GB1374440A - System for measuring the rotational speed of an internal combustion engine and the cam and ignition angle thereof - Google Patents

Abstract

1374440 Measuring ignition timing of I C engines SAAB-SCANIA AB 17 Dec 1971 [23 Dec 1970] 58720/71 Heading G1N [Also in Division G4] The engine speed, ignition angle and cam angle of an internal combustion engine are measured digitally by applying pulses to associated counters 30, Fig. 1, under the control of transducers sensing conditions in the engine. The engine speed is measured by counting a predetermined number of pulses for each rotation of a drive wheel 3 connected to the crank-shaft. This is effected by setting a bi-stable 45 whenever a recess 4 corresponding to the top dead centre position of the piston is sensed by a magnetic transducer 5 to allow pulses to pass from oscillator 27 via gate 24 to a counter 30 until a predetermined number of oscillator pulses have been passed when the output of a counter 38 also receiving the pulses resets the bi-stable. At the end of a predetermined time interval a memory 31 is strobed to read in the count which is decoded and displayed on Nixie tubes, the counter 30 being subsequently reset. The cam angle, which represents the time when cut-out contacts 19, 20 are closed so that a high voltage current can be induced in the ignition coil 21 of the engine, is measured by enabling a gate 26 whilst the contacts are closed to supply pulses from oscillator 29 to the counter 30 which is similarly read out for decoding and display at the end of the time interval. The ignition angle which is the angle between the top dead centre position of the piston and the angle at which the contacts 19, 20 are closed is measured by setting a bi-stable 39 when the contacts close to pass pulses from an oscillator 28 via gate 25 to a third counter 30, the bi-stable being reset by the output of transducer 5 sensing the recess 4. The counter 30 is similarly read out and displayed. This measures advanced ignition. A sensing circuit may be included between the bistable 39 and gate 25 so that if retarded ignition is sensed the gate is enabled by the top dead centre position pulse and closed by the ignition pulse, a lamp being additionally lit. The frequency of the pulses from the oscillator 28 is divided by an amount dependent on the engine speed In a modification Fig. 3 (not shown), pulses are fed via gate 25 to the counter 30 between the ignition pulse and the top dead centre position pulse but the transfer is effected to the memory at a time determined by the transducer sensing the top dead centre position. Simultaneously pulses from the oscillator 28 after division by 360 are counted in a further counter which is read out after the same time interval to a memory. The ignition angle is then obtained by dividing the contents of the memory and decoding and displaying the quotients so found. Modification: The ignition pulse may be inductively sensed and the top dead centre position optically sensed by reading a reflective mark.