Work vehicles

Abstract

To improve acceleration performance after end of modulation operation while suppressing fuel consumption during the modulation operation.SOLUTION: A work vehicle includes: a generator motor connected to an engine; a travel driving device which can drive a wheel by power generated by the generator motor and enables regenerative brake of the wheel; an engine rotation speed sensor for detecting rotation speed of the engine; and a control device for controlling a fuel injection amount so that the rotation speed of the engine detected by the engine rotation speed sensor coincides with first target rotation speed. The control device reduces the fuel injection amount of the engine, when modulation operation of switching a travel direction of a vehicle body by the regenerative brake is performed, and the rotation speed of the engine increases than the first target rotation speed, and increases the fuel injection amount of the engine, when the rotation speed of the engine is less than predetermined second target rotation speed higher than the first target rotation speed.SELECTED DRAWING: Figure 9

Description

[Technical Field]

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

[0002] A wheel loader or other work vehicle is known that includes an engine, a generator motor mechanically connected to the engine, and a travel drive device that can drive wheels with electric power generated by the generator motor and that can perform regenerative braking on the wheels. The engine is equipped with a fuel injection device. The fuel injection device adjusts the amount of fuel injected, thereby controlling the engine rotation speed and output torque and generating power.

[0003] The higher the engine's rotational speed, the higher the upper limit of the power it can generate. On the other hand, the higher the engine rotational speed, the worse the fuel efficiency. Therefore, during work requiring a large amount of engine power, the engine rotational speed is controlled to be high in response to operation by the operator, and during standby when the required engine power is low, the engine rotational speed is controlled to be low.

[0004] In a basic transport operation of a work vehicle such as a wheel loader, the vehicle excavates an excavation target such as soil and sand, scoops it into a bucket, moves backward a certain distance to move away from the excavation target, then moves forward toward a loading target such as a dump truck and loads the soil and sand into the loading target. To perform this transport operation quickly, the operator switches the forward / reverse switch from reverse to forward while continuing to depress the accelerator pedal. This causes the work vehicle to perform a modulating operation that quickly changes direction from reverse to forward.

[0005] In the case of a work vehicle equipped with a travel drive unit capable of regenerative braking of the wheels, when regenerative braking is performed by modulating operation, regenerative energy is generated and regenerated into the engine. When this action causes the actual engine rotation speed to become higher than the target engine rotation speed, the fuel injection device reduces the amount of fuel injection. When regenerative braking ends and the work vehicle begins to move forward, the actual engine rotation speed becomes lower than the target engine rotation speed. When the actual engine rotation speed becomes lower than the target engine rotation speed, the fuel injection device increases the amount of fuel injection.

[0006] In this case, the fuel injection amount does not increase until the actual engine speed becomes lower than the target engine speed, and the actual engine speed falls far below the target engine speed due to the response delays of the fuel injection device and the engine, resulting in poor acceleration performance after the end of the modulating operation.

[0007] Patent Document 1 discloses a work vehicle in which, in order to improve acceleration performance after the end of the modulating operation, the regenerative energy generated during regenerative braking is consumed in a brake resistor via a chopper circuit, thereby allowing fuel injection to continue even during the modulating operation. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 2019-38365 Summary of the Invention [Problem to be solved by the invention]

[0009] However, in the technology described in Patent Document 1, fuel injection continues even during the modulating operation, so there is room for improvement in terms of fuel economy.

[0010] The present invention has been made to solve these technical problems, and aims to provide a work vehicle that can reduce fuel consumption during modulating operation while improving acceleration performance after modulating operation ends. [Means for solving the problem]

[0011] A work vehicle according to one aspect of the present invention comprises a vehicle body, wheels provided on the vehicle body, an engine mounted on the vehicle body, a generator motor mechanically connected to the engine, a travel drive device capable of driving the wheels with electric power generated by the generator motor and capable of regenerative braking of the wheels, an engine rotation speed sensor that detects the rotation speed of the engine, and a control device that controls the amount of fuel injected into the engine so that the engine rotation speed detected by the engine rotation speed sensor matches a first target rotation speed. ,before Modulation action to change the direction of travel of the vehicle By using this regenerative braking, When the rotation speed of the engine increases above the first target rotation speed, a fuel injection amount of the engine is reduced; When the increase in the rotation speed of the engine due to regenerative braking has ended and the rotation speed of the engine is decreasing, When the rotation speed of the engine becomes lower than a predetermined second target rotation speed that is higher than the first target rotation speed, the amount of fuel injected into the engine is increased. [Effects of the Invention]

[0012] According to the present invention, it is possible to provide a work vehicle that can reduce fuel consumption during modulating operation and improve acceleration performance after modulating operation ends. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a side view of a wheel loader. [Figure 2] FIG. 2 is a system configuration diagram of a wheel loader. [Figure 3] FIG. 3 is a diagram for explaining the basic transport operation of the wheel loader. [Figure 4] FIG. 4 is a functional block diagram of the main controller according to the first embodiment. [Figure 5] FIG. 5 is a block diagram illustrating a method for calculating a target engine rotation speed by the target speed calculation unit. [Figure 6] FIG. 6 is a diagram showing an example of a correlation map showing the relationship between the rotation speed deviation of the engine and the fuel injection amount. [Figure 7] FIG. 7 is a diagram showing an example of a correlation map showing the relationship between the amount of negative overshoot of the actual engine rotation speed and the target correction value. [Figure 8] FIG. 8 is a flowchart of engine control executed by the main controller according to the first embodiment. [Figure 9] FIG. 9 is a diagram showing time series changes in each parameter of the wheel loader (accelerator operation amount, forward / reverse switch operation position, command rotation speed, actual engine rotation speed, fuel injection amount, engine acceleration power, and vehicle speed). [Figure 10] FIG. 10 is a functional block diagram of a main controller according to the second embodiment. [Figure 11] FIG. 11 is a functional block diagram of a main controller according to the third embodiment. [Figure 12] FIG. 12 is a functional block diagram of a main controller according to the fourth embodiment. [Figure 13] FIG. 13 is a diagram showing an example of a correlation map showing the relationship between the accelerator operation amount and the estimated negative overshoot value. [Figure 14] FIG. 14 is a flowchart of engine control executed by the main controller according to the fourth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0014] An embodiment of the present invention will now be described with reference to the drawings. In the description of the drawings, the same elements are given the same reference numerals, and duplicated description will be omitted. In this embodiment, an example will be described in which the work vehicle is an electrically driven wheel loader. Note that in this embodiment, a wheel loader equipped with a hybrid system using an engine and a generator motor as a drive source will be described as an example, but the present invention can be applied to various work vehicles equipped with an engine and a traveling drive device capable of regenerative braking. In the following description, the up / down, left / right, and front / rear directions and positions are based on the normal use state of the work vehicle, i.e., a state in which each wheel is in contact with the ground.

[0015] First Embodiment - Wheel loader configuration - A wheel loader 1 according to a first embodiment of the present invention will be described with reference to Figures 1 to 9. Figure 1 is a side view of the wheel loader 1. As shown in Figure 1, the wheel loader 1 comprises a vehicle body 8 on which an electric travel drive unit 45 is mounted, and an articulated working device 6 attached to the front of the vehicle body 8. The vehicle body 8 is of an articulated steering type (vehicle body articulation type), and has a front vehicle body 8A, a rear vehicle body 8B, and a center joint 10 that connects the front vehicle body 8A and the rear vehicle body 8B.

[0016] A working implement 6 is attached to the front body 8A. A driver's cab 12 and an engine room 16 are arranged in the rear body 8B. The driver's cab 12 is provided with a seat for an operator and operating devices operated by the operator. The engine room 16 is equipped with an engine 20 (see FIG. 2), hydraulic pumps 30A, 30B, 30C (see FIG. 2) driven by the engine 20, and hydraulic equipment such as valves.

[0017] The working device 6 has a lift arm (hereinafter simply referred to as arm) 2 attached to the front vehicle body 8A so as to be freely rotatable in the vertical direction, a hydraulic cylinder (hereinafter also referred to as arm cylinder) 4 that drives the arm 2, a bucket 3 attached to the tip of the arm 2 so as to be freely rotatable in the vertical direction, and a hydraulic cylinder (hereinafter also referred to as bucket cylinder) 5 that drives the bucket 3. The arm 2, which is the member to be driven, is moved in accordance with the extension and retraction movement of the arm cylinder 4. The bucket 3, which is also the member to be driven, is moved in accordance with the extension and retraction movement of the bucket cylinder 5. Note that one arm 2 and one arm cylinder 4 are provided on each side of the front vehicle body 8A. In this embodiment, a Z-link (bell crank) type link mechanism is used as the link mechanism for operating the bucket 3.

[0018] The wheel loader 1 is equipped with a travel drive device 45 that drives the wheels 7 provided on the vehicle body 8. The travel drive device 45 has a travel motor 43 and a power transmission device that transmits power from the travel motor 43 to the wheels 7. The power transmission device is configured to include an axle, a differential device, a propeller shaft, etc. The wheels 7 include front wheels 7A attached to the front vehicle body 8A and rear wheels 7B attached to the rear vehicle body 8B. Power from the travel motor 43 is transmitted to at least one of the front wheels 7A and the rear wheels 7B.

[0019] The traveling motor 43 is an electric motor that drives the wheels 7. The traveling motor 43 is driven to rotate by electric power generated by a generator motor that is rotated by the power of the engine 20.

[0020] The wheel loader 1 is steered by a steering device having a pair of left and right hydraulic cylinders (hereinafter also referred to as steering cylinders) 15 provided to connect the front vehicle body 8A and the rear vehicle body 8B.

[0021] Fig. 2 is a system configuration diagram of the wheel loader 1. As shown in Fig. 2, the wheel loader 1 includes an engine 20, a fuel injection device 23 that supplies fuel to the engine 20, a generator motor 40 mechanically connected to the engine 20, hydraulic pumps 30A, 30B, and 30C mechanically connected to the engine 20 and the generator motor 40, a working device 6 driven by hydraulic oil discharged from the hydraulic pump 30A, a front control unit 31 that controls the operation of the working device 6, a braking device 21 driven by hydraulic oil discharged from the hydraulic pump 30B, a brake control unit 32 that controls the operation of the braking device 21, a steering device 22 driven by hydraulic oil discharged from the hydraulic pump 30C, a steering control unit 33 that controls the steering device 22, and a traveling drive device 45 that can drive the wheels 7 with electric power generated by the generator motor 40 and that is capable of regenerative braking of the wheels 7.

[0022] The working device 6 and the traveling drive device 45 are driven independently of each other by the power of the engine 20. The engine 20, which is a prime mover, is configured by an internal combustion engine such as a diesel engine. The generator motor 40 is rotated by the torque output from the engine 20 and functions as a generator that generates electricity.

[0023] The hydraulic pumps 30A, 30B, and 30C are driven by the torque output by the engine 20 to discharge hydraulic oil. When the generator motor 40 functions as an electric motor, the hydraulic pumps 30A, 30B, and 30C are driven by the torque output by the engine 20 and the generator motor 40.

[0024] The hydraulic cylinders 4, 5, 15, 17, and 18 are expanded and contracted by hydraulic oil (pressurized oil) discharged from hydraulic pumps 30A, 30B, and 30C, which are rotated by torque output by the engine 20.

[0025] The front control unit 31 controls the pressure, flow rate, and direction of the hydraulic oil supplied from the hydraulic pump 30A to the arm cylinder 4 and the bucket cylinder 5. This controls the extension and retraction operations of the arm cylinder 4 and the bucket cylinder 5. The brake control unit 32 controls the pressure, flow rate, and direction of the hydraulic oil supplied from the hydraulic pump 30B to the brake cylinder 17 and the parking brake cylinder 18. This controls the extension and retraction operations of the brake cylinder 17 and the parking brake cylinder 18. The steering control unit 33 controls the pressure, flow rate, and direction of the hydraulic oil supplied from the hydraulic pump 30C to the steering cylinder 15. This controls the extension and retraction operation of the steering cylinder 15.

[0026] The wheel loader 1 comprises a main controller 100 that controls the entire vehicle, and an engine controller 120 that controls the fuel injector 23 based on an engine rotation speed command from the main controller 100. The wheel loader 1 also comprises the fuel injector 23 that controls the fuel injection amount based on a fuel injection amount command from the engine controller 120, a generator motor inverter (hereinafter referred to as the power generation inverter) 41 that controls the generator motor 40 based on a power generation voltage command input from the main controller 100, a traveling motor inverter (hereinafter referred to as the traveling inverter) 42 that controls the torque of the traveling motor 43 based on a traveling drive torque command input from the main controller 100, and various operating devices (51 to 57) that are provided in the cab 12 and are operated by an operator.

