Wheel decoupling device for a motor vehicle in bistable design

Abstract

Wheel decoupling device (1) for a motor vehicle, comprising a drive element (4), an output element (5), a displaceably arranged shifting sleeve (6) which can be connected in a rotationally fixed manner to the drive element (4) and the output element (5), and an actuating device (7) which acts in an adjusting manner on the shifting sleeve (6), wherein the actuating device (7) further comprises a ramp system (8) and the ramp system (8) is designed such that, upon rotation of an adjusting gear (9), a sliding ring (10) which is axially fixedly supported on the shifting sleeve (6) is displaced axially between a first position in which the drive element (4) and the output element (5) are rotationally decoupled from one another, and a second position in which the shifting sleeve (6) positively connects the drive element (4) and the output element (5) to one another in a rotationally fixed manner, and wherein a position securing device (30) is provided is,which axially secures the sliding ring (10) both in the first position and in the second position, wherein the position securing device (30) comprises a preload spring unit (13), characterized in that the preload spring unit (13) comprises at least one spring element (31) which is operatively inserted between a housing (14) and the shift sleeve (6).

Description

[0001] The invention relates to a wheel decoupling device for a motor vehicle, i.e., a device for selectively decoupling / coupling a wheel / wheel hub of a motor vehicle from / to a drive shaft. The invention also relates to a drive unit with this wheel decoupling device.

[0002] Both US 2018 / 0345785 A1 and DE 31 19 447 A1 disclose corresponding wheel decoupling devices for a motor vehicle.

[0003] The object of the invention is to provide a decoupling device that is as close to the tire as possible to enable efficient operation of a motor vehicle, in particular optimal coasting. The decoupling device should also be as compact as possible and, at the same time, be controllable quickly and precisely. Functional reliability should also be ensured.

[0004] This is achieved according to the invention by the subject matter of claim 1. A wheel decoupling device for a motor vehicle is claimed, which device has a drive element, an output element, a displaceably arranged shifting sleeve that can be connected in a rotationally fixed manner to the drive element and the output element, and an actuating device that acts on the shifting sleeve in an adjusting manner. The actuating device further has a ramp system. The ramp system is designed such that, upon rotation of an adjusting gear, a sliding ring supported axially fixedly on the shifting sleeve is displaced axially between a first position, in which the drive element and the output element are rotationally decoupled from one another, and a second position, in which the shifting sleeve positively connects the drive element and the output element to one another in a rotationally fixed manner.Furthermore, there is a position securing device that axially secures / supports the sliding ring in both the first position and the second position.

[0005] This provides a positive-locking wheel decoupling device that requires minimal installation space and can be integrated directly into and / or near a wheel hub of a motor vehicle in a space-saving manner. This allows a wheel of the motor vehicle to be decoupled during operation, which contributes to a significant increase in efficiency, particularly when the vehicle is coasting. Furthermore, the clutch is designed to be bistable, meaning that it functions reliably both in its open position and in its closed position in the event of a failure of one actuation.

[0006] Further advantageous embodiments are claimed in the subclaims and explained in more detail below.

[0007] Accordingly, according to the invention, the position securing device comprises a preload spring unit. Thus, the position securing device is designed to be as robust and reliable as possible in its operation.

[0008] If the preload spring unit is inserted in such a way that the sliding ring is preloaded into the first position, the position of the sliding ring in the first position is secured by simple means.

[0009] In this context, it is in accordance with the invention that the preload spring unit comprises at least one spring element that is operatively inserted / clamped between a housing and the shift sleeve. The preload spring unit preferably comprises several spring elements arranged in series, furthermore preferably several wave springs. This also enables a compact design.

[0010] It is also advantageous if the ramp system is implemented in a self-releasing manner. Further preferably, the ramp system is designed in such a way that, when the torque driving the adjusting gear during operation ceases (or when a certain torque driving the adjusting gear during operation is undershot), the sliding ring is automatically pushed back (by the preload spring unit) into the first position outside of / at a distance from the second position. This further increases functional reliability.

