Electricity: measuring and testing – Electrical speed measuring – Including speed-related frequency generator
Reissue Patent
2001-05-29
2003-04-29
Patidar, Jay (Department: 2862)
Electricity: measuring and testing
Electrical speed measuring
Including speed-related frequency generator
C324S161000, C073S116070, C073S117020
Reissue Patent
active
RE038100
ABSTRACT:
BACKGROUND OF THE INVENTION
An alternator which charges the battery in a vehicle causes a ripple to be superimposed on the DC battery voltage, the frequency of which ripple is related to the engine speed. There are prior-art tachometers that calculate engine speed by measuring the frequency of the ripple. To convert ripple frequency to RPM requires knowledge of the relationship between such frequency and the rotational speed of mechanical parts of the engine. For example, it is known that the alternator speed is approximately one to three times the speed of the crank shaft. However, to obtain precise RPM readings the exact relationship in a particular vehicle must be determined. Prior-art approaches to calibration have not been sufficiently accurate.
Also known are tachometers that calculate RPM based on mechanical oscillations in the engine. For example, it is known to measure the frequency of the exhaust. As each cylinder fires, a pulse is produced in the exhaust. Measurement of the frequency of these pulses yields information on the engine speed. In such a tachometer, a microphone is placed near the exhaust pipe. The microphone picks up the exhaust sounds and the tachometer uses the frequency of those sounds to calculate RPM. A second type of mechanical oscillation is vibration of the engine. An accelerometer is placed near or on the engine to measure the frequency of such vibration, which frequency is related to engine speed.
At low engine speed, true RPM is very accurately related to the frequency of mechanical oscillations. But, the higher the engine speed, the lower the accuracy.
It has become important to provide virtually instantaneous measurement of the engine speed. This is because government specifications in various countries require measurement of certain parameters as a function of engine speed. For example, in Germany, there are specifications for the opacity of engine emissions in the range of 1,000 RPM to 10,000 RPM. Currently available tachometers do not have the capability of instantaneously keeping track of such extreme variations in engine speed.
SUMMARY OF THE INVENTION
It is, therefore, an important object of the present invention to provide a tachometer which accurately displays engine speed even though it is changing very rapidly.
Another object is to provide a tachometer that calculates engine speed based on the ripple in the vehicle's electrical system, and uses mechanical oscillation of the engine for calibration.
Another object is to provide a tachometer that calculates engine speed based on the ripple in the vehicle's electrical system, and uses exhaust sound frequency of the engine for calibration.
In summary, there is provided a tachometer for determining the speed of the engine in a vehicle that includes a battery-operated electrical system which produces a DC voltage having a ripple thereon, the engine producing mechanical oscillations during operation, the tachometer comprising first means for coupling to the electrical system for providing first signals representative of the frequency of the ripple, second means for coupling to the engine for providing second signals representative of the frequency of the mechanical oscillations, third means coupled to the first and second means for calculating a constant representing the relationship of the frequencies of the first and second signals and for responding to the first signals and the constant to provide third electrical signals corresponding to the speed of the engine.
The invention consists of certain novel features and a combination of parts hereinafter fully described, illustrated in the accompanying drawings, and particularly pointed out in the appended claims, it being understood that various changes in the details may be made without departing from the spirit, or sacrificing any of the advantages of the present invention.
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Pohl Olaf
Rentsch Wolfgang
Patidar Jay
Shaw Seyfarth
Sun Electric Deutschland GmbH
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