JP2002286137A - Manufacturing method for sliding member - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture sliding members having a proper clearance assuring good productivity without applying any additional machining process. SOLUTION: The manufacturing method is for sliding members having a minute clearance between two sliding members, whereby a first sliding member 1 and a second sliding member 2 are formed having a clearance C1 a little greater than the proper sliding clearance C3, and then the difference ΔC between C3 and C1 as actual is measured, and a hard film 5 having a thickness the same as or similar to ΔC is formed on the sliding parts 1a and 3a of the first sliding member 1 and/or the second sliding member 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method of manufacturing a sliding member, and more particularly to a method of manufacturing a fuel-based sliding member having a small clearance between the sliding members.

[0002]

2. Description of the Related Art A sliding member of a fuel system such as a needle piston and a piston bore of a fuel injection injector or a plunger and a plunger barrel of a fuel injection pump is slid due to a balance between its sliding resistance and the amount of fuel leakage. It is necessary to adjust the gap (clearance) between the members to an appropriate value. For example, dimethyl ether (hereinafter DME)
) As a fuel, the appropriate value of the clearance between the members is a very small value of several μm, so that a highly accurate clearance adjustment is required.

For this reason, conventionally, in order to adjust the clearance within an appropriate range, a sliding member of a fuel system, for example, a needle piston and a piston bore are manufactured mainly using the following two methods. Was. A large number of needle pistons are manufactured in advance using an ordinary grinding machine. Thereafter, while actually measuring the inner diameter of a certain piston bore, the outer diameter of a certain piston head is ground so that the clearance between the members falls within an appropriate range, and pairing of the needle piston and the piston bore is performed. A large number of needle pistons are manufactured in advance using an ordinary grinding machine. Then, by measuring the outer diameter of the piston head (or by sensual or empirical judgment), needle pistons that form an appropriate clearance with a certain piston bore are selected, and pairing of these needle pistons and the piston bore is performed. Do.

[0004]

However, in the case of
An internal length measuring device is provided because additional machining is performed on a certain needle piston so as to form an appropriate clearance with a certain piston bore, that is, a needle piston is formed to a certain piston bore. In addition, a precision cylindrical grinder capable of feeding back the measured value of the inner diameter to the grinding of the piston head is required. This grinding machine is very expensive and is not suitable for mass production. As a result, there is a problem that the production cost of the needle piston is increased.

In addition, in the case of (1), it is not necessary to perform additional machining on the needle piston, and the manufacturing cost of the needle piston itself is low. However, since the outer diameter of the piston head varies within a certain range, the needle piston has Requires a sorting step. Since this sorting process is a single item process, there is a problem that the processing lead time is long, that is, the productivity is not good.

An object of the present invention, which has been made in view of the above circumstances, is to provide a sliding member capable of manufacturing a sliding member having an appropriate clearance without performing additional machining and with good productivity. An object of the present invention is to provide a method for manufacturing a member.

[0007]

In order to achieve the above object, a method of manufacturing a sliding member according to the present invention is directed to a method of manufacturing a sliding member having a small clearance between the sliding members. After forming the first sliding member and the second sliding member slightly larger than each other, the clearance difference between the proper clearance and the actual clearance is measured, and the sliding of the first sliding member and / or the second sliding member is performed. A hard coating having the same thickness or substantially the same thickness as the clearance difference is formed on the portion.

According to the above-described method, the first and second sliding members having the final clearance between the sliding members substantially equal to the appropriate clearance can be obtained without performing additional machining. .

It is preferable that the film formation time is determined based on the clearance difference and the hard film formation speed to control the film thickness.

Preferably, the hard coating is formed by a plasma PVD method.

Further, a hard coating having a high surface hardness and a low coefficient of friction is formed on at least one of the first sliding member and the second sliding member, and the sliding member after the formation of the hard coating is formed. Preferably, the final clearance between them is less than 5 μm.

On the other hand, the fuel injector according to the present invention is composed of a piston bore and a needle piston that slides in the piston bore. The piston bore and the needle piston are formed slightly larger than the proper clearance, and at least one of the sliding portions of the piston bore or the needle piston has a hard material having the same thickness or substantially the same thickness as the clearance difference between the appropriate clearance and the actual clearance. A film was formed and the final clearance after forming the hard film was formed to less than 5 μm.

The fuel injection pump according to the present invention comprises a plunger barrel and a plunger that slides in the plunger barrel. In a fuel injection pump in which the clearance between the sliding members is minute, the clearance is appropriate. Form a plunger barrel and plunger slightly larger than the clearance, and form a hard coating with the same thickness or substantially the same thickness as the clearance difference between the appropriate clearance and the actual clearance on at least one of the sliding portions of the plunger barrel or the plunger. Then, the final clearance after the formation of the hard film was formed to be less than 5 μm.

