JPH0735237A - Piston and manufacture thereof - Google Patents

Abstract

PURPOSE:To reduce the number of parts or manufacturing manhours by composing a piston main body of a part diametrially out protruded from an end part of one piston rod, and a part welded with the protruded part and diametrially out protruded from an end part of the other piston rod. CONSTITUTION:A piston of a rack and pinion type hydraulic power steering device is provided with piston rods 4b, 4c extended from both sides of a piston main body 4a, and a rack teeth 4b with which a pinion is engaged are formed in an outer circumference of the piston rod 4b. In this case, parts 4a', 4a'' are formed diametrically out protruded from end parts of the piston rods 4b, 4c respectively, both protruded parts 4a', 4a'' are welded with each other to form the piston main body 4a, and a circumferential groove 4e is formed around a welded part for engagement of a seal ring. A pair of cylindrical hollow rods are friction-pressure welded with the protruded parts 4a', 4a'' at their end surfaces facing each other, burrs protruded diametrically out are press-moulded to be circular, and they are then machine-worked.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piston used in a hydraulic / pneumatic cylinder, a rack and pinion type hydraulic power steering device, and a method for manufacturing the piston.

[0002]

2. Description of the Related Art For example, as a piston used in a hydraulic / pneumatic cylinder, one having a piston body axially reciprocating relative to the cylinder and a piston rod extending from both sides of the piston body is known. It is commonly used. The rack and pinion hydraulic power steering device includes a piston body that reciprocates in the axial direction relative to the cylinder, and piston rods extending from both sides of the piston body. A piston with rack teeth is used, and a steering wheel is connected to at least one of both piston rods via a ball joint, a tie rod, etc., and a pinion that rotates by steering is meshed with the rack and is partitioned by the piston body. Pressure oil is supplied to the oil chamber according to the steering resistance and the steering direction, and the hydraulic pressure acts on the piston body to generate a steering assist force.

Conventionally, a piston body constituting the piston and both piston rods are separate members. For example, as shown in FIG.
1, a ring-shaped member 102 fitted to the outer periphery of the rod 101 constitutes a piston body, and the rod 101 and the ring-shaped member 102 are circlip 103.
1 connected to each other by the ring-shaped member 102
The ring-shaped member 102 was fixed to the bar 101 by caulking 02a and pressing it against the bar 101.

Further, in the piston used in the rack and pinion type hydraulic power steering device, the piston rod is hollow in order to reduce the weight or prevent the internal pressure of the expandable cover covering both ends of the piston rod from rising. Is being done. In this case, since the portion of the piston rod where the rack teeth are formed needs to have a large wall thickness in order to secure strength, the portion where the rack teeth are formed is made hollow by processing with a gun drill. However, since the processing cost increases if the processing is performed by the gun drill, as shown in FIG. 7, the piston rod is configured by frictionally welding the solid rod member 111 and the hollow rod member 112. It has been proposed that the rack teeth 113 are formed on the actual bar material 111 to reduce the weight and to secure the wall thickness necessary for forming the rack teeth 113 (see Japanese Patent Laid-Open No. 3-138042).

[0005]

In the conventional structure that requires a circlip or a caulking process to connect the piston body and the piston rod, the number of parts increases and the management process for the caulking work increases. The cost increases. Further, in the conventional structure in which the solid rod member 111 and the hollow rod member 112 are friction-welded to each other to form a piston rod and the rack teeth 113 are formed on the solid rod member 111,
When the piston body is connected to the hollow rod 112,
Based on the supporting reaction force that acts from the inner peripheral surface of the cylinder on the outer peripheral surface of the piston body and the hydraulic pressure that acts on the piston main body, stress due to bending moment acts on the friction pressure contact portion, and strength reliability is low. Become.

An object of the present invention is to provide a piston and a method for manufacturing the piston, which can solve the above-mentioned problems of the prior art.

[0007]

SUMMARY OF THE INVENTION The present invention relates to a piston having a piston body and piston rods extending from both sides of the piston body, the piston body comprising:
It consists of a portion that projects radially outward from the end of one piston rod, and a portion that is welded to this protruding portion and projects radially outward from the end of the other piston rod. Characterize. It is preferable that rack teeth are formed on the outer circumference of one of the piston rods and at least the other piston rod is hollow.

According to the method of the present invention, when a piston having a piston body and piston rods extending from both sides of the piston body is manufactured, a pair of rod members are friction-welded at their respective end faces, and both rod members are pressure-welded. It is characterized in that a burr that projects radially outward from the portion is formed into a piston body and both rods are formed into piston rods.

