GB2034624A

GB2034624A - Hydraulically actuated hollow clamping cylinder for clamping devices on a rotating spindle

Info

Publication number: GB2034624A
Application number: GB7937973A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1978-11-04
Filing date: 1979-11-02
Publication date: 1980-06-11
Also published as: BR7906992A; IT7968995A0; DE2847951C2; IT1119395B; FR2440800B1; JPS5570508A; FR2440800A1; DE2847951A1; CH640444A5

Abstract

Internal space is economized and oil friction reduced in a clamping cylinder having a housing (1), for connection to a rotating spindle, and having an annular chamber (3) containing a piston (4) with a collar (5), for connection to a traction member for actuating a clamping device, and passing through a gap (6) to a supporting bore (7) in a housing cap (2). This assembly rotates on a stationary unit (16) with connections (17.1, 17.2) for supply and discharge of pressure oil to and from opposite faces of piston (4) to actuate the traction member. Part of this oil is leaked through a bearing gap (21) surrounding a projecting portion (13) of housing (1). Cooling air is fed through cooling chamber (22) by fan blades (24.1). Safety valves are provided between the ducts of each of two pairs of ducts leading to chamber (3) for said oil supply and discharge. These safety valves prevent inadvertent movement of the piston and unintentional clamping device release. <IMAGE>

Description

SPECIFICATION Hydraulically actuated hollow clamping cylinder for clamping devices on a rotating spindle The invention relates to a hydraulically actuated hollow clamping cylinder for actuating clamping devices on a rotating spindle, in particular lathe spindles, comprising a cylinder housing which can be connected to the spindle, and a clamping piston which is axially displaceable in the cylinder chamber in the cylinder housing and which can be connected to a traction member, in particular a traction tube, which is disposed in the hollow spindle, wherein the cylinder housing and the clamping piston rotate with the spindle and its traction member, and further comprising a stationary connection housing for permitting the external feed and discharge of the pressure fluid, which connection housing is mounted externally on a hollow-cylindrical guide projection portion of the cylinder housing, coaxially with respect to the axis of the cylinder, by means of a cylindrical internal bore which has at least one annular groove and a pressure fluid duct opening therein, the hollow-cylindrical guide portion having connecting passages to the cylinder spaces on both sides of the clamping piston, the connecting passages joining the annular grooves, and the hollowcylindrical guide portion forming between itself and the connection housing an annular gap seal means which is filled with the pressure fluid.

Hollow clamping cylinders of this kind are known from DAS No. 1 018 696 and are used in particular in machine tools for actuating the clamping device which is carried on the machine spindle, in machining bar or rod material which, because of its length, requires a free central opening not only in the clamping device but also in the spindle and its traction member and in the clamping cylinder. For this purpose, the cylinder chamber, in the hollow clamping cylinder, is closed towards the central opening by a tube member which is fixedly connected to the annular clamping piston and which extends into the guide projection portion, is guided therein, and thereby in turn guides the clamping piston in the cylinder chamber.The properties of boundary layers or the films of fluid which cling to the internal bore in the stationary connection housing and the rotating guide projection portion are utilised to provide the seal in the annular gap between the above-mentioned bore and guide projection portion, in order to prevent the escape of pressure fluid or to meter the amount of fluid which escapes, in a given manner.This is achieved in that the clearance between the internal bore in the stationary connection housing and the outside surface of the rotating guide projection portion is selected at such a small value, by means of roller bearings arranged between the guide projection portion and the connection housing, that the annular gap is sealed off as a result of the adhesion effect of both surfaces, which is applied to the pressure fluid, and only a controlled amount of fluid, which is desired for example, for lubricating and cooling the roller bearings, issues through the above-mentioned annular gap, the axial length of the annular gap being such that the leakage fluid on issuing from the annular gap is already relieved of load.The components which rotate relative to each other do not come into contact with each other so that the major friction losses and thus the heat produced are caused solely by internal oil friction. The amount of heat produced increases in proportion to increasing periphery of the annular gap, for a greater periphery for the annular gap results in particular in an increasing relative speed between the boundary surfaces which are moving relative to each other.

