Work machine and work machine control method

Abstract

A work machine and a control method for the work machine are provided, in which automatic braking control is stably performed. [Solution] A wheel loader (100) performs automatic braking control, automatically braking the travel of the wheel loader (100) depending on the distance to an obstacle. Brake circuits (42a, 42b) brake the travel of the wheel loader (100). An EPC valve (46) opens and closes a hydraulic circuit that supplies hydraulic oil to the brake circuits (42a, 42b) during automatic braking control. A pressure sensor detects the pressure in the hydraulic circuit. If a controller (26) determines that there is an abnormality in the EPC valve (46) or the pressure sensor (25b), it disables control of the brake circuits (42a, 42b) during automatic braking control.

Description

[Technical Field]

[0001] The present disclosure relates to a work machine and a method for controlling a work machine. [Background technology]

[0002] A technology for automatically driving a vehicle equipped with various types of work equipment is disclosed, for example, in Japanese Patent Laid-Open Publication No. 6-193099 (Patent Document 1). In Patent Document 1, the vehicle's powertrain and brakes are controlled to automatically control the vehicle's forward movement, backward movement, stopping, and driving speed. Deviations from a predetermined driving route are also detected, and the vehicle's steering mechanism is automatically controlled to minimize such deviations. If an abnormality occurs in the operating conditions of any part, the vehicle is controlled to a safe side, and the location of the abnormality is reported. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 6-193099 Summary of the Invention [Problem to be solved by the invention]

[0004] However, Patent Document 1 does not describe detecting obstacles in the direction of travel of a work machine, nor does it describe automatic braking control that automatically brakes travel when interference with an obstacle is predicted. For such automatic braking control, a work machine and a control method for a work machine that can execute automatic braking control stably are required.

[0005] An object of the present disclosure is to provide a work machine and a control method for a work machine in which automatic braking control is executed stably. [Means for solving the problem]

[0006] The work machine disclosed herein is a work machine that performs automatic braking control to automatically brake travel depending on the distance to an obstacle, and includes a brake circuit, a proportional pressure reducing valve, a pressure sensor, and a controller. The brake circuit brakes travel. The proportional pressure reducing valve opens and closes a hydraulic circuit that supplies hydraulic oil to the brake circuit during automatic braking control. The pressure sensor detects pressure in the hydraulic circuit. If the controller determines that there is an abnormality in the proportional pressure reducing valve or the pressure sensor, it disables control of the brake circuit during automatic braking control.

[0007] A control method for a work machine disclosed herein is a control method for a work machine that performs automatic braking control, which automatically brakes the work machine's traveling in accordance with the distance to an obstacle. The work machine has a brake circuit that brakes the work machine's traveling, a proportional pressure reducing valve that opens and closes a hydraulic circuit that supplies hydraulic oil to the brake circuit during automatic braking control, and a pressure sensor that detects the pressure in the hydraulic circuit. The control method for a work machine includes the steps of determining whether there is an abnormality in the proportional pressure reducing valve or the pressure sensor, and disabling control of the brake circuit during automatic braking control if it is determined that there is an abnormality in the proportional pressure reducing valve or the pressure sensor. [Effects of the Invention]

[0008] According to the present disclosure, it is possible to realize a work machine and a control method for a work machine in which automatic braking control is executed stably. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a side view showing the configuration of a wheel loader 100 (an example of a work machine) according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is a block diagram showing a braking system of the wheel loader of FIG. 1. [Figure 3] FIG. 3 is a hydraulic circuit diagram showing the configuration of the braking device of FIG. 2. [Figure 4] FIG. 3 is a functional block diagram showing the configuration of a controller in FIG. 2. [Figure 5] FIG. 10 is a diagram showing a state in which an obstacle M is present behind the wheel loader 100 according to the embodiment. [Figure 6] 3 is a flow chart showing a control method for the wheel loader 100 according to the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0011] In the specification and drawings, the same or corresponding components are denoted by the same reference numerals, and redundant explanations will not be repeated. In addition, in the drawings, configurations may be omitted or simplified for the sake of convenience.

[0012] <Wheel loader configuration>

[0013] The configuration of a wheel loader 100 in this embodiment will be described with reference to FIG.

[0014] FIG. 1 is a side view showing the configuration of a wheel loader 100 (an example of a work machine) according to an embodiment of the present disclosure. As shown in FIG. 1, the wheel loader 100 according to this embodiment has a vehicle body 1 and an object sensor 25a. The vehicle body 1 has a traveling body 2 and a work implement 3. The work implement 3 is disposed on the traveling body 2. The traveling body 2 has a body frame 10, a pair of front tires 4, a cab 5, an engine compartment 6, a pair of rear tires 7, and a steering cylinder 9. The wheel loader 100 performs work such as loading earth and sand using the work implement 3.

[0015] In the following description, the terms "front," "rear," "right," "left," "up," and "down" refer to directions based on the state seen from the operator seated in the driver's seat 5s in the cab 5. In FIG. 1, the front-to-rear direction is indicated by Z, with Zf indicating the front direction and Zb indicating the rear direction.

[0016] The body frame 10 is of a so-called articulated (swinging) type and has a front frame 11, a rear frame 12, and a connecting shaft 13. The front frame 11 is disposed in a forward direction Zf of the rear frame 12. The connecting shaft 13 is provided in the center of the body frame 10 in the left-right direction (vehicle width direction), and connects the front frame 11 and the rear frame 12 to each other so that they can swing. A pair of front tires 4 are attached to the left and right of the front frame 11. Furthermore, a pair of rear tires 7 are attached to the left and right of the rear frame 12.

[0017] The work implement 3 is driven by hydraulic oil from a hydraulic pump 61 (FIG. 2), not shown. The work implement 3 has a boom 14, a bucket 15, a lift cylinder 16, a bucket cylinder 17, and a bell crank 18. The boom 14 is attached to the front frame 11. The bucket 15 is attached to the tip of the boom 14.

[0018] The lift cylinder 16 and the bucket cylinder 17 are hydraulic cylinders. One end of the lift cylinder 16 is attached to the front frame 11, and the other end of the lift cylinder 16 is attached to the boom 14. The extension and contraction of the lift cylinder 16 causes the boom 14 to swing up and down. One end of the bucket cylinder 17 is attached to the front frame 11, and the other end of the bucket cylinder 17 is attached to the bucket 15 via a bell crank 18. The extension and contraction of the bucket cylinder 17 causes the bucket 15 to swing up and down.

