Two-speed gear train assembly

A two-speed gear train (200) including a first gear (118) and a second gear (120) and drive members (11, 114, 106) for driving the second gear faster than the first gear. A double acting clutch (126) splined to a shaft (28A) has a first and second position for clutching either the first gear (118) or second gear (120) to the shaft (28A). The clutch teeth (134, 136, 138, 140) are provided with specially configured ramps (222) on certain edges (208, 210, 212, 214) to improve clutch engagement.

BACKGROUND OF THE INVENTION 
1. Field of The Invention 
The present invention relates to a two-speed gear train assembly, such as a 
splitter type auxiliary section or subsection of a compound multi-speed 
transmission. In particular, the present invention relates to a two-speed 
gear train utilizing non-synchronized, clash type jaw clutches which are 
specifically configured to provide relatively simple and reliable 
clutching structures for smooth and easy shifting without the need for 
complicated control devices or the like. 
2. Brief Description of the Prior Art 
Compound change gear transmissions of the type having one or more auxiliary 
sections connected in series with a main transmission section are well 
known in the prior art. Briefly, by utilizing main and auxiliary 
transmission sections connected in series, assuming proper sizing of the 
ratio steps, the total of available transmission ratios is equal to the 
product of the main and auxiliary section ratios. 
Auxiliary transmission sections are of three general types: range type, 
splitter type or combined range/splitter type. 
In compound transmissions having a range type auxiliary section, the ratio 
step or steps are greater than the total ratio coverage of the main 
transmission section and the main section is shifted progressively through 
its ratios in each range. Examples of compound transmissions having range 
type auxiliary sections may be seen by reference to U.S. Pat. Nos. 
3,105,395; 2,637,222 and 2,637,221, the disclosures of which are hereby 
incorporated by reference. 
In compound transmissions having a splitter type auxiliary section, the 
ratio steps of the splitter auxiliary section are less than the ratio 
steps of the main transmission section and each main section ratio is 
split, or subdivided, by the splitter section. Examples of compound change 
gear transmissions having splitter type auxiliary sections may be seen by 
reference to U.S. Pat. Nos. 4,290,515; 3,799,002; 4,375,172; 4,440,037 and 
4,527,447, the disclosures of which are hereby incorporated by reference. 
In a combined range and splitter type auxiliary section, or sections, both 
range and splitter type ratios are provided allowing the main section to 
be progressively shifted through its ratios in at least two ranges and 
also allowing the main section ratios to be split in at least one range. 
One example of a compound transmission having a single combined 
range/splitter type auxiliary section may be seen by reference to U.S. 
Pat. Nos. 3,283,613; 3,648,546, the disclosures of which are hereby 
incorporated by reference and to publication Small Scale Print No. 016-AD; 
Fuller Transmissions; Models RT-14613, RTO-14613, RTOO-14613, published 
March 1981 by Eaton Corporation, assignee of this invention, the 
disclosure of which is hereby incorporated by reference. Another example 
is the "Ecosplit" model of transmission sold by Zahnradfabrik 
Friedrichshafen Aktiengeseushaft of Friedrichshafen, Federal Republich of 
Germany which utilizes a separate splitter auxiliary section in front of, 
and a separate range auxiliary section behind, the main transmission 
section. 
A preferred example of a compound transmission having a three-layer, 
four-speed combined range/splitter type auxiliary section may be seen by 
reference to U.S. Pat. No. 4,754,665, the disclosure of which is 
incorporated by reference. 
It should be noted that the terms main and auxiliary sections are relative 
and that if the designations of the main and auxiliary sections are 
reversed, the type of auxiliary section (either range or splitter) will 
also be reversed. In other words, given what is conventionally considered 
a four-speed main section with two-speed range type auxiliary section, if 
the normally designated auxiliary is considered the main section, the 
normally designated main section would be considered a four-speed splitter 
type auxiliary section therefor. By generally accepted transmission 
industry convention, and as used in this description of the invention, the 
main transmission section of a compound transmission is that section which 
contains the largest (or at least no less) number of forward speed ratios, 
which allows selection of a neutral position, which contains the reverse 
ratio(s) and/or which is shifted (in manual or semiautomatic 
transmissions) by manipulation of a shift bar or shift rail or shift 
shaft/shift finger assembly as opposed to master/slave valve/cylinder 
arrangements or the like. 
