Floating bush bearing device and turbocharger provided with the bearing device

A floating bush bearing device, comprising:

• a casing including a bearing hole;
• a rotary shaft disposed rotatably inside the bearing hole;
• a floating bush disposed rotatably inside the bearing hole and surrounding the rotary shaft;
• an oil-feed hole of lubricant oil, the oil-feed hole having an opening on an inner peripheral surface of the bearing hole;
• a plurality of communication holes formed on the bush, each of the communication holes extending between an inner peripheral surface and an outer peripheral surface of the floating bush, and disposed at intervals in a circumferential direction of the floating bush;
• and
• a circumferential groove formed on the outer peripheral surface of the floating bush or the inner peripheral surface of the bearing hole and extending over an entire circumference of the outer peripheral surface of the floating bush or the inner peripheral surface of the bearing hole, the circumferential groove passing through openings of the plurality of communication holes or facing the openings of the plurality of communication holes,
• wherein the communication groove has a cross-sectional area which varies in accordance with a circumferential position,
• wherein the circumferential groove is formed on the inner peripheral surface of the bearing hole,
• wherein the circumferential groove includes a plurality of first regions dispose corresponding to the intervals of the plurality of communication holes in the circumferential direction of the bearing hole, and a plurality of second regions each extending between the plurality of first regions,
• therein a cross-sectional area of each of the plurality of first regions is greater than a cross-sectional area of each of the plurality of second regions,
• wherein the width of each of the plurality of first regions is in a range of from 0.9 to 1.3 times a width of each of the plurality of communication holes,
• wherein at least one of the plurality of first regions includes a part at which a width of the circumferential groove reaches a maximum width, and
• wherein the width of each of the plurality of second regions is in a range of from 0.2 to 0.4 times the maximum width of the circumferential groove.

A floating bush bearing device, comprising:

• a casing including a bearing hole;
• a rotary shaft disposed rotatably inside the bearing hole;
• a floating bush disposed rotatably inside the bearing hole and surrounding the rotary shaft;
• an oil-feed hole of lubricant oil, the oil-feed hole having an opening on an inner peripheral surface of the bearing hole;
• a plurality of communication holes formed on the floating bush, each of the communication holes extending between an inner peripheral surface and an outer peripheral surface of the floating bush, and disposed at intervals in a circumferential direction of the floating bush;
• and
• a circumferential groove formed on the outer peripheral surface of the floating bush or the inner peripheral surface of the bearing hole and extending over an entire circumference of the outer peripheral surface of the floating bush or the inner peripheral surface of the bearing hole, the circumferential groove passing through openings of the plurality of communication holes or facing the openings of the plurality of communication holes,
• wherein the circumferential groove has a cross-sectional area which varies in accordance with a circumferential position,
• wherein a cross-sectional area of a downstream region of the circumferential groove joined to a downstream side of the communication hole in a rotational direction of the floating bush increases toward the communication hole in the circumferential direction of the floating bush.