[0027] Within the cab 12 are provided a forward / reverse switch 51 which is a forward / reverse switching device that switches the traveling direction of the vehicle body 8, an arm operating device 52 that operates the arm cylinder 4 (arm 2) of the working device 6, a bucket operating device 53 that operates the bucket cylinder 5 (bucket 3) of the working device 6, an accelerator operating device 56 that operates the traveling drive device 45, a brake operating device 57 that operates the brake cylinder 17, a parking brake operating device 54 that operates the parking brake cylinder 18, and a steering operating device 55 that operates the pair of left and right steering cylinders 15. The forward / reverse switch 51 has a forward position (F), a standby position (N), and a reverse position (R) as its operating positions.

[0028] The arm operating device 52 includes an arm operating lever and an arm operation amount sensor 52a that detects the operation amount of the arm operating lever (hereinafter also referred to as the arm operation amount). The bucket operating device 53 includes a bucket operating lever and a bucket operation amount sensor 53a that detects the operation amount of the bucket operating lever (hereinafter also referred to as the bucket operation amount). The accelerator operating device 56 includes an accelerator pedal and an accelerator operation amount sensor 56a that detects the operation amount of the accelerator pedal (hereinafter also referred to as the accelerator operation amount). The brake operating device 57 includes a brake pedal and a brake operation amount sensor 57a that detects the operation amount of the brake pedal (hereinafter also referred to as the brake operation amount). The steering operating device 55 includes a steering wheel and a steering operation amount sensor 55a that detects the operation amount of the steering wheel (hereinafter also referred to as the steering operation amount). The arm operation amount sensor 52a, the bucket operation amount sensor 53a, the accelerator operation amount sensor 56a, the brake operation amount sensor 57a, and the steering operation amount sensor 55a are, for example, potentiometers that output a voltage according to the operation position of an operating member (operation lever or pedal) to the main controller 100.

[0029] -Wheel loader control device- The control device 11, which controls each part of the wheel loader 1, includes a main controller 100 and an engine controller 120. The main controller 100 and the engine controller 120 exchange data with each other. The main controller 100 is made up of a microcomputer that includes a CPU (Central Processing Unit) 101 as a processing device (operating circuit), a ROM (Read Only Memory) 102 and RAM (Random Access Memory) 103 as storage devices, an input interface 104, an output interface 105, and other peripheral circuits. Like the main controller 100, the engine controller 120 is also made up of a microcomputer that includes a processing device, storage device, input / output interface, etc. The main controller 100 and the engine controller 120 may each be made up of a single microcomputer, or may be made up of multiple microcomputers. The functions of the main controller 100 and the engine controller 120 may also be realized by a single computer.

[0030] The ROM 102 of the main controller 100 is a non-volatile memory such as an EEPROM, and stores programs capable of executing various calculations. In other words, the ROM 102 of the main controller 100 is a storage medium from which the programs that realize the functions of this embodiment can be read. The RAM 103 is a volatile memory, and serves as a work memory that directly inputs and outputs data to and from the CPU 101. The RAM 103 temporarily stores necessary data while the CPU 101 is executing the programs. The main controller 100 may further include a storage device such as a flash memory or a hard disk drive.

[0031] The CPU 101 is an arithmetic unit that loads a program stored in the ROM 102 into the RAM 103 and executes the program, and performs predetermined arithmetic processing on signals received from the input interface 104, the ROM 102, and the RAM 103 in accordance with the program.

[0032] Operation signals from the various operation devices (51 to 57) and sensor signals from the various sensors are input to the input interface 104. The input interface 104 converts the input signals into data that can be calculated by the CPU 101. The output interface 105 generates output signals according to the calculation results of the CPU 101, and outputs the signals to the front control unit 31, the brake control unit 32, the steering control unit 33, the power generation inverter 41, the traveling inverter 42, the engine controller 120, etc.

[0033] The main controller 100 comprehensively controls the front control unit 31, the brake control unit 32, the steering control unit 33, the power generation inverter 41, the driving inverter 42, and the engine controller 120 based on operation signals input from various operating devices and sensor signals input from various other sensors.

[0034] The operation signals input to the main controller 100 include the accelerator operation amount detected by the accelerator operation amount sensor 56a, the brake operation amount detected by the brake operation amount sensor 57a, the arm operation amount detected by the arm operation amount sensor 52a, the bucket operation amount detected by the bucket operation amount sensor 53a, the steering operation amount detected by the steering operation amount sensor 55a, and a signal output from the forward / reverse switch 51 indicating the operation position of the forward / reverse switch 51.

[0035] The sensor signals input to the main controller 100 include a signal representing the angle detected by an arm relative angle sensor 62 provided on the connecting shaft connecting the vehicle body 8 and the arm 2, and a signal representing the angle detected by a bucket relative angle sensor 63 provided on the connecting shaft connecting the arm 2 and the bucket 3. The arm relative angle sensor 62 is a potentiometer that detects the relative angle (tilt angle) of the arm 2 with respect to the vehicle body 8 and outputs a signal representing the detected angle to the main controller 100. The bucket relative angle sensor 63 is a potentiometer that detects the relative angle (tilt angle) of the bucket 3 with respect to the arm 2 and outputs a signal representing the detected angle to the main controller 100. Because the angle of the vehicle body 8 with respect to the ground (traveling surface) is constant, the angle detected by the arm relative angle sensor 62 can be said to correspond to the relative angle (tilt angle) of the arm 2 with respect to the ground.

[0036] Furthermore, the sensor signals input to the main controller 100 include a signal representing the vehicle speed (traveling speed of the vehicle) detected by a vehicle speed sensor 61. The vehicle speed sensor 61 detects the vehicle speed of the wheel loader 1 and outputs a signal representing the detected vehicle speed to the main controller 100. Further sensor signals input to the main controller 100 include signals representing the rotational speeds of the engine 20, the generator motor 40, the hydraulic pumps 30A, 30B, 30C, and the traveling motor 43 detected by a plurality of rotational speed sensors, signals representing the discharge pressures of the hydraulic pumps 30A, 30B, 30C detected by first, second, and third discharge pressure sensors 71, 72, 73, and signals representing the pressures (load pressures) of the hydraulic cylinders detected by cylinder pressure sensors (not shown), etc.

[0037] The multiple rotation speed sensors include an engine rotation speed sensor 64 that detects the actual rotation speed of the engine 20 (hereinafter also referred to as the actual engine rotation speed NEG_ACT), and a motor speed sensor 58 such as a resolver that detects the rotation speed of the traveling electric motor 43 (hereinafter also referred to as the motor speed). The engine rotation speed sensor 64 is, for example, a rotary encoder provided on the output shaft of the engine 20, and outputs a signal indicative of the detected actual engine rotation speed NEG_ACT to the main controller 100. Note that the engine rotation speed sensor 64 is not limited to detecting the rotation speed of the output shaft of the engine 20, and may also be one that detects the rotation speed of any shaft constituting the power transmission device. In this case, the main controller 100 calculates the actual engine rotation speed NEG_ACT based on the detection result of the engine rotation speed sensor 64.

[0038] In the illustrated example, the engine speed sensor 64 is connected to the main controller 100, but may be connected to the engine controller 120. In this case, the main controller 100 acquires the actual engine speed NEG_ACT detected by the engine speed sensor 64 via the engine controller 120.

[0039] The main controller 100 outputs a front control command based on the operation direction and operation amount of the arm operation device 52 and the bucket operation device 53. The front control unit 31 adjusts the pressure, flow rate, and direction of the hydraulic oil discharged from the hydraulic pump 30A based on the front control command from the main controller 100, and operates the arm cylinder 4 and the bucket cylinder 5. The front control unit 31 has a directional control valve that controls the flow of the hydraulic oil discharged from the hydraulic pump 30A, a solenoid valve that generates pilot pressure that is input to a pilot chamber of the directional control valve, and the like.

[0040] The main controller 100 outputs a brake control command based on the operation amount of the brake operating device 57 and the operation position of the operation switch of the parking brake operating device 54. The brake control unit 32 adjusts the pressure, flow rate, and direction of the hydraulic oil discharged from the hydraulic pump 30B based on the brake control command from the main controller 100, and operates the brake cylinder 17 and the parking brake cylinder 18. The brake control unit 32 has a directional control valve that controls the flow of the hydraulic oil discharged from the hydraulic pump 30B, a solenoid valve that generates pilot pressure that is input to a pilot chamber of the directional control valve, and the like.

[0041] The main controller 100 outputs a steering control command based on the direction and amount of operation of the steering wheel of the steering operation device 55. The steering control unit 33 adjusts the pressure, flow rate, and direction of the hydraulic oil discharged from the hydraulic pump 30C based on the steering control command from the main controller 100, and operates the steering cylinder 15. The steering control unit 33 has a directional control valve that controls the flow of the hydraulic oil discharged from the hydraulic pump 30C, a solenoid valve that generates pilot pressure that is input to a pilot chamber of the directional control valve, and the like.

[0042] The power generation inverter 41 and the traveling inverter 42 are connected by a DC section (DC bus) 44. The wheel loader 1 according to this embodiment does not include a power storage device connected to the DC section 44. The power generation inverter 41 controls the bus voltage of the DC section 44 using the power supplied from the generator motor 40 based on a power generation voltage command from the main controller 100. The traveling inverter 42 drives the traveling motor 43 using the power of the DC section 44 based on a traveling drive torque command from the main controller 100.

[0043] In this embodiment, hydraulic pumps 30A, 30B, and 30C are driven by torque output from the engine 20, and hydraulic oil discharged from the hydraulic pumps 30A, 30B, and 30C drives the working device 6, the braking device 21, and the steering device 22. Also, in this embodiment, the generator motor 40 is driven by torque output from the engine 20, and the traveling motor 43 is driven by electric power generated by the generator motor 40.

[0044] When the arm operation lever of the arm operation device 52 is operated, the arm 2 rotates up and down (moves up and down) due to the extension and contraction of the arm cylinder 4. When the bucket operation lever of the bucket operation device 53 is operated, the bucket cylinder 5 rotates up and down (crowd operation or dump operation).

[0045] When the steering wheel of the steering operation device 55 is operated, the front body 8A is turned (steered) left and right relative to the rear body 8B around the center joint 10 in accordance with the extension and contraction of the steering cylinder 15. When the accelerator pedal of the accelerator operation device 56 is operated, the wheels 7 are rotated by the drive of the traveling motor 43, and the wheel loader 1 travels.

[0046] When the forward / reverse switch 51 is operated to the forward position (F) and the accelerator pedal of the accelerator operating device 56 is depressed, the wheels 7 rotate in the forward direction, and the vehicle body 8 travels forward. When the forward / reverse switch 51 is operated to the reverse position (R), and the accelerator pedal of the accelerator operating device 56 is depressed, the wheels 7 rotate in the reverse direction, and the vehicle body 8 travels backward. Note that when the forward / reverse switch 51 is operated to the standby position (N), the wheels 7 do not rotate and the vehicle body 8 does not travel, even if the accelerator pedal of the accelerator operating device 56 is depressed.

[0047] - Excavation work using a wheel loader - Next, the basic transporting operation of the wheel loader 1 will be described with reference to Fig. 3. In the transporting operation, the wheel loader 1 performs an excavation operation to excavate an excavation target 91 such as earth and sand or minerals, and then performs a loading operation to transport the excavated material and load it onto a loading target 92 such as a dump truck. Fig. 3 shows V-shaped loading, which is one method for performing this transporting operation.

[0048] As shown by arrow X1 in FIG. 3 , the operator operates the accelerator operating device 56 to move the wheel loader 1 forward toward the excavation target 91, such as natural ground, and penetrates the bucket 3 into the excavation target 91. The operator operates the arm operating device 52 and the bucket operating device 53 to raise the arm 2 and place earth, sand, minerals, etc. into the bucket 3. The operator then operates the bucket operating device 53 to perform a crowding operation on the bucket 3. At this time, the operator operates the bucket operating device 53 to scoop up the bucket 3 toward him, taking care not to spill the earth, sand, minerals, etc. that have been placed in the bucket 3. This completes the excavation work.

[0049] After completing the excavation work, the operator moves the wheel loader 1 backward to return to its original position, as shown by arrow X2 in FIG. 3. Then, the operator moves the wheel loader 1 forward toward the loading target 92, such as a dump truck, as shown by arrow Y1 in FIG. 3, while raising the arm 2. The operator stops the wheel loader 1 in front of the loading target 92. Note that in FIG. 3, the wheel loader 1 stopped in front of the loading target 92 is shown by a dashed line. Then, the operator operates the bucket operating device 53 to perform a dump operation on the bucket 3, thereby releasing the transported material in the bucket 3 onto the bed of the loading target 92. This loads the transported material in the bucket 3 onto the bed of the loading target 92, completing the loading work. After completing the loading work, the operator moves the wheel loader 1 backward to return to its original position, as shown by arrow Y2 in FIG. 3.

[0050] This series of operations, including excavation and loading, is called "V-shape loading" because it is performed while tracing a V-shaped trajectory, and is performed repeatedly. V-shape loading accounts for the majority of the total working time of the wheel loader 1. For this reason, in order to improve the working efficiency of the wheel loader 1, it is effective to increase the acceleration performance after switching from reverse to forward during V-shape loading.

