Wheel type work vehicle

Abstract

To provide a wheel type work vehicle that is able to immediately actuate steering by means of a steering operation lever when runaway occurs while preventing occurrence of steering operation unintended by an operator due to erroneous operation.SOLUTION: A wheel loader including a steering lever 34 and a setting switch 36 including a setting position for validating / invalidating an operation of the steering lever, has a controller 5 that controls actuation of steering cylinders 41, 42. When a vehicle body is in a traveling state, the controller 5 actuates the steering cylinders 41, 42 according to the operation of the steering lever 34 regardless of the setting position of the setting switch 36.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to a wheel-type work vehicle provided with a plurality of wheels.

Background Art

[0002] In wheel-type work vehicles such as wheel loaders, since work is performed while traveling on the road surface, frequent steering operations are required to change the traveling direction of the vehicle. As types of steering operation devices, in addition to a general wheel-type steering operation device arranged in front of the driver's seat, in recent years, for the purpose of reducing the operator's fatigue, a lever-type steering operation device arranged near the armrest has been developed so that the operator can perform steering operations in a comfortable posture with elbows on the armrest. Depending on the specifications of the work vehicle, the cab may be provided with both a wheel-type and a lever-type device, or may be provided with either one of them.

[0003] The lever-type steering operation device is easier to operate than the wheel-type steering operation device. However, on the other hand, the operator's clothes or equipment may get caught on the operation lever, or the operator may accidentally touch the operation lever, causing it to easily tilt, and there is a possibility that the steering may operate at an unexpected timing for the operator. Therefore, some work vehicles are equipped with a function to switch between enabling and disabling the operation lever in order to prevent the steering from operating due to an accidental operation of the operation lever.

[0004] For example, in Patent Document 1, when a steering lever switch for switching between the operation and non-operation of a steering operation lever is in the operating position, if it is detected by a seating sensor that the operator is not seated in the driver's seat, the vehicle speed is below a predetermined speed, and the travel lever is in the neutral position and the brake pedal is not depressed, a work vehicle is disclosed that includes a control unit that makes the steering operation by the steering operation lever impossible.

Prior Art Documents

[0005] [Patent Document 1] Japanese Patent Publication No. 2019-157543 [Overview of the project] [Problems that the invention aims to solve]

[0006] Movement of work vehicles includes runaway, which is movement unintended by the operator. Runaway can occur, for example, when a work vehicle is stopped on a steep slope with the parking brake applied and is hit by another vehicle, causing it to start moving. Alternatively, even on a gentle slope, the operator may forget to apply the parking brake, causing a stopped work vehicle to start moving. In such cases, when a work vehicle runs away, the operator must immediately apply the steering.

[0007] However, in the work vehicle described in Patent Document 1, steering operation is possible only when the steering lever switch is in the activated position, the seating sensor detects that an operator is seated in the driver's seat, the vehicle speed is faster than a predetermined speed, the travel lever is in the forward or reverse position, and the brake pedal is pressed. Therefore, it is difficult to immediately activate the steering lever when the work vehicle runs away. In particular, if the vehicle runs away when the steering lever switch is in the non-activated position, the steering lever becomes completely inoperable, and the operator cannot operate the steering lever.

[0008] Therefore, the object of the present invention is to provide a wheeled work vehicle that can suppress unintended steering movements caused by operator error, while also allowing immediate steering activation via a steering lever in the event of runaway movement. [Means for solving the problem]

[0009] To achieve the above objective, the present invention provides a vehicle body provided with a plurality of wheels, a driver's cab provided on the vehicle body, a steering cylinder for steering the plurality of wheels, a hydraulic pump for supplying hydraulic fluid to the steering cylinder, a steering control valve for controlling the flow of hydraulic fluid discharged from the hydraulic pump and supplied to the steering cylinder, a pilot pump for supplying pilot pressure oil to the steering control valve, a steering lever provided in the driver's cab for performing steering operations, a setting switch including an activation setting position that enables the operation of the steering lever and operates the steering cylinder in accordance with the operation of the steering lever, and a deactivation setting position that disables the operation of the steering lever and deactivates the steering cylinder, and an electromagnetic control for controlling the pilot pressure oil discharged from the pilot pump and acting on the steering control valve. A wheeled work vehicle comprising a valve, a controller for controlling the electromagnetic control valve, and a vehicle speed sensor for detecting the vehicle speed of the vehicle, wherein the controller determines whether the vehicle is stopped or in motion based on the vehicle speed detected by the vehicle speed sensor, and if it is determined that the vehicle is stopped and the setting switch is set to the activation setting position, it outputs an activation signal to the electromagnetic control valve to activate the steering cylinder in response to the operation of the steering lever, if it is determined that the vehicle is stopped and the setting switch is set to the deactivation setting position, it outputs a deactivation signal to the electromagnetic control valve to deactivate the operation of the steering cylinder in response to the operation of the steering lever, and if it is determined that the vehicle is in motion, it outputs the activation signal to the electromagnetic control valve. [Effects of the Invention]

[0010] According to the present invention, while preventing unintended steering movements caused by operator error, if runaway occurs, steering can be immediately activated by the steering lever. Problems, configurations, and effects other than those described above will be clarified by the following description of embodiments. [Brief explanation of the drawing]

[0011] [Figure 1] This is an external side view showing one example of the configuration of a wheel loader according to an embodiment of the present invention. [Figure 2] This is a top view showing a wheel loader with the steering wheel turned to the left. [Figure 3] This is a perspective view of the driver's cab, seen from the left rear. [Figure 4] This is a perspective view of the driver's cab, seen from the front right. [Figure 5] This is a system configuration diagram showing one example of a steering drive system configuration. [Figure 6] This is a functional block diagram showing the functions of the controller. [Figure 7] This flowchart shows the flow of processing performed by the controller. [Figure 8] This is a state transition diagram showing the transitions in the state of the steering drive system. [Modes for carrying out the invention]

[0012] Hereinafter, as one embodiment of the wheeled work vehicle according to the present invention, a wheel loader that performs cargo handling operations such as excavating soil, minerals, etc., and loading them onto a dump truck or hopper will be described.

