Adjusting device for adjusting a vehicle seat along a sliding axis

Abstract

An adjusting device for adjusting a vehicle seat along a sliding axis, having a first and a second lower rail, both of which are fixedly connected with the vehicle, a first upper rail, which is slidably supported in the first lower rail in parallel to the sliding axis and a second upper rail, which is slidably supported in the second lower rail in parallel to the sliding axis. The first lower rail and the first upper rail can enclose a first cavity and the second lower rail and the second upper rail enclose a second cavity. A first spindle can be arranged in the first cavity and non-rotatably connected to the first lower rail and a second spindle can be arranged in the second cavity and non-rotatably connected to the second lower rail.

Claims

1. An adjusting device for adjusting a vehicle seat along a sliding axis, comprising: a first lower rail, which is fixedly connected with a vehicle and a second lower rail, which is fixedly connected with the vehicle, a first upper rail, which is slidably supported in the first lower rail in parallel to a sliding axis and a second upper rail, which is slidably supported in the second lower rail in parallel to the sliding axis, wherein the first lower rail and the first upper rail enclose a first cavity and the second lower rail and the second upper rail enclose a second cavity, a first spindle arranged in the first cavity and rotatably supported around a first rotation axis and a second spindle arranged in the second cavity and rotatably supported around a second rotation axis, a first spindle nut interacting with the first spindle and at least partially arranged within the first cavity and fixedly connected with the first upper rail and a second spindle nut, interacting with the second spindle and at least partially arranged within the second cavity and fixedly connected with the second upper rail; a first drive motor, which is operatively connected, on a driven side, with the first spindle for driving the first spindle; and a second drive motor, which is operatively connected, on the driven side, with the second spindle, for driving the second spindle.

2. The adjusting device of claim 1, wherein the first drive motor comprises a first driven shaft and the second drive motor comprises a second driven shaft; and wherein the first driven shaft is aligned with the first rotation axis and the second driven shaft is aligned with second rotation axis.

3. The adjusting device of claim 1, wherein the adjusting device comprises: a first gear, which is operatively connected, on a drive side, to the first drive motor for driving the first spindle and which is operatively connected, on the driven side, to the first spindle, and a second gear, which is operatively connected, on the drive side, to the second drive motor for driving the second spindle and which is operatively connected, on the driven side, to the second spindle.

4. The adjusting device of claim 3, wherein the first gear is formed as a first planetary gear and the second gear is formed as a second planetary gear.

5. The adjusting device of claim 4, wherein the first planetary gear, the second planetary gear, or both, are formed as a helical planetary gear.

6. An adjusting device for adjusting a vehicle seat along a sliding axis, comprising: a first lower rail, which is fixedly connected with the vehicle and a second lower rail, which is fixedly connected with the vehicle, a first upper rail, which is slidably supported in the first lower rail in parallel to the sliding axis and a second upper rail, which is slidably supported in the second lower rail in parallel to the sliding axis, wherein the first lower rail and the first upper rail enclose a first cavity and the second lower rail and the second upper rail enclose a second cavity, a first spindle arranged in the first cavity and non-rotatably connected to the first lower rail and a second spindle arranged in the second cavity and non-rotatably connected to the second lower rail, a first gear interacting with the first spindle and at least partially arranged in the first cavity and which is fixedly connected with the first upper rail and a second gear interacting with the second spindle and at least partially arranged within the second cavity and which is fixedly connected with the second upper rail, a drive motor arranged between the first upper rail and the second upper rail, a drive train extending between the drive motor and the first gear and between the drive motor and the second gear, wherein the drive motor is offset, by a distance relative to the sliding axis to the first gear and to the second gear and the drive train comprises connecting element for bridging the distance.

7. The adjusting device of claim 6, wherein the connecting element comprises a flexible first drive shaft and a flexible second drive shaft.

8. The adjusting device of claim 6, wherein the first gear and the second gear are formed by a respective worm gear.

9. The adjusting device of claim 8, wherein the worm gear comprises a worm with a worm axis and a worm wheel having a worm wheel axis, wherein the worm axis and the worm wheel axis form an axis angle which is less than 90 degrees.

