Electric Power Steering Worm Axial Displacement
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Solution Overview
Problem
Conventional electric power steering systems face challenges in suppressing gear rattle while maintaining good steering feeling during fine steering, as increasing the urging load reduces steering feeling due to increased frictional resistance, and decreasing it fails to suppress gear rattle effectively.
Innovation Solution
The system employs a worm with a first and second end portion, a worm wheel, a speed reducer, and bearings with elastic members and an urging member that adjusts frictional resistance to ensure the sum of frictional torques is less than the engagement frictional torque, allowing fine axial displacement of the worm without rotating the worm wheel, thus preventing gear rattle and improving steering feeling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the urging load of the urging member is increased, then gear rattle is suppressed, but steering feeling during fine steering is deteriorated due to increased frictional resistance
Solution Approach 1:
The patent applies dynamics by making the urging load adjustable rather than fixed. The urging member's load can be dynamically changed based on operating conditions (steering angle, vehicle speed) to optimize performance across different scenarios, resolving the contradiction between maintaining consistent gear contact and enabling smooth fine steering movements.
Solution Approach 2:
The patent changes the parameter of urging load from a constant value to a variable parameter that can be adjusted according to operating conditions. By modifying the urging load parameter dynamically, the system achieves both gear rattle suppression when needed and reduced friction during fine steering operations.
2Ease of operation
If the urging load of the urging member is decreased, then steering feeling during fine steering is improved due to decreased frictional resistance, but gear rattle cannot be suppressed
Solution Approach 1:
The system dynamically adjusts the urging load based on real-time operating conditions. During fine steering operations, the urging load is decreased to reduce friction and improve steering feel, while during normal or high-speed driving, the urging load is increased to suppress gear rattle, thus resolving the contradiction through temporal separation of optimization goals.
Solution Approach 2:
The urging load parameter is changed from a fixed low value to a dynamically adjustable parameter that can be increased or decreased based on operating conditions, enabling the system to achieve both improved steering feel and gear rattle suppression at different times as needed.
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 effectively prevents gear rattle and enhances steering feeling during fine steering by optimizing frictional resistance through the use of elastic members and an urging member, ensuring the system operates with reduced axial rigidity and improved alignment of components.
Implementation Method 1
first elastic member and a second elastic member that are disposed on respective sides of the inner ring of the first bearing in the axial direction, and that elastically support the worm in the axial direction with respect to the inner ring of the first bearing
Implementation Method 2
an urging member that urges an outer circumference of the outer ring of the second bearing in the direction in which the inter-center distance decreases. A sum of first frictional resistance in the axial direction between the inner ring of the first bearing and the worm and second frictional resistance in the axial direction between the urging member and the outer circumference of the outer ring of the second bearing is less than engagement frictional resistance in the axial direction of the worm
Data Source
AI summary
In a speed reducer of an electric power steering system, a first bearing (30) supports a first end portion (18a) of a worm (18) so that the first end portion (18a) is movable in an axial direction (X). Elastic members (32, 33) elastically support the worm (18) in the axial direction (X). A second bearing (31) supports a second end portion (18b) of the worm (18). An urging member (60) oscillates and urges the worm (18). The sum of first frictional resistance (G1) in the axial direction (X) between an inner ring (34) of the first bearing (30) and the worm (18) and second frictional resistance (G2) in the axial direction (X) between the urging member (60) and an outer circumference (54a) of an outer ring (54) of the second bearing (31) is less than engagement frictional resistance (Gm) in the axial direction (X) of the worm (18).