JP2013177927A - Work vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent an engine stop from being caused by a sudden starting or a lack of driving torque when a sub-transmission tool is shifted to a high-speed region, in a configuration provided with the sub-transmission tool for changing a speed changing region to a plurality of stages by a main transmission tool for performing continuously variable transmission operation for HST and a gear shift transmission.SOLUTION: In a motive force transmission system from an engine 5 to wheels 2 and 3, a work vehicle is provided with: a main transmission tool 18 for changing a traveling speed via a hydraulic continuously variable transmission 21, for changing a speed by rotating both the swash plate of a variable capacity pump 21a and the swash plate of a variable capacity motor 21b, and a mechanical transmission part 22 having a plurality of speed changing stages; and a sub-transmission tool 15 for changing the speed of the mechanical transmission part 22. When the sub-transmission tool 15 is set to a high-speed region, control is performed to start to change a speed of the variable motor 21b from the lowest speed at the time of starting.

Description

  The present invention relates to a work vehicle, and in particular, a hydraulic continuously variable transmission (hereinafter referred to as “HST”) is provided in a traveling drive power transmission system, and the HST is subjected to shift control by an automatic control unit to respond to a shift position of a main transmission. The present invention relates to a shift control device that obtains a traveling vehicle speed.

As shown in Patent Document 1, a normal HST transmission mechanism has a variable displacement pump and a fixed displacement motor, and rotates the swash plate of the variable displacement pump to change the rotation speed of the HST output shaft.
Moreover, as shown in Patent Document 2, the control pressure is an HST configured by a variable hydraulic pump and a variable displacement hydraulic motor, and performs capacity control according to the pressure in the hydraulic circuit on the discharge side of the variable hydraulic pump. There is a hydraulic continuously variable transmission that has different characteristics in forward and reverse by connecting a pressure control valve to the part and performing displacement control of the variable hydraulic pump and variable displacement hydraulic motor.

JP 2002-250437 A JP 2007-85404 A

  According to the present invention, a main transmission that operates the HST without change and a sub-transmission that changes the shift range to a plurality of stages by gear shifting are provided, and sudden start or drive when the sub-shift is shifted to a high speed range. It is an object to prevent engine stop due to unexpected torque.

The problems of the present invention are solved by the following technical means.
According to the first aspect of the present invention, a hydraulic continuously variable transmission that shifts and shifts the swash plate of the variable displacement pump 21a and the swash plate of the variable displacement motor 21b in the power transmission system from the engine 5 to the wheels 2 and 3 together. In a work vehicle provided with a main transmission 18 that changes the traveling speed and a sub-transmission 15 that changes speed of the mechanical transmission 22, the sub-transmission 15 is provided. When the high speed range is set, the work vehicle is characterized in that the variable motor 21b is controlled to start shifting from the lowest speed when starting.

  With this configuration, when the sub-transmission 15 is set to the high speed range and the main transmission 18 is set to the lowest speed, the variable displacement motor 21b is shifted from the lowest speed to prevent a sudden high-speed start, The engine stop due to an excessive engine load can be prevented by the high drive torque at the lowest speed of the variable displacement motor 21b when starting with the work machine mounted or when starting uphill.

  According to the second aspect of the present invention, a hydraulic continuously variable transmission that shifts the swash plate of the variable displacement pump 21a and the swash plate of the variable displacement motor 21b in the power transmission system from the engine 5 to the wheels 2 and 3 to change gears. 21. In a work vehicle having a main transmission 18 for changing and setting the traveling speed and a sub-transmission 15 for shifting the mechanical transmission unit 22 through a mechanical transmission unit 22 having a plurality of shift ranges and a variable transmission motor, A work vehicle is characterized in that 21b is always controlled to start shifting from the lowest speed side.

  With this configuration, the variable displacement motor 21b starts from a state where the drive torque is high at the lowest speed regardless of whether the auxiliary transmission 15 is high or low. Even on an uphill start, engine stop due to excessive engine load can be prevented.

