Work vehicle and method for controlling the work vehicle

Abstract

Utilize regenerative power efficiently. [Solution] When the amount of regenerative power generated in the electric motor by the regenerative braking of the traction unit exceeds the amount of power required by the hydraulic pump, a portion of the regenerative power is stored in a power storage device.

Description

Technical Field

[0001] The present disclosure relates to a work vehicle and a method for controlling a work vehicle.

Background Art

[0002] There is known a hybrid work vehicle having an engine, a generator that generates electricity by the rotational force of the engine, and an electric motor that is driven by the electric power of the generator. Patent Document 1 discloses a technique in which when the regenerative power generated by regenerative braking exceeds the allowable charging power of the power storage device, the surplus power is consumed by the generator.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By driving the generator as a motor, a rotational force can be applied to the engine. On the other hand, since the engine has a large frictional resistance, driving the generator by regenerative power has lower energy efficiency compared to storing the regenerative power in the power storage device. The technique described in Patent Document 1 preferentially charges the power storage device with regenerative power, but when the amount of charged power in the power storage device reaches the upper limit, it is necessary to consume all of the regenerative power by the generator, resulting in a decrease in energy efficiency. An object of the present disclosure is to provide a work vehicle and a method for controlling a work vehicle that can utilize regenerative power with high energy efficiency.

Means for Solving the Problems

[0005] According to one aspect of the present invention, a work vehicle comprises an engine, a generator driven by the engine, a hydraulic pump driven by the engine and the generator, an electric motor electrically connected to the generator and driving a running gear, a power storage device electrically connected to the generator and the electric motor, and a control device, wherein the control device stores a portion of the regenerative power in the power storage device when the amount of regenerative power generated by the electric motor to provide braking force to the running gear exceeds the amount of power required by the hydraulic pump. [Effects of the Invention]

[0006] According to the above embodiment, the work vehicle can utilize regenerative power in an energy-efficient manner. [Brief explanation of the drawing]

[0007] [Figure 1] This is a side view of a work vehicle according to the first embodiment. [Figure 2] This is a schematic diagram showing the power system of a work vehicle according to the first embodiment. [Figure 3] This is a schematic block diagram showing the configuration of the control device for the work vehicle according to the first embodiment. [Figure 4] This is a flowchart showing a control method for a work vehicle according to the first embodiment. [Figure 5] This figure shows an example of a constraint function according to the first embodiment. [Figure 6] This is a time chart showing an example of regenerative power distribution according to the first embodiment. [Modes for carrying out the invention]

[0008] <First Embodiment> 《Composition of work vehicles》 The embodiments will be described in detail below with reference to the drawings. Figure 1 is a side view of a work vehicle according to the first embodiment. The work vehicle 100 according to the first embodiment is a wheel loader. The work vehicle 100 comprises a body 110, a work implement 120, and wheels 130.

[0009] The vehicle body 110 is equipped with a driver's cab 111 in which the operator sits. Inside the driver's cab 111 is an operating device 112 for operating the work vehicle 100. The operating device 112 includes an accelerator pedal, a brake pedal, a steering wheel, a forward / reverse selector switch, a shift switch, a boom lever, and a bucket lever.

[0010] The vehicle body 110 consists of a front vehicle body 110a and a rear vehicle body 110b. The front vehicle body 110a and the rear vehicle body 110b are rotatably connected around a steering axis that extends vertically through the vehicle body 110. A front wheel 130a, which is a wheel 130, is provided at the lower part of the front vehicle body 110a. A rear wheel 130b, which is a wheel 130, is provided at the lower part of the rear vehicle body 110b. A steering cylinder 113 is provided between the front body 110a and the rear body 110b. The steering cylinder 113 is a hydraulic cylinder. The base end of the steering cylinder 113 is attached to the rear body 110b, and the tip end is attached to the front body 110a. The steering cylinder 113 expands and contracts due to the hydraulic fluid, thereby defining the angle between the front body 110a and the rear body 110b. In other words, the steering angle of the front wheels 130a is defined by the expansion and contraction of the steering cylinder 113.

[0011] The work implement 120 is used for excavating and transporting materials such as soil and sand. The work implement 120 is mounted at the front of the vehicle body 110. The work implement 120 comprises a boom 121, a bucket 122, a bell crank 123, a lift cylinder 124, and a bucket cylinder 125.

