Variable valve timing system

Details Variable valve timing system Variable valve timing system

2000-12-26

2002-09-17

Lo, Weilun (Department: 3748)

Internal-combustion engines

Poppet valve operating mechanism

With means for varying timing

Reexamination Certificate

active

06450137

ABSTRACT:

This application is based on and claims priority under 35 U.S.C. §119 with respect to Japanese Application No. 11-365755 filed on Dec. 24, 1999, the entire content of which is incorporated herein by reference.
FIELD OF THE INVENTION
This invention generally relates to vehicle engines. More particularly, the present invention pertains to a variable valve timing system for controlling the opening and closing timing of an intake valve and an exhaust valve of a vehicle engine while the engine is actuated or operating.
BACKGROUND OF THE INVENTION
Known variable valve timing systems are described in Japanese Patent Laid-Open Publication H01-92504 and Japanese Patent Laid-Open Publication H09-250310. The disclosed variable valve timing systems include a rotation transmitting member rotatably supported in a predetermined range relative to a rotation member rotating with a cam shaft. The rotation transmitting member transmits a rotation force from a crank sprocket or a pulley of a crankshaft, and is provided with a recessed portion at its inner peripheral portion. The variable valve timing system also includes a plurality of vanes provided on the rotation member, a fluid pressure chamber formed between the recess portion and the rotation member and divided into an advanced angle chamber and a retarded angle chamber by the vane, a first fluid conduit supplying fluid to and discharging the fluid from the advanced angle chamber, a second fluid conduit supplying fluid to and discharging the fluid from the retarded angle chamber, and a relative phase restricting mechanism restricting a relative phase between the rotation member and the rotation transmitting member when the relative phase between the rotation member and the rotation transmitting member corresponds to the predetermined phase.
In the variable valve timing system disclosed in the publications mentioned above, the rotation member is rotated relative to the rotation transmitting member to move the vanes in the advanced angle direction of the recess portion to a certain position until reaching the most advanced angle position to advance the angle of the valve opening and closing timing by supplying the operation fluid to the advanced angle chamber via the first fluid conduit and discharging the operation fluid from the retarded angle chamber via the second fluid conduit. The rotation member is rotated relative to the rotation transmitting member to move the vane of the recess portion in the retarded angle direction to a certain position until reaching the most retarded angle position to retard the angle of the valve opening and closing timing by supplying operation fluid to the retarded angle chamber via the second fluid conduit and by discharging the operation fluid from the advanced angle chamber via the first fluid conduit.
With further regard to the variable valve timing system disclosed in the publications mentioned above, the rotation member is always affected by the force in the retarded angle direction by a variable torque affecting the cam shaft during the engine operation. When the supply of operation fluid to the fluid pressure chamber stops as the engine stops, the vane is not able to be locked by the fluid pressure of the fluid pressure chamber, the rotation member is rotated in the retarded angle direction relative to the rotation transmitting member (until the crankshaft is completely stopped) to stop the rotation member and the rotation transmitting member at the relative phase in accordance with the relative phase therebetween immediately before the engine stops. When the engine is started in this condition, the rotation member is rotated in the retarded angle direction relative to the rotation transmitting member by the fluid pressure in the retarded angle direction and the vane reaches the phase at the most retarded angle position where the vane contacts the peripheral direction end surface of the advanced angle side of the recess portion. When the engine is started in this condition, the vane stays unstable until the fluid pressure in the fluid pressure chamber is increased to lock the vane, and the vane is vibrated by the variable torque affecting the cam shaft to contact a peripheral end surface of the recess portion and thus generates noise. To avoid this drawback, the relative phase between the rotation member and the rotation transmitting member is restricted at the most retarded angle position by the relative phase restricting mechanism.
In general, the volumetric efficiency is improved by delaying the closing timing of the intake valve to improve the output of the engine because the intake air enters the cylinder by inertia even after the piston starts to move towards the top dead center at the high speed velocity area of the engine.
However, in the case of the variable valve timing systems disclosed in the aforementioned publications for controlling the opening and closing timing of the intake valve, because the valve timing for opening and closing at the most retarded angle position is required to be determined at the time when the air can be taken in at the start of the engine, it is difficult to improve the volumetric efficiency by retarding the closing timing of the intake valve to utilize the inertia of the intake air at the high speed velocity area. When the valve opening and closing timing at the most retarded angle position is determined at the time capable of improving the volumetric efficiency by the inertia of the intake air, the intake valve is opened even after the piston passes the bottom dead center position and moves towards the top dead center position at the engine start at the most retarded angle position. Moreover, because the intake air is not accompanied by inertia, once sucked or drawn-in intake air is reversely moved to be discharged not to raise the compression ratio to generate the condition which cannot achieve the combustion. This may cause difficulty with respect to the engine start. This problem tends to be generated at the place with low pressure when the closing timing of the intake valve is determined after the piston passes the bottom dead center position even when the valve opening and closing timing at the most retarded angle position is determined at the time capable of taking in the air at the engine start and even when the valve opening and closing timing at the most retarded angle position is not determined at the time capable of improving the volumetric efficiency by the inertia of the intake air.
When the variable valve timing system in the aforementioned publications is used for controlling the opening and closing of the exhaust valve, the retarded closing timing of the exhaust valve elongates or extends the overlapping period of the intake valve and the exhaust valve, thus deteriorating the engine start by increasing the internal EGR volume (exhaust gas re-circulation volume).
To address the aforementioned problems, Japanese Patent Laid-Open Publication H09-324613 describes a system in which the relative phase between the rotation member and the rotation transmitting member is restricted by the relative phase restricting mechanism at a middle position moved to the advanced angle by a predetermined angle compared to the most retarded angle position in accordance with the valve opening and closing timing capable of improving the volumetric efficiency by the inertia of the intake air. However, in this system, it is only for a brief moment that the relative phase of the rotation member and the rotation transmitting member is positioned at the predetermined middle position when the rotation member rotates in the retarded angle direction relative to the rotation transmitting member at the engine stop. Accordingly, the relative phase between the rotation member and the rotation transmitting member cannot be completely restricted at the predetermined middle position by the relative phase restricting mechanism and noise may be generated by contact between the vane and the peripheral end surface of the recess portion of the rotation transmitting member at the engine st

Affiliated with

Also associated with

Rating

Variable valve timing system does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Variable valve timing system, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Variable valve timing system will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2825410