Continuously variable transmission structure

Abstract

To provide a continuously variable transmission structure enabling both a single transmission operation member to perform tilting operation of both a pump volume adjustment device and a motor volume adjustment device while simplifying and downsizing a structure.SOLUTION: A pump operation piston neutrally energized with a neutral spring mechanism and a motor operation piston energized in a direction to increase a volume with a volume increase operation spring directly or indirectly tilt a pump volume adjustment device and a motor volume adjustment device respectively. A first pressure control valve commonly supplies and discharges hydraulic oil when pressing the pump operation piston in a first slide direction and the motor operation piston in a volume reduction direction. A second pressure control valve supplies and discharges the hydraulic oil when pressing the pump operation piston in a second slide direction. Energizing force of the neutral spring mechanism and the volume increase operation spring is set so that the motor operation piston is started to move in the volume reduction direction after the pump operation piston is moved a predetermined distance in the first slide direction.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a continuously variable transmission structure including a hydraulic continuously variable transmission mechanism (HST) having a variable displacement hydraulic pump and a variable displacement hydraulic motor.

Background Art

[0002] Conventionally, there has been proposed a continuously variable transmission structure including an HST having a variable displacement hydraulic pump and a variable displacement hydraulic motor, the structure including a single shift operation member, a pump operation arm provided at an operation end portion of a movable swash plate in the hydraulic pump, a motor operation arm provided at an operation end portion of a movable swash plate in the hydraulic motor, and a push-pull rod operatively connected to the shift operation member with free end portions of the pump operation arm and the motor operation end portion connected to each other (see Patent Document 1 below).

[0003] A first accommodation mechanism is provided at a connection portion between the push-pull rod and the motor operation arm. The first accommodation mechanism is configured such that in an operation range corresponding to a zero speed to a predetermined speed of an output rotation speed of the HST, the motor operation arm is not operated while the pump operation arm is operated in response to an operation of the shift operation member.

[0004] Furthermore, a second accommodation mechanism is provided at a connection portion between the push-pull rod and the pump operation arm. The second accommodation mechanism is configured such that in an operation range corresponding to the predetermined speed or more of the output rotation speed of the HST, the pump operation arm is not operated while the motor operation arm is operated in response to an operation of the shift operation member.

[0005] The stepless speed change structure described in Patent Document 1 is useful in that the volume changes of both the hydraulic pump and the hydraulic motor can be made possible by the single speed change operation member. However, for this purpose, since the first and second accommodation mechanisms are provided, it is difficult to adjust the timing for moving the motor operation arm without interruption with respect to the movement of the pump operation arm, and there is a problem that the mechanical link mechanism between the speed change operation member, the pump operation arm, and the motor operation arm becomes large and complicated.

[0006] In addition, another stepless speed change structure has been proposed in which the volumes of both a variable displacement hydraulic pump and a variable displacement hydraulic motor can be changed by a single speed change operation member (see Patent Document 2 below).

[0007] However, the stepless speed change structure described in Patent Document 2 also has a problem that it is difficult to adjust the timing for starting the volume change of the hydraulic motor, and the mechanical link mechanism connecting the speed change operation member, the operation end of the swash plate of the hydraulic pump, and the operation end of the swash plate of the hydraulic motor becomes large and complicated.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0009] The present invention has been made in view of the above prior art, and an object of the present invention is to provide a stepless speed change structure including a hydraulic stepless speed change mechanism including a variable displacement hydraulic pump and a variable displacement hydraulic motor, while achieving a simplified and downsized structure, and enabling the volume changes of both the hydraulic pump and the hydraulic motor by a single speed change operation member.

Means for Solving the Problems

[0010] To achieve the above object, a first aspect of the present invention is a variable displacement hydraulic pump in which the volume of the pump body changes according to the operation of a pump volume adjuster, and a variable displacement hydraulic motor in which the volume of the motor body changes according to the operation of a motor volume adjuster, a hydraulic continuously variable transmission mechanism including the above, a shift operation member for operating the shift state of the hydraulic continuously variable transmission mechanism, and a pump operation piston movable in a bidirectional manner in a first slide direction on one side in the axial direction and a second slide direction on the other side, the pump operation piston being directly or indirectly engaged with an operation end portion of the pump volume adjuster so as to operate the pump volume adjuster in a first operation direction and a second operation direction respectively according to the movement in the first and second slide directions, a neutral spring mechanism that generates a biasing force toward the neutral position when the pump operation piston is moved in the first and second slide directions from the neutral position while holding the pump operation piston in the neutral position in a state where no external force is applied to the pump operation piston, first and second slide oil chambers configured to push the pump operation piston in the first and second slide directions respectively against the biasing force of the neutral spring mechanism by the supplied pressure oil, a motor operation piston movable in a bidirectional manner in a volume reduction direction on one side in the axial direction and a volume increase direction on the other side, the motor operation piston being directly or indirectly engaged with an operation end portion of the motor volume adjuster so as to operate the motor volume adjuster in the volume reduction direction and the volume increase direction respectively according to the movement in the volume reduction direction and the volume increase direction, a volume increase operation spring that biases the motor operation piston in the volume increase direction, a volume reduction operation oil chamber configured to push the motor operation piston in the volume reduction direction against the biasing force of the volume increase operation spring by the supplied pressure oil, a first pressure control valve that commonly switches the supply and discharge of pressure oil to the first slide oil chamber and the volume reduction operation oil chamber according to the operation of the shift operation member, and a second pressure control valve that switches the supply and discharge of pressure oil to the second slide oil chamber according to the operation of the shift operation member, and the pressure oil in the first slide oil chamber when the pump operation piston is moved from the neutral position the first slide direction to move andand then, after the neutral spring mechanism reaches a predetermined retained elastic state, the urging forces of the neutral spring mechanism and the volume increasing operation spring are set such that the motor operation piston starts to move in the volume decreasing direction while elastically deforming the volume increasing operation spring by the pressure oil in the volume decreasing operation oil chamber, thereby providing a continuously variable transmission structure. the pump operation piston is biased toward the neutral position with a predetermined biasing force After the neutral spring mechanism reaches a predetermined retained elastic state, the urging forces of the neutral spring mechanism and the volume increasing operation spring are set such that the motor operation piston starts to move in the volume decreasing direction while elastically deforming the volume increasing operation spring by the pressure oil in the volume decreasing operation oil chamber, thereby providing a continuously variable transmission structure.

[0011] In the first configuration of the first aspect, the neutral spring mechanism is configured to reach the predetermined retained elastic state when the pump operation piston positions the pump volume adjuster at the first operation direction moving end.

[0012] In the second configuration of the first aspect, the neutral spring mechanism is configured to reach the predetermined retained elastic state when the pump operation piston positions the pump volume adjuster at a predetermined position in front of the first operation direction moving end.

[0013] In the first example of the second configuration of the first aspect, the urging forces of the neutral spring mechanism and the volume increasing operation spring are set such that when the pump operation piston causes the pump volume adjuster to reach the first operation direction moving end, the motor operation piston positions the motor volume adjuster at the volume decreasing direction moving end.

[0014] In the second example of the second configuration of the first aspect, the urging forces of the neutral spring mechanism and the volume increasing operation spring are set such that when the pump operation piston causes the pump volume adjuster to reach the first operation direction moving end, the motor operation piston positions the motor volume adjuster at a predetermined position in front of the volume decreasing direction moving end.

[0015] The continuously variable transmission structure according to the first aspect may further include a first supply / drain line fluidly connected to the first slide oil chamber and the volume decreasing operation oil chamber, and a second supply / drain line fluidly connected to the second slide oil chamber.

[0016] In this case, the first pressure control valve is configured to be able to take a supply position for fluidly connecting the first supply / drain line to a charge line for supplying hydraulic fluid to the hydraulic continuously variable transmission mechanism, and a discharge position for draining the first supply / drain line, and the second pressure control valve is configured to be able to take a supply position for fluidly connecting the second supply / drain line to the charge line, and a discharge position for draining the second supply / drain line.

[0017] The continuously variable transmission structure according to the first aspect of the first form may further include a pump hydraulic servo mechanism for hydraulically operating the pump volume adjuster based on the movement of the pump operation piston, and a motor hydraulic servo mechanism for hydraulically operating the motor volume adjuster based on the movement of the motor operation piston.

[0018] The motor hydraulic servo mechanism may include a motor servo piston, a volume increasing servo spring, a spring chamber for housing the spring, a volume decreasing servo oil chamber, and a motor servo switching valve.

[0019] The motor servo piston is configured to be movable in two directions, i.e., a volume decreasing servo direction on one side in the axial direction and a volume increasing servo direction on the other side, in cooperation with the switching operation of the motor servo switching valve. As it moves in the volume decreasing servo direction, it operates the motor volume adjuster in the volume decreasing direction, and when it is positioned at the minimum volume servo position, it positions the motor volume adjuster at the minimum volume position. On the other hand, as it moves in the volume increasing servo direction, it operates the motor volume adjuster in the volume increasing direction, and when it is positioned at the maximum volume servo position, it positions the motor volume adjuster at the maximum volume position, and is engaged with the operation end of the motor volume adjuster.

[0020] The volume increasing servo spring is configured to bias the motor servo piston in the volume increasing servo direction. The volume decreasing servo oil chamber is configured to push the motor servo piston in the volume decreasing servo direction against the biasing force of the volume increasing servo spring by the supplied pressure oil. The motor servo switching valve is operatively connected to the motor operating piston so as to take a volume increasing position and a volume decreasing position respectively in accordance with the movement of the motor operating piston in the volume increasing direction and the volume decreasing direction. The volume increasing servo spring urges the motor servo piston in a volume increasing servo direction, and the volume increasing operation spring urges the motor operating piston in a volume increasing direction, and these two directions are made to coincide.

[0021] In the continuously variable transmission structure according to the second form of the first aspect, the pump operating piston is mechanically connected to the operating end of the pump volume adjuster so as to operate the pump volume adjuster in the first and second operating directions respectively in accordance with the movement in the first and second slide directions, and the motor operating piston is mechanically connected to the operating end of the motor volume adjuster so as to operate the motor volume adjuster in the volume decreasing direction and the volume increasing direction respectively in accordance with the movement in the volume decreasing direction and the volume increasing direction.

[0022] To achieve the above object, a second aspect of the present invention provides a hydraulic continuously variable transmission mechanism including a variable displacement hydraulic pump whose volume changes according to the operation of a pump volume adjuster and a variable displacement hydraulic motor whose volume changes according to the operation of a motor volume adjuster, a shift operation member that can be operated bidirectionally about an axis between a first operation direction operation end on one side and a second operation direction operation end on the other side with respect to a neutral position, a pump operation connection mechanism that operates the pump volume adjuster from the neutral position in the first and second operation directions, and a motor operation connection mechanism that operates the motor volume adjuster in the volume reduction direction and the volume increase direction, respectively. The pump operation connection mechanism has a pump spool operatively connected to the shift operation member such that when the shift operation member is operated to the neutral position, the pump spool assumes a pump spool neutral position, and when the shift operation member is operated from the neutral position in the first and second operation directions, the pump spool moves from the pump spool neutral position in a first slide direction on one side and a second slide direction on the other side of the axial direction, respectively. The motor operation connection mechanism includes a motor spool coaxially and abuttingly arranged in series on one side in the axial direction of the pump spool and capable of moving bidirectionally in the volume reduction direction on one side and the volume increase direction on the other side of the axial direction, and a volume increase operation spring that biases the motor spool in the volume increase direction. The motor operation connection mechanism is configured to operate the motor volume adjuster in the volume reduction direction and the volume increase direction on the other side according to the movement of the motor spool in the volume reduction direction and the volume increase direction, respectively. A clearance portion having a predetermined distance in the first slide direction is provided between the pump spool located at the pump spool neutral position and the motor spool located at the volume increase direction movement end. When the pump spool is moved to the end of the clearance portion in response to the operation of the shift operation member in the first operation direction, only the pump spool moves in the first slide direction while the motor spool is held at the volume increase direction movement end. When the pump spool moves beyond the clearance portion in the first slide direction, the pump spool is configured to abut against the motor spool and move the motor spool in the volume reduction direction, thereby providing a continuously variable transmission structure.

[0023] In the second aspect, preferably, when the shift operation member positions the pump volume adjuster at the first operation direction moving end via the pump operation connection mechanism, the pump spool is configured to be positioned at the end of the accommodation portion.

[0024] Preferably, the continuously variable transmission structure according to the second aspect may include a neutral spring mechanism that directly or indirectly holds the pump spool at the pump spool neutral position and generates a biasing force directed toward the pump spool neutral position directly or indirectly on the pump spool when the pump spool is moved in the first and second slide directions from the pump spool neutral position.

[0025] In the continuously variable transmission structure according to the second aspect, preferably, the pump operation connection mechanism may include a pump hydraulic servo mechanism that hydraulically operates the pump volume adjuster based on the operation of the shift operation member.

[0026] The pump hydraulic servo mechanism is assumed to include a pump servo piston, a volume increasing servo oil chamber, a volume decreasing servo oil chamber, and a pump servo switching valve. The pump servo piston is movable in a first servo direction on one side in the axial direction and a second servo direction on the other side in cooperation with the switching operation of the pump servo switching valve. When moving in the first servo direction, it operates the pump volume adjuster in the first operation direction, and when moving to the second servo position, it is engaged with the operation end portion of the pump volume adjuster so as to operate the pump volume adjuster in the second operation direction.

[0027] In response to the operation up to a predetermined position in front of the first operation direction operation end of the shift operation member, the pump servo switching valve is operated via the pump operation connection mechanism so that the pump spool is positioned at the end position of the accommodation portion and the pump volume adjuster is positioned at the first operation direction moving end by the pump servo piston.

[0028] When the shift operation member is being operated between the predetermined position and the operation end in the first operation direction, while maintaining the state in which the pump servo piston positions the pump volume adjuster at the first operation direction moving end, the pump spool is positioned at a slide position corresponding to the operation position of the shift operation member via the pump operation connection mechanism.

[0029] To achieve the above object, a third aspect of the present invention includes a variable displacement hydraulic pump whose volume of the pump body changes according to the operation of a pump volume adjuster and a variable displacement hydraulic motor whose volume of the motor body changes according to the operation of a motor volume adjuster. When the pump volume adjuster is positioned at the neutral position, the output rotational power becomes zero speed. When the pump volume adjuster is positioned in the forward rotation region and the reverse rotation region from the neutral position, the rotational direction of the output rotational power is configured to be the forward rotation direction and the reverse rotation direction, respectively. A hydraulic continuously variable transmission mechanism; a shift operation member that performs a switching operation of the rotational direction of the output of the hydraulic continuously variable transmission mechanism and a speed change operation of the rotational speed; a pump operation piston that is movable in a bidirectional manner in a first slide direction on one side in the axial direction and a second slide direction on the other side, and the pump operation piston is directly or indirectly engaged with the operation end of the pump volume adjuster so as to operate the pump volume adjuster in a first operation direction and a second operation direction according to the movement in the first and second slide directions; a neutral spring mechanism that holds the pump operation piston at the neutral position when no external force is applied to the pump operation piston, and generates a biasing force toward the neutral position when the pump operation piston is moved in the first and second slide directions from the neutral position; first and second slide oil chambers configured to push the pump operation piston in the first and second slide directions against the biasing force of the neutral spring mechanism by the supplied pressure oil; a motor operation piston that is movable in a bidirectional manner in a volume reduction direction on one side in the axial direction and a volume increase direction on the other side, and the motor operation piston is directly or indirectly engaged with the operation end of the motor volume adjuster so as to operate the motor volume adjuster in the volume reduction direction and the volume increase direction on the other side according to the movement in the volume reduction direction and the volume increase direction; a volume increase operation spring that biases the motor operation piston in the volume increase direction; a volume reduction operation oil chamber configured to push the motor operation piston in the volume reduction direction against the biasing force of the volume increase operation spring by the supplied pressure oil; a first pressure control valve configured to supply and discharge pressure oil to and from the first slide oil chamber according to the operation of the shift operation member that operates the pump volume adjuster in the first and second operation directions.A second pressure control valve configured to discharge and supply pressure oil to the second slide oil chamber in accordance with the operation of the shift operation member that operates the pump volume adjuster in the first and second operation directions, and when the shift operation member is positioned in the forward rotation operation region and the reverse rotation operation region, a flow path switching valve configured to introduce the pressure oil in the first and second slide oil chambers into the volume reduction operation oil chamber respectively. By the pressure oil in the first and second slide oil chambers, when the pump operation piston is moved from the neutral position corresponding slide direction to moves and so that the neutral spring mechanism the pump operation piston is biased toward the neutral position with a predetermined biasing force After reaching a predetermined holding elastic state, the urging forces of the neutral spring mechanism and the volume increasing operation spring are set so that the motor operation piston starts to move in the volume decreasing direction while elastically deforming the volume increasing operation spring by the pressure oil in the volume decreasing operation oil chamber. A continuously variable transmission structure is provided.

[0030] In the first configuration of the third aspect, the neutral spring mechanism is configured to be in the predetermined holding elastic state when the pump operation piston positions the pump volume adjuster at the first operation direction moving end and the second operation direction moving end.

[0031] In the second configuration of the third aspect, the neutral spring mechanism is configured to be in the predetermined holding elastic state when the pump operation piston positions the pump volume adjuster at a predetermined position in front of the moving ends in their respective operation directions when operating the pump volume adjuster in the first and second operation directions.

[0032] In the first example of the second configuration of the third aspect, the urging forces of the neutral spring mechanism and the volume increasing operation spring are set so that when the pump volume adjuster reaches the first operation direction moving end and the second operation direction moving end by the pump operation piston, the motor operation piston positions the motor volume adjuster at the volume decreasing direction moving end.

[0033] In the second example of the second configuration of the third aspect, the biasing forces of the neutral spring mechanism and the volume increasing operation spring are set such that when the pump volume adjuster reaches the first and second operation direction moving ends by the pump operation piston, the motor operation piston positions the motor volume adjuster at a predetermined position before the volume decreasing direction moving end.

