Internal-combustion engines – Charge forming device – Exhaust gas used with the combustible mixture
Reexamination Certificate
1999-06-07
2001-05-08
Wolfe, Willis R. (Department: 3747)
Internal-combustion engines
Charge forming device
Exhaust gas used with the combustible mixture
C701S108000
Reexamination Certificate
active
06227182
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the improvements of an exhaust gas recirculation control system for an internal combustion engine, particularly to techniques for feedback-controlling an exhaust gas recirculation rate depending upon a flow rate of intake air flowing through an air-intake pipe on diesel engines.
2. Description of the Prior Art
In order to minimize atmospheric pollution, specifically nitrogen oxide (NO
x
) emissions, from automotive vehicles, there have been proposed and developed various automotive tune-up and exhaust-emission control techniques. An exhaust-gas-recirculation control system, often abbreviated to “EGR system”, is used to reduce NO
x
emissions from exhaust gases of the internal combustion engine by way of the fall of combustion temperature, caused by recycling of some of the inert exhaust gas back through an intake manifold. One such EGR system has been disclosed in Japanese Patent Provisional Publication No. 60-230555. On one hand, EGR is useful to decrease the formation of NO
x
. On the other hand, undesiredly excessive EGR deteriorates combustion, thus dropping engine power output, and also reducing driveability of the vehicle. In recent years, it is desirable to achieve high-precision EGR control in due consideration of various factors, namely (i) engine temperature (during cold engine start, during warming-up period, or in the engine warmed-up state), (ii) the reduced effective opening of an EGR control valve occurring owing to lubricating oil (engine oil) or a product of combustion (carbon deposits) adhered to the EGR control valve, (iii) changes in an intake-air flow rate occurring due to changes in air density, arising from changes in environment from low-land driving to high-land driving under constant engine speed and load, and (iv) the delay in boost pressure (often called “turbo-lag”) on turbo-charged engines in a transient state, such as in a transition from normal-straight ahead driving to heavy vehicle acceleration. To avoid the problem of deviation from a desired EGR rate, resulting from changes in the intake-air flow rate occurring due to the drop in air density from low-land driving to high-land driving, Japanese Patent Provisional Publication No. 59-74364 proposes to feedback-control a desired EGR rate on the basis of a detected value of an actual flow rate of intake air flowing through an intake-air pipe of an induction system of a diesel engine.
SUMMARY OF THE INVENTION
In order to achieve the previously-noted high-precision EGR control, it is necessary to correct or compensate for an EGR rate or an EGR amount (an opening of an EGR control valve) depending on various engine operating conditions (engine temperature for example engine coolant temperature, automatic transmission oil temperature, or the like, a fuel-injection timing, atmospheric pressure, and so forth) except engine speed and load, and to execute feed-back correction for the EGR rate depending on changes in an actual intake-air flow rate. Assuming that an EGR rate is corrected depending on engine temperature such as engine coolant temperature, an intake-air flow rate also varies owing to the corrected EGR rate. Therefore, it is necessary to estimate the intake-air flow rate varied, and to correct the EGR rate (or the opening of the EGR control valve) while comparing the estimated intake-air flow rate with an actual intake-air flow rate. According to a typical method for correcting the opening of the EGR control valve, a plurality of characteristic maps each showing the relationship among a basic intake-air flow rate and engine operating conditions such as engine speed and load, for each engine-coolant-temperature dependent EGR-control-valve-opening correction value, must be first prepared. Second, a correction factor for the EGR control valve opening is calculated on the basis of a rate of the basic intake-air flow rate, which is interpolated and corrected by the engine-coolant-temperature dependent EGR-control-valve-opening correction value, to an actual intake-air flow rate (or the actual volume of air flowing into the engine cylinders) actually measured or detected by means of an air flow meter. Third, a desired EGR control valve opening, which is calculated on the basis of engine speed and load, is finally corrected by the calculated correction factor for the EGR control valve, to execute feedback control, so that the opening of the EGR control valve is adjusted toward the finally-corrected desired opening. In the previously-described method for correcting the EGR control valve opening, a plurality of characteristic maps must be prepared for each engine coolant temperature and be stored in memories of an electronic control unit with a microcomputer, since the engine coolant temperature dependent EGR-control-valve-opening correction and the EGR control valve opening correction based on changes in the intake-air flow rate would be made independently of each other. This results in an undesirably large amount of data stored in the memories (containing a fixed-data memory and an operating-data memory). Additionally, there is the problem of more complicated interpolation and arithmetic calculations owing to a plurality of corrections made independently of each other. Furthermore, a plurality of characteristic maps different from each other for every sorts of internal combustion engines must be prepared. This induces the problem of reduced flexibility in different types of internal combustion engine.
Accordingly, it is an object of the invention to provide an exhaust gas recirculation (EGR) control system for internal combustion engines which avoids the aforementioned disadvantages of the prior art.
It is another object of the invention to provide an exhaust gas recirculation control system for internal combustion engines, in which a first EGR-rate correction (or a first EGR-valve-opening correction) and a second EGR-rate feedback correction (or a second EGR-valve-opening feedback-correction) based on the result of comparison between the actual intake-air flow rate and the estimated intake-air flow rate are interrelatively simply made to the desired EGR rate as a series of EGR rate control procedures.
It is a further object of the invention to provide an exhaust gas recirculation control system for internal combustion engines having enhanced flexibility in different types of internal combustion engine, by virtue of simple arithmetic calculations or estimations needed for deriving an intake-air flow rate varied due to a first desired-EGR-rate correction being made to a basic EGR rate (the basic EGR rate being based on a first predetermined engine operating condition indicative parameter including at least one of engine speed and engine load), on the basis of a second predetermined engine operating condition indicative parameter (the engine temperature, the fuel-injection timing, the atmospheric pressure or the like) except the first predetermined engine operating condition indicative parameter, and by virtue of a second desired-EGR-rate correction made in response to the deviation of the estimated intake-air flow rate from an actual intake-air flow rate.
In order to accomplish the aforementioned and other objects of the present invention, an exhaust gas recirculation control system for an internal combustion engine equipped with an exhaust-gas recirculation system that recycles part of inert exhaust gas back through the engine, comprises sensors detecting operating conditions-of the engine, an air-flow meter detecting an actual intake-air flow rate, an exhaust-gas-recirculation passage adapted to connect an exhaust manifold with an intake manifold, an exhaust-gas-recirculation control valve device disposed in the exhaust-gas-recirculation passage for regulating an EGR rate, and a control unit configured to be electronically connected to the sensors and the exhaust-gas-recirculation control valve device for automatically regulating the EGR rate to a final desired EGR rate, the control unit comprising a basic EGR r
Muraki Hirotada
Yonetamari Sadayuki
Foley & Lardner
Nissan Motor Co,. Ltd.
Wolfe Willis R.
LandOfFree
Exhaust gas recirculation control system for internal... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Exhaust gas recirculation control system for internal..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Exhaust gas recirculation control system for internal... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2457686