JP2003042039A - Fuel injector and fuel injection pump - Google Patents

Abstract

(57) [Problem] To provide a fuel injection injector and a fuel injection pump which are free from abrasion and galling in a sliding portion. SOLUTION: A fuel injector 21 according to the present invention.
Is composed of a piston bore 1 and a needle piston 12 that slides in the piston bore 1 and opens and closes an ejection port of the piston bore 1, and at least one of the piston bore 1 and the needle piston 2 slides. Moving parts 1a, 3
a, a microcrystalline chromium nitride film 5 having a high surface hardness and a low coefficient of friction was formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel injection injector and a fuel injection pump, and more particularly to a fuel injection injector and a fuel injection pump having a small sliding clearance.

[0002]

2. Description of the Related Art In a fuel system sliding member 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, when a highly viscous fuel such as light oil or gasoline is used, Since the fuel itself also serves as a lubricant, it was not necessary to consider the wear resistance of the sliding portion.

On the other hand, when a low-viscosity fuel, such as dimethyl ether (hereinafter referred to as DME) or alcohol fuel, is used, the lubrication action of the fuel itself cannot be expected, so that the sliding portion is worn. In order to prevent this, a hard coating having excellent wear resistance is formed on the sliding portion.

Examples of conventional hard coatings formed on the sliding portion include TiN coatings and DLC (Diamond Like Carbon) coatings.

[0005]

The TiN coating film has a high hardness of about 2000 HV or more, but has a large friction coefficient, so that it has a problem of high aggression with respect to the mating material.

On the other hand, the DLC film has a hardness of 3000 HV or more, which is higher than that of the TiN film, and a friction coefficient smaller than that of the TiN film. Therefore, the DLC film is very useful as a hard film formed on the sliding portion.

[0007] However, in the sliding portion using the fuel of low viscosity, if the sliding clearance is the same as that of the sliding portion using the fuel of high viscosity, the amount of fuel leakage increases (leakage increases). Therefore, the sliding clearance is smaller than that of the sliding part that uses fuel with high viscosity (for example,
Must be less than 10 μm). In addition, it is also a problem to prevent "galling (seizure)" in sliding parts that use low viscosity fuel. Even if a DLC film is used as a hard film, it is possible to prevent galling. Was difficult.

An object of the present invention, which has been devised in consideration of the above circumstances, is to provide a fuel injection injector and a fuel injection pump which are free from wear and galling at sliding parts.

[0009]

To achieve the above object, a fuel injection injector according to the present invention comprises a piston bore,
In a fuel injection injector that is composed of a needle piston that slides in the piston bore and opens and closes the injection port of the piston bore, at least one sliding part of the piston bore and the needle piston has high surface hardness and low surface hardness. A microcrystalline chromium nitride film having a friction coefficient is formed.

Further, the fuel injection pump according to the present invention is such that the plunger barrel slides in the plunger barrel,
A fuel injection pump composed of a plunger for pumping fuel, in which at least one sliding portion of a plunger barrel and a plunger is provided with a microcrystalline chromium nitride coating having a high surface hardness and a low friction coefficient. .

According to the above construction, even if the piston bore and the needle piston (or the plunger barrel and the plunger) have a small sliding clearance at the sliding portion, the sliding portion may be worn or galled. Disappear.

[0012]

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

FIG. 1 is a sectional view of the piston bore and needle piston of the fuel injection injector immediately after being manufactured by machining, and FIG. 1 is a sectional view of the piston bore and needle piston of the fuel injection injector according to the first embodiment. The figure is shown in FIG.

As shown in FIG. 1, the piston bore 1 immediately after being manufactured by machining has a bore surface 1a having an inner diameter D1, and the needle piston 2 has a head portion 3 having an outer diameter d1. It has a rod portion 4. That is, the clearance between the piston bore 1 and the needle piston 2 is C
1 (= (D1-d1) / 2).

As shown in FIG. 2, the fuel injection injector 21 according to the first embodiment is a sliding portion of the piston bore 1 and the needle piston 2 immediately after being manufactured by the machining shown in FIG. 1, that is, a bore. Of the surface 1a and the outer surface 3a of the head portion 3, at least one sliding portion (in FIG. 2, only the outer surface 3a of the head portion 3) has a high surface hardness, a low friction coefficient, and a film thickness t Microcrystalline chromium nitride (Cr _x
The coating film 5 of N _y ) is formed.

By forming the microcrystalline chromium nitride coating 5 having a film thickness t on the outer surface 3a of the head portion 3, the outer diameter of the needle piston 12 becomes d2 (= d1 + 2t). That is, the piston bore 1 after forming the microcrystalline chromium nitride coating 5
And the needle piston 12 sliding clearance is C2
It is expressed as (= (D1-d2) / 2).

