Gear unit and motor-driven gear unit for cable window lift systems

Abstract

Gear unit and a motor-driven gear unit for cable window lift systems of motor vehicles, including drive and gear mechanism which cooperates with the drive and is coupled to rotatably mounted cable drum for winding and unwinding cable of the cable window lift system. According to the invention a diameter of the cable drum of the gear unit or motor-driven gear unit is in a range from about 22 mm to about 30 mm, wherein a gear ratio of the gear mechanism ranges from about 1:38 to about 1:55. A cable drum has, on its end side, claws which engage in correspondingly designed recesses on the end side of a worm wheel. Electric motors having a maximum driving torque of only about 5.7 Nm can be used. Overall, the size of the gear unit or motor-driven gear unit can be reduced by about 40-50%.

Description

FIELD OF INVENTION

The present invention relates to a gear unit and to a motor-driven gear unit for cable window lift systems of motor vehicles.

RELATED ART

The many requirements on motor-driven gear units for cable window lift systems in motor vehicles mean in practice relatively narrow parameter ranges in terms of the structural design. In particular, the following constraints must be taken into account in the structural design: the output power of the electric motor used for the electric drive; the available on-board power of motor vehicles, which has an effect on the maximum output power; the friction forces brought about by the structural design of the window lift system, which predefine the necessary minimum output power; the structural design both for window lift systems of motor vehicle front doors and also for window lift systems of motor vehicle rear doors; the required maximum travel for adjusting the window; the expected maximum number of actuations of the window lift system during the service life of the motor vehicle; the optional design both for manual and electric drive of the window lift system; the flexural strength and durability of the cable used. In practice, a large number of other constraints must also be taken into account.

In practice, these requirements have led to window lift system drives with worm wheel reduction always having a gear ratio in the range from about 1:62 to about 1:84, wherein the cable drums always have a diameter in the range from about 36 mm to about 48 mm and the output power of the electric motors always is about 20 W. Deviations from these relatively narrow parameter ranges are in practice very difficult since in any modification a large number of conditions have to be optimized, as mentioned above.

Some of the abovementioned parameters and also other parameters can rarely be changed in practice because serious technical problems would arise. For example, a possible reduction in the diameter of the cable drum entails the disadvantages that the cable winds up relatively high on the drum, which poses great problems in terms of cable guidance and also the structural design of cable window lift systems, and that the cable is bent to a considerably greater extent, which adversely affects the durability of the cable which is to be ensured throughout the entire service life of the motor vehicle.

The automotive industry nowadays is increasingly demanding standardized ancillary components which are used universally. This reduces the cost in terms of construction, storage and assembly. In particular, the fact that for this reason electric cable window lift systems both for the front door and for the rear door are nowadays provided as a unit with electric motors having a possible output power of 20 W nevertheless has the disadvantage that too great a structural volume has to be provided in the rear door, which is actually not necessary. This is because the rear windows usually also have dual guidance in the door and the drive force is usually introduced at one point, so that friction or tilting problems are of lesser importance. For reasons of space and also reasons of cost, it would therefore be desirable to provide electric cable window lift systems with electric motors having a lower output power. However, the comparatively high requirements in terms of adjusting a front window, particularly relatively complex window guides with a poorer mechanical efficiency and the like, prevent this.

In all this, account must be taken of the fact that even very small improvements in the design of gear units or motor-driven gear units for cable window lift systems are of considerable economic significance given the current cost pressure in the automotive ancillary industry.

FIG. 8 shows, in a sectional view, a gear unit according to the prior art for electric cable window lift systems. Only the gear housing section 6 of the gear unit is shown, in which a worm wheel 10 of a worm gear is accommodated. A drive shaft (not shown) extends through a cylindrical hole at the right edge of the gear housing section 6, at the front end of which drive shaft there is seated a drive worm 15, the toothing of which engages in the toothing 11 of the worm wheel 10. For the abovementioned reasons, in the prior art the gear ratio of the worm gear designed in this way is in the range from about 1:62 to about 1:84.

