Spacing mechanism for the plates of a fluid friction coupling

A fluid friction coupling comprises a coupling hub (1) and a coupling housing (2) rotatably supported on the coupling hub. The coupling also comprises sets of plates (6; 7) non-rotatably mounted on the hub and housing. One set of plates has spacing teeth (8) which, while eliminating the previously used spacer rings, permit accurate spacing of the set of plates. A predetermined number of spacing teeth (8) of the axially immovable plates (7) are bent out of the plane of the respective plate so as to be Z-shaped with both bending angles approximately 90 degrees. This measure ensures that the plates for a friction coupling are designed in such a way that they are accurately spaced at predetermined distances and that they are suitable for automatic assembly purposes.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a fluid friction coupling comprising at least one 
coupling hub, a coupling housing rotatably supported on the coupling hub, 
and two sets of plates, one non-rotatably connected to the coupling hub 
and one non-rotatably connected to the coupling housing, the plates of the 
sets of plates being disposed in an alternating sequence with the plates 
of a first of the sets being held at predetermined spacings from one 
another while the plates of the other set are axially movable. 
2. Description of Prior Art 
With such fluid friction couplings such as they are known from West German 
Patent Specification No. 38 28 421 C1 and its British equivalent No. 2 222 
232, spacing between the first set of plates is achieved by so-called 
spacer rings of a predetermined thickness. These spacer rings are slotted 
and as compared to the inner diameter of the coupling housing, they have a 
slightly increased outer diameter so that they rest against the inner 
housing wall in a prestressed condition. However, a disadvantage of this 
design is that automatic assembly of the plates is either not possible at 
all or causes great difficulties, which is the reason why the plates are 
still fitted by hand. 
From U.S. Pat. No. 4,058,027, it is known to arrange a certain number of 
teeth on the plates in an angular position in order to achieve a 
spring-loaded return. However, for spacing the plates such an angular 
position is not suitable because the tolerances of the outer diameter and 
especially centering of the plates have to be very close to achieve 
uniform dimensions for the distances to be observed, whereas an 
articulated position, because of its spring-loaded return forces, does not 
permit such tolerances or only with considerable effort. 
From West German Patent Specification No. 37 26 641 C1 and its British 
equivalent No. 2 207 983 it is known to provide one of the sets of plates 
with cam-like pressed-out regions which are aligned relative to each other 
in one direction of rotation and which increase the distance between the 
associated plates. However, it is the purpose of this design to provide 
the fluid friction coupling with different torque characteristics for the 
two directions of rotation; a predetermined distance between the plates 
cannot be achieved with such pressed-out regions. 
SUMMARY OF THE INVENTION 
It is the object of the present invention to provide a fluid friction 
coupling of the initially described type which, while eliminating the 
previously used spacer rings, permits accurate spacing of the plates. 
The invention provides a fluid friction coupling comprising at least one 
coupling hub, a coupling housing rotatably supported on the coupling hub, 
and two sets of plates, one non-rotatably connected to the coupling hub 
and one non-rotatably connected to the coupling housing, the plates of the 
sets of plates being disposed in an alternating sequence with the plates 
of a first of the sets being held at predetermined spacings from one 
another while the plates of the other set are axially movable, wherein the 
plates of the first set have a predetermined number of spacing teeth each 
of which is bent out of the plane of the plate to form a Z-shape having 
two bending angles which are both approximately 90 degrees. 
Each spacing tooth, thus, has a first portion which extends substantially 
normally of the plane of the plate and a second portion which extends from 
the end of the first portion substantially parallel to the plane of the 
plate. 
In this way, it is possible for the plates of the fluid friction coupling 
to be spaced accurately at predetermined distances. Such plates are 
suitable for automatic assembly, and the invention permits the inner or 
outer plates to be provided with bent teeth. As bending angles of approx 
90 degrees are used for the Z-shape, the dimensional accuracy of the axial 
bends is determined exclusively by the accuracy of the tool used. Other 
tolerances such as those of the outer diameter, inner diameter or material 
thickness do not affect the dimensional accuracy of the bends. A further 
advantage of the bends in accordance with the invention consists in the 
fact that the bent teeth are not subject to bending moments. Any axial 
forces acting on the bent regions can only affect the axial webs in the 
form of compressive forces. 
In a preferred embodiment in the case of which assembly is particularly 
easy, the first set of plates having the spacing teeth is a set of outer 
plates non-rotatably connected t the coupling housing. However, the first 
set may be a set of inner plates non-rotatably connected t the coupling 
hub. 
A fluid friction coupling may be designed as a torque splitter which 
comprises two sets of inner plates, with a predetermined number of teeth 
of both sets of inner plates non-rotatingly connected to separate coupling 
hubs and either the outer plates or both sets of inner plates having 
spacing teeth.

