Electronic control of a spark plug for an internal combustion engine

1. An internal-combustion-engine electronic control system comprising:

a power switching device that applies or shuts off a primary current of an ignition coil of an internal combustion engine so that at the secondary side of the ignition coil, there is generated a voltage for making an ignition plug of the internal combustion engine produce a spark discharge; and

a control unit that turns on or off the power switching device,

wherein the control unit is provided with a circuit unit that softly shuts off the power switching device so as to prevent the ignition plug from producing the spark discharge, in the case where at least one of the power switching device, the control unit, the ignition coil, and the ignition plug is in a predetermined state; and based on a change in the conduction state of the power switching device, the characteristics of the soft shutoff is changed halfway through the shutoff operation,

wherein the circuit unit includes a capacitor, a first slow-discharge circuit that makes electric charge in the capacitor discharge with a first predetermined time constant, and a second slow-discharge circuit that makes electric charge in the capacitor discharge with a second predetermined time constant that is smaller than the first predetermined time constant,

wherein when the soft shutoff is started, the control unit causes electric charge in the capacitor to discharge by use of the second slow-discharge circuit so as to make the power switching device begin a soft shutoff operation, and then causes electric charge in the capacitor to discharge by use of the first slow-discharge circuit, until completion of the soft shutoff operation, and

wherein in the control unit, the circuit unit is provided with a function of suppressing a secondary voltage from making the ignition plug produce a spark discharge when energization of the ignition coil with the primary current is started.

2. The internal-combustion-engine electronic control system according to claim 1 , wherein the control unit is provided with a current limiting circuit that limits the primary current flowing in the ignition coil.

3. An internal-combustion-engine electronic control system comprising:

a power switching device that applies or shuts off a primary current of an ignition coil of an internal combustion engine so that at the secondary side of the ignition coil, there is generated a voltage for making an ignition plug of the internal combustion engine produce a spark discharge; and

a control unit that turns on or off the power switching device,

wherein the control unit is provided with a circuit unit that makes the power switching device softly shut off so as to prevent the ignition plug from producing the spark discharge, in the case where at least one of the power switching device, the control unit, the ignition coil, and the ignition plug is in a predetermined state,

wherein the circuit unit includes a capacitor, a first slow-discharge circuit that makes electric charge in the capacitor discharge with a predetermined time constant, and a second slow-discharge circuit that makes electric charge in the capacitor discharge with a time constant that is smaller than the time constant of the first slow-discharge circuit, and

wherein based on the predetermined state, the control unit selects one of the first slow-discharge circuit and the second slow-discharge circuit and makes the capacitor discharge electric charge so as to perform the soft shutoff, and

wherein in the control unit, the circuit unit is provided with a function of suppressing a secondary voltage from making the ignition plug produce a spark discharge when energization of the ignition coil with the primary current is started.

4. The internal-combustion-engine electronic control system according to claim 3 , wherein the control unit is provided with a current limiting circuit that limits the primary current flowing in the ignition coil.

5. The internal-combustion-engine electronic control system according to claim 3 , wherein the control unit is provided with a current detection circuit that detects the primary current flowing in the ignition coil, and when the current detection circuit detects the fact that the primary current is the same as or larger than a predetermined value, the control unit selects one of the first slow-discharge circuit and the second slow-discharge circuit so as to perform the soft shutoff.

6. The internal-combustion-engine electronic control system according to claim 3 , wherein the control unit is provided with an overheating detection circuit that detects overheating in at least one of the constituent elements included in the control unit, and when the overheating detection circuit detects the overheating, the control unit selects one of the first slow-discharge circuit and the second slow-discharge circuit so as to perform the soft shutoff.

7. The internal-combustion-engine electronic control system according to claim 3 , wherein the control unit is provided with a timer circuit that detects a continuous energization duration of the primary current flowing in the ignition coil, and when the timer circuit detects the fact that the continuous energization duration is the same as or longer than a predetermined value, the control unit selects one of the first slow-discharge circuit and the second slow-discharge circuit so as to perform the soft shutoff.

