Patent ID: 8516811

Claim:
An oil pressure system comprising: an engine; a first oil pressure pump and a second oil pressure pump driven by the engine and configured to vary discharge quantity of pressure oil in accordance with rotational speed of the engine; a first flow passage arranged to feed the pressure oil discharged from the first oil pressure pump to a predetermined high-pressure circuit; a second flow passage connected to a low-pressure circuit; a third flow passage connected to the second oil pressure pump; a relief flow passage connecting the first flow passage and the second flow passage; a relief valve configured to close the relief flow passage when the pressure of the pressure oil that flows through the first flow passage is at a relief pressure or less, the relief valve being configured to open the relief flow passage and relieve the pressure oil of the first flow passage into the second flow passage when the pressure of the pressure oil that flows through the first flow passage is greater than the relief pressure; a flow passage changeover valve configured to switch between a merging state wherein the third flow passage is connected to the first flow passage, and the pressure oil discharged from the first oil pressure pump and the pressure oil discharged from the second oil pressure pump are merged and fed to the first flow passage, and a branching state wherein the third flow passage is connected to the second flow passage, the pressure oil discharged from the first oil pump is fed to the first flow passage, and the pressure oil discharged from the second oil pump is fed to the second flow passage; a relief pressure changeover unit configured to switch the relief pressure of the relief valve between a predetermined high relief pressure, and a predetermined low relief pressure that is lower than the high relief pressure; and a control unit configured and arranged to set the flow passage changeover valve to be in the merging state and to use the relief pressure changeover unit to set the relief pressure to the low relief pressure in the case that the rotational speed of the engine is lower than a predetermined threshold level, and to set the flow passage changeover valve to be in the branching state and to use the relief pressure changeover unit to set the relief pressure to the high relief pressure in the case that the rotational speed of the engine is equal to or higher than the predetermined threshold level.