Electric Power Steering Motor Phase Control
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Solution Overview
Problem
Existing electric power steering devices with three-phase AC motors experience fluctuations in steering assist force due to abnormal phase occurrences, leading to driver discomfort and potential increased power supply currents that may blow vehicle fuses, necessitating current limitations which reduce steering assist force and cause steering wheel stickiness.
Innovation Solution
An electric power steering device with a three-phase AC motor, a drive circuit, a drive control device, and abnormal phase detection unit, which stops energization of the abnormal phase and reduces current to the remaining phases as vehicle speed increases, or sets steering assist force to zero at high speeds, and adjusts current values based on steering angle to minimize driver discomfort and ensure stable vehicle travel.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the motor is driven by abnormality occurrence state energization control using remaining two phases, then the motor can continue to operate, but the current fluctuation range increases causing driver discomfort
Solution Approach 1:
The patent applies dynamics by making the current command value adjustable based on operating conditions. Specifically, the control device reduces the current command value when the vehicle is traveling at high speed or when the steering handle is within a predetermined range including the neutral point, thereby dynamically adapting the steering assist force to minimize current fluctuations and driver discomfort while maintaining motor operation.
Solution Approach 2:
The patent changes the current parameter adaptively based on vehicle speed and steering angle. By reducing the current command value under specific conditions (high speed or near neutral steering position), the system modifies the electrical parameter to suppress excessive current fluctuations that cause steering force variations, thus resolving the contradiction between maintaining operation and ensuring smooth steering.
2Force
If the power supply current is increased to maintain steering assist force when magnetic pole passes through abnormal phase, then the steering assist force is maintained, but the vehicle fuse may be blown
Solution Approach 1:
The patent applies partial action by not maintaining full steering assist force under all conditions. Instead, it selectively reduces the current command value when vehicle speed is high or steering angle is near neutral, allowing sufficient assist force during normal operation while preventing excessive current that could blow fuses. This partial reduction strategy balances assist force maintenance with power supply protection.
Solution Approach 2:
The control device acts as an intermediary between the motor and power supply system. By introducing conditional current reduction logic, it mediates between the need for steering assist force and the risk of power supply damage, preventing fuse blowout while maintaining adequate steering assistance during critical operating conditions.
3Object-affected harmful factors
If the power supply current is limited to prevent fuse blowout, then the power supply system is protected, but the steering assist force decreases causing steering wheel stickiness
Solution Approach 1:
The patent makes the current command value dynamic rather than fixed. By conditionally reducing current only when necessary (high speed or near neutral position), the system maintains high steering assist force during normal steering operations while limiting current only when it would cause power supply damage, thus avoiding steering wheel stickiness during normal use.
Solution Approach 2:
The patent applies local quality by selectively reducing current in specific operating conditions rather than uniformly limiting it. The current command value is reduced only when vehicle speed exceeds a threshold or steering angle is within a predetermined range, while maintaining normal current levels in other conditions, thus preserving steering assist force quality where needed while protecting the power supply system.
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 reduces driver discomfort by stabilizing the steering assist force during high-speed travel and preventing power supply issues, ensuring a smooth and stable driving experience by adjusting current values in response to vehicle speed and steering angle.
Implementation Method 1
An electric power steering device generates a steering assist force by driving an electric motor. As the electric motor, for example, a three-phase alternating current (AC) motor having U-phase, V-phase and W-phase windings is used.
Implementation Method 2
a vehicle speed sensor detecting a vehicle speed
Data Source
AI summary
An electric power steering device is provided, easing a sense of incongruity that a driver feels with respect to steering. If an abnormal phase is detected, an electronic control unit (ECU) 50 stops energizing a winding (any one of windings 86u, 86v and 86w) of the abnormal phase and energizes windings (two of the windings 86u, 86v and 86w) of the two phases other than the abnormal phase, and, as a vehicle speed V increases, the ECU 50 reduces a current value applied to the windings (two of the windings 86u, 86v and 86w) of the two phases other than the abnormal phase.