Power plants – Fluid motor means driven by waste heat or by exhaust energy... – With supercharging means for engine
Reexamination Certificate
2000-12-07
2001-11-27
Nguyen, Hoang (Department: 3748)
Power plants
Fluid motor means driven by waste heat or by exhaust energy...
With supercharging means for engine
C060S611000
Reexamination Certificate
active
06321536
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates generally to internal combustion engines and, more particularly, to a pneumatic throttle system for the maintaining sufficient engine exhaust gas pressure to maintain flow of exhaust gasses through an EGR emission control system.
BACKGROUND OF THE INVENTION
Internal combustion engines produce exhaust gasses containing by-products of inefficient or incomplete combustion. Among these by-products are such pollutants as carbon monoxide, nitrous oxides, and a variety of hydrocarbons. Even diesel engines, which use a higher air-to-fuel ratio than do gasoline (Otto cycle) engines, produce excessive nitrous oxides along with hydrocarbons and carbon monoxide. These combustion by-products are undesirable because they are both harmful to the environment and wasteful.
Carbon monoxide is a known greenhouse gas and is also toxic in large quantities, since it is preferentially absorbed over oxygen in red blood cells. Some nitrous oxides are also toxic, and contribute to acid rain. And among the plethora of hydrocarbons produced by inefficient combustion are carcinogenic benzpyrene and nitroaromates. Inefficient combustion is also wasteful insofar as the carbon monoxides, nitrous oxides, and hydrocarbons may yet be further oxidized to release potential chemical energy stored within.
One known method of removing the by-products of inefficient combustion is to pass the exhaust stream through an exhaust gas recirculation (EGR) system, as illustrated schematically in FIG.
1
. In general, EGR systems
10
direct a portion of the gas exiting an engine exhaust manifold
12
back into the engine intake manifold
14
, such that the recirculated exhaust gas may participate in the combustion process a second time. At least some of the by-products of inefficient combustion present in the recirculated exhaust gas are completely oxidized as they once again pass through the engine
16
and are exposed to the combustion process ongoing therein. While this method is efficient in reducing the level of inefficient combustion by-products (especially nitrous oxides and carbon monoxide) ultimately emitted by the engine
16
, the exhaust gasses must first be cooled before being reintroduced into the engine
16
in order to control the combustion process. Cooling is accomplished by routing the hot exhaust gasses through a cooling chamber
18
. One requirement of any EGR system
10
is that the pressure of the gasses exiting the engine exhaust manifold
12
be greater than the pressure of the gasses entering the engine air intake manifold
14
so that the exhaust gasses will flow into the intake manifold
14
. Compressor
20
and turbine
22
sizes and efficiencies determine this manifold pressure gradient in the absence of a pressure assist device. Without a pressure assist device to maintain the exhaust gas at a pressure greater than the intake manifold pressure, the EGR system
10
will not function under all engine conditions (such as when torque is relatively high and revolutions are relatively low—see FIG.
2
). Electronic throttle systems for maintaining an elevated exhaust gas back-pressure are known in the art. One such system is described in U.S. Pat. No. 5,806,308 to Khair, et al., EXHAUST GAS RECIRCULATION SYSTEM FOR SIMULTANEOUSLY REDUCING NO
X
AND PARTICULATE MATTER. These systems include electromechanically actuates throttle mechanisms. The electromechanical throttle mechanism requires microprocessors for performing the control functions. These devices also require gas pressure sensors (such as a differential pressure sensor or a mass flow transducer) for measuring the exhaust gas flow rate or pressure. The exhaust gas data is transmitted to the microprocessor, which calculates the current exhaust gas pressure, compares the calculated exhaust gas pressure to the desired exhaust gas pressure, and actuates throttling to approach the desired exhaust gas pressure. One disadvantage of systems of this type is the requirement of a plethora of electrical devices, such as the electromechanical throttle, microprocessor, and sensor. In addition to adding bulk and expense, such a system is vulnerable to the degradation or failure of any one of a number of electrical connections. Further, the increased complexity of the system increases the time and expense of repairs when a problem develops.
There is therefore a need for a cheap and reliable system for controlling exhaust gas pressure such that exhaust gas pressure is substantially always maintained at a desired level. The present invention is directed towards meeting this need.
SUMMARY OF THE INVENTION
The present invention relates to a pneumatic throttle system for the maintaining sufficient engine exhaust gas pressure to maintain flow of exhaust gasses through an EGR emission control system. The throttle system includes a throttle plate positioned to selectively restrict the flow of exhaust gasses exiting the engine. The throttle plate is operationally connected to a pneumatic piston assembly such that movement of the piston operates to control the throttle plate. The piston assembly includes a piston movably mounted within a chamber. The piston head functionally divides the chamber into two portions of variable volume. A first portion of the chamber is pneumatically connected to the engine intake manifold, while a second portion of the chamber is pneumatically connected to the engine exhaust manifold. The position of the piston in the chamber (and, therefore, the degree to which the throttle plate restricts exhaust gas flow from the engine) is determined by the relative intake and exhaust gas pressures. If the intake manifold pressure increases such that it is greater than the exhaust manifold pressure, the piston is displaced to allow the volume of the first portion to increase at the expense of the volume of the second portion. This displacement of the piston also operates to move the throttle plate to further restrict the flow of the exhaust gasses from the engine, thereby increasing the exhaust gas back-pressure.
Careful selection of the parameters of the system (i.e., the dimensions of the gas conduits, the dimensions of the chamber and piston, the mass of the piston, the size of the throttle plate, the dimensions and calibration of the members connecting the piston and the throttle plate, etc. . . . ) allow for precise control of the exhaust gas pressure range. If an EGR system is connected to the engine, the pneumatic throttle system may be calibrated to ensure proper exhaust gas flow through the EGR system over the widest possible range of engine operating conditions.
One object of the present invention is to provide an improved pneumatic throttle for maintaining the exhaust gas of an internal combustion engine system at a pressure greater than that of the intake manifold. Related objects and advantages of the present invention will be apparent from the following description.
REFERENCES:
patent: 4083188 (1978-04-01), Kumm
patent: 4349004 (1982-09-01), Matsuda
patent: 4350013 (1982-09-01), Yoshiba
patent: 4484445 (1984-11-01), Gillbrand
patent: 4669442 (1987-06-01), Nakamura et al.
patent: 5440800 (1995-08-01), Ceynow et al.
patent: 5806308 (1998-09-01), Khair et al.
patent: 26 20 594 (1976-05-01), None
patent: 32 18 156-A (1982-05-01), None
patent: 0 531 277 (1992-08-01), None
patent: 54-148927 (1979-11-01), None
Henderson Gregory H.
Henry Scott A.
Cummins Engine Company, Inc.
Nguyen Hoang
Woodard Emhardt Naughton Moriarty & McNett
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