Seated on the upper end of the gear housing section 6 is a driven pawl 40 which at its upper end has a conical notched toothing 41 on which a cable drum (not shown) with an inner toothing is placed such that it is fixed in rotation. The worm wheel 10 is designed as a hollow body in which retaining ribs (not shown) are arranged at angular spacings from one another. The rubber damping elements 39, which are arranged at corresponding angular spacings from one another, engage in the retaining ribs in order to connect the pawl 40 to the worm wheel 10 such that it is fixed in rotation. The driven pawl 40 and the worm wheel 10 are mounted such that they can rotate together about the pivot pin 9. The driven pawl 40 and the worm wheel 10 are secured against displacement in the axial direction by the securing ring 35. The cable drum (not shown) serves to wind and unwind the cable of a cable window lift system in the known manner.

Seated on the gear housing section 6 is an upper housing cover 32, wherein a seal 30 with sealing lips 31 is seated in the annular gap between the inner peripheral wall of the upper housing cover 32 and the outer peripheral edge at the upper end of the worm wheel 10, in order to seal off the worm wheel 10 and the driven pawl 40 with respect to the gear housing section 6.

The relatively high output power (20 W) of the electric motor according to the prior art and a correspondingly high driving torque make a certain degree of damping absolutely necessary in the conventional motor-driven gear unit shown. The multi-part design of the driven train, comprising the driven pawl, the deformable rubber damping elements connected to the pawl—which engage in a form-fitting manner in corresponding retaining ribs in the inner periphery of the worm wheel—and the worm wheel, is comparatively complex and expensive.

DE 198 12 875 C1, corresponding to WO 99/47779, of the applicant discloses a cable actuated window lift drive mechanism, which is made up of only a few components with modest tolerance requirements. The motor shaft is integrated in one of the bearing covers of the gear drive unit. A seal is provided on the peripheral edge of the cable drum and/or a gear element of the geard drive unit.

SUMMARY OF INVENTION

It is an object of the present invention to provide a gear unit or motor-driven gear unit which can be used universally for cable window lift systems of both rear and front vehicle doors, is of even simpler design and can be produced even more cost-effectively.

According to the present invention, a gear unit for cable window lift systems of motor vehicles is provided, which comprises a drive and a gear mechanism which cooperates with the drive and is coupled to a rotatably mounted cable drum for winding and unwinding a cable of the cable window lift system. According to the invention, the gear unit is characterized in that a diameter of the cable drum is in a range from about 22 mm to about 30 mm and more preferably in a range from about 24 mm to about 28 mm, wherein the gear ratio of the gear mechanism is in a range from about 1:38 to about 1:55 and more preferably in a range from about 1:42 to about 1:51.

By virtue of the surprisingly simple measure according to the invention of making the diameter of the cable drum considerably smaller than in conventional gear units and at the same time correspondingly changing the gear ratio of the gear mechanism, according to the invention it is possible to use, for rear cable window lift systems, smaller and lesser-powered drive motors. In particular, according to the invention, it is possible to use drive motors having a maximum output power of only about 10 W and a maximum driving torque of only about 6.0 Nm. It has been found that this design modification is critical in order that the gear unit according to the invention can be used both for electric and for manual cable window lift systems.

This is because extensive studies by the Applicant have shown that, contrary to the preconception that such a small cable drum diameter leads to unacceptably high stressing of the cable and thus to breaking of the cable or the like before the end of the customary service life of motor vehicles, the maximum cable stress in the case of the significantly lesser-powered motors to be used according to the invention is low enough that the cable lasts until the end of the customary service life of motor vehicles.

In particular, it has been found that the rear windows of motor vehicles are not used as often and also the maximum travel in respect of rear windows is often smaller than in the case of front windows. Therefore, contrary to the abovementioned preconception, smaller cable drum diameters can indeed be used for rear cable window lift systems and/or the axial length of the cable drum, despite its smaller diameter, is nevertheless sufficient without the cable winding too high onto the drum.

