Work vehicles

Abstract

To provide a work vehicle capable of restricting drive force when a wheel is slipped, which detects the slip of the wheel in an earlier stage, and thereby can improve work efficiency.SOLUTION: A work vehicle includes: a vehicle body having wheels; a hydraulic pump mounted on the vehicle body; a work device having a hydraulic actuator driven by hydraulic oil discharged from the hydraulic pump; a pressure sensor for detecting the pressure of the hydraulic actuator; a travel driving device for driving the wheels; a drive force sensor for detecting the drive force of the travel driving device; and a control device for controlling the drive force of the travel driving device. The control device calculates thrust of the hydraulic actuator according to reaction force of the work device received from a work object, on the basis of the detection result of the pressure sensor, and restricts the drive force, when a slip determination condition including non-increase of the thrust of the hydraulic actuator is established even though the drive force of the travel driving device is increasing.SELECTED DRAWING: Figure 3

Description

[Technical Field]

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

[0002] A known example of a work vehicle is a wheel loader equipped with a travel device for moving the vehicle body and a work device having a bucket and arm for excavating earth and sand, etc. Excavation work, which is one type of work performed by such a work vehicle, involves an operator operating, for example, an accelerator pedal to increase the driving force for moving the vehicle body forward, while penetrating the bucket into a work object such as natural ground and lifting the bucket to scoop up the work object.

[0003] When a work vehicle is excavating, if the driving force for moving the vehicle forward exceeds the maximum static friction force between the tires and the ground, the tires will slip. If slippage occurs during excavation work, the bucket cannot penetrate sufficiently into the work object, reducing work efficiency. The operator must adjust the driving force by feel to a level that prevents slippage during excavation work, which places a heavy burden on the operator.

[0004] Therefore, a technology has been proposed that automatically suppresses the occurrence of slippage when a work vehicle is performing excavation work (see Patent Document 1). Patent Document 1 discloses "a driving force control device for a work vehicle that is equipped with a work implement and in which engine power is transmitted as driving force to tires via a driving force transmission path, characterized in that the device comprises driving force variable means that is provided in the driving force transmission path and is capable of freely changing the driving force transmitted to the tires, tire slip detection means that detects the occurrence of tire slippage, driving force measurement means that measures the driving force, and driving force control means that controls the driving force variable means so that the driving force is less than the driving force at the time tire slippage is detected." [Prior art documents] [Patent documents]

[0005] [Patent Document 1] WO2008 / 146846A1 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in a technology that detects slip based on wheel speed (tire speed), such as the technology described in Patent Document 1, if slip occurs in which the wheel speed increases gradually, it takes time for the wheel speed to reach the threshold value for slip determination, which can cause a delay in detecting the slip.If there is a delay in detecting the slip, the time that the slip occurs will be longer, which will reduce work efficiency.

[0007] The present invention aims to provide a work vehicle that can reduce the burden on the operator by automatically limiting the driving force when the wheels slip, and that can improve work efficiency by detecting wheel slippage earlier and shortening the duration of the slip. [Means for solving the problem]

[0008] A work vehicle according to one aspect of the present invention includes a vehicle body having wheels, a hydraulic pump mounted on the vehicle body, a working device having a hydraulic actuator driven by hydraulic fluid discharged from the hydraulic pump, a pressure sensor that detects the pressure of the hydraulic actuator, a traveling drive device that drives the wheels, a driving force sensor that detects the driving force of the traveling drive device, and a control device that controls the driving force of the traveling drive device. The control device calculates a thrust of the hydraulic actuator corresponding to a reaction force that the working device receives from a work object based on the detection result of the pressure sensor, and limits the driving force when a slip determination condition is met, which condition includes the thrust of the hydraulic actuator not increasing even though the driving force of the traveling drive device is increasing. [Effects of the Invention]

[0009] According to the present invention, a work vehicle can be provided that can reduce the operating burden on the operator by automatically limiting the driving force when the wheels slip, and that can improve work efficiency by detecting wheel slippage earlier and shortening the duration of the slip. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a side view of a wheel loader. [Figure 2] FIG. 2 is a configuration diagram of a wheel loader control system. [Figure 3] FIG. 3 is a functional block diagram of the main controller. [Figure 4] FIG. 4 is a diagram showing an example of a correlation map that defines the relationship between the thrust force during slip and the estimated value of the friction coefficient. [Figure 5] FIG. 5 is a diagram showing an example of a correlation map that defines the relationship between the estimated friction coefficient value and the driving force upper limit value. [Figure 6] FIG. 6 is a flowchart showing an example of a main flow of the driving force control executed by the main controller. [Figure 7] FIG. 7 is a flowchart showing an example of the process of setting the excavation determination flag in FIG. [Figure 8] FIG. 8 is a flowchart showing an example of the slip determination flag setting process of FIG. [Figure 9] FIG. 9 is a diagram showing time series changes in the parameters (bucket operation amount, arm operation amount, travel driving force, arm cylinder thrust, wheel speed, and slip determination flag) of the wheel loaders according to this embodiment and the comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, an embodiment of a work vehicle according to the present invention will 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, but the work vehicle of the present invention is not limited to wheel loaders and may be a bulldozer or the like. In addition, in this embodiment, an example will be described in which a hybrid system using an engine and a generator motor as a drive source is employed, but a system using an engine alone as a drive source may also be employed. Furthermore, 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 all four wheels are in contact with the traveling surface.

[0012] - Wheel loader configuration - Figure 1 is a side view of a 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.

[0013] 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.

[0014] 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 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 rotatable in the front-rear 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.

[0015] The wheel loader 1 is equipped with a traveling drive device 45 that drives the wheels 7 provided on the vehicle body 8. The traveling drive device 45 includes a traveling motor 43 and a traveling device 11 that receives driving force (hereinafter also referred to as traveling drive force) from the traveling motor 43. The traveling device 11 has front wheels 7A that are wheels 7 attached to the front vehicle body 8A, rear wheels 7B that are wheels 7 attached to the rear vehicle body 8B, and a power transmission device that transmits the traveling drive force (power) from the traveling motor 43 to the wheels 7. The power transmission device is configured to include an axle, a differential device, a propeller shaft, etc. Power from the traveling motor 43 is transmitted to at least one of the front wheels 7A and the rear wheels 7B via the power transmission device.

[0016] The traveling motor 43 is an electric motor that drives the wheels 7 of the traveling device 11. The traveling motor 43 is driven to rotate by electric power generated by a generator motor 40 (see FIG. 2) that is rotated by the power of the engine 20.

[0017] The wheel loader 1 is steered by a steering device 22 (see FIG. 2) 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.

[0018] -Wheel loader control system- Fig. 2 is a configuration diagram of the control system 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 driven by electric power generated by the generator motor 40.

[0019] 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.

[0020] 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.

[0021] The hydraulic cylinders (hydraulic actuators) 4, 5, 15, 17, and 18 are driven to expand and contract by hydraulic oil (pressurized oil) discharged from hydraulic pumps 30A, 30B, and 30C which are rotated by torque output from an engine 20 (see FIG. 2).

[0022] 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.

[0023] The wheel loader 1 is equipped with a main controller 100 which is a control device that controls the entire vehicle, an engine controller 25 which controls the fuel injector 23 based on an engine rotation speed command from the main controller 100, the fuel injector 23 which controls the fuel injection amount based on a fuel injection amount command from the engine controller 25, a generator motor inverter (hereinafter referred to as the power generation inverter) 41 which 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 which controls the torque of the traveling motor 43 (i.e., the traveling driving force generated by the traveling drive device 45) based on a traveling drive torque command input from the main controller 100, and various operating devices (51 to 57) provided in the driver's cab 12.