[0012] The base end of the boom 121 is attached to the front of the front body 110a via a pin. The bucket 122 comprises a cutting edge for excavating the workpiece and a container for transporting the excavated workpiece. The base end of the bucket 122 is attached to the tip of the boom 121 via a pin. The bell crank 123 transmits power from the bucket cylinder 125 to the bucket 122. The first end of the bell crank 123 is attached to the bottom of the bucket 122 via a link mechanism. The second end of the bell crank 123 is attached to the tip of the bucket cylinder 125 via a pin.

[0013] The lift cylinder 124 is a hydraulic cylinder. The base end of the lift cylinder 124 is attached to the front of the front body 110a. The tip end of the lift cylinder 124 is attached to the boom 121. The boom 121 is driven in the upward or downward direction by the extension and retraction of the lift cylinder 124 by hydraulic fluid. The bucket cylinder 125 is a hydraulic cylinder. The base end of the bucket cylinder 125 is attached to the front of the front body 110a. The tip of the bucket cylinder 125 is attached to the bucket 122 via a bell crank 123. The bucket cylinder 125 expands and contracts due to the hydraulic fluid, causing the bucket 122 to swing in the tilt or dump direction.

[0014] Power System Configuration Figure 2 is a schematic diagram showing the power system 200 of a work vehicle according to the first embodiment. The power system 200 of the work vehicle 100 includes an engine 210, a generator 220, a power storage device 230, a resistor 240, an electric drive motor 250, and a variable displacement pump 260.

[0015] The engine 210 is, for example, a diesel engine. The engine 210 is driven by the combustion of fuel, which rotates the drive shaft. A flywheel 211 may be provided on the drive shaft. The engine 210 is equipped with an engine controller 212 that controls the engine 210. The engine controller 212 monitors the rotational speed of the engine 210 and controls the engine 210 according to commands from the control device 300. The generator 220 has a rotor that rotates together with the drive shaft of the engine 210. The generator 220 generates electricity when the rotor is driven by the rotation of the engine 210. The generator 220 includes a generator converter 221. The generator converter 221 converts the alternating current power generated by the generator 220 into direct current power and supplies it to the bus bar B. Also, the generator converter 221 drives the generator 220 as a motor by converting the power of the bus bar B into alternating current power and supplying it to the generator 220. A generator controller 222 for controlling the generator 220 is provided in the generator 220. The generator controller 222 monitors the generated power of the generator 220 and controls the generator converter 221 so that the voltage of the bus bar B becomes a predetermined target voltage. When the voltage of the bus bar B is lower than the target voltage, the generator controller 222 outputs a power command for causing the generator converter 221 to output the generated power of the generator 220 to the bus bar B. When the voltage of the bus bar B is higher than the target voltage, the generator controller 222 outputs a power command for causing the generator converter 221 to output the power of the bus bar B to the generator.

[0016] The power storage device 230 stores and discharges electric power. The power storage device 230 may be, for example, a capacitor or a battery. The power storage device 230 includes a power storage device converter 231. The power storage device converter 231 exchanges direct current power between the bus bar B and the power storage device 230. That is, the power storage device converter 231 charges and discharges the power storage device 230. A power storage device controller 232 for controlling the power storage device 230 is provided in the power storage device 230. The power storage device controller 232 monitors the charge amount of the power storage device 230 and controls the power storage device converter 231 according to a command from the control device 300.

[0017] The resistor 240 converts electric power into thermal energy and releases it to the atmosphere. The resistor 240 includes a resistor converter 241 and a resistor controller 242. The resistor controller 242 controls the resistor converter 241 according to a power command from the control device 300.

[0018] The electric drive motor 250 is driven by power supplied from the busbar B and rotates the wheels 130. The power of the electric drive motor 250 is transmitted to the wheels 130, for example, via the axle 131. The electric drive motor 250 is equipped with a drive motor converter 251. The drive motor converter 251 supplies power to the electric drive motor 250 for driving when the work vehicle 100 is in motion. The drive motor converter 251 releases the regenerative power generated by the electric drive motor 250 when the work vehicle 100 is braking to the busbar B. The electric drive motor 250 may be provided on each of the front wheels 130a and the rear wheels 130b, and may be provided on the left and right wheels of the front wheels 130a, and on the left and right wheels of the rear wheels 130b. The electric drive motor 250 is equipped with a drive motor controller 252 that controls the electric drive motor 250. The travel motor controller 252 monitors the rotational speed of the electric travel motor 250 and controls the travel motor converter 251 according to commands from the control device 300.