This means that, at high speeds of rotation, the oil which passes through the clamping cylinder is heated to such an extent that it needs to be cooled before it is returned to the clamping cylinder. It will be seen that this problem becomes more critical, as the speed of rotation increases. With the known hollow clamping cylinders however, it is not readily possible for this problem to be solved by using an annular gap sealing means of smaller annular diameter, because the tube portion which carries the clamping piston and whose diameter also determines the diameter of the guide projection portion must carry the traction tube, so that in any case the above-mentioned tube portion cannot be of smaller diameter than the traction tube itself.However, the internal diameter of the traction tube is predetermined by the operating requirements in respect of which the clamping cylinder is to be adapted or used. The annular diameter of the annular gap sealing means in the known hollow clamping cylinders is larger than the radius required in respect of the central opening, by at least the wall thicknesses of both the guide projection portion and also the above-mentioned tube portion.

The invention is based on the problem of providing a hydraulically actuated hollow clamping cylinder of the kind set out hereinbefore, in such a way that, with a predetermined internal diameter in the opening through the cylinder, the annular diameter and thus the length of the periphery of the annular gap sealing means can be as small as possible.

According to the invention, this problem is solved in that the cylinder chamber is in the form of annular chamber between an outerannularwall and an inner annular wall of the cylinder housing and an annular gap is left free between the inner annular wall and an internal bore in the cylinder end wall which is arranged for connection to the spindle, said internal bore being coaxial with respect to the axis of the chuck, wherein a collar member extends through the annular gap, the collar member being fixedly connected to the clamping piston and guiding it on the inner annular wall and sealing the cylinder end wall and being arranged, at its end which projects out of the annular gap, for connection to the traction member. Preferably, the cylinder end wall which is arranged for connection to the spindle is held at the edge of the outer annular wall.The internal diameter of the inner annular wall may be equal to or larger than that of the guide projection portion for the connection housing.

The technical advance achieved by the invention is essentially that the hollow clamping cylinder accord ing to the invention does not require a guide member for the clamping piston, which guide member extends into the guide projection portion. On the contrary, the clamping piston is guided by means of the collar member which is fixedly connected to the clamping piston, on the outside of the inner annular wall which internally closes off the annular cylinder chamber. The free internal cross-section of the guide projection portion is therefore fully available for the passage therethrough of the hollow clamping chuck, and does not need to be larger than the required diameter therefor. This involves a corresponding reduction in the diameter and the periphery of the annular gap sealing means.As a result of such reduction, the amount of heat produced due to internal oil friction in the annular gap sealing means is reduced.

The invention is described in greater detail hereinafter in an embodiment which is illustrated in the drawings in which: Figure 1 shows a view in axial section of a hydraulically actuated hollow clamping cylinder according to the invention; Figure 2 shows a view in section taken along line Il-Il in Figure 1; and Figure 3 shows a view in section taken along line Ill-Ill in Figure 1.

The drawings show the hollow clamping cylinder in a vertical position which however does not correspond to its actual position of installation, in which the hollow clamping cylinder is arranged with its axis 12 extending horizontally, and with the oil discharge connection 16.7 directed downwardly. The cylinder housing is denoted by reference numeral 1.

At its front end wall 2, the cylinder housing 1 is adapted for connection to a machine spindle (not shown) of a lathe. Disposed in the cylinder housing 1 is a cylinder chamber 3 which is incorporated into the cylinder housing 1 in the form of an annular chamber which is open forwardly towards the spindle, that is to say, the chamber is formed between an outerannularwall 1.1 and an inner annular wall 1.2 of the cylinder housing. The cylinder chamber 3 is closed off at the spindle end by an annular cylinder cover member 1.4 which is held to the edge of the outer annular wall 1.1 by screw means 1.3. The cylinder cover member 1.4 carries screw-threaded blind holes 1.5 to which the machine spindle (not shown) is connected.The cylinder piston 4 which is axially displaceable in the cylinder chamber 3 and which is shown in its rearward limit position in Figure 1 carries at its front side a collar member 5 which is fixedly connected to the piston and which guides the piston 4 on the outside surface of the inner annular wall 1.2 and which projects outwardly through an annular gap 6 which is left free between an internal bore 7 in the cylinder cover member 1.4 and the end of the inner annular wall 1.2.The clamping piston 4 is sealed with respect to the inner and outer annular walls 1.1 and 1.2 of the cylinder chamber 3 by sealing means 8 and sealed with respect to the cylinder cover member 1.4 by a sealing means 9, by way of its collar portion 5 which projects out of the annular gap 6, so that the pressure fluid which passes into the cylinder chambers 3.1 and 3.2 on both sides of the clamping piston cannot escape. The part of the collar member 5 which projects freely from the annular gap 6 is provided at 10 with an internal screwthread for connection of the clamping tube (not shown) which is disposed in the machine spindle (also not shown).

