Hydrostatic transmission

Abstract

According to the present invention, provided is a hydrostatic transmission comprising: a hydraulic pump (110) which discharges a fluid; a hydraulic motor (120) which is operated by the fluid discharged by the hydraulic pump (110) and outputs a torque that varies depending on the tilt angle of a swash plate (121); a piston (130) which advances and retracts in an advance / retraction section (Sar) so as to adjust the tilt angle of the swash plate (121); and a piston body (140) accommodating the piston (130).

Description

hydrostatic transmission

[0001] The present invention relates to a hydrostatic transmission capable of two-speed control.

[0002] Hydrostatic transmissions (HSTs) facilitate the maintenance of high torque output because they transmit power via hydraulics. Additionally, they enable easy implementation of continuously variable speeds, making them suitable for fine-tuning the output delivered to implements via a Power Take-Off (PTO).

[0003] Accordingly, it is mainly adopted by work vehicles such as tractors.

[0004] The hydrostatic transmission includes a hydraulic pump and a hydraulic motor.

[0005] In a hydraulic pump, a piston linked to a rotating input shaft slides on a swash plate, thereby inducing a change in volume inside the piston block into which the piston is inserted, and accordingly discharges hydraulic fluid.

[0006] The hydraulic fluid discharged from the hydraulic pump is supplied to the hydraulic motor through a path extending to the hydraulic motor. The hydraulic pressure resulting from the fluid supply causes a change in volume within the hydraulic motor's piston block, and as the piston slides on the swash plate, the piston block rotates to transmit power to the output shaft.

[0007] Hydrostatic transmissions typically controlled output torque by rotating the pump-side swash plate. However, a wider range of output control was required, and accordingly, hydrostatic transmissions capable of 2-speed control (switching) that also varied the motor-side swash plate emerged.

[0008] Hydrostatic transmissions capable of 2-speed control have a problem in that the shifting shock is large when the motor-side swash plate is switched. Prior art recognizing this problem has been disclosed (Registered Patent Publication No. 10-1988413).

[0009] Figure 1 is a cross-sectional view of a conventional hydrostatic transmission capable of 2-speed control.

[0010] Referring to FIG. 1, the conventional hydrostatic transmission discloses a hydraulic pump (10') and a hydraulic motor (20').

[0011] The hydraulic pump (10') performs speed change by discharging a flow rate that varies according to the angle of inclination of the pump swash plate (12').

[0012] The hydraulic motor (20') is driven by hydraulic fluid from the hydraulic pump (10') and rotates in a low-speed mode or a high-speed mode as the angle of the motor swash plate (22') is operated between the maximum tilt angle (a2) or the minimum tilt angle (a1) to drive the hydraulic equipment.

[0013] At this time, hydraulic fluid supplied from the hydraulic pump (10') through the flow path (Ls) and port (A) flows into the lower outer surface of the motor plate (22') and acts as a control pressure.

[0014] Figure 2 shows the rotational speed of the hydraulic motor - load pressure - torque of the hydraulic motor according to Figure 1.

[0015] As shown in FIG. 2, when the load pressure exceeds a certain value, the rotational speed and torque of the hydraulic motor change rapidly. In other words, the hydrostatic transmission according to FIG. 1 experiences significant shifting shock when switching between two speeds.

[0016] Accordingly, the prior art attempts to solve this problem by proposing the following hydrostatic transmission.

[0017] Figure 3 is a cross-sectional view of a hydrostatic transmission according to the prior art.

[0018] According to FIG. 3, a hydrostatic transmission according to the prior art discloses a hydraulic motor (20) comprising a hydraulic pump (10) and a swash plate (22) capable of turning at two turning angles.

[0019] In addition to this, the prior art discloses a proportional control valve (30) that takes hydraulic pressure supplied from a hydraulic pump (10) as input and outputs a control pressure for controlling a swash plate (22).

[0020] The description of the operation of the proportional control valve (30) is replaced with the content disclosed in the prior art document (Registered Patent Publication No. 10-1988413).

