Title:
Roll-up window shade with reduced-friction drive
Kind Code:
A1


Abstract:
Two drive gears are provided as an extension of the guide rails for driving a roll-up window shade for a motor vehicle. The drive gears are coupled to the winding shaft in a rotationally elastic manner. The driving is carried out via a geared motor, which acts either on the gears or on the winding shaft. The positioning of the drive gears as an extension of the guide rails avoids the guide tubes used in prior art arrangements. Thus, the friction losses found in the prior art, which consume up to 80% of the drive force, are avoided. Furthermore, manufacturing is simplified because the connection tubes having a complicated shape are not needed.



Inventors:
Hansen, Melf (Gondelsheim, DE)
Stark, Wolfgang (Denkendorf, DE)
Application Number:
11/904589
Publication Date:
03/27/2008
Filing Date:
09/27/2007
Assignee:
BOS GmbH & Co. KG (Ostfildern, DE)
Primary Class:
International Classes:
B60J1/20
View Patent Images:
Related US Applications:
20040003903Extruded rigid plastic storm shutter slat having a co-extruded rigid foam coreJanuary, 2004Wenrick et al.
20060196617Sound absorbing composite blind systemsSeptember, 2006Barkman et al.
20070277938Portal covering for controlled environmentsDecember, 2007Crider
20090294077Easy access hanging structure for window origami panelsDecember, 2009Zimmer
20070012411Tensioning sheet materialJanuary, 2007Weight
20080202005DECORATIVE DECAL SYSTEM ON LOUVERED BLINDSAugust, 2008Floyd et al.
20070277935CURTAINDecember, 2007Lin
20060289122Multi-stage window coveringDecember, 2006Lin
20080302290Membrane Body and Relative Production MethodDecember, 2008Molta et al.
20090038762CORD FIXER FOR VENETIAN BLINDFebruary, 2009Hsieh
20080230188Doorway screening apparatusSeptember, 2008Albert



Primary Examiner:
JOHNSON, BLAIR M
Attorney, Agent or Firm:
LEYDIG VOIT & MAYER, LTD (CHICAGO, IL, US)
Claims:
1. A roll-up window shade for motor vehicles comprising: a rotatably supported winding shaft; a shade having a first edge affixed to the winding shaft; a tension rod connected to a second edge of the shade spaced away from the winding shaft; two guide rails each extending on a respective side of the shade when the shade is an extended position, the two guide rails guide the tension rod in a positive-locking manner; two push elements each being conducted in a respective one of the guide rails, each push element carrying a gear-tooth system that acts on the tension rod; two drive gears arranged at first and second ends of the winding shaft, each drive gear being allocated to a respective one of the push elements, wherein the push elements are operatively arranged between the drive wheels and the tension rod; an electric drive motor; and a spring compensating element for compensating for differences in the length of the shade as it is extended as compared to the corresponding length of travel of the push elements in the guide rails.

2. The roll-up window shade according to claim 1, wherein the tension rod is configured so that its length is selectively variable.

3. The roll-up window shade according to claim 1, wherein a first end of the each of the guide rails is arranged in the vicinity of the winding shaft.

4. The roll-up window shade according to claim 1, wherein the guide rails extend parallel to one another.

5. The roll-up window shade according to claim 1, wherein each guide rail contains a guide groove.

6. The roll-up window shade according to claim 5, wherein the guide groove has a cross sectional configuration including a groove chamber and a groove slit, a diameter of the groove chamber being larger than an inside width of the slit so as to define an undercut guide groove.

7. The roll-up window shade according to claim 6, wherein each push element is conducted in a buckle-resistant manner in the respective groove chamber.

8. The roll-up window shade according to claim 1, wherein the gear tooth system of each push element extends around the push element.

9. The roll-up window shade according to claim 1, wherein each drive gear is a front gear.

10. The roll-up window shade according to claim 1, wherein each of the drive gears is connected to the winding shaft.

11. The roll-up window shade according to claim 1, wherein each of the drive gears is arranged coaxial relative to a rotational axis of the winding shaft.

