Engine valve actuation system

Abstract

A valve actuation system includes an engine valve moveable between a first position at which engine valve prevents a flow of fluid relative to the engine valve second position at which the fluid flows relative to the engine valve. The system also has a cam follower operatively connected to the engine valve. A first cam is adapted to engage the cam follower such that the rotation of the first cam acts to move the engine valve from the first position to the second position during a first lift period. A second cam is adapted to engage the cam follower such that a rotation of the second cam acts to affect movement of the engine valve between the first position and the second position during a second lift period. A phase shifting device is operatively connected to the second cam and adapted to adjust the relative timing between the first lift period and the second lift period.

Description

TECHNICAL FIELD [0001] The present invention is directed to a system and method for actuating an engine valve and, more particularly, to a variable engine valve actuation system. BACKGROUND [0002] The operation of an internal combustion engine such as, for example, a diesel, gasoline, or natural gas engine, may cause the generation of undesirable emissions. These emissions, which may include particulates and oxides of nitrogen (NOx), are generated when fuel is combusted in a combustion chamber of the engine. An exhaust stroke of the engine piston forces exhaust gas, which may include these emissions, from the engine. If no emission reduction measures are in place, these undesirable emissions will eventually be exhausted to the environment. [0003] Research is currently being directed towards decreasing the amount of undesirable emissions that are exhausted to the environment during the operation of the engine. It is expected that improved engine design and improved control over engin...

AI Technical Summary

Benefits of technology

[0010] In another aspect, the present disclosure is directed to a method of actuating an engine valve having a first position at which the engine valve prevents a flow of fluid relative to the engine valve and a second position at which the fluid flows relative to the engine valve. A first cam is rotated to engage a cam follower associated with the engine valve to thereby move the engine valve between the first position and the second position during a first lift period. A second cam is rotated to engage the cam follower to thereby affect movement of the engine valve between the first position and the second position during a second lift period. The rotational phase of the second cam is adjusted to thereby adjust the relative timing between the first lift period and the second lift period.

Problems solved by technology

The operation of an internal combustion engine such as, for example, a diesel, gasoline, or natural gas engine, may cause the generation of undesirable emissions.

If no emission reduction measures are in place, these undesirable emissions will eventually be exhausted to the environment.

Unfortunately, the implementation of these emission reduction approaches typically results in a decrease in the overall efficiency of the engine.

However, while valve actuation timing adjustments may provide efficiency benefits, these actuation timing adjustments may also result in detrimental engine performance under certain operating conditions.

For example, a late intake Miller cycle may be inefficient when the engine is starting, operating under cold conditions, or experiencing a transient condition, such as a sudden increase in engine load.

This detrimental engine performance is caused by a decrease in the mass of air flowing through the engine.

Especially under cold ambient conditions, the delayed start of compression may lead to cylinder temperatures insufficient to support good combustion and startability.

Because the shape of the cam is fixed, this type of arrangement is inflexible and may only be changed during the operation of the engine through the use of complex mechanical mechanisms.

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