JPH0513983Y2 - - Google Patents

Description

[Detailed description of the invention] [Field of industrial application] This invention relates to a heat shielding device for a fuel injection valve, particularly a mounting structure for a heat shield attached to the tip of a fuel injection valve in a pre-chamber type diesel engine. be.

[Conventional technology]

In general, the function of a heat shield is to protect the surface of the fuel injector from the high-temperature combustion gas in the combustion chamber, to minimize heat received from the combustion gas, and to prevent the needle valve of the fuel injector from becoming stuck. The goal is to keep the fuel atomization condition optimal at all times by reducing the accumulation of fuel.

Various types of structures have been adopted for attaching this heat shield to the tip of the mounting hole of the fuel injection valve.
Publications No. 1 and Figure 1 are examples. As shown in these figures, a flange part 3 is formed at the upper end of the heat shield 1, and ring-shaped packings 4, 4 are interposed on the front and back surfaces of the flange part 3, and a step part provided in the mounting hole and a fuel It is sandwiched between a stepped portion formed at the boundary between the large diameter portion and the small diameter portion of the tip of the injection valve 5,
The distal end of the heat shield 1 is configured so as not to be pressed by the cylinder head 2, and to receive the distal end of the fuel injection valve 5 inserted therein.

[Problem that the invention attempts to solve]

Such a conventional heat shield 1 properly protects the surface of the fuel injection valve 5 from the high temperature combustion gas generated within the swirl chamber 6 formed in the cylinder head 2. However, since the gap h between the conventional heat shield 1 and the tip of the fuel injector 5 is extremely small, the heat received by the heat shield 1 is transferred to the fuel injector 5, especially in high-speed and high-load engines. easy to be

As a result, carbon accumulates on the needle valve 7 that protrudes from the front end surface of the fuel injection valve 5, which obstructs normal fuel injection and causes fuel spray cracks, resulting in deterioration of exhaust gas and worsening of noise. There was a problem that caused

Further, in the conventional heat shield 1, it is necessary to form a flange portion at the upper end and a groove portion for a heat insulating space on the outer peripheral surface of the side wall portion. and packings 4, 4 are provided on both sides of the flange portion, respectively,
Furthermore, it is necessary to form a step part on the inner surface of the mounting hole of the fuel injection valve 5 formed in the cylinder head 2 to receive the flange part 3, etc.
Another problem is that the work of the cylinder head 2 becomes complicated and the packing 4 is required, resulting in an increase in the number of parts. Note that 8 is a cylinder, 9 is a piston, and 10 is a combustion chamber.

This idea was developed by focusing on the problems of conventional devices, and its purpose is to minimize the transmission of the high temperature of combustion gas to the fuel injection valve, so that the needle valve By effectively preventing clogging of the nozzle holes due to carbon accumulation, and by forming the tip of the heat shield into a truncated cone shape, we improved the structure of the heat shield and the shape of the fuel injection valve mounting hole. The present invention provides a heat shielding device for a fuel injection valve in a pre-chamber type diesel engine that is simplified and has a reduced number of parts, such as by omitting packing.

[Means to solve the problem]

In order to achieve the above object, the heat shielding device for a fuel injection valve according to this invention has a receiving surface at the tip of the heat shield mounting hole opened in the swirl chamber of the cylinder head formed in a truncated conical shape, and the heat shield is attached to the receiving surface. It is formed by a truncated conical front end having an angle smaller than the truncated conical angle of the surface, a cylindrical side wall, and a ring-shaped rear end, and the rear end is connected to the step end face of the fuel injection valve and the fuel injection valve. The side wall portion contacts the circumferential surface of the tip of the valve, the side wall portion contacts the wall surface of the mounting hole, and the front end portion contacts the truncated conical receiving surface, and the side wall portion of the heat shield and the tip portion of the fuel injection valve contact each other. The gist is that a heat insulating air layer is formed between it and the surrounding surface.

[Effect]

The front end of the heat shield is formed into a truncated cone shape, and this part is received by the truncated cone-shaped receiving surface at the bottom of the fuel injection valve mounting hole in the cylinder head, and the rear end is formed into a truncated cone shape. Since it is in contact with the step at the boundary of the section, various packing is not necessary.
The mounting hole for the heat shield or the fuel injection valve is simplified, and a sufficient gap can be formed between the tip of the fuel injection valve and the heat shield.

〔Example〕

Embodiments of this invention will be described below based on the accompanying drawings.

Note that parts that are the same as those of the conventional example explained in FIG.

FIG. 2 shows a cross-sectional view of a pre-combustion chamber of a diesel engine, in which 8 is a cylinder, 9 is a piston, 2 is a cylinder head provided with a swirl chamber 6, and 10 is a combustion chamber. Glow plug 11
and a fuel injection valve 5 having a main nozzle hole 12 are attached via a heat shield 1.

The heat shield 1 is composed of a ring-shaped rear end 1a, a cylindrical side wall 1b, and a truncated cone-shaped front end 1c. A pocket is formed between the small diameter portion and the circumferential surface to form a gap. The rear end portion 1a comes into contact with the inner surface of a mounting hole 2c provided in the cylinder head 2, the end surface of the step portion 5a of the fuel injection valve 5, and the circumferential surface of the tip portion 5b. The side wall portion 1b is in contact with the inner surface of the mounting hole 2c, and the front end portion 1c is mounted at a predetermined distance h from the tip portion 5b of the fuel injection valve 5, forming an insulating air layer 13 from combustion gas in that space. are doing.

