JP2503975B2 - Fuel injection device for internal combustion engine - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a fuel injection device of a type in which a control hydraulic pressure is generated by a piezoelectric element to open the valve.

[Conventional technology]

As a fuel injection device for a diesel engine, there has been proposed a device including a fuel pump and a fuel injection valve driven by a piezoelectric element. There is a pressure accumulator in the fuel path from the fuel pump, and it is intended to suppress the pressure pulsation of the fuel from the pump. A constant pressure from the fuel pump is applied to the needle of the fuel injection valve, and the hydraulic pressure generated by the expansion and contraction of the piezoelectric element acts on the needle to open the valve and inject fuel. In this constant pressure type fuel injection device, the fuel injection amount is exactly proportional to the valve opening time of the fuel injection valve, that is, the time during which a voltage signal for opening the fuel injection valve is applied to the piezoelectric element. Therefore, the fuel injection amount can be determined by the valve opening time of the fuel injection valve. As a constant pressure fuel injection device, for example, Japanese Patent Application No. 60-140
See issue 417.

[Problems to be solved by the invention]

In the conventional constant pressure type fuel injection device, the pulsation of the fuel pressure is prevented by installing the pressure accumulating chamber, but its volume is limited. Therefore, by opening and closing the fuel injection valve,
The pressure wave generated in the fuel passage from the fuel injection pump to the needle of the fuel injection valve cannot be completely suppressed. If there is a pressure wave, it will not be a constant pressure injection substantially, it will be difficult to control the injection rate constant, the linearity between the injection time and the injection amount will be poor, and further there will be problems such as unintended irregular injection. there were.

[Means for solving problems]

According to the present invention, the fuel pump has a fuel pump for generating a constant fuel pressure, and the fuel injection valve is opened by the fuel hydraulic pressure from the piezoelectric element. The main body of the fuel injection valve is formed in the cylinder head. In a fuel injection device inserted into and attached to a fuel injection valve hole, a first pressure accumulation chamber is installed in a fuel supply pipe in the vicinity of a fuel pump, and a second pressure accumulation chamber is installed in the fuel supply pipe in the vicinity of a fuel injection valve. The fuel for an internal combustion engine, wherein the second pressure accumulating chamber is formed by an annular recess formed on at least one of an outer periphery of a main body of the fuel injection valve and an inner periphery of a fuel injection valve hole. An injector is provided.

〔Example〕

In FIG. 1, reference numeral 7 denotes a cylinder head of a diesel engine, which has a fuel injection valve hole 7A.
The fuel injection valve 9 is inserted in and attached to. The fuel injection valve 9 has a main body 10, a spacer 12, and a nozzle 14, which are vertically connected and fastened and fixed to each other by a nozzle holder 16. The needle 28 is installed in the nozzle holder 16 so as to be vertically movable, and the injection port 30 formed at the lower end of the nozzle holder 16 is opened and closed. A fuel storage chamber 31 is formed in the nozzle holder 14, and this fuel storage chamber 31 is communicated with the injection port 30 when the needle 28 is lifted, and fuel injection is performed. Nozzle holder 14, spacer
12, fuel passages 32, 34, 36 communicating with the main body 10 are formed, and are connected to a fuel supply pipe 40 via a union 38 screwed to the cylinder head 7. The fuel supply pipe 40 is connected to a fuel tank 44 via a fuel pump 42.

A pressurizing pin 44 and a control rod 46 are arranged in series with the needle 28 in the main body 10 of the fuel injection valve so as to contact each other at their ends. The compression spring 47 urges the pressure pin 44 downward in the drawing, that is, in the valve closing direction of the needle 28. A fuel chamber 48 is formed on the upper end surface of the control rod 46, and the fuel chamber 48 is a fuel passage.
It communicates with the fuel passage 36 via 50. Therefore, the control rod 46 is urged downward by the fuel pressure from the pump 42, that is, in the valve closing direction of the needle 28. Control rod 46
A pressurizing chamber 51 is formed at the lower end of the.

