Internal-combustion engines – Poppet valve operating mechanism – With means for varying timing
Reexamination Certificate
1999-12-03
2001-02-06
Lo, Weilun (Department: 3748)
Internal-combustion engines
Poppet valve operating mechanism
With means for varying timing
C123S090180, C123S090310
Reexamination Certificate
active
06182623
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
This application is based upon and claims priority from Japanese Patent Application No. Hei 10-349856 filed Dec. 9, 1998, the contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a variable valve control device for changing opening/closing timing and lift stroke of at least one of an intake valve and an exhaust valve for an internal combustion engine (hereinafter referred to simply as an “engine”) according to engine operating conditions.
2. Description of Related Art
There has been known a vane type variable valve control device for controlling opening/closing timing of at least one of the intake and exhaust valves in a manner that a camshaft is driven via a timing pulley or a chain sprocket which rotates in synchronism with an engine crank shaft with a phase difference by relative rotation between the timing pulley or the chain sprocket and the camshaft. Such a variable valve control device is operative for changing a mutually overlapping valve-open period of the intake and exhaust valves to secure more stable engine operation, less fuel consumption and lower exhaust emission.
Further, as disclosed in JP-A-9-32519, there is also a known variable valve control device in which the valve-open period and the lift stroke of at least one of the intake valve and the exhaust valve are changed by axially moving a camshaft provided with a cam having an axially different profile.
Furthermore, according to the variable valve control device shown in JP-A-9-32519, the valve-open period and the lift stroke is changed by controlling the pressure to a hydraulic actuator according to engine operating conditions so that more stable engine operation, less fuel consumption and lower exhaust emission may be further secured.
However, the conventional variable valve control device, in which phase control means for adjusting the angular phase of the camshaft relative to the crankshaft and axial movement control means for changing the valve-open period and the lift stroke of one of the intake and exhaust valves are combined and controlled independently of each other, has the following problems.
At first, in the cam having an axially different profile, a camshaft receives a thrust force acting toward a lower lift stroke position due to an axially tapered cam profile. When a movable piston as a hydraulic actuator is held at the lowest lift stroke position, the movable piston is in contact with and is pushed onto an axial end surface of a pressure chamber at the lowest lift stroke position by the thrust force. Therefore, a responsiveness of the angular phase control is adversely affected by a friction between the piston and the axial end surface.
Secondly, when the movable piston is held at the highest lift stroke position by supplying sufficient oil to a high lift side pressure chamber, the movable piston is in contact with and is pushed onto the other axial end surface restricting the cam shaft stroke. Thus, a friction between the piston and the other axial end surface causes a worse responsiveness of the angular phase control.
Thirdly, when the movable piston is at the lowest lift stroke position and air is invaded into the high lift side pressure chamber or when the movable piston is at the highest lift stroke position and air is invaded into the low lift side pressure chamber, a responsiveness of shifting the movable piston from the lowest lift stroke position toward the higher lift stroke position or from the highest lift stroke position toward the lower lift stroke position is adversely affected.
SUMMARY OF THE INVENTION
The present invention is made in light of the foregoing problems, and it is an object of the present invention to provide a variable valve control device having a better control responsiveness for changing the angular phase.
Another object of the present invention is to provide a variable valve control device having a better control responsiveness for changing the valve-open period and the lift stroke.
To achieve the above objects, in the variable valve control device, a rotatable and axially movable driven shaft (camshaft) is provided with a cam having axially and radially different profile for opening and closing an intake or exhaust valve. the cam is rotated by angular phase control means for hydraulically changing an angular phase of the driven shaft relative to a drive shaft (crankshaft) to adjust opening/closing timing of the valve. Further, the cam is axially moved by axial movement control means for hydraulically controlling an axial movement of the driven shaft to adjust a valve-open period and a lift stroke of the valve.
The angular phase control means and the axial movement control means are operative independently of each other. Therefore, the valve-opening/closing timing, the valve-open period and the lift stroke of at least one of the intake and exhaust valves are optimally controlled according to engine operating conditions so that more stable engine operation, lower fuel consumption and less exhaust emission may be secured.
In the above device, the axial movement control means have a pressure chamber and a piston fixed with the driven shaft and axially moving in the pressure chamber. It is arranged in such a manner that pressure more than minimum operating pressure necessary for axially moving the piston is always ready to be applied to the axial movement control means at the time when the angular phase control means actually changes the angular phase of the driven shaft relative to the drive shaft. In particular, in case that a pump supplies hydraulic pressure to both the axial movement control means and the angular phase control means, the axial movement control means and the angular phase control means are constructed, preferably, to have a feature that the minimum operating hydraulic pressure to the angular phase control means necessary for changing the angular phase of the driven shaft is higher than that to the axial movement control means for axially moving the piston.
As a result, whenever the angular phase is actually changed, the hydraulic pressure sufficient enough to move the piston may be always ready to be applied to the axial movement member. Therefore, when the driven shaft is at the lowest lift stroke position, the driven shaft may be easily shifted via the piston from the lowest lift stroke position to the higher lift stroke position without time delay so that a highly accurate angular phase control of the driven shaft may be secured, while a better responsiveness of the angular phase control of the driven shaft may be also assured.
Further, even when the driven shaft is at the lowest lift stroke position or at the highest lift stroke position, at least the high lift side pressure chamber or the low lift side pressure chamber is hydraulically controlled to the extent that the driven shaft can not be moved from the lowest lift position to the higher lift stroke position or from the highest lift stroke position to the lower lift stroke position. Preferably, when the driven shaft is at the lowest lift stroke position, the hydraulic pressure is applied to the piston in a manner that a force almost equal to and slightly less than a thrust force of the driven shaft is given to the piston so as to act in a direction of moving the driven shaft toward the higher lift stroke position.
As at least the high lift side pressure chamber or the low lift side pressure chamber is hydraulically controlled as mentioned above, the friction between the piston and the stopper is less or, preferably, is none so that the interference between the angular phase control and the axial movement control may be minimized, thus resulting in the better responsiveness of the angular phase control.
Further, as the hydraulic pressure difference necessary for axially shifting the piston from the lowest lift stroke position to the higher lift stroke position or from the highest lift stroke position to the lower lift stroke position is relatively small or, p
Iden Noriyuki
Kikuoka Shinichiro
Moriya Yoshihito
Sato Osamu
Sugie Nobuhiko
Denso Corporation
Lo Weilun
Nixon & Vanderhye P.C.
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