[0011] For the lowest possible wear-related operation of the ramp system, it is also beneficial if the adjusting gear and the sliding ring are supported on one another in the axial direction via a rolling element (more preferably arranged over several rolling elements distributed in the circumferential direction), for example in the form of balls. Further preferably, the rolling element lies directly against a ramp contour (preferably continuously increasing in the circumferential direction) of the adjusting gear and / or a ramp contour (preferably continuously increasing in the circumferential direction) of the sliding ring, and a holding section is provided in the circumferential direction adjacent to the at least one ramp contour, by means of which the rolling element is secured / blocked from further rolling in the second position of the sliding ring by means of a positive-locking and / or frictional-locking engagement.

[0012] If the holding section is integrated directly into a raceway that accommodates the rolling element (of the sliding ring or the adjusting gear), the structure is further simplified.

[0013] In this context, it has also been found to be expedient for the holding section to have a reduced gradient compared to the at least one ramp contour or no gradient in the circumferential direction (preferably designed as a 0° flank).

[0014] Furthermore, it is advantageous if the retaining section has a recess / trough in the raceway accommodating the rolling element, into which the rolling element can be positively engaged. This ensures that the rolling element is locked in place with as little wear as possible.

[0015] If the sliding ring is supported on the shift sleeve by means of a spring unit, the ramp system is in turn subjected to a certain axial preload force, which further reduces wear.

[0016] If the adjusting gear is axially fixed to a housing, preferably by means of an axial bearing, the actuating device is stably accommodated in the housing.

[0017] It is also advantageous if the shift sleeve has a sleeve area with a toothing of constant diameter, preferably designed as an internal toothing. In the second position, this toothing is positively connected in the direction of rotation with both a counter toothing of the drive element and a counter toothing of the output element. This keeps the shift sleeve as simple as possible in its design.

[0018] If the adjusting gear is driven by an electric actuator, the wheel decoupling device is actuated as efficiently as possible during operation of the motor vehicle.

[0019] Furthermore, the invention relates to a drive unit for a motor vehicle, comprising a drive shaft (preferably designed as an output of a tripod), a wheel hub and a wheel decoupling device according to the invention, accommodated in a steering knuckle, according to at least one of the previously described embodiments, wherein the drive element of the wheel decoupling device is connected to the drive shaft or is formed directly by the drive shaft and the output element of the wheel decoupling device is connected to the wheel hub or is formed directly by the wheel hub.

[0020] In other words, according to the invention, a wheel separation unit (wheel decoupling device) is designed by means of which the wheel is decoupled or coupled from the rest of the drive train depending on the respective driving mode of the motor vehicle. Bistability is achieved by a ramp system and a return spring (preload spring unit). If the clutch (wheel decoupling device) is open, i.e. the shift sleeve is (only) engaged with the tripod (drive shaft), the shift sleeve is held in this stable state by the force of the corrugated spring assembly (preload spring unit). If the ramp mechanism (ramp system) is actuated by the spur gear (adjusting gear), the shift sleeve is displaced and brought into engagement with the output-side hub toothing (second counter toothing).If a failure occurs during engagement of the clutch, the selector sleeve is repositioned into the open state (first position) by the wave spring assembly. The spur gear is not self-locking, which means that the return process is not blocked. Two different variants are available to keep the clutch closed in the event of a failure. In the first variant, the gradient of the ramp changes to 0° (end position without gradient) at the end of the ball tracks (ramp contours). This corresponds to a flat plateau on which the ball (rolling element) remains in the closed state. Due to the arrangement of the wheel decoupling device directly on the wheel and the associated undamped mechanical loads, a second variant provides an end position with a hollow (recess) for the ball.Once the balls have engaged in the grooves at the end of the tracks (ramp contours), the clutch remains closed even in the event of a failure (second position). Unlike the first variant, the balls are held in position by positive engagement rather than friction. By reversing the speed and applying torque from the electric motor (actuator), the ramp / adjustment gear can be reversed and the wheel decoupling device can be disengaged.

