Clamping device for tool holder

1 . A clamping device arranged for releasably holding a tool holder shank, the clamping device comprising:

a housing having a front end, a rear end, and a bore which intersects the front end and extends rearwardly therefrom, wherein a mounting portion arranged for receiving the tool holder shank is provided at a front end of the bore;

a drawbar slidably mounted inside the bore so as to be moveable in the bore along a longitudinal axis thereof in a first axial direction from an advanced releasing position to a retracted locking position, and further moveable in an opposite second axial direction from the retracted locking position to the advanced releasing position;

engagement members arranged around the drawbar at a front end thereof, wherein the engagement members, under the effect of a movement of the drawbar from the advanced releasing position to the retracted locking position, are moveable from a first position, in which the engagement members allow the tool holder shank to move into and out of said mounting portion, to a second position, in which the engagement members are in locking engagement with the tool holder shank and keep the tool holder shank secured to the housing;

a hydraulically operated actuating member arranged in the bore, wherein the actuating member is axially moveable in relation to the drawbar;

at least one wedge arranged in the bore and configured to transfer an axial movement of the actuating member in the first axial direction in relation to the drawbar into a movement of the drawbar from the advanced releasing position to the retracted locking position; and

a piston slidably mounted in a space inside the bore and configured to divide this space into a first hydraulic chamber on a first side of the piston and a second hydraulic chamber on an opposite second side of the piston,

wherein the actuating member is fixed to the piston and moveable together with the piston in the first axial direction by feeding of hydraulic fluid into the first hydraulic chamber and in the second axial direction by feeding of hydraulic fluid into the second hydraulic chamber,

wherein the at least one wedge is arranged on the outside of the drawbar and is configured to press the drawbar towards the retracted locking position when the at least one wedge is pressed inwards towards a longitudinal center axis of the drawbar,

wherein the at least one wedge comprises includes an outwardly facing first pressure receiving surface,

wherein the actuating member has a form of a sleeve and surrounds a part of the drawbar,

wherein the actuating member on an inner side thereof is provided with a first pressure applying surface which faces inwards for contacting the first pressure receiving surface on the at least one wedge, the first pressure applying surface having a radial distance to the longitudinal axis that increases in the first axial direction; and

wherein the first pressure applying surface is configured to press the at least one wedge inwards towards the longitudinal center axis of the drawbar by pressing against the first pressure receiving surface on the at least one wedge when the actuating member is moved in the first axial direction.

2 . The clamping device according to claim 1 , further comprising;

a support element which is arranged in the bore and is fixed to the housing,

wherein the support element is configured to support the at least one wedge, and

wherein the at least one wedge includes an inclined wedge surface, which faces towards the front end of the housing and which slidably abuts against an inclined slide surface on the support element facing towards the rear end of the housing.

3 . The clamping device according to claim 2 ,

wherein the at least one wedge includes a contact surface, which faces towards the rear end of the housing and which abuts against a shoulder on the drawbar facing towards the front end of the housing,

wherein the at least one wedge, when being pressed inwards towards the longitudinal center axis of the drawbar under the effect of the actuating member, is configured to exert a pushing force on the drawbar by pressing against said shoulder via the contact surface.

4 . The clamping device according to claim 3 ,

wherein the drawbar includes an elongated main part and an annular part, which is fixed to the main part at a rear end thereof and which projects radially from the main part,

wherein said shoulder is provided on the annular part.

5 . The clamping device according to claim 2 , wherein the support element is provided with guiding means, which are configured to co-operate with corresponding guiding means on the at least one wedge in order to keep the at least one wedge correctly positioned on the support element while allowing the at least one wedge to slide longitudinally along the associated slide surface on the support element.

6 . The clamping device according to claim 2 ,

wherein the support element surrounds the drawbar, and

wherein the drawbar is slidably mounted to the support element and extends through a central opening in the support element.

7 . The clamping device according to claim 1 , wherein the piston is configured to come into contact with a rear end of the drawbar and to push the drawbar in the second axial direction under the effect of a hydraulic pressure generated in the second hydraulic chamber by feeding of the hydraulic fluid into the second hydraulic chamber.

8 . The clamping device according to claim 1 , wherein the first pressure applying surface and the first pressure receiving surface are curved as seen in a cross-sectional plane perpendicular to the longitudinal axis.

9 . The clamping device according to claim 1 , wherein the first pressure applying surface and the first pressure receiving surface are inclined in relation to the longitudinal axis by such an angle α that the at least one wedge keeps the actuating member in a self-locking axial position in the bore when the drawbar has been forced into the retracted locking position under the effect of the actuating member and the at least one wedge.

10 . The clamping device according to claim 9 ,

wherein the at least one wedge includes an outwardly facing second pressure receiving surface,

wherein the actuating member on an inner side thereof is provided with a second pressure applying surface which faces inwards for contacting the second pressure receiving surface on the at least one wedge, the second pressure applying surface having a radial distance to the longitudinal axis that increases in said first axial direction,

wherein the second pressure applying surface and the second pressure receiving surface are inclined in relation to the longitudinal axis by an angle ß which is larger than the angle α, and

wherein the first and second pressure applying surfaces and the first and second pressure receiving surfaces are arranged consecutively on the actuating member and on the at least one wedge, respectively, such that, upon a movement of the actuating member in the first axial direction, the second pressure applying surface is configured to slide and to press against the second pressure receiving surface during a first phase of the movement and the first pressure applying surface is configured to slide and to press against the first pressure receiving surface during a subsequent second phase of the movement.

11 . The clamping device according to claim 10 , wherein the second pressure applying surface and the second pressure receiving surface are curved as seen in a cross-sectional plane perpendicular to the longitudinal axis.

12 . The clamping device according to claim 1 , wherein the at least one wedge includes two or more wedges spaced apart from one another in a circumferential direction of the drawbar.

13 . The clamping device according to claim 12 , wherein said two or more wedges are three in number.

14 . The clamping device according to claim 12 , wherein said two or more wedges are evenly distributed in the circumferential direction of the drawbar.

15 . The clamping device according to claim 1 , wherein the actuating member and the piston are formed in one piece.