JP2007196917A - Power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power steering device not to make the sound from a stepping motor conspicuous in initial control to decide an initial position of the stepping motor. <P>SOLUTION: This power steering device to assist steering by hydraulic pressure which a hydraulic pressure control valve controls with a rotating position of the stepping motor when a variable throttle valve is totally closed set as its standard position by actuating the stepping motor driven by a pulse of specified frequency, controlling a pressure oil flow rate of the hydraulic control valve by the variable throttle valve provided on the outlet side of the hydraulic control valve in correspondence with car velocity (c) detected by a car velocity detector and driving the stepping motor by the pulse number equivalent to a total driving range of the variable throttle valve (d) in starting (a)(b). It is furnished with a (d) driving means to drive the stepping motor by the pulse number equivalent to the total driving range by frequency different from the specified frequency so as to reduce the generated sound from the stepping motor in starting (a)(b). <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  In the present invention, the flow rate of the hydraulic control valve is controlled by a variable throttle valve on the outlet side driven by the stepping motor, and the stepping motor is driven at the number of pulses corresponding to the entire drive range of the variable throttle valve at the start. The present invention relates to a power steering device in which the rotation position of a stepping motor when a throttle valve is fully closed is used as a reference position of the stepping motor.

  2. Description of the Related Art Conventionally, a hydraulic power steering apparatus that supplies hydraulic oil from an oil pump to a power cylinder coupled to a steering mechanism and generates a steering assist force from the power cylinder is used in vehicles. Such a power steering device is provided with a hydraulic control valve having a plurality of throttle portions whose opening degree changes according to the steering torque, and an appropriate steering assist force is supplied from a power cylinder to which hydraulic pressure is supplied according to the steering torque. Is supposed to occur.

  The hydraulic power steering device is provided on the outlet side of the hydraulic control valve in order to change the relationship of the steering resistance to the hydraulic pressure acting on the power cylinder according to the vehicle speed, and controls the pressure oil flow rate of the hydraulic control valve Some have a variable throttle valve. The variable throttle valve has a housing, a spool inserted in the housing so as to be axially movable, and a screw member that is screwed into the spool, and the spool moves in the axial direction as the screw member rotates. Thus, the opening degree is changed.

  The screw member is rotated by a stepping motor, and the stepping motor is driven and controlled by a controller including a microcomputer. Since the rotation position (number of steps) of the stepping motor corresponds to the opening of the variable throttle valve on a one-to-one basis, the controller can control the opening of the variable throttle valve by controlling the rotation position of the stepping motor. The hydraulic pressure can be controlled by controlling the pressure oil flow rate of the hydraulic control valve.

  The rotational position of the stepping motor is generally controlled by an open loop control method. In the open loop control method, the rotation position of the stepping motor when the spool is at a predetermined position is used as a reference position, and the number of stepping motor drive pulses (steps) required to move the spool to the target position based on this reference position. Number, rotational position).

Actually, the stepping motor is driven with the number of pulses (number of steps) corresponding to the entire movement range of the spool (the entire drive range of the variable throttle valve) at the time of start-up, and the spool is moved to the full moving position (predetermined position). The rotation position of the stepping motor when the variable throttle valve is fully closed is the initial position (reference position) of the stepping motor. In this case, after the variable throttle valve is fully closed, the stepping motor will step out even if a pulse is given, so the rotational position does not change.
JP 2002-233189 A

As described above, in the conventional power steering device, the initial position of the stepping motor is determined by driving the stepping motor with the number of pulses corresponding to the entire driving range of the variable throttle valve at the time of startup (initial control). Since this is a quiet period during non-running, there is a problem that the sound generated from the stepping motor becomes annoying.
In Patent Document 1, paying attention to the fact that the required torque during driving of the variable throttle valve is smaller than the required torque at the start of driving, the pulse rate during driving at the initial control is larger than the pulse rate at the start of driving. An origin positioning device for a stepping motor that shortens the time required for initial control is disclosed.

  The present invention has been made in view of the above-described circumstances, and an object thereof is to provide a power steering device in which sound generated from a stepping motor is not noticeable at the time of initial control for determining an initial position of the stepping motor. .

