Internal-combustion engines – Charge forming device – Exhaust gas used with the combustible mixture
Reexamination Certificate
2000-08-01
2001-07-03
Wolfe, Willis R. (Department: 3747)
Internal-combustion engines
Charge forming device
Exhaust gas used with the combustible mixture
C123S568290
Reexamination Certificate
active
06253749
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to design and control of a vacuum actuated valve for an internal combustion engine.
BACKGROUND OF THE INVENTION
Vacuum actuated valves have long been used in the automotive industry for controlling the flow of various gasses, including exhaust gas recirculation (EGR). EGR systems use the valves for allowing exhaust gas from the exhaust manifold to flow into the intake manifold. Thus, the exhaust gas is recirculated through the engine. Controlling EGR flowis typically used for meeting regulated emissions and maximizing fuel economy. Poor EGR flow control can have detrimental effects, such as engine misfires, engine speed surging, and lost fuel economy.
In particular, good control at low exhaust gas recirculation flow rates is a challenge because of the relationship between the controllable signal sent to the valve and the actual flow through the valve. In one particular system, a vacuum signal is sent to a vacuum actuated valve. The vacuum actuated valve mechanically converts the vacuum signal to a valve pintle position through a spring and diaphragm assembly. The valve pintle then defines the flow area and thus the flow rate of exhaust gasses through the valve and into the engine. Because the pintle is designed to resist sticking and deposit coating, the flow to position characteristics are such that at low openings, a small change in valve position creates a large change in flow. In addition, at high openings, a large change in valve position creates a small change in flow. These relationships cause a high mechanical gain in the feedback control system at low openings. Further; when high gains are coupled with sensors that have delays, with low vacuum command resolution, or with low vacuum command repeatability, all of which are typical in EGR control systems, the result is poor control.
One method of eliminating the problems of poor control at low opening areas is to calibrate the command so that low EGR flow rates are not commanded. This eliminates the control problem by disallowing operating in a certain flow rate region. Another method of improving control of low flow rates would be to increase vacuum control resolution, vacuum control repeatability and sensor bandwidth. This would allow the control system to more accurately maintain a desired low flow rate despite the high gain between control vacuum and EGR flow rate.
The inventors herein have recognized numerous disadvantages with the above approaches. A disadvantage with removing commands of low flow rates is that this eliminates the benefit for which the EGR system is installed on an engine. In other words, there is both a fuel economy and regulated emission benefit for using low flow rates of EGR in certain engine operation regions. A disadvantage with increasing vacuum control resolution, vacuum control repeatability, or sensor bandwidth is that this generally adds cost and is unacceptable.
SUMMARY OF THE INVENTION
An object of the invention claimed herein is to provide an exhaust gas recirculation system with a generally linear relationship between the controlled input and exhaust gas recirculation flow rate across the entire operating region of the system.
The above object is achieved, and problems of prior approaches overcome, by providing a valve for controlling a flow entering and internal combustion engine. The valve comprises a pintle having one end connected to a diaphragm and another end slidably coupled to a seat valve so that flow through said seat valve is related to position of said pintle, a vacuum chamber operatively connected to said diaphragm to move said pintle away from said seat valve, a vacuum source coupled to said vacuum chamber for providing a vacuum thereto in relation to a signal, and a spring operatively coupled to said diaphragm to move said pintle toward said seat valve, said spring having a spring rate as a function of said pintle position such that a relationship between the flow and said signal is linear.
Using a spring with a certain characteristic relationship between spring rate and valve position counteracts the nonlinear relationship that is encountered between control vacuum and EGR flow rate which otherwise occurs when using a conventional spring. Using the relationship between valve position and EGR flow rate, which is determined analytically or experimentally, the relationship between spring rate and valve position is found such that the overall relationship between control vacuum and EGR flow rate is generally linear.
An advantage of the above aspect of the invention is that the feedback control quality is maintained throughout the entire operating region of EGR flow rates.
Another advantage of the above aspect of the invention is that the consistent feedback control quality yields better fuel economy and driveability.
Yet another advantage of the above aspect of the invention is that the consistent feedback control quality yields lower emissions.
In another aspect of the present invention, the above object is achieved, and problems of prior approaches overcome, by providing an exhaust gas recirculation valve for controlling an exhaust gas recirculation amount entering and internal combustion engine, said valve having a nonlinear flow relationship between a valve flow and a valve position. The valve comprises a housing portion of the valve having a vacuum port adapted to be connected to a vacuum control line, a vacuum chamber within said housing portion communicating with said vacuum port, having a vacuum volume, and having a vacuum pressure, a vent chamber within said housing portion communicating with atmospheric pressure, a flexible diaphragm having a vacuum side and a vent side, said diaphragm separating said vacuum chamber from said vent chamber, a shaft having a vent end and an orifice end, with said vent end connected to said diaphragm on said vent side of said diaphragm, a pintle located on said orifice end of said shaft, with said orifice position defining a flow rate, and a spring located in said vacuum chamber acting to move said diaphragm in such a way as to increase said volume of said vacuum chamber, with said spring contacting said vacuum side of said diaphragm, said spring having a spring rate dependent on said valve position such that a relationship between said vacuum pressure and said flow rate is linear. In a preferred embodiment, a spring with a relatively large spring rate at low positions and a relatively small spring rate at high positions is used.
An advantage of the above aspect of the invention is that a linear relationship between control vacuum and EGR flow rate is provided when the valve position to EGR flow characteristics are such that at low positions, a small change in position creates a large change in flow and at high positions, a large change in position creates a small change in flow.
Other objects, features and advantages of the present invention will be readily appreciated by the reader of this specification.
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Blaha George
Kotwicki Allan Joseph
Russell John David
Ford Global Technologies Inc.
Russell John D.
Wolfe Willis R.
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