[0021] The invention will now be explained in more detail below with reference to figures.

[0022] They show: Fig. 1 a longitudinal sectional view of a wheel decoupling device according to the invention according to a preferred embodiment, wherein the wheel decoupling device is already used in a drive unit of a motor vehicle having a steering knuckle and is arranged in a decoupling state / open state, Fig. 2 a perspective view of a wheel decoupling device according to Fig. 1 drive unit, wherein an actuator actuating the wheel decoupling device is also shown, Fig. 3 a longitudinal section of the wheel decoupling device according to Fig. 1 in the area of tooth contact between an adjusting gear and another gear operatively connected to the actuator, the gear decoupling device again being in the decoupling state, Fig. 4 a further longitudinal section of the wheel decoupling device according to Fig. 1, whereby the wheel decoupling device is now in a coupling state / closed state, Fig. 5 a perspective view of the Fig. 1 to 4, wherein a recess in a raceway of the adjusting gear securing a rolling element in a closed state of the wheel decoupling device can be seen, and Fig. 6 a perspective view of an alternative design of the adjusting gear compared to that shown in Fig. 5, whereby the raceway of the adjusting gear now only has a section that has no pitch (in the circumferential direction).

[0023] The figures are merely schematic in nature and serve exclusively to facilitate understanding of the invention. The same elements are provided with the same reference numerals. Furthermore, the different features of the various embodiments can, in principle, be freely combined with one another.

[0024] With Fig. 1 shows a detailed view of a wheel decoupling device 1 according to the invention. The wheel decoupling device 1 is a decoupling device in the sense of a clutch / disconnect clutch for separating a wheel / a wheel hub 2 that is non-rotatably connected to the tire-equipped wheel of the motor vehicle from the adjacent rotating components of the drive train, here a drive shaft 3. The wheel decoupling device 1 is therefore inserted directly between the drive shaft 3 and the wheel hub 2 of a motor vehicle. The drive shaft 3 is also designed as a component (output / a component facing the wheel) of a cardan shaft, namely a tripod.

[0025] It can also be seen that a housing 14 of the wheel decoupling device 1 is directly received / integrated in a steering knuckle 19 of a wheel suspension.

[0026] The terms axial / radial and circumferential direction used herein refer to various directions that are to be understood in relation to a central axis of rotation 23. The axis of rotation 23 forms a rotation axis of the wheel hub 2 and the drive shaft 3. The axial / axial direction is to be understood as a direction along / parallel to the axis of rotation 23, the radial / radial direction is to be understood as a direction perpendicular to the axis of rotation 23, and the circumferential direction is to be understood as a direction along a circular line concentric with the axis of rotation 23.

[0027] The wheel decoupling device 1 is in the Fig. 1 and Fig. 2 in a decoupling state / open state and in Fig. 3 is shown in a coupled / closed state. The wheel decoupling device 1 is designed as a positive-locking coupling / positive-locking coupling.

[0028] The wheel decoupling device 1 has a shift sleeve 6, which is relatively displaceable relative to an end region of the drive shaft 3, referred to as the drive element 4, and an end region of the wheel hub 2, referred to as the output element 5. The shift sleeve 6 has a toothing 16 designed as an internal toothing, which interacts with counter-toothings 17a, 17b of the drive element 4 and the output element 5 and can be connected to them in a rotationally fixed, positive-locking manner.

[0029] According to Fig. 1, the shift sleeve 6 is displaced into a first position corresponding to the uncoupling state, in which its toothing 16 is only in meshing engagement with the first counter-toothing 17a of the drive element 4, but is disengaged from the second counter-toothing 17b of the output element 5. This first position is supported / supported by a preload spring unit 13 described in more detail below. In a second position corresponding to the coupling state, the shift sleeve 6 is axially displaced relative to the first position to such an extent that the toothing 16 is in form-fitting, non-rotatable contact with both the first counter-toothing 17a and the second counter-toothing 17b. In the coupling state / in the second position, the shift sleeve 6 thus connects the drive element 4 and the output element 5 in a non-rotatable manner.

