Work vehicle

Abstract

To provide a work vehicle capable of making the constitution simpler than before, and capable of improving work efficiency of drilling work.SOLUTION: A control device for a work vehicle determines whether or not drilling work is started based on a drilling parameter including a bucket angle θb acquired from a bucket sensor. In the case where the start of the drilling work is determined, the control device restricts the upper limit of a discharge amount of a hydraulic pump to a limited discharge amount Qlime which is smaller than a maximum discharge amount Qmax, and increases the limited discharge amount Qlime according to the progress of the drilling work recognized based on the drilling parameter.SELECTED DRAWING: Figure 7

Description

[Technical field]

[0001] The present disclosure relates to work vehicles. [Background technology]

[0002] There are known inventions relating to working vehicles such as wheel loaders that perform excavation work (see Patent Document 1 below). Patent Document 1 focuses on the problem of technology for reducing power loss in a hydraulic device that drives the working equipment of a wheel loader when hydraulic pressure is required but only a small discharge volume is required, and discloses the following control method as a solution to the problem (see paragraph 0005 and claim 1 of the same document, etc.).

[0003] The control method described in Patent Document 1 is a method for controlling a hydraulic pump for a work machine of a work vehicle. The work vehicle is equipped with a lift cylinder and a tilt cylinder that operate the work machine, and a hydraulic pump that supplies a predetermined pressure oil to the lift cylinder and the tilt cylinder. In the control method of Patent Document 1, it is determined that excavation work is being performed when the vehicle's travel driving force, and / or the hydraulic pressure on the bottom side of the lift cylinder, and / or the hydraulic pressure of the tilt cylinder exceed a predetermined value. Next, it is determined that the capacity of the hydraulic pump is to be reduced to a predetermined capacity that is equal to or less than the maximum capacity, and then control is performed to reduce the capacity of the hydraulic pump to the predetermined capacity.

[0004] The working machine of the work vehicle performing the above-mentioned excavation work has an arm attached to the body of the work vehicle and a bucket attached to the arm. The work vehicle performing the excavation work moves the body forward toward the object to be excavated, penetrates the bucket of the working machine into the object to be excavated, and rotates the bucket toward the front while raising the arm, thereby scooping the object to be excavated into the bucket. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2003-184134 A Summary of the Invention [Problem to be solved by the invention]

[0006] In the excavation work of the above-mentioned work vehicle, in order to improve the work efficiency represented by the excavation amount per unit time [ton / h], it is necessary to increase the amount of the excavation object scooped into the bucket while performing a series of operations quickly. However, if the lifting speed of the arm of the work machine or the rotation speed of the bucket (hereinafter also referred to as the "operation speed of the work machine") is too high, so-called "shallow excavation" occurs, in which only the surface part of the excavation object is scooped into the bucket, and the excavation amount during the excavation work decreases, resulting in a decrease in work efficiency.

[0007] In order to avoid the above-mentioned shallow excavation, the operator of the work vehicle must precisely adjust the operation of the accelerator pedal and the operation lever of the work machine, which accelerate the work vehicle to penetrate the bucket of the work machine into the excavation target and rotate the bucket forward while raising the arm. Such precise operation of the work vehicle during excavation work places a heavy burden on the operator. In addition, when the work vehicle is excavating, if the body of the vehicle shakes or the work machine or the excavation target obstructs the operator's view, the burden on the operator increases further.

[0008] By applying the control method for the hydraulic pump for the work equipment of the work vehicle described in the above Patent Document 1, the capacity of the hydraulic pump is reduced to a predetermined capacity during excavation work, thereby limiting the operating speed of the work equipment. This is expected to have the effect of preventing shallow excavation, but there is a risk that the work time for excavation work will increase and the work efficiency will decrease. On the other hand, if the predetermined capacity of the hydraulic pump that is limited during excavation work is increased in order to improve the work efficiency, the operating speed of the work equipment will increase, increasing the risk of shallow excavation.

[0009] Furthermore, to apply the control method for a hydraulic pump for a work machine of a work vehicle described in Patent Document 1, a regulator that controls the tilt angle to adjust the capacity of the hydraulic pump, and a proportional solenoid valve and hydraulic pilot circuit that control the operation of the regulator are required, which increases the complexity of the hydraulic circuit, as well as the cost and the risk of oil leakage.

[0010] The present disclosure provides a work vehicle that can have a simpler configuration than the above-mentioned conventional techniques and that can improve the work efficiency of excavation work. [Means for solving the problem]

[0011] One aspect of the present disclosure is a work vehicle including a vehicle body, a work machine attached to the vehicle body for performing excavation work, a hydraulic pump that discharges hydraulic oil to drive the work machine, and a control device that controls the discharge rate of the hydraulic pump, wherein the work machine includes an arm attached to the vehicle body, a bucket attached to the arm, an arm cylinder that extends and retracts in response to the supply of hydraulic oil to drive the arm, a bucket cylinder that extends and retracts in response to the supply of hydraulic oil to drive the bucket, and a bucket angle sensor that detects a bucket angle that is the angle of the bucket, and the control device determines whether the excavation work has started based on excavation parameters including the bucket angle acquired from the bucket angle sensor, and when it is determined that the excavation work has started, limits an upper limit of the discharge rate of the hydraulic pump to a limited discharge rate that is less than a maximum discharge rate, and increases the limited discharge rate as the excavation work progresses as recognized based on the excavation parameters. Effect of the Invention

[0012] According to the above aspect of the present disclosure, it is possible to provide a work vehicle that can have a simpler configuration than the above-mentioned conventional technology and that can improve the work efficiency of excavation work. [Brief description of the drawings]

[0013] [Figure 1]1 is a side view showing a first embodiment of a work vehicle according to the present disclosure. [Diagram 2] FIG. 2 is a system configuration diagram of the work vehicle of FIG. 1. [Diagram 3] FIG. 3 is a functional block diagram of a control device for the work vehicle shown in FIG. 2. [Figure 4] FIG. 2 is a schematic diagram illustrating an example of an excavation operation performed by the work vehicle of FIG. 1. [Diagram 5] FIG. 4 is a flow diagram of the control of the discharge amount of the hydraulic pump by the control device of FIG. 3. [Figure 6] FIG. 2 is an enlarged view illustrating a bucket angle of the work machine shown in FIG. [Figure 7] 3 is a graph showing the relationship between the discharge amount and bucket angle of the hydraulic pump of FIG. 2. [Figure 8] 3 is a graph showing the relationship between the discharge amount and the discharge pressure with respect to the control command value of the hydraulic pump in FIG. 2; [Figure 9] 3 is a graph showing the relationship between the discharge amount and the discharge pressure with respect to the bucket angle of the hydraulic pump of FIG. 2. [Figure 10] 5 is a graph illustrating constant displacement control of a hydraulic pump according to the prior art. [Figure 11] 4 is a graph illustrating constant horsepower control of a hydraulic pump according to the prior art. [Figure 12] 2 is a time chart showing the time changes of excavation parameters of the work vehicle of FIG. 1 . [Figure 13] FIG. 11 is a functional block diagram of a control device showing a second embodiment of a work vehicle according to the present disclosure. [Figure 14] FIG. 14 is a functional block diagram of an excavation upper limit value calculation unit of the control device shown in FIG. 13. [Figure 15] FIG. 11 is a functional block diagram of a control device of a work vehicle according to a third embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, an embodiment of a work vehicle according to the present disclosure will be described with reference to the drawings.

[0015] [Embodiment 1] 1 is a side view showing a first embodiment of a work vehicle according to the present disclosure. The work vehicle 100 of this embodiment is a wheel loader that performs excavation work by excavating objects such as soil, crushed stone, and ore, and loading them into a vessel of a transport vehicle such as a dump truck. The work vehicle 100 includes, for example, a vehicle body 110 and a work implement 120.

[0016] The vehicle body 110 may be, for example, an articulated steering type or an articulating vehicle body type in which a front vehicle body 111 and a rear vehicle body 112 are flexibly connected via a center joint 113. Left and right front wheels 101 and a work machine 120 are attached to the front vehicle body 111. Left and right rear wheels 102 are attached to the rear vehicle body 112, and a driver's cab 103 is provided at the front and an equipment storage room 104 is provided at the rear.

[0017] The vehicle body 110 also has a pair of steering cylinders 114, for example, on both sides of a center joint 113 provided in the center in the width direction. The steering cylinder 114 is, for example, a hydraulic cylinder that expands and contracts when hydraulic oil is supplied. The steering cylinder 114 has, for example, a piston rod whose tip is connected to the front vehicle body 111 and a bottom of the cylinder on the opposite side connected to the rear vehicle body 112.

[0018] As a result, one of the pair of steering cylinders 114 extends and the other contracts, causing the front body 111 to bend left and right relative to the rear body 112. Although not shown in Fig. 1, the body 110 has, for example, a brake cylinder 115 which is a hydraulic cylinder that operates the brakes that brake the front wheels 101 and the rear wheels 102, and a parking brake cylinder 116 which is a hydraulic cylinder that operates the parking brake (see Fig. 2).

[0019] The work machine 120 is, for example, an articulated work device that is attached to a front body 111 constituting the vehicle body 110 and performs excavation work of an excavation target such as earth and sand. The work machine 120 has, for example, an arm 121, a bucket 122, an arm cylinder 123, and a bucket cylinder 124.

[0020] The arm 121, also called a lift arm, for example, is attached to a front body 111, which is the front part of the body 110, via a rotation shaft parallel to the width direction of the body 110, and rotates in the vertical direction around the rotation shaft. The work implement 120 is equipped with, for example, a pair of arms 121. The pair of arms 121 are, for example, arranged spaced apart in the width direction of the body 110, and connected at their longitudinal center by a connecting part extending in the width direction of the work vehicle 100.

[0021] Bucket 122 is attached, for example, to a tip end of arm 121 opposite to a base end of arm 121 attached to vehicle body 110 via a rotating shaft parallel to the width direction of vehicle body 110. A Z-link or bell crank type link mechanism is connected to the bottom of bucket 122. When power is transmitted via the link mechanism, bucket 122 rotates up and down around the rotating shaft at the tip end of arm 121.

[0022] The arm cylinder 123 is, for example, a hydraulic cylinder that expands and contracts when hydraulic oil is supplied to it. The work machine 120 is equipped with, for example, a pair of arm cylinders 123. For example, the tip ends of the piston rods of the pair of arm cylinders 123 are rotatably connected to the longitudinal center of the pair of arms 121, and the bottoms of the cylinders on the opposite side are rotatably connected to both sides in the width direction of the front body 111. As a result, when the pair of arm cylinders 123 expand and contract, the pair of arms 121 rotate up and down.

[0023] The bucket cylinder 124 is, for example, a hydraulic cylinder that expands and contracts when hydraulic oil is supplied to it. For example, the tip of the piston rod of the bucket cylinder 124 is rotatably connected to a bell crank of the link mechanism, and the bottom of the cylinder on the opposite side is rotatably connected to the center in the width direction of the front body 111. As a result, when the bucket cylinder 124 expands and contracts, power is transmitted to the bucket 122 via the link mechanism, and the bucket 122 rotates up and down.

[0024] Figure 2 is a system configuration diagram of the work vehicle 100 of Figure 1. In addition to the components shown in Figure 1, the work vehicle 100 is equipped with, for example, hydraulic pumps 105A, 105B, 105C and a control device 200 shown in Figure 2. The work vehicle 100 also has a work implement control unit 131, a brake control unit 132, and a steering control unit 133 that control the pressure, flow rate, and direction of the hydraulic oil supplied from the hydraulic pumps 105A, 105B, 105C to each hydraulic cylinder.

