Abstract:
A heavy goods vehicle has several wheel pairs forming a driven wheel axle, which wheel pairs are each supported by a separate rocker arm, which extends between the wheels of the respective wheel pairs and carries on opposite sides two wheel hubs on which the wheels can be attached. For each wheel of the wheel pair there is provided an independent wheel drive which consists of an electric motor and a reduction stage, which transfers the drive motion of the electric motor to the respective wheel hub. For each wheel of the wheel pair there is provided an independent wheel brake, which is arranged on an outside of the respective electric motor and/or the respective reduction stage facing away from the respective rocker arm and which is arranged, together with the respective electric motor and the respective reduction stage, inside the respective wheel hub and the associated wheel axle.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to a travel drive for heavy goods vehicles, in particular bulk material dumping trucks of the so-called large dump truck type, with several wheel pairs forming a driven wheel axle, which wheel pairs are each supported by a separate rocker arm, which extends between the wheels of the respective wheel pairs and carries on opposite sides two wheel hubs on which the wheels can be attached, whereby there is provided for each wheel of the wheel pair an independent wheel drive consisting of an electric motor and a reduction stage, which transfers the drive motion of the electric motor to the respective wheel hub. 
   The so-called large dump trucks are chiefly used in mining operations for the transport of mined minerals and ores. These bulk material dumping trucks are produced in a size of several hundred tonnes in tare weight and payload, so that special travel drives are necessary to handle the corresponding huge forces and drive conditions. 
   A large dump truck with an independent wheel drive of the type mentioned at the outset is known for example from WO 92/04196. The rear axle of this large dump truck is formed by four wheels, which are combining in pairs and are mounted on two rocker arms supported in a mobile manner on the vehicle frame. The rocker arms extending between the wheel pairs carry on the right and left a pair of wheel hubs, on which the wheels are mounted. A separate electric motor is assigned to each of the wheels so that the wheels can be driven separately also at different speeds, particularly in order to prevent grinding of the wheels when travelling round tight corners. 
   Proceeding from the prior art, the problem underlying the present invention is to provide an improved travel drive for heavy duty vehicles of the type mentioned at the outset, which avoids drawbacks of the prior art and develops the latter in an advantageous way. A structurally improved design of the travel drive is preferably to be achieved. 
   SUMMARY OF THE INVENTION 
   According to the invention, a travel drive is provided to solve this problem. Preferred developments of the invention are the subject-matter herein. 
   According to the invention, therefore, there is provided for each wheel of the wheel pair an individual wheel brake, which is arranged on an outside of the respective electric motor and/or the respective reduction stage facing away from the respective rocker arm and which is arranged, together with the respective electric motor and the respective reduction stage, inside the respective wheel hub and the associated wheel axle. The external arrangement of the brakes inside the wheel hub creates a protected arrangement of the operating components as well as a compact structure of the travel drive. The electric motors with the associated reduction stages lie on the inside towards the respective rocker arm, whilst the brakes lie on the outside of the drive units. 
   In order to be able, in the limited internal space of the wheel axle and wheel hub, to achieve nonetheless a large transmission ratio, a planet gear is provided as the reduction stage in a development of the invention, said planet gear gearing down the drive motion of the electric motors. In particular, a dual planet gear stage with a gearing down in the range from 20 to 40 can be provided. When operating with the electric motors at speeds of the order of magnitude of 3500 revolutions per minute, speeds of approx. 100 revolutions per minute can be achieved on the wheels. 
   The electric motor and the reduction stage are preferably arranged with all their rotary axes parallel to the rotary axis of the respective wheel hub. The electric motor sits with its rotary axis preferably coaxial with the rotary axis of the corresponding wheel hub and drives a first planet carrier, which in turn drives the wheel hub via a further reduction stage. 
   In a development of the invention, the wheel axle, on which the wheel hub is mounted in a rotary manner, is formed by a casing of the electric motor or a casing of the reduction stage. Preferably, the motor casing and the gear casing are designed separately. The electric motors can each be accommodated in a central motor casing, which is rigidly connected to the respective rocker arm and on which the gear casing is flange-mounted. The gear casing at the same time forms the wheel axle, which supports the respective wheel hub in a rotary manner. The dual function of the gear casing leads to a weight-saving design and makes excellent use of the given space conditions. 
