Technical Field

The present document relates to a hydraulic clamping device, to a system comprising such a clamping device and to a method of connecting a hub to a shaft.

Background

Hydraulic friction couplings, or hydraulic clamping devices, are known from e.g. US 3,747,445 and WO 9832562 A1 . They are used to provide a mechanical connection between two machine parts, which can generally be referred to as a shaft and a hub, the connection allowing power and/or torque to be transmitted between the shaft and the hub.

The terms "hub" and "shaft", as used herein, should be understood as schematic terms, i.e. they shall be deemed to apply to any type of structures that are attached to each other by introduction of a shaft into a recess and preventing relative rotation of the shaft and recess.

Shaft-and-hub joints are used for industrial purposes in various applications, for example in mechanical engineering, as tool holders (chucks) in machine tools, and as safety locks in hydraulic and pneumatic cylinders. Joints of this type often have to meet exacting requirements regarding precision, consecutive working properties and safety, while at the same time satisfying demands for a good overall economy, sufficient compactness and rapid assembly.

Hydraulic clamping devices usually comprise an inner sleeve for frictional locking to a shaft surrounded by the inner sleeve, and an outer sleeve for frictional locking to a hub. One type of known friction couplings comprises a pressure chamber, which by means of contact surfaces bearing against the sleeves transmits a force to said sleeves. By making the sleeves from an expandable material it is possible, using the pressure in the pressure chamber, to control a deformation of the sleeves to obtain frictional locking to a machine part which surrounds the sleeves or is housed in the sleeves, such as a hub or a shaft.

While there are many different types of hydraulic clamping devices, there remain applications where hydraulic clamping devices presently cannot be used, e.g. since they take up too much space. It would be desirable to be able to integrate the hydraulic clamping device into the device which it is to operate in or on. However, hydraulic clamping devices present challenges in terms of selection of materials and in terms of tolerances, which cannot always be combined with the production technology that is used to form the rest of the product.

Hence, there is a need for a hydraulic clamping device which may be readily integrated with the device which it is to operate in or on.

Summary

It is an object of the present disclosure to provide a hydraulic clamping device which can be readily integrated with a shaft axle that it is to operate on to provide a connection to a hub.

The invention is defined by the appended independent claims, with embodiments being set forth in the dependent claims, in the following description and in the drawings.

According to a first aspect, there is provided a hydraulic clamping device, comprising a rigid core, a radially deformable sleeve, which envelops the core, such that a pressure chamber is formed between the core and the sleeve, and means for pressurizing the pressure chamber. The pressurization means is arranged in the core, and thus enveloped by the sleeve, such that the clamping device generally exhibits the form of a cylinder.

The terms "hub" and "shaft", as used herein, should be understood as schematic terms, i.e. they shall be deemed to apply to any type of structures that are attached to each other by introduction of a shaft into a recess and preventing relative rotation of the shaft and recess.

The core may be substantially cylindrical. The sleeve may also be substantially cylindrical. The term "rigid" should be understood as a relative term, i.e. the core does not deform radially to any significant extent. In particular, the core may be solid, but for any pressurization means received therein.

Such a clamping device may be arranged inside a hollow body and when activated, cause the hollow body to expand, such that a hub which is arranged on the hollow body will be frictionally engaged to the hollow body. Such a hollow body should preferably have a shape which fits snugly with the clamping device. The fit may be a press fit, i.e. with a negative play, an exact fit, with substantially a zero play, or a fit with some, but not too great, play.

The pressurization means may comprise an activation device, which is accessible at an axial surface of the clamping device.

The pressurization means may comprise a fluid chamber holding an amount of fluid and a pressurization piston, which is movable so as to force the fluid into the pressure chamber.

In the alternative, the pressurization means may comprise a valve, such as a non-return valve, for connection to a pressurization and/or depressurization device.

The sleeve may be connected to the core by a weld or solder, wherein the weld or solder preferably may be provided in a substantially annular area.

The clamping device may comprise a substantially annular area presenting a smaller outer diameter than an area radially outside the pressure chamber.

A sealing device in the form of a separate component may be provided between the sleeve and the core.

The core and the sleeve may be made of different materials.

The sleeve may be made from a material having a lower modulus of elasticity than steel, preferably lower than 150 GPa, such as a polymeric material or a polymer composite material.

The core may be made from a metallic material.

Alternatively, the core may be made from a non-metallic materials, such as plastic material.

