JPH10159687A - Fuel injection valve for in-cylinder injection type internal combustion engine - Google Patents

Abstract

(57) [Problem] To provide a fuel injection valve of an in-cylinder injection type internal combustion engine with improved ability to suppress deposit adhesion. SOLUTION: In a fuel injection valve of a direct injection internal combustion engine, a coating solution containing a metal alkoxide and a fluoroalkyl group-substituted alkoxide in which a part of an alkoxyl group is substituted with a fluoroalkyl group is applied to the surface of a fuel injection hole. Having a coating film formed by sintering and baking, wherein the film thickness of the coating film is 10 nm to 100 nm, and the concentration of the fluoroalkyl group-substituted alkoxide in the coating solution is adjusted to the total concentration in the coating solution. 5 to 20 mol% of the alkoxide amount.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a fuel injection valve for a direct injection internal combustion engine. More specifically, the present invention relates to a fuel injection valve of a direct injection internal combustion engine having a coating film having excellent liquid repellency and high durability on the surface of a fuel injection hole.

[0002]

2. Description of the Related Art In a fuel injection valve of an internal combustion engine, it is necessary to reliably shut off fuel or control an appropriate flow rate by opening and closing the valve. Oil, additives,
Foreign matter such as moisture is present and accumulates on the fuel injection valve, particularly on the injection holes during operation, and deposits called deposits impede the flow of fuel and the like. Therefore, even if the fuel injection valve is configured with high accuracy, the flow of fuel or the like is obstructed by the presence of such deposits, and the function of the fuel injection valve cannot be exhibited.

[0003] In order to solve such a problem, it has been conventionally proposed to suppress the adhesion of the deposit by performing a liquid repellent treatment. As one of them, for example, in JP-A-7-246365, a metal alkoxide and a fluoroalkyl group-substituted metal alkoxide in which a part of an alkoxyl group is substituted with a fluoroalkyl group are used for sol-forming.
A method of forming a liquid-repellent film by a gel method has been proposed.
That is, it is known that a substance containing a fluoroalkyl group has water and oil repellency. By providing the fluoroalkyl group on the surface of the coating film, liquid repellency is imparted and adhesion of the deposit is prevented. ing.

[0004]

By the way, when the fuel injection system is classified according to the position where the fuel is injected, it can be divided into in-cylinder injection directly injecting into the cylinder and intake pipe injection injecting into the intake pipe. In the case of in-cylinder injection, since the fuel injection valve is exposed in the combustion chamber, it is necessary to withstand high temperature and explosion pressure, and there is an environment where deposits are likely to adhere. Since the injection valve in the in-cylinder injection internal combustion engine is placed in such a severe environment, there is a problem that the conventional coating film as described above does not have a sufficient effect of suppressing the deposit adhesion. In addition, since this fuel injection valve injects fuel at a high injection pressure of 12 MPa, a coating film that can withstand such pressure is required, but the conventional coating film also has a problem in this respect.

[0005]

According to the present invention, there is provided a fuel injection valve for a direct injection internal combustion engine, wherein a metal alkoxide and a part of an alkoxyl group are formed on the surface of the fuel injection hole. Has a coating film formed by applying and baking a coating solution containing a fluoroalkyl group-substituted alkoxide substituted with a fluoroalkyl group, and the coating film has a thickness of 10 nm to 100 nm, The concentration of the fluoroalkyl group-substituted alkoxide in the coating solution is 5 to 20 mol% of the total alkoxide amount in the coating solution.

[0006] As described above, by limiting the concentration of the fluoroalkyl group-substituted alkoxide in the coating solution and the thickness of the obtained coating film to a predetermined range, a deposit having excellent heat resistance and peeling resistance can be obtained. A coating film that suppresses adhesion can be provided.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Formation of Coating Film on Injection Valve of the Present Invention
Is a metal alkoxide used in the following formula: M (OR)_n (1) wherein M is a metal, and R is
Alkyl and n is the oxidation number of the metal M. With metal M
Metal can be used as the target metal
A material corresponding to the oxide is used. Examples of metals include
Although not specified, Li, Na, Cu, Ca, S
r, Ba, Zn, B, Al, Ga, Y, Si, Ge, P
b, P, Sb, V, Ta, W, La, Nd, etc.
Can be. Alkyl includes methyl, ethyl, pro
Pill, butyl and the like can be used. Therefore, metal
As alkoxide, LiOCH_Three, NaOCH_Three, Cu (OCH_Three)_Two, Ca
(OCH_Three) _Two, Sr (OCH_Three)_Two, Ba (OCH_Three)_Two, Zn (OCH_Three)_Two, B (OC
H_Three)_Three, Al (i-OC_ThreeH₇)_Three, Ga (OC_TwoH_Five)_Three, Y (OC_FourH₉)_Three, Si (OC_Two
H_Five)_Four, Ge (OC_TwoH_Five)_Four, Pb (OC_FourH₉)_Three, PO (OCH_Three)_Three , Sb (OC
_TwoH_Five)_Three, VO (OC_TwoH_Five)_Three, Ta (OC_ThreeH₇)_Five, W (OC_TwoH_Five)₆, La (OC_ThreeH
₇)_Three, Nd ((OC_TwoH_Five)_Three Is exemplified.

