DE202008008477U1 - Rod-shaped linear sensor - Google Patents

Abstract

Inductive linear sensor with
A stator element (18) having a coil arrangement (26) which extends over a linear measuring range (L),
And an index element (20, 120) which is arranged to be movable relative to the stator element (18), wherein the index element (20, 120) has at least one coupling element (40a, 40b, 140a, 140b),
characterized in that
- The stator (18) is rod-shaped and the index element (20) is arranged annularly around the rod-shaped stator element (18).

Description

The The invention relates to an inductive linear sensor.

With Help of a linear sensor can be a linear displacement of two Elements against each other determined as a sensor value and in electrical Form - for example, as an analog or digital signal - output. Such linear sensors are for a variety of uses usable, for example in the automotive sector.

In the WO2003 / 038379 is described an inductive linear sensor. This has a linear stator element in the form of a printed circuit board on which a coil arrangement extends over the linear measuring range. The coil assembly comprises two excitation and a receiver coil, wherein the excitation coils are formed as periodically varying patterns which are spatially displaced in the direction of the course of the measuring range. An alternating current signal applied to the excitation coils generates a temporally and spatially varying electromagnetic field. This generates in a arranged on a movable index element inductive coupling element, a current that leads in the receiver coil to a coupled signal. The position of the index element within the measuring range relative to the stator element can be determined from the coupled signal.

While The technique described for position sensors extraordinarily Nevertheless, it is necessary for a precise detection of an exact linear movement of the index element is present along the measuring range. While this with some relative movements to be sensed in a simple manner may be given, in which the index element always in a as constant as possible a distance exactly parallel to the measuring range moved, put in a variety of sensor applications, the Conditions much more complicated dar.

It Object of the invention to provide a linear sensor, with in a simple way a relative movement between index and Stator element can be reliably determined.

These The object is achieved by a sensor according to claim 1. In particular, the problem is solved by a brake wear sensor according to claim 11, a level sensor according to claim 12 and a shock absorber according to claim 13.

According to the invention the stator is rod-shaped. Below this is an elongated (i.e., the longitudinal dimension is larger as the largest transverse dimension, for example, more than twice so large, preferably more than 4 times as large), at least substantially cylindrical shape (i.e., the outer Cross-section is substantially over the longitudinal extent constant). The outer cross-sectional shape may preferably be round, but are also flat, polygonal or differently shaped cross sections conceivable. Inside, the rod-shaped Stator element constructed arbitrarily, so for example. Both hollow and be massive.

The Index element is annular and around the rod-shaped Statorelement arranged around. It is then in the longitudinal direction slidable on the rod-shaped stator. By the annular formation is automatically a guide ensured the index element on the stator. By an appropriate Game, d. H. Difference between the inner surface of the ring and the outer surface of the stator element on the one hand ensures a very easy mobility and On the other hand, a transverse displacement can be prevented. It can by a corresponding guide twisting of the ring be prevented around the longitudinal axis of the rod element, but preferably the ring element is freely rotatable about the stator element.

One Such linear sensor is for a variety of applications very well suited because on the one hand the two sensor parts are good against each other on the other hand - especially with rotatability of the ring - many degrees of freedom of Keep moving.

So may, for example, a brake wear sensor on a brake device be formed, in which a screw for tracking a Bremsklotzes a brake is provided after wear Ver. The rod-shaped stator element can then be designed to be stationary be while the annular index element moved with the screw. The position of the index element is thus Information about the degree of wear of the Brake pad.

A Another possible application is a level sensor to determine the level of a liquid in a container. The rod-shaped sensor element can be arranged substantially vertically. The index element includes a float element that floats in the liquid. Thus, a different position of the index element along the stator depending on the current fluid level to adjust. The swimmer can move relatively freely, so that the risk of jamming is low.

