Planetary roller screw drive for an actuator of a vehicle, and actuator comprising such a planetary roller screw drive

Abstract

The invention relates to a planetary roller screw drive for an actuator (1) of a vehicle, wherein a plurality of planetary rollers (2) are in engagement with a thread profile of a spindle (3), wherein the planetary rollers (2) are rotatably arranged at both ends by means of planetary roller journals (4, 5) in recesses (6, 7), each recess being formed in a planetary roller carrier (8, 9), wherein, during operation of the planetary roller screw drive, the planetary rollers (2) come into contact, at least in part, with a sleeve (10) surrounding the planetary rollers (2), wherein, during operation of the planetary roller screw drive, radial forces of the planetary rollers (2) can be transmitted via rolling contact to a smooth inner circumferential surface of the sleeve (10), and axial forces of the planetary rollers (2) can be transmitted via the axial ends of the planetary roller journals (4, 5) into the recesses (6, 7) and at least indirectly into the associated planetary roller carrier (8, 9), wherein each planetary roller carrier (8, 9) contains a centring element (13, 14) for concentrically supporting the spindle (3) relative to said planetary roller carrier, wherein the centring elements (13, 14) rotate together with the planetary roller carriers (8, 9) and are axially freely guided in the associated planetary roller carrier (8, 9).

Description

[0001] Planetary roller screw drive for a vehicle actuator and actuator with such a planetary roller screw drive

[0002] The invention relates to a planetary roller screw drive for a vehicle actuator and an actuator with such a planetary roller screw drive. Actuators can convert the rotary motion of one component into an axial motion of another component.

[0003] A planetary roller screw drive (PWG), also called a planetary roller screw drive, consists of a spindle, a spindle nut or ring gear, and planetary rollers arranged around the circumference between these and mounted in a planetary roller carrier. The spindle, spindle nut, and planetary rollers have profiles to transmit rotary motion between the spindle and spindle nut. One of the components—the spindle or spindle nut—is driven by rotation, while the other component, in a rotationally fixed arrangement, is displaced along the longitudinal axis of the spindle by an axial path corresponding to the set gear ratio.In this design, the planetary rolling elements have two different profile sections that mesh with the spindle on one side and with the ring gear on the other, with one profile section on the planetary rolling element being groove-shaped and the other profile section on the planetary rolling element typically being groove-shaped, and depending on the embodiment, a complementary threaded section is arranged on the spindle or the spindle nut and, accordingly, the grooved section on the other component.

[0004] For example, DE 10 2018 104 095 A1 discloses a planetary roller screw drive, an actuator, and a release system for a clutch device. The planetary roller screw drive comprises a threaded spindle and several planetary rollers mechanically engaged with the threaded spindle and rotatable about their own longitudinal axis. Each planetary roller has a cylindrical shoulder in which several circumferential grooves form a structure that meshes with the thread of the threaded spindle. The planetary roller screw drive further comprises at least one planetary roller carrier that supports the planetary rollers at least in the axial direction.The planetary rollers are surrounded on their radial outer side by an essentially hollow cylindrical planetary sleeve, which serves to radially support the planetary rollers and on its inner side, at least in the area of ​​radial overlap with the structures of the planetary rollers, is essentially so smooth that no positive-locking transmission of an axial force from the structures of the planetary rollers to the planetary sleeve is possible.

[0005] The object of the invention is to provide an alternative planetary roller screw drive. In particular, the planetary roller screw drive should be inexpensive and easy to manufacture. Furthermore, the positioning of the planetary rollers and spindle, as well as the positioning of the planetary roller carrier and spindle, should be improved. This object is achieved by the subject matter of claim 1. Preferred embodiments can be found in the dependent claims, the description, and the figures.

[0006] According to a planetary roller screw drive according to the invention for an actuator of a vehicle, several planetary rollers engage with a profiled spindle, wherein the planetary rollers are rotatably arranged at both ends by means of planetary roller journals in respective recesses on a respective planetary roller carrier, wherein, during operation of the planetary roller screw drive, the planetary rollers come into contact at least partially with a sleeve surrounding the planetary rollers, wherein, during operation of the planetary roller screw drive, radial forces of the planetary rollers can be transmitted by means of a rolling contact on a smooth inner circumferential surface of the sleeve, and axial forces of the planetary rollers can be transmitted at least indirectly to the respective planetary roller carrier via the axial ends of the planetary roller journals in the respective recesses.wherein a respective centering element is arranged in the respective planetary roller carrier for the concentric mounting of the spindle to the respective planetary roller carrier, wherein the centering elements rotate together with the planetary roller carriers and are axially freely guided in the respective planetary roller carrier.

