GB2120322A - Electrohydraulic displacing device - Google Patents

Abstract

The device comprises a housing (18), an electric drive motor (36), and a pump (21) to pump an operating liquid which acts on a setting piston (31) guided in a cylinder (17). Present between the cylinder (17) and the housing (18) is an annular chamber (29) for the liquid, this chamber being connected through a passage (26) with the cylinder bore (30). When the device is vertical, an air space lies above the liquid; to avoid mixing of air with the liquid during each flow phase and thus avoid a reduction in the displacing force of the device, the housing (18) is parallelepipedonal and the passage (26) has a step (37) in one housing side wall (38) bounded by a curved guide surface (25) so that liquid enters the bore (30) below the liquid surface (12). A partition (14) with a bore (13) is provided, for the formation of a compensating volume, between the housing (18) and the cylinder (17), when the device is used horizontally. <IMAGE>

Description

SPECIFICATION Electrohydraulic displacing device The present invention relates to an electrohydraulic displacing device.

In German (Federal Republic) patent specification (Offenlegungsschrift) No. 2 729 343 there is disclosed an electrohydraulic displacing device which is illustrated in a vertical installation orientation and which comprises a housing, an electric drive motor, a single-stage or multi-stage pump driven by the motor to pump an operating liquid, a single-stage piston loadable by the pumped liquid and guided in a cylinder, the piston being connected through a piston rod with a pressure strap, a guide ring with guide blades disposed between the pump and the piston, and a restoring spring arranged between piston and the housing or a counterweight acting on the pressure strap.An annular space is present between the cylinder and the housing for the operating liquid and a connecting space connects the annular space with the piston space, wherein in the vertical installation position (pressure strap at the top) of the device the level of the liquid lies above the connecting space and an air space is situated above that level.

In a non-operative state of the electrohydraulic displacing device, the piston with piston rod and pressure strap is disposed in a lower end position.

After switching on of the drive motor, a pump wheel of the pump forces the operating liquid through the guide ring under the piston and thereby displaces the piston with the piston rod and pressure strap, against the force of a restoring spring or a counterweight, into an upper end position. In that case, the liquid flows from the space above the piston through the connecting space and the annular space between the cylinder and the housing to the pump suction inlet. After the switching off of the drive motor, the piston returns to its initial setting due to the restoring spring or the counterweight.The liquid then flows in opposite direction from the pump suction inlet through the annular space and the connecting space back into the space above the piston, in which case the liquid flowing out of the connecting space is deflected so that it does not come into contact with the liquid surface.

An air space is present above the liquid so as to prevent excessive increase in the pressure in the housing due to the expansion of the liquid when heated. This air space is disposed externally at the housing in known electrohydraulic displacing devices. As a result, the enclosed space becomes rather large. Air from the air space is mixed with the operating liquid at the surface thereof in each flow phase so that the air space becomes smaller and the pressure in the housing rises. Due to the intermixing with air, the specific weight of the liquid is reduced so that the lifting force of the displacing device is also reduced. Moreover, the intermixing with air is enhanced through volume displacement by the raising of the operating liquid level on introduction of the piston rod into the housing.

There is accordingly a need for an electrohydraulic displacing device in which mixing of the hydraulic fluid with air is avoided and the aforementioned enclosed space is kept as small as possible.

According to the present invention there is provided an electrohydraulic displacing device comprising a generally block-shaped housing containing a hydraulic fluid and air in a space above the fluid, a cylinder disposed in the housing to define an annular hydraulic fluid chamber therebetween, the chamber communicating with the bore of the cylinder by way of a flow passage which is bounded by a deflecting guide surface at a step in one side wall of the housing and which, in a first one of two mutually perpendicular alternative mounting orientations of the device, lies below the surface of the hydraulic fluid in the housing so as to conduct the fluid between the cylinder bore and the annular chamber without reaching the surface of the fluid, a piston slidably engaged in the cylinder and connectible externally of the housing to means to be displaced by the device, a pump drivable by an electric motor to pump hydraulic fluid to displace the piston against a restoring force, fluid guide means between the pump and the piston to guide the pumped fluid, and a partition which extends parallel to and at a spacing from each of said one housing side wall and the housing side wall opposite thereto to connect the housing to the cylinder at two circumferentially spaced regions thereof and which is spaced further from said one side wall than from said opposite side wall, the partition being disposed, in the second one of said orientations of the device, below the surface of the hydraulic fluid in the housing and being provided with a flow bore to permit an equaiising flow of hydraulic fluid from one side of the partition to the other.

In a preferred embodiment, the housing is parallellepipedonal in shape with a nearly rectangular profile and the connecting flow passage is formed by a step in one side wall, which bounds the passage with an arcuate guide surface in such a manner than, for a vertical installation orientation of the device, the flow of the operating liquid is conducted between the annular chamber and the piston space without reaching the level of the liquid. The housing is connected with the cylinder at both sides thereof by a partition which is inserted parallel to two side walls of the housing, namely the one with the step and the parallel wall opposite thereto, and which has a greater spacing from said one side wall than from the other side wall.In a horizontal installation orientation of the device, the partition lies entirely in the liquid, and is provided with a passage bore, whereby the part of the liquid volume above the partition serves as a compensating space of the liquid.

