Hydraulic tensioner

Abstract: A hydraulic tensioner for tensioning a threaded connector has a substantially tubular housing (1) having an axis, one axial end to abut against an object and another opposite axial end, a substantially tubular engaging element (2) arranged radially inside the housing (1) so as to form a space therebetween and provided with engaging means (11) for engaging a threaded connector, a plurality of pistons (4-6) arranged in the space and spaced axially from one another so as to form a plurality of chambers in the space, and passages (7-10) for supplying a working liquid into the chambers so as to apply a force to the housing (1) and to the engaging element (2) whereby when the housing (1) abuts against the object in one axial direction, the engaging element (2) is displaced axially in an opposite direction and thereby axially pulls the threaded connector in an opposite axial direction. The radially outer dimension of the chambers reduces in a direction from the another axial end to the one axial end of the housing (1).

Description: This invention relates to a hydraulic tensioner of the kind disclosed in the pre-characterising portion of claim 1. Stud tensioning requires the use of a tool with a small diameter and possibly a low height, so that it can be used in multiple applications. In the past, a user had to determine if a customer required a low height tensioner or a small diameter tensioner, since it was impossible to make a tensioner that would meet both parameters. While small-diameter tensioners utilised a multi-stage system with several cylinder chambers staged on top of each other so as to obtain the required pulling load, low height tensioners have usually been provided with one single-cylinder chamber. A multi-stage system includes a plurality of individual cylinder chambers mounted on top of each other so that the bottom piston is connected with the piston in the cylinder chamber above to push that piston, while it is also being pushed by the hydraulic pressure. In other words each piston located above another piston would generate the combined force of both. Such a tensioner is disclosed for example in WO-94/14578. Another known hydraulic tensioner of the kind defined in the preamble of claim 1 is disclosed in GB-A-1 249 979. As most applications, however, have smaller radial clearances around the bolt than above it, it has in many instances not been possible to make a tensioner small enough in its lower diameter to fit such bolts having a small radial clearance. In addition the manufacture and assembly of the known tensioners is time consuming and expensive. Accordingly, it is an object of the present invention to provide a hydraulic tensioner which avoids the disadvantages of the prior art. In keeping with these objects and with others which will become apparent hereinafter, the present invention resides in a hydraulic tensioner for tensioning a threaded connector which has a substantially tubular, integral housing having an axis, one axial end to abut against an object, another opposite axial end, an outer surface, and an inner surface comprising cylindrical portions and shoulder portions joining axially adjacent cylindrical portions, the cylindrical portions reducing in diameter from said another axial end to said one axial end and defining with said shoulder portions a plurality of steps; a substantially tubular engaging element arranged radially inside said housing so as to form a space therebetween and provided with engaging means for engaging a threaded connector; a plurality of piston means arranged in said space with parts of said piston means abutting against said shoulders and said piston means being spaced axially from one another so as to form in said space a plurality of chambers having radially inner walls and radially outer walls defined by said inner surface of the housing; and means for supplying a working liquid into said chambers so as to apply a force directly or indirectly via each of said piston means to said housing and to said engaging element whereby when said housing abuts against the object in one axial direction, said engaging element is displaced axially in an opposite direction and thereby axially pulls the threaded connector in an opposite axial direction, characterised in that said outer surface of said housing has a diameter reducing in the direction from said another end toward said one end at least in the region radially outwardly of the stepped inner surface of the housing. When the hydraulic tensioner is designed in accordance with the present invention, the lower end of the tensioner cooperating with the threaded connector has a small diameter and can fit in small radial clearances around the threaded connector. The manufacturing and assembly costs of the tensioner are reduced. Only one engaging element and only one housing need to be used in the inventive multi-stage tensioner. The housing can change its inner diameter with every cylinder chamber, while the engaging element can change its outer diameter with every cylinder chamber, so that at the location of each piston the outside diameter of the engaging element and the inside diameter of the housing are increased relative to the cylinder chamber below. By taking advantage of the fact that each piston only applies a given force and that the tensioning force applied to the engaging element by the bottom piston is less than the combined force of two or three pistons, less material to transfer this force onto the engaging element is required, so that the outer diameter of the tensioner in the region which is close to the stud to be tensioned can be smaller. The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, in which: Figure 1 is a cross-sectional view of a hydraulic tensioner in accordance with one embodiment of the present invention; Figure 2 is a cross-sectional view of a hydraulic tensioner in accordance with another embodiment of the present invention; and Figure 3 is a cross-sectional view of a hydraulic tensioner in accordance with a further embodiment of the invention. Figure 1 shows a tensioner in accordance with the present invention having a tubular housing 1 and a tubular engaging element 2 located radially inwardly of the housing 1 so as to form a space 3 therebetween. The radially outer surface of the engaging