JP2007203963A - Steering device of work vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a steering device of a work vehicle which can increase a steering force without a large time lag of synchronization between the steering angles of the front/rear wheels even when a steering resistance becomes large at the time of simultaneous steering of the front/rear wheels. <P>SOLUTION: The steering device is provided with a line-communicating means and a power-mode control means. The line-communicating means connects supply/discharge lines to each other, which are at least on one side of the supply/discharge line used for the supply and discharge of pressure oil to steering cylinders for the front/rear wheels. Then the power-mode control means controls the continuity and the non-continuity of the line-communicating means, and makes the steering cylinder for the front wheel and the steering cylinder for the rear wheel stroke alternately at a predetermined time interval. Thus, at the time of simultaneous steering of the front/rear wheels, the steering force can be increased without a large time lag of synchronization between the steering angles of the front/rear wheels even when the steering resistance becomes large. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to a steering device provided in a working vehicle such as a crane or a lift truck, and more particularly to a steering device for a working vehicle capable of steering front and rear wheels.

  Conventionally, many work vehicles such as cranes and lift trucks are provided with a plurality of steering modes as steering devices in order to improve workability. The multiple steering modes include a 2WS mode in which only the front wheels are steered, a 4WS mode in which the front and rear wheels are steered in opposite phases, and a crab mode in which the front and rear wheels are steered in the same phase. By switching the position of the mode selector switch, the mode can be switched to either 2WS mode, 4WS mode, or crab mode.

  In such a steering device, when the 4WS mode or the crab mode in which the front and rear wheels are steered simultaneously is selected, the front wheel steering cylinder and the rear wheel are synchronized in order to synchronize the steering angle of the front wheels and the steering angle of the rear wheels. The steering cylinder is connected to the series.

  When both steering cylinders are connected to the series, the front and rear wheels are steered simultaneously with the pressure oil obtained from one power steering unit, so in order to obtain sufficient steering force, It is necessary to adopt a steering cylinder having a larger pressure receiving area as compared with steering, or to supply pressure oil at a higher pressure from the power steering unit.

  However, since the steering cylinder is usually attached to the lower side of the vehicle, a vertical space that can be attached by providing a load clearance is restricted, so that it is difficult to install a steering cylinder having a large pressure receiving area.

  In addition, steering wheel steering resistance increases when the steering wheel is turned off while the vehicle is stopped on a muddy ground or a rough ground, etc., but the circuit pressure is also from the viewpoint of the characteristics and life of the hydraulic equipment. Since there is an upper limit, it is difficult to set the pressure corresponding to the steering resistance of the front and rear wheels, which may cause a problem that the steering operation becomes impossible.

  In order to solve such a problem of simultaneous steering of front and rear wheels, Japanese Patent Publication No. 7-5091 discloses power steering of a steering cylinder for front and rear wheels when steering resistance increases. Proposals have been made to increase the steering force by switching the connection of the unit to the pressure oil port (pressure oil source) from series to parallel.

Japanese Patent Publication No. 7-5091

  As described above, when the front and rear steering cylinders are connected in parallel when the steering resistance is large, the following problems occur.

  When the work vehicle is carrying heavy loads and there is a large difference between the load applied to the front wheel shaft and the load applied to the rear wheel shaft, or when only one of the front and rear wheels is muddy, When there is a large difference in the steering resistance of the rear axle, if the front and rear wheel steering cylinders are connected in parallel to the pressure oil source, most of the hydraulic oil flows to the cylinder with the smaller steering resistance. As a result, only the steering cylinder on one side strokes, and the steering angle of the front wheels and the rear wheels is greatly out of synchronization. For this reason, the steering performance is extremely deteriorated against the will of the operator.

  The present invention has been made to solve such deficiencies in the prior art, and the object of the present invention is to reduce the front and rear wheels even when the steering resistance increases when the front and rear wheels are steered simultaneously. An object of the present invention is to provide a steering device for a working vehicle that can increase the steering force without greatly shifting the synchronization of the steering angles.

(1) In order to achieve the above object, the present invention includes a front wheel and a rear wheel attached to a vehicle body, a front wheel steering cylinder for steering the front wheel, a rear wheel steering cylinder for steering the rear wheel, A hydraulic pump that supplies pressure oil to the front wheel steering cylinder and the rear wheel steering cylinder; a steering valve that controls a flow of pressure oil supplied from the hydraulic pump to the front wheel steering cylinder and the rear wheel steering cylinder; A steering mode switching direction control valve for controlling the flow of pressure oil between the steering valve, the front wheel steering cylinder and the rear wheel steering cylinder and a steering position for changing the switching position of the direction control valve according to a switching position. In the steering apparatus for a working vehicle, comprising a mode switching means, a pressure is applied to the front wheel steering cylinder. A pipe connecting means for communicating at least one of a supply / discharge pipe for supplying and discharging pressure oil to and from the supply / discharge pipe for supplying and discharging pressure oil to the rear wheel steering cylinder; and the pipe connecting means Power mode control means for controlling the communication state and the non-communication state to alternately stroke the front wheel steering cylinder and the rear wheel steering cylinder at predetermined time intervals.
In the present invention configured as described above, when the front and rear wheels are steered at the same time, even if the steering resistance increases, the supply / exhaust line of the front wheel steering cylinder or the rear wheel steering cylinder is not provided. By alternately controlling the communication state and the non-communication state, the front wheel steering cylinder and the rear wheel steering cylinder can be alternately stroked at predetermined time intervals. It is possible to increase the steering force without greatly shifting the synchronization.