[0051] When the forward / reverse switch 51 is switched from the reverse position (R) to the forward position (F) while the wheel loader 1 is moving in reverse, the wheel loader 1 performs a "modulating operation" in which the wheels 7 are braked by the regenerative operation of the travel drive device 45 shown in FIG. 2 and the traveling direction of the vehicle body 8 is switched from reverse to forward. In this paper, the operation of the wheel loader 1 in which the forward / reverse switch 51 is switched to the side opposite the traveling direction while the wheel loader 1 is traveling, thereby reducing the vehicle speed in the traveling direction at the time the forward / reverse switch 51 is switched, by regenerative braking, is referred to as a "modulating operation." For example, when the forward / reverse switch 51 is switched from the reverse position (R) to the forward position (F) while the wheel loader 1 is moving in reverse, the vehicle speed in the reverse direction is reduced by regenerative braking without operating the brake pedal of the brake operating device 57, and if the accelerator pedal of the accelerator operating device 56 is kept depressed during this deceleration, acceleration in the forward direction will begin after the modulating operation ends (after deceleration in the reverse direction ends). In this embodiment, as will be described later, the work efficiency of V-shape loading is improved by improving the acceleration performance after the end of the modulating operation. Here, the work efficiency (t / h) means the weight (t) of the transported goods loaded onto the loading target 92 per predetermined time (h).

[0052] Basically, the magnitude of engine power increases as the actual engine rotation speed NEG_ACT increases and as the fuel injection amount increases. However, the higher the actual engine rotation speed NEG_ACT, the higher the engine load. Therefore, the main controller 100 lowers the first target rotation speed (hereinafter also referred to as target engine rotation speed) NEG_TGT of the engine 20 when not working to improve fuel efficiency. On the other hand, when working, the main controller 100 sets the target engine rotation speed NEG_TGT at which the engine power required for work (i.e., desired engine power) can be obtained, based on the amount of operation of the accelerator operation device 56, arm operation device 52, and bucket operation device 53 by the operator, etc.

[0053] Here, the problem will be explained using a comparative example in which the engine controller 120 adjusts the fuel injection amount by the fuel injector 23 so that the actual engine speed NEG_ACT matches the target engine speed NEG_TGT, regardless of whether modulation operation is in progress, thereby generating the desired engine power.

[0054] During the modulating operation, regenerative energy generated by regenerative braking is returned from the traveling drive device 45 to the engine 20. Specifically, the regenerative power generated by the traveling motor 43 causes the generator motor 40 to function as an electric motor, and the power of the generator motor 40 is transmitted to the engine 20. As a result, when the actual engine rotation speed NEG_ACT becomes higher than the target engine rotation speed NEG_TGT, there is no longer a need to generate engine power, and the engine controller 120 reduces the amount of fuel injected by the fuel injector 23 until it becomes zero. In this way, by performing regenerative braking and reducing the amount of fuel injection during the modulating operation, fuel economy is improved compared to when braking is performed by the brake device 21.

[0055] After reverse travel ends and the vehicle switches to forward travel, i.e., after the modulating operation ends, no regenerative energy is generated, so the actual engine speed NEG_ACT gradually decreases. Then, when the actual engine speed NEG_ACT falls below the target engine speed NEG_TGT, the engine controller 120 determines the amount of fuel injection by the fuel injector 23 based on the difference between the actual engine speed NEG_ACT and the target engine speed NEG_TGT, and restarts fuel injection.

[0056] When fuel injection is resumed, the generated engine power increases the actual engine rotation speed NEG_ACT, and the wheel loader 1 accelerates in the forward direction. Note that the absolute value of the maximum negative value of the rotation speed deviation when the actual engine rotation speed NEG_ACT becomes less than the target engine rotation speed NEG_TGT after the modulating operation ends is called the "amount of negative overshoot."

[0057] After the modulating operation ends, from the point at which the actual engine speed NEG_ACT becomes less than the target engine speed NEG_TGT until engine power is generated, delays occur in the detection of the actual engine speed, the calculation processing by the control device, the operation of the fuel injector 23, and the response of the engine 20. For this reason, if the timing of restarting the fuel injector 23 is late, the actual engine speed NEG_ACT will not start to increase until it has fallen significantly below the target engine speed NEG_TGT. In this case, much of the generated engine power is used to increase the actual engine speed NEG_ACT, and the amount used to accelerate the wheel loader 1 in the forward direction is reduced. As a result, vehicle acceleration performance after the modulating operation ends decreases, leaving room for improvement.

[0058] In order to prevent a decrease in vehicle acceleration performance after the modulating operation ends, it is possible to allocate more power to the traveling drive device 45 than to the engine 20. However, this method further delays the timing at which the actual engine rotation speed NEG_ACT increases, increasing the time required to produce the desired engine power. As a result, the improvement in vehicle acceleration performance is small.

[0059] Another possible method is to increase the gain of proportional control of the fuel injection amount by the engine controller 120 to increase the response speed of the actual engine rotation speed NEG_ACT relative to the target engine rotation speed NEG_TGT. However, this method may result in a large increase or decrease in the fuel injection amount relative to the rotation speed deviation, which may cause engine control to become unstable. Furthermore, a response delay due to the calculation processing of the control device remains, making it impossible to significantly improve the amount of negative overshoot.

[0060] Therefore, as a result of extensive research, the inventors of the present application have found that, in order to suppress the amount of negative overshoot in the actual engine rotation speed after the end of the modulating operation, a command rotation speed NEG_CMD is calculated by correcting the target engine rotation speed NEG_TGT by adding a rotation speed correction value NC to the target engine rotation speed NEG_TGT, and the fuel injection amount is controlled based on the difference between the command rotation speed NEG_CMD and the actual engine rotation speed NEG_ACT. This suppresses the amount of negative overshoot caused by the control characteristics of the engine controller 120 and response delays of each device, thereby improving vehicle acceleration performance without deteriorating fuel economy.

[0061] As will be described later, the main controller 100 calculates a target engine rotation speed NEG_TGT based on the accelerator operation amount, the arm operation amount, the bucket operation amount, etc. The main controller 100 calculates a command rotation speed NEG_CMD based on the target engine rotation speed NEG_TGT and outputs it to the engine controller 120. The main controller 100 also outputs an actual engine rotation speed NEG_ACT detected by the engine rotation speed sensor 64 to the engine controller 120.

[0062] The engine controller 120 compares the command rotation speed NEG_CMD obtained from the main controller 100 with the actual engine rotation speed NEG_ACT detected by the engine rotation speed sensor 64, and controls the fuel injector 23 so that the actual engine rotation speed NEG_ACT matches the command rotation speed NEG_CMD. The command rotation speed NEG_CMD is calculated by adding a rotation speed correction value NC to the target engine rotation speed NEG_TGT.

[0063] That is, when no correction is made (NC=0), the engine controller 120 controls the fuel injection amount of the engine 20 so that the actual engine speed NEG_ACT detected by the engine speed sensor 64 matches the target engine speed (first target speed) NEG_TGT. On the other hand, when correction is made (NC≠0), the engine controller 120 controls the fuel injection amount of the engine 20 so that the actual engine speed NEG_ACT detected by the engine speed sensor 64 matches the command speed (second target speed) NEG_CMD, which is the corrected target engine speed. Note that when correction is made (NC≠0), if the actual engine speed NEG_ACT changes from a state higher than the command speed (second target speed) NEG_CMD to a state lower than the command speed (second target speed) NEG_CMD, the fuel injection amount of the engine 20 is controlled to increase. Therefore, the command speed (second target speed) NEG_CMD functions as a threshold for determining the start of an increase in the fuel injection amount of the engine 20.

[0064] The fuel injection device 23 controls the fuel injection amount based on a fuel injection command output from the engine controller 120 to operate the engine 20. For example, in this embodiment, when the command rotation speed NEG_CMD is higher than the actual engine rotation speed NEG_ACT, the engine controller 120 executes integral control to gradually increase the fuel injection amount until the difference between the actual engine rotation speed NEG_ACT and the command rotation speed NEG_CMD becomes 0 (zero).

[0065] In this way, the main controller 100 and the engine controller 120 cooperate to form a control device 11 that controls the operation of the engine 20 .

[0066] The functions of the main controller 100 according to this embodiment and the content of the arithmetic processing executed by the main controller 100 will be described in detail below.

[0067] -Main controller functions- Fig. 4 is a functional block diagram of the main controller 100. As shown in Fig. 4, the main controller 100 executes a program stored in the ROM 102 to function as a target speed calculation unit 110, a modulation determination unit 111, a correction value calculation unit 112, and a command value calculation unit 113.

[0068] The target speed calculation unit 110 calculates the target engine rotation speed NEG_TGT based on at least the detection result of the operation amount detection device 150. In this embodiment, the target speed calculation unit 110 calculates the target engine rotation speed NEG_TGT based on the detection result of the operation amount detection device 150, the detection result of the motor speed sensor 58, and the detection result of the discharge pressure detection device 151. The operation amount detection device 150 includes the arm operation amount sensor 52a, bucket operation amount sensor 53a, accelerator operation amount sensor 56a, brake operation amount sensor 57a, and steering operation amount sensor 55a described above. The discharge pressure detection device 151 includes the first discharge pressure sensor 71, second discharge pressure sensor 72, and third discharge pressure sensor 73 described above.

[0069] An example of a method for calculating the target engine rotation speed NEG_TGT will be described with reference to Fig. 5. Fig. 5 is a block diagram illustrating a method for calculating the target engine rotation speed NEG_TGT by the target speed calculation unit 110. As shown in Fig. 5, the target speed calculation unit 110 has a traveling required power calculation unit 121, a first pump required power calculation unit 122, a second pump required power calculation unit 123, a third pump required power calculation unit 124, a maximum value selection unit 125, an addition unit 126, and a target speed calculation unit 127.

[0070] The traveling power requirement calculation unit 121 has a traveling motor torque calculation unit 121a and a multiplication unit 121b. The traveling motor torque calculation unit 121a calculates the traveling motor torque based on the rotation speed (motor speed) of the traveling motor 43 detected by the motor speed sensor 58 and the accelerator operation amount detected by the accelerator operation amount sensor 56a.

[0071] A travel motor torque table used for calculating the travel motor torque is stored in the ROM 102 of the main controller 100. The travel motor torque table stores a plurality of torque curves corresponding to the accelerator operation amount so that the torque of the travel motor 43 increases or decreases according to an increase or decrease in the accelerator operation amount. The travel motor torque table is set so that the greater the accelerator operation amount, the greater the travel motor torque, and the faster the rotation speed of the travel motor 43, the smaller the travel motor torque.

[0072] The traveling electric motor torque calculation unit 121a selects a torque curve corresponding to the magnitude of the accelerator operation amount, and calculates the traveling electric motor torque based on the rotation speed of the traveling electric motor 43. For example, when the accelerator operation device 56 is fully operated, the traveling electric motor torque calculation unit 121a selects the torque curve indicated by the solid line, and calculates the traveling electric motor torque based on the rotation speed of the traveling electric motor 43 by referring to the selected torque curve.

[0073] The multiplication unit 121b multiplies the traveling motor torque calculated by the traveling motor torque calculation unit 121a, the rotation speed of the traveling motor 43 detected by the motor speed sensor 58, and a coefficient for unit conversion to calculate the required traveling power.

[0074] The first pump required power calculation unit 122 has a pump required flow rate calculation unit 122a and a multiplication unit 122b. The pump required flow rate calculation unit 122a calculates the pump required flow rate of the hydraulic pump 30A based on the arm operation amount and bucket operation amount detected by the arm operation amount sensor 52a and bucket operation amount sensor 53a of the operation amount detection device 150, and the discharge pressure of the hydraulic pump 30A detected by the first discharge pressure sensor 71 of the discharge pressure detection device 151. The arm operation amount and bucket operation amount are also collectively referred to as lever operation amount.

[0075] A required flow rate table used for calculating the required pump flow rate of the hydraulic pump 30A is stored in the ROM 102 of the main controller 100. The required flow rate table is set so that the required pump flow rate increases from the minimum discharge flow rate as the lever operation amount increases.

[0076] The pump required flow rate calculation unit 122a refers to a required flow rate table and calculates the pump required flow rate based on the lever operation amount. The pump required flow rate table includes a table based on the arm operation amount and a table based on the bucket operation amount, and the larger of the flow rates determined by each table is determined as the pump required flow rate.

[0077] The multiplication unit 122b multiplies the pump required flow rate of the hydraulic pump 30A calculated by the pump required flow rate calculation unit 122a, the discharge pressure of the hydraulic pump 30A detected by the first discharge pressure sensor 71 of the discharge pressure detection device 151, and a coefficient for unit conversion to calculate the required power of the hydraulic pump 30A.

[0078] Although not shown, the second pump required power calculation unit 123 has the same function as the first pump required power calculation unit 122, and calculates the required power of the hydraulic pump 30B based on the brake operation amount detected by the brake operation amount sensor 57a of the operation amount detection device 150 and the discharge pressure of the hydraulic pump 30B detected by the second discharge pressure sensor 72 of the discharge pressure detection device 151.