The prior art comPound change gear transmissions of the type having both 
range and splitter type auxiliary section gearing, such as the 
"Roadranger" type offered by Eaton Corporation and the "Ecosplit" type 
offered by Zahnradfabrik Friedrichshafen Aktiengesbushaft, are well 
received and widely used in manually shifted heavy duty vehicles. However, 
these and other types of prior art compound change gear transmissions are 
not totally satisfactory as rather sensitive shifting procedures were 
required for splitter types of shifts or the splitter clutches required 
synchronizing mechanisms and/or master clutch interlocks were required to 
protect the splitter clutch synchronizers. Referring specifically to 
auxiliary sections where the splitter clutches were not synchronized, the 
operation of the usually air actuated non-synchronized jaw clutches 
involved controlling the greatest out of synchronous rotation at which the 
clutches would engage by controlling shift yoke engagement force and 
clutch backlash. The correct balance between backlash and engaging force 
was difficult to achieve and maintain. Too much backlash and/or engagement 
force resulted in unacceptably harsh clutch engagements while too little 
force and/or backlash resulted in missed shifts. 
SUMMARY OF THE INVENTION 
In accordance with the present invention, the drawbacks of the prior art 
have been overcome to the extent that a two-speed gear train, such as the 
splitter auxiliary section or subsection of a compound transmission, 
having a relatively simple and reliable easily shifted, smoothly engaging, 
non-synchronized, clutching mechanism is provided. 
The above is accomplished in a two-speed gear train having a first and 
second gear selectively clutchable to a common shaft, the second gear 
always driven at a greater rotational speed than the first gear, and a 
clutching mechanism having only a first selectable position for clutching 
the first gear to the shaft and a second position for clutching the second 
gear to the shaft, the clutching mechanism including first clutch members 
fixed for rotation with the gears and complimentary second clutch members 
fixed for rotation with the shaft. 
In such a drive train, as the clutch mechanism is moved directly from one 
of the two positions to the other, the shaft and second clutch members 
fixed thereto will be rotating at substantially the speed of the just 
disengaged gear and will always have the same relative rotation relative 
to the gear being engaged and the clutch members rotating therewith. 
AccordinglY, for a given direction of shaft rotation, such as the 
direction corresponding to forward movement of a vehicle in which a 
transmission is installed, disengaging the first gear from, and engaging 
the second gear to, the shaft will cause the leading edges of the engaging 
first clutch member clutch teeth and the trailing edges of the engaging 
second clutch member clutch teeth to engage as the shaft and second gear 
move toward synchronous rotation. Conversely, in the given direction of 
rotation, disengaging the second gear from, and engaging the first gear 
to, the shaft will cause the trailing edges of the engaging first clutch 
member clutch teeth and the leading edges of the engaging second clutch 
members clutch teeth to engage as the shaft and first gear move towards 
synchronous rotation. 
In the present invention, the leading edges of the first clutch member 
clutch teeth and/or the trailing edges of the second clutch member clutch 
teeth associated with ;the second gear, and the trailing edges of the 
first clutch member clutch teeth and/or the leading edges of the second 
clutch member clutch teeth associated with the first gear are provided 
with ramped surfaces which, under the relatively light engagement force 
urging the clutch members into engagement, will interact to cause the 
clutch members to be urged axially apart and ratchet out of axial 
engagements. As soon as the engaging clutch members achieve synchronous 
rotation, the ramp surfaces of the engaging clutch teeth will not be urged 
into engagement and, due to the relatively large initial penetration of 
the interengaging clutch teeth due to engagement occurring along a ramp, 
the clutch members will achieve a rapid and smooth engagement. 
Additionally, the clutches are relatively insensitive to backlash and thus 
less expensive to produce. 
Accordingly, it is an object of the invention to provide a two-sPeed gear 
train assembly having a relatively simple and reliable nonsynchronized jaw 
clutch assemblY for Providing relatively smooth and easily accomplished 
shifts. 
This and other objects and advantages of the present invention will become 
aPParent from a reading of the detailed description of the preferred 
embodiment taken in connection with the attached drawings.

DESCRIPTION OF THE EMBODIMENT 
Certain terminology will be used in the following description for 
convenience only and will not be limiting. The words "upwardly", 
"downwardly", "rightwardly" and "leftwardly" will designate directions in 
the drawings to which reference is made. The words "forward" and 
"rearward" will refer respectively to the front and rear ends of the 
transmission as conventionally mounted in the vehicle, being respectively 
to the left and right sides of the transmission as illustrated in FIG. 3. 
The words "inwardly" and "outwardly" will refer to directions toward and 
away from, respectively, the geometric center of the device and designated 
parts thereof. Said terminology includes the words above specifically 
mentioned, derivatives thereof and words of similar import. 
