Column Torque Estimation in Motor-Driven Power Steering
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Solution Overview
Problem
In motor-driven power steering systems, the sudden failure of a torque sensor can lead to inappropriate assist forces, degrading driving safety and causing a sense of heterogeneity during steering, especially in low-speed cornering situations, as the system is switched to manual mode without accurate driver torque sensing.
Innovation Solution
An apparatus and method that estimate column torque using vehicle speed, steering angle, and yaw rate to generate assist torque, incorporating a vehicle speed sensing unit, steering sensing unit, and yaw rate sensor, with a column torque estimation unit that calculates self-aligning torque and adjusts angular velocity gains to output a final column torque, compensating for differences between measured and estimated yaw rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the torque sensor breaks down, then the system switches to manual mode, but the driver experiences sudden heavy steering feel and safety is degraded
Solution Approach 1:
The patent introduces a column torque estimation unit that acts as an intermediary to provide virtual torque sensor data when the actual torque sensor fails. This estimation unit uses alternative sensors (steering angle sensor, vehicle speed sensor, yaw rate sensor) to calculate and provide column torque information to the control unit, maintaining the power steering assist function during torque sensor failure
Solution Approach 2:
The patent creates a virtual copy of the torque sensor function through the column torque estimation unit. Instead of relying on the failed physical torque sensor, the system generates estimated torque values that replicate the expected torque sensor output based on data from other sensors, allowing the power steering system to continue operating in automatic mode
2Reliability
If the MDPS system switches to manual mode when torque sensor fails, then the system avoids providing inappropriate assist force, but the driver feels strong heterogeneity during steering
Solution Approach 1:
The patent implements preliminary action by continuously monitoring the torque sensor status and preparing the column torque estimation mechanism in advance. When torque sensor failure is detected, the estimation unit is already ready to immediately provide torque information, preventing any interruption or sudden change in steering assist characteristics
Solution Approach 2:
The column torque estimation unit serves as an intermediary that smooths the transition between normal operation and failure mode. By providing continuously adjusted estimated torque values based on multiple sensor inputs, it maintains steering smoothness and eliminates the sudden heterogeneity that would occur with abrupt mode switching
3Measurement precision
If the torque sensor is used to determine driving condition, then the assist torque is accurately controlled, but the system becomes vulnerable to torque sensor breakdown
Solution Approach 1:
The patent implements universality by making the column torque estimation unit capable of providing torque information under multiple conditions - both normal operation (as backup) and torque sensor failure (as primary source). The estimation unit uses multiple sensors (steering angle, vehicle speed, yaw rate) to provide a universal torque measurement solution that works regardless of torque sensor status
Solution Approach 2:
The patent applies parameter changes by dynamically adjusting the weighting and combination of parameters from different sensors (steering angle, vehicle speed, yaw rate) in the column torque estimation calculation. The estimation algorithm modifies these parameters based on driving conditions and sensor reliability to maintain accurate torque measurement
Data Source
AI summary
An apparatus for estimating a column torque in a motor-driven power steering system includes a vehicle speed sensing unit configured to sense a vehicle speed; a steering sensing unit configured to sense a steering state of a driver; a yaw rate sensor configured to output a measured yaw rate by sensing a tilted state of a vehicle; and a column torque estimation unit configured to calculate a self-aligning torque and an estimated yaw rate based on the vehicle speed and the steering state inputted from the vehicle speed sensing unit and the steering sensing unit, estimate a column torque by adjusting angular velocity compensation gains with respect to a steering angular velocity for each of the estimated yaw rate and the vehicle speed, and output a final column torque by adjusting the estimated column torque according to a difference between the measured yaw rate and the estimated yaw rate.