Work vehicle

Abstract

To provide a work vehicle configured so that electric power generated when the vehicle is braked is adjusted in accordance with a state of an engine, which can supply power from the engine more smoothly when the vehicle is braked and the started, in modulate operation.SOLUTION: A work vehicle is equipped with an electric motor for running that makes a vehicle body run by electric power from an electricity generator that is driven by an engine, a forward / backward running-switching switch, and an external resistor that consumes regenerative electric power from the electric motor for running, which when a running direction of the vehicle body shown by the forward / backward running-switching switch is different from a running direction of the vehicle body shown by a rotating direction of the electric motor for running, controls the electric power generator so that electric power generated by the electricity generator increases, when a difference between a preset fuel injection limit value and a fuel injection volume which are preset for the engine is larger than a first threshold, and controls the electricity generator so that electric power generated by the electricity generator decreases, when the difference between fuel injection limit value and the fuel injection amount is smaller than the first threshold.SELECTED DRAWING: Figure 7

Description

[Technical field]

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

[0002] Some work vehicles generate electricity by driving a motor generator with an engine, and use the power from the motor generator to rotate and drive wheels with a traveling motor. For example, Patent Document 1 discloses an electrically driven work vehicle that includes a generator motor mechanically connected to the engine, a generator inverter that controls the amount of electricity generated by the generator motor based on a generation voltage command, a traveling motor that drives a vehicle body, a traveling inverter that controls the torque of the traveling motor based on a motor torque command, a forward / reverse switching device that switches between forward and reverse travel of the vehicle body, a brake resistor, a chopper circuit that is electrically connected to the generator inverter and the traveling inverter, and that consumes the power generated by the generator motor and the traveling motor by electrically connecting the generator inverter and the traveling inverter to the brake resistor when the input voltage exceeds a set voltage, and a generation voltage command that drives the generator motor with the engine to generate a voltage exceeding a set voltage while the electrically driven work vehicle is modulated by selecting a direction opposite to the traveling direction of the vehicle body by the forward / reverse switching device, and outputs to the generator inverter a generation voltage command. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2019-38365 A Summary of the Invention [Problem to be solved by the invention]

[0004] An example of a work vehicle is a wheel loader that excavates and transports earth and sand using the bucket of a hydraulic work device at the front while traveling, and loads it into a dump truck or the like. With a wheel loader, the work efficiency, such as the amount of material transported per unit time, is one indicator of the vehicle's performance. To improve the work efficiency of a wheel loader, it is necessary to move the vehicle as quickly as possible and perform work promptly.

[0005] For example, one of the operations that a wheel loader performs during operation is a so-called modulated operation, in which the wheel loader suddenly brakes, reverses its direction of travel, and then suddenly accelerates when moving between an excavation position and a loading position.

[0006] In the above-mentioned conventional technology, since power generation is performed without considering the engine state during the modulating operation, the engine output may become excessive when the vehicle starts moving after braking, resulting in a drop in engine speed and making it difficult to start the vehicle smoothly. Also, if the generated power is reduced to avoid a drop in engine speed, it may take time to supply the power required for the vehicle to start, resulting in a delay in starting the vehicle.

[0007] The present invention has been made in consideration of the above, and aims to provide a work vehicle that can supply power from the engine more smoothly when starting off after braking by adjusting the generated power during vehicle braking in accordance with the state of the engine during modulated operation. [Means for solving the problem]

[0008] The present application includes multiple means for solving the above-mentioned problems, and one example is a work vehicle equipped with a generator driven by an engine, a traveling motor that drives the vehicle body to travel using power from the generator, a forward / reverse switch that switches the traveling direction of the vehicle body between forward and reverse, an external resistor that consumes regenerative power from the traveling motor, and a vehicle control device, wherein when a difference occurs between the traveling direction of the vehicle body indicated by the forward / reverse switch and the traveling direction of the vehicle body indicated by the rotation direction of the traveling motor, the vehicle control device controls the generator to increase or decrease the generated power based on the difference between a fuel injection limit value preset for the engine and the fuel injection amount. Effect of the Invention

