GB1601793A

GB1601793A - Transmission

Info

Publication number: GB1601793A
Application number: GB983178A
Authority: GB
Original assignee: Rolls Royce Motors Ltd
Current assignee: Bentley Motors Ltd
Priority date: 1978-03-08
Filing date: 1978-03-08
Publication date: 1981-11-04

Description

(54) A TRANSMISSION (71) We, ROLLS-ROYCE MOTORS LIMITED, a British Company of Pym's Lane, Crewe, CWi 3PL, Cheshire, 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 present invention relates to a transmission. It is particularly, but not exclusively, concerned with automatic transmissions for vehicles.

Known transmissions of this type comprises a plurality of clutches and brakes which, when suitably operated enable a chosen one of a plurality of transmission ratios to be selected. The application of clutches and brakes leads to wear which in turn leads to unreliability. Furthermore, the repetitive application of such clutches and brakes calls for complex control means which is expensive and is in itself undesirable. Some known transmissions require more than one clutch or brake to be released and/or more than one clutch or brake to be applied in order to change gear and this results in three or four operations which produces a jerky "double gear-change" effect. Such a gearchange is difficult to control smoothly and quickly and tends to produce not only jerky gearchanges but also excessive clutch and/or brake wear mentioned previously. Some other known transmissions overcome the problem of smooth gearchanges by complex and bulky solutions. An object of the present invention is to simplify presently known transmissions and to reduce the number of clutch and brake applications required for given changes in transmission ratios.

According to one aspect of the present invention, there is provided a transmission comprising an input. an output, planetary gearing disposed between the input and the output providing two reverse and four forward transmission ratios, first, second and third reaction brakes and first and second clutches the planetary gearing comprising first, second and third eipicyclic gear trains each comprising a sun wheel, planet pinion, planet pinion carrier and internally toothed annulus and providing first, second, third and fourth intermediate transmission members, the first intermediate member consisting of the sun wheels of the first and second epicyclic gear trains arranged for connection to the input by means of the first friction clutch. the second intermediate member consisting of the planet pinion carrier of the second epicyclic gear train attached to the internally toothed annuli of the first and third epicyclic gear trains the said second intermediate member being arranged in operation to be held stationary by the first reaction brake, the third intermediate member consisting of the planet pinion carrier of the third epicyclic gear train attached to the internally toothed annulus of the second epicyclic gear train which is arranged in operation to be held stationary by the second reaction brake and the fourth intermediate member consisting of the sun wheel of the third epicyclic gear train, which is arranged in operation to be held stationary by the third reaction brake in one of the four forward ratios or alternatively to be connected to the input by the second clutch in another of the four forward ratios. the second intermediate member being arranged to be connected in operation to the input by a third friction clutch to provide an additional speed increasing 'over drive' ratio.

According to another aspect of the present invention there is provided a transmission comprising an input, an output, planetary gearing disposed between the input and the output providing two reverse and four forward transmission ratios, first, second and third reaction brakes and first and second clutches the planetary gearing comprising first, second and third epicyclic gear trains each comprising a sun wheel, planet pinion, planet pinion carrier and internally toothed annulus and providing first, second, third and fourth intermediate transmission members, the first intermediate member consisting of the sun wheels of the first and second epicyclic gear trains arranged for connection to the input by means of the first friction clutch, the second intermediate member consisting of the planet pinion carrier of the second epicyclic gear train attached to the internally toothed annuli of the first and third epicyclic gear trains the said second intermediate member being arranged in operation to be held stationary by the first reaction brake, the third intermediate member consisting of the planet pinion carrier of the third epicyclic gear train attached to the internally toothed annulus of the second epicylic gear train which is arranged in operation to be held stationary by the second reaction brake and the fourth intermediate member consisting of the sun wheel of the third epicyclic gear train, which is arranged in operation to be held stationary by the third reaction brake in one of the four forward ratios or alternatively to be connected to the input by the second clutch in another of the four forward ratios, the third intermediate member being arranged to be connected in operation to the input by a third friction clutch to provide an additional speed increasing 'over drive' ratio.

In order that the invention may be more clearly understood, two embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure I diagrammatically shows a first assembly of epicyclic gear trains and associated friction clutches and reaction brakes comprising three epicyclic gear trains, three friction clutches and three reaction brakes.

