阅读说明：本技术 作业车辆的控制装置、作业车辆、及作业车辆的控制方法 (Control device for work vehicle, and control method for work vehicle ) 是由 山田贤一 池田裕明 于 2020-06-08 设计创作，主要内容包括：作业车辆具备动力源、行驶装置、将动力源的动力向行驶装置传递的动力传递装置。动力传递装置具备具有能够设定安全压的安全阀的静液压式无级变速器。作业车辆的控制装置具备根据行驶装置的目标输出值设定安全阀的安全压的安全压设定部。(The work vehicle includes a power source, a travel device, and a power transmission device that transmits power of the power source to the travel device. The power transmission device is provided with a hydrostatic continuously variable transmission having a relief valve capable of setting a relief pressure. The control device for a work vehicle is provided with a safety pressure setting unit that sets a safety pressure of a safety valve in accordance with a target output value of a traveling device.)

1. A control device for a work vehicle, comprising:

a power source;

a running device;

a power transmission device that is provided with a hydrostatic continuously variable transmission having a safety valve capable of setting a safety pressure, and that transmits power of the power source to the traveling device;

and a relief pressure setting unit that sets the relief pressure of the relief valve based on a target output value of the travel device.

2. The control device for a work vehicle according to claim 1,

a target circuit pressure specifying unit that specifies a target circuit pressure that is a pressure of a hydraulic circuit of the hydrostatic continuously variable transmission for achieving a target output value of the traveling device,

the safe pressure setting portion sets the safe pressure based on the specified target circuit pressure.

3. The control device for the working vehicle according to claim 1 or 2, comprising:

a working state specifying unit that specifies a working state of the working vehicle;

a remaining amount determination unit that determines a remaining amount pressure of a hydraulic circuit of the hydrostatic continuously variable transmission based on the specified operation state,

the relief pressure setting portion sets the relief pressure based on the determined surplus pressure.

4. The control device for a work vehicle according to claim 3, wherein,

the remaining amount determining unit sets the remaining amount pressure when the operating state is an excavation state to be smaller than the remaining amount pressure when the operating state is a travel state.

5. The control device for a work vehicle according to claim 3 or 4, wherein,

the remaining amount determining unit sets the remaining amount pressure when the operating state is a braking state to be smaller than the remaining amount pressure when the operating state is another state.

6. The control device for a work vehicle according to claim 5,

the residual pressure when the operating state is the braking state is a negative value.

7. The control device for the working vehicle according to any one of claims 3 to 6,

the remaining amount determination unit sets the remaining amount pressure to be smaller as the travel speed is lower when the operation state of the travel device is a travel state.

8. A work vehicle is provided with:

a power source;

a running device;

a power transmission device that transmits power of the power source to the travel device;

a control device that controls the power transmission device;

the power transmission device is provided with a hydrostatic continuously variable transmission having a relief valve capable of setting a relief pressure,

the control device includes a control unit that sets the relief pressure of the relief valve based on a target output value of the travel device.

9. A method for controlling a work vehicle, the work vehicle comprising:

a power source;

a running device;

a power transmission device that is provided with a hydrostatic continuously variable transmission having a safety valve capable of setting a safety pressure, and that transmits power of the power source to the traveling device;

the method for controlling the working vehicle includes a step of setting the relief pressure of the relief valve based on a target output value of the travel device.

Technical Field

The present invention relates to a control device for a work vehicle, and a control method for a work vehicle.

The present application claims priority based on Japanese application No. 2019-108554, 6/11/2019, the contents of which are incorporated herein by reference.

Background

A work vehicle such as a wheel loader equipped with a continuously variable transmission is known. Examples of the continuously variable Transmission include HST (hydrostatic Transmission) and HMT (hydro-Mechanical Transmission). Patent document 1 discloses a technique for controlling the pump capacity of an HST in order to reduce a rapid acceleration feeling generated when a clutch of an HST of a one-pump two-motor type is operated.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open No. 2012-231331

Disclosure of Invention

Problems to be solved by the invention

As described in patent document 1, the pressure in the HST circuit of the continuously variable transmission mounted on the work vehicle may become higher than necessary due to various factors. For example, when a load fluctuation due to work such as excavation and dozing occurs or a load fluctuation due to braking occurs, the pressure of the HST circuit suddenly changes. When the pressure of the HST circuit sharply rises, the output torque becomes higher than necessary, and the riding comfort of the work vehicle deteriorates.

An object of the present invention is to provide a control device for a work vehicle, and a control method for a work vehicle, which can prevent a sudden change in output torque of a continuously variable transmission due to a load fluctuation.

Means for solving the problems

According to one aspect of the present invention, there is provided a control device for a work vehicle, comprising: a power source; a running device; a power transmission device that is provided with a hydrostatic continuously variable transmission having a safety valve capable of setting a safety pressure, and that transmits power of the power source to the traveling device; and a relief pressure setting unit that sets the relief pressure of the relief valve based on a target output value of the travel device.

Effects of the invention

According to the above aspect, the control device for a work vehicle can prevent a sudden change in output torque of the power transmission device due to a load variation.

Drawings

Fig. 1 is a side view of a work vehicle according to a first embodiment.

Fig. 2 is a diagram showing the internal structure of the cab according to the first embodiment.

Fig. 3 is a schematic diagram showing a power system of the work vehicle of the first embodiment.

Fig. 4 is a diagram showing a structure of an HST provided in the transmission according to the first embodiment.

Fig. 5 is a schematic block diagram showing the configuration of the control device for a work vehicle according to the first embodiment.

Fig. 6 is a flowchart illustrating a method of controlling the work vehicle according to the first embodiment.

Fig. 7 is a diagram showing an example of setting of the relief pressure in the first embodiment.

Fig. 8 is a diagram showing an effect of setting the relief pressure by the control device of the first embodiment.

Detailed Description

First embodiment

Hereinafter, embodiments will be described in detail with reference to the drawings.

