JPH05546B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an improvement of a high-pressure fuel injection device suitable for a direct fuel injection type internal combustion engine typified by a diesel engine.

(Prior Art) A distribution type fuel injection pump as shown in FIG. 5 is known as a fuel supply device suitable for small high-speed diesel engines.

To explain this, a plunger 12 is attached to the pump shaft 10, which is driven to make one revolution for every two revolutions of the crankshaft in synchronization with the engine rotation, so as to be able to move relative to the pump shaft in the axial direction. 16, the plunger 12 reciprocates by the number of engine cylinders each time the pump shaft 10 rotates once. Fuel introduced into the internal pump chamber 18 via the feed pump 20 is sucked from the suction port 22 by the rotational reciprocating motion of the plunger 12, and is forced into the injection nozzle (not shown) from the distribution port 24 through the delivery valve 26. will be done.

The amount of fuel injected at this time is determined by the amount of fuel that is
0, e.g. spill port 2
When the opening 8 crosses the right end surface of the sleeve 30 in the figure as the plunger 12 moves to the right, the fuel that had been pumped from the plunger pressure chamber 13 to the distribution port 24 passes through the spill port 28 to the pump chamber 18. The pump is released and the pumping ends. In other words, if the sleeve 30 is displaced to the right relative to the plunger 12, the fuel injection end time will be delayed and the injection amount will increase, and if the sleeve 30 is similarly displaced to the left, the injection end time will be earlier and the injection amount will be decreased. .

The position of the sleeve 30 is controlled via a link mechanism 32 linked to the accelerator pedal and a centrifugal governor 34 so that the fuel injection amount is in accordance with the required load and rotational speed, and the injection start timing is controlled by the internal pressure of the pump chamber 18. A timer piston 36 (actually arranged in the rotational tangential direction of the pump shaft 10) operates based on the roller 1 relative to the face cam 14.
Automatically controlled by changing the phase of 6. (March 20, 1980, published by Sankaido Co., Ltd., “Automotive Engineering Complete Book Volume 5 Diesel Engine” pp.192-194
reference. ) (Problems to be Solved by the Invention) By the way, in such a plunger type fuel injection pump, high pressure is used to communicate between the injection nozzle and the pump in order to prevent the phenomenon of fuel dripping at the end of injection and to prepress the injection pipe. A delivery valve 26 is provided in the middle of the fuel passage. This delivery valve is basically a check valve, but a part of its valve body has a piston structure, and the pressure drop at the end of injection prevents the flow of fuel from the injection nozzle side during the valve stroke until it seats. By sucking back a portion of the fuel, the fuel pressure acting on the injection nozzle is quickly reduced, thereby preventing the dripping phenomenon. At the same time, in order to obtain stable injection characteristics, the fuel pressure (hereinafter referred to as "residual pressure") in the high-pressure fuel passage leading to the injection nozzle during non-injection is
It also has the function of keeping the temperature constant.

However, the residual pressure actually fluctuates under the influence of the rotational speed and injection amount, and becomes higher in the high-speed, high-load operating range. This tendency is particularly noticeable in injection pumps for direct injection engines, where the injection pressure is set high in order to obtain good fuel spray, and this cannot be completely prevented even if the Angleich mechanism is used. . On the other hand, if the residual pressure is too high, secondary injection is likely to occur due to the influence of fuel pressure waves after injection in a high-load operating range. Therefore, the residual pressure is set with emphasis on the high load range from the perspective of preventing secondary injection after considering pressure fluctuations, but as a result, the residual pressure is low in the low speed and low load operation range. This creates the problem of becoming too much. In other words, if the residual pressure is too low, the invalid stroke from when the plunger 12 starts its discharge stroke until it reaches the opening pressure of the injection nozzle becomes long, and when this is seen in relation to the lift curve of the cam 14, the result is Since injection is performed at a portion where the oil feeding speed is high, the injection rate becomes high and knocking or combustion noise increases.

The present invention has been made in view of these problems, and aims to solve these problems by variably controlling the residual pressure in the high-pressure fuel passage during non-injection.

(Means for Solving the Problems) In order to achieve the above object, in this invention, an equal-pressure delivery valve is interposed in the middle of a high-pressure fuel passage communicating between a fuel injection pump and an injection nozzle, and
A pressure control passage that communicates the high-pressure fuel passage between the equal-pressure delivery valve and the injection nozzle with a low-pressure part of the fuel system, a pressure control valve that variably controls the opening degree of the pressure control passage; A control means for controlling the drive according to the engine operating state is provided. The equal pressure delivery valve sets the residual pressure characteristic so that fuel injection starts in the low oil delivery speed range at the beginning of the pressure lift of the fuel injection pump, while the control means sets the residual pressure characteristic so that fuel injection starts in the low oil delivery speed range at the beginning of the pressure lift of the fuel injection pump. The pressure control valve is configured to open the pressure control valve to reduce the residual pressure in the high pressure fuel passage.