In that case, in the horizontal installation orientation, the flow space for the liquid, which space is separated off by the partition and formed between the cylinder and the nearly rectangular housing, is disposed in the lower region. The connecting flow passage with the guide surface is disposed in the flow space. Disposed above the partition is a compensating space, which is connected with the bore and in which the level of the liquid can adjust itself according to the coldness or heat of the liquid as well as at small displacement volumes and low speeds of the piston rod. The formation of flow eddies in the air space is thereby prevented. No flow takes place in this compensating space. Disposed above the compensating space is the air space, for which the cross-section of the rectangular housing is utilized.

As a result, it is ensured that the liquid in the flow space does not come into contact with the air space. The enclosed space is arranged to be as small as possible through inclusion of the air space in the nearly rectangular cross-section.

In the case of the vertical installation orientation, the liquid flows through the connecting flow passage and in that case is guided by the guide surface so that it does not reach the liquid surface. Through the separation of the flow space by the partition, it is ensured that air-free liquid from the flow space is conducted through the pump suction inlet to the pump wheel.

Preferably, the spacing of the inside edge of the housing at the inner end of the curved guide surface from the piston rod is smaller than half the diameter of the piston.

An electrohydraulic displacing device embodying the present invention may have the advantage of avoiding problems of the prior art in the horizontal installation orientation as well as in any desired (inclined) installation orientation between horizontal and vertical. The invention is also applicable to displacing devices with a lifting and lowering valve.

An embodiment of the present invention will now be more particularly described by way of example with reference to the accompanying drawings, in which Fig. 1 is a cross-sectional view of an electrohydraulic displacing device embodying the present invention, parts of the device being omitted for clarity; and Fig. 2 is a sectional elevation of the device.

Referring now to the drawings, there is shown an electrohydraulic displacing device which is illustrated in the switched-off pressure-free state, i.e. with a drive motor thereof stationary.

The device comprises a housing 3/1 8 with ribs supporting a cylinder 6/17 in which a piston 31 is slidably engaged. A piston rod 28 with a pressure strap 10 is fastened to the piston 31. A guide ring 19 with guide blades 20 is mounted adjacent to the piston 31. A pump wheel 21 is mounted on a shaft 35 of an electric motor 36, the shaft being mounted in a ball bearing 34 and sealed by a sealing ring 23. The pump suction space 33 is disposed in the suction side 22 of the pump wheel 21.

The housing 3/1 8 is constructed to be nearly rectangular in cross-section while an annular space 9/29 is disposed between the housing and the cylinder. This space is utilized as far as the corners 7 of the housing. Disposed in the upper part (according to Fig. 2) of the annular space 9/29 is a connecting space 26 with arcuate guide surfaces 25, which space 26 is effective on a vertical installation orientation of the device and the shape of which is determined by the side wall of the housing bounding it outwardly, into which wall is shaped a step aligned perpendicularly to the piston rod. As a result, the flow 27 of a hydraulic operating liquid in the housing is so guided that it does not reach the surface 12 of the liquid.

The housing possesses a partition 8/14, which separates a compensating space 5/11 from the flow space 9/29. Disposed in the partition is a compensating bore 1/13, through which - in the horizontal installation orientation of the device (Fig. 1) -- the liquid can equalize in both directions when temperature changes occur as well as during the to-and-fro movement of the piston 31 and the piston rod 28. In the case of the horizontal installation orientation of the device, an air space 2/1 5 lies above the compensating space 5/11 and the surface 4/16 of the liquid.

The piston rod 28, which is connected at one end to the piston 31, is guided at the other end to be axially displaceable in a bearing 24 of the housing.

Claims (5)

1. An electrohydraulic displacing device comprising a generally block-shaped housing containing a hydraulic fluid and air in a space above the fluid, a cylinder disposed in the housing to define an annular hydraulic fluid chamber therebetween, the chamber communicating with the bore of the cylinder by way of a flow passage which is bounded by a deflecting guide surface at a step in one side wall of the housing ard which, in a first one of two mutually perpendicular alternative mounting orientations of the device, lies below the surface of the hydraulic fluid in the housing so as to conduct the fluid between the cylinder bore and the annular chamber without reaching the surface of the fluid, a piston slidably engaged in the cylinder and connectible externally of the housing to means to be displaced by the device, a pump drivable by an electric motor to pump hydraulic fluid to displace the piston against a restoring force, fluid guide means between the pump and the piston to guide the pumped fluid, and a partition which extends parallel to and at a spacing from each of said one housing side wall and the housing side wall opposite thereto to connect the housing to the cylinder at two circumferentially spaced regions thereof and which is spaced further from said one side wall than from said opposite side wall, the partition being disposed, in the second one of said orientations of the device, below the surface of the hydraulic fluid in the housing and being provided with a flow bore to permit an equalising flow of hydraulic fluid from one side of the partition to the other.

2. A device as claimed in claim 1, comprising a spring arranged between the housing and the piston to provide the restoring force.

3. A device as claimed in either claim 1 or claim 2, the fluid guide means comprising a guide ring provided with guide blades.

4. A device as claimed in any one of the preceding claims, wherein the radial spacing from the rod of the inwardly facing surface of said one housing wall at a radially inner end of said guide surface is less than half the diameter of the piston.

5. An electrohydraulic displacing device substantially as hereinbefore described with reference to the accompanying drawings.