WO2009043394A1 - Rotatory-translatory converter, actuator arrangement and clutch arrangement - Google Patents

Abstract

The invention relates to a rotatory-translatory converter (40) having rolling body rotation, comprising a spindle (23) on the outer circumference of which a first part (62) of a running groove (66) is formed, a nut (36) on the inner circumference of which a second part (64) of the running groove (66) is formed, a plurality of rolling elements (68) disposed in the running groove (66), and a return channel (70) connecting opposite ends of the running groove (66) to one another in order to allow the rolling elements (68) to rotate, wherein the return channel (70) is configured on the spindle (23).

Description

 Rotation-translation converter. Actuator assembly and clutch assembly

The present invention relates to a rotation-displacement converter with Wälzkörperumlauf, comprising a spindle, on whose outer periphery a first part of a raceway groove is formed, a nut on the inner periphery of which a second part of the raceway groove is formed, a plurality of rolling elements arranged in the raceway groove and a return passage connecting opposite ends of the raceway to allow the rolling elements to circulate.

Such a rotary-to-translation converter in the form of a ball screw is well known.

The present invention further relates to an actuator assembly for axially displacing an actuator by means of a driving force generated by an electric machine, in particular for a clutch assembly of a step change gear, wherein the actuator is mounted axially displaceable with respect to a rotary shaft, the electric machine fixed to a housing Stator and a rotor which is coupled to the actuator and disposed coaxially with the actuator. Such an actuator arrangement is known from the document DE 101 03 664 Al.

The present invention further relates to a clutch assembly for a variable speed transmission, in particular for motor vehicles, having a guide sleeve which is fixed to a rotary shaft and having a guide sleeve toothing, with a sliding sleeve, which has a sliding sleeve toothing, which is in engagement with the guide sleeve toothing, so that Shift sleeve in relation to the rotary shaft rotatably and axially displaceably mounted, and with a coupling body which is fixed to a loose wheel, which is rotatably mounted on the rotary shaft, and having a Kupplungsungskörperverzahnung into which the sliding sleeve toothing can be inserted to the idler gear rotatably connected to the rotary shaft, wherein the shift sleeve is axially displaceable by means of an actuator assembly.

From the document DE 100 21 368 A1, a mechatronic actuator is known in which a rotor of an electric motor is designed as a ring gear, as a planetary carrier or integrated into the planet gears of a planetary gear set. A sun gear of the planetary gear set is designed as a spindle for a linear drive.

An electromechanically actuated disc brake is known from the document DE 195 11 287 B4. A rotor is formed as a hollow shaft and surrounds a reduction gear in the form of a roller screw whose output member serves as an actuator for the disc brake. Between the rotor and the roller screw, a planetary gear can be switched.

The document DE 10 2004 013 450 B4 relates to a switching device for a variable speed transmission. Switching and synchronization processes are realized electromagnetically. A loose wheel and a guide sleeve are designed to guide a magnetic flux generated by a stator. On the guide sleeve shift pins are mounted axially displaceable, which serve to produce a positive connection with a loose wheel. From the document DE 199 47 405 Al a stepped change gear in countershaft design is known in which a shift sleeve of a synchronous clutch can be actuated by means of an electric linear stepping motor. The stepper motor can be designed as a reluctance motor and accommodated in the transmission housing.

Furthermore, the above-mentioned document DE 101 03 664 A1 discloses a synchronizer in which the shift sleeve is formed as part of the electric drive. In this case, the drive can be designed as a linear motor or as a rotary drive. In the latter case, the shift sleeve via rolling or sliding bearing with respect to a spindle is rotatable, but slidably mounted with this. The spindle carries an electromotive component and forms a rotation-translation converter with two spindle nuts supported on the housing.

From the document DE 10 2005 017 026 Al an actuator arrangement for a clutch assembly is known, which includes a concentric to a rotational axis arranged electrical machine with a housing fixed stator and a rotor. The rotor is coupled via a pin and a coil spring with a ring member. The ring member is axially displaceable by suitable measures relative to the stator, but not rotatable. The ring member has on the inner circumference of an annular projection which engages in a circumferential groove of a shift sleeve of the clutch assembly. Here, the rotor is only driven when an axial displacement of the shift sleeve is desired.