  According to the third aspect of the present invention, the rear axle rotation sensor 26 for detecting the rotational speed of the rear wheel drive shaft 27 is provided, and the rotational speed of the engine 5 and the variable capacity are fed back by feeding back the detected rotational speed of the rear axle rotation sensor 26. The work vehicle according to claim 1 or 2, wherein the shift positions of the pump 21a and the variable displacement motor 21b are controlled.

With this configuration, the traveling speed calculated from the rotational speed of the rear wheel drive shaft 27 and the wheel diameter of the rear wheel can be maintained and controlled at an accurate traveling speed according to the shift positions of the main transmission 18 and the auxiliary transmission 15.
According to a fourth aspect of the present invention, there is provided the work vehicle according to any one of the first to third aspects, further comprising an engine rotation setting unit that sets the rotation speed of the engine 5 independently.

  With this configuration, at the time of high load work or climbing work, the engine rotation setting means 14 sets the rotation of the engine 5 to a high rotation state and effectively uses the output of the engine 5 in an optimum state depending on the work state. I can do it.

  According to the first aspect of the present invention, when the sub-transmission 15 is set to a high speed range and the main transmission 18 is set to the lowest speed, the variable displacement motor 21b is changed from the lowest speed, so that the rapid high-speed start. In addition, it is possible to prevent the engine from being stopped due to an excessive engine load by the high drive torque at the lowest speed of the variable capacity motor 21b when starting with the work machine mounted or when starting uphill.

  In the invention according to claim 2, since the variable displacement motor 21b starts from a state where the driving torque is high at the lowest speed regardless of whether the auxiliary transmission 15 is high or low, a heavy working machine is mounted. Even if the vehicle starts or starts up a steep hill, it can prevent the engine from being stopped due to excessive engine load.

  According to the third aspect of the present invention, the traveling speed calculated from the rotational speed of the rear wheel drive shaft 27 and the wheel diameter of the rear wheel is maintained at an accurate traveling speed according to the shift positions of the main transmission 18 and the auxiliary transmission 15. I can control it.

  In the invention according to claim 4, the output of the engine 5 is in an optimum state depending on the work state such as traveling while setting the rotation of the engine 5 to the high rotation state by the engine rotation setting means 14 at the time of high load work or climbing work. Can be used effectively.

It is the whole tractor side view. It is the whole tractor top view except a cabin. It is a power transmission block diagram. It is a control block diagram of automatic control. It is a graph showing the relationship between a drive current and HST output-shaft rotation speed. It is a top view of a maximum speed dial. It is a graph showing the relationship between the operation position of a speed change operation tool, and a drive current value.

A tractor 1 will be described below as an example of the work vehicle.
In the present specification, the left and right directions in the forward direction of the work vehicle are referred to as left and right, respectively, the forward direction is referred to as front, and the reverse direction is referred to as rear.

  As shown in FIGS. 1 and 2, the tractor 1 includes a pair of left and right front wheels 2 and 2 and a pair of left and right rear wheels 3 and 3 at the front and rear portions of the fuselage, and the rotational power of the engine 5 mounted on the front of the fuselage. The HST 21 in the transmission case 8 and the auxiliary transmission 22 are appropriately decelerated and transmitted to the front wheels 2 and 2 and the rear wheels 3 and 3.

  A steering handle 7 is provided at the handle post 6 in the cabin 4 at the center of the machine body, and a seat 9 is provided behind the steering handle 7. Below the steering handle 7 is provided a forward / reverse lever 10 for switching the advancing direction of the airframe to the front / rear direction. When the forward / reverse lever 10 is rotated forward, the airframe moves forward, and when it is rotated rearward, it moves backward.

  An accelerator lever 11 for adjusting the engine speed is provided on the opposite side of the forward / reverse lever 10 with the handle post 6 in between, and an accelerator pedal 18 (for adjusting the traveling speed) is provided at the right front corner of the step floor 13. In the present invention, the "main transmission" is provided, and left and right brake pedals 19R and 19L for operating the left and right rear wheels 3 and 3 are provided.

