A fluid friction clutch of this type is known from EP 1 731 787 Bl, the content of disclosure of which is hereby made the content of disclosure of the present application by explicit reference.

It is an object of the present invention to provide a fluid friction clutch of the type specified in the preamble of claim 1, by way of which it is possible in a simple way to increase the clutch efficiency.

This object is achieved by the features of claim 1.

The provision of an oil cooler improves the slip heat capacity with the aid of a cooling circuit which runs through the housing parallel to the main fluid circuit which connects the working chamber and the reservoir chamber. This additional fluid circuit serves exclusively for the purpose of cooling the fluid, in particular oil, but has no function at all relating to the emptying of the working chamber.

The arrangement and/or position of the oil-cooler delivery pump causes said oil-cooler delivery pump to operate only when the system is situated in the range of medium slip heat, with the result that no further idling losses of the fluid friction clutch according to the invention are produced.

Since it is possible to expose the oil circuit to the surrounding air as a result of the arrangement of the oil cooler of the fluid friction clutch according to the invention, this results in a maximization of the heat reduction of the fluid.

For this purpose, the oil cooler is preferably arranged in the cover of the housing.

The dependent claims contain advantageous developments of the invention.

As a result of the provision of a rotatably mounted supply pump element which defines a shear gap with the housing, it is made possible in a simple way, by utilization of a differential speed between the pump element and the housing or the secondary side of the fluid friction clutch, to generate a volumetric flow from the reservoir chamber into the working chamber, which volumetric flow is dependent on the differential speed. One of the special advantages of the fluid friction clutch according to the invention is first of all that only a small quantity of clutch fluid is required, since an active delivery pump is formed in the oil reservoir on account of the above-described arrangement, which is advantageous with regard to the clutch fluid quantity in comparison with the known utilization of centrifugal forces to fill the working chamber.

Furthermore, the response behavior of the fluid friction clutch according to the invention becomes more rapid on account of the lower clutch fluid component.

Furthermore, it results in an extremely compact design, since the external diameter of the reservoir chamber and/or the reservoir can be made larger than the internal diameter of the working chamber.

It is to be noted in summary that excellent clutch performance can be achieved on account of the circumstance that the supply pump element rotates at primary speed (speed of the shaft) and strips off clutch fluid with respect to the housing.

The clutch performance can be improved further by virtue of the fact that a recirculating pump is provided which rotates at secondary or primary speed and strips off clutch fluid on account of its arrangement between the clutch plate and housing.

Further details, advantages and features of the present invention will emerge from the following description of exemplary embodiments with reference to the drawing, in which:

fig. 1 A shows a sectional illustration of a fluid friction clutch according to the invention from a first viewing direction,

fig. IB shows a perspective, sectioned illustration of the fluid friction clutch according to fig. 1A,

figs. 1C-1E show illustrations of an alternative embodiment of the fluid friction clutch according to the invention,

fig. 2 A shows an illustration, corresponding to fig. 1A, of the fluid friction clutch from a second viewing direction,

fig. 2B shows an illustration, corresponding to fig. IB, of the fluid friction clutch from the viewing direction according to fig. 2 A,

fig. 3 shows a perspective plan view of the fluid friction clutch without housing cover,

fig. 4 shows a partial illustration, corresponding to fig. 3, of the fluid friction clutch,

fig. 5 shows a partial illustration, corresponding to fig. 4, of another region of the fluid friction clutch,

fig. 6 shows a detailed illustration of a valve element which is shown in fig. 5, fig. 7 shows a first embodiment of a hydraulic circuit diagram for the fluid friction clutch according to the invention, and

fig. 8 shows an illustration, corresponding to fig. 3, of a second embodiment of the hydraulic circuit diagram for the fluid friction clutch according to the invention.

Fig. 1A shows a sectional illustration of a fluid friction clutch 1 according to the invention which has a housing which is usually constructed from a housing body 2 and a cover 3.

A clutch plate 4 which can be rotated with respect to the housing 2, 3 is arranged in the housing 2, 3. Here, the clutch plate 4 which can be rotated with respect to the housing 2, 3 is arranged in a rotationally fixed manner at one end 5 of a shaft 6 which is mounted centrally within the housing 2, 3. A drivable active element 7 which is shown diagrammatically in a slightly simplified form and can be configured, for example, as a fan wheel is fixed on the housing 2, 3.

A working chamber 9 is arranged between the housing 2, 3 and the clutch plate 4, which working chamber 9 has working gaps 15, as can be seen from fig. 1A, which make a transmission of torque possible on account of a shearing action on the clutch fluid which is fed to the working chamber 9.

Furthermore, a reservoir chamber 10 is provided for said clutch fluid, a feed channel 11a, l ib leading from the reservoir chamber 10 to the working chamber 9 and therefore forming the supply.

Furthermore, according to the invention, a return pump system or a recirculating pump 16 is provided which serves to return clutch fluid from the working chamber 9 to the reservoir chamber 10. Said recirculating pump is either formed by the centrifugal force which is produced and pumps fluid to the reservoir chamber 10 to the outside in order to evacuate the working chamber 9. As an alternative, it is possible to provide a separate component in the form of an active recirculating pump, as is indicated diagrammatically in the hydraulic diagram of figs. 7 and 8, which acts via shearing force.

Furthermore, the fluid friction clutch 1 has a stationary clutch part 13 which can be rotated with respect to the housing 2, 3 and is preferably configured as a magnet, in particular an electromagnet.