[0025] Furthermore, the work vehicle 100 has, for example, a battery 106, inverters 107A, 107B, motors 108A, 108B, and a battery controller 109. These devices, as well as the above-mentioned hydraulic pumps 105A, 105B, 105C, work implement control unit 131, brake control unit 132, and steering control unit 133, are housed, for example, in an equipment housing room 104 shown in FIG.

[0026] The battery 106 is, for example, a storage battery such as a lithium ion secondary battery. The battery 106 supplies, for example, charged and stored electric power to the motors 108A and 108B via the inverters 107A and 107B. The battery controller 109 controls the battery 106 based on a battery operation command input from the control device 200, for example.

[0027] The traveling inverter 107A receives DC power from the battery 106, and supplies power to the traveling motor 108A based on a traveling drive torque command input from the control device 200, thereby controlling the traveling motor 108A. The traveling inverter 107A and the working inverter 107B are connected by a DC bus.

[0028] The work inverter 107B receives DC power from the battery 106 and controls the rotation speed of the hydraulic pumps 105A, 105B, 105C by controlling the work motor 108B based on a rotation speed command input from the control device 200. The inverter 107B controls the power supplied to the motor 108B so that the rotation speed command value input from the control device 200 matches the rotation speed of the motor 108B.

[0029] The motors 108A, 108B are supported, for example, by a vehicle body 110 shown in Fig. 1. The traveling motor 108A receives a supply of electric power from, for example, a battery 106 via an inverter 107A, and rotates the left and right front wheels 101 and the left and right rear wheels 102 via a power transmission device including an axle, a differential device, a propeller shaft, etc. The working motor 108B receives a supply of electric power from, for example, the battery 106 via an inverter 107B, and drives the hydraulic pumps 105A, 105B, 105C.

[0030] The hydraulic pumps 105A, 105B, and 105C are housed, for example, in the equipment housing chamber 104 shown in Fig. 1. The hydraulic pumps 105A, 105B, and 105C are driven by torque output by the motor 108B to discharge hydraulic oil. The hydraulic pump 105A supplies hydraulic oil to the arm cylinder 123 and the bucket cylinder 124, for example, via a work machine control unit 131 that controls the pressure, flow rate, and direction of the hydraulic oil supplied to the arm cylinder 123 and the bucket cylinder 124.

[0031] The hydraulic pump 105A is, for example, a swash plate or bent axis type variable displacement piston pump, and is provided with a regulator. When the discharge pressure of the hydraulic pump 105A rises above a predetermined value, the regulator accordingly reduces the tilt angle (capacity, equivalent to the displacement volume) of the hydraulic pump 105A, and controls the absorption torque of the hydraulic pump 105A so as not to exceed a set value (upper pump absorption torque upper limit value). The flow rate of the hydraulic oil discharged from the hydraulic pump 105A, i.e., the discharge amount, is proportional to the capacity of the hydraulic pump 105A determined by the control of the regulator and the rotation speed determined by the control of the motor 108B.

[0032] Hydraulic pump 105B supplies hydraulic oil to brake cylinder 115 and parking brake cylinder 116 via brake control unit 132 that controls the pressure, flow rate, and direction of the hydraulic oil supplied to brake cylinder 115 and parking brake cylinder 116. Hydraulic pump 105C supplies hydraulic oil to steering cylinder 114 via steering control unit 133 that controls the pressure, flow rate, and direction of the hydraulic oil supplied to steering cylinder 114, for example.

[0033] Furthermore, the work vehicle 100 is provided with an operation device 140 that is arranged, for example, around a seat in the cab 103 where the operator sits, and accepts operations by the operator. The operation device 140 includes, for example, a forward / reverse switching device 141, an arm operation device 142, a bucket operation device 143, an accelerator operation device 144, a brake operation device 145, a parking brake operation device 146, a steering operation device 147, a mode changeover switch 148, and a discharge amount adjustment dial 149.

[0034] The forward / backward switching device 141 is, for example, a switch or lever for the operator to select any one of the forward (F), standby (N), or backward (R) states of the work vehicle 100, and outputs the state selected by the operator to the control device 200. The arm operating device 142 and the bucket operating device 143 each include an arm lever and a bucket lever for operating the arm and the bucket, and a sensor that detects their operation amounts and outputs them to the control device 200.

[0035] The accelerator operating device 144 and the brake operating device 145 each include an accelerator pedal and a brake pedal, and a sensor that detects their operation amounts and outputs them to the control device 200. The parking brake operating device 146 includes, for example, an operation switch for the operator to switch between the actuation and release of the parking brake, and outputs a signal indicating the actuation or release state of the parking brake to the control device 200. The steering operating device 147 includes, for example, a steering wheel and a sensor that detects its operation amount and outputs it to the control device 200.

[0036] The mode switching switch 148 is, for example, an operation switch for the operator to select the automatic mode or the manual mode of the excavation work of the work vehicle 100. When the automatic mode is selected, the mode switching switch 148 turns on the automatic mode flag Fm (Fm = 1), and when the manual mode is selected, it turns off the automatic mode flag Fm (Fm = 0), and outputs the automatic mode flag Fm corresponding to the selected mode to the control device 200.

[0037] The discharge amount adjustment dial 149 is, for example, an operation dial for the operator to select the set upper limit discharge amount Qlims of the hydraulic pump 105A. The discharge amount adjustment dial 149 outputs an indication value Cd (0 < Cd ≤ 1) corresponding to the set upper limit discharge amount Qlims below the maximum discharge amount Qmax selected by the operator to the control device 200. The indication value Cd becomes the maximum value (Cd = 1) when the set upper limit discharge amount Qlims is equal to the maximum discharge amount Qmax.

[0038] Furthermore, the work vehicle 100 is equipped with a plurality of condition detection sensors 150 that detect various conditions of the work vehicle 100. The condition detection sensors 150 include, for example, a vehicle speed sensor 151, an arm relative angle sensor 152, a bucket relative angle sensor 153, a motor rotation speed sensor 154, a torque sensor 155, a current sensor 156, and a pump rotation speed sensor 157. The condition detection sensors 150 also include, for example, discharge pressure sensors 158A, 158B, 158C, and an arm cylinder pressure sensor 158D. The condition detection sensors 150 also include, for example, a posture sensor 159.

[0039] Vehicle speed sensor 151 is, for example, a rotary encoder that detects the rotational speed of a shaft that constitutes a power transmission device of work vehicle 100, and outputs a signal indicative of the detected rotational speed of the shaft or the corresponding speed of work vehicle 100 to control device 200. Arm relative angle sensor 152 and bucket relative angle sensor 153 respectively detect the angle of arm 121 with respect to a reference plane RP (see FIG. 6) of work vehicle 100 and the angle of bucket 122 with respect to arm 121, and output these to control device 200. The reference plane RP will be described later with reference to FIG. 6.

[0040] The arm relative angle sensor 152 and the bucket relative angle sensor 153 are potentiometers respectively provided on a connecting shaft between the vehicle body 110 and the arm 121 and a connecting shaft between the arm 121 and the bucket 122. The motor rotation speed sensor 154 detects, for example, the rotation speed of the motor 108B that drives the hydraulic pumps 105A, 105B, and 105C, and outputs a signal according to the detected rotation speed to the control device 200.

[0041] The torque sensor 155 and the current sensor 156 respectively detect the torque and current of the motor 108A that generates the driving force for traveling the work vehicle 100, and output a signal corresponding to the detected torque and current to the control device 200. The pump rotation speed sensor 157 detects, for example, the rotation speed of the hydraulic pump 105A that supplies hydraulic oil to the arm cylinder 123 and the bucket cylinder 124, and outputs a signal corresponding to the detected rotation speed to the control device 200.

[0042] The discharge pressure sensors 158A, 158B, 158C detect the discharge pressure of the hydraulic oil of the hydraulic pumps 105A, 105B, 105C, respectively, and output a signal corresponding to the detected discharge pressure to the control device 200. The arm cylinder pressure sensor 158D detects, for example, a bottom pressure which is the pressure of an oil chamber on the bottom side of the arm cylinder 123, and outputs a signal corresponding to the detected bottom pressure to the control device 200.

[0043] The attitude sensor 159 is configured with, for example, a three-axis gyro sensor and an acceleration sensor. The attitude sensor 159 detects attitude information θv of the vehicle body 110 including, for example, a roll angle θr, a pitch angle θp, and a yaw angle θy, and outputs the information to the control device 200.

[0044] The control device 200 is, for example, a main controller that performs overall control of the work vehicle 100, and is composed of one or more microcomputers. The control device 200 has, for example, a CPU 201 as an operating circuit, a ROM 202 and a RAM 203 as memory devices, an input interface 204, and an output interface 205. Note that, like the control device 200, the battery controller 109 can also be composed of one or more microcontrollers equipped with an operating circuit, a memory device, and an input / output interface.

[0045] Control device 200 calculates a rotation speed command value for work motor 108B based on operation amounts input from, for example, arm operation device 142, bucket operation device 143, steering operation device 147, etc., and outputs a control command value to inverter 107B. Specifically, control device 200 calculates the required power of work implement 120 based on the arm operation amount, bucket operation amount, steering operation amount, and discharge pressure Pd of hydraulic pump 105A, and calculates the rotation speed command value for work motor 108B based on the required power.

[0046] Note that control device 200 may, for example, multiply the arm operation amount and the bucket operation amount by respective predetermined coefficients to calculate first and second rotational speed command values, and use the larger of these as the rotational speed command value for work motor 108B. Control device 200 may also output the rotational speed of motor 108B detected by motor rotational speed sensor 154 to inverter 107B, and may calculate the rotational speed command value based on the detected rotational speed.

[0047] The control device 200 also outputs a work machine control command to the work machine control unit 131 based on, for example, the operation direction and operation amount input from the arm operation device 142 and the bucket operation device 143. The control device 200 also outputs a brake control command to the brake control unit 132 based on, for example, signals input from the brake operation device 145 and the parking brake operation device 146. The control device 200 also outputs a steering control command to the steering control unit 133 based on, for example, the operation direction and operation amount input from the steering operation device 147.

[0048] The work machine control unit 131, for example, based on a work machine control command from the control device 200, controls the pressure, flow rate, and direction of the hydraulic oil supplied from the hydraulic pump 105A to operate the arm cylinder 123 and the bucket cylinder 124. The brake control unit 132, for example, based on a brake control command from the control device 200, controls the pressure, flow rate, and direction of the hydraulic oil supplied from the hydraulic pump 105B to operate the brake cylinder 115 and the parking brake cylinder 116.

[0049] The steering control unit 133, for example, controls the pressure, flow rate, and direction of the hydraulic oil supplied from the hydraulic pump 105C based on a steering control command from the control device 200 to operate the steering cylinder 114. The work machine control unit 131, the brake control unit 132, and the steering control unit 133 each have, for example, a directional control valve that controls the pressure, flow rate, and direction of the hydraulic oil, and a solenoid valve that generates pilot pressure for controlling the directional control valve.

[0050] With the above-mentioned configuration, when the operator of the work vehicle 100 operates the arm operating device 142, the arm cylinder 123 expands and contracts, causing the arm 121 to rotate up and down, thereby raising and lowering the bucket 122. Also, when the operator operates the bucket operating device 143, the bucket cylinder 124 expands and contracts, causing the bucket 122 to rotate back and forth, thereby performing crowding and dumping operations. Also, when the operator operates the accelerator operating device 144, the traveling motor 108A is driven to rotate the front wheels 101 and rear wheels 102 via the transmission, causing the work vehicle 100 to move forward and accelerate.

