JP2011020566A - Power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power steering device equipped with a solenoid valve that can inhibit difference in pressure loss due to the flow direction of hydraulic oil. <P>SOLUTION: The solenoid valve has a fixed orifice 21 and a variable orifice 22 therein both so arranged as to be allocated in series on oil passage circuit. The fixed orifice 21 is constituted so that a pressure loss YΔP1 in the flow in the other direction Y becomes greater than a pressure loss XΔP1 in the flow in one direction X, and the variable orifice 22 is constituted so that a pressure loss XΔP2 in the flow in the one direction X becomes greater than a pressure loss YΔP2 in the flow in the other direction Y. Thereby, the differences in pressure losses Xdp, Ydp, occurring both on the orifices 21, 22 respectively due to the differences in the flow directions of the hydraulic fluid are offset each other. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an improvement of a so-called power steering device applied to a vehicle such as an automobile.

  As a conventional power steering device applied to a vehicle, for example, one described in Patent Document 1 below is known.

  Briefly, this power steering device supplies hydraulic oil to a pressure chamber on one side of a power cylinder through a control valve configured as a so-called rotary valve, so that the pressure chamber on the one side of the power cylinder is supplied. A steering assist force is generated in the power cylinder based on a differential pressure between the internal pressure and the internal pressure of the pressure chamber on the other side, and the steering force of the driver is assisted with the steering assist force. A part of the hydraulic oil supplied to the engine is returned to the reservoir tank and the internal pressure of the pressure chamber on one side is adjusted to generate an optimum steering assist force for the power cylinder.

  That is, the power steering device includes a first oil passage that connects the control valve and the pressure chamber on one side, a second oil passage that connects the control valve and the pressure chamber on the other side of the power cylinder, A third oil passage that connects the oil passage and the reservoir tank, and a fourth oil passage that connects the second oil passage and the reservoir tank, and the third oil passage and the fourth oil passage are predetermined The communication passage is configured to communicate with each other, and a solenoid valve is provided in the communication passage. From this configuration, for example, when supplying hydraulic oil to the pressure chamber on one side of the power cylinder, a part of the hydraulic oil supplied to the pressure chamber on one side passes through the third oil passage and the communication passage. Thus, together with the hydraulic oil in the pressure chamber on the other side of the power cylinder returned to the control valve through the second oil passage, the oil is returned to the reservoir tank through the fourth oil passage. The internal pressure of the pressure chamber on the one side is adjusted by controlling the flow rate of the hydraulic oil in the pressure chamber on the one side to be returned to the solenoid valve by a solenoid valve.

JP 2002-46634 A

  As described above, the conventional power steering apparatus has a configuration in which hydraulic oil flows in both directions through the solenoid valve via the communication path. However, the shape of the oil passage formed in the solenoid valve is not symmetric with respect to the flow direction. In other words, it is difficult to configure the oil passage symmetrically. For this reason, in the conventional power steering device, the pressure loss varies depending on the steering direction, and as a result, a difference occurs in the steering assist force generated in the power cylinder. As a result, the steering feeling is reduced. There was a problem of losing.

  The present invention has been devised in view of such technical problems, and provides a power steering device including a solenoid valve that can suppress a difference in pressure loss due to the flow direction of hydraulic oil.

  The present invention relates to a power cylinder that applies a steering assist force to a steered wheel based on a differential pressure between a pair of pressure chambers separated inside, and hydraulic oil supplied from an external hydraulic source to each pressure of the power cylinder. A control valve that selectively leads to the chamber, a first oil passage that connects the pressure chamber on one side of the power cylinder and the control valve, and a pressure chamber on the other side of the power cylinder and the control valve. A second oil path, a first oil path and a reservoir tank in which hydraulic oil is stored, a third oil path for returning the hydraulic oil returned from the first oil path to the reservoir tank; A fourth oil path connecting the second oil path and the reservoir tank and returning the hydraulic oil returned from the second oil path to the reservoir tank; the third oil path; and the fourth oil path. A communication path for communicating, and The flow rate of the working oil in the one-way flow of the working oil that is provided in the passage and flows from the third oil passage side to the fourth oil passage side and in the other direction of the working oil that flows from the fourth oil passage side to the third oil passage side. A variable restrictor for controlling the flow rate of hydraulic fluid flowing through the communication passage by changing the flow passage area in the solenoid valve, and a fixed restrictor that does not change the flow passage area. Is a power steering device configured to be arranged in series on the oil passage circuit, wherein the variable throttle portion is configured such that the pressure loss in the one-way flow of hydraulic oil is the pressure loss in the other-direction flow. The fixed throttle portion is configured such that the pressure loss in the other direction flow of hydraulic oil is larger than the pressure loss in the one direction flow. It is characterized by being configured to so that.