  A power steering device according to a first aspect of the present invention operates a stepping motor driven by a pulse of a predetermined frequency, and a vehicle speed detector detects a pressure oil flow rate of the hydraulic control valve by a variable throttle valve provided on an outlet side of the hydraulic control valve. The stepping motor rotates when the variable throttle valve is fully closed by driving the stepping motor with the number of pulses corresponding to the full drive range of the variable throttle valve at the time of start-up. In the power steering device configured to assist the steering by the hydraulic pressure controlled by the hydraulic control valve with the position as the reference position of the stepping motor, at the start-up, the generated sound from the stepping motor is reduced. A driver that drives the stepping motor by a number of pulses corresponding to the entire driving range at a frequency different from the predetermined frequency. Characterized in that it comprises a.

  The power steering device according to a second aspect of the present invention is the power steering device, wherein the driving means drives the stepping motor with a pulse having a frequency different from the predetermined frequency, and the driving is detected when the vehicle speed detector detects a vehicle speed exceeding 0. The stepping motor is driven with a pulse of the predetermined frequency, with the rotational position of the stepping motor when the driving is interrupted as a temporary reference position, and the pressure oil is driven by a variable throttle valve. And a means for controlling the flow rate, and when the means controls, when the vehicle speed detector detects 0, the driving means is resumed from the temporary reference position. It is characterized by being.

  According to the power steering device of the first aspect of the present invention, at the time of start-up, the driving means reduces the generated sound from the stepping motor by the number of pulses corresponding to the entire driving range at a frequency different from the predetermined frequency. Therefore, it is possible to realize a power steering device in which the sound generated from the stepping motor is not noticeable during the initial control for determining the initial position of the stepping motor.

  According to the power steering apparatus of the second invention, when the driving means drives the stepping motor with a pulse having a frequency different from the predetermined frequency, when the vehicle speed detector detects a vehicle speed exceeding 0, the driving means The driving is interrupted, the rotational position of the stepping motor at the time of the interruption is set as a temporary reference position, the stepping motor is driven with a pulse of a predetermined frequency, and the pressure oil flow rate is controlled by the variable throttle valve. If the vehicle speed detector detects 0 in this control, the driving means restarts from the temporary reference position. Therefore, a pulse with a lower frequency is used for the initial control for determining the initial position of the stepping motor. Can be used, and a power steering device in which the sound generated from the stepping motor is not noticeable can be realized.

Hereinafter, the present invention will be described with reference to the drawings showing embodiments thereof.
FIG. 1 is a longitudinal cross-sectional view showing a main configuration of a power steering apparatus according to the present invention. In this power steering apparatus 1, an input shaft 2 is connected to a steering member (handle) (not shown) of a vehicle, and an output shaft 3 is connected to the input shaft 2 via a torsion bar 6. The torsion bar 6 is connected to the input shaft 2 by a pin 4 and is connected to the output shaft 3 by a serration 5.
The input shaft 2 is supported by the valve housing 7 via a bearing 8 and supported by the output shaft 3 via a bearing 12. The output shaft 3 is supported by the rack housing 9 via bearings 10 and 11.

A pinion 15 is formed below the output shaft 3, and a steering wheel (not shown) is connected to the rack 16 that meshes with the pinion 15. As a result, the rotation of the input shaft 2 by steering is transmitted to the pinion 15 via the torsion bar 6, and the rotation of the pinion 15 is converted into the movement of the rack 16 in the vehicle width direction, thereby turning the steered wheels. Is done.
A hydraulic cylinder 20 is provided as an actuator for generating a steering assist force. The hydraulic cylinder 20 includes a cylinder tube constituted by the rack housing 9 and a piston 21 integrated with the rack 16. In order to supply pressure oil to the oil chambers 22 and 23 partitioned by the piston 21 according to the steering direction and the steering resistance, a rotary hydraulic control valve 30 is provided.

The hydraulic control valve 30 includes a cylindrical first valve member 31 that is inserted into the valve housing 7 so as to be relatively rotatable, and a second valve member 32 that is coaxially inserted into the first valve member 31 so as to be relatively rotatable. It has.
The first valve member 31 is connected to the output shaft 3 so as to rotate along with the output shaft 3, and the second valve member 32 is formed integrally with the input shaft 2. That is, the second valve member 32 is configured by the outer peripheral portion of the input shaft 2, and the second valve member 32 rotates along with the input shaft 2. Thereby, the 1st valve member 31 and the 2nd valve member 32 rotate relatively coaxially by twisting the torsion bar 6 according to steering resistance.