Fig. 1 is a side view of a work vehicle according to a first embodiment.

The work vehicle 100 of the first embodiment is a wheel loader. The work vehicle 100 includes: vehicle body 110, work implement 120, front wheel portion 130, rear wheel portion 140, and cab 150. Work vehicle 100 is an example of a power machine.

The vehicle body 110 includes a front vehicle body 111, a rear vehicle body 112, and a steering cylinder 113. The front vehicle body 111 and the rear vehicle body 112 are mounted to be rotatable about a steering shaft extending in the up-down direction of the vehicle body 110. The front wheel portion 130 is provided at a lower portion of the front vehicle body 111, and the rear wheel portion 140 is provided at a lower portion of the rear vehicle body 112.

The steering cylinder 113 is a hydraulic cylinder. The steering cylinder 113 is attached at its base end to the rear vehicle body 112 and at its tip end to the front vehicle body 111. The steering cylinder 113 extends and contracts by hydraulic oil, thereby defining an angle formed by the front vehicle body 111 and the rear vehicle body 112. That is, the steering angle of the front wheel unit 130 is defined by the expansion and contraction of the steering cylinder 113.

The work implement 120 is used for excavating and conveying a work object such as earth and sand. Work implement 120 is disposed at a front portion of vehicle body 110. The work implement 120 includes an arm 121, a bucket 122, a crank 123, a lift cylinder 124, and a bucket cylinder 125.

The base end of the boom 121 is attached to the front portion of the front vehicle body 111 via a pin.

The bucket 122 includes a shovel for excavating a work object and a container for transporting the excavated work object. The base end of the bucket 122 is attached to the tip end of the boom 121 via a pin.

The bell crank 123 transmits the power of the bucket cylinder 125 to the bucket 122. A first end of a bell crank 123 is mounted to the bottom of the bucket 122 via a linkage. The second end of the bell crank 123 is attached to the front end of the bucket cylinder 125 via a pin.

The lift cylinder 124 is a hydraulic cylinder. The base end of the lift cylinder 124 is attached to the front portion of the front vehicle body 111. The front end of the lift cylinder 124 is attached to the large arm 121. The lift cylinder 124 extends and contracts by the hydraulic oil, and thereby the boom 121 is driven in the ascending direction or the descending direction.

The bucket cylinder 125 is a hydraulic cylinder. The base end of the bucket cylinder 125 is attached to the front portion of the front vehicle body 111. The front end of the bucket cylinder 125 is attached to the bucket 122 via a crank 123. The bucket cylinder 125 expands and contracts with hydraulic oil, and thereby the bucket 122 moves in the tilting direction or the dumping direction.

Cab 150 is a space in which an operator sits and is used to perform operations of work vehicle 100. The cab 150 is provided at an upper portion of the rear vehicle body 112.

Fig. 2 is a diagram showing the internal structure of the cab according to the first embodiment. A seat 151, an accelerator pedal 152, a brake pedal 153, a steering wheel 154, a front-rear selector switch 155, a shift switch 156, a boom lever 157, and a bucket lever 158 are provided in the cab 150. The work vehicle 100 may include one brake pedal 153, or may include a plurality of brake pedals 153. For example, in the case where work vehicle 100 includes two brake pedals 153 as shown in fig. 2, the same function as that of right brake pedal 153 may be assigned to left brake pedal 153 when viewed from behind. In addition, different functions may be assigned to the left brake pedal 153 and the right brake pedal 153. In this case, for example, the degree of engagement of the clutch may be changed in accordance with the operation amount of the left brake pedal 153 so that the engagement of the clutch is released by the operation of the left brake pedal 153.

Accelerator pedal 152 is operated to set a driving force (traction force) for traveling generated by work vehicle 100. The larger the operation amount of the accelerator pedal 152, the higher the target driving force (target traction force) is set.

Brake pedal 153 is operated to set a braking force for traveling generated by work vehicle 100. The larger the operation amount of the brake pedal 153, the stronger the braking force is set.

Steering wheel 154 is operated to set the steering angle of work vehicle 100.

Front-rear changeover switch 155 is operated to set the traveling direction of work vehicle 100. The traveling direction of the work vehicle is either Forward (F), reverse (R), or Neutral (N).

The shift switch 156 is operated to set the speed range of the power transmission device. A speed range is selected from, for example, 1 st, 2 nd, 3 rd, and 4 th gears by operation of the shift switch 156.

The large arm lever 157 is operated to set the movement amount of the raising operation or the lowering operation of the large arm 121. The upper arm 157 receives a lowering operation by being inclined forward and receives a raising operation by being inclined rearward.

The bucket lever 158 is operated to set the movement amount of the dumping operation or the tilting operation of the bucket 122. The bucket lever 158 receives a dumping operation by being tilted forward, and receives a tilting operation by being tilted backward.

Power system

Fig. 3 is a schematic diagram showing a power system of the work vehicle of the first embodiment.

The work vehicle 100 includes: an engine 210, a PTO220(Power Take Off), a transmission 230, a front axle 240, a rear axle 250, a variable capacity pump 260, and a fixed capacity pump 270.

The engine 210 is, for example, a diesel engine. Engine 210 is provided with fuel injection device 211 and engine tachometer 2101. Fuel injection device 211 controls the driving force of engine 210 by adjusting the amount of fuel injected into the cylinder of engine 210. The engine tachometer 2101 measures the rotational speed of the engine 210.

PTO220 transmits a part of the driving force of engine 210 to variable displacement pump 260 and fixed displacement pump 270. That is, PTO220 distributes the driving force of engine 210 to transmission 230, variable capacity pump 260, and fixed capacity pump 270.

