Work machine and work machine control method

Abstract

Improves the responsiveness of automatic braking and reduces shock when braking begins. [Solution] A work machine that performs automatic braking control, which automatically brakes travel based on the results of detecting an obstacle in the travel direction, includes a brake circuit, a proportional pressure reducing valve, 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 controller outputs a first command current C1 to the proportional pressure reducing valve for a predetermined trigger time in an initial stage of automatic braking control, outputs a third command current C3 smaller than the first command current C1 to the proportional pressure reducing valve for a predetermined second trigger time after the trigger time has elapsed, and outputs a second command current C2 smaller than the third command current to the proportional pressure reducing valve after the second trigger time has elapsed.

Description

[Technical Field]

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

[0002] Japanese Patent Application Laid-Open Publication No. 2021-54307 (Patent Document 1) discloses a work machine that automatically brakes when an obstacle is detected behind the vehicle body while reversing. If it is determined that the state of the vehicle body would become unstable if automatic braking with a preset braking force were to be activated, the braking force of the automatic brake is suppressed. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-54307 Summary of the Invention [Problem to be solved by the invention]

[0004] The automatic brake activates when it detects the possibility of a collision with an obstacle, but activating it too early reduces work efficiency, so it is best to delay activation as long as possible.If a high command current is output to the proportional pressure reducing valve in order to shorten the time until the automatic brake activates and the braking distance, the shock at the start of braking will be greater.

[0005] The present disclosure proposes a work machine and a control method for the work machine that can improve the responsiveness of automatic braking and suppress shock when braking begins. [Means for solving the problem]

[0006] A work machine according to one aspect of the present disclosure is a work machine that performs automatic braking control to automatically brake travel based on the result of detection of an obstacle in the travel direction, and includes a brake circuit, a proportional pressure reducing valve, 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 controller outputs a first command current to the proportional pressure reducing valve for a predetermined trigger time in an initial stage of the automatic braking control, outputs a third command current smaller than the first command current to the proportional pressure reducing valve for a predetermined second trigger time after the trigger time has elapsed, and outputs a second command current smaller than the third command current to the proportional pressure reducing valve after the second trigger time has elapsed.

[0007] A control method for a work machine according to one aspect of the present disclosure includes the following steps. A first step is to output a first command current for a predetermined trigger time to a proportional pressure reducing valve that opens and closes a hydraulic circuit that supplies hydraulic oil to a brake circuit that brakes the work machine, during automatic braking control that automatically brakes the work machine based on the detection result of an obstacle in the travel direction. A second step is to output a third command current that is smaller than the first command current to the proportional pressure reducing valve for a predetermined second trigger time after the trigger time has elapsed. A third step is to output a second command current that is smaller than the third command current to the proportional pressure reducing valve after the second trigger time has elapsed. [Effects of the Invention]

[0008] According to the present disclosure, the responsiveness of the automatic brake can be improved and the shock at the start of braking can be suppressed. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a side view showing a configuration 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 is present behind the wheel loader according to the embodiment. [Figure 6] FIG. 4 is a diagram showing changes over time in command current and brake cylinder pressure before the present invention is applied. [Figure 7] FIG. 4 is a first diagram showing changes over time in command current and brake cylinder pressure according to the first embodiment. [Figure 8] FIG. 6 is a second diagram showing changes over time in command current and brake cylinder pressure according to the first embodiment. [Figure 9] FIG. 10 is a diagram showing changes over time in command current and brake cylinder pressure when the oil temperature is high. [Figure 10] FIG. 3 is a flowchart showing a control method for a wheel loader according to the first embodiment. [Figure 11] FIG. 10 is a flowchart showing a control method for a wheel loader according to a second embodiment. [Figure 12] FIG. 10 is a first diagram showing changes over time in command current and brake cylinder pressure according to the second embodiment. [Figure 13] FIG. 10 is a second diagram showing changes over time in command current and brake cylinder pressure according to the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, the embodiments will be described with reference to the drawings. In the following description, the same parts and components are denoted by the same reference numerals. Their names and functions are also the same. Therefore, detailed descriptions thereof will not be repeated. In the drawings, configurations may be omitted or simplified for the sake of convenience. It is also intended from the beginning that any configurations may be extracted from the embodiments and arbitrarily combined.