[0034] To achieve the above object, a fourth aspect of the present invention includes a variable displacement hydraulic pump in which the volume of a pump body changes according to the operation of a pump volume adjuster between a first operation direction moving end on one side and a second operation direction moving end on the other side, and a variable displacement hydraulic motor in which the volume of a motor body changes according to the operation of a motor volume adjuster, a hydraulic continuously variable transmission mechanism, a drive source, and the hydraulicA planetary gear mechanism that inputs the rotational power from a continuously variable transmission mechanism to a first element and a second element respectively, combines these rotational powers, and outputs them from a third element; a shift operation member that operates the shift state of the hydraulic continuously variable transmission mechanism; a pump operation piston that is movable in a bidirectional manner in a first slide direction on one side in the axial direction and a second slide direction on the other side, and is directly or indirectly engaged with an operation end portion of the pump volume adjuster so as to operate the pump volume adjuster in first and second operation directions respectively in response to movement in the first and second slide directions; a second slide spring that biases the pump operation piston in the second slide direction; a first slide oil chamber configured to push the pump operation piston in the first slide direction against the biasing force of the second slide spring by the supplied pressure oil; a motor operation piston that is movable in a bidirectional manner in a volume reduction direction on one side in the axial direction and a volume increase direction on the other side, and is directly or indirectly engaged with an operation end portion of the motor volume adjuster so as to operate the motor volume adjuster in the volume reduction direction and the volume increase direction on the other side respectively in response to movement in the volume reduction direction and the volume increase direction; a volume increase operation spring that biases the motor operation piston in the volume increase direction; a volume reduction operation oil chamber configured to push the motor operation piston in the volume reduction direction against the biasing force of the volume increase operation spring by the supplied pressure oil; and a pressure control valve that commonly switches the supply and discharge of pressure oil to the first slide oil chamber and the volume reduction operation oil chamber in response to the operation of the shift operation member. The planetary gear mechanism has a gear ratio set such that the combined rotational power becomes zero speed when the pump volume adjuster is positioned at the second operation direction moving end, and the combined rotational power is increased in speed in one direction as the pump volume adjuster is operated from the second operation direction moving end to the first operation direction moving end. By the pressure oil in the first slide oil chamber when the pump operation piston is moved against the biasing force of the second slide spring the first slide direction to move and so that the second slide spring the pump operation piston is biased in the first slide direction with a predetermined biasing forceAfter reaching a predetermined holding spring state, the urging forces of the second slide spring and the volume increasing operation spring are set such that the motor operation piston starts to move in the volume decreasing direction while elastically deforming the volume increasing operation spring by the pressure oil in the volume decreasing operation oil chamber.

[0035] In the fourth aspect, preferably, in the hydraulic continuously variable transmission mechanism, when the pump volume adjuster is positioned at the second operation direction moving end, the output rotational power becomes the maximum reverse speed, and as the pump volume adjuster is operated in the first operation direction from the second operation direction moving end to the neutral position between the second operation direction moving end and the first operation direction moving end, the output rotational power is decelerated from the maximum reverse speed to zero speed, and as the pump volume adjuster is operated in the first operation direction from the neutral position to the first operation direction moving end, the output rotational speed is accelerated from zero speed to the maximum forward speed.

[0036] In the first configuration of the fourth aspect, the second slide spring is configured to be in the predetermined holding spring state when the pump operation piston positions the pump volume adjuster at the first operation direction moving end.

[0037] In the second configuration of the fourth aspect, the second slide spring is configured to be in the predetermined holding spring state when the pump operation piston positions the pump volume adjuster at a predetermined position in front of the first operation direction moving end.

[0038] In the first example of the second configuration of the fourth aspect, the urging forces of the second slide spring and the volume increasing operation spring are set such that when the pump volume adjuster reaches the first operation direction moving end by the pump operation piston, the motor operation piston positions the motor volume adjuster at the volume decreasing direction moving end.

[0039] In the second example of the second configuration of the fourth aspect, when the pump operation piston reaches the first operation direction moving end of the pump volume adjuster, the motor operation piston positions the motor volume adjuster at a predetermined position in front of the volume decreasing direction moving end. In this way, the biasing forces of the second slide spring and the volume increasing operation spring are set.

[0040] The continuously variable transmission structure according to the first form of the fourth aspect preferably further includes a pump hydraulic servo mechanism that hydraulically operates the pump volume adjuster based on the movement of the pump operation piston, and a motor hydraulic servo mechanism that hydraulically operates the motor volume adjuster based on the movement of the motor operation piston.

[0041] In the continuously variable transmission structure according to the second form of the fourth aspect, the pump operation piston is mechanically connected to the operation end of the pump volume adjuster so as to operate the pump volume adjuster in the first and second operation directions respectively in response to movement in the first and second slide directions, and the motor operation piston is mechanically connected to the operation end of the motor volume adjuster so as to operate the motor volume adjuster in the volume decreasing direction and the volume increasing direction respectively in response to movement in the volume decreasing direction and the volume increasing direction.

[0042] The continuously variable transmission structure according to the first to fourth aspects preferably further includes a biasing force adjustment mechanism capable of adjusting the biasing force of the volume increasing operation spring.

[0043] When the continuously variable transmission structure includes a motor operation piston case that forms the accommodation space of the motor operation piston, the motor operation piston is accommodated in the accommodation space in a state where it can move in both axial directions while defining a spring chamber that accommodates the volume increasing operation spring on the side opposite to the volume decreasing operation oil chamber and the volume decreasing operation oil chamber. The biasing force adjustment mechanism has a spring receiver that is supported by the motor operation piston case in a state where it can be adjusted in a fixed position while engaging with the base end side of the volume increasing operation spring, which is opposite to the tip end side that is the engagement end with the motor operation piston.

Advantages of the Invention

[0044] According to the continuously variable transmission structure of the present invention, while achieving structural simplification and miniaturization, with a single shift operation member, in a state where the motor volume adjuster is held at the maximum volume position, the pump volume adjuster is moved according to the operation of the shift operation member, and after the pump volume adjuster is positioned at or near the moving ends in the first and second operation directions or the moving ends in the first and second operation directions, a shift state in which the motor volume adjuster is moved alone or together with the pump volume adjuster according to the operation of the shift operation member can be obtained.

Brief Description of the Drawings

[0045]

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Embodiments for Carrying Out the Invention

[0046] Embodiment 1 Hereinafter, an embodiment of a continuously variable transmission structure according to the present invention will be described with reference to the accompanying drawings. FIG. 1 shows a cross-sectional view of a hydraulic continuously variable transmission mechanism (HST) 10 in a continuously variable transmission structure 1A according to the present embodiment. Also, FIG. 2 shows a cross-sectional view taken along line II-II in FIG. 1. Furthermore, FIG. 3(a) shows a cross-sectional view taken along line IIIa-IIIa in FIG. 2, and FIG. 3(b) shows a cross-sectional view taken along line IIIb-IIIb in FIG. 3(a).

[0047] The continuously variable transmission structure 1A includes the HST 10 and a speed change operating member (not shown) such as a speed change lever for operating the HST 10.

[0048] The HST10 is configured such that the volume of the pump body 20 changes according to the operation of the pump volume adjuster, and the volume of the motor body 50 changes according to the operation of the motor volume adjuster.

[0049] As shown in FIG. 1, in the present embodiment, the HST10 is of an axial piston type. That is, the HST10 includes a pump shaft 15 that is rotationally driven about an axis by rotational power operatively input from a drive source (not shown), a pump body 20 supported by the pump shaft 15 so as to rotate about the axis together with the pump shaft 15, a pump movable swash plate 30 that acts as the pump volume adjuster and changes the volume amount of the pump body 20 according to the tilting about a pump swing axis PA, a motor shaft 45 that outputs rotational power after continuously variable transmission, a motor body 50 supported by the motor shaft 45 so as to rotate about the axis together with the motor shaft 45, a motor movable swash plate 60 that acts as the motor volume adjuster and changes the volume amount of the motor body 50 according to the tilting about a motor swing axis MA, and a pair of HST lines (not shown) that fluid-connect the pump body 20 and the motor body 50. The motor body 50 is hydraulically rotationally driven by the pump body 20 via the pair of HST lines.

[0050] As shown in FIG. 1, the pump body 20 includes a pump cylinder block 21 that is supported non-rotatably relative to the pump shaft 15 and has a plurality of cylinder holes arranged around the axis of the pump shaft 15, and a plurality of pump pistons 22 that are slidably accommodated in the plurality of cylinder holes and have free ends engaged with a swash plate body 32 of the pump movable swash plate 30.

[0051] Similarly, the motor main body 50 includes a motor cylinder block 51 that is non-rotatably supported relative to the motor shaft 45 and has a plurality of cylinder holes arranged around the axis of the motor shaft 45, and a plurality of motor pistons 52 that are slidably accommodated in the plurality of cylinder holes and have free ends engaged with the swash plate body 62 of the motor swash plate 60.

[0052] As shown in FIG. 1, in the present embodiment, the pump swash plate 30 and the motor swash plate 60 are cradle-type swash plates.

[0053] That is, the pump swash plate 30 and the motor swash plate 60 have swash plate bodies 32, 62 and operation ends 35, 65.

[0054] The swash plate bodies 32, 62 have piston engagement surfaces that engage with the corresponding pistons 22, 52 and backs on the side opposite to the piston engagement surfaces, and the backs are guided by the guide members 38, 68 so as to be tiltable around the corresponding swing axes PA, MA.

[0055] The operation ends 35, 65 are provided on the swash plate bodies 32, 65 so as to tilt around the corresponding swing axes PA, MA together with the corresponding swash plate bodies 32, 62.

[0056] Alternatively, the pump swash plate 30 and the motor swash plate 60 can be trunnion-type swash plates. In this case, the pump swash plate and the motor swash plate may include a swash plate body having a piston engagement surface that engages with the corresponding pistons 22, 52, and an operation end connected to the swash plate body so as to tilt the swash plate body around the swing axis in response to rotation around the axis and arranged on the corresponding swing axes PA, MA.

[0057] In the present embodiment, the HST 10 is capable of outputting bidirectional rotational power continuously variable from the motor shaft 45. That is, the pump volume adjuster is operable between a first operation direction moving end that rotates the motor shaft 45 at the maximum speed in the forward rotation direction and a second operation direction moving end that rotates the motor shaft 45 at the maximum speed in the reverse rotation direction, with a neutral position that sets the volume of the pump body 20 (the hydraulic oil discharge amount discharged according to one rotation of the pump body 15) to zero in between.

[0058] As described above, in this embodiment, the pump movable swash plate 30 is used as the pump volume adjuster. In this case, the tilting end (first tilting direction moving end) on one side around the pump rocking axis PA from the neutral position becomes the first operation direction moving end, and the tilting end (second tilting direction moving end) on the other side around the pump axis PA from the neutral position becomes the second operation direction moving end.

[0059] That is, when the pump volume adjuster (the pump movable swash plate 30) is positioned within the forward rotation region on the first operation direction side (first tilting direction side) from the neutral position, as the pump volume adjuster (the pump movable swash plate 30) is operated in the first operation direction (tilted in the first tilting direction) toward the first operation direction moving end (first tilting direction moving end), the hydraulic oil discharge amount (forward rotation direction discharge amount) of the pump body 20 in the direction of rotating the motor body 50 in the forward rotation direction increases, and the rotation speed of the motor body 50 (that is, the motor shaft 45) in the forward rotation direction increases. On the other hand, within the forward rotation region, as the pump volume adjuster (the pump movable swash plate 30) is operated in the second operation direction (tilted in the second tilting direction) toward the neutral position, the forward rotation direction discharge amount of the pump body 20 decreases, and the rotation speed of the motor body 50 (that is, the motor shaft 45) in the forward rotation direction decreases.

[0060] When the pump volume adjuster (the pump movable swash plate 30) positioned within the forward rotation region is operated in the second operation direction (tilted in the second tilting direction) and positioned at the neutral position, the hydraulic oil discharge amount of the pump body 20 becomes zero, and the rotation speed of the motor body 50 (that is, the motor shaft 45) becomes zero.

[0061] Further, when the pump volume adjuster (the pump swash plate 30) is positioned within the reverse region on the second operation direction side (second tilting direction side) from the neutral position, as the pump volume adjuster (the pump swash plate 30) is operated in the second operation direction (tilted in the second tilting direction) toward the second operation direction moving end (second tilting direction moving end), the hydraulic oil discharge amount (reverse direction discharge amount) of the pump body 20 in the direction of rotating the motor body 50 in the reverse direction increases, and the rotational speed of the motor body 50 (i.e., the motor shaft 45) in the reverse direction increases. As the pump volume adjuster (the pump swash plate 30) is operated in the first operation direction (tilted in the first tilting direction) toward the neutral position within the reverse region, the reverse direction discharge amount of the pump body 20 decreases, and the rotational speed of the motor body 50 (i.e., the motor shaft 45) in the reverse direction decreases.

[0062] The first tilting direction moving end that becomes the first operation direction moving end can be set, for example, by a first tilting direction stop member that restricts further tilting of the pump swash plate 30 in one side in the first tilting direction (e.g., forward rotation direction) around the pump swing axis PA when the pump swash plate 30 is tilted in one side in the first tilting direction (e.g., forward rotation direction) around the pump swing axis PA. In the present embodiment, as will be described later, a pump servo piston 210P that swings the pump swash plate 30 is accommodated in a pump servo space formed in a housing body 75 of an HST housing 70 so as to be slidable in two directions of first and second servo directions SV1 and SV2. A portion of the pump servo space that defines the moving end of the pump servo piston 210P in the first servo direction SV1 forms the first tilting direction stop member.

[0063] The second tilting direction moving end that becomes the second operation direction moving end can be set, for example, by a second tilting direction stop member that restricts further tilting of the pump swash plate 30 in the other side in the second tilting direction (e.g., reverse direction) around the pump swing axis PA when the pump swash plate 30 is tilted in the other side in the second tilting direction (e.g., reverse direction) around the pump swing axis PA. In the present embodiment, a portion of the pump servo space that defines the moving end of the pump servo piston 210P in the second servo direction SV2 forms the second tilting direction stop member.

[0064] The motor volume adjuster is operable between a maximum volume position that makes the volume of the motor body 50 the maximum volume and a minimum volume position that makes the volume of the motor body 50 the minimum volume.

[0065] As described above, in the present embodiment, the motor movable swash plate 60 is used as the motor volume adjuster. The motor movable swash plate 60 is swingable about the motor swing axis MA between a maximum volume position that makes the volume of the motor body 50 the maximum volume and a minimum volume position that makes the volume of the motor body 50 the minimum volume.

[0066] The minimum volume position can be set, for example, by a minimum volume side stop member that restricts the motor movable swash plate 60 from further swinging to one side (e.g., the volume decrease direction) about the motor swing axis MA when the motor movable swash plate 60 is swung to one side about the motor swing axis MA.

[0067] In the present embodiment, as will be described later, a motor servo piston 210M that swings the motor movable swash plate 60 is accommodated in a motor servo space formed in the housing body 75 so as to be slidable in both the volume increase servo direction SVL and the volume decrease servo direction SVS. A portion of the motor servo space that defines the moving end of the motor servo piston 210M in the volume decrease servo direction SVS forms the minimum volume side stop member.

[0068] Similarly, the maximum volume position can be set, for example, by a maximum volume side stop member that restricts the motor movable swash plate 60 from further swinging to the other side (e.g., the volume increase direction) about the motor swing axis MA when the motor movable swash plate 60 is swung to the other side about the motor swing axis MA. In the present embodiment, a portion of the motor servo space that defines the moving end of the motor servo piston 210M in the volume increasing servo direction SVL forms the maximum volume side stop member.

[0069] When the motor volume adjuster (the motor movable swash plate 60) is positioned at the maximum volume position and the motor body 50 is in the maximum volume state, the amount of working oil required to rotate the motor body 50 once around the axis increases. On the other hand, when the motor volume adjuster (the motor movable swash plate 60) is positioned at the minimum volume position and the motor body 50 is in the minimum volume state, the amount of working oil required to rotate the motor body 50 once around the axis decreases.

[0070] Therefore, assuming that the working oil discharge amount of the pump body 20 is constant, as the motor volume adjuster (the motor movable swash plate 60) is operated from the maximum volume position to the minimum volume position, the rotational speed of the motor body 50 (i.e., the motor shaft 45) increases.

[0071] In the present embodiment, as shown in FIG. 1, the HST 10 further includes an HST housing 70 that houses the pump body 20, the pump movable swash plate 30, the motor body 50, and the motor movable swash plate 60, and rotatably supports the pump shaft 15 and the motor shaft 45 around the axis.

[0072] The HST housing 70 has a housing body 75 provided with an opening through which the pump body 20 and the motor body 50 can be inserted, and a port block 80 connected to the housing body 75 so as to close the opening.

[0073] The housing body 75 has a peripheral wall 76 that surrounds the pump body 20 and the motor body 50, and an end wall 77 that closes one side in the axial direction of the peripheral wall 76. The side of the peripheral wall 76 opposite to the end wall 77 is the opening. The guide members 38 and 68 are disposed between the swash plate bodies 32 and 62 and the end wall 77.

[0074] An oil passage for forming the pair of HST lines is formed in the port block 80. Furthermore, a charge oil passage 82 (see FIG. 1) for forming a charge line for guiding supply oil to the pair of HST lines is provided in the port block 80. One end of the charge oil passage 82 opens to the outer surface to form a charge port 82P. Note that reference numeral 85 in FIG. 1 is a charge relief valve for setting the hydraulic pressure of the charge line.

[0075] Naturally, the present invention including the present embodiment and the following embodiments can also be provided with a radial piston type HST 10' instead of the axial piston type HST 10.

[0076] FIG. 4 shows a cross-sectional view of an example of a radial piston type HST 10' applicable to the continuously variable transmission structure according to the present invention. The HST 10' includes a pintle 80' in which an oil passage is formed, a pump shaft 15, a pump body 20', a motor shaft 45, and a motor body 50'.

[0077] The pump body 20' has a pump cylinder 21' in which a plurality of cylinder holes opening radially outward are arranged around the axis, and a plurality of pump pistons 22' that are slidably accommodated in the plurality of cylinder holes. The pump cylinder 21' is rotatably supported by the pintle 80' while being connected to the pump shaft 15 so as to rotate around the axis together with the pump shaft 15.

[0078] The motor body 50' has a motor cylinder 51' in which a plurality of cylinder holes opening radially outward are arranged around the axis, and a plurality of motor pistons 52' that are slidably accommodated in the plurality of cylinder holes. The motor cylinder 51' is rotatably supported by the pintle 80' while being connected to the motor shaft 65 so as to rotate about the axis together with the motor shaft 65.

[0079] The pintle 80' is formed with a pair of HST lines 90a that fluidly connect the pump body 20' (the pump cylinder 21') and the motor body 50' (the motor cylinder 51').

[0080] The HST 10' further includes a pump movable cam ring 30' that acts as the pump volume adjuster and a motor movable cam ring 60' that acts as the motor volume adjuster.

[0081] The pump movable cam ring 30' has an inner peripheral surface that engages with the outer ends of the plurality of pump pistons 22' in the pump body 20' and a pump movable cam ring body 32' that is swingable about a pump swing shaft 39', and an operation end 35' that swings the pump movable cam ring body 32' about the pump swing shaft 39'.

[0082] The pump movable cam ring 30' is swingable in a first operation direction on one side and a second operation direction on the other side about the pump swing shaft with a neutral position where the center position of the pump movable cam ring body 32' coincides with the center position of the pump cylinder 21' interposed therebetween in response to an operation on the operation end 35'.

[0083] The motor movable cam ring 60' has an inner peripheral surface that engages with the outer ends of the plurality of motor pistons 52' in the motor body 51' and a motor movable cam ring body 62' that is swingable about a motor swing shaft 69', and an operation end 65' that swings the motor movable cam ring body 62' about the motor swing shaft 69'.