As results from the illustration of figs. 1A, IB, 2A and 2B and 4, an inner reservoir 18 is provided, furthermore, which is connected via the feed channel 11 to the reservoir chamber 10. Here, the valve 17 is connected into the feed channel 11a, l ib, and the reservoir chamber 10 is arranged so as to lie on the outside, as results in detail from figs. 1 A to 2B.

Furthermore, a non-return valve 19 is provided which is arranged between the valve 17 and the reservoir 18. Said non-return valve 19 can be, for example, a small tube which protrudes beyond the fluid level into the reservoir 18.

As results from figs. 1A to 2B and 4 and 5, furthermore, a return valve 20 is provided which is operatively connected to the valve 17 and opens and closes a return channel 23 to the reservoir chamber 10.

The valve 17 which is preferably configured as a multiway valve has a valve element 24 which has a through bore 25 and a fluid inlet recess 26 for introducing fluid into the working chamber 9, which results above all from fig. 5 and the detailed illustration of fig. 6.

Furthermore, an actuator 27 is provided for actuating the valve 17 and the return valve 20. The actuator 27 preferably has an armature 28 which can be rotated relative to the shaft 26 and a flux ring 29 which can be rotated with the shaft 6 and can be excited by the stationary clutch part in the form of the magnet 13 (see fig. 3).

The actuator 27 can also be moved by a bimetallic strip (not shown) instead of the armature and the magnet.

In one particularly preferred embodiment, the reservoir chamber 10 is provided on the secondary side of the fluid friction clutch 1 and the inner chamber 18 is provided on the primary side of the fluid friction clutch 1.

Finally, in an alternative embodiment according to fig. 7, the fluid friction clutch 1 has a return bore 30 for pressure relief which connects the feed channel or feed channel section 11a via a further fluid inlet opening (not shown) of the valve 17 to the reservoir chamber 10. In this embodiment, no inner volume is provided, with the result that the oil is not conveyed back via the inner reservoir. This embodiment of the fluid friction clutch 1 according to the invention can be used in relatively small clutch designs which do not require an inner volume, since the drag moments are low in said designs.

Figs. 1C to IE show a further embodiment of a fluid friction clutch 1 according to the invention. All components which correspond to those of figs. 1A and IB are labeled with the same designations, with the result that reference can be made to their description above.

The embodiment according to figs. 1C to IE is distinguished by the provision of an oil cooler 31. The oil cooler 31 is arranged in the housing 2, 3, the illustration which is selected in figs. 1C to IE showing a particularly preferred embodiment, in which the oil cooler 31 is arranged in the cover 3.

The oil cooler 31 has first of all an oil-cooler delivery pump 32 which can be rotated with the housing, with the cover 3 in the case of the example, relative to the clutch plate 4, adjacently to which the oil-cooler delivery pump 32 is arranged, as results from figs. 1C to IE. The oil-cooler delivery pump is arranged in the reservoir chamber 10.

Furthermore, the oil cooler 31 has an oil feed channel 33. A first end 33 A of said oil feed channel is flow-connected to the oil-cooler delivery pump 32. A second end 33B of the oil feed channel 33 is flow-connected to a first end 34A of an oil cooling channel 34.

As results, in particular, from the illustration of figs. 1C and ID, said oil cooling channel 34 extends at least substantially transversely with respect to the longitudinal axis L of the fluid friction clutch 1 and runs through the entire cover 3 in this transverse direction in the case of the example which is shown. The second end 34B of the oil cooling channel 34 is again flow-connected to the reservoir chamber 10. In the embodiment which is shown in figs. 1C and ID, this further flow connection to the reservoir chamber 10 is brought about via a feed channel 35 which adjoins the second end 34B.

As has already been explained at the outset, the fluid circuit which is formed by the oil-cooler delivery pump 32, the oil feed channel 33 and the oil cooling channel 34 is formed parallel to the main actuation fluid circuit which connects the working chamber 9 and the reservoir chamber 10 to one another and has been explained using the preceding embodiment.

The oil cooler 31 acts only in the medium slip heat range of the fluid friction clutch 1 according to the invention, since the fluid or the oil can only reach the delivery pump 32 at all in this range, since there is a sufficient quantity of oil in the reservoir chamber 10 in this operating state in order to supply the delivery pump 32 with oil. In this case, the oil-cooler delivery pump 32 pumps hot oil into the oil cooling channel 34, from which cooled oil is conveyed back into the working chamber 9.

In addition to the above written disclosure of the invention, reference is made hereby explicitly to the diagrammatic illustration of the invention in figs. 1 to 4 in order to complete the disclosure of the invention.

LIST OF REFERENCE SIGNS

1 Fluid friction clutch

2, 3 Housing (2: housing body, 3: cover)

4 Clutch plate

5 End of the shaft 6

6 Shaft

7 Active element (for example, im

8 Second end of the shaft 6

9 Working chamber

10 Reservoir chamber

11a, l ib Feed channel

12 Shear gap

13 Stationary clutch parts (magnet)

14 Supply pump element

15 Working gaps

16 Recirculating pump

17 Valve

18 Inner reservoir

19 Non-return valve

20 Return valve

21 Valve arm

22 Connecting bore

23 Return channel

24 Valve element

25 Through bore

26 Fluid inlet recess

27 Actuator

28 Armature

29 Flux ring

30 Return bore

31 Oil cooler

32 Oil-cooler delivery pump Oil feed channel Oil cooling channel Feed channel