  According to the present invention, the difference in the pressure loss generated in each of the variable throttle portion and the fixed throttle portion cancels each other based on the difference in the hydraulic oil flow direction, and the difference in the hydraulic oil flow direction in the solenoid valve. It is possible to reduce the difference in pressure loss that occurs based on the above. As a result, the pressure loss difference as a whole device generated based on the difference in the flow direction of hydraulic oil is reduced.

It is the schematic which shows the structure of the power steering apparatus which concerns on this invention. FIG. 2 is a hydraulic circuit diagram of the power steering device shown in FIG. 1. It is a principal part expanded sectional view which shows the structure of the solenoid valve shown in FIG. FIG. 2 is a hydraulic circuit diagram of the solenoid valve shown in FIG. 1. It is the schematic of the fixed orifice shown in FIG. It is a graph which shows the relationship between the passage diameter ratio before and behind the fixed orifice shown in FIG. 5, and a loss coefficient. It is sectional drawing which follows the AA line of the fixed orifice shown in FIG. It is sectional drawing equivalent to FIG. 7 which shows the conventional fixed orifice. 5 is a graph showing a relationship between a solenoid exciting current and a pressure loss in the variable orifice with respect to a flow direction of hydraulic oil in the variable orifice shown in FIG. 4. 5 is a graph showing the relationship between the excitation current of the solenoid and the pressure loss in the entire solenoid valve with respect to the flow direction of hydraulic oil in the entire solenoid valve shown in FIG. 4. It is the schematic which concerns on the other example of a structure of the fixed aperture | diaphragm | squeeze part shown in FIG.

  Hereinafter, an embodiment of a power steering device according to the present invention will be described in detail with reference to the drawings. In this embodiment, an example in which the power steering apparatus is applied to, for example, a rack and pinion type steering apparatus for an automobile is shown.

  That is, as shown in FIG. 1, this power steering apparatus is connected to a steering shaft 1 that is an input shaft linked to a steering wheel (not shown) on one end side, and to the other end of the steering shaft 1 via a torsion bar 2. A pinion shaft 3 which is an output shaft having pinion teeth 3a on the outer periphery on the front end side, and rack teeth 4a meshing with the pinion teeth 3a in a predetermined range in the axial direction. The rack shaft 4 linked to the left and right steered wheels via outer knuckles, and the rack shaft 4 is used as a piston rod, and hydraulic pressure is applied to the first and second pressure chambers P1 and P2 described later. The power cylinder 5 that generates the steering assist force by the action of, the reservoir tank 6 that stores the hydraulic oil circulating in the power cylinder 5, and the hydraulic oil is sucked up from the reservoir tank 6 The steering shaft 1 and the pinion shaft 3 are rotated relative to each other by the torsion of the oil pump 7 that pumps this to the power cylinder 5 and the torsion bar 2 is twisted. A control valve 8 that controls the amount of hydraulic oil supplied to the power cylinder 5 in accordance with the torsion amount of the torsion bar 2, and the flow rate of hydraulic oil that is provided adjacent to the control valve 8 and supplied to the power cylinder 5 in accordance with the vehicle speed. And a solenoid valve 10 that variably controls.

  With such a configuration, when the steering operation is performed by the driver, the steering shaft 1 rotates relative to the pinion shaft 3 and the torsion bar 2 is twisted, and the torsion restoring force of the torsion bar 2 is restored. As a result, the pinion shaft 3 rotates to move the rack shaft 4 in the axial direction, thereby changing the direction of the steered wheels. At this time, the hydraulic pressure corresponding to the rotational torque of the steering wheel based on the steering operation of the driver is applied to the first and second pressure chambers P1 and P2 described later in the power cylinder 5 through the rotary valve 8. Thus, the steering operation of the driver is assisted.

