GB2090634A - Planetary Gear Transmissions - Google Patents

Abstract

In a transmission comprising first and second serially connected planetary gear sets P1, P2, each set comprises a planetary pinion carrier 16, 62 fast with the output member of that set, a plurality of planetary pinions 21, 22, 23, 24 and 74, 81 mounted in the carrier, at least two pinions in each carrier being of different gearing diameters, an input and centrally disposed gear (ring gear 14 of the first set and sun 60 or 79 of the second set) meshing with one of the planetary pinions and at least two other centrally disposed gears (suns 41, 42, 43, ring gear 44, and ring gears 75, 82) also meshing with pinions, each of these centrally disposed gears having brake means 51, 52, 53, 54, 76, 83, a separate input centrally disposed gear 60, 79 for each of the pinions of the second gear set mounted on the input shaft X, Y of the second gear set, and the two pinions 74, 81 of the second gear set being journalled on the carrier 62 independently of each other. <IMAGE>

Description

SPECIFICATION Improvements In and Relating to Planetary Gears and Power Shift Planetary Gear Transmissions This invention relates to a planetary gear and a multi-speed power shift planetary gear transmission incluidng such planetary gears. The transmission according to the invention is especially suitable for use with buses, lorries, earth moving equipment and military vehicles. More particularly, the invention relates to a 9- to 1 2-speed transmission of the power shift type comprising a first planetary gear set in combination with a range planetary gear set for multiplying the gear ratios of the first set.

The present invention is a further development of the transmission described and claimed in my British Patent Nos. 1559491 and 1559492 and one aim of the present invention is to provide a relatively small multi-speed power shift planetary gear transmission which, with a minimum number of changes in structure, can be adapted to provide a wide range of gear ratios necessary for a "range" gear as hereinafter defined. Another aim of the present invention is to provide such an improved planetary gear transmission which has certain characteristics of the transmission of my aforesaid British Patents.

According to the present invention, there is provided a multi-speed planetary gear transmission suitable for use with buses, lorries, earth moving equipment and military vehicles comprising first and second planetary gear sets arranged in series, each set comprising a planetary gear carrier having associated planetary pinions spaced around its axis. In each of the two planetary gear sets, the planetary pinions include at least two gearing of different diameters, and in each planetary gear set, the planetary pinions mesh with at least three sun and/or ring gears, which shall be referred to below generically as "centrally disposed gears", and at least one of the said sun and/or ring gears comprises the input member of that planetary gear set while the carrier for the planetary pinions comprises the output from that planetary gear set.Each of the remaining sun and/or ring gears of that set have associated therewith a friction brake controlled by a servo motor stationarily mounted in the housing; and wherein the two different gearing diameters on the planetary pinions of the second gear set are driven from the secondary side of the first planetary gear set, and wherein each of the two different diameters of the planetary pinions of the second gear set are individually journalled on a planetary pinion holder which constitutes the output member for the secondary planetary gear set.

The multi-speed planetary gear transmission of the present invention includes a first section having a number of gear trains in parallel with each other and a second section which utilizes the gear trains of the first section a number of different times, which in turn requires that each gear step in the second section have a relatively large gear ratio. The type of planetary gear sets having such a relatively large gear ratio between each step is herein referred to as a "range" gear, because it multiplies the range of the gear steps of the first section. By way of definition, another way to multiply the number of gear steps of a first section is to provide an additional section which includes steps smaller than the steps of the first section so that it divides each step of the first section into a plurality of different steps.Such a transmission is commonly referred to as a "spit" gear. While the present invention is directed to the combination of a first section combined with a range gear, the transmission of the present invention can also be used in combination, that is, in series with such a split gear.

Preferably, the first planetary gear set of a transmission according to the invention has three or four gear steps, and the second planetary gear set has three steps. This preferred form of the transmission will, therefore, have nine or twelve gear ratios, depending on whether the first planetary gear set has three or four gear steps.

