Transmission for a wheel- or tracktype vehicle comprising a braking device and a steering unit

Disclosed is a transmission having an input shaft coupled to a motor unit on one side of the transmission and a braking device located on the other side of the unit. Planetary gear trains are located together on one side of the gear box with shafts coupled to the drive wheels or tracks extending through the braking unit on one side and through the gear box on the other. The gear box is connected to the planetary gear train by an output shaft and housing which is also connected to the braking device. Finally, a steering device is located within the transmission housing and serves to controllably interconnect the planetary gear of the planetary gear trains. This advantageously permits the brake unit to be mounted outside of the transmission housing which includes the planetary gear trains, the gear box and the steering device.

BACKGROUND OF THE INVENTION 
The present invention relates to a transmission for a vehicle with 
propelling means, such as wheels or tracks, on each of the longitudinal 
sides thereof, said transmission comprising a right output shaft and a 
left output shaft coupled to the propelling means, a gear box with input 
and output shafts respectively coupled to a motor unit and to the right 
and left output shafts, a braking device which can reduce the rotational 
speed of the right and left output shafts and a steering unit comprising a 
shaft with, fitted thereon, a first and a second pinions, a third pinion 
engaged with the first pinion, and two planetary gear trains coaxial with 
the right and left output shafts, including each a planetary gear, a ring 
gear, planet wheels and a planet carrier and controlled by the second and 
third pinions for varying the rotational speeds of the right and left 
output shafts with respect to each other and thus changing the vehicle 
direction. 
The planetary gear trains and the brakes in the transmissions of this type 
are located on either side of the gear box, in the vicinity of the 
longitudinal walls of the vehicles. In fact, because of their particular 
positioning within such transmissions, they make the motor-transmission 
coupling difficult and thus form an obstacle to an arrangement of the 
motor unit parallel to the right and left output shafts, which is a 
disadvantage for the manufacturers who generally have only a very confined 
space available to install the transmissions and motors in the vehicles. 
SUMMARY OF THE INVENTION 
The object of the present invention is to remedy such a disadvantage and, 
to this effect, it is directed to a transmission of the above mentioned 
type, characterized in that the input shaft of the gear box is coupled to 
the motor unit through a coupling mechanism extending along one of the 
longitudinal sides of the vehicle, in that the braking device is located 
in the vicinity of the other longitudinal side of the vehicle and 
comprises a rotating part coaxial with the right and left output shafts, 
and in that the planetary gear trains are disposed back to back between 
the gear box and the braking device, with their planet carriers integral 
with each other and coupled one to the output shaft of the gear box and 
the other to the rotating part of the braking device, while their ring 
gears are respectively coupled to the right and left output shafts, one 
through the rotating part of the braking device and the other through the 
gear box, and their planetary gears are rotatably integral with toothed 
wheels, respectively engaged with the third and second pinions. 
The transmission according to the invention has such a structure that its 
motor unit can now be installed parallel to the right and left output 
shafts, in the close vicinity of one of the longitudinal walls of the 
vehicle. It thus provides the manufacturers with an additional means for 
solving the problem raised by the little space available on certain 
vehicles to accommodate the transmission and the motor. 
Preferably, the gear box, the right and left output shafts, the steering 
unit and the coupling mechanism are accommodated in a main casing, while 
the braking device is either located externally or accommodated in an 
auxiliary casing carried by the main casing. 
As the braking device is located outside the main housing, very easy access 
is of course provided for carrying out its maintenance. 
The motor coupling mechanism is advantageously formed by a set of pinions 
the rotation axes of which are parallel to the right and left output 
shafts, and contributes, in turn, to increase the size of the space 
intended for the motor unit. 
In some cases, the transmission according to the present invention 
comprises preferably step-up planetary gear trains, that is to say with a 
single set of planet wheels meshing both with their planetary gear and 
ring gear. 
In other cases, it is on the contrary desirable that the planetary gear 
trains be step-down planetary gear trains having two sets of planet wheels 
meshing some with their planetary gear and some with their ring gear, the 
planet wheels of one set further meshing with those of the other set. 
To build vehicles at better cost, it may be judicious to equip their 
transmission with a steering unit comprising a large turning-radius brake 
and a small turning-radius brake, these two brakes being advantageously 
located externally or housed in a third casing carried by the main casing, 
in the vicinity of the braking device.

