CA1053931A - Variable speed planetary transmission - Google Patents

Abstract

Abstract of the Disclosure A transmission comprises an input member; a driven member; a torque converter driven by the input member; a first planetary gear assembly includ-ing a first sun gear, a plurality of first planet gears, and a first ring gear which is connected to the torque converter to be driven thereby; a clutch selectively engageable for transmitting torque applied to the input member directly to the first planetary ring gear; a second planetary gear assembly including a second sun gear which is constrained to rotate with the first sun gear of the first planetary gear assembly, a second planet gear arrangement, and a second ring gear; a common planet carrier having rotatingly mounted thereupon the first planet gears and the second planet gear arrangement, the common planet carrier driving the driven member; first brake means selectively actuable for stopping rotation of the second ring gear so that the first planetary gear assembly and the second planetary gear arrangement operate in a split-torque relationship transmitting torque applied to the first ring gear from the input member to the driven member through the common planet carrier;
second brake means selectively actuable for stopping rotation of the first and second sun gears so that torque applied to the first gear ring is transmitted to the driven member through the common planet carrier; and a second clutch selectively engageable for drivingly connecting the input member directly with the common planet carrier and driven member so that the driven member is driven at a speed of rotation equal to the speed of rotation of the input member.
This provides the basic component for a transmission for a vehicle utilizing four planetary gear sets to provide seven output ratios in the highly efficient mechanical range with almost identical step ratios throughout a broad range of output speeds. The torque converter is provided for operation primarily in the first range but also available in any one of the speed ratios, while a fifth planetary arrangement provides a reverse drive.

Description

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This invention relates to a transmission to couple a vehlcle engine with the vehicle drive wheels, in particular the transmission disclosed herein combi.nes a torque converter with a plurality o~ planetary gear arrangements to provlde a large number o~ gear ratios.
Transmission o~ power ~rom a vehicle engine ~o the vehicle wheels ldeallg will allow the vehlcle engine to operate at or near a most e~icient constan~ speed throughou~ the complete range o~ vehicle speedsO From a practical standpoint this goal is una~tainable in vlew o~ the ~act that the vehicle must be started ~rom a standing positlon. ~urthermoxe, while using a geared transmission, engine speed must vary throughout the range o~ the particular gear set engaged~ The u~ zation ~ a torque converter helps to overcome problems o~ ~nitial start-up and ~urther provldes a br~ader torque transmiss~Dn range;
however~ .~luid drive ~ relatively less e~iclent than a mechanlcal dr-lve. A mechanlcal drive~ although more e~icient than a ~luld drlve~ requires a relatively high number o~ gear ratios in order to allow the engine to operate in its most e~flcient speed range~ ~lowever~ in adding more gear ratlos, ef~iciency is sacri~iced through ~riction losses and the like i~ lnactive gear ratios. ~ccordin~ly~ compromise transmissions incorporatlng ~eatures of a ~luid drlve or torque converter and .
a mechanical transmlssion have been designed to take advantage o.~ the beet characteristics o~ ho~h tran5missionsO
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A problem encountered ;n the design and construc~ion of xuch combi-nation transmissions is the attainment of uni~orm step ratios betwcen thc mechanical shifts. Uniform step ratios are ideally most efficient in such transmissions, as such uniform step ratios eliminate less efficient matches between engine speeds and desired vehicle speed inherent in a transmission which couples lar~e step ratios with smaller step ratios.
An example of a combination torque converter and planetary gear arrangement is found in lJnited States Patent 3,347,113 issued to Ramsel on October 17, 1967. Ramsel~s patent, which was designed for use in scrapers of the kind used in earth-moving operations, provides six forward speed ratios of mechanical drive at high ground speeds while allowing for a fluid drive at lower ground speeds. Such fluid drive in lower speeds has been found acceptable in scraper operations. Although Ramsel's patent approaches a uniform step ratio, there still remain certain uneven steps. In order to provide more efficient operation at lower speeds required for other types of vehicles, either additional mechanical gear sets mus~ be provided or the arrangement of ~he various planetary units and the sizing of the planetary elements must be modified to provide cons~ant step ratios throughout a broad range of output speeds.
Summary of the Invention In accordance with the invention, there is provided a transmission comprising an input member; a d'r;ven member; a torque converter driven by the input member; a flrst planetary gear assembly including a firs~ sun gear, a ~'~
plurality of first planet gears, and a first ring gear which is conn0cted to :
~ the torque converter to be driven thereby; a clutch selectively engageable ~ .
for transmi~ting ~orque applied to the inpu~ member directly to the first planetary ring gear; a second planetary gear assembly including a second sun ~ -~ gear which is constrained ~o rota~e wi~h the first sun gear of tlle firs~
;~ planetary gear assembly, a second plane~ gear arrangement, and a second ring gear; a common planet carrier having rotatingly mounted thereupon the first planet gears and the second planet gear arrange~ent, the common planet carrier driving the driYen member; first brake means selectively actua'ble for stopping ' .

