Internal-combustion engines – Charge forming device – Exhaust gas used with the combustible mixture
Reexamination Certificate
2000-05-30
2001-10-09
Wolfe, Willis R. (Department: 3747)
Internal-combustion engines
Charge forming device
Exhaust gas used with the combustible mixture
C123S295000, C123S399000, C123S568200
Reexamination Certificate
active
06298835
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an EGR control system for an internal combustion engine.
2. Description of the Related Art
In internal combustion engines, EGR (Exhaust-Gas Recirculation) control for recirculating part of the exhaust gas is conducted in order to improve fuel economy and reduce exhaust gas pollutants.
Recent years have seen the development of direct-injection spark ignition internal combustion engines where gasoline fuel is injected directly into the combustion chamber to achieve lean stratified-charge combustion. EGR control has also been applied to this type of engine. An example can be found in Japanese Laid-open Patent Application No. Hei 9 (1997)-32651.
When a direct-injection spark ignition engine is operating in the low engine speed and low engine load region, gasoline fuel is injected during the compression stroke to cause stratified-charge combustion (ultra-lean burn combustion) at an air-fuel ratio of, for instance, 30:1 or greater. When the engine is operating in the high engine speed and high engine load region, gasoline fuel is injected during the intake stroke to cause premix-charge combustion (uniform combustion) at an air-fuel ratio of, for instance, 20:1 or less.
In the stratified-charge combustion region, the EGR amount (or rate) should preferably be increased to reduce the NOx (nitrogen oxides) content. As can be seen from
FIG. 27
, if the EGR amount is increased, stratified-charge combustion does not fluctuate greatly and remains stable, since the marginal limit of EGR is high owing to the stratification. In the premix-charge combustion region, however, combustion grows increasingly unstable with increasing EGR amount. Thus, the marginal limit of EGR is lower than in the stratified combustion region and the required EGR amount is relatively small.
Viewing this from a different point, as shown in
FIG. 28
, a large amount of EGR gas is required for NOx reduction in the stratified-charge combustion region. However, introduction of EGR gas is difficult, since the pressure difference between the intake air and the exhaust gas becomes small when the engine operates with full-throttle.
In the premix-charge combustion region, on the other hand, the pressure difference between the intake air and the exhaust gas is sufficient, since the engine load is regulated through the throttle opening, similarly to the case of an ordinary engine where gasoline fuel is injected before the intake valve(s). As shown in
FIG. 27
, however, increasing the EGR amount destabilizes combustion and the margin of EGR is therefore not high. This means that the diameter or capacity of an EGR control valve need be only about the same as that in an ordinary engine where fuel is injected before the intake valve(s).
It can thus be seen that the marginal limit of EGR differs between the stratified-charge combustion region and the premix-charge combustion region in the direct-injection spark ignition engine. However, the combustion mode must frequently be switched between the stratified-charge combustion and the premix-charge combustion in response to the engine operating conditions.
Therefore, if the characteristic of the EGR control valve is designed or set with the focus on the premix-charge combustion region where the marginal limit of EGR is relatively low, then, as shown in
FIGS. 29A and 29B
, the EGR control valve response is deficient when the combustion mode is switched to the stratified-charge combustion in response to a change in the engine operating condition. The EGR amount is therefore insufficient. On the other hand, if the characteristic of the EGR valve is designed or set with focus on the stratified-charge combustion region, the EGR control valve response becomes too high when the combustion mode is switched to the premix-charge combustion. The EGR amount therefore becomes excessive.
As shown in
FIG. 29C
, the deficient/excessive EGR amount destabilizes combustion to cause misfiring and degraded drivability, and further, as shown in
FIG. 29D
, increases unburnt HCs (hydrocarbons) that degrade emission performance. While designing the EGR amount low prevents misfiring etc., this expedient is undesirable, since it makes full utilization of the expected engine performance impossible and is also disadvantageous in terms of fuel economy.
The technique proposed in the aforesaid prior art of coping with these problems is to drive the EGR control valve at a high speed when the combustion mode is switched from the stratified-charge combustion to the premix-charge combustion and to drive it at a lower speed when the combustion mode is switched from the premix-charge combustion to the stratified-charge combustion.
However, the aim of this prior art technique is to achieve exhaust gas purification by conducting EGR control in the stratified-charge combustion region and the premix-charge combustion region, and to prevent engine output deficiency and to lower torque shock when the combustion mode is switched, while preventing transient deterioration of combustion when the EGR amount (or ratio) is changed. Specifically, in this prior art, the purpose in increasing the EGR valve driving speed when the combustion mode is switched to premix-charge combustion is to improve response to demand for increased engine output without causing combustion deterioration. And the purpose in decreasing the EGR driving speed when the combustion mode is switched to the stratified-charge combustion is to avoid combustion deterioration at the time of transition.
It has also been proposed in this prior art to make the driving speed of the EGR control valve higher in the closing direction than in the opening direction. However, the principle involved in this prior art is the same as that just explained.
In other words, the prior art is limited to changing the driving speed of the EGR valve in response to the combustion mode and does not propose an improved EGR mechanism for an engine with different combustion modes that is responsive to the combustion mode for realizing an EGR amount that is neither deficient nor excessive.
SUMMARY OF THE INVENTION
An object of this invention is therefore to overcome the foregoing shortcomings by providing an EGR control system for an internal combustion engine having different combustion modes with an improved EGR mechanism which can ensure an EGR amount that is neither deficient nor excessive required for the combustion mode, while preventing misfire from happening and preventing the degradation of drivability, fuel economy and emission performance from occurring.
For realizing this object, the present invention provides a system for controlling an EGR mechanism, installed in an internal combustion engine, having an EGR passage connecting an air intake system and an exhaust system of the engine to recirculate a portion of exhaust gas produced by the engine to the air intake system and an EGR control valve equipped at the EGR passage to regulate an amount of the exhaust gas to be recirculated; comprising; engine operating condition detecting means for detecting operating conditions of the engine; combustion mode determining means for determining one of a plurality of combustion modes of the engine based on the detected operating conditions of the engine; and EGR mechanism operating means for operating an EGR control valve of the EGR mechanism based on the detected operating conditions of the engine. The system includes at least one of a flow rate control valve equipped at the EGR passage to regulate flow rate of the exhaust gas to be recirculated and an actuator for regulating an opening of a throttle valve provided at the air intake system; and the EGR mechanism operating means operates the EGR control valve and at least one of the flow rate control valve and the actuator, when the one combustion mode is determined to be changed to other of a plurality of the combustion modes.
REFERENCES:
patent: 4366799 (1983-01-01), Suda
patent: 4924840 (1990-05-01), Wade
patent: 5950595 (1999-09-01), Yoshioka et al.
patent: 5
Horie Kaoru
Kubodera Masao
Matsuura Hiromi
Shinohara Michio
Takahashi Hitoshi
Arent Fox Kintner & Plotkin & Kahn, PLLC
Honda Giken Kogyo Kabushiki Kaisha
Wolfe Willis R.
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