10. The adjusting device of claim 9, wherein the first gear and the second gear are formed as a respective spur gear.

11. The adjusting device of claim 6, wherein the connecting element comprises a first belt gear and a second belt gear.

12. The adjusting device of claim 6, wherein the connecting element comprises a flexible first drive shaft and a flexible second drive shaft, wherein the first belt gear has, on the drive side, a first drive wheel which is connected to the first drive shaft and on a driven side, a first driven wheel, which is configured as a first spindle nut interacting with the first spindle, and the second belt gear has, on the drive side, a second drive wheel which is connected to the second drive shaft and on the driven side, a second driven wheel, which is configured as a second spindle nut interacting with the second spindle.

13. The adjusting device of claim 11, wherein the drive train comprises a first drive shaft and a second drive shaft, wherein the first gear is configured as a first worm gear and the second gear is configured as a second worm gear, wherein the first belt gear comprises, on the drive side, a first drive wheel connected to the first drive shaft and on the driven side, a first driven wheel interacting with the first worm gear and wherein the second belt gear comprises, on the drive side, a second drive wheel connected to the second drive shaft and, on the driven side, a second driven wheel interacting with the second worm gear.

14. The adjusting device of claim 6, wherein the drive train, the first and the second gear and the first and the second spindle are provided in such a way that between torque provided by the drive motor and torque applied to spindles, a total transmission ratio from 6 to 7 is applied, wherein the first and the second spindle have a thread pitch, which is reduced or increased with respect to a normal thread pitch and wherein the drive train, the first and the second gear, or both, are adapted to a reduced or increased thread pitch in such a way that the total transmission ratio is preserved.

15. The adjusting device of claim 6, wherein the drive train, the first and the second gear and the first and the second spindle are provided in such a way that between torque provided by the drive motor and torque applied to spindles a total transmission ratio from 6 to 7 is applied, wherein the drive train comprises a further motorized worm gear, and the first and the second spindle, the first and the second gear, or both are adapted to the further gear in such a way that the total transmission ratio is preserved.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0039] Exemplary embodiments of the present disclosure are explained in the following with reference to the annexed drawings. In particular:

[0040] FIG. 1 shows a perspective illustration of an adjusting device known in the art,

[0041] FIG. 2A shows a schematic plan view of an adjusting device known in the art,

[0042] FIG. 2B shows a separate schematic view of a worm gear, which is used in the adjusting device of FIG. 2A,

[0043] FIG. 3 shows a first example of a proposed adjusting device based on a schematic plan view,

[0044] FIG. 4 shows a second example of a proposed adjusting device based on a schematic plan view,

[0045] FIG. 5A shows a partially cut-out view through a helical planetary gear,

[0046] FIG. 5B shows a perspective view of the helical planetary gear of FIG. 5A,

[0047] FIG. 6A shows a third example of a proposed adjusting device based on a schematic plan view,

[0048] FIG. 6B shows the first worm gear shown in FIG. 6A based on a schematic separate illustration,

[0049] FIG. 7 shows a fourth example of a proposed adjusting device based on a schematic plan view,

[0050] FIG. 8 shows a fifth example of a proposed adjusting device based on a schematic plan view,

[0051] FIG. 9 shows a sixth example of a proposed adjusting device based on a schematic plan view, and

[0052] FIG. 10 shows a seventh example of a proposed adjusting device based on a schematic plan view.

DETAILED DESCRIPTION

[0053] In FIG. 1 a known adjusting device 10P for longitudinal seat adjustment of a vehicle seat, not shown, is illustrated, in perspective, along a sliding axis L, wherein the sliding axis L approximately coincides with the longitudinal axis of the vehicle, which is also not shown.

[0054] The adjusting device 10P has a first lower rail 12.sub.1 fixedly connected with the vehicle, and a second lower rail 12.sub.2 fixedly connected with the vehicle, wherein in FIG. 1 only the first lower rail 12.sub.1 is shown. The lower rails 12.sub.1, 12.sub.2 may be fixed to the floor of the vehicle passenger compartment. The adjusting device 10P also has a first upper rail 14.sub.1 which is slidably supported within the first lower rail 12.sub.1 in parallel to the sliding axis L and a second upper rail 14.sub.2 which is slidably supported within the second lower rail 12.sub.2 in parallel to the sliding axis L, wherein also in this case only the first upper rail 14.sub.1 is shown. The upper rails 14.sub.1, 14.sub.2 slide directly or via adjusting and/or supporting elements, not shown, on the lower rails 12.sub.1, 12.sub.2. A vehicle seat, not shown, is secured to both upper rails 14.sub.1, 14.sub.2.