(Function) As is well known, the above-mentioned equal pressure delivery valve has the function of opening based on the fuel pressure applied from the injection nozzle side after injection is completed, and the residual pressure is determined by the set load of the spring. The fuel on the injection nozzle side is returned to the injection pump side until the pressure drops below a predetermined pressure. Therefore, it is less affected by operating conditions such as the amount of fuel injected and the number of revolutions.
A relatively stable residual pressure is obtained. In this invention, as described above, the residual pressure is controlled through the equal pressure delivery valve so that the actual injection starts in the low oil delivery speed range of the injection pump lift at the start of the injection stroke.
In other words, the pressure is set to be relatively higher than the conventional one. As a result, fuel is injected at a low injection rate during low-speed, low-load operation, so the proportion of premixed combustion caused by ignition delay is reduced, and combustion noise is reduced.

However, if this continues, the residual pressure may become excessive during high-speed, high-load operation, leading to problems such as secondary injection, but in such operating ranges, the pressure control valve and pressure control passage must be closed in synchronization with the non-injection period. This causes a portion of the fuel in the high-pressure fuel passage to escape into a low-pressure part of the fuel system, such as a pump chamber in a distributor fuel injection pump, thereby reducing the residual pressure. Therefore, inconveniences such as secondary injection are avoided, and subsequent injections are started in the high oil delivery speed range of the cam lift, ensuring a high injection rate compatible with high-speed or high-load operation. .

The control means for controlling the opening and closing of such a pressure control valve is well known and can be easily configured. For example, an electromagnetically actuated pressure control valve may be used, and this may be controlled by the output from the crank angle sensor. Alternatively, the injection timing (non-injection timing) is determined based on the signal from the piezoelectric lift sensor attached to the injection nozzle.
and a control circuit configured to determine the injection amount.

Next, an embodiment in which the present invention is applied to a distribution type fuel injection pump as shown in FIG. 5 will be described based on the drawings. Note that substantially the same parts as in FIG. 5 are designated by the same reference numerals.

(Example) In FIG. 1A or B, 40 is a plunger barrel fixed to one end of the pump body 4;
is a plurality of (four in this case) distribution ports formed radially so as to sequentially face the distribution port 24 of the plunger 12 that is slidably and rotatably fitted into the plunger barrel 40 as the plunger 12 rotates. 42 is an equal pressure delivery valve screwed onto the pump body 4 so as to be connected to the outlet end of each distribution passage 41; 43 is a pressure outlet connected to the outlet end of each equal pressure delivery valve 42 via a nut 44; It is a control valve.

The pressure control valve 43 is provided with a plurality of high-pressure passages 46 that axially penetrate the main body 45 corresponding to the distribution passage 41 and the equal-pressure delivery valve 42, and a base 47 at the inlet end of the high-pressure passage 46 is provided. As described above, it is connected to the equal pressure delivery valve 42 via the nut 44, and its outlet end is connected via the nut 49 to an injection pipe 48 leading to a fuel injection nozzle (not shown), thereby creating a series of high pressure fuel passages. 50
It consists of Furthermore, first pressure control passages 52 are branched from each high-pressure passage 46 and converge toward a cylindrical valve chamber 51 formed in the center of the main body 45 in the axial direction.

A spool 53 having an annular group 53A is slidably housed in the cylindrical valve chamber 51. This spool 53 is normally biased to close based on the tension of a spring 54 interposed on one end side (right side in the figure), and normally the valve chamber 51
The opening of each pressure control passage section 52 facing is closed. However, the spool 53 is connected via a rod 56 to an electromagnetic solenoid 55 attached to the right end surface of the main body 45, and when the solenoid 55 is energized, it moves to the right against the spring 54 due to its attractive force. , the pressure control passage portions 52 are opened and communicated with each other (as shown). Further, a second pressure control passage section 57 is formed in the main body 45 at this time, which communicates with the plurality of first pressure control passage sections 52 at the same time via the groove 53A (see Fig. 1B).
reference). This second pressure control passage section 57 is connected to the main body 45
A series of pressures are It constitutes a control passage 61.