element 2 is stepped to join a plurality of different diameter outer cylindrical surfaces, whilst the radially inner surface of the housing 1 is also stepped to join different diameter inner cylindrical surfaces of the housing. The hydraulic tensioner further has a plurality of piston means identified by reference numerals 4, 5, 6. The piston means 4 is formed as a single piston or floating body abutting against an axially upper surface of the lower end of the housing 1 and against a lower shoulder of the engaging element 2 formed between the two lower different diameter outer cylindrical surfaces of the element 2. The piston means 5 and 6 each include two pistons located adjacent to one another, the lower piston of each pair abutting against a shoulder of the housing formed between two different diameter inner cylindrical surfaces of the housing 1 and the upper piston of each pair abutting against a shoulder of the engaging element formed between two different diameter outer cylindrical surfaces of the element 2 as can be seen in Figure 1. As Figure 1 shows, the stepped shapes of the radially inner surfaces of the housing 1 and of the radially outer surface of the engaging element 2 are such that the radial dimensions of steps diminish from the upper end toward the lower end of the tensioner. The tensioner further has means for supplying a hydraulic liquid including a lengthwise extending or substantially axial passage 7 and transverse or substantially radial passages 8, 9 and 10. The passage 8 leads into a region underneath the lower piston means 4, whereas the passages 9 and 10 each lead into regions between the individual pistons of piston means 5 and the individual pistons of piston means 6, respectively. The engaging element 2 is provided with engaging means 11 which can be formed in particular as a screw thread or threads provided in an inner opening 12 of the engaging element. Since at least the radially outer diameter, or in other words the radially outer surface, of the engaging element 2 and the radially inner surface of the housing 1 have radial dimensions diminishing in the direction from the upper end to the lower end of the tensioner, the outer surface of the housing 1 can also have a diameter diminishing in the same direction as is shown in Figure 1. An annular recess 18 is provided in the housing 1 to reduce the weight of the tensioner. The hydraulic tensioner described above operates in the following manner: The tensioner is first arranged on a threaded connector (not shown), e.g. a threaded stud, so that the threaded engaging means 11 of the engaging element 2 is screwed on the threaded connector. The hydraulic liquid is then supplied through the passages 7, 8, 9 and 10. The liquid flows through the passage 8, enters underneath the piston 4 and presses or urges the housing 1 downwardly and the piston 4 upwardly. The hydraulic liquid flowing through the passages 9 and 10 presses or urges the lower piston of each piston means 5 and 6 downwardly and the upper piston of each piston means 5 and 6 upwardly. Since the housing 1 is placed on an object, for example on a flange in which the threaded stud is screwed, the housing cannot move downwardly, and therefore the engaging element 2 is displaced or urged upwardly so as to pull, and therefore to tension, the stud in the flange. As can be seen from Figure 1, the engaging element 2 can include a radially inner puller member 13, which is provided with the opening 12 having the thread 11, and a radially outer transmission member 14 which surrounds the puller member 13 and has the radially outer stepped surface described hereinabove. The transmission member 14 is not connected with the puller member 13 but instead, during operation, axially abuts against the puller member 13 due to the cooperation between the shoulders of the puller member 13 and the transmission member 14. In such a construction the puller member 13 can be easily removed from the transmission member 14 and can be replaced with another puller member having, for example, different engaging means, i.e. a different opening 12 with a different thread 11 corresponding to a specific threaded connector. The upper end of the puller member 13 can be provided with means, for example a knurled flange, to be engaged by a user to assist in removal of the old puller member and insertion of the replacement puller member. It is of course understood that the engaging element 2, instead of being composed of two members 13 and 14, can be formed as a one-piece element. As shown in Figure 1, the radial widths of the pistons, and of the chambers in which the pistons are axially displaced, are identical for all pistons and all chambers. However, such an arrangement is not necessary, and it is possible to provide the pistons and the chambers with different radial dimensions. The hydraulic tensioner in accordance with the second embodiment shown in Figure 2 is substantially similar to the hydraulic tensioner of Figure 1. However, here the piston means 5' and 6' are formed somewhat differently. Each piston means 5' and 6' has a first piston 5", 6" and a second piston 5"' and 6"', which are formed and arranged so that the piston 5''' , 6''' surrounds the piston 5", 6" radially inwardly and extends axially downwardly to abut against a neighbouring, downwardly located piston. Also, the piston means are connected with one another by return springs 16. The hydraulic tensioner of Figure 3 is substantially similar to the hydraulic tensioners of Figures 1 and 2. The piston means in this tensioner are, however, different. Each piston means 26, with the exception of the lowermost piston means, has an upper piston 17 provided with a radially inner ring-shaped projection 28 which extends axially upwardly, and a lower piston 29 provided with a radially outer ring-shaped projection 30 which extends axially downwardly. The radially inner projections 28 of the pistons 27 abut axially against the steps of the engaging element 2, while the radially outer projections 30 of the pistons 29 abut against the steps of the housing 1. In such a construction the seals in the pistons are reliably protected, and at the same time the overall axial height of the tensioner is reduced. It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of constructions differing from the types described above.