  Further, an emergency stop pedal 70 is provided on the right side on the seat 9 side on the step floor 13, and a differential lock lever 71 and a parking lever 72 are also provided on the left side on the seat 9 side. When the emergency stop pedal 70 is used, the engine 5 is stopped and the vehicle stops suddenly. Therefore, the emergency stop pedal 70 can be stopped more quickly than when the brake pedals 19R and 19L are used. However, if the HST 21 is returned to neutral, the stop distance can be shortened. A switch for switching the stopping method may be provided near the emergency stop pedal 70. If the parking lever 72 is pulled to apply the brake, the parking is stopped and the auto-cruise function is canceled.

The emergency stop pedal 70 may be provided in combination with the brake pedals 19R and 19L.
The accelerator pedal 18 changes and controls the rotation of the engine 5 together with the shift of the HST 21. However, the accelerator pedal 18 is divided into the shift pedal of the HST 21 and the shift pedal of the engine 5 and arranged side by side, and the shift of the HST 21 and the shift of the engine 5 are selectively used. Alternatively, the shift of the HST 21 and the shift of the engine 5 may be linked.

In addition, you may provide the clutch pedal which cut | disconnects the clutch in the transmission case 8 along with brake pedal 19R, 19L.
A meter panel 16 is provided on the front side of the steering handle 7 at the upper part of the handle post 6 to display the vehicle status such as traveling speed, and an engine rotation setting dial (referred to as “engine rotation setting means” in the present invention) 14 at the lower right part thereof. Is provided, and the maximum number of revolutions of the engine 5 can be set. On the meter panel 16, the operation amount of the response setting dial 55 and the operation amount of the maximum speed setting dial 54 may be displayed.

  Further, the left front side portion of the seat 9 is provided with a sub-transmission lever 15 (referred to as “sub-transmission” in the present invention) that can select any of a low speed, a medium speed, a high speed, and a neutral position. A lever 12 is provided.

  A maximum speed setting dial 54, a response setting dial 55, and an auto cruise set switch 56 are provided on the right side of the seat 9. The drive current value set by the maximum speed setting dial 54 is determined based on the control data stored in the adjustment mode to be described later, and as shown in FIG. Set evenly. In order to cancel the auto-cruise traveling by turning on the auto-cruise set switch 56, the brake pedals 19R and 19L are depressed, the accelerator pedal 18 is depressed again, and the auto-cruise set switch 56 is turned on again. An auto cruise cancel sensitivity adjustment switch for adjusting the auto cruise cancel sensitivity may be provided near the auto cruise set switch 56.

Further, an auto cruise switching switch for turning on / off the auto cruise may be provided so that the auto cruise is not canceled even in the auto cruise cancel operation.
Further, a sensor for detecting that the driver is seated on the seat 9 may be provided, and the engine 5 may be stopped when it is detected that the driver has left the seat 9 during auto-cruising so that safety can be achieved. .

A rotary working machine 17 is attached to the rear of the tractor 1.
FIG. 3 is a power transmission block diagram, in which the rotation of the output shaft of the engine 5 is transmitted to the rear wheel drive shaft 27 of the differential case 23 via the damper 20 in the transmission case 8, the HST 21, and the auxiliary transmission unit 22. , 3 are driven. The HST 21 is composed of a variable displacement pump 21a and a variable displacement motor 21b, and shifts by rotating the swash plate of the variable displacement pump 21a and the swash plate of the variable displacement motor 21b by a travel system ECU 50 described later. Further, the sub-transmission unit 22 shifts in three stages of high, medium, and low by gear shift.