[0024] 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 operating positions including a forward position (F), a standby position (N), and a reverse position (R). For ease of explanation, the operating devices 52, 53 of the working device 6 and the operating device 56 of the traveling drive device 45 will also be collectively referred to as operating device 50.

[0025] 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.

[0026] The main controller 100 is configured as a microcomputer having a CPU (Central Processing Unit) 101 as a processing device (operating circuit), a ROM (Read Only Memory) 102 and a 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 25 is also configured as a microcomputer having a processing device (operating circuit), a storage device, an input / output interface, etc. The main controller 100 and the engine controller 25 may each be configured as one microcomputer or as multiple microcomputers.

[0027] 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.

[0028] The CPU 101 is a processing device 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.

[0029] 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 25, etc.

[0030] 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 25 based on operation signals input from various operating devices and sensor signals input from various other sensors.

[0031] 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.

[0032] 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.

[0033] Further, the sensor signals input to the main controller 100 include a signal representing the wheel speed (rotation speed of the wheels (drive wheels) 7) detected by a wheel speed sensor 61. The wheel speed detected by the wheel speed sensor 61 can be converted into the traveling speed (vehicle speed) of the vehicle. The wheel speed sensor 61 detects the wheel speed and outputs a signal representing the detected wheel speed to the main controller 100. Further, the sensor signals input to the main controller 100 include signals representing the rotation 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 rotation speed sensors, and a signal representing the pressure (load pressure) of the arm cylinder 4 detected by an arm cylinder pressure sensor 75.

[0034] The multiple rotation speed sensors include an engine rotation speed sensor 64 that detects the actual rotation speed of the engine 20, 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 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 representing the detected actual engine rotation speed 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 detect the rotation speed of any shaft constituting the power transmission device. In this case, the main controller 100 calculates the actual engine rotation speed based on the detection result of the engine rotation speed sensor 64.

[0035] The motor speed sensor 58 detects the motor speed and outputs a signal indicating the detection result to the main controller 100 and a driving force sensor 65 (described later). The motor speed detected by the motor speed sensor 58 is correlated with the wheel speed. In other words, the motor speed detected by the motor speed sensor 58 can be converted into vehicle speed.

[0036] In the illustrated example, the engine rotation speed sensor 64 is connected to the main controller 100, but it may also be connected to the engine controller 25. In this case, the main controller 100 acquires the actual engine rotation speed detected by the engine rotation speed sensor 64 via the engine controller 25.

[0037] Further, the sensor signals input to the main controller 100 include a signal representing the driving force of the traveling drive device 45 detected by the driving force sensor 65. The driving force sensor 65 calculates the driving force of the traveling drive device 45 based on the command value of the driving torque calculated by the main controller 100, the motor speed input from the motor speed sensor 58, the radius of the wheel 7, and the inertia constant of the wheel 7, and outputs a signal representing the calculation result to the main controller 100. The radius and inertia constant of the wheel 7 are stored, for example, in a memory provided in the driving force sensor 65. Note that the data stored in the memory of the driving force sensor 65 (such as the radius and inertia constant of the wheel 7) can be updated by data output from the main controller 100.

[0038] The driving force sensor 65 detects the traveling driving force F according to the following equation (1): M Calculate the following. F M =(T M_COM -M×ΔS M ) / R···(1) where T M_COM is the command value of the driving torque calculated by the main controller 100, M is the inertia constant of the wheel 7, and R is the radius of the wheel 7. ΔS M is the angular acceleration of the traveling motor 43 and is calculated based on the motor speed detected by the motor speed sensor 58.

[0039] The driving force sensor 65 is not limited to the above configuration. For example, the driving force sensor 65 may calculate the driving force based on the output torque (motor torque) of the traveling motor 43 detected by a torque sensor, or may calculate the driving force based on the current flowing through the traveling motor 43 detected by a current sensor. The functions of the driving force sensor 65 may also be performed by the main controller 100. In this case, the driving force sensor 65 is omitted, and the motor speed sensor 58 functions as a driving force sensor that detects a physical quantity related to the driving force (motor speed), and the main controller 100 calculates the driving force F based on the detection result of the motor speed sensor 58. M Calculate the following.

[0040] The main controller 100 calculates a target rotation speed of the engine 20 (hereinafter also referred to as a target engine rotation speed) based on the accelerator operation amount, the arm operation amount, the bucket operation amount, etc. The main controller 100 calculates a rotation speed command value based on the target engine rotation speed and outputs it to the engine controller 25. The main controller 100 also outputs an actual engine rotation speed detected by the engine rotation speed sensor 64 to the engine controller 25.

[0041] The engine controller 25 compares the rotation speed command value acquired from the main controller 100 with the actual engine rotation speed detected by the engine rotation speed sensor 64, and controls the fuel injector 23 so that the actual engine rotation speed becomes the rotation speed command value. The fuel injector 23 controls the fuel injection amount based on the fuel injection command output from the engine controller 25, and operates the engine 20.

[0042] In this way, the main controller 100 , the engine controller 25 and the fuel injector 23 cooperate to configure an engine control device that controls the operation of the engine 20 .

[0043] 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 (flow rate 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 this directional control valve, and the like.

[0044] 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 (flow rate 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 this directional control valve, and the like.

[0045] The main controller 100 outputs a steering control command based on the operation direction and operation amount 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 (flow rate 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 this directional control valve, and the like.

[0046] The power generation inverter 41 and the traveling inverter 42 are connected by a DC section (DC bus) 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.

[0047] 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.

[0048] 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, causing the bucket 3 to rotate back and forth (dump operation or crowd operation).

[0049] 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.

[0050] When the forward / reverse switch 51 is set 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 set 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. When the forward / reverse switch 51 is set 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. Note that when the forward / reverse switch 51 is set to the forward position (F) or the reverse position (R), the vehicle body 8 travels forward or backward (creep) at an extremely low speed, even if the accelerator pedal is not depressed.

[0051] -Main controller functions- 3 is a functional block diagram of the main controller 100. The main controller 100 generates a traveling drive torque command based on detection signals from each sensor and outputs it to the traveling inverter 42, thereby controlling the traveling drive force generated by the traveling drive device 45. Below, with reference to FIG. 3, details of each function when the main controller 100 generates a traveling drive torque command will be described.

[0052] As shown in FIG. 3, by executing the programs stored in ROM 102, main controller 100 functions as a motor speed change amount calculation unit 112, a thrust force calculation unit 110, a thrust force change amount calculation unit 111, a driving force change amount calculation unit 113, an excavation operation determination unit 114, a slip determination unit 115, a thrust force retention unit during slip 116, a friction coefficient estimation unit 117, a driving force upper limit value calculation unit 118, a traveling required driving force calculation unit 119, a minimum value selection unit 120, and a torque command generation unit 121.

[0053] The motor speed change amount calculation unit 112 calculates the motor speed S detected by the motor speed sensor 58. M The time rate of change of (hereinafter also referred to as the speed rate of change) ΔS M Calculate the motor speed S M is a positive value when the vehicle body 8 moves forward, and is a negative value when the vehicle body 8 moves backward. The motor speed change amount calculation unit 112 calculates the motor speed S M Previous value S M a and the current value S M The difference between b and (S M bS M a) is the previous value S M The current value S from the time ta when a was detected M By dividing b by the time Δt (= tb - ta) until the time tb is detected, the speed change rate ΔS M (=(S M bS M a) / (tb-ta)) is calculated. Therefore, the speed change rate ΔS M is a positive value when the advancing vehicle body 8 is accelerating, and is a negative value when the advancing vehicle body 8 is decelerating. Mis 0 when the vehicle body 8 is traveling at a constant speed.

