192 clutches and power-stop control – Clutches – Fluent material
Reexamination Certificate
1997-12-12
2001-02-06
Bonck, Rodney H. (Department: 3681)
192 clutches and power-stop control
Clutches
Fluent material
C192S058430, C192S085060, C192S1030FA
Reexamination Certificate
active
06182810
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to an automatic coupling comprising two parts which are supported inside one another, which are rotatable around a common longitudinal axis and which form an annular chamber filled with a highly viscous fluid, for the purpose of generating a locking effect between the two parts when the two parts rotate relative to one another. In referring herein to a “locking” effect between the two parts, it is to be appreciated that in practice the effect is one of an inhibition or braking of relative rotation between the parts rather than a complete prevention of relative rotation, and the term “locking” is to be interpreted accordingly.
Couplings of this type are known as viscous couplings and described in GB 1 357 106. These couplings are used in combination with differential drives or on their own in the drivelines of motor vehicles. In the former application they generate a differential-speed-dependent locking effect at the axle differentials or in central differentials. In the latter application they serve as so-called visco-transmissions which have the function of a differential-speed-dependent engageable coupling for the second driving axle which is normally the rear axle of motor vehicle with a permanent front wheel drive.
Furthermore, a coupling of this type is known from DE 37 25 103 C1 wherein the coupling plates of a viscous coupling operate in a highly viscous fluid and wherein a conveying worm also operating in the highly viscous fluid is intended to reduce the locking effect as a function of the fluid level in the region of the coupling plates in the case of a relative rotation.
Furthermore, DE 37 43 434 C2 describes a friction coupling operated by a pressure agent, which is combined with a viscous coupling, with the latter being included in the power flow between a housing and a hub when the friction coupling is loaded, whereas the parts rotate freely relative to one another when the friction coupling is not loaded.
Finally, P 43 43 307.3 proposes a Visco-Lok coupling wherein a highly viscous fluid in a chamber—as a result of shear processes in the highly viscous fluid—increases the pressure in such a way that there is displaced a piston which delimits the chamber and which loads a conventional multi-plate friction coupling in the sense of closing same.
SUMMARY OF THE INVENTION
It is the object of the present invention to provide a coupling of the initially mentioned type which, in the form of a viscous coupling, even at a small speed differential and after an extremely short reaction time, contributes towards building up a known locking effect and which, at a greater speed differential and thus with increased traction requirements, generates a greater locking effect.
The objective is achieved in that, in the annular chamber, there is arranged an annular piston which divides the annular chamber into two compartments and which, in the annular chamber, is connected to one of the parts in a rotationally fast and axially displaceable way by means of driving elements; and which, by means of a cylindrical outer face, closely fits into a cylindrical counter face of the other one of the parts; and that between the outer face and the counter face there is provided at least one shear channel which extends helically relative to the longitudinal axis and which connects the two compartments to one another, which compartments are separated by the annular piston; and that end faces of the annular chamber are formed by the other one of the parts and that the annular piston, by means of end faces, is able to support itself at least indirectly at the end faces of the annular chamber for the purpose of generating braking forces.
This coupling embodiment shows that when the annular piston is in a centered position, the coupling, in respect of design and function, corresponds to a viscous coupling and that if the annular piston is in a position of support in one compartment, the coupling becomes a friction coupling whereas, in the other compartment, it continues to operate as a viscous coupling with changed characteristics, with the effect of both couplings being added up.
In consequence, there are obtained three major characteristic curve portions which are advantageously adapted to and cover three operating conditions as follows:
small speed differential, determined entirely by the characteristics of a viscous coupling, initially with a low locking moment: suitable for tight cornering; avoids wind-up in the driveline.
higher speed differential, determined entirely by the characteristics of a viscous coupling, with higher, moderately increasing locking moment; suitable for normal driving conditions; no negative influence on vehicle handling.
high speed differential, largely determined by the characteristics of a friction coupling; progressively increasing locking moment as a starting aid in the case of wheel spin.
If there exists a relative speed between the two parts rotatable relative to one another, fluid shear takes place in the shear channel, as a result of which the fluid is conveyed from the one compartment into the other compartment, with the piston being axially displaced in the annular chamber.
If the annular piston is in a centered position in the annular chamber, the coupling has the locking effect and the advantageous vibration damping effect of a viscous coupling. In the case of a predetermined higher speed differential, the coupling additionally acts as a mechanical friction coupling. It is particularly advantageous that between the housing and hub there are provided only rotating seals and not also axially displaceable seals.
According to a preferred embodiment it is proposed that between the annular piston and one of the parts, there are arranged axially effective spring means which axially center the annular piston in the annular chamber and which, with a reproducible reaction time, do not allow the coupling to operate as a friction coupling until there exists a higher predetermined speed differential.
In this way it is ensured that the reaction behavior in both directions of relative rotation is always the same due to the annular piston being centered, and that it is not influenced by previous locking processes. When the annular piston is centered, pressure compensation takes place through the helical shear channel.
When eliminating such spring means, a similar effect can be achieved by a plurality of shear channels with a steep gradient in respect of the circumferential direction. In this case it is necessary to provide a higher speed differential to build up a piston pressure sufficient for closing the friction coupling.
According to a first embodiment it is proposed that the end faces of the annular piston and/or the end faces of the annular chamber are provided with friction linings and are able to contact one another directly. According to a further embodiment it is proposed that between the end faces of the annular piston and the end faces of the annular chamber, there are arranged sets of inner plates and outer plates which, in a rotationally fast and axially movable way, are alternately connected to the one and the other of the parts rotatable relative to one another, and which are able to contact one another directly.
By designing the friction linings in the two compartments in different ways or by providing different numbers of coupling plates in the two compartments, it is possible to achieve different characteristics as a function of the direction of relative rotation between the housing and the hub.
According to a preferred embodiment, the inner or outer plates directly contacting the end faces of the annular piston are connected in a rotationally fast way to the same one of the rotatable parts as is the annular piston. Any wear at the annular faces of the annular piston is thus avoided. According to a further embodiment it is proposed that the driving elements consist of longitudinal teeth at the one of the rotatable parts and of counter teeth at the annular piston, which teeth engage one another with a cleara
Bonck Rodney H.
Carten Francis N.
GKN Viscodrive GmbH
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