JPH11198838A - Power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent occurrence of an abnormal rise of working oil pressure in its supply path leading from a hydraulic pump to a power cylinder via a servo valve by displacing a movable body (spool valve) of a differential pressure sensor when the pressure in the supply path is, going to rise abnormally and actuating a steering situation sensing means to issue a specified output signal so as to stop an electric motor. SOLUTION: A power steering device includes no conventional relief valve, and when the inside of a supply path reaches the relief pressure, a check valve 13 (pressure sinking mechanism) is opened to sink the pressure in the second pressure chamber of a differential pressure sensor 12, and a spool valve (movable body) is displaced to the position at which a steering situation sensing means 1 issues an output signal to stop an electric motor 2. Thus the motor 2 is stopped.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power steering device used in an automobile, and more particularly to an electric pump type power steering device in which a hydraulic pump, which is a supply source of hydraulic fluid for power assist, is driven by an electric motor. It concerns the device.

[0002]

2. Description of the Related Art For many years, a power steering apparatus which performs a power assisting operation by hydraulic oil supplied from a hydraulic pump has been mainly driven by an engine. However, in such an engine driven type, since the hydraulic pump is driven regardless of whether power assist is required or not, the load is constantly applied to the engine, which results in loss of engine output and, consequently, energy consumption. Loss was a problem.

In order to solve the above-mentioned problem, a system has been proposed in which a hydraulic pump is driven by an electric motor separate from the engine, and the operation of the electric motor is controlled according to a steering condition. Being offered. For example, as shown in FIG. 5, the pressure Po in the pump outlet passage 800 connecting the discharge side of the hydraulic pump 300 and the inlet port 410 of the center close type servo valve 400, the cylinder port 420 of the servo valve 400 Power cylinder 500
Cylinder passages 900 connecting the cylinder chambers 520 with each other
Of the pressure Pa in the cylinder passage 900 on the high pressure side
(Or Pb) is determined by the differential pressure detector 120
The electronic control unit 200a controls the electric motor 200 that drives the hydraulic pump 300 based on the detected steering state. The hydraulic pump 300 is, for example, a vane pump. The suction side of the hydraulic pump 300 and the reservoir tank 600 are connected by a pump inlet passage 700, and the return port 430 of the servo valve 400 is connected to the reservoir tank 600. I have.

[0004]

Incidentally, the hydraulic pump 300 has a relief valve 310, which is a known relief valve having a valve 310a and a spring 310b for urging the valve 310a. It has a configuration. The relief valve 310 is disposed in a relief passage 320 that short-circuits the pump outlet passage 800 and the pump inlet passage 700.
b is pushed to the relief passage 320
And is opened when the pressure in the pump outlet passage 800 rises to a predetermined value, and the hydraulic oil discharged from the hydraulic pump 300 is returned to the suction side of the hydraulic pump 300. Become. Thereby, the hydraulic pump 30
Abnormal pressure increase in the hydraulic oil supply path from the discharge side of 0 to the cylinder chamber 520 of the power cylinder 500 via the servo valve 400 is avoided.

With this configuration, when the relief valve 310 operates (opens), the high-pressure hydraulic oil pushes the valve element 310a of the relief valve 310 and passes as a high-speed jet, so that the driver Noise and vibrations may be generated that cause discomfort to the user. Also, at this time, the hydraulic oil continues to circulate in the closed circuit from the discharge side to the suction side of the hydraulic pump 300. Therefore, if this state continues for a predetermined time or more, the oil temperature rises abnormally and the viscosity of the hydraulic oil decreases. I do. Then, the oil film may be broken at each sliding portion inside the hydraulic pump 300, and seizure may occur to impair the function of the hydraulic pump 300.

In addition, when the relief valve 310 is operating, in other words, when power assist is not necessary, the hydraulic pump 300 does not stop rotating even in such a state, and the driving power of the electric motor 200 is not increased. Will continue to be wasted.

