Roller Screw Steering Spindle for Return-Direction Self-Locking
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Solution Overview
Problem
Steer-by-wire steering systems face challenges in maintaining wheel alignment and preventing unintended steering angle adjustments due to lateral forces during cornering, often requiring additional braking or locking mechanisms to prevent self-locking in the return direction.
Innovation Solution
The use of a roller screw drive with different efficiencies in the drive and return directions, designed to be non-self-locking in the drive direction for efficient operation and self-locking in the return direction to maintain wheel alignment without additional inhibiting units, utilizing a low torque in the return direction to prevent axial displacement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a conventional roller screw drive with high efficiency in both directions is used, then drive torque is reduced and installation space is minimized, but the spindle becomes self-locking in the return direction causing unintended steering angle adjustments under lateral forces
Solution Approach 1:
The roller screw drive is designed with direction-dependent efficiency characteristics. In the drive direction, the efficiency is high (low friction) to minimize drive torque and installation space. In the return direction, the efficiency is reduced (higher friction) to prevent self-locking and maintain wheel alignment stability under lateral forces. This local differentiation of friction properties resolves the contradiction between power efficiency and alignment reliability.
Solution Approach 2:
The invention changes the friction parameter of the roller screw drive based on operation direction. By adjusting the efficiency parameter - high efficiency for driving motion, low efficiency for return motion - the system achieves both reduced drive torque requirements and prevented unintended steering adjustments, resolving the contradiction between power consumption and positioning reliability.
2Reliability
If a braking or locking mechanism is added to prevent self-locking in the return direction, then wheel alignment stability is improved, but device complexity and installation space increase
Solution Approach 1:
The roller screw drive itself provides the alignment stability function through its direction-dependent friction characteristics, without requiring external braking or locking mechanisms. The system serves its own positioning requirement through the inherent properties of the roller screw drive, eliminating the need for additional complexity.
Solution Approach 2:
The invention extracts the alignment stability function from separate braking/locking mechanisms and integrates it directly into the roller screw drive's friction characteristics. By taking out the need for additional locking components and embedding the stability function within the drive mechanism itself, device complexity is reduced while maintaining reliability.
3Reliability
If friction is increased in the return direction to prevent self-locking, then wheel alignment stability is improved, but drive torque requirements increase
Solution Approach 1:
The friction property is differentiated by direction rather than uniformly increased. High friction is applied only in the return direction to prevent self-locking, while the drive direction maintains low friction for minimal torque requirements. This localized application of friction resolves the contradiction between alignment stability and power efficiency.
Solution Approach 2:
The roller screw drive exhibits asymmetric friction characteristics - low friction in the drive direction and high friction in the return direction. This asymmetry allows the system to achieve both goals: minimal drive torque during normal operation and prevented unintended adjustments during lateral loading, resolving the contradiction between power and reliability.
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
This design achieves efficient and cost-effective integration with reduced installation space, low noise, and long service life, ensuring that wheels remain aligned without unintended steering adjustments, even under maximum lateral forces, without the need for additional braking or locking units.
Implementation Method 1
the roller screw drive has different efficiencies in the drive direction and in the return direction
Data Source
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AI summary
The invention relates to a steer-by-wire steering system for a motor vehicle, comprising a spindle drive (20) having a linearly movable leadscrew (27), the spindle drive (20) being designed as a roller screw drive. The invention is characterized by a roller screw drive having different efficiencies in the driving direction thereof and in the reverse-driving direction thereof.