[0007] The planetary rollers can roll on the smooth inner circumference of the sleeve. Rolling friction can occur between the two contacting surfaces as the planetary rollers roll. In the planetary roller screw drive of interest here, rolling contact exists between a flattened outer surface of each planetary roller and the macroscopically smooth inner surface of the surrounding sleeve: The two cylindrical bodies touch at a narrow contact ellipse, over which they roll – with negligible sliding; the resulting Hertzian contact pressures generate the normal force through which the radial forces occurring during operation are positively transmitted into the sleeve.

[0008] In contrast, rolling friction (rolling resistance) is the small loss component that opposes rolling, resulting from the elastic deformation of the contact partners, internal damping of the material, and microslip at the edges of the contact area; it generates a braking force FR = cr N, but does not significantly affect the transmission of the radial load. In short: Rolling contact describes the load-bearing, virtually slip-free rolling contact, while rolling friction refers to its unavoidable energy losses that are not required for the force path itself.

[0009] By distributing guide surfaces and force application / dissipation surfaces between the planetary rollers, planetary roller carrier, sleeve, and centner elements, a cost-effective design can be achieved, resulting in high efficiency. The planetary rollers are arranged essentially parallel to the longitudinal axis of the spindle, with this concentricity being improved by the centner elements. For example, the planetary roller carriers are configured to be rotationally fixed to the rotor of an actuator. Alternatively, the spindle can be connected to the rotor of the actuator. The sleeve is designed as a "floating sleeve" and thus has a clearance or air gap to the planetary roller carriers. The sleeve is designed to absorb radial forces from the planetary rollers via a rolling contact during operation of the planetary roller screw drive.Since the sleeve cannot absorb axial forces, it is designed without rolling bearings or other sliding bearings and is guided only by axial contact surfaces in the planetary roller carrier.

[0010] The axial adjustability of the centering elements relative to the planetary roller carriers prevents axial forces from the planetary rollers from being transmitted to the centering elements. This allows the centering elements to adjust themselves according to the support of the planetary roller journals in the planetary roller carriers. Regardless of the axial direction in which the planetary rollers approach, the centering elements follow this axial direction. This ensures optimal concentricity of the spindle to the respective planetary roller carrier at all times, even if the planetary rollers wear down. In particular, this extends the service life and efficiency of the planetary roller screw drive.

[0011] According to one embodiment, each centner element has a profiled inner circumferential surface that engages with the profile of the spindle. Thus, the profiled inner circumferential surface of each centering element corresponds to the profile of the spindle. For example, each centner element is rotationally fixed to the respective planetary roller carrier via a positive locking mechanism. Alternatively, each centner element has a smooth cylindrical outer circumferential surface that is connected to the respective planetary roller carrier via a key or a drive element. The centner element may also have the outer geometry of a polygonal hollow cylinder, particularly a hexagonal cylinder. The spindle's mounting via the centner elements in the planetary roller carriers prevents the spindle from tilting relative to the planetary rollers. For example, the centner elements are made of plastic.

[0012] According to one embodiment, at least one starting element is arranged axially in the respective recess between the respective planetary roller journal and the respective planetary roller carrier. For example, exactly two starting elements are provided for each planetary roller, wherein one starting element is arranged axially between the first planetary roller journal and the first planetary roller carrier in the recess, and wherein another starting element is arranged axially between the second planetary roller journal and the second planetary roller carrier in the recess. For example, the starting elements are designed as plates and have a diameter that essentially corresponds to the diameter of the planetary roller journals.Alternatively, exactly two starting elements are provided for all planetary rollers, with one starting element arranged axially between the first planetary roller journal and the first planetary roller carrier in the recesses, and another starting element arranged axially between the second planetary roller journal and the second planetary roller carrier in the recesses. For example, the two starting elements are designed as star-shaped plates. The radial legs of the starting elements designed as star-shaped plates are, in particular, axially stepped such that the steps follow the spindle pitch and thus rise in a helical staircase-like fashion in the circumferential direction. The starting elements are, in particular, made of a wear-resistant material and are designed to absorb the axial forces of the planetary rollers. Consequently, the planetary roller carriers can be made of a cost-effective and lightweight material.This allows the service life of the planetary roller screw drive to be increased in a simple and cost-effective manner. Alternatively, instead of the starting elements, at least the starting surface, which is designed to absorb the axial forces from the planetary rollers, can be hardened or coated, thereby locally increasing wear resistance.