At the same time, the gear unit according to the invention can also be used for front cable window lift systems. This is because, despite the considerably smaller diameter of the cable drum according to the invention, there is a sufficient lever arm available, including for front cable window lift systems, to adjust the window even in the case of a lesser-powered electric motor with sufficient driving torque. Sufficient durability of the cable can thus be ensured even for front cable window lift systems.

According to the invention, the gear ratio of the gear mechanism, in particular of the worm gear, is also reduced compared to the prior art in the same ratio as that of the cable drum diameter. It is advantageous that the cable force/cable speed characteristic curve of a cable window lift system according to the invention thus corresponds essentially to that of a conventional cable window lift system.

The considerably lower output torque of the electric motor and the lower output power of the latter, which have become possible according to the invention, make it possible according to the invention for the cable drum to be coupled, preferably also directly, to the gear mechanism, in particular to a worm wheel of the gear mechanism. According to the invention, the use of additional damping elements for damping between the drive shaft and the driven shaft, as required in the prior art, can thus be omitted. The surprisingly simple design modification according to the invention thus has the additional advantage that the gear unit can be designed in a less complicated manner, and according to the invention this leads to a considerable cost saving both in terms of the design and in terms of the assembly.

According to the invention, the cable drum is coupled to the worm wheel by means of at least two engagement elements which are arranged on its end side and engage in a form-fitting manner in at least two counterelements on an end side of the worm wheel, said counterelements being designed to correspond to the engagement elements. The engagement elements are preferably designed as protrusions, for example as claws, which engage in correspondingly designed recesses.

Because a driven pawl coupled to the worm wheel is no longer required according to the invention, the gear housing section of the gear unit according to the invention can also be sealed in a much simpler manner. For this purpose, a sealing means is seated, in a manner such that it is fixed in rotation, preferably either on an outer peripheral edge of the worm wheel or on an upper edge of the gear housing section.

This feature allows a manufacturing and assembly process which is changed considerably compared to the prior art. For instance, the sealing means may also be formed in one operation together with other sealing means, for example seals of the electronics housing section, for sealing off an electric motor with respect to the housing and the like. For this purpose, use may also be made in particular of two-component injection molding (2C injection molding) in which, once the first component, for example the relatively hard housing, has solidified, the cavity in the mold is enlarged and then the second component, for example the relatively soft sealing means, is injected by means of a second injection device. Furthermore, the worm wheel can be pushed through the already applied sealing means into the gear housing section, whereas according to the prior art (cf. FIG. 8) the sealing means can only be placed on the worm wheel subsequently, together with the upper housing cover. A number of operations can thus be saved.

Because the cable drum according to the invention is coupled directly to the worm wheel, in particular engaged in a form-fitting manner in an end side of the worm wheel, the window lift system can according to the invention optionally be designed for a manual or an electric drive without further design modifications being required. In particular, an identical cable drum, an identical baseplate (for fixing the gear unit or motor-driven gear unit, for example to a guide rail of the cable window lift system) and an identical coverplate can be used both for manual and for electric cable window lift systems.

In order to receive a brake spring or wrap spring for a manual cable window lift system, one engagement element, in particular one claw, may comprise a shoulder in order to form a seat for receiving the brake spring or wrap spring.

According to a further aspect of the present invention, a motor-driven gear unit for cable window lift systems of motor vehicles is also provided. According to the invention, this motor-driven gear unit is characterized in that an electric motor is coupled to the gear unit, said electric motor having a driving torque of at most about 5.7 Nm and/or an output power of at most about 10 W.

According to the invention, such a motor-driven gear unit can be used both for a cable window lift system for a front motor vehicle door and for a cable window lift system for a rear motor vehicle door.

Because the electric motor according to the invention can have a considerably smaller maximum torque, the external dimensions of a motor-driven gear unit according to the invention can be considerably smaller. According to the invention, the structural volume to be contained in a vehicle door or in a door module that is to be integrated in the door can be reduced by about 40% or even by 50%. Overall, this leads to a further considerable cost saving compared to the prior art.

