JP2023122685A - work vehicle - Google Patents

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

The present invention relates to work vehicles.

Conventionally, a combine harvester, which is an example of a work vehicle, has a hydraulic continuously variable transmission that changes the power of the engine using a hydraulic pump and a hydraulic motor, and a main transmission operating device that changes the output of the hydraulic continuously variable transmission. and is configured to transmit the shifting power of the hydraulic continuously variable transmission to the traveling portion in accordance with the amount of operation of the main shift operating tool. An example of this type of combine is disclosed in Patent Document 1 and the like.

JP 2010-183855 A

In the above-described conventional configuration, when the main speed change operation device is operated to return to the neutral position, the swash plate of the hydraulic pump becomes neutral, the output of the hydraulic motor (rotation of the motor output shaft) stops, and the combine stops running. For this reason, if an emergency situation arises in which the combine does not stop running even if the main gear shift operation tool is returned to the neutral position due to a problem with the hydraulic continuously variable transmission, the engine will be forcibly stopped, or the sub gear shift operation tool will be released. If so, there was no choice but to stop the combine by neutralizing the auxiliary gear shift operation tool.

However, if the engine is forcibly stopped, all the functions of the combine harvester cannot be used, and if the sub-transmission operating device is of a manually operated type, the operator must manually operate the sub-transmission operating device one by one. was there.

SUMMARY OF THE INVENTION An object of the present invention is to provide a work vehicle improved by examining the above-mentioned current situation.

A first aspect of the present invention is a work vehicle comprising a hydraulic continuously variable transmission that shifts the power of an engine using a hydraulic pump and a hydraulic motor, and a shift operating device that shifts the output of the hydraulic continuously variable transmission. A closed circuit of the hydraulic continuously variable transmission is provided with a bypass oil passage for bypassing between the hydraulic pump and the hydraulic motor. A bypass valve is disposed, and control means for controlling the bypass valve is provided, and the control means operates the speed change operation device to return the speed change operation tool to a neutral position to open the bypass valve. When the neutral return time of the device exceeds a preset time, the opening speed of the bypass valve is made slower than when the time is less than the set time.

According to a second aspect of the present invention, there is provided a work vehicle comprising a hydraulic continuously variable transmission that shifts the power of an engine using a hydraulic pump and a hydraulic motor, and a shift operating device that shifts the output of the hydraulic continuously variable transmission. A closed circuit of the hydraulic continuously variable transmission is provided with a bypass oil passage for bypassing between the hydraulic pump and the hydraulic motor. A bypass valve is disposed, and control means for controlling the bypass valve is provided, and the control means operates the speed change operation device to return the speed change operation tool to a neutral position to open the bypass valve. When the tool's neutral return time is less than a preset set time, the opening speed of the bypass valve is made faster than when the set time is exceeded.

In the work vehicle of the present invention, the control means may gradually increase the degree of opening of the bypass valve when the neutral return time of the shift operation device exceeds the set time.

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 operation tool falls below the set time.

In the work vehicle of the present invention, the control means may brake the traveling portion to which the speed change power of the hydraulic continuously variable transmission is transmitted in accordance with the full opening of the bypass valve.

According to the present invention, the bypass valve is opened in conjunction with the return operation of the speed change operation tool to the neutral position. By both neutralizing the swash plate of the hydraulic pump and opening the bypass valve, it is possible to reliably stop the output of the hydraulic motor.

Therefore, even if a problem occurs in the hydraulic continuously variable transmission, such as the swash plate of the hydraulic pump not being in a neutral state, by simply adopting a simple configuration in which a bypass oil passage and a bypass valve are added in the closed circuit, Without forcibly stopping the engine, the output of the hydraulic motor can be reliably stopped, the output (vehicle speed) of the hydraulic continuously variable transmission can be set to zero, and the work vehicle can be reliably stopped. It is also possible to bring the work vehicle to a sudden stop simply by returning the speed change operation tool to the neutral position. In addition, since there is no need to stop the engine, operations such as threshing and discharging can be performed as they are.

In addition, the operating oil pressure for the hydraulic motor can be reduced by changing the degree of opening of the bypass valve in accordance with the speed of the return operation of the shift operating tool, and the output of the hydraulic motor can be shifted to a stop. operation followability can be ensured.

It is a side view of a combine. It is a top view of a combine. It is a power transmission system diagram of a mission case. 2 is a hydraulic circuit diagram of the hydraulic continuously variable transmission in the first embodiment; FIG. It is a functional block diagram of a controller. It is a flowchart of travel stop control. It is a hydraulic circuit diagram showing another example of a bypass valve. It is a power transmission system diagram of a transmission case in the second embodiment. 1 is a hydraulic circuit diagram of a hydraulic continuously variable transmission; FIG. It is a functional block diagram of a controller. It is a flowchart of travel stop control. It is a hydraulic circuit diagram showing another example of a bypass valve.

EMBODIMENT OF THE INVENTION Below, embodiment which actualized this invention is described based on drawing at the time of applying it to the combine which is an example of a working vehicle. In the following description, the terms "front and back", "left and right", and "up and down" are used to specify directions, but the directions of left and right and up and down 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.

As shown in FIGS. 1 and 2, the combine has a running body 1 supported by a pair of left and right running crawlers 2 . A reaping device 3 for reaping and taking in grain culms is attached to the front part of the traveling body 1 so as to be vertically adjustable 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 for storing grains taken out from the threshing device 5 are mounted side by side on the traveling body 1 . A driving control unit 9 is provided on the right side of the harvesting device 3 and in front of the grain tank 7 .