[0079] Although not shown, the third pump required power calculation unit 124 has the same function as the first pump required power calculation unit 122, and calculates the required power of the hydraulic pump 30C based on the steering operation amount detected by the steering operation amount sensor 55a of the operation amount detection device 150 and the discharge pressure of the hydraulic pump 30C detected by the third discharge pressure sensor 73 of the discharge pressure detection device 151.

[0080] The maximum value selection unit 125 selects the largest of the required power of the hydraulic pump 30A calculated by the first pump required power calculation unit 122, the required power of the hydraulic pump 30B calculated by the second pump required power calculation unit 123, and the required power of the hydraulic pump 30C calculated by the third pump required power calculation unit 124, and determines the selected required power as the work required power.

[0081] The adder 126 calculates the engine required power by adding the required traveling power calculated by the required traveling power calculation unit 121 and the required work power selected by the maximum value selection unit 125 .

[0082] The target speed calculation unit 127 calculates the target engine rotation speed NEG_TGT based on the engine required power calculated by the addition unit 126. A speed table used for calculating the target engine rotation speed NEG_TGT is stored in the ROM 102 of the main controller 100. The speed table is set so that the target engine rotation speed NEG_TGT increases from the minimum rotation speed NEG_TGT_min as the engine required power increases. The target speed calculation unit 127 refers to the speed table and calculates the target engine rotation speed NEG_TGT based on the engine required power.

[0083] In this way, the target speed calculation unit 110 determines the target engine rotation speed NEG_TGT so as to generate engine power that satisfies, as much as possible, the total value of the required traveling power and the required work power.

[0084] The modulation determination unit 111 determines whether the wheel loader 1 is in a modulated state (i.e., during modulated operation) or not in a non-modulated state (i.e., during non-modulated operation) based on the command rotational speed NEG_CMD calculated by the command value calculation unit 113 and the actual engine rotational speed NEG_ACT detected by the engine rotational speed sensor 64. If the wheel loader 1 is in a modulated state, the modulation determination unit 111 sets the modulation determination flag FL to on (FL=1). If the wheel loader 1 is in a non-modulated state, the modulation determination unit 111 sets the modulation determination flag FL to off (FL=0).

[0085] The modulate determination unit 111 calculates the rotation speed deviation ΔNEG using the following equation (1). ΔNEG=NEG_ACT-NEG_CMD (1) In equation (1), NEG_ACT is the actual engine rotation speed detected by the engine rotation speed sensor 64, and NEG_CMD is the command rotation speed calculated by the command value calculation unit 113.

[0086] When the modulation determination flag FL is set to off and the calculated rotational speed deviation (first rotational speed deviation) ΔNEG becomes larger than a first rotational speed threshold (predetermined first threshold) NTH1, the modulation determination unit 111 determines that the wheel loader 1 is performing a modulating operation and switches the modulation determination flag FL from off to on (F=1). The first rotational speed threshold NTH1 corresponds to the rotational speed deviation ΔNEG when the modulating operation is started, and is stored in advance in the ROM 102. The first rotational speed threshold NTH1 corresponds to, for example, a rotational speed of approximately 5 to 10% when the maximum engine rotational speed is 100%.

[0087] As will be described later, when the modulate determination flag FL is set to off, the rotation speed correction value NC is 0 (zero), and the command rotation speed NEG_CMD is equal to the target engine rotation speed NEG_TGT (NEG_CMD=NEG_TGT). Therefore, when the modulate determination flag FL is set to off, the rotation speed deviation (first rotation speed deviation) ΔNEG corresponds to the difference between the actual engine rotation speed NEG_ACT and the target engine rotation speed NEG_TGT (ΔNEG=NEG_ACT-NEG_TGT).

[0088] When the modulation determination flag FL is set to on and the calculated rotational speed deviation (second rotational speed deviation) ΔNEG becomes less than a second rotational speed threshold (predetermined second threshold) NTH2, the modulation determination unit 111 determines that the wheel loader 1 is in non-modulated operation and switches the modulation determination flag FL from on to off (F=0). The second rotational speed threshold NTH2 corresponds to the rotational speed deviation ΔNEG when the modulating operation is completed, and is stored in advance in the ROM 102. The second rotational speed threshold NTH2 is equal to or less than the first rotational speed threshold NTH1, and corresponds to an operation amount of, for example, about 0 to 5% when the maximum engine rotational speed is 100%.

[0089] As will be described later, the rotational speed deviation (second rotational speed deviation) ΔNEG when the modulation determination flag FL is set to on corresponds to the difference between the actual engine rotational speed NEG_ACT and the command rotational speed (second target rotational speed) NEG_CMD, which is the corrected target engine rotational speed, and can therefore also be called the corrected rotational speed deviation (ΔNEG=NEG_ACT-NEG_CMD, NEG_CMD>NEG_TGT).

[0090] When the modulation determination flag FL is set to ON, the correction value calculation unit 112 sets the rotation speed correction value NC to a target correction value (predetermined correction value) NC_TGT. The target correction value NC_TGT is a fixed value greater than 0, and is stored in advance in the ROM 102. The target correction value NC_TGT corresponds to the negative overshoot amount NMOD_ERR of the actual engine rotation speed NEG_ACT after the modulating operation ends when the target engine rotation speed NEG_TGT is not corrected (comparative example).

[0091] A method for determining the target correction value NC_TGT will be described with reference to Figures 6 and 7. Figure 6 is a diagram showing an example of a correlation map Mf that shows the relationship between the rotation speed deviation ΔNEG of the engine 20 and the fuel injection amount FEG. As shown in Figure 6, the characteristics of the engine controller 120 shown in this correlation map Mf are determined in advance by calculation or experiment. As shown in the correlation map Mf, when the rotation speed deviation ΔNEG is less than 0 (zero), the engine controller 120 increases the fuel injection amount FEG as the rotation speed deviation ΔNEG increases in the negative direction. Furthermore, when the rotation speed deviation ΔNEG is 0 (zero) or more, the engine controller 120 sets the fuel injection amount FEG to 0 (zero).

[0092] Therefore, during modulating operation, when regenerative braking of the traveling drive device 45 causes regenerative energy to be regenerated in the engine 20, causing the rotational speed deviation ΔNEG to exceed 0, the fuel injection amount FEG is cut to 0 (zero). Thereafter, regenerative braking ends, and when the rotational speed deviation ΔNEG of the engine 20 begins to decrease and becomes less than 0 (zero), fuel injection is resumed. Then, when the engine power generated by fuel injection and the engine power required by the wheel loader 1 are balanced, the decrease in the rotational speed deviation ΔNEG stops. Thereafter, the rotational speed deviation ΔNEG increases, and the fuel injection amount FEG is adjusted so that the rotational speed deviation ΔNEG approaches 0 (zero).

[0093] At this time, the absolute value of the rotational speed deviation ΔNEG when the decrease in the rotational speed deviation ΔNEG stops corresponds to the negative overshoot amount NMOD_ERR of the actual engine rotational speed NEG_ACT. The larger the negative overshoot amount NMOD_ERR, the less engine power is distributed to the traveling drive device 45, and therefore the vehicle acceleration performance after the modulating operation ends deteriorates.

[0094] Therefore, in this embodiment, the target engine rotation speed NEG_TGT is corrected by adding the target correction value NC_TGT, which corresponds to the amount of negative overshoot NMOD_ERR obtained from the results of calculations, experiments, etc. on the wheel loader 1 according to the comparative example, to the target engine rotation speed NEG_TGT, to obtain the command rotation speed NEG_CMD.

[0095] FIG. 7 is a diagram showing an example of a correlation map Mc showing the relationship between the negative overshoot amount NMOD_ERR of the actual engine rotation speed NEG_ACT and the target correction value NC_TGT. As shown in FIG. 7, the larger the negative overshoot amount NMOD_ERR, the larger the set target correction value NC_TGT. Note that the negative overshoot amount NMOD_ERR and the target correction value NC_TGT do not need to be perfectly equal. The correlation map Mc shown in FIG. 7 is determined in advance based on calculations or experiments.

[0096] 4 sets the rotation speed correction value NC to an initial correction value NC_INI when the modulation determination flag FL is set to OFF. In this embodiment, the initial correction value NC_INI is 0 (zero) and is stored in advance in the ROM 102.

[0097] When the modulation determination flag FL is set to ON, the correction value calculation unit 112 sets the rotation speed correction value NC to the target correction value NC_TGT. In this embodiment, the target correction value NC_TGT is a fixed value determined by calculation, experiment, etc. as described above, and is stored in advance in the ROM 102.

[0098] When the modulation determination flag FL switches from on to off, the correction value calculation unit 112 performs delay processing to hold the rotation speed correction value NC at the target correction value NC_TGT for a predetermined time. When the modulation determination flag FL switches from on to off, the correction value calculation unit 112 performs rate limiting processing on the rotation speed correction value NC after the delay processing. Furthermore, when the modulation determination flag FL switches from off to on, the correction value calculation unit 112 does not perform delay processing but performs rate limiting processing on the rotation speed correction value NC.

[0099] Therefore, when the modulate determination flag FL switches from off to on, the rotation speed correction value NC gradually increases from the initial correction value NC_INI to the target correction value NC_TGT over time. Also, when the modulate determination flag FL switches from on to off, the rotation speed correction value NC is held at the target correction value NC_TGT for a predetermined time, and then gradually decreases from the target correction value NC_TGT to the initial correction value NC_INI over time.

[0100] This prevents the rotation speed correction value NC from changing abruptly when the modulation determination flag FL is switched, and also prevents fuel injection from being resumed at an unintended timing when the modulation determination flag FL is switched from on to off.

[0101] As shown in FIG. 4, the command value calculation unit 113 calculates the command rotation speed NEG_CMD using the target engine rotation speed NEG_TGT and the rotation speed correction value NC according to the following equation (2). NEG_CMD=NEG_TGT+NC (2) As described above, the target engine rotation speed NEG_TGT is calculated by the target speed calculation unit 110, and the rotation speed correction value NC is calculated by the correction value calculation unit 112.

[0102] In this way, the command value calculation unit 113 corrects the target engine rotation speed NEG_TGT using the rotation speed correction value NC calculated by the correction value calculation unit 112. The command rotation speed NEG_CMD, which is the corrected target engine rotation speed, is output to the engine controller 120 as an engine speed command. Note that in a state where it is not determined that the wheel loader 1 is in modulating operation, the rotation speed correction value NC is 0 (zero). For this reason, the command value calculation unit 113 does not actually correct the target engine rotation speed NEG_TGT using the rotation speed correction value NC. On the other hand, when it is determined that the wheel loader 1 is in modulating operation, the command value calculation unit 113 adds a predetermined correction value (target correction value NC_TGT>0) to the target engine rotation speed (first target rotation speed) NEG_TGT to calculate the command rotation speed (second target rotation speed) NEG_CMD.

[0103] When it is determined that the wheel loader 1 is in non-modulated operation, the engine controller 120 controls the fuel injection amount of the engine 20 so that the actual engine rotational speed NEG_ACT matches the command rotational speed (second target rotational speed) NEG_CMD until a predetermined time has elapsed. When a predetermined time has elapsed since the modulation determination flag FL was set to off, the rotational speed correction value NC decreases and becomes 0 (zero). Therefore, after the predetermined time has elapsed and the rotational speed correction value NC becomes 0 (zero), the engine controller 120 controls the fuel injection amount so that the actual engine rotational speed NEG_ACT matches the target engine rotational speed (first target rotational speed) NEG_TGT.

[0104] -Engine control flow- An example of engine control executed by the main controller 100 will be described below with reference to Fig. 8. Fig. 8 is a flowchart of engine control executed by the main controller 100. The process shown in the flowchart of Fig. 8 is started, for example, when an ignition switch (engine key switch) is turned on, and after initial setting (not shown) is performed, it is repeatedly executed at a predetermined control period. In the initial setting, the modulation determination flag FL is set to off.

[0105] As shown in FIG. 8, in step S110, the target speed calculation unit 110 calculates the target engine rotation speed NEG_TGT based on the detection results of the operation amount detection device 150, the discharge pressure detection device 151, and the motor speed sensor 58, and proceeds to step S120.

[0106] In step S120, the modulate determination unit 111 calculates the rotational speed deviation ΔNEG (see equation (1)) based on the previous value of the command rotational speed NEG_CMD (for example, the value calculated in step S210 of the previous control cycle) and the actual engine rotational speed NEG_ACT detected by the engine rotational speed sensor 64, and proceeds to step S130.

[0107] In step S130, the modulation determination unit 111 determines whether the currently set modulation determination flag FL is on. If the currently set modulation determination flag FL is off, the process proceeds to step S140, and if the currently set modulation determination flag FL is on, the process proceeds to step S160.

