Capacitive Rack Shaft Position Detection for Vibration-Resistant Steering
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Solution Overview
Problem
Existing position detection devices for rack shafts in vehicle steering systems suffer from accuracy errors due to vibrations caused by vehicle movement, leading to inaccuracies in detecting the rack shaft's position.
Innovation Solution
A position detection device that incorporates a capacitance member arranged around the rack shaft to form a capacitive load, where the capacitance between the rack shaft and the capacitance member changes with the rack shaft's position, allowing for accurate position calculation using a calculation unit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If magnetoresistive elements are used to detect rack shaft position, then position detection is achieved, but detection accuracy deteriorates due to vibrations causing rack shaft movement
Solution Approach 1:
The patent replaces the magnetoresistive detection system with a capacitance-based detection system. The capacitance member and rack shaft form a capacitor where the capacitance value changes with the relative position between them. This substitution eliminates the mechanical contact and magnetic field interactions that are sensitive to vibration-induced movements, thereby improving detection accuracy under vibrational conditions.
Solution Approach 2:
The patent utilizes the change in capacitance parameter as the detection basis. As the rack shaft moves axially, the distance between the capacitance member and the rack shaft changes, causing the capacitance value to vary. This parameter change provides a direct and stable relationship for position detection that is less susceptible to vibration effects compared to magnetoresistive methods.
2Measurement precision
If capacitance member is arranged around rack shaft periphery, then detection accuracy improves, but device complexity increases
Solution Approach 1:
The capacitance member serves multiple functions: it acts as both the detection element for position measurement and as a structural component of the steering device housing. By integrating the detection function into the existing structure, the patent avoids adding separate complex detection mechanisms, thereby limiting the increase in device complexity while achieving improved detection accuracy.
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 significantly enhances the detection accuracy of the rack shaft's position, reducing susceptibility to vibrations and enabling precise positioning over the entire stroke range.
Implementation Method 1
a capacitance member that is arranged around a periphery of the rack shaft and forms a capacitive load together with the rack shaft; and a calculation unit that calculates the position of the rack shaft based on a capacitance between the rack shaft and the capacitance member
Data Source
AI summary
A position detection device for detecting a position of a rack shaft having a rack teeth portion that meshes with a pinion gear in a part in an axial direction, is provided with a capacitance member that is arranged around a periphery of the rack shaft and forms a capacitive load together with the rack shaft, and a calculation unit that calculates the position of the rack shaft based on a capacitance between the rack shaft and the capacitance member. The capacitance member is arranged to face at least a part of the rack teeth portion. The capacitance changes in accordance with the position of the rack shaft.