Contactor Status Detection via Coil Inductance and Current Decay
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Solution Overview
Problem
In electrified vehicles, contactors often experience unintended open conditions and contact welding, where they fail to open or close properly, posing challenges for reliable operation and safety, and traditional diagnosis methods require voltage measurements across terminals, which can be unreliable and invasive.
Innovation Solution
The system employs a controller to manage the contactor coil current through PWM control, determining the contactor's status by measuring the inductance and time constant of the coil without direct voltage measurements, using methods that differentiate between closed and open states based on current decay and peak current analysis, and sets a fault flag for improper conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If voltage measurements across terminals are used to diagnose contactor status, then contactor status can be determined, but the measurement becomes unreliable and invasive
Solution Approach 1:
The patent uses the contactor coil as an intermediary element to infer contactor status. Instead of directly measuring voltage across the contactor terminals, the system measures electrical characteristics (current, impedance, time constant) of the coil circuit, which indirectly reflect the contactor's actual status. This intermediary measurement approach avoids the harmful effects of direct terminal measurements while maintaining detection accuracy.
Solution Approach 2:
The patent replaces the traditional electrical voltage measurement method with an alternative electrical characterization method. By measuring current decay characteristics and time constants of the coil circuit, the system substitutes direct voltage measurement with a different electrical parameter measurement that provides the same diagnostic information without the associated reliability and invasiveness problems.
2Reliability
If traditional diagnosis methods are used, then contactor status can be monitored, but the system complexity increases due to additional wiring and measurement requirements
Solution Approach 1:
The patent makes the existing coil circuit serve multiple functions: it remains the actuating element for the contactor while simultaneously serving as the sensing circuit for status detection. The same coil that drives the contactor also provides the electrical characteristics (inductance, time constant, current decay) used to determine contactor status, eliminating the need for separate sensing wires or measurement circuits.
Solution Approach 2:
The contactor coil circuit performs self-diagnosis by providing its own electrical characteristics for status monitoring. The system uses the inherent electrical properties of the coil (inductance, resistance, time constant) to determine whether the contactor is properly closed or open, without requiring external diagnostic infrastructure. The coil essentially monitors itself through its electrical behavior.
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
This approach allows for reliable detection of unintended open and contact welding conditions without extra wires, enhancing the reliability and safety of contactor operation by identifying issues without direct voltage measurement, thereby preventing vehicle start in faulty states.
Implementation Method 1
a contactor, including a coil, arranged to close responsive to current magnitude through the coil exceeding a first threshold
Implementation Method 2
determining the contactor's status by measuring the inductance and time constant of the coil without direct voltage measurements, using methods that differentiate between closed and open states based on current decay and peak current analysis
Data Source
AI summary
A system for a vehicle includes a controller and contactor arranged to close responsive to current magnitude through a coil thereof exceeding a first threshold. The controller, following a request to open the contactor, applies current to the coil at a magnitude less than the first threshold for a duration, and responsive to peak current through the contactor during the duration being less than a second threshold, prevents start of the vehicle.