[0011] [First embodiment] <Wheel loader configuration> 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.

[0012] 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.

[0013] The body frame 10 is of a so-called articulated 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 so that they can rotate relative to each other. 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.

[0014] The work implement 3 is driven by hydraulic oil from a hydraulic pump 61 (see FIG. 2), not shown in FIG. 1. 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.

[0015] 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 boom 14 moves up and down as the lift cylinder 16 extends and retracts. 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 bucket 15 moves up and down as the bucket cylinder 17 extends and retracts.

[0016] 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).

[0017] <Braking system for wheel loader 100> Next, the braking system of the wheel loader 100 in this embodiment will be described with reference to FIGS.

[0018] 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.

[0019] 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.

[0020] 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. The detection device 25 also detects the oil pressure of the hydraulic circuit, the oil temperature in the hydraulic circuit, the travel speed of the wheel loader 100, etc. 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.

[0021] (Driver 21) As shown in FIG. 2, the drive unit 21 includes an engine 31, an HST (Hydro Static Transmission) 32, a transfer case 33, an axle 34, front tires 4, and rear tires 7.

[0022] The engine 31 is, for example, a diesel engine, and the driving force generated by the engine 31 drives a pump 32 a of the HST 32 .

[0023] 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.

[0024] 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.

[0025] The transfer 33 distributes the output from the engine 31 to the front and rear axles 34 . 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.

[0026] (braking device 22) 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.

[0027] 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.

[0028] An accumulator, a pump, etc. are connected to the hydraulic oil supply passages 44a, 44b, and hydraulic oil is supplied thereto.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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 .

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] (Operating device 23) 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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] (Detection device 25) The detection device 25 has an object sensor 25a, a pressure sensor 25b, a temperature sensor 25c, and a speed sensor 25d.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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 equipment (pressure sensor 25b, EPC valve 46, etc.) that executes automatic braking control based on the pressure in the hydraulic circuit detected by the pressure sensor 25b.

[0063] Temperature sensor 25c detects the temperature of the hydraulic oil in the hydraulic circuit and generates a signal of the detected oil temperature. Temperature sensor 25c may detect the oil temperature in brake circuits 42a, 42b, may detect the oil temperature in the hydraulic circuit between shuttle valve unit 47 and brake circuits 42a, 42b, or may detect the temperature of the hydraulic oil supplied to shuttle valve unit 47.

[0064] Information detected by the temperature sensor 25c is sent to the controller 26. The controller 26 determines the time for outputting a command current to the EPC valve 46 based on the oil temperature detected by the temperature sensor 25c.

[0065] The speed sensor 25d detects the traveling speed (vehicle speed) of the wheel loader 100 and generates a signal of the detected vehicle speed. The speed sensor 25d may detect the vehicle speed of the vehicle body 1, for example, by detecting the rotational speed of the output shaft of the transmission. The speed sensor 25d may also detect the vehicle speed of the vehicle body 1, for example, by detecting the rotational speed of the front tires 4 or the rear tires 7. The speed sensor 25d may also be an IMU (Inertial Measurement Unit) that detects the acceleration of the traveling vehicle body 1. In this case, the vehicle speed is calculated from the integrated value of the acceleration of the vehicle body 1 detected by the IMU.

[0066] Information detected by the speed sensor 25d is sent to the controller 26. The controller 26 determines a command current to be output to the EPC valve 46 based on the vehicle speed detected by the speed sensor 25d.

[0067] (Operating device 24) 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 31, and operates the lift cylinder 16 and the bucket cylinder 17 with 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.

[0068] 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.

[0069] 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.

[0070] (Controller 26) 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).

[0071] 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 operating device 24, 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.

[0072] 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.

