Vehicle Weld Detection Using Capacitor Voltage Comparison
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Solution Overview
Problem
Conventional weld detection methods for System Main Relays (SMRs) in vehicles are inaccurate due to the influence of smoothing capacitors in the boosting circuit, leading to unreliable detection results.
Innovation Solution
A weld detection apparatus using a microcomputer that measures voltages of a capacitor in different switch states to determine if SMRs are welded, with a second capacitor in the load circuit and a predetermined timing for voltage measurement, allowing for accurate and speedy weld detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional weld detection method using flying capacitor voltage is used, then weld detection can be performed, but smoothing capacitor in boosting circuit influences the charging of flying capacitor causing inaccurate detection
Solution Approach 1:
The patent extracts and removes the harmful influence of the smoothing capacitor from the detection system by introducing a separate detection capacitor that is isolated from the boosting circuit. The detection capacitor charges only through the SMR and insulation resistance, excluding the smoothing capacitor's parasitic effects, thereby achieving accurate weld detection.
Solution Approach 2:
The patent introduces a detection capacitor as an intermediary element between the power supply and the detection circuit. This intermediary capacitor serves as a dedicated sensing element that transfers only the relevant electrical characteristics (voltage drop across insulation resistance) without being affected by the smoothing capacitor, enabling accurate weld detection.
2Measurement precision
If voltage measurement is performed at arbitrary timing, then detection process is simple, but smoothing capacitor charging state causes detection errors
Solution Approach 1:
The patent applies preliminary action by controlling the detection capacitor to charge only after the SMR has been confirmed to be in the ON state and the boosting operation has stabilized. This timing control ensures that the smoothing capacitor's charging transient has settled, allowing accurate voltage measurement that reflects only the insulation resistance characteristics.
Solution Approach 2:
The patent implements periodic action by repeatedly performing the weld detection process at specific intervals during vehicle operation. The detection is triggered by a measurement accepting signal from an external apparatus, creating a periodic measurement cycle that ensures accurate detection while coordinating with the boosting circuit's operational phases.
3Reliability
If weld detection is performed continuously, then detection accuracy is maintained, but detection time and processing load increase
Solution Approach 1:
The patent uses periodic action by implementing weld detection at regular intervals triggered by a measurement accepting signal from an external apparatus. This periodic detection strategy maintains reliability by regularly monitoring the SMR condition while minimizing time loss by not performing continuous detection, thus reducing processing load and coordination overhead.
Solution Approach 2:
The patent implements feedback by using the voltage measurement result to determine weld status and by coordinating with the external apparatus through the measurement accepting signal. The detection system provides feedback about the SMR condition to the vehicle control system, enabling timely responses while optimizing detection timing based on operational conditions.
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 enables accurate and swift weld detection for SMRs by minimizing the impact of smoothing capacitors and other factors, improving detection accuracy and efficiency.
Implementation Method 1
measure a first voltage of a first capacitor and measure a second voltage of the first capacitor, the first voltage being measured when the first capacitor is charged while connected in series to a power supply and a ground of a vehicle body
Data Source
AI summary
A weld detection apparatus is mounted on a vehicle and measures first and second voltages of a first capacitor. The first voltage is measured when the first capacitor is charged while connected in series to a power supply and a ground of a vehicle body while switches that connect the power supply to a load circuit are controlled to be in a first state. The second voltage is measured at a predetermined timing, when the first capacitor is charged while connected in series to the power supply and the ground of the vehicle body while the switches are controlled to be in a second state different from the first state. The apparatus performs a weld detection process to decide which of the switches is welded in an ON-state when a difference between the first and second voltages is equal to or smaller than a predetermined threshold value.