Spark timing control system for an internal combustion engine

Claim 2

A spark timing system for an internal combustion engine comprising, at least one spark electrode for igniting the combustible mixture of said engine, means responsive to a spark firing control signal for causing spark firing energy to be applied to said spark electrode device, means driven by the crankshaft of said engine for generating a crankshaft position voltage which represents engine crankshaft position, engine speed advance means responsive to engine speed for phase shifting said crankshaft position voltage in the spark advance direction as a function of increasing engine speed, vacuum advance means responsive to engine manifold vacuum for phase shifting said crankshaft position voltage in the spark advance direction with increasing manifold vacuum, said engine speed and vacuum advance means jointly providing continuously variable spark advance functions which under some conditions are more advanced than desirable for certain conditions of engine operation and under all conditions providing the maximum spark advance for said system, spark timing control means for causing firing of said spark electrode device either at substantially the time of occurrence of a predetermined voltage transition of said crankshaft position voltage as determined by said engine speed and vacuum advance means or at either of at least first or second spark retards corresponding respectively to predetermined timing value that are retarded by predetermined crankshaft angles of rotation from the occurrence of said voltage transition, said spark timing control means comprising bidirectional ramp voltage generating means, an electronic spark selection logic network responsive to a binary input voltage having an output coupled to said spark timing control means for determining the spark timing mode of operation, and a plurality of engine condition responsive sensors each sensing a respective engine operating condition and each coupled to the input of said spark selection logic network to provide respective bits of binary input voltage thereto, the bit voltage provided by each sensor being a function of whether a respective engine operating condition is above or below a predetermined magnitude, said spark selection logic network and engine condition responsive sensors being so arranged that the simultaneous occurrence of a first predetermined combination of engine sensor outputs causes said spark timing to be controlled by said crankshaft position voltage, operative during a second combination of sensor outputs to provide said first spark retard and operative during a third combination of engine sensor outputs to cause said second spark retard.

Claim 3

A spark timing control system for an internal combustion engine comprising, a voltage pulse generator driven by the crankshaft of said engine having engine speed and vacuum advance mechanisms responsive respectively to engine speed and manifold vacuum for generating a spark advance control signal related to engine crankshaft position by the advance functions provided respectively by said engine speed and vacuum advance mechanisms, said engine speed and vacuum advance mechanisms operative to provide the maximum spark advance obtainable with said system from an initial spark advance setting, a bidirectional ramp voltage generating means, means for at times causing said ramp voltage generating means to initiate a ramp voltage of one sense substantially at the occurrence of said spark advance control signal, means for terminating said ramp voltage of said one sense and for causing said ramp voltage generating means to initiate a ramp voltage of an opposite sense when said ramp voltage of said one sense reaches a predetermined magnitude, means for generating a spark retard control signal when the ramp voltage of said one sense attains said predetermined magnitude, the time period required for said ramp voltage of said one sense to attain said predetermined magnitude corresponding to an angle of rotation of said engine crankshaft of a predetermined magnitude which does not vary substantially with changes in engine speed, a plurality of engine condition responsive sensors each sensing a respective engine operating condition, each sensor providing a control signal as a function of whether an engine operating condition is above or below a predetermined value, electronic spark timing selector means coupled to said sensors and responsive to a plurality of different combinations of engine operating conditions for providing spark selection signals, means responsive to said spark selection signals for causing the engine spark timing to be controlled by said spark advance control signal when said spark timing selector means has an input representing a first predetermined combination of engine operating conditions, means responsive to said spark selection signals for causing engine spark timing to be controlled by said spark retard control signal to thereby retard spark timing when said selector means has an input representing a second combination of engine operating conditions, and means responsive to a third combination of engine operating conditions for varying the slope of said ramp voltage of said one sense to provide a spark timing value that differs from that provided in response to either said first or second combination of engine operating conditions.

