Electric Power Steering Ball-Screw Assembly
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional hydraulic power steering systems are not suitable for electric and/or hybrid commercial vehicles, necessitating a more effective and efficient power steering solution.
Innovation Solution
An electric power steering system utilizing a ball-screw assembly with a ball nut and ball shaft, coupled with an electric motor and gearset, which provides a mechanical advantage for steering, is implemented. This system includes a housing with splines to limit rotation and facilitate linear motion, and concertinaed jackets to manage air flow, offering a compact, robust, and cost-effective solution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If hydraulic power steering is used in conventional commercial vehicles, then steering assistance is provided, but it is not suitable for electric and/or hybrid commercial vehicles
Solution Approach 1:
The patent replaces the hydraulic power steering system with an electric power steering system that uses an electric motor to drive a ball-screw assembly. This substitution eliminates the need for hydraulic pumps, fluid reservoirs, and associated components, making the system suitable for electric and hybrid vehicles while maintaining steering assistance functionality.
Solution Approach 2:
The patent extracts and removes the hydraulic components (pump, fluid system) from the power steering system, retaining only the essential mechanical elements (ball-screw assembly, electric motor) needed to provide steering assistance. This extraction creates a simplified system that is compatible with electric vehicle architectures.
2Power
If a ball-screw assembly is used to convert rotational motion to linear motion, then mechanical advantage is provided, but the ball shaft may rotate relative to the housing
Solution Approach 1:
The patent introduces splines as an intermediary mechanism between the ball shaft and housing. These splines engage with corresponding splines in the housing to prevent relative rotation while allowing the ball shaft to translate axially. This intermediary element maintains the mechanical advantage of the ball-screw assembly while ensuring rotational stability.
3Ease of operation
If the ball shaft is constrained to prevent rotation, then linear motion is facilitated, but the system complexity increases
Solution Approach 1:
The patent segments the constraint function into discrete spline elements distributed around the circumference of the ball shaft. Rather than using a single complex constraint mechanism, multiple simple spline teeth are distributed around the shaft, each providing a portion of the rotational constraint. This segmentation simplifies the overall design while effectively preventing rotation and facilitating linear motion.
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 electric power steering system effectively supplements driver torque, enabling easier steering of heavy commercial vehicles, providing a mechanically robust, safe, and cost-effective alternative to hydraulic systems, while allowing for features like automatic driver assist and reduced power consumption.
Implementation Method 1
A plurality of bearings are circulatable through the helical track when the ball nut rotates relative to the ball shaft in order to translate the ball shaft relative to the ball nut
Implementation Method 2
An outer surface of the ball shaft includes at least one spline received by the housing in order to limit rotation of the ball shaft relative to the housing
Data Source
AI summary
An electric power steering assembly includes an electric motor, a gearset, and a ball-screw assembly. The gearset couples the electric motor and a ball nut of the ball-screw assembly such that the electric motor is operable to rotate the ball nut relative to the ball shaft. A plurality of bearings are circulatable through a helical track, which is defined between the ball nut and a ball shaft of the ball-screw assembly, when the ball nut rotates relative to the ball shaft in order to translate the ball shaft relative to the ball nut.