12. The roll-up window shade according to claim 1, wherein the two drive gears are seated on a connection shaft which is conducted through the winding shaft.

13. The roll-up window shade according to claim 1, wherein the two drive gears are seated on a connection shaft which runs parallel to the winding shaft.

14. The roll-up window shade according to claim 1, wherein the electric drive motor is coupled to the winding shaft.

15. The roll-up window shade according to claim 12, wherein the electric drive motor is coupled to the connection shaft.

16. The roll-up window shade according to claim 13, wherein the electric drive motor is coupled to the connection shaft.

17. The roll-up window shade according to claim 12, wherein the spring compensating element is located between the connection shaft and the winding shaft and the drive gears are connected to the connection shaft without rotational play.

18. The roll-up window shade according to claim 13, wherein the spring compensating element is located between the connection shaft and the winding shaft and the drive gears are connected to the connection shaft without rotational play.

19. The roll-up window shade according to claim 13, wherein a gear pair is provided with one of the gear pair being coupled to the winding shaft and the other of the gear pair being coupled to the connection shaft.

20. The roll-up window shade according to claim 1, wherein the spring compensating element comprises a coil spring.

21. The roll-up window shade according to claim 1, wherein the spring compensating element comprises a spiral spring.

22. The roll-up window shade according to claim 21, wherein the spiral spring is seated in a recess of one of the drive gears.

23. The roll-up window shade according to claim 13, wherein the spring compensating element comprises two springs, one of the two springs being located between one of the drive gears and the connection shaft.

24. The roll-up window shade according to claim 1, wherein the spring compensating element comprises two springs, one of the two springs being located between the winding shaft and a corresponding one of the drive gears.

25. The roll-up window shade according to claim 1, wherein the spring compensating element comprises two springs, one of the two springs being located between the tension rod and one of the push elements and the other of the two springs being located between the tension rod and the other push element.

26. The roll-up window shade according to claim 25, wherein the springs are compression springs.

27. The roll-up window shade according to claim 1, wherein each push element has an associated engagement mechanism for keeping the respective push element engaged with its associated drive gear.

28. The roll-up window shade according to claim 1, where a separate gear housing is provided for each drive gear.

29. The roll-up window shade according to claim 1, wherein each push element has a corresponding storage tube for receiving an empty rail of the push element when the shade is in a retracted position.

30. The roll-up window shade according to claim 29, wherein each storage tube is made of a flexible material.

Description:

FIELD OF THE INVENTION

This invention relates to roll-up window shades for motor vehicles.

BACKGROUND OF THE INVENTION

Electrically driven rear window roll-up shades are known from the prior art. These prior art roll-up window shades have a winding shaft that is pivotably supported below the rear shelf and on which one edge of the shade is affixed. The other edge of the shade is connected to a tension rod that is guided at its end by guide rails. The guide rails are arranged next to the lateral edges of the rear window and extend from the rear shelf or below it to the vicinity of the upper edge of the window. In order to pretension the shade, there is generally a spring motor in the winding shaft or next to it. This motor biases the winding shaft in the shade wind-up direction.

The unwinding or unfolding of the shade is carried out with the aid of linear push elements that run in a buckle resistant manner in the groove or slot chamber of the guide rails. A common gear motor is provided next to the winding shaft approximately at the level of its center. Guide tubes are provided in order to connect the gear motor to the lower ends of the guide rails. The guide tubes end at the gear housing of the geared motor. With the aid of these guide tubes, the push elements are conducted in a buckle-proof manner between the drive motor and the guide rails, so that they can carry out the pushing function.

Since the motor sits relatively close to the winding shaft because of space considerations, the guide tubes run more or less parallel to the winding shaft in the vicinity of the geared motor and must be deflected in the guide rails in a direction perpendicular to the winding shaft. In turn, for space considerations, the radius of curvature of the guide tubes next to the point where they lead into the guide rails is relatively very narrow.

