JPH06288317A - Fuel injection device for diesel engine - Google Patents

Abstract

(57) [Abstract] [Object] The present invention relates to a fuel injection device for a diesel engine, and an object of the present invention is to improve the air utilization rate and realize good combustion. A fuel pressurizing means 200 for pressurizing fuel to a pressure higher than the pressure in the combustion chamber at the time of fuel injection, and a required fuel amount that changes depending on operating conditions of each engine are injected. The fuel pressure control means 100 and 600 are provided to raise the fuel pressure and gradually decrease it just before the end of injection so that the pressure becomes substantially equal to the above-mentioned pressure in the combustion chamber.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel injection device for a diesel engine.

[0002]

2. Description of the Related Art A diesel engine supplies fuel into a combustion chamber at the top dead center of compression of a piston and ignites the fuel to burn it. Therefore, the fuel injection device must inject fuel with the fuel pressure higher than the pressure in the combustion chamber at this time.

A typical fuel injection device for a diesel engine uses a plunger or the like to pressurize the fuel and inject the fuel when the valve opening pressure of a valve element provided near the injection port is reached. The fuel pressure during injection is maintained at this valve opening pressure.

[0004]

Such fuel injection is performed at other positions in the combustion chamber because the fuel injected at each instant reaches a specific position in the combustion chamber all with the same velocity. There is a problem in that the air existing in the air is not used for combustion so much, the air utilization rate decreases, and a large amount of black smoke is generated.

Therefore, an object of the present invention is to provide a fuel injection device for a diesel engine which can improve the air utilization rate and realize good combustion.

[0006]

A fuel injection device for a diesel engine according to the present invention comprises a fuel pressurizing means for pressurizing fuel to a pressure higher than a pressure in a combustion chamber at a fuel injection timing,
When injecting a required fuel amount that changes depending on each engine operating state, a fuel pressure control means that makes the fuel pressure the highest immediately after the start of injection and gradually decreases it so as to be almost equal to the pressure in the combustion chamber immediately before the end of injection, And is provided.

[0007]

In the fuel injection device for a diesel engine described above, the fuel pressurizing means pressurizes the fuel to a pressure higher than the pressure in the combustion chamber at the time of fuel injection, and the fuel pressure control means adjusts the required fuel amount that changes depending on the engine operating state. At the time of injection, the fuel pressure is made highest immediately after the start of injection and gradually decreased so as to be equal to the pressure in the combustion chamber immediately before the end of injection.

[0008]

1 is a schematic sectional view of a fuel injection device for a diesel engine according to the present invention. In the figure, 100 is an injection valve for injecting fuel into the combustion chamber, and 200 is an injection pump for supplying fuel to the injection valve 100. The injection valve 100 and the injection pump 200 are connected by a fuel supply passage 300. This injection pump 200 is a general distribution type injection pump, and when the drive shaft 201 is driven by the rotation of the crankshaft, the pump 20
The fuel is taken into the housing from the fuel tank 400 by 2, and the plunger 205 is moved left and right by the cam disk 203 and the spring 204 while rotating.

When the plunger 205 moves leftward in FIG. 1, the fuel in the housing is taken into the pressure chamber 207 formed between the tip of the plunger 205 and the plunger case 206, and the pressure moves by the rightward movement. The fuel in the chamber 207 passes through the fuel passage 205 a in the plunger 205, the delivery passage 208, and the fuel passage 300 to inject the fuel into the injection valve 10.
Pumped to 0. Although only one delivery passage 208 is shown in FIG. 1, it is actually formed so as to surround the plunger 205 by the number of cylinders, and each delivery passage is connected to the injection valve of each cylinder via the fuel supply passage. The fuel is sequentially fed under pressure to each injection valve as the plunger 205 rotates.

A fuel passage 205a in the plunger 205
Is in communication with the spill passage 205b on the side of the cam disc, and when the plunger 205 moves rightward, the spill passage 205b surrounds the spill ring 2b.
When it comes off from 09 and communicates with the internal space of the housing, the pressure feeding of fuel is stopped. Therefore, the spill ring 209
1 can be moved leftward in FIG. 1 to reduce the amount of fuel to be pressure-fed to the injection valve 100, and to supply the required amount of fuel to the injection valve 100 according to the engine operating condition. The left and right movements of the spill ring 209 are performed by the accelerator lever 2 which is linked to the accelerator pedal 500.
It is performed with the rotation of 10.

Each injection valve 10 by this injection pump 200
The pressure feeding of fuel to 0 is normally synchronized with the fuel injection into each combustion chamber, but in the present embodiment, it is set to be completed before the fuel injection timing.

