Internal-combustion engines – Poppet valve operating mechanism – Hydraulic system
Reexamination Certificate
1998-08-28
2002-07-02
Lo, Weilun (Department: 3748)
Internal-combustion engines
Poppet valve operating mechanism
Hydraulic system
C123S090490, C123S090550
Reexamination Certificate
active
06412457
ABSTRACT:
FIELD OF INVENTION
This invention relates to the control of engine valves associated with the combustion chamber of an internal combustion engine. In particular, the present invention is directed to an apparatus for controlling the seating of engine valves.
BACKGROUND OF THE INVENTION
Engine combustion chamber valves, such as intake and exhaust valves, are almost universally of a poppet type. These engine valves are typically spring loaded toward a valve closed position. A number of means exist for opening such valves, including hydraulic pressure. In many systems, hydraulic pressure acts on an actuator piston within a housing or cylinder. The piston may be operatively connected to the valve stem of an engine valve. In response to hydraulic pressure on the top of the piston, the piston translates downward, forcing the engine valve open against the force of a valve spring, opening the engine valve. This hydraulic piston arrangement is commonly referred to as a hydraulic actuator.
A variety of systems exist to regulate the timing of engine valve opening by controlling the hydraulic pressure within the actuator at the top of the actuator piston. These systems include “common rail” systems in which a solenoid control valve, or other valve, opens a path from a source of high pressure fluid to the top of the slave piston at precisely timed instants. One such common rail system is described in Cosma et al., U.S. Pat. No. 5,619,964, assigned to the assignee of the present application.
Another type of system for applying hydraulic pressure to the actuator piston is a hydraulically linked master and slave piston arrangement. In such systems, a cam or other device causes motion of a master piston. Master piston motion is transferred to the actuator (“slave”) piston by means of the hydraulic link between the two pistons. The motion of the slave piston, in relation to the basic cam motion imparted to the master piston, may be modified by draining and filling fluid from the hydraulic link at precise times. In this way, only selected portions of the cam-driven motion may be transferred to the slave piston. These systems are sometimes therefore called “lost motion” systems. One such lost motion system is described in Hu, U.S. Pat. No. 5,537,976, assigned to the assignee of the present application.
Engine valves are required to open and close very quickly, therefore the valve spring is typically very stiff. When the valve closes, it impacts the valve seat at a velocity that can create forces which may eventually erode the valve or the valve seat or even fracture or break the valve. In mechanical valve actuation systems that use a valve lifter to follow a cam profile, the cam lobe shape provides built-in valve-closing velocity control. In common rail hydraulically actuated valve assemblies, however, there is no cam to self-dampen the closing velocity of an engine valve. Likewise, in hydraulic lost motion systems, a rapid draining of fluid from the hydraulic link between the master and slave pistons may allow an engine valve to “free fall” and seat with an unacceptably high velocity.
As a result, in engine valve and cylinder head design, there is a need to limit valve seating velocities. With hydraulically actuated systems, however, this need for restriction is in conflict with the need for unrestricted valve opening rates. Some attempts have been made to solve the problem by providing separate fill and drain ports. U.S. Pat. No. 5,577,468 discloses a system for limiting valve seating velocity, however, the system disclosed is both costly and inaccurate. Other existing methods for controlling engine valve seating velocity do so for the entire range of valve closing. These methods may cause excessive valve closing variations. Existing systems also fail to accommodate the need for adjustments due to variations in engine valve lash between cylinders.
In addition to excessive valve closing speed, piston overtravel can also cause severe engine damage. It is therefore necessary, to precisely control and limit the return stroke of the engine valve and the actuator piston during engine operation. There are several methods of controlling piston stroke: mechanical stops, mechanisms that cut off the flow of fluid to the piston, and mechanisms that apply high pressure oil to the backside of the piston. Each of these designs, however, have shortcomings. Mechanical stops have durability problems unless seating velocity is controlled. Systems that cut off the oil supply may allow overtravel due to the formation of vapor or the evolution of gas bubbles. Systems that bleed high pressure oil behind the piston place an excessive load on the oil pump.
Accordingly, there is a need for a simple and effective stroke-limiting design that is fail-safe. For mechanical stop methods of stroke-limiting, there is a particular need for a design that reduces the risk of damage to the stops. Furthermore, existing systems do not fill the need for valve seating velocity control which allows free, unrestricted return of the engine valve for a set distance and restricted, controlled return as the valve approaches the valve seat.
The present invention meets the aforementioned needs and provides other benefits as well.
OBJECTS OF THE INVENTION
It is therefore an object of the present invention to provide a hydraulic engine valve control system which allows free valve return over the majority of the valve's return distance, and provides velocity control over a limited range of the valve's travel just prior to seating.
A further object of the present invention is to provide faster, more consistent controlled valve seating.
It is a further object of the present invention to provide a method of free valve return with controlled seating velocity.
Another object of the present invention is to provide an adjustable range over which valve seating velocity is controlled.
It is another object of the present invention to provide an engine valve actuator which allows free, unrestricted opening of an engine valve.
Still another object of the present invention is to provide a means for adjusting, either manually or automatically, an engine valve hydraulic actuation system for variations in engine valve height or lash.
It is also an object of the present invention to provide an improved apparatus for limiting the stroke of the actuator piston.
It is another object of the present invention to provide a piston stroke-limiting means that is fail-safe and low-cost.
It is another object of the present invention to provide slave piston stroke-limiting without a separate stroke-controlling piston.
It is another object of the present invention to provide slave piston stroke-limiting means comprising at least one fixed mechanical stop.
It is another object of the present invention to provide a hydraulic damper that controls the valve seating velocity and thereby reduces damage to the mechanical stop(s).
Additional objects and advantages of the invention are set forth, in part, in the description which follows and, in part, will be apparent to one of ordinary skill in the art from the description and/or from the practice of the invention.
BRIEF SUMMARY OF THE INVENTION
In response to this challenge, applicants have developed an innovative, economical apparatus for controlling the seating velocity of an engine valve. The present invention includes a hydraulic valve actuator for operating an engine valve comprising: an actuator housing; an actuator piston having upper and lower ends, wherein the piston is reciprocally disposed within the housing and is adapted to be moved upward and downward in response to hydraulic pressure; the lower end of the actuator piston is operatively connected to the engine valve so that the engine valve opens when the actuator piston is displaced downward in response to hydraulic pressure upon the upper end, and when the hydraulic pressure is removed from the upper end the actuator piston returns upward and the engine valve shuts; a feed and drain passage in the housing to allow hydraulic fluid to move to and from the upp
Israel Mark A.
Kinerson Kevin J.
Vorih Joseph M.
Collier Shannon Scott PLLC
Diesel Engine Retarders, Inc.
Lo Weilun
Yohannan David R.
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