[0055] In the mounted state, the first lower rail 12.sub.1 and the first upper rail 14.sub.1 enclose a first cavity 16.sub.1 and the second lower rail 12.sub.2 and the second upper rail 14.sub.2 enclose a second cavity 16.sub.2. In the first cavity 16.sub.1 a first spindle 18.sub.1 is positioned, which is non-rotatably connected to the first lower rail 12.sub.1 by means of fixing elements 20. Correspondingly, in the second cavity 16.sub.2 a second spindle 18.sub.2 is positioned, which is non-rotatably connected with the second lower rail 12.sub.2 (not shown).

[0056] The adjusting device 10P also has a first gear 22.sub.1, interacting with the first spindle 18.sub.1 and positioned, at least partially, within the first cavity 16.sub.1 and which is fixedly connected with the first upper rail 14.sub.1 and a second gear 22.sub.2, interacting with the second spindle 18.sub.2 and positioned, at least partially, within the second cavity 16.sub.2 and which is fixedly connected with the first upper rail 14.sub.1.

[0057] A support 24 extends between the first upper rail 14.sub.1 and the second upper rail 14.sub.2, wherein the support is secured to the first and second upper rail 14.sub.1, 14.sub.2. On the support 24, a drive motor 26 having securing brackets 27 is secured, which is usually an electric motor. The provision of the support 24 is not strictly necessary. The support 24 may be omitted by securing the drive motor 26 to the vehicle seat. Between the drive motor 26 and the first gear 22.sub.1 and between the drive motor 26 and the second gear 22.sub.2 a drive train 28 extends, which comprises a linear first drive shaft 30.sub.1 and a linear second drive shaft 30.sub.2.

[0058] FIG. 2A shows the adjusting device 10 based on a schematic plan view.

[0059] The gears 22.sub.1, 22.sub.2 in the example shown are formed by a respective worm gear 32, which comprises a worm 34 and a worm wheel 36, which is a spindle nut 41, which mesh with each other. The worm gear 32 is separately shown by means of a schematic representation in FIG. 2B. The spindle nut 41 has an inner thread, not shown, in which the spindle 18.sub.1 is screwed. The drive shafts 30 are non-rotatably connected with the worms 34.

[0060] The adjusting device 10P operates in the following way: by actuating the drive motor 26, both drive shafts 30.sub.1, 30.sub.2 are set in rotation. The rotation of the drive shafts 30.sub.1, 30.sub.2 is transmitted to the worms 34, whereby in turn the spindle nuts 41 are rotated. Due to this rotation, the spindle nuts 41 move along the spindles 18.sub.1, 18.sub.2. Since gears 22.sub.1, 22.sub.2 are fixedly connected with upper rails 14.sub.1, 14.sub.2, they move together with the upper rails 14.sub.1, 14.sub.2 along the sliding axis L within the lower rails 12.sub.1, 12.sub.2. The support 24, the drive train 28, the drive motor 26 and the vehicle seat, not shown, follow this movement.

[0061] The length of the maximum adjustment stroke of the vehicle seat along the sliding axis L is essentially equal to the length of spindles 18.sub.1, 18.sub.2. The surface A swept by the support 24 and drive train 28 is approximately indicated by a hatched portion in FIG. 2A. In order to ensure the sliding of the vehicle seat over the entire adjustment stroke, in the area A between the two lower rails 12.sub.1, 12.sub.2 no obstacle should be present, against which the drive train 28 and/or the drive motor 26 may collide.

[0062] FIG. 3 shows a first example of an inventive adjusting device 10.sub.1 based on a schematic plan view. The structure of the inventive adjusting device 10.sub.1 according to the first exemplary embodiment differs from the structure of known adjusting device 10P in particular in following aspects:

[0063] The first and second spindle 18.sub.1, 18.sub.2 in this case are rotatably supported around a rotation axis T and are directly connected, at one end, with a respective driven shaft 39 of a drive motor 40.sub.1, 40.sub.2. Thus, a first drive motor 40.sub.1 is associated to the first spindle 18.sub.1 and a second drive motor 26 is associated to the second spindle 40.sub.2. The first drive motor 40.sub.1 or its driven shaft 39 is aligned with the rotation axis T of the first spindle 18.sub.1 and the second drive motor 40.sub.2 or its driven shaft 39 is aligned with the rotation axis T of the second spindle 18.sub.2. The adjusting device 10 in this example also comprises a first spindle nut 41.sub.1 and a second spindle nut 41.sub.2, which are fixedly connected with the first and second upper rail 14.sub.1, 14.sub.2, respectively, and which interact with the first spindle 18.sub.1 and second spindle 18.sub.2, respectively. A support 24 is not required.

