CA1249354A

CA1249354A - Arrangement for determining the travel of a piston

Info

Publication number: CA1249354A
Application number: CA000462181A
Authority: CA
Inventors: Bernd Moser
Original assignee: Boge GmbH
Current assignee: ZF Boge GmbH
Priority date: 1983-08-30
Filing date: 1984-08-30
Publication date: 1989-01-24

Abstract

ARRANGEMENT FOR DETERMINING THE TRAVEL OF A PISTON

ABSTRACT OF THE INVENTION

A contactlessly, measuring arrangement for determining the position of a piston in a suspension component such as a vibra-tion damper, gas spring or hydro-pneumatic suspension. In one embodiment, the piston and/or the piston rod of the suspension component and a further electrode are mounted inside the cylinder of the suspension component to form a variable capacitor which, with the aid of other circuitry, measures the position of the piston. The further electrode preferably is in the form of a tube extending from the base of the cylinder into a hollow cylinder formed within the piston rod which receives the tube.
In the capacitive embodiment, additionally, there may be provided a further tube within the first tube to form a reference, second capacitor which is sensitive to pressure and temperature in the same manner as the first capacitor. The first capacitor serves as the variable capacitor for making a position measurement of the piston and the two tubes fixed relative to one another are employed to form the reference capacitor. In an alternative capacitive embodiment, a medium, such as a ceramic or epoxy resin cylinder enters between two electrodes, the extent of the entry of the dielectric medium being made to be proportional to the relative travel of the piston in the cylinder. In a further alternative embodiment, the outer surface of the cylinder has an inductive coil wound therearound for producing a magnetic field which is variable dependent upon the position of the piston within the cylinder. Both measuring arrangements when connected in a Wheatstone Bridge circuit produce an electrical signal indicative of the position of the piston.

Description

~;~4~354 NHL-BGG-02 Canada ARRANGEMENT FOR DETERMINING THE TRAVEL OF A PISTON
_ _ _ BACKGROUND OF TXE INVENTION

FIELD OF TEE INVENTION

The invention relates generally to an arrangement for determining ~he position or travel of a piston in hydraulic, pneumatic or hydro-pneumatic assemblies, such as vibration dampers, gas springs and hydro-pneumatic suspensions, and more particularly, to vi.bration dampers having the piston arranged to slide axially by means of a piStQn rod in a cylinder filled with at least one damping medium.

DESCRIPTION OF PRIOR ART

Suspensions are, for example, known from British Laid-Open Patent Application No. 8110972 and its corresponding German Laid-Open Patent Application DE-OS 32 12 433 in which each suspension unit of a vehicle has a sensor for adjusting its platform height producing an output magnitude which changes progressively with the platform height. The drawback here is that for adjusting the height of the platform, i.e. the spacing between the sprung and unsprung parts of the vehicle, a platform height sensor is provided at each respective suspension unit. Such a device is particularly expensive as the corresponding measured values between the vehicle suspension and the actual suspension unit or strut must be ascertained. Further, this determination of the measured value is expensive as corresponding measurement trans-ducers must be provided on the widely different parts of the vehicle.

In arrangements for the contactless measurement of the travel of a piston relating to some aspects of the invention, it has been found that because of different relatively moving $

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NHL BGG-02 Canada eLectLode components, precise evaluation of the electric signals produced by the electrodes becomes difficult owing to disturbing influences arising through unfavorable lengths of lead.
OBJECTS OF THE INVENTION
Taking the above as a starting point, it is the object of the invention to provide a method of measuring the piston travel, the apparatus of which operates without physical contact between the parts of the transducer thereby providing a high degree of reliability.
It is a further object of the invention to integrate the measuring aLrangement into the suspension of a vehicle, which arrangement has relatively small dimensions with respect to its incorporating unit and thereby requires no major modifications to existing hydraulic, pneumatic or hydro-pneumatic assemblies such as vibration dampers, gas springs and hydro-pneumatic suspensions.
It is yet a further object of this invention to substantially eliminate movable connecting leads so that disturbing influences arising from external variations of the measured value are avoided as far as possible so that a reliable evaluation of the variable capacitance is achieved.
SUMMARY OF THE INVENTION
One aspect of the invention resides broadly in a cylinder having an arrangement for determining a position of piston means therewithin, said cylinder having a space therewithin with said piston means disposed in said space for axial slidable movement ~49~54 N~L-BGG-02 Canada within said cylinder; at least one damping medium being disposed within said cylinder for damping sald axlal movement of said piston means with respect to said cylinder; said arrangement for determining the position of said piston means comprising: means for sensing a position of said piston means within said cylinder;
said position sensing means having a first element and a second element; said first element of said position sensing means being disposed to be movable with said piston means; said second element of said position sensing means being disposed to be substantially stationary with respect to said cylinder; said first element and said second element being electrically insulated one from the other; said two elements forming a variable impedance component which is subs~antially electrically reactive; said variable reactive electrical impedance varying, in operation, with said position of said piston means in said cylinder; an electrical signal being generated by at least one of said elements and being indicative of said position of said piston means; electrical connecting means, connected to at least one of said elements, for sensing said electrical signal, indicative of said position of said piston means; said first element comprising a first electrode and said second element comprising a second electrode of a capacitor; dielectric means being disposed at least in part between said first and second electrodes of said capacitor; said electrical connecting means being connected to said first electrode and to said second electrode; said piston means including a piston rod; said first electrode comprising at least a portion of said piston rod; said piston rod having a hollow portion; said cylinder having a base at one end thereof; said second electrode comprising a first, cylindrical tube which is disposed on and extends from said base of said cylinder means into said space within said cylinder; said hollow portion of said piston rod having a longitudinal axis NHL-BGG-02 Canada ~;~4g354 being substantially axially aligned with a longitudinal axis of said first tube; and said first tube at least during operation extending, at least partially, into said hollow portion of said piston rod.

Arother aspect of the invention resides in a cylinder having an arrangement for determining a position of piston means there-within, said cylinder having a space therewithin with said piston means disposed in said space for axial slidable movement within said cylinder; at least one damping medium being disposed within said cylinder for damping said axial movement of said piston means with respect to said cylinder; said arrangement for determining the position of said piston means comprising: means for sensing a position of said piston means within said cylinder;
said position sensing means having a first element and a second element; said first element of said position sensing means being disposed to be movable with said piston means; said second element of said position sensing means being disposed to be substantially stationary with respect to said cylinder; said first element and said second element being electrically insulated one from the other; said two elements forming a variable impedance component which is substantially electrically reactive; said variable reactive electrical impedance varying, in operation, with said position of said piston means in said cylinder; an electrical signal being generated by at least one of said elements and being indicative of said position of said piston means; electrical connecting means, connected to at least one of said elements, for sensing said electrical signal, indicative of said position of said piston means; said first element comprising a first electrode and said second element comprising a second electrode of a capacitor; dielectric means being disposed at least in part between said first and second ~4~3~ NHL-BGG-02 Canada electrodes o said capacitor; said electrical connecting means being connected to said first electrode and to said second electrode; said cylinder having a base; said piston means having a face disposed towards said base, said base of said damper cylinder being insulated from the cylinder to form said second electrode of said capacitor; and said face of said piston means forming said first electrode of said capacitor.

Yet another aspect of the invention resides broadly in a cylinder having an arrangement for determining a position of piston means therewithin, said cylinder having a space there-within with said piston means disposed in said space for axial slidable movement within said cylinder; at least one damping medium being disposed within said cylinder for damping said axial movement of said piston means with respect to said cylinder; said arrangement for de~ermining the position of said piston means comprising: means for sensing a position of said piston means within said cylinder; said position sensing means having a first element and a second element; said first element of said position sensing means being disposed to be movable with said piston means; said second element of said position sensing means being disposed to be substan~ially stationary with respect to said cylinder; said first element and said second element being electrically insulated one from the other; said tWG elements forming a variable impedance component which is substantially electrically reactive; said variable reactive electrical impedance varying, in operation, with said position of said piston means in said cylinder; an electrical signal being generated by at least one of said elements and being indicative of said position of said piston means; electrical connecting means, connected to at least one of said elements, for sensing 4a ~4~3~ NHL-BGG-02 Canada said electrical signal, indicative of said position of said piston means; and an impedance bridge, connected to said connecting means, for generating an electrical signal indicative of a position of said piston means.

A further aspect of the invention resides in a cylinder having an arrangement for determining a position of piston means therewithin, said cylinder having a space therewithin with said piston means disposed in said space for axial slidable movement within said cylinder; at least one damping medium being disposed within said cylinder for damping said axial movement of said piston means with respect to said cylinder; said arrangement for determining the position of said piston means comprising: means for sensing a position of said piston means within said cylinder;
said position sensing means having a first element and a second element; said first element of said position sensing means being disposed to be movable with said piston means; said second element of said position sensing means being disposed to be substantially stationary with respect to said cylinder; said first element and said second element being electrically insulated one from the other; said two elements forming a variable impedance component which is substantially electrically reactive; said variable reactive electrical impedance varying, in operation, with said position of said piston means in said cylinder; an electrical signal being generated by at least one of said elements and being indicative of said position of said piston means; electrical connecting means, connected to at least one of said elements, for sensing said electrical signal, indicative of said position o~ said piston means; said first element comprising a first electrode and said second element comprising a second electrode of a capacitor; dielectric means 4b NHL-BGG-02 Canada being disposed at least in part between said first and second electrodes of said capacitor; said electricaI connecting means being connected to said first electrode and to said second electrode; said piston means including a piston rod;
said first electrode comprising at least a portion of said piston rod; capacitance measuring circuitry for connection to said capacitor; said capacitance measuring circuitry comprising a capacitor bridge; said variable capacitor forming one of the arms of one half of sai.d capacitor bridge; and an amplifier being connected to said capacitor bridge for generating an electrical signal corresponding to the position of said piston in said damper cylinder.

A yet further aspect of the invention resides broadly in a cylinder having an arrangement for determining a position of piston means therewithin, said cylinder having a space therewithin with said piston means disposed in said space for axial slidable movement within said cylinder; at least one damping medium being disposed within said cylinder for damping said axial movement of said piston means with respect to said cylinder; one of said at least one damping medium being hydraulic damping oil; said arrangement for determining the position of said piston means comprising: said piston means including a circular, hollow piston rod; said cylinder having a base at one end thereof from which a hollow circular cylindrical, first tube extends into said space and also into said hollow piston in a telescopic relationship therewith, thereby forming, with a dielectrical material, comprising said hydraulic damping oil, disposed between said first tube and said piston rod, a variable, first capacitor; a longitudinal axis of said piston rod being substantially aligned with a longitudinal axis of said first 4c g NHL-BGG-02 Canada tube; said first tube being insulated from said cylinder and said hollow piston rod; a first lead being connected to said first tube; and a second lead being connected to said hollow piston rod.

Yet another further aspect of the invention resides broadly in an arrangement for measuring relative travel of a piston in a cylinder, comprising: a supporting member housing a first electrode which is mounted substantially fixed but substantially electrically insulated with respect to the supporting member; a second electrode spaced from the first electrode to define a space therebetween, said second electrode being substantially fixed with respect to the first electrode and being substantially electrically insulated from the supporting member, said first and second electrodes in use forming a capacitive reactance; a reactance varying member which is mounted to move in accordance with said relative travel between the piston and the cylinder, said reactance varying member being so disposed that its movement changes the capacitance between said first and second electrodes in accordance with said relative movement between the piston and the cylinder; and electrical connecting means being connected to said fixed first and second electrodes for measuring the capaci-tance formed therebetween and for producing a signal indicative of relative movement between the piston and the cylinder.