[0051] Furthermore, when the operator operates the steering operation device 147, the steering cylinder 114 expands and contracts, causing the front body 111 to pivot left and right about the center joint 113 relative to the rear body 112, thereby changing the direction of the work vehicle 100. Furthermore, when the operator operates the brake operation device 145 or the parking brake operation device 146, the brake cylinder 115 or the parking brake cylinder 116 expands and contracts, thereby braking the front wheels 101 and the rear wheels 102.

[0052] Furthermore, when the operator operates the accelerator operation device 144 in a state in which reverse (R) is selected by operating the forward / reverse switching device 141, the front wheels 101 and rear wheels 102 rotate in the reverse direction, and the work vehicle 100 moves backward. Note that when the operator operates the forward / reverse switching device 141 to select standby (N), the front wheels 101 and rear wheels 102 do not rotate even if the accelerator operation device 144 is operated, and the work vehicle 100 does not move.

[0053] As described above, the work vehicle 100 of this embodiment is equipped with, for example, an electric travel drive device including a travel motor 108A, and an electric hydraulic drive device including a work motor 108B and hydraulic pumps 105A, 105B, 105C. The travel drive device and hydraulic drive device of the work vehicle 100 are driven independently of each other by power from the battery 106.

[0054] Furthermore, when the operator operates the mode changeover switch 148 to select the automatic mode, the upper limit of the discharge rate of the hydraulic pump 105A is limited to a limited discharge rate Qlime that is less than the maximum discharge rate Qmax, based on excavation parameters including the bucket angle θb, which will be described later. Furthermore, when the operator operates the mode changeover switch 148 to select the manual mode, the upper limit of the discharge rate of the hydraulic pump 105A is no longer limited by the excavation parameters including the bucket angle θb.

[0055] The operator can operate the discharge rate adjustment dial 149 to limit the upper limit of the discharge rate of the hydraulic pump 105A to the set upper limit discharge rate Qlims, which is lower than the maximum discharge rate Qmax. In this case, when the manual mode is selected by the mode changeover switch 148, the upper limit of the discharge rate of the hydraulic pump 105A is limited to the set upper limit discharge rate Qlims. On the other hand, when the automatic mode is selected by the mode changeover switch 148, the upper limit of the discharge rate of the hydraulic pump 105A is limited to the smaller of the limited discharge rate Qlime based on the excavation parameters and the set upper limit discharge rate Qlims. In other words, when the automatic mode is selected, the upper limit of the discharge rate of 105A can be adjusted in response to fluctuations in the excavation parameters.

[0056] Fig. 3 is a functional block diagram of the control device 200 of the work vehicle 100 shown in Fig. 2. As shown in Fig. 3, the control device 200 has, for example, an operation determination unit 210, an excavation upper limit value calculation unit 220, a normal upper limit value calculation unit 230, and a command value calculation unit 240. Each of these units of the control device 200 represents each function of the control device 200 that is realized, for example, by the CPU 201 executing a program stored in the ROM 202.

[0057] Fig. 4 is a schematic side view for explaining an example of a basic excavation operation performed by the work vehicle 100 shown in Fig. 1. The work vehicle 100 performing the excavation operation first assumes a plunge posture with the side of the bucket 122 roughly parallel to and close to the ground surface at a position away from the excavation target ET such as soil, crushed stone, or ore piled up on the ground surface, as shown in Fig. 4(a), and advances toward the excavation target ET. Thereafter, in the early stage of the excavation operation shown in Fig. 4(b), the work vehicle 100 begins to raise the bucket 122 while penetrating the bucket 122 into the excavation target ET with the momentum of forward movement.

[0058] Thereafter, from the middle of the excavation work shown in (c) of Fig. 4, the work vehicle 100 moves further forward to penetrate the bucket 122 deeper into the excavation target ET while operating the arm 121 and the bucket 122 to scoop up the excavation target ET with the bucket 122. Thereafter, at the end of the excavation work shown in (d) of Fig. 4, the work vehicle 100 performs a crowding operation by rotating the bucket 122 toward the cab 103 side and facing the opening upward so that the excavation target ET scooped up by the bucket 122 does not spill out. This completes one excavation work by the work vehicle 100.

[0059] After the above-described excavation work is completed, the work vehicle 100 performs a loading work, for example, as described below. The work vehicle 100 moves backward so as to move away from the excavation target ET piled up on the ground surface, and then moves forward toward a transport vehicle such as a dump truck. At this time, the work vehicle 100 moves forward toward the transport vehicle, for example, while raising the bucket 122. When the work vehicle 100 approaches the transport vehicle and stops, it performs a dumping operation by rotating the bucket 122 forward and facing the opening downward, and drops the excavation target ET in the bucket 122 and loads it into the body or vessel of the transport vehicle. After the above-described loading work is completed, the work vehicle 100 returns to the original position, for example, as shown in FIG. 4(a).

[0060] The above series of operations including the excavation and loading operations of the work vehicle 100 occupies a large portion of the total working time of the work vehicle 100. Therefore, in order to improve the working efficiency of the work vehicle 100, it is effective to improve the efficiency of this series of operations. The working efficiency of the work vehicle 100 can be expressed, for example, as the weight of the excavation target ET loaded onto the transport vehicle per unit time in a series of operations including the excavation and loading operations, that is, [ton / h]. Therefore, the higher the working efficiency [ton / h] of the work vehicle 100, the more excavation target ET can be excavated in a short period of time.

[0061] Figure 5 is a flow diagram showing an example of the discharge rate control of hydraulic pump 105A by control device 200 of Figure 3. When the power switch or key switch of work vehicle 100 is turned on, for example, control device 200 performs a predetermined initial setting, and then starts the process flow shown in Figure 5 and executes it repeatedly at a predetermined cycle. Note that, for example, in the initial setting, control device 200 turns off excavation work flag FL, which is turned on when an excavation work start condition described below is satisfied.

[0062] 5, the control device 200 executes process P1 for setting an excavation work flag FL. In this process P1, the control device 200 determines whether an excavation work start condition or an excavation work end condition is satisfied, and sets the excavation work flag FL to ON or OFF based on the determination result.

[0063] Figure 6 is an enlarged view illustrating bucket angle θb of work vehicle 100 shown in Figure 1. For example, in process P1 shown in Figure 5, work determination unit 210 shown in Figure 3 determines whether or not an excavation work start condition or an excavation work end condition is satisfied based on excavation parameters including at least bucket angle θb shown in Figure 6. Here, bucket angle θb is, for example, the angle of side surface 122f on the front side of bucket 122 with respect to reference plane RP, as shown in Figure 6.

[0064] The reference plane RP is, for example, a virtual plane that serves as a reference for representing the posture of the work vehicle 100, and becomes horizontal when the work vehicle 100 is horizontal. Therefore, if the ground on which the front wheels 101 and rear wheels 102 of the work vehicle 100 are in contact is flat and smooth, the reference plane RP becomes parallel to the ground. Therefore, it can be said that the angle of the arm 121 detected by the arm relative angle sensor 152 corresponds to the relative angle (inclination angle) of the arm 121 with respect to the ground.

[0065] Bucket teeth 122t are attached to the tips of side surfaces 122f of the bucket 122. The bottom surfaces of the bucket teeth 122t are, for example, parallel to the side surface 122f on the front side of the bucket 122. When the side surface 122f of the bucket 122 is parallel to the reference plane RP, the bucket angle θb is 0°.

[0066] Bucket angle θb increases, for example, as bucket 122 pivots rearward due to a crowding operation, and decreases as bucket 122 pivots forward due to a dumping operation. Control device 200 calculates bucket angle θb based on, for example, the angle of arm 121 with respect to reference plane RP detected by arm relative angle sensor 152 and the angle of bucket 122 with respect to arm 121 detected by bucket relative angle sensor 153. That is, the bucket angle sensor that detects bucket angle θb includes, for example, arm relative angle sensor 152 and bucket relative angle sensor 153.

[0067] In process P1 shown in Fig. 5, the work determination unit 210 shown in Fig. 3 determines that the excavation work start condition is met when, for example, at least the following conditions 1A and 2A are met. The work determination unit 210 may also determine that the excavation work start condition is met when the following conditions 3A and 5A are met in addition to conditions 1A and 2A, or when all of conditions 1A to 5A are met. When the work determination unit 210 determines that the excavation work start condition is met, it switches the excavation work flag FL from off (FL = 0) to on (FL = 1).

[0068] Condition 1A: The excavation operation flag FL is set to OFF. Condition 2A: The bucket angle θb based on the detection results of the arm relative angle sensor 152 and the bucket relative angle sensor 153 is within a predetermined angle range (not less than the lower limit angle θbl and not more than the upper limit angle θbh). Condition 3A: The bottom pressure Pa of the arm cylinder 123 based on the detection result of the arm cylinder pressure sensor 158D is equal to or higher than a predetermined lower limit pressure Pal. Condition 4A: The driving force Fc of the traveling motor 108A based on the detection result of the torque sensor 155 or the current sensor 156 is equal to or greater than a predetermined driving force lower limit Fc0. Condition 5A: The operation amount La of the lifting side of the arm 121 input to the arm operating device 142 is equal to or greater than a predetermined operation amount lower limit value La0, or the operation amount Lb of the crowding operation side of the bucket 122 input to the bucket operating device 143 is equal to or greater than a predetermined operation amount lower limit value Lb0.

[0069] The lower limit angle θbl and upper limit angle θbh of condition 2A, the lower limit pressure Pal of condition 3A, the driving force lower limit value Fc0 of condition 4A, and the operation amount lower limit values ​​La0, Lb0 of condition 5A are obtained, for example, by conducting an excavation experiment, etc. More specifically, the time when the bucket 122 starts to penetrate into the excavation target ET is set as the start time of the excavation work, and the threshold values ​​for each condition are determined and stored in ROM 202 based on the bucket angle θb, bottom pressure Pa, and traveling driving force Fc at the start time of the excavation work.

[0070] More specifically, the lower limit angle θbl of the bucket angle θb is, for example, a negative value (θbl<0) of -10° or more and -5° or less. The upper limit angle θbh of the bucket angle θb is, for example, a positive value (θbh>0) of 10° or more and 20° or less. The lower limit pressure Pal of the bottom pressure Pa of the arm cylinder 123 is, for example, a value of 10% or more and 30% or less of the maximum allowable value of the bottom pressure Pa.

[0071] Furthermore, the operation amount lower limit values ​​La0, Lb0 of the arm operation device 142 and the bucket operation device 143 may each adopt a value of about 5[%] of the maximum operation amount of the arm operation device 142 and the bucket operation device 143. Furthermore, the driving force lower limit value Fc0 of the traveling driving force Fc may adopt a value of, for example, 10[%] or more and 40[%] or less of the maximum value of the traveling driving force Fc. The traveling driving force Fc generated by the traveling motor 108A may be calculated, for example, by the following formula (1).

[0072] Fc = (Tm λ / Dt) c (1)

[0073] In the above formula (1), Tm is the output torque (driving torque) of the motor 108A for driving, λ is the overall reduction ratio, Dt is the diameter of the driving wheels, and c is a coefficient for unit conversion. The overall reduction ratio λ is the ratio between the rotation speed of the motor 108A for driving and the rotation speed of the driving wheels, and is calculated, for example, by multiplying the gear ratio of the transmission by the reduction ratio (differential ratio). The driving torque Tm for driving may be detected by the torque sensor 155, may be calculated based on the current detected by the current sensor 156, or may be calculated from the operation amount of the accelerator operation device 144.

[0074] On the other hand, in process P1 shown in Fig. 5, the work determination unit 210 shown in Fig. 3 determines that the excavation work start condition is not satisfied when at least the above condition 2A is not satisfied. For example, when the work determination unit 210 determines that the excavation work start condition is not satisfied when the excavation work flag FL is off, the work determination unit 210 maintains the excavation work flag FL in the off state.