[0064] In this embodiment of the proposed adjusting device 10.sub.1, between both lower rails 12.sub.1, 12.sub.2 no component of the adjusting device 10.sub.1 is disposed, so that the space between both lower rails 12.sub.1, 12.sub.2 may be completely used for arranging vehicle components of any kind such as storage compartments, fire extinguishers, subwoofers, batteries, and/or other electronic components.

[0065] The second exemplary embodiment shown in FIG. 4 of the adjusting device 10.sub.2 is predominantly identical to the first example of the adjusting device 10.sub.1 shown in FIG. 3. Herein, again, the first and second spindle 18.sub.1, 18.sub.2 are rotatably supported, although the first and second spindle 18.sub.1, 18.sub.2 are not directly connected with the driven shaft 39 of the first and second drive motors 40.sub.1, 40.sub.2. Instead, the first spindle 18.sub.1 is connected, at one end, with the first gear 22.sub.1 and the second spindle 18.sub.2 is connected with one end to the second gear 22.sub.2. In the second example the first gear 22.sub.1 and second gear 22.sub.2 are respective planetary gears 38.sub.1, 38.sub.2. Each planetary gear 38.sub.1, 38.sub.2 is connected, on the drive side, to the driven shaft 39 of the first and second drive motor 40.sub.1, 40.sub.2, respectively. Thus, a first drive motor 40.sub.1 is associated to the first spindle 18.sub.1 and a second drive motor 26 is associated to the second spindle 40.sub.2. The first drive motor 40.sub.1 or its driven shaft 39 and the first planetary gear 38.sub.1 are aligned with the rotation axis T of the first spindle 18.sub.1 and the second drive motor 40.sub.2 or its driven shaft 39 and the second planetary gear 38.sub.2 are aligned with the rotation axis T of the second spindle 18.sub.2.

[0066] The first planetary gear 381 and the second planetary gear 382 may be conventional planetary gears or so called helical planetary gears 43. Such a helical planetary gear 43 is shown in FIGS. 5A and 5B, in parts and in an unmounted state, respectively. In this case, the driven shaft 39 has a helical gear 45, whereby the driven shaft 39 is also called a helical shaft 47, which may rotate around a helical shaft axis A.sub.SW. As in conventional planetary gears, a satellite carrier 49 is present, in which, in this case, three satellite wheels 51 (see in particular FIG. 5B) are rotatably supported about respective satellite wheel axis AP. The satellite wheels 51 have a satellite wheel toothing 53, which is adapted to the helical toothing 45, so that an essentially optimal meshing between the helical shaft 47 and the satellite wheels 51 is provided. A special characteristic of the helical planetary gear 43 is that the satellite axis AP are skewed with respect to the helical shaft axis Asw.

[0067] As shown in FIG. 5B, the helical planetary gear 43 also has a crown wheel 53, which in this case is provided as an inner screw gear 55 with an inner toothing 59, wherein the inner toothing 59 is adapted to the planetary toothing 53 in such a way that an essentially optimal meshing between the satellite wheels 51 and the crown wheel 47 is provided. The satellite carrier 49 is rotatably supported within the inner screw gear 55. As in conventional planetary gears, in case of a rotating helical shaft 47, either the satellite carrier 49 or the inner screw gear 47 may be stationary and the respective other part may rotate. In this example, the inner screw gear 47 may be non-rotatably connected to a housing, not shown, of the drive motor 40 and the spindle may be non-rotatably connected to the satellite carrier 49. Thus, the helical shaft axis A.sub.SW and the rotation axis T coincide.

[0068] In FIG. 6A, a third example of the proposed adjusting device 103 is shown, which is also shown in a schematic plan view. In this example, the adjusting device 10.sub.2 has the support 24 extending between the first and second upper rail 14.sub.1, 14.sub.2, on which the drive motor 26 is disposed.

[0069] The first gear 22.sub.1 is a first worm gear 42.sub.1 and the second gear 22.sub.2 is a second worm gear 42.sub.2. The first worm gear 42.sub.1 is separately shown in FIG. 6B. The worm gears 42.sub.1, 42.sub.2 comprise a respective worm 44 having a worm axis 46 and a worm wheel 48 having a worm wheel axis 50, which form an angle between them. In this case, the angle is less than 90, approximately equal to 30.

