JPH0355786Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an air intake control device for a diesel engine.

[Conventional technology]

Conventionally, in diesel engines, adiabatic compression by introducing exhaust gas into the combustion chamber has been used as a means to improve the ignition performance at the time of starting and promote starting, as shown in Japanese Utility Model Application Publication No. 55-139236. A device is known that uses work to increase the initial temperature of the air in the combustion chamber during the compression stroke. In other words, this device provides an on-off valve in the engine exhaust system in addition to the engine exhaust valve, and operates this on-off valve when the engine starts to block the exhaust gas, and also closes the exhaust valve from the end of the suction stroke to the beginning of the compression stroke. By opening the cylinder in between, exhaust gas is allowed to flow into the combustion chamber whose pressure has been reduced between the end of the intake stroke and the beginning of the compression stroke when the engine is started, thereby performing adiabatic compression work.

[Purpose of invention]

The present invention uses a means to improve low-temperature startability by increasing the initial temperature of the compression stroke of the air in the combustion chamber through adiabatic compression work as described above.
It is an object of the present invention to provide an air intake control device for a diesel engine that can reduce mechanical stress and thermal load when the engine is under high load and high rotation speed.

[Structure of the idea]

In order to achieve this purpose, the intake control device for a diesel engine according to the present invention has an intake valve whose one end opens into the combustion chamber of the diesel engine and whose closing timing is set at a crank angle of 20 degrees or earlier after bottom dead center. an exhaust passage having one end open to the combustion chamber and having an exhaust valve; an auxiliary passage having one end opening to the combustion chamber and the other end opening to the intake passage; a supercharger disposed in the intake passage; and the auxiliary passage, which performs opening and closing operations later than the opening and closing operations of the intake valve, respectively, so that the valve opens from the end of the intake stroke to the beginning of the compression stroke. an auxiliary valve provided in the intake passageway, and an auxiliary valve located downstream of a branch point between the intake passage and the auxiliary passageway;
a first valve means for selectively opening and closing the intake passage leading to the combustion chamber; a second valve means selectively opening and closing the auxiliary passage; and a first valve means for selectively opening and closing the auxiliary passage; and valve opening/closing control means for closing and opening the second valve means, opening the first valve means and closing the second valve means at least when the diesel engine is under high load and at high speed.

〔Example〕

FIG. 1 is a schematic diagram showing a four-cylinder diesel engine incorporating an intake control device according to an embodiment of the present invention.

The diesel engine 1 has four cylinders 2, and each cylinder 2 is formed with an intake port 5 and an exhaust port 6 each having an intake valve 3 and an exhaust valve 4. Each intake port 5 has an intake passage 7,
An exhaust passage 8 is connected to each exhaust port 6. The engine 1 has a mechanical supercharger 9 in the intake passage 7, and heated air sent by the supercharger 9 is cooled in a cooler 10.

The combustion chamber of each cylinder 2 and the intake passage 7 are connected to an auxiliary passage 51
connected via. Each cylinder 2 is formed with an auxiliary port 12 which is a third port.
The auxiliary passage 51 has one end connected to each cylinder 2 via this auxiliary port 12 and the other end connected to the cooler 1 connected to the intake passage 7.
It communicates immediately downstream of 0. Each auxiliary port 12
includes an auxiliary valve 13 that opens and closes the auxiliary port 12.
is provided.

A first on-off valve 52 for opening and closing the intake passage 7 is provided in the intake passage 7 downstream of the confluence point of the intake passage 7 and the auxiliary passage 51.
A second on-off valve 53 opens and closes the auxiliary passage 51.
is provided. A diaphragm device 54 is connected to the first on-off valve 52, and the diaphragm device 54 has a diaphragm 55, an atmospheric chamber 56, and a negative pressure chamber 57. A spring 58 is arranged inside the negative pressure chamber 57, and this spring 5
8 biases the diaphragm 55 in the direction to open the first on-off valve 52. On the other hand, the second on-off valve 53
A diaphragm device 59 is connected to the
This diaphragm device 59 includes a diaphragm 6
0, an atmospheric chamber 61 and a negative pressure chamber 62. A spring 63 is arranged inside the negative pressure chamber 62,
This spring 63 biases the diaphragm 60 in a direction to open the second on-off valve 53. Negative pressure chambers 57, 62 of diaphragm devices 54, 59
is connected to a vacuum pump 66 via a negative pressure passage 64 and a negative pressure passage 65 branched from the negative pressure passage 64. Negative pressure passages 64 and 65 are provided with switching valves 67 and 68, respectively. Switching valve 67
is a first position (first position) that communicates the atmosphere with the negative pressure chamber 57.
position shown in the figure) and the vacuum pump 66 into the negative pressure chamber 57.
The second position communicates with the second position. On the other hand, the switching valve 68 connects the vacuum pump 66 to the negative pressure chamber 62.
The first position (the position shown in FIG. 1) communicates with the negative pressure chamber 62, and the second position communicates the atmosphere with the negative pressure chamber 62.

These switching valves 67 and 68 are connected to a control circuit 69 composed of, for example, a microcomputer, and are controlled by this control circuit 69 to take either the first position or the second position. controlled. This control circuit 69 includes an engine rotation speed sensor 38 that detects the engine rotation speed N and outputs a rotation speed signal S _N , and an engine load sensor 3 that detects the engine load L and outputs a load signal S _L.
9 is connected.