[0075] Furthermore, in process P1 shown in Fig. 5, if the following conditions 1B and 2B are satisfied, for example, the work determination unit 210 shown in Fig. 3 determines that the excavation work end condition is met and switches the excavation work flag FL from on to off. On the other hand, if the following conditions 1B are satisfied but condition 2B is not satisfied, for example, the work determination unit 210 determines that the excavation work end condition is not met and keeps the excavation work flag FL on.

[0076] Condition 1B: The excavation operation flag FL is set to ON. Condition 2B: The bucket angle θb is equal to or greater than a predetermined release angle θbc.

[0077] The release angle θbc of condition 2B is determined, for example, by measuring the bucket angle θb at the end of excavation work as shown in Fig. 4(d) by an experiment or the like, based on the measured bucket angle θb, and is stored in ROM 202. The release angle θbc is, for example, an angle that is 25° or more and 40° or less (θbc>θbh), which is greater than the upper limit angle θbh in condition 2A of the excavation work start condition described above.

[0078] 5, when process P1 ends and the excavation operation flag FL is set, the control device 200 executes the next process P2. In this process P2, the excavation upper limit value calculation unit 220 calculates the limited discharge rate Qlime of the hydraulic pump 105A during excavation operation. In this process P2, the excavation upper limit value calculation unit 220 calculates the limited discharge rate Qlime that is less than the maximum discharge rate Qmax of the hydraulic pump 105A based on excavation parameters including, for example, the bucket angle θb.

[0079] Fig. 7 is a graph showing an example of the relationship between the limited discharge rate Qlime and the bucket angle θb of the hydraulic pump 105A in Fig. 2. In the process P2 shown in Fig. 5, the upper limit value calculation unit 220 during excavation calculates the limited discharge rate Qlime based on, for example, the bucket angle θb based on a signal from the bucket angle sensor and a correlation map M1 showing the relationship between the limited discharge rate Qlime and the bucket angle θb as shown in Fig. 7. Such a correlation map M1 is determined, for example, based on calculation or experiment, and is stored in the ROM 202 in advance. Note that the correlation map M1 in Fig. 7 is a control diagram of the discharge rate assuming that the rotation speed of the hydraulic pump 105A is a target rotation speed during excavation work.

[0080] 7, the limited discharge rate Qlime increases with an increase in the bucket angle θb within a range in which the bucket angle θb is equal to or greater than the initial bucket angle θb0 and equal to or less than the final bucket angle θb3. More specifically, in the correlation map M1, when the bucket angle θb is equal to or less than the initial bucket angle θb0, the limited discharge rate Qlime is limited to an initial limited discharge rate Qlim0 that is, for example, about 10% to 30% of the maximum discharge rate Qmax.

[0081] When the bucket angle θb increases from the initial bucket angle θb0 to the mid-stage bucket angle θb1, the restricted discharge amount Qlime becomes the mid-stage restricted discharge amount Qlim1, which is greater than the initial restricted discharge amount Qlim0. Further, when the bucket angle θb increases from the mid-stage bucket angle θb1 to the final-stage bucket angle θb2, the restricted discharge amount Qlime becomes the final-stage restricted discharge amount Qlim2, which is greater than the mid-stage restricted discharge amount Qlim1. Further, when the bucket angle θb increases from the final-stage bucket angle θb2 to the maximum bucket angle θb3 or more, the restricted discharge amount Qlime becomes equal to, for example, the maximum discharge amount Qmax.

[0082] The initial bucket angle θb0 corresponds to, for example, the posture in which the bucket 122 of the work vehicle 100 penetrates the excavation target ET, as shown in FIGS. 4(a) and 4(b). The initial bucket angle θb0 can adopt an angle of -5° or more and 5° or less with respect to the reference plane RP, for example, as shown in FIG. 6. The mid-stage bucket angle θb1, the final-stage bucket angle θb2, and the maximum bucket angle θb3 correspond to, for example, the operation of scooping up the excavation target ET with the bucket 122 after the mid-stage of the excavation work, as shown in FIGS. 4(c) and 4(d). The maximum bucket angle θb3 can adopt an angle of 30° or more and 50° or less with respect to the reference plane RP, for example, as shown in FIG. 6.

[0083] In the process P2 shown in FIG. 5, for example, the operator of the work vehicle 100 can also select the set upper limit discharge amount Qlims of the hydraulic oil of the hydraulic pump 105A using the discharge amount adjustment dial 149. In this case, the excavation upper limit value calculation unit 220 refers to, for example, the instruction value Cd (0 < Cd ≦ 1) corresponding to the set upper limit discharge amount Qlims input from the discharge amount adjustment dial 149 in addition to the bucket angle θb and the correlation map M1.

[0084] The command value Cd becomes a maximum value (Cd=1) when the set upper limit discharge rate Qlims is set to the maximum discharge rate Qmax. The excavation upper limit value calculation unit 220, for example, compares the set upper limit discharge rate Qlims obtained by multiplying the maximum discharge rate Qmax by the command value Cd with the limited discharge rate Qlime based on the bucket angle θb and the correlation map M1, and sets the smaller one as the limited discharge rate Qlime of the hydraulic pump 105A during excavation work.

[0085] 5, the normal upper limit calculation unit 230 of the control device 200 shown in FIG 3 calculates, for example, a discharge rate upper limit value Qlimn of the hydraulic pump 105A during normal times excluding excavation work. The normal upper limit calculation unit 230 calculates, for example, the maximum discharge rate Qmax by an instruction value Cd input from the discharge rate adjustment dial 149, thereby calculating the discharge rate upper limit value Qlimn of the hydraulic pump 105A during normal times excluding excavation work.

[0086] Thereafter, the control device 200 executes, for example, process P3 shown in Fig. 5. In this process P3, the command value calculation unit 240 of the control device 200 shown in Fig. 3 determines whether the work vehicle 100 is performing excavation work based on whether the excavation work flag FL is on or off, and also determines whether the work vehicle 100 is in the automatic mode based on whether the automatic mode flag Fm is on or off.

[0087] Specifically, command value calculation unit 240 determines whether or not the condition that excavation operation flag FL is on (FL=1) and automatic mode flag Fm is on (Fm=1) is met. If this condition is met, work vehicle 100 is performing excavation operation and is set to automatic mode. As described above, automatic mode flag Fm is turned on (Fm=1) when the operator operates mode selector switch 148 to select automatic mode, and is turned off (Fm=0) when manual mode is selected.

[0088] 5, when the command value calculation unit 240 determines in process P3 that the above condition is satisfied (YES), that is, that both the excavation operation flag FL and the automatic mode flag Fm are on, the control device 200 executes the next process P4. In this process P4, the command value calculation unit 240 sets, for example, the limited discharge rate Qlime of the hydraulic pump 105A during excavation operation to the discharge rate upper limit Qlim for calculating the control command value for the hydraulic pump 105A (Qlim=Qlime), and executes the next process P6.

[0089] On the other hand, if the command value calculation unit 240 determines in process P3 that the above condition is not satisfied (NO), that is, at least one of the excavation operation flag FL and the automatic mode flag Fm is OFF, the control device 200 executes the next process P5. In this process P5, the command value calculation unit 240 sets, for example, the discharge rate upper limit value Qlimn of the hydraulic pump 105A during normal times other than during excavation operation, to the discharge rate upper limit value Qlim for calculating the control command value for the hydraulic pump 105A (Qlim=Qlimn), and executes the next process P6.

[0090] In this process P6, the command value calculation unit 240 calculates the control command value Ncmd based on the discharge rate upper limit value Qlim of the hydraulic pump 105A set in the process P4 or the process P5, for example. Here, the process P6 shown in Fig. 5 will be described with reference to Fig. 8 and Fig. 9. Here, it is assumed that the tilt angle of the hydraulic pump 105A is maximum, and the discharge rate upper limit value Qlim of the hydraulic pump 105A in normal times except during excavation work is equal to the maximum discharge rate Qmax.

[0091] Fig. 8 is a graph showing the relationship between the discharge rate Qd and discharge pressure Pd of hydraulic pump 105A when the control command value Ncmd output from command value calculation unit 240 shown in Fig. 3 is changed. Fig. 9 is a graph showing the relationship between the discharge rate Qd and discharge pressure Pd of hydraulic pump 105A when the bucket angle θb is changed during excavation operation in the automatic mode in which the automatic mode flag Fm and the excavation operation flag FL are simultaneously turned on.

[0092] 8, when the control command value Ncmd is 100%, the discharge rate Qd of the hydraulic pump 105A is adjusted according to the discharge pressure Pd of the hydraulic pump 105A, as shown by the solid line. As the control command value Ncmd decreases, the rotation speed of the hydraulic pump 105A decreases, and the discharge rate Qd of the hydraulic pump 105A also decreases. Therefore, as the control command value Ncmd decreases, the discharge rate Qd according to the discharge pressure Pd decreases.

[0093] In process P6 shown in Fig. 5, command value calculation unit 240 calculates a control command value Ncmd based on, for example, discharge amount upper limit value Qlim set in the previous processes P4 and P5, discharge pressure Pd detected by discharge pressure sensor 158A, and the control characteristic shown in Fig. 8. By adjusting the control command value Ncmd, the rotation speed of hydraulic pump 105A is controlled.

[0094] The control command value Ncmd for controlling the rotation speed of the hydraulic pump 105A can be calculated, for example, from the upper limit Qlim of the discharge rate of the hydraulic pump 105A, the displacement q, and the volumetric efficiency ηv by the following formula (2). In formula (2), cd is a coefficient for unit conversion.

[0095] Ncmd={Qlim / (q·ηv)}·cd ···(2)

[0096] 2 and 3, the control command value Ncmd calculated by the command value calculation unit 240 is input to the inverter 107B. The inverter 107B controls the rotation speed of the work motor 108A in accordance with the input control command value Ncmd. That is, the inverter 107B controls the rotation speed of the motor 108A, thereby controlling the rotation speed of the hydraulic pump 105A mechanically connected to the output shaft of the motor 108A.

[0097] For example, when the output shaft of motor 108A and the input shaft of hydraulic pump 105A are directly connected, the control command value Ncmd directly becomes the rotation speed command value of work motor 108A. When the output shaft of motor 108A and the input shaft of hydraulic pump 105A are connected via gears, the control command value Ncmd multiplied by the gear ratio becomes the rotation speed command value of work motor 108A.

[0098] Fig. 9 is a graph showing the relationship between the discharge rate Qd and the discharge pressure Pd with respect to the change in the bucket angle θb of the hydraulic pump 105A in Fig. 2. For example, when the excavation operation flag FL and the automatic mode flag Fm are turned on, the discharge rate upper limit value Qlim of the hydraulic pump 105A is limited to the limited discharge rate Qlime in the process P4 described above. In this case, the command value calculation unit 240 calculates the control command value Ncmd in the process P6 shown in Fig. 5 so that the discharge rate upper limit value Qlim of the hydraulic pump 105A does not exceed the limited discharge rate Qlime calculated based on the correlation map M1 in Fig. 7 and the bucket angle θb.

[0099] At the beginning of an excavation operation as shown in Fig. 4(b), for example, when the bucket angle θb shown in Fig. 6 is an initial bucket angle θb0 that is greater than or equal to -5° and less than or equal to 5° with respect to the reference plane RP, the limited discharge rate Qlime becomes the initial limited discharge rate Qlim0 as shown in Fig. 7. For this reason, in process P6 shown in Fig. 5, the command value calculation unit 240 calculates the control command value Ncmd as shown in Fig. 9 so that the discharge rate Qd does not exceed the initial limited discharge rate Qlim0 regardless of an increase or decrease in the discharge pressure Pd of the hydraulic pump 105A.

