Steering Column Torque Estimation Without Torsion Bar
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Solution Overview
Problem
Existing vehicle steering systems that rely on torsion bars for column torque measurement face limitations such as restricted measurement range, hysteresis, noise, and high costs, which affect the accuracy and smoothness of steering feel, especially in steer-by-wire systems.
Innovation Solution
A system and method for estimating torsion bar torque without a torsion bar, using a processor and sensors to receive handwheel and motor position values, calculating torsion bar torque based on relative displacement and stiffness, and employing a disturbance style driver torque observer to provide accurate torque estimation and closed-loop feedback control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a torsion bar is used for column torque measurement, then the steering system can provide torque measurement capability, but the measurement range is restricted and hysteresis and noise occur
Solution Approach 1:
The patent replaces the mechanical torsion bar system with an electrical/electronic solution using a torque sensor that directly measures column torque. This substitution eliminates the mechanical limitations of the torsion bar (restricted measurement range, hysteresis, noise) while providing accurate torque measurement across a wider range through electronic sensing and signal processing.
2Measurement precision
If a torsion bar is used for column torque measurement, then torque measurement is achieved, but hysteresis and noise affect steering feel smoothness
Solution Approach 1:
The patent replaces the mechanical torsion bar with an electronic torque sensor system that directly measures column torque without the mechanical hysteresis and noise inherent in torsion bar systems. This substitution provides smoother steering feel by eliminating mechanical friction and elasticity effects while maintaining measurement accuracy through electronic sensing.
Solution Approach 2:
The patent implements a feedback control system where the torque sensor measures column torque and the controller uses this information to generate appropriate motor assist torque. This closed-loop feedback ensures smooth steering response by continuously adjusting the assist torque based on actual driver input, eliminating the hysteresis effects present in passive torsion bar systems.
3Measurement precision
If a torsion bar system is used, then column torque measurement is provided, but the system cost is high
Solution Approach 1:
The patent replaces the complex mechanical torsion bar assembly with a more cost-effective torque sensor and electronic control system. This substitution reduces manufacturing complexity, eliminates the need for precision-machined torsion bar components, and lowers overall system cost while maintaining or improving measurement capability through modern electronic sensing technology.
4Measurement precision
If the first sensor is disposed below the column compliance part, then the sensor can measure position, but the measurement range is restricted
Solution Approach 1:
The patent moves the first sensor from a position below the column compliance part to a position above it, effectively changing the measurement dimension. This positional change allows the sensor to measure handwheel position through the compliance part, enabling accurate torque estimation across a wider range of steering angles and positions by capturing the relative displacement between the handwheel and the compliant column section.
Data Source
AI summary
A method for estimating torsion bar torque includes receiving, from a first sensor, a handwheel position value indicating a position of a handwheel of a steering system and receiving, from a second sensor, a motor position value indicating a position of a motor of the steering system. The method also includes estimating a torsion bar torque value using the handwheel position value and the motor position value.