[0073] 4, controller 26 has automatic braking control unit 27 and memory 26A. Memory 26A may be provided separately from controller 26. Automatic braking control unit 27 has driving direction information acquisition unit 27A, driving direction determination unit 27B, object information acquisition unit 27C, object determination unit 27D, EPC valve control unit 27E, oil temperature acquisition unit 27F, and vehicle speed acquisition unit 27G.

[0074] <Method for controlling a work machine> Next, the control of the work machine in this embodiment will be described. Figure 5 is a diagram showing a state in which an obstacle M is present behind the wheel loader according to this embodiment.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] 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 there is a high possibility that vehicle main body 1 will interfere with obstacle M based on the detection result of object sensor 25a, etc., and outputs the determination result to EPC valve control unit 27E.

[0079] 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 obtains, 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 obstacle M, EPC valve control unit 27E outputs a command current to EPC valve 46 as an open command to open EPC valve 46. A solenoid of EPC valve 46 is operated based on this command current, and EPC valve 46 is opened. When EPC valve 46 is opened, hydraulic oil is supplied from rear shuttle valve 47a and front shuttle valve 47b to brake circuits 42a, 42b, and braking operation is performed.

[0080] A state in which a braking operation is being performed (ON state) means that a 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, in the case of a wet multi-disc brake, the disc is sandwiched and pressed between the plates, braking the rotation of the disc. On the other hand, a state in which a braking operation is not being performed (OFF state) means that no braking force is being applied by the brake circuits 42a, 42b. An example of a state in which a braking operation is not being performed is when, in the case of a wet multi-disc brake, the pressure between the plates and the disc is released, causing the disc to move away from the plates.

[0081] In this way, the controller 26 executes automatic braking control to automatically brake the vehicle body 1 based on the detection result of the obstacle M 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.

[0082] Figure 6 is a diagram showing the change over time in command current and brake cylinder pressure before the application of the present invention. The horizontal axis of the graph shown in Figure 6(A) represents time, and the vertical axis represents the command current to the EPC valve 46. The horizontal axis of the graph shown in Figure 6(B) represents time, and the vertical axis represents the hydraulic pressure in the brake cylinder. The physical quantities represented by the horizontal and vertical axes of each graph in the subsequent Figures 7 to 9 and Figures 12 to 13 are the same as those in Figure 6. The scales of the horizontal and vertical axes of each graph in Figures 6 to 9 and Figures 12 to 13 are also the same.

[0083] The opening degree of the EPC valve 46 is adjusted by a command current output from the controller 26 (EPC valve control unit 27E) to the EPC valve 46. In the example shown in FIG. 6, the controller 26 determines a target brake cylinder pressure based on the traveling speed of the vehicle body 1 when 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. The controller 26 determines a command current C0 to be sent to the EPC valve 46 that corresponds to that brake cylinder pressure. The EPC valve control unit 27E outputs a constant command current C0 to the EPC valve 46.

[0084] The timing of "command ON" in the graph of FIG. 6 and the graphs of the subsequent figures indicates the start of a braking command, i.e., the time when a command current is output to the EPC valve 46. The timing of "brake operation start" in the graph of FIG. 6 and the graphs of the subsequent figures indicates the time when the hydraulic oil pressure (brake cylinder pressure) in the brake cylinders reaches a pressure at which braking operation starts (braking begins to work) in the brake circuits 42a, 42b. The time from when an automatic braking command is issued until braking starts is hereinafter referred to as the fill time. The pressure of the hydraulic oil at which braking operation starts is also referred to as the fill pressure.

[0085] In Figure 6, the fill time is relatively long, and there is a large time lag between when an automatic braking command is issued and when braking begins. If the fill time can be shortened, the responsiveness of the automatic brake can be improved. Below, we will explain a control method for improving the responsiveness of the brake in automatic braking control.

[0086] FIG. 7 is a first graph showing changes over time in command current and brake cylinder pressure according to the first embodiment. For example, a command current as shown in FIG. 7(A) is applied to the EPC valve 46. The command current of the braking command shown in FIG. 7(A) includes a first command current C1 (trigger current) and a second command current C2 (execution current). The first command current C1 may be the maximum current value that can be output to the EPC valve 46. The value of the first command current C1 is determined in advance and stored in the memory 26A.

