JPH07259655A - Exhaust gas circulating device - Google Patents

Abstract

PURPOSE:To attain an exhaust gas circulating current of a variable compression ratio engine at a low EGR rate in the case of high load and at a high EGR rate in the case of low load. CONSTITUTION:Two intake and exhaust valves are provided on a cylinder head 1, and operated by a first cam shaft 10 and a second cam shaft 20. In the intake stroke, the second exhaust valve 5 is operated through a lever 23 and a locker arm 15 by a cam 22 of the second cam shaft 20 to circulate exhaust gas. In the case of high load, the second exhaust valve 5 opens and closes near the top dead center of a piston in a quick close mirror cycle with a low compression ratio to attain a low EGR rate. The phase of the second cam shaft is changed, and in the case of high load, the second exhaust valve 5 openes and closes at 90+ or - before the bottom dead point in a normal cycle with a high compression ratio to attain a high EGR rate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas recirculation system for an internal combustion engine, and more particularly to an exhaust gas recirculation system for a variable compression ratio engine that enables conversion between a normal cycle and a Miller cycle.

[0002]

2. Description of the Related Art Conventionally, in a vehicle engine, in order to reduce NOx contained in exhaust gas, exhaust gas, which is an inert gas, is recirculated into intake air and exhaust gas recirculation (EGR) is performed to lower the combustion gas temperature. ) Is done.

By the way, when the engine load is high, EGR
The lower the gas temperature, the higher the volumetric efficiency, and the larger the EGR gas amount, the lower the combustion temperature and the NOx. The combustion temperature becomes unstable when the temperature of the EGR gas is low when the load is light, so the temperature of the EGR gas is preferably high. Therefore, EG
There is a method in which a cooling means for the R gas is provided to cool the EGR gas when the load is high and to control the EGR gas not to cool when the load is light.

[0004]

However, if EGR is performed under high load, adverse effects such as deterioration of fuel consumption and reduction of output occur. Therefore, the supply amount of EGR gas (EGR rate)
Needs to be high at low load and low at high load.

The present invention has been made by paying attention to the above-mentioned problems. It is possible to increase the EGR rate when the load is low and decrease the EGR rate when the load is high so that the normal cycle and the Miller cycle can be converted. An object of the present invention is to provide an exhaust gas recirculation system that always performs optimum EGR over a wide operating range of a variable compression ratio engine.

[0006]

[Means for Solving the Problems] To achieve the above object,
In the first aspect of the exhaust gas recirculation system according to the present invention, an internal combustion engine including an exhaust gas recirculation system that recirculates a part of exhaust gas into intake air is provided with means for opening and closing an exhaust valve during an intake stroke.

In the second invention, in the internal combustion engine, two or more intake valves per cylinder and at least one intake valve are provided.
A first camshaft provided with at least one exhaust valve and provided with a cam for operating the intake valve and the exhaust valve; and a second camshaft provided with at least one intake valve and a cam for operating the exhaust valve Equipped.

In the third invention, in the internal combustion engine, the valve timing of at least one intake valve and exhaust valve is made variable by changing the phase of the cam of the second cam shaft which opens and closes these valves. .

In the fourth aspect of the invention, in the intake stroke of the internal combustion engine, the closing timing of the intake valve is set before the piston bottom dead center, and the opening and closing timing of the exhaust valve is set near the piston top dead center for operation. Depending on the conditions, a valve drive device that can set the closing timing of at least one intake valve near the piston bottom dead center and set the opening and closing timing of the exhaust valve before piston bottom dead center was provided.

In the fifth aspect of the invention, in the intake stroke of the internal combustion engine, the closing timing of the intake valve is set near the bottom dead center of the piston, and the opening and closing timing of the exhaust valve is set before the bottom dead center of the piston. Depending on the conditions, the closing timing of at least one intake valve is set after the piston bottom dead center, and
A valve drive device that can set the opening / closing timing of the exhaust valve near the fulcrum below the piston was provided.

