Internal-combustion engines – Engine speed regulator – Responsive to deceleration mode
Reexamination Certificate
2000-12-20
2002-09-17
Wolfe, Willis R. (Department: 3747)
Internal-combustion engines
Engine speed regulator
Responsive to deceleration mode
C123S090160
Reexamination Certificate
active
06450144
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to valve actuation in internal combustion engines that include compression release-type engine retarders. In particular, it relates to methods and apparatus for controlling valve lift and duration for compression release valve events and main exhaust valve events.
BACKGROUND OF THE INVENTION
Engine retarders or brakes 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 compression-ignition type into an air compressor. In doing so, the engine develops retarding horsepower to help slow the vehicle 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 in positive power.
Functionally, compression release-type retarders supplement 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. Patent No. 3,220,392 (November 1965) for a Vehicle Engine Braking And Fuel Control System.
The compression release-type engine retarder disclosed in the Cummins '
392
patent employs a hydraulic system or linkage. The hydraulic linkage of a typical compression release-type engine retarder may be linked to the valve train of the engine. When the engine is under positive power, the hydraulic linkage may be disabled from providing valve actuation. When compression release-type retarding is desired, the hydraulic linkage is enabled such that valve actuation is provided by the hydraulic linkage responsive to an input from the valve train.
Among the hydraulic linkages that have been employed to control valve actuation (both in braking and positive power), are so-called “lost-motion” systems. Lost-motion, per se, is not new. It has been known that lost-motion systems are useful for variable valve control for internal combustion engines for decades. In general, lost-motion systems work by modifying the hydraulic or mechanical circuit connecting the actuator (typically the cam shaft) and the valve stem to change the length of that circuit and lose a portion or all of the cam actuated motion that would otherwise be delivered to the valve stem to produce a valve opening event. In this way lost-motion systems may be used to vary valve event timing, duration, and the valve lift.
Compression release-type engine retarders may employ a lost motion system in which a lash piston is included in the valve train (e.g. a linkage of a push tube, cam, and/or rocker arm) of the engine. When the retarder is engaged, the lash piston is hydraulically extended to cause the exhaust valve of the internal combustion engine to open at a point near the end of a piston's 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 and radiator systems of the engine. By dissipating energy developed from the work done in compressing the cylinder gases, the compression release-type retarder dissipates the kinetic energy of the vehicle, which may be used to slow the vehicle down.
Regardless of the specific actuation means chosen, inherent limits were imposed on operation of the compression release-type retarder based on engine parameters. One such engine parameter is the physical relationship of an engine cylinder valve used for compression release braking and the piston in the same cylinder. If the extension of the valve into the cylinder was unconstrained during compression release braking, the valve could extend so far down into the cylinder that it impacts with the piston in the cylinder.
There may be a significant risk of valve-to-piston contact when a unitary cam lobe is used to impart the valve motion for both the compression release valve event and the main exhaust valve event. Use of a unitary cam lobe for both events means that the relatively large main exhaust lobe motion will be imparted to the hydraulic linkage, or more particularly to the slave piston. Because there is typically little or no lash between the lash piston and the exhaust valve during engine braking, input of the main exhaust event motion to the lash piston may produce a greater than desired main exhaust event. A means for limiting the downward stroke of an exhaust valve for its main exhaust event during engine braking is needed.
Some systems do not use a unitary cam lobe for both the compression release valve event and the main exhaust valve event. These systems may operate using a dedicated braking cam lobe to drive a dedicated braking rocker arm, and a dedicated main exhaust cam lobe to drive a dedicated main exhaust rocker arm. The braking and main exhaust rocker arms may actuate different or the same exhaust valves using one or more bridges or similar arrangements to convey the rocker arm motions to the selected exhaust valves. Although these “dedicated” systems do not run the same risks of valve-to-piston contact as the “unitary cam” systems, they may also benefit from inclusion of a means to limit the downward stroke of the exhaust valves.
One way of limiting the downward stroke of an exhaust valve used for compression release valve events and/or main exhaust valve events is to limit the extension of the hydraulic lash piston that is responsible for pushing the valve into the cylinder during compression release braking. A device that may be used to limit piston extension or motion is disclosed in Cavanagh, U.S. Pat. No. 4,399,787 (Aug. 23, 1983) for an Engine Retarder Hydraulic Reset Mechanism, which is incorporated herein by reference. Another device that may be used to limit piston motion is disclosed in Hu, U.S. Pat. No. 5,201,290 (Apr. 13, 1993) for a Compression Relief Engine Retarder Clip Valve, which is also incorporated herein by reference. Both of these (reset valves and clip valves) may comprise means for blocking a passage in a lash piston during the downward movement of the lash piston (such as the passage 344 of the slave piston 340 of FIG.
6
). After the lash piston reaches a threshold downward displacement, the reset valve or clip valve may unblock the passage through it and allow the oil displacing it to drain there through, causing the lash piston to return to its upper position under the influence of a return spring.
A reset valve, such as the one disclosed in Cavanagh, may be provided as part of a lash adjuster or a lash piston. A reset valve may comprise a hydraulically actuated means for unblocking a passage through the lash piston to limit its displacement. In Cavanagh, compression release retarding is carried out by opening one of two valves connected by a crosshead member or bridge. A purpose of the reset valve used in Cavanagh is to reseat the exhaust valve used for the compression release event before a subsequent main exhaust valve event so that the rocker arm will not push down on an unbalanced crosshead during the main exhaust event and transmit a bending force to the crosshead guide pin or to the non-braking valve stem.
A clip valve, such as the one disclosed in Hu, may comprise a mechanically actuated means for unblocking the passage through a hydraulically extendable piston to limit its extension.
As evident from the foregoing, compression release retarding systems have historically been implemented as bolt-on systems added to an existing engine as an optional or after-market item. As the market for compression release-type engine retarders has developed and matured, the direction of technological development has moved away from bolt-on systems towards compact, cost-efficient int
Bergmann Michael
Janak Robb
Lak Stephen
Collier Shannon Scott PLLC
Diesel Engine Retarders, Inc.
Wolfe Willis R.
Yohannan David R.
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