[0087] At the initial stage of automatic braking control, a first command current C1 is applied to the EPC valve 46. The time during which the first command current C1 is applied to the EPC valve 46 is hereinafter referred to as the trigger time. By applying a high current value of the first command current C1 to the EPC valve 46 immediately after the start of a braking command, the brake cylinder pressure can quickly reach the pressure at which braking operation begins, and the fill time can be shortened. This improves the responsiveness of the automatic brake.

[0088] The second command current C2 is smaller than the first command current C1. After the trigger time has elapsed, the second command current C2, which has a lower current value, is applied to the EPC valve 46. By setting the trigger time to be shorter than the fill time, the command current is reduced from the first command current C1 to the second command current C2 before the brake operation begins. If the brakes are operated while the first command current C1, which has a high current value, is being output to the EPC valve 46, a deceleration shock will occur, but by reducing the current value to the second command current C2 before the brakes start to operate, the deceleration shock is suppressed and a sudden stop of the wheel loader 100 is avoided.

[0089] Before the start of braking, for example, simultaneously with the output of the first command current C1 to the EPC valve 46, the throttle opening of the engine 31 may be reduced. For example, the throttle opening may be set to 0%, so that even if the operator operates the accelerator 55, the rotation speed of the engine 31 based on the accelerator operation amount is not changed. By reducing the driving force of the engine 31, the braking distance of the brakes can be shortened. Typically, the braking distance can be minimized by cutting unnecessary driving force.

[0090] Before the start of braking, for example, the transmission may be placed in neutral simultaneously with the output of the first command current C1 to the EPC valve 46. By disconnecting the engine 31 from the axle 34, the inertia that is used to stop the vehicle by braking can be reduced, thereby shortening the braking distance.

[0091] Fig. 8 is a second diagram showing time-dependent changes in command current and brake cylinder pressure according to the first embodiment. Fig. 8 shows an example of automatic braking control when the vehicle speed is slower than the example shown in Fig. 7. The controller 26 determines the value of the second command current C2 based on the traveling speed of the vehicle body 1. For example, the controller 26 can determine a target brake cylinder pressure based on the vehicle speed detected by the speed sensor 25d at the start of a braking command, and the current value corresponding to that brake cylinder pressure can be set as the second command current C2.

[0092] When the vehicle speed is low, a small brake cylinder pressure may be required to stop the vehicle body 1 before colliding with the obstacle M. Therefore, the value of the command current corresponding to the target brake cylinder pressure may also be small. The second command current C2 in FIG. 8, where the vehicle speed is low, is set to be smaller than the second command current C2 in FIG. 7, where the vehicle speed is high. By determining the brake cylinder pressure corresponding to the vehicle speed and setting the second command current C2 to be small in accordance with that brake cylinder pressure, deceleration shock is suppressed.

[0093] 9 is a diagram showing the change over time in the command current and the brake cylinder pressure when the oil temperature is high. In Fig. 9 and the subsequent figures, the allowable pressure of the axle 34 is shown by the dashed line extending in the left-right direction in the graph (B).

[0094] When the temperature of the hydraulic oil is high, the flow rate of the hydraulic oil increases. Because the flow rate of hydraulic oil per unit time into the brake cylinder increases, the brake cylinder pressure increases in a short period of time, and the fill time becomes shorter. The trigger time shown in Figure 9(A) is the same as in Figures 7 and 8, but because the fill time is shorter, the fill time is shorter than the trigger time. When the brakes are activated while a high first command current C1 is being output to the EPC valve 46, the brake cylinder pressure increases rapidly, and pressure that exceeds the allowable pressure of the axle acts.

[0095] To prevent the pressure from exceeding the allowable pressure, the controller 26 determines the trigger time based on the oil temperature. When the oil temperature is high, as shown in Figure 9, the trigger time is shortened and set to be shorter than the fill time, so that the command current drops from the first command current C1 to the second command current C2 before braking begins, as in Figures 7 and 8. This keeps the pressure acting on the axle below the allowable pressure, preventing axle malfunctions.

