Vehicle Load Path Diagnosis Using Dynamic Test Current
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Solution Overview
Problem
Existing methods for diagnosing low-side load circuits in vehicles, particularly those with low-resistance loads, struggle to distinguish between normal operating states and short circuits due to the inability to differentiate between reactive and nonreactive resistance values, leading to potential misdiagnosis and damage.
Innovation Solution
A method and circuit arrangement that utilize a switchable test current and test switch to produce defined diagnosis cases, including static and dynamic evaluations, allowing for the differentiation between nominal loads, shorts, and open circuits by sensing and evaluating voltages under various switching states, employing a test voltage source, signal conditioning unit, and evaluation unit to accurately diagnose load path conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a high-value pull-up resistor is used to monitor voltage for diagnosis, then the diagnosis can detect open circuits and disconnected cables, but it cannot distinguish between a shorted load circuit and a normal operating state
Solution Approach 1:
The patent applies dynamics by switching the test current between different states (on/off) to create dynamic measurement conditions. The test current is activated only during diagnosis mode, allowing the system to transition from normal operation to diagnostic measurement, enabling distinction between static and dynamic circuit states that reveals short circuit conditions
Solution Approach 2:
The diagnosis procedure uses periodic action by implementing sequential diagnosis steps: first checking voltage with load switch open, then activating test current, measuring again, and deactivating test current. This periodic switching of measurement conditions allows differentiation between various fault types including short circuits that static measurements cannot detect
2Reliability
If the load switch is closed during diagnosis to test normal operation, then the system can verify load functionality, but it becomes impossible to detect short circuits between output connection and positive pole
Solution Approach 1:
The patent segments the diagnosis into distinct phases: Phase 1 with load switch open for safety checks, Phase 2 with test current activation for short circuit detection, and Phase 3 with load switch closure for functionality verification. This segmentation allows each phase to focus on specific diagnostic objectives without interference from other conditions
Solution Approach 2:
The system performs preliminary actions by checking for short circuits and open circuits before activating the load switch or applying full operating current. This preliminary diagnosis prevents potential damage and ensures safe operation by identifying faults that would be masked during normal operation
3Device complexity
If a simple voltage monitoring approach is used for diagnosis, then the device complexity is low, but the measurement precision is insufficient to distinguish between different fault types
Solution Approach 1:
The patent introduces a test current as an intermediary element that mediates between the voltage source and the load circuit during diagnosis. This test current acts as a probe that reveals circuit conditions without requiring complex measurement equipment, enabling precise fault detection while maintaining relatively simple circuit architecture
Solution Approach 2:
The system changes measurement parameters by switching between different current levels (normal operating current vs. test current) and different switching states (load switch open/closed). These parameter changes enable the same simple circuit to perform multiple diagnostic functions with varying measurement conditions, achieving high measurement precision without increasing device complexity
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
Effectively distinguishes between different diagnosis cases, including recognizing short circuits, open loads, and broken cables, even in inductive loads with low nonreactive resistance, preventing misdiagnosis and thermal damage, and ensuring safe operation of electronic controllers.
Implementation Method 1
at least one test resistance RT is used to produce a test current IT having a defined level and to output the test current IT to the switchable load 34 at an output connection OUT
Implementation Method 2
a signal conditioning unit 18 which, during the diagnosis, senses a resultant voltage UOUT at the output connection OUT and outputs a conditioned test voltage UIO to an evaluation and control unit 20 for evaluation
Data Source
AI summary
A method and circuit assembly for the diagnosis of a load path in a vehicle. The load path comprises a DC voltage source, a switchable load permanently connected to a negative pole and a load switch permanently connected to a positive pole, controlled by a load control signal, wherein in the closed state of the load switch a load current can be conducted through the switchable load (34). During diagnosis a test current having a defined level is generated and is output to the switchable load in accordance with a test control signal via a test switch on an output terminal, wherein a resulting voltage is detected, processed and evaluated at the output terminal, wherein the load switch (36) is opened during the diagnosis, and wherein at least two different diagnostic cases are generated via the test control signal and the resulting switching state of the test switch.