Figure 2 diagrammatically illustrates a modification of the embodiment of Figure 1 in which one of the three friction clutches is differently connected, Figure 3 diagrammatically illustrates another modification of the embodiment of Figure 1 showing a different arrangement of the reaction brakes, and Figure 4 shows part of a cross-section of a practical application of the embodiment of Figure 1.

Referring to Figure 1, the assembly comprises three epicyclic gear trains respectively referenced El, E2, and E3, three friction clutches respectively referenced C1, C2 and C3 and three reaction brakes respectively referenced B1, B2 and B3. Each epicyclic gear train comprises a sun wheel, planet pinions, planet pinion carrier and an internally toothed annulus. Each friction clutch and each reaction brake comprises hub inner plates attached to the hub and outer plates attached to an outer drum. The input to the assembly is an input shaft 10 and the output from the assembly is an output shaft 12.

The input shaft 10, which may be the crankshaft of an engine or the output shaft of a hydrokinetic coupling or torque converter, drives a drum 11 which carries the outer plates of each friction clutch C1, C2 and C3. The output shaft 12 is attached to the carrier 13 of the planet pinions 14 of the first epicyclic gear train El. Transmission between input shaft 10 and output shaft 12 may be considered as being achieved via four intermediate transmission members. The first intermediate member consists of a shaft 15 attached to the sun wheel 16 of the first epicyclic gear train El, the sun wheel 17 of the second epicyclic gear train E2 and a hub 18 which carries the inner plates of the first friction clutch C1.

The second intermediate member consists of the carrier 19 of the planet pinions 20 of the second epicyclic train E2, to which are attached the internally toothed annulus 21 of the first epicyclic gear train El and the internally toothed annulus 22 of the third epicyclic gear train E3, and carries the inner plates of the first friction reaction brake B1.

The third intermediate member consists of the carrier 23 of the planet pinions 24 of the third epicylic gear train E3 attached to the internally toothed annulus 25 of the second epicyclic gear train E2 and to the sleeve 26 which surrounds the shaft 15 and is connected to a hub 27 of the inner plates of the second friction clutch C2.

The fourth intermediate member consists of the sleeve 28, which surrounds the sleeve 26, the sun wheel 29 of the third epicyclic gear train E3, the hub 30 which carries the inner plates of the third friction clutch C3 and the hub 31 which carries the inner plates of the third reaction brake B3.

The outer plates of the reaction brakes B1, B2 and B3 are carried in the drum 32 which is attached to or part of the transmission casing.

The assembly provides five forward and two reverse gear ratios by appropriate operation of the friction clutches and reaction brakes as follows.

First gear The clutch C1 is engaged to drive the sun wheel 16 of the first epicyclic gear train El causing the associated planet pinions 14 to roll round the associated annulus 21, which is held stationary by the reaction brake B1 and the planet pinions 14 drive the carrier 13 and the output shaft 12 at reduced speed.

Second gear The clutch C1 is engaged to drive the sun wheel 17 of the second epicyclic gear train E2.

The associated planet pinions 20 roll round the associated annulus 25 which is held stationary by the reaction brake B2 causing the associated carrier 19 and annulus 21 to rotate forwards at reduced speed instead of being held stationary as in first gear. The sun wheel 16 of the first epicyclic gear train is also driven by the clutch C1 and the carrier 13 and the output shaft 12 are therefore driven forward at reduced speed, but at a higher speed than in first gear.

Third gear The clutch C1 is engaged to drive the sun wheel 17 of the second epicyclic gear train causing the associated planet pinions 20 to roll round the associated annulus 25 and drive the associated carrier 19 together with the annuli 21 and 22 of respective gear trains El and E3 forward. The planet pinions 24 of gear train E3 therefore roll round the sun wheel 29 which is held stationary by the reaction brake B3 causing the carrier 23 and the annulus 25 to rotate forwards at reduced speed instead of being stationary as in second gear. The speed of the carrier 19 and the annulus 21 is therefore higher than in second gear and; because the sun wheel 16 is still driven by the clutch C1, the speed of the carrier 13 and the output shaft 12 is further increased, but is still lower than the input shaft speed.

Fourth gear The clutches C1 and C2 are both engaged driving the sun wheels 16 and 17 of respective epicyclic gear trains El and E2 and the planet carrier 23 of gear train E3 and the annulus 25 of gear train E2 at input shaft speed. The carrier 19 of gear train E2 and the annulus 21 of gear train El and therefore the carrier 13 of gear train El and the output shaft 12 are thus constrained to rotate at input shaft speed providing a 1:1 direct drive.

