GB1579380A

GB1579380A - Planetary gear mechanism

Info

Publication number: GB1579380A
Application number: GB1673877A
Authority: GB
Original assignee: Northern Engineering Industries PLC
Current assignee: Rolls Royce Power Engineering PLC
Priority date: 1978-04-12
Filing date: 1978-04-12
Publication date: 1980-11-19

Description

(54) PLANETARY GEAR MECHANISM (71) We, NORTHERN ENGINEERING IN DUSTRIES LIMITED, a British Company of NEI House, Regent Centre, Newcastle on Tyne, NE3 3SB, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement : - The invention relates to planetary gear mechanism.

Planetary gear mechanism, according to the invention comprises first and second gears rotatable about a first axis, a carrier assembly having two or more planetary gear assemblies which engage the first and second gears and which are equiangularly disposed about the first axis and which comprise members having helical formations concentric with respective axes of rotation of the members parallel to the first axis, the members being capable of endwise movement in the direction of their respective rotational axes, the mechanism comprising counterbalance means arranged to transmit from any planetary gear assembly in response to endwise movement of a member thereof in a first sense an equal thrust to a member of the or each of the other planetary gear assemblies in the direction of the respective rotational axis of the member in a second sense opposite to said first sense to cause the planetary gear assemblies mutually to react each against the other or others.

Each planetary gear assembly may comprise but one member the helical formations of which are teeth meshing with helical teeth on one of the first and second gears.

Alternatively, each planetary gear assembly may comprise two members the helical formations of which are interengaged. In that case, for example, the helical formations of one member may be teeth meshing with corresponding teeth forming the helical formations of the other member.

One form of counterbalance means comprises a ring arranged normally to the first axis so as to be movable radially relative thereto, the ring having for each planetary assembly means by which thrust from members of the planetary gear assemblies are transmitted to the ring. For example, the ring may have for each gear assembly a face at 45" to the first axis, and the members of the planetary gear assemblies act on abutments which have corresponding faces engaging the respective faces on the ring.

In another form of counterbalance means the members of the planetary gear assemblies act upon hydrostatic capsules which are hydraulically interconnected. This form of means is especially suitable where the planetary gear assemblies are relatively numerous.

In yet another form the counterbalance means comprise a body of material which is closely confined and which is only very slightly compressible and which transmits counterbalancing forces in a manner similar to a liquid, members of the planetary gear assemblies being arranged to act upon the body of material.

Where the mechanism is required to be operable in both rotational senses two such rings are provided; or two arrays of capsules or two bodies of material are provided; and the planetary gear assemblies are arranged between the two rings or between the two arrays or two bodies as the case may be.

Two forms of mechanism will now be described by way of example to illustrate the invention with reference to the drawings accompanying the provisional specification, in which: Figures 1 and 2 are, respectively, a sideelevation partly in section and an end elevation with parts removed of one form of planetary gear mechanism; Figure 3 is a section showing a second form of mechanism on the line III-III in Figure 4; Figure 4 is a section on the line IV-IV in Figure 3; Figure 5 is a sectional view of the second form of mechanism similar to Figure 4; Figures 6 and 7 are diagrammatic views in the directions A and B respectively in Figure 5 illustrating forces arising in the mechanism.

Figures 1 and 2 show planetary gear mechanism consisting of a "first" gear in the form or a ring gear 10 mounted between two parts of an annular housing 12 secured together by bolt 13 and having internal helical teeth 14 and external teeth 16. A drive input, for example, can be applied to the mechanism from a shaft 18 through a gear 20 meshing with the external teeth 16 of the ring gear 10.

The housing 12 is carried by central bearings 22, 24 supported by a carrier assembly 26, which includes tubular stub-shafts 28, 30 protruding from the housing 12. The shaft 28 carries a gear 32 keyed to it at which an output drive can be taken.

The shafts 28, 30 are supported by bearings 34, 36, respectively carried by a framework.

Another input shaft 38 is supported in a bearing 40 carried by the framework and by a bearing 42 carried within the shaft 28. The shaft 38 has an integral sun gear 44, which forms the "second" gear of the mechanism.

The carrier assembly 26 includes a flange 46 and a spider 48 integral with the stubshafts 28, 30, respectively and secured together by screws (not shown). The flange 46 and the spider 48 have three pairs of opposed equiangularly separated openings 51 in which, in the flange 46, are mounted first respective cup-shaped abutments 52 and in which the spider 48 are mounted second respective cup-shaped abutments 54. The pairs of abutments 52, 54 accommodate the first and second end portions, respectively, of a respective non-rotatable pin 56 (three in total), each pin and its abutments being movable endwise relatively to the carrier assembly 26 parallel to the principal axis 58 of rotation of the mechanism.