(2) In the above (1), preferably, the power mode control means includes steering resistance detection means, and when the steering resistance is determined to be a predetermined value or more, the front wheel steering cylinder and the rear wheel The steering cylinder is alternately stroked at predetermined time intervals.
Thus, when the steering resistance becomes equal to or higher than a predetermined value, the steering force is automatically increased to control so as not to shift the synchronization of the steering angles of the front and rear wheels.

(3) In the above (2), more preferably, the conduit communication means is a direction control valve provided in a supply / exhaust conduit for supplying / exhausting pressure oil to / from a front wheel steering cylinder, and the power mode control means is When the steering resistance exceeds a predetermined value, the directional control valve has means for switching the communication state and the non-communication state of the supply / exhaust pipe at predetermined time intervals.

  Thus, one directional control valve is provided in the supply / exhaust conduit of the front wheel steering cylinder, and the front wheel steering cylinder and the rear wheel steering cylinder are alternately stroked at predetermined time intervals simply by controlling the direction switching valve. be able to.

(4) In the above (1), preferably, power mode switching means is provided for alternately making strokes of the front wheel steering cylinder and the rear wheel steering cylinder at predetermined time intervals as selected by an operator.

  As a result, the operating force can be increased while synchronizing the front wheel steering cylinder and the rear wheel steering cylinder as determined by the operator.

According to the present invention, when the steering of the front and rear wheels is performed simultaneously, the steering force is increased without greatly shifting the synchronization of the steering angles of the front and rear wheels even if the steering resistance increases. Therefore, it is possible to provide a steering device for a working vehicle having good steering performance.

  Embodiments of a steering apparatus for a work vehicle according to the present invention will be described below with reference to the drawings.

FIG. 1 is a hydraulic circuit diagram showing a hydraulic power steering provided in the steering apparatus according to the first embodiment of the present invention, and FIGS. 2 and 3 are for work to which the steering apparatus of the present invention is applied. It is a figure which shows the external appearance of a lift truck as an example of a vehicle.
1 to 3, reference numerals 1 and 1 denote left and right front wheels of a lift truck 200 which is a working vehicle, and reference numerals 2 and 2 denote left and right rear wheels. The front wheels 1 and 1 are attached to the front axle 4 in a steerable manner, and the rear wheels 2 and 2 are attached to the rear axle 5 in a steerable manner. Steering of the front wheels 1, 1 and the rear wheels 2, 2 is performed by a hydraulic power steering 50.

  2 and 3, the lift truck 200 is supported by a support deck structure 202 constituting a wheel mounting structure to which the front wheels 1, 1 and the rear wheels 2, 2 are attached, and the support deck structure 202. A telescopic lift arm 206 pivotally supported at the rear end of the upright plate 204 is provided. An operation / operating room 208 is supported on the upper surface of one side of the support deck structure 202 and on one side of the axis LL in the vehicle length direction of the lift truck 200.

  The housing 210 is supported by the support deck structure 202 on the side opposite to the operation / operator cab 208 with respect to the axis LL, and the internal combustion engine 214 extends in the vehicle length direction and is accommodated in the housing 210. ing. The housing 210 is disposed at a distance that opens a gap 216 from the side of the operation / cab 208, and the lift arm 206 is a horizontal pin 218 that forms a horizontal axis that is perpendicular to the axis LL in the vehicle length direction. The horizontal pin 218 is disposed at such a height that most of the lift arm 206 is accommodated in the gap 216 at the lowest position.

  In FIG. 2, the telescopic lift arm 206 is shown in a fully retracted position, with the dashed line outline partially showing the raised position and the solid and dotted lines showing the fully lowered position. Has been.

  The lift arm 206 is rotated around the horizontal pin 218 by the hydraulic jack 220, and the lower portion 222 of the hydraulic jack 220 is pivotally supported by the central portion of the support deck structure 202.

  An end element 224 that is slidable inside the telescopic lift arm 206 supports a head portion 226, and a working tool 230 that is rotated by a jack 228 is pivotally supported by a pin 232 on the head portion 226. Yes.

  In the illustrated example, the working tool 230 is configured as a fork-like lifting platform, but may be replaced with another type of working tool such as a bucket instead of the lifting platform.

Returning to FIG. 1, the hydraulic power steering 50 includes a steering wheel (hereinafter referred to as “steering operation member”) 3, direction control valves 10 and 16, a steering valve 11, a hydraulic pump 12, a pressure oil tank 13, and a front wheel steering cylinder 14. The rear wheel steering cylinder 15 is provided, and these hydraulic devices are connected by pipe lines 40-48.
The steering operation member 3 is provided in the operation / driver's cab 208. The direction control valve 10 and the direction control valve 16 are solenoid valves that are operated by solenoids 30A, 30B, and 30C.

  The hydraulic pump 12 and the steering valve 11 are connected by a pipeline 40, and the tank 13 and the steering valve 11 are connected by a pipeline 41. The steering valve 11 and the direction control valve 10 are connected by a pipeline 42, the steering valve 11 and the direction control valve 16 are connected by a pipeline 43, and the direction control valve 10 and the direction control valve 16 are connected by a pipeline 44. The front wheel steering cylinder 14 and the direction control valve 16 are connected by lines 47 and 48, and the rear wheel steering cylinder 15 and the direction control valve 10 are connected by lines 45 and 46.

