WO2003043162A1

WO2003043162A1 - Geared motor drive with torque sensing

Info

Publication number: WO2003043162A1
Application number: PCT/EP2002/013492
Authority: WO
Inventors: François BREYNAERT; Dan Mirescu
Original assignee: Arvinmeritor Light Vehicle Systems - France
Priority date: 2001-11-15
Filing date: 2002-11-15
Publication date: 2003-05-22

Abstract

A geared motor drive for a vehicle window lifter comprises an electric motor with a motor shaft; a transmission system comprising an input driven by the motor shaft and a drive output; a shock absorber (6) coupling the input to the output of the transmission system; and a sensor for the torque transmitted by the shock absorber. A vehicle window glass lifter incorporating this geared motor drive is also provided. This arrangement reduces the response time before the presence of an object impeding lifting of the window glass is detected.

Description

GEARED MOTOR DRIVE WITH TORQUE SENSING

The invention relates, generally, to geared motor drives for vehicle window lifters and, more particularly, to window lifter geared motor drives with torque sensing.

Vehicle windows are being more and more frequently driven by electric motors. It can happen that an object or a person's hand gets accidentally located in the lifting path of the window, getting trapped between the top of the window glass and the door frame, which can lead to pain or wounding. Various devices are known for stopping movement of the window glass or for causing it to re-descend.

United States Patent 5,296,658 employs window glass seals that contain capacitors or optical fibres. The seal characteristics are modified when an object gets trapped, supplying a signal indicating trapping, operating on the window glass drive.

However, such seals, firstly, are expensive and secondly impact negatively on vehicle aesthetics as they are voluminous and apparent.

United States Patent 6,086,177, German patent 3,034,114 and German Patent 4,442,171 disclose processing of information concerning the drive motor, for detecting trapping. In German patent 3,034,114, the speed of rotation of the electric motor is measured, in German Patent 4,442,171, it is motor current that is measured and in United States Patent 6,086,177, another characteristic of the motor is measured. Some change in the measured information allows trapping of an object to be determined. These methods nevertheless have their disadvantages. Because of the characteristics of the electric motor, notably its inertia, impedance or speed or flux, a relatively long response time exists between an object getting trapped and its detection. Response time is typically of the order of 25 milliseconds. The window glass drive force may in the meantime have significantly increased, leading to wounding. The trapping force can also exceed the limits defined in standards, which makes it difficult to get approval for the vehicle.

It is also known to process measured information, in order to compensate for response time. However, the electrical components employed for such processing have characteristics which drift with ageing. A considerable response time can then reappear.

European patent application 318,345 discloses a geared motor drive drive device with an input shaft, a speed reduction gear and a shock absorber between the shaft and the speed reduction unit. It further comprises a sensor for the torque exercised on the shock absorber. The sensor includes electrically conducting tracks which are mechanically integral with, respectively, the output shaft and a wheel of the reduction gear. European Patent Application 753,727 discloses a torque measuring device, notably for a geared motor drive for operating a functional member of an automobile vehicle. This device comprises means for determining angular displacement, with angle encoders for position associated one with the reduction gear wheel and the other with an output member of the geared motor drive. The wheel and output member are connected by a shock absorber.

The disadvantage of such devices is that the measurement of torque by the sensor is not accurate, as torque variations detected by the sensor are of small amplitude.

United States Patent 4,723,450 discloses a system for measuring torque between a driving shaft and a driven shaft, the shafts sharing the same axis of rotation. The system includes loads cells located at a certain number of interfaces between the two shafts and includes shock absorbers located at the interfaces remote from those occupied by the load cells.

United States Patent 6,084,368 discloses an arrangement for contactless measurement of rotor torque.

These systems and arrangements do not relate to the field of geared motor drives. Further, they do not allow accurate measurement of torque as variations in torque detected by the sensor are of small amplitude.

There is consequently a need for a geared motor drive, a window lifter or a method which resolves one or several of these disadvantages. In particular, there is a need for a geared motor drive in which measurement of torque and trapping is more accurate. Thus, this invention provides an geared motor drive for a window lifter comprising: an electric motor with a motor shaft ; a transmission system comprising: an input driven by the motor shaft and a drive output ; a shock absorber coupling the input to the output of the transmission system; and a sensor for torque transmitted by the shock absorber.

