DE102020113895A1 - Central slave cylinder - Google Patents

Abstract

The invention relates to a central release (1), in particular for a hydraulic release system (2) of a clutch system (3) of a motor vehicle (4), comprising a central release housing (5) with an annular central release piston space (6) in which the central release piston space (6) feedable hydraulic fluid (7) a central release piston (8) is axially movably received, characterized in that an inductive sensor unit (9) is arranged on the central release housing (5) which connects an electronic sensor control (10) and the electronic sensor control (10) Induction conductor tracks (11), and a metallic sensor body (12) is coupled to the central release piston (8) that a linear offset of the central release piston (8) causes a linear offset of the metallic sensor body (12), wherein the induction conductor tracks (11) extend in an axially parallel direction to the central release piston (8) and the metallic sensor body (12) is arranged in the radial direction between the central release housing (5) and the induction conductor tracks (11).

Description

The invention relates to a central release, in particular for a hydraulic release system of a clutch system of a motor vehicle, comprising a central release housing with an annular central release piston chamber in which a central release piston is axially movably received by a hydraulic fluid that can be fed to the central release piston.

It is basically known from the prior art that central release mechanisms can have a position sensor for detecting the position of the central release piston. EP1898111B1 describes, for example, a central release for a hydraulic clutch actuation, which has a housing having a cylindrical through-hole and a tubular sleeve arranged concentrically within the through-hole and at one end centered on the housing, on which an annular piston that can be effectively connected to the clutch is guided in an axially displaceable manner the outer end of which is attached to the inner ring of a release bearing, with a sensor for detecting the axial position of the annular piston relative to the housing being fixedly attached to the housing, and with the sensor being assigned an axially displaceable magnet body, which is attached to an annular body attached to the inner ring for entrainment is connected axially free of play by the annular piston during its axial displacements; the magnet body is guided displaceably with a constant distance to the sensor on the housing over its displacement path and engages with a guide shoe in a circumferential groove of the ring body axially free of play but radially movable.

It is therefore the object of the present invention to at least partially overcome the disadvantages known from the prior art. In particular, it is the object of the present invention to provide a solution by means of which the accuracy of the measurement of the position of a central release piston can be improved. It is also the object of the present invention to provide a central release device which is designed to be particularly compact in its radial structure.

This object is achieved by a central release piston, in particular for a hydraulic release system of a clutch system of a motor vehicle, comprising a central release housing with an annular central release piston space in which a central release piston is axially movably received by a hydraulic fluid that can be fed to the central release piston space, an inductive sensor unit being arranged on the central release housing, which comprises an electronic sensor control and induction conductor tracks connected to the electronic sensor control, and a metallic sensor body is coupled to the central release piston in such a way that a linear displacement of the central release piston causes a linear displacement of the metallic sensor body, with the induction conductor tracks extending in an axially parallel direction to the central release piston and the metallic sensor body in the radial direction between the central release housing and the inductors onsleiterbahnen is arranged.

Such a central release piston is easy to manufacture and allows, in particular, a particularly precise determination of the axial position of the central release piston while at the same time having a compact structure in the radial direction. Such a central release device can thus have significant advantages over the configurations from the prior art.

First, the individual elements of the claimed subject matter of the invention are explained in the order in which they are named in the set of claims and particularly preferred embodiments of the subject matter of the invention are described below.

Fully hydraulic clutch systems of motor vehicles can be equipped with a central slave cylinder, which is often also referred to as a Concentric Slave Cylinder (CSC). This can in particular consist of an annular hydraulic central release cylinder with an integrated release bearing, which is preferably arranged in the clutch housing between the gearbox and the clutch in the middle of the gearbox input shaft, which means that the lever in the gearbox bell housing, as used in arrangements with a conventional slave cylinder, can be omitted .

A hydraulic release system usually has a master cylinder that transmits the pressure generated on the master cylinder to the slave cylinder via a hydraulic pressure line.