[0011]

According to the above construction, in an internal combustion engine equipped with an exhaust gas recirculation device, two or more intake valves per cylinder, one or more exhaust valves, and a first cam for driving the intake valves and the exhaust valves. By providing a shaft and a second cam shaft that operates at least one intake valve and an exhaust valve, and changing the phase of the second cam shaft, the valve timing of at least one intake valve and exhaust valve can be adjusted. It was variable.

In the intake stroke, the closing timing of the intake valve is set before the piston bottom dead center, the opening and closing timing of the exhaust valve is set near the piston top dead center, and at least one intake valve is closed depending on operating conditions. The timing is set near the piston bottom dead center, and the opening / closing timing of the exhaust valve is set before the piston bottom dead center. Therefore, when the load is high, a low compression ratio early closing mirror cycle is performed. In that case, exhaust gas recirculation is hardly performed, and when the load is low, a high compression ratio normal cycle is performed, in which case exhaust gas recirculation is performed.

Alternatively, in the intake stroke, the closing timing of the intake valve is set near the piston bottom dead center and the opening / closing timing of the exhaust valve is set before the piston bottom dead center, and at least one intake valve is closed depending on operating conditions. The timing is set after the piston bottom dead center, and the opening / closing timing of the exhaust valve is set near the piston bottom dead center. Therefore, when the load is low, a normal cycle with a high compression ratio is performed, in which case exhaust gas recirculation is performed, and when the load is high, a slow closing mirror cycle with a low compression ratio is performed, and in that case, exhaust gas recirculation is hardly performed.

[0014]

Embodiments of the exhaust gas recirculation system according to the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a plan sectional view of a cylinder head portion of a diesel engine having two intake valves and two exhaust valves in one cylinder, FIG. 2 is a side sectional view thereof, and FIG. 3 is an X section of FIG.
It is a side sectional view showing a -X section. A first intake valve 2, a second intake valve 3, a first exhaust valve 4, a second exhaust valve 5, a first camshaft 10 and a second camshaft 20 are mounted on the cylinder head 1. The first camshaft 10 is provided with cams 11, 12, and 13 for the first intake valve 2, the first exhaust valve 4, and the second exhaust valve 5, respectively.
Directly actuates the first exhaust valve 4, and the cam 11 and the cam 1
3 operates the first intake valve 2 and the second exhaust valve 5 via rocker arms 14 and 15, respectively. The second camshaft 20 is provided with a cam 21 and a cam 22, the cam 21 directly operates the second intake valve 3, and the cam 22 operates a lever 23 mounted on the cylinder head 1 as shown in FIG. The rocker arm 15 is swung around the pin 24.
Is operated to open and close the second exhaust valve 5. The second cam shaft 20 is adapted to rotate by a predetermined angle by a drive device (not shown), and by shifting the phases of the cam 21 and the cam 22, the second intake valve 3 and the second exhaust valve 5 can be rotated. The valve timing can be delayed. Reference numeral 25 is a piston, 26 and 27 are intake passages, and 28 is an exhaust passage.

Next, the operation will be described. FIG. 4 is a diagram showing the relationship between the movement of the piston 25 and the opening areas of the intake and exhaust valves when the load is high. The vertical axis represents the opening area and the horizontal axis represents the position of the piston 22. The solid line is the opening area of one valve, and the thin two-dot chain line is the total opening area of two valves. In the figure, A is an exhaust valve, B is an intake valve, and C is a second exhaust valve. That is, the first and second exhaust valves 4, 5 start to open before the piston bottom dead center and close near the piston top dead center. And the phase is always the same. The phases of the first and second intake valves 2 and 3 are the same, and the first and second intake valves 2 and 3 start to open near the top dead center of the piston and close at about 90 ° before the bottom dead center of the piston. When the second intake valve 3 opens near the top dead center of the piston, the second exhaust valve 5 opens at the same time for a short time as indicated by C, but almost all the exhaust gas recirculates during intake because it is near the top dead center of the piston. do not do. Therefore, there is no fear of deterioration of fuel consumption and output reduction.