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rotation of the second ring gear so ~hat the first planetary gear assembly and the second planetary gear arrangement operate in a split-torque r01ation-ship transmitting torque applied to the first ring gear from the input member to the driven member through the common planet carr;er; second hrake means selectively actuable for stopping rotation of the first an<l second sun gears so that torque applied to the first ring gear is transmitted to the driven member through the common planet carrier; and a second clutch selectively engageable for drivingly connecting the input member directly with the common planet carrier and driven member so that the driven member is driven at a speed of rotation equal to the speed of rota~ion of the input memher.
As will be described this provides the basic component for a ~
transmission for a vehicle utilizing four planetary gear sets to provide :
seven output ratios in t~e highly efficient mechanical range ~ h almost identical step ratios throughout a broad range of output speeds. The torque ~ :
converter is provided for operation primarily in the first range but also available in any one of the speed ratios, while a fifth planetary arrange- :~
ment provides a reverse drive.

Brief Descrip~ion of the Drawings :
In the accompanying drawings:
Pigure 1 is a schematic diagram of a transmission embodying the invention;

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Fig. 2 is a chart showing the particular clutches and brakes which are engaged in a particular embodiment of the transmission of Fig. 1 to establish the different drive ra-tios provided therein, and which shows the speed reductions, along with the step ratios associated with the speed reductions.
Fig. 3 is a graphical depiction of transmission input horsepower plotted against transmission output speed, and Fig. 4 depicts a transmission partly sectionalized incorporating the provisions of this invention and showing -the various gearing, clutching and braking elements.
Detailed Description of the Preferred Embodiment Referring to Fig. 1, a transmission 10 is shown schematically. Input to the transmission 10 is provided by shaft 12 driving a speed unit 14 which provides a plurality of reduction ratios and is comprised of a first planetary gear arrangement 16 and a second planetary gear arrangement 18. First planetary gear arrangement 16, driven by input shaft 12, is comprised of a ring gear 16R in intermeshing relationship with a plurality of the first planet gears 16P, which in turn are in intermeshing rela-tionship with a first `sun gear 16S. Ring gear 16R is drivingly connected to input shaft 12. Second planetary gear arrangement 18 is comprised of a ring gear 18R, a plurality of intermediate planet gears 18X, a plurality of second planet gears 18P and a sun gear 18S. Sun gear 18S intermeshes with the plurality of inter-18~
~'mediate planet gears ~ff~ which intermesh with the plurality of planet gears 18P, while planet gears 18P intermesh with ring gear 18R. A common plane-t carrier 20 has mounted thereon the plurality of first planet gears 16P and a~ially separated, but immediately adjacent thereto, in-termediate :
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planet gears 18X along with planet gears l~P. F'irst sun gear 16S and second sun gear 18S are integrally formed on a coaxial shaft 22 mounted about sha~t 12 to enable ~irst sun gear 16S and second sun gear 18S to rotate together as a unit. A clutch means 28 is provided to directly interconnect input shaft 12 with common carrier 20~ common carrier 20 providing input to a range unit 30 by means of a sha~t 32.
Coaxial shaft 22 is also provided with a b:rake means 2~
allowing selective stopping of rotation o~ sun gears 16S and ;i :

