Clamping device for tool holder

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

• a housing;
• a spindle rotatably mounted inside the housing and having a front end, a rear end and a bore which intersects the front end and extends rearwardly therefrom, wherein a mounting portion 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 reciprocally moveable in the bore along a longitudinal axis thereof between an advanced releasing position and a retracted locking 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 of the bore, to a second position, in which the engagement members are in locking engagement with the tool holder shank and keep it secured to the spindle;
• an actuating member arranged inside the housing, wherein the actuating member is slidably mounted to the spindle so as to be moveable in relation to the spindle in the axial direction thereof;
• a motion transferring mechanism arranged inside the housing, wherein the motion transferring mechanism is mounted to the spindle and configured to transfer an axial movement of the actuating member in a first axial direction in relation to the spindle into a movement of the drawbar from the advanced releasing position to the retracted locking position;
• a hydraulic actuator arranged in or mounted on the housing and configured to move the actuating member axially in relation to the spindle, wherein the hydraulic actuator includes a piston unit slidably received in a space of the hydraulic actuator and configured to divide this space into first and second hydraulic chambers;
• a first hydraulic line connected to the first hydraulic chamber, wherein hydraulic fluid is feedable into and dischargeable from the first hydraulic chamber via the first hydraulic line;
• a second hydraulic line connected to the second hydraulic chamber, wherein hydraulic fluid is feedable into and dischargeable from the second hydraulic chamber via the second hydraulic line wherein the piston unit is moveable in a first direction by feeding of hydraulic fluid into the first hydraulic chamber via the first hydraulic line in order to allow the piston unit to exert, directly or via a connecting element, a pulling or pushing force on the actuating member in said first axial direction and thereby effect a movement of the drawbar from the advanced releasing position to the retracted locking position, the piston unit being moveable in an opposite second direction by feeding of hydraulic fluid into the second hydraulic chamber via the second hydraulic line, wherein the actuating member is rotatable in relation to the piston unit together with the spindle;
• and
• a first valve assembly arranged in the second hydraulic line, the first valve assembly including first and second flow channels arranged in parallel with each other, a first check valve in the form of a spring-loaded check valve, which is arranged in the first flow channel and which is configured to allow flow of hydraulic fluid through the first flow channel towards the second hydraulic chamber and obstruct flow of hydraulic fluid through the first flow channel away from the second hydraulic chamber, and a second check valve in the form of a spring-loaded check valve, which is arranged in the second flow channel and which is configured to allow flow of hydraulic fluid through the second flow channel away from the second hydraulic chamber when the hydraulic pressure in the second hydraulic chamber exceeds a cracking pressure of the second check valve and obstruct flow of hydraulic fluid through the second flow channel towards the second hydraulic chamber, wherein the actuating member is a sleeve, and wherein the actuating member is arranged around a peripheral wall of the spindle and slidably mounted to the peripheral wall so as to be axially moveable in relation to the spindle, the motion transferring mechanism including two or more wedges spaced apart in a circumferential direction of the spindle, each wedge being received in a respective aperture that extends radially through the peripheral wall of the spindle, wherein the wedges are configured to press the drawbar towards the retracted locking position when they are pressed radially inwards in the associated apertures, wherein each wedge includes a first pressure receiving surface which faces outwards from the spindle, wherein the actuating member on its inner side is provided with a first pressure applying surface which faces inwards for contacting the first pressure receiving surface on each wedge, the first pressure applying surface having a radial distance to the longitudinal axis that increases as seen in said first axial direction, and wherein the first pressure applying surface is configured to press each wedge radially inwards in the associated aperture by pressing against the first pressure receiving surface on each wedge when the actuating member is moved in said first axial direction.