Harmonic drive

Abstract

A harmonic drive (1), including a wave generator (8), a flexible, externally toothed gear component (14), in particular in the form of a flex ring, which can be deformed by said wave generator, and at least one internally toothed gear component (4, 5) that meshes with the flexible, externally toothed gear component (14). The flexible, externally toothed gear component (14) has a non-circular basic shape in relation to its mechanically non-loaded state.

Claims

1. A harmonic drive, comprising a wave generator, a flexible, externally toothed gear component that is deformable by the wave generator, at least one internally toothed gear component engaging the flexible, externally toothed gear component, and in an unstressed state, the flexible, externally toothed gear component comprises a convex basic shape, wherein the flexible, externally toothed gear component has an elliptic basic form, with a spring energy (E) stored in said flexible, externally toothed gear component having two minima E(dw_g-d1) and two maxima E(dw_g-d2) per one full revolution of the flexible, externally toothed gear component.

2. The harmonic drive according to claim 1, wherein an amount of a difference between a teeth count of external teeth of the flexible gear component and a teeth count of internal teeth of the internally toothed gear component is maximally equivalent to 1/60.

3. The harmonic drive according to claim 1, wherein the spring energy at the minima E(dw_g-d1) stored in the flexible, externally toothed gear component is equivalent to less than half of the spring energy at the maxima E(d2_g-d2) stored in said gear component.

4. The harmonic drive according to claim 1, wherein the flexible, externally toothed gear component has a basic form of a polygon with rounded edges.

5. The harmonic drive according to claim 1, wherein the flexible, externally toothed gear component is a flex ring.

6. The harmonic drive according to claim 5, wherein there are two of the internally toothed gear components, and one of the two internally toothed gear components comprises a driven sprocket.

7. The harmonic drive according to claim 1, wherein the flexible, externally toothed gear component comprises a flex cup which is adapted to be a driven element.

8. A control gear of an electric camshaft adjuster or a device for adjusting a compression ratio of an internal combustion engine comprising the harmonic drive according to claim 1.

9. A method for operating a harmonic drive comprising a wave generator, a flexible, externally toothed gear component, that by the wave generator, as well as at least one internally toothed gear component that engages the flexible, externally toothed gear component, with the flexible, externally toothed gear component having an out-of-round basic form in a mechanically unstressed state, the method comprising the externally toothed gear component adjusting itself into a desired position in a period in which no relative adjustment shall occur via a spring energy (E) stored in said flexible, externally toothed gear component, and said flexible, externally toothed gear component applying an inherent holding torque that reduces a holding torque applied for driving the wave generator.

10. A harmonic drive, comprising a wave generator adapted to be connected to an adjustment shaft, a flexible, externally toothed gear component that is deformable by the wave generator, that in an unstressed state, comprises a convex basic shape, a first internally toothed gear component engaging the flexible, externally toothed gear component that is adapted to be connected to a drive shaft, and a second internally toothed gear component engaging the flexible, externally toothed gear component that is adapted to be connected to a driven shaft, and wherein the flexible, externally toothed gear component has an elliptic basic form, with a spring energy (E) stored in said flexible, externally toothed gear component having two minima and two maxima per one full revolution of the flexible, externally toothed gear component.

11. The harmonic drive according to claim 10, wherein the spring energy at the minima stored in the flexible, externally toothed gear component is equivalent to less than half of the spring energy at the maxima.

12. The harmonic drive according to claim 10, wherein the first and second internally toothed gear components have a different number of teeth.

13. The harmonic drive according to claim 10, wherein the transmission ratio is at least 60:1.

14. The harmonic drive according to claim 10, wherein the wave generator includes an internal ring, an external ring on which the flexible, externally toothed gear component is located, and roller bodies located between the internal and external rings.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the following, an exemplary embodiment of the invention is explained based on a drawings. Shown here are:

(2) FIG. 1 a harmonic drive in a symbolized cross-section,

(3) FIG. 2 states of a flexible gear component of the harmonic drive,

(4) FIG. 3 status changes of the flexible gear component in the form of a diagram.

DETAILED DESCRIPTION

(5) FIG. 1 shows a sketch of the design of a harmonic drive, marked with the reference character 1 in its entirety, with here reference being made to prior art with regards to its principle function.

(6) The harmonic drive 1 comprises a housing 2, which is connected fixed to the drive wheel 3. The drive wheel 3 can be driven, for example by a traction mechanism or a sprocket. Additionally, a drive sprocket 4 is connected to the housing 2 as a gear component, which includes internal teeth. In addition to the drive sprocket 4, a driven component 5 is provided as another gear component, which also exhibits internal teeth and is coupled fixed via a driven wheel 6 to a driven shaft 7.