FIG. 5 is a PV diagram under high load. In the intake stroke, suction is started from 0, and in 1a, the first and second intake valves 2 and 3 are closed, so that the cylinder pressure decreases,
Follow the arrow to 1b. The compression stroke goes from 1b to 1a to 2a, the combustion and expansion strokes go from 2a to 3 and 4, the exhaust stroke goes from 4 to 1c, and 1c to 0.
That is, the early closing Miller cycle is performed, and since the expansion and compression of 1a-1b-1a are only performed near the end of the intake stroke, the substantial compression ratio becomes low, and the compression ratio at this time is around 11 to 13. Therefore, high output can be achieved.

FIG. 6 is a diagram showing the relationship between the movement of the piston 25 and the opening areas of the intake and exhaust valves when the load is low.
In this case, the second camshaft 20 is rotated by the drive device to change the phases of the cams 21 and 22, and the closing position of the second intake valve 3 is delayed so as to be near the piston bottom dead center.
In the figure, B1 indicates the first intake valve 2 and B2 indicates the second intake valve 3.
Indicates. Therefore, the second exhaust valve 5 is at the position indicated by C, that is, near 90 ° before the piston bottom dead center, the exhaust gas is recirculated into the intake air, the EGR rate is increased, and the generation of NOx is reduced.

FIG. 7 is a PV diagram at a low load, which is a normal intake stroke 0-1, compression stroke 1-2, combustion stroke 2-3, expansion stroke 3-4, and exhaust stroke 4-1-0. It becomes a cycle operation. The compression ratio at this time is 15 to 17, and good startability and combustion conditions can be obtained.

The relationship between the engine load and the compression ratio or EGR rate is summarized as follows. Figure 8
FIG. 4 is a diagram showing a relationship between an engine load and a compression ratio, where the vertical axis represents the engine load and the horizontal axis represents the engine speed. The outermost curve is the torque curve at maximum engine output. As shown in the figure, the compression ratio decreases as the load increases, and the compression ratio increases as the load decreases.

FIG. 9 is a diagram showing the relationship between the engine load and the EGR rate. As with FIG. 8, the vertical axis represents the engine load and the horizontal axis represents the engine speed. As shown in the figure, the EGR rate decreases as the load increases, and the EGR rate increases as the load decreases.

FIG. 10 shows two intakes per cylinder,
FIG. 12 is a plan sectional view of a cylinder head portion of a gasoline engine provided with an exhaust valve, FIG. 11 is a side sectional view, and FIG. 12 is a side sectional view showing a section YY of FIG. 10. The cylinder head 31 includes a first intake valve 32, a second intake valve 33, a first exhaust valve 34, a second exhaust valve 35, and a first camshaft 4.
0, the second camshaft 50 is mounted. The first camshaft 40 is provided with cams 41, 42, and 43 for the first intake valve 32, the first exhaust valve 34, and the second exhaust valve 35, and the cam 41 has a first rocker arm 44 and a first camshaft 41. The intake valve 32 is operated, and the cam 42 directly connects the first exhaust valve 3
4 is operated, the cam 43 moves the pin 45 to the cylinder head 31.
The second exhaust valve 35 is actuated via the lever 46 pivotally attached by the. The cam 5 is provided on the second cam shaft 50.
1 and 52 are provided, the cam 51 directly operates the second intake valve 33, and the cam 52 connects the cylinder head 31 with the pin 5
The lever 46 pivotally mounted by 3 swings the lever 46 to open and close the second exhaust valve 35. The second camshaft 50 is configured to rotate by a predetermined angle by a drive device (not shown), and by shifting the phases of the cams 51 and 52, the valves of the second intake valve 33 and the second exhaust valve 35 are shifted. You can delay the timing. 55 is a piston, 56 and 57 are intake passages, 58
Is an exhaust passage.

