Hydraulic tensioner and method of tensioning

A hydraulic tensioner (1), comprising: abase (2); a piston (3) mounted for sliding motion relative to the base (2), the base (2) and the piston (3) defining a pressure space (4) therebetween and being arranged to be urged apart along an axis (8) upon introduction of a fluid into the pressure space (4), the tensioner (1) having an internal bore (6) along the axis (8) having first and second ends along the axis and comprising a threaded component having an internally threaded portion (7) at the first end and coupled to the piston (3); the tensioner (1) further comprising: a threaded stud (10) having an exterior thread which engages the internally threaded portion (7) of the threaded component; and a drive mechanism (12) arranged to transmit rotational motion from the second end of the internal bore (9) to the threaded stud; the tensioner being arranged such that rotational motion applied to the drive mechanism (12) at the second end causes rotation of the stud (10) relative to the threaded component, with the engagement of the exterior thread of the stud (10) and the internal thread of the threaded component causing the stud to move along the axis as it rotates.

This invention relates to a hydraulic tensioner and a method of tensioning using such a tensioner.

Hydraulic tensioners are well known; we describe such a tensioner in our earlier United Kingdom Patent number GB2 457 138 B. They generally comprise a body and a piston, with a pressure space defined therebetween such that introduction of (e.g.) hydraulic fluid into the pressure space forces the piston and body apart. If the piston is coupled to the work piece to be tensioned (e.g. though a threaded stud), then this can be used to tension the work piece.

Many applications for hydraulic tensioners have limited space in which the tensioner can be used. In particular, height (that is, distance above the tensioner in the direction in which the tensioner pulls) can be limited significantly. Furthermore, for applications with limited access—for example, in the nacelle of wind turbines—it is often desired to take as few items as possible with a user making use of the tensioner. Previous attempts at solving this problem have generally used multiple components that must be assembled in the application space, which is undesirable.

Prior art single unit tools have generally involved a captive stud, but the length of the stud protruding from the tensioner in such a case has meant that such tensioners have been sufficiently long not be to acceptable in some applications.

As such, it would be desirable to provide a hydraulic tensioner with limited height requirements, and that required as few discrete items as possible.

According to a first aspect of the invention, there is provided a hydraulic tensioner, comprising:a base;a piston mounted for sliding motion relative to the base,the base and the piston defining a pressure space therebetween and being arranged to be urged apart along an axis upon introduction of a fluid into the pressure space, the tensioner having an internal bore along the axis having first and second ends along the axis and comprising a threaded component having an internally threaded portion at the first end and coupled to the piston;the tensioner further comprising:a threaded stud having an exterior thread which engages the internally threaded portion of the threaded component; anda drive mechanism arranged to transmit rotational motion from the second end of the internal bore to the threaded stud;the tensioner being arranged such that rotational motion applied to the drive mechanism at the second end causes rotation of the stud relative to the threaded component, with the engagement of the exterior thread of the stud and the internal thread of the threaded component causing the stud to move along the axis as it rotates.

This allows for a reduced-height tensioner that can be provided as a single unit, which is useful in confined spaces and in situations where it is desired to make use of the minimum number of units.

Typically, the internal bore will comprise a wider section having a larger diameter than the internally threaded portion. The drive mechanism can then comprise a sleeve member in the wider section passing from the second end to the internally threaded portion, with the sleeve being coupled to the stud so as to transmit rotation of the sleeve to the stud.

The drive mechanism may comprise a coupling between the sleeve and the stud arranged so as to permit movement of the stud relative to the sleeve along the axis but to fix the stud and the sleeve relative to each other rotationally. The coupling may be a splined coupling, comprising complementary splines on the sleeve (typically internally) and on a member fixed to the stud.

The drive mechanism may comprise a drive member at the second end, having an engagement means for being driven by a user, rotation of the engagement means causing rotation of the sleeve. Typically, the engagement means will comprise a protrusion or recess to engage with a tool by means of which the drive member can be rotated.

The piston may also be provided with location for a tool to rotate the piston. This will allow the piston to be rotated so as to close up any gap that might be present once the stud is fully engaged in the item to be tensioned.

The threaded component may be the piston, or a part thereof. Alternatively, the threaded component may comprise an insert received within and which bears against the piston. In a further alternative, the threaded component may comprise a reaction nut which is threaded onto the stud and which is received within a recess in the piston, or which bears against an end surface of the piston.