An additional aspect of the invention resides broadly in an arrangement for measuring relative travel of a piston in a cylinder which is part of a hydro-pneumatic assembly, comprising:
a suppor~ing member in the form of a hollow piston rod and housing having fixed first and second spaced substantially 4d ~93 NHL-BGG-02 Canada coaxial tubular electrodes which are bo~h substantially electri-call~ insulated from the supporting member and mounted in a substantially fixed relationship with respect to each other to form a substantially annular gap; electrical leads connected to said first and second electrodes, said first and second elec-trodes in use forming a variable capacitance; a sleeve-like member which is mounted for movement reflecting said relative travel of the piston in said cylinder, said sleeve-like member being disposed to enter said substantially annular gap to vary in use said capacitance between said first and second electrodes;
and said variable capacitance producing in use a signal indica-tive of relative travel of said piston in said cylinder.

A yet additional aspect of the invention resides broadly in an arrangement for measuring relative travel of a piston in a cylinder which is part of a mechanical suspension assembly, comprising: a hollow piston rod housing first and second, substantially coaxial tubular electrodes which are spaced from one another and which are both substantially electrically insulated from the piston rod and mounted in a substantially fixed relationship with respect to each other to form a substantially annular gap, said first and second electrodes forming a variable capacitance; a sleeve-like member which is mounted for movement reflecting said relative travel of the piston in said cylinder, said sleeve-like member being disposed to slidingly enter said substantially annular gap to vary said variable capacitance; a third electrode substantially electri-cally insulated from both the first and second electrodes and spaced from the second electrode to form a substantially fixed reference capacitance in use; and electrical connecting means connected to said fixed first, second and third electrodes.

4e ~2~5~ NHL-BGG-02 Canada A further additional aspect of the invention resides broadly in an arrangement for measuring relative travel of a piston in a cylinder, comprising: a supporting member housing a first electrode which is mounted fixed but electrically insulated with respect to the supporting member; a second electrode spaced from the first electrode to define a space therebetween, said second electrode being immovable with respect to the first electrode and being electrically insulated from the supporting member, said first and second electrodes in use forming a capacitive reac-tance; a reactance varying member which is mounted to move in accordance with said relative travel between the piston and the cylinder, said reactance varying member being so disposed that its movement changes the capacitance between said first and second electrodes in accordance with said relative movement between the piston and the cylinder; and electrical measuring means being connected to said fixed first and second electrodes to measure the capacitance formed therebetween and produce a signal indicative of relative movement between the piston and the cylinder.

A yet further additional aspect of the invention resides broadly in an arrangement for measuring relative travel of a piston in a cylinder which is part of a hydro-pneumatic assembly, comprising: a supporting member in the form of a hollow piston rod and housing fixed first and second spaced substantially coaxial tubular electrodes which are both electrically insulated from the supporting member and mounted in fixed relationship with respect to each other to form a substantially annular gap; elec-trical leads connected to said first and second electrodes, said first and second electrodes in use forming a variable capaci-tance; a sleeve-like member which is mounted for movement ~2~S~ NHL-BGG-02 Canada reflecting said relative travel of the piston in said cylinder, said sleeve-like member being disposed to enter said substan-tially annular gap to vary said capaci~ance between said first and second electrodes; and electrical measuring means being connected to said electrical leads to produce a signal indicative of relative travel of said piston in said cylinder.

Another further additional aspect of the invention resides broadly in an arrangement for measuring relative travel of a piston in a cylinder which is part of a mechanical suspension assembly, comprising: a hollow piston rod housing first and spaced substantially coaxial tubular electrodes which are both electrically insulated from the piston rod and mounted in fixed relationship with respect to each other to form a substantially annular gap, said first and second electrodes forming a variable capacitance; a sleeve-like member which is mounted for movement reflecting said relative travel o~ the piston in said cylinder, said sLeeve-like member being disposed to slidingly enter said substantially annular gap to vary said variable capaci~ance; a third electrode electrically insulated from both the second electrode and spaced from the second electrode to form a fixed capacitance in use; electrical leads connected to said fixed first, second and third electrodes; and an electrical measuring bridge connected to at least said first, second and third electrodes to measure said variable capacitance to produce a signal, by using said fixed capacitance as a reference, said signal indicating the extent of movement of said piston in said cylinder.

A yet another additional aspect of the invention resides broadly in a damping cylinder of a vibration damper, said damping 4g ~?J~9 ~ NHL-BGG-02 Canada cylinder having an arrangement for determining a position of piston means therewithin, said cylinder having a space there-within with said piston means disposed in said space for axial slidable movement within said cylinder; at least one damping medium being disposed within said cylinder for damping said a~ial movement of said piston means with respect to said cylinder; said arrangement for deter~ining the position of said piston means comprising: means for sensing a position of said piston means within said cylinder; said position sensing means having a first element and a second element; said first element of said position sensing means being disposed to be movable with said piston means; said second element of said position sensing means being disposed to be substantially stationary with respect to said cylinder; said first element and said second element being electrically insulated one from the other; said two elements forming a variable impedance component which is substantially electrically reactive; said variable reactive electrical impedance varying, in operation, with said position of said piston means in said cylinder; an electrical signal being generated by at least one of said elements and being indicative of said position of said piston means; electrical connecting means, being connected to at least one of said elements, for sensing said electrical signal, indicative of said position of said piston means; said first element comprising a first electrode and said second element comprising a second electrode of a capacitor; dielectric means being disposed at least in part between said first and second electrodes of said capacitor; said electrical connecting means being connected to said first elec-trode and to said second electrode; said piston means including a piston rod; said first electrode comprising at least a portion of said piston rod; said piston rod having a hollow portion; said 4h ~z~ 35~ NHL-BGG-02 Canada cylinder having a base at one end thereof; said second electrode comprising a first, cylindrical tube which is disposed on and extends from said base of said cylinder means into said space within said cylinder; said hollow portion of said piston rod having a longitudinal axis being substantially axially aligned with a longitudinal axis of said first tube; and said first tube at least during operation extending, at least partially, into said hollow portion of said piston rod.

Another yet further aspect of the invention resides broadly in a damping cylinder of a vibration damper, said damping cylinder having an arrangement for determining a position of piston means therewithin, said cylinder having a space there-within with said piston means disposed in said space for axial slidable movement within said cylinder; at least one damping medium being disposed within said cylinder for damping said axial movement of said piston means with respect to said cylinder; said arrangement for determining the position of said piston means comprising: means for sensing a position of said piston means within said cylinder; said position sensing means having a first element and a second element; said first element of said position sensing means being disposed to be movable with said piston means; said second element of said position sensing means being disposed to be substantially stationary with respect to said cylinder; said first element and said second element being electrically insulated one from the other; said two elements forming a variable impedance component which is substantially electrically reactive; said variable reactive electrical impedance varying, in operation, with said position of said piston means in said cylinder; an electrical signal being generated by at least one of said elements and being indicative 4i NHL-BGG-02 Canada ~Z~935~
of said position of said piston means; electrical connecting means, being connected to at least one of said elements, for sensing said electrical signal, indicative of said position of said piston means; said first element comprising a first electrode and said second element comprising a second electrode of a capacitor; dielectric means disposed at least in part between said first and second electrodes of said capacitor; and said electrical connecting means being connected to said first electrode and to said second electrode; said cylinder having a base; said piston means having a face disposed towards said base, said base of said damper cylinder being insulated from the cylinder to form said second electrode of said capacitor; and said face of said piston means forming said first electrode of said capacitor.

A still further aspect of the invention resides broadly in a damping cylinder of a vibration damper, said damping cylinder having an arrangement for determining a position of piston means therewithin, said cylinder having a space therewithin with said piston means disposed in said space for axial slidable movement within said cylinder; at least one damping medium being disposed within said cylinder for damping said axial movement of said piston means with respect to said cylinder; said arrangement for determining the position of said piston means comprising:
means for sensing a position OI said piston means within said cylinder; said position sensing means having a first element and a second element; said first element of said position sensing means being disposed ~o be movable with said piston means; said second element of said position sensing means being disposed to be substantially stationary with respect to said cylinder; said first element and said second element being electrically 4j ~ 35~ NHL-B~G-02 Canada insulated one from the other; said ~wo elements forming a variable impedance component which is subst&ntially electrically reactive; said variable reactive electrical impedance varying, in operation, with said position of said piston means in said cylinder; an electrical signal being generated by at least one of said elements and bein8 indicative of said position of said piston means; and electrical connecting means, being connected to at least one of said elements, for sensing said electrical signal, indicative of said position of said piston means; and an impedance bridge, being connected to said connecting means, for generating an electrical signal indicative of a position of said piston means.

A still further additional aspect of the invention resides broadly in a damping cylinder of a vibration damper, said damping cylinder having an arrangement for determining a position of piston means therewithin, said cylinder having a space there-within with said piston means disposed in said space for axial slidable movement within said cylinder; at least one damping medium being disposed within said cylinder for damping said axial movement of said piston means with respect to said cylinder; said arrangement for determining the position of said piston means comprising: means for sensing a position of said piston means within said cylinder; said position sensing means having a first element and a second element; said first element of said position sensing means being disposed to be movable with said piston means; said second element of said position sensing means being disposed to be substantially stationary with respect to said cylinder; said first element and said second element being electrically insulated one from the other; said two elements forming a variable impedance component which is substantially 4k ~93~4~ NHL-BGG-02 Canada electrically reactive; said variable reactive electrical impedance varying, ln operation, with said position of said piston means in said cylinder; an electrical signal being generated by at least one of said elements and being indicative of said position of said piston means; electrical connecting means, being connected to at least one of said elements, for sensing said electrical signal, indicative of said position of said piston means; said first element comprising a first electrode and said second element comprising a second electrode of a capacitor; dielectric means being disposed at least in part between said first and second electrodes of said capacitor; and said electrical connecting means being connected to said first electrode and to said second electrode; said piston means including a piston rod; said first electrode comprising at least a portion of said piston rod; capacitance measuring circuitry for connection to said capacitor; said capacitance measuring circuitry comprising a capacitor bridge; said variable capacitor forming one of the arms of one half of said capacitor bridge; and an amplifier being connected to said capacitor bridge for generating an electrical signal corresponding to the position of said piston in said damper cylinder.

Another still further additional aspect of the invention resides broadly in a damping cylinder of a vibration damper, said cylinder having an arrangement for determining a position of piston means therewithin, said cylinder having a space there-within with said piston means disposed in said space for axial slidable movement within said cylinder; at least one damping medium being disposed within said cylinder for damping said axial movement of said piston means with respect to said cylinder; one of said at least one damping medium being hydraulic damping oil;

NHL-BGG-02 Canada ~LZ49354 said arrangement for determining the position of said piston means comprising: said piston means including a circular, hollow piston rod; said cylinder having a base at one end thereof from which a hollow circular cylindrical, first tube extends into said space and also into said hollow piston in a telescopic relationship therewith> thereby forming, with a dielectric material, comprising said hydraulic damping oil, disposed between said first tube and said pi.ston rod, a variable, first capacitor;
a longitudinal axis of said piston rod being substantially aligned with a longitudinal axis of said first tube; said first tube being insulated from said cylinder and said hollow piston rod; a first ].ead being connected to said first tube; and a second lead being connected to said hollow piston rod.

