JPH11263241A - Steering device for working vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a steering device for vehicle capable of switching a mode among front wheel steering mode for steering the only front wheels, a rear wheel steering mode for steering the only rear wheels, a front and rear wheels opposite phase steering mode for steering the front and rear wheels in the opposite directions, and a front and rear wheels same phase steering mode for steering the front and rear wheels in the same direction. SOLUTION: Any one of a front wheel steering hydraulic actuator 22 and a rear wheel steering hydraulic actuator 28 is operated by a hydraulic steering mechanism 37 directly connected to a steering operating tool 5, and the operation of the other actuator is controlled by a steering valve 38. In this case, the oil passage structure for operating the front wheel steering hydraulic actuator 22 with a hydraulic steering mechanism 37 and for controlling the operation of the rear wheel steering hydraulic actuator 28 with a steering valve 38 and the oil passage structure for operating the rear wheel steering hydraulic actuator 28 with the hydraulic steering mechanism 37 and for controlling the operation of the front wheel steering actuator 22 with the steering valve 38 are switched by oil passage switching valves 39, 40.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a front wheel steering mode in which only the front wheels are steered, a rear wheel steering mode in which only the rear wheels are steered, and a front-rear wheel steering mode in which the front wheels and the rear wheels are steered in opposite directions. The present invention relates to a steering device for a work vehicle that can be switched to a front and rear wheel in-phase steering mode in which front and rear wheels are steered in the same direction.

[0002]

2. Description of the Related Art The above-mentioned steering apparatus for a work vehicle operates a front-wheel steering hydraulic actuator and a rear-wheel steering hydraulic actuator by a hydraulic circuit comprising a hydraulic steering mechanism and a plurality of direction control valves. The desired steering mode is selected by switching the oil path with the direction control valve.

For example, a steering apparatus described in Japanese Patent Application Laid-Open No. 3-148384 has a front-wheel steering hydraulic actuator ("hydraulic cylinder" 18 in the publication) and a rear-wheel steering hydraulic actuator (also "hydraulic cylinder" 1).
9) are connected in series, and are provided with two electromagnetic valves (25) and (28) for switching an oil path connecting the hydraulic steering mechanism (35) and both hydraulic actuators (18) and (19). In the case of the front wheel steering mode or the rear wheel steering mode, one of the electromagnetic valves (25 or 28) is set to a position where the hydraulic steering mechanism (35) and the hydraulic actuator (18 or 19) on the steering side communicate with each other. The hydraulic actuator (18 or 19) is operated with the oil supplied from (35). At this time, the other electromagnetic valve (28 or 25) is fixed at a position where oil does not flow. In the case of the front and rear wheel reverse phase steering mode or the front and rear wheel in-phase steering mode, both the electromagnetic valves (25) and (28) are communicated with the hydraulic steering mechanism (35) and the hydraulic actuators (18) and (19). And one of the hydraulic actuators is operated by the oil directly supplied from the hydraulic steering mechanism (35), and the other hydraulic actuator is operated by the return oil of the hydraulic actuator.

[0004]

In the conventional steering apparatus described above, in the front wheel steering mode or the rear wheel steering mode, the electromagnetic valve (28 or 25) is fixed at a position where oil does not flow, so that it can be used on a slope or the like. There was a problem that even if the wheel on the non-steered side changed its direction due to external force, this could not be corrected. In addition, in the case of the front-rear wheel reverse phase steering mode or the front-rear wheel in-phase steering mode, since the other hydraulic actuator is operated by the return oil of one hydraulic actuator, the ratio of the front wheel steering amount and the rear wheel steering amount is always constant, There is a problem that even if it is preferable to change the above ratio depending on the weight of the working machines to be connected or the difference in the work load, it is not possible to cope with it.