According to one embodiment, the sensor is on the shock absorber. According to one embodiment, the sensor comprises a two-terminal circuit having an impedance varying with shock absorber transmission torque. According to one embodiment, the transmission system comprises a gear unit coupled at the input and a drum coupled at the output; the shock absorber has a deformable slot with the gear unit acting on a first face thereof and the drum acting on a second face thereof; and the sensor is arranged in the slot.

According to a further embodiment, the shock absorber has an overall cylindrical shape, the slot extending in a radial direction of the shock absorber.

According to yet a further embodiment, the faces of the slot each have a conducting surface adapted to jointly constitute a variable contact surface area. According to yet a further embodiment, one of the surfaces is of metal and the other surface is of carbon.

According to another embodiment, the sensor is a piezo-resistive sensor. According to yet a further embodiment, the geared motor drive further comprises a transformer, the sensor being connected to a secondary winding of the transformer.

According to a further embodiment, the shock absorber is arranged against one face of the gear unit and the secondary winding is arranged on the opposing face of the gear unit.

According to a further embodiment, the gear unit is arranged inside a casing of the geared motor drive and a primary winding of the transformer is arranged on a face of the casing facing the secondary winding.

According to one embodiment, the geared motor drive for a window lifter comprises

- at least one transmission member driven by the motor; the torque sensor being located on the transmission member;

- a measurement circuit for the state of the sensor, the measurement circuit having:

- a part that is fixed with respect to a stator of the motor, supplying a signal that is dependent on the state of the sensor. According to one embodiment, the transmission member is the shock absorber.

According to a further embodiment, the measurement circuit further has a rotary transformer one winding of which is connected to the sensor and the other winding of which is included in the fixed part.

According to yet a further embodiment, the fixed part is supplied with an alternating current.

According to yet a further embodiment, a winding of the fixed part is connected in one arm of a heatstone bridge.

According to yet a further embodiment, the winding of the fixed part is connected in series with a shunt resistor. According to another embodiment, the circuit formed by the measurement circuit and the sensor has a resonant frequency comprised between 95 and 105 KHz when the sensor is not under load.

According to another embodiment, the measurement circuit comprises a temperature compensating device. According to another embodiment, the sensor is a resistive sensor.

According to another embodiment, the sensor is a capacitive sensor. According to another embodiment, the geared motor drive further comprises:

- a casing on which the winding of the fixed part is provided; - a transmission gear unit housed in the casing, carrying the winding (connected to the sensor, facing the winding of the fixed part.

A window lifter is aso provided, comprising:

- a geared motor drive as above; and - a slider for a window glass driven by the output from the transmission system.

The window lifter can further comprise a switch that stops the drive of a slider when a signal from the measurement circuit exceeds a triggering threshold.

It can also further comprises a switch that stops the drive of a window glass when a signal from the measurement circuit exceeds a triggering threshold. A method for determining the torque of a geared motor drive is also provided, comprising the steps of:

- sensing a torque of the geared motor drive using a sensor located on a transmission member of the geared motor drive driving a window glass;

- recovering the state of the sensor at a fixed part of a measurement circuit; - providing a signal that is a function of the state of the sensor.

The method can comprises the steps of comparing the signal with a predetermined threshold, and stopping drive of the window glass when the signal exceeds this threshold.

In the method, the transmission member can be a shock absorber. Further characteristics and advantages of the invention will become more clear from reading the description below of some embodiments of the invention provided by way of example and with reference to the attached drawings which show:

In Figure 1, a diagrammatic view of a window lifter with a geared motor drive according to the invention; hi Figure 2 a detailed view of a wheel and shock absorber of the transmission system in Figure 1 in the idle position;

In Figure 3, a detailed view of a wheel and shock absorber of the transmission system of figure 2 while a window glass is being lifted;

In Figure 4, a detailed view of a wheel and shock absorber of the transmission system in the idle state, of a further embodiment; hi Figure 5, a detailed view of the wheel and a shock absorber of the transmission system of figure 4 while a window glass is being lifted; hi Figure 6, a diagram showing electrical impedance of an unloaded sensor, like in figures 3 and 5; In Figure 7, a diagram showing electrical impedance of a loaded sensor, like in figures 3 and 5;

In Figure 8, a detailed view of a wheel and shock absorber according to a third embodiment; In Figure 9, a perspective view of a wheel, turned round, with a secondary winding; hi Figure 10, a diagrammatic perspective view of a gear unit of the invention, including a measuring circuit; i Figure 11, a diagrammatic view of one embodiment of the measuring circuit with the sensor;

In Figure 12, a diagrammatic view of a second embodiment of a measuring circuit and a sensor.