[0019] The variable displacement pump 260 is driven by a rotating shaft that rotates together with the drive shaft of the engine 210 and discharges hydraulic fluid. The discharge capacity of the variable displacement pump 260 is changed, for example, by controlling the tilt angle of a swash plate located inside the variable displacement pump 260. The hydraulic fluid discharged from the variable displacement pump 260 is supplied to the lift cylinder 124, bucket cylinder 125, and steering cylinder 113 via a control valve 261. The control valve 261 controls the flow rate of the hydraulic fluid discharged from the variable displacement pump 260 and distributes the hydraulic fluid to the lift cylinder 124, bucket cylinder 125, and steering cylinder 113.

[0020] Control device The work vehicle 100 is equipped with a control device 300 for controlling the work vehicle 100. The control device 300 outputs control signals to the engine 210, generator converter 221, energy storage device converter 231, travel motor converter 251, variable displacement pump 260, and control valve 261 according to the amount of operation of the operating device 112.

[0021] Figure 3 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 comprising a processor 310, main memory 330, storage 350, and interface 370.

[0022] Storage 350 is a tangible, non-temporary storage medium. Examples of storage 350 include HDDs (Hard Disk Drives), SSDs (Solid State Drives), magnetic disks, magneto-optical disks, CD-ROMs (Compact Disc Read Only Memory), DVD-ROMs (Digital Versatile Disc Read Only Memory), and semiconductor memory. Storage 350 may be an internal medium directly connected to the bus of the control device 300, or an external medium connected to the control device 300 via the interface 370 or a communication line. Storage 350 stores a program for controlling the work vehicle 100.

[0023] The program may be for implementing a part of the functions to be performed by the control device 300. For example, the program may perform functions in combination with other programs already stored in the storage 350, or in combination with other programs implemented in other devices. 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, some or all of the functions implemented by the processor 310 may be implemented by the integrated circuit.

[0024] If the program is delivered to the control device 300 via a communication line, the control device 300 that receives the program may load it into the main memory 330 and execute the above processing. Furthermore, the program may be intended to implement some of the functions described above. In addition, the program may be a so-called differential file (differential program) that implements the functions described above in combination with other programs already stored in the storage 350.

[0025] The processor 310, by executing a program, includes a manipulated variable acquisition unit 311, a measured value acquisition unit 312, a required power calculation unit 313, and a control unit 314.

[0026] The manipulated variable acquisition unit 311 acquires the manipulated variable from the operating device 112 via the interface 370. The measurement value acquisition unit 312 acquires measurement data from the engine controller 212, the energy storage device controller 232, and the drive motor controller 252 via the interface 370. Specifically, the measurement value acquisition unit 312 acquires the following data: The measurement value acquisition unit 312 acquires measurement data of the rotational speed of the engine 210 from the engine controller 212. The measurement value acquisition unit 312 acquires measurement data of the charge amount of the energy storage device 230 from the energy storage device controller 232. The measurement value acquisition unit 312 acquires measurement data of the regenerative power of the electric drive motor 250 from the drive motor controller 252. In addition, the measurement value acquisition unit 312 may acquire measurement data of the drive motor torque and drive motor rotational speed from the drive motor controller and calculate the regenerative power from the measurement data of the drive motor torque and drive motor rotational speed.

[0027] The power request calculation unit 313 calculates the power (requested power) value required by the electric drive motor 250 and the variable displacement pump 260 based on the manipulated variable acquired by the manipulated variable acquisition unit 311 and the pump pressure of the variable displacement pump 260. The power requirement calculation unit 313 determines the required power of the electric drive motor 250, for example, by following the procedure below. The power requirement calculation unit 313 determines the target vehicle speed of the work vehicle 100 from the amount of operation of the operating device 112. The power requirement calculation unit 313 determines the target traction force based on the difference between the target vehicle speed and the current vehicle speed of the work vehicle 100. The power requirement calculation unit 313 determines the required power of the electric drive motor 250 based on the target traction force, the rotational speed of the electric drive motor 250, and a predetermined reduction ratio. Note that if the target vehicle speed is less than the current vehicle speed, the required power will be a negative number. A negative required power number means that regenerative power equivalent to the required power will be generated in order to apply braking force to the electric drive motor 250. The power requirement calculation unit 313 determines the required power of the variable displacement pump 260, for example, by following the procedure below. The power requirement calculation unit 313 determines the required flow rate for each actuator from the manipulated amount, based on a conversion function that defines the relationship between the manipulated amount and the required flow rate of the hydraulic fluid, which is defined for each actuator. The power requirement calculation unit 313 determines the required power of the variable displacement pump 260 from the sum of the required flow rates and the pump pressure of the variable displacement pump 260.

