JPH0698930B2 - Full hydraulic power steering device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an all-hydraulic power steering device used for vehicles such as a forklift truck and having no steering gear or mechanical link.

(Prior Art) As a conventional full hydraulic power steering device, for example, a device as shown in FIG. 13 is known. ("Nissan Technology No. 19" December 1983, Nissan Motor Co., Ltd .; 17
This conventional device 100 includes a steering unit 102 (valve mechanism) operated by a handle 101 and a steering cylinder 104 (actuator) for steering steered wheels 103.
And hydraulic lines 105, 106 connecting the steering unit 102 and the steering cylinder 104.

Reference numeral 107 in the drawing is a steering pump, 108 is a hydraulic oil tank, 109 is a vehicle body, 110 is a steering chain, 111 is a fixed wheel, and 112 is a steering wheel spoke. This figure shows a state at the time of left steering, and by turning the steered wheels 103 to the right, the vehicle can be turned to the left.

Therefore, by rotating the steering wheel 101 in the steering direction, the amount of pressure oil sent from the steering pump 107, which is proportional to the steering wheel rotation angle, is sent from the steering unit 102 to the steering cylinder 104 according to the arrow in the figure.

Then, the pressure oil sent to the steering cylinder 104 enters the steering cylinder 104 through the hollow portion of the cylinder rod 141, and the cylinder tube 141 is fixed to the vehicle body 109. Accordingly, the steered wheels 103 connected by the steering chain 110 are rotated by an angle corresponding to the rotation angle of the handle 101.

(Problems to be Solved by the Invention) However, in such a conventional all-hydraulic power steering device, the steering unit 102 and the steering cylinder 104 are connected only by the hydraulic lines 105 and 106, and the steering gear and mechanical Since there is no link, the amount of oil sent to the steering cylinder 104 and the rotation angle of the steering wheel 101 deviate due to an oil leak in the steering unit 102, which causes the steering wheel spoke 112 and the steering wheel 103 to shift. The direction relative position may change.

In particular, when the steering wheel 103 is in the straight-ahead neutral position but the steering wheel 101 is displaced from the neutral position,
As an operator, even if the operator tries to bend the position of the handlebar 101, the vehicle may actually go straight.

In order to solve such problems, the present applicant has filed an application (Japanese Patent Application No. 59-1178) with the content shown in FIG.
No. 81, filed on June 8, 1984) as a prior art.

In this prior art, the hydraulic oil lines 105 and 106 are provided with drain oil lines 113 and 114 and an electromagnetic switching valve 122, and the electromagnetic switching valve 112 is provided.
The first and second solenoids 123 and 124 of the above are driven by the control signals (a) and (b) from the controller 125 to move the handle 101 to the cylinder stroke (corresponding to the steering angle of the steered wheels).
It is intended to correct the rotation angle according to.

That is, the controller 125 inputs the angle signal (θ) from the steering wheel rotation angle detecting means 120 provided on the steering shaft 121 and the stroke signal (s) from the cylinder stroke detecting means 119 provided on the steering cylinder 104. , The actual values from these signals (θ) and (s) are compared with a target value stored in advance in the controller 125, and if the difference exceeds a predetermined value, the actual value matches the target value. As described above, the drive signals (a) and (b) are output.

However, in this prior art, when an error of a predetermined value or more occurs in the relationship between the cylinder stroke and the steering wheel rotation angle, one of the hydraulic lines 105 and 106 is drained with pressurized oil to idle the steering wheel 101 to correct the steering wheel position. Therefore, as shown in FIG. 15, at the time of steering wheel position correction, looking at the pressure change of the steering cylinder 104 on the side where pressurized oil is supplied, the position correction start point is taken as the boundary. The pressure drastically drops to the atmospheric pressure level by the drain, the pressure is not transmitted to one of the pistons in the steering cylinder 104, and the pressure applied to the left and right of the piston becomes a large unbalance, resulting in a steered wheel.
The situation in which the position of the steering cylinder 104 cannot be maintained as it is against the external force applied from 103 has occurred.

