It is well known that in some applications it is advantageous to aim at attaining such a pretensioning state in the shank part of the bolt structure when installing the bolt structure, that the nut functioning as an abutment piece can be screwed onto the shank part freely without generating a tensile stress state that produces tightening force in the shank part. In the state of art, for which reference is made to publications CH-552,448, US-5398574 and WO-96/02363, this pretensioning state is produced by means of a tool separate from the bolt structure, which is fixed to the shank part in connection with the fitting of an abutment piece, by means of which tool a temporary strain state is generated in the shank part. On the other hand, there are known bolt structure solutions in which a heating resistance is placed inside the shank part, which heating resistance is heated in connection with the fitting of the abutment piece, wherein the heating of the shank part causes a temporary strain state in the shank part.

When the effect caused by the separate tool or heating resistance is removed, the shank part is restored into its original length and a predetermined tightening force is generated in the bolt structure.

Solutions of prior art can also be used in the opening of screw couplings attained by means of a bolt structure.

There are, however, many problems related to the applying of prior art.

It is often difficult and tedious to fix a separate tool in the shank part that changes the length of the shank part, and it is not even possible to use the tool in all targets, especially due to the lack of space at the point of location of the bolt structure. On the other hand, it is not

possible to use heating resistances in all targets because of the temperature requirements set by environment in which the installation takes place. Furthermore, the use of a heating resistance increases work safety risks especially when the abutment piece is fitted manually.

It is an aim of the present invention to eliminate the above-presented problems related to the act of applying prior art to a large extent, thus improving the state of the art prevailing in the field. To attain these purposes, the bolt structure according to the invention is primarily characterized in that at least the stationary, second abutment piece comprises a pressurized medium chamber in which the second end of the shank part is placed to adjust the longitudinal force effect exerted on the shank part and acting between the shank part and the second abutment piece.

By means of the above-presented solution it is possible in a simple and rapid manner, by coupling the pressurized medium chamber with a coupling means, for example with a quick-action connector, through pressurized medium circuitry to a pressurized medium source without a separate tool, to attain such a pretensioning state in the shank part which is necessary when installing or dismounting said bolt structure for example manually. Because it not necessary to bring other equipment except the small-sized coupling means to the location where the bolt structure will be positioned, the bolt structure according to the invention can also be placed in very narrow spaces. The change in the length of the shank part can be easily adjusted, and thus the bolt structure enables an accurate tightening force. The pressurized medium chamber and the moving structural parts in connection with the same can be protected effectively, and the bolt structure can be easily maintained.

The other dependent claims present some preferred embodiments of the bolt structure according to the invention.

The invention will be illustrated in more detail in the description hereinbelow, in which reference is made to the embodiments shown in the appended drawings. In the drawings, Figs 1 to 3 show three embodiments of the bolt structure in longitudinal cross-sections of the

shank part, Fig. 4 shows substantially an embodiment of the bolt structure according to Fig. 1 in an installation situation in the longitudinal cross-section of the shank part as well, and Fig. 5 shows an advantageous embodiment with respect to the detachment of the bolt structure.

The bolt structure shown in Figs 1 to 3 comprises a substantially cylindrical elongated shank part 1, whose first end 1 a contains a fastening means 2, such as a threading on the outer surface of the shank part 1 in the longitudinal direction of the same, for fastening to the bolt structure a first abutment piece 3, such as a nut equipped with an internal threading which abutment piece is fastened in a releasable manner to the bolt structure when the bolt structure is taken in use. The bolt structure also includes a stationary second abutment piece 4 in connection with the second end 1b of the shank part 1, said second abutment piece comprising a pressurized medium chamber PVT to which the second end 1b of the shank part 1 is placed, to adjust the longitudinal force effect exerted on the shank part, and effective between the shank part 1 and the second abutment piece 4. In the embodiments according to Figs 1 and 2, the pressurized medium supplied to the pressurized medium chamber PVT generates a temporary reversible change in the length of the shank part 1, and in the embodiment according to Fig. 3, a corresponding pressurized medium supplied to the pressurized medium chamber PVT generates a shift in the shank part with respect to the second abutment piece 4 in the longitudinal direction of the bolt structure. In both ways, i. e. by means of the change in length (Figs 1 and 2) and by means of the shift (Fig. 3) it is possible to attain an increase in the distance between the fastening means 2 and the second abutment piece 4 at the installation stage of the bolt structure, wherein the first abutment piece 3 can be easily placed in connection with the fastening means 2 without generating a tightening force at the installation stage. When said change in length or shift is reversed when the pressure prevailing in the pressurized medium chamber PVT and producing the change in length or shift is removed, the desired tightening force producing a tensile stress in the shank part 1 is attained, said tightening force being exerted on a machine element between the first 3 and the second abutment piece 4.