[0007]

In order to solve the above-mentioned problems, the following configuration is adopted. According to a first aspect of the present invention, there is provided a hydraulic pump driven by an electric motor, a servo valve for controlling a flow of hydraulic oil discharged from the hydraulic pump in accordance with an operation of a steering wheel, and the servo valve. A power cylinder that receives supplied hydraulic oil into one of two cylinder chambers partitioned by a power piston to perform a power assisting operation, and a differential pressure between a discharge pressure of the hydraulic pump and a high-pressure cylinder chamber of the power cylinder. In a power steering apparatus having a steering condition detecting means configured to detect a steering condition by detecting, and control means for controlling the operation of the electric motor based on an output signal from the steering condition detecting means, The steering condition detecting means is operated and displaced according to a pressure difference between a discharge pressure of a hydraulic pump and a high pressure side cylinder chamber of the power cylinder. It has a differential pressure detector composed of a moving body and a displacement detection mechanism for detecting the working displacement of the movable body, and the pressure in the supply path of the working oil from the hydraulic pump to the power cylinder via the servo valve is set to a predetermined value. A power steering device configured to actuate and displace the movable body of the differential pressure detector to a position where an output signal for stopping the electric motor is issued from the steering situation detecting means when the relief pressure is reached. It is the gist.

According to a second aspect of the present invention, in the first aspect, the movable body of the differential pressure detector includes a first pressure chamber in which the discharge pressure of the hydraulic pump is guided in the differential pressure detector. The pressure in the high pressure side cylinder chamber of the power cylinder is divided into a second pressure chamber guided through a fixed throttle, and the steering situation detecting means detects when the pressure in the supply path reaches a predetermined relief pressure. (2) A power steering device having a pressure drop mechanism for lowering the pressure of a pressure chamber and displacing the movable body by a differential pressure generated between the first pressure chamber and the second pressure chamber. It is.

According to a third aspect of the present invention, in the second aspect, the pressure dropping mechanism comprises a check valve which opens when the pressure in the supply path reaches a predetermined relief pressure, The gist is that the check valve is a power steering device provided in a passage connecting the second pressure chamber of the differential pressure detector and the reservoir tank. According to a fourth aspect of the present invention, in the second or third aspect, the steering condition detecting means has a volume increasing mechanism including a volume chamber connected to the second pressure chamber of the differential pressure detector. The gist of the invention is that the volume chamber is a power steering device configured so that the volume can be increased at a predetermined pressure lower than the relief pressure.

[0010]

FIG. 1 shows a first embodiment of the present invention.
A description will be given based on FIG. The electric motor 2 is controlled by an electronic control unit 2a based on a detection result of the steering condition detecting means 1, and a hydraulic pump which is driven by the electric motor 2, for example, a vane pump. 3, this hydraulic pump 3
Center-closed type servo valve 4 for controlling the flow of hydraulic oil discharged from the cylinder, two cylinder chambers 52 (52a, 52b) partitioned by a power piston 51 for receiving hydraulic oil supplied through the servo valve 4. ), And a reservoir tank 6 for storing the hydraulic oil as main components.

The servo valve 4 is operated by operating a steering wheel.
The pump outlet passage 8 has a cylinder port 42 (42).
a, 42b) include the cylinder chamber 52 of the power cylinder 5.
(52a, 52b) and the cylinder passage 9 (9a, 9b).
b), the reservoir tank 6 is connected to the return port 43 (43a, 43b). And
In the non-steering state, the inlet port 41 is closed, and the cylinder port 42 communicates with the return port 43. In the steering state, the inlet port 41 is connected to the cylinder port 4
3 (43a, 43b), and the other of the cylinder ports 43 (43a, 43b) communicates with the return port 43.

