The disclosure proceeds from a linear travel measurement apparatus for a compression travel of an electrically conductive spring of the generic type of the following description. A spring unit comprising a linear travel measurement apparatus of this kind and a measurement method for a compression travel of an electrically conductive spring are also subjects of the present disclosure.
Externally fitted measurement systems are known from the prior art for detecting a linear travel in a system which is spring-mounted by means of a telescopic spring arrangement, such as in a motorcycle suspension fork for example. Said measurement systems measure the linear travel or the insertion depth of the suspension fork with the aid of a potentiometer and a sliding contact. Disadvantages of this can be considered to include firstly the wear of the measurement system and secondly the exposed position on the outside of the slider tube which can lead to soiling and accordingly to reduced reliability of the measurement system.
Furthermore, MacPherson spring legs which are used, for example, for wheel suspension in motor vehicles are known from the prior art. Here, measurement of the compression can be performed, for example, by means of relatively expensive pressure force sensors.
DE 10 2007 017 308 B4 discloses a spring unit comprising a linear travel sensor which ascertains the changes in distance between two spring turns. Furthermore, the total compression travel is then deduced. The linear travel sensor used is based in one embodiment on the “coupled-coils” principle, that is to say a target on the spring changes the inductive coupling between two sensor coils. In a second embodiment, the target is of resonant design and comprises a resonant circuit. However, measurement of the inductive coupling remains substantially identical.