The invention provides a window lifter geared motor drive, including an electric motor with a motor shaft. The geared motor drive also comprises a transmission system with an input driven by the motor shaft and a driving output, and a shock absorber which couples the input to the output of the transmission system. The geared motor drive includes a sensor for the torque transmitted by the shock absorber.

The invention also enables trapping in a window lifter to be detected, by using a sensor located in a transmission member of the geared motor drive. The sensor measures the torque applied to the transmission member and transmits the measured value to a measuring circuit that includes a part that is fixed with respect to the geared motor drive stator.

The invention makes it possible to obtain an electric signal indicating trapping that can be exploited directly to detect trapping.

Figure 1 shows a window lifter 1 according to an embodiment of the invention. This window lifter comprises a slider 2 which acts on a window glass, not illustrated. Slider 2 is itself driven by a cable 3. Cable 3 is driven by a drum 4 of geared motor drive 5. A shock absorber 6 couples drum 4 to a wheel 7 of the gearing. Coupling the drum to the wheel via a shock absorber allows their relative angular position to be varied, with absorption of shocks. Toothed wheel 7 meshes with a worm gear 8 provided, for example, on the end of a motor shaft 9. Motor 10 and the transmission by wheel 7 and worm gear 8 can the implemented in a manner known per se.

Figure 2 shows detail of the shock absorber and wheel of the window lifter according to a first embodiment. Shock absorber 6 has, overall, a cylindrical shape with notches 11 and 16 on its radial periphery. The shock absorber is housed in a casing of geared motor drive 5. It has a central opening. Shock absorber 6 is guided and maintained axially by a shaft 21 passing through this central opening. The shaft can be fixed to the casing 22 of geared motor drive 5. Shock absorber 6 has three securing notches 18 into which ribs 12 of a wheel 7 are inserted. A rib 12 can apply a force to a face of the corresponding notch 18. Toothed wheel 7 and shock absorber 6 are thereby coupled. The shock absorber also has three notches 16 for insertion of studs 17 on a drum 4, these being shown in cross section. One face of a notch 16 can thus apply a force to a corresponding stud. Shock absorber 6 and drum 4 our thus coupled in rotation about shaft 21. The notches 12 are offset with respect to the notches 18. There is preferably an even number of notches 16 and 18 and the angle between a notch 16 and an adjacent notch 18 is approximately the same for all the notches.

A deformable slot 11 is provided in the shock absorber between one notch 16 and one notch 18. This slot preferably extends radially from the central opening out to the radial periphery. This slot can also separate the shock absorber at both sides. Slot 11 has two opposing faces on which conducting surfaces 13 and 14 are provided, i the idle state, contact surface area SI between conducting surfaces 13 and 14 is minimal or nonexistent. Portion 23 of the shock absorber supporting conducting surface 13 is wedged against a rib 12. The portion 24 of the shock absorber supporting conducting surface 14 is wedged against a stud 17. A portion 23 which is fixed with respect to rib 12, or only slightly deformable, can be used. Portion 24 now gets deformed thereby increasing the contact surface area between conducting surfaces 13 and 14. The slot and the contact surfaces consequently form a transmission torque sensor for the shock absorber, as will be explained below.

Thus, preferably, the sensor is on the shock absorber. The shock absorber acts as a carrier for the sensor. Geared motor drive torque measurement by the sensor is more accurate as the sensor is arranged on a part, the transmission member which can be the shock absorber, which has higher magnitudes of deformation than exist in the prior art where sensors are located on members having smaller magnitudes of deformation. Further, the sensor is on one and the same part, the transmission member which can be the shock absorber, where deformations are more homogeneous than the case where the sensor is between different parts. Trapping detection is consequently improved.

Figure 3 shows a wheel and shock absorber under load while a window glass is being lifted. A rib 13 drives portion 23 of the shock absorber. A stud 17 applies a reaction force to portion 23 of the shock absorber. We consequently have a driving portion 23 and a driven portion 24. In view of the reaction force, portion 24 of the shock absorber gets deformed or displaced. The contact area between conducting surfaces 13 and 14 increases now up to a value S2, higher than SI.