In prior British Patent No. 1559491 there is described a multi-speed planetary gear transmission of the type described above which can produce nine or twelve gear speeds. However, the structure of the second planetary gear set shown in said British Patent has certain limitations as to the size of the gear stps and the present invention seeks to overcome these problems.

This invention includes a multi-speed transmission, first and second serially connected multiple speed planetary gears, each planetary gear comprising a planet carrier having associated planet gear wheels at least two of which planet gear wheels are of different diameters and which, in each planetary gear, mesh with at least three internally and/or externally toothed centrally disposed gear wheels, at least one of the centrally disposed wheels in each planetary gear constituting an input member with the planet carriers constituting an output member, each remaining centrally disposed gear wheel having an associated friction brake controlled by a servo motor having a non-rotatable housing characterised in that each of the two gear wheels of different diameters of the said second gear are driven from the secondary side of the said first gear and in that each of the said two planetary gear wheels are individually journalled in a planet gear holder which constitutes the output shaft.

It is another aim of the present invention to provide a planetary gear for use in the above defined as well as other gear transmissions. Accordingly, the invention also includes a planetary gear comprising: a casing; and input shaft rotatably mounted in the casing; a carrier rotatably mounted in the casing and comprising the output member of the planetary gear; a plurality of planetary pinions mounted in the carrier and spaced about the axis of the planetary gear, each planetary pinion having at least two different gearing diameters; a first sun gear connected to the input shaft and meshing with the smaller gearing diameter, a second sun gear connected to the input shaft and meshing with the larger gearing diameter, and each of the said two gearing diameters being journalled on the carrier independently of each other.

A transmission according to the present invention provides a relatively small 9- to 12-to 1 5speed transmission of the power shift type which also has a relatively low weight as compared to existing 9- or 12- or 1 5-speed transmission.

The invention will now be described by way of example, with reference to the accompanying drawings in which: Figure 1 is a longitudinal sectional view of a 12-speed planetary gear transmission having gear steps of approximately 1.25:1 and a total gear ratio of approximately 11.5::1; Figure 1 A is a longitudinal cross-sectional view through a planetary gear transmission showing another embodiment of the present invention with the second planetary gear transmission modified in a way which permits greater variation of the gear ratios obtainable in said second planetary gear set; Figure 1 B is a modification of gear P 1 of Figure 1 and provides five steps giving a 1 5-speed transmission; Figure 2 shows schematically, for purposes of comparison, a 12-speed planetary gear transmission of the type shown in British Patent No. 1,559,491; Figure 3 is a schematic illustration of the planetary gear transmission of Figure 1; Figure 4 is a schematic illustration of the planetary gear transmission of Figure 1 A;; Figure 5 is a schematic view of a planetary gear transmission showing another embodiment of the present invention wherein another means is illustrated for varying the size of the gear step in the second planetary gear set; Figure 6 is a schematic view of a planetary gear transmission according to the present invention and showing another embodiment thereof wherein the bearing structure of the second planetary gear set has been modified; Figure 7 is a graph showing the gear ratios, the primary speeds and tractive effort obtained with the planetary gear transmission of Figure 2; Figure 8 is a graph showing speed ratios and primary speeds and tractive effort for the planetary gear transmissions shown in Figures 3 to 6.

In the drawings, like elements are represented by like numerals throughout the several views.

Although the figures will be described in detail, many specific features will not be described in detail because they are illustrated and described in the said commonly owned U.S. Patent No. 4,142,425.

Sun and ring gears may be referred to below by the generic phrase "centrally disposed gear".

Referring to Figure 1, (which Figure is also shown schematically in Figure 3), the planetary gear transmission comprises an input shaft I, an output shaft 0 with intermediate shafts X and Y. The shafts are supported within a stationary casing C, by means of bearings 10, 11 and 12. Between the bearings 10 and 11 there is illustrated first planetary gear set P 1 which has four forward gears and one reverse gear. Between bearings 11 and 12 there is illustrated a second planetary gear set P2 which is a "range" gear having three forward gears and no reverse gear.Each of the steps of the second planetary gear set is greater than the total of the steps in the first planetary gear set P . In the first set P 1 the input is via a ring gear while the output is via the planetary pinion carrier, whereas, in the second set P2, the input is via a sun gear and the output is via the planetary pinion carrier.

