Steering Rack Force Detection via Dual Pinion Sensors
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Solution Overview
Problem
Existing steering actuators have limited resolution in detecting rack forces, especially at lower magnitudes (less than 300 Newtons), leading to inaccurate control and friction-related errors in steering systems, particularly in steer-by-wire and autonomous vehicles.
Innovation Solution
The implementation of a steering actuator system that includes a rack coupled to a steering knuckle, a ball nut, a motor, and sensors to detect the rotation of the pinion and shaft, which directly measures the force on the rack by accounting for axial deflection and spring washer compression, reducing friction effects and enhancing precision.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional single-sensor motor encoder is used to detect motor shaft rotation, then the device complexity is low, but the measurement precision of rack force is insufficient especially at lower magnitudes
Solution Approach 1:
The patent divides the detection function into two separate sensors: a motor encoder for detecting motor shaft rotation and a second sensor for detecting ball nut rotation. This segmentation allows each sensor to specialize in measuring specific rotational parameters, improving the overall precision of rack force detection while maintaining manageable system complexity through functional decomposition
Solution Approach 2:
The patent introduces a second sensor as an intermediary measurement device that indirectly measures rack force through ball nut rotation detection. This intermediary approach enables precise force measurement at lower magnitudes by measuring the rotational movement of the ball nut, which provides a more sensitive indicator of small forces than direct motor shaft measurement
2Extent of automation
If mechanical linkage assembly is eliminated in steer-by-wire systems, then the ease of operation and automation are improved, but the reliability of force feedback and control accuracy deteriorate due to friction errors
Solution Approach 1:
The patent implements a feedback mechanism by using two sensors to detect rotational positions and calculating rack force based on the relationship between motor shaft rotation and ball nut rotation. This feedback system continuously monitors and compensates for friction effects in the ball nut mechanism, maintaining reliable force feedback in automated steer-by-wire systems without mechanical linkages
Solution Approach 2:
The patent replaces traditional mechanical force feedback mechanisms with an electronic sensing and calculation system. By using rotational position sensors and computational algorithms to determine rack force from the relationship between motor and ball nut rotations, the system eliminates friction-prone mechanical force transmission while maintaining accurate force feedback for automated control
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
This solution allows for precise control of vehicle steering with improved accuracy and reduced friction errors, enabling better road and tire dynamics, even at lower force magnitudes, compared to traditional systems.
Implementation Method 1
a ball nut engaged with the rack, a first ring gear coupled to the ball nut... the motor to rotate the ball nut, via the first pinion and the first ring gear, to move the rack
Implementation Method 2
a motor encoder to detect a rotation of the first pinion... a sensor fixed to a second pinion, the second pinion engaged with the second ring gear, the second pinion to rotate as the second ring gear rotates, the sensor to detect a rotation of the second pinion
Data Source
AI summary
Methods and apparatus to determine rack force are disclosed. An example apparatus includes a rack to couple to a steering knuckle of a vehicle, a ball nut engaged with the rack, a first ring gear coupled to the ball nut, a first pinion fixed to a motor, the first pinion engaged with the first ring gear, the motor to rotate the ball nut to move the rack, a motor encoder to detect a rotation of the first pinion, a second ring gear coupled to the ball nut, and a sensor fixed to a second pinion, the second pinion engaged with the second ring gear, the second pinion to rotate as the second ring gear rotates, the sensor to detect a rotation of the second pinion, the rotation of the second pinion and the rotation of the first pinion corresponding to a force on the rack.