  The valve housing 7 includes an inlet port 34 connected to the pump 70, a first port 37 connected to one oil chamber 22 of the hydraulic cylinder 20, and a second port 38 connected to the other oil chamber 23. A first outlet port 36 directly connected to the tank 71 and a second outlet port 61 connected to the tank 71 via a variable throttle valve 60 described later are provided. Each port 34, 36, 37, 38, 61 is connected to each other through an inter-valve flow path 27 between the inner and outer periphery of the first valve member 31 and the second valve member 32.

  That is, as shown in the cross-sectional view of FIG. 2, eight concave portions 50a, 50b, 50c are formed on the inner periphery of the first valve member 31 at equal intervals in the circumferential direction. In addition, eight recesses 51a, 51b, 51c are formed at equal intervals in the circumferential direction. The recesses 51a, 51b, 51c formed in the second valve member 32 are located between the recesses 50a, 50b, 50c formed in the first valve member 31.

The recesses formed in the first valve member 31 constitute two right steering recesses 50a, two left steering recesses 50b, and four communication recesses 50c.
The two right steering recesses 50a are connected to the oil chamber 22 for generating the right steering assist force of the hydraulic cylinder 20 through the flow path 53 and the first port 37 formed in the first valve member 31, and are mutually connected. They are arranged 180 degrees apart in the circumferential direction.
The two left steering recesses 50b are connected to the oil chamber 23 for generating the left steering assist force of the hydraulic cylinder 20 through the flow path 54 formed in the first valve member 31 and the second port 38, and are mutually connected. They are arranged 180 degrees apart in the circumferential direction.

The recesses formed in the second valve member 32 constitute four pressure oil supply recesses 51a, two first pressure oil discharge recesses 51b, and two second pressure oil discharge recesses 51c. To do.
The four pressure oil supply recesses 51a are connected to the pump 70 via the pressure oil supply passage 55 formed in the first valve member 31 and the inlet port 34, and are arranged 90 ° apart from each other in the circumferential direction. ing.

The two first pressure oil discharge recesses 51b pass between the input shaft 2 and the torsion bar 6 from the flow path 52a formed in the input shaft 2, and the flow path 52b formed in the input shaft 2 (FIG. 1). And the first outlet port 36 are connected to the tank 71 and spaced apart from each other by 180 ° in the circumferential direction.
The two second pressure oil discharge recesses 51c are connected to the variable throttle valve 60 via the flow path 59 formed in the first valve member 31 and the second outlet port 61, and are separated from each other by 180 ° in the circumferential direction. Are arranged.

Each first pressure oil discharge recess 51b is disposed between the right steering recess 50a and the left steering recess 50b, and each second pressure oil discharge recess 51c is disposed between the communication recesses 50c and 50c. A pressure oil supply recess 51a is disposed between the right steering recess 50a and the communication recess 50c, and between the left steering recess 50b and the communication recess 50c.
The gap between the edges along the axial direction of the recesses 50a, 50b and 50c formed in the first valve member 31 and the edges along the axial direction of the recesses 51a, 51b and 51c formed in the second valve member 32 Parts A, A ', B, B', C, C ', D, D' are configured. As described above, the throttle portions A, A ′, B, B ′, C, C ′, D, and D ′ are arranged in the inter-valve flow path 27 that connects the pump 70, the tank 71, and the hydraulic cylinder 20. .

  Each throttle part between the first valve member 31 and the second valve member 32 includes a first group composed of a plurality of throttle parts A, B, C, D, and each throttle part A belonging to the first group. They are grouped into a second group consisting of a plurality of apertures A ′, B ′, C ′, D ′ having a larger closing angle than B, C, D. The throttle portions belonging to the second group are the throttle portions A ′ and C ′ between the pressure oil supply concave portion 51a and the communication concave portion 50c, and the communication concave portions having a larger closing angle than the throttle portions A ′ and C ′. There are two types of throttle portions B ′ and D ′ between the portion 50c and the second pressure oil discharge recess 51c.

  The input shaft 2 and the output shaft 3 are rotated relative to each other by the torsion of the torsion bar 6 due to the resistance transmitted from the road surface via the steering wheel. By the relative rotation of the first valve member 31 and the second valve member 32 due to this relative rotation, the flow passage areas of the throttle portions A, B, C, D, A ′, B ′, C ′, and D ′ are increased. As a result, the hydraulic cylinder 20 generates a steering assist force according to the steering direction and the steering resistance. The throttle portions A, B, C, and D belonging to the first group have smaller closing angles than the throttle portions A ′, B ′, C ′, and D ′ belonging to the second group, so that the change in the steering resistance can be prevented. The rate of change in hydraulic pressure increases.