The term "compound transmission" is used to designate a change speed or 
change gear transmission having a main transmission section and an 
auxiliary transmission section connected in series whereby the selected 
gear reduction in the main transmission section may be compounded by 
further selected gear reduction in the auxiliary transmission section. The 
term "upshift" as used herein shall mean the shifting from a lower speed 
gear ratio to a higher speed gear ratio. The term "downshift" as used 
herein shall mean the shifting from a higher speed gear ratio to a lower 
speed gear ratio. The terms "low speed gear" or "low gear" as used herein 
shall designate a gear ratio utilized for relatively lower forward speed 
operation in a transmission, i.e., a set of gears having a higher ratio of 
reduction of output shaft speed relative to the speed of the input shaft. 
"Synchronize clutch assembly" and words of similar import shall designate 
a clutch assembly utilized to nonrotatably couple a selected gear to a 
shaft by means of a positive clutch in which attempted engagement of said 
clutch is prevented until the members of the clutch are at substantially 
synchronous rotation and relative large capacity friction means are 
associated with the clutch members and are sufficient, upon initiation of 
a clutch engagement, to cause the clutch members and all members rotating 
therewith to rotate at a substantially synchronous speed. 
Referring to FIGS. 3, 3A, 4A and 4B, there is illustrated a compound 
eighteen-forward speed transmission 100 comprising a multi-speed main 
transmission section 12A and an auxiliary section 102 connected in series 
therewith. Transmission 100 is disclosed and described in detail in 
above-mentioned U.S. Pat. No. 4,754,655. 
Typically, transmission 100 is housed within a single housing and includes 
an input shaft 16 driven by a prime mover such as diesel engine E through 
a selectively disengaged, normally engaged friction master clutch C having 
an input or driving section 18 drivingly connected to the engine crank 
shaft 20 and a driven portion 22 rotatably fixed to the transmission input 
shaft 16. 
Preferably, each of the main section mainshaft gears encircles the 
mainshaft 28A and is in continuous meshing engagement with and is 
floatingly supported by the associated countershaft gear group, which 
mounting means and a special advantages resulting therefrom are explained 
in greater detail in U.S. Pat. Nos. 3,105,395 and 3,335,616, the 
disclosures of which are hereby incorporated by reference. Typically, 
clutch collars are axially positioned by means of shift forks (not 
illustrated) associated with a shift bar housing assembly (not 
illustrated) as well known in the prior art. 
Auxiliary transmission section 102 includes two substantially identical 
auxiliary countershaft assemblies 104 and 104A, each comprising an 
auxiliary countershaft 106 supported by bearings 108 and 110 in housing H 
and carrying three auxiliary section countershaft gears 112, 114 and 116 
fixed for rotation therewith. Auxiliary countershaft gears 112 are 
constantly meshed with and support auxiliary section splitter gear 118 
which surrounds mainshaft 28A. Auxiliary countershaft gears 114 are 
constantly meshed with and support auxiliary section splitter/range gear 
120 which surrounds the output shaft 122 at the end thereof adjacent the 
coaxial end of mainshaft 28A. Auxiliary section countershaft gears 116 
constantly mesh and support auxiliary section range gear 124, which 
surrounds the output shaft 122. Accordingly, auxiliary section 
countershaft gears 112 and splitter gear 118 define a first gear layer, 
auxiliary section countershaft gears 114 and splitter/range gear 120 
define a second gear layer and auxiliary section countershaft gears 116 
and range gear 124 define a third layer, or gear group of the combined 
splitter and range type auxiliary transmission section 102. 
A sliding two position jaw clutch collar 126 is utilized to selectively 
couple either the splitter gear 118 or the splitter/range gear 120 to the 
mainshaft 28A, while a two position synchronized assembly 128 is utilized 
to selectively couple the splitter/range gear 120 or the range gear 124 to 
the output shaft 122. The structure and function of double acting sliding 
jaw clutch collar 126 is substantially identical to the structure and 
function of sliding clutch collar 96 utilized in connection with 
transmission 10 while the structure and function of double acting 
synchronized clutch assembly 128 is substantially identical to the 
structure and function of synchronized clutch assembly 92 utilized in 
connection with transmission 10. Synchronized clutch assembly 128 are well 
known in the prior art and examples thereof may be seen by reference to 
U.S. Pat. Nos. 4,462,489; 4,125,179 and 2,667,955, the disclosures of all 
of which are incorporated by reference. 
