JPS63120850A - Fuel injection device for diesel engine - Google Patents

Abstract

PURPOSE:To enable ensurance of an optimum injection factor responding to a running condition, by providing a cam of cam lift characteristics having a low speed region at a front stage and a high speed region at a rear stage, and a feed valve with an adaptation mechanism, a suction return amount of which is inceased according to an increase in the number of revolutions of an engine and the like. CONSTITUTION:A fuel injection pump 1 axially reciprocates a pulnger 6 each time a cam 11 rides over a roller 10 resulting from rotation of a cam disc 5. The reciprocation of the plunger result in pressurization of fuel in a pump chamber 14 to feed the fuel to a fuel injection nozzle 40 through a distribution groove 15 and a delivery valve 17. In this case, the cam 11 is formed so that the cam lift speed characteristics having an approximately constant low speed region at a front stage end a high speed region at a rear stage can be provided in relation to a cam rotation angle by setting a profile. And the delivery valve 17 is provided with an adaptation mechanism, increaing a suction return amount with the increase in the number of revolutions of an engine, and the injection nozzle 4 is of structure in that the area of nozzle hole of a throttle region is of structure in that it is gradually increased with the increase in a nozzle lift.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a fuel injection device for a diesel engine,
In particular, the present invention relates to a fuel injection device that can achieve an optimal injection rate depending on operating conditions.

<Prior art> As a conventional fuel injection device for a diesel engine, the one described in "Automobile Engineering Complete Book Volume 5 Diesel Engine" published by Sankaido, March 20, 1980, pages 193 and 194 is well known. A known pumping mechanism consisting of a cylinder and a plunger fitted into the cylinder,
a cam provided between a drive shaft rotatably driven by the engine and the plunger of the pumping mechanism, which converts the rotation of the drive shaft into reciprocating motion and transmits it to the plunger; and a cam pressurized by the pumping mechanism. The fuel injection pump includes a fuel injection pump including a delivery valve provided in a pressure passage through which fuel is delivered, and an injection nozzle that injects the fuel delivered by the fuel injection pump.

In general, the injection rate at which fuel is injected from the fuel injection pump through the injection nozzle has a direct effect on combustion, and for example, in low speed regions such as idling, combustion noise (diesel knock)
It is known that lowering the injection rate in order to lower the engine speed, and increasing the injection rate in the medium-high speed range enables efficient combustion and increases output.

Referring to FIG. 15, the function of the fuel injection pump is to perform compression work W0 to increase the pressure (residual pressure) P of fuel filled in the injection pipe and injection nozzle to the injection nozzle opening pressure P0 by force feeding with the plunger. , and the injection work W that continues fuel injection until a predetermined injection amount is injected after the injection nozzle is opened.
It can be broadly divided into

θ in FIG. is the compression path (start of injection) angle, θ1 is the pressure path angle, and t is the pressure propagation delay from the delivery valve to the nozzle chamber (injection pipe).

Since the injection rate is controlled by the injection work W per unit time, its characteristics are almost determined by the cam lift speed after the injection nozzle is opened.

<Problems to be Solved by the Invention> However, in conventional diesel engine fuel injection systems, the aforementioned residual pressure generally tends to increase as the speed decreases, but it is not noticeable and the range of compression work at cam lift speed increases. was almost constant regardless of operating conditions, making it difficult to obtain the optimum injection rate by changing the cam lift speed after the injection nozzle opens depending on operating conditions such as engine speed or load. If you reduce the cam lift speed and lower the injection rate at low speeds and low loads,
There is a problem in that stable injection rate characteristics cannot be obtained due to variations in the area of the injection hole in the throttle area of the injection nozzle or changes over time such as carbon clogging.

<Means for Solving the Problems> In order to solve these conventional problems, the present invention provides a cam with a cam lift speed characteristic that has a low speed region in the front stage and a high speed region in the rear stage with respect to the cam rotation angle. In addition, the delivery valve is equipped with an Angleich mechanism that increases the amount of suction and return as the engine speed or fuel injection amount increases. The structure is such that the amount increases gradually as the amount increases.

In other words, by using the delivery valve attached to the side of the Angleich machine, the residual pressure is increased under operating conditions of low speed and low injection amount,
By combining this with a cam with the aforementioned cam lift speed characteristics, an optimal injection rate can be obtained depending on the operating conditions, and by combining this with an injection nozzle whose nozzle hole area changes in the throttle area, stable injection rate characteristics can be achieved. You get it.

<Example> The present invention will be explained below based on embodiments shown in the drawings.

In FIG. 1, 1 is a fuel injection pump, 2 is its pump housing, and 3 is a drive shaft rotationally driven by the engine.One is a drive shaft that drives a feed pump 4 to draw fuel into the pump housing 2. .

A plunger 6 having a cam disc 5 connected to the drive shaft 3 so as to be movable relative to the drive shaft 3 in the axial direction is disposed coaxially with the plunger 6, and as the plunger 6 reciprocates inside the cylinder 7, high-pressure pumping is performed. perform the operation.