[0009]

The piston body constituting the piston of the present invention is
Since it is composed of a portion that projects radially outward from the end of one piston rod, and a portion that is welded to this protruding portion and projects radially outward from the end of the other piston rod, Compared with the case where the piston body is made of a member separate from the piston rod and is fixed to the piston rod by a circlip or a caulking process, the number of components can be reduced. Also, since the welding position of both piston rods coincides with the axial center position of the piston body, supporting reaction force acts on the outer peripheral surface of the piston body from the inner peripheral surface of the cylinder, and fluid pressure acts on the piston body. However, the moment-based stress does not act on the welded portion. Rack teeth are formed on the outer circumference of one of the piston rods, and at least the other piston rod is hollow, so that it is possible to reduce the weight of the piston and secure a wall thickness necessary for forming the rack teeth. Further, by forming the hollow piston rod from a pipe material, gun drilling can be eliminated. In this case, both piston rods may be hollow, and the wall thickness of one piston rod forming the rack teeth may be larger than the wall thickness of the other piston rod.

By friction-welding a pair of rod members at their respective end faces, forming a burr projecting radially outward from the pressure-contact portion of both rod members on the piston body, and making both rod members a piston rod, Since the piston body and the piston rod are integrated at the same time when the piston rod is welded, the number of manufacturing steps of the piston can be reduced. The burr may be formed in the piston body by press working, machining, or the like, and each rod may be machined or strain-relieved as necessary to form the piston body.

[0011]

Embodiments of the present invention will be described below with reference to the drawings.

The rack and pinion type hydraulic power steering apparatus 1 shown in FIGS. 3 and 4 has an input shaft 2 which is connected to a steering wheel of a vehicle and a pinion which is connected to the input shaft 2 through a hydraulic control valve 15 in a housing 5. 3, a cylinder 20 connected to the housing 5, and a piston 4 inserted into the housing 5 and the cylinder 20 and supported by a support yoke 29 in the housing 5 and a bush 22 in the cylinder 20. There is. The piston 4
Includes a piston body 4a that reciprocates in the axial direction (left and right direction in FIG. 3) with respect to the cylinder 20, and piston rods 4b and 4c that extend from both sides of the piston body 4a in one axial direction and the other axial direction. The pinion 3 meshes with rack teeth 4d formed on the outer circumference of one piston rod 4b. Ball joints 6 and 7 are connected to the respective ends of the piston rods 4b and 4c, and steering wheels (not shown) are connected to the ball joints 6 and 7 via tie rods 8 and 9. As a result, the pinion 3 is steered.
Is rotated and the piston 4 moves axially with respect to the cylinder 20, whereby the vehicle is steered.

A pair of seal members 1 for sealing between the outer circumference of the other piston rod 4c and the inner circumference of the cylinder 20.
0, 11 are provided, and the pair of oil chambers 13, 14 in which the space between the seal members 10, 11 is partitioned by the piston body 4a
It is said that. A seal ring 12 is fitted around the outer circumference of the piston body 4a. Pressure oil is supplied to one of the oil chambers 13 and 14 from the pump 70 via the hydraulic control valve 15 and the pipes 16 and 17 according to steering resistance and steering direction, and oil is supplied from the other of the oil chambers 13 and 14 to a tank. By returning to 71, steering assist force is generated.

The end portions of the piston rods 4b and 4c are covered with bellows-shaped expandable covers 25 and 26, respectively. One end of each expandable cover 25 and 26 is connected to the tie rods 8 and 9, and the other end thereof is the housing 5. Or cylinder 20
And prevents muddy water, foreign matter, dust, etc. from entering the housing 5 and the cylinder 20. Both piston rods 4b and 4c are hollow, and the piston 4 has a through hole 36 extending along the axial direction. The through hole 36 and a pair of radial holes 37 and 38 communicating with the through hole 36 are provided. The inside of one elastic cover 25 communicates with the inside of the other elastic cover 26. Thus, when the piston 4 moves in the axial direction, the air inside the expandable covers 25, 26 is moved from one side to the other to prevent the internal pressure of each expandable cover 25, 26 from rising and prevent the piston 4 from moving. Are prevented.

As shown in FIG. 1, its piston body 4a
Is a portion 4a 'which projects radially outward from the end of one piston rod 4b, and a portion which is welded to this projecting portion 4a' and projects radially outward from the end of the other piston rod 4c. 4a ″, and a peripheral groove 4e for fitting the seal ring 12 is formed on the outer periphery thereof by machining. Both ends of the through hole 36 are integrated with the ball joints 6 and 7. The internal thread portions 36a, 36b into which the external thread portions (not shown) are screwed in. The inner diameter of the through hole 36 is the internal thread portions 36a, 3b.
Except for 6b, one of the piston rods 4b formed with the rack teeth 4d has the other one.
The piston rods 4b and 4c have the same outer diameter. As a result, the one piston rod 4b has a larger wall thickness than the other piston rod 4c, and the wall thickness for forming the rack teeth 4d is secured.