[0096] 10 is a flow diagram showing a control method for the wheel loader 100 according to the first embodiment. Although some of the description overlaps with the above description, the flow of processing for automatic braking control according to the first embodiment will be described in order.

[0097] 10, in step S1, it is determined whether or not to execute automatic braking control. When the traveling direction determination unit 27B determines the traveling direction of the vehicle body 1, the object sensor 25a detects that an obstacle M exists in the traveling direction, and the object determination unit 27D determines that there is a possibility that the vehicle body 1 will interfere with the obstacle M, the controller 26 determines that the automatic braking control will be executed (YES in step S1).

[0098] In step S2, the vehicle speed is detected. The speed sensor 25d detects the traveling speed of the vehicle body 1 and outputs the detected vehicle speed to the vehicle speed acquisition unit 27G of the controller 26. The vehicle speed acquisition unit 27G acquires the detection result of the traveling speed of the vehicle body 1 from the speed sensor 25d. The vehicle speed acquisition unit 27G outputs the acquired vehicle speed to the EPC valve control unit 27E.

[0099] In step S3, a second command current value is determined. The value of the second command current C2 corresponding to the vehicle speed of the vehicle body 1 is stored in advance in the memory 26A. The relationship between the vehicle speed and the second command current C2 may be stored in the memory 26A in the form of a table, or the second command current C2 may be calculated by applying the vehicle speed to a relational expression stored in the memory 26A. The controller 26 (EPC valve control unit 27E) determines an appropriate value of the second command current C2 corresponding to the vehicle speed of the vehicle body 1 using the relationship between the vehicle speed and the second command current C2 stored in the memory 26A.

[0100] In step S4, the oil temperature is detected. Temperature sensor 25c detects the temperature of the hydraulic oil in the hydraulic circuit that supplies the hydraulic oil to brake circuits 42a, 42b. Temperature sensor 25c outputs the detected oil temperature to oil temperature acquisition unit 27F of controller 26. Oil temperature acquisition unit 27F acquires the detection result of the hydraulic oil temperature from temperature sensor 25c. Oil temperature acquisition unit 27F outputs the acquired oil temperature to EPC valve control unit 27E.

[0101] In step S5, the trigger time is determined. The fluidity of the hydraulic oil varies according to the oil temperature, and the responsiveness of the automatic brake changes. An appropriate trigger time according to the oil temperature is determined in advance and stored in memory 26A. The relationship between the oil temperature and the trigger time may be stored in the memory 26A in the form of a table, or the trigger time may be calculated by applying the oil temperature to a relational expression stored in memory 26A. The controller 26 (EPC valve control unit 27E) determines an appropriate trigger time according to the oil temperature using the relationship between the oil temperature and the trigger time stored in advance in memory 26A. Specifically, the controller 26 (EPC valve control unit 27E) determines the trigger time according to the oil temperature so that it is shorter than the fill time.

[0102] By varying the trigger time in response to the oil temperature rather than setting it to a constant value, braking can be prevented from starting during the trigger time even when the oil temperature is high and the hydraulic oil flow rate increases, and the hydraulic oil pressure can be prevented from exceeding the allowable axle pressure.

[0103] In step S6, the controller 26 (EPC valve control unit 27E) outputs a first command current C1 to the EPC valve 46. Based on the first command current C1, the EPC valve 46 opens. Typically, the EPC valve 46 opens fully. Hydraulic oil is supplied to the brake circuits 42a, 42b via the shuttle valve unit 47, and the brake cylinder pressure starts to increase.

[0104] In step S7, it is determined whether or not a trigger time has elapsed since the start of output of the first command current C1 to the EPC valve 46. The controller 26 determines whether or not the trigger time has elapsed by comparing the time measured by a timer (not shown) with the trigger time determined in the previous step S5. If it is determined that the trigger time has not elapsed (NO in step S7), the determination in step S7 is repeated.