The input shaft I is drivingly engaged with the generally disc shaped input member 13 which has an aperture 1 3a passing therethrough for a purpose to be described below. The outer periphery of disc input member 13 is engaged with longitudinally extending splines on a ring gear 14. Mounted within the planetary gear set P1 and spaced around its axis are a plurality of planetary pinions 15, all of which pinions 1 5 are mounted in a carrier 16, supported therein by bearings 1 7 and 1 8. The carrier 1 6 is connected via splines 1 9 to the shaft X. Pinion 1 5 includes a large gearing diameter 21, an intermediate gearing diameter 22 and a smaller gearing diameter 23.In this illustration, the gearings 21 and 22 are connected by splines onto a basic cylindrical central element of the pinions 15 which includes on its periphery the smaller gearing diameter 23. On the right hand side of the bearing 18 when viewed in Figure 1, there is a further gearing diameter 24.

The input shaft I, acting via the ring gear 14 provides the input to the planetary gear set P 1 via the larger diameter gearing 21. In the gearings 21,22 and 23 each have associated therewith a sun gear designated 41, 42 and 43, respectively, and each of which can be braked independently of the other by associated disc brakes 51, 52 and 53, respectively. Each of the three disc brakes is operated by stationarily (i.e. non-rotatably) mounted servo motors 51 A, 52A and 53A, respectively. The gearing 24 is connected to a ring gear 44 and constitutes a reverse gear upon braking of brake 54 which is also operated by a servo motor 54A which is non-rotatably mounted in the casing C.

The gear set P 1 also includes a direct drive facility for operatively connecting the input shaft I to the output shaft X. To this end the gear set P 1 includes a direct drive clutch 30 operation of which is controlled by an annular piston 31 which moves longitudinaily on the splines of ring gear 14 under the agency of a Belleville spring 32. When the spring 32 urges the piston 31 to the left, the clutch 30 is disengaged. To engage this clutch, there is provided a lever 33 which passes through opening 1 3a in the disc input member 13. At its iower end, the lever 33 is engaged by element 34 which is a rotatable part of a servo piston. The element 34 abuts an axial thrust bearing 36, across which is provided an element 35 in the form of an annular servo piston which is non-rotatably mounted in the casing C.

Such a servo piston is also shown in British Patent No. 1,559,491 in Figure 1 thereof.

Figure 1 B is a modification of gear P 1 (of Figure 1) and is designated P 1 A. The main difference between P 1 A (in which, where appropriate, the same reference numerals have been used as in Figure 1) and P 1 is that whereas P 1 provides four gear steps and reverse, P 1 A provide five gear steps and reverse. Thus, whereas the combination of P 1 and P2 produces a 9- to 12-speed transmission, the combination of P 1 A and P2 produces a 9- to 12- to 15-speed transmission. Further, when combined with a "split" gear, the number of gear steps can, of course, be doubled.

From a comparison between Figures 1 and 1 B it will be seen that the extra and fifth gear in the gear P 1 A is obtained using additional sun gear 45 and additional servo operated brake 50/50A. The servo operated brake 50/50A serves to brake or release sun gear 42 relative to the casing C.

The ratios of the five gears of planetary gear P 1 A are

The shaft X is connected via splines to the shaft Y which is drivingly engaged with three separate input members to the second planetary gear set P2, namely input members 60, 65 and 79. The second planetary "range" gear set P2 includes a plurality of planetary pinions 61 spaced about the axis of the planetary gear set. The pinions are mounted in a carrier 62 (the full extent of which is best illustrated in the lower portion of Figure 1). Pinions 61 are mounted in the carrier 62 by means of bearings 63 and 64.

