JPS62241768A - Power steering device - Google Patents

Abstract

PURPOSE:To secure excellent stability, by installing a device which determines a desired value of return speed, and driving and controlling a return assist mechanism by a control signal complying with the desired value, in the case of a device provided with the return assist mechanism restoring a steering system to a rectilinear state. CONSTITUTION:In case of a device which controls an electric motor (return assist mechanism) 11 by a controller 15 according to each output of respective sensors 12-14 for steering torque, a steering angle and a car speed and secures auxiliary steering force, a restoring state judging circuit 18, which judges whether a steering system is restoring to a rectilinear state or not, is installed in this controller 15. And, also there is provided with a return speed control circuit 20 which carries out return speed control at the time of restoring. And, this return speed control circuit 20 is constituted of a setting part 21 calculating a desired value of return speed on the basis of each output of a steering angle sensor 13 and a car speed sensor 14, a calculating part 22 differentiating the detected steering angle value and calculating the actual return speed and a converting part 23 outputting the driving current desired value based on the desired value and the actual value.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a power steering device for a vehicle such as an automobile.

[Conventional technology]

As a conventional power steering device, for example, Japanese Patent Application Laid-Open No. 59-19
There is one described in Japanese Patent No. 5470.

This thing has an electric motor connected to the vehicle's steering system.
When returning the steering wheel to the straight-ahead state after steering, the electric motor generates a predetermined return assist force to return the steering system to the straight-ahead state.

[Problem that the invention seeks to solve]

However, in such conventional power steering devices, the voltage (or current) to the electric motor is controlled according to the torsional torque of the steering shaft, and the rotational force of the electric motor is used to return the steering wheel to a straight-ahead state. As a result, the return speed when the steering wheel is released varies greatly due to driving conditions such as vehicle speed and steering angle, or the frictional force of the entire steering system due to variations in component parts, etc., making it difficult for the driver to steer the steering wheel. There was a problem that a different phase window was generated.

This invention has been made by focusing on such conventional problems, and it sets a target value for the return speed based on the vehicle speed, steering angle, etc. that affect the return speed of the steering system, and sets the target value for the return speed. The purpose of this invention is to solve the above problems by controlling the actual return speed to match the actual return speed.

[Means for solving problems]

In order to solve the above-mentioned problems, the present invention provides a power steering system having a return assist mechanism capable of returning a steering system to a straight-ahead state, including return speed target value determining means for determining a target value of return speed; The present invention is characterized by comprising a control means for outputting a control signal based on a return speed target value to drive and control the return assist mechanism.

[Effect]

Accordingly, in the present invention, the driving state detecting means detects the driving state such as the vehicle speed and the steering angle that affect the return speed of the steering system, and the returning speed target value determining means determines the return speed based on the driving state. In addition to determining the target value, the control means outputs a control signal based on the return speed target value to drive and control the return assist mechanism, so that the actual return speed matches the return speed target value, and the steering system moves straight. Improve state recovery performance.

〔Example〕

The present invention will be explained below based on illustrated embodiments.

FIGS. 1 to 3 are diagrams showing one embodiment of the present invention.

First, to explain the structure, l shown in Fig. 1 is a steering shaft, and this steering shirt l-1 is
It is composed of an upper shaft 1a and a lower shaft lb that are connected via a universal joint 2. Upper shaft 1
A steering wheel 3 is fixed to the upper end of the lower shaft lb, and a pinion shaft 5 is connected to the lower end of the lower shaft lb via a universal joint 4. , meshes with the rack 6a of the rack shaft 6 inside a steering gear box (not shown). Furthermore, tie lofts 7 (only the left half is shown) are swingably connected to both ends of the rack shaft 6, and a front wheel 8, which is a steered wheel, is rotatably supported at the outer end of each tie rod 7. The knuckles 9 are swingably connected to each other.