[0013] According to one embodiment, the recesses in the respective planetary roller carrier are arranged in a star shape and designed as grooves. In particular, each groove in the respective planetary roller carrier extends radially outwards from the center, essentially to the circumference of the planetary roller journals. The recesses can be produced, for example, by stamping or machining.

[0014] According to one embodiment, the recesses in the respective planetary roller carrier are designed as cylindrical bores. In particular, the cylindrical bore extends only partially axially into the respective planetary carrier, and a collar can be formed at least partially or completely around the cylindrical bore, which is designed to ensure that all planetary roller journals have the same overlap length on the respective planetary roller carrier, thereby ensuring identical torque transmission between the planetary roller carriers and the planetary rollers.

[0015] According to one embodiment, at least one radial dimension of the respective recess in the respective planetary roller carrier is larger than one radial dimension of the respective planetary roller journal. This not only optimizes wear but also prevents radial forces from being introduced into the planetary roller carrier. Essentially, no frictional forces arise from the relative rotation between the cylindrical surfaces of the planetary roller journals and the planetary roller carriers. For example, the recesses are at least partially round, elliptical, or oval.

[0016] According to one embodiment, the profile of each planetary roller is cylindrically flattened to increase the contact area between the planetary rollers and the sleeve. Thus, each planetary roller has an enclosing cylindrical surface designed to at least temporarily contact the inner circumferential surface of the sleeve, thereby transmitting a radial force from the respective planetary roller to the sleeve. Consequently, no thread peaks are formed on the outer circumferential surface of the planetary rollers, which reduces wear due to Hertzian contact stress on the profile of the planetary rollers and extends the service life of the planetary roller screw drive.

[0017] According to one embodiment, all planetary rollers are identically designed.

[0018] This improves not only manufacturing but also assembly. In particular, the planetary rollers are arranged axially offset from each other in the planetary roller carriers, following the pitch of the spindle profile.

[0019] According to one embodiment, at least one end face of the planetary roller journal is convexly shaped. Preferably, both end faces of the planetary roller journal are convexly shaped. This improves the transmission of the axial force between the planetary rollers and the planetary roller carrier and simultaneously reduces the frictional torque. This extends the service life of the planetary roller screw drive.

[0020] Furthermore, the invention also relates to an actuator for a vehicle, comprising an electric machine and a planetary roller screw drive according to the invention, effectively connected thereto. In particular, the actuator can be arranged for actuating a clutch in a transmission or in a steering system of the vehicle. Preferably, the vehicle is designed as a motor vehicle.

[0021] Further measures improving the invention are described in more detail below, together with a description of preferred embodiments of the invention, with reference to the figures. Figure 1 shows a section of a schematic perspective sectional view of an actuator according to the invention with a planetary roller screw drive.

[0022] Figure 2 shows a simplified schematic view of a planetary roller of the planetary roller screw drive according to Figure 1.

[0023] Figure 3 shows a section of a schematic detailed sectional view of the planetary roll according to Figure 2.

[0024] Figure 4 shows a section of a schematic perspective view of a planetary roller carrier according to one embodiment and

[0025] Figure 5 shows a schematic perspective view of a planetary roller carrier according to a further embodiment.

[0026] Figure 1 shows a section of an actuator 1 according to the invention for a vehicle not shown in detail. The actuator 1 comprises an electric machine 20 and a planetary roller screw drive connected to it for drive purposes. In this case, the electric machine 20 and the planetary roller screw drive are arranged coaxially to each other in a common housing 16 with a housing cover 17. A rotor of the electric machine 20 is non-rotatably connected to two planetary roller carriers 8, 9. The first planetary roller carrier 8 is rotatably mounted in the housing cover 17 via a first bearing element. The second planetary roller carrier 9 is rotatably mounted in the housing 16 via a second bearing element. The two planetary roller carriers 8, 9 are axially screwed together and thus non-rotatably connected.

[0027] Several planetary rollers 2, of which only two are shown here, engage with a profiled spindle 3 that extends axially through the actuator 1. The spindle 3 is arranged on a central axis 18, with the planetary rollers 2 arranged coaxially thereto. The planetary rollers 2 are rotatably mounted at both ends by means of planetary roller journals 4, 5 in respective recesses 6, 7 on the respective planetary roller carriers 8, 9. Furthermore, a wear-resistant starting element 11, 12 is arranged axially in the respective recesses 6, 7 between the respective planetary roller journals 4, 5 and the respective planetary roller carriers 8, 9.