The document DE 33 23 345 Al discloses a recirculating ball screw classic design. DE 33 23 347 A1 discloses a similar recirculating ball screw drive in which a flexible band secures balls from falling out of a channel.

Furthermore, it is known from the document DE 103 33 909 A1 to realize the return channel of a ball screw by means of a deflecting piece which returns the rolling elements to the starting point after a little less than one revolution from the end point and in the axial projection lies approximately on the circular profile formed by the track groove. As a result, space is saved in the radial direction. However, a plurality of such revolutions with respective deflection piece is provided in the mother.

The connection of end points of a raceway with multiple revolutions, however, takes place in the prior art via a return channel, which is arranged outside the raceway, in particular radially outside in a special return channel of the mother. Such a return channel lies in the axial projection outside the circular profile formed by the track groove.

Against this background, it is the object of the invention to specify an improved actuator arrangement and an improved rotational-translation converter, which can be used in particular for an actuator arrangement according to the invention. Furthermore, it is the object of the invention to provide a clutch assembly for a variable speed transmission.

The above object is achieved according to a first aspect of the present invention by a rotation-translation converter having the features of claim 1.

Characterized in that the return channel is formed on the spindle, it is possible to form the rotation-translation converter in the radial direction compact. Overall, this results in a space savings.

It is particularly advantageous if the nut is longer in the axial direction than the spindle.

Here, the principle of a ball screw is reversed by the mother is longer than the spindle and thus moves the inner spindle along the mother. In this case, it is possible to make the spindle compact in the axial direction, so that it is particularly suitable for use in an actuator assembly for a clutch assembly.

It is also advantageous if the spindle is designed as a hollow spindle.

In this way, the spindle, for example, surround other components, such as a shift sleeve of a clutch assembly for vehicle transmission.

Furthermore, it is advantageous if the return passage is formed as a channel through the spindle. In this way, the spindle can be made compact even in the form of a hollow spindle in the radial direction. It is also advantageous here that the return channel can be arranged through the spindle outside the circular projection of the track groove in order to bridge more than one revolution of the track groove in this way. In this way, the spindle can be made compact even in the axial direction.

Furthermore, it is advantageous if the return channel follows the course of a secant in an axial projection onto the spindle.

In this embodiment, the return passage can be connected in a substantially straight line from one end of the raceway groove located on the outer circumference of the spindle to another end of the raceway groove which is also located on the outer circumference of the spindle.

The manufacturing costs can be simplified thereby. In the best case, the return passage can be formed as a bore, which passes through the body of the spindle.

Alternatively, it is also possible to provide the return channel with an arcuate course, especially in casting or sintered components. According to a further preferred embodiment, a plurality of grooves, each having an associated return channel is formed between the spindle and the nut.

Although a running groove with a gear is generally sufficient for use in an actuator arrangement for a clutch, it is naturally also possible, if appropriate, to make the rotational-translation converter more smoothly. The return channels do not have to end in the same groove. Rather, the rolling elements can also be guided into another raceway (another gear), so that the rolling elements then pass through several raceways or passages in succession.

Overall, it is advantageous if the rolling elements are balls.

Alternatively, it is also possible that the rolling elements are each formed as cylindrical rollers, which are referred to below for the sake of simplicity as a cylinder.

In the latter case, the cylinder axes of adjacent cylinders in the raceway groove are preferably each entangled with each other by an angle greater than zero or offset from one another. As a result, axial forces can be transmitted efficiently to the spindle (or the nut).

It is particularly advantageous if the cylinders are arranged alternately folded by 90 ° in the Laufπlle.

In general, with the rotation-translation converter according to the invention, a low-friction conversion of a rotational movement into an axial movement for actuating an actuator arrangement or a clutch can be converted, for example for adjusting a shift sleeve by means of a hollow-shaft electric motor in a vehicle transmission. In general, the use in all automated manual transmissions and dual-clutch transmissions is conceivable, which have switchable clutches on the gear ratios. Particularly interesting here is the application for an automated manual transmission or dual-clutch transmission or automatic transmission, which can be designed without a hydraulic system.

As rolling elements, as mentioned, balls or other rolling elements such as cylinders can be used. It is understood that between the rolling elements, spacers, such as e.g. Spacer balls can be arranged. The grooves may be circular in cross-section or with other shapes to achieve the most possible flat or selective contact as possible between the rolling elements and the track groove as needed.

