Steering Device Fault Torque Shock Reduction
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Solution Overview
Problem
In steering devices with electric motor drive systems, faults can lead to loss of assist torque during automatic steering, causing vehicle behavior disturbances and torque shocks when shifting from automatic to assist control, especially if the driver is not holding the steering wheel.
Innovation Solution
A steering device with multiple electric motor systems and a controller that maintains automatic steering using a fault-free system until the driver intervenes, then adjusts output limits to reduce torque shock during assist control, setting lower output limits after fault detection to prevent vehicle behavior disturbances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the maximum current limit value is set to zero when vehicle speed is lower than predetermined threshold after fault detection, then heat generation of electric motor is suppressed and driver can notice fault, but assist torque cannot be generated and vehicle behavior is disturbed
Solution Approach 1:
The patent changes the parameter of maximum current limit value from zero (prior art) to a non-zero value that is lower than the normal operation limit. This allows the electric motor to generate limited assist torque after fault detection, preventing vehicle behavior disturbance while still suppressing excessive heat generation and allowing driver awareness of the fault condition.
2Ease of operation
If torque equivalent to before fault is output after shifting to assist control, then steering assist function is restored, but torque shock is transmitted to driver and vehicle behavior is disturbed when fault occurs in other normal systems
Solution Approach 1:
The patent applies beforehand cushioning by setting the maximum current limit value to a level that prevents torque shock before it can occur. When fault is detected and system shifts to assist control, the limited current limit ensures that even if other systems fail, the torque output remains within safe boundaries that prevent sudden torque shocks to the driver, while still providing necessary steering assist.
3Extent of automation
If driver takes hand off steering wheel during automatic steering and fault occurs, then automatic steering continues, but torque is not generated and vehicle behavior is disturbed until driver holds steering wheel
Solution Approach 1:
The patent implements feedback by continuously monitoring the operational status of electric motor systems and dynamically adjusting the maximum current limit value based on fault detection. When a fault is detected during automatic steering, the system provides feedback by setting an appropriate current limit that maintains stable vehicle behavior, and this information is used to control the assist torque generation even when driver hand position is not detected.
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
Ensures stable and continuous vehicle operation by minimizing torque shocks and maintaining vehicle control during faults, allowing safe driving even when a fault occurs in one electric motor system during automatic steering.
Implementation Method 1
an electric drive device which includes a plurality of systems having electric motors composed of a combination of driving circuits and winding sets
Data Source
AI summary
Provided is a steering device which allows continued safe travel in the event of a fault during automatic steering control. The steering device is equipped with an electric drive device composed of a plurality of systems of electric motors and has an assist control function for assisting a driver in steering and an automatic steering control function for automatically controlling the steering angle of steered wheels on the basis of a steering angle instruction value. In the event a fault occurs in one of the electric motor systems of the electric drive device during control under automatic operation control, a controller in the steering device maintains automatic operation control S36 using the electric motor of a normally operating system not suffering from a fault, and then, upon shifting to assist control S21, the controller sets the output limit value of the electric motor to a fault-time output limit value, which is less than a normal-time output limit value set when all electric motor systems are operating normally.