[0108] In step S140, the modulation determination unit 111 determines whether the rotational speed deviation ΔNEG calculated in step S120 has become larger than the first rotational speed threshold NTH1. In step S140, if the rotational speed deviation ΔNEG has become larger than the first rotational speed threshold NTH1, the modulation determination unit 111 determines that the wheel loader 1 is in modulated operation, and the process proceeds to step S150. In step S140, if the rotational speed deviation ΔNEG is equal to or smaller than the first rotational speed threshold NTH1, the modulation determination unit 111 determines that the wheel loader 1 is in unmodulated operation, and the process proceeds to step S180.

[0109] In step S150, the modulation determination section 111 sets the modulation determination flag FL to ON, and the process proceeds to step S180.

[0110] In step S160, the modulation determination unit 111 determines whether the rotational speed deviation ΔNEG calculated in step S120 has become less than the second rotational speed threshold NTH2. If the rotational speed deviation ΔNEG has become less than the second rotational speed threshold NTH2 in step S160, the modulation determination unit 111 determines that the wheel loader 1 is in unmodulated operation, and the process proceeds to step S170. If the rotational speed deviation ΔNEG is equal to or greater than the second rotational speed threshold NTH2 in step S160, the modulation determination unit 111 determines that the wheel loader 1 is in modulated operation, and the process proceeds to step S180.

[0111] In step S170, the modulation determination section 111 sets the modulation determination flag FL to OFF, and the process proceeds to step S180.

[0112] In step S180, correction value calculation unit 112 determines whether the currently set modulation determination flag FL is on. If the currently set modulation determination flag FL is on, the process proceeds to step S190, and if the currently set modulation determination flag FL is off, the process proceeds to step S200.

[0113] In step S190, correction value calculation unit 112 sets rotation speed correction value NC to target correction value NC_TGT, and proceeds to step S210. Note that correction value calculation unit 112 applies rate limiting processing to rotation speed correction value NC when modulate determination flag FL switches from off to on. In step S200, correction value calculation unit 112 sets rotation speed correction value NC to initial correction value NC_INI, and proceeds to step S210. Note that correction value calculation unit 112 applies delay processing and rate limiting processing to rotation speed correction value NC when modulate determination flag FL switches from on to off.

[0114] In step S210, command value calculation unit 113 calculates command rotation speed NEG_CMD based on target engine rotation speed NEG_TGT calculated in step S110 and rotation speed correction value NC calculated in step S190 or step S200 (see equation (2)). When the processing of step S210 is completed, the processing of the flowchart shown in Fig. 8 for this control cycle is terminated, and the processing from step S110 to step S210 is executed again in the next control cycle.

[0115] -Operation- Below, the main operations and effects of the wheel loader 1 according to this embodiment will be explained with reference to Figure 9. Figure 9 is a diagram showing time series changes in each parameter of the wheel loader 1 according to this embodiment (accelerator operation amount RA, operation position of the forward / reverse switch 51, command rotation speed NEG_CMD, actual engine rotation speed NEG_ACT, fuel injection amount FEG, engine acceleration component power PEG_ACC, and vehicle speed VVHCL).

[0116] An example of the operation of the wheel loader 1 when performing modulating operation will be described below. In order to clarify the effects of this embodiment, the explanation will be made in comparison with a comparative example in which the target engine rotation speed NEG_TGT is not corrected by the rotation speed correction value NC. It should be noted that the wheel loader 1 according to this embodiment and the wheel loader according to the comparative example for this embodiment have the same operating procedures and operation amounts for the various operating devices by the operator.

[0117] In FIG. 9, the time series changes of each parameter in this embodiment are indicated by solid lines, and the time series changes of each parameter in the comparative example are indicated by dashed lines. The horizontal axis in FIGS. 9(a) to 9(g) represents time (elapsed time). The vertical axis in FIG. 9(a) represents the accelerator operation amount RA detected by the accelerator operation amount sensor 56a. The vertical axis in FIG. 9(b) represents the operation position of the forward / reverse switch 51. The vertical axis in FIG. 9(c) represents the command rotation speed NEG_CMD calculated by the command value calculation unit 113. Note that in the comparative example, the target engine rotation speed is not corrected. Therefore, the command rotation speed in the comparative example corresponds to the uncorrected target engine rotation speed NEG_TGT (dashed line). The vertical axis in FIG. 9(d) represents the actual engine rotation speed NEG_ACT detected by the engine rotation speed sensor 64. The vertical axis in FIG. 9(e) represents the fuel injection amount FEG injected by the fuel injection device 23. The vertical axis of Figure 9(f) represents the engine acceleration power component PEG_ACC (solid line) allocated by the main controller 100 to make the actual engine rotation speed NEG_ACT coincide with the command rotation speed NEG_CMD, and the engine acceleration power component PEG_ACC (dashed line) allocated by the main controller 100 to make the actual engine rotation speed NEG_ACT coincide with the uncorrected target engine rotation speed NEG_TGT. The vertical axis of Figure 9(g) represents the vehicle speed VVHCL of the wheel loader 1. Note that the vehicle speed VVHCL is a positive value when the wheel loader 1 is moving forward, and a negative value when the wheel loader 1 is moving backward.

[0118] 9, time t0 is the time when the operator starts operating the accelerator operation device 56. In other words, time t0 is the time when the vehicle body 8 starts to move backward. Time t1 is the time when the operator switches the forward / reverse switch 51 from the reverse position (R) to the forward position (F), and starts to reverse the direction of the drive torque of the traveling motor 43.

[0119] Time t2 is the time when the rotation speed deviation ΔNEG becomes larger than the first rotation speed threshold NTH1. That is, time t2 is the time when the modulation determination flag FL is switched from off to on. Time t3 is the time when the rotation speed deviation ΔNEG becomes smaller than the second rotation speed threshold NTH2. That is, time t3 is the time when the modulation determination flag FL is switched from on to off.

[0120] Time t4 is the time when the fuel injector 23 starts to restart fuel injection in this embodiment, and time t5 is the time when the fuel injector 23 starts to restart fuel injection in the comparative example.

[0121] As shown in Figure 9(a), the accelerator operation amount RA is small until time t0. This is because the operator has not operated the accelerator operation device 56 until time t0, and the wheel loader 1 is stopped. At time t0, the vehicle body 8 starts to move backward, and the accelerator operation amount RA increases rapidly.

[0122] As shown in Figure 9(b), the forward / reverse switch 51 is in the reverse position (R) until time t1. For this reason, the traveling motor 43 generates drive torque in a direction that moves the wheel loader 1 backward until time t1. At time t1, the forward / reverse switch 51 is operated to switch the traveling direction of the wheel loader 1 from reverse to forward, and the operating position of the forward / reverse switch 51 is changed from the reverse position (R) to the forward position (F).

[0123] 9(c), in this embodiment and the comparative example, the command rotation speed NEG_CMD increases from the low rotation speed NL to the medium rotation speed NM in response to the sudden increase in the accelerator operation amount RA from time t0. After that, when the forward / reverse switch 51 is switched to the forward position (F) at time t1, the actual engine rotation speed NEG_ACT increases as shown in FIG.

[0124] In the comparative example, as shown in FIG. 9(d), the actual engine rotation speed NEG_ACT increases from time t1, and then decreases, but as shown in FIG. 9(c), the command rotation speed NEG_CMD is maintained at the medium rotation speed NM.

[0125] In contrast to this, in this embodiment, the command rotation speed NEG_CMD starts to increase from the medium rotation speed NM from time t2. As shown in Fig. 9(d), time t2 is a time during which the actual engine rotation speed NEG_ACT increases from the medium rotation speed NM to the high rotation speed NH from time t1. As shown in Fig. 9(c), the command rotation speed NEG_CMD increases from time t2 because the modulation determination flag FL switches from off to on at time t2 and the rotation speed correction value NC quickly increases from 0 (zero).

[0126] In this embodiment, the command rotation speed NEG_CMD starts to decrease toward the medium rotation speed NM after a predetermined time has elapsed since time t3 (for example, between time t4 and time t5). This is because there is a slight delay after the modulation determination flag FL switches from on to off at time t3, and then the rotation speed correction value NC quickly decreases from the target correction value NC_TGT to 0 (zero).

[0127] In this embodiment and the comparative example, as shown in Fig. 9(d), the actual engine rotation speed NEG_ACT increases in accordance with the increase in the command rotation speed NEG_CMD from time t0. The actual engine rotation speed NEG_ACT quickly increases from the low rotation speed NL to a value slightly lower than the medium rotation speed NM, and then maintains a value slightly lower than the medium rotation speed NM. This is because the engine load and engine power are balanced when the actual engine rotation speed NEG_ACT is slightly lower than the medium rotation speed NM.

[0128] Then, when the forward / reverse switch 51 is switched from the reverse position (R) to the forward position (F) at time t1, the actual engine rotation speed NEG_ACT increases to the high rotation speed NH and then decreases. Specifically, as shown in FIG. 9(g), regenerative braking is performed from when the forward / reverse switch 51 is switched at time t1 until the vehicle speed VVHCL becomes greater than 0 (zero), and regenerative energy is regenerated from the traveling electric motor 43 to the engine 20, thereby increasing the actual engine rotation speed NEG_ACT. While the regenerative energy is greater than the load on the engine 20, the actual engine rotation speed NEG_ACT increases. While the regenerative energy is less than the load on the engine 20, the actual engine rotation speed NEG_ACT decreases. In other words, when the power of the generator motor 40, which operates as an electric motor using regenerative energy, is greater than the load on the hydraulic pumps 30A to 30C, the actual engine rotation speed NEG_ACT increases. Thereafter, when the regenerative energy decreases and the power of the generator motor 40 becomes smaller than the load on the hydraulic pumps 30A to 30C, the actual engine rotation speed NEG_ACT starts to decrease.

[0129] In this embodiment and the comparative example, as shown in Figures 9(c) and 9(d), shortly after time t1, the engine controller 120 detects that the rotation speed deviation ΔNEG has become larger than 0 (zero), and reduces the fuel injection amount FEG to 0 (zero), as shown in Figure 9(e). Therefore, fuel economy during the modulating operation can be improved.

[0130] In the comparative example, as shown in Figures 9(c) and 9(d), at time t5, the engine controller 120 detects that the rotation speed deviation ΔNEG has become less than 0 (zero), and starts to increase the fuel injection amount FEG, as shown in Figure 9(e). Therefore, in the comparative example, the rate at which the actual engine rotation speed NEG_ACT decreases becomes gentler from time t5, as shown in Figure 9(d). The actual engine rotation speed NEG_ACT stops decreasing between the low rotation speed NL and the medium rotation speed NM, and then increases to a value slightly lower than the medium rotation speed NM.

[0131] Here, there is a time delay between when the engine controller 120 detects that the rotation speed deviation ΔNEG has become less than 0 (zero), when it outputs a command to increase the fuel injection amount FEG of the fuel injector 23, when the fuel injector 23 actually increases the fuel injection amount FEG, and when the engine 20 actually increases its power. For this reason, in the comparative example, as shown in FIG. 9(d), the actual engine rotation speed NEG_ACT drops to approximately the middle between the low rotation speed NL and the medium rotation speed NM. Thus, in the comparative example, a large negative overshoot amount NMOD_ERR occurs.

[0132] In contrast, in this embodiment, as shown in FIG. 9(c), the command rotation speed NEG_CMD is maintained at a value greater than the target engine rotation speed NEG_TGT by a predetermined correction value (target correction value NC_TGT) until a little after time t4. Therefore, in this embodiment, the rotation speed deviation ΔNEG becomes less than 0 (zero) at an earlier timing than in the comparative example. As a result, the timing at which the engine controller 120 issues a command to increase the fuel injection amount FEG, the timing at which the fuel injector 23 actually increases the fuel, and the timing at which the engine 20 actually increases the power are advanced. For this reason, in this embodiment, fuel injection is resumed from time t4 as shown in FIG. 9(e), and the rate at which the actual engine rotation speed NEG_ACT decreases becomes gradual as shown in FIG. 9(d). Thereafter, the actual engine rotation speed NEG_ACT stops decreasing at a value slightly lower than the medium rotation speed NM and remains at that value.

[0133] In this way, as shown in Figures 9(c) to 9(e), the control device 11 of this embodiment performs a modulating operation to switch the direction of travel of the vehicle body 8 by regenerative braking, and when the actual engine rotation speed NEG_ACT detected by the engine rotation speed sensor 64 increases above the command rotation speed NEG_CMD (= target engine rotation speed NEG_TGT), it reduces the fuel injection amount FEG of the engine 20 (time t1 to time t2).

[0134] Furthermore, the control device 11 according to this embodiment increases the fuel injection amount FEG of the engine 20 (time t2 to time t4) when the actual engine rotation speed NEG_ACT detected by the engine rotation speed sensor 64 becomes less than the command rotation speed (second target rotation speed) NEG_CMD, which is a value that is greater than the target engine rotation speed NEG_TGT by a predetermined correction value (target correction value NC_TGT).

[0135] As a result, in this embodiment, by restarting fuel injection by the fuel injection device 23 at an earlier timing than in the comparative example, it is possible to suppress the amount of decrease in the actual engine rotation speed NEG_ACT after the modulating operation ends.

