JP2010203497A - Power cylinder and hydraulic power steering device using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power cylinder capable of reducing cost, and a hydraulic power steering device using the same. <P>SOLUTION: This power cylinder 10 has a piston ring 16 arranged in a peripheral groove 15 formed on the outer peripheral side of a piston 12 and sealing a part between an inner wall 11a of a cylinder tube 11 and the piston 12. A bottom surface 17 of the peripheral groove 15 is formed with an inclined face 17a inclining inside in the radial direction toward the center in the axial direction of the peripheral groove 15 from an inside end 18a in the radial direction of a sidewall surface 18 of the peripheral groove 15 and capable of abutting on a corner part 16d on the inside in the radial direction of the piston ring 16 in a state of contacting the piston ring 16 with the inner wall 11a of the cylinder tube 11. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a power cylinder for assisting a rack shaft and a hydraulic power steering apparatus using the same.

  A rack-and-pinion type hydraulic power steering apparatus used in an automobile includes a power cylinder that generates a steering assist force by supplying hydraulic pressure. The power cylinder includes a cylinder tube, a rack shaft that functions as a piston rod that moves in the axial direction in the cylinder tube, and a piston that is fixed to the rack shaft and divides the cylinder tube into two oil chambers. I have. A piston ring for sealing between the piston and the cylinder tube is interposed.

FIG. 5 is a partial cross-sectional view around the piston of a conventional power cylinder. As shown in the figure, the piston 101 is fixed to the rack shaft 102 and the inside of the cylinder tube 103 is divided into first and second oil chambers 104 and 105. A circumferential groove 106 that is recessed radially inward is formed on the outer circumferential surface of the piston 101, and a piston ring 107 and an O-ring 108 are disposed inside the circumferential groove 106.
The piston ring 107 is disposed in the circumferential groove 106 in contact with the inner peripheral surface of the cylinder tube 103. The O-ring 108 is interposed between the piston ring 107 and the inner peripheral surface of the piston ring 107 and the bottom surface of the peripheral groove 106.

  FIG. 5 shows a case where the hydraulic pressure in the first oil chamber 104 is higher than the hydraulic pressure in the second oil chamber 105. When the hydraulic pressure in the first oil chamber 104 is higher than the hydraulic pressure in the second oil chamber 105, the piston ring 107 and the O-ring 108 move to the side wall on the second oil chamber 105 side of the circumferential groove 106 due to the hydraulic pressure difference. Further, when the O-ring 108 is pressed by hydraulic pressure, the piston ring 107 is deformed so as to be pressed toward the inner peripheral surface of the cylinder tube 103. As a result, the piston ring 107 is pressed against the cylinder tube 103 to ensure a sealing property between the two (for example, see Patent Document 1).

JP-A-10-252711

The above-described conventional power cylinder has a relatively simple structure in which an O-ring 108 is interposed between the piston 101 and the piston ring 107 to ensure the sealing performance between the piston ring 107 and the cylinder tube 103. On the other hand, in recent years, there has been a strong demand for lowering the cost of automobile parts, and measures for further lowering the cost of power cylinders have been desired.
The present invention has been made in view of such circumstances, and provides a power cylinder capable of reducing the cost by using a simpler configuration, and a hydraulic power steering apparatus using the same. With the goal.

  In order to achieve the above object, the present invention includes a cylinder tube, a piston rod that is movable in the axial direction in the cylinder tube, and two cylinders that are fixed to the piston rod and are supplied with hydraulic pressure in the cylinder tube. It is divided into oil chambers, a piston that moves in the axial direction in the cylinder tube due to a hydraulic pressure difference between these two oil chambers, a circumferential groove formed on the outer peripheral side of the piston, an inner wall of the cylinder tube, and a piston And a piston ring that seals between each of the circumferential grooves, the bottom surface of the circumferential groove has a radially inner side from a radially inner end of a side wall surface of the circumferential groove toward an axial center of the circumferential groove. Inclined surface that can be in contact with the radially inner corner of the piston ring while the piston ring is in contact with the inner wall of the cylinder tube It is characterized by being formed.