Another possible application is a car level sensor for determining the position of a suspension relative to the chassis of a motor vehicle. Index and stator are arranged on two mutually movable parts, wherein the The position of the parts changes when the suspension is deflected in relation to the chassis. This results in a guided by the rod and the ring relative movement, which can be queried as the sensor value. Preferably, such a sensor can be mounted directly on a shock absorber. The shock absorber has a piston rod which can slide linearly in a piston, wherein this movement in a known manner - for example. Hydraulically - is damped. A stator element of the sensor described above is now mounted so that it is fixed relative to one of the two mounting points, while the index element is fixed relative to the second mounting point. A displacement of the piston rod results in a movement of the sensor parts and thus a sensor value for the displacement. Preferably, the stator element of the sensor is mounted externally on the piston, while the index element surrounds the piston as a ring, preferably as part of a tube arranged thereon, for example a dust protection tube.

According to one Further development of the invention is the coil arrangement of the stator formed as a flat coil carrier with flat coils arranged thereon. Here is particularly suitable a circuit board on which the coils are applied as tracks. As a result, a coil arrangement is very cost-effectively mass-produced. It is also possible, additional electronics for control and to provide evaluation on the same circuit board.

According to one Further development of the invention is also the coupling element with at least a capacitor and a coil arrangement provided. The coil arrangement has a circumferentially extending, spatially in Lengthwise varying arrangement of conductors on. in this connection are surface areas between intersecting ladders formed, which are bounded by the ladders. A changing magnetic Flow through these areas induces a corresponding current through the conductors. The coupling element with capacity and inductance (coil arrangement) acts like a resonant circuit with a certain resonant frequency. This creates a high frequency-selective behavior and - when excited in the Near the resonance frequency - by resonance peaking a high signal strength of the coupled signal in the receiver coil.

According to one Essential development of the invention comprises the coupling element two electrically isolated resonant circuits, each comprise a coil assembly with a capacitance. The Coil arrangements of the two resonant circuits are in the circumferential direction of the annular index element spatially to each other postponed. That is, that between the crossing Ladders formed surface areas of the two oscillating circuits different positions. Particularly preferred are the Coil arrangements shifted from each other so that always the crossing of conductors of the first coil arrangement within - preferably substantially centrally within - the surface areas formed on the second coil arrangement lies and vice versa. For a periodic pattern with at least two each Intersections and surface areas per period this becomes eg. achieved by shifting against each other by a quarter period. By this shifted arrangement of the two coil arrangements is ensured that when excited with a directed in a radial direction electromagnetic field always in at least one of the coil arrangements a signal is induced. Because the field is centered on a conductor crossing, so in the corresponding coil arrangement is substantially no Signal induced. However, the shifted arrangement ensures that in that position at least in the second coil arrangement a current is induced. The resonant circuits preferably have one at least substantially the same resonant frequency, with at least a frequency component of the excitation signal matches.

Therefore is in this arrangement at any rotation of the ring given to the stator around a secure detection of the position. hereby the scope of the sensor is significantly expanded, namely on the capture of elements that are adjacent to each other in addition to the linear Move movement can also perform a rotary motion. A linear guide becomes superfluous, so that the associated effort is also eliminated like possible mechanical problems, for example with jamming.

According to one Further development of the invention is provided that the stator a plastic body, in which the coil assembly is arranged on a bobbin. D. h., That the coil assembly not freely accessible and thus protected is. The coil assembly can be easily manufactured Spool carrier particularly simple and inexpensive be formed, which then within one for the relative guidance of the index element particularly suitably shaped stator element to be arranged is, for example, in a hollow bar.

Preferably, the coil arrangement comprises at least one exciter coil for generating an alternating magnetic field and at least one receiver coil for receiving portions of the alternating field, which are coupled over the coupling element. The exciter and / or the receiver coil can be designed as a pattern that varies along the measuring range and periodically varies in the transverse direction. Particularly preferred is the sensor principle of WO2003 / 038379 , in which two excitation coils are formed as a periodically varying pattern, wherein the patterns are spatially out of phase with each other in the direction of the course of the measuring range, and wherein a receiver coil is formed as at least one loop around the measuring range.