[0008] The fluoroalkyl group-substituted alkoxide is
In the following formulas _{Rf m -M (OR) nm (} 2) ( the above formula, Rf is a fluoroalkyl group, M is the metal, n is the valence of the metal M, and m is a fluoroalkyl group The metal alkoxide is obtained by substituting a part of the alkoxyl group OR with a fluoroalkyl group.

[0009] The fluoroalkyl group Rf, the following formula _{CF 3 (CF 2) x -C} 2 H 4 - is represented by (3). Here, x is preferably 5 to 10 in order for CF ₃ groups to be arranged neatly on the substrate surface.

[0010] The presence of the fluoroalkyl group imparts liquid repellency to the resulting coating and prevents deposition of deposits. In this fluoroalkyl group-substituted alkoxide, the number of fluoroalkyl groups, that is, the above formula (2)
The larger the number m of Rf is, the higher the liquid repellency of the obtained coating film is. However, if the number of fluoroalkyl groups is too large,
Since the steric hindrance may prevent the fluoroalkyl group from being densely arranged on the surface of the coating film, the number m of the fluoroalkyl group is preferably 1.

The coating film in the injection valve of the present invention is formed by a so-called sol-gel method using these alkoxides. The sol-gel method is generally a method in which a metal organic or inorganic compound is made into a solution, and a hydrolysis / polycondensation reaction of the compound proceeds in the solution to solidify the sol into a gel and solidify the gel. This is a method in which a coating film is formed by applying the composition to a substrate and then heating it.

Specifically, a coating solution is prepared by adding water (for hydrolysis), alcohol (for preparing a homogeneous solution), acid or base (catalysis) to the metal alkoxide and the fluoroalkyl group-substituted alkoxide. As the alcohol, for example, methanol, ethanol, propanol, butanol and the like are used. Examples of the acid used as the catalyst include hydrochloric acid, sulfuric acid, acetic acid, and hydrofluoric acid. As the base, ammonia that can be removed by volatilization after the treatment is used. Further, a known additive such as acetylacetone may be added to this solution in the sol-gel method.

The effect is higher as the amount of the fluoroalkyl group-substituted alkoxide in the coating solution is larger. However, when the amount is larger, the properties are close to those of the resin. Accordingly, the amount is 5 to 20 mol% of the total amount of all alkoxides, that is, metal alkoxide and fluoroalkyl group-substituted alkoxide in the coating solution. If it is less than 5 mol%, sufficient liquid repellency cannot be obtained, and if it is more than 20 mol%, abrasion resistance and peel resistance are inferior.

The coating solution thus prepared is stirred at a predetermined temperature and aged as necessary to proceed the hydrolysis and polycondensation reaction of the alkoxide to form a gel.
Then, the fuel injection valve is immersed in the solution, and then the solution is removed from the injection hole to form a wet coating film of the coating solution on the surface of the injection hole. At this time, the thickness of the obtained film can be adjusted by adjusting the amount of the solvent in the coating solution, in particular, the amount of the alcohol. In the present invention, the thickness of the obtained coating film is set to 10 to 100 nm. If the film thickness is less than 10 nm, the heat resistance of the coating film is low, while if it is greater than 100 nm, the coating film cannot withstand the injection pressure of the fuel from the injection hole and is easily peeled off. More preferably, this thickness is 50 nm or less.

Finally, the coating film is fired. Usually, a drying step for removing water and a solvent is performed before this firing step. In this drying step, the fluoroalkyl groups concentrate on the surface of the coating film. As a result, many fluoroalkyl groups are unevenly distributed on the surface of the obtained coating film, which greatly contributes to liquid repellency. The firing step may be performed by a general method in the sol-gel method, and is performed at 200 to 500 ° C. in the air or in a non-oxidizing atmosphere. When calcination is performed in the air, 35%
It is preferable to carry out at 0 ° C. or lower. Thus, the fuel injection valve of the present invention having the coating film having excellent liquid repellency on the surface of the fuel injection hole is obtained.

[0016]

【Example】

Example 1 The following components: tetraethoxysilane (Si (OC ₂ H ₅ ) ₄ ) 3 g heptadecafluorodecyl trimethoxysilane (CF ₃ (CF ₂ ) ₇ C ₂ H ₄ Si (OCH ₃ ) ₃ ) 1 g ethanol 10 to 100 g 3 g of 0.05N HCl was put into a 50 ml beaker and mixed with stirring for 30 minutes. This solution was then transferred to a sealed container and left at 25 ° C. for 24 hours.
The amount of ethanol was adjusted so as to obtain a desired film thickness. The concentration of the fluoroalkyl group-substituted alkoxide in the solution is about 10 mol% of the total alkoxide.
Is equivalent to

A fuel injection valve for a direct injection engine is immersed in the coating solution thus obtained, and the solution is blown off from the injection hole.
A wet coating film was formed on the inner surface of the injection hole. Next, this coating film was baked at 250 ° C. for 1 hour to form coating films having different thicknesses.

