Work vehicles

Abstract

To enable the travel stop of a work vehicle only by operating a shift operation tool 12 to be returned to a neutral position even when trouble occurs in a hydraulic continuously variable transmission 30.SOLUTION: The work vehicle according to this invention includes a hydraulic continuously variable transmission 30 using a hydraulic pump 31 and a hydraulic motor 32 for shifting the motive power of an engine 17, and a shift operation tool 12 for applying shift operation to the output of the hydraulic continuously variable transmission 30. In a closed circuit 51 of the hydraulic continuously variable transmission 30, a bypass oil path 60 is provided for the bypass between the hydraulic pump 31 and the hydraulic motor 32. In the bypass oil path 60, a bypass valve 61 is arranged, the opening of the bypass valve being adjustable. Control means 70 for controlling the bypass valve 61 operates the shift operation tool 12 to be returned to a neutral position to open the bypass valve 61 while making the opening speed of the bypass valve 61 lower when a neutral return time Tn for the shift operation tool 12 exceeds a preset time TS than when it falls below the preset time TS.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a work vehicle. [Background technology]

[0002] A conventional combine harvester, which is an example of a work vehicle, is equipped with a hydraulic continuously variable transmission that uses a hydraulic pump and a hydraulic motor to change the speed of the engine power, and a main speed change operating device that changes the speed of the output of the hydraulic continuously variable transmission, and is configured to transmit the speed-changing power of the hydraulic continuously variable transmission to a traveling part in accordance with the amount of operation of the main speed change operating device. An example of this type of combine harvester is disclosed in Patent Document 1, etc. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-183855 Summary of the Invention [Problem to be solved by the invention]

[0004] In the conventional configuration, when the main speed change device is returned to the neutral position, the swash plate of the hydraulic pump is placed in a neutral state, stopping the output of the hydraulic motor (rotation of the motor output shaft), and the combine harvester stops running. Therefore, if an emergency situation occurs in which the combine harvester does not stop running even when the main speed change device is returned to the neutral position due to a malfunction of the hydraulic continuously variable transmission, the only way to stop the combine harvester running is to forcibly stop the engine or, if there is an auxiliary speed change device, to operate the auxiliary speed change device in neutral.

[0005] However, if the engine is forcibly stopped, all of the combine's functions become unusable, and if the auxiliary speed change device is manually operated, the operator must manually operate the auxiliary speed change device each time, which is a hassle. [Means for solving the problem]

[0006] SUMMARY OF THE INVENTION The present invention has as its technical object to provide a work vehicle that has been improved upon by considering the current situation described above.

[0007] The invention of claim 1 is a work vehicle equipped with a hydraulic continuously variable transmission that changes the speed of engine power using a hydraulic pump and a hydraulic motor, and a speed change operating device that changes the speed of the output of the hydraulic continuously variable transmission, wherein a bypass oil passage is provided in the closed circuit of the hydraulic continuously variable transmission to bypass between the hydraulic pump and the hydraulic motor, a bypass valve whose opening is adjustable is arranged in the bypass oil passage, and the control means has control means for controlling the bypass valve, wherein the control means operates the speed change operating device to return to a neutral position to open the bypass valve, and when the neutral return time of the speed change operating device exceeds a predetermined set time, the opening speed of the bypass valve is slower than when the neutral return time is less than the set time.

[0008] The invention of claim 2 is a work vehicle equipped with a hydraulic continuously variable transmission that changes the speed of engine power using a hydraulic pump and a hydraulic motor, and a speed change operating device that changes the speed of the output of the hydraulic continuously variable transmission, wherein a bypass oil passage is provided in the closed circuit of the hydraulic continuously variable transmission to bypass between the hydraulic pump and the hydraulic motor, a bypass valve whose opening is adjustable is arranged in the bypass oil passage, and the control means has control means for controlling the bypass valve, wherein the control means operates the speed change operating device to return to a neutral position to open the bypass valve, and when the neutral return time of the speed change operating device falls below a predetermined set time, the control means opens the bypass valve faster than when the set time is exceeded.

[0009] In the work vehicle of the present invention, the control means may gradually increase the opening of the bypass valve when the neutral return time of the speed change device exceeds the set time.

[0010] In the work vehicle of the present invention, the control means may instantly fully open the bypass valve when the neutral return time of the speed change device falls below the set time.

[0011] In the work vehicle of the present invention, the control means may brake a traveling section to which the speed-changing power of the hydrostatic continuously variable transmission is transmitted in synchronization with the bypass valve being fully opened. [Effects of the Invention]

[0012] According to the present invention, the bypass valve is opened in conjunction with the return operation of the speed change device to the neutral position, so the operating oil pressure to the hydraulic motor is released regardless of whether the swash plate of the hydraulic pump is in the neutral state, and the output of the hydraulic motor can be reliably stopped by both neutralizing the swash plate of the hydraulic pump and opening the bypass valve.

[0013] Therefore, by simply adopting a simple configuration in which a bypass oil line and a bypass valve are added to the closed circuit, even if a malfunction occurs in the hydraulic continuously variable transmission, such as the hydraulic pump swash plate not being in the neutral state, the output of the hydraulic motor can be reliably stopped without forcibly stopping the engine, the output of the hydraulic continuously variable transmission (vehicle speed) can be set to zero, and the work vehicle can be reliably stopped.The work vehicle can also be brought to a sudden halt simply by returning the speed change operating device to the neutral position.In addition, because there is no need to stop the engine, tasks such as threshing and discharge can be carried out as is.

[0014] Furthermore, the opening of the bypass valve is changed to match the speed of the return operation of the speed change device, reducing the hydraulic pressure to the hydraulic motor and even stopping the output of the hydraulic motor, thereby ensuring extremely good operation response in the speed change device. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. [Figure 2] FIG. [Figure 3]FIG. 2 is a power transmission system diagram of the transmission case. [Figure 4] 1 is a hydraulic circuit diagram of a hydraulic continuously variable transmission according to a first embodiment. [Figure 5] FIG. 2 is a functional block diagram of a controller. [Figure 6] 10 is a flowchart of a travel stop control. [Figure 7] FIG. 10 is a hydraulic circuit diagram showing another example of a bypass valve. [Figure 8] FIG. 10 is a power transmission system diagram of a transmission case according to a second embodiment. [Figure 9] FIG. 2 is a hydraulic circuit diagram of a hydraulic continuously variable transmission. [Figure 10] FIG. 2 is a functional block diagram of a controller. [Figure 11] 10 is a flowchart of a travel stop control. [Figure 12] FIG. 10 is a hydraulic circuit diagram showing another example of a bypass valve. DETAILED DESCRIPTION OF THE INVENTION

[0016] An embodiment of the present invention will be described below with reference to drawings showing the application of the present invention to a combine harvester, which is an example of a work vehicle. In the following description, terms such as "front / rear," "left / right," and "up / down" are used to specify directions, but the left / right and up / down directions are determined based on the forward direction of the traveling body 1. However, these terms are used for convenience of explanation and do not limit the technical scope of the present invention.

