WO1995004232A1

WO1995004232A1 - Clearance-free planetary gear

Info

Publication number: WO1995004232A1
Application number: PCT/EP1994/002449
Authority: WO
Inventors: Horst Schulz
Original assignee: Zf Friedrichshafen Ag
Priority date: 1993-07-28
Filing date: 1994-07-25
Publication date: 1995-02-09
Also published as: DE4325295A1; AU7532594A; EP0710335A1

Abstract

A clearance-free planetary gear (1) is disclosed. The planetary gear (1) is of the Wolfrom gear type and allows big reduction ratios. Such gears are preferably used in handling technology. They must have a small torsional clearance during a change in the load direction and must have a torsionally stiff, light and compact design. In order to improve the accuracy of manufacture and the total efficiency, the planetary axes (5) are inclined, enclosing an acute angle with a center line (15) of the planetary gear (1). The teeth of the ring gears (10, 11) may be conical or straight. Spacing washers eliminate the clearance between the teeth.

Description

Backlash-free planetary gear

The invention relates to a planetary gear with a driven sun gear, two internally toothed

Ring gears, one of which is fixed and the other is rotatably mounted and forms the output. Several planet gears are provided, which are mounted on planet axes in a planet carrier. The planet gears are in constant mesh with the sun gear and the ring gears.

Many tasks in drive technology require the implementation of extreme translations. Planetary gears are particularly well suited to combine high gear ratios with a compact design. Such a planetary gear is the Wolfrom coupling gear, which still has good efficiencies with a high gear ratio. A Wolfrom gear is a special, simple coupling gear. The drive is connected to a sun gear which cooperates with a planetary gear block. The planet gear is supported on the internally toothed ring gear, which is fixed to the housing. The web as a planet carrier runs along empty. The movement is passed on via the planet carrier and the planet gear (s) (stepped planet). The planet gear in turn meshes with an internally toothed ring gear that forms the output. The arrangement described is suitable for a compact construction which enables high transmission densities in a small space (cf. Klein: Theoretical principles for the design of Wolfrom coupling gears, in Maschinenmarkt 1982, pages 341 to 344).

In handling technology in particular, power is high for high-speed drive motors reducing gear needed. These gears should have a small backlash when changing the load direction. Furthermore, they should be characterized by a rigid, light and compact design.

In the case of planetary gears of the type mentioned, the overall efficiency is a decisive factor for their usability. Internal tension, for example, has a serious influence on the overall efficiency due to the resulting increased internal rolling power.

From US Pat. No. 4,106,366 a backlash-free planetary gear has become known, in which an internally toothed ring gear is pressed onto the conically manufactured planetary gears by helical compression springs. Because of the increased tooth rolling performance due to internal tension, the overall efficiency is lowered inadmissibly.

The present invention has for its object to provide a backlash-free planetary gear, in which the achievable accuracy in manufacture, which forms the basis for a narrow backlash setting, is great. Accordingly, the achievable overall efficiency should be high. In addition, the manufacturing costs are to be reduced.

The object on which the invention is based is achieved in that the planetary axes are inclined at an acute angle with respect to a central axis of the planetary gear. The inclination of the planet axes enables two designs to be realized. In a first preferred embodiment, the toothing of the ring gears are conical. Straight toothed planet gears are used here. This design variant is also particularly advantageous because the backlash between the ring gears and the planetary wheels can be adjusted separately. The position of the planet gears in relation to the ring gears is set such that the cylindrical tooth flanks of the planet gears and the conical tooth flanks of the ring gears touch approximately uniformly along their common engagement width.

In the further construction variant, the hollow wheels are provided with cylindrical internal teeth. In this case, the toothing of the planet gears is conical.

In order to absorb the axial thrust with conical planet gears with low friction, each planet gear or planet axis is supported by an axial bearing in the planet carrier.

A particularly compact design can be achieved if the planetary gear has a tubular housing. This housing encloses two rows of balls, via which the second ring gear and / or the output flange is rotatably mounted.

The bearing is very precise when the second ring gear is rotatably supported in the housing via a row of balls in the housing and the output flange is rotatably mounted in the housing via the further row of balls.