[0084] The motor movable cam ring 60' is operable between a minimum volume position that causes the motor body 50' to be in a minimum volume state and a maximum volume position that causes the motor body to be in a maximum volume state around the motor swing axis 69' in response to an operation on the operation end portion 65'. In the illustrated form, the pump swing axis 39' and the motor swing axis 69' are a single axis.

[0085] As shown in FIG. 3, the continuously variable transmission structure 1A further includes a pump operation piston 110, a neutral spring mechanism 120, first and second slide oil chambers 131 and 132, a motor operation piston 140, a volume increase operation spring 150, and a volume decrease operation oil chamber 160.

[0086] The pump operation piston 110 is movable in two directions, i.e., a first slide direction S1 on one side in the axial direction and a second slide direction S2 on the other side. In response to the movement in the first slide direction S1, the pump volume adjuster is operated in the first operation direction, and when positioned at the movement end in the first slide direction, the pump volume adjuster is positioned at the movement end in the first operation direction. On the other hand, in response to the movement in the second slide direction S2, the pump volume adjuster is operated in the second operation direction, and when positioned at the movement end in the second slide direction, the pump volume adjuster is positioned at the movement end in the second operation direction. It is operatively connected to the operation end portion of the pump volume adjuster.

[0087] As described above, in the present embodiment, the HST 10 is of an axial piston type and has the pump movable swash plate 30 as the pump volume adjuster. In this case, the movement end in the first tilting direction around the pump swing axis PA of the pump movable swash plate 30 corresponds to the movement end in the first operation direction of the pump volume adjuster, and the movement end in the second tilting direction around the pump swing axis PA of the pump movable swash plate 30 corresponds to the movement end in the second operation direction of the pump volume adjuster.

[0088] Note that, as shown in FIG. 3, in the present embodiment, the pump operation piston 110 is indirectly connected to the operation end portion of the pump volume adjuster (the operation end portion 35 of the pump movable swash plate 30 in the present embodiment) via the pump hydraulic servo mechanism 200. The configuration of the pump hydraulic servo mechanism 200P will be described later.

[0089] The neutral spring mechanism 120 is configured to generate a biasing force toward the neutral position when the pump operation piston 110 is moved from the neutral position corresponding to the neutral position of the pump movable swash plate 30 to the first and second slide directions S1 and S2 while holding the pump operation piston 110 at the neutral position in a state where no external force is applied to the pump operation piston 110.

[0090] As shown in FIG. 3, in the present embodiment, the neutral spring mechanism 120 has first and second slide springs 121 and 122 that bias the pump operation piston 110 in the first and second slide directions S1 and S2, respectively. The biasing forces of the first and second slide springs 121 and 122 are set to hold the pump operation piston 110 at the neutral position in a state where no external force is applied to the pump operation piston 110.

[0091] As shown in FIG. 3, in the present embodiment, the base end sides (the sides opposite to the tip end sides engaged with the pump operation piston 110) of the first and second slide springs 121 and 122 are engaged with a position adjustment plug, and the biasing forces of the first and second slide springs 121 and 122 can be adjusted by the position adjustment plug.

[0092] The first and second slide directions 131 and 132 are configured such that the supplied pressure oil pushes the pump operation piston 110 in the first and second slide directions S1 and S2 against the biasing force of the neutral spring mechanism 120.

[0093] In the present embodiment, the first slide oil chamber 131 is configured to push the pump operation piston 110 in the first slide direction S1 against the biasing force of the second slide spring 122 by the supplied pressure oil.

[0094] On the other hand, the second slide oil chamber 132 is configured to push the pump operation piston 110 in the second slide direction S2 against the biasing force of the first slide spring 121 by the supplied pressure oil.

[0095] As shown in FIG. 3, in the present embodiment, a pump operation piston case 115 for housing the pump operation piston 110 is connected to the HST housing 70.

[0096] Specifically, the pump operation piston case 115 is provided with a housing space for housing the pump operation piston 110, and the pump operation piston 110 is housed in the housing space in a state where it can move in the first and second slide directions while defining the first and second slide oil chambers 131 and 132.

[0097] As described above, in the present embodiment, the neutral spring mechanism 120 has the first and second slide springs 121 and 122, and the first and second slide springs 121 and 122 are disposed in the first and second slide oil chambers 131 and 132, respectively.

[0098] The motor operation piston 140 is movable in both the volume reduction direction VS on one side in the axial direction and the volume increase direction VL on the other side. In response to the movement in the volume increase direction VL, the motor volume adjuster is operated in the volume increase direction, and when positioned at the maximum volume position which is the movement end in the volume increase direction VL, the motor volume adjuster is positioned at the maximum volume position. On the other hand, in response to the movement in the volume reduction direction VS, the motor volume adjuster is tilted in the volume reduction direction, and when positioned at the minimum volume position which is the movement end in the volume reduction direction, the motor volume adjuster is positioned at the minimum volume position. It is operatively connected to the operation end of the pump volume adjuster.

[0099] As described above, in the present embodiment, the HST10 is of an axial piston type and has the motor movable swash plate 60 as the motor volume adjuster. In this case, the moving end of the motor movable swash plate 60 in the volume increasing direction around the motor rocking axis MA corresponds to the maximum volume position of the motor volume adjuster, and the moving end of the motor movable swash plate 60 in the volume decreasing direction around the motor rocking axis MA corresponds to the minimum volume position of the motor volume adjuster.

[0100] As shown in FIG. 3, in the present embodiment, the motor operation piston 140 is indirectly connected to the operation end portion of the motor volume adjuster (the operation end portion 65 of the motor movable swash plate 60 in the present embodiment) via the motor hydraulic servo mechanism 200M. The configuration of the motor hydraulic servo mechanism 200M will be described later.

[0101] The volume increasing operation spring 150 biases the motor operation piston 140 in the volume increasing direction VL toward the maximum volume position which is the initial reference position. Here, the maximum volume position of the motor operation piston 140 is the position where the motor movable swash plate 60 is positioned at the maximum volume position.

[0102] The volume decreasing operation oil chamber 160 is configured to push the motor operation piston 140 in the volume decreasing direction VS against the biasing force of the volume increasing operation spring 150 by the supplied pressure oil.

[0103] As shown in FIG. 3, in the present embodiment, a motor operation piston case 145 for housing the motor operation piston 140 is connected to the HST housing 70.

[0104] Specifically, the motor-operated piston case 145 is provided with an accommodation space for accommodating the motor-operated piston 140. The motor-operated piston 140 is accommodated in the accommodation space in a state where it can move axially in both directions while defining the volume reduction operation oil chamber 160 and the spring chamber 152 on the side opposite to the volume reduction operation oil chamber 160. The volume increase operation spring 150 is disposed in the spring chamber 152.

[0105] The continuously variable transmission structure 1A further includes a first pressure control valve 171 that commonly switches the supply and discharge of pressure oil to the first slide oil chamber 131 and the volume reduction operation oil chamber 160 in response to the operation of the transmission operation member, and a second pressure control valve 172 that switches the supply and discharge of pressure oil to the second slide oil chamber 132 in response to the operation of the transmission operation member.

[0106] The first pressure control valve 171 is configured to be able to take a supply position for supplying pressure oil from a pressure oil source to both the first slide oil chamber 131 and the volume reduction operation oil chamber 160, and a discharge position for discharging the pressure oil in both the first slide oil chamber 1311 and the volume reduction operation oil chamber 160. In the present embodiment, the first pressure control valve 171 is of a pressure reducing valve type, and is configured to increase the oil pressure in the oil chambers 131 and 160 to which pressure oil is supplied as the control current to the electromagnetic solenoid shown in FIG. 3 increases.

[0107] The second pressure control valve 172 is configured to be able to take a supply position for supplying pressure oil from a pressure oil source to the second slide oil chamber 132, and a discharge position for discharging the pressure oil in the second slide oil chamber 132. In the present embodiment, the second pressure control valve 172 is also of a pressure reducing valve type, and is configured to increase the oil pressure in the oil chamber 132 to which pressure oil is supplied as the control current to the electromagnetic solenoid shown in FIG. 3 increases.

[0108] The stepless speed change structure 1A further includes a control device (not shown) that controls the first and second pressure control valves 171 and 172 according to the operating state of the speed change operating member.

[0109] The control device performs the operation control of the first and second pressure control valves 171 and 172 based on, for example, a signal from an operation position sensor that detects the operation position of the speed change operating member.

[0110] The biasing forces of the neutral spring mechanism 120 and the volume increasing operation spring 150 are set as follows. That is, after the neutral spring mechanism 120 reaches a predetermined holding elastic state due to the movement of the pump operation piston 110 in the first slide direction S1 by the pressure oil in the first slide oil chamber 131, the motor operation piston 140 starts to move in the volume decreasing direction VS while compressing the volume increasing operation spring 150 by the pressure oil in the volume decreasing operation oil chamber 160 where the supply and discharge of the pressure oil are performed together with the first slide oil chamber 131. The biasing forces of the neutral spring mechanism 120 and the volume increasing operation spring 150 are set.

[0111] As described above, in the present embodiment, the neutral spring mechanism 120 has the first and second slide springs 121 and 122, and when the pump operation piston 110 is pushed in the first slide direction S1 from the neutral position, the second slide spring 122 is elastically deformed (compressed).

[0112] Therefore, in the present embodiment, after the second slide spring 122 reaches a predetermined compressed state due to the movement of the pump operation piston 110 in the first slide direction S1 by the pressure oil in the first slide oil chamber 131, the motor operation piston 140 starts to move in the volume decreasing direction VS while compressing the volume increasing operation spring 150 by the pressure oil in the volume decreasing operation oil chamber 160. The biasing forces of the second slide spring 122 and the volume increasing operation spring 150 are set.

[0113] In addition, in the present embodiment, the timing at which the motor operation piston 140 starts moving in the volume reduction direction VS is when the pump operation piston 110 is positioned at the first slide direction moving end, and accordingly, when the pump movable swash plate 30 is positioned at the first tilting direction moving end.

[0114] Fig. 5 shows a graph representing the relationship between the operation position of the speed change operation member, the output speed of the continuously variable transmission structure 1A (when the continuously variable transmission structure 1A is used in the traveling system transmission path of the work vehicle, the vehicle speed), the tilting position of the pump movable swash plate 30, and the tilting position of the motor movable swash plate 60.

[0115] As shown in Fig. 5, when the speed change operation member is positioned at the neutral position, the control device stops the control current to the first and second pressure control valves 171 and 172, and positions the first and second pressure control valves 171 and 172 at the discharge position.

[0116] Thereby, the pump operation piston 110 is held at the neutral position by the neutral spring mechanism 120 (in the present embodiment, the first and second slide springs 121 and 122), and the pump movable swash plate 30 is positioned at the neutral position. Therefore, the output rotational speed of the continuously variable transmission 1A becomes zero speed.

[0117] When the speed change operation member is operated from the neutral position in the second operation direction (for example, the reverse direction), the control device keeps the first pressure control valve 171 positioned at the discharge position and supplies a control current corresponding to the operation position of the speed change operation member to the second pressure control valve 172 to position the second pressure control valve 172 at the supply position according to the operation position of the speed change operation member.

[0118] Thereby, pressure oil is supplied from the pressure oil source to the second slide oil chamber 132, and the pump operation piston 110 is pushed in the second slide direction S2 while elastically deforming the neutral spring mechanism 120 (in the present embodiment, while compressing the first slide spring 121).

[0119] That is, as the shift operation member is operated from the neutral position in the second operation direction (e.g., the reverse direction), the pump movable swash plate 30 is tilted from the neutral position in the second tilting direction, and the output of the continuously variable transmission structure 1A is increased in speed in the second direction (e.g., the reverse direction) from zero speed to the maximum speed Rmax in the second direction.

[0120] On the other hand, when the shift operation member is operated from the neutral position in the first operation direction (e.g., the forward direction), the control device supplies a control current corresponding to the operation position of the shift operation member to the first pressure control valve 171 while keeping the second pressure control valve 172 in the discharge position, and positions the first pressure control valve 171 in the supply position according to the operation position of the shift operation member.

[0121] Thereby, pressure oil is supplied from the pressure oil source to the first slide oil chamber 131 and the volume reduction operation oil chamber 160. The pump operation piston 110 receives a pressing force in the first slide direction, and the motor operation piston 140 receives a pressing force in the volume reduction direction VS.

[0122] As described above, after the neutral spring mechanism (the second slide spring 132 in the present embodiment) reaches a predetermined holding elastic state due to the movement of the pump operation piston 110 in the first slide direction S1 by the pressure oil in the first slide oil chamber 131, the motor operation piston 140 starts to move in the volume reduction direction VS while compressing the volume increase operation spring 150 by the pressure oil in the volume reduction operation oil chamber 160. The biasing forces of the neutral spring mechanism (the second slide spring 132 in the present embodiment) and the volume increase operation spring 150 are set.

[0123] Therefore, by supplying pressure oil from the pressure oil source to the first slide oil chamber 131 and the volume reduction operation oil chamber 160, first, only the pump operation piston 110 is pushed in the first slide direction S1 while elastically deforming the neutral spring mechanism 120 (while compressing the second slide spring 122 in the present embodiment).

[0124] Here, in the present embodiment, the predetermined holding elastic state of the neutral spring mechanism 120 (the second slide spring 132 in the present embodiment) means a state that appears when the pump operation piston 110 is moved in the first slide direction S1 to the first slide direction moving end that positions the pump volume adjuster at the first operation direction moving end (the operation position that makes the pump body 20 have the maximum volume).

[0125] That is, when the shift operation member is operated from the neutral position to the motor volume switching start position (the operation position that positions the pump volume adjuster at the first operation direction moving end. In the present embodiment, it is the operation position that positions the pump movable swash plate 30 at the first tilting direction moving end), the motor volume adjuster (the motor movable swash plate 60) remains held at the maximum volume position, and the pump volume adjuster (the pump movable swash plate 30) is tilted from the neutral position in the first operation direction (the first tilting direction) (to the first tilting direction moving end in the present embodiment) according to the operation of the shift operation member to the motor volume switching start position. As a result, the output of the continuously variable transmission structure 1A is increased in speed from zero speed to a predetermined speed (the first direction intermediate speed Fc) in the first direction (for example, the forward direction).

[0126] When the shift operation member is further operated in the first operation direction from the motor volume switching start position, the hydraulic pressures in the first slide oil chamber 121 and the volume reducing oil chamber 160 are further increased. Here, since the pump operation piston 110 has been moved to the first slide direction moving end, the neutral spring mechanism 120 (the second slide spring 122) remains in the predetermined holding elastic state.

[0127] Therefore, when the shift operation member is operated in the first operation direction beyond the motor volume switching start position (the maximum volume position in the first direction of the pump in the present embodiment), as the shift operation member approaches the operation end in the first operation direction, the motor operation piston 140 is pushed in the volume decreasing direction VS against the biasing force of the volume increasing operation spring 150 by the pressure oil in the volume decreasing oil chamber 160. When the shift operation member is positioned at the operation end in the first operation direction, the motor operation piston 140 is positioned at the minimum volume position, and the motor movable swash plate 60 is positioned at the minimum volume position. As a result, the output of the continuously variable transmission structure 1A becomes the highest speed Fmax in the first direction.

[0128] Thus, in the continuously variable transmission structure 1A according to the present embodiment, without requiring a complicated mechanical link mechanism that was necessary in the past, when the shift operation member is operated between the operation end in the second operation direction and the motor volume switching start position, while holding the motor movable swash plate 60 at the maximum volume position, by tilting the pump movable swash plate 30 to a tilting position corresponding to the operation position of the shift operation member, a desired output speed can be obtained. Further, when the shift operation member is operated between the motor volume switching start position and the operation end in the first operation direction, while holding the pump movable swash plate 30 at the moving end in the first tilting direction, by tilting the motor movable swash plate 60 to a tilting position corresponding to the operation of the shift operation member, a desired high-speed output state can be obtained.

[0129] In the present embodiment, the timing at which the motor operation piston 140 starts to move in the volume decreasing direction is set to be the time when the pump operation piston 110 is positioned at the moving end in the first slide direction. However, the present invention is not limited to such a configuration.

[0130] For example, it is also possible to set the biasing forces of the neutral spring mechanism 120 (the second slide spring 122 in the present embodiment) and the volume increasing operation spring 150 so that the motor operation piston 140 starts to move in the volume decreasing direction when the pump operation piston 110 reaches an arbitrary position before the moving end in the first slide direction.

[0131] The biasing force of this spring can be set, for example, by replacing the corresponding spring 150 or changing the thickness of the shim interposed between the base of the spring 150 and the spring chamber 152.

[0132] Alternatively, the biasing force of the corresponding spring 150 can also be set to a desired value according to the modification shown in FIG. 6. FIG. 6 is a partial cross-sectional view of the continuously variable transmission structure 1B according to a modification of the present embodiment, and is a partial cross-sectional view of a portion corresponding to the VI portion in FIG. 3. As shown in FIG. 6, the continuously variable transmission structure 1B has a biasing force adjustment mechanism 155 for adjusting the biasing force of the corresponding spring 150.

[0133] The biasing force adjustment mechanism 155 includes a spring receiver 156 that can engage with the proximal end side of the corresponding spring 150, and the spring receiver 156 is configured such that its fixed position can be adjusted artificially from the outside. The biasing force of the corresponding spring 150 can be set to a desired value by the spring receiver 156. Note that reference numeral 157 in FIG. 6 is a lock nut for holding the spring receiver 156 in a fixed position.

[0134] In the present embodiment, the pump operation piston 110 is configured to reach the first slide direction movement end and then the motor operation piston 140 starts to move in the volume decreasing direction. However, it is also possible to operate the pump operation piston 110 (i.e., the pump movable swash plate 30) and the motor operation piston 140 (i.e., the motor movable swash plate 60) at different timings.

[0135] Fig. 7 shows a graph representing the relationship between the operating position of the shift operation member, the output speed of the continuously variable transmission structure 1A (vehicle speed when the continuously variable transmission structure 1A is used in the traveling system transmission path of the work vehicle), the tilting position of the pump movable swash plate 30, and the tilting position of the motor movable swash plate 60 when the pump operation piston 110 and the motor operation piston 140 are configured to operate in another operation pattern (first modified pattern).

[0136] The first modified pattern is configured such that when the pump operation piston 110 reaches an arbitrary position before the first slide direction moving end, the motor operation piston 140 starts to move in the volume decreasing direction.

[0137] In the first modified pattern, as shown in Fig. 7, · When the shift operation member is positioned between the second operation direction operation end and the motor volume switching start position, the motor operation piston 140 is held at the maximum volume position to keep the motor movable swash plate 60 at the maximum volume position, and as the shift operation member is operated in the first operation direction, the pump operation piston 110 is pushed in the first slide direction S1 to tilt the pump movable swash plate 30 in the first tilting direction, · When the shift operation member reaches the motor volume switching start position, the motor operation piston 140 is held at the maximum volume position, and the pump operation piston 110 is positioned at an intermediate position before the first slide direction moving end to position the pump movable swash plate 30 at an intermediate position in the first tilting direction before the first tilting direction moving end, · When the shift operation member is positioned between the motor volume switching start position and the first operation direction pump maximum volume operation position, as the shift operation member is operated in the first operation direction, the pump operation piston 110 is pushed from the intermediate position to the first slide direction moving end to move the pump movable swash plate 30 from the intermediate position in the first tilting direction to the first tilting direction moving end, and the motor operation piston 140 is pushed in the volume decreasing direction from the maximum volume position to the intermediate volume position to move the motor movable swash plate from the maximum volume position in the volume decreasing direction, The biasing forces of the neutral spring mechanism 120 and the volume increasing spring 150 are set.