[0013] (Overall configuration of wheel loader 1) First, the overall configuration of the wheel loader 1 according to an embodiment of the present invention will be described with reference to Figures 1 and 2.

[0014] FIG. 1 is an external side view showing a configuration example of a wheel loader 1 according to an embodiment of the present invention. FIG. 2 is a top view showing the wheel loader 1 in a state where the steering is turned to the left direction.

[0015] The wheel loader 1 is an articulated work vehicle that is steered by the body being bent in the vicinity of the center. Specifically, a front frame 1A that is the front part of the body and a rear frame 1B that is the rear part of the body are connected to be rotatable in the left - right direction by a center joint 10. When the operator performs a steering operation, a pair of left - right steering cylinders 41, 42 operate, and the front frame 1A bends in the left - right direction with respect to the rear frame 1B.

[0016] In the following description, among the left - right direction of the body, the left - hand side of the operator facing the forward direction is defined as the "left direction", and the right - hand side of the operator is defined as the "right direction". FIG. 2 shows the wheel loader 1 in a state where the steering is turned to the left direction and it is turning left. The specific configuration of the steering operation system will be described later.

[0017] Four wheels 11 are provided on the body. Two wheels 11 are provided as front wheels 11A on both the left and right sides of the front frame 1A, and the remaining two wheels 11 are provided as rear wheels 11B on both the left and right sides of the rear frame 1B, respectively. In FIG. 1, only the front wheel 11A and the rear wheel 11B provided on the left side among the four wheels 11 are shown. Note that there is no particular limitation on the specific number of the plurality of wheels 11 provided on the body.

[0018] At the front part of the front frame 1A, a working device 2 for carrying out loading and unloading operations is attached. The working device 2 includes a lift arm 21 attached to the front frame 1A so as to be rotatable in the vertical direction, two lift arm cylinders 22L and 22R for driving the lift arm 21, a bucket 23 attached to the tip of the lift arm 21 so as to be rotatable in the vertical direction, a bucket cylinder 24 for driving the bucket 23, and a bell crank 25 rotatably connected to the lift arm 21 and constituting a link mechanism between the bucket 23 and the bucket cylinder 24.

[0019] The lift arm 21 rotates upward with respect to the front frame 1A when the rods 220 of the two lift arm cylinders 22L and 22R extend, and rotates downward with respect to the front frame 1A when the rods 220 of the two lift arm cylinders 22L and 22R contract. As shown in FIG. 2, the two lift arm cylinders 22L and 22R are arranged side by side at a predetermined interval in the left - right direction of the vehicle body. In FIG. 1, since both of the two lift arm cylinders 22L and 22R are arranged at positions hidden by the front wheel 11A provided on the left side, they are not shown.

[0020] The bucket 23 rotates upward with respect to the lift arm 21 when the rod 240 of the bucket cylinder 24 extends (tilt operation), and rotates downward with respect to the lift arm 21 when the rod 240 of the bucket cylinder 24 contracts (dump operation). Thereby, the bucket 23 can scoop up the work object and discharge (dump soil) it to the loading destination. The bucket 23 can be replaced with various attachments such as a blade, for example. The wheel loader 1 can perform various operations such as snow removal work and earth - pushing work in addition to the loading and unloading work using the bucket 23.

[0021] The rear frame 1B is provided with a driver's cab 12 where the operator sits, a machine room 13 that houses the equipment necessary for driving the wheel loader 1, and a counterweight 14 that maintains balance with the work device 2 to prevent the vehicle body from tilting. In the rear frame 1B, the driver's cab 12 is located at the front, the counterweight 14 is located at the rear, and the machine room 13 is located between the driver's cab 12 and the counterweight 14.

[0022] In this embodiment, the wheel loader 1's movement is controlled by a torque converter type drive system. The drive system comprises an engine 131, a torque converter 132 connected to the output shaft of the engine 131, and a transmission 133 connected to the output shaft of the torque converter 132.

[0023] The driving force generated by the rotation of the engine 131 is shifted by the torque converter 132 and the transmission 133, and then transmitted to the four wheels 11 via the propeller shaft 134 and the axle 135 (see Figure 2), thereby causing the wheel loader 1 to move. In Figure 1, the engine 131, torque converter 132, transmission 133, and propeller shaft 134 are shown by dashed lines.

[0024] (Configuration of the driver's cab 12) Next, the configuration of the driver's cab 12 will be explained with reference to Figures 3 and 4.

[0025] Figure 3 is a perspective view of the interior of the driver's cab 12, seen from the left rear. Figure 4 is a perspective view of the interior of the driver's cab 12, seen from the right front.

[0026] In the center of the driver's cab 12 is a driver's seat 31 where the operator sits. In front of the driver's seat 31 is a console 32 equipped with a monitor that displays the vehicle's running status and the operating status of the work device 2, as well as various control switches.

[0027] To the right of the driver's seat 31, two work control levers 33 are provided side by side in the left-right direction as operating devices for the work device 2. Each of the two work control levers 33 is a lever that can be tilted in the front-back direction.

