Drive having an energy recovery and retarder function

#The invention relates to a drive having an energy recovery and retarder function.

#In utility vehicles, such as, for example, construction site vehicles or fork lift trucks, the vehicle is often accelerated and subsequently braked again during working operation. In addition to the primary drive, working hydraulic units are provided in most cases and are operated by means of an additional hydrostatic piston engine. For the driving operation, these hydrostatic piston engines can be connected to the drive and consequently to the primary energy source of the drive. In order to store the energy which is released during the braking of either an operating device or the travel drive, it is known from DE 32 47 335 C2 to connect a store to the hydrostatic piston engine. By charging the store, kinetic energy is converted into pressure energy. To this end, the hydrostatic piston engine draws pressure medium from a pressure medium reservoir and conveys it into the store with the pressure being increased. Owing to the increasing pressure as the pressure medium is conveyed, the vehicle or the operating device is subjected to a braking effect. In addition, it is possible to use a pressure limitation valve in order to brake the operating device or the vehicle. The pressure medium conveyed by the hydrostatic piston engine is depressurised via the pressure limitation valve.

#The drive known from DE 32 47 335 C2 has the disadvantage that, for example, in the event of a relatively long hill start, the capacity of the store is reached. Further braking of the vehicle or only maintaining the selected travel speed by conveying pressure medium counter to the pressure in the store then becomes impossible. In order to achieve an adequate braking effect, the corresponding kinetic energy at the pressure limitation valve must consequently be converted into heat. This leads to a significant rise in the temperature of the pressure medium.

#Advantageous configurations of the drive according to the invention are illustrated in the drawings and are explained in greater detail in the following description:

#FIG. 1 is a first preferred embodiment of a drive according to the invention, and

#FIG. 2 is a second embodiment having an alternative connection of the hydraulic motor.

#FIG. 1 schematically illustrates a drive 1 according to the invention. The drive 1 according to the invention comprises a primary drive source which is schematically constructed as a drive motor 2 in the embodiment illustrated. The drive motor 2 is, for example, an internal combustion engine of a utility vehicle. The drive motor 2 is connected to a hydraulic pump 4 by means of a drive shaft 3. The hydraulic pump 4 is preferably constructed for conveying in two directions and can be adjusted in terms of the supply volume thereof. A motor 5 is connected to the hydraulic pump 4 and can be adjusted in terms of the absorption volume thereof. The hydraulic pump 4 and the hydrostatic motor 5 are, for example, hydrostatic axial piston engine of the construction type involving inclined plates or inclined shafts.

#The pressure medium conveyed by the hydraulic pump 4 in accordance with the selected supply direction in a first operating line 6 or a second operating line 7 flows through the motor 5 and produces an output torque at the ends 8 and 8′ of an output shaft. The output shaft may be constructed, for example, as a continuous output shaft which extends through the motor 5. The end 8 of the output shaft is, for example, connected to a travel drive of a fork lift truck or a construction vehicle. The output shaft may also be connected to a load type gear which is arranged downstream or an additional switching gear.

#The end of the 8′ output shaft is connected to a gear stage 10 by means of a decoupler 9. By means of the decoupler 9, the torque produced by the motor 5 can be transferred to the gear stage 10. It is insignificant whether the motor 5 is driven by the hydraulic pump 4 during a normal travel operation or the torque is instead produced at the end 8 of the output shaft during overrun operation of the vehicle, owing to the mass inertia of the vehicle. Further reference is made below to the various travel situations in the functional description of the drive 1.