JPS6357870A - Fuel injection device - Google Patents

Abstract

PURPOSE:To surely decrease a rate of injection to a small value, by high holding the internal pressure in an injection pipe by a constant pressure valve while using a leakless nozzle holder in a fuel injection valve so that only a low speed region of a cam is used in the time of low speed and low load in no relation to cold and warm states. CONSTITUTION:Since fuel in a high pressure chamber 8 is pressurized by reciprocating a plunger 5 if a driving shaft 2 rotates, the fuel, passing through an injection pipe 14 to reach an injection valve 17, is injected from a nozzle 20 in accordance with a lift of a needle valve 24. Here a device, which holds the residual pressure in the injection pipe 14 to a high level by a constant pressure valve 16, increases the injection pressure of fuel in an injection valve 17 higher than the valve opening pressure in the point of time a cam 7 is in a small rotary angle. And in the time of low speed and low load, a rate of injection is small decreased by using only a low speed region of the cam 7. While in the time of high speed and high load, the rate of injection is large increased by using also a high speed region of the cam 7. While the injection valve 17, using a leakless nozzle holder 19, prevents the leakage of fuel, and the residual pressure in the injection pipe 14 is always held to a high level.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a fuel injection device, particularly to a fuel injection device used in a diesel engine such as an automobile.

(Prior Art) In this type of fuel injection device, a fuel injection pump and a fuel injection valve are connected via an injection pipe. As shown in Japanese Patent Laid-Open No. 60-50268, for example, a fuel injection pump has a pressurizing mechanism consisting of a cylinder and a plunger fitted into the cylinder, and the rotation of the drive shaft is caused by the reciprocation of the plunger. It is designed to be converted into motion via a cam.

(Problem to be solved by the invention) However, the injection rate of the fuel injection device is constant regardless of the engine speed, and at low speeds and low loads, the injection rate is reduced to cause gentle combustion and knock. Attempts to reduce noise have the problem of insufficient horsepower and increased emissions of NOx and other substances at high speeds and high loads.

For this reason, the applicant of this application previously filed Japanese Patent Application No. 61-9481.
Therefore, we proposed using a cam with a low-speed section at the front stage and a high-speed section at the rear stage (see Figure 2). This prior invention differs from the present invention in that it uses a delivery valve device having an Angleich mechanism, but the principle is the same in that the residual pressure in the injection pipe is maintained high. In other words, by keeping the residual pressure in the injection pipe high, injection is started from a point when the plunger stroke is small, and at low speeds and low loads, only the low speed section of the front stage of the cam is used, thereby achieving a low injection rate. This is what we are trying to achieve.

However, as a result of experiments by the inventor of the present application, when the temperature of the internal combustion engine is low (hereinafter referred to as cold time).

) and when the temperature of the internal combustion engine is high (hereinafter referred to as warm time).

), it became clear that there is a difference in the injection rate characteristics.

In other words, as shown in Fig. 3 of the 21211, when the cam is cold, only the low-speed portion of the cam is used to obtain an appropriate injection rate characteristic, but when the cam is warm, as shown by the dotted line in the figure, , the high-speed part of the cam is also used, increasing the injection rate.

The cause of this is that fuel injection valves are usually equipped with a leak passage, and when the fuel injection valve is warm, the clearance between the needle valve in the fuel injection valve and the insertion hole into which the needle valve is inserted increases, causing leakage. This is considered to be because the residual pressure in the injection pipe becomes low as the amount increases, and the rise in the internal pressure of the injection pipe is delayed relative to the stroke of the plunger, causing a shift in the actual injection start timing.

Therefore, this invention solves the above problems, eliminates leakage from the fuel injection valve, and increases the injection rate by using only the front stage portion where the cam speed is slow at low speeds and low loads regardless of whether it is cold or warm. It is an object of the present invention to provide a fuel injection device that can reliably lower the fuel injection rate.