The input member 65 is a flanged disc connected to the shaft section Y to provide an input for direct drive directly between the shaft Y and the carrier 62 and hence the output shaft 0. For this purpose, the flanged disc 65 includes discs which form a part of direct drive clutch 66, the other discs of which are engaged with the carrier 62. Direct drive clutch 66 includes an annular piston 67 which is urged into the disengaged position by a Belleville spring 68. To close the direct drive clutch 66, radial inner portions of a number of levers 69 are urged to the right by a servo motor system which, like the system in a planetary gear set P 1, includes a rotational portion 70 of the servo motor, an axial thrust bearing 72, and non-rotatably mounted servo part 71.

For intermediate speed reduction through the planetary gear set P2, the transmission includes a ring gear 75, the outer portion of which is connected by a spline to discs of a brake 76 operated by a servo motor 77 which is non-rotatably mounted in the casing.

For the greatest speed reduction through planetary gear set P2, the input member 79 (a sun gear) of the shaft section Y engages a very large diameter pinion 81 which is mounted, via bearings 80, on a hub shaped portion 85 of the carrier 62. Outwardly of this gear 81 there is a ring gear 82 which is operatively connected to a brake 83 which in turn is operated by a servo motor 84 which is non-rotatably mounted in the casing.

Although not illustrated in detail, it will be understood that all of the non-rotatably mounted servo motors include suitable means such as spring means, hydraulic means or pneumatic means or the like for returning the servo motors to a released position upon release of the pressurised fluid behind the servo motor piston.

The following table illustrates the gear ratios through the planetary gear set P 1 , taken alone, the planetary gear set P2, taken alone, and the combined gear reductions through the overall planetary gear transmission, including twelve forward speeds and three reverse speeds.

As will be apparent from the preceding description, the construction of P2 allows relatively large gear steps to be obtained between the three gear ratios. This is made possible by the use of the relatively large gearing 81 which is constructed by mounting the same on bearings journalled on the exterior of a hub portion 85 of the carrier 62. Additionally, a greater variation in gear ratios is obtained by constructing the reverse gear 24 in P 1 separately from the gearings 21, 22 and 23 which are utilised for forward drive.

Figure 1 A and Figure 4 illustrates a modification of the embodiment of Figures 1 and 3 wherein the gearing in planetary gear set P2 is slightly modified. In these figures like numerals represent like parts to those of Figures 1 and 3, but, for clarity, many numerals for like parts have been omitted; parts which are similar to Figure 1 but slightly modified are followed by the letter "A" and new elements are indicated by new numerals 91 and 92.

Specifically, in the embodiment of Figure 1 A and Figure 4, input sun gear 60A meshes with teeth 91 on pinion 61 A and there a second gearing 92 is mounted separately from 91 and adjacent thereto for engagement with a ring gear 75A for producing the second gear step when braked by brake 76.

Although the gear ratios obtained in the embodiment of Figures 1A and 4 are the same as in the embodiment of Figure 1 and listed in the table above, the embodiment of Figures 1 A and 4 has the advantage that the separate gearings 91 and 92 allow greater freedom in varying the level of the gear ratio of the second gear.

Figure 2 illustrates diagrammatically the arrangement as shown in British Patent No. 1,559,491 of which the present invention is an improvement. In the arrangement shown therein, input sun gear 60B meshes with pinions 61 B and a direct drive clutch 66B and a carrier 62B are also included.

However, in this arrangement both gearings 95 and 96 are carried directly on the pinions 61 B; and in this construction, there are definite physical limitations on the magnitude of the highest gear ratio, i.e.