  The pipe 47 and the pipe 48 constitute a supply / discharge pipe for the front wheel steering cylinder 14, and the pipes 45 and 46 constitute a supply / discharge pipe for the rear wheel steering cylinder 15.

  The front wheels 1 and 1 are steered by supplying pressure oil to the front wheel steering cylinder 14, and the rear wheels 2 and 2 are steered by supplying pressure oil to the rear wheel steering cylinder 15. The front wheel 1 is steered rightward by flowing the pressure oil supplied from the hydraulic pump 12 into the right chamber 14a of the front wheel steering cylinder 14, and the front wheel 1 is moved leftward by flowing the pressure oil into the left chamber 14b. Steered. Similarly, the rear wheel 2 is steered leftward by flowing pressure oil into the right chamber 15a of the rear wheel steering cylinder 15, and the rear wheel 2 steered rightward by flowing pressure oil into the left chamber 15b. Is done.

  The steering valve 11 sends pressure oil corresponding to the rotation direction and the rotation amount of the steering operation member 3 provided in the operation / driver's cab 208 to the pipelines 42 and 43. When the steering operation member 3 is rotated leftward, the conduit 40 and the conduit 43 are communicated with each other, and the steering operation member 3 is rotated in the left direction. And the pipe line 42 and the pipe line 41 and the pipe line 43 are communicated. Further, the steering valve 11 is a kind of servo valve, and the communication is cut off when pressure oil having a flow rate corresponding to the rotation amount of the steering operation member 3 flows from the pipeline 40 to the pipeline 42 or 43.

  The connection between the steering valve 11, the front wheel steering cylinder 14 and the rear wheel steering cylinder 15 is switched by the direction control valve 10. The direction control valve 10 has three switching positions 10a, 10b, and 10c. By switching the excitation states of the solenoids 30A and 30B, one of these three switching positions 10a, 10b, and 10c can be selected. It has become. The switching position 10a is a position corresponding to the crab mode, the switching position 10b is a position corresponding to the 2WS mode, and the switching position 10c is a position corresponding to the 4WS mode. These switching positions are controlled via the control device 111 by signals output by switching the steering mode setting switch 100 provided in the cab 208 to the crab mode, 2WS mode, and 4WS mode positions, respectively.

  The direction control valve 16 switches between the normal mode and the power mode, and has two switching positions 16a and 16b. In the normal mode, the switching position (communication position) 16a is selected, and in the power mode, the solenoid 30C is turned on. The excitation state (ON) and the non-excitation state (OFF) are switched at a predetermined time interval to switch between the switching position 16a and the switching position 16b, and between the pipe line 43 and the pipe line 48 and between the pipe line 44 and the pipe line 47. It is designed to repeatedly communicate and block.

  A relief valve 17 is installed in the pipeline 40 to regulate the maximum pressure of the hydraulic pump 12.

  Further, a pressure sensor 70 is installed on the pipe line 40 to detect the discharge pressure of the hydraulic pump 12.

  A steering mode setting switch 100 is provided in the operation and cab 208, and a discharge pressure signal from the pressure sensor 70 and a signal related to the switching position of the steering mode setting switch 100 are input to the control device 111, and solenoids 30A, 30B, The direction switching valves 10 and 16 are controlled by controlling the excitation state of 30C.

  FIG. 4 is a flowchart showing the contents of control in the control device 111. FIG. 5 is a chart showing the excitation states of the solenoids 30A, 30B, 30C in each situation in the flowchart of FIG. In FIG. 4, S100 to S114 show each step of the flowchart.

  First, as an initial setting, the power mode is set to OFF (S100).

  In S101, it is determined whether or not the steering mode is the 2WS mode based on a signal relating to the switching position of the steering mode setting switch 100. If YES (2WS mode), the solenoids 30A to 30C are excited with the pattern I (see FIG. 5). (S102). In the pattern I, the solenoids 30A to 30C are all OFF, so the direction control valve 10 is in the 10b position and the direction control valve 16 is in the 16a position.

  In this state, when the steering operation member 3 is rotated in the right direction, the pressure oil corresponding to the rotation amount of the steering operation member 3 is supplied from the hydraulic pump 12 to the pipeline 40, the pipeline 43, the direction control valve 16, and the pipeline 48. And flows into the right chamber 14a of the front wheel steering cylinder 14, and the front wheel 1 is steered rightward. The pressure oil discharged from the right chamber 14 b of the front wheel steering cylinder 14 is returned to the tank 13 through the pipe 47, the direction control valve 16, the pipe 44, the direction switching valve 10, the pipe 42, and the pipe 41.

  Similarly, when the steering operation member 3 is rotated in the left direction, pressure oil corresponding to the rotation amount of the steering operation member 3 is supplied from the hydraulic pump 12 to the pipelines 40 and 42, the direction control valve 10, the pipeline 44, and the direction control. It flows into the left chamber 14b of the front wheel steering cylinder 14 through the valve 16 and the pipe 47, and the front wheel 1 is steered leftward. The pressure oil discharged from the right chamber 14 a of the front wheel steering cylinder 14 is returned to the tank 13 through the pipe 48, the direction control valve 16, the pipe 43, and the pipe 41.

  If S101 is NO and the state of the steering mode setting switch 100 is set to 4WS mode or crab mode other than 2WS, it is determined in step S103 whether the power mode is ON or OFF.

  When step S103 is NO (power mode is OFF), the solenoids 30A to 30C are excited in pattern III (see FIG. 5) in step S104.

