Internal-combustion engines – Poppet valve operating mechanism – With means for varying timing
Reexamination Certificate
2000-03-22
2001-04-24
Lo, Weilun (Department: 3748)
Internal-combustion engines
Poppet valve operating mechanism
With means for varying timing
C123S090390, C123S308000, C123S19800E
Reexamination Certificate
active
06220212
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to automotive valve rocker arms. Such rocker arms are of course well known and form part of the mechanism in automotive engines by which the exhaust and inlet valves of the engine are opened and closed. More specifically, the invention relates to automotive valve rocker arms comprising an elongate lever which comprises a valve engagment portion and a cam engagement portion and is mounted at a position intermediate its ends to rock about a rocker shaft transverse to its length.
In use, the cam engagement region is engaged periodically by the associated cam, either directly or indirectly via a push rod and/or tappet which results in movement of the associated end of the rocker arm in one direction and thus in rocking or pivotal movement of the rocker arm about the rocking axis. This results in movement of the other end of the rocker arm and thus of the valve engagement region in the opposite direction and the valve engagement region bears against the stem of the associated valve and moves it, e.g. into the open position.
DESCRIPTION OF THE PRIOR ART
Continuing pressure for improved fuel economy is leading automotive engine manufacturers to seek improved engine technologies which can lower fuel consumption. These include the ability to disable selected valves or selected cylinders during low load operation. In the case of an engine with two or more inlet valves of swirl-inducing type per cylinder, the swirling velocity of the air or air/fuel mixture within the cylinder may drop to unacceptably low levels at low engine loads, thereby resulting in incomplete combustion or increased emission levels. It is known to counteract this problem by disabling one of the inlet valves, that is to say ensuring that it does not open or close with the other inlet valve(s), whereby the air speed through the other inlet valve(s) is increased and the swirling velocity of the air within the cylinder is increased also. It is also known to disable entire cylinders, that is to say to disable all the inlet valves associated with a selected cylinder so that the cylinder in question does not contribute at all to the power output of the engine at low load. This increases fuel economy because it permits the engine to operate with the throttle more widely open than would otherwise be the case, thereby reducing pumping losses. Pumping losses are further reduced if the exhaust valve(s) associated with the disabled cylinder are also disabled. The fuel supply and ignition associated with the disabled cylinder are preferably also disabled.
Whilst the technique of selective valve or cylinder disablement has been shown to be effective, very few engines with this feature have actually been produced commercially. The reason for this is that the deactivation mechanisms are complex and costly and typically require an additional actuator for each cylinder or valve that is to be disabled.
It is therefore the object of the invention to provide a valve actuation mechanism, specifically a rocker arm, which is cheap, simple and reliable and may be used to disable selected valves of an automotive engine and in which only a single actuator is required for disabling a number of valves or cylinders.
SUMMARY OF THE INVENTION
According to the present invention an automotive valve rocker arm of the type referred to above is characterised in that the valve engagement portion and the cam engagement portion constitutes separate, relatively movable components and selectively actuable locking means are provided which are movable between a first position in which relative movement of the valve engagement portion and the cam engagement portion is permitted and a second position in which they are locked together and such relative movement is prevented.
Thus the rocker arm in accordance with the invention does not constitute a single unitary component, as is conventional, but constitutes two separate components which may be selectively locked together, which means that they will then act as a single component, or may be unlocked, in which event they are capable of independent movement and the force transmitted by the cam to one end of the rocker arm is not transmitted through to the associated valve, whereby the associated valve is disabled.
It is preferred that the valve engagement portion and the cam engagement portion are mounted for independent rocking movement about the rocker shaft. This may be effected in a number of ways but in the preferred embodiment one of the cam engagement portion and the valve engagement portion affords a first bush or sleeve which accommodates and is rotatable about the rocker shaft and the other of which affords a second bush or sleeve which accommodates the first bush or sleeve and is rotatable about the first bush or sleeve and thus about the rocker shaft also.
In one embodiment, the first bush has an aperture formed therein which accommodates a locking member and is in registry with a recess in the inner surface of the second bush, in one relative position of the valve engagement portion and the cam engagement portion, and the locking means includes a lock actuator arranged to move the locking member between a locked position in which it is accommodated in both the aperture and the recess and thus locks the cam engagement portion and the valve engagement portion together and an unlocked position in which it is not within the recess and relative pivotal movement of the cam engagement portion and the valve engagement portion is thus possible.
The locking member and the aperture partially accommodating it may take various forms and there may be one locking member provided for each rocker arm or two or more such locking members. In the preferred embodiment, the aperture in the first bush is elongate in the direction of the length of the rocker shaft and the locking member comprises a pin or roller.
It is preferred that the rocker shaft is rotatable about its axis and has a recess in its outer periphery and constitutes the lock actuator, the rocker shaft being rotatable between an unlocked position in which the locking member is accommodated in both the aperture and the recess in the rocker shaft and a locked position in which the locking member is not accommodated within the recess in the rocker shaft. In the preferred embodiment the recess in the rocker shaft extends in the peripheral direction and is of progressively increasing depth in that direction.
The invention also embraces an internal combustion engine of reciprocating piston type including one or more such rocker arms. These rocker arms may be used selectively to disable one of two or more inlet valves per cylinder at low engine loads so as to increase the velocity of air flow through the remaining inlet valves. Thus the invention embraces such engine having a plurality of cylinders, each of which has two inlet valves and at least one exhaust valve, at least one inlet valve of each cylinder being operated by a cam shaft via a respective rocker arm of the type referred to above mounted on a common rocker shaft, the rocker shaft having a respective recess in its outer periphery associated with each said rocker arm and being connected to a rotary actuator, the recesses in the rocker shaft being so positioned that the rocker shaft is rotatable between a position in which all the rocker arms associated with the said one inlet valves are locked and a position in which the two portions of all the said rocker arms are capable of relative movement, whereby the said one inlet valves are all disabled.
The rocker arm in accordance with the present invention also finds application in an engine of reciprocating piston type with a plurality of cylinders for the purpose of selectively disabling one or more entire cylinders. Thus the invention embraces such an engine in which each cylinder has at least one inlet valve and at least one exhaust valve, all the inlet valves, and preferably all the exhaust valves also, associated with at least one cylinder being operated by a cam shaft via respective rocker arms of the
Lo Weilun
Ricardo Inc.
Rosenthal & Osha L.L.P.
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