The pressurized medium chamber PVT is formed in such a manner that a housing 5, or the like, having the form of a circular cylinder, is formed inside the stationary second abutment piece 4. On the second end 1 b of the shank part 1, there is a flange 8 located in the housing 5 and sealed with an O-ring seal 22 with respect to the axial inner surface 5a of the housing 5, said flange protruding from the outer surface of the shank part 1 in the radial direction. Thus, the face 8a of the flange 8 that is substantially perpendicular to the longitudinal direction of the shank part 1, is directed towards the second end 1 b of the shank part 1 and is equipped with an opening recess 7, forms a part of the inner surface of the pressurized medium chamber PVT, which is otherwise defined according to the volume of the pressurized medium chamber PVT by the first radial end surface 5b of the housing 5 (no pressure in the pressurized medium chamber PVT) or by the inner surface 5a and the first radial end surface 5b together (pressure prevailing in the pressurized medium chamber PVT).

In the embodiments of Figs 1 to 3, the stationary second abutment piece 4 is composed of a cup-shaped part 9 especially to form the housing 5, wherein the open end 10 of the cup-shaped part 9 is directed towards the first end 1a of the shank part 1. Thus, the housing 5 is formed in the space defined by the cup-shaped part 9 closed by means of a cover part 11 at the location of the open end 10. At the location of the open end 10 of the cup-shaped part 9, on the inner surface of the cup-shaped part 9 (on the surface joining to the axial inner surface 5a of the housing 5) there are fastening means, preferably a threading 9a to fasten the cover part 11 by means of a threading 11 a located on the outer edge of the substantially plate-like cover part 11.

In the embodiments according to Figs 1 and 3, the housing 5 is also provided with spring members 6 effective between the housing 5 and the second end 1b of the shank part 1 to produce a force effect in the longitudinal direction of the shank part 1 between the shank part 1 and the abutment piece 4. The spring members 6 are preferably a set of ring-like flat springs, which are positioned around the shank part 1 according to Figs 1 and 3.

According to Figs 1 and 3, the pressurized medium chamber PVT and the spring members 6 are positioned on the opposite sides of the flange 8. Thus, the pressurized medium chamber PVT is formed in connection with the housing 5 between the first face 8a (the surface directed towards the second end 1 b of the shank part) of the flange 8 protruding from the outer surface of the shank part 1 substantially perpendicularly to the longitudinal direction of the shank part 1 and the first radial end surface 5b (the inner surface of the bottom of the cup- shaped part 9) of the housing 5, the surface extending substantially perpendicularly to the longitudinal direction of the shank part 1. The spring members 6 or the like are, in turn, placed in connection with the housing 5 between the second face 8b (the surface directed towards the first end 1a of the shank part 1) of the flange 8 protruding from the outer surface of the shank part 1 substantially perpendicularly to the longitudinal direction of the shank part 1, and the second radial end surface 5c (the inner surface of the cover part 11) of the housing 5, the surface extending substantially perpendicularly to the longitudinal direction of the shank part 1.

To attain the necessary transfer connection for the pressurized medium, the second stationary abutment piece 4 and/or the shank part 1 contain a channel arrangement 12 and 13 passing through the wall of the bolt structure (either the shank part 1 and/or the cup-shaped part 9) at the respective location. The channel arrangement transfers the pressurized medium to the pressurized medium chamber PVT, and the outlets of the channel arrangement 12 and 13 contain in the outer wall of the bolt structure a suitable connector arrangement 14 and 15 that can be closed and opened, to quick-couple the pressurized medium duct to the respective channel 12 or 13 in the channel arrangement. In the embodiments according to Figs 1 to 3, to attain the transfer connection of the pressurized medium to the pressurized medium chamber PVT, there are two alternative channels 12 and 13 that can also be used simultaneously, the first of the channels being an axial channel 12 arranged in the shank part 1 and extending through the same centrally between the first 1 a and the second 1 b end of the shank part 1, and the second channel 13 being formed in such a manner that it extends through the wall of the abutment piece 4 i. e. the cup-shaped

part 9, in the presented embodiments the bottom of the cup-shaped part 9 centrally.

In the embodiments according to Figs 1 and 2, in which the pressurized medium supplied to the pressurized medium chamber PVT brings about a temporary change in the length of the shank part 1, the shank part 1 contains substantially two parts comprising a sleeve part 16 or the like and a rod 17 or the like as its main parts. Thus, a sleeve part 16 or the like, that is stationary with respect to the second stationary abutment piece 4 and forms the outer surface part of the shank part 1, is fixed to the end of the second stationary abutment piece 4 (i. e. to the outer surface of the cover part 11), which extends substantially in radial direction and faces the first end 1a of the shank part 1. In the case of Figs 1 and 2, the cover part 11 is integrated in the same piece with the sleeve part 16, thus forming the flange-like projecting part of the sleeve part. Inside the sleeve part 16 or the like, in the inner hole of the same, a rod 17 or the like is arranged by sliding fit, which rod forms the inner part of the shank part 1 and is connected to the housing 5 (pressurized medium chamber PVT). The above-mentioned flange 8 located in the pressurized medium chamber PVT and protruding from the outer surface of the shank part 1 is fixed to the corresponding end of the rod 17. The rod, in turn, is substantially in the area of the first end 1a of the shank part 1 connected to the first end 16a of the sleeve part 16 or the like in a manner transmitting longitudinal force of the shank part 1 thereto. In Figs 1 and 2 the inner surface of the sleeve part 16 is threaded in the first end 16a of the sleeve part 16 or the like, and the threading is provided with (point 17b) an adjustment member located in the inner hole of the sleeve part 16, such as a sleeve nut 19 whose face 19a directed towards the second end 1b of the shank part 1 is connected to a ring shoulder 17a formed to the end of the rod 17 or the like, to transmit longitudinal force of the shank part 1. In the area directed towards the opposite end 1 b from this point, the end of the rod 17 is connected to the inner threading (point 17c) of the end 16a of the sleeve part. Thus, the rod 17 can transmit force in its longitudinal direction to the end 16a of the sleeve part 16 in both directions. When the position of the sleeve nut 19 is changed, the desired pretensioning tensile stress is obtained in the sleeve part 16. The sleeve part 16 or the like is attached to a ring flange forming the cover part 11 of the