[0030] It should also be noted that the toothing 16 of the shift sleeve 6 has a constant (inner) diameter. Therefore, the counter toothings 17a, 17b preferably also have the same (outer) diameter.

[0031] An actuating device 7 is provided for actuating / displacing the shift sleeve 6 between its first position and second position. The actuating device 7 has a ramp system 8. The ramp system 8 further includes an adjusting gear 9 and a sliding ring 10. Furthermore, the ramp system 8 includes a plurality of rolling elements 12 distributed in the circumferential direction, which are shaped as balls here. The adjusting gear 9 is axially supported on the sliding ring 10 via the rolling elements 12.

[0032] When considering the Fig. 1 to 3, it should be noted that both the adjusting gear 9 and the sliding ring 10 form ramp contours 11a, 11b, which directly form the raceway 34 for the rolling elements 12. Each ramp contour 11a, 11b rises continuously axially along its extension in the circumferential direction. The ramp contours 11a, 11b rise in a circumferential direction, in particular axially opposite to one another. The ramp contours 11a, 11b are therefore designed as spindle-shaped / helical tracks.

[0033] The ramp contours 11a, 11b are coordinated with one another in such a way that when the adjusting gear 9 is rotated in a first direction of rotation relative to the sliding ring 10, the rolling elements 12 roll along the ramp contours 11a, 11b, thereby pushing the sliding ring 10 away from the adjusting gear 9. When the adjusting gear 9 is rotated in the opposite direction in a second direction of rotation, the sliding ring 10 is in turn pushed back towards the adjusting gear 9. This results in the corresponding decoupling or coupling state of the wheel coupling device 1 by rotating the adjusting gear 9. The sliding ring 10 is furthermore received / guided on the housing 14 in a rotationally fixed manner.

[0034] It can also be seen that the sliding ring 10 is supported on the shift sleeve 6 on its side axially facing away from the adjusting gear 9 / the rolling element 12. For this purpose, the sliding ring 10 is supported on the shift sleeve 6 at its end via a (first) axial bearing 24a and a spring unit 25 (here comprising at least one wave spring) radially outside a sleeve region 15 comprising the toothing 16. The sliding ring 10, like the shift sleeve 6, is therefore displaced between the first position and the second position.

[0035] Axially opposite to the sliding ring 10, the shift sleeve 6 continues to be spring-loaded relative to the housing 14. For this purpose, the preload spring unit 13 is provided, which serves to press the shift sleeve 6 with an axial preload in the direction of the adjusting gear 9.

[0036] This preload spring unit 13 also forms a position securing device 30 according to the invention, which preloads the sliding ring 10 and consequently also the shift sleeve 6 into the first position, i.e., axially secures / supports it in the first position. The ramp system 8 is designed to be self-releasing, so that when a torque driving the adjusting gear 9 during operation ceases, the sliding ring 10 is automatically pushed back into the first position outside of the second position, i.e., in any intermediate position axially between the first position and the second position.

[0037] The preload spring unit 13 has at least one spring element 31, here even several spring elements 31 arranged axially in series with one another in the form of wave springs, which are inserted axially between the housing 14 and the shift sleeve 6.

[0038] In this context, it should also be noted that both the preload spring unit 13 and the spring unit 25 may also comprise other mechanical springs, such as spiral springs, disc springs or spring assemblies.

[0039] The preload spring unit 13 is supported on the shift sleeve 6 by means of a (second) axial bearing 24b. The preload spring unit 13 is thus essentially fixed to the housing and the shift sleeve 6 is mounted / supported so as to be rotatable relative to the preload spring unit 13. For the sake of clarity, the preload spring unit 13 is shown in Fig. 4 with a reduced number of wave springs compared to Fig. 1 and Fig. 2 shown.

[0040] In this embodiment, the position securing device 30 is even bistable and secures the sliding ring 10 and consequently also the shift sleeve 6 not only in their first position, but also in the second position. Once the sliding ring 10 reaches the second position, it is automatically locked in this second position, so that the sliding ring 10 remains in the second position when the torque driving the adjusting gear 9 during operation is removed.