Claim 4

A spark timing control system for an internal combustion engine comprising, a voltage pulse generator driven by the crankshaft of said engine having engine speed and vacuum advance mechanisms responsive respectively to engine speed and manifold vacuum for generating a spark advance control signal related to engine crankshaft position by the advance functions provided respectively by said engine speed and vacuum advance mechanisms, said engine speed and vacuum advance mechanisms operative to provide the maximum spark advance obtainable with said system from an initial spark advance setting, a bidirectional ramp voltage generating means, means for at times causing said ramp voltage generating means to initiate a ramp voltage of one sense substantially at the occurrence of said spark advance control signal, means for terminating said ramp voltage of said one sense and for causing said ramp voltage generating means to initiate a ramp voltage of an opposite sense when said ramp voltage of said one sense reaches a predetermined magnitude, means for generating a spark retard control signal when the ramp voltage of said one sense attains said predetermined magnitude, the time period required for said ramp voltage of said one sense to attain said predetermined magnitude corresponding to an angle of rotation of said engine crankshaft of a predetermined magnitude which does not vary substantially with changes in engine speed, a plurality of engine condition responsive sensors each sensing a respective engine operating condition, each sensor providing a control signal as a function of whether an engine operating condition is above or below a predetermined value, electronic spark timing selector means coupled to said sensors and responsive to a plurality of different combinations of engine operating conditions for providing spark selection signals, means responsive to said spark selection signals for causing the engine spark timing to be controlled by said spark advance control signal when said spark timing selector means has an input representing a first predetermined combination of engine operating conditions, means responsive to said spark selection signals for causing engine spark timing to be controlled by said spark retard control signal to thereby retard spark timing when said selector means has an input representing a second combination of engine operating conditions, and means responsive to a third combination of engine operating conditions for varying the slope of said ramp voltage of said one sense to provide a spark timing value that differs from that provided in response to either said first or second combination of engine operating conditions.

Claim 5

A spark timing control system for an internal combustion engine comprising, a voltage pulse generator driven by the crankshaft of said engine having engine speed and vacuum advance mechanisms responsive respectively to engine speed and manifold vacuum for continuously generating a spark advance control signal related to engine crankshaft position by the advance functions provided respectively by said engine speed and vacuum advance mechanisms, a bidirectional ramp voltage generating means comprising an operational amplifier and a capacitor, said capacitor connected between the output and one input of said operational amplifier, said ramp voltage generating means generating a ramp voltage of one sense when said capacitor is being charged and generating a ramp voltage of an opposite sense when said capacitor is discharging, means for at times causing said ramp voltage generating means to initiate said ramp voltage of one sense substantially at the occurrence of said spark advance control signal, means for terminating said ramp voltage of said one sense and for causing the ramp voltage of said opposite sense to be generated when said ramp voltage of said one sense attains a predetermined magnitude, means for generating a spark retard control signal when said ramp voltage of said one sense reaches said predetermined magnitude, the time period required for said ramp voltage of said one sense to attain said predetermined magnitude from its initiation corresponding to an angle of rotation of said engine crankshaft of a predetermined magnitude which does not vary substantially with changes in engine speed, a plurality of engine condition responsive sensor means each sensing a respective engine operating condition, each sensor means providing signals indicative of whether an engine operating condition is above or below a predetermined value, electronic spark timing selector means coupled to said sensor means and responsive to a plurality of different combinations of engine operating conditions for providing spark selection signals, means responsive to said spark selection signals for causing the engine spark timing to be controlled by said spark advance control signal when said spark timing selector means has an input from said sensor means representing a first predetermined combination of engine operating conditions, means responsive to said spark selection signals for causing engine spark timing to be controlled by said spark retard control signal when said selector means has an input from said sensor means representing a second combination of engine operating conditions, and means for varying the slope of said ramp voltage of said one sense to provide a spark timing value that differs from that provided in response to either of said first or second combination of engine operating conditions when said selector means has an input from said sensor means representing a third combination of engine operating conditions.