  The power cylinder 5 includes a cylinder tube 5a formed in a substantially cylindrical shape, a piston 5b provided in the cylinder tube 5a so as to be movable in the axial direction, and a non-illustrated fitting on the outer periphery of the piston 5b. The piston tube seal divides the inside of the cylinder tube 5a into a first pressure chamber P1 on the left side and a second pressure chamber P2 on the right side in FIG.

  As shown in FIGS. 1 and 2, the control valve 8 includes the pressure chambers P1 and P2 and the reservoir tank of the power cylinder 5 through first to fourth oil passages 9a to 9d configured by predetermined piping. 6 is connected. That is, as shown in FIG. 2, the control valve 8 and the first pressure chamber P1 are connected via the first oil passage 9a, and the control valve 8 and the second pressure chamber P2 are connected via the second oil passage 9b. The first oil passage 9a and the reservoir tank are connected via the third oil passage 9c, and the second oil passage 9b and the reservoir tank 6 are connected via the fourth oil passage 9d. It is configured. From such a configuration, the hydraulic oil discharged from the oil pump 7 is selected into the corresponding pressure chamber on the one side of the power cylinder 5 via the first oil passage 9a or the second oil passage 9b according to the steering direction. The hydraulic oil in the pressure chamber on the other side of the power cylinder 5 returned to the control valve 8 via the first oil passage 9a or the second oil passage 9b is supplied to the third oil passage 9c or the fourth oil passage 9c. The oil is recirculated to the reservoir tank through the oil passage 9d.

  Here, the third oil passage 9c and the fourth oil passage 9d are, as shown in FIGS. 1 and 2, a gear box 11 in which the control valve 8 is accommodated and a valve housing 12 fixed to the gear box 11. A part of the hydraulic oil supplied to the pressure chamber on the one side is transferred to the control valve 8 through the communication path 20. The fluid is returned to the reservoir tank 6 together with the returned hydraulic oil in the pressure chamber on the other side. The solenoid valve 10 is provided in the middle of the communication path 20, and the hydraulic pressure supplied to the pressure chamber on the one side by controlling the flow rate of the hydraulic oil flowing through the communication path 20 by the solenoid valve 8. Thus, an appropriate steering assist force is generated in the power cylinder 5. In the present embodiment, the flow of hydraulic oil from the third oil passage 9c side to the fourth oil passage 9d side is defined as a one-way flow X according to the present invention, and the fourth oil passage 9d side to the third oil passage 9c side. The flow of the hydraulic oil to the flow is defined as the other direction flow Y according to the present invention. Hereinafter, for convenience of explanation, the unidirectional flow X will be described as an example.

  As shown in FIG. 2, the solenoid valve 10 is controlled by a control current from the electronic control unit 30 based on detection results of a torque sensor and a vehicle speed sensor (not shown) connected to the electronic control unit 30 that is an ECU. The drive is controlled. The torque sensor is usually provided on the steering shaft 1 and used for detection of steering torque, and the vehicle speed sensor is usually provided on the steered wheels and used for detection of the traveling speed of the vehicle. is there.

  As shown in FIG. 3, the solenoid valve 10 has a valve housing 12 in which a valve body housing hole 12a forming a part of the communication passage 20 is formed on one side, and one end side of the valve body housing hole 12a. A valve body 13 made of a substantially cylindrical magnetic material, a valve body 14 arranged in a fixed state in a valve body housing hole 13a which is an inner peripheral portion on one end side of the valve body 13, and a valve body 13 A core 15 made of a substantially cylindrical magnetic material disposed in a confronting state on the other end side and connected to the other end portion of the valve body 13 via a tubular member, and an inner peripheral side mainly of the other end portion of the valve body 13 The armature 16 is accommodated in the valve body 14 so as to be movable relative to the valve body 14, and is screwed through an internal thread portion formed on the inner peripheral portion of the core 15. rear The adjustment plug 17 that adjusts the urging force (preload) of the urging member 18 and the retainer attached to the end of the armature 16 facing the core 15 and the adjustment plug 17 are interposed between the armature 16 and the core. And an urging member 18 for urging in a direction of separating from 15.

  The housing 12 is provided with a third oil passage side passage 20a and a fourth oil passage side passage 20b that communicate with each other via a valve body accommodation hole 12a and constitute the series of communication passages 20 together with the valve accommodation hole 12a. These passages 20a, 20b are connected to the pressure chamber on the side where one of the passages is increased in the power cylinder 5 (the side supplying hydraulic oil) when the control valve 8 is opened, These passages are configured to be connected to the reservoir tank 6.

