FIELD OF THE INVENTION

[0001] The present invention relates to a superimposing drive with an input axle and an output axle. BACKGROUND OF THE INVENTION

[0002] As illustrated on figure 1, superimposing drives in general are drives with an input axle and an output axle. An input rotational angle applied on the input axle is transmitted (mechanically) to the output axle as an output rotational angle. Depending on the type of drive, the opposite is also true, i.e. an output rotational angle applied on the output axle is transmitted by the drive to the first rotational axle. In addition, a superimposing angle can be applied on the output axle, the thus resulting output rotational angle equaling the sum of the input rotational angle and the superimposing angle.

[0003] However, existing superimposing drives are too complex and therefore expensive and too bulky. Furthermore, the high complexity of the existing drives results in a high level of noise and vibrations generated by these drives. For example, quite often, the superimposing rotation is introduced into the drive by means of planetary gears or strain wave gears which are not only bulky and expensive but generate a high amount of noise and vibrations as well .

[0004] In many applications where reliability of the drive is of upmost importance, such as in the automotive industry, a permanent mechanical connection between the two axles is mandatory. The construction of a superimposing drive fulfilling all the above requirements and also providing a permanent mechanical connection between its axes poses further difficulties.

TECHNICAL PROBLEM TO BE SOLVED

[0005] The objective of the present invention is therefore to provide a superimposing drive with a compact and efficient construction, providing a quiet and vibration-free operation while allowing high torques to be

transferred and providing a permanent mechanical connection between the two axles (input axle and output axle) of the drive.

[0006] A further requirement is to provide a solution with a reduced number of moving parts in order to reduce maintenance efforts and to ensure increased reliability.

SUMMARY OF THE INVENTION

[0007] The above-identified objectives are solved by a superimposing drive according to the present invention, the superimposing drive comprising : - an input axle and an output axle configured to be rotatable about a first axis;

a worm drive with a worm gear configured to be rotatable about a second axis and connected with the input axle such as to be rotatable about said first axis and a worm wheel, configured to provide a rotation about said first axis and being drivingly connected with the output axle, the worm gear and the worm wheel being arranged with respect to each other such that the worm wheel to be drivable by said worm gear;

a spiral drive with a driven gear drivingly connected to the worm gear and mounted to provide a rotation about said second axis, the spiral drive further comprising a spiral-toothed gear wheel with at least one spiral tooth, the spiral-toothed gear wheel being mounted to provide a rotation about said first axis and configured to drivingly engage with said driven gear,

the superimposing drive providing for a superimposing rotational angle of the spiral-toothed gear wheel to be mechanically superimposable on the output rotational angle of the output axle and/or on the input rotational angle (φ _Α ) of the input axle (10).

ADVANTAGEOUS EFFECTS

[0008] The most important advantages of the present invention are its simple construction allowing for a compact drive and the smooth transmission of the torques by means of the worm drive and spiral drive. Even though worm drives and spiral drives are known to be running quietly and smoothly, there is no superimposing drive known which achieves all the requirements (mechanical superimposition and permanent mechanical connection between the input and output axles) of a mechanical superimposing drive exclusively by means of worm and spiral drive(s).

[0009] Furthermore, the simple construction with relatively few moving parts ensures great reliability and reduced maintenance requirements. The simple and compact construction also leads to reduced costs of the

superimposing drive of the present invention. INDUSTRIAL APPLICABILITY

[0010] The superimposing drive of the present invention finds

application in various fields, where a superimposing rotational angle has to be imposed on an input rotational angle.

