Fluid Friction Clutch

The invention relates to a fluid friction clutch for a cooling fan of an internal combustion engine.

From Fed. German Patent Application No. 3,246,783 a fluid friction clutch for a cooling fan of an internal combustion engine is known in which a substantially U-shaped holder for a bimetallic element is fitted on the front of a housing enclosing the driven rotor so as to form shear gaps. The bimetallic element is a component of a regulating device which controls the shear fluid level in the working gap in dependence upon temperature. In the known fluid friction clutch the bimetallic element has a substantially rectangular configuration and is inserted in the region of its short sides into openings of the holder. It is resiliently held in the openings by the relatively slight initial stress force of a valve element arranged in the interior of the housing, which valve element is in connection with the bimetallic element through a thrust piece displaceably passing through the front of the housing. The manner of fastening has the advantage that the bimetallic element can easily be fitted and also replaced. However it has the disadvantage that in the case of heavy vibrations of the internal combustion engine the zones with which the bimetallic element is seated in the retaining fitting are knocked out, so that the bimetallic element can slip out of the retaining fitting due to unintended contact and the cooling fan loses its temperature-regulating properties.

The main concern of the invention is to avoid the above disadvantages and in a manner of simple design to secure the bimetallic element to the front of the housing, namely in such a way that it can be subjected without problem to even heavy vibrations.

Within the scope of the invention, flexible retaining tabs are integrally formed on the longitudinal ends of the bimetallic element, which tabs are angled off towards the front and are firmly fastened, preferably riveted, to the front. The retaining tabs are integral components of the bimetallic element and compensate for its variation of length, even though slight, in its temperature-caused flexure. The non-losable fastening is not disengaged even by heavier vibrations caused by the internal combustion engine.

In order to increase the flexibility of the retaining tabs, the cross-sectional area of the retaining tabs is expediently smaller than the cross-sectional area of the actual bimetallic element. For preference each of the retaining tabs consists of two flexible retaining bridge pieces arranged with spacing from one another which, by pairs in each case, connect the longitudinal end of the bimetallic element with a flange tab which contains the hole provided for the rivet connection. The interval between the two retaining bridge pieces at the same time forms a passage opening for the riveting tool needed for closing the rivet connection.

It has also proved to be favourable if the apertures formed between the retaining bridge pieces continue in the form of slots towards the centre of the bimetallic element. The slots reduce the tendency of the bimetallic element to curve not only in longitudinal direction but also in the transverse direction.

The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which there are illustrated and described preferred embodiments of the invention .

Examples of embodiment of the invention will be explained in greater detail below by reference to drawings wherein:

FIG. 1 shows an axial longitudinal section through a fluid friction clutch for a cooling fan of an internal combustion engine;

FIG. 2 shows a partial view of the fluid friction clutch seen in the direction towards the front and

FIG. 3 shows an axial longitudinal section through a variant of the fluid friction clutch according to FIG. 1.

The fluid friction clutch as represented in FIGS. 1 and 2 comprises a housing designated generally by 1, which is rotatably mounted with a housing basic part 3, by means of a bearing 5, on a shaft 9 driven by the internal combustion engine about an axis 7 of rotation. The housing basic part 3 carries fan blades indicated at 11 and is closed in sealed manner by a cover 13 forming the front of the housing 1. A partition 15 divides the interior of the housing 1 into a reservoir chamber 17 for shear fluid and a working chamber 19 lying axially therebeside. In the working chamber 19 there is situated a rotor 21 of substantially disc form which, together with the housing basic part 3 and the partition 15, forms shear gaps 23 which, when they are filled with shear fluid, transmit the drive torque of the shaft 9 to the housing 1. When the shear fluid is conducted away out of the shear gaps 23 the clutch is disengaged.

The operation of the clutch is controlled by a bimetallic element 25 in dependence upon the ambient temperature. The bimetallic element 25 is secured in the manner as explained below on the outside of the cover 13 and acts through a central thrust piece 27, guided displaceably in the cover 13, upon a resilient valve lever 29 secured on the partition 15, which valve lever 29 in turn controls an opening 31 of the partition 15. Through the opening 31 shear fluid can pass from the reservoir chamber 17 into the working chamber 19 for the engagement of the clutch. A dynamo pressure pump device (not shown further), on relative rotation between the housing 1 and the rotor 21, ensures the return of the shear fluid from the working chamber 19 into the reservoir chamber 17 for the disconnection of the clutch. An adjusting screw 33 on the bimetallic element 25 permits the adjustment of the change-over behaviour of the clutch. The manner of operation of such fluid friction clutches is known and is therefore not to be explained in greater detail.

As shown best by FIG. 2, the bimetallic element 25 has a substantially rectangular elongated configuration on each of the longitudinal ends of which two retaining bridge pieces 37 are formed by apertures 35. The retaining bridge pieces 37 lie opposite to one another with spacing, in the transverse direction of the bimetallic element 25 and, as shown best by FIG. 1 for the longitudinal central plane of the bimetallic element 25, are angled in U-form and connected with one another at their ends by a common flange tab 39 in each case. The flange tab 39 and the retaining bridge pieces 37 are formed in one piece on the bimetallic element 25. The flange tabs 39 have holes 41 through which there pass rivets 45 seated in holes 43 of the cover 13, securing the bimetallic element 25 durably to the cover 13. The apertures 35 between the two retaining bridge pieces 37 at each of the two longitudinal ends extend, in a view of the cover 13, to over the rivets 45 and at the same time form passage openings for the riveting tools necessary for closing the rivets. Furthermore the apertures 35 reduce the cross-sectional area of the retaining bridge pieces in relation to the cross-sectional area in the middle region of the bimetallic element 25, so that the retaining bridge pieces 37 are sufficiently flexible to be able to compensate for the variation of length, even though slight, of the bimetallic element in the case of a temperature-caused flexure. The flexibility of the retaining bridge pieces 37 further has the function of a hinge.

The apertures 35 extend from the flange tabs 39, resting on the cover 13, to above the rivets 45. In the longitudinal central place of the bimetallic element 25 however the apertures 35 continue as slots 47 which are narrower in the transverse direction of the bimetallic element 25. The slots 47 terminate at a distance from the centre of the bimetallic element and the unslotted central region of the bimetallic element 25 amounts to more than about 30% of the overall length, represented in the axial view in FIG. 2, of the bimetallic element 25 including the projections of the retaining bridge pieces 37. The slots 47 improve the controlling properties of the bimetallic element 25, in that they reduce the transverse doming occurring transversely of the longitudinal direction of the bimetallic element 25.

FIG. 3 shows a variant of a fluid friction clutch. Parts of like effect are designated in FIG. 3 by the reference numerals of FIGS. 1 and 2, and reference is made to the description of these figures for explanation.

The clutch according to FIG. 3 differs from the clutch according to FIGS. 1 and 2 merely in that the securing rivets 45 are not conducted through holes 43 of the cover 13, but are formed, for example by injection moulding, on the cover 13 as one-piece rivet projections. This design reduces the danger of leakages. The rivet projections 45 can be deformed by wobble devices or the like after the fitting-on of the bimetallic element 45.

The direct riveting of the bimetallic element 25 on the front of the cover 13 improves the strength of the fastening, in comparison with conventional types of fastening of bimetallic elements, so that durable fastening is achieved even in the case of heavily vibrating internal combustion engines. Unintended release of the bimetallic element, such as could occur hitherto, is prevented.

While specific embodiments of the invention have been shown and described in detail to illustrate the application of the inventive principles, it will be understood that the invention may be embodied otherwise without departing from such principles.