According to the above arrangement, a piston bore and a needle having an appropriate clearance, a plunger barrel and a plunger can be obtained at low cost and with good productivity.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a sectional view of a main part of a piston bore and a needle piston of a fuel injector immediately after being manufactured by machining, and FIG. 1 shows a piston bore of a fuel injector formed by using the method of manufacturing a sliding member according to the present invention. FIG. 2 is a sectional view of a main part of the needle piston. Here, FIG. 1B is an enlarged view of a main part A of FIG. 1A.

In the method for manufacturing a sliding member according to the present invention, first, as shown in FIGS.
1 forms a piston bore (first sliding member) 1 and a needle piston (second sliding member) 2 slightly larger than an appropriate clearance C2 (<C1) by machining. Here, the needle piston 2 has a head portion 3 having an outer diameter d1.
The outer surface 3a of the head 3 slides on the inner surface 1a of the piston bore 1 having an inner diameter of D1. The clearance C1 is represented by (D1-d1) / 2.

Next, a clearance difference ΔC between the proper clearance C2 and the actual clearance C1 is measured. Thereafter, as shown in FIG. 2, the clearance difference Δ is provided on the sliding portion of the piston bore 1 and / or the needle piston 2 (only the outer surface 3a of the head portion 3 of the needle piston 2 in FIG. 2).
Hard coating 5 having the same thickness (or substantially the same thickness) as C and a thickness t
To form

As a result, the outer diameter of the head portion 13 becomes d2
(= D1 + 2t) needle piston 12 is obtained.
Here, the final clearance C3 between the piston bore 1 and the needle piston 12 and the appropriate clearance C2 have substantially the same value, for example, C3 = C2 ± about 0.2 μm.

The method for forming the hard coating 5 is PVD.
Method, plasma PVD method, etc.
The VD method is preferred.

The hard coating 5 can be adjusted to a film thickness t in the range of about 1 to 10 μm to enable clearance adjustment, has a high surface hardness, and has a low friction coefficient. For example, a CrN film, a TiN film and the like can be mentioned.

Next, the operation of the present invention will be described.

To eliminate the clearance difference ΔC between the actual clearance C1 between the piston bore 1 and the needle piston 2 and the appropriate clearance C2, the needle piston 2
By forming a hard coating 5 having the same thickness (or substantially the same thickness) as the clearance difference ΔC on the head portion 3 of
The final clearance C3 having substantially the same value as the target value of the appropriate clearance C2 is obtained.

Further, since the film formation time of the hard film 5 is determined based on the clearance difference ΔC and the film formation speed of the hard film 5, the film formation time of the hard film 5 is appropriately adjusted to obtain the hard film 5. 5 is about 1 to
It can be controlled freely within the range of 10 μm. In other words, without performing additional machining on the piston bore 1 or the needle piston 2 as in the conventional manufacturing method described above, the film formation time is appropriately adjusted, that is, while the film thickness t is accurately controlled. By forming the hard coating 5 on the head portion 3 of the needle piston 2, the final clearance C3 can be kept within an appropriate range.

Further, the thickness t of the hard coating 5 is set to about 1 to 10
Since it can be freely controlled in the range of μm, even if the clearance difference ΔC is somewhat large, it is possible to obtain a final clearance C3 having substantially the same value as the target value of the appropriate clearance C2. If the machining accuracy of the bore 1 and the needle piston 2 is within a certain range (for example, ± 6 μm or less), it can be used.
No high precision piston bore 1 and needle piston 2 are required.

An amorphous CrN film is used as the hard film 5 and plasma PVD is used as the film forming method.
When the method is used, the deposition rate of the amorphous CrN film is about 1 μm.
m / hr, which is very slow, and the film thickness of this amorphous CrN film is uniform over the entire surface of the film formation portion.
More accurate film thickness t (for example, on the order of 0.1 μm)
The formation of the hard coating 5 can be performed while controlling.

Further, the formation of the hard coating 5 is a batch-type processing, which can be simultaneously performed on a plurality of needle pistons 2. Therefore, the productivity is higher than the conventional manufacturing method described above. Is good.

Further, the hard coating 5 is formed using a normal PVD method.
When forming, the processing temperature is high (500 to 700
° C), the member to be processed may be subject to thermal distortion due to high temperature. However, when the hard coating 5 is formed by using the plasma PVD method, the processing temperature is as low as 200 to 250 ° C. In 2, the head portion 13) of the needle piston 12 is hardly subject to thermal distortion.

Further, conventionally, the piston bore 1
In addition, heat treatment (for example, nitriding treatment, carburizing treatment, etc.) was required to prevent abrasion of the sliding portion of the needle piston 2, but in the present invention, by forming the hard coating 5 for clearance control. At the same time, the wear resistance can be improved, so that the manufacturing process can be simplified and the shape deformation accompanying the heat treatment can be avoided.

The piston bore and the needle piston of the fuel injector obtained according to the present invention are particularly suitable for the piston bore and the needle piston of the common rail type injector using a high supply pressure and low viscosity DME as fuel. It is valid.