That is, the steered wheels 103 have a self-recovery function such as an elastic return force due to the contact pressure distribution with the road surface in the steered state, and this self-recovery force becomes a force for moving the steering cylinder 104 at the time of position correction, and is originally Tries to correct the position of the steering wheel 101 without changing the steered position of the steered wheels 103, whereas the steered wheels 103 sometimes rotate in a straight traveling direction at the time of position correction due to hydraulic oil outflow.

Therefore, even if the operator is steering in a predetermined direction,
On the contrary, the steered wheels 103 may return in the straight traveling direction, which caused an uncomfortable feeling in steering, and the vehicle behavior was also unstable.

(Means for Solving Problems) The present invention has been made for the purpose of solving the above-mentioned problems, and in order to achieve this object, the present invention provides the following solving means. did.

The solution means of the present invention will be described with reference to the conceptual diagram of claims shown in FIG. 1. A steering unit 2 operated by a steering wheel 1, a steering cylinder 3 for steering steered wheels, the steering unit 2 and a steering cylinder 3. And hydraulic lines 4 and 5, which connect the
The steering unit 2 has a valve mechanism that can be switched by a steering wheel 1. One of two input ports of this valve mechanism is connected to a steering pump 14, the other is connected to a hydraulic oil tank 11, and two outputs of the valve mechanism are connected. In the all-hydraulic power steering device in which the ports are respectively connected to the two hydraulic lines 4 and 5, in the drain oil lines 12 and 13 provided in the two hydraulic lines 4 and 5, control signals for steering wheel position correction ( a),
The hydraulic oil outflow means 6 and 7 for connecting the drain oil lines 12 and 13 and the hydraulic oil tank 11 by switching according to (b) are provided,
A handle rotation angle signal (θ ₁ ) is supplied to the hydraulic oil outflow means 6 and 7.
And a signal corresponding to the wheel turning angle (θ ₂ ) are input to calculate the difference between the actual detected value and the control target value, and when this difference exceeds a predetermined value, a control signal (a ), (B) is provided to the operating oil outflow means 6 and 7, and a control means 8 is provided, and the operating oil outflow means 6 and 7 are provided with a pressure to maintain the position of the steering cylinder 3 when the operating oil flows out. It is characterized in that residual pressure mechanisms 9 and 10 to be left are provided. The hydraulic oil outflow means 6 and 7 are provided in the hydraulic line, and the steering wheel rotation angle signal (θ ₁ ) and the wheel turning angle equivalent signal (θ ₂ ) are input to the hydraulic oil outflow means 6 and 7 for actual detection. A control means 8 is provided which calculates a difference between the value and the control target value, and outputs control signals (a) and (b) for position correction of the steering wheel 1 when the difference exceeds a predetermined value, and the operation is performed. The oil outflow means 6 and 7 are provided with residual pressure mechanisms 9 and 10 which leave a pressure that allows the steering cylinder 3 to hold its position when the operating oil flows out.

Here, the control signals (a) of the hydraulic oil outflow means 6 and 7,
In order to directly connect the drain oil lines 12 and 13 and the hydraulic oil tank 11 by switching according to (b), the drain oil lines 12 and 13 are branched from the two hydraulic lines 4 and 5, respectively. It may be a line communicating with.

Further, the control signals (a) of the hydraulic oil outflow means 6 and 7,
By switching according to (b), the drain oil lines 12, 13 are connected to the hydraulic oil tank 11 via one hydraulic line 4 or 5 and the valve mechanism of the steering unit 2 so that the drain oil lines 12, 13 are connected to each other. Two hydraulic lines 4,5
May be a line connecting the two.