The piston 4 is formed of a pair of cylindrical hollow rod members 4B and 4C shown in (1) of FIG. As the two rods 4B and 4C, steel pipes having the same outer diameter and smaller inner diameter in one rod 4B than in the other rod 4C are used. The two rods 4B, 4C are frictionally pressure-welded at their respective end faces, and by this frictional pressure welding, burrs B, C projecting radially outward from the pressure-contacting portions of both rods 4B, 4C as shown in (2) of FIG. 2 is press-formed into an annular shape as shown by the solid line in (3) of FIG. 2 and is then machined as shown by the broken line to form the piston body 4a. Then, the rack teeth 4d, the female screw portion 36a, and the radial hole 37 are formed on the one rod member 4B, and the female screw portion 36b and the radial hole 38 are formed on the other rod member 4C. By performing the removal, the piston rods 4b and 4c are molded. The rack teeth 4d of the piston rods 4b and 4c, the female screw portions 36a and 36b, and the radial holes 37 and 38.
May be formed before friction welding of both rods 4B, 4C.

According to the above structure, the piston body 4a is
A portion 4a 'which projects radially outward from the end of one piston rod 4b, and a portion 4a "which is welded to the projecting portion 4a' and projects radially outward from the end of the other piston rod 4c". Therefore, the number of components can be reduced as compared with the case where the piston body is formed of a member separate from the piston rod and is fixed to the piston rod by a circlip or a caulking process. By friction-welding the rod members 4B, 4C at the respective end faces, both piston rods 4b, 4c
At the same time as welding of the piston body 4a and piston rod 4
Since it is integrated with b and 4c, the number of manufacturing steps of the piston can be reduced. Since the welding positions of the two piston rods 4b and 4c coincide with the position of the piston body 4a, the cylinder 2 is attached to the outer peripheral surface of the piston body 4a.
Even if a supporting reaction force acts from the inner peripheral surface of 0 or a hydraulic pressure acts on the piston body 4a, stress based on the moment does not act on the welded portion. Both piston rods 4b, 4c are made of hollow steel pipe material, and rack teeth 4
Since the thickness of one piston rod 4b in which d is formed is made larger than the thickness of the other piston rod 4c, the weight of the piston 4 should be reduced as compared with the case where the piston rod is made of a solid material. Therefore, the wall thickness required for forming the rack teeth 4d can be secured, and the gun drilling process can be eliminated.

The present invention is not limited to the above embodiment. For example, as shown in FIG. 5, both piston rods 4b and 4c are hollow and one piston rod 4b is
The inner diameter may be smaller at the portion where the rack teeth 4d are formed, and may be equal to the inner diameter of the other piston rod at other portions. As a result, the wall thickness for forming the rack teeth 4d can be ensured, and the thinner the respective thicknesses of the friction welding parts, the faster the temperature rises. Since the shape of C is made uniform, friction welding of both rods 4B, 4C can be performed smoothly. Further, one of both piston rods may be solid and the other may be hollow, or both may be solid, or both may be made of rods having the same inner and outer diameters. Further, the present invention can be applied to pistons of hydraulic / pneumatic cylinders other than the rack and pinion type hydraulic power steering device.

[0019]

According to the present invention, the number of parts of the piston and the number of manufacturing steps can be reduced to reduce the cost, and the cost can be reduced by using the pipe material as the material of the piston, and the strength reliability can be improved. Can be increased.

[Brief description of drawings]

FIG. 1 is a sectional view of a piston according to an embodiment of the present invention.

FIG. 2 is a diagram showing a manufacturing process of a piston according to an embodiment of the present invention.

FIG. 3 is a front view of a rack and pinion type hydraulic power steering device according to an embodiment of the present invention.

FIG. 4 is a sectional view of a rack and pinion type hydraulic power steering system according to an embodiment of the present invention.

FIG. 5 is a sectional view of a piston of a modified example of the invention.

FIG. 6 is a partial sectional view of a conventional piston.

FIG. 7 is a partial sectional view of a conventional piston.

[Explanation of symbols]

 4 Piston 4a Piston body 4b, 4c Piston rod 4d Rack tooth 20 Cylinder

Claims (3)

[Claims] 1. A piston comprising a piston body and a piston rod extending from both sides of the piston body, wherein the piston body has a portion projecting radially outward from an end of one piston rod, A piston which is welded to the projecting portion and which projects radially outward from the end of the other piston rod. 2. The piston according to claim 1, wherein rack teeth are formed on the outer circumference of one piston rod, and at least the other piston rod is hollow. 3. When manufacturing a piston comprising a piston body and piston rods extending from both sides of the piston body, a pair of rod members are frictionally pressure-welded at their respective end faces, and a diameter is obtained from the pressure-contacting portions of both rod members. A method for manufacturing a piston, characterized in that a burr protruding outward in the direction is formed into a piston body and both rods are formed into a piston rod.