[0041] In general, this is a Fig. 5, a (first) holding section 32 is provided, which can be seen in more detail, by means of which one of the rolling elements 12 is positively secured / prevented from further rolling along the raceway 34 in the second position of the sliding ring 10. The (first) holding section 32 is integrated directly into the raceway 34 receiving the rolling element 12. In this embodiment, the (first) holding section 32 is formed in the adjusting gear 9, but in other embodiments, it can also be formed alternatively in the sliding ring 10. The (first) holding section 32 has Fig. 5 has a recess 35 which is formed in the raceway 34. The recess 35 is dimensioned such that the rolling element 12 engages in the second position in a form-fitting manner (form-fitting action in the circumferential direction / direction of rotation).

[0042] Because the sliding ring 10 is supported axially on the adjusting gear 9 via the rolling element 12, the rolling element 12 is permanently and directly in contact with both the first ramp contour 11a of the adjusting gear 9 and the second ramp contour 11b of the sliding ring 10. The (first) holding section 32 with the recess 35 directly adjoins the first ramp contour 11a, so that the rolling element 12 engages in the recess 35 in the second position and is thus blocked relative to the adjusting gear 9 (with a specific holding force).

[0043] According to Fig. 6, the (first) holding section 32 can alternatively be replaced by a (second) holding section 33, which, in the second position of the sliding ring 10, essentially blocks the rolling element 12 from further rolling by frictional support. In this embodiment, the second holding section 33 is designed with a reduced gradient compared to the first ramp contour 11a, or with no gradient at all in the circumferential direction / forming a 0° flank. This also secures the second position of the sliding ring 10 / the shift sleeve 6.

[0044] Combined with Fig. 2, in which an entire drive unit 20 is indicated, it should be noted that the adjusting gear 9 is preferably adjustable via a gear 21 that is drivable / driven by an electric actuator 18. The actuator 18 is designed as a purely electric actuator 18 (rotary motor). The gear 21 preferably engages directly with a toothing, here designed as external toothing 36, of the adjusting gear 9. The gear 21 is designed here as an intermediate gear and is in tooth engagement with a pinion 37 located on a rotor shaft of the actuator 18. The actuator 18 thus drives the adjusting gear 9 via a gear 38 (here in the form of a spur gear), which includes the gear 21, the pinion 37, and the external toothing 36.

[0045] With regard to the housing 14, considering the Fig.1 also points out that this preferably consists of two parts 29a, 29b, which are connected to one another in a connecting region 22. Here, it is again advantageous if a seal 26, for example in the form of an O-ring, is present in the connecting region 22 / contact region between the two parts of the housing 14. A corresponding static seal 27 can also be provided between the steering knuckle 19 and the housing 14. Furthermore, a radial shaft seal 28 is preferably present radially between the housing 14 and the drive element 4.

[0046] Furthermore, a further (third) axial bearing 24c is provided on a side of the adjusting gear 9 axially facing away from the shift sleeve 6. The adjusting gear 9 is supported on the housing 14 by means of this (third) axial bearing 24c.

[0047] In other words, in the wheel decoupling device according to the invention, a shifting sleeve 6 is displaced by a ramp geometry (ramp contours 11a, 11b) for switching / adjusting the wheel decoupling device. In particular, a return spring (preload spring unit 13) is provided for quickly bridging the frictional connection of the wheel decoupling device 1 near the tire. A further return spring (spring unit 25) also serves to center the ramp unit (ramp system 8). The return spring (preload spring unit 13) for the decoupling / separating function can also be implemented as a disc spring, a spring assembly, or a coil spring.