(Operation) Therefore, in the all-hydraulic power steering apparatus of the present invention, by adopting the solving means as described above, when the steering wheel is steered, the wheel steering angle θ _{2 with} respect to the steering wheel rotation signal (θ ₁ ). If there is an error, the control means 8 calculates the difference between the actual detected value and the control target value. If this difference exceeds a predetermined value, the control signal (a) for correcting the position of the handle 1 is obtained. , (B) are output to the hydraulic oil outflow means 6, 7.

With this control, in the invention according to claim 2, the hydraulic oil tank passes from one hydraulic line of the two hydraulic lines 4,5 to the drain oil line 12 or 13 communicating therewith. The hydraulic oil flows out to 11, and the handle 1 idles, whereby the position of the handle 1 is corrected.

Further, in the invention described in claim 3,
Of the two hydraulic lines 4,5, hydraulic oil flows to the other hydraulic line after passing through the drain oil lines 12 and 13 that are connected to each other, and the hydraulic oil is operated from the hydraulic line via the valve mechanism of the steering unit 2. The hydraulic oil flows out into the oil tank 11, whereby the handle 1 idles to correct the position of the handle 1.

When the steering wheel position is corrected, even if the self-returning force acts on the steering cylinder 3 from the steered wheels, the residual pressure mechanisms 9 and 10 are provided in the hydraulic oil outflow means 6 and 7, so that the residual pressure mechanism 9 and The transmission of the pressure into the steering cylinder 3 is not interrupted by 10 and the position of the steering cylinder 3 can be maintained as it is.

The operation of the handle position correction of the present invention is described in
This is compared with the handle position correction device described in the microfilm of No. 25920 (Japanese Utility Model Publication No. 59-132470).

Control Timing of Neutral Position Correction In the case of the prior application example, the steering wheel position correction control signal is output only when the steering angle neutral position is passed, and the steering wheel position correction is executed under the condition that the hydraulic motor is operating. On the other hand, according to the present invention, when a predetermined deviation occurs, the control signal for correcting the steering wheel position is output without any time limitation. In the invention according to the second aspect of the present invention, the hydraulic oil is allowed to flow out directly from the drain oil line 12 or 13 to the hydraulic oil tank 11 so that the steering wheel position can be corrected. There is no limitation on the execution time, and the steering wheel position correction by the drain is executed whenever the control signal is output. Further, in the invention according to the third aspect of the invention, since the hydraulic oil is made to flow out to the hydraulic oil tank 11 via the valve mechanism of the steering unit 2, the handle 1 is moved to the right or left. If the cut-off valve mechanism is removed from the shut-off position, the handle position correction by the drain is executed.

Neutral position correction method In the case of the previous application example, the neutral position correction is a method that utilizes internal leakage in the metering part of the hydraulic motor in the steering unit, and the hydraulic motor is operating under the condition that the hydraulic motor is stopped. The position correction is not performed, and the position correction response is delayed when the hydraulic motor is slowly rotating.

On the other hand, in the present invention, since the neutral position correction method by the drain is used, the operation of the hydraulic motor is not a condition, and the position correction is always performed with high response to the occurrence of the deviation.

(Examples) Hereinafter, examples of the present invention will be described in detail with reference to the drawings.

In describing the embodiments, an all-hydraulic power steering device for a three-wheel forklift truck will be taken as an example.

First, the structure of a first embodiment (corresponding to the invention described in claims 1 and 2) shown in FIGS. 2 to 8 will be described.

Reference numeral 10 is a handle, and handle spokes 11 are provided on the handle 10 to improve operability.

Reference numeral 12 denotes a steering unit, which is directly operated by the steering wheel 10.
Reference numeral 12 has a valve mechanism that can be switched by the steering wheel 10 and has a function of sending to the steering cylinder 14 an amount of pressure oil sent from a steering pump 13, which will be described later, in proportion to the steering wheel rotation angle. 132470).

A steering cylinder 14 includes cylinder rods 16 and 16 fixed to the vehicle body 15, a cylinder tube 17 that is a movable member, and a piston 18 that reciprocates in the cylinder tube 17.