[0009] According to the present invention, in the modulating operation, the generated power during vehicle braking is adjusted in accordance with the state of the engine, so that power can be supplied from the engine more smoothly when starting off after braking. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a side view showing a schematic external appearance of a wheel loader. [Diagram 2] FIG. 1 is a diagram illustrating a schematic configuration of an electric drive system of a wheel loader. [Diagram 3] FIG. 4 is a diagram illustrating an example of the operation of a wheel loader. [Figure 4] FIG. 4 is a diagram illustrating a schematic diagram of a flow of electric power during fuel efficiency improvement control. [Diagram 5] FIG. 4 is a diagram illustrating a schematic diagram of a flow of power in a work efficiency improvement control. [Figure 6] FIG. 2 is a functional block diagram showing the processing contents in a controller function unit of the generator inverter. [Figure 7] 2 is a functional block diagram illustrating functional units related to control of the electric power drive system of the vehicle control device. FIG. [Figure 8] 4 is a flowchart showing the processing contents of a modulation determination unit and an MG control mode switching unit of the vehicle control device. [Figure 9] 4 is a functional block diagram showing the processing contents in a power generation amount calculation unit of the vehicle control device. FIG. [Figure 10] FIG. 11 is a diagram showing state quantities of each part during modulation operation in the prior art shown as a comparative example. [Figure 11] 5A and 5B are diagrams illustrating state quantities of each part during modulation operation. [Figure 12] FIG. 4 is a functional block diagram showing the content of a process for limiting regenerative power. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, an embodiment of the present invention will be described with reference to FIGS.

[0012] In the following description, a wheel loader will be used as an example of a work vehicle, but this is not limited to this, and the present invention can also be applied to other work machines that use a so-called diesel-electric system.

[0013] 1 is a side view showing a schematic view of the exterior of a wheel loader according to this embodiment. In the following description, unless otherwise specified, the front, rear, left and right of the wheel loader are based on the viewpoint of an operator who rides on and operates the wheel loader.

[0014] In Fig. 1, the wheel loader 100 is made up of a front frame 102 disposed at the front (left direction in Fig. 1) and a rear frame 103 disposed at the rear (right direction in Fig. 1) that constitute the vehicle body. The front frame 102 and the rear frame 103 are connected by a center pin 109 so as to be rotatable in the left-right direction.

[0015] A pair of left and right lift arms 108, the base ends of which are connected to the front frame 102 so as to be vertically rotatable relative to the front frame 102, a bucket 107 connected to the tip of the lift arm 108 so as to be vertically rotatable, and a pair of left and right wheels (front wheels 11a, 11b) are attached to the front frame 102. The lift arm 108 and bucket 107, together with the lift cylinder 52, bucket cylinder 51, etc., constitute the front hydraulic working device 5 that performs work of excavating earth and sand, etc.

[0016] The lift arm 108 and the front frame 102 are connected by a lift cylinder 52. When the lift cylinder 52 extends or retracts, the lift arm 108 rotates vertically together with the bucket 107.

[0017] The bucket 107 and the lift arm 108 are connected by a bucket cylinder 51. The bucket cylinder 51 extends and retracts, thereby causing the bucket 107 to rotate in the vertical direction.

[0018] A cab 104 in which an operator sits and a pair of left and right wheels (rear wheels 12a, 12b) are attached to the rear frame 103. A forward / reverse changeover switch 104a is disposed in the cab 104 to change the traveling direction of the wheel loader between forward and reverse.

[0019] The front frame 102 and the rear frame 103 are connected by a pair of left and right steering cylinders 53. By extending one of the pair of left and right steering cylinders 53 while simultaneously retracting the other, the front frame 2 and the rear frame 3 are bent in the left-right direction around a center pin 109.

[0020] FIG. 2 is a diagram showing a schematic configuration of an electric drive system for a wheel loader.

[0021] In FIG. 2 , the electric drive system is connected to the output shaft of an engine 1 (for example, a diesel engine) arranged on the rear frame 103 or the like and is generally composed of a generator 6 (motor generator: MG) driven by the engine 1, a generator inverter 7 that controls the operation of the generator 6, a travel motor 9 that uses power from the generator 6 to rotate and drive a propeller shaft 8, related to the travel drive of the wheel loader 100, as an output shaft, a travel motor inverter 10 that controls the operation of the travel motor 9 by controlling the power supplied from the generator 6 to the travel motor 9 via the generator inverter 7, an external resistor 14 for consuming regenerative power from the travel motor 9, and a vehicle control device 15 that controls the overall operation of the electric drive system.