[0011] One exemplary application is a steering column for a vehicle comprising a superimposing drive according to the present invention, the input axle being drivingly connectable to the steering wheel of said vehicle and the output axle being drivingly connectable to a steering input of one or more wheels of said vehicle. The superimposing drive superimposing correctional and/or autonomous driving control signals over the controls imposed by the driver via the steering wheel. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Further characteristics and advantages of the invention will in the following be described in detail by means of the description and by making reference to the drawings. Which show: Fig . 1 a symbolic illustration of a superimposing drive;

Fig . 2A an exploded perspective view of a worm drive comprising a worm gear and a worm wheel, according to the present invention;

Fig . 2B a perspective view of the worm drive of figure 2A;

Fig . 3A an exploded perspective view of a spiral drive with a driven gear and a first embodiment of the spiral-toothed gear wheel;

Fig . 3B a perspective view of the spiral drive of figure 3A;

Fig . 3C a cross section of the spiral drive of figure 3A, showing a first

(convex pitch surface) embodiment of the spiral-tooth of the present invention;

Fig . 4 a cross section of a spiral drive, showing a second (plane pitch surface) embodiment of the spiral-tooth of the present invention; Fig . 5 a cross section of a spiral drive, showing a third (concave pitch surface) embodiment of the spiral-tooth of the present invention; Fig . 6A a perspective view of a spiral drive with a driven gear and a

second embodiment of the spiral-toothed gear wheel, according to the present invention comprising an inner spiral tooth arranged on its inner surface;

Fig . 6B a cross section of the spiral drive of figure 6A, showing a first embodiment of the inner spiral-tooth of the present invention; Fig . 7 a cross section of the spiral drive, showing a second embodiment of the inner spiral-tooth of the present invention;

Fig . 8 a cross section of the spiral drive, showing a third embodiment of the inner spiral-tooth of the present invention;

Fig . 9 a perspective view of the spiral drive of the present invention, showing a first embodiment of the driving mechanism for driving the spiral-toothed gear wheel;

Fig . 10A a perspective view of the superimposing drive according to the present invention, a front view of the superimposing drive of figure 10A;

a side view of the superimposing drive of figures 10A and 10B; a perspective view of the superimposing drive according to the present invention showing a first embodiment of the driving mechanism for driving the spiral-toothed gear wheel; a front view of the superimposing drive of figure 11A; an exploded perspective view of a further embodiment of the worm drive comprising a worm wheel and three rotationally symmetrically arranged worm gears;

a perspective view of the worm drive of figure 12A; an exploded perspective view of a further embodiment of the spiral drive comprising a spiral-toothed gear wheel and three rotationally symmetrically arranged driven gears;

a perspective view of the spiral drive of figure 13A; a perspective view of a further embodiment of the superimposing drive according to the present invention, comprising the worm drive of figure 12A and the spiral drive of figure 13A; a front view of the superimposing drive of figure 14A; a side view of the superimposing drive of figures 14A and 14B; a front view of a further embodiment of the superimposing drive, with two rotationally symmetrically arranged worm gears and two rotationally symmetrically arranged driven gears; and a symbolic illustration of a steering column of a vehicle comprising a superimposing drive according to the present invention.

Note : The figures are provided as illustration only and serve only for better understanding but not for defining the scope of the invention. No limitations of any features of the invention should be implied form these figures.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0013] Certain terms will be used in this patent application, the formulation of which should not be interpreted to be limited by the specific term chosen, but as to relate to the general concept behind the specific term [0014] The term worm drive shall be used throughout the specification to refer to a drive comprising a worm gear and worm wheel, the exact type of the worm gear and worm wheel not affecting the inventive concept of the application . [0015] The term spiral drive shall be used throughout the specification to refer to a drive comprising a driven gear and a spiral-toothed gear wheel, the exact type of driven gear and a spiral-toothed gear wheel not affecting the inventive concept of the application .

[0016] Fig . 1 depicts a symbolic illustration of a superimposing drive 100, illustrating its function, i .e. adding/superimposing a superimposing rotational angle φ _ζ to an input rotational angle φ _Α οί the drive 100 so that its resulting output rotational angle φ _Β will be the sum of the superimposing rotational angle φ _ζ multiplied by the gear ratio of the worm drive Ri and multiplied by the gear ratio of the spiral drive R ₂ and of the input rotational angle φ _Α (φ _Β = ΦΑ+ i * R ₂ * Φζ) .