[0019] The cab 5 is mounted on the rear frame 12. Inside the cab 5, there are arranged a driver's seat 5s for an operator to sit in, a handle for steering, levers for operating the work equipment 3, various switches, display devices, etc. The engine room 6 is arranged on the rear frame 12 in the rear direction Zb of the cab 5, and houses an engine 31 (FIG. 2).

[0020] <Braking system for wheel loader 100>

[0021] Next, the braking system of the wheel loader 100 in this embodiment will be described with reference to FIGS.

[0022] Fig. 2 is a block diagram showing a braking system of the wheel loader of Fig. 1. Fig. 3 is a hydraulic circuit diagram showing the configuration of the braking device of Fig. 2. Fig. 4 is a functional block diagram showing the configuration of the controller of Fig. 2.

[0023] As shown in FIG. 2, the braking system of the wheel loader 100 includes a drive device 21, a braking device 22, an operation device 23, an operating device 24, a detection device 25, and a controller 26.

[0024] The drive device 21 drives the wheel loader 100. The brake device 22 brakes the travel of the wheel loader 100. The operation device 23 is operated by an operator. The operating device 24 operates the work equipment 3. The detection device 25 detects objects (obstacles) around the vehicle body 1, and also detects the hydraulic pressure of the hydraulic circuit. The controller 26 controls the operation of the drive device 21, brake device 22, and operating device 24 based on the operation of the operation device 23 by the operator and detection by the detection device 25.

[0025] (Driver 21)

[0026] As shown in FIG. 2, the drive unit 21 includes an engine 31, an HST 32, a transfer case 33, an axle 34, front tires 4, and rear tires 7.

[0027] The engine 31 is, for example, a diesel engine, and the driving force generated by the engine 31 drives a pump 32 a of an HST (Hydro Static Transmission) 32 .

[0028] The HST 32 has a pump 32a, a motor 32b, and a hydraulic circuit 32c. The pump 32a is, for example, a swash plate type variable displacement pump, and the angle of the swash plate can be changed by a solenoid 32d. The pump 32a is driven by the engine 31 to discharge hydraulic oil. The discharged hydraulic oil is sent to the motor 32b through the hydraulic circuit 32c. The motor 32b is, for example, a swash plate type pump, and the angle of the swash plate can be changed by a solenoid 32e.

[0029] Hydraulic circuit 32c connects pump 32a and motor 32b. Hydraulic circuit 32c has a first drive circuit 32c1 and a second drive circuit 32c2. Hydraulic oil is supplied from pump 32a to motor 32b through first drive circuit 32c1, thereby driving motor 32b in one direction (for example, the forward direction). Hydraulic oil is supplied from pump 32a to motor 32b through second drive circuit 32c2, thereby driving motor 32b in the other direction (for example, the reverse direction). The direction of hydraulic oil discharge to first drive circuit 32c1 or second drive circuit 32c2 can be changed by solenoid 32d.

[0030] The transfer 33 distributes the output from the engine 31 to the front and rear axles 34 .

[0031] A pair of front tires 4 are connected to the front axle 34, and rotate with the distributed power from the engine 31. A pair of rear tires 7 are connected to the rear axle 34, and rotate with the distributed power from the engine 31.

[0032] (braking device 22)

[0033] The braking device 22 has a braking unit 40 and a shutoff valve 45. The braking unit 40 brakes the traveling of the vehicle body 1 based on the operation of the brake pedal 54, and performs automatic braking control of the vehicle body 1 based on a command from the controller 26. The shutoff valve 45 puts the braking unit 40 in a state where it can or cannot exert braking force through automatic braking control.

[0034] The braking section 40 includes a brake valve unit 41, brake circuits 42a and 42b (an example of a service brake), a parking brake 43, hydraulic oil supply passages 44a and 44b, an EPC (Electric Proportional Control) valve 46, a shuttle valve unit 47, and a tank 48. The EPC valve 46 corresponds to the proportional pressure reducing valve of the present disclosure.

[0035] An accumulator, a pump, etc. are connected to the hydraulic oil supply passages 44a, 44b, and hydraulic oil is supplied thereto.

[0036] 3, the brake valve unit 41 is operated by a brake pedal 54 (described later). The brake valve unit 41 has a rear brake valve 41a and a front brake valve 41b. Each of the rear brake valve 41a and the front brake valve 41b is a three-position selector valve having three ports.

[0037] A first port of the rear brake valve 41a is connected to a hydraulic oil supply passage 44a. A second port of the rear brake valve 41a is connected to a tank 48. A third port of the rear brake valve 41a is connected to a rear shuttle valve 47a of the shuttle valve unit 47.

[0038] In the first state, the rear brake valve 41a connects the first port to the third port, connects the hydraulic oil supply passage 44a to the rear shuttle valve 47a, and supplies hydraulic oil to the rear shuttle valve 47a. In the second state, the rear brake valve 41a closes all ports. In the third state, the rear brake valve 41a connects the second port to the third port, and discharges hydraulic oil between the rear shuttle valve 47a and the rear brake valve 41a to the tank 48. In the second and third states, the rear brake valve 41a stops the supply of hydraulic oil to the rear shuttle valve 47a.

[0039] A first port of the front brake valve 41b is connected to the hydraulic oil supply passage 44b. A second port of the front brake valve 41b is connected to the tank 48. A third port of the front brake valve 41b is connected to the front shuttle valve 47b of the shuttle valve unit 47.

[0040] In the first state, the front brake valve 41b connects the first port to the third port, connects the hydraulic oil supply passage 44b to the front shuttle valve 47b, and supplies hydraulic oil to the front shuttle valve 47b. In the second state, the front brake valve 41b closes all ports. In the third state, the front brake valve 41b connects the second port to the third port, and discharges hydraulic oil between the front shuttle valve 47b and the front brake valve 41b to the tank 48. In the second and third states, the front brake valve 41b stops the supply of hydraulic oil to the front shuttle valve 47b.