  In Pattern III, the excitation states of 30A to 30C are further determined by the state of the steering mode setting switch 100.

  When the steering mode setting switch 100 is in the 4WS mode, the solenoid 30A is controlled OFF, 30B is ON, and 30C is OFF, so that the direction control valve 10 is in the 10c position and the direction control valve 16 is in the 16a position.

  In this state, when the steering operation member 3 is rotated in the right direction, the pressure oil corresponding to the rotation amount of the steering operation member 3 passes from the hydraulic pump 12 through the pipelines 40 and 43 and the direction control valve 16 to the front wheel steering cylinder. 14 flows into the right chamber 14a, the front wheel 1 is steered rightward, and the pressure oil discharged from the left chamber 14b of the front wheel steering cylinder 14 is the conduit 47, the direction control valve 16, the conduit 44, and the direction control. It flows into the right chamber 15a of the rear wheel steering cylinder 15 through the valve 10 and the pipe 46, and the rear wheel 2 is steered leftward. Therefore, the work vehicle can be turned to the right with a small turning radius.

  Similarly, when the steering operation member 3 is rotated in the left direction, the pressure oil corresponding to the rotation amount of the steering operation member 3 is supplied from the hydraulic pump 12 to the pipeline 40, the pipeline 42, the direction control valve 10, and the pipeline 45. It flows into the left chamber 15b of the rear steering cylinder 15 and the rear wheel 2 is steered in the right direction, and the pressure oil discharged from the right chamber 15a of the rear wheel steering cylinder 15 is connected to the pipe 46, the direction control valve. 10, the pipe 44, the direction control valve 16, and the pipe 47 flow into the left chamber 14b of the front wheel steering cylinder 14, and the front wheel 1 is steered leftward. Therefore, the work vehicle can be turned left with a small turning radius.

  In Pattern III, when the steering mode setting switch 100 is in the crab mode, the solenoid 30A is ON, 30B is OFF, and 30C is OFF, so the direction control valve 10 is in the 10a position and the direction control valve 16 is in the 16a position. It becomes.

  In this state, when the steering operation member 3 is rotated in the right direction, the pressure oil corresponding to the rotation amount of the steering operation member 3 passes from the hydraulic pump 12 through the pipelines 40 and 43 and the direction control valve 16 to the front wheel steering cylinder. 14 flows into the right chamber 14a, the front wheel 1 is steered rightward, and the pressure oil discharged from the left chamber 14b of the front wheel steering cylinder 14 is the conduit 47, the direction control valve 16, the conduit 44, and the direction control. It flows into the left chamber 15b of the rear wheel steering cylinder 15 through the valve 10 and the pipe 45, and the rear wheel 2 is steered rightward. Therefore, the work vehicle can be moved in the right direction (crab movement) without changing the direction of the work vehicle.

  Similarly, when the steering operation member 3 is rotated in the left direction, pressure oil corresponding to the rotation amount of the steering operation member 3 is supplied from the hydraulic pump 12 to the pipeline 40, the pipeline 42, the direction control valve 10, and the pipeline 46. And flows into the right chamber 15a of the rear wheel steering cylinder 15, the rear wheel 2 is steered leftward, and the pressure oil discharged from the left chamber 15b of the rear wheel steering cylinder 15 is connected to the pipe 45, the direction control valve. 10, the pipe 44, the direction control valve 16, and the pipe 47 flow into the left chamber 14b of the front wheel steering cylinder 14, and the front wheel 1 is steered leftward. Therefore, it is possible to perform a width-alignment traveling in which the work vehicle is moved leftward without changing the direction of the work vehicle.

  When the steering operation is performed by excitation by the pattern III, the discharge pressure P of the hydraulic pump 12 is input to the control device 111 by the pressure sensor 70, and is larger than the set pressure P0 compared to the pressure P0 set in advance in S105. In this case, the power mode is turned on (S106).

  When the power mode is turned on, the timer is reset (S107), and the process returns to S101.

When the power mode is ON (S103), the excitation pattern I and the excitation pattern II are switched and controlled, for example, every 0.5 seconds through S108 to S112. (When timer> 0.5 is N0, pattern I, and when timer> 0.5 is YES, pattern II)
In the pattern I, as described above, in the pattern II in which the front wheel 1 is steered left and right by an amount corresponding to the left and right rotation direction and the rotation amount of the steering operation member 3, further, depending on the state of the steering mode setting switch 100, 30A to 30C The excitation state is determined.

  When the steering mode setting switch 100 is in the 4WS mode, the solenoid 30A is controlled to be OFF, 30B is ON, and 30C is ON, so that the direction control valve 10 is in the 10c position and the direction control valve 16 is in the 16b position.

  In this state, when the steering operation member 3 is rotated in the right direction, pressure oil corresponding to the rotation amount of the steering operation member 3 is supplied from the hydraulic pump 12 to the pipelines 40 and 43, the direction control valve 16, the pipeline 44, and the direction. The air flows into the right chamber 15a of the rear wheel steering cylinder 15 through the control valve 10 and the pipe 46, and the rear wheel 2 is steered leftward. The pressure oil discharged from the right chamber 15 b of the rear wheel steering cylinder 15 is returned to the tank 13 through the pipe 45 direction switching valve 10, the pipe 42, and the pipe 41.