Above steering wheel 3, steering shaft 1
, universal joints 2, 4, pinion shaft 5, rack shaft 6,
The tie rod 7 and knuckle 9 constitute a steering system.

Further, the pinion shaft 5 is connected to a rotating shaft 1)a of an electric motor 1), which is a specific example of a return assist mechanism capable of returning the steering system to a straight-ahead state, via a reduction gear mechanism IO. This reduction gear mechanism IO includes a casing 10
A driving gear tob and a driven gear 10c that mesh with each other in a
The driven gear IOC is fixed to the pinion shaft 5, and the drive gear 10b is fixed to the rotating shaft 1)a. The electric motor 1) is composed of, for example, a DC servo motor, and its rotational force is transmitted to the steering system via the reduction gear mechanism 10, thereby providing steering assist torque during steering and steering return torque during restoration. is assigned to the steering system.

Further, the steering shaft 1 is provided with a steering torque sensor 12 that detects the steering torque applied manually to the steering shaft 1 from the steering wheel 3. The steering torque sensor 12 is composed of, for example, a strain gauge fixed to the steering shaft 1, and detects the torsion that occurs in the steering shaft 1 when the driver turns the steering wheel 3, and detects the magnitude of the torsion. A steering torque detection signal DT consisting of a corresponding analog voltage is output.

Reference numeral 13 denotes a steering angle sensor that detects the steering angle, and is composed of a rotation detector made of, for example, a disk with a slit attached to the steering shaft 1 and a photocoupler having two sets of detectors facing the slit. , outputs a steering angle detection signal Dθ which is a pulse signal according to the rotational direction and rotational speed of the steering shaft l.

Further, 14 is a vehicle speed sensor that detects the vehicle speed, and detects, for example, the rotational speed of the output shaft of the transmission, and outputs a vehicle speed detection signal DV that is a pulse signal with a period corresponding to this.

The steering angle sensor 13 and the vehicle speed sensor 14 constitute a driving state detection means, and the detected steering angle and vehicle speed are driving state information that affects the steering return speed,
The steering angle detection signal Dθ and the vehicle speed detection signal DV constitute a driving state detection signal.

These driving state detection signals Dθ, DV and steering torque detection signal DT are supplied to the control device 15 as a control means, and based on these, the control device 15 determines whether the steering is being performed or the state is being restored to the straight-ahead state (steering angle = 0). When it is determined that restoration is in progress, the control switching circuit 16 is switched to the return speed control side, and a drive current, which is a control signal, is output to the electric motor 1) via the drive circuit 17. The return assist force of the electric motor 1) is controlled to return the steering angle to O based on the return speed target value, thereby restoring the steering system to the straight-ahead state.

As shown in FIG. 2, this control device 15 includes a restoring state determination circuit 18 that determines whether or not the steering system is restoring to the straight-ahead state, and a restoring state determination circuit 18 that executes returning speed control when the steering system is restoring to the straight-ahead state. It is composed of a speed control circuit 20. The restoration state determination circuit 18 is supplied with the steering torque detection signal DT of the steering torque sensor 12 and the steering angle detection signal Dθ of the steering angle sensor 13, and based on these, the steering torque detection value is below a predetermined value and the steering angle detection value is is greater than a predetermined value, it is determined that the steering system is in the restoring state, and the restoring state determination signal R3 is output to the control switching circuit 16.

The control switching circuit 16 is a circuit that selects whether to perform steering assist torque control during steering or return speed control when restoring after steering. When the restoration state determination signal R3 is supplied in the subsequent restoring state, the switch is made to the return speed control circuit 20 side, and as a result, the return speed control signal output from the return speed control circuit 20 is It is supplied to the electric motor 1) via a drive circuit 17.

