Conventionally, a valve timing control device is known, which can achieve a proper driving condition in response to a rotation speed of the crankshaft by adjusting the opening/closing timing of the intake valves and the exhaust valves of the internal combustion engine. The valve timing control device of such conventional structure is disclosed in a Japanese Patent Publication 2006-037886A (particularly in FIG. 1 and pages 5 and 6 in the specification). The disclosed valve timing control device includes a phase control unit having a drive side rotation member rotating in synchronization with the crankshaft, a driven side rotation member arranged coaxially with the drive side rotation member and rotating in synchronization with the camshaft and a hydraulic chamber formed between the drive side and the driven side rotation members and divided into an advance angle chamber and a retard angle chamber by a vane. The phase control unit is formed at an end portion of the camshaft for unitary rotation therewith. The valve timing control device further includes a hydraulic circuit for supplying the operation fluid to the hydraulic chamber of the phase control unit. The valve opening or closing timing of the intake and exhaust valves of the internal combustion engine is controlled to an advanced angle side or a retarded angle side by the supply of the operation fluid to one of or both of the advance angle chamber and the retard angle chamber from the hydraulic circuit.
One of such hydraulic circuit is disclosed in Japanese Patent Publication 2004-060572A (particularly in FIG. 1 and pages 4 and 5 of the specification). This structure is illustrated in FIG. 12 of the drawing attached to this application. The valve timing control device according to FIG. 12 includes a phase control unit 101 which changes the rotation phase of the camshaft relative to the rotation of the crankshaft of the internal combustion engine by using the hydraulic pressure of the operation fluid to adjust opening/closing timing of the valves driven by the camshaft, a mechanical pump 102 driven by rotation of the crankshaft for supplying the operation fluid to the phase control unit 101, a hydraulic circuit 103 for valve operating system hydraulically connecting the phase control unit 101 and the mechanical pump 102, a hydraulic circuit 105 for cylinder block system branched from the hydraulic circuit 103 for the valve operating system for supplying the operation fluid into a cylinder block portion 104, a filter device 106 provided in the hydraulic circuit 103 for filtering operation of the operation fluid discharged from the mechanical pump 102 and an electric pump 107 provided in the hydraulic circuit 103 between the phase control unit 101 and the filter device 106 and driven by a motor.
The mechanical pump 102 and the electric pump 107 are arranged in series and the electric motor 107 is positioned at downstream of the filter device 106. Accordingly, any foreign material or object may be prevented from entering into the electric pump 107. The mechanical pump 102 is driven in correlation with the engine rotation speed (rpm), and accordingly, operation fluid may be insufficient when the engine rotation speed is low. However, according to this structure, the electric pump 107 is actuated when the engine rotation speed is low to compensate for the insufficient supply of the operation fluid.
In the engine with V-type or horizontally oppositely placed type (Boxer type), each set of camshaft is supported respectively in each bank of the engine block. One or two camshafts usually form a set of camshaft. In more detail, SOHC (Single Over Head Camshaft) type engine has only one camshaft and DOHC (Double Over Head Camshaft) engine has two camshafts. The engine type having a plurality of banks includes a phase control unit at a set of camshaft. Accordingly, each phase control unit is separately arranged with each other according to the distance between each set of camshafts.
Since the plurality of phase control units is separately positioned, the operation fluid supply circuit between the electric pump and the phase control unit has to be branched off in plural because of the position situation. The total length of the conduit from the electric pump to each phase control unit has to be elongated and it is necessary to use a high power electric pump to effectively function against a large flow resistance in the conduit generated especially when the temperature of the fluid is low and the viscosity of the fluid is high. Also, if the length of the conduit is long, it takes a relatively longer time to fill the operation fluid in the empty conduit when the engine is started.
On the other hand, a plurality of electric pumps can be arranged corresponding to the number of the phase control units to dispose the electric pumps close to the units. The length of the conduit from the electric pump to the phase control unit becomes shorter and the power of the electric pump can be reduced to prevent a slow operation of the phase control unit due to the hitherto use of a large powered electric pump. However, the number of the electric pump is increased which may lead to the cost increase of the total system and the consumption of the electricity becomes large.
Accordingly, it is an object of the invention to provide a valve opening and closing timing control device having a prompt operation of the phase control device at the start of the engine and to reduce the cost of manufacturing and less consumption of the energy.