[0070] The worm gears 42.sub.1, 42.sub.2 are offset, relative to the sliding axis L, by a distance D to the drive motor 26. The drive train 28 comprises a distance bridging means 52, which is formed by a flexible first drive shaft 54.sub.1 and a flexible second drive shaft 54.sub.2.

[0071] Again, as in FIG. 2A, an area A is approximately shown, which is the maximum surface swept by the support 24, the drive train 28 and the drive motor 26 during the adjustment of the vehicle seat between the lower rails 12.sub.1, 12.sub.2. It may be noticed that a portion of space between the lower rails 12.sub.1, 12.sub.2 is not being swept and thus may be used for arranging components.

[0072] FIG. 7 shows a fourth example of the inventive adjusting device 10.sub.4, also by means of a schematic plan view. In this case, the first gear 22.sub.1 is provided as a first spur gear 58.sub.1 and the second gear 22.sub.2 is provided as a second spur gear 58.sub.2 which is offset with respect to the drive motor 26 the distance D along the sliding axis L. The drive train 28 also comprises the flexible drive shafts 54.sub.1, 54.sub.2, which are non-rotatably connected, at one end, to an upper spur wheel 60. The upper spur wheel 60 meshes with a rotatable lower spur wheel 62, which is formed by the spindle nut 41, and which interacts with the spindle 18.sub.1.

[0073] The flexible drive shafts 54.sub.1, 54.sub.2 are connected, by the other end, to a further gear 64, in this case, to a motorized worm gear 66, which is connected, on the drive side, to a driven shaft 68 of the drive motor 26. A direct connection to the drive motor 26 may also be conceived. The further gear 64 is used as a case gear. The drive train 28, the spur gear 58 and the spindle 18 provide a total transmission ratio i. To this end, the spindles 18.sub.1, 18.sub.2 have a normal thread pitch PN, between 2.5 and 3.5 mm, as in known adjusting devices 10P.

[0074] Due to the arrangement of the upper spur wheel 60 and lower spur wheel 62, the flexible drive shafts 54.sub.1, 54.sub.2 extend above the upper rails 14.sub.1, 14.sub.2, and do not pass through the space between both lower rails 12.sub.1, 12.sub.2, thus making it more usable for arranging components. This however presupposes that the axis distance X between the upper spur wheel 60 and the lower spur wheel 62 is correctly selected. In particular, the axis distance X should be big enough for the upper spur wheel 60 to sufficiently protrude from the cavity 16, in order to connect the flexible drive shaft 54 to the upper spur wheel 60. The axis distance X in spur gears 58 is determined by diameters of the upper spur wheel 60 and lower spur wheel 62. The diameter of the lower spur wheel 62 cannot be arbitrary, since otherwise it would collide with the upper rail 12 or lower rail 14. The further gear 64 already reduces the speed of the flexible drive shafts 54.sub.1, 54.sub.1 to a certain extent, so that the spur gear 58 is required to provide a small or no transmission ratio at all. The lower the transmission ratios, the closer get the diameters of the upper and lower spur wheel 60, 62, whereby the axis distance X may be adapted to the constructive needs. The noise emission in spur gears at low speeds may also be kept at a low level.

[0075] In FIG. 8 a fifth exemplary embodiment of the inventive adjusting device 10.sub.5 is shown, again in a schematic plan view. The structure of the fifth example is essentially identical to the structure of the fourth example, wherein, however, the drive train 28 is lacking the further gear 64. The spindles 18.sub.1, 18.sub.2 have a thread pitch P which is about 60 to 70% smaller than the normal thread pitch P of the fourth example, for example. Due to the reduced thread pitch P, the spur gears 58.sub.1, 58.sub.2 have a low transmission ratio about 1. As already indicated with reference to the fourth example, the axis distance X may thus be adapted to constructive requirements, without modifying the total transmission ratio i.

[0076] In FIG. 9 a sixth exemplary embodiment of the inventive adjusting device 10.sub.6 is shown, again in a schematic plan view. In this case, the drive train 28 comprises a first belt gear 70.sub.1 and a second belt gear 70.sub.2, which are offset to the drive motor 26 by a distance D along the sliding axis L. The first belt gear 70.sub.1 has, on the drive side, a first drive wheel 72.sub.1, which is rotatably connected to the flexible first drive shaft 54.sub.1. The first belt gear 70.sub.1 also comprises, on the driven side, a first driven wheel 74.sub.1, which is provided as the spindle nut 41, and which interacts with the first spindle 18.sub.1. A first belt 76.sub.1 is disposed between the first drive wheel 72.sub.1 and the first driven wheel 74.sub.1. The second belt gear 70.sub.2 is constructed correspondingly. The drive shafts 54.sub.1, 54.sub.2 extend above the upper rails 14.sub.1, 14.sub.2.