[0041] The opening degrees of the rear brake valves 41 a and the front brake valves 41 b are adjusted in accordance with the amount of operation of the brake pedal 54, and the amount of hydraulic oil supplied to the shuttle valve unit 47 is changed. For example, when the amount of operation of the brake pedal 54 is large, the amount of hydraulic oil supplied from the rear brake valves 41 a and the front brake valves 41 b to the shuttle valve unit 47 increases.

[0042] The brake circuit 42a is provided on the rear axle 34 (FIG. 2). The brake circuit 42a is connected to the rear shuttle valve 47a. The brake circuit 42b is provided on the front axle 34 (FIG. 2). The brake circuit 42b is connected to the front shuttle valve 47b.

[0043] The brake circuits 42a and 42b are hydraulic brakes. The braking force of the brake circuit 42a increases as the amount or pressure of hydraulic oil supplied from the rear shuttle valve 47a increases. The braking force of the brake circuit 42b increases as the amount or pressure of hydraulic oil supplied from the front shuttle valve 47b increases. The brakes that can be switched between a braking state and a non-braking state by the brake circuits 42a and 42b are, for example, wet multi-disc brakes.

[0044] The EPC valve 46 is connected to the hydraulic oil supply line 44b. The EPC valve 46 is a solenoid valve having three ports. A first port of the EPC valve 46 is connected to the hydraulic oil supply line 44b. A second port of the EPC valve 46 is connected to the tank 48. A third port of the EPC valve 46 is connected to the shut-off valve 45.

[0045] The EPC valve 46 is opened and closed based on commands from the controller 26. Specifically, the EPC valve 46 is set to an open state (on state) when energized by an open command from the controller 26, and is set to a closed state (off state) when de-energized by a close command from the controller 26.

[0046] In the open state, the EPC valve 46 connects the first port with the third port, and supplies hydraulic oil supplied from the hydraulic oil supply passage 44b to the shuttle valve unit 47 via the shut-off valve 45. As a result, the pressure (hydraulic pressure) in the hydraulic circuit for supplying hydraulic oil to the brake circuits 42a, 42b increases to a level at which the brakes in the brake circuits 42a, 42b can be operated. The opening of the EPC valve 46 is adjusted based on a command from the controller 26. By adjusting the opening of the EPC valve 46, the amount of hydraulic oil supplied to the shuttle valve unit 47 is changed.

[0047] When the EPC valve 46 is in the closed state, the first port is closed, the second port is connected to the third port, and the hydraulic oil in the flow path from the EPC valve 46 to the shuttle valve unit 47 is discharged to the tank 48. As a result, when the EPC valve 46 is in the closed state, the supply of hydraulic oil from the shutoff valve 45 to the shuttle valve unit 47 is stopped.

[0048] The shutoff valve 45 is disposed in a flow path connecting the EPC valve 46 and the shuttle valve unit 47. The shutoff valve 45 is a solenoid valve having three ports and two states: an open state and a closed state. A first port of the shutoff valve 45 is connected to the EPC valve 46. A second port of the shutoff valve 45 is connected to the tank 48. A third port of the shutoff valve 45 is connected to the shuttle valve unit 47.

[0049] The shutoff valve 45 is opened and closed based on commands from the controller 26. Specifically, the shutoff valve 45 is closed (on) when energized by a close command from the controller 26, and is opened (off) when de-energized by an open command from the controller 26. Under normal conditions, the shutoff valve 45 is in an open state with no current flowing through it.

[0050] When the shutoff valve 45 is open, it connects the first port to the third port and supplies the hydraulic oil from the EPC valve 46 to the shuttle valve unit 47 .

[0051] In the closed state, the shutoff valve 45 closes the first port. As a result, in the closed state, the shutoff valve 45 stops the supply of hydraulic oil from the EPC valve 46 to the shuttle valve unit 47. In addition, in the closed state, the shutoff valve 45 connects the second port and the third port, and discharges the hydraulic oil in the hydraulic circuit between the shutoff valve 45 and the shuttle valve unit 47 to the tank 48.

[0052] In this embodiment, the controller 26 controls the EPC valve 46 to an open state when it is determined that the wheel loader 100 is traveling in a predetermined direction (for example, the backward direction Zb) and there is a high possibility that the wheel loader 100 will interfere with an obstacle in the traveling direction. In this state, the controller 26 does not energize the shut-off valve 45, and the shut-off valve 45 is controlled to an open state. Movement of the vehicle body 1 in the traveling direction (for example, the backward direction Zb) is determined by the controller 26 based on a signal indicating the lever position in the traveling direction switching device 52 and an opening degree signal indicating the accelerator operation amount of the accelerator 55.

[0053] The shuttle valve unit 47 has a rear shuttle valve 47a and a front shuttle valve 47b. The rear shuttle valve 47a supplies the hydraulic oil having a higher pressure, either the hydraulic oil supplied via the rear brake valve 41a or the hydraulic oil supplied via the EPC valve 46, to the brake circuit 42a. The front shuttle valve 47b supplies the hydraulic oil having a higher pressure, either the hydraulic oil supplied via the front brake valve 41b or the hydraulic oil supplied via the EPC valve 46, to the brake circuit 42b.

[0054] With this configuration, even if the brake pedal 54 is not operated and hydraulic oil is not supplied from the brake valve unit 41, when the shutoff valve 45 and the EPC valve 46 are opened by a command from the controller 26, hydraulic oil is supplied to the brake circuits 42a, 42b from the rear shuttle valve 47a and the front shuttle valve 47b, and automatic braking control is performed.

[0055] 2, the parking brake 43 is provided on the transfer 33. As the parking brake 43, for example, a wet multi-stage brake or a disc brake that can be switched between a braking state and a non-braking state can be used.

[0056] (Operating device 23)

[0057] The operation device 23 is operated by an operator seated in the cab 5 (FIG. 1). The operation device 23 has a work machine operation unit 51, a travel direction switching device 52, a parking switch 53, a brake pedal 54, and an accelerator 55.

[0058] The work machine operation unit 51 is provided inside the cab 5. The work machine operation unit 51 controls the operation of the work machine 3 and is, for example, an operation lever operated by an operator. The amount of operation of the work machine operation unit 51 is detected, for example, by a potentiometer, a Hall IC (Integrated Circuit), or the like. When the work machine operation unit 51 is operated, an operation signal indicating the amount of operation of the work machine operation unit 51 is sent to the controller 26. The controller 26 sends the operation signal to the EPC valves 62 for the lift cylinder 16 and the bucket cylinder 17 as operation commands.

