Rear Wheel Steering Actuator Positioning for Positive Ackermann
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Solution Overview
Problem
Space constraints in vehicle suspensions often prevent the achievement of desired Ackermann geometry, leading to negative rear wheel Ackermann, which results in excessive tire wear, scrubbing, and reduced vehicle maneuverability and performance.
Innovation Solution
A rear wheel steering apparatus is designed with a steering actuator positioned aft of the rear axle and a tie rod/knuckle interface forward of the axle, utilizing a dual transfer linkage to generate positive Ackermann, allowing the inner rear wheel to steer at a greater angle than the outer rear wheel, thereby overcoming space constraints and achieving improved Ackermann geometry.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If conventional rear wheel steering components are mounted in traditional locations, then the structure is simple, but negative Ackermann geometry occurs reducing vehicle maneuverability
Solution Approach 1:
The patent positions the steering actuator in the longitudinal direction (aft of the rear axle) rather than laterally, creating a new spatial dimension for steering component arrangement. This longitudinal positioning, combined with the transfer linkage, enables positive Ackermann geometry without increasing lateral space requirements, thus improving maneuverability without compromising structural simplicity.
Solution Approach 2:
The transfer linkage acts as an intermediary mechanism between the steering actuator and the wheel knuckles. It translates the linear motion of the actuator into the appropriate angular motion at the wheels, enabling positive Ackermann geometry to be achieved while maintaining a relatively simple overall structure. The intermediary linkage resolves the conflict between simple mounting and optimal steering geometry.
2Ease of operation
If space constraints are ignored to achieve desired Ackermann geometry, then positive Ackermann can be achieved, but component mounting locations are blocked by driveshaft and brake packages
Solution Approach 1:
The patent moves the steering actuator from traditional lateral mounting positions to a longitudinal position aft of the rear axle. This dimensional change in component placement allows the actuator to be positioned in available space without interfering with the driveshaft and brake packages, while still achieving the desired positive Ackermann geometry through the transfer linkage mechanism.
Solution Approach 2:
The steering system is segmented into distinct functional components: the steering actuator positioned aft of the axle, the transfer linkage connecting the actuator to the wheels, and the wheel knuckles. This segmentation allows each component to be optimally positioned in available space, with the actuator in the longitudinal region and the linkages bridging the space to the wheels, avoiding interference with brake and driveshaft packages.
3Ease of operation
If inner rear wheel steers at greater angle than outer rear wheel, then positive Ackermann is generated improving handling, but linkage configuration becomes more complex
Solution Approach 1:
The transfer linkage serves as an intermediary that automatically generates the differential steering angles between inner and outer rear wheels. As the steering actuator moves, the transfer linkage mechanically ensures that the inner wheel turns at a greater angle than the outer wheel, achieving positive Ackermann geometry. This intermediary mechanism produces the desired handling performance without requiring complex control systems or additional components.
Solution Approach 2:
The transfer linkage is configured with asymmetric geometry where the inner linkage has different dimensions or positioning compared to the outer linkage. This asymmetric configuration naturally produces the asymmetric steering angles required for positive Ackermann, with the inner wheel turning at a greater angle than the outer wheel, thereby improving handling performance through inherent geometric design rather than complex active control.
Data Source
AI summary
Vehicle suspension systems are described herein. An example wheel steering apparatus includes a steering actuator to couple to a rear axle, a tie rod, and a transfer link to couple the steering actuator and the tie rod. The steering actuator is positioned on a first side of a first longitudinal axis of the rear axle and the tie rod positioned on a second side of the first longitudinal axis of the rear axle opposite the first side.