The steering condition detecting means 1 includes a switching valve 1
1 and a differential pressure detector 12. In the switching valve 11, a ball valve 112 is disposed in a space at the intersection of the internal passage 111 intersecting in a T shape, and ends 111a, 111 of the internal passage 111 opposed to each other with the ball valve 112 interposed therebetween.
b is connected to the cylinder passage 9 (9a, 9b), and the remaining end 111c is connected via a fixed throttle 113 to a second pressure chamber 122b of the differential pressure detector 12, which will be described later. With such a configuration, the high pressure side of the cylinder passage 9 (9a, 9b) is connected to the second pressure chamber 122b by the movement of the ball valve 112.

Next, the differential pressure detector 12 is slidably fitted into a housing 121 and a sliding hole 122 of the housing 121, and has a shaft portion 123a and a shaft portion 123a.
A spool valve 123 as a movable body comprising a piston portion 123b provided at one end of the shaft portion;
and a differential transformer 124 as a displacement detection mechanism provided on the other end side of FIG. The inside of the sliding hole 122 is divided into a first pressure chamber 122a and a second pressure chamber 122b by a piston portion 123b of a spool valve 123, and a spring 125 biases the piston portion 123b toward the first pressure chamber 122a. I have. The first pressure chamber 122a is connected to the pump outlet passage 8, and the second pressure chamber 122b is connected to the switching valve 11, respectively.
The spool valve 123 moves according to the difference between the two pressures guided to the pressure chambers 122a and 122b.

The above-described differential transformer 124 includes a core 124 provided at an end of a shaft portion 123a of the spool valve 123.
and a coil 124b surrounding the core 124a. The movement of the core 124a is detected by a change in electromotive force generated in the coil 124b.
3 transmits an electric signal corresponding to the amount of movement. The electronic signal transmitted in this manner is received by the electronic control unit 2a, and the first and second pressure chambers 122a,
When it is determined that the differential pressure of the motor 122b has become equal to or less than a predetermined value, the electric motor 2 is operated.

The configuration of the steering situation detecting means 1 is the same as that of the conventional steering situation detecting means 1, except that a check valve 13 as a pressure drop mechanism is added to the steering situation detecting means 1. is there. That is, check valve 1
3 is provided in a drain passage 14 connecting the second pressure chamber 122b of the differential pressure detector 12 and the reservoir tank 6, and includes, for example, a valve body and a spring for urging the valve body in a valve closing direction. It has a configuration known per se.
This check valve 13 has a predetermined pressure value (relief pressure P
Each parameter is set so that the valve is opened toward the reservoir tank 6 in r). The relief pressure Pr is set near an allowable limit value when the pressure in the hydraulic oil supply path from the hydraulic pump 3 to the cylinder chamber 52 of the power cylinder 5 via the servo valve 4 increases. It is.

The operation of the electric pump-type power steering device having the above-described configuration is as follows. When the hydraulic pump 3 is driven by the electric motor 2, the hydraulic oil is
From the pump outlet passage 8, and is guided to the inlet port 41 of the servo valve 4 and the first pressure chamber 122 a of the differential pressure detector 12. At this time, if the steering wheel is in the non-steering state in the neutral position, the inlet port 41 of the servo valve 4 is closed, and the pump outlet passage 8 is connected to the cylinder passage 9 (9).
a, 9b), the cylinder passage 9
(9a, 9b) is the cylinder port 42 of the servo valve 4.
(42a, 42b) and the return port 43 (43
a, 43b) and the reservoir tank 6. Therefore, the pump outlet passage 8 and the differential pressure detector 12
Is high, the pressure Pa = Pb in the left and right cylinder chambers 52a, 52b is low, and the second pressure chamber 122b of the differential pressure detector 12 is also low. Therefore, the differential pressure between the first and second pressure chambers 122a and 122b becomes equal to or more than a predetermined value, and the spool valve 123
Is displaced toward the second pressure chamber 122b against the urging force of the electric motor 2, and the operation of the differential transformer 124 electrically detects that the vehicle is not in a steering state.
To stop.