The clamping device may further comprise a channel connecting opposite axial sides of the clamping device. According to a second aspect there is provided a system comprising a shaft, adapted for transferring a torque, a hub, which is connectable to the shaft, and a clamping device as described above. The shaft presents a hub receiving portion having an outer diameter adapted for receiving the hub, wherein the hub receiving portion presents an axially open substantially cylindrical recess. The recess presents an inner diameter and axial length, which are adapted such that the clamping device fits therein, and

the hub receiving portion is radially deformable upon pressurization of the clamping device, such that the hub is frictionally connected to the shaft.

According to a third aspect there is provided a system comprising a rigid core, a shaft having a portion presenting a hollow space adapted such that the rigid core fits therein such that a pressure chamber is formed between the rigid core and a wall of the hollow space, a sealing device in the form of a separate component provided between the wall and the core to seal the pressure chamber, means for pressurizing the pressure chamber, the means being arranged in the core and thus enveloped by the wall, wherein the wall is radially deformable upon pressurization of the pressure chamber.

The hollow space may be axially open and have the form of a sleeve, which may be formed in one piece with and/or otherwise integrated with the shaft. A thickness of the sleeve walls may be selected so as to be thin enough to allow sufficient deformation, while being thick enough to enable transfer of torque and axial forces from the hub to the shaft.

According to a fourth aspect there is provided a method for connecting a shaft to a hub, comprising providing a shaft having an axially open, substantially cylindrical recess, arranging a clamping device having a radially deformable outer sleeve in said recess, arranging the hub on the shaft, and causing the outer sleeve to expand such that a wall of the recess expands whereby the hub is frictionally connected to the shaft.

According to a fifth aspect, there is provided a method of connecting a shaft to a hub, comprising providing a shaft having an axially open, substantially cylindrical recess, arranging a rigid core enclosing pressurization means in the recess, such that a pressure chamber is formed between the rigid core and a wall of the cylindrical recess, providing a sealing device in the form of a separate component between the wall and the core to seal the pressure chamber, and pressurizing the pressure chamber. The wall is radially deformed such that the hub is frictionally connected to the shaft. Brief Description of the Drawings

Fig. 1 is a schematic exploded view of a shaft-hub system including a clamping device according to a first embodiment.

Fig. 2a is a perspective view of the clamping device of the first embodiment obliquely from a first axial surface.

Fig. 2b is a perspective view of the clamping device of the first embodiment obliquely from a second axial surface.

Fig. 2c shows the clamping device of the first embodiment straight from the first axial surface.

Fig. 2d is a cross-sectional side view of the clamping device of the first embodiment.

Fig. 2e is an enlargement of an encircled portion of Fig. 2d.

Fig. 3a shows the shaft-hub system of Fig. 1 straight from a first axial surface.

Fig. 3b is a cross-sectional side view of the shaft-hub system of Fig. 1 . Fig. 3c is an enlargement of an encircled portion of Fig. 3b.

Fig. 4 is a schematic exploded view of a shaft-hub system including a clamping device according to a second embodiment

Fig. 5a is a perspective view of the clamping device of the second embodiment obliquely from a first axial surface.

Fig. 5b is a perspective view of the clamping device of the second embodiment obliquely from a second axial surface.

Fig. 5c shows the clamping device of the second embodiment straight from the first axial surface.

Fig. 5d is a cross-sectional side view of the clamping device of the second embodiment.

Fig. 6a shows the shaft-hub system of Fig. 4 straight from a first axial surface.

Fig. 6b is a cross-sectional side view of the shaft-hub system of Fig. 4. Fig. 6c is an enlargement of an encircled portion of Fig. 6b.

Fig. 7a is a cross-sectional side view of a system comprising a shaft and a rigid core comprising pressurization means.

Fig. 7b shows the system of Fig. 7a straight from a first axial surface. Fig. 7c is an enlargement of an encircled portion of Fig. 7a.

Detailed Description

In Fig. 1 is shown a schematic exploded view of a shaft-hub system 1 . The system 1 comprises a shaft 2, a hub 3 and a hydraulic clamping device 4 of a first embodiment. The shaft 2 may comprise a substantially cylindrical hollow portion and shaft portion 5, which may present an arbitrary length and which may be adapted to be releasably or fixedly mounted, with a first axial end thereof, in for example a rotary machine tool (not shown), for instance in a lathe machine, a milling machine, a drilling machine etc.

The shaft 2 has a hub receiving portion 6, an axially open substantially cylindrical recess, having an outer diameter adapted for receiving the hub 3, which hub 3 may be one or more working tools or work pieces which are releasably secured on the shaft 2. The cylindrical recess 6 extends in the axial direction of the shaft 2 from a second axial end 7 towards the shaft portion 5. The outer diameter of the shaft 2 in the recessed area may be 85- 99%, 90-99% or 95-99% of the outer diameter of the shaft 2 in a neighboring, in the axial direction, non-recessed area 8.