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18$ to provic3e a mid-range range output .rom planetar~ gear - arrangement 16 to common carrier 200 Second r~ng gear lgR ls provlded with a brake means 26 aLlowing ~3e~ective stopping o~
rota~:ion o~ ring gear 18R to provlde a low-rangc spl-lt~torque output ~rom planetary gear arrangemen~s 16 an~ 18 to common carrier~ 20.
Range unit 30 provides additional reductivn ratlos and is compr~sed o~ a pair o~ plane~ary gear arrangements 34 and 36. Mid~range planetary gear arrangement 34 has a mld-Yange sun gear 34S drivingly connected to sha~t 32 while low xange planekar~ gear arrangemen~ 36 has a low range sun gear 36S similarly drlvingly connected to sha~t 32, Mid range planetary gear arrangement 34 lncluces a pluralit~ of mid-range planet gears 3L~p in intermeshing relationship with mid-range sun gear 34S~ and a mid-range ring gear 34R in intermeshing relationshlp with the plurallty of mid~-range planet gears 34P0 A bra~e means 38 is provided for selectively stQpping ~rotation o~ mid-range ring gear 3~R~ A clutch means ~0 selectively interconnects sha~t 32 wlth the pluraliky o~ mid-range planet gears 34P through a mld-range planet carrier 420 Mid-range planet carrler ~2 is drivingly lnterconnected with low range ring gear 36R o~
lo~ range planetar~ gear arrangement 36~ Low range ring gear 36R is provided with a brake means 4~ to allow selective stoppîng o~ rotation o~ low range ring gear 36R. A plurality o~ low range planet gears 36P completes low range planetary gear arrangement 36~ the plurality o~ low range planet gears 36P lntermeshing with low range sun gear 36S and also intermeshing wi'h low range ring gear 3~R. The pluralit~ o~ low range planet gears 36P ar~
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rotatingl~ mounted on a low range planet carrier 46 which is drivingly connected to an output sha~t 48.
Range unit 30 is sized so thak actuation oL` brake means 1~4 to stop rotation of ring gear 36R provides a low range reducti.on in range unlt 30 with output torque delivered ~rom plane~ carrier 46 to output sha~t 48. Actuaklon o~ brake means 38 to stop rotation o~ ring gear 34R provides a mid~range reduction ln range unit 30 w~th output torque delivered through planet carrier 42 ~o ring gear 36R thence planet gears 36P to planet carrier 46 and output sha~t 48O Engagement of clutch means 40 without actuation of either brake means 24 or 26 or clutch means 2~ ~ .
o~ speed unit 1~ provides a neutral range with no transmisslon o~ torque, such torque transmitted to ring gear 16 b~ lnput sha~t 12 being dissipated in speed unit 11~ However, e~gagement o~ clutch means ~0 with an actuated drive engaging device in speed unit 14 results in ca~rrier 42 rotatirlg xing gear 36R
at the same speed and in the same d~rectlon as sun gear 36S
thus rotatlng planet carrier 46 to transmit tcrque to output sha~ 489 A reverse drive planetary unit 50~ to provide selective reverse rotatlon of output sha~t ~8, is coaxially mounted about output sha~t 48 and is drivingly connected ~o low range ring gear 36R by means o~ a coaxial shaft 52. Reverse planetar~ unit 50 is comprised o~ a sun gear 50S drivingly mounte~ on coaxial sha~t 52 and in inter~eshing relationship with a plurality o~
reverse planet gears 50P rotatingly mounted on a reverse planet carr~er 56. The pluralit~ o~ reverse planet gears 50P
intermesh with a reverse ring gear 50~ o~ reverse planetar~