(Means for Solving the Problems) Therefore, the gist of the present invention is to provide a fuel injection device in which a fuel injection pump and a fuel injection valve are connected via an injection pipe, in which the fuel injection pump is driven. A pressurizing mechanism consisting of a shaft, a cylinder, and a plunger fitted into the cylinder; and a pressurizing mechanism provided between the plunger of the pressurizing mechanism and the drive shaft to convert rotation of the drive shaft into reciprocating motion of the plunger. and a delivery valve device provided between the pressurizing mechanism and the fuel outlet, and the cam has a cam characteristic in which a low speed region is at the front stage and a high speed region at the rear stage with respect to the cam rotation angle. The delivery valve device has an equal pressure valve that maintains a high residual pressure in the injection pipe, and the fuel injection valve has a leakless nozzle holder that prevents leakage of fuel to the outside. . In other words, it is characterized in that it combines a cam with a low speed range, an equal pressure valve, and a fuel injection valve with a leakless nozzle holder.

(Function) Therefore, in a fuel injection pump, when the drive shaft is rotated, the plunger is reciprocated by the cam, and the fuel is sent out from the fuel outlet via the delivery valve device, and the fuel sent out from the fuel injection pump is sent through the injection pipe. This leads to the fuel injection valve, from which the fuel is injected, but since the internal pressure of the injection pipe is kept high by the equal pressure valve, at low speeds and low loads, only the low speed part of the cam is used to inject. Therefore, a low injection rate can be achieved. Moreover, since a leakless nozzle holder is used in the fuel injection valve, there is no leakage of fuel regardless of whether it is cold or warm, and therefore the above object can be achieved.

(Example) In FIG. 1, a fuel injection pump 1 has a drive shaft 2 that is connected to a crankshaft of an internal combustion engine (not shown) and rotates. Further, this fuel injection pump 1 has a pump body 3, a cylinder 4 is formed in this pump body 3, a plunger 5 is slidably inserted into this cylinder 4, and the cylinder 4 and plunger 5 form a pressurizing mechanism. 6 are configured. The plunger 5 is pressed by a cam 7 formed on the drive shaft 2 to reciprocate, and a high pressure chamber 8 surrounded by the cylinder 4 and the plunger 5 has a volume corresponding to the reciprocating movement of the plunger 4. The fuel in the high pressure chamber 8 is pressurized until the control groove 9 formed in the plunger 5 and the cutoff port 10 formed in the pump body 3 communicate with each other.

As shown in FIG. 2, the cam 7 has a cam characteristic that has a low speed region A at the front stage and a high speed region B at the rear stage with respect to the rotation angle.

A fuel outlet 11 is formed at the upper end of the pump body 3;
A delivery valve device 12 is provided between this fuel outlet 11 and the high pressure chamber 8 mentioned above. This delivery valve device 12 includes a discharge valve 13 that opens when the fuel pressure in the high pressure chamber 8 rises above a predetermined value, and an equal pressure valve 16 provided in a return passage 15 to maintain the residual pressure in the injection pipe 14 at a predetermined value. It consists of The injection pipe 14 connects between the fuel outlet 11 of the fuel injection pump 1 and the fuel inlet 18 of the fuel injection valve 17, which will be described below.

In the fuel injection valve 17, a nozzle holder 19 in which a fuel population 18 is formed and a nozzle body 21 in which a nozzle hole 20 is formed are fixed with an intermediate member 22 in between, and a needle valve insertion hole 23 is formed in the nozzle body 21. The needle valve 24 is inserted into this needle valve insertion hole 23.
is slidably inserted. A fuel reservoir chamber 25 is formed in the nozzle body 21 near the tip of the needle valve 24, and the fuel reservoir chamber 25 and the fuel inlet 18 at the front end 3A are connected via a fuel passage 26. A pressure stage 27 formed on the needle valve 24 faces this fuel reservoir chamber 25 , and a spring receiver 28 is in contact with the upper end of the needle valve 24 . A spring 29 is loaded, and when the fuel pressure in the fuel reservoir chamber 25 increases, this acts on the pressure stage 27 of the needle valve 24 and lifts the needle valve 24 against the spring 28, so that fuel is discharged from the nozzle hole 20. Inject.