The transmission 230 is a continuously variable transmission provided with an HST231 (hydrostatic continuously variable transmission). The transmission 230 may be a transmission that performs shift control only by the HST231, or may be an HMT (hydro-mechanical continuously variable transmission) that performs shift control by a combination of the HST231 and a planetary gear mechanism. The transmission 230 changes the speed of the driving force input to the input shaft and outputs the changed speed from the output shaft. The transmission 230 has an input shaft connected to the PTO220 and an output shaft connected to the front axle 240 and the rear axle 250. That is, transmission 230 transmits the driving force of engine 210 distributed by PTO220 to front axle 240 and rear axle 250. An input shaft speed table 2301 and an output shaft speed table 2302 are provided in the transmission 230. The input shaft speed table 2301 measures the speed of the input shaft of the transmission 230. An output shaft tachometer 2302 measures the rotational speed of the output shaft of the transmission 230. An HST pressure gauge 2303 is provided in the HST231 of the transmission 230. An HST pressure gauge 2303 measures the pressure of the HST 231.

Front axle 240 transmits the driving force output from transmission 230 to front wheel portion 130. Thereby, the front wheel portion 130 rotates.

The rear axle 250 transmits the driving force output from the transmission 230 to the rear wheel portion 140. Thereby, the rear wheel part 140 rotates.

The front axle 240 and the rear axle 250 are examples of traveling devices.

Variable displacement pump 260 is driven by the driving force from engine 210. The discharge capacity of the variable capacity pump 260 is changed by controlling the tilt angle of a swash plate provided in the variable capacity pump 260, for example. The hydraulic oil discharged from the variable displacement pump 260 is supplied to the lift cylinder 124 and the bucket cylinder 125 via the control valve 261, and is supplied to the steering cylinder 113 via the steering valve 262.

The control valve 261 controls the flow rate of the hydraulic oil discharged from the variable capacity pump 260, and distributes the hydraulic oil to the lift cylinder 124 and the bucket cylinder 125. The steering valve 262 controls the flow rate of the hydraulic oil supplied to the steering cylinder 113.

The variable displacement pump 260 is provided with a first pump pressure gauge 2601 and a pump displacement gauge 2602. The first pump pressure gauge 2601 measures the discharge pressure of the hydraulic oil discharged from the variable capacity pump 260. The pump capacity meter 2602 measures the capacity of the variable capacity pump 260 based on the swash plate angle of the variable capacity pump 260 and the like.

Variable displacement pump 260 is an example of a device that distributes power from PTO 220. In another embodiment, the variable capacity pump 260 may be constituted by a plurality of pumps, and may be provided with a supply destination such as a hydraulically driven fan, not shown, instead of or in addition to the variable capacity pump 260.

A lift pressure sensor 2603 is provided in the lift cylinder 124. The lift pressure sensor 2603 measures the bottom pressure of the lift cylinder 124.

The fixed capacity pump 270 is driven by the driving force from the engine 210. The hydraulic oil discharged from the fixed capacity pump 270 is supplied to a brake valve 271 in the transmission 230. The brake valve 271 controls the pressure of hydraulic oil supplied to a brake cylinder, not shown, provided in each axle. By supplying the brake cylinder with the hydraulic oil, the brake disk that rotates together with the rotation shafts of the front wheel portion 130 and the rear wheel portion 140 is pressed against the plate that does not rotate, and braking force is generated. A second pump pressure gauge 2701 is provided in the fixed capacity pump 270. The second pump pressure gauge 2701 measures the discharge pressure of the working oil discharged from the fixed capacity pump 270. The fixed capacity pump 270 is an example of a device that distributes power from the PTO 220. The fixed capacity pump 270 may be constituted by a plurality of pumps, or may have a supply destination such as a lubrication circuit, not shown.

Structure of HST

Fig. 4 is a diagram showing a structure of an HST provided in the transmission according to the first embodiment.

The HST231 includes: an HST pump 2311, an HST motor 2312, a first relief valve 2313, a first check valve 2314, a second relief valve 2315, and a second check valve 2316. The HST pump 2311 and the HST motor 2312 are connected to each other via a first hydraulic path P1 and a second hydraulic path P2.

The HST pump 2311 supplies the working oil to the HST motor 2312 via the first hydraulic path P1 or the second hydraulic path P2. The HST motor 2312 is driven by the hydraulic oil supplied from the HST pump 2311.

The first relief valve 2313 connects the first hydraulic path P1 and the relief bypass P3. When the pressure in the first hydraulic pressure path P1 is higher than that in the second hydraulic pressure path P2 and the differential pressure exceeds a predetermined relief pressure, the hydraulic oil flowing through the first hydraulic pressure path P1 flows through the relief bypass P3.

The first check valve 2314 is provided in parallel with the first relief valve 2313, blocks the hydraulic oil flowing through the first hydraulic pressure path P1, and flows the hydraulic oil flowing through the pressure reducing bypass P3 to the first hydraulic pressure path P1.

The second relief valve 2315 connects the second hydraulic pressure passage P2 and the pressure reducing bypass P3. When the pressure of the second hydraulic passage P2 is higher than the pressure of the first hydraulic passage P1 and the differential pressure exceeds a predetermined relief pressure, the hydraulic oil flowing through the second hydraulic passage P2 flows through the pressure reduction bypass P3.

The second check valve 2316 is provided in parallel with the second relief valve 2315, blocks the hydraulic oil flowing from the second hydraulic pressure path P2, and flows the hydraulic oil flowing from the pressure reducing bypass P3 to the second hydraulic pressure path P2.

That is, when the pressure of the first hydraulic pressure path P1 is higher than that of the second hydraulic pressure path P2 and the differential pressure exceeds a predetermined relief pressure, the hydraulic oil flowing through the first hydraulic pressure path P1 flows into the second hydraulic pressure path P2 via the first relief valve 2313, the pressure reducing bypass P3, and the second check valve 2316. On the other hand, when the pressure of the second hydraulic pressure passage P2 is higher than the first hydraulic pressure passage P1 and the differential pressure exceeds a predetermined relief pressure, the hydraulic oil flowing through the second hydraulic pressure passage P2 flows through the second relief valve 2315, the pressure reduction bypass passage P3, and the first check valve 2314 to the first hydraulic pressure passage P1. In order to compensate for the reduction in the oil amount due to the leakage of the hydraulic oil from the HST231, for example, a hydraulic pump, not shown, may be provided for supplying the hydraulic oil to the pressure reducing bypass P3.