According to a second aspect of the present invention, the above object is achieved by an actuator assembly according to claim 11. In this case, the rotor is coupled to the actuator via a rotational-translation converter. Further, the rotor is axially supported at an axial bearing portion having first and second annular ridges disposed on axially opposite sides of the rotor.

In this way, the rotor can be axially fixed in the actuator assembly.

Preferably, the axial bearing portion is formed fixed to the housing.

Although it is also conceivable to fix the axial bearing section, for example, on the rotary shaft, a construction fixed to the housing is preferred for structural reasons. The housing may in particular be a housing of the actuator arrangement, but in particular a housing of a transmission in which the actuator arrangement according to the invention is used for actuating a clutch assembly. It is advantageous if the rotation-translation converter has a converter section on the inner periphery of the rotor.

In this embodiment, the rotor (or a component rigidly connected thereto) forms a "nut" of the rotation-translation converter.

According to a further preferred embodiment, the rotational-translation converter has a converter section on the outer circumference of a switching member, which is coupled to the actuating member in the axial direction.

In this embodiment, the rotor is indirectly coupled to the actuator, via a switching member which is coupled to the actuator in the axial direction.

The actuator may be a shift sleeve in a clutch for a motor vehicle transmission. The switching member may be formed as a ring member which is formed in the manner of a spindle.

It is particularly advantageous if guide means extend between the first and the second ring web, on which the switching member is displaceably guided in the axial direction.

In this way, the ring lands fulfill a double function, on the one hand the axial bearing of the rotor and on the other hand the guiding function for the switching element.

It is particularly advantageous if the guide means have a plurality of axial pins which are distributed over the circumference of the actuator assembly.

In this way, the leadership of the switching element can be realized structurally simple. According to a further preferred embodiment, at least one of the annular webs passes through the stator in the radial direction.

In this way, a comparatively compact actuator arrangement can be realized.

Alternatively, the stator is arranged between the ring lands. This has the advantage that not only the rotor but also the stator are arranged as a closed unit between the ring lands, which consequently can form a kind of housing.

It is particularly preferred if the stator, the rotor, the switching member and the associated annular webs and the associated axial bearing of the rotor is designed as a preassembled actuator, which can be mounted later in a simple manner to a clutch of a transmission (in gearbox manufacturing ).

In addition, the pre-assembled unit can be tested in advance in a comparatively simple manner.

Overall, it is preferred if the rotation-translation converter of the actuator assembly according to the invention is designed as a rotational-translation converter according to the first aspect of the present invention.

Here, as mentioned above, the mother of the rotation-translation converter is connected to the rotor of the actuator assembly and formed by this.

Furthermore, it is advantageous if the spindle of the rotation-translation converter is connected to the switching member which is coupled to the actuator in the axial direction. It is particularly advantageous if the switching element has a width which corresponds to the width of a groove of the actuating element.

In this embodiment, the spindle is thus formed as a ring whose width may correspond, for example, a shift sleeve.

It is understood that the features mentioned above and those yet to be explained below can be used not only in the particular combination given, but also in other combinations or in isolation, without departing from the scope of the present invention.

Embodiments of the invention are illustrated in the drawings and are explained in more detail in the following description. Show it:

Fig. 1 is a schematic longitudinal sectional view through a first embodiment of a clutch assembly according to the invention;

FIG. 2 shows a schematic longitudinal sectional view through a second embodiment of a clutch assembly according to the invention; FIG.

3 shows a highly schematic longitudinal sectional view through a third embodiment of a clutch assembly according to the invention;

4 is a perspective, partially broken away view of part of a clutch assembly according to the invention with a rotation-translation converter of a first embodiment according to the invention;

5 shows a plan view of a switching ring in the form of a spindle of a further embodiment of a rotation-translation converter according to the invention; Fig. 6 is a sectional view taken along line VI-VI of Fig. 5; and

Fig. 7 is a partial perspective view of another embodiment of a rotation-translation converter according to the invention.

In Fig. 1, a first embodiment of an actuator assembly is generally designated 10.

The actuator assembly 10 is used to actuate a clutch assembly 12 of a variable speed transmission 13th

The clutch assembly 12 is associated with a rotary shaft 14. On opposite sides of the clutch assembly 12, a first idler gear 16 and a second idler gear 18 are arranged, which are rotatably mounted on the rotary shaft 14.