The operation control unit 9 includes a control lever 10, a driver's seat 11, a main gear shift lever 12 as a gear change operation tool, an auxiliary gear shift lever 13, a threshing clutch lever 14 for turning on and off a threshing clutch, and a reaper clutch for turning on and off a threshing clutch. A lever 15 is provided. An engine 17 as a drive source is mounted below the driver's seat 11 . A transmission case 18 is arranged in front of the engine 17 to appropriately shift the power of the engine 17 and transmit it to the left and right traveling crawlers 2 . A parking brake pedal 27 for braking the left and right traveling crawlers 2, 2 at the same time is provided at the lower front portion of the driver's seat 11 in the driving control unit 9. As shown in FIG.

As shown in FIG. 1 , left and right track frames 21 are arranged on the underside of the traveling body 1 . The track frame 21 is provided with a driving sprocket 22 that transmits the power of the engine 17 to the traveling crawler 2 .

Next, mainly referring to FIG. 3, a traveling drive structure for transmitting power from the engine 17 to the traveling crawler 2 will be described. A transmission case 18 (hydraulic transmission) arranged in front of the engine 17 includes a hydraulic continuously variable transmission 30 formed by combining a hydraulic pump 31 and a hydraulic motor 32 . An output shaft 19 of the engine 17 is interlocked with a pump input shaft 33 of a hydraulic pump 31 which is an input shaft of the transmission case 18 via a transmission belt 35 . The power from the engine 17 drives the hydraulic pump 31 , and the hydraulic motor 32 drives the hydraulic fluid discharged from the hydraulic pump 31 . A charge pump 20 is attached to the engine 17 to supply a supplementary amount of hydraulic oil circulating between the hydraulic pump 31 and the hydraulic motor 32 . The charge pump 20 is also driven by the power of the engine 17 .

A motor output shaft 34 of the hydraulic motor 32 is interlocked with a counter shaft 37 and a PTO output shaft 38 via a spur gear mechanism 36 . Left and right axles 26, 26 protruding outward from the transmission case 18 are connected to the counter shaft 37 via an auxiliary transmission gear mechanism 39, left and right side clutches 41, 42, and left and right side brakes 43, 44 of hydraulic switching multi-plate type. are interlocked. The power transmitted to the counter shaft 37 rotates the drive sprocket 22 connected to the left and right axles 26 and 26 via the sub-transmission gear mechanism 39, the left and right side clutches 41 and 42, and the left and right side brakes 43 and 44. It is transmitted to the left and right traveling crawlers 2, 2 as parts. That is, the power of the engine 17 is changed by the hydraulic continuously variable transmission 30 and transmitted to the left and right traveling crawlers 2 , 2 . Note that the PTO output shaft 38 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 .

Next, referring to FIG. 4, the hydraulic circuit structure of the hydraulic continuously variable transmission 30 according to the first embodiment will be described. A 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 by a closed circuit 51 so as to circulate working oil. The engine 17 drives the hydraulic pump 31 and the charge pump 20 . By controlling the swash plate angle of the hydraulic pump 31 according to the manual operation of the main shift lever 12, the discharge direction and discharge amount of the hydraulic oil of the hydraulic pump 31 are changed, and the hydraulic motor 32 rotates forward/reverse and steplessly. Increase/decelerate.

Here, in FIG. 4, for convenience of explanation, in the closed circuit 51, when the hydraulic motor 32 is rotated forward to move the traveling 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 forward oil. An oil passage through which hydraulic oil is sent from the hydraulic motor 32 to the hydraulic pump 31 is called a reverse oil passage 51b. Therefore, when the hydraulic motor 32 is reversed to move the traveling body 1 backward, hydraulic oil is supplied from the hydraulic pump 31 to the hydraulic motor 32 in the reverse oil passage 51b, and from the hydraulic motor 32 to the hydraulic pump 31 in the forward oil passage 51a. Hydraulic oil is supplied to

As shown in FIG. 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 has a shift valve 53 that switches in response to manual operation of the main shift lever 12 and a shift cylinder 54 that is connected to the charge pump 20 via the shift valve 53 . When the shift valve 53 is switched in conjunction with the manual operation of the main shift lever 12, the shift cylinder 54 operates to change the swash plate angle of the hydraulic pump 31, thereby increasing the rotation speed of the motor output shaft 34 of the hydraulic motor 32. A speed change operation is executed in which the speed is steplessly changed or reversed.

Check relief valves 56 a and 56 b are provided between the forward oil passage 51 a and the reverse oil passage 51 b and the charge oil passage 55 to which the charge pressure from the charge pump 20 is applied. When the pressure in one of the oil passages 51a (or 51b) becomes too high, the check relief valve 56a (or 56b) does not supply hydraulic fluid to the hydraulic motor 32 or the hydraulic pump 31, and the other oil passage 51b is closed. (or 51a) or the hydraulic continuously variable transmission 30 (and thus the mission case 18) to release the hydraulic oil to relieve the abnormal pressure generated when the hydraulic motor 32 is overloaded. The relief pressures set in the check relief valves 56a and 56b are defined to correspond to the above-described abnormal pressures.

When the hydraulic oil in one oil passage 51a (or 51b) runs short, the check relief valve 56a (or 56b) operates from the charge oil passage 55 via the check relief valve 56a (or 56b) to the one oil passage 51a. (or 51b) is supplied with hydraulic oil. That is, the check relief valves 56a and 56b have both the function of a check valve and the function of a relief valve.

The charge oil passage 55 is connected to both the forward oil passage 51 a and the reverse oil passage 51 b that form the closed circuit 51 . Therefore, while the engine 17 is running, the closed circuit 51 is always replenished with hydraulic oil from the charge pump 20 . A surplus relief valve 57 that regulates the discharge pressure of the charge pump 20 to the charge pressure is provided in the charge oil passage 55 halfway to the check relief valves 56a and 56b. The charge oil passage 55 is connected to the transmission case 18 via the hydraulic continuously variable transmission 30 via the surplus relief valve 57 . Therefore, the surplus hydraulic oil from the charge pump 20 is returned to the mission case 18 via the surplus relief valve 57 and the hydraulic continuously variable transmission 30 .