[0136] Next, the behavior of the fuel injection amount FEG, engine acceleration power component PEG_ACC, and vehicle speed VVHCL will be described with reference to Figures 9(e) to 9(g). As shown in Figure 9(e), in this embodiment and the comparative example, the fuel injection amount FEG increases from a small amount FEL in response to an increase in the command rotation speed NEG_CMD from time t0. Thereafter, although not shown, the fuel injection amount FEG increases to a large amount FEH in response to an increase in the boost pressure of the engine 20. Then, when regenerative braking is started at time t1, the fuel injection amount FEG decreases to 0 (zero) in response to a decrease in the power required of the engine 20.

[0137] In the comparative example, the rotation speed deviation ΔNEG becomes less than 0 (zero) at time t5, and the fuel injection amount FEG begins to increase. In contrast, in this embodiment, the rotation speed deviation ΔNEG becomes less than 0 (zero) at time t4, which is before time t5. Therefore, the fuel injection amount FEG begins to increase before the actual engine rotation speed NEG_ACT becomes less than the medium rotation speed NM.

[0138] 9(f), in this embodiment and the comparative example, the engine acceleration component power PEG_ACC increases from a value slightly lower than the low power PL to the high power PH in response to an increase in the command rotation speed NEG_CMD from time t0. Thereafter, as the absolute value of the rotation speed deviation ΔNEG decreases in response to an increase in the actual engine rotation speed NEG_ACT, the engine acceleration component power PEG_ACC decreases from the high power PH to the low power PL. Then, at time t1, a modulating operation is started, and when the rotation speed deviation ΔNEG becomes greater than 0 (zero), the engine acceleration component power PEG_ACC decreases to 0 (zero).

[0139] In the comparative example, when the rotation speed deviation ΔNEG becomes less than 0 (zero) at time t5, the engine acceleration component power PEG_ACC starts to increase and then reaches a value between the medium power PM and the high power PH. Then, as the actual engine rotation speed NEG_ACT increases to a value slightly lower than the medium rotation speed NM, the engine acceleration component power PEG_ACC decreases to the low power PL.

[0140] In contrast to this, in this embodiment, the engine acceleration component power PEG_ACC starts to increase at time t4, which is before time t5, and then reaches the low power PL. Since the actual engine rotation speed NEG_ACT is maintained at a value slightly lower than the medium rotation speed NM, the engine acceleration component power PEG_ACC stabilizes at the low power PL.

[0141] As described above, in this embodiment, at time t4, the command rotation speed NEG_CMD is maintained at a value slightly higher than the medium rotation speed NM (see FIG. 9(c)), and the timing at which the engine controller 120 issues a command to increase the fuel injection amount FEG, the timing at which the fuel injector 23 actually discharges fuel, and the timing at which the engine 20 actually increases power are all earlier than in the comparative example. Because the fuel injection timing is earlier, after the modulating operation ends, the actual engine rotation speed NEG_ACT stops decreasing at a value slightly lower than the medium rotation speed NM without decreasing to near the middle between the low rotation speed NL and the medium rotation speed NM (see FIG. 9(d)). As a result, in this embodiment, the rotation speed deviation ΔNEG is prevented from falling significantly below 0 (zero), and the engine acceleration component power PEG_ACC does not become larger than the low power PL.

[0142] As shown in FIG. 9(g), in this embodiment and the comparative example, the vehicle speed VVHCL increases from 0 (zero) in the negative direction in response to the sudden increase in accelerator operation amount RA from time t0 (see FIG. 9(a)), i.e., the vehicle is accelerating in reverse. Then, when the engine acceleration component power PEG_ACC decreases from high power PH to low power PL (see FIG. 9(f)), the rate of increase in the absolute value of the vehicle speed VVHCL decreases. Then, at time t1, the forward / reverse switch 51 switches from the reverse position (R) to the forward position (F) (see FIG. 9(b)) and the modulating operation begins, the absolute value of the vehicle speed VVHCL decreases toward 0 (zero). Shortly before time t3, the vehicle speed VVHCL becomes greater than 0 (zero) and increases in the positive direction. In other words, the wheel loader 1 begins to accelerate forward.

[0143] In the comparative example, the rate of increase of the vehicle speed VVHCL then decreases from time t5, and after a short time has passed, the rate of increase of the vehicle speed VVHCL increases. This is because, from time t5 until the actual engine rotation speed NEG_ACT increases to a value slightly lower than the medium rotation speed NM (see FIG. 9(d)), the engine acceleration component power PEG_ACC increases to a value between the medium power PM and the high power PH (see FIG. 9(f)), thereby reducing the engine power allocated to the traveling drive device 45.

[0144] In contrast, in this embodiment, after the wheel loader 1 starts accelerating forward slightly before time t3, the rate of increase in the vehicle speed VVHCL increases without temporarily decreasing as in the comparative example. This is because, as described above, in this embodiment, fuel is injected from the fuel injector 23 at an early timing before the actual engine rotation speed NEG_ACT becomes less than the medium rotation speed NM (see FIGS. 9(d) and 9(e)). By resuming fuel injection at an early timing, the actual engine rotation speed NEG_ACT stops decreasing at a value slightly lower than the medium rotation speed NM (see FIG. 9(d)), and the engine acceleration power PEG_ACC does not increase above the low power PL (see FIG. 9(f)). In other words, because the timing of fuel injection is advanced, there is no reduction in the engine power allocated to the traveling drive device 45. As a result, as shown in the figure, after the modulating operation ends, the rate of increase in the vehicle speed VVHCL of the wheel loader 1 increases without temporarily decreasing, improving acceleration performance.

[0145] As described above, when the wheel loader 1 performs modulating operation during transport work, in the comparative example, the amount of negative overshoot of the actual engine rotation speed NEG_ACT after the modulating operation ends becomes large. This reduces the engine power distributed to the traveling drive device 45, and the vehicle acceleration performance remains low for a long time. As a result, the efficiency of transport work decreases.

[0146] In contrast to this, in this embodiment, the main controller 100 sets the rotational speed correction value NC (target correction value NC_TGT) so as to offset the amount of negative overshoot of the actual engine rotational speed NEG_ACT. Then, the main controller 100 adds the rotational speed correction value NC to the target engine rotational speed NEG_TGT to determine the command rotational speed NEG_CMD. The main controller 100 outputs the calculated command rotational speed NEG_CMD to the engine controller 120. This makes it possible to suppress a decrease in engine power distributed to the traveling drive device 45 after the modulating operation is completed, thereby improving vehicle acceleration performance. As a result, in this embodiment, the efficiency of transport work by the wheel loader 1 can be improved compared to the comparative example.

[0147] Furthermore, in this embodiment, since the fuel injector 23 does not need to continue injecting fuel during the modulating operation, the desired vehicle acceleration performance can be obtained without wasting fuel. Although the timing at which fuel injection is resumed after the modulating operation starts is slightly earlier than in the comparative example, this is offset by the increased work efficiency due to the improved vehicle acceleration performance, and therefore, the deterioration of fuel economy compared to the comparative example can be suppressed.

[0148] The configuration, operation, and effects of the first embodiment of the present invention configured as above can be summarized as follows.

[0149] (1) A wheel loader (work vehicle) 1 includes a vehicle body 8, wheels 7 provided on the vehicle body 8, an engine 20 mounted on the vehicle body 8, a generator motor 40 mechanically connected to the engine 20, a travel drive device 45 capable of driving the wheels 7 with electric power generated by the generator motor 40 and capable of regenerative braking of the wheels 7, an accelerator operation device 56 operated by an operator, and an engine rotation speed sensor 64 that detects the rotation speed of the engine 20 (actual engine rotation speed NEG_ACT) (see FIG. 2). The wheel loader 1 also includes a control device 11 (main controller 100 and engine controller 120) that controls the fuel injection amount of the engine 20 so that the actual engine rotation speed NEG_ACT detected by the engine rotation speed sensor 64 matches a target engine rotation speed (first target rotation speed) NEG_TGT (see FIG. 2). The control device 11 increases the target engine rotation speed NEG_TGT as the operation amount of the accelerator operation device 56 increases (see FIG. 5).

[0150] When a modulating operation for switching the traveling direction of the vehicle body 8 is performed by regenerative braking and the actual engine rotation speed NEG_ACT becomes higher than the target engine rotation speed (first target rotation speed) NEG_TGT, the control device 11 reduces the fuel injection amount of the engine 20. When the actual engine rotation speed NEG_ACT becomes lower than a command rotation speed (predetermined second target rotation speed) NEG_CMD that is higher than the target engine rotation speed (first target rotation speed) NEG_TGT, the control device 11 increases the fuel injection amount of the engine 20.

[0151] In this configuration, during modulating operation, regenerative braking is performed by the traveling drive device 45, and the generator motor 40 operates as an electric motor using regenerative energy. As a result, the actual engine rotation speed NEG_ACT increases above the target engine rotation speed NEG_TGT, and the fuel injection amount decreases. Therefore, according to this embodiment, fuel efficiency can be improved compared to when fuel injection is continued even during modulating operation.

[0152] Furthermore, in this embodiment, the control device 11 reduces the fuel injection amount during the modulating operation, and then increases the fuel injection amount when the actual engine speed NEG_ACT becomes less than the commanded engine speed NEG_CMD, which is greater than the target engine speed NEG_TGT, immediately after the modulating operation ends. As a result, according to this embodiment, the fuel injection amount FEG can be increased after the modulating operation ends and before the actual engine speed NEG_ACT becomes less than the target engine speed NEG_TGT. In other words, according to this embodiment, the actual engine speed NEG_ACT is prevented from falling significantly below the target engine speed NEG_TGT, and good acceleration performance is obtained.

[0153] As described above, according to this embodiment, it is possible to provide a wheel loader (work vehicle) 1 that is capable of suppressing fuel consumption during modulating operation and improving acceleration performance after modulating operation ends.

[0154] (2) The wheel loader 1 includes a hydraulic pump 30A driven by the engine 20, hydraulic cylinders 4 and 5 that are extended and retracted by hydraulic oil discharged from the hydraulic pump 30A, and a working device 6 having driven members (an arm 2, a bucket 3) that are moved in response to the extension and retraction of the hydraulic cylinders 4 and 5 (see FIG. 2).

[0155] In this embodiment, the actual engine speed NEG_ACT is prevented from falling significantly below the target engine speed NEG_TGT after the modulating operation is completed. As a result, a sufficient flow rate of the hydraulic pump 30A, which is proportional to the actual engine speed NEG_ACT, can be ensured after the modulating operation is completed. In other words, according to this embodiment, the operating speed of the working implement 6 can be improved compared to the comparative example. Therefore, according to this embodiment, when the arm 2 is raised while the wheel loader 1 is moved forward toward the loading target 92, such as a dump truck, after the modulating operation is completed, the lifting speed of the arm 2 is increased, thereby improving work efficiency.

[0156] Second Embodiment A wheel loader 1 according to a second embodiment of the present invention will be described with reference to Figure 10. Components that are the same as or equivalent to those described in the first embodiment will be given the same reference numerals, and differences will be mainly described. In the second embodiment, the determination method used by the modulate determination unit 111A differs from that in the first embodiment.

[0157] Figure 10 is a functional block diagram of the main controller 100A according to the second embodiment. As shown in Figure 10, a modulate determination unit 111A determines whether or not the wheel loader 1 is in a modulating operation based on the command rotation speed NEG_CMD calculated by the command value calculation unit 113, the actual engine rotation speed NEG_ACT detected by the engine rotation speed sensor 64, and the accelerator operation amount RA detected by the accelerator operation amount sensor 56a of the operation amount detection device 150.

[0158] When the modulation determination flag FL is set to off, the accelerator operation amount RA is greater than a predetermined operation amount threshold RTH, and the calculated rotational speed deviation (first rotational speed deviation) ΔNEG becomes greater than a first rotational speed threshold (first threshold) NTH1, the modulation determination unit 111A determines that the wheel loader 1 is in a modulating operation and switches the modulation determination flag FL from off to on (F=1). The operation amount threshold RTH is a threshold for determining whether or not the accelerator operation device 56 is being operated, and is stored in advance in the ROM 102. The operation amount threshold RTH corresponds to, for example, 5 to 30% when the maximum value of the accelerator operation amount RA is 100%.

[0159] When the modulation determination flag FL is set to on and the calculated rotational speed deviation (second rotational speed deviation) ΔNEG becomes less than a second rotational speed threshold (second threshold) NTH2, the modulation determination unit 111A determines that the wheel loader 1 is in non-modulated operation, and switches the modulation determination flag FL from on to off (F=0).

