Steer-by-Wire Twin-Motor Torque Feedback Eliminates Gear Rattle
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Solution Overview
Problem
In steer-by-wire steering systems, the use of a single electric motor for torque feedback can result in gear rattling during sinusoidal motions or sharp position changes due to insufficient connection between the motor and gearing.
Innovation Solution
The implementation of a twin-motor torque feedback unit, where two motors are actively controlled to provide torque feedback and ensure continuous contact with their gearing, minimizing rattle and actively managing friction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single electric motor is used in the torque feedback unit, then the device complexity is reduced, but gear rattling occurs during sinusoidal motions or sharp position changes due to insufficient connection between the motor and gearing
Solution Approach 1:
The single motor is segmented into two separate motors (first torque feedback motor and second torque feedback motor). Each motor independently drives its own gearing, ensuring continuous contact and eliminating the connection instability that causes gear rattling. This segmentation resolves the contradiction by maintaining simple overall structure while improving local connection reliability.
2Reliability
If a spring is used to hold the motor in locked contact with the gearing, then the connection is maintained, but the spring is a passive component that relies on inherent properties and is not sufficiently firm in certain driving conditions
Solution Approach 1:
The system uses active control where the motors themselves generate the force to maintain locked contact with the gearing, rather than relying on a passive spring. The motors actively adjust their torque output to ensure continuous engagement, making the system self-sufficient and eliminating the need for separate passive connection components.
Solution Approach 2:
The control system monitors the operational state of the steering system and actively adjusts the torque output of both motors to maintain optimal engagement with the gearing. This feedback mechanism ensures the motors remain firmly connected during various driving conditions, replacing the passive spring's inherent properties with active, adaptive control.
3Reliability
If two motors are used to actively control torque feedback and ensure continuous contact with gearing, then gear rattling is minimized, but the device complexity increases
Solution Approach 1:
Both motors serve multiple functions: they provide torque feedback to the steering column and simultaneously maintain locked contact with their respective gearing. This multi-functionality allows the system to achieve reliable gear engagement without adding separate components, thereby reducing the overall complexity increase despite using two motors.
Solution Approach 2:
The functions of torque feedback provision and gear engagement maintenance are merged into the same two motors. Rather than having separate components for each function, the motors perform both roles, which optimizes the system structure and minimizes the complexity increase associated with using dual motors.
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
The twin-motor system effectively eliminates or significantly reduces gear rattling while providing a sensation of road feel to the driver, by actively managing the torque applied to the steering shaft.
Implementation Method 1
first and second torque feedback motors having output shafts connected to the steering shaft and each being operable to apply either a feedback torque or an offset torque to the steering shaft
Data Source
AI summary
A steer-by-wire steering system for a vehicle comprises: a rotatable steering shaft; a driver-operated steering input member connected to the steering shaft; and first and second torque feedback motors having output shafts connected to the steering shaft and each being operable to apply either a feedback torque or an offset torque to the steering shaft. The system further comprises: an angular position measuring arrangement for measuring the angular position of the steering shaft; an angular acceleration determination arrangement for determining the angular acceleration of the steering shaft; an envelope determination arrangement for establishing or determining an envelope of the measured or calculated angular acceleration of the steering shaft; a magnitude determination arrangement for determining the magnitude of the offset torque to be applied by the motors as a function of the envelope of the angular acceleration of the steering shaft, as modified by a scaling factor whereby a maximum defined offset torque is applied at a maximum defined amplitude and angular acceleration of the steering shaft.