Next, the valve timings of the intake valve 3, exhaust valve 4, and auxiliary valve 13 will be explained with reference to FIG. The exhaust valve 4 is located at the bottom dead center like a normal exhaust valve.
It is set to open just before BDC and close just after top dead center TDC. Intake valve 3 opens at the same timing as a normal intake valve, but closes earlier than normal, depending on the nature of the engine, for example, from 60 degrees before bottom dead center BDC to 20 degrees after bottom dead center. It is now set at a certain time. Further, the auxiliary valve 13 is configured to perform its opening and closing operations later than the opening and closing operations of the intake valve 3, so that the auxiliary valve 13 opens from the end of the intake stroke to the beginning of the compression stroke.

Next, the control of the first on-off valve 52 and the second on-off valve 53 by the control circuit 69 will be explained with reference to FIG.

The control circuit 69 first reads the engine load L and the engine speed N, and then determines whether or not the engine load L is smaller than the set load _L1 , which is the load that separates the high load from the low load.
When NO, the engine is in a high-load operating region indicated by the symbol D in FIG. 4, and in this region D, the first on-off valve 52 is opened and the second on-off valve 53 is closed. As a result, supercharging is performed while the intake valve 3 is closing early, so a so-called Miller cycle is performed, which reduces thermal load and mechanical stress during high-load, high-speed engine operation. In addition, you can enjoy the benefits of Miller Cycle.

On the other hand, when the determination whether L<L ₁ is YES,
Next, it is determined whether the engine rotation speed N is smaller than the set rotation speed _N1 , which is the rotation speed that separates the high rotation speed and the low rotation speed, and if this determination is YES,
Since the engine is in the low-load, low-speed operating region A,
The first on-off valve 52 is closed and the second on-off valve 53 is opened to perform a cycle including adiabatic compression of the air-fuel mixture in the cylinder 2 by intake air.

Also, when the determination of whether N<N ₁ is NO,
Since this is the general operating range B of the engine, both the first on-off valve 52 and the second on-off valve 53 are opened to perform a cycle suitable for normal operation.

In this embodiment, the intake (air) valve opens from the end of the intake stroke to the beginning of the compression stroke.
The air is introduced into the combustion chamber via an auxiliary valve that opens and closes later than the intake valve opens and closes, respectively. At the time of this introduction, the piston descends and the volume inside the combustion chamber increases, so
When a large amount of intake air is supplied into this combustion chamber at once, a compression effect occurs. Therefore, the intake air temperature increases and the ignitability improves. In particular, when exhaust gas is supplied, the intake air temperature is further increased by the heat held by the exhaust gas, and the ignitability can be further improved.

[Effect of idea]

As described above, according to the present invention, in the low-load, low-speed range of the engine, the intake air is adiabatically compressed to raise the temperature of the intake air.
The startability is improved, and the mirror cycle can be performed at least at high speeds under high load, so the benefits of the mirror cycle can be enjoyed.

In other words, in this invention, the intake valve closing timing is set before 20 degrees after bottom dead center in terms of crank angle, so a large amount of supercharging air is supplied, increasing the pressure inside the combustion chamber and increasing the maximum combustion pressure. restrain from doing. In other words, since the supply of supercharging air is stopped at early closing, the pressure in the combustion chamber does not become excessively large, and the necessary and sufficient amount of intake air can be secured through supercharging, so a supercharger is not required. Compared to an engine, the amount of work (effective compression ratio) can be increased, and output can be improved.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of an intake control device for a diesel engine according to an embodiment of the present invention, Fig. 2 is a diagram showing valve timings of an intake valve, an exhaust valve, and an auxiliary valve, and Fig. 3 is a diagram of a control circuit. FIG. 4, a flowchart showing the operation, is a diagram showing the relationship between engine load, rotation speed, and opening/closing of each valve. Explanation of symbols, 1... Diesel engine, 2...
...Cylinder, 3...Intake valve, 4...Exhaust valve, 7...Intake passage, 8...Exhaust passage, 9...Supercharger, 10...
...Cooler, 13...Auxiliary valve, 51...Auxiliary passage,
52...first on-off valve, 53...second on-off valve.

Claims (1)

[Scope of claim for utility model registration] (1) One end is open in the combustion chamber of a diesel engine, and the closing timing is 20 degrees after bottom dead center at the crank angle.
an intake passage with an intake valve previously set; an exhaust passage with one end opening into the combustion chamber and an exhaust valve; one end opening into the combustion chamber and the other end with the intake passage. an auxiliary passage that is open; a supercharger disposed in the intake passage; and an opening operation that is delayed from the opening and closing operations of the intake valve so that the valve opens from the end of the intake stroke to the beginning of the compression stroke. and an auxiliary valve provided in the auxiliary passage which performs a closing operation, and which is located downstream of a branch point between the intake passage and the auxiliary passage and selectively opens and closes the intake passage leading to the combustion chamber. a first valve means; a second valve means for selectively opening and closing the auxiliary passage; when the diesel engine is under low load and at low speed, the first valve means is closed and the second valve means is opened; An intake air control device for a diesel engine, comprising: valve opening/closing control means that opens the first valve means and closes the second valve means at least at high speeds when the engine is under high load. (2) The diesel engine according to claim 1, wherein the valve opening/closing control means opens both the first valve means and the second valve means when the diesel engine is at low load and high speed. intake control device.