Work vehicle

Abstract

To prevent an operator from switching between position and speed control modes at an unintended timing.SOLUTION: A work vehicle (1) comprises: vehicle bodies (5, 9), traveling wheels (4, 8) supported by the vehicle bodies, actuators (221, 222) for changing a steering angle of the traveling wheel (4) to the right or left from a predetermined neutral angle, a steering lever (215), and a controller (210) for switching a control mode of the steering lever between a speed control mode for controlling the actuators so as to allow a speed corresponding to an operation amount of the steering lever by changing the steering angles of the traveling wheels, and a position control mode for controlling the actuators so as to allow the steering angles of the traveling wheels to correspond to the operation amount of the steering lever. The controller calculates bending angles (θ) of the vehicle bodies based on the operation of the steering lever, and switches the control mode from one to the other between the speed control mode and the position control mode when the bending angles of the vehicle bodies are less than a predetermined threshold (θ1).SELECTED DRAWING: Figure 7

Description

[Technical Field]

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

[0002] Work vehicles, such as wheel loaders, are equipped with a steering member, such as a steering wheel or a steering lever, for steering the running wheels left and right. The control modes for the steering angle controlled by the operation of the steering member include a position control mode and a speed control mode. Specifically, in the position control mode, the steering angle is set to an angle that corresponds to the amount of operation of the steering member. On the other hand, in the speed control mode, the steering angle changes at a speed that corresponds to the amount of operation of the steering member.

[0003] In Patent Document 1, the first steering member can be operated within any of a left steering range, a right steering range, and a neutral range. In this way, the steering range is divided into a left steering range, a right steering range, and a neutral range. Then, when the first steering member is located within the left steering range or the right steering range, the actuator is controlled at a speed corresponding to the amount of operation of the first steering member. On the other hand, when the first steering member is located within the neutral range, the actuator is controlled to return the steering angle to the neutral angle. In this way, when the first steering member is located within the left steering range or the right steering range, a speed control type is used to enable smooth, small steering angle operations. On the other hand, a technology is known in which, when the first steering member is located within the neutral range, the steering angle is returned to the neutral angle to easily move the work machine straight. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2023-13527 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the technique of Patent Document 1 controls the actuator (controls the steering angle) according to the steering range of the steering member, so that the position control mode and the speed control mode may be switched at a timing not intended by the operator.

[0006] Therefore, an object of the present invention is to prevent switching between the position control mode and the speed control mode at a timing not intended by the operator. [Means for solving the problem]

[0007] In order to achieve the above object, a representative aspect of the present invention is a work vehicle including a bendable body, running wheels supported on the body, an actuator that changes the steering angle of the running wheels to the left or right from a predetermined neutral angle, a steering lever that operates the actuator, and a controller that switches the control mode of the steering lever between a speed control mode that controls the actuator to change the steering angle of the running wheels at a speed corresponding to the amount of operation of the steering lever, and a position control mode that controls the actuator to change the steering angle of the running wheels to a value corresponding to the amount of operation of the steering lever, wherein the controller, when it determines that a predetermined switching condition is met, calculates the bending angle of the body based on the operation of the steering lever, and switches the control mode from one of the speed control mode and the position control mode to the other when the bending angle of the body is less than a predetermined threshold value. [Effects of the Invention]

[0008] According to the present invention, it is possible to prevent switching between the position control mode and the velocity control mode at a timing not intended by the operator. Note that problems, configurations, and effects other than those described above will become clear from the description of the following embodiments. [Brief explanation of the drawings]

[0009] [Figure 1]1 is a side view of a wheel loader according to a first embodiment of the present invention. [Figure 2] 1 is an overall configuration diagram of a hydraulic system of a wheel loader. [Figure 3] FIG. 2 illustrates an example of a hardware configuration. [Figure 4] FIG. 4 is a diagram showing the relationship between the operation amount of the steering wheel and the pilot pressure. [Figure 5] FIG. 4 is a diagram showing the relationship between the operation amount of the steering lever and the command current. [Figure 6] FIG. 4 is a diagram showing the relationship between the accelerator pedal depression amount and the required engine rotation speed. [Figure 7] 10 is a flowchart illustrating an example of overall processing. [Figure 8] 10A and 10B are diagrams illustrating examples of a speed control mode and a position control mode. [Figure 9] 10 is a flowchart illustrating an example of a process for setting a switching flag. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, various embodiments of a wheel loader, which is an example of a work vehicle according to the present invention, will be described with reference to the drawings.