BRIEF DESCRIPTION OF DRAWINGS

The invention will be described below by way of example and with reference to the appended figures, from which one can derive further features, advantages and objects to be achieved and wherein:

FIG. 1 shows, in a sectional view, a gear unit according to the present invention;

FIG. 2 shows, in schematic section, the engagement of a worm wheel and of a cable drum according to the present invention;

FIG. 3 shows, in a perspective exploded view, the worm wheel and the cable drum of FIG. 2;

FIG. 4 shows, in a sectional view, a gear unit according to a second embodiment of the present invention;

FIG. 5 shows, in a perspective partial section, a motor-driven gear unit as shown in FIG. 4;

FIGS. 6 a and 6b show, in a perspective view, an electric cable window lift system according to the present invention in two different phases of its assembly;

FIGS. 7 a and 7b show, in a perspective view, a manual cable window lift system according to the present invention in two different phases of its assembly; and

FIG. 8 shows, in a sectional view, a gear unit according to the prior art for an electric cable window lift system.

In the figures, identical references refer to elements or groups of elements which are identical or perform essentially the same function.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 1 shows, in a sectional view, a gear unit according to the present invention. As shown in FIG. 1, the worm wheel 10 is accommodated in the gear housing section 6 which is formed by a housing bottom 7 and side walls 8 which extend perpendicular to the housing bottom 7. Projecting vertically from the housing bottom 7 is a pivot pin 9 which may be designed as a metal or plastic pin and is connected rigidly to the housing bottom 7. The pivot pin 9 serves as an axis of rotation for the worm wheel 10 and a cable drum as shown in FIG. 3. A drive shaft of an electric motor extends through a cylindrical hole at the left edge of the gear housing section 6, which drive shaft has at its front end a drive worm 15 which meshes with the worm wheel 10. The worm wheel 10 and the drive worm 15 form a worm gear, the gear ratio of which is defined by the toothing of the drive worm 15 and the toothing 11 of the worm wheel 10.

According to the present invention, the gear ratio of the worm gear is in the range from about 1:38 to about 1:55, more preferably in a range from about 1:42 to about 1:51, and is even more preferably about 1:47. The gear ratio according to the present invention differs considerably from the conventional gear ratio for cable window lift systems, which is in the range from about 1:62 to about 1:84.

Above the toothing 11, the worm wheel 10 has an essentially smooth-walled peripheral edge which lies opposite an upper edge 29 of the side wall 8. The upper peripheral edge of the worm wheel 10 is surrounded in a friction-tight manner by an essentially C-shaped seal, so that the seal 30 is seated on the worm wheel 10 essentially in a manner such that it is fixed in rotation with the latter. An annular gap formed between the upper peripheral wall of the worm wheel 10 and the upper edge 29 of the side wall 8 is bridged by two hook-like sealing lips 31 which protrude from the seal 30, which sealing lips bear against the inner peripheral wall of the upper edge 29 of the side wall 8. The worm wheel 10 is thus sealed with respect to the gear housing section 6. For assembly, the worm wheel 10 can be placed together with the seal 30 on the pivot pin and pushed into the gear housing section 6.

As shown in FIG. 1, formed on the lower end side of the worm wheel 10 is an annular bead 36 on which the worm wheel 10 rests in the gear housing section 6, in order to reduce friction forces. Alternatively, a corresponding annular bead may also be formed on the lower end side of the worm wheel 10. The upper end side of the worm wheel 10 is designed to be essentially flat and has two recesses 13, 14 which serve to couple a cable drum (FIG. 2) to the worm wheel 10 in a manner such that it is fixed in rotation, as described below with reference to FIGS. 2 and 3.

FIG. 2 shows, in schematic section, the engagement of a worm wheel and of a cable drum according to the present invention. As shown in FIG. 2, the cable drum 17 has, on its lower end side, two claws 19, 20 which project axially from the lower end side and extend in a ring-like manner in the circumferential direction. As shown in FIG. 2, the claws 19, 20 engage essentially without play in the correspondingly designed recesses 13, 14 on the upper end side of the worm wheel 10, so that the cable drum 17 engages in a form-fitting manner in the worm wheel 10.