[0048] The subject of the application is therefore a wheel decoupling device 1 (in English "Disconnect Unit (DCU)"), which is integrated into the drive train directly on the wheel between the drive shaft 3 and the hub (wheel hub 2). Depending on the respective driving mode, the wheel decoupling device 1 disconnects or connects the wheel from the rest of the drive train. By moving the shift sleeve 6, the drive-side toothing (first counter-toothing 17a) of the tripod is positively connected to the output-side toothing (second counter-toothing 17b) of the hub. The axial displacement of the shift sleeve 6 is achieved by a ramp system 8, which converts a rotational movement into an axial movement. The ramp system 8 consists of an adjusting gear 9, balls (rolling elements 12), and an axially displaceable ramp (sliding ring 10). The raceways 34 (having ramp contours 11a, 11b) of the balls can be designed according to the required travel path.

[0049] The ramp system 8 is actuated by an electric motor (actuator 18) with a spur gear (gear 38), which engages the adjusting gear 9. The axially displaceable ramp (sliding ring 10) is fixed in the housing 14 of the wheel decoupling device 1 by a toothing. When the adjusting gear 9 is actuated, the balls are axially displaced due to the helical raceways 34. The rotationally fixed bearing of the ramp (sliding ring 10) leads to their axial displacement. Due to the pressure angle, the adjusting gear 9 is centered, which is why no separate radial bearing is necessary. The relative movement of the adjusting gear 9 to the housing 14 is compensated by an axial needle bearing (third axial bearing 24c).

[0050] When open, the shift sleeve 6 engages only with the drive-side gearing (first counter-gearing 17a) of the tripod. When the wheel decoupling device 1 is closed, the shift sleeve 6 is displaced equivalent to the axial movement of the ramp. The relative movement between the ramp and the shift sleeve 6 is compensated by an additional axial bearing / axial needle bearing (first axial bearing 24a). A wave spring (spring unit 25) is integrated between the axial bearing (first axial bearing 24a) and the shift sleeve 6 to ensure a defined degree of compliance in the event of tooth-to-tooth contact.

[0051] The ramp system 8 requires axial preload, which is implemented via a wave spring assembly (preload spring unit 13). The wave spring (preload spring unit 13) is positioned in the housing 14 and connected to the shift sleeve 6 via another axial bearing / axial needle bearing (second axial bearing 24b). When the shift sleeve 6 is opened by the actuator 18, the wave spring assembly (preload spring unit 13) relaxes and pushes the shift sleeve 6 back to its initial state (decoupling state).

[0052] Bistability according to the invention is achieved by the ramp system 8 and the return spring (preload spring unit 13). If the clutch is opened, i.e. the shift sleeve 6 is engaged with the tripod (drive shaft 3), the shift sleeve 6 is held in this stable state by the force of the wave spring assembly (preload spring unit 13). If the ramp mechanism is actuated by the spur gear, the shift sleeve 6 is displaced, as described above, and brought into engagement with the output-side hub toothing (second counter toothing 17b). If a failure occurs during engagement of the clutch, the shift sleeve 6 is repositioned into the open state (decoupling state) by the wave spring assembly. The spur gear is not designed to be self-locking, which means that the return process is not blocked.

[0053] Two different variants are available to keep the clutch closed in the engaged state (coupling state) in the event of failure. At the end of the ball raceways (i.e. at one end region of the raceways 34 in the circumferential direction), the gradient of the ramp (here the first ramp contour 11a) changes to 0° (end position without gradient). This corresponds to a flat plateau on which the ball remains in the engaged state. Due to the arrangement of the wheel decoupling device 1 directly on the wheel and the associated undamped mechanical loads, the other variant provides an end position with a recess (depression 35) for the ball. As soon as the balls have engaged in the recesses at the end of the raceways 34, the clutch remains closed even in the event of failure. In this case, in contrast to the first variant, the balls are held in position by positive locking and not by friction.By reversing the speed and motor torque of the electric motor, the ramp (adjusting gear 9) can be turned back and the wheel decoupling device 1 can be disengaged.