There are three pins 56 equiangularly disposed about the axis 58.

Each pin carries two part-spherical roller bearing assemblies 60, 62 one at each side of a central larger diameter portion 64 of the pin 56. The bearing assemblies 60, 62 carry a planetary gear member 66 which has an integral row of straight teeth 68 meshing with the internal teeth 14 of the ring gear 1.0. The gear 66 also has an integral row of helical teeth 70 which mesh with the sun gear 44. The inner rings of the bearing assemblies 60, 62 engage the inner ends of the first and second abutments 52, 54, respectively.

The first abutments 52 each have a plane face 72 which is inclined at 45" to the axis 58 and which engages a correspondingly inclined plain surface 74 on a first ring 76.

The ring 76 is retained by a nut 78 and a lock-nut 80 screwed onto a threaded portion on the shaft 28. The ring 76 can move slightly radially but not axially of the shaft 28. There is a surface 74 for each abutment and the surfaces 74 are equiangularly spaced around the ring 76.

The first abutments 52 and the first ring 76 form a first equalising means. A second similar means is formed by the second abutments 54, which have inclined faces 82, and by a second ring 84, which has three equiangularly spaced surfaces 86 engaging the respective faces 82.

The ring 84 is retained by a nut 89 and a locknut 90 so as to be radially, but not axially, movable.

The mechanism just described may, typically, be suitable for use in transmitting a 400 horsepower drive at 980 revolutions per minute in a hoist of an electric overhead crane.

Two similar electric motors are used to drive the shafts 18 and 38, respectively, the motors normally both used simultaneously, the output to the winding barrel being taken at the gear 32.

In the event of failure of either motor, the other is capable of handling full load on the barrel at half hoisting speed. The planetary gear mechanism gives a 2:1 speed reduction when one input shaft 18 or 38 is stationary. If either motor fails a brake (not shown) is automatically immediately applied to hold the respective shaft 18 or 38 stationary.

The planetary gears in the planetary gear mechanism are balanced and they equally share the torque transmitted by the mechanism even though they and the other gears are gears manufactured to ordinary commercial tolerances. Furthermore, the mechanism can be readily assembled despite the normal manufacturing tolerances present in the gears and needs no special adjustment to achieve the balanced functions when in use. The high performance is maintained throughout the life of the mechanism. The loads on the gear teeth are still equalised even where permanent or temporary sets arise in the mechanism and in the presence of war and deflections under load.

The balancing capability of the mechanism is achieved by the equalising means.

When torque is applied to the ring gear 10 and to a planetary gear 66 the force on the helical teeth 70 instantaneously engaging the sun gear 44 has a component acting axially on the gearwheel. The force is transmitted through, say, the bearing 60 to the first abutment 52 and thence to the ring 76. The ring transmits the force equally to the other two first abutments 52 so that all three planetary gears 66 are obliged to bear equal shares of the applied torque. Any movement of any gear necessary for it to assume its full share of load is provided for by very slight axial movement of gears and their abutments and by very slight radial movement of the rings 76, 84. The faces 72 and the surface 74 on the one hand, and the faces 82 and the surface 86 on the other hand slide slightly relatively to one another to produce such movements. The friction at the sliding surfaces acts to damp the motions and so give stable performance of the equalising means and of the mechanism.

The movements of the pins 56 are very small, of the order of only a few thousandths of an inch to preserve equalisation during operation of the mechanism. As wear occurs the pins will have progressively more "play" but once loads have been exerted by applied torque and equalised the movements necessary to maintain equalisation are still only a few thousandths of an inch.

No special assembly techniques are required to make the mechanism. The parts are simply assembled and the nuts 78 and 89 screwed up to comfortably tighten the assembly.

The pitch error of gears usually diminshes with wear; on the other hand radial displacement due to external forces will increase as bearings wear. However, the movements will remain practically unchanged throughout the life of the gear.

This eliminates lost motion between the teeth of the planetary gears and the "first" and "second" gears 10 and 44, respectively.

The counterbalance rings 76 and 84 thus act to facilitate simple assembly and automatically to adjust the planetary gear assemblies simultaneously. No individual adjustment of the planetary gear assemblies is required. The locknuts 80, 90 are tightened.

The slight wear which occurs initially will soon ease any tightness. No special machining tolerances, lapping or matching or "one off" procedures are needed for the gears or other parts and up to 1000 horsepower say can be transmitted by gears made of EN 24 steel without the need for induction hardening, using three planetary gears only.

The equalising facility virtually triples the power transmitting capacity of the mechanism compared with known unbalanced mechanism.

Seven variations in tooth pitching can be tolerated without loss of the equalising facility.

Figures 3 to 7 show another form of mechanism and also illustrate the way in which forces arise and are equalised.