[0022] A hydraulic pump 4 driven by the engine 1 is connected to the output shaft of the engine 1. The flow rate and direction of the pressure oil discharged from the hydraulic pump 4 are controlled by a control valve 50, thereby controlling the extension and retraction of each of a bucket cylinder 51, a lift cylinder 52, and a steering cylinder 53.

[0023] The propeller shaft 8, which is rotated by the traveling motor 9, is attached to the front wheels 11a, 11b via a center joint 13 (CJ), a differential gear 11e (Dif), and gears 11c, 11d, and to the rear wheels 12a, 12b via a differential gear 12e (Dif) and gears 12c, 12d (G).

[0024] In the electric drive system of this embodiment, the engine 1 drives the generator 6, and the power generated by the generator 6 is used as input to generate torque in the travel motor 9, which is transmitted to the wheels 11a, 11b, 12a, and 12b via the propeller shaft 8 and the like to rotate and drive the wheel loader 100. At this time, the voltage (i.e. DC bus voltage) of the DC coupling portion electrically connecting between the generator inverter 7 that controls the generator 6 and the travel motor inverter 10 that controls the travel motor 9 is controlled.

[0025] Here, the basic operation of the wheel loader 100 at a work site will be described.

[0026] FIG. 3 is a diagram showing an example of the operation of the wheel loader.

[0027] As shown in FIG. 3, the basic operation of the wheel loader is an operation called V-shaped excavation work. In V-shaped excavation work, the wheel loader 100 first advances toward an excavation target such as a pile of earth and sand, and loads the transported material such as earth and sand into the bucket 107 by thrusting the hydraulic working device 5 into the excavation target 200. After that, it moves backward to return to the original position, and moves forward toward a transport vehicle such as a dump truck 300 while operating the steering wheel and lifting the bucket 107 of the hydraulic working device 5. Then, after loading the transported material into the transport vehicle (discharging the earth from the bucket 107), it moves backward again to return to the original position. In this way, the basic operation of the wheel loader 100 is called V-shaped excavation work because this operation is repeated while tracing a V-shaped trajectory, and this operation occupies the majority of the working time of the wheel loader 100. The operation of suddenly braking, switching the traveling direction to the opposite direction, and suddenly starting when the wheel loader 100 moves between the excavation position and the loading position is called so-called modulated operation.

[0028] One of the basic performance indexes of the wheel loader 100 in V-shaped excavation work is the work efficiency [t / h] (t represents the weight of the transported material, and h represents the work time). In order to improve the work efficiency [t / h] in V-shaped excavation work, it is possible to increase the amount [t] of earth and sand loaded into the bucket 107, or to improve the traveling performance during work to shorten the work time [t].

[0029] In this embodiment, the working efficiency [t / h] is improved by shortening the working time [t]. The working time [t] of the V-shaped excavation work of the wheel loader 100 can be shortened, for example, by performing an operation (modulation operation) of shifting from reverse to forward suddenly. Specifically, when the wheel loader 100 is in a state where it is applying sudden braking from a reverse state (for example, a full brake state in a reverse state), the forward / reverse selector switch 104a switches the forward direction indication signal (FNR signal) to the forward direction (i.e., the forward / reverse selector switch 104a is switched to forward) and transitions to a sudden start in the forward direction, thereby shortening the working time [t]. Hereinafter, such control is referred to as working efficiency improvement control.

[0030] Another basic performance index of the wheel loader 100 during V-shaped excavation work is the ratio of the weight of the transported load to the amount of fuel consumed (so-called fuel efficiency). In order to improve fuel efficiency during V-shaped excavation work, it is possible to consider efficiently generating power using the generator 6. Specifically, fuel efficiency can be improved by not generating power using the generator 6 during braking, when regenerative power is generated by the travel motor 9 and consumed by the external resistor 14. Hereinafter, this type of control will be referred to as fuel efficiency improvement control.

