JP2002266963A - Producing method of hydraulic auto tensioner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a sleeve with excellent forming accuracy and wear resistance at a low cost for an auto tensioner wherein a hydraulic fluid chamber in a cylinder is divided into a pressure chamber and a reserver chamber by inserting a piston into the sleeve in the cylinder. SOLUTION: A rod of free-cutting steel is cut and honing processed to scrape out the sleeve. The formed article is nitro-carburized to form a hard layer on a surface of the sleeve. The processing stress of the free-cutting steel is small, thereby deformation is not caused in the sleeve even by nitro-carburizing after processing and the sleeve is formed in the high accuracy. Further, the enhanced wear resistance is achieved by providing the hard layer on the surface.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a hydraulic auto-tensioner used for adjusting a tension of a timing belt of an automobile engine.

[0002]

2. Description of the Related Art Conventionally, as this type of hydraulic auto-tensioner, there is a hydraulic auto-tensioner in which a separate sleeve 2 into which a piston 3 is inserted is provided inside a cylinder 1 as shown in FIG.

In this structure, the hydraulic oil chamber 5 provided inside the cylinder 1 is moved by the piston 3 to the pressure chamber 6 and the reservoir chamber 7.
The piston 3 is provided with a passage 8 for communicating the pressure chamber 6 with the reservoir chamber 7 and a check valve 9 for closing the passage 8 when the hydraulic oil pressure on the pressure chamber 6 side increases from the reservoir chamber 7 side. Provided.

Further, a wear ring 1 sliding on the inner wall of the cylinder 1 is attached to a piston rod 10 connected to the piston 3.
The return spring 4 is brought into contact with the wear ring 11 to apply a spring force to the piston rod 10 so as to project outward.

In FIG. 1, reference numeral 12 denotes a retainer, 13 denotes a spring for connecting the piston 3 and the piston rod 10, 14 denotes a tension pulley, 15 denotes a support arm thereof, and 16 denotes a timing belt.

In the above structure, when the tension of the belt 16 is increased and the piston rod 10 and the piston 3 are pushed below the cylinder, the check valve 9 is closed, the oil pressure in the pressure chamber 6 is increased, and the force from the belt is increased. At the same time, the hydraulic oil in the pressure chamber 6 leaks little by little from the minute gap between the piston 3 and the sleeve 2 into the reservoir chamber 7, and the piston 3 is pushed in by that amount to adjust the excessive tension of the belt 16.

Conversely, when the tension of the belt 16 decreases and the piston rod 10 projects outward due to the spring force of the return spring 4, the pressure in the pressure chamber 6 decreases and the check valve 9 opens the passage 8. As a result, the hydraulic oil in the reservoir chamber 7 flows into the pressure chamber 6 and the piston rod 1
0 rapidly projects and keeps the tension of the slack belt 16 constant.

[0008]

In the hydraulic auto-tensioner having the above structure, the piston 3 slides inside the sleeve 2, so that the surface of the sleeve 2 tends to be worn. When the surface of the sleeve 2 is worn, the gap between the sleeve and the piston 3 is increased, and the leak down time of the hydraulic oil is reduced, and the damping force is reduced.

For this reason, it is desirable to increase the hardness of the sleeve 2 and increase the abrasion resistance against sliding of the piston. Is required.
However, such a grinding process has a problem of increasing the number of working steps and increasing the manufacturing cost.

As a method of avoiding the above-mentioned grinding, a method of subjecting the sleeve 2 to a tempering treatment with a hardness of about HRC 25 and machining the inner diameter surface by cutting is considered.
No improvement in abrasion resistance can be expected at about RC25.
May exceed the limit.

It is also effective to provide a hard layer on the sleeve surface by a hardening treatment such as soft nitriding after the completion of the forming of the sleeve 2 to increase the wear resistance of the sleeve.
In the hardening treatment such as soft nitriding, the sleeve 2 needs to be heated to a temperature of about 600 ° C., so that the residual stress generated inside the sleeve by the work forming is released, and the sleeve is deformed.

It is an object of the present invention to solve the above-mentioned problems and to provide a method of manufacturing a hydraulic auto-tensioner capable of forming a sleeve excellent in shape accuracy and wear resistance at low cost.

[0013]

Means for Solving the Problems In order to solve the above problems, a first means of the present invention is to cut a free-cutting steel to form a bottomed cylindrical sleeve having a small residual stress, and then form the sleeve. A hard layer is formed on the surface of a molded article by nitrocarburizing.

A second means of the present invention is that a heat treatment for removing residual stress is performed after press working to form a bottomed cylindrical sleeve, and then the formed product is subjected to cutting or honing. Soft nitriding was performed to provide a hard layer on the surface of the sleeve.