Reference numeral 19 denotes a steered wheel, which is connected to the cylinder tube 17 by steering chains 20, 20 and steered by the movement of the cylinder tube 17.

Reference numerals 21, 22 are hydraulic lines for connecting the steering unit 12 and the steering cylinder 14,
One of the hydraulic lines 21 and 22 serves as a feed line for feeding the pressurized hydraulic oil from the steering pump 13 during steering, and the other line serves as a return line for returning the oil to the hydraulic oil tank 23.

It should be noted that pressurized oil is sent to the steering cylinder 14 through the hollow portion of the cylinder rod 16, and oil is returned through the hollow portion. 24 and 25 are drain oil lines, Line 21,
This is connected to the drain oil lines 24, 25, and electromagnetic switching valves 26, 27 (operating oil outflow means) are provided in the middle of the drain oil lines 24, 25. The electromagnetic switching valves 26, 27 enable the hydraulic lines to open when one of them is opened. One of the hydraulic oils 21 and 22 is caused to flow into the hydraulic oil tank 23, and the handle position is corrected.

As shown in FIG. 3, the electromagnetic switching valves 26, 27 include solenoids 31, 32 and springs 37, 38 for switching between one-way valve portions 33, 34 and drain portions 35, 36, and the drain oil line. Orifices 39 and 40 (residual pressure mechanism) provided in the middle of 24 and 25 are respectively provided.

A specific example of the electromagnetic switching valve 26 will be described with reference to FIG. 4. Structurally, the solenoid 31, the spring 37, the movable spool 41, the check sleeve 42, the orifice 39, the one-way valve port 43, the valve frame 44, Port frame 45, input port 46,
It has an output port 47 and a guide 48. A drain oil line 24 on the hydraulic line 21 side is connected to the input port 46, and a drain oil line 24 on the hydraulic oil tank 23 side is connected to the output port 47.

Therefore, when the solenoid 31 is not excited, the one-way valve port 43 is closed at the tip of the movable spool 41 that is biased by the spring 37, and only the flow from the output port 47 to the input port 46 via the orifice 39 is allowed. , A so-called one-way valve is interposed (switched to the one-way valve portion 33 side), and when the solenoid 31 is excited, the spring 37
By pulling up the movable spool 41 against the force, the input port 46 and the output port 47 are in communication with each other via the orifice 39 (switching state to the drain portion 35 side).

Reference numeral 28 denotes a control unit, which inputs the handle rotation signal (θ) from the handle rotation angle sensor 29 and the cylinder stroke signal (s) from the cylinder position sensor 30, and inputs these input signals (θ) and (s). The control signals (a) and (b) are output to the solenoids 31 and 32 of the electromagnetic on-off valves 26 and 27, respectively.

A specific example of the steering wheel rotation angle sensor 29 will be described with reference to FIGS. 5 and 6. Structurally, the worm 51 is fixed to the steering shaft 50, and the worm wheel 53 meshing with the worm 51 is a potentiometer. It is fixed to the shaft 54 of the steering wheel rotation angle sensor 29 of the structure, and the steering wheel rotation angle sensor 29 is a steering column 55.
Is attached to.

Therefore, when the steering shaft 50 is rotated during steering, the rotation reduced by the worm 51 and the worm wheel 53 is input to the shaft 54, and the degree of rotation of the shaft 54 is converted into an electric signal by the handle rotation angle sensor 29. By that,
The handle rotation angle is measured.

The control unit 28 includes an A / D conversion circuit 281, an A / D conversion circuit 282, a RAM, as shown in FIG.
(Random access memory) 283, ROM (read only memory) 284, clock circuit 285, CPU (central processing unit) 286, position correction signal generation circuit 287.

The A-D conversion circuit 281 is a circuit for converting a steering wheel rotation angle signal (θ) input as an electric signal into a digital signal that can be processed by the CPU 286.

