Torque-measurinα device.

The invention relates to a torque-measuring device with a torsion shaft, the shaft having a magnetically non-permeable sleeve surrounding the shaft, the ends of which sleeve are fixedly joined to the shaft and which carries an armature which, when the sleeve ends rotate in opposite directions, shifts axially and alters a magnetic field; the invention also relates to an arrangement for detecting the change in field.

In a known torque-measuring device of this kind (DE 39 18 862 C2), the torsion shaft consists of a metal which likewise affects the magnetic field of the measuring device. If the measuring device is subseguently to be used with a shaft made of a different material, this can impair the measuring sensitivity of the measuring device as well, because the shaft can cause too extreme a change in the magnetic field.

The invention is based on the problem of providing a torque-measuring device of the kind mentioned in the introduction, in which the influence of different shaft materials on the magnetic field of the measuring device is largely avoided.

According to the invention, this problem is solved in that a magnetically permeable foil surrounding the I ^' f shaft is arranged between the sleeve and the shaft.

This magnetically permeable foil causes the magnetic field to be screened from the shaft. Irrespective of the material of the shaft, the magnetic field, and therefore also the measuring signal, remains largely unaffected by the shaft.

Preferably, provision is made for a torsion tube surrounding the shaft to be arranged between the sleeve and the shaft, by means of which tube the ends of the sleeve are connected to the shaft and which supports the foil. That makes mounting of the foil simple.

The tube and the cylindrical foil can be longer than the sleeve. In that manner, screening is also effected axially outside the sleeve.

The foil is preferably secured to the inside of the tube. The tube can therefore be connected directly to the ends of the sleeve, without having to transfer the torque by way of the foil.

Furthermore, it is advantageous if the ends of the tube are connected to the shaft by way of rings surrounding the shaft. In that case, the inner diameter of the rings can be matched to the particular diameter of the shaft , without the other dimensions of the measuring device, in particular the diameter of the cylindrical foil and thus the magnetic properties of the magnetic circuit of the measuring device, having to be changed. A change in the magnetic resistance of the shaft combined with a different choice of shaft diameter likewise has no effect on the magnetic field of the measuring device owing to the screening provided by the foil.

If the tube consists of plastics material, the magnetic field is also not affected thereby.

Preferably, the foil consists of mumetal, which has a high permeability.

The invention and its developments are described in detail hereinafter with reference to the drawing of a preferred embodiment.

The torque-measuring- device illustrated has a torsion shaft 1, transferring the torque to be measured, Carranged) ^1' coaxially in a torsion tube 2 of

Word in brackets added for clarity - translator

thermoplastic plastics material, to the ends of which tube rings 3 are secured coaxially, for example, adhesively. The rings 3 can consist of metal and surround the shaft 1, and are fixed to the shaft 1, for example, adhesively or by welding, so that they cannot rotate. The inner diameter of the rings 3 is matched to the particular diameter of the shaft 1 so that an otherwise unchanged torque-measuring device can be used for shafts 1 of different diameter.

A cylindrical foil 4 of magnetically permeable material, preferably mumetal, is arranged between the tube 2 and the shaft 1, so that it surrounds the shaft 1. The foil 4 is preferably secured to the inside of the tube 2.

The tube 2 is surrounded by a sleeve 5, also capable of torsion, made of thermoplastic plastics material, which is secured, for example, adhesively or by welding, by its ends to the tube 2. The sleeve 5 is divided by a slot 6 running in the circumferential direction into two sleeve parts 7 and 8. In the slot 6, two tongues 9 and 10 are joined by narrow webs to the two sleeve parts 7 and 8. The tongues 9 and 10 lie diametrically opposite one another in relation to the shaft 1 and extend for a part of the circumference of the sleeve. The free ends of the tongues 9, 10 are both linked to an armature 12.

When a torque is exerted on the shaft 1, the shaft 1, the tube 2 , the foil 4 and the sleeve 5 are twisted, so that the sleeve parts 7 and 8 rotate in opposite directions. The tongues 9, 10 are thereby deflected axially towards the one sleeve part, and in so doing carry the armature 12 with them in the same direction coaxially with respect to the shaft 1.