The charge oil passage 55 is connected to the hydraulic servomechanism 52 via a servo oil passage 58 . Servo pressure for operating the transmission cylinder 54 is supplied to the hydraulic servo mechanism 52 from a charge oil passage 55 via a servo oil passage 58 . The suction side of the charge pump 20 in the charge oil passage 55 is connected through a strainer 59 to the mission case 18 which is also a hydraulic oil tank.

A bypass oil passage 60 that bypasses between 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 capable of releasing the hydraulic pressure to the hydraulic motor 32 is provided in the bypass oil passage 60 . The bypass valve 61 of the first embodiment is of a proportional electromagnetic type whose degree of opening is adjustable and of a normally open type. In other words, the bypass valve 61 of the first embodiment 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 demagnetizing the electromagnetic solenoid. This is a port 2 position switching type normally open proportional solenoid valve.

In the first embodiment, the bypass valve 61 is in the open position when the main gear lever 12 is in the neutral position, and the bypass valve 61 is in the closed position when the main gear 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, and the operating oil pressure for the hydraulic motor 32 is bypassed to the bypass oil passage 60 side. The working oil pressure for the hydraulic motor 32 is reduced according to the opening of the . Ultimately, although the charge pressure acts on the hydraulic motor 32, since the differential pressure between the forward oil passage 51a and the reverse oil passage 51b disappears, the swash plate of the hydraulic pump 31 is in the neutral state. Regardless, the output of the hydraulic motor 32 (rotation of the motor output shaft 34) stops.

Next, referring to FIGS. 5 and 6, the control structure of the hydraulic continuously variable transmission 30 and, in turn, the traveling system, and an example of its control mode will be described. The combine is equipped with a controller 70 as a 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. It has The controller 70 is connected to a battery 72 via a key switch 71 for applying power.

On the input side of the controller 70 are a steering angle potentiometer 73 for detecting the operating position of the steering lever 10, a main gear shifting potentiometer 74 for detecting the operating position of the main gear shifting lever 12, and an auxiliary gear shifting potentiometer for detecting the operating position of the auxiliary gear shifting lever 13. 75, a parking brake sensor 76 for detecting depression of the parking brake pedal 27, a vehicle speed sensor 77 for detecting the vehicle speed of the traveling body 1, and the like are electrically connected.

On the output side of the controller 70 are a shift valve 53 for a shift cylinder 54 which is a shift actuator, left and right clutch electromagnetic valves 91 and 92 for left and right clutch cylinders 81 and 82 for connecting and disconnecting the left and right side clutches 41 and 42, and left and right side brakes 43. , 44 are electrically connected to the left and right brake solenoid valves 93 and 94, the bypass valve 61 and the like to the left and right brake cylinders 83 and 84 as brake actuators for braking the actuators .

The controller 70 opens the bypass valve 61 in conjunction with returning the main shift lever 12 to the neutral position, and stops the combine by both neutralizing the swash plate of the hydraulic pump 31 and opening the bypass valve 61. It is configured to execute travel stop control.

That is, as shown in the flow chart of FIG. 6, following the start of the travel stop control, the controller 70 detects the operating state of the main gear shift lever 12 to a position other than the neutral position by the main gear shift potentiometer 74, and detects the vehicle speed by the vehicle speed sensor 77. If it is determined that the combine is running based on the detection of a running state other than zero (S01: YES), the detected value of the main shift potentiometer 74 is read and the main shift lever 12 is returned to the neutral position. It is determined whether or not (S02).

When the combine is running, the main shift 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 gear shift lever 12 is operated to return to the neutral position (S02: YES), the neutral return time Tn of the main gear shift lever 12 is calculated from the detected value of the main gear shift potentiometer 74, and the neutral return time Tn is set in advance. It is determined whether or not the time is equal to or longer than the time TS (S03). The set time TS may be set to about 0.5 seconds, for example.

If the neutral return time Tn is equal to or longer than the set time TS (if it exceeds the set time TS, S03: YES), it means that the operator is relatively slowly returning the main shift lever 12 to the neutral position. By the electromagnetic solenoid, for example, the bypass valve 61 is gradually switched to the open position by duty control corresponding to the neutral return time Tn, the bypass oil passage 60 is opened, and the working oil pressure for the hydraulic motor 32 is supplied to the bypass oil passage 60 side. (bypass, S04). That is, the opening speed of the bypass valve 61 in step S04 is slower than in step S07, which will be described later.

Then, the hydraulic pressure applied to the hydraulic motor 32 is reduced according to the degree of opening of the bypass valve 61, and although the charge pressure acts on the hydraulic motor 32, the forward oil passage 51a side and the reverse oil passage 51b side are eventually separated. There is no differential pressure therebetween, and regardless of whether the swash plate of the hydraulic pump 31 is in a neutral state or not, the output of the hydraulic motor 32 (rotation of the motor output shaft 34) stops.

Here, since the main gear shift lever 12 is returned to the neutral position, the bypass valve 61 is fully opened and the output of the hydraulic motor 32 (rotation of the motor output shaft 34) is stopped. swashplate is in neutral. Therefore, upon detection of depression of the parking brake pedal 27 (S05: YES), the controller 70 switches the left and right brake electromagnetic valves 93 and 94, and operates the left and right brake cylinders 83 and 84 to operate the left and right side brakes 43 and 44. The brake is applied to reliably stop the combine harvester (S06).