[0138] In the first deformation pattern, the output of the continuously variable transmission structure 1A is shifted from the maximum speed Rmax in the second direction to the first intermediate speed Fc1 in the first direction via a vehicle speed of zero as the pump movable swash plate 30 is moved in the first tilting direction from the second tilting direction moving end to the first tilting direction intermediate position while the motor movable swash plate 60 is held at the maximum volume position.

[0139] Next, the output of the continuously variable transmission structure 1A is shifted from the first intermediate speed Fc1 in the first direction to the second intermediate speed Fc2 in the first direction as the pump movable swash plate 30 is moved from the first tilting direction intermediate position to the first tilting direction moving end and the motor movable swash plate 60 is moved from the maximum volume position to the intermediate volume position.

[0140] Then, the output of the continuously variable transmission structure 1A is shifted from the second intermediate speed Fc2 in the first direction to the maximum speed Fmax in the first direction as the pump movable swash plate 30 is held at the first tilting direction moving end and the motor movable swash plate 60 is moved from the intermediate volume position to the minimum volume position.

[0141] Also with such a first deformation pattern, the tilting operations of the pump movable swash plate 30 and the motor movable swash plate 60 are continuously performed without interruption, and it is possible to effectively prevent or reduce the jerking of the output speed (travel speed) during the switching transient period.

[0142] FIG. 8 shows a graph representing the relationship between the operation position of the shift operation member, the output speed of the continuously variable transmission structure 1A (the vehicle speed when the continuously variable transmission structure 1A is used in the transmission path of the traveling system of the work vehicle), the tilting position of the pump movable swash plate 30, and the tilting position of the motor movable swash plate 60 when the pump operation piston 110 and the motor operation piston 140 are configured to be operated in still another operation pattern (second deformation pattern).

[0143] When the pump operation piston 110 reaches an arbitrary position before the moving end in the first slide direction, the motor operation piston 140 is configured to start moving in the volume decreasing direction in the second deformation pattern.

[0144] When the speed change operation member is positioned between the operation end in the second operation direction and the motor volume switching start position, the second deformation example shown in FIG. 8 performs the same speed change operation as the first deformation example shown in FIG. 7.

[0145] That is, when the speed change operation member is being operated between the operation end in the second operation direction and the motor volume switching start position, the motor operation piston 140 is held at the maximum volume position to position the motor movable swash plate 60 at the maximum volume position. As the speed change operation member is operated in the first operation direction, the pump operation piston 110 is pushed in the first slide direction S1 to tilt the pump movable swash plate 30 in the first tilting direction. When the speed change operation member reaches the motor volume switching start position, the pump operation piston 110 is positioned at an intermediate position before the moving end in the first slide direction, and the pump movable swash plate 30 is positioned at an intermediate position in the first tilting direction before the moving end in the first tilting direction. The biasing forces of the neutral spring mechanism 120 and the volume increasing spring 150 are set accordingly.

[0146] On the other hand, when the speed change operation member is positioned between the motor volume switching start position and the operation end in the first operation direction, the second deformation example shown in FIG. 8 performs a speed change operation different from that of the first deformation example shown in FIG. 7.

[0147] That is, in the second deformation example, when the speed change operation member is positioned between the motor volume switching start position and the operation end in the first operation direction, as the speed change operation member is operated in the first operation direction, the pump movable swash plate 30 is tilted toward the moving end in the first tilting direction while the motor movable swash plate 60 is tilted from the maximum volume position toward the minimum volume position.

[0148] When the shift operation member is positioned at the operation end in the first operation direction, the pump movable swash plate 30 is positioned at the movement end in the first tilting direction and the motor movable swash plate 60 is positioned at the minimum volume position.

[0149] In the second modification, the output of the continuously variable transmission structure 1A is shifted from the maximum speed Rmax in the second direction via vehicle speed zero to the first intermediate speed Fc1 in the first direction as the pump movable swash plate 30 is moved from the movement end in the second tilting direction to the intermediate position in the first tilting direction in the first tilting direction while the motor movable swash plate 60 is held at the maximum volume position. As the pump movable swash plate 30 is moved from the intermediate position in the first tilting direction to the movement end in the first tilting direction and the motor movable swash plate 60 is moved from the maximum volume position to the minimum volume position, the speed is increased from the first intermediate speed Fc1 in the first direction to the maximum speed Fmax in the first direction.

[0150] Also in such a second modification, the tilting operations of the pump movable swash plate 30 and the motor movable swash plate 60 are continuously performed without interruption, and it is possible to effectively prevent or reduce the jerky change in the output speed (travel speed) during the switching transient period.

[0151] Here, the pump hydraulic servo mechanism 200P and the motor hydraulic servo mechanism 200M will be described.

[0152] As shown in FIG. 3 and the like, the pump hydraulic servo mechanism 200P includes a pump servo piston 210P, first and second servo oil chambers 220P1 and 220P2, and a pump servo switching valve 230P.

[0153] The pump servo piston 210P is movable in both the first servo direction SV1 on one side in the axial direction and the second servo direction SV2 on the other side, and is engaged with the operation end portion 35 of the pump movable swash plate 30 so as to tilt the pump movable swash plate 30 in the first and second tilting directions around the pump swing axis PA in response to the movement in the first and second servo directions SV1 and SV2.

[0154] The first and second servo oil chambers 220P1 and 220P2 are configured to push the pump servo piston 210P in the first and second servo directions SV1 and SV2, respectively, by the supplied pressure oil.

[0155] In the present embodiment, as shown in FIGS. 2 and 3, a pump servo space is formed in the housing main body 75, and the pump servo piston 210P is accommodated in the pump servo space so as to be movable in both the first and second servo directions SV1 and SV2 while defining the first and second servo oil chambers 220P1 and 220P2.

[0156] The pump servo switching valve 230P takes a holding position, a first servo position, and a second servo position relative to the pump servo piston 210P. When it is located at the first servo position, it guides the pressure oil from the pressure oil source to the first servo oil chamber 220P1 while discharging the pressure oil in the second servo oil chamber 220P2. When it is located at the second servo position, it discharges the pressure oil in the first servo oil chamber 220P1 while guiding the pressure oil from the pressure oil source to the second servo oil chamber 220P2. When it is located at the holding position, it is configured to block the first and second servo oil chambers 220P1 and 220P2.

[0157] The pump servo switching valve 230P is operatively connected to the pump operation piston 110 so as to take the first and second servo positions in response to the movement of the pump operation piston 110 in the first and second slide directions S1 and S2, respectively.

[0158] In the present embodiment, a central hole is formed in the pump servo piston 210P along the axial direction, and the pump servo switching valve 230P is accommodated in the central hole so as to be axially movable in both directions while being connected to the pump operation piston 110 via a pump connection rod 250P inserted into an access opening formed in the pump servo piston 210P. Here, the pump servo switching valve 230P is interlocked with the pump operation piston 110 via the pump connection rod 250P without play.

[0159] As shown in FIG. 3 and the like, the motor hydraulic servo mechanism 200M includes a motor servo piston 210M, a volume increasing servo spring 240M, a volume decreasing servo oil chamber 220M, and a motor servo switching valve 230M.

[0160] The motor servo piston 210M is movable in both the volume decreasing servo direction SVS on one side in the axial direction and the volume increasing servo direction SVL on the other side.

[0161] As the motor servo piston 210M moves in the volume decreasing servo direction SVS, it tilts the motor movable swash plate 60 in the volume decreasing direction around the motor rocking axis MA, and when it is positioned at a predetermined minimum volume servo position, it positions the motor movable swash plate 60 at the minimum volume position. On the other hand, as the motor servo piston 210M moves in the volume increasing servo direction SVL, it tilts the motor movable swash plate 60 in the volume increasing direction around the motor rocking axis MA, and when it is positioned at a predetermined maximum volume servo position, it positions the motor movable swash plate 60 at the maximum volume position. It is engaged with the operating end portion 65 of the motor movable swash plate 60.

[0162] The volume increasing servo spring 240M biases the motor servo piston 210M in the volume increasing servo direction SVL toward the maximum volume servo position.

[0163] The volume decreasing servo oil chamber 220M is configured to push the motor servo piston 210M in the volume decreasing servo direction SVS against the biasing force of the volume increasing servo spring 240M by the supplied pressure oil.

[0164] In the present embodiment, as shown in FIGS. 2 and 3, a motor servo space is formed in the housing main body 75, and the motor servo piston 210M defines a spring chamber 245 disposed on the opposite side in the axial direction from the volume decreasing servo oil chamber 220M and the volume decreasing servo oil chamber 220M, and is accommodated in the motor servo space so as to be movable in both the volume decreasing servo direction SVS and the volume increasing servo direction SVL. The volume increasing servo spring 240 is housed in the spring chamber 245.

[0165] The motor servo switching valve 230M takes a holding position, a volume decreasing position, and a volume increasing position relative to the motor servo piston 210M. When it is positioned at the volume decreasing position, it guides the pressure oil from the pressure oil source to the volume decreasing servo oil chamber 220M while discharging the pressure oil in the spring chamber, and when it is positioned at the volume increasing position, it discharges the pressure oil in the volume decreasing servo oil chamber 220M while guiding the pressure oil from the pressure oil source to the spring chamber 245. When it is positioned at the holding position, it is configured to block the volume decreasing servo oil chamber 220M and the spring chamber 245.

[0166] The motor servo switching valve 230M is operatively connected to the motor operating piston 140 so as to take the volume increasing position and the volume decreasing position respectively in response to the movement of the motor operating piston 140 in the volume increasing direction VL and the volume decreasing direction VS.

[0167] In the present embodiment, a central hole is formed in the motor servo piston 210M along the axial direction, and the motor servo switching valve 230M is accommodated in the central hole so as to be axially movable in both directions while being connected to the motor operating piston 140 via a motor connecting rod 250M inserted into an access opening formed in the motor servo piston 210M. Here, the motor servo switching valve 230M is interlocked with the motor operating piston 140 via the motor connecting rod 250M without play.

[0168] In the present embodiment, the pressure oil for pushing the pump operating piston 110 and the motor operating piston 140 is taken out from the charge line.

[0169] Fig. 9 shows a hydraulic circuit diagram of the continuously variable transmission structure 1A. As shown in FIGS. 1, 3, and 9, the stepless transmission structure 1A includes a pressure oil supply line 180 having a base end fluid-connected to the charge line (the charge oil passage 82), a first supply / discharge line 181 having a tip end fluid-connected to the first slide oil chamber 131 and the volume reduction operation oil chamber 160, and a second supply / discharge line 182 having a tip end fluid-connected to the second slide oil chamber 132.

[0170] When the first pressure control valve 171 is in the supply position, it is configured to fluid-connect the first supply / discharge line 181 to the pressure oil supply line 180, and when in the discharge position, it is configured to drain the first supply / discharge line 181.

[0171] Also, when the second pressure control valve 172 is in the supply position, it is configured to fluid-connect the second supply / discharge line 182 to the pressure oil supply line 180, and when in the discharge position, it is configured to drain the second supply / discharge line 182.

[0172] In this embodiment, the pressure oil supplied to the pump hydraulic servo mechanism 200P and the motor hydraulic servo mechanism 200M is also taken out from the charge line (the charge oil passage 82).

[0173] That is, the stepless transmission structure 1A has a pump servo line 185P that fluid-connects the pressure oil supply line 180 to the inlet port of the pump servo switching valve 230P, and a motor servo line 185M that fluid-connects the pressure oil supply line 180 to the inlet port of the motor servo switching valve 230M.

[0174] Embodiment 2 Hereinafter, a stepless transmission structure according to another embodiment of the present invention will be described with reference to the accompanying drawings. FIG. 10 shows a partial cross-sectional view of the stepless transmission structure 2A according to this embodiment, which is a cross-sectional view corresponding to FIG. 3 in Embodiment 1. In the figure, the same members as those in Embodiment 1 are denoted by the same reference numerals, and the description thereof will be omitted as appropriate.

[0175] The continuously variable transmission structure 2A according to this embodiment is different from the continuously variable transmission structure 1A according to Embodiment 1 mainly in that the pump hydraulic servo mechanism 200P and the motor hydraulic servo mechanism 200M are deleted, and the pump operation piston 110 and the motor operation piston 140 are changed to the pump operation piston 310 and the motor operation piston 320.

[0176] That is, as shown in FIG. 10, in this embodiment, the pump operation piston 310 is mechanically connected to the operation end portion 35 of the pump movable swash plate 30 so as to tilt the pump movable swash plate 30 in the first and second tilting directions around the pump swing axis PA in accordance with the movement in the first and second slide directions S1, S2.

[0177] Further, the motor operation piston 320 is mechanically connected to the operation end portion 65 of the motor movable swash plate 60 so as to tilt the motor movable swash plate 60 in the volume decrease direction and the volume increase direction around the motor swing axis MA in accordance with the movement in the volume decrease direction VS and the volume increase direction VL.

[0178] The continuously variable transmission structure 2A according to this embodiment has a neutral spring mechanism 330 instead of the neutral spring mechanism 120 (the first and second slide springs 121, 122) as compared with the continuously variable transmission structure 1A.

[0179] The pump operation piston 310 is different from the pump operation piston 110 in that it has a hollow portion along the first and second slide directions S1, S2.

[0180] The neutral spring mechanism 330 includes a support rod 340 that extends along the first and second slide directions S1 and S2 and is supported by the pump operation piston case 115 so that the tip side enters the hollow portion, a tip-side spring receiver 350 and a base-end-side spring receiver 360 that are located within the hollow portion and are axially relatively movable with respect to the support rod 340, and are respectively supported on the tip side and the base end side of the support rod 340, a tip-side stop portion 355 provided on the support rod 340 so as to define a moving end of the tip-side spring receiver 350 toward the tip side with respect to the support rod 340, a base-end-side stop portion 365 provided on the support rod 340 so as to define a moving end of the base-end-side spring receiver 360 toward the base end side with respect to the support rod 340, and a single biasing spring 370 having a tip side locked to the tip-side spring receiver 350 and a base end side locked to the base-end-side spring receiver 360.

[0181] In the present embodiment, when the hydraulic pressure in the oil chamber located on the tip side of the support rod 340 (the first slide oil chamber 121 in the present embodiment) among the first and second slide oil chambers 121 and 122 increases, the pump operation piston 310, together with the tip-side spring receiver 350, expands the oil chamber located on the tip side of the support rod 340 (the first slide oil chamber 121) and is pushed in a direction (the first slide direction S1 in the present embodiment) to reduce the opposite oil chamber (the second slide oil chamber 122).

[0182] At this time, since the movement of the base-end-side spring receiver 360 toward the base end side of the support rod 340 is stopped by the base-end-side stop portion 365, as the pump operation piston 310 is pushed in a direction (the first slide direction S1 in the present embodiment) to expand the oil chamber located on the tip side of the support rod 340 and reduce the opposite oil chamber, the elastic amount (compression amount) held by the biasing spring 370 increases.

[0183] Here, the biasing force of the biasing spring 370 is set such that, after the biasing spring 370 reaches a predetermined holding elastic state due to the movement of the pump operation piston 310 in the first slide direction S1, the motor operation piston 140 starts to move in the volume reduction direction VS while elastically deforming the volume increase operation spring 150 by the pressure oil in the volume reduction operation oil chamber 160.

[0184] In addition, as shown in FIG. 10, in the present embodiment, the pump operation piston case 115 and the motor operation piston case 145 are integrally formed.

[0185] Further, reference numeral 190 in FIG. 10 is a drive source, and reference numeral 192 is a hydraulic pump that is driven by the drive source 190 and discharges pressure oil to the charge line.

[0186] Embodiment 3 Hereinafter, a continuously variable transmission structure according to another embodiment of the present invention will be described with reference to the accompanying drawings. FIG. 11 shows a partial cross-sectional view of a continuously variable transmission structure 3A according to the present embodiment, which is a cross-sectional view corresponding to FIG. 2 in the first embodiment. FIG. 12 shows a cross-sectional view taken along line XII-XII in FIG. 11. Further, FIG. 13 shows a cross-sectional view taken along line XIII-XIII in FIG. 12. In the drawings, the same members as those in the first and second embodiments are denoted by the same reference numerals, and the description thereof will be omitted as appropriate.

[0187] The continuously variable transmission structure 3A includes the HST 10, a shift operation member 410, a pump hydraulic servo mechanism 200P, a pump operation connection mechanism 430, and a motor operation connection mechanism.

[0188] As shown in FIGS. 11 and 13, the shift operation member 410 is operable bidirectionally about the axis between a first operation direction maximum operation position D1max on one side and a second operation direction maximum operation position D2max on the other side with respect to the neutral position N interposed therebetween.

[0189] In the present embodiment, the shift operation member 410 includes an operation shaft 412 rotatable about an axis, and an operation arm 414 connected to the operation shaft 412 so as to be rotatable about the axis by an external operation.

[0190] The pump operation connection mechanism 430 has a pump spool 450 movable in a first slide direction S1 on one side in the axial direction and a second slide direction S2 on the other side.

[0191] The motor operation connection mechanism is coaxially and serially arranged on one side in the axial direction of the pump spool 430, and includes a motor spool 480 movable in both a volume reduction direction VS on one side in the axial direction and a volume increase direction VL on the other side, a volume increase operation spring 490 biasing the motor spool 480 in the volume increase direction VL, and a motor spool maximum volume position setting member 495 directly or indirectly setting a motor spool maximum volume position which is a moving end of the motor spool 480 in the volume increase direction. The motor swash plate 60 is configured to be tilted in a volume reduction direction on one side and a volume increase direction on the other side about the motor swing axis MA in accordance with the movement of the motor spool 480 in the volume reduction direction and the volume increase direction.

[0192] In the present embodiment, as shown in FIGS. 11 and 12, a spool case 500 having a spool accommodation space for integrally accommodating the pump spool 450 and the motor spool 480 is connected to the HST housing 70. The operation shaft 412 is supported by the spool case 500 in a state where an inner end portion extends into a space provided at a connection portion between the spool case 500 and the HST housing 70 and an outer end portion extends outward.

[0193] In the present embodiment, the pump operation connection mechanism 430 has the pump hydraulic servo mechanism 200P. The pump hydraulic servo mechanism 200P is configured to tilt the pump movable swash plate 30 in the first and second tilting directions in response to operations of the shift operation member 410 in the first and second operation directions D1 and D2.