[0017] In a preferred embodiment of the present invention, the drive 100 is configured such that the superimposing rotational angle φ _ζ of the spiral-toothed gear wheel 53 is mechanically superimposable on the output rotational angle φ _Β of the output axle 20 such that the superimposing rotational angle φ _ζ is not transmitted back to the input rotational angle φ _Α of the input axle 10. Thus the superimposing rotational angle φ _ζ has no effect on the input rotational angle φ _Α .

[0018] For ease of understanding, the axles and rotational angles are referred to throughout the application as input/output axles and input/output rotational angles. However, the wording input/output shall not be treated as limiting the role of these axes/angles as the construction of the drive according to the present invention allows for the input/output sides of the drive to be reversed without affecting the inventive concept behind . Whether the superimposing rotational angle φ _ζ is superimposed on the input axle 10 or on the output axle 20 or both, depends on the relative resistance against rotation of the input axle 10 and output axle 20. In the examples shown, it is assumed that the axle 20 has no resistance against rotation and therefore the superimposing rotational angle φ _ζ is superimposed fully on the output axle 20.

[0019] However, the superimposing drive of the present invention 100 is reversible in that if the input axle 10 has no resistance against rotation

(purely theoretically, as practically there will always be a resistance, even if very small), then the superimposing rotational angle φ _ζ is superimposed on the input axle 10 (and not on the output axle 20) . In this case the

superimposing drive 100 adds/superimposes the superimposing rotational angle φ _ζ to the output rotational angle φ _Β of the drive 100 so that the input rotational angle φ _Α will be the sum of the superimposing rotational angle φ _ζ multiplied by the gear ratio of the worm drive Ri and multiplied by the gear ratio of the spiral drive R ₂ and of the output rotational angle φ _Β . Thus the formula - if the input axle 10 has the lower resistance against rotation - would be φ _Α = ΦΒ + RI * R ₂ * Φζ - In practice however different fractions of the superimposing rotational angle φ _ζ will be applied on both axles simultaneously.

[0020] Fig . 2A shows an exploded perspective view of a worm drive comprising a worm gear 15 and a worm wheel 25, according to the present invention . Two axes are depicted on figure 2A: the first axis A and the second axis C, the first axis A and the second axis C being non-coplanar (non- intersecting) axes, i.e. the second axis C is arranged with an offset relative to the first axis A.

[0021] The worm gear 15 is configured to be rotatable about a second axis C and is connected with the input axle 10 such as to be rotatable about said first axis A. For example - as shown on the figures - the connection between the worm gear 15 and the input axle 10 can be achieved by an arm 12 extending radially from said first axle 10 and providing a mount 14, preferably a pair of mounts, for the worm gear 15 to be arranged to rotate about the second axis C.

The worm wheel 25 is configured to provide a rotation about said first axis A and is drivingly connected with the output axle 20. The depicted examples show the worm wheel 25 itself rotatable around the first axis A and directly connected with the output axle 20, the worm wheel 25 being co-axially arranged with the first axis A. However other arrangements are possible without departing from the concept of the present invention, for example by positioning the worm wheel 25 offset or at an ang le with respect to the first axis A. The rotation around said first axis A being provided for example by means of an add itional transmission, such as a pair of gears, the first of said pair of gears being rotatably mounted coaxially with the worm wheel 25 and the second gear of said pair being mounted to rotate around the first axis. In such a case, the gear ratio of such an add itional transmission will be factored in when calcu lating the gear ratio of the worm d rive Ri . [0022] The worm gear shown is arranged perpend icu larly to the worm wheel, however other arrangements are possible .

[0023] Fig ure 2A also shows the input axle 10 and output axle 20 config ured to be rotatable about said first axis A. The input rotational ang le φ _Α and the output rotational ang le φ _Β of the input axle 10 respectively output axle 20 are also illustrated .

