Abstract:
The invention relates to a work machine, in particular in the form of a dump truck or truck, having a diesel electric traction drive, wherein at least one alternator is or can be driven by at least one internal combustion engine of the work machine. In accordance with the invention, the current generation can also be reliably interruptible with a running internal combustion engine by interruption of the excitation circuit by means of a breaker switch.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a work machine, in particular in the form of a dump truck or truck, having a diesel electric drive, wherein a alternator is or can be driven by at least one internal combustion engine of the work machine. 
     Dump trucks or so-called large dump trucks are predominantly used in coal mining operations or ore mining operations for the transport of the mined coal, minerals and ores. These bulk material dumpers are manufactured in sizes of more than 90 metric tons (t) up to several 100 t in weight and payload so that they have very large dimensions overall. 
     A diesel electric drive is used as the traction drive, wherein the mechanical energy generated by this diesel engine is converted with the aid of a alternator into electrical energy for the supply of the electric traction drives. The reason for this process is that diesel engines, like all internal combustion engines, can only be operated with ideal efficiency in a very restricted speed range and cannot be started under load. The AC motors for the driving axle which are used can also produce the desired torque in the lower speed range for starting. The internal combustion engine used can be operated continuously in the ideal speed range. Corresponding work machines are described, for example, in DE 10 2014 003 374, DE 10 2014 003 203 and DE 10 2014 003 375. 
     In such work machines, a large number of components are at high voltage so that corresponding service or maintenance work for the service engineers is associated with great risks. The deployment of especially trained technical personnel is necessary due to this. 
     A possibility of safely carrying out corresponding service, maintenance and repair work is also switching off the diesel engine. This is, however, frequently not desired since the further systems which are driven by the diesel engine and which are not electrically operated, for example the hydraulic systems and the mechanically driven systems, are to continue to be available during the maintenance work on the electrical system. Solutions are also generally already known from the prior art in which the internal combustion engines continue to run during the maintenance work. A known solution comprises mechanically separating the driving internal combustion engine from the alternator. Another solution comprises short-circuiting and grounding the DC current lines. These solutions are, however, complex and/or expensive since they have to be carried out with a larger mechanical effort and using special electrical tools and trained personnel. 
     SUMMARY OF THE INVENTION 
     It is now the object of the present invention also to make possible a simple and safe separation of the current generating circuit during service, maintenance or repair work on work machines of this category by personnel not especially trained for this. 
     This object is achieved in accordance with the invention by a work machine having the features herein. For this purpose, in a work machine having a diesel electric traction drive in which at least one alternator is or can be driven by at least one internal combustion engine of the work machine, the current generation can also be safely interrupted with a running internal combustion engine by interrupting the excitation circuit of the alternator by means of a breaker switch. 
     The magnetic field of the alternator is attenuated or reduced by the interruption of the excitation current. The alternator consequently also no longer generates any electrical energy with an unchanged mechanical power at the inlet; the alternator is ideally de-energized at the output side. A regulation, decoupling or even a switching off of the internal combustion engine is not necessary. It is ensured by this solution in accordance with the invention that no high voltages are transmitted despite a running internal combustion engine. The breaker switches for switching off the voltage generation itself are each arranged in low-voltage circuits. 
     Preferred embodiments of the invention result from the description herein. 
     In accordance with a first embodiment of the invention, the breaker switch can be arranged in the voltage supply of the excitation circuit. The excitation circuit is typically operated by a 24 volt voltage source. The excitation circuit can be interrupted in a simple manner by interrupting the voltage supply line. 
     A further preferred embodiment comprises likewise interrupting the excitation circuit in a safe manner by interrupting the line for the control signals. 
     A combination of the two aforesaid embodiment variants is generally also possible. A breaker switch can thus be arranged both in the voltage supply line of the excitation circuit and additionally in the supply line extending in parallel therewith for the control signals to control the excitation voltage. The switches are ideally coupled with one another such that the manual actuation of a breaker switch triggers an interrupting switching of the second switch. 
     A further preferred solution of the invention comprises a breaker switch being arranged in the supply line of the excitation circuit to the alternator. A safe switching off of the electrical supply of the work machine is also possible by this interruption despite a running internal combustion engine. 
     The respective breaker switches can particularly advantageously be secured via a lock. It can hereby be ensured that only the staff interrupts the current generation who have admittedly not been especially trained as a high-voltage electrician, but who have been commission to carry out maintenance work or repair work. 
     As already presented above with reference to an example, one or more breaker switches can advantageously be arranged at a position of the work machine accessible from the outside. 
     A breaker switch can, for example, be arranged close to the electrical drive motors. The staff can hereby operate the breaker switch in the direct environment of the electrical components and thus in the region in which the maintenance and service or repair work is to be carried out. 
     Alternatively or additionally, a breaker switch can also be arranged in a switch cabinet for low-voltage switches which is located in the region of the maintenance and service access in the frontal region of the work machine. Such a breaker switch can otherwise naturally also advantageously be at a different position in the region of the maintenance and service access in the frontal region of the work machine. Alternatively, a breaker switch can, however, also be arranged at the upper deck of the work machine, preferably in the region of the operators cabin or even in the operator&#39;s cabin itself. 