[0021] This specification describes the effects of the prior art by introducing a proportional control valve (30).

[0022] Figure 4 shows the rotational speed - load pressure - torque of the hydraulic motor (20) according to Figure 3.

[0023] As shown in FIG. 4, the hydraulic motor (20) has a proportional control section in which the rotational speed gradually decreases and the torque increases as the load pressure increases.

[0024] That is, according to the prior art, a technology is provided that can mitigate shifting shock when switching between two speeds of a hydrostatic transmission.

[0025] However, according to Fig. 4, the curves of rotational speed and torque show a bending shape at both ends of the proportional control section. That is, even according to the prior art, shifting shock still occurs in the hydraulic motor when entering the proportional control section and when exiting the proportional control section.

[0026] 2-speed control technology has a clear advantage in that it expands the shifting range of hydrostatic transmissions. However, the shifting shock during 2-speed switching is a factor that undermines the advanced advantage of hydrostatic transmissions, which enables precise output control. As such, technology to reduce shifting shock during 2-speed switching is urgently needed in hydrostatic transmissions.

[0027] [Prior Art Literature]

[0028] [Patent Literature]

[0029] (Patent Document 1) Registered Patent Publication No. 10-1988413

[0030] The present invention was invented in an attempt to reduce the shifting shock that occurs at the start and end of the switching operation of the motor swash plate during the 2-speed switching of a hydrostatic transmission capable of 2-speed control.

[0031] According to one embodiment of the present invention, the invention comprises: a hydraulic pump (110) for discharging fluid; a hydraulic motor (120) that operates by the fluid discharged by the hydraulic pump (110) and outputs a torque that varies according to the tilt angle of the swash plate (121); a piston (130) capable of adjusting the tilt angle of the swash plate (121) by moving back and forth in a forward / backward section (Sar); and a piston body (140) for housing the piston (130), wherein the piston body (140) includes a placement space (141) in which the piston (130) is placed; and a supply passage (142) that communicates the placement space (141) with the outside (OR) so that operating fluid can be supplied to the piston (130). A discharge passage (143) is formed to communicate the outside (OR) and the placement space (141) so that working fluid can be discharged from the piston (130); and the piston (130) moves forward and backward by the operating hydraulic pressure of the working fluid supplied through the supply passage (142), and when the piston (130) advances in the buffer section (Sd), which is part of the advance / retreat section (Sar), the working fluid is discharged into the discharge passage (143), thereby lowering the operating hydraulic pressure, thereby providing a constant hydraulic transmission (100).

[0032] The above piston (130) may be formed with a hydraulic chamber (131) for filling with hydraulic fluid capable of applying operating hydraulic pressure; an inlet port (132) connecting the supply passage (142) and the hydraulic chamber (131); and an outlet port (133) connecting the hydraulic chamber (131) and the discharge passage (143) in the buffer section (Sd) as the piston (130) moves back and forth, and being blocked by the piston body (140) in the section excluding the buffer section (Sd).

[0033] According to the above hydraulic transmission, the hydraulic fluid supplied through the supply passage (142) is filled into the hydraulic chamber (131) through the inlet port (132) to apply hydraulic pressure to the piston (130), and a portion of the hydraulic fluid filled in the hydraulic chamber (131) in the buffer section (Sd) can be discharged through the discharge port (133) to the discharge passage (143).

[0034] The above buffer section (Sd) includes a point where the piston (130) begins to advance, and as the piston (130) advances in the buffer section (Sd), the communication area (CF) in which the discharge hole (133) and the discharge passage (143) communicate with each other can be gradually narrowed.

[0035] The above buffer section (Sd) includes a point where the piston (130) ends its forward movement, and when the piston (130) moves forward in the buffer section (Sd), the communication area (CF) in which the discharge hole (133) and the discharge passage (143) communicate with each other can be gradually widened.

[0036] The above discharge hole (133) may have an expanded diameter on the side of the piston body (140).

