JPH068608B2 - Intake device for diesel engine - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an intake system for a diesel engine in which an intake temperature is raised by adiabatic compression in order to accelerate start-up of the diesel engine and improve emission.

(Prior Art) Conventionally, as disclosed in Japanese Utility Model Laid-Open No. 59-107936, in order to improve the ignitability at the time of starting in a diesel engine, the intake air supplied to the combustion chamber is adiabatically compressed to raise the intake air temperature. An intake device (start promotion device) is known. This device is provided with an opening / closing valve that opens in the intake passage in the middle of the intake stroke, specifically, an intake throttle valve is provided in the main intake passage, and an opening / closing valve is provided in a bypass intake passage that bypasses the intake throttle valve. During a low load operation state from start-up to warm-up, the above-mentioned open / close valve is opened in the middle of the intake stroke by a valve mechanism or a pressure-responsive open / close valve with the main intake passage being throttled by the intake throttle valve. I am trying to make it work. By such operation of the on-off valve, introduction of intake air into the combustion chamber is restricted until the middle of the intake stroke, and intake air is rapidly introduced into the combustion chamber from the middle of the intake stroke to perform adiabatic compression. According to this device, much energy is not consumed as electric power as compared with the case where the intake air is heated by the air heater, and the intake air temperature can be efficiently raised in the combustion chamber. In the above-mentioned conventional device, the on-off valve is operated during the startup warm-up operation,
Even during normal operation, for example, by operating the on-off valve in an operation region where the rotation speed is relatively low and the load is low, the combustibility is improved due to the rise in intake air temperature and the generation of white smoke and HC is prevented.

The on-off valve that opens during the intake stroke in this device is one that is driven by the engine output shaft through a valve mechanism or an interlocking mechanism, or automatically when the negative pressure in the cylinder reaches a predetermined negative pressure. Although a pressure-responsive type that opens can be adopted, in particular, if a pressure-responsive type is used, it is possible to perform adiabatic compression of intake air with a simple structure without requiring a valve operating mechanism or an interlocking mechanism.

By the way, when such a pressure-responsive on-off valve is used, in the conventional device, the negative pressure in the cylinder is reduced to near atmospheric pressure after the on-off valve is simply opened at a preset valve opening negative pressure. Since it is only closed at this time, there is a problem that the adiabatic compression effect of intake air is likely to decrease due to the early closing of the on-off valve, especially during cranking in a low rotation speed below the idle speed. It was That is, when such an on-off valve is used, normally, in the rotational speed range of the idle speed or higher, the opening negative pressure of the on-off valve is set in advance so that the on-off valve is in the open state from the middle of the intake stroke to the end of the intake stroke. Although it is set, when cranking at a speed lower than the idle speed, the time from the point at which the negative pressure in the cylinder reaches the valve opening negative pressure and the opening / closing valve opens to the end of the intake stroke becomes longer. , The negative pressure becomes small before the end of the intake stroke and the on-off valve closes early. If the on-off valve closes early in this way, then the intake air is again blocked and the pressure in the cylinder decreases, which causes adiabatic expansion to lower the temperature, which reduces the filling amount and the adiabatic compression effect. There is a problem that is.

(Object of the Invention) In view of such circumstances, the present invention aims to improve combustibility and emission by adiabatic compression of intake air with a simple structure using a pressure-responsive on-off valve, and in particular, engine speed. The present invention provides an intake device for a diesel engine that can exhibit a good adiabatic compression effect even during low cranking.

(Structure of the Invention) According to the present invention, a pressure-responsive on-off valve that opens when a negative pressure in a cylinder reaches a predetermined negative pressure is provided in an intake passage for each cylinder of an engine. In the intake system of a diesel engine, which limits the introduction of intake air into the combustion chamber until the middle of the intake stroke, and rapidly introduces intake air into the combustion chamber from the middle of the intake stroke to achieve adiabatic compression, A delay means for delaying the opening operation timing of the on-off valve by a predetermined amount when rotating is provided compared to other times.

In other words, the opening / closing valve is set to obtain proper opening / closing timing at idle speed or higher in advance. Is to prevent.

(Embodiment) FIGS. 1 and 2 show an embodiment of the present invention. In these drawings, reference numeral 1 denotes each cylinder of a diesel engine, and a combustion chamber 3 is formed above the piston 2 inside the cylinder. The combustion chamber 3 has an intake port 5 equipped with an intake valve 4. , And an exhaust port (not shown) provided with an exhaust valve is open. In the intake passage 6 communicating with the intake port 5, the introduction of intake air into the combustion chamber 3 is restricted by the pressure-responsive on-off valve 10 until the middle of the intake stroke, and the intake air is rapidly introduced into the combustion chamber 3 from the middle of the intake stroke. An intake air introduction restricting device is provided to introduce and perform adiabatic compression. In this intake air introduction restricting device, in this embodiment, an intake passage 6 including a main intake passage 6a and a sub intake passage 6b having a downstream end opening to the main intake passage 6a is formed for each cylinder 1, and the main intake passage 6a is formed. The intake throttle valve 7 is provided upstream of the opening position of the auxiliary intake passage 6b of 6a.
Is provided, and the opening / closing valve 1 is provided in the auxiliary intake passage 6b.
It is configured by providing 0. In addition,
The main intake passage 6a and the sub intake passage 6b are connected to an air cleaner (not shown) via surge tanks 8 and 9, respectively.