The return speed control circuit 20 is supplied with the steering angle detection signal Dθ from the steering angle sensor 13 and the vehicle speed detection signal DV from the vehicle speed sensor 14, and is operated based on the steering angle θ and vehicle speed V corresponding to these input signals as shown in FIG. A setting unit 21 that calculates and determines a target value υref of the return speed from the steering angle θ using the vehicle speed ■ shown in as a parameter, and outputs the target value signal θref.
and a calculation unit 22 which is supplied with the steering angle detection signal Dθ, differentiates the steering angle value θ corresponding to the steering angle detection signal Dθ, calculates the actual return speed υ, and outputs the actual value signal σ; It is comprised of a converting section 23 that converts a deviation signal (i ref-υ) obtained by adding the target value signal 0 ref and the actual value signal 0 into a current value and outputs it as a drive current target value i ref.

In Fig. 3, the horizontal axis shows the steering angle θ, and the vertical axis shows the return speed target value υref, and the target value changes as the vehicle speed increases (VI < Vz < V3 < Va). It is set so that θref is large. For example, it is defined as follows.

(1) When vehicle speed≠0■ For the return speed target value/1ref, the vehicle speed 4Qkm/h is taken as the reference value θrefa.

drefo= dref (V = 40) ■ At other vehicle speeds lj ref (V = 20) = a refo X
(20/40) “”7ref (V = 60) =
4refoX (60/40)””i ref (V
=80) = lI refo X (80/40)
"" (2) When vehicle speed = 0, θref (V-0) = constant value. Note that the restorability of the steering system increases as the speed increases, so
When the vehicle speed exceeds a certain level, the restorability improvement operation by the electric motor 1) is discontinued. Thereby, it is possible to save the current consumption of the electric motor 1).

Drive current target value i re output from the converter 23
After passing through the control switching circuit 16, f is added to the current value i of the drive current flowing through the motor 1) fed back from the motor 1) at the summing point, and the current value i is calculated according to the current difference value (iraf i). A current signal of the value is supplied to the drive circuit 17. As a result, the drive circuit 17
outputs a drive current corresponding to the input current difference value (iref-i) to the electric motor 1), and by feedback-controlling the electric motor 1) in this way, a steering return torque is generated in the electric motor 1). The steering system is restored to a straight-ahead state.

Next, the effect will be explained.

Now, assuming that the vehicle is in a running state, the steering torque detection signal DT from the steering torque sensor 12, the steering angle detection signal Dθ from the steering angle sensor 13, and the vehicle speed detection signal DV from the vehicle speed sensor 14, which represent the running state, are Each is supplied to the control device 15.

At this time, when the vehicle is running straight ahead, the detected steering torque value is 0 (or less than a predetermined value), and the detected steering angle value is also 0 (or less than a predetermined value), and the restoration state judgment circuit 18 Since the AND condition (steering torque is below a predetermined value and steering angle is above a predetermined value) is not satisfied, the restoring state determination circuit 18 does not output the restoring state determination signal R3. As a result, since the control switching circuit 16 maintains the normal connection state on the steering torque control circuit side, return speed control for restoring the steering system to the straight-ahead state (neutral position) is not performed.

In this running state, when the driver steers the steering wheel 3 to the right (or left), both the detected steering torque value and the detected steering angle value become greater than a predetermined value, and in this case also, the restoration state determination circuit 18 Since the AND condition is not satisfied, the restoration state determination signal R3 is not output, and therefore, the return speed control is not executed in this case as well.

Next, after the above-mentioned steering, the steering wheel 3 is turned back, and it is assumed that only the detected steering torque value falls below a predetermined value, while the detected steering angle value remains above a predetermined value. Since the state determination circuit 18 determines that the steering system is being restored to the straight-ahead state, the restoration state determination signal R3 is output and the control switching circuit 16 is switched to the return speed control circuit 20 side.

At this time, in the return speed control circuit 20, the vehicle speed sensor 14
The setting unit 21 is based on the current vehicle speed based on the vehicle speed detection signal DV from
The target value υref of the return speed is determined at , and the steering angle change litυ is calculated by differentiating the detected steering angle value in the calculation unit 22 , and the target value signal υref and the change amount signal υ are added at a point 24 added at,
The sum signal (θref-7) is converted into a current value by the counter 23 and outputted from the control device 15 as a drive current target value i ref.