[0017] As shown in Figures 1 and 2, the combine harvester has a traveling body 1 supported by a pair of left and right traveling crawlers 2. A reaping device 3 that harvests and collects grain stalks is attached to the front of the traveling body 1 so that it can be adjusted in elevation around a reaping input case 16 via a single-acting lifting hydraulic cylinder 4. A threshing device 5 having a feed chain 6 and a grain tank 7 that stores grain removed from the threshing device 5 are mounted side by side on the traveling body 1. A driver's control panel 9 is provided to the right of the reaping device 3 and in front of the grain tank 7.

[0018] The driving control unit 9 is provided with a control lever 10, a driver's seat 11, a main speed change lever 12 and a sub-speed change lever 13 as speed change controls, a threshing clutch lever 14 for operating the threshing clutch on and off, and a reaping clutch lever 15 for operating the reaping clutch on and off. An engine 17 is mounted below the driver's seat 11 as a drive source. A transmission case 18 is disposed in front of the engine 17, which appropriately changes the speed of the power of the engine 17 and transmits it to the left and right traveling crawlers 2. A parking brake pedal 27 is provided in front of the driver's seat 11 below the driver's seat 11 in the driving control unit 9, which simultaneously brakes the left and right traveling crawlers 2.

[0019] 1, left and right track frames 21 are arranged on the underside of the traveling body 1. The track frames 21 are provided with drive sprockets 22 that transmit the power of the engine 17 to the traveling crawlers 2.

[0020] Next, with primary reference to FIG. 3 , a travel drive structure that transmits power from the engine 17 to the travel crawler 2 will be described. A transmission case 18 (hydraulic transmission) disposed in front of the engine 17 is equipped with a hydraulic continuously variable transmission 30 that combines a hydraulic pump 31 and a hydraulic motor 32. The output shaft 19 of the engine 17 is operatively connected to a pump input shaft 33 of the hydraulic pump 31, which serves as the input shaft of the transmission case 18, via a transmission belt 35. Power from the engine 17 drives the hydraulic pump 31, and hydraulic motor 32 is driven by hydraulic oil discharged from the hydraulic pump 31. A charge pump 20 is attached to the engine 17 and supplies replenishment oil to circulate between the hydraulic pump 31 and the hydraulic motor 32. The charge pump 20 is also driven by the power of the engine 17.

[0021] A countershaft 37 and a PTO output shaft 38 are interlocked with the motor output shaft 34 of the hydraulic motor 32 via a spur gear mechanism 36. The countershaft 37 is interlocked with the left and right axles 26, 26 protruding outward from the transmission case 18 via an auxiliary transmission gear mechanism 39, left and right side clutches 41, 42, and left and right hydraulically switched multi-plate side brakes 43, 44. The power transmitted to the countershaft 37 rotates the drive sprockets 22 connected to the left and right axles 26, 26 via the auxiliary transmission gear mechanism 39, left and right side clutches 41, 42, and left and right side brakes 43, 44, and is transmitted to the left and right traveling crawlers 2, 2 serving as the traveling unit. In other words, the power of the engine 17 is speed-changed by the hydraulic continuously variable transmission 30 and transmitted to the left and right traveling crawlers 2, 2. The PTO output shaft 38 also protrudes outward from the transmission case 18. The power transmitted to the PTO output shaft 38 is transmitted to each part of the reaping device 3.

[0022] Next, the hydraulic circuit structure of the hydraulic continuously variable transmission 30 in the first embodiment will be described with reference to Figure 4. The hydraulic circuit 50 of the hydraulic continuously variable transmission 30 includes a hydraulic pump 31, a hydraulic motor 32, and a charge pump 20. The hydraulic pump 31 and the hydraulic motor 32 are connected to circulate hydraulic oil through a closed circuit 51. The hydraulic pump 31 and the charge pump 20 are driven by the engine 17. The swash plate angle of the hydraulic pump 31 is controlled in response to manual operation of the main shift lever 12, thereby changing the discharge direction and discharge amount of hydraulic oil from the hydraulic pump 31, and the hydraulic motor 32 operates in forward / reverse rotation and infinitely increases / decreases speed.

[0023] 4, for convenience of explanation, in the closed circuit 51, when the hydraulic motor 32 is rotated forward to move the traveling machine body 1 forward, the oil passage through which the hydraulic oil is sent from the hydraulic pump 31 to the hydraulic motor 32 is referred to as the forward oil passage 51a, and the oil passage through which the hydraulic oil is sent from the hydraulic motor 32 to the hydraulic pump 31 is referred to as the reverse oil passage 51b. Therefore, when the hydraulic motor 32 is rotated in the reverse direction to move the traveling machine body 1 backward, the hydraulic oil is supplied from the hydraulic pump 31 to the hydraulic motor 32 in the reverse oil passage 51b, and the hydraulic oil is supplied from the hydraulic motor 32 to the hydraulic pump 31 in the forward oil passage 51a.

[0024] As shown in Figure 4, the hydraulic circuit 50 includes a hydraulic servomechanism 52 that controls the swash plate angle of the hydraulic pump 31. The hydraulic servomechanism 52 includes a speed change valve 53 that is switched in response to manual operation of the main speed change lever 12, and a speed change cylinder 54 that is connected to the charge pump 20 via the speed change valve 53. When the speed change valve 53 is switched in conjunction with manual operation of the main speed change lever 12, the speed change cylinder 54 operates to change the swash plate angle of the hydraulic pump 31, thereby performing a speed change operation that continuously changes or reverses the rotational speed of the motor output shaft 34 of the hydraulic motor 32.

[0025] Check relief valves 56a and 56b are provided between the forward oil passage 51a and the reverse oil passage 51b and the charge oil passage 55 to which charge pressure from the charge pump 20 is applied. When the pressure in one oil passage 51a (or 51b) becomes too high, the check relief valve 56a (or 56b) does not supply hydraulic oil to the hydraulic motor 32 or the hydraulic pump 31, but instead releases the hydraulic oil to the other oil passage 51b (or 51a) or the hydraulic continuously variable transmission 30 (and thus the transmission case 18), thereby relieving abnormal pressure that occurs when an overload acts on the hydraulic motor 32. The relief pressure set in the check relief valves 56a and 56b is specified to be equivalent to the abnormal pressure described above.

