Internal-combustion engines – Charge forming device – Exhaust gas used with the combustible mixture
Reexamination Certificate
1999-10-13
2001-04-24
Wolfe, Willis R. (Department: 3747)
Internal-combustion engines
Charge forming device
Exhaust gas used with the combustible mixture
C123S568210
Reexamination Certificate
active
06220233
ABSTRACT:
TECHNICAL FIELD
The present invention relates to internal combustion engines, and, more particularly, to exhaust gas recirculation systems in such engines.
BACKGROUND ART
An exhaust gas recirculation (EGR) system is used for controlling the generation of undesirable pollutant gases and particulate matter in the operation of internal combustion engines. Such systems have proven particularly useful in internal combustion engines used in motor vehicles such as passenger cars, light duty trucks, and other on-road motor equipment. EGR systems primarily recirculate the exhaust gas by-products into the intake air supply of the internal combustion engine. The exhaust gas which is reintroduced to the engine cylinder reduces the concentration of oxygen therein, which in turn lowers the maximum combustion temperature within the cylinder and slows the chemical reaction of the combustion process, decreasing the formation of nitrous oxides (NOx). Furthermore, the exhaust gases typically contain unburned hydrocarbons which are burned on reintroduction into the engine cylinder, which further reduces the emission of exhaust gas by-products which would be emitted as undesirable pollutants from the internal combustion engine.
When utilizing EGR in a turbocharged diesel engine, the exhaust gas to be recirculated is preferably removed upstream of the exhaust gas driven turbine associated with the turbocharger. In many EGR applications, the exhaust gas is diverted directly from the exhaust manifold. Likewise, the recirculated exhaust gas is preferably introduced to the intake air stream downstream of the compressor and air-to-air after cooler (ATAAC). Introducing the exhaust gas downstream of the compressor and ATAAC is preferred due to the reliability and maintainability concerns that arise if the exhaust gas passes through the compressor is and ATAAC. An example of such an EGR system is disclosed in U.S. Pat. No. 5,802,846 (Bailey) issued on Sep. 8, 1998, which is assigned to the assignee of the present invention.
With conventional EGR systems as described above, the exhaust gas may be drawn from only a subset of the combustion cylinders within the engine, and driven back into the intake manifold. For example, the exhaust gas may be drawn from only a single cylinder of a multi-cylinder engine. In the case of a six cylinder engine, such a single cylinder EGR system would provide one-sixth of the available exhaust gases to the intake manifold, thereby providing an EGR rate of approximately 17 percent. Such an EGR rate, however, is too high under certain operating conditions, such as when the engine is operating under a peak torque condition.
Also, it is known to control the operation of the EGR valve of such conventional EGR systems by using a negative pressure source, such as an intake manifold, to sense low load conditions. However, operation of the EGR valve based on pressure changes can be adversely affected by leaks in the negative pressure source, and leaks or blockages in the control line coupling the EGR valve to the negative pressure source.
The present invention is directed to overcoming one or more of the problems as set forth above.
DISCLOSURE OF THE INVENTION
In one aspect of the invention, an internal combustion engine comprises a block defining a plurality of combustion cylinders, each combustion cylinder of the plurality of combustion cylinders having a displacement volume. An intake manifold provides combustion air to each combustion cylinder. An exhaust manifold includes cylinder ports fluidly connected to each combustion cylinder for selectively transporting exhaust gas therefrom through at least one of a primary exhaust outlet and a secondary exhaust outlet. An exhaust gas recirculation valve is fluidly connected between the intake manifold and the secondary exhaust outlet, and wherein the exhaust gas recirculation valve is controllably positioned in one of a first position and a second position. When the exhaust gas recirculation valve is in the first position the exhaust gas from each combustion cylinder is transported through the primary exhaust outlet, and when the exhaust gas recirculation valve is in the second position an exhaust gas flow from at least one of the plurality of combustion cylinders is transported through the secondary exhaust outlet. An actuator communicates with the exhaust gas recirculation valve for effecting a position change of the exhaust gas recirculation valve. A controller is coupled to the actuator to control a timing of movement of the exhaust gas recirculation valve between the first position and the second position based on at least one cyclical engine operation characteristic.
Another aspect of the invention is an exhaust gas recirculation system for an internal combustion engine. The internal combustion engine has a crankshaft, a block defining a plurality of combustion cylinders, a cylinder head having an exhaust valve, an intake manifold for providing combustion air to each cylinder of the plurality of combustion cylinders, and an exhaust manifold having cylinder ports fluidly connected to each cylinder for selectively transporting exhaust gas therefrom through at least one of a primary exhaust outlet and a secondary exhaust outlet.
The exhaust gas recirculation system comprises an exhaust gas recirculation valve adapted for coupling to the intake manifold and adapted for connection to the secondary exhaust outlet, the exhaust gas recirculation valve being controllably positioned in one of a first position and a second position, wherein when the exhaust gas recirculation valve is in the first position the exhaust gas from each cylinder is transported through the primary exhaust outlet, and when the exhaust recirculation valve is in the second position an exhaust gas flow from at least one of the plurality of combustion cylinders is transported through the secondary exhaust outlet. Also, the exhaust gas recirculation system comprises an actuator in communication with the exhaust gas recirculation valve for effecting a position change of the exhaust gas recirculation valve and a controller coupled to the actuator to control a timing of movement of the exhaust gas recirculation valve between the first position and the second position based on at least one cyclical engine operation characteristic of the internal combustion engine.
In still another aspect of the invention, a is method of recirculating exhaust gas in an internal combustion engine comprises the steps of providing a plurality of combustion cylinders having a displacement volume; providing an intake manifold for providing combustion air to each combustion cylinder; providing an exhaust manifold having cylinder ports fluidly connected to each combustion cylinder for selectively transporting exhaust gas therefrom through at least one of a primary exhaust outlet and a secondary exhaust outlet; providing an exhaust gas recirculation valve fluidly connected between the intake manifold and the secondary exhaust outlet; and controlling a timing of movement of the exhaust gas recirculation valve between a first position and a second position based on at least one cyclical engine operation characteristic, wherein when the exhaust gas recirculation valve is in the first position the exhaust gas from each combustion cylinder is transported through the primary exhaust outlet, and when the exhaust gas recirculation valve is in the second position an exhaust gas flow from at least one of the plurality of combustion cylinders is transported through the secondary exhaust outlet.
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patent:
Caterpillar Inc.
Taylor Todd T.
Wolfe Willis R.
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