Next, the operation will be described. FIG. 13 is a diagram showing the relationship between the movement of the piston 55 under low load and the opening areas of the intake and exhaust valves, where the vertical axis represents the intake and exhaust valve opening areas and the horizontal axis represents the position of the piston 55. There is. The solid line shows the opening area of one valve, and the thin two-dot chain line shows the total opening area of two valves. In the figure, A is an exhaust valve, B is an intake valve, and C
Indicates the second exhaust valve. That is, the first and second exhaust valves 3
Nos. 4 and 35 start to open before the piston bottom dead center and close near the piston top dead center. And the phase is always the same. The first and second intake valves 32 and 33 have the same phase and start to open near the top dead center of the piston and close at the bottom dead center of the piston. At this time, the second exhaust valve 35 opens for a short time near 90 ° before the piston lower fulcrum, the exhaust gas is recirculated into the intake air, the EGR rate is high, and the generation of NOx is reduced.

FIG. 14 is a PV diagram when the load is low, in which the intake stroke 0-1, the compression stroke 1-2, the combustion stroke 2-3, the expansion stroke 3-4, and the exhaust stroke 4-1-0 are cycled. I do.
At this time, the compression ratio is set to around 11 to 13 to improve the startability and the thermal efficiency, and it is possible to reduce fuel consumption and CO ₂ generation amount.

FIG. 15 is a diagram showing the relationship between the movement of the piston 55 under high load and the opening areas of the intake and exhaust valves. In the figure, A is the exhaust valve, B1 is the first intake valve 32, and B2 is The second intake valve 33, C indicates the second exhaust valve 35. In this case, the second camshaft 50 is rotated by a drive device (not shown) so that the closing timing of the second intake valve 33 is 90 ° after the piston bottom dead center.
And Therefore, the opening / closing timing of the second exhaust valve 35 is near the piston bottom dead center, and the exhaust gas is hardly recirculated into the intake air. Therefore, the fuel consumption does not deteriorate and the output does not decrease.

FIG. 16 is a PV diagram at the time of high load, in which the intake stroke is 0-1 and the compression stroke is 1-1d, the second intake valve 33 is open, so the pressure is not increased and the first stroke is made at the 1d point. Since the 2 intake valve 33 is closed, the compression stroke is 1d-2b. After that, combustion stroke 2b-3, expansion stroke 3-4, exhaust stroke 4-1
It becomes a delayed closing mirror cycle operation of -0. The compression ratio at this time is in the vicinity of 8 to 10, high output can be generated, and knocking at high output can be prevented.

[0027]

As described above in detail, the present invention has two or more intake valves per cylinder and at least one or more exhaust valves, and has two camshafts for intake and exhaust valves. In operation, the phase of one camshaft was changed to make the valve timing of at least one intake valve and exhaust valve variable.

Since the closing timing of the intake valve is set before the piston bottom dead center in the intake stroke and the opening and closing timing of the exhaust valve is set near the piston top dead center, the compression ratio becomes low.
The early closing Miller cycle operation enables high output, but since exhaust gas recirculation is hardly performed, deterioration of fuel efficiency and output reduction at high output do not occur. Also, at low load, the closing timing of at least one intake valve is set near the piston bottom dead center, and the opening and closing timing of the exhaust valve can be set before piston bottom dead center. The operation is started, the startability is good, the combustion state is good, the EGR rate is high, and the generation of NOx is reduced.