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), it means that the operator is quickly returning the main shift lever 12 to the neutral position. Then, the bypass valve 61 is instantaneously switched fully open by the electromagnetic solenoid, the bypass oil passage 60 is opened, and the operating oil pressure for the hydraulic motor 32 is bypassed to the bypass oil passage 60 side (bypassed, S07). That is, the opening speed of the bypass valve 61 in step S07 is faster than in step S04.

As a result, the differential pressure between the forward oil passage 51a side and the reverse oil passage 51b side disappears more quickly than in step S04, and the hydraulic motor 32 is operated regardless of whether the swash plate of the hydraulic pump 31 is in the neutral state or not. output (rotation of the motor output shaft 34) stops. In this case also, the swash plate of the hydraulic pump 31 is in the neutral state before and after the bypass valve 61 is fully opened and the output of the hydraulic motor 32 (rotation of the motor output shaft 34) is stopped. Moving to step S05, upon detection of depression of the parking brake pedal 27 (step S05: YES), the controller 70 switches the left and right brake electromagnetic valves 93, 94 to operate the left and right brake cylinders 83, 84 to The brakes 43 and 44 are applied to reliably stop the combine harvester (S06).

After that, when the release of the parking brake pedal 27 is detected (S08: YES), the left and right brake electromagnetic valves 93 and 94 are switched, and the left and right brake cylinders 83 and 84 are released to brake the left and right side brakes 43 and 44. It is released (S09), and the combine is returned to a state in which it can run. Note that the set time TS itself may be included on the lower side or may be included on the higher side. In the first embodiment, it is included in the higher side.

With the control described above, the bypass valve 61 is opened in conjunction with the return operation of the main gear shift lever 12 to the neutral position. The hydraulic pressure is released, and by both neutralizing the swash plate of the hydraulic pump 31 and opening the bypass valve 61, the output of the hydraulic motor 32 (rotation of the motor output shaft 34) can be reliably stopped.

Therefore, by adopting a simple configuration of adding the bypass oil passage 60 and the bypass valve 61 in the closed circuit 51, even if the swash plate of the hydraulic pump 31 does not go into the neutral state, the problem of the hydraulic continuously variable transmission 30 can be eliminated. Even if this occurs, the output of the hydraulic motor 32 (rotation of the motor output shaft 34) can be reliably stopped without forcibly stopping the engine 17 or neutrally operating the auxiliary transmission lever 13, and the hydraulic continuously variable transmission 30 output (vehicle speed) can be set to zero, and the combine can be reliably stopped. It is also possible to bring the combine harvester to a sudden stop simply by returning the main shift lever 12 to the neutral position. In addition, since there is no need to stop the engine, operations such as threshing and discharging can be performed as they are.

In addition, the degree of opening of the bypass valve 61 is changed in accordance with the speed of the return operation of the main shift lever 12 to reduce the hydraulic pressure applied to the hydraulic motor 32, thereby stopping the output of the hydraulic motor 32 (rotation of the motor output shaft 34). , and extremely good operation followability of the main shift lever 12 can be ensured.

FIG. 7 illustrates another bypass valve 62 . A bypass valve 62 of another example shown in FIG. 7 has three ports that can be switched between two positions, an open position for opening the bypass oil passage 60 and a closed position for closing the bypass oil passage 60, by energizing and demagnetizing an electromagnetic solenoid. This is a 2-position switching type normally open proportional solenoid valve. In this case, when the bypass valve 62 is switched to the open position by the electromagnetic solenoid, the working oil pressure for the hydraulic motor 32 is drained to the mission 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 obtained.

Next, the hydraulic circuit structure of the hydraulic continuously variable transmissions 130, 160 according to the second embodiment will be described with reference to FIGS. 8 to 11. FIG. Although detailed illustration is omitted, the combine having the hydraulic continuously variable transmissions 130 and 160 of the second embodiment employs a circular steering handle 110 instead of the steering lever 10 .

In the second embodiment, the steering handle 110, the main transmission lever 12, and the hydraulic continuously variable transmissions 130, 160 are
(1) When the steering handle 110 is rotated to a position other than the neutral position while the main gearshift lever 12 is operated to a position other than the neutral position, the traveling machine body 1 turns left or right with a smaller turning radius as the amount of turning operation increases. and the smaller the turning radius, the slower the vehicle speed of the traveling machine body 1 (turning speed when traveling forward and backward).
(2) Regardless of whether the main transmission lever 12 is operated forward or backward, the turning operation direction of the steering handle 110 and the turning direction of the traveling machine body 1 are the same (when the steering handle 110 is turned to the right, the traveling machine body 1 turns to the right, and if the steering handle 110 is turned to the left, the traveling machine body 1 turns to the left),
(3) When the main shift lever 12 is in the neutral position, turning the steering handle 110 does not work.
, are electrically or mechanically linked to control the hydraulic continuously variable transmissions 130 and 160 in conjunction with the operation of the main shift lever 12 and the steering handle 110 .

Hydraulic continuously variable transmissions 130 and 160 of the second embodiment are composed of a linear hydraulic continuously variable transmission 130 for traveling speed change having a linear pump 131 and a linear motor 132, and a turning pump 161 and a turning motor 162 for steering. Hydraulic continuously variable transmission 160. That is, the hydraulic continuously variable transmissions 130 and 160 of the second embodiment are equipped with two hydraulic continuously variable transmissions, one for running speed change and one for steering.

A traveling drive structure of a combine harvester according to the second embodiment will be described with reference to FIG. 8 . The transmission case 18 includes a linear hydraulic continuously variable transmission 130 for traveling speed change having a linear pump 131 and a linear motor 132, and a turning hydraulic continuously variable transmission 160 for steering having a turning pump 161 and a turning motor 162. there is The transmission input shaft 120 of the transmission case 18 is gear-connected to the pump shaft 133 of the linear pump 131 and the pump shaft 163 of the orbiting pump 161 so as to be driven. 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 rotary pump 161 via the pulley belt transmission system 119 and the transmission input shaft 120 .