     The provision of the breaker switches makes it possible safely to shut down the current-conductive parts without electrical switch cabinets having to be opened to switch off the components at high voltage. An opening of these switch cabinets is only possibly by especially trained personnel due to the following high voltage and such personnel is also not immediately available in the mining sector or at construction sites. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further features, details and advantages of the invention will be explained in more detail with reference to an embodiment shown in the drawing. There are shown: 
         FIG. 1 : a perspective representation of a dump truck in accordance with the invention; 
         FIG. 2 : a schematic representation of the drivetrain in accordance with the invention; and 
         FIGS. 3 to 5 : different schematic representations of the drivetrain with different solution possibilities for arranging a breaker switch in accordance with the solution of the present invention; and 
         FIG. 6 : illustrate a view of the breaker switch being secured by a lock. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A dump truck  10  is shown in  FIG. 1 . It is here a so-called large dump truck such as is used in ore mines. Front wheels  14  and rear wheels  16 , driven via electric motors not shown in any more detail in  FIG. 1 , are supported at a rigid frame. The rear wheels  16  are designed with dual tires (cf.  FIG. 2 ). 
     A skip  18  is pivotally connected to the frame and is pivotable via hydraulic lifting cylinders provided at both sides at the vehicle. The vehicle  10  is bounded by the bumper  22  in the region of the vehicle at the front in the direction of travel. A radiator module  24  is arranged above the bumper  22 . An upper deck  26  in turn extends over the width of the dump truck  10  above the radiator module  24 . An operators cabin  28  is positioned on a side of the upper deck  26 , on the side of the upper deck  26  at the left in the direction of travel. The operator&#39;s cabin  28  thus lies above the front left wheel  14 . 
     The dump truck  10  comprises a diesel electric drive which is shown in the schematic detailed view in  FIG. 2 . The drive comprises a diesel engine  40  in the region of the front wheels  14  beneath the upper deck  26  and the operators cabin  28 . 
     The internal combustion engine  40  drives an alternator  60  mechanically to generate the required electrical energy for the electrical traction drive. Two AC motors  80 , which are integrated to the left and right with the rear wheels  16 , serve as the traction drive. The use of separate motors per vehicle side for the rear wheels  16  optimizes the cornering and maneuvering since different speeds can be selected for the driven wheels. Power electronics  100  with the required power components such as frequency converters, etc. are available for the control or regulation of the electric motors and of the alternator  60 . 
     In the dump truck of the present invention, a number of secondary consumers of the dump truck are not electrically driven by the generated energy of the alternator  60 , but are instead supplied hydraulically. For this purpose, it is made possible via a pump transfer case  50 , which is mounted directly at the engine  40 , that a small portion of the engine output power is branched off and is used for the drive of the secondary consumers. This small portion of the engine output power is picked up via the secondary drives (PTO)  51  and  52  and is supplied in a manner not shown in any more detail here to the hydraulic consumers. Alternatively, the pump transfer case  50  could also be attached to the alternator  60  or could be a component of the alternator  60 . 
     The alternator  60  used in the present invention is a separately excited synchronous alternator. For this purpose, an excitation winding  62  is integrated in the alternator  60  in a known manner and is supplied via an excitation circuit  64 . The excitation circuit  64  is connected to a supply line  66  for the control signals for controlling the excitation voltage. It is connected via a switch cabinet to a voltage supply  68  of the excitation circuit. 
     Different embodiments of the invention are shown in  FIGS. 3 to 5 . 
     In the embodiment in accordance with  FIG. 3 , a breaker switch  90  is arranged in the voltage supply of the excitation circuit. The power supply for the excitation circuit can therefore be interrupted by actuating the breaker switch. The power generation by the alternator  60  is hereby effectively and safely interrupted. 
     In the embodiment in accordance with  FIG. 4 , a different, alternative arrangement of a breaker switch  92  is shown. It is arranged in a supply line  66  for the control signals for controlling the excitation voltage. An indirect switch  94  arranged in the voltage supply line of the excitation circuit is additionally actuated by the breaker switch  92 . Alternatively, the indirect switch  94  can also be configured as a manual switch so that both the supply line  66  of the control signals of the excitation circuit  64  and the voltage supply  68  of the excitation circuit  64  can be manually interrupted. 
     Finally, a third embodiment of the invention is shown in  FIG. 5  in which a breaker switch  96  is arranged in the supply line  64  which extends between the power electronics  100  and the alternator  60 . 
     In  FIG. 1 , three different positions are indicated in the region of the dump truck  10  at which the breaker switch can respectively be particularly advantageously arranged since it can be actuated there in an easily reachable manner by the operating personnel. A first preferred position in the region of the dump truck  10  is marked by  110 . The breaker switch is here arranged close to the electric motors  80  and to the power electronics  100  not shown in any more detail here in  FIG. 1 . At this position, the operating personnel can actuate the breaker switch directly before the start of the maintenance or repair work. 
     A further preferred position results at  112  in the region of a switch cabinet for low-voltage switches, not shown in any more detail here, which is arranged at the maintenance and service access in the frontal region of the work machine. 
     Finally, a preferred arrangement of the breaker switch on the upper deck  26  of the dump truck  10  results at  114  close to the operator&#39;s cabin  28 . 
     A particular property of the invention is that a dump operation can also be ensured due to the running internal combustion engine even with a safe interruption of the power supply. The skip can thereby be easily used for purposes other than intended as an auxiliary crane. Some machine components can be raised by the tilt movement. For example, some electronic components which were previously switched without current can be raised from the frame by means of the skip and can be easily replaced during the service or maintenance.