Internal-combustion engines – Charge forming device – Exhaust gas used with the combustible mixture
Reexamination Certificate
2000-04-20
2001-09-18
Wolfe, Willis R. (Department: 3747)
Internal-combustion engines
Charge forming device
Exhaust gas used with the combustible mixture
C123S568120, C123S399000
Reexamination Certificate
active
06289883
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an exhaust gas recirculation system for an engine.
2. Description of the Related Art
In recent years, engines, in particular diesel engines, are equipped with an exhaust gas recirculation system for recirculating a large amount of exhaust gas into an intake air stream. In order to admit a large amount of exhaust gas into an air stream, there have been proposed exhaust gas recirculation systems equipped with an intake air throttle valve located in an intake path upstream an exhaust gas inlet port. The intake air throttle valve operates in a closing direction in a region of engine operating conditions in which recirculation of a large amount of exhaust gas is demanded so as to reduce an effective aperture of intake air passage with the result of increasing negative pressure acting at the exhaust gas inlet port of the intake path so as to intensify suction of exhaust gas into the intake air path. One of such exhaust gas recirculation systems is known from, for example, Japanese Unexamined Patent Publication 8-193534. Further, because recirculation of a large amount of exhaust gas causes aggravation of combustibility, feedback control of the amount of exhaust gas recirculation is implemented to bring a ratio of the amount of exhaust gas recirculation is feedback controlled to bring a ratio of the amount of exhaust gas relative to an amount of fresh air that is introduced into the intake air path to a specified ratio by controlling an amount of intake air that is actually detected by an air flow meter so as to bring it to a target value.
In the exhaust gas recirculation system which is equipped with an intake air throttle valve operative to increase the amount of exhaust gas recirculation, it was ascertained that, when closing the intake air throttle valve or, in particular, fully closing the intake air throttle valve so as to provide a smallest effective aperture of intake air path with the intention to increase the amount of exhaust gas recirculation, there possibly occurs such a situation that the amount of exhaust gas recirculation is made zero in an excessive case. As a result of having pursued causes of an occurrence of this situation, it has been proven that fully closing the intake air throttle valve imposes restraints on the largest amount of air which is actually introduced and, as a result of which, the actual amount of air becomes too smaller than the target amount of air. That is to say, the feedback control of the recirculation amount of exhaust gas function to reduce the recirculation amount of exhaust gas so as to increase the actual amount of air, and the exhaust gas recirculation finally comes to a standstill. The present invention has its object to provide an exhaust gas recirculation system for an engine which feedback controls a recirculation amount of exhaust gas so as to bring an amount of air that is actually introduced to a target amount of air with a certain effect of reflecting an increase in the recirculation amount of exhaust gas.
SUMMARY OF THE INVENTION
The foregoing object of the present invention is accomplished by an exhaust gas recirculation control system of a type having an intake air throttle valve between an air flow sensor operative to detect an actual amount of air introduced into an intake air passage and an exhaust gas inlet port of the intake air passage through which exhaust gas is admitted into an intake air stream for feedback controlling a recirculation amount of exhaust gas so as to bring an actual amount of intake air to a target amount of air, the exhaust gas recirculation system being characterized by changing an operated condition of the intake air throttle valve when an engine operating condition falls in an engine operating region specified for implementation of feedback control of the recirculation amount of exhaust gas, and changing the target amount of air according to the operated condition of the intake air throttle valve. The target amount of air is determined to be small for a smaller valve lift of the intake air throttle valve as compared with a larger valve lift of the intake air throttle valve.
The valve lift of the intake air throttle valve is reduced in a specified engine operating region for an increase in exhaust gas recirculation amount, which may be predetermined for lower engine speeds or lower engine loads, or otherwise both lower engine speeds and lower engine loads. Further, the target amount of air may be reduced by an amount of air that occurs due to a reduction in valve lift of the intake air throttle valve.
According to the exhaust gas recirculation of the present invention, an amount of air that is actually introduced reliably reaches a target amount of air during the feedback control of the recirculation amount of exhaust gas by changing the target amount of air according to a valve lift of the intake air throttle valve that has a strong effect on the actual amount of air, so as to provide an effect of reflecting an increase in the recirculation amount of exhaust gas by controlling the intake air throttle valve. This effect is more reliably secured by making the target amount of air small for a smaller valve lift of the intake air throttle valve as compared with a larger valve lift of the intake air throttle valve.
An increase in the recirculation amount of exhaust gas is made certain by reducing a valve lift of the intake air throttle valve in a specified engine operating region where an increase in exhaust gas recirculation amount is intended, specifically in a region for lower engine speeds or lower engine loads, or for both lower engine speeds and lower engine loads where there is a strong demand for lowering a level of NOx emissions.
Reducing the target amount of air by an amount of air that occurs due to a reduction in valve lift of the intake air throttle valve is desirable in the viewpoint of making a reduction in the target amount of air as small as possible, which is always desirable for an increase in air utilization factor for combustion.
REFERENCES:
patent: 4763264 (1988-08-01), Okuno et al.
patent: 6016788 (2000-01-01), Kibe et al.
patent: 6039025 (2000-03-01), Iwano et al.
patent: 6079387 (2000-06-01), Mamiya et al.
patent: 08193534 (1996-07-01), None
patent: 10-184408-A (1998-07-01), None
patent: 10-339191-A (1998-12-01), None
patent: 11-351068-A (1999-12-01), None
Matsuo Yuji
Wakutani Shinichi
Brooks & Kushman P.C.
Mazda Motor Corporation
Wolfe Willis R.
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