Power plants – Fluid motor means driven by waste heat or by exhaust energy... – With supercharging means for engine
Reexamination Certificate
2000-09-15
2001-04-17
Wolfe, Willis R. (Department: 3747)
Power plants
Fluid motor means driven by waste heat or by exhaust energy...
With supercharging means for engine
C123S568120, C123S568210
Reexamination Certificate
active
06216461
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to internal combustion engines and more particularly relates to an exhaust gas recirculation system for an internal combustion engine having a charged intake.
BACKGROUND OF THE INVENTION
In internal combustion engines, a process known as exhaust gas recirculation (“EGR”) is used to reduce NO
x
emissions. In general, EGR involves routing a portion of exhaust gas back into the intake air flow. In an engine wherein exhaust backpressure is greater than the intake air pressure (e.g., most normally aspirated engines) an EGR flow can be realized simply by connecting a conduit between the exhaust and the intake ducts. Because of the negative pressure differential, the flow from the exhaust manifold is drawn to the lower pressure of the intake. However, in an engine having a charged intake, an unfavorable pressure differential must be overcome.
More particularly, in turbocharged diesel engines, the recirculated exhaust gas flow is typically introduced into the intake downstream of turbo-compressor and intercooler components in order to avoid degradation of these components. Unfortunately, the intake air is pressurized at this location, presenting an unfavorable intake-to-exhaust manifold pressure.ratio for transporting EGR gases. Diesel engines with efficient, well-matched turbochargers have an insufficient exhaust-to-intake manifold pressure differential during virtually all operating states to induce useful amounts of EGR.
Various EGR systems are known which attempt to overcome this unfavorable pressure differential. One known system provides a pump or compressor that creates a pressure differential sufficient to force the desired exhaust-to-intake flow from the exhaust stack into the intake manifold. However, this requires a significant amount of energy to pump the exhaust from a low or near-zero gauge pressure up to more than the intake manifold pressure. As a result, these known devices tend to substantially sacrifice fuel economy.
An EGR system for a turbocharged engine is disclosed in U.S. Pat. No. 5,564,275 in which exhaust gas flow is drawn from upstream of the exhaust turbine and pumped to the intake by a separate EGR turbocompressor that is driven by a separate branch of the exhaust. A rate of EGR flow is adjustable by a control valve located in that exhaust flow branch driving the EGR turbine. This exhaust-driven type of EGR compressor system can have a response lag from spooling the EGR turbocompressor. Moreover, such a system produces an EGR flow which is limited in capacity, because its pumping capacity is directly dependent on the engine exhaust flow rate.
A need exists for an EGR system which is fuel efficient and which is capable of producing a desired amount of EGR flow on demand.
SUMMARY OF THE INVENTION
The present invention overcomes the problems with the prior art by providing an improved exhaust gas recirculation delivery and control system using a dedicated full authority EGR compressor which is positively driven in an independently controllable manner. The EGR compressor is driven by an independent EGR drive which is controllable to provide a desired output on demand and not limited by an operating condition of the engine, such as exhaust flow rate. This provides greater control and versatility over prior art EGR systems which do not provide independent control of the EGR drive, such as a turbine-powered EGR compressor whose output is directly dependent on the exhaust pressure and flow rate of the engine. This independence of EGR flow rate from engine pressure differential makes the present invention most desirable from an economy point of view.
Specifically, the invention provides a system for use in a diesel engine to draw exhaust gas from upstream of a turbine and pass it through an EGR cooler to lower the gas temperature. The cooled EGR gas is then compressed by a dedicated EGR compressor which delivers it into the fresh, compressed aftercooled intake air stream between an intercooler and an intake manifold. The system of the invention draws exhaust gas from the exhaust manifold instead of the lower-pressure exhaust gas downstream of the exhaust turbine, thereby dramatically reducing an amount of pumping energy needed to deliver the EGR flow. According to the invention, the EGR compressor is driven by a dedicated drive such as an electric motor, hydraulic motor, pneumatic motor, or a variable-ratio coupling between the engine crankshaft and the EGR compressor via a variably controllable transmission means.
The EGR flow rate output of the EGR compressor, and hence a desired intake charge composition, is controlled by a corresponding controller which modulates power delivery to the EGR compressor. For example, in various embodiments of the invention, the controller modulates (1) the voltage delivered to the electric motor EGR drive, (2) air supply to the pneumatic motor EGR drive, (3) hydraulic fluid flow to the hydraulic motor EGR drive, or (4) a variable coupling means varying the transmission of mechanical rotational force from the crankshaft to the EGR compressor. Modulating the drive energy delivery to the EGR compressor drive allows the system to provide full authority control or metering of EGR flow. Moreover, the system can provide a desired amount of EGR flow on demand because the EGR compressor is independently powered and controlled. The EGR drive according to the invention is advantageously not limited in driving capacity by engine operating states, unlike prior art turbine-powered EGR drives which are dependent on exhaust pressure and flow rate.
In order to optimize transient torque response or in engine operating conditions where EGR is unnecessary or may adversely effect the engine system, the EGR delivery system includes a shut-off valve operable to turn off flow through the EGR duct.
An advantage of the present invention is that it provides an EGR system which is economical and versatile. Another advantage of the invention is that it is fuel efficient. A further advantage of the present invention is that it provides an improved system for reducing NO
x
emission output, which is regulated in most parts of the world. Furthermore, the EGR system of the invention eliminates the need for a second EGR cooler to transfer away heat from compression, had the EGR been drawn from downstream of the exhaust turbine.
Additional features and advantages of the present invention are described in, and will be apparent from, the disclosure, drawings, and claims.
REFERENCES:
patent: 4373498 (1983-02-01), Ushimura
patent: 5657630 (1997-08-01), Kjemtrup et al.
patent: 5771868 (1998-06-01), Khair
patent: 5791146 (1998-08-01), Dungner
patent: 5794445 (1998-08-01), Dungner
patent: 5937650 (1999-08-01), Arnold
patent: 5937651 (1999-08-01), Braun et al.
patent: 5-71426 (1993-03-01), None
Charlton Stephen J.
Hwang Long Kung
Miller Paul R.
Shao Josh S.
Cummins Engine Company, Inc.
Leydig , Voit & Mayer, Ltd.
Wolfe Willis R.
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