[0054] The excavation operation determination unit 114 determines whether the current state is an excavation operation state in which the work implement 6 is excavating a work object such as natural ground, or a non-excavation operation state in which the work implement 6 is not excavating a work object. If the excavation operation determination unit 114 determines that the current state is an excavation operation state, it sets the excavation determination flag FLdig on (FLdig = 1), and if the current state is a non-excavation operation state, it sets the excavation determination flag FLdig off (FLdig = 0).

[0055] The excavation determination flag FLdig indicates whether the wheel loader 1 is in an excavation work state or a non-excavation work state. Therefore, the main controller 100 can determine whether the wheel loader 1 is in an excavation work state based on the setting state of the excavation determination flag FLdig.

[0056] The excavation work determination unit 114 determines that the excavation work state is in progress when the excavation work conditions are met. When the wheel loader 1 moves forward toward a work object such as a mound of natural ground and then the working implement 6 enters the work object, the vehicle body 8 decelerates and the reaction force that the working implement 6 receives from the work object increases. As the reaction force increases, the thrust of the arm cylinder 4 also increases. For this reason, in this embodiment, the excavation work conditions include the following (Condition I) and (Condition II). (Condition I) The advancing vehicle 8 is decelerating. (Condition II) The thrust of the arm cylinder 4 is equal to or greater than a predetermined value.

[0057] Whether the advancing vehicle body 8 is decelerating or not is determined by the speed change rate ΔS calculated by the motor speed change amount calculation unit 112. M The excavation operation determination unit 114 can determine the speed change rate ΔS M is equal to or smaller than a predetermined speed change rate threshold value S1, the excavation operation determination unit 114 determines that (Condition I) is satisfied. Mis greater than the speed change rate threshold S1, it is determined that (Condition I) is not satisfied. The speed change rate threshold S1 is stored in advance in ROM 102. The speed change rate threshold S1 is a threshold for determining whether the advancing vehicle body 8 is decelerating as a result of the wheel loader 1 entering a work object, and is a value obtained by subtracting a margin value (>0) from 0. In other words, the speed change rate threshold S1 is smaller than 0 (S1<0). This margin value is determined in advance by calculation or experiment in order to prevent erroneous determinations due to changes in the speed of the traveling motor 43 caused by vibrations of the vehicle body 8, detection errors of the motor speed sensor 58, etc.

[0058] The thrust of the arm cylinder 4, which increases when the working device 6 receives a reaction force from the work object, is proportional to the pressure of the hydraulic oil in the bottom-side oil chamber (not shown) of the arm cylinder 4. For this reason, in this embodiment, the arm cylinder pressure P A Based on this, it is determined whether (Condition II) is satisfied.

[0059] As shown in FIG. 2, the arm cylinder pressure sensor 75 is a pressure sensor provided in an oil passage connecting a bottom-side oil chamber (not shown) of the arm cylinder 4 and the front control section 31, and detects the pressure of the hydraulic oil in the bottom-side oil chamber of the arm cylinder 4 (arm cylinder pressure) P A and outputs a signal representing the detection result to the main controller 100. The excavation operation determination unit 114 shown in FIG. A is equal to or greater than the cylinder pressure threshold value P1, it is determined that (Condition II) is satisfied. A is less than the cylinder pressure threshold P1, it is determined that (Condition II) is not satisfied. The cylinder pressure threshold P1 corresponds to the arm cylinder pressure detected when the excavation work is started in calculation or experiment, and is stored in advance in ROM 102.

[0060] When the excavation determination flag FLdig is set to off and both (Condition I) and (Condition II) are satisfied, the excavation work determination unit 114 determines that the excavation work conditions are met. That is, the excavation work determination unit 114 determines that the state of the wheel loader 1 has transitioned from a non-digging work state to an excavation work state, and switches the excavation determination flag FLdig from off to on (FLdig = 1). Note that when the excavation determination flag FLdig is set to off and either (Condition I) or (Condition II) is not satisfied, the excavation work determination unit 114 determines that the excavation work conditions are not met. That is, the excavation work determination unit 114 determines that the non-digging work state is continuing. That is, the excavation determination flag FLdig remains off.

[0061] When the wheel loader 1 finishes excavation work, it travels in reverse and moves away from the work object. Therefore, the excavation work determination unit 114 according to this embodiment determines whether or not an excavation work end condition has been met, that is, whether or not the wheel loader 1 has shifted from a working state to a non-working state, based on the operating position of the forward / reverse switch 51. The excavation work end condition includes the forward / reverse switch 51 being operated to the reverse position (R).

[0062] When the excavation determination flag FLdig is set to on and the forward / reverse switch 51 is operated to the reverse position (R), the excavation work determination unit 114 determines that the excavation work end condition is met. In other words, the excavation work determination unit 114 determines that the wheel loader 1 has transitioned from a working state to a non-working state, and switches the excavation determination flag FLdig from on to off (FLdig = 0). When the excavation determination flag FLdig is set to on and the forward / reverse switch 51 is not operated to the reverse position (R), the excavation work determination unit 114 determines that the excavation work end condition is not met. In other words, the excavation work determination unit 114 determines that the excavation work state is continuing. In other words, the excavation determination flag FLdig remains on.

[0063] The thrust calculation unit 110 calculates the arm cylinder thrust F by the following equation (2):A Calculate the following. F A =P A ×S A ···(2) where P A is the arm cylinder pressure detected by the arm cylinder pressure sensor 75, and S A is the pressure-receiving area (cross-sectional area) of the arm cylinder 4 stored in advance in the ROM 102. Arm cylinder thrust F A increases in accordance with an increase in the reaction force that the work implement 6 receives from the work object during excavation work.

[0064] The thrust force change amount calculation unit 111 calculates the arm cylinder thrust F calculated by the thrust force calculation unit 110. A The time rate of change of the thrust force (hereinafter also referred to as the thrust rate of change) ΔF A The thrust force change amount calculation unit 111 calculates the arm cylinder thrust F A Previous value of F A a and the current value F A Difference from b (F A bF A a) is the previous value F A The current value F from the time ta when a was detected A By dividing b by the time Δt (= tb - ta) until the detection time tb, the thrust change rate ΔF A (=(F A bF A a) / (tb-ta)) is calculated. Therefore, the thrust change rate ΔF A is the arm cylinder thrust F A When the force F increases, it becomes a positive value. A When the thrust change rate ΔF A is the arm cylinder thrust F A is constant, it is 0.

[0065] The driving force change amount calculation unit 113 calculates the traveling driving force F detected by the driving force sensor 65. M The time rate of change of the driving force (hereinafter also referred to as the driving force change rate) ΔF MThe driving force change amount calculation unit 113 calculates the traveling driving force F M Previous value of F M a and the current value F M Difference from b (F M bF M a) is the previous value F M The current value F from the time ta when a was detected M The driving force change rate ΔF is calculated by dividing b by the time Δt (= tb - ta) from the time b to the time tb. M (=(F M bF M a) / (tb-ta)) is calculated. Therefore, the driving force change rate ΔF M is the driving force F M When the driving force F M When the driving force change rate ΔF M is the driving force F M is constant, it is 0.