In the mechanism shown in Figures 3 to 7 there are two input shafts 100, 102 and there is an output gear 104 keyed to one stub-shaft 106 of the planetary gear mechanism. There is no ring gear.

The construction of the mechanism is generally similar to that described above with reference to Figures 1 and 2 so far as the mounting of the pins 108 (a total of six) and the arrangement of first abutments 110, first ring 112, second abutments 114, second ring 116 and second stub shaft 118 are concerned.

In this mechanism, however, the planetary gear assemblies each comprise a pair of pins 108 with their respective planetary gear members 120, 122. The three planetary gear assemblies as equiangularly disposed about the main axis 123.

In each pair the gears are similar but are oppositely mounted, end for end, on their pins 108. Each gear, as before, has an integral row of straight teeth 124 and an integral row of helical teeth 126. In each pair the helical teeth 126 mesh with each other.

The straight teeth 124 of the gear 120 mesh with a "first" sun gear 130 integral with the input shaft 100. The straight teeth of the gear 122 mesh with a "second" sun gear 132 integral with the input shaft 102.

The two inputs thus combine and an output is available from the carrier assembly which here is shown as made up of a cupshaped member 134 integral with the stubshaft 106 and a flange 136 secured to the member 134 by screws 138. The flange 136 is integral with the stub shaft 118.

Figure 5 shows equal force and reaction R1 arising at the engaged inclined surfaces of the first abutment 110 of one of the gears 120 and the first ring 112 for one sense of rotation of the mechanism and equal force and reaction R4 arising at the engaged inclined surfaces of the second abutment 114 and the second ring 116 of that same gear 120 for the opposite sense of rotation of the mechanism.

The gear 120 shown in Figures 3 and 5 reacts against its partner gear 122 in its pair through the helical row of teeth. Therefore a force R1 is exerted by the partner gear 122 in the opposite direction upon the ring 116.

Figures 6 and 7 show how the forces arising are distributed.

Figure 6 shows how the force or reaction R1 gives rise to two other forces or reactions R2 and R3 at 1200 to R1 applied by the ring 112 to the respective abutments.

The forces depicted at R1, R2 and R3 in Figures 6 and 7 appertain when the mechanism is transmitting torque in one sense of rotation. The leftward thrust R1 from the planetary gear member 120 shown in Figure 5 produces thrusts on the other two gear members 120.

The gear member 122 meshing with the gear member 120 shown in Figure 5 exerts a rightward thrust R1 on the gear ring 116 which transmits it so as to produce thrusts R2, R3 in the opposite sense on the other two gear members 122, as shown in Figure 7.

Therefore, in each planetary gear assembly, the two gear members act mutually opposite upon one another to take up lost motion between themselves and between their respective "first" and "second" gears 130, 132. The planetary gear assemblies therefore transmit equal portions of the total torque transmitted by the planetary gear mechanism.

Planetary gear mechanisms employing the invention may take many different forms.

The carrier assembly need not rotate about the main axis of the mechanism but may merely be held stationary. Therefore, "planetary" is not to be taken to meaning that the carrier is necessarily rotatable.

Drive input may be applied to the "first" or "second"gears or to the carrier assembly; or outputs may be taken from those items.

The mechanism may have one input with two outputs; one input with one output; or two inputs with one output.

The mechanism will usually be required to be reversible so as to transmit torque in both senses, whether to equal or different in which case the counterbalancing means must be double-acting as described above.

However, the invention is applicable where the mechanism is required to operate in only one sense in which case the counterbalance means need only be single-acting.

The helical teeth described above may in modifications be dispensed with and other kinds of helical formations used instead.

The helical formations must be arranged to derive rotational loading of the gear members in response to axial thrusts applied by the counterbalancing means. There are various possibilities and examples are de scribed below.

The mechanisms particularly described above provide another advantage in that all the bearing duties in the case of the carrier and planetary gear members are rendered less stringent. The distribution of loads about the main axis means that cyclic radial loads on the main carrier bearing (e.g. 24) are greatly reduced compared with mechanisms having a single planetary gear with only crude balancing by counterweight.

Yet another advantage gained is that where the mechanism experiences unbalanced eccentric loading (as is the case where it is used to transmit drive in crane hoists for example in which loads additional to pure torque are sustained by this mechanism) such loads are shared by the several planetary gears and, very importantly, the gear teeth have ample tolerance to absorb small discrepancies without excessive tooth loads. By contrast, where known constructions without counterbalancing are provided with fitted gears having lapped teeth, only pure torque can be transmitted. No eccentric loads can be tolerated and the application of such mechanism is very limited.

Mechanisms according to the invention are made by assembling components of normal standard having normal tolerances.