According to one Development of the invention comprises the index element a Plastic sleeve to the at least one coil assembly wrapped as a wire. It is particularly preferred that the Plastic sleeve on the circumference elevations or depressions corresponding to the winding pattern of the coil assembly, so that this can be made very easy. Alternatively, it is also possible that the Coil assembly is formed on a flexible circuit board, the is arranged around the plastic sleeve.

following Be embodiments of the invention with reference to drawings described in more detail. In the drawings show:

1 a perspective view of an inductive linear sensor;

2 an exploded perspective view of the stator of the sensor 1 ;

3 in schematic form, a coil arrangement of the stator 2 ;

4 as a perspective exploded view of a first embodiment of an index element;

5 in a perspective, enlarged view of a winding arrangement of the index element 4 ;

6 in a perspective exploded view, a second embodiment of an index element;

7 a schematic side view of a brake wear sensor;

8th a schematic side view of a level sensor and

9 a view of a level sensor on a vehicle shock absorber.

In 1 is an embodiment of an inductive linear sensor 10 shown. The sensor 10 includes a stator 18 with a connection housing 12 and a superb stator rod 16 , The housing 12 and the hollow stator rod 16 are designed as plastic injection molded parts. Around the stator rod 16 around is an annular index element 20 arranged. This is freely displaceable along the longitudinal direction L.

The internal structure of the stator element 18 is in exploded view of 2 recognizable. Here, however, the housing is shown in a different variant. While the case 12 in 1 as electrical connection, a connector housing 14 having protruding, by means of a plug electrically contacted terminals, the housing 12a in 2 with a direct connection 15 intended for a cable.

The stator element 18 points inside the hollow bar 16 a coil carrier 22 in the form of a conventional epoxy resin circuit board and a circuit board carrier 24 made of plastic. The PCB carrier 24 takes the circuit board 22 and fixes them inside the hollow bar 16 in about the middle.

How out 3 recognizable includes the circuit board 22 a coil arrangement 26 with two in the measuring direction L sinusoidal exciting coils 26a and a receiver coil formed as a conductor loop 26b , Next is on the circuit board 22 a driver and evaluation electronics 28 provided to the electrical connection 15 (or to the plug connection 14 ) is electrically connected.

A first, preferred embodiment of the index element 20 is in 4 shown in detail. It comprises a plastic sleeve 32 with an outer ring on which as a coupling element two resonant circuits 40a . 40b are formed. As seen from the view of a wired element in 5 As can be seen, each of the resonant circuits comprises a coil winding and a capacitor element. The capacitor elements 42a . 42b are as SMD capacitor elements on contacted printed circuit boards with pins 44 intended. For encapsulation of the element 20 this is molded onto its ring after manufacturing the windings and the capacitor elements with plastic.

The respective coils 46a . 46b are with the capacitor elements 42a . 42b connected to resonant circuits by connecting the coil wires to the pins 44 are contacted. The spools 46a . 46b are on the ring of the sleeve 32 between structural elements formed there 48 (Projections or grooves between these) wound and electrically isolated from each other. Each of the coils 46a . 46b In the example shown, there are five turns, each of the turns successively crossing regions (clearly visible in FIG 5 front for the coil 46a and on the right edge for the coil 46b ) and surface areas formed between the conductors. The spools 46a . 46b are here gegeneinan phase-shifted by a quarter period so that each crossing region of the first winding 46a centrally in a formed area of the second winding 46b falls and vice versa. So are for each of the coils 46a . 46b formed over the circumference two surface area and two Überkeuzungen. As a result, the two surface areas of each coil 46a . 46b arranged diametrically opposite and wound electrically gegensinning. As a result, a radially acting electromagnetic field generated between and exiting through the areas induces a non-zero sum signal in the respective coil.

6 shows an alternative embodiment of the index element 120 , Unlike the first embodiment ( 4 . 5 ) are resonant circuits here 140a . 140b not with wire windings, but each formed with flat coils on a flexible circuit board. On the circuit board, the flat coils of two mutually insulated, rotated by ¼ turn against each other resonant circuits are applied as a conductor track structure and each form an SMD capacitor 142a . 142b a resonant circuit.

The following is the function of the sensor 10 with his stator 18 and index element 20 described.

The coil arrangement 26 is from the driver electronics 28 during operation of the sensor as in WO2003 / 038379 explained operating by applying to the two excitation coils AC signals of a carrier frequency, the resonant frequency of the two resonant circuits 40a . 40b of the index element 20 equivalent. The signals of the two transmitting coils are as in WO2003 / 038379 described, temporally out of phase modulated with a signal of lower frequency, so that a resulting temporally and spatially varying magnetic field results, the direction of which is substantially perpendicular to the two opposite surfaces of the circuit board 22 is.