[0011] (First embodiment) FIG. 1 is a side view of a wheel loader 1 according to a first embodiment of the present invention.

[0012] As shown in FIG. 1, the wheel loader 1 includes a front frame 5 (vehicle body) having a lift arm 2, a bucket 3, a pair of front wheels 4, etc., and a rear frame 9 (vehicle body) having a driver's cab 6, an engine compartment 7, a pair of rear wheels 8, etc. An engine 30 serving as a prime mover is mounted in the engine compartment 7, and a counterweight 10 is attached to the rear of the rear frame 9. Note that an electric motor may be used as the prime mover instead of the engine 30. The front frame 5 and the rear frame 9 are connected to each other by a center pin 15 so that they can rotate freely, and the front frame 5 bends left and right relative to the rear frame 9 due to the extension and contraction of steering cylinders 221, 222 (see FIG. 2) which serve as actuators. Note that in the following description, the front wheels 4 and rear wheels 8 may be collectively referred to as "wheels 4, 8." The wheels 4, 8 are an example of traveling wheels.

[0013] The lift arm 2 rotates (elevates) in the vertical direction by driving a pair of lift arm cylinders 11, and the bucket 3 rotates (tilts or dumps) in the vertical direction by driving a bucket cylinder 12. A link mechanism including a bell crank 13 is interposed between the bucket cylinder 12 and the bucket 3, and the bucket cylinder 12 rotates the bucket 3 via this link mechanism. The lift arm 2, bucket 3, pair of lift arm cylinders 11, bucket cylinder 12, bell crank 13, etc. constitute a work machine 14 (front device).

[0014] A lift arm angle sensor 27 is attached to the connection between the lift arm 2 and the front frame 5, and this lift arm angle sensor 27 detects the rotation angle of the lift arm 2. The bucket cylinder 12 is equipped with a proximity switch 28, which turns on when the rod of the bucket cylinder 12 is retracted by a predetermined amount. This makes it possible to detect the posture of the bucket 3.

[0015] The operator's cab 6 mounted on the front of the rear frame 9 is equipped with a driver's seat where the operator sits, operation levers 213, 214 (see FIG. 2) for operating the work equipment 14, a steering wheel 212 that controls the steering angle of the wheel loader 1, a steering lever 215 (see FIG. 2), an accelerator pedal 230, a key switch for starting and stopping the wheel loader 1, a parking brake 231, and a monitor 60 that displays information to the operator. The monitor 60 is, for example, a touch panel type liquid crystal monitor.

[0016] The cab 6 is also provided with a controller 210 that controls the overall operation of the wheel loader 1 (see FIG. 3). The cab 6 may also be provided with an IMU (Inertial Measurement Unit) that detects vehicle acceleration and vehicle angular velocity.

[0017] Fig. 2 is an overall configuration diagram of the hydraulic system of the wheel loader 1. As shown in Fig. 2, when the key switch is turned on and the engine 30 starts, the pump 217 (hydraulic pump) draws hydraulic oil from a tank (not shown) and supplies pressure oil to the lift arm directional control valve 223, the bucket directional control valve 224, and the steering directional control valve 220.

[0018] When the operation lever 213 is operated, the position of the lift arm directional control valve 223 is switched, and pressure oil from the pump 217 is supplied to the pair of lift arm cylinders 11, causing the pair of lift arm cylinders 11 to extend and retract. In this way, the lift arm 2 rotates up and down. When the operation lever 214 is operated, the position of the bucket directional control valve 224 is switched, and pressure oil from the pump 217 is supplied to the bucket cylinder 12, causing the bucket cylinder 12 to extend and retract. In this way, the bucket 3 rotates up and down. Note that operation signals from the operation levers 213, 214 are input to the controller 210, and the controller 210 monitors the operating state of the work implement 14.

[0019] Furthermore, when the steering lever 215 is operated, a right steering electromagnetic control valve 218 or a left steering electromagnetic control valve 219 is actuated via the controller 210 in accordance with the direction and amount of operation, and the position of the steering direction control valve 220 is switched. Then, pressure oil from the pump 217 is supplied to the steering cylinder 221 or the steering cylinder 222 in accordance with the position of the steering direction control valve 220, and one of the steering cylinders 221, 222 extends and the other retracts. In this way, the front frame 5 bends left and right relative to the rear frame 9. Here, the right steering electromagnetic control valve 218 and the left steering electromagnetic control valve 219 are examples of steering proportional valves of the present invention.

