Steer-by-Wire Steering Wheel Holding via Motor Phase Shorting
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Solution Overview
Problem
In steer by wire systems, the steering wheel can become out of sync with the steering rack when the vehicle is stationary and powered off, as drivers may inadvertently rotate the steering wheel for support, leading to potential disturbances during synchronization.
Innovation Solution
A steering wheel holding system using an emulator motor, switching system, and controller that determines the vehicle's mode to either enable steer by wire operations or resist rotational movement by generating resistive torque when the vehicle is off, utilizing a multi-phase emulator motor and switching mechanisms like SPDT relays or MOSFETs to manage power and ground connections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the steering wheel is left free to rotate when the vehicle is stationary and powered off, then the driver can use it for support during entry and exit, but the steering wheel becomes out of sync with the steering rack
Solution Approach 1:
The emulator motor dynamically changes its operational state based on vehicle conditions. When the vehicle is off, the motor generates resistive torque to hold the steering wheel position. When the vehicle is on, the motor becomes free to rotate and follows the steering rack position, enabling synchronization. This dynamic state change resolves the contradiction between allowing free rotation for driver support and maintaining synchronization reliability.
2Reliability
If the steering rack is moved automatically during synchronization when the vehicle is powered off, then the steering wheel and steering rack can be synchronized, but the driver experiences disturbance
Solution Approach 1:
Instead of moving the steering rack automatically to synchronize with the steering wheel (which disturbs the driver), the system inverts the approach by holding the steering wheel in position using resistive torque from the emulator motor. This prevents the steering wheel from rotating freely while the vehicle is off, maintaining synchronization without requiring automatic movement of the steering rack that would disturb the driver.
3Reliability
If the emulator motor is continuously powered to maintain steering wheel position, then the steering wheel remains synchronized, but energy consumption increases
Solution Approach 1:
The emulator motor operates periodically rather than continuously. It generates resistive torque only when needed (when the vehicle is off and the steering wheel needs to be held). When the vehicle is on, the motor is free to rotate and follows the steering rack position without active power consumption for position holding. This periodic operation maintains reliability while minimizing energy consumption.
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
Effectively maintains steering wheel synchronization with the steering rack by preventing unintended rotation when the vehicle is off, ensuring smooth transition to driving mode with synchronized steering wheel positioning.
Implementation Method 1
short the plurality of phases of the emulator motor to ground resulting in the emulator motor generating a resistive torque
Data Source
AI summary
A steer by wire includes a steering wheel holding system. An emulator controller receives vehicle data from vehicle systems and determines whether a vehicle is in one of a driving mode and a non-driving mode. When the vehicle is in the driving mode, the emulator controller transmits a command to an emulator switching system to electrically couple the phases of an emulator motor to a power source to enable the emulator motor to implement steer by wire operations placing the steering wheel in an un-hold mode. When the vehicle is in the non-driving mode, the emulator controller transmits a command to the emulator switching system to electrically couple the phases of the emulator motor to ground to short the phases of the emulator motor to ground to generate a resistive torque to resist rotational movement of a steering wheel of the vehicle placing the steering wheel in a hold mode.