Occasionally the hydraulic pressure is also increased by means of a so-called Powerpacks provided, which consists of a hydraulic pump and a hydraulic pressure accumulator that can be acted upon by the hydraulic pump. Here, a pressure chamber of the slave cylinder can also be hydraulically pressurized, for example, by a master cylinder controlled by a control unit by means of an electric motor, or by a hydraulic pump, possibly with the assistance of a pressure accumulator. A so-called power pack can be used in an advantageous manner, which switches several pressure circuits via a particularly central hydraulic pump and corresponding valves.

By means of an axially displaceable piston and with the interposition of a clutch release bearing, the slave cylinder transmits the hydraulic pressure to a lever system, which can be formed, for example, by a plate spring. The diaphragm spring acts on a clutch pressure plate connected to a clutch housing in a rotationally fixed and axially displaceable manner and is braced against a pressure plate firmly connected to the clutch housing. A clutch disc with a clutch lining is arranged between the pressure plate and the clutch pressure plate, which, depending on the tension between the pressure plate and the clutch pressure plate, form a frictional connection and either close the friction clutch or open it when the frictional connection is canceled.

A clutch system for motor vehicles has the function of coupling or decoupling the driving engine side in a drive train of a vehicle in a switchable manner from the transmission side and thus enabling a gear change of the transmission while driving and thereby operating the driving motor in a preferred speed / torque range to be able to.

A basic distinction is made between manually operated clutch systems and automatic clutch systems. In a manually operated clutch system, the clutching and disengaging process is triggered and controlled manually by the driver, for example by muscle-operated actuation of a clutch pedal. In automatic clutch systems, this control and actuation is taken over by an electronic control and actuators, so that the driver no longer needs to intervene to change gears while driving. As a result, automatic clutch systems usually do not have a clutch pedal either.

Motor vehicles in the sense of this application are land vehicles that are moved by machine power without being tied to railroad tracks. A motor vehicle can be selected, for example, from the group of passenger cars (cars), trucks (trucks), small motorcycles, light motor vehicles, motorcycles, motor buses (KOM) or tractors.

The central release housing has the function of receiving components of the central release, in particular the movable central release piston, and protecting them from external mechanical or chemical influences. Furthermore, the central release housing has the function of allowing simple assembly and fixing of the central release within the drive train. The central release housing can be designed in one piece or in several pieces. The central release housing can preferably be formed from a plastic, a metallic material and / or a ceramic material.

The central release piston space formed in the central release housing serves to receive and guide the central release piston, which is mounted in the central release housing so that it can move linearly.

In a hydraulic release system of a motor vehicle, the hydraulic fluid has the function of transmitting energy in the form of pressure with as little loss as possible, for example within a clutch system of a vehicle.

In addition to this main task, the hydraulic fluid can also provide lubrication and corrosion protection for the moving parts and the metal surfaces of the hydraulic release system. In addition, it can in particular also dissipate impurities (for example due to abrasion), water and air as well as waste heat.

The function of the central release piston is to convert a hydraulic pressure application into a linear displacement of the central release piston, with the effect that the clutch system can be transferred from an engaged operating state to a disengaged operating state. The central release piston can have an annular central release piston or several central release pistons (multi-piston release mechanism).

According to a preferred embodiment of the invention, it can be advantageous that the metallic sensor body has a plate-like three-dimensional shape with a height in the radial direction between 0.2-5 mm, preferably between 0.5-3 mm. In this way, a particularly radially compact design of the central release device can be implemented.

It can furthermore be advantageous that the metallic sensor body is arranged in or on a carrier element, which results in greater structural flexibility with regard to the arrangement and coupling of the sensor body with the other components, in particular with the fastening ring.

In a further development of the invention, it can furthermore be preferred that the carrier element is formed from a material that is different from the material of the metallic sensor body, in particular the carrier element is formed from a plastic. This allows the construction to be further simplified. In particular, the metallic sensor body can be completely or be partially enclosed by a plastic material from which the carrier element is formed. By embedding it in a preferably closed pocket within the carrier element, the sensor body can be protected from harmful mechanical and chemical influences, whereby the measurement accuracy can also be ensured over a long period of operation.

