The present invention relates to a torque-limiting clutch arrangement which comprises two mutually coaxial clutch elements which are non-rotatably connected to a driving shaft and a driven shaft respectively and which engage one another through the intermediary of two mutually opposing, pressurized surfaces, therewith forming a friction joint which is dimensioned to slip when the torque on the clutch exceeds a predetermined value; and a device which is operative to detect slip occurrences in the friction joint and to disengage or separate the clutch elements when slip occurs.

Torque-limiting clutches or couplings of this kind are known to the art in many different forms. The clutch normally has the form of a conventional disc-clutch comprising a pressure plate which is applied by means of a powerful spring force. When slip occurs, a device comes into function and relieves the pressure on the pressure plate, so as to disengage the clutch. In the case of one simple design, described and illustrated in DE 22 15 053, the spring pressure is generated by compressed-air springs which are pressurized via a compressed-air conduit. This conduit communicates with an outwardly projecting nipple mounted on one clutch element. The nipple is closed at one end and when rela¬ tive rotation occurs between the two clutch elements, the nipple is punctured by a moveable member provided on the other of said clutch-elements.

Such a clutch arrangement is both complicated and space- demanding, particularly when intended for high torques. Another drawback with a clutch of this kind is that once

the clutch is overloaded, so that the clutch is dis¬ engaged and the driven shaft has stopped, the clutch cannot be reengaged until the nipple has been replaced and the compressed-air springs repressurized.

The object of the present invention is to provide a clutch of the kind described in the introduction which is of simple and reliable construction and which will remain reliable, even after several years in use; which is particularly adapted for high torques; and which when disengaged under overload conditions is ready for re-use immediately, without needing to replace any of the clutch components or to take any other form of remedial action with respect to the clutch.

This object is achieved with a clutch constructed in accordance with the invention and having the char¬ acteristic features set forth in the following claims. Considered as a clutch arrangement, the inventive arran- gement has the simplest and most-compact construction possible, namely a cylindrical sleeve which is clamped rigidly, preferably shrink-fitted, onto a cylindrical part. Moveable parts, i.e. pump means driven by mutual rotation of the cylindrical parts, do not begin to function until slip occurs between the cylindrical parts as a result of an overload. Pressure fluid is delivered to a pressure conduit at the requisite pressure, such as to force the fluid through openings provided in at least one of said friction surfaces and produce a hydrostatic layer which separates the two cylindrical parts so that the friction generated therebetween will be at a mini¬ mum. Immediately upon cessation of the mutual rotation of said parts, the pump means will cease to operate and the hydrostatic layer is dispersed so as to reestablish

frictional contact between the clutch elements. A closed pressure-fluid circuit is obtained, by providing drain¬ age channels in at least one of said friction surfaces, said circuit enabling the clutch to be held disengaged over a long period of time, if necessary.

The invention will now be described in more detail with reference to the accompanying drawing, in which Figure 1 is a longitudinal sectional view of a preferred embodi- ment of an inventive clutch arrangement, and Figure 2 illustrates schematically alternative positioning of the pump units of said arrangement.

Shown in the drawing is a drive shaft 1 which is keyed by a key 2 to a first clutch or coupling element comprising a first cylindrical sleeve 3 which is press- fitted on one end of the drive shaft and the free-end of which has a first hub 4 firmly mounted thereon. A second or outer sleeve 5 having mounted thereon a second hub 6 and belonging to a second clutch element is shrink- fitted on the outer cylindrical surface of the first sleeve 3. The second hub 6 has provided therein a cen¬ tral hole in which there is firmly mounted a journal pin 7, the end of which facing the drive shaft 1 is con- nected to said shaft through the intermediary of a roller bearing 8. The second hub 6 is configured as a flange-connection for a driven shaft, e.g. a cardan shaft in an electrically driven unit intended for a track-driven vehicle or the like.

The first hub 4 incorporates six radially extending piston pumps 10, which are uniformly placed around the hub. Each pump includes a radial bore 11 which accom¬ modates a piston 12, said piston being driven by a

strong pressure-spring 13, located between the outer end of the piston and a closure 14. The spring 13 presses the inwardly located end of the piston 12 against an outer-ring 15 of a needle-bearing, the inner-ring 16 of which is mounted on an excentric 17 formed on the jour¬ nal pin 7. The piston 12 is provided in a conventional manner with a suction opening 18, an axial through-flow channel 19, a suction valve 20 mounted in said channel, and a pressure opening 21.

