Patent ID: 7581576

Claim:
An automatic air-feeding mechanism for a pneumatic tire for automatically supplying air to a pneumatic tire mounted on a wheel body rotatable about an axle of a vehicle, comprising: a compressed air producing section for producing compressed air when the wheel body is rotated about the axle, wherein the compressed air produced in the compressed air producing section is supplied to the pneumatic tire, wherein the compressed air producing section has a compression chamber for compressing the air therein, an air intake port for introducing outside air into the compression chamber, and a waterproof mechanism for preventing water from entering the compression chamber through the air intake port, wherein the wheel body has a hub rotatably supported by the axle and the compressed air producing section is attached to the hub of the wheel body, wherein the waterproof mechanism has a first air passage connecting the air intake port in air flow communication with the interior of the hub so that air can be taken in from the interior of the hub into the compression chamber through the first air passage in order to prevent water from entering the compressed air producing section, wherein the hub has a cylindrical hub drum, and supporting parts for supporting the hub drum from both sides, the supporting parts being rotatably supported on the axle, whereby the hub is rotatable about the axle and a partitioned space is defined in the hub by the hub drum and the supporting parts; and the waterproof mechanism has a second air passage formed through the supporting parts and communicating the partitioned space in the hub with the outside, wherein each one of the supporting parts of the hub has a steel ball receiving part for rotatably receiving a plurality of steel balls, and an axle hole formed radially inside the steel ball receiving part for rotatably receiving the axle, and the steel ball receiving parts are rotatably supported by the axle extending through the axle hole via a plurality of steel balls, whereby the hub is rotatable about the axle and an axle-gap air passage extending from the partitioned space through an axle gap formed between the inner surface of the axle hole and the axle and steel ball gaps formed between the steel balls and in air flow communication with the partitioned space is formed through each of the supporting parts of the hub; and the second air passage includes at least one of the axle-gap air passages as a constituent element.