At the second axial end 7 of the shaft there is provided an opening into the hollow space of the shaft 2, through which opening the clamping device 4 may be inserted. The cylindrical recess 6 of the shaft 2 has an inner diameter and axial length, which are adapted such that the clamping device 4 fits therein. The wall thickness of the shaft 2 at the cylindrical recess may vary between different applications but is typically between 1 -5 mm, 1 -4 mm, 1 -3 mm or 1 -2 mm. A play between the clamping device 4 and the shaft 2 may be -0.1 -0.1 mm, preferably 0-0.1 or 0.01 -0.05 mm.

The clamping device 4, a hydraulic clamping device, is shown from different views in Figs 2a-2e. The clamping device 4 comprises a rigid core 10, which may be substantially cylindrical, see the cross-sectional side view of the clamping device in Fig. 2d. A radially deformable outer sleeve 1 1 , which also may be substantially cylindrical, envelops the core 10. A

circumferential, substantially annular pressure chamber 12 is formed between the core 10 and the outer sleeve 1 1 . The pressure chamber 12 may be filled with a pressure medium, which may be a hydraulic pressure medium. Upon pressurization of the pressure medium, the outer sleeve 1 1 of the clamping device 4 expands radially outwards. When a clamping device 4 is arranged in the hollow body of a shaft 2, as shown in Figs 3a-3c, and activated, i.e. by being pressurized, its outer sleeve 1 1 expands radially outwards against the inner surface of the cylindrical recess 6 of the shaft 2, causing the shaft 2 to expand radially outwards, such that a hub 3 arranged on the hub receiving portion 6 of the shaft 2 will be frictionally engaged/connected to the outer surface of the recess 6 of the shaft 2, preventing relative rotation between the shaft 2 and the hub 3.

Pressurization means used for pressurizing the pressure chamber 12 are arranged in the core 10 of the clamping device 4 (see Figs 2d and 3b), and thus enveloped by the outer sleeve 1 1 , such that the clamping device 4 generally exhibits the form of a cylinder. The pressurization means may include a displaceable pressurization piston 1 6 arranged to force a fluid, pressure medium, into the pressure chamber 12. The piston 1 6 may be threaded into the cylinder wherein it is displaceable. The pressurization means may also comprise a fluid chamber 19 holding an amount of fluid and when moving the pressurization piston 1 6, the fluid is forced into the pressure chamber 12.

In the alternative, the pressurization means may comprise a valve through which an external pressurization/depressurization device can be connected (not shown).

The clamping device 4 may also comprise a filling port (not shown) for pressure medium, which may be accessible from either of the axial surfaces of the clamping device 4.

The pressurization means comprises an activation device 17, which is accessible at a first axial surface 18 of the clamping device 4 (Figs 2a, 2c, 3a). The activation device 17 may connect to an axial bore which, at the inner end thereof, has one or more cross channels 20 opening into the pressure chamber 12 (Figs 2d, 3b). In the axial bore is the displaceable piston 1 6 defining the fluid chamber 19, which is filled with the pressure medium. The activation device 17 may comprise pushing means which co-operates with inner threads of the bore. The pushing means may have an inner connection bore for a wrench or similar, for instance a hexagonal wrench of T-handle type. Upon activation with the activation device 17, the pushing means and thereby also the pressurization piston 16 may be tightened by means of the wrench and pressure medium is forced from the fluid chamber 19, through the cross channel 20 and into the all around extending pressure chamber 12 thereby providing a radial expansion of the outer sleeve 1 1 .

Upon deactivation of the activation device 17, when untightening the pushing means, the outer sleeve 1 1 of the clamping device 4 regains its non- expanded shape, the shaft 2 regains its non-expanded shape and the hub 3 becomes released.

The core 10 of the clamping device 4 does not deform radially to any significant extent. The core 10 may thus be seen as solid, but for the pressurization means.

The clamping device 4 may comprise a channel 30 connecting opposite axial sides of the clamping device, see e.g. Fig. 2 and 2b. The channel facilitates fitting of the clamping device 4 into the shaft 3, as air may escape through the channel 30.

With the shaft-hub system 1 discussed above most of the load flow is provided on the shaft 2 and almost no load flow is provided on the clamping device 4 due to the integration of the clamping device 4 into the shaft 2. With known prior art solutions, where the clamping device is not integrated into the shaft, a major part of the load flow is provided on the clamping device itself. Hence, the clamping device itself will be subjected to less shear and tensional forces.