Fifth gear The clutch C2 is engaged to drive the planet carrier 23 of gear train E3 and the annulus 25 of gear train E2. The planet pinions 24 of gear train E3 roll round the sun wheel 29 gear train E3 which is held stationary by the reaction brake B3 causing the annulus 22 of gear train E3, carrier 19 of gear train E2 and the annulus 21 of gear train El to rotate forward at increased speed. The planet pinions 20 of gear train E2 therefore roll around the annulus 25 of gear train E2 causing the sun wheels 17 and 16 of gear trains E2 and El respectively to be driven at a still higher speed and the planet carrier 13 of gear train El and the output shaft 12 are therefore driven forward at increased speed.

Low reverse The reaction brake Bl, is engaged to hold the annulus 21 of gear train El and the annulus 22 of gear train E3 and the planet pinion carrier 23 of gear train E3 stationary. The friction clutch C3 is engaged to drive the sun wheel 29 of gear train E3 causing the planet carrier 23 of gear train E3 and the annulus 25 of gear train E2 to be driven forward at reduced speed.

The sun wheels 17 and 16 of gear trains E2 and El respectively on the shaft 15 are driven in the reverse direction and the planet carrier 13 of gear train El and the output shaft 12 are therefore driven at reduced speed in the reverse direction.

High reverse The reaction brake B2 is engaged to hold the planet carrier 23 of gear train E3 and the annulus 25 of gear train E2 stationary. The friction clutch C3 is engaged to drive the sun wheel 29 of gear train E3 causing the annulus 22 of gear train E3 and the planet carrier 19 of gear train E2 and the annulus 21 of gear train El to be driven in the reverse direction at reduced speed. The planet pinions 20 roll around the stationary annulus 25 of gear train E2 causing the sun wheel 17 of that gear train together with the shaft 15 and the sun wheel 16 of gear train El to be driven in the reverse direction at a high speed. The planet pinion carrier 13 of gear train El and the output shaft 12 are therefore driven at a speed intermediate between the low reverse speed of the annulus 21 of gear train El and the high reverse speed of the sun wheel 16 of gear train El.

Referring to Figure 2, a slightly different embodiment of the invention to that shown in Figure 1 is illustrated.

In this embodiment, the friction clutch C2 is connected by a sleeve 226 to the planet carrier 219 of the second gear train 2E2 instead of to the planet carrier 23 of the third gear train E3 in Figure 1. The effect of this difference is to alter the fifth (overdrive) forward speed ratio without affecting any of the other forward or reverse speed ratios. For example, if the annuli 21, 22 and 25 (221, 222 and 225 in Figure 2) each have three times as many teeth as their respective sun wheels 16, 29 and 17 (216, 229 and 217 in Figure 2) the ratios obtained would be as follows.

4th 1:1 C1 and C2 engaged 3rd 1.474:1 C1 and B3 engaged 2nd 2.286:1 C1 and B2 engaged 1st 4.000:1 C1 and B1 engaged Low reverse 5.333:1 C3 and B1 engaged High reverse 1.714:1 C3 and B2 engaged The fifth (overdrive) ratio will be .631:1 in the arrangement shown in Figure 1 and .842:1 in the arrangement shown in Figure 2. Clutch C2 and brake B3 are engaged in both cases.

Figure 3 shows a further alternative which may be applied to either of the embodiments shown in Figures 1 and 2. In this arrangement, the diameter of the unit is reduced at the expense of increased length, by arranging the reaction brake 3B1 at the rear of the epicyclic gear assembly and the brakes 3B2 and 3B3 between the clutch assembly and the epicyclic gear assembly instead of around the gear assembly.

Figure 4 shows a partial view of a section taken through the axis of a practical automatic transmission arrangement corresponding to the arrangement shown diagrammatically in Figure 1. As with the other figures corresponding parts carry the same reference prefixed by the numeral 4. Thus, as in Figure 1, there are three friction clutches 4C1, 4C2 and 4C3, three reaction brakes 4B 1, 4B2 and 4B3 and three epicyclic gear trains 4E1, 4E2 and 4E3.