[0059] The travel direction switching device 52 is provided inside the cab 5. The operator operates the travel direction switching device 52 to set the travel direction of the wheel loader 100. The travel direction switching device 52 is, for example, an FNR lever. The FNR lever can be positioned in forward (F), neutral (N), or reverse (R). An operation signal indicating the lever position of the FNR lever is sent to the controller 26, and the controller 26 switches the travel direction to forward, neutral, or reverse by controlling the solenoid 32d.

[0060] A potentiometer may be used as a position detection sensor for detecting the lever position of the FNR lever, or switches may be provided for the forward position, reverse position, and neutral position. Also, both the potentiometer and the switch may be provided so that erroneous operation of either one can be detected.

[0061] The brake pedal 54 is provided inside the cab 5. The brake pedal 54 adjusts the opening degree of the rear brake valve 41a and the front brake valve 41b of the brake valve unit 41.

[0062] The accelerator 55 is provided inside the cab 5. The operator sets the throttle opening by operating the accelerator 55. The accelerator 55 generates an opening signal indicating the accelerator operation amount and transmits it to the controller 26. The controller 26 controls the rotation speed of the engine 31 based on the transmitted signal.

[0063] The parking switch 53 is provided inside the cab 5 and is a switch that can be switched between an on and off state, and transmits a signal indicating the state to the controller 26. The controller 26 puts the parking brake 43 into a braking state or a non-braking state based on the transmitted signal.

[0064] (Detection device 25)

[0065] The detection device 25 includes an object sensor 25a and a pressure sensor 25b.

[0066] The object sensor 25a detects objects (obstacles) around the vehicle body 1. The object sensor 25a detects obstacles located in the traveling direction of the wheel loader 100. Specifically, the object sensor 25a is a rear detection unit that detects obstacles in the rear direction Zb of the vehicle body 1 when the wheel loader 100 travels in the rear direction Zb. The object sensor 25a is a front detection unit that detects obstacles in the forward direction Zf of the vehicle body 1 when the wheel loader 100 travels in the forward direction Zf.

[0067] When the object sensor 25a is a rear detection unit, the rear detection unit is attached to the rear end of the vehicle body 1 as shown in Fig. 1, for example, but may be attached to a location other than the rear end. When the object sensor 25a is a front detection unit, the front detection unit may be attached to the cab 5, the front frame 11, or a location other than these.

[0068] The object sensor 25a is, for example, a LiDAR (Light Detection and Ranging) that emits laser light to acquire information about an object (obstacle). The object sensor 25a may also be a Radar (Radio Detection and Ranging) that emits radio waves to acquire information about an object (obstacle). The Radar may also be, for example, a millimeter-wave radar that uses a receiving antenna to detect how millimeter-wave band radio waves emitted from a transmitting antenna are reflected off the surface of the object and returned. The object sensor 25a may also be a visual sensor including a camera. The object sensor 25a may also be an infrared sensor.

[0069] Information detected by the object sensor 25a is transmitted to the controller 26, which determines whether or not an obstacle exists in the traveling direction of the vehicle body 1. The controller 26 also calculates the distance to the detected obstacle. The controller 26 may determine whether or not there is a high possibility that the vehicle body 1 will interfere with the obstacle based on the distance to the detected obstacle, etc.

[0070] 3, the pressure sensor 25b detects the pressure (oil pressure) of the hydraulic circuit that supplies hydraulic oil to the brake circuits 42a, 42b. Specifically, the pressure sensor 25b detects the oil pressure in the hydraulic circuit between the EPC valve 46 and the brake circuits 42a, 42b. More specifically, the pressure sensor 25b detects the oil pressure in the hydraulic circuit between the shutoff valve 45 and the brake circuits 42a, 42b. In this example, the pressure sensor 25b detects the pressure of the hydraulic oil supplied to the shuttle valve unit 47.

[0071] 2, information detected by the pressure sensor 25b is transmitted to the controller 26. The controller 26 determines whether or not there is an abnormality in the device (such as the pressure sensor 25b) that executes the automatic braking control, based on the pressure in the hydraulic circuit detected by the pressure sensor 25b.

[0072] The controller 26 also determines whether or not there is an abnormality in the device that executes the automatic braking control (such as the EPC valve 46) based on the content of the command output to the EPC valve 46 and the pressure of the hydraulic circuit. The controller 26 also determines whether or not there is an abnormality in the device that executes the automatic braking control (such as the EPC valve 46) based on the potential of the input terminal of the EPC valve 46.

[0073] (Operating device 24)

[0074] The operating device 24 has work machine cylinders 16, 17, an EPC valve 62, and a hydraulic pump 61. The work machine cylinders 16, 17 are, for example, a lift cylinder 16 and a bucket cylinder 17. A portion of the driving force of the engine 31 is transmitted to the hydraulic pump 61. The hydraulic pump 61 is driven by the engine, and operates the lift cylinder 16 and the bucket cylinder 17 by the hydraulic oil that it discharges. The hydraulic oil discharged from the hydraulic pump 61 is supplied to the lift cylinder 16 and the bucket cylinder 17 via the EPC valve 62.

[0075] The EPC valve 62 is opened and closed based on commands from the controller 26. Specifically, the EPC valve 62 is opened when energized by an open command from the controller 26, and is closed when de-energized by a close command from the controller 26.

[0076] When in the open state, the EPC valve 62 connects the hydraulic pump 61 to the lift cylinder 16 and the bucket cylinder 17, and supplies hydraulic oil from the hydraulic pump 61 to the lift cylinder 16 and the bucket cylinder 17. When in the closed state, the EPC valve 62 stops the supply of hydraulic oil from the hydraulic pump 61 to the lift cylinder 16 and the bucket cylinder 17.

[0077] (Controller 26)

[0078] The controller 26 includes a processor, a main memory, and a storage. The processor is, for example, a central processing unit (CPU). The main memory includes, for example, a nonvolatile memory such as a read-only memory (ROM) and a volatile memory such as a random access memory (RAM).