A hydraulic piston 54 is vertically slidably fitted on the upper end of the main body 10. A hydraulic chamber 56 is formed below the hydraulic piston 54,
The hydraulic chamber 56 communicates with the pressurizing chamber 51 via a hydraulic passage 58. The hydraulic pressure generated by the hydraulic piston 54 acts on the pressurizing chamber 51, and the control rod 46 is biased upward by this hydraulic pressure, which is the opening direction of the needle 28.

A driving device 60 drives the hydraulic piston 54, and includes a casing 62 and a piezoelectric element 64 arranged in the casing 62. The lower end of the piezoelectric element 64 is a plate
It is connected to the piston 54 by 66, a plate 68 is arranged at the upper end, and has a lead wire 70 for energizing the piezoelectric element 64. The piezoelectric element 64 is configured as a laminated structure of thin plate piezoelectric elements. The piezoelectric element 64 expands when energized,
As a result, the liquid in the pressurizing chamber 56 is pressurized, and a force for raising the control rod 46 is generated. Then, by releasing the energization, the piezoelectric element 64 contracts to the original state,
The pressure in the pressurizing chamber 56 is reduced. Such expansion and contraction of the piezoelectric element 64 is achieved at an extremely high speed, and high responsiveness of fuel injection operation can be obtained.

When the pressure chamber 56 is not under pressure, the needle
A downward force acting on the control rod 46 from the fuel chamber 48, a downward force acting on the pressurizing pin 44 from the compression spring 47, and an upward force acting on the needle 28 from the fuel reservoir chamber 31 are applied to 28. . Then, the area of the pressure receiving surface 46a of the control rod 46, the pressure of the compression spring 47, and the area of the pressure receiving surface 28a of the needle 28 are determined so that the total of the downward force is slightly larger than the upward force. Therefore, the valve is closed during normal operation when the piezoelectric element 64 is not energized. When the piezoelectric element 64 is energized, the piston
The pressure generated in the pump chamber 56 when 54 is lowered acts on the control rod 46 upward from the pressurizing chamber 51, and as a result,
Although the hydraulic pressure generated in the hydraulic chamber 56 is not so large, the upward force is predominant, the needle 28 is lifted, and the fuel is injected from the injection port 30.

According to this invention, in order to make the pressure of the fuel piping system from the fuel pump 42 to the injection port 30 constant, the first pressure accumulation chamber 80 close to the fuel pump 42 and the second pressure accumulation chamber 82 close to the injection port 30 are provided. Prepare The first pressure accumulation chamber 80 is installed in the fuel supply passage 40. On the other hand, the second pressure accumulating chamber 82 is formed in the hole 7A of the cylinder head 7 in which the fuel injection valve 9 is mounted. That is, the cylinder head hole 7A has an annular recess 84, and the second pressure accumulation chamber 82 is formed between the cylinder head hole 7A and the main body 10 of the fuel injection valve. Fuel passage of body 10
36 is communicated with this second pressure accumulating chamber 82 through a lateral hole 86,
The pressure accumulating chamber 82 is communicated with the fuel passage 40 via the union 38,
The fuel is supplied from the pump 42.

As in the present invention, the first pressure accumulating chamber 42 and the second pressure accumulating chamber 82
By installing the fuel pump 42, the pressure of the fuel pipe from the fuel pump 42 to the injection port 30 can be kept constant, and since the fuel pressure supplied from the fuel pump 42 is constant, the fuel injection amount of the fuel injection valve is It is determined only by the opening time, and the desired injection rate characteristics can be secured.

The pressure wave generated when the needle valve is opened disappears in the second pressure accumulating chamber, so that pressure pulsation does not occur. Conventionally, only the first accumulator 80 was installed, but in this case, the size of the accumulator 80 is limited and the distance to it is long, so it is difficult to completely suppress the pressure wave. . That is, the pressure wave generated when the valve is closed cannot be completely attenuated there when the volume of the pressure accumulating chamber is small, and is reflected toward the nozzle.
The time t until the pressure wave returns is t = (2l / a), where l is the distance to the accumulator and a is the speed of sound. Then, the time required from the start to the end of valve closing is t
when the _a (FIG. 2 (b)), the pulsation of the fuel pressure is generated under the condition of t _a <t, affects the injection of the next cycle, and the pressure pulsation caused by injection is amplified (B), the injection rate Has a wavy characteristic as shown in FIG. Since l This invention is reduced it is possible to t _a> t, it is possible to solve the state waving seen in the injection rate characteristic of FIG. 2 (c).