The clutch assembly 12 has a guide sleeve 20 with an unspecified outer guide sleeve toothing. The guide sleeve 20 is rotatably fixed to the rotary shaft 14. Furthermore, the clutch assembly 12 has a shift sleeve 22 with an internal shift sleeve toothing. The shift sleeve toothing is engaged with the guide sleeve toothing, such that the shift sleeve 22 with respect to the rotary shaft 14 rotatably and axially displaceably mounted. The shift sleeve 22 is externally circumferentially provided in a conventional manner with a circumferential groove. A switching element in the form of a switching ring 23 is displaceable in the axial direction by means of the actuator assembly 10 and engages in this groove. The switching ring 23 is rotatably mounted with respect to the housing 34.

At the first idler gear 16, a first coupling body 24 is fixed, which has an outer coupling body toothing. In a corresponding manner, a second coupling body 26 is fixed to the second idler gear 18, which has a corresponding outer coupling body toothing. The shift sleeve 22 can be axially displaced so that the shift sleeve toothing is inserted into each one of the coupling body teeth so as to connect the respective associated idler gear 16, 18 rotatably connected to the rotary shaft 14.

The axial force 27 required for the axial displacement of the shift sleeve 22 is generated by an electric machine which will be described below.

The clutch assembly 12 may include any conventional synchronization, such as with a synchronizer ring (not shown in FIG. 1), but may also be configured as a dog clutch (without synchronization).

In Fig. 1, a ball-spring locking system is shown at 28, as it is also generally used in Kegel synchronization.

Further, at 30 in Fig. 1, an axis of rotation of the rotary shaft 14 is shown.

As mentioned above, the driving force 27 is generated by means of an electric machine 33 having a stator 32 and a rotor 36.

The stator 32 is fixed to a housing 34 of the step change gearbox.

The electric machine 33 is designed as a rotary machine concentric with the axis of rotation 30. The electric machine 33 may be, for example, a brushless machine with a permanently energized rotor or a rotor similar to a three-phase asynchronous machine.

The electric machine 33 is arranged radially around the clutch assembly 12 around. The stator 32 includes electrically energized coils (field coils) 38 which are wound on a stator core 37 and may be electrically connected through the housing 34, for example. The rotor 36 is generally aligned with the stator 32 in the axial direction and is axially supported for this purpose. This can be done via sliding, preferably via roller bearings.

Between the rotor 36 and the switching ring 23, a rotation-translation converter 40 is provided, for example in the form of a screw, a slotted guide, a ball screw or the like.

The rotational-translation converter 40 converts a rotational movement of the rotor 36 generated by the electric machine 33 into an axial movement of the switching ring 23. The switching ring 23 engages, as I said, in a circumferential groove of the shift sleeve 22 and thus actuates thereby the clutch assembly 12. As a result, either the idler gear 16 or the idler gear 18 rotatably connected to the rotary shaft 14 to insert in the transmission 13, for example, a specific gear or like.

The actuator assembly 10 has for axial support of the rotor 36, a first annular ridge 42 and a second annular ridge 44, which are formed as radial webs and receive the rotor 36 between them. More specifically, a first thrust bearing 46 is disposed between the rotor 36 and the first ring land 42, for example, a rolling bearing. Between the opposite end of the rotor 36 and the second ring land 44, a second thrust bearing 48 is arranged, which may be formed identical to the first thrust bearing 46th

The ring lands 42, 44 further receive the stator core 37 of the stator 32 therebetween, and the field windings 38 of the stator are externally wound around the ring lands 42, 44. In other words, enforce the annular webs 42, 44 the stator 32. In this way, a total of a compact arrangement of the annular webs 42, 44 can be achieved. At the radially inner ends of the annular webs 42, 44 guide pins 50 are provided (in the present case, for example, three or more guide pins), which extend between the ends of the two annular webs 42, 44. The guide pins 50 are distributed over the circumference of the actuator assembly 10 and serve to guide the switching ring 23 in the axial direction and to secure against rotation.

Furthermore, the annular webs 42, 44 may be formed as axial stops for the switching ring 23, so that a control of the electric motor 33 can be configured according to simple. In Fig. 1, the switching ring 23 is shown in a position in which he has taken the shift sleeve 22 so far to the left that the shift sleeve teeth has entered the teeth of the coupling body 24 of the idler gear 16 to rotatably in this way, the rotary shaft 14 with to connect the idler gear 16.