Claim 6

A spark timing control system for an internal combustion engine comprising, a voltage pulse generator driven by the crankshaft of said engine having engine speed and vacuum advance mechanisms responsive respectively to engine speed and manifold vacuum for continuously generating a spark advance control signal related to engine crankshaft position by the advance functions provided respectively by said engine speed and vacuum advance mechanisms, a bidirectional ramp voltage generating means comprising an operational amplifier and a capacitor, said capacitor connected between the output and one input of said operational amplifier, said ramp voltage generating means generating a ramp voltage of one sense when said capacitor is being charged and generating a ramp voltage of an opposite sense when said capacitor is discharging, means for at times causing said ramp voltage generating means to initiate said ramp voltage of one sense substantially at the occurrence of said spark advance control signal, means for terminating said ramp voltage of said one sense and for causing the ramp voltage of said opposite sense to be generated when said ramp voltage of said one sense attains a predetermined magnitude, means for generating a spark retard control signal when said ramp voltage of said one sense reaches said predetermined magnitude, the time period required for said ramp voltage of said one sense to attain said predetermined magnitude from its initiation corresponding to an angle of rotation of said engine crankshaft of a predetermined magnitude which does not vary substantially with changes in engine speed, a plurality of engine condition responsive sensor means each sensing a respective engine operating condition, each sensor means providing signals indicative of whether an engine operating condition is above or below a predetermined value, electronic spark timing selector means coupled to said sensor means and responsive to a plurality of different combinations of engine operating conditions for providing spark selection signals, means responsive to said spark selection signals for causing the engine spark timing to be controlled by said spark advance control signal when said spark timing selector means has an input from said sensor means representing a first predetermined combination of engine operating conditions, means responsive to said spark selection signals for causing engine spark timing to be controlled by said spark retard control signal when said selector means has an input from said sensor means representing a second combination of engine operating conditions, and means for varying the slope of said ramp voltage of said one sense to provide a spark timing value that differs from that provided in response to either of said first or second combination of engine operating conditions when said selector means has an input from said sensor means representing a third combination of engine operating conditions.

Claim 7

A spark timing control system for an internal combustion engine comprising, a voltage pulse generator driven by the crankshaft of said engine having engine speed and vacuum advance mechanisms responsive respectively to engine speed and manifold vacuum for generating a spark advance control signal related to engine crankshaft position by the advance functions provided respectively by said engine speed and vacuum advance mechanisms, a bidirectional ramp voltage generating means, means for at times causing said ramp voltage generating means to initiate a ramp voltage of one sense substantially at the occurrence of said spark advance control signal, means for terminating said ramp voltage of said one sense and for causing said ramp voltage generating means to initiate a ramp voltage of an opposite sense when said ramp voltage of said one sense attains a predetermined magnitude, means for generating a spark retard control signal when said ramp voltage of said one sense attains said predetermined magnitude, the time required for said ramp voltage of said one sense to attain said predetermined magnitude from its initiation corresponding to an angle of rotation of said engine crankshaft of a predetermined magnitude which does not vary substantially with changes in engine speed, at least first, second and third switching means responsive respectively to engine speed, engine manifold vacuum and engine temperature, the state of operation each switching means being determined by whether an engine operating condition is above or below a predetermined value, electronic spark timing selector means coupled to said switching means and responsive to a plurality of different combinations of states of operation of said switching means for providing spark selection signals, means responsive to said spark selection signals for causing engine spark timing to be controlled by said spark advance control signal when said spark timing selector means has an input from said switching means representing a first predetermined combination of engine operating conditions, means responsive to said spark selection signals for causing engine spark timing to be controlled by said spark retard control signal when said selector means has an input from said switching means representing a second combination of engine operating conditions, and means for varying the slope of said ramp voltage of said one sense to provide a spark timing value that differs from that provided in response to either said first or second combination of engine operating conditions when said selector means has an input from said switching means representing a third combination of engine operating conditions.