When the steering is not performed, the throttle portions A, B, C, D, A ′, B ′, C ′, and D ′ between the valve members 31 and 32 are all opened, and the inlet port 34 and the outlet port 36 and 61 communicate with each other through the inter-valve channel 27. Therefore, the oil flowing into the hydraulic control valve 30 from the pump 70 returns to the tank 71 and no steering assist force is generated.
When the two valve members 31 and 32 are rotated relative to each other by steering resistance generated by steering to the right from this state, as shown in FIG. 2, the restriction between the pressure oil supply recess 51a and the right steering recess 50a. The flow path area of the throttle portion A ′ between the pressure oil supply recess 51a adjacent to the portion A and the left steering recess 50b and the communication recess 50c is increased.

  Further, the throttle portion B between the right steering recess 50a and the first pressure oil discharge recess 51b, the communication recess 50c adjacent to the pressure oil supply recess 51a adjacent to the left steering recess 50b, and the second pressure. The flow path area of the narrowed portion B ′ between the oil discharge recess 51c is reduced. Further, the throttle C between the pressure oil supply recess 51a and the left steering recess 50b, and the throttle C 'between the pressure oil supply recess 51a adjacent to the right steering recess 50a and the communication recess 50c. The flow path area of is reduced.

Further, the throttle portion D between the left steering recess 50b and the first pressure oil discharge recess 51b, the communication recess 50c adjacent to the pressure oil supply recess 51a adjacent to the right steering recess 50a, and the second pressure. The flow path area of the narrowed portion D ′ between the oil discharge concave portion 51c increases.
2 is supplied to the oil chamber 22 for generating the right steering assist force of the hydraulic cylinder 20 by the flow of the pressure oil indicated by the arrow in FIG. Oil flows back from the auxiliary force generating oil chamber 23 to the tank 71, and a steering assist force to the right of the vehicle acts on the rack 16 from the hydraulic cylinder 20.

  When steered to the left, both valve members 31, 32 rotate relative to each other in the opposite direction to that steered to the right, reducing the flow passage area of the restrictors A, A 'and reducing the flow of the restrictors B, B'. The path area increases, the flow area of the throttles C and C ′ increases, and the flow area of the throttles D and D ′ decreases. Thereby, the steering assist force to the left of the vehicle acts on the rack 16 from the hydraulic cylinder 20.

  The variable throttle valve 60 (FIG. 1) communicating with the second outlet port 61 includes a second valve housing 7 ′ connected to the valve housing 7 and a second valve, as shown in an enlarged longitudinal sectional view in FIG. A spool 62 inserted in an insertion hole 66 formed in the housing 7 ′ so as to be movable in the axial direction (vertical direction in FIGS. 1 and 3), and a male screw formed at the inner peripheral lower portion of a through hole 62 d penetrating the spool 62. The screw member 64 is screwed into the hole 62d '.

A circumferential groove 62a is formed on the outer periphery of the spool 62, a circumferential groove 66a is formed on the inner periphery of the insertion hole 66, and a constricted portion 67 is formed between the circumferential grooves 62a and 66a. The opening degree of the throttle portion 67 changes with the movement of the spool 62 in the axial direction. That is, when the spool 62 is displaced downward in FIG. 3, the opening degree of the throttle portion 67 is increased, and when the spool 62 is displaced upward, the opening degree of the throttle portion 67 is decreased.
A stopper 68 is screwed into one end of the insertion hole 66, and the stopper 68 prevents the spool 62 from moving in a predetermined position (in the upward direction in FIG. 3) in the direction of decreasing the opening of the throttle portion. A compression coil spring 90 is provided between the stopper 68 and the spool 62 to impart an axial elasticity to the spool 62, and rattling of the spool 62 is prevented by the elasticity of the compression coil spring 90. .

The above-described screw member 64 is inserted into and supported by the second support hole 73 that communicates the insertion hole 66 and the actuator chamber 72 formed in the second valve housing 7 '. The actuator chamber 72 has a built-in stepping motor 80 that rotationally drives the screw member 64.
The block 91 is press-fitted into the output shaft 80a of the stepping motor 80, and the end of the screw member 64 is fitted into the block 91 via the recess 64a. Thereby, the rotation of the output shaft 80a of the stepping motor 80 is transmitted to the screw member 64, and the spool 62 moves in a direction corresponding to the rotation direction.

