Internal-combustion engines – Poppet valve operating mechanism – Hydraulic system
Patent
1991-11-29
1996-11-26
Lo, Weilun
Internal-combustion engines
Poppet valve operating mechanism
Hydraulic system
123 9049, F01L 902
Patent
active
055774687
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
Hydraulically actuated engine poppet valves, and more particularly, hydraulically actuated engine poppet valves having a hydraulic snubber for decelerating the valve during valve closing to an acceptable impact velocity before the valve contacts the valve seat.
BACKGROUND ART
Engine combustion chamber valves are almost universally of a poppet type. A number of means exist for opening such valves including a cam on a rotating cam shaft, hydraulic pressure, electromagnetics, and others. Hydraulically actuated valves are typically spring loaded toward a valve-closed position and opened against the spring bias by the hydraulic pressure.
Because the valve should open and close very quickly, the spring is typically very stiff and is loaded to a high force under the relatively high hydraulic pressure needed to open the valve quickly against the high internal pressures of the combustion chamber. Therefore, when the valve closes, it impacts the valve seat at velocities that can create forces which eventually erode the valve or the valve seat or even fracture or break the valve.
Therefore, it is an object of the present invention to provide a means whereby the valve will be slowed or snubbed as it nears the valve seat so that the valve seats at an acceptable velocity.
It is an additional object of the present invention to provide a hydraulically actuated poppet valve having a snubbing valve positioned upstream therefrom, wherein the snubbing valve restricts fluid flow exiting the hydraulic cavity between the engine valve and the snubbing valve as the engine valve closes, thereby slowing the engine valve to an acceptable impact velocity.
DISCLOSURE OF THE INVENTION
In a first aspect of the present invention, a system is provided for opening an engine valve by hydraulic force and for slowing the engine valve by hydraulic force to an acceptable impact velocity when the engine valve closes. The engine valve is biased towards its closed position by a return spring. A rail communicates high pressure fluid to a first end of the engine valve for opening the engine valve against the spring bias force. Situated between the rail and the first end of the engine valve is a snubbing valve. The snubbing valve and its surrounding structures are adapted to allow relatively unrestricted flow of the high pressure fluid from the rail to the first end of the engine valve to quickly open the engine valve.
When the engine valve is to return to its closed position, communication of the high pressure fluid with the rail is ceased. The force of the return spring then causes the engine valve to return towards its closed position. The snubbing valve and its surrounding structures are also adapted to then restrict the flow of fluid from the cavity between the snubbing valve and the first end of the engine valve to a rate that will maintain hydraulic pressure in the cavity adequate to slow the engine valve to an acceptable impact velocity as it closes.
In a preferred embodiment, the snubbing valve includes a check displaceable between a first seat and a second seat. When high pressure fluid is in the rail, the check seats against the first seat and the check and first seat are adapted to allow relatively unrestricted flow of the fluid to the first end of the engine valve. When communication of the high pressure fluid to the rail ends, the differential hydraulic pressure between the relatively high pressure fluid still in the cavity between the snubbing valve and the first end of the engine valve and the relatively low pressure fluid now in the rail causes the check to seat against the second seat. The check and the second seat are adapted to then restrict the flow of fluid being essentially pumped out of the cavity by the return of the engine valve to a rate that will maintain hydraulic pressure in the cavity adequate to slow the engine valve to an acceptable impact velocity.
In a second aspect of the present invention, a method for performing the above described functions is provided.
BRIEF DESCRIPTION OF THE DRAWINGS
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Caterpillar Inc.
Keen Joseph W.
Lo Weilun
Skarvan Dennis C.
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