Next, the structure of the injection valve 100 will be described. Inside the injection valve 100, a fuel passage 102 that communicates with the injection port 101 from the connection portion of the fuel supply passage 300 is formed.
In the middle of this fuel passage, first and second check valves 103 and 104 which allow only a flow in the downstream direction are arranged in series, and the fuel passage 102 is provided with a first check valve 103 upstream of the first check valve 103. The passage 102a, the third passage 102c downstream of the second check valve 104, and the first passage
And a second passage 102b between the second check valves 103 and 104. A pressure accumulating chamber 106 having a relatively large capacity is formed in the third passage 102c.
A valve body 105 for closing the nozzle 101 by its tip
The valve body 105 is formed such that the pressure receiving area on the front end side is equal to the pressure receiving area on the back surface on the opposite side, and the fuel pressure in the third passage 102c is on the front end side and on the back surface side. The fuel pressure in the second passage 102b acts via the pressure passage 107.

The second passage 102b communicates with a variable volume chamber 111 in which a piston 109 installed at the tip of the PZT actuator 108 is arranged. Thereby, PZ
By applying a voltage to the T actuator 108, the PZ
The T actuator 108 contracts, the piston 109 moves upward in FIG. 1 by the spring 110, and the volume of the variable volume chamber 111 increases from the initial value.
The fuel pressure in the passage 102b drops. Further, in the pressure passage 107, a spring 112 is provided which abuts on the back side of the valve body 105 and biases the valve body 105 toward the injection port 101.

In the fuel injection device for a diesel engine of the present embodiment constructed as described above, a voltage is applied to the PZT actuator 108 and contracts at the end of the previous fuel injection, and the delivery of the injection pump 200 is completed. Passage 208
To the injection port 101 of the injection valve 100 are filled with fuel having a pressure V0 equivalent to that in the combustion chamber at the time of fuel injection. At this time, the same pressure V0 acts on the tip side and the back side of the valve body 105, so that the valve body 105 closes the injection port 101 by the urging force of the spring 112.

At the time of fuel injection this time, first, the required amount of fuel corresponding to the engine operating state is pressure-fed to the injection valve 100 by the injection pump 200, the voltage application to the PZT actuator 108 is stopped, and the volume of the variable volume chamber 110 is initially set. Is returned to the value of. As a result, the fuel pressure from the delivery passage 205 of the injection pump 200 to the injection port 101 of the injection valve 100 increases from V0 to V, and the third passage 1 of the injection valve 100 increases.
Since the pressure accumulating chamber 106 formed in 02b has a larger capacity than other portions, the required fuel amount described above is stored in this portion. Of course, the fuel pressure V at this time is
The value varies depending on the amount of fuel pumped to the injection valve 100. Even at this time, since the same pressure V acts on the tip side and the back side of the valve body 105, the spring 112
The valve body 105 closes the injection port 101 by the urging force of.

At the fuel injection timing, a voltage is applied to the PZT actuator 108. The contraction amount of the PZT actuator 108 depends on the voltage value applied to it, and the voltage value at this time is such that the increase in the volume of the variable volume chamber 110 is the current fuel pressure V in the second passage 102b of the injection valve 100. Is determined by the control device 600 by estimating the fuel amount pumped based on the signal of the accelerator pedal stroke sensor 501 so as to reduce the above-mentioned V0 to V0.

When the fuel pressure in the second passage 102b is reduced to V0, the fuel pressures acting on the tip side and the back side of the valve body 105 become V and V0, respectively, and the valve body 105 opposes the biasing force of the spring 112. 1, the nozzle 101 is opened by opening upward, and the fuel in the third passage 102c is injected from the nozzle 101.

The fuel pressure V in the third passage 102c decreases every time fuel is injected, and when it reaches V0, the valve body 1
05 closes the injection port 101 and the fuel injection is stopped. The amount of fuel injected during this period is equal to the amount stored in the pressure accumulating chamber 106 before the fuel injection, and it is possible to realize the required fuel amount injection in each engine operating state.

FIG. 2 shows a time chart of the fuel pressure in this fuel injection. In the figure, the solid line indicates the engine high load with a relatively large fuel injection amount, the dotted line indicates the engine medium load, and the alternate long and short dash line indicates the engine low load with a relatively small fuel injection amount. The larger the fuel injection amount, the higher the pressure at the start of injection and the longer the injection time. However, in any case, the pressure at the end of injection is equal to V0, that is, the pressure in the combustion chamber at the fuel injection timing.

As shown in FIG. 3, the injection valve 100 of the present embodiment has a substantially circular combustion chamber 1a formed in a concave shape on the top surface of the engine piston 1 in the vicinity of the compression top dead center.
The fuel is injected from around the
As shown in FIG. 4, the shape is such that the fuel is injected in a fan shape.