The detailed structure of the preferred embodiment of auxiliary section 102 
is illustrated in FIG. 3, wherein it may be seen that the rearward end of 
mainshaft 28A extending into the auxiliary transmission section 102 is 
provided with external splines 130 which mate with internal splines 132 
provided on clutch collar 126 for rotationally coupling clutch collar 126 
to the mainshaft 28A while allowing relative axial movement therebetween. 
The clutch collar 126 is provided with clutch teeth 134 and 136 for 
selective axial engagement with clutch teeth 138 and 140 provided on gears 
118 and 120, respectively.The clutch collar 126 is also provided with a 
groove 141 for receipt of a shift fork 142. 
Gear 118 surrounds mainshaft 28A and is normally free to rotate relative 
thereto and is axially retained relative to the mainshaft 28A by means of 
retainers 144. Clutch teeth 136 and 138 present tapered surfaces 146 and 
148 which are inclined at about 35.degree. relative to the axis of the 
mainshaft 28A which provides an advantageous interaction tending to resist 
nonsynchronous engagement and also tending to cause a synchronous rotation 
as is described in greater detail in U.S. Pat. No. 3,265,173, the 
disclosure of which is hereby incorporated by reference. Clutch teeth 136 
and 140 are provided with similar complementary tapered surfaces. 
Splitter/range gear 120 is rotatably supported at the inward end 150 of 
output shaft 122 by means of a pair of thrust bearings 152 while range 
gear 124 surrounds the output shaft 122 and is axially retained thereon by 
means of thrust washers 154 and 156. Located axially between gears 120 and 
124, and rotationally fixed to output shaft 122 by means of external 
splines 158 and internal splines 160, is the double acting two Position 
synchronized clutch assembly 128. Many of the well known synchronized 
positive clutch structures are suitable for use in the auxiliary 
transmission section of the present invention. The synchronized clutch 
assembly 128 illustrated is of the pin type described in above mentioned 
U.S. Pat. No. 4,462,489. Briefly, the synchronized clutch assembly 128 
includes a slidable jaw clutch member 162 axially positioned by a shift 
fork 164 and carrying clutch teeth 166 and 168, respectively, for axial 
engagement with clutch teeth 170 and 172, respectively, carried by gears 
120 and 124, respectively. Gears 120 and 124 define cone friction surfaces 
174 and 176, respectively, for frictional synchronizing engagement with 
matching frictional cone surfaces 178 and 180, respectively, carried by 
the friction rings 182 and 184, respectively, of the synchronized clutch 
assembly. Blocker pins 186 and 188 are rotationally fixed to the friction 
rings 184 and 182, respectively, and interact with blocker openings 190 
carried by the sliding member 162 to provide the blocking function as is 
well known in the prior art. Synchronizing assembly 128 may also include a 
plurality of spring pins (not shown) for providing initial engagement of 
the conical friction surfaces at the initiation of a clutch engagement 
operation. 
Output shaft 122 is supported by bearings 192 in housing H and extends 
therefrom for attachment of a yolk member Y or the like which typically 
forms a portion of a universal joint for driving a propeller shaft to a 
differential or the like. The output shaft 122 may also carry a 
speedometer gear 194 and/or various sealing elements (not shown). 
As may be seen by reference to FIGS. 5 and 6, by selectively axially 
positioning both the splitter clutch 126 and the range clutch 128 in the 
forward and rearward axial positions thereof, four distinct ratios of main 
shaft rotation to output shaft rotation may be provided. Accordingly, 
auxiliary transmission section 102 is a 3-layer auxiliary section of the 
combined range and splitter type providing four selectable speeds or drive 
ratios between the input (countershaft 28A) and output (output shaft 122) 
thereof. In compound transmission 100 the main section 12A provides a 
reverse and five potentially selectable forward speeds. However, one of 
these selectable forward gear ratios is often a creeper or low gear not 
intended to be used in the high range. Thus transmission 100 is properly 
designated as a (4+1).times.(2).times.(2) type transmission providing 17 
or 18 selectable forward speeds depending upon the desirability and/or 
practicality of splitting the low or creaper gear. 
While clutch 128, the range clutch, should be a synchronized clutch, double 
acting clutch collar 126, the splitter clutch, according to the present 
invention, is a specially configured non-synchronized clutch. 
The shift pattern for shifting transmission 100 is schematically 
illustrated in FIG. 3A. Divisions in the vertical direction illustrate 
range shifts while divisions in the horizontal direction illustrate 
splitter shifts. 