Claims: A hydraulic tensioner for tensioning a threaded connector, comprising a substantially tubular, integral housing (1) having an axis, one axial end to abut against an object, another opposite axial end, an outer surface, and an inner surface comprising cylindrical portions and shoulder portions joining axially adjacent cylindrical portions, the cylindrical portions reducing in diameter from said another axial end to said one axial end and defining with said shoulder portions a plurality of steps; a substantially tubular engaging element (2) arranged radially inside said housing (1) so as to form a space (3) therebetween and provided with engaging means (11) for engaging a threaded connector; a plurality of piston means (4-6) arranged in said space (3) with parts of said piston means abutting against said shoulders and said piston means being spaced axially from one another so as to form in said space a plurality of chambers having radially inner walls and radially outer walls defined by said inner surface of the housing; and means (7-10) for supplying a working liquid into said chambers so as to apply a force directly or indirectly via each of said piston means to said housing (1) and to said engaging element (2) whereby when said housing abuts against the object in one axial direction, said engaging element (2) is displaced axially in an opposite direction and thereby axially pulls the threaded connector in an opposite axial direction, characterised in that said outer surface of said housing (1) has a diameter reducing in the direction from said another end toward said one end at least in the region radially outwardly of the stepped inner surface of the housing. A hydraulic tensioner according to claim 1, characterised in that said engaging element (2) has a radially outer surface provided with a plurality of steps against which this parts of said piston means (4-6) abut. A hydraulic tensioner according to claim 2, characterised in that said engaging element (2) includes a radially inner pulling member (13) and a radially outer transmission member (14) axially abutting against said pulling member (13), said radially inner pulling member (13) having an opening (12) provided with said engaging means (11), said radially outer transmission member (14) being provided with said radially outer surface. A hydraulic tensioner according to any one of the preceding claims, characterised in that said piston means includes a piston (4) located closer to said one end of said housing and forming a floating base, the remaining ones (5,6) of said piston means each including two pistons located axially adjacent to one another, said means (7-10) for supplying a hydraulic liquid being formed so as to supply the hydraulic liquid in an area between said floating body and said one end of said housing and also in areas between two pistons of each of said remaining piston means. A hydraulic tensioner according to any one of claim 1 to 3, characterised in that at least some of said piston means includes a first piston (5", 6") and a second piston (5"',6"') arranged so that said second piston radially inwardly surrounds said first piston (5",6") of a respective one of said piston means, and said second piston (5"',6"') of one of said piston means axially abuts against said second piston (5"', 6"') of another of said piston means. A hydraulic tensioner according to claim 1 2, or 3 or claim 4 or 5 when not dependent on claim 3, characterised in that said engaging element (2) is formed as an element which is uninterrupted in the axial direction. A hydraulic tensioner according to any of the preceding claims, characterised in that at least some of said piston means includes a first piston provided with a radially inner ring-shaped projection (28) and abutting against said engaging element and a second piston provided with a radially outer ring-shaped projection (30) abutting against an associated one of said shoulders of said housing. A hydraulic tensioner according to claim 7, characterised in that said projections (28,30) of each of said some piston means extend in opposite axial directions and axially abut against said engaging element and one of said shoulders of said housing, respectively.

Inventors: JUNKERS JOHN K, JUNKERS, JOHN K.
Applicants: JUNKERS JOHN K, JUNKERS, JOHN K.
Application year: 1995
Main classification: B25B29
IPC codes: B23P19, B25B29