[0028] A sleeve 10 with a smooth inner and outer circumferential surface is arranged around the planetary rollers 2. The sleeve 10 is spaced from the planetary carriers 8, 9 by an air gap 15 and can, at least temporarily, contact the planetary carriers 8, 9 during operation of the actuator 1, particularly when the planetary rollers 2 come into contact with the sleeve 10 during operation of the planetary roller screw drive and deform it radially due to the profiling on the spindle 1 and the associated explosive forces. Due to this arrangement of the planetary rollers 2 in the planetary roller carriers 8, 9, radial forces of the planetary rollers 2 are transmitted via a rolling contact to the macroscopically smooth inner circumferential surface of the sleeve 10 during operation of the planetary roller screw drive, whereby axial forces of the planetary rollers 2 are transmitted via the axial ends of the planetary roller journals 4, 5 in the respective recess 6, 7 indirectly via the thrust elements 11, 12 to the respective planetary roller carrier 8, 9.This results in a favorable distribution of forces in the planetary rollers 2, which in particular enables a compact and efficient design of the planetary roller screw drive. Specifically, this eliminates the need for additional rolling and sliding bearings and increases the number of identical parts. All planetary rollers 2 are identical and arranged axially offset from one another in their respective planetary roller carriers 8, 9, following the pitch of the spindle 3 profile.

[0029] To improve the concentric bearing of the spindle 3 relative to the respective planetary roller carrier 8, 9, a centering element 13, 14 is arranged in each planetary roller carrier 8, 9. The centering elements 13, 14 rotate together with the planetary roller carriers 8, 9 and are axially guided freely within the respective planetary roller carrier 8, 9. The respective centering element 13, 14 is, for example, made of plastic and has a smooth outer circumferential surface and a profiled inner circumferential surface that engages with the profile of the spindle 3.

[0030] The axial displacement of the centering elements 13, 14 relative to the planetary roller carriers 8, 9 prevents axial forces from the planetary rollers being transmitted into the centering elements 13, 14. This allows the centering elements 13, 14 to adjust themselves in accordance with the support of the planetary rollers 2 via the planetary roller journals 4, 5 in the planetary roller carriers 8, 9. Regardless of the axial direction in which the planetary rollers 2 engage the planetary roller carriers 8, 9, the centering elements 13, 14 follow in this axial direction. This ensures optimal concentricity of the spindle 3 to the respective planetary roller carrier 8, 9 even in the event of wear of the planetary rollers 2, thereby extending the service life and efficiency of the planetary roller screw drive. Consequently, the longitudinal axis 19 of the respective planetary roller 2 and the central axis 18 are always parallel to each other.

[0031] Figure 2 shows one of the identical planetary rollers 2 according to Figure 1, and Figure 3 shows a detailed sectional view of the planetary roller 2 according to Figure 2. The planetary roller 2 is formed in one piece and has a profile 21 that corresponds to the profile of the spindle 3 and is arranged axially between the two planetary roller journals 4, 5. Figures 2 and 3 show that the profile 21 of the planetary rollers 2 is cylindrically flattened, which increases the contact area between the planetary rollers 2 and the sleeve 10. It is also evident that the end faces on the planetary roller journals 4, 5 are convexly shaped and thus have a crown 22. When the planetary rollers 2 axially engage with the respective planetary carrier 8, 9, the force transmission is optimized via the crown 22 on the planetary roller journals 4, 5.

[0032] Figure 4 shows another embodiment of a planetary roller carrier 9. In this embodiment, the planetary roller carrier 9 has five star-shaped recesses 7, which are designed as grooves. The grooves extend radially outwards from a central bore for the passage of the spindle 3. It is also evident that the five recesses 7 have different depths, with the recess 7 to which the arrow of the reference numeral points being the deepest recess in the axial direction. Moving counterclockwise, the recesses become shallower, so that in this illustration they rise in a spiral, stepped fashion. This allows the planetary rollers 2 to be arranged axially offset from one another in the planetary roller carrier 9, following the slope of the spindle 3's profile.Except for the deepest recess 7, a collar 23 is formed at least partially around the other four recesses 7, which is designed to ensure that all planetary roller journals have the same overlap length on the planetary roller carrier 9, thereby making the torque transmission between the planetary roller carrier 9 and the respective planetary roller 2 mounted on it identical.