Actual practice shows that with such shades, the push elements in the guide tubes consume the majority of the drive force produced by the motor. Only a comparatively small fraction of the drive force is actually needed to extend the shade.

The guide tubes generally have a relatively complicated, three-dimensional shape. As a result, their production and their adaptation to motor vehicle conditions are difficult.

In addition, the push elements must also be protected in the section that lies behind the motor relative to the line of sight. The length of this part of the push element, which projects above the motor, depends on the distance the shade extends. The push element projects least when the shade is extended, whereas the projection is greatest when the shade is completely retracted. Since the travel is usually greater than half the width of the winding shaft, the storage tube taking up the excess part must also be adapted in a complicated three-dimensional manner to the available space in the motor vehicle. Thus, not only is the manufacturing of the roll-up window shade cumbersome, it also is difficult to install in a motor vehicle.

The problems with known designs have been described in the context of a rear window roll-up shade. Similar problems are found with roll-up window shades for sunroofs, which are driven in a comparable manner. The high friction losses of the push elements in the guide and storage tubes also create complications with regard to the design and dimensioning of an electric-based pinch protection system, which is based on the measurement of the motor current. Depending on the magnitude of the friction losses, more or less force may be available at the given interruption current to catch or pinch body parts.

OBJECTS AND SUMMARY OF THE INVENTION

In view of the foregoing, a general object of the present invention is to provide a roll-up window shade for motor vehicles having a drive with lower friction losses.

The roll-up window shade of the invention includes a rotatably supported winding shaft. In the usual manner, one edge of the shade is affixed to this winding shaft. The other edge of the shade is connected to a tension rod, the ends of which run in guide rails. The guide rails extend on both sides of the extended shade and define the path which the tension rod travels between the retracted and extended positions of the shade.

The drive of the tension rod operates with the aid of two push elements. Each of the push elements is conducted by a corresponding guide rail. The ends of the two push elements act on the tension rod, so as to be able to move the tension rod away from the winding shaft.

Each push element is provided with its own drive gear. The drive gear can be provided adjacent the foot end of the guide rail—i.e., in the vicinity of the winding shaft. Thus, a substantial piece of guide tube between the foot end of the guide rail and the drive gear can be omitted. The push element exiting from the individual guide rail can run substantially directly into a gear housing that is arranged adjacent to the foot end of the guide rail. In this way, it is possible to reduce the cost of the connection tube.

Reducing the cost of the connection tube enables the drive force to be saved in two ways. First, the drive force which is required to move the corresponding length of push element through a perhaps even straight-running guide tube can be omitted. Second, the friction force is minimized because the connection tube does not have a curved shape, which caused the push element to encounter increased friction in the connection tube. As a result, the drive force supplied by the motor is essentially entirely available for moving the shade. The friction force produced by the push elements in the guide rails is comparatively small because the guide rails run almost straight.

An electrical drive motor is provided for driving the shade. The drive motor simultaneously produces the force which is needed to wind up the shade during the retraction on the winding shaft and to move back the push elements.

Additionally, a compensation mechanism is provided to compensate for the length difference between the advance movement of the shade and the push element. The push element runs over a drive gear, whose diameter is constant. Thus, for each turn of the drive gear, the same length of the push element is always moved. The situation is different with the shade. The shade forms a spiral-shaped roll on the winding shaft. When the shade is unwound, the effective diameter of the roll, and thus the quantity of shade that is drawn from the winding shaft per turn, changes. The length difference is not excessively large but must be controlled. This is where the compensation mechanism is used. The compensation mechanism produces the cloth tension on the shade.