The nozzle holder 19 of this fuel injection valve 17 is not formed with an overflow passage for returning fuel leaking from between the needle valve insertion hole 23 and the needle valve 24 to the tank side, so that the fuel injection valve 17 is leak-free. Such a Thales nozzle holder 19 is well known, and for example, the one shown in Japanese Utility Model Publication No. 14966/1988 can be used.

In the above configuration, when the drive shaft 2 rotates, the rotation is converted into a reciprocating motion of the plunger 5, and the fuel sucked into the high pressure chamber 8 from the fuel inlet (not shown) is pressurized, and the injection pipe 14
The fuel passes through the fuel injection valve 17, the needle valve 24 lifts, and the fuel is injected from the nozzle hole 20. Here, since the residual pressure in the injection pipe 14 is kept high by the equal pressure valve 16, the fuel injection valve 17 When the fuel injection pressure exceeds the valve opening pressure at low speed and low load, only the low speed region A of the cam 7 is used, as shown by the solid line in FIG. 2, and the injection rate can be reduced. At high speeds and high loads, the high speed region B of the cam 7 is also used to increase the injection rate.

Since the fuel injection valve 17 uses the nozzle holder 19 with large dripping, the clearance between the needle valve insertion hole 23 and the needle valve 24 becomes large during warm conditions, and fuel leaks out of the nozzle holder 19. The residual pressure in the injection pipe 14 can be kept high at all times, and even during warm conditions, only the low speed region B of the cam 7 shown by the solid line in Fig. 2 is used, as in the case of cold conditions. It is something that can be done.

(Effects of the Invention) As described above, according to the present invention, since the fuel injection pump is provided with a cam having a low speed region and an equal pressure valve at the front stage, the residual pressure in the injection pipe can be maintained, and at low speeds and low loads, It uses only the low speed region of the cam and can lower the injection rate.
In addition to reducing knocking noise at low speeds and low loads, the high-speed region of the cam is also used at high speeds and high loads, making it possible to increase the injection rate, increasing horsepower at high speeds and high loads, and reducing emissions. It can be reduced. In addition, since a Thales nozzle holder is used for the fuel injection valve, the residual pressure inside the injection pipe can be kept high regardless of whether it is cold or warm, and the injection rate can be reliably kept low at low speeds and low loads. This has the effect of making it possible to

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an embodiment of the present invention, FIG. 2 is a diagram showing cam characteristics, and FIG. 3 is a diagram showing characteristics of injection pressure and injection rate. DESCRIPTION OF SYMBOLS 1... Fuel injection pump, 2... Drive shaft, 4... Cylinder, 5... Plunger, 7... Cam, 11...
- Fuel outlet, 12... Delivery valve device, 14... Injection pipe, 16... Equal pressure valve, 17... Fuel injection valve, 19...
・Leakless nozzle holder. Figure 2 Rotation angle -

Claims (1)

[Claims] In a fuel injection device in which a fuel injection pump and a fuel injection valve are connected via an injection pipe, the fuel injection pump includes a drive shaft, a pressurizing mechanism consisting of a cylinder and a plunger fitted into the cylinder, and the pressurizing mechanism. a cam provided between the plunger of the pressure mechanism and the drive shaft to convert rotation of the drive shaft into reciprocating motion of the plunger; and a delivery valve device provided between the pressure mechanism and the fuel outlet. The cam is provided with a cam characteristic that has a low speed region in the front stage and a high speed region in the rear stage with respect to the rotation angle, and the delivery valve device has an equal pressure valve that maintains a high residual pressure in the injection pipe, The fuel injection device is characterized in that the fuel injection valve has a leakless nozzle holder that prevents leakage of fuel to the outside.