[0066] The slip determination unit 115 determines that the wheel 7 is slipping if the slip determination condition is met, and determines that the wheel 7 is not slipping if the slip determination condition is not met. The slip determination conditions include the following (Condition 1) to (Condition 5). If all of (Condition 1) to (Condition 5) are met, the slip determination unit 115 determines that the slip determination condition is met and sets the slip determination flag FLslip to on (FLslip=1). Note that if any of (Condition 1) to (Condition 5) is not met, the slip determination unit 115 determines that the slip determination condition is not met and sets the slip determination flag FLslip to off (FLslip=0). (Condition 1) Excavation work must be carried out. (Condition 2) The arm cylinder thrust is not increasing. (Condition 3) The driving force is increasing. (Condition 4) The arm operating device is not being operated. (Condition 5) The bucket operating device is not being operated.

[0067] The slip determination unit 115 determines whether or not (Condition 1) is satisfied based on the setting state of the excavation determination flag FLdig. If the excavation determination flag FLdig is set to on (FLdig=1), the slip determination unit 115 determines that (Condition 1) is satisfied, and if the excavation determination flag FLdig is set to off (FLdig=0), the slip determination unit 115 determines that (Condition 1) is not satisfied.

[0068] The slip determination unit 115 determines the thrust change rate ΔF A The slip determination unit 115 determines whether or not the condition 2 is satisfied based on the thrust force change rate ΔF A is the thrust change rate threshold F A If it is less than 1, it is determined that (Condition 2) is met, and the thrust change rate ΔF A is the thrust change rate threshold F A If it is greater than 1, it is determined that (Condition 2) is not satisfied. A 1 is a threshold value for determining whether a sudden decrease (loss) in the arm cylinder thrust has occurred at the start of slippage, and is determined by calculation or experiment. A 1 is a value less than or equal to 0 and is stored in the ROM 102.

[0069] The slip determination unit 115 determines the driving force change rate ΔF M The slip determination unit 115 determines whether or not the condition 3 is satisfied based on the driving force change rate ΔF M If is greater than 0, it is determined that (Condition 3) is met, and the driving force change rate ΔF M If is less than or equal to 0, it is determined that (Condition 3) is not satisfied.

[0070] The slip determination unit 115 detects the arm operation amount R detected by the arm operation amount sensor 52a. A The slip determination unit 115 determines whether or not the condition 4 is satisfied based on the arm operation amount R A Absolute value of |R A | is the arm operation amount threshold R AIf it is less than 1, it is determined that (Condition 4) is satisfied, and the arm operation amount R A Absolute value of |R A | is the arm operation amount threshold R A If it is greater than 1, it is determined that (Condition 4) is not satisfied. A The arm operation amount threshold R1 is a threshold value for determining whether the arm operation device 52 is being operated or not, and is stored in the ROM 102. A For example, when the maximum operation amount for raising the arm is 100% and the maximum operation amount for lowering the arm is -100%, 1 corresponds to an operation amount of about 5%.

[0071] The slip determination unit 115 determines the bucket operation amount R detected by the bucket operation amount sensor 53a. B The slip determination unit 115 determines whether or not the condition 5 is satisfied based on the bucket operation amount R B Absolute value of |R B | is the bucket operation amount threshold R B If it is less than 1, it is determined that (Condition 5) is satisfied, and the bucket operation amount R B Absolute value of |R B | is the bucket operation amount threshold R B If it is greater than 1, it is determined that (Condition 5) is not satisfied. B The bucket operation amount threshold R1 is a threshold for determining whether the bucket operation device 53 is being operated, and is stored in the ROM 102. B For example, when the maximum operation amount on the bucket dump side is 100% and the maximum operation amount on the bucket cloud side is -100%, 1 corresponds to an operation amount of about 5%.

[0072] The slip time thrust holding unit 116 holds the arm cylinder thrust F when the slip determination flag FLslip is switched from off to on. A , that is, the arm cylinder thrust F when the slip determination condition is met A Thrust force F when slipping A_slip (F A_slip =F A ) Thrust force during slip FA_slip is maintained at least until the slip determination flag FLslip is switched from ON to OFF. A_slip After the slip determination flag FLslip is switched from on to off, the value may be held until the flag FLslip is switched on again.

[0073] The friction coefficient estimation unit 117 uses the correlation map M μ (see FIG. 4), the slip thrust F held by the slip thrust holding unit 116 is A_slip The estimated friction coefficient μ is calculated based on the correlation map M μ is the thrust force during slip F A_slip The correlation map M is a prescribed data that defines the relationship between the estimated friction coefficient μ and the μ may be stored in a lookup table format or in a function format (approximation formula), for example.

[0074] Correlation map M in Fig. 4 μ As shown in the figure, the slip thrust F A_slip The friction coefficient estimate μ for the correlation map M μ is the thrust force during slip F A_slip When is 0, the estimated friction coefficient μ is 0, and the thrust F A_slip The correlation map M μ The characteristics of the correlation map M are determined in advance by calculation or experiment. μ The larger the slope of (increase in estimated friction coefficient / increase in thrust during slip), the greater the thrust during slip F A_slip The estimated coefficient of friction μ at

[0075] The driving force upper limit calculation unit 118 shown in FIG. 3 calculates the driving force upper limit value by using a correlation map M L 5, the driving force upper limit F is calculated based on the estimated friction coefficient μ calculated by the friction coefficient estimating unit 117. M_LIM The correlation map M Lis the estimated friction coefficient μ and the driving force upper limit F M_LIM The correlation map M L may be stored in a lookup table format or in a function format (approximation formula), for example.

[0076] As shown in Figure 5, the correlation map M L When the estimated friction coefficient μ is 0, the driving force upper limit F M_LIM is the minimum value F M_LIM_MIN As the friction coefficient estimated value μ increases from 0 to the predetermined value μp, the driving force upper limit value F M_LIM becomes large, and when the estimated friction coefficient μ is equal to or greater than the predetermined value μp, the driving force upper limit F M_LIM is the maximum value F M_LIM_MAX The upper limit of driving force F M_LIM The maximum value of F M_LIM_MAX corresponds to the maximum driving force that the traveling motor 43 can output. M_LIM The minimum value of F M_LIM_MIN corresponds to the minimum driving force that can move the wheel loader 1 forward. L The characteristics of the correlation map M are determined in advance by calculation or experiment. L The larger the slope of the equation (increase in the driving force upper limit value / increase in the estimated friction coefficient value), the greater the driving force upper limit value F M_LIM becomes larger.

[0077] In addition, the driving force upper limit F M_LIM The correlation map M is used only when the slip determination flag FLslip is set to ON. L When the slip determination flag FLslip is set to OFF, the driving force upper limit value calculation unit 118 uses the result calculated based on the characteristics of M_LIM to the maximum value F M_LIM_MAX Therefore, when the slip determination condition is met, the correlation map M L The driving force upper limit F is set according to the characteristics of M_LIM The driving force F MOn the other hand, if the slip determination condition is not met, the driving force upper limit F M_LIM to the maximum value F M_LIM_MAX is set, the driving force is not substantially limited.