The transmission shown on FIG. 1 has been developed to equip a vehicle 
having propelling means 1a, 1b, such as wheels or tracks with their 
step-down gears, on each of the longitudinal sides 2a, 2b thereof. 
In a manner known in itself, it comprises a right output shaft 3a and a 
left output shaft 3b respectively coupled to the propelling means 1a, 1b, 
a gear box 4 comprising an input shaft 5 and an output shaft 6 
respectively coupled to a motor unit 7 and to the output shafts 3a and 3b, 
a braking device 8 which can reduce the rotational speed of the output 
shafts 3a and 3b, and a steering unit 9 comprising a shaft 10 with, fitted 
thereon, two pinions 11 and 12, a third pinion 13 engaged with the pinion 
11 and two planetary gear trains 14, 15 coaxial with the output shafts 3a, 
3b and including each a planetary gear 16a, 16b, respectively, a ring gear 
17a, 17b, respectively, planet wheels 18a, 18b, respectively, and a planet 
carrier 19a, 19b, respectively, whereby the planetary gear trains 14, 15 
are respectively controlled by the pinions 13 and 12 for varying the 
rotational speeds of the output shafts 3a, 3b with respect to each other 
and thus changing the direction of the vehicle. 
To permit the installation of the motor unit 7, for example, a gas turbine 
or a piston engine, parallel to the output shafts 3a and 3b, the input 
shaft 5 of the gear box 4 is coupled to the motor unit 7 through a 
coupling mechanism 20 extending along the longitudinal side 2b of the 
vehicle. Besides, the braking device 8 is located in the vinicity of the 
longitudinal side 2a of the vehicle and has a rotating part 8a coaxial 
with the output shafts 3a, 3b, while the planetary gear trains 14, 15 are 
disposed back to back between the gear box 4 and the braking device 8. 
Namely, the planet carriers 19a, 19b are integral with each other and 
coupled the first one to the rotating part 8a of the braking device and 
the second one to the output shaft 6 of the gear box 4. The ring gears 
17a, 17b are for their part respectively coupled to the output shafts 3a 
and 3b, the first one through the rotating part 8a of the braking device 
and the second one through the gear box 4. As for the planetary gears 16a, 
16b, they are rotatably integral with toothed wheels 21, 22 respectively 
engaged with the pinions 13 and 12. 
In the examplary embodiment shown on FIG. 1, the coupling mechanism 20 is 
formed by a set of 4 pinions 20a, 20b, 20c, 20d meshing together and the 
rotation axes of which are parallel to the output shafts 3a, 3b. 
The pinion 20d of this set is fitted on the input shaft 5 of the gear box 
4. It will be understood, however, that this pinion could be coupled to 
the shaft 5 through a resilient coupling, a torque converter or a clutch 
without departing from the present invention. 
It is to be noted here that the number of the pinions of the coupling 
mechanism 20 is not imposed and could be different from 4, should 
technical considerations so require. 
Concerning the steering unit 9, it is to be pointed out that in the example 
illustrated on FIG. 1, its shaft 10 is not different from the output shaft 
of a hydrostatic assembly 23, the input shaft 24 of which carries a pinion 
25 meshing with a pinion 26 meshing itself with the pinion 20d. Of course, 
the coupling between the pinion 25 and the engine could be different from 
the one illustrated on FIG. 1. Thus, the pinion 26 could, for example, be 
replaced by at least two pinions coupling the pinions 25 and 20d or 25 and 
2a, 2b or 20c. 
Moreover, it must be noted that the gear box 4, the output shafts 3a and 
3b, the steering unit 9 and the coupling mechanism 20 are accommodated in 
a main casing 27, while the braking device 8 is housed in an auxiliary 
casing 28 carried by casing 27. 
As the braking device is located outside the main casing, it thus provides 
very easy access for an operator in charge of its maintenance to carry out 
his work. 
For a complete description, it must be further indicated that the braking 
device 8, owing to the fact it is external to the main casing 27, could 
operate dry, the casing 28 being possibly suppressed, or in a fluid 
identical to or different from the one normally contained in the main 
casing. 
The transmission shown on FIG. 2 differs from the one described above in 
that it incorporates a steering unit 29 which, instead of a hydrostatic 
assembly, such as the one designated in 23 on FIG. 1, comprises a 
mechanical assembly including an auxiliary gear box 30, a large 
turningradius brake 31, a small turning-radius brake 32 and two clutches 
33 and 34. 
The auxiliary gear box 30 has an input shaft 35 with, fitted thereon, a 
pinion 36 rotatably integral with the pinions of the coupling mechanism 
20, to control members 37, 38 respectively coupled to the brakes 31 and 32 
and an output through a toothed wheel 45. 
As for the clutches 33 and 34, they comprise, for the first one, a rotating 
part 39 provided with a pinion 40 meshing with the toothed wheel 21 of the 
planetary gear 16a of the gear train 14 and, for the second one, a 
rotating part 41 provided with a pinion 42 meshing with the toothed wheel 
22 of the planetary gear 16b of the gear train 15. They further have a 
common shaft 43 carrying a pinion 44 which meshes with the toothed wheel 
45 forming the output of the auxiliary gear box. 
Like in the transmission represented on FIG. 1, the gear box 4, the output 
shafts 3a and 3b, the steering unit 29 and the coupling mechanism 20 are 
housed in a main casing 46, while the braking device 8 can be accommodated 
in an auxiliary casing 47 carried by the main casing. 
The brakes 31 and 32 can, for their part, be housed in a third casing 48 
carried by the main casing 46, in the vicinity of the braking device 8 and 
can thus be of the type operating dry or of the type operating in a 
liquid, which, besides, could be identical or different from the one 
normally contained in the main casing. 
The planetary gear trains 14 and 15 of the transmissions represented on 
FIGS. 1 and 2 are step-up planetary gear trains since they comprise a 
single set of planet wheels meshing both with their planetary gear and 
ring gear. 
These step-up gear trains, however, could be replaced by stepdown gear 
trains 49, such as those represented on FIGS. 3 and 4 and comprising a 
first set of planet wheels 50 meshing with their ring gear 51 and a second 
set of planet wheels 52 meshing with their planetary gear 53, the planet 
wheels 50 and 52 meshing together and being carried by a planet carrier 54 
(shown on FIG. 3 only) ; such replacement will of course be considered as 
being within the scope of the present invention. 
Finally, it will be noted that, should space problems be encountered, the 
motor unit 7 could be positioned parallel to the longitudinal sides 2a, 2b 
of the vehicle by interposing a bevel gear between same and the coupling 
mechanism 20.