Since a three-dimensional deflection of the push element does not occur with the present invention, a push element that has a gear-tooth system only on one side can be used. Alternatively, a push element that has a gear-tooth system all around can be used. The all-around gear-tooth system enables positioning of the push element in the guide rail via a kind of helical movement. Due to this helical movement, the push element is “turned past,” so to speak, the fixed drive gear.

Depending on the vehicle body conditions, the push elements can either run freely in the vehicle body or can run in storage tubes that are made of a flexible material. The storage tubes can be placed anywhere in the automobile body and do not have to be pre-shaped by the manufacturer of the roll-up window shade.

Very simple drive conditions can be produced if the drive motor is coupled via gears directly to the winding shaft. With such an arrangement, either the drive gears are coupled in an elastically rotating manner with the winding shaft, or they sit on a connection shaft that is conducted through or runs over the winding shaft. Use of a separate connection shaft also allows the gears to fixed on the connection shaft without rotational play and the connection shaft to be coupled to the winding shaft in a rotationally elastic manner. When using a separate connection shaft, it is also possible to drive the connection shaft via the motor.

The elastic elements which bring about the rotation compensation can be coil springs or spiral springs, similar to the mainspring of a watch. The spiral spring can be accommodated in the drive gear and in particular in a pocket-shaped extension in the drive gear. The rotating parts can be coupled rigidly and inelastically with one another and the compensation can be produced by placing a compression spring between the tension rod and the push element associated the pertinent end of the tension rod.

The length of the tension rod can vary in accordance with the geometry of the window.

In order to conduct the push elements in a bend-resistant manner, the use of guide rails that contain an undercut guide groove is advantageous. The undercut guide groove is composed of in cross-section of a groove chamber and a groove slit.

The following description of the figures is limited to an explanation of the aspects necessary to understand the invention. A number of modifications are clearly possible. As will be appreciated, one of skill in the art will understand the less important details that are not described in the drawings.

The following drawings are not necessarily to scale. For instance, to promote a better understanding of the invention it may be that certain areas have been enlarged. Moreover, the drawings are schematic in nature and do not contain every detail which may be present.

Exemplary embodiments of the invention are shown in the drawings.

Other objects and advantages of the invention will become apparent upon reading the following detailed description and upon reference to the drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partially cutaway perspective view of the rear passenger compartment of an exemplary motor vehicle equipped with a roll-up window shade according to the present invention.

FIG. 2 is a partially cutaway front view of the roll-up window shade of FIG. 1.

FIG. 3 is a schematic exploded perspective view of the connection between one of the drive gears and the winding shaft of the window roll-up shade of FIG. 1.

FIG. 4 is a partially cutaway front view of an alternative embodiment of a roll-up window shade according to the present invention in which the drive gears are arranged on the connection shaft without rotational play.

FIG. 5 is a partially cutaway front view of an alternative embodiment of a roll-up window shade according to the present invention in which the connection shaft runs coaxially through the winding shaft.

FIG. 6 is a partially cutaway plan view of an alternative embodiment of a roll-up window shade according to the present invention in which the compensation of the shade is accomplished with the aid of compression springs.

While the invention is susceptible of various modifications and alternative constructions, a certain illustrative embodiment thereof has been shown in the drawings and will be described below in detail. It should be understood, however, that there is no intention to limit the invention to the specific form disclosed, but on the contrary, the intention is to cover all modifications, alternative constructions, and equivalents falling within the spirit and scope of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1 of the drawings, the rear passenger compartment of a an exemplary motor vehicle is shown. The right interior side is shown in FIG. 1. The right side is the mirror image of the left interior side. Unless otherwise indicated, the explanations for the right automobile body side are also apply to the left automobile body side. The depiction in FIG. 1 is simplified; thus, for example, automobile body interior structures, such as the reinforcements, affixing elements are not shown since they are not necessary for an understanding of the invention.