Hence, with the present clamping device 4 it is possible to use a material for the core 10 which has a lower hardness and yield point than the core material used in prior art clamping devices, as low or no load flow is provided on the clamping device 4 itself. One example of such a core material is unhardened steel, e.g. OVAKO 280 (19MnVS6). For example, the core material may have a yield point of less than 550 MPa, preferably less than 400 MPa or less than 300 MPa.

The outer sleeve 1 1 material may typically be of metallic material, such as stainless steel.

The material of the outer sleeve 1 1 may alternatively be made from a material having a lower modulus of elasticity than steel, such as a polymeric material or a polymer composite material. The choice of material may depend on in which environment the clamping device 4 is to be used, which temperatures and which loads the shaft-hub system will experience.

Examples of different such outer sleeve 1 1 materials are polyoxymethylene plastic, polyetherketone, polyamide, polytetrafluoroethylene, polyethylene, polycarbonate, aluminum, aluminum bronze etc.

For a clamping device 4 with an outer sleeve 1 1 and core 10 of a weldable or solderable material, the sleeve 1 1 may be connected to the core 10 by a weld or solder, see e.g. Figs 2a and 2b. The weld or solder may be provided in a substantially annular area of the clamping device 4.

A substantially annular area 41 may be provided on the clamping device 4 presenting a smaller outer diameter than an area radially outside the pressure chamber 12, thereby enabling force fit (i.e. providing negative play) of the clamping device 4 to the shaft 2 without affecting the outer diameter of the shaft 2, especially when the shaft 2 is heated prior to the insertion of the clamping device 4. Further, it may be possible to obtain an exactly defined contact length between the shaft 2 and the clamping device 4.

By using sleeve materials having a lower modulus of elasticity than stainless steel (i.e. lower than about 180 GPa) the clamping device 4 may exert a higher contact pressure against the inner surface of the cylindrical recess 6 of the shaft 2 and, hence, against the hub 3 as the pressure needed for expanding such outer sleeve materials is less than for outer sleeves of steel. Examples of suitable moduli of elasticity may be 1 -150 GPa.

Thereby, it is also possible to use a shaft 2 with a thicker wall than in the case of a clamping device having an outer sleeve of steel but still obtaining the same contact pressure against the inner surface of the shaft and against the hub. The thicker wall of the shaft which here is possible may be advantageous as such a shaft may sustain load better than a shaft having thinner walls.

In an alternative embodiment it is possible to replace the weld or solder connecting the sleeve 1 1 and the core 10 to each other with a sealing device 200 in the form of a separate component provided between the sleeve 1 1 ^' and the core 10 ^' . Such a clamping device 4 ^' and shaft-hub system 1 ^' is illustrated in Figs 4, 5a-5d and 6a-6c. In this second embodiment like reference numbers are used for like parts shown for the first embodiment in Figs 1 , 2a-2e and 3a-3c.

The material of the core 10 ^' could in this embodiment be from a metallic or non-metallic material, such as plastics.

The sealing device 200 may be provided as a separate part, such as an O-ring. The O-ring may have any cross section, including circular, elliptic or polygonal. As an alternative, a sealing device 200 may be formed in situ, e.g. by application of a hardening or setting compound. Such an in situ formed sealing device may be allowed to harden or seal before or after assembly of the sleeves.

The O-ring may be formed from a rubber elastic material, including rubber materials, polyurethane and thermoplastic elastomeric materials.

In the system 1 ^" shown in Figs 7a-7c, the core 10 ^" is directly inserted into the shaft 2, such that the shaft 2 forms a sleeve for the core. A pressure chamber 12 is formed between the shaft 2 and the core 10. Sealing devices 200 ^' may be used for sealing between the core and the shaft. In this embodiment like reference numbers are used for like parts shown for the first and second embodiments discussed above. The material of the core 10 ^" may be a metallic material or a non-metallic material.

The system disclosed herein may find use in a variety of applications. As non-limiting examples may be mentioned: a pump, wherein the shaft may be a motor shaft and the hub may be an impeller; a gearbox, wherein the shaft may be an input- or output shaft and the hub may be a gearwheel; a packaging machine, wherein the shaft may be an actuator (e.g. outgoing axle of motor) and the hub may be a lever; a printing machine, wherein the shaft may be a cylinder and the hub may be a roller; a brake, wherein the shaft may be a drive shaft and the hub may be a brake disc; a test equipment, wherein the hub may be a test piece, which is arranged on the shaft; or a turbine, wherein the shaft may be an output shaft and the hub may be a turbine impeller.