The relief pressures of the first relief valve 2313 and the second relief valve 2315 can be changed in response to a control signal. For example, the first relief valve 2313 and the second relief valve 2315 may include a solenoid that presses a spring for closing the valve, and the relief pressure may be set by changing the position of the solenoid in accordance with the current.

Note that the HST pressure gauge 2303 measures a differential pressure between the first hydraulic path P1 and the second hydraulic path P2. It should be noted that a pressure sensor may be provided in each of the first hydraulic path P1 and the second hydraulic path P2, and a differential pressure between the first hydraulic path P1 and the second hydraulic path P2 may be measured from a difference between the measurement values of the two pressure sensors.

Control device

Work vehicle 100 includes a control device 300 for controlling work vehicle 100. Control device 300 is provided in vehicle body 110, preferably in cab 150.

The control device 300 outputs control signals to the fuel injection device 211, the transmission 230, the variable capacity pump 260, and the control valve 261 in accordance with the operation amounts of the respective operation devices (the accelerator pedal 152, the brake pedal 153, the steering wheel 154, the front-rear switching switch 155, the shift switch 156, the boom lever 157, and the bucket lever 158) in the cab 150.

Fig. 5 is a schematic block diagram showing the configuration of the control device for a work vehicle according to the first embodiment. The control device 300 is a computer including a processor 310, a main memory (memory)330, a storage (storage)350, and an interface 370.

Memory 350 is a non-transitory tangible storage medium. Examples of the memory 350 include: HDD (Hard Disk Drive), SSD (Solid State Drive), magnetic Disk, magneto-optical Disk, CD-ROM (Compact Disk Read Only Memory), DVD-ROM (Digital Versatile Disk Read Only Memory), semiconductor Memory, etc. The memory 350 may be an internal medium directly connected to the bus of the control device 300, or may be an external medium connected to the control device 300 via the interface 370 or a communication line. The memory 350 stores a program for controlling the work vehicle 100.

The program may be a program for realizing a part of the functions to be performed by the control device 300. For example, the program may be a program that functions by being combined with another program already stored in the memory 350 or with another program installed in another device. In other embodiments, the control Device 300 may include a custom LSI (Large Scale Integrated Circuit) such as a PLD (Programmable Logic Device) in addition to or instead of the above configuration. Examples of PLDs include PAL (Programmable Array Logic), GAL (Generic Array Logic), CPLD (Complex Programmable Logic Device), and FPGA (Field Programmable Gate Array). In this case, a part or all of the functions realized by the processor may be realized by the integrated circuit.

When a program is distributed to the control device 300 via a communication line, the control device 300 that has received the distribution may expand the program in the main memory 330 and execute the above-described processing.

The program may be a program for realizing a part of the above-described functions. The program may be a so-called differential file (differential program) that realizes the above-described functions by combining with another program already stored in the memory 350.

The processor 310 executes a program, and includes: an operation amount acquisition portion 311, a measured value acquisition portion 312, a vehicle state calculation portion 313, a requested PTO torque determination portion 314, a requested output torque determination portion 315, a travel load estimation portion 316, a work state specification portion 317, a target rotation speed determination portion 318, an acceleration torque determination portion 319, a target engine torque determination portion 320, an engine control portion 321, a target HST pressure determination portion 322 (target circuit pressure determination portion), a margin determination portion 323, a relief pressure setting portion 324, a target speed ratio determination portion 325, and a transmission control portion 326.

The operation amount obtaining unit 311 obtains the operation amount from each of the accelerator pedal 152, the brake pedal 153, the steering wheel 154, the front/rear changeover switch 155, the shift switch 156, the boom lever 157, and the bucket lever 158. Hereinafter, the operation amount of the accelerator pedal 152 is referred to as an accelerator operation amount, the operation amount of the brake pedal 153 is referred to as a brake operation amount, the operation amount of the steering wheel 154 is referred to as a steering operation amount, a value corresponding to the operation position of the front/rear switch 155 is referred to as an FNR operation amount, a value corresponding to the operation position of the shift switch 156 is referred to as a shift operation amount, the operation amount of the boom lever 157 is referred to as a boom operation amount, and the operation amount of the bucket lever 158 is referred to as a bucket operation amount.

The measured value acquisition portion 312 acquires measured values from the fuel injection device 211, the engine revolution meter 2101, the input shaft revolution meter 2301, the output shaft revolution meter 2302, the HST pressure meter 2303, the first pump pressure meter 2601, the pump capacity meter 2602, the lift pressure sensor 2603, and the second pump pressure meter 2701. That is, the measured value acquisition unit 312 acquires the measured values of the fuel injection amount of the engine 210, the rotation speed of the input shaft of the transmission 230, the rotation speed of the output shaft of the transmission 230, the pressure of the HST231, the pump pressure of the variable capacity pump 260, the capacity of the variable capacity pump 260, the bottom pressure of the lift cylinder 124, and the pump pressure of the fixed capacity pump 270, respectively.

Vehicle state calculation unit 313 calculates the output torque of engine 210, the upper limit torque of engine 210, the angular acceleration of engine 210, the torque (PTO torque) distributed from PTO220 to variable capacity pump 260 and fixed capacity pump 270, the input/output speed ratio of transmission 230, the angular acceleration of the output shaft of transmission 230, and the traveling speed of work vehicle 100, based on the measurement value acquired by measurement value acquisition unit 312. The output torque of engine 210 is the torque actually exerted by engine 210 calculated based on the fuel injection amount. The upper limit torque of the engine 210 is the maximum torque that the engine 210 can exert.