The above problems can be solved only by adopting a method of operating the front wheel and the rear wheel by separate hydraulic steering mechanisms, and a method of electrically controlling the steering of the front and rear wheels by a microcomputer or the like. Although the former method requires two hydraulic steering mechanisms, it has the drawback that the cost increases and the amount of hydraulic oil used increases, and the latter method has a control response delay. Another problem arises in that steering performance is deteriorated by a certain amount.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and in order to solve the problems of the conventional device,
The present invention has the following configuration. That is, the steering apparatus for a work vehicle according to the present invention includes a front wheel steering mode in which only the front wheels are steered, a rear wheel steering mode in which only the rear wheels are steered, and front and rear wheel reverse phase steering in which the front wheels and the rear wheels are steered in opposite directions. Mode and
A steering device for a work vehicle that can be switched to a front and rear wheel in-phase steering mode in which front and rear wheels are steered in the same direction, comprising a front wheel steering hydraulic actuator and a rear wheel steering hydraulic actuator, and a hydraulic pressure for operating these hydraulic actuators. The apparatus includes: a hydraulic steering mechanism that operates a front-wheel steering hydraulic actuator or a rear-wheel steering hydraulic actuator so that a front wheel or a rear wheel is steered according to an operation position of a steering operating tool; and a side that is operated by the hydraulic steering mechanism. A state in which the other hydraulic actuator for the hydraulic actuator is operated so as to maintain the steering position of the wheel steered by the latter hydraulic actuator at neutral, A state in which the steered wheels are operated to be steered in the same direction; A steering valve that controls the wheels that are steered by the latter hydraulic actuator to operate so that the wheels steered by the latter hydraulic actuator are steered in the opposite direction, and a hydraulic actuator for front wheel steering by a hydraulic steering mechanism. An oil passage configuration that operates and controls the operation of a rear-wheel steering hydraulic actuator with a steering valve, a hydraulic steering mechanism that operates a rear-wheel steering hydraulic actuator, and a steering valve that controls the operation of a front-wheel steering actuator An oil passage switching valve for switching to an oil passage configuration.

The hydraulic steering mechanism operates a front wheel steering hydraulic actuator, and the steering valve controls the operation of the rear wheel steering hydraulic actuator. When the operation of the steering hydraulic actuator is controlled, the front wheel steering mode is set.

The hydraulic steering mechanism operates a rear-wheel steering hydraulic actuator and the steering valve controls the operation of the front-wheel steering hydraulic actuator. The front-wheel steering hydraulic actuator is configured to maintain the front-wheel steering position neutral. When the operation of the hydraulic actuator is controlled, the rear wheel steering mode is set.

The hydraulic steering mechanism operates a front-wheel steering hydraulic actuator or a rear-wheel steering actuator, and controls the operation of the other hydraulic actuator with respect to the hydraulic actuator operated by the hydraulic steering mechanism by a steering valve. When the wheels steered by the former hydraulic actuator are controlled so that the wheels steered by the latter hydraulic actuator are steered in the opposite direction, the front and rear wheel reverse phase steering mode is set.

The hydraulic steering mechanism operates a front-wheel steering hydraulic actuator or a rear-wheel steering actuator, and controls the operation of the other hydraulic actuator with respect to the hydraulic actuator operated by the hydraulic steering mechanism by a steering valve. If the wheels steered by the former hydraulic actuator are controlled so that the wheels steered by the latter hydraulic actuator are steered in the same direction, the front and rear wheel in-phase steering mode is set.

[0011]

Preferred embodiments of the present invention will be described below with reference to the drawings. FIGS. 1 and 2 show a tractor which is a kind of work vehicle. The tractor 1 includes a pair of left and right front wheels 2 and 2 and rear wheels 3 and 3, and a hood 4 is provided at a front portion of the vehicle body. A steering handle 5 is provided as a steering operation tool, and a seat 6 is further provided behind the steering handle 5.

A lift arm 8,
8 is provided rotatably up and down, and a working machine is connected to a hitch 9 attached to a rear end of the lift arm. When the lift cylinders 11, 11 are extended and retracted, the lift arms 8, 8 rotate up and down. In addition, when the rolling cylinder 12 provided on one side of the hitch is operated to expand and contract, the hitch 9 rotates around the PTO shaft 13, and the inclination of the working machine connected to the hitch is changed.

FIG. 3 is a side view of the steering device of the tractor,
FIG. 4 is a plan view thereof. The front wheels 2, 2 are supported by front wheel support cases 20, 20 which are rotatable about a substantially vertical axis. Left and right knuckle arms 21, 21 integral with the front wheel support case are connected to each other by tie rods 22. A front wheel steering cylinder 22, which is a front wheel steering hydraulic actuator, is provided so that the front wheel support case 20 can be rotated. When the front wheel steering cylinder 22 is extended, the front wheels 2, 2 are steered to the right, and when the front wheel steering cylinder 22 is contracted, the front wheels 2, 2 are steered to the left. Front wheel 2,
The turning angle of No. 2 is detected by a front wheel turning angle sensor 23 which is a means for detecting a steering amount of the front wheels.