Each friction clutch 4C1, 4C2, 4C3 comprises six outer friction plates respectively referenced OP1, OP2 and OP3 and six inner friction plates IP1, IP2 and IP3. The outer plates are supported in the common drum 411 which in turn is driven by the input shaft 410 through the splined coupling 110 and the end cover 111. The-sets of inner plates are respectively supported on three hubs 418, 427 and 430 which are respectively connected to shafts 415, 426 and 428 by means of respective axial splines 41, 42 and 43. As can be seen the shafts 415, 426 and 428 are coaxially arranged, 415 being solid and shafts 426 and 428 being tubular. The connection of each individual friction plate, inner or outer, to the appropriate outer drum or hub is also a splined connected allowing relative axial movement of the plates. The plates are moved by oil pressure upon corresponding annular pistons to operate the corresponding clutch. Thus clutch 4C1 is operated by annular piston 44 acting on the right-handmost (looking at the drawing of Figure 4) outer plate, clutch 4C2 is operated by annular piston 45 acting on the left-handmost (looking at the drawing) outer plate and clutch 4C3 is operated by annular piston 46. Operation of the pistons pushes the corresponding inner and outer plates into mutual contact under pressure to lock them together. The pistons are sealed to the casing parts in which they are housed by pressure fluid seals. Thus, pistons 44, 45 and 46 are sealed at their outer peripheries by respective seals 47, 48 and 49 and at their inner peripheries by respective seals 50, 51 and 52. The pistons 44 and 45 have a common annular housing 54 which coaxially surrounds the shaft 415 and the piston 46 has an annular housing 54 which coaxially surrounds the shaft 428.

Circumferential bearings for the housing 53 are shown at 55 and 56 and axial thrust bearing at 57 and 58. A circumference bearing for the housing 54 is shown at 59 and an axial bearing at 60. Pressure fluid is supplied to the clutches (behind the pistons) via ducting 61 provided by appropriate drillings (not wholly shown) in the various parts of the transmission. Piston return springs are provided at 62, 63 and 64.

The construction of the reaction brakes 4B1, 4B2 and 4B3 is very similar to that of the clutches. Although the clutches are all of substantially the same size, the torque capacity of the brakes is increased towards the transmission output side by varying the number of plates. Thus brakes 4B1, 4B2 and 4B3 respectively comprises outer friction plates OP4, OP5 and OP6 and inner friction plates IP4, IP5 and IP6. Respective annular pistons 70, 71 and 72 are provided from the brakes 4B1, 4B2 and 4B3. These pistons 70, 71 and 72 are provided with respective inner peripheral seals 74, 75 and 76 and respective outer peripheral seals 77, 78 and 79. Pistons 70 and 71 have a common housing 80 and piston 72 has a housing 81. Operation of these brakes is, as with the clutches, by supply of pressure fluid to the pistons via drillings (not shown) in the transmission parts. The outer brake plates are splined as described above for the clutches into the common drum 432 which is secured to the casing.

The three epicyclic gear trains 4E1, 4E2 and 4E3 each comprises a sun wheel, planet pinion carrier, planet pinions and internally toothed annulus. Thus train 4E1 comprises a sun wheel 416, planet pinion carrier 413, planet pinions 414 and internally toothed annulus 421. Train 4E2 comprises a sun wheel 417, planet pinion carrier 419, planet pinions 420 and internally toothed annulus 425. Train 4E3 comprises a sun wheel 429, planet pinion carrier 423, planet pinion 424 and internally toothed annulus 422. The pinions 414, are mounted on roller bearings 90 in the planet pinion carrier 413, the pinions 420 on roller bearings 91 in the planet pinion carrier 419 and the pinions 424 on roller bearings 92 in the planet pinion carrier 423.

The sun wheels 416 and 417 of the first and second epicyclic gear trains are connected to the output shaft 415 via respective axially extending splines 93 and 94. The sun wheel 429 of the fluid epicylic gear train is integral with intermediate shaft 428. The planet pinion carrier 423 is splined to the intermediate shaft 426 by axially extending splines 96 and this same shaft 426 is splined to the hub of the innner plates of the clutch 4C2 as previously mentioned. The annulus 421 of the first gear train 4E1 forms the hub for the inner plates IP4 of brake 4B 1. The annulus 425 of the second gear train 4E2 forms the hub for the inner plates IP5 of brakes 4B2 and an extension of the annulus 422 of the third gear train 4E3 is connected to the planet pinion carrier 423 of the third train 4E3 by teeth engaging in slots 97 and retained therein by means of a spring ring 98.