Next, the operation of this embodiment will be described.

An X-ray diffraction chart of the microcrystalline chromium nitride coating film is shown in FIG. Here, in FIG. 3, the target is Cu,
Tube voltage 30kV, tube current 30mA, fixed angle 2 °
2 shows the X-ray diffraction pattern of the microcrystalline chromium nitride (CrxNy) coating when

In this embodiment, at least one sliding portion of the piston bore 1 and the needle piston 2 immediately after being manufactured by machining has a high surface hardness (for example, about 1500 to 2500 HV) and a low friction coefficient. A microcrystalline chromium nitride coating 5 (e.g., 0.12-0.18 with steel) is formed. This microcrystalline chromium nitride coating 5 has a friction coefficient substantially equal to or less than that of the above-mentioned DLC (conventional hard coating), but has a low hardness and an appropriate "familiarity". Slide clearance C2
Even if the value is very small (for example, less than 10 μm), there is no risk of abrasion or galling at the sliding portion between the piston bore 1 and the needle piston 12.

Further, by using the reactive sputtering method as the method for forming the microcrystalline chromium nitride coating 5, the film formation rate of the microcrystalline chromium nitride coating 5 is about 0.5 to 5 μm /
It can be controlled with high accuracy in the range of hr, and the film thickness t of the microcrystalline chromium nitride coating film 5 can be made uniform over the entire surface of the coating film forming portion. For this reason, the film thickness t of the microcrystalline chromium nitride coating film 5 can be freely and accurately controlled in the range of about 1 to 10 μm (for example, on the order of 0.1 μm) to form the coating film. As a result, the microcrystalline chromium nitride coating 5 can be formed on the outer surface 3a of the head portion 3 while controlling the film thickness t with high accuracy, so that even when the coaxiality of the allowable sliding clearance is severe (for example, less than 5 μm). The sliding clearance C2 can be kept within an appropriate range.

Further, as can be seen from the X-ray diffraction chart shown in FIG. 3, the crystal structure of the microcrystalline chromium nitride coating 5 has a broad diffraction peak and a dense fine crystal structure. The surface of the coating 5 becomes very smooth. For example, the surface roughness of the microcrystalline chromium nitride coating of the present embodiment obtained by the reactive sputtering method is less than half that of the conventional TiN coating obtained by the PVD method. As a result, the coefficient of friction of the microcrystalline chromium nitride coating 5 in the fuel injection injector 21 of the present embodiment is smaller than that of the conventional TiN coating.

When the chromium nitride film 5 is formed by PVD method such as vacuum arc discharge ion plating or HCD (hollow cathode discharge) ion plating, the treatment temperature is high (300 to 700 ° C.). Although the head piston 3 of the needle piston 12 may be thermally distorted due to high temperature, the microcrystalline chromium nitride coating 5 of the fuel injection injector 21 of the present embodiment is formed by the reactive sputtering method. Processing temperature is 20
The temperature is as low as 0 to 250 ° C., and there is almost no risk of thermal strain occurring in the head portion 3 of the needle piston 12.

Further, even when the allowable coaxiality of the sliding clearance is strict, an appropriate sliding clearance C2 can be obtained for the above-mentioned reason. Therefore, the piston bore 1 and the needle piston which are produced in a lot are manufactured. The processing accuracy of 2 is within a certain fixed range (for example, ± 6μ
m or less), it is applicable to the fuel injection injector 21 of the present embodiment, and it is not necessary to use the piston bore 1 and the needle piston 2 which are machined with high precision.

Further, the film formation of the microcrystalline chromium nitride film 5 is a batch type process, and since a plurality of needle pistons 2 can be processed simultaneously, the productivity is good.

The fuel injection injector 21 of the present embodiment
The piston bore 1 and the needle piston 12 are particularly effective as a piston bore and a needle piston of a common rail injection injector that uses a fuel having a high supply pressure and a low viscosity (such as DME or alcohol fuel).

Further, although the case where the microcrystalline chromium nitride coating 5 is formed only on the outer surface 3a of the head portion 3 of the needle piston 2 has been described in the present embodiment, only the bore surface 1a of the piston bore 1 is described. Alternatively, the microcrystalline chromium nitride coating 5 may be formed on both the outer surface 3a of the head portion and the bore surface 1a, and it is needless to say that the same effects as those of the present embodiment can be obtained in those cases as well. Here, when the microcrystalline chromium nitride coating 5 is formed on both the outer surface 3a of the head portion and the bore surface 1a, the case where the microcrystalline chromium nitride coating 5 is formed only on one of the outer surface 3a of the head portion or the bore surface 1a In comparison, the film formation time can be shortened to about half, and a new effect of improving productivity can be obtained.

