The invention relates to a hydraulic coupling assembly of the type comprising an annular working chamber, one wall of which is expandable in response to pressurization of the hydraulic fluid in-the chamber, whereby to engage a conform surface on a.machine element which is to be coupled to the assembly.

Devices have been known for a long while for connecting to¬ gether two machine parts formed with rotationally generated surfaces shaped alike, said surfaces being coaxial at the coupling, and, by utilizing hydraulic pressure, said devices bring about expansion of one of the rotationally generated surfaces to give coupling contact with the other one. Examples on such known devices are revealed in U.S.. Patent 4,093,052 and French Patent 1,092,416. The hydraulic systems used up to now for this _. purpose contain an annular working chamber arranged in side one of the rotationally generated surfaces, said chamber having a wall thickness towards the coupling surface ^' such that this wall, when the specific pressure on the hydraulic medium enclosed in the chamber is increased, elastically expands to give the desired coupling connection. The working chamber in the known devices has been uniformly thick, with relatively large space (in order of millimeters) between its coaxial inner defining surfaces in relation to the space or clearance (some hundre hs of a millimeter) between the rotationally generated surfaces which are to be coupled together. Such a construction has in many cases been found to give unsatisfactory mechanical stability to the device, e.g. in the cases where the load on the expanding wall varies along the longitudinal direct¬ ion thereof.

in object of the invention is therefore to provide an assembly of the above-mentioned type having enhanced mech¬ anical stability against radical dynamic loads.

In his attempts to improve the stability of such hydraulic couplings, and thereby expand the area of heir use, the inventor has started from the known fact that the thin ^• lubricating oil ^' filling between a journal and the bearing surface in a plain bearing has strength properties which give this bearing the high mechanical stability. Against this background, the working chamber in a hydraulic coupl¬ ing, for achieving great mechanical stability,should be given the same gap width or spacing between its rotational generated inner ^' surfaces as the clearance between shaft an bearing surface in a plain bearing. It is, however, obviou that such a construction must bring with it great difficul ies, especially with regard to complete filling the hydrau ic medium, and to the desired rapid and uniform propagatio of pressure variations through the whole of the enclosed mass of hydraulic medium, e.g. when coupling and uncouplin machine parts by means of the hydraulic device.

The invention is defined in the appended claims, and com¬ prises, broadly speaking, two substantial features, namely that the chamber width, in the pressurized state of the chamber, is of the same order as the gap in a correspondin plain bearing wherein the hydraulic fluid would be used as lubricant. Said width is preferably less than about 0.3 mm. Formally the width should be about 0.1 mm or less and pre- ferably be about 0.05 mm or less. By prescribing such a dimensioning for the chamber width, the approach between opposed surfaces in the chamber is retarded due to i.a. squeezing effects in the intermediate oil film. However, with such narrow gap or small width between the chamber su faces it would be very difficult or at least time consumin to propagate the oil and pressure throughout the chamber a pressurization thereof. To overcome that problem the inven tion also prescribes that the working chamber should be regularly divided into zones with alte natingly very small and relatively large distances between the coaxial walls o

the chamber, so that when filled by hydraulic ^* medium, it forms an intermediate body of oil or lubricant consisting of one or a series of thin films kept together by thicker bands. Such thicker bands provide for the propagating of the oil film into the narrow gaps and the pressure through¬ out the chamber.

As far as structure is .concerned, the invention signifies that one of the coaxial inner walls of the working chamber is provided with uniformly distributed ridges or flanges with a height such.that their crests, the surfaces of which are formed alike with the opposing working chamber wall will be situated at only clearance spacing from said wall. Such clearance spacing relates to the pressurized state of the chamber when the expandable wall thereof fully, engages the machine element to be coupled. In the non-pressurized state of the chamber, the gap or clearance between the crest sur¬ faces and the opposing working chamber wall could well be zero. The ^" grooves between the ridges or flanges will simul¬ taneously be channels for facilitating filling hydraulic medium to form a simple cohesive mass or body, and enabling relatively rapid evening-out of pressure variations.

The ridges or flanges can be axial, circular or helical, with one or more threads along the length. Said threads can be the most suitable from the point of view of manufacture. If the flanges are circular, the intermediate spaces between them should be interconnected by channels for facilitating the filling of hydraulic medium.

The invention will be described in more detail in the following while referring to the attached drawings.

The drawings illustrate in section a pair of embodiments with the helical inner walls for the working chamber.

Figure 1 illustrates a first embodiment applied to the clamping up of a plurality of tools on a common shaft, e.g. circular sawblades provided with bushings. Figure 2 shows an embodiment applied to a tool chuck for clamping a mill- ing cutter.

In figure 1 there is a shaft, denoted by the numeral 1, in the surface of which the working chamber in the hydraulic system has been formed* as a helical groove 2, at one end connected to the pressure side of a piston 4 in a pressure cylinder 5, via a canal 3, and at the other end to a closable filling nipple for hydraulic medium via a canal 6. The outer wall of the working chamber consists, in the illustrated embodiment, of a sleeve 9 drawn over the ^* helica flange 8 with clearance 7 a-nd welded _. (10) to the shaft 1, said flange defining the groove 2. Circular sawblades mount ed on the sleeve 9 are denoted by 11, said sawblades being coupled to the sleeve 9 by the radial expansion of the latter when the pressure of the hydraulic medium is increas by pressing in the pressure piston 4.

In figure 2, the numeral 1 denotes a wall in the working chamber in the hydraulic system, the surface of said wall being formed as a helical groove 2, one end of the groove being connected to the pressure side of a piston 4 in a pressure system 5 via a canal 3. In the embodiment shown the outer wall 9 of the working chamber is welded to the wall 1 at the places denoted by 10, as in figure 1, and is also welded to the remaining portion of the chuck at the places which are denoted by 12. The canal 3, and the pressure cylinder are formed in the outer wall 9 of the working chamber, in which a thread 13 is also,made, for taking the pressure piston 4 in and out of the pressure cylinder by turning the sleeve 14.

In figure 2, the numeral 11 denotes the end of the milling cutter which the hydraulic device is intended to clamp.

In the two embodiments shown, the clearance ^" 7 is preferably zero in the nonrpressurized state of the device. In the pressurized state of the device, when the expandable wall engages the machine element to be coupled, said clearance should be less than about 0.3 mm. Normally the clearance should however be about 0.1 mm or less,- and _^ preferably be in the order of 0.05 mm or- less.

The dimensions of the surfaces delimited by the grooves should be as large as possible. The surface dimensions are then deterinined by the time required to provide a full oil and pressure propagation throughout the chamber. Said time should preferably be less than a few seconds.

In the tested embodiments of the invention, the groove system is in the shape of a helical groove, the hydraulic medium consists of multi purpose grease and the clearance is about 0.05 mm in the area of engagement between the expandable chamber wall and the coupled machine element, in the pressurized state of the working chamber.