Browse Prior Art Database

HIGH RESOLUTION, DUAL TIMEBASE SPARK FUNCTION

IP.com Disclosure Number: IPCOM000009406D
Original Publication Date: 1999-Jun-01
Included in the Prior Art Database: 2002-Aug-21
Document File: 3 page(s) / 130K

Publishing Venue

Motorola

Related People

Richard Soja: AUTHOR

Abstract

This invention permits high resolution place- ment of angle based events which are synchronized to a rotating body such as an automobile engine crankshaft. The occurence of the event could result in the generation of an output pulse to control the timing of spark in the combustion cycle of the engine. Alternatively an event could initiate the reading of an analog value such as engine load or knock detection, or generate a pulse to control fuel delivery to the engine.

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Developments Technical 0 M MOTOROLA

HIGH RESOLUTION, DUAL TIMEBASE SPARK FUNCTION

by Richard Soja

  This invention permits high resolution place- ment of angle based events which are synchronized to a rotating body such as an automobile engine crankshaft. The occurence of the event could result in the generation of an output pulse to control the timing of spark in the combustion cycle of the engine. Alternatively an event could initiate the reading of an analog value such as engine load or knock detection, or generate a pulse to control fuel delivery to the engine.

  An automobile engine has to operate over a wide range of engine speeds, typically from approx- imately 2Orpm to SOOOrpm. In addition, the pulses which control spark and fuel are often required to be delivered with a resolution approaching 0.1 degree.

  Pulses are usually repeated every crankshaft revolution or engine cycle. An engine cycle is 2 crankshaft cycles in a 4 stroke engine. This puts a bound on the maximum angular displacement of any pulse or event to 360 degrees or 720 degrees, and the maximum required angular resolution at approx- imately l/7200. This can be accomodated by 13 bits of resolution.

  Because resolution is given in terms of degrees, the corresponding time resolution required to achieve 0.1 degree will vary with engine speed. Figure 1 shows an example of this.

  For example at SOOOrpm, 0.1 degree is equiva- lent to approximately 2 microseconds of time. At SOOrpm, 0.1 degree is equivalent to approximately

20 microseconds of time.

  In most microcontroller applications which con- trol rotating systems, a constant timebase is used to generate angular events. This means that a 2 microsecond timebase would provide 10 times more

resolution man is needed at 8OOrpm. So, to provide high resolution at high speed and operate over the full dynamic range, a fixed timebase system would require at least 21 bit counters, data registers and computation.

  This invention avoids the need for such large data registers and computations by defining a time- base system in which one or other of two timebases is selected depending on the current engine speed. One timebase is clocked at a higher rate than the other. The high rate timebase is used to schedule events and pulses at high engine speeds, while the low rate timebase is used at low speeds.

  The criteria for switching between timebases is the presence or absence of an overflow of the high rate timebase.

  Because events in an automobile engine control system occur relative to each other, a timebase over- flow can be defined in terms of the duration between two consecutive reads of the timebase. If the timebase can be read within the maxi...