The invention relates to a -method and an apparatus, by means of which driving or braking powers are transmitted to the wheels of a vehicle in unusual situations. Powers are trans¬ mitted to wheels which are not connected to the proper vehicle drive system.

Previously known are auxiliary driving apparatus, where two parallel axles form a boggie, only the other axle which is driving. In this construction a drive wheel is known to be used, which rotates freely and is pressed between the wheels in the parallel axles in order to transmit the rotative moment from the drive wheel also to the wheel on the other boggie axle. When the drive wheel of the boggie runs onto a sliding surface, the auxiliary drive wheel is pressed down between the wheels and thus even the freely rotating wheel is made driv¬ ing.

Bogging problems occur also with vehicles with trailer, where the major load weight is in the trailer, which has no drive wheels at all. The risk of bogging down lessens the use of such vehicles in poor conditions.

The object of this invention is to achieve a solution in order to accomplish an auxiliary driving apparatus for freely rotat¬ ing vehicle wheels, close to which there are no drive wheels from which auxiliary drive power could be transmitted in accordance with previously known methods. The method and appa¬ ratus as per the invention utilize previously known technology provided that it includes a drive wheel, which can be forced into contact with the tread of the vehicle wheel which is used to transmit rotating power. The method and appararatus as per this invention are characterized in what is presented in the patent claims.

As major advantages of this invention can be considered the facts that driving power can be transmitted from one single independent drive motor to the boggie where, due to the con¬ struction of the auxiliary drive wheel system, either forced rotation/braking, similar to that of a differential lock, is produced into the boggie wheels or, into the wheels on one side of the boggie, independent driving or braking is pro¬ duced, regardless of the other side wheels. In the last men¬ tioned way the slewing boggie can be turned with respect to the vehicle chassis, which means remarkable improvments of trailer handling in difficult and complicated situations.

In the following the invention is presented in detail with reference to the enclosed drawing, where

Fig. 1 is an auxiliary drive wheel system viewed from one side. Fig. 2 is an auxiliary driv wheel system viewed from the rear. Fig. 3 is an auxiliary drive wheel system viewed from above. Fig. 4 is an another drive wheel system viewed from above. Fig. 5 is an auxiliary boggie construction viewed from one side. Fig. 6 is a trailer viewed from one side.

Fig. 7 is the chassi of trailer in fig. 6 viewed from above. Fig. 8 is a trailer viewed from one side. Fig. 9 is the trailer in fig. 8 viewed from the rear. Fig. 10 is the chassi of trailer in fig. 8 viewed from above.

Figure 1 shows a drive wheel system with a pair of drive wheels, both the wheels 2 of which are pressed against the vehicle wheels. Drive wheels 2 rest on pivoted arms 7 and and can thus be pulled apart in pressing the power transmis¬ sion gear 4 in between them. The power transmission gear 4 rests also on pivoted arms 8 and is pressed with cylinder 9 between the drive wheels. The drive is transmitted from gear 4 to drive wheels 2 by means of coggings on the surface of wheels 2 and 4 and by peripherical force. The power transmis-

sion wheel 4 on this side of boggie can be, independently, pressed down and pulled off from between wheels 2 by cylinder 9.

Figure 2 shows the same drive wheel system viewed from the rear. The width of drive wheel 2 is dimensioned to correspond to the width of one vehicle wheel only.

Figure 3 shows the same drive wheel system viewed from above. Rotating force from the driving motor comes to power transmis¬ sion gear 4 along axle 6. The same axle transmits rotating force also to the other side of the boggie. The axle is pivot¬ ed in the way that both its ends can be, individually, pressed down and pulled up in order to get the power transmission gears 4 individually or simultaneously pressed in or pulled up from between drive wheels 2. Further, the apparatus is fur¬ nished with a spring 10, that pulls the drive wheels together and secures their remaining off the vehicle wheels at stand¬ still.

Figure 4 show another drive wheel system, where the friction surfaces of the drive wheels 2 ' are parted into two ones with a toothed ring between them. Likewise, a cogged gear 4' on axle 6 functions as power transmission gear.

Figure 5 shows the drive system location in working position. The power transmission gear 4 is pressed by cylinder 9 bet¬ ween drive wheels 2. By means of the drive wheel system the drive or the braking can be transmitted to wheels 1. The figure shows how the drive wheel system can be installed without disturbing the use of boggies 5 on the boggie wheels.

Figures 6 and 7 show a semi-trailer from one side and its chassis from above. In the rear end of the trailer there is a movable boggie. The chassis is furnished with rails 11, along which the boggie, can be moved lengthwise under the chassis. The figure shows the boggie both in its front and its rear

position. The boggie is moved in the rails in the chassis by means of cylinders 12. Figute 7 shows a drive motor 3, which is a hydraulic motor on axle 6, whereby its rotating power is transmitted over axle 6 to drive wheels 2 on both side of the boggie. Both motor 3 and axle 6 are pivoted to the chassis. The movability of the boggie with respect to the chassis im¬ proves roadholding in different situations of transportation and, even on being bogged down, it is possible, by moving the boggie and utilizing its power transmission, to drive, among others, the truck forward and, at standstill, the boggie can in its turn be pulled forward and in that way one can get out of awkard places.

Figures 8,9 and 10 show a full trailer, also with the possibi¬ lity to shift the boggie 15 under and in parallel to the chas¬ sis. Further, boggie 15 is fitted with a slewing gear ring 16. The front boggie 13 is furnished with an auxiliary drive wheel system as is also boggie 15, which is pivoted to the rear. In the chassis there is an individual drive unit 14, advantage¬ ously a combustion engine, by utilization of which a hydraulic system has been formed in the trailer. Thus the trailer can be transported individually by means of its own power source and by using the auxiliary drive wheel systems. Boggie 15 can also be moved in operating the drive wheel system 2, whereat the front boggie 13 is braked by means of its own drive wheels 2 and boggie 15 moves forward or backward along the rails in the chassis. Boggie 15 is slewed by transmitting power to the drive wheel system on one side of boggie 15 only. The locking of the slewing gear ring is released and the boggie can turn in various ways. One method is to keep boggie 13 braked while driving with the one side drive wheels of boggie 15, whereby the boggie turns. Another method is to move the trailer and to brake with the one side drive wheels of boggie 15, whereby the boggie turns by the braking effect. With the above driving and braking methods, the boggie 15 can be slewed also while moving it. The possibility to slew the boggie makes trailer driving in narrow spaces lighter and the truck can, for instance, be

backed even to very difficult and complicated places.

The invention is not restricted to the above embodiments but several modifications are possible within the limits of the inventional concept determined in the enclosed patent claims. The impact of the invention can be intesified, among others, with a sanding gear connected to drive wheels 2.