[0028] One of the two operating levers 33 is used to operate the lift arm 21. For example, when the operator pushes one of the operating levers 33 forward, the lift arm 21 rotates downward relative to the front frame 1A, and when the operator pushes it backward (towards them), the lift arm 21 rotates upward relative to the front frame 1A.

[0029] One of the two operating levers 33 corresponds to the lever that operates the bucket 23. For example, when the operator pushes the other operating lever 33 forward, the bucket 23 performs a dumping operation, and when the operator pushes it backward (towards them), the bucket 23 performs a tilting operation.

[0030] Furthermore, the operating device for operating the work device 2 does not necessarily have to consist of two operating levers 33. For example, both the lift arm 21 and the bucket 23 may be operated using a single operating lever 33 that can be tilted in two directions: forward, backward, left, and right.

[0031] A steering lever 34, which serves as a steering control device for steering, is provided to the left of the driver's seat 31. In this embodiment, the steering lever 34 is an electrically operated lever that can be tilted left and right.

[0032] For example, when the operator pushes the steering lever 34 to the left, the wheel loader 1 turns left according to the steering signal output from the steering lever 34 (left turn). On the other hand, when the operator pushes the steering lever 34 to the right, the wheel loader 1 turns right according to the steering signal output from the steering lever 34 (right turn). Note that the steering lever 34 does not necessarily have to be an electric lever; it may be a mechanical lever.

[0033] A support base 35 is installed behind the steering lever 34 to support the operator's left elbow. The operator can operate the steering lever 34 while resting their left elbow on this support base 35.

[0034] As shown in Figure 4, a setting switch 36 for enabling or disabling the operation of the steering lever 34 is mounted on the front lower side of the support base 35. In this embodiment, the setting switch 36 includes an enable setting position for enabling the operation of the steering lever 34, a disable setting position for disabling the operation of the steering lever 34, and a holding position for holding the enable or disable setting.

[0035] For example, when the operator pushes the setting switch 36 forward, the setting switch 36 is set to the enabled position, and the wheel loader 1's steering operates according to the operating direction and amount (tilt direction and amount) of the steering lever 34. On the other hand, when the operator pushes the setting switch 36 backward (towards the operator), the setting switch 36 is set to the deactivated position, and the steering becomes inoperable.

[0036] In wheel loader 1, a lever-type steering control device (steering lever 34) is used as the steering control device. Therefore, if the operator's clothing or equipment gets caught on the steering lever 34, or if the operator unconsciously touches the steering lever 34, it can easily tilt, making it more prone to misoperation compared to a wheel-type steering control device.

[0037] Therefore, the wheel loader 1 is equipped with a setting switch 36 that enables or disables the operation of the steering lever 34, thereby preventing unintended steering movements caused by erroneous operation of the steering lever 34.

[0038] Furthermore, when the setting switch 36 is in a neutral position and not pressed forward or backward, it enters a hold position, and the setting immediately preceding the hold position is retained. Note that the setting switch 36 only needs to include at least an enable setting position and a disable setting position, and does not necessarily need to include a hold position.

[0039] The work lever 33, steering lever 34, and setting switch 36 do not necessarily have to be located in the positions shown in Figures 3 and 4. Their placement may be changed according to the specifications of the driver's cab 12, as long as they are within the range of operation for an operator seated in the driver's seat 31.

[0040] (Configuration of steering drive unit 4) Next, the configuration of the steering drive unit 4 that operates the steering of the wheel loader 1 will be explained with reference to Figure 5.

[0041] Figure 5 is a system configuration diagram showing one example of the configuration of the steering drive unit 4.

[0042] The steering drive unit 4 comprises a pair of steering cylinders 41, 42 for steering the four wheels 11 (a pair of front wheels 11A and a pair of rear wheels 11B), a hydraulic pump 44 driven by the engine 131 to supply hydraulic fluid to each of the pair of steering cylinders 41, 42, a steering control valve 45 for controlling the flow (direction and flow rate) of hydraulic fluid discharged from the hydraulic pump 44 and supplied to each of the pair of steering cylinders 41, 42, a pilot pump 46 driven by the engine 131 to supply pilot pressure oil to the steering control valve 45, a pair of electromagnetic control valves 47, 48 for controlling the pilot pressure oil discharged from the pilot pump 46 and acting on the steering control valve 45, and a hydraulic fluid tank 49 for storing hydraulic fluid.

[0043] A pair of steering cylinders 41 and 42 are arranged side by side in the left-right direction of the vehicle body and connect the front frame 1A and the rear frame 1B. Specifically, the tips of the rods 41A and 42A of the pair of steering cylinders 41 and 42 are attached to the front frame 1A, and the ends on the bottom chamber 41B and 42B side are attached to the rear frame 1B. In this embodiment, of the pair of steering cylinders 41 and 42, the one located on the left is referred to as the "left steering cylinder 41," and the one located on the right is referred to as the "right steering cylinder 42."

[0044] When the rod 41A of the left steering cylinder 41 retracts and the rod 42A of the right steering cylinder 42 extends, the wheel loader 1 steers to the left (turns left), as shown in Figure 5, and when the rod 41A of the left steering cylinder 41 extends and the rod 42A of the right steering cylinder 42 retracts, it steers to the right (turns right).

[0045] The steering control valve 45 has a first switching position 45A for turning the wheel loader 1 to the left, a second switching position 45B for turning the wheel loader 1 to the right, and a neutral position 45N for moving the wheel loader 1 straight. These first switching position 45A, second switching position 45B, and neutral position 45N are switched between each other by the movement of a spool provided inside the steering control valve 45. The first switching position 45A, second switching position 45B, and neutral position 45N are aligned along the direction of movement of the spool such that the neutral position 45N is positioned between the first switching position 45A and the second switching position 45B.

