Work vehicles

Abstract

To provide a work vehicle capable of reducing work time while preventing shallow digging during excavation work.SOLUTION: A work vehicle comprises: a vehicle body; a work device attached to the vehicle body; a power source mounted on the vehicle body; a hydraulic pump driven by the power source and supplying hydraulic oil to an arm cylinder and a bucket cylinder; a bucket angle sensor detecting an angle of a bucket; and a control device controlling capacity of the hydraulic pump which is proportional to a discharge volume of the hydraulic pump so that the discharge volume does not exceed an upper limit value of the discharge volume. The control device determines whether or not an excavation operation is in progress based on at least detection result of the bucket angle sensor, and when it is determined that an excavation operation is in progress, reduces the upper limit value to a predetermined discharge volume that is smaller than the maximum discharge volume of the hydraulic pump, and increases the upper limit value in accordance with an increase in the angle of the bucket detected by the bucket angle sensor.SELECTED DRAWING: Figure 8

Description

Technical Field

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

Background Art

[0002] There is known a work vehicle such as a wheel loader provided with a traveling device for traveling the vehicle body and a work device for excavating an excavation target such as an earth and sand mountain (see Patent Document 1). The work device has an arm attached to the vehicle body and a bucket attached to the arm. In such a work vehicle, an excavation operation is performed in which the vehicle body is advanced toward the excavation target to penetrate the bucket into the excavation target, the bucket is lifted and scooped forward while the bucket is being lifted, and earth and sand are loaded into the bucket.

[0003] In the excavation operation, in order to increase the work efficiency [ton / h] represented by the loading amount per working hour, it is necessary to quickly perform a series of operations and increase the amount of earth and sand scooped into the bucket. In the excavation operation, if the speed at which the bucket is lifted by rotating the arm upward (hereinafter also referred to as the operating speed of the work device) or the bucket is operated to the crowd side (cab side) to scoop up earth and sand is too high, it will result in "shallow excavation" where only near the surface of the excavation target can be scooped up by the bucket. As a result, the loading amount of earth and sand loaded into the bucket decreases, and as a result, the work efficiency decreases.

[0004] In order for the operator to quickly perform "deep excavation" in which the excavation target is deeply dug and the loading amount increases, the operator needs to simultaneously perform operations of operating the accelerator pedal to penetrate the bucket into the excavation target, operating the arm operation lever to lift the bucket, and operating the bucket operation lever to rotate the bucket forward, while adjusting the respective operation amounts in a well-balanced manner. That is, the excavation operation is a work with a large work load for the operator.

[0005] Furthermore, the vehicle may experience shaking during excavation work. Visibility from the driver's seat may also be poor due to the work equipment and the object being excavated. In such cases, the workload on the operator increases even further.

[0006] Patent Document 1 discloses a hydraulic pump capacity control device for a work vehicle that automatically controls the hydraulic pump to reduce its capacity to a predetermined capacity below its maximum capacity during excavation work. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2003-184134 [Overview of the project] [Problems that the invention aims to solve]

[0008] In the technology described in Patent Document 1, the capacity of the hydraulic pump is automatically reduced during excavation work, thereby limiting the operating speed of the work device. This is expected to prevent shallow excavation. However, in the technology described in Patent Document 1, the operating speed of the bucket is limited even in the middle and later stages of excavation work when the bucket has sufficiently penetrated the object to be excavated, which may lead to longer working times. Furthermore, in the technology described in Patent Document 1, if the amount of reduction in the capacity of the hydraulic pump during excavation work is reduced in order to suppress the decrease in the operating speed of the bucket, the operating speed of the bucket in the initial stages of excavation immediately after the bucket penetrates the object to be excavated may be too high, which may lead to shallow excavation.

[0009] The present invention aims to provide a work vehicle that can shorten working time while preventing shallow excavation during excavation work. [Means for solving the problem]

[0010] A work vehicle according to one aspect of the present invention comprises a vehicle body, a work device having an arm attached to the vehicle body, an arm cylinder for driving the arm, a bucket attached to the arm, and a bucket cylinder for driving the bucket, a power source mounted on the vehicle body, a hydraulic pump driven by the power source and supplying hydraulic fluid to the arm cylinder and the bucket cylinder, a bucket angle sensor for detecting the angle of the bucket, and a control device that controls the capacity of the hydraulic pump in proportion to the discharge amount so that the discharge amount of the hydraulic pump does not exceed the upper limit of the discharge amount. The control device determines whether or not an excavation work state is in place, based at least on the detection result of the bucket angle sensor, and if it is determined that an excavation work state is in place, it reduces the upper limit to a predetermined discharge amount smaller than the maximum discharge amount of the hydraulic pump, and increases the upper limit in accordance with the increase in the angle of the bucket detected by the bucket angle sensor. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide a work vehicle that can shorten the working time while preventing shallow excavation during excavation work. [Brief explanation of the drawing]

[0012] [Figure 1] Figure 1 is a side view of a wheel loader. [Figure 2] Figure 2 is a system configuration diagram of a wheel loader. [Figure 3] Figure 3 illustrates the basic excavation operations of a wheel loader. [Figure 4] Figure 4 is a PQ diagram illustrating constant-capacity control of a hydraulic pump. [Figure 5] Figure 5 is a PQ diagram illustrating constant horsepower control of a hydraulic pump. [Figure 6] Figure 6 is a functional block diagram of the main controller according to the first embodiment, showing the functions necessary for pump control. [Figure 7] Figure 7 illustrates the bucket angle θb. [Figure 8] FIG. 8 is a diagram showing an example of a correlation map M1 that defines the relationship between the bucket angle θb and the upper limit value Qlime of the discharge amount during excavation. [Figure 9] FIG. 9 is a diagram showing an example of the relationship between the discharge pressure Pd and the discharge amount Qd of the hydraulic pump when the control command value Icmd of the hydraulic pump is varied. [Figure 10] FIG. 10 is a diagram showing an example of the relationship between the discharge pressure Pd and the discharge amount Qd of the hydraulic pump with respect to the bucket angle θb when the AUTO mode flag Fm is set to on and the excavation work flag FL is set to on. [Figure 11] FIG. 11 is a flowchart showing an example of the processing flow in the discharge amount control executed by the main controller. [Figure 12] FIG. 12 is a diagram showing the time-series changes of each parameter (accelerator operation amount Ra, arm operation amount La, bucket operation amount Lb, discharge pressure Pd of the hydraulic pump, discharge amount Qd of the hydraulic pump, arm angle θa, and bucket angle θb) of the wheel loader according to the first embodiment. [Figure 13] FIG. 13 is a functional block diagram of the main controller according to the second embodiment. [Figure 14] FIG. 14 is a functional block diagram of the main controller according to the third embodiment. [Figure 15] FIG. 15 is a diagram showing the function of the upper limit value calculation unit during excavation according to the third embodiment.

Mode for Carrying Out the Invention

[0013] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant descriptions are omitted. In the present embodiment, an example in which the work vehicle is an electric drive wheel loader will be described. In the present embodiment, a wheel loader equipped with a hybrid system including an engine as a drive source, a power generation motor driven by the engine, and a travel drive device that runs the vehicle body with the power generated by the power generation motor will be described as an example. However, the present invention may be applied to a work vehicle in which the drive source is in another form such as a storage battery, or the travel drive device uses a mechanical torque converter or the like. In the following description, the up-down, left-right, and front-back directions and positions are based on the normal use state of the work vehicle, that is, the state in which the traveling device is grounded on a horizontal ground.

[0014] - First Embodiment - <Configuration of Wheel Loader> Referring to FIGS. 1 to 12, the wheel loader 1 according to the first embodiment of the present invention will be described. FIG. 1 is a side view of the wheel loader 1. As shown in FIG. 1, the wheel loader 1 includes a vehicle body 8 equipped with an electric travel drive device 45, and a multi-joint work device 6 attached to the front portion of the vehicle body 8. The vehicle body 8 is of an articulated steering type (vehicle body folding 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.

[0015] The work device 6 is attached to the front vehicle body 8A. A driver's cab 12 and an engine room 16 are arranged in the rear vehicle body 8B. Inside the driver's cab 12, a seat on which an operator sits and an operating device operated by the operator are provided. In the engine room 16, an engine 20 (see FIG. 2) as a power source, hydraulic pumps 30A, 30B, 30C (see FIG. 2) driven by the engine 20, and hydraulic equipment such as valves are mounted.

[0016] The work device 6 includes a lift arm (hereinafter simply referred to as "arm") 2 that is rotatably mounted vertically to the front body 8A, a hydraulic cylinder (hereinafter also referred to as "arm cylinder") 4 that drives the arm 2, a bucket 3 that is rotatably mounted vertically to the tip of the arm 2, and a hydraulic cylinder (hereinafter also referred to as "bucket cylinder") 5 that drives the bucket 3. The arm 2 is moved in accordance with the extension and retraction of the arm cylinder 4. The bucket 3 is moved in accordance with the extension and retraction of the bucket cylinder 5. One arm 2 and one arm cylinder 4 are provided on each side of the front body 8A. In this embodiment, a Z-link type (bell crank type) link mechanism is used as the link mechanism for operating the bucket 3.

[0017] The wheel loader 1 is equipped with a travel drive system 45 that drives the wheels 7. The travel drive system 45 includes a travel motor 43 and a travel device 11 to which driving force is supplied by the travel motor 43. The travel device 11 has front wheels 7A, which are wheels 7 attached to the front body 8A, rear wheels 7B, which are wheels 7 attached to the rear body 8B, and a power transmission device that transmits power from the travel motor 43 to the wheels 7. The power transmission device is composed of an axle, a differential device, a propeller shaft, etc.

[0018] The traction motor 43 is an electric motor that operates the wheels 7 of the traction device 11. The traction motor 43 is rotationally driven by electricity generated by the regenerator motor 40, which is rotated by the power of the engine 20.

[0019] 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 that are provided to connect the front body 8A and the rear body 8B.

[0020] Figure 2 is a system configuration diagram of wheel loader 1. As shown in Figure 2, wheel loader 1 comprises an engine 20, a fuel injector 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 work device 6 driven by hydraulic fluid discharged from hydraulic pump 30A, a front control unit 31 that controls the operation of the work device 6, a brake device 21 driven by hydraulic fluid discharged from hydraulic pump 30B, a brake control unit 32 that controls the operation of the brake device 21, a steering device 22 driven by hydraulic fluid discharged from hydraulic pump 30C, a steering control unit 33 that controls the steering device 22, and a travel drive device 45 driven by electricity generated by the generator motor 40.

[0021] The work device 6 and the travel drive device 45 are driven independently of each other by the power of the engine 20. The prime mover, the engine 20, is composed of an internal combustion engine such as a diesel engine. The generator motor 40 rotates using the torque output from the engine 20 and functions as a generator that produces electricity.

[0022] The hydraulic pumps 30A, 30B, and 30C are driven by the torque output by the engine 20 to discharge hydraulic fluid. When the generator-motor 40 functions as an electric motor, the hydraulic pumps 30A, 30B, and 30C are driven by the torque output by both the engine 20 and the generator-motor 40. The hydraulic pump 30A is a swashplate or slanted-shaft variable displacement piston pump. The hydraulic pump 30A is equipped with a regulator 34. When the discharge pressure of the hydraulic pump 30A rises above a certain value, the regulator 34 reduces the tilt angle (corresponding to the capacity, displacement volume) of the hydraulic pump 30A accordingly, controlling the absorption torque of the hydraulic pump 30A so that it does not exceed a set value (upper limit of pump absorption torque). The set value of the regulator 34 (upper limit of pump absorption torque) is variable and is controlled by a control solenoid valve 35. The control solenoid valve 35 operates in response to an electrical command signal and outputs a control pressure corresponding to the command signal. The flow rate (discharge volume) of the hydraulic fluid discharged from the hydraulic pump 30A is proportional to the capacity of the hydraulic pump 30A (discharge volume per revolution), which is determined by the control of the regulator 34, and the rotational speed of the hydraulic pump 30A, which is determined by the control of the engine 20 (pump discharge volume = pump capacity × pump rotational speed).