Figures 4 and 5 show a second embodiment of the invention. In this embodiment, both of the portions 23 and 24 get deformed. The surfaces 13 and 14 have, in the idle state, a separation which decreases as one moves towards the radial periphery of the shock absorber. In Figure 5, the shock absorber is under load while a window is being lifted. The portions 23 and 24, along with the conducting surfaces 13 and 14 get deformed. Contact surface area increases substantially in proportion to the load. This embodiment makes it possible to obtain a contact surface area between conducting surfaces 13 and 14 which is substantially proportional to the drive torque.

The conducting surfaces and shock absorber are shaped so that the contact surface area increases still further when the trapping force threshold is exceeded. Figure 6 shows the sensor of figures 2 or 4 in the idle state in the form of a rheostat. Contact surface area between the conducting surfaces of the slot varies as a function of load. The electrical impedance of the sensor is inversely proportional to this contact surface area. Thus, as shown in Figure 7, the impedance of the sensor of figures 3 and 5 decreases under load. An increase in the drive force of the slider, and, consequently, in the drive torque then brought about, leads to a reduction of contact impedance.

Preferably, low resistivity materials are used for providing the conducting surfaces of the slot. The conducting surfaces can be made with a layer of copper or carbon. It is preferable to use a copper layer on the fixed face of the slot. It is then preferable to use a carbon layer on the movable face of the slot. The carbon layer is more flexible than the copper layer. It consequently gets deformed better when the shock absorber is loaded. The sensitivity of the sensor to deformation is consequently increased as the carbon layer adapts itself better to the shape of the copper layer. The use of carbon coatings also facilitates production of the sensor. These surfaces can be provided in the form of thin sheets bonded onto the faces of the slot.

According to another embodiment illustrated in Figure 8, the two faces of the slot are in contact with a piezo-resistive sensor 15. A piezo-resistive sensor that is known per se and commercially available can be used, the electrical impedance of which increases in proportion to the force applied to its two faces. The sensor can also employ a sensing element having a capacitance, inductance or, more generally, an impedance the value of which varies as a function of the force applied thereto. Such a sensor is compact and can be pre-equipped with terminals ready for connection.

In the framework of this invention, the sensor can be provided on other members of the transmission apart from those described above. The sensor is nevertheless preferably arranged on a transmission member having an elasticity modulus of the order of 2500 N/mm², in order to have a high degree of deformation with, consequently, accurate torque measurement. One can obviously also use a deformable conducting surface provided on the shock absorber, acting on a conducting surface provided for example on a stud of the drum. It is nevertheless preferable to employ conducting surfaces provided on the same part, in this case the shock absorber in the first two embodiments described.

The conducting surfaces 13 and 14 each have an electrical connection, respectively 25 and 26. These connections 25 and 26 each connect the conducting surfaces to one end of a secondary winding 27 shown in figure 9. The secondary winding forms a transformer with a primary winding which is stationary with respect to the motor stator and which will be described below. This transformer can for example be included in a measurement circuit for transmitting the signal from the sensor to a part that is fixed with respect to the rotor of the measurement circuit. The toothed wheel can thus have two passages to allow the connections to pass to the rear face 28 of the toothed wheel. The secondary winding can be mounted on the rear face of the toothed wheel. One can for example provide a groove 29 in this face for inserting the secondary winding 27. Secondary winding 27 does not consequently project with respect to rear face 28.

The secondary widening interacts with a primary winding. The electric current through the primary winding is inversely proportional to the overall impedance of the unit constituted by the sensor, including the secondary winding. The current through the primary winding is thus representative of the state of the sensor. The signal from the sensor can now be transmitted from the moving wheel to the fixed part of a measurement circuit without using electrical contact between the fixed and moving parts. The window lifter consequently is of simple manufacture with a low risk of wear of the sensor and measuring device.

The primary winding can optionally be located on the casing 22 opposite the secondary winding. Primary winding 31 is preferably placed on an outer wall of the casing 22. The distance between the primary winding and the secondary winding is preferably less than 10 mm. It is preferable to use a casing thickness less than 3 mm where the primary winding is located. The casing is also made from a material having a magnetic permeability greater than unity where the primary winding is located. One can for example use PBT with a 30% glass fiber filling or yet again PA 6-6 for this part of the casing. Provisions can also be made to increase magnetic permeability using metallic filler incorporated into a matrix forming the casing. These various characteristics make it possible to increase signal level picked up by the primary winding. This also limits the danger of interference with other electromagnetic components. Depending on the embodiment, it can be arranged to provide the windings 27 or 31 respectively by printing on the toothed wheel or the casing.

We shall now describe in detail various measurements circuits able to be connected to the sensor.