The A-D conversion circuit 282 is a circuit for converting a cylinder stroke signal (s) (an analog signal based on a current value) from the cylinder position sensor 30 using a variable resistance into a digital signal which can be processed by the CPU 286.

The RAM 283 is a writable and readable memory, and is a circuit for temporarily storing the steering wheel rotation signal (θ) and the cylinder stroke signal (s) by digital signals until the arithmetic processing time comes.

The ROM 284 is a read-only memory, and the relationship between the steering wheel rotation signal θ that is a control target value and the cylinder stroke x is stored in advance in the ROM 284 in the form of a table. As shown in the graph A of FIG. 7, the control target value is set so that the ratio of the cylinder stroke x to the steering wheel rotation signal θ is set smaller than the ratio of both θ and x in the ideal control value (shown in the graph B). ing.

The clock circuit 285 is a circuit for setting the arithmetic processing time in the CPU 286.

The CPU 286 is called a central processing unit and has a RAM 283.
And the signal written in the ROM 284 is read and arithmetic processing is performed in accordance with a predetermined procedure, and a position correction signal generation circuit
It is a circuit that outputs the result signal to 287.

The position correction signal generation circuit 287 is a circuit that outputs control signals (a) and (b) to the solenoids 31 and 32 based on the result signal from the CPU 286. The control signals (a) and (b) are This is an electric signal for operating the solenoid. When this signal is output to one of the solenoids 31 and 32, one of the electromagnetic switching valves 26 and 27 is switched to the drain side, and the hydraulic oil is drained for the signal output time.

Next, the operation of the first embodiment will be described.

First, the control operation of the steering wheel position correction will be described with reference to the flowchart showing the flow of the operation of the CPU 286 of the control unit 28 shown in FIG.

First, in step 200, a handle rotation angle signal (θ) indicating the actual handle rotation angle θn obtained by rotating the handle 10 in one direction is read from the RAM 283.

In step 201, the target cylinder stroke xn is looked up from the target value A stored in the ROM 284 based on the steering wheel rotation angle θn read in step 200.

For example, in FIG. 7, the handle rotation angle θn is θ ₁
If so, the target cylinder stroke xn becomes x ₁ .

In step 202, the cylinder stroke signal (x) indicating the actual cylinder stroke xn at the actual handle rotation angle θn is read from the RAM 283.

For example, in FIG. 7, the actual cylinder stroke xn
Be x ₂ .

In step 203, the actual cylinder stroke xn is taken as a function f (t) of time t, and the steering direction is right depending on the slope of this function, that is, whether the value differentiated at time t is positive or negative. Determine if it is the left.

It should be noted that this steering direction determination may be performed using the steering wheel rotation angle θn or the target cylinder stroke xn.

If the value differentiated with respect to time t is zero in step 203, it means that steering is not performed, and step 20
Proceeding to 4, the result signal is not output from the CPU 286.

Here, in the case of right steering, in the case of right steering, the routine proceeds from step 203 to step 205, and in this step 205, the stroke difference δ between the actual cylinder stroke xm and the target cylinder stroke xn is calculated. To be done.
For example, as shown in FIG. 7, when xm is x ₂ and xn is x ₁ , the stroke difference δ is obtained by the calculation of δ ₁ = x ₂ −x ₁ .

In the next step 206, the stroke difference δ obtained in step 205 is the predetermined stroke error δ set in advance.
It is determined whether it is larger or smaller than n.

Then, if δ ≦ δn, it is determined that the position correction control is not required, and the process proceeds to step 204, and δ> δ
If the relationship is n, it is determined that position correction control is required, and the process proceeds to step 207, and in step 207, the CPU 286 outputs a result signal for operating the solenoid 32.

That is, when steering to the right, contrary to FIG. 2, hydraulic oil is sent from the steering unit 12 to the steering cylinder 14 via the hydraulic line 22.
By operating 32, the electromagnetic switching valve 27 is switched to the drain section 36 side, and the hydraulic oil is released to the hydraulic oil tank 23 via the drain oil pipe 25 and the electromagnetic opening / closing valve 27 provided in this hydraulic line 22, and the cylinder The position of the steering wheel 10 is corrected by idling the steering wheel 10 in the steering direction without changing the stroke.