Next, when the steering handle is operated, the inlet port 41 of the servo valve 4 is opened and the cylinder port 42 is opened.
(42a, 42b), and the pump outlet passage 8 communicates with any of the cylinder passages 9 (9a, 9b). Therefore, the first pressure chamber 12 of the differential pressure detector 12
The pressure Po introduced into the second pressure chamber 122b through the switching valve 11 becomes equal to the pressure Pa (or Pb) of the high-pressure side cylinder passage 9 through the switching valve 11, so that
The pressure difference between the second pressure chambers 122a and 122b is equal to or less than a predetermined value. Thus, the spool valve 123 of the differential pressure detector 12 is urged toward the first pressure chamber 122a by the spring 125, and the operation of the differential transformer 124 electrically detects that the steering is in the steering state. 2a drives the electric motor 2. Then, the hydraulic pump 3 is operated, and the hydraulic oil discharged from the hydraulic pump 3 is guided to one of the cylinder chambers 52 (52a, 52b) of the power cylinder 5 to urge the power piston 51 to one side. Power assist action is performed.

In the above steering state,
When the driver holds the steering wheel in the operating state even after the power piston 51 of the power cylinder 5 reaches the moving end, or when the wheel hits a curb and cannot be turned despite the operation of the steering wheel, the power cylinder When the power piston 51 cannot move while the hydraulic oil is supplied to the cylinder chamber 52 of No. 5, the check valve 13, which is a feature of the present embodiment, operates (opens).

That is, at this time, since the driver is operating the steering wheel, the pump outlet passage 8 communicates with one of the cylinder passages 9 (9a, 9b), and the first pressure of the differential pressure detector 12 The pressure Po in the chamber 122a is equal to the pressure Pa (or Pb) in the second pressure chamber 122b, and the differential pressure is equal to or less than a predetermined value. For this reason, it is in a steering state,
The hydraulic pump 3 is operated. However,
As described above, the power piston 51 of the power cylinder 5
Is not movable, the pressure in the hydraulic oil supply path from the hydraulic pump 3 to one of the cylinder chambers 52 rises, and the pressure Po of the first pressure chamber 122a and the pressure Po of the second pressure chamber 12
2b and the pressure Pa (or Pb) rises at the same pressure,
Eventually, the pressure reaches the relief pressure Pr. Then, the check valve 13 set to open with the relief pressure Pr as described above is opened, and the second pressure chamber 122b and the reservoir tank 6 are communicated via the drain passage 14. At this time,
Since the fixed throttle 113 is provided between the second pressure chamber 122b and the switching valve 11 to restrict the flow of the hydraulic oil, the hydraulic oil in the second pressure chamber 122b is guided from the drain passage 14 to the reservoir tank 6. I will As a result, the first pressure chamber 122
a and a predetermined pressure difference or more is generated between the second pressure chamber 122b and the second pressure chamber 122b, and the spool valve 123 is allowed to be displaced toward the second pressure chamber 122b against the urging force of the spring 125. By the signal from the electronic control device 2a based on
The electric motor 2 and the hydraulic pump 3 are stopped to avoid the abnormal pressure increase in the hydraulic oil supply path.

According to the first embodiment described in detail above, the following effects are obtained. First, in the present embodiment, as means for avoiding abnormal pressure rise in the supply path of hydraulic oil from the hydraulic pump 3 to the cylinder chamber 52 of the power cylinder 5,
Since the hydraulic oil discharged from the hydraulic pump 3 is not recirculated from the pump outlet passage 8 to the pump inlet passage 7 via the relief valve, (1) Conventionally, when high-pressure hydraulic oil passes through the relief valve, Harmful noises and vibrations occurring in the vehicle can be suppressed.

(2) There is no closed circuit in which the hydraulic oil continues to circulate from the discharge side to the suction side of the hydraulic pump 3, and therefore the oil temperature does not rise abnormally. There is no danger of the hydraulic pump seizing which occurred with the rise. Then, by means of stopping the electric motor 2 by the action of the check valve 13 connected to the differential pressure detector 12, abnormal pressure increase in the hydraulic oil supply path is avoided. (3) The cylinder of the power cylinder 5 In a steering situation in which the power piston 51 cannot move while the hydraulic oil is supplied to the chamber 52, the electric motor 2 that drives the hydraulic pump 3 can be stopped. Therefore, there is no need to operate the electric motor 2 unnecessarily in a situation where power assist is not required, and energy saving is improved.