The suction opening 18 communicates with a suction passage 22 which extends axially through the first hub 4, whereas the pressure opening 21 communicates with a pressure passage 23 which also extends through the first hub 4. Located opposite the orifice of the pressure passage 23 is an axial outlet channel 24. The channel 24 incorporates a pressure valve 25 which coacts with the pump 10, in a known manner.

A radial channel 26 connects the outlet channel 24 with a peripheral groove 27 in the outer cylindrical wall 28 of the first sleeve 3. Each of the other five pumps 10 is provided with a peripheral groove, in a corresponding manner. As illustrated in the upper part of Figure 1, a further outlet channel 24' is connected to a further peripheral groove 27', via a further radial channel 26'. The peripheral grooves 27, 27' are uniformly spaced in the axial direction. Arranged externally of the groove 27" distal from the first hub 4 is a peripheral drainage groove 29 which communicates, via a drainage passage 30, with an annular pressure-fluid storage container 31 located between the clutch elements. The container 31 communicates solely with the suction passages 22 of respective piston pumps 10 and with the drainage pasage

30. Two closing devices 32 and 33, not shown in detail, are provided for the purpose of filling the system with pressure fluid, preferably oil, and of ventilating the closed fluid system.

In normal operation, the inventive clutch arrangement functions as a friction clutch having two clutch sleeves which are joined by a shrink-joint, said joint being adapted so that clutch-slip will only occur when the torque applied to the clutch reaches a predetermined, maximum permitted value.

When this value is reached, the first sleeve 3 and the first hub 4 will rotate relative to the second sleeve 5 and the second hub 6 carrying the journal pin 7 and the excentric 17. The pistons 12 will then be forced out¬ wards in succession and with great force, by the ex¬ centric needle-bearing 15, 16, and then returned by the springs 13. When the pressure-fluid system is filled with oil, oil will consequently be pressed into the peripheral grooves 27, thereby separating the two sleeves 3, 5 sufficiently to enable the oil to leave the grooves 27 and enter the drainage passage 29, from where the oil flows through the drainage pasage 30 and back to the container 31. There is thus formed between the first and second sleeves 3 and 5 a hydrostatic layer which will permit the sleeves to rotate mutually with only very little friction therebetween.

Slipping between the sleeves 3 and 5 will stop immedi¬ ately the torque acting on the clutch has fallen to a sufficiently low level. The pumps 10 will then cease to work and the oil in the grooves 27 will lose its pres¬ sure. Consequently, the oil is forced away from the

interspace between the grooves 27, and the two sleeves 3 and 5 are then restored to frictional engage ment as a result of the shrink joint.

The illustrated and described clutch arrangement is intended primarily for use with rapid-speed clutches or couplings which operate with one pump-stroke per revolution and pump. In the case of slower clutches it may be more expedient to use a cam-curve which enables more pump-strokes to be effected per revolution and pump. In this case, the pump units can then be disposed axially, as shown schematically in Figure 2. This illu¬ stration shows separate piston-pumps 40 mounted exter¬ nally on the outer or second sleeve 5 of the clutch arrangement, and a cam-curve 41 mounted rigidly on the shaft 1. Piston rods 42 provided with roller-type cam-followers 42 transmit pumping movement from the cam- curve 41 to the pistons of the pumps (not shown) when relative movement occurs between the outer sleeve 5 and the shaft 1. With the exception of the pumps 10 and the excentric 17, the clutch shown in Figure 2 is the same as that shown in Figure 1, although in the case of the Figure 2 embodiment it may be expedient to form the peripheral grooves 27 with associated passages in the outer sleeve 5, since the pumps ^' 40 are mounted on said sleeve.

It will be understood that the invention is not restric¬ ted to the illustrated and described emnbodiments and that various modifications can be made within the scope of the invention defined in the foolowing claims, for instance, the piston-pumps 40 of the Figure 2 embodiment can be mounted in axial bores in the wall of the outer sleeve 5, in a manner corresponding to the pumps 10 in

the radial bores II provided in the first hub 4. The number of pumps can, of course, vary in dependence on the pressure-fluid requirement.