As shown in FIG. 1, in the illustrated position of the worm wheel 10 a conical shoulder 37 of the pivot pin 9 projects out of the plane formed by the upper end side of the worm wheel 10. The conical shoulder 37 serves for the exact positioning of the cable drum 17 in the axial direction. As shown in FIG. 2, in the illustrated position of the cable drum 17, when the claws 19, 20 are completely received in the recesses 13, 14 and the conically widening section of the through-opening 21 of the cable drum 17 bears against the conical shoulder 37 of the pivot pin 9, a comparatively narrow gap is formed in the axial direction between the upper end side of the worm wheel 10 and the lower end side of the cable drum 17, which narrow gap can serve to compensate for any manufacturing tolerances.

As shown in FIG. 2, formed on the peripheral edge of the lower end side of the cable drum 17 is a radially protruding circumferential protrusion 23 which in the illustrated position of the cable drum 17 bears against the inner peripheral edge of the seal 30 (FIG. 1) or slightly overlaps the latter and thus completes the sealing of the worm wheel 10 with respect to the gear housing section 6.

As shown in FIG. 2, according to the invention the cable drum 17 engages directly in the worm wheel 10 by means of the claws 19, 20. According to the invention, no additional damping elements, for example deformable rubber blocks, are thus required in order to dampen the driving torque of an electric motor. This simpler and more cost-effective design is a direct consequence of the fact that according to the invention, on account of the considerably smaller gear ratio of the worm gear and of the correspondingly smaller diameter of the cable drum 17 compared to the previously known prior art, the maximum driving torque of an electric motor according to the invention can be selected to be considerably smaller.

FIG. 3 shows, in a perspective exploded view, the worm wheel and the cable drum of FIG. 2. As shown in FIG. 3, the two recesses 13, 14 lie on diametrically opposite sides of the through-opening 16. Each of the recesses 13, 14 is formed by two peripheral walls running concentrically with respect to the through-opening and by two side walls which connect said peripheral walls to one another and extend in the radial direction. As shown in FIG. 3, the profile of the two recesses 13, 14 and of the correspondingly designed claws 19, 20 differ from one another so that the angle of the cable drum 17 with respect to the worm wheel 10 is clearly defined. As will be readily obvious to the person skilled in the art, any other locking or latching elements may also be used to connect the cable drum 17 to the worm wheel 10 in a manner such that it is fixed in rotation.

Spiral guide grooves 18 run on the outer periphery of the cable drum 17, in which guide grooves the cable of a cable window lift system (FIG. 7) is guided. Formed on the upper end side 25 of the cable drum 17 is a cable nipple receptacle 26 for receiving the cable nipple of the cable of the cable window lift system, said cable nipple receptacle extending essentially tangentially. The cable nipple receptacle 26 opens into a cable bushing 27 and into the deflection region 28 where the cable is deflected into the uppermost guide groove 18. A corresponding cable nipple receptacle is formed on the lower end side of the cable drum 17 in order to receive the other end of the cable of the cable window lift system.

As shown in FIG. 3, the claw 20 has a projection or protrusion 24 in the axial direction so that, as shown in FIG. 7a, in the event of use for a manual cable window lift system, a receptacle is available for receiving the inwardly bent end 58 of the wrap spring or brake spring 57 of the manual cable window lift system 100 (FIG. 7a).

According to the invention, the external diameter of the cable drum 17 is considerably smaller than in the case of conventional cable drums for electric cable window lift systems. According to the invention, the diameter of the cable drum 17 is in a range from about 22 mm to about 30 mm, more preferably in a range from about 24 mm to about 28 mm, and is even more preferably about 26 mm. According to the invention, the gear unit shown can be used both for a manual and for an electric cable window lift system both for front and for rear doors of motor vehicles.

