Abstract: A system for use with an automotive vehicle supported on front and rear pairs of road wheels to detect a drop in a tire air pressure for each of the road wheels. When the vehicle is detected as operating substantially in a steady straight line driving condition, the road wheel having a dropped tire air pressure is specified based on the angular speeds of rotation of the respective road wheels. This detection is made based on the angular road wheel speeds in view of changes in loads exerted in the respective road wheels caused by the tire air pressure drop.

Abstract: A seal device is adapted to be mounted at an area of relative rotation between two mounting portions of a tire pressure-adjusting device. The seal device includes a pair of first and second seal rings which are disposed in opposed relation to each other. Each of the first and second seal rings includes a main seal of an annular shape having a radially inwardly-directed lip formed on an inner periphery of the main seal, the lip having at its distal end a lip sliding surface to which a self-lubricating thin plate for sliding contact with one of the two mounting portion. Each seal ring further includes an auxiliary seal of an annular shape having a radially inwardly-directed lip which is formed on an inner periphery of the auxiliary seal and is adapted for sliding contact with the one mounting portion, the auxiliary seal being connected to the main seal to form therebetween a closed space for holding grease.

Abstract: A four-wheel drive system comprises a first drive train that is mechanically engageable for transmitting a driving force from an engine to a set of front wheels and a second drive train that is provided with a viscous coupling for transmitting a driving force from the engine to a set of rear wheels by way of the viscous coupling. The second drive train is constructed so as to satisfy the relation that the speed of rotation of an input shaft of the viscous coupling divided by the speed of rotation of the front wheels is larger than the result of the speed of rotation of an output shaft of the viscous coupling divided by the speed of rotation of the rear wheels.