[0046] In the first switching position 45A, the discharge side of the hydraulic pump 44 is connected to the rod chamber 41C of the left steering cylinder 41 and the bottom chamber 42B of the right steering cylinder 42, and the bottom chamber 41B of the left steering cylinder 41 and the rod chamber 42C of the right steering cylinder 42 are connected to the hydraulic fluid tank 49.

[0047] Therefore, when the steering control valve 45 is switched to the first switching position 45A, the hydraulic fluid discharged from the hydraulic pump 44 flows into the rod chamber 41C of the left steering cylinder 41 and the bottom chamber 42B of the right steering cylinder 42, respectively. As a result, the rod 41A of the left steering cylinder 41 contracts and the rod 42A of the right steering cylinder 42 extends, causing the wheel loader 1 to turn left.

[0048] In the second switching position 45B, the discharge side of the hydraulic pump 44 is connected to the bottom chamber 41B of the left steering cylinder 41 and the rod chamber 42C of the right steering cylinder 42, and the rod chamber 41C of the left steering cylinder 41 and the bottom chamber 42B of the right steering cylinder 42 are connected to the hydraulic fluid tank 49.

[0049] Therefore, when the steering control valve 45 switches to the second switching position 45B, the hydraulic fluid discharged from the hydraulic pump 44 flows into the bottom chamber 41B of the left steering cylinder 41 and the rod chamber 42C of the right steering cylinder 42, respectively. As a result, the rod 41A of the left steering cylinder 41 extends and the rod 42A of the right steering cylinder 42 retracts, causing the wheel loader 1 to turn right.

[0050] In the neutral position 45N, the discharge side of the hydraulic pump 44 is connected to the hydraulic fluid tank 49. Therefore, when the steering control valve 45 is switched to the neutral position 45N, hydraulic fluid is not supplied to the left steering cylinder 41 and the right steering cylinder 42, so the wheel loader 1 does not steer and moves in a straight line.

[0051] The steering control valve 45 switches to the first switching position 45A when the pilot pressure Pi1 acting on the first pilot oil chamber 451 located on the first switching position 45A side is greater than the pilot pressure Pi2 acting on the second pilot oil chamber 452 located on the second switching position 45B side (Pi1 > Pi2). On the other hand, it switches to the second switching position 45B when the pilot pressure Pi2 acting on the second pilot oil chamber 452 is greater than the pilot pressure Pi1 acting on the first pilot oil chamber 451 (Pi2 > Pi1).

[0052] Furthermore, the steering control valve 45 switches to the neutral position 45N when the pilot pressure Pi1 acting on the first pilot oil chamber 451 and the pilot pressure Pi2 acting on the second pilot oil chamber 452 are the same pressure (Pi1=Pi2) or zero (Pi1=Pi2=0).

[0053] Furthermore, the steering of the wheel loader 1 will operate even if the steering control valve 45 is not fully switched to the first switching position 45A or the second switching position 45B, as soon as the internal spool of the steering control valve 45 begins to move toward the first switching position 45A or the second switching position 45B, and the hydraulic fluid discharged from the hydraulic pump 44 begins to be supplied to the pair of steering cylinders 41 and 42.

[0054] The pilot pressure Pi acting on the first pilot oil chamber 451 and the pilot pressure Pi2 acting on the second pilot oil chamber 452 are controlled by a pair of electromagnetic control valves 47 and 48. In this embodiment, of the pair of electromagnetic control valves 47 and 48, the one that controls the pilot pressure Pi acting on the first pilot oil chamber 451 is referred to as the "first electromagnetic control valve 47," and the one that controls the pilot pressure Pi2 acting on the second pilot oil chamber 452 is referred to as the "second electromagnetic control valve 48." The first electromagnetic control valve 47 and the second electromagnetic control valve 48 are controlled according to command signals output from the controller 5.

[0055] The controller 5 is electrically connected to the steering lever 34, the setting switch 36, the vehicle speed sensor 60 mounted on the transmission 133 (shown by a dashed line in Figures 1 and 5) for detecting vehicle speed, the first electromagnetic control valve 47, and the second electromagnetic control valve 48.

[0056] The controller 5 receives the operation signal output from the steering lever 34, the setting signal output from the setting switch 36, and the vehicle speed signal output from the vehicle speed sensor 60.

[0057] The operation signal output from the steering lever 34 is a signal based on the operator's operation and includes data related to the direction and amount of operation (tilt direction and amount) of the steering lever 34. If the steering lever 34 is a mechanical lever, the controller 5 receives data output from the operation state sensor that detects the operating state of the steering lever 34, i.e., the direction and amount of operation of the steering lever 34.

[0058] The setting signal output from the setting switch 36 includes an activation setting signal for an activation setting position (shown as "ON" in Figure 5) that enables the operation of the steering lever 34 and operates the pair of steering cylinders 41 and 42 in response to the operation of the steering lever 34, and a deactivation setting signal for a deactivation setting position (shown as "LOCK" in Figure 5) that disables the operation of the steering lever 34 and deactivates the pair of steering cylinders 41 and 42.

[0059] The vehicle speed signal output from the vehicle speed sensor 60 is a data signal related to the vehicle speed detected by the vehicle speed sensor 60. The vehicle speed sensor 60 may also be replaced with, for example, a rotational speed sensor that detects the rotational speed of the propeller shaft.