[0024] Fig . 2B shows a perspective view of the worm drive of fig ure 2A as assembled together, il lustrating how the worm gear 15 and the worm wheel 25 are arranged with respect to each other such that the worm wheel 25 to be d rivable by said worm gear 15. [0025] It is clear from figure 2B, that in the embod iment where the worm drive is configu red as a self-locking worm d rive, then any in put rotational ang le φ _Α applied on the in put axle 10 is d irectly transmitted to the output rotational ang le φ _Β of the output axle 20 and vice versa .

[0026] As an alternative to a self- locking worm d rive as means for rotational ly locking the input axle 10 with respect to the output axle 20, external means for locking the worm d rive may be provided preventing the worm gear 15 from rotating about the second axis C. As an even further alternative to a self-locking worm d rive as means for rotational ly locking the input axle 10 with respect to the output axle 20, the input axle 10 and output axle 20 may be d irectly connected , e .g . by a releasable brake inbetween . [0027] Fig . 3A depicts an exploded perspective view of a spiral drive of the present invention, comprising a driven gear 55 and a first embodiment of the spiral-toothed gear wheel 53 with at least one spiral tooth 54.

[0028] The depicted examples show the driven gear 55 itself rotatable around the second axis C and arranged co-axially with the second axis C.

However other arrangements are possible without departing from the concept of the present invention, for example by positioning the driven gear 55 on an axis arranged offset or at an angle with respect to the second axis C, but providing for a rotation around said second axis C, for example by means of an additional transmission, such as a pair of gears, the first of said pair of gears being rotatably mounted coaxially with the worm gear 15 and the second gear of said pair being rotatably mounted coaxially with the driven gear 55. In such a case, the gear ratio of such an additional transmission will be factored in when calculating the gear ratio of the spiral drive R ₂ .

[0029] As depicted on figure 3A, the spiral-toothed gear wheel 53 is mounted to provide a rotation about said first axis A. The depicted examples show the spiral-toothed gear wheel 53 itself rotatable around the first axis A and arranged co-axially with the first axis A. However other arrangements are possible without departing from the concept of the present invention, for example by positioning the spiral-toothed gear wheel 53 on an axis arranged with an offset or at an angle with respect to the first axis A, but providing for a rotation around said first axis A, for example by means of an additional transmission, such as a pair of gears, the first of said pair of gears being rotatably mounted coaxially with the spiral-toothed gear wheel 53 and the second gear of said pair being rotatably mounted to rotate about said first axis A. In such a case, the gear ratio of such an additional transmission will be factored in when calculating the gear ratio of the spiral drive R ₂ .

[0030] Figures 3A through 5 show a first embodiment of the spiral- toothed gear wheel 53, wherein the spiral-toothed gear wheel 53 is a face gearwheel with the at least one spiral tooth 54 following a spiral course on the gear face. [0031] Exemplary details of spiral drives with a face gearwheel with at least one spiral tooth following a spiral course on the gear face are described for example in the international patent application WO2003004904.

[0032] Fig . 3B shows a perspective view of the spiral drive of figure 3A, the curved outer toothing 56 of the driven gear 55 drivably engaging with the spiral tooth 54 on the gear face of the spiral-toothed gear wheel 53. As illustrated on this figure, a rotation of the spiral-toothed gear wheel 53 by a superimposing rotational angle φ _ζ results by means of the spiral drive in a rotation of the driven gear 55 by an intermediary rotational angle φ _Ρ . [0033] In an alternative embodiment of the present invention, instead of - or in addition to- configuring the worm drive as a self-locking worm drive, the spiral drive may be configured as a self-locking spiral drive, i.e. any input rotational angle φ _Α applied on the input axle 10 is directly transmitted to the output rotational angle φ _Β of the output axle 20 and vice versa. To achieve this, the spiral tooth 54 of the gear wheel 53 and the toothing 56 of the driven gear 55 are configured such that rotating the driven gear 55 around the second axis C does not drive the gear wheel 53, instead doing so locks the spiral drive. In this case, the rotation of the worm gear 15 about the second axis C (even if the worm gear 15 would be drivable by the worm wheel 25) is prevented by the self-locking of the spiral drive, which results in the input axle 10 being directly mechanically connected to the output axle 20 and therefore an input rotational angle φ _Α οί the input axle 10 is directly

transmitted to the output rotational angle φ _Β of the output axle 20 and vice- versa. [0034] As an alternative to a self-locking spiral drive, external means for locking the spiral drive may be provided .