Figure 10 is a diagrammatic perspective view of a geared motor drive according to the invention including a measurement circuit and a torque sensor. The torque sensor 15 is comiected to the secondary winding 27 of the transformer of measurement circuit 30. The respective arrangement of primary winding 31 and secondary winding 27 can be chosen as described above. Primary winding 31 is thus fixed to a face of the casing opposite the toothed wheel. Primary winding 31 is included in a fixed part of the measurement circuit. The fixed part is stationary with respect to the stator of motor 10.

Figure 11 shows one alternative embodiment in which a piezo-resistive sensor is employed. The measurement circuit is supplied from an alternating voltage source 32. For a given force applied to sensor 15, a given impedance is obtained at the unit constituted by sensor 15 and the windings 27 and 31. For a given impedance of this unit, a corresponding voltage is obtained at the terminals of primary winding 31. Primary winding 31 is here integrated into a Wheatstone bridge 34. Thus, the motor transmission torque causes unbalance of the Wheatstone bridge. This unbalance produces a corresponding voltage at the terminals of an amplifier 35. The transmission torque is thus transformed into a voltage signal available in a stationary part of the geared motor drive. This voltage signal is for example sent to a switch or auxiliary processing device 33.

This processing device 33 can for example extrapolate a slider drive force value or a torque supplied by the motor from the sensor signal. This signal can then be compared with a predetermined trapping threshold. The processing device or auxiliary microprocessor can then cut off the motor supply to stop the window glass lifting should trapping be detected. Preferably, the electrical supply to the motor is reversed in order to lower the window glass should trapping be detected. The processing device can also control mechanical braking of the motor to reinforce the slowing-down of the lifting of the window glass.

Processing device 33 can also comprise a temperature compensating device. The signal supplied by the measurement circuit can thus be corrected as a function of ambient temperature. This consequently limits the danger of erroneous trapping detection.

Figure 12 shows another embodiment in which a piezo-capacitive sensor 15 is employed. Primary winding 31 is in this case placed in series with a shunt resistor 36. For a given impedance of the unit formed by the sensor and the windings, a corresponding voltage is obtained across resistor 36. The transmission torque is thus also transformed into a voltage signal available in a stationary part of the geared motor drive.

It is preferable to use a unit that includes a sensor and associated measurement circuit having a resonant frequency comprised between 95 and 105 KHz when no torque is applied to the sensor. It can for example be arranged to excite the measurement circuit with a power signal having a frequency of 100 KHz. Variations in load due to torque applied to the transmission then bring about a variation in the resonant frequency of the unit including the measurement circuit and sensor, and this variation can be measured. The invention also provides a window lifter that includes a geared motor drive of the type described previously. It can be arranged to mount the fixed or stationary part of the measurement circuit on a structural member of the window lifter and not on the geared motor drive itself. Generally, a measurement circuit can be provided having a fixed part which is not directly integral with the geared motor drive. This window lifter can comprise a general structure known per se, including a cable wmding drum, a slider drive cable, a slider guide rail and a window glass secured to the slider.

Obviously, this invention is not limited to the examples and embodiments described and illustrated, but may be subject to numerous variations available to those skilled in the art. Thus, regarding the sensor, although a drum has been described having three notches 16 and three notches 18, a different number of notches could obviously be provided. Ribs and studs of differing shape could also be employed. Any suitable means for coupling between the shock absorber and the drum and between the shock absorber and the toothed wheel could also be employed. The invention is also not limited to signal transfer from the sensor to a fixed part via a transformer. Other means such as brushes rubbing against a contact track could also be envisaged. The invention is also not limited to the combinations of sensor and measuring circuits described.

Claims

1. A geared motor drive (5) for a window lifter (1) comprising:

- an electric motor (10) with a motor shaft (9); - a transmission system comprising:

- an input (7) driven by said motor shaft (9) and a drive output (4);

- a shock absorber (6) coupling said input (7) to said output (4) of the transmission system; and

- a sensor (13, 14, 50) for torque transmitted by said shock absorber (6).

2. The geared motor drive (5) for a window lifter (1) of claim 1 , characterised in that the sensor is on the shock absorber.

3. The geared motor drive (5) for a window lifter (1) of claim 1 or 2, characterised in that the sensor (15) comprises a two-terminal circuit having an impedance varying with shock absorber transmission torque.