The requested PTO torque determination unit 314 determines a requested value of torque (requested PTO torque) to be distributed from the PTO220 to the variable capacity pump 260 and the fixed capacity pump 270, based on the steering operation amount, the boom operation amount, and the bucket operation amount acquired by the operation amount acquisition unit 311, and the measured values of the pump pressure of the variable capacity pump 260, the capacity of the variable capacity pump 260, and the pump pressure of the fixed capacity pump 270 acquired by the measured value acquisition unit 312. For example, the requested PTO torque determination unit 314 determines the requested flow rate of the variable capacity pump 260 from the steering operation amount based on a PTO conversion function that specifies the relationship between the operation amount and the requested flow rate. Further, for example, requested PTO torque determination unit 314 determines the requested flow rate of variable displacement pump 260 from the boom operation amount and the bucket operation amount based on the PTO conversion function. Then, the requested PTO torque determination unit 314 determines the requested PTO torque based on the pump pressure of the variable capacity pump 260, the capacity of the variable capacity pump 260, the measured value of the pump pressure of the fixed capacity pump 270, and the specified requested flow rate of the variable capacity pump 260.

The requested output torque determining portion 315 determines a requested value of torque (requested output torque) of the output shaft of the transmission 230 based on the accelerator operation amount, the brake operation amount, the shift operation amount, and the FNR operation amount acquired by the operation amount acquiring portion 311, and the traveling speed calculated by the vehicle state calculating portion 313. For example, the requested output torque determination unit 315 determines the requested output torque from the travel speed calculated by the vehicle state calculation unit 313 based on a travel conversion function that specifies a relationship between the travel speed and the requested output torque. At this time, the requested output torque determining portion 315 determines the characteristics of the running conversion function based on the accelerator operation amount, the brake operation amount, the shift operation amount, and the FNR operation amount.

Specifically, the requested output torque determination portion 315 specifies the travel conversion function corresponding to the speed range specified by the shift operation amount among the plurality of travel conversion functions corresponding to the plurality of speed ranges. The requested output torque determination unit 315 deforms the travel conversion function specified based on the magnification of the accelerator operation amount when the accelerator operation is performed. The requested output torque determination unit 315 deforms the travel conversion function specified based on the magnification of the brake operation amount when the brake operation is performed. The requested output torque determination portion 315 determines the sign of the requested output torque based on the FNR operation amount. When the requested output torque and the running speed do not match each other in sign (when the product of the requested output torque and the running speed has a negative sign), the torque on the braking side is generated by the transmission 230.

According to the travel conversion function, when the travel speed exceeds a predetermined speed, the requested output torque is a value on the braking side. Therefore, when the traveling speed calculated by the vehicle state calculating unit 313 exceeds the upper limit of the speed range specified by the shift operation amount, the accelerator operation amount, and the brake operation amount, the requested output torque determining unit 315 determines that the requested output torque is a value on the braking side (a sign opposite to the traveling speed).

Traveling load estimation unit 316 calculates output torque T of engine 210 based on vehicle state calculation unit 313_engAngular acceleration a of engine 210_engPTO Torque T_PTOInput-output speed ratio i of transmission 230, and angular acceleration α of output shaft of transmission 230_outEstimating a running load torque T relating to running_load。

Running load torque T_loadCan be calculated based on the following formula (1).

[ number 1 ]

I_engIs the rotational inertia of the engine 210. I is_vIs the moment of inertia of work vehicle 100. Eta_tIs the torque efficiency of the transmission 230. N is a distance from an output shaft of transmission 230 to front wheel section 130 and rear wheel section 140And (4) reducing the speed ratio of the vehicle axle. Moment of inertia I_engMoment of inertia I_vTorque efficiency η_tAnd the axle reduced speed ratio N is a constant. Expression (1) can be expressed in terms of the output torque T of the engine 210_engAnd output torque T of the transmission 230_outExpression (2) representing the relationship between the output torque T of the transmission 230 and the torque_outAnd acceleration a of work vehicle 100_outThe relation (3) therebetween. In other embodiments, the running load torque T is set to be equal to or greater than the running load torque T_loadThe calculation may be performed based on an expression other than expression (1). For example, instead of equation (2), a capacity command indicating the pressure of the HST231 measured by the HST231 and the HST231 of the variable displacement pump, or the pump capacity and the output torque T measured by a pump capacity meter provided in the variable displacement pump may be used_outExpression of the relationship therebetween, deriving the specific running load torque T_loadThe formula (II) is shown in the specification. In another embodiment, when the transmission 230 includes an electric motor, the specific travel load torque T may be derived using a torque command of the electric motor or an electric motor output torque estimated from a voltage or a current_loadThe formula (II) is shown in the specification.

Number 2

[ number 3 ]

The work state specifying unit 317 specifies the work state of the work vehicle 100 based on the operation amount acquired by the operation amount acquiring unit 311 and the measurement value acquired by the measurement value acquiring unit 312. The values of the working state are, for example, "low-speed travel state", "high-speed travel state", "excavation state", and "braking state".

The "low-speed travel state" is a state in which work vehicle 100 travels at a low speed. For example, when the absolute value of the travel speed is lower than a predetermined value, the working state specification unit 317 may determine that the working state is the "low-speed travel state". For example, when the shift operation amount is 1 st or 2 nd, the operating state specifying unit 317 may determine that the operating state is the "low-speed travel state".

The "high-speed travel state" is a state in which work vehicle 100 is moving forward or backward. For example, when the absolute value of the travel speed is equal to or greater than a predetermined value, the working state specifying unit 317 may determine that the working state is the "high-speed travel state". For example, when the shift operation amount is 3 th or 4 th gear, the operating state specifying unit 317 may determine that the operating state is the "high-speed travel state".

The "excavation state" is a state in which work vehicle 100 performs excavation work by work implement 120. For example, the working state specification unit 317 may determine that the working state is the "excavation state" when the measured value of the bottom pressure of the lift cylinder 124 is equal to or greater than a predetermined value.