[0105] When it is determined that the trigger time has elapsed (YES in step S7) and that the time during which the first command current C1 is being output to the EPC valve 46 has reached the trigger time, in step S8 the controller 26 (EPC valve control unit 27E) outputs a second command current C2 to the EPC valve 46. The opening of the EPC valve 46 is changed based on the second command current C2. Specifically, the opening of the EPC valve 46 becomes smaller. With the second command current C2 being output to the EPC valve 46, the brake cylinder pressure reaches the fill pressure. Operation of the automatic brake is initiated, and braking force is exerted by the automatic braking. In this way, the wheel loader 100 can be stopped in front of the obstacle M by the automatic braking.

[0106] In the determination in step S1, if it is determined that automatic braking control is not to be performed because no obstacle M is detected in the traveling direction of the vehicle body 1 (NO in step S1), the process ends immediately ("END" in FIG. 10).

[0107] The processing of steps S2 to S6 shown in Fig. 10 does not necessarily have to be performed in this order. For example, when it is determined in step S1 that automatic braking control is to be performed, output of the first command current C1 to the EPC valve 46 may immediately be started (step S6), followed by processing to determine a trigger time according to the oil temperature (steps S4, S5), and then processing to determine the second command current C2 according to the vehicle speed (steps S2, S3).

[0108] [Second embodiment] The wheel loader 100 according to the second embodiment does not have to be equipped with the temperature sensor 25c shown in Figures 2 and 4. The temperature of the hydraulic oil supplied to the brake circuits 42a, 42b does not have to be detected. If the temperature of the hydraulic oil supplied to the brake circuits 42a, 42b is not used, the trigger time is predetermined as a fixed time and stored in the memory 26A. A relatively short time is set as the trigger time so that the trigger time is shorter than the fill time even when the oil temperature is high and the flow rate of the hydraulic oil is large.

[0109] In addition, a third command current C3 is set that is smaller than the first command current C1 and larger than the second command current C2. The value of the third command current C3 is predetermined and stored in the memory 26A. The third command current C3 may be smaller than half the sum of the first command current C1 and the second command current C2. A second trigger time during which the third command current C3 is applied to the EPC valve 46 is also predetermined as a fixed time and stored in the memory 26A. The second trigger time may be longer than the first trigger time.

[0110] Figure 11 is a flow diagram showing a control method for the wheel loader 100 according to the second embodiment. The control method of the second embodiment shown in Figure 11 does not include step S4 of detecting the oil temperature and step S5 of determining the trigger time based on the oil temperature, which were described with reference to Figure 10. Once the second command current C2 is determined based on the vehicle speed in step S3, the process proceeds to step S6, where the controller 26 outputs the first command current C1 to the EPC valve 46.

[0111] If it is determined in step S7 that the trigger time has elapsed (YES in step S7), in step S9, the controller 26 (EPC valve control unit 27E) outputs a third command current C3 to the EPC valve 46. The opening degree of the EPC valve 46 is changed based on the third command current C3. Specifically, the opening degree of the EPC valve 46 is reduced.

[0112] In step S10, it is determined whether a second trigger time has elapsed since the output of the third command current C3 to the EPC valve 46 started. The controller 26 determines whether the second trigger time has elapsed by comparing the time measured by a timer (not shown) with a predetermined second trigger time. If it is determined that the trigger time has not elapsed (NO in step S10), the determination in step S10 is repeated.

[0113] If it is determined that the second trigger time has elapsed (YES in step S10), in step S8, the controller 26 (EPC valve control unit 27E) outputs a second command current C2 to the EPC valve 46. The opening degree of the EPC valve 46 is changed based on the second command current C2. Specifically, the opening degree of the EPC valve 46 is further reduced.

[0114] FIG. 12 is a first graph showing changes over time in the command current and the brake cylinder pressure according to the second embodiment. FIG. 12 shows an example when the oil temperature is relatively low. In the example shown in FIG. 12, the brake cylinder pressure reaches the fill pressure while the third command current C3 is being output to the EPC valve 46. The automatic brake operation is initiated during the second trigger time after the trigger time has elapsed. Because the trigger time is shorter than the fill time, the brake is not operated while the first command current C1, which has a high current value, is being output to the EPC valve 46, thereby suppressing deceleration shock.