[0078] The driving force requirement calculation unit 119 shown in FIG. 3 calculates the motor speed S detected by the motor speed sensor 58. M and the accelerator operation amount detected by accelerator operation amount sensor 56a. A required traveling driving force table used for calculating the required traveling driving force is stored in ROM 102. The required traveling driving force table stores a plurality of driving force curves corresponding to the accelerator operation amount so that the required traveling driving force increases or decreases according to an increase or decrease in the accelerator operation amount. The required traveling driving force table is set so that the required traveling driving force increases as the accelerator operation amount increases, and decreases as the rotation speed (motor speed) of traveling electric motor 43 increases.

[0079] The traveling required driving force calculation unit 119 selects a driving force curve corresponding to the magnitude of the accelerator operation amount, and calculates the rotation speed (motor speed) S of the traveling motor 43. M Based on the driving demand F M_REQ For example, when the accelerator operation device 56 is fully operated, the traveling required driving force calculation unit 119 selects the driving force curve indicated by the solid line, and calculates the traveling required driving force F based on the rotation speed of the traveling motor 43 by referring to the selected driving force curve. M_REQ Calculate.

[0080] The minimum value selection unit 120 selects the driving force upper limit value F calculated by the driving force upper limit calculation unit 118. M_LIM , and the required driving force F calculated by the required driving force calculation unit 119 M_REQ The smallest one is selected and the selected value is used as the driving target driving force F M_TGT It is determined as follows.

[0081] The torque command generator 121 generates the driving target driving force F selected by the minimum value selector 120. M_TGT Based on this, the driving torque command TM_COM The travel driving torque command T generated by the torque command generating unit 121 is M_COM is output to the traveling inverter 42 and the driving force sensor 65, and the traveling motor 43 is controlled so that the traveling driving force detected by the driving force sensor 65 becomes the target traveling driving force.

[0082] -Driving force control flow- The contents of the control executed by the main controller 100 to suppress slipping will be described with reference to Figures 6 to 8. Figure 6 is a flowchart showing an example of a main flow of the travel driving force control executed by the main controller 100, Figure 7 is a flowchart showing an example of the process of setting the excavation determination flag in Figure 6, and Figure 8 is a flowchart showing an example of the process of setting the slip determination flag in Figure 6.

[0083] The process shown in the flowchart of FIG. 6 is started, for example, when an ignition switch (engine key switch) is turned on, and after an initial setting (not shown) is performed, it is repeatedly executed at a predetermined control period. In the initial setting, the slip determination flag FLslip and the excavation determination flag FLdig are set to OFF. Furthermore, the process shown in the flowcharts of FIGS. 6 to 8 is executed based on the detection results (for example, arm cylinder pressure P A , arm operation amount R A , bucket operation amount R B ), the calculation results of each calculation unit (for example, arm cylinder thrust F A , Thrust force change rate ΔF A , velocity change rate ΔS M , driving force change rate ΔF M ) and a signal indicating the operation position from the forward / reverse switch 51, etc.

[0084] As shown in Fig. 6, in step S100, excavation operation determination unit 114 executes a process for setting an excavation determination flag FLdig. As shown in Fig. 7, when the process for setting an excavation determination flag starts, in step S110, excavation operation determination unit 114 determines whether the currently set excavation determination flag FLdig is on. If it is determined that the currently set excavation determination flag FLdig is off, the process proceeds to step S120. If it is determined that the currently set excavation determination flag FLdig is on, the process proceeds to step S150.

[0085] In step S120, the excavation operation determination unit 114 calculates the speed change rate ΔS, which is the time change rate of the motor speed calculated by the motor speed change amount calculation unit 112. M is equal to or less than the speed change rate threshold S1. M If it is determined that the speed change rate ΔS is equal to or less than the speed change rate threshold S1, the process proceeds to step S130. M is determined to be greater than the speed change rate threshold value S1, the excavation determination flag setting process shown in FIG. 7 ends.

[0086] In step S130, the excavation operation determination unit 114 determines whether the arm cylinder pressure P A It is determined whether the arm cylinder pressure P is equal to or greater than the cylinder pressure threshold value P1. A If it is determined that the arm cylinder pressure P is equal to or greater than the cylinder pressure threshold value P1, the process proceeds to step S140. A If it is determined that the cylinder pressure is less than the cylinder pressure threshold value P1, the excavation determination flag setting process shown in FIG. 7 ends.

[0087] In step S140, the digging operation determination unit 114 sets the digging determination flag to ON (FLdig=1), and ends the digging determination flag setting process shown in FIG.

[0088] In step S150, the excavation operation determination unit 114 determines whether the forward / reverse switch 51 is operated to the reverse position (R) based on the operation position signal from the forward / reverse switch 51. If it is determined that the forward / reverse switch 51 is operated to the reverse position (R), the process proceeds to step S160. If it is determined that the forward / reverse switch 51 is not operated to the reverse position (R), the excavation determination flag setting process shown in Figure 7 ends.

[0089] In step S160, the digging operation determination unit 114 sets the digging determination flag to off (FLdig=0), and ends the digging determination flag setting process shown in FIG.

[0090] When the excavation determination flag setting process is completed, the process proceeds to step S200 in FIG. 6. As shown in FIG. 6, in step S200, slip determination unit 115 executes the process of setting the slip determination flag FLslip. As shown in FIG. 8, when the slip determination flag setting process is started, in step S210, slip determination unit 115 determines whether the currently set excavation determination flag FLdig is on, similar to step S110 above. If it is determined that the currently set excavation determination flag FLdig is on, the process proceeds to step S220. If it is determined that the currently set excavation determination flag FLdig is off, the process proceeds to step S270.

[0091] In step S220, the slip determination unit 115 determines whether the driving force F M The driving force change rate ΔF M Determine whether or not is greater than 0. M If it is determined that the driving force change rate ΔF is greater than 0, the process proceeds to step S230. M If it is determined that is equal to or less than 0, the process proceeds to step S270.

[0092] In step S230, the slip determination unit 115 determines whether the arm cylinder thrust F calculated by the thrust force change amount calculation unit 111 is greater than the arm cylinder thrust F A The thrust change rate ΔF is the time rate of change of A is the thrust change rate threshold F A Determine whether it is equal to or less than 1. Thrust change rate ΔF A is the thrust change rate threshold F A If it is determined that the thrust force change rate ΔF is equal to or less than 1, the process proceeds to step S240. A is the thrust change rate threshold F A If it is determined that the value is greater than 1, the process proceeds to step S270.

[0093] In step S240, the slip determination unit 115 calculates the arm operation amount R detected by the arm operation amount sensor 52a. A is the arm operation amount threshold R A Determine whether it is 1 or less. Arm operation amount R A is the arm operation amount threshold R A If it is determined that the arm operation amount R is equal to or less than 1, the process proceeds to step S250. A is the arm operation amount threshold R A If it is determined that the value is greater than 1, the process proceeds to step S270.

[0094] In step S250, slip determination unit 115 calculates the bucket operation amount R detected by bucket operation amount sensor 53a. B is the bucket operation amount threshold R B Determine whether the bucket operation amount R is equal to or less than 1. B is the bucket operation amount threshold R B If it is determined that the bucket operation amount R is equal to or less than 1, the process proceeds to step S260. B is the bucket operation amount threshold R B If it is determined that the value is greater than 1, the process proceeds to step S270.

[0095] In step S260, slip determination unit 115 sets the slip determination flag to ON (FLslip=1), and ends the slip determination flag setting process shown in Fig. 8. In step S270, slip determination unit 115 sets the slip determination flag to OFF (FLslip=0), and ends the slip determination flag setting process shown in Fig. 8. When the slip determination flag setting process ends, the process proceeds to step S310 in Fig. 6.

