Abstract:
The invention relates to a vehicle having a drive engine/motor ( 2 ) for driving a locomotive drive ( 6 ) and for operating at least one hydraulic working circuit ( 4 ). The vehicle has a hydraulic accumulator ( 11 ) which is connected to a hydraulic machine ( 12 ). The hydraulic machine ( 12 ) is connected to an output shaft ( 5 ) which connects the drive engine/motor ( 2 ) to the locomotive drive ( 6 ).

Description:
BACKGROUND 
     The invention relates to a vehicle with a drive engine for driving a traction drive and for driving at least one working hydraulic system. 
     In the case of machines or utility vehicles, it is the norm that only one prime mover is provided, with which the different consumers of the vehicle are driven. In particular, it is usual to provide a single diesel engine. In the case of several different functions, for example a traction drive as well as an additional working hydraulic system, the power produced by the diesel engine is branched. A portion of the available overall power of the diesel combustion engine is allotted to the respective consumers in this case according to a defined control strategy. If short-term peak loads occur, this results for example in a reduction in the engine speed. Utility vehicles and construction machinery, such as fork lift trucks, wheel-type loaders or even refuse vehicles are frequently accelerated to low velocities and then braked to a stop again. At the same time or in the traction intervals occurring, work is carried out using the working hydraulic system. To be able to use the energy released in the braking process, it is known from DE 32 35 825 A1 to provide a device for storing energy. 
     On the vehicle known from DE 32 35 825 A1, a prime mover is connected to a drive axle via a characteristics converter. The power take-off shaft of the prime mover is coupled to an auxiliary drive, which is connected to a working hydraulic system via a clutch and an overrunning clutch. A hydromachine can be coupled to the working hydraulic system via a further clutch, this hydromachine being connected via a line to an accumulator. Due to this, when the corresponding clutches are closed, the hydromachine can convert the kinetic energy of the vehicle into storable pressure energy in overrunning of the vehicle. If the accumulator is to be recharged without overrunning occurring, driving of the hydromachine indirectly via the auxiliary drive and the clutches is also possible. 
     In the case of the proposed vehicle, it is disadvantageous that the hydromachine has to be activated in a complex manner via a branching gearbox as well as at least one clutch. This not only increases the losses when storing energy, so that only a portion of the braking energy can be stored in the accumulator, but also increases the losses again when recovering the stored energy. At any rate, it is necessary to carry the working hydraulic system along also when recovering the energy, due to which considerable losses arise in spite of the working hydraulic system not being used. In an alternative execution, a coupling with the drive axle of the vehicle can be produced, bypassing the working device. However, an additional transfer gearbox is necessary in this case to achieve speed matching of the hydromachine. 
     SUMMARY 
     According to an exemplary aspect of the invention, there is provided a vehicle with a simple option for energy storage and for transferring the energy between at least one working hydraulic system and a traction drive. 
     The vehicle according to the exemplary aspect of the invention has a drive engine for driving a traction drive and for driving at least one working hydraulic system. Furthermore, the vehicle has a hydraulic accumulator, which is connected to a hydromachine. The hydromachine is connected to a power take-off shaft connecting the drive engine to the traction drive. The vehicle has the advantage that the coupling of the hydromachine to the traction drive takes place at the power take-off shaft of the engine, where the torque of the drive engine is also coupled into the traction drive. This has the advantage that the power flow is unchanged, regardless of whether the torque produced is present due to the stored energy or due to driving on the part of the drive engine. Furthermore, it is advantageous that the hydromachine for charging the accumulator is coupled directly to the traction drive. A complex rerouting of power via an auxiliary drive or a transfer gearbox can be omitted. 
     It is advantageous to connect the hydromachine for storage purposes to a low-pressure accumulator as well as to a high-pressure accumulator. Such a connection with a low-pressure accumulator and a high-pressure accumulator has the advantage that a minimum pressure can always be maintained even on the suction side of the hydromachine by the low-pressure accumulator. The occurrence of cavitation is thus prevented when drawing pressure medium in. The low-pressure accumulator and the high-pressure accumulator work together to produce a hydraulic cradle. Due to the maintenance of a minimum pressure on the suction side of the hydromachine, even hydromachines that are problematic when sucking pressure medium in from a pressure-free tank volume can be used. 
     According to an exemplary embodiment, the traction drive of the vehicle is formed as a hydrostatic gearbox. The formation of the traction drive as a hydrostatic gearbox has the advantage, in interaction with the storage of energy in an accumulator that can be filled via a hydromachine, that during a braking process a continuous change can take place in the gear ratio in the hydrostatic gearbox. Thus the braking force can be set individually on the one hand, while on the other hand the speed at which the hydromachine is operated can be adjusted. At an adjusted speed, the hydromachine for storing energy can be operated in a particularly preferred speed range, due to which the losses can be reduced in turn. A consequence of this is efficient storage of the braking energy released. 