[0023] Hydraulic cylinders 4, 5, 15, 17, and 18 are supplied with hydraulic fluid (pressurized oil) discharged from hydraulic pumps 30A, 30B, and 30C, which are rotated by the torque output of engine 20 (see Figure 2), causing them to extend and retract.

[0024] The front control unit 31 controls the pressure, flow rate, and direction of the hydraulic fluid supplied from the hydraulic pump 30A to the arm cylinder 4 and bucket cylinder 5. This controls the extension and retraction of the arm cylinder 4 and bucket cylinder 5. The brake control unit 32 controls the pressure, flow rate, and direction of the hydraulic fluid supplied from the hydraulic pump 30B to the brake cylinder 17 and parking brake cylinder 18. This controls the extension and retraction of the brake cylinder 17 and parking brake cylinder 18. The steering control unit 33 controls the pressure, flow rate, and direction of the hydraulic fluid supplied from the hydraulic pump 30C to the steering cylinder 15. This controls the extension and retraction of the steering cylinder 15.

[0025] The wheel loader 1 includes a main controller 100, which is a control device that controls the entire vehicle; an engine controller 120 that controls the fuel injector 23 based on an engine rotation speed command from the main controller 100; a 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 41 (hereinafter referred to as the generator inverter) 41 that controls the generator motor 40 based on a generator voltage command input from the main controller 100; a traction motor inverter 42 (hereinafter referred to as the traction inverter) 42 that controls the torque of the traction motor 43 based on a traction drive torque command input from the main controller 100; and various operating devices (51-59) provided in the driver's cab 12.

[0026] The driver's cab 12 is equipped with a forward / reverse switch 51, which is a forward / reverse switching device for switching the vehicle body 8 forward (F), standby (N), and reverse (R); an arm operating device 52 for operating the arm cylinder 4 (arm 2); a bucket operating device 53 for operating the bucket cylinder 5 (bucket 3); an accelerator operating device 56 for accelerating the vehicle body 8; a brake operating device 57 for operating the brake cylinder 17; a parking brake operating device 54 for operating the parking brake cylinder 18; a steering operating device 55 for operating a pair of left and right steering cylinders 15; a mode switching switch (mode switching device) 58 for switching between AUTO mode and MANUAL mode; and an adjustment dial 59 for manually adjusting the upper limit of the discharge amount of the hydraulic pump 30A. For the sake of explanation, the operating devices 52, 53, and 56 will be collectively referred to as the operating device 50.

[0027] The arm operating device 52 includes an arm operating lever and an arm operating amount sensor 52a that detects the amount the arm operating lever is operated (hereinafter also referred to as the arm operating amount). The bucket operating device 53 includes a bucket operating lever and a bucket operating amount sensor 53a that detects the amount the bucket operating lever is operated (hereinafter also referred to as the bucket operating amount). The accelerator operating device 56 includes an accelerator pedal and an accelerator operating amount sensor 56a that detects the amount the accelerator pedal is operated (hereinafter also referred to as the accelerator operating amount). The brake operating device 57 includes a brake pedal and a brake operating amount sensor 57a that detects the amount the brake pedal is operated (hereinafter also referred to as the brake operating amount). The steering operating device 55 includes a steering wheel and a steering operating amount sensor 55a that detects the amount the steering wheel is operated (hereinafter also referred to as the steering operating amount). 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 are, for example, potentiometers that output a voltage to the main controller 100 according to the operating position of an operating member (operating lever or pedal).

[0028] The mode selector switch 58 is a switch that allows manual switching between AUTO mode and MANUAL mode. AUTO mode is a control mode in which the upper limit of the discharge volume of the hydraulic pump 30A is set based on the bucket angle, as described later. In contrast, MANUAL mode is a control mode in which the upper limit of the discharge volume of the hydraulic pump 30A is not set based on the bucket angle. The mode selector switch 58 has two operating positions: an AUTO mode position and a MANUAL mode position, and outputs a signal to the main controller 100 corresponding to the operating position. When the mode selector switch 58 is operated to the AUTO mode position, the main controller 100 turns on the AUTO mode flag Fm to set the control mode to AUTO mode (Fm=1). When the mode selector switch 58 is operated to the MANUAL mode position, the main controller 100 turns off the AUTO mode flag Fm to set the control mode to MANUAL mode (Fm=0).

[0029] When the control mode is set to MANUAL mode, the upper limit of the discharge volume of the hydraulic pump 30A is set to a fixed value corresponding to the operating position of the adjustment dial 59. When the control mode is set to AUTO mode, the upper limit of the discharge volume of the hydraulic pump 30A is adjusted to a value corresponding to the bucket angle, ranging from the initial upper limit Qlim0 (described later) to the maximum value, with the operating position of the adjustment dial 59 as the maximum value. In other words, by manually changing the value of the adjustment dial 59, the amount by which the upper limit of the discharge volume of the hydraulic pump 30A changes in response to changes in the bucket angle can be adjusted.

[0030] <Wheel loader control system> The main controller 100 is composed of a microcomputer equipped with a CPU (Central Processing Unit) 101 as an operating circuit, 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. The engine controller 120 is also composed of a microcomputer equipped with an operating circuit, storage devices, and input / output interfaces, similar to the main controller 100. The main controller 100 and the engine controller 120 may each be composed of one microcomputer or multiple microcomputers.

[0031] The ROM 102 of the main controller 100 is a non-volatile memory such as an EEPROM, and stores a program capable of executing various calculations. In other words, the ROM 102 of the main controller 100 is a storage medium from which the program realizing the functions of this embodiment can be read. The RAM 103 is a volatile memory and is 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 calculations in the program. The main controller 100 may also be further equipped with storage devices such as flash memory or a hard disk drive.

[0032] The CPU 101 is a processing unit that loads a program stored in the ROM 102 into the RAM 103 and performs calculations on it. It performs predetermined calculations on signals received from the input interface 104 and the ROM 102 and RAM 103 according to the program.

[0033] The input interface 104 receives operation signals from various control devices (51-59) and sensor signals from various sensors. The input interface 104 converts the input signals into data that can be processed by the CPU 101. The output interface 105 generates output signals according to the calculation results of the CPU 101 and outputs these signals to the front control unit 31, brake control unit 32, steering control unit 33, power generator inverter 41, drive inverter 42, and engine controller 120, etc.

[0034] The main controller 100 comprehensively controls the front control unit 31, brake control unit 32, steering control unit 33, power generation inverter 41 and drive inverter 42, and engine controller 120 based on operation signals input from various operating devices and sensor signals input from other various sensors.

[0035] 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, a signal output from the forward / reverse switch 51 indicating the operating position of the forward / reverse switch 51, a signal output from the mode selector switch 58 indicating the operating position of the mode selector switch 58, and a signal output from the adjustment dial 59 indicating the operating position of the adjustment dial 59.

[0036] The sensor signals input to the main controller 100 include a signal representing the angle detected by the arm relative angle sensor 62 and a signal representing the angle detected by the bucket relative angle sensor 63. The arm relative angle sensor 62 is installed on the connecting shaft that connects the vehicle body 8 and the arm 2. 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. The bucket relative angle sensor 63 is installed on the connecting shaft that connects the arm 2 and the bucket 3. 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.

[0037] Since the angle of the vehicle body 8 with respect to the ground (running surface) is constant, the angle θa detected by the arm relative angle sensor 62 (hereinafter also referred to as the arm angle) can be said to correspond to the relative angle (inclination angle) of the arm 2 with respect to the ground. Furthermore, the angle θb of the bucket 3 with respect to the ground (running surface) (hereinafter also referred to as the bucket angle) can be calculated based on the detection results of the arm relative angle sensor 62 and the bucket relative angle sensor 63. In other words, the arm relative angle sensor 62 and the bucket relative angle sensor 63 function as bucket angle sensors that detect the bucket angle θb with respect to the ground (running surface).

[0038] In addition, the sensor signals input to the main controller 100 include a signal representing the vehicle speed of the wheel loader 1 (the travel speed of the vehicle body 8) detected by the vehicle speed sensor 61. The vehicle speed sensor 61 is, for example, a rotary encoder that detects the rotational speed of the shafts that constitute the power transmission device.

[0039] Furthermore, the sensor signals input to the main controller 100 include signals representing the rotational speeds of the engine 20, generator motor 40, hydraulic pumps 30A, 30B, 30C, and traction motor 43, which are detected by multiple rotational speed sensors. The rotational speed of the engine 20 is detected by the engine rotational speed sensor 64, and the rotational speed of the hydraulic pump 30A is detected by the pump rotational speed sensor 67.

[0040] Furthermore, the sensor signals input to the main controller 100 include the discharge pressure of the hydraulic pumps 30A, 30B, and 30C detected by the discharge pressure sensors 71, 72, and 73, and the pressure of the bottom oil chamber of the arm cylinder 4 (hereinafter also referred to as bottom pressure) detected by the arm cylinder pressure sensor 74.

[0041] The main controller 100 calculates the rotational speed command value (target engine rotational speed) for the engine 20 based on the accelerator operation amount, arm operation amount, bucket operation amount, etc., and outputs it to the engine controller 120. The main controller 100 also outputs the actual engine rotational speed detected by the engine rotational speed sensor 64 to the engine controller 120. The engine controller 120 compares the rotational speed command value obtained from the main controller 100 with the actual engine rotational speed detected by the engine rotational speed sensor 64 and controls the fuel injection device 23 so that the actual engine rotational speed becomes the rotational speed command value. The fuel injection device 23 controls the fuel injection amount based on the fuel injection command output from the engine controller 120 and operates the engine 20.

[0042] The main controller 100 outputs a control command value for the hydraulic pump 30A based on the operating direction and amount of the arm operating device 52 and the bucket operating device 53, and the discharge pressure of the hydraulic pump 30A. The control solenoid valve 35 adjusts the pump capacity (displacement volume) proportional to the discharge amount of the hydraulic pump 30A based on the control command value from the main controller 100. The main controller 100 can perform constant torque control (or constant horsepower control). In constant torque control, the control command value (upper limit of pump absorption torque) is not changed by the magnitude of the discharge pressure of the hydraulic pump 30A, and the pump capacity is controlled so that the torque absorbed from the engine 20 does not exceed the set upper limit. The main controller 100 can also perform constant capacity control. In constant capacity control, the control command value (upper limit of pump absorption torque) is changed by the magnitude of the discharge pressure of the hydraulic pump 30A, and the pump capacity of the hydraulic pump 30A is controlled so that it does not exceed the set upper limit. With constant capacity control, the pump capacity does not change depending on the magnitude of the discharge pressure of the hydraulic pump 30A. Therefore, the upper limit of the discharge volume of the hydraulic pump 30A is determined by multiplying the set upper limit of the pump capacity by the rotational speed of the hydraulic pump 30A.

[0043] The main controller 100 outputs a front control command based on the operating direction and amount of the arm operating device 52 and the bucket operating device 53. Based on the front control command from the main controller 100, the front control unit 31 adjusts the pressure, flow rate, and direction of the hydraulic fluid discharged from the hydraulic pump 30A to operate the arm cylinder 4 and the bucket cylinder 5. The front control unit 31 includes a directional control valve that controls the flow of hydraulic fluid discharged from the hydraulic pump 30A, and a solenoid valve that generates the pilot pressure input to the pilot chamber of the directional control valve.

[0044] The main controller 100 outputs a brake control command based on the amount of operation of the brake operating device 57 and the operating position of the operating switch of the parking brake operating device 54. Based on the brake control command from the main controller 100, the brake control unit 32 adjusts the pressure, flow rate, and direction of the hydraulic fluid discharged from the hydraulic pump 30B to operate the brake cylinder 17 and the parking brake cylinder 18. The brake control unit 32 includes a directional control valve that controls the flow of hydraulic fluid discharged from the hydraulic pump 30B, and a solenoid valve that generates pilot pressure input to the pilot chamber of the directional control valve.

[0045] The main controller 100 outputs a steering control command based on the operating direction and amount of the steering wheel of the steering control device 55. Based on the steering control command from the main controller 100, the steering control unit 33 adjusts the pressure, flow rate, and direction of the hydraulic fluid discharged from the hydraulic pump 30C to operate the steering cylinder 15. The steering control unit 33 includes a directional control valve that controls the flow of hydraulic fluid discharged from the hydraulic pump 30C, and a solenoid valve that generates pilot pressure input to the pilot chamber of the directional control valve.