[0026] When the hydraulic oil in one oil passage 51a (or 51b) is insufficient, the check relief valve 56a (or 56b) supplies hydraulic oil to the other oil passage 51a (or 51b) from the charge oil passage 55 via the check relief valve 56a (or 56b). In other words, the check relief valves 56a and 56b function as both a check valve and a relief valve.

[0027] Charge oil passage 55 is connected to both forward oil passage 51a and reverse oil passage 51b that constitute closed circuit 51. Therefore, while engine 17 is running, hydraulic oil from charge pump 20 is constantly replenished to closed circuit 51. An excess relief valve 57 that regulates the discharge pressure of charge pump 20 to the charge pressure is provided in charge oil passage 55 at a portion thereof that leads to check relief valves 56a and 56b. Charge oil passage 55 is connected to transmission case 18 via excess relief valve 57 and hydrostatic continuously variable transmission 30. Therefore, excess hydraulic oil from charge pump 20 is returned to transmission case 18 via excess relief valve 57 and hydrostatic continuously variable transmission 30.

[0028] Charge oil passage 55 is connected to hydraulic servomechanism 52 via servo oil passage 58. Servo pressure for operating speed change cylinder 54 is supplied to hydraulic servomechanism 52 from charge oil passage 55 via servo oil passage 58. The suction side of charge pump 20 in charge oil passage 55 is connected via strainer 59 to transmission case 18, which also serves as a hydraulic oil tank.

[0029] A bypass oil passage 60 that bypasses the hydraulic pump 31 and the hydraulic motor 32 is connected to the forward oil passage 51a and the reverse oil passage 51b. A bypass valve 61 that can release the hydraulic oil pressure to the hydraulic motor 32 is provided in the bypass oil passage 60. The bypass valve 61 of the first embodiment is a proportional solenoid valve of a normally open type that has an adjustable opening. In other words, the bypass valve 61 of the first embodiment is a two-port two-position switching type normally open proportional solenoid valve that can be switched between two positions: an open position that opens the bypass oil passage 60, and a closed position that closes the bypass oil passage 60, by energizing and de-energizing an electromagnetic solenoid.

[0030] In the first embodiment, the bypass valve 61 is configured to be in the open position when the main shift lever 12 is in the neutral position, and to be in the closed position when the main shift lever 12 is in a position other than the neutral position. When the bypass valve 61 is switched to the open position by the electromagnetic solenoid while the engine 17 is running, the bypass oil passage 60 is opened, the hydraulic oil pressure for the hydraulic motor 32 is bypassed to the bypass oil passage 60 side, and the hydraulic oil pressure for the hydraulic motor 32 is reduced according to the opening degree of the bypass valve 61. Then, although charge pressure still acts on the hydraulic motor 32, there is no longer a differential pressure between the forward oil passage 51a and the reverse oil passage 51b, and therefore the output of the hydraulic motor 32 (rotation of the motor output shaft 34) stops regardless of whether the swash plate of the hydraulic pump 31 is in the neutral state.

[0031] Next, an example of the control structure and control mode of the hydraulic continuously variable transmission 30 and the traveling system will be described with reference to Figures 5 and 6. The combine harvester is equipped with a controller 70 as the control means of the present invention. Although not shown in detail, the controller 70 includes a CPU that executes various arithmetic processes and controls, a ROM that stores control programs and data, a RAM that temporarily stores control programs and data, an input / output interface, and the like. The controller 70 is connected to a battery 72 via a key switch 71 for applying power.

[0032] The input side of the controller 70 is electrically connected to a steering angle potentiometer 73 that detects the operating position of the steering lever 10, a main speed change potentiometer 74 that detects the operating position of the main speed change lever 12, an auxiliary speed change potentiometer 75 that detects the operating position of the auxiliary speed change lever 13, a parking brake sensor 76 that detects the depression of the parking brake pedal 27, and a vehicle speed sensor 77 that detects the vehicle speed of the traveling vehicle body 1.

[0033] The output side of the controller 70 is electrically connected to the speed change valve 53 for the speed change cylinder 54, which is a speed change actuator, left and right clutch solenoid valves 91, 92 for the left and right clutch cylinders 81, 82 that engage and disengage the left and right side clutches 41, 42, left and right brake solenoid valves 93, 94 for the left and right brake cylinders 83, 84 that are brake actuators that apply the left and right side brakes 43, 44, and a bypass valve 61, etc.

[0034] The controller 70 is configured to open the bypass valve 61 in conjunction with returning the main speed change lever 12 to the neutral position, and to execute travel stop control to stop the combine by both neutralizing the swash plate of the hydraulic pump 31 and opening the bypass valve 61.

[0035] That is, as shown in the flowchart of FIG. 6, following the start of travel stop control, if the controller 70 determines that the combine is traveling based on the detection by the main speed change potentiometer 74 of the main speed change lever 12 being operated to a position other than the neutral position and the detection by the vehicle speed sensor 77 of a traveling state other than zero vehicle speed (S01: YES), it reads the detection value of the main speed change potentiometer 74 and determines whether the main speed change lever 12 has been operated back to the neutral position (S02).

[0036] If the combine is traveling, the main speed change lever 12 is operated to a position other than the neutral position, so the bypass valve 61 is in the closed position and the bypass oil passage 60 is closed. If the main speed change lever 12 is operated to return to the neutral position (S02: YES), the neutral return time Tn of the main speed change lever 12 is calculated from the detection value of the main speed change potentiometer 74, and it is determined whether the neutral return time Tn is equal to or greater than a preset set time TS (S03). The set time TS may be set to, for example, about 0.5 seconds.

[0037] If the neutral return time Tn is equal to or greater than the set time TS (if it exceeds the set time TS, S03: YES), this means that the operator is returning the main speed change lever 12 to the neutral position relatively slowly, and therefore the bypass valve 61 is gradually switched to the open position by the electromagnetic solenoid, for example, under duty control corresponding to the neutral return time Tn, the bypass oil passage 60 is opened, and the hydraulic pressure for the hydraulic motor 32 is bypassed (diverted) to the bypass oil passage 60 side, S04. In other words, the opening speed of the bypass valve 61 in step S04 is slower than in step S07, which will be described later.

[0038] As a result, the operating oil pressure to the hydraulic motor 32 is reduced according to the opening of the bypass valve 61, and ultimately, although charge pressure acts on the hydraulic motor 32, there is no differential pressure between the forward oil passage 51a side and the reverse oil passage 51b side, and the output of the hydraulic motor 32 (rotation of the motor output shaft 34) stops regardless of whether the swash plate of the hydraulic pump 31 is in the neutral state or not.

[0039] Here, because the main speed change lever 12 is returned to the neutral position, the bypass valve 61 is fully opened and the swash plate of the hydraulic pump 31 is in the neutral state around the time that the output of the hydraulic motor 32 (rotation of the motor output shaft 34) stops. Therefore, upon detecting depression of the parking brake pedal 27 (S05: YES), the controller 70 switches and operates the left and right brake solenoid valves 93, 94, and operates the left and right brake cylinders 83, 84 to brake the left and right side brakes 43, 44, thereby reliably stopping the combine harvester from traveling (S06).