In order to switch off the bearing play between the second ring gear and the housing, a spacer is connected between the output flange and the second ring gear.

In order to switch off the tooth flank backlash, the first ring gear can be axially adjusted with respect to the planet gears via a spacer. The spacer is preferably inserted between the first ring gear and the housing. Another measure also serves to eliminate the backlash. The planet carrier can be adjusted in the axial direction - based on a longitudinal center axis of the planetary gear - using a spacer.

Since the planet carrier runs along empty, it is advantageous to mount it on a bushing with low friction via a ball bearing. The socket is preferably located on the side of the planet carrier facing away from the sun gear. It is guided in a bore in the discharge flange.

In order to be able to determine the axial position of the planet carrier exactly, the bushing rests on one end over a shoulder on the ball bearing and can be fixed on the spacer by means of a locking ring.

The input shaft and the bushing are preferably provided with a through hole, that is to say they are designed as hollow components.

In order to protect the transmission from external influences, a seal is connected between the housing and the output flange.

Further features essential to the invention and the advantages resulting therefrom can be found in the following description of exemplary embodiments of a play-free planetary gear according to the invention. Show it :

Fig. 1 shows a first embodiment of a planetary gear in a longitudinal half-section with outer central wheels with a conical toothing and

2 shows a modified embodiment of a planetary gear, in which the outer central gears are straight-toothed.

In the planetary gear 1 shown in longitudinal half-section in FIG. 1, a high-speed rotating input shaft 2 drives a sun gear 3 (small central gear). In the present case, the sun gear 3 and the input shaft 2 are made in one piece.

The sun gear 3 is in constant meshing connection with several planet gears 4. One of these planet gears 4 is shown in the drawing. A total of four planet gears 4 are provided, for example.

A planetary axis 5 is rotatably supported in a planet carrier 8 via bearings 6 and 7, preferably needle bearings. Each planet gear 4 is connected to its planetary axis 5 in a non-displaceable manner via a fixed fit.

The planet gears 4 are in constantly meshing connection with a first ring gear 10 (first large central gear). At the same time, they are constantly in engagement with a second ring gear 11 (second large central gear).

The planet carrier 8 has no direct connecting shafts, so that no torque is supplied or removed. As a result, it runs along empty. The first ring gear 10 is arranged in a fixed manner, while the second ring gear 11 is fixedly connected to an output flange 12.

From the drawing it can also be seen that the

Ring gears 10 and 11 are surrounded by an annular housing 13. The ring-shaped housing 13 is preferably fixedly connected to the ring gear 10 via fastening elements 9 (not shown). For this purpose, the housing 13 can be screwed to the ring gear 10.

The gears mentioned can have the following number of teeth:

Sun gear 3 37 teeth, planet gear 4 33 teeth, first ring gear 10 (stator) 107 teeth and second ring gear 11 (output) 111 teeth.

The input shaft 2 or the sun gear 3 is driven at a high speed at a relatively low torque. The output flange 12 (it can be connected to an output shaft, not shown itself) rotates at a low speed at a high torque. Such a gearbox is particularly suitable for use in handling technology.

Since the number of teeth of the ring gears 10 and 11 differ from one another, different pitch circle diameters are set. By shifting the profile, it is possible to compensate for the diameters of both ring gears 10, 11 so that both can mesh with the planet gears 4 at the same time.

1, the teeth of the ring gears 10 and 11 are conical. Here the amount of profile shift changes continuously, based on the width of these ring gears. The base and top circles each lie on the surface of the cone.

In contrast, the planet gears 4 are cylindrical. The center lines 14 of the planetary axes 5 intersect with the center axis 15 of the planetary gear 1 at an acute angle alpha. This angle is 3 °, for example. A preferred range for the size of this angle alpha extends from 1.5 ° to 15.0l'O

The inclination of the flank lines on the ring gears 10, 11 (a measure of their taper) is chosen so that the cylindrical tooth flanks of the planet gears 4 and the conical tooth flanks of the ring gears 10, 11 touch approximately uniformly along their common engagement width. This applies mutatis mutandis to the engagement of the sun gear 3, which also has conical tooth flanks. Because of the much lower specific load on the tooth flanks of the sun gear 3, the requirements to be placed on the precision (inclination of the essential flank lines) are less critical.