[0028] The control unit 314 outputs power commands to each converter. When the electric drive motor 250 is generating regenerative power, the control unit 314 determines the distribution of regenerative power to the generator 220 and the energy storage device 230 based on the power request of the variable displacement pump 260 determined by the manipulated variable acquisition unit 311. In the first embodiment, the control unit 314 outputs power commands to the converters, but is not limited to this; the control unit 314 may also output torque commands that cause the converters to output torque equivalent to the power distributed to them.

[0029] Control methods for work vehicles Figure 4 is a flowchart showing the control method for a work vehicle according to the first embodiment. First, the manipulated variable acquisition unit 311 acquires the manipulated variable from the operating device 112 (step S1). The measured value acquisition unit 312 acquires measurement data from the engine controller 212, the energy storage device controller 232, and the travel motor controller 252 (step S2). The requested power calculation unit 313 calculates the requested power for the electric travel motor 250 and the variable displacement pump 260 based on the manipulated variable and the measurement data (step S3). The control unit 314 determines the power to be supplied to the travel motor converter 251 based on the requested power for the electric travel motor 250 and outputs a power command to the travel motor controller 252 (step S4).

[0030] The control unit 314 determines whether or not the electric drive motor 250 generates regenerative power based on the requested power value of the electric drive motor 250 (step S5). The control unit 314 determines that regenerative power is generated if the requested power value is negative. If regenerative power is not generated (step S5: NO), i.e., the work vehicle 100 is being powered, the control unit 314 outputs a control command for the engine 210 to the engine controller 212 based on the requested power of the electric drive motor 250 and the variable displacement pump 260.

[0031] If regenerative power is being generated (Step S5: YES), the control unit 314 determines whether the absolute value of the power required by the electric drive motor 250 (magnitude of regenerative power) is greater than the absolute value of the power required by the variable displacement pump 260 (Step S6). If the regenerative power is less than or equal to the power required by the variable displacement pump 260 (Step S6: NO), the control unit 314 outputs a power command to the energy storage device controller 232 that sets the power supply from busbar B to the energy storage device 230 to zero (Step S7). Due to the constant busbar voltage control by the generator controller 222, all of the regenerative power generated by the electric drive motor 250 is output to the generator 220 and used to drive the variable displacement pump 260. Based on the difference between the power required by the electric drive motor 250 and the variable displacement pump 260 and the regenerative power, the control unit 314 outputs a control command for the engine 210 to the engine controller 212.

[0032] If the regenerative power exceeds the required power of the variable capacity pump 260 (step S6: YES), the control unit 314 determines the maximum charging power of the energy storage device 230 (step S8). The maximum charging power is the maximum power that satisfies the constraints on the voltage, current, and power that can be input to the energy storage device 230. The control unit 314 determines the maximum charging power from the voltage of the energy storage device 230 based on a predetermined constraint function that shows the relationship between the voltage of the energy storage device 230 and the maximum charging power. Figure 5 is a diagram showing an example of a constraint function according to the first embodiment. The constraint function F represents the minimum value of the voltage constraint function F1 that determines the maximum power that satisfies the input voltage constraint, the current constraint function F2 that determines the maximum power that satisfies the input current constraint, and the power constraint function F3 that represents the specification upper limit of the input power of the energy storage device 230. The voltage constraint function F1 is expressed as the product of the current obtained by dividing the difference between the upper limit of the input voltage of the energy storage device 230 and the voltage of the energy storage device 230 by the internal resistance of the energy storage device 230, and the voltage of the energy storage device 230. In other words, the voltage constraint function F1 is a quadratic function that is concave upwards. The current constraint function F2 is expressed as the product of the upper limit of the input current to the energy storage device 230 and the voltage of the energy storage device 230. In other words, the current function F2 is a linear function with a positive slope. The power constraint function F3 represents a constant upper limit of the input power of the energy storage device 230, regardless of the voltage of the energy storage device 230. Furthermore, in addition to the upper limit value determined by the constraint function, the control unit 314 may further determine the upper limit value of the input voltage to the energy storage device 230 from the voltage value of bus B so that the voltage value of bus B does not fall below a predetermined lower limit value. Normally, the voltage value of bus B does not fall below the lower limit value when regenerative power is generated, but there may be cases where the voltage value of bus B falls below the lower limit value, such as when the regenerative power determined in step S3 is overestimated and the power generated by the generator 220 is low.