A roller 1 is mounted on the flange surface of the cam disc 5 and is held in a roller holder 9 whose position is adjustable by a timer piston 8.
A plurality of cams 11 corresponding to the number of cylinders in contact with the cam disk 5 are formed at equal intervals, and the plunger 6 is reciprocated in the axial direction every time the cam 11 is overlaid by the roller 10 by rotation of the cam disk 5. Therefore, the plunger 6 rotates coaxially with the drive shaft 3 and reciprocates by the number of cams 11 per unit rotation.

Here, when the plunger 6 is in the suction stroke moving to the left in the figure, the fuel in the pump housing 2 is sucked into the pumping chamber 14 from the suction port 12 through the suction groove 13 of the plunger 6, and the plunger 6 moves to the left in the figure. When the pumping stroke moves to the right, the fuel in the pumping chamber 14 is compressed and delivered to the discharge port 16 from the distribution groove 15 of the plunger 6, passes through the delivery valve 17 and the injection pipe 30, and is injected into the cylinder from the injection nozzle 40. be done.

In addition, a control sleeve 18 is slidably fitted into the portion of the plunger 6 that exists outside the cylinder 7, and when the cut-off port 19 of the plunger 6 comes off the inner peripheral surface of the control sleeve 18 and is exposed, the pumping chamber 14
The fuel flows in waves from the cut-off port 19 and forms an injection path. Therefore, by adjusting the position of the control sleeve 18 using the governor mechanism 20, the injection path can be adjusted.
Therefore, the injection amount can be controlled.

The above configuration is basically the same as that of a conventional distribution type fuel injection pump.

In the configuration according to the present invention, by setting the profile of the cam 11, a cam lift speed characteristic as shown in FIG. 2 is obtained. That is, the cam lift speed characteristic has a substantially constant low speed region at the front stage and a high speed region at the rear stage with respect to the cam rotation angle.

Further, as shown in FIGS. 3 and 4, the delivery valve 17 is composed of a valve seat member 21 and a valve body 22 on which a suction/return piston 23 is formed. This is an Angleich mechanism that increases the amount of suction and return according to the increase, that is, a notch 24 is provided on the outer circumferential surface of the suction and return piston 23.

Furthermore, as for the injection nozzle 40, as shown in FIG. As shown in the figure, the structure is such that the nozzle lift gradually increases as the nozzle lift increases.

Next, the action will be explained.

When the plunger 6 starts pressure feeding and the pressure in the pumping chamber 14 becomes equal to or higher than the delivery valve opening pressure+residual pressure, the delivery valve 17 starts to lift and pressure propagation to the injection nozzle 40 begins.

As shown in FIGS. 3 and 4, the delivery valve 17 is provided with a suction and return piston 23, and after fuel injection is completed and before the valve body 22 is seated on the seat portion of the valve seat member 21, the suction and return piston 23 is disposed. 23 closes and seats while regulating the flow before and after the delivery valve 17 by the throttling effect, so the volume inside the injection pipe 30 and the injection nozzle 40 downstream of the delivery valve 17 is calculated as the cross-sectional area of the suction piston 23 x the suction and return stroke. (Re in FIGS. 3 and 5), the injection pipe 30 and the injection nozzle 40
to reduce the residual pressure within by a predetermined value.

This suction-back stroke is determined by the lift amount of the delivery valve 17, but the lift characteristics of conventional delivery valves are such that the opening area is narrowed until the suction-back stroke is reached, and under normal operating conditions, the lift exceeds the suction-back stroke. Therefore, the residual pressure is constant regardless of the operating conditions, and the cam angle until the injection nozzle opens, that is, the cam lift speed after the valve opens, is also approximately constant.

In the present invention, a notch 24 is provided in the suction and return piston 23 as shown in FIGS. 3 and 4, and the flow rate characteristics with respect to lift are increased as shown in FIG. Under conditions where the momentum applied to the delivery valve 17 is small, the conventionally required valve flow rate Q is secured with a lift amount less than the suction stroke R0, and the lift of the delivery valve 17 is reduced from R1 to R2 (R+ >Re>Rz)
By reducing the above-mentioned suction back amount, the residual pressure can be increased as shown in FIG. 6 under conditions of low speed or low injection amount.

Due to this effect, the above-mentioned injection work area with respect to the cam rotation angle can be changed depending on the operating conditions as shown in FIG. In addition, the optimum injection rate can be obtained by lowering the injection rate under operating conditions of low speed and low injection quantity, and increasing the injection rate under operating conditions of high speed and high injection quantity.

In addition, when injecting fuel at a low injection rate under conditions such as idling and low speed and low injection quantity, it is possible to inject fuel at a low injection rate under conditions such as idling, etc., as shown in Figures 10 and 11. When using an injection nozzle, if the area of the injection hole is large, even if the pressure increase applied to the needle is gradual, the injection amount per unit time will increase, and the injection rate will increase as shown in Figure 12 to achieve the desired level. If the nozzle area becomes smaller than the specified value, or due to changes over time due to carbon clogging, the effect will no longer be obtained.
As shown in FIG. 12, the injection rate drops too much, causing problems such as poor exhaust and unstable idling due to the occurrence of secondary injection.