[0077] FIG. 10 shows a seventh example of the inventive adjusting device 10.sub.7, again in a schematic plan view. In this case also the drive train 28 comprises the first and second belt gear 70.sub.1, 70.sub.2, which, however, are arranged in a slightly different way. The drive train 28 comprises two drive shafts 78.sub.1, 78.sub.2, which may be of the rigid type and extend linearly along the support 24. The first gear 22.sub.1 and the second gear 22.sub.2 are configured as worm gears 42.sub.1, 42.sub.2 having an axis angle of 90 and are offset by a distance D along the sliding axis L to the drive motor 26. The belt gears 70.sub.1, 70.sub.2 are disposed between the drive shafts 78.sub.1, 78.sub.2 and the worm gears 42.sub.1, 42.sub.2. The first belt gear 70.sub.1 comprises, on the drive side, the first drive wheel 72.sub.1 which is non-rotatably connected to the drive shaft 78.sub.1 and on the drive side the first driven wheel 74.sub.1, which is interacting with the worm gear 42.sub.1. The first belt 76.sub.1 between the first drive wheel 72.sub.1 and the first driven wheel 74.sub.1 is parallel to the upper rail 14.sub.1, whereby the distance D is bridged. The first belt gear 70.sub.1 is disposed in a housing 80. The construction of the second belt gear 70.sub.2 is analogous to the one of the first belt gear 70.sub.1.

REFERENCE LIST

[0078] 10, 10.sub.1-107 adjusting device [0079] 10P known adjusting device [0080] 12, 12.sub.1, 12.sub.2 lower rail [0081] 14, 14.sub.1, 14.sub.2 upper rail [0082] 16, 16.sub.1, 16.sub.2 cavity [0083] 18, 18.sub.1, 18.sub.2 spindle [0084] 20 mount [0085] 22, 22.sub.1, 22.sub.2 gear [0086] 24 support [0087] 26 drive motor [0088] 27 securing bracket [0089] 28 drive train [0090] 30, 30.sub.1, 30.sub.2 drive shaft [0091] 32 worm gear [0092] 34 worm [0093] 36 worm wheel, spindle nut [0094] 38, 38.sub.1, 38.sub.2 planetary gear [0095] 39, 39.sub.1, 39.sub.2 driven shaft [0096] 40, 40.sub.1, 40.sub.2 drive motor [0097] 41, 41.sub.1, 41.sub.2 spindle nut [0098] 42, 42.sub.1, 42.sub.2 worm gear [0099] 43 helical planetary gear [0100] 44 worm [0101] 45 helical toothing [0102] 46 worm axis [0103] 47 worm wheel axis [0104] 48 worm wheel [0105] 49 satellite carrier [0106] 50 worm wheel axis [0107] 51 satellite wheel [0108] 52 distance bridging means [0109] 53 satellite wheel toothing [0110] 54, 54.sub.1, 54.sub.2 flexible drive shaft [0111] 55 crown gear [0112] 56, 56.sub.1, 56.sub.2 bevel gear [0113] 57 inner thread gear [0114] 58, 58.sub.1,58.sub.2 spur gear [0115] 59 inner toothing [0116] 60 upper spur wheel [0117] 62 lower spur wheel [0118] 64 further gear [0119] 66 motorized worm gear [0120] 68 driven shaft [0121] 70, 70.sub.1,70.sub.2 belt gear [0122] 72, 72.sub.1, 72.sub.2 drive wheel [0123] 74, 74.sub.1, 74.sub.2 driven wheel [0124] 76, 76.sub.1, 76.sub.2 belt [0125] 78, 78.sub.1, 78.sub.2 linear drive shaft [0126] 80 housing [0127] A surface [0128] A.sub.P satellite wheel axis [0129] A.sub.SW helical shaft axis [0130] D distance [0131] i transmission ratio [0132] L sliding axis [0133] P thread pitch [0134] P.sub.N thread normal pitch [0135] T, T.sub.1, T.sub.2 axis of rotation [0136] X axis distance [0137] axis angle