According to the power cylinder configured as described above, there is an inclined surface on the bottom surface of the circumferential groove on which the piston ring can come into contact with the radially inner corner of the piston ring in a state where the piston ring is in contact with the inner wall of the cylinder tube. As a result, the hydraulic pressure of one oil chamber increases, and when the piston ring is pressed in the axial direction toward the side wall surface of the circumferential groove by the hydraulic pressure, the piston ring is in the radial direction before contacting the side wall surface. The inner corner contacts the inclined surface. When the oil pressure is further pressed to the side wall surface side, the radially inner corner of the piston ring is pushed radially outward along the inclined surface, and the force that pushes the entire piston ring radially outward. Works. Thereby, a piston ring is pressed by the wall surface of a cylinder tube, As a result, the sealing performance between a piston ring and a cylinder tube can be ensured.
Thus, according to the present invention, the sealing performance between the piston ring and the cylinder tube can be ensured without using an O-ring as in the above-described conventional example, so that the number of parts can be reduced and simpler. By adopting a simple configuration, the cost can be reduced.

In the power cylinder, it is preferable that the inclined surface is in contact with a radially inner corner of the piston ring in a state where there is no difference in hydraulic pressure between the two oil chambers.
In this case, when a hydraulic pressure difference occurs between the two oil chambers, the radially inner corner of the piston ring that is already in contact with the inclined surface is pushed up radially outward by the inclined surface, and the piston ring and the cylinder tube The space is sealed. That is, in the case of the above-described configuration, it is not necessary to move the piston ring in the axial direction in order to bring the corner portion into contact with the inclined surface after the hydraulic pressure difference occurs, so that the responsiveness of the power cylinder can be improved.

  In addition, a corner portion on the radially inner side of the piston ring may be formed on an inclined surface corresponding to the inclination of the inclined surface. In this case, the corner portion of the piston ring by the inclined surface of the circumferential groove Can be smoothly pushed up, and the piston ring can be more reliably pressed against the wall surface of the cylinder tube.

According to the present invention, in the hydraulic power steering apparatus including a power cylinder that generates a steering assist force by supplying hydraulic pressure, the power cylinder is the above-described power cylinder.
According to the hydraulic power steering apparatus having the above-described configuration, as described above, cost reduction can be achieved.

  According to the power cylinder and the hydraulic power steering apparatus of the present invention, the cost can be reduced by adopting a simpler configuration.

1 is a schematic diagram illustrating a configuration of a rack and pinion type hydraulic power steering apparatus including a power cylinder according to a first embodiment of the present invention. It is a fragmentary sectional view around the piston of a power cylinder, (a) has shown the state where the oil pressure difference between both oil chambers has not arisen, and (b) has shown the state where oil pressure difference has arisen. It is a fragmentary sectional view around the piston of the power cylinder concerning a second embodiment of the present invention. (A) is a partial sectional view around a piston showing a modification, and (b) is a partial sectional view showing a further different modification. It is a fragmentary sectional view around the piston of the conventional power cylinder.

Next, preferred embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a schematic diagram showing a configuration of a rack and pinion type hydraulic power steering apparatus including a power cylinder according to a first embodiment of the present invention.
In FIG. 1, a hydraulic power steering apparatus PS includes an input shaft 1 to which a steering wheel S is attached, a pinion 2 provided at an end of the input shaft 1, a rack shaft 3 constituting a rack pinion, and a rack shaft 3 And a hydraulic control valve 4 that is connected to a hydraulic pump (not shown) and supplies hydraulic power to the power cylinder 10 in accordance with the rotation (steering) of the input shaft 1. Steering wheels W are connected to both ends of the rack shaft 3 via tie rods (not shown), respectively.

  The power cylinder 10 includes a cylinder tube 11 constituted by a housing or the like that covers the rack shaft 3 and a piston 12 that is fixed to the rack shaft 3 as a piston rod and moves in the cylinder tube 11 in the axial direction.

The piston 12 divides the inside of the cylinder tube 11 into two oil chambers (a first oil chamber 13 and a second oil chamber 14). Hydraulic pipes 13 a and 14 a extending from the hydraulic control valve 4 are connected to the first oil chamber 13 and the second oil chamber 14, respectively, and hydraulic pressure is supplied into both the oil chambers 13 and 14.
The hydraulic control valve 4 adjusts the hydraulic pressure supplied to both the oil chambers 13 and 14 according to the rotation of the input shaft 1, and causes a hydraulic pressure difference between the both oil chambers 13 and 14. Due to the hydraulic pressure difference between the oil chambers 13 and 14, the piston 12 moves in the axial direction within the cylinder tube 11 and generates a steering assist force that moves the rack shaft 3 in the axial direction.

