GB2232454A - Asymmetric planetary gear assembly - Google Patents

Abstract

A planetary gear assembly in which each planetary gear (2) consists of a planetary gear part (8) in the middle, a disc part (6) smaller than the tooth-root circle of the planetary gear part on one side and another disc part (7) bigger than the tooth-edge circle of the planetary gear part (8) on the other side thereof. An internal ring gear (3) includes an internal gear part (25) in the middle, a cylindrical part (26) smaller than the tooth- edge circle of the internal gear part on one side thereof and another cylindrical part (27) bigger than the tooth-root circle of the internal gear part on another side. The planetary smaller disc parts (6) roll on the smaller cylindrical part (26) of the internal gear and the planetary bigger disc parts (7) roll on the bigger cylindrical part (27) of the internal gear. The planetary gear part (8), two disc parts (6, 7) are integrally formed as a single body. The internal ring gear (3) is made of nylon or polypropylen. <IMAGE>

Description

UNIFIED ASYMMETRIC PLANETARY GEAR ASSEMBLY DESCRIPTION This invention relates to a planetary gear assembly having wide applications for decelerator or accelerator, especially to an asymmetric planetary gear assembly with unified asymmetric planetary gears and an asymmetric internal gear.

Planetary gear assembly consists of a sun gear, three or four planetary gears, an internal gear and a carrier.

At six or eight points planetary gears mesh with a sun gear or an internal gear.

The number of engagement points exceeds the number of parts. Therefore it is difficult to equalize all the transmitting forces acting upon the engagement points. Owing to very small size errors the transmitting forces are likely to be uneven.

Uneven engagement means too deep engagement on the one hand and too shallow engagement on the other hand.

Deep engagement between planetary gears and a sun gear or an internal gear causes great vibration, loud noise and big energy loss.

To solve the problem of uneven engagement, improved planetary gear assemblies having planetary gears with discs and an internal gear with rings on both sides or on one side thereof have been proposed.

The diameters of the planetary discs or the internal rings are equal to the diameters of pitch circles of the planetary gear or the internal gear respectively.

FIG.8 shows a planetary gear of this improvement.

The planetary discs contact with and roll on the internal rings. These pitch discs and pitch rings effectively forbid an excess engagement between planetary gears and an internal gear. Now this type of improvement is called as a pitch circle type for convenience.

Many variations of this type have been proposed so far. This is because the pitch circle is a unique circle for a gear.

When pitch discs and pitch rings are rotated at the same speeds with their gears, the line velocities of the pitch discs and pitch rings are equal at the contact points. No slipping occurs between the pitch discs and pitch rings.

Therefore transmitting efficiency is not reduced.

The defacements of pitch discs and rings are trivial.

However the pitch circle type of planetary gear assembly has a drawback that a great number of parts are required to construct an assembly. Pitch circle has an intermediate size between -a tooth-edge circle and a tooth-root circle. Thus two pitch discs and a planetary gear cannot be made in a body. Similarly pitch rings and an internal gear cannot be made in a body.

In the case of the pitch circle type, a planetary gear consists of three parts and an internal gear consists of three parts. Because the number of parts is big, the cost for manufacturing parts is heighten.

Furthermore because an internal gear consists of three parts ------- a gear in the middle and two pitch rings on sides, a problem of misalignment occurs among three parts in radial directions.

Then this applicant has invented a novel planetary gear assembly, which is now called as toothedge circle type ( Japanese Patent Application No.56193113, Laying Open No.58-94656 Laying Open Date 4, June, 1983 ).

In this type, a planetary gear has two discs larger than the tooth-edge circle on both sides.

An internal gear has two ring portions larger than the tooth edge circle on both sides. Because side ring portions are larger than the tooth-edge circle, two side ring portions can be made in a body with a central gear portion.

Therefore an internal gear can be made as one part. In practice an internal gear is made by injection molding of polyacethaS The number of parts are reduced by two, because an internal gear consists of one part instead of three.

This fact reduces not only the cost for manufacturing parts but also the cost for constructing an assembly.

At first there was a theoretical question whether all the gears of the planetary gear assembly could smoothly rotate, because the contacting and rolling circles deviated from the pitch circles. However when the applicant had constructed such a planetary gear assembly and had examined the rotational property of the gear assembly, all the gear rotated as smooth as one of the pitch circle type.