[0033] Figure 5 shows another embodiment of a planetary roller carrier 9. In this embodiment, the planetary roller carrier 9 has a plurality of recesses 7, which are designed as cylindrical bores. The recesses 7 have different depths, and the bottom of each recess is not visible.

[0034] Counterclockwise, the recesses become shallower, so that in the present illustration they rise in a spiral, stepped fashion. This allows the planetary rollers 2 to be arranged axially offset from one another in the planetary roller carrier 9, following the slope of the spindle 3's profile. A collar 23 is formed around the recesses 7, ensuring that all planetary roller journals have the same overlap length on the planetary roller carrier 9, thus guaranteeing identical torque transmission between the planetary roller carrier 9 and the respective planetary roller 2 mounted on it.

[0035] List of reference signs

[0036] 1 actuator

[0037] 2 planetary roles

[0038] 3 spindles

[0039] 4 planetary roller pivots

[0040] 5 planetary roller pivots

[0041] 6 Exclusion

[0042] 7 Exclusion

[0043] 8 planetary roller carriers

[0044] 9 planetary roller carriers

[0045] 10 sleeve

[0046] 11 Starting element

[0047] 12 Starting element

[0048] 13 hundredweight element

[0049] 14 hundredweight element

[0050] 15 air gap

[0051] 16 cases

[0052] 17 Housing covers

[0053] 18 Central axis

[0054] 19 Longitudinal axis of the planetary roll

[0055] 20 electric machine

[0056] 21 Flattening

[0057] 22 Balliness

[0058] 23 collars

Claims

Patent claims 1. Planetary roller screw drive for an actuator (1) of a vehicle, wherein several planetary rollers (2) engage with a profiled spindle (3), wherein the planetary rollers (2) are rotatably arranged at both ends by means of planetary roller journals (4, 5) in respective recesses (6, 7) on a respective planetary roller carrier (8, 9), wherein, during operation of the planetary roller screw drive, the planetary rollers (2) come into contact at least partially with a sleeve (10) surrounding the planetary rollers (2), wherein, during operation of the planetary roller screw drive, radial forces of the planetary rollers (2) can be transmitted via a rolling contact to a smooth inner circumferential surface of the sleeve (10), and axial forces of the planetary rollers (2) can be transmitted at least indirectly to the respective planetary roller carrier (8, 9) via the axial ends of the planetary roller journals (4, 5) in the respective recesses (6, 7), characterized in that in the respective planetary roller carrier (8, 9)9) a respective centering element (13, 14) is arranged for the concentric mounting of the spindle (3) to the respective planetary roller carrier (8, 9), wherein the centering elements (13, 14) rotate together with the planetary roller carriers (8, 9) and are axially guided freely in the respective planetary roller carrier (8, 9).

2. Planetary roller screw drive according to claim 1, wherein the respective centering element (13, 14) has a profiled inner circumferential surface which engages with the profile of the spindle (3).

3. Planetary roller screw drive according to one of the preceding claims, characterized in that at least one starting element (11 , 12) is arranged axially in the respective recess (6, 7) between the respective planet roller journal (4, 5) and the respective planet roller carrier (8, 9).

4. Planetary roller screw drive according to one of the preceding claims, characterized in that the recesses (6, 7) in the respective planetary roller carrier (8, 9) are arranged in a star shape and are designed as grooves.

5. Planetary roller screw drive according to one of the preceding claims, characterized in that the recesses (6, 7) in the respective planetary roller carrier (8, 9) are designed as cylindrical bores.

6. Planetary roller screw drive according to one of the preceding claims, characterized in that at least a radial dimension of the respective recess (6, 7) in the respective planetary roller carrier (8, 9) is larger than a radial dimension of the respective planetary roller journal (4, 5).

7. Planetary roller screw drive according to one of the preceding claims, characterized in that a respective profile (21 ) of the planetary rollers (2) is cylindrically flattened, so that no thread peaks are formed on an outer circumferential surface of the planetary rollers (2) in order to increase the contact area between the planetary rollers (2) and the sleeve (10).

8. Planetary roller screw drive according to one of the preceding claims, characterized in that all planetary rollers (2) are identically designed.

9. Planetary roller screw drive according to one of the preceding claims, characterized in that at least one end face on the planetary roller journal (4, 5) is convexly formed.

10. Actuator (1 ) for a vehicle, comprising an electric machine (21) and a planetary roller screw drive connected thereto in a drive-effective manner according to one of the preceding claims.

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