Each planet pinion carrier comprises two pieces 100 and 101 connected together by dowels 102 and set screws 103. Each brake is provided with a release spring 104 supported on a guide pin 105 and pushing on ears 106 formed on the end one of the series of outer plates to effect release of the brake. The output shaft 412 is an extension of planet carrier part 101 and is supported in two roller bearings 107 and 108 disposed on opposite sides respectively of a gear wheel 109 through which in this instance the output power is transmitted.

Although the friction reaction brakes are indicated in Figures 1 and 2 in the form of multi-plate clutches, they may alternatively be of the band and drum expanding shoe or axially applied conical brake types.

The above described embodiment provides a simple and compact assembly of epicyclic gear trains and associated friction clutches and reaction brakes which will provide five forward speed ratios and two reversing speed ratios and in which changes of operative ratios are made by releasing only one clutch or reaction brake and engaging only one other clutch or reaction brake.

The principle may be extended to provide additional forward and reverse ratios by adding further epicyclic gear trains and reaction brakes.

WHAT WE CLAIM IS: 1. A transmission comprising an input, an output, planetary gearing disposed between the input and the output providing two reverse and four forward transmission ratios, first, second and third reaction brakes and first and second clutches the planetary gearing comprising first, second and third epicyclic gear trains each comprising a sun wheel, planet pinion, planet pinion carrier and internally toothed annulus and providing first, second, third and fourth intermediate transmission members, the first intermediate member consisting of the sun wheels of the first and second epicyclic gear trains arranged for connection to the input by means of the first friction clutch, the second intermediate member consisting of the planet pinion carrier of the second epicyclic gear train attached to the internally toothed annuli of the first and third epicyclic gear trains the said second intermediate member being arranged in operation to be held stationary by the first reaction brake, the third intermediate member consisting of the planet pinion carrier of the third epicyclic gear train attached to the internally toothed annulus of the second epicyclic gear train which is arranged in operation to be held stationary by the second reaction brake and the fourth intermediate member consisting of the sun wheel of the third epicyclic gear train, which is arranged in operation to be held stationary by the third reaction brake in one of the four forward ratios or alternatively to be connected to the input by the second clutch in another of the four forward ratios, the second intermediate member being arranged to be connected in operation to the input by a third friction clutch to provide an additional speed increasing 'over drive' ratio.

2. A transmission comprising an input, an output, planetary gearing disposed between the input and the output providing two reverse and four forward transmission ratios, first, second and third reaction brakes and first and second clutches the planetary gearing comprising first, second and third epicyclic gear trains each comprising a sun wheel, planet pinion, planet pinion carrier and internally toothed annulus and providing first, second, third and fourth intermediate transmission members, the first intermediate member consisting of the sun wheels of the first and second epicyclic gear trains arranged for connection to the input by means of the first friction clutch, the second intermediate member consisting of the planet pinion carrier of the second epicyclic gear train attached to the internally toothed annuli of the first and third epicyclic gear trains the said second intermediate member being arranged in operation to be held stationary by the first reaction brake, the third intermediate member consisting of the planet pinion carrier of the third epicyclic gear train attached to the internally toothed annulus of the second epicyclic gear

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. 423, planet pinion 424 and internally toothed annulus 422. The pinions 414, are mounted on roller bearings 90 in the planet pinion carrier 413, the pinions 420 on roller bearings 91 in the planet pinion carrier 419 and the pinions 424 on roller bearings 92 in the planet pinion carrier 423. The sun wheels 416 and 417 of the first and second epicyclic gear trains are connected to the output shaft 415 via respective axially extending splines 93 and 94. The sun wheel 429 of the fluid epicylic gear train is integral with intermediate shaft 428. The planet pinion carrier 423 is splined to the intermediate shaft 426 by axially extending splines 96 and this same shaft 426 is splined to the hub of the innner plates of the clutch 4C2 as previously mentioned. The annulus 421 of the first gear train 4E1 forms the hub for the inner plates IP4 of brake 4B 1. The annulus 425 of the second gear train 4E2 forms the hub for the inner plates IP5 of brakes 4B2 and an extension of the annulus 422 of the third gear train 4E3 is connected to the planet pinion carrier 423 of the third train 4E3 by teeth engaging in slots 97 and retained therein by means of a spring ring 98. Each planet pinion carrier comprises two pieces 100 and 101 connected together by dowels 102 and set screws 103. Each brake is provided with a release spring 104 supported on a guide pin 105 and pushing on ears 106 formed on the end one of the series of outer plates to effect release of the brake. The output shaft 412 is an extension of planet carrier part 101 and is supported in two roller bearings 107 and 108 disposed on opposite sides respectively of a gear wheel 109 through which in this instance the output power is transmitted. Although the friction reaction brakes are indicated in Figures 1 and 2 in the form of multi-plate clutches, they may alternatively be of the band and drum expanding shoe or axially applied conical brake types. The above described embodiment provides a simple and compact assembly of epicyclic gear trains and associated friction clutches and reaction brakes which will provide five forward speed ratios and two reversing speed ratios and in which changes of operative ratios are made by releasing only one clutch or reaction brake and engaging only one other clutch or reaction brake. The principle may be extended to provide additional forward and reverse ratios by adding further epicyclic gear trains and reaction brakes. WHAT WE CLAIM IS:

