Transmission structure

Abstract

To provide a transmission structure capable of smoothly switching first to third speed stages according to vehicle speed.SOLUTION: A transmission structure includes: a speed change output device in which a continuously variable output between first and second speeds is input in a planetary third element; input side first to third transmission paths which can transmit driving source power to a planetary first or second element; output side first to third transmission paths which can transmit synthetic power from the planetary second or first element to a travel output shaft. When vehicle speed is a first speed stage up to first vehicle speed and a third speed stage which is equal to or higher than second vehicle speed, the first element becomes a reference power input section in which the driving source power is input and the second element becomes a synthetic output section. When the vehicle speed is a second speed stage between the first and second vehicle speed, the first element becomes the synthetic output section, and the second element becomes the reference power input section. Rotational speed of the second element when an output of the speed change output device is the second speed at the time of the first speed stage is made substantially the same as rotational speed at the time of the second speed stage. Rotational speed of the planetary first element when an output of the speed change output device is first speed at the time of the second speed stage is made substantially the same as rotational speed at the third speed stage.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a transmission structure having a planetary gear mechanism that combines and outputs rotational power from a drive source and rotational power from a speed-changing output device.

Background Art

[0002] A transmission structure having a planetary gear mechanism that combines and outputs rotational power from a drive source and rotational power from a hydrostatic continuously variable transmission mechanism (HST) acting as a speed-changing output device is suitably used, for example, in the running system transmission path of work vehicles such as combines and tractors, and various configurations have been proposed to expand the vehicle speed variable range.

[0003] For example, Patent Document 1 below discloses a transmission structure in which a hydrostatic-mechanical continuously variable transmission structure (HMT) formed by the HST and the planetary gear mechanism and a multi-stage transmission having three speed stages of a low speed stage, a medium speed stage, and a high speed stage are arranged in series in the running system transmission path to expand the vehicle speed variable range. However, the transmission structure described in Patent Document 1 is intended to perform the shift operation of the multi-stage transmission in advance before the vehicle starts running. When the shift operation of the multi-stage transmission is performed during vehicle running, the following disadvantages occur.

[0004] Regarding this point, a case will be described as an example in which the HMT is operated with the multi-stage transmission engaged in the low speed stage to increase the running vehicle speed, and when the running vehicle speed reaches a predetermined vehicle speed, the multi-stage transmission is shifted from the low speed stage to the medium speed stage.

[0005] In this case, when the output of the HMT reaches the maximum speed or near the maximum speed in the low speed stage engagement state of the multi-stage transmission, the multi-stage transmission is shifted from the low speed stage to the medium speed stage while the output of the HMT is maintained at the maximum speed or near the maximum speed. As a result, a large vehicle speed change occurs during shifting, the riding comfort deteriorates, and an excessive load is applied to the running system transmission path.

[0006] Regarding this point, the applicant of the present application has proposed a transmission structure including an HST, a planetary gear mechanism having first to third elements, an input of the HST output to the third element, a traveling output shaft operatively driven by a planetary output portion of the planetary gear mechanism, an input-side first transmission mechanism and an input-side second transmission mechanism capable of operatively transmitting the rotational power of a drive source to the first and second elements of the planetary gear mechanism respectively, an input-side first clutch mechanism and an input-side second clutch mechanism for respectively engaging and disengaging the power transmission of the input-side first transmission mechanism and the input-side second transmission mechanism, an output-side first transmission mechanism and an output-side second transmission mechanism capable of operatively transmitting the rotational power of the second and first elements to the traveling output shaft respectively, an output-side first clutch mechanism and an output-side second clutch mechanism for respectively engaging and disengaging the power transmission of the output-side first transmission mechanism and the output-side second transmission mechanism, an output-side third transmission mechanism and an output-side third clutch mechanism for engaging and disengaging the output-side third transmission mechanism, a shift operation member, and a control device (see Embodiments 8 and 9 of Patent Document 2 below).

[0007] In a first gear stage transmission state where the rotational speed of the traveling output shaft is less than a predetermined first vehicle speed X (see FIG. 7), the control device makes the input-side and output-side first clutch mechanisms engaged and the input-side and output-side second clutch mechanisms disengaged, so as to cause the first element to act as a planetary input portion for inputting reference power from the drive source and the second element to act as a planetary output portion, while presenting a first transmission state. While operating the output adjustment member so that the HST output shifts from the first HST speed to the second HST speed in response to a speed increase operation of the shift operation member. In a second gear stage transmission state where the rotational speed of the traveling output shaft is equal to or higher than the first vehicle speed X and less than a predetermined second vehicle speed Y, the control device makes the input-side and output-side first clutch mechanisms disengaged and the input-side and output-side second clutch mechanisms engaged, so as to cause the first element to act as a planetary output portion and the second element to act as a planetary input portion, while presenting a second transmission state. While operating the output adjustment member so that the HST output shifts from the second HST speed to the first HST speed in response to a speed increase operation of the shift operation member.

[0008] The reduction ratio of the input-side first transmission mechanism (input-side first reduction ratio) and the reduction ratio of the input-side second transmission mechanism (input-side second reduction ratio) are set such that when the HST output is set to the second HST speed in the first transmission state, the rotational speed of the second element is substantially the same as the rotational speed of the second element due to the rotational power transmitted through the input-side second transmission mechanism in the second transmission state, and when the HST output is set to the second HST speed in the second transmission state, the rotational speed of the first element is substantially the same as the rotational speed of the first element due to the rotational power transmitted through the input-side first transmission mechanism in the first transmission state.

[0009] The reduction ratio of the output-side first transmission mechanism (output-side first reduction ratio) and the reduction ratio of the output-side second transmission mechanism (output-side second reduction ratio) are set such that the rotational speed appearing on the transmission output shaft when the HST output is set to the second HST speed is substantially the same in the first and second transmission states.

[0010] Furthermore, in Patent Document 2, as shown in FIG. 7, when the speed change operation member is operated in the speed increasing direction in the second transmission state and the rotational speed of the traveling output shaft reaches the second vehicle speed Y, the control device shifts the output-side second clutch mechanism from the engaged state to the disengaged state and shifts the output-side third clutch mechanism from the disengaged state to the engaged state, and operates the output adjustment member so that the output of the HST changes from the rotational speed (first HST speed) that rotates the traveling output shaft at the second vehicle speed Y in the second transmission state to the rotational speed (third HST speed in FIG. 7) that rotates the traveling output shaft at the second switching speed Y or a speed in the vicinity thereof in the third transmission state.

[0011] The transmission structure described in Patent Document 2 is useful in that it can expand the transmission width of the transmission output shaft without causing a rapid change in the rotational speed of the transmission output shaft as compared with the transmission structure described in Patent Document 1.

[0012] However, regarding the switching between the second-speed transmission state and the third-speed transmission state, the switching of the second and third clutch mechanisms and the speed adjustment between the second and third HST speeds of the HST (the output adjustment member) must be controlled simultaneously, making the control complex and leaving room for improvement.

Prior Art Documents

Patent Documents

[0013]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0014] The present invention has been made in view of the above prior art, and includes a transmission output device that outputs continuously variable rotational power, a planetary gear mechanism, input-side first to third transmission paths capable of transmitting rotational power from a drive source to the planetary gear mechanism, and output-side first to third transmission paths capable of transmitting the combined rotational power output from the planetary gear mechanism to a traveling output shaft. By switching the input-side first to third transmission paths and the output-side first to third paths, a transmission structure capable of presenting first to third speed transmission states, and an object thereof is to provide a transmission structure capable of smoothly switching the first to third speed transmission states.

Means for Solving the Problems

[0015] To achieve the above object, a first aspect of the present invention is a transmission structure that steplessly changes the rotational power of a drive shaft operatively connected to a drive source and transmits the rotational power to a traveling output shaft that outputs the rotational power toward drive wheels, including a speed-changing output device that outputs rotational power for speed change that is steplessly changed at least between a first speed and a second speed, a planetary gear mechanism having first to third elements and inputting the rotational power for speed change to the third element, an input-side first transmission path that transmits the rotational power of the drive shaft to the first element, an input-side second transmission path that transmits the rotational power of the drive shaft to the second element, an input-side third transmission path that transmits the rotational power of the drive shaft to the first element, input-side first to third clutch mechanisms respectively inserted into the input-side first to third transmission paths, an output-side first transmission path that transmits the rotational power of the second element to the traveling output shaft, an output-side second transmission path that transmits the rotational power of the first element to the traveling output shaft, an output-side third transmission path that transmits the rotational power of the second element to the traveling output shaft, output-side first to third clutch mechanisms respectively inserted into the output-side first to third transmission paths, a speed-changing operation member, and a control device that controls the operation of the speed-changing output device, the input-side first to third clutch mechanisms, and the output-side first to third clutch mechanisms. The control device, when the absolute value of the rotational speed of the traveling output shaft is in the range up to a first vehicle speed, engages the input-side and output-side first clutch mechanisms and releases the remaining input-side clutch mechanisms and output-side clutch mechanisms to exhibit a first-speed-stage transmission state, and when the speed-changing operation member is operated to the vehicle stop position, changes the output of the speed-changing output device to the first speed to make the rotational speed of the second element zero, and changes the output of the speed-changing output device toward the second speed in response to the speed increase operation of the speed-changing operation member to increase the rotational speed of the second element. When the absolute value of the rotational speed of the traveling output shaft is in the range from the first vehicle speed to the second vehicle speed, engages the input-side and output-side second clutch mechanisms and releases the remaining input-side clutch mechanisms and output-side clutch mechanisms to exhibit a second-speed-stage transmission state, and changes the output of the speed-changing output device toward the first speed in response to the speed increase operation of the speed-changing operation member to increase the rotational speed of the first element. When the absolute value of the rotational speed of the traveling output shaft exceeds the second vehicle speed,By engaging the input-side third clutch mechanism and the output-side third clutch mechanism and disengaging the remaining input-side clutch mechanisms and output-side clutch mechanisms, a third-speed transmission state is exhibited, and in response to an upshift operation of the shift operation member, the output of the transmission output device is shifted toward the second speed to increase the rotational speed of the second element. When the output of the transmission output device is set to the second speed in the first-speed transmission state, the rotational speed of the second element is substantially the same as the rotational speed of the second element in the second-speed transmission state. When the output of the transmission output device is set to the second speed in the first-speed transmission state, the rotational speed of the first element is substantially the same as the rotational speed of the first element in the second-speed transmission state. When the output of the transmission output device is set to the first speed in the second-speed transmission state, the rotational speed of the first element is substantially the same as the rotational speed of the first element in the third-speed transmission state. When the output of the transmission output device is set to the first speed in the second-speed transmission state, the rotational speed of the second element is substantially the same as the rotational speed of the second element in the third-speed transmission state. A transmission structure is provided.