The embodiment of the present invention may employ the following configuration in addition to the first embodiment.
The same components as those in the first embodiment are denoted by the same reference numerals, and a duplicate description of the same configuration and operation as those in the first embodiment is partially omitted. Here, what is described as the second embodiment is obtained by adding a volume increasing mechanism 15 to the configuration of the first embodiment, and is as shown in FIGS.

As described in the description of the first embodiment, in the non-steering state (at the time of neutral operation), the servo valve 4 cuts off the communication between the pump outlet passage 8 and the cylinder passage 9, and Since the passage 9 and the reservoir tank 6 communicate with each other, the pressure Po of the first pressure chamber 122a of the differential pressure detector 11 becomes high, and the pressure Pa = Pb of the second pressure chamber 122b becomes low. Of the spool valve 123 tends to be displaced toward the second pressure chamber 122b against the urging force of the spring 125. At this time, since the pressure Pa = Pb in the second pressure chamber 122b is a low pressure that does not reach the relief pressure Pr, the check valve 13 as a pressure drop mechanism is closed, and the hydraulic oil in the second pressure chamber 122b is discharged. The displacement of the spool valve 123 is allowed by being pushed away from the switching valve 11 and the cylinder passage 9 side.

However, when the hydraulic oil is in a low temperature state and the viscosity is high, for example, immediately after the start of the vehicle, the fixed throttle 113 provided between the second pressure chamber 122b of the differential pressure detector 12 and the switching valve 11 is obstructed. And the second pressure chamber 122b
In some cases, there is a response delay in the movement of the hydraulic oil from the valve to the switching valve 11 and the cylinder passage 9 side. For this reason, the response of the displacement of the spool valve 123 of the differential pressure detector 12 is also delayed, so that it is not possible to quickly detect the steering state, and even in a non-steering state in which the electric motor 2 should be stopped, the electric motor 2 is stopped. You might end up driving.

Therefore, in this embodiment, a volume increasing mechanism 15 as a volume increasing mechanism for increasing the volume of the second pressure chamber 122b of the differential pressure detector 12 as necessary is added to the configuration of the first embodiment. The configuration was adopted. The volume increasing mechanism 15 includes a partition member 15 housed in the case 151.
2 and a spring 153 for urging the partition member 152 in one direction. Inside the case 151, the partition member 15
The pressure chamber 12 is divided into a volume chamber 154 and a spring chamber 155 by the second pressure chamber 12 of the differential pressure detector 12.
2b, and the spring chamber 155 is connected to the reservoir tank 6 and is open to the atmosphere. The spring 153 urges the partition member 152 toward the volume chamber 154, but the second pressure chamber 122b
Is introduced into the volume chamber 154 from the relief pressure P
The parameters of the volume increasing mechanism 15 are set such that the partition member 152 can be displaced toward the spring chamber 155 at a pressure value Pv smaller than r and a relatively low pressure. Since the volume increasing mechanism 15 having such a configuration is provided, the differential pressure detector 1
2, the pressure in the second pressure chamber 122b is relatively low.
When v reaches v, the partition member 152 is displaced toward the spring chamber 155 to increase the volume of the volume chamber 154 and substantially increase the volume of the second pressure chamber of the differential pressure detector 12. Accordingly, as described above, even when the hydraulic oil has a high viscosity at a low temperature and the movement of the hydraulic oil from the second pressure chamber 122b of the differential pressure detector 12 to the switching valve 11 and the cylinder passage 9 is difficult, The amount of increase in the volume of the volume chamber 154 receives hydraulic oil that allows displacement of the spool valve 123 of the differential pressure detector 12. As a result, the spool valve 123 can be displaced to the second pressure chamber 122b side without resistance, and the electronic control unit 2a stops the electric motor 2 by quickly detecting the non-steering state by the operation of the differential transformer 124.