8. An internal-combustion-engine electronic control system comprising:

a power switching device that applies or shuts off a primary current of an ignition coil of an internal combustion engine so that at the secondary side of the ignition coil, there is generated a voltage for making an ignition plug of the internal combustion engine produce a spark discharge; and

a control unit that turns on or off the power switching device,

wherein the control unit is provided with a circuit unit that softly shuts off the power switching device so as to prevent the ignition plug from producing the spark discharge, in the case where at least one of the power switching device, the control unit, the ignition coil, and the ignition plug is in a predetermined state,

wherein the circuit unit includes a capacitor, a first slow-discharge circuit that makes electric charge in the capacitor discharge with a predetermined time constant, and a second slow-discharge circuit that makes electric charge in the capacitor discharge with a time constant that is smaller than the time constant of the first slow-discharge circuit,

wherein the control unit is provided with an overheating detection circuit that detects overheating in at least one of the constituent elements included in the control unit, and when the overheating detection circuit detects the overheating, the control unit selects one of the first slow-discharge circuit and the second slow-discharge circuit so as to perform the soft shutoff, and

wherein in the control unit, the circuit unit is provided with a function of suppressing a secondary voltage from making the ignition plug produce a spark discharge when energization of the ignition coil with the primary current is started.

9. The internal-combustion-engine electronic control system according to claim 8 , wherein the control unit is provided with a current detection circuit that detects the primary current flowing in the ignition coil, and when the current detection circuit detects the fact that the primary current is the same as or larger than a predetermined value, the control unit selects one of the first slow-discharge circuit and the second slow-discharge circuit so as to perform the soft shutoff.

10. The internal-combustion-engine electronic control system according to claim 8 , wherein the control unit is provided with a timer circuit that detects a continuous energization duration of the primary current flowing in the ignition coil, and when the timer circuit detects the fact that the continuous energization duration is the same as or longer than a predetermined value, the control unit selects one of the first slow-discharge circuit and the second slow-discharge circuit so as to perform the soft shutoff.

11. The internal-combustion-engine electronic control system according to claim 9 , wherein the time constant of the selected slow-discharge is set such that if a fluctuation in engine rotation speed prolongs an energization duration of the primary current in the ignition coil, the power switching device shuts off the primary current of the ignition coil at a regular ignition timing so that at the secondary side of the ignition coil, there is generated a voltage for making an ignition plug of the internal combustion engine produce a spark discharge.

12. An internal-combustion-engine electronic control system comprising:

a power switching device that applies or shuts off a primary current of an ignition coil of an internal combustion engine so that at the secondary side of the ignition coil, there is generated a voltage for making an ignition plug of the internal combustion engine produce a spark discharge; and

a control unit that turns on or off the power switching device,

wherein the control unit is provided with a circuit unit that softly shuts off the power switching device so as to prevent the ignition plug from producing the spark discharge, in the case where at least one of the power switching device, the control unit, the ignition coil, and the ignition plug is in a predetermined state; and based on a change in the conduction state of the power switching device, the characteristics of the soft shutoff is changed halfway through the shutoff operation,

wherein the circuit unit includes a capacitor, a first slow-discharge circuit including a first resistor that makes electric charge in the capacitor discharge with a first predetermined time constant, and a second slow-discharge circuit including a second resistor that makes electric charge in the capacitor discharge with a second predetermined time constant that is smaller than the first predetermined time constant,

wherein when the soft shutoff is started, the control unit causes electric charge in the capacitor to discharge by use of the second slow-discharge circuit so as to make the power switching device begin a soft shutoff operation, and then causes electric charge in the capacitor to discharge by use of the first slow-discharge circuit, until completion of the soft shutoff operation, and

wherein in the control unit, the circuit unit is provided with a function of suppressing a secondary voltage from making the ignition plug produce a spark discharge when energization of the ignition coil with the primary current is started.