4. The geared motor drive (5) according to one of Claims 1-3, characterised in that:

- said transmission system comprises a gear unit (7) coupled at the input and a drum (4) coupled at the output;

- said shock absorber (6) has a deformable slot (11) with said gear unit acting on a first face thereof and said drum acting on a second face thereof; and - said sensor (13, 14, 15) is arranged in said slot (11).

5. The geared motor drive according to claim 4, characterised in that the shock absorber has an overall cylindrical shape, said slot extending in a radial direction of the shock absorber.

6. The geared motor drive of claim 4 or 5, characterised in that said faces of said slot each have a conducting surface (13, 14), adapted to jointly constitute a variable contact surface area.

7. The geared motor drive of claim 6, characterised in that one of said surfaces is of metal and the other surface is of carbon.

8. The geared motor drive according to one of Claims 1-5, characterised in that said sensor is a piezo-resistive sensor (15).

9. The geared motor drive of one of Claims 1-8, characterised in that it further comprises a transformer, said sensor (13, 14, 15) being connected to a secondary winding (27) of said transformer.

10. The geared motor drive according to claim 9, characterised in that said shock absorber is aπanged against one face of said gear unit and said secondary winding is arranged on the opposing face of the gear unit.

11. The geared motor drive according to claim 10, characterised in that:

- said gear unit is arranged inside a casing (22) of the geared motor drive;

- a primary winding of the transformer is arranged on a face of said casing facing said secondary winding.

12. The geared motor drive (5) for a window lifter (1) according to claim 1 comprising:

- at least one transmission member (6) driven by said motor; the torque sensor (15) being located on said transmission member;

- a measurement circuit (30) for the state of said sensor, said measurement circuit having:

- a part that is fixed with respect to a stator of said motor, supplying a signal that is dependent on the state of said sensor.

13. The geared motor drive (5) for a window lifter (1) according to claim 12, characterised in that said transmission member is the shock absorber.

14. The geared motor drive of claim 12 or 13, characterised in that the measurement circuit further has a rotary transformer (27, 31) one winding of which is comiected to said sensor and the other winding of which is included in said fixed part.

15. The geared motor drive of claim 14, characterised in that the fixed part is supplied with an alternating current.

16. The geared motor drive of claim 14 or 15, characterised in that a winding of the fixed part is connected in one arm of a Wheatstone bridge (34).

17. The geared motor drive of claim 14 or 15, characterised in that the winding of the fixed part is comiected in series with a shunt resistor (36).

18. The geared motor drive of one of claims 12 to 17, characterised in that the circuit formed by the measurement circuit and the sensor has a resonant frequency comprised between 95 and 105 KHz when the sensor is not under load.

19. The geared motor drive according to one of claims 12 to 18, characterised in that the measurement circuit (30) comprises a temperature compensating device.

20. The geared motor drive according to one of claims 12 to 19, characterised in that the sensor is a resistive sensor.

21. The geared motor drive according to one of claims 12 to 19, characterised in that the sensor is a capacitive sensor.

22. The geared motor drive according to one of Claims 12 to 21, characterised in that the geared motor drive further comprises:

- a casing (22) on which the winding of the fixed part is provided;

- a transmission gear unit (7) housed in said casing, caπying said winding (27) connected to the sensor, facing the winding (31) of said fixed part.

23. A window lifter (1) comprising:

- a geared motor drive (5) according to one of the preceding claims; and

- a slider for a window glass (2) driven by the output from the transmission system.

24. The window lifter according to Claim 23, characterised in that it further comprises a switch that stops the drive of a slider when a signal from said measurement circuit exceeds a triggering threshold.

25. The window lifter according to Claim 23, characterised in that it further comprises a switch that stops the drive of a window glass when a signal from said measurement circuit exceeds a triggering threshold.

26. A method for determining the torque of a geared motor drive, comprising the steps of:

- sensing a torque of said geared motor drive using a sensor located on a transmission member of the geared motor drive driving a window glass;

- recovering the state of said sensor at a fixed part of a measurement circuit;

- providing a signal that is a function of the state of said sensor.

27. The method of claim 26, characterised in that it further comprises the steps of comparing said signal with a predetermined threshold, and stopping drive of the g nrllaos.-is.-i t wT rlh*Λ αeιn-ι - thl-ieα c suigmnualil o evxc»oeoeπdcsι + thlτiιsπ " tfrihιτr*Qesohr_{- -}oOld/-ι,

28. The method according to claim 26 or 27, characterised in that the transmission member is a shock absorber.