The "braking state" is a state in which work vehicle 100 is braked. For example, when the brake operation amount is larger than 0, the working state specification unit 317 may determine that the working state is the "braking state".

Target rotational speed determination portion 318 determines a target engine rotational speed used in the control of engine 210 based on the sum of the requested travel power calculated from the requested output torque and the travel speed and the requested PTO output calculated from the measurement values of the requested PTO torque and the rotational speed of engine 210, that is, the requested engine output. Target engine speed determination portion 318 determines a target engine speed based on a speed conversion function that specifies a relationship between the requested engine output and the engine speed, which is determined by a pre-design or the like. The rotation speed conversion function may be designed to suppress the rotation of the engine 210 to a low rotation side as much as possible within a range in which the requested engine output can be exhibited without hindering the engine acceleration, for example.

Further, the target rotational speed determination portion 318 determines the rotational speed of the engine (PTO necessary rotational speed) required to achieve the requested flow rate of the variable capacity pump 260, which is calculated by the requested PTO torque determination portion 314. Target rotation speed determination unit 318 determines the PTO required rotation speed based on a rotation speed conversion function that specifies the relationship between the requested flow rate of variable capacity pump 260 and the engine rotation speed, which is determined by a pre-design or the like. When the target engine speed is lower than the PTO required speed, target speed determination unit 318 determines the target engine speed as the PTO required speed.

Acceleration torque specifying unit 319 calculates a target acceleration torque required to rotate engine 210 at the target engine speed, based on the measured value of the rotational speed of engine 210 acquired by measured value acquisition unit 312 and the target engine speed specified by target rotational speed specifying unit 318. That is, acceleration torque specifying unit 319 determines a target engine acceleration from the rotation speed of the difference between the measurement value of the rotation speed of engine 210 and the target engine rotation speed, and multiplies the target engine acceleration by the moment of inertia of engine 210, thereby calculating the target acceleration torque.

Target engine torque determination unit 320 determines a target engine torque, which is a torque to be output by engine 210, based on the PTO torque calculated by vehicle state calculation unit 313, the upper limit torque of engine 210, the input/output speed ratio of transmission 230, the requested output torque determined by requested output torque determination unit 315, and the measured value of the rotation speed of engine 210. Target engine torque determination unit 320 calculates a requested input torque, which is a torque of engine 210 required to obtain the requested output torque, by multiplying the requested output torque by the input/output speed ratio of transmission 230. The target engine torque determination unit 320 determines the smaller one of the sum of the PTO torque and the requested input torque and the maximum value of the engine torque as the target engine torque.

The engine control unit 321 outputs an engine torque command to the fuel injection device 211. Specifically, the engine control portion 321 outputs an engine torque command indicating the target engine torque determined by the target engine torque determination portion 320.

The target HST pressure specifying unit 322 specifies the pressure of the HST231 corresponding to the requested output torque specified by the requested output torque specifying unit 315 as a target HST pressure (target circuit pressure) that is a control target of the HST 231. The relationship of the output torque of the transmission 230 and the pressure of the HST231 is determined according to the relationship of the gear ratio between the output shaft and the HST motor 2312, which is determined by the design of the transmission 230, and the capacity of the HST motor 2312 at that time. That is, the larger the capacity of the HST motor 2312, the smaller the target HST pressure, and the larger the requested output torque, the larger the target HST pressure.

The remaining amount determining unit 323 determines the remaining amount pressure that should be allowed with respect to the difference between the relief pressure of the first relief valve 2313 and the second relief valve 2315 and the target HST pressure, based on the operation state of the work vehicle 100 specified by the operation state specifying unit 317.

The excess pressure is determined in advance for each operation state. When the remaining pressures in the respective working states are arranged in order of decreasing, the remaining pressures in the braking state, the remaining pressures in the excavation state, the remaining pressures in the low-speed travel state, and the remaining pressures in the high-speed travel state are set. The remaining amount pressure in the braking state may be set to monotonically decrease with respect to the depression amount of the brake pedal 153. In addition, when a strong braking force is to be applied, the residual pressure in the braking state may be set to a negative value.

The relief pressure setting unit 324 sets the relief pressure of the first relief valve 2313 and the second relief valve 2315 of the HST231 to the sum of the target HST pressure specified by the target HST pressure specifying unit 322 and the residual pressure specified by the residual amount specifying unit 323.

Target speed ratio determination unit 325 determines a target input/output speed ratio of transmission 230 based on the measured value of the rotation speed of the input shaft of transmission 230, the measured value of the rotation speed of the output shaft of transmission 230, the running load torque estimated by running load estimation unit 316, the target output torque determined by requested output torque determination unit 315, and the target engine acceleration specified by acceleration torque determination unit 319. Specifically, target speed ratio determination unit 325 estimates the rotation speed of the output shaft of transmission 230 after the lapse of a time period associated with a predetermined control cycle, based on the rotation speed of the output shaft of transmission 230, the running load torque, and the target output torque, and sets the rotation speed as the target rotation speed of the output shaft. Target speed ratio determination unit 325 estimates the rotation speed of the input shaft of transmission 230 after the elapse of a time period associated with a predetermined control cycle, based on the rotation speed of the input shaft of transmission 230 and the target engine acceleration, and sets the rotation speed as the target rotation speed of the input shaft. The target speed ratio determination unit 325 determines a target input-output speed ratio by dividing the target rotation speed of the output shaft by the target rotation speed of the input shaft.

The transmission control unit 326 outputs a control command for the transmission 230 to achieve the target input/output speed ratio determined by the target speed ratio determination unit 325. The transmission control unit 326 outputs, for example, a capacity command of the HST231 included in the transmission 230.

The pump control unit 327 outputs a control command for the variable capacity pump 260 in order to realize the requested PTO torque determined by the requested PTO torque determination unit 314.

