Compact multi-stage gear with a planetary gear and a strain wave gear adjacent to said multi-stage gear

Abstract

A multi-stage gear is provided with a planetary gear and a strain wave gear adjacent to the multi-stage gear, wherein a output of the planetary gear maintains a drive connection with a wave generator of the strain wave gear, and wherein the planetary gear is arranged at least partially radially within the strain wave gear. It is provided that the wave generator is mounted radially on a ring gear of the planetary gear.

Claims

1. A multi-stage gear with a planetary gear and a strain wave gear adjacent to said planetary gear, wherein a drive of the planetary gear maintains a drive connection with a wave generator of the strain wave gear, and wherein the planetary gear is arranged at least partially radially within the strain wave gear, wherein the wave generator is mounted radially on a ring gear of the planetary gear.

2. The multi-stage gear according to claim 1, wherein the output of the planetary gear is a planetary carrier of the planetary gear, wherein this planetary carrier is formed as one part with the wave generator.

3. The multi-stage gear according to claim 1, wherein the wave generator is mounted with at least one roller bearing on the ring gear of the planetary gear.

4. The multi-stage gear according to claim 3, wherein the wave generator is mounted on the ring gear of the planetary gear with two roller bearings that are axially spaced from one another.

5. The multi-stage gear according to claim 4, wherein the effective axial distance between the two roller bearings amounts to at least half of the axial overlap of the wave generator and the ring gear.

6. The multi-stage gear according to claim 1, wherein the planetary gear is formed in a multi-stage way, wherein the wave generator encloses the ring gear over a maximum of half of the axial length of the ring gear.

7. The multi-stage gear according to claim 1, wherein the planetary gear is formed in a single-stage way, wherein the wave generator encloses the ring gear over the entire axial length of the ring gear.

8. The multi-stage gear according to claim 1, wherein the axial overlap of the planetary gear and the strain wave gear amounts to at least 80% of the axial length of the planetary gear.

9. The multi-stage strain wave gear according to claim 8, wherein the planetary gear is enclosed over its entire axial length by the strain wave gear.

10. A drive unit with a multi-stage gear according to claim 1, wherein the gear unit has an electric motor, wherein the planetary gear is driven by the electric motor, and wherein the electric motor is an internal rotor motor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) An embodiment of the present invention will be described in greater detail based on a drawing in the following.

(2) FIG. 1 shows a longitudinal section through an embodiment of a drive unit 1 according to the invention with an electric motor 15 and a multi-stage gear according to the invention. The multi-stage gear consists of a three-stage planetary gear and a downstream strain wave gear. The planetary gear is arranged radially within the strain wave gear. The planetary gear and the strain wave gear share a common longitudinal axis 7. The planetary gear is driven by the electric motor 15. The electric motor 15 is an internal rotor motor. It therefore has an external stator 19, which is connected firmly to the bearing 18 of the electric motor, and an internal rotor 20. The rotor 20 comprises the motor shaft 16 that protrudes from the bearing 18 of the electric motor in the illustration on the left side and whose end carries the input sun wheel 17 of the first stage A of the three-stage planetary gear. Each of the three planetary stages A, B and C consists of a respective sun wheel, a planetary carrier as well as planetary wheels 6 that are mounted in a rotatable way on said planetary carrier and that mesh on one hand with the respective sun wheel of the corresponding planetary stage and on the other hand with the internal teething 5 of an external ring gear 4 of the planetary gear.

DETAILED DESCRIPTION

(3) The planetary carrier 2 of the last planetary stage C forms the output of the three-stage planetary gear. It is formed as one part with the wave generator 3 of the downstream strain wave gear. Said strain wave gear, in turn, is installed radially on the ring gear 4 of the planetary gear with two ball drives 8 and 9 that are spaced axially from one another. As becomes clear from the drawing, the wave generator 3 encloses the ring gear 4 approximately over half of the axial length of the ring gear 4. The two ball bearings 8 and 9 are positioned in such a way that they are arranged essentially on the opposite ends of the wave generator 3.

(4) The wave generator 3 has a well-known elliptic form and causes during a rotation a circulating deformation of the external flexible spur gear 11 of the strain wave gear. Between the wave generator 3 and the flexspline 11, a respective roller bearing 21 is arranged in the known way. In the shown embodiment, the flexspline 11 is connected in a torque-proof way with the ring gear 4 of the planetary gear. For this purpose, it can for example be screwed with an extension 12 of the ring gear 4, which, however, cannot be counted as part of the planetary gear but which is part of the external strain wave gear. Here, also a separate component can be used instead of an extension of the ring gear 4.

(5) The flexspline 11 has an external teething that, during rotation of the wave generator, is set to encroach with an internal teething of the external ring gear 10 of the strain wave gear in a sectionally circulating way. The ring gear 10 forms the output of the multi-stage gear according to the invention. It is installed flexibly on the extension 12 of the ring gear 4 of the planetary gear by means of two ball bearings 13 and 14. In a similar way as the two ball bearings 8 and 9, the two ball bearings 13 and 14 are arranged in a spaced way from one another in order to ensure a particularly stable mounting of the ring gear 10.