[0037] According to one embodiment, the hydrostatic transmission may further include an elastic spring (ES) connected to the piston (130) and applying an elastic force in the retracting direction to the piston (130) as it advances.

[0038] The above hydrostatic transmission can be configured so that the angle of tilt of the swash plate (121) decreases as the piston (130) advances.

[0039] According to the present invention, the "amount of change" in rotational speed / torque at the start and end points of the switching operation of the motor swash plate can be gradually changed by simply adding a simple piston structure.

[0040] Therefore, the effect of reducing shift shock is maximized at the start and end points of the switching operation.

[0041] As a result, it is possible to apply 2-speed control technology for a wider gear range while minimizing damage to the continuously variable transmission, which is an inherent characteristic of hydrostatic transmissions, and thus provide a work vehicle capable of precise output control over a wider range.

[0042] In addition, various additional effects may be available according to different embodiments of the present invention. These are described in the description of the relevant embodiments.

[0043] Figure 1 is a cross-sectional view of a conventional hydrostatic transmission capable of 2-speed control.

[0044] Figure 2 shows the rotational speed of the hydraulic motor - load pressure - torque of the hydraulic motor according to Figure 1.

[0045] Figure 3 is a cross-sectional view of a hydrostatic transmission according to the prior art.

[0046] Figure 4 shows the rotational speed of the hydraulic motor - load pressure - torque of the hydraulic motor according to Figure 3.

[0047] FIG. 5 is a cross-sectional view of a hydrostatic transmission (100) according to one embodiment of the present invention.

[0048] Figure 6 is an enlarged view of area A according to Figure 5.

[0049] Figure 7 is a cross-sectional view of a piston body according to Figure 6.

[0050] Figure 8 is an enlarged view of the other side of the supply channel and one side of the inlet hole according to Figure 6.

[0051] Figure 9 is an enlarged view of the surface where the discharge passage and the discharge hole come into contact when the piston is in the buffer section.

[0052] FIG. 10 is an enlarged view of the point where the discharge hole and the discharge channel meet according to another embodiment.

[0053] FIG. 11 illustrates the positional relationship between the discharge passage and the discharge port during the forward and backward sections, from when the piston starts moving forward until it ends (in order from (a) to (e)) or from when it starts moving backward until it ends (in order from (e) to (a)).

[0054] Figure 12 shows the rotational speed - load pressure of a hydraulic motor according to Figure 5, which can be compared with Figures 2 and 4.

[0055] FIG. 13 illustrates a hydrostatic transmission in which the angle of inclination of the swash plate increases as the piston advances.

[0056] Preferred embodiments according to the present invention are described with reference to the accompanying drawings, provided that for the sake of brevity, descriptions of well-known configurations are omitted or compressed as much as possible.

[0057] Since the hydrostatic transmission (100) according to the present invention is also a type of hydrostatic transmission capable of 2-speed control introduced above, it includes a hydraulic pump (110) and a hydraulic motor (120).

[0058] Therefore, detailed descriptions of configurations that are not necessary to explain the technical concept of the present invention and that a person skilled in the art can easily implement through known inventions will be omitted.

[0059] The technical concept of the present invention is clarified below by describing several embodiments of the invention.

[0060] <Explanation of the Components of a Hydrostatic Transmission>

[0061] FIG. 5 is a cross-sectional view of a hydrostatic transmission (100) according to one embodiment of the present invention.

[0062] The hydrostatic transmission (100) according to the present invention includes a hydraulic pump (110), a hydraulic motor (120), a piston (130), and a piston body (140).

[0063] A hydraulic pump (110) is provided to discharge fluid and supply it to a hydraulic motor (120).

[0064] The pressure from the fluid discharged by the hydraulic pump (110) can apply pressure to the swash plate (121) of the hydraulic motor (120) in a direction that reduces the tilt angle.

[0065] The hydraulic pump (110) is a standard type and can be easily implemented by a person of ordinary skill, so a detailed description is omitted.