[0194] That is, in the present embodiment, the pump hydraulic servo mechanism 200P is operatively connected to the shift operation member 410 so as to position the pump movable swash plate 30 at the neutral position in response to an operation of the shift operation member 410 to the neutral position N and to tilt the pump movable swash plate 30 in the first and second tilting directions in response to operations of the shift operation member 410 in the first and second operation directions D1 and D2.

[0195] In the present embodiment, as shown in FIGS. 11 to 13, the pump operation connection mechanism 430 further includes a relay arm 432 connected to the inner end portion of the operation shaft 412, and a pump servo engagement pin 435 provided on the free end side of the relay arm 432. The pump servo engagement pin 435 is engaged with the pump servo switching valve 230P through the access opening formed in the pump servo piston 210P.

[0196] The relay arm 432 and the pump servo engagement pin 435 are disposed in the space provided at the connecting portion of the spool case 500 and the HST housing 70.

[0197] The pump servo engagement pin 435 is engaged with the pump servo switching valve 230P such that when the shift operation member 410 is operated in the first operation direction D1, the pump servo switching valve 230P is positioned at the first servo position, and when the shift operation member 410 is operated in the second operation direction D2, the pump servo switching valve 230P is positioned at the second servo position.

[0198] The pump spool 450 assumes a pump spool neutral position in response to an operation of the shift operation member 410 to the neutral position N, and moves from the pump spool neutral position to a first slide direction moving end on one side in the axial direction and a second slide direction moving end on the other side in the axial direction in response to operations of the shift operation member 410 from the neutral position N to the operation ends D1max and D2max in the first and second operation directions, respectively, and is operatively connected to the shift operation member 410.

[0199] Specifically, the pump operation connection mechanism 430 is further provided with a pump spool engagement pin 440 having a base end connected to the relay arm 432 and a front end engaged with the pump spool 450.

[0200] The pump spool engagement pin 440 engages with the pump spool 450 so as to position the pump spool 450 at the pump spool neutral position in response to an operation of the shift operation member 410 to the neutral position N, move the pump spool from the pump spool neutral position to the first slide direction moving end in response to an operation of the shift operation member 410 from the neutral position N to the operation end D1max in the first operation direction, and move the pump spool 450 from the pump spool neutral position to the second slide direction moving end in response to an operation of the shift operation member 410 from the neutral position N to the operation end D2max in the second operation direction.

[0201] In the present embodiment, as shown in FIG. 12, the pump spool 450 includes a first spool 451 that is pushed in the first slide direction S1 via the pump engagement pin 440 when the shift operation member 410 is operated from the neutral position N in the first operation direction D1, and a second spool 452 that is separate from the first spool 451 and is pushed in the second slide direction S2 when the shift operation member 410 is operated from the neutral position N in the second operation direction D2.

[0202] Furthermore, in the continuously variable transmission structure 3A according to the present embodiment, a neutral spring mechanism 460 is provided that directly or indirectly holds the pump pulley 450 at the pump pulley neutral position and generates a biasing force directed toward the pump pulley neutral position directly or indirectly on the pump pulley 450 when the pump pulley 450 is moved from the pump pulley neutral position in the first and second slide directions S1 and S2.

[0203] In the present embodiment, the neutral spring mechanism 460 includes a support rod 462 having a shaft portion 463 supported by the spool case 500 so as to extend along the slide direction within the slide range of the pump pulley 450, a first slide spring 471 that biases the second spool 452 in the first slide direction S1, and a second slide spring 472 that biases the first spool 451 in the second slide direction S2.

[0204] A through hole extending in the slide direction of the pump pulley 450 is formed in the spool case 500, and the spool accommodation space is formed by closing the side of the pump pulley 450 and the side of the motor pulley 480 of the through hole with first and second lid members 511 and 513, respectively.

[0205] In addition to the shaft portion 463, the support rod 462 has an intermediate locking portion 465 having a larger diameter than the shaft portion 462 provided between the tip side and the base end side of the shaft portion 463, and a tip locking portion 467 having a larger diameter than the shaft portion 462 provided on the tip side of the shaft portion 463.

[0206] The first and second spools 451 and 452 are externally inserted and supported on the shaft portion 463 on both sides in the axial direction with the intermediate locking portion 465 interposed therebetween.

[0207] The first spool 451 is externally inserted and supported on the shaft portion 463 so as to be axially movable between the intermediate locking portion 465 and the tip locking portion 467. On the other hand, the second spool 452 is externally inserted and supported so as to be axially movable on the shaft portion 463 between the intermediate locking portion 465 and the first lid member 511.

[0208] Then, the second slide spring 472 is inserted between the tip locking portion 467 and the first spool 451, and biases the first spool 451 in the second slide direction S2 toward the intermediate locking portion 465. Also, the first slide spring 471 is inserted between the first lid member 511 and the intermediate locking portion 465, and biases the second spool 452 in the first slide direction S1 toward the intermediate locking portion 465.

[0209] With such a configuration, the pump spool 450 moves as follows according to the operation of the speed change operation member 410.

[0210] When the speed change operation member 410 is operated from the neutral position N in the first operation direction D1, the second spool 452 remains pressed against the intermediate locking portion 465 by the first slide spring 471, and the first spool 452 is moved in the first slide direction S1 against the biasing force of the second slide spring 472 according to the operation amount of the speed change operation shaft 410 via the pump operation connection mechanism 430.

[0211] When the operating force on the speed change operation shaft 410 is released in a state where the speed change operation shaft 410 is located in a region on the first operation direction side from the neutral position or the speed change operation shaft 410 is operated in the second operation direction S2, the first spool 451 is returned in the second slide direction S2 by an amount corresponding to the operation amount of the speed change operation member 410 in the second operation direction D2 by the biasing force of the second slide spring 471.

[0212] On the one hand, when the shift operation member 410 is operated from the neutral position N in the second operation direction D2, the first spool 451 remains pressed against the intermediate locking portion 465 by the second slide spring 471, and the second spool 452 is pushed in the second slide direction S2 against the biasing force of the first slide spring 471 according to the operation amount of the shift operation shaft 410 via the pump operation connection mechanism 430.

[0213] When the operating force on the shift operation shaft 410 is released in a state where the shift operation shaft 410 is located in a region on the second operation direction side from the neutral position N or the shift operation shaft 410 is operated in the first operation direction D1, the second spool 452 is returned in the first slide direction S1 by an amount corresponding to the operation amount of the shift operation member 410 in the first operation direction D1 by the biasing force of the first slide spring 471.

[0214] In the present embodiment, the neutral spring mechanism 460 is configured to directly bias the pump spool 450 to the pump spool neutral position. Instead, it is also possible to configure the shift operation member 410 to be biased to the neutral position N so as to indirectly bias the pump spool 450 to the pump spool neutral position.

[0215] In this case, the pump spool 450 is a single member, and the pump engagement pin 440 is connected to the single pump spool 450 such that the single pump spool 450 moves in the first and second slide directions S1 and S2 according to the operation of the shift operation member 410 in the first and second operation directions D1 and D2.

[0216] The motor spool 480 is coaxially arranged in series on one side in the axial direction of the pump spool 450 and is movable in both the volume reduction direction VS on one side in the axial direction and the volume increase direction VL on the other side.

[0217] As described above, in the present embodiment, the motor spool 480 is coaxially arranged on one axial side of the pump spool 450 within the spool accommodation space of the spool case 500.

[0218] The volume increasing direction spring 490 biases the motor spool 480 in the volume increasing direction VL. In the present embodiment, the volume increasing direction spring 490 is disposed between the motor spool 480 and the second lid member 513.

[0219] The motor spool maximum volume position setting member 495 directly or indirectly sets the spool maximum volume position which is the end in the volume increasing direction of the motor spool 480. In the present embodiment, the support rod 462 of the neutral spring mechanism 460 is also used as the motor spool maximum volume position setting member 495.

[0220] That is, the motor spool 480 biased in the volume increasing direction VL by the volume increasing direction spring 490 engages with the tip locking portion 467 of the support rod 460, thereby defining the motor spool maximum volume position.

[0221] In the present embodiment, the motor operation connection mechanism further has the motor hydraulic servo mechanism 200M. The motor hydraulic servo mechanism 200M is configured to tilt the motor movable swash plate 60 in the volume decreasing direction on one side and the volume increasing direction on the other side around the motor swing axis MA in accordance with the movement of the motor spool 480 in the volume decreasing direction VS and the volume increasing direction VL.

[0222] That is, in the present embodiment, the motor servo switching valve 230M is operatively connected to the motor spool 480 so as to take the volume decreasing position and the volume increasing position respectively in accordance with the movement of the motor spool 480 in the volume increasing direction VL and the volume decreasing direction VS.

[0223] As shown in FIG. 12, between the pump pool 450 positioned at the pump pool neutral position and the motor pool 480 positioned at the motor pool maximum volume position, a flexible portion 520 is provided that allows the pump pool 450 to move a predetermined distance in the first slide direction while keeping the motor pool 480 at the motor pool maximum volume position.

[0224] In the present embodiment, when the pump pool 450 is positioned to the slide position where the pump pool 450 positions the pump movable swash plate 30 at the first tilting direction moving end via the pump hydraulic servo mechanism 200P, the axial length of the flexible portion 520 is set so that the pump pool 450 is positioned at the end of the flexible portion 520 (that is, so that the pump pool 450 abuts on the motor pool 480).

[0225] That is, when the shift operation member 410 is operated from the neutral position N in the first operation direction D1 and reaches the motor volume switching start position (the pump first direction maximum volume position P1max in the present embodiment) before reaching the first operation direction operation end D1max, the shift operation connection mechanism 430 is configured so that the pump pool 450 moves to the slide position where the pump pool 450 positions the pump movable swash plate 30 at the first tilting direction moving end via the pump hydraulic servo mechanism 200P.

[0226] And at this time, the axial length of the flexible portion 520 is set so that the pump pool 450 abuts on the motor pool 480.

[0227] Therefore, while the pump pool 450 is being moved within the range where it does not abut on the motor pool 480, only the pump pool 450 moves while the motor pool 480 is held at the motor pool maximum volume position by the volume increasing direction spring 490, and when the pump pool 450 moves beyond the flexible portion 520 in the first slide direction, the pump pool 450 pushes the motor pool 480 in the volume decreasing direction.

[0228] Figure 14 shows a cross-sectional view of the pump sump 450, the motor sump 480, the pump hydraulic servo mechanism 200P, and the motor hydraulic servo mechanism 200M. Figure 14(a) shows a state in which the pump sump 450 is moved from the pump sump neutral position shown in FIG. 12 to a position where it abuts against the motor sump 480 in the first slide direction. Figure 14(b) shows, in a mirror image relationship with FIG. 14(a), a state in which the pump sump 450 has passed through the accommodation portion 520 and is moved in the first slide direction (the volume reduction direction VS for the motor sump 480) together with the motor sump 480.

[0229] That is, the shift operation member 410 is operable between the first operation direction operation end D1max and the second operation direction operation end D2max. When it is positioned at the neutral position N between the first and second operation direction operation ends D1max and D2max, the pump hydraulic servo mechanism 200P operates neutrally via the shift operation link mechanism 430, and the pump movable swash plate 30 is positioned at the neutral position (see FIG. 12).

[0230] First, the case where the shift operation member 410 is operated from the neutral position N in the second operation direction D2 will be described. When the shift operation member 410 is operated from the neutral position N in the second operation direction D2, the pump servo switching valve 230P moves in a direction corresponding to the operation direction of the shift operation member 430 via the pump operation link mechanism 430.

[0231] As a result, the pump servo switching valve 230P relatively moves from the relatively neutral state with respect to the pump servo piston 210P in the direction corresponding to the second operation direction D2, the pressure oil supply state to the second servo oil chamber 220P2 appears, and the pump servo piston 210P is pushed in the second servo direction SV2 to tilt the pump movable swash plate 30 in the second tilting direction.

[0232] When the pump movable swash plate 30 is moved to the tilting position corresponding to the operating position of the shift operating member 410, the pump servo switching valve 230P and the pump servo piston 210P will return to the relatively neutral state, and the first and second servo oil chambers 220P1, 220P2 will be blocked. Therefore, the pump servo piston 210P holds the pump movable swash plate 30 in its tilting position.

[0233] By such an operation, the pump movable swash plate 30 is tilted in the second tilting direction according to the operation of the shift operating member 410, and when the shift operating member 410 is positioned at the second operation direction operation end D2max, the pump movable swash plate 30 is positioned at the second tilting direction movement end.

[0234] When the shift operating member 410 is being operated in the second operation direction D2, the pump spool 450 does not contact the motor spool 480, and the motor spool 480 remains held at the motor spool maximum volume position by the volume increasing direction spring 490. Therefore, the motor movable swash plate 60 is held at the maximum volume position.

[0235] Next, the case where the shift operating member 410 is operated from the neutral position N in the first operation direction D1 will be described.

[0236] First, the case where the shift operating member 410 is operated to the pump first direction maximum volume position P1max will be described. When the shift operating member 410 is operated in the first operation direction D1, the pump servo switching valve 230P moves in the direction corresponding to the operation direction of the shift operating member 430 via the pump operation connection mechanism 430.

[0237] As a result, the pump servo switching valve 230P is relatively moved from the relatively neutral state with respect to the pump servo piston 210P in the direction corresponding to the first operation direction D1, and the pressure oil supply state to the first servo oil chamber 220P1 appears. Accordingly, the pump servo piston 210P is pushed in the first servo direction SV1 to tilt the pump movable swash plate 30 in the first tilting direction.

[0238] Then, when the pump servo piston 210P moves the pump movable swash plate 30 to the tilting position corresponding to the operation position of the shift operation member 410, the pump servo switching valve 230P and the pump servo piston 210P return to the relatively neutral state, and the first and second servo oil chambers 220P1, 220P2 are closed. Accordingly, the pump servo piston 210P holds the pump movable swash plate 30 at its tilting position.

[0239] By such an operation, the pump movable swash plate 30 is tilted in the first tilting direction in response to the operation of the shift operation member 410 in the first operation direction D1, and when the shift operation member 410 is positioned at the pump first direction maximum volume position P1max, the pump movable swash plate 30 is positioned at the moving end in the first tilting direction.

[0240] On the other hand, when the shift operation member 410 is positioned at the pump first direction maximum volume position P1max, the pump spool 450 is positioned at the end of the accommodation portion 520. Accordingly, at this time, the motor spool 480 does not receive the pushing force from the pump spool 450 and is held in the state of being held at the motor spool maximum volume position by the volume increasing direction spring 490. Accordingly, the motor movable swash plate 60 is held at the maximum volume position.

[0241] Next, when the shift operation member 410 is operated between the pump first direction maximum volume position P1max and the first operation direction operation end D1max beyond the pump first direction maximum volume position P1max, regardless of the operation position of the shift operation member 410, the pump movable swash plate 30 is maintained in a state of being held at the first tilting direction movement end.

[0242] That is, when the shift operation member 410 is positioned at the pump first direction maximum volume position P1max, the pump servo piston 210P is positioned at the first slide direction movement end that positions the pump movable swash plate 30 at the first tilting direction movement end.

[0243] When the shift operation member 410 is further operated in the first operation direction D1 from the state where it is positioned at the pump first direction maximum volume position P1max, the pump servo switching valve 230P relatively moves in a direction corresponding to the first operation direction D1 from the relatively neutral state with respect to the pump servo piston 210P positioned at the first slide direction movement end, and the pressure oil supply state to the first servo oil chamber 220P1 appears.

[0244] Here, since the pump servo piston 210P is positioned at the first slide direction movement end, it does not move further in the first servo direction SV1. As a result, when the shift operation member 410 is operated between the pump first direction maximum volume position P1max and the first operation direction operation end D1max, the pump movable swash plate 30 will be held at the first tilting direction movement end (Fig. 14(b)).

[0245] On the other hand, when the shift operation member 410 is operated between the pump first direction maximum volume position P1max and the first operation direction operation end D1max, the pump spool 450 is positioned in a region beyond the accommodation portion 520 by the pump operation connection mechanism 430, and is positioned at a position corresponding to the operation position of the shift operation member 410 together with the motor spool 480.

[0246] That is, when the shift operation member 410 is operated between the pump first direction maximum volume position P1max and the first operation direction operation end D1max, the pump spool 450 moves integrally with the motor spool 480 that is biased in the volume increasing direction VL by the volume increasing operation spring 490 in response to the operation of the shift operation member 410.

[0247] By such movement of the motor servo switching valve 230M, a relative positional deviation occurs between the motor servo switching valve 230M and the motor servo piston 210M, and the motor servo piston 210M moves in the corresponding direction, and the motor movable swash plate 60 is moved to a tilting position corresponding to the operation position of the shift operation member.

[0248] When the motor servo piston 210M is positioned at a tilting position corresponding to the operation position of the shift operation member, the relative positional deviation between the motor servo switching valve 230M and the motor servo piston 210M is eliminated, and the motor servo piston 210M holds the motor movable swash plate 60 at its tilting position.

[0249] By such an operation, as the shift operation member 410 is operated from the pump first direction maximum volume position P1max to the first operation direction operation end D1max, the motor movable swash plate 60 is moved from the maximum volume position to the minimum volume position.

[0250] Embodiment 4 Hereinafter, a continuously variable transmission structure according to still another embodiment of the present invention will be described with reference to the accompanying drawings. FIG. 15 shows a partial cross-sectional view of a continuously variable transmission structure 4A according to the present embodiment, which is a cross-sectional view corresponding to FIG. 3 in Embodiment 1. FIG. 16 shows a hydraulic circuit diagram of the continuously variable transmission structure 4A. In the drawings, the same members in the above embodiments are denoted by the same reference numerals, and the description thereof will be appropriately omitted.

[0251] In the stepless transmission structures 1A to 3A according to the first to third embodiments, when the pump movable swash plate 30 is moved to the first tilting direction moving end or near the first tilting direction moving end, the motor movable swash plate 60 is moved. On the other hand, when the pump movable swash plate 30 is moved to the second tilting direction moving end or near the second tilting direction moving end, the motor movable swash plate 60 is fixed at the initial position (volume increasing position).

[0252] In contrast, in the stepless transmission structure 4A according to the present embodiment, in addition to when the pump movable swash plate 30 is moved to the first tilting direction moving end or near the first tilting direction moving end, even when the pump movable swash plate 30 is moved to the second tilting direction moving end or near the second tilting direction moving end, the motor movable swash plate 60 is configured to be moved.

[0253] Specifically, as shown in FIGS. 15 and 16, the stepless transmission structure 4A includes the HST 10, a shift operation member (not shown), the pump operation piston 110, the neutral spring mechanism 120, the first and second slide oil chambers 131 and 132, the motor operation piston 140, the volume increasing operation spring 150, the volume decreasing operation oil chamber 160, the first pressure control valve 171, the second pressure control valve 172, a flow path switching valve 175, and a control device (not shown).

[0254] The first pressure control valve 171 is configured to be able to take a supply position for supplying pressure oil from a pressure oil source to the first slide oil chamber 131 and a discharge position for discharging the pressure oil in the first slide oil chamber 131.

