Valve timing control apparatus for engine

A valve timing control apparatus for an engine having an intake valve and an exhaust valve alternately opened and closed in a valve timing sequence according to a rotation of a cam shaft coupled to a crank shaft by way of a rotatable member securely mounted on the cam shaft, wherein said cam shaft is rotatable in synchronism with the crank shaft of the engine, wherein said cam shaft is arranged to be selectively advanced and retarded between two opposite limits with respect to the crank shaft so as to converge the valve timing sequence to a target value computed based on a running condition of the engine detected by detecting means which includes a sensor for detecting a rotational speed of the engine, said apparatus comprising:

• said rotatable member including a timing pulley mounted on the cam shaft to operably connect the cam shaft to the crank shaft and a housing securely connected to the timing pulley and accommodating the plunger to define the first pressure chamber and the second pressure chamber;
• a sleeve secured to the cam shaft within the housing;
• said plunger having an inner spline and an outer spline respectively formed in the inner surface and in the outer surface of the plunger;
• said housing having an inner surface with a spline in mesh with the outer spline of the plunger to form a first spline connection;
• a first pressure chamber and a second pressure chamber sealed with respect to each other in the rotatable member;
• a hollow plunger movable between the first pressure chamber and the second pressure chamber, said plunger having an inner surface and an outer surface respectively in mesh with the sleeve and the rotatable member, said plunger being arranged to move in an axial direction between a first extreme position in the first pressure chamber and a second extreme position in the second pressure chamber to selectively advance and retard the cam shaft based on differential pressure between the first pressure chamber and the second pressure chamber, wherein said cam shaft is advanced to one of said limits when said plunger is in the first extreme position and retarded to the other one of said limits when the cam shaft is in the second extreme position;
• a first fluid passage connected to the first pressure chamber;
• a second fluid passage connected to the second fluid passage;
• an electromagnetic valve for adjusting a flow amount in each of said fluid passages to move the plunger;
• a controller for controlling the electromagnetic valve, said controller computing a specific control value to adjust the fluid pressure to be supplied to the first pressure chamber and the second pressure chamber so as to keep the valve timing sequence converged to the target value, said controller correcting said specific value based on the detected rotational speed of the engine when the plunger is in one of the extreme positions, wherein said controller adjusts the fluid pressures based on the corrected specific value.

A valve timing control apparatus for an engine having an intake valve and an exhaust valve alternately opened and closed in a valve timing sequence according to a rotation of a cam shaft coupled to a crank shaft by way of a rotatable member securely mounted on the cam shaft, wherein said cam shaft is rotatable in synchronism with the crank shaft of the engine, wherein said cam shaft is arranged to be selectively advanced and retarded between two opposite limits with respect to the crank shaft so as to converge the valve timing sequence to a target value computed based on a running condition of the engine detected by detecting means which includes a sensor for detecting a rotational speed of the engine, said apparatus comprising:

• said rotatable member including a timing pulley mounted on the cam shaft to operably connect the cam shaft to the crank shaft and a housing securely connected to the timing pulley and accommodating the plunger to define the first pressure chamber and the second pressure chamber;
• a sleeve secured to the cam shaft within the housing;
• a first pressure chamber and a second pressure chamber sealed with respect to each other in the rotatable member;
• a hollow plunger movable between the first pressure chamber and the second pressure chamber, said plunger having an inner surface and an outer surface respectively in mesh with the sleeve and the rotatable member, said plunger being arranged to move in an axial direction between a first extreme position in the first pressure chamber and a second extreme position in the second pressure chamber to selectively advance and retard the cam shaft based on differential pressure between the first pressure chamber and the second pressure chamber, wherein said cam shaft is advanced to one of said limits when said plunger is in the first extreme position and retarded to the other one of said limits when the cam shaft is in the second extreme position, said plunger having an inner spline and an outer spline respectively formed in the inner surface and in the outer surface of the plunger;
• said housing having an inner surface with a spline in mesh with the outer spline of the plunger to form a first spline connection;
• said sleeve having an outer surface with a spline in mesh with the inner spline of the plunger to form a second spline connection;
• and
• at least one of the spline connections being a helical spline connection;
• a first fluid passage connected to the first pressure chamber;
• a second fluid passage connected to the second fluid passage;
• an electromagnetic valve for adjusting a flow amount in each of said fluid passages to move the plunger;
• and
• a controller for controlling the electromagnetic valve, said controller computing a specific control value to adjust the fluid pressure to be supplied to the first pressure chamber and the second pressure chamber so as to keep the valve timing sequence converged to the target value, said controller correcting said specific value based on the detected rotation speed of the engine when the plunger is in one of the extreme positions, wherein said controller adjusts the fluid pressures based on the corrected specific value, wherein said controller computes an offset value based on the rotational speed of the engine, wherein said offset value is proportionally variable to the rotational speed of the engine, and wherein said specific control value is indicative of a specific duty cycle to be corrected by the offset value so as to hold a plunger in a desired position and converge the valve timing to the specific value.