This tooth-edge type of was symmetric with regard to the axial direction.

The applicant has further invented a novel planetary gear asembly asymmetric with regard to the axial direction.

(a) Patent Laying Open No.60-34553 Laying Open Date ; 22, February,1985 (b) Patent Laying Open No.60-252845 Laying Open Date ; 13, December, 1985 (c) Patent Laying Open No.61-27337 Laying Open Date ; 6, February, 1986 (a) is an asymmetric planetary gear assembly ih which every gear has a disc or a ring on one side.

(b) and (c) are asymmetric planetary gear assembly in which every planetary gear and an internal gear have two discs or two rings on both sides.

However the discs and the rings are asymmetric with regard to the axial direction. A disc mounted on either side of a planetary gear is larger than the tooth-edge circle of planetary gear, but another disc mounted on another side is smaller than the tooth-root circle. A matter of course a ring formed on one side of an internal gear is larger than the tooth-edge circle of internal gear, and another ring formed on other side is smaller than the tooth-root circle of internal gear. At first in the same way to the former invention of the tooth-edge type, there was a theoretical question whether such an asymmetric planetary gear assembly could smoothly rotate, because the line velocities of side discs and side rings are different at the contacting and rolling points on both sides.

Then the applicant had constructed such an asymmetric assembly, had examined its rotational property, and had confirmed smooth rotations of all gears.

The asymmetric type of planetary gear assembly has an advantage that a sun gear or a sun gear shaft can be inserted from a side after construction.

So far the applicant has been inventing various kinds of anomalous planetary gear assembly for groping an ideal planetary gear assembly with low vibration, high transmission efficiency and low cost for construction.

Both in the cases of the tooth-edge circle type or the asymmetric type, a planetary gear consists of three parts. They are a gear in the middle and two side discs which hold the gear therebetween.

A planetary gear assembly has three or four planetary gears and each planetary gear consists of three parts.

Then a great number of parts have been required to construct an assembly. This fact has heightened the cost for manufacturing parts and the cost for assemblying them.

If a planetary gear could be made in a single body, the costs for manufacturing and for assemblying would significantly reduced.

In the pitch circle type a planetary gear consists of three parts. It might be possible to make a planetary gear in two parts, but such an asymmetric structure would cause an undesirable unbalance of a planetary gear.

In the tooth-edge circle type , it is unavoidable to constitute a planetary gear with three parts, because it is equipped with two discs larger than the gear part on both sides of the gear part.

A purpose of this invention is to provide a planetary gear assembly having planetary gears unified in a single part.

Another purpose of the invention is to provide a planetary gear assembly with low noise and low vibration by improving an internal gear from a material point of view.

The planetary gear assembly of this invention use the unified planetary gears which consist of unified three parts - a gear part, a side disc larger than the tooth-edge circle and another side disc smaller than the tooth-root circle. Namely in this invention a gear part and two side discs are unified in a body.

Furthermore the internal gear of this invention is made from elastic material with low rigidity e.g.

nylon 66, nylon 6 or polypropylene instead of polyacethal.

The invention will be more fully understood from the following description given by way of example only with reference to the several figures of the accompanying drawings in which FIG. 1 is a partially sectioned front view of a unified asymmetric planetary gear assembly as an embodiment of the invention.

FIG.2 is a partially sectioned rear view.

FIG. 3 is a sectional view taken along a line III - III in FIG. 1 FIG.4 is an enlarged sectional view only of a planetary gear shown in FIG.3.

FIG.5 is a front view of a planetary gear.

FIG.6 is a sectional view near a planetary gear of another embodiment of this invention.

FIG.7 is a sectional view of a planetary gear of the tooth-edge type.

FIG.8 is a sectional view of a planetary gear of the pitch circle type.

Referring now to the drawings a unified asymmetric planetary gear assembly consists of a sun gear (1), planetary gear (2), an internal gear (3) and a carrier (4).

There is a sun gear (1) in the center.

In this example four planetary gears (2) enclose and mesh with the sun gear (1). Three planetary gears (2) are also available instead of four.

