Patent GB-1321990-A (GB)
Title: Engine control systems
IPC: F02D41/24
Filed: 1969-12-31
Abstract: 1321990 Controlling I C engines JOSEPH LUCAS (INDUSTRIES) Ltd 21 Sept 1970 [ 31 Dec 1969 23 Sept 1969] 63410/69 Divided out of 1321989 Heading F1B [Also in Division G4] An engine control system comprises a transducer 8 producing a digital signal representing a first parameter and a transducer 9 for a second parameter also giving a digital signal a coder store to which both signals are fed, the store being arranged to produce a predetermined output code dependent on the values of the two digital signals, control means operated by the output code from the store for controlling a characteristic of the engine, and means to add a cyclic waveform to the first parameter so that the output oscillates between one code and the next to provide an accurate representation of the input parameters. The signals from transducers 8 and 9, both being a combination on three leads, are each recoded at 11 and 12 to mark one of eight lines. The eight row lines 13 are connected by diodes to different combinations of five vertical lines in each of eight groups. One of the groups is selected by the input from decoder 12 and the corresponding pattern of five bits is presented on lines 21. Control circuit 22 responds to this signal to control the supply of fuel to the engine 23. Because of the stepped response of the transducers 8 and 9 the final signal is likely to be an inaccurate representation of the two input parameters. To overcome this a cyclic triangular voltage with no D. C. component is added to the each input of amplitude equal to one step. The marking will therefore repeatedly appear first on one line and then on the adjacent line, spending proportionately more time on the line than the other if the parameter value is nearer one reference value than the next. A similar cyclic voltage may be added to the other parameter signal phase-displaced by 90 degrees. These oscillations are reflected in the output from the coding matrix, the output value changing between two or more values spending an appropriate time in each to represent the exact value of the input parameters. The digital signals may be varied as shown in Fig. 3 in which the analogue parameter signal is applied to resistor 31 and passed via summing amplifier 32 to two threshold circuits 33, 34 responding respectively to positive and negative signals of a predetermined amplitude. The outputs enable gates 35, 36 so that clock pulses from 37 can pass to counter 38 to count up or down respectively. An input signal, if greater than the minimum set by threshold circuit 33, serves to enable gate 35 so that the counter counts up applying a combination of feedback signals to balance the input via transistors 41-43. The cyclic triangular voltage is generated by a Schmitt trigger 44 feeding an integrator 45 which is connected to the input of amplifier 32. In one state of trigger 44 the integrator produces a rising voltage, in the other state a falling voltage resulting in a triangular waveform. The 90 degrees phasedisplaced waveform for the other input is derived by a comparator 47 which compares the first waveform with zero and passes the difference signal to an integrator 48. The matrix of Fig. 1 may be replaced by a series of groups of resistors, each resistor having a switch. The input signal is applied to a switch control circuit which closes the same switch in each group. The output of one of the groups is selected by switches one of which is closed by a circuit controlled by the other input signal. The triangular waveform of one-step amplitude may be replaced by other waveforms.