Furthermore, it can be advantageous that a fastening ring is coupled to the central release piston, so that an axial offset of the central release piston causes an axial offset of the fastening ring, the carrier element being fixable on the fastening ring. This results in a particularly flexible possibility of connecting the carrier element to the central release piston. The fixation of the carrier element on the fastening ring is preferably carried out without play.

According to a further advantageous embodiment of the invention, it can be preferred that the inductive sensor unit can be coupled to the central release housing. As a result, the sensor unit can be arranged and mounted on an existing central release device in a particularly simple manner.

According to a preferred embodiment of the invention, it can be advantageous that the metallic sensor body is formed from aluminum and / or copper. These materials have proven to be particularly advantageous as sensor targets for inductive position determination of the central release piston.

It can furthermore be advantageous that the induction conductor tracks comprise a first transmission coil as well as a first receiver coil and at least one second receiver coil, whereby a particularly precise inductive position determination can be achieved.

Furthermore, it is advantageous that an alternating voltage can be induced in the first receiver coil and in the second receiver coil via the electronic sensor control by means of the transmitter coil, and the transmitter coil as well as the first receiver coil and the second receiver coil each as a conductor track structure extending in one plane in a common circuit board are arranged, wherein the transmitter coil surrounds the first receiver coil and the second receiver coil circumferentially.

In a further, preferred embodiment of the invention it can be provided that the first receiver coil and the second receiver coil have a conductor track structure which is designed such that individual series-connected receiver coil turns of each receiver coil are nested in one another. This has the advantage that the clamping voltage of the receiver coils is increased compared to conventional sinusoidal or cosinusoidal receiver coils running in the circuit board and the distance between the position sensor and the target to be detected by the position sensor can be increased without compromising the quality of the measurement result Need to become.

The invention is explained in more detail below with reference to figures without restricting the general inventive concept. The figures are merely of a schematic nature and serve exclusively for the understanding of the invention. The same elements are provided with the same reference symbols. The different features of the various exemplary embodiments can also be freely combined with one another within what is technically feasible.

• 1 eine Seitenansicht auf einen erfindungsgemäßen Zentralausrücker,
• 2 eine schematische Querschnittsansicht eines erfindungsgemäßen Zentralausrückers,
• 3 ein Kraftfahrzeug mit einem erfindungsgemäßen Zentralausrücker, und
• 4 den Aufbau einer möglichen Ausführung an Induktionsleiterbahnen, wobei in der oberen Darstellung eine mögliche Ausgestaltung einer ersten Empfängerspule in einer ersten Layerschicht einer Leiterplatte und wobei in der unteren Darstellung eine mögliche Ausgestaltung einer zweiten Empfängerspule in einer weiteren Layerschicht der Leiterplatte gezeigt sind.

Show it:

• 1 a side view of a central slave cylinder according to the invention,
• 2 a schematic cross-sectional view of a central slave cylinder according to the invention,
• 3 a motor vehicle with a central slave cylinder according to the invention, and
• 4th the structure of a possible design on induction conductor tracks, the top illustration showing a possible design of a first receiver coil in a first layer of a circuit board and the bottom illustration showing a possible design of a second receiver coil in a further layer of the circuit board.

1 and the 2 show a possible embodiment of a central slave cylinder according to the invention 1 for a hydraulic release system 2 a coupling system 3 of a motor vehicle 4th as exemplified in the 3 is shown. The dash-dot line in the 2 indicates the axis of rotation of the coupling system 3 at.

The central slave cylinder 1 includes a central slave cylinder 5 with an annular central release piston chamber 6th in the one through the central release piston chamber 6th hydraulic fluid that can be supplied 7th a central release piston 8th is axially movably received. On the central slave cylinder 5 is an inductive sensor unit 9 arranged which an electronic sensor control 10 and with the electronic sensor control 10 connected induction tracks 11 includes.