"first" gear. Since the ratio of each gear step in the "range" gear (in order to be a true range gear) must be greater than that of the highest reduction ratio (lowest gear) in the first planetary gear set P 1 then, if the steps in P2 cannot be made very large, it follows that the total range of gear ratios in P 1 is limited to smaller levels in the previous arrangement as shown in Figure 2, i.e. British Patent No. 1,559,491, than is possible with the present invention. For example, as described in British Patent No. 1,559,491, whe greatest gear ratio is 5.73:1. In contrast and as apparent from the above, the present invention renders possible the achievement of a higher gear reduction of 11.09:1.Indeed, to achieve the same high reduction ratio with the embodiment as shown in said British Patent, the diameter of gearing 96 for the lowest gear would have to be so large that it would not be feasible to mount the same within the diameter of the gear box within a practical installation of the overall transmission. Further, there would be certain definite gear ratio limitations which will not permit proper coverage of the overall field within which it is desired to operate.

A comparison of the relatively narrow field of operation of the transmission shown in British Patent No. 1,559,491, s shown in the graph of Figure 7 which is to be compared with the graph of Figure 8 which illustrates the field for the present invention. It is apparent from Figure 7 that it is not possible to spread the gear ratios sufficiently to obtain twelve different gear ratios since the ratios of gears 95 and 96 overlap with the ratios of the firt planetary gear P 1. Moreover, due to this overlap, it was not possible to obtain complete multiplication of the gear ranges of the first planetary gear set P1 (as was discussed above) and hence smaller gear steps were obtained at low speeds.

These limitations are overcome by the present invention and Figure 8 shows the gear ratios and the tractive effort for a 12-speed gear. Above the speed range fields are shown the four gear steps, the first section P 1 repeated three times, one for each step of the range gear P2. The figure designates which gear ratios should be connected in the second planetary gear set P2 to obtain these fields. In other words, a 4-speed gear set P 1 with a range gear set P2 changes the fields of the first gear set P 1 in relation to each other to obtain, in principle, three fields with four gear steps each which do not overlap.

Figure 5 illustrates diagrammatically a modification of the present invention and for simplicity many elements identical to those in previous figures are not designated by numerals whereas other identical elements are represented by identical numerals. Certain elements which are similar to those in previous figures are followed by the subscript "C" while new elements are designated by numerals 104106.

Instead of the single gear 81 engaging with both the input sun gear 79 and the annular gear 82 of Figures 1 and 2, in the case of Figure 5 the input sun gear 79C engages a gearing 81 C mounted on hub 85 via bearings 80C. A separate gearing 104 is also provided adjacent the bearings 80C and this gearing 104 is then engaged with a ring gear 105 which is operated by brake 106. This construction has the advantage of greater design flexibility to vary the magnitude of the reduction ratio through this first gear step of P2 without changing the planetary gear carrier. Moreover, it is only necessary to change the design of gearings 79C, 81 C, 104 and 105.

Figure 6 illustrates diagrammatically still another embodiment of the present invention. For simplicity most numerals are omitted for elements identical to previous figures but certain elements which are similar but slightly different from corresponding elements in earlier Figures are followed by the subscript D. Additional numerals 110 and 111 are used in Figure 6 to illustrate elements which are new in that figure.

Figure 6 differs from Figure 1 by showing a modified journalling arrangement for the second planetary gear set P2 and this modification can also be employed in the previously described embodiments. specifically, in Figure 6 each of the separate gearings 74D and 110, being separately journalled from each other, need not be coaxial, i.e. the carrier structure can be more complex so that the respective gearings are located at different positions around the axis of the planetary gear set P2.

As illustrated in Figure 6, the first gear (gear having greatest gear reduction ratio) 110 is journalled in a carrier portion 112, journalled thereon at 111, whereas a separate pinion 74D engaged with input sun gear 60D isjournalled in bearings 63D and 64D.

Hence, with the present invention, as shown for example in the four illustrated embodiments, the disadvantages of the prior arrangement of Figure 2 are overcome by having planetary pinions which are torsionally disconnected and independently journalled in the same planetary pinion carrier and each is driven by its own sun gear. Further, each planetary pinion gearing has its own ring gear on the outer side thereof which is braked to cause operation of that planetary pinion gearing. As noted above, Figure 6 differs from Figure 3 in that it not only provides separate journalling of the two planetary pinion gearings of the second planetary gear set, but it also permits the different gearings to be located at different points around the axis of P2.