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uni~ 50. A brake means 54 is provided to selectively s~op rotation of reverse rlng gear 50R and ~hus prov:lcle outpu~ tu sha~t 48 through reverse planet carrler 56 which ls ~riv:lngly connected to output sha~t 1~83 such ou~put ~,eing available onl~ while clutch means 2S is engaged or al,ternatively while e:Lther brake means 21~ or 26 is actuated.
Input sha~t 12 has mounted ~hereon a drive gea.r 58 whlch may be driven alternatlvely by the output o~ a conven~ional torque converter 60 to pxovide a fluid drive or directly by a prlme mover~ Tor~ue converter 60 has a pump element 62 inter- -connected with an output sha~t 64 o~ an engine (not shown). The turbine element 66 o~ tor~ue converter 60 is drivingly connected 'GO a turbine sha~t 68 which is prov:ided wi~h a un-lversal ~oint 69 and has mounted thereon a drive gear 70 intermeshing wlth drive gear 58. Reaction element 72 is provide~ with a conventional overrunning clutch 74 associated with a stationary structure 76 such as the transmission housing assembly. ~ drive engaæement means 65 is included~ interconnecting engine output shaf~ 64 directly to turbine sha~t 68~ thereb~ providlng a direct drive ~rom the engine (not shown) to drive gear 700 ~Iaving generall~ descr.ibed the schematlc arrangement o~ the transmlssion3 reference is made to Figure 2 ~or discussion o~ the varlous speed reduction and range reduction ratios with appropriate clu~ches and brakes engagedO The transm~ssion as ,.,'.
:25 described above provides ~or a possible nine forward speeds '~ :
by selection o~ a brake or clutch unit in range unit 30 and :~
selection of a b.rake or clutch in speed unit 140 In practice~ ~
however~ it has been determined that seven reduction ra~ios are , . .

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; su~ficient to serve the needs o~ most transmisslons, In khe embodiment discussed herein khe primary obJective is to provlde a kransmission which has a uni~orm step ratio over the seven speeds. A second objective o~ khis kransmission is to provide a minimum Or clutch changes between the various output ra~es.
These two objeckives are attained in this transmlssion in the three lowest ranges by actuating bral~e 44 of range unit 30 coupled with actuation of brake 26 ~or a ~irst rangeJ brake 24 ~or a seconcl range and clutch 28 ~or a third range.
The unlque arrangement o~ speed unit 14 is such that ln the ~irst range forward when brake 26 is energlzed, khe two planetary gear arrangements 16 and 18 provide a spli~-t~rque ' oukput. Split torque ls available to CQmmon carrier 20 ~rom j ~irst planet gear 16P in planetary gear arrangemant 16 and planet gears 18P and l~X ln planetary gear arrangement 18.
Particular selection of appropriate gearing in the planetar~
gear arrangements ma~ provlde a reduction ratio of 1.84 in the speed unit as shown in Fig. 20 AS noted above~ input ko speed unik 14 is at rlng gear 16Ro The planetary gear arrangements o~ range unit 30 may be proportioned so thak actuation o~' brake 26 ln speed unit 14 and brake 44 ln range unit 30 in the transmission herein described provides an overall reduc-tion o~ 6.083 t,he range unit reduction ln low range planetary gear arrangement 36 being adapted ~o provide a reduction of 3,31 coupled with the a~oresald ratlo o~ 1~84 in ~he speed UnitD In ~he same application~
actuation o~ brake 24 while maintaining brake 44 in an actuated state may provide a total reduction ratio o~ 4O4 with this con~
~lguration the reduction available ~n the speed unit being 1.35.
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Deactivation of brake 2~ ancl actuation o~ clu~ch 28 prov;~es a st.raight through drlve ln the speed unit with no rcductlon and thereby the total reduction of the ~ransmisslon .ls dependent upon low range planetary gear arrangement 36 or 3~31. It is emphasized that in all three o~ these low :range ratlos, bral~e 41 remains actuated with shl~ts occurring only as a result o~
actuation o~ the brakes or clutch in speed unit 14D
To shi~t to a ~ourth range forward;, brake 44 i.s deactùated and brake 38 is actuated both belng in range unit 30/ along w~th brake 24 in speed unit 14~ the speed unit providing a reduction o~ 1.34 and the range unit providing a reduction of 1.83 for a total reduction o~ 2.4~ Deactuation o~ brake 24 and engagement o~ clutch 28 whlle retaln:lng brake 38 in an actuated state provides a ri~th range ~orward with the ratios as lllustrated in FICT~ 2~ ~ sixth range ~orward is pro~ided by actuation o~ brake 24 and engagement o~ clu~ch 40, ~hile a seventh ;~
range is provided by engagement o~ the two clutches 28 and 40 thereby providing a straight through drive with no reduction.
It is speciflcally pointed out that by proper propor-~ionlng o~ the various planetary gear arrangements to provide the con~iguration shown ln FICTO 2, the step ratlo between the varlous reduction ratios is practically constant at 1035, varying to 1034 only between the third and ~ourth ratios~ whlch is one o~ the prime object-ives o~ the transmission~ ~n additlonal ~ a~ure o~ this transmission is, as no~ed above, that during the ~;
~irst three shi~ts only one drive engagement means is involved, brake 44 remaining actuated throughout these three shi~ts, and ~or the entlre seven ranges a total o~ ten changes in drive engagement means occursO