In the linear hydraulic continuously variable transmission 130 , hydraulic fluid is appropriately fed from the linear pump 131 to the linear motor 132 by the power transmitted to the pump shaft 133 . Similarly, in the swing hydraulic continuously variable transmission 160 , hydraulic fluid is appropriately fed from the swing pump 161 to the swing motor 162 by the power transmitted to the pump shaft 163 . A charge pump 20 is attached to a pump shaft 163 of the swivel pump 161 to supply working oil to the rectilinear pump 131 , the rectilinear motor 132 , the swivel pump 161 and the swivel motor 162 .

The linear hydraulic continuously variable transmission 130 changes the discharge direction and 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 operation amount of the main shift lever 12 . . As a result, the direction of rotation and the number of revolutions of the linear motor shaft 134 projecting from the linear motor 132 are arbitrarily adjusted. The rotational power of the rectilinear motor shaft 134 is transmitted from the rectilinear transmission gear mechanism 135 to the auxiliary transmission gear mechanism 136 . The sub-transmission gear mechanism 136 includes a sub-transmission low-speed gear 139, a sub-transmission medium-speed gear 140, and a sub-transmission high-speed gear 141 that are switched by sub-transmission shifters 137 and 138 that interlock with each other.

The low-speed sub-transmission shifter 137 is supported by a parking brake shaft 143 (sub-transmission output shaft) located on the output side of the sub-transmission gear mechanism 136 . The high-speed sub-transmission shifter 138 is pivotally supported by a sub-transmission counter shaft 142 that constitutes the rectilinear transmission gear mechanism 135 . By operating the sub-transmission lever 13 arranged in the operation control unit 9, the output rotation speed of the linear motor shaft 134 is selectively switched to one of three gear stages, ie, low speed, medium speed or high speed.

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 the sub-transmission output gear 145 fixed to the parking brake shaft 143 to the planetary gear mechanism 146, which is a left and right differential mechanism. A straight pulsar 121 is provided on the parking brake shaft 144 . A straight traveling vehicle speed sensor 122 is arranged on the outer peripheral side of the straight traveling pulsar 121 so as to face it. A straight running vehicle speed sensor 122 detects the rotation speed of the straight running output (straight running vehicle speed, which can also be said to be the shift output of the auxiliary transmission output gear 145).

The left and right planetary gear mechanisms 146 include a sun gear 147 meshing with the sub-transmission output gear 145, a plurality of planetary gears 148 meshing with the sun gear 147, a ring gear 149 meshing with the planetary gears 148, and a plurality of planetary gears 148 on the same circumference. and a rotatably arranged carrier 150 . 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 therebetween. The left and right sun gears 147 are fixed to both ends of the sun gear shaft 151 in the axial direction. A center gear 152 is fixed to the axially intermediate portion of the sun gear shaft 151 .

The left and right ring gears 149 are arranged concentrically with the sun gear shaft 151 with the inner teeth of the inner peripheral surfaces meshing with the plurality of planetary gears 148 . The outer teeth 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 to left and right forced differential output shafts 153 projecting left and right outward 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 a final gear mechanism 154 . The rotational power transmitted from the sub-transmission gear mechanism 136 to the left and right planetary gear mechanisms 146 is transmitted from the left and right axles 26 to the drive sprockets 22 at the same rotation speed in the same direction, and the left and right traveling crawlers 2 are rotated in the same direction. It is driven by the number of revolutions, and the traveling machine body 1 is moved straight (forward, backward).

The swing hydraulic continuously variable transmission 160 changes and adjusts the swash plate angle of the swing pump 161 according to the operation amount of the steering wheel 110, thereby changing the discharge direction and discharge amount of hydraulic oil to the swing motor 162. , the rotation direction and the number of revolutions of a turning motor shaft 164 projecting from the turning motor 162 are arbitrarily adjusted. A turning pulser 123 is provided on a steering counter shaft 167, which will be described later. A turning vehicle speed sensor 124 is arranged on the outer peripheral side of the turning pulser 123 so as to face the turning pulser 123 . A turning vehicle speed pulser 123 detects the number of rotations of the turning output (also referred to as turning vehicle speed).

Inside the transmission case 18 are a wet multi-plate type turning brake 165 provided on a turning motor shaft 164, a steering counter shaft 167 connected to the turning motor shaft 164 via an upstream reduction gear 166, and a steering counter shaft. A steering output shaft 169 connected to 167 via a downstream reduction gear 168 is provided. Rotational power of the turning motor shaft 164 is transmitted to the steering counter shaft 167 via the upstream reduction gear 166 . The rotational power transmitted from the steering counter shaft 167 to the steering output shaft 169 is transmitted to the left ring gear 149 as reverse rotational power via the left intermediate gear 170 and the reverse gear 171 on the steering output shaft 169. , is transmitted to the right ring gear 149 as forward rotational power via the right intermediate gear 172 on the steering output shaft 169 .

When the auxiliary transmission gear mechanism 136 is set to 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 stage 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 set to the neutral state and the swing brake 165 is set to the on state, 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 set to a disengaged state, the rotational power of the swing motor 162 is applied to the steering counter shaft 167, the steering output shaft 169, the left intermediate gear 170 and the reverse gear. 171 and the like to the left ring gear 149, and the steering counter shaft 167, the steering output shaft 169, the right intermediate gear 172 and the like to the right ring gear 149.

When the swing motor 162 rotates forward (reverse), the left and right ring gears 149 rotate at the same rotational speed in opposite directions. That is, the speed change output of each motor shaft 134, 164 is transmitted to the left and right driving sprockets 22 via the sub-transmission gear mechanism 136 or the left and right planetary gear mechanisms 146, respectively, and the vehicle speed (running speed) of the running body 1 is and direction of travel are determined.

