GB2245367A

GB2245367A - Apparatus for monitoring the temperature of a moving component, in particular of a friction clutch

Info

Publication number: GB2245367A
Application number: GB9111409A
Authority: GB
Inventors: Hans-Joachim Schmidt-Bruecken
Original assignee: Fichtel and Sachs AG
Current assignee: ZF Sachs AG
Priority date: 1990-06-01
Filing date: 1991-05-28
Publication date: 1992-01-02
Anticipated expiration: 2011-05-28
Also published as: FR2662799B1; FR2662799A1; GB9111409D0; GB2245367B

Description

APPARATS FOR MONITORING THE TEMPERATURE OF A MOVING COMPONENT, IN PARTICULAR OF A FRICTION CLUTCH The invention relates to an apparatus for monitoring the temperature of a component which moves relative to a stationary component, in particular of a rotating component, forming a friction face, of a friction clutch. The invention also relates to a friction clutch constructed using such apparatus.

Measuring devices for the friction effect of a friction clutch are known in which the heating of the clutch components is calculated from the friction effect. Examples of them are known from German Offenlegungsschriften 35 05 992 and 36 01 708. Such methods of calculation have to operate with many unknowns. Thus, for example, the cooling of the heated components is a variable which cannot be detected exactly. It is also assumed that the vehicle is equipped with an electronic computer.

On the other hand, it has been known for a long time that temperature measurements can be taken with thermocouples. However, the use of such thermocouples has not been achieved satisfactorily hitherto with a rotating component. Sliding contacts used hitherto have in many cases proven unusable owing to the low voltages occurring with the thermocouples. t.

An object of the present invention is to provide apparatus for monitoring the temperature of a moving component, in particular for monitoring the temperature in the region of the friction faces of a friction clutch, which allows reliable, contact-free transmission of the measured temperature information from the moving component to an adjacent stationary component and in particular transmission of the temperature information from the interior of the clutch.

According to the invention there is provided apparatus comprising a thermoelectric current generator and an induction coil connected to the thermoelectric current generator is held on the moving component, the thermoelectric current generator producing a current of which the value depends on the temperature of the moving component and the induction coil producing a magnetic field corresponding to the value of the current and in that a receiver which responds to the magnetic field without contact is held on the stationary component. The thermoelectric current generator, which can be a conventional thermocouple but also a different element which converts thermal energy into electric current as a function of temperature, produces a direct current of which the value is a measure of the temperature. The intensity of the magnetic field produced according to the current by the induction coil is in turn a measure of the temperature and is converted by the receiver, which is held on the stationary component and responds to the magnetic field, into an electric signal containing the temperature information.

The induction coil can be constructed or arranged such that it is continuously located in the region of the receiver independently of the movement of the component. As this demands comparatively large coils under certain circumstances, it is preferably proposed, for reducing the induction coil with a component rotating round an axis of rotation for decreasing the dimensions of the induction coil, that this induction coil be arranged eccentrically to the axis of rotation on the component. The induction coil can be a flat coil which is constructed, in particular, as a wire loop and projects radially from the rotating component substantially in a plane extending normally to the axis of rotation. With such a coil, the receiver can be arranged without difficulty axially next to the induction coil.

The receiver can be an element which is sensitive to magnetic fields such as a Hall sensor or the like. In addition to measurement of the field strength of the induction coil moving past the receiver, the magnetic induction can also be utilised for contact-free measurement of the magnetic field which represents the temperature of the component and is produced by the induction coil. It is preferably proposed that the receiver comprise a secondary induction coil past which the induction coil connected to the thermoelectric current generator can be moved during rotation of the component. As the primary induction coil passes by, the secondary induction coil produces a voltage pulse of which the value is a measure of the field strength and therefore of the temperature of the rotating component. As the value of the voltage pulse is also dependent on the speed at which the induction coils are moved past one another and therefore on the speed of the rotating component, speeddependent compensating measures may be necessary in individual cases when evaluating the temperature information, unless measurement is carried out at a uniform speed. To increase the magnetic induction, the secondary induction coil is preferably arranged on a core with air gap through which the primary induction coil runs.

In a preferred embodiment, the thermoelectric current generator has at least one thermocouple, optionally several thermocouples connected to form a thermopile, each thermocouple comprising two pairs of thermal contacts which are connected in series and of which a first pair is arranged in a region of the moving component, in particular the friction face of the friction clutch and the second pair is aranged in a region with a temperature which varies in operation, in particular in the ambient air of the moving part. Together with the primary induction coil, the thermocouple forms a closed circuit which is constructed, in particular with secondary induction coils, coupling by magnetic induction, of the receiver, as a low-resistance circuit in order to produce comparatively high current intensities and therefore sufficiently great magnetic fields.

As normal with thermocouples, the magnetic field is proportional to the temperature difference of the two pairs of thermal contacts.

