JPH06219297A - Rack and pinion type power steering device - Google Patents

Abstract

PURPOSE:To prevent a cam part from buckling in a piston for opening/closing a bypass valve thereby, in a rack and pinion type power steering device formed so that depressurization can be performed by using the bypass valve in a stroke end of the piston. CONSTITUTION:A piston 4 is divided into a cam part 6 having a cam surface 6b coming into contact with a lower end of an operating shaft 37 of a bypass valve 31 and a fixed part 7 having a protrusion part 7a fixedly calked relating to a rack shaft 2, and by using a quenching material for the cam part 6 and a soft material for the fixed part 7, both the parts are connected by press fitting.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rack-and-pinion type power steering system capable of releasing pressure at the stroke end of a piston.

[0002]

2. Description of the Related Art Generally, in a power steering system, when the piston of the power cylinder reaches the stroke end during stationary operation, the pressure of the pump rises to the relief pressure, the load on the engine increases, and the relief action of the relief valve increases. Causes the diaphragm sound to be generated. For this,
Conventionally, as shown in FIG. 3, a relief valve 52 that opens and closes when a cam portion 50a formed on a piston 50 abuts, and connects the left and right cylinder chambers 51a and 51b formed on the power cylinder 51 to each other, is formed by the stroke of the piston 50. Each is provided near the end. In this type, when the piston 50 is moved to the stroke end, the cam portion 50a of the piston 50 contacts the tip of the operating shaft 52a of the relief valve 52,
The ball 52b of the relief valve 52 is moved through the operation shaft 52a, the relief valve 52 is opened, and the left and right cylinder chambers 51 are opened.
The pressure relief of the cylinder chamber on the pressure oil supply side is performed by allowing the a and 51b to communicate with the relief valve 52 via the pipe 55.

Here, conventionally, the rack shaft 5 of the piston 50 is used.
As shown in FIG. 3, first, the rack shaft 53 is fixed to the rack shaft 53.
The locking member 54 is fitted into the locking groove 53a formed in the rack shaft 53, and the piston 50 is fitted into the rack shaft 53 up to the position where the piston 50 is locked by the locking member 54. In addition, the protrusion 50b formed by protruding in the axial direction of the rack shaft 53 is caulked and fixed to the piston 50.

[0004]

In the prior art, when the steering wheel is steered, pressure oil is supplied to one of the left and right cylinder chambers 51a and 51b by the operation of the servo valve. For example, if pressure oil is supplied to the cylinder chamber 51a, as shown in FIG.
Will be moved. Here, the cylinder chamber 51a on the pressure oil supply side
The relief valve provided on the pressure oil supply side is opened by the oil pressure of the pressure oil supplied to the relief valve 52, which blocks the communication of the pressure oil with the cylinder chamber 51b on the oil return side via the pipe 55. When the pressure is released at the stroke end of the piston 50, that is, the piston 50
Cam portion 50a pushes up the ball 52b upward in FIG. 3 via the actuating shaft 52a to open the relief valve 52, the ball 52b has an oil pressure on the pressure oil supply side and a spring 52c.
Is applied, the surface pressure of the cam portion 50a of the piston with which the operating shaft 52a comes into contact increases, and the cam portion 50a
There was a risk of buckling or the like at a. Also, in order to prevent buckling, it is necessary to quench the piston 50.
As shown in (4), the protrusion 50b formed on the piston 50 was caulked and fixed to the rack shaft 53, so that quenching could not be performed.

[0005]

The rack-and-pinion type power steering apparatus of the present invention has been made to solve the above-mentioned problems, and a power cylinder is slid on a rack shaft meshing with a pinion shaft. A rack-and-pinion type power supply is provided with a movably fitted piston, and a relief valve that opens and closes when the cam part formed on this piston comes into contact and connects the left and right cylinder chambers near the stroke end of the piston. In the steering apparatus, the piston is divided into a cam portion having a cam surface that comes into contact with the relief valve and a sliding contact surface that slidably contacts the power cylinder, and a fixed portion that is caulked and fixed to the rack shaft. And a hardened material is used for the cam portion, a soft material is used for the fixed portion, and the cam portion is fixed on the rack shaft by the fixed portion. Characterized in that was.