[0066] The hydraulic motor (120) is operated by the fluid discharged by the hydraulic pump (110) and is provided to output a torque that varies according to the tilt angle of the swash plate (121).

[0067] The method of operation of the hydraulic motor (120) by means of the fluid discharged by the hydraulic pump (110) is the same as that of a known hydraulic motor (120), and since it is easy enough for a person skilled in the art to implement the present invention, a detailed description is omitted.

[0068] The swash plate (121) is configured to allow rotation between the maximum rotation angle and the minimum rotation angle, similar to the swash plate (121) of the conventional 2-speed control hydrostatic transmission (100) introduced earlier. For reference, according to FIG. 5, the swash plate (121) is located at the maximum rotation angle.

[0069] When the swash plate (121) tilts to the maximum tilt angle, the rotational speed of the hydraulic motor (120) decreases and the torque increases. When the swash plate (121) tilts to the minimum tilt angle, the rotational speed of the hydraulic motor (120) increases and the torque decreases.

[0070] As in the embodiment according to FIG. 5, the angle of inclination of the swash plate (121) may decrease as the piston (130) advances, but embodiments in which the angle of inclination of the swash plate increases as the piston advances are not excluded from the scope of the present invention.

[0071] The piston (130) is configured to adjust the tilt angle of the swash plate (121) by moving back and forth in the advance / retreat section (Sar).

[0072] The advance / retreat section (Sar) is defined as a set of positions in which the piston (130) may exist to adjust the tilt angle of the swash plate (121). That is, according to the present invention, the piston (130) functions by being positioned within the advance / retreat section (Sar).

[0073] The piston (130) can be configured to advance by the hydraulic pressure of the supplied hydraulic fluid.

[0074] The piston body (140) is provided to accommodate the piston (130).

[0075] The piston body (140) may be implemented in a manner such that it is connected to a source of hydraulic pressure (not shown) for moving the swash plate (121) forward and backward, and is mounted on the motor-side swash plate (121) of an existing hydrostatic transmission. In this embodiment, the piston body (140) may function as a piston case (not shown).

[0076] When hydraulic fluid is supplied to the piston (130) through the piston body (140), the hydraulic fluid applies hydraulic pressure to the piston (130), and the piston (130) moves forward by the hydraulic pressure.

[0077] When the piston (130) advances, the tilt angle of the swash plate (121) decreases or increases, and accordingly, the torque and rotational speed of the hydraulic motor (120) are controlled.

[0078] The hydraulic fluid for applying operating hydraulic pressure to the piston (130) may be controlled by passing through a proportional control valve (not shown) as in the prior art, or it may even be supplied directly from a hydraulic pump, as in the conventional hydrostatic transmission that motivated the invention of the prior art. In other words, the method or source of supply for moving the piston (130) forward and backward according to the present invention is irrelevant as long as it is capable of applying operating hydraulic pressure to the piston (130).

[0079] Below, we will examine in detail the configuration of the piston (130) and the piston body (140).

[0080] <Explanation of Piston and Piston Body>

[0081] Figure 6 is an enlarged view of area A according to Figure 5.

[0082] FIG. 7 is a cross-sectional view of the piston body (140) according to FIG. 6.

[0083] Refer to FIGS. 6 and FIGS. 7 below.

[0084] A placement space (141), a supply passage (142), and a discharge passage (143) may be formed in the piston body (140).

[0085] A placement space (141) is formed to accommodate a piston (130).

[0086] The piston (130) placed in the placement space (141) is inserted into the placement space (141) and must be positioned so that it can move back and forth through lubrication by the lubricating oil.

[0087] The placement space (141) can be connected to the outside (OR) of the piston body (140) (hereinafter referred to as 'outside (OR)') through the supply path (142) and the discharge path (143).

[0088] The supply channel (142) is formed to connect the outside (OR) and the placement space (141) so that working fluid can be supplied to the piston (130).

[0089] One side of the supply channel (142) is connected to the outside (OR), and the other side is connected to the placement space (141).