[0046] The power generator inverter 41 and the travel inverter 42 are connected by a DC section (DC bus) 44. Note that the wheel loader 1 according to this embodiment does not have a power storage device connected to the DC section 44. The power generator inverter 41 controls the bus voltage of the DC section 44 using power supplied from the generator motor 40 based on a power generation voltage command from the main controller 100. The travel inverter 42 drives the travel motor 43 using power from the DC section 44 based on a travel drive torque command from the main controller 100.

[0047] In this embodiment, the torque output by the engine 20 drives the hydraulic pumps 30A, 30B, and 30C, and the hydraulic fluid discharged from the hydraulic pumps 30A, 30B, and 30C drives the work device 6, the brake device 21, and the steering device 22. In addition, in this embodiment, the torque output by the engine 20 drives the generator motor 40, and the electricity generated by the generator motor 40 drives the drive motor 43.

[0048] When the arm operating lever of the arm operating device 52 is operated, the arm 2 rotates vertically (up and down) due to the extension and retraction of the arm cylinder 4. When the bucket operating lever of the bucket operating device 53 is operated, the bucket 3 rotates vertically (clouding or dumping) due to the extension and retraction of the bucket cylinder 5.

[0049] When the steering wheel of the steering control device 55 is operated, the front body 8A bends (steers) to the left and right around the center joint 10 relative to the rear body 8B as the steering cylinder 15 extends and retracts. When the accelerator pedal of the accelerator control device 56 is operated, the wheels 7 rotate due to the drive of the traction motor 43, and the wheel loader 1 moves.

[0050] When the forward / reverse switch 51 is set to forward (F), and the accelerator pedal of the accelerator control device 56 is pressed, the wheels 7 rotate in the forward direction and the vehicle body 8 moves forward. When the forward / reverse switch 51 is set to reverse (R), and the accelerator pedal of the accelerator control device 56 is pressed, the wheels 7 rotate in the reverse direction and the vehicle body 8 moves in reverse. However, when the forward / reverse switch 51 is set to standby (N), even if the accelerator pedal of the accelerator control device 56 is pressed, the wheels 7 will not rotate and the vehicle body 8 will not move.

[0051] <Excavation work> Next, with reference to Figure 3, an example of the basic excavation work of the wheel loader 1 will be described. In the excavation work, the wheel loader 1 first moves forward toward the object to be excavated, such as a pile of soil, with the bucket 3 positioned horizontally and close to the ground (entry position), as shown in Figure 3(a). Next, in the initial stages of the excavation work, as shown in Figure 3(b), the wheel loader 1 begins to raise the bucket 3 while penetrating the object to be excavated 91 in a manner that resembles plunging into the object to be excavated 91. Next, from the middle stages of the excavation work onward, as shown in Figure 3(c), the wheel loader 1 operates the arm 2 and bucket 3 while penetrating the object to be excavated 91 with the bucket 3, loading soil and other transported materials into the bucket 3. Finally, as shown in Figure 3(d), the wheel loader 1 scoops up the bucket 3 towards itself (cloud operation) to prevent spilling the soil and other transported materials loaded into the bucket 3, and sets the work device 6 to the transport position. This completes the excavation work.

[0052] Once the excavation work is complete, the wheel loader 1 reverses and then moves forward towards a transport vehicle such as a dump truck. At this time, the wheel loader 1 moves forward towards the dump truck while raising the bucket 3. After stopping in front of the dump truck, the wheel loader 1 loads the transported material (load) in the bucket 3 onto the dump truck's bed by performing a dumping operation with the bucket 3. Once the loading is complete, the wheel loader 1 reverses again and returns to its original position.

[0053] This series of operations, including excavation and loading, accounts for the majority of the wheel loader 1's total working time. Therefore, improving the efficiency of this series of operations is an effective way to improve the wheel loader 1's operational efficiency. Operational efficiency, for example, corresponds to the weight of excavated material loaded onto the transport vehicle per unit of time [tons / hour] during the series of operations including excavation and loading. A higher efficiency means that a larger volume of material can be excavated in a shorter time.

[0054] <Challenges in excavation work> In the early stages of the excavation work, as shown in Figure 3(b), if the bucket 3 is raised too early or at too high a speed, the bucket 3 will dig close to the surface of the material to be excavated 91. This type of excavation is called shallow digging. In shallow digging, the amount of soil loaded into the bucket 3 is reduced, thus decreasing work efficiency.

[0055] On the other hand, if the timing of raising the bucket 3 is too late, or if the bucket raising speed is too low, the wheels 7 may slip, causing the vehicle 8 to stall and become unable to move forward. In addition, the pressure of the hydraulic fluid supplied to the hydraulic cylinders 4 and 5 may exceed the threshold (relief setting pressure), causing pressure relief in which the hydraulic fluid is discharged into the tank. In excavation work, if pressure relief occurs, the work device 6 cannot be operated. When wheel 7 slip, vehicle 8 stall, and work device 6 pressure relief occur, operations are required to resolve these phenomena, which increases working time and reduces work efficiency.

[0056] Based on these operating characteristics, the operator adjusts the amount of movement of the accelerator pedal, arm control lever, and bucket control lever during excavation work, operating the wheel loader 1 to gradually increase the bucket lifting speed from the beginning to the end of the excavation work, thereby increasing work efficiency. To perform highly efficient excavation work, the operator needs to perform complex and precise operations in a short amount of time, requiring high concentration and skill. If the operator's concentration decreases over time, work efficiency will decrease.

[0057] Therefore, in order to maintain high work efficiency, it is important to reduce the operator's workload and to appropriately control the operation of the work device 6. Here, workload refers to the number of times the operator changes the amount of operation of operating members such as the accelerator pedal, arm operating lever, and bucket operating lever during a series of operations including excavation and loading. In other words, if the number of times the amount of operation of the operating members is changed can be reduced, the operator's workload can be said to have been reduced.

[0058] Here, "simplified excavation operation" is defined as when, after the bucket 3 begins to penetrate the excavation target 91, the operator operates the arm operating lever and bucket operating lever to their fullest extent (full lever operation) and the accelerator pedal to its fullest extent (full accelerator operation), and operates the work device 6 until it reaches the transport position while maintaining the full lever and full accelerator operation state. In this embodiment, when this simplified excavation operation is performed, the operating speed of the work device 6 is increased in accordance with the increase in the bucket angle θb, thereby preventing wheel slippage, vehicle stalling, pressure relief of the work device 6, and shallow excavation, thereby reducing the workload on the operator and improving work efficiency.

[0059] <Challenges in constant-volume control> Referring to Figure 4, the challenges in improving work efficiency in conventional constant-capacity control will be explained. Figure 4 is a PQ diagram illustrating constant-capacity control of a hydraulic pump. In the PQ diagram of Figure 4, the horizontal axis represents the discharge pressure Pd of the hydraulic pump 30A, and the vertical axis represents the discharge volume Qd of the hydraulic pump 30A. In constant-capacity control, as shown in Figure 4, the discharge volume Qd of the hydraulic pump 30A is reduced to a predetermined value during excavation work. For example, the PQ characteristic that defines the relationship between the discharge pressure Pd and the discharge volume Qd in constant-capacity control is changed from a 100% characteristic to a 50% characteristic, as shown in the figure. In other words, the upper limit of the discharge volume Qd is set to 50% of the maximum discharge volume Qmax. As a result, power loss of the work device 6 is reduced and the driving force for travel is increased.

[0060] This method is thought to be effective in preventing shallow drilling because the upward speed of bucket 3 is low in the early stages of the excavation. However, in the middle and later stages of the excavation, when bucket 3 has sufficiently penetrated the excavated object 91, the operating speed of the work device 6 is low, resulting in longer excavation times. In addition, slippage of the wheels 7, stalling of the vehicle body 8, and pressure relief of the work device 6 may occur, which may also extend the working time. By reducing the reduction in the discharge volume of the hydraulic pump 30A, it is possible to ensure the operating speed of the work device 6 in the middle and later stages of the excavation and suppress the extension of working time. However, in this case, the upward speed of bucket 3 in the early stages of the excavation is too high, making shallow drilling more likely.

[0061] <Challenges in constant horsepower control> Referring to Figure 5, the challenges in improving work efficiency in conventional constant horsepower control will be explained. Figure 5 is a PQ diagram illustrating constant horsepower control of a hydraulic pump. In the PQ diagram of Figure 5, the horizontal axis represents the discharge pressure Pd of the hydraulic pump 30A, and the vertical axis represents the discharge volume Qd of the hydraulic pump 30A. In constant horsepower control, as shown in Figure 5, the set value of the absorption torque of the hydraulic pump 30A (upper limit of pump absorption torque) is reduced to a predetermined value during excavation work. For example, the PQ characteristic that defines the relationship between discharge pressure Pd and discharge volume Qd in constant horsepower control is changed from a 100% characteristic to a 50% characteristic, as shown in the figure. In other words, the upper limit of the output of the hydraulic pump 30A (= discharge volume Qd × discharge pressure Pd) is set to 50% of the maximum horsepower. As a result, power loss of the work device 6 is reduced and the driving force for travel is increased.

[0062] However, in the early stages of excavation, the reaction force (excavation reaction force) acting on the wheel loader 1 from the excavation target 91 is small. In other words, the discharge pressure Pd of the hydraulic pump 30A is low. Therefore, in the early stages of excavation, the discharge volume Qd is hardly reduced. This means that the upward speed of the bucket 3 is hardly reduced, which may lead to shallow excavation. Furthermore, in the middle and later stages of excavation, the excavation reaction force increases, and the discharge pressure of the hydraulic pump 30A increases. As a result, the discharge volume Qd is suppressed more than necessary. Consequently, in the middle and later stages of excavation, the operating speed of the work device 6 is greatly reduced, which may decrease work efficiency.

[0063] <Gradual increase in discharge volume according to bucket angle> As described above, there is room for improvement in terms of work efficiency with the constant capacity control and constant horsepower control mentioned above. Therefore, the inventors of this application have diligently researched the operator's operation during excavation work, the control of the hydraulic pump 30A, and work efficiency (work time and load capacity). As a result, a method has been found in which the upper limit of the discharge amount of the hydraulic pump 30A is reduced to a predetermined value at the start of excavation, and the hydraulic pump 30A is controlled so that the upper limit of the discharge amount Qd is increased as the bucket angle θb increases, without changing the upper limit of the discharge amount Qd due to fluctuations in the discharge pressure Pd of the hydraulic pump 30A.

[0064] According to this method, even if the operator keeps the arm and bucket control levers constant during excavation, the operating speed of the work device 6 will be low in the initial stages of excavation, and will gradually increase as the bucket angle θb increases from the beginning to the end of the excavation. Therefore, shallow excavation becomes difficult in the initial stages of the excavation. In addition, the working time in the middle and later stages of the excavation can be shortened. Furthermore, slippage of the wheels 7, stalling of the vehicle body 8, and pressure relief of the work device 6 can be prevented. As a result, it is possible to provide a wheel loader 1 that can improve work efficiency with easy operation.

[0065] The functions of the main controller 100 according to this embodiment, and the content of the calculation processing performed by the main controller 100, will be described in detail below.

[0066] <Controller Functions> Figure 6 is a functional block diagram of the main controller 100, showing the functions necessary for pump control. As shown in Figure 6, the main controller 100 functions as a work determination unit 110, an upper limit calculation unit 111a during excavation, an upper limit calculation unit 111b during normal operation, and a command value calculation unit 112 by executing a program stored in the ROM 102.

[0067] The work determination unit 110 determines whether the working state of the wheel loader 1 is an excavation work state, based at least on the bucket angle θb.

[0068] The work determination unit 110 determines whether the conditions for starting excavation work have been met. If the conditions for starting excavation work are met while the system is in a non-excavation state, the work determination unit 110 switches the excavation work flag FL from off to on. If the conditions for starting excavation work have not been met, the work determination unit 110 keeps the excavation work flag FL off. The work determination unit 110 also determines whether the conditions for ending excavation work have been met. If the conditions for ending excavation work are met while the system is in an excavation state, the work determination unit 110 switches the excavation work flag FL from on to off. If the conditions for ending excavation work have not been met, the work determination unit 110 keeps the excavation work flag FL on. The command value calculation unit 112, described later, determines whether the work state is an excavation state based on the on / off state of the excavation work flag FL. The command value calculation unit 112 determines that the working state of the wheel loader 1 is an excavation operation state if the excavation operation flag FL is set to ON, and determines that the working state of the wheel loader 1 is a non-excavation operation state if the excavation operation flag FL is set to OFF.

