Abstract: A control coupling, particularly for use with a differential gearing, the coupling including an enclosure containing a viscous liquid and first and second mutually interleaved sets of annular plates arranged for rotation about a common axis within the enclosure. The first set of plates are arranged to be connected with a first rotatable member and the second set of plates being arranged to be connected with a second rotatable member, and the plates of at least one set are free to move in directions parallel to the common axis. One of the sets of plates are mounted on a hollow hub which projects within the enclosure and which has a bore which is open to, and forms part of, the enclosure volume. A piston is slidable in this bore to vary the volume of the enclosure and springs are located in the bore to urge the piston towards a limit position in which the volume of the bore in communication with the remainder of the enclosure is at a minimum.

Abstract: A coupling for controlling or limiting the angular velocity or angular acceleration between first and second rotatable members. The coupling has an enclosure containing viscous liquid in which first and second sets of interleaved elements and third and fourth sets of interleaved elements are arranged for rotation about a common axis. The first and third sets of elements have driving connections with the first rotatable member and the second and fourth sets of elements have driving connections with the second rotatable member. Spacing means are provided to space apart the facing surfaces of adjacent elements of at least one of said first and second sets and also at least one of said third and fourth sets so that the facing surfaces of adjacent elements of each spaced set are spaced apart by distances greater than the thicknesses of the portions of the elements of the other set interleaved between said facing surfaces. The spacing means provided for one or both of the third and fourth sets are resilient.

Abstract: A control coupling in which an enclosure houses first and second sets of mutually interleaved elements in a viscous liquid. The first and second sets of elements are arranged for rotation about a common axis and for driving connection with first and second rotatable members respectively. A clutch is provided outside the enclosure and resilient means are arranged to urge the clutch into a disengaged state. A pressure responsive means which is in communication with the enclosure is arranged to engage the clutch against the action of the resilient means when the pressure in the liquid in the enclosure attains a predetermined level.

Abstract: Viscous shear couplings for controlling the action of an interaxle or interwheel differential gear in a vehicle transmission are described. The couplings comprise a pack of interleaved annular plates which are free to float axially in an annular enclosure containing a viscous liquid. The enclosure incorporates a spring-loaded piston shiftable to vary the enclosure volume. The quantity of viscous liquid, in the range 85% to 100% of the minimum volume at ambient temperature, and the spring strength are chosen to give a predetermined pressure build-up within the enclosure with rise in temperature during shearing of the viscous liquid to tailor the torque-transmitting characteristics of the coupling to particular needs.

Abstract: A control coupling in which an enclosure houses first and second sets of mutually interleaved elements in a viscous fluid. The first and second sets of elements are arranged for rotation about a common axis and for driving connection with first and second rotatable members respectively. The quantity of liquid within the enclosure and the construction of the enclosure are such that, at a predetermined working temperature of at least 100.degree. C, the pressure of the liquid in the enclosure rises substantially above ambient. At least one set of the elements is free to move in directions parallel to the common axis of rotation and at least one set of the elements is provided with facings of friction material.