[0096] 6, in step S310, slip thrust holding unit 116 and driving force upper limit calculation unit 118 determine whether the currently set slip determination flag FLslip is on. If it is determined that the currently set slip determination flag FLslip is on, the process proceeds to step S320. If the currently set slip determination flag FLslip is off, the process proceeds to step S350.

[0097] In step S320, the thrust force holding unit 116 at the time of slipping holds the arm cylinder thrust F calculated by the thrust force calculation unit 110. A Thrust force F when slipping A_slip That is, the slip thrust holding unit 116 holds the arm cylinder thrust F when the slip determination flag FLslip is switched from off to on. A Thrust force F when slipping A_slip When the process of step S320 ends, the process proceeds to step S330.

[0098] In step S330, the friction coefficient estimation unit 117 calculates the slip thrust F A_slip Based on the correlation map M μ The estimated friction coefficient μ is calculated based on the characteristics (see FIG. 4), and the process proceeds to step S340.

[0099] In step S340, the driving force upper limit calculation unit 118 calculates the correlation map M based on the estimated friction coefficient μ calculated in step S330. L (See Figure 5)M_LIM Calculate the following.

[0100] In step S350, the driving force upper limit calculation unit 118 calculates the driving force upper limit F M_LIM Maximum value F M_LIM_MAX When the processing of step S340 or step S350 is completed, the processing of the flowchart shown in Fig. 6 for this control cycle ends, and in the next control cycle, the processing from step S100 to step S340 or step S350 is executed again.

[0101] In this way, when a slip is detected by switching the slip determination flag from off to on, the thrust F A_slip Based on the driving force upper limit F M_LIM Therefore, the driving force F M F M_LIM_MIN More than F M_LIM_MAX The driving force upper limit F is set within the following range: M_LIM On the other hand, if no slip is detected, the driving force upper limit is always limited to the maximum value F M_LIM_MAX Therefore, the driving force is not limited. M is the required driving force F calculated based on the detection results of the accelerator operation amount sensor 56a and the motor speed sensor 58. M_REQ The control is performed so that

[0102] -Operation- An example of the operation and effects of the wheel loader 1 according to this embodiment during excavation work will be described below with reference to Fig. 9. Fig. 9 shows the respective parameters (bucket operation amount R B , arm operation amount R A , driving force F M , arm cylinder thrust F A , wheel speed V W , and a slip determination flag FLslip) over time.

[0103] In order to clarify the effect of this embodiment, the wheel speed V detected by the wheel speed sensor 61 is W The following description will be made in comparison with a comparative example in which the slip determination flag setting process is executed based on the above. Note that the wheel loader 1 according to this embodiment and the wheel loader according to the comparative example of this embodiment are assumed to have the same operation procedures and operation amounts by the operator.

[0104] The main controller of the wheel loader according to the comparative example determines whether or not slippage is occurring using the following (Condition 2') instead of the above (Condition 2). In other words, when all of (Condition 1), (Condition 2'), (Condition 3) to (Condition 5) are met, the main controller of the wheel loader according to the comparative example determines that the slip determination condition is met and switches the slip determination flag FLslip from off to on. (Condition 2') Wheel speed V W is the wheel speed threshold V W 0 or more (V W ≧V W 0) Here, the wheel speed threshold V W 0 is stored in advance in the ROM 102. W 0 is determined based on the wheel speed when slip occurs through experiments, etc. W In order to prevent false detection of slip due to changes in wheel speed caused by vibration of the vehicle body 8 or detection errors of the wheel speed sensor 61, 0 is adopted as the value obtained by adding a margin value (>0) to the wheel speed when slip occurs in an experiment, etc.

[0105] 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 Fig. 9(a) to (g) represents time (elapsed time). The vertical axis in Fig. 9(a) represents the bucket operation amount R detected by the bucket operation amount sensor 53a. B 9(b) represents the arm operation amount R detected by the arm operation amount sensor 52a. A The vertical axis of FIG. 9(c) represents the traveling driving force F detected by the driving force sensor 65 in the comparative example. M9(d) represents the running driving force F detected by the driving force sensor 65 in this embodiment. M The vertical axis of FIG. 9(e) represents the arm cylinder thrust F calculated by the thrust calculation unit 110. A 9(f), the vertical axis of FIG. 9(f) represents the wheel speed V detected by the wheel speed sensor 61. W 9(g), and the vertical axis of FIG. 9(g) represents the slip determination flag FLslip.

[0106] Fig. 9 shows the time series changes after the wheel loader 1 enters the work object and the excavation determination flag FLdig is switched from off to on. In Fig. 9, time t0 is the time when, with the bucket 3 having penetrated the work object such as a mound of natural ground, the operator begins to further depress the accelerator pedal in order to cause the bucket 3 to penetrate further into the work object. In other words, at time t0, the travel driving force F in the direction moving the vehicle body 8 forward M ,F M The accelerator pedal is depressed slowly. At time t1, the arm cylinder thrust F A In this embodiment, the slip detection is performed based on the wheel speed V. W In the comparative example in which slip is detected based on the above, this is the time when the slip determination flag FLslip is switched from OFF to ON.

[0107] As shown in Fig. 9(a) and Fig. 9(b), when the bucket 3 penetrates the work object, the bucket operation amount R B and arm operation amount R A does not change. In other words, the work implement 6 maintains the attitude of penetrating into the work object (the attitude shown in FIG. 1). In this attitude, the bottom surface of the bucket 3 is parallel to the ground so that the bucket 3 can easily penetrate into the work object.

[0108] As shown in FIG. 9(c) and FIG. 9(d), as the accelerator operation amount (not shown) increases from time t0, the driving force F M ,F M' gradually increases. Also, as shown in Fig. 9(e), the arm cylinder thrust F A gradually increases. Driving force F M When the maximum static friction force generated in the wheel 7 exceeds the maximum static friction force, slippage occurs. When slippage occurs, the friction force generated in the wheel 7 switches from the maximum static friction force to a kinetic friction force, and the arm cylinder thrust F A begins to decrease rapidly.

[0109] As shown in FIG. 9(f) and FIG. 9(g), in the wheel loader according to the comparative example, the wheel speed V W The wheel speed threshold V is set so that slip is not detected falsely. W 0, the slip determination flag FLslip is switched from off to on. As shown in FIG. 9(c), in the wheel loader according to the comparative example, the slip determination flag FLslip is switched from off to on at time t2, and thereafter the traveling drive force F M ' is the driving force upper limit F M_LIM The driving force F is limited so as not to exceed '. M ' is the driving force upper limit F M_LIM ', thereby preventing further slippage.

[0110] In contrast, in this embodiment, the wheel speed V W Instead, arm cylinder thrust F A As shown in Fig. 9(e), the arm cylinder thrust F A is immediately and suddenly reduced by the occurrence of slippage. For this reason, in this embodiment, as shown in FIG. 9(g), the slip determination flag FLslip is switched from off to on at time t1, which is earlier than in the comparative example. As shown in FIG. 9(d), in the wheel loader 1 according to this embodiment, the slip determination flag FLslip is switched from off to on at time t1, and thereafter the traveling drive force F M is the driving force upper limit F M_LIM By limiting the slip to , the occurrence of subsequent slip is prevented.