A controller 63 including a microcomputer is connected to the stepping motor 80. The stepping motor 80 is supplied with power from the in-vehicle battery 100 through the fail safe relay contact ry. The relay driving circuit 101 for the fail-safe relay contact ry is ON / OFF controlled by the controller 63.
The controller 63 is supplied with power through a power switch interlocked with an ignition switch (not shown). In addition, a vehicle speed signal from the vehicle speed sensor 105 that detects the vehicle speed is given, and the controller 63 performs open loop control based on the given vehicle speed signal so that the throttle unit 67 has an appropriate opening according to the vehicle speed. The rotational position of the stepping motor 80 is controlled by the method.

  In the second valve housing 7 ′, a communication flow path 58 that connects the inner circumferential groove 66 a of the insertion hole 66 and the second outlet port 61 is formed. Further, a radial hole 62 c that communicates the circumferential groove 62 a on the outer periphery of the spool 62 and the through hole 62 d of the spool 62 is formed in the spool 62, and the through hole 62 d communicates with the space above the spool 62. . An upper space of the spool 62 communicates with the first outlet port 36 by a flow path 76 formed between the valve housing 7 and the second valve housing 7 '.

  As a result, the pressure oil supplied from the pump 70 is guided to the communication channel 58 from the inter-valve channel 27 and the second outlet port 61, reaches the throttle unit 67 from the communication channel 58, and is supplied from the throttle unit 67 to the first channel. The tank 71 is reached through the outlet port 36. The spool 62 has a drain passage 62h formed in parallel with the through hole 62d, and connects the upper space and the lower space of the spool 62.

  With this configuration, when the variable throttle valve 60 is operated, the flow path area between the throttle portions A ′, B ′, C ′, D ′ belonging to the second group and the tank 71 changes. That is, the pressure controlled by the throttle parts A ′, B ′, C ′, D ′ belonging to the second group of the pressure oil flow rate controlled by the throttle parts A, B, C, D belonging to the first group. The ratio to the oil flow rate is changed by the operation of the variable throttle valve 60.

  When traveling at low speed, the spool 62 is displaced upward in FIGS. 1 and 3, and the throttle portion 67 of the variable throttle valve 60 is fully closed. In this case, even if the steering input torque is small and the relative rotation angles of the valve members 31 and 32 are small, the flow passage areas of the throttle portions A, B, C, and D belonging to the first group are reduced, and the steering assist force is reduced. It is possible to increase the rate of increase of the hydraulic pressure that generates a high pressure and satisfy the high response performance of steering during low-speed driving.

  During high speed travel, the spool 62 is displaced downward in FIGS. 1 and 3, so that the flow passage area of the throttle portion 67 of the variable throttle valve 60 becomes the throttle portions A ′, B ′, C belonging to the second group. It becomes more than the maximum value of the total channel area of ', D'. In this case, unless the steering input torque is increased and the relative rotational angles of the valve members 31 and 32 are increased, the flow passage areas of the throttle portions A ′, B ′, C ′, and D ′ belonging to the second group are Since the rate of increase of the hydraulic pressure that is maintained large without being reduced and generates the steering assist force is small, it is possible to satisfy the stability of steering during high-speed traveling.

  During medium speed running, the flow path area of the throttle part 67 of the variable throttle valve 60 is the minimum of the total flow path areas of the throttle parts A ′, B ′, C ′, D ′ belonging to the second group due to the displacement of the spool 62. Greater than the value and less than its maximum value. As a result, the steering assist force is controlled according to the steering resistance.

FIG. 4 is a timing chart showing an initial control procedure for determining an initial position of the stepping motor 80. As described above, since the stepping motor 80 is driven and controlled by the open loop control method, it is necessary to set the initial position of the stepping motor 80 at the start-up prior to the drive control of the stepping motor 80.
In the initial control of the stepping motor 80, the stepping motor 80 is driven with the number of pulses (step number) corresponding to the entire movement range of the spool 62 of the variable throttle valve 60, and the spool 62 is brought into contact with the stopper 68. The rotational position of the stepping motor 80 when 60 (the aperture 67) is fully closed is set as the initial position. In this case, since the stepping motor 80 steps out after the spool 62 contacts the stopper 68, the rotational position of the stepping motor 80 does not change.