[0160] In this way, the control device 11 according to the second embodiment determines whether or not the wheel loader 1 is in modulating operation, taking into account the amount of operation of the accelerator operating device 56. With this configuration, when regenerative braking is not being performed, it is not determined that the wheel loader 1 is in modulating operation, even if the rotational speed deviation (first rotational speed deviation) ΔNEG becomes larger than the first rotational speed threshold (first threshold) NTH1. This prevents the wheel loader 1 from being erroneously determined to be in modulating operation when the vehicle body 8 is naturally decelerated without regenerative braking while traveling. Furthermore, when the load on the engine 20 fluctuates depending on the state of the wheel loader 1, it prevents the wheel loader 1 from being erroneously determined to be in modulating operation.

[0161] <Third embodiment> A wheel loader 1 according to a third embodiment of the present invention will be described with reference to Figure 11. Components that are the same as or equivalent to those described in the first embodiment will be given the same reference numerals, and differences will be mainly described. In the third embodiment, the determination method used by the modulate determination unit 111B differs from that in the first embodiment.

[0162] The modulating operation is an operation in which the forward / reverse switch 51 is used to select a direction opposite to the actual traveling direction of the vehicle body 8 while the wheel loader 1 is traveling, thereby reducing the vehicle speed in the traveling direction before the forward / reverse switch 51 is switched (the actual traveling direction of the vehicle body 8).

[0163] Therefore, the main controller 100B according to the third embodiment determines whether or not the traveling drive device 45 is generating a drive torque in the opposite direction to the rotation direction of the wheels 7, and taking into account the result of this determination, determines whether or not the wheel loader 1 is in modulated operation.

[0164] Figure 11 is a functional block diagram of the main controller 100B according to the third embodiment. As shown in Figure 11, the modulation determination unit 111B determines whether the wheel loader 1 is in a modulating operation based on the command rotational speed NEG_CMD calculated by the command value calculation unit 113, the actual engine rotational speed NEG_ACT detected by the engine rotational speed sensor 64, a signal indicating the operation position from the forward / reverse switch 51, and the rotational speed (motor speed) NMOT of the traveling motor 43 detected by the motor speed sensor 58. Here, when the traveling motor 43 is rotating in a direction that moves the vehicle body 8 forward, the motor speed NMOT will be a positive (+) value (N>0), and when the traveling motor 43 is rotating in a direction that moves the vehicle body 8 backward, the motor speed NMOT will be a negative (-) value (N<0).

[0165] The modulation determination unit 111B determines the rotation direction of the wheel 7 based on the detection result of the motor speed sensor 58. If the motor speed NMOT detected by the motor speed sensor 58 is a positive value, the modulation determination unit 111B determines that the rotation direction of the wheel 7 is a forward direction. If the motor speed NMOT detected by the motor speed sensor 58 is a negative value, the modulation determination unit 111B determines that the rotation direction of the wheel 7 is a reverse direction. In this way, the motor speed sensor 58 functions as a wheel rotation direction detection device that detects the rotation direction of the wheel 7.

[0166] The modulate determination unit 111B determines the direction of the drive torque generated by the traveling drive device 45 based on the operation position of the forward / reverse switch 51. When the operation position of the forward / reverse switch 51 is the forward position, the modulate determination unit 111B determines that the direction of the drive torque generated by the traveling drive device 45 is the forward direction. When the operation position of the forward / reverse switch 51 is the reverse position, the modulate determination unit 111B determines that the direction of the drive torque generated by the traveling drive device 45 is the reverse direction. In this way, the forward / reverse switch 51 functions as a torque direction detection device that detects the direction of the drive torque generated by the traveling drive device 45.

[0167] When a forward / reverse switching operation is performed and the traveling motor 43 is rotating in the direction opposite to the traveling direction of the vehicle body 8 selected by the switching operation (i.e., the rotation direction before the switching operation), the modulate determination unit 111B determines that the following auxiliary condition is met. Auxiliary condition: The direction of the drive torque generated by the traveling drive device 45 is opposite to the rotation direction of the wheels 7.

[0168] Specifically, the modulate determination unit 111B determines that the auxiliary condition is met when the forward / reverse switch 51 is switched from the reverse position to the forward position and the traveling motor 43 is rotating in the reverse direction. Also, the modulate determination unit 111B determines that the auxiliary condition is met when the forward / reverse switch 51 is switched from the forward position to the reverse position and the traveling motor 43 is rotating in the forward direction.

[0169] Even if a forward / reverse switching operation is performed, the modulate determination unit 111B determines that the auxiliary condition is not met if the traveling motor 43 is not rotating in the direction opposite to the traveling direction of the vehicle body 8 selected by the switching operation.

[0170] When the modulate determination flag FL is set to off, the auxiliary condition is met, and the calculated rotational speed deviation (first rotational speed deviation) ΔNEG is greater than a first rotational speed threshold (first threshold) NTH1, the modulate determination unit 111B determines that the wheel loader 1 is in a modulating operation, and switches the modulate determination flag FL from off to on (F=1).

[0171] When the modulation determination flag FL is set to on and the calculated rotational speed deviation (second rotational speed deviation) ΔNEG becomes less than the second rotational speed threshold NTH2, the modulation determination unit 111A determines that the wheel loader 1 is in non-modulated operation, and switches the modulation determination flag FL from on to off (F=0).

[0172] In this way, the control device 11 according to the third embodiment determines that the wheel loader 1 is in modulating operation when the direction of the drive torque generated by the traveling drive device 45, detected by the forward / reverse switch 51 as a torque direction detection device, is opposite to the rotational direction of the wheels 7, detected by the motor speed sensor 58 as a wheel rotation direction detection device, and the rotational speed deviation (first rotational speed deviation) ΔNEG becomes larger than the first rotational speed threshold (first threshold) NTH1. With this configuration, as with the second embodiment, when regenerative braking is not being performed, it is not determined that the wheel loader 1 is in modulating operation even if the rotational speed deviation (first rotational speed deviation) ΔNEG becomes larger than the first rotational speed threshold (first threshold) NTH1. This prevents the wheel loader 1 from being erroneously determined to be in modulating operation when regenerative braking is not being performed.

[0173] In the third embodiment, as in the second embodiment, the amount of operation of the accelerator operation device 56 may also be taken into consideration when determining whether the wheel loader 1 is in modulated operation. Furthermore, although an example has been described in which the motor speed sensor 58 is used as the wheel rotation direction detection device that detects the rotation direction of the wheels 7, the wheel rotation direction detection device is not limited to this. For example, a vehicle speed sensor 61 may be used as the wheel rotation direction detection device. Although an example has been described in which the forward / reverse switch 51 is used as the torque direction detection device that detects the direction of the drive torque generated by the traveling drive device 45, the torque direction detection device is not limited to this. A current sensor that detects the current of the traveling electric motor 43, a torque sensor that detects the torque of the traveling electric motor 43, or the like may be used as the torque direction detection device.

[0174] <Fourth embodiment> A wheel loader 1 according to a fourth embodiment of the present invention will be described with reference to Figures 12 to 14. Note that components that are the same as or equivalent to those described in the first embodiment are given the same reference numerals, and differences will be mainly described. In the first embodiment, an example was described in which the target correction value NC_TGT is a fixed value.

[0175] In contrast to this, the control device 11 according to the fourth embodiment changes the target correction value NC_TGT in real time according to the state of the wheel loader 1. Below, the functions of the main controller 100C according to the fourth embodiment of the present invention and the contents of the calculation processing executed by the main controller 100C will be explained in detail.

[0176] Fig. 12 is a functional block diagram of a main controller 100C according to the fourth embodiment. As shown in Fig. 12, the main controller 100C has functions as a negative overshoot estimation unit 310 and a target correction value calculation unit 311 in addition to the functions described in the first embodiment.

[0177] The negative overshoot estimation unit 310 calculates a negative overshoot estimated value NMOD_ERR_EST based on the accelerator operation amount RA detected by the accelerator operation amount sensor 56 a of the operation amount detection device 150 .

[0178] The ROM 102 of the main controller 100C stores a correlation map Mo between the accelerator operation amount RA and the negative overshoot estimated value NMOD_ERR_EST, as shown in Fig. 13. Fig. 13 is a diagram showing an example of the correlation map indicating the relationship between the accelerator operation amount RA and the negative overshoot estimated value NMOD_ERR_EST.

[0179] The negative overshoot estimation unit 310 refers to a correlation map Mo and calculates a negative overshoot estimated value NMOD_ERR_EST based on the accelerator operation amount RA. This correlation map Mo shows the relationship in which the torque generated by the traveling electric motor 43 increases as the accelerator operation amount RA increases, and the negative overshoot amount NMOD_ERR increases as the required traveling power increases. The characteristics shown by this correlation map Mo are determined in advance by calculation or experiment. Specifically, the correlation map Mo is created by determining the relationship between the accelerator operation amount RA and the negative overshoot amount NMOD_ERR and replacing this negative overshoot amount NMOD_ERR with the negative overshoot estimated value NMOD_ERR_EST.

[0180] The negative overshoot amount NMOD_ERR is determined according to the required traveling power, the inertia of the engine shaft, the hydraulic load, the sampling rate of the engine speed sensor 64, the calculation cycle of the engine controller 120, the response time constants of the fuel injector 23 and the engine 20, and the boost pressure of the engine 20. As described above, the required traveling power is determined based on the accelerator operation amount RA and the motor speed NMOT.

[0181] In the modulating operation, all the parameters except for the accelerator operation amount RA are fixed or approximately determined. Therefore, a correlation map between the accelerator operation amount RA and the amount of negative overshoot can be created, as shown in Figure 13. Note that because of the presence of creep torque, the negative overshoot estimated value NMOD_ERR_EST is greater than 0 (zero) in the correlation map Mo when the accelerator operation amount RA is 0 (zero).

[0182] 12, the target correction value calculation unit 311 calculates the target correction value NC_TGT based on the negative overshoot estimated value NMOD_ERR_EST calculated by the negative overshoot estimation unit 310. The ROM 102 of the main controller 100C stores a correlation map Mc (see FIG. 7) between the amount of negative overshoot NMOD_ERR and the target correction value NC_TGT.

[0183] The target correction value calculation unit 311 refers to the correlation map Mc and calculates the target correction value NC_TGT based on the overshoot estimated value NMOD_ERR_EST. Note that the target correction value calculation unit 311 calculates the target correction value NC_TGT using the overshoot estimated value NMOD_ERR_EST as the amount of overshoot NMOD_ERR in the correlation map Mc. The characteristics indicated by this correlation map Mc are determined in advance by calculation or experiment.

[0184] When the modulate determination flag FL is set to ON, the correction value calculation unit 112C sets the rotation speed correction value NC to the target correction value NC_TGT calculated by the target correction value calculation unit 311. When the modulate determination flag FL is set to OFF, the correction value calculation unit 112C sets the rotation speed correction value NC to the initial correction value NC_INI (=0).

[0185] Next, an example of engine control executed by the main controller 100C according to the fourth embodiment will be described with reference to Fig. 14. Fig. 14 is a diagram similar to Fig. 8, and is a flowchart of engine control executed by the main controller 100C. The main controller 100C according to the fourth embodiment executes the processes of steps S310 and S311 between steps S110 and S120 in the flowchart of Fig. 8.

[0186] In step S310, the negative overshoot estimation unit 310 refers to the correlation map Mo (FIG. 13) and calculates the negative overshoot estimated value NMOD_ERR_EST based on the accelerator operation amount RA detected by the accelerator operation amount sensor 56a of the operation amount detection device 150, and then proceeds to step S311.

[0187] In step S311, the target correction value calculation unit 311 refers to the correlation map Mc (FIG. 7) and calculates the target correction value NC_TGT based on the negative overshoot estimated value NMOD_ERR_EST calculated in step S310, and the process proceeds to step S120.

[0188] Then, in step S190, correction value calculation unit 112C sets rotation speed correction value NC to target correction value NC_TGT calculated in step S311, and the process proceeds to step S210.

[0189] The processing in the other steps is the same as that in the flowchart of FIG. 8, and therefore the description thereof will be omitted.

[0190] As described above, the control device 11 according to the fourth embodiment increases the rotation speed correction value NC as the operation amount of the accelerator operation device 56 (accelerator operation amount RA) increases (see FIGS. 7 and 13). That is, the control device 11 increases the command rotation speed NEG_CMD as the second target rotation speed as the operation amount of the accelerator operation device 56 increases. This achieves a balance between the rotation speed correction value NC and the negative overshoot amount NMOD_ERR regardless of the magnitude of the accelerator operation amount RA. That is, regardless of the degree of depression of the accelerator pedal by the operator, the actual engine rotation speed NEG_ACT after the modulating operation ends will not fall significantly below or exceed the target engine rotation speed NEG_TGT. Therefore, acceleration performance after the modulating operation ends can be improved over a wider operating range of the accelerator operation device 56.

[0191] The following modified examples are also within the scope of the present invention, and it is possible to combine the configuration shown in the modified example with the configuration described in the above embodiment, to combine the configurations described in the different embodiments above, or to combine the configurations described in the different modified examples below.

