Electric Power Steering Controller Current Amplitude Dynamics
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Solution Overview
Problem
Existing electric power steering apparatuses face limitations in the number of repetitions and continuous time of 'stationary steering' and 'end contact' due to high heat generation and cost increases from large electric current amplitudes, especially when rotational speed is low, leading to deteriorated steering feeling.
Innovation Solution
An electric power steering apparatus with a controller that adjusts the allowed electric current amplitude of the rotating AC machine, allowing it to increase at higher rotational speeds and decrease at lower speeds, optimizing the power supply capability of the semiconductor power converter to reduce heat generation and extend the operational time of 'stationary steering' and 'end contact'.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If the electric current amplitude of the rotating AC machine is increased to generate large auxiliary torque in stationary steering, then the steering assistance is improved, but the heat generation increases and the number of repetitions and continuous time of stationary steering is limited
Solution Approach 1:
The patent applies dynamics by making the electric current amplitude dynamically adjustable based on rotational speed. At low rotational speeds (stationary steering), a larger electric current amplitude is permitted to provide sufficient auxiliary torque. At high rotational speeds, the permitted electric current amplitude is reduced. This dynamic adjustment resolves the contradiction by allowing high torque when needed (low speed) while preventing excessive heat generation when speed is high and torque demand is lower.
Solution Approach 2:
The patent changes the parameter of electric current amplitude based on rotational speed conditions. The control device adjusts the permitted electric current amplitude as a variable parameter: increasing it at low rotational speeds to maintain steering assistance, and decreasing it at high rotational speeds to reduce heat generation. This parameter change strategy directly addresses the technical contradiction between torque requirement and heat generation.
2Ease of operation
If the electric current amplitude is increased to maintain steering assistance at low rotational speeds, then the steering feeling is improved, but the cost and size of the semiconductor power converter increase
Solution Approach 1:
The patent implements dynamic adjustment of the permitted electric current amplitude based on real-time rotational speed feedback. The control device monitors rotational speed and dynamically modifies the current amplitude limit accordingly. This ensures that the semiconductor power converter is sized for moderate current requirements, while still delivering high current when needed during stationary steering, thus avoiding the need for an oversized converter and reducing cost and complexity.
Solution Approach 2:
The patent changes the operational parameter of electric current amplitude based on rotational speed conditions. By permitting larger current amplitude only when rotational speed is low (stationary steering), the system maintains good steering feeling without requiring the semiconductor power converter to be designed for continuously high current capacity. This parameter change approach reduces the converter size and cost while preserving steering performance when needed.
3Power
If the rotational speed of the rotating AC machine is increased, then the power output is improved, but the load becomes large requiring increased electric current amplitude
Solution Approach 1:
The patent applies dynamics by implementing speed-dependent control of the permitted electric current amplitude. At high rotational speeds where power output is naturally high, the system reduces the permitted electric current amplitude to prevent excessive load and heat generation. At low rotational speeds where power output is low, the system increases the permitted electric current amplitude to maintain sufficient torque. This dynamic control resolves the contradiction between power output and electric current amplitude requirements.
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 configuration reduces heat generation and maintains the power supply capability of the semiconductor power converter, allowing for longer operation without deteriorating the steering feeling, even during continuous or repeated 'stationary steering' and 'end contact' scenarios.
Implementation Method 1
an electric power steering apparatus which generates an auxiliary torque for a steering torque of a steering system using an rotating AC machine
Implementation Method 2
an alternating current is decomposed into a magnetic flux component electric current and a torque component electric current by means of a technique which is called coordinate transformation
Data Source
AI summary
An electric power steering apparatus includes an rotating AC machine which generates an auxiliary torque for assisting a steering torque of a steering system; and a controller which performs control so that the allowed electric current amplitude of the rotating AC machine becomes large if a rotational speed of the rotating AC machine is increased. Accordingly, it is possible to release or lessen the limit on the number of repetitions or continuous time of the “stationary steering” or the “end contact”.