A metallic sensor body 12th is the same with the central release piston 8th coupled that one linear offset of the central release piston 8th a backlash-free linear offset of the metallic sensor body in the axial direction 12th causes. The induction tracks 11 extend in an axially parallel direction to the central release piston 8th . The metallic sensor body 12th is in the radial direction between the central slave cylinder 5 and the induction tracks 11 arranged.

The metallic sensor body 12th has a plate-like three-dimensional shape with a height in the radial direction between 0.2-5mm, preferably between 0.5-3mm, so that a very compact radial design of the central slave cylinder is achieved 1 can be realized.

The metallic sensor body 12th is in or on a support element 13th arranged. In the example shown, it is formed from aluminum and / or copper. The carrier element 13th is formed from a material that of the material of the metallic sensor body 12th is different. The carrier element 13th is formed from a plastic in the embodiment shown.

In principle, however, it would also be conceivable that the metallic sensor body 12th and the support element 13th are made of the same material. In particular, it would then also be possible for the metallic sensor body 12th and the support element 13th are monolithic.

The fastening ring 14th is backlash-free in the axial direction with the central release piston 8th coupled so that an axial offset of the central release piston 8th an axial offset of the fastening ring 14th causes the carrier element 13th play-free in the axial direction on the fastening ring 14th is fixable. The fastening ring 14th protrudes in the radial direction over the central slave cylinder 5 addition, so that the carrier element 13th in the radial direction between the central release housing 5 and the sensor unit 9 is arranged.

The carrier element 13th has to be arranged on the fastening ring 14th a groove by means of which the carrier element 13th on the circumference of the fastening ring 14th can be attached. The fixation of the carrier element 13th on the fastening ring 14th can take place in a force-locking and / or form-locking and / or cohesive manner. About the in the carrier element 13th formed groove, it is possible for the carrier element 13th in the radial direction on the fastening ring 14th to move something in order to minimize the radial distance to the sensor unit 9 to manufacture.

As from the 2 is the inductive sensor unit 9 with the central slave cylinder 5 connectable. One recognizes by means of 2 also good that the electronic sensor control 10 in the embodiment shown in the axial direction of the induction conductor tracks 11 as well as from the metallic sensor body 12th is spaced and in no operating state an axial overlap area with the induction conductor tracks 11 and the sensor body 12th having.

The structure and configuration of the induction tracks 11 is explained below using the 4th explained in more detail. 4th shows the structure of an inductive sensor unit 9 according to the invention, in a possible embodiment in a schematic representation. The induction tracks 11 can in particular on a circuit board 18th be designed, as in the following embodiment of the 4th is shown. In this context it is of course advantageous that the electronic sensor control 10 also on the circuit board 18th is arranged.

The induction tracks 11 include a first transmitter coil 15th and a first receiver coil 16 and at least one second receiver coil 17th . Via the electronic sensor control 10 is by means of the transmitter coil 15th an AC voltage in the first receiver coil 16 and into the second receiver coil 17th inducible, the transmitter coil 15th as well as the first receiver coil 16 and the second receiver coil 17th each as a conductor track structure extending in one plane in a common circuit board 18th are arranged. The transmitter coil 15th surrounds the first receiver coil 16 and the second receiver coil 16 extensive.

The first receiver coil 16 and the second receiver coil 17th have a conductor track structure which is designed in such a way that individual receiver coil turns connected in series 300 ; 400 each receiver coil 16 ; 17th are formed arranged nested in one another.

The structure of the induction tracks 11 is in 4th For the sake of clarity, shown in separate layer views - instead of superimposing them.