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Although three reverse ranges are theoreticall~
possible by combining brake 24 or b.rake 2S or clutch 28 with brake 54, it has been determined that proper ratloint~ o~
reverse planetar~ gear unit 50 provld~s an adecluate reverse range unit reduction, thus the speed unit reduction capabillty ls not utilized in the reverse mode ot operation~
Re~erring to FIGo 3~ the specific advantages o~
the constant or nearl~ constant step ratios between shi~ts become apparent when compared with earlier transmissions o~
multiple drive ratlos. FIG 3 shows graphically the input horsepower plotted against output speed both in percent of maximumO It is evident that once a 10% maximum output speed is achieved, the step ra~ios o~ the various mechanical drives are then evelg spaced providing a utilizat~on approaching 100%
o~ input horsepower at the peak o~ each drive ratio and ensuring the most ef~icient part o~ each drive ratio~ ~hat is~ the upper portion o~ the curves~ is ~ully utilizedO Comparlson wi~h earlier transmisslons show uneven peaks and valle~s as compared ~o ~he :~
present inventionO
~eferring to FIGo 4J mechanical constructlon o~ a pre~erred embodiment is 111ustrated partly in cross section.
The torque converter 60, illustrated in FIG~ 1 schema~ically, has not been included in FIGo 4 as such torque converters are ~ell kno~n in the art0 In the ernbodiment envlsioned in FIG~ 4 a torque converter of the type set ~orth in U~S ~atent 3,347,113 issued to Ramsel on October 17, 1967 would be applicable to this inventionO I~ is emphasized~ however~ that the torq~e converter utilized ln U,SO Pa~ent 3g34~,113 is not provided with a drive : ~ . : ~; . . .

