Variable valve timing apparatus for internal combustion engine

Abstract

A variable valve timing apparatus includes a variable valve timing mechanism that includes a first rotating body and a second rotating body that are rotating bodies that rotate about the same rotational axis; advance chambers and retard chambers that serve as hydraulic pressure chambers into which hydraulic fluid is supplied from an oil pump; and a discharge passage that discharges hydraulic fluid from the hydraulic pressure chambers. At least one of the hydraulic pressure chambers that is communicated with the discharge passage in a position vertically higher than the rotational axis when the first rotating body and the second rotating body have stopped rotating at a given phase, and from which hydraulic fluid is discharged into the discharge passage, is placed in a state constantly open to ambient air regardless of the phase at which the first rotating body and the second rotating body have stopped.

1 . A variable valve timing apparatus for an internal combustion engine, comprising:
 a variable valve timing mechanism that changes a valve timing of at least one of an intake valve or an exhaust valve by changing a relative rotation phase of a camshaft with respect to a crankshaft; and   a lock mechanism that fixes the valve timing at an intermediate angle between a most advanced angle and a most retarded angle,   wherein the variable valve timing mechanism includes i) a first rotating body and a second rotating body that are rotating bodies that rotate about the same rotational axis, the first rotating body being drivingly connected to the crankshaft and having a plurality of housing chambers surrounding the rotational axis, and the second rotating body being drivingly connected to the camshaft and having a plurality of vanes that extend in a radial direction of the rotational axis and are arranged in the housing chambers, one vane being housed in each housing chamber; ii) an advance chamber formed on one side of the vane in each housing chamber and a retard chamber formed on the other side of the vane in each housing chamber, the advance chambers and the retard chambers serving as hydraulic pressure chambers into which hydraulic fluid is supplied from an oil pump; iii) a discharge passage that extends from each of the hydraulic pressure chambers on the rotational axis side and discharges hydraulic fluid from the hydraulic pressure chambers; and iv) an opening mechanism that communicates the hydraulic pressure chambers with an ambient air space to open the hydraulic pressure chambers to ambient air at least when the first rotating body and the second rotating body have stopped rotating,   and wherein the opening mechanism places at least one of the hydraulic pressure chambers that is communicated with the discharge passage in a position vertically higher than the rotational axis when the first rotating body and the second rotating body have stopped rotating at a given phase, and from which hydraulic fluid is discharged into the discharge passage, in a state constantly open to ambient air regardless of the phase at which the first rotating body and the second rotating body have stopped.   
     
     
         2 . The variable valve timing apparatus according to  claim 1 , wherein the hydraulic pressure chambers that the opening mechanism opens to ambient air are the retard chambers. 
     
     
         3 . The variable valve timing apparatus according to  claim 1 , wherein the hydraulic pressure chambers that the opening mechanism opens to ambient air are the advance chambers. 
     
     
         4 . The variable valve timing apparatus according to  claim 1 , wherein the hydraulic pressure chambers that the opening mechanism opens to ambient air are the retard chamber positioned on one side of a specific vane and the advance chamber positioned on the other side of the specific vane. 
     
     
         5 . The variable valve timing apparatus according to  claim 1 , wherein the opening mechanism includes an ambient air communication passage that communicates the hydraulic pressure chambers with the ambient air space, and an on-off valve that is provided in the ambient air communication passage and selectively opens and closes the ambient air communication passage; and the opening mechanism displaces a valve body of the on-off valve to a position that closes the ambient air communication passage while the engine is operating, and displaces the valve body to a position that opens the ambient air communication passage when the engine is stopped. 
     
     
         6 . The variable valve timing apparatus according to  claim 5 , wherein the on-off valve includes the valve body that is displaced to the position that closes the ambient air communication passage based on hydraulic pressure of hydraulic fluid supplied from the oil pump while the engine is operating, and that is displaced to the position that opens the ambient air communication passage based on the supply of hydraulic fluid from the oil pump being stopped when the engine is stopped. 
     
     
         7 . The variable valve timing apparatus according to  claim 6 , further comprising:
 a flow control valve that switches the state of the lock mechanism between a locked state and an unlocked state by controlling a supply/discharge state of hydraulic fluid with respect to the lock mechanism,   wherein the opening mechanism switches a communication state between the hydraulic pressure chambers and the ambient air space based on hydraulic pressure of hydraulic fluid that is directly circulated from the oil pump, regardless of a control state of the flow control valve.   
     
     
         8 . The variable valve timing apparatus according to  claim 6 , further comprising:
 a flow control valve that switches the state of the lock mechanism between a locked state and an unlocked state by controlling a supply/discharge state of hydraulic fluid with respect to the lock mechanism,   wherein the opening mechanism controls the supply and discharge of hydraulic fluid via the flow control valve.   
     
     
         9 . The variable valve timing apparatus according to  claim 5 , wherein the on-off valve includes the valve body that is displaced to the position that closes the ambient air communication passage by centrifugal force generated as the first rotating body and the second rotating body rotate while the engine is operating, and that is displaced to the position that opens the ambient air communication passage by urging force of a spring when the first rotating body and the second rotating body have stopped rotating when the engine has stopped.