The counterbalance means is positioned and automatically adjusts all the planetary gear members to take up lost motions between them and the "first" and "second" gears.

It is to be noted that the straight gear teeth may be replaced by helical gear teeth if desired, providing that there is a resultant axial force proportional to the applied torque.

Helical teeth may be eliminated entirely where other helical formations are used in the planetary gear assemblies as shown in Figures 3 to 7 (or in analogous fashion) so that no helical teeth are needed on the ring gear or on any other gear.

It is possible to use helical teeth on the ring gear and straight teeth on the sun gear 44 in a modification of Figures 1 and 2, the planetary gears being modified accordingly; or helical teeth may be used on the ring gear and on the sun gear and for both rows on each planetary gear, provided axial thrust induced by torque is still present.

In the embodiment of Figures 3 to 7, it is possible to use helical teeth on both sun gears and to replace the straight teeth on the planetary gears.

In other modifications larger numbers of planetary gears or pairs of planetary gears may be used; or the planetary gears may be used in threes or larger numbers on the planetary gear assemblies.

In other modifications the counterbalancing means shown in the drawings may be altered by replacing or modifying the 45" faces by other means of transmitting thrust in similar manner. For example, rollers may be interposed between the faces with roller entrapment to maintain the rollers in place; if preferred one face may be normal to the line of motion of the ring or abutment as the case may be. Another alternative is to use levers such as bellcranks; or a toggle mechanism may be used at each abutment; the toggle having the end of one link pivoted on the housing 12 says, the knuckle being acted on by the abutment and the end of the other link connected to the ring.

In another modification the ring may have its inclined faces on its inner periphery and so act in tension rather than compression. Similarly, the abutments may be arranged to act in tension rather than compression if preferred.

WHAT WE CLAIM IS: 1. Planetary gear mechanism comprising first and second gears rotatable about a first axis, a carrier assembly having two or more planetary gear assemblies which engage the first and second gears and which are equiangularly disposed about the first axis and which comprise members having helical formations concentric with respective axes of rotation of the members parallel to the first axis, the members being capable of endwise movement in the direction of their respective rotational axes, the mechanism comprising counterbalance means arranged to transmit from any planetary gear assembly in response to endwise movement of a member thereof in a first sense an equal thrust to a member of the or each of the other planetary gear assemblies in the direction of the respective rotational axis of the member in a second sense opposite to said first sense to cause the planetary gear assemblies mutually to react against the other or others.

2. Mechanism according to claim 1, in which each planetary gear comprises but one member the helical formations of which are teeth meshing with helical teeth on one of the first and second gears.

3. Mechanism according to claim 1, in which each planetary gear assembly comprises two members the helical formations of which are interengaged.

4. Mechanism according to claim 3, in which the helical formations of one member are teeth meshing with corresponding teeth forming the helical formations of the other member.

5. Mechanism according to any preceding claim, in which the counterbalanco means comprises a ring arranged normally to the first axis so as to be movable radially relative thereto, the ring having for each planetary assembly means by which thrust from members of the planetary gear assemblies are transmitted to the ring.

6. Mechanism according to claim 5, in which the ring has for each gear assembly a face at 45C to the first axis and the members of the planetary gear assemblies act on abutments which have corresponding faces engaging the respective faces on the ring.

7. Mechanism according to any claim of claims 1 to 4, in which the counterbalance means comprises hydrostatic capsules which are hydraulically interconnected and upon which the members of the planetary gear assemblies act.

8. Mechanism according to any claim of claims 1 to 4, in which the counterbalance means comprises material which is closely confined and which is only very slightly compressible and which transmits counterbalancing forces in a manner similar to a liquid, members of the planetary gear assemblies being arranged to act upon the material.

9. Planetary gear mechanism substantially as herein described with reference to Figures 1 and 2 of the drawings accompanying the provisional specification.

10. Planetary gear mechanism substantially as herein described with reference to Figures 3 to 5 of the drawings accompanying the provisional specification.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. have its inclined faces on its inner periphery and so act in tension rather than compression. Similarly, the abutments may be arranged to act in tension rather than compression if preferred. WHAT WE CLAIM IS:

1. Planetary gear mechanism comprising first and second gears rotatable about a first axis, a carrier assembly having two or more planetary gear assemblies which engage the first and second gears and which are equiangularly disposed about the first axis and which comprise members having helical formations concentric with respective axes of rotation of the members parallel to the first axis, the members being capable of endwise movement in the direction of their respective rotational axes, the mechanism comprising counterbalance means arranged to transmit from any planetary gear assembly in response to endwise movement of a member thereof in a first sense an equal thrust to a member of the or each of the other planetary gear assemblies in the direction of the respective rotational axis of the member in a second sense opposite to said first sense to cause the planetary gear assemblies mutually to react against the other or others.