Claim 8

A spark timing control system for an internal combustion engine comprising, a voltage pulse generator driven by the crankshaft of said engine having engine speed and vacuum advance mechanisms responsive respectively to engine speed and manifold vacuum for generating a spark advance control signal related to engine crankshaft position by the advance functions provided respectively by said engine speed and vacuum advance mechanisms, a bidirectional ramp voltage generating means, means for at times causing said ramp voltage generating means to initiate a ramp voltage of one sense substantially at the occurrence of said spark advance control signal, means for terminating said ramp voltage of said one sense and for causing said ramp voltage generating means to initiate a ramp voltage of an opposite sense when said ramp voltage of said one sense attains a predetermined magnitude, means for generating a spark retard control signal when said ramp voltage of said one sense attains said predetermined magnitude, the time required for said ramp voltage of said one sense to attain said predetermined magnitude from its initiation corresponding to an angle of rotation of said engine crankshaft of a predetermined magnitude which does not vary substantially with changes in engine speed, at least first, second and third switching means responsive respectively to engine speed, engine manifold vacuum and engine temperature, the state of operation each switching means being determined by whether an engine operating condition is above or below a predetermined value, electronic spark timing selector means coupled to said switching means and responsive to a plurality of different combinations of states of operation of said switching means for providing spark selection signals, means responsive to said spark selection signals for causing engine spark timing to be controlled by said spark advance control signal when said spark timing selector means has an input from said switching means representing a first predetermined combination of engine operating conditions, means responsive to said spark selection signals for causing engine spark timing to be controlled by said spark retard control signal when said selector means has an input from said switching means representing a second combination of engine operating conditions, and means for varying the slope of said ramp voltage of said one sense to provide a spark timing value that differs from that provided in response to either said first or second combination of engine operating conditions when said selector means has an input from said switching means representing a third combination of engine operating conditions.

Claim 9

A spark timing system for an internal combustion engine comprising, a voltage pulse generator driven by the crankshaft of said engine for generating a crankshaft position voltage which represents engine crankshaft position, centrifugal advance means responsive to engine speed for continuously phase shifting said crankshaft position voltage, vacuum advance means responsive to engine manifold vacuum for continuously phase shifting said crankshaft position voltage, said centrifugal and vacuum advance means providing continuously variable spark advance functions more advanced than desirable for certain conditions of engine operation, spark timing control means for generating a spark timing control signal either at substantially the time of occurrence of a predetermined voltage transition of said crankshaft position voltage as determined by said centrifugal and vacuum advance means or at either of at least first or second spark retards corresponding respectively to predetermined timing values that are retarded by predetermined crankshaft angles of rotation from the occurrence of said voltage transition, said spark timing control means comprising bidirectional ramp voltage generating means, an electronic spark selection logic network having an output coupled to said spark timing control means for determining the spark timing mode of operation, at least first, second, third and fourth switching means responsive respectively to engine speed, engine manifold vacuum, a first engine coolant temperature and a second engine coolant temperature of a higher value coupled to the input of said spark selection network, the state of operation of each switching means being determined by whether a corresponding engine operating condition is above or below a predetermined value, said spark selection logic network and said switching means being so arranged that the simultaneous occurrence of a first predetermined combination of states of operation of said switching means causes said spark timing to be controlled by said crankshaft position voltage, operative during a second combination of states of operation of said switching means to provide said first spark retard and operative during a third combination of states of operation of said switching means to cause said second spark retard.