[0040] Returning to step S03, if the neutral return time Tn is less than the set time TS (if it is less than the set time TS, S03: NO), this means that the operator is quickly returning the main speed change lever 12 to the neutral position, so the electromagnetic solenoid is caused to instantly switch the bypass valve 61 to full open, opening the bypass oil passage 60 and causing the hydraulic pressure for the hydraulic motor 32 to bypass (detour) to the bypass oil passage 60 side. That is, the opening speed of the bypass valve 61 in step S07 is faster than that in step S04.

[0041] As a result, the pressure difference between the forward oil passage 51a and the reverse oil passage 51b disappears more quickly than in step S04, and the output of the hydraulic motor 32 (rotation of the motor output shaft 34) stops regardless of whether the swash plate of the hydraulic pump 31 is in the neutral state. In this case, too, the swash plate of the hydraulic pump 31 is in the neutral state around the time when the bypass valve 61 is fully opened and the output of the hydraulic motor 32 (rotation of the motor output shaft 34) stops. Therefore, the process proceeds to step S05. When depression of the parking brake pedal 27 is detected (step S05: YES), the controller 70 switches and operates the left and right brake solenoid valves 93, 94, and operates the left and right brake cylinders 83, 84 to brake the left and right side brakes 43, 44, thereby reliably stopping the combine harvester from traveling (S06).

[0042] Thereafter, when it is detected that the parking brake pedal 27 has been released (S08: YES), the left and right brake solenoid valves 93, 94 are switched, and the left and right side brakes 43, 44 are released by the release operation of the left and right brake cylinders 83, 84 (S09), thereby returning the combine to a state in which it can travel. Note that the set time TS itself may be included on the shorter side or the longer side. In the first embodiment, it is included on the longer side.

[0043] When controlled as described above, the bypass valve 61 is opened in conjunction with the return operation of the main shift lever 12 to the neutral position, so that the operating oil pressure to the hydraulic motor 32 is released regardless of whether the swash plate of the hydraulic pump 31 is in the neutral state or not, and the output of the hydraulic motor 32 (rotation of the motor output shaft 34) can be reliably stopped by both the neutralization of the swash plate of the hydraulic pump 31 and the opening of the bypass valve 61.

[0044] Therefore, by simply adopting the simple configuration of adding a bypass oil passage 60 and a bypass valve 61 to the closed circuit 51, even if a malfunction occurs in the hydraulic continuously variable transmission 30, such as the swash plate of the hydraulic pump 31 not being in the neutral state, the output of the hydraulic motor 32 (rotation of the motor output shaft 34) can be reliably stopped, the output of the hydraulic continuously variable transmission 30 (vehicle speed) can be set to zero, and the combine can be reliably stopped from traveling, without forcibly stopping the engine 17 or operating the sub-transmission lever 13 to neutral. The combine can also be brought to an emergency stop simply by returning the main transmission lever 12 to the neutral position. Furthermore, because there is no need to stop the engine, tasks such as threshing and discharge can be performed as is.

[0045] Furthermore, the opening of the bypass valve 61 is changed in accordance with the speed of the return operation of the main shift lever 12, thereby reducing the hydraulic pressure to the hydraulic motor 32 and bringing the output of the hydraulic motor 32 (rotation of the motor output shaft 34) to a halt, thereby ensuring extremely good operation response of the main shift lever 12.

[0046] Fig. 7 illustrates another example of a bypass valve 62. The bypass valve 62 of the other example shown in Fig. 7 is a three-port, two-position, normally open proportional solenoid valve that can be switched between two positions: an open position that opens the bypass oil passage 60, and a closed position that closes the bypass oil passage 60, by energizing and de-energizing an electromagnetic solenoid. In this case, when the bypass valve 62 is switched to the open position by the electromagnetic solenoid, the hydraulic pressure for the hydraulic motor 32 is drained to the transmission case 18 via the hydraulic continuously variable transmission 30. Even when configured in this manner, the same effects as those of the first embodiment can be achieved.

[0047] Next, the hydraulic circuit structure of the hydraulic continuously variable transmissions 130, 160 in the second embodiment will be described with reference to Figures 8 to 11. Although detailed illustrations are omitted, the combine harvester having the hydraulic continuously variable transmissions 130, 160 of the second embodiment employs a round-shaped control handle 110 instead of the control lever 10.

[0048] In the second embodiment, the steering handle 110, the main shift lever 12, and the hydraulic continuously variable transmissions 130 and 160 are (1) When the main speed change lever 12 is operated to a position other than the neutral position and the steering handle 110 is rotated to a position other than the neutral position, the traveling vehicle 1 turns left or right with a smaller turning radius as the rotation amount increases, and the smaller the turning radius, the slower the vehicle speed (turning speed when traveling forward or backward) of the traveling vehicle 1 becomes. (2) When the main speed change lever 12 is operated in either the forward or reverse direction, the direction of rotation of the steering handle 110 coincides with the direction of rotation of the traveling vehicle 1 (when the steering handle 110 is turned to the right, the traveling vehicle 1 turns to the right, and when the steering handle 110 is turned to the left, the traveling vehicle 1 turns to the left). (3) When the main speed change lever 12 is in the neutral position, the steering handle 110 does not function even if it is rotated. In order to perform the above-mentioned various operations, the hydraulic continuously variable transmissions 130 and 160 are electrically or mechanically linked to the main shift lever 12 and the operating handle 110 so as to control them in conjunction with the operation of the main shift lever 12 and the operating handle 110.

[0049] The hydraulic continuously variable transmissions 130, 160 of the second embodiment are made up of a linear hydraulic continuously variable transmission 130 for traveling speed change having a linear pump 131 and a linear motor 132, and a swing hydraulic continuously variable transmission 160 for steering having a swing pump 161 and a swing motor 162. That is, the hydraulic continuously variable transmissions 130, 160 of the second embodiment are equipped with two hydraulic continuously variable transmissions, one for traveling speed change and one for steering.

[0050] The travel drive structure of the combine harvester in the second embodiment will be described with reference to Figure 8. The transmission case 18 is equipped with a linear hydraulic continuously variable transmission 130 for travel speed change, which has a linear pump 131 and a linear motor 132, and a swing hydraulic continuously variable transmission 160 for steering, which has a swing pump 161 and a swing motor 162. A transmission input shaft 120 of the transmission case 18 is gear-coupled to a pump shaft 133 of the linear pump 131 and a pump shaft 163 of the swing pump 161, respectively, for driving. Power output from the output shaft 19 of the engine 17 is transmitted to the pump shaft 133 of the linear pump 131 and the pump shaft 163 of the swing pump 161 via a pulley belt transmission system 119 and the transmission input shaft 120.

