An outer rotor and an inner rotor are formed of sintered aluminum alloy. The sintered aluminum alloy contains 0.5 wt % to 11 wt % of aluminum nitride. Porosity of the sintered aluminum alloy for outer rotor is 3 vol % to 15 vol %. Porosity of the sintered aluminum alloy for inner rotor is 2 vol % to...http://www.google.com.au/patents/US6089843?utm_source=gb-gplus-sharePatent US6089843 - Sliding member and oil pump