Similarly, the rear wheels 3, 3 are supported by rear wheel support cases 25, 25 rotatably provided about a substantially vertical axis, and left and right knuckle arms 26 integrated with the rear wheel support case. , 26 are connected to each other by a tie rod 27, and a rear wheel steering cylinder 28, which is a rear wheel steering hydraulic actuator, is provided so that one rear wheel support case 25 can be rotated. When the rear wheel steering cylinder 28 is extended, the rear wheels 3, 3 are steered to the right, and when the rear wheel steering cylinder 28 is contracted, the rear wheels 3, 3 are steered to the left. The turning angles of the rear wheels 3, 3 are detected by a rear wheel turning angle sensor 29 which is a means for detecting the steering amount of the rear wheels.

FIG. 5 is a hydraulic circuit diagram of the entire hydraulic system. The hydraulic circuit includes a steering circuit section 31 for operating the front wheel steering cylinder 22 and the rear wheel steering cylinder 28, and a lifting circuit for operating the lift cylinders 11, 11. And a rolling circuit 33 for operating the rolling cylinder 12. The hydraulic pump 34 supplies hydraulic oil to the steering circuit 31, and the hydraulic pump 35 applies pressure to the lifting circuit 32 and the rolling circuit 33. It is designed to supply oil.

Next, the configuration of the steering circuit section 31 will be described. The steering circuit unit 31 includes a hydraulic steering mechanism 37, a steering valve 38, a first oil passage switching valve 39, a second oil passage switching valve 40, and other valves.

The hydraulic steering mechanism 37 is composed of a combination of a pump and a direction control valve interlocked with the operation of the steering handle 5. When the steering handle 5 is at the neutral position, the P port and the T port are connected and the steering valve is connected. The oil supplied via 38 is returned to the oil tank 41 as it is, and the steering wheel 5
When the is turned to the right of the neutral position, the P port and the R port are connected, and oil at a flow rate corresponding to the amount of rotation of the steering wheel is supplied via the first oil passage switching valve 39 to the extension side cylinder chamber of the front wheel steering cylinder 22. 22a or the contraction side cylinder chamber 28b of the rear wheel steering cylinder 28,
The port is connected, and the return oil from the contraction side cylinder chamber 22b of the front wheel steering cylinder 22 or the extension side cylinder chamber 28a of the rear wheel steering cylinder 28 is returned to the oil tank 41 via the second oil path switching valve 40, and the steering handle When the dial 5 is turned to the left of the neutral position, the P port and the L port are connected to each other, and the oil having a flow rate corresponding to the turning amount of the steering wheel is supplied via the second oil passage switching valve 40 to the contraction side cylinder of the front wheel steering cylinder 22. In addition to the supply to the chamber 22b or the extension cylinder chamber 28a of the rear wheel steering cylinder 28, the T port and the R port are connected, and the extension cylinder chamber 22a of the front wheel steering cylinder 22 is provided.
Or, the compression side cylinder chamber 22b of the rear wheel steering cylinder 28
Is returned to the oil tank 41 via the first oil passage switching valve 39.

The steering valve 38 is a 3 position, 4 port solenoid valve.
At the neutral position, the P port and the T port are connected to supply oil from the hydraulic pump 34 to the hydraulic steering mechanism 37, and when the solenoid 38a is excited, the P port and the A port are connected and the oil from the hydraulic pump 34 The extension side cylinder chamber 28a of the rear wheel steering cylinder 28 via the oil passage switching valve 40
Or, the compression side cylinder chamber 22b of the front wheel steering cylinder 22
And T port and B port are connected,
The return oil from the contraction side cylinder chamber 28b of the rear wheel steering cylinder 28 or the extension side cylinder chamber 22a of the front wheel steering cylinder 22 passes through the first oil passage switching valve 39 and the hydraulic steering mechanism 3
7, when the solenoid 38b is excited, the P port and the B port are connected, and the oil from the hydraulic pump 34 passes through the first oil passage switching valve 39 and the contraction side cylinder chamber 28b of the rear wheel steering cylinder 28 Alternatively, while being supplied to the extension side cylinder chamber 22a of the front wheel steering cylinder 22, the T port and the A port are connected, and the return from the extension side cylinder chamber 28a of the rear wheel steering cylinder 28 or the contraction side cylinder chamber 22b of the front wheel steering cylinder 22 is performed. The oil is supplied to the hydraulic steering mechanism 37 via the second oil passage switching valve 40.