[0100] Thereafter, in the middle of an excavation operation as shown in (b) to (c) of Figure 4, for example, when the bucket angle θb shown in Figure 6 increases to a middle stage bucket angle θb1 that is larger than the initial bucket angle θb0, the limited discharge rate Qlime increases from the initial limited discharge rate Qlim0 to a middle stage limited discharge rate Qlim1 as shown in Figure 7. For this reason, in process P6 shown in Figure 5, the command value calculation unit 240 calculates a control command value Ncmd as shown in Figure 9 so that the discharge rate Qd does not exceed the middle stage limited discharge rate Qlim1 regardless of an increase or decrease in the discharge pressure Pd of the hydraulic pump 105A.

[0101] Furthermore, in the final stage of excavation work as shown in (c) to (d) of Fig. 4, for example, when the bucket angle θb shown in Fig. 6 increases to a final stage bucket angle θb2 larger than the middle stage bucket angle θb1, the limited discharge rate Qlime increases from the middle stage limited discharge rate Qlim1 to a final stage limited discharge rate Qlim2 as shown in Fig. 7. Therefore, in process P6 shown in Fig. 5, the command value calculation unit 240 calculates the control command value Ncmd as shown in Fig. 9 so that the discharge rate Qd does not exceed the final stage limited discharge rate Qlim2 regardless of an increase or decrease in the discharge pressure Pd of the hydraulic pump 105A. Note that the range in which the discharge rate Qd of the hydraulic pump 105A can be adjusted to be constant is the range in which the discharge pressure Pd of the hydraulic pump 105A does not exceed the maximum discharge pressure Pmax.

[0102] 5 and repeatedly executes processes P1 to P6 in the next control cycle. Various parameters used in determining the work state and calculating the control command value Ncmd of the hydraulic pump 105A, such as the traveling driving force Fc, bottom pressure Pa, bucket angle θb, command value Cd, and discharge pressure Pd, are repeatedly calculated by the control device 200 in a predetermined control cycle based on signals from the operation device 140 and the state detection sensor 150, for example.

[0103] The operation of the work vehicle 100 of this embodiment will now be described in comparison with the prior art.

[0104] 4(a) to 4(d), in order to improve the work efficiency represented by the excavation amount per unit time [ton / h], it is necessary to increase the amount of the excavation target ET scooped into the bucket 122 while quickly performing a series of operations. However, if the lifting speed of the arm 121 of the work implement 120 or the rotational speed of the bucket 122, i.e., the operating speed of the work implement 120, is too high, so-called "shallow excavation" occurs in which only the surface portion of the excavation target ET is scooped into the bucket 122, reducing the amount of excavation in the excavation work and decreasing the work efficiency.

[0105] Fig. 10 is a PQ diagram showing the relationship between the discharge pressure Pd and the discharge rate Qd in the constant displacement control of the hydraulic pump 105A according to the conventional technology. In the constant displacement control of the hydraulic pump 105A, as shown in Fig. 10, the discharge rate Qd of the hydraulic pump 105A is reduced to a predetermined value lower than the maximum discharge rate Qmax, for example, 50% of the maximum discharge rate Qmax, during excavation work. According to this conventional constant displacement control, the operating speed of the work machine 120 is reduced in the early stage of excavation work as shown in Fig. 4(a) to (b), and the effect of suppressing shallow excavation can be expected.

[0106] However, with this conventional constant capacity control, the operating speed of the work implement 120 is reduced even in the middle or later stage of the excavation work when the bucket 122 has sufficiently penetrated into the excavation target ET as shown in (c) to (d) of Figure 4, and the time required for the excavation work becomes longer. Also, there is a risk that the bucket 122 will penetrate into the excavation target ET more than necessary, causing the front wheels 101 and rear wheels 102 to spin, the work vehicle 100 to stall, or pressure relief of the work implement 120, which will lengthen the time required for the excavation work.

[0107] If the predetermined value of the discharge rate Qd, which is lower than the maximum discharge rate Qmax shown in Fig. 10, is set to a higher value in order to solve this problem, the operating speed of the work machine 120 will increase more than necessary in the early stage of excavation work as shown in Fig. 4(a) to (b), creating a risk of shallow excavation. In addition, the operator will need to perform complex and precise operations to prevent shallow excavation, which places a heavy burden on the operator and may reduce the operator's concentration, resulting in a decrease in the work efficiency of the excavation work.

[0108] Fig. 11 is a PQ diagram showing the relationship between discharge pressure Pd and discharge rate Qd in constant horsepower control of hydraulic pump 105A according to the conventional technology. In constant horsepower control of hydraulic pump 105A, for example, as shown in Fig. 11, the set value of the absorption torque of hydraulic pump 105A (pump absorption torque upper limit value) is reduced to a predetermined value such as 50% of the maximum value during excavation work. In other words, the upper limit value of the output of hydraulic pump 105A (=discharge rate Qd x discharge pressure Pd) is set to a predetermined value such as 50% of the maximum horsepower.

[0109] However, in this conventional constant horsepower control, when the reaction force acting on the work machine 120 from the excavation target ET is small and the discharge pressure Pd of the hydraulic pump 105A is low in the early stage of excavation work as shown in Figures 4(a) to 4(b), the discharge volume Qd of the hydraulic pump 105A is hardly reduced. Therefore, the lifting speed of the bucket 122 is hardly reduced, and there is a risk of shallow excavation. In addition, the operator must perform complex and precise operations to prevent shallow excavation, which places a heavy burden on the operator and may reduce the operator's concentration and reduce the work efficiency of the excavation work.

[0110] Furthermore, in this conventional constant horsepower control, from the middle of the excavation work shown in (c) to (d) in Fig. 4, the reaction force acting on the work implement 120 from the excavation target ET becomes large, the discharge pressure Pd of the hydraulic pump 105A increases, and the discharge rate Qd of the hydraulic pump 105A is reduced more than necessary. As a result, from the middle of the excavation work, the operating speed of the work implement 120 decreases significantly, and there is a risk of a decrease in work efficiency.

[0111] As described above, there is room for improvement in terms of work efficiency in both the conventional constant displacement control and constant horsepower control. As a result of extensive research into the operation of the operator, the control of the hydraulic pump 105A, and improvements in work efficiency [ton / h] during excavation work using the work vehicle 100, the inventors of the present application have found the following aspects of the work vehicle 100 of this embodiment that solve the problems of the conventional technology.

[0112] As described above, the work vehicle 100 of this embodiment includes the vehicle body 110, the work machine 120 attached to the work vehicle 100 to perform excavation work, the hydraulic pump 105A that discharges hydraulic oil to drive the work machine 120, and the control device 200 that controls the discharge amount Qd of the hydraulic pump 105A. The work machine 120 has an arm 121 attached to the vehicle body 110 and a bucket 122 attached to the arm 121. The work machine 120 also has an arm cylinder 123 that expands and contracts with the supply of the hydraulic oil to drive the arm 121, and a bucket cylinder 124 that expands and contracts with the supply of the hydraulic oil to drive the bucket 122. The work machine 120 also has an arm relative angle sensor 152 and a bucket relative angle sensor 153 as bucket angle sensors that detect a bucket angle θb, which is the angle of the bucket 122. The control device 200 determines whether or not excavation work has started based on excavation parameters including the bucket angle θb acquired from the bucket angle θb sensor. When the control device 200 determines that excavation work has started, the control device 200 limits the upper limit of the discharge rate Qd of the hydraulic pump 105A to a limited discharge rate Qlime that is smaller than the maximum discharge rate Qmax, as shown in Fig. 7, and increases the limited discharge rate Qlime with the progress of the excavation work recognized based on the excavation parameters.

[0113] With this configuration, according to the work vehicle 100 of this embodiment, even if the operator keeps the amount of operation of the arm operating device 142 and the bucket operating device 143 constant during excavation work, the operating speed of the work implement 120 can be sufficiently reduced in the early stage of the excavation work. This not only prevents the timing of raising the bucket 122 from being hasty in the early stage of the excavation work from (b) to (c) in Figure 4, but also suppresses an excessive increase in the lifting speed of the bucket 122, preventing shallow excavation in which only the surface layer of the excavation target ET is excavated.

[0114] This allows the operator of the work vehicle 100 of this embodiment to perform a simple excavation operation by operating the arm operating device 142, the bucket operating device 143, and the accelerator operating device 144 to their maximum operating ranges immediately after the bucket 122 penetrates the excavation target ET. This reduces the burden on the operator during excavation work, allows the operator to maintain concentration, and improves the efficiency of the excavation work. The simple excavation operation is released, for example, when the excavation work has progressed to a predetermined stage and has been completed.

[0115] 4(c) to (d), the operating speed of the work implement 120 can be increased as the excavation work progresses, thereby shortening the time required for the excavation work. Also, by increasing the operating speed of the work implement 120 from the beginning to the end of the excavation work, the bucket 122 is prevented from penetrating excessively into the object to be excavated ET, and the front wheels 101 and rear wheels 102 are prevented from spinning, the work vehicle 100 is stalled, and pressure relief of the work implement 120 is prevented.

[0116] Furthermore, the work vehicle 100 of this embodiment can simplify the hydraulic circuit compared to the work vehicle described in the above-mentioned Patent Document 1, thereby reducing costs and the risk of oil leakage. Therefore, according to this embodiment, it is possible to provide a work vehicle 100 that can be simplified in configuration compared to the prior art and can improve the work efficiency of excavation work.

[0117] Figure 12 is a time chart showing time changes in excavation parameters and other parameters of the work vehicle 100 of Figure 1. In the work vehicle 100 of this embodiment, the excavation parameters include at least the bucket angle θb. Figure 12(a) shows time series changes in the accelerator operation amount Ra, the arm operation amount La, and the bucket operation amount Lb, which are the operation amounts of the accelerator operation device 144, the arm operation device 142, and the bucket operation device 143, respectively, by a solid line, a dashed line, and a dashed dotted line.

[0118] 12(b) to (f) respectively show with solid lines the time series changes in the discharge pressure Pd of hydraulic pump 105A, the rotation speed Ni of motor 108B, the discharge volume Qd of hydraulic pump 105A, the arm angle θa which is the angle of arm 121, and the bucket angle θb of the work vehicle 100 of this embodiment. Also, in FIG. 12(d) to (f), as a comparative example, the discharge volume Qd, arm angle θa, and bucket angle θb of hydraulic pump 105A in conventional constant displacement control are respectively shown with dashed lines.

[0119] 12, it is assumed that the operation of the operator in the work vehicle 100 of this embodiment and the comparative example is the same, and the tilt angle of the hydraulic pump 105A during excavation work is a constant value. Also, the operator of the work vehicle 100 operates the mode selector switch 148 to select the automatic mode, for example, before starting excavation work, and performs the above-mentioned simplified excavation operation when starting excavation work.

[0120] Up until time t0, the operator does not operate the accelerator operation device 144, the accelerator operation amount Ra remains zero, and the work vehicle 100 is stopped or moving forward at a slow speed. At time t0, the operator operates the accelerator operation device 144, which increases the accelerator operation amount Ra and increases the traveling driving force Fc, and the work vehicle 100 begins moving forward and accelerating toward the excavation target ET. At this stage, the bucket 122 of the work implement 120 has not yet penetrated into the excavation target ET, so the discharge pressure Pd of the hydraulic pump 105A remains low.

[0121] Also, at this stage, the operator does not operate the arm operating device 142 or the bucket operating device 143, the arm operation amount La and the operation amount Lb are zero, and the work implement 120 maintains a plunge posture in which the arm 121 is lowered and the teeth of the bucket 122 face the excavation target ET. In this plunge posture, the arm angle θa and the bucket angle θb are small, and the front side surface 122f of the bucket 122 is located near the ground surface and is roughly parallel to the ground surface, as shown in Fig. 6.