[0020] Similarly, the steering cylinder 221 and the steering cylinder 222 of the steering wheel 212 extend and retract in accordance with the operation direction (rotation direction) and operation amount (rotation amount / rotation angle). The operation amount of the steering wheel 212 is detected by a steering wheel operation amount detector 204 and input to the controller 210.

[0021] The rotation speed of the engine 30 is input to the controller 210, which monitors the operating state of the engine 30 (has the function of operating as a motor rotation speed determining unit).

[0022] (Example of hardware configuration) 3 is a diagram showing an example of the hardware configuration. For example, the wheel loader 1 is equipped with a parking brake operation position detector 201, a pump pressure sensor 202, a vehicle speed detector 203, a steering wheel operation amount detector 204, a steering lever operation amount detector 205, and an accelerator pedal operation amount detector 206.

[0023] The wheel loader 1 further includes a controller 210, a monitor 60, and a changeover switch 211 (a changeover operation receiving unit), etc. The controller 210 includes, for example, a central processing unit (hereinafter referred to as "CPU 210a"), a memory 210b, and a control device 210c, etc.

[0024] The parking brake operation position detector 201 is a sensor that detects the position at which the parking brake 231 is operated by the operator.

[0025] The pump pressure sensor 202 is a sensor that detects the pressure (discharge pressure) P in the pump 217 .

[0026] The vehicle speed detector 203 is a sensor that measures the traveling speed (vehicle speed V) of the wheel loader 1. Specifically, it measures the number of rotations (rotational speed) of the propeller shaft that drives the wheels 4, 8 to rotate.

[0027] The steering wheel operation amount detector 204 is a sensor that measures the rotation angle (steering wheel operation amount Sa) of the steering wheel 212 operated by the operator, and is, for example, a rotary encoder.

[0028] The steering lever operation amount detector 205 is a sensor that measures the operation amount (operation amount Sb) of the steering lever 215 operated by the operator.

[0029] Accelerator pedal operation amount detector 206 is a sensor that measures the operation amount (operation amount AP) of accelerator pedal 230 operated by the operator, and is, for example, a potentiometer.

[0030] The CPU 210a is an example of a computing device, and therefore executes processing in cooperation with hardware such as the memory 210b.

[0031] The control device 210c performs control. For example, the control device 210c switches the control mode related to the steering operation between a speed control mode and a position control mode based on the operation of a changeover switch 211 by an operator (described in detail later).

[0032] The hardware is not limited to the above. For example, the wheel loader 1 may have a hardware configuration that includes other devices such as a calculation device, a control device, a storage device, an input device, an output device, a communication device, a sensor, or an auxiliary device.

[0033] 4 is a diagram showing an example of the relationship between the operation amount Sa of the steering wheel 212 and the pilot pressure Pa acting on the steering direction control valve 220. For example, when the operation amount Sa of the steering wheel 212 is a value between an eleventh set value Sa1 and a twelfth set value Sa2, the pilot pressure Pa is proportional to the value from the first pilot pressure Pa1 to the second pilot pressure Pa2. In this way, the steering angle is configured to change in proportion to the operation amount Sa of the steering wheel 212. Note that the range in which the operation amount Sa of the steering wheel 212 is less than the eleventh set value Sa1 is a play portion in which operation of the steering wheel 212 is not effective.

[0034] 5 is a diagram showing an example of the relationship between the command current I of the left and right steering electromagnetic control valves 218, 219 and the operation amount Sb of the steering lever 215. The magnitude of the command current I is synonymous with the magnitude of the output of the steering electromagnetic control valves 218, 219. In other words, when the command current I is large, the output of the steering electromagnetic control valves 218, 219 is also large.

[0035] The operation amount Sb is the amount of operation of the operator with respect to the steering lever 215, and is "0" when the operator is not operating the steering lever 215. Then, when the steering lever 215 is tilted and the tilt angle increases, the operation amount Sb becomes a large value.

[0036] When the operation amount Sb of the steering lever 215 is equal to or less than the 21st set value Sb1, the command current I becomes the current A1, which is the minimum output. That is, when the operation amount Sb is sufficiently small and the steering lever 215 is hardly operated, the command current I becomes the current A1. That is, when the operation amount Sb of the steering lever 215 is equal to or less than the 21st set value Sb1, the outputs of the left and right steering electromagnetic control valves 218, 219 become the minimum.