  That is, when P> P0 and the power mode is turned on while the steering operation member 3 is rotated to the right in the 4WS mode, the front wheel 1 is steered to the right when the pattern I is excited, and the pattern II Since it is repeated that the rear wheel 2 is steered leftward in the excited state, the front wheel steering cylinder 14 and the rear wheel steering cylinder 15 are alternately stroked at a predetermined time interval by the pressure oil of the hydraulic pump 12. be able to. Therefore, it becomes possible to increase the steering force without greatly shifting the synchronization of the steering angles of the front and rear wheels. Sufficient steering force can be obtained even on road surfaces with high steering resistance, and small rotation It becomes possible to turn the work vehicle to the right at the radius.

Similarly, when the steering operation member 3 is rotated leftward, pressure oil corresponding to the rotation amount of the steering operation member 3 passes from the hydraulic pump 12 through the pipelines 40 and 42, the direction control valve 10, and the pipeline 45. It flows into the left chamber 15b of the rear wheel steering cylinder 15, and the rear wheel 2 is steered rightward.
In other words, when P> P0 and the power mode is turned on while the steering operation member 3 is turned counterclockwise in the 4WS mode, the front wheel 1 is steered to the left when the pattern I is excited, and the pattern Since it is repeated that the rear wheel 2 is steered rightward in the excitation state of II, it is sufficient even on a road surface with a large steering resistance without greatly shifting the steering angle of the front and rear wheels. A steering wheel is obtained, and the work vehicle can be turned to the left with a small turning radius.

  Similarly, when the steering mode setting switch 100 is in the crab mode in pattern II, the solenoid 30A is ON, 30B is OFF, and 30C is ON, so the direction control valve 10 is in the 10a position and the direction control valve 16 is 16b position.

  In this state, when the steering operation member 3 is rotated in the right direction, pressure oil corresponding to the rotation amount of the steering operation member 3 is supplied from the hydraulic pump 12 to the pipelines 40 and 43, the direction control valve 16, the pipeline 44, and the direction. It flows into the left chamber 15a of the rear wheel steering cylinder 15 through the control valve 10 and the pipe 45, and the rear wheel 2 is steered rightward. In other words, when P> P0 and the power mode is turned on while the steering operation member 3 is turned to the right in the crab mode, the front wheel 1 is steered to the right when the pattern I is in the excited state. Since it is repeated that the rear wheel 2 is steered rightward in the excitation state of II, it is sufficient even on a road surface with a large steering resistance without greatly shifting the steering angle of the front and rear wheels. A steering wheel is obtained, and width-shifting traveling is possible in which the work vehicle is moved in the right direction without changing the direction of the work vehicle.

  Similarly, when the steering operation member 3 is rotated leftward, pressure oil corresponding to the rotation amount of the steering operation member 3 passes from the hydraulic pump 12 through the pipelines 40 and 42, the direction control valve 10, and the pipeline 46. It flows into the right chamber 15a of the rear wheel steering cylinder 15, and the rear wheel 2 is steered leftward. That is, when P> P0 and the power mode is turned on while the steering operation member 3 is turned to the left in the crab mode, the front wheel 1 is steered to the left when the pattern I is in the excited state, and the pattern II Since it is repeated that the rear wheel 2 is steered to the left when in the excited state, sufficient steering power can be obtained even on road surfaces with high steering resistance without greatly shifting the synchronization of the steering angles of the front and rear wheels. Thus, it is possible to perform a width-alignment traveling in which the work vehicle is moved in the left direction without changing the direction of the work vehicle.

  When the power mode is ON in S113, the power mode is turned OFF when the discharge pressure P of the hydraulic pump 12 becomes smaller than the preset pressure P1 (S114).

  The pressure P0 at which the power mode is turned on is set to a pressure close to the set pressure of the relief valve 17, and the pressure P1 at which the power mode is turned off is, for example, approximately ½ of P0.

  According to this embodiment configured as described above, when steering is performed in the 4WS mode or the crab mode, the steering cylinder for front and rear wheels is alternately stroked when the steering resistance is large. Since the front and rear wheels are steered alternately with the pressure oil obtained from the steering unit, a sufficiently large steering force to overcome steering resistance can be achieved without greatly shifting the synchronization of the steering angles of the front and rear wheels. Obtainable.

  Next, a second embodiment of the present invention will be described with reference to FIGS.

In the figure, parts that are the same as those shown in FIG.
In FIG. 6, the hydraulic power steering 50B according to the present embodiment is provided with a power mode changeover switch 300 for switching between a normal mode and a power mode in a cab (not shown).
The changeover switch 300 is, for example, a button switch and is connected to the control device 112. When the changeover switch 300 is turned on, the power mode is turned on.
FIG. 7 is a flowchart showing control contents in the control device 113.
The excitation states of the solenoids 30A, 30B, and 30C in each situation in the flowchart of FIG. 7 are the same as those in FIG.

First, timer is reset as an initial setting. (S200)
In S201, it is determined whether or not the steering mode is the 2WS mode based on a signal related to the switching position of the steering mode setting switch 100. If YES (2WS mode), the solenoids 30A to 30C are excited with the pattern I (see FIG. 5). (S202). In the pattern I, since the solenoids 30A to 30C are all OFF, the direction control valve 10 is in the 10b position and the direction control valve 16 is in the 16a position, and the rotation direction and the rotation amount of the steering operation member 3 are the same as in the first embodiment. Accordingly, the front wheel 1 is steered left and right.

  If S201 is NO and the state of the steering mode setting switch 100 is set to 4WS mode or crab mode other than 2WS, it is determined in step 203 whether the power mode changeover switch 300 is ON or OFF.