The first oil passage switching valve 39 is an electromagnetic valve having two positions and four ports. Under normal conditions, the R port of the hydraulic steering mechanism 37 communicates with the extension side cylinder chamber 22a of the front wheel steering cylinder 22, and the steering valve 38 B port and rear wheel steering cylinder 28
Communicates with the contraction side cylinder chamber 28b of the solenoid 39a.
Is excited, the R port of the hydraulic steering mechanism 37 communicates with the contraction cylinder chamber 28b of the rear wheel steering cylinder 28, and the B port of the steering valve 38 communicates with the extension cylinder chamber 22a of the front wheel steering cylinder 22. It has become.

The second oil passage switching valve 40 is also an electromagnetic valve having two positions and four ports. Under normal conditions, the L port of the hydraulic steering mechanism 37 communicates with the compression side cylinder chamber 22b of the front wheel steering cylinder 22, and the steering valve 38 A port and rear wheel steering cylinder 28
Communicates with the extension side cylinder chamber 28a of the solenoid 40a.
Is excited, the L port of the hydraulic steering mechanism 37 communicates with the extension cylinder chamber 28a of the rear wheel steering cylinder 28, and the A port of the steering valve 38 communicates with the compression cylinder chamber 22b of the front wheel steering cylinder 22. It has become.

The positions of the solenoid valves 38, 39, and 40 are switched by a command from a controller 43 described later, and the following steering modes are selected by a combination of the switching positions (see Table 1). Here, the first oil passage switching valve 39 and the second oil passage switching valve 40 are OFF in the normal state, and ON when the solenoids 39a and 40a are excited. Steering valve 3
The “neutral control”, “in-phase control”, and “reverse-phase control” of No. 8 will be described later.

[0022]

[Table 1]

When the steering valve 38 is neutrally controlled and the first and second oil passage switching valves 39 and 40 are turned off, a front wheel steering mode is performed in which only the front wheels are steered. When the steering valve 38 is neutrally controlled and the first and second oil passage switching valves 39 and 40 are turned on, a rear wheel steering mode in which only the rear wheels are operated is set. When the steering valve 38 is controlled in-phase and the first and second oil passage switching valves 39 and 40 are turned off, the front wheel and the rear wheel are steered in the same direction and the front and rear wheels are driven in the same-phase steering mode. When the steering valve 38 is in-phase controlled and the first and second oil passage switching valves 39 and 40 are turned ON, the vehicle is traveling backward when the front and rear wheels are in phase. When the steering valve 38 is controlled in the opposite phase and the first and second oil passage switching valves 39 and 40 are turned off, the front wheel and the rear wheel are steered in opposite directions, and the front and rear wheels are in the reverse phase steering mode. When the steering valve 38 is controlled in the reverse phase and the first and second oil passage switching valves 39 and 40 are turned on, the vehicle is traveling backward in the front and rear wheel reverse phase steering mode.

FIG. 6 is a block diagram of a steering control device for controlling the switching of the solenoid valves 38, 39, 40. This steering control device includes a controller 43 composed of a microcomputer or the like. The input section 43a has a front wheel turning angle sensor 23, a rear wheel turning angle sensor 29, a turning angle adjustment dial 44, a front wheel steering switch 45, a rear wheel steering switch 46, The front and rear wheel in-phase steering switch 47, the front and rear wheel reverse-phase steering switch 48, and the back detection switch 50 are connected, and the solenoids 38a and 38b of the steering valve, the solenoid 39a of the first oil passage switching valve, and the second Solenoid 40a of oil passage switching valve
Is connected. The turning angle adjustment dial 44 and the switches 45, 46, 47, 48 for switching the steering mode are used.
Is provided near the seat 6 and operated by an operator. These switches 45, 46, 47, 48
Only one of them becomes "enter". In addition, the back detection switch 50 is turned on when the change lever is operated to the back, for example.

