Motorcycle Front Fork Stroke Detection via Coil Inductance
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Solution Overview
Problem
Existing stroke detection devices for motorcycles require complex processing inside the stem shaft cylinder, increasing costs and complexity.
Innovation Solution
A stroke detection device with a cylindrical stem shaft made of conductive material and a movable coil, where the coil's inductance variation is used to detect changes in front fork length, without the need for internal processing, and optionally includes a shield member with an insulator to prevent eddy currents and improve detection precision.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the coil is fixed inside the cylinder of the stem shaft, then the coil can be retained securely, but processing must be performed on the inner circumferential surface of the cylinder to provide retaining portions
Solution Approach 1:
Instead of fixing the coil to the inner surface of the stem shaft cylinder (which requires complex internal processing), the patent inverts the arrangement by having the conductor bar extend into the cylinder and the coil wrap around the outer surface of the conductor bar. This eliminates the need for internal retaining portions while securing the coil through the conductor bar's presence.
Solution Approach 2:
The patent extracts the coil from the internal space of the stem shaft cylinder and relocates it to the external surface of the conductor bar. This extraction eliminates the need for internal processing of the cylinder while maintaining the functional relationship between the coil and the moving components.
2Measurement precision
If the conductor bar extends upward through the stem shaft cylinder, then stroke detection is enabled, but eddy currents may be generated that affect detection precision
Solution Approach 1:
The patent acknowledges that the conductor bar extending into the cylinder may generate eddy currents, but converts this potential harm into a benefit by positioning the coil to detect both the useful inductance changes from stroke movement and the eddy current effects. The system uses the total inductance variation, which includes eddy current contributions, as part of the detection signal.
Solution Approach 2:
The coil acts as an intermediary that mediates between the conductor bar's movement and the detection system. It transforms the mechanical stroke and electromagnetic effects (including eddy currents) into measurable inductance variations, allowing the system to detect stroke while accounting for eddy current effects.
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 reduces processing costs, prevents eddy currents, and enhances detection precision and reliability by eliminating the need for internal stem shaft processing and using a shield member to stabilize the coil and prevent deflection.
Implementation Method 1
a variation in inductance of the coil based on change in length in which the coil entering the cylinder of the stem shaft through a lower end opening of the cylinder of the stem shaft and the cylinder of the stem shaft overlap each other is output as a value for obtaining the variation in length with respect to the reference length of the front forks
Implementation Method 2
a shield member with an insulator to prevent eddy currents and improve detection precision
Data Source
Figure 1~2
Figure 3
Figure 4~6
AI summary
A stroke detection device (1) includes a stem shaft (2) which is formed of a conductor in a shape of a cylinder, in which a center line of the cylinder is located in parallel to center lines of inner tubes (12) and outer tubes (11) of front forks (10) coupled to a bracket, and which serves as a steering center axis of handlebars (9a) of a motorcycle, and a coil (3) which is formed of a conductor and provided so as to be movable in a direction along the center line of the cylinder (2c) of the stem shaft (2) with movement in a direction along the center line of the inner tubes (12) and the outer tubes (11) of the front forks (10), in which a variation in inductance of the coil (3) based on change in length in which the coil (3) and the cylinder (2c) of the stem shaft (2) overlap each other is output.