[0051] In the linear hydraulic continuously variable transmission 130, hydraulic oil is appropriately sent from the linear pump 131 to the linear motor 132 by power transmitted to the pump shaft 133. Similarly, in the swing hydraulic continuously variable transmission 160, hydraulic oil is appropriately sent from the swing pump 161 to the swing motor 162 by power transmitted to the pump shaft 163. A charge pump 20 is attached to the pump shaft 163 of the swing pump 161, supplying hydraulic oil to the linear pump 131, the linear motor 132, the swing pump 161, and the swing motor 162.

[0052] The linear hydraulic continuously variable transmission 130 changes the discharge direction and discharge amount of hydraulic oil to the linear motor 132 by changing and adjusting the swash plate angle of the linear pump 131 in accordance with the amount of operation of the main speed change lever 12. As a result, the rotation direction and rotation speed of the linear motor shaft 134 protruding from the linear motor 132 are adjusted as desired. The rotational power of the linear motor shaft 134 is transmitted from a linear transmission gear mechanism 135 to an auxiliary transmission gear mechanism 136. The auxiliary transmission gear mechanism 136 includes an auxiliary low-speed gear 139, an auxiliary medium-speed gear 140, and an auxiliary high-speed gear 141 that are switched by auxiliary transmission shifters 137, 138 that are linked to one another.

[0053] The low-speed auxiliary speed change shifter 137 is journalled on a parking brake shaft 143 (auxiliary speed change output shaft) located on the output side of the auxiliary speed change gear mechanism 136. The high-speed auxiliary speed change shifter 138 is journalled on an auxiliary speed change counter shaft 142 which constitutes the linear travel transmission gear mechanism 135. By operating the auxiliary speed change lever 13 arranged on the driving operation unit 9, the output rotation speed of the linear travel motor shaft 134 can be selectively switched to one of three speed stages: low speed, medium speed, or high speed.

[0054] The parking brake 143 is provided with a parking brake 144, such as a drum type. Rotational power from the sub-transmission gear mechanism 136 is transmitted from a sub-transmission output gear 145 fixed to the parking brake shaft 143 to a planetary gear mechanism 146, which is a left and right differential mechanism. A straight-line pulsar 121 is provided on the parking brake shaft 144. A straight-line vehicle speed sensor 122 is disposed opposite the outer periphery of the straight-line pulsar 121. The straight-line vehicle speed sensor 122 detects the rotation speed of the straight-line output (straight-line vehicle speed, which can also be said to be the speed change output of the sub-transmission output gear 145).

[0055] The left and right planetary gear mechanisms 146 each include a sun gear 147 that meshes with the subtransmission output gear 145, multiple planetary gears 148 that mesh with the sun gear 147, a ring gear 149 that meshes with the planetary gears 148, and a carrier 150 on which the multiple planetary gears 148 are rotatably arranged on the same circumference. The left and right carriers 150 face each other on the same axis (on the axis of the sun gear shaft 151 and the forced differential output shaft 153) with an appropriate gap between them. The left and right sun gears 147 are fixed to both axial ends of the sun gear shaft 151. A center gear 152 is fixed to the middle of the axial portion of the sun gear shaft 151.

[0056] The left and right ring gears 149 are arranged concentrically with the sun gear shaft 151, with the internal teeth on their inner peripheral surfaces meshing with the multiple planetary gears 148. The external teeth on the outer peripheral surfaces of the left and right ring gears 149 are connected to the steering output shaft 169 via left and right intermediate gears 170, 172 and a reverse gear 171, which will be described later. Each ring gear 149 is rotatably fitted onto left and right forced differential output shafts 153 that protrude outward to the left and right from the outer surface of the carrier 150. The left and right forced differential output shafts 153 are connected to the left and right axles 26 via final gear mechanisms 154. The rotational power transmitted from the auxiliary transmission gear mechanism 136 to the left and right planetary gear mechanisms 146 is transmitted from the left and right axles 26 to the respective drive sprockets 22 at the same rotational speed in the same direction, driving the left and right traveling crawlers 2 at the same rotational speed in the same direction, and moving the traveling body 1 straight (forward and backward).

[0057] The swing hydraulic continuously variable transmission 160 changes and adjusts the swash plate angle of the swing pump 161 in accordance with the amount of operation of the steering handle 110, thereby changing the discharge direction and discharge amount of hydraulic oil to the swing motor 162, and as a result, the rotation direction and rotation speed of the swing motor shaft 164 protruding from the swing motor 162 are adjusted as desired. A swing pulser 123 is provided on a steering counter shaft 167, which will be described later. A swing vehicle speed sensor 124 is disposed opposite the outer periphery of the swing pulser 123. The swing vehicle speed pulser 123 detects the rotation speed of the swing output (which can also be said to be the swing vehicle speed).

[0058] A wet-type multi-plate swing brake 165 is provided on the swing motor shaft 164, a steering countershaft 167 connected to the swing motor shaft 164 via an upstream reduction gear 166, and a steering output shaft 169 connected to the steering countershaft 167 via a downstream reduction gear 168. The rotational power of the swing motor shaft 164 is transmitted to the steering countershaft 167 via the upstream reduction gear 166. The rotational power transmitted from the steering countershaft 167 to the steering output shaft 169 is transmitted to the left ring gear 149 as reverse rotational power via a left intermediate gear 170 and a reverse gear 171 on the steering output shaft 169, and is transmitted to the right ring gear 149 as forward rotational power via a right intermediate gear 172 on the steering output shaft 169.

[0059] When the auxiliary transmission gear mechanism 136 is in neutral, power transmission from the linear motor 132 to the left and right planetary gear mechanisms 146 is blocked. When the auxiliary transmission gear mechanism 136 is set to a gear position other than neutral, power is transmitted from the linear motor 132 to the left and right planetary gear mechanisms 146 via the auxiliary transmission gear mechanism 136. When the output of the swing pump 161 is in neutral and the swing brake 165 is on, power transmission from the swing motor 162 to the left and right planetary gear mechanisms 146 is blocked. When the output of the swing pump 161 is set to a state other than neutral and the swing brake 165 is turned off, the rotational power of the swing motor 162 is transmitted to the left ring gear 149 via the steering countershaft 167, steering output shaft 169, left intermediate gear 170, and reverse gear 171, etc., and is also transmitted to the right ring gear 149 via the steering countershaft 167, steering output shaft 169, and right intermediate gear 172, etc.