Also with the features of the present invention, one can more freely select the different gear ratios in the two gear trains associated with the two different diameter gearings of P2 by changing each gear train independently of the other. One can therefore determine both the sequence of operation as well as the magnitude of the gear ratio of these two gear trains of P2 to obtain the correct distribution of gear steps in association with P 1, as desired for a specific operation.

The embodiments of Figures 4 and 5 illustrate how in either of the two gear trains of P2 one can separate the sun engaging and ring engaging portions and thereby provide a considerably greater design latitude to vary the reduction ratio of that gear step.

Table Gear Ratios in P 1 Gear Ratio First gear 21-Sun gear 43 braked by 53 1.96:1 Second gear 22-Sun gear 42 braked by 52 1.53:1 Third gear 23-Sun gear 41 braked by 51 1.25:1 Direct Drive--clutch 30 engaged 1:1 Reverse gearing gear 24 braked by 54 1.38:1 Gear ratios in P2 First gear 81-Ring gear 82 braked by 83 5.60:1 Second gear 74-Ring gear 75 braked by 76 2.44:1 Direct Drive-Clutch 66 engaged 1:1 Combined Gear Ratios P 1, P2 Gear Brakes Braked Clutch Combined Gear Step P1 P2 P1 P2 Gear Ratio 1 43 82 53 83 11.09:1 2 42 82 52 83 8.64:1 3 41 82 51 83 7.07:1 4 - 82 30 83 6.66:1 5 43 75 53 76 4.74:1 6 42 75 52 76 3.69:1 7 41 75 51 76 3.02: :1 8 - 75 30 76 2.42:1 9 43 - 53 66 1.96:1 10 42 - 52 66 1.53:1 11 41 - 51 66 1.25:1 12 - - 30 66 1.00:1 Reverse 1 44 82 54 83 -7.82:1 Reverse 2 44 75 54 76 -8.34:1 Reverse 3 44 - 54 66 -1.38:1

Claims (34)

Claims

1. A multi-speed transmission comprising first and second serially connected planetary gear sets, the output shaft of the first set operatively connected to the input shaft of the second set; each planetary gear set comprising a planetary pinion carrier which includes the output member of its planetary gear set, a plurality of planetary pinions mounted in the carrier, each pinion having at least two different gearing diameters, an input and centrally disposed gear meshing with one of the gearing diameters and at least two other centrally disposed gears meshing one with each of the gearing diameters, a brake means for braking each of the other centrally disposed gears relative to the casing; a separate input centrally disposed gear for each of the gearing diameters of the second planetary gear set with the input shaft of the second planetary gear set connected to each of said input centrally disposed gear, and with the two gearing diameters of the second planetary gear set journalled on the carrier independently of each other.

2. A multi-speed transmission according to Claim 1, wherein the first planetary gear set has at least three different gearing diameters, the input centrally disposed gear constituting a ring gear meshing with the largest gearing diameter, and each other centrally disposed gear constituting a sub gear in mesh one with each of the three gearing diameters, and friction brake for each of the sun gears.

3. A multi-speed transmission according to Claim 2, wherein the other centrally disposed gears include a further ring gear in mesh with one of the gearing diameters other than the largest gearing diameter to provide a reverse drive, and a friction brake for the further ring gear.

4. A multi-speed transmission according to claim 2 or claim 3 wherein the first planetary gear set includes a direct drive clutch for connecting the input shaft of the first planetary gear set with the carrier thereof to establish direct drive therethrough.

5. A multi-speed transmission according to any one of claims 1 to 4, including a direct drive clutch means in the second planetary gear set for connecting the input shaft thereof to the carrier thereof for direct drive therethrough.

6. A multi-speed transmission according to any one of claims 1 to 4, wherein the input centrally disposed gears of the second planetary gear set are sun gears and the bther centrally disposed gears of the second planetary gear set are ring gears, and wherein the carrier of the second planetary gear set forms a hub portion coaxial with each planetary pinion and located at a radius from the axis of its planetary pinion greater than the radius to the bearings for the smaller gearing diameter with the journal bearings for the larger gearing diameter mounted on the hub portion.