Yet another still further additional aspect of the invention resides broadly in a damping cylinder in a vibration damper, said cylinder having an arrangement for measuring relative travel of a piston in said cylinder, comprising: a supporting member housing a first electrode which is mounted substantially fixed but sub-stantially electrically insulated with respect to the supporting member; a second electrode being spaced from the first electrode to define a space therebetween, said second electrode being substantially fixed with respect to the first electrode, said first and second electrodes in use forming a capacitive reactance; a reactance varying member which is mounted to move in accordance with said relative travel between the piston and the cylinder, said reactance varying member being so disposed that its movement changes the capacitance between said first and second electrodes in accordance with said relative movement between the piston and the cylinder; and electrical connecting means connected to said fixed first and second electrodes for measuring the capacitance formed therebetween and for producing a signal indicative of relative movement between the piston and the cylinder.

4m ~9 354 NHL-BGG-02 Canada Still another yet further additional aspect of the invention resides broadly in a damping cylinder ln a vibration damper, said cylinder having an arrangement for measuring relative travel of a piston in said cylinder, comprising: a supporting member in the form of a hollow piston rod and housing having fixed first and second spaced substantially coaxial tubular electrodes which are both substantially electrically insulated from the supporting member and mounted in a substantially fixed relationship with respect to each other to form a substantially annular gap;
electrical leads connected to said first and second electrodes, said first and second electrodes in use forming a variable capacitance; a sleeve-like member which is mounted for movement reflecting said relative travel of the piston in said cylinder, said sleeve-like member being disposed to enter said substan-tially annular gap to vary in use said capacitance between said first and second electrodes; and said variable capacitance producing in use a signal indicative of relative travel of said piston in said cylinder.

Another still further yet additional aspect of the invention resides broadly in an arrangement for measuring relative travel of a piston in a damping cylinder of a vibration damper for a mechanical suspension assembly for a vehicle, comprising: a hollow piston rod housing first and second, substantially coaxial tubular electrodes which are spaced from one another and which are both substantially electrically insulated from the piston rod and mounted in a substantially fixed relationship with respect to each other to form a substantially annular gap, said first and second electrodes forming a variable capacitance; a sleeve-like member which is mounted for movement reflecting said relative travel of the piston in said cylinder, said sleeve-like member 4n ~935~ NHL-BGG-02 Canada being disposed to slidingly enter said substantially annular gap to vary said variable capacitance; a third electrode substantially electrically insulated from both the first and second electrodes and spaced from the second electrode to form a substantially fixed reference capacitance in use; and electrical connecting means connected to said fixed first, second and third electrodes.

The problems related to the prior art are solved, according to one embodiment of the invention, by providing a capacitor which is formed in the interior of the cylinder in such a way that a first axially displaceable electrode is formed directly or indirectly by the piston and/or the piston rod and a second electrode, insulated from the first, is held fixed within the cylinder. These first and second electrodes are separated from one another by a dielectric.

NHL-BGG-02 Canada 3~4 In this first embodiment, it is preferable that a compact measuring system assem~ly is provided by a physical contactlessly workable method of measurement, so that the measuring system can be integrated into, for example, a vibration damper, a gas spring or a hydro-pneumatic suspPnsion without major modifications.
Further advantages of this embodiment of the invention are the low-cost o~ manufacture and the providing of vehicle suspension which can readily f~nction together with the arrangement for determining the travel or position of a piston therein, as a self-contained unitary system.

According to a further important feature of the invention, it is provided that the piston rod is made hollow, thereby forming the first electrode. A second electrode comprising a tube, is provided and disposed within the hollow space in the piston rod and spaced therefrom. This tube is secured in the base of the cylinder and is insulated from the first electrode and also preferably from the cylinder. The second electrode is disposed substantially coaxially with the first electrode and at least partially therewithin. The first electrode is axially displaceable in a telescopical fashion relative to the second electrode.

It has been found particularly desirable to design and make a hydro-pneumatic vibration damper so that a cylindrical capacitor can be provided therein with minimal structural modifications. The typically oil-filled vibrational damper cylinder and its often hollow piston rod have associated there-with an additional hollow cylinder which is held by an insulating body in the base o~ the vibration damper cylinder. The hollow piston rod and the additional cylinder form a cylindrical ~ 3~ NnIL-BGG-02 Canada capacitor which, as a result of the varying overlapping surfaces9 form a first and second electrode, which arrangement produces a variation in capacitance so that the desired value of a physical magnitude to be measured is provided by a change in the capacitance between the electrodes.

The travel of the piston results in the change of capaci-tance as a function of the piston displacement. The position of the piston is uniquely related to the capacitance. The capaci-tance of the cylindrical capacitor as a function of piston position (L) or travel from the position just before any portion of the two circular cylinders telescope together or become radially adjacent to one another is:

Cylinder 2~ x Eo x Er x L
ln 2 r where ACCylinder = change in capacitance Eo = the dielectric constant of free space Er = the relative dielectric constant of the oil in the damper L = length of piston travel r2 = radius of the bore of the piston rod rl = outer radius of the hollow cylinder secured to the cylinder base ~ = 3.14159 This equation follows from the fact that the movable circular piston rod is displaced from and concentrically disposed over the inner hollow circular cylinder which inner cylinder is secured in an insulating manner to the base o~ the outer, ~ 3~ NHL-BGG-02 Canada vibration damper cylinder. This results in a variation of the cylinder surfaces being radially adjacent to one another and results in the variation of the capacitance in accordance with ~he travel or position of the piston. The electrodes are formed by the structure, such that, one electrode on the one hand is formed by the hollow piston rod ancl the other electrode on the other hand is formed by the tube fixed to the base of ~he cylinder.

According to an alternative capacitive embodiment, it is provided that the base of the cylinder is arranged to be insulated from the cylinder to form the second electrode and the first electrode is formed by that face of the piston which faces towards the base of the cylinder.

Also, in this alternative embodiment, the capacitor is formed by the components of the assembly itself provided to form the suspension which includes the vibrational damper of which the capacitor is a part. Here the change in capacitance is produced by the varying spacing or distance between the two electrodes which capacitance is expressed by the equation:

C = Eo x Er x A
L

where, Eo = dielectric constant of free space Er = relative dielectric constant of oil dielectric or in the vibrational damper A = effective surface area of the electrodes ~faces of piston and base of cylinder) C - capacitance L = distance between the electrodes ~24~354 NHL-BGG-02 Canada By calculating the capacitance for two different positions of the piston, this equation shows that a change in the spacing, between the piston and the cylinder base, produces a change in the capacitance by which the corresponding position change or travel can be derived.

To produce a corresponding electric signal, which can be used, for example, for controlling the height of a vehicle, it is provided according to a yet further embodiment that the elec-trodes of the capacitor are connected in a capacitance measuring bridge and produce an electric signal corresponding to position.
This signal is fed through an amplifier for use in making adjust-MentS to the pressure of the damping medium, thereby changing the position of the piston to a desired position.

It is a further aim to arrange such a device so that, in addition to the evaluation of the variable capacitance, a simultaneous compensation for pressure and temperature is made possible such that the pressure is regulated by the position and/or change and/or rate of change of position of the piston in operation.

To solve this problem, it is provided in a yet further and third, capacitive embodiment of the invention that, within the cylindrical interior of the inner, first tube, forming an electrode, is secured in the base of the vibrational damper cylinder, there is arranged and spaced from it, a further second inner fixed tube which forms an additional electrode defining, with the first tube, a second capacitor having a fixed capacitance value under conditions of a fixed temperature and a fixed pressure.

~g354 NHL-BG~-02 Canada An advantage of this third embodiment is that by the insulated incorporation of an additional, second, metallic, circular cylinder, as a further third electrode within the electrode already present on the base of the vibrational damper cylinder, a second capacitor having a fixed capacitance under specific condition is produced. This gives the advantage of a capacitive half-bridge which is made up of the variable capacitance (varied by displacement of the piston rod~ and the fixed capacitance secured in the base of the cylinder which fixed, second capacitor varies in capacitance in the same way that the variable first capacitor varies from influences other than displacement of the piston and/or piston rod.

This arrangement in the th~rd capacitive embodiment not only allows improved evaluation of the variable capaci~ance but also achieves a simultaneous compensation for at least pressure a~d temperature in that, by means of a suitable electronic circuit, e.g. a Wheatstone Bridge, the ratio of the two capacitances is taken into account.

In one embodiment of the invention, it is provided that the first tube and the further, second tube are arranged to be insulated from one another. The further, second tube can like-wise be secured in the base of the cylinder.

In an alternative, magnetic or inductive, embodiment of the invention, it is provided for solving the problem posed according to the invention that the outer surface of the cylinder has, over at least a portion of the region of the piston travel, at least one winding producing a magnetic field.

It is advantageous that an inductive or magnetic field should be produced. The piston and piston rod of the vibration ~ ~ NHL-BGG-02 Canada damper, being disposed in this magnetic field, produces an increase in the inductance as the piston and piston rod move further into the damper cylinder so that after measuring and converting the inducta~ce into an electrical magnitude the determination of the piston position and thus travel can likewise be obtained. Also this embodiment is suitable for the output signal to be able to be used as a basis for, for example, vehicle height control.

A further, inductive embodiment of the invention envisages that two windings are provided, having longitudinal axes which are substantially coextensive with the longitudinal axis of the cylinder of the vibration damper. Each of the windings covers preferably the distance of half the piston travel. In these versions it is advantageous that the piston rod can be made solid and not necessarily hollow. Ferromagnetic materials with rela-tively high permeance are advantageously used for making at least portions of the piston and/or the piston rod.

By such an arrangement of the windings, two inductances are formed which can be used directly as the series components of one side of an inductance measuring bridge .

To solve the problem of disturbing influences arising from external variations of the measured value because of the movement of movable connecting leads, according to one embodiment of the invention, there is provided in a vibration damper a first electrode insulated with respect to a supporting component that receives it, and a second electrode arranged non-displaceably within the interior of the first electrode and spaced from it; a dielectric member having a known dielectric constant is disposed so as to be able to enter between ~he first and second electrodes, during the functioning of the vibration damper.

~ 35~ NHL-BGG-02 Canada In such an arrangement, it is significant that no unfavor-able lengths of lead are present. The electric connections for the two electrodes are taken out of the supporting components that receive ~hem and accordingly are close to one another. By the avoidance of unnecessary lengths of lead, any disturbing in-fluences Erom outside are largely eliminated, so that a reliable evaluation of the measured values can be achieved. Further, it is of advantage that the mounting of a measuring arrangement can be selected according to the type of vehicle so that measuring means are mounted either on the piston rod or on the cylinder, and this allows one to avoid mounting on the unsprung mass of the vehicle and allows mounting on the bodywork to be achieved without difficulty.

According to an important feature of the invention, the first and second electrodes are arranged advantageously in the interior of the piston rod, and the dielectric medium used is secured in the cylinder.