   The brakes arranged inside the wheel hub, which in principle are designed separate from the drive units, have in a manner known per se a stationary part and a rotating part. The stationary part of the brakes is preferably fixed to the end face of the wheel axles, in particular to the end face of the gear casing. The rotating part of the brakes could in principle be fixed to the wheel hub. 
   Preferably, however, the stationary part is fixed to the reduction stage element and rotates with respect to the wheel hub with a geared speed. In particular, the rotating part of the brakes can be coupled to the planet carrier, which is driven by the motor shaft, and rotate at its speed. The speed of the rotating part of the brakes geared with respect to the wheel hub permits particularly effective braking. 
   The brakes themselves can be designed differently. According to a preferred embodiment of the invention, the brakes can be designed as a disc brake. An alternative form of embodiment of the brakes consists in providing multiple disc brakes. 
   Each of the brakes preferably has a service brake and a parking brake, which preferably act on a common brake disc, or have common multiple brake discs. 
   In order to prevent a defective independent wheel drive from locking up the whole vehicle, provision is made in a preferred development of the invention such that the reduction stage has an axially disengageable gear element, in particular an axially displaceable gear wheel, for interrupting the power train in the reduction stage. By this means, the respective wheel can, as it were, be uncoupled. If the electric motor locks up, the vehicle is nonetheless able to travel onward with the remaining independent wheel drives. It goes without saying that the gear element interrupts the power train at a point which leaves the power train from the brake to the wheel hub unaffected. As described above, the rotating part of the brake can be fixed to a reduction stage element. The interruption of the power train in the reduction stage takes place on the electric motor side, whilst the power train from the brake to the wheel hub remains in place even in the retracted state of the displaceable gear element. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be explained below in greater detail with the aid of preferred examples of embodiment and respective drawings. The drawings show the following: 
       FIG. 1  a diagrammatic representation of the chassis of a bulk material dumping truck of the large dump truck type with a travel drive according to a preferred embodiment of the invention, 
       FIG. 2  an enlarged representation of a rear wheel pair from  FIG. 1 , which is mounted on a rocker arm supported in a mobile manner on the vehicle frame, to the left and right of said rocker arm, whereby each wheel is driven separately by an independent wheel drive and the independent wheel drives are supplied with cooling air through the rocker arm, 
       FIG. 3  an enlarged representation of a rear wheel pair similar to  FIG. 2  according to an alternative embodiment of the invention, according to which the independent wheel drives are supplied with cooling agent through cooling agent lines inside the rocker arm, 
       FIG. 4  an enlarged sectional view of an independent wheel drive of a rear wheel from the preceding figures, which shows the arrangement of an electric motor, a planet gear stage and the wheel brake, whereby a disc brake is provided as the brake, and 
       FIG. 5  a sectional view of the independent wheel drive of a rear wheel from the preceding figures in a representation similar to  FIG. 4 , whereby a multiple disc brake is provided as the brake. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The chassis of a so-called large dump truck shown in  FIG. 1  comprises a rigid vehicle frame  1 , to which are coupled two front wheels  6  controllable respectively about an axle  5 . A pair of parallel rocker arms  2  projecting backwards are coupled on a rear section of vehicle frame  1 , which are supported in a suitable manner and capable of swivelling, relative to vehicle frame  1 , about a horizontal axis extending at right angles to the travel direction, such as is shown in WO 92/04196. The two rocker arms  2  each carry a pair of rear wheels  8 . As  FIG. 1  shows, rocker arms  2  extend in each case between a pair of rear wheels  8 , which are mounted to the right and left on respective rocker arm  2 . The four rear wheels  8  form the drive axle of the vehicle. As  FIG. 1  shows, an independent wheel drive  3  is assigned to each of rear wheels  8 , so that rear wheels  8  can be driven independently of one another and at different speeds, which is of advantage particularly when tight bends are taken and prevents grinding of the wheels on account of different curved paths. 