[0016] The transmission structure according to the first aspect may further include a first transmission shaft operatively connected to the first element, a second transmission shaft operatively connected to the second element, an input-side first and third drive gears rotatably supported relative to the drive shaft while being operatively connected to the first transmission shaft, and an input-side second drive gear rotatably supported relative to the drive shaft while being operatively connected to the second transmission shaft.

[0017] The input-side first to third clutch mechanisms may be configured to engage and disengage the power transmission from the drive shaft to the input-side first to third drive gears, respectively. The second transmission shaft may be arranged coaxially with the planetary gear mechanism. The first transmission shaft may be externally inserted in a state rotatable relative to the second transmission shaft.

[0018] A second aspect of the present invention is a transmission structure that steplessly changes the rotational power of a drive shaft operatively connected to a drive source and transmits the rotational power to a traveling output shaft that outputs the rotational power toward drive wheels. The transmission structure includes a speed-changing output device that outputs rotational power for speed change that is steplessly changed at least between a first speed and a second speed, a planetary gear mechanism having first to third elements and inputting the rotational power for speed change to the third element, an input shaft, an input-side first transmission path operatively connected to the first element, an input-side second transmission path that transmits the rotational power of the drive shaft to the second element, an input-side third transmission path operatively connected to the first element, an input shaft clutch mechanism that engages and disengages power transmission from the drive shaft to the input shaft, a shifter that can selectively operatively connect the input shaft to the input-side first and third transmission paths, an input-side second clutch mechanism inserted in the input-side second transmission path, an output-side first transmission path that transmits the rotational power of the second element to the traveling output shaft, an output-side second transmission path that transmits the rotational power of the first element to the traveling output shaft, an output-side third transmission path that transmits the rotational power of the second element to the traveling output shaft, output-side first to third clutch mechanisms respectively inserted in the output-side first to third transmission paths, a speed-changing operation member, and a control device that controls the operation of the speed-changing output device, the input-side first to third clutch mechanisms, and the output-side first to third clutch mechanisms. The control device, when the absolute value of the rotational speed of the traveling output shaft is in the range up to a first vehicle speed, engages the input shaft clutch mechanism and the output-side first clutch mechanism and disengages the remaining clutch mechanisms with the input shaft operatively connected to the input-side first transmission path by the shifter to exhibit a first-speed transmission state. When the speed-changing operation member is operated to the vehicle stop position, the control device changes the output of the speed-changing output device to the first speed, sets the rotational speed of the second element to zero speed, and changes the output of the speed-changing output device toward the second speed in response to an upshifting operation of the speed-changing operation member to increase the rotational speed of the second element. When the absolute value of the rotational speed of the traveling output shaft is in the range from the first vehicle speed to the second vehicle speed, the control device engages the input-side and output-side second clutch mechanisms and disengages the remaining clutch mechanisms to exhibit a second-speed transmission state, and changes the output of the speed-changing output device toward the first speed in response to an upshifting operation of the speed-changing operation member to increase the rotational speed of the first element.When the absolute value of the rotational speed of the traveling output shaft exceeds the second vehicle speed, with the input shaft operatively connected to the input-side third transmission path by the shifter, the input shaft clutch mechanism and the output-side third clutch mechanism are engaged and the remaining clutch mechanisms are disengaged to exhibit a third gear transmission state. Then, in response to the speed increasing operation of the shift operation member, the output of the transmission output device is shifted toward the second speed to increase the rotational speed of the second element. It is configured such that the rotational speed of the second element when the output of the transmission output device is set to the second speed in the first gear transmission state is substantially the same as the rotational speed of the second element in the second gear transmission state, the rotational speed of the first element in the first gear transmission state is substantially the same as the rotational speed of the first element when the output of the transmission output device is set to the second speed in the second gear transmission state, the rotational speed of the first element when the output of the transmission output device is set to the first speed in the second gear transmission state is substantially the same as the rotational speed of the first element in the third gear transmission state, and the rotational speed of the second element in the second gear transmission state is substantially the same as the rotational speed of the second element when the output of the transmission output device is set to the first speed in the third gear transmission state. A transmission structure is provided.

[0019] In one form of the second aspect, when upshifting from the second gear transmission state to the third gear transmission state, the control device causes the shifter to pre-connect the input shaft to the input-side third transmission path to exhibit a third gear preparation state when the rotational speed of the traveling output shaft reaches a shift-up preparation speed that is a predetermined speed lower than the second vehicle speed. When downshifting from the second gear transmission state to the first gear transmission state, the control device causes the shifter to pre-connect the input shaft to the input-side first transmission path to exhibit a first gear preparation state when the rotational speed of the traveling output shaft reaches a downshift preparation speed that is a predetermined speed higher than the first vehicle speed.

[0020] In another form of the second aspect, when the rotational speed of the traveling output shaft is increasing in the second speed stage transmission state, the control device causes the input shaft to be connected to the input side third transmission path by the shifter to exhibit a third speed stage preparation state, and when the rotational speed of the traveling output shaft is decreasing in the second speed stage transmission state, the control device causes the input shaft to be connected to the input side first transmission path by the shifter to exhibit a first speed stage preparation state.

[0021] The transmission structure according to the second aspect further includes a first transmission shaft operatively connected to the first element, a second transmission shaft operatively connected to the second element, an input side first and third drive gears rotatably supported relative to the input shaft while being operatively connected to the first transmission shaft, and an input side second drive gear rotatably supported relative to the drive shaft while being operatively connected to the second transmission shaft.

[0022] The shifter may be configured to selectively engage the input shaft with the input side first and third drive gears. The input side second clutch mechanism may be configured to engage and disengage power transmission from the drive shaft to the input side second drive gear. The second transmission shaft may be arranged coaxially with the planetary gear mechanism. The first transmission shaft may be externally inserted in a state of being relatively rotatable with respect to the second transmission shaft.

[0023] The transmission structure according to the present invention may further include an input side first and third driven gears supported non-rotatably relative to the first transmission shaft and operatively connected to the input side first and third drive gears respectively, and an input side second driven gear supported non-rotatably relative to the second transmission shaft and operatively connected to the input side second drive gear.

[0024] In this case, the input-side first drive gear, the input-side first driven gear, and the first transmission shaft form the input-side first transmission path, the input-side second drive gear, the input-side second driven gear, and the second transmission shaft form the input-side second transmission path, and the input-side third drive gear, the input-side third driven gear, and the first transmission shaft form the input-side third transmission path.

[0025] The transmission structure according to the present invention may further include an intermediate shaft disposed between the first and second transmission shafts and the traveling output shaft in the transmission direction, an output-side first gear rotatably supported on the intermediate shaft while being operatively connected to the second transmission shaft, an output-side second gear rotatably supported on the intermediate shaft while being operatively connected to the first transmission shaft, and an output-side third gear rotatably supported on the traveling output shaft while being operatively connected to the second transmission shaft.

[0026] In this case, the output-side first and second clutch mechanisms may be configured to engage and disengage the power transmission from the output-side first and second gears to the intermediate shaft, respectively. The output-side third clutch mechanism may be configured to engage and disengage the power transmission from the output-side third gear to the traveling output shaft.

[0027] Preferably, the output-side first gear is operatively connected to the second transmission shaft via the input-side second driven gear, the output-side second gear is operatively connected to the first transmission shaft via the input-side first driven gear, and the output-side third gear is operatively connected to the second transmission shaft via the output-side first gear.

[0028] More preferably, the transmission structure according to the present invention includes an output-side intermediate gear rotatably supported on the intermediate shaft and non-rotatably connected to the output-side first gear. The output-side third gear is operatively connected to the output-side intermediate gear.

[0029] More preferably, the transmission structure according to the present invention includes a forward transmission mechanism and a reverse transmission mechanism that can operatively transmit the rotational power of the intermediate shaft to the traveling output shaft as forward rotational power and reverse rotational power, respectively, and a forward clutch mechanism and a reverse clutch mechanism that engage and disengage the power transmission of the forward transmission mechanism and the reverse transmission mechanism, respectively. In this case, the forward transmission mechanism and the reverse transmission mechanism form part of the output-side first and second transmission paths.

Advantages of the Invention

[0030] According to the transmission structure of the present invention, it is possible to smoothly switch the first to third gear transmission states exhibited by the switching of the input-side first to third transmission paths and the output-side first to third transmission paths. Further, in the first to third gear transmission states, the speed-changing output device in the transmission structure only reciprocates its output between the first speed and the second speed, so the control is also simplified.