[0037] On the other hand, when the operation amount Sb of the steering lever 215 is a value between the 21st set value Sb1 and the 22nd set value Sb2, the command current I is proportional from the current A1 to the current A2, with the maximum current A2 being the upper limit. In other words, when the operation amount Sb of the steering lever 215 is the 22nd set value Sb2, the outputs of the left and right steering electromagnetic control valves 218, 219 are maximum.

[0038] 6 is a diagram showing an example of the relationship between the required engine speed N and the operation amount (depression amount) AP of accelerator pedal 230. The operation amount AP of accelerator pedal 230 is the input amount by which the operator depresses accelerator pedal 230.

[0039] When the operation amount AP of accelerator pedal 230 is equal to or less than 31st set value AP1, i.e., when the accelerator pedal is not operated (idling), requested engine speed N becomes equal to first threshold value E1. Then, when the operator depresses accelerator pedal 230 and operation amount AP increases to a value higher than 31st set value AP1, requested engine speed N becomes proportional to operation amount AP of accelerator pedal 230. Accelerator pedal 230 can be operated by depressing it up to 32nd set value AP2. Therefore, requested engine speed N increases in proportion to the value of operation amount AP up to engine speed upper limit value E2.

[0040] When the requested engine speed E is equal to or less than the first threshold value E1, the engine 30 is in an idling state, and the wheel loader 1 is said to be in a stopped state (non-traveling state).

[0041] (Overall processing example) Next, there will be explained the flow of the overall processing of the wheel loader 1. Fig. 7 is a flowchart showing an example of the overall processing.

[0042] In step S10, the controller 210 accepts a switching operation by the operator on the changeover switch 211. The switching operation by the operator may be accepted by other hardware.

[0043] In step S20, the controller 210 determines whether the switching flag is ON. Next, if the switching flag is ON (YES in step S20), the controller 210 proceeds to step S30. On the other hand, if the switching flag is not ON (NO in step S20), the controller 210 proceeds to step S31.

[0044] In step S30, the controller 210 acquires the vehicle body bending angle θ. Specifically, the controller 210 acquires the operation amount Sa from the steering wheel operation amount detector 204 or the operation amount Sb from the steering lever operation amount detector 205, and calculates the angle of the front frame 5 with respect to the rear frame 9, i.e., the vehicle body bending angle θ, from these operation amounts Sa and Sb.

[0045] In step S31, the controller 210 maintains the current control mode. That is, unless the switching flag is ON, the controller 210 does not switch the current control mode related to steering.

[0046] In step S40, the controller 210 determines whether the vehicle body bending angle θ is equal to or less than the third threshold value θ1. Next, if the vehicle body bending angle θ is equal to or less than the third threshold value θ1 (YES in step S40), the controller 210 proceeds to step S50. On the other hand, if the vehicle body bending angle θ is not equal to or less than the third threshold value θ1 (NO in step S40), the controller 210 proceeds to step S60.

[0047] The third threshold value θ1 is a predetermined value that may be determined as appropriate taking into consideration the specifications of the wheel loader 1, the working environment, etc., but for example, the third threshold value θ1 is a value at which the posture of the wheel loader 1 can be determined to be neutral if the absolute value of the vehicle body bending angle θ (hereinafter referred to as absolute value |θ|) is equal to or less than the third threshold value θ1.

[0048] In step S50, the controller 210 turns the vehicle body so that the absolute value |θ| becomes less than the third threshold value θ 1. In other words, if the vehicle body bending angle θ is a large value and the attitude of the wheel loader 1 is not neutral, the controller 210 controls the steering cylinders 221, 222 so that the attitude of the wheel loader 1 becomes neutral.

[0049] In step S60, controller 210 determines whether the current steering control mode is the position control mode. Next, if the current steering control mode is the position control mode (YES in step S60), controller 210 proceeds to step S70. On the other hand, if the current steering control mode is not the position control mode (NO in step S60), controller 210 proceeds to step S71.

[0050] In step S70, the controller 210 switches the steering control mode to a speed control mode.

[0051] On the other hand, in step S71, the controller 210 switches the steering control mode to the position control mode.