To detect the axial displacement of the armature 12, a differential-transformer transducer 13 is provided, comprising a primary winding 14 and two secondary windings 15, 16. The three windings also

surround the shaft 1 concentrically. The primary winding 14 is arranged between the two secondary windings 15, 16. All three windings are arranged on a carrier 17 which consists, for example, of a plastics material or resin-impregnated paper. The carrier 17 is rotatably mounted on the sleeve 5 by means of two bearings 18, 19. The bearings 18, 19 are preferably radial ball bearings with no axial play. The inner rings 20 of the bearings are secured on the sleeve 5 while the outer rings 21 is (sic) connected to the carrier 17. This mounting arrangement enables the shaft 1 to rotate while the differential-transformer transducer 13 remains stationary. The transformer transducer connections 22, 23, 24 can therefore be led without problems out of the windings 14, 15, 16 in order to transmit electrical input and output signals from and to an evaluator. In the axial direction the differential-transformer transducer 13 is mounted so that the armature 12 in the rest position, that is to say, when no torque is being exerted on the shaft 1, lies exactly symmetrically with respect to the primary winding 14 and to the two secondary windings 15, 16. Furthermore, the differential-transformer transducer 13 is located centrally between the two rings 3, the tube 2 and the foil 4 projecting axially beyond the ends of the sleeve 5.

In operation, the primary winding 14 has a current flowing through it, thereby generating a magnetic field which passes through the two secondary windings 15, 16 and induces in these an electric potential. The electric potential is dependent, inter alia, on how many turns of the secondary windings 15, 16 the magnetic field passes through. The armature 12, which consists of magnetically permeable material, conducts the magnetic field. In the rest or neutral position, the armature 12 projects an equal distance into the two secondary windings 15, 16. The same potential is

consequently induced in each secondary winding. If the two potentials are subtracted from one another, the signal 0 appears at the output, which indicates that there is no torque acting on the shaft 1. By displacing the armature 12 in the axial direction relative to the windings 14, 15, 16, the symmetrical field distribution is destroyed. In the secondary winding into which the armature 12 projects further, the magnetic field passes through a larger number of turns than in the other secondary winding, from which the armature 12 has been withdrawn somewhat. A greater potential is therefore induced in the first secondary winding than in the second one. Forming the difference of the two potentials enables an electrical signal which indicates the magnitude of the torque acting on the shaft to be obtained.

Without the magnetically permeable foil 4, the magnetic field of the primary winding 14 would also pass in part through the shaft 1, which generally consists of magnetically permeable material. If a shaft 1 of a different diameter or of a different material is then used, the magnetic field would also be influenced thereby. The magnetically permeable foil 4 is therefore provided as a screen in order to prevent the shaft 1 from influencing the magnetic field. The material and/or the diameter of the shaft 1 can therefore be arbitrarily chosen, without the measurement result being influenced thereby, provided that the dependence of the angle of torsion of the shaft 1 on the torque applied remains unchanged.

Because the tube 2 and the foil 4 project far beyond the ends of the sleeve 5, a screening over a correspondingly greater axial length is also achieved by the foil 4.

Departing from the embodiment illustrated, it is also possible to provide the shaft 1 centrally between the rings 3 with a portion of reduced diameter, as in

the case of the torque-measuring device according to DE 39 18 862 C2. Furthermore, the tube 2 may also consist of steel; in that case, it can then be provided with slots in a similar manner to the sleeve 5. If desired, the magnetically permeable foil 4 then surrounds the steel tube 2 on its outside between the tube 2 and the sleeve 5. The illustrated arrangement is preferred , however, in order to avoid torque being transferred by the tube 2 to the sleeve 5 by way of the foil 4.

The measuring device is arranged in a housing, not illustrated, so that the interior of the measuring device is also sealed by the tube 2 or, in the case of a slotted tube 2, at least by the foil 4, against ingress of contaminants, for example, oil, by way of the slot 6 into the interior of the measuring device, while the shaft 1 remains unmounted. If, on the other hand, the rings 3 are not sealed by a medium to the shaft 1, but are mounted with a force fit or with an interlocking fit, in the case of a tube 2 which has been slotted to increase its ability to twist, the foil 4 also provides a seal against penetration of oil between the shaft 1 and the rings 3 into the measuring device when the shaft l is installed.