[0090] The operating fluid introduced into the supply channel (142) through one side can be discharged into the placement space (141) through the other side.

[0091] The external (OR) beyond one side of the supply channel (142) may be understood as any configuration (not shown) capable of supplying hydraulic fluid to the piston body (140) or the piston (130) to apply hydraulic pressure for the reciprocating of the piston (130).

[0092] The supply channel (142) can be connected to the hydraulic chamber (131) formed in the piston (130) through the inlet hole (132) formed in the piston (130).

[0093] The position and diameter of the supply channel (142) can be determined in relation to the position and diameter of the inlet hole (132) formed in the piston (130), so the explanation will be given later.

[0094] The discharge passage (143) is formed to connect the outside (OR) and the placement space (141) so that working fluid can be discharged from the piston (130).

[0095] One side of the discharge channel (143) is connected to the placement space (141), and the other side is connected to the outside (OR).

[0096] The working fluid introduced into the discharge channel (143) through one side can be discharged to the outside (OR) through the other side.

[0097] The discharge passage (143) can be connected to the hydraulic chamber (131) formed in the piston (130) through the discharge hole (133) formed in the piston (130) according to the movement of the piston (130).

[0098] It is sufficient to understand that the outside (OR) beyond the other side of the discharge channel (143) is any space or configuration in which at least a portion of the working fluid supplied to the piston (130) through the supply channel (142) can be drained so as not to apply working hydraulic pressure to the piston (130).

[0099] The location of the discharge channel (143) is determined relatively in relation to the discharge hole (133) depending on where the location of the buffer section (Sd) is to be set within the advance / retreat section (Sar), so it will be explained in detail later.

[0100] According to FIGS. 6 and 7, two discharge channels (143) are formed to form two buffer sections (Sd), but it is also possible to form one buffer section (Sd) by forming them alternatively.

[0101] Referring to FIG. 6, the piston (130) may have a hydraulic chamber (131), an inlet port (132), and an outlet port (133) formed therein.

[0102] The hydraulic chamber (131) is formed to be filled with hydraulic fluid capable of applying operating hydraulic pressure.

[0103] The hydraulic chamber (131) can be connected to the outside (OR) beyond one side of the supply channel (142) through the inlet port (132) and the supply channel (142).

[0104] The hydraulic fluid filling the hydraulic chamber (131) can be supplied to the hydraulic chamber (131) from the outside (OR) through the supply passage (142) and the inlet port (132).

[0105] As hydraulic fluid is continuously filled into the hydraulic chamber (131), the pressure inside the hydraulic chamber (131) increases, and the increased pressure inside the hydraulic chamber (131) acts as operating hydraulic pressure to advance the piston (130).

[0106] When the pressure inside the hydraulic chamber (131) increases, the discharge port (133) connects the hydraulic chamber (131) and the discharge passage (143) according to the movement of the piston (130), so that the hydraulic fluid can be discharged to the outside (OR) through the discharge port (133) and the discharge passage (143). At this time, the speed of the piston (130) moving back and forth according to the hydraulic pressure decreases. This section of the movement section (Sar) is called the buffer section (Sd) (details will be described later).

[0107] The inlet port (132) is formed to connect the supply channel (142) and the hydraulic chamber (131).

[0108] One side of the inlet port (132) is connected to the other side of the supply channel (142), and the other side of the inlet port (132) is connected to the hydraulic chamber (131). The hydraulic fluid supplied through the supply channel (142) is filled into the hydraulic chamber (131) through the inlet port (132), thereby applying hydraulic pressure to the piston (130).

[0109] FIG. 8 is an enlarged view of the other side of the supply channel (142) and one side of the inlet port (132) according to FIG. 6. The dotted line indicates the position of the inlet port (132) when the piston (130) has advanced all the way.

[0110] As referenced in FIG. 8, the diameter (w-142) of the supply channel (142) is preferably greater than or equal to the sum of the diameter (w-132) of the inlet port (132) and the length (w-Sar) of the reciprocating section (Sar). According to this embodiment, the inlet port (132) and the supply channel remain connected throughout the entire reciprocating section (Sar).