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engagement means analogous to drive engagement means 65 shown schematically ln FIG, l and interconnecting output shart 6I~ of the engine (not shown) to turbine sha~t 68~ Re~erring again to FI~. 4, drive gear 58 is shown splLned to sha~t 12, shaft 12 drivlng ring gear 16R ~hrough drive ~lange 90 by means o.~ spline connection 78. Coaxial sha~t 22, which has integrally formed there-with ~irst sun gear 15S and second sun gear 18S3 has mounted thereon the rotating member 25 o~ bra~e means 24~ bra~e means 24 being of a conventional lnterleaved disc type~ by a spllne 80~ Rotating member 25 is provlded wlth a bearing 82 to provide ~ree rotation .
o.~ rotating member 25 ln the transmlssion houslng. Co~mon planet carrler 20, in the ll~ustrated embodiment, substantially encompasses ~irst planetary gear arrangement 16 and is interconnected to : sha~t 32 by a spline connection 840 Clutch means 28~ which selectivelg interconnects shaft 12 with common planet carrier 20, is similarly substantially encompassed by common plane~ carrier 20.
Clutch means 28 is o~ the conventional rotating interleaved disc : -tgpe and is provided with resllient means 86 which mag be a spring o~ the ~elleville-type urging clutch means 28 to the disengaged stateO Common planet carrier 20 is rotatingly mo~mted bg bearing -~
means 88 d~sposed between common planet carrier 20 and drlve ~lange 90 with drlve ~lange 90 driving ~lrst ring gear 16Ro ~6 Second bearing means 92 is provided at the opposite end of~common planet carrier and is disposed between rotatlng member 25 o~ :~
brake means 249 which may also be o~ the interleaved disc tgpe, and common planet carrler 20. A thlrd bearing means 94 is disposed between common planet carrler 20 and portion 96 o~ the transmlssion houslng whlch ~orms a separation between speed UIlit 14 and range . ~ .... . .

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unit 30, Bearing meàns 9~ ~ovIdes ror rota~ion o.f common planet carrier 20 and sha.~'t 32.
Range unit 30~ as noted above in -~,he discussion relatlr~
to ~IG. 1, provides output through plallct carriar 46 to out~ut sha~t 48 which is coax~ally mounted about s~la~t 3~0 ~ bearing means 98 allows free rotatlon of output sha~t 48 about s~la~t 32. Reverse planet carrler 56 is splined to output sha~t 4~ by spline connec~ion 99, and ma~ have integrally ~ormed there~
with an output spline 101. Planetarg units 34 and 36 are mounted about sha~t 32 with sun gears 34S and 36S splined theretoO
Sun gear 34S which is splined to shaft 32 has extending outwardlg thererrom a M ange lQ3 wlth which clutch means 40 is assoclated. Engagement o~ clutch means 40 therefore associates sha~t 32 through sun gear 34S with planet carrier 42 o:~ range unit 30. A bearing means 105 is provlded between planet carrier 42 and porkion 96 o~ the transmisslon housing wh~ch along wi~h a bearing means 107 located on the opposite side o~ sun ~ear 34S allows free rotation o~ planet carrier 42. Brake means 38 and brake means 44 mag be o~ the interleaved disc type and are associated wi~h the transmission housing to stop rotation of rlng gears 34R and 36R respectively~
Operation of the preferred embodiment should be evident from the discussion o~ the structure above; however, certaln points of operation are herein reiterated~ Initiall~ :
it is pointed out that the transmission mag be operated with the torque converter provlding input to drive gear 58 or b~ a direct connection between engine output shaft 64 and drive gear 58, bg engagement o~ clutch 65~ Other than operatlon in ~irst 3~
range forward and seventh range ~orward, the transtnlssio~ til:lzes one or two planetary gear arrangements to accomplish the necessary reductionO In the ~irst range ~orward, a split torque output is provided by engagement of brake means 26 and bra}ce means 44.
Thus ~irst planetary gear arrangement 16 ancl second plane~ary ~ gear arrangement 18 combine to provide output torque to shaft ; 32 which in turn drives low range planetary gear arrangement 36 through sun gear 36S. In the seventh range ~orward, engagement o~ clutch 28 and clutch 40 provicles a direct drive through both ~he speed unit 14 and range unit 30 to output sha~ 48~
While the lnvention has been describec1 with respect to a single embodiment, it wi.ll be apparent ~hat many modi.~ications are posslble and it is not lntended to limit the in~ention except as de~ined in the followlng cla Ds.