Claim 10

A spark timing system for an internal combustion engine comprising, a voltage pulse generator driven by the crankshaft of said engine for generating a crankshaft position voltage which represents engine crankshaft position, centrifugal advance means responsive to engine speed for continuously phase shifting said crankshaft position voltage, vacuum advance means responsive to engine manifold vacuum for continuously phase shifting said crankshaft position voltage, said centrifugal and vacuum advance means providing continuously variable spark advance functions more advanced than desirable for certain conditions of engine operation, spark timing control means for generating a spark timing control signal either at substantially the time of occurrence of a predetermined voltage transition of said crankshaft position voltage as determined by said centrifugal and vacuum advance means or at either of at least first or second spark retards corresponding respectively to predetermined timing values that are retarded by predetermined crankshaft angles of rotation from the occurrence of said voltage transition, said spark timing control means comprising bidirectional ramp voltage generating means, an electronic spark selection logic network having an output coupled to said spark timing control means for determining the spark timing mode of operation, at least first, second, third and fourth switching means responsive respectively to engine speed, engine manifold vacuum, a first engine coolant temperature and a second engine coolant temperature of a higher value coupled to the input of said spark selection network, the state of operation of each switching means being determined by whether a corresponding engine operating condition is above or below a predetermined value, said spark selection logic network and said switching means being so arranged that the simultaneous occurrence of a first predetermined combination of states of operation of said switching means causes said spark timing to be controlled by said crankshaft position voltage, operative during a second combination of states of operation of said switching means to provide said first spark retard and operative during a third combination of states of operation of said switching means to cause said second spark retard.

Claim 11

A spark timing system for an internal combustion engine comprising, a voltage pulse generator including a pick-up coil and a rotor driven by the crankshaft of said engine for generating a crankshaft position voltage which represents engine crankshaft position, centrifugal advance means responsive to engine speed for continuously phase shifting said crankshaft position voltage, vacuum advance means responsive to engine manifold vacuum for continuously phase shifting said crankshaft position voltage, said centrifugal and vacuum advance means providing continuously variable spark advance functions more advanced than desirable for certain conditions of engine operation, spark timing control means for generating a spark timing control signal either at substantially the time of occurrence of a predetermined voltage transition of said crankshaft position voltage as determined by said centrifugal and vacuum advance means or at either of at least first or second spark retards corresponding respectively to predetermined timing values that are retarded by predetermined crankshaft angles of rotation from the occurrence of said voltage transition, said spark timing control means comprising bidirectional ramp voltage generating means including an operational amplifier and a capacitor connected between the output of the amplifier and one input of the amplifier, an electronic spark selection logic network comprising a plurality of condutors connected by a plurality of diodes in a predetermined configuration and having an output coupled to said spark timing control means for determining the spark timing mode of operation, at least first, second, third and fourth switching means responsive respectively to engine speed, engine manifold vacuum, a first engine coolant temperature and a second engine coolant temperature of a higher value coupled to the input of said spark selection logic network, the state of operation of each switching means being determined by whether a corresponding engine operating condition is above or below a predetermined value, said spark selection logic network and said switching means being so arranged that the simultaneous occurrence of a first predetermined combination of states of operation of said switching means causes said spark timing to be controlled by said crankshaft position voltage, operative during a second combination of states of operation of said switching means to provide said first spark retard and operative during a third combination of states of operation of said switching means to cause said second spark retard.

Claim 12

A spark timing system for an internal combustion engine comprising, a voltage pulse generator including a pick-up coil and a rotor driven by the crankshaft of said engine for generating a crankshaft position voltage which represents engine crankshaft position, centrifugal advance means responsive to engine speed for continuously phase shifting said crankshaft position voltage, vacuum advance means responsive to engine manifold vacuum for continuously phase shifting said crankshaft position voltage, said centrifugal and vacuum advance means providing continuously variable spark advance functions more advanced than desirable for certain conditions of engine operation, spark timing control means for generating a spark timing control signal either at substantially the time of occurrence of a predetermined voltage transition of said crankshaft position voltage as determined by said centrifugal and vacuum advance means or at either of at least first or second spark retards corresponding respectively to predetermined timing values that are retarded by predetermined crankshaft angles of rotation from the occurrence of said voltage transition, said spark timing control means comprising bidirectional ramp voltage generating means including an operational amplifier and a capacitor connected between the output of the amplifier and one input of the amplifier, an electronic spark selection logic network comprising a plurality of condutors connected by a plurality of diodes in a predetermined configuration and having an output coupled to said spark timing control means for determining the spark timing mode of operation, at least first, second, third and fourth switching means responsive respectively to engine speed, engine manifold vacuum, a first engine coolant temperature and a second engine coolant temperature of a higher value coupled to the input of said spark selection logic network, the state of operation of each switching means being determined by whether a corresponding engine operating condition is above or below a predetermined value, said spark selection logic network and said switching means being so arranged that the simultaneous occurrence of a first predetermined combination of states of operation of said switching means causes said spark timing to be controlled by said crankshaft position voltage, operative during a second combination of states of operation of said switching means to provide said first spark retard and operative during a third combination of states of operation of said switching means to cause said second spark retard.