The electronic sensor control 10 is set up by means of the transmitter coil 15th an AC voltage in the first receiver coil 16 and into the second receiver coil 17th to induce. Via the electronic sensor control 10 becomes a high frequency alternating current in the transmitter coil 15th impressed (which is the terminal voltage u1 at the terminals of the transmitter coil 2 resulting in), which in turn generates an alternating magnetic field which is in the windings of the receiver coils 16 , 17th a voltage u2, u3 induced. In the event that there is no electrically conductive part or metallic sensor body 12th influences the alternating magnetic field of the inductive position sensor, the clamping voltage is u2, u3 at the receiver coils 16 , 17th zero mV. Is now in the area of the inductive sensor unit 9 an electrically conductive metallic sensor body 12th moved on / in the sensor body 12th Eddy currents induced, which in turn generate a target magnetic field, which is the magnetic field of the inductive sensor unit 9 is opposite. This changes the terminal voltage u2, u3 of the receiver coils 16 , 17th which in turn affects the position of the metallic sensor body 12th closes.

The transmitter coil 15th as well as the first receiver coil 16 and the second receiver coil 17th are each as a conductor track structure extending in one plane in a common circuit board 18th arranged, the transmitter coil 15th the first receiver coil 16 and the second receiver coil 17th surrounds extensively.

In the upper illustration of the 4th is a possible embodiment of a first receiver coil 16 in a first layer of a printed circuit board 18th shown. In the illustration below is a possible configuration of a second receiver coil 17th in another layer of the circuit board 18th shown. Also the connections of the receiver coils 16 , 17th as well as the connections of the coil parts 30, 40 are preferably made in separate layers in order to avoid unnecessary line crossings.

By the coil arrangement of the first receiver coil shown above 16 a sinusoidal course of the coil windings is simulated without arranging the coil windings sinusoidally. In the illustrated embodiment, the first receiver coil is 16 in two axially spaced, similarly constructed coil parts 16 divided up. Each coil part 16 comprises five nested, rectangular receiver coil windings connected in series 300 . Starting from the starting point of the winding P1 becomes in five increasingly larger receiver coil turns 300 (see arrow direction - clockwise) the first part of the coil 16 built up. Here are the adjacent receiver coil turns 300 from the inside to the outside with an ever decreasing distance d spaced from each other. From the outermost receiver coil winding 300 starting out, is at a distance D. , starting with an outermost receiving coil winding 300 of the second (left) coil part 30, with five nested, increasingly smaller, rectangularly designed and series-connected receiver coil windings 300 (counterclockwise) that in point P2 end, the second coil part 16 built up. Here are the adjacent receiver coil turns 300 from the outside to the inside with an ever increasing distance d spaced from each other.

By the coil arrangement of the second receiver coil shown below 17th a cosine-shaped curve of the coil windings is simulated without arranging the coil windings sinusoidally. In the illustrated embodiment, the second receiver coil is 17th into three axially spaced coil parts 17th split, with the middle coil part 17th analogous to one of the coil parts 30 of the first receiver coil 16 (namely depicting a full half-wave) and wherein the two coil parts arranged on the right and left adjacent thereto 17th each half of the middle part of the coil 17th (each half of a half-wave). Each coil part 17th comprises five nested, rectangular receiver coil windings connected in series 400 .

Analogous to the coil structure of the first receiver coil 16 is also used for the second receiver coil 17th starting from a winding starting point P3 in five increasingly larger receiver coil turns 400 (see arrow direction - clockwise) the first part of the coil 17th (right) built. Here are the adjacent receiver coil turns 400 from the inside to the outside with an ever decreasing distance d spaced from each other. From the outermost receiver coil winding 400 of the first coil part 17th starting out, is at a distance D. , starting with an outermost receiver coil winding 400 of the second (middle) coil part 17th , with five nested, increasingly smaller, rectangularly designed and series-connected receiver coil windings 400 (counterclockwise) that in the intermediate point of the winding P4 end, the second coil part 40 built up. Here are the neighboring Receiver coil turns 400 from the outside to the inside with an ever increasing distance d spaced from each other.