[0031] In this embodiment, a control ON / OFF switch 104b that switches between enabling and disabling work efficiency improvement control is provided inside the cab 104, and when the control ON / OFF switch 104b is ON, work efficiency improvement control is performed, and when it is OFF, fuel efficiency improvement control is performed. In other words, when it is desired to prioritize the work efficiency of work performed by the wheel loader 100, the operator turns the control ON / OFF switch 104b ON and performs the work. Also, when the work performed by the wheel loader 100 is time-permissible, the operator turns the control ON / OFF switch 104b OFF in consideration of fuel efficiency and performs the work.

[0032] Fig. 4 is a diagram showing the flow of power in fuel efficiency improvement control, and shows the flow of regenerative power during braking in modulated operation for V-shaped excavation work. Note that in Fig. 4, some components are added or omitted for simplicity of explanation.

[0033] As shown in FIG. 4, in the fuel economy improvement control, during braking in the modulated operation, a braking force is applied to the traveling motor 9 from the wheel side, and the traveling motor 9 generates electricity due to the braking force. The generated power (regenerated power) from the traveling motor 9 is consumed by the external resistor 14 and consumed by rotating and driving the generator 6 (by motoring). At this time, the output shaft of the engine 1 is rotated by the rotation of the generator 6, so the rotation of the output shaft of the engine 1 increases, and as a result, the engine 1 suspends fuel injection during that time. In the case of the modulated operation, that is, when transitioning to a sudden start after a sudden braking, since the engine 1 suspends fuel injection, a large engine output cannot be immediately output, and a sudden start cannot be made. In other words, since the effect of shortening the time required for the modulated operation is not obtained, an improvement in the working efficiency [t / h] is not expected, but a deterioration in fuel economy is expected to be suppressed.

[0034] Fig. 5 is a diagram showing a schematic diagram of the flow of power in the work efficiency improvement control, and shows the flow of regenerative power during braking in the modulated operation of the V-shaped excavation work. Note that in Fig. 5, some components are added or omitted for the sake of simplicity of explanation.

[0035] As shown in Fig. 5, in the work efficiency improvement control, when braking in modulated operation, the output of engine 1 is increased in advance so that the large output of engine 1 required for a sudden start after sudden braking can be immediately output. In other words, by suppressing the delay in the output of engine 1, it becomes possible to perform a sudden start in modulated operation, so that the effect of shortening the time required for modulated operation, that is, improvement of work efficiency [t / h] can be expected.

[0036] Here, the control for improving the working efficiency of the electric drive system will be described in detail.

[0037] FIG. 6 is a functional block diagram showing the processing contents in the controller function unit of the generator inverter.

[0038] In FIG. 6, the controller function unit of the generator inverter 7 includes a voltage control unit 71 that calculates a command value so as to reduce the difference between the DC bus voltage command and the DC bus voltage, a conversion gain calculation unit 72 that calculates a command value corresponding to an MG torque command, a command value selection unit 73 that selects the command value of either the voltage control unit 71 or the conversion gain calculation unit 72 in response to an MG mode control command from the vehicle control device 15, a current limiting unit 74 that specifies an upper limit of the command value selected by the command value selection unit 73, and a current control unit 75 that calculates and outputs a command value (MG inverter voltage command) that controls the operation of the generator inverter 7 so as to reduce the difference between the MG current command via the current limiting unit 74 and the MG current.

[0039] As shown in FIG. 6, when the MG control mode command indicates voltage control (described later), the generator inverter 7 selects a command value from a voltage control unit 71 in a command value selection unit 73, and performs feedback control so that the voltage of the DC bus electrically connecting the generator inverter 7 and the traction motor inverter 10 becomes the desired voltage (the voltage indicated by the DC bus voltage command).

[0040] In addition, when the MG control mode command indicates torque control (described later), the generator inverter 7 selects a command value from the conversion gain calculation unit 72 in a command value selection unit 73, and controls the output torque of the generator 6 to be the value indicated by the MG torque command from the vehicle control device 15.

[0041] FIG. 7 is a functional block diagram showing functional units related to control of the electric power drive system of the vehicle control device.

