Drive of a cross-country vehicle

A cross-country vehicle comprising an all-wheel drive is driven by a reciprocating engine installed transversely close to the front axle and by means of a change speed transmission which is also disposed transversely in the front. From the change speed transmission, the drive torque flows onto a planetary transmission operating as a center differential. The ring gear of the planetary transmission drives the front axle; the sun gear drives a low-high change-over unit. The planetary transmission, the change-over unit and the wheel sets connected behind it are constructed such that, during the high operation, the major portion of the torque is available at the front axle, and, in the low operation, is available on the rear axle. The center differential can be locked in the high and in the low operation.

BACKGROUND AND SUMMARY OF THE INVENTION 
This invention relates to a drive of a cross-country vehicle comprising an 
all-wheel drive and a high/low reduction gear whose engine and 
change-speed transmission are arranged transversely on the front axle. 
In the case of a front transverse arrangement of the engine-transmission 
unit, the transmission output shaft is not accessible. The reduction gear 
must therefore be arranged behind the final drive, where, because of the 
high torques, it would have to be dimensioned to be so large that it could 
no longer be housed in the engine/front-axle area. 
When driving on roads in the high operation, cross-country vehicles must 
have an understeering vehicle handling and avoid a swerving of the rear 
axle in marginal situations. During cross-country driving in the low 
operation, it is important to obtain a good steerability of the 
cross-country vehicle whose front axle is loaded by the weight of the 
reciprocating engine and of the change speed transmission. 
It is an object of the invention to meet the requirements of directional 
control on the road and good steerability when driving cross-country in 
the low operation by a drive that can be manufactured at reasonable cost 
while a shiftable reduction gear is housed at the same time. 
This object is achieved according to the invention by providing a change 
over unit for the change over from cross-country low operation to a road 
high operation, said change over unit being arranged in a transmission 
line to the rear axle, wherein the change over unit serves to transmit the 
majority portion of the torque to the front axle during the high operation 
and to the rear axle during the low operation. 
If, during the high operation, the larger portion of the torque is guided 
to the front axle and, during the low operation, it is guided to the rear 
axle, the requirements of directional control and steerability of the 
cross-country vehicle can be optimally met in both cases. 
A remaining problem to be solved by especially preferred embodiments of the 
invention will then be the design and the physical arrangement of the 
all-wheel drive and of the change-over unit via which these high torques 
are to be guided to the rear axle. This problem is addressed and solved by 
providing an arrangement wherein the center differential is connected 
between the change speed transmssion and the change-over unit, wherein 
only a fraction of the transmission output torque is transmitted to the 
change-over unit, and wherein a torque transmission to the desired higher 
value takes place in gear sets which are connected behind the change-over 
unit.

DETAILED DESCRIPTION OF THE DRAWINGS 
By means of a reciprocating engine 1 which is arranged transversely with 
respect to the longitudinal dimension of the cross-country vehicle close 
to the front axle 2, a change-speed transmission 3 is driven which is also 
arranged transversely. The gear 4 of the change-speed transmission 3 mates 
with a master gear 5 which drives a planet carrier 6 of a planetary 
transmission 7 acting as a center differential. The planet gears 8 
disposed on the planet carrier 6 mate with a ring gear 9 and a sun gear 
10. 
The front axle 2 is driven by the ring gear 9 by way of a front axle 
differential 11 which is constructed of four bevel gears. For this 
purpose, the housing 12 of the differential 11 is connected with the ring 
gear 9 by way of an internal hollow shaft 13. The right axle drive shaft 
15 is driven by one bevel gear 14 arranged on the front axle 2; the left 
axle drive shaft 17, which penetrates the hollow shaft 13 along its whole 
length, is driven by the other bevel gear 16 which is disposed coaxially 
to bevel gear 14. The tooth number of the diameters of the ring gear 9 is 
approximately twice as large as in the case of the sun gear 10. Therefore, 
approximately two thirds of the drive torque supplied by the change-speed 
transmission 3 is guided to the front axle during high operation. One 
third of the drive torque is fed by the sun gear 10 to the change-over 
unit 18 which drives, by way of a forward bevel gear drive 19, a propeller 
shaft 20, which extends into the longitudinal direction of the vehicle, 
and the rear axle 22 by way of a rear bevel gear drive 21. 
The change-over unit 18 comprises a low gear pair 23, 24, a high gear pair 
25, 26 and a coupling sleeve 27 disposed between the two gear pairs. By 
way of an external hollow shaft or transmission member 28, the coupling 
sleeve 27 is connected with the sun gear 10. According to the position of 
the longitudinally displaceable coupling sleeve, the loose gear 23 of the 
low gear pair can be connected with the sun gear 10 in a 
torque-transmitting manner by the closing of clutch 29, or the loose gear 
25 of the high gear pair can be connected with the sun gear 10 in a torque 
transmitting manner by the closing of the clutch 30. The fixed gears 24 
and 26 of the two gear pairs are disposed on an auxiliary shaft 31 which 
is in parallel to the front axle 2 and which introduces the torque into 
the forward angle drive 19. The torque ratio of the output torque to the 
input torque in the low gear pair amounts to approximately 2:1; in the 
high gear pair to approximately 0.5:1; in the forward bevel gear drive to 
approximately 0.5:1; in the rearward bevel gear drive to approximately 
4:1. 
The front axle also receives approximately two thirds of the torque 
existing at the master gear 5 during high operation. During the low 
operation, approximately two thirds of this torque flow to the rear axle; 
thus, approximately twice as much as to the front axle. During the high 
operation, the rear axle receives approximately one third of the torque; 
thus approximately half as much as the front axle. 
In the high operation, when the rotational speeds of the front axle and the 
rear axle are the same, the planetary transmission rotates as a block. In 
contrast, in the low operation, it operates as a torque-splitting running 
transmission. 
The planetary transmission can therefore not be locked directly but only 
indirectly. In order to implement an all-wheel lock on it, a locking 
clutch 32 is mounted between the loose wheel 25 of the high gear pair and 
the internal hollow shaft 13. For this purpose, an externally controllable 
clutch or an automatically closing clutch which responds to the rotational 
speed difference between the front axle and the rear axle may be provided. 
During the low operation, only the locking torques generated according to 
the degree of lock flow by way of the high gear pair 25, 26. 
Although the invention has been described and illustrated in detail, it is 
to be clearly understood that the same is by way of illustration and 
example, and is not to be taken by way of limitation. The spirit and scope 
of the present invention are to be limited only by the terms of the 
appended claims.