[0006]

With the steering wheel steering, the rack shaft moves in the axial direction via the pinion shaft, and at the same time, pressure oil is introduced into one of the cylinder chambers to move the piston. When the piston reaches the stroke end, the left and right cylinder chambers communicate with each other by opening the relief valve provided in the cylinder on the oil recirculation side by the cam portion of the piston, and the pressure in the cylinder chamber on the oil supply side is released. . Here, at the time of pressure release, the load acting in the direction of closing the relief valve provided in the oil recirculation side cylinder chamber is large, so the surface pressure of the cam portion of the piston increases and buckling or the like of the cam portion of the piston occurs. There was a fear that it would occur.
However, in the present invention, the piston is split,
The cam that contacts the relief valve is made of a hardened material, and the fixed part that is caulked and fixed to the rack shaft is made of a soft material.
Since the cam portion is fixed on the rack shaft by the fixing portion, buckling of the piston can be prevented.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. In FIG. 1, reference numeral 1 denotes a gear housing. A rack shaft 2 is slidably penetrated through the gear housing 1, and both ends of the rack shaft 2 are connected to steering wheels through ball joints or the like not shown. . Rack teeth 2a are formed on the outer periphery of one end of the rack shaft 2. The rack teeth 2a are formed on the gear housing 1
It is meshed with a pinion shaft 3 which is rotatably supported. The pinion shaft 3 is connected to a steering handle (not shown) via a servo valve 15.

A piston 4 is provided on the rack shaft 2, and the piston 4 is slidably fitted in the power cylinder 5. Here, as shown in FIG. 2, the piston 4 is composed of a cam portion 6 made of a hardened material in which the SCM 15 and the like are hardened, and a fixing portion 7 made of a soft material such as S45C. On the outer periphery of the cam portion 6, a sliding contact surface 6a that slidably contacts the power cylinder 5, a cam surface 6b that is tapered from the sliding contact surface 6a toward both ends, and an annular groove 6c.
Are formed. An O-ring 8 and a resin-based seal member 9 are sequentially fitted into the annular groove 6c to seal the inner circumference of the power cylinder 5. A step portion 6d having a diameter larger than the diameter of the rack shaft 2 is formed on the inner circumference of the cam portion 6.

The fixing portion 7 is joined to the cam portion 6 by being press-fitted into the step portion 6d, and the fixing portion 7 is formed with a protrusion portion 7a protruding in the axial direction of the rack shaft 2. Further, a locking groove 10 and a concave groove 11 are formed on the rack shaft 2, a locking member 12 such as a snap ring is fitted into the locking groove 10, and the concave groove 11 has the fixing portion. Protrusion 7
a is fixed by crimping. As a result, the piston 4 is fixed to the rack shaft 2.

One end of the power cylinder 5 is fitted to one end of the gear housing 1, and a cylinder end (not shown) is fixed to the other end. In this way, with the piston 4,
The inside of the power cylinder 5 is divided into a cylinder left chamber 5a and a cylinder right chamber 5b. A port 1 for introducing or discharging pressure oil is provided at the ends of the cylinder chambers 5a, 5b.
3 and 14 are provided, and the ports 13 and 14 are connected to a servo valve 15. The servo valve 15 is operated by relative rotation of an input shaft and an output shaft (not shown), and pressure oil supplied from a pump 16 is supplied. The cylinder chamber 5a of the power cylinder 5,
5b is distributed to one side and the oil from the other side is returned to the tank 17.

Further, pressure release ports 18 and 19 are provided near the piston stroke end, and these pressure release ports 18 and 19 are connected to each other via a pipe connecting device 20. As shown in FIG. 2, on the outer periphery of the power cylinder 5, a fitting hole 25 is provided at a position corresponding to the pressure relief port 19.
The fixing member 21 having the is formed is fixed.