An internal gear (3) encloses and meshes with all the planetary gears (2).

A carrier (4) is built with a main carrier disc (4a) and a sub-carrier disc (4b). The carrier (4) rotatably supports the planetary gears (2) by planetary shafts (5).

The main carrier disc (4a) has four ( or three ) first convex parts (10) on the inner surface.

Correspondingly the sub-carrier disc (4b) has four ( or three ) second convex parts (11) on the inner surface.

A plug part (12) is formed on second convex part (11) of the sub-carrier disc (4b). A socket (13) is perforated in the axial direction in the first convex part (10) of the main carrier disc (4a).

To connect two carrier discs, an operator inserts the plug parts (12) of the sub-carrier disc (4b) into the sockets (13) of the main carrier disc (4a) till the ends of the plug parts (12) project out of cavities (29). And the projecting ends are crushed round. The crushed ends (28) firmly couple the main carrier disc (4a) with the sub-carrier disc (4b).

This method of connection is available if the main carrier disc (4a) and the sub-carrier disc (4b) are made from sintered alloy or alminium die-casting.

If the carrier discs (4a) and (4b) are made from plastics, the projecting ends (28) of the plug parts (12) are bonded to the sockets (13) by the ultra sonic bonding.

Four ( or three ) third convex parts (18) perforated with shaft-supporting holes (16) are formed on the inner surface of the main carrier disc (4a). The Third convex parts (18) are positioned at the middle of two neighboring first convex parts (10).

Similarly four ( or three ) fourth convex parts (19) perforated with shaft-supporting holes (16) are formed on the inner surface of the sub-carrier disc (4b).

Boths ends of the planetary shafts (5) are fixed in the shaft-supporting holes (16) of the main carrier disc (4a) and the sub-carrier disc (4b).

The shape of the planetary gear is one of novel features of this invention. Therefore it will be explained in detail with referring to FIG.4 and FIG.5.

The planetary gear (2) has a planetary gear part (8) in the middle, a planetary smaller disc part (6) and a planetary bigger disc part (7) on both sides. Thus the planetary gear (2) is asymmetric regarding axial direction.

Inner portion of the planetary gear part (8) connects with a planetary boss (9) through which a shaft hole (21) is perforated. A planetary shaft (5) pierces the shaft hole (21).

The planetary smaller disc part (6) is smaller than the tooth-root circle of planetary gear. On the contrary the planetary bigger disc parts (7) is bigger than the tooth-edge circle of planetary gear.

The important matter is that the planetary gear part (8), planetary smaller disc part (6), planetary bigger disc part (7) and planetary boss (9) are made in a body. The planetary gear (2) is not divided in three parts but is unified in a single part. This is one of the characteristics of the invention. Such an asymmetric planetary gear is able to be made by plastic injection molding or sintering of powder metal.

In correspondence with the planetary gear (2), the internal gear (3) consists of three parts.

Namely the internal gear (3) has an internal gear part (23) in the middle, an smaller inner cylindrical part (26.) and a bigger inner cylindrical part (27) on both sides.

The internal gear part (25) meshes with the planetary gear part (8) to transmit rotation torque thereto. The planetary smaller disc part (6) contacts with and rolls on the smaller inner cylindrical part (26) of the internal gear (3). Of course there is some clearance between two rolling surfaces. Sometimes two parts (6) and (26) touch each other but other times they untouch.

Similarly the planetary bigger disc part (7) contacts with and rolls on the bigger inner cylindrical part (27). There is also some clearances between two rolling surfaces. Two parts (7) and (27) sometimes touch but other times untouch each other.

Owing to the contact between the planetary smaller disc part (6) and the smaller inner cylindrical part (26) and the contact between the planetary bigger disc part (7) and the bigger inner cylindrical part (27), radial forces are transmitted from the planetary gears (2) to the internal gear (3).

A sun shaft hole (14) is axially perforated in the sun gear (1). Spline, Serration or D-shape hole is formed on the inner surface of the sun shaft hole (14).

Boss part of the main carrier disc (4a) is thickened to reinforce it. A carrier shaft hole (15) is axially perforated in the thickened boss part. Spline, Serration or other coupling device is formed also on the inner surface of the carrier shaft hole (15).

