HYDRAULIC ACTUATOR

Abstract: The aim has been to provide a simplified and improved hydraulic actuator in the form of a hydraulic piston type cylinder (10) meant for use under water or in other environments, in which the actuator is exposed to elevated ambient pressure. The actuator comprises a force-exerting element in the form of a piston (14), forming a movable partition wall between two chambers (24, 26). This force-exerting element, the piston, is driven in one of two opposite directions, when different pressures prevail in the two chambers (24, 26). According to the invention, each of the two chambers (24, 26) are to allow evacuation, as at least one chamber, the first chamber (24), is to be provided with an inlet (36) with a shut-off valve (38) arranged thereto, and in contact with the ambient medium. By an open inlet (36) water or other surrounding medium is admitted into a first chamber (24) and drives the piston (14) into said second evacuated chamber (26) against the action of a return spring (28).

Description: HYDRAULIC ACTUATOR This invention relates to a hydraulic actuator meant to be used under water or in other environments of elevated ambient pressure compared to atmospheric pressure, comprising a force-exerting element such as a piston in a hydraulic piston type cylinder, a vane of a hydraulic vane motor or other corresponding force element forming a movable partition wall between two chambers of said cylinder, said chambers being changeable in volume, the housing of said hydraulic engine, or similar defined cavity accommodating such a power element, wherein the force-exerting element is displaced in one direction or other because of the pressure differential of said two chambers. Hydraulic actuators of the above or similar kind, operating underwater equipment, receive their supply of energy from a hydraulic energy source, which can be submerged or be placed above water. In subsea operations on great depths, the transfer of energy from the energy source to the actuator is not very efficient, and it may be necessary to make use of hydraulic accumulators and place them immediately adjacent to, for example, an underwater actuator, with the purpose of providing the required actuator effect. This complicates subsea hydraulic actuators and associated hydraulic underwater equipment and makes them/it more expensive. The purpose of the invention has been to provide a simplified cheaper actuator arranged for use in water or in other environment with elevated ambient pressures, thus representing a constructive improvement to known technique. The purpose is realized by forming an actuator of the kind stated in the introductory part of Claim 1, in accordance with the characterizing part of Claim 1. According to the invention each chamber, for example each cylinder chamber, is arranged to allow evacuation thereof, at least one chamber being provided with an openable/closable inlet, which permits, in its open condition, the entering of water or other medium, forming the surrounding environment, into the associated chamber. The initially mentioned force-exerting element, the force element, which has two distinct, extreme positions, may conveniently be biased towards one extreme position. The actuator is formed by a piston type cylinder, and said force element is formed by a piston which can be displaced linearly in the cylinder, and which is spring-biased towards one end of the cylinder, and wherein the adjacent chamber, the first cylinder chamber, exhibits the minimum volume when the piston is in this extreme position, whereas the chamber on the piston rod side of the piston, the second cylinder chamber, exhibits its maximum volume in the same piston position. The first chamber is provided with an outlet with a first shut-off valve and, downstream of this, a first pump. Further, the first chamber provided with said inlet is provided with a second shut-off valve. The inlet communicates with the surroundings, the cylinder end cap at the opposite end of the cylinder being formed - in this embodiment - with a central passage for the end portion of the piston rod, which may have the form of a pipe socket with a bore therethrough for the guided displacing movement of the piston rod. in a second embodiment there is also provided, at the stationary end of the second cylinder chamber, a (second) outlet which has a (third) valve and a (second) pump arranged thereto. In this second embodiment there may advantageously be provided a water detector monitoring the second chamber and arranged to respond to water in the second chamber, and in that case produce a signal to a control circuit, which again is arranged to produce a signal to said third valve and said second pump, in order thereby to initiate an emptying sequence with respect to the second chamber. The operation of the two different embodiments of an actuator will be explained in