[0060] Based on these input signals, namely the operation signal from the steering lever 34, the setting signal from the setting switch 36, and the vehicle speed signal from the vehicle speed sensor 60, the controller 5 generates command signals for the first electromagnetic control valve 47 and the second electromagnetic control valve 48.

[0061] (Controller 5 configuration) Next, the configuration of controller 5 will be explained with reference to Figure 6.

[0062] Figure 6 is a functional block diagram showing the functions of the controller 5.

[0063] Controller 5 is configured with a CPU, RAM, ROM, HDD, input interface, and output interface all connected to each other via a bus. Various operating devices such as the steering lever 34 and setting switch 36, as well as sensors such as the vehicle speed sensor 60, are connected to the input interface, while the first electromagnetic control valve 47 and the second electromagnetic control valve 48 are connected to the output interface.

[0064] In this hardware configuration, the CPU reads the control program (software) stored in a recording medium such as ROM, HDD, or optical disc, expands it onto RAM, and executes the expanded control program. The control program and hardware then work together to realize the functions of the controller 5.

[0065] In this embodiment, the controller 5 is described as a computer composed of a combination of software and hardware. However, it is not limited to this configuration. For example, an integrated circuit that implements the functions of the control program executed on the wheel loader 1 may be used as an example of another computer configuration.

[0066] The controller 5 includes a data acquisition unit 51, a determination unit 52, an elapsed time measurement unit 53, a command signal output unit 54, and a storage unit 55.

[0067] The data acquisition unit 51 acquires the operation signal output from the steering lever 34, the setting signal output from the setting switch 36, and data related to the vehicle speed (vehicle speed signal) detected by the vehicle speed sensor 60.

[0068] The determination unit 52 includes a setting determination unit 52A, a vehicle body state determination unit 52B, and a lever position determination unit 52C.

[0069] The setting determination unit 52A determines whether the setting position of the setting switch 36 is the enable setting position or the disable setting position, based on the setting signal acquired by the data acquisition unit 51. In other words, the setting determination unit 52A determines whether the setting signal acquired by the data acquisition unit 51 is an enable setting signal or a disable setting signal.

[0070] The vehicle state determination unit 52B determines whether the vehicle is in a running state or not based on the vehicle speed acquired by the data acquisition unit 51. The vehicle state determination unit 52B does not determine the vehicle is stopped only when the vehicle speed detected by the vehicle speed sensor 60 matches 0 (zero); rather, it determines whether the vehicle is stopped within a range that includes the detection error of the vehicle speed sensor 60. The threshold values ​​for determining the vehicle's running state (or stopped state) are stored in the storage unit 55 beforehand.

[0071] The lever position determination unit 52C determines the operating state (tilt direction and amount) of the steering lever 34, that is, to what position the operator tilted the steering lever 34, based on the operation signal acquired by the data acquisition unit 51. In particular, the lever position determination unit 52C determines whether the steering lever 34 is in the neutral position or has been operated to the maximum tilt position.

[0072] Here, the "neutral position" of the steering lever 34 is the position where the supply of hydraulic fluid from the hydraulic pump 44 to the pair of steering cylinders 41 and 42 is stopped. The "maximum tilt position" of the steering lever 34 includes the "maximum left tilt position" and the "maximum right tilt position," and is the position where the amount of hydraulic fluid supplied from the hydraulic pump 44 to the pair of steering cylinders 41 and 42 is set to a preset maximum amount.

[0073] More specifically, the "maximum left tilt position" is the position where the amount of hydraulic fluid supplied from the hydraulic pump 44 to the rod chamber 41C of the left steering cylinder 41 and the bottom chamber 42B of the right steering cylinder 42 is set to the preset maximum amount. In other words, when the operator wants to turn the steering wheel to the maximum left, they operate the steering lever 34 to the maximum left tilt position.

[0074] Furthermore, the "maximum right tilt position" is the position where the amount of hydraulic fluid supplied from the hydraulic pump 44 to the bottom chamber 41B of the left steering cylinder 41 and the rod chamber 42C of the right steering cylinder 42 is set to the preset maximum amount. In other words, when the operator wants to turn the steering wheel to the maximum extent to the right, they operate the steering lever 34 to the maximum right tilt position.

[0075] Furthermore, the "maximum tilt position" does not necessarily have to be the position that allows for the maximum amount of hydraulic fluid to be supplied from the hydraulic pump 44 to the pair of steering cylinders 41 and 42. It may be a position that is arbitrarily set as the maximum amount of hydraulic fluid supplied from the hydraulic pump 44 to the pair of steering cylinders 41 and 42 (a preset maximum amount).

[0076] The elapsed time measurement unit 53 measures the time T that has elapsed since the vehicle body state determination unit 52B determined that the vehicle body has stopped, and determines whether the measured time T has exceeded a predetermined time Tth. This "predetermined time Tth" is an arbitrary time (for example, less than 10 seconds) that is stored in advance in the storage unit 55, and is set to a time that takes into account the possibility that the vehicle body may start moving again after the vehicle body state determination unit 52B has determined that the vehicle body is stopped.

[0077] The command signal output unit 54 outputs either an activation signal to the first electromagnetic control valve 47 and the second electromagnetic control valve 48, respectively, in accordance with the determination result in the determination unit 52, which activates the pair of steering cylinders 41 and 42 in response to the operation of the steering lever 34, or a deactivation signal to the first electromagnetic control valve 47 and the second electromagnetic control valve 48, which deactivates the pair of steering cylinders 41 and 42 in response to the operation of the steering lever 34.