Further, in the present embodiment, the piston bore 1 and the needle piston 12 of the fuel injection injector 21 have been described as the sliding members of the fuel system, but the sliding members of the fuel system include the piston bores. It is not limited to 1 and the needle piston 12, but may be other sliding members such as a plunger barrel and a plunger of a fuel injection pump. Needless to say, in those cases, the same effects as those of the present embodiment can be obtained.

[0028]

EXAMPLES <Test 1> Cr-Mo steel SCM415
(JIS standard) is used to form the piston bore and needle piston of the fuel injection injector to obtain three sets of test materials.

(Example 1) A needle piston was placed in a chamber, and a microcrystalline chromium nitride coating film with a film thickness of 4 µm was formed on the surface of its head portion by a reactive sputtering method. The test material is 1.

Various conditions of the reactive sputtering method are as follows: chamber volume is about 100 L, target cathode size of Cr material is 150 mm × 450 mm, target cathode output is 10 kW, base material heating temperature is 250 ° C., base material bias voltage. -100V, target shutter open,
Argon gas flow rate is 35 sccm, nitrogen gas flow rate is 40
sccm, the total pressure in the chamber during film formation is 0.4
Pa, film formation time is 60 minutes.

(Comparative Example 1) A needle piston was placed in a chamber, and a TiN coating film having a film thickness similar to that of Example 1 was formed on the surface of the head portion by the PVD method, and after polishing, it was combined with the piston bore. And used as the test material of Comparative Example 1.

(Comparative Example 2) A needle piston was placed in a chamber, and a DLC film having a film thickness similar to that of Example 1 was formed on the surface of the head portion by the PVD method. After polishing, the needle piston was combined with the piston bore. And used as the test material of Comparative Example 2.

The surface hardness, the coefficient of friction, and the surface roughness of the coatings of the test materials of Example 1 and Comparative Examples 1 and 2 were evaluated. Here, the coefficient of friction is a value for steel.

The surface hardness of the microcrystalline chromium nitride film in the test material of Example 1 was 2000 HV, the friction coefficient was 0.15, and the surface roughness (Ra) was 6 nm.

On the other hand, the surface hardness of the TiN film in the test material of Comparative Example 1 was 2300 HV, which was almost the same as that of Example 1. However, the coefficient of friction was 0.40 and the surface roughness (Ra) was 14 nm, which was more than twice that of Example 1.

The surface hardness of the DLC coating in the test material of Comparative Example 2 was 3000 to 5000 HV, which was higher than that of Example 1. The coefficient of friction was 0.10, which was lower than that in Example 1.

<Test 2> Cr-Mo steel SCM41
5 (JIS standard), a pin member that is a rotating member and a tightening member that tightens the peripheral surface of the pin member and slides on the peripheral surface of the rotating pin member are formed. After that, the pin member and the tightening member having a surface hardness of 60.0 (HRC) are sequentially subjected to carburizing and quenching treatment with a carburizing depth of 1 mm, tempering treatment, and cutting finish processing to obtain three sets of test materials.

Example 2 A pin member after cutting was placed in a chamber, and a microcrystalline chromium nitride coating film was formed on its surface by a reactive sputtering method. Use as material.

Various conditions of the reactive sputtering method are the same as those in the first embodiment.

Comparative Example 3 A pin member after cutting is placed in a chamber, a DLC film is formed on the surface of the pin member by a plasma CVD method, and the pin member is combined with a tightening member.
The test material of.

Various conditions of the plasma CVD method are as follows: chamber volume is about 100 L, size of target cathode made of Ti material is 150 mm × 450 mm, output of target cathode is 10 kW, base material heating temperature is 250 ° C., base material bias voltage is The target shutter is closed at −140 V, the plasma current is 8 A, the argon gas flow rate is 85 sccm, the acetylene gas flow rate is 120 sccm, the total pressure in the chamber during film formation is 2 Pa, and the film formation time is 60 minutes.

(Comparative Example 4) The pin member and the block material after cutting are used as they are (no surface treatment), and together with the tightening member, the test material of Comparative Example 4 is obtained.

The test material of each example was tested with a friction and wear tester (FAVILLE
FL-2) and friction and wear tests were conducted. The various conditions of the friction and wear test are as follows: the test environment is in a lubricating state (lubricant; paraffin-based 100N), and the number of rotations of the pin member is 33.
0 rpm, the sliding speed is 110 mm / sec, and the load condition is the increasing load mode (the tightening load for tightening the pin member is increased by 100 kgf in the range of 200 to 2500 kgf).