The stud may have a length measured along the axis, which may be at most the same as a length of the internal bore along the same axis. The stud may have a retracted position where it is entirely received within the internal bore. The stud may also have an extended position, when it extends from the internal bore. Typically, at least 50%, if not 80% of a length of the stud will extend from the internal bore in the extended position.

The base and the piston may define a second chamber therebetween, which may be provided with a connection for a gas (such as air). Whilst a fluid can fill the (main) pressure space in order to apply tension, the second chamber can be used to return the tensioner to its original position (i.e. zero stroke). The connection may comprise a one-way valve, which allows has (such as air) to enter the second chamber but not escape. This has been found to function as a spring (a so-called “air spring”).

According to a second aspect of the invention, there is provided a method of tensioning a work piece having a threaded bore, comprising:positioning the tensioner of the first aspect of the invention adjacent to the bore;using the drive mechanism to rotate the stud such that it extends from the tensioner and engages the threaded bore of the work piece; andintroducing fluid into the pressure space in order to force the base and piston apart, so as to apply tension to the work piece.

The method may also comprise the step of rotating the piston once the stud has engaged the threaded bore of the work piece, so that the tensioner abuts a surface of the work piece adjacent to the threaded bore of the work piece.

The work piece may comprise a plurality of threaded bores. The method may comprise providing a plurality of the threaded bores with tensioners in accordance with the first aspect of the invention. The method may also comprise providing those threaded bores which have not been provided with tensioners with threaded tension retaining members, such as bolts with heads, or threaded studs with nuts. The method may comprise retaining the tension applied to the workspace with the tension retaining members, for example by rotating the bolts or nuts such that the heads or nuts are adjacent to a surface of the workpiece.

The method may also comprise, after the tension has been applied, returning the piston to a zero stroke position by pressurising the second chamber with a gas, such as air. The method may then comprise rotating the piston so as to bring the tensioner closer to the work piece.

The method can further comprise using the drive mechanism to retract the stud from the workpiece, and then typically removing the tensioner from the work piece.

Typically, the work piece may comprise a shrink disc.

A hydraulic tensioner in accordance with a first embodiment of the invention is shown inFIGS.1and2of the accompanying drawings. The tensioner1comprises a body2and a piston3. The piston3can more relative to the body2, and there is a pressure space4defined between the piston3and the body2. The pressure space4is provided with a fluid connection5by means of which fluid—typically hydraulic fluid—can be introduced into the pressure space4. Doing so forces the piston3and body2apart along axis8, such that (as shown inFIGS.1and2), the piston3will move upwards relative to the body2.

A second pressure space15is formed between the body2and piston3, which is provided with a connection16for gas (e.g. air). As explained in our United Kingdom Patent GB 2 457 138B, this connection16is provided as a one-way valve, such that air is introduced into the space as the second pressure space15increases in size, but cannot escape when the second pressure space15decreases in size. As such, the second pressure space acts in a similar manner as a spring, tending to counteract the force generated by the introduction of hydraulic fluid into the (main) pressure space4. The force generated by the second pressure space15is significantly lower than that generated by the introduction of hydraulic fluid into the main pressure space4, but once that force is released, it tends to return the piston3to its original position relative to the body2(which is shown inFIGS.1and2).

The piston3is provided with an internal bore6having an internally threaded part7at a first, bottom end and a wider (in terms of diameter) part9at the second, top end, all coaxial with axis8. Within this bore6is provided a threaded stud10, the external thread of which engages the internal thread of the internally threaded part7of the internal bore6. The stud has a head11fixed to it.

Within the wider part9of the internal bore6, there is provided a cylindrical sleeve12. This is coupled to a drive member13at the top end, but runs the length of the wider portion9. The sleeve12is internally splined, the head11having complementary splines. The drive member13has a square recess14(quarter inch/0.635 cm) for attachment of a tool.

As such, rotation of the drive member13at the top end will cause rotation of the sleeve12. The internal splines of the sleeve12will cause the stud10to rotate. The threaded engagement of the stud10in the threaded portion7will then cause the stud10to move along the axis, from the retracted position shown inFIG.1where the stud10is entirely within the bore6, to the extended position shown inFIG.2where the stud10is largely extended out of the bore6. As the stud10moves along the axis8, the splined connection of the head11and the sleeve12allows linear motion of the head11and the stud10along the axis8, but does not allow the head11and the stud10to rotate relative to the sleeve12.

The operation of this tensioner in tensioning (in this example) a shrink disc can be demonstrated with reference toFIGS.3to12of the accompanying drawings, which sequentially show the tensioner's use.