Although not shown, the driving force is branched in the transmission case 8 so that the front wheels 2 and 2 are also driven.
The rotation of the output shaft of the HST 21 is detected by the HST output shaft sensor 25 as the rotation of the rotation sensor gear 24, and the output shaft rotation of the auxiliary transmission unit 22 is detected by the rear axle rotation sensor 26 as the rotation speed of the rear wheel drive shaft 27. Since the HST output shaft sensor 25 and the rear axle rotation sensor 26 calculate the time required to detect the predetermined number of teeth of the sensor gear, the number of rotations at a high speed can be obtained by setting the number of teeth to 1 at low speed and 3 teeth at high speed. It can detect accurately and stop quickly.

  FIG. 4 is a control block diagram of automatic control for controlling the operation of each part of the tractor. The engine ECU 29 for controlling the output of the engine E, the work machine lifting / lowering system ECU 40 for controlling the lifting / lowering of the work machine 17, the front wheels 2, and the rear wheels 3. It is composed of a traveling system ECU 50 that controls the traveling speed by controlling the rotation, and exchanges control signals by CAN communication.

  Input of control data to the engine ECU 29 includes boost pressure from the boost pressure sensor 30, correction signal from the boost pressure correction control switch 36, exhaust temperature from the engine exhaust temperature sensor 31, and engine from the engine rotation sensor 32. The rotation speed of the output shaft, the oil pressure from the engine oil pressure sensor 33, the radiator water temperature from the engine water temperature sensor 34, the fuel pressure on the common rail from the rail pressure sensor 35, and the depression angle of the accelerator pedal 18 of the accelerator sensor 28 The control output from the engine ECU 29 is the rail pressure to the fuel high pressure pump 37 and the injection signal to the high pressure injector 38.

The boost pressure correction control switch 36 turns on / off the control for gradually increasing the fuel injection amount when the accelerator lever 11 rotates when the boost pressure is low.
Input of control data to the work implement lifting system ECU 40 includes an operation position signal of the position control lever 41 for raising and lowering the work implement 17, a lift position signal from the lift arm sensor 42, a raising position regulating dial 43 and a lowering speed adjustment. The control output from the work implement elevating system ECU 40, such as an adjustment signal of the dial 44, is an ascending or descending signal to the main ascending sol 45 and the main descending sol 46 of the hydraulic cylinder.

Further, the work implement lifting system ECU 40 communicates with the work implement controller 47 and the communication unit 48 with GPS.
Input of control data to the travel system ECU 50 includes the output shaft rotational speed of the HST 21 of the HST output shaft sensor 25, the rotational speed of the rear wheel drive shaft 27 of the rear axle rotational sensor 26, and the maximum speed set by the maximum speed setting dial 54. , The response of the response setting dial 55, the set signal of the auto cruise set switch 56, the operating position of the forward / reverse lever operating position sensor 64 of the forward / reverse lever 10, and the auxiliary transmission lever operating position sensor 57 of the auxiliary transmission lever 15. The accelerator pedal sensor 58, the engine rotation setting signal of the accelerator sensor 59 provided on the accelerator lever 11, the oil temperature in the transmission case 8 of the oil temperature sensor 60, The brake pedal depression signal of the brake pedal operation detection sensor 61 The control output from the travel system ECU 50 based on the travel acceleration of the acceleration detection sensor 52, the engine speed of the engine rotation sensor 66 of the engine 5 and the like, the swash plate angle output signal to the pump swash plate solenoid 62, and the motor swash plate solenoid 63. Is a swash plate angle output signal or the like.

The traveling speed, the shift position, the engine water temperature, and other data are displayed on the meter panel 16 and the operation panel 65 provided in front of the steering handle 7.
FIG. 5 shows the relationship between the drive current value applied to the pump swash plate solenoid 62 and the motor swash plate solenoid 63 for controlling the hydraulic cylinder that rotates the trunnion shaft of the HST 21 and the HST output shaft rotational speed detected by the HST output shaft sensor 25. The measured drive current value and the measured data of the HST output shaft rotation speed are assumed to fluctuate in the design change line A indicated by the solid line in the design, but the actual measured data is the maximum of the shift width B and the maximum depending on the characteristics of each HST 21 and the aircraft. There is a variation in the rotational speed width C. The drive current value and the measurement data of the HST output shaft rotational speed which are different for each aircraft are stored in the traveling system ECU 50 as control data.