The pressure control valve 43 is driven to open and close via a control means (not shown), and this control means determines the presence or absence of injection and the amount of injection based on, for example, a signal from a well-known lift sensor attached to the injection nozzle. It is configured to detect this and supply a drive current to the electromagnetic solenoid 55 in synchronization with the non-injection period of each cylinder of the engine during high load operation where the injection amount is greater than or equal to a predetermined reference value (see FIG. 3C). Through such a control means, when the solenoid 55 is turned on and the pressure control valve 43 is opened during the non-injection period, the first and second pressure control passages 52 and 57 are connected to each other as described above. In this state, the pressure control passage 61 and the high-pressure fuel passage section 46 communicate with each other, so that the pressure within the high-pressure fuel passage 50 after injection is completed is released to the pump chamber 18 on the low-pressure side. Therefore, the residual pressure decreases during high-load operation with a large amount of fuel injection. However, in a relatively low-load operating state where the fuel injection amount is less than a predetermined reference value, no drive current is supplied to the solenoid 55, and the pressure control valve 43 remains closed regardless of the presence or absence of injection. The pressure will be maintained at a relatively high pressure set via an equal pressure delivery valve 42, which will be described next.

Next, an example of the above-mentioned equal pressure delivery valve 42 will be explained based on FIG. 2. This is because a check valve 74 biased to close via a coil spring 73 is seated on a seat portion 72 of an annular sleeve 71 that is fitted into a cylindrical main body 70 from the injection pump side, which is the left side in the figure. There is. The check valve 74 lifts against the coil spring 73 when injection pressure from the injection pump acts through the inlet passage 75, allowing fuel to pass to the outlet passage 76 and the high-pressure fuel passage 50 toward the injection nozzle. However, when the injection is finished and the pressure on the inlet side decreases, it seats on the seat portion 72 to prevent backflow of fuel. However, unlike a simple delivery valve, the check valve 74 has a fuel passage section 77 that passes through its center and communicates upstream and downstream, and a seat section 78 at the open end on the pump side is provided with a coil. The ball-shaped equal pressure valve 8 is activated by the tension of the spring 79.
0 is seated. When the pressure in the high-pressure fuel passage 50 after injection is higher than the set value, the equal-pressure valve 80 receives this high pressure and lifts while compressing the coil spring 79 to open the fuel passage part 77 and supply high-pressure fuel. A portion is allowed to escape to the inlet passage 75 and the injection pump side.

Due to this operation, the internal pressure of the high-pressure fuel passage 50 after the end of injection is kept almost constant by the equal-pressure delivery valve 42 without being affected by the operating conditions, so that during low-speed, low-load operation with little injection charge, Highly accurate injection quantity control characteristics can be expected.

Next, the overall operation of the fuel injection device based on the above configuration will be explained.

First, regarding the fuel injection pump, this is the same as that shown in FIG. 5, that is, high-pressure fuel is sequentially discharged from the pressure chamber 13 to the four distribution passages 41 as the plunger 12 reciprocates and rotates. As a result, when the pressure on the downstream side of the distribution passage 41 becomes high, the equal-pressure delivery valve 42 and the injection nozzle connected to the end of the high-pressure fuel passage 50 each open due to this high pressure, and a predetermined amount of fuel flows into the engine cylinder. and is supplied by injection. Then, when the discharge pressure of the injection pump decreases at the end of injection, the injection nozzle and the equal pressure delivery valve 42 close in response to this pressure decrease. At this time, since the pressure control valve 43 is closed during low-load operation, the internal pressure, that is, the residual pressure, in the high-pressure fuel passage 50 is maintained at a relatively high predetermined value by the action of the above-mentioned equal pressure delivery valve 42. It will be done. On the other hand, during high-load operation, the pressure control valve 43 is opened after injection ends, so the residual pressure becomes relatively low or zero (see FIGS. 3A and 3B).

The residual pressure setting of the above-mentioned equal pressure delivery valve 42 is determined at the initial stage of the lift when the lift speed of the cam (face cam 14...see Fig. 5) that drives the plunger 12 or the oil supply speed is relatively slow, as described above. It is set higher than the conventional method so that the injection starts, and specifically, it is set so that the injection starts at point A of the cam angle θ ₁ as shown in Fig. 4 (pre-lift _H1 ). Therefore, during low load operation when the residual pressure on the high pressure side set by this equal pressure delivery valve 42 is maintained as it is, A
Injection starts at the point. On the other hand, if the residual pressure was set at a low level with an emphasis on high loads as in the past, an extra cam lift would be required to reach the opening pressure of the injection nozzle.
For example, injection does not begin until the cam angle θ ₂ (θ ₂ >θ ₁ ) reaches point B (prelift H ₂ ).