The drive current target value 1ref is determined by the following addition point 25
The drive current detection value i of the electric motor 1) is subtracted, and the difference value (iref-i) between the two types of flow values is output as a control amount to the electric motor 1) via the drive circuit 17. As a result, the electric motor 1) is drive-controlled to restore the steering system to the straight-ahead state at a return speed that corresponds to the steering angle and vehicle speed during control, and the return speed control continues until the steering system is returned to the straight-ahead state. be done.

As shown in Fig. 3, by storing the relationship between the steering angle θ and the return speed target value υref in the storage device in advance in the form of a storage table using the vehicle speed as a parameter, it is possible to avoid using too much memory capacity. Smooth return speed control can be achieved.

FIG. 4 (al and (bl are return speed target value θref)
Here is another example of determining. In addition, (a) and (b) of the same figure
In both cases, the horizontal axis represents the steering angle θ, and the vertical axis represents the return speed target value υref.

The graph shown in FIG. 4(a) indicates that the speed target value 4 is returned to a predetermined value regardless of both the steering angle θ and the vehicle speed V.
This is set as a ref. In this case, since it is only necessary to set one reference value, the configuration can be made the simplest and cheapest.

The graph shown in FIG. 6(b) is related only to the steering angle θ, regardless of the vehicle speed V, and is set so that the return speed target value υref increases proportionally as the steering angle θ increases. . In this case, the return speed target value θref may be stored in the storage device of the microcomputer in the form of a storage table, or in the case of an electronic circuit configuration, a function generator may be provided as a function of the steering angle θ. good.

5 and 6 show other examples of the control method in the conversion section 23 of the return speed control circuit 20.

In the converter 23 of the embodiment described above, the return speed target value θr
The drive current target value 1ref is calculated by proportionally controlling the deviation ε=θref−shield between ef and the steering angle change scale (see Fig. 6).
Although the example a)) has been described, by providing the proportionality coefficient k as a function of the deviation ε, it is possible to smooth the return speed of the steering system and eliminate the strange feeling during steering.

That is, FIG. 5 shows the steering angle θ at a certain vehicle speed Vex.
The absolute value 1θ1 (the absolute value is used to treat right steering and left steering equally) and the return speed target value θref
It is a graph showing the relationship with the absolute value 1θref l,
As is clear from the figure, when the hand is suddenly released from the holding state at the steering angle θ, the initial deviation ε1 at that time is large, so the proportionality coefficient k is too large, as shown by the dashed-dotted curve X. Then, the return speed target value #ref (X) increases rapidly, and the return speed target value ref (V
ex), and then the target value 1) re
The vibration vibrates around f (V ex) and converges, and the return speed of the steering wheel 3 fluctuates greatly, causing a strange feeling in steering. On the contrary, if the proportionality coefficient k is too small as shown by the broken line curve Y, the return speed target value υref (Y ) will not reach the return speed target value &ref (Vex) during continuous steering, and the steering Responsiveness deteriorates.

Therefore, the proportionality coefficient k is a function of the deviation ε (k=k(ε)
), and this function is stored in advance in the form of a storage table in the storage device of a microcomputer, for example, and then converted into a proportional coefficient as shown in the graph 81 shown by the solid line in FIG. 6(b) or the graph T1 shown by the broken line. The relationship between the deviation ε and the current target value i ref can be determined by changing the value of ε according to the deviation ε, increasing the proportional coefficient k when the deviation ε is small, and setting the proportional coefficient k small when the deviation ε is large. The relationship can be set as shown in the graph shown in FIG. 6 (C1 (graph T2 corresponds to graph T, and graph St corresponds to graph S1).