The varying magnetic field penetrates the plastic sleeve 16 and acts on the coil assemblies 40a . 40b of the index element 20 one. In this case it induces in a coil arrangement 46a . 46b whose surface areas are approximately perpendicular to the field components, a corresponding signal. On the other hand, the field components merely encounter crossing regions of a coil arrangement 46a . 46b Thus, because the field components cancel each other out on opposite surfaces, essentially no signal is induced.

By the relative to each other shifted arrangement of the coils 46a . 46b ensures that at any rotational position of the index element 20 always at least one of the two coils around the longitudinal axis L around 46a . 46b is excited by the magnetic field.

By the excitation of at least one of the oscillating circuits 40a . 40b at its resonant frequency, there is a resultant signal coming from the receiver coil 26b at the stator 18 is recorded. As in WO2003 / 038379 the signal is described in the receiver coil 26b evaluated with respect to the phase of the modulation signal contained therein and thereby the position of the index element 20 determined along the measuring range L. The sensor value thus determined is provided by the electronics 28 at the electrical connection 14 respectively. 15 as a sensor value, for example. Digital or analog electrical output value output.

7 shows a first possible application of the sensor 1 , In a brake arrangement 50 is in a known manner a brake pad 52 next to a brake disc 54 arranged. During operation of the brake assembly 50 it comes to the wear of the brake pad 52 (dashed line). This is the brake pad 52 via a tracking device with a screw 56 tracked. With the help of the sensor 10 the current brake wear should be determined.

The rod-shaped stator 18 of the sensor 10 is fixed while the index element 20 moved relative to this. The index element 20 is on the screw 56 attached so that it moves with this and this shifts in the longitudinal direction L of the sensor.

At advanced wear of the brake pad 52 shifts the screw 56 in the longitudinal direction L (shown in dashed lines). This also shifts the index element 20 under rotation with respect to the stator element 18 , As explained above, despite the rotation in each orientation of the index element 20 always a determination of Po position possible, as always at least one of the two resonant circuits 40a . 40b is excited. So can the position of the index element 20 queried and thus the current value of the brake wear are detected as a sensor value.

In 8th is a second application of the sensor 10 out 1 in which this as a level sensor for the level of a liquid 72 in a container 70 is used. The rod-shaped stator 18 is aligned vertically. The index element 20 has a - in the example shown disk-shaped - float 74 on top of the surface of the liquid 72 swims.

With variation of the level of the liquid 72 results (dashed lines) a entspre pending shift of the index element 20 in the longitudinal direction L of the sensor 10 , Here is the float 74 through the rod-shaped stator element 18 Well guided in the movement. Nevertheless, there is enough clearance between the sleeve 32 and the rod-shaped stator element 18 not to jamming. Also by the swimmer 74 triggered rotations about the longitudinal axis L, a sensor value for the level can always be determined due to the described sensor arrangement.

9 schematically shows a further application possibility of the sensor described above. A shock absorber 80 , which may be part of a vehicle wheel suspension, for example, comprises a piston rod 82 at a first mounting point and a piston tube 84 at a second mounting point. The piston rod 82 can be linear with respect to the piston tube 84 and in this case, in a manner known to those skilled in the art, is damped. About the penetration depth of the piston rod 82 in the piston tube 84 can the chassis condition, eg. Spring deflection, load, etc. determine. This value is thus relevant for a variety of interesting in the automotive field control and regulatory tasks, eg. For a chassis control, headlamp control, etc.

At the in 9 shown shock absorbers 80 is a dust tube 86 provided, which is connected to the first mounting point and the piston tube 84 variable absorbs. At the dust protection tube 86 is the index element of a sensor formed as described above, by coil windings as described and connected thereto capacitor elements in the plastic material of the dust tube 86 are embedded. On the cylinder 86 Outside is a flexible conductor foil 88 applied with the (flat) coil arrangement described above, the curvature of the outer wall of the cylinder 84 follows, but not completely surrounds, but only covers an angular range of, for example, 30 ° in the circumferential direction thereof.

