JP2006299807A - Diesel engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve fuel economy and an exhaust gas characteristic by optimally controlling a temperature rise caused by compression of a diesel engine. <P>SOLUTION: Generation of NOx in combustion is restrained by preventing the cylinder inside temperature from becoming high more than necessary in response to compression, by arranging a combustion chamber 1, an auxiliary chamber 2, a normally closed valve 4 for communicating the auxiliary chamber 1 with the combustion chamber 2 only for a compression stroke latter stage from the compression stroke initial stage of the engine, and a control unit for controlling the valve 4 in an operation state and an unoperated state on the basis of an operation state of the engine in a switching system. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a diesel engine, and more particularly, to a diesel engine capable of optimally controlling a temperature rise accompanying compression to improve fuel consumption and exhaust gas characteristics.

  A premixed compression ignition type engine in which a part of fuel is preliminarily injected into the combustion chamber from the beginning of the intake stroke to the middle of the compression stroke, and the remaining fuel is mainly injected near the compression top dead center. In this case, it is well known that the generation of NOx accompanying combustion can be suppressed and the emission of black smoke can be prevented to improve fuel efficiency.

However, in such a premixed compression ignition type engine, depending on the operating state of the engine, the fuel preliminarily injected before the main injection may be ignited. Thus, by providing a variable volume auxiliary chamber communicated and held in the combustion chamber, or by providing an auxiliary chamber having a pressure valve pressed and urged by an elastic body as seen in Patent Document 2, preliminary injection is performed. It has been studied to suppress ignition by the fuel itself.

However, when an auxiliary chamber communicated with the combustion chamber is provided as in the invention shown in Patent Document 1, the auxiliary chamber is exposed to high-temperature combustion gas, so that the cooling load on the engine increases. In addition, the cylinder head becomes larger as the volume of the auxiliary chamber increases. Further, when an auxiliary chamber having a pressure valve pressed and urged by an elastic body is provided as in the invention of Patent Document 2, the pressure valve is opened by the combustion pressure, so that the expansion energy is always effectively used. There was a possibility of incurring a side effect of being unable to do so.
Japanese Patent Application Laid-Open No. 11-107772 JP 2000-230439 A

  The problem to be solved is that an increase in engine cooling load and an increase in the size of the cylinder head cannot be prevented.

  The present invention includes a combustion chamber and an auxiliary chamber, a normally closed valve for communicating the auxiliary chamber with the combustion chamber only during an early stage of the compression stroke of the engine and a later stage of the compression stroke, and the valve based on the operating state of the engine. The main feature is that a control unit for controlling switching between an operating state and a non-operating state is provided. The invention of claim 2 is characterized in that the auxiliary chambers of the cylinders in which the compression strokes do not continue are mutually connected and held, and the invention of claim 3 supports the porous material rich in thermal conductivity. It is characterized by being loaded into the chamber.

  In the diesel engine according to the present invention, the auxiliary chamber is communicated with the combustion chamber only during the period from the initial stage of the compression stroke to the latter stage of the compression stroke, so that the temperature rise due to compression is optimally controlled. The combustion gas does not flow into the auxiliary chamber, and the temperature of the auxiliary chamber is kept low, so that the cooling load of the engine does not increase. According to the invention of claim 2, since the auxiliary chambers of the cylinders in which the compression strokes do not continue are shared, even when a large-capacity auxiliary chamber is provided, an increase in the size of the cylinder head is suppressed. In the case where a porous material having a high thermal conductivity is loaded in the auxiliary chamber as in the invention of claim 3, there is an advantage that the cooling efficiency of the auxiliary chamber becomes higher.

  FIG. 1 is a schematic configuration diagram showing a basic structure of a diesel engine according to the present invention, in which an auxiliary chamber 2 connected to a combustion chamber 1 is formed in a cylinder head 3 and a porous material having a high thermal conductivity (not shown). ) Is filled in the auxiliary chamber 2. The normally closed valve 4 is attached to the opening of the auxiliary chamber 2 in the combustion chamber 1 so that the auxiliary chamber 2 is normally disconnected from the combustion chamber 1 and the auxiliary chamber 2 is combusted only when the valve 4 is opened. Communication with the chamber 1 is made. Reference numeral 5 denotes a piston having a cavity formed on the top surface, and an intake valve, an exhaust valve, a fuel injection valve, etc. (not shown) are attached to the combustion chamber 1 to constitute a premixed compression ignition type diesel engine. .

The valve 4 normally shuts off the auxiliary chamber 2 from the combustion chamber 1, but when a control unit (not shown) detects that the engine is operating in the middle / high speed range, it starts from the early stage of the compression stroke to the late stage of the compression stroke. During this period, the valve-opening drive is performed so that the auxiliary chamber 2 communicates with the combustion chamber 1.
That is, in the premixed compression ignition type engine, when the pre-injected fuel is not likely to be ignited during the compression stroke, the auxiliary chamber 2 is separated from the combustion chamber 1 to increase the compression ratio. Make fuel ignition more reliable.