Claim 13

A spark timing system for an internal combustion engine comprising, a voltage pulse generator driven by the crankshaft of said engine for generating a crankshaft position voltage which represents engine crankshaft position, centrifugal advance means responsive to engine speed for continuously phase shifting said crankshaft position voltage, vacuum advance means responsive to engine manifold vacuum for continuously phase shifting said crankshaft position voltage, said centrifugal and vacuum advance means providing continuously variable spark advance functions more advanced than desirable for certain conditions of engine operation, spark timing control means for generating a spark timing control signal either at substantially the time of occurrence of a predetermined voltage transition of said crankshaft position voltage as determined by said centrifugal and vacuum advance means or at either of at least first or second spark retards corresponding respectively to predetermined timing values that are retarded by predetermined crankshaft angles of rotation from the occurrence of said voltage transition, said spark timing control means comprising a bidirectional ramp voltage generating means including an operational amplifier and a capacitor connected between the output of said amplifier and one input of the amplifier, said spark timing control means having a circuit bypassing said operational amplifier for at times providing said spark timing control signal substantially at the occurrence of said voltage transition when such spark timing operation is desired, an electronic spark selection logic network having an output coupled to said spark timing control means for determining the spark timing mode of operation, at least first, second, third and fourth switching means responsive respectively to engine speed, engine manifold vacuum, a first engine coolant temperature and a second engine coolant temperature of a higher value coupled to the input of spark selection network, the state of operation of each switching means being determined by whether a corresponding engine operating condition is above or below a predetermined value, said spark selection logic network and said switching means being so arranged that the simultaneous occurrence of a first predetermined combination of states of operation of said switching means causes said spark timing to be controlled by said crankshaft position voltage, operative during a second combination of states of operation of said switching means to provide said first spark retard and operative during a third combination of states of operation of said switching means to cause said second spark retard.

Claim 14

A spark timing system for an internal combustion engine comprising, a voltage pulse generator driven by the crankshaft of said engine for generating a crankshaft position voltage which represents engine crankshaft position, centrifugal advance means responsive to engine speed for continuously phase shifting said crankshaft position voltage, vacuum advance means responsive to engine manifold vacuum for continuously phase shifting said crankshaft position voltage, said centrifugal and vacuum advance means providing continuously variable spark advance functions more advanced than desirable for certain conditions of engine operation, spark timing control means for generating a spark timing control signal either at substantially the time of occurrence of a predetermined voltage transition of said crankshaft position voltage as determined by said centrifugal and vacuum advance means or at either of at least first or second spark retards corresponding respectively to predetermined timing values that are retarded by predetermined crankshaft angles of rotation from the occurrence of said voltage transition, said spark timing control means comprising a bidirectional ramp voltage generating means including an operational amplifier and a capacitor connected between the output of said amplifier and one input of the amplifier, said spark timing control means having a circuit bypassing said operational amplifier for at times providing said spark timing control signal substantially at the occurrence of said voltage transition when such spark timing operation is desired, an electronic spark selection logic network having an output coupled to said spark timing control means for determining the spark timing mode of operation, at least first, second, third and fourth switching means responsive respectively to engine speed, engine manifold vacuum, a first engine coolant temperature and a second engine coolant temperature of a higher value coupled to the input of spark selection network, the state of operation of each switching means being determined by whether a corresponding engine operating condition is above or below a predetermined value, said spark selection logic network and said switching means being so arranged that the simultaneous occurrence of a first predetermined combination of states of operation of said switching means causes said spark timing to be controlled by said crankshaft position voltage, operative during a second combination of states of operation of said switching means to provide said first spark retard and operative during a third combination of states of operation of said switching means to cause said second spark retard.