further detail in connection with the following particular part of the specification, with reference to the accompanying drawings. Non-limiting examples of embodiments of the invention are described in the following, with reference to the drawings, in which a first embodiment is shown in Pigs. 1 and 2, whereas a modified embodiment is shown in Fig. 3, and wherein: Fig. 1 shows schematically a coupling of a hydraulic actuator in the form of a single-acting hydraulic piston type cylinder, in which the piston is in one of two end positions; Fig. 2 corresponds to Fig. 1, but here the piston is driven linearly towards the left, and is in an approximately mid position, whereby it divides the cylinder volume into two approximately equally large changeable chambers; and Fig. 3 shows a modified coupling similar to that in Figs. 1 and 2 , but in which there is further provided means for after-emptying of a cylinder chamber. Reference is made to the drawings, first to the embodiment according to Figs. 1 and 2, in which the reference numeral 10 generally identifies a piston type cylinder, whose cylinder element 12 accommodates a piston 14 reciprocatingly displaceable, whose piston rod 16 has a central socket 18 arranged thereto and acting as a guide passage for the piston rod 16 at the first end cap 20 of the cylinder 12. The second end cap is identified by 22. The piston 14 divides the internal cylinder volume into a first chamber 24 changeable in length, and a second chamber 26 changeable in length. A pre-tensioned helical compression spring 28 arranged in the second chamber 26 between the first end cap 20 and the piston 14, seeks to push the piston 14 towards an end/start position, Fig. 1, in which the volume of the first chamber 24 has its minimum value, and in which the volume of the second chamber 26 consequently has its maximum value. The first chamber 24 is . provided with a first outlet 30, which can be opened and closed by means of a first remotely controlled shut-off valve 32. Downstream of the valve 32 the outlet 30 has a first remotely controlled pump 34 arranged thereto, which is arranged to allow the first chamber 24 to be emptied through the outlet 30 when the valve 32 is open. Further, the first chamber 24 is provided with an inlet 36, which communicates with the surroundings, which can consist of water or other medium causing the hydraulic actuator (piston type cylinder) 10 to be subjected to elevated ambient pressure, which inlet 36 can be opened and closed by means of a second remotely controlled valve 38. Thus, the first chamber 24 can be filled with water from the surroundings when the second valve 38 is open. In a practical embodiment the remotely controlled first and second valves 32, 38 and the first remotely controlled pump 34 will be connected to a not shown control system, and be arranged to respond to signals therefrom. The second chamber 26 has been emptied of water (liquid) in advance and evacuated to a low absolute pressure. In the initial position shown in Fig. 1, both valves 32 and 38 are closed, and the first pump 34 has been switched off. The first chamber 24 is empty or contains a small trapped amount of liquid from the surrounding liquid medium (water) . By opening of the second valve 38 of the inlet 36, water at ambient pressure is let into the first chamber 24, and the pressure of water in the first chamber 24, which is higher than the low absolute pressure of the second chamber 26, drives the piston 14 towards the left, the length, and thereby the volume, of the first chamber 24 increasing, and the length, and thereby the volume, of the second chamber 26 decreasing. Fig. 2 shows the piston in an approximately mid position relative to the length of the cylinder 12, the first and second chambers 24, 26 being of approximately the same volume . Since the second chamber 26 was evacuated in the initial position, Fig. 1, no pressure increase or just an insignificant one occurs in the second chamber 26. At great depths, for example of two thousand metres or more, a hydraulic actuator in the form of such a single-acting piston type cylinder 10 according to the invention, may provide a power corresponding to the dynamic efficiency of an ordinary hydraulic piston type cylinder of the same dimensions and driven by hydraulic pressure fluid at a work pressure of more than two hundred bar. The piston 14 is brought to return to its initial position by opening of the first valve 32 at the outlet 30, closing the second valve 38 of the inlet 36 and starting the first pump 34 at the outlet 30, so that water in the first chamber 24 is pumped out. Thereby the actuator is brought back into its initial position, in which the first chamber 24 exhibits its minimum volume, whereas the second chamber 26 is evacuated to a low absolute pressure, provided reliable sealing conditions. However, the second chamber 26 may be subjected to