Electric Power Steering Output Shaft Backlash Control
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Solution Overview
Problem
Conventional electric power-steering apparatuses experience vibration and noise due to inadequate suppression of backlash in the output shaft of the electric motor over time, leading to a decrease in preload and performance degradation.
Innovation Solution
The apparatus employs a tandem arrangement of single-row ball bearings with an elastic member, such as a compression coil spring, to apply a consistent preload to both bearings, ensuring stable backlash suppression and preventing noise and vibration by maintaining the elastic force over a long period.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a plate spring is used to apply preload to ball bearings supporting the output shaft, then backlash is suppressed initially, but the elastic force decreases over time due to repeated compression, leading to preload loss and increased vibration
Solution Approach 1:
The elastic member is segmented into multiple independent coil springs arranged in parallel, where each spring independently contributes to the total preload. This segmentation allows the load to be distributed across multiple elements, reducing the compression ratio of each individual spring and preserving their elastic force over time, thus maintaining stable preload and backlash suppression throughout the service life.
Solution Approach 2:
The invention changes the physical parameters of the elastic member by using multiple coil springs with smaller individual compression ratios instead of a single plate spring with large compression ratio. This parameter change ensures that each spring operates within its elastic limit over extended periods, preventing elastic force degradation and maintaining consistent preload application.
2Object-generated harmful factors
If the output shaft is pressed in the axial direction to eliminate backlash, then gear rattling noise is prevented, but the elastic member's stroke is reduced over time, causing preload loss
Solution Approach 1:
By dividing the elastic member into multiple coil springs, the total required preload is distributed across several elements. Each spring undergoes smaller axial displacement for the same preload force, thereby maintaining their elastic stroke capability over time while still achieving the necessary backlash elimination and preventing gear rattling noise.
Solution Approach 2:
The multiple coil springs are pre-configured to provide the necessary preload force from the outset, cushioning against axial displacements that would cause backlash. This beforehand cushioning effect is maintained over time because the smaller compression ratio of each spring preserves its elastic potential, continuing to prevent gear rattling noise throughout the service life.
3Device complexity
If a single elastic member is used to apply preload, then the structure is simple, but the preload becomes unstable over time due to elastic force degradation
Solution Approach 1:
The elastic member is segmented into multiple coil springs arranged in parallel, where each spring independently provides a portion of the total preload. This segmentation enhances reliability because the failure or degradation of one spring does not compromise the entire preload system, and the distributed load reduces the compression ratio of each spring, preserving elastic force and ensuring stable preload over time.
Solution Approach 2:
The invention changes from a single elastic member with high compression ratio to multiple elastic members with lower individual compression ratios. This parameter change maintains or reduces overall system complexity while dramatically improving preload stability through reduced elastic force degradation in each individual spring.
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 stabilizes backlash in the output shaft, reducing vibration and noise during operation by ensuring a consistent preload is applied to both ball bearings, even under changing torque directions and loads.
Implementation Method 1
an elastic member that has an elastic force in the axial direction is held in an elastically compressed state in the axial direction between the back end surface of the engagement hole and the tip end surface of the engagement rod section
Implementation Method 2
an elastic member, such as a compression coil spring
Data Source
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AI summary
Construction of an electric power-steering apparatus is achieved that, by stably suppressing backlash of an output shaft 6a of an electric motor 5 over a long period of time, is able to stably reduce vibration and strange noise that occurs during operation. The front end section of the output shaft 6a and the base end section of a worm 7 are connected such that torque can be transmitted and such that relative displacement in the axial direction is possible An elastic member 31 having an elastic force in a direction that separates the output shaft 6a and worm 7 is provided in the connecting section between the output shaft 6a and the worm 7. Due to the elastic force of the elastic member 31, together with the tandem arrangement contact angles, the preload is applied to a pair of ball bearings 14a, 14b that support the output shaft 6a with respect to the motor case 13 such that the output shaft 6a can rotate freely.