[0069] Figure 7 illustrates the bucket angle θb. As shown in Figure 7, the bucket angle θb is the inclination angle of the bucket 3 from the reference plane 90. In this embodiment, the reference plane 90 is a plane set parallel to the horizontal ground (the running surface of the wheel loader 1). When the bottom surface of the blade portion 39 of the bucket 3 is parallel to the reference plane 90, the bucket angle θb is 0 [°]. When the bucket 3 rotates due to a clouding operation, the bucket angle θb increases with that rotation. In other words, when the bucket 3 rotates due to a dumping operation, the bucket angle θb decreases with that rotation. The bucket angle θb is calculated by the main controller 100 based on the relative angle of the arm 2 with respect to the reference plane 90 detected by the arm relative angle sensor 62 and the relative angle of the bucket 3 with respect to the arm 2 detected by the bucket relative angle sensor 63.

[0070] In this embodiment, the work determination unit 110 determines that the excavation work start condition has been met if all of the following conditions (1A) to (5A) are met, and switches the excavation work flag FL from off to on (FL=1). The work determination unit 110 determines that the excavation work start condition has not been met if at least one of conditions (1A) to (5A) is not met. If condition (1A) is met, and at least one of conditions (2A) to (5A) is not met, the work determination unit 110 determines that the excavation work start condition has not been met and leaves the excavation work flag FL off. (Condition 1A) The excavation work flag FL is set to OFF. (Condition 2A) The bucket angle θb is within a predetermined angle range (lower threshold θba or greater, upper threshold θbb or less). (Condition 3A) The bottom pressure Pa of the arm cylinder 4 is greater than or equal to a predetermined pressure threshold Pa0. (Condition 4A) The driving force Fc required to move the vehicle body 8 forward is equal to or greater than a predetermined driving force threshold Fc0. (Condition 5A) The arm operation amount La on the arm-raising side is greater than or equal to the first operation amount threshold La0, or the bucket operation amount Lb on the bucket cloud side is greater than or equal to the second operation amount threshold Lb0.

[0071] The bucket angle θb used in (Condition 2A) is calculated by the main controller 100 based on the detection results of the arm relative angle sensor 62 and the bucket relative angle sensor 63. The bottom pressure Pa of the arm cylinder 4 used in (Condition 3A) is calculated by the main controller 100 based on the detection results of the arm cylinder pressure sensor 74. The travel driving force Fc used in (Condition 4A) is calculated by the main controller 100 based on the detection results of the torque sensor 65 of the travel motor 43 or the current sensor 66 of the travel motor 43. The arm operating amount La used in (Condition 5A) is calculated by the main controller 100 based on the detection results of the arm operating amount sensor 52a. The bucket operating amount Lb used in (Condition 5A) is calculated by the main controller 100 based on the detection results of the bucket operating amount sensor 53a.

[0072] The lower threshold θba, upper threshold θbb, pressure threshold Pa0, and driving force threshold Fc0 are determined based on the bucket angle θb, bottom pressure Pa, and travel driving force Fc measured by experiments, etc., at the start of the excavation work (when the bucket 3 begins to penetrate the object to be excavated 91). The first operation amount threshold La0 and the second operation amount threshold Lb0 are set to determine whether or not the arm operation lever and bucket operation lever have been operated. These thresholds θba, θbb, Pa0, Fc0, La0, and Lb0 are stored in the ROM 102.

[0073] The lower threshold θba is a negative value (θba < 0). For example, a value between -10° and -5° is adopted for the lower threshold θba. The upper threshold θbb is a positive value (θbb > 0). For example, a value between 10° and 20° is adopted for the upper threshold θbb. For the pressure threshold Pa0, for example, a value between 10% and 30% of the maximum operating pressure of the arm cylinder 4 is adopted. For the first operating amount threshold La0, a value of about 5% of the maximum operating amount of the arm operating lever is adopted. For the second operating amount threshold Lb0, a value of about 5% of the maximum operating amount of the bucket operating lever is adopted. For the driving force threshold Fc0, for example, a value between 10% and 40% of the maximum travel driving force is adopted.

[0074] The driving force Fc generated by the traction motor 43 can be calculated, for example, by the following equation (1) based on the output torque (driving torque) Tm of the traction motor 43, the overall reduction ratio λ, and the diameter Dt of the wheel 7.

[0075]

number

[0076] The overall reduction ratio λ is the ratio of the rotational speed of the engine 20 to the rotational speed of the wheels 7. If a transmission is provided, it is calculated by multiplying the transmission's gear ratio by the reduction ratio (differential ratio). c is a coefficient for unit conversion. The driving torque (motor output torque) Tm may be detected by the torque sensor 65, or calculated from the motor current detected by the current sensor 66. Alternatively, the driving torque Tm may be calculated from the accelerator pedal input.

[0077] The work determination unit 110 determines that the excavation work completion condition has been met and switches the excavation work flag FL from on to off (FL=0) if both (condition 1B) and (condition 2B) below are met. The work determination unit 110 determines that the excavation work completion condition has not been met if at least one of (condition 1B) and (condition 2B) is not met. The work determination unit 110 determines that the excavation work completion condition has not been met and leaves the excavation work flag FL on if (condition 1B) is met but (condition 2B) is not met. (Condition 1B) The excavation work flag FL is set to ON. (Condition 2B) The bucket angle θb is greater than or equal to a predetermined release threshold θbc.

[0078] The bucket angle θb used in (Condition 2B) is calculated by the main controller 100 based on the detection results of the arm relative angle sensor 62 and the bucket relative angle sensor 63.

[0079] The release threshold θbc is determined based on the bucket angle θb at the end of the excavation work (when the bucket 3 has finished scooping up the excavation target 91), as measured by experiments, etc. The release threshold θbc is stored in the ROM 102. A value greater than the upper threshold θbb is adopted for the release threshold θbc (θbc > θbb). For example, a value of 25[°] or more and 40[°] or less is adopted for the release threshold θbc. In this way, the work determination unit 110 determines that the excavation work completion condition has been met when the bucket angle θb becomes greater than or equal to the release threshold θbc while the excavation work is in progress.

[0080] The drilling limit calculation unit 111a shown in Figure 6 calculates the upper limit of the discharge volume of the hydraulic pump 30A used during drilling operations (hereinafter also referred to as the drilling limit) Qlime, based at least on the bucket angle θb. The relationship between the bucket angle θb and the drilling limit Qlime will be explained with reference to Figure 8. Figure 8 is a diagram showing an example of a correlation map M1 that defines the relationship between the bucket angle θb and the drilling limit Qlime. This correlation map M1 is determined in advance based on calculations or experiments and stored in the ROM 102. Note that the correlation map M1 in Figure 8 is a control diagram of the discharge volume assuming that the rotational speed of the hydraulic pump 30A is the target rotational speed during drilling operations. The drilling limit calculation unit 111a refers to this correlation map M1 and calculates the drilling limit Qlime of the discharge volume based on the bucket angle θb.

[0081] As shown in Figure 8, the correlation map M1 defines a characteristic in which the upper limit Qlime during drilling increases as the bucket angle θb increases, within the range from the initial bucket angle θb0 to the final bucket angle θb3.

[0082] The initial bucket angle θb0 corresponds to the bucket angle θb suitable for the posture (hereinafter also referred to as the penetration posture) when the wheel loader 1 enters the excavation target 91 and the bucket 3 penetrates the excavation target 91. For example, a value of -5[°] or more and 5[°] or less is adopted for the initial bucket angle θb0. The final bucket angle θb3 corresponds to the bucket angle θb at the end of the excavation work, that is, at the stage when the bucket 3 scoops up to the very end. For example, a value of 30[°] or more and 50[°] or less is adopted for the final bucket angle θb3.

[0083] When the bucket angle θb is greater than or equal to the initial bucket angle θb0, the upper limit Qlime of the discharge rate during excavation is the initial upper limit Qlim0. The initial upper limit Qlim0 corresponds to a discharge rate that is less likely to result in shallow excavation even with simple excavation operations. For example, the initial upper limit Qlim0 is set to a value between 10% and 30% of the maximum discharge rate Qmax, which is set to 100%. When the bucket angle θb is greater than or equal to the final bucket angle θb3, the upper limit Qlime of the discharge rate during excavation is the maximum discharge rate Qmax of the hydraulic pump 30A.

[0084] The bucket angle θb is small at the beginning of the excavation work and gradually increases as the excavation work approaches its end. Therefore, when the upper limit of the discharge volume is adjusted based on the correlation map M1 shown in Figure 8, even if the amount of operation of the arm operation lever and the bucket operation lever remains constant, the operating speed of the work device 6 is low at the beginning of the excavation work and increases as the excavation work approaches its end. Thus, the operator can improve work efficiency without having to perform complex operations.

[0085] Furthermore, as shown in Figure 6, the drilling upper limit calculation unit 111a in this embodiment calculates the drilling upper limit Qlime by also taking into account the indicated value Cd (Cd ≤ 1) of the adjustment dial 59. Specifically, the drilling upper limit calculation unit 111a compares the value calculated based on the correlation map M1 with the value obtained by multiplying the maximum discharge rate Qmax by the indicated value Cd of the adjustment dial 59, and determines the smaller of the two as the drilling upper limit Qlime.

[0086] The normal upper limit calculation unit 111b calculates the upper limit of the discharge volume of the hydraulic pump 30A (hereinafter also referred to as the normal upper limit) Qlimn by multiplying the indicated value Cd (Cd ≤ 1) of the adjustment dial 59 by the maximum discharge volume Qmax. The normal upper limit Qlimn is used in non-excavation work conditions when AUTO mode is set, and when MANUAL mode is set, as will be described later.

[0087] The command value calculation unit 112 calculates the control command value Icmd for the hydraulic pump 30A based on the excavation work flag FL, the AUTO mode flag Fm, the upper limit value Qlime for the discharge volume during excavation, the upper limit value Qlimn for the discharge volume during normal operation, the upper limit value Tp for the pump absorption torque, and the discharge pressure Pd of the hydraulic pump 30A detected by the discharge pressure sensor 71.

[0088] The command value calculation unit 112 determines the normal upper limit Qlimn as the upper limit Qlim of the discharge amount used in calculating the control command value Icmd when the AUTO mode flag Fm is set to ON and the drilling operation flag FL is set to OFF. Similarly, the command value calculation unit 112 determines the normal upper limit Qlimn as the upper limit Qlim of the discharge amount used in calculating the control command value Icmd when the AUTO mode flag Fm is set to OFF. The command value calculation unit 112 determines the drilling upper limit Qlime as the upper limit Qlim of the discharge amount used in calculating the control command value Icmd when the AUTO mode flag Fm is set to ON and the drilling operation flag FL is set to ON.

[0089] The upper limit Tp of the pump absorption torque is calculated by the main controller 100. For example, the main controller 100 calculates the rotational speed command value of the engine 20 based on the accelerator operation amount, arm operation amount, bucket operation amount, etc. As a specific example, the main controller 100 calculates the required power of the travel motor 43 (hereinafter also referred to as the travel required power) based on the accelerator operation amount and the rotational speed of the travel motor 43. The main controller 100 calculates the required power of the work device 6 (hereinafter also referred to as the work required power) based on the arm operation amount, bucket operation amount, and the discharge pressure Pd of the hydraulic pump 30A. The main controller 100 calculates the required power of the engine 20 based on the sum of the travel required power and the work required power. The main controller 100 calculates the rotational speed command value (target engine rotational speed) of the engine 20 based on the required power of the engine 20.

[0090] The main controller 100 calculates the upper limit Tp of the pump absorption torque by multiplying the calculated target engine rotational speed by a predetermined coefficient. The upper limit Tp of the pump absorption torque is set to increase as the target engine rotational speed increases.