[0255] The second pressure control valve 172 is configured to be able to take a supply position for supplying pressure oil from a pressure oil source to the second slide oil chamber 132 and a discharge position for discharging the pressure oil in the second slide oil chamber 132.

[0256] The stepless transmission structure 4A according to the present embodiment is provided with the pressure supply line 180, a first supply / discharge line 181' fluidly connected to the first slide oil chamber 131, and the second supply / discharge line 182.

[0257] When the first pressure control valve 171 is positioned at the supply position, the first supply / discharge line 181' is fluidly connected to the pressure oil supply line 180, and when it is positioned at the discharge position, the first supply / discharge line 181' is drained.

[0258] When the second pressure control valve 172 is positioned at the supply position, the second supply / discharge line 182 is fluidly connected to the pressure oil supply line 180, and when it is positioned at the discharge position, the second supply / discharge line 182 is drained.

[0259] The flow path switching valve 175 is configured to be able to take a first position for introducing the pressure oil in the first slide oil chamber 131 into the volume reduction operation oil chamber 160 and a second position for introducing the pressure oil in the second slide oil chamber 132 into the volume reduction operation oil chamber 160.

[0260] The continuously variable transmission structure 4A according to the present embodiment includes a first slide line 281 fluidly connected directly or indirectly to the first slide oil chamber 131, a second slide line 282 fluidly connected directly or indirectly to the second slide oil chamber 132, and a volume reduction line 285 fluidly connected to the volume reduction operation oil chamber 160.

[0261] When the flow path switching valve 175 is positioned at the first position, the volume reduction line 285 is fluidly connected to the first slide line 281, and when it is positioned at the second position, the volume reduction line 285 is fluidly connected to the second slide line 282.

[0262] In the present embodiment, the first pressure control valve 171, the second pressure control valve 172, and the flow path switching valve 175 are operationally controlled by the control device as follows.

[0263] When the control device recognizes that, based on the signal from the operation position sensor, the shift operation member is positioned in the operation region (i.e., the forward rotation operation region) that causes the output rotation direction of the continuously variable transmission structure 4A to be the forward rotation direction, the control device positions the flow path switching valve 175 at the first position. As a result, a state appears in which the volume reduction oil chamber 160 is pressure-controlled in conjunction with the first slide oil chamber 131.

[0264] On the other hand, when the control device recognizes that, based on the signal from the operation position sensor, the shift operation member is positioned in the operation region (i.e., the reverse rotation operation region) that causes the output rotation direction of the continuously variable transmission structure 4A to be the reverse rotation direction, the control device positions the flow path switching valve 175 at the second position. As a result, a state appears in which the volume reduction oil chamber 160 is pressure-controlled in conjunction with the second slide oil chamber 132.

[0265] In the present embodiment, as shown in FIG. 15, the flow path switching valve 175 includes a pilot type switching valve 176 that can selectively take the first position and the second position, and an electromagnetic switching valve 177 whose position is controlled by the control device.

[0266] The pilot type switching valve 176 is biased by a spring or the like toward one of the first position and the second position (the first position in FIG. 15), takes one of the first and second positions in the initial state of not receiving the pilot pressure, and is configured to take the other of the first and second positions (the second position in FIG. 15) when receiving the pilot pressure.

[0267] The electromagnetic switching valve 177 has an electromagnetic switching valve that can selectively take an operating position for supplying a pilot pressure to the pilot type switching valve 176 and an initial position for blocking the supply of the pilot pressure to the pilot type switching valve 176.

[0268] In this embodiment, when the electromagnetic switching valve 177 is positioned at the operating position, it supplies the pressure oil from the pressure oil supply line 180 to the pilot line 176a of the pilot-operated switching valve 176, and when positioned at the initial position, it is configured to cut off the supply of pressure oil to the pilot line 176a.

[0269] With such a configuration, when the shift operation member is positioned in the forward rotation operation region, the control device does not send a control signal to the switching solenoid valve 177, and the switching solenoid valve 177 remains positioned at the initial position. Therefore, the pilot-operated switching valve 176 is positioned at the first position, and the volume reduction oil chamber 160 is pressure-controlled in conjunction with the first slide oil chamber 131.

[0270] On the other hand, when the shift operation member is positioned in the reverse rotation operation region, the control device transmits a control signal to the switching solenoid valve 177, and the switching solenoid valve 177 is positioned at the operating position. Therefore, the pilot-operated switching valve 176 receives the pilot pressure and is positioned at the second position, and the volume reduction oil chamber 160 is pressure-controlled in conjunction with the second slide oil chamber 132.

[0271] Instead of the flow path switching valve 175, it is also possible to use a flow path switching valve 175' formed by a single electromagnetic switching valve. FIG. 17 shows a partial cross-sectional view of a continuously variable transmission structure 4B according to a first modification having a flow path switching valve 175' formed by a single electromagnetic switching valve.

[0272] In the continuously variable transmission structure 4B, the flow path switching valve 175' is configured to selectively assume a first position where the volume reduction line 285 is fluid-connected to the first slide line 281 and a second position where the volume reduction line 285 is fluid-connected to the second slide line 282 according to the operation position of the shift operation member.

[0273] In this case, when the shift operation member is positioned in the forward rotation operation region, the control device positions the flow path switching valve 175' at the first position, whereby a state in which the volume reduction oil chamber 160 is pressure-controlled in conjunction with the first slide oil chamber 131 appears.

[0274] Further, when the shift operation member is positioned in the reverse rotation operation region, the control device positions the flow path switching valve 175' at the second position, whereby a state in which the volume reduction oil chamber 160 is pressure-controlled in conjunction with the second slide oil chamber 132 appears.

[0275] In the present embodiment, the pump movable swash plate 30 and the motor movable swash plate 60 are moved at the following timing.

[0276] FIG. 18 shows a graph representing the relationship between the operation position of the shift operation member, the tilting position of the pump movable swash plate 30, the tilting position of the motor movable swash plate 60, and the output speed of the continuously variable transmission structure 4A in the continuously variable transmission structure 4A.

[0277] As shown in FIG. 18, in the present embodiment, when the shift operation member is operated in an intermediate region between the second operation direction motor volume switching start position in front of the second operation direction operation end with the neutral position interposed therebetween and the first operation direction motor volume switching start position in front of the first operation direction operation end, the motor operation piston 140 is positioned at the maximum volume position and holds the motor movable swash plate 60 at the maximum volume position, and the pump operation piston 110 is positioned at a slide position corresponding to the operation position of the shift operation member, and is configured to position the pump movable swash plate 30 at a corresponding tilting position.

[0278] Specifically, as the shift operation member is operated in the first operation direction within the intermediate region, the pump operation piston 110 is pushed in the first slide direction S1 to move the pump movable swash plate 30 in the first tilting direction.

[0279] In this embodiment, when the shift operation member is operated in the first operation direction and reaches the first operation direction side motor volume switching start position, the motor operation piston 140 remains at the maximum volume position, and the pump operation piston 110 is positioned at the first slide direction moving end, and the urging forces of the neutral spring mechanism 120 and the volume increasing operation spring 150 are set so as to move the pump movable swash plate 30 to the first tilting direction moving end.

[0280] At this time, the output of the continuously variable transmission structure 4A becomes the speed (first direction intermediate speed Fc) when the pump movable swash plate 30 is at the first tilting direction moving end and the motor movable swash plate 60 is at the maximum volume position (see FIG. 18).

[0281] When the shift operation member is operated in the region between the first operation direction side motor volume switching start position and the first operation direction operation end, the pump operation piston 110 is held at the first slide direction moving end and the pump movable swash plate 30 is positioned at the first operation direction moving end, and according to the operation of the shift operation member in the first operation direction, the motor operation piston 140 is pushed in the volume decreasing direction VS to move the motor movable swash plate 60 in the volume decreasing direction.

[0282] And when the shift operation member is positioned at the first operation direction operation end, the urging force of the volume increasing operation spring 150 is set so that the motor operation piston 140 is positioned at the minimum volume position and the motor movable swash plate 60 is moved to the minimum volume position.

[0283] At this time, the output of the continuously variable transmission structure 4A becomes the speed (first direction maximum speed Fmax) when the pump movable swash plate 30 is at the first tilting direction moving end and the motor movable swash plate 60 is at the minimum volume position (see FIG. 18).

[0284] When the shift operation member is operated in the second operation direction within the intermediate region, the pump operation piston 110 is pushed in the second slide direction S2 to move the pump movable swash plate 30 in the second tilting direction.

[0285] Then, when the speed change operation member reaches the second operation direction side motor volume switching start position, the pump operation piston 110 is positioned at the second slide direction movement end, and the pump movable swash plate 30 is moved to the second tilting direction movement end.

[0286] At this time, the output of the continuously variable transmission structure becomes the speed (second direction intermediate speed Rc) when the pump movable swash plate 30 is at the second tilting direction movement end and the motor movable swash plate 60 is at the maximum volume position (see FIG. 18).

[0287] When the speed change operation member is being operated in the region between the second operation direction side motor volume switching start position and the second operation direction operation end, the pump operation piston 110 is held at the second slide direction movement end and the pump movable swash plate 30 is positioned at the second operation direction movement end. Then, as the speed change operation member is operated in the second operation direction, the motor operation piston 140 is pushed in the volume decreasing direction VS to move the motor movable swash plate 60 in the volume decreasing direction.

[0288] Then, when the speed change operation member is positioned at the second operation direction operation end, the motor operation piston 140 is positioned at the minimum volume position to move the motor movable swash plate 60 to the minimum volume position.

[0289] At this time, the output of the continuously variable transmission structure 4A becomes the speed (second direction maximum speed Rmax) when the pump movable swash plate 30 is at the second tilting direction movement end and the motor movable swash plate 60 is at the minimum volume position (see FIG. 18).

[0290] It is also possible to move (tilt) the pump operation piston 110 (i.e., the pump movable swash plate 30) and the motor operation piston 140 (i.e., the motor movable swash plate 60) at different timings.

[0291] Fig. 19 shows a graph representing the relationship between the operating position of the shift operation member, the tilting position of the pump movable swash plate 30, the tilting position of the motor movable swash plate 60, and the output speed of the continuously variable transmission structure 4A when the pump operation piston 110 and the motor operation piston 140 are configured to operate in another operation pattern (first modified pattern).

[0292] As shown in Fig. 19, in the first modified pattern, when the shift operation member is being operated in the intermediate region, the motor operation piston 140 is positioned at the maximum volume position to hold the motor movable swash plate at the maximum volume position, and the pump operation piston 110 positions the pump movable swash plate 30 at the tilting position corresponding to the operating position of the shift operation member. In this regard, it is common with the operation pattern in the present embodiment. However, the tilting position of the pump movable swash plate 30 when the shift operation member is positioned at the first operation direction side motor volume switching start position and the second operation direction side motor volume switching start position is different from the operation pattern in the present embodiment.

[0293] Specifically, in the first modified pattern, when the shift operation member is operated in the first operation direction and reaches the first operation direction side motor volume switching start position, the motor operation piston 140 remains positioned at the maximum volume position, and the pump operation piston 110 is positioned at the first slide direction intermediate position in front of the first slide direction movement end to position the pump movable swash plate 30 at the first tilting direction intermediate position. In this way, the biasing forces of the neutral spring mechanism 120 and the volume increasing operation spring 150 are set.

[0294] That is, in the first modified pattern, at the time when the shift operation member is operated to the first operation direction side motor volume switching start position, the output of the continuously variable transmission structure 4A becomes the speed (first direction first intermediate speed Fc1) when the pump movable swash plate 30 is at the first tilting direction intermediate position and the motor movable swash plate 60 is at the maximum volume position (see Fig. 19).

[0295] When the shift operation member is operated in the region between the first operation direction motor volume switching start position and the first operation direction pump maximum volume operation position in front of the first operation direction operation end, as the shift operation member is operated in the first operation direction, the pump operation piston 110 is pushed in the first slide direction S1 to move the pump movable swash plate 30 toward the first tilting direction moving end, and the motor operation piston 140 is pushed in the volume decreasing direction to move the motor movable swash plate 60 in the volume decreasing direction.

[0296] And when the shift operation member is positioned at the first operation direction pump maximum volume operation position, the pump operation piston 110 is positioned at the first slide direction moving end to position the pump movable swash plate 30 at the first tilting direction moving end.

[0297] At this point, the biasing force of the volume increasing operation spring 150 is set so that the motor operation piston 140 is positioned at an intermediate volume position between the maximum volume position and the minimum volume position to position the motor movable swash plate 60 at an intermediate volume position between the maximum volume position and the minimum volume position.

[0298] The output of the continuously variable transmission structure 4A at this point becomes the speed (first direction second intermediate speed Fc2) when the pump movable swash plate 30 is at the first tilting direction moving end and the motor movable swash plate 60 is at the intermediate volume position (see FIG. 19).

[0299] When the shift operation member is operated in the region between the first operation direction pump maximum volume operation position and the first operation direction operation end, the pump operation piston 110 is held at the first slide direction moving end to keep the pump movable swash plate 30 positioned at the first operation direction moving end, and as the shift operation member is operated in the first operation direction, the motor operation piston 140 is pushed in the volume decreasing direction to move the motor movable swash plate 60 in the volume decreasing direction.

[0300] When the shift operation member is positioned at the first operation direction operation end, the motor operation piston 140 is positioned at the minimum volume position to move the motor movable swash plate 60 to the minimum volume position.

[0301] The output of the continuously variable transmission structure 4A at this time becomes the speed (the highest speed Fmax in the first direction) when the pump movable swash plate 30 is at the first tilting direction moving end and the motor movable swash plate 60 is at the minimum volume position (see FIG. 19).

[0302] On the other hand, when the shift operation member is operated in the second operation direction within the intermediate region, the pump operation piston 110 is pushed in the second slide direction S1 to move the pump movable swash plate 30 in the second tilting direction.

[0303] When the shift operation member reaches the second operation direction motor volume switching start position, the pump operation piston 110 is positioned at the second slide direction intermediate position before the second slide direction moving end, and the pump movable swash plate 30 is positioned at the second tilting direction intermediate position.

[0304] The output of the continuously variable transmission structure 4A at this time becomes the speed (the second direction first intermediate speed Rc1) when the pump movable swash plate 30 is at the second tilting direction intermediate position and the motor movable swash plate 60 is at the maximum volume position (see FIG. 19).

[0305] When the shift operation member is being operated in the region between the second operation direction motor volume switching start position and the second operation direction pump maximum volume operation position before the second operation direction operation end, as the shift operation member is operated in the second operation direction, the pump operation piston 110 is pushed in the second slide direction S2 to move the pump movable swash plate 30 toward the second tilting direction moving end, and the motor operation piston 140 is pushed in the volume decreasing direction to move the motor movable swash plate 60 in the volume decreasing direction.

[0306] And when the shift operation member is positioned at the second operation direction pump maximum volume operation position, the pump operation piston 110 is positioned at the second slide direction movement end to position the pump movable swash plate 30 at the second tilt direction movement end.

[0307] At this time, the motor operation piston 140 is positioned at an intermediate volume position between the maximum volume position and the minimum volume position to position the motor movable swash plate 60 at an intermediate volume position between the maximum volume position and the minimum volume position.

[0308] The output of the continuously variable transmission structure 4A at this time becomes the speed (second direction second intermediate speed Rc2) when the pump movable swash plate 30 is at the second tilt direction movement end and the motor movable swash plate 60 is at the intermediate volume position (see Fig. 19).

[0309] When the shift operation member is being operated in a region between the second operation direction pump maximum volume operation position and the second operation direction operation end, the pump operation piston 110 is held at the second slide direction movement end to keep the pump movable swash plate 30 positioned at the second operation direction movement end, and as the shift operation member is operated in the second operation direction, the motor operation piston 140 is pushed in the volume decreasing direction to move the motor movable swash plate 60 in the volume decreasing direction.

[0310] And when the shift operation member is positioned at the second operation direction operation end, the motor operation piston 140 is positioned at the minimum volume position to move the motor movable swash plate 60 to the minimum volume position.

[0311] The output 4A of the continuously variable transmission structure at this time becomes the speed (second direction maximum speed Rmax) when the pump movable swash plate 30 is at the second tilt direction movement end and the motor movable swash plate 60 is at the minimum volume position.

[0312] Fig. 20 shows a graph representing the relationship between the operating position of the shift operation member, the tilting position of the pump swash plate 30, the tilting position of the motor swash plate 60, and the output speed of the continuously variable transmission structure 4A when the pump operation piston 110 and the motor operation piston 140 are operated in still another operation pattern (second modified pattern).

[0313] As shown in Fig. 20, in the second modified pattern, when the shift operation member is being operated in the intermediate region, the motor operation piston 140 holds the motor swash plate at the maximum volume position, and the pump operation piston 110 moves the pump swash plate 30 according to the operating position of the shift operation member. Also, when the shift operation member reaches the first and second operation direction motor volume switching start positions, the pump swash plate 30 is positioned at the first and second tilting direction intermediate positions, which is common to the first modified pattern. However, the timing at which the pump swash plate 30 reaches the first and second tilting direction moving ends is different from that in the first modified pattern.

[0314] Specifically, in the second modified pattern, when the shift operation member is being operated in the region between the first operation direction motor volume switching start position and the first operation direction operating end, as the shift operation member is operated in the first operation direction, the pump operation piston 110 is pushed in the first slide direction S1 to move the pump swash plate 30 toward the first tilting direction moving end, and the motor operation piston 140 is pushed in the volume decreasing direction to move the motor swash plate 60 toward the minimum volume position. When the shift operation member reaches the first operation direction operating end, the pump operation piston 110 is positioned at the first slide direction moving end to position the pump swash plate 30 at the first tilting direction moving end, and the motor operation piston 140 is positioned at the minimum volume position to position the motor swash plate 60 at the minimum volume position. The biasing forces of the neutral spring mechanism 120 and the volume increasing operation spring 150 are set accordingly.

[0315] The output of the continuously variable transmission structure 4A in the second deformation pattern becomes the speed (first direction intermediate speed Fc) when the pump movable swash plate 30 is at the first tilting direction intermediate position and the motor movable swash plate 60 is at the maximum volume position when the shift operation member is at the first operation direction motor volume switching start position. As the shift operation member is operated in the first operation direction from the first operation direction motor volume switching start position, the speed increases according to the movement of the movable swash plate 30 in the first tilting direction and the movement of the motor movable swash plate 60 in the volume decreasing direction. When the shift operation member is at the first operation direction operation end, it becomes the speed (first direction maximum speed Fmax) when the pump movable swash plate 30 is at the first tilting direction movement end and the motor movable swash plate 60 is at the minimum volume position (see FIG. 20).

[0316] On the other hand, when the shift operation member is being operated in the region between the second operation direction motor volume switching start position and the second operation direction operation end, as the shift operation member is operated in the second operation direction, the pump operation piston 110 is pushed in the second slide direction S2 to move the pump movable swash plate 30 toward the second tilting direction movement end, and the motor operation piston 140 is pushed in the volume decreasing direction to move the motor movable swash plate 60 toward the minimum volume position.