[0035] The spiral tooth 54 of the spiral-toothed gear wheel 53 can have various configurations, a few examples being shown in the following figures 3C, 4 and 5. The exact configuration is chosen based on the specific

requirements of the application and chosen to optimize the spiral drive for smooth and quiet transmission and if the case is, for self-locking . [0036] Fig . 3C depicts a cross section of the spiral drive of figure 3A along the line X-X' of figure 10B, showing a first embodiment of the spiral- tooth 54 of the gear wheel 53, the spiral-tooth 54 having a convex pitch surface. [0037] Fig . 4 depicts a cross section of a spiral drive, showing a second embodiment of the spiral-tooth 54 having a plane pitch surface.

[0038] Fig . 5 shows a cross section of a spiral drive, showing a third embodiment of the spiral-tooth 54, having a concave pitch surface.

[0039] It must be pointed out, that only a few exemplary pitch surfaces of the spiral tooth 54 are shown and that an infinite number of pitch surfaces are possible. Additionally the various angular positionings (for example as shown on figures 6B, 7 and 8) can be combined with various spiral teeth 54 (such as the examples shown on figures 3C, 4 and 5 with a concave, convex or plane pitch surfaces). Also it is important to note that the position where the toothing 56 of the driven gear 55 engages the spiral tooth 54 of the spiral-toothed gear wheel 53 can be chosen at any angle (0-360°) around the driven gear 55.

[0040] However, the spiral-toothed gear wheel 53 need not be a face gearwheel with the spiral tooth 54 on the gear face. Fig . 6A shows a perspective view of a spiral drive with a driven gear 55 and a second embodiment of the spiral-toothed gear wheel 53, wherein the spiral tooth 54 is arranged on its inner surface. As it can be seen on this figure, the spiral tooth 54 is configured to drivingly engage with the driven gear 55.

[0041] Figures 6B, 7 and 8 show cross sections of the spiral drive having an spiral tooth 54 arranged on the inner surface of the spiral-toothed gear wheel 53, depicting various exemplary arrangements of the spiral tooth 54 of the present invention. The exact configuration is chosen based on the specific requirements of the application and chosen to optimize the spiral drive for smooth and quiet transmission and if the case is, for self-locking . It must be pointed out, that only a few exemplary arrangements are shown and that an infinite number of arrangements are possible, the spiral tooth 54 being arranged at various angles inbetween. Additionally, the spiral teeth with a concave, convex or plane pitch surfaces (as shown on figures 3C, 4 and 5) can all be freely combined with various angular positionings of the spiral teeth as shown on figures 6B, 7 and 8. [0042] Therefore figures 3C, 4 and 5 depict various exemplary pitch surfaces of the spiral tooth and figures 6B, 7 and 8 depict various exemplary angular arrangements of any of the various spiral teeth.

[0043] Fig . 9 shows a perspective view of the spiral drive of the present invention, showing a first embodiment of the driving mechanism 70 for driving the spiral-toothed gear wheel 53 so as to impose said superimposing rotational angle φ _ζ . The depicted embodiment of the driving mechanism 70 is a belt driven mechanism comprising a belt engaging with a driving contact surface 82 of the spiral-toothed gear wheel 53, preferably a toothed belt 80 engaging with corresponding teeth arranged on said driving contact surface 82 of the gear wheel 53.

[0044] However, other driving mechanism 70 for driving the spiral- toothed gear wheel 53 are also possible without departing from the concept of the invention, such as for example a spur gear mechanism comprising a first spur gear engaging with corresponding teeth arranged on an outer driving contact surface 82 of the spiral-toothed gear wheel 53 (not shown on the figures).