[0111] According to this, the hydraulic pressure in the path between the external (OR) on one side of the supply path supplying the hydraulic fluid and the hydraulic chamber (131) is maintained constant throughout the entire advance / retreat section (Sar).

[0112] The discharge port (133) is formed to communicate the hydraulic chamber (131) and the discharge passage (143) in the buffer section (Sd) as the piston (130) moves back and forth, and to be shielded by the piston body (140) in the section excluding the buffer section (Sd).

[0113] FIG. 9 is an enlarged view of the surface where the discharge passage (143) and the discharge hole (133) come into contact when the piston (130) is in the buffer section (Sd).

[0114] Referring to FIG. 9, the buffer section (Sd) can be understood as a section in which a portion of the hydraulic fluid filled in the hydraulic chamber (131) in the advance / retreat section (Sar) is discharged through the discharge port (133) to the discharge path (143). The advance of the piston (130) is performed by filling the hydraulic chamber (131) with hydraulic fluid and applying hydraulic pressure to the piston (130). If the hydraulic chamber (131) and the discharge path (143) are connected by the discharge port (133), the hydraulic fluid in the hydraulic chamber (131) moves to the discharge path (143) through the discharge port (133), and accordingly, the speed of the piston (130), which advances and retreats according to the hydraulic pressure of the hydraulic chamber (131), is reduced. Of course, the hydraulic fluid moved to the discharge path (143) is discharged to the outside (OR).

[0115] In FIG. 9, the solid line indicates the position of the discharge port (133) when the piston (130) is fully retracted, and the dotted line indicates the position of the discharge port (133) when the piston (130) is fully advanced. According to this, the buffer section (Sd) may include both the point where the piston (130) begins to advance and the point where the piston (130) ends to advance.

[0116] FIG. 10 is an enlarged view of the point where the discharge hole (133) and the discharge channel (143) meet according to another embodiment. The dotted line shows the location of the discharge hole (133) in the buffer section (Sd), and the solid line shows the location of the discharge hole (133) in the advance / retreat section (Sar) other than the buffer section (Sd).

[0117] According to FIG. 10, the discharge port (133) may have an expanded diameter (w-133') on the side of the discharge channel (143). According to this, a lubrication space (LP) is formed on the side of the piston (130) block of the discharge port (133) so that working fluid can be contained therein even when it is not in the buffer section (Sd). The working fluid contained in the lubrication space (LP) can be continuously supplied between the piston body (140) and the piston (130). Therefore, there is no need to separately supply lubricating fluid for the smooth movement of the piston (130).

[0118] <Explanation of the Operation of Hydrostatic Transmissions>

[0119] 1. When the piston moves forward

[0120] FIG. 11 illustrates the positional relationship between the discharge passage (143) and the discharge port (133) in the advance / retreat section (Sar) from the start of the piston (130) until it finishes advancing (in order from (a) to (e)) or from the start of the reverse movement until it finishes retracting (in order from (e) to (a)).

[0121] FIGS. 11(a) and FIGS. 11(b) show the buffer section (Sd) including the point where the piston (130) begins to advance, and FIGS. 11(d) and FIGS. 11(e) show the buffer section (Sd) including the point where the piston (130) ends to advance.

[0122] FIG. 12 shows the rotational speed - load pressure of a hydraulic motor (120) according to FIG. 5, which can be compared with FIG. 2 and FIG. 4. The torque has been omitted as it moves in the opposite direction to the rotational speed.

[0123] According to FIG. 11(a), at the point where the piston (130) begins to advance, the communication area (CF) between the discharge port (133) and the discharge passage (143) becomes maximum. Consequently, the discharge amount of hydraulic fluid becomes maximum, and the reduction in the speed of the piston (130) is also maximum, so that the swash plate (121) does not begin to rotate abruptly. As a result, as referenced in FIG. 12, the abrupt increase in the rotational speed of the hydraulic motor (120) is prevented.

