Rear Wheel Steering Cam Mechanism 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 Ackermann, which results in reduced vehicle maneuverability, increased tire scrubbing, and wear.
Innovation Solution
A rear wheel steering apparatus featuring a cam pivotably coupled to a rear axle with inner and outer tie rods arranged in a cross-tie configuration, allowing the tie rods to move different lateral distances, thereby increasing Ackermann and enabling positive Ackermann even in vehicles with solid rear axles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If traditional steering components are mounted on solid axles, then the vehicle suspension structure is simple, but negative Ackermann geometry occurs due to space constraints from driveshaft and brake packages
Solution Approach 1:
The patent introduces a cam mechanism that converts linear actuator motion into rotational cam motion, which then drives the tie rods through a cross-tie arrangement. This dimensional transformation allows the inner and outer tie rods to move different lateral distances, achieving positive Ackermann geometry without complicating the overall suspension structure.
Solution Approach 2:
The cam acts as an intermediary between the linear actuator and the tie rods. By positioning the cam pivot point and designing the cam profile, the system mediates the motion transfer to create the required differential lateral movement of the tie rods, thereby achieving the desired Ackermann geometry while maintaining structural simplicity.
2Ease of operation
If Ackermann geometry is not achieved due to space constraints, then component mounting is easier, but vehicle maneuverability and handling are reduced
Solution Approach 1:
The cross-tie arrangement with the cam mechanism transforms the motion from a single-plane linear movement to a differential lateral movement in multiple dimensions. This allows the tie rods to achieve the necessary different lateral distances for positive Ackermann, improving maneuverability within the constrained mounting space of solid axle vehicles.
Solution Approach 2:
The cam profile is specifically designed to change the motion parameters of the tie rods. By varying the cam rotation angle and profile shape, the system adjusts the lateral movement distances of the inner and outer tie rods to achieve optimal Ackermann geometry, thereby improving vehicle maneuverability without requiring additional mounting space.
3Object-affected harmful factors
If tie rods move equal lateral distances, then the steering mechanism is simpler, but tire scrubbing and wear increase due to negative Ackermann
Solution Approach 1:
The cam mechanism serves as an intermediary that differentiates the motion of the inner and outer tie rods. The cam profile is designed so that as the cam rotates, it pushes the inner and outer tie rods by different amounts, creating the differential lateral movement needed to eliminate tire scrubbing and wear caused by negative Ackermann geometry.
Solution Approach 2:
The cross-tie arrangement combined with the cam mechanism introduces a differential motion dimension. Instead of both tie rods moving equally in one dimension, the system creates differential lateral movements in the same plane, which eliminates the harmful tire scrubbing effect while maintaining a relatively simple mechanical structure.
Data Source
AI summary
Vehicle suspension systems are described herein. An example apparatus includes a cam pivotably coupled to a rear axle. The example apparatus also includes a first tie rod having a first end pivotably coupled to the cam and a second end pivotably coupled to a steering knuckle. The example apparatus also includes a second tie rod having a first end pivotably coupled to the cam outboard relative to the first end of the first tie rod and a second end coupled to a steering actuator.