[0033] Step S9 determines whether the surplus power, which is the difference between the regenerated power and the power required by the variable displacement pump 260, exceeds the maximum charging power of the energy storage device 230. If the surplus power does not exceed the maximum charging power (Step S9: NO), the control unit 314 outputs a power command to the energy storage device controller 232 to supply power equivalent to the surplus power from busbar B to the energy storage device 230 (Step S10). Due to the constant busbar voltage control by the generator controller 222, the difference between the regenerated power and the surplus power, i.e., power equivalent to the required power, is output to the generator 220. As a result, the power equivalent to the required power from the regenerated power is used to drive the variable displacement pump 260, and the remaining power is used to charge the energy storage device 230. The control unit 314 outputs a control command to the engine controller 212 to set the output of the engine 210 to zero. However, in other embodiments of the control device 300, a control command for the engine 210 that does not have a zero output may be output for control such as changing the rotational speed of the engine 210. In this case, the energy storage device 230 is charged with the remaining power from the regenerated power that was used for the required power and engine control.

[0034] If the surplus power exceeds the maximum charging power (step S9: YES), the control unit 314 determines whether the rotational speed of the drive shaft of the engine 210 is below the set upper limit of the rotational speed (step S11). The set upper limit may be equal to the specification upper limit of the engine 210, or it may be a value with a margin above the specification upper limit. If the rotational speed of the drive shaft is below the set upper limit (step S11: YES), the control unit 314 outputs a power command to the energy storage device controller 232 to supply power equivalent to the maximum charging power from the bus B to the energy storage device 230 (step S12). Due to the constant bus voltage control by the generator controller 222, the power equivalent to the difference between the regenerative power and the maximum charging power is output to the generator 220. Of the power output to the generator 220, power equivalent to the required power is used to drive the variable capacity pump 260, and the remaining power is used to accelerate the drive shaft of the engine 210. This allows the portion of regenerative power exceeding the sum of the required power and the maximum charging power to be stored as rotational kinetic energy of the flywheel 211. However, energy storage as rotational kinetic energy of the flywheel 211 is affected by friction losses and is therefore less efficient than energy storage by charging the energy storage device 230. The control unit 314 outputs a control command to the engine controller 212 that sets the output of the engine 210 to zero. However, in other embodiments of the control device 300, the control device 300 may output a control command for the engine 210 that does not have a zero output, for control purposes such as changing the rotational speed of the engine 210. In this case, the energy storage device 230 is charged with the required power and the remaining power used for engine control from the regenerative power.

[0035] If the rotational speed of the drive shaft reaches the set upper limit (step S11: NO), the control unit 314 outputs a power command to the energy storage device controller 232 to supply power equivalent to the maximum charge power from bus B to the energy storage device 230, and outputs a power command to the resistor controller 242 to supply power equivalent to the difference between the surplus power and the maximum charge power from bus B to the resistor 240 (step S13). Due to the constant bus voltage control by the generator controller 222, power equivalent to the required power, which is the regenerative power minus the maximum charge power and the power consumed by the resistor 240, is output to the generator 220. As a result, power equivalent to the required power from the regenerative power is used to drive the variable capacity pump 260, power equivalent to the maximum charge power is charged to the energy storage device 230, and the remaining power is consumed by the resistor 240. The control unit 314 outputs a control command to the engine controller 212 to set the output of the engine 210 to zero. However, in other embodiments, the control device 300 may output a control command for the engine 210 that does not output zero in order to control the rotational speed of the engine 210. In this case, the energy storage device 230 is charged with the remaining power from the regenerated power that was used for the requested power and engine control. In other embodiments, even when the rotational speed of the drive shaft has reached a set upper limit, the power difference between the regenerated power and the upper limit power for charging may be output to the generator 220, and the amount of oil supplied to the hydraulic load (steering cylinder 113, lift cylinder 124, bucket cylinder 125, accumulator (not shown), bleed valve, etc.) connected to the variable displacement pump 260 may be increased so as not to increase the rotational speed.