[0124] According to FIG. 11(b), when the piston (130) advances, the communication area (CF) in which the discharge port (133) and the discharge passage (143) communicate with each other can be gradually narrowed. That is, in this section, the discharge port (133) and the discharge passage (143) form a variable orifice structure that is gradually created. Accordingly, the discharge amount of hydraulic fluid is also gradually reduced, and the amount of reduction in the speed of the piston (130) is also gradually reduced, and the rotational speed of the swash plate (121) can be gradually increased. As a result, as referenced in FIG. 12, the amount of increase in the rotational speed of the hydraulic motor (120) increases gradually.

[0125] According to FIG. 11(c), in the forward / backward section (Sar) rather than the buffer section (Sd), the discharge hole (133) and the discharge passage (143) do not form a mutually communicating area (CF). Therefore, the hydraulic fluid is not discharged, and the hydraulic pressure also remains at the pressure corresponding to the control pressure. Consequently, the swash plate (121) can rotate at a constant speed, and as a result, the rotational speed also increases at a constant rate.

[0126] According to FIG. 11(d), when the piston (130) advances, the communication area (CF) in which the discharge hole (133) and the discharge passage (143) communicate with each other can be gradually widened. That is, in this section, the discharge hole (133) and the discharge passage (143) form a variable orifice structure that gradually disappears. Accordingly, the discharge amount of hydraulic fluid also gradually increases, and the amount of reduction in the speed of the piston (130) accordingly also gradually increases, and the rotational speed of the swash plate (121) can be gradually reduced. As a result, as referenced in FIG. 12, the amount of increase in the rotational speed of the hydraulic motor (120) gradually decreases.

[0127] According to FIG. 11(e), at the point where the piston (130) ends its forward movement, the communication area (CF) in which the discharge port (133) and the discharge passage (143) communicate with each other becomes maximum. Therefore, the amount of hydraulic fluid discharged becomes maximum, and the corresponding reduction in the speed of the piston (130) also becomes maximum, and the swash plate (121) does not end its forward movement abruptly. As a result, the abrupt end of the increase in the rotational speed of the hydraulic motor (120), as referenced in FIG. 12, is prevented.

[0128] 2. When the piston retracts

[0129] When the piston (130) retracts, the change in operating hydraulic pressure also exhibits a reverse order of the above-described sequence due to the variable orifice structure formed by the discharge port (133) and the discharge passage (143). Therefore, even when the piston (130) retracts, the hydraulic motor (120) has a rotational speed that gradually changes at the start and end points of the speed change (swash plate switching) as shown in FIG. 12.

[0130] However, the force that overcomes the operating hydraulic pressure and retracts the piston (130) needs to be explained.

[0131] According to the embodiment introduced above, the tilt angle of the swash plate (121) decreases as the piston (130) advances. Therefore, as the piston (130) advances, the swash plate (121) of the hydraulic motor (120) receives a load from the drive shaft (PA) to increase the tilt angle (hereinafter referred to as 'drive shaft load').

[0132] Therefore, a net force in the retraction direction is applied to the piston (130) by the drive shaft load.

[0133] That is, when the operating hydraulic pressure is reduced, the piston (130) naturally retracts.

[0134] FIG. 13 illustrates a hydrostatic transmission (100) in which the angle of rotation of the swash plate (121) increases as the piston (130) advances.

[0135] As referenced in FIG. 13, in another embodiment, the hydrostatic transmission (100) may further include an elastic spring.

[0136] The elastic spring (ES) is connected to the piston (130) and can apply an elastic force in the direction of retraction to the piston (130) that has advanced.

[0137] The elastic spring (ES) can be positioned in the hydraulic chamber (131) with both ends connected to the piston body (140) and the piston (130).