[0060] When the swing motor 162 rotates forward (reverse), the left and right ring gears 149 rotate at the same rotation speed in opposite directions. In other words, the speed-change outputs of the motor shafts 134, 164 are transmitted to the left and right drive sprockets 22 via the sub-transmission gear mechanism 136 or the left and right planetary gear mechanisms 146, respectively, and the vehicle speed (traveling speed) and traveling direction of the traveling machine body 1 are determined.

[0061] Next, a hydraulic circuit 200 of the hydraulic continuously variable transmissions 130, 160 in the second embodiment will be described with reference to Fig. 9. The straight hydraulic continuously variable transmission 130 and the turning hydraulic continuously variable transmission 160 in the second embodiment have basically the same configuration as the hydraulic continuously variable transmission 30 (see Fig. 4) described in the first embodiment.

[0062] The hydraulic circuit 200 of the second embodiment includes a linear hydraulic continuously variable transmission 130 and a swing hydraulic continuously variable transmission 160. That is, the hydraulic circuit 200 includes a linear pump 131, a linear motor 132, a swing pump 161, a swing motor 162, and a charge pump 20. The linear pump 131 and the linear motor 132 are connected in a closed loop by a first linear oil passage 201a and a second linear oil passage 201b. The first linear oil passage 201a and the second linear oil passage 201b form a linear closed circuit 201. The swing pump 161 and the swing motor 162 are connected in a closed loop by a first swing oil passage 202a and a second swing oil passage 202b. The first swing oil passage 202a and the second swing oil passage 202b form a swing closed circuit 202.

[0063] The rotational power of the engine 17 drives the linear pump 131 and the swing pump 161, and by controlling the swash plate angle of the linear pump 131 and the swing pump 161, the discharge direction and discharge amount of hydraulic oil to the linear motor 132 and the swing motor 162 are changed, and the linear motor 132 and the swing motor 162 operate in forward and reverse directions and with infinitely increased and decreased speed.

[0064] The hydraulic circuit 200 of the second embodiment includes a linear valve 203 that switches in response to manual operation of the main shift lever 12, and a linear cylinder 204 connected to the charge pump 20 via the linear valve 203. When the linear valve 203 is switched, the linear cylinder 204 operates to change the swash plate angle of the linear pump 131, thereby performing a linear speed change operation in which the rotation speed of the linear motor shaft 134 of the linear motor 132 is continuously changed or reversed. The hydraulic circuit 200 also includes a hydraulic servomechanism 205 for linear speed change. The hydraulic servomechanism 205 performs a feedback operation in which the linear valve 203 returns to neutral by controlling the swash plate angle of the linear pump 131, thereby changing the swash plate angle of the linear pump 131 in proportion to the amount of operation of the main shift lever 12, thereby changing the rotation speed of the linear motor shaft 134 of the linear motor 132.

[0065] The hydraulic circuit 200 of the second embodiment includes a swing valve 206 that switches in response to the operation of the control handle 110, and a swing cylinder 207 connected to the charge pump 20 via the swing valve 206. When the swing valve 206 is switched, the swing cylinder 207 operates to change the swash plate angle of the swing pump 161, thereby performing left and right swing operations by continuously changing or reversing the rotation speed of the swing motor shaft 164 of the swing motor 162. The hydraulic circuit 200 also includes a hydraulic servo mechanism 208 for swing speed change. The hydraulic servo mechanism 208 performs a feedback operation in which the swing valve 206 returns to neutral by controlling the swash plate angle of the swing pump 161, thereby changing the swash plate angle of the swing pump 161 in proportion to the amount of operation of the control handle 110, and changing the rotation speed of the swing motor shaft 164 of the swing motor 162.

[0066] As shown in Fig. 9, a charge branch oil passage 213 is connected to all of the oil passages 201a, 201b, 202a, and 202b of both closed circuits 201 and 202. Check relief valves 209a and 209b are provided between the straight-travel first oil passage 201a and the straight-travel second oil passage 201b and the charge branch oil passage 213. Check relief valves 210a and 210b are also provided between the swing-travel first oil passage 202a and the swing-travel second oil passage 202b and the charge branch oil passage 213. The functions of the straight-travel side check relief valves 209a and 209b and the swing-side check relief valves 210a and 210b are the same as the check relief valves 56a and 56b of the first embodiment.

[0067] A strainer 211 located inside the transmission case 18 is connected to the suction side of the charge pump 20. A charge oil passage 212 is connected to the discharge side of the charge pump 20. A charge branch oil passage 213 is connected downstream of the charge oil passage 212. As described above, the charge branch oil passage 213 is connected to all of the oil passages 201a, 201b, 202a, and 202b of both closed circuits 201 and 202. Therefore, while the engine 17 is running, hydraulic oil from the charge pump 20 is constantly replenished to both closed circuits 201 and 202.

[0068] The charge branch oil passage 213 is connected to the straight valve 203 and therefore to the straight cylinder 204 via a straight servo oil passage 214, and is also connected to the swing valve 206 and therefore to the swing cylinder 207 via a swing servo oil passage 215. Servo pressure is supplied to the hydraulic servo mechanism 205 for straight speed change from the charge oil passage 212 and the charge branch oil passage 213 via the straight servo oil passage 214, and servo pressure is supplied to the hydraulic servo mechanism 208 for swing speed change from the charge oil passage 212 and the charge branch oil passage 213 via the swing servo oil passage 215.

[0069] Charge branch oil passage 213 is connected to transmission case 199, which houses straight hydraulic continuously variable transmission 130 and turning hydraulic continuously variable transmission 160, and ultimately to transmission case 18, via surplus relief valve 216. Therefore, surplus hydraulic oil supplied from charge pump 20 is returned to transmission case 18 via transmission case 199 and surplus relief valve 216.

[0070] A straight bypass oil passage 220 that bypasses the straight pump 131 and the straight motor 132 is connected to the first straight oil passage 201a and the second straight oil passage 201b. A straight bypass valve 221 that can release the hydraulic pressure to the straight motor 132 is provided in the straight bypass oil passage 220. In addition, a swing bypass oil passage 222 that bypasses the swing pump 161 and the swing motor 162 is connected to the first swing oil passage 202a and the second swing oil passage 202b. A swing bypass valve 223 that can release the hydraulic pressure to the swing motor 162 is provided in the swing bypass oil passage 222.

[0071] The straight bypass valve 221 and the swing bypass valve 223 of the second embodiment are basically configured in the same way as the bypass valve 61 of the first embodiment. However, the swing bypass valve 223 is an on-off type solenoid switching valve that does not have an opening adjustment. In the second embodiment, when the main shift lever 12 is in the neutral position, the straight bypass valve 221 is in the open position, and the swing bypass valve 223 is also in the open position regardless of the operating state of the steering wheel 110. When the main shift lever 12 is in a position other than the neutral position, the straight bypass valve 221 is in the closed position. Furthermore, when the steering wheel 110 is in the neutral position (steering angle zero), the swing bypass valve 223 is in the open position, and when the steering wheel 110 is in a position other than the neutral position, the swing bypass valve 223 is in the closed position.