The adjustment mode is performed in a state where the assembly of the tractor 1 is finished and the sub-shift lever 15 is neutral and the driving after the HST 21 is turned off and no traveling load is applied at the final adjustment.
First, in the measurement on the forward side, as the data at the time of acceleration, the drive current is changed from near zero where the HST 21 does not rotate to the maximum drive current value D sufficient to obtain the maximum rotational speed J, and the output shaft rotation of the HST 21 The number of rotations is measured, and the driving start current value F at the start of rotation and the maximum acceleration speed H near the maximum driving current value E of 90% of the maximum driving current D are stored in the traveling system ECU 50 as control data.

  Further, as data at the time of deceleration, the drive current is changed from the maximum drive current value D to near zero, and the maximum deceleration near rotation speed I and the drive stop current value G are stored in the traveling system ECU 50 as control data. The drive stop current value G can be accurately detected by actually running the tractor 1 and measuring it.

Similarly to the above, on the reverse side, the deceleration side control data is stored in the traveling ECU 50.
In addition, since there is a slight time lag when the drive current is applied and the rotation of the HST 21 is output, the rotation speed after a predetermined time has elapsed from the application of the drive current is used as control data.

  The rotation speed of the HST 21 depending on the depression depth of the accelerator pedal 18 uses the speed increase side drive start current value F, the speed increase maximum vicinity speed H, the speed reduction maximum vicinity speed I, and the drive stop current value G. The drive current value calculated from the calculated control change rate is applied to the pump swash plate solenoid 62 and the motor swash plate solenoid 63.

  As shown in FIG. 7, an HST neutral region in which output is prohibited is provided in the depression start range of the accelerator pedal 18, and the travel system ECU 50 outputs the drive start current value F at the acceleration start position at the end of the HST neutral region. To control. When the accelerator pedal 18 is depressed from the acceleration start position, the drive current value is rapidly increased so that the drive current linearly changes (proportional change) from zero rotation of the HST 21 to the maximum acceleration vicinity H. Further, a maximum maintenance margin angle is provided at the maximum depression position of the accelerator pedal 18 so that the maximum rotation speed J is output at the maximum drive current value.

  The maximum speed J is determined by the engine speed regulation. However, when the oil temperature sensor 60 detects a predetermined temperature or higher, the maximum drive current value D is set to the maximum speed setting dial 54 and the current value range and near the maximum. By further reducing the regulated drive current value to the lower drive current value E, further increase in the oil temperature is suppressed. The return of the drive current is lower than a predetermined temperature to prevent the occurrence of hunting.

The regulated drive current value is determined by the drive current value calculated from the control change rate.
When the depression of the accelerator pedal 18 is stopped and the driving of the HST 21 is stopped, the driving current for driving forward or backward driving is stopped and a driving current slightly larger than the driving start current value F in the reverse direction after a predetermined time has elapsed. Is applied for a short time (several tens of milliseconds), and the trunnion shaft is returned to the neutral position after returning to the normal position.

  When the accelerator pedal 18 is depressed to a predetermined high speed position or a predetermined high speed position or higher, a change rate of the depression speed is calculated, and according to the change rate, up to a constant change rate that does not overload the engine load, up to the pedal position corresponding speed. Change the speed increase rate. In addition, when the accelerator pedal 18 is stepped on beyond a predetermined high speed position, the speed acceleration rate is decreased when the predetermined speed acceleration rate elapses for a predetermined time, and the speed acceleration rate is canceled when the target speed is reached.

  From the traveling system ECU 50, the set traveling speed is obtained at the depression position of the accelerator pedal 18 using the control data of the maximum vicinity driving current value E, the driving start current value F, and the driving stop current value G detected above. A drive current is output to the pump swash plate solenoid 62 and the motor swash plate solenoid 63 to control the rotation of the trunnion shaft of the HST 21.