It is generally conceivable that the rotor 36 is supported on annular webs in the axial direction, which are fixed (for example via corresponding recesses in the sliding sleeve 22) on the guide sleeve 20 and not on the housing 34th

The actuator assembly 10 according to the invention and the clutch assembly 12 controlled by the invention can be used in all conceivable stage change transmissions 13, in particular in automated manual transmissions, in dual-clutch transmissions etc. It is particularly advantageous here that a hydraulic system is generally no longer necessary at all. This can be particularly advantageous if, for example, the associated starting clutch (or dual clutch) is not adjusted hydraulically but by electric motor.

In the actuator assembly 10 of FIG. 1, it is also advantageous for mounting purposes, when the rotor 36 and / or the stator 32 are formed divided. In the stages change gear 13, a separate actuator assembly 10 is preferably provided for each clutch assembly 12. Accordingly, it is also possible to operate the different clutch assemblies 12 associated gears in an overlapping manner.

Furthermore, it is advantageous in the invention that no shift linkage and no auxiliary drives, such. Shift drums, are necessary. This results in a total of a compact design and a reduced overall space.

The path control can either be detected by sensors and then controlled. However, it is also possible to perform the path control without path detection by the shift sleeve 22 is driven in their end positions against attacks. In this way it can be ensured that the rotor 36 always remains in the field region of the stator 32.

However, the end stops can also be scanned by sensors.

FIG. 2 shows an alternative embodiment of an actuator arrangement 10 'according to the invention. The actuator assembly 10 'generally corresponds in terms of structure and operation of the actuator assembly 10 of FIG. 1. The same elements are therefore indicated by the same reference numerals. In the following, only the differences are discussed.

The ring lands 42 ', 44' in the actuator assembly 10 'include not only the rotor 36' but also the entire stator 32 'and together form an actuator housing which may be fixed to, for example, the housing 34 of a transmission or the like.

Furthermore, it can be seen that the switching ring 23 'is shorter in the axial direction than the rotor 36'. The switching ring 23 'has such a width that it is exactly in the Circumferential groove of the shift sleeve 22 'fits. In other words, the axial length of the switching ring 23 corresponds to the axial length of the circumferential groove of the sliding sleeve 22 '.

In both actuator assemblies 10, 10 'of Figures 1 and 2, it is possible to provide these as a preassembled unit that is mounted in gearbox manufacturing. This preassembled unit then preferably contains in each case the electric machine 33 including the stator 32 and the rotor 36, the annular webs 42, 44, the axial guide for the switching ring 23 and the switching ring 23 itself. The unit can preferably be tested for function before assembly in the transmission, so that the test methods for the transmission are simplified as a whole. The housing of such a preassembled unit formed with the annular webs 42, 44 and shown in FIG. 2 is designated 60 in FIG. 2.

3 shows in a very schematic form a further alternative embodiment of an actuator arrangement 10 "according to the invention. The actuator arrangement 10" generally corresponds in terms of structure and mode of operation to the actuator arrangement 10 of FIG. 1. The same elements are therefore also indicated by the same reference numbers. In the following, only the differences are discussed.

Thus, in FIG. 3, the preassembled unit described above is indicated by dot-dash lines and denoted by 61. The rotation-translation converter 40 "shown in FIG. 3 is indicated schematically as a ball screw drive.

4 shows a further alternative embodiment of an actuator arrangement 10 'according to the invention, which generally corresponds in terms of structure and mode of operation to the actuator arrangement 10' of Fig. 2. The same elements are therefore also indicated by the same reference numerals. FIG. 4 particularly shows details of a rotational-translation converter 40 '"as it is usable for the actuator arrangement 10'" (and also for the actuator arrangements described above).

The rotation-translation converter 40 '"is formed as a ball screw and includes a spindle in the form of the switching ring 23'" and a nut in the form of the rotor 36 '". It is understood that the rotation-translation converter 40'" with other types of Spindles and nuts can be trained. However, for ease of illustration, these elements will be referred to hereafter by rotor or switching ring.