[0015]

According to the first means, since the free-cutting steel can be machined with a small force and the residual stress generated inside the material by the working is small, the deformation of the sleeve is suppressed even if soft nitriding is performed after the working. Can be

In the second means, the residual stress generated by the press working is removed by heat treatment, and a molded product having no residual stress is subjected to cutting or honing.
By performing soft nitriding, deformation of the sleeve can be suppressed.

In each of the first and second means, since the grinding process can be omitted from the processing of the sleeve, the sleeve can be formed efficiently at low cost.

[0018]

Embodiments of the present invention will be described below.
The basic structure and operation of the hydraulic auto-tensioner manufactured in the present invention are the same as those in FIG. 1 described above, except that the sleeve 2 is a molded product formed by cutting or pressing. It is in.

First, in the first embodiment, as shown in FIG. 2, a round bar made of free-cutting steel to which sulfur (S) or lead (Pb) or the like is added is subjected to cutting such as outer diameter cutting and honing. As a result, a bottomed cylindrical sleeve 2 as shown in FIG. 1 is cut out, and the molded product is subjected to soft nitriding to form a hard compound layer having a thickness of about several μm on the sleeve surface.

In this example, the free-cutting steel can be machined with a small force and the processing stress during the machining of the inner surface is small, so that the residual stress is small, and the deformation of the sleeve is small even if nitrocarburizing is performed after the forming. The sleeve can be formed with high accuracy.

In addition, the grinding process for the inner diameter of the sleeve can be omitted, and the cycle time of machining can be shortened by using free-cutting steel. Can be.

On the other hand, in the second embodiment, as shown in FIG. 3, first, a metal flat plate is deep drawn by a press machine to form a bottomed cylindrical sleeve shape.

In the molded product subjected to the plastic working by press working as described above, an excessive residual stress is generated inside the molded product. Next, the molded product is subjected to an annealing treatment to remove the internal residual stress. I have.

Next, after the above-mentioned molded product is subjected to machining and honing to a predetermined shape and dimensions, it is subjected to soft nitriding to form a hard layer on the surface of the sleeve.

Forming by such a press has a high material yield and a high processing speed, so that the production efficiency is high.
It can be adopted as a method suitable for mass production.

[0026]

As described above, according to the manufacturing method of the present invention, the grinding process can be omitted from the processing of the sleeve, the hardness of the sleeve surface is high due to the nitrocarburized hard layer, and the deformation of the sleeve after nitrocarburizing is eliminated. Since the precision can be increased, the abrasion resistance of the sleeve can be improved without lowering the damping characteristics, and there is an effect that the durability life of the auto tensioner can be improved and the manufacturing cost can be reduced.

[Brief description of the drawings]

FIG. 1 is a sectional view showing the structure of a hydraulic auto tensioner.

FIG. 2 is a block diagram showing a flow of manufacturing a sleeve in the first embodiment.

FIG. 3 is a block diagram showing a flow of manufacturing a sleeve in the second embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Cylinder 2 Sleeve 3 Piston 4 Return spring 5 Hydraulic oil chamber 6 Pressure chamber 7 Reservoir chamber 8 Passage 9 Check valve 10 Piston rod 16 Timing belt

Claims (2)

[Claims] 1. A cylinder having a bottomed cylindrical sleeve provided inside a cylinder, and a hydraulic oil chamber inside the cylinder is divided into a pressure chamber and a reservoir chamber by a piston slidably inserted into the sleeve. A passage communicating the pressure chamber and the reservoir chamber, and a check valve for closing the passage when the hydraulic oil pressure on the pressure chamber side is increased from the reservoir chamber side,
In the method for manufacturing a hydraulic auto-tensioner in which a spring force in a direction protruding outward from a cylinder is applied to the piston and a piston rod coupled to the piston, by cutting free-cutting steel, a bottomed bottom having a small residual stress is formed. A method for manufacturing a hydraulic auto-tensioner, comprising: forming a cylindrical sleeve, and then providing a hard layer by soft nitriding on the surface of the sleeve. 2. A cylinder having a bottomed cylinder inside a cylinder, and a hydraulic oil chamber inside the cylinder is divided into a pressure chamber and a reservoir chamber by a piston slidably inserted into the sleeve. A passage communicating the pressure chamber and the reservoir chamber, and a check valve for closing the passage when the hydraulic oil pressure on the pressure chamber side is increased from the reservoir chamber side,
In the method for manufacturing a hydraulic auto tensioner in which a spring force in a direction protruding outward from a cylinder is applied to the piston and a piston rod coupled to the piston, a heat treatment for removing residual stress is performed after press working, and A method for producing a hydraulic auto-tensioner, comprising: forming a sleeve in a shape, cutting or honing the formed product, and then performing soft nitriding to provide a hard layer on the surface of the sleeve.