The illustrated automobile body section 1 has a roof 2. A C column 3 leads downwards from a side of the roof to a car bottom assembly. A corresponding C column can also be provided on the opposite side of the motor vehicles. In this case, the interior side of the C column 3 is provided with a lining 4. A rear window 5 extends downward from the rear edge of the roof 2. The rear window 5 is bound on the upper side by a window upper edge 6. The side edges 7 of the windows extend toward each other. The side edge 7 shown in FIG. 1 extends into a corner area 8 into the window upper edge 6.

The width of the rear window 5 is greater at the level of the beltline of the automobile body than in the area of the window upper edge 6. A B column 9 is provided at a distance in front of the C column 3. A rear right-side door 11 is hinged to the B column in a known manner. The right rear-side door 11 contains a window section 12, which is divided up by a vertical brace 13 into a substantially rectangular section 14 and an approximately triangular section 15. The interior of the vehicle further includes a back seat bench 15, with a back seat area 16 and a back seat back 17. The back seat area 17 lies on a floor assembly 18. A rear shelf 19 extends between the upper rear edge of the back seat back 17 and the rear window 5.

In accordance with the invention, the rear window 5 is provided with a rear window roll-up shade 21 of which only the shade 22 is shown in FIG. 1. Other window shades are provided for the side window 12. Specifically, a shade 23 is provided for the rectangular window section 14 and a shade 24 is provided for the triangular section 15. The drive for the shades 23 and 24 is the same as the drive for the rear window shade 21. Accordingly, only the structure of the drive for the rear window shade will be described in detail herein.

As shown in FIG. 2, the rear window shade 21 includes two guide rails 25 and 26 and a drive system 27. The guide rails 25 and 26 are arranged in a mirror image to one another and follow the side edge of the rear window 5. Unlike as shown in FIG. 2, the guide rails 25 and 26 converge as they extend in the direction of the roof 2.

Since the two guide rails 25 and 26 are identical, a description of the interior structure of the guide rail 26 is sufficient for an understanding of the invention. Such description is also applies for the guide rail 25. In the guide rail 26, an undercut guide groove 27 is provided. The profile of the undercut guide groove 27 is composed of a groove chamber 28 and a groove slit 29. The width of the slit 29 is smaller than the inside width of the groove chamber 28, wherein the undercut structure is produced.

The two guide rails 25 and 26 conduct a tension rod 31 on which one edge of the shade 22 is affixed. The tension rod 31 includes a middle piece in which two end pieces 32 and 33 are supported in a telescoping manner. The middle piece can sit in a hose-like loop formed on the shade 22. Each of the end pieces 32 and 33 has a telescoping rod 34 with a slide piece 35 sitting on its free end. The telescoping rod 34 has cross-sectional dimensions in that enable it to be conducted through the slit 29 with clearance. The cross-sectional configuration of the slide piece 35 is adapted to the cross-sectional configuration of the groove chamber 28, which can be, for example, circular. The end of the shade 22 opposite the tension rod 31 is affixed to a winding shaft 36.

The drive device 27 is used to move the shade 22 between an extended position in which it is extended over the rear window 5 and a retracted position in which the tension rod 31 either lies on the rear shelf 19 or is retracted into the slit provided in the rear shelf. The drive device 25 includes two identical linear flexible push elements 38 and 39. Each of the push elements 38, 39 includes a core 41 having a circular cross section and a coil 42 that is affixed on the outside of the circular core 41. This produces a kind of elastically flexible toothed rack with teeth all around. The outside diameter of the push elements 38, 39 corresponds to the inside width of the groove chamber 28. In this way, the two push elements 38, 39 are conducted in their corresponding guide rails 25 and 26 in a buckle-free manner and can transfer compression forces. The diameter of the push elements is larger than the slit width 29 so that they cannot be buckled laterally through the slit 29 even with compression stress.

