Vehicle Test Mode Circuit Reset Logic for Erroneous Switching
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Solution Overview
Problem
Control circuits in vehicles are prone to erroneous switching into test mode due to mechanical stresses or electrical noise, leading to malfunction and requiring a fail-safe mechanism to revert to normal mode, especially when nonvolatile memory is not rewritable or when external noises cause incorrect switching.
Innovation Solution
A test mode circuit that utilizes an ON/OFF switch to manage the transition between test and normal modes by resetting the logic circuit section using signal levels from external terminals and an ignition relay, ensuring reliable operation even under harsh conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the control circuit is configured to operate in test mode to improve testability, then test coverage is improved, but the control circuit becomes vulnerable to erroneous switching due to mechanical causes or electric noises
Solution Approach 1:
A dedicated test mode setting circuit is introduced as an intermediary component between the external test mode operation switch and the logic circuit section. This circuit includes a test mode setting flag that must be explicitly set to activate test mode, creating a mediating layer that prevents direct or erroneous switching. The intermediary circuit ensures that test mode activation requires both the external switch operation and the flag setting condition, thereby improving reliability while maintaining testability.
2Reliability
If a nonvolatile memory is used to store a test mode operation check signal, then test mode activation control is improved, but additional external rewriting work is required and the system becomes more complex
Solution Approach 1:
The test mode setting circuit is designed to automatically manage the test mode setting flag based on the operation of the test mode operation switch, without requiring external intervention for flag management. The circuit self-updates the flag state when the switch is operated, eliminating the need for external rewriting work associated with nonvolatile memory while maintaining reliable test mode activation control. This self-service approach reduces device complexity while preserving the reliability benefits of check signal control.
3Adaptability or versatility
If the control circuit operates in test mode during vehicle travel, then function testing is enabled, but the control circuit may be disabled due to mechanical vibrations or electric noises
Solution Approach 1:
The test mode setting flag is set in advance as a preliminary condition before the control circuit can operate in test mode. This preliminary action creates a pre-established state that must be present for test mode activation, adding a layer of protection against transient disturbances. When mechanical vibrations or electric noises occur during vehicle travel, the requiring both the external switch operation and the pre-set flag condition prevents erroneous mode switching, while still allowing intentional function testing when properly configured.
Data Source
AI summary
A power control circuit is provided in a vehicle control ECU mounted in a vehicle. The control circuit, when making a shift to a test mode by a test mode circuit, closes a relay to supply a power voltage from a battery to a power line in the similar manner as an ignition main switch is turned on. A logic circuit section of the test mode circuit is reset by an OR logic of a set level of a test terminal and a level of the power line.