1. A transmission comprising an input, an output, planetary gearing disposed between the input and the output providing two reverse and four forward transmission ratios, first, second and third reaction brakes and first and second clutches the planetary gearing comprising first, second and third epicyclic gear trains each comprising a sun wheel, planet pinion, planet pinion carrier and internally toothed annulus and providing first, second, third and fourth intermediate transmission members, the first intermediate member consisting of the sun wheels of the first and second epicyclic gear trains arranged for connection to the input by means of the first friction clutch, the second intermediate member consisting of the planet pinion carrier of the second epicyclic gear train attached to the internally toothed annuli of the first and third epicyclic gear trains the said second intermediate member being arranged in operation to be held stationary by the first reaction brake, the third intermediate member consisting of the planet pinion carrier of the third epicyclic gear train attached to the internally toothed annulus of the second epicyclic gear train which is arranged in operation to be held stationary by the second reaction brake and the fourth intermediate member consisting of the sun wheel of the third epicyclic gear train, which is arranged in operation to be held stationary by the third reaction brake in one of the four forward ratios or alternatively to be connected to the input by the second clutch in another of the four forward ratios, the second intermediate member being arranged to be connected in operation to the input by a third friction clutch to provide an additional speed increasing 'over drive' ratio.

train which is arranged in operation to be held stationary by the second reaction brake and the fourth intermediate member consisting of the sun wheel of the third epicyclic gear train, which is arranged in operation to be held stationary by the third reaction brake in one of the four forward ratios or alternatively to be connected to the input by the second clutch in another of the four forward ratios, the third intermediate member being arranged to be connected in operation to the input by a third friction clutch to provide an additional speed increasing 'over drive' ratio.

3. A transmission as claimed in any preceding claim, in which additional ratios are obtained by additional epicyclic trains and associated reaction brakes.

4. A transmission as claimed in any preceding claim in which the input is connected to a coupling.

5. A transmission as claimed in Claim 4, in which the coupling is a hydrodynamic torque converter.

6. A transmission as claimed in any preceding claim, in which each clutch comprises an inner hub and clutch plates and an outer drum and clutch plates.

7. A transmission as claimed in any preceeding claim, in which the three reaction brakes are of the multi-plate type brake.

8. A transmission as claimed in Claim 7, in which the three reaction brakes having a common drum which is attached to or forms part of the transmission casing.

9. A transmission as claimed in any of Claims 1 to 6, in which each reaction brake comprises a drum and a brake secured to the transmission casing.

10. A transmission as claimed in Claim 9, in which the brake comprises an external contracting band.

11. A transmission as claimed in Claim 9, in which the brake comprises an internal expanding shoe.

12. A transmission as claimed in Claim 9, in which the brake comprises a conical brake applied axially.

13. A transmission as claimed in any preceding claim, in which the three clutches and three epicyclic gear trains are coaxially arranged in line and the brakes coaxially surround the gear trains.

14. A transmission as claimed in any of Claims 1 to 12, in which the three clutches, brakes and three epicyclic gear trains are coaxially arranged in line, one brake being disposed axially between the clutches and gear trains and another brake being disposed axially on that side of the gear train remote from the clutches.

15. A transmission substantially as hereinbefore described with reference to Figures 1, 2, 3 or 4 of the accompanying drawings.

16. A vehicle comprising a transmission as claimed in any preceding claim.