The cylindrically shaped planet gears 4 are particularly easy to manufacture. The tooth flanks are ground in order to improve the overall efficiency of the planetary gear through high precision. Since no step planet is used, there are no problems due to deviations in the position assignment. Such problems are irrelevant due to the continuous, ground teeth. The bearings 6 and 7 of the planetary axes 5 are essentially spared axial thrusts. This is a further advantage since axial thrusts, insofar as they are accommodated by thrust bushings, can easily reduce the overall efficiency by several percentage points.

The basic design of the planetary gear, likewise shown in longitudinal half-section in FIG. 2, corresponds to the planetary gear of FIG. 1. The same reference numbers are used for the same components.

In this planetary gear as well, the planet axes 14 run at an acute angle alpha.

In contrast to the planetary gear according to FIG. 1, the ring gears 10 and 11 have cylindrical internal teeth. As a result, the toothing of the planet gears 4 is conical. Ring gears with cylindrical internal teeth are comparatively easy to manufacture. However, the conically shaped planet gears 4 cause an axial thrust which is to be taken up in roller bearings. For this purpose, each planet gear 4 or each planetary axis 5 is additionally supported via an axial bearing 16 in the planet carrier 8.

The exemplary embodiments according to FIGS. 1 and 2 have in common that the tubular housing 13 encloses two rows of balls 17 and 18. For each row of balls 17 and 18 there are pairs of interacting ball raceways 19 and 20 or 21 and 22. The ball raceways 19 to 22 are incorporated directly into the output flange 12, the housing 13 and the ring gear 11. This eliminates the need for separate (complete) bearings or separate inner and outer rings. Overall, a compact design with acceptable manufacturing costs can be achieved. The planetary gear 1 represents a combined bearing-drive unit, so to speak. This is important because it allows gear play to be reduced to a minimum. Elastic deformations of the planetary gear add up with bearing play and bearing elasticities. Both influences, bearing play and gear play, are equally disadvantageous.

The gear and bearing clearances are set in the explained planetary gears via three spacers 23, 24 and 25.

The spacer 23 is located between the ring gear 11 and the driven flange 12. The thickness of this spacer is adjusted so that a desired bearing play is established on the rows 17 and 18 of balls. This bearing play can also be a moderate preload.

The axial position of the planet carrier 8 with respect to the ring gear 11 is set via the spacer 24. For this purpose, the planet carrier 8 is additionally supported on a bushing 27 via a ball bearing 26. The bushing 27 is guided in a bore 28 of the output flange 12 and axially secured by a locking ring 29.

The thickness of the spacer disk 24 is determined by selection or by combining a plurality of individual disks of different thicknesses or also by grinding. This thickness measure causes the desired game setting.

Ultimately, the axial position of the ring gear 10 is determined by the spacer 25. For this, the Thickness dimension of this disk, which is located between the ring gear 10 and the housing 13, is selected until the desired tooth flank play between the ring gear 10 and the planet wheels 4 is reached.

The backlash should be as tight as possible. Clamping or tensioning states (also in partial areas of a revolution) should be avoided.

After a longer period of operation, the tooth flank backlash increases due to the wear that occurs. In this case, the spacer 24 can be exchanged for another with a greater thickness. The tooth flank backlash can thus be reduced again simultaneously on both ring gear interventions.

The above-described exemplary embodiments of a backlash-free planetary gear according to the invention allow the representation of large translations. Assuming that a lower gear ratio is sufficient, the sun gear 3 can be omitted. Then the input shaft 2 is connected directly to the planet carrier 8. The planet carrier 8 is then preferably driven via a spur gear stage which is formed from a toothing on the planet carrier 8 and a drive pinion. This drive pinion is then arranged eccentrically with respect to the central axis 15 of the planetary gear. The eccentric arrangement is a prerequisite for the trouble-free use of drive motors that have no central output. Reference sign

