Modular drive axle having a three-speed transmission

A modular drive axle having left and right drive wheels and axles that are coupled to a differential. The left and right axles are in line and define a transverse axis. A bevel gear assembly having first and second bevel gears mounted on a drive shaft directs rotary motion from a transmission to the differential for driving the drive wheels. The bevel gear assembly drive shaft is perpendicular to the transverse axis and the transmission which is operatively coupled to the bevel gear assembly and arranged parallel to the transverse axis. The transmission is a collar shift transmission having an input collar with two output surfaces. The first output surface of the input collar drives a fixed countershaft gear having first and second output surfaces. The first and second output surfaces drive first and second intermediate gears. A gear selector collar is slidably positioned on a drive shaft and selectively engages either the first intermediate gear, the second intermediate gear, or the second output surface of the input collar. The selector collar is provided with bi-directional self centering surfaces.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention is directed to a modular drive axle having a sliding gear 
transmission. 
2. Description of the Prior Art 
A conventional power train for a work vehicle comprises a prime mover or 
internal combustion engine applying rotary motion to a main clutch. The 
main clutch engages a transmission which manipulates the speed of the 
rotary motion. The transmission in turn is coupled to a differential which 
applies the rotary motion to right and left axles. The axles are provided 
with final drives for driving wheels that propel the vehicle. In work 
vehicles the final drives may comprise planetary reduction units. 
Hydrostatic drive systems provide an infinitely variable method of 
adjusting the speed of the final drives. In a hydrostatic drive system the 
internal combustion engine drives a fluid pump which supplies fluid to a 
fluid motor. The motor in turn is operatively coupled to the final drives 
for driving the vehicle. The pumping unit can be a reversible variable 
displacement pump, so that the operator by adjusting the position of the 
swash plate can drive the vehicle at any speed over a specified range, in 
forward or reverse. 
The hydrostatic drive only operates efficiently over a limited speed range, 
as such shiftable transmissions have been added between the hydrostatic 
motor and the final drives to increase the efficient range of the 
hydrostatic unit. More specifically, on combines the hydrostatic units 
have been provided with four-speed transmissions to increase the effective 
speed range of the combine. 
One type of mechanical transmission is the collar shift transmission. The 
collar shift transmission has parallel shafts with gears in constant mesh. 
In neutral, the gears are free-running but when shifted, they are locked 
to their shafts by sliding collars. When a gear is engaged, it is secured 
to its shaft by a collar or coupling device. The gear is disengaged when 
the collar is released and the gear turns freely again. 
To insure that the gears are correctly held in place, it is known to angle 
the side surface of the gear tooth and the root of the sliding gear so 
that the gear is biassed against a stop during rotation. It has been found 
that the canted surfaces need be only five to seven degrees.

SUMMARY 
It is an object of the present invention to provide a modular and compact 
drive axle for a work vehicle. 
It is another object of the present invention to provide a compact collar 
shift transmission. 
It is a feature of this transmission that it is provided with a 
self-centering collar. 
The present invention comprises a drive axle having left and right wheels 
that are provided with planetary reduction units. The planetary reduction 
units are coupled to left and right axles that are coupled at their other 
end to a differential. The left and right axles define a transverse axis. 
The input to the differential is perpendicular to transverse axis and 
comprises a drive shaft having two bevel gear surfaces. The first bevel 
gear is coupled to the differential whereas the second bevel gear is 
driven by a collar shift transmission The collar shift transmission is 
arranged parallel to the transverse axis and in turn is driven by a 
hydraulic motor. The bevel gear drive shaft is also provided with an 
output assembly in line with the drive shaft which is coupled to an 
emergency brake. 
The collar shift transmission of the present invention comprises an input 
collar having two output surfaces. The first output surface of the input 
collar is used to drive three stationary countershaft gears arranged 
radially about the input collar. The countershaft gears are mounted to 
three fixed and parallel countershafts and are each provided with two 
output surfaces. Each of the two output surfaces of the countershaft gears 
drive two independent intermediate gears that are concentrically arranged 
around an output drive shaft. A gear selector collar is selectively 
positioned on the output shaft and can be selectively positioned to engage 
the second output surface of the input collar, the first intermediate 
gear, or the second intermediate gear. Neutral positions are provided by 
first and second spaces that are formed between the second output surface 
of the input collar and the second intermediate gear; and the second 
intermediate gear and the first intermediate gear, respectively. 
To insure that the selector collar is properly positioned in relation to 
one of the intermediate gears or the second output surface of the input 
collar, the gear selector sleeve is provided with the self centering 
surfaces. The self centering surface comprises concave gear teeth 
sidewalls and an axially concave root on the gear selector collar. 
DETAILED DESCRIPTION 
FIG. 1 illustrates a modular drive axle for a work vehicle. The drive axle 
-0 comprises left and right wheels 12 and 14 respectively that are coupled 
to left and right planetary reduction units 16 and 18. The planetary 
reduction units in turn are coupled to left and right axles 20 and 22 
which are joined together at differential 24. The left and right axles 
define a transverse axis that passes through the differential. A bevel 
drive shaft 26, best illustrated in FIG. 2, drives the differential and is 
arranged perpendicular to the transverse axis. Collar shift transmission 
28 is also coupled to the bevel drive shaft and is arranged parallel to 
the transverse axis. Hydraulic motor 30 drives the transmission and in 
turn the bevel drive shaft, the differential, the left and right axles, 
and the left and right drive wheels. The bevel drive shaft is also 
provided with an in line output assembly which is coupled to emergency 
brake 32. 
