US Patent 7895980 Valve timing adjusting device

A valve timing adjusting device includes a housing, a first vane rotor, a second vane rotor, a biasing device, and a limiting device. The second vane rotor is coaxial with the first vane rotor. The biasing device has a first end engaged with the first vane rotor and a second end engaged with the second vane rotor. The biasing device biases one of the first and second vane rotors in the advance direction, and biases the other one in the retard direction. The limiting device allows the first vane rotor to rotate relative to the second vane rotor when pressure of working fluid is lower than a preset level, and limits the first vane rotor from rotating relatively when the pressure is not lower than the preset level.