Power steering system having a mechanical safety breaker

DETAILED DESCRIPTION We claim: 1.
A power steering system for assisting steering operation of a manual steering system having a rack and pinion steering means, a steering shaft connected with the rack-and-pinion means for steering operation thereof, and a steering wheel connected with the steering shaft for driving the steering shaft in either of opposite steering directions by a driver, said power steering system comprising: a motor for generating a force for assisting said steering operation of said manual steering system, and means for torque transmittingly connecting said motor with said manual steering system, wherein said torque transmitting connection means includes a mechanical safety breaker element for breaking the torque transmitting connection of said motor with the manual steering system when the torque transmitted exceeds a predetermined limit value, said breaker element being made substantially of a ceramic material, said ceramic material substantially maintaining its fracture strength over a relatively long period of use under repeated applications of load.
2.
A power steering system according to claim 1, wherein said breaker element is a plate element adapted to transmit said force via a sheering along a cross sectional region at a middle portion thereof in a plane extension thereof.
3.
A power steering system according to claim 2, wherein said cross sectional region of said plate element is defined by a pair of notches formed in opposite surfaces of said plate element to be substantially aligned to one another across the thickness thereof.
4.
A power steering system according to claim 3, wherein said plate element has a sectoral configuration with said notches being formed in parallel with a straight edge thereof to traverse a middle portion of said sectoral configuration, the depth of said notches being changed along a length thereof so as to be smallest at a central portion of the length and to be largest at opposite ends of the length.
5.
A power steering system according to claim 4, wherein the depth of said notches is changed arcuately so as to define arcuately convex opposite edges of said cross sectional region