DESCRIPTION OF PREFERRED EMBODIMENTS 
FIG. 1 shows the drive concept of a four wheel drive vehicle 15 the basic 
concept of which is that of a front wheel drive vehicle. The two front 
wheels 16 are driven by the engine 18 via a gearbox 19 and a front axle 
differential 20 as well as via the front sideshafts 21. The drive for the 
rear wheels 17 is branched off the drive of the front axle differential 
20. For this purpose, the front axle differential is associated with a 
central differential 22 which is equipped with a fluid friction coupling 
as illustrated in FIG. 2 in order to achieve a speed-dependent locking 
effect of the central differential. Via a propeller shaft 23, the central 
differential 22 is connected to the rear axle differential 24 which drives 
the rear wheels 17 via rear sideshafts 25. 
The fluid friction coupling illustrated in FIG. 2 essentially comprises a 
coupling hub 1 and a coupling housing 2 rotatably supported on the hub 1 
and sealed by seals 3. The inner wall of the coupling housing 2 is 
provided with inner teeth 4, whereas the coupling hub 1 comprises outer 
teeth 5. In the outer teeth 5 there are arranged correspondingly toothed 
plates 6 of a set of inner plates so as to be non-rotatable, but axially 
movable on the coupling hub 1. Plates 7 of a set of outer plates provided 
with teeth 9 are non-rotatingly connected to the coupling housing 2 via 
the inner teeth 4. 
The interior 11 of the coupling housing 2 accommodates the inner plates 6 
and the outer plates 7 which are disposed in an alternating sequence. The 
plates 7 are held at predetermined spacings from one another while the 
plates 6 are axially movable. To achieve the spacing, each plate 7 has a 
predetermined number of its radially outer teeth 9 formed into spacing 
teeth 8. 
The spacing teeth 8 are each bent out of the plane of the plate 7 to form a 
Z-shape. Between the inner plates 6 and the outer plates 7 there is a free 
space 12 in which the inner plates 6 are axially movable, whereas the 
outer plates 7 are spaced at a fixed distance from one another due to the 
teeth 8 bent so as to be Z-shaped. The orientation of adjacent plates 7 is 
different so that, at their bent ends, the Z-shaped teeth 8 cooperate with 
the non-deformed teeth 9 of the adjacent outer plate 7. 
As can be seen in FIG. 3, the Z-shaped teeth 8 are bent by a right angle 14 
out of the plane of the respective outer plate 7. After forming an axial 
web 13 of a predetermined length which depends on the required spacing, 
the respective tooth 8 bent so as to be Z-shaped is again bent by a second 
right angle 14a in a direction parallel to the plane of the outer plate. 
In consequence, the axial web 13 extends at a right angle relative to the 
plate of the respective outer plate 7 and when ensuring the distance 
relative to the adjacent outer plate (not illustrated) it does not have to 
accommodate any bending moments. 
The embodiment illustrated in FIG. 4 is provided with five teeth 8 bent so 
as to be Z-shaped. However, the number of Z-shaped teeth depends on the 
division of the outer teeth, but there should be at least 3 teeth of each 
plate bent so as to be Z-shaped. The illustrated outer plate 7 is provided 
with slot-shaped perforations 10. When fitting the outer plates 7, the 
Z-shaped teeth 8 are intended, in each case, to rest against a tooth 9 of 
the next adjacent outer plate. This objective can be achieved by providing 
index markings (not illustrated) on the plates and by making suitable 
provisions at the automatic feeding device. 
As shown in FIG. 5, the axial webs 13 resulting from the bent teeth 8 
permit a kind of spacing which has a sufficiently high degree of 
dimensional accuracy. A fluid friction coupling provided with outer plates 
7 spaced in this way may be associated for example with the central 
differential 22 of a motor vehicle such as it is illustrated in the drive 
concept of FIG. 1. In the case of the embodiment shown, the coupling hub 1 
is the driving part, whereas the coupling housing 2 is the driven part 
connected to the rear axle differential via the propeller shaft 23. The 
interior of the coupling housing 2 is at least partially filled with a 
viscous medium, preferably a silicone oil. 
FIG. 6 shows an arrangement of Z-shaped spacing teeth 8a on an inner plate 
6 of an alternative fluid friction coupling. 
FIG. 7 illustrates the basic concept of a vehicle drive where the central 
differential 22 is replaced by a torque splitter 28. This torque splitter 
28 replaces the central differential 22 and at the same time the usual 
rear axle differential (24). The torque splitter consists of the housing 
26 which is driven by the angular drive 27 and to which a set of outer 
plates is non-rotatingly connected, and of two sets of inner plates each 
of which is associated with a wheel drive. The invention may be used to 
great advantage here because this application requires a large number of 
plates so that automation has favourable effects.