Method for controlling work vehicle

Fig. 6 is a flowchart illustrating a method of controlling the work vehicle according to the first embodiment.

First, the operation amount acquisition unit 311 acquires an operation amount from each of the accelerator pedal 152, the brake pedal 153, the steering wheel 154, the front-rear switching switch 155, the shift switch 156, the boom lever 157, and the bucket lever 158 (step S1). The measured value acquisition unit 312 acquires measured values from the fuel injection device 211, the engine rpm table 2101, the input shaft rpm table 2301, the output shaft rpm table 2302, the HST pressure table 2303, the first pump pressure table 2601, the pump capacity table 2602, and the second pump pressure table 2701 (step S2).

Next, vehicle state calculation unit 313 calculates the output torque of engine 210, the upper limit torque of engine 210, the angular acceleration of engine 210, the PTO torque, the input/output speed ratio of transmission 230, the angular acceleration of the output shaft of transmission 230, and the traveling speed of work vehicle 100, based on the measurement values acquired in step S2 (step S3).

The requested PTO torque determination portion 314 determines the requested PTO torque based on the steering operation amount, the boom operation amount, and the bucket operation amount acquired in step S1, the pump pressure and the capacity of the variable capacity pump 260, and the measured value of the pump pressure of the fixed capacity pump 270 acquired in step S2 (step S4). The requested output torque determination portion 315 determines the requested output torque based on the operation amount related to the running acquired in step S1 and the running speed calculated in step S3 (step S5). The running load estimation unit 316 estimates a running load torque based on the value of the vehicle state calculated in step S3 (step S6).

The work state specifying unit 317 specifies the work state of the work vehicle 100 based on the operation amount acquired in step S1 and the measurement value acquired in step S2 (step S7). That is, the working state specifying unit 317 specifies which of the "low-speed travel state", the "high-speed travel state", the "excavation state", and the "braking state" the working state is.

Target rotational speed determination portion 318 determines the target engine rotational speed based on the requested travel power calculated from the requested output torque and the travel speed, and the sum of the requested PTO output calculated from the measured values of the requested PTO torque and the rotational speed of engine 210, that is, the requested engine output (step S8). Acceleration torque specifying part 319 calculates a target acceleration torque based on the measured value of the rotation speed of engine 210 and the target engine rotation speed determined in step S8 (step S9). The target engine torque determination portion 320 determines the target engine torque based on the requested output torque, the PTO torque calculated in step S3, the upper limit torque of the engine, the input/output speed ratio of the transmission 230, and the measured value of the rotation speed of the engine 210 acquired in step S2 (step S10). The engine control portion 321 outputs an engine torque command indicating the target engine torque determined in step S10 (step S11).

The target HST pressure specifying portion 322 determines the target HST pressure based on the requested output torque determined in step S5 and the latest capacity command of the HST motor 2312 (step S12). The remaining amount determination part 323 determines the remaining amount pressure based on the operation state of the work vehicle 100 specified in step S7 (step S13). Then, the relief pressure setting unit 324 sets the relief pressures of the first relief valve 2313 and the second relief valve 2315 of the HST231 to the sum of the target HST pressure determined in step S12 and the residual pressure determined in step S13 (step S14).

The target speed ratio determination unit 325 determines a target input/output speed ratio based on the measured value of the rotation speed of the input shaft of the transmission 230, the measured value of the rotation speed of the output shaft of the transmission 230, the load torque, the target output torque, and the target engine acceleration (step S15). The transmission control unit 326 outputs a control command for the transmission 230 to achieve the target input-output speed ratio (step S16).

The control device 300 executes the control processing described above for each predetermined control cycle.

Example of setting safety pressure

Here, the setting of the relief pressure by the control device 300 will be described with reference to a specific example. Fig. 7 is a diagram showing an example of setting of the relief pressure in the first embodiment. It should be noted that, as described above, the safety press_HST＿reliefBy pressing P at the target HST_HST＿targetPlus a residual pressure P_HST＿marginAnd obtaining the compound.

Work vehicle 100 starts traveling at time T0. The travel speed of work vehicle 100 reaches a threshold speed that distinguishes between the low-speed travel state and the high-speed travel state at time T1. At this time, from time T0 to time T1, working state specification unit 317 specifies that the working state of work vehicle 100 is the low-speed travel state. Therefore, the remaining amount determination unit 323 will match the target HST pressure P_HST＿targetAdded residual pressure P_HST＿marginThe remaining pressure in the low-speed running state is determined. When work vehicle 100 travels at a low speed, a fine acceleration operation is required, and there is a high possibility of shifting to the excavation operation. Therefore, the control device 300 sets a value smaller than the high-speed running state as the residual pressure P_HST＿marginThis can prevent the pressure of the HST231 from greatly deviating from the target HST pressure P_HST＿target。

From time T1 to time T2, the travel speed of work vehicle 100 further increases. At this time, from time T1 to time T2, operation state specification unit 317 specifies that the operation state of work vehicle 100 is the high speed travel state. Therefore, the remaining amount determination unit 323 sets the remaining amount pressure P_HST＿marginIs determined to be a value larger than the low-speed running state. When work vehicle 100 travels at a high speed, there is a low possibility that a sudden load is generated. Therefore, the control device 300 sets a value larger than the low-speed running state as the excess pressure P_HST＿marginThis can reduce the pressure reduction loss of the HST 231.

Next, during a period from time T2 to time T3, the operator of work vehicle 100 depresses brake pedal 153. Thus, the travel speed of work vehicle 100 is lower than the threshold speed at time T3. At this time, from time T2 to time T3, working state specification unit 317 specifies that the working state of work vehicle 100 is the braking state. Therefore, the remaining amount determination unit 323 sets the remaining amount pressure P_HST＿marginIs determined as a value that monotonically decreases to the amount of depression of the brake pedal 153. In the example shown in fig. 7, the residual pressure P is_HST＿marginBecomes a negative value. As a result, the control device 300 actively promotes the pressure reduction of the hydraulic oil to suppress the traction force, thereby improving the braking performance.