[0115] 12, when the fill time has elapsed, a third command current C3 that is greater than the second command current C2 corresponding to the vehicle speed of the vehicle body 1 is output to the EPC valve 46. While the third command current C3 is being output to the EPC valve 46, the brake cylinder pressure increases, but because the brake cylinder pressure is maintained lower than the allowable pressure of the axle, a malfunction of the axle is avoided.

[0116] FIG. 13 is a second graph showing the change over time in the command current and the brake cylinder pressure according to the second embodiment. FIG. 13 shows an example when the oil temperature is relatively high. When the temperature of the hydraulic oil is high, the brake cylinder pressure increases in a short period of time. The fill time shown in FIG. 13 is shorter than the fill time shown in FIG. 12.

[0117] 13, the brake cylinder pressure reaches the fill pressure immediately after the trigger time has elapsed and the command current output to the EPC valve 46 is reduced from the first command current C1 to the third command current C3. During the second trigger time after the trigger time has elapsed, automatic braking begins. Because the trigger time is shorter than the fill time, the brakes are not activated while the high-current first command current C1 is being output to the EPC valve 46, and deceleration shock is avoided.

[0118] In the second embodiment, the trigger time and the second trigger time are constant regardless of the oil temperature. In the example shown in FIG. 13, the fill time is shorter than in FIG. 12, so the time during which the third command current C3 is output to the EPC valve 46 after the fill time has elapsed is longer. The brake cylinder pressure exceeds the maximum value shown in FIG. 12 and reaches a pressure corresponding to the third command current C3, at which point it becomes substantially constant. Even in this case, the brake cylinder pressure is maintained within a range lower than the axle's allowable pressure, preventing axle malfunction.

[0119] [Action and effect] The characteristic configurations of the above-described embodiment, as well as their actions and effects, can be listed as follows:

[0120] 11 to 13, in an initial stage of automatic braking control, the controller 26 outputs a first command current C1 to the EPC valve 46 for a predetermined trigger time. After the trigger time has elapsed, the controller 26 outputs a third command current C3, which is smaller than the first command current C1, to the EPC valve 46 for a predetermined second trigger time. After the second trigger time has elapsed, the controller 26 outputs a second command current C2, which is smaller than the third command current C3, to the EPC valve 46.

[0121] By increasing the current value when a brake command is initiated, the responsiveness of the automatic brake can be improved. By decreasing the current value before the brake starts to operate, the shock at the start of braking can be suppressed. By decreasing the current value in two stages, a command with good responsiveness and that does not exceed the allowable pressure can be achieved with a simple configuration that does not use the temperature sensor 25c that detects the temperature of the hydraulic oil.

[0122] 12 and 13, the trigger time may be shorter than the fill time from when an automatic braking command is issued until braking starts. By setting the trigger time and fill time in this way, the current value can be reduced before the brake starts to operate, and shock at the start of braking can be reliably suppressed.

[0123] 2 and 4, the wheel loader 100 is further equipped with a speed sensor 25d that detects the traveling speed, and the controller 26 may determine the second command current C2 based on the detection result of the speed sensor 25d, as shown in Fig. 11. In this way, it is possible to reliably stop the traveling vehicle body 1 in front of the obstacle M.

[0124] In the embodiment, a case has been described in which automatic braking is performed when the object sensor 25a detects the presence of an obstacle M behind the wheel loader 100 while the wheel loader 100 is moving backward, but the present invention can also be applied to a configuration in which automatic braking is performed not only when moving backward but also when moving forward.

[0125] In the above embodiment, a wheel loader has been used as an example of a work machine, but the work machine is not limited to a wheel loader and may be other types of work machines that travel and perform work, such as a motor grader, bulldozer, etc. The work machine may also be a work machine equipped with a rotating body, such as a hydraulic excavator, whose rotating body may rotate during work.

[0126] <Additional Notes> The above description includes the following additional features.