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Claims (7)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A transmission comprising an input member; a driven member; a torque converter driven by the input member; a first planetary gear assembly inclu-ding a first sun gear, a plurality of first planet gears, and a first ring gear which is connected to the torque converter to be driven thereby; a clutch selectively engageable for transmitting torque applied to the input member directly to the first planetary ring gear; a second planetary gear assembly including a second sun gear which is constrained to rotate with the first sun gear of the first planetary gear assembly, a second planet gear arrangement, and a second ring gear; a common planet carrier having rotatingly mounted thereupon the first planet gears and the second planet gear arrangement, the common planet carrier driving the driven member; first brake means selectively actuable for stopping rotation of the second ring gear so that the first planetary gear assembly and the second planetary gear arrangement operate in a split-torque relationship transmitting torque applied to the first ring gear from the input member to the driven member through the common planet carrier; second brake means selectively actuable for stopping rotation of the first and second sun gears so that torque applied to the first ring gear is transmitted to the driven member through the common planet carrier; and a second clutch selectively engageable for drivingly connecting the input member directly with the common planet carrier and driven member so that the driven member is driven at a speed of rotation equal to the speed of rotation of the input member.

2. A transmission according to Claim 1, wherein the second planet gear arrangement comprises a plurality of intermediate gears intermeshing with the second sun gear and a plurality of second planet gears intermeshing with the intermediate gears and the second ring gear.

3. A transmission according to Claim 1 or Claim 2, wherein the first planetary gear assembly is sized and adapted so that at a constant speed of rotation of the input member, the speed of rotation of the driven member is relatively slower with the first brake means actuated than with the second brake means actuated, and further with the second brake means actuated speed of rotation of the driven member is slower than the constant speed of rotation of the input member.

4. A transmission according to Claim 1, wherein the driven member com-prises a plurality of planetary gear arrangements; an output shaft; and a plurality of drive engagement means selectively actuable for drivingly asso-ciating the common planet carrier with the output shaft whereby speed of rotation of the output shaft is at most equal to the speed of rotation of the common planet carrier.

5. A transmission according to Claim 4, further comprising a reverse planetary gear arrangement including a sun gear drivingly connected to the plurality of planetary gear arrangements, a plurality of reverse planet gears, a reverse planet carrier having mounted thereon the plurality of reverse pla-net gears, a reverse ring gear, and a reverse brake means actuable for selectively stopping rotation of the reverse ring gear; the plurality of reverse planet gears being in intermeshing relationship with the reverse sun gear and the reverse ring gear, and the reverse planet carrier drivingly con-nected with the output shaft.

6. A transmission according to Claim 5, wherein the plurality of plan-etary gear arrangements comprises a low range planetary gear arrangement and a mid-range planetary gear arrangement, the low range planetary gear arrangement comprising a low range sun gear drivingly connected to the common planet carrier of the speed unit, a low range planet carrier, a plurality of low range planet gears rotatingly mounted on the low range planet carrier, and a low range ring gear; the mid-range planetary gear arrangement comprising a mid-range sun gear drivingly connected with the common planet carrier, a mid-range planet carrier, a plurality of mid-range planet gears rotatingly mounted on the mid-range planet carrier and a mid-range ring gear; the mid-range planet carrier drivingly connected with the low range ring gear, and the low range planet carrier drivingly connected with the output shaft, and the low range ring gear drivingly connected with the reverse sun gear.

7. A transmission according to Claim 6, further comprising range clutch means selectively actuable for drivingly connecting the common planet carrier with the mid-range planet carrier and further wherein the plurality of drive engagement means comprise low range brake means, and mid-range brake means;
the low range brake means being selectively actuable for stopping rotation of the low range ring gear, the mid-range brake means being selectively actuable for stopping rotation of the mid-range ring gear; the low range and mid-range planetary gear arrangements being sized and adapted so that at a constant speed of rotation of the common planet carrier rotation of the output shaft is relatively slower upon actuation of the low range brake means than upon actuation of the mid-range brake means, further with the common planet carrier operating at the same constant speed of rotation, rotation of the output shaft is relatively slower upon actuation of the mid-range brake means than upon actuation of the range clutch means, and further with the common planet carrier operating at the same constant speed of rotation, rotation of the output shaft is equal to the constant speed of rotation of the common planet carrier upon actuation of the range clutch means.