Thus, the switching ring 23 '"has on its outer circumference a first part 62 of a raceway groove 66. The rotor 36'" has on its inner circumference a second part 64 of the raceway groove 66. More specifically, these parts are formed by approximately semicircular, helically encircling grooves, which together form the track groove 66 and the thread. In the raceway 66, a plurality of rolling elements in the form of balls 68 is used. Further, one end of the raceway groove 66 is connected to the opposite end of the raceway groove 66 via a return passage 70 provided on the shift ring 23 ''. The rotation-translation converter 40 '' thus has a rolling element circulation. The rolling elements may be introduced directly adjacent to each other in the raceway 66, or spacer balls may be interposed. It is also possible to combine the balls into a ball chain, which can be made in one piece or endless. The cross section of the track groove 66 is on the one hand designed so that forces in the axial direction are transferable and on the other hand, the rolling elements and optionally the spacers (or links of the ball chain) as low friction can be performed by this track 66.

The spacers may be formed for example in the form of balls or as elements with concave recesses on both sides. The spacers preferably exert no pressure on the thread flanks of the raceway 66 and are therefore not subject to the compulsion to run along or to pass. It can also be seen in FIG. 4 that the track groove 66 includes approximately two revolutions around the circumference. As shown, the return channel 70 can be formed on the outside of the switching ring 23 '"or inside the switching ring 23'".

The switching ring 23 '"is formed shorter in the axial direction than the rotor 36'". The axial length of the switching ring 23 '"is denoted in Fig. 4 with L ₂ , the axial length of the rotor 36'" with Li. Da L ₂ <Li, the return channel 70 is preferably formed on the switching ring 23 '".

The axial length L _{2 of} the switching ring 23 '"preferably corresponds to the axial length L _{3 of} an annular groove 72 of a shift sleeve 22'" a clutch assembly, as has been described above.

Fig. 5 shows a preferred embodiment of a switching ring 23 ™ forming a spindle for a rotary-to-translational transducer according to the present invention, which may be used, for example, in the rotary-to-translation converter 40 '' of Fig. 4. It will be appreciated that the return channel 70 ™ may be used as a 5 is formed as a secant in the axial projection shown in Fig. 5. Fig. 6, which shows a section along the line VI-VI in Fig. 5, reveals that the return channel 70 ™ is formed as a straight bore and extends slightly obliquely to a longitudinal axis 30, to connect the opposite ends of the raceway 66 ^ιv each other.

In Fig. 5 it is further shown that the switching ring 23 ™ has three distributed over the circumference axial bores 74 through which the guide pins 50 of the actuator assembly according to the invention can be performed.

Fig. 7 shows in schematic form an alternative embodiment of a rotational translation converter 40 ^v . The rotation-translation converter 40 ^v corresponds in terms of structure and operation generally the rotation-translation converter of Figures 4 to 6. The same elements are therefore indicated by the same reference numerals. In the following, only the differences are discussed.

Thus, as rolling elements in the rotation-translation converter 40 ^v no balls but cylinder 68 ^{V is} provided, which are alternately offset by 90 ° within the groove 66 ^V are arranged. Between the cylinders 68 ^V respectively intermediate body are arranged, which prevent rotation of the cylinder against each other. About the cylinder 68 ^V relatively high forces can be transmitted in the axial direction. It is understood that the track groove 66 ^V in cross-section adapted to the shape of the cylinder, in particular is executed edged. Preferably, the length of the cylinder 68 ^{V is} equal to the diameter thereof, so that the raceway 66 ^V can be made compact.

Preferred embodiments of the electric machine 33 are described in the German patent application 10 2006 015 688, the disclosure content of which is fully incorporated herein by reference.

In the actuator arrangements, an energy recovery during braking of the rotor can take place. Furthermore, the electric machine 33, depending on the configuration of the rotational-translation converter 40, support critical synchronous operations.