[0036] Example of operation Figure 6 is a time chart showing an example of regenerative power distribution according to the first embodiment. In the example shown in Figure 6, regenerative power is generated at time t1. During the period from time t1 to time t2, the regenerative power is insufficient to meet the power requirements of the variable capacity pump 260. Therefore, the control device 300 distributes all of the regenerative power to drive the generator 220 during the period from time t1 to time t2. At time t2, the regenerative power exceeds the power requirements of the variable capacity pump 260. Therefore, the control device 300 distributes power equivalent to the power requirements of the variable capacity pump 260 to drive the generator 220, and distributes the remainder to the energy storage device 230. At time t3, the surplus power exceeds the charging limit power. Therefore, the control device 300 distributes power equivalent to the charging limit power to the energy storage device 230, and distributes the remainder to drive the generator 220. Of the rotational force generated by the generator 220, the amount equivalent to the required power is consumed by the variable displacement pump 260, and the remainder is stored in the flywheel 211 as inertial energy of the drive shaft of the engine 210. At time t4, the surplus power falls below the maximum charging power limit. Therefore, the control device 300 distributes the power equivalent to the required power of the variable displacement pump 260 from the regenerated power to drive the generator 220, and distributes the remainder to the energy storage device 230. At time t5, the required power of the variable displacement pump 260 exceeds the regenerated power. Therefore, the control device 300 distributes all of the regenerated power to drive the generator 220.

[0037] "effect" Thus, in the first embodiment, the control device 300 stores a portion of the regenerated power in the energy storage device 230 when the amount of regenerated power exceeds the amount of power required by the variable capacity pump 260. When the magnitude of regenerated power exceeds the power requirement of the variable displacement pump 260, all of the regenerated power is distributed to drive the generator 220, and the surplus can be stored as inertial energy of the engine 210's rotating shaft. However, as the rotational speed of the rotating shaft increases, the frictional force increases, and a portion of the power supplied to the generator 220 is lost due to frictional losses. Since the charge and discharge losses are smaller than the frictional losses of the engine 210, the control device 300 can store a portion of the regenerated power in the energy storage device 230, as in the first embodiment, thereby suppressing the energy loss due to frictional losses.

[0038] Furthermore, in the first embodiment, if the surplus power obtained by subtracting the power required by the variable displacement pump 260 from the amount of regenerative power exceeds the maximum charging power of the energy storage device 230, the control device 300 stores power equivalent to the maximum charging power from the regenerative power in the energy storage device 230. As a result, the difference between the regenerative power and the charging power of the energy storage device 230 is distributed to drive the generator 220. The amount of power distributed to the generator 220 that exceeds the power required by the variable displacement pump 260 is stored as inertial energy of the rotating shaft of the engine 210.

[0039] Thus, the control device 300 according to the first embodiment can utilize regenerative power in an energy-efficient manner.

[0040] <Other Embodiments> Although one embodiment has been described in detail above with reference to the drawings, the specific configuration is not limited to that described above, and various design changes are possible. In other embodiments, the order of the above-described processes may be changed as appropriate. Also, some processes may be executed in parallel. The control device 300 according to the above embodiment may be composed of a single computer, or the configuration of the control device 300 may be divided among multiple computers, and the multiple computers may cooperate with each other to function as the control device 300. In this case, some of the computers constituting the control device 300 may be mounted inside the work vehicle, while the other computers may be provided outside the work vehicle.