     In this regard it is advantageous, furthermore, to form the hydromachine as an adjustable hydrostatic piston engine. By adjusting the absorption volume of the hydromachine during a braking process, the braking power can likewise be varied. It is advantageous to use a hydrostatic gearbox as a traction drive and in addition to execute the hydrostatic piston engine adjustably. With suitable control of the gear ratio of the hydrostatic gearbox and of the absorption volume of the hydromachine, particularly efficient usage of the available kinetic energy of the vehicle can thus be achieved. 
     Furthermore, it is advantageous to provide a working hydraulic system which comprises at least one hydropump operating in a closed circuit. When using a hydropump operating in a closed circuit, not only can the energy released by the traction drive on braking of the vehicle be used, but it is also possible to drive the hydromachine for storing energy by means of the working hydraulic system. If a double-acting lifting cylinder, for example, is connected to a hydropump in a closed circuit of the working hydraulic system, then the hydropump of the working hydraulic system can be driven when lowering a load. The hydropump, then acting as a hydromotor, then mechanically drives the hydromachine, which for its part conveys pressure medium to the accumulator. A regenerative utilization of energy both from the traction drive in the direction of the working hydraulic system and from the working hydraulic system in the direction of the traction drive is thus possible. The stored energy can also be re-used in the same circuit, thus the working hydraulic system or the traction drive. 
     It is also advantageous to execute the hydromachine disconnectably. In the arrangement according to the exemplary embodiments of the invention, the hydromachine is coupled to a drive shaft connecting the drive engine to the traction drive, such a disconnectable arrangement is especially advantageous. Thus when the accumulator is completely filled, for example, if carrying the hydromachine along were to result for example in churning losses, the hydromachine can be disconnected. Connection is always possible as required, if recovery of the energy is necessary. In the intervening period, in which a transport journey is carried out for example at constant velocity, the disconnected hydromachine does not cause any losses, on the other hand. 
     The exemplary embodiments of the vehicle according to the exemplary aspect of invention are illustrated in the drawing and are described in greater detail in the following description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a schematic representation to clarify the arrangement according to the invention; 
         FIG. 2  shows a schematic representation of a first embodiment of a vehicle according to the invention; 
         FIG. 3  shows a schematic representation of a second embodiment of a vehicle according to the invention. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     In  FIG. 1 , the basic structural elements of a vehicle with a hydraulic working circuit and a traction drive are shown first of all. The vehicle  1  has a drive engine  2  used jointly by the elements to be driven. The drive engine  2  drives the vehicle by driving a drive axle  3 . In order to be able to operate further working devices in addition to the driving tasks, the drive engine  2  is connected to a hydraulic working circuit  4 . 
     The drive engine  2  transmits its output torque via a power take-off shaft  5  to a vehicle drive  6 , which acts via a vehicle power take-off shaft  7  on a differential gearbox  8  of the drive axle  3 . The differential gearbox  8  is connected to a first half-shaft  9  and a second half-shaft  9 ′, which are connected to the driven vehicle wheels  10 ,  10 ′. The vehicle drive  6  can be executed in any way. In particular, it can be designed as a purely mechanical drive, so that the vehicle drive  6  preferably consists of a mechanical manual gearbox. In this case a decoupler is provided at the vehicle drive  6  on the input side. The traction drive  6  can likewise be executed as an automatic gearbox, which is connected via a hydrodynamic converter to the power take-off shaft  5 . For the sake of simplicity, only one driven vehicle axle  3  is shown in  FIG. 1 . However, it is also possible that the traction drive  6  comprises a transfer case of an all-wheel drive. 
     In the embodiment shown, the hydraulic working circuit  4  is an open circuit. If the vehicle  1  is braked, overrunning occurs due to the mass inertia. Opposite to normal driving operation, the torque introduced at the vehicle wheels  10 ,  10 ′ is continued via the half-shaft  9 ,  9 ′, the differential gearbox  8  as well as the vehicle power take-off shaft  7  and the vehicle drive  6  as far as the power take-off shaft  5 . On normal vehicles without an accumulator device, this torque led via the power take-off shaft  5  to the drive engine  2  is reinforced at the drive engine  2 . In a drive with energy recovery, an accumulator  11  is provided for storing pressure energy, as shown in  FIG. 1 . The accumulator  11  is equipped with a compressible volume, so that a pressure medium can be conveyed to the accumulator  11  under compression of the compressible volume. To facilitate the transport of pressure medium, a hydromachine  12  is provided, which is connected to the power take-off shaft  5 . The hydromachine  12  transports pressure medium via an accumulator line  13  to the accumulator  11 . The pressure medium is sucked from a tank volume  15  via a suction line  14 . The hydromachine  12  is preferably executed adjustably. The adjustable hydrostatic piston engine is provided for transporting pressure medium in two directions and can be operated both as a pump and during recovery of the stored energy as a hydromotor. When recovering the stored energy, the pressure medium, which is under pressure, is supplied from the accumulator  11  via the accumulator line  13  to the hydromachine. The hydromachine  12  then acts as a hydromotor and by expansion of the pressure medium produces a torque, which is transferred from the hydromachine  12  to the power take-off shaft  5 . 