FIG. 2A is a partial cross-sectional view around the piston of the power cylinder, and shows a state where no hydraulic pressure difference is generated between the hydraulic chambers 13 and 14.
As shown in the figure, the piston 12 is fixed to the rack shaft 3 and divides the inside of the cylinder tube 11 into a first oil chamber 13 and a second oil chamber 14.
A circumferential groove 15 recessed radially inward is formed on the outer peripheral surface 12a of the piston 12 over the entire circumference. A piston ring 16 for sealing between the inner wall 11 a of the cylinder tube 11 and the piston 12 is disposed in the circumferential groove 15.

  The piston ring 16 is an annular member formed of synthetic resin or the like, and has a substantially rectangular shape whose cross section is longer in the axial direction than in the radial direction. Each corner is rounded to a predetermined rounded surface. The outer peripheral surface 16a of the piston ring 16 is in contact with the inner wall 11a of the cylinder tube 11 so as to be slidable.

The piston 12 is an annular member fixed to the outer peripheral surface of the rack shaft 3, and a slight gap is provided between the outer peripheral surface 12 a and the inner wall 11 a of the cylinder tube 11.
The circumferential groove 15 formed in the outer peripheral surface 12a of the piston 12 is constituted by a bottom surface 17 and side wall surfaces 18 on both axial sides. Further, the depth dimension and the axial width dimension of the circumferential groove 15 are set such that a slight gap can be formed with respect to the inner circumferential surface 16b and both end surfaces 16c of the piston ring 16, respectively.

The side wall surface 18 of the circumferential groove 15 is formed so as to be orthogonal to the axial direction.
The bottom surface 17 of the circumferential groove 15 connects the pair of inclined surfaces 17a with a pair of inclined surfaces 17a inclined from the radially inner ends 18a of the side wall surfaces 18 on both axial sides toward the axial center of the circumferential groove 15. It is comprised by the cylindrical surface 17b.
The inclined surface 17a is formed in the shape of a conical surface inclined at a uniform angle with respect to the axial direction, and the piston ring 16 contacts the inner wall 11a of the cylinder tube 11 in the radial direction of the piston ring 16. The corner 16d is formed so as to be able to come into contact therewith.

  FIG. 2B shows the periphery of the piston in a state where a hydraulic pressure difference between the hydraulic chambers 13 and 14 is generated. FIG. 2B shows a case where the hydraulic pressure of the first oil chamber 13 is higher than that of the second oil chamber 14 and the piston 12 is about to move to the right side of the drawing.

  In the figure, the piston ring 16 is pressed in the axial direction toward the second oil chamber 14 in the circumferential groove 15 by the hydraulic pressure from the first oil chamber 13, and the outer periphery toward the side wall surface 18 on the second oil chamber 14 side. The surface 16a moves while being in sliding contact with the inner wall 11a.

  In the power cylinder 10 of the present embodiment, the corner 16d on the radially inner side of the piston ring 16 can come into contact with the bottom surface 17 of the circumferential groove 15 in a state where the piston ring 16 is in contact with the inner wall 11a of the cylinder tube 11. Since the inclined surface 17a is formed, when the piston ring 16 is pressed and moved in the axial direction toward the side wall surface 18 on the second oil chamber 14 side by hydraulic pressure, the piston ring 16 is not in contact with the side wall surface 18. The corner 16d on the radially inner side is in contact with the inclined surface 17a (the position of the broken line H in FIG. 2B).

When the oil pressure is further pressed toward the side wall surface 18 on the second oil chamber 14 side, the radially inner corner 16d of the piston ring 16 is pushed up radially outward along the inclined surface 17a, and the piston ring The force pushed up radially outward acts on the entire 16. As a result, the piston ring 16 is pressed against the wall surface 11a of the cylinder tube 11 as shown in FIG. 2B, and as a result, the sealing performance between the piston ring 16 and the cylinder tube 11 can be ensured. .
Thus, in the power cylinder 10 of this embodiment, the sealing performance between the piston ring 16 and the cylinder tube 11 can be ensured without using an O-ring as in the above-described conventional example, so the number of parts is reduced. The cost can be reduced by using a simpler configuration. Furthermore, since it is not necessary to form the circumferential groove 15 deep in the radial direction in order to secure the space for arranging the O-ring, the processing for forming the circumferential groove 15 is facilitated, and also in this respect, the cost is reduced. be able to.

