An engine valve actuation
system includes an engine valve movable between a first position that blocks a
flow of fluid and a second position that allows a flow of fluid. The system
also includes a valve actuation assembly connected to move the engine valve
between the first position and the second position and a fluid actuator
configured to selectively modify a timing of the engine valve in moving from
the second position to the first position. The fluid actuator includes a first piston.
The system further includes an accumulator including a second piston, wherein
the second piston is slidably movable in the first piston.
Background:
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 nitrous oxide (NOx), are generated then
fuel is combusted in a combustion chamber of the engine. An exhaust stroke of
an 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. Reduced internal combustion
engine exhaust gas emissions and improved engine performance of a diesel engine
may be achieved by adjusting the actuation timing of the engine valves. For
example, the actuation timing of the intake and exhaust valves may be modified
to implement a variation on the typical diesel or Otto cycle known as the
Miller cycle. In a "late intake" type Miller cycle, the intake values
are kept open during a portion of the compression stroke of the piston.
Engines implementing a late intake
miller cycle may include a fluid actuator capable of varying the closing timing
of mechanically operated intake valves. In such systems the fluid actuator may
also experience impact forces against an actuator chamber wall associated with
the closing of the intake valves by the stiff return springs. Therefore the
fluid actuator may also suffer erosion, fracture and/or breakage.
Some engines may include a snubbing
valve to reduce the flow of fluid from the fluid actuator, and thereby reduce
the intake valve seating velocity. Additionally or alternatively, an actuator
may be required to dampen fluid pressure spikes and pressure waves during
operation of the fluid actuators. However in these engines the piston of the
fluid actuator, the snubbing valve and the accumulator are implemented
separately from one another, thus requiring independent manufacture and
occupying valve space in the engine compartment which may result in increased
cost to the manufacturer.
