Value mechanism of internal combustion engine

Details Value mechanism of internal combustion engine Value mechanism of internal combustion engine

1999-11-03

2001-08-21

Lo, Weilun (Department: 3748)

Internal-combustion engines

Poppet valve operating mechanism

With means for varying timing

C123S090420, C123S090440, C123S090600

Reexamination Certificate

active

06276320

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a valve mechanism of a multi-cylinder internal combustion engine, particularly such a valve mechanism in which a pair of air-intake valves provided on a cylinder can be closed together to make the cylinder pause and lift, of each air-intake valve can be changed independently in accordance with engine operation regions.
Hitherto, a valve mechanism of a multi-cylinder internal combustion engine in which a pair of air-intake valves provided on a cylinder can be closed together to make the cylinder pause and lift of each air-intake valve can be changed independently in accordance with engine operation regions is known (see Japanese Laid-Open Patent Publication No. 8-61031.
The above-mentioned valve mechanism comprises first and second drive rocker arms which are operatively connected to the respective air-intake valves and contacted with circular pause sections of a cam shaft, a first free rocker arm contacted with a substantial pause cam enabling the air-intake valve to open slightly, a second free rocking arm contacted with a low-speed cam for making the air-intake valve open with a small lift, and a third free rocker arm contacted with a high-speed cam for making the air-intake valve open with a large lift.
The first and second drive rocker arms and the first, second and third free rocker arms are connected or disconnected with each other suitably by switchover means so that the operation mode of the air-intake valves can be switched over. Namely, both the air-intake valves are closed by the pause sections in an engine pause state, one of the air-intake valves is made to perform opening-closing motion by the low-speed cam while another air-intake valve is made to substantially pause by the substantial pause cam in an engine low-speed operation region to produce swirl within a combustion chamber for improvement of combustion, and both the air-intake valves are made to perform opening-closing motion by the high-speed cam in an engine high-speed operation region to improve engine output.
In a rocker arm shaft of the valve mechanism are formed two switching oil-pressure supply passages of circular cross sections for supplying oil-pressure to the connection switchover means.
In the above valve mechanism, the operation mode of the air-intake valves is shifted from a state that one air-intake valve is made to perform opening-closing motion by the low-speed cam as well as another air-intake valve is made to substantially pause by the substantial pause cam in an engine low-speed operation region, to a state that both the air-intake valves are made to perform opening-closing motion by the high-speed cam in an engine high-speed operation. Accordingly, in a part of the engine low-speed operation region near the high-speed region where only one air-intake valve opens with the small lift, sufficient engine output cannot be obtained.
Since a plurality of the switching oil-pressure supply passages, which are usually formed by mechanical work and of relatively small diameter, must be provided within the rocker arm shaft, the working takes much time. Further, since each of the two switching oil-pressure supply passages formed in the rocker arm shaft has a circular cross section, the inner space of the rocker arm shaft is not necessarily utilized efficiently. Therefore, in order to ensure a necessary passage area of the switching oil-pressure supply passage, sometimes the diameter of the rocker arm shaft must be enlarged and it obstructs miniaturization of the valve mechanism.
The present invention has been accomplished in order to overcome the above difficulties, and a subject of the invention is to improve the nature of combustion in the combustion chamber and output of the engine, by increasing the number of operation modes of the air-intake valves depending on engine operation regions, in a valve mechanism of a multi-cylinder internal combustion engine having a cylinder provided with a pair of air-intake valves. Another subject of the invention is cost reduction and miniaturization of the valve mechanism.
SUMMARY OF THE INVENTION
The present invention provides a valve mechanism of an internal combustion engine having a cylinder with a pair of air-intake valves, comprising: a cam shaft having a pair of pause sections for holding the air-intake valves substantially in closing pause states, a first operation cam with a profile capable of causing the air-intake to perform opening-closing motion, a second operation cam with a profile capable of causing the air-intake valve to perform opening-closing motion, and a third operation cam with a profile capable of causing the air-intake valve to perform opening-closing motion with a larger lift compared to the first and second operation cams; a first drive rocker arm operatively connected to one of the air-intake valves and contacted with one of the pause sections of the cam shaft; a second drive rocker arm operatively connected to another air-intake valve and contacted with another pause section of the cam shaft; a first free rocker arm contacted with the first operation cam; a second free rocker arm contacted with the second operation cam; a third free rocker arm contacted with the third operation cam; a first connection switchover means for connecting and disconnecting the first drive rocker arm with the first free rocker arm; a second connection switchover means for connecting and disconnecting the second drive rocker arm with the second free rocker arm; and a third connection switchover means for connecting and disconnecting the first drive rocker arm and the second drive rocker arm with the third free rocker arm.
According to the invention, the air-intake valves provided on one cylinder can take a first state in which both the air-intake valves are substantially closed to pause, a second state in which one air-intake valve is made to perform opening-closing motion substantially by the first or second operation cam as well as another air-intake valve is substantially closed to pause, a third state in which one air-intake valve is made to perform opening-closing motion substantially by the first operation cam as well as another air-intake valve is made to perform opening-closing motion substantially by the second operation cam, and a fourth state in which both the air-intake valves are made to perform opening-closing motion substantially by the third operation cam. Therefore, desirable operation modes of the air-intake valves can be set according to engine operation regions, in view of cylinder pause, swirl generation in the combustion chamber to improve combustion nature or improvement of engine output.
More concretely, in the first state, the engine can be operated with the cylinder pausing. In the second state, only one air-intake valve is made to perform opening-closing motion to cause a vortex or a swirl in the combustion chamber so that combustion nature is improved and circulation of a large amount of exhaust gas and lean mixture combustion become possible. In the third state, since both the air-intake valves are made to perform opening-closing motion with a lift smaller than that in the fourth state, engine output can be improved compared to prior art in a transition region between an engine operation region by the second state and an engine operation region by the fourth state. Further, since profiles of the first and second operation cams can be made identical or different, formation of the swirl in the combustion chamber and amount of intake air into the combustion chamber can be set with increased freedom. In the fourth state, since both the air-intake valves are made to perform opening-closing motion with the largest lift, a high engine output can be obtained.
The above valve mechanism may be provided with a control means by which in an engine operation region with the cylinder pausing, the first, second and third connection switchover means are in disconnecting states; in an engine operation region with a small amount of intake air, the first connection switchover means is i

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