The intermediate point of the winding that now emerges in the middle of the central coil part 40 P4 of the second coil part 17th the second receiver coil 17th is now, in order to avoid line crossings, in a separate layer of the circuit board, not shown 18th further guided axially to the left to a defined starting point, intermediate winding point P5 , for the third part of the coil 17th again in the layer of the second receiver coil 17th to be continued. From the outermost receiver coil winding 400 of the middle / second coil part 17th starting out, is at a distance D. , starting with an outermost receiver coil winding 400 of the third (left) coil part 17th , with again five nested, increasingly smaller, rectangularly designed and series-connected receiver coil windings 400 (clockwise) that in the winding end point P6 end, the third coil part 17th built up. Here are the adjacent receiver coil turns 400 from the outside to the inside with an ever increasing distance d spaced from each other.

The terminal connections of the receiver coil 16 , 17th are not explicitly shown. The winding ends of the first receiver coil 16 as well as the winding ends of the second receiver coil 17th can be taken anywhere from the circuit board 18th be led out.

Both the first receiver coil 16 as well as the second receiver coil 17th have a conductor track structure which is designed in such a way that individual receiver coil turns connected in series 300 , 400 each receiver coil 16 , 17th are formed arranged nested in one another. The first receiver coil 16 and the second receiver coil 17th each comprise five receiver coil turns connected in series 300 , 400 . The receiver coil turns 300 the first receiver coil 16 and the receiver coil turns 400 the second receiver coil 17th are like this on the circuit board 18th arranged that the coil parts 16 , 17th and their receiver coil turns 300 , 400 are spaced from one another in the axial direction in such a way that individual positions ws _n , toilet _n can be generated which, viewed over the direction of movement, are positioned in analogy to an ideal sine or cosine shape. These individual positions are transverse to the direction of movement X of the metallic sensor body 12th extending coil turn portions of the coil parts 16 , 17th from the first and second receiver coil 16 , 17th Are defined.

• Sinus/Empfängerspule 16: $$\text{Position }[°]=\text{arcsin}\left({\text{n}}_{\text{n}}/{\text{n}}_{\text{gesamt}}+1\right)),$$
  
• Cosinus/Empfängerspule 17: $$\text{Position }[°]=\text{arcsin}\left({\text{n}}_{\text{n}}/{\text{n}}_{\text{gesamt}}+1\right))-90°,$$
  

wobei jeweils
Position [°] - der Position der Empfängerspulenwindung 300, 400 entspricht,
n_n - der Nummer der Empfängerspulenwindung 300, 400 entspricht, und
n_gesamt (Anzahl der Empfängerspulenwindung) - der Anzahl der Empfängerspulenwindungen 300, 400 der jeweiligen Empfängerspule 16, 17 entspricht.The position ws _n of the receiver coil turns 300 the first receiver coil 16 (Sine) and the position toilet _n of the receiver coil turns 400 the second receiver coil 17th (Cosine) positioned or spaced according to the following formula:

• Sine / receiver coil 16 : $$\text{position}[°]=\text{arcsin}\left({\text{n}}_{\text{n}}/{\text{n}}_{\text{total}}+1\right)),$$
  
• Cosine / receiver coil 17th : $$\text{position}[°]=\text{arcsin}\left({\text{n}}_{\text{n}}/{\text{n}}_{\text{total}}+1\right))-90°,$$
  

where each
Position [°] - the position of the receiver coil turn 300 , 400 is equivalent to,
n _n - the number of the receiver coil turn 300 , 400 corresponds to, and
n _total (number of receiver coil turns) - the number of receiver coil turns 300 , 400 the respective receiver coil 16 , 17th is equivalent to.

The axial, radial, tangential and / or circumferential directions used in this application relate to an imaginary axis of rotation of the respective component in question or described.

The invention is not limited to the embodiments shown in the figures. The above description is therefore not to be regarded as restrictive, but rather as explanatory. The following claims are to be understood in such a way that a named feature is present in at least one embodiment of the invention. This does not exclude the presence of further features. If the patent claims and the above description define “first” and “second” features, this designation serves to distinguish between two similar features without defining an order of precedence.

