Ignition Coil Soft Shutdown Circuit for Spark-Free Current Ramp-Down
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Solution Overview
Problem
Existing ignition systems face challenges in shutting down the ignition coil without creating an unwanted spark, particularly when the coil current is not abruptly stopped, which can lead to overheating and undesirable combustion.
Innovation Solution
A current limiter circuit with a transistor, current sensor, and controller is used to gradually reduce the coil current through a ramp signal and variable feedback resistor, ensuring a soft shutdown and preventing sparks by maintaining stability and accuracy during the shutdown process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the coil current is abruptly stopped to shut down the ignition coil, then the shutdown speed is improved, but unwanted sparks are generated at the spark gap
Solution Approach 1:
The patent applies dynamics by making the shutdown process adjustable rather than fixed. The controllable switch allows the coil current to be reduced gradually over a configurable time period, transforming the static abrupt shutdown into a dynamic controlled process. This enables the system to adapt the shutdown speed to prevent sparks while maintaining operational flexibility.
Solution Approach 2:
The patent employs periodic action by implementing a time-based ramp-down profile where the coil current decreases continuously over a specified shutdown period. Instead of an instantaneous cutoff, the current follows a time-dependent decay pattern, allowing the magnetic field to collapse gradually and preventing the voltage spike that causes unwanted sparks.
2Object-generated harmful factors
If the coil current is reduced gradually to prevent sparks, then the harmful factors are reduced, but the shutdown time is increased
Solution Approach 1:
The controllable switch enables dynamic adjustment of the shutdown characteristics. By configuring the switch to operate with specific timing parameters, the system optimizes the balance between gradual current reduction (to prevent sparks) and shutdown duration. The dynamic control allows flexibility in setting the shutdown period to minimize time loss while maintaining spark prevention.
3Device complexity
If a simple switch is used to stop coil current, then the device complexity is reduced, but control precision is insufficient to prevent sparks
Solution Approach 1:
The patent implements feedback control through the controllable switch that responds to control signals to regulate coil current. The switch is driven by a control circuit that monitors and adjusts the current decay profile, providing closed-loop control precision without requiring complex additional components. This feedback mechanism ensures accurate current reduction to prevent sparks while maintaining reasonable circuit simplicity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively prevents unwanted sparks by gradually reducing the coil current, maintaining stability in low current regions, and ensuring accurate control in high current regions, thus preventing damage to the ignition system and ensuring proper engine operation.
Implementation Method 1
a transistor (e.g., an insulated gate bipolar transistor) that is coupled to the coil and configured to allow a coil current to flow through the switch at a current level that is based on a voltage at a terminal (e.g., the gate) of the transistor
Implementation Method 2
a current sensor that is coupled to the transistor that senses the current level of the coil current
Implementation Method 3
The controller is configured to adjust the voltage at the terminal of the transistor to reduce a difference between the sensed current level and a reference level
Implementation Method 4
a signal generator that is coupled to the controller and that generates a ramp signal. The ramp signal controls the reference level of the controller so the coil current is reduced gradually over a shutdown period
Implementation Method 5
The open-loop gain of the controller is determined by a resistance of a variable feedback resistor. The ramp signal also controls the resistance of the variable feedback resistor so that the open loop gain of the controller is reduced over the shutdown period
Data Source
AI summary
A circuit and method for gradually reducing a coil current during a shutdown period is disclosed. The circuit and method include a controller that is configured in a control loop with a current sensor that measures the current in the coil and a transistor that can be controller to limit the current in the coil. The open-loop gain of the controller is determined by a resistance of a variable feedback resistor, and the resistance of the variable feedback resistor is reduced during the shutdown period as the coil current becomes small. The reduction of the resistance maintains a suitable phase margin by lowering the open loop gain of the circuit for low coil currents. Thus during shutdown, the circuit provides control accuracy for high coil currents and control stability for low coil currents.