FIGS. 2 and 3 are cross sectional views of the modular axle assembly. FIG. 
3 is a partial cross sectional view of right axle 22 having axle housing 
34 and drive axle 36. Drive axle 36 is provided with a bearing collar 38 
and external splines 40 which drive three planetary gears 42, only one 
shown. The planetary gears in turn drive ring gear 44 which is fixably 
mounted to wheel flange 46 for driving right wheel 14. The left planetary 
reduction unit is identical to the right planetary reduction unit. Both of 
these planetary reduction units are convention and are well known in the 
art. 
Right drive axle 36 is coupled at its other end to differential 24. It is 
also provided with hydraulic brake 48 located immediately outside of the 
differential housing. The left drive axle has a similar hydraulic brake. 
The differential and the hydraulic brake assembly are of well known 
configurations. The differential is modular in nature so that different 
differential assemblies may be slipped into and out of differential 
housing 50. For example, a standard differential, a limited slip 
differential, or an anti-spin differential could be inserted into the 
differential housing 50. 
The differential is driven by perpendicular bevel drive shaft 26 having a 
first bevel gear surface 52 and a second bevel gear surface 54. The bevel 
gear drive shaft is also provided with an in line output assembly 56. The 
first bevel gear surface 52 is used to drive the differential 24. Whereas, 
the second bevel gear surface 54 is driven by transmission 28. The in line 
output assembly 56 is coupled to emergency brake 32. Emergency brake 32 is 
also of a conventional configuration well known in the art. 
The second bevel gear surface is driven by output drive shaft 58 of 
transmission 28. The transmission is located in housing 60 and has three 
speeds. The transmission itself is best illustrated in FIG. 4. The 
transmission comprises an input means formed by input collar 62 having 
internal splines 64 which are coupled to the output shaft of a hydraulic 
motor 30. The input collar is also provided with a first output surface 66 
and a second output surface 68. The first output surface 66 drives a 
transfer means comprising three radially arranged countershaft gears 70 
(only one shown), having an input surface 72 that cooperates with the 
first output surface 66. The three radially arranged countershaft gears, 
as illustrated in FIG. 5, are rotatably mounted on countershafts 74 which 
extend parallel to output drive shaft 58. Each of the countershaft gears 
are provided with first and second output surfaces 76 and 78, 
respectively. Housing 60 is provided with base portion 61 having inwardly 
projecting portions 63. Base portion 61 together with inwardly projecting 
portions 63 form mounting assemblies for the three countershafts. Annular 
holding plate 82 is mounted to portions 63 by bolts 80. 
The first and second output surfaces 76 and 78 of countershaft gear 70 are 
used to drive independent first and second intermediate gears 84 and 86, 
having input surfaces 88 and 90 respectively. Intermediate gears 84 and 86 
are concentrically arranged around drive shaft 58 and are held in place by 
the three radially arranged countershaft gears and holding plate 82. First 
intermediate gear 84 is provided with output surface 92, and second 
intermediate gear 86 is provided with output surface 94. 
Slidably positioned on drive shaft 58 is a gear selection means comprising 
gear selector collar 96. Gear selector collar 96 transmits rotary motion 
to drive shaft 58 through cooperating splines 98. The selector collar is 
provided with an input surface 100 which is selectively coupled to second 
output surface 68 of input collar 62, output surface 94 of second 
intermediate gear 86 and output surface 92 of first intermediate gear 84. 
The selector collar is slidably positioned on output shaft 58 by fork 102 
cooperating with channel 104 formed on the selector collar. The fork is 
slidably positioned by rod 106 having bearing detents 108 identifying the 
gear shift positions of the transmission. Rod 106 can be manipulated by 
any suitable linkage. 
The two intermediate gears and the second output surface of the input 
collar defines three different output speeds of the transmission. By 
selectively engaging each of these output surfaces, the output speed of 
the drive shaft 58 is changed relative to the input speed of the hydraulic 
motor. First and second neutral spaces are formed between the output 
surfaces. More specifically, a first neutral space 110 is formed between 
output surface 94 and second output gear surface 68 of the input collar. A 
second neutral space 112 is formed between output gear surface 94 and 
output gear surface 92. In these neutral spaces input surface 100 of the 
selector collar is no longer driven by the hydraulic motor. 
As illustrated in FIG. 4a, input surface 100 of selector collar 90 is 
provided with a plurality of radially outwardly extending teeth. Each 
tooth is provided with two concave sidewalls 118 which act to center the 
input surface 100 of the selector collar into mesh with the output 
surfaces. In addition, root 120 is also axially concave having an axially 
concave root configuration 120. These concave surfaces act as 
bi-directional self-centering surfaces. By having these concave surfaces, 
the selector collar tends to center on the output surfaces. 
It is desirable that the hydraulic motor 30 be driven by a reversible 
variable displacement pump, not shown, so that there is an infinite range 
of speed selections in each gear shift and the motor can be readily 
reversed without requiring a reversing gear for the transmission. 
The present invention provides a compact modular drive axle assembly having 
an infinite range of speeds. The transmission mounted to the drive axle is 
simple and rugged and provides a compact unit for the axle. 
The present invention should not be limited by the above described 
embodiment, but should be limited solely by the claims that followed.