Brief Description of the Drawings

[0031]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Embodiments for Carrying Out the Invention

[0032] Embodiment 1 Hereinafter, an embodiment of the transmission structure according to the present invention will be described with reference to the accompanying drawings. FIG. 1 shows a transmission schematic diagram of a work vehicle 200 to which a transmission structure 1A according to this embodiment is applied. Further, FIG. 2 shows a longitudinal side view of the transmission structure 1A.

[0033] As shown in FIG. 1, the work vehicle 200 includes a drive source 210, a drive shaft 212 operatively connected to the drive source 210, drive wheels 220, a traveling output shaft 47 that outputs rotational power toward the drive wheels 220, and the transmission structure 1A that transmits rotational power from the drive shaft 212 to the traveling output shaft 47. Note that reference numeral 210a in FIGS. 1 and 2 is a flywheel included in the drive source 210.

[0034] The work vehicle 200 has a pair of left and right main drive wheels as the drive wheels 220. Therefore, as shown in FIG. 1, the work vehicle 200 further includes a pair of main drive axles 250 that respectively drive the pair of main drive wheels 220, and a differential mechanism 260 that differentially transmits the rotational power of the traveling output shaft 47 to the pair of main drive axles 250.

[0035] As shown in FIG. 1, the work vehicle 200 further includes a traveling brake mechanism 255 that selectively applies a braking force to the main drive axle 250, a deflock mechanism 265 that forcibly synchronously drives the pair of main drive axles 250 by the rotational power from the traveling output shaft 47, and a drive force extraction mechanism 270 for sub-drive wheels that can selectively output the rotational power taken out from the traveling output shaft 47 toward sub-drive wheels.

[0036] In addition, the work vehicle 200 includes a PTO shaft 280 that outputs rotational power to the outside, and a PTO clutch mechanism 285 and a PTO multi-stage speed change mechanism 290 that are inserted into a PTO transmission path from the drive source 210 to the PTO shaft 280.

[0037] The transmission structure 1A includes a speed change output device, a planetary gear mechanism 30, input side first to third transmission paths 50(1) to 50(3), input side first to third clutch mechanisms 60(1) to 60(3), output side first to third transmission paths 70(1) to 70(3), output side first to third clutch mechanisms 80(1) to 80(3), a speed change operation member, and a control device 100.

[0038] The speed change output device is configured to output rotational power for speed change that is steplessly changed at least between the first speed and the second speed. The speed change output device is operationally controlled by the control device 100.

[0039] As shown in FIGS. 1 and 2, the transmission structure 1A according to the present embodiment includes a hydrostatic continuously variable transmission mechanism (HST) 10 as the speed change output device. The HST 10 cooperates with the planetary gear mechanism 30 to form an HMT (hydrostatic-mechanical continuously variable transmission structure). Note that it is also possible to provide the transmission structure 1A with two electric motors capable of outputting continuously variable rotation by manual operation instead of the HST 10 as the speed change output device. One of the electric motors drives one element of the three planetary elements constituting the planetary gear mechanism 30 at a constant speed, and the other of the electric motors is configured to be able to switch between forward and reverse rotation and drives another element of the three planetary elements with speed change.

[0040] As shown in FIGS. 1 and 2, the HST 10 includes a pump shaft 12 that is operatively rotationally driven by the drive source 210, an HST pump 14 that is supported non-rotatably relative to the pump shaft 12, an HST motor 18 that is fluidly connected to the HST pump 14 via a pair of first and second HST lines and is hydraulically rotationally driven by the HST pump 14, a motor shaft 16 that supports the HST motor 18 non-rotatably, and an output adjusting member 20 that changes the volume of at least one of the HST pump 14 and the HST motor 18.

[0041] The HST 10 is capable of steplessly changing the ratio of the rotational speed of the HST output output from the motor shaft 16 to the rotational speed of the power input to the pump shaft 12 (i.e., the gear ratio of the HST 10) according to the operating position of the output adjusting member 20.

[0042] That is, when the rotational speed of the rotational power operatively input from the drive source 210 to the pump shaft 12 is defined as the reference input speed, the HST 10 steplessly changes the rotational power of the reference input speed from at least the first speed to the rotational power between the second speeds according to the operating position of the output adjusting member 20 and outputs it from the motor shaft 16. Note that reference numeral 195a in FIG. 1 is a shift output sensor that detects the output rotational speed of the shift output device (the HST 10 in the present embodiment).

[0043] Note that in the present embodiment, as shown in FIGS. 1 and 2, the pump shaft 12 is connected to the drive shaft 212 operatively connected to the drive source 210 via an HST input gear train 214.

[0044] FIG. 4 shows the relationship between the output rotational speed of the HST 10 and the rotational speed (vehicle speed) of the driving rotational power of the transmission structure 1A. As shown in FIG. 4, in the present embodiment, the HST 10 is capable of switching the rotational direction of the HST output between forward and reverse.

[0045] That is, when the rotation direction of the reference input speed is the forward rotation direction, when the output adjustment member 20 is located at the first operating position, the rotation power of the first speed (for example, the maximum reverse rotation speed Rmax) with the rotation direction being one side of the forward and reverse directions (for example, the reverse rotation direction) is output from the motor shaft 16, and when the output adjustment member 20 is located at the second operating position, the rotation power of the second speed (the maximum forward rotation speed Fmax) with the rotation direction being the other side of the forward and reverse directions (for example, the forward rotation direction) is output from the motor shaft 16.

[0046] In this case, when the output adjustment member 20 is located at the neutral position between the first and second operating positions, the rotational speed of the HST output becomes the neutral speed (zero speed).

[0047] In the present embodiment, as the output adjustment member 20, the HST 10 is a swash plate that is swung around a swing shaft, which is common as an axial piston pump, and changes the volume of the HST pump 14, and has a swash plate that can swing to one side and the other side around the swing shaft with a neutral position where the discharge amount discharged from the HST pump 14 is zero (see FIG. 2).

[0048] When the swash plate is located at the neutral position, the discharge of the pressure oil from the HST pump 14 stops, and the HST 10 becomes a neutral state where the output of the HST motor 18 is zero.

[0049] When the swash plate is swung from the neutral position to the forward rotation side on one side around the swing shaft, pressure oil is supplied from the HST pump 14 to one of the pair of HST lines, the one first HST line becomes the high pressure side, and the other second HST line becomes the low pressure side. As a result, the HST motor 18 is rotationally driven to the forward rotation side, and the HST 10 becomes a forward rotation output state.

[0050] Conversely, when the movable swash plate is swung from the neutral position to the reverse side on the other side around the swing axis, pressure oil is supplied from the HST pump 14 to the other second HST line of the pair of HST lines, the other second HST line becomes the high-pressure side, and one first HST line becomes the low-pressure side. As a result, the HST motor 18 is rotationally driven to the reverse side, and the HST 10 enters the reverse output state. In the HST 10, the volume of the HST motor 18 is fixed by a fixed swash plate.

[0051] The output adjusting member 20 is operationally controlled by the control device 100 according to the operation of the shift operation member.

[0052] That is, the transmission structure 1 according to the present embodiment has an HST shift actuator for operating the output adjusting member 20, and the control device 100 operates the output adjusting member 20 via the HST shift actuator according to the operation of the shift operation member.

[0053] The HST shift actuator can take various configurations such as an electric motor or a hydraulic mechanism (e.g., a hydraulic servo mechanism) as long as it can be operationally controlled by the control device 100. Reference numeral 112 in FIG. 1 is a valve block in which electromagnetic valves and the like in the hydraulic mechanism are housed.

[0054] As shown in FIG. 1, the transmission structure 1A according to the present embodiment has an accelerator pedal 190a and a main shift lever 190b as the shift operation members. Reference numerals 192a and 192b in FIG. 1 are sensors for detecting the operation positions of the accelerator pedal 190a and the main shift lever 190b, respectively.

[0055] As shown in FIGS. 1 and 2, the planetary gear mechanism 30 includes a sun gear 32, a planetary gear 34 meshing with the sun gear 32, an internal gear 36 meshing with the planetary gear 34, and a carrier 38 that rotatably supports the planetary gear 34 about its axis and rotates about the axis of the sun gear 32 in conjunction with the revolution of the planetary gear 34 around the sun gear 32. The sun gear 32, the carrier 38, and the internal gear 36 form three planetary elements.

[0056] One of the three planetary elements, i.e., the third element, acts as a variable power input portion for inputting the rotational power for shifting. In the present embodiment, the sun gear 32 is the third element.

[0057] As described above, in the present embodiment, the HST 10 is provided as the shifting output device. Therefore, the third element (sun gear 32) is operatively connected to the motor shaft 16. In the present embodiment, the sun gear 32 is operatively connected to the motor shaft 16 via the HST output gear train 216.

[0058] The input-side first and third transmission paths 50(1) and 50(3) are configured to transmit the rotational power of the drive shaft 212 to the first element, and the input-side second transmission path 50(2) is configured to transmit the rotational power of the drive shaft 212 to the second element. In the present embodiment, the internal gear 36 is the first element, and the carrier 38 is the second element.

[0059] As shown in FIGS. 1 and 2, the transmission structure 1A according to the present embodiment includes a first transmission shaft 150 operatively connected to the first element (the internal gear 36), a second transmission shaft 152 operatively connected to the second element (the carrier), and input-side first and third drive gears 52(1), 52(3) rotatably supported relative to the drive shaft 212 while being operatively connected to the first transmission shaft 150, and an input-side second drive gear 52(2) rotatably supported relative to the drive shaft 212 while being operatively connected to the second transmission shaft 152.