The controller 43 performs control in the order shown in the flowchart of FIG. That is, after reading signals from the respective sensors and switches, the state of each steering mode switching switch is determined. If the front wheel steering switch 45 is “ON”, the front wheel steering control is executed, and the front and rear wheel reverse phase steering switch is executed. If 48 is "ON", the front and rear wheels are subjected to reverse phase steering control. If the rear wheel steering switch 46 is "ON", rear wheel steering control is executed. If the front and rear wheels in-phase steering switch 47 is "ON", front and rear wheels are controlled. In-phase steering control is performed. The order of judging the state of each switch is arranged in descending order of the frequency of being operated as “ON”.

In the front wheel steering control, as shown in the flowchart of FIG. 8, the rear wheel turning angle sensor value is determined, and if it matches the stored neutral value of the rear wheel previously stored in the controller, the steering valve 38 is controlled. The output to both solenoids 38a and 38b is turned off, and if there is a difference from the stored neutral value, the output to the solenoid 38a or 38b that brings the rear wheel turning angle sensor value closer to the stored neutral value is turned on. While performing the control, the solenoid 39a of the first oil passage switching valve 39 and the solenoid 40a of the second oil passage switching valve 40 are kept OFF.

With this control, in the front-wheel steering mode, the front-wheel steering cylinder 22 is operated by the hydraulic steering mechanism 37 directly connected to the operation of the steering wheel 5 to steer the front wheels 2 and 2. Also, by appropriately switching the steering valve 38,
Control (neutral control) for operating the rear wheel steering cylinder 28 is performed so that the rear wheel turning angle sensor value matches the stored neutral value stored in the controller in advance, and the rear wheels 3 and 3 are always maintained neutral.

In the rear wheel steering control, as shown in the flowchart of FIG. 9, the front wheel turning angle sensor value is determined, and if it matches the stored neutral value of the front wheel previously stored in the controller, the steering valve 38 is controlled. The control to turn off the output to both solenoids 38a and 38b and to turn on the output to the solenoid 38a or 38b on the side that brings the front wheel turning angle sensor value closer to the stored neutral value if there is a difference from the stored neutral value. While performing, the solenoid 39a of the first oil passage switching valve 39 and the solenoid 40a of the second oil passage switching valve 40 are kept OFF.

With this control, in the rear wheel steering mode, the rear wheel steering cylinder 28 is operated by the hydraulic steering mechanism 37 to steer the rear wheels 3 and 3. Further, by appropriately switching the steering valve 38, control (neutral control) for operating the front wheel steering cylinder 22 is performed so that the front wheel turning angle sensor value is adjusted to the stored neutral value stored in the controller in advance. Is always kept neutral.

As described above, in the front-wheel steering mode and the rear-wheel steering mode, the turning angle of the unsteered wheel is controlled so as to match the neutral value stored in the controller in advance. Even if the direction of the wheel that is not steered due to the change is changed, this is immediately corrected to the neutral position, so that stable running can always be maintained.

In the front and rear wheel in-phase steering control, as shown in the flowchart of FIG. 10, the state of the back detection switch 50 is determined, and different control is performed when the back detection switch 50 is "on" and "off". When the back detection switch 50 is turned off, that is, when the vehicle is moving forward, first, a rear wheel turning angle sensor correction value is calculated by adding the turning angle adjustment dial value to the rear wheel turning angle sensor value (see FIG. 14), and then the wheel is turned off. The angle sensor correction value and the front wheel turning angle sensor value are compared, and if they match, the output to the two solenoids 38a and 38b of the steering valve 38 is turned off. If there is a difference between them, the rear wheel turning angle sensor correction value The solenoid 39a of the first oil passage switching valve 39 and the second oil passage switching valve 4 are controlled while turning on the output to the solenoid 38a or 38b on the side that approaches the front wheel turning angle sensor value.
The output to the solenoid 40a of 0 is maintained OFF. When the back detection switch 50 is "on", that is, when the vehicle is traveling backward, the front wheel turning angle sensor value and the rear wheel turning angle sensor value are compared, and if they match, the output to the solenoids 38a, 38b of the steering valve 38 is output. Is turned off, and if there is a difference between them, the first oil passage switching valve is controlled while turning on the output to the solenoid 38a or 38b on the side that brings the front wheel turning angle sensor value closer to the rear wheel turning angle sensor value. The output to the solenoid 39a of the solenoid valve 39 and the solenoid 40a of the second oil passage switching valve 40 is maintained ON.