[0091] However, the method for calculating the upper limit Tp of the pump absorption torque is not limited to this. For example, the main controller 100 calculates the first target engine rotational speed by multiplying the arm operating amount by a predetermined coefficient, and calculates the second target engine rotational speed by multiplying the bucket operating amount by a predetermined coefficient. The main controller 100 adopts the larger of the first target engine rotational speed and the second target engine rotational speed as the rotational speed command value for the engine 20. The main controller 100 calculates the upper limit Tp of the pump absorption torque by multiplying the adopted rotational speed command value (target engine rotational speed) by a predetermined coefficient.

[0092] Furthermore, the main controller 100 may calculate the upper limit value Tp of the pump absorption torque based on the actual engine rotation speed detected by the engine rotation speed sensor 64.

[0093] The command value calculation unit 112 calculates the control command value Icmd such that the discharge amount Qd of the hydraulic pump 30A does not exceed the upper limit value Qlim, and the absorption torque of the hydraulic pump 30A does not exceed the upper limit value Tp.

[0094] Figure 9 shows an example of the relationship between the discharge pressure Pd and discharge volume Qd of the hydraulic pump 30A when the control command value Icmd of the hydraulic pump 30A is varied. It is assumed that the rotational speed of the hydraulic pump 30A is at its maximum rotational speed. It is also assumed that the indicated value Cd of the adjustment dial 59 is set to 1, and the upper limit value of the discharge volume Qlim is set to the maximum discharge volume Qmax.

[0095] When the control command value Icmd is 0%, the discharge rate Qd is adjusted according to the discharge pressure Pd of the hydraulic pump 30A so that the characteristics are represented by the solid line in Figure 9. As the control command value Icmd increases, the capacity of the hydraulic pump 30A decreases. Therefore, as the control command value Icmd increases, the discharge rate Qd corresponding to the discharge pressure Pd decreases. The command value calculation unit 112 calculates the control command value Icmd based on the upper limit value Qlim of the discharge rate, the discharge pressure Pd, and the control characteristics shown in Figure 9. By adjusting the control command value Icmd, the capacity of the hydraulic pump 30A is controlled so that the discharge rate Qd does not exceed its upper limit value Qlim (= maximum discharge rate Qmax), and the absorption torque of the hydraulic pump 30A does not exceed its upper limit value Tp.

[0096] As shown in Figure 6, the control command value Icmd calculated by the main controller 100 is input to the regulator 34. The regulator 34 controls the capacity of the hydraulic pump 30A based on the control command value Icmd.

[0097] Figure 10 shows an example of the relationship between the discharge pressure Pd and discharge volume Qd of the hydraulic pump 30A with respect to the bucket angle θb when the AUTO mode flag Fm is set to ON and the excavation operation flag FL is set to ON. Note that this assumes the rotational speed of the hydraulic pump 30A is at its maximum rotational speed.

[0098] When the AUTO mode flag Fm is set to ON and the excavation work flag FL is set to ON, the command value calculation unit 112 calculates the control command value Icmd such that the discharge amount of the hydraulic pump 30A does not exceed the upper limit Qlim (=Qlime) calculated based on the correlation map M1 and the bucket angle θb, and the absorption torque of the hydraulic pump 30A does not exceed the upper limit Tp.

[0099] In the early stages of excavation, for example, when the bucket angle θb = θb0, the upper limit of the discharge volume Qlim = Qlim0, as shown in Figure 8. Therefore, as shown in Figure 10, the command value calculation unit 112 calculates a control command value Icmd so that the discharge volume Qd does not exceed the initial upper limit Qlim0, regardless of the height of the discharge pressure Pd of the hydraulic pump 30A. Subsequently, in the middle stages of excavation, for example, when the bucket angle θb = θb1, the upper limit of the discharge volume Qlim = Qlim1, as shown in Figure 8 (θb1 > θb0, Qlim1 > Qlim0). Therefore, as shown in Figure 10, the command value calculation unit 112 calculates a control command value Icmd so that the discharge volume Qd does not exceed Qlim1, regardless of the height of the discharge pressure Pd of the hydraulic pump 30A. Then, towards the end of the excavation work, for example, when the bucket angle θb = θb2, the upper limit of the discharge volume Qlim = Qlim2, as shown in Figure 8 (θb3 > θb2 > θb1, Qmax > Qlim2 > Qlim1). For this reason, as shown in Figure 10, the command value calculation unit 112 calculates the control command value Icmd so that the discharge volume Qd does not exceed Qlim2, regardless of the height of the discharge pressure Pd of the hydraulic pump 30A. The range in which the discharge volume Qd can be adjusted to be constant is the range in which it does not exceed the maximum discharge pressure Pmax or the upper limit of the pump absorption torque Tp.

[0100] -Processing flow in discharge volume control- The discharge rate control performed by the main controller 100 will be explained with reference to Figure 11. Figure 11 is a flowchart showing an example of the processing flow in the discharge rate control performed by the main controller 100. The processing shown in the flowchart of Figure 11 is started, for example, when the ignition switch (engine key switch) is turned on, and after initial settings (not shown) are performed, it is repeatedly executed at a predetermined control cycle. In the initial settings, the drilling operation flag FL is set to off.

[0101] In step S110, the work determination unit 110 determines whether the excavation start conditions and excavation end conditions are met, based at least on the excavation work flag FL and the bucket angle θb, sets the excavation work flag FL according to the determination result, and proceeds to step S120.

[0102] In step S120, the drilling upper limit calculation unit 111a calculates the drilling upper limit Qlime of the discharge volume of the hydraulic pump 30A based on the bucket angle θb and the indicated value Cd of the adjustment dial 59. The normal upper limit calculation unit 111b also calculates the normal upper limit Qlimn of the discharge volume of the hydraulic pump 30A based on the indicated value Cd of the adjustment dial 59. Once the calculations for the drilling upper limit Qlime and the normal upper limit Qlimn are complete, the process proceeds to step S130.

[0103] In step S130, the command value calculation unit 112 determines whether the currently set excavation work flag FL is on and whether the currently set AUTO mode flag Fm is on. If both the excavation work flag FL and the AUTO mode flag Fm are on, the process proceeds to step S140. If at least one of the excavation work flag FL and the AUTO mode flag Fm is off, the process proceeds to step S150.

[0104] In step S140, the command value calculation unit 112 sets the upper limit value Qlime during drilling as the upper limit value Qlim for calculating the control command value, and proceeds to step S160. In step S150, the command value calculation unit 112 sets the upper limit value Qlimn during normal operation as the upper limit value Qlim for calculating the control command value, and proceeds to step S160.

[0105] In step S160, the command value calculation unit 112 calculates the control command value Icmd for the hydraulic pump 30A based on the upper limit value Qlim of the discharge volume, the upper limit value Tp of the pump absorption torque, the discharge pressure Pd of the hydraulic pump 30A, and the control characteristics of the hydraulic pump 30A shown in Figures 9 and 10.

[0106] Once the processing in step S160 is completed, the flowchart shown in Figure 11 for this control cycle is terminated, and in the next control cycle, the processing from step S110 to step S160 is executed again. Although not shown in the figure, the parameters used to determine the working state (Fc, Pa, θb) and the parameters used to calculate the control command value Icmd for the hydraulic pump 30A (θb, Cd, Tp, Pd) are repeatedly calculated by the main controller 100 at a predetermined control cycle based on signals from various sensors and operating devices.

[0107] -Operation- Referring to Figure 12, the main operation and effects of the wheel loader 1 according to this embodiment will be explained. Figure 12 is a diagram showing the time-series changes of each parameter of the wheel loader 1 according to this embodiment (accelerator operation amount Ra, arm operation amount La, bucket operation amount Lb, discharge pressure Pd of hydraulic pump 30A, discharge amount Qd of hydraulic pump 30A, arm angle θa, and bucket angle θb). Figure 12 shows an example in which the wheel loader 1 performs excavation work on an excavation target object 91 such as a pile of earth, and the operator performs a simple excavation operation. In this embodiment, the control mode is set to AUTO mode.

[0108] To clarify the effects of this embodiment, the effects of this embodiment will be explained by comparing it with a comparative example (corresponding to the case where MANUAL mode is set in this embodiment) in which the upper limit of the discharge amount of the hydraulic pump 30A is not adjusted based on the bucket angle θb. It will be assumed that the operator's operating procedures and operating amounts for various operating devices, and the discharge pressure Pd of the hydraulic pump 30A are the same for the wheel loader 1 according to this embodiment and the wheel loader according to the comparative example of this embodiment. Furthermore, it is assumed that the rotational speed Np of the hydraulic pump 30A is constant during excavation work.

[0109] In Figure 12, the time-series changes of each parameter in this embodiment are shown by solid lines, and the time-series changes of each parameter in the comparative example are shown by dashed lines. The horizontal axis in Figures 12(a) to (g) represents time (elapsed time). The vertical axis in Figure 12(a) represents the accelerator operation amount Ra detected by the accelerator operation amount sensor 56a, and the vertical axis in Figure 12(b) represents the arm operation amount La detected by the arm operation amount sensor 52a. The vertical axis in Figure 12(c) represents the bucket operation amount Lb detected by the bucket operation amount sensor 53a. The vertical axis in Figure 12(d) represents the discharge pressure Pd of the hydraulic pump 30A, and the vertical axis in Figure 12(e) represents the discharge amount Qd of the hydraulic pump 30A. The vertical axis in Figure 12(f) represents the arm angle θa, and the vertical axis in Figure 12(g) represents the bucket angle θb.

[0110] In Figure 12, time t0 is when the operator operates the accelerator control device 56, the driving force Fc increases, and the vehicle body 8 begins to move forward. Time t1 is when the bucket 3 penetrates the excavation target 91, and the bottom pressure Pa of the arm cylinder 4 and the discharge pressure Pd of the hydraulic pump 30A begin to increase. Time t2 is when the operator operates the arm control device 52, and the bucket 3 begins to rise. Also, time t2 is when the excavation work flag FL is switched from off to on. Time t3 is when the operator operates the bucket control device 53, and the bucket 3 begins to rotate towards the operator. Time t4 is in the middle of the excavation work, and is the time when the relative magnitudes of the discharge volume Qd of the hydraulic pump 30A in this embodiment and the discharge volume Qd of the hydraulic pump 30A in the comparative example begin to reverse. Time t5 is when the operator stops operating the control device 50, and the excavation work is completed.

[0111] As shown in Figure 12(a), the accelerator pedal input Ra is 0 (zero) until time t0. This indicates that until time t0, the operator has not operated the accelerator control device 56, and the wheel loader 1 is stopped or moving forward at a slow speed. At time t0, the operator presses down on the accelerator pedal, causing the accelerator pedal input Ra to increase sharply and initiating forward acceleration of the vehicle 8.

[0112] As shown in Figure 12(b), the arm operation amount La is 0 (zero) until time t2. This indicates that the wheel loader 1 was driven into the excavation target 91 at time t1, and until time t2, the operator was not operating the arm operating device 52, and the wheel loader 1 was maintaining the entry position. In the entry position, as shown in Figure 12(f), the arm angle θa is small, and the height of the bucket 3 is near the ground. Note that in this entry position, the bucket 3 is nearly parallel to the ground, and corresponds to the initial state of the penetration position. From time t2, the arm operation amount La increases rapidly as the operator operates the arm operating device 52 upwards. As a result, the bucket 3 begins to rise.

[0113] As shown in Figure 12(c), the bucket maneuver amount Lb is 0 (zero) until time t3. This indicates that the operator has not operated the bucket maneuvering device 53 until time t3, and the wheel loader 1 is maintaining the penetration position. In the penetration position, as shown in Figure 12(g), the bucket angle θb is small, and the bucket 3 is approximately parallel to the ground. From time t3, the bucket maneuver amount Lb increases sharply when the operator operates the bucket maneuvering device 53 toward the cloud. This initiates the scooping of the excavation target 91 by the bucket 3.

[0114] As shown in Figure 12(d), the discharge pressure Pd of the hydraulic pump 30A is small until time t1. This indicates that the bucket 3 has not yet penetrated the excavated object 91. At time t1, the discharge pressure Pd of the hydraulic pump 30A increases as the bucket 3 begins to penetrate the excavated object 91.

