Squib Driver Diagnostic Circuit for Airbag Control
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Solution Overview
Problem
Existing airbag control circuits in vehicles may be damaged during installation, leading to insufficient current to detonate squibs during crashes, and there is a risk of 'dudding' where a sub-threshold current renders squibs unusable, necessitating a self-diagnostic system to ensure proper function post-installation without prematurely activating or damaging the squibs.
Innovation Solution
A driving current diagnostic circuit with a field-effect transistor, switches, current sources, and an error-detecting circuit that provides test and drive currents to verify the airbag control circuit's functionality, ensuring sufficient current for squib detonation while avoiding dudding by using a test current below the threshold for activation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the airbag control circuit is tested before installation, then manufacturing defects can be detected, but installation damage cannot be detected
Solution Approach 1:
The patent implements a self-service diagnostic system where the airbag control circuit tests itself after installation. The control circuit automatically selects appropriate test parameters, activates the test current source, monitors squib response, and determines whether the circuit is functioning properly. This self-diagnostic capability eliminates the need for external testing equipment and enables post-installation verification.
Solution Approach 2:
The patent performs preliminary diagnostic testing as part of the installation process itself. Before the airbag system is activated for normal operation, the control circuit executes a self-diagnostic routine that verifies both the control circuit functionality and squib integrity. This preliminary action ensures that any installation damage is detected before the system enters service.
2Reliability
If a high current is passed through the squib to ensure detonation capability, then the squib will reliably detonate, but the squib may be damaged or dudded during testing
Solution Approach 1:
The patent dynamically changes the current parameter based on the testing phase. During diagnostic testing, the current parameter is set to a low value (10 mA or less) to avoid damage. During actual deployment, the current parameter is switched to a high value (1.0-1.2 A) to ensure reliable detonation. This parameter change is controlled by the control circuit which selects the appropriate current source based on operational context.
Data Source
AI summary
A diagnostic circuit is provided that includes a FET having a source connected to a first node, a drain, and a gate; a first switch connecting a current-supply node to one of the gate and a second node; a second switch connecting the first node and the second node; a variable current source providing one of a drive current and a test current to the current-supply node; a fire current source configured to provide a fire current to the drain; an error-detecting circuit connected to the second node, a reference terminal, and an error node, the error-detecting circuit generating an error signal to the error node indicating whether an error-detecting parameter at the second node exceeds a reference parameter at the reference terminal; and a control circuit generating control signals to control the variable current source, and the first and second switches.