[0072] In the second embodiment, as described above, when the main speed change lever 12 is in the neutral position, the straight bypass valve 221 is in the open position, and the swing bypass valve 223 is also in the open position regardless of the operating state of the control handle 110. Therefore, even if the operator inadvertently hits the main speed change lever 12 and operates it to the neutral position while the combine is swinging left or right (while turning the control handle 110), the hydraulic pressure to the swing motor 162 is released, and the output of the swing motor 162 (rotation of the swing motor shaft 164) can be reliably stopped by both neutralizing the swash plate of the swing pump 161 and opening the swing bypass valve 223, thereby zeroing the output of the swing hydraulic continuously variable transmission 160. As a result, there is no risk of the combine performing a spin turn (pivot turn) due to inadvertent operation of the main speed change lever 12 to neutral. Furthermore, by operating the main speed change lever 12 to the neutral position, the output of the linear hydraulic continuously variable transmission 130 becomes zero, so that the combine can be stopped without fail.

[0073] Next, an example of the control structure and control mode of the hydraulic continuously variable transmissions 130, 160 and, ultimately, the traveling system in the second embodiment will be described with reference to Figures 10 and 11. The basic structure of the controller 70 in the second embodiment is the same as that in the first embodiment. The input side of the controller 70 in the second embodiment is electrically connected to a steering angle potentiometer 73 that detects the operating position of the steering wheel 110, a main speed change potentiometer 74 that detects the operating position of the main speed change lever 12, an auxiliary speed change potentiometer 75 that detects the operating position of the auxiliary speed change lever 13, a parking brake sensor 76 that detects depression of the parking brake pedal 27, a straight vehicle speed sensor 122, and a turning vehicle speed sensor 124, etc.

[0074] The output side of the controller 70 is electrically connected to a straight valve 203 for the straight cylinder 204, a swing valve 206 for the swing cylinder 207, a parking brake solenoid valve 218 for the parking brake cylinder 217 as a brake actuator that activates the parking brake 144, a straight bypass valve 221, and a swing bypass valve 223.

[0075] The controller 70 of the second embodiment is configured to open the straight and swing bypass valves 221, 223 in conjunction with returning the main speed change lever 12 to the neutral position, and to perform travel stop control to stop the combine by both neutralizing the swash plate of the hydraulic pump 31 and opening the straight and swing bypass valves 221, 223.

[0076] That is, as shown in the flowchart of FIG. 11, following the start of travel stop control, if the controller 70 determines that the combine is traveling based on the detection by the main speed change potentiometer 74 of the main speed change lever 12 being operated to a position other than the neutral position and the detection by both vehicle speed sensors 122, 124 of a traveling state other than zero vehicle speed (S11: YES), it reads the detection value of the main speed change potentiometer 74 and determines whether the main speed change lever 12 has been operated back to the neutral position (S12).

[0077] If the combine is traveling, the main speed change lever 12 is operated to a position other than the neutral position, so the straight bypass valve 221 is in the closed position and the straight bypass oil passage 220 is closed. The open / closed state of the swing bypass valve 223 (swing bypass oil passage 222) depends on the operating state of the control handle 110. If the main speed change lever 12 is operated to return to the neutral position (S12: YES), the neutral return time Tn of the main speed change lever 12 is calculated from the detection value of the main speed change potentiometer 74, and it is determined whether the neutral return time Tn is equal to or greater than a preset set time TS (S13). The set time TS may be set to, for example, about 0.5 seconds.

[0078] If the neutral return time Tn is equal to or greater than the set time TS (if it exceeds the set time TS, S13: YES), this means that the operator is returning the main speed change lever 12 to the neutral position relatively slowly, and therefore the electromagnetic solenoid gradually switches the straight travel bypass valve 221 to the open position using, for example, duty control corresponding to the neutral return time Tn, opens the straight travel bypass oil passage 222, and causes the hydraulic pressure for the straight travel motor 132 to bypass (detour) to the straight travel bypass oil passage 220 side (S14). That is, the opening speed of the straight travel bypass valve 221 in step S14 is slower than in step S17, which will be described later.

[0079] As a result, the hydraulic pressure to the linear motor 132 is reduced according to the opening of the linear bypass valve 221, and ultimately, although charge pressure acts on the linear motor 132, there is no pressure difference between the linear first oil passage 201a side and the linear second oil passage 201b side, and the output of the linear motor 132 (rotation of the linear motor shaft 134) stops regardless of whether the swash plate of the linear pump 131 is in a neutral state or not.

[0080] In step S12, if the steering handle 110 is rotated to a position other than the neutral position, in parallel with the switching operation of the straight bypass valve 221, the swing bypass valve 223 is switched to fully open by an electromagnetic solenoid, the swing bypass oil passage 222 is opened, the operating oil pressure for the swing motor 162 is bypassed to the swing bypass oil passage 222 side, and the output of the swing motor 162 (rotation of the swing motor shaft 164) is stopped regardless of whether the swash plate of the swing pump 161 is in the neutral state or not.

[0081] At this stage, the main speed change lever 12 is returned to the neutral position, so the swash plates of the straight and swing pumps 131, 161 are in the neutral state around the time that the straight and swing bypass valves 221, 223 are fully opened and the outputs of the straight and swing motors 132, 162 are stopped. Then, upon detecting depression of the parking brake pedal 27 (S15: YES), the controller 70 switches the parking brake solenoid valve 218 to operate the parking brake cylinder 217 to apply the parking brake 144, thereby reliably stopping the combine harvester from traveling (S16).

[0082] Returning to step S13, if the neutral return time Tn is less than the set time TS (if it is less than the set time TS, S13: NO), this means that the operator is quickly returning the main speed change lever 12 to the neutral position, so the electromagnetic solenoid is caused to instantly switch the straight travel bypass valve 221 to full open, opening the straight travel bypass oil passage 220 and causing the hydraulic pressure for the straight travel motor 132 to bypass (detour) to the straight travel bypass oil passage 220 side. That is, the opening speed of the straight travel bypass valve 221 in step S17 is faster than in step S14.

[0083] As a result, the pressure difference between the first straight oil passage 201a and the second straight oil passage 201b disappears more quickly than in step S14, and the output of the straight motor 132 (rotation of the straight motor shaft 134) stops regardless of whether the swash plate of the straight pump 131 is in the neutral state. In this case as well, if the operating handle 110 is rotated to a position other than the neutral position, the electromagnetic solenoid switches the swing bypass valve 223 to full open in parallel with the switching operation of the straight bypass valve 221, as described above, and the output of the swing motor 162 (rotation of the swing motor shaft 164) stops regardless of whether the swash plate of the swing pump 161 is in the neutral state.