  The valve body 13 is attached to the pump body 12 via a flange portion having an enlarged diameter near one end side in the axial direction, and is inserted into the valve body housing hole 12a. An annular constricted portion 13c is continuously provided in the circumferential direction at an intermediate portion of 13b, and an outer peripheral surface of the constricted portion 13c and an inner periphery of the valve body housing hole 12a are provided on the outer peripheral side of the constricted portion 13c. An annular passage 23 is defined between the two surfaces. The valve body 13 is provided with an armature accommodating portion 13d on the inner circumference on one end side thereof, which is formed with an enlarged diameter relative to the inner diameter of the valve element accommodating hole 13a and accommodates the armature 16 so as to be movable in the axial direction. A communication hole 24 that communicates the armature accommodating portion 13d and the annular passage 23 is provided at a predetermined position in the circumferential direction of the constricted portion 13c of the valve body 13, and the fixed hole according to the present invention is provided in the communication hole 24. A fixed orifice 21 as a throttle portion is configured (see FIG. 4).

  The valve body 14 has a cylindrical shape with one end opened and the other end closed, and an oil passage 25 facing the fourth oil passage side passage 20b is formed on the inner peripheral side through the one end opening. In addition, a plurality of valve holes 14a functioning as orifices are formed through the circumferential wall in the vicinity of the other end of the oil passage 25 along the radial direction. The outer peripheral side communicates.

  The armature 16 is mainly accommodated in the armature accommodating portion 13d of the valve body 13 so as to be movable in the axial direction, and an exciting current is applied to a coil (not shown) arranged so as to straddle both opposing ends of the valve body 13 and the core 15. By being energized, the coil is displaced toward the core 15 by using the outer peripheral surface of the valve body 14 as a guide by the magnetic force of the coil. In addition, the armature 16 has an introduction hole 16a along the axial direction that guides the hydraulic oil flowing into the armature housing portion 13d to the valve holes 14a on the end surface of one end portion facing the inner end portion of the armature housing portion 13d. In addition, an annular groove 16b is formed in the inner peripheral surface of the armature 16 along the circumferential direction so as to communicate with the inner end of the introduction hole 16a.

  Here, the solenoid valve 10 is configured as a so-called normally open solenoid valve, and each of the above-described solenoid valves 10 is not energized to a coil (not shown) provided in the solenoid valve 10. The valve hole 14a and the annular groove 16b communicate with each other, that is, the third oil passage side passage 20a and the fourth oil passage side passage 20b communicate with each other. On the other hand, in a state in which the exciting current is applied to the coil, the flow passage area of the communication portion between each valve hole 14a and the annular groove 16b changes depending on the amount of current supplied. As shown in FIG. 3, the communication between each valve hole 14a and the annular groove 16b, that is, the communication between the third oil passage side passage 20a and the fourth oil passage side passage 20b is blocked. A variable orifice 22 which is a variable restricting portion of the present invention is configured by a communicating portion between each valve hole 14a and the annular groove 16b whose flow area changes depending on the amount of current supplied to the coil (see FIG. 4). ).

  With the above configuration, in the solenoid valve 10, for example, in a non-energized state, in the case of the one-way flow X in which the hydraulic oil is introduced from the third oil passage side passage 20 a, the hydraulic oil flows from the annular passage 23. The oil passage 25 is guided to the armature housing portion 13d through the fixed orifice 21 (communication hole 24), and from the armature housing portion 13d through the introduction hole 16a through the variable orifice 22 (annular groove 16b and valve hole 14a). And flows into the fourth oil passage side passage 20b through the oil passage 25. On the other hand, in the case of the other direction flow Y in which the hydraulic oil is introduced from the fourth oil passage side passage 20b side, the state of the hydraulic oil flow is opposite to that of the one-way flow X.

  This flow of hydraulic oil is represented as a hydraulic circuit as shown in FIG. That is, in the solenoid valve 10, the fixed orifice 21 and the variable orifice 22 are arranged in series. In the case of the one-way flow X, the flow flows from right to left in the figure, and in the case of the other-direction flow Y, It will flow from left to right inside. In the figure, XΔP1 and XΔP2 represent pressure losses at the fixed orifice 21 and the variable orifice 22 of the unidirectional flow X, respectively. YΔP1 and YΔP2 are variable with the fixed orifice 21 of the other direction flow Y. The pressure loss at each of the orifices 22 is represented.