[0078] (Processing within Controller 5) Next, we will explain the specific processing flow executed by controller 5 with reference to Figure 7.

[0079] Figure 7 is a flowchart showing the processing flow executed by controller 5.

[0080] In the controller 5, first, the setting determination unit 52A determines whether the setting position of the setting switch 36 is the enable setting position or the disable setting position based on the setting signal acquired by the data acquisition unit 51 (step S501). In other words, in step S501, it is determined whether the setting switch 36 is set to the enable setting or the disable setting.

[0081] If it is determined in step S501 that the setting position of the setting switch 36 is the disabled setting position (step S501 / disabled), the setting determination unit 52A then determines whether or not the setting position of the setting switch 36 has been switched to the enabled setting position, that is, whether or not there has been no operation to enable the setting switch 36 and it remains in the disabled setting position (step S502).

[0082] If it is determined in step S502 that the setting switch 36 has not been switched to the enable setting position (it remains in the disable setting position) (step S502 / YES), the vehicle state determination unit 52B determines whether the vehicle is moving or not, that is, whether it is in a driving state, based on the vehicle speed signal acquired by the data acquisition unit 51 (step S503).

[0083] If it is determined in step S503 that the vehicle body is moving (step S503 / YES), the lever position determination unit 52C determines whether the steering lever 34 is in the neutral position or has been operated to the maximum tilt position (step S504).

[0084] On the other hand, if it is determined in step S502 that the vehicle body has not moved, i.e., the vehicle body is in a stationary state (step S503 / NO), the process does not proceed to step S504 until the vehicle body starts moving (becomes in a driving state).

[0085] If, in step S504, it is determined that the steering lever 34 is in the neutral position or has been operated to the maximum tilt position (step S504 / YES), the command signal output unit 54 outputs an activation signal to the first electromagnetic control valve 47 and the second electromagnetic control valve 48, respectively (step S505). In other words, when the steering lever 34 is in the neutral position or has been operated to the maximum tilt position, the controller 5 outputs an activation signal to the first electromagnetic control valve 47 and the second electromagnetic control valve 48, respectively, even if the setting switch 36 is in the deactivation setting position.

[0086] On the other hand, if it is determined in step S504 that the steering lever 34 is not in the neutral position and has not been operated to the maximum tilt position (step S504 / NO), the process will not proceed to step S505 until the steering lever 34 returns to the neutral position or is operated to the maximum tilt position.

[0087] Next, the setting determination unit 52A determines, based on the setting signal acquired by the data acquisition unit 51, whether or not the setting switch 36 has been switched to the enable setting position, that is, whether or not an enable setting operation has been performed on the setting switch 36 (step S506).

[0088] If it is determined in step S506 that the setting switch 36 has been switched to the enable setting position (step S506 / YES), the command signal output unit 54 continues to output enable signals to the first electromagnetic control valve 47 and the second electromagnetic control valve 48, respectively (step S507).

[0089] Next, the setting determination unit 52A determines, based on the setting signal acquired by the data acquisition unit 51, whether the setting position of the setting switch 36 has been switched to the disabled setting position, that is, whether a disabled setting operation has been performed on the setting switch 36 (step S508).

[0090] When it is determined in step S508 that the setting position of the setting switch 36 has been switched to the invalidation setting position (step S508 / YES), the vehicle body state determination unit 52B determines whether or not the vehicle body has stopped based on the vehicle speed signal acquired by the data acquisition unit 51 (step S509).

[0091] On the other hand, when it is determined in step S508 that the setting position of the setting switch 36 has not been switched to the invalidation setting position, that is, it remains in the validation setting position (step S508 / NO), the process returns to step S507, and the command signal output unit 54 continues to output the validation signal to the first electromagnetic control valve 47 and the second electromagnetic control valve 48.

[0092] Next, when it is determined in step S509 that the vehicle body has stopped (step S509 / YES), the elapsed time measurement unit 53 measures the time T since the stop of the vehicle body was determined, and determines whether or not the measured time T has elapsed the predetermined time Tth (step S510).

[0093] On the other hand, when it is not determined in step S509 that the vehicle body has stopped, that is, when it is determined that the vehicle body remains in the traveling state (step S509 / NO), the process does not proceed to step S510 until the vehicle body stops.

[0094] Subsequently, when it is determined in step S510 that the measured time T has elapsed the predetermined time Tth (T≧Tth) (step S510 / YES), the command signal output unit 54 outputs an invalidation signal to the first electromagnetic control valve 47 and the second electromagnetic control valve 48, respectively (step S511), and the processing in the controller 5 ends.

[0095] On the other hand, when it is determined in step S510 that the measured time T has not elapsed the predetermined time Tth (T<Tth) (step S510 / NO), the process does not proceed to step S511 until the measured time T has elapsed the predetermined time Tth (T≧Tth).

[0096] If, in step S506, it is determined that the setting switch 36 has not been switched to the enable setting position, i.e., it remains in the disable setting position (step S506 / NO), the process proceeds to step S509, where the vehicle body state determination unit 52B determines the state of the vehicle body.

[0097] Furthermore, if it is determined in step S501 that the setting position of the setting switch 36 is the enable setting position (step S501 / enablement), the process proceeds to step S508, where the setting determination unit 52A determines whether or not a deactivation setting operation has been performed on the setting switch 36.

[0098] Furthermore, if it is determined in step S502 that the setting position of the setting switch 36 has been switched to the activation setting position, that is, that an activation setting operation has been performed on the setting switch 36 (step S502 / NO), the lever position determination unit 52C determines whether or not the steering lever 34 is in the neutral position (step S512).