Expediently, in such an arrangement, a contactlessly operating method of making the physical measurement can be received in the interior of the piston rod as a compact assembly so that simple integration is possible. Since all the components employed are tubular, they are matched without any problems, to the geometry of the piston rod. Such a system can be employed without major modifications, for example, in the piston rod of a vibration damper, a gas spring or a hydro-pneumatic suspension.

In another preferred embodiment of the invention, the first and second electrodes are mounted in the cylinder whereas the dielectric is provided inside the piston rod.

~4~5~ NHL-BGG-02 Canada Preferably, the dielectric comprises a ceramic tube; by the use of such a tube because of the characteristics of the ceramic material, compensation for pressure and temperature in the measuring system will not be necessary.

In an improvement of the foregoing embodiment, the cylindri-cal inner surface of the ceramic tube is advantageously connected electrically to the cylindrical outer surface of the second electrode. By such a conducting inner layer, the oil gap which would otherwise be made necessary by the tolerances can be eliminated. This oil gap acts in principle as a further dielec-tric because of the tolerances and the consequently varying spacing, whereby variations arise in the measured values; such undesirable variations can be eliminated by the electrically conducting connection. In order to further ~acilitate formation of the electrically conducting connection, the cylindrical inner surface of the ceramic tube may be provided with a metallic layer. In order to additionally amplify effectiveness of the electric conducting layer, preferably, an electrically conducting ring is mounted on the cylindrical outer surface of the second electrode, this ring having an outside diameter corresponding to the inside diameter of the dielectric.

To evaluate the variable capacitance with simultaneous com-pensation for pressure and temperature, it is proposed according to a further embodiment that all the electrodes should be fixed relative to one another and should be insulated from the sup-porting component that receives them, the firs~ and second electrodes being separated from each other by a dielectric.
Also, a third electrode is spaced from the second electrode in such a way that a tubular body can enter the space between them.

NHL-BGG-02 Canada 3 Z~35~
In such an arrangement, it is of significance that no ~mfavorable lengths of conduc~ing lead are present. The electric connections for the individual electrodes are taken directly out of ~he component and accordingly lie close to one another. By elimi nating unnecessary lengths of lead, disturbing influences from outside are largely eliminated, so that a reliable evaluation of the measured signals can be achieved. Furthermore, it is an advantage that the mounting of the measuring system can be chosen in accordance with the type of vehicle so that the apparatus is mounted ei~her on the piston rod or on the cylinder, which allows one to avoid mounting the arrangement on the ~msprung mass of the vehicle and allows it to be mounted on the bodywork.

According to a further important feature of the invention, all ~he electrodes are mounted in the interior of the piston rod, an insulating body being provided between the outer surface of the first electrode and the cylindrical inner surface of the piston rod, the tubular body being connected rigidly to the cylinder.

In this embodiment, it is advantageous that the contactless arrangement of making the physical measurement can be received in the interior of the piston rod as a compact assembly unit so that simple integration is possible with the components which are all of tubular shape.

It is furthermore advantageous that all the connections and the actual capacitor are received within the piston rod. This allows the possibility of mounting the evaluating electronic circuits without ups~tting acceleration influences, since the piston rod is usually mounted on the bodywork, so that during operation of the vehicle no noticeable acceleration acts on the piston rod.

NHL-BGG-02 Canada In order ~o take advan~age of the geometry of the hollow piston rod and simultaneously realize all cost-favorable and manufacturing advantages, a tube of synthetic resin, such as an epoxy resin, is used as the insulating body in another embodiment.

In a further important modifieation, an earthed electrically conducting tube is provided as the tubular body. This tubular body is secured in the base of the cylinder and3 on inward movement of the piston rod it enters between the second and third electrodes. The first and second electrodes form a fixed capaci-tance which is introduced for compensation of varying temperature and pressure influences on the measurement.

The second and third electrodes, between which the tube enters, produce a resultant variable capacitance for determining the travel of the piston. In this connection it is advantageous that the penetration of the earthed tube between the second and third electrodes reduces the capacitance since the effective capacitive surface area is reduced.

In an important modification, it is envisaged that the tubular body comprises an electrically non-conducting tube. In this way, full use is made of the fact that the non-conducting tube acts as a dielectric and accordingly on entry between the second and third electrodes, a parallel circuit of two capaci-tances is obtained. This parallel circuit is a consequence of the two different dielectrics, since the insulating tube and the medium (e.g. mineral oil, such as commercially available shock absorber oil) present in the remaining part have different dielectric constants. During the measurement of the variable capacitance, this characteristic is represented by a parallel connection of two capacitances, the overall capacitance being ~2~93~4 NHL-BGG-02 Canada derived by addition of the two individual capacitances.

A particularly preferred material for the tubular body comprises synthetic resin.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention by way of example are illustrated diagrammatically in the accompanying drawings wherein:

Figure 1 shows a sectional view of a vibration damper, in which the hollow piston rod forms a variable capacitor in conjunction with a tube in a cavity of the damper.
Figure 2 shows a sectional view of a diagrammatic represen-tation of a cylindrical capacitor.
Figure 3 shows a diagram of capacitance of the cylindrical capacitor of Figure 2 with respect to piston position or piston travel.
Figure 4 shows a sectional view of a further embodiment of a vibration damper, in which the face of the piston and the base of the cylinder form plates of a capacitor.
Figure 5 shows a sectional view of a cylindrical vibration damper wherein an inductive coil is disposed on the surface of the cylinder.
Figure 6 shows a sectional view of a vibration damper wi~h another coil arrangement.
Figure 7 shows a sectional view of a vibration damper in which the tube forms, with a further cylindrical tube, a second fi~ed capacitor.
Figure 8 shows schematically the embodiments of Figure 1 and Figure 7 arranged in an impedance measuring bridge.

NHL-BGG-02 Canada ~24~3S~
Figure 9 shows schematically the inductive coil arrangement oE Figure 5 connected into an impedance measuring bridge.
Figure 10 shows schematically the coil arrangement of Figure 6 connected into an impedance measuring bridge.
Figure 11 shows a sectional view of another embodiment of which a tubular capacitor is arranged in the interior or the piston rod.
Figure 12 shows a sectional view of a vibration damper in which a compensator is mounted in the in~erior of the piston rod.
Figure 13 depicts a piston travel/capacitance diagram for a cylindrical capacitor with compensation for $emperature.

DESCRIPTION OF THE, PREFERRED EMBODIMENTS

The vibration damper illustrated in Figure 1 comprises substantially a cylinder 1, a piston 2 and a piston rod 3, well-known in the prior art. In the interior cavity 4 of the cylinder 1 there is at least one damping medium serving for damping vibrations of the piston 2. Attachment means 5 and 6, well-known in the prior art, are provided for mounting the vibration damper in a vehicle. The piston rod 3, which is made hollow, slides telescopically over a tube 7, the tube 7 being located in the cylinder 1, and at~ached thereto by an insulating body 8 which insulates the tube 7 from the remainder of the components of the damper. The hollow piston rod 3 and the tube 7 form together a variable circular cylindrical capacitor. The damping medium present in the interior cavity 4 for~s a dielectric for the capacitor. The hollow piston rod 3 forms the first electrode and is connected through a lead 10 connected through an insulating terminal (not shown) to appropriate ter~inals of an appropriate measurement device. The piston rod 3 forms a second electrode ~2~93~5~ NHL BGG~02 Canada which is connected ~hrough a lead 9 to appropriate terminals of the measurement device.

The steepness of the change in capacitance is dependent upon the spacing between the outer surface of the tube 7 and the inner surface of the hollow piston rod 3, and on the medium present between them. The hollow piston rod 3 is arranged coaxially with and is concentrically spaced from the tube 7; a space between them receives the dielectric which may be a damping medium such as oil, or even a dielectric solid between the facing surfaces of the tube 7 and the piston rod 3. In Figure 2, there is diagrammatically illustrated a cylindrical capacitor, ~he firs~
elec~rode thereof comprising the hollow piston rod 3 and the second electrode comprising tube 7. The spacing 11 indicates a practical minimum overlap. The spacing 12 indicates the maximum overlap between the two surfaces when the piston 2 is as far to the right in Figure 1 as it can move. These overlaps produce a minimum and maximNm capacitance when appropriately converted, and represent the minimum and maximum travel positions of the piston.
By interpolating between these extremes, the position of the piston in the cylinder is indicated by a capacitance therein-between. The leads 9 and 10 serve, for example, for connection to a capacitance measuring bridge as shown in Figure 8 infra.

Figure 3 shows a diagram in which the capacitance of such a cylindrical capacitor is plotted against piston position or travel. It is seen from Figure 3 that the change in capacitance is proportional to the travel of the piston, and the steepness of the curve is dependent on the ratio of the inside radius of the bore in the piston rod to the outside radius of the tube 7 as well as the relative dielectric constant Er The relative ~93~4 NHL-BGG-02 Canada dielectr;c constant Er is predeterm:ined in any known embodiment by the characteristics of the damping medium used. The two solid straight lines show two different cylindrical capacitor arrangements having, for example, d:ifferent maximum overlap-spacings between the piston rod 3 and the cylinder, or relative dielectric constants Er of the dielectric.

Figure 4 shows diagrammatically an alternative, second capacitive embodiment of the invention illustrating a vibration damper again having a cylinder 1, a piston 2 and a piston rod 3.
The piston 2 and the base 13 of the cylinder respectively form the first and second electrodes of a capacitor. The base 13 of the cylinder 1 is mounted in this cylinder 1 but insulated therefrom so that a desired change in capacitance ca~ be obtained by varying the distance between the piston 2 and the base 13 of the cylinder 1. By appropriate conversion of the measured value, likewise in this embodiment, the position of the piston can be obtained.

As an alternative inductive embodiment, there is shown in section in Figure 5, a vibration damper wherein again the princi-pal components are the cylinder 1, the piston 2 and the piston rod 3.

The outer surface 14 of the vibration damper cylinder 1 is provided with windings 15, comprising a first coil 16 and a second coil 17, for respective generation of a magnetic field.
The coils 16 and 17 when connected appropriately as the arms of a half-bridge generate a positional signal indicative of the position of the piston 2.

The resultant inductive half-bridge generates a bridge voltage determined by the degree or position of the insertion of ~2~3~ NHL-BGG-02 Canada the piston 2 in the damper cylinder, so that, a suitable signal corresponding to the piston travel is produced.

Figure 6 shows a modified inductive embodiment. The prin-cipal components of a vibration damper are here again the cylinder 1, the piston 2 and the piston rod 3 which in the embodiments using inductance; this piston rod 3 does not have to be made hollow. A winding is disposed on the outer surface of the vibration damper cylinder 1 extending preferably over at least the entire range of travel of the piston. On insertion of the piston within this region, there is a resulting change in inductance which can be correspondingly evaluated. The piston rod 3, at least, in Figure 5 and Figure 6, is preferably made of a ferromagnetic material in order to vary the inductance as much as possible from one relative position of the piston 2 and piston rod 3 to another position thereof.