In FIG. 2, reference numeral 22 is an eye union, and a through hole 26 for inserting a bolt union described later is formed in the eye union 22, and a pipe mounting port communicating with the through hole 26 in the radial direction of the eye union 22. 27 is formed. The pipe 23 is fixed to the pipe mounting port 27.
24 is a bolt union, and this bolt union 24
Penetrates through the insertion hole 26 of the eye union 22 and is screwed into the fitting hole 25 of the fixing member 21, and communicates with the pressure relief port 19 in the axial direction of the bolt union 24 inside the bolt union 24. A shaft hole 28 is formed, and a communication hole 29 that connects the shaft hole 28 and the pipe mounting port 27 of the eye union 22 is formed in the radial direction of the bolt union 24.

The pressure release port 18 side is also provided in the same manner, that is, the pipe connecting device 20 is composed of a fixing member 21, an eye union 22, a pipe 23 and a bolt union 24. Further, in FIG. 2, 30 is a packing, which is inserted between the fixing member 21 and the eye union 22 and between the eye union 22 and the bolt union 24, respectively. Further, a relief valve 31 is provided inside each bolt union 24 of the pipe connecting device 20 configured as described above.

As shown in FIG. 2, the bolt union 2
4. The valve seat 32 formed by projecting annularly in the axial hole 28 of No. 4
A ball 33 that contacts and closes the valve seat 32 in an upper space defined by the valve seat 32, a pressing member 34 that abuts on the ball 33, and a plug 35 that closes the upper part of the axial hole 28. And the stopper 35 and the pressing member 3
4, a spring 36 that presses the pressing member 34 toward the ball 33 to press the ball 33 against the valve seat 32, and a spring 36 that is slidably inserted into a space defined by the valve seat 32. The relief valve 31 is constituted by the actuated shaft 37 and the stopper 38 fixed below the axial hole 28 and restricting the lower movable end of the actuated shaft 37.

A communication groove 39 is formed on the outer circumference of the operating shaft 37 so that pressure oil can communicate with the front and rear of the operating shaft 37. Further, the upper and lower ends of the operating shaft 37 have a small diameter, and the lower end penetrates the pressure relief port 19 and projects into the cylinder right chamber 5b of the power cylinder 5, so that the piston 4 is
The cam surface 6b of the piston 4 comes into contact when moving to the middle right. On the other hand, the upper end of the operating shaft 37 has a diameter that allows the valve seat 32 to be inserted, and the cam surface 6b of the piston 4 causes the ball 33 and the upper end of the operating shaft 37 to come into contact when the operating shaft 37 is moved upward. The relief valve 31 is opened by moving the ball 33 against the urging force of the spring 36.

A relief valve 31 is similarly provided on the pressure relief port 18 side. Next, the assembling order of the piston 4 to the rack shaft 2 will be described. First, the locking member 12 is fitted into the locking groove 10 formed in the rack shaft 2. Next, the cam portion 6
The piston 4 integrated by press-fitting the fixing portion 7 into the stepped portion 6d is fitted into the rack shaft 2 to a position where it is locked by the locking member 12. Next, the piston 4 is fixed to the rack shaft 2 by caulking and fixing the protrusion 7a of the fixing portion 7 in the groove 11 formed in the rack shaft 2.

Next, the operation of the rack-and-pinion type power steering system of the present embodiment will be described based on the above-mentioned structure.
When the steering handle (not shown) is steered, the pinion shaft 3 is rotated, and the rack teeth 2a, that is, the rack shaft 2 is moved, for example, in the right direction in FIG. Pressure oil is supplied from the port 13 to the cylinder left chamber 5a of the power cylinder 5, and the piston 4
Is moved to the right in FIG. In this way, when the piston 4 is at a position other than the piston stroke end, power assist is added to the steering of the steering wheel by all the pressure oil supplied to the cylinder left chamber 5a, and the traveling wheels at both ends of the rack shaft 2 have the desired direction. Biased to.