[0052] Figure 8 is a diagram showing examples of the speed control mode and the position control mode. For example, in the speed control mode, when the operator inputs a first operation amount Sb10 that operates the steering lever 215 greatly, the wheel loader 1 moves in the steered direction at a high speed V10 (turns right in Figure 8). On the other hand, in the speed control mode, when the operator inputs a second operation amount Sb20 that operates the steering lever 215 slightly, the wheel loader 1 moves in the steered direction at a low speed V20.

[0053] The first operation amount Sb10 is a larger operation amount than the second operation amount Sb20. Furthermore, the high speed V10 is a speed faster than the low speed V20. In this way, the steering speed is controlled by the operation amount Sb.

[0054] On the other hand, in the position control mode, when the operator inputs the third operation amount Sb30 to the steering lever 215, the wheel loader 1 moves to a position where the angle is θ30 according to the third operation amount Sb30. Also, in the position control mode, when the operator does not operate the steering lever 215, that is, when the operation amount Sb is "0", the wheel loader 1 reaches a neutral angle (does not bend).

[0055] The position control mode and the speed control mode are switched in step S70 or step S71. The steering angle is controlled by the pump 217 and the steering cylinders 221 and 222 based on the amount of operation of the steering lever 215.

[0056] 9 is a flowchart showing the procedure for setting the switching flag. For example, before the switching flag is referenced in step S20, the switching flag is set to ON or OFF by the following process. That is, FIG. 9 shows the processing procedure for setting whether a predetermined switching condition is met.

[0057] In step S80, the controller 210 acquires parameters. Specifically, the parameters include position information of the parking brake 231, the pressure P in the pump 217, the vehicle speed V, the steering wheel operation amount Sa, the steering lever operation amount Sb, state information of the work implement 14 (front device), state information of the steering wheel 212, state information of the steering lever 215, state information of the accelerator pedal 230, and information on the control current (steering proportional output) of the solenoid control valves 218, 219. Note that the parameters may be other information as long as it is information that can be used to make decisions in the following steps S90 to S180. Furthermore, the parameters may be used for multiple decisions.

[0058] In step S90, the controller 210 determines whether or not the parking brake 231 is in an actuated state based on the position information of the parking brake 231 (operates as a parking brake actuation determination unit). If the parking brake 231 is in an actuated state, the wheel loader 1 is in a stopped state. Next, if the parking brake 231 is in an actuated state (YES in step S90), the controller 210 proceeds to step S100. On the other hand, if the parking brake 231 is not in an actuated state (NO in step S90), the controller 210 proceeds to step S180.

[0059] In step S100, the controller 210 determines whether the work implement 14 (front equipment) is in an inoperative state based on the state information of the work implement 14 (front equipment) (operates as a front equipment operation determination unit). Next, if the work implement 14 is in an inoperative state (YES in step S100), the controller 210 proceeds to step S110. On the other hand, if the work implement 14 is not in an inoperative state (NO in step S100), the controller 210 proceeds to step S180.

[0060] In step S110, the controller 210 determines whether or not the vehicle speed V is equal to or less than a second threshold value based on the vehicle speed V (operating as a vehicle speed determination unit). The second threshold value is a preset value. A vehicle speed V equal to or less than the second threshold value is a speed at which the vehicle speed V is sufficiently small and the wheel loader 1 is stopped. Next, if the vehicle speed V is equal to or less than the second threshold value (YES in step S110), the controller 210 proceeds to step S120. On the other hand, if the vehicle speed V is not equal to or less than the second threshold value (NO in step S110), the controller 210 proceeds to step S180.

[0061] In step S120, the controller 210 determines whether the steering wheel 212 is in an inoperative state based on the state information of the steering wheel 212 (operating as a steering wheel operation determination unit). Next, if the steering wheel 212 is in an inoperative state (YES in step S120), the controller 210 proceeds to step S130. On the other hand, if the steering wheel 212 is not in an inoperative state (NO in step S120), the controller 210 proceeds to step S180.

[0062] In step S130, the controller 210 determines whether the steering lever 215 is in an inoperative state based on the state information of the steering lever 215 (operating as a steering lever operation determination unit). Next, if the steering lever 215 is in an inoperative state (YES in step S130), the controller 210 proceeds to step S140. On the other hand, if the steering lever 215 is not in an inoperative state (NO in step S130), the controller 210 proceeds to step S180.

[0063] In step S140, controller 210 determines whether accelerator pedal 230 is in a non-operated state based on the state information of accelerator pedal 230 (operating as a pedal operation state determination unit). Next, if accelerator pedal 230 is in a non-operated state (YES in step S140), controller 210 proceeds to step S150. On the other hand, if accelerator pedal 230 is not in a non-operated state (NO in step S140), controller 210 proceeds to step S180.