The vibration damper illustrated in Figure 7 comprises a fourth capacitance embodiment of the invention which is made up of basically the cylinder l, the piston 2 and the piston rod 3 as in Figure 1. Within the interior cavity 4 of the cylinder 1, there is the damping medium serving for damping vibrations.
As in the embodiment of Figure 1, mounting means 5 and 6 are provided for mounting the damper in the vehicle in a manner well-known in the prior art. The piston rod 3, w~ich is made hollow, can slide telescopically over the tube 7, the tube 7 being secured in the cylinder in an insulating body 8 and being insulated with respect to the remainder of the components of the damper. The hollow piston rod 3 and the tube 1 form together the cylindrical capacitor. The damping medium present in the ~2~35~ NHL-B&G-02 Canada interior cavity ~ preferably forms the dielectric for the capaci-tor as in Figure l. The hollow piston rod 3 forms the first electrode and the tube 7 forms the second fixed electrode and is connected through the lead 10, passing through an insulated terminal arrangement (not shown), to the input of an appropriate measurement device such as shown in Figure 8 infra.

The steepness of the changP in capacitance is dependent ~pon the spacing between the outer surface of the tube 7 and the inner surface of the hollow piston rod 3 and on the dielectric medium present between them. The hollow piston rod 3 is arranged to be coaxial with and spaced from the tube 7; the space between them receives a suitable dielectric~

The spacing ll represents the minimum overlap and the spacing 12 the maximum overlap between the two surfaces, produc-ing accordingly a minimum and a maximum capacitance, which, appropriately converted, indicate the momentary piston travel, i.e., the position of the piston in the cylinder.

Secured within the cylindrical interior 19 of the tube 7 is a further tube 18 which is likewise arranged spaced from the tube 7. Between the two tubes, the damping fluid here again acts preferably as a dielectric as in Figure l; the dielectric may be solid. By the fixed arrangement of the two tubes 7 and 18 with respect to one another, there is produced a capacitor having a fixed capacitance at a particular temperature and pressure. The cylindrical tube 18 which acts as the further electrode is mounted in the insulating body 8 of the cylinder again in an insulating manner and is connected to the measurement receiver through a lead 20. The tube 7 and the tube 18 again form a tubular circular capacitor which serves for compensating for at ~g35~ NHL-BGG-02 Canada least the pressure and temperature of the dielectric medium between the tube 7 and the piston rod 3. The manner of operation of the overall system is well-known in the prior art of Wheatstone Bridge as a capacitive half-bridge.

In Figure 8, a schematic diagram is shown representing a bridge circuit 108, e.g., an impedance Wheatstone Bridge, for sensing the changes in capacitance of a variable capacitor 110 formed by the tube 7 and the hollow piston rod 3. The leads 9 and 10 are connected in the bridge 108 so that the capacitor 110 forms half on one arm of the bridge 108. Either a fixed capaci-tor external to the vibration damper or a temperature variable capacitor, as shown in Figure 7, and formed by the tube 7 and the tube 18, comprises a capacitor 112 forming one-half of the bridge 108 connected to the capacitor 110. Two other impedance elements, preferably capacitors 114 and 116 form the other half of the bridge 108. Series capacitors 110 and 112 form one arm and the series capacitors 114 and 116 form the other arm of the bridge 108. A generator 118, preferably supplying alternating current, is connected across the bridge 108 at the connectors between the capacitors 110 and 114 and the capacitors 112 and 116. The operation of a Wheatstone Bridge is well-known in the electrical prior art.

It is within the purview of the invention that this gener-ator 118 may also be a generator of direct voltage if the imped-ance levels of the bridge 108 are appropriate therefor. Alterna-tively, within the purview of the invention, a pulse generator may also be used under special circumstances. The terminal 10 forms one input of an amplifier 120; a junction of the capacitors 114 and 116 forms ~he other input of the amplifier 120 which N~L-BGG-02 Canada 935~
generates a signal proportional to the position of the piston 2.

In the case of the inductive coil embodiment of the inven-tion as shown in Figure 5 being adapted to the circuit in Figure 8, the first coil 16 replaces the capacitor 110 and the second coil 17 replaces the capacitor 112 as in shown in Figure 9. The other capacitors 114 and 116 are preferably replaced by impedances.
However, other impedance elements may be used for capacitors 114 and 116 if their impedance is chosen appropriately in a manner which is well known in the impedance bridge art.

For example, if the capacitive impedances llO and 112 in Figure 8 both increase by the same percentage amount due to change in the mutual dielectric because of temperature, pressure, etc., the voltage at the terminal 10 will remain constant, as is well-known in the art of electrical bridge measurements such as the Wheatstone Bridge.

Fig1lre 10 shows the coil arrangement 22 of Figure 6 con-nected into the bridge 108 replacing the capacitor 110.

The vibration damper illustrated in Figure 11 generally comprises the cylinder 201, the piston 202 and the piston rod 203. In the interior cavity 204 of the piston 201, there is provided a damping medium serving for damping the vibrations.
Attachment means 205 and 206 are provided for mounting the vibration damper on the vehicle.

The piston rod 203 is made hollow, and there~ithin are disposed a first elec~rode 208 and the second electrode 211. The first electrode 208 is insulated from the piston rod 203 by an insulating layer 207. Between the first electrode 208 and the second electrode 211 is a gap 212.

354 MHL-BGG-02 Canada Since the first electrode 208 i.s substantially concentric to and spaced away from the second electrode 211, the tubular body

2.13, which is secured to the base 214 of the cylinder 201, can enter the gap 212 axially during operation of the damper in the vehicle. By the entry of the tubular body 213, a variation occurs in the capacitance between the first electrode 208 and the second electrode 211.

In the specific embodiment of Figure 11, a ceramic tube is provided as the tubular body 213. The variation in capacitance arises because of different dielectric characteristic~. of the ceramic tube and the rest of the medium which may be oil.

The ceramic tube and the mineral oil which is present as the damping fluid each have a different dielectric constant, and on insertion of the ceramic tube 213 in the gap 212, the immersed surface of the ceramic tube acts as a different dielectric from oil.

In order to eliminate as far as possible the effect of the oil in the gap, between the electrode 211 and the ceramic tube 213, the ceramic tube 213 is provided with an electrically conducting surface on its inner cylindrical surface 209. This conducting surface is electrically connected to the second electrode 211 by an electrically conducting ring 210 provided on the outer surface of the second electrode 211. Since the inner cylindrical surface 209 electrically becomes a part of the second electrode 211, the oil in the gap between the second electrode 211 and the ceramic tube 213 does not have any electric filed generated therein. Therefore, this gap does not produce any capacitive effect and thereby variations in this gap due to NHL-BGG-02 Canada ~;~4935~:

tolerances, wear of the parts, etc., do not deleteriously affect the performance accuracy.

By virtue of the arrangement of the electrodes 208 and 211 either in the hollow piston rod 203 or in the cylinder 201, structurally preferred possibilities are provided for making the connections for the leads 215. The leads could be made to terminate as connecting terminals on the outer surface either of the cylinder 201 or the piston rod 203. The electrodes 208 and 211 are held fixed relative to one another. The tubular body 213 is fixed also; however, the tubular body is mounted in the cylinder 201 so that during operation of the vibration damper, a telescopic displacement of the components within each other take~
place, and the tubular capacitor can perform as desired.

The vibration damper illustrated in Figure 12 comprises substantially the cylinder 201, the piston 202 and the piston rod 203. In the interior cavity 204 of the cylinder 201, there is the damping medium serving for damping the oscillations. Securing devices 205 and 206 are provided as attachment means for mounting the damper in the vehicle.

Provided in the piston rod 203, which is made hollow, are the first electrode 217 and the second electrode 218. The first electrode 217 is insulated with respect to the piston rod 203 by a tube 219 of, for example, synthetic resin. A dielectric 220 is disposed between the first electrode 217 and ~he second electrode 218.

Spaced away ~rom the second electrode 218 is a third elec-trode 221. The tubular body 223 is disposed to be able to enter the intermediate space 222 between the second electrode 218 and the third electrode 221 during active functioning of the damper NHL-BGG-02 Canada ~2~93~4 in the vehicle. By the insertion of the tubular body 223 into the space 222, there occurs a change of capacitance between the second electrode 218 and the third electrode 221. The first electrode 217 forms, together with the second electrode 218, a fixed capacitance by contrast. The space 222 may be filled with a dielectric fluid, e.g., mineral oil.

Preferably, as illustrated, the tubular body is metallic;
with the use of an electrically conducting tubular body 223, the latter must be earthed through the insulating body 224 of the cylinder. This results in the following manner of operation:
with the piston rod 203 extended, the three electrodes form two fixed capacitances of known magnitude. 0~ inward movement of the grounded electrically conducting tubular body 223, the capacitance between the second electrode 218 and the third electrode 221 is reduced because the effective capacitive surface area is diminished.

As an alternative in regard to the material of the tubular body 223, it is also possible for the tubular body 223 to be made in the form of an electrically non-conducting tube. For example, a tube of synthetic resin is suitable for this purpose. If a synthetic resin tube is provided to form the tubular body 223 then on entry of the synthetic resin tube between the second electrode 218 and the third electrode 221, there is produced a parallel circuit of two capacitors. The two capacitances of different values arise by the different dielectrics so that the overall capacitance of the second electrode 218 and the third electrode 221 results from the addition of the two individual capacitances. These different values of capacitance arise partly since the synthetic resin tube and the mineral oil which may be ~æ~35~ NHL-~GG-02 Canada present as the damping fluid, each have different dielectric constants. If the tubular body 223 is made of synthetic resin, on insertion of the synthetic resin tube, the inserted surface area of the tubular body 223 acts as a dielectric.

The variable capacitance follows the formula:

CgeS (1) - Ca + Cb where:

Cges ~ overall capaci~ance Ca = the individual capacitance of the first medium (e.g. Mineral oil) Cb = the individual capacitance of the second medium (e.g. Synthetic resin) In Figure 13, a diagram is shown in which the capacitance for such a cylindrical capacitor is drawn against piston travel or displacement. The individual capacitance Ca falls steadily on insertion of the piston 202, whereas the individual capacitance Cb, in which the tubular body 223 is used as the dielectric, steadily increases. The two individual capacitances add up and form the resultant characteristic line Cges.

By the disposition of the electrodes 217, 218 and 221, either within the hollow piston rod 203 or in the cylinder 201, there are advantageous possibilities for making connections to the leads 225 since these only need to be mounted as connecting pins on the outside surace of either the cylinder 201 or the piston rod 203. The electrodes are advantageously kept fixed relative to one another, and the tubular body 223 is likewise fixed, but in the other component. Accordingly during the action of a vibration damper, a telescopic displacement of the parts ~z~93$4 N~L-B&G-02 Canada within one another takes place, so that the desired measured variable capacitance is formed.