On the other hand, when the control unit detects that the engine is operating in the middle / high speed range, the valve 4 is driven to open from the initial stage of the compression stroke to the latter stage of the compression stroke, and the auxiliary chamber 2 communicates with the combustion chamber 1. . Then, since the compression ratio is reduced and the temperature rise is suppressed, the pre-injected fuel does not ignite and start combustion in the stage before the main injection is performed, and the main injection is performed. Even later, the generation of NOx accompanying combustion is suppressed.
In FIG. 1, (A) is the state of the compression stroke start, (B) is the initial state of the compression stroke where the valve 4 starts to open, (C) is the state of the late stage of the compression stroke where the valve 4 is closed, and (D) is A state at the time when ignition / combustion is started by main injection, (E) shows an expansion stroke.

  As described above, when the valve 4 is opened from the initial stage of the compression stroke to the latter stage of the compression stroke, a part of the compressed air flows into the auxiliary chamber 2 and heat exchange with the cylinder head is performed in a state where the temperature is lowered. When the valve is opened in the cycle, it is returned to the combustion chamber. If the temperature of the air returned to the combustion chamber in this way is high, it is predicted that the heat load of the engine increases and causes various adverse effects. However, the combustion gas does not flow into the auxiliary chamber 2 and is filled with a porous material. Therefore, since the air flowing into the auxiliary chamber 2 is efficiently heat-exchanged with the cylinder head 3 through the porous material, there is no concern that the high-temperature air is returned to the combustion chamber 1.

  The valve 4 is driven to open only during the period from the initial stage of the compression stroke to the latter stage of the compression stroke, and is kept closed in other areas. For this reason, in the unlikely event that high-temperature combustion gas does not flow into the auxiliary chamber 2, it is confined in the combustion chamber (inside the cylinder). Therefore, an output equivalent to that of a normal engine can be obtained, and the degree of freedom in selecting a porous material filled in the auxiliary chamber 2 is high.

  By the way, in the high compression engine, when it is intended to increase the degree of reduction in the compression ratio caused by the opening of the valve 4, it is necessary to increase the volume of the auxiliary chamber 2. Therefore, when the auxiliary chambers 2 of the respective cylinders are made independent, the cylinder head is enlarged as the volume of the auxiliary chamber 2 is increased. However, for example, in an engine in which the ignition order is set to 1-4-2-3, for example, the group of the first cylinder and the fourth cylinder is divided into the group of the second cylinder and the third cylinder, and the ignition order is set to 1-3. In the case of an engine set to -5-2-6-4, the group of the first cylinder to the third cylinder and the group of the fourth cylinder to the sixth cylinder, or the group of the first and second cylinders, A plurality of cylinder groups are formed only by cylinders in which the compression strokes are not continuous, such as a group of 3 and 4 cylinders, and a group of 5 and 6 cylinders, and a common auxiliary chamber 2 for each cylinder group. By forming the cylinder head, it is possible to suppress the increase in size of the cylinder head, which is a concern when a large-capacity auxiliary chamber 2 is provided. FIG. 2 shows an example in which the auxiliary chamber 2 of two cylinders is shared.

  The valve 4 is driven to open while there is almost no pressure difference between the combustion chamber 1 and the auxiliary chamber 2. Therefore, for example, as shown in the embodiment, when a valve of the type that is seated and closed from the combustion chamber 1 side is provided, the valve 4 can be opened with a slight force. The valve 4 can be accurately driven to open and close by an arbitrary actuator such as an electromagnetic actuator, a fluid actuator using hydraulic pressure or air pressure, or a composite actuator thereof.

  In the above embodiment, the present invention is applied to a premixed compression ignition type diesel engine. However, the present invention is also applied to a normal type diesel engine that does not perform premixing, and the temperature at the compression top dead center is applied. NO can be suppressed by avoiding that it becomes higher than necessary. Furthermore, in order to improve the heat exchange efficiency of the auxiliary chamber 2, in the said embodiment, although the auxiliary chamber 2 is filled with the porous material which is rich in heat resistance, the inner surface of the auxiliary chamber 2 is a brush-like body or flagella-like. The same heat exchange effect can be obtained even if the body is attached.

It is a schematic block diagram which shows the basic structure of the diesel engine which concerns on this invention. It is a schematic plan view which shows the example which shared the auxiliary chamber 2 of two cylinders.

Explanation of symbols

1 Combustion chamber 2 Auxiliary chamber 3 Cylinder head 4 Valve

Claims (3)

  A combustion chamber (1) and an auxiliary chamber (2), and a normally closed valve (4) for communicating the auxiliary chamber (2) with the combustion chamber (1) only from the early stage to the late stage of the compression stroke of the engine. A diesel engine comprising a control unit that switches the valve between an operating state and a non-operating state based on an operating state of the engine.   The diesel engine according to claim 1, wherein the auxiliary chamber (2) of the cylinders in which the compression strokes do not continue is shared. The diesel engine according to claim 1 or 2, wherein a porous material rich in thermal conductivity is loaded in the auxiliary chamber (2).

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