   As  FIG. 2  shows, the independent wheel drives are integrated into the interior of the rocker arm and the wheel axles and wheel hubs attached thereto. Each of rocker arms  2  widen towards the axis of wheels  8  and forms a central motor casing  9 , in which two separate electric motors  4  are accommodated, which are both arranged coaxial with the rotary axis of the two rear wheels  8  fixed to rocker arm  2 . Motor casing  9  formed integrally in one piece on rocker arm  2  has two openings facing the wheels. In the area of these openings, two gear casings  10  lying opposite one another are flange-mounted on motor casing  9 , which gear casings are designed essentially pot-shaped and at the same time form the wheel axles for the two rear wheels  8 . Wheel hubs  11 , which carry rear wheels  8  and which will be described in greater detail, are fixed in a rotary manner on gear casings  10 . 
   As  FIG. 2  shows, electric motors  4  are air-cooled inside motor casing  9 . The cooling air is fed through the interior of rocker arm  2 , which in the interior has a cooling-air channel or is designed as a cooling-air channel. 
   The cooling air preferably circulates through rocker arm  2  and motor casing  9 . Suitable inlet and outlet channels are provided for this.  FIG. 2  shows inlet channel  12 , through which the cooling air can be fed. 
   In an alternative embodiment of the invention, electric motors  4  can also be liquid-cooled. Here too, it is expedient for the cooling agent channels to be passed inside rocker arm  2 . As  FIG. 3  shows, cooling agent channels  13  emerge from rocker arm  2  in the immediate vicinity of the coupling point of rocker arm  2  and are conveyed from there to vehicle frame  1 . The cooling agent is also circulated here. One of cooling agent lines  13  acts as a cooling agent feed and leads to the electric motors, whilst the other of the two cooling agent lines  13  acts as a cooling agent discharge. The two electric motors can be connected in series one after the other as regards the cooling agent circulation. 
     FIG. 4  shows the more detailed structure of each independent wheel drive and the brake assigned to each wheel. Electric motor  4 , which can preferably be a frequency-regulated asynchronous motor, is arranged with its motor shaft  14  coaxial with rotary axis  15  of each wheel, whereby motor shaft  14  projects to the exterior, i.e. away from rocker arm  2  through corresponding motor casing opening  9  into gear casing  10 . Said gear casing  10  is designed essentially rotation-symmetric and tapers towards the exterior, i.e. away from the rocker arm, step-by-step to a smaller diameter. Wheel hub  16  sits in a rotary-mounted manner on the outer periphery of gear casing  10 , in particular on its section with reduced diameter. It is supported on motor casing  9  by means of two inclined cylindrical roller bearings  17 . 
   A two-stage planet gear  18  is provided inside motor casing  9 . A planet carrier  20  sits coaxially above motor shaft  14  and carries a plurality of planet wheels  21 , which are mounted in a rotary manner on planet carrier  20 . Planet wheels  21  engage on the one hand with toothed motor shaft  14  of electric motor  4 . On the other hand, they engage with a toothed ring  22 , which is arranged rigid with the gear casing and coaxially surrounds planet carrier  20 . Planet carrier  20  is driven by motor shaft  14  of electric motor  4  via planet wheels  21 . As  FIG. 4  shows, planet carrier  20  has a toothed shoulder  23  projecting axially over motor shaft  4 , said toothed shoulder engaging with a sleeve  24  arranged coaxial with the rotary axis of wheel  8 . As  FIG. 4  shows, sleeve  24  has an external tooth system, with which it sits in an internal tooth system of toothed shoulder  23 . Sleeve  24  thus rotates with planet carrier  21 . 
   Via sleeve  24 , planet carrier  20  drives a further set of planet wheels  25 , which are arranged distributed around rotary axes  15  and are mounted in a rotary manner on gear casing  10 . Gear wheels  25  mesh on the one hand with sleeve  24 . On the other hand, they engage with an internal tooth system of wheel hub  16 , so that they drive wheel hub  16 . As  FIG. 4  shows, the internal tooth system of wheel hub  16  is provided between two roller bearings  17  on the inner periphery of the wheel hub. 