When the planetary gear assembly is used as decelerator, an input shaft shall be inserted into the sun shaft hole (14) and an output shaft shall be inserted into the carrier shaft hole (15). On the contrary when it is used as accelerator, an input shaft shall be inserted into the carrier shaft hole (15) and an output shaft shall be inserted into the sun shaft hole (14).

The internal gear (3) shall be mounted in a casing.

To prevent the internal gear (3) from rotating with regard to the casing, several radial projections (31) are formed on smooth cylindrical surface (32). The casing shall be formed to have complementary projections on its inner surface. In this example the internal gear (3) shall rather loosely mounted in the casing.

Of course another kinds of mounting are also available. For instance perforating axial holes on an internal gear and the flange of a casing, one can fix the internal gear to the casing by screwing bolts in the holes.

In the embodiment shown in figures, the radial projections (31) deviate from the middle plane.

The plane for receiving torque axially distances from the plane on which the radial projections (31) exist.

If a strong torque acts on, the internal gear (3) can distort in a spiral manner between two planes.

Such spiral distortion is effective to absorb an abrupt, strong shock.

Furthermore the internal gear (3) of this invention is molded in a body from nylon 66, nylon 6 or polypropylene.

These materials are more elastic than polyacethal which the applicant has been employing so far as the material of internal gear. Because of their high elasticity nylon 66, nylon 6 or polypropylene is effective to alleviate vibration or noise-generation.

In the example shown by FIG.3 the third concave parts (18) and fourth concave parts (19) are formed on the inner surface of carrier discs (4a) and (4b) to prevent the planetary gears (2) from displacing axially by holding the planetary boss (9) therebetween.

The planetary bigger disc parts (7) prevent the sun gear (1) from coming out leftward in FIG.3.

An inner boss (22) of the thickened main carrier disc (4a) prevents the sun gear (1) from coming out rightward.

Thus the sun gear (1) is kept at a right axial position.

Furthermore in this example, the main disc (4a) is larger than the smaller inner cylindrical part (26) of the internal gear. This fact prevents the carrier (4) from coming out of the internal gear (3) leftward.

Another embodiment of this invention is shown in FIG. 6. Fundamental structure is common with the former embodiment. In this embodiment circular protrusions (36) and (37) are shaped on the inner surfaces of the main carrier disc (4a) and sub-carrier disc (4b) to prevent the planetary gears (2) from displacing in axial direction. Because the sides of planetary smaller disc part (6) and bigger part (7) touch with the circular protrusions (36) and (37), the planetary gears (2) are kept at a right axial position. Besides in this embodiment bolt holes (38) are perforated in axial direction.

By inserting bolts in the bolt holes (38) and screwing them into screw holes of a casing, the internal gear (3) is safely fixed on the casing.

The sun gear (1) is made from plastics, sintered alloy, zinc or steel. The planetary gear (2) is made from plastics or sintered alloy. In spite of the anomalous shape, the planetary gear can be made in a body by molding. The carrier (4) is made from plastics, aluminium, aluminium alloy, sintered alloy, zinc or steel.

The internal gear (3) can be molded from nylon 66, nylon 6 or polypropylene.

In the embodiment shown in FIG.1 to FIG.6, the planetary smaller disc part (6) neighbours to the main carrier disc (4a) and the planetary bigger disc part (7) neighbours to the sub-carrier disc (4b) to prevent the sun gear (1) from coming out.

This disposition can be safely reversed. If the disposition is reversed, the sun gear (1) can be freely inserted or drawn out after construction.

Desirable size relations of gears, disc and cylindrical parts will now be explained.

The planetary smaller disc part (6) of the planetary gear (2) is 0 to 2 modules smaller in radius than the tooth-root circle of planetary gear. The planetary bigger disc part (7) is 0 to 2 modules bigger in radius than the tooth-edge circle of planetary gear. The smaller inner cylindrical part (26) of the internal gear (3) is 0 to 2 modules smaller in radius than the toothedge circle of internal gear. The bigger inner cylindrical part (27) is O to 2 modules bigger in radius than the tooth-root circle of internal gear.

The functions of the planetary gear assembly will now be explained.