[0111] As described above, in the comparative example, the wheel speed V W The wheel speed threshold V is set so that slip is not detected falsely. W 0 or more. In contrast, in this embodiment, slip cannot be detected. W Since slippage can be detected based on the behavior of the arm cylinder thrust immediately after slippage begins without using a control signal, excavation work can be performed more smoothly. Furthermore, in this embodiment, the slippage time is shorter than in the comparative example, so the time during which the running surface at the work site is scraped by the wheels 7 can be shortened. As a result, the effort required for subsequent repair work on the running surface can be reduced compared to the comparative example. Furthermore, since the slippage time is shorter in this embodiment than in the comparative example, the amount of tire wear can be reduced compared to the comparative example. Note that the drive force is limited automatically upon detection of slippage, regardless of the operator's operation, so the operational burden on the operator can be reduced.

[0112] According to the above-described embodiment, the following advantageous effects are achieved.

[0113] (1) A wheel loader (work vehicle) 1 comprises a body 8 having wheels 7, a hydraulic pump 30A mounted on the body 8, a working device 6 having an arm cylinder (hydraulic actuator) 4 driven by hydraulic oil discharged from the hydraulic pump 30A, an arm cylinder pressure sensor (pressure sensor) 75 that detects the pressure of the arm cylinder 4, a traveling drive device 45 that drives the wheels 7, a driving force sensor 65 that detects the driving force of the traveling drive device 45, and a main controller (control device) 100 that controls the driving force of the traveling drive device 45. Based on the detection result of the arm cylinder pressure sensor 75, the main controller 100 calculates the thrust of the arm cylinder 4 in accordance with the reaction force that the working device 6 receives from the work object. The main controller 100 calculates the driving force of the traveling drive device 45 (traveling driving force F M ) is rising, the thrust of arm cylinder 4 (arm cylinder thrust F A) has not increased (that is, when the slip determination conditions including (Condition 2) and (Condition 3)) are met, the driving force is limited.

[0114] According to this embodiment, when the wheels 7 slip, the driving force is automatically limited to eliminate the slip state, and work can be continued while preventing further slippage, thereby reducing the operational burden on the operator. Furthermore, according to this embodiment, compared to technology that detects slippage based on wheel speed (for example, the comparative example described above), slippage of the wheels 7 can be detected earlier, thereby shortening the duration of slippage and improving the work efficiency of excavation work.

[0115] (2) The slip determination conditions include an excavation operation state in which the work implement 6 is excavating a work object (i.e., (Condition 1)). When the excavation operation state is in progress and (Condition 2) to (Condition 5) are met, the main controller 100 determines whether the travel driving force F M On the other hand, when the excavation work is not being performed, the main controller 100 limits the traveling driving force F M Do not restrict.

[0116] This configuration makes it possible to properly detect slippage of the wheels 7 that occurs when excavation work is being performed, and to prevent erroneous detection of slippage when excavation work is not being performed.

[0117] (3) The wheel loader 1 is equipped with a motor speed sensor 58 that detects the rotation speed (motor speed) of the traveling motor 43 provided in the traveling drive device 45. The main controller 100 determines whether the advancing vehicle body 8 is decelerating based on the detection result of the motor speed sensor 58. The main controller 100 determines that the vehicle is in an excavation work state when the following conditions for determining excavation work are met: (Condition I) The advancing vehicle body 8 is decelerating; and (Condition II) The thrust of the arm cylinder 4 is equal to or greater than a predetermined value. In this embodiment, the main controller 100 detects the speed change rate ΔS of the traveling motor 43.M is equal to or less than the speed change rate threshold value S1, it is determined that (Condition I) is satisfied, and the pressure P A is equal to or greater than the cylinder pressure threshold P1, it is determined that (Condition II) is met. The speed change rate threshold S1 is smaller than 0 (S1<0). The predetermined value of (Condition II) above corresponds to the value obtained by multiplying the cylinder pressure threshold P1 by the pressure receiving area of ​​the arm cylinder 4.

[0118] According to this configuration, when the wheel loader 1 enters the work object, it is immediately determined that the work is in an excavation work state. This makes it possible to appropriately determine that the work is in an excavation work state at the start of excavation work by the wheel loader 1.

[0119] (4) The main controller 100 calculates the driving force change rate ΔF M is calculated, and the thrust change rate ΔF A The slip determination conditions also include the condition that the working implement 6 is not being operated (i.e., (Condition 4) and (Condition 5)). The main controller 100 according to this embodiment determines whether the working implement 6 is in an excavation operation state, the driving force change rate ΔF M is greater than 0, and the thrust change rate ΔF A is the thrust change rate threshold F A 1 or less, and the arm 2 and bucket 3 that constitute the working device 6 are not being operated, it is determined that the wheel 7 is slipping.

[0120] The thrust of the arm cylinder 4 may change when the working device 6 is operated. In this embodiment, the slip determination conditions include the fact that the working device 6 is not being operated, so it is possible to limit the sudden decrease (loss) in the thrust of the arm cylinder 4 to cases where it is caused by slip. Therefore, according to this embodiment, it is possible to prevent erroneous detection of slip when the working device 6 is operated.

[0121] (5) The main controller 100 calculates the estimated friction coefficient μ based on the thrust of the arm cylinder 4 when the slip determination condition is met (thrust during slip), and determines the driving force upper limit F based on the calculated estimated friction coefficient μ. M_LIM Furthermore, the main controller 100 calculates the driving force F of the traveling drive device 45. M is the driving force upper limit F M_LIM The driving force is controlled so as not to exceed

[0122] According to this configuration, the thrust F of the arm cylinder 4 A After calculating the friction coefficient estimate μ, which changes nonlinearly depending on M_LIM By setting the above, the driving force can be increased up to the limit of the driving force within the range where slippage does not occur, thereby further improving the efficiency of excavation work.

[0123] 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, or to combine the configurations described in the different modified examples below.

[0124] <Variation 1> In the above embodiment, the main controller 100 calculates the estimated friction coefficient μ and calculates the driving force upper limit F M_LIM However, the present invention is not limited to this. For example, the main controller 100 may calculate the slip thrust F A_slip The main controller 100 may calculate the upper limit value of the driving force by using a correlation map that defines the relationship between the driving force F detected by the driving force sensor 65 when slippage is detected. M The driving force upper limit (fixed value) may be set to about 95% of the above.

[0125] <Variation 2> The method of limiting the driving force is not limited to the example of controlling the driving force so as not to exceed the driving force upper limit value. For example, when the main controller 100 detects a slip, the main controller 100 may limit the slip thrust F A_slipCalculate the correction coefficient c according to the situation, and multiply the driving force F required for running M_REQ by the correction coefficient c to obtain the target driving force F for running M_TGT It may be calculated. The correction coefficient c is a value greater than 0 and less than 1 (0 < c < 1). Also, the correction coefficient c is such that the thrust F during slip A_slip becomes larger as it becomes larger.

[0126] <Modified Example 3> The method for determining whether or not the non-excavation work state has shifted to the excavation work state is not limited to the method described in the above embodiment. That is, the excavation work conditions are not limited to the examples described in the above embodiment. For example, the excavation work determination unit 114 determines that the excavation work conditions are satisfied when the accelerator operation amount of the accelerator operation device 56 is a predetermined value or more and the rate of change in speed ΔS M is less than or equal to the rate-of-change-in-speed threshold value S1. According to this modified example, when the wheel loader 1 enters the work object with the accelerator pedal depressed, it is determined that the excavation work state has been reached. Whether or not (Condition I) is satisfied is determined based on the rate of change in speed ΔS M Although the example of determination based on has been described, it may be determined whether or not (Condition I) is satisfied based on the rate of change over time of the speed of the wheel (drive wheel) detected by the wheel speed sensor 61.

