Patent GB-1434309-A (GB)
Title: Systems for controlling the ignition timing of internal combustion engines
IPC: F02P5/15
Filed: 1973-06-08
Abstract: 1434309 Ignition systems; timing ignition ROBERT BOSCH GmbH 8 June 1973 [10 June 1972] 27372/73 Heading F1B A system for controlling the ignition timing of an ignition system for a single or multi-cylinder internal combustion engine comprises a tachogenerator 10 for providing at least one pulse output signal per revolution of the crank-shaft of the engine, a generator responsive to output signals from the tachogenerator and comprising a binary counter 15 and a digital-analogue converter 17 for supplying a signal proportional to the angle of rotation of the crank-shaft from a predetermined angular position, a signal source responsive to at least one parameter available for influencing the ignition timing and a comparator 21 responsive to the signals from the generator and from the source and connected to a switching amplifier 24 for releasing ignition processes. The tachogenerator 10 supplies at least one starting pulse per revolution of the crank-shaft of the internalcombustion engine which marks a specific angular position of the crank-shaft. By means of this pulse the bi-stable circuit 12 is triggered into a starting state as a result of which via the OR gate 13 and the reset input 151 the counting process of the binary counter 15 is released. The starting pulse may occur for example 60 degrees before the top dead centre of a piston. The tachogenerator 10 also provides at its output 109 a considerable number of counting pulses for example one counting pulse per degree of revolution of the crank-shaft. These counting pulses are transmitted to a binary counter 15 where they are counted. The digital counter reading of the binary counter 15 is converted in the digital-analogue converter 17 into an angle proportional voltage which is applied to the input of the comparator 21. To the other comparator input which is connected to the summer 35 there is applied a voltage which is according to a desired adjustment of the ignition timing. When the voltages on the inputs of the comparator 21 are equal the latter provides an output signal in response to which the bi-stable trigger circuit 23 is changed over. This operates the ignition switching amplifier 24 and results in an ignition spark. The output signal occurring at the output of the bi-stable circuit 23 is converted in the differentiator 26 to a momentary pulse which is passed to the OR gate 13 and thereby to the reset input 151 of the binary counter 15 as a result of which the latter is momentarily set to zero. The binary counter 15 again counts the counting pulses received from the tachogenerator 10. The new counting process is evaluated by the decoder 19 so that when a predetermined count is reached the bi-stable circuit 23 is reset by an output signal of the decoder 19. The output signal of the bi-stable circuit 23 is converted in the differentiator 26 to a pulse which resets the bi-stable circuit 12 which then in the reset condition resets the binary counter 15 and retains it in its zero condition until a new starting pulse again triggers the bi-stable circuit 12. On the supply side of the summer 35 are a speed voltage transducer 27  and a first function generator 29 and for example a pressure voltage transducer serving as a load voltage transducer 31 and a second function generator 34. The pressure voltage transducer 31 may be responsive to the vacuum in the induction manifold of the engine. Signals responsive to other parameters can be fed to the summer 35 via further function generators. In a modification the voltage dependent upon the load may be derived for example in connection with electronic fuel injection systems from injection pulses the lengths of which represent measures of the loading of the engine. In another modification a current comparator is employed in place of the voltage comparator 21. It is stated that a signal proportional to the load can be derived from the air-flow to the engine. The tachogenerator 10 may operate electro-dynamically, photoelectrically or by magnetic induction.