[0079] The controller 26 and the operation device 23 may each be mounted on the wheel loader 100, or may be located remotely outside the wheel loader 100. When the controller 26 and the operation device 23 are each located remotely outside the wheel loader 100, the controller 26 and the operation device 23 may each be connected wirelessly to the drive device 21, the braking device 22, the operation device 23, the detection device 25, etc. The controller 26 may be stored in a server remote from the wheel loader 100. Furthermore, since the operation device 23 is located remotely from the wheel loader 100, the operator may operate the wheel loader 100 remotely without getting inside the cab 5 of the wheel loader 100.

[0080] The controller 26 reads the program stored in the storage, loads it into the main memory, and executes predetermined processing in accordance with the program. The controller 26 may be divided into a collision detection controller and an HST controller. The collision detection controller and the HST controller may have separate CPUs. The program may also be distributed to the controller 26 via a network.

[0081] When the controller 26 determines that there is an abnormality in the EPC valve 46 or the pressure sensor 25b, it disables the control of the brake circuits 42a, 42b in the automatic braking control. When the controller 26 acquires information indicating an abnormality in the EPC valve 46 or the pressure sensor 25b, it disables the control of the brake circuits 42a, 42b in the automatic braking control by outputting a signal to close the shutoff valve 45.

[0082] The controller 26 determines that there is an abnormality in the pressure sensor 25b when the pressure in the hydraulic circuit that supplies hydraulic oil to the brake circuits 42a, 42b is outside a predetermined range. The controller 26 determines that there is an abnormality in the EPC valve 46 when the input terminal of the EPC valve 46 is electrically short-circuited to the power supply. The controller 26 determines that there is an abnormality in the EPC valve 46 when the hydraulic pressure in the hydraulic circuit that supplies hydraulic oil to the brake circuits 42a, 42b is a pressure that activates the brake circuits 42a, 42b even though the output to the EPC valve 46 is off.

[0083] 4, controller 26 has, for example, automatic braking control unit 27, automatic braking control disabling unit 28, and memory 26A. Memory 26A may be provided separately from controller 26. Automatic braking control unit 27 has traveling direction information acquisition unit 27A, traveling direction determination unit 27B, object information acquisition unit 27C, object determination unit 27D, and EPC valve control unit 27E. Automatic braking control disabling unit 28 has hydraulic pressure acquisition unit 28A, hydraulic pressure determination unit 28B, shutoff valve control unit 28C, input voltage acquisition unit 28D, and voltage determination unit 28E.

[0084] <Method for controlling a work machine>

[0085] Next, a control method for a work machine in this embodiment will be described with reference to FIGS.

[0086] Fig. 5 is a diagram showing a state in which an obstacle M is present behind the wheel loader according to the embodiment. Fig. 6 is a flow diagram showing a control method for a wheel loader according to the embodiment.

[0087] First, the automatic braking control of the work machine in this embodiment will be described. As shown in Figure 4, in automatic braking control, the traveling direction information acquisition unit 27A acquires a switching signal from the traveling direction switching device 52. The traveling direction information acquisition unit 27A outputs the acquired switching signal from the traveling direction switching device 52 to the traveling direction determination unit 27B.

[0088] When the traveling direction determination unit 27B acquires the switching signal of the traveling direction switching device 52, it determines whether the traveling direction of the wheel loader 100 is a predetermined direction (for example, the backward direction Zb) based on the switching signal of the traveling direction switching device 52. The traveling direction determination unit 27B outputs the determination result to the EPC valve control unit 27E.

[0089] In addition, the driving direction determination unit 27B may determine that the vehicle body 1 is driving in a predetermined direction (reverse state) when the lever position of the driving direction switching device 52 is in a predetermined direction (for example, the backward direction Zb) even if the wheels 4, 7 are in a stopped state and not rotating.

[0090] Meanwhile, object information acquisition unit 27C acquires the detection result of object sensor 25a. Object information acquisition unit 27C outputs the acquired detection result of object sensor 25a to object determination unit 27D. Object determination unit 27D determines whether or not there is a high possibility that vehicle main body 1 will interfere with an obstacle based on the detection result of object sensor 25a, etc., and outputs the determination result to EPC valve control unit 27E.

[0091] During execution of automatic braking control, EPC valve control unit 27E controls the opening and closing operation of EPC valve 46 based on the determination results of traveling direction determination unit 27B and object determination unit 27D. Specifically, during execution of automatic braking control, if EPC valve control unit 27E acquires, for example, a determination result from traveling direction determination unit 27B that the traveling direction is backward Zb and a determination result from object determination unit 27D that there is a high possibility that vehicle main body 1 will interfere with an obstacle, it outputs an open command (command current) to EPC valve 46 so that EPC valve 46 is in an open state. A solenoid of EPC valve 46 is operated based on this command current, and EPC valve 46 is in an open state. When EPC valve 46 is in an open state, hydraulic oil is supplied from rear shuttle valve 47a and front shuttle valve 47b to brake circuits 42a, 42b, and braking operation is performed.

[0092] A state in which a braking operation is being performed (ON state) means that braking force is being applied by the brake circuits 42a, 42b. An example of a state in which a braking operation is being performed is when the brake is a wet multi-disc brake and the plate is sandwiched and pressed between multiple discs. On the other hand, a state in which a braking operation is not being performed (OFF state) means that braking force is not being applied by the brake circuits 42a, 42b. An example of a state in which a braking operation is not being performed is when the brake is a wet multi-disc brake and the plate is not sandwiched and pressed between multiple discs.

[0093] In this way, the controller 26 executes automatic braking control to automatically brake the vehicle body 1 based on the detection result of an obstacle in the traveling direction. As a result, as shown in Figure 5, if an obstacle M is detected in the backward direction Zb while the vehicle body 1 of the wheel loader 100 is traveling in the backward direction Zb, for example, automatic braking control is implemented and braking force is exerted even without the operator operating the brake pedal 54. This allows the vehicle body 1 to stop before the obstacle M.