The drive device 27 further includes a geared motor 43 whose outlet shaft 44 is rigidly connected to the axle pins 45 of the winding shaft 36. A spur gear 47 or 48 sits on the two shaft journals 45 and 46. The spur gear is provided with a gear-tooth system on its circumferential surface that permits a positive-locking meshing with the corresponding push element 38, 39. The two push elements 38, 39 are pressed in a radial direction against the corresponding drive gear 47, 48, so that the engagement is consistently maintained. The push elements 38, 39 lie on the same side relative to the axis of rotation of the corresponding drive gear 47, 48 on which the shade 22 is extended from the winding shaft 36.

The gear 47 is rotatably supported on the shaft journal 45 and the gear 48 is rotatably supported on the shaft journal 46. The operative drive connection, via which a driving torque is transferred, is shown in FIG. 3. The details shown in FIG. 3 apply for both drive gears 47 and 48.

The drive gear 47 has a disk-like shape with a cylindrical circumferential surface area 50 in which grooves 51 comprise the gear tooth system. The grooves 51 run at an incline and take up the pertinent section of the coil 42. The gear 47 includes an extension 52 coaxial to the outside circumferential area 50. A bearing borehole 53 is contained concentrically in the extension 52 that enables the gear 47 to be rotatably supported on the shaft journal 45. In this case, the extensions 52 each comprise a spring housing for a spiral spring 54 that produces a rotationally elastic connection between the shaft journal 45 and the gear 57. In this respect, the shaft journal 45 includes a turned-up lip 46 at the corresponding location, which is used as an abutment for an opening 47 provided on the inner spring end. The outside spring end also has an opening 48, which can be connected, in a positive-locking manner, with a lip 49. The lip 49 points radially inwardly from the outside circumferential area of the extension 52.

As can be understood from the operational description below, a relative rotation with respect to the winding shaft 36 is achieved via a corresponding dimensioning of the effective diameter of the gear 47 relative to the roll body that is formed on the winding shaft 36 by the wound shade 22. The dimension of this relative rotation is approximately and at most one rotation. In this way, a spiral spring 54 which has a relatively short effective path can be used.

The figures are not to scale and are intended to illustrate the important features of the drive concept according to the invention. The pertinent dimensions of the guide rails 25 and 26 and the outside diameter of the two elastic, pliable push elements 38, 39 can be readily determined from actual practice.

An elastically flexible storage tube 61 or 62 is arranged on the opposite side of the pertinent gear 47, 48 from the individual guide rails 25, 26. To a large extent, the storage tubes 61, 62 can be placed freely in the motor vehicle in accordance with the spatial conditions. A description of the measures which are taken in order to keep the storage tubes 61 and 62 stationary is not necessary for the understanding of the invention. Additionally, a housing may be provided to surround the gear 47 or 48. The housing can contain a corresponding tangential borehole for the passage of the pertinent flexibly-elastic push element 38, 39.

The operation of the illustrated embodiment is as follows. It is assumed that initially the shade 22 is completely (i.e., as much as possible) wound on the winding shaft 36. When wound, the spiral springs 54 contained in the two gears 47, 48 are slightly biased. As a result of the bias, the push elements 38 and 39, meshed and thus coupled in a positive-locking manner are elastically biased in the direction of the two slide pieces 35 of the tension rod 31 and fit snugly there. The bias force of the spiral springs 54 holds the shade 22 between the winding shaft 36 and the tension rod 31 so that it is taut.

Beginning from this position, if a user wishes to extend the rear window roll-up shade 21, he starts the geared motor 43 with an electric switch. The running geared motor 43 turns the winding shaft 36, together with the two shaft journals 45 and 46, which are coupled without rotational play, in the unwinding direction of the shade 22. The two drive gears 47 and 48 move in the same direction of rotation. Since their effective diameter coincides with the outside diameter of the roll body on the winding shaft 36 when the shade 22 is completely wound (i.e., with the window shade opened), the two push elements 38 and 39 first move at exactly the same speed as the tension rod 31 at the movable front edge of the shade 22.