According to the above-described second embodiment, the following effects are obtained in addition to the effects obtained by the above-described first embodiment. (1) Spool valve 123 (movable body) of differential pressure detector 12
Since the spool valve 123 can be easily displaced by the action of the pressure increasing section 13 even at a low temperature of the hydraulic oil, which is difficult to be displaced, the steering situation detecting means 1 detects the steering situation without error,
The electronic control device 2a can control the electric motor 2 accurately.

[0027]

As described in detail above, the following effects can be obtained by employing the power steering apparatus according to the present invention.
According to the first aspect of the present invention, when the power piston of the power cylinder reaches the moving end, and the driver holds the steering wheel in the steering state, or the wheel hits the curb regardless of the operation of the steering wheel. When hydraulic oil is supplied to the cylinder chamber of the power cylinder but the power assist function cannot be performed, such as when turning is not possible, and the hydraulic oil supply path from the hydraulic pump to the power cylinder via the servo valve is about to abnormally increase the pressure. Then, the movable body (spool valve) of the differential pressure detector is operated and displaced, and the steering condition detecting means can emit a predetermined output signal to stop the electric motor. Prevent beforehand.

In addition, since the hydraulic oil discharged from the hydraulic pump is not recirculated from the discharge side to the suction side of the hydraulic pump via the relief valve, conventionally, high-pressure hydraulic oil passes through the relief valve. Harmful abnormal noises and vibrations that are sometimes generated can be suppressed. Also, since there is no closed circuit in which the hydraulic oil continues to circulate from the discharge side to the suction side of the hydraulic pump, and therefore the oil temperature does not rise abnormally,
Conventionally, there is no risk of seizure of the hydraulic pump, which has been caused by an abnormal rise in oil temperature.

In addition, in a steering situation in which the power assist operation cannot be performed as described above, the electric motor that drives the hydraulic pump can be stopped. There is no such problem, and energy saving is improved. According to the second aspect of the present invention, the differential pressure detector includes a first pressure chamber into which the discharge pressure of the hydraulic pump is led, and a second pressure chamber into which the pressure of the high pressure side cylinder chamber is led via a fixed throttle. When the pressure in the supply path of the hydraulic oil reaches a predetermined relief pressure, the pressure in the second pressure chamber is reduced, and the first pressure chamber and the second pressure chamber are divided by a movable body (spool valve). By providing a pressure drop mechanism for operating and displacing the movable body by a differential pressure generated between the first and second embodiments, the operation and effect of the first aspect can be obtained.

According to the third aspect of the present invention, the pressure drop mechanism is constituted by a check valve that opens when the pressure in the supply path of the hydraulic oil reaches a predetermined relief pressure, and this check valve is provided. Is provided in the passage connecting the second pressure chamber of the differential pressure detector and the reservoir tank, so that when the pressure in the supply path reaches the relief pressure, a part of the hydraulic oil in the second pressure chamber is removed. Then, the pressure is guided to the reservoir tank through the opened check valve to generate a pressure difference between the first pressure chamber and the second pressure chamber.

According to the fourth aspect of the present invention, the steering state detecting means has a volume chamber connected to the second pressure chamber of the differential pressure detector, and the volume of the volume is adjusted at a predetermined pressure lower than the relief pressure. The volume chamber is configured to be able to increase in volume, so that in addition to the function and effect of claim 2 or 3, the volume chamber can be formed even at a low temperature of hydraulic oil in which the movable body (spool valve) of the differential pressure detector is difficult to be displaced. The amount of increase in volume of the differential pressure detector accepts hydraulic oil enough to allow displacement of the movable body, and the movable body can be easily displaced, so that the steering situation detecting means quickly detects the steering situation and controls There is an operational effect that the means (electronic control device) can control the electric motor without delay.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an entire configuration of a hydraulic circuit and an electric circuit of a power steering device according to a first embodiment of the present invention.