In the present invention, as shown in FIGS. 7 and 8, the injection nozzle 4
By setting 0 as a throttle nozzle in which the nozzle area in the throttle area gradually increases as the nozzle lift increases, the nozzle area does not vary due to variations in the nozzle area or decrease due to carbon clogging, as shown in Figure 9. It has been made possible to obtain stable injection rate characteristics. In other words, even if the nozzle hole area changes as shown in Figure 8, approximately the same nozzle hole area A can be obtained by changing the nozzle lift, so for example, in the case of a large nozzle hole area, the unit Even if the injection amount per hour increases, the pressure applied to the needle decreases due to fuel injection, so the nozzle lift decreases (St-3υ), and approximately the same nozzle hole area (A) can be secured. Equivalent injection rates can be obtained.

In the opposite case, the pressure applied to the needle increases, increasing the nozzle lift (Sz = Ss) and increasing the nozzle area (A
), and the same injection rate can be obtained.

In addition, in order to obtain a structure in which the nozzle hole area in the throttle area of the injection nozzle is gradually increased according to an increase in the nozzle lift, a small-angle taper α may be provided on the needle 42 side as shown in FIG. Nozzle body 4 as shown in the figure
Small angle taper α1 on both the 1 side and the needle 42 side
．． Even if α2 is provided, the same effect as in FIG. 7 can be obtained.

(Effects of the Invention) As explained above, according to the present invention, the cam has a cam lift speed characteristic that has a low speed region in the front stage and a high speed region in the rear stage with respect to the cam rotation angle, and a cam that is suitable for increasing the engine speed or the fuel injection amount. The system uses a combination of a delivery valve attached to the side of the Angleich machine, which increases the suction amount as the nozzle lift increases, and an injection nozzle, whose nozzle hole area in the throttle area gradually increases as the nozzle lift increases, resulting in a synergistic effect. This makes it possible to achieve the optimum injection rate depending on the operating conditions with a simple configuration, and, especially when performing fuel injection at a low injection rate, stable characteristics can be obtained regardless of variations in the injection hole area of the injection nozzle. So the idle noise, exhaust performance.

The effect is that the output etc. can be greatly improved.

[Brief explanation of the drawing]

Fig. 1 is a sectional view of a fuel injection device showing an embodiment of the present invention, Fig. 2 is a characteristic diagram of cam lift speed, Fig. 3 is a sectional view of a delivery valve, and Fig. 4 is a perspective view of a valve body of the delivery valve. Figure 5 is a characteristic diagram of the static flow rate of the delivery valve, Figure 6 is a characteristic diagram of residual pressure, Figure 7 is a sectional view of the injection nozzle, Figure 8 is a characteristic diagram of the nozzle hole area, and Figure 9 is a characteristic diagram of the nozzle area. An injection rate characteristic diagram, FIG. 10 is a cross-sectional view of a conventional injection nozzle, FIG. 11 is a characteristic diagram of the nozzle hole area in the case of FIG. 10,
Fig. 12 is a characteristic diagram of the injection rate in the case of Fig. 10, Figs. 13 and 14 are cross-sectional views of injection nozzles showing other embodiments, and Fig. 15 shows the functions of a conventional fuel injection device. It is a diagram. 1...Fuel injection pump 3...Drive shaft 6...
・Plunger 7... Cylinder 11... Cam 14... Pumping chamber 17... Delivery valve
23... Suction/return piston 24... Notch 4
0... Injection nozzle Fig. 2 Fig. 5 Fig. 10 Fig. 11 Fig. 12 Fig. 13 n α Fig. 14 U α2

Claims (1)

[Claims] A pumping mechanism consisting of a cylinder and a plunger fitted into the cylinder is provided between a drive shaft rotationally driven by an engine and the plunger of the pumping mechanism to convert the rotation of the drive shaft into reciprocating motion. A fuel injection pump including a cam that transmits to the plunger and a delivery valve provided in a pressure passage through which fuel pressurized by the pumping mechanism is discharged, and an injection nozzle that injects the fuel discharged by the fuel injection pump. In the fuel injection device for a diesel engine, the cam is provided with a cam profile having a cam lift low speed region at the front stage and a cam lift high speed region at the rear stage with respect to the cam rotation angle, and the delivery valve is provided with a cam profile having a cam lift low speed region at the front stage and a cam lift high speed region at the rear stage with respect to the cam rotation angle. Equipped with an Angleich mechanism that increases the amount of suction back as the amount increases,
A fuel injection device for a diesel engine, characterized in that the injection nozzle has a structure in which the area of the injection hole in the throttle region gradually increases as the nozzle lift increases.