The planetary gear parts (7) of the planetary gears (2) mesh with the internal gear part (25) to transmit rotation torque.

The planetary bigger disc parts (7) contact with and roll on the bigger inner cylindrical parts (27) of the internal gear (3). The planetary smaller disc parts (6) contact with and roll on the smaller inner cylindrical parts (26).

Radial forces are transmitted from the side disc parts (6) and (7) to the side cylindrical parts (26) and (27). The contacts of the side disc parts and cylindrical parts forbid excess engagement between the planetary gears and the internal gear.

Although the line velocities of the disc parts and the inner cylindrical parts are different at the rolling points, the difference of line velocities does not hinder a smooth rotation of gears.

Some amounts of tolerances are usually allocated to the side disc parts (6) or (7) and the side inner cylindrical parts (26) or (27). The disc parts and the inner cylindrical parts are not always contacting each other. But they are separated nearly all time owing to tolerances.

By the reason the difference of line velocities does not hinder smooth rotation of gears.

The assembly of gears will now be explained.

(1) A sub-carrier disc (4b) is put on a table as the second convex parts (11) face upward.

(2) Planetary shafts (5) are inserted into the shaft supporting holes (16).

(3) Planetary gears (2) are inserted around the planetary shaft (5) as the planetary bigger disc parts (7) face downward.

(4) An internal gear (3) is inserted around the planetary gears (2) as the bigger inner cylindrical part (27) face downward.

(5) A sun gear (1) is slightly rotated and inserted into the center of planetary gears (2).

(6) A main carrier disc (4a) is fitted onto the sub-carrier disc (4b).

(7) Top ends of plug parts (12) projecting on the cavities (24) are pressed and flattened.

The advantages of this invention will now be explained.

First of all, a planetary gear is unified.

It consists of one parts instead of three.

The reason why the planetary gear can be unified in a body is able to be understood by referring FIG.3, FIG.5 or FIG.6. One side of a planetary gear part (8) is a planetary smaller disc part (6) smaller than the tooth root circle. Another side of a planetary gear part (8) is a planetary bigger disc part (7) bigger than the tooth-edge circle. The peripheral diameter changes monotonously in axial direction.

Therefore such an anomalous planetary gear can be made by injection molding with a paired metallic mold. On the contrary such planetary gears shown in FIG.7 or FIG.8 cannot be molded at a time, because the peripheral diameter does not change monotonously.

The unified planetary gear reduces the costs for manufacturing and assemblying parts.

Because the internal gear is made from elastic material-nylon 66, nylon 6 or polypropylene, the internal gear distorts elastically and alleviates the abnormal torque when an excess torque acts on the gears.

The elastic distortion of the internal gear reduces noise-generation and vibration.

To confirm this advantage of the invention, the Inventor has tried the following examination.

Four kinds of planetary gear assemblies with same size and matter except the matter of internal gears have been manufactured. The internal gears have been made from nylon 66, nylon 6, polypropylene or polyacethal.

The outer diameter of internal gears is 75 mm.

The module of gears is 0.75. The tooth number of internal gears is 75. The reduction ratio is 4.8.

The tooth number of sun gears is 20. The tooth number of planetary gears is 28. The sun gears are made of sintered alloy. The planetary gears are made of polyacethal. These planetary gear assemblies have been mounted in electric washers for testing the noise-generation property. 4 kg of clothes have been thrown into each of the electric washer. Then the electric washers have been switched on. Then the Inventor has measured the noise loudness at a point distanced 1 meter from the electric washer. The number of sample is ten for each kind. The results of measurements are shown in Table 1.

Table 1 Measurement of noise-loudness of electric washers equipped with different kinds of planetary gear assemblies

Material of internal gear Noise loudness nylon 66 48 - 43 phon nylon 6 49 - 43 phon phon polypropylene 49 - 46 phon polyacethal 54 - 47 phon These results have proved that the planetary gear assemblies of this invention can reduce noise loudness about 4 to 6 phons in comparison with the case of polyacethal.

Radial forces are transmitted in two ways one way is between the planetary bigger disc parts (7) and the bigger inner cylindrical part (27) and the other way is between the planetary smaller disc parts (6) and the smaller inner cylindrical part (26).