[0060] In such a configuration, the input-side first drive gear 52(1) and the first transmission shaft 150 form the input-side first transmission path 50(1), the input-side second drive gear 52(2) and the second transmission shaft 152 form the input-side second transmission path 50(2), and the input-side third drive gear 52(3) and the first transmission shaft 150 form the input-side third transmission path 50(3).

[0061] In the present embodiment, as shown in FIGS. 1 and 2, the second transmission shaft 152 is disposed coaxially with the planetary gear mechanism 30, and the first transmission shaft 150 is externally inserted in a state of being relatively rotatable with respect to the second transmission shaft 152.

[0062] As shown in FIGS. 1 and 2, the transmission structure 1A according to the present embodiment further includes input-side first and third driven gears 54(1), 54(3) non-rotatably supported with respect to the first transmission shaft 150 and operatively connected to the input-side first and third drive gears 52(1), 52(3) respectively, and an input-side second driven gear 54(2) non-rotatably supported with respect to the second transmission shaft 152 and operatively connected to the input-side second drive gear 52(2).

[0063] The input-side first to third driven gears 54(1) to 54(3) each form a part of the input-side first to third transmission paths 50(1) to 50(3).

[0064] The input-side first to third clutch mechanisms 60(1) to 60(3) are respectively inserted into the input-side first to third transmission paths 50(1) to 50(3).

[0065] As shown in FIGS. 1 and 2, in the present embodiment, the input-side first to third clutch mechanisms 60(1) to 60(3) are each configured to engage and disengage the power transmission from the drive shaft 212 to the input-side first to third drive gears 52(1) to 52(3).

[0066] In the present embodiment, the input-side first to third clutch mechanisms 60(1) to 60(3) are hydraulic friction plate clutches.

[0067] The input-side first and third clutch mechanisms 60(1), 60(3) have a common clutch housing that is supported on the drive shaft 212 so as not to rotate relative to each other.

[0068] Specifically, the input-side first clutch mechanism 60(1) includes an input-side common clutch housing 62, a first drive-side friction plate supported on the input-side common clutch housing 62 so as not to rotate relative to each other, and a first driven-side friction plate supported on the input-side first drive gear 52(1) so as not to rotate relative to each other in a state of facing the first drive-side friction plate, and an input-side first piston (not shown) that frictionally engages the input-side first friction plate group 64(1).

[0069] The input-side third clutch mechanism 60(3) includes an input-side common clutch housing 62, a third drive-side friction plate supported on the input-side common clutch housing 62 so as not to rotate relative to each other, and a third driven-side friction plate supported on the input-side third drive gear 52(3) so as not to rotate relative to each other in a state of facing the third drive-side friction plate, and an input-side third piston (not shown) that frictionally engages the input-side third friction plate group 64(3).

[0070] The input-side second clutch mechanism 60(2) includes an input-side second clutch housing 62(2) that is non-rotatably supported on the drive shaft 212, an input-side second friction plate group 64(2) including a second drive-side friction plate that is non-rotatably supported on the input-side second clutch housing 62(2) and a second driven-side friction plate that is non-rotatably supported on the input-side second drive gear 52(2) in a state of facing the second drive-side friction plate, and an input-side second piston (not shown) that frictionally engages the input-side second friction plate group 64(2).

[0071] The output-side first and third transmission paths 70(1) and 70(3) transmit the rotational power of the second element to the traveling output shaft 47, and the output-side second transmission path 70(2) is configured to transmit the rotational power of the first element to the traveling output shaft 47.

[0072] As shown in FIGS. 1 and 2, the transmission structure 1A according to the present embodiment includes an intermediate shaft 155 disposed between the first and second transmission shafts 150 and 152 and the traveling output shaft 47 in the transmission direction, an output-side first gear 72(1) that is rotatably supported on the intermediate shaft 155 in a state of being operatively connected to the second transmission shaft 152, an output-side second gear 72(2) that is rotatably supported on the intermediate shaft 155 in a state of being operatively connected to the first transmission shaft 150, and an output-side third gear 72(3) that is rotatably supported on the traveling output shaft 47 in a state of being operatively connected to the second transmission shaft 152.

[0073] In such a configuration, the second transmission shaft 152, the output-side first gear 72(1), and the intermediate shaft 155 form a part of the output-side first transmission path 70(1), the first transmission shaft 150, the output-side second gear 72(2), and the intermediate shaft 155 form a part of the output-side second path 70(2), and the second transmission shaft 152 and the output-side third gear 72(3) form a part of the output-side third path 70(3).

[0074] As shown in FIGS. 1 and 2, the output-side first gear 72(1) is operatively connected to the second transmission shaft 152 via the input-side second driven gear 54(2). That is, in the present embodiment, the input-side second driven gear 54(2) forms a part of the input-side second transmission path 50(2) and also forms a part of the output-side first transmission path 70(1).

[0075] Further, the output-side second gear 72(2) is operatively connected to the first transmission shaft 150 via the input-side first driven gear 54(1). That is, in the present embodiment, the input-side first driven gear 54(1) forms a part of the input-side first transmission path 50(1) and also forms a part of the output-side second transmission path 70(2).

[0076] Furthermore, the output-side third gear 72(3) is operatively connected to the second transmission shaft 152 via the output-side first gear 72(1). That is, in the present embodiment, the input-side second driven gear 54(2) and the output-side first driven gear 72(1) also form a part of the output-side third transmission path 70(3).

[0077] More specifically, the transmission structure 1A according to the present embodiment includes an output-side intermediate gear 74 that is relatively rotatably supported by the intermediate shaft 155 and is non-rotatably connected to the output-side first gear 72(1), and the output-side third gear 72(3) is operatively connected to the output-side intermediate gear 74.

[0078] The output-side first to third clutch mechanisms 80(1) to 80(3) are respectively inserted into the output-side first to third transmission paths.

[0079] As shown in FIGS. 1 and 2, in the present embodiment, the output-side first and second clutch mechanisms 80(1) and 80(2) are respectively configured to engage and disengage the power transmission from the output-side first and second gears 72(1) and 72(2) to the intermediate shaft 155.

[0080] In this embodiment, the output-side first and second clutch mechanisms 80(1) and 80(2) are hydraulic friction plate clutches. The output-side first and second clutch mechanisms 80(1) and 80(2) have a common clutch housing that is non-rotatably supported on the intermediate shaft 155.

[0081] Specifically, the output-side first clutch mechanism 80(1) includes an output-side common clutch housing 82 that is non-rotatably supported on the intermediate shaft 155, a first driving-side friction plate that is non-rotatably supported on the output-side common clutch housing 82, and a first driven-side friction plate that is non-rotatably supported on the output-side first gear 72(1) in a state of facing the first driving-side friction plate, and an output-side first friction plate group 84(1), and an output-side first piston (not shown) that frictionally engages the output-side first friction plate group 84(1).

[0082] The output-side second clutch mechanism 80(2) includes the output-side common clutch housing 82, a second driving-side friction plate that is non-rotatably supported on the output-side common clutch housing 82, and a second driven-side friction plate that is non-rotatably supported on the output-side second gear 72(2) in a state of facing the second driving-side friction plate, and an output-side second friction plate group 84(2), and an output-side second piston (not shown) that frictionally engages the output-side second friction plate group 84(2).

[0083] As shown in FIGS. 1 and 2, the output-side third clutch mechanism 80(3) is configured to engage and disengage the power transmission from the output-side third gear 72(3) to the traveling output shaft 47.

[0084] In this embodiment, the output-side third clutch mechanism 80(3) is a hydraulic friction plate clutch.

[0085] Specifically, the output-side third clutch mechanism 80(3) includes an output-side third clutch housing 82(3) that is non-rotatably supported on the traveling output shaft 47, a third driving-side friction plate that is non-rotatably supported on the output-side third clutch housing 82(3), and an output-side third friction plate group 84(3) including a third driven-side friction plate that is non-rotatably supported on the output-side third gear 72(3) in a state of facing the third driving-side friction plate, and an output-side third piston (not shown) that frictionally engages the output-side third friction plate group 84(3).

[0086] The transmission structure 1A further includes a transmission state switching actuator that switches the engagement and disengagement of the input-side first to third clutch mechanisms 60(1) to 60(3) and the output-side first to third clutch mechanisms 80(1) to 80(3).

[0087] The transmission state switching actuator can have various configurations such as an electric motor or a hydraulic mechanism as long as it can be operationally controlled by the control device 100. When a hydraulic mechanism is provided as the transmission state switching actuator, a solenoid valve or the like in the hydraulic mechanism can be housed in the valve block 112.

[0088] As shown in FIGS. 1 and 2, the transmission structure 1A according to the present embodiment further includes a forward transmission mechanism 400F and a reverse transmission mechanism 400R that can operatively transmit the rotational power of the intermediate shaft 155 to the traveling output shaft 47 as forward rotational power and reverse rotational power, respectively, and a forward clutch mechanism 410F and a reverse clutch mechanism 410R that respectively engage and disengage the power transmission of the forward transmission mechanism 400F and the reverse transmission mechanism 400R.

[0089] In the present embodiment having such a configuration, the forward transmission mechanism 400F and the reverse transmission mechanism 400R respectively form a part of the output-side first transmission path 70(1) and the output-side second transmission path 70(2).

[0090] As shown in FIGS. 1 and 2, the forward transmission mechanism 400F includes a forward gear train including a forward drive gear 402F supported by the intermediate shaft 155 and a forward driven gear 404F meshed with the forward drive gear 402F while being supported by the traveling output shaft 47.