The clamping piston 4 is moreover prevented from rotating relative to the cylinder housing 1, by guide pins 11.

At its rearward end, the cylinder housing 1 carries a hollow-cylindrical guide projection portion 13 which is coaxial with respect to the axis 12 of the cylinder and whose internal cross-section, together with that of the inner annular wall 1.2 of the cylinder housing 1 forms the opening or passage 14 of the hollow clamping cylinder.

The guide projection portion 13 participates in the rotary movement of the spindle and the traction tube, together with the cylinder housing 1 and the piston 4. Mounted on the outside of the guide projection portion 13 by way of roller bearings 15 is a stationary connection housing 16 which therefore does not rotate with the guide projection portion 13 and which permits the external feed and discharge of the pressure fluid, by way of pressure duct connections 17.1 and 17.2. Forthis purpose the connection housing 16 has an internal bore 16.1 with, in the embodiment illustrated, two annular grooves 18.1 and 18.2 which are connected to the pressure duct connections 17.1 and 17.2.Connecting passages which are only partly shown in the drawing, at 19.1, 19.2,20.1 and 20.2 and which connect to the annular grooves 18.1 and 18.2 extend in the guide projection portion 13 to the cylinder chambers 3.1 and 3.2 on both sides of the clamping piston 4.

Disposed between the guide projection 13 and the connection housing 16 isthe annular gap sealing means which is filled with the pressure fluid and which represents a gap 21 of only a few hundredths of a millimetre in width. The pressure oil which flows through the annular grooves 18.1 and 18.2 into the connecting passages 19.1 or 19.2 or vice-versa and which thus passes across the gap 21 spreads out laterally in the gap 21.Part of the oil which escapes from the gap 21 at the end can pass into an oil collecting chamber 16.6 directly through annular grooves 16.2 which are provided in the internal bore 16.1 in the connection housing 6, and ducts 16.3 which are connected to the annular grooves 16.2, while the other part of the oil issuing from the gap 21 at the end thereof passes into the oil collecting chamber 16.6 after lubriucting and cooling the roller bearings 15, by passing through annular passages 16.4 which are provided in two end closure caps 16.5 of the connection housing 16. The leakage oil can escape from the oil collecting chamber 16.6 by way of an oil discharge connection 16.7. The oil collecting chamber 16.6 is closed outwardly by an annular wall 16.8 which is delimited at both ends by the caps 16.5.

The annular wall 16.8, together with a further outer annular wall 16.9 which is also held axially at both ends on the caps 16.5, forms a cooling chamber 22 which is in communication with the exterior axially at both ends by way of openings 23 provided in the caps 16.5. The openings 23 each extend over a substantial angular peripheral distance of the caps 16.5, as Figure 2 particularly shows. Like the connection housing 16, the annular walls 16.8 and 16.9 are also stationary, together with the two axial closure caps 16.5.Disposed on the end wall, which is towards the connection housing 16, of the cylinder housing 1 which rotates relative to the stationary connection housing 16, is a fan wheel 24 which suitably rotates with the cylinder housing 1 and whose fan blades 24.1 are so arranged and constructed that they draw in through openings indicated at 25 a flow of cooling air which flows through the cooling chamber 22 by way of the openings 23 in the caps 16.5, so that the heat produced in the annular gap sealing means due to internal oil friction is removed from the connection housing 16 by convection. Radial ribs 26 may be provided between the annular walls 16.8 and 16.9, in order to increase the heat exchange area for the flow of cooling air.

