Sintered bearing for an EGR valve and manufacturing method thereof

A sintered bearing for an EGR valve, comprising,

• 9% by weight to 12% by weight of aluminum, 0.1% by weight to 0.6% by weight of phosphorus, 3% by weight to 10% by weight of graphite, and the balance comprising copper as a main component, and inevitable impurities, wherein:
• the sintered bearing has a structure of a sintered aluminum-copper alloy,
• the sintered bearing further comprises free graphite distributed in pores formed so as to be dispersed,
• the sintered bearing does not contain tin,
• a portion in which a copper simple substance is concentrated does not substantially exist in the sintered bearing,
• the sintered bearing has a bearing surface on an inner circumference and a radially outer surface,
• the sintered bearing has compressed layers on the radially outer surface and the bearing surface, respectively,
• a density ratio αo of the compressed layer on the radially outer surface side is 80%≤αo≤95%, and a density ratio αb of the compression layer on the bearing surface side is 80%≤αb≤95%,
• the density ratio αo of the compressed layer on the radially outer surface side and the density ratio αb of the compressed layer on the bearing surface side are both higher than a density ratio of an inside, and
• when an average value of depths of the compressed layer on the radially outer surface side is defined as To, an average value of depths of the compressed layer on the bearing surface side is defined as Tb, and ratios of To and Tb to an inner diameter dimension D1 of the bearing surface are defined as To/D1 and Tb/D1, respectively, To/D1 are set to 1/100≤To/D1≤ 1/15 and Tb/D1 are set to 1/100≤Tb/D1≤ 1/15.