US Patent 7997804 Rolling bearing apparatus

A rolling bearing apparatus includes inner and outer rings in which a preload applying unit applies a preload to the outer ring. If a fluid pressure in a fluid supply passage is higher than a first set pressure, then fluid is supplied to a pressure chamber via a check valve, and if a pressure becomes lower than the first set pressure, then fluid is supplied from a hydraulic pump to the pressure chamber via the check valve. If the pressure becomes higher than a second set pressure, then the fluid is discharged from the pressure chamber via a relief valve, and if the pressure within the pressure chamber becomes higher than a third set pressure, which is higher than the first set pressure but is lower than the second set pressure, then the supply of fluid is stopped. Thus, the pressure within the pressure chamber is maintained between the first and second set pressures.