When the engine of the vehicle is started and the power switch is turned on (FIG. 4 (a)), the controller 63 turns on the fail-safe relay contact ry in the relay drive circuit 101 (b), and then turns the stepping motor 80 clockwise. Drive to (CW) at a pulse rate of 200 pps (pulse per second) to execute initial control (d).
When the number of steps for driving the stepping motor 80 in the clockwise direction reaches the number of steps corresponding to the entire movement range of the spool 62 (here, 220), the controller 63 starts running (c). The initial control is interrupted (d). Next, the rotational position of the stepping motor 80 at that time is set as a temporary initial position, and the stepping motor 80 is driven at a pulse rate of 100 pps (pulse of a predetermined frequency), and (c) the position of the spool 62 is changed according to the vehicle speed. Then, normal control for controlling the pressure oil flow rate is executed by adjusting the opening degree of the variable throttle valve 60 (d).

  When the vehicle stops (c), the controller 63 finishes the normal control based on the temporary initial position of the stepping motor 80 (d) (at this time, the stepping motor 80 has returned to the temporary initial position), and the stepping motor 63 Initial control (origin return control) for the remaining number of steps is resumed from the temporary initial position of the motor 80. After the position of the spool 62 changes and comes into contact with the stopper 68 (mechanical stopper), the stepping motor 80 steps out, so the rotational position of the stepping motor 80 does not change and the position of the spool 62 does not change (d).

  When the number of steps in which the stepping motor 80 is driven clockwise reaches 220 (d), the controller 63 sets the rotation position of the stepping motor 80 at that time as an initial position (d). Thereafter, the stepping motor 80 is driven at a pulse rate of 100 pps, and the normal control for adjusting the opening degree of the variable throttle valve 60 is performed by changing the position of the spool 62 according to the vehicle speed (c) (d).

As described above, in the power steering apparatus according to the present embodiment, during initial control, the pulse rate for driving the stepping motor 80 is changed from 100 pps to 200 pps to reduce the torque for driving the stepping motor 80 for each pulse. Therefore, the sound generated from the stepping motor during initial control is reduced.
Note that, by changing the pulse rate for driving the stepping motor 80 from 100 pps to 50 pps during initial control, the generated sound from the stepping motor 80 becomes a low frequency of 50 Hz, which makes it difficult to hear and occurs during initial control. Sound can be made inconspicuous (reduced). In this case, the time required for the initial control becomes longer, but if the initial control can be interrupted and resumed as in the present embodiment, the effect is small.

It is a longitudinal section showing the important section composition of the power steering device concerning the present invention. It is a cross-sectional view which shows the principal part structure of the power steering apparatus which concerns on this invention. It is a longitudinal cross-sectional view which expands and shows the variable throttle valve of the power steering apparatus which concerns on this invention. It is a timing chart which shows the procedure of the initial control which determines the initial position of the stepping motor of the power steering apparatus which concerns on this invention.

Explanation of symbols

1 Power steering device, 2 input shaft, 3 output shaft, 6 torsion bar, 15 pinion, 16 rack, 20 hydraulic cylinder, 30 hydraulic control valve, 60 variable throttle valve, 62 spool, 63 controller, 68 stopper, 70 pump, 80 Stepping motor, 100 vehicle-mounted battery, 101 relay drive circuit, 105 vehicle speed sensor, ry fail-safe relay contact

Claims (2)

A stepping motor driven by a pulse of a predetermined frequency is operated, and the pressure oil flow rate of the hydraulic control valve is controlled by a variable throttle valve provided on the outlet side of the hydraulic control valve according to the vehicle speed detected by the vehicle speed detector, The rotational position of the stepping motor when the stepping motor is driven at the number of pulses corresponding to the entire driving range of the variable throttle valve at the start and the variable throttle valve is fully closed is set as the reference position of the stepping motor. In the power steering apparatus configured to assist steering by the hydraulic pressure controlled by the hydraulic control valve,
Drive means for driving the stepping motor by a number of pulses corresponding to the entire drive range at a frequency different from the predetermined frequency so as to reduce sound generated from the stepping motor at startup. Power steering device.   Means for interrupting driving of the driving means when the vehicle speed detector detects a vehicle speed exceeding 0 when the driving means drives the stepping motor with a pulse having a frequency different from the predetermined frequency; Means for driving the stepping motor with a pulse of the predetermined frequency using the rotational position of the stepping motor when the driving is interrupted as a temporary reference position, and controlling the pressure oil flow rate with a variable throttle valve, 2. The power steering apparatus according to claim 1, wherein when the vehicle is controlled, and the vehicle speed detector detects 0, the drive of the drive device is resumed from the temporary reference position.

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