[0094] In the above-described automatic braking control, if a device that executes the automatic braking control (for example, pressure sensor 25b, EPC valve 46, etc.) malfunctions, the EPC valve 46 will not operate according to the commands of the controller 26. For example, if the spool of the EPC valve 46 is stuck and does not move or is difficult to move, it becomes difficult for the EPC valve 46 to open and close, and the EPC valve 46 will not operate according to the commands of the controller 26. Furthermore, for example, if the input terminal of the EPC valve 46 is electrically shorted to the power supply (a so-called power short state), the EPC valve 46 will remain closed and will not open, and the EPC valve 46 will not operate according to the commands of the controller 26.

[0095] If the EPC valve 46 does not operate as instructed by the controller 26 and malfunctions, there is a risk that excessive deceleration will occur due to sudden braking during automatic braking control, or that the vehicle will be braked even though there is no possibility of interference with an obstacle.

[0096] Therefore, in this embodiment, the automatic braking control disabling unit 28 disables the control of the brake circuits 42a, 42b in the automatic braking control when it determines that there is an abnormality in the pressure sensor 25b or the EPC valve 46. A control method for disabling the control of the brake circuits 42a, 42b in the automatic braking control will be described below.

[0097] 4 and 6, the controller 26 acquires the pressure of the hydraulic circuit that supplies hydraulic oil to the brake circuits 42a and 42b (step S1a), and also acquires the state of the EPC valve 46 (step S1b).

[0098] To acquire the pressure of the hydraulic circuit, the hydraulic pressure acquisition unit 28A of the controller 26 acquires the pressure (hydraulic pressure) of the hydraulic oil in the hydraulic circuit from the pressure sensor 25b. The hydraulic pressure acquisition unit 28A outputs the acquired pressure to the hydraulic pressure determination unit 28B. The hydraulic pressure determination unit 28B determines whether or not there is an abnormality in the device that executes the automatic braking control (e.g., pressure sensor 25b) based on the acquired pressure (step S2). This determination is made, for example, by determining whether or not the acquired pressure is within a predetermined range. The predetermined pressure range is stored in advance in, for example, memory 26A. When making the above determination, the hydraulic pressure determination unit 28B refers to the predetermined pressure range stored in memory 26A.

[0099] If the acquired pressure is within a predetermined range of pressure, the hydraulic pressure determination unit 28B determines that the device that executes the automatic braking control is operating normally. In this case, steps S1a and S1b are repeated.

[0100] On the other hand, if the acquired pressure is outside the predetermined range, hydraulic pressure determination unit 28B determines that there is an abnormality in the device that executes automatic braking control. In this case, hydraulic pressure determination unit 28B outputs a signal indicating the determination result to shutoff valve control unit 28C.

[0101] Based on the signal indicating the acquired determination result, shutoff valve control unit 28C outputs a close command to shutoff valve 45 and energizes shutoff valve 45. Upon receiving the close command, shutoff valve 45 enters a closed state and closes the first port. This stops the supply of hydraulic oil from EPC valve 46 to shuttle valve unit 47. In addition, the second and third ports of shutoff valve 45 are connected, and hydraulic oil in the hydraulic circuit between shutoff valve 45 and shuttle valve unit 47 is discharged to tank 48.

[0102] As described above, the supply of hydraulic oil from the EPC valve 46 to the shuttle valve unit 47 is stopped, and thus the control of the brake circuits 42a, 42b in the automatic braking control is disabled (step S3).

[0103] Furthermore, if the EPC valve 46 is shorted to power or if the command to the EPC valve 46 does not match the pressure in the hydraulic circuit, the control of the brake circuits 42a, 42b in the automatic braking control may be disabled. Such a case will be described below.

[0104] Regarding a power fault of the EPC valve 46, the input voltage acquisition unit 28D of the controller 26 acquires information about the voltage applied to the input terminal of the EPC valve 46 (step S1b). The input voltage acquisition unit 28D outputs the acquired voltage information to the voltage determination unit 28E. The voltage determination unit 28E determines whether or not there is an abnormality in the device that executes automatic braking control (e.g., the EPC valve 46) based on the acquired voltage information (step S2). Specifically, the voltage determination unit 28E determines whether or not a voltage greater than a predetermined voltage value is applied to the input terminal of the EPC valve 46. The predetermined voltage value is stored in advance in, for example, the memory 26A. The hydraulic pressure determination unit 28B refers to the predetermined voltage value stored in the memory 26A when making the above determination.

[0105] Here, the predetermined voltage value is, for example, a voltage value (e.g., 4 V) that is input to place the EPC valve 46 in a normally open state. If the EPC valve 46 is shorted to power, a power supply potential (e.g., 24 V) is applied to the input terminal of the EPC valve 46. Therefore, if the voltage value applied to the input terminal of the EPC valve 46 is greater than the predetermined voltage value, there is a possibility that the EPC valve 46 is shorted to power.

[0106] Therefore, if the acquired voltage value is greater than a predetermined voltage value, voltage determination unit 28E determines that there is an abnormality in the device that executes automatic braking control (for example, EPC valve 46). In this case, hydraulic pressure determination unit 28B outputs a signal indicating the determination result to shutoff valve control unit 28C.

[0107] Based on the signal indicating the acquired determination result, shutoff valve control unit 28C outputs a close command to shutoff valve 45, as described above, and energizes shutoff valve 45. Upon receiving the close command, shutoff valve 45 enters a closed state and closes the first port. This stops the supply of hydraulic oil from EPC valve 46 to shuttle valve unit 47, and disables control of brake circuits 42a, 42b in the automatic braking control (step S3).

[0108] Furthermore, in response to a mismatch between the command to the EPC valve 46 and the pressure in the hydraulic circuit, the EPC valve control unit 27E of the controller 26 outputs a control command for the EPC valve 46 to the hydraulic pressure determination unit 28B. The hydraulic pressure determination unit 28B determines an abnormality in the equipment that executes automatic braking control based on the pressure of the hydraulic circuit acquired from the hydraulic pressure acquisition unit 28A and the control command for the EPC valve 46 acquired from the EPC valve control unit 27E (step S2). Specifically, if the control command for the EPC valve 46 acquired from the EPC valve control unit 27E is off but the pressure of the hydraulic circuit acquired from the hydraulic pressure acquisition unit 28A is a pressure that activates the brake circuits 42a, 42b, the hydraulic pressure determination unit 28B determines that an abnormality exists in the EPC valve 46. In this case, the hydraulic pressure determination unit 28B outputs a signal indicating the determination result to the shutoff valve control unit 28C.

