Differential-speed-dependent automatic coupling with reduction switching means

A Viscotrac® coupling (111) comprising inner and outer parts (121, 141) supported inside one another and rotatable relative to one another around a common longitudinal axis, and forming an annular space (131) which is filled with a highly viscous medium in which there are arranged inner plates (127, 129) which are non-rotatably connected to said inner part (121) and form a set of inner plates, as well as outer plates (148) which are non-rotatably connected to said outer part (141) and form a set of outer plates, said inner plates (127, 129) and outer plates (148) being arranged so as to alternate in the longitudinal direction for the purpose of generating a coupling effect between said inner and outer parts (121, 141) when the latter rotate relative to one another, wherein in the annular space (131) an annular piston (171) is arranged axially between said plates to axially divide said annular space (131) into two chambers (173, 175), and is connected to one of said inner part (121) and said outer part (141) by means of driving elements (172) in a non-rotatable and axially movable way, wherein said annular piston (171) by means of one of its cylindrical faces, rests against a counter face of the other one of said inner part (121) and said outer part (141) and wherein, between said one cylindrical face and said counter face, there is formed at least one channel (179) which extends helically relative to the longitudinal axis and which connects said two chambers (173, 175) to one another wherein said annular piston (171) is carried directly by a sleeve (125) which is coupled to that one of said inner part (121) and said outer part (141) of the coupling which carries said annular piston (171) in such a way it can be uncoupled in respect of relative rotation at a raised rotational speed in that it provides a two-part characteristic curve with a declining jump function of coupling forces over rotational speed.

An improvement in a Viscotrac® coupling which comprises inner and outer parts supported inside one another and rotatable relative to one another around a common longitudinal axis, and forming an annular space which is filled with a highly viscous medium;

• inner plates non-rotatably connected to said inner part and forming a set of inner plates arranged within said annular space;
• outer plates non-rotatably connected to said outer part and forming a set of outer plates, said inner plates and outer plates being arranged so as to alternate in the longitudinal direction for the purpose of generating a coupling effect between said inner and outer parts when said inner and outer parts rotate relative to one another, wherein in said annular space an annular piston is arranged axially between said plates to axially divide said annular space into two chambers, and is connected to one of said inner and outer parts by means of driving elements in a non-rotatable and axially movable way, wherein said annular piston, by means of one of its cylindrical faces, rests against a counter face of the other one of said inner and outer parts and wherein, between said one cylindrical face and said counter face, there is formed at least one channel which extends helically relative to said longitudinal axis and which connects said two chambers to one another, the improvement comprising:
• said annular piston is carried directly by a sleeve which is coupled to that one of said inner and outer parts which carries said annular piston in such a way it can be uncoupled in respect of relative rotation at a raised rotational speed in that it provides a two-part characteristic curve with a declining jump function of coupling forces over rotational speed.