With friction clutches, the two components forming the friction faces, i. e. the flywheel and the pressure plate, usually consist of iron. During temperature measurement in the region of the friction face of these components, the first pair is preferably formed by the component forming the friction face and a copper conductor which stands in a blind hole of the component reaching close to the friction face, in contact with the iron material thereof. The second pair is formed by an iron conductor which is connected in a conducting manner to the rotating component and said copper conductor, the copper conductor also forming the induction coil.

The invention can be employed both for measuring the temperature of the friction face of the flywheel of a friction clutch and for measuring the temperature of the friction face of the pressure plate. If the friction face temperature of the pressure plate which is axially movably guided relative to a clutch casing is to be measured, the primary induction coil is preferably fastened in an electrically insulated manner on the clutch casing and is connected to the thermoelectric current generator by flexible pieces of line. It has proven beneficial to measure the friction face temperature of the pressure plate as the maximum rise in temperature can be observed with peak loading of the friction clutch and the risk of overheating is therefore highest at this point. On the other hand, flexible pieces of line between thermoelectric current generator and primary induction coil can be dispensed with if the friction face temperature of the flywheel is measured instead of the axially movable pressure plate. The comparatively low heat absorption capacity of the pressure plate can be determined experimentally in this case and the heating thereof can be allowed for and monitored by corrective action.

The invention is described in more detail hereinafter with reference to an example.

Figure 1 is a partial section of the measuring arrangement in an elementary diagram.

Figure 2 is section II-II in Figure 1.

Figure 3 is the partial longitudinal section through a motor vehicle friction clutch with a measuring device according to Figures 1 and 2.

Figures 1 and 2 show a flywheel 2 which consists of steel and is rotatably mounted round an axis of rotation 11.

This flywheel 2 has a friction face 3 connected, for example, to a clutch plate. The heating caused by the friction between the friction face 3 and the clutch plate is measured and transmitted in the following manner: in a blind hole of the flywheel 2 which is introduced from the side remote from the friction face 3 and leads close to the friction face 3 there is arranged, in an insulated manner, a copper conductor 20 which, with its end face on the base of the blind hole, forms a first pair of thermal contacts 17. The copper conductor 20 extends outside the flywheel in a plane substantially perpendicularly to the axis of rotation 11 and forms a wire loop 13 in this plane. In the region of the wire loop 13 there is arranged a second pair of thermal contacts 18 with which transmission is effected from the copper conductor 20 to an iron conductor 22. This iron conductor 22 is rigidly connected by its other end directly to the flywheel 2. The wire loop 13 forms, with the two conductors 20 and 22 and the flywheel 2, a circuit which, during a temperature rise at the first thermal contact pair 17, allows a current to flow, which current is dependent on the temperature difference between the two thermal contact pairs 17 and 18. For contact-free transmission of this temperature information, the wire loop 13 runs, while the flywheel 2 is revolving, through an air gap or slot of a soft iron core 19 provided with a secondary coil 14. The core 19 is stationarily mounted. The magnetic field formed in the wire loop 13 by the flowing current produces in the secondary coil, on passing through the secondary coil, a comparatively high change of magnetic flux which leads to a corresponding voltage pulse. This can then be displayed and evaluated on a measuring instrument 24 and a corresponding evaluating instrument.

Figure 3 shows a motor vehicle friction clutch 1 in which the first thermal contact pair 17 is arranged in the pressure plate 4 in the vicinity of the friction face 5 thereof. The pressure plate 4 is usually non-rotatably but axially movably arranged in a clutch casing 6 and is loaded by a diaphragm spring 7 which is held by spacer bolts 12. The clutch casing 6 is screwed on the flywheel 2 which is connected to a crankshaft 8 of an internal combustion engine, not shown. Between the flywheel 2 and the pressure plate 4 there can be clamped a clutch plate 9 which is arranged nonrotatably but axially movably on a gear shaft, not shown.

Furthermore, a release means 10 which actuates the diaphragm spring 7 and thus controls a clutch engagemet and disengagement process, is arranged concentrically to the axis of rotation 11. The first thermal contact pair 17 is arranged in the pressure plate 4 consisting of iron and is formed by the pressure plate 4 and the copper conductor 20 which is led in an insulated manner from the pressure plate 4 and is guided radially outwardly. It passes into an elastic connecting member 21 of copper which is in turn connected to the copper wire loop 13 arranged rigidly in the clutch casing 6. Insulation is also provided at the passage through the clutch casing 6. The iron conductor 22 which is connected at 18 to the wire loop 13 also penetrates the clutch casing 6 and is directly connected to the material of the pressure of iron plate 4 via an elastic connecting member 23/The elastic connecting members 21 and 23 correspond, with regard to the material, to the copper and the iron and are preferably produced from a wire mesh which-as the other components in this circuit-has a large cross section in order to produce a low-resistance connection. The plane of the wire loop 13 extends substantially perpendicularly to the axis of rotation 11 and, during its rotation together with the friction clutch 1, penetrates the air gap in the core 19 which acts as a receiver and is rigidly connected via a lid 16 to the gear casing 15. The core 19 carries a secondary coil 14 of which the ends are connected to the measuring/evaluating instrument 24 (Figure 1).