The invention, as described hereinabove in the context of a preferred Pmbodiment, is not be taken as limited to all of the provided details thereof, since modifications and variations thereof may be made without departing from the spirit and scope of the invention.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A cylinder having an arrangement for determining a position of piston means therewithin, said cylinder having a space therewithin with said piston means disposed in said space for axial slidable movement within said cylinder;
at least one damping medium being disposed within said cylinder for damping said axial movement of said piston means with respect to said cylinder;
said arrangement for determining the position of said piston means comprising:
means for sensing a position of said piston means within said cylinder;
said position sensing means having a first element and a second element;
said first element of said position sensing means being disposed to be movable with said piston means;
said second element of said position sensing means being disposed to be substantially stationary with respect to said cylinder;
said first element and said second element being electri-cally insulated one from the other;
said two elements forming a variable impedance component which is substantially electrically reactive;
said variable reactive electrical impedance varying, in operation, with said position of said piston means in said cylinder;
an electrical signal being generated by at least one of said elements and being indicative of said position of said piston means;
electrical connecting means, connected to at least one of said elements, for sensing said electrical signal, indicative of said position of said piston means;
said first element comprising a first electrode and said second element comprising a second electrode of a capacitor;
dielectric means being disposed at least in part between said first and second electrodes of said capacitor;
said electrical connecting means being connected to said first electrode and to said second electrode;

said piston means including a piston rod;
said first electrode comprising at least a portion of said piston rod;
said piston rod having a hollow portion;
said cylinder having a base at one end thereof;
said second electrode comprising a first, cylindrical tube which is disposed on and extends from said base of said cylinder means into said space within said cylinder;
said hollow portion of said piston rod having a longitudinal axis being substantially axially aligned with a longitudinal axis of said first tube; and said first tube at least during operation extending, at least partially, into said hollow portion of said piston rod.

2. The cylinder having an arrangement for determining a position of piston means therewithin, according to Claim 1, wherein first tube is hollow and has disposed therein a second cylindrical tube secured to the base of said cylinder; said second tube being spaced from said first tube, and comprising an additional electrode which together with the first tube from a further capacitor, said first tube and said second tube being substantially stationary with respect to one another.

3. The cylinder having an arrangement for determining a position of piston means therewithin, according to Claim 2, wherein said first tube and said second tube have the same type of dielectric material therebetween as the dielectric material which is between said first tube and said hollow portion of said piston rod.

4. The cylinder having an arrangement for determining a position of piston means therewithin, according to Claim 3, wherein said second tube is also secured in the base of the damper cylinder.

5. The cylinder having an arrangement for determining a position of piston means therewithin, according to Claim 4, wherein said first tube is insulated from the base of the cylin-der.

6. A cylinder having an arrangement for determining a position of piston means therewithin, said cylinder having a space therewithin with said piston means disposed in said space for axial slidable movement within said cylinder;
at least one damping medium being disposed within said cylinder for damping said axial movement of said piston means with respect to said cylinder;
said arrangement for determining the position of said piston means comprising:
means for sensing a position of said piston means within said cylinder;
said position sensing means having a first element and a second element;
said first element of said position sensing means being disposed to be movable with said piston means;
said second element of said position sensing means being disposed to be substantially stationary with respect to said cylinder;
said first element and said second element being electri-cally insulated one from the other;
said two elements forming a variable impedance component which is substantially electrically reactive;
said variable reactive electrical impedance varying, in operation, with said position of said piston means in said cylinder;
an electrical signal being generated by at least one of said elements and being indicative of said position of said piston means;
electrical connecting means, connected to at least one of said elements, for sensing said electrical signal, indicative of said position of said piston means;
said first element comprising a first electrode and said second element comprising a second electrode of a capacitor;

dielectric means being disposed at least in part between said first and second electrodes of said capacitor;
said electrical connecting means being connected to said first electrode and to said second electrode;
said cylinder having a base;
said piston means having a face disposed towards said base, said base of said damper cylinder being insulated from the cylinder to form said second electrode of said capacitor; and said face of said piston means forming said first electrode of said capacitor.

7. A cylinder having an arrangement for determining a position of piston means therewithin, said cylinder having a space therewithin with said piston means disposed in said space for axial slidable movement within said cylinder;
at least one damping medium being disposed within said cylinder for damping said axial movement of said piston means with respect to said cylinder;
said arrangement for determining the position of said piston means comprising:
means for sensing a position of said piston means within said cylinder;
said position sensing means having a first element and a second element;
said first element of said position sensing means being disposed to be movable with said piston means;
said second element of said position sensing means being disposed to be substantially stationary with respect to said cylinder;
said first element and said second element being electri-cally insulated one from the other;
said two elements forming a variable impedance component which is substantially electrically reactive;

said variable reactive electrical impedance varying, in operation, with said position of said piston means in said cylinder;
an electrical signal being generated by at least one of said elements and being indicative of said position of said piston means;
electrical connecting means, connected to at least one of said elements, for sensing said electrical signal, indicative of said position of said piston means; and an impedance bridge, connected to said connecting means, for generating an electrical signal indicative of a position of said piston means.

8. A cylinder having an arrangement for determining a position of piston means therewithin, said cylinder having a space therewithin with said piston means disposed in said space for axial slidable movement within said cylinder;
at least one damping medium being disposed within said cylinder for damping said axial movement of said piston means with respect to said cylinder;
said arrangement for determining the position of said piston means comprising:
means for sensing a position of said piston means within said cylinder;
said position sensing means having a first element and a second element;
said first element of said position sensing means being disposed to be movable with said piston means;
said second element of said position sensing means being disposed to be substantially stationary with respect to said cylinder;
said first element and said second element being electri-cally insulated one from the other;
said two elements forming a variable impedance component which is substantially electrically reactive;

said variable reactive electrical impedance varying, in operation, with said position of said piston means in said cylinder;
an electrical signal being generated by at least one of said elements and being indicative of said position of said piston means;
electrical connecting means, connected to at least one of said elements, for sensing said electrical signal, indicative of said position of said piston means;
said first element comprising a first electrode and said second element comprising a second electrode of a capacitor;
dielectric means being disposed at least in part between said first and second electrodes of said capacitor;
said electrical connecting means being connected to said first electrode and to said second electrode;
said piston means including a piston rod;
said first electrode comprising at least a portion of said piston rod;
capacitance measuring circuitry for connection to said capacitor;
said capacitance measuring circuitry comprising a capacitor bridge;
said variable capacitor forming one of the arms of one half of said capacitor bridge; and an amplifier being connected to said capacitor bridge for generating an electrical signal corresponding to the position of said piston in said damper cylinder.

9. The cylinder having an arrangement for determining a position of piston means therewithin, according to Claim 3, wherein said further capacitor provides at least a temperature compensating capacitor being connectable in a said capacitance measuring circuitry.

10. The cylinder having an arrangement for determining a position of piston means therewithin, according to Claim 6, including an impedance bridge, connected to said connecting means, for generating an electrical signal indicative of a position of said piston means.

11. A cylinder having an arrangement for determining a position of piston means therewithin, said cylinder having a space therewithin with said piston means disposed in said space for axial slidable movement within said cylinder;
at least one damping medium being disposed within said cylinder for damping said axial movement of said piston means with respect to said cylinder;
one of said at least one damping medium being hydraulic damping oil;
said arrangement for determining the position of said piston means comprising:
said piston means including a circular, hollow piston rod;
said cylinder having a base at one end thereof from which a hollow circular cylindrical, first tube extends into said space and also into said hollow piston in a telescopic relationship therewith, thereby forming, with a dielectrical material, com-prising said hydraulic damping oil, disposed between said first tube and said piston rod, a variable, first capacitor;
a longitudinal axis of said piston rod being substantially aligned with a longitudinal axis of said first tube;
said first tube being insulated from said cylinder and said hollow piston rod;
a first lead being connected to said first tube; and a second lead being connected to said hollow piston rod.

12. The cylinder having an arrangement for determining a position of piston means therewithin, according to Claim 11, wherein first tube is hollow and has disposed therein a second cylindrical tube secured to the base of said cylinder and in-sulated from said first tube; said second tube being spaced from said first tube, and comprising an additional electrode which together with the first tube form a further capacitor, said first tube and said second tube being substantially stationary with respect to one another; and said first tube and said second tube having the same type of dielectric material thereinbetween as the dielectric material which is between said first tube and said hollow portion of said piston rod.

13. An arrangement for measuring relative travel of a piston in a cylinder, comprising:
a supporting member housing a first electrode which is mounted substantially fixed but substantially electrically insulated with respect to the supporting member;
a second electrode spaced from the first electrode to define a space therebetween, said second electrode being substantially fixed with respect to the first electrode and being substantially electrically insulated from the supporting member, said first and second electrodes in use forming a capacitive reactance;
a reactance varying member which is mounted to move in accordance with said relative travel between the piston and the cylinder, said reactance varying member being so disposed that its movement changes the capacitance between said first and second electrodes in accordance with said relative movement between the piston and the cylinder; and electrical connecting means being connected to said fixed first and second electrodes for measuring the capacitance formed therebetween and for producing a signal indicative of relative movement between the piston and the cylinder.

14. The arrangement according to Claim 13 wherein said reactance varying member is made of a substantially electrically insulating material which on entering said space, acts as a dielectric medium.

15. The arrangement according to Claim 14 wherein said reactance varying member comprises a ceramic sleeve.

16. The arrangement according to Claim 14 wherein said reactance varying member comprises a sleeve made of epoxy resin.

17. The arrangement according to Claim 13 wherein said first and second electrodes are tubular and substantially co-axial t and wherein said supporting member comprises a hollow piston rod which is substantially coaxial with said first and second electrodes.

18. The arrangement according to Claim 13 wherein said cylinder is filled with a dielectric fluid so as to fill said space, and wherein said reactance varying member at least partly displaces said dielectric fluid upon entering said space, whereby said capacitive reactance is a sum of a first capacitive reac-tance formed by the electrically insulating reactance varying member, and a second capacitive reactance formed by said di-electric fluid.

19. The arrangement according to Claim 13 wherein the reac-tance varying member comprises electrically conductive material and wherein the cylinder is filled with a dielectric fluid to fill said space, whereby the reactance varying member upon entering said space partly displaces said dielectric fluid, thereby reducing the measured capacitance between the first and second electrodes.

20. The arrangement according to Claim 14 wherein said reactance varying member of insulating material includes an electrically conductive coating.

21. An arrangement for measuring relative travel of a piston in a cylinder which is part of a hydro-pneumatic assembly, comprising:
a supporting member in the form of a hollow piston rod and housing having fixed first and second spaced substantially coaxial tubular electrodes which are both substantially electri-cally insulated from the supporting member and mounted in a substantially fixed relationship with respect to each other to form a substantially annular gap;

electrical leads connected to said first and second elec-trodes, said first and second electrodes in use forming a vari-able capacitance;
a sleeve-like member which is mounted for movement reflect-ing said relative travel of the piston in said cylinder, said sleeve-like member being disposed to enter said substantially annular gap to vary in use said capacitance between said first and second electrodes; and said variable capacitance producing in use a signal indica-tive of relative travel of said piston in said cylinder.

22. The arrangement according to Claim 21 wherein said sleeve-like member comprises insulating material.

23. The arrangement according to Claim 22 wherein said sleeve-like member comprises a ceramic sleeve.

24. The arrangement according to Claim 22 wherein said sleeve-like member comprises a sleeve made of epoxy resin.

25. The arrangement according to Claim 24 wherein said cylinder is substantially filled with a fluid having dielectric properties so as substantially to fill said space, and wherein said reactance varying member at least partly displaces said dielectric fluid upon entering said space, whereby said capaci-tance becomes a combination of a first capacitance formed by said first and second electrodes and said sleeve-like member, and a second capacitance formed by said dielectric fluid in association with said first and second electrodes.

