Rear-Axle Steering Linear Actuator With Inductive Position Sensing
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Solution Overview
Problem
Existing linear actuators for rear axle steering in motor vehicles face issues with expensive magnetic-inductive sensors that are prone to demagnetization at high temperatures and require precise alignment, and the pushrod is susceptible to unwanted deflections affecting measurement accuracy.
Innovation Solution
The use of an inductive linear travel sensor with a position transmitter made of metal and a curved contour to compensate for deflections, allowing for contactless and precise position detection without complex constructive measures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a magnetic-inductive linear travel sensor is used for position detection, then position detection can be performed, but the sensor is prone to demagnetization at high temperatures and requires precise alignment
Solution Approach 1:
The patent replaces the magnetic-inductive position transmitter (permanent magnet) with an inductive position transmitter made of electrically conductive metal. This substitution eliminates the magnetic field generation requirement and replaces it with eddy current-based sensing, thereby avoiding demagnetization issues at high temperatures while maintaining contactless position detection capability
Solution Approach 2:
The patent changes the fundamental operating principle from magnetic-inductive to purely inductive by using an electrically conductive metal target instead of a permanent magnet. This parameter change in the sensing mechanism allows the system to operate reliably at high temperatures without the magnetic field stability issues that plague magnetic-inductive sensors
2Measurement precision
If a permanent magnet is used as position transmitter, then position detection is enabled, but the magnet is expensive and requires precise pole alignment
Solution Approach 1:
The patent substitutes the permanent magnet with an electrically conductive metal target that interacts with the inductive sensor through eddy currents. This replacement eliminates the need for expensive rare-earth magnets and complex pole alignment procedures, while maintaining accurate position detection through the inductive sensing principle
Solution Approach 2:
The patent uses a simple electrically conductive metal target instead of an expensive permanent magnet. The metal target can be made from common conductive materials that are inexpensive and easy to manufacture, replacing the costly magnetic components while achieving the same functional goal of position detection
3Force
If the pushrod is subjected to forces from drive connection and wheel carriers, then the actuator can transmit force, but unwanted deflections occur affecting measurement accuracy
Solution Approach 1:
The patent replaces the magnetic-inductive sensing system with an inductive system using an electrically conductive metal target. This substitution makes the position detection immune to mechanical deflections because the inductive field is less sensitive to positional variations caused by pushrod deflection, thereby maintaining measurement accuracy even when force transmission causes unwanted movements
Solution Approach 2:
The patent introduces an electrically conductive metal target as an intermediary between the inductive sensor and the pushrod. This intermediary element decouples the measurement system from the mechanical forces acting on the pushrod, allowing force transmission while maintaining accurate position detection through eddy current interactions that are less sensitive to deflection
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
Enables accurate and cost-effective position detection of the pushrod, resistant to heating and deflections, ensuring reliable operation of the linear actuator.
Implementation Method 1
A position receiver arranged on the housing side is provided with a receiver section which can be provided with a plurality of, for example, imprinted coils which generate the magnetic field
Implementation Method 2
A position transmitter, also referred to as a target, interacting with the position receiver is associated with the pushrod. The position transmitter has metallic sections or is formed of metal and is electrically conductive
Implementation Method 3
The coil usually emits a magnetic field as part of an oscillating circuit/oscillator, which causes eddy currents in the passing, electrically conductive position transmitter
Data Source
AI summary
The disclosure relates to a linear actuator, the housing of which encloses a pushrod which is guided displaceably along a longitudinal axis. The linear actuator includes a linear travel sensor intended for determining a position of the pushrod. A housing-side position receiver of the linear travel sensor includes a receiver section extending along the longitudinal axis, and a pushrod-side position transmitter that interacts contactlessly with the position receiver. The position transmitter is made from an electrically conductive material, and a transmitter contour of the linear travel sensor is curved about at least one dimensional axis.