When pressure oil is supplied to the cylinder left chamber 5a,
Due to the hydraulic pressure, the relief valve provided on the cylinder left chamber 5a side is opened, and pressure oil is supplied through the pipe 24 to the relief valve 31 provided on the cylinder right chamber 5b side. As a result, the ball 33 of the relief valve 31 on the cylinder right chamber 5b side is brought into pressure contact with the valve seat 32 by the biasing force of the spring 36 and the oil pressure of the pressure oil supplied to the cylinder left chamber 5a, and the cylinder left chamber 5a. And the cylinder right chamber 5b are cut off from each other.

Further, when the piston 4 is moved rightward in FIG. 1 and the piston 4 reaches the vicinity of the piston stroke end, the cam surface 6b of the piston 4 contacts the lower end of the operating shaft 37, and the cam surface 7b causes the operating shaft to move. Push 37 up in FIG. As a result, the upper end of the operating shaft 37 abuts the ball 33, and the ball 33 is moved against the biasing force of the spring 36 and the hydraulic pressure of the pressure oil supplied to the cylinder left chamber 5a to open the relief valve 31. , The cylinder left chamber 5a and the cylinder right chamber 5b are communicated with each other. The pressure oil supplied to the cylinder left chamber 5a is passed through the relief valve 31 and the pipe 24 to the cylinder right chamber 5b.
Is supplied to the tank 17 from the port 14 of the cylinder right chamber 5b, and the cylinder left chamber 5a, which is the pressure oil supply side, is depressurized, and the pressure of the pump 16 is reduced to the relief pressure at the piston stroke end. Does not rise until.

Here, when the cam surface 6b of the piston 4 pushes up the ball 33 via the operating shaft 37, the ball 33 is biased by the spring 36 and the hydraulic pressure of the pressure oil supplied to the cylinder left chamber 5a. As a result, since the surface pressure of the cam surface 6b of the piston 4 that contacts the lower end of the actuating shaft 37 increases, there is a risk that the cam surface 6b may buckle or the like. As shown in FIG. 3, the piston 4 has a cam portion 6 having a cam surface 6 b that contacts the lower end of the operating shaft 37.
And a fixing portion 7 having a protrusion 7a that is caulked and fixed to the rack shaft 2, and since the cam portion 6 is made of a hardened material, buckling of the cam surface 6b of the piston 4 is prevented. be able to. Further, since the fixing portion 7 is formed of a soft material, it can be caulked and fixed to the rack shaft 2.

[0021]

The rack-and-pinion type power steering apparatus of the present invention hardens the cam portion which divides the piston of the power cylinder and has a cam surface for contacting the relief valve and a sliding surface for sliding contact with the power cylinder. Material, and the fixed part that is caulked and fixed to the rack shaft is made of a soft material, and the cam part is fixed on the rack shaft by the fixed part. Buckling of the piston due to the relief valve for pressure relief can be prevented.

[Brief description of drawings]

FIG. 1 is a sectional view of a rack-and-pinion type power steering apparatus showing an embodiment of the present invention.

FIG. 2 is an enlarged sectional view of an essential part showing a state in which a piston has moved to the vicinity of a stroke end.

FIG. 3 is an enlarged sectional view of an essential part showing a state in which a piston of a conventional rack-and-pinion type power steering apparatus has moved to near a stroke end.

[Explanation of symbols]

 2 Rack shaft 3 Pinion shaft 4 Piston 5 Power cylinder 5a Cylinder left chamber 5b Cylinder right chamber 6 Cam part 7 Fixed part 31 Relief valve

Claims (1)

[Claims] 1. A rack shaft that meshes with a pinion shaft,
Providing a piston that slidably fits into the power cylinder,
In a rack-and-pinion type power steering device in which a cam portion formed on this piston is opened and closed by abutting, and a relief valve that connects the left and right cylinder chambers is provided near the stroke end of the piston, A cam portion having a cam surface that comes into contact with a valve and having a sliding contact surface that slidably contacts the power cylinder, and a fixed portion that is caulked and fixed to the rack shaft, and a hardened material is used for the cam portion. A rack-and-pinion type power steering apparatus, wherein a soft material is used for the fixing portion, and the cam portion is fixed on the rack shaft by the fixing portion.