Steering System Magnetic Torque Overlay Lash Compensation
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Solution Overview
Problem
Steering systems experience degradation in steering feel due to lash between the steering wheel and road wheels, which is not effectively addressed by existing technologies, leading to undesirable steering sensations like jerky or disconnected movements, especially in the on-center position.
Innovation Solution
A method and system that determine a rack pressure value and compensation friction value based on driver torque, differential pressure, and vehicle speed to generate a torque command that compensates for lash, using a control module to adjust the steering system's assist torque, thereby maintaining a lash-free connection between the steering wheel and road wheels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If traditional hydraulic steering systems are used, then steering assist is provided to the driver, but lash between the steering wheel and road wheels degrades steering feel
Solution Approach 1:
The control module proactively determines compensation friction values based on predicted lash conditions before they significantly degrade steering feel. By calculating required compensation torque in advance based on steering angle and velocity, the system maintains smooth steering characteristics before lash becomes problematic.
Solution Approach 2:
The system dynamically changes the assist torque parameter by adding compensation friction values to the base assist torque. This parameter adjustment compensates for lash effects across different steering conditions, transforming the steering feel from jerky to smooth while preserving the hydraulic assist function.
2Reliability
If lash compensation is implemented through torque overlay, then steering feel is improved, but system complexity increases
Solution Approach 1:
The control module performs multiple functions using the same computational resources: it determines base assist torque, calculates compensation friction values, and generates torque commands all within a single integrated control system. This multi-functionality approach adds lash compensation capability without requiring separate dedicated hardware systems.
Solution Approach 2:
The patent replaces mechanical lash compensation mechanisms (such as mechanical preloading devices or adjustable clearances) with an electronic torque overlay system. The control module computes compensation torque based on steering parameters and applies it through electronic control, substituting complex mechanical adjustment mechanisms with a more compact electronic control approach.
3Reliability
If friction compensation is dynamically adjusted, then steering smoothness is enhanced, but computational requirements increase
Solution Approach 1:
The control module applies friction compensation selectively based on operating conditions rather than continuously at maximum level. By determining compensation values based on actual lash conditions (steering angle, velocity), the system applies just enough computational effort to maintain smoothness without excessive processing requirements during all steering maneuvers.
Solution Approach 2:
The system updates compensation friction values at appropriate intervals during steering operation, recalculating based on changing steering parameters. This periodic recalculation maintains steering smoothness through dynamic adaptation while avoiding continuous high-frequency computation that would increase processing demands unnecessarily.
Data Source
AI summary
Technical solutions for compensating for lash in a steering system are described. An example method includes determining a rack pressure value based on a driver torque value and a differential pressure across a rack of the steering system. The method also includes determining a compensation friction value based on a position of a handwheel of the steering system and a speed of a vehicle equipped with the steering system. The method also includes computing a pressure value based on the rack pressure value and the compensation friction value. The method also includes generating a torque command using the pressure value, the torque command being added to the driver assist torque for the steering system.