Electric Power Steering Control Unit Damping Signal Strategy
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Solution Overview
Problem
Existing electric power steering devices fail to effectively suppress collision noise produced by mechanical stoppers, which occurs when the rack bar movement is restricted, leading to further twisting of the torsion bar and increased noise.
Innovation Solution
An electric power steering device with a control unit that calculates and applies damping signals to the electric motor based on steering torque and torsion bar twist signals, incorporating a mechanical stopper with first and second stopper parts to control relative rotation between shafts, thereby minimizing collision noise from both the rack and mechanical stoppers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the rack bar movement is restricted by the electric motor output control to suppress rack stopper collision noise, then the rack stopper collision noise is reduced, but the torsion bar is more easily twisted and mechanical stopper collision noise increases
Solution Approach 1:
The control unit applies a counter torque to the rack bar in advance when detecting that the rack bar is approaching the terminal end, preventing the torsion bar from excessive twisting before the mechanical stopper engagement occurs, thereby suppressing mechanical stopper collision noise while maintaining rack stopper noise suppression
Solution Approach 2:
The control unit continuously monitors the rack bar position and torsion bar twist amount, and dynamically adjusts the electric motor output based on this feedback information to coordinate the engagement timing of both rack stopper and mechanical stopper, preventing excessive torsion bar twisting that would cause mechanical stopper collision noise
2Ease of operation
If the electric motor applies steering power to assist steering operation, then steering assist performance is improved, but collision noise from stoppers increases under certain conditions
Solution Approach 1:
The control unit dynamically adjusts the steering assist torque based on real-time detection of rack bar position and torsion bar twist amount, reducing or suspending assist torque when the rack bar approaches terminal ends to prevent stopper collision noise, while providing full assist torque during normal steering operations to maintain steering assist performance
3Stability of the object's composition
If the mechanical stopper is designed to suppress further relative rotation between shafts, then shaft rotation limitation is improved, but torsion bar twisting increases leading to more collision noise
Solution Approach 1:
The control unit performs preliminary action by applying counter torque to the rack bar before the mechanical stopper engagement occurs, preventing excessive torsion bar twisting that would lead to collision noise, while still allowing the mechanical stopper to effectively limit shaft rotation when needed
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 solution effectively reduces collision noise and enhances the durability of shock absorbers by controlling the contact between stopper parts, ensuring smooth steering operations and minimizing noise.
Implementation Method 1
a second shaft connected to the first shaft through a torsion bar
Implementation Method 2
a first damping signal calculation part that calculates a first damping signal representing a damping force against a steering force produced by the electric motor
Data Source
AI summary
In order to suppress an electric power steering device from generating a contact noise due to operation of a mechanical stopper and a rack stopper, there is provided a control unit in which a command signal Io applied to an electric motor used for assisting the steering power is calculated taking into consideration both a rack stopper side damping correction represented by a rack side damping correction signal Dr calculated in a rack side damping correction amount calculation part 21 and a mechanical stopper side damping correction represented by a mechanical side damping correction signal Dm calculated in a mechanical side damping correction amount calculation part 23.