Internal-combustion engines – Spark ignition timing control – Electronic control
Reexamination Certificate
2000-01-13
2001-08-14
Yuen, Henry C. (Department: 3747)
Internal-combustion engines
Spark ignition timing control
Electronic control
C123S435000, C073S035040
Reexamination Certificate
active
06273064
ABSTRACT:
TECHNICAL FIELD
The invention relates to the control of internal combustion engines for achieving optimum combustion stability.
BACKGROUND OF THE INVENTION
It is known design practice to calculate indicated mean effective pressure (IMEP) for an internal combustion piston engine using measured in-cylinder pressure obtained with an in-cylinder pressure sensor. The sensor provides cylinder pressure data at various crank angles. As described by Haywood in a publication entitled “Internal Combustion Engine Fundamentals” (1988, p.715), IMEP is a measure of the amount of work delivered to the piston during the compression and expansion stroke for each cycle per unit displaced volume. This information is used to establish optimum valve timing, air/fuel ratio, and optimum exhaust gas recirculation to achieve increased fuel economy and reduced emissions. The use of in-cylinder pressure sensors in this way for high volume production applications is costly, however, because the pressure sensors themselves are expensive. Further, locating the sensors in the cylinder is difficult and each cylinder requires its own sensor.
The calculation of indicated mean effective pressure for production engine applications using such pressure sensor data requires engine control microprocessors with substantial processing power and speed. Further, such control methods are characterized by sensor degradation and variability in system components.
BRIEF DESCRIPTION OF THE INVENTION
The invention includes an engine-mounted accelerometer to obtain measured characteristic values for cylinder combustion energy. Other combustion measurements, including mean effective pressure and torque, also can be correlated to the accelerometer output.
A single accelerometer may be used to obtain engine vibration data. The accelerometer is mounted on the exterior of the engine block and measures output from each cylinder. The calculation of indicated mean effective pressure can be performed in real-time by a typical electronic engine control microprocessor. If the engine is equipped with a broad band accelerometer as part of a knock control system, the same accelerometer may be used in practicing the invention. An example of a knock control system using an engine accelerometer of this kind may be seen by referring to U.S. Pat. No. 5,535,722.
The more efficiently the engine converts chemical energy of the fuel, the greater the power that is available at the crankshaft. But increased combustion efficiency with normal combustion also results in more energy being transferred to the engine block in the form of vibrations. There is a distinct and detectable correlation between in-cylinder combustion energy and engine block vibrations sensed by the accelerometer. The engine-mounted accelerometer is able to detect variations in combustion energy and the system of the invention will control that variation to a predetermined level.
Indicated mean effective pressure (IMEP) is one element of the total combustion energy. The other components are the energy absorbed by the mass of the engine in the form of vibrations, etc.
According to one aspect of the invention, the combustion energy information is monitored and a corrective action can be taken in a closed loop fashion if the combustion energy varies more than a predetermined amount. The deviation can be either from a statistical mean, or from recent combustions or from a predetermined value. Corrective action can be achieved by appropriately adjusting air/fuel ratio, spark timing or exhaust gas recirculation.
An engine normally is operated at stoichiometry with the spark timing set at the mean best torque value (MBT). Under certain conditions, however, an engine may be operated purposely under conditions where stability must be compromised. This may occur, for example, when the engine is running with a high spark retard and a lean air/fuel ratio during cold starts. This will quickly bring the catalytic converter of the engine to a desired operating temperature. Deviations from the optimum engine combustion stability may be intentionally incurred also when the engine is operating lean of stoichiometry for fuel economy reasons or when the engine is running with a large percentage of exhaust gas recirculation for purposes of exhaust gas emission reduction. Unlike prior art systems where such control of engine stability is done open loop with results that vary from engine-to-engine, non-standard engine operation can be achieved in a closed loop fashion using the teachings of the invention. This will permit the engine to tolerate a spark retard and a lean air/fuel ratio, for example, without objectionable erratic combustion occurring.
The invention is capable of using the engine vibration data obtained from the engine-mounted accelerometer to keep track of the characteristics of the combustion event and the associated energy level of the combustion and to take corrective action if the variation of the combustion event is greater than a desired amount.
The invention may use a single accelerometer or multiple accelerometers to detect the combustion energy in each cylinder of a multiple cylinder engine. The engine vibration data sensed by an accelerometer is sampled during a defined window in the combustion cycle during which combustion occurs. The window is calculated using camshaft and crankshaft position sensor data. This same data will identify the cylinder where the engine vibrations originate.
The accelerometer data, after being filtered and rectified, is measured (i.e., integrated) to obtain cylinder combustion energy. This computed value can be compared to normal combustion energy values with stable combustion. If the computed value deviates more than a desired amount, the system will appropriately adjust spark timing, air/fuel ratio or exhaust gas recirculation.
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Carlstrom Kevin Ronald
Hahn Stephen L.
Scholl David James
Drouillard Jerome R.
Ford Global Technologies Inc.
Gimie Mahmoud
Yuen Henry C.
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