InFIG.3, the tensioner1is brought to the work piece20(here, a shrink disc), which has a plurality of threaded bores21. As shown inFIG.4, the tensioner1is positioned so that the bottom face of the tensioner1is on the surface of the work piece, with the stud10over one of the threaded bores21. As can be seen, the work piece comprises an overhang22, so there is not a great deal of space available vertically over the threaded bores21. Typically, a tensioner1would be provided for every other threaded bore21; the remaining threaded bores would be provided with threaded nuts with hexagonal heads.

InFIG.5, a ratchet drive tool23has engaged recess14in drive member13. The tool23rotates the drive member13, which rotates sleeve12, which in turn rotates the head11fixed to stud10. This causes the stud10to rotate. Because the stud10is engaged with threaded portion7, the stud10is drive along axis8out of the bore6, as shown inFIG.6. The thread of the stud10engages that of the threaded bore21.

Once the stud10has reached its maximum travel, there will potentially be a gap of up to one pitch of the stud10thread between the tensioner1and the workpiece20. In order to close this up, the piston3is provided with drive holes17by means of which the piston3can be rotated. By inserting a tommy bar24into one of these holes17, the piston can be rotated so that any gap25is closed up as shown inFIG.7.

The pressure space4can then be filled with pressurised hydraulic fluid, so as to drive the piston3upwards with respect to body2. This has the effect of pulling the stud10up in the threaded bore21, thus tensioning the work piece20. The tensioner1can be pressurised so as to produce its maximum stroke, which is demonstrated by a thin red line (not shown) appearing at the top edge of the piston3.

When the appropriate loading is reached, the nuts (not shown) in the other threaded bores (not shown) would be run down so as to capture the tension created.

The hydraulic pressure in space4can then be released, and the air captured in second pressure space15will cause the piston3to retract back to its original position as shown inFIG.9. This will lift the tensioner1off the surface of the work piece20.

If there is now insufficient space between the overhang22to engage ratchet tool23, the tommy bar24can again be used in hole17to rotate the tensioner1so that it is flush against the surface of work piece20, as shown inFIG.10.

The ratchet tool23can then be reintroduce into drive member13as shown inFIG.11, and used to drive the stud in the opposite direction as previously, in order to retract the stud10from threaded bore21, as shown inFIG.11.

Once stud10is retracted as shown inFIG.12, the tensioner1can be removed from workpiece20. The work piece20has been tensioned; the nuts can be tightened with a torque wrench if desired.

Thus, a single unit tensioner that has limited height requirements is provided.

A second embodiment of the invention is shown inFIG.13of the accompanying drawings; equivalent features to those of the first embodiment have been given corresponding reference numerals, raised by 50.

In this embodiment, the threaded portion57is formed in an insert80separate from the piston53. This insert80is a sliding fit within the piston53and has a flange81at the second end which bears against the piston53. Thus, as the piston53is forced apart from the body52, the piston will react against the flange81, transmitting force from the piston53through the insert80to the threaded stud60. The internal bore56is therefore formed within the insert80, which then contains the sleeve62. This embodiment otherwise functions as described above with respect to the first embodiment of the invention.

A third embodiment of the invention can be seen inFIG.14of the invention equivalent features to those of the first embodiment have been given corresponding reference numerals, raised by 100.

In this embodiment, rather than the piston or an insert carrying the internally threaded portion, this is carried on a reaction nut120. The internal bore106is within the piston103once more, and has a tapered recess121for the reaction nut120. As such, when the piston is urged upwards (as shown inFIG.14) by the introduction of hydraulic pressure, the piston will force reaction nut120upwards. Reaction nut120is threaded onto the stud110, so as to have the force from piston103transferred to it by the reaction nut120. A separate load retaining nut123is provided, which can be run down the stud110once load has been applied to it.

Again, the third embodiment otherwise functions as the first embodiment, with the sleeve112working within the internal bore106in the piston103.

A fourth embodiment of the invention can be seen inFIG.14of the invention equivalent features to those of the first embodiment have been given corresponding reference numerals, raised by 150.

In this embodiment, the piston153again provides the internally threaded portion157and is threaded onto stud160. However, the internal bore156is formed in multiple components: the piston153and a floating member170. The sleeve162therefore sits within these two components. This is advantageous because it results in less wear on the pressure seals171and less effort for the operator as they only need to rotate the piston153against one set of seals171rather than against 3 or 4 as in the first embodiment.

Otherwise, this embodiment functions as described in the first embodiment.