  When the accelerator pedal 18 is depressed most, a predetermined large drive current value is output to the pump swash plate solenoid 62 and the motor swash plate solenoid 63 instead of the drive current value based on the control data. Make sure they are not different.

  Further, even if the drive current value (rate) is increased, if the travel speed increase amount (rate) is lower than a predetermined value, the travel load is large, so that the increase in the drive current value is interrupted to prevent an engine stall. Further, when the engine speed reduction is larger than a predetermined rate, the drive current is reduced to prevent engine stall, and when the engine speed is close to the idling speed, the drive current is turned off and the HST 21 is made neutral. After that, when the engine speed returns to the set speed, the engine speed is slowly returned to a predetermined drive current at a predetermined change rate.

  In addition to the control using the measurement data of the drive current value and the HST output shaft rotation speed, the acceleration / deceleration acceleration is set by the response setting dial 55 so that the acceleration of the machine body detected by the acceleration detection sensor 52 becomes the set acceleration. It is also possible to control it. The control using the acceleration is not performed because it takes too much time to detect the acceleration in the low speed state, and the control is performed with the immediately preceding acceleration / deceleration rate.

In addition, since control using this acceleration is difficult to detect a change in acceleration at a low speed, acceleration / deceleration is controlled by a drive current change rate of a separately set change rate line.
The response setting dial 55 controls acceleration / deceleration at a predetermined drive current change rate according to the dial position without performing acceleration control. At the start of deceleration, the speed change after a certain time has elapsed since the current change. Is corrected by the acceleration detected by the acceleration detection sensor 52. The correction at the time of switching in the reverse direction immediately after the forward / reverse switching (forward → reverse or reverse → forward) is performed on the predetermined drive current change rate with the same amount of increase / decrease correction as the correction increase / decrease amount on the deceleration side.

  Further, the rotational speed of the engine 5 is regulated so that the rotational speed detected by the engine rotational sensor 66 does not exceed a predetermined rotational speed, but is slightly higher than that using the restricted rotational speed of the maximum speed setting dial 54. Set to the number of revolutions. Note that the maximum speed setting dial 54 may limit the travel shift range by limiting the rotation range of the trunnion shaft of the variable displacement pump 21a.

The traveling speed is set by the accelerator pedal 18 and the auxiliary transmission lever 15, and the shift control is performed as follows.
First, when the rotary work is performed at a low speed, the auxiliary transmission lever 15 is set to “low” and the vehicle starts running while gradually depressing the accelerator pedal 18. Then, the shift position of the auxiliary transmission lever 15 is read by the auxiliary transmission lever operating position sensor 57, the depression depth of the accelerator pedal 18 is read by the accelerator pedal sensor 58, and is input to the travel system ECU 50. A swash plate angle output signal is output to the plate solenoid 63, and the variable displacement pump 21a and the variable displacement motor 21b are shifted from the lowest speed to the traveling speed set by the accelerator pedal 18 and the auxiliary transmission lever 15.

  When the sub-shift lever 15 is set to “low” or “medium” to start traveling, the variable displacement motor 21b may shift from a medium speed other than the lowest speed while shifting the variable displacement pump 21a from the lowest speed. However, when the sub-shift lever 15 is set to “high” to start traveling, the variable displacement motor 21b is shifted from the lowest speed to prevent sudden start and start with a high driving torque.

  Further, the engine load factor is input from the engine ECU 29 to the traveling system ECU 50, and when the engine load factor is lower than the predetermined load factor, the auxiliary transmission lever 15 can be switched to the high gear shift range, so that the engine rotation at the time of speed increase is achieved. Decline can be prevented.

  Further, when the auxiliary transmission lever 15 is switched to the low speed change range, the engine 5 may be rotated at a low speed to prevent the engine from increasing due to a light load change and to achieve a smooth speed change.