7. A multi-speed transmission according to claim 6, wherein the smaller gearing diameter of the second planetary gear set has two gear surfaces of different diameters and where the sun input gear of the second planetary gear meshes with the smaller gear surface, and a ring gear, which is one of said other centrally disposed gears, meshes with the other gear surface.

8. A multi-speed transmission according to claim 6, wherein the said larger gearing diameter of the second planetary gear set has two gear surfaces of different diameters, and the said sun input gear thereof meshes with the smaller gear surface thereof, and wherein a ring gear, which is one of said other centrally disposed gears, meshes with the other gear surface.

9. A multi-speed transmission according to claim 6, wherein each of the smaller and larger gearing diameters have two gear surfaces of different diameters, the sun input gear for each of said gearing diameters meshing with the smaller gear surface and a ring gear, which is one of said other centrally disposed gears, meshing with the other gear surface.

10. A multi-speed transmission according to claim 6, wherein the said hub portion includes a central axial opening, at least a portion of the journal bearings for the smaller gearing diameter located in said opening, and the journal bearing for the large gearing diameter mounted on the outer side of the hub generally in the same radial plane with the said portion of the joumal bearing for the smaller gearing diameter.

11. A multi-speed transmission according to claim 6, wherein the large and small gearing diameters of the second planetary gear set are coaxial.

12. A multi-speed transmission according to claim 6, including a direct drive clutch means in said second planetary gear set for connecting the input shaft thereof to the carrier thereof for direct drive therethrough.

13. A multi-speed transmission according to any one of claims 1 to 4, wherein the input centrally disposed gears of the second planetary gear set are sun gears and the other centrally disposed gears thereof are ring gears, and wherein the carrier of the second planetary gear set includes a first portion for mounting the smaller gearing diameter and a second portion for mounting the larger gearing diameter.

14. A multi-speed transmission according to claim 13, wherein the axes of the large gearing diameters are spaced circumferentially about the axis of the second planetary gear set from the axes of the smaller gearing diameters.

1 5. A multi-speed transmission according to any one of claims 1 to 4, wherein the input centrally disposed gears of the second planetary gear set are sun gears and the other centrally disposed gears thereof are ring gears, and wherein the smaller gearing diameter of the second planetary gear set has two gear surfaces of different diameters, and with the sun input gear thereof in mesh with the smaller gear surface, and wherein a ring gear, which is one of said other centrally disposed gears, in mesh with the other gear surface.

1 6. A multi-speed transmission according to any one of claims 1 to 4, wherein the input centrally disposed gears of the second planetary gear set are sun gears and the other centrally disposed gears thereof are ring gears, and wherein the said larger gearing diameter of the second planetary gear set has two gear surfaces of different diameters and with the sun input gear thereof in mesh with the smaller gear surface thereof, and wherein a ring gear, which is one of said other centrally disposed gears, in mesh with the other gear surface.

1 7. A multi-speed transmission according to any one of claims 1 to 4, wherein the input centrally disposed gears of the second planetary gear set are sun gears and the other centrally disposed gears thereof are ring gears, and wherein each of the smaller and larger gearing diameters have two gear surfaces of different diameters, the sun input gear for each of said gearing diameters meshing with the smaller gear surface and a ring gear, which is one of said other centrally disposed gears, meashing with the other gear surface.

1 8. A planetary gear comprising a casing; an input shaft rotatably mounted in the casing; a carrier rotatably mounted in the casing and comprising the output member of the planetary gear; a plurality of planetary pinions mounted in the'carrier and spaced about the axis of the planetary gear, each planetary pinion having at least two different gearing diameters; a first sun gear connected to the input shaft and meshing with the smaller gearing diameter, a second sun gear connected to the input shaft and meshing with the larger gearing diameter, and each of the said two gearing diameters being journalled on the carrier independently of each other.