[0317] And when the shift operation member is at the second operation direction pump maximum volume operation position, the pump operation piston 110 is at the second slide direction movement end to position the pump movable swash plate 30 at the second tilting direction movement end, and the motor operation piston 140 is at the minimum volume position to position the motor movable swash plate 60 at the minimum volume position.

[0318] The output of the continuously variable transmission structure 4A at this point becomes the speed (second direction maximum speed Rmax) when the pump movable swash plate 30 is at the second tilting direction movement end and the motor movable swash plate 60 is at the minimum volume position (see FIG. 20).

[0319] The continuously variable transmission structure 4A according to the present embodiment can also include the biasing force adjustment mechanism 155. Figure 21 shows a partial cross-sectional view of a continuously variable transmission structure 4C according to a second modification of the present embodiment including the biasing force adjustment mechanism 155.

[0320] By providing the biasing force adjustment mechanism 155, it is possible to easily adjust the timing at which the pump movable swash plate 30 moves (tilts) and the timing at which the motor movable swash plate 60 moves (tilts).

[0321] Embodiment 5 Hereinafter, a continuously variable transmission structure according to still another embodiment of the present invention will be described with reference to the accompanying drawings. Figure 22 shows a partial cross-sectional view of a continuously variable transmission structure 5A according to the present embodiment, which is a cross-sectional view corresponding to FIG. 15 in Embodiment 4. In the drawings, the same members as those in the above embodiment are denoted by the same reference numerals, and the description thereof will be omitted as appropriate.

[0322] The continuously variable transmission structure 5A according to the present embodiment is different from the continuously variable transmission structure 4A according to Embodiment 4 mainly in that the pump hydraulic servo mechanism 200P and the motor hydraulic servo mechanism 200M are deleted, and the pump operation piston 110 and the motor operation piston 140 are changed to the pump operation piston 310 and the motor operation piston 320.

[0323] Similar to Embodiment 2, the pump operation piston 310 and the motor operation piston 320 are mechanically connected to the operation end portion 35 of the pump movable swash plate 30 and the operation end portion 65 of the motor movable swash plate 60, respectively.

[0324] Further, the continuously variable transmission structure 5A according to the present embodiment has a neutral spring mechanism 330 instead of the mechanism 120 (the first and second slide springs 121, 122) compared to the continuously variable transmission structure 4A.

[0325] The continuously variable transmission structure 5A can also be provided with the biasing force adjustment mechanism 155. Fig. 23 shows a partial cross-sectional view of a continuously variable transmission structure 5B according to a modified example of the present embodiment, which is provided with the biasing force adjusting mechanism 155.

[0326] Embodiment 6 Hereinafter, a continuously variable transmission structure according to still another embodiment of the present invention will be described with reference to the accompanying drawings. Fig. 24 shows a transmission schematic diagram of a work vehicle 100 to which the continuously variable transmission structure 6A according to the present embodiment is applied. Figs. 25 and 26 show a partial cross-sectional view and a hydraulic circuit diagram of the continuously variable transmission structure 6A, respectively. In the drawings, the same members as those in the above embodiment are denoted by the same reference numerals, and the description thereof will be omitted as appropriate.

[0327] As shown in Fig. 24, the continuously variable transmission structure 6A is inserted into the traveling system transmission path from the drive source 190 to the drive wheels 390 in the work vehicle 100. Note that reference numerals 350 and 360 in Fig. 24 are a forward / reverse switching mechanism and a sub-transmission mechanism inserted into the traveling system transmission path. Reference numeral 400 is a PTO shaft, and reference numerals 410 and 420 are a PTO clutch mechanism and a PTO transmission mechanism inserted into the PTO system transmission path from the drive source 190 to the PTO shaft 400.

[0328] The continuously variable transmission structure 6A according to the present embodiment includes the HST 10, a planetary gear mechanism 300, the shift operation member, the pump operation piston 110, the second slide direction spring 122, the first slide oil chamber 131, the volume increase operation spring 150, the volume decrease operation oil chamber 160, the first pressure control valve 171, and the control device that controls the operation of the first pressure control valve 171.

[0329] The planetary gear mechanism 300 includes a sun gear 302, a planetary gear 304 meshing with the sun gear 302, an internal gear 306 meshing with the planetary gear 304, and a carrier 308 that rotatably supports the planetary gear 304 about an axis and rotates about the axis of the sun gear 302 in conjunction with the revolution of the planetary gear 304 around the sun gear 302. The sun gear 302, the carrier 308, and the internal gear 306 form three planetary elements.

[0330] In the planetary gear mechanism 300, a reference rotational power from the drive source 190 is operatively input to a first element among the three planetary elements, and an HST output from the motor shaft 45 is operatively input to a second element, and a combined rotational power obtained by combining the reference rotational power and the HST output is output from a third element.

[0331] As shown in FIG. 24, in the present embodiment, the internal gear 306 acts as the first element, the sun gear 302 acts as the second element, and the carrier 308 acts as the third element.

[0332] FIG. 27 shows a graph representing the relationship between the operating position of the shift operation member in the continuously variable transmission structure 6A, the tilting position of the pump movable swash plate 30, the tilting position of the motor movable swash plate 60, and the output speed of the continuously variable transmission structure 6A (i.e., the rotational speed of the combined rotational power output from the third element of the planetary gear mechanism 300).

[0333] In the present embodiment, when the pump movable swash plate 30 is positioned at the second tilting direction moving end (for example, the reverse direction moving end) and the HST output input to the second element is set to the maximum speed in the second operation direction (for example, the reverse direction maximum speed), the combined rotational power output from the third element (i.e., the output of the continuously variable transmission structure) becomes zero speed. The gear ratio of the planetary gear mechanism 300 is set such that the combined rotational power (the output of the continuously variable transmission structure) is increased in one direction as the pump movable swash plate 30 is operated from the second tilting direction moving end through the neutral position to the first tilting direction moving end (for example, the forward direction moving end).

[0334] The first pressure control valve 171 integrally supplies and discharges pressure oil to and from the first slide oil chamber 131 and the volume reduction operation oil chamber 160.

[0335] As shown in FIGS. 25 and 26, the stepless transmission structure according to the present embodiment has a pressure oil supply line 180 fluidly connected to a pressure oil source, and a first supply / discharge line 181 fluidly connected to the first slide oil chamber 131 and the volume reduction operation oil chamber 160.

[0336] In this case, the first pressure control valve 171 is configured to selectively take a supply position where the first supply / discharge line 181 is fluidly connected to the pressure oil supply line 180 and a discharge position where the first supply / discharge line 181 is drained, according to a control signal from the control device.

[0337] As shown in FIGS. 25 and 26, the stepless transmission structure 6A according to the present embodiment further includes a pump hydraulic servo mechanism 200P that moves the pump movable swash plate 30 based on the movement of the pump operation piston 110, and a motor hydraulic servo mechanism 200M that moves the motor movable swash plate 60 based on the movement of the motor operation piston 140. Furthermore, as shown in FIG. 25, the stepless transmission structure 6A includes the biasing force adjustment mechanism 155.

[0338] As shown in FIG. 27, in the present embodiment, after the pump operation piston 110 is positioned at the first slide direction movement end and the pump movable swash plate is positioned at the first tilting direction movement end, the urging forces of the second slide spring 122 and the volume increase operation spring 150 are set such that the motor operation piston 140 starts to slide in the volume reduction direction VS and moves the motor movable swash plate 60 in the volume reduction direction.

[0339] The stepless transmission structure 6A having such a configuration operates as follows. As shown in FIG. 27 and as described above, when the shift operation member is positioned at the second operation direction operation end and the pump operation piston 110 is positioned at the second slide direction movement end to position the pump movable swash plate at the second tilting direction movement end, the combined rotational power output from the planetary gear mechanism 300 (the output of the continuously variable transmission structure 6A) becomes zero speed.

[0340] When the shift operation member is operated in a region between the second operation direction operation end and the motor volume switching start position in front of the first operation direction operation end with the neutral position (the position for making the output of the HST 10 zero speed) interposed therebetween, while the motor operation piston 140 is held at the maximum volume position to hold the motor movable swash plate 60 at the maximum volume position, in response to the operation of the shift operation member in the first operation direction from the second operation direction operation end to the motor volume switching start position, the pump operation piston 110 is pushed in the first slide direction S1 from the second slide direction movement end to the first slide direction movement end to move the pump movable swash plate 30 in the first tilting direction from the second tilting direction movement end to the first tilting direction movement end.

[0341] In response to the output change of the HST 10 due to the movement of the pump movable swash plate from the second tilting direction movement end to the first tilting direction movement end with the motor movable swash plate held at the maximum volume position, the combined rotational power of the planetary gear mechanism 300 (the output of the continuously variable transmission structure 6A) is increased in speed from zero speed to the intermediate speed Fc (see FIG. 27).

[0342] When the shift operation member is operated between the motor volume switching start position and the first operation direction operation end, the pump operation piston 110 is held at the first slide direction movement end to keep the pump movable swash plate 30 positioned at the first operation direction movement end, and as the shift operation member is operated in the first operation direction from the motor volume switching start position to the first operation direction operation end, the motor operation piston 140 is pushed in the volume decreasing direction VS from the maximum volume position to the minimum volume position to move the motor movable swash plate 60 from the maximum volume position to the minimum volume position.

[0343] In a state where the pump movable swash plate 30 is held at the first tilting direction moving end, as the motor movable swash plate 60 moves from the maximum volume position to the minimum volume position, in response to the output change of the HST 10, the combined rotational power of the planetary gear mechanism 300 (the output of the stepless transmission structure 6A) is increased in speed from the intermediate speed Fc to the maximum speed Fmax (see FIG. 27).

[0344] Also in the present embodiment, the pump operation piston 110 (that is, the pump movable swash plate 30) and the motor operation piston 140 (that is, the motor movable swash plate 60) can be moved at different operating timings.

[0345] FIG. 28 shows a graph representing the relationship between the operation position of the speed change operation member, the tilting position of the pump movable swash plate 30, the tilting position of the motor movable swash plate 60, and the output speed of the stepless transmission structure 6A when the pump operation piston 110 and the motor operation piston 140 are configured to operate in another operation pattern (first modified pattern).

[0346] As shown in FIG. 28, in the first modified pattern, when the speed change operation member is operated in a region between the second operation direction operation end and the motor volume switching start position, the motor operation piston 140 is positioned at the maximum volume position and holds the motor movable swash plate 60 at the maximum volume position, and the pump operation piston 110 positions the pump movable swash plate 30 at a tilting position corresponding to the operation position of the speed change operation member. In this regard, it is common with the present embodiment, but the tilting position of the pump movable swash plate 30 when the speed change operation member is positioned at the motor volume switching start position is different from that of the present embodiment.

[0347] That is, in the first modified example, · When the speed change operation member is operated in the first operation direction from the second operation direction operation end to the motor volume switching start position, with the motor operation piston 140 held at the maximum volume position, the pump operation piston 110 is pushed from the second slide direction moving end to the intermediate position in the first slide direction. · When the shift operation member is operated in the first operation direction from the motor volume switching start position to the first operation direction pump maximum volume position, the pump operation piston 110 is pushed from the intermediate position to the first slide direction moving end, and the motor operation piston 140 is pushed from the maximum volume position to the intermediate volume position. · When the shift operation member is operated in the first operation direction from the first operation direction pump maximum volume position to the first operation direction operation end, the pump operation piston 110 is held at the first slide direction moving end, and the motor operation piston 140 is pushed from the intermediate volume position to the minimum volume position. The biasing forces of the second slide spring 122 and the volume increasing operation spring 150 are set.

[0348] In the first deformation pattern, with the motor operation piston 140 positioned at the maximum volume position and the motor movable swash plate 60 held at the maximum volume position, the pump operation piston 110 is pushed from the second slide direction moving end to the intermediate position, and the pump movable swash plate 30 is moved from the second tilting direction moving end to the first tilting direction intermediate position. According to the output change of the HST 10, the combined rotational power of the planetary gear mechanism 300 (the output of the continuously variable transmission structure 6A) is increased from zero speed to the first intermediate speed Fc1 (see Fig. 28).

[0349] Next, while the pump operation piston 110 is pushed from the intermediate position to the first slide direction moving end and the pump movable swash plate 30 is moved from the first tilting direction intermediate position to the first tilting direction moving end, the motor operation piston 140 is pushed from the maximum volume position to the intermediate volume position and the motor movable swash plate 60 is moved from the maximum volume position to the intermediate volume position. According to the output change of the HST 10, the combined rotational power of the planetary gear mechanism 300 (the output of the continuously variable transmission structure 6A) is increased from the first intermediate speed Fc1 to the second intermediate speed Fc2 (see Fig. 28).

[0350] Then, with the pump operation piston 110 positioned at the first slide direction moving end and the pump movable swash plate 30 held at the first tilting direction moving end, in response to the output change of the HST 10 caused by the motor operation piston 140 being pushed from the intermediate volume position to the minimum volume position and the motor movable swash plate 60 being moved from the intermediate volume position to the minimum volume position, the combined rotational power of the planetary gear mechanism 300 (the output of the continuously variable transmission structure 6A) is increased from the second intermediate speed Fc2 to the maximum speed Fmax (see Fig. 28).

[0351] Fig. 29 shows a graph representing the relationship between the operating position of the speed change operating member, the tilting position of the pump movable swash plate 30, the tilting position of the motor movable swash plate 60, and the output speed of the continuously variable transmission structure 6A when the pump operation piston 110 and the motor operation piston 140 are configured to operate in still another operation pattern (second modified pattern).

[0352] The second modification is common with the first modified pattern in that when the speed change operating member is operated in the region between the second operation direction operating end and the motor volume switching start position, the motor operation piston 140 is positioned at the maximum volume position to hold the motor movable swash plate 30 at the maximum volume position, and the pump operation piston 110 positions the pump movable swash plate 30 at a tilting position corresponding to the operating position of the speed change operating member, and when the speed change operating member reaches the motor volume switching start position and the pump movable swash plate 30 is positioned at the first tilting direction intermediate position. However, it is different from the first modified pattern in the timing at which the pump movable swash plate 30 is positioned at the first tilting direction moving end.

[0353] That is, in the second modification,[[]] · When the speed change operating member is operated in the first operation direction from the second operation direction operating end to the motor volume switching start position, with the motor operation piston held at the maximum volume position, the pump operation piston is pushed from the second slide direction moving end to the intermediate position in the first slide direction. · When the speed change operation member is operated in the first operation direction from the motor volume switching start position to the first operation direction operation end, the pump operation piston is pushed from the intermediate position to the first slide direction moving end, and the motor operation piston is pushed from the maximum volume position to the minimum volume position, The biasing forces of the second slide spring 122 and the volume increasing operation spring 150 are set.

[0354] In the second modification, with the motor operation piston 140 held at the maximum volume position and the motor movable swash plate 60 held at the maximum volume position, as the pump operation piston 110 is pushed from the second slide direction moving end to the intermediate position in the first slide direction and the pump movable swash plate 30 is moved from the second tilting direction moving end to the first tilting direction intermediate position, according to the output change of the HST 10, the combined rotational power of the planetary gear mechanism 300 (the output of the continuously variable transmission structure 6A) is increased from zero speed to the first intermediate speed Fc1 (see FIG. 29).

[0355] Next, as the pump operation piston 110 is pushed from the intermediate position to the first slide direction moving end and the pump movable swash plate 30 is moved from the first tilting direction intermediate position to the first tilting direction moving end, and the motor operation piston 140 is pushed from the maximum volume position to the minimum volume position and the motor movable swash plate 60 is moved from the maximum volume position to the minimum volume position, according to the output change of the HST 10, the combined rotational power of the planetary gear mechanism 300 (the output of the continuously variable transmission structure 6A) is increased from the first intermediate speed Fc1 to the maximum speed Fmax (see FIG. 29).

[0356] Embodiment 7 Hereinafter, a continuously variable transmission structure according to still another embodiment of the present invention will be described with reference to the accompanying drawings. FIG. 30 shows a partial cross-sectional view of a continuously variable transmission structure 7A according to the present embodiment, which corresponds to FIG. 25 in Embodiment 6. In the figure, the same members as those in the above embodiment are denoted by the same reference numerals, and the description thereof will be omitted as appropriate.

[0357] The continuously variable transmission structure 7A according to this embodiment is different from the continuously variable transmission structure 6A according to Embodiment 6 mainly in that the pump hydraulic servo mechanism 200P and the motor hydraulic servo mechanism 200M are deleted, and the pump operation piston 110 and the motor operation piston 140 are changed to the pump operation piston 310 and the motor operation piston 320.

[0358] Similar to those in Embodiments 2 and 5, the pump operation piston 310 and the motor operation piston 320 are mechanically connected to the operation end 35 of the pump movable swash plate 30 and the operation end 65 of the motor movable swash plate 60, respectively.

[0359] Further, the continuously variable transmission structure 7A according to this embodiment has a neutral spring mechanism 330 instead of the neutral spring mechanism 120 (the first and second slide springs 121, 122) compared with the continuously variable transmission structure 4A.

Explanation of Signs

[0360] 1A to 7A Continuously variable transmission structure 10 Hydraulic continuously variable transmission mechanism (HST) 30 Pump movable swash plate (pump volume adjuster) 60 Motor movable swash plate (motor volume adjuster) 82 Charge oil passage (charge line) 110, 310 Pump operation piston 121, 122 First and second slide springs of the neutral spring mechanism 131, 132 First and second slide oil chambers 140, 320 Motor operation piston 150 Volume increase direction spring 160 Volume decrease operation oil chamber 330 Neutral spring mechanism 171, 172 First and second pressure control valves 180 Pressure oil supply line 181, 182 First and second supply and discharge lines 200P Pump hydraulic servo mechanism 210P Pump servo piston 220P1, 220P2 First and second servo oil chambers 230P Pump servo switching valve 200M Motor hydraulic servo mechanism 210M Motor servo piston 220M Volume reduction servo oil chamber 230M Motor servo switching valve 240M Volume increase servo direction spring 410 Shift operation member 430 Pump operation connection mechanism 450 Pump spool 460 Neutral spring mechanism 480 Motor spool 490 Volume increase direction spring 495 Motor spool maximum volume position setting member 520 Flexible part S1 First slide direction S2 Second slide direction SV1 First servo direction SV2 Second servo direction VS Volume reduction direction VL Volume increase direction SVS Volume reduction servo direction SVL Volume increase servo direction PA Pump swing axis MA Motor swing axis

Claims

1. A hydraulic continuously variable transmission mechanism including a variable displacement hydraulic pump whose volume changes in response to the operation of a pump volume adjuster and a variable displacement hydraulic motor whose volume changes in response to the operation of a motor volume adjuster, a shift operation member for operating the shift state of the hydraulic continuously variable transmission mechanism, a pump operation piston movable in two directions, a first slide direction on one side in the axial direction and a second slide direction on the other side, and directly or indirectly engaged with an operation end of the pump volume adjuster so as to operate the pump volume adjuster in a first operation direction and a second operation direction respectively in response to movement in the first and second slide directions, a neutral spring mechanism that holds the pump operation piston in a neutral position when no external force is applied to the pump operation piston and generates a biasing force toward the neutral position when the pump operation piston is moved from the neutral position in the first and second slide directions, first and second slide oil chambers configured to push the pump operation piston in the first and second slide directions respectively against the biasing force of the neutral spring mechanism by the supplied pressure oil, a motor operation piston movable in two directions, a volume reduction direction on one side in the axial direction and a volume increase direction on the other side, and directly or indirectly engaged with an operation end of the motor volume adjuster so as to operate the motor volume adjuster in the volume reduction direction and the volume increase direction respectively in response to movement in the volume reduction direction and the volume increase direction, a volume increase operation spring that biases the motor operation piston in the volume increase direction, a volume reduction operation oil chamber configured to push the motor operation piston in the volume reduction direction against the biasing force of the volume increase operation spring by the supplied pressure oil, a first pressure control valve that commonly switches the supply and discharge of pressure oil to the first slide oil chamber and the volume reduction operation oil chamber in response to the operation of the shift operation member, a second pressure control valve that switches the supply and discharge of pressure oil to the second slide oil chamber in response to the operation of the shift operation member, After the pressure oil in the first slide oil chamber moves the pump operation piston from the neutral position in the first slide direction and the neutral spring mechanism biases the pump operation piston toward the neutral position with a predetermined biasing force to reach a predetermined holding elastic state, the biasing forces of the neutral spring mechanism and the volume increasing operation spring are set so that the pressure oil in the volume decreasing operation oil chamber starts to move the motor operation piston in the volume decreasing direction while elastically deforming the volume increasing operation spring. A continuously variable transmission structure characterized by this.