26. The arrangement according to Claim 22 wherein said cylinder is substantially filled with a fluid having dielectric properties so as substantially to fill said space, and wherein said reactance varying member at least partly displaces said dielectric fluid upon entering said space, whereby said capaci-tance becomes a combination of a first capacitance formed by the electrically insulating reactance varying member, and a second capacitance formed by said dielectric fluid.

27. The arrangement according to Claim 22 wherein said reactance varying member of insulating material has an electri-cally conductive coating.

28. An arrangement for measuring relative travel of a piston in a cylinder which is part of a mechanical suspension assembly, comprising:
a hollow piston rod housing first and second, substantially coaxial tubular electrodes which are spaced from one another and which are both substantially electrically insulated from the piston rod and mounted in a substantially fixed relationship with respect to each other to form a substantially annular gap, said first and second electrodes forming a variable capacitance;
a sleeve-like member which is mounted for movement reflect-ing said relative travel of the piston in said cylinder, said sleeve-like member being disposed to slidingly enter said sub-stantially annular gap to vary said variable capacitance;
a third electrode substantially electrically insulated from both the first and second electrodes and spaced from the second electrode to form a substantially fixed reference capacitance in use; and electrical connecting means connected to said fixed first, second and third electrodes.

29. The arrangement according to Claim 28 wherein said sleeve-like member comprises an epoxy resin sleeve.

30. The arrangement according to Claim 28 wherein said sleeve-like member comprises a ceramic cylinder.

31. The arrangement according to Claim 28 wherein said sleeve-like member comprises a metallic cylinder.

32. The arrangement according to Claim 28 wherein said mechanical suspension assembly comprises a liquid dielectric filled and sealed assembly, whereby said sleeve-like member by its movement displaces said liquid dielectric from said annular gap.

33. The arrangement according to Claim 28 wherein an electrical measuring bridge connected to at least said first, second and third electrodes to measure said variable capacitance to produce a signal, by using said fixed capacitance as a refer-ence, said signal indicating the extent of movement of said piston in said cylinder.

34. An arrangement for measuring relative travel of a piston in a cylinder, comprising:
a supporting member housing a first electrode which is mounted fixed but electrically insulated with respect to the supporting member;
a second electrode spaced from the first electrode to define a space therebetween, said second electrode being immovable with respect to the first electrode and being electrically insulated from the supporting member, said first and second electrodes in use forming a capacitive reactance;
a reactance varying member which is mounted to move in accordance with said relative travel between the piston and the cylinder, said reactance varying member being so disposed that its movement changes the capacitance between said first and second electrodes in accordance with said relative movement between the piston and the cylinder; and electrical measuring means being connected to said fixed first and second electrodes to measure the capacitance formed therebetween and produce a signal indicative of relative movement between the piston and the cylinder.

35. The arrangement as in Claim 34 wherein said reactance varying member is made of an electrically insulating material which on entering said space, acts as a dielectric medium.

36. The arrangement as in Claim 35 wherein said reactance varying member comprises a ceramic sleeve.

37. The arrangement as in Claim 35 wherein said reactance varying member comprises a sleeve made of epoxy resin.

38. The arrangement as in Claim 34 wherein said first and second electrodes are tubular and substantially coaxial, and wherein said supporting member comprises a hollow piston rod which is substantially coaxial with said first and second elec-trodes.

39. The arrangement as in Claim 35 wherein said cylinder is filled with a dielectric fluid so as to fill said space, and wherein said reactance varying member at least partly displaces said dielectric fluid upon entering said space, whereby said capacitive reactance is a sum of a first capacitive reactance formed by the electrically insulating reactance varying member, and a second capacitive reactance formed by said dielectric fluid.

40. The arrangement as in Claim 34 wherein the reactance varying member comprises electrically conductive material and wherein the cylinder is filled with a dielectric fluid to fill said space, whereby the reactance varying member upon entering said space partly displaces said dielectric fluid, thereby reducing the measured capacitance between the first and second electrodes.

41. The arrangement as in Claim 35 wherein said reactance varying member of insulating material includes an electrically conductive coating.

42. An arrangement for measuring relative travel of a piston in a cylinder which is part of a hydro-pneumatic assembly, comprising:
a supporting member in the form of a hollow piston rod and housing fixed first and second spaced substantially coaxial tubular electrodes which are both electrically insulated from the supporting member and mounted in fixed relationship with respect to each other to form a substantially annular gap;
electrical leads connected to said first and second elec-trodes, said first and second electrodes in use forming a vari-able capacitance;

a sleeve-like member which is mounted for movement reflect-ing said relative travel of the piston in said cylinder, said sleeve-like member being disposed to enter said substantially annular gap to vary said capacitance between said first and second electrodes; and electrical measuring means being connected to said elec-trical leads to produce a signal indicative of relative travel of said piston in said cylinder.

43. The arrangement as in Claim 42 wherein said sleeve-like member comprises insulating material.

44. The arrangement as in Claim 43 wherein said sleeve-like member comprises a ceramic sleeve.

45. The arrangement as in Claim 44 wherein said sleeve-like member comprises a sleeve made of epoxy resin.

46. The arrangement as in Claim 45 wherein said cylinder is filled with a dielectric fluid so as to fill said space, and wherein said reactance varying member at least partly displaces said dielectric fluid upon entering said space, whereby said capacitive reactance becomes the sum of a first capacitive reactance formed by said first and second electrodes and said sleeve-like member, and a second capacitive reactance formed by said dielectric fluid in association with said first and second electrodes.

47. The arrangement as in Claim 43 wherein said cylinder is filled with a dielectric fluid so as to fill said space, and wherein said reactance varying member at least partly displaces said dielectric fluid upon entering said space, whereby said capacitive reactance becomes the sum of a first capacitive reactance formed by the electrically insulating reactance varying member, and a second capacitive reactance formed by said di-electric fluid.

48. The arrangement as in Claim 47 wherein said reactance varying member of insulating material includes an electrically conductive coating.

49. An arrangement for measuring relative travel of a piston in a cylinder which is part of a mechanical suspension assembly, comprising:
a hollow piston rod housing first and spaced substantially coaxial tubular electrodes which are both electrically insulated from the piston rod and mounted in fixed relationship with respect to each other to form a substantially annular gap, said first and second electrodes forming a variable capacitance;
a sleeve-like member which is mounted for movement reflect-ing said relative travel of the piston in said cylinder, said sleeve-like member being disposed to slidingly enter said sub-stantially annular gap to vary said variable capacitance;
a third electrode electrically insulated from both the second electrode and spaced from the second electrode to form a fixed capacitance in use;
electrical leads connected to said fixed first, second and third electrodes; and an electrical measuring bridge connected to at least said first, second and third electrodes to measure said variable capacitance to produce a signal, by using said fixed capacitance as a reference, said signal indicating the extent of movement of said piston in said cylinder.

50. The arrangement as in Claim 49 wherein said sleeve-like member comprises an epoxy resin sleeve.

51. The arrangement as in Claim 49 wherein said sleeve-like member comprises a ceramic cylinder.

52. The arrangement as in Claim 49 wherein said sleeve-like member comprises a metallic cylinder.

53. The arrangement as in Claim 49 wherein said mechanical suspension assembly comprises a liquid dielectric filled and sealed in said cylinder, whereby said sleeve-like member by its movement displaces said liquid dielectric from said annular gap.

54. A damping cylinder of a vibration damper, said damping cylinder having an arrangement for determining a position of piston means therewithin, said cylinder having a space there-within with said piston means disposed in said space for axial slidable movement within said cylinder;
at least one damping medium being disposed within said cylinder for damping said axial movement of said piston means with respect to said cylinder;
said arrangement for determining the position of said piston means comprising:
means for sensing a position of said piston means within said cylinder;
said position sensing means having a first element and a second element;
said first element of said position sensing means being disposed to be movable with said piston means;
said second element of said position sensing means being disposed to be substantially stationary with respect to said cylinder;
said first element and said second element being electri-cally insulated one from the other;
said two elements forming a variable impedance component which is substantially electrically reactive;
said variable reactive electrical impedance varying, in operation, with said position of said piston means in said cylinder;
an electrical signal being generated by at least one of said elements and being indicative of said position of said piston means;
electrical connecting means, being connected to at least one of said elements, for sensing said electrical signal, indicative of said position of said piston means;

said first element comprising a first electrode and said second element comprising a second electrode of a capacitor;
dielectric means being disposed at least in part between said first and second electrodes of said capacitor;
said electrical connecting means being connected to said first electrode and to said second electrode;
said piston means including a piston rod;
said first electrode comprising at least a portion of said piston rod;
said piston rod having a hollow portion;
said cylinder having a base at one end thereof;
said second electrode comprising a first, cylindrical tube which is disposed on and extends from said base of said cylinder means into said space within said cylinder;
said hollow portion of said piston rod having a longitudinal axis being substantially axially aligned with a longitudinal axis of said first tube; and said first tube at least during operation extending, at least partially, into said hollow portion of said piston rod.

55. The damping cylinder of said vibration damper, said cylinder having an arrangement for determining a position of piston means therewithin, according to Claim 54, wherein first tube is hollow and has disposed therein a second cylindrical tube secured to the base of said cylinder; said second tube being spaced from said first tube, and comprising an additional elec-trode which together with the first tube form a further capacitor, said first tube and said second tube being substan-tially stationary with respect to one another.

56. The damping cylinder of said vibration damper, said cylinder having an arrangement for determining a position of piston means therewithin, according to Claim 55, wherein said first tube and said second tube have the same type of dielectric material therebetween as the dielectric material which is between said first tube and said hollow portion of said piston rod.

57. The damping cylinder of said vibration damper, said cylinder having an arrangement for determining a position of piston means therewithin, according to Claim 56, wherein said second tube is also secured in the base of the damper cylinder.

58. The damping cylinder of said vibration damper, said cylinder having an arrangement for determining a position of piston means therewithin, according to Claim 57, wherein said first tube is insulated from the base of the cylinder.

59. A damping cylinder of a vibration damper, said damping cylinder having an arrangement for determining a position of piston means therewithin, said cylinder having a space there-within with said piston means disposed in said space for axial slidable movement within said cylinder;
at least one damping medium being disposed within said cylinder for damping said axial movement of said piston means with respect to said cylinder;
said arrangement for determining the position of said piston means comprising:
means for sensing a position of said piston means within said cylinder;
said position sensing means having a first element and a second element;
said first element of said position sensing means being disposed to be movable with said piston means;
said second element of said position sensing means being disposed to be substantially stationary with respect to said cylinder;
said first element and said second element being electri-cally insulated one from the other;
said two elements forming a variable impedance component which is substantially electrically reactive;
said variable reactive electrical impedance varying, in operation, with said position of said piston means in said cylinder;

an electrical signal being generated by at least one of said elements and being indicative of said position of said piston means;
electrical connecting means, being connected to at least one of said elements, for sensing said electrical signal, indicative of said position of said piston means;
said first element comprising a first electrode and said second element comprising a second electrode of a capacitor;
dielectric means disposed at least in part between said first and second electrodes of said capacitor; and said electrical connec-ting means being connected to said first electrode and to said second electrode;
said cylinder having a base;
said piston means having a face disposed towards said base, said base of said damper cylinder being insulated from the cylinder to form said second electrode of said capacitor; and said face of said piston means forming said first electrode of said capacitor.