As described above, in the present invention, the piston bore and the needle piston of the fuel injector have been described, but the sliding member manufactured by the method of manufacturing a sliding member according to the present invention includes a piston bore. The present invention is not limited to the needle piston and the needle piston, but can be applied to the manufacture of other sliding members, for example, a plunger barrel and a plunger of a fuel injection pump. Needless to say.

In the present invention, the case where the hard coating 5 is formed only on the outer surface 3a of the head portion 3 of the needle piston 2 has been described, but only the inner surface 1a of the piston bore 1 or the outer surface 3a of the head portion 3 The hard coating 5 may be formed on both the bore inner surface 1a, and it is needless to say that the same operation and effect as those of the present invention can be obtained in those cases. Here, when the hard coating 5 is formed on both the head outer surface 3a and the bore inner surface 1a, the coating formation time is shorter than when the hard coating 5 is formed on only one of the head outer surface 3a or the bore inner surface 1a. It can be shortened to about half, and a new operation and effect that productivity is further improved can be obtained.

[0033]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Sixteen sets of piston bores and needle pistons are prepared in advance. After that, the inner diameter of each piston bore and the outer diameter of the head part of each needle piston are measured, the average value thereof is calculated, and the actual average clearance (7 μm) is obtained from each average value.

Next, the clearance difference (5 μm) from the appropriate clearance (2 μm) and the actual average clearance (7 μm)
μm) is calculated. Then, using a plasma PVD method, the non-crystalline C
An rN coating (surface hardness 2500 HV, coefficient of friction against steel 0.15) is simultaneously formed. At this time, the thickness of the amorphous CrN film is 5 ± 5 which is almost the same value as the clearance difference (5 μm).
The film formation time is set to 0.8 to 1.
The film thickness is controlled by adjusting within a range of 2 hours.

The formation of the amorphous CrN coating allows the proper clearance between the piston bore and the needle piston 2
For μm, a final clearance of 1.8-2.2 μm was obtained. Here, the variation in the thickness of the CrN film to be crystallized is as small as about 0.1 μm, and most of the variation in the obtained final clearance of 0.4 μm is due to the bore inner diameter of each piston bore and the needle piston. This is due to the processing accuracy of the outer diameter of the head.

As described above, the embodiments of the present invention are not limited to the above-described embodiments, and it is needless to say that various other embodiments are also conceivable.

[0037]

In summary, according to the present invention, the first sliding member and the second sliding member having the final clearance between the sliding members having substantially the same value as the proper clearance without additional machining.
An excellent effect that a sliding member can be obtained is exhibited.

[Brief description of the drawings]

FIG. 1 is a sectional view of a main part of a fuel injector immediately after being manufactured by machining.

FIG. 2 is a sectional view of a main part of a piston bore and a needle piston of a fuel injection injector formed by using the method for manufacturing a sliding member according to the present invention.

[Explanation of symbols]

Reference Signs List 1 piston bore (first sliding member) 1a bore inner surface (sliding portion of first sliding member) 2 needle piston (second sliding member) 3a head outer surface (sliding portion of second sliding member) 5 hard Coating 12 Needle piston (second sliding member after forming hard coating) C1 Clearance (actual clearance) C2 Final clearance C3 Proper clearance (proper sliding clearance) ΔC Clearance difference

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Claims (6)

[Claims] In a method for manufacturing a sliding member having a small clearance between the sliding members, after forming a first sliding member and a second sliding member whose clearance is slightly larger than an appropriate clearance, an appropriate clearance is provided. And the actual clearance is measured, and the first sliding member and / or
Alternatively, a method for manufacturing a sliding member, wherein a hard coating having the same thickness or substantially the same thickness as the clearance difference is formed on the sliding portion of the second sliding member. 2. The method for manufacturing a sliding member according to claim 1, wherein a film forming time is determined based on the clearance difference and the film forming speed of the hard film to control the film thickness. 3. The method according to claim 1, wherein the hard coating is formed by a plasma PVD method. 4. A sliding member having a high surface hardness and a low coefficient of friction formed on at least one sliding portion of the first sliding member or the second sliding member. The method for manufacturing a sliding member according to any one of claims 1 to 3, wherein a final clearance therebetween is formed to be less than 5 µm. 5. A fuel injection injector comprising a piston bore and a needle piston sliding in the piston bore, wherein the clearance between the sliding members is small, and the clearance between the piston bore and the clearance is slightly larger than an appropriate clearance. Forming a needle piston, forming a hard coating of the same thickness or substantially the same thickness as the clearance difference between the appropriate clearance and the actual clearance on at least one sliding portion of the piston bore or the needle piston,
A fuel injection injector characterized in that the final clearance after the formation of the hard coating is less than 5 μm. 6. A fuel injection pump comprising a plunger barrel and a plunger that slides in the plunger barrel, wherein the clearance between the sliding members is small, and the clearance is slightly larger than an appropriate clearance. And forming a hard coating of the same thickness or substantially the same thickness as the clearance difference between the proper clearance and the actual clearance on at least one of the sliding portions of the plunger barrel or the plunger, and the final clearance after the formation of the hard coating. A fuel injection pump characterized by having a thickness of less than 5 μm.