[0127] (Appendix 1) A work machine that performs automatic braking control to automatically brake travel based on the detection result of an obstacle in the travel direction, 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 controller that outputs a first command current to the proportional pressure reducing valve for a predetermined trigger time in an initial stage of the automatic braking control, outputs a third command current smaller than the first command current to the proportional pressure reducing valve for a predetermined second trigger time after the trigger time has elapsed, and outputs a second command current smaller than the third command current to the proportional pressure reducing valve after the second trigger time has elapsed.

[0128] (Appendix 2) 2. The work machine of claim 1, wherein the trigger time is shorter than the time between when automatic braking is commanded and when braking begins.

[0129] (Appendix 3) a speed sensor for detecting a traveling speed of the work machine; The work machine according to claim 1 or 2, wherein the controller determines the second command current based on a detection result of the speed sensor.

[0130] (Appendix 4) In an automatic braking control that automatically brakes traveling based on a detection result of an obstacle in the traveling direction, outputting a first command current for a predetermined trigger time to a proportional pressure reducing valve that opens and closes a hydraulic circuit that supplies hydraulic oil to a brake circuit that brakes traveling; after the trigger time has elapsed, outputting a third command current smaller than the first command current to the proportional pressure reducing valve for a predetermined second trigger time; outputting a second command current smaller than the third command current to the proportional pressure reducing valve after the second trigger time has elapsed.

[0131] (Appendix 5) 5. A work machine control method according to claim 4, wherein the trigger time is shorter than the time from when an automatic braking command is issued to when braking starts.

[0132] (Appendix 6) A control method for a work machine according to claim 4 or 5, wherein the second command current is determined based on a detection result of a speed sensor that detects a traveling speed of the work machine.

[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, 7 rear tire, 10 vehicle frame, 14 boom, 15 bucket, 21 drive unit, 22 braking unit, 23 operation unit, 24 operating unit, 25 detection unit, 25a object sensor, 25b pressure sensor, 25c temperature sensor, 25d speed sensor, 26 controller, 26A memory, 27 automatic braking control unit, 27A travel direction information acquisition unit, 27B travel direction determination unit, 27C object information acquisition unit, 27D object determination unit, 27E EPC valve control unit, 27F oil temperature acquisition unit, 27G vehicle speed acquisition unit, 31 engine, 34 axle, 40 braking unit, 41 brake valve unit, 41a rear brake valve, 41b front brake valve, 42a, 42b Brake circuit, 44a, 44b hydraulic oil supply line, 45 shutoff valve, 46, 62 EPC valve, 47 shuttle valve unit, 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, C1 to C3 command current, M obstacle.

Claims

1. A work machine that performs automatic braking control to automatically brake travel based on the detection result of an obstacle in the travel direction, 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 controller that outputs a first command current to the proportional pressure reducing valve for a predetermined trigger time in an initial stage of the automatic brake control, outputs a third command current smaller than the first command current to the proportional pressure reducing valve for a predetermined second trigger time after the trigger time has elapsed, and outputs a second command current smaller than the third command current to the proportional pressure reducing valve after the second trigger time has elapsed.

2. The work machine according to claim 1 , wherein the trigger time is shorter than the time between when an automatic braking command is issued and when braking is initiated.

3. a speed sensor for detecting a traveling speed of the work machine; The work machine according to claim 1 , wherein the controller determines the second command current based on a detection result of the speed sensor.

4. In an automatic braking control for automatically braking the traveling of the vehicle based on the detection result of an obstacle in the traveling direction, a first command current is output for a predetermined trigger time to a proportional pressure reducing valve that opens and closes a hydraulic circuit that supplies hydraulic oil to a brake circuit that brakes the traveling of the vehicle; outputting a third command current smaller than the first command current to the proportional pressure reducing valve for a predetermined second trigger time after the trigger time has elapsed; outputting a second command current smaller than the third command current to the proportional pressure reducing valve after the second trigger time has elapsed.

5. 5. The method for controlling a work machine according to claim 4, wherein the trigger time is shorter than the time from when an automatic braking command is issued until braking is initiated.

6. 5. The method for controlling a work machine according to claim 4, wherein the second command current is determined based on the detection result of a speed sensor that detects the traveling speed of the work machine.

Images