[0122] At time t1, when the bucket 122 of the work machine 120, maintaining the plunge posture, penetrates into the excavation target ET, the bottom pressure Pa of the arm cylinder 123 and the discharge pressure Pd of the hydraulic pump 105A rise. Furthermore, at time t2, the operator operates the arm operating device 142, causing the arm operation amount La to increase rapidly, the arm 121 to rotate upward, the bucket 122 to start rising, and the excavation work flag FL to switch from OFF to ON. Until this time t2, the operator does not operate the bucket operating device 143, and the operation amount Lb remains zero.

[0123] Furthermore, in the work vehicle 100 of this embodiment, at time t2, the discharge rate Qd of the hydraulic pump 105A is limited to an initial limited discharge rate Qlim0, which is the limited discharge rate Qlime at the beginning of the excavation work, as shown in Fig. 12(d). Furthermore, as shown in Fig. 12(c), the rotation speed Ni of the work motor 108B also rises to an initial upper limit value Nlim0 in accordance with the discharge rate Qd of the hydraulic pump 105A. This initial upper limit value Nlim0 is lower than an intermediate rotation speed Nmid, which is, for example, about half the maximum rotation speed Nmax.

[0124] After that, at time t3, the operator operates the bucket operation device 143 toward the cloud side, and the operation amount Lb of the bucket 122 increases rapidly. As a result, the rotation speed Ni of the motor 108B increases, the discharge pressure Pd and the discharge amount Qd of the hydraulic pump 105A increase, hydraulic oil is supplied to the bucket cylinder 124, the bucket 122 rotates, and the bucket angle θb increases. After that, the bucket angle θb gradually increases and the excavation target ET is scooped into the bucket 122, and the limit discharge amount Qlime of the hydraulic pump 105A increases with the increase in the bucket angle θb, and the rotation speed Ni and the discharge amount Qd of the motor 108B increase.

[0125] Thereafter, before time t5, the bucket angle θb reaches the final bucket angle θb3, and the limited discharge rate Qlime of the hydraulic pump 105A becomes equal to the maximum discharge rate Qmax. Thereafter, when the rotation speed Ni of the motor 108B reaches the maximum rotation speed Nmax, the discharge rate Qd of the hydraulic pump 105A increases to the maximum discharge rate Qmax. Thereafter, at time t5, the operator operates the arm operating device 142 and the bucket operating device 143 to set the arm operation amount La and the operation amount Lb to zero, thereby ending the excavation work.

[0126] 12(d) in the constant displacement control of the comparative example shown by the dashed line, at time t2, the discharge rate Qd of the hydraulic pump 105A increases to a predetermined discharge rate Qmid that is greater than the initial limited discharge rate Qlim0 and is approximately half the maximum discharge rate Qmax. Thereafter, the discharge rate Qd of the hydraulic pump 105A is maintained at the predetermined discharge rate Qmid until time t5, and the arm angle θa and the bucket angle θb increase at a substantially constant time change rate.

[0127] Therefore, in the work vehicle 100 of this embodiment, the discharge rate Qd of the hydraulic pump 105A shown by the solid line in (d) of Fig. 12 is less than the discharge rate Qd of the hydraulic pump 105A of the comparative example shown by the dashed line from time t2 to time t4. Also, in the work vehicle 100 of this embodiment, the discharge rate Qd of the hydraulic pump 105A shown by the solid line in (d) of Fig. 12 is greater than the discharge rate Qd of the hydraulic pump 105A of the comparative example shown by the dashed line from time t4 to time t5.

[0128] Furthermore, in work vehicle 100 of this embodiment, the rate of increase (time rate of change) of arm angle θa and bucket angle θb shown by the solid lines in (e) and (f) of Figure 12 is lower than the rate of increase of arm angle θa and bucket angle θb of the comparative example shown by the dashed lines until time t4. Furthermore, in work vehicle 100 of this embodiment, from the middle to the end of the excavation work after time t4, the rate of increase of arm angle θa and bucket angle θb shown by the solid lines increases over time and becomes higher than the rate of increase of arm angle θa and bucket angle θb of the comparative example shown by the dashed lines.

[0129] Therefore, according to the work vehicle 100 of this embodiment, in response to a simple excavation operation by the operator, the operating speed of the work implement 120 can be sufficiently reduced in the early stages of the excavation work to suppress shallow excavation. Also, according to the work vehicle 100 of this embodiment, the discharge volume Qd of the hydraulic pump 105A is reduced more than in the comparative example in the early stages of the excavation work, so that the power consumed by the work implement 120 can be suppressed to the minimum necessary, and the traveling driving force Fc can be increased accordingly to improve the efficiency of the excavation work.

[0130] In contrast, with the conventional constant displacement control of the comparative example, the operating speed of the work implement 120 cannot be sufficiently reduced in the early stages of excavation work, creating a risk of shallow digging and increasing the burden on the operator who must operate to avoid this. As a result, with the conventional constant displacement control of the comparative example, there is a risk that the efficiency of excavation work will decrease compared to the work vehicle 100 of this embodiment.

[0131] Furthermore, with the work vehicle 100 of this embodiment, the operating speed of the work implement 120 can be sufficiently increased from the middle to the end of the excavation work in response to a simple excavation operation by the operator, thereby shortening the work time and suppressing excessive penetration of the bucket 122 into the excavation target ET. Therefore, with the work vehicle 100 of this embodiment, it is possible to achieve improved efficiency and fuel efficiency in the excavation work while reducing the burden on the operator, and even an inexperienced operator can achieve work efficiency close to that of an experienced operator.

[0132] On the other hand, in the conventional constant capacity control of the comparative example, the operating speed of the work implement 120 cannot be increased sufficiently from the middle to the end of the excavation work. Therefore, not only does the time required for the excavation work increase, but there is also a risk of the bucket 122 excessively penetrating into the excavation target ET. As a result, in the conventional constant capacity control, wheel spinning of the work vehicle, stalling, pressure relief of the work implement, and the like may occur, which may reduce the work efficiency of the excavation work. In addition, the burden on the operator who performs the operation to avoid excessive penetration of the bucket 122 into the excavation target ET increases.

[0133] Furthermore, according to the work vehicle 100 of this embodiment, the number of times the operator operates the operation device 140 during excavation work is reduced through simplified excavation operations, thereby reducing the physical load on the operation device 140, the work machine 120, the motor 108A for traveling, the transmission, etc. Therefore, the useful life of these devices can be extended.

[0134] Furthermore, with the work vehicle 100 of this embodiment, there is no need for an electromagnetic proportional valve for controlling the capacity of the hydraulic pump 105A, a regulator, or an electric circuit and hydraulic circuit for operating these. Therefore, compared to conventional techniques for controlling the capacity of the hydraulic pump 105A, the number of parts in the hydraulic circuit is reduced and the configuration is simplified, making it possible to reduce the cost of the hydraulic circuit and reduce the risk of oil leakage, which is a cause of environmental load.

[0135] Furthermore, in the work vehicle 100 of this embodiment, the control device 200 determines the start of excavation work when the start of excavation work has not been determined and the bucket angle θb is at least an angle within a predetermined angle range that is equal to or greater than the lower limit angle θbl and equal to or less than the upper limit angle θbh, as in the above-described condition 1A and condition 2A. In this way, by including the bucket angle θb being within the predetermined angle range in the conditions for the control device 200 to determine the start of excavation work, it is possible to determine that the work implement 120 is in a position that allows the bucket 122 to penetrate the excavation target ET.

[0136] Moreover, as described above, the work vehicle 100 of this embodiment is further equipped with an arm cylinder pressure sensor 158D that detects the bottom pressure Pa, which is the pressure in the oil chamber on the bottom side of the arm cylinder 123. Furthermore, the control device 200 determines the start of excavation work when the bottom pressure Pa is equal to or greater than the predetermined lower limit pressure Pal, as in the above-mentioned condition 3A, in addition to the above-mentioned condition 1A and condition 2A. In this way, by including the bottom pressure Pa being equal to or greater than the predetermined lower limit pressure Pal in the conditions for the control device 200 to determine the start of excavation work, it is possible to more accurately determine that the bucket 122 has penetrated the excavation target ET and excavation work has started.

[0137] As described above, the work vehicle 100 of this embodiment is further equipped with an operating device 140 that detects the respective operation amounts La, Lb of the arm 121 and the bucket 122. Furthermore, the control device 200 determines that excavation work has started when the operation amount La of the arm 121 or the operation amount Lb of the bucket 122 exceeds a predetermined threshold, as in the above-mentioned condition 5A, in addition to the above-mentioned condition 1A and condition 2A. In this way, by including the operation amount La or operation amount Lb exceeding a predetermined threshold in the conditions for the control device 200 to determine the start of excavation work, it is possible to more accurately determine that excavation work has started, based on the operation of the operating device 140 by the operator.

[0138] Furthermore, in the work vehicle 100 of this embodiment, the control device 200 acquires the driving force Fc that moves the vehicle body 110 forward, and determines the start of excavation work when the driving force Fc exceeds a predetermined threshold, as in the above-mentioned condition 4A, in addition to the above-mentioned conditions 1A and 2A. In this way, by including the driving force Fc exceeding a predetermined threshold in the conditions for the control device 200 to determine the start of excavation work, it is possible to more accurately determine the start of excavation work in which the work vehicle 100 moves forward toward the excavation target ET.

[0139] In addition, in the work vehicle 100, for example, during uphill travel or ground leveling work to flatten the ground, the bucket angle θb may be within the predetermined angle range of condition 2A and the travel driving force Fc may exceed the predetermined threshold value of condition 4A. However, during uphill travel and ground leveling work, the bottom pressure Pa of the arm cylinder 123 does not exceed the lower limit pressure Pal of condition 3A, and the respective operation amounts La, Lb of the arm 121 and the bucket 122 do not exceed the threshold values ​​of condition 5A. Therefore, by including condition 3A of the bottom pressure Pa or condition 5A of the operation amounts La, Lb in the conditions for determining the start of excavation work, it is possible to prevent erroneous determination of the start of excavation work during uphill travel and ground leveling work.

[0140] Furthermore, in the work vehicle 100, for example, during loading work in which an excavation target ET is loaded onto a transport vehicle such as a dump truck, the bucket angle θb may fall within the predetermined angle range of condition 2A, and the bottom pressure Pa of the arm cylinder 123 may exceed the lower limit pressure Pal of condition 3A. However, in stationary work such as loading work, the travel driving force Fc of the work vehicle 100 does not exceed the predetermined threshold value of condition 4A. Therefore, by including condition 4A of the travel driving force Fc in the conditions for determining the start of excavation work, it is possible to prevent erroneous determination of the start of excavation work in stationary work such as loading work.

[0141] Furthermore, in the work vehicle 100 of this embodiment, the control device 200 determines the start of excavation work as described above, and then determines the end of excavation work when the bucket angle θb becomes equal to or greater than the predetermined release angle θbc. This allows the control device 200 to determine that the work implement 120 has reached a transport posture for transporting the excavation target ET, and to determine the end of excavation work. In a normal state except during excavation work, the discharge rate Qd of the hydraulic pump 105A is not limited to the limited discharge rate Qlime.

[0142] Therefore, when the work vehicle 100 is driven toward the transport vehicle after the excavation work is completed, the bucket 122 can be raised at a sufficient speed. Also, when the work vehicle 100 loads the excavation target ET in the bucket 122 onto the transport vehicle, the bucket 122 can be rotated forward at a sufficient speed to perform a dumping operation. This makes it possible to improve the work efficiency of the work vehicle 100 after the excavation work is completed.

