Electric Power Steering Ball Screw Anti-Rotate Pins to Eliminate Lash
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Solution Overview
Problem
Conventional anti-rotational features in electric power steering gears allow for undesirable free rotational movement (lash) due to manufacturing tolerances and normal wear, compromising the stability of the steering mechanism.
Innovation Solution
Incorporation of anti-rotational pins with tapered ends and grooves in the housing, biased by a spring to ensure a tight fit, preventing rotation of the ball screw relative to the housing while allowing axial translation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional anti-rotational features (pin in hole through ball screw engaging axial groove in housing) are used, then the ball screw is rotationally fixed relative to the housing, but undesirable free rotational movement (lash) occurs due to manufacturing tolerances and normal wear
Solution Approach 1:
The invention changes the geometric parameters of the anti-rotational feature by introducing tapered surfaces on the pin and matching tapered grooves in the housing. The taper angle creates a wedge effect that converts radial compression forces into axial clamping forces, maintaining constant contact pressure between the pin and groove surfaces despite manufacturing tolerances and wear, thereby eliminating lash while preserving rotational fixation.
Solution Approach 2:
The invention introduces a spring element that dynamically adjusts the radial compression force applied to the tapered pin. The spring maintains constant contact pressure between the pin and tapered grooves, compensating for variations in manufacturing tolerances and wear over time. This dynamic adjustment ensures the anti-rotational feature remains effective without causing excessive friction or binding.
2Reliability
If tapered anti-rotational pins with spring bias are used to eliminate lash, then rotational fixation stability is improved, but device complexity increases
Solution Approach 1:
The invention segments the anti-rotational function into distinct components: a tapered pin element, matching tapered grooves in the housing, and a spring bias mechanism. This segmentation allows each component to be optimized independently and facilitates assembly and maintenance. The modular approach reduces overall system complexity compared to attempting to achieve the same function with a single monolithic anti-rotational feature.
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
Eliminates lash by ensuring a constant tight fit between the anti-rotational pins and grooves, enhancing the stability and precision of the steering mechanism.
Implementation Method 1
a spring disposed between the first anti-rotational pin and the second anti-rotational pin and configured to bias the first anti-rotational pin and the second anti-rotational pin in a radially outward direction
Implementation Method 2
the at least one tapered end of the first anti-rotational pin and the at least one tapered end of the second anti-rotational pin engage the first and second grooves respectively and thereby restrict rotation of the ball screw
Data Source
AI summary
An electric powered steering assembly includes a housing with a cylindrical portion, an interior wall of the cylindrical portion defining a first and second grooves extending in an axial direction, the first and second grooves having inwardly tapered walls. A ball screw is disposed in the housing, extending in the axial direction, and defining a through hole extending in a radial direction having a first and second ends. A ball nut is disposed in the housing surrounding the ball screw and configured to rotate relative to the housing. A first anti-rotational pin is disposed in the first end of the through hole, a second anti-rotational pin is situated in the second end of the through hole, and a spring is disposed between the anti-rotational pins. The spring is configured to bias the first and second anti-rotational pins in a radially outward direction towards the first and the second groves respectively.