[0064] In step S150, the controller 210 determines whether the outputs of the steering electromagnetic control valves 218, 219 are at minimum output or not based on information about the control currents (outputs) of the left and right steering electromagnetic control valves 218, 219 (operating as a steering proportional valve output determination unit). Next, if the outputs of the steering electromagnetic control valves 218, 219 are at minimum output (YES in step S150), the controller 210 proceeds to step S170. On the other hand, if the outputs of the steering electromagnetic control valves 218, 219 are not at minimum output (NO in step S150), the controller 210 proceeds to step S180.

[0065] In step S160, the controller 210 determines whether the vehicle body bending angle θ is equal to or less than the third threshold value θ1 (operating as a vehicle body bending angle determination unit). Next, if the vehicle body bending angle θ is equal to or less than the third threshold value θ1 (YES in step S160), the controller 210 proceeds to step S170. On the other hand, if the vehicle body bending angle θ is not equal to or less than the third threshold value θ1 (NO in step S160), the controller 210 proceeds to step S180.

[0066] The order of steps S90 to S160 is not limited to the above order, and steps may be performed in other orders or in parallel.

[0067] In step S170, the controller 210 turns on the switching flag.

[0068] In step S180, the controller 210 turns off the switching flag.

[0069] If the switching flag is not turned ON in step S170, step S70 or step S71 is not executed, and the position control mode and the speed control mode are not switched.

[0070] As described above, when the switching flag is ON, it is possible to prevent switching between the position control mode and the speed control mode at a timing not intended by the operator.

[0071] For example, in the speed control mode, when the steering lever 215 is in the neutral position and the body bending angle θ is not straight, if the mode is switched to the position control mode, the body may return to the neutral position without the operator's intention.

[0072] Furthermore, in the position control mode, when the steering lever 215 is tilted (the amount of operation is not the maximum amount of tilting) and the vehicle body is at a vehicle body bending angle θ corresponding to the amount of operation, if the mode is switched to the speed control mode, the vehicle body may turn in the direction in which the steering lever 215 is tilted unintentionally by the operator.

[0073] If the above cases are judged as switch flags and the vehicle body bending angle θ is judged as a switchable condition, it is possible to prevent the vehicle body from moving unintentionally even when switching between the position control mode and the speed control mode, thereby ensuring better operability and safety.

[0074] (Second embodiment) Next, a second embodiment of the present invention will be described. The second embodiment is characterized in that the time since it is determined that the switchable condition is met (condition met time) is further used as a switchable condition.

[0075] Specifically, the condition fulfillment time is measured by a timer implemented in the controller 210. When it is determined that the switchable condition is fulfilled, the timer starts measuring the condition fulfillment time, and measures the time during which the switchable condition is fulfilled (operates as a time measurement unit).

[0076] Next, the controller 210 determines whether the condition fulfillment time has elapsed a predetermined time (operating as a time elapse determination unit). The predetermined time is a time that is set in advance. For example, the predetermined time is preferably a time that does not keep the operator waiting too long and that can be said to be a time that the switchable condition, such as the vehicle being sufficiently stopped, is fulfilled for a certain period of time. Specifically, the predetermined time is about 1 to 10 seconds. However, the predetermined time differs depending on the type of the changeover switch 211.

[0077] If the condition is satisfied for a predetermined time, the controller 210 switches to the position control mode or the speed control mode as in steps S60 to S71. By adding a time condition in this way, switching is not performed even if the operator unintentionally performs a switching operation (for example, if a button is pressed by mistake), thereby ensuring better operability and safety.

[0078] For example, even if an erroneous switching operation such as repeatedly pressing the changeover switch 211 occurs, it is possible to prevent the process of switching to the position control mode or the speed control mode from being frequently executed.

[0079] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the gist of the present invention. The present invention covers all technical matters included in the technical ideas described in the claims. The above-described embodiments are preferred examples, but a person skilled in the art can realize various alternatives, modifications, variations, or improvements from the contents disclosed in this specification, and these are included in the technical scope described in the appended claims.