Figure 3 shows in detail that the connecting passages 19.1, 19.2,20.1 and 20.2 are provided with safety valves which are only indicated at 30 in Figure 1 and which, in the event of trouble in the supply of pressure fluid, prevent inadvertent movement of the clamping piston and thus unintentional release of the clamping device, which could result in an accident. Each of the safety valves comprise a ball-shaped valve member 31.1 and 31.2 which is displaceably mounted in a valve cage 30.1 and 30.2 and which bears against an associated valve seat 33.1 and 33.2, under the force of a valve spring 32.1 and 32.2.Disposed between the two valve members 31.1 and 31.2 is a displaceably mounted control piston 34 which, depending on its position, can lift one or other of the two valve balls from their valve seat, against the force applied thereto by the respective valve spring. If for example pressure fluid flows in through the connecting passage indicated at 19.2 in Figure 3, it displaces the left-hand valve ball 31.2 in Figure 3 towards the left against the force of its valve spring 32.2, and thereby opens the communication through the valve to the connecting passage indicated at 20.2, which leads to the rearward cylinder chamber shown at 3.2 in Figure 1.Atthe same time, the pressure fluid flowing through the connecting passage 19.2 displaces the control piston 34 towards the right in Figure 3, so that the control piston 34 also lifts the right-hand valve ball 31.1 in Figure 3 from its valve seat 33.1, so that the pressure fluid can escape from the connecting passage indicated at 20.1 in Figure 3, into the connecting passage indicated at 19.1, and thus can escape from the forward cylinder chamber 3.1 in Figure 1. This causes the clamping piston 4 to move forwardly. If the above-indicated direction of flow of the pressure fluid in the connecting passages is reversed, the direction of movement of the clamping piston is correspondingly reversed.If, due to any trouble, the pressure fluid supply breaks down, so that pressure fluid no longer flows into the valve arrangement through either of the two connecting passages 19.1 and 19.2, the two safety valves close under the pressure of their valve springs 32.1 and 32.2 and thereby close off the two cylinder chambers 3.1 and 3.2 so that the clamping piston is no longer capable of further movement. In the event of a breakdown in the pressure fluid supply therefore, the clamping piston 4 can no longer move into a position which corresponds to the opening condition of the clamping device.

The guide projection portion 13 and the inner annular wall 1.2 may be of the same internal diameter, as in the embodiment illustrated, although it is obviously possible for the internal diameter of the inner annular wall 1.2 to be larger than that of the guide projection portion 13. At any event, the internal diameter of the guide projection portion 13 does not need to be larger than the required diameter of the opening through the hollow clamping cylinder, thus ensuring that the annular gap sealing means is of the optimum small annular diameter and thus annular periphery.

Claims

1. A hydraulically actuated clamping cylinder for actuating clamping devices on a rotary spindle, comprising a cylinder housing which can be connected to the spindle, and a clamping piston which is axially displaceable in the cylinder chamber in the cylinder housing and which can be connected to a traction member, which is disposed in the spindle, wherein the cylinder housing and the clamping piston rotate with the spindle and its traction member, and further comprising a stationary connection housing for permitting the external feed and discharge of the pressure fluid, which connection housing is mounted externally on a cylindrical guide projection portion of the cylinder housing, coaxially with respect to the axis of the cylinder, by means of a cylindrical internal bore which has at least one annular groove and a pressure fluid duct opening therein, the cylindrical guide portion having connecting passages to the cylinder spaces on both sides of the clamping piston, the connecting passages leading to the annular grooves, and the cylindrical guide portion forming between itself and the connection housing a cylindrical gap seal which is filled with the pressure gluid, the cylinder chamber being in the form of an annular chamber between an outer annular wall and an inner annular wall of the cylinder housing and an annular gap being left free between the inner annular wall and a bore in a cylinder end wall which is arranged for connection to the spindle, said internal bore being coaxial with respect to the axis of the clamping devices wherein a collar member extends through the annular gap and is fixed to the clamping piston for guiding it on the inner annular wall and sealing the cylinder end wall and being arranged, at its end which projects out of the annular gap, for connection to the traction member.

2. A clamping cylinder according to Claim 1, in which the cylinder end wall is arranged for connection to the spindle and is fixed at the edge of the outer annular wall.

3. A clamping cylinder according to Claim 1 or Claim 2, in which the inside diameter of the inner annular wall of the cylinder chamber is equal to or greater than that of the guide portion for the connection housing.

4. A hydraulically actuated hollow clamping cylinder substantially as hereinbefore described with reference to the accompanying drawings.