With this control, in the front-rear wheel in-phase steering mode, the hydraulic steering mechanism 37 operates the forward-direction steering cylinder (the front-wheel steering cylinder 22 for forward traveling, and the rear-wheel steering cylinder 28 for backward traveling), thereby turning the forward-facing wheel. (Front wheels 2 and 2 for forward travel, rear wheels 3 and 3 for reverse travel), and steering on the opposite side to the traveling direction is controlled by the steering valve 38 so that the front wheel turning angle sensor value matches the rear wheel turning angle sensor value. The cylinder (the rear wheel steering cylinder 28 in the forward direction, the front wheel steering cylinder 28 in the reverse direction) is operated to follow and steer the wheels opposite to the traveling direction (the rear wheels 3 and 3 in the forward direction and the front wheels 2 and 2 in the forward direction).

The turning angle adjustment dial 44 can be set in three levels of "strong", "standard" and "weak". For example, "strong" indicates that the rear wheel turning angle sensor correction value is the rear wheel turning angle sensor value. 25% reduction, "Standard" means that the rear wheel turning angle sensor correction value is equal to the rear wheel turning angle sensor value, and "Weak" means that the rear wheel turning angle sensor correction value is 20% higher than the rear wheel turning angle sensor value Have been. Therefore, if the turning angle adjustment dial 44 is set to “strong”, the steering amount of the rear wheels becomes larger than the steering amount of the front wheels. When the turning angle adjustment dial 44 is set to “weak”, the steering amount of the rear wheels becomes smaller than the steering amount of the front wheels.

In the front-rear wheel reverse-phase steering control, as shown in the flowchart of FIG. 11, the state of the back detection switch 50 is determined, and different control is performed when the back detection switch 50 is "on" and "off". . When the back detection switch 50 is "OFF", that is, when the vehicle is moving forward, the reverse phase value of the rear wheel turning angle sensor value and the front wheel turning angle sensor value are compared, and if they match, the two solenoids 38a and 38b of the steering valve 38 are operated. Is turned off, and if there is a difference between them, the solenoid 38a on the side that brings the reverse phase value of the rear wheel turning angle sensor value closer to the rear wheel turning angle sensor value
Alternatively, the output to the solenoid 39a of the first oil passage switching valve 39 and the output to the solenoid 40a of the second oil passage switching valve 40 are maintained OFF while performing control to turn on the output to the 38b. When the back detection switch 50 is "ON", that is, when the vehicle is moving backward, the reverse phase value of the front wheel turning angle sensor value is compared with the rear wheel turning angle sensor value.
Output to both solenoids 38a and 38b is turned off,
If there is a difference between them, the first oil passage switching valve is controlled while turning on the output to the solenoid 38a or 38b on the side that brings the reverse phase value of the front wheel turning angle sensor value closer to the rear wheel turning angle sensor value. 39 solenoid 39a and second oil passage switching valve 4
The output of 0 to the solenoid 40a is kept ON.

With this control, in the front / rear wheel reverse phase steering mode, the hydraulic steering mechanism 37 operates the steering cylinder on the traveling direction side (the front wheel steering cylinder 22 for forward traveling, and the rear wheel steering cylinder 28 for backward traveling), and operates in the traveling direction side. The wheels (front wheels 2 and 2 for forward travel, rear wheels 3 and 3 for reverse travel) are steered, and the traveling direction is controlled by the control of the steering valve 38 so that the front wheel disconnection angle sensor value and the rear wheel disconnection angle sensor value match in opposite phases. Operate the opposite steering cylinder (the rear wheel steering cylinder 28 for forward travel, the front wheel steering cylinder 28 for reverse travel) and follow the wheel opposite to the direction of travel (rear wheels 3, 3 for forward travel, front wheels 2, 2 for forward travel). Steer.

As described above, in the front and rear wheel in-phase steering mode and the front and rear wheel opposite phase steering mode, the front wheel steering cylinder 22
And one of the rear wheel steering cylinders 28 is operated by oil supplied from a hydraulic steering mechanism 37, and the other is operated by oil supplied from a hydraulic pump 34 via a steering valve. The ratio between the front wheel steering amount and the rear wheel steering amount can be changed in accordance with the weight and the work load of the working machine to be operated. In the present embodiment, this ratio change is employed in the front and rear wheel in-phase steering mode during forward movement. Further, since the steering cylinder in the traveling direction is operated by oil supplied from the hydraulic steering mechanism 37 directly connected to the operation of the steering handle 5, a sense of unity is felt between the steering operation and the actual steering. Easy to do.

