Electric Power Steering Viscoelastic Model Control
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Solution Overview
Problem
Conventional electric power steering apparatuses experience uncomfortable shocks and noisy sounds when reaching the maximum steering angle, due to inadequate control over assist torque and lack of consideration for steering velocity, and fail to effectively handle various road surface conditions.
Innovation Solution
An electric power steering apparatus that employs a viscoelastic model as a reference model to control the assist torque, using a model-following control system that adjusts parameters based on rack axial force, displacement, and steering state to suppress shocks and noises, and limits input to prevent uncomfortable reactions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional electric power steering apparatus performs feedback control of motor current to accurately generate assist torque, then the steering assist accuracy is improved, but shock and noisy sound occur at rack end hitting
Solution Approach 1:
The control apparatus performs preliminary action by detecting when the rack shaft approaches the rack end position and proactively reducing the assist torque before actual contact occurs. This preventive measure eliminates shock and noisy sound by avoiding sudden impacts, while maintaining accurate torque control through the feedback mechanism during the approach phase.
Solution Approach 2:
The system dynamically adjusts the assist torque characteristic based on the rack shaft position. When the rack shaft is far from the rack end, normal feedback control maintains accurate torque. When approaching the rack end, the control apparatus transitions to a different control mode that reduces torque, creating a dynamic adaptation that prevents end-hitting shock while preserving control accuracy in the operational range.
2Power
If the assist torque is increased to improve steering performance, then the steering responsiveness is improved, but the striking energy at rack end increases
Solution Approach 1:
The control apparatus applies local quality by creating different torque characteristics in different spatial zones. In the normal steering range, high assist power is provided for responsive steering. In the zone near the rack end, the assist torque is reduced to prevent excessive striking energy. This spatial differentiation allows high performance where needed while eliminating harmful effects at the boundary.
3Stability of the object's composition
If the motor current is controlled to provide consistent steering assist, then the steering uniformity is improved, but uncomfortable reaction occurs near rack end
Solution Approach 1:
The control apparatus changes the control parameters dynamically based on rack shaft position. The motor current command is adjusted according to the distance from the rack end, creating a position-dependent torque characteristic. This parameter change ensures consistent and comfortable steering assist throughout the normal range while preventing uncomfortable reactions near the rack end by reducing torque in that specific zone.
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 system provides robust end-hitting suppression, improved controllability, and reduced shock forces, enhancing the steering experience by attenuating motor inertia and adapting to different road conditions.
Implementation Method 1
a viscoelastic model as a reference model within a predetermined angle at front of a rack end so as to suppress a rack end hitting
Data Source
AI summary
A high-performance electric power steering apparatus that includes a control system based on a physical model, includes a model following control that an output (a distance to a rack end) of a controlled object follows-up to a reference model, eliminates or reduces the occurrences of a noisy sound and a shock force at an end hitting without giving any uncomfortable steering feeling to a driver, and reduces the end hitting. The electric power steering apparatus calculates a current command value based on at least a steering torque and performs an assist-control of a steering system by driving a motor based on the current command value, including: a configuration of a model following control including a viscoelastic model as a reference model within a predetermined angle at front of a rack end so as to suppress a rack end hitting.