[0109] Based on the signal indicating the acquired determination result, shutoff valve control unit 28C outputs a close command to shutoff valve 45, as described above, and energizes shutoff valve 45. Upon receiving the close command, shutoff valve 45 enters a closed state and closes the first port. This stops the supply of hydraulic oil from EPC valve 46 to shuttle valve unit 47, and disables control of brake circuits 42a, 42b in the automatic braking control (step S3).

[0110] The control method for a work machine in this embodiment is carried out as described above.

[0111] The above-mentioned abnormality based on the pressure of the hydraulic circuit, the abnormality based on a power fault of the EPC valve 46, and the abnormality based on a mismatch between the command to the EPC valve 46 and the pressure of the hydraulic circuit may be determined individually or in combination.

[0112] <Effects>

[0113] Next, the effects of this embodiment will be described.

[0114] 4, in this embodiment, when it is determined that there is an abnormality in the EPC valve 46 or the pressure sensor 25b, the controller 26 disables the control of the brake circuits 42a, 42b (FIGS. 2 and 3) in the automatic braking control. This makes it possible to suppress malfunction of the brakes due to equipment failure in the automatic braking control, and the automatic braking control is executed stably.

[0115] 4, in this embodiment, when controller 26 detects an abnormality in EPC valve 46 or pressure sensor 25b, it disables control of brake circuits 42a, 42b in the automatic braking control by outputting a signal to close shutoff valve 45. By closing shutoff valve 45 in this manner, it is possible to disable control of brake circuits 42a, 42b and suppress malfunction of brakes in the automatic braking control.

[0116] 4, in this embodiment, the controller 26 determines that there is an abnormality in the pressure sensor 25b when the pressure in the hydraulic circuit that supplies hydraulic oil to the brake circuits 42a, 42b is outside a predetermined range. In this way, it is possible to identify the device that has an abnormality.

[0117] 4, in this embodiment, the controller 26 determines that an abnormality has occurred in the EPC valve 46 when the input terminal of the EPC valve 46 is electrically shorted to the power supply. This makes it possible to identify an abnormality in the EPC valve 46 due to a short to power.

[0118] 4, in this embodiment, the controller 26 determines that there is an abnormality in the EPC valve 46 when the hydraulic pressure of the hydraulic circuit that supplies hydraulic oil to the brake circuits 42a, 42b is high enough to operate the brake circuits 42a, 42b, even though the output to the EPC valve 46 is off. This makes it possible to identify the abnormality in the EPC valve 46.

[0119] Furthermore, if the shutoff valve 45 is disposed upstream of the EPC valve 46 with respect to the flow direction of hydraulic oil from the hydraulic oil supply path 44b to the brake circuits 42a, 42b, even when the shutoff valve 45 is closed, hydraulic oil in the hydraulic circuit between the shutoff valve 45 and the shuttle valve unit 47 is less likely to drain to the tank 48. This is because the spool of the EPC valve 46, disposed downstream of the shutoff valve 45, is moved and controlled based on the hydraulic pressure output by the EPC valve 46 itself, thereby adjusting the pressure by gradually changing the degree of opening of the EPC valve 46 connecting the shutoff valve 45 and the shuttle valve unit 47. This small change in the degree of opening makes it difficult to maintain a large degree of opening, making it difficult for the hydraulic oil between the EPC valve 46 and the shuttle valve unit 47 to be discharged to the tank 48.

[0120] 2 and 3, in this embodiment, the shutoff valve 45 is disposed downstream of the EPC valve 46 in the direction of hydraulic oil flow from the hydraulic oil supply passage 44b to the brake circuits 42a, 42b. Therefore, it is possible to discharge the hydraulic oil between the shutoff valve 45 and the shuttle valve unit 47 from the shutoff valve 45 to the tank 48, regardless of the movement control of the spool of the EPC valve 46. This makes it easier for the hydraulic oil between the shutoff valve 45 and the shuttle valve unit 47 to drain to the tank 48 through the shutoff valve 45, even when the EPC valve 46 is operating.

[0121] <Additional Notes>

[0122] The above description includes the following additional features.

[0123] (Appendix 1) A work machine that performs automatic braking control to automatically brake travel depending on the distance to an obstacle, A brake circuit that brakes the vehicle; a proportional pressure reducing valve that opens and closes a hydraulic circuit that supplies hydraulic oil to the brake circuit during automatic braking control; a pressure sensor for detecting the pressure of the hydraulic circuit; a controller that disables control of the brake circuit in automatic braking control when it is determined that there is an abnormality in the proportional pressure reducing valve or the pressure sensor.

[0124] (Appendix 2) a shutoff valve connected to the hydraulic circuit; 2. The working machine according to claim 1, wherein the controller, when detecting an abnormality in the proportional pressure reducing valve or the pressure sensor, disables control of the brake circuit in automatic braking control by outputting a signal to close the shutoff valve.

[0125] (Appendix 3) The work machine according to claim 1 or 2, wherein the controller determines that an abnormality exists in the pressure sensor when the pressure in the hydraulic circuit is outside a predetermined range.

[0126] (Appendix 4) The work machine according to any one of Supplementary Note 1 to Supplementary Note 3, wherein the controller determines that an abnormality exists in the proportional pressure reducing valve when an input terminal of the proportional pressure reducing valve is electrically short-circuited to a power source.

[0127] (Appendix 5) The working machine according to any one of Supplementary Note 1 to Supplementary Note 4, wherein the controller determines that there is an abnormality in the proportional pressure reducing valve when the hydraulic pressure in the hydraulic circuit is at a pressure that activates the brake circuit even though the output to the proportional pressure reducing valve is off.

[0128] (Appendix 6) A control method for a work machine that performs automatic braking control to automatically brake travel in accordance with the distance to an obstacle, comprising: the work machine has a brake circuit that brakes travel, a proportional pressure reducing valve that opens and closes a hydraulic circuit that supplies hydraulic oil to the brake circuit under automatic braking control, and a pressure sensor that detects pressure in the hydraulic circuit, The work machine control method includes: determining whether or not there is an abnormality in the proportional pressure reducing valve or the pressure sensor; and when it is determined that there is an abnormality in the proportional pressure reducing valve or the pressure sensor, disabling control of the brake circuit in automatic braking control.

