Electric Power Steering Relay Current Control
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Solution Overview
Problem
Conventional electric power steering systems face challenges with high current flow in motor relays during prolonged steering wheel holding, leading to expensive and large-sized relays, and difficulties in diagnosing open failures in relay contacts, which can cause uncomfortable steering and increased costs.
Innovation Solution
The system employs an electromagnetic type motor relay with a steering status detecting section to control motor current based on steering status, limiting continuous energization time and temperature estimation to manage relay current, allowing the use of smaller, less expensive relays and preventing overheating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a large capacity relay is used to handle high current during prolonged steering wheel holding, then the relay can tolerate continuous high current, but the relay becomes expensive and large-sized
Solution Approach 1:
The patent applies dynamics by making the relay current capacity adaptable through control strategies. Instead of using a fixed large capacity relay, the system dynamically adjusts the current flow based on steering status detection, allowing a smaller relay to handle variable current demands effectively
Solution Approach 2:
The patent changes the parameter of relay current capacity from a fixed large value to a dynamically adjusted value based on steering conditions. By detecting steering status and controlling current accordingly, the system optimizes relay utilization without requiring oversized hardware
2Reliability
If a large capacity relay is used to handle high current during prolonged steering wheel holding, then the relay can tolerate continuous high current, but the relay becomes expensive
Solution Approach 1:
The system dynamically controls relay current based on steering status, allowing a smaller, less expensive relay to replace costly large capacity relays while maintaining reliability through adaptive current management
Solution Approach 2:
By changing the current capacity parameter from fixed high to dynamically adjusted based on steering conditions, the system reduces relay cost without sacrificing operational reliability
3Power
If high current flows continuously in the motor relay during prolonged steering wheel holding, then the motor receives sufficient power, but torque variations increase causing uncomfortable steering sensations
Solution Approach 1:
The patent applies periodic action by controlling the motor relay current in pulses or cycles rather than continuous flow. By periodically adjusting current based on steering status detection, the system maintains adequate motor power while reducing torque variations that cause uncomfortable sensations
Solution Approach 2:
The system uses feedback by detecting steering status and using this information to control relay current. This closed-loop approach ensures smooth torque delivery by adjusting power supply based on actual steering conditions, eliminating uncomfortable vibrations
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 reduces torque variations, suppresses uncomfortable steering sensations, and enables a cost-effective, compact system configuration by controlling motor current based on steering status and temperature, eliminating the need for large capacity relays and expensive semiconductor relays.
Implementation Method 1
an electromagnetic type motor relay that supplies a current to a brushless DC motor
Data Source
AI summary
An electric power steering apparatus for generating a PWM signal based on a calculated steering assist command value, PWM-controlling a motor via a motor drive circuit including switching elements, and assist-controlling a steering system that a motor relay is inserted between the motor drive circuit and the motor, includes a steering status detecting section that detects a steering status of a steering wheel, outputs a longtime steering holding signal when detecting that the steering status is a longtime steering holding status, and outputs a normal steering signal when detecting that the steering status is a normal steering status, and a motor current control section that determines a motor current control value for controlling a motor current flowing in the motor relay in accordance with the longtime steering holding signal or the normal steering signal.