[0115] As shown in Figure 12(e), in the comparative example, the discharge rate Qd of the hydraulic pump 30A increases to Qmid in response to the rapid increase in the arm operating amount La at time t2. Qmid is approximately half of the maximum discharge rate Qmax. Subsequently, the discharge rate Qd remains constant until the arm operating amount La and bucket operating amount Lb rapidly decrease at time t5. As a result, as shown in Figure 12(f), the arm angle θa increases at a nearly constant rate (rate of change over time) from time t2 to time t5. Similarly, as shown in Figure 12(g), the bucket angle θb also increases at a nearly constant rate (rate of change over time) from time t3 to time t5.

[0116] On the other hand, as shown in Figure 12(e), in this embodiment, in response to the rapid increase in the arm operation amount La at time t2, the discharge amount Qd of the hydraulic pump 30A increases to an initial upper limit Qlim0, which is less than Qmid. Subsequently, in line with the increase in the bucket angle θb, the discharge amount Qd gradually increases until the arm operation amount La rapidly decreases at time t5. As a result, as shown in Figure 12(f), in this embodiment, the rate of increase of the arm angle θa (rate of change over time, slope) is lower than in the comparative example during the early and middle stages of the excavation work (times t1 to t4). In this embodiment, the rate of increase of the arm angle θa increases with the passage of time. Therefore, in this embodiment, the rate of increase of the arm angle θa is higher than in the comparative example during the final stages of the excavation work (times t4 to t5). Similarly, as shown in Figure 12(g), in this embodiment, the rate of increase of the bucket angle θb (rate of change over time, slope) is lower than in the comparative example during the early and middle stages of the excavation work. In this embodiment, the rate at which the bucket angle θb rises becomes higher than in the comparative example towards the end of the excavation operation.

[0117] As described above, in the comparative example, when the operator performs a simplified excavation operation, the upward speed of the arm angle θa and bucket angle θb is somewhat high in the initial stages of the excavation work. Therefore, in the comparative example, in order to prevent shallow excavation that goes close to the surface of the object to be excavated 91, the operator needs to adjust the arm control lever and bucket control lever according to the penetration distance, vehicle speed, bucket height 3, and bucket angle θb. As a result, the workload on the operator increases. The penetration distance refers to the distance traveled from the time the bucket 3 begins to penetrate the object to be excavated 91.

[0118] Furthermore, in the comparative example, when a simple excavation operation is performed by the operator, the rate of increase (rate of change over time) of the arm angle θa and bucket angle θb remains almost constant from the beginning to the end of the excavation work. In other words, in the comparative example, the operating speed of the work device 6 is kept low. In the comparative example, because the operating speed of the work device 6 does not increase sufficiently from the middle of the excavation work onward, the work time becomes longer and the work efficiency decreases. Moreover, the ratio of the bucket 3's upward distance to the penetration distance is also suppressed more than necessary. For this reason, in the comparative example, in order to prevent wheel slippage, vehicle stalling, and pressure relief of the work device 6, the operator needs to reduce the amount of accelerator operation according to the penetration distance, vehicle speed, bucket 3 height, and bucket angle θb. As a result, the operator's workload increases, the work time becomes longer, and the work efficiency decreases.

[0119] In contrast, in the wheel loader 1 according to this embodiment, the discharge rate Qd of the hydraulic pump 30A is kept lower than in the comparative example from the beginning to the middle of the excavation work. The main controller 100 increases the upper limit Qlim of the discharge rate of the hydraulic pump 30A in accordance with the increase in the bucket angle θb. The discharge rate Qd of the hydraulic pump 30A is adjusted based on the upper limit Qlim. As a result, in this embodiment, the upward speed of the arm angle θa and bucket angle θb in the beginning of the excavation work is lower than in the comparative example. In other words, according to this embodiment, even if a simple excavation operation is performed by the operator, the upward speed of the bucket in the beginning of the excavation work is suppressed, thus preventing shallow excavation. Furthermore, the upward speed (rate of change over time) of the arm angle θa and bucket angle θb from the middle of the excavation work onward is higher than in the comparative example. Therefore, according to this embodiment, even if a simple excavation operation is performed by the operator, slippage of the wheels 7, stalling of the vehicle body 8, and pressure relief of the work device 6 can be prevented. Moreover, according to this embodiment, the operating speed of the work device 6 from the middle of the excavation work onward can be sufficiently increased, thus shortening the working time. In other words, according to this embodiment, it is possible to improve work efficiency while reducing the workload on the operator.

[0120] Furthermore, in this embodiment, the power consumed by the work device 6 in the initial stages of excavation can be kept to a minimum. By reducing the power consumption of the work device 6, the power consumed by increasing the rotational speed of the engine 20 and the power consumed by the travel drive device 45 can be increased. In other words, in this embodiment, the power of the engine 20 can be increased and the travel driving force can be increased in the initial stages of excavation, thereby improving work efficiency.

[0121] Furthermore, in this embodiment, shallow digging, wheel slippage, vehicle body stalling, and pressure relief of the work device 6 can be prevented with simple digging operations, allowing even inexperienced operators to achieve digging efficiency close to that of skilled operators.

[0122] Furthermore, in this embodiment, it is possible to prevent wheel slippage 7, stalling of the vehicle body 8, and pressure relief of the work device 6, which consume unnecessary power. As a result, unnecessary fuel consumption is prevented, and fuel efficiency (fuel consumption rate) can be improved.

[0123] Furthermore, in this embodiment, the number of times the operator changes the operating amount of the control device 50 during excavation work is reduced. As a result, the physical load on the control device 50, the work device 6, and the travel drive device 45 is reduced, and the lifespan of these devices can be extended.

[0124] According to the above-described embodiment, the following effects are achieved.

[0125] (1) The wheel loader (work vehicle) 1 is equipped with a main controller (control device) 100 that controls the capacity of the hydraulic pump 30A, which is proportional to the discharge rate, so that the discharge rate of the hydraulic pump 30A does not exceed the upper limit value Qlim of the discharge rate. The main controller 100 determines whether the working state of the wheel loader 1 is an excavation work state, based at least on the detection results of the bucket angle sensors (arm relative angle sensor 62 and bucket relative angle sensor 63). If the main controller 100 determines that the working state of the wheel loader 1 is an excavation work state, it reduces the upper limit value Qlim to a predetermined discharge rate (initial upper limit value Qlim0) which is smaller than the maximum discharge rate Qmax of the hydraulic pump 30A, and increases the upper limit value Qlim in accordance with the increase in the bucket angle (angle of the bucket 3 relative to the ground) θb detected by the bucket angle sensors (62, 63).

[0126] This configuration provides a wheel loader 1 that can prevent shallow excavation while shortening working time during excavation work. Preventing shallow excavation and shortening working time leads to an improvement in the work efficiency [ton / h] during excavation work.

[0127] (2) The main controller 100 determines whether the conditions for starting excavation work have been met, and considers the working state after the conditions for starting excavation work have been met as the excavation work state. The conditions for starting excavation work are composed of a combination of various conditions. Preferably, the conditions for starting excavation work include at least one of the following: the pressure (bottom pressure) Pa of the arm cylinder is greater than or equal to the pressure threshold Pa0; the operating amount La on the arm-lifting side of the arm operating device 52 is greater than or equal to the first operating amount threshold La0; and the operating amount Lb on the bucket cloud side of the bucket operating device 53 is greater than or equal to the second operating amount threshold Lb0; and the bucket angle θb is less than or equal to the upper threshold (first angle threshold) θbb. By including the condition that the bucket angle θb is less than or equal to the upper threshold θbb as a condition for starting excavation work, it is possible to determine that the working device 6 is in a position to insert the bucket 3 into the object to be excavated 91. Furthermore, by including the condition that the bottom pressure Pa of the arm cylinder 4 is greater than or equal to the pressure threshold Pa0 as a condition for starting excavation work, it is possible to appropriately determine that the working device 6 has entered the object to be excavated 91. Furthermore, by including the condition that the arm operation amount La or bucket operation amount Lb is equal to or greater than the operation amount threshold as a condition for starting excavation work, it is possible to determine that an excavation operation has been performed by the operator.

[0128] In this case, during uphill driving and leveling work where the bucket 3 flattens the ground (driving surface), the bucket angle θb may be between the lower threshold θba and the upper threshold θbb, and the driving force Fc may be greater than or equal to the driving force threshold Fc0. On the other hand, during uphill driving and leveling work, the bottom pressure Pa of the arm cylinder 4 never exceeds the pressure threshold Pa0. Therefore, by including at least one of (condition 3A) and (condition 5A) as the excavation work start condition, it is possible to prevent the system from mistakenly determining that excavation work has started while driving uphill or leveling work is in progress.

[0129] (3) The conditions for starting excavation work include that the driving force Fc for moving the vehicle body 8 forward is equal to or greater than the driving force threshold Fc0. This makes it possible to appropriately determine that the vehicle body 8 is moving forward in order to approach the object to be excavated 91.

[0130] In stationary operations such as loading onto a dump truck, where the vehicle body 8 is stationary, the bucket angle θb may be between the lower threshold θba and the upper threshold θbb, and the bottom pressure Pa of the arm cylinder 4 may be above the pressure threshold Pa0. On the other hand, in stationary operations, the driving force Fc never exceeds the driving force threshold Fc0. Therefore, by including (condition 4A) as a condition for starting excavation work, it is possible to prevent the system from mistakenly determining that excavation work has started while stationary work is in progress.

[0131] (4) As described in (2) and (3) above, the conditions for starting excavation work consist of multiple conditions, so it is possible to appropriately determine when the work has transitioned from a non-excavation state to an excavation state.

[0132] (5) The main controller 100 determines whether the excavation work completion condition has been met and considers the working state after the excavation work completion condition has been met as a non-excavation work state. The excavation work completion condition includes the bucket angle θb becoming greater than or equal to the release threshold (second angle threshold) θbc, which is greater than the upper threshold (first angle threshold) θbb, when the excavation work state is in place. This makes it possible to determine that the work device 6 is in a transport position. In the non-excavation work state, the upper limit value Qlim of the discharge amount is not controlled according to the bucket angle θb. For this reason, when the vehicle body 8 is driven toward the dump truck after the excavation work is completed, the bucket 3 can be raised at a sufficient speed. Also, when releasing soil into the dump truck, the bucket 3 can be dumped at a sufficient speed. In other words, the work efficiency in the non-excavation work state can be improved.

[0133] -A variation of the first embodiment- In the first embodiment described above, an example was described in which the main controller 100 calculates the upper limit value Qlim of the discharge amount according to the bucket angle θb when the drilling operation flag FL is switched from off to on. However, when the drilling operation flag FL is switched from off to on, the main controller 100 may set the upper limit value Qlim of the discharge amount to an initial upper limit value Qlim0 regardless of the bucket angle θb. In this case, after the drilling operation flag FL is switched from off to on, the main controller 100 increases the upper limit value Qlim of the discharge amount in accordance with the increase in the bucket angle θb after a change occurs in the bucket angle θb.

[0134] -Second Embodiment- A wheel loader 1 according to a second embodiment of the present invention will be described with reference to Figure 13. Components identical or equivalent to those described in the first embodiment will be given the same reference numerals, and the differences will be primarily explained. Figure 13 is a functional block diagram of the main controller 200 according to the second embodiment.

[0135] In this second embodiment, the method by which the command value calculation unit 212 calculates the control command value Icmd for the hydraulic pump 30A differs from that of the first embodiment. Specifically, as shown in Figure 13, the command value calculation unit 212 calculates the control command value Icmd for the hydraulic pump 30A based on the excavation work flag FL, the AUTO mode flag Fm, the upper limit value Qlime for the discharge volume during excavation, the upper limit value Qlimn for the discharge volume during normal operation, the upper limit value Tp for the pump absorption torque, the discharge pressure Pd of the hydraulic pump 30A detected by the discharge pressure sensor 71, and the rotational speed Np of the hydraulic pump 30A detected by the pump rotational speed sensor 67 (see Figure 2).

[0136] In this second embodiment, the control when at least one of the excavation work flag FL and the AUTO mode flag Fm is set to off is the same as in the first embodiment, so a description is omitted.