[0091] In the present embodiment, the forward drive gear 402F is supported by the intermediate shaft 155 so as not to be relatively rotatable, and the forward driven gear 404F is supported by the traveling output shaft 47 so as to be relatively rotatable.

[0092] The reverse transmission mechanism 400R includes a reverse gear train including a reverse drive gear 402R supported by the intermediate shaft 155 and a reverse driven gear 404R meshed with the reverse drive gear 402R via an idle gear 403 (see FIG. 1) while being supported by the traveling output shaft 47.

[0093] In the present embodiment, the reverse drive gear 402R is supported by the intermediate shaft 155 so as not to be relatively rotatable, and the reverse driven gear 404R is supported by the traveling output shaft 47 so as to be relatively rotatable.

[0094] In the present embodiment, the forward clutch mechanism 410F and the reverse clutch mechanism 410R are each supported by the traveling output shaft 47 so as to engage and disengage the forward driven gear 404F and the reverse driven gear 404R with the traveling output shaft 47.

[0095] In the present embodiment, the forward and reverse clutch mechanisms 410F, 410R are hydraulic friction plate clutches. The forward and reverse clutch mechanisms 410F, 410R have a common clutch housing supported by the traveling output shaft 47 so as not to be relatively rotatable.

[0096] Specifically, the forward clutch mechanism 410F includes a forward-reverse clutch housing 412 that is non-rotatably supported on the traveling output shaft 47, a forward driven-side friction plate that is non-rotatably supported on the forward-reverse clutch housing 412, and a forward drive-side friction plate that is non-rotatably supported on the forward driven gear 404F in a state of facing the forward driven-side friction plate, and a forward piston (not shown) that frictionally engages the forward friction plate group 414F.

[0097] The reverse clutch mechanism 410R includes the forward-reverse clutch housing 412, a reverse driven-side friction plate that is non-rotatably supported on the forward-reverse clutch housing 412, and a reverse drive-side friction plate that is non-rotatably supported on the reverse driven gear 404R in a state of facing the reverse driven-side friction plate, and a reverse piston (not shown) that frictionally engages the reverse friction plate group 414R.

[0098] The control device 100 controls the operation of the transmission output device (the HST 10 in this embodiment), the input-side first to third clutch mechanisms 60(1) to 60(3), and the output-side first to third clutch mechanisms 80(1) to 80(3).

[0099] In this embodiment, the control device 100 also controls the operation of the forward and reverse clutch mechanisms 410F and 410R.

[0100] As shown in FIG. 1, the transmission structure 1A is provided with a forward-reverse switching operation member 816 that can be manually operated, and a forward-reverse actuator (not shown) that operates the forward clutch mechanism 410F and the reverse clutch mechanism 410R. The control device 100 operates the forward-reverse actuator so that the forward clutch mechanism 410F and the reverse clutch mechanism 410R are in a transmission state corresponding to the operation of the forward-reverse switching operation member 816. Note that reference numeral 817 in FIG. 1 is a sensor that detects the operation position of the forward-reverse switching operation member 816.

[0101] As long as the forward and backward actuator can be operationally controlled by the control device 100, it can have various configurations such as an electric motor or a hydraulic mechanism. When the hydraulic mechanism is provided as the forward and backward actuator, the solenoid valve and the like in the hydraulic mechanism can be housed in the valve block 112.

[0102] When the control device 100 recognizes that the forward and backward switching operation member 816 has been operated to the forward side F, the control device 100 operates the forward and backward actuator so that the forward clutch mechanism 410F is engaged and the reverse clutch mechanism 410R is released. When the control device 100 recognizes that the forward and backward switching operation member 816 has been operated to the reverse side R, the control device 100 operates the forward and backward actuator so that the forward clutch mechanism 410F is released and the reverse clutch mechanism 410R is engaged. When the control device 100 recognizes that the forward and backward switching operation member 816 has been operated to the neutral position N, the control device 100 operates the forward and backward actuator so that both the forward and reverse clutch mechanisms 410F and 410R are released.

[0103] Here, the gear ratios of the input-side first to third transmission paths 50(1) to 50(3), the planetary gear mechanism 30, and the output-side first to third transmission paths 70(1) to 70(3) are set as follows.

[0104] In the first-speed transmission state achieved by engaging the input-side first clutch mechanism 60(1) and the output-side first clutch mechanism 80(1) and releasing the remaining input-side clutch mechanisms (the input-side second and third clutch mechanisms 60(2), 60(3)) and output-side clutch mechanisms (the output-side second and third clutch mechanisms 80(2), 80(3)), the rotational power of the drive shaft 212 is transmitted to the traveling output shaft 47 via the input-side first transmission path 50(1), the planetary gear mechanism 30, and the output-side first transmission path 70(1).

[0105] In this first speed transmission state, the first element of the planetary gear mechanism 30 (the internal gear 36 in the present embodiment) acts as a reference power input portion for inputting reference rotational power from the drive shaft 212, and the second element (the carrier 38 in the present embodiment) acts as a combined power output portion for outputting traveling rotational power toward the traveling output shaft 47.

[0106] As shown in FIG. 2, the transmission case 300 that houses the transmission structure 1A has a front case portion 301 detachably attached to the front surface thereof with the HST 10, and a rear case portion 302 that houses the PTO clutch mechanism 285 (see FIG. 1), the PTO multi-speed transmission mechanism 290 (see FIG. 1), and the differential mechanism 260. The front case portion 301 and the rear case portion 302 are connected along the longitudinal direction of the machine body.

[0107] The planetary gear mechanism 30, the input-side first to third transmission paths 50(1) to 50(3), the input-side first to third clutch mechanisms 60(1) to 60(3), the output-side first to third transmission paths 70(1) to 70(3), and the output-side first to third clutch mechanisms 80(1) to 80(3) that constitute the transmission structure 1A are housed and supported by the front case portion 301. The forward transmission mechanism 400F, the reverse transmission mechanism 400R, the forward clutch mechanism 410F, and the reverse clutch mechanism 410R that form the output-side first to third transmission paths 70(1) to 70(3) are housed and supported by the rear case portion 302.

[0108] In the present embodiment, the rear case portion 302 has an opening at the front end and has an intermediate wall 3021 for bearing support in the middle of the longitudinal direction, and has a connection space portion 303 in front of the intermediate wall 3021. The drive shaft 212, the intermediate shaft 155, and the traveling output shaft 47 have a front portion rotatably supported by the front case portion 301 and a rear portion rotatably supported by the rear case portion 302. When connecting the front case portion 301 and the rear case portion 302 in a state where the rear end wall 3011 of the front case portion 301 is in contact with the mounting flange formed around the front end of the rear case portion 302, the front half portions of the drive shaft 212, the intermediate shaft 155, and the traveling output shaft 47, and the rear half portions of the drive shaft 212, the intermediate shaft 155, and the traveling output shaft 47 rotatably supported by the rear case portion 302 face each other within the space portion 303 and are operatively connected to each other via couplings.

[0109] An oil passage relay cylinder 800 for supplying and discharging hydraulic oil and supplying lubricating oil to the clutch mechanisms 60(1) to 60(3) from the valve block 112 (not shown) is mounted on the rear end portion of the drive shaft 212 protruding from the rear end wall 3011 of the front case portion 301. Similarly, oil passage relay cylinders 810 and 820 are respectively mounted on the rear end portions of the intermediate shaft 155 and the traveling output shaft 47 for the clutch mechanisms 80(1) to 80(3).

[0110] The rear shaft end of the second transmission shaft 152 that operatively connects the carrier 38 of the planetary gear mechanism 30 and relatively rotatably supports the input-side first and third driven gears 54(1) and 54(3) protrudes from the rear end wall 3011 of the front case portion 301, and an oil passage relay cylinder 830 for supplying lubricating oil to each lubricated portion located around the second transmission shaft 152 through the oil passage in the second transmission shaft 152 is mounted.

[0111] An oil passage relay cylinder 840 for supplying and discharging hydraulic oil and supplying lubricating oil to the forward clutch mechanism 410F and the reverse clutch mechanism 410R is mounted on the front end portion of the traveling output shaft 47 protruding from the intermediate wall 3021 of the rear case portion 302.

[0112] In this way, since the oil passage relay cylinders 800 to 840 are intensively arranged in the space portion 303 provided at the connection portion between the front case portion 301 and the rear case portion 302, the assembly of the transmission structure 1A and the connection piping of the oil passage relay cylinders 800 to 840 to the valve block 112 can be efficiently performed.

[0113] FIG. 3 is an enlarged view of the main part of FIG. 2. A hollow sun gear shaft 32a is integrally formed on the sun gear 32 that is coaxially arranged at the front end of the second transmission shaft 152. The sun gear shaft 32a is rotatably supported by bearings between the front end wall of the front case portion 301 and the HST case, and the sun gear 32 is provided at the rear end portion that penetrates into the front case portion 301. The tip of the second transmission shaft 152 is inserted into the hollow portion of the sun gear shaft 32a, and the sun gear shaft 32a and the second transmission shaft 152 are relatively rotatably supported by each other via a needle bearing 152a arranged at the same position as the sun gear 32 in the axial direction.

[0114] Lubricating oil from the oil passage relay cylinder 830 is supplied to the needle bearing 152a, which is one of the lubricated parts, via the oil passage 152b in the second transmission shaft 152. Further, lubricating oil is also supplied as the lubricated parts to the bearings arranged on the second transmission shaft 152 for rotatably supporting the input side first and third driven gears 54(1), 54(3) relatively rotatably, and to the splines for fixedly supporting the carrier 38 and the input side second driven gear 54(2) non-rotatably, respectively branched from the oil passage 152b.