water entering from the surroundings, for example by piston seals and/or piston rod seals not tightening completely. In a preferred, modified embodiment of the invention, Fig. 3, also the second chamber 26 is provided with a (second) outlet 40, which can be opened and closed by means of a third remotely controlled shut-off valve 42, which is connected downstrea of the valve 42 to a (second) pump 44, arranged to allow the second chamber 26 to be emptied when the valve 42 is open. The third valve 42 is normally closed, and the second pump 44 is normally not used. The second chamber 26 may be emptied of possible liquid (water) and be evacuated to a low absolute pressure in an emptying sequence, in which the second pump 44 is started and the third valve 42 is opened, and in which the third valve 42 is closed and the second pump 44 is stopped on completion of a predetermined emptying period. The emptying sequences can be initiated periodically by means of a timer not shown, which may similarly be arranged to control the duration of the individual emptying periods. Said emptying sequences may also be initiated and controlled on the basis of signals from a water detector 46 inside the second chamber 26. In Fig. 3 is suggested such a water detector 46, which is arranged to respond to water in the second cylinder chamber 26 and if positive, generate signals to a control circuit 48. The control circuit 48 responds to the signals from the water detector 46 and starts an emptying sequence with respect to the second chamber 26 by providing a signal to the third valve 42 and the second pump 44. It should be readily apparent that the hydraulic actuator 10 in the form of a single-acting piston type cylinder might just as well consisted in a double-acting piston type cylinder, simply by providing the second chamber 26 in the embodiment according to Fig. 3 with a not shown inlet controlled by a valve. Through evacuation of one cylinder chamber 24, 26, while the inlet of the second chamber is open, the piston 14 may be driven in the desired direction. It will be appreciated directly that the invention may be realized by other types of actuators than the actuators with linearly displaceable pistons, such as by single- and double- acting piston type cylinders driven by pressure fluid, for example actuators with rotationally force-exerting elements, for example in the form of a hydraulic vane motor, in which a vane that has a rotor arranged thereto, forms a movable partition between two chambers changeable in volume.

Claims: C L A I M S 1. A hydraulic actuator for use under water or in other environments of elevated ambient pressure, comprising a force-exerting element such as a piston (14) in a hydraulic piston type cylinder (10), a vane of a hydraulic vane motor or similar, in which the force- exerting element (14) forms a movable partition wall between the chambers (24, 26), changeable in volume, and in whic . he force-exerting element (14) is arranged to o be driven in one of two opposite directions, when the pressures prevailing in the two chambers (24, 26) are different from each other, and in which the housing of the actuator, such as the cylinder of said piston type cylinder accommodating the two changeable chambers (24, s 26), is provided with openable/closable inlets/outlets (36, 30 and 40), c har a c te r i z ed i n that each chamber (24, 26) is arranged to be evacuated, each chamber (24, 26) being provided with partly an openable/closable inlet (36) communicating with water or 0 other medium of an environment of elevated ambient pressure, and on opening, admitting water or said other medium into the chamber (24, 26) in question, provided that provisions have been made, so that in this chamber there is a pressure lower than said elevated ambient 5 pressure, partly an openable/closable outlet (30, 40). 2. An actuator according to claim 1, c h ar a c te r i z ed i n that the openable/closable outlet (30, 40) of each chamber (24, 26) has a pump (34, 44) arranged thereto for periodically emptying the respective chamber o (24, 26). An actuator according to claim 1 or 2, c harac t e r i z e d i n that the force-exerting element (14) is a piston (14), which can be reciprocated linearly, and which has two extreme positions adjacent to a respective end cap (20, 22) of the cylinder (12) of the piston type cylinder (10), and is spring-biased (28) towards the extreme position, in which the first chamber (24) is defined by a first cylinder end cap (22), and that the second chamber (26) has a water detector (46) arranged thereto and which is interconnected in a control circuit (48), in which also shut-off valve (42) and the pump (44) of the associated outlet (40) are included.

Inventors: GJEDEBO JON GRUDE, GJEDEBO, JON, GRUDE
Applicants: GJEDEBO JON GRUDE, HITEC ASA, GJEDEBO, JON, GRUDE
Application year: 2000
Main classification: F15B15
IPC codes: F15B11