Next, the hydraulic circuit 200 of the hydraulic continuously variable transmissions 130, 160 in the second embodiment will be described with reference to FIG. A linear hydraulic continuously variable transmission 130 and a turning hydraulic continuously variable transmission 160 of the second embodiment basically have the same configuration as the hydraulic continuously variable transmission 30 (see FIG. 4) described in the first embodiment.

A hydraulic circuit 200 of the second embodiment includes a straight hydraulic continuously variable transmission 130 and a turning hydraulic continuously variable transmission 160 . That is, the hydraulic circuit 200 includes a rectilinear pump 131 , a rectilinear motor 132 , a swing pump 161 , a swing motor 162 and a charge pump 20 . The straight pump 131 and the straight motor 132 are connected in a closed loop by a first straight oil passage 201a and a second straight oil passage 201b. The straight first oil passage 201a and the straight second oil passage 201b constitute a straight closed circuit 201. As shown in FIG. 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 turning oil passage 202 a and the second turning oil passage 202 b constitute a closed turning circuit 202 .

The linear pump 131 and the turning pump 161 are driven by the rotational power of the engine 17, and the swash plate angles of the linear pump 131 and the turning pump 161 are controlled. The amount of discharge is changed, and the linear motor 132 and the turning motor 162 are operated to rotate forward and reverse, and to steplessly increase and decrease speed.

The hydraulic circuit 200 of the second embodiment includes a straight valve 203 that switches in response to manual operation of the main shift lever 12, and a straight cylinder 204 that is connected to the charge pump 20 via the straight valve 203. . When the straight advance valve 203 is switched, the straight advance cylinder 204 operates to change the swash plate angle of the straight advance pump 131, thereby steplessly changing or reversing the rotation speed of the straight advance motor shaft 134 of the straight advance motor 132. Action is performed. The hydraulic circuit 200 also includes a hydraulic servomechanism 205 for straight forward gear shifting. The hydraulic servomechanism 205 executes a feedback operation in which the rectilinear valve 203 returns to neutral by controlling the swash plate angle of the rectilinear pump 131, and the swash plate angle of the rectilinear pump 131 is changed in proportion to the amount of operation of the main gear shift lever 12 to move straight. The rotation speed of the linear motor shaft 134 of the motor 132 is changed.

A hydraulic circuit 200 according to the second embodiment includes a turning valve 206 that switches according to the operation of the steering handle 110 and a turning cylinder 207 that is connected to the charge pump 20 via the turning valve 206 . When the turning valve 206 is switched, the turning cylinder 207 is actuated to change the swash plate angle of the turning pump 161, and the rotation speed of the turning motor shaft 164 of the turning motor 162 is steplessly changed or reversed. Action is performed. The hydraulic circuit 200 also includes a hydraulic servomechanism 208 for rotation speed change. The hydraulic servomechanism 208 executes a feedback operation in which the swivel valve 206 returns to neutral by controlling the swash plate angle of the swivel pump 161, changes the swash plate angle of the swivel pump 161 in proportion to the amount of operation of the steering handle 110, and controls the swivel motor. 162 rotation motor shaft 164 rotation speed is changed.

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

A strainer 211 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 to the downstream side of the charge oil passage 212 . As described above, the charge branch oil passage 213 is connected to all the oil passages 201a, 201b, 202a, 202b of both closed circuits 201,202. Therefore, both closed circuits 201 and 202 are constantly replenished with hydraulic oil from the charge pump 20 while the engine 17 is running.

The charge branch oil passage 213 is connected to the straight valve 203 and thus to the straight cylinder 204 via a straight servo passage 214, and is connected to the swing valve 206 and thus to the swing cylinder 207 via a swing servo passage 215. there is Servo pressure is supplied from a charge oil passage 212 and a charge branch oil passage 213 to the hydraulic servo mechanism 205 for straight gear shift via a straight servo oil passage 214, and a charge oil is supplied to the hydraulic servo mechanism 208 for turning gear shift. Servo pressure is supplied from path 212 and charge branch path 213 via turning servo path 215 .

The charge branch oil passage 213 is connected via a surplus relief valve 216 to a transmission case 199 that houses the linear hydraulic continuously variable transmission 130 and the turning hydraulic continuously variable transmission 160 , and thus to the transmission case 18 . Therefore, the excess hydraulic fluid supplied from the charge pump 20 is returned to the mission case 18 via the transmission case 199 via the excess relief valve 216 .

A straight bypass oil passage 220 that bypasses between 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 capable of releasing hydraulic pressure to the straight motor 132 is provided in the straight bypass oil passage 220 . A turning bypass oil passage 222 that bypasses between the turning pump 161 and the turning motor 162 is connected to the first turning oil passage 202a and the second turning oil passage 202b. A swing bypass valve 223 capable of releasing hydraulic pressure to the swing motor 162 is provided in the swing bypass oil passage 222 .