The on-off valve 10 is arranged in the opening of the auxiliary intake passage 6b to the surge tank 9, and is provided in the valve chamber 11 and is in contact with the valve seat 12 from the upstream side.
A diaphragm 15 which is connected to the via a connecting shaft 14,
Two chambers 16 partitioned by this diaphragm 15,
17 and a return spring 18 that is provided in one of the chambers 16 and biases the valve body 13 in the valve closing direction. The one chamber 16 communicates with the auxiliary intake passage 6b downstream of the valve body 13 through a communication hole 19 penetrating the valve body 13, the connecting shaft 14 and the diaphragm 15, and the other chamber 1
7 communicates with the surge tank 9 and is maintained at substantially atmospheric pressure. Thus, when the negative pressure introduced from the auxiliary intake passage 6b downstream of the valve body 13 into the one chamber 16 reaches a predetermined valve opening negative pressure, the on-off valve 10 and the urging force of the return spring 18 and the valve body 13 are closed. The valve element 13 is opened against the negative pressure acting on itself, and is closed when the negative pressure becomes sufficiently small after opening the valve.

The opening / closing valve 10 is provided with a delay unit that delays the opening operation timing of the opening / closing valve 10 by a predetermined amount when the rotation speed is lower than the idle speed and when the rotation speed is low.
In the present embodiment, this delay means is controlled by a control circuit 25, which will be described later, to throttle the communication hole 19, and the communication hole throttle valve 20.
It is composed of. The communication hole throttle valve 20 restricts the communication hole 19 to reduce the passage area when it receives the delay means actuation signal a, and otherwise fully opens the communication hole 19.

On the other hand, with respect to the intake throttle valve 7, an actuator 21 formed by a diaphragm device for opening and closing the intake throttle valve 7 is provided.
And the passage 2 for operating this actuator 21
2, a drive means including a vacuum pump 23 and a switching valve 24 is provided, and the intake throttle valve 7 is provided by the drive means.
The intake system can be switched between an open / close valve operating state in which the intake valve is closed to operate the open / close valve 10 and an operation stop state in which the operation mechanism of the intake throttle valve 7 is stopped by opening the intake throttle valve 7 to open the main intake passage 6a. I am trying.

Further, reference numeral 25 is a control circuit using a microcomputer or the like, which receives a signal for detecting an operating state from the rotation speed detecting means 26, the load detecting means 27, etc., and performs a cranking operation and a relatively low rotation and low load operation. On-off valve 10 in the area
Is operated and the main intake passage 6a is opened in the operating region on the high rotation and high load side where it is not necessary to perform adiabatic compression of the intake air so that the on-off valve 10 is deactivated.
The drive means is controlled by the control signal b output to the. Further, the control circuit 25 sends the delay means actuation signal a to the communication hole throttle valve 20 based on the engine speed detection signal when the engine speed is lower than the idle speed (when cranking).
I am trying to output to.

According to the intake device as described above, the opening / closing valve 10 operates in a state where the main intake passage 6a is throttled by the intake throttle valve 7 during cranking or in an operating region of relatively low rotation and low load, that is, the intake air intake Up to the middle of the stroke, the introduction of intake air into the combustion chamber 3 is restricted, and the negative pressure in the cylinder 1 gradually increases,
When this negative pressure is introduced into one chamber 16 of the opening / closing valve 10 and reaches the valve opening negative pressure, the opening / closing valve 10 is opened and the auxiliary intake passage 6 is opened.
A large amount of intake air is rapidly introduced into the combustion chamber 3 from b. As a result, adiabatic compression of the intake air is performed and the temperature in the combustion chamber 3 rises, so that ignitability and combustibility are enhanced, and white smoke, HC, etc. in the exhaust gas are reduced.

By the way, when the engine speed is equal to or higher than the idle speed, the communication hole throttle valve 20 does not operate and the communication hole 19 of the on-off valve 10 is fully opened. The pressure is immediately introduced into one chamber 16 of the on-off valve 10. In this state, the opening / closing valve 10 is opened at a substantially constant crank angle at which the negative pressure in the cylinder 1 reaches the opening negative pressure of the opening / closing valve 10, and then the negative pressure in the cylinder 1 is sufficiently reduced by the inflow of intake air. Open / close valve 10
Is closed. At the idling speed or higher, the closing timing of the on-off valve 10 substantially coincides with the end of the intake stroke in this state so that the adiabatic compression is favorably performed.
The valve opening negative pressure of the on-off valve 10 is set in advance.

