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Hydraulic circuit arrangement with recovery of energy

Hydraulic circuit arrangement with recovery of energy description/claims

The invention relates to a hydraulic circuit arrangement having a first pump which is driven by an electric motor and is assigned to a lifting cylinder, wherein, in order to recover energy, the electric motor can be operated as a generator and the first pump can be operated as a hydraulic motor in order to recover potential energy of the lifting cylinder, and having a second pump supplying at least one further load according to the preamble of Claim 1.

Such a circuit arrangement for battery-driven industrial trucks is known from DE 43 17 782 C2. In said document, a direct current or asynchronous electric motor drives a pump P which makes available the hydraulic pressure for the lifting cylinder. When the load is lowered, the circuit arrangement clears a path on which the fluid can flow back virtually without loss of pressure from the lifting cylinder to the pump P. In this context, the potential energy which is stored in the lifting cylinder is recovered by virtue of the fact that the pump then operates as a hydraulic motor and the electric motor then operates as a generator G for recharging the battery. The particular advantages lie in the fact that the expenditure is relatively low and no pressure losses due to the principle occur.

In the known arrangement, it also possible to connect other loads. For this purpose, a separate circuit with a further pump and separate drive motor is provided. Furthermore, additional functions can be provided by the first-mentioned working circuit. However, the lowering function must then be respectively interrupted for this purpose.

DE 299 11 686 U1 discloses a further electrohydraulic lifting module which can be operated in an energy-saving mode. In this context, a single pump supplies both main loads and secondary loads which can be connected into the circuit via an electromagnetically actuated valve. A separate return line is provided for the lowering process of the lifting cylinder, and when said return line is opened it connects the lifting cylinder to the intake side of the pump, wherein a non-return valve prevents the direct emptying into the reservoir. The working line, otherwise provided for the lifting mode, of the pump then functions as a return line and is connected to the tank via an electromagnetic valve.

The invention is based on the object of specifying an improved, more cost-effective circuit for recovering energy from a lifting cylinder while simultaneously operating with other loads.

According to the invention, this is achieved in a hydraulic circuit arrangement according to the preamble of Claim 1 by virtue of the fact that the electric motor, the first pump and the second pump are embodied as a motor/double pump assembly, wherein in the lowering mode of the lifting cylinder the first pump acts as a hydraulic motor with reversal of the rotational direction while the second pump always operates as a pump with a constant delivery direction, and wherein provided between the first pump and the lifting cylinder is a priority valve which, depending on requirements, distributes the volume flow which flows in from the first pump to the lifting cylinder on the one hand, and to the at least one further load on the other, and the volume flow which flows in from the lifting cylinder in the lowering mode accordingly to the at least one load and the first pump.

This solution reduces quite considerably the complexity of known circuit arrangements in terms of valve technology for supplying a plurality of loads.

As preference, arranged in the working line of the first pump between the priority valve and the lifting cylinder is an electrically controllable lifting valve which is partially opened during simultaneous operation of the lifting cylinder and of the at least one further load, and in its two limiting positions switches the working line of the first pump to the closed and open positions, wherein when the lifting cylinder and the at least one further load are not operating simultaneously, the lifting valve opens fully. The lifting valve ensures, together with the priority valve, that excess volume flow of the first pump can flow to the further loads, wherein it is added to the volume flow of the second pump. The second pump can therefore be given relatively small dimensions because it is assisted by the first pump.

It is particularly advantageous if the priority valve is embodied in such a way that it is controlled by the pressure difference which occurs at the lifting valve, wherein in a first extreme position of the priority valve, the first pump is connected, on the one hand, to the lifting valve via a throttle and, on the other hand, to the at least one further load, while in a second opposed extreme position of the priority valve, the working line which comes from the first pump is switched to the open position and at the same time is connected to the at least one further load, and the priority valve also has a central position in which the working line of the first pump is switched to the open position and the line to the at least one further load is closed.

Preferably provided in the line leading from the priority valve to the at least one further load is a non-return valve which then opens if in the working line leading from the first pump to the lifting cylinder there is excess pressure above the pressure generated by the second pump.

The supply of further loads can advantageously be carried out by a constant flow system which is of particularly simple design and is sufficient for a large number of practical applications. However, a load-sensing system which permits better pressure adaptation and volume adaptation to the instantaneous requirements of the individual loads can preferably also be provided for this purpose.

In a further advantageous embodiment of the invention, an electrically controllable load-lowering valve is provided, and in the lowering mode said load-lowering valve diverts the volume flow from the lifting cylinder to the reservoir without the recovery of energy and switches in the cases in which the recovery of energy is to be dispensed with. Such a case can occur, for example, when a small lifting load is lowered and there is simultaneous operation of further loads. If, in this context, only a small amount of energy is available for recovering, it is, according to circumstances, preferable to divert the volume flow into the reservoir. Such situations can preferably be detected by means of pressure sensors which are provided in the respective working lines of the first and the second pumps and are used to actuate the load-lowering valve.

Further features and advantages of the invention emerge from the following description of the figures:

In said figures:

FIG. 1: shows a first exemplary embodiment of the invention in which the further loads are supplied by a load-sensing system.

FIG. 2: shows the exemplary embodiment from FIG. 1 with a load-lowering valve for optionally bypassing the recovery of energy, and

FIG. 3: shows a further exemplary embodiment in which the additional loads are supplied by a constant flow system.

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