[0115] The front end face of the second transmission shaft 152 is located inside the sun gear shaft 32a, and the oil passage 152b is opened to the hollow portion of the sun gear shaft 32a. A seal ring 32b is interposed between the outer peripheral surface portion extending forward from the front end bearing support portion of the sun gear shaft 32a and the inner peripheral surface of the recessed portion of the HST case that receives this. By setting a slight gap between the seal ring 32b and the HST case, lubricating oil can be supplied toward the front end bearing that supports the sun gear shaft 32a while being stored in the sun gear shaft 32a.

[0116] As shown in Fig. 4, when the output of the speed change output device (the HST 10 in this embodiment) is set to the first speed, the input-side first transmission path 50(1) and the output-side first transmission path 70(1) that are the power transmission paths in this first-speed transmission state, and the planetary gear mechanism 30 are set such that the rotational speed of the second element (i.e., the rotational speed of the traveling output shaft 47) becomes zero speed, and the rotational speed of the second element (i.e., the rotational speed of the traveling output shaft 47) increases as the output of the speed change output device is shifted from the first speed to the second speed.

[0117] In the second-speed transmission state presented by engaging the input-side second clutch mechanism 60(2) and the output-side second clutch mechanism 80(2) and releasing the remaining input-side clutch mechanisms (the input-side first and third clutch mechanisms 60(1), 60(3)) and the output-side clutch mechanisms (the output-side first and third clutch mechanisms 80(1), 80(3)), the rotational power of the drive shaft 212 is transmitted to the traveling output shaft 47 via the input-side second transmission path 50(2), the planetary gear mechanism 30, and the output-side second transmission path 70(2).

[0118] In this second-speed transmission state, the second element of the planetary gear mechanism 30 acts as the reference power input portion, and the first element acts as the combined power output portion.

[0119] Here, the input-side first and second transmission paths 50(1) and 50(2), the planetary gear mechanism 30, and the output-side first and second transmission paths 70(1) and 70(2) are configured such that when the output of the speed-changing output device is set to the second speed in the first gear stage transmission state, the rotational speed of the second element is substantially the same as the rotational speed of the second element that is rotationally driven by the driving force transmitted via the input-side second transmission path 50(2) in the second gear stage transmission state. Further, the rotational speed of the first element that is rotationally driven by the driving force transmitted via the input-side first transmission path 50(1) in the first gear stage transmission state is substantially the same as the rotational speed of the first element when the output of the speed-changing output device is set to the second speed in the second gear stage transmission state. Note that "substantially the same" includes not only the case obtained by strictly setting the gear ratios of the respective transmission paths 50(1), 50(2), 70(1), 70(2) and the planetary gear mechanism 30, but also a state in which there is a rotational speed difference to such an extent that it can be absorbed by the slippage between the friction plates when the hydraulic friction plate type clutches described later are engaged, which form the respective running system transmission paths.

[0120] As shown in FIG. 4, in this second gear stage transmission state, the variable speed range of the first element acting as the combined power output unit is higher than the variable speed range of the second element acting as the combined power output unit in the first gear stage transmission state. In the second gear stage transmission state, as the output of the speed-changing output device is shifted from the second speed toward the first speed, the rotational speed of the first element (i.e., the rotational speed of the traveling output shaft 47) increases.

[0121] In the third gear stage transmission state presented by engaging the input-side third clutch mechanism 60(3) and the output-side third clutch mechanism 80(3) and releasing the remaining input-side clutch mechanisms (the input-side first and second clutch mechanisms 60(1) and 60(2)) and output-side clutch mechanisms (the output-side first and second clutch mechanisms 80(1) and 80(2)), the rotational power of the drive shaft 212 is transmitted to the traveling output shaft 47 via the input-side third transmission path 50(3), the planetary gear mechanism 30, and the output-side third transmission path 70(3).

[0122] In this third-speed transmission state, the first element of the planetary gear mechanism 30 acts as the reference power input portion, and the second element acts as the combined power output portion.

[0123] Here, the input-side second and third transmission paths 50(2), 50(3), the planetary gear mechanism 30, and the output-side second and third transmission paths 70(2), 70(3) are configured such that the rotational speed of the first element when the output of the speed-changing output device is set to the first speed in the second-speed transmission state and the rotational speed of the first element that is rotationally driven by the driving force transmitted through the input-side third transmission path 50(3) in the third-speed transmission state are substantially the same, and further, the rotational speed of the second element that is rotationally driven by the driving force transmitted through the input-side second transmission path 50(2) in the second-speed transmission state and the rotational speed of the second element when the output of the speed-changing output device is set to the first speed in the third-speed transmission state are substantially the same.

[0124] As shown in FIG. 4, the variable speed range of the second element acting as the combined power output portion in this third-speed transmission state is higher than the variable speed range of the first element acting as the combined power output portion in the second-speed transmission state. In the third-speed transmission state, as the output of the speed-changing output device is shifted from the first speed to the second speed, the rotational speed of the second element (i.e., the rotational speed of the traveling output shaft 47) increases.

[0125] As shown in FIG. 4, the control device 100 changes the rotational speeds of the first element and the second element as follows according to the vehicle speed. ·For example, when the absolute value of the rotational speed of the traveling output shaft 47 detected by the vehicle speed sensor 195b (see FIG. 1) is within the range up to the first vehicle speed X (i.e., the rotational speed of the traveling output shaft 47 is in the range of -X to +X), the control device 100 exhibits the first gear stage transmission state, and when the shift operation member is operated to the vehicle stop position, the output of the transmission output device is shifted to the first gear to make the rotational speed of the second element zero, and the output of the transmission output device is shifted toward the second gear in response to the speed increasing operation of the shift operation member to increase the rotational speed of the second element. ·When the absolute value of the rotational speed of the traveling output shaft 47 is within the range from the first vehicle speed X to the second vehicle speed Y (i.e., the rotational speed of the traveling output shaft 47 is in the ranges of -X to -Y and +X to +Y), the control device 100 exhibits the second gear stage transmission state, and the output of the transmission output device is shifted toward the first gear in response to the speed increasing operation of the shift operation member to increase the rotational speed of the first element. ·When the absolute value of the rotational speed of the traveling output shaft 47 exceeds the second vehicle speed Y (i.e., when the rotational speed of the traveling output shaft 47 exceeds +Y), the control device 100 exhibits the third gear stage transmission state, and the output of the transmission output device is shifted toward the second gear in response to the speed increasing operation of the shift operation member to increase the rotational speed of the second element.

[0126] As shown in FIG. 1, the transmission structure 1A further has a lowest speed setting member 851 and a highest speed setting member 853 near the driver's seat of the vehicle 200. Reference numerals 852 and 853 in FIG. 1 are sensors for detecting the operation positions of the lowest speed setting member 851 and the highest speed setting member 853, respectively.

[0127] FIG. 5 shows a transmission schematic diagram of a work vehicle 200 to which a transmission structure 1B according to a modification of the present embodiment is applied. In the figure, the same members as those in the present embodiment are denoted by the same reference numerals.

[0128] The transmission structure 1B according to the modified example is different from the transmission structure 1A according to the present embodiment in that the output-side third clutch mechanism 80(3) is supported by the intermediate shaft 155.

[0129] Specifically, the transmission structure 1B according to the modified example has an output-side third transmission path 75(3) instead of the output-side third transmission path 70(3) as compared with the transmission structure 1A according to the present embodiment.

[0130] As shown in FIG. 5, the output-side third transmission path 75(3) includes the second transmission shaft 152, an output-side third drive gear 77(3) supported on the second transmission shaft 152 in a non-rotatable relative manner, and an output-side third gear 72(3) meshed with the output-side third drive gear 77(3) while being supported on the intermediate shaft 155 in a relatively rotatable manner.

[0131] In the transmission structure 1B according to the modified example, the output-side third clutch mechanism 80(3) is supported on the intermediate shaft 155 so as to engage and disengage the power transmission from the output-side third gear 72(3) to the intermediate shaft 155.

[0132] In the transmission structure 1B having such a configuration, the forward transmission mechanism 400F and the reverse transmission mechanism 400R form a part of the output-side first and second transmission paths 70(1) and 70(2), and also form a part of the output-side third transmission path 75(3).

[0133] Embodiment 2 Hereinafter, another embodiment of the transmission structure according to the present invention will be described with reference to the accompanying drawings. FIG. 6 shows a transmission schematic diagram of a work vehicle 200 to which the transmission structure 2 according to the present embodiment is applied. In the figure, the same members as those in the above embodiment are denoted by the same reference numerals.

[0134] The transmission structure 2 according to the present embodiment is different from the transmission structure 1A according to the first embodiment mainly in that the input-side first and third transmission paths 50(1) and 50(3) are changed to the input-side first and third transmission paths 55(1) and 55(3).

[0135] Specifically, as shown in FIG. 6, the transmission structure 2 includes the speed-changing output device (the HST 10), the planetary gear mechanism 30, the input shaft 170, the input-side first transmission path 55(1), the input-side second transmission path 50(2), the input-side third transmission path 55(3), the input shaft clutch mechanism 90, the shifter, the input-side second clutch mechanism 60(2), the output-side first to third transmission paths 70(1) to 70(3), the output-side first to third clutch mechanisms 80(1) to 80(3), the speed-changing operation members (the accelerator pedal 190a and the main speed-changing lever 190b), and the control device 100.

[0136] The input shaft clutch mechanism 90 is configured to engage and disengage the power transmission from the drive shaft 212 to the input shaft 170.

