Abstract:
A drive for a hydraulic excavator having an electric motor as a main drive. In order to provide a compact, low-maintenance and reliable drive system, at least one diesel engine is arranged on the excavator vehicle itself and can be switched on as required and supplies the chassis with power independently of the main drive.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    Diesel engines and electric motors are used for the drive of hydraulic excavators. In both cases, the installed power is converted into hydraulic power, which is preferably suited to transmission, control and safeguarding against overload.  
           [0002]    The main arguments for the two drive systems are:  
           [0003]    Electric motor:  
           [0004]    high efficiency  
           [0005]    high reliability  
           [0006]    low maintenance effort  
           [0007]    this is therefore overall an economic drive.  
           [0008]    Diesel engine:  
           [0009]    great mobility of the excavator  
           [0010]    the appliance can be moved easily and quickly in the mine.  
           [0011]    For the main task of an excavator, to loosen and load material, an electric motor is the more economical drive. The diesel engine has its advantages only when moving (relocating) the excavator.  
           [0012]    One known possible solution envisages arranging a diesel-hydraulic unit on a separate vehicle (trailer). This solution, also called a “power pack” has not become widespread. Coupling the various hydraulic lines is cumbersome, time-consuming and susceptible to faults.  
         SUMMARY OF THE INVENTION  
         [0013]    The invention is based on the object of providing a compact, low-maintenance and reliable drive system which also ensures a high degree of mobility of the excavator.  
           [0014]    Pursuant to this object, and others which will become apparent hereafter, one aspect of the present invention resides in a drive for a hydraulic excavator, which drive includes an electric motor as a main drive and at least one separate diesel engine arranged on the excavator so as to be startable as required. The diesel engine is operatively arranged to supply the chassis of the excavator with power independently of the main drive.  
           [0015]    In another embodiment of the invention both the electric motor and the diesel engine, together with hydraulic pumps respectively associated with the electric motor and the diesel engine, form a separate drive unit.  
           [0016]    In still another embodiment of the invention the electric motor is designed to have two shaft ends. A coupling is arranged to connect the second shaft end to the diesel engine so that the hydraulic pumps can be driven both by the electric motor and by the diesel engine connected to the electric motor via the second shaft end.  
           [0017]    The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of the disclosure. For a better understanding of the invention, its operating advantages, and specific objects attained by its use, reference should be had to the drawing and descriptive matter in which there are illustrated and described preferred embodiments of the invention.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]    [0018]FIG. 1 shows a drive unit with a separate diesel engine;  
         [0019]    [0019]FIG. 2 shows a drive unit with two diesel engines and through drive of the electric motors; and  
         [0020]    [0020]FIG. 3 shows a drive unit with two separately connectable diesel engines.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0021]    Large appliances are designed with two separate drives arranged in parallel. The reasons for this are substantially that, in the case of the electrical design, a reduction in the starting current is to be achieved by starting up the two motors with a time delay.  
         [0022]    [0022]FIG. 1 shows a drive unit according to the invention with a separate diesel engine. Since the relevant large appliances are designed with two drive units and, in principle, only a lower power is needed for the driving operation as compared with the overall system, it is possible for a diesel-hydraulic unit, comprising a diesel engine  1 , hydraulic pumps  2 , a radiator  3  and a pump distributor gearbox  5 , to be mounted transversely in front of the main drives, each comprising an electric motor  4 , a pump distributor gearbox  5  and hydraulic pumps  2 . The hydraulic pumps  2  are supplied with oil (hydraulic tank  7 ) via a separate suction tank  6 . The pressurized oil is fed into the control blocks of the main drive.  
         [0023]    As FIG. 2 shows, two diesel engines  1  can be connected via through drive of the electric motors  4 .  
         [0024]    Electric motors  4  with two shaft ends  8  are used. One shaft end drives the main pumps  2  via a pump distributor gearbox  5 , as usual. Via the additional shaft end  8 , virtually as a through drive, the additional diesel engine  1  is connected via a coupling  9 . The idea in this design is, therefore, when the electric motor  4  is switched off, to drive the hydraulic pumps  2  by means of the diesel engines  1 , the respective electric motor  4  is used as a through drive.  
         [0025]    The third variant according to FIG. 3 envisages both the electric motors  4  and the diesel engines  1  being capable of being connected up to the drive of the hydraulic pumps  2  via couplings  9  respectively associated with the diesel engines  1  and via the same pump distributor gearbox  5 .  
         [0026]    The coupling  9  illustrated can be a switching clutch and/or a hydrodynamic clutch. In the case of mechanical coupling, before the changeover to diesel operation, the diesel engine would first have to be brought to approximately the rotational speed of the electric motor before a changeover was made. In the design as a hydrodynamic coupling, the diesel units can be started even when the electric motor is at a standstill.  
         [0027]    In the exemplary embodiments, only two hydraulic pumps  2  for each pump distributor gearbox  5  are shown. There are usually at least three or up to six pumps.  
         [0028]    The solutions proposed can also be used for an excavator having only one drive.  
         [0029]    Thus, while there have been shown and described and pointed out fundamental novel features of the present invention as applied to a preferred embodiment thereof, it will be understood that various omissions and substitutions and changes in the form and details of the devices illustrated, and in their operation, may be made by those skilled in the art without departing from the spirit of the present invention. For example, it is expressly intended that all combinations of those elements and/or method steps which perform substantially the same function in substantially the same way to achieve the same results are within the scope of the invention. Substitutions of elements from one described embodiment to another are also fully intended and contemplated. It is also to be understood that the drawings are not necessarily drawn to scale but that they are merely conceptual in nature. It is the intention, therefore, to be limited only as indicated by the scope of the claims appended hereto.