[0045] The provision of the driving mechanism 70 allows for an other alternative for rotationally locking the input axle 10 with respect to the output axle 20 by means of the driving mechanism 70 being configured for imposing on the spiral-toothed gear wheel 53 a superimposing rotational angle φ _ζ of such a magnitude, so as to ensure the output rotational angle φ _Β of the output axle 20 is kept essentially identical with the input rotational angle φ _Α of the input axle 10 and vice-versa.

[0046] Fig . 10A shows a perspective view of a first embodiment of the superimposing drive 100 according to the present invention as assembled together, depicting its essential elements: - the input axle 10 and output axle 20 arranged to rotate about the first axis A;

- the worm drive with the worm gear 15 and the spiral-toothed worm wheel 53;

- the spiral drive with the driven gear 55 and the spiral-toothed gear wheel 53.

[0047] This figure illustrates very well just how compact the assembled superimposing drive 100 is and how all the functionalities of a superimposing drive are achieved in an inventive manner by a very low number of moving parts and exclusively with worm gears and spiral gears allowing for a smooth and noise-free operation.

[0048] In a preferred embodiment of the present invention, the drive

100 is configured such that that the superimposing rotational angle φ _ζ of the spiral-toothed gear wheel 53 is mechanically superimposable on the output rotational angle φ _Β of the output axle 20 such that the superimposing rotational angle φ _ζ is not transmitted back to the input rotational angle φ _Α of the input axle 10. Thus the superimposing rotational angle φ _ζ has no effect on the input rotational angle φ _Α .

[0049] Fig . 10B shows a front view of the superimposing drive 100 of figure 10A illustrating well the coaxial arrangement of the first axle 10, the worm wheel 25 and the spiral-toothed gear wheel 53 and the axial offset (non-coplanarity) of the second axis C with respect to the first axis A.

[0050] A side view of the superimposing drive 100 of figures 10A and 10B is shown on figure IOC. The embodiments depicted show a second axis C arranged perpendicularly to the first axis A. However, according to the choice of the particular worm drive, this must not be the case.

[0051] Figures 11A and 11B show various views of the assembled superimposing drive 100 according to the present invention, showing the belt- driven embodiment of the driving mechanism 70 for driving the spiral-toothed gear wheel 53. [0052] According to further embodiments of the present invention, the worm drive further comprises n additional worm gear(s) 15.1 - 15. n, each configured to rotate about a corresponding additional second axis CI - Cn and each connected with the input axle 10 such as to be rotatabie about said first axis A, the n additional worm gear(s) 15.1 - 15. n being arranged with respect to the worm wheel 25 such that the worm wheel 25 to be collaboratively drivable by the worm gear 15 and the n additional worm gear(s) 15.1 - 15. n . The number n is an integer number greater or equal to 1.

[0053] In addition, the spiral drive may further comprise m additional driven gear(s) 55.1 - 55. m, the driven gear 55 respectively the m additional driven gear(s) 55.1 - 55. m being arranged such as to be simultaneously driven by said spiral-toothed gear wheel 53.. The number m is an integer number greater or equal to 0.

[0054] The additional worm gear(s) 55.1 - 55. m aid in the distribution of an input torque applied on the input axle 10 among the worm gear 15 respectively the n additional worm gear(s) 15.1 - 15. n. Thus additional worm gear(s) allow the superimposing drive 100 to transfer even greater torques between the input axle 10 and output axle 20 in a smooth and reliable manner. [0055] Similarly, the additional driven gear(s) 55.1 - 55. m aid in distributing a superimposing torque applied to the gear wheel 53 among the driven gear 55 respectively the m additional driven gear(s) 55.1 - 55. m. Thus, the additional driven gear(s) of the spiral drive allow greater superimposing torques to be applied on the superimposing drive 100 as the superimposing torque is transmitted to the output axle 20 as distributed torques applied on m + 1 contact surfaces between the spiral-toothed gear wheel 53 and the m additional driven gear(s) 55.1 - 55. m respectively the driven gear 55. As a result, the sum of the input torque and the superimposing torque are transmitted to the output axle 20 as distributed torques applied on n + 1 contact surfaces between the worm gear 15 respectively the n additional worm gear(s) 15.1 - 15. n and the worm wheel 25. [0056] In all embodiments where the worm drive is a self-locking worm drive, the number n of additional worm gear(s) 15.1 - 15. n is equal to the number m of additional driven gear(s) 55.1 - 55. m, and each additional driven gear(s) 55.1 - 55. m is drivingly connected to a corresponding additional worm gear(s) 15.1 - 15. n and mounted to provide a rotation about a corresponding additional second axis CI - Cn.