Further, since the pressure pulsation is suppressed, the linearity of the injection time and the injection amount can be improved in the present invention.
If there is pressure pulsation, the linearity of the characteristic of the injection amount with respect to the injection time deteriorates. That is, if the positive pressure wave acts on the needle, the closing time of the needle is delayed, and conversely, if the expansion wave acts, the closing time is shortened, and if the ideal linear characteristic is n in FIG. It comes off like m.
If deviation from the ideal characteristic is performed by an electrical correction circuit, the circuit becomes complicated and technically difficult.

In addition, irregular pressure injection can be prevented by suppressing the pressure wave. That is, if the second accumulator 82 is not provided, the pressure wave is generated at the tip of the needle as shown in FIG. 5A because the fuel flow is suddenly stopped when the needle is closed. At this time, since the needle is closed and the pressure accumulator side is open, the pressure pulsation cycle is t = (4l) / a, which is twice that in the previous case. Since the sine wave generated when the needle is closed returns after t seconds have elapsed, the force that tries to open the needle acts, and when this phenomenon occurs under high pressure, as shown by q in Fig. 4 (b), However, the irregular injection is an unintended injection. As is well known, irregular injection causes smoke, poor output controllability, and noise.

In the embodiment, the second pressure accumulating chamber 82 is installed in the cylinder head 7 around the fuel injection valve 9. This does not require any cost because it is only necessary to slightly change the mounting shape of the fuel injection valve. The maximum pulsation reduction effect can be obtained. However, it is not necessary to form the cylinder head integrally with the cylinder head, and it is not limited to the cylinder head, and it is not limited to the cylinder head and the second part may be provided on other parts such as the cylinder head cover and the cylinder block.
A pressure accumulating chamber 82 can be installed.

Further, the second pressure accumulating chamber does not have to be installed for each cylinder, but can be shared by all the cylinders or shared by some of the cylinders.

〔effect〕

According to the present invention, by installing the second pressure accumulating chamber close to the fuel injection valve in addition to the first pressure accumulating chamber immediately downstream of the pump, the pressure wave can be generated without increasing the volume of the pressure accumulating chamber so much. It is possible to effectively damp, it is possible to ideally perform constant pressure injection, the controllability of the injection rate is improved, and irregular injection can be prevented.

Further, in the present invention, the second pressure accumulating chamber 82 adjacent to the fuel injection valve 9 is formed by utilizing the wall surface of the main body 10 of the fuel injection valve or the cylinder head 7, so that the size is reduced, the number of parts is reduced, and the cost is reduced. There are also effects such as reduction and increase in design freedom.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a fuel injection device of the present invention. 2 to 4 are views for explaining the operation of the conventional fuel injection device. 7 …… Cylinder head 9 …… Fuel injection valve 28 …… Needle 40 …… Fuel supply pipe 42 …… Fuel pump 44 …… Pressure pin 46 …… Control rod 60 …… Drive device 64 …… Piezo piezoelectric element 80… … First accumulator 82… Second accumulator

Claims (1)

(57) [Claims] 1. A fuel pump having a fuel pump for generating a constant fuel pressure and a fuel injection valve which is opened by fuel oil pressure from a piezoelectric element. The main body of the fuel injection valve is formed in a cylinder head. In a fuel injection device inserted into and attached to a fuel injection valve hole, a first pressure accumulation chamber is installed in a fuel supply pipe adjacent to a fuel pump, and a second pressure accumulation chamber is installed in the fuel supply pipe adjacent to a fuel injection valve. However, the second pressure accumulating chamber is formed by an annular recess formed in at least one of the outer periphery of the body of the fuel injection valve and the inner periphery of the fuel injection valve hole. apparatus.