housing 5 and protruding in the radial direction from the second end 16b of the sleeve part 16, said ring flange being attached to the location of the open end 10 of the cup-shaped part 9 in a manner described above, preferably by means of a threaded coupling.

When the pressure of the pressurized medium chamber PVT is increased via the channels 12 and/or 13 by means of a pressurized medium effect exerted on the pressurized medium chamber PVT, the rod 17 or the like moves upwards in the embodiments according to Figs 1 and 2, wherein a reversible change in length is generated in the sleeve part 16 or the like. In the embodiment according to Fig. 1, the spring members 6 are used in connection with the housing 5, and in the embodiment according to Fig. 2 said spring members are not used in the housing 5, but in both cases the pressurized medium causes a reversible increase in length in the sleeve part 16 or the like, produced by the movement of the rod 17 or the like. When the spring members 6 are used, the rod 17 (Fig. 1) or the integral shank part 1 (Fig. 3) participates in the generation of tensioning force in a tightened coupling when it transmits the spring force produced by the spring members 6 to the other side of the coupling (to the first end 1 a of the shank part) In the embodiments according to Figs 1 and 2 it is obvious that the axial central first channel 12 extending through the shank part 1, between the first 1 a and second 1 b end of the shank part 1 composed of two parts (16,17), is formed in connection with the rod 17 or the like, and that the fastening means 2 on the first end 1 a of the shank part 1, such as the threading in the longitudinal direction of the shank part 1, in the outer surface of the same, is formed on the outer surface of the sleeve part 16.

In the embodiment according to Fig. 3, the shank part 1 composed of one integral piece is arranged to extend through the end surface of the second, stationary abutment piece 4, which extends substantially in the radial direction and faces the first end 1 a of the shank part 1. The entire shank part 1 moves with respect to the stationary, second abutment piece 4 (upwards in Fig. 3 when the stationary abutment piece 4 is fixed for example according to Fig. 4) when the pressure of the pressurized medium chamber PVT is increased by means of a

pressurized medium effect exerted on the pressurized medium chamber PVT, wherein the spring members 6 are compressed and return the shank part 1 and the abutment piece 4 to their mutual position according to Fig. 3, when the effect of the pressurized medium is removed. The end of the abutment piece 4 on the side of the first end 1a is formed of a separate cover part 11, which is fixed to the cup- shaped part 9 immovable in the longitudinal direction of the shank part.

The plate part forming the cover part 11 is provided with a central hole 20 or the like, through which the shank part 1 is guided to the housing 5. The cover part 11 is fixed to the location of the open end of the cup- shaped part 9 by means of a threaded coupling 9a, 11 a.

As shown in Fig. 4 (the bolt structure corresponds substantially to the embodiment of Fig. 1), the bolt structure can be fixed to the base A by means of fastening means 21 formed in connection with the second stationary abutment piece 4. The fastening means 21 for fixing the bolt structure to the base A are formed on the cylindrical outer surface of the cup-shaped part 9, extending in the axial direction of the shank part 1, advantageously as a screw thread, wherein the base A comprises a recess equipped with a corresponding threading. The pressurized medium is conveyed to the pressurized medium chamber PVT by means of the channel 12.

Fig. 5 shows a preferred embodiment in view of opening the coupling, and corresponding parts are marked with the same reference numerals as above. Here, the abutment piece 4 is formed as a cylindrical structure of such a length that the entire shank part 1 can be pulled into the pressurized medium chamber PVT when the coupling is detached, wherein the connectable part B can be moved away in the direction of the joint surface C without having to release the abutment piece 4 from its mounting base A. The condition is that the free travel length of the flange 8 functioning as a piston to the opposite direction (D1) is at least equally large as the distance (D2) of the outer free end of the shank part 1 from the joint surface C. The drawing also shows how the flange on the second end 16b of the sleeve part 16 can be located entirely inside the abutment piece 4, against the inner surface of that end wall of the abutment piece that faces the first end, thus forming the end surface of the housing 5.