[0042] 7, the vehicle control device 15 comprises a modulation determination unit 151 which determines whether or not the wheel loader 100 is performing a modulated operation based on the vehicle speed obtained via CAN communication or the like and a signal from the forward / reverse switch 104a, an MG control mode switching unit 152 which outputs an MG control mode command instructing either voltage control or torque control to the generator inverter 7 depending on the determination result of the modulation determination unit 151, a power generation amount calculation unit 153 which calculates a target value for the amount of power generation in the generator 6 based on the fuel injection upper limit value and engine torque obtained via CAN communication or the like, and an MG torque calculation unit 154 which calculates an MG torque command based on the target value of the amount of power generation calculated by the power generation amount calculation unit 153 and the engine speed obtained via the power generation amount calculation unit CAN communication or the like, and outputs the MG torque command to the generator inverter 7.

[0043] FIG. 8 is a flowchart showing the process contents of the modulation determination unit and the MG control mode switching unit of the vehicle control device.

[0044] As shown in FIG. 8, the vehicle control device 15 first inputs a vehicle speed signal from CAN communication or the like to the modulating determination unit 151, and also inputs a signal from the forward / reverse changeover switch 104a (step S101).

[0045] Next, it is determined whether the vehicle speed and the traveling direction indicated by the signal from the forward / reverse switch 104a have the same sign, that is, whether the current traveling direction of the wheel loader 100 and the traveling direction indicated by the operator using the forward / reverse switch 104a are the same (step S102).

[0046] If the determination result in step S102 is YES, that is, if the direction indicated by the forward / reverse switch 104a matches the traveling direction of the wheel loader 100 (unmodulated operation), an MG control mode command instructing voltage control of the generator 6 is generated and output to the generator inverter 7 (step S103), and the process ends.

[0047] Furthermore, if the determination result in step S102 is NO, that is, if the direction indicated by the forward / reverse switch 104a differs from the traveling direction of the wheel loader 100 (if there is a possibility of modulated operation), it is determined whether or not the vehicle speed is equal to or greater than a predetermined threshold value (step S104).

[0048] If the determination result in step S104 is NO, that is, if the vehicle speed is lower than the threshold value, it is determined that a vehicle is skidding down a slope (non-modulated operation) and an MG control mode command instructing voltage control of the generator 6 is generated and output to the generator inverter 7 (step S103), and the process ends.

[0049] Also, if the determination result in step S104 is YES, that is, if the vehicle speed is equal to or higher than the threshold value (if the vehicle is in non-modulated operation), an MG control mode command instructing torque control of the generator 6 is generated and output to the generator inverter 7 (step S103), and the processing ends.

[0050] Thus, in this embodiment, in parallel with the process of determining the MG control mode command based on detection of modulated operation, the MG torque command is calculated when the generator 6 is under torque control. Calculation of the MG torque command makes it possible to optimize the amount of power generated by the generator 6 during regenerative operation in modulated operation of the wheel loader 100, enabling a highly responsive and smooth start-up operation without reducing the rotation speed of the engine 1 even during subsequent sudden starts.

[0051] Next, the processing contents of the power generation amount calculation unit 153 will be described in detail.

[0052] FIG. 9 is a functional block diagram showing the processing contents in the power generation amount calculation unit of the vehicle control device.

[0053] As shown in FIG. 9, the power generation amount calculation unit 153 determines the power generation amount of the generator 6 based on the fuel injection state of the engine 1 (the output ratio of the engine torque). The power generation amount calculation unit 153 first inputs the fuel injection upper limit value and the engine torque (more precisely, a value corresponding to the fuel injection amount obtained from a table determined by measuring in advance the relationship between the engine torque and the fuel injection amount for the engine 1) contained in the CAN signal from the engine ECU (not shown) and determines the power generation amount. At this time, the difference between the fuel injection upper limit value and the engine torque (both are expressed in units of [%], for example, indicating a ratio to a rated value) is calculated by the calculation unit 153a, and the power generation amount is determined by the determination unit 153b according to the magnitude of the difference. For example, when the difference between the fuel injection upper limit value and the engine torque is small, it indicates that the output of the engine 1 is close to the upper limit, and if an attempt is made to output more than that, it is considered that the rotation speed of the engine 1 will decrease. On the other hand, when the difference between the fuel injection upper limit value and the engine torque is large, it indicates that the engine output has a large margin with respect to the upper limit, and it is considered that it takes some time to increase the output. Therefore, when a relatively large output is required in the modulated operation of the wheel loader 100, that is, when transitioning from a sudden braking state to a sudden start, it is effective to maintain the difference between the fuel injection upper limit value and the engine torque at an appropriate value.