In the front-rear wheel in-phase steering mode or the front-rear wheel reverse-phase steering mode, the steering wheel 38 controls the rear wheel turning angle sensor value to follow the front wheel turning angle sensor value, or the front wheel turning angle to the rear wheel turning angle sensor value. When following the sensor value,
As shown in the flow chart of FIG. 12, the steering valve 38 is controlled by continuous output until the control wheel turning angle approaches the target value, and the steering valve 38 is controlled by pulse output after approaching the target value. FIG. 15 is a time chart of an example of the steering valve output.

The switching of each steering mode is executed as soon as the steering mode switching switches 45, 46, 47, 48 are turned on. Therefore, even if the steering mode changeover switch is erroneously operated, it is immediately known, so that the section in which the vehicle is traveling in the wrong steering mode can be shortened, and the adverse effect on the work is small.

However, when switching from the front-rear wheel in-phase steering mode to the front-rear wheel reverse-phase steering mode, control is performed as shown in the flowchart of FIG. That is, if the front mode is the front-rear wheel in-phase steering mode when the front-rear and rear-wheel reverse-phase steering switch 48 is turned on, the steering valve 38 is set so that the rear wheel turning angle sensor value once becomes the stored neutral value. Solenoid 38
a, 38b, and switches to the front and rear wheel reverse phase steering mode when the rear wheel turning angle sensor value matches the stored neutral value. Here, the fact that the rear wheel turning angle sensor value becomes the stored neutral value means that the vehicle is in the front wheel steering mode. After the mode change operation, a predetermined set time (for example, 1
If the mode is not switched to the front wheel steering mode even after the elapse of (sec), switching to the front and rear wheel reverse phase steering mode is executed.

Switching from the front-rear wheel in-phase steering mode to the front-rear wheel reverse-phase steering mode is generally performed as shown in FIG. 16 when the aircraft is working along a contour line on a slope (slope α). Since the vehicle is turned to the valley side, if the front and rear wheel in-phase steering mode is directly switched to the front and rear wheel opposite-phase steering mode, immediately after the front and rear wheel reverse-phase steering switch 48 is operated, contrary to the intention of the operator. As shown in FIG. 16 (a), it is dangerous because the aircraft starts to turn sharply toward the mountain side. On the other hand, when the control is performed as described above, as shown in FIG. 16B, the front and rear wheel in-phase steering mode is once relayed to the front wheel steering mode and then switched to the front and rear wheel reverse phase steering mode, so that a sharp turn to the mountain side is avoided. Is safe. Further, if it is difficult to switch to the front wheel steering mode due to the influence of the condition of the field or the like, it is rather dangerous as it is. Therefore, the mode is switched to the front and rear wheel reverse phase steering mode after the set time has elapsed.

As shown in the flowchart of FIG. 17, when the front-rear wheel reverse-phase steering switch 48 is turned on when the front-rear wheel front-rear wheel in-phase steering mode is switched to the front-rear wheel reverse-phase steering mode, the mode is switched immediately. Alternatively, after the mode change operation, the front and rear wheel in-phase steering mode may be continued as it is until a predetermined set time (for example, 1 second) elapses, and the front and rear wheel in-phase steering mode may be switched after the set time elapses. Good. By doing so, the operator starts operating the steering wheel toward the valley within the set time,
When the mode is switched to the front and rear wheel reverse phase steering mode, the aircraft does not make a sharp turn to the mountain side.

FIG. 18 is a hydraulic circuit diagram of a different configuration. This hydraulic circuit is different from the hydraulic circuit of FIG.
9 and the second oil passage switching valve 40 is used to switch the oil passage.
The configuration is such that the operation is performed by the oil passage switching valve 60 at the 8-port position.