As the shade 22 is increasingly unwound, the roll body on the winding shaft decreases in size. Consequently, less shade is released per rotation of the winding shaft 36 than the two elastically flexible but shear-resistant push elements 38, 39 would traverse with a rigid coupling and at the same angular rotation. As a result of the rigid coupling with the shade 22, the push elements 38, 39 are forced to move at the same speed as the shade 22, which as a result leads to the slowing down of the rotational movement of the two drive gears 47 and 48 as compared to the rotational movement of the winding shaft 36. In this way, the spiral spring 54 is substantially wound up in a manner similar to the mainspring of a watch. However, depending on the dimensions and the length of the shade has extended, the extent of the relative rotation is limited to approximately one rotation between the winding shaft 36 and the drive gear 47 or 48. At the end of the extension movement, when the tension rod 21 has arrived at the upper edge of the window, the cloth tension in the shade 22 will thus be somewhat greater than at the beginning.

The retraction of the shade is carried out analogously in the reverse direction, wherein the two spiral springs 54 once again relax by the corresponding extent. At the end of the retraction movement, the tension rod 31 is again on the rear shelf 19 and the remaining residual tension in the two spiral springs 54 provides the required cloth tension in the shade 22. Since the spiral springs 54 have identical dimensions, the same forces also act on the tension rod 31 on both ends.

As a result of the illustrated arrangement, the two shaft journals 45 and 46 that are coupled rigidly to the geared motor 43 move at the same rotational speed and thus produce the same drive effect for the two drive gears 47 and 48. Furthermore, the push elements 38 and 39 now move in an essentially stretched state. Since the drive effect is introduced right at the foot end of the two guide rails 25 and 26, complex deflections are not required to bring the two push elements 38, 39 to one common drive source. Each push element 38, 39 has its own drive source, which is arranged in such a manner that a minimal deflection of the push element 38, 39 from the completely stretched, straight condition is required. In this way, the friction is enormously reduced, compared with the arrangements found in the prior art. Also the storage tubes 61 and 62 move primarily in a straight line, and since they are flexible, they can be placed in the motor vehicle in any manner.

The force which must be produced by the motor 43 corresponds to the force which is required to further wind up the two spiral springs 54 with the rotational travel, in comparison with the winding shaft 36, as well as the very small friction to which the two push elements 38, 39 are subjected. This friction is very small since the two guide rails 25, 26 move primarily in a straight line. The radius of curvature is also extremely large at the most narrow location.

The illustrated embodiment is a fundamental arrangement. The illustrated motor 43 is a geared motor that acts on the outside end of the shaft journal 45 so that the drive gear 47 is located between the winding shaft 36 and the geared motor 43. Those skilled in the art will readily appreciate that the drive can also be introduced at the shaft journal 45 between the drive gear 39 and the winding shaft 36.

In the embodiment of FIG. 2, each drive gear 47, 48 is coupled by itself in a rotationally elastic manner. An embodiment in which the two drive gears 47 and 48 are seated on a connection shaft 65 is shown in FIG. 4. The connection shaft 65 moves like a bearing axle through the tube-shaped winding shaft 36 as shown in the cut away portion of FIG. 4. The other end of the connection shaft 65 is in turn coupled without rotational play to the outlet shaft 44 of the geared motor 43.

The diameter of the connection shaft 65 is clearly smaller than the inside width of the tube-shaped winding shaft 36. An annular space 66 is produced in which a coil spring 67 is located. The coil spring is anchored at one end in a bearing ring 68 that is coupled to the connection shaft 65 without rotational play via a pin 69. The pertinent end of the winding shaft 36 is supported on the bearing ring 68. The other end of the coil spring 67 is connected without rotational play to a ring piece 71, which in turn is also connected without rotational play to the winding shaft 36 with the aid, for example, of reinforcing seams 72. The other end of the winding shaft 36 is supported, with little clearance, on the connection shaft 65. Otherwise, the structure of this rear window roll-up shade 21 is not different from the rear window roll-up shade 21 of FIGS. 2 and 3.