[0137] As shown in FIG. 6, in the present embodiment, the input shaft 170 is externally inserted into the drive shaft 212 so as to be relatively rotatable.

[0138] The input shaft clutch mechanism 90 is a hydraulic friction plate type clutch. Specifically, the input shaft clutch mechanism 90 includes an input shaft clutch housing 92 supported on the drive shaft 212 so as not to be relatively rotatable, an input shaft friction plate group 94 including an input shaft drive-side friction plate supported on the input shaft clutch housing 92 so as not to be relatively rotatable and an input shaft driven-side friction plate supported on the input shaft so as not to be relatively rotatable in a state of facing the input shaft drive-side friction plate, and an input shaft piston (not shown) for frictionally engaging the input shaft friction plate group.

[0139] In addition, in the present embodiment, the input-side second clutch mechanism 60(2) is configured to also serve as the input shaft clutch housing 92 of the input shaft clutch mechanism 90 (that is, in the present embodiment, the input-side second clutch housing 62(2) is omitted).

[0140] The input-side first transmission path 55(1) transmits rotational power from the input shaft 170 to the first element. Specifically, as shown in FIG. 6, the input-side first transmission path 55(1) includes an input-side first drive gear 56(1) rotatably supported relative to the input shaft 170, an input-side first driven gear 54(1), and the first transmission shaft 150.

[0141] The input-side third transmission path 55(3) transmits rotational power from the input shaft 170 to the first element. Specifically, as shown in FIG. 6, the input-side third transmission path 55(3) includes an input-side third drive gear 56(3) rotatably supported relative to the input shaft 170, an input-side third driven gear 54(3), and the first transmission shaft 150.

[0142] The shifter 180 is configured to selectively connect the input shaft 170 to the input-side first and third transmission paths 55(1) and 55(3).

[0143] In the present embodiment, the shifter 180 is non-rotatable relative to the input shaft 170 and axially movable, and can take a first transmission path selection position connected to the input-side first drive gear 56(1), a third transmission path selection position connected to the input-side third drive gear 56(3), and a non-selection position not connected to any of the input-side first and third drive gears 56(1) and 56(3).

[0144] The shifter 180 is actuated by an electric actuator such as an electric motor or a push-pull type linear solenoid that is actuated and controlled by the control device 100.

[0145] In this embodiment, the control device 100 performs operation control as follows. · When the absolute value of the rotational speed of the traveling output shaft 47 is in the range up to the first vehicle speed X, the control device 100 engages the input shaft clutch mechanism 90 and the output-side first clutch mechanism 80(1) with the input shaft 170 operatively connected to the input-side first transmission path 55(1) by the shifter 180, and disengages the remaining clutch mechanisms (i.e., the input-side second clutch mechanism 60(2), the output-side second and third clutch mechanisms 80(2), 80(3)), thereby realizing the first-speed transmission state. When the shift operation member is operated to the vehicle stop position, the output of the transmission output device is shifted to the first speed to make the rotational speed of the second element zero, and the output of the transmission output device is shifted toward the second speed in response to the speed increase operation of the shift operation member to increase the rotational speed of the second element. · When the absolute value of the rotational speed of the traveling output shaft 47 is in the range from the first vehicle speed X to the second vehicle speed Y, the control device 100 engages the input-side second clutch mechanism 60(2) and the output-side second clutch mechanism 80(2), and disengages the remaining clutch mechanisms (i.e., the input shaft clutch mechanism 90, the output-side first and third clutch mechanisms 80(1), 80(3)), thereby realizing the second-speed transmission state. In response to the speed increase operation of the shift operation member, the output of the transmission output device is shifted toward the first speed to increase the rotational speed of the first element. · When the absolute value of the rotational speed of the traveling output shaft 47 exceeds the second vehicle speed Y, the control device 100 engages the input shaft clutch mechanism 90 and the output-side third clutch mechanism 80(3) with the input shaft 170 operatively connected to the input-side third transmission path 55(3) by the shifter 180, and disengages the remaining clutch mechanisms (i.e., the input-side second clutch mechanism 60(2), the output-side first and second clutch mechanisms 80(1), 80(2)), thereby realizing the third-speed transmission state. In response to the speed increase operation of the shift operation member, the output of the transmission output device is shifted toward the second speed to increase the rotational speed of the second element.

[0146] When the control device 100 shifts up from the second gear transmission state to the third gear transmission state, when the rotational speed of the traveling output shaft 47 reaches the shift-up preparation speed that is lower than the second vehicle speed Y by a predetermined speed, the shifter 180 pre-connects the input shaft 170 to the input-side third transmission path 55(3) to present the third gear preparation state. When shifting down from the second gear transmission state to the first gear transmission state, when the rotational speed of the traveling output shaft 47 reaches the shift-down preparation speed that is higher than the first vehicle speed X by a predetermined speed, the shifter 180 pre-connects the input shaft 170 to the input-side first transmission path 55(1) to present the first gear preparation state. It can be configured in this way.

[0147] Alternatively, when the rotational speed of the traveling output shaft 47 is increasing in the second gear transmission state, the control device 100 connects the input shaft 170 to the input-side third transmission path 55(3) by the shifter 180 to present the third gear preparation state. When the rotational speed of the traveling output shaft 47 is decreasing in the second gear transmission state, the control device 100 connects the input shaft 170 to the input-side first transmission path 55(1) by the shifter 180 to present the first gear preparation state. It can be configured in this way.

[0148] Alternatively, when the control device 100 shifts up from the second gear transmission state to the third gear transmission state, the shift from the engaged state to the released state of the input-side and output-side second clutch mechanisms 60(2), 80(2), the shift from the released state to the engaged state of the input shaft clutch mechanism 90, the movement of the shifter 180 to the third transmission path selection position, and the shift from the released state to the engaged state of the output-side third clutch mechanism 80(3) are performed substantially simultaneously. When shifting down from the second gear transmission state to the first gear transmission state, the shift from the engaged state to the released state of the input-side and output-side second clutch mechanisms 60(2), 80(2), the shift from the released state to the engaged state of the input shaft clutch mechanism 90, the movement of the shifter 180 to the first transmission path selection position, and the shift from the released state to the engaged state of the output-side first clutch mechanism 80(1) are performed substantially simultaneously. It can be configured in this way.

Explanation of Signs

[0149] 1A, 1B, 2 Transmission Structures 10 HST (Output Device for Speed Change) 30 Planetary Gear Mechanism 32 Sun Gear (Third Element) 36 Internal Gear (First Element) 38 Carrier (Second Element) 47 Travel Output Shaft 50(1) - 50(3) Input Side First - Third Transmission Paths 52(1) - 52(3) Input Side First - Third Driving Gears 54(1) - 54(3) Input Side First - Third Driven Gears 55(1) Input Side First Transmission Path 55(3) Input Side Third Transmission Path 56(1) Input Side First Driving Gear 56(3) Input Side Third Driving Gear 60(1) - 60(3) Input Side First - Third Clutch Mechanisms 70(1) - 70(3) Output Side First - Third Transmission Paths 72(1) - 72(3) Output Side First - Third Gears 74 Output Side Intermediate Gear 75(3) Output Side Third Transmission Path 77(3) Output Side Third Driving Gear 80(1) - 80(3) Output Side First - Third Transmission Paths 90 Input Shaft Clutch Mechanism 100 Control Device 150 First Transmission Shaft 152 Second Transmission Shaft 155 Intermediate Shaft 170 Input Shaft 180 Shifter 190a Accelerator Pedal (Shift Operating Member) 190b Main Shift Lever (Shift Operating Member) 400F, 400R Forward and Reverse Transmission Mechanisms 410F, 410R Forward and Reverse Clutch Mechanisms

Claims

1. A transmission structure that steplessly changes the rotational power of a drive shaft operatively connected to a drive source and transmits the rotational power to a traveling output shaft that outputs the rotational power to drive wheels, comprising: A speed-changing output device that outputs rotational power for speed change that is steplessly changed at least between a first speed and a second speed; A planetary gear mechanism having first to third elements and inputting the rotational power for speed change to the third element; An input-side first transmission path that transmits the rotational power of the drive shaft to the first element; An input-side second transmission path that transmits the rotational power of the drive shaft to the second element; An input-side third transmission path that transmits the rotational power of the drive shaft to the first element; Input-side first to third clutch mechanisms respectively inserted into the input-side first to third transmission paths; An output-side first transmission path that transmits the rotational power of the second element to the traveling output shaft; An output-side second transmission path that transmits the rotational power of the first element to the traveling output shaft; An output-side third transmission path that transmits the rotational power of the second element to the traveling output shaft; Output-side first to third clutch mechanisms respectively inserted into the output-side first to third transmission paths; A shift operation member; A control device that controls the operation of the speed-changing output device, the input-side first to third clutch mechanisms, and the output-side first to third clutch mechanisms; The control device: When the absolute value of the rotational speed of the traveling output shaft is in the range up to the first vehicle speed, the input-side and output-side first clutch mechanisms are engaged and the remaining input-side clutch mechanisms and output-side clutch mechanisms are released to exhibit a first-speed transmission state. When the shift operation member is operated to the vehicle stop position, the output of the speed-changing output device is shifted to the first speed to make the rotational speed of the second element zero, and in response to the speed increase operation of the shift operation member, the output of the speed-changing output device is shifted toward the second speed to increase the rotational speed of the second element. When the absolute value of the rotational speed of the traveling output shaft is in the range from the first vehicle speed to the second vehicle speed, the input-side and output-side second clutch mechanisms are engaged and the remaining input-side clutch mechanisms and output-side clutch mechanisms are released to exhibit a second-speed transmission state. In response to the speed increase operation of the shift operation member, the output of the speed-changing output device is shifted toward the first speed to increase the rotational speed of the first element. When the absolute value of the rotational speed of the traveling output shaft exceeds the second vehicle speed, the input-side third clutch mechanism and the output-side third clutch mechanism are brought into an engaged state, and the remaining input-side clutch mechanisms and output-side clutch mechanisms are brought into a disengaged state to exhibit a third-speed transmission state. While doing so, in response to the speed increasing operation of the shift operation member, the output of the transmission output device is shifted toward the second speed to increase the rotational speed of the second element. In the first-speed transmission state, the rotational speed of the second element when the output of the transmission output device is set to the second speed is made substantially the same as the rotational speed of the second element in the second-speed transmission state. In the first-speed transmission state, the rotational speed of the first element is made substantially the same as the rotational speed of the first element when the output of the transmission output device is set to the second speed in the second-speed transmission state. In the second-speed transmission state, the rotational speed of the first element when the output of the transmission output device is set to the first speed is made substantially the same as the rotational speed of the first element in the third-speed transmission state. A transmission structure characterized in that the rotational speed of the second element in the second-speed transmission state is made substantially the same as the rotational speed of the second element when the output of the transmission output device is set to the first speed in the third-speed transmission state.