For example, if δ ₁ > δn in FIG. 7, only the steering wheel rotation angle θ advances in the direction of arrow E.

Also, in the case of left steering, as in the case of right steering, step 20
After 8 and step 209, the process proceeds to either step 204 or step 210, and the position of the handle 10 is corrected. The above control operation is repeated every predetermined time to correct the position of the handle 10 in the delay direction.

The hydraulic oil drained to correct the position of the handle 10 due to the hydraulic oil outflow is carried out after passing through one of the orifices 39, 40, so the outflow flow rate is the orifices 39, 40.
The pressure in the steering cylinder 14 is not sharply reduced by the limitation.

In other words, draining is performed in the same state as when a part of the pressurized oil supplied from one of the hydraulic lines 21 and 22 is diverted to the drain side.
Even if pressure transmission to the inside of the steering wheel 14 is not interrupted, the position of the steering cylinder 14 can be maintained as it is even if the self-returning force from the steered wheels 19 acts on the steering cylinder 14.

In this way, by holding the position of the steering cylinder 14, it is possible to prevent the steered wheels 19 from rotating in a straight traveling direction opposite to the steering direction at the time of position correction, thereby eliminating the feeling of strange steering. The stability of the vehicle behavior during steering is also increased.

When the position of the steering wheel 10 is corrected, the steering wheel 19
Excessive self-restoring force from the steering cylinder
When 14 is moved to some extent, the hydraulic line and the cylinder chamber on the side where the drain is not formed have an increased volume corresponding to the movement, and bubbles or the like are generated due to the negative pressure, and the pressure cannot be transmitted.

However, the one-way valve portions 33, 34 of the solenoid operated directional control valves 26, 27 allow the operating oil to flow through the drain oil line 24 from the hydraulic oil tank 23 side to the hydraulic pressure lines 21, 22 side. As a result, the hydraulic oil is supplied to the hydraulic line on the side that is not drained due to the pressure difference, and the aforementioned bubbles and the like do not occur.

Further, in the first embodiment, the ratio (x / θ) between the steering wheel rotation angle θ and the cylinder stroke x at the control target value A.
Is set to be smaller than the ratio in the control ideal value B, the stroke difference δ becomes larger than a predetermined error δn in most cases, and the position correction of the handle 10 due to hydraulic oil outflow can be frequently performed. At the same time, because the position control is performed in the delay direction, even as a steering feeling,
There is no discomfort and it is preferable.

Next, a second embodiment shown in FIG. 9 (corresponding to the invention described in claims 1 and 3) will be described.

In the second embodiment, as hydraulic oil outflow means and residual pressure mechanism, hydraulic lines 21 and 22 are connected by a connecting line 60 (drain oil line connected to each other), and an electromagnetic switching valve is provided in the middle of the connecting line 60. 61 or 62, 62 are provided, and the electromagnetic switching valve 61
Or, when the 62,62 is excited (when the position is corrected), the connecting line 60
This is an example in which the hydraulic lines 21 and 22 are communicated with each other.

Here, a variable orifice 63 is added to the continuous line 60 to further enhance the residual pressure function.

Since the other structures are similar to those of the first embodiment, some of them are omitted from the drawing, and the same components as those of the first embodiment are designated by the same reference numerals.

Therefore, in the second embodiment, when the position of the handle 10 is corrected, the hydraulic lines 21 and 22 are communicated with each other by the connecting line 60 so that the hydraulic line 21 or 22 is connected to the connecting line 60.
→ The other hydraulic line 22 or 21 → Steering unit
The hydraulic oil can be discharged to the hydraulic oil tank 23 via the 12 valve mechanism, and the pressure level is set to the left and right hydraulic lines.
By making 21,22 almost equal, pressure can be left in the hydraulic line on the hydraulic oil outflow side.