  The traveling speed set by the accelerator pedal sensor 58 and the auxiliary transmission lever 15 is fed back to the pump swash plate solenoid 62 and the motor swash plate solenoid 63 by feeding back the rotational speed of the rear wheel drive shaft 27 detected by the rear axle rotation sensor 26. Adjust the swash plate angle output signal.

The engine rotation setting dial 14 is used to set the rotation speed of the engine 5 to an arbitrary rotation speed lower than the maximum rotation speed, and is used when working at a low speed.
The engine speed to be used is set at the engine speed indicated by the accelerator lever 11, but if an engine speed higher than the used engine speed is indicated by the accelerator pedal 18, the higher engine speed is given priority.

  When the sub-shift lever 15 is shifted from “medium” to “high” or from “low” to “medium”, the engine speed is low when the rotation speed detected by the rear axle rotation sensor 26 is low, and the engine rotation is not performed. Is not changed, but the rotational speed detected by the rear axle rotation sensor 26 is high and the rotational speed of the engine 5 is adjusted in the running state so as to eliminate a shift shock such as sudden acceleration. At that time, after the engine speed is reduced at once, the vehicle speed difference before and after the change is returned to the indicated rotational speed within a specified range within a specified acceleration.

When the engine load factor at the time of returning to the commanded rotational speed is equal to or greater than a predetermined value, priority is given to setting a restriction on the subsequent engine rotational speed lowering instruction rather than the regulation within the vehicle speed difference regulation range.
When the sub-shift lever 15 is shifted from “high” to “middle” or “middle” to “low”, the engine speed is increased at a stroke and then returned to the indicated rotational speed. At this time, if the pre-change engine speed instruction is in the vicinity of the large base speed, the shift change speed is adjusted with a variable iris or the like so as to be slower than normal. Further, when the engine load factor before the change is near the maximum output, the engine speed is increased or decreased so as to be within the vehicle speed acceleration regulation.

  Further, the vehicle speed acceleration after shifting is monitored, and the engine speed is increased or decreased so that the acceleration is within the range. At that time, when it can be estimated that the engine load factor increases when the engine load factor is large, acceleration priority is stopped and load stabilization is prioritized.

2 Front wheel 3 Rear wheel 5 Engine 14 Engine rotation setting means (engine rotation setting dial)
15 Sub transmission (sub transmission lever)
18 Main transmission (accelerator pedal)
21 HST
21a Variable displacement pump 21b Variable displacement motor

Claims (4)

  Hydraulic stepless transmission that changes speed by rotating both the swash plate of the variable displacement pump (21a) and the swash plate of the variable displacement motor (21b) in the power transmission system from the engine (5) to the wheels (2) and (3). A main transmission (18) for changing the traveling speed and a sub-transmission (15) for changing the speed of the mechanical transmission unit (22) are interposed by a device (21) and a mechanical transmission unit (22) having a plurality of shift stages. In the provided work vehicle, when the auxiliary transmission (15) is set in a high speed range, the variable motor (21b) is controlled to start shifting from the lowest speed when starting.   Hydraulic stepless transmission that changes speed by rotating both the swash plate of the variable displacement pump (21a) and the swash plate of the variable displacement motor (21b) in the power transmission system from the engine (5) to the wheels (2) and (3). A main transmission (18) for changing the traveling speed and a sub-transmission (15) for changing the speed of the mechanical transmission unit (22) are interposed by a device (21) and a mechanical transmission unit (22) having a plurality of shift stages. A work vehicle in which the variable motor (21b) is controlled to always start shifting from the lowest speed side in the provided work vehicle.   A rear axle rotation sensor (26) for detecting the rotational speed of the rear wheel drive shaft (27) is provided, and the rotational speed of the engine (5) and the variable displacement pump are fed back by feeding back the detected rotational speed of the rear axle rotation sensor (26). The work vehicle according to claim 1 or 2, wherein a shift position of the variable motor (21a) and the variable displacement motor (21b) is controlled.   The work vehicle according to any one of claims 1 to 3, further comprising engine rotation setting means (14) for independently setting a rotation speed of the engine (5).

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