[0054] The wheel decoupling device 1 is completely enclosed and thus protected against the ingress of ambient media and leaking lubricants. The housing 14 is mounted on the wheel axle using several mounting screw connections (not shown for clarity). The housing 14 is sealed against the tripod with a dynamic seal (radial shaft seal 28). A static O-ring seal (static seal 27) is installed opposite the steering knuckle 19. Due to the assembly, the housing 14 is split in the area of the screwing points. The flange connection (connection area 22) of the housing 14 is also sealed with an O-ring (seal 26). List of reference symbols 1 wheel decoupling device 2 wheel hub 3 Drive shaft 4 Drive element 5 Output element 6 Shift sleeve 7 Actuating device 8 Ramp system 9 Adjusting gear 10 sliding ring 11a Ramp contour of the adjusting gear 11b Ramp contour of the sliding ring 12 rolling elements 13 Preload spring unit 14 housings 15 Sleeve area 16 Gearing 17a first counter toothing 17b second counter toothing 18 Actuator 19 Steering knuckles 20 drive unit 21 gear 22 Connection area 23 axis of rotation 24a first axial bearing 24b second axial bearing 24c third thrust bearing 25 spring unit 26 Seal 27 static seal 28 Radial shaft seal 29a first part of the housing 29b second part of the housing 30 Position securing device 31 spring element 32 first stopping section 33 second stopping section 34 Career 35 Deepening 36 external teeth 37 pinions 38 gearboxes

Claims

[1] Wheel decoupling device (1) for a motor vehicle, comprising a drive element (4), an output element (5), a displaceably arranged shifting sleeve (6) which can be connected in a rotationally fixed manner to the drive element (4) and the output element (5), and an actuating device (7) which acts in an adjusting manner on the shifting sleeve (6), wherein the actuating device (7) further comprises a ramp system (8) and the ramp system (8) is designed such that, upon rotation of an adjusting gear (9), a sliding ring (10) which is axially fixedly supported on the shifting sleeve (6) is displaced axially between a first position in which the drive element (4) and the output element (5) are rotationally decoupled from one another, and a second position in which the shifting sleeve (6) positively connects the drive element (4) and the output element (5) to one another in a rotationally fixed manner, and wherein a position securing device (30) is present,which axially secures the sliding ring (10) both in the first position and in the second position, wherein the position securing device (30) has a preload spring unit (13), , characterized by that the preload spring unit (13) has at least one spring element (31) which is inserted between a housing (14) and the shift sleeve (6). [2] Wheel decoupling device (1) according to claim 1, characterized by that the ramp system (8) is designed to be self-releasing in such a way that when a torque driving the adjusting gear (9) during operation ceases, the sliding ring (10) is automatically pushed back into the first position outside the second position. [3] Wheel decoupling device (1) according to one of claims 1 to 2, characterized byin that the adjusting gear (9) and the sliding ring (10) are supported on one another in the axial direction via a rolling body (12), wherein the rolling body (12) bears directly against a ramp contour (11a) of the adjusting gear (9) and / or a ramp contour (11b) of the sliding ring (10) and a holding section (32, 33) is provided in the circumferential direction adjacent to the at least one ramp contour (11a, 11b), by means of which holding section the rolling body (12) is secured in the second position of the sliding ring (10) in a form-fitting and / or friction-fitting manner against further rolling. [4] Wheel decoupling device (1) according to claim 3, characterized by that the holding section (32, 33) is directly integrated into a raceway (34) receiving the rolling element (12). [5] Wheel decoupling device (1) according to claim 3 or 4, characterized by that the holding section (33) has a reduced gradient compared to the at least one ramp contour (11b, 11a) or no gradient in the circumferential direction. [6] Wheel decoupling device (1) according to claim 3 or 4, characterized by that the holding section (32) has a recess (35) in the raceway (34) receiving the rolling element (12), into which recess (35) the rolling element (12) can be positively engaged. [7] Drive unit (20) for a motor vehicle, with a drive shaft (3), a wheel hub (2) and a wheel decoupling device (1) accommodated in a steering knuckle (19) according to one of claims 1 to 6, wherein the drive element (4) of the wheel decoupling device (1) is connected to the drive shaft (3) or is formed directly by the drive shaft (3) and the output element (5) of the wheel decoupling device (1) is connected to the wheel hub (2) or is formed directly by the wheel hub (2).

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