  When the operator does not select the power mode, the changeover switch 300 is OFF, and the solenoids 30A to 30C are excited in pattern III (see FIG. 5) in step S204.

  In pattern III, steering control when the steering mode setting switch 100 is in the 4WS mode is exactly the same as in the first embodiment. When the steering operation member 3 is rotated in the right direction, the front wheel 1 is moved in the right direction. And the rear wheel 2 is steered leftward (turning right), and when the steering operation member 3 is rotated leftward, the rear wheel 2 is steered rightward and the front wheel 1 is steered leftward. Thus, the work vehicle can turn left and right with a small turning radius of the steering operation member 3.

  Further, when the steering mode setting switch 100 is in the crab mode, the steering control is exactly the same as in the first embodiment, and when the steering operation member 3 is rotated in the right direction, the front wheel 1 is steered in the right direction. In addition, the rear wheel 2 is steered in the right direction, and the work vehicle can be moved in the right direction (crab movement) without changing the direction of the work vehicle. Similarly, when the steering operation member 3 is rotated to the left, both the front wheels 1 and the rear wheels 2 are steered to the left, and width-shifting travel is performed in which the work vehicle is moved to the left without changing the direction of the work vehicle. It becomes possible.

  When the operator turns on the changeover switch 300 and selects the power mode, S203 becomes YES and the process proceeds to step S205. The excitation pattern I and the excitation pattern II are switched and controlled, for example, every 0.5 seconds by S206 to S209. The

  In the pattern II, the excitation states of 30A to 30C are further determined by the state of the steering mode setting switch 100.

  The steering control in S205 to S209 is exactly the same as the steering control in S108 to S112 of the first embodiment. When the steering mode setting switch 100 is in the 4WS mode, the right steering of the front wheel 1 and the rear wheel 2 are performed. Left-hand steering or left-hand steering of the front wheel and right-hand steering of the rear wheel 2 are repeated every 0.5 seconds, so that the road surface having a large steering resistance can be obtained without greatly shifting the steering angle of the front and rear wheels. In such a case, sufficient steering force can be obtained, and the work vehicle can be turned left and right with a small turning radius.

  When the steering mode setting switch 100 is in the crab mode, the steering to the right of the front wheel 1 and the right steering of the rear wheel 2 or the left steering of the front wheel and the left steering of the rear wheel 2 takes 0.5 seconds. Since it is repeated every time, sufficient steering force can be obtained even on road surfaces with high steering resistance without greatly synchronizing the steering angle of the front and rear wheels, and the work vehicle without changing the direction of the work vehicle It is possible to perform width-shifting travel that moves in the left-right direction.

  According to the present embodiment, when steering in the 4WS mode or the crab mode, the operator can sufficiently overcome the steering resistance while synchronizing the front wheel steering cylinder and the rear wheel steering cylinder according to the operator's judgment. A large steering force can be obtained. Maneuvering power can be increased.

  Next, a third embodiment of the present invention will be described with reference to FIGS.

  The hydraulic power steering 50C according to the present embodiment is an application of the present invention to a 4WS dedicated work vehicle. The steering valve 11 and the right chamber 14a of the front wheel steering cylinder 14 are connected to a pipe 53, a direction switching valve 16A, The steering valve 11 and the left chamber 15b of the rear wheel steering cylinder 15 are connected via a pipe 52, a direction switching valve 16B, and a pipe 58, and are connected to the left of the front wheel steering cylinder 14. The chamber 14b and the right chamber 15a of the rear wheel steering cylinder 15 are connected via a pipe 56, a direction switching valve 16A, a pipe 54, a direction switching valve 16B, and a pipe 57.

  The direction control valve 16A switches between the normal mode and the power mode, and has two switching positions, 16Aa and 16Ab. In the normal mode, the communication position 16Aa is selected, and in the power mode, the solenoid 30D 'is set for a predetermined time. The excitation state (ON) and the non-excitation state (OFF) are switched at intervals, and the switching position 16Aa and the switching position 16Ab are switched to switch between the pipe line 53 and the pipe line 55 and between the pipe line 44 and the pipe line 47. Intercommunication / interruption is repeated.

  Similarly, the direction control valve 16B switches between the normal mode and the power mode, and has two switching positions 16Ba and 16Bb. In the normal mode, the communication position 16Ba is selected, and in the power mode, the solenoid 30E ′ is turned on. The excitation state (ON) and the non-excitation state (OFF) are switched at a predetermined time interval to switch between the switching position 16Ba and the switching position 16Bb, and between the pipe line 53 and the pipe line 55 and between the pipe line 44 and the pipe line 47. Communication and disconnection are repeated.

  The pipe 55 and the pipe 56 constitute a supply / discharge pipe for the front wheel steering cylinder 14, and the pipe 57 and the pipe 58 constitute a feed / discharge pipe for the rear wheel steering cylinder 15.

  And since it is a 4WS dedicated work vehicle, unlike Embodiments 1 and 2, the flow of pressure oil between the steering valve, the front wheel steering cylinder, and the rear wheel steering cylinder is changed according to the switching position. A steering mode switching direction control valve to be controlled and a steering mode switching means for changing the switching position of the direction control valve are not provided.

  The control device 113 receives a discharge pressure signal from the pressure sensor 70 and controls the excitation state of the solenoids 30D 'and 30E', thereby switching the direction switching valve! 6A and 16B are controlled.