FIG. 2 also shows a power steering device according to the first embodiment;
FIG. 3 is a hydraulic circuit diagram showing a main part (a rudder situation detecting means).

FIG. 3 is a circuit diagram showing an overall configuration of a hydraulic circuit and an electric circuit of a power steering device according to a second embodiment of the present invention.

FIG. 4 shows a power steering device according to a second embodiment,
FIG. 3 is a hydraulic circuit diagram showing a main part (a rudder situation detecting means).

FIG. 5 is a circuit diagram showing the overall configuration of a hydraulic circuit and an electric circuit of a conventional power steering device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Steering condition detection means 11 Switching valve 113 Fixed throttle 12 Differential pressure detector 122a First pressure chamber 122b Second pressure chamber 123 Spool valve (movable body) 123a Shaft part 123b Piston part 124 Differential transformer (displacement detection mechanism) 124a Core 124b Coil 13 Check valve (pressure drop mechanism) 14 Drain passage 15 Volume increase mechanism 151 Case 152 Partition member 153 Spring 154 Volume chamber 155 Spring chamber 2 Electric motor 2a Electronic control unit (control means) 3 Hydraulic pump 4 Servo valve 41 Inlet port 42 Cylinder port 43 Return port 5 Power cylinder 51 Power piston 52 Cylinder chamber 6 Reservoir tank 7 Pump inlet passage 8 Pump outlet passage 9 Cylinder passage

Claims (4)

[Claims] 1. A hydraulic pump driven by an electric motor, a servo valve for controlling a flow of hydraulic oil discharged from the hydraulic pump in accordance with an operation of a steering wheel, and an operation supplied via the servo valve. By detecting the pressure difference between the discharge pressure of the hydraulic pump and the high-pressure side cylinder chamber of the power cylinder, the power cylinder receiving oil into one of the two cylinder chambers defined by the power piston to perform a power assisting operation. A power steering apparatus comprising: a steering condition detecting means configured to detect a steering condition; and control means for controlling operation of the electric motor based on an output signal from the steering condition detecting device. A movable body that is operated and displaced in accordance with a pressure difference between a discharge pressure of the hydraulic pump and a high pressure side cylinder chamber of the power cylinder. And has a differential pressure detector which is composed of a displacement detecting mechanism for detecting the operating displacement of the movable body,
When the pressure in the supply path of hydraulic oil from the hydraulic pump to the power cylinder via the servo valve reaches a predetermined relief pressure, the movable body of the differential pressure detector stops the electric motor from the steering state detecting means. A power steering apparatus characterized in that the power steering apparatus is configured to be operated and displaced to a position where an output signal is issued. 2. The movable body of the differential pressure detector is configured such that the pressure in the first pressure chamber into which the discharge pressure of the hydraulic pump is guided and the pressure in the high pressure side cylinder chamber of the power cylinder are guided through a fixed throttle in the differential pressure detector. And a second pressure chamber to be operated.
When the pressure in the supply path reaches a predetermined relief pressure, the pressure in the second pressure chamber is reduced, and the movable body is actuated by a differential pressure generated between the first pressure chamber and the second pressure chamber. The power steering device according to claim 1, further comprising a pressure drop mechanism for displacing the power steering device. 3. A pressure drop mechanism comprising a check valve that opens when the pressure in the supply path reaches a predetermined relief pressure, wherein the check valve is connected to a second pressure chamber of a differential pressure detector. 3. The power steering device according to claim 2, wherein the power steering device is provided in a passage connecting to the reservoir tank. 4. A steering condition detecting means, comprising:
4. The method according to claim 2, further comprising a volume increasing mechanism having a volume chamber connected to the pressure chamber, wherein the volume chamber is configured to be capable of increasing its volume at a predetermined pressure lower than the relief pressure. A power steering device as described in the above.