Claims

claims 1. Rotary translation converter (40) with Wälzkörperumlauf, comprising a spindle (23), on the outer circumference of a first part (62) of a raceway (66) is formed, a nut (36), on the inner circumference of a second part (64) the running groove (66) is formed, a plurality of rolling elements (68) arranged in the raceway groove (66), and a return channel (70) connecting opposite ends of the raceway groove (66) to the rolling elements (68) to be able to circulate, wherein the return channel (70) on the spindle (23) is formed. 2. Rotation-translation converter according to claim 1, wherein the nut (36) is longer in the axial direction than the spindle (23). 3. Rotation-translation converter according to claim 1 or 2, wherein the spindle (23) is designed as a hollow spindle. 4. Rotation-translation converter according to one of claims 1 to 3, wherein the return passage (70) is formed as a channel through the spindle (23) therethrough. 5. Rotation-translation converter according to one of claims 1 to 4, wherein the return channel (70) in an axial projection on the spindle (23) follows the course of a secant. 6. Rotation-translation converter according to one of claims 1 to 5, wherein between the spindle (23) and the nut (36) is formed a plurality of grooves, each having an associated return channel (70). 7. rotational-translation converter according to one of claims 1 to 6, wherein the rolling elements (68) are balls. 8. Rotation-translation converter according to one of claims 1 to 6, wherein the rolling elements (68 ^ are cylinders. 9. Rotation-translation converter according to claim 8, wherein the cylinder axes of adjacent cylinders (68 ^ 0 in the groove (66 ^ are each an angle greater than zero against each other entangled. 10. rotational-translation converter according to claim 9, wherein the cylinders (68 ^ alternately crossed by 90 ° in the groove (66 ^ are arranged. 11. Actuator assembly (10) for axially displacing an actuating member (22) by means of a driving force (27), which is generated by an electric machine (33), in particular for a clutch assembly (12) of a stepped change gear (13), wherein the actuating member (22 ) is axially displaceably mounted with respect to a rotary shaft (14), the electric machine (33) having a stator (32) fixed to the housing and a rotor (36) coupled to the actuator (22) and coaxial with the actuator (22 ), wherein the rotor (36) is coupled to the actuator (22) via a rotation-translation converter (40), and wherein the rotor (36) is axially journaled to an axial bearing portion (42-48) having a first and a second ring land (42, 44) disposed on axially opposite sides of the rotor (36). 12. actuator assembly according to claim 11, wherein the Axiallagerungsabschnitt (42-48) is formed fixed to the housing. 13. actuator assembly according to claim 11 or 12, wherein the rotational-translation converter (40) has a converter section on the inner circumference of the rotor (36). 14. Actuator arrangement according to one of claims 11 to 13, wherein the rotation ons translation converter (40) has a converter section on the outer circumference of a switching member (23) which is coupled to the actuating member (22) in the axial direction. 15. Actuator arrangement according to claim 14, wherein between the first and the second annular web (42, 44) guide means (50) extend, on which the switching member (23) is guided displaceably in the axial direction. 16. An actuator assembly according to claim 15, wherein the guide means (50) comprises a plurality of axial pins (50) which are arranged distributed over the circumference of the actuator assembly (10). 17. Actuator arrangement according to one of claims 11 to 16, wherein at least one of the annular webs (42, 44) passes through the stator (32) in the radial direction. 18. Actuator arrangement according to one of claims 11 to 16, wherein the stator (32 ') between the annular webs (42', 44 ') is arranged. 19. Actuator arrangement according to one of claims 11 to 18, wherein the rotation ons translation converter is designed as a rotational-translation converter according to one of claims 1 to 10. 20. Actuator assembly according to claim 19, wherein the nut is connected to the rotor (36). 21. Actuator arrangement according to claim 19 or 20, wherein the spindle of the rotation ons translation converter with a switching member (23) is connected, which is coupled to the actuating member (22) in the axial direction. 22. Actuator arrangement according to claim 21, wherein the switching member (23) has a width (L ₂ ) corresponding to the width (L ₃ ) of a groove of the actuating element (22). 23. A clutch assembly (12) for a variable speed transmission (13), in particular for motor vehicles, with a guide sleeve (20) which is fixed to a rotary shaft (14) and has a guide sleeve toothing, with a sliding sleeve (22) having a sliding sleeve teeth, which is engaged with the guide sleeve teeth, so that the shift sleeve (22) with respect to the rotary shaft (14) rotatably and axially displaceably mounted, and with a coupling body (24, 26) fixed to a loose wheel (16, 18) is, which is rotatably mounted on the rotary shaft (14), and having a Kupplungsungskörperverzahnung into which the sliding sleeve toothing can be inserted to the idler gear (16, 18) rotatably connected to the rotary shaft (14), wherein the sliding sleeve (22 ) as an actuating member by means of an actuator assembly (10; 50) according to one of claims 11 to 22 axially displaceable.