60. A damping cylinder of a vibration damper, said damping cylinder having an arrangement for determining a position of piston means therewithin, said cylinder having a space therewithin with said piston means disposed in said space for axial slidable movement within said cylinder;
at least one damping medium being disposed within said cylinder for damping said axial movement of said piston means with respect to said cylinder;
said arrangement for determining the position of said piston means comprising:
means for sensing a position of said piston means within said cylinder;
said position sensing means having a first element and a second element;
said first element of said position sensing means being disposed to be movable with said piston means;

said second element of said position sensing means being disposed to be substantially stationary with respect to said cylinder;
said first element and said second element being electri-cally insulated one from the other;
said two elements forming a variable impedance component which is substantially electrically reactive;
said variable reactive electrical impedance varying, in operation, with said position of said piston means in said cylinder;
an electrical signal being generated by at least one of said elements and being indicative of said position of said piston means; and electrical connecting means, being connected to at least one of said elements, for sensing said electrical signal, indicative of said position of said piston means; and an impedance bridge, being connected to said connecting means, for generating an electrical signal indicative of a position of said piston means.

61. A damping cylinder of a vibration damper, said damping cylinder having an arrangement for determining a position of piston means therewithin, said cylinder having a space there-within with said piston means disposed in said space for axial slidable movement within said cylinder;
at least one damping medium being disposed within said cylinder for damping said axial movement of said piston means with respect to said cylinder;
said arrangement for determining the position of said piston means comprising:
means for sensing a position of said piston means within said cylinder;
said position sensing means having a first element and a second element;

said first element of said position sensing means being disposed to be movable with said piston means;
said second element of said position sensing means being disposed to be substantially stationary with respect to said cylinder;
said first element and said second element being electri-cally insulated one from the other;
said two elements forming a variable impedance component which is substantially electrically reactive;
said variable reactive electrical impedance varying, in operation, with said position of said piston means in said cylinder;
an electrical signal being generated by at least one of said elements and being indicative of said position of said piston means;
electrical connecting means, being connected to at least one of said elements, for sensing said electrical signal, indicative of said position of said piston means;
said first element comprising a first electrode and said second element comprising a second electrode of a capacitor;
dielectric means being disposed at least in part between said first and second electrodes of said capacitor; and said electrical connecting means being connected to said first electrode and to said second electrode;
said piston means including a piston rod;
said first electrode comprising at least a portion of said piston rod;
capacitance measuring circuitry for connection to said capacitor;
said capacitance measuring circuitry comprising a capacitor bridge;
said variable capacitor forming one of the arms of one half of said capacitor bridge; and an amplifier being connected to said capacitor bridge for generating an electrical signal corresponding to the position of said piston in said damper cylinder.

62. The damping cylinder of said vibration damper, said cylinder having an arrangement for determining a position of piston means therewithin, according to Claim 56 wherein said further capacitor provides at least a temperature compensating capacitor being connectable in a capacitance measuring circuitry.

63. The damping cylinder of said vibration damper, said cylinder having an arrangement for determining a position of piston means therewithin, according to Claim 59 including an impedance bridge, connected to said connecting means, for gen-erating an electrical signal indicative of a position of said piston means.

64. A damping cylinder of a vibration damper, said cylinder having an arrangement for determining a position of piston means therewithin, said cylinder having a space therewithin with said piston means disposed in said space for axial slidable movement within said cylinder;
at least one damping medium being disposed within said cylinder for damping said axial movement of said piston means with respect to said cylinder;
one of said at least one damping medium being hydraulic damping oil;
said arrangement for determining the position of said piston means comprising:
said piston means including a circular, hollow piston rod;
said cylinder having a base at one end thereof from which a hollow circular cylindrical, first tube extends into said space and also into said hollow piston in a telescopic relationship therewith, thereby forming, with a dielectric material, compris-ing said hydraulic damping oil, disposed between said first tube and said piston rod, a variable, first capacitor;

a longitudinal axis of said piston rod being substantially aligned with a longitudinal axis of said first tube;
said first tube being insulated from said cylinder and said hollow piston rod;
a first lead being connected to said first tube; and a second lead being connected to said hollow piston rod.

65. The damping cylinder of said vibration damper, said cylinder having an arrangement for determining a position of piston means therewithin, according to Claim 64 wherein first tube is hollow and has disposed therein a second cylindrical tube secured to the base of said cylinder and insulated from said first tube; said second tube being spaced from said first tube, and comprising an additional electrode which together with the first tube form a further capacitor, said first tube and said second tube being substantially stationary with respect to one another; and said first tube and said second tube having the same type of dielectric material thereinbetween as the dielectric material which is between said first tube and said hollow portion of said piston rod

66. A damping cylinder in a vibration damper, said cylinder having an arrangement for measuring relative travel of a piston in said cylinder, comprising:
a supporting member housing a first electrode which is mounted substantially fixed but substantially electrically insulated with respect to the supporting member;
a second electrode being spaced from the first electrode to define a space therebetween, said second electrode being substantially fixed with respect to the first electrode, said first and second electrodes in use forming a capacitive reactance;
a reactance varying member which is mounted to move in accordance with said relative travel between the piston and the cylinder, said reactance varying member being so disposed that its movement changes the capacitance between said first and second electrodes in accordance with said relative movement between the piston and the cylinder; and electrical connecting means connected to said fixed first and second electrodes for measuring the capacitance formed therebetween and for producing a signal indicative of relative movement between the piston and the cylinder.

67. The damping cylinder in said vibration damper, said cylinder having an arrangement according to Claim 66 wherein said reactance varying member is made of a substantially electrically insulating material which on entering said space, acts as a dielectric medium.

68. The damping cylinder in said vibration damper, said cylinder having an arrangement according to Claim 67 wherein said reactance varying member comprises a ceramic sleeve.

69. The damping cylinder in said vibration damper, said cylinder having an arrangement according to Claim 67 wherein said reactance varying member comprises a sleeve made of epoxy resin.

70. The damping cylinder in said vibration damper, said cylinder having an arrangement according to Claim 66 wherein said first and second electrodes are tubular and substantially co-axial, and wherein said supporting member comprises a hollow piston rod which is substantially coaxial with said first and second electrodes.

71. The damping cylinder in said vibration damper, said cylinder having an arrangement according to Claim 66 wherein said cylinder is filled with a dielectric fluid so as to fill said space, and wherein said reactance varying member at least partly displaces said dielectric fluid upon entering said space, whereby said capacitive reactance is a sum of a first capacitive reactance formed by the electrically insulating reactance varying member, and a second capacitive reactance formed by said dielectric fluid.

72. The damping cylinder in said vibration damper, said cylinder having an arrangement according to Claim 66 wherein the reactance varying member comprises electrically conductive material and wherein the cylinder is filled with a dielectric fluid to fill said space, whereby, the reactance varying member upon entering said space partly displaces said dielectric fluid, thereby reducing the measured capacitance between the first and second electrodes.

73. The damping cylinder in said vibration damper, said cylinder having an arrangement according to Claim 67, wherein said reactance varying member of insulating material includes an electrically conductive coating.

74. A damping cylinder in a vibration damper, said cylinder having an arrangement for measuring relative travel of a piston in said cylinder, comprising:
a supporting member in the form of a hollow piston rod and housing having fixed first and second spaced substantially coaxial tubular electrodes which are both substantially electri-cally insulated from the supporting member and mounted in a substantially fixed relationship with respect to each other to form a substantially annular gap;
electrical leads connected to said first and second elec-trodes, said first and second electrodes in use forming a var-iable capacitance;
a sleeve-like member which is mounted for movement reflect-ing said relative travel of the piston in said cylinder, said sleeve-like member being disposed to enter said substan-tially annular gap to vary in use said capacitance between said first and second electrodes; and said variable capacitance producing in use a signal indica-tive of relative travel of said piston in said cylinder.

75. The damping cylinder in said vibration damper, said cylinder having an arrangement according to Claim 74 wherein said sleeve-like member comprises insulating material.

76. The damping cylinder in said vibration damper, said cylinder having an arrangement according to Claim 75 wherein said sleeve-like member comprises a ceramic sleeve.

77. The damping cylinder in said vibration damper, said cylinder having an arrangement according to Claim 75 wherein said sleeve-like member comprises a sleeve made of epoxy resin.

78. The damping cylinder in said vibration damper, said cylinder having an arrangement according to Claim 77 wherein said cylinder is substantially filled with a fluid having dielectric properties so as substantially to fill said space, and wherein said reactance varying member at least partly displaces said dielectric fluid upon entering said space, whereby said capaci-tance becomes a combination of a first capacitance formed by said first and second electrodes and said sleeve-like member, and a second capacitance formed by said dielectric fluid in association with said first and second electrodes.

79. The damping cylinder in said vibration damper, said cylinder having an arrangement according to Claim 75 wherein said cylinder is substantially filled with a fluid having dielectric properties so as substantially to fill said space, and wherein said reactance varying member at least partly displaces said dielectric fluid upon entering said space, whereby said capaci-tance becomes a combination of a first capacitance formed by the electrically insulating reactance varying member, and a second capacitance formed by said dielectric fluid.

80. The damping cylinder in said vibration damper, said cylinder having an arrangement according to Claim 75, wherein said reactance varying member of insulating material has an electrically conductive coating.

81. An arrangement for measuring relative travel of a piston in a damping cylinder of a vibration damper for a mechan-ical suspension assembly for a vehicle, comprising:
a hollow piston rod housing first and second, substantially coaxial tubular electrodes which are spaced from one another and which are both substantially electrically insulated from the piston rod and mounted in a substantially fixed relationship with respect to each other to form a substantially annular gap, said first and second electrodes forming a variable capacitance;
a sleeve-like member which is mounted for movement reflect-ing said relative travel of the piston in said cylinder, said sleeve-like member being disposed to slidingly enter said sub-stantially annular gap to vary said variable capacitance;

a third electrode substantially electrically insulated from both the first and second electrodes and spaced from the second electrode to form a substantially fixed reference capacitance in use; and electrical connecting means connected to said fixed first, second and third electrodes.

82. The arrangement for measuring relative travel of a piston in a damping cylinder of a vibration damper for a mechan-ical suspension assembly for a vehicle according to Claim 81 wherein said sleeve-like member comprises an epoxy resin sleeve.

83. The arrangement for measuring relative travel of a piston in a damping cylinder of a vibration damper for a mechan-ical suspension assembly for a vehicle according to Claim 81 wherein said sleeve-like member comprises a ceramic cylinder.

84. The arrangement for measuring relative travel of a piston in a damping cylinder of a vibration damper for a mechan-ical suspension assembly for a vehicle according to Claim 81 wherein said sleeve-like member comprises a metallic cylinder.

The arrangement for measuring relative travel of a piston in a damping cylinder of a vibration damper for a mechan-ical suspension assembly for a vehicle according to Claim 81 wherein said mechanical suspension assembly comprises a liquid dielectric filled and sealed assembly, whereby said sleeve-like member by its movement displaces said liquid dielectric from said annular gap.

86. The arrangement for measuring relative travel of a piston in a damping cylinder of a vibration damper for a mechan-ical suspension assembly for a vehicle according to Claim 81 wherein an electrical measuring bridge connected to at least said first, second and third electrodes to measure said variable capacitance to produce a signal, by using said fixed capacitance as a reference, said signal indicating the extent of movement of said piston in said cylinder.