The present invention refers to a hub-bearing assembly allowing pressurized air to be supplied to the tire of a motor vehicle wheel.
There are known hub-bearing units allowing to inflate air pressurized by a source of pressurized air mounted on board of the vehicle to the tire in order to adjust and/or monitor the air pressure of the tires.
In some known solutions, as for example in U.S. Pat. No. 5,642,946 and EP-A-0 362 921, radial bores are formed in the outer and inner races of the bearing for allowing pressurized air to pass to the rotating part of the hub-bearing assembly. Forming such bores involves a constructional complication which may adversely affect the bearing raceways, which—as known—are made of hardened steel and have very low admissible tolerances.
In other known solutions, as for example in U.S. Pat. No. 5,221,381, air is conveyed to the wheel through an axial bore formed in the rotating hub.
In both the above-mentioned cases, pressurized air is let into the hub-bearing assembly very near the rolling bodies. It is therefore necessary to fit special high duty sealing devices preventing pressurized air from penetrating directly into the inner part of the bearing, where the lubricating grease for lubricating the rolling parts is contained. The sealing devices are expensive and develop considerable friction. Moreover, the passage of pressurized air through the bearing can shorten considerably its life, in case the above-mentioned sealing devices should be or become faulty. In addition, the sealing devices are normally mounted proximate to the bearing raceways, and therefore have to be miniaturized due to the available space, that is minimum in those zones.
U.S. Pat. No. 5,584,949 discloses a system for inflating air to the tires through the axle of the wheels of a trailer. A threaded ring, constituting an airtight barrier, is screwed onto the end of the axle.
In view of the foregoing state of the art, it is a general object of the present invention to inflate pressurized air to a hub-bearing assembly, avoiding the problems concerning the formation of bores of the passage of air near the bearing raceways.