1 9. A planetary gear according to claim 18, including a direct drive clutch means for connecting the input shaft and the carrier for direct drive.

20. A planetary gear according to claim 19, wherein the direct drive includes an element directly connecting the input shaft to the direct drive clutch.

21. A planetary gear according to claim 1 8 or claim 1 9, wherein the carrier forms a hub portion coaxial with each planetary pinion and located at a radius from the axis of its planetary pinion greater than the radius to the bearing for the smaller gearing diameter, and wherein the journal bearings for the larger gearing diameter is mounted on the hub portion.

22. A planetary gear according to claim 21 wherein the smaller gearing diameter has two gear surfaces of different diameters, and its said sun input gear meshes with the gear surface of the smaller diameter, and wherein a ring gear, which is one of the other centrally disposed gears, meshes with the other gear surface.

23. A planetary gear according to claim 21, wherein the said larger gearing diameter has two gear surfaces of different diameters, and its sun input gear meshes with the gear surface of smallest diameter, and wherein a ring gear, which is one of said other centrally disposed gears, meshes with the other gear surface.

24. A planetary gear according ta claim 21, wherein each of said larger and smaller gearing diameters have two gear surfaces of different diameters, the sun input gear for each of said gearing diameters meshing with the smaller gear surface and a ring, gear, which is one of said other centrally disposed gears, meshing with the other gear surface.

25. A planetary gear according to claim 21, wherein the said hub portion includes a central axial opening with at least a portion of the journal bearings for the smaller gearing diameter located in the opening, and wherein the journal bearing for the large gearing diameter is mounted on the outer side of the hub portion generally in the same radial plane with the said portion of the journal bearing for the smaller gearing diameter.

26. A planetary gear according to claim 21, wherein the different gearing diameters are coaxial.

27. A planetary gear according to either of claims 1 8 or 19, wherein the carrier comprises a first portion for mounting the small gearing diameter and a second portion for mounting the large gearing diameter.

28. A planetary gear according to claim 27, wherein the axes of the large gearing diameter and the small gearing diameter are spaced apart about the axis of the planetary gear.

29. A planetary gear acccording to any one of claims 1 8 or 1 9, wherein the smaller gearing diameter has two gear surfaces of different diameters, and with its sun input gear in mesh with the smaller gearing diameter, and wherein a ring gear, which is one of the other centrally disposed gears, meshes with the other gear surface thereof.

30. A planetary gear according to either one of claims 18 or 19, wherein the said larger gearing diameter has two gear surfaces of different diameters, and with its sun input gear in mesh with the smaller gear surface thereof, and wherein a ring gear, which is one of said other centrally disposed gears, meshes with the other gear surface.

31. A planetary gear according to any one of claims 18 or 19, wherein each of said larger and smaller gearing diameters have two gear surfaces of different diameters with the sun input gear for each of the said gearing diameters in mesh with the smaller gear surface and wherein a ring gear, which is one of said other centrally disposed gears, is in mesh with the other gear surface.

32. A multi-speed transmission comprising first and second serially connected multiple speed planetary gears, each planetary gear comprising a planet carrier having associated planet gear wheels at least two of which planet gear wheels are of different diameters and which, in each planetary gear, mesh with at least three internally and/or externally toothed centrally diposed gear wheels, at least one of the centrally disposed wheels in each planetary gear constituting an input member with the planet carriers constituting an output member, each remaining centrally disposed gear wheel having an associated friction brake controlled by a servo motor having a non-rotatable housing characterised in that each of the two gear wheels of different diameters of the said second gear are driven from the secondary side of the said first gear and in that each of the said two planetary gear wheels are individually journalled in a planet gear holder which constitutes the output shaft.

33. A multi-speed transmission constructed and arranged substantially as hereinbefore described with reference to and as shown in Figures 1, 1 A and 3 to 6.

34. A planetary gear according to claim 1 8 and constructed and arranged substantially as hereinbefore described with reference to and as shown in any one of Figures 1, 1 A and 3 to 6.