     The torque transferred to the power take-off shaft  5  can be used in the same way as were possible if generated by the drive engine  2 . This means that the torque produced by the energy recovery can be made available both to the vehicle drive  6  and to the hydraulic working circuit. The hydraulic working circuit  4  likewise comprises an adjustable hydropump  17 . The adjustable hydropump  17  is likewise provided for transportation in both directions. The hydropump  17  sucks in pressure medium via a second suction line  16  from a further tank volume  15 ′ and pumps this via a working line  18  to a working hydraulic system  19 . In the embodiment shown, the hydraulic working circuit  4  is executed as an open circuit. 
     In  FIG. 2 , a further embodiment of the vehicle according to the invention is shown. To avoid repetition, the features corresponding to  FIG. 1  are not described afresh and are provided with the same reference signs in  FIG. 2 . In contrast to the hydraulic working circuit  4  in  FIG. 1 , the hydraulic working circuit  4  is executed as a closed circuit. The hydropump  17  is consequently connected to a first working line  20  and a second working line  21 . The working lines  20  and  21  are connected to a double-acting hydraulic cylinder  19 ′ and open there into a first pressure chamber  22  and a second pressure chamber  23 . The first pressure chamber  22  and the second pressure chamber  23  are arranged in the hydraulic cylinder  19  on different sides of a piston  24 . As a consequence of the pressure difference between the first pressure chamber  22  and the second pressure chamber  23 , displacement of the piston  24  results. The piston movement of the piston  24  is transmitted via a piston rod  25  to an arm of an excavator, for example, or a lifting arm of a wheel-type loader. Due to the piston rod  25 , there is a difference between the supplied and the displaced volume in the pressure chambers  22 ,  23 . To equalize the differential volume, the first working line  20  and the second working line  21  are connected to one another via a valve manifold  26 . The valve manifold  26  facilitates a volume flow required to equalize the difference. In the formation shown of a closed circuit, the hydraulic circuit  6  can also have a separate energy storage device in the form of a further hydroaccumulator. 
     The vehicle drive  6  is executed as a hydrostatic gearbox with a second embodiment of  FIG. 2 . The hydrostatic gearbox comprises a hydropump  30 , which is adjustable and is provided for transportation in two directions. The hydrostatic pump  30  is coupled via a first gearbox line  31  and a second gearbox line  32  to a hydromotor  33 . In the embodiment shown in  FIG. 2 , the hydromotor  33  is designed as a fixed displacement motor, through which a flow can pass in two directions. For further functions, such as e.g. the supply of pressure medium to the circuit of the traction drive  6 , which circuit is initially pressureless following the start-up of the vehicle, a feed pump  34  is provided. Like the pump  30  and the hydrostatic piston engine  17  of the hydraulic working circuit  4 , the feed pump  34  is connected to the power take-off shaft  5 . 
     A third embodiment is shown in  FIG. 3 . The traction drive  6  and the hydraulic working circuit  4  correspond to the embodiment in  FIG. 2 . In addition to the accumulator  11  formed as a high-pressure accumulator, which is provided for the storage of braking energy, a second accumulator  35  is provided in the embodiment in  FIG. 3 . The second accumulator  35  is connected to the suction line  141 . During the storage of pressure energy in the accumulator  11 , the hydromachine  12  accordingly no longer sucks pressure medium from a tank volume, which is normally pressureless, but from a second accumulator  35 . The second accumulator  35  is designed as a low-pressure accumulator. In the second accumulator  35  designed as a low-pressure accumulator, a slight excess pressure prevails, so that even when drawing in a large volume flow, sufficient admission pressure exists in each case to avoid cavitation on the suction side of the hydromachine  12 . This enables hydromachines to be used which are unsuitable for sucking pressure medium in independently from a pressureless tank volume due to their low suction capacity. 
     The embodiments described make it possible to store energy released both by braking of the vehicle  1  via the traction drive  6  and during the lowering of a load via the hydraulic circuit  4 , for example, in the accumulator  11 , which is designed as a high-pressure accumulator. The energy stored there can then be recovered via the hydromachine  12  operated in the reverse direction, which then acts as a motor. The torque produced by the hydromachine  12  is made available, like the torque of the prime mover  2 , via the power take-off shaft  5 . Due to the torque available at the power take-off shaft  5 , the power flow direction both in the traction drive  6  and in the hydraulic circuit  4  is unchanged compared with production of the torque by the drive engine  2 . 
     The invention is not limited to the embodiments shown. In particular, diverging combinations of individual features of the individual embodiments are conceivable.