2. A first transmission shaft operatively connected to the first element, A second transmission shaft operatively connected to the second element, Input-side first and third drive gears rotatably supported relative to the drive shaft while being operatively connected to the first transmission shaft, An input-side second drive gear rotatably supported relative to the drive shaft while being operatively connected to the second transmission shaft, The input-side first to third clutch mechanisms are each configured to engage and disengage the power transmission from the drive shaft to the input-side first to third drive gears. The second transmission shaft is arranged coaxially with the planetary gear mechanism. The transmission structure according to claim 1, characterized in that the first transmission shaft is externally inserted in a state of being relatively rotatable with respect to the second transmission shaft.

3. A transmission structure that continuously variable-transmits the rotational power of a drive shaft operatively connected to a drive source and transmits it to a traveling output shaft that outputs rotational power toward drive wheels, A transmission output device that outputs continuously variable-transmitted rotational power for transmission, at least between the first speed and the second speed, A planetary gear mechanism having first to third elements, with the continuously variable-transmitted rotational power for transmission input to the third element, An input shaft, an input-side first transmission path operably connected to the first element; an input-side second transmission path for transmitting the rotational power of the drive shaft to the second element; an input-side third transmission path operably connected to the first element; an input shaft clutch mechanism for engaging and disengaging the power transmission from the drive shaft to the input shaft; a shifter capable of selectively operably connecting the input shaft to the input-side first and third transmission paths; an input-side second clutch mechanism inserted in the input-side second transmission path; an output-side first transmission path for transmitting the rotational power of the second element to the traveling output shaft; an output-side second transmission path for transmitting the rotational power of the first element to the traveling output shaft; an output-side third transmission path for transmitting the rotational power of the second element to the traveling output shaft; output-side first to third clutch mechanisms respectively inserted in the output-side first to third transmission paths; a shift operation member; a control device for controlling the operation of the transmission output device, the input-side first to third clutch mechanisms, and the output-side first to third clutch mechanisms; the control device is configured to: when the absolute value of the rotational speed of the traveling output shaft is in the range up to the first vehicle speed, engage the input shaft clutch mechanism and the output-side first clutch mechanism with the input shaft operably connected to the input-side first transmission path by the shifter and release the remaining clutch mechanisms to exhibit a first-gear transmission state, and when the shift operation member is operated to the vehicle stop position, shift the output of the transmission output device to the first gear to set the rotational speed of the second element to zero speed and shift the output of the transmission output device toward the second gear in response to the upshift operation of the shift operation member to increase the rotational speed of the second element; when the absolute value of the rotational speed of the traveling output shaft is in the range from the first vehicle speed to the second vehicle speed, engage the input-side and output-side second clutch mechanisms and release the remaining clutch mechanisms to exhibit a second-gear transmission state, and shift the output of the transmission output device toward the first gear in response to the upshift operation of the shift operation member to increase the rotational speed of the first element; When the absolute value of the rotational speed of the traveling output shaft exceeds the second vehicle speed, with the input shaft operatively connected to the input-side third transmission path by the shifter, the input shaft clutch mechanism and the output-side third clutch mechanism are engaged, and the remaining clutch mechanisms are disengaged, thereby presenting a third-gear transmission state. In addition, in response to the speed-up operation of the shift operation member, the output of the transmission output device is shifted toward the second speed to increase the rotational speed of the second element. In the first-gear transmission state, the rotational speed of the second element when the output of the transmission output device is set to the second speed is substantially the same as the rotational speed of the second element in the second-gear transmission state. In the first-gear transmission state, the rotational speed of the first element is substantially the same as the rotational speed of the first element when the output of the transmission output device is set to the second speed in the second-gear transmission state. In the second-gear transmission state, the rotational speed of the first element when the output of the transmission output device is set to the first speed is substantially the same as the rotational speed of the first element in the third-gear transmission state. A transmission structure characterized in that the rotational speed of the second element in the second-gear transmission state is substantially the same as the rotational speed of the second element when the output of the transmission output device is set to the first speed in the third-gear transmission state.

4. The control device is configured as follows: During an upshift from the second-gear transmission state to the third-gear transmission state, when the rotational speed of the traveling output shaft reaches a shift-up preparation speed that is a predetermined speed lower than the second vehicle speed, the shifter pre-connects the input shaft to the input-side third transmission path to present a third-gear preparation state. During a downshift from the second-gear transmission state to the first-gear transmission state, when the rotational speed of the traveling output shaft reaches a downshift preparation speed that is a predetermined speed higher than the first vehicle speed, the shifter pre-connects the input shaft to the input-side first transmission path to present a first-gear preparation state. The transmission structure according to claim 3, characterized by this configuration.

5. The control device is configured as follows: When the rotational speed of the traveling output shaft is increasing in the second-speed stage transmission state, the shifter connects the input shaft to the input-side third transmission path to present a third-speed stage preparation state. When the rotational speed of the traveling output shaft is decreasing in the second-speed stage transmission state, the shifter connects the input shaft to the input-side first transmission path to present a first-speed stage preparation state. The transmission structure according to claim 3, characterized in that it is configured as such.

6. A first transmission shaft operatively connected to the first element, A second transmission shaft operatively connected to the second element, Input-side first and third drive gears supported so as to be relatively rotatable with respect to the input shaft while being operatively connected to the first transmission shaft, An input-side second drive gear supported so as to be relatively rotatable with respect to the drive shaft while being operatively connected to the second transmission shaft, and comprising: The shifter is configured to selectively engage the input shaft with the input-side first and third drive gears, The input-side second clutch mechanism is configured to engage and disengage the power transmission from the drive shaft to the input-side second drive gear, The second transmission shaft is arranged coaxially with the planetary gear mechanism, The first transmission shaft is externally inserted in a state where it can rotate relative to the second transmission shaft. The transmission structure according to claim 3, characterized in that it is as such.

7. Input-side first and third driven gears supported so as not to be rotatable relative to the first transmission shaft and operatively connected to the input-side first and third drive gears respectively, An input-side second driven gear supported so as not to be rotatable relative to the second transmission shaft and operatively connected to the input-side second drive gear, and comprising: The input-side first drive gear, the input-side first driven gear, and the first transmission shaft form the input-side first transmission path, The input-side second drive gear, the input-side second driven gear, and the second transmission shaft form the input-side second transmission path, The input-side third drive gear, the input-side third driven gear, and the first transmission shaft form the input-side third transmission path. The transmission structure according to any one of claims 1 to 6, characterized in that it is as such.

8. An intermediate shaft disposed between the first and second transmission shafts and the traveling output shaft with respect to the transmission direction, An output-side first gear supported so as to be relatively rotatable with respect to the intermediate shaft while being operatively connected to the second transmission shaft, An output-side second gear supported so as to be relatively rotatable with respect to the intermediate shaft while being operatively connected to the first transmission shaft, An output-side third gear rotatably supported relative to the traveling output shaft while being operatively connected to the second transmission shaft; The output-side first and second clutch mechanisms are each configured to engage and disengage power transmission from the output-side first and second gears to the intermediate shaft; The transmission structure according to any one of claims 1 to 6, wherein the output-side third clutch mechanism is configured to engage and disengage power transmission from the output-side third gear to the traveling output shaft.

9. The output-side first gear is operatively connected to the second transmission shaft via the input-side second driven gear; The output-side second gear is operatively connected to the first transmission shaft via the input-side first driven gear; The transmission structure according to claim 8, wherein the output-side third gear is operatively connected to the second transmission shaft via the output-side first gear.

10. An output-side intermediate gear non-rotatably connected to the output-side first gear while being rotatably supported relative to the intermediate shaft; The transmission structure according to claim 9, wherein the output-side third gear is operatively connected to the output-side intermediate gear.

11. A forward transmission mechanism and a reverse transmission mechanism capable of operatively transmitting the rotational power of the intermediate shaft to the traveling output shaft as forward-direction rotational power and reverse-direction rotational power, respectively; A forward clutch mechanism and a reverse clutch mechanism for engaging and disengaging the power transmission of the forward transmission mechanism and the reverse transmission mechanism, respectively; The transmission structure according to claim 10, wherein the forward transmission mechanism and the reverse transmission mechanism form a part of the output-side first and second transmission paths.

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