1 planetary gear

2 input shaft

3 sun gear

4 planet gears

5 planetary axis

6 bearings

7 bearings

8 planet carriers

9 fasteners

10 first ring gear

11 second ring gear

12 output flange

13 housing

14 planetary axis

15 central axis of the planetary gear

16 thrust bearings

17 row of balls

18 row of balls

19 ball tracks

20 ball tracks

21 ball tracks

22 ball tracks

23 spacer

24 spacer

25 spacer

26 ball bearings

27 socket

28 hole

29 circlip

Claims

Expectations

1. Planetary gear (1) with a driven sun gear (3), a first (10) and a second (11), each internally toothed ring gear, of which the first is fixed and the second is rotatably driven and the output forms and planet gears, which are mounted on planet axes (5) in a planet carrier (8) in such a way that they are in constant tooth mesh with the sun gear (3) and the ring gears (10, 11), characterized ¬ characterized in that the Planetary axes (5) are inclined at an acute angle (alpha) with respect to a central axis (15) of the planetary gear (1).

2. Planetary gear according to claim 1, characterized in that the toothings of the hollow wheels (10, 11) are conical.

3. Planetary gear according to claims 1 and 2, da¬ by g e k e n n z e i c h n e t that the planet wheels (4) are spur-toothed.

4. Planetary gear according to claims 1 to 3, thereby g e k e n n z e i c h n e t that the cylindrical tooth flanks of the planet gears (4) and the conical tooth flanks of the ring gears (10, 11) touch approximately evenly along their common engagement width.

5. Planetary gear according to claim 1, characterized ¬ indicates that the ring gears (10, 11) have a cylindrical internal toothing.

6. Planetary gear according to claim 5, characterized in that the toothing of the planet wheels (4) is conical.

7. Planetary gear according to claims 5 and 6, da¬ by g e k e n n z e i c h n e t that each Plane¬ tenrad (4) or each planetary axis (5) via an axial bearing (16) in the planet carrier (8) is supported.

8. Planetary gear according to claim 1, characterized ge ¬ indicates that it has a tubular Ge ¬ housing (13) which um¬ includes two rows of balls (17, 18), via which the second ring gear (11) and / or the output flange ( 12) is rotatably mounted.

9. Planetary gear according to claim 7, characterized ge ¬ indicates that the second ring gear (11) via a row of balls (18) in the housing (13) and the Abtriebs¬ flange (12) via a row of balls (17) in the housing (13) rotatable is stored.

10. Planetary gear according to claims 1 and 9, da¬ by g e k e n n z e i c h n e t that between the output flange (12) and the second ring gear (11), a spacer (23) is switched on for setting the bearing play.

11. Planetary gear according to claim 1, characterized ¬ indicates that the first ring gear (10) with respect to the planet gears (4) via a spacer (25) is adjustable in the axial direction.

12. Planetary gear according to claim 11, characterized in that the spacer (25) between the first ring gear (10) and the housing (13) is switched on.

13. Planetary gear according to claim 1, characterized in that the planet carrier (8) in the axial direction - based on a longitudinal central axis (15) - is adjustable via a spacer (24).

14. Planetary gear according to claim 1, characterized in that the planet carrier (8) is rotatably supported via a ball bearing (26) on a bushing (27) on its side facing away from the sun gear (3).

15. Planetary gear according to claim 1, characterized in that the bushing (27) is guided in a bore (28) of the output flange (12).

16. Planetary gear according to claims 13 and 14, characterized in that the Buch¬ se (27) abuts at one end via a shoulder on the ball bearing (26) and at the other end via a locking ring (29) on the spacer (24) in Axial direction is set.

17. Planetary gear according to claims 1 and 14, characterized in that the input shaft (2) and the bushing (27) are designed as hollow components.

18. Planetary gear according to claim 1, characterized ¬ indicates that between the housing (13) and the output flange (12) a seal is turned on.

19. Planetary gear according to claim 1, characterized g e ¬ k e n n z e i c h n e t that the teeth are ground.

20. Planetary gear according to claim 1, characterized in that the planet carrier (8) - with the omission of the sun gear (3) - is driven directly via a spur gear stage.

21. Planetary gear according to claim 20, characterized in that the planet carrier (8) has an external toothing in which engages an eccentrically arranged drive pinion with respect to the central axis (15) of the planetary gear.