FIG. 5 is a diagram showing a fuel distribution state in the combustion chamber when the above-mentioned fuel injection is executed by the injection valve having such an injection port shape. FIG.
(B) shows the engine with a medium load, and (C) shows the engine with a low load. In each engine load state, the fuel injected immediately after the start of injection has the highest pressure, and therefore reaches farther from the injection port 101, and the pressure decreases as the injection progresses. The approach point of the fuel gradually approaches the injection port 101, and the arrival point of the fuel injected immediately before the end of the injection is near the injection port 101.

As a result, in each engine load state, the fuel injected at each moment has different reaching points, and is ignited and burned by utilizing the air existing in that portion in the combustion chamber 1a, and the fuel is burned in the combustion chamber 1a. Since all of the air is used, good combustion with high air utilization is realized. On the other hand, in the conventional case where the fuel pressure is equal at each moment, all of the injected fuel reaches the same position in the combustion chamber 1a, so that the air in the vicinity of the nozzle 101 is not used for combustion and the air utilization rate is low. It produces a lot of black smoke.

Further, in order to make the arrival point of the fuel in the combustion chamber 1a at each moment different, it is conceivable to gradually increase the fuel pressure in the course of injection, contrary to the present embodiment. Since the combustion is started, the fuel injected thereafter passes there, and at that time, because it burns and ignites, the air existing outside it in the combustion chamber is not used for this combustion, and the air utilization rate is also low. Will be things.

The injection valve of the fuel injection device according to the present invention is
The arrangement and the shape of the injection port are not limited to those shown in the embodiment, and for example, as shown in FIG. 6 similar to FIG. 3, the injection valve 100 that injects fuel radially from the center of a general combustion chamber 1a. The same effect can be obtained with '.

However, in such a radial fuel injection, since there are many ignition combustion points, combustion is likely to be rapid, and the combustion pressure and the combustion temperature rapidly increase.
The noise may increase and a large amount of NOx may be generated. On the other hand, in the fuel injection of the present embodiment, since the ignition and combustion occur in a continuous range, the combustion becomes gentle, and such a problem does not occur.

Further, in the prior art, the spring for urging the valve element of the injection valve maintains the valve element in the closed position against a considerably high fuel pressure immediately before the injection, and therefore has a relatively large size. However, a similar spring of this embodiment has a structure in which the fuel pressure acts on both ends of the valve body at the closed position at the same time. In order to maintain it, a small one can be used, and the vicinity of the injection port of the injection valve can be made small, so that the degree of freedom in disposing the injection valve is considerably improved.

[0027]

As described above, according to the fuel injection device for a diesel engine of the present invention, the fuel pressurizing means pressurizes the fuel to a pressure higher than the pressure in the combustion chamber at the fuel injection timing, and the fuel pressure control means operates each engine. When injecting the required amount of fuel that changes depending on the state, the fuel pressure is injected immediately after the start of injection in order to increase the fuel pressure immediately after the start of injection and gradually decrease it to almost equal the pressure in the combustion chamber immediately before the end of injection. Further, the fuel reaches a position farther from the injection port in the combustion chamber, and as the injection progresses, the arrival point of the fuel gradually approaches the injection port, and the arrival point of the fuel injected immediately before the end of the injection is near the injection port. Therefore, the fuel injected at each moment has different reaching points, and there is no overlap of the injected fuel due to the fact that the relative velocities of the injected fuels do not reverse, so the air existing in that part of the combustion chamber is used. Then, it is ignited and burned, and the entire air in the combustion chamber is used. As a result, good combustion with high air utilization is realized.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a fuel injection device for a diesel engine according to the present invention.

FIG. 2 is a time chart of fuel pressure.

FIG. 3 is a perspective view showing an arrangement of injection valves.

4A and 4B are views showing the shape of the injection port of the injection valve, where FIG. 4A is a perspective view in the vicinity of the injection port of the injection valve, FIG. 4B is a sectional view taken along the line PP of FIG. 4A, and FIG. It is a QQ sectional view.

FIG. 5 is a diagram showing a fuel distribution state in a combustion chamber,
(A) when the engine has a high load, (B) when the engine has a medium load, (C)
Is at low engine load.

FIG. 6 is a perspective view showing the arrangement of another injection valve having another injection port shape.

[Explanation of symbols]

 100,100 '... Injection valve 106 ... Accumulation chamber 108 ... PZT actuator 111 ... Variable volume chamber 200 ... Injection pump 600 ... Control device

Claims (1)

[Claims] 1. A fuel pressurizing means for pressurizing fuel to a pressure higher than the pressure in the combustion chamber at the time of fuel injection, and when injecting a required fuel amount that changes depending on each engine operating state, the fuel pressure is immediately after the start of injection. And a fuel pressure control means for gradually decreasing the fuel pressure so that the pressure becomes the same as the combustion chamber pressure immediately before the end of injection.