Internal-combustion engines – Poppet valve operating mechanism – With means for varying timing
Reexamination Certificate
2000-09-08
2002-07-23
Walberg, Teresa (Department: 3742)
Internal-combustion engines
Poppet valve operating mechanism
With means for varying timing
C123S090160, C123S090430, C123S090460, C123S090550
Reexamination Certificate
active
06422186
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to a rocker arm system for controlling exhaust valves during positive power and engine braking. In particular, the present invention is directed to a rocker arm system having a lost motion piston for modifying a valve motion profile of the exhaust valve during positive power and different operating conditions. The present invention is also directed to a valve actuation mechanism that automatically adjusts for tolerance stack up in the valve train.
BACKGROUND OF THE INVENTION
For many internal combustion engine applications, such as for powering heavy trucks, it is desirable to operate the engine in a braking mode. This approach involves converting the engine into a compressor by cutting off the fuel flow and opening the exhaust valve(s) for at least one engine cylinder near the end of the compression stroke for that cylinder.
An early technique for accomplishing the braking effect is disclosed in U.S. Pat. No. 3,220,392 to Cummins (incorporated herein by reference), wherein a slave hydraulic piston located over an exhaust valve opens the exhaust valve near the end of the compression stroke of an engine piston with which the exhaust valve is associated. To place the engine into braking mode, three-way solenoids are energized which cause pressurized lubricating oil to flow through a control valve, creating a hydraulic link between a master piston and a slave piston. The master piston is displaced inward by an engine element (such as a fuel injector actuating mechanism) periodically in timed relationship with the compression stroke of the engine which in turn actuates the slave piston through hydraulic force to open the exhaust valves. The compression brake system as originally disclosed in the '392 patent has evolved in many aspects, including improvements on the control valves (see U.S. Pat. Nos. 5,386,809 to Reedy et al. and U.S. Pat. No. 4,996,957 to Meistrick) and the piston actuation assembly (see U.S. Pat. No. 4,475,500 to Bostelman). In a typical modem compression braking system the exhaust valves are normally operated during the engine's power mode by an exhaust rocker lever. To operate the engine in a braking mode, a control valve separates the braking system into a high pressure circuit and a low pressure circuit using a check valve which prevents the flow of high pressure fluid back into the low pressure supply circuit, thereby allowing the formation of a hydraulic link in the high pressure circuit.
Various problems have been discovered with conventional compression braking systems. First, an inherent time delay exists between the actuation of the three-way solenoid valve and the onset of the braking mode. This time delay is in part due to the positioning of the solenoid valve a spaced distance from the control valve creating longer than desired fluid passages and thus response time. Also long fluid passages between the master and slave pistons, that is, in the high pressure circuit, disadvantageously increase the compressed fluid volume and thus the response time. In addition, in conventional compression braking systems, the braking system is a bolt-on accessory that fits above the overhead. In such systems, in order to provide space for mounting the braking system, a spacer is positioned between the cylinder head and the valve cover which is bolted to the spacer. This arrangement adds unnecessary height, weight, and costs to the engine. Many of the above-noted problems result from viewing the braking systems as an accessory to the engine rather than as part of the engine itself.
One possible solution is to integrate components of the braking system with the rest of the engine components. One attempt at integrating parts of the compression braking system is found in U.S. Pat. No. 3,367,312 to Jonsson, which discloses an engine braking system including a rocker arm having a plunger, or slave piston, positioned in a cylinder integrally formed in one end of the rocker arm wherein the plunger can be locked in an outer position by hydraulic pressure to permit braking system operation. Jonsson also discloses a spring for biasing the plunger outward from the cylinder into continuous contact with the exhaust valve to permit the cam-actuated rocker lever to operate the exhaust valve in both the power and braking modes. In addition, a control valve is used to control the flow of pressurized fluid to the rocker arm cylinder so as to permit selective switching between braking operation and normal power operation. However, the control valve unit is positioned separately from the rocker arm assembly, resulting in unnecessarily long fluid delivery passages and a longer response time. This also leads to an unnecessarily large amount of oil that must be compressed before activation of the braking system can occur, resulting in less control over the timing of the compression braking. Furthermore, the control valve is used to control the flow of fluid to a predetermined set of cylinders in the engine thereby undesirably preventing individual engine cylinders or different groups of engine cylinders from being selectively operated in the braking mode. Moreover, the control valve is a manually operated rotary type valve requiring actuation by the driver and often resulting in unreliable and inefficient braking operation. Also, rotary valves are subject to undesirable fluid leakage between the rotary valve member and its associated cylindrical bore.
U.S. Pat. No. 3,332,405 to Haviland discloses a compression braking system wherein a control valve unit, for enabling the formation of a hydraulic link, is mounted in a cavity formed in a rocker arm that operates the exhaust valves during the braking mode. Separate cam lobes are used for normal power operation and braking operation. However, a single rocker arm is used to actuate the exhaust valves during both normal and braking modes possibly causing the braking cam lobe profile design, and therefore the braking system operation, to be at least partially dependent on, or influenced by, the design of the cam lobe used for operating the exhaust valve during normal engine operation.
U.S. Pat. No. 4,251,051 to Quenneville discloses a solenoid valve assembly having an inlet communicating with a supply of fluid, and on e or more outlet passages communicating with respective loads requiring intermittent fluid supply and a design passage. A respective ball valve is positioned b between the inlet and each outlet and spring biased t o block flow between the supply and outlet passage while opening the drain passage. An armature and pin are actuated to move the ball valve s o to connect the supply to the outlet, and close the drain passage. However, when the valve assembly in the actuated position permits supply flow to the outlet passage, it does not prevent the return flow of fluid from the outlet passage into the supply passage and therefore could not permit the formation of a hydraulic link between different pressurized circuits as required by a control valve during compression braking system operation. Also see U.S. Pat. No. 5,146,890 to Gobert, et al., which discloses a method and device for compression braking.
Consequently, there is a need for a simple, yet effective braking system which is capable of minimizing the size and weight of the associated engine while ensuring optimum operation of a the compression braking system.
It is often desirable t o combine multiple profiles on a single cam lobe, e.g. a positive power or main event exhaust valve bump or motion, a compression-release brake bump or motion, and/or an exhaust gas recirculation (EGR) bump or motion. When this is done there must be a mechanism to select which profile(s)/bump(s) are to be active. Improved operation can be obtained if the main event motion is not altered by the addition of