Internal-combustion engines – Poppet valve operating mechanism – With means for varying timing
Reexamination Certificate
2000-02-04
2001-07-17
Walberg, Teresa (Department: 3742)
Internal-combustion engines
Poppet valve operating mechanism
With means for varying timing
C123S090160, C123S090170
Reexamination Certificate
active
06260523
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a variable-valve-actuation (VVA) apparatus for an internal combustion engine, which can change, particularly, the valve lift of an intake or exhaust valve in accordance with the engine operating conditions.
One of the VVA apparatus is shown in JP-A 11-
107725. This VVA apparatus, applied to intake valves, comprises a crank cam arranged on the outer periphery of a driving shaft rotated together with a crankshaft and having an axis eccentric to an axis of the driving shaft, and a valve operating (VO) cam to which torque of the crank cam is transmitted through a transmission mechanism to have a cam face coming in slide contact with the top face of a valve lifter arranged at the upper end of the intake valve for operation thereof.
The transmission mechanism includes a rocker arm disposed above the VO cam and swingably supported to a control shaft, a crank arm having an annular base engaged with the outer peripheral surface of the crank cam and an extension rotatably connected to a first arm of the rocker arm through a pin, and a link rod having a first end rotatably connected to a second arm of the rocker arm through a pin and a second end rotatably connected to an end of the VO cam through a pin.
Moreover, fixed on the outer peripheral surface of the control shaft is a control cam having an axis eccentric to an axis of the control shaft by a predetermined amount and rotatably fitted in a support hole formed substantially in the center of the rocker arm. The control cam changes a rocking fulcrum of the rocker arm in accordance with the rotated position to change the position of contact of the cam face of the valve operating cam with respect to the top face of the valve lifter, carrying out variable control of the valve lift of the intake valve.
Specifically, when the engine operating conditions are in the high-rotation and high-load range, in order to urge an actuator to rotate the control cam in one direction through the control shaft for rotation of the control cam in the same direction, the rocking fulcrum of the rocker arm is moved to approach the driving shaft. Then, an end or a cam nose of the VO cam is pushed downward by the link rod, etc. to move the position of contact of the cam face of the VO cam with respect to the top face of the valve lifter to a lift section of the cam face. Thus, the intake valve is controlled to have the maximum valve-lift characteristic.
On the other hand, when the engine operating conditions are in the low-rotation and low-load range, the actuator rotates the control shaft in another direction for rotation of the control cam in the same direction, moving the rocking fulcrum of the rocker arm to separate from the driving shaft. Then, the pivotal point of the rocker arm and the link rod is moved upward to draw up the cam nose of the VO cam, moving the position of contact of the cam face of the VO cam with respect to the top face of the valve lifter to separate from the lift section of the cam face. Thus, the intake valve is controlled to have the minimum valve-lift characteristic.
Therefore, the VVA apparatus allows full achievement of the engine performance in accordance with the engine operating conditions, i.e., an improvement in fuel efficiency and in engine output.
With the above VVA apparatus, however, though the valve-lift characteristic can be changed by changing the rocking fulcrum of the rocker arm in accordance with the rotated position of the control cam, a full consideration is not made with regard to the direction of rotation of the control cam, particularly, the direction of rotation from the maximum valve-lift control position to the minimum valve-lift control position, and the position of rotation for minimum valve-lift control. This may raise a problem that a full reduction is impossible in the minimum valve lift due to the direction of rotation of the control cam. Moreover, this may raise another problem that during minimum valve-lift control, the line connecting the axes of first and second end pins of the link rod and the line connecting the axis of the second end pin and the axis of the driving shaft form a straight line to produce locking of the link rod, disturbing smooth rotation of the link rod and the VO cam upon transition of operation of the intake valve from closing to opening.
It is, therefore, an object of the present invention to provide a VVA apparatus for an internal combustion engine, which contributes to an improvement in the engine performance and a smooth operation of the apparatus components.
SUMMARY OF THE INVENTION
One aspect of the present invention lies in providing a variable-valve-actuation apparatus for an internal combustion engine with a cylinder head, a crankshaft and a valve, comprising:
a driving shaft rotated in synchronism with the crankshaft, said driving shaft including a crank cam on an outer periphery;
a control shaft arranged substantially parallel to said driving shaft;
a valve lifter movably arranged with respect to the cylinder head, said valve lifter including a top face;
a valve operating (VO) cam swingably supported by said driving shaft, said VO cam opening and closing the valve through said valve lifter, said VO cam including a cam face;
a crank arm including a base and an extension, said base being slidably engaged with an outer periphery of said crank cam;
a rocker arm including first and second arms, said first arm being rotatably connected to said extension of said crank arm, which forms a first pivotal point;
a link rod having a first end rotatably connected to an end of said VO cam, which forms a second pivotal point, and a second end rotatably connected to said second arm of said rocker arm, which forms a third pivotal point; and
a control cam mounted to said control shaft on an outer periphery, said control cam having an axis eccentric to an axis of said control shaft, said control cam changing a rocking fulcrum of said rocker arm in accordance with a rotated position of said control shaft,
whereby a position of contact of said cam face of said VO cam with respect to said top face of said valve lifter is changed in accordance with a change in said rocking fulcrum of said rocker arm to alter a lift of the valve,
wherein a maximum lift of the valve is obtained in a first rotated position of said control shaft where said axis of said control cam is adjacent to said driving shaft,
wherein a minimum lift of the valve is obtained in a second rotated position of said control shaft where said axis of said control cam is positioned near said first pivotal point of said rocker arm and said crank arm with respect to a first line connecting said axis of said control shaft and said axis of said control cam upon said maximum lift.
Another aspect of the present invention lies in providing a variable-valve-actuation apparatus for an internal combustion engine with a cylinder head, a crankshaft and a valve, comprising:
a driving shaft rotated in synchronism with the crankshaft, said driving shaft including a crank cam on an outer periphery;
a valve lifter movably arranged with respect to the cylinder head, said valve lifter including a top face;
a valve operating (VO) cam swingably supported by said driving shaft, said VO cam opening and closing the valve through said valve lifter, said VO cam including a cam face;
a rocker arm including first and second arms, said first arm being mechanically connected to said crank cam;
a link rod having a first end rotatably connected to an end of said VO cam, which forms a first pivotal point, and a second end rotatably connected to said second arm of said rocker arm, which forms a second pivotal point;
an alteration mechanism altering a rocking fulcrum of said rocker arm in accordance with operating conditions of the engine; and
a restriction mechanism restricting an angle formed by a first line connecting an axis of said driving shaft during lift control of the valve and said first pivotal point of said link rod and said VO cam and a second line connecting said first pivotal point and said
Hibi Tsutomu
Miyazato Yoshiaki
Nakamura Makoto
Nohara Tsuneyasu
Takemura Shinichi
Dahbour Fadi H.
Sughrue Mion Zinn Macpeak & Seas, PLLC
Unisia Jecs Corporation
Walberg Teresa
LandOfFree
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