[0041] In the work vehicle 100 according to the above embodiment, the voltage of bus B is controlled to a constant level by the generator controller 222, but this is not limited to this. For example, in the work vehicle 100 according to other embodiments, the voltage of bus B may be controlled to a constant level by the energy storage device controller 232. In this case, the control device 300 outputs a power command to the generator controller 222 instructing it to supply power to the generator 220. That is, in step S7 above, the control device 300 outputs a power command to the generator controller 222 to supply all the regenerative power generated from bus B to the generator 220. Also, in step S10 above, the control device 300 outputs a power command to the generator controller 222 to supply power equivalent to the power required by the variable capacity pump 260 from bus B to the generator 220. Also, in steps S12 and S13 above, the control device 300 outputs a power command to the generator controller 222 to supply power obtained by subtracting the charging limit power from the regenerative power from bus B to the generator 220.

[0042] The work vehicle 100 according to the above-described embodiment is a wheel loader, but is not limited to this. The work vehicle 100 according to other embodiments may be other work vehicles such as a dump truck, hydraulic excavator, or bulldozer. [Explanation of Symbols]

[0043] 100…Work vehicle 110…Body 110a…Front body 110b…Rear body 111…Driver's cab 112…Control device 113…Steering cylinder 120…Work equipment 121…Boom 122…Bucket 123…Bell crank 124…Lift cylinder 125…Bucket cylinder 130…Wheels 130a…Front wheels 130b…Rear wheels 131…Axle 200…Power system 210…Engine 211…Flywheel 212…Engine controller 220…Generator 221…Generator converter 222…Generator controller 230…Energy storage device 231…Energy storage device converter 232…Energy storage device controller 240…Resistor 241…Resistor converter 242…Resistor controller 250…Electric travel motor 251…Travel motor converter 252…Travel motor controller 260... Variable displacement pump 261... Control valve 300... Control device 310... Processor 311... Manipulated variable acquisition unit 312... Measured value acquisition unit 313... Required power calculation unit 314... Control unit 330... Main memory 350... Storage 370... Interface B... Busbar

Claims

1. The engine and A generator driven by the aforementioned engine, A hydraulic pump driven by the engine and the generator, An electric motor electrically connected to the aforementioned generator and driving the traction device, A power storage device electrically connected to the generator and the electric motor, Control device and Equipped with, The control device is When the amount of regenerative power generated by the electric motor to apply braking force to the traction device exceeds the amount of power required by the hydraulic pump, a portion of the regenerative power is stored in the energy storage device. Work vehicle.

2. The control device is If the surplus power, which is the value obtained by subtracting the required power from the regenerative power, does not exceed the maximum charging power of the energy storage device, then the power equivalent to the surplus power from the regenerative power is stored in the energy storage device. When the surplus power exceeds the charging limit power, the regenerative power equivalent to the charging limit power is stored in the energy storage device. The work vehicle according to claim 1.

3. The control device is If the magnitude of the regenerated power does not exceed the required power, the generator is driven with the regenerated power. If the magnitude of the regenerated power exceeds the required power, the generator is driven with the portion of the regenerated power equivalent to the required power. The work vehicle according to claim 1.

4. The control device is If the surplus power, which is the value obtained by subtracting the required power from the regenerative power, does not exceed the maximum charging power of the energy storage device, then the power equivalent to the surplus power from the regenerative power is stored in the energy storage device. When the surplus power exceeds the charging limit power, the regenerative power equivalent to the charging limit power is stored in the energy storage device, and the remaining regenerative power is used to drive the generator. The work vehicle according to claim 3.

5. If the surplus power exceeds the charging limit power and the engine speed exceeds the set upper limit, the regenerative power equivalent to the charging limit power is stored in the energy storage device, and the remaining regenerative power is consumed by the resistor or hydraulic load. The work vehicle according to claim 4.

6. The aforementioned charging limit power is the power that satisfies the constraints on the input voltage of the energy storage device, the constraints on the input current of the energy storage device, and the constraints on the input power of the energy storage device. The work vehicle according to claim 4.

7. The engine and the generator are equipped with a flywheel mounted coaxially with their respective rotating shafts. The work vehicle according to claim 1.

8. The engine and A generator driven by the aforementioned engine, A hydraulic pump driven by the engine and the generator, An electric motor electrically connected to the aforementioned generator and driving the traction device, A power storage device electrically connected to the generator and the electric motor, Control device and A control method for a work vehicle equipped with, The control device, when the amount of regenerative power generated in the electric motor to apply braking force to the traction device exceeds the amount of power required by the hydraulic pump, stores a portion of the regenerative power in the energy storage device. A method for controlling a work vehicle having a certain feature.

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