Then, during the period from time T3 to time T4, the work vehicle continues to travel at a speed lower than the threshold speed. At this time, from time T3 to time T4, working state specification unit 317 specifies that the working state of work vehicle 100 is the low-speed travel state. Therefore, the remaining amount determination unit 323 sets the remaining amount pressure P_HST＿marginThe excess pressure for low speed travel is determined. Note that the margin pressure P is set from the time T3 to the time T4_HST＿marginIs equal to the residual pressure P from the time T0 to the time T1_HST＿marginThe same value.

At time T4, when bucket 122 of work vehicle 100 pushes against the earth and sand, the pressure of lift cylinder 124 increases. At this time, after time T4, work state specification unit 317 specifies that the work state of work vehicle 100 is the excavation state. Therefore, the remaining amount determination unit 323 sets the remaining amount pressure P_HST＿marginIs determined to be a value smaller than the low-speed running state. When work vehicle 100 excavates, there is a high possibility that sudden load fluctuations occur, such as sudden load drops due to a tilting operation during excavation and sudden load drops due to the end of excavation. Therefore, the control device 300 controls the residual pressure P_HST＿marginThe engine speed is set to a value smaller than that in the low-speed running state, and the reduction in the engine speed and the vehicle can be prevented from flying out.

Action and Effect

Fig. 8 is a diagram showing an effect of setting a relief pressure by the control device of the first embodiment.

Control device 300 of the first embodiment presses P according to the target HST_HST＿targetThe relief pressure P of the first relief valve 2313 and the second relief valve 2315 is set_HST＿relief. The relief pressure P of the first relief valve 2313 and the second relief valve 2315 is set_HST＿reliefThe same value is also possible. As a result, as shown in fig. 8, when a load variation such as an external force is applied to work vehicle 100, internal pressure P of HST231 can be adjusted_HSTInhibit at the HST pressure P_HST＿targetThe corresponding pressure. Therefore, according to the first embodiment, a sudden change in output torque due to a load variation of the transmission 230 can be prevented.

As a comparative example, fig. 8 also discloses that the non-set relief pressure P is set_HST＿reliefThe behavior at the time, but the safety pressure P is not set_HST＿reliefIn the case of (3), the internal pressure P of the HST231 is varied according to the load_HST＿cpGreatly increasing. Then, control device 300 makes the internal pressure of HST231 approach the target HST pressure P_HST＿targetThe control is performed, and thereby, a backswing of the internal pressure is generated. This swinging back causes the pitch of the vehicle body to swing, and the riding comfort is reduced. In contrast, according to the first embodiment, the internal pressure P of the HST231 is adjusted_HSTInhibit at the HST pressure P_HST＿targetThe internal pressure can be brought to the target HST pressure P earlier by suppressing the swing back by a pressure lower than the corresponding pressure_HST＿target。

Referring to fig. 8, in the control of the comparative example, the engine speed significantly decreases after the load fluctuation occurs. This is because an abrupt load is transmitted from the HST231 to the engine 210. In contrast, according to the first embodiment, the load can be prevented from being transmitted to the engine 210 by reducing the pressure of the HST231, and the decrease in the engine speed can be suppressed.

While one embodiment has been described in detail with reference to the drawings, the specific configuration is not limited to the above, and various design changes and the like can be made.

The work vehicle 100 according to the first embodiment is a wheel loader, but is not limited thereto. For example, the work vehicle 100 according to another embodiment may be another work vehicle 100 such as a bulldozer or a tractor. In another embodiment, control device 300 may be applied to a power machine other than a work vehicle.

For example, according to the above-described embodiment, the control device 300 sets the relief pressure based on the target HST pressure regardless of the operation state, but the present invention is not limited to this in other embodiments. For example, in another embodiment, the control device 300 may set the relief pressure in a case where the operation state is the high speed travel state, without setting the relief pressure in another state.

In the above-described embodiment, the control device 300 varies the residual pressure depending on the operation state, but the present invention is not limited thereto. For example, in another embodiment, the control device 300 may always set the relief pressure using the same margin pressure.

Industrial applicability

According to the above disclosure of the present invention, the control device of the work vehicle can prevent a sudden change in the output torque due to a load variation of the power transmission device.

Description of the reference numerals

100 … work vehicle 110 … vehicle body 111 … front vehicle body 112 … rear vehicle body 113 … steering cylinder 120 … working device 121 … large arm 122 … bucket 123 … crank 124 … lift cylinder 125 … bucket cylinder 130 … front wheel section 140 … rear wheel section 150 … cab 151 … seat 152 … accelerator pedal 153 … brake pedal 154 … steering wheel 155 … front axle 250 … rear axle 260 … variable displacement pump 270 … fixed displacement pump 211 … fuel injection device 2101 … engine speed table … t … input axle speed table 2302 … output shaft … speed table 2303 HST 261 … control valve 262 steering valve 2601 … steering valve 26072 first pump 26072 pressure table 2602 pump 26072 pressure table … lift valve 27072 pressure table … lift valve 2703672 control valve … first pump … pressure table … lift pressure table … pressure table 2703672 The main memory 350 … of the device 330 … main memory 350 … the memory 370 … interface 2311 … HST pump 2312 … HST motor 2313 … first relief valve 2314 … first check valve 2315 … second relief valve 2316 … second check valve 311 … operation amount acquisition section 312 … measured value acquisition section 313 … vehicle state calculation section 314 … requests the PTO torque determination section 315 … to request the output torque determination section 316 … running load estimation section 317 … operation state determination section 318 … target rotation speed determination section 319 … acceleration torque determination section 320 … target engine torque determination section 321 … engine control section 321 … target HST pressure determination section 323 … margin determination section 324 … relief pressure setting section 325 … target speed ratio determination section 326 … transmission control section.