Belt Speed Reducing Apparatus for Electric Power Steering
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Solution Overview
Problem
Existing electric power steering systems face challenges in reducing operating sound and maintaining excellent steering feel while avoiding layout difficulties and high fabrication costs, particularly due to issues with backlash adjustment in gear speed reducing mechanisms and belt tension control.
Innovation Solution
A belt speed reducing apparatus with a drive pulley and driven pulley having helical gears, where the twist angle and friction coefficient relationship is optimized to minimize thrust force and face pressure, and a tension adjusting mechanism using materials with different thermal expansion coefficients to maintain constant belt tension, eliminating the need for elastic members and reducing temperature-induced tension variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a gear speed reducing mechanism is used, then speed reduction is achieved, but backlash adjustment becomes difficult and fabrication cost increases
Solution Approach 1:
The patent changes the physical parameters of the belt (thickness, material properties) to directly control backlash. By selecting belt thickness within a specific range (0.5-2.0 times the tooth height), the system achieves automatic backlash adjustment without complex mechanical adjustment mechanisms, resolving the contradiction between speed reduction and ease of manufacture.
Solution Approach 2:
The patent replaces the traditional gear meshing mechanism with a belt-pulley system. This substitution eliminates the need for precise gear tooth meshing and backlash adjustment mechanisms, simplifying manufacturing while maintaining speed reduction functionality through the belt's elastic deformation.
2Power
If belt tension is increased, then power transmission improves, but operating noise increases
Solution Approach 1:
The patent optimizes belt thickness parameters to achieve optimal tension distribution. By controlling belt thickness within a specific range relative to tooth height, the system maintains sufficient tension for power transmission while reducing excessive face pressure that causes noise, thus resolving the contradiction between power transmission and noise reduction.
3Reliability
If elastic members are used for tension adjustment, then belt tension control improves, but device complexity increases
Solution Approach 1:
The patent enables the belt system to self-regulate tension through the elastic deformation properties of the belt itself. The belt's inherent elasticity allows it to automatically accommodate tension variations during operation without requiring external elastic members or complex adjustment mechanisms, resolving the contradiction between reliability and device complexity.
4Ease of operation
If helical gears are used, then smooth operation improves, but thrust force increases
Solution Approach 1:
The patent replaces helical gears with a belt-pulley system featuring helical grooves. This substitution maintains the smooth operation benefits of helical engagement through the grooved belt design while eliminating the axial thrust force generated by traditional helical gears, as the belt system does not produce the same directional force components.
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 operating noise, enhances durability, simplifies backlash adjustment, and maintains optimal belt tension, thereby improving steering feel and reducing fabrication costs by integrating the motor shaft and gear components.
Implementation Method 1
a friction coefficient μ and a twist angle β are selected such that a relationship of tan β>μ is established
Implementation Method 2
a speed reducing mechanism comprising a drive pulley and a driven pulley
Implementation Method 3
a canceling expansion portion (274) comprising a material different from a material of the housing (251)
Data Source
AI summary
A belt speed reducing apparatus for an electric power steering apparatus includes a drive pulley having a first helical gear, a driven pulley having a second helical gear and a drive belt having a third helical gear in which a relationship of tan β<μ is established between a twist angle β of the respective helical gears and a friction coefficient μ between the first or the second helical gear and the third helical gear. Further, an electric power steering apparatus for adjusting a backlash between gears of a speed reducing apparatus brought in mesh with each other or adjusting a tension of a belt of a speed reducing apparatus.