[0099] If it is determined in step S512 that the steering lever 34 is in the neutral position (step S512 / YES), the command signal output unit 54 outputs activation signals to the first electromagnetic control valve 47 and the second electromagnetic control valve 48, respectively (step S513), and proceeds to step S508.

[0100] On the other hand, if it is determined in step S512 that the steering lever 34 is not in the neutral position (step S512 / NO), the process will not proceed to step S513 until the steering lever 34 is operated to the neutral position.

[0101] (State transitions of steering drive unit 4) Next, the state transitions of the steering drive unit 4 due to processing by the controller 5 will be explained with reference to Figures 7 and 8.

[0102] Figure 8 is a state transition diagram showing the state transitions of the steering drive unit 4.

[0103] First, if the vehicle is stationary and the setting switch 36 is in the disabled position (step S501 / disabled → step S502 / YES), the steering drive unit 4 is in a disabled state ST1 where the steering does not operate.

[0104] When the steering drive unit 4 is in the disabled state ST1, and the vehicle body enters a driving state and it is detected that the steering lever 34 is in the neutral position or has been operated to the maximum tilt position (for example, the amount of operation to the maximum tilt position is detected based on the operation signal output from the steering lever 34), the controller 5 outputs activation signals to the first electromagnetic control valve 47 and the second electromagnetic control valve 48, respectively (step S503 / YES → step S504 / YES → step S505). As a result, the steering drive unit 4 transitions to a temporarily enabled state ST2 in which the steering operates regardless of the setting position of the setting switch 36 (arrow X1 shown in Figure 8).

[0105] Thus, even if the wheel loader 1 enters a driving state (runaway) while the steering drive unit 4 is in the disabled state ST1, if the controller 5 determines that the steering lever 34 is in the neutral position or has been operated to the maximum tilt position, the steering drive unit 4 transitions to a temporarily enabled state ST2. Therefore, the operator can immediately operate the steering with the steering lever 34, regardless of whether the setting switch 36 is in the enabled or disabled setting position.

[0106] As a result, the wheel loader 1, by providing a setting switch 36, suppresses accidental operation of the steering lever 34, while also allowing the steering to be immediately activated with the steering lever 34 in the event of runaway.

[0107] In this embodiment, the conditions for the steering drive unit 4 to transition from a disabled state ST1 to a temporarily enabled state ST2 (transition conditions from disabled state ST1 to temporarily enabled state ST2) include, in addition to the vehicle being in motion, the steering lever 34 being in the neutral position or operated to the maximum tilt position (the amount of operation to operate to the maximum tilt position is detected). However, the conditions are not limited to these, and at least the vehicle being in motion (runaway occurring) is sufficient as a transition condition from disabled state ST1 to temporarily enabled state ST2.

[0108] However, by including the condition that the steering lever 34 is in the neutral position as a transition condition from the disabled state ST1 to the temporarily enabled state ST2, it is possible to suppress situations in which the steering suddenly operates when the steering drive unit 4 transitions to the temporarily enabled state ST2.

[0109] Furthermore, by including the condition that the steering lever 34 is operated to the maximum tilt position (i.e., the amount of operation that resulted in the maximum tilt position is detected) as a transition condition from the disabled state ST1 to the temporarily enabled state ST2, the controller 5 can confirm the operator's intention to operate the steering in response to runaway, thereby enabling it to determine with greater accuracy whether runaway has occurred.

[0110] Next, when the steering drive unit 4 is in the temporarily enabled state ST2, and the setting position of the setting switch 36 is switched to the enabled setting position (step S506 / YES), the steering drive unit 4 transitions from the temporarily enabled state ST2 to the enabled state ST3 in which the steering is operated (arrow X2 shown in Figure 8).

[0111] Next, when the steering drive unit 4 is in the enabled state ST3, if the setting switch 36 is switched to the disabled setting position (step S508 / YES), the controller 5 outputs a disabled signal to the first electromagnetic control valve 47 and the second electromagnetic control valve 48, respectively, after the vehicle body has stopped and a predetermined time Tth has elapsed (step S509 / YES → step S510 / YES → step S511).

[0112] In other words, when the steering drive unit 4 is in the enabled state ST3, simply switching the setting position of the setting switch 36 from the enabled setting position to the disabled setting position does not transition to the disabled state ST1, but rather enters a temporarily enabled state ST2 (arrow Y1 shown in Figure 8). As a result, even if runaway occurs when the setting position of the setting switch 36 is in the disabled setting position, the operator can immediately operate the steering with the steering lever 34.

[0113] Then, when the steering drive unit 4 is in the temporarily enabled state ST2, after the vehicle body has stopped and a predetermined time Tth has elapsed, it transitions from the temporarily enabled state ST2 to the disabled state ST1 (arrow Y2 shown in Figure 8). In other words, when the controller 5 determines that the vehicle body has stopped and there is no possibility of it becoming mobile again, the steering drive unit 4 is disabled in state ST1, thereby reliably preventing erroneous operation of the steering lever 34.

[0114] In this embodiment, the condition for the steering drive unit 4 to transition from a temporarily enabled state ST2 to a disabled state ST1 (the transition condition from the temporarily enabled state ST2 to the disabled state ST1) includes the elapsed time Tth from the vehicle body stopping. However, it is not limited to this, and at least the vehicle body stopping is sufficient as the transition condition from the temporarily enabled state ST2 to the disabled state ST1. However, by including the elapsed time Tth from the vehicle body stopping as the transition condition from the temporarily enabled state ST2 to the disabled state ST1, the steering can be immediately operated with the steering lever 34 in cases where the vehicle body starts moving immediately after stopping.