FIG. 4 shows, in a sectional view, a gear unit according to a second embodiment of the present invention. As shown in FIG. 4, according to the second embodiment the annular seal 30 surrounds the upper edge 29 of the side wall 8 of the gear housing section 6. From the seal 30, an upper sealing lip 31 projects radially inwards and a lower sealing lip 31 projects in an essentially hook-like manner radially inwards. The seal 30 is seated on the upper edge 29 in a friction-tight manner and in a manner such that it is fixed in rotation. In the illustrated position of the worm wheel 10, the sealing lips 31 bear against the upper peripheral edge of the worm wheel 10 in order to seal the worm wheel 10 with respect to the gear housing section 6. For assembly, firstly the seal 30 can be placed on the upper edge 29 or formed there. Then, the worm wheel 10 is placed on the pivot pin 9 and pushed into the gear housing section 6 through the seal 30.

Preferably, the gear unit is produced in a two-component injection molding method. Firstly, the housing is injected into a mold using a first, relatively rigid component, then the cavity of the mold is enlarged and a second, relatively soft component is injected by means of a second injection device in order to inject all the seals (for example for sealing plug-in electronics and an electric motor (cf. FIG. 6b) and for sealing the worm wheel) onto the housing in one operation.

FIG. 5 shows, in a perspective partial section, a motor-driven gear unit for a cable window lift system as shown in FIG. 4. As shown in FIG. 5, the gear housing section 6 is located at the front end of the housing 2, which has a motor housing section 3 for fixing an electric motor (FIG. 6a) and for receiving the drive shaft 14. A number of fixing regions 4 are provided on the housing 2 for fixing the motor-driven gear unit 1 to a vehicle door. Carbon brushes and plug-in electronics which control the electric motor are pushed into the housing 2 from the side through an insertion opening 5, so that the carbon brushes bear against the commutator on the drive shaft 14. Seated at the front end of the drive shaft 14 is a drive worm (not shown) which meshes with the worm wheel 10.

On account of the considerably smaller diameter of the cable drum compared to the prior art and the correspondingly smaller gear ratio of the worm gear, according to the invention use can be made of electric motors having considerably lower maximum driving torques and a lower power output. Overall, the motor-driven gear unit 1 is thus characterized by a considerably smaller structural volume so that according to the invention a considerably smaller structural volume for accommodating the motor-driven gear unit of a cable window lift system has to be contained in a vehicle door or in a door module that is to be received by the latter.

FIGS. 6 a and 6b show, in a perspective view, an electric cable window lift system according to the invention in two different phases of its assembly. The cable window lift system 100 comprises the cable 53 which is guided in a circulatory or revolving manner and is deflected at the deflection regions 55 by means of deflection rollers 56 and the ends of which are received in the upper cable nipple receptacle 26 and the lower cable nipple receptacle of the cable drum 17. The baseplate 52 serves to fix the motor-driven gear unit 1 to the guide rail 54 and/or to a door module and/or to a door. For assembly, firstly, as shown in FIG. 6a, the cable drum 17 is placed on a pivot pin of the baseplate 52 and the two cable nipples of the cable 53 are secured in the cable nipple seats. Then, as shown in FIG. 6b, the motor-driven gear unit 1 is placed on the baseplate 52, with the electric motor 50 fixed to the housing 2, such that the claws 19, 20 of the cable drum 17 engage in the corresponding recesses of the worm wheel. The motor-driven gear unit is then connected to the baseplate 52.

FIGS. 7 a and 7b show, in a perspective view, a manual cable window lift system according to the present invention in two different phases of its assembly. According to the invention, the cable window lift system 100 is preliminarily configured in an identical manner. According to the invention, use may be made of a baseplate 52 which is identical to the baseplate of the electric cable window lift system shown in FIGS. 6a and 6b. As shown in FIG. 7a, the cable drum 17 is placed on a pivot pin of the baseplate 52 and the cable nipples of the cable 53 are secured in the associated cable nipple receptacles of the cable drum 17. As can be seen from FIG. 7a, the claw 20 of the cable drum 17 has a projection 24 so that a seat is provided for receiving the inwardly bent end 58 of the of the wrap spring or brake spring 57 shown in FIG. 7a. As shown in FIG. 7b, placed on the cable drum 17 is a cylindrical housing or brake cup 61 with a plate 62 in which the crank bolt 59 of a manual window lift system engages. The crank bolt 59 has a toothing 60 at its front end. The wrap spring or brake spring 57 is secured in the known manner.