2. The continuously variable transmission structure according to claim 1, characterized in that the neutral spring mechanism is configured to be in the predetermined holding elastic state when the pump operation piston positions the pump volume adjuster at the moving end in the first operation direction.

3. The continuously variable transmission structure according to claim 1, characterized in that the neutral spring mechanism is configured to be in the predetermined holding elastic state when the pump operation piston positions the pump volume adjuster at a predetermined position in front of the moving end in the first operation direction.

4. The continuously variable transmission structure according to claim 3, characterized in that the biasing forces of the neutral spring mechanism and the volume increasing operation spring are set so that when the pump volume adjuster reaches the moving end in the first operation direction by the pump operation piston, the motor operation piston positions the motor volume adjuster at the moving end in the volume decreasing direction.

5. The continuously variable transmission structure according to claim 3, characterized in that the biasing forces of the neutral spring mechanism and the volume increasing operation spring are set so that when the pump volume adjuster reaches the moving end in the first operation direction by the pump operation piston, the motor operation piston positions the motor volume adjuster at a predetermined position in front of the moving end in the volume decreasing direction.

6. A first supply / drain line fluidly connected to the first slide oil chamber and the volume decreasing operation oil chamber, A second supply / drain line fluidly connected to the second slide oil chamber, The first pressure control valve is configured to be able to take a supply position that fluidly connects the first supply / drain line to a charge line for supplying hydraulic oil to the hydraulic continuously variable transmission mechanism and a discharge position that drains the first supply / drain line. The second pressure control valve is configured to be able to take a supply position that fluidly connects the second supply / discharge line to the charge line and a discharge position that drains the second supply / discharge line, and is characterized in that it is the stepless transmission structure according to any one of claims 1 to 5.

7. A pump hydraulic servo mechanism that hydraulically operates the pump volume adjuster based on the movement of the pump operation piston, and A motor hydraulic servo mechanism that hydraulically operates the motor volume adjuster based on the movement of the motor operation piston, and is characterized in that it is the stepless transmission structure according to any one of claims 1 to 6.

8. The motor hydraulic servo mechanism has a motor servo piston, a volume increasing servo spring, a spring chamber that houses the spring, a volume decreasing servo oil chamber, and a motor servo switching valve. The motor servo piston is configured to be movable in two directions, a volume decreasing servo direction on one side in the axial direction and a volume increasing servo direction on the other side, in cooperation with the switching operation of the motor servo switching valve. As it moves in the volume decreasing servo direction, it operates the motor volume adjuster in the volume decreasing direction, and when it is positioned at the minimum volume servo position, it positions the motor volume adjuster at the minimum volume position. On the other hand, as it moves in the volume increasing servo direction, it operates the motor volume adjuster in the volume increasing direction, and when it is positioned at the maximum volume servo position, it positions the motor volume adjuster at the maximum volume position, and is engaged with the operation end of the motor volume adjuster. The volume increasing servo spring biases the motor servo piston in the volume increasing servo direction. The volume decreasing servo oil chamber is configured to push the motor servo piston in the volume decreasing servo direction against the biasing force of the volume increasing servo spring by the supplied pressure oil. The motor servo switching valve is operatively connected to the motor operation piston so as to take a volume increasing position and a volume decreasing position, respectively, according to the movement of the motor operation piston in the volume increasing direction and the volume decreasing direction. The volume increasing servo direction in which the volume increasing servo spring biases the motor servo piston coincides with the volume increasing direction in which the volume increasing operation spring biases the motor operation piston, and is characterized in that it is the stepless transmission structure according to claim 7.

9. The pump operation piston is mechanically connected to the operation end of the pump volume adjuster so as to operate the pump volume adjuster in the first and second operation directions respectively in response to movement in the first and second slide directions. The continuously variable transmission structure according to any one of claims 1 to 6, wherein the motor operation piston is mechanically connected to the operation end of the motor volume adjuster so as to operate the motor volume adjuster in the volume reduction direction and the volume increase direction respectively in response to movement in the volume reduction direction and the volume increase direction.

10. A hydraulic continuously variable transmission mechanism including a variable volume type hydraulic pump whose volume changes in response to the operation of a pump volume adjuster and a variable volume type hydraulic motor whose volume changes in response to the operation of a motor volume adjuster, A speed change operation member that is operable bidirectionally about an axis between a first operation direction operation end on one side and a second operation direction operation end on the other side about the axis with a neutral position interposed therebetween, A pump operation connection mechanism that operates the pump volume adjuster from the neutral position in the first and second operation directions, And a motor operation connection mechanism that operates the motor volume adjuster in the volume reduction direction and the volume increase direction respectively. The pump operation connection mechanism has a pump spool operatively connected to the speed change operation member so as to take a pump spool neutral position in response to the operation of the speed change operation member to the neutral position, and move in the first slide direction on one side in the axial direction and the second slide direction on the other side from the pump spool neutral position in response to the operation of the speed change operation member from the neutral position in the first and second operation directions. The motor operation connection mechanism has a motor spool coaxially and abuttingly arranged in series on one side in the axial direction of the pump spool and capable of moving bidirectionally in the volume reduction direction on one side in the axial direction and the volume increase direction on the other side, and a volume increase operation spring that biases the motor spool in the volume increase direction, and is configured to operate the motor volume adjuster in the volume reduction direction and the volume increase direction on the other side respectively in response to the movement of the motor spool in the volume reduction direction and the volume increase direction. A clearance portion having a predetermined distance in the first slide direction is provided between the pump spool located at the pump spool neutral position and the motor spool located at the volume increase direction movement end. When the pump spool is moved to the end of the bypass portion in response to an operation of the speed change operation member in the first operation direction, the motor spool remains held at the end position in the volume increasing direction, and only the pump spool moves in the first slide direction. When the pump spool moves in the first slide direction beyond the bypass portion, the pump spool abuts against the motor spool to move the motor spool in the volume decreasing direction. A continuously variable transmission structure characterized by this.

11. When the speed change operation member positions the pump volume adjuster at the end position in the first operation direction via the pump operation connection mechanism, the pump spool is configured to be positioned at the end of the bypass portion. The continuously variable transmission structure according to claim 10, characterized by this.

12. A neutral spring mechanism that directly or indirectly holds the pump spool at the pump spool neutral position, and generates a biasing force directed toward the pump spool neutral position directly or indirectly on the pump spool when the pump spool is moved in the first and second slide directions from the pump spool neutral position. The continuously variable transmission structure according to claim 10 or 11, characterized by this.

13. The pump operation connection mechanism includes a pump hydraulic servo mechanism that hydraulically operates the pump volume adjuster based on an operation of the speed change operation member. The pump hydraulic servo mechanism has a pump servo piston, a volume increasing servo oil chamber, a volume decreasing servo oil chamber, and a pump servo switching valve. The pump servo piston is movable in a first servo direction on one side in the axial direction and a second servo direction on the other side in cooperation with a switching operation of the pump servo switching valve. When moving in the first servo direction, it operates the pump volume adjuster in the first operation direction, and when moving to the second servo position, it operates the pump volume adjuster in the second operation direction, and is engaged with an operation end portion of the pump volume adjuster. In response to an operation up to a predetermined position in front of the first operation direction operation end of the speed change operation member, the pump spool is positioned at the end position of the bypass portion via the pump operation connection mechanism, and the pump servo switching valve is operated so that the pump volume adjuster is positioned at the end position in the first operation direction by the pump servo piston. When the shift operation member is being operated between the predetermined position and the operation end in the first operation direction, while maintaining the state in which the pump volume adjuster is positioned at the first operation direction moving end by the pump servo piston, the pump spool is positioned at a slide position corresponding to the operation position of the shift operation member via the pump operation link mechanism. The continuously variable transmission structure according to any one of claims 10 to 12, characterized in that.

14. A variable displacement hydraulic pump in which the volume of the pump body changes in response to the operation of the pump volume adjuster and a variable displacement hydraulic motor in which the volume of the motor body changes in response to the operation of the motor volume adjuster. When the pump volume adjuster is positioned at the neutral position, the output rotational power becomes zero speed. When the pump volume adjuster is positioned in the forward rotation region and the reverse rotation region from the neutral position, the rotational direction of the output rotational power is configured to be the forward rotation direction and the reverse rotation direction, respectively. A hydraulic continuously variable transmission mechanism, A shift operation member for performing a switching operation of the rotational direction of the output of the hydraulic continuously variable transmission mechanism and a speed change operation of the rotational speed, A pump operation piston movable in both the first slide direction on one side in the axial direction and the second slide direction on the other side. The pump operation piston is directly or indirectly engaged with the operation end portion of the pump volume adjuster so as to operate the pump volume adjuster in the first operation direction and the second operation direction in response to the movement in the first and second slide directions. A neutral spring mechanism that generates a biasing force toward the neutral position when the pump operation piston is moved from the neutral position in the first and second slide directions while holding the pump operation piston at the neutral position when no external force is applied to the pump operation piston. First and second slide oil chambers configured to push the pump operation piston in the first and second slide directions against the biasing force of the neutral spring mechanism by the supplied pressure oil. A motor operation piston movable in both the volume reduction direction on one side in the axial direction and the volume increase direction on the other side. The motor operation piston is directly or indirectly engaged with the operation end portion of the motor volume adjuster so as to operate the motor volume adjuster in the volume reduction direction and the volume increase direction on the other side in response to the movement in the volume reduction direction and the volume increase direction. A volume increase operation spring that biases the motor operation piston in the volume increase direction. A volume reduction operation oil chamber configured to push the motor operation piston in a volume reduction direction against the biasing force of the volume increase operation spring by the supplied pressured oil; A first pressure control valve configured to supply and discharge pressured oil to and from the first slide oil chamber in accordance with the operation of the shift operation member that operates the pump volume adjuster in the first and second operation directions; A second pressure control valve configured to discharge and supply pressured oil to and from the second slide oil chamber in accordance with the operation of the shift operation member that operates the pump volume adjuster in the first and second operation directions; A flow path switching valve configured to introduce the pressured oil in the first and second slide oil chambers into the volume reduction operation oil chamber when the shift operation member is positioned in the forward rotation operation region and the reverse rotation operation region; After the pressured oil in the first and second slide oil chambers moves the pump operation piston from the neutral position in the corresponding slide direction to a predetermined holding elastic state in which the neutral spring mechanism biases the pump operation piston toward the neutral position with a predetermined biasing force, the pressured oil in the volume reduction operation oil chamber causes the motor operation piston to start moving in the volume reduction direction while elastically deforming the volume increase operation spring. The biasing forces of the neutral spring mechanism and the volume increase operation spring are set. A continuously variable transmission structure characterized by this.

15. The continuously variable transmission structure according to claim 14, characterized in that the neutral spring mechanism is configured to be in the predetermined holding elastic state when the pump operation piston positions the pump volume adjuster at the first operation direction moving end and the second operation direction moving end.

16. The continuously variable transmission structure according to claim 14, characterized in that the neutral spring mechanism is configured to be in the predetermined holding elastic state when the pump operation piston is positioned at a predetermined position in front of the moving ends in their respective operation directions when the pump volume adjuster is operated in the first and second operation directions.

17. The continuously variable transmission structure according to claim 16, characterized in that the biasing forces of the neutral spring mechanism and the volume increase operation spring are set such that when the pump volume adjuster reaches the first operation direction moving end and the second operation direction moving end by the pump operation piston, the motor operation piston positions the motor volume adjuster at the volume reduction direction moving end.

18. The neutral spring mechanism and the urging force of the volume increasing operation spring are set such that when the pump volume adjuster reaches the first and second operation direction moving ends by the pump operation piston, the motor operation piston positions the motor volume adjuster at a predetermined position in front of the moving end in the volume decreasing direction. The continuously variable transmission structure according to claim 16, characterized in that.

19. A variable volume type hydraulic pump in which the volume of the pump body changes according to the operation of the pump volume adjuster between the first operation direction moving end on one side and the second operation direction moving end on the other side, and a variable volume type hydraulic motor in which the volume of the motor body changes according to the operation of the motor volume adjuster, and A planetary gear mechanism that inputs the rotational power from the drive source and the hydraulic continuously variable transmission mechanism to the first element and the second element respectively, and synthesizes these rotational powers and outputs them from the third element, and A shift operation member that operates the shift state of the hydraulic continuously variable transmission mechanism, and A pump operation piston that is movable in both the first slide direction on one side in the axial direction and the second slide direction on the other side, and directly or indirectly engages with the operation end of the pump volume adjuster so as to operate the pump volume adjuster in the first and second operation directions according to the movement in the first and second slide directions. A pump operation piston, and A second slide spring that urges the pump operation piston in the second slide direction, and A first slide oil chamber configured to push the pump operation piston in the first slide direction against the urging force of the second slide spring by the supplied pressure oil, and A motor operation piston that is movable in both the volume decreasing direction on one side in the axial direction and the volume increasing direction on the other side, and directly or indirectly engages with the operation end of the motor volume adjuster so as to operate the motor volume adjuster in the volume decreasing direction and the volume increasing direction on the other side according to the movement in the volume decreasing direction and the volume increasing direction. A motor operation piston, and A volume increasing operation spring that urges the motor operation piston in the volume increasing direction, and A volume decreasing operation oil chamber configured to push the motor operation piston in the volume decreasing direction against the urging force of the volume increasing operation spring by the supplied pressure oil, and A pressure control valve that commonly switches the supply and discharge of the pressure oil to the first slide oil chamber and the volume decreasing operation oil chamber according to the operation of the shift operation member. The planetary gear mechanism is configured such that when the pump volume adjuster is positioned at the moving end in the second operation direction, the combined rotational power becomes zero speed, and as the pump volume adjuster is operated from the moving end in the second operation direction toward the moving end in the first operation direction, the combined rotational power is increased in speed in one direction, and the gear ratio is set accordingly. A continuously variable transmission structure, characterized in that the urging forces of the second slide spring and the volume increasing operation spring are set such that, after the pressure oil in the first slide oil chamber moves the pump operation piston in the first slide direction against the urging force of the second slide spring to a predetermined holding spring state in which the second slide spring urges the pump operation piston in the first slide direction with a predetermined urging force, the pressure oil in the volume decreasing operation oil chamber starts to move the motor operation piston in the volume decreasing direction while elastically deforming the volume increasing operation spring. Claim 20 The hydraulic continuously variable transmission mechanism according to claim 19, wherein when the pump volume adjuster is positioned at the moving end in the second operation direction, the output rotational power reaches the maximum reverse speed, and as the pump volume adjuster is operated in the first operation direction from the moving end in the second operation direction to a neutral position between the moving end in the second operation direction and the moving end in the first operation direction, the output rotational power is decelerated from the maximum reverse speed to zero speed, and as the pump volume adjuster is operated in the first operation direction from the neutral position to the moving end in the first operation direction, the output rotational speed is increased from zero speed to the maximum forward speed. Claim 21 The continuously variable transmission structure according to claim 19 or 20, characterized in that the second slide spring is configured to be in the predetermined holding spring state when the pump operation piston positions the pump volume adjuster at the moving end in the first operation direction. Claim 22 The continuously variable transmission structure according to claim 19 or 20, characterized in that the second slide spring is configured to be in the predetermined holding spring state when the pump operation piston positions the pump volume adjuster at a predetermined position in front of the moving end in the first operation direction. Claim 23 When the pump volume adjuster reaches the moving end in the first operation direction by the pump operation piston, the urging forces of the second slide spring and the volume increasing operation spring are set so that the motor operation piston positions the motor volume adjuster at the moving end in the volume decreasing direction. The stepless speed change structure according to claim 22, characterized in that.

24. When the pump volume adjuster reaches the moving end in the first operation direction by the pump operation piston, the urging forces of the second slide spring and the volume increasing operation spring are set so that the motor operation piston positions the motor volume adjuster at a predetermined position in front of the moving end in the volume decreasing direction. The stepless speed change structure according to claim 22, characterized in that.

25. Based on the movement of the pump operation piston, a pump hydraulic servo mechanism for hydraulically operating the pump volume adjuster, A motor hydraulic servo mechanism for hydraulically operating the motor volume adjuster based on the movement of the motor operation piston is provided. The stepless speed change structure according to any one of claims 14 to 24, characterized in that.

26. The pump operation piston is mechanically connected to the operation end of the pump volume adjuster so as to operate the pump volume adjuster in the first and second operation directions respectively in response to movement in the first and second slide directions, The motor operation piston is mechanically connected to the operation end of the motor volume adjuster so as to operate the motor volume adjuster in the volume decreasing direction and the volume increasing direction respectively in response to movement in the volume decreasing direction and the volume increasing direction. The stepless speed change structure according to any one of claims 14 to 24, characterized in that.

27. An urging force adjustment mechanism capable of adjusting the urging force of the volume increasing operation spring is provided. The stepless speed change structure according to any one of claims 1 to 9 and 14 to 26, characterized in that.

28. A motor operation piston case forming a housing space for the motor operation piston is provided, The motor operation piston is housed in the housing space in a state where it can move in both axial directions while defining a spring chamber for housing the volume increasing operation spring on the side opposite to the volume decreasing operation oil chamber and the volume decreasing operation oil chamber, The urging force adjustment mechanism has a spring receiver that engages with the base end side of the volume increasing operation spring, which is opposite to the tip end side that is the engagement end with the motor operation piston. The stepless speed change structure according to claim 27, characterized in that the spring receiver is supported by the motor operation piston case in a fixed position adjustable manner.

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