Electric Power Assisted Steering for Solid Front Axle
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Solution Overview
Problem
Existing power assisted steering systems are not commercially available or capable of proper operation in vehicles with a solid front axle and significant gross axle weight rating, such as heavy-duty pickup trucks with a cab on frame architecture.
Innovation Solution
An electronically controlled power assisted steering assembly that integrates an electric motor with a recirculating ball nut mechanism and a drag link steering geometry, eliminating the need for hydraulic assistance and optimizing packaging for vehicles with a solid front axle, reducing power consumption and improving fuel efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If hydraulic power assisted steering is used in vehicles with solid front axle and high GAWR, then steering assistance is provided, but the system becomes complex and expensive with hydraulic components
Solution Approach 1:
The patent replaces the hydraulic power assisted steering system with an electric motor-driven recirculating ball mechanism. The electric motor (part number 240) directly drives the recirculating ball nut (part number 150) to provide steering assistance, eliminating hydraulic pumps, reservoirs, hoses, and fluid management systems while maintaining the ability to assist steering in high GAWR vehicles with solid front axles
2Reliability
If column-mounted EPAS is used to directly drive the steering column, then steering assistance is provided, but the cost increases significantly
Solution Approach 1:
The patent introduces a recirculating ball mechanism as an intermediary between the electric motor and the steering linkage. The recirculating ball nut converts the rotary motion of the electric motor into linear motion of the rack, which then moves the steering linkage. This intermediary mechanism provides the necessary mechanical advantage and motion conversion while keeping the overall system cost-effective for heavy-duty applications
3Reliability
If rack and pinion EPAS is used with electric motor directly driving the pinion, then steering assistance is provided, but the system is not suitable for solid front axle vehicles with high GAWR
Solution Approach 1:
The patent employs a recirculating ball mechanism that provides dynamic mechanical advantage adjustment. The recirculating ball nut allows for variable gear ratios and mechanical advantage depending on the steering position and load conditions, making the system adaptable to the high torque requirements of solid front axle vehicles while maintaining responsiveness. This dynamic characteristic enables the system to handle both light and heavy steering conditions effectively
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
Enables efficient steering assistance for vehicles with high front gross axle weight ratings, enhancing operational capabilities and fuel economy by eliminating hydraulic components and optimizing steering assembly design.
Implementation Method 1
an electric motor coupled to a gear train for rotating within the mechanism and thereby transferring the rotary motion of the ball nut to the steering gear
Data Source
AI summary
A wheeled vehicle includes a solid vehicle frame and a solid front axle including wheels movable to change the direction of the vehicle, a steering assembly including a steering wheel, a steering shaft coupled with the steering wheel, and a rotary output member having an end selectively movable in response to an input to the steering wheel, the solid front axle vehicle includes an electric power assist steering (EPAS) system for selectively steering the vehicle separately from any input to the steering wheel. The EPAS system includes a motor having a rotary output coupled to a steering gear and a steering rack having a longitudinal extent defining an axis having an end coupled a tie rod of the steering assembly. The longitudinal axis of the EPAS assembly is aligned with or transverse to the forward vehicle direction so its output is coupled to the output of the steering wheel and can be actuated independently.