  FIG. 9 is a flowchart showing the contents of control in the control device 114. FIG. 10 is a chart showing excitation states of the solenoids 30D ′ and 30E ′ in each situation in the flowchart of FIG.

  In S300, the power mode is turned off.

  Next, in S301, it is determined whether the power mode is ON or OFF.

  When the power mode is OFF (NO in S301), the solenoids 30D 'and 30E' are excited with the pattern I (see FIG. 10) in step S102.

  In the pattern I, the solenoids 30D 'and 30E' are controlled to be OFF, so that the direction switching valves 16A and 16B become the communication positions 16Aa and 16Ba.

  In this state, when the steering operation member 3 is rotated in the right direction, the pressure oil corresponding to the rotation amount of the steering operation member 3 passes from the hydraulic pump 12 through the pipelines 40 and 53, the direction switching valve 16A, and the pipeline 55. Then, the oil flows into the right chamber 14a of the front wheel steering cylinder 14 and the front wheel 1 is steered in the right direction, and the pressure oil discharged from the left chamber 14b of the front wheel steering cylinder 14 is connected to the pipe 56, the direction switching valve 16A, It flows into the right chamber 15a of the rear wheel steering cylinder 15 through the pipe 54, the direction switching valve 16B, and the pipe 57, and the rear wheel 2 is steered leftward. Therefore, the work vehicle can be turned to the right with a small turning radius. Similarly, when the steering operation member 3 is rotated in the left direction, pressure oil corresponding to the rotation amount of the steering operation member 3 is supplied from the hydraulic pump 12 to the pipeline 40, the pipeline 52, the direction switching valve 16B, and the pipeline 58. Then, it flows into the left chamber 15b of the rear steering cylinder 15 and the rear wheel 2 is steered rightward, and the pressure oil discharged from the right chamber 15a of the rear wheel steering cylinder 15 is connected to the pipe 57, the direction switching valve. It flows into the left chamber 14b of the front wheel steering cylinder 14 through 16B, the pipe line 54, the direction switching valve 16A, and the pipe line 56, and the front wheel 1 is steered leftward. Therefore, the work vehicle can be turned left with a small turning radius.

  When the steering operation is performed by being excited by the pattern I, the discharge pressure P1 of the hydraulic pump 12 is input to the control device 113 by the pressure sensor 70, and is larger than the set pressure P0 compared with the pressure P0 set in advance in S303. In this case, the power mode is turned on (S304). When the power mode is turned on, the timer is reset and the process returns to S301.

  When the power mode is ON (YES in S301), the excitation pattern II (S307) and the excitation pattern III (S308) are switched and controlled, for example, every 0.5 seconds through S306 to S310 (timer> 0.5 is N0). In pattern III, if timer> 0.5 is YES, pattern II).

  In the pattern II, the solenoid 30D 'is controlled to be ON and 30E' is controlled to be OFF, so that the direction switching valve 16A is in the 16Ab position and the direction switching valve 16B is in the 16Ba position.

  In this state, when the steering operation member 3 is rotated rightward, the pressure oil corresponding to the rotation amount of the steering operation member 3 is supplied from the hydraulic pump 12 to the pipeline 40, the pipeline 53, and the direction switching valve 16A pipeline 54. Then, the air flows into the right chamber 15a of the rear wheel steering cylinder 15 through the direction switching valve 16B and the pipeline 57, and the rear wheel 2 is steered leftward.

  The pressure oil discharged from the left chamber 15 b of the rear wheel steering cylinder 15 is returned to the tank 13 through the pipe line 58 and the pipe line 52.

  In the pattern III, the solenoid 30D 'is controlled to be OFF and 30E' is controlled to be ON, so that the direction switching valve 16A is in the 16Aa position and the direction switching valve 16B is in the 16Bb position.

  In this state, when the steering operation member 3 is rotated rightward, the pressure oil corresponding to the rotation amount of the steering operation member 3 is supplied from the hydraulic pump 12 to the pipeline 40, the pipeline 53, the direction switching valve 16A, the pipeline. After passing through 55, it flows into the right chamber 14a of the front wheel steering cylinder 14, and the front wheel 4 is steered rightward. Pressure oil discharged from the left chamber 14b of the front wheel steering cylinder 14 is returned to the tank 13 through the pipe 56, the direction switching valve 16A, through the pipe 54, the direction switching valve 16B, the pipe 52, and the pipe 41. .

  In other words, when P1> P0 and the power mode is turned on while the steering operation member 3 is rotated to the right, the front wheel 1 is steered to the right when the pattern III is excited, and the excitation state of the pattern II is Since the rear wheel 2 is sometimes steered to the left, the front wheel steering cylinder 14 and the rear wheel steering cylinder 15 can be alternately stroked at predetermined time intervals by the pressure oil of the hydraulic pump 12. Therefore, the steering force can be increased without greatly shifting the synchronization of the steering angles of the front and rear wheels, and a sufficient steering force can be obtained even on a road surface with a large steering resistance.

  Similarly, when the steering operation member 3 is rotated leftward in the pattern II, the pressure oil corresponding to the rotation amount of the steering operation member 3 is supplied from the hydraulic pump 12 to the pipeline 52, the direction switching valve 16B, and the pipeline 58. And then flows into the left chamber 15b of the rear wheel steering cylinder 15 and the rear wheels are steered rightward.