Therefore, in this embodiment, the return speed of the steering system is controlled to a large proportional coefficient when the initial deviation ε is small, and when the initial deviation ε is large, it is initially controlled to a small proportional coefficient, and then the deviation ε becomes smaller. By controlling the steering system to a relatively large proportional coefficient, it is possible to smooth the return speed of the steering system to the straight-ahead state, eliminate the sense of discomfort during steering, and prevent deterioration in steering responsiveness.

FIG. 7 shows a second embodiment of the invention.

In this embodiment, the return assist mechanism in the previous embodiment is constructed by a hydraulic cylinder 30 installed in relation to the rack shaft 6, and a hydraulic control valve 31 for switching and controlling this hydraulic cylinder 30.

The hydraulic cylinder 30 includes a cylinder body 32 through which a rack shaft 6 passes, and a piston 3 that partitions the inside of this cylinder body 32 into two pressure chambers A and B, and is fixed to the rank shaft 6.
3, and the cylinder body 32 is fixed to the vehicle body side. The hydraulic control valve $1 is a 4-point, 3-position, spring offset electromagnetic type directional switching valve, and a drive current, which is a control signal from the control device 15, is applied to the control switching circuit 16 and the electromagnetic solenoid 31a. Drive circuit 17
The spool 31b is moved forward and backward by the excitation of the electromagnetic solenoid 31a, and the hydraulic pressure supplied from the hydraulic pump 34 is supplied to the two pressure chambers A.

B and discharged to the reservoir tank 35.

Note that the other configurations are the same as those in the embodiment described above, and the same effects as in the embodiment described above can also be obtained by configuring in this manner.

Furthermore, FIGS. 8 and 9 show a third embodiment of the present invention.

In this embodiment, a selection switch is provided in the device shown in FIG. to operate the return assist force.
This allows the driver to select whether or not to operate according to his or her preference.

As shown in FIG. 8, the selection switch 40 is connected to the control device 15, and a selection signal DS indicating its on or off state is input to the control device 15.

Generally, the steering system has a self-centering function that returns the vehicle to a straight-ahead state even when the vehicle speed is O. However, in some cases, this self-centering function may not be necessary. For example, when parallel parking, keeping the same steering angle as when the vehicle was parked will make it easier to get out of the vehicle next time. In addition, parking on slopes is legally regulated in the United States and other countries, i.e., parking with the wheels turned against the curb to prevent the vehicle from going down the slope even if the parking brake breaks. This is the case.

Therefore, when the vehicle speed is 0 or close to 0, it would be very convenient if the driver could select whether to activate or deactivate the restoration function according to his preference.

Next, the operation when the selection switch 4o is used will be explained with reference to FIG. 9 showing an example thereof.

The control device 15 according to this embodiment has at least a microcomputer having, for example, an input/output interface circuit, an arithmetic processing unit, a storage device, etc., and the storage device includes:
The graphs shown in steps ■, ■, and [phase] in the same figure are each stored in a predetermined storage area in the form of a memory table, and the graphs shown in steps ■, ■, and [phase] are respectively stored in a predetermined storage area in the form of a memory table, and depending on the corresponding vehicle speed (■□〉VM > Vt) and according to the steering angle θ. The return speed target value υref can be searched and determined using the table run query. Then, the arithmetic processing unit executes arithmetic processing according to the timer interrupt processing program shown in the figure, for example, which is stored in advance in the storage device.

First, in step (2), the selection signal DS from the selection switch 4o is read and temporarily stored in a predetermined storage area of the storage device. At this time, assuming that the selection switch 40 selects the off state in which no restoration assisting force is generated,
A value representing an off state is stored in the storage device.

In the next step (2), the steering angle detection signal Dθ of the steering angle sensor 13 is read, and the detected steering angle value θ is temporarily stored in a predetermined storage area of the storage device.In the following step (2), the vehicle speed detection signal DV of the vehicle speed sensor 14 is is read, and the detected vehicle speed value V is temporarily stored in a predetermined storage area of the storage device.