List of reference symbols

1

Central slave cylinder

2

hydraulic release system

3

Coupling system

4th

Motor vehicle

5

Central slave cylinder

6th

Central release piston space

7th

Hydraulic fluid

8th

Central release piston

9

inductive sensor unit

10

electronic sensor control

11

Induction tracks

12th

metallic sensor body

13th

Support element

14th

Fastening ring

15th

first transmitter coil

16

first receiver coil / coil part

17th

second receiver coil / coil part

18th

Circuit board

300

Receiver coil turns (first receiver coil)

400

Receiver coil turns (second receiver coil)

D.

Distance between the coil parts

d

Distance between the receiver coil turns within a coil part

wsn (ws1, .., ws20)

axial position of the receiver coil winding sections of the first receiver coil arranged transversely to the direction of movement of a target

wcn (wc1, ..., wc20)

axial position of the receiver coil winding sections of the second receiver coil arranged transversely to the direction of movement of a target

P1

Winding starting point (first coil part, first receiver coil)

P2

Winding end point (second coil part, first receiver coil)

P3

Starting point of winding (first coil part (right), second receiver coil)

P4

Intermediate winding point (second coil part (middle), second receiver coil)

P5

Intermediate winding point (third coil part (left), second receiver coil)

P6

Winding end point (third coil part (left), second receiver coil)

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• EP 1898111 B1 [0002]

Claims (10)

Central release device (1), in particular for a hydraulic release system (2) of a clutch system (3) of a motor vehicle (4), comprising a central release housing (5) with an annular central release piston space (6) in the hydraulic fluid (7) which can be fed to the central release piston space (6) ) a central release piston (8) is accommodated in an axially movable manner, characterized in that an inductive sensor unit (9) is arranged on the central release housing (5), which has an electronic sensor control (10) and induction conductor tracks (11) connected to the electronic sensor control (10) comprises, and a metallic sensor body (12) is coupled to the central release piston (8) so that a linear offset of the central release piston (8) causes a linear offset of the metallic sensor body (12), the induction conductor tracks (11) in an axially parallel direction to the central release piston (8) and the metallic sensor body r (12) is arranged in the radial direction between the central release housing (5) and the induction conductor tracks (11). Central slave cylinder (1), according to Claim 1 , characterized in that the metallic sensor body (12) has a plate-like three-dimensional shape with a height in the radial direction between 0.2-5 mm, preferably between 0.5-3 mm. Central release device (1) according to one of the preceding claims, characterized in that the metallic sensor body (12) is arranged in or on a carrier element (13). Central release device (1) according to one of the preceding claims, characterized in that the carrier element (13) is formed from a material that is different from the material of the metallic sensor body (12), in particular the carrier element (13) is formed from a plastic . Central release mechanism (1) according to one of the preceding claims, characterized in that a fastening ring (14) is coupled to the central release piston (8) so that an axial offset of the central release piston (8) causes an axial offset of the fastening ring (14), wherein the carrier element (13) can be fixed on the fastening ring (14). Central release device (1) according to one of the preceding claims, characterized in that the inductive sensor unit (9) can be coupled to the central release device housing (5). Central release device (1) according to one of the preceding claims, characterized in that the metallic sensor body (12) is formed from aluminum and / or copper Central release device (1) according to one of the preceding claims, characterized in that the induction conductor tracks (11) comprise a first transmitter coil (15) and a first receiver coil (16) and at least one second receiver coil (17). Central slave cylinder (1), according to Claim 8 , characterized in that an alternating voltage can be induced in the first receiver coil (16) and in the second receiver coil (17) via the electronic sensor control (10) by means of the transmitter coil (15), and the transmitter coil (15) and the first receiver coil ( 16) and the second receiver coil (17) are each arranged as a conductor track structure extending in one plane in a common circuit board (18), the transmitter coil (15) circumferentially surrounding the first receiver coil (16) and the second receiver coil (16). Central slave cylinder (1), after one of the Claims 8 - 9 , characterized in that the first receiver coil (16) and the second receiver coil (17) have a conductor track structure which is designed such that individual series-connected receiver coil turns (300; 400) of each receiver coil (16; 17) are nested in one another .

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