A method of selecting desirable gear ratios is schematically illustrated by 
reference to FIG. 5. Disregarding the creeper (illustrated in dashed 
lines) and reverse ratios, and assuming that it is desirable that a 
transmission have generally equal ratio steps, the main section ratio 
steps should be generally equal, the splitter step should be generally 
equal to the square root of the main section ratio steps and the range 
step should equal about the main section ratio step raised to the N power 
where N equals the number of main section ratio steps occurring in both 
ranges (i.e. N=4 in the (4+1).times.(2).times.(2) transmission). Given the 
desired ideal ratios, gearing to approximate these ratios is selected. 
Referring to FIGS. 3, 4A and 4B and assuming by way of example that gears 
118, 120, 124, 112, 114 and 116, respectively, have 40, 38, 54, 41, 45 and 
19 teeth each, respectively, the following four auxiliary section ratios 
are obtainable: 
(1). Clutch 126 engaged to gear 120 and clutch 128 engaged to gear 124 
provides an auxiliary section reduction of about 3.365:1; 
(2). Clutch 126 engaged to gear 118 and clutch 128 engaged to gear 124 
provides an auxiliary section reduction of about 2.913:1; 
(3) Clutch 126 engaged to gear 120 and clutch 128 engaged to gear 120 
provides an auxiliary section reduction about 1.000:1; and 
(4). Clutch 126 engaged to gear 118 and clutch 128 engaged to gear 120 
provides an auxiliary section reduction of about 0.865:1. 
In the above example, the splitter steps are about 15.6% while the range 
step is about 336.6% which is generally suitable for a "4+1" main 
transmission section having about 35% steps as the square root of 1.35 
equals about 1.16 and 1.35 raised to fourth power (i.e. N=4) equals about 
3.32. FIG. 6 illustrates the various gears engaged for the various 
selectable forward speeds of transmission 100. 
The above example illustrates an "overdrive" type transmission. As is known 
in the transmission art, a "direct drive" transmission may be provided 
utilizing the auxiliary transmission section of the present invention by 
reversing the splitter and splitter/range gear sets and also reversing the 
sequence of operation of splitter clutch 126. By way of example, for such 
a transmission, gears 118, 120, 112 and 114 would have 38, 40, 45 and 41 
teeth each, respectively, and splitter clutch 126 would engage gear 118 in 
gears ratios 1, 3, 5, 7, 9, 11, 13, 15 and gear 120 in gear ratios 2, 4, 
6, 8, 10, 12, 14 and 16. Such a transmission would, by way of example, 
provide the same splitter step as discussed above but a somewhat smaller 
range step. Of course, by modifying the numbers of teeth on the various 
auxiliary section gears, acceptable range and splitter steps may be 
provided. 
Referring to FIG. 1, the splitter type auxiliary subsection 200 of the 
present invention is schematically illustrated. The two-speed gear train 
assembly 200 comprises the mainshaft 28A which is surrounded by splitter 
gear 118 and splitter/range gear 120, both rotatable relative to shaft 28A 
and selectively clutchable one at a time thereto by two position sliding 
clutch collar 126. Sliding clutch 126 is fixed to shaft 28A by splines 
130/132 for rotation therewith and is axially positioned by shift fork 142 
and two-position pressurized fluid actuation 202 to a first position for 
engaging gear 118 to shaft 28A or to a second position (FIG. 4A) for 
engaging gear 120 to shaft 28A. 
Gear 118 constantly meshes with auxiliary countershaft gear 112, gear 120 
constantly with auxiliary countershaft gear 114. Both auxiliary 
countershaft gears 112 and 114 are fixed for rotation with auxiliary 
countershaft 106. 
Gear 118 carries clutch teeth 138 for selective engagement with clutch 
teeth 134 carried by sleeve 126 while gear 120 carries clutch teeth 140 
for selective engagement with clutch teeth 136 carried by sleeve 126. 
Accordingly, clutch teeth 138 and 134 define a first positive clutch 204 
associated with engagement and disengagement of gear 118 and shaft 28A 
while clutch teeth 140 and 136 define a second positive clutch 206 
associated with engagement and disengagement of gear 120 and shaft 28A. 
The actuator 202 is preferably fluid (gas) actuated to urge the clutch 
teeth into engagement in a resilient manner and the clutch members, 138, 
134, 140 and/or 136 may be resiliently movable as illustrated in 
above-mentioned U.S. Pat. No. 3,799,002. 