[0137] The command value calculation unit 212 calculates the control command value Icmd such that the discharge amount of the hydraulic pump 30A does not exceed its upper limit Qlim, and the absorption torque of the hydraulic pump 30A does not exceed its upper limit Tp. Furthermore, if both the excavation work flag FL and the AUTO mode flag Fm are set to ON, the command value calculation unit 212 considers the work state at that time to be an excavation work state. When the command value calculation unit 212 considers the state to be an excavation work state, it increases the capacity of the hydraulic pump 30A as the rotational speed Np of the hydraulic pump 30A decreases.

[0138] In this second embodiment, the command value calculation unit 212 adjusts the control command value Icmd so that the discharge amount Qd does not fluctuate due to fluctuations in the rotational speed Np of the hydraulic pump 30A. The control command value Icmd is calculated, for example, by the following equation (2).

[0139]

number

[0140] In equation (2), Icmd1 is the control command value in the first embodiment. Also in equation (2), Np is the rotational speed of the hydraulic pump 30A, Npr is the rated rotational speed of the hydraulic pump 30A, and α is the conversion coefficient (correction coefficient). The conversion coefficient α is a dimensionless number and is set in advance by the correlation between the control command value Icmd of the regulator 34 and the discharge amount Qd of the hydraulic pump 30A. For example, a value of 0.5 or more and 2.0 or less is used for the conversion coefficient α.

[0141] For example, if the rotational speed Np is reduced from 100% (rated value) to 90%, the command value calculation unit 212 reduces the control command value Icmd. This increases the capacity of the hydraulic pump 30A, and the discharge volume of the hydraulic pump 30A increases to the rated value.

[0142] Thus, in this second embodiment, by correcting the control command value Icmd1 described in the first embodiment based on the rotational speed Np of the hydraulic pump 30A, the discharge volume Qd does not fluctuate due to fluctuations in the rotational speed Np of the hydraulic pump 30A. Therefore, even when there is a large discrepancy between the actual rotational speed of the engine 20 and the target rotational speed, and the rotational speed Np of the hydraulic pump 30A is lower than the set rotational speed, the discharge volume Qd of the hydraulic pump 30A can be made to match the upper limit value Qlim. Consequently, even when the actual rotational speed of the engine 20 fluctuates at the beginning of the excavation work and in the middle of the excavation work, the operating speed of the work device 6 can be stabilized. In other words, according to this second embodiment, the workload of the operator can be further reduced.

[0143] -Modified form of the second embodiment- In the second embodiment described above, an example was given in which the control command value is corrected based on the rotational speed Np of the hydraulic pump 30A. However, the correction method is not limited to this. The main controller 200 only needs to be able to increase the capacity of the hydraulic pump 30A as the rotational speed Np of the hydraulic pump 30A decreases. For example, the main controller 200 can obtain the same effect as in the second embodiment by correcting the upper limit Qlim of the discharge amount of the hydraulic pump 30A instead of the control command value. In this modified version of the second embodiment, the upper limit Qlim of the discharge amount is calculated by, for example, the following equation (3).

[0144]

number

[0145] In equation (3), Qlim1 is the upper limit of the discharge volume in the first embodiment. In equations (2) and (3), the target rotational speed of the hydraulic pump 30A may be used instead of the rotational speed Np of the hydraulic pump 30A. In this case as well, fluctuations in the rotational speed Np of the hydraulic pump 30A, which fluctuate with the operator's input, can be absorbed, and the upward speed of the bucket 3 can be stabilized to some extent, thereby reducing the operator's workload. Furthermore, by using the target rotational speed of the hydraulic pump 30A, responsiveness can be improved compared to using the actual rotational speed. However, in order to respond to changes in the actual rotational speed due to load fluctuations, it is preferable to use the rotational speed Np detected by the pump rotational speed sensor 67.

[0146] -Third Embodiment- A wheel loader 1 according to the third embodiment of the present invention will be described with reference to Figures 14 and 15. Note that the same or equivalent components as those described in the first embodiment will be denoted by the same reference numerals, and the differences will be primarily explained. Figure 14 is a functional block diagram of the main controller 300 according to the third embodiment.

[0147] The main controller 300 according to this third embodiment has the functions of the main controller 100 of the first embodiment and the function of a penetration distance calculation unit 313. Furthermore, the method for determining the start of excavation work by the work determination unit 310 and the method for calculating the upper limit value Qlim of the discharge amount by the excavation upper limit value calculation unit 311a differ from those of the first embodiment.

[0148] As shown in Figure 14, the work determination unit 310 determines whether the conditions for starting excavation work have been met based on the travel driving force Fc, the bottom pressure Pa of the arm cylinder 4, and the bucket angle θb. In this third embodiment, the conditions for starting excavation work do not include (condition 5A) as described in the first embodiment. In other words, if all of (condition 1A) to (condition 4A) are met, the work determination unit 310 determines that the conditions for starting excavation work have been met and switches the excavation work flag FL from off to on (FL=1). In other words, in this third embodiment, the excavation work flag FL switches from off to on regardless of the arm operating amount La and the bucket operating amount Lb.

[0149] The work determination unit 310 determines that the conditions for starting excavation work are not met if at least one of (Condition 1A) to (Condition 4A) is not met. If (Condition 1A) is met, but at least one of (Condition 2A) to (Condition 4A) is not met, the work determination unit 310 determines that the conditions for starting excavation work are not met and leaves the excavation work flag FL off.

[0150] As shown in Figure 14, the penetration distance calculation unit 313 calculates the penetration distance Ld based on the excavation work flag FL and the vehicle speed v detected by the vehicle speed sensor 61 (see Figure 2). The penetration distance Ld corresponds to the distance the vehicle body 8 moves from the time the wheel loader 1 enters the excavation target 91 and the bucket 3 begins to penetrate. If the excavation work flag FL is set to off, the penetration distance calculation unit 313 sets the penetration distance Ld to 0 (zero). In other words, when the excavation work flag FL is switched from on to off, the penetration distance Ld is reset to its initial value of 0 (zero).

[0151] The penetration distance calculation unit 313, when the excavation work flag FL is set to ON, considers the current work state as an excavation work state and calculates the penetration distance Ld based on the vehicle speed v and time. The penetration distance Ld is calculated, for example, by accumulating the vehicle speed v [m / control cycle] for each control cycle of the main controller 100. In other words, the penetration distance calculation unit 313 calculates the penetration distance Ld as the distance traveled by the vehicle body 8 since it was deemed to be in an excavation work state.

[0152] The drilling limit calculation unit 311a calculates the drilling limit Qlime of the discharge volume of the hydraulic pump 30A based on the bucket angle θb, the arm angle θa, the penetration distance Ld, and the indicated value Cd of the adjustment dial 59. Figure 15 is a diagram showing the functions of the drilling limit calculation unit 311a according to the third embodiment. As shown in Figure 15, the drilling limit calculation unit 311a has a first limit calculation unit 3111, a second limit calculation unit 3112, a third limit calculation unit 3113, and a maximum value selection unit 3114.

[0153] The first upper limit calculation unit 3111 refers to the correlation map M1 and calculates the first upper limit Qlime1 of the discharge volume based on the bucket angle θb. The second upper limit calculation unit 3112 refers to the correlation map M2 and calculates the second upper limit Qlime2 of the discharge volume based on the arm angle θa. The third upper limit calculation unit 3113 refers to the correlation map M3 and calculates the third upper limit Qlime3 of the discharge volume based on the penetration distance Ld.

[0154] Correlation map M1 defines the relationship between the bucket angle θb and the first upper limit of the discharge volume, Qlime1. Correlation map M2 defines the relationship between the arm angle θa and the second upper limit of the discharge volume, Qlime2. Correlation map M3 defines the relationship between the penetration distance Ld and the third upper limit of the discharge volume, Qlime3. Correlation maps M1, M2, and M3 are pre-stored in ROM 102.

[0155] The correlation map M1 corresponds to the correlation map described in the first embodiment (see Figure 8). The correlation map M1 defines the characteristic that the first upper limit Qlime1 increases in accordance with the increase in the bucket angle θb. Specifically, the correlation map M1 defines the following characteristics: When the bucket angle θb is less than or equal to the initial bucket angle θb0, the first upper limit Qlime1 becomes the initial upper limit Qlim0. Furthermore, when the bucket angle θb is between the initial bucket angle θb0 and the final bucket angle θb3, the first upper limit Qlime1 increases in accordance with the increase in the bucket angle θb. Moreover, when the bucket angle θb is greater than or equal to the final bucket angle θb3, the first upper limit Qlime1 becomes the maximum discharge rate Qmax.

[0156] The correlation map M2 defines the characteristic that the second upper limit Qlime2 increases in accordance with the increase in the arm angle θa. Specifically, the correlation map M2 defines the following characteristics: When the arm angle θa is less than or equal to the initial arm angle θa0, the second upper limit Qlime2 is the initial upper limit Qlim0. Furthermore, when the arm angle θa is between the initial arm angle θa0 and the final arm angle θax, the second upper limit Qlime2 increases in accordance with the increase in the arm angle θa. Moreover, when the arm angle θa is greater than or equal to the final arm angle θax, the second upper limit Qlime2 becomes the maximum discharge rate Qmax.

[0157] The correlation map M3 defines the characteristic that the third upper limit Qlime3 increases in accordance with the increase in penetration distance Ld. Specifically, the correlation map M3 defines the following characteristics: When the penetration distance Ld is less than or equal to the initial penetration distance Ld0, the third upper limit Qlime3 is the initial upper limit Qlim0. Furthermore, when the penetration distance Ld is between the initial penetration distance Ld0 and the final penetration distance Ldx, the third upper limit Qlime3 increases in accordance with the increase in penetration distance Ld. In addition, when the penetration distance Ld is greater than or equal to the final penetration distance Ldx, the third upper limit Qlime3 becomes the maximum discharge amount Qmax.

[0158] The maximum value selection unit 3114 selects the largest of the first to third upper limit values ​​Qlime1 to Qlime3 calculated by the first to third upper limit value calculation units 3111 to 3113 as the drilling upper limit value Qlime and outputs it to the command value calculation unit 112.

[0159] In the first embodiment, the upper limit Qlim of the discharge volume of the hydraulic pump 30A increases in accordance with the increase in the bucket angle θb. In other words, if the operator does not operate the bucket operating lever and the arm operating lever after the bucket 3 has penetrated the workpiece 91, the discharge volume of the hydraulic pump 30A will not increase. Therefore, if the operation of the bucket operating lever and the arm operating lever is delayed after the bucket 3 has penetrated the workpiece 91, the penetration distance Ld may become too large before the upward speed of the bucket 3 becomes sufficiently high, which may cause the wheels 7 to slip, the vehicle body 8 to stall, and the work device 6 to experience pressure relief.

[0160] In contrast, the main controller 300 according to this third embodiment calculates the penetration distance Ld, which is the distance traveled by the vehicle body 8 since it was deemed to be in an excavation work state. When the main controller 300 is deemed to be in an excavation work state, it increases the upper limit of the discharge amount Qlim in accordance with the increase in the penetration distance Ld. For example, even if the bucket operating lever and arm operating lever are not operated until the middle of the excavation work, once the bucket 3 penetrates the excavation target 91, the upper limit of the discharge amount Qlim increases in accordance with the increase in the penetration distance Ld. Therefore, even if the operation of the bucket operating lever and arm operating lever is delayed after the bucket 3 has penetrated the excavation target 91, the bucket 3 can be raised at a sufficient speed. In other words, according to this third embodiment, it is possible to prevent the occurrence of wheel slippage 7, stalling of the vehicle body 8, and pressure relief of the work device 6 due to the bucket 3 penetrating too far into the excavation target 91 due to delays in operator operation.

[0161] Furthermore, when the main controller 300 determines that excavation work is in progress, it increases the upper limit of the discharge volume Qlim in accordance with the increase in the arm angle θa detected by the arm relative angle sensor (arm angle sensor) 62. This ensures that the operating speed of the work device 6 is more appropriate.

