Electric Power Steering Rack Retainer Biasing for Smooth Torque
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Solution Overview
Problem
Conventional electric power steering systems face difficulties in smooth operation due to high set load of the rack retainer, leading to increased steering torque before the rack bar starts moving, which results in poor steering feeling.
Innovation Solution
An electric power steering apparatus with a biasing member that adjusts the set load to ensure smooth movement by defining specific regions of steering torque and rotation, where the boundary points of these regions are strategically set to minimize initial steering torque and maximize smooth steering characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the set load of the rack retainer is increased to improve steering stability, then the steering torque before rack bar movement becomes excessively large, but this deteriorates smooth operation at the start of steering
Solution Approach 1:
The rack retainer is designed to dynamically change its state from a fixed biased position to a swinging position based on steering input. The retainer swings about its rotation axis when the rack bar moves, allowing the biasing force to be effectively reduced during operation while maintaining stability when stationary. This dynamic behavior resolves the contradiction between stability and smooth operation.
Solution Approach 2:
The biasing force parameter is optimized to a specific range (50-150 N) that balances two opposing requirements: providing enough force to maintain steering stability when the rack bar is stationary, while being low enough to allow smooth initiation of movement. This parameter optimization resolves the technical contradiction.
2Stability of the object's composition
If the biasing force of the rack retainer is increased to maintain steering position, then the steering torque required to initiate rack bar movement increases, but this causes overshoot and discomfort
Solution Approach 1:
The rack retainer transitions from a static biased state to a dynamic swinging state during rack bar movement. This dynamic transition allows the system to maintain position stability when needed while reducing the harmful torque overshoot during movement initiation, as the retainer swings rather than rigidly resists movement.
Solution Approach 2:
The biasing member applies a partial biasing force (optimized range of 50-150 N) rather than a strong excessive force. This partial action is sufficient to maintain steering position stability while avoiding the excessive torque that would cause overshoot and driver discomfort.
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 achieves improved steering feeling by ensuring smooth movement and stable steering torque characteristics, reducing the likelihood of overshoot and discomfort during steering operations.
Implementation Method 1
a biasing member (coil spring) arranged to bias the rack retainer toward the rack bar
Data Source
AI summary
An electric power steering apparatus according to the present invention has a biasing member arranged to bias a rack retainer toward a rack bar, wherein a biasing force of the biasing member is set such that, in a two-axis coordinate system with a rotation amount of a steering wheel on a horizontal axis and a steering torque on a vertical axis, the steering torque increases with increase in the rotation amount of the steering wheel in a region before the start of relative movement of the rack bar and the rack retainer.