Internal-combustion engines – Poppet valve operating mechanism
Reexamination Certificate
2000-09-15
2002-05-28
Walberg, Teresa (Department: 3742)
Internal-combustion engines
Poppet valve operating mechanism
C123S090390, C123S090450, C123S090160
Reexamination Certificate
active
06394050
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to an actuator piston assembly for use on a rocker arm system in an engine. In particular, the present invention relates to the construction of an actutaor piston assembly that can take up a preset lash and be easily manufactured.
BACKGROUND OF THE INVENTION
With many engines it is desirable to have both a positive power mode of operation (in which the engine produces power for such purposes as propelling an associated vehicle) and a braking mode operation (in which the engine absorbs power for such purposes as slowing down an associated vehicle). It is well known that a highly effective way of operating an engine in braking mode is to cut off the fuel supply to the engine and to then open the exhaust valves in the engine near top dead center of the compression strokes of the engine cylinders. This allows air that the engine has compressed in its cylinders to escape to the exhaust system of the engine before the engine can recover the work of compressing the air during the subsequent “power” strokes of the engine pistons. This type of engine braking is known as compression release engine braking.
It takes a great deal more force to open an exhaust valve to produce a compression release event during compression release engine braking than to open either an intake or exhaust valve during positive power mode operation of the engine. During positive power mode operation the intake valves typically open while the piston is moving away from the valves, thereby creating a low pressure condition in the engine cylinder. Thus the only real resistance to intake valve opening is the force of the intake valve return spring which normally holds the intake valve closed. Similarly, during positive power mode operation the exhaust valves typically open near the end of the power strokes of the associated piston after as much work as possible has been extracted from the combustion products in the cylinder. The piston is again moving away from the valves and the cylinder pressure against which the exhaust valves must be opened is again relatively low. (Once opened, the exhaust valves are typically held open throughout the subsequent exhaust stroke of the associated piston, but this only requires enough force to overcome the exhaust valve return spring force.)
The additional exhaust valve opening associated with compression release retrading is achieved by adding components that actuate an exhaust valve independently from the normal actuating mechanisms. This is typically achieved by actuating the lifting mechanism of the exhaust valve by way of a secondary hydro-mechanical system that can be deactivated when the engine is operating in its positive power mode. In summary, the secondary system lifts the exhaust valve, at an appropriate time, and does not interfere with, nor interrupt, the normal valve lifting mechanism, and is inactive during positive power operation. Timing of the secondary system's valve lifting is usually derived from the activation of an adjacent cylinder's normal intake or exhaust valve's opening or the injection actuation mechanism. A neighboring cylinder, wherein a valve opening occurs nearest to the desired time for the active cylinder's exhaust valve opening is chosen. This approach, deriving timing from an adjacent cylinder's normal operation, eliminates the need for the secondary system to contain its own timing control.
The most common type of engine brake derives its motion from the injector cam of the same cylinder.
Conventional single-cycle engine braking systems have inherent limitations. These limitations are introduced primarily by (1) secondary valve actuating systems derive their timing from an adjacent cylinder's normal valve opening timing via hydromechanical links; and (2) secondary systems do not interrupt the normal opening and closing of the cylinder intake and exhaust valves during positive power. The first circumstance generally results in a sub-optimum realization of the full engine braking potential. This occurs because the timing and duration of the exhaust valve opening to vent the cylinder at the completion of the compression braking stroke is fixed by an adjacent cylinder's normal timing or injector timing of that cylinder during valve opening duration. The second circumstance prevents exploiting a second compression braking cycle because the exhaust valve is open during the exhaust stroke. Otherwise, the second cycle is available for compression braking Consequently, a system that takes control of the actuation of the cylinder intake and exhaust valves enables or disables their opening. This can optimize engine performance in an engine braking mode.
Other internal combustion engine limitations have emerged in the thirty years since engine braking technology has been introduced. Emission controls, turbo-chargers, and exhaust braking have affected the performance of engine braking. The net effect is a reduction in conventional engine braking performance, particularly at low speeds when the turbo-charged air volume, available for compression, is small. During the same time, demand and reliance on conventional engine braking has increased. A further motivation for improved engine braking performance has emerged.
Engine retarders of the compression release-type are well-known in the art. Engine retarders are designed to convert, at least temporarily, an internal combustion engine of either the spark-ignition or compression-ignition type into an air compressor. In doing so, the engine develops retarding horsepower to help slow the engine down. This can provide the operator increased control over the vehicle, and substantially reduce wear on the service brakes of the vehicle. A properly designed and adjusted compression release-type engine retarder can develop retarding horsepower that is a substantial portion of the operating horsepower developed by the engine on positive power.
A compression release-type retarder of this type supplements the braking capacity of the primary vehicle wheel braking system. In so doing, it extends substantially the life of the primary (or wheel) braking system of the vehicle. The basic design for a compression release engine retarding system of the type involved with this invention is disclosed in Cummins, U.S. Pat. No. 3,220,392.
The compression release-type engine retarder disclosed in the Cummins '392 patent employs a hydraulic control system. The hydraulic control system of typical compression release-type engine retarders used prior to the present invention engage the valve actuation system of the engine. When the engine is under positive power, the hydraulic control system of a typical compression release engine retarder is disengaged from the valve control system. When compression release-type retarding is desired, the fuel supply is stopped and the hydraulic control system of the compression release brake causes the compression release brake to engage the valve control system of the engine.
Compression release-type engine retarders typically employ a hydraulic system in which a master piston engages the valve control or injector system of the engine. When the retarder is activated, a solenoid valve allows lube oil to fill a hydraulic circuit which actuates the master piston which is hydraulically connected to a slave piston. The motion of the master piston controls the motion of the slave piston, which in turn typically opens the exhaust valve of the internal combustion engine at a point near the end of the compression stroke. In doing so, the work that is done in compressing the intake air cannot be recovered during the subsequent expansion (or power) stroke of the engine. Instead, it is dissipated through the exhaust. By dissipating energy developed from the work done in compressing the intake gases, the compression release-type retarder dissipates energy from the engine, slowing the vehicle down.
The master piston in typical compression release engine retarders of the type known prior to the present invention i
Custer Dennis R.
Little, Jr. Richard J.
McCarthy Donald J.
Collier Shannon Scott PLLC
Coulby John N.
Dahbour Fadi H.
Diesel Engine Retarders, Inc.
Rygiel Mark W.
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