The relative rotation between the winding shaft 36 and the drive gears 47 and 48 required during operation is brought about here via a coil spring 67, which produces the rotationally elastic connection between the connection shaft 65 and the winding shaft 36. Otherwise, the operation is also the same as the embodiment of FIGS. 2 and 3.

An arrangement in which the connection shaft 65 does not pass coaxially through the tube-shaped winding shaft 36, as in the embodiment of FIG. 4, but rather is located parallel to and next to it is shown in FIG. 5. The two gears 47 and 48 sit on the connection shaft 65—again in such a way that they, as with all the illustrated embodiment, are largely aligned with an extension of the guide rails 25, 26, so as to produce a minimal deflection of the push elements 38, 39 and thereby the friction forces remain small. A gear 75, which meshes with a front gear 76 located on the shaft journal 65, is seated on the connection shaft 65.

In the embodiment of FIG. 5, there are several possibilities of compensating for the rotation between the drive gears 47 and 48 and the winding shaft 36. First, the two gears 47 and 48 could be coupled with the connection shaft 65, in a rotationally elastic manner, as with the embodiment of FIGS. 2 and 3. In that embodiment, the drive gears 47 and 48 are rotationally elastically connected to the bearing journals 45 and 46, which in turn are coupled to the winding shaft 36 without rotational play. Another possibility for attaining the required rotation compensation is by coupling the front gear 76 in a rotationally elastic manner to the shaft journal 65, as in the embodiment of FIG. 3.

Instead of accommodating the rotationally elastic coupling in the front gear 76, the rotationally elastic coupling can also be carried out between the gear 75 and the connection shaft 65. In each case, the operation is described as above. The advantages explained in this connection are also attained.

An alternative embodiment as to how the travel path difference between the front edges of the shade 22 and the push elements 38, 39 can be controlled is shown in FIG. 6. The basic structure of the shade 21, according to FIG. 6, corresponds to the structure shown in FIG. 2. However, the two drive gears 47 and 48 are seated on the shaft journals 45 and 46 without rotational play, so that in this case a relative rotation between the winding shaft 36 and the two drive gears 47 and 48 is possible. The travel path difference is controlled with the aid of compression springs 79. The cutaway part of the guide rail 26 in Fig. shows how the coil compression spring 79 is inserted between the free end of the push element 39 and the slide piece 35. The dimensions are selected such that the compression spring 79, which is supported on the free end of the push element 39, constantly exerts a pre-push force on the tension rod 31. The compression spring 79 exhibits the largest length when the shade 22 is wound on the winding shaft 36. When the winding shaft 36 together with the two gears 47 and 48 are rotated by the geared motor 43, the tension rod 31 begins to slow increasingly down, as compared with the free ends of the two push elements 38, 39. In this way, the compression springs 79 contained in the two guide rails 25 and 26 are increasingly compressed. Since the two drive gears 47 and 48 are located directly below the lower end of the two guide rails 25 and 26, connection tubes for a common drive gear are avoided, and correspondingly, the friction loss is reduced.

Those skilled in the art will appreciate that the drive concept for shades explained above in connection with FIGS. 2-6, is not limited to use with rear window roll-up shades. This drive concept can also be used in connection with other type of shades, for example, side roll-up window shades for the rectangular window section 14 of the rear side door or with a sunroof roll-up window shade.

Two drive gears are provided as an extension of the guide rails for driving a roll-up window shade for a motor vehicle. The drive gears are coupled to the winding shaft in a rotationally elastic manner. The driving is carried out via a geared motor, which acts either on the gears or on the winding shaft. The positioning of the drive gears as an extension of the guide rails avoids the guide tubes used in prior art arrangements. Thus, the friction losses found in the prior art, which consume up to 80% of the drive force, are avoided. Furthermore, manufacturing is simplified because the connection tubes having a complicated shape are not needed.