[0043]

As is apparent from the above description, the steering apparatus for a work vehicle according to the present invention is a hydraulic circuit having a hydraulic steering mechanism, a steering valve, and a switching valve. Operating the front hydraulic steering actuator, selectively switching between the front wheel steering mode, the rear wheel steering mode, the front and rear wheel in-phase steering mode, and the front and rear wheel simultaneous reverse steering mode, and is not steered in the front wheel steering mode and the rear wheel steering mode. The turning angle of the side wheel is controlled to match the stored neutral value stored in the microcomputer or the like in advance, so that the wheel can always be maintained at the neutral position, and the front and rear wheel in-phase steering mode and the front and rear wheel reverse mode can be maintained. In the phase steering mode, one hydraulic actuator is operated by oil supplied from a hydraulic steering mechanism, and the other hydraulic actuator is operated by a hydraulic pump through a steering valve. It is operated with oil supplied from the vehicle, so that the ratio between the front wheel steering amount and the rear wheel steering amount can be changed according to the weight and work load of the working machine connected to the work vehicle. Was.

Further, the steering apparatus for a working vehicle can perform steering sensitively to the operation of the steering operation tool by using both the steering by the hydraulic steering mechanism and the steering by the electric control, and can compare the cost. The amount of oil used can be reduced while reducing the amount of oil used.

[Brief description of the drawings]

FIG. 1 is a side view of a tractor.

FIG. 2 is a plan view of the tractor.

FIG. 3 is a side view of the steering device.

FIG. 4 is a plan view of the steering device.

FIG. 5 is an overall hydraulic circuit diagram of the tractor.

FIG. 6 is a block diagram of a steering control device.

FIG. 7 is an overall flowchart of control.

FIG. 8 is a flowchart of front wheel steering control.

FIG. 9 is a flowchart of rear wheel steering control.

FIG. 10 is a flowchart of front and rear wheel in-phase steering control.

FIG. 11 is a flowchart of front and rear wheel reverse phase steering control.

FIG. 12 is a flowchart of steering valve output control.

FIG. 13 is a flowchart of control at the time of switching from the front-rear wheel in-phase steering mode to the front-rear wheel reverse-phase steering mode.

FIG. 14 is a graph showing a relationship between a rear wheel turning angle sensor value and a rear wheel turning angle sensor correction value.

FIG. 15 is a time chart of a steering valve output.

FIGS. 16 (a) and (b) are schematic diagrams each showing a steering state of a work vehicle on a slope.

FIG. 17 is a flowchart of control at the time of switching from different front and rear wheel in-phase steering modes to front and rear wheel opposite-phase steering modes.

FIG. 18 is a hydraulic circuit diagram of a different configuration.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Tractor 2 Front wheel 3 Rear wheel 5 Steering handle (Steering operation tool) 22 Front wheel steering cylinder (Front wheel steering hydraulic actuator) 23 Front wheel steering angle sensor 28 Rear wheel steering cylinder (Rear wheel steering hydraulic actuator) 29 Rear wheel steering angle sensor 37 Hydraulic steering mechanism 38 Steering valve 39 First oil path switching valve 40 Second oil path switching valve

Claims (1)

[Claims] 1. A front wheel steering mode for steering only front wheels,
Switchable between a rear wheel steering mode in which only the rear wheels are steered, a front and rear wheel opposite phase steering mode in which the front and rear wheels are steered in opposite directions, and a front and rear wheel in phase steering mode in which the front and rear wheels are steered in the same direction. BACKGROUND ART A steering device for a work vehicle includes a hydraulic actuator for steering a front wheel and a hydraulic actuator for steering a rear wheel. In a hydraulic device that operates these hydraulic actuators, a front wheel or a rear wheel is steered according to an operation position of a steering operation tool. The hydraulic steering mechanism for operating the front wheel steering hydraulic actuator or the rear wheel steering hydraulic actuator, and the other hydraulic actuator for the hydraulic actuator on the side operated by the hydraulic steering mechanism are used for the wheels steered by the latter hydraulic actuator. A state in which the steering position is maintained to be neutral, and a vehicle steered by the former hydraulic actuator On the other hand, the wheel operated by the latter hydraulic actuator is operated to be steered in the same direction, and the wheel operated by the latter hydraulic actuator is steered in the opposite direction to the wheel operated by the former hydraulic actuator. A steering valve for controlling the operating state so as to be operated,
An oil path configuration for operating a front-wheel steering hydraulic actuator with a hydraulic steering mechanism and controlling the operation of a rear-wheel steering hydraulic actuator with a steering valve, a hydraulic steering mechanism for operating a rear-wheel steering hydraulic actuator, and a steering valve An oil passage switching valve for switching to an oil passage configuration for controlling the operation of the front wheel steering actuator.