   The two-stage design of planet gear  19  between electric motor  4  and wheel hub  11  produces a large transmission ratio in the smallest possible space. In the form of embodiment shown, a transmission ratio of approx. 30 to 35 is provided, i.e. the speed of electric motor  4  is 30 to 35 times as great as the initial speed of wheel hub  16 . 
   Brake  26  is designed as a disc brake in the embodiment according to  FIG. 4 . Brake  26  sits on the outside, i.e. on the side of planet gear  18  facing away from rocker arm  2 . It is arranged inside the inner periphery of wheel hub  16 . As  FIG. 4  shows, it is enclosed by a wheel hub cap  27 , which is connected on the end face with wheel hub  16 . 
   Disc brake  28  forms the rotating part of the brake. Brake disc  28 , however, is not fixed directly to wheel hub  16 , but rotates with the speed of planet carrier  20 . As  FIG. 4  shows, brake disc  28  sits torsion-resistant on a sleeve-shaped brake disc carrier  29 , which is mounted in a rotary manner on gear casing  10  by means of two inclined roller bearings  30  and engages with sleeve  24 . Brake disc carrier  29 , which is arranged coaxial with rotary axis  15  of the wheels, has an internal tooth system which sits on the external tooth system of sleeve  24 . 
   The stationary part of brake  26  is formed by brake shoes  31 , which are screwed to the end face of motor casing  10 . Several brake shoes are preferably provided, in particular service brake shoes and parking brake shoes, which act on common brake disc  28 . 
   Gear casing  10 , which is shown in  FIG. 4 , sits with its inner flange  32  on motor casing  9 , which is fixed rigidly to rocker arm  2  or is formed by the latter, as shown in  FIG. 2 . The operation of brake  26  preferably takes place hydraulically. As  FIG. 4  shows, there are incorporated in gear casing  10  hydraulic channels  33 , which connect a hydraulic line  34  inside motor casing  9  with the interior of wheel hub  16 , in particular wheel hub cap  27 , so that the brake shoes can be accordingly closed. 
   The fixing of the wheels on wheel hub  11  takes place in a manner known per se by means of a wheel hub flange  34  and suitable screw-bolt connections. 
     FIG. 5  shows an alternative embodiment of brake  26 . As for the rest, the design of the independent wheel drive corresponds to that of  FIG. 4 , so that in this respect reference may be made to the description thereof. Brake  26  according to  FIG. 5  is designed as a multiple disc brake. On the one hand, a rotating multiple disc carrier  35  is provided. The latter, like the previously described brake disc carrier  29 , is not coupled directly with the wheel hub, but with the planet carrier. In particular, multiple disc carrier  35  engages with sleeve  24 . Multiple disc carrier  35  possesses for this purpose a sleeve section  36 , which is mounted in a rotary manner on gear casing  10  by means of roller bearings  30  and sits with an internal tooth system on the external tooth system of sleeve  24 . Radially outside multiple disc carrier  35 , the latter carries a set of rotating multiple brake discs  36 . Between rotating multiple brake discs  36  are arranged stationery multiple brake discs  37 , which are held in a torsion-resistant manner by a multiple disc carrier  38 . As  FIG. 5  shows, multiple disc carrier  38  that is not rotating is screwed down to gear casing  10  on its end face. Circular multiple brake discs  36  and  37  arranged axially one behind the other can be pressed next to one another by hydraulic pressure in a manner known per se. The hydraulic supply also takes place here through a hydraulic channel  33  extending through gear casing  10 . 
   In order to be able to uncouple the wheel hub, reduction stage  19  can have a disengageable, in particular axially displaceable, gear element. In particular, provision can be made such that sleeve  24  with the external tooth system is mounted in an axially displaceable manner. For example, provision can be made such that sleeve  24  can be displaced a little far to the right according to  FIGS. 4 and 5 , so that it becomes disengaged from toothed shoulder  23  of planet carrier  20 . In this way, the wheel hub can rotate with respect to planet carrier  20  and thus with respect to electric motor  4 . On the other hand, the brake still remains engaged with the wheel hub.