The results of the friction and wear test of the test materials of Example 2 and Comparative Examples 3 and 4 are shown in Table 1, and the test materials of each example in the friction and wear test were tested for the durable load (kgf) and seizure. The average friction coefficient over time is shown in FIG.

[0045]

[Table 1]

As shown in Table 1 and FIG. 4, the coefficient of friction of the test material of Example 2 was measured at the beginning of the test.
Although it is larger than the friction coefficient of the test materials of Comparative Examples 3 and 4 (0.174), the friction coefficient gradually decreases over the entire test time, and the minimum friction coefficient (0.048) is at the end of the test (115 seconds after the start of the test). ), The average friction coefficient over the entire test time was 0.068. Further, the durable load (2500 kgf) and the durable time (115 sec) of the test material of Example 2 were values when the tightening load of the friction and wear tester reached the upper limit, and seizure did not occur.

On the other hand, the friction coefficients of the test materials of Comparative Examples 3 and 4 gradually decreased over a fixed time from the start of the test, but the load was 1000 after 42,12 seconds from the start of the test. At 500 kgf, seizure occurred.
The final coefficient of friction when seizure occurs is 0.137 and 0.435, and the average coefficient of friction over the test time is 0.070 and 0.212.
The final coefficient of friction and the average coefficient of friction increase in the order of Comparative Examples 3 and 4.

From the results of Test 1 and Test 2, when the TiN coating film was formed, the hardness was high, but the friction coefficient was large, so the aggressiveness against the mating material was high, and although the friction and wear test was not conducted, it is probably seizure. It is presumed that (galling) is likely to occur. Further, it was confirmed that in the case where the hard coating was not formed, seizure (galling) easily occurred even if a small load was applied for a short time, although the coefficient of friction was small because of the low hardness. Furthermore, it was confirmed that when the DLC film was formed, it had high hardness and low friction, and had a larger durable load and a longer durability time than the TiN film, but it was not possible to prevent seizure from occurring. .

On the other hand, when the microcrystalline chromium nitride film is formed, the hardness is lower and the friction (initial friction) is larger than when the DLC film is formed, but the durable load and the durable time are DLC. It was confirmed that the film was more than twice as thick as the coating and that no seizure occurred.

It is needless to say that the embodiments of the present invention are not limited to the above-mentioned embodiments, and various other embodiments are possible.

[0051]

In summary, according to the present invention, even if the piston bore and the needle piston (or the plunger barrel and the plunger) have a small sliding clearance in the sliding portion, the sliding portion is not worn or galled. It has an excellent effect that it does not occur.

[Brief description of drawings]

FIG. 1 is a sectional view of essential parts of a piston bore and a needle piston of a fuel injection injector immediately after being manufactured by machining.

FIG. 2 is a cross-sectional view of essential parts of a piston bore and a needle piston of the fuel injection injector according to the first embodiment.

FIG. 3 is an X-ray diffraction chart of a microcrystalline chromium nitride film.

FIG. 4 is a diagram showing an endurance load (kgf) at the time of seizure and an average friction coefficient over the entire test time of the test material of each example in the friction and wear test.

[Explanation of symbols]

1 Piston bore 1a Bore surface (sliding part) 2 Needle piston (needle piston before film formation) 3 Head part 3a Head outer surface (sliding part) 5 Microcrystalline chromium nitride film 12 Needle piston (after film formation) Needle piston) 21 Fuel injection injector C2 Sliding clearance

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Kisaburo Shimamura             2-1-19 Kanda Surugadai, Chiyoda-ku, Tokyo             Rubergo Ochanomizu 1006 F-term (reference) 3G066 AA01 AA07 AB04 AC01 AD02                       AD07 BA49 CA08 CA09 CC03                       CC14 CD14 CD21 CD30

Claims (4)

[Claims] 1. A fuel injection injector comprising a piston bore and a needle piston that slides in the piston bore and opens and closes an ejection port of the piston bore, in a sliding portion of at least one of the piston bore and the needle piston. A fuel injection injector, characterized in that a microcrystalline chromium nitride coating film having a high surface hardness and a low friction coefficient is formed. 2. The fuel injection injector according to claim 1, wherein the sliding clearance between the piston bore and the needle piston is less than 5 μm. 3. A fuel injection pump comprising a plunger barrel and a plunger that slides in the plunger barrel and pumps fuel, wherein at least one sliding portion of the plunger barrel and the plunger has a high surface hardness.
A fuel injection pump characterized in that a microcrystalline chromium nitride film having a low coefficient of friction is formed. 4. The fuel injection pump according to claim 3, wherein the sliding clearance between the plunger barrel and the plunger is less than 5 μm.