(7) A wave generator 8 is located radially inside the two gear components 4, 5 with internal teeth, which is driven by an adjustment shaft 9. The adjustment shaft 9 is coupled via a self-aligning coupling 10 to a servomotor, particularly an electric motor, not shown. The internal ring 11 of the wave generator 8 shows a stiff, elliptic form. A resilient external ring 12 of the wave generator 8 adjusts permanently to the elliptic form of the internal ring 11 during the rotation of the adjustment shaft 9, with balls 13 rolling as roller bodies between the internal ring 11 and the external ring 12.

(8) A flexible, externally toothed transmission element 14, namely a flex ring, is located directly around the external ring 12. During the rotation of the adjustment shaft 9 of the wave generator 8 the flex ring 14 permanently assumes the form of the external ring 12. Here, the external teeth of the flex ring 14 are made to engage the internal teeth of the gear components 4, 5 at two diametrically opposite points. By slightly different teeth counts of the above-mentioned gear components 4, 5, 14 a high transmission ratio is given of the harmonic drive 1, in the present case a transmission ratio of 90:1.

(9) In FIG. 2 the form of the flex ring 14 is sketched in the mechanically unstressed state, i.e. here the harmonic drive 1 is not installed. A first external dimension d1 is given along the large semi-axes, a second external dimension d2 along the small semi-axes. Circles tangent to the flex ring 14 at the respective points, are identified as external circle K.sub.a and as internal circle K.sub.i. The difference of the semi-axes of the flex ring 14 marked x0 is equivalent to the difference between the radius of the external circle K.sub.a and the radius of the internal circle K.sub.i, and is also called deviation from roundness.

(10) In FIG. 3 the angle of the adjustment shaft 9 is marked with a and the angle of the driven shaft 7 is marked with β. The target angle of the adjustment shaft 9 is marked with α0 and a target angle of the driven shaft 7 with β0. The energy E stated in Joule represents the spring energy stored in the flex ring 14 and dependent on the angular position of the adjustment shaft 9. As discernible from FIG. 3, the spring energy stored in the flex ring 14 is varied in a sinusoidal fashion over the rotation of the adjustment shaft 9 between a minimum value E(dw_g-d1) and a maximum value E(dw_g-d2). The minimum energy E(dw_g-d1) is then stored in the flex ring 14 when the large semi-axis of the elliptic internal ring 11 is aligned parallel to the large semi-axis of the flex ring 14 in reference to the status sketched in FIG. 2.

(11) Conditions of minimal energy are marked A1, A2, a status of maximum energy is marked with B. In the status B the flex ring 14 is deformed maximally in reference to its mechanically unstressed form. The transition from the status B into one of the lower energy states A1, A2 is equivalent to an adjustment of the adjustment shaft 9 by ±90° as well as an adjustment of the driven shaft 7 by ±1°. At a requested setting accuracy, i.e. control quality, of the driven shaft 7 of ±1°, here always a state of minimal energy A1, A2 can be approached, with the transition being possible by exclusively using the snapping moment of the flex ring 14. In the state A1, A2 the harmonic drive 1 can be held with little energy effort, even without applying any torque upon the adjustment shaft 9.

(12) LIST OF REFERENCE CHARACTERS

(13) 1 Harmonic drive

(14) 2 Drive element, housing

(15) 3 Drive wheel

(16) 4 Drive sprocket, gear component

(17) 5 Driven sprocket, gear component

(18) 6 Driven disk

(19) 7 Driven shaft

(20) 8 Wave generator

(21) 9 Adjustment shaft

(22) 10 Self-aligning coupling

(23) 11 Internal ring

(24) 12 External ring

(25) 13 Roller body

(26) 14 Flexible, externally toothed gear element, flex ring

(27) αAngle of the adjustment shaft

(28) βAngle of the driven shaft

(29) α0 Target angle of the adjustment shaft

(30) β0 Target angle of the driven shaft

(31) A1, A2 States of minimal energy

(32) B Status of maximal energy

(33) d1, d2 External dimensions

(34) E Stored spring energy

(35) E(dw_g-d1) Minimum value of energy

(36) E(dw_g-d2) Maximum value of energy

(37) K.sub.a External circle

(38) K.sub.i Internal circle

(39) x0 Deviation from roundness, difference of the semi-axes