After the fuel injection valve having the coating film formed thereon was tested for 200 hours with an actual machine, the contact angle of water in the injection hole was measured. Since the contact angle of water in the injection hole cannot be measured directly as in a normal method, it was measured indirectly. That is, when the fuel injection valve is brought into contact with water with the injection hole facing down,
In the case of a fuel injection valve that has not been treated, that is, does not have a lyophobic coating film, water enters the injection holes. On the other hand, in a fuel injection valve having a lyophobic coating, water hardly enters the injection hole. In other words, those having high liquid repellency have smaller weight changes after immersion in water than those having low liquid repellency. Using this principle, the contact angle was determined from the weight change before and after immersion in water. FIG. 1 shows the relationship between the formed film thickness and the contact angle of the film after the durability test.

It is said that the critical value of the contact angle is 70 ° for suppressing the adhesion of the deposit, and FIG.
For thinner and thicker than 100 nm, the contact angle is 70
° lower. As a result of analyzing the coating film, a decrease in the fluorine concentration in the coating film was observed at a film thickness of less than 10 nm. On the other hand, when the thickness exceeds 50 nm, peeling of the coating film was observed, and when the thickness was 100 nm or more, the amount of the peeling increased, and exposure of the base of SUS as the base material was observed.

Example 2 The following components: tetraethoxysilane (Si (OC ₂ H ₅ ) ₄ ) 3 g heptadecafluorodecyl trimethoxysilane (CF ₃ (CF ₂ ) ₇ C ₂ H ₄ Si (OCH ₃ ) ₃ ) 0.1 to 3 g ethanol 40 g 0.05 N HCl 3 g was put into a 50 ml beaker and mixed by stirring for 30 minutes. This solution was then transferred to a sealed container and left at 25 ° C. for 24 hours.
The amount of CF ₃ (CF ₂ ) ₇ C ₂ H ₄ Si (OCH ₃ ) ₃ was adjusted so as to obtain film thicknesses having different contents.

A fuel injection valve for a direct injection engine is immersed in the coating solution thus obtained, and the solution is blown off from the injection hole.
A wet coating film was formed on the inner surface of the injection hole. Next, this coating film was baked at 250 ° C. for 1 hour to form a coating film having a thickness of 30 nm with different addition amounts of the fluoroalkyl group-substituted alkoxide.

The coated film was subjected to a 200-hour test in an actual machine in the same manner as in Example 1, and the contact angle of water was measured. FIG. 2 shows the relationship between the contact angle and the addition amount of the fluoroalkyl group-substituted alkoxide. .

FIG. 2 shows that the contact angle was lower than 70 ° when the addition amount of the fluoroalkyl group-substituted alkoxide was less than 5% or more than 20%. As a result of analyzing the coating film, when the content was less than 5%, the fluorine concentration in the coating film was extremely low (F / Si atomic ratio: 0.3). On the other hand, when it exceeded 20%, peeling of the coating film was observed.

[0024]

According to the present invention, a liquid repellent film formed by a sol-gel method from a coating solution containing a metal alkoxide and a fluoroalkyl group-substituted alkoxide in which a part of the alkoxyl group is substituted with a fluoroalkyl group. 10nm ~
By setting the concentration of the fluoroalkyl group-substituted alkoxide in the coating solution to 5 to 20 mol% of the total alkoxide amount in the coating solution, heat resistance and peeling resistance are improved, and the in-cylinder injection type internal combustion The effect of suppressing deposit adhesion can be exhibited in the fuel injection valve of the engine.

[Brief description of the drawings]

FIG. 1 is a graph showing a relationship between a coating film thickness and a contact angle after a durability test.

FIG. 2 is a graph showing the relationship between the amount of fluoroalkyl group-substituted alkoxide in a coating solution for forming a coating film with respect to all alkoxides and the contact angle of the coating film after a durability test.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI // F02M 51/06 F02M 51/06 R

Claims (1)

[Claims] 1. A fuel injection valve for an in-cylinder injection internal combustion engine, wherein a coating containing a metal alkoxide and a fluoroalkyl group-substituted alkoxide in which a part of an alkoxyl group is substituted with a fluoroalkyl group is provided on a surface of the fuel injection hole. A coating film formed by applying and baking the solution, wherein the thickness of the coating film is 10 nm to 100 nm, and the concentration of the fluoroalkyl group-substituted alkoxide in the coating solution is A fuel injection valve for a direct injection internal combustion engine, characterized in that the amount is 5 to 20 mol% of the total alkoxide content in the fuel injection valve.