For longitudinally variable intake of the piston rod 82 in the piston 84 , depending on the chassis condition, moves so the index element 20 over the coil circuit 88 so that with the help of an attached electronics 89 As described above, a sensor value can be provided.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• WO 2003/038379 [0003, 0018, 0038, 0038, 0041]

Claims (13)

Inductive linear sensor with - a stator element ( 18 ) with a coil arrangement ( 26 ), which extends over a linear measuring range (L), - and an index element ( 20 . 120 ), which is opposite to the stator element ( 18 ) is movably arranged, wherein the index element ( 20 . 120 ) at least one coupling element ( 40a . 40b . 140a . 140b ), characterized in that - the stator element ( 18 ) is rod-shaped and the index element ( 20 ) annularly around the rod-shaped stator element ( 18 ) is arranged. Sensor according to claim 1, in which - the coil arrangement ( 26 ) as a conductor on a flat coil carrier ( 22 ) is trained. Sensor according to one of the preceding claims, in which - the coupling element ( 40a . 40b . 140a . 140b ) at least one capacity ( 42a . 42b . 142a . 142b ) and a coil arrangement ( 46a . 46b ), wherein the coil arrangement ( 46a . 46b ) has a circumferentially extending, spatially in the longitudinal direction (L) varying arrangement. Sensor according to claim 3, in which - the coupling element comprises two oscillating circuits ( 40a . 40b . 140a . 140b ), each having a coil arrangement ( 46a . 46b ) and a capacity ( 42a . 42b . 142a . 142b ), - where coil arrangements ( 46a . 46b ) of the two oscillating circuits ( 40a . 40b . 140a . 140b ) are arranged spatially displaced in the circumferential direction. Sensor according to one of the preceding claims, in which - the stator element ( 18 ) a plastic body ( 16 ), in which the coil arrangement ( 26 ) on a bobbin carrier ( 22 ) is arranged. Sensor according to one of the preceding claims, in which - the coil arrangement ( 26 ) at least one exciting coil ( 26a ) for generating an alternating magnetic field and at least one receiver coil ( 26b ) for receiving portions of the alternating field, which are coupled over the coupling element comprises, - of which at least one coil ( 26a ) is formed as along the measuring range (L) extending, periodically varying in the transverse direction pattern. Sensor according to Claim 6, in which - at least two exciter coils ( 26a ) are formed as periodically varying patterns, wherein the patterns are spatially out of phase with each other in the direction of the course of the measuring range (L), - wherein a receiver coil ( 26b ) is formed as at least one loop around the measuring range. Sensor according to one of the preceding claims, in which - the index element ( 20 ) a plastic sleeve ( 32 ) to the at least one coil assembly ( 46a . 46b ) is formed as a wound conductor. Sensor according to claim 8, wherein - the plastic sleeve ( 32 ) on the perimeter elevations ( 48 ) or depressions corresponding to the winding pattern of the coil arrangement ( 46a . 46b ) having. Sensor according to one of the preceding claims 1-7, wherein - at least one coil arrangement of the index element ( 120 ) as a flat coil on a flexible printed circuit board ( 140a . 140b ) is formed, - wherein the index element ( 20 ) a sleeve ( 32 ), to which the flexible circuit board is attached annularly. Brake wear sensor with - a screw ( 56 ) for tracking a brake pad ( 52 ) a brake ( 50 ) after wear, - wherein a linear sensor according to one of the preceding claims is provided so that the index element ( 20 ) with the screw ( 56 ), so that a Nachführweg can be determined as a sensor value. Level sensor for determining the level of a liquid ( 72 ) in a container ( 70 ), with a sensor according to one of claims 1-10, in which - the rod-shaped stator element ( 18 ) is arranged vertically, and the index element ( 20 ) a floating element ( 74 ). A shock absorber with a sensor according to any one of claims 1-10, wherein - a piston rod connected to a first mounting point ( 82 ) for variable-length recording in a piston connected to a second mounting point ( 84 ) is provided, - one of the two sensor elements - stator ( 18 ) or index element ( 20 ) - are connected to the first mounting point and the other element to the second mounting point, - so that during a displacement of the piston rod ( 82 ) opposite the piston ( 84 ) results in a movement of the sensor parts, so that a shift value can be determined as a sensor value.