In the next step ■, the first vehicle speed reference value vl stored in advance in the storage device and the detected vehicle speed value ■ stored in step ■ are used.
It is determined whether the detected vehicle speed value V is less than the first vehicle speed reference value 71 or not.

In this case, the determination is made by checking whether the vehicle is in an extremely sluggish running state with a vehicle speed of less than 71 or in a stopped state with a vehicle speed of 0. If V<V, the process moves to step (2).

In this step (2), it is determined whether the selection switch 40 is in the off state. The determination in this case is to see whether the driver does not require the restoring assist force, and is made by checking the switch selection state stored in step (3).

Here, assuming that the driver turns off the selection switch 40 and selects the non-operation of the return assist mechanism,
Loading the off state at step ■, and step ■～
After the process in ■, it is determined that the off state is selected in this step ■, so the next step is to proceed to step ■.
The return speed target value υrcf is determined to be O. Then, in the next step (2), a control signal having a value corresponding to the return speed target value υref determined in step (2) is output.

However, since the return speed target value 1/ref=0, no drive current is output from the drive circuit 17, and the motor 1
) is held non-rotating. As a result, the reduction gear mechanism 10 and the steering system are held in a non-rotating state, and the wheels 8 and steering wheel 3 similarly remain in the steered state.

On the other hand, assuming that the vehicle is running at an extremely low speed of less than vehicle speed (1) and the driver has selected the operation of the return assist mechanism by turning on the selection switch 40, in step (2), the selection switch 40 is turned on. Since it is determined that the return speed control is selected in the on state, in this case, the process moves to step 2, and the return speed control corresponding to the absolute value 1θ1 of the steering angle θ is performed based on the low speed characteristic ■ and the conversion table. The absolute value 14refl of the speed target value υref is searched.

Then, in the next step 0, a control signal having a value corresponding to the return speed target value θref determined in step (2) is output.

As a result, through the operation of the control switching circuit 16 and the drive circuit 17, the electric motor 1) is rotationally driven to return the steering system to the straight-ahead state at a speed corresponding to the vehicle speed, thereby moving the steering wheel 3 into neutral at the same speed. returned to the state.

Further, if the vehicle is running at a speed equal to or higher than the first vehicle speed reference value (■1), the process proceeds to step (2) based on the determination of step (step) and (b), and the detected vehicle speed value V is set to the first vehicle speed reference value. ■
It is determined whether the vehicle speed is lower than a second vehicle speed reference value V2 which is higher than V1. As a result of that determination, the detected vehicle speed value ■ is the second
If the detected vehicle speed value 12 or more is equal to or higher than the second vehicle speed reference value 12, the process moves to step (2), while if the detected vehicle speed value (2) is less than the second vehicle speed reference value 72, the process moves to step [phase]. In these steps (2) and [phase], the absolute value Iθref1 of the return speed target value 4ref is searched and determined in the same manner as in the step (2), and in the following step (2), a control signal is output in the same manner as described above.

Therefore, in this embodiment, the vehicle speed V is equal to the first vehicle speed reference value 7.
When it is 1 or more, the return assist force is applied regardless of whether the selection switch 40 is on or off, but V
<V, when the return assist force is applied only when the selection switch 40 is in the ON state, and when the same switch 40 is in the OFF state, the return assist force is not applied, and the steering state at that time is maintained as it is. .

Therefore, in the case of this embodiment, when the selection switch 40 is turned off and the restoration function is selected to be inactive, if the vehicle speed decreases below a predetermined vehicle speed, the steering angle of the wheels is maintained as it is, for example. It is possible to easily take out a vehicle that is parallel parked, and it is also possible to satisfy a specific parking method stipulated by law.

It should be noted that the processing of Steps (2) to (Phase) above constitutes a return speed target value determining means, and the processing of Step (2), the control switching circuit 16, and the drive circuit 17 constitute a control means.