Radial forces are not transmitted from gears to gears. Because of little radial forces, teeth of gears do not deeply mesh each other.

Even if strong centrifugal forces, or other abnormal forces e.g. The forces induced by size errors are applied to the input or output shafts, the gears can smoothly rotate by the actions of the discs and the inner cylindrical surfaces.

Claims (1)

1. (1) A unified asymmetric planetary gear assembly comprising a sun gear, a plurality of planetary gears meshing with the sun gear, an internal gear meshing with the planetary gears, a carrier rotatably supporting the planetary gears with planetary shafts; characterized in that the planetary gear consists of a planetary gear part in the middle, a planetary smaller disc part smaller than the tooth-root circle of the planetary gear part on a side thereof,a planetary bigger disc part bigger than the tooth-edge circle of the planetary gear part on another side thereof and a planetary boss axially perforated with a shaft hole, the planetary gear part, the planetary smaller disc part, the planetary bigger disc part and the planetary boss are unified in a body the internal gear includes an internal gear part meshing with planetary gear part, a smaller inner cylindrical part smaller than the tooth-edge circle of the internal gear part on a side thereof and a bigger inner cylindrical part bigger than the tooth-root circle of the internal gear part on another side thereof the internal gear part, the smaller inner cylindrical part and the bigger inner cylindrical part remade of nylon or polypropylen ; the planetary smaller disc parts roll on smaller inner cylindrical part and the planetary bigger disc parts roll on the bigger inner cylindrical part (2) A unified asymmetric planetary gear assembly as claimed in claim (1), wherein the planetary smaller disc part is 0 to 2 modules smaller in radius than the tooth-root circle of the planetary gear part and the smaller inner cylindrical part is 0 to 2 modules smaller in radius than the tooth-edge circle of the inner gear part.

   (3) A unified asymmetric planetary gear assembly as claimed in claim (2), wherein the planetary bigger disc part is 0 to 2 modules bigger in radius than the tooth-edge circle of the planetary gear part and the bigger inner cylindrical part is 0 to 2 modules bigger in radius than the tooth-root circle of the inner gear part.

   (4) A unified asymmetric planetary gear assembly as claimed in claim (3), wherein a carrier consists of a main carrier-disc having a carrier shaft hole for fitting an output shaft and a sub-carrier disc with a wide opening, , and the planetary bigger disc part and the bigger inner cylindrical part are located on the side neighboring to the sub-carrier disc.

   (5) A unified asymmetric planetary gear assembly as claimed in claim (5), wherein a carrier consists of a main carrier disc having a carrier shaft hole for fitting an output shaft and a sub-carrier disc with a wide opening and the planetary bigger disc part and the bigger inner cylindrical part are located on the side neighboring to the main disc.

   (or) A unified asymmetric planetary gear assembly as claimed in claim (4) or(5), wherein the main carrier disc has an inner boss inwardly projecting on the inner wall for:forbidding the sun gear from displacing in the axial direction.

   (7) A unified asymmetric planetary gear assembly as claimed in claim (3), wherein the internal gear has a flat smooth cylinder surface and several number of radial projections , for forbidding the relative rotation of the internal gear in a casing and the radial projections lie in a plane axially distanced from a middle plane of the internal gear.

   (8) A unified asymmetric planetary gear assembly as claimed in claim (7), wherein the planetary gears are made of plastics or sintered alloy.

   (9) A unified asymmetric planetary gear assembly as claimed in claim (8), wherein the main carrier disc has third convex parts projecting inwardly with axial shaft-supporting holes, the sub-carrier disc has fourth convex parts projecting inwardly with axial shaft-supporting holes and the shaft supporting holes support both sides of the planetary shaft.

   (10) A unified asymmetric planetary gear assembly as claimed in claim (9), wherein the sun gear is made of plastics, sintered alloy, zinc, steel or quenched steel.

   (11) A unified asymmetric planetary gear assembly as claimed in claim (9), wherein the carrier is made of plastics, fiber-reinforced plastic, aluminium, aluminium alloy, sintered alloy, zinc or steel.

   (12) A unified asymnetric planetary gear assembly substantially as hereinbefore described with reverence to the accomtany-ing drawings.