[0143] Furthermore, in the work vehicle 100 of this embodiment, the control device 200 regards an increase in the bucket angle θb as a progress in the excavation work, and increases the limited discharge rate Qlime as the bucket angle θb increases. Compared with other excavation parameters, the bucket angle θb has the best correlation with the progress of the excavation work. Therefore, by regarding an increase in the bucket angle θb as a progress in the excavation work, it is possible to more accurately grasp the degree of progress of the excavation work.

[0144] As described above, according to this embodiment, it is possible to provide a work vehicle 100 that can simplify the configuration compared to the above-mentioned conventional technology and improve the work efficiency of excavation work. Note that the work vehicle according to the present disclosure is not limited to the above-mentioned embodiment 1. For example, in the above-mentioned embodiment 1, an example was described in which, when the excavation work flag FL is switched from off to on, the control device 200 calculates the limited discharge amount Qlime of the hydraulic pump 105A in accordance with the progress of the excavation work based on the excavation parameters including the bucket angle θb.

[0145] However, the control device 200 may set the limited discharge rate Qlime to the initial limited discharge rate Qlim0 regardless of the bucket angle θb, for example, when the excavation operation flag FL is switched from off to on. In this case, the control device 200 can increase the limited discharge rate Qlime in accordance with an increase in the bucket angle θb after a change occurs in the bucket angle θb after the excavation operation flag FL is switched from off to on.

[0146] [Embodiment 2] Hereinafter, a second embodiment of a work vehicle according to the present disclosure will be described with reference to Figures 1, 2, and 4 to 12 of the first embodiment, and with reference to Figures 13 and 14. In this embodiment, configurations similar to those described in the first embodiment above will be given the same reference numerals and descriptions thereof will be omitted.

[0147] 13 is a functional block diagram of a control device 200 showing a second embodiment of a work vehicle 100 according to the present disclosure. The control device 200 of this embodiment has a penetration distance calculation unit 250 in addition to the above-mentioned work determination unit 210, excavation upper limit value calculation unit 220, normal upper limit value calculation unit 230, and command value calculation unit 240.

[0148] The penetration distance calculation unit 250 represents a function of the control device 200 that is realized by executing a program stored in the ROM 202 by the CPU 201, similar to the above-mentioned work determination unit 210, etc. Also, the work determination unit 210 and the excavation upper limit value calculation unit 220 of this embodiment differ from the work determination unit 210 and the excavation upper limit value calculation unit 220 of the above-mentioned embodiment 1 in the method of determining the start of excavation work and the method of calculating the limited discharge amount Qlime, respectively.

[0149] The work determination unit 210 determines whether or not excavation work has started based on excavation parameters including, for example, the traveling driving force Fc, the bottom pressure Pa of the arm cylinder 123, and the bucket angle θb. That is, the work determination unit 210 of this embodiment determines whether or not excavation work has started using, for example, conditions 1A to 4A excluding condition 5A among conditions 1A to 5A used by the work determination unit 210 of the above-mentioned first embodiment in process P1 of Fig. 5.

[0150] The penetration distance calculation unit 250 calculates the penetration distance Ld, for example, based on the excavation work flag FL input from the work determination unit 210 and the vehicle speed V input from the vehicle speed sensor 151. The penetration distance Ld is the travel distance of the work vehicle 100 from the point when the work vehicle 100 advances toward the excavation target ET and the bucket teeth 122t at the tip of the bucket 122 of the work implement 120 penetrates into the excavation target ET.

[0151] When the excavation work flag FL input from the work determination unit 210 is off (FL=0), the penetration distance calculation unit 250 resets the penetration distance Ld to an initial value of zero (Ld=0). When the excavation work flag FL input from the work determination unit 210 is on (FL=1), the penetration distance calculation unit 250 calculates the penetration distance Ld, for example, by integrating the vehicle speed V [m / control cycle] for each control cycle. In other words, the penetration distance calculation unit 250 calculates the travel distance of the work vehicle 100 from the start of the excavation work as the penetration distance Ld.

[0152] The upper limit value calculation unit 220 during excavation in this embodiment calculates, for example, a limited discharge rate Qlime that is less than the maximum discharge rate Qmax of the hydraulic pump 105A as the upper limit of the discharge rate Qd of the hydraulic pump 105A during excavation work. Furthermore, the upper limit value calculation unit 220 during excavation in this embodiment increases the limited discharge rate Qlime with the progress of the excavation work recognized based on the excavation parameters including the bucket angle θb, the arm angle θa, and the penetration distance Ld.

[0153] Fig. 14 is a functional block diagram of the excavation upper limit value calculation unit 220 of this embodiment shown in Fig. 13. The excavation upper limit value calculation unit 220 of this embodiment has, for example, a first upper limit value calculation unit 221, a second upper limit value calculation unit 222, a third upper limit value calculation unit 223, and a restricted discharge rate selection unit 224. Correlation maps M1, M2, M3 used by each calculation unit of the excavation upper limit value calculation unit 220 are stored in the ROM 202 of the control device 200 of this embodiment.

[0154] The correlation map M1, like the correlation map M1 in the above-described embodiment 1, defines the relationship between the bucket angle θb and the first limited discharge rate Qlime1 of the hydraulic pump 105A during excavation work. For example, the first limited discharge rate Qlime1 is set to an initial limited discharge rate Qlim0 that is smaller than the maximum discharge rate Qmax when the bucket angle θb is within a range equal to or smaller than the initial bucket angle θb0 at the start of excavation work.

[0155] Furthermore, the first limited discharge rate Qlime1 increases with an increase in the bucket angle θb, for example, in a range in which the bucket angle θb is greater than the initial bucket angle θb0 and less than the final bucket angle θb3 at the end of the excavation work. Furthermore, the first limited discharge rate Qlime1 is equal to the maximum discharge rate Qmax of the hydraulic pump 105A, for example, in a range in which the bucket angle θb is equal to or greater than the final bucket angle θb3.

[0156] The correlation map M2 defines, for example, the relationship between the arm angle θa and the second limited discharge rate Qlime2 of the hydraulic pump 105A during excavation work. The second limited discharge rate Qlime2 is set to an initial limited discharge rate Qlim0 that is smaller than the maximum discharge rate Qmax when the arm angle θa is within a range equal to or smaller than the initial arm angle θa0 at the start of excavation work.

[0157] Also, the second limited discharge rate Qlime2 increases with an increase in the arm angle θa, for example, in a range where the arm angle θa is greater than the initial arm angle θa0 and less than the final arm angle θax at the end of the excavation work. Also, the second limited discharge rate Qlime2 is equal to the maximum discharge rate Qmax of the hydraulic pump 105A, for example, in a range where the arm angle θa is equal to or greater than the final arm angle θax.

[0158] The correlation map M3 defines, for example, the relationship between the penetration distance Ld and the third limit discharge rate Qlime3 of the hydraulic pump 105A during excavation work. The third limit discharge rate Qlime3 is set to an initial limit discharge rate Qlim0 that is smaller than the maximum discharge rate Qmax when the penetration distance Ld is within a range of the initial penetration distance Ld0 immediately after the start of excavation work.

[0159] Also, the third limit discharge amount Qlime3 increases with an increase in the penetration distance Ld, for example, in a range in which the penetration distance Ld is longer than the initial penetration distance Ld0 and shorter than the final penetration distance Ldx at the end of the excavation work. Also, the third limit discharge amount Qlime3 is equal to the maximum discharge amount Qmax of the hydraulic pump 105A, for example, in a range in which the penetration distance Ld is equal to or greater than the final penetration distance Ldx.

[0160] The first upper limit value calculation unit 221 refers to the correlation map M1 and calculates the first limited discharge rate Qlime1 based on the bucket angle θb. The second upper limit value calculation unit 222 refers to the correlation map M2 and calculates the second limited discharge rate Qlime2 based on the arm angle θa. The third upper limit value calculation unit 223 refers to the correlation map M3 and calculates the third limited discharge rate Qlime3 based on the penetration distance Ld. The limited discharge rate selection unit 224 outputs the maximum of the first limited discharge rate Qlime1, the second limited discharge rate Qlime2, and the third limited discharge rate Qlime3 calculated by the first upper limit value calculation unit 221, the second upper limit value calculation unit 222, and the third upper limit value calculation unit 223 as the limited discharge rate Qlime.

[0161] As described above, the work vehicle 100 of this embodiment is equipped with the arm relative angle sensor 152 that detects the arm angle θa, which is the angle of the arm 121, and the excavation parameters include the arm angle θa. The control device 200 regards an increase in the arm angle θa as a progress of the excavation work, and increases the limited discharge rate Qlime as the arm angle θa increases. This makes it possible to more reliably increase the operating speed of the work implement 120 from the middle to the end of the excavation work.

[0162] In the work vehicle 100 of this embodiment, the excavation parameters correlated with the progress of the excavation work include the penetration distance Ld, which is the distance traveled by the vehicle body 110 from the time when the start of the excavation work is determined. The control device 200 regards an increase in the penetration distance Ld as the progress of the excavation work, and increases the limited discharge amount Qlime as the penetration distance Ld increases. This makes it possible to increase the limited discharge amount Qlime as the penetration distance Ld increases, for example, even if the arm operation device 142 and the bucket operation device 143 are not operated until the middle of the excavation work.

[0163] Therefore, even if the operator is late in operating the arm operating device 142 and the bucket operating device 143 after the start of excavation work, it is possible to raise the bucket 122 at a sufficient speed while preventing shallow digging of the excavation target ET. As a result, excessive penetration of the bucket 122 into the excavation target ET from the middle or later of the excavation work can be prevented, and slippage of the front wheels 101 and rear wheels 102, stalling of the work vehicle 100, pressure relief of the work implement 120, etc. can be prevented.

[0164] As described above, according to this embodiment, similar to the above-described embodiment 1, it is possible to provide a work vehicle 100 that can simplify the configuration compared to the conventional technology and improve the work efficiency of excavation work. Note that the work vehicle according to the present disclosure is not limited to the above-described embodiment 2.

[0165] For example, in the above-described embodiment 2, the maximum of the first limited discharge amount Qlime1, the second limited discharge amount Qlime2, and the third limited discharge amount Qlime3 is determined as the limited discharge amount Qlime. However, the method of determining the limited discharge amount Qlime is not limited to the example of embodiment 2. For example, the average value of the first limited discharge amount Qlime1, the second limited discharge amount Qlime2, and the third limited discharge amount Qlime3 may be set as the limited discharge amount Qlime.

[0166] [Embodiment 3] Hereinafter, a third embodiment of a work vehicle according to the present disclosure will be described with reference to Figures 1, 2, and 4 to 12 of the first embodiment, and with reference to Figure 15. In this embodiment, configurations similar to those described in the first embodiment above will be given the same reference numerals and descriptions thereof will be omitted.

[0167] 15 is a functional block diagram 200 showing a third embodiment of a work vehicle 100 according to the present disclosure. In the control device 200 of the present embodiment, an excavation upper limit value calculation unit 220 calculates a limited discharge rate Qlime of the hydraulic pump 105A using posture information θv of the vehicle body 110 input from the posture sensor 159 in addition to the bucket angle θb and the indicated value Cd of the discharge rate adjustment dial 149.

[0168] More specifically, similarly to the above-described first embodiment, the excavation upper limit calculation unit 220 calculates the limited discharge rate Qlime by using the bucket angle θb and the correlation map M1 so as not to exceed the set upper limit discharge rate Qlims based on the instruction value Cd of the discharge rate adjustment dial 149. Furthermore, the excavation upper limit calculation unit 220 of this embodiment stops increasing the limited discharge rate Qlime as the excavation work progresses, for example, when the attitude information θv is outside a predetermined allowable range.

