Digital dwell circuit

#The present invention is related to the inventions described and claimed in copending U.S. patent application Ser. No. 049,016, filed June 15, 1979 entited "Spark and Dwell Ignition Control System Using Digital Circuitry" by Robert S. Wrathall; and described and claimed in copending U.S. patent application Ser. No. 049,013, filed June 15, 1979 entitled "Dwell Circuitry for an Ignition Control System" by Rupin Javeri. Both of the copending U.S. applications referred to above are assigned to the same assignee as the present invention.

#The present invention relates generally to the field of digital signal processing circuitry, and more particularly to the field of digital electronic dwell circuits used in ignition control systems which control spark and dwell occurrence.

#In internal combustion engines the time occurrence at which a spark is produced to ignite a fuel and air mixture in a cylinder is a primary operational consideration. Similarly, producing an appropriate excitation signal (dwell) for an ignition coil immediately prior to the coil producing spark ignition is also a major design consideration. Mechanical spark control ignition systems have been found not to be reliable over long periods of time thus necessitating frequent readjustment of the mechanical controls. Thus electronic dwell and spark control ignition systems having greater reliability have been developed.

#For a more complete understanding of the invention, reference should be made to the drawings, in which:

#FIG. 1, comprising drawings 1A, 1B and 1C, is a combination block and schematic diagram illustrating an engine ignition control system for an internal combustion engine;

#FIG. 2 is a schematic diagram illustrating a typical configuration for a dwell circuit illustrated in FIG. 1;

#FIG. 1 illustrates an electronic ignition control system 10 for a two cylinder internal combustion engine (not shown). Essentially the control system 10 receives sensor input signals and develops control signals that determine the spark timing and dwell (coil excitation time) for a distributorless inductive ignition system. The term "distributorless" contemplates the fact that no rotating mechanical distributor will be utilized, and that instead sparks will be created in each of the two cylinders simultaneously but at different times with respect to the compression cycle of each cylinder. In other words, when a spark is generated for cylinder 1 at the proper time of its compression cycle, a spark will also be generated in cylinder 2 but this spark will occur during the exhaust cycle of cylinder two and therefore will not result in igniting a fuel mixture. Distributorless ignition systems are known and do not form an essential part of the present invention.

#The control system 10 illustrated in FIG. 1 will now be described. For a better understanding of FIG. 1, drawings 1A, 1B and 1C should be arranged with drawing 1B located between drawings 1A and 1C.

#The control system 10 includes a rotating cam 11 synchronously rotatable with a crankshaft of a two cylinder engine, the crankshaft being shown schematically as an axis of rotation 12. The cam 11 has a peripheral projection 13 spaced from the axis 12 and the cam 11 is contemplated as rotating in a clockwise direction.