Pump housing having a high pressure portion and a low pressure portion

A pump comprising a housing having a shaft bore and a pump chamber, a bearing provided for an inner periphery of the shaft bore, a shaft rotatively supported by the shaft bore through the bearing, and an impeller connected to one end portion of the shaft for transporting fluid by imparting mechanical energy to the fluid sucked in the pump chamber,

• two bearings provided in an axial direction so as to be apart from each other, and one of said two bearings provided at a side of the pump chamber being constituted as a sliding bearing while another of said two bearings provided at a side opposing to the pump chamber being constituted as a rolling bearing and wherein a sealing member for sealing a gap between the shaft bore formed to the housing and the shaft being provided at a portion between the sliding bearing and the rolling bearing, and said impeller being arranged off-set inside the housing and constructed such that a high-pressure portion and a low-pressure portion of lower pressure than the high-pressure portion being formed inside the pump chamber when a fluid passage is formed, a first region of a sliding surface formed to the sliding bearing being communicated with the high pressure portion to be formed so as to provide a high pressure when constructed as the fluid passage, while a second region of the sliding surface formed to the sliding bearing being communicated with the low-pressure portion to be formed so as to have a relatively lower pressure than that of the high-pressure portion when constructed as the fluid passage, so that the fluid is supplied to the sliding surface of the sliding bearing by the action of a differential pressure between the high-pressure portion and the low-pressure portion of the fluid passage so as to lubricate the sliding surface.