[0115] Furthermore, when the steering drive unit 4 is in the disabled state ST1, if the setting switch 36 is switched to the enabled setting position and the steering lever 34 is operated to the neutral position (for example, the amount of operation to the neutral position is detected based on the operation signal output from the steering lever 34), the controller 5 outputs an enable signal to the first electromagnetic control valve 47 and the second electromagnetic control valve 48, respectively (step S502 / NO → step S512 / YES → step S513). As a result, the steering drive unit 4 transitions from the disabled state ST1 to the enabled state ST3 (arrow X3 shown in Figure 8).

[0116] In this way, by including the condition that the steering lever 34 is in the neutral position as a condition for the steering drive unit 4 to transition from the disabled state ST1 to the enabled state ST3, it is possible to suppress situations in which the steering suddenly operates when the steering drive unit 4 transitions to the enabled state ST3.

[0117] Embodiments of the present invention have been described above. It should be noted that the present invention is not limited to the embodiments described above, and various modifications are included. For example, the embodiments described above are described in detail to make the present invention easier to understand, and are not necessarily limited to those having all the described configurations. Furthermore, it is possible to replace some of the configurations of this embodiment with those of other embodiments, and it is also possible to add configurations from other embodiments to the configuration of this embodiment. Moreover, it is possible to add, delete, or replace some of the configurations of this embodiment with those of other embodiments.

[0118] For example, in the above embodiment, a wheel loader 1 was specifically described as one form of a wheeled work vehicle, but it is not necessarily limited to a wheel loader 1. Any wheeled work vehicle equipped with multiple wheels may be used instead of a wheel loader 1.

[0119] Furthermore, in the above embodiment, since the steering lever 34 was an electrically operated lever, pilot pressurized oil was generated by the pressure of the pressurized oil discharged from the pilot pump 46 being reduced in pressure by the first electromagnetic control valve 47 and the second electromagnetic control valve 48. However, if the steering lever 34 is a mechanically operated lever, pilot pressurized oil is generated by the pressure of the pressurized oil discharged from the pilot pump 46 being reduced in pressure by the pilot valve. In this case, the first electromagnetic control valve 47 and the second electromagnetic control valve 48 control whether or not to allow the pilot pressurized oil generated by the pilot valve to act on the steering control valve 45. [Explanation of Symbols]

[0120] 1: Wheel loader (wheeled work vehicle) 5: Controller 11,11A,11B: Wheel 12: Driver's cab 34: Steering lever 36: Setting switch 41: Left steering cylinder (steering cylinder) 42: Right steering cylinder (steering cylinder) 44: Hydraulic pump 45: Steering control valve 46: Pilot pump 47: First electromagnetic control valve (electromagnetic control valve) 48: Second electromagnetic control valve (electromagnetic control valve) 60: Vehicle speed sensor

Claims

1. A vehicle body having a plurality of wheels; A cab provided on the vehicle body; a steering cylinder for steering the plurality of wheels; a hydraulic pump for supplying hydraulic oil to the steering cylinder; a steering control valve for controlling a flow of hydraulic oil discharged from the hydraulic pump and supplied to the steering cylinder; a pilot pump for supplying pilot pressure oil to the steering control valve; A steering lever provided in the driver's cab for performing a steering operation; a setting switch for setting an enabled setting state in which the operation of the steering lever is enabled and the steering cylinder is actuated in response to the operation of the steering lever, and a disabled setting state in which the operation of the steering lever is disabled and the steering cylinder is not actuated; an electromagnetic control valve for controlling pilot pressure oil discharged from the pilot pump and acting on the steering control valve; A controller for controlling the solenoid control valve; a vehicle speed sensor for detecting a vehicle speed of the vehicle body; In a wheeled work vehicle equipped with The controller: determining whether the vehicle body is in a stopped state or a moving state based on the vehicle speed detected by the vehicle speed sensor; When it is determined that the vehicle body is in the stopped state and the setting switch is in the enabled setting state, an enable signal for operating the steering cylinder in response to operation of the steering lever is output to the electromagnetic control valve, When it is determined that the vehicle body is in the stopped state and the setting switch is in the disabled setting state, a disable signal for disabling the operation of the steering cylinder in response to the operation of the steering lever is output to the electromagnetic control valve, When it is determined that the vehicle body is in the traveling state, the enabling signal is output to the electromagnetic control valve. A wheeled work vehicle characterized by:

2. The wheeled work vehicle according to claim 1, The controller: When it is determined that the vehicle body is in the traveling state, the setting switch is in the disabled setting state, and the operation state of the steering lever is in a neutral state in which the supply of hydraulic oil from the hydraulic pump to the steering cylinder is stopped, or When it is determined that the vehicle body is in the traveling state, the setting switch is in the disabled setting state, and the operation state of the steering lever is in a maximum tilt state in which the amount of hydraulic oil supplied from the hydraulic pump to the steering cylinder is a preset maximum amount, outputting the enabling signal to the solenoid control valve; When it is determined that the vehicle body is in the traveling state, the setting switch is in the disabled setting state, and the operation state of the steering lever is an operation state different from the neutral state and the maximum tilt state, The disabling signal is output to the electromagnetic control valve. A wheeled work vehicle characterized by:

3. The wheeled work vehicle according to claim 2, The controller: When the vehicle body is determined to be in the stopped state while the enabling signal is being output to the electromagnetic control valve, and a predetermined time has elapsed since the setting switch was in the disabled setting state, The disabling signal is output to the electromagnetic control valve. A wheeled work vehicle characterized by:

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