The value of the current pulses in the secondary coil 14 is proportional to the number of windings of the secondary coil, proportional to the speed and proportional to the primary magnetic field. The primary magnetic field is proportional to the current in the wire loop 13 and this current is dependent on the temperature difference between the two thermal contact pairs 17,18. When using copper and iron, an ohmic resistance within the primary circuit of 1 to 1.5 m Q can substantially be allowed for. A thermoelectromotive force of 1.1 mV per 100 degrees between iron and copper therefore produces a current intensity of about 0.8 ampere. With a relatively high primary current of this type, it is possible to provide sufficiently high voltage pulses on the secondary side. The speed dependency of the inductive transmission of the temperature information may however necessitate measures for allowing for the speed on the primary side or the secondary side.

The arrangement of the thermocouple directly in the flywheel is accompanied by constructional simplifications as no axial movability of current-carrying components has to be allowed for here. The lower heat absorption capacity of the pressure plate can be established experimentally and can be allowed for.

The embodiments described hereinbefore merely show a single thermocouple consisting of two pairs of thermal contacts. Several such thermocouples can also be connected in series with one another to increase the output voltage and therefore the power. Instead of a wire loop with a single turn, the primary induction coil can also comprise several windings and, in particular, can also be provided with a core to increase the magnetic flux density. It goes without saying that a different receiver responding to the magnetic field strength of the primary induction coil, for example a Hall probe or the like, can be provided instead of the secondary coil 14.

Claims

CLAIMS: 1. Apparatus for monitoring the temperature of a component (2; 4) moving relative to a stationary component (15), in particular of a rotating component, forming a friction face, of a friction clutch (1), comprising a thermoelectric current generator (17,18) and an induction coil (13) connected to the thermoelectric current generator (17,18) for mounting on the moving component (2; 4), the thermoelectric current generator (17, 18) serving to produce a current of which the value depends on the temperature of the moving component (2; 4) and the induction coil (13) serving to produce a magnetic field corresponding to the value of the current, and a receiver (14,19) serving to respond to the magnetic field in a contact-free manner for mounting on the stationary component (15).
2. Apparatus as claimed in claim 1, in which the moving component (2; 4) rotates round an axis of rotation (11), wherein the induction coil (13) is arranged eccentrically to the axis of rotation (11) on the moving component (2; 4).
3. Apparatus as claimed in claim 2, wherein the induction coil (13) is constructed as a flat coil and projects radially from the rotating component (2; 4) substantially in a plane extending normally to the axis of rotation.
4. Apparatus as claimed in claim 1,2 or 3, wherein the induction coil is constructed as a wire loop (13).
5. Apparatus as claimed in any one of claims 2 to 4, wherein the receiver (14,19) comprises a secondary induction coil (14) past which the induction coil (13) connected to the thermoelectric current generator (17,18) can be moved during rotation of the component (2; 4) when inductively coupled to the secondary induction coil (14).
6. Apparatus as claimed in claim 5, wherein the secondary induction coil (14) i s arranged on a core (19) with an air gap through which the induction coil (13) connected to the thermoelectric current generator (17,18) runs.
7. Apparatus as claimed in any one of claims 1 to 6, wherein the thermoelectric current generator has at least one thermocouple (17,18) to which the induction coil (13) is connected in an, in particular, low-resistance circuit, each thermocouple (17,18) comprising two pairs of thermal contacts which are connected in series and of which a first pair (17) is arranged in a region of the moving component (2; 4) in particular of a friction face (3; 5) of the friction clutch and the second pair (18) is arranged in a region with a temperature which varies in operation, in particular in the ambient air of the moving component (2; 4).
8. Apparatus as claimed in claim 7, wherein the component (2; 4) forming the friction face (3; 5) consists of iron, in that the first pair (17) is formed by the component (2; 4) forming the friction face (3; 5) and a copper conductor (20) which stands in a blind hole, reaching close to the friction face (3; 5), of the component (2; 4) in contact with the iron material thereof, and in that the second pair (18) is formed by an iron conductor (22) conductively connected to the rotating component (2; 4) and the above-mentioned copper conductor (20) and in that the copper conductor (20) forms the induction coil (13).
9. Apparatus as claimed in any one of claims 1 to 8, wherein the thermoelectric current generator (17,18) detects the temperature of the friction face (15) of pressure plate (4), guided non-rotatably but axially movably relative to a clutch casing (6), of a friction clutch (1) and in that the induction coil (13) is fastened in an electrically insulated manner on the clutch casing (6) and is connected by flexible pieces of line (21,23) to the thermoelectric current generator (17,18).
10. Apparatus as claimed in claim 9, wherein the receiver (14,19) is held on a gear casing (15) adjacent to the friction clutch (1).
11. A friction clutch including apparatus as claimed in any one of claims 1 to 10 for monitoring the temperature of the friction face (3; 5) of a flywheel (2) or a pressure plate (4).

Apparatus as claimed in claim 1 substantially as described with reference to Figures 1 and 2 or Figure 3 of the accompanying drawings.