Circuits and methods to control a current in a coil are disclosed. The circuit and methods provide over-dwell protection and soft shut-down functionality to safely discharge the coil. The safe discharge of the coil is facilitated by a soft-start ramp signal that reduces the coil current gradually by controlling a switching device according. A profile of the soft-start ramp signal over time determines the gradual reduction. The profile of the soft-start ramp signal can be adjusted to set (i) an over-dwell period of the coil current, after which the coil current is shut down, and (ii) a soft shut-down period, over which the coil current is gradually reduced.

A current control circuit for an ignition system (i.e., igniter current limiter) is disclosed. The current control circuit can reduce a coil current over a soft shut down (SSD) period using an insulated gate bipolar transistor (IGBT) that is controlled by a negative feedback loop, which controls the current limit of the IGBT according to a SSD profile. In order to prevent an unwanted current rise during the soft shut down period, the current control circuit compares a gate voltage of the IGBT to a reference signal and based on the comparison can enable the SSD profile to include a fast ramp. The fast ramp quickly lowers the current limit of the IGBT so that the coil current equals the current limit and can be controlled by the negative feedback loop.

Circuits and methods for controlling a coil current are disclosed. The control utilizes current sources to source/sink charge to/from a capacitance of a switching device to turn the switching device ON/OFF. When turned OFF, the switching device blocks coil current from flowing, which can create a large kickback voltage on the coil. To reduce the large kickback voltage, the capacitance can be discharged slowly by a small discharge current. The disclosed circuits and methods provide a gradual reduction of the coil current at a rate that is slow enough to prevent a spark while minimizing a period for shutdown to prevent overheating. The disclosed systems and methods may be simpler than other approaches because the soft shutdown is no ramp signal is required for the reduction. Instead, a rate of gate capacitance discharge is controlled to maintain the kickback voltage at a particular level.

An ignition system including a spark plug control unit adapted to control at least two coil stages to provide a current to a spark plug, including two stages including a first transformer including a first primary winding inductively coupled to a first secondary winding; a second transformer including a second primary winding inductively coupled to a second secondary winding; the control unit enabled to simultaneously switch on and off two corresponding switches to maintain a continuous ignition fire, and includes a step-down converter stage with a switch and a diode. The method includes i) switching off the switch; and ii) toggling the two corresponding switches.

A method for determining the wear rate of a spark plug electrode of an ignition system of an internal combustion engine comprises determining a risetiine number indicating the time required for raising the current and thereby the primary energy which is supplied to an ignition coil of the spark plug from an inactive level to a predetermined level, determining an operating condition indicator configured to indicate an operating condition of the ignition system, determining a wear rate of the spark plug electrode based on a difference of a first spark plug state indicator at a first time instance and a second spark plug state indicator at a second time instance, wherein the first time instance and the second time instance are separated by a predetermined time interval, wherein the spark plug state indicator is determined as a value based on the risetime number and the operating condition indicator.

In an ignition control device for an internal-combustion engine, signal separation circuitry receives and separates an ignition control signal that is an integrated signal of a main ignition signal for controlling the main ignition operation, an energy input signal for controlling the energy input operation, and a target secondary current command signal. The ignition control signal is formed of a first signal and a second signal that are pulsed signals. The signal separation circuitry is configured to generate, from the ignition control signal, the main ignition signal based on rising edges of the first signal and the second signal as pulse-waveform information of the first signal and the second signal, generate the energy input signal based on a pulse width of the second signal as pulse-waveform information of the second signal, and generate the target secondary current command signal based on pulse-waveform information of the first signal.

The invention provides an internal combustion engine combustion state detecting device such that ascertaining a combustion state using ionic current detection is carried out accurately over a wide operating range of an internal combustion engine. The internal combustion engine combustion state detecting device includes a spark plug that has a central electrode and a grounding electrode opposing across a gap, and a discharge stopping-induced current detecting device that estimates an induced current caused by a stopping of a spark discharge generated in the gap between the central electrode and the grounding electrode, wherein an ionic current detection threshold is set to a threshold value that is not affected by the induced current using the induced current estimated by the discharge stopping-induced current detecting device.

There is provided an ignition apparatus that makes it possible that after a spark discharge starts, a secondary current is reduced so that a plug is suppressed from being consumed. The ignition apparatus is provided with an ignition coil including a primary coil, a secondary coil, and a tertiary coil, a first switching circuit for performing on/off-switching of energization of the primary coil from a power source, a second switching circuit for performing on/off-switching of energization of the tertiary coil, and a controller that performs on/off-control of the first switching circuit so as to generate a secondary current in the secondary coil, thereby causing a spark discharge in an ignition plug, and then turns on the second switching circuit so as to reduce the secondary current through a change in flux in the tertiary coil.

A current control circuit for an ignition system (i.e., igniter current limiter) is disclosed. The current control circuit can reduce a coil current over a soft shut down (SSD) period using an insulated gate bipolar transistor (IGBT) that is controlled by a negative feedback loop, which controls the current limit of the IGBT according to a SSD profile. In order to prevent an unwanted current rise during the soft shut down period, the current control circuit compares a gate voltage of the IGBT to a reference signal and based on the comparison can enable the SSD profile to include a fast ramp. The fast ramp quickly lowers the current limit of the IGBT so that the coil current equals the current limit and can be controlled by the negative feedback loop.

An ignition system includes a primary coil, a secondary coil, a first switch, a second switch, a third switch, a fourth switch, and a switch control section. The primary coil includes a first winding, and a second winding which is connected in series with the first winding. The secondary coil is connected to an ignition plug and is magnetically coupled to the primary coil. The first switch connects and disconnects an electrical path between a first terminal and a ground. The second switch connects and disconnects an electrical path between a power supply and a second terminal. The third switch connects and disconnects an electrical path between the power supply and the first terminal. The fourth switch connects and disconnects an electrical path between a contact point and the ground. The switch control section controls opening and closing of each switch to connect and disconnect the associated electrical path.