In summary, according to the invention the following advantages can thus be achieved in particular:

• • (1) The gear unit can be used optionally for a manual or electric drive of cable window lift systems.
  • (2) The motor-driven gear unit can be used optionally for front or rear windows of motor vehicles.
  • (3) The cable drum, the baseplate and the gear housing section can be designed in an identical manner.
  • (4) Electric motors having a considerably lower maximum driving torque can be used.
  • (5) Damping elements in the gear housing, for example between the worm wheel and the cable drum, can be omitted; a conical notched toothing on the cable drum for connecting it to the worm wheel or the component bearing the damping elements is not required.
  • (6) The structural volume of a motor-driven gear unit according to the present invention is considerably smaller.
  • (7) All seals can be formed on the gear housing in one operation by means of two-component injection molding.
  • (8) An additional coverplate for covering the worm wheel accommodated in the gear housing section can be omitted.

As will be readily obvious to the person skilled in the art upon studying the present description, numerous variations and modifications can be carried out without departing from the concept and scope of protection of the present invention as defined in the appended patent claims. Such variations and modifications are therefore intended to be expressly included in the present invention.

The present application claims priority from German Patent Application no. 103 42 074.6, filed on Sep. 10, 2003, the whole contents of which are hereby explicitly incorporated by reference.

Claims

1. A gear unit for cable window lift systems of motor vehicles, comprising a drive and a gear mechanism which cooperates with the drive and is coupled to a rotatably mounted cable drum for winding and unwinding a cable of the cable window lift system, wherein a diameter of the cable drum is in a range from about 22 mm to about 30 mm and more preferably in a range from about 24 mm to about 28 mm and wherein a gear ratio of the gear mechanism is in a range from about 1:38 to about 1:55 and more preferably in a range from about 1:42 to about 1:51.

2. A gear unit as claimed in claim 1, in which the cable drum is designed such that the gear unit can be used optionally for one of an electric and a manual drive.

3. A gear unit as claimed in claim 1, in which the cable drum is designed optionally for one of a cable-operated window lift system for a front motor vehicle door and a cable-operated window lift system for a rear motor vehicle door.

4. A gear unit as claimed in claim 1, in which the cable drum is coupled directly and without the use of additional damping elements to the gear mechanism.

5. A gear unit as claimed in claim 4, in which the cable drum has on an end side at least two engagement elements which engage in a form-fitting manner in at least two counterelements on an end side of the worm wheel, said counterelements being designed to correspond to the engagement elements.

6. A gear unit as claimed in claim 5, in which the engagement elements are arranged on diametrically opposite sides of the cable drum.

7. A gear unit as claimed in claim 5, in which the engagement elements are designed as protrusions on the end side of the cable drum and the counterelements are designed as recesses on the end side of the worm wheel, said recesses being designed to correspond to the protrusions.

8. A gear unit as claimed in claim 4, in which a worm wheel of the gear mechanism is accommodated in a housing section such that a sealing means seals off the worm wheel with respect to the housing section.

9. A gear unit as claimed in claim 8, in which the sealing means surrounds an upper edge of the worm wheel.

10. A gear unit as claimed in claim 8, in which the sealing means surrounds an upper edge of the housing section.

11. A gear unit as claimed in claim 6, which is designed optionally for one of a manual and an electric drive.

12. A gear unit as claimed in claim 11, in which an engagement element has a shoulder for receiving a brake spring or wrap spring of a manual cable window lift system.

13. A gear unit as claimed in claim 11, in which provided on a housing are fixing regions for fixing the gear unit, wherein the fixing regions are identical for a manual and for a motor-driven gear unit.

14. A motor-driven gear unit for cable window lift systems of motor vehicles, comprising an electric motor which is coupled to the gear unit, wherein a driving torque of the electric motor is at most about 5.7 Nm and/or an output power of the electric motor is at most about 10 W.

15. A motor-driven gear unit as claimed in claim 14, in which the electric motor is designed both for a cable window lift system for a front motor vehicle door and for a cable window lift system for a rear motor vehicle door.