However, in the second embodiment, as the steering wheel position correction time, the steering wheel 10 is turned to the left and the valve mechanism of the steering unit 12 is in the communication position instead of the shut-off position. In such cases, the frequency of turning traveling is higher than the frequency of traveling straight ahead, and there is practically no restriction on the steering wheel position correction timing.

Next, a third embodiment shown in FIGS. 10 and 11 (corresponding to the invention described in claims 1 and 2) will be described.

In the third embodiment, a diversion valve (stoichiometric diversion valves 64, 64 or return line side priority valves 65, 65) is provided as a residual pressure mechanism at the rear of the hydraulic oil outflow means, and one diversion side of the diversion valve is provided. Is connected to the hydraulic oil tank 23 through the drain oil lines 24 and 25, and the other shunt side is returned through the return lines 66 and 67 to the hydraulic line 21,
It is connected to 22.

In the figure, 68 and 68 are solenoid switching valves for switching between opening and closing.
An orifice 69 is provided in the flow path of each of the diversion valves 64 and 65.

Since the other structures are similar to those of the first embodiment, some of them are omitted from the drawing, and the same components as those of the first embodiment are designated by the same reference numerals.

Therefore, in this third embodiment, when the position of the handle 10 is corrected, of the amount of oil flowing out of the hydraulic line on the hydraulic oil outflow side,
A part of the amount of oil is made to flow out to the hydraulic oil tank 23, and the remaining amount of oil is returned from one return line to the hydraulic line, whereby a rapid decrease in pressure can be suppressed.

Next, a fourth embodiment shown in FIG. 12 (corresponding to the invention described in claims 1 and 2) will be described.

The fourth embodiment is an example in which relief valves 70, 70 are provided as a residual pressure mechanism at the rear part of the hydraulic oil outflow means.

In the figure, 71 and 71 are solenoid switching valves for switching between opening and closing.

Since the other structures are similar to those of the first embodiment, some of them are omitted from the drawing, and the same components as those of the first embodiment are designated by the same reference numerals.

Therefore, in the fourth embodiment, when the position of the handle 10 is corrected, even if one of the electromagnetic switching valves 71, 71 is switched to the drain side and the hydraulic oil flows out, the predetermined pressure set by the relief valves 70, 70 or more is exceeded. The hydraulic oil flows out only at the time of, and becomes a cutoff state at a predetermined pressure or less, so that the hydraulic line on the hydraulic oil outflow side can be held at least at the pressure set by the relief valves 70, 70.

Although the embodiment of the present invention has been described in detail above with reference to the drawings, the specific configuration is not limited to this embodiment, and the present invention can be applied even if there is a design change or the like within a range not departing from the gist of the present invention. included.

For example, in the embodiment, the cylinder stroke signal is used as the signal corresponding to the wheel turning angle, but a turning angle signal obtained by directly detecting the turning angle of the steered wheels may be used.

Further, the residual pressure mechanism is not limited to the embodiment as long as it is a mechanism capable of leaving the line pressure on the hydraulic oil outflow side.

Further, as the steering cylinder, a cylinder that operates linearly is shown, but a cylinder that performs a rotational operation or a curved operation may be used.

(Effects of the Invention) As described above, in the all-hydraulic power steering device of the present invention, the drain is provided by switching the control signal for steering wheel position correction in the middle of the drain oil lines provided in the two hydraulic lines. Providing hydraulic oil outflow means for communicating the oil line with the hydraulic oil tank, and outputting a control signal for steering wheel position correction to the hydraulic oil outflow means when the difference between the actual detected value and the control target value exceeds a predetermined value. Since the control means is provided, a control signal for correcting the position of the steering wheel is immediately output without a time limit when a predetermined amount of deviation occurs, and based on this control signal, the steering wheel position with respect to the position of the steered wheels is changed to hydraulic oil. The effect that it can be corrected by the outflow is obtained.