[0054] The power generation amount calculation unit 153 inputs the fuel injection upper limit value and engine torque, which are state quantities output from the engine ECU (not shown) by CAN communication, and calculates the difference in the calculation unit 153a. The determination unit 153b determines a provisional value of the power generation amount command so as to increase or decrease the power generation amount of the generator 6 according to the calculated difference. For example, if the difference is greater than a threshold value X1 (e.g., 20[%]), the provisional value of the power generation amount command is increased by a preset appropriate value (e.g., +α[kW]) so as to increase the power generation amount. If the difference is smaller than a threshold value X2 (e.g., 10[%]), the output of the engine 1 is determined to be close to the upper limit, and the power generation amount of the generator 6 is reduced by an appropriate value so as to reduce it further. If the difference between the fuel injection upper limit value and the engine torque is equal to or less than the threshold value X1 and equal to or greater than the threshold value X2, the power generation amount is determined so as to maintain the current output.

[0055] The threshold values ​​X1 and X2 can be adjusted arbitrarily according to the acceleration of the vehicle. For example, the threshold value X1 can be set to a value that results in a relatively large difference between the fuel injection upper limit value and the engine torque (a difference that slows down the start of the vehicle when the vehicle starts moving), while the threshold value X2 can be set to a relatively small value that results in a relatively small difference between the fuel injection upper limit value and the engine torque (a difference that reduces the engine speed when the vehicle starts moving). In this embodiment, the power generation amount of the generator 6 is increased or decreased by αkW (an arbitrary value) in increments. This is to suppress fluctuations in the speed of the engine 1 caused by a sudden change in load.

[0056] The power generated by the generator 6 (generated power) is consumed by the external resistor 14 together with the regenerated power from the traveling motor 9. Therefore, as shown in FIG. 12, it is necessary to limit the total value of the generated power from the generator 6 and the regenerated power from the traveling motor 9 so as not to exceed the capacity (rated) of the external resistor 14. When the wheel loader 100 is braking, limiting the regenerative power of the traveling motor 9 may reduce the vehicle's motion (braking) performance, so maintaining the regenerative power of the traveling motor 9 is given priority and the generated power of the generator 6 is limited. Note that, since the regenerative power of the traveling motor 9 decreases as the vehicle speed decreases during regeneration, the generated power of the generator 6 may be increased accordingly.

[0057] The effects of the present embodiment configured as above will be described with reference to the drawings.

[0058] Fig. 10 is a diagram showing the state quantities of each part during modulation operation in the prior art shown as a comparative example, while Fig. 11 is a diagram showing the state quantities of each part during modulation operation in this embodiment.

[0059] As shown in FIG. 11, in the comparative example, regenerative power is generated from the traction motor 9 during deceleration ((a) in the figure), and the regenerative power is consumed (motoring) in the generator 6, so that the MG power becomes positive, the rotation speed of the engine 1 increases, and the engine 1 stops fuel injection. In other words, the engine torque becomes zero. After that, at the start of acceleration ((b) in the figure), there is a sudden need for generated power from the generator 6, and a load is applied to the engine 1, so that the rotation speed of the engine 1 decreases, and thereafter, the MG power does not increase smoothly ((c) in the figure), and as a result, the start of the vehicle is delayed.

[0060] In contrast to this, in this embodiment, as shown in Fig. 13, regenerative power is generated from the travel motor 9 during deceleration ((a) in the figure), but the generator 6 is not motored and power generation is forcibly started in the generator 6 as well, so that the MG power gradually increases on the negative side (power generation side). As a result, the engine 1 continues to inject fuel, increasing engine torque, and when the wheel loader transitions to a forward movement, output can be continued smoothly without a sudden change in output, that is, without an unintended drop in the rotation speed of the engine 1. As a result, it is possible to handle a sudden start-up operation following sudden braking of the vehicle.

