CROSS-REFERENCE TO RELATED APPLICATION

This application claims foreign priority benefits under 35 U.S.C. § 119 to European Patent Application No. 19170757.9 filed on Apr. 24, 2019, the content of which is hereby incorporated by reference in its entirety.

TECHNICAL FIELD

The present invention relates to a hydraulic actuator arrangement comprising a hydraulic actuator having a pressure chamber, a cylinder in a cylinder housing and a piston connected to a piston rod, a hydraulic pump connected to the pressure chamber, and an electric motor driving the hydraulic pump, wherein the pump and the motor are arranged with the actuator.

BACKGROUND

Such a hydraulic actuator arrangement is known, for example, from DE 10 2016 224 970 A1.

Such a hydraulic actuator arrangement can be realized in a rather compact unit. The compactness can be, however, in some cases a bar for the usability.

SUMMARY

The object underlying the invention is to provide an actuator arrangement with many application possibilities.

This is solved with a hydraulic actuator arrangement as described at the outset in that a hydraulic pressure amplifier is arranged between the hydraulic pump and the pressure chamber.

The hydraulic pressure amplifier can be used to increase the pressure supplied to the pressure chamber, so that the hydraulic actuator arrangement can be used despite its compactness to produce lager forces, for example to lift larger loads. With such an arrangement it is possible to have a hydraulic actuator arrangement having only electrical wires to the hydraulic actuator arrangement. No other energy supply is necessary. Anything else (components, hydraulic, etc.) can be contained in the actuator arrangement.

In an embodiment of the invention the pressure amplifier is arranged in the piston rod. In this way the pressure amplifier, which can be, for example, a pressure amplifier cartridge, does not need any additional space so that the compactness of the actuator arrangement can be maintained.

In an embodiment of the invention the motor and the pump are arranged in the piston rod. Again, the internal volume of the piston rod can be used to accommodate the motor and the pump, so that no additional space is needed. The pump can be, for example, a pump having a variable displacement. In an alternative embodiment, the pump can be a pump with a fixed displacement. In this case, the rotational speed of the electrical motor could be varied, for example by way of a frequency converter. In principle, any electric motor could be used.

When all components are integrated into the piston rod, it is possible to provide a “finished unit” which just needs to be placed in a corresponding cylinder.

In an embodiment of the invention the pressure amplifier comprises switching means which in response to a pressure in the pressure chamber activate or inactivate the pressure amplifier. In this way it is possible under “low load” conditions to supply “normal” pressure which can be produced by the hydraulic pump to the pressure chamber. Only in case where a higher pressure is required, the pressure amplifier is activated. Such an activation can be made automatically.

In an embodiment of the invention the motor is arranged in a section of the piston rod extending out of the cylinder in an extracted state of the piston rod. This has the advantage that the motor can be cooled by the ambient air when the piston rod is extracted.

In an embodiment of the invention the motor is arranged in a section of the piston rod surrounded by an oil volume, when the piston rod is in a retracted position. The motor is at least partly oil-cooled. In this way that is possible to prevent an overheating of the motor. The term “oil” is used as an abbreviation for “hydraulic fluid”. It is of course possible to use other hydraulic fluids than oil.

In an embodiment of the invention the oil volume is unpressurized in a retracted position of the piston rod. This means that the oil can be kept at a low temperature.

In an embodiment of the invention an accumulator is arranged within the cylinder housing. The accumulator is used to balance the oil volume when the pressure chamber and a retraction chamber have different pressure areas.

In an embodiment of the invention the accumulator is arranged between the cylinder housing and the cylinder. The accumulator does not interfere with other parts of the actuator.

In an embodiment of the invention the accumulator is ring-shaped. In this way the whole outer circumference of the cylinder can be used to accommodate the accumulator.

In an embodiment of the invention the accumulator extends over the length of the cylinder. Thus, the accumulator can have a sufficiently large volume. The accumulator can be pressurized, if necessary, by a volume of air under a certain pressure.

In an alternative embodiment the pressure chamber is arranged with the piston rod.

In an embodiment of the invention a retraction chamber surrounds the piston rod, wherein a first pressure area of the retraction chamber is equal to a second pressure area of the pressure chamber. In this way it is possible to shift the oil from the pressure chamber to the retraction chamber or vice versa without the need for an additional space accommodating hydraulic oil.

In an embodiment of the invention a buffer tank is arranged within the piston rod. The buffer tank can be used for temperature and tolerance compensation without the necessity to accommodate a difference volume of oil or hydraulic fluid between the pressure chamber and the retraction chamber. Thus, the buffer tank can be kept quite small, so that the overall size of the actuator arrangement can be kept small as well.

In an embodiment of the invention a volume of compressed air limits the buffer tank. The air volume can be further compressed, when temperature or tolerance compensation needs a larger volume of the buffer tank or it can be expanded when the needed volume of the buffer tank decreases.