The straight bypass valve 221 and the swivel bypass valve 223 of the second embodiment basically have the same configuration as the bypass valve 61 of the first embodiment. However, the turning bypass valve 223 employs an on/off type electromagnetic switching valve that does not adjust the degree of opening. In the second embodiment, when the main gear lever 12 is in the neutral position, the straight bypass valve 221 is in the open position, and the turning bypass valve 223 is in the open position regardless of the operating state of the steering handle 110. is in a position other than the neutral position, the straight bypass valve 221 is in the closed position. Further, when the steering handle 110 is in the neutral position (steering angle is zero), the turning bypass valve 223 is in the open position, and when the steering handle 110 is in a position other than the neutral position, the turning bypass valve 223 is in the closed position. there is

In the second embodiment, as described above, the straight bypass valve 221 is in the open position when the main gearshift lever 12 is in the neutral position, and the turning bypass valve 223 is also in the open position regardless of the operating state of the steering handle 110. Therefore, even if the operator inadvertently touches the main shift lever 12 and operates it to the neutral position while the combine is turning left or right (during the turning operation of the steering handle 110), the turning motor 162 The hydraulic pressure is released, and the output of the swing motor 162 (rotation of the swing motor shaft 164) can be reliably stopped by both the swash plate neutralization of the swing pump 161 and the opening of the swing bypass valve 223. 160 output can be zeroed. As a result, the possibility of the combine turning into a spin turn due to an inadvertent neutral operation of the main shift lever 12 is reliably eliminated. In addition, when the main shift lever 12 is neutrally operated, the output of the straight hydraulic continuously variable transmission 130 becomes zero, so that the combine can be reliably stopped.

Next, with reference to FIGS. 10 and 11, an example of hydraulic continuously variable transmissions 130, 160 and, in turn, a travel system control structure and its control mode in the second embodiment will be described. The basic structure of the controller 70 in the second embodiment is similar to that of the first embodiment. On the input side of the controller 70 in the second embodiment, a steering angle potentiometer 73 for detecting the operating position of the steering wheel 110, a main transmission potentiometer 74 for detecting the operating position of the main gearshift lever 12, and an operating position of the auxiliary gearshift lever 13 are provided. A sub-transmission potentiometer 75 for detection, a parking brake sensor 76 for detecting depression of the parking brake pedal 27, a straight traveling vehicle speed sensor 122, a turning vehicle speed sensor 124, and the like are electrically connected.

On the output side of the controller 70 are a straight travel valve 203 for the straight travel 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 for braking the parking brake 144, a straight bypass valve 221, and the swivel bypass valve 223 and the like are electrically connected.

The controller 70 of the second embodiment opens the straight and turning bypass valves 221 and 223 in conjunction with the return operation of the main gear shift lever 12 to the neutral position, neutralizes the swash plate of the hydraulic pump 31 and straight and turning bypass. By both opening the valves 221 and 223, the travel stop control for stopping the travel of the combine is executed.

That is, as shown in the flow chart of FIG. 11, following the start of the travel stop control, the controller 70 detects the state of operation of the main shift lever 12 to a position other than the neutral position by the main shift potentiometer 74, If it is determined that the combine is running based on the detection of the vehicle speed other than zero by 124 (S11: YES), the detected value of the main shift potentiometer 74 is read, and the main shift lever 12 is returned to the neutral position. It is determined whether or not an operation has been performed (S12).

When the combine is running, the main shift 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 turning bypass valve 223 (turning bypass oil passage 222 ) depends on the operation state of the steering handle 110 . If the main shift lever 12 is operated to return to the neutral position (S12: YES), the neutral return time Tn of the main shift lever 12 is calculated from the detected value of the main shift potentiometer 74, and the neutral return time Tn is set in advance. It is determined whether or not the time is longer than the time TS (S13). The set time TS may be set to, for example, about 0.5 seconds.

If the neutral return time Tn is equal to or longer than the set time TS (if it exceeds the set time TS, S13: YES), it means that the operator is relatively slowly returning the main shift lever 12 to the neutral position. By means of an electromagnetic solenoid, the straight bypass valve 221 is gradually switched to the open position by, for example, duty control corresponding to the neutral return time Tn, and the straight bypass oil passage 222 is opened, so that the operating oil pressure for the straight motor 132 is changed to the straight bypass oil. Bypass to the road 220 side (detour, S14). That is, the opening speed of the straight bypass valve 221 in step S14 is slower than in step S17, which will be described later.

As a result, the operating oil pressure for the straight motor 132 is reduced according to the opening degree of the straight bypass valve 221, and finally, although the charge pressure acts on the straight motor 132, the straight first oil passage 201a and the second straight oil passage 201a are charged. The differential pressure with the path 201b disappears, and the output of the straight motor 132 (the rotation of the straight motor shaft 134) stops regardless of whether the swash plate of the straight pump 131 is in a neutral state.

In step S12, if the steering handle 110 has been turned to a position other than the neutral position, the electromagnetic solenoid causes the turning bypass valve 223 to be fully opened in parallel with the switching operation of the straight bypass valve 221. The bypass oil passage 222 is opened to bypass the operating oil pressure for the swing motor 162 to the swing bypass oil passage 222 side, and the output of the swing motor 162 (swing motor rotation of shaft 164) is stopped.

At this stage, since the main gearshift lever 12 is returned to the neutral position, the straight and turning bypass valves 221 and 223 are fully opened and the outputs of the straight and turning motors 132 and 162 are stopped. and the swash plates of the rotary pumps 131 and 161 are in the neutral state. Therefore, upon detection of the depression of the parking brake pedal 27 (S15: YES), the controller 70 switches the parking brake electromagnetic valve 218, and operates the parking brake cylinder 217 to brake the parking brake 144, thereby reliably operating the combine. The vehicle is stopped (S16).

Returning to step S13, if the neutral return time Tn is less than the set time TS (if less than the set time TS, S13: NO), it means that the operator is quickly returning the main shift lever 12 to the neutral position. Then, the straight bypass valve 221 is instantaneously switched to fully open by the electromagnetic solenoid, the straight bypass oil passage 220 is opened, and the operating oil pressure for the straight traveling motor 132 is bypassed to the straight bypass oil passage 220 side (bypassed, S17). ). That is, the opening speed of the straight bypass valve 221 in step S17 is faster than in step S14.