  The pressure oil discharged from the right chamber 15a of the rear wheel steering cylinder 15 is returned to the tank 13 through the pipe 57, the direction switching valve 16B, the pipe 54, the direction switching valve 16A, the pipe 53, and the pipe 41. .

  Further, when the steering operation member 3 is rotated leftward in the pattern III, the pressure oil corresponding to the rotation amount of the steering operation member 3 is supplied from the hydraulic pump 12 to the pipeline 52, the direction switching valve 16B, the pipeline 54, It flows into the left chamber 14b of the front wheel steering cylinder 14 through the direction switching valve 16A and the pipe 56, and the front wheels are steered leftward. The pressure oil discharged from the right chamber 14a of the front wheel steering cylinder 14 is returned to the tank 13 through the pipe 55, the direction switching valve 16A, the pipe 53, and the pipe 41.

  In other words, when P1> P0 and the power mode is turned on while the steering operation member 3 is turned to the left, the front wheel 1 is steered to the left when the pattern III is excited, and the excitation state of the pattern II is Sometimes the rear wheel 2 is steered in the right direction repeatedly, so that sufficient steering force can be obtained even on road surfaces with high steering resistance without greatly shifting the steering angle of the front and rear wheels. .

  In S311, when the power mode is ON, if the discharge pressure P of the hydraulic pump 12 becomes lower than the preset pressure P1, the power mode is turned OFF (S312).

  According to the fourth embodiment configured as described above, when the steering resistance is large in a 4WS exclusive vehicle, the front and rear wheel steering cylinders are alternately stroked. Since the front and rear wheels are steered alternately with the pressure oil that is produced, a sufficiently large steering force can be obtained to overcome the steering resistance without greatly shifting the synchronization of the steering angles of the front and rear wheels. .

1 is a hydraulic circuit diagram of a hydraulic power steering of a steering apparatus according to a first embodiment of the present invention. It is a side view which shows the external appearance of the lift truck which is an example of the working vehicle carrying the steering apparatus of this invention. It is a top view which shows the external appearance of the lift truck which is an example of the working vehicle by which the steering apparatus of this invention is mounted. It is a flowchart which shows the control content of the control apparatus concerning the 1st Embodiment of this invention. It is a figure which shows the control content which a control apparatus performs in response to the signal of a steering mode change switch in the flowchart of FIG. It is a hydraulic circuit diagram of the hydraulic power steering of the steering apparatus concerning the 2nd Embodiment of this invention. It is a flowchart which shows the control content of the control apparatus concerning the 2nd Embodiment of this invention. It is a hydraulic circuit diagram of the hydraulic power steering of the steering apparatus concerning the 3rd Embodiment of this invention. It is a flowchart which shows the control content of the control apparatus concerning the 3rd Embodiment of this invention. It is a figure which shows the control content which a control apparatus receives in response to the signal of a steering mode switch in the chart of FIG.

Explanation of symbols

1 Front Wheel 2 Rear Wheel 3 Steering Wheel 4 Front Axle 5 Rear Axle 10 Directional Control Valve 11 Steering Valve 12 Hydraulic Pump 13 Tank 14 Front Wheel Steering Cylinder 15 Rear Wheel Steering Cylinder 16, 16A, 16B Control Valve (Pipe Connection Means)
17 Relief valve 30A, 30B, 30C, 30D ', 30E' Solenoid 40-48, 52-58 Pipe line 50, 50B, 50C Hydraulic power steering 70 Pressure detector 100 Steering mode setting switch 111, 112, 113 Controller ( Control means)
300 pushbutton switch

Claims (4)

Pressure oil is supplied to the front and rear wheels attached to the vehicle body, the front wheel steering cylinder for steering the front wheel, the rear wheel steering cylinder for steering the rear wheel, and the front wheel steering and rear wheel steering cylinders. A hydraulic pump that controls the flow of pressure oil supplied from the hydraulic pump to the front-wheel steering cylinder and the rear-wheel steering cylinder, the steering valve and the front-wheel steering cylinder according to a switching position, A steering device for a working vehicle, comprising: a steering mode switching direction control valve for controlling the flow of pressure oil to and from the rear wheel steering cylinder; and a steering mode switching means for changing a switching position of the direction control valve. In
Pipe line communication for connecting a supply / discharge line for supplying / exhausting pressure oil to / from the front wheel steering cylinder and a supply / discharge line for supplying / exhausting pressure oil to / from the rear wheel steering cylinder. And a power mode control means for controlling the communication state and the non-communication state of the pipe communication means to alternately stroke the front wheel steering cylinder and the rear wheel steering cylinder at predetermined time intervals. A steering device for a working vehicle.   2. The steering device according to claim 1, wherein the power mode control means includes steering resistance detection means, and when the steering resistance is determined to be equal to or greater than a predetermined value, the front wheel steering cylinder and the rear wheel steering cylinder are determined. A steering device for a working vehicle, characterized in that strokes are alternately made at predetermined time intervals.   3. The steering apparatus according to claim 2, wherein the pipe communication means is a direction control valve provided in a supply / discharge pipe for supplying and discharging pressure oil to and from a front wheel steering cylinder, and the power mode control means is a steering resistance. A steering device for a working vehicle, comprising means for switching the communication state and the non-communication state of the supply / exhaust pipe at predetermined time intervals when the directional control valve exceeds a predetermined value.   2. The steering apparatus according to claim 1, further comprising power mode switching means that alternately strokes the front wheel steering cylinder and the rear wheel steering cylinder at predetermined time intervals according to an operator's selection. Vehicle steering device.

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