On the other hand, at the time of cranking at a low rotation speed equal to or lower than the idle speed, the communication hole throttle valve 20 operates to throttle the communication hole 19 of the opening / closing valve 10, thereby delaying the opening operation of the opening / closing valve 10. This prevents the on-off valve 10 from being closed early. This action will be described with reference to FIG. 3. In the conventional device which does not have the delay means, the negative pressure in the cylinder (negative pressure introduced into the on-off valve) is the valve opening negative pressure as indicated by the chain double-dashed line A. The on-off valve opens at time t ₁ when P is reached, but the time from this time t ₁ to the end of the intake stroke becomes longer during cranking, so that the negative pressure is increased at time t ₂ earlier than the BDC time at the end of the intake stroke. It becomes smaller and the on-off valve closes, and from this time point t ₂ , the introduction of intake air is interrupted again, and the negative pressure increases. Then, due to the adiabatic expansion at this time, the intake air temperature that has been increased by the adiabatic compression up to that point will be lowered, and the intake charge ratio will also decrease. On the other hand, in the above-described embodiment of the present invention, the communication hole 19 of the opening / closing valve 10 is throttled by the communication hole throttle valve 20 during cranking, and the introduction of the negative pressure to the one chamber 16 of the opening / closing valve 10 is restricted. As a result, as shown by the solid line B, one chamber 16 of the on-off valve 10 is
The increase of the negative pressure in the inside slows down and the open / close valve opening operation time point t _{3 at} which the negative valve opening pressure is reached is delayed, and accordingly, the timing when the negative pressure becomes sufficiently small is delayed until near BDC. Therefore, the on-off valve 10 is prevented from prematurely closing, adiabatic expansion does not occur after the on-off valve 10 is closed, the adiabatic compression effect is not impaired, and the filling amount is prevented from decreasing.

In the above embodiment, the communication hole 19 of the on-off valve 10 is throttled by a certain amount during cranking, but the communication hole throttle valve 20
May have a structure in which the opening degree is adjustable, and the delay time of the opening operation of the on-off valve 10 may be controlled according to the rotation speed during cranking.

Further, as the delaying means of the opening operation of the on-off valve 10, various structures other than the above-mentioned embodiment can be adopted. For example, a throttle valve may be provided in the auxiliary intake passage 6b downstream of the on-off valve 10, and this throttle valve may be set to a small opening during cranking to delay the introduction of negative pressure into the on-off valve 10. Alternatively, the volume of the intake passage 6 downstream of the on-off valve 10 is made variable, and for example, a chamber whose volume can be changed by a piston or the like is used as the on-off valve 10
It is also possible that the intake passage 6 on the downstream side is communicated with the intake passage 6 and the volume thereof is increased at the time of cranking to delay the increase of the negative pressure. Alternatively, the amount of intake leak to the cylinder 1 may be increased by slightly opening a throttle valve provided in the main intake passage 6a during cranking or by opening a separately provided leak passage.

In the above embodiment, the intake passage 6 for each cylinder is divided into a main intake passage 6a and a sub intake passage 6b, and the sub intake passage 6b is divided.
Although the on-off valve 10 is provided in each of the cylinders, one intake passage may be provided for each cylinder and the pressure-responsive on-off valve 10 may be provided in the intake passage. When the intake valve is rotatable to the retracted position and the operation is stopped, the on-off valve 10 may be rotated to the retracted position to open the intake passage. Also in this case, by providing the opening / closing valve 10 with the delay means as described above, the same operation as that of the above embodiment can be obtained.

(Effects of the Invention) As described above, according to the present invention, the adiabatic compression of intake air is performed with a simple structure by the pressure-responsive on-off valve that opens when the negative pressure in the cylinder reaches a predetermined negative pressure. Combustibility and emission can be improved. Moreover, in the present invention, since the opening operation of the opening / closing valve is delayed particularly at low rotation speeds equal to or lower than the idle rotation speed, the opening / closing valve of the opening / closing valve is changed depending on the low rotation speed corresponding to cranking and the idle rotation speed or higher. The opening / closing timing is properly adjusted, and the adiabatic compression effect of the intake air can be exhibited satisfactorily over these rotation speed ranges.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of an apparatus according to an embodiment of the present invention, FIG. 2 is an enlarged cross-sectional view of an on-off valve, and FIG. 3 is an explanatory diagram showing changes in negative pressure introduced into the on-off valve. 1 ... Cylinder, 3 ... Combustion chamber, 4 ... Intake valve, 6 ... Intake passage, 10 ... Open / close valve, 20 ... Communication hole throttle valve (delay means),
25 ... Control circuit.

Claims (1)

[Claims] 1. A pressure-responsive on-off valve that opens when a negative pressure in a cylinder reaches a predetermined negative pressure is provided in an intake passage for each cylinder of an engine. In the intake system of the diesel engine, which restricts the introduction of intake air into the combustion chamber and suddenly introduces intake air into the combustion chamber during the intake stroke to perform adiabatic compression,
An intake system for a diesel engine, comprising: a delay unit that delays the opening operation timing of the on-off valve by a predetermined amount when the engine speed is lower than the idle speed and when the engine speed is low.