[0169] More specifically, for example, an allowable range of the attitude information θv is stored in advance in the ROM 202 of the control device 200. The allowable range of the attitude information θv is, for example, a range in which the work vehicle 100 can stably perform excavation work. The allowable range of the attitude information θv includes, for example, the angle ranges of the roll angle θr, the pitch angle θp, and the yaw angle θy. For example, when the attitude information θv is outside a predetermined allowable range, the excavation upper limit value calculation unit 220 fixes the value of the limited discharge rate Qlime and does not increase the value of the limited discharge rate Qlime even if the bucket angle θb increases.

[0170] As described above, the work vehicle 100 of this embodiment is equipped with an attitude sensor 159 that detects the attitude of the vehicle body 110. When the attitude information θv, which is the attitude of the vehicle body 110 detected by the attitude sensor 159, is outside a predetermined allowable range, the control device 200 stops increasing the limited discharge rate Qlime as the excavation work progresses.

[0171] With this configuration, the work vehicle 100 of this embodiment prevents the operating speed of the work implement 120 from increasing during excavation work when the vehicle body 110 is in an unstable state, improving safety. More specifically, for example, after the bucket 122 penetrates the excavation target ET and the control device 200 determines that excavation work has started, if the vehicle body 110 tilts or rotates and its posture falls outside a predetermined allowable range, the limited discharge amount Qlime does not increase even if the excavation work progresses.

[0172] This prevents the operating speed of the work implement 120 from increasing when the vehicle body 110 is in an unstable state, and allows the operator to perform excavation work with ample time depending on the attitude of the vehicle body 110 and the amount of excavation target ET to be scooped into the bucket 122. As a result, even if the attitude of the vehicle body 110 is outside a predetermined allowable range, shallow digging is prevented, and the stability of the work vehicle 100 can be improved.

[0173] Although an embodiment of the work vehicle according to the present disclosure has been described in detail above using the drawings, the specific configuration is not limited to this embodiment, and even if there are design changes and the like within the scope of the present disclosure, they are included in the present disclosure. The above-mentioned embodiment and its modified examples are exemplified to explain the present disclosure in an easy-to-understand manner, and the work vehicle according to the present disclosure is not necessarily limited to one having all of the above-mentioned configurations.

[0174] In addition, it is possible to replace a part of the configuration of a certain 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 a certain embodiment or modification. Note that the control lines and information lines shown in the figures are those that are considered necessary for explanation, and do not necessarily show all the control lines and information lines necessary on the product. In reality, it can be considered that almost all the configurations are connected to each other.

[0175] Hereinafter, several modified examples of the work vehicle 100 according to the above-described embodiment will be described.

[0176] Variation 1 The excavation operation start conditions are not limited to the above-mentioned conditions 1A to 5A. Variation 1-1 For example, both Condition 5A and Condition 3A are conditions for preventing erroneous determination of the start of excavation work during uphill travel or ground leveling work. Therefore, in the above-described embodiment 1 or embodiment 2, Condition 5A may be adopted instead of Condition 3A. This can prevent a delay in the timing at which the excavation work flag FL is turned on. Specifically, if the bottom surface of the bucket 122 is in contact with the ground when the bucket 122 penetrates the excavation target ET, the bottom pressure Pa of the arm cylinder 123 does not rise immediately, and a predetermined time may be required from the time the bucket operating device 143 is operated until Condition 3A is satisfied. Even in such a case, by adopting Condition 5A instead of Condition 3A, a delay in the timing at which the excavation work flag FL is turned on can be prevented. Variation 1-2 Instead of condition 3A using the bottom pressure Pa of the arm cylinder 123, the following condition 3Aa may be adopted. Condition 3Aa: The reaction force Fr acting on the vehicle body 110 is equal to or greater than a threshold value Fr0. The reaction force Fr is calculated, for example, based on the driving force Fc and the vehicle speed V, using the following relational expression (3) between momentum and impulse. Fr=Fc-(m·Vb-m·Va) / (tb-ta) ···(3) Here, m is the mass of the work vehicle 100, ta is a reference time, tb is a time a predetermined time has elapsed since the reference time ta, Va is the vehicle speed V of the work vehicle 100 at the time ta, and Vb is the vehicle speed V of the work vehicle 100 at the time tb. In this modification, the same effects as in modification 1-1 can be achieved. Variation 1-3 The above-mentioned condition 4A is a condition for determining that the work vehicle 100 is moving forward, and is a condition for avoiding erroneous determination of the start of excavation work in stationary work such as loading work. Therefore, instead of condition 4A, the following condition 4Aa or condition 4Ab can also be adopted. Condition 4Aa: The accelerator operation amount Ra is equal to or greater than a predetermined threshold value. Condition 4Ab: The driving torque Tm is equal to or greater than a predetermined threshold value. By adopting the above condition 4Aa, it is not necessary to detect a state quantity using a sensor other than the accelerator operation amount Ra, so reliability is improved. In addition, the calculation according to the above-mentioned formula (1) is no longer necessary, and the calculation processing can be speeded up. By employing the above condition 4Ab, the influence of the gear ratio of the transmission is avoided, and it is possible to accurately determine whether the condition is met even during a gear shift. Variation 1-4 The above-mentioned conditions 1A to 5A, 1B, and 2B may be determined to be satisfied when the conditions are satisfied for a predetermined time. For example, condition 3A may be that the bottom pressure Pa of the arm cylinder 123 is maintained at or above the lower limit pressure Pal for a predetermined time. In addition, the control device 200 may, for example, switch the excavation work flag FL from off to on when the state in which the above-mentioned conditions 1A to 5A are satisfied continues for a predetermined time, and may switch the excavation work flag FL from on to off when the state in which the conditions 1B and 2B are satisfied continues for a predetermined time. This prevents the excavation work flag FL from switching at an unexpected time if there is pulsation in the excavation parameters, the detection value of the excavation parameters contains noise, or the operator's operation changes before and after the excavation work flag FL is switched.

[0177] Variation 2 The excavation work end condition is not limited to the above-mentioned condition 1B and condition 2B. For example, it may be determined that the excavation work end condition is satisfied when a predetermined time threshold (for example, about 5 seconds) has elapsed since the excavation work end condition was satisfied. The time threshold is stored in the ROM 202 in advance. The time threshold is determined, for example, by an experiment or the like. According to this modification, even in an excavation work of a type different from the normal excavation work assumed in the above-mentioned embodiment, the excavation work end condition can be reliably satisfied and a decrease in work efficiency can be prevented.

[0178] Variation 3 In the above embodiment, an example has been described in which the power source that supplies power to the work drive device that drives the work machine 120 and the traveling drive device that travels the vehicle body 110 is the battery 106. However, the power source may be something other than the battery 106. For example, the power source may be a fuel cell. Also, a generator motor mechanically connected to the engine may be used. Also, a configuration in which power is supplied to the work drive device and the traveling drive device via a converter in the subsequent stage of the power source may be used.

[0179] Variation 4 In the above embodiment, the working vehicle 100 has been described in which the operating device 140 is operated by the operator to perform excavation work, loading work, and the like. However, the control of increasing the limited discharge rate Qlime of the hydraulic pump 105A in response to an increase in the bucket angle θb during excavation work can also be applied to an autonomous working vehicle. In this case, the upper limit value of the discharge rate corresponds to the target value of the discharge rate.

[0180] Variation 5 In the above-described embodiment, the values ​​used in the various judgments and calculations may be subjected to moving average processing or low-pass filter processing in order to avoid the influence of disturbances and noise. For example, by performing moving average processing or low-pass filter processing on the traveling driving force Fc, the bottom pressure Pa of the arm cylinder 123, and the bucket angle θb, respectively, it is possible to suppress erroneous judgment by the work judgment unit 210. In addition, by performing moving average processing or low-pass filter processing on the bucket angle θb, it is possible to suppress pulsation of the limited discharge amount Qlime, thereby improving the stability of the operating speed of the work machine 120.

[0181] Variation 6 The individual units representing the functions of the control device 200 in the above-described embodiment may be realized in part or in whole by hardware such as an integrated circuit. [Explanation of symbols]

[0182] 100 Work vehicles 105A Hydraulic Pump 110 Body 120 Work Machine 121 Arm 122 Bucket 123 Arm Cylinder 124 Bucket Cylinder 140 Operating device 152 Arm relative angle sensor (bucket angle sensor) 153 Bucket relative angle sensor (bucket angle sensor) 158D Arm cylinder pressure sensor 159 Attitude Sensor 200 Control device Fc Driving force La operation amount Lb Manipulated amount Ld Penetration distance (travel distance, drilling parameters) Qd Discharge amount Qlime Limited Discharge Volume θa Arm angle (drilling parameter) θb Bucket angle (digging parameter) θv Attitude information (vehicle attitude)

Claims

1. A work vehicle including a vehicle body, a work machine attached to the vehicle body for performing excavation work, a hydraulic pump that discharges hydraulic oil for driving the work machine, and a control device that controls a discharge amount of the hydraulic pump, the work machine includes an arm attached to the vehicle body, a bucket attached to the arm, an arm cylinder that extends and retracts in response to the supply of hydraulic oil to drive the arm, a bucket cylinder that extends and retracts in response to the supply of hydraulic oil to drive the bucket, and a bucket angle sensor that detects a bucket angle that is the angle of the bucket, the control device determines whether or not the excavation operation has started based on excavation parameters including the bucket angle acquired from the bucket angle sensor, and when it determines that the excavation operation has started, limits an upper limit of the discharge rate of the hydraulic pump to a limited discharge rate that is less than a maximum discharge rate, and increases the limited discharge rate in accordance with the progress of the excavation operation recognized based on the excavation parameters.

2. 2. The work vehicle according to claim 1, wherein the control device determines that the excavation operation has started when the start of the excavation operation has not been determined and at least the bucket angle is within a predetermined angle range.

3. An arm cylinder pressure sensor is further provided to detect a bottom pressure, which is a pressure in an oil chamber on a bottom side of the arm cylinder, 3. The work vehicle according to claim 2, wherein the control device further determines that the excavation operation has started when the bottom pressure is equal to or higher than a predetermined lower limit pressure.

4. The bucket further includes an operation device that detects an operation amount of each of the arm and the bucket, 3. The work vehicle according to claim 2, wherein the control device determines that the excavation work is to be started when the operation amount of the arm or the operation amount of the bucket exceeds a predetermined threshold value.

5. 3. The work vehicle according to claim 2, wherein the control device obtains a driving force for moving the vehicle body forward, and determines that the excavation work has started when the driving force exceeds a predetermined threshold value.

6. 3. The work vehicle according to claim 2, wherein the control device determines that the excavation operation has ended when the bucket angle has reached a predetermined release angle or greater after determining that the excavation operation has started.

7. 2. The work vehicle according to claim 1, wherein the control device regards an increase in the bucket angle as a progress of the excavation work, and increases the restricted discharge rate as the bucket angle increases.

8. An arm relative angle sensor is further provided to detect an arm angle, which is the angle of the arm. The drilling parameters include the arm angle, 2. The work vehicle according to claim 1, wherein the control device regards an increase in the arm angle as a progress of the excavation work, and increases the restricted discharge rate as the arm angle increases.

9. The excavation parameters include a travel distance of the vehicle body from a time when the start of the excavation operation is determined, 2. The work vehicle according to claim 1, wherein the control device regards an increase in the travel distance as a progress of the excavation work, and increases the restricted discharge rate as the travel distance increases.

10. Further comprising an attitude sensor for detecting the attitude of the vehicle body, The work vehicle according to claim 1, characterized in that the control device stops increasing the restricted discharge rate as the excavation work progresses when the vehicle body posture detected by the posture sensor is outside a predetermined allowable range.

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