[0162] -A modified example of the third embodiment- In the third embodiment described above, an example was described in which the largest value among the first upper limit Qlime1, the second upper limit Qlime2, and the third upper limit Qlime3 of the discharge volume is determined as the drilling upper limit Qlime of the discharge volume. However, the method for determining the drilling upper limit Qlime of the discharge volume is not limited to this. For example, the drilling upper limit calculation unit 311a may determine the average value of the first upper limit Qlime1, the second upper limit Qlime2, and the third upper limit Qlime3 of the discharge volume as the drilling upper limit Qlime of the discharge volume.

[0163] The following modifications are also within the scope of the present invention, and it is possible to combine the configurations shown in the modifications with the configurations described in the embodiments described above, or to combine the configurations described in the different embodiments described above, or to combine the configurations described in the following different modifications.

[0164] <Example 1> The conditions for initiating excavation work are not limited to the examples described above.

[0165] <Variation Example 1-1> For example, (Condition 5A) and (Condition 3A) are both conditions to prevent misjudgments during uphill driving and ground leveling work. For this reason, in the first and second embodiments, (Condition 5A) may be adopted instead of (Condition 3A).

[0166] <Variation 1-2> Instead of using the pressure of arm cylinder 4 (condition 3A), the following (condition 3Aa) may be adopted. (Condition 3Aa) The reaction force Fr acting on the vehicle body 8 is greater than or equal to the reaction force threshold Fr0.

[0167] The reaction force Fr is calculated, for example, based on the driving force Fc and vehicle speed v, using the following momentum-impulse relationship equation (4).

[0168]

number

[0169] Here, m is the mass of the wheel loader 1, ta is the reference time, tb is the time after a predetermined time has elapsed from the reference time ta, va is the vehicle speed v of the wheel loader 1 at the reference time ta, and vb is the vehicle speed v of the wheel loader 1 at time tb.

[0170] <Variation 1-3> Condition 4A is a condition for determining whether the vehicle body 8 is moving forward, and is provided to prevent misjudgments during stationary work. For this reason, instead of using Condition 4A, which uses the driving force Fc, the following Condition 4Aa or Condition 4Ab may be adopted. (Condition 4Aa) The amount of accelerator operation is equal to or greater than a predetermined threshold amount. (Condition 4Ab) The driving torque (motor output torque) Tm is equal to or greater than a predetermined torque threshold.

[0171] <Variation 1-4> In the above embodiment, an example was described in which, when all of (Condition 1A) to (Condition 5A) are met, the excavation work flag FL is immediately switched from off to on, and when both (Condition 1B) and (Condition 2B) are met, the excavation work flag FL is immediately switched from on to off. However, in this case, if there is pulsation in the parameters used to determine the excavation start conditions and excavation end conditions, or if the parameters contain noise, or if the operator's operation changes before or after the excavation work flag FL is switched, the excavation work flag FL may not be switched at the expected timing.

[0172] Therefore, the main controller 100 may include the fact that a predetermined maintenance time has elapsed for each of (Condition 1A) to (Condition 5A), (Condition 1B), and (Condition 2B). For example, (Condition 3A) may be defined as "the state in which the bottom pressure Pa of the arm cylinder 4 is equal to or greater than the pressure threshold Pa0 has elapsed for the maintenance time." Alternatively, the main controller 100 may switch the drilling operation flag FL from off to on when the drilling operation start condition has been met for a predetermined time. Similarly, the main controller 100 may switch the drilling operation flag FL from on to off when the drilling operation end condition has been met for a predetermined time. This prevents the drilling operation flag FL from switching at an unexpected timing if there is pulsation in the parameters used for determination, noise is included in the detected values ​​of the parameters, or the operator's operation changes before or after the drilling operation flag FL is switched.

[0173] <Modification 2> The conditions for completing the excavation work are not limited to the examples described above. For example, the conditions for completing the excavation work may be determined to be met when a predetermined time threshold (for example, about 5 seconds) has elapsed since the conditions for starting the excavation work were met. The time threshold is stored in ROM 105 in advance. The time threshold is determined in advance through experiments or other means.

[0174] <Variation 3> In the above embodiment, an example was described in which the power source supplying power to the work device 6 and the travel drive device 45 is an engine 20. However, the power source may be something else. For example, the power source may be an electric motor. The wheel loader 1 may be configured such that, for example, a battery or fuel cell is used to drive the hydraulic pumps 30A, 30B, and 30C with electric motors, and the travel motor 43 is driven by electricity from the battery or fuel cell.

[0175] <Modification 4> In the above embodiment, an example of applying the present invention to a wheel loader 1 in which the operating device 50 is operated by an operator to perform excavation work, loading work, etc. was described. However, the control that increases the discharge amount of the hydraulic pump 30A in accordance with the increase in the bucket angle θb during excavation work can also be applied to an automatically operated wheel loader 1. In this case, the upper limit of the discharge amount corresponds to the target value of the discharge amount.

[0176] <Modification 5> In the above embodiment, the values ​​used for various judgments and calculations may be subjected to moving average processing or low-pass filtering to avoid the influence of disturbances and noise. For example, by applying moving average processing or low-pass filtering to the travel driving force Fc, the bottom pressure Pa of the arm cylinder 4, and the bucket angle θb, erroneous judgments by the work judgment unit 110 can be suppressed. Furthermore, by applying moving average processing or low-pass filtering to the bucket angle θb, pulsation of the upper limit value Qlim of the discharge amount can be suppressed, thereby improving the stability of the operating speed of the work device 6.

[0177] <Variation 6> The functions of the main controllers 100, 200, and 300 described in the above embodiment may be partially or entirely implemented in hardware (for example, by designing the logic for performing each function using an integrated circuit).

[0178] Although embodiments of the present invention have been described above, these embodiments represent only a portion of the applications of the present invention and are not intended to limit the technical scope of the present invention to the specific configurations of these embodiments. The embodiments and modifications described above are illustrative examples provided to facilitate understanding of the present invention and are not necessarily limited to those comprising all the configurations described. Furthermore, it is possible to replace parts of the configuration of one embodiment or modification with the configuration of another embodiment or modification, and it is also possible to add the configuration of another embodiment or modification to the configuration of one embodiment or modification. Note that the control lines and information lines shown in the figures are those considered necessary for explanation and do not necessarily represent all the control lines and information lines required in the product. In practice, it can be assumed that almost all configurations are interconnected. [Explanation of symbols]

[0179] 1...Wheel loader, 2...Arm, 3...Bucket, 4...Arm cylinder, 5...Bucket cylinder, 6...Working device, 7...Wheels, 8...Body, 11...Running gear, 16...Engine room, 20...Engine, 30A...Hydraulic pump, 34...Regulator, 40...Generator motor, 43...Traction motor, 45...Traction drive system, 50...Operating device, 52...Arm operating device, 52a...Arm operating amount sensor, 53...Bucket operating device, 53a...Bucket operating amount sensor, 56...Accelerator operating device, 56a...Accelerator operating amount sensor, 58...Mode selector switch (mode selector), 59...Adjustment dial, 61...Vehicle speed sensor, 62...Arm relative angle sensor (arm angle sensor, bucket angle sensor), 63...Bucket relative angle sensor (bucket angle sensor), 64...Engine rotation speed sensor, 65...Torque sensor, 66...Current sensor, 67...Pump Rotation speed sensor, 71… Discharge pressure sensor, 74… Arm cylinder pressure sensor, 91… Excavation target, 100, 200, 300… Main controller (control device), 110, 310… Work determination unit, 111a, 311a… Excavation upper limit calculation unit, 111b… Normal upper limit calculation unit, 112, 212… Command value calculation unit, 120… Engine controller, 313… Penetration distance calculation unit, 3111… First upper limit calculation unit, 3112 ...2nd upper limit calculation unit, 3113...3rd upper limit calculation unit, 3114...Maximum value selection unit, Cd...Indicated value of adjustment dial, Fc...Travel driving force, Fc0...Driving force threshold, FL...Excavation work flag, Fm...AUTO mode flag, Fr...Reaction force, Fr0...Reaction force threshold, Icmd...Control command value, La...Arm operation amount, La0...1st operation amount threshold, Lb...Bucket operation amount, Lb0...2nd operation amount threshold, Ld...Penetration distance, M1, M2,M3…Correlation map, Np…Hydraulic pump rotation speed, Pa…Arm cylinder bottom pressure (arm cylinder pressure), Pa0…Pressure threshold, Pd…Hydraulic pump discharge pressure, Pmax…Maximum discharge pressure, Qd…Hydraulic pump discharge volume, Qlim…Upper limit of discharge volume, Qlim0…Initial upper limit, Qlime…Upper limit of discharge volume during drilling, Qlime1…First upper limit, Qlime2…Second upper limit, Qlime3…Third upper limit, Qlimn…Normal upper limit of discharge volume, Qmax…Maximum discharge volume, Ra…Accelerator operation amount, Tm…Travel drive torque (motor output torque), Tp…Upper limit of pump absorption torque, v…Vehicle speed, θa…Arm angle (Arm angle), θb…Bucket angle (Bucket angle), θba…Lower threshold, θbb…Upper threshold (First angle threshold), θbc…Release threshold (Second angle threshold)

Claims

1. The car body and, A work device having an arm attached to the vehicle body, an arm cylinder for driving the arm, a bucket attached to the arm, and a bucket cylinder for driving the bucket, The power source mounted on the aforementioned vehicle body, A hydraulic pump driven by the aforementioned power source supplies hydraulic fluid to the arm cylinder and the bucket cylinder, A bucket angle sensor for detecting the angle of the bucket, A work vehicle equipped with a control device that controls the capacity of the hydraulic pump in proportion to the discharge amount so that the discharge amount of the hydraulic pump does not exceed the upper limit of the discharge amount, The control device is At least based on the detection results of the bucket angle sensor, it is determined whether or not an excavation operation is in progress. If the aforementioned excavation work state is determined, the upper limit is reduced to a predetermined discharge amount smaller than the maximum discharge amount of the hydraulic pump, and the upper limit is increased in accordance with the increase in the angle of the bucket detected by the bucket angle sensor. A work vehicle characterized by the following features.

2. In the work vehicle described in claim 1, An arm operating device for operating the aforementioned arm, A bucket operating device for operating the bucket, The system includes a pressure sensor for detecting the pressure of the arm cylinder, The control device is Determine whether the conditions for starting excavation work have been met. The state of work after the aforementioned conditions for starting excavation work are met is considered to be the excavation work state. The aforementioned conditions for commencing the excavation work are: At least one of the following: the pressure of the arm cylinder is equal to or greater than a pressure threshold; the amount of operation on the arm-lifting side of the arm operating device is equal to or greater than a first operation amount threshold; and the amount of operation on the bucket-cloud side of the bucket operating device is equal to or greater than a second operation amount threshold. The angle of the bucket is less than or equal to a first angle threshold, including A work vehicle characterized by the following features.

3. In the work vehicle described in claim 2, The aforementioned conditions for starting the excavation work include the driving force for moving the vehicle forward being equal to or greater than the driving force threshold. A work vehicle characterized by the following features.

4. In the work vehicle described in claim 2, The control device is Determine whether the conditions for completing the excavation work have been met. The working state after the aforementioned excavation completion conditions are met is considered a non-excavation working state. The excavation completion condition includes the condition that, while in the excavation state, the angle of the bucket becomes greater than or equal to a second angle threshold which is greater than the first angle threshold. A work vehicle characterized by the following features.

5. In the work vehicle described in claim 1, The system includes an arm angle sensor that detects the angle of the arm, When the control device determines that the excavation work is in progress, it increases the upper limit value in accordance with the increase in the arm angle detected by the arm angle sensor. A work vehicle characterized by the following features.

6. In the work vehicle described in claim 1, The control device is The distance traveled by the vehicle body since the aforementioned excavation work state was assumed is calculated, When the excavation work state is assumed to be in effect, the upper limit is increased in accordance with the increase in the travel distance. A work vehicle characterized by the following features.

7. In the work vehicle described in claim 1, The hydraulic pump is equipped with a rotational speed sensor for detecting the rotational speed of the hydraulic pump, The discharge volume of the hydraulic pump is proportional to the capacity of the hydraulic pump and the rotational speed of the hydraulic pump. When the control device is deemed to be in the excavation work state, it increases the capacity of the hydraulic pump as the rotational speed of the hydraulic pump decreases. A work vehicle characterized by the following features.

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