[0129] (Appendix 7) the work machine further includes a shutoff valve connected to the hydraulic circuit; 7. A working machine control method as described in Appendix 6, wherein, in the step of disabling control of the brake circuit, when an abnormality is detected in the proportional pressure reducing valve or the pressure sensor, control of the brake circuit in automatic braking control is disabled by outputting a signal to close the shutoff valve.

[0130] (Appendix 8) 8. A control method for a work machine according to claim 6 or 7, wherein in the step of determining whether or not there is an abnormality in the pressure sensor, it is determined that there is an abnormality in the pressure sensor if the pressure in the hydraulic circuit is outside a predetermined range.

[0131] (Appendix 9) The work machine control method according to any one of Supplementary Note 6 to Supplementary Note 8, wherein in the step of determining whether or not an abnormality exists in the pressure sensor, it is determined that an abnormality exists in the proportional pressure reducing valve if an input terminal of the proportional pressure reducing valve is electrically short-circuited to a power source.

[0132] (Appendix 10) 10. A working machine control method according to any one of Supplementary Note 6 to Supplementary Note 9, wherein in the step of determining whether or not an abnormality exists in the pressure sensor, it is determined that an abnormality exists in the proportional pressure reducing valve if the hydraulic pressure in the hydraulic circuit is a pressure that activates the brake circuit even though the output to the proportional pressure reducing valve is off.

[0133] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is defined by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0134] 1 vehicle body, 2 travelling body, 3 work equipment, 4 front tire, 5 cab, 5s driver's seat, 6 engine room, 7 rear tire, 9 steering cylinder, 10 vehicle frame, 11 front frame, 12 rear frame, 13 connecting shaft section, 14 boom, 15 bucket, 16 lift cylinder, 17 bucket cylinder, 18 bell crank, 21 drive device, 22 braking device, 23 operation device, 24 operating device, 25 detection device, 25a object sensor, 25b pressure sensor, 26 controller, 26A memory, 27 automatic braking control section, 27A travel direction information acquisition section, 27B travel direction determination section, 27C object information acquisition section, 27D object determination section, 27E valve control section, 28 automatic braking control invalid section, 28A hydraulic pressure acquisition section, 28B hydraulic pressure determination section, 28C Shut-off valve control unit, 28D input voltage acquisition unit, 28E voltage determination unit, 31 engine, 32a pump, 32b motor, 32c1 first drive circuit, 32c2 second drive circuit, 32c hydraulic circuit, 32d, 32e solenoid, 33 transfer, 34 axle, 40 braking unit, 41 brake valve unit, 41a rear brake valve, 41b front brake valve, 42a, 42b brake circuit, 43 parking brake, 44a, 44b hydraulic oil supply line, 45 shut-off valve, 46, 62 EPC valve, 47 shuttle valve unit, 47a rear shuttle valve, 47b front shuttle valve, 48 tank, 51 work equipment operation unit, 52 travel direction switching device, 53 parking switch, 54 brake pedal, 55 accelerator, 61 hydraulic pump, 100 Wheel loader.

Claims

1. A work machine that performs automatic braking control to automatically brake travel depending on the distance to an obstacle, A brake circuit that brakes the vehicle; a proportional pressure reducing valve that opens and closes a hydraulic circuit that supplies hydraulic oil to the brake circuit during automatic braking control; a pressure sensor for detecting the pressure of the hydraulic circuit; a controller that disables control of the brake circuit in automatic braking control when it is determined that there is an abnormality in the proportional pressure reducing valve or the pressure sensor.

2. a shutoff valve connected to the hydraulic circuit; 2. The work machine according to claim 1, wherein the controller, when detecting an abnormality in the proportional pressure reducing valve or the pressure sensor, disables control of the brake circuit in automatic braking control by outputting a signal to close the shutoff valve.

3. 2. The work machine according to claim 1, wherein the controller determines that an abnormality exists in the pressure sensor when the pressure in the hydraulic circuit is outside a predetermined range.

4. The work machine according to claim 1 , wherein the controller determines that the proportional pressure reducing valve has an abnormality when an input terminal of the proportional pressure reducing valve is electrically short-circuited to a power source.

5. 2. The work machine according to claim 1, wherein the controller determines that the proportional pressure reducing valve is malfunctioning when the hydraulic pressure in the hydraulic circuit is at a pressure that activates the brake circuit even though the output to the proportional pressure reducing valve is off.

6. A control method for a work machine that performs automatic braking control to automatically brake travel in accordance with the distance to an obstacle, comprising: the work machine has a brake circuit that brakes travel, a proportional pressure reducing valve that opens and closes a hydraulic circuit that supplies hydraulic oil to the brake circuit under automatic braking control, and a pressure sensor that detects pressure in the hydraulic circuit, The work machine control method includes: determining whether or not there is an abnormality in the proportional pressure reducing valve or the pressure sensor; and when it is determined that there is an abnormality in the proportional pressure reducing valve or the pressure sensor, disabling control of the brake circuit in automatic braking control.

7. the work machine further includes a shutoff valve connected to the hydraulic circuit; 7. The working machine control method according to claim 6, wherein in the step of disabling control of the brake circuit, when an abnormality in the proportional pressure reducing valve or the pressure sensor is detected, a signal to close the shutoff valve is output, thereby disabling control of the brake circuit in automatic braking control.

8. 7. The control method for a work machine according to claim 6, wherein in the step of determining whether or not the pressure sensor is abnormal, it is determined that the pressure sensor is abnormal if the pressure in the hydraulic circuit is outside a predetermined range.

9. 7. The control method for a work machine according to claim 6, wherein in the step of determining whether or not an abnormality exists in the pressure sensor, it is determined that an abnormality exists in the proportional pressure reducing valve when an input terminal of the proportional pressure reducing valve is electrically short-circuited to a power source.

10. 7. A control method for a work machine according to claim 6, wherein in the step of determining whether or not an abnormality exists in the pressure sensor, it is determined that an abnormality exists in the proportional pressure reducing valve if the hydraulic pressure in the hydraulic circuit is a pressure that activates the brake circuit even though the output to the proportional pressure reducing valve is off.

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