Claim 15

A spark timing system for an internal combustion engine comprising, a voltage pulse generator having a single pickup coil and a rotor driven by the crankshaft of said engine for generating a crankshaft position voltage which represents engine crankshaft position, centrifugal advance means responsive to engine speed for continuously phase shifting said crankshaft position voltage, vacuum advance means responsive to engine manifold vacuum for continuously phase shifting said crankshaft position voltage, said centrifugal and vacuum advance means providing continuously variable spark advance functions more advanced than desirable for certain conditions of engine operation and operative to provide the maximum spark advance for said system from an initial spark advance setting, spark timing control means for generating a spark timing control signal either at substantially the time of occurrence of a predetermined voltage transition of said crankshaft position voltage as determined by said centrifugal and vacuum advance means or at either of at least first or second spark retards corresponding respectively to predetermined timing values that are retarded by predetermined crankshaft angles of rotation from the occurrence of said voltage transition, said spark timing control means comprising bidirectional ramp voltage generating means including an operational amplifier and a capacitor connected between the output of the amplifier and one input of the amplifier, an electronic spark selection logic network having an output coupled to said spark timing control means for determining the spark timing mode of operation, a plurality of switching means, each switching means responsive to a respective engine operating condition, the state of operation of each switching means being determined by whether a corresponding engine operating condition is above or below a predetermined value, said switching means coupled to the input of said spark selection logic network, said spark selection logic network and said switching means being so arranged that the simultaneous occurrence of a first predetermined combination of states of operation of said switching means causes said spark timing to be controlled by said crankshaft position voltage, operative during a second combination of states of operation of said switching means to provide said first spark retard and operative during a third combination of states of operation of said switching means to cause said second spark retard.

Claim 16

A spark timing system for an internal combustion engine comprising, a voltage pulse generator having a single pickup coil and a rotor driven by the crankshaft of said engine for generating a crankshaft position voltage which represents engine crankshaft position, centrifugal advance means responsive to engine speed for continuously phase shifting said crankshaft position voltage, vacuum advance means responsive to engine manifold vacuum for continuously phase shifting said crankshaft position voltage, said centrifugal and vacuum advance means providing continuously variable spark advance functions more advanced than desirable for certain conditions of engine operation and operative to provide the maximum spark advance for said system from an initial spark advance setting, spark timing control means for generating a spark timing control signal either at substantially the time of occurrence of a predetermined voltage transition of said crankshaft position voltage as determined by said centrifugal and vacuum advance means or at either of at least first or second spark retards corresponding respectively to predetermined timing values that are retarded by predetermined crankshaft angles of rotation from the occurrence of said voltage transition, said spark timing control means comprising bidirectional ramp voltage generating means including an operational amplifier and a capacitor connected between the output of the amplifier and one input of the amplifier, an electronic spark selection logic network having an output coupled to said spark timing control means for determining the spark timing mode of operation, a plurality of switching means, each switching means responsive to a respective engine operating condition, the state of operation of each switching means being determined by whether a corresponding engine operating condition is above or below a predetermined value, said switching means coupled to the input of said spark selection logic network, said spark selection logic network and said switching means being so arranged that the simultaneous occurrence of a first predetermined combination of states of operation of said switching means causes said spark timing to be controlled by said crankshaft position voltage, operative during a second combination of states of operation of said switching means to provide said first spark retard and operative during a third combination of states of operation of said switching means to cause said second spark retard.