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

Also, before and after the straight and turning bypass valves 221 and 223 are fully opened and the outputs of the straight and turning motors 132 and 162 are stopped, the swash plates of the straight and turning pumps 131 and 161 are in the neutral state. Next, the process proceeds to step S15, and upon detection of depression of the parking brake pedal 27 (step S15: YES), the controller 70 switches the parking brake electromagnetic valve 218, and operates the parking brake cylinder 217 to operate the parking brake 144. is braked to reliably stop the combine harvester (S16).

After that, when it is detected that the parking brake pedal 27 is released (S18: YES), the parking brake electromagnetic valve 218 is switched, and the parking brake cylinder 217 is released to release the parking brake 144 (S19). is restored to a drivable state. Note that the set time TS itself may be included on the lower side or on the higher side, as in the first embodiment.

By controlling as described above, the same effects as those of the first embodiment can be obtained. That is, both the neutralization of the swash plate of the straight pump 131 and the opening of the straight bypass valve 221 can reliably stop the output of the hydraulic motor 32 (the rotation of the motor output shaft 34). Even if the linear hydraulic continuously variable transmission 130 malfunctions, such as the swash plate of the linear pump 131 not being in the neutral state, there is no need to forcibly stop the engine 17 or operate the sub-transmission lever 13 to neutral. In addition, according to the speed of the return operation of the main shift lever 12, the opening degree of the straight bypass valve 221 is changed to reduce the operating oil pressure for the straight motor 132, thereby reducing the output of the straight motor 132 (rotation of the straight motor shaft 134). It is possible to shift to a stop, and extremely good operation followability of the main shift lever 12 can be ensured.

Particularly in the second embodiment, as described above, when the main gearshift lever 12 is operated to the neutral position, the turning bypass valve 223 is also switched to the open position regardless of the operating state of the steering handle 110, so that for example, the combine harvester can turn left or right. Even if the operator inadvertently touches the main gear shift lever 12 and moves it to the neutral position during the turning operation of the steering handle 110, the operating oil pressure for the turning motor 162 is released and the swash plate of the turning pump 161 is released. Both the neutralization and the opening of the turning bypass valve 223 can reliably stop the output of the turning motor 162 (rotation of the turning motor shaft 164) and make the output of the turning hydraulic continuously variable transmission 160 zero. As a result, the possibility of the combine turning into a spin turn due to an inadvertent neutral operation of the main shift lever 12 is reliably eliminated. In addition, when the main shift lever 12 is neutrally operated, the output of the straight hydraulic continuously variable transmission 130 becomes zero, so that the combine can be reliably stopped.

As described above, the straight and turning bypass valves 221 and 223 of the second embodiment basically have the same configuration as the bypass valve 61 of the first embodiment, but the bypass valve shown in FIG. 62 may be employed as straight and swivel bypass valves 225, 227 (see FIG. 12). In this case, when the straight and swing bypass valves 225 and 227 are switched to the open position, the operating oil pressure for the straight and swing motors 132 and 162 is drained to the transmission case 18 via the transmission case 199 . However, in this case as well, the turning bypass valve 227 is sufficient if it adopts an on/off type electromagnetic switching valve that does not adjust the degree of opening. It is also possible to use a combination of the charge pressure actuation type shown in FIG. 9 and the drain type shown in FIG. 12 as straight and swivel bypass valves.

Note that the present invention is not limited to the above-described embodiments, and can be embodied in various aspects. For example, the hydraulic transmission is not limited to combine harvesters and can be widely applied to various work vehicles such as tractors, rice transplanters, forklift cars and backhoes, ships, and the like. In addition, the configuration of each part is not limited to the illustrated embodiment, and various modifications can be made without departing from the scope of the present invention.

2 Traveling crawler (traveling part)
12 Main shift lever (shift operation tool)
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 Paths 61, 62 Bypass Valve 70 Controller (Control Means)
130 Linear hydraulic continuously variable transmission 131 Linear pump 132 Linear motor 144 Parking brake 160 Turning hydraulic continuously variable transmission 161 Turning pump 162 Turning motor 199 Transmission case 200 Hydraulic circuit 201a First straight oil passage 201b Second straight oil passage 202a Turning No. 1 oil passage 202b turning second oil passage 220 straight bypass oil passages 221, 225 straight bypass valve 222 turning bypass oil passages 223, 227 turning bypass valve

Claims (5)

A work vehicle comprising: a hydraulic continuously variable transmission that shifts the power of an engine using a hydraulic pump and a hydraulic motor;
A closed circuit of the hydraulic continuously variable transmission is provided with a bypass oil passage for bypassing between the hydraulic pump and the hydraulic motor. is arranged, and has a control means for controlling the bypass valve,
When the control means returns the gear shift operation tool to a neutral position to open the bypass valve, if the time for returning the gear shift operation tool to neutral exceeds a preset set time, the control means is less than the set time. slowing the opening speed of the bypass valve to less than
work vehicle. A work vehicle comprising: a hydraulic continuously variable transmission that shifts the power of an engine using a hydraulic pump and a hydraulic motor;
A closed circuit of the hydraulic continuously variable transmission is provided with a bypass oil passage for bypassing between the hydraulic pump and the hydraulic motor. is arranged, and has a control means for controlling the bypass valve,
When the control means returns the gear shift operation tool to a neutral position to open the bypass valve, if the time for returning the gear shift operation tool to neutral is less than a preset set time, the control means may exceed the set time. opening the bypass valve faster than
work vehicle. The control means gradually increases the degree of opening of the bypass valve when the time to return to neutral of the speed change operation tool exceeds the set time.
A work vehicle according to claim 1 or 2. The control means instantly fully opens the bypass valve when the time to return to neutral of the speed change operation tool falls below the set time.
A work vehicle according to claim 1 or 2. The control means brakes the traveling portion to which the speed change power of the hydraulic continuously variable transmission is transmitted in accordance with the full opening of the bypass valve.
A work vehicle according to any one of claims 1 to 4.

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