[0138] At this time, the operating hydraulic pressure for advancing the piston (130) is sufficient to overcome the elastic force of the elastic spring (ES) by combining with the drive shaft load applied to the swash plate (121) (at this time, the drive shaft load is in the direction to advance the piston (130)) and to apply a net force in the forward direction to the piston (130) (operating hydraulic pressure + drive shaft load > elastic force). That is, according to FIG. 13, the pressure for forming the operating hydraulic pressure does not necessarily have to be formed by a large pressure such as the hydraulic pressure generated by the hydraulic pump (110), and is sufficient with a small pressure that can be generated by a simple hydraulic device.

[0139] When the operating hydraulic pressure decreases, the piston (130) retracts due to the elastic force of the elastic spring (ES), and as the piston (130) retracts, the swash plate (121) connected to the front end of the piston (130) rotates in a direction in which the angle of rotation decreases.

[0140] By describing the above embodiment, an embodiment provided in a hydrostatic transmission (100) in which the angle of inclination of the swash plate (121) decreases as the piston (130) advances is not excluded from the scope of rights.

[0141] The above-described embodiments are merely preferred examples of the present invention and may have various applications. Therefore, the present invention should not be understood as being limited only to the contents described above. Instead, the scope of the present invention should be understood as the separately described claims and their equivalents.

Claims

1. A hydraulic pump (110) that discharges fluid; A hydraulic motor (120) that operates by the fluid discharged by the above hydraulic pump (110) and outputs a torque that varies according to the tilt angle of the swash plate (121); A piston (130) capable of adjusting the tilt angle of the sway plate (121) by moving back and forth in the advance / retreat section (Sar); and It includes a piston body (140) that accommodates the above piston (130), and The above piston body (140) A placement space (141) in which the above piston (130) is placed; A supply passage (142) that connects the outside (OR) and the placement space (141) so that working fluid can be supplied to the piston (130); and A discharge passage (143) is formed to connect the outside (OR) and the placement space (141) so that working fluid can be discharged from the piston (130), and The above piston (130) moves back and forth by the hydraulic pressure of the operating fluid supplied through the supply path (142), and When the piston (130) moves back and forth in the buffer section (Sd), which is part of the above-mentioned advance / retreat section (Sar), the working fluid is discharged into the discharge passage (143). Hydrostatic transmission (100).

2. In Paragraph 1 The above piston (130) A hydraulic chamber (131) for filling with hydraulic fluid capable of applying hydraulic pressure; An inlet hole (132) connecting the supply channel (142) and the hydraulic chamber (131); and As the piston (130) moves back and forth, the hydraulic chamber (131) and the discharge passage (143) are connected in the buffer section (Sd), and a discharge hole (133) is formed that is shielded by the piston body (140) in the section excluding the buffer section (Sd). The hydraulic fluid supplied through the above supply channel (142) is filled into the hydraulic chamber (131) through the above inlet hole (132) to apply hydraulic pressure to the piston (130), and In the above buffer section (Sd), a portion of the hydraulic fluid filled in the above hydraulic chamber (131) is discharged through the above discharge port (133) to the above discharge path (143). Hydrostatic transmission (100).

3. In Paragraph 2 The above buffer section (Sd) includes the point where the piston (130) begins to advance, and When the piston (130) advances in the above buffer section (Sd), the communication area (CF) in which the discharge hole (133) and the discharge passage (143) communicate with each other gradually narrows. Hydrostatic transmission (100).

4. In Paragraph 2 The above buffer section (Sd) includes a point where the piston (130) ends its forward movement, and When the piston (130) advances in the above buffer section (Sd), the communication area (CF) in which the discharge hole (133) and the discharge passage (143) communicate with each other gradually widens. Hydrostatic transmission (100).

5. In Paragraph 2 The above discharge hole (133) has an expanded diameter on the side of the piston body (140). Hydrostatic transmission (100).

6. In Paragraph 2 The apparatus further includes an elastic spring (ES) connected to the piston (130) and applying an elastic force in a retracting direction to the piston (130) that has advanced. Hydrostatic transmission (100).

7. In Paragraph 2 The tilt angle of the above plate (121) decreases as the above piston (130) advances. Hydrostatic transmission (100).

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