[0057] However, if the worm gear is not a self-locking worm gear and if the superimposing torques are not too high, the number m of additional driven gear(s) 55.1 - 55. m may be less than the number n of additional worm gear(s) 15.1 - 15. n or even 0.

[0058] Thus generally speaking, the number n of additional worm gear(s) 15.1 - 15. n is dependent on the amount input/output torques on the input/output axles 10 resp. 20 and the number m of additional driven gear(s) 55.1 - 55. m is dependent on the amount of superimposing torque applied on the spiral-toothed gear wheel 53. Distribution of the torques further reduces friction and vibrations and ensures even wear of all components reducing the chance of uneven loads applied on certain parts.

[0059] In the most preferred embodiments of the present invention, the worm gear 15 and the n additional worm gear(s) 15.1 - 15. n are arranged rotationally symmetric with respect to the first axis A. The driven gear 55 respectively the m additional driven gear(s) 55.1 - 55. m are also arranged rotationally symmetrical with respect to said first axis A.

[0060] Fig . 12A shows an exploded perspective view of a further embodiment of the worm drive comprising a worm wheel 25 and three rotationally symmetrically arranged worm gears 15 and n = 2 additional worm gears 15.1 and 15. n. The n = 2 additional worm gears 15.1 and 15. n are configured to rotate about a corresponding additional second axis CI to Cn and are connected with the input axle 10 such as to be rotatable about said first axis A. For example - as shown on the figures - the connection between the additional worm gear(s) 15.1 - 15. n and the input axle 10 can be achieved by additional arm(s) 12.1 - 12. n each extending radially from said first axle 10 and providing additional mount(s) 14.1 - 14. n, preferably n pair(s) of mounts, for the additional worm gear(s) 15.1 - 15. n to be arranged to rotate about the second axis C. Fig . 12B shows a perspective view of the worm drive of figure 12A as assembled, the sum of the input torque and the superimposing torque being transmitted to the output axle 20 as distributed torques applied on n + l = 3 contact surfaces between the n + l = 3 worm gears 15, 15.1 - 15. n and the worm wheel 25.

[0061] Fig . 13A depicts an exploded perspective view of a further embodiment of the spiral drive comprising a spiral-toothed gear wheel 53 and three rotationally symmetrically arranged driven gears 55, 55.1 and 55. m. This spiral drive corresponds to the worm drive of figures 12A and 12B, that is the embodiment of the superimposing drive where the number of additional worm gears and additional driven gears n = 2. The m = 2 additional driven gear(s) 55.1 - 55. m are each drivingly connected to the corresponding additional worm gear (shown on figures 14A to 14C) and mounted to provide a rotation about a corresponding additional second axis CI respectively Cn.

[0062] Fig . 13B shows a perspective view of the spiral drive of figure 13A showing the driven gear 55 and the m = 2 additional driven gears 55.1 - 55. m being arranged such as to be simultaneously driven by the spiral- toothed gear wheel 53, thus the superimposing torque being transmitted to the output axle 20 as distributed torques applied on m+ l = 3 contact surfaces between the spiral-toothed gear wheel 53 and the m = 2 additional driven gear(s) 55.1 - 55. m and the driven gear 55.

