Electric Power Steering Relay Diagnostic Method
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In electric power steering systems, dry relay contacts in harsh environments can lead to film buildup and corrosion, causing delays in system start-up due to the inefficiency of traditional relay wetting methods, which either increase start-up time or apply high torque to the motor.
Innovation Solution
A diagnostic method that involves closing the relay, demanding a predetermined current, measuring the phase current's characteristics after a short period, comparing it to a reference, and repeating the process to ensure correct relay closure, with the option to use a Woodpecker strategy for cleaning the contacts and applying a wetting current to burn off film.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional relay wetting is used to burn off film buildup, then relay contact reliability is improved, but system start-up time increases and high torque is applied to the motor
Solution Approach 1:
The patent applies preliminary diagnostic action by measuring relay contact resistance before closing the relay. This allows the system to detect film buildup on contacts in advance and take corrective measures (such as cleaning or conditioning the contacts) before the relay is closed, thereby ensuring reliable contact operation without requiring extended wetting current application that would delay system start-up.
Solution Approach 2:
The patent implements feedback by continuously monitoring relay contact resistance and using this information to control relay operation. The measured resistance value provides feedback about the contact condition, allowing the control system to adjust its behavior - such as applying cleaning currents or conditioning pulses - to maintain reliable operation without the need for prolonged high-current wetting that would increase start-up time.
2Reliability
If high current is applied to wet the relay contacts, then film buildup is removed, but high torque is applied to the motor which is felt through the steering wheel
Solution Approach 1:
The patent measures relay contact resistance before closing the relay, allowing preliminary detection of film buildup conditions. This enables the system to apply contact conditioning or cleaning currents while the relay is still open, isolating the motor circuit. Consequently, high currents can be applied to remove film without transmitting torque to the motor or steering wheel, as the relay remains open during the cleaning process.
Solution Approach 2:
The patent uses real-time feedback from contact resistance measurements to control when and how relay conditioning is performed. By monitoring resistance values, the system can identify when film buildup is present and apply appropriate cleaning currents during periods when the relay is open and the motor circuit is isolated, thereby eliminating film without causing unwanted motor torque that would be transmitted to the steering wheel.
3Ease of operation
If relay contacts are left open for extended periods in harsh environments, then film buildup occurs on contacts, but relay operation becomes unreliable
Solution Approach 1:
The patent applies preliminary diagnostic measurement of contact resistance before relay closure. This early detection mechanism identifies film buildup that has occurred during extended periods in harsh environments, allowing the system to take corrective action (such as applying cleaning currents or conditioning pulses) before the relay is closed, thereby ensuring reliable operation despite prolonged exposure to harsh conditions.
Solution Approach 2:
The patent implements continuous feedback monitoring of relay contact resistance that detects the effects of harsh environmental exposure and film buildup. This feedback enables the control system to automatically apply contact maintenance currents or cleaning pulses to prevent reliability degradation, ensuring the relay operates reliably even after extended periods in harsh environments where film buildup would normally occur.
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 method allows for timely and reliable system start-up by ensuring proper relay operation, reducing delays and torque fluctuations, while preventing film buildup through effective cleaning and diagnostic fault detection.
Implementation Method 1
a high current, equal to the wetting current specified for the relay, is applied to the relay immediately that it is closed and held for a defined period of time. This current burns through the film and conditions the relay contact.
Data Source
AI summary
A method and apparatus diagnoses a correct operation of a phase or star point isolation relay in an electric power steering system of the kind including a motor drive circuit and at least one phase isolation relay which connects a part of the drive circuit to a phase of the motor. The relay is opened during shutdown to isolate the motor phase from the part of the drive circuit and is normally closed during operation of the motor to connect the phase to the part of the drive circuit. The method includes the steps of: closing the relay; demanding a current through the motor phase associated with the relay that is equal to a predetermined value; measuring at least one characteristic of the phase current in that phase after a predetermined period of time has elapsed, the elapsed time being less than a time needed for the phase current to reach the demanded current value; comparing the measured characteristic of the phase current with a reference characteristic of the phase current; and, in the event that the measured characteristic does not correspond with the reference characteristic, opening the relay and subsequently repeating the steps.