The heat shield 1 has its front end 1c bent at a predetermined angle toward the tip center X (main nozzle hole 12) of the fuel injector 5 to form a truncated conical surface. The curved portion 14 is brought into contact with the inclined surface of the heat shield receiving surface 2a (seating portion) formed in a truncated cone shape having a large inclination by an appropriate angle θ with respect to the tip portion 1a of the heat shield 1 of the cylinder head 2. The tip portion 5b of the fuel injection valve 5 is elastically supported in an upwardly pushed state.
Therefore, the front end 1c having a slightly sharper slope is pressed against the truncated conical receiving surface 2a, so that the front end 1c contacts the receiving surface 2a linearly or over a fairly narrow area. As a result, good sealing performance can be obtained.

Further, as the material of the heat shield 1, stainless steel material with poor heat transfer properties is used.

The heat shielding device for the fuel injection valve of this invention is configured as described above, so that the combustion gas heat in the combustion chamber 10 is transferred to the fuel injection valve 5 via the heat shield 1.
However, since the heat insulating air layer 13 is formed between the fuel injector 5 and the heat shield 1, the heat transfer is significantly reduced, especially at high speeds.
It is possible to eliminate exhaust gas deterioration and noise aggravation due to carbon adhesion to nozzle needle valves (not shown), which are problems in high-load engines.

In addition, the fuel injector 5 has a heat shield 1 at its tip.
The heat shield 1 is formed into a truncated cone shape having an angle smaller than the angle of the truncated cone shape of the receiving surface 2a of the heat shield 1, which forms an annular contact surface and is elastically supported with increased surface pressure. This improves sealing performance, making it unnecessary to use parts such as packing as in the past, significantly reducing the number of parts, and improving ease of assembly. It is.

[Effect of idea]

The receiving surface at the tip of the heat shield mounting hole that opens into the swirl chamber of the cylinder head is formed in the shape of a truncated cone.
The heat shield is formed of a truncated conical front end having an angle smaller than the truncated conical angle of the receiving surface, a cylindrical side wall, and a ring-shaped rear end; The end face of the heat shield and the circumferential surface of the tip of the fuel injector, the side wall part abuts the wall surface of the mounting hole, and the front end abuts the truncated conical receiving surface, and the side wall part of the heat shield and the fuel injector Since an insulating air layer is formed between the valve tip and the circumferential surface of the valve, the amount of combustion gas heat transferred from the heat shield to the fuel injection valve is extremely small, and as a result, the needle valve is prevented from clogging due to carbon deposits. At the same time, it effectively prevents the occurrence of fuel spray cracking, and also prevents exhaust gas deterioration and noise aggravation, thereby significantly improving the durability of the fuel injection valve.

Further, the peripheral surface of the tip of the fuel injection valve is covered by a heat shield, and this heat shield has a truncated conical front end having a smaller angle than the truncated conical shape of the receiving surface of the cylinder head. The front end is in contact with the truncated conical receiving surface of the heat shield, and the contact between both truncated conical surfaces increases the surface pressure and is elastically supported, improving sealing performance and improving the sealing performance compared to conventional heat shields. It is not necessary to use members such as packing as in the device, and the number of parts can be significantly reduced, and at the same time, the assembly work can be made easier. In addition, since the structure is simple, it can be provided at low cost, and maintenance is also easy.

Furthermore, since the ring-shaped rear end of the heat shield is brought into contact with the stepped end face and the circumferential surface of the tip of the fuel injector, the heat of the tip is transmitted to the cylinder head via the rear end. The effect of preventing clogging due to carbon deposition at the tip,
This has the effect of further improving the effect of preventing the occurrence of fuel spray cracking and the effect of preventing deterioration of exhaust gas and noise.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a conventional pre-chamber type combustion chamber, FIG. 2 is a cross-sectional view of a pre-chamber type combustion chamber in which this invention is implemented, and FIG. 3 is an explanatory view of the front end of a heat shield. 1... Heat shield, 1a... Rear end of heat shield, 1b... Side wall, 1c... Front end,
2...Cylinder head, 2a...Receiving surface of heat shield, 5...Fuel injection valve, 13...Insulating air layer, 14...Bend portion of heat shield, X...Center of tip of fuel injection valve.

Claims (1)

[Scope of utility model registration request] The receiving surface at the tip of the heat shield mounting hole that opens into the swirl chamber of the cylinder head is formed in the shape of a truncated cone.
The heat shield is formed of a truncated conical front end having an angle smaller than the truncated conical angle of the receiving surface, a cylindrical side wall, and a ring-shaped rear end; The end face of the heat shield and the circumferential surface of the tip of the fuel injector, the side wall part abuts the wall surface of the mounting hole, and the front end abuts the truncated conical receiving surface, and the side wall part of the heat shield and the fuel injector A heat shielding device for a fuel injection valve that forms a heat insulating air layer between the valve tip and the circumferential surface of the valve.