  As shown in FIG. 5, the fixed orifice 21 is formed in a stepped diameter in the communication hole 24 by a small diameter portion 21 a having a relatively small inner diameter and a large diameter portion 21 b having a relatively large inner diameter. In the case of the unidirectional flow X, the hydraulic oil flows from the small diameter portion 21a side to the large diameter portion 21b side, and in the case of the other direction flow Y, the hydraulic oil operates from the large diameter portion 21b side to the small diameter portion 21a side. Oil will flow. In the fixed orifice 21, the inner diameter d1 of the small diameter portion 21a and the inner diameter d2 of the large diameter portion 21b are set so that the pressure loss XΔP1 in the unidirectional flow X is larger than the pressure loss YΔP1 in the other direction flow Y. Each is set (see FIG. 6). In other words, the inner diameters d1 and d2 of the respective diameter portions 21a and 21b have a value obtained by squaring the ratio (d1 / d2) in the unidirectional flow X in FIG. Each is set to be in the tuning region Z range.

  Further, a plurality of the fixed orifices 21 are provided in the circumferential direction, and the pressure loss characteristics can be tuned by increasing or decreasing the number. In the present embodiment, the fixed orifices 21 are arranged at three locations in the circumferential direction (see FIG. 7) as compared to the conventional technique provided at four locations in the circumferential direction (see FIG. 8).

  On the other hand, as shown in FIG. 9, the variable orifice 22 has a pressure loss YΔP2 in the other direction flow Y indicated by a broken line in the drawing rather than a pressure loss XΔP2 in the one direction flow X indicated by a solid line in the drawing. It is configured to be large. In other words, the variable orifice 22 has a pressure loss characteristic opposite to the pressure loss characteristic of the fixed orifice 21 such that the pressure loss of the unidirectional flow X is larger than the pressure loss of the other direction flow Y. The pressure loss characteristics cancel each other out with respect to the pressure loss characteristics in the orifice 21.

  With such a configuration, in the solenoid valve 10, the pressure loss difference Xdp (= XΔP1−XΔP2) respectively generated in the fixed orifice 21 and the variable orifice 22 in the unidirectional flow X and the fixed orifice 21 in the other direction flow Y are variable. The pressure loss differences Ydp (= YΔP1−YΔP2) generated in the orifices 22 cancel each other. Therefore, the pressure loss difference Ydp−Xdp generated based on the difference in the flow direction of the hydraulic oil in the entire solenoid valve 10 is at least the hydraulic oil when flowing only through the variable orifice 22 as shown in FIG. Is smaller than the pressure loss difference YΔP2 due to the difference in the flow direction.

  As described above, in this embodiment, the fixed orifice 21 and the variable orifice 22 are arranged in series on the hydraulic circuit of the solenoid valve 10, and the pressure loss characteristics of the orifices 21 and 22 conflict with each other. Because of the configuration, the difference in pressure loss generated in each of the orifices 21 and 22 cancels out based on the difference in the flow direction of the hydraulic oil, and the flow direction of the hydraulic oil in the solenoid valve 10 The pressure loss difference generated based on the difference can be reduced as much as possible. As a result, the pressure loss difference as a whole of the power steering device generated based on the difference in the flow direction of the hydraulic oil is reduced.

  Specifically, the pressure loss difference Ydp−Xdp generated based on the difference in the flow direction of the hydraulic oil in the entire solenoid valve 10 is at least the flow direction of the hydraulic oil when only the variable orifice 22 flows. Since it is configured to be smaller than the pressure loss difference YΔP2 due to the difference, the entire power steering device that is generated based on the difference in the flow direction of the hydraulic oil as compared with the prior art in which the solenoid valve is configured by only the variable orifice As a result, the pressure loss difference can be reduced.

  Further, the fixed orifice 21 is set so that the pressure loss XΔP1 in the one-way flow X is larger than the pressure loss YΔP1 in the other-direction flow Y, that is, the ratio between the inner diameters d1 and d2 of the respective diameter portions 21a and 21b. Is within the range of the tuning region Z. In this tuning region Z, as shown in the graph of FIG. 6, the difference in pressure loss between the orifices 21 and 22 based on the difference in the flow direction of hydraulic oil is large. Therefore, there is a merit that the pressure loss characteristics in these orifices 21 and 22 can be easily verified and tuned.