Now, the injection from prelift H ₁ is at cam angle θ ₃
Assuming that the injection from the prelift H ₂ ends at point D at a cam angle θ ₄ , and the pumping strokes up to that point are the same at H ₀ (that is, the same injection amount), the cam Since the profile draws a buffer curve in the initial region of the lift, θ ₃ −θ ₁ >θ ₄ −θ ₂ is satisfied. In other words, since the average oil feeding speed is low at the beginning of the cam lift, the injection period for the same injection amount becomes longer, that is, the injection rate decreases.

Knotting and excessive combustion noise during low-load operation in diesel engines are caused by a large amount of fuel particles that have become premixed due to ignition delay and start burning at the same time. By reducing the amount of fuel injected during the period responsible for ignition delay, engine noise is also significantly reduced.

On the other hand, during high-load operation, the residual pressure is lower than during low-load operation, so as is clear from the above, fuel injection is performed at a high oil feeding speed, and the injection rate increases. Therefore, a relatively large amount of fuel can be supplied in a short period of time to achieve the desired engine output performance. Further, secondary injection is prevented due to the decrease in residual pressure. Needless to say, during high-load operation, the combustion chamber temperature rises and the ignition delay period is shortened, so combustion noise does not become a problem.

By the way, although the above embodiment has been explained on the premise that the residual pressure is controlled in two stages, high and low,
For example, the residual pressure can be controlled in a continuously variable manner by driving the pressure control valve 43 with a high-frequency pulse signal and controlling the valve opening time ratio, thereby controlling the residual pressure in a wide range of operating conditions. It is possible to provide a more appropriate injection rate. In addition, in this invention, as described above, since the cam lift at which injection starts, that is, the prelift, can be changed, the face cam (1
4) and the plunger (12) are not required, and therefore it is also possible to reduce the manufacturing cost of the injection pump.

(Effects of the Invention) As described above, according to the present invention, a relatively high residual pressure can be stably obtained by interposing an equal pressure delivery valve in the middle of the high pressure fuel passage that communicates the fuel injection pump and the injection nozzle. On the other hand, a pressure control passage is provided that communicates the high-pressure fuel passage from the equal-pressure delivery valve to the injection nozzle with a low-pressure part of the fuel system, and a pressure control valve that opens and closes this passage. During low-load operation when the amount of fuel injected is small, it is closed to maintain the residual pressure at a relatively high pressure, thereby suppressing the injection rate.On the other hand, during high-load operation when the amount of fuel injected increases, it is closed to reduce the residual pressure and increase the injection rate. This makes it possible to reduce combustion noise during low-load operation while satisfying the requirements of securing engine output during high-load operation and preventing secondary injection.

[Brief explanation of the drawing]

FIG. 1A is a front view of essential parts of an embodiment of the present invention;
FIG. 1B is a sectional view thereof, and FIG. 2 is a longitudinal sectional view of an example of the equal pressure delivery valve. 3 and 4 are characteristic diagrams for explaining the operation of the embodiment, and FIGS. 3A and 3B show pressure waveforms in the injection pipe during low-load operation and high-load operation, respectively. Fig. 3C shows the waveform of the drive current applied to the pressure control valve in relation to the pressure inside the pipe, and Fig. 4 shows the relationship between the oil feeding speed, cam lift, and cam rotation angle. It is. FIG. 5 is a longitudinal sectional view of a conventional example. 4...Pump body, 12...Plunger, 14
... Face cam, 16 ... Roller, 18 ... Pump chamber, 24 ... Distribution port, 40 ... Plunger barrel, 41 ... Distribution passage, 42 ... Equal pressure delivery valve, 43 ... Pressure control valve, 45 ... ... Main body of pressure control valve, 46 ... High pressure fuel passage section, 48 ... Injection pipe, 50 ... High pressure fuel passage, 52 ... First pressure control passage section, 53 ... Spool, 54 ... Spring, 55 ... ...Electromagnetic solenoid, 57...Second pressure control passage section, 61...Pressure control passage.

Claims (1)

[Claims] 1. An equal-pressure delivery valve is interposed in the middle of a high-pressure fuel passage that communicates between the fuel injection pump and the injection nozzle, and the high-pressure fuel passage between the equal-pressure delivery valve and the injection nozzle is communicated with the low-pressure part of the fuel system. a pressure control passage for controlling the pressure control passage; a pressure control valve for variably controlling the opening degree of the pressure control passage; and a control means for driving and controlling the pressure control valve according to the engine operating state,
In addition, the equal-pressure delivery valve sets the residual pressure characteristics so that fuel injection starts in the low oil delivery speed range at the beginning of the pressure lift of the fuel injection pump, while the control means A fuel injection device for an internal combustion engine, characterized in that the pressure control valve is opened to reduce residual pressure in a high-pressure fuel passage.