[0192] <Variation 1> In the first embodiment, an example has been described in which the wheel loader 1 is determined to be in modulated operation when the rotational speed deviation (first rotational speed deviation) ΔNEG becomes larger than the first rotational speed threshold (first threshold) NTH1, and the wheel loader 1 is determined to be in unmodulated operation when the rotational speed deviation (second rotational speed deviation) ΔNEG becomes smaller than the second rotational speed threshold (second threshold) NTH2. However, a delay may be introduced in the determination of whether the wheel loader is in modulated operation or unmodulated operation.

[0193] In step S140 of FIG. 8, if the state in which the rotational speed deviation (first rotational speed deviation) ΔNEG is greater than the first rotational speed threshold (first threshold) NTH1 continues for the first time (predetermined time) Tt1, the modulate determination unit 111 determines that the wheel loader 1 is performing a modulating operation, and proceeds to step S150.

[0194] In step S160 of FIG. 8, if the state in which the rotational speed deviation (second rotational speed deviation) ΔNEG is less than the second rotational speed threshold (second threshold) NTH2 continues for a second time (predetermined time) Tt2, the modulation determination unit 111 determines that the wheel loader 1 is in non-modulated operation, and proceeds to step S170.

[0195] The first time Tt1 and the second time Tt2 are threshold values ​​for preventing unstable operation of the wheel loader 1, and are stored in advance in the ROM 102. The first time Tt1 and the second time Tt2 may be the same value or different values.

[0196] According to this modification, it is possible to prevent unstable operation caused by the modulation determination flag FL being switched due to pulsation of the actual engine rotation speed NEG_ACT. Similarly, it is possible to prevent unstable operation caused by the modulation determination flag FL being switched due to noise contained in the detected value of the actual engine rotation speed NEG_ACT. Furthermore, it is possible to prevent unstable operation caused by the modulation determination flag FL being momentarily switched when the amount of operation of the accelerator operation device 56 or the lever of the working device 6 is changed before and after the modulation determination flag FL is switched.

[0197] In the first embodiment, an example was described in which a delay was introduced in determining whether a modulated operation or a non-modulated operation was in progress, but in the second to fourth embodiments, a delay may be introduced in determining whether a modulated operation or a non-modulated operation was in progress.

[0198] <Variation 2> In the above embodiment, an example has been described in which the amount of negative overshoot is suppressed by correcting the target engine rotation speed NEG_TGT to calculate the command rotation speed NEG_CMD and controlling the fuel injection amount of the engine 20 so that the actual engine rotation speed NEG_ACT coincides with the command rotation speed NEG_CMD. However, the present invention is not limited to this.

[0199] For example, the fuel injection amount may be controlled as follows. The engine controller 120 according to this modified example controls the fuel injection amount of the fuel injector 23 so that the actual engine rotation speed NEG_ACT coincides with the target engine rotation speed NEG_TGT. Furthermore, when it is determined that the wheel loader 1 is in a modulated operation, the main controller 100 according to this modified example calculates a value that is greater than the target engine rotation speed NEG_TGT by a predetermined value (a value equivalent to the target correction value NC_TGT) as a determination threshold value (second target rotation speed) NEG_TH. When the modulate determination flag FL is set to on and the actual engine rotation speed NEG_ACT becomes less than the determination threshold value NEG_TH, the main controller 100 transmits a compulsory fuel injection signal to the engine controller 120.

[0200] When the engine controller 120 receives the forced fuel injection signal, it increases the fuel injection amount and injects fuel for a certain period of time regardless of the actual engine speed NEG_ACT and the target engine speed NEG_TGT. After the certain period of time has elapsed, the engine controller 120 controls the fuel injector 23 so that the actual engine speed NEG_ACT coincides with the target engine speed NEG_TGT.

[0201] According to this modification, it is possible to obtain the same effects as those of the first embodiment.

[0202] <Variation 3> The wheel loader 1 may also include a chopper circuit electrically connected to the power generation inverter 41 and the traveling inverter 42 (see FIG. 2), and a discharge resistor electrically connected to the power generation inverter 41 and the traveling inverter 42 by the switching operation of the chopper circuit. In this configuration, when the input voltage of the chopper circuit exceeds a set voltage, the chopper circuit is operated so that unnecessary power can be consumed by the discharge resistor. By applying the present invention to a wheel loader 1 equipped with a chopper circuit and a discharge resistor, the operation frequency of the chopper circuit and the discharge resistor can be reduced, and the mechanical life of these devices can be improved.

[0203] <Variation 4> Furthermore, the traveling drive device 45 according to the above embodiment has been described as an example in which a single traveling motor 43 is provided. However, the present invention is not limited to this. The traveling drive device 45 may be provided with multiple traveling motors 43. For example, the traveling drive device 45 may be configured using two traveling motors 43 directly connected to the front wheels 7A in a one-to-one relationship, or may be configured using four traveling motors 43 directly connected to the four wheels 7 in a one-to-one relationship. Furthermore, the traveling motors 43 and the wheels 7 may be integrated.

[0204] <Variation 5> Furthermore, in the above embodiment, the case has been described where the system that drives the working device 6 is a hydraulic drive system that transmits the power of the engine 20 to the working device 6 (see FIG. 2). In the hydraulic drive system of the above embodiment, the hydraulic oil discharged from the hydraulic pump 30A is converted into mechanical energy by the arm cylinder 4 and the bucket cylinder 5. However, the present invention is not limited to this. The drive system that drives the working device 6 may also be an electric drive system. In an electric drive system, the arm cylinder 4 and the bucket cylinder 5 are not hydraulic cylinders, but electric cylinders that are driven by electric power generated by the generator motor 40.

[0205] <Variation 6> In the above embodiment, values ​​used in various determinations and calculations may be subjected to moving average processing or low-pass filtering to avoid the effects of disturbances and noise. Furthermore, by performing moving average processing or low-pass filtering on the rotation speed correction value NC, it is possible to suppress a sudden fluctuation in the rotation speed correction value NC immediately after an increase in the actual engine rotation speed NEG_ACT, thereby improving the stability and operability of engine control.

[0206] <Variation 7> Some or all of the functions of the control device (main controller and engine controller) 11 described in the above embodiment may be realized by hardware (for example, by designing logic for executing each function as an integrated circuit).

[0207] Although the embodiments of the present invention have been described above, these embodiments merely illustrate some of the application examples of the present invention, and the technical scope of the present invention is not intended to be limited to the specific configurations of the above embodiments. The above-described embodiments and variations are provided as examples to facilitate understanding of the present invention, and are not necessarily limited to those including all of the described configurations. Furthermore, it is possible to replace part of the configuration of one embodiment or variation with the configuration of another embodiment or variation, and it is also possible to add the configuration of another embodiment or variation to the configuration of one embodiment or variation. Note that the control lines and information lines shown in the figures are those considered necessary for explanation, and do not necessarily represent all control lines and information lines required in the product. In reality, it can be assumed that almost all configurations are interconnected.

[0208] Furthermore, in the above embodiment, an example was described in which the work vehicle was a wheel loader 1, but the present invention can be applied to various work vehicles, such as wheeled excavators and forklifts, that are equipped with a traveling drive device capable of regenerative braking using engine power. [Explanation of symbols]

[0209] 1...wheel loader (work vehicle), 2...arm (driven member), 3...bucket (driven member), 4...arm cylinder (hydraulic cylinder), 5...bucket cylinder (hydraulic cylinder), 6...working device, 7...wheel, 7A...front wheel, 7B...rear wheel, 8...body, 8A...front body, 8B...rear body, 10...center joint, 11...control device, 12...operator's cab, 20...engine, 23...fuel injection device, 30A, 30B, 30C...hydraulic pump, 31...front control unit, 32...brake control unit, 33...steering control unit, 40...generator motor, 41...generator inverter, 42 ...Travel inverter, 43...Travel motor, 45...Travel drive device, 51...Forward / reverse switch (torque direction detection device), 56...Accelerator operation device, 56a...Accelerator operation amount sensor, 58...Motor speed sensor (wheel rotation direction detection device), 61...Vehicle speed sensor (wheel rotation direction detection device), 64...Engine rotation speed sensor, 91...Excavation target, 92...Loading target, 100, 100A, 100B, 100C...Main controller, 110...Target speed calculation unit, 111, 111A, 111B...Modulation determination unit, 112, 112C...Correction value calculation unit, 113...Command value calculation unit, 120 ...engine controller, 150...operated variable detection device, 151...discharge pressure detection device, 310...overshoot estimation unit, 311...target correction value calculation unit, FL...modulation judgment flag, NC...rotation speed correction value, NC_INI...initial correction value, NC_TGT...target correction value (predetermined correction value), NEG_ACT...actual engine rotation speed, NEG_CMD...command rotation speed (second target rotation speed), NEG_TGT...target engine rotation speed (first target rotation speed), NEG_TH...judgment threshold (second target rotation speed), NMOD_ERR...overshoot amount, NMOD_ERR_ EST...estimated overshoot value, NMOT...motor speed (rotation speed of the traveling electric motor), NTH1...first rotation speed threshold (predetermined first threshold), NTH2...second rotation speed threshold (predetermined second threshold), PEG_ACC...engine acceleration component power, RA...accelerator operation amount (operation amount of accelerator operation device), RTH...operation amount threshold, Tt1...first time (predetermined time), Tt2...second time (predetermined time), ΔNEG...rotation speed deviation (first rotation speed deviation when the modulation determination flag is set to off, second rotation speed deviation when the modulation determination flag is set to on)

Claims

1. The car body and a wheel provided on the vehicle body; an engine mounted on the vehicle body; a generator motor mechanically connected to the engine; a travel drive device capable of driving the wheels using electric power generated by the generator motor and capable of regenerative braking of the wheels; an engine rotation speed sensor for detecting a rotation speed of the engine; a control device that controls a fuel injection amount of the engine so that the rotation speed of the engine detected by the engine rotation speed sensor matches a first target rotation speed, The control device When the rotation speed of the engine increases above the first target rotation speed due to regenerative braking being performed by a modulating operation that switches the traveling direction of the vehicle body, a fuel injection amount of the engine is reduced; When the increase in the rotation speed of the engine due to regenerative braking has ended and the rotation speed of the engine is decreasing, and the rotation speed of the engine becomes less than a predetermined second target rotation speed that is greater than the first target rotation speed, the amount of fuel injected into the engine is increased. A work vehicle characterized by:

2. The work vehicle according to claim 1, The control device calculating a first rotation speed deviation that is a difference between the rotation speed of the engine and the first target rotation speed; If the calculated first rotational speed deviation becomes larger than a predetermined first threshold value, it is determined that the work vehicle is in a modulated operation; When it is determined that the work vehicle is in a modulating operation, a predetermined correction value is added to the first target rotation speed to calculate the second target rotation speed; calculating a second rotation speed deviation that is a difference between the rotation speed of the engine and the calculated second target rotation speed; If the calculated second rotational speed deviation is less than a predetermined second threshold, it is determined that the work vehicle is in unmodulated operation; When it is determined that the work vehicle is in unmodulated operation, the amount of fuel injection of the engine is controlled so that the rotation speed of the engine coincides with the second target rotation speed until a predetermined time has elapsed, and after the predetermined time has elapsed, the amount of fuel injection is controlled so that the rotation speed of the engine coincides with the first target rotation speed. A work vehicle characterized by:

3. The work vehicle according to claim 2, An accelerator operation device operated by an operator is provided, The control device the first target rotation speed is increased as the operation amount of the accelerator operation device is increased, When the operation amount of the accelerator operation device is larger than a predetermined operation amount threshold and the first rotation speed deviation is larger than the first threshold, it is determined that the work vehicle is in a modulating operation. A work vehicle characterized by:

4. The work vehicle according to claim 2, The control device If the state in which the first rotational speed deviation is greater than the first threshold continues for a predetermined time, it is determined that the work vehicle is performing a modulated operation; When the second rotational speed deviation remains less than the second threshold value for a predetermined period of time, it is determined that the work vehicle is in unmodulated operation. A work vehicle characterized by:

5. The work vehicle according to claim 2, a torque direction detection device that detects the direction of the drive torque generated by the traveling drive device; a wheel rotation direction detection device that detects the rotation direction of the wheel, The control device When the direction of the drive torque generated by the traveling drive device, detected by the torque direction detection device, is opposite to the rotation direction of the wheels, detected by the wheel rotation direction detection device, and the first rotation speed deviation becomes larger than the first threshold value, it is determined that the work vehicle is in a modulated operation. A work vehicle characterized by:

6. The work vehicle according to claim 1, a hydraulic pump driven by the engine; a working device having a hydraulic cylinder that is extended and retracted by hydraulic oil discharged from the hydraulic pump, and a driven member that is moved in accordance with the extension and retraction of the hydraulic cylinder; A work vehicle characterized by:

7. The work vehicle according to claim 1, The traveling drive device has a traveling motor that is driven by the electric power generated by the generator motor. A work vehicle characterized by:

8. The work vehicle according to claim 1, An accelerator operation device operated by an operator is provided, The control device the first target rotation speed is increased as the operation amount of the accelerator operation device is increased, The greater the operation amount of the accelerator operation device, the greater the second target rotation speed. A work vehicle characterized by:

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