  Furthermore, since the boundary between the two diameter portions 21a and 21b is formed in a stepped diameter in the fixed orifice 21, the pressure loss characteristics of the two orifices 21 and 22 based on the difference in the flow direction of hydraulic oil are exhibited. As a result, there is also an advantage that tuning of the pressure loss characteristics of both the orifices 21 and 22 is facilitated.

  The present invention is not limited to the configuration of the above embodiment. For example, the oil path configuration in the solenoid valve 10 is configured such that the fixed orifice 21 and the variable orifice 22 are arranged in series on the hydraulic circuit. What is necessary is just to be able to change freely about the handling of a detailed oil path according to the specification etc. of the object vehicle and the power steering apparatus used for this vehicle.

  In the above embodiment, the boundary between the diameter portions 21a and 21b in the fixed orifice 21 is described as an example of a step diameter. However, the boundary between the diameter portions 21a and 21b is illustrated in FIG. It is also possible to configure so-called tapered diameter as shown in FIG.

  Furthermore, the fixed orifice 21 corresponding to the fixed throttle portion according to the present invention is not limited to a clear throttle, and has an inner diameter smaller than the inner diameter of the third oil passage side passage 20a. However, it may be anything that exhibits a diaphragm effect.

21 ... Fixed orifice (fixed restrictor)
22 ... Variable orifice (variable restrictor)
X ... one-way flow Y ... other-direction flow XΔP1 ... pressure loss YΔP1 in a fixed orifice in one-way flow ... pressure loss XΔP2 in a fixed orifice in other direction flow ... pressure loss YΔP2 in a variable orifice in one-way flow ... variable in other direction flow Pressure loss at the orifice Xdp ... Pressure loss difference in one direction flow Ydp ... Pressure loss difference in other direction flow

Claims (5)

A power cylinder for applying a steering assist force to the steered wheels based on a differential pressure between a pair of pressure chambers separated inside;
A control valve that selectively guides hydraulic oil supplied from an external hydraulic source to each pressure chamber of the power cylinder;
A first oil passage connecting the pressure chamber on one side of the power cylinder and the control valve;
A second oil passage connecting the pressure chamber on the other side of the power cylinder and the control valve;
A third oil passage that connects the first oil passage to a reservoir tank in which hydraulic oil is stored, and returns the hydraulic oil returned from the first oil passage to the reservoir tank;
A fourth oil path that connects the second oil path and the reservoir tank and returns the hydraulic oil returned from the second oil path to the reservoir tank;
A communication passage for communicating the third oil passage with the fourth oil passage;
The hydraulic fluid is provided in the communication passage and flows in one direction of hydraulic oil flowing from the third oil passage side to the fourth oil passage side and in the other direction flow of hydraulic oil flowing from the fourth oil passage side to the third oil passage side. A solenoid valve for controlling the flow rate,
In the solenoid valve, a variable throttle part that controls the flow rate of the hydraulic fluid flowing through the communication path by changing the flow path area, and a fixed throttle part that does not change the flow path area are on the oil path circuit. A power steering device configured to be arranged in series,
The variable restrictor is configured such that the pressure loss in the one-way flow of hydraulic oil is greater than the pressure loss in the other-direction flow,
The power throttle device, wherein the fixed throttle portion is configured such that a pressure loss in the other direction flow of hydraulic oil is larger than a pressure loss in the one direction flow. The fixed throttle portion has a pressure loss difference due to a difference in a flow direction of hydraulic oil flowing only in the variable throttle portion due to a difference in a flow direction of hydraulic fluid flowing through the variable throttle portion and the fixed throttle portion. The power steering apparatus according to claim 1, wherein the power steering apparatus is configured to be smaller. The power steering apparatus according to claim 1, wherein the fixed throttle portion includes a plurality of throttle passages. The said fixed throttle part is comprised so that a pressure loss may become large when hydraulic fluid flows from the small diameter part side to the large diameter part side, The Claim 1 characterized by the above-mentioned. Power steering device. The power steering device according to claim 4, wherein a boundary between the small diameter portion and the large diameter portion is formed in a step shape.

Images