As gears 118, 120, 112 and 114 have 40, 38, 41 and 48 teeth, respectively, 
gear 120 will always rotate at about one-hundred fifteen and six-tenths 
percent (115.6%) of the rotational speed of gear 118. Further, as clutch 
sleeve 126 is shifted directly between the first and second Positions 
thereof (i.e. no neutral position for gear train 200), during a shift 
transient, the shaft 28A and clutch sleeve 126, and the clutch members 134 
and 136, will be rotating at substantially the same speed as the just 
disengaged gear 118 or 120. 
Accordingly, for shifts of gear train 200 in a given direction of rotation 
for shaft 28A, during an engagement of clutch 204, clutch teeth 134 will 
be initially rotating faster than clutch teeth 138 and the leading edge 
208 of clutch teeth 134 will be in contact with the trailing edge 210 of 
clutch teeth 138. For shifts of gear train 200 in the given direction of 
rotation for shaft 28A, during an engagement of clutch 206, clutch teeth 
136 will initially rotate slower than clutch teeth 140 and the trailing 
edge 212 of clutch teeth 136 will be contacted by the leading edge 214 of 
clutch teeth 140. 
Referring to FIG. 2 a layout view, arrows 216, 218 and 220 represent the 
rotational speeds of gear 118, clutch sleeve 126/shaft 28A and gear 120, 
respectively. The value of 220 is always about 115.6% of the value of 216. 
The arrows CR and AX, respectively, indicate the circumferential direction 
and axial direction, respectively, of relative movement in FIGS. 2 and 7. 
Rotational movement of clutch member 120 relative to clutch member 126 
will result in a relative movement of clutch teeth 214 relative to clutch 
teeth 136 in the circumferential direction. 
The leading edges 208 of clutch teeth 134 and trailing edges 212 of clutch 
teeth 136 are provided with ramps 222. Alternatively, ramps could be 
provided on trailing edges 210 and leading edges 214 or on all of the 
initial contact edges 208, 210, 212 and 214. 
The ramps 222 are dimensioned such that under the relatively light engaging 
force provided by actuator 202, if clutch 126 is overspeeding gear 118, 
(i.e. rotating at about speed of just disengaged gear 120) the ramps will 
cause an axially separating or ratcheting force sufficient to prevent 
engagement of clutch 204. However, as clutch 126 is caused to rotate at an 
equal and then relatively slower speed than gear 118, the ramps 222 will 
not contact teeth 138 under force and the relatively large initial 
penetration will allow the clutch members or teeth 134 and 138 of positive 
clutch 204 to quickly and smoothly engage at substantially synchronous 
speed. 
Similarly, ramps 222 are dimensioned such that under the relatively light 
engaging force provided by actuator 202, if clutch 126 is underspeeding 
gear 120 (i.e. rotating at about speed of just disengaged gear 18) the 
ramps will cause an axially separating or ratcheting force sufficient to 
prevent engagement of clutch 206. However, as clutch 126 is caused to 
rotate at an equal and then relatively faster speed than gear 120, the 
ramps 222 will not be forced into contact with clutch teeth 140 and the 
relatively large initial penetration will allow a rapid and smooth 
engagement of clutch 206 at substantially synchronous conditions. 
In the engaging position, the clutch members, 134 and 138 of clutch 204 or 
136 and 140 of clutch 206, are being resiliently urged into, or are 
maintained in, axial engagement. 
The resiliency is provided by spring biasing devices as illustrated in 
above-mentioned U.S. Pat. No. 3,799,002 and/or by the use of pressurized 
compressible fluid operators. 
Referring to FIG. 7, when clutch teeth 140 are caused to rotate slightly in 
the direction of arrow 220A relative to clutch teeth 136, i.e. just as the 
clutch 206 passes through synchronous, the surfaces 214 of teeth 140 will 
ride down ramps 222 to achieve a large initial axial penetration 230 at 
the time of maximum backlash 224 between the engaging teeth. Due to this 
large initial penetration, the clutch will engage "one tooth past 
synchronous" for smooth, positive engagements which are relatively 
insensitive to clutch tooth backlash. 
While the present invention relates to many types of two-speed gear trains, 
it is especially advantageous in splitter type gearing wherein the ratio 
steps are relatively small. 
Accordingly, it may be seen that an improved two-speed gear train, such as 
the splitter type auxiliary section or subsection of a compound 
transmission is provided. 
The description of the preferred embodiments of the present invention is by 
way of example only and various modifications and/or rearrangement of the 
parts are contemplated without deParting from the spirit and the scope of 
the invention as hereinafter claimed.