[0127] <Modified Example 4> Also, the method for determining whether or not the excavation work state has shifted to the non-excavation work state is not limited to the method described in the above embodiment. That is, the excavation work end conditions are not limited to the examples described in the above embodiment. For example, when the posture of the work device 6 changes from the intrusion posture in which the bottom surface of the bucket 3 is parallel to the ground to the transport posture in which the angle formed by the extension line of the bottom surface of the bucket 3 and the ground is a predetermined value or more by the crowding operation of the bucket 3, it may be determined that the excavation work end conditions are satisfied. The posture of the work device 6 can be detected by the arm relative angle sensor 62 and the bucket relative angle sensor 63.

[0128] <Modified Example 5> In the above embodiment, the main controller 100 may perform moving average processing or low-pass filtering on the values ​​used in various determinations and calculations to avoid the influence of disturbances and noise. By performing moving average processing or low-pass filtering, the estimated friction coefficient μ and the driving force upper limit value F M_LIM As a result, it is possible to improve stability and operability when the driving force is limited during excavation work.

[0129] <Variation 6> In the above embodiment, an example has been described in which the wheel loader 1 is equipped with a single travel motor 43 that supplies power to the traveling device 11, but the present invention is not limited to this. The present invention may also be applied to a wheel loader 1 that is equipped with a plurality of travel motors 43. For example, the present invention can be applied to a wheel loader 1 that is equipped with a travel motor 43 that drives the left front wheel 7A and a travel motor 43 that drives the right front wheel 7A. The present invention can also be applied to a wheel loader 1 that is equipped with four travel motors 43 that drive each of a pair of left and right front wheels 7A and a pair of left and right rear wheels 7B. The travel motor 43 may be connected to the wheels 7 via a transmission, or may be configured to be integrated into the wheels 7.

[0130] <Variation 7> In the above embodiment, an example has been described in which the work vehicle is an electrically driven wheel loader 1, but the present invention is not limited to this. The present invention may also be applied to, for example, a torque converter driven wheel loader or a hydraulic static transmission (HST) driven wheel loader that converts the power of the engine 20 into hydraulic power and transmits it to the wheels 7. The present invention may also be applied to a wheel loader equipped with a differential limiting device that limits the speed difference between the left and right wheels 7.

[0131] <Variation 8> Some or all of the functions of the main controller 100 described in the above embodiment may be realized by hardware (for example, by designing logic for executing each function as an integrated circuit).

[0132] <Variation 9> In the above embodiment, an example has been described in which the work vehicle is a wheel loader 1, but the present invention is not limited to this. The present invention can be applied to various work vehicles equipped with work implements such as a bulldozer.

[0133] Although the embodiments of the present invention have been described above, the above 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 having all of the described configurations. Note that the control lines and information lines shown in the figures are those considered necessary for explanation, and do not necessarily represent all of the control lines and information lines required in the product. In reality, it can be assumed that almost all of the configurations are interconnected. [Explanation of symbols]

[0134] 1...wheel loader (work vehicle), 2...arm, 3...bucket, 4...arm cylinder (hydraulic cylinder, hydraulic actuator), 5...bucket cylinder (hydraulic cylinder, hydraulic actuator), 6...working device, 7...wheel, 8...body, 8A...front body, 8B...rear body, 10...center joint, 11...traveling device, 20...engine, 25...engine controller, 30A, 30B, 30C...hydraulic pump, 31...front control unit, 32...brake control unit, 33...steering control unit, 40...generator motor, 41...generator inverter, 42...traveling inverter, 43...traveling motor, 45...traveling drive device, 50...operation device, 51...forward / reverse switch, 52...arm operation device, 52a...arm operation amount sensor, 53 ...Bucket operation device, 53a...Bucket operation amount sensor, 56...Accelerator operation device, 56a...Accelerator operation amount sensor, 58...Motor speed sensor, 61...Wheel speed sensor, 62...Arm relative angle sensor, 63...Bucket relative angle sensor, 65...Driving force sensor, 75...Arm cylinder pressure sensor (pressure sensor), 100...Main controller (control device), 110...Thrust calculation unit, 111...Thrust change amount calculation unit, 112...Motor speed change amount calculation unit, 113...Driving force change amount calculation unit, 114...Excavation operation determination unit, 115...Slip determination unit, 116...Thrust force retention unit during slip, 117...Friction coefficient estimating unit, 118...Driving force upper limit value calculation unit, 119...Traveling required driving force calculation unit, 120...Minimum value selecting unit, 121...Torque command generating unit, F A …Arm cylinder thrust, F A_slip …Thrust during slip, F A 1...Thrust force change rate threshold, FLdig...Drilling judgment flag, F M … Driving force (driving force), F M_LIM …Drive force upper limit, F M_LIM_MAX …Maximum driving force limit, F M_LIM_MIN …Minimum upper limit of driving force, F M_REQ …Drive force required for driving, F M_TGT …Traveling target driving force, M L ,M μ …correlation map, P1…cylinder pressure threshold, P A …Arm cylinder pressure, R A …Arm operation amount, R A 1...Arm operation amount threshold, R B …Bucket operation amount, RB 1...Bucket operation amount threshold, S1...Speed ​​change rate threshold, S M …motor speed, T M_COM …Travel drive torque command, V W ...Wheel speed, V W 0...Wheel speed threshold, ΔF A …Thrust change rate (time change rate of thrust of hydraulic actuator), ΔF M … Driving force change rate (time rate of change of driving force), ΔS M …speed change rate (time change rate of the rotational speed of the traveling motor), μ…estimated friction coefficient

Claims

1. a vehicle body having wheels; a hydraulic pump mounted on the vehicle body; a working device having a hydraulic actuator driven by hydraulic oil discharged from the hydraulic pump; a pressure sensor for detecting the pressure of the hydraulic actuator; a travel drive device that drives the wheels; a driving force sensor that detects the driving force of the traveling drive device; a control device for controlling the driving force of the traveling drive device, The control device calculating a thrust of the hydraulic actuator corresponding to a reaction force that the working device receives from a work object based on the detection result of the pressure sensor; When a slip determination condition is established, which includes a state in which the driving force of the traveling drive device is increasing but the thrust of the hydraulic actuator is not increasing, the driving force is limited. A work vehicle characterized by:

2. The work vehicle according to claim 1, The slip determination condition includes an excavation operation state in which the work device is performing an excavation operation on the work object. A work vehicle characterized by:

3. The work vehicle according to claim 2, a motor speed sensor for detecting a rotation speed of a traveling motor provided in the traveling drive device; The control device determining whether the forward moving vehicle body is decelerating based on the detection result of the motor speed sensor; When an excavation operation determination condition is met, the condition includes that the forward moving vehicle body is decelerating and that the thrust of the hydraulic actuator is equal to or greater than a predetermined value, the excavation operation state is determined to be in the excavation operation state. A work vehicle characterized by:

4. The work vehicle according to claim 2, The slip determination conditions include a condition in which the working device is not being operated. A work vehicle characterized by:

5. The work vehicle according to claim 1, The control device calculating a friction coefficient estimate value based on the thrust of the hydraulic actuator when the slip determination condition is met; calculating a driving force upper limit value based on the estimated friction coefficient value; The driving force of the traveling drive device is controlled so that the driving force does not exceed the driving force upper limit value. A work vehicle characterized by:

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