[0084] Also, since the swash plates of the straight and swing pumps 131, 161 are in the neutral state around the time when the straight and swing bypass valves 221, 223 are fully opened and the output of the straight and swing motors 132, 162 stops, the process proceeds to step S15, and upon detecting that the parking brake pedal 27 is depressed (step S15: YES), the controller 70 switches the parking brake solenoid valve 218 to operate, and the parking brake cylinder 217 is operated to apply the parking brake 144, thereby reliably stopping the combine harvester from traveling (S16).

[0085] Thereafter, when the release of the parking brake pedal 27 is detected (S18: YES), the parking brake solenoid valve 218 is switched and the parking brake cylinder 217 is released to release the parking brake 144 (S19), returning the combine to a state in which it can travel. Note that the set time TS itself may be included on the lower side or the upper side, as in the first embodiment.

[0086] The above control provides the same operational effects as those of the first embodiment. That is, the output of the hydraulic motor 32 (rotation of the motor output shaft 34) can be reliably stopped by both neutralizing the swash plate of the linear pump 131 and opening the linear bypass valve 221. Even if a malfunction occurs in the linear hydraulic continuously variable transmission 130, such as the swash plate of the linear pump 131 not being neutralized, there is no need to forcibly stop the engine 17 or operate the auxiliary shift lever 13 to neutral. Furthermore, the opening of the linear bypass valve 221 is changed in accordance with the speed of the return operation of the main shift lever 12 to reduce the hydraulic pressure for the linear motor 132, thereby enabling the output of the linear motor 132 (rotation of the linear motor shaft 134) to be stopped, ensuring extremely good operation response of the main shift lever 12.

[0087] In particular, in the second embodiment, as described above, when the main speed change lever 12 is operated to the neutral position, the swing bypass valve 223 is also switched to the open position regardless of the operating state of the steering handle 110. Therefore, even if the operator accidentally hits the main speed change lever 12 and operates it to the neutral position while the combine is swinging left or right (while rotating the steering handle 110), the hydraulic pressure to the swing motor 162 is released, and the output of the swing motor 162 (rotation of the swing motor shaft 164) is reliably stopped by both the neutralization of the swash plate of the swing pump 161 and the opening of the swing bypass valve 223, thereby zeroing the output of the swing hydraulic continuously variable transmission 160. As a result, the risk of the combine performing a spin turn (pivot turn) due to an inadvertent operation of the main speed change lever 12 to neutral is reliably eliminated. Furthermore, because the output of the straight-line hydraulic continuously variable transmission 130 is zeroed by operating the main speed change lever 12 to neutral, the combine can be reliably stopped.

[0088] As described above, the straight driving and swing bypass valves 221, 223 of the second embodiment are basically of the same configuration as the bypass valve 61 of the first embodiment. However, instead of these, the bypass valve 62 shown in FIG. 7 may be used as the straight driving and swing bypass valves 225, 227 (see FIG. 12). In this case, when the straight driving and swing bypass valves 225, 227 are switched to the open position, the hydraulic pressure for the straight driving and swing motors 132, 162 is drained to the transmission case 18 via the transmission case 199. However, in this case as well, it is sufficient to use an on-off type solenoid switching valve that does not adjust the opening degree as the swing bypass valve 227. It is also possible to use a combination of a charge pressure action type valve shown in FIG. 9 and a drain type valve shown in FIG. 12 as the straight driving and swing bypass valve.

[0089] The present invention is not limited to the above-described embodiment and can be embodied in various forms. For example, the hydraulic transmission can be widely applied not only to combine harvesters but also to various work vehicles such as tractors, rice transplanters, forklift trucks, and backhoes, as well as ships. Furthermore, the configuration of each part is not limited to the illustrated embodiment and can be modified in various ways without departing from the spirit of the present invention. [Explanation of symbols]

[0090] 2 Traveling crawler (traveling part) 12 Main shift lever (shifting device) 17 Engine 18 Mission Case 30 Hydraulic continuously variable transmission 31 Hydraulic pump 32 Hydraulic motor 50 Hydraulic circuit 51 Closed circuit 60 Bypass oil passage 61,62 Bypass valve 70 Controller (control means) 130 Straight-line hydraulic continuously variable transmission 131 Straight pump 132 Linear motor 144 Parking brake 160 Swing hydraulic continuously variable transmission 161 Swirl pump 162 Swing motor 199 gear case 200 Hydraulic circuit 201a Straight oil passage No. 1 201b Straight 2nd oilway 202a Swing No. 1 oilway 202b Swinging 2nd oilway 220 Straight bypass oil passage 221,225 Straight bypass valve 222 Swing bypass oil passage 223,227 Swing bypass valve

Claims

1. A work vehicle equipped with a hydraulic continuously variable transmission that changes the speed of engine power using a hydraulic pump and a hydraulic motor, and a speed change operating device that changes the speed of the output of the hydraulic continuously variable transmission, a bypass oil passage that bypasses between the hydraulic pump and the hydraulic motor is provided in the closed circuit of the hydraulic continuously variable transmission, a bypass valve whose opening degree is adjustable is arranged in the bypass oil passage, and a control means is provided that controls the bypass valve; When the speed change device is returned to the neutral position to open the bypass valve, if a time taken for the speed change device to return to neutral exceeds a preset time, the control device slows down the opening speed of the bypass valve compared to when the time is less than the preset time. Work vehicle.

2. A work vehicle equipped with a hydraulic continuously variable transmission that changes the speed of engine power using a hydraulic pump and a hydraulic motor, and a speed change operating device that changes the speed of the output of the hydraulic continuously variable transmission, a bypass oil passage that bypasses between the hydraulic pump and the hydraulic motor is provided in the closed circuit of the hydraulic continuously variable transmission, a bypass valve whose opening degree is adjustable is arranged in the bypass oil passage, and a control means is provided that controls the bypass valve; When the speed change device is returned to the neutral position to open the bypass valve, if a time taken for the speed change device to return to neutral falls below a preset time, the control device increases the opening speed of the bypass valve compared to when the time exceeds the preset time. Work vehicle.

3. the control means gradually increases the opening of the bypass valve when the neutral return time of the speed change device exceeds the set time. A work vehicle according to claim 1 or 2.

4. the control means instantly fully opens the bypass valve when the neutral return time of the speed change device falls below the set time. A work vehicle according to claim 1 or 2.

5. the control means brakes a traveling unit to which the speed-changing power of the hydraulic continuously variable transmission is transmitted in accordance with the bypass valve being fully opened. A work vehicle according to any one of claims 1 to 4.

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