FIG. 10 shows a fourth embodiment of the invention.

In this embodiment, the selection switch 40 shown in FIG. 8 is added to the device shown in FIG. 7. With this configuration as well, the same effects as in the embodiment shown in FIG. 8 can be obtained.

In the above embodiment, the steering angle sensor 13 and the vehicle speed sensor 14 constitute the driving state detection means, but at least one of the sensors may constitute the same detection means.

Furthermore, it goes without saying that the aforementioned selection switch is not limited to one for selecting whether or not to execute return speed control, but may also be a switch for selecting a control mode such as a return speed control pattern.

〔Effect of the invention〕

As described above, according to the present invention, in a power steering system having a steering system return assist mechanism, means for determining a target value of the return speed is provided, and the actual return speed is made to match the target value. Because it is configured to control as much as possible,
When returning the steering system to a straight-ahead state, the return speed can be made natural and clean, eliminating delay in response and strange feeling during steering, and achieving high restoring performance. You can get the effect that you can.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of the present invention, FIG. 2 is a block diagram showing an example of a control device according to the present invention,
FIG. 3 is a graph showing the relationship between the steering angle and the return speed target value, which is used to explain the present invention, and FIGS. 4(a) to (C1 and FIG. Graphs showing other examples, FIGS. 6(a) to 6(C) are graphs for explaining the graph in FIG. 5, FIG. 7 is a schematic diagram showing the second embodiment of the present invention, and FIG. The figure is the third part of this invention.
FIG. 9 is a flowchart showing an example of the processing procedure of the control device according to the third embodiment;
FIG. 10 is a schematic configuration diagram showing a fourth embodiment of the present invention. 1... Steering shaft, 3...
Steering wheel, 5... Binion shaft, 6... Rack shaft, 10... Reduction gear mechanism, 1)... Electric motor (return assist mechanism)
, 12... Steering torque sensor, 13...
・Steering angle sensor, 14...Vehicle speed sensor, 15・
... Control device (control means), 16 ... Control switching circuit, 18 ... Restoration state judgment circuit, 20
... Return speed control circuit, 30 ... Hydraulic cylinder, 31 ... Hydraulic control valve, 40 ...
...Selection switch Figure 1 Figure 7 Figure 8 Procedure owner's official document (method) June 25, 1985 Michibu Uga, Commissioner of the Patent Office, 1986 Patent Application No. 82851 2, Name of invention Power Steering device 3ura 1) Relationship with the case of person who takes corrective action Patent applicant name (399) Nissan Motor Co., Ltd. 4, agent address 628-ku 8, 6th floor, Tokyo Bank Building, 4-2 Marunouchi-chome, Chiyoda-ku, Tokyo Sakae Patent Office 6, Column 7 for a brief explanation of drawings in the specification subject to amendment, Contents of amendment (1) Page 27 of the specification, line 3 “Figure 4 (a) to fc
) and'' should be corrected to ``4 Figure (al, (b) and'').

Claims (5)

[Claims] (1) In a power steering system having a return assist mechanism capable of returning a steering system to a straight-ahead state, a return speed target value determining means for determining a target return speed, and a control signal based on the return speed target value. A power steering device comprising: a control means for driving and controlling the return assist mechanism by outputting an output. (2) The power steering system according to claim (1), wherein the target value of the return speed is determined based on a detected value of at least one of vehicle speed and steering angle. (3) The power rudder according to claim (1) or (2), wherein the control means varies a control constant according to a deviation between the target return speed value and the actual return speed value. removal device. (4) The target value of the return speed is determined based on the detected value of the vehicle speed, and the control means stops outputting the control signal and stops the return speed control when the vehicle speed is equal to or higher than a predetermined value. A power steering device according to claims (1) to (3). (5) The control means has a selection switch that can select whether or not to execute return speed control or select any control mode from among a plurality of return speeds. The power steering device described in items 1) to (4) of the same.