Alternatively, since the closing timing of the intake valve is set near the piston bottom dead center in the intake stroke and the opening / closing timing of the exhaust valve is set before the piston bottom fulcrum, the compression ratio becomes high and the normal cycle operation is performed, and the startability is improved. Is good, the combustion state is good, the EGR rate is high, and the generation of NOx is reduced. Also, at the time of high load, the closing timing of at least one intake valve is set after the piston bottom dead center and the opening and closing timing of the exhaust valve can be set near the piston bottom dead center. Although it becomes a cycle operation and high output can be achieved, since exhaust gas recirculation is hardly performed, fuel consumption deterioration and output reduction at high output do not occur.

[Brief description of drawings]

FIG. 1 is a plan sectional view of a cylinder head portion of a diesel engine equipped with an exhaust gas recirculation device of the present invention.

FIG. 2 is a side sectional view of the engine.

FIG. 3 is a side sectional view of an exhaust valve drive system of the engine.

[Fig. 4] The movement of the piston under high load of the engine,
It is a figure which shows the relationship with the opening area of an intake and an exhaust valve.

FIG. 5 is a PV diagram when the engine is under high load.

FIG. 6 shows the movement of the piston when the engine has a low load,
It is a figure which shows the relationship with the opening area of an intake and an exhaust valve.

FIG. 7 is a PV diagram when the engine is under a low load.

FIG. 8 is a diagram showing a relationship between a load of the engine and a change in compression ratio.

FIG. 9 is a diagram showing a relationship between a load of the engine and a change in EGR rate.

FIG. 10 is a plan sectional view of a cylinder head portion of a gasoline engine equipped with the exhaust gas recirculation device of the present invention.

FIG. 11 is a side sectional view of the engine.

FIG. 12 is a side sectional view of an exhaust valve drive system of the engine.

FIG. 13 shows the movement of the piston when the engine has a low load,
It is a figure which shows the relationship with the opening area of an intake and an exhaust valve.

FIG. 14 is a PV diagram when the engine is under a low load.

FIG. 15 shows the movement of the piston when the engine is under high load,
It is a figure which shows the relationship with the opening area of an intake and an exhaust valve.

FIG. 16 is a PV diagram when the engine is under high load.

[Explanation of symbols]

1, 31 ... Cylinder head, 2, 32 ... First intake valve, 3, 33 ... Second intake valve, 4, 34 ... First exhaust valve, 5, 35 ... Second exhaust valve, 10, 40 ... 1st camshaft, 20, 50 ... 2nd camshaft, 14, 1
5, 44 ... Rocker arm, 46, 54 ... Lever.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display area F02D 15/00 E

Claims (4)

[Claims] 1. An exhaust gas recirculation system for an internal combustion engine, comprising: an exhaust gas recirculation system for recirculating a part of exhaust gas into intake air; and means for opening and closing an exhaust valve during an intake stroke. A first cam shaft provided with an intake valve and at least one exhaust valve and provided with a cam for operating the intake valve and the exhaust valve, and a cam for operating at least one intake valve and the exhaust valve An exhaust gas recirculation device comprising a second camshaft. 2. The internal combustion engine is characterized in that the valve timing of at least one intake valve and exhaust valve is variable by changing the phase of a cam of a second cam shaft that opens and closes these valves. The exhaust gas recirculation device according to claim 1. 3. In the intake stroke of the internal combustion engine, the closing timing of the intake valve is set before the piston bottom dead center, and the opening and closing timing of the exhaust valve is set near the piston top dead center. The exhaust system according to claim 2, further comprising a valve drive device capable of setting the closing timing of each intake valve near the piston bottom dead center and setting the opening / closing timing of the exhaust valve before piston bottom dead center. Reflux device. 4. In the intake stroke of the internal combustion engine, the closing timing of the intake valve is set near the piston bottom dead center, and
The opening / closing timing of the exhaust valve is set before the piston bottom dead center, the closing timing of at least one intake valve is set after the piston bottom dead center, and the exhaust valve opening / closing timing is set near the piston bottom dead center depending on operating conditions. The exhaust gas recirculation device according to claim 2, further comprising a valve drive device that can be set.