with a second plunger 22 housed in part in a second hydraulic control chamber 23 opposite to the first hydraulic control chamber 25 a pretensioned spring 28 inside the first hydraulic control chamber 25 exerts a pushing force on the first plunger 24 both hydraulic control chambers 25 23 are formed inside and by the pump housing 11 the pump housing 11 also comprises a pump intake port 20 to suck the lubricant from the lubricant tank 50 and a pump outlet port 21 to feed lubricant with a discharge pressure to the internal combustion engine 70 a conduit 80 extends from the pump outlet port 21 to supply the internal combustion engine 70 the lubricant which is supplied to the internal combustion engine 70 is conducted to the second hydraulic control chamber 23 via a pressure conduit 81 and the lubricant is fed to the first hydraulic control chamber 25 via pressure conduits 82 87 more specifically the lubricant in pressure conduit 82 is finally fed to the first hydraulic control chamber 25 via pressure conduit 87 through a pressure throttle valve 67 in which a calibrated pressure drop occurs as the lubricant flows through the pressure conduits 82 88 are connected to a control port of a first pressure control valve 60 by a conduit the first pressure control valve 60 comprises a.