[0061] Thus, in this embodiment, when modulating operation of the wheel loader 100 is detected, by having the generator 6 generate power during braking (regeneration) with an amount of power generation that takes into account the state of the engine 1, it becomes possible to smoothly output the power required for the next sudden start from the engine 1. In other words, by adjusting the generated power during vehicle braking in accordance with the state of the engine in modulating operation, it is possible to supply power from the engine more smoothly when starting off after braking.

[0062] <Additional Notes> The present invention is not limited to the above-described embodiments, and includes various modifications and combinations within the scope of the gist of the present invention. The present invention is not limited to those having all the configurations described in the above-described embodiments, and includes those in which some of the configurations are deleted. The above-described configurations, functions, etc. may be realized by designing some or all of them as an integrated circuit, for example. The above-described configurations, functions, etc. may be realized by software, in which a processor interprets and executes a program that realizes each function. [Explanation of symbols]

[0063] 1...engine, 2...front frame, 3...rear frame, 4...hydraulic pump, 5...hydraulic working device, 6...generator, 7...generator inverter, 8...propeller shaft, 9...travel motor, 10...travel motor inverter, 11a, 11b...front wheels, 11c, 11d...gear, 11e...differential gear, 12a, 12b...rear wheels, 12c, 12d...gear, 12e...differential gear, 13...center joint, 14...external resistor, 15...vehicle control device, 50...control valve, 51...bucket cylinder, 52...lift cylinder, 53...steering cylinder, 71...electric pressure control unit, 72...conversion gain calculation unit, 73...command value selection unit, 74...current limiting unit, 75...current control unit, 100...wheel loader, 102...front frame, 103...rear frame, 104...cab, 104a...forward / reverse switch, 104a...forward / reverse switch, 104b...control ON / OFF switch, 107...bucket, 108...lift arm, 109...center pin, 151...modulate determination unit, 152...MG control mode switching unit, 153...power generation amount calculation unit, 153a...calculation unit, 153b...determination unit, 154...MG torque calculation unit, 200...excavation object, 300...dump truck

Claims

1. A generator driven by an engine, A traveling motor that drives the vehicle body to travel by the power from the generator, A forward / reverse switching switch that switches the traveling direction of the vehicle body between forward and reverse, An external resistor that consumes the regenerative power from the traveling motor, In a work vehicle equipped with a vehicle control device, The vehicle control device, When there is a difference between the traveling direction of the vehicle body indicated by the forward / reverse switching switch and the traveling direction of the vehicle body indicated by the rotational direction of the traveling motor, A work vehicle characterized in that it controls to increase or decrease the generated power of the generator based on the difference between the fuel injection upper limit value and the fuel injection amount preset for the engine.

2. In the work vehicle according to Claim 1, The vehicle control device, When there is a difference between the traveling direction of the vehicle body indicated by the forward / reverse switching switch and the traveling direction of the vehicle body indicated by the rotational direction of the traveling motor, When the difference between the fuel injection upper limit value and the fuel injection amount preset for the engine is greater than a first threshold value, it controls to increase the generated power of the generator, A work vehicle characterized in that when the difference between the fuel injection upper limit value and the fuel injection amount is smaller than a second threshold value preset as a value smaller than the first threshold value, it controls the generator to decrease the generated power of the generator.

3. In the work vehicle according to Claim 1, The vehicle control device, A work vehicle characterized in that when there is a difference between the traveling direction of the vehicle body indicated by the forward / reverse switching switch and the traveling direction of the vehicle body indicated by the rotational direction of the traveling motor, it switches the control of the generator from voltage control to torque control.

4. In the work vehicle according to Claim 1, The vehicle control device, A work vehicle characterized in that it limits the generated power of the generator so that the sum of the generated power of the generator and the regenerative power from the traveling motor does not exceed the rated power of the external resistor.

5. In the work vehicle according to Claim 1, Further provided with a control ON / OFF switch, The vehicle control device, When the control ON / OFF switch is in the OFF state, when there is a difference between the traveling direction of the vehicle body indicated by the forward / reverse switching switch and the traveling direction of the vehicle body indicated by the rotational direction of the traveling motor, it does not generate electricity by the generator.

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