[0080] (Relationship between the present invention and the embodiments) In this embodiment, the "front device operation determination unit," "steering lever operation determination unit," "pedal operation state determination unit," "parking brake operation determination unit," "motor rotation speed determination unit," "vehicle speed determination unit," "vehicle body bending angle determination unit," "steering proportional valve output determination unit," "time measurement unit," and "time elapsed determination unit" of the present invention are realized by the functions of controller 210. [Explanation of symbols]

[0081] 1: Wheel loader 2: Lift arm 3: Bucket 4: Front wheel 5: Previous frame 6: Driver's cab 8: Rear wheel 9: Rear frame 11: Lift arm cylinder 12: Bucket cylinder 13: Bell crank 14: Work equipment (front device) 15: Center pin 30: Engine (prime mover) 60: Monitor 201: Parking brake operation position detector 202: Pump pressure sensor 203: Vehicle speed detector 204: Steering wheel operation amount detector 205: Steering lever operation amount detector 210: Controller 211: Changeover switch (changeover operation reception part) 212: Steering wheel 213: Operating lever 214: Control lever 215: Steering lever 217: Pump (hydraulic pump) 218: Right steering electromagnetic control valve (steering proportional valve) 219: Left steering solenoid control valve (steering proportional valve) 220: Steering directional control valve 223: Directional control valve for lift arm 224: Bucket directional control valve 230: Accelerator pedal 231: Parking brake

Claims

1. A bendable body; a running wheel supported on the vehicle body; an actuator that changes the steering angle of the running wheels to the left or right from a predetermined neutral angle; a steering lever for operating the actuator; a controller that switches the control mode of the steering lever between a speed control mode that controls the actuator to change the steering angle of the running wheels at a speed corresponding to the amount of operation of the steering lever, and a position control mode that controls the actuator to change the steering angle of the running wheels according to the amount of operation of the steering lever, The controller when it is determined that a predetermined switching condition is met, a bending angle of the vehicle body is calculated based on the operation of the steering lever, and when the bending angle of the vehicle body is less than a predetermined threshold value, the control mode is switched from one of the speed control mode and the position control mode to the other. A work vehicle characterized by:

2. The work vehicle according to claim 1, when the bending angle of the vehicle body is equal to or greater than the predetermined threshold, the controller controls the actuator so that the bending angle of the vehicle body becomes less than the predetermined threshold, and then switches the control mode from one of the speed control mode and the position control mode to the other. A work vehicle characterized by:

3. The work vehicle according to claim 2, a prime mover mounted on the vehicle body; a hydraulic pump driven by the prime mover; a front device provided at a front portion of the vehicle body and driven by pressure oil supplied from the hydraulic pump; a steering proportional valve that operates in response to an operation amount of the steering lever and controls a flow rate of hydraulic oil supplied to the actuator; an accelerator pedal for adjusting the rotation speed of the prime mover; a parking brake that stops the vehicle body, the actuator is driven by pressure oil supplied from the hydraulic pump, The controller a front device operation determination unit that determines the operation state of the front device; a steering lever operation determination unit that determines the operation state of the steering lever; a pedal operation state determination unit that determines the operation state of the accelerator pedal; a parking brake operation determination unit that determines an operation state of the parking brake; a prime mover rotation speed determination unit that determines the rotation speed of the prime mover; a vehicle speed determination unit that determines a vehicle speed of the vehicle body; a vehicle body bending angle determination unit that determines a bending angle of the vehicle body; a steering proportional valve output determination unit that determines an output of the steering proportional valve, The controller The predetermined switching condition is determined to be met when the front device is in an inoperative state, the steering lever is in an inoperative state, the accelerator pedal is not operated, the parking brake is in an activated state, the rotation speed of the prime mover is equal to or less than a first threshold value, the vehicle speed is equal to or less than a second threshold value, the bending angle of the vehicle body is equal to or less than a third threshold value, and the output of the steering proportional valve is at a minimum output. A work vehicle characterized by:

4. The work vehicle according to claim 3, The controller a time measurement unit that measures the time during which the predetermined switching condition is satisfied; a time lapse determination unit that determines whether the time has passed a predetermined time, when the controller determines that the time has elapsed the predetermined time, the controller switches the control mode from one of the speed control mode and the position control mode to the other. A work vehicle characterized by:

5. The work vehicle according to claim 4, a switching operation receiving unit that receives an operator's operation to switch between the speed control mode and the position control mode, The controller when the switching operation is input from the switching operation receiving unit, the control mode is switched from one of the speed control mode and the position control mode to the other. A work vehicle characterized by:

Images