  In the present embodiment, the angle of the inclined surface 17a with respect to the axial direction is preferably set in the range of 20 to 60 degrees. If the angle is smaller than 20 degrees, the piston ring 16 may not be able to ensure a sufficient amount of radial outward movement when attempting to move along the inclined surface 17a, and the angle is more than 60 degrees. If it is larger, it is difficult for the piston ring 16 to move smoothly along the inclined surface 17a, and there is a possibility that sufficient force to push the piston ring 16 outward in the radial direction may not be obtained.

  FIG. 3 is a partial cross-sectional view of the periphery of the piston of the power cylinder according to the second embodiment of the present invention, showing a state in which there is no hydraulic pressure difference between the two oil chambers. The difference between the present embodiment and the first embodiment described above is that the inclined surface 17a of the circumferential groove 15 has a corner 16d on the radially inner side of the piston ring 16 in a state where there is no difference in hydraulic pressure between the oil chambers 13 and 14. It is the point which is in contact with.

  As shown in the drawing, in the present embodiment, in the state where there is no hydraulic pressure difference between the two oil chambers 13, 14, the corner portions 16 d on both axial sides on the radially inner side are at both axial ends of the bottom surface 17 of the circumferential groove 15. It is comprised so that it may contact | abut on the provided inclined surface 17a.

  In this case, when a hydraulic pressure difference occurs between the oil chambers 13 and 14, the radially inner corner 16d of the piston ring 16 that is already in contact with the inclined surface 17a is pushed up radially outward by the inclined surface 17a. The space between the ring 16 and the cylinder tube 11 is sealed. That is, in the case of the above-described configuration, it is not necessary to move the piston ring 16 in the axial direction in order to bring the corner portion 16d into contact with the inclined surface 17a after the hydraulic pressure difference occurs. Can do.

The present invention is not limited to the above embodiments. In each of the above embodiments, the corner portion 16d on the radially inner side of the piston ring 16 is rounded to form an R surface so that the corner portion 16d can be smoothly pushed up by the inclined surface 17a of the circumferential groove 15. However, for example, as shown in FIG. 4A, an inclined surface corresponding to the inclined surface 17a of the circumferential groove 15 may be used.
In this case, the corner portion 16d of the piston ring 16 can be pushed up more smoothly by the inclined surface 17a of the circumferential groove 15, and the direction in which the corner portion 16d is pushed up can be reliably directed radially outward. For this reason, the piston ring 16 can be more reliably pressed against the wall surface 11 a of the cylinder tube 11.

  Further, in each of the above embodiments, the case where the inclined surface 17a of the circumferential groove 15 is formed in the shape of a conical surface inclined at a uniform angle with respect to the axial direction is exemplified. For example, FIG. Thus, it can also be formed in a curved surface having a concave cross section.

3 Rack shaft (piston rod)
DESCRIPTION OF SYMBOLS 10 Power cylinder 11 Cylinder tube 11a Inner wall 12 Piston 13 First oil chamber 14 Second oil chamber 15 Circumferential groove 16 Piston ring 16d Corner portion 17 Bottom surface 17a Inclined surface 18 Side wall surface 18a Radial inner end PS Hydraulic power steering device

Claims (4)

A cylinder tube;
A piston rod movable in the axial direction in the cylinder tube;
A piston that is fixed to the piston rod and is divided into two oil chambers in which oil pressure is supplied to the inside of the cylinder tube, and a piston that moves in the cylinder tube in the axial direction due to a hydraulic pressure difference between the two oil chambers;
In a power cylinder that is disposed in a circumferential groove formed on the outer peripheral side of the piston, and includes a piston ring that seals between the inner wall of the cylinder tube and the piston,
The bottom surface of the circumferential groove is inclined radially inward from the radially inner end of the sidewall surface of the circumferential groove toward the axial center of the circumferential groove, and the piston ring is in contact with the inner wall of the cylinder tube The power cylinder is characterized in that an inclined surface is formed on which a radially inner corner of the piston ring can abut.   2. The power cylinder according to claim 1, wherein the inclined surface is in contact with a radially inner corner of the piston ring in a state where there is no difference in hydraulic pressure between the two oil chambers.   The power cylinder according to claim 1 or 2, wherein a corner portion on the radially inner side of the piston ring is formed on an inclined surface corresponding to the inclination of the inclined surface. In a hydraulic power steering apparatus having a power cylinder that generates a steering assist force by supplying hydraulic pressure,
The hydraulic power steering device according to any one of claims 1 to 3, wherein the power cylinder is the power cylinder according to any one of claims 1 to 3.

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