Further, since the hydraulic oil outflow means is provided with a residual pressure mechanism that leaves a pressure that allows the steering cylinder to hold its position when the hydraulic oil flows out, the transmission of pressure to the steering cylinder is not interrupted when the position of the steering wheel is corrected. The effect of being able to hold the position of the steering cylinder is obtained.

[Brief description of drawings]

FIG. 1 is a conceptual diagram of a claim showing an all-hydraulic power steering device of the present invention, FIG. 2 is a plan view showing a three-wheel forklift truck equipped with the first embodiment device, and FIG. 3 is a block of the first embodiment device. Diagram, FIG. 4 is a cross-sectional view showing a specific example of the electromagnetic switching valve of the first embodiment device, and FIGS. 5 and 6 are cross-sectional views showing a specific example of the handle rotation angle sensor of the first embodiment device. FIG. 7 is a partially cutaway side view, FIG. 7 is a graph showing a control target value stored in advance in a control unit of the embodiment apparatus, and FIG. 8 is a flow chart diagram showing a flow of operation in the CPU of the control unit of the embodiment apparatus, FIG. 9 is a schematic view of an essential part showing the device of the second embodiment, FIGS. 10 and 11 are schematic views of an essential part showing the device of the third embodiment, and FIG. 12 is an outline of an essential part showing the device of the fourth embodiment. Figures and 13 show a conventional full hydraulic power steering system. Plan view illustrating the mounting the three-wheel forklifts truck, Fig. 14 view block diagram showing an apparatus of the prior art, FIG. 15 is a graph showing changes in the hydraulic oil outlet side steering cylinder pressure in the prior art device. 1 …… Handle 2 …… Steering unit 3 …… Steering cylinder 4,5 …… Hydraulic line 6,7 …… Hydraulic oil outflow means 8 …… Control means 9,10 …… Residual pressure mechanism 11 …… Hydraulic oil tank 12 , 13 …… Drain oil line 14 …… Steering pump (θ ₁ ) …… Handle rotation angle signal (θ ₂ ) …… Wheel steering angle equivalent signal (a) …… Control signal (b) …… Control signal

Claims (3)

[Claims] 1. A steering unit operated by a steering wheel, a steering cylinder for steering a steered wheel, and two hydraulic lines connecting the steering unit and the steering cylinder, wherein the steering unit is switched by the steering wheel. Has a valve mechanism, one of two input ports of the valve mechanism is connected to a steering pump, the other is connected to a hydraulic oil tank, and two output ports of the valve mechanism are respectively connected to two hydraulic lines. In the all-hydraulic power steering system, a hydraulic oil outflow means for connecting the drain oil line and the hydraulic oil tank by switching by a control signal for steering wheel position correction is provided in the middle of the drain oil lines provided in the two hydraulic lines, Handle rotation to the hydraulic oil outflow means The signal and the signal corresponding to the wheel turning angle are input, the difference between the actual detected value and the control target value is calculated, and if this difference exceeds a predetermined value, a control signal for correcting the position of the steering wheel is output from the hydraulic oil. Means for outputting to the means, and the hydraulic oil outflow means is provided with a residual pressure mechanism for leaving a pressure sufficient to maintain the position of the steering cylinder when the hydraulic oil flows out. . 2. The drain oil line is branched from each of the two hydraulic lines to a hydraulic oil tank so that the drain oil line and the hydraulic oil tank are directly communicated with each other by switching by the control signal of the hydraulic oil outflow means. The all-hydraulic power steering device according to claim 1, characterized in that the line is a communication line. 3. The drain oil line is connected to two drain oil lines so that the drain oil line and the hydraulic oil tank communicate with each other via one hydraulic line and a valve mechanism of a steering unit by switching by a control signal of the hydraulic oil outflow means. The all-hydraulic power steering device according to claim 1, wherein the hydraulic lines are connected to each other.