[0063] Fig . 14A shows a perspective view of a further embodiment of the superimposing drive 100 according to the present invention, where the number of additional worm gears (of the worm drive) and additional driven gear(s) (of the spiral drive) n = m = 2, the drive 100 comprising the worm drive of figures 12A, 12B and the spiral drive of figures 13A, 13B, depicting its essential elements:

- the input axle 10 and output axle 20 arranged to rotate about the first axis A; - the worm drive with a spiral-toothed worm wheel 53, a worm gear 15 and n = 2 two additional worm gears 15.1 - 15. n, the worm gear(s) 15, 15.1 - 15. n being arranged with respect to the worm wheel 25 such that the worm wheel 25 to be collaboratively drivable by the worm gears 15, 15.1 - 15. n;

- the spiral drive with the spiral-toothed gear wheel 53, the driven gear 55 and m = 2 additional driven gears 55.1 - 55. m, mounted to provide a rotation about the corresponding second axes C, CI - Cn, the driven gears 55, 55.1 - 55. m being arranged such as to be simultaneously driven by said spiral-toothed gear wheel 53.

[0064] Fig . 14B shows a front view of the superimposing drive 100 of figure 14A, illustrating well how the n + l = 3 worm gears 15, 15.1 and 15. n are arranged rotationally symmetric with respect to said first axis A, the intersection of their axes C, CI and Cn (shown with dotted-dashed lines) forming an equilateral triangle centered around the first axis A.

[0065] Fig . 14C depicts a side view of the superimposing drive 100 of figures 14A and 14B.

[0066] Figures 14A-14C illustrate well, that even the embodiment with multiple worm gears and driven gears for the transmission of high input and superimposing torques, the superimposing drive 100 remains very compact.

[0067] Figure 15 shows a front view of a further embodiment of the superimposing drive 100, where the number of additional worm gears (of the worm drive) and additional driven gear (of the spiral drive) n = m = l, the second axis C and the additional second axis CI being preferably parallel and equidistant with respect to said first axis A.

[0068] Fig . 16 shows a highly symbolic illustration of a vehicle with a steering column SC comprising a superimposing drive 100 according to the present invention. The input axle 10 (or the output axle 20) is drivingly connectable to a steering input of one or more wheel(s) S of the vehicle and the output axle 20 (or the input axle 10) is drivingly connectable to one or more wheels W of said vehicle. The driving mechanism 70 for driving the spiral-toothed gear wheel 53 is connected to a control unit CU providing correctional and/or autonomous driving control signals CS to said driving mechanism 70. The driving mechanism 70 is configured to convert said control signals CS into superimposing rotational angle φ _ζ applied on the spiral- toothed gear wheel 53, superimposing said superimposing rotational angle φ _ζ multiplied by the gear ratio of the worm drive Ri and multiplied by the gear ratio of the spiral drive R ₂ on the output rotational angle φΒ of the output axle 20 (or input axle 10), thus adding the superimposing rotational angle φ _ζ multiplied by the gear ratio of the worm drive Ri and multiplied by the gear ratio of the spiral drive R ₂ to controls (input rotational angle) applied by the driver through the steering wheel.

[0069] It will be understood that many variations could be adopted based on the specific structure hereinbefore described without departing from the scope of the invention as defined in the following claims.

REFERENCE LIST: superimposinq drive 100 input axle 10 arm 12 additional armfs ^' ) 12.1 - 12. n mount 14 additional mountfs ^' ) 14.1 - 14.2 worm aear 15 additional worm qear(s ^' ) 15.1 - 15. n first axis A output axle 20 worm wheel 25 second axis C additional second axis CI, Cn additional driven aearfs ^' ) 55.1 - 55. m spiral-toothed qear wheel 53 spiral tooth 54 driven qear 55 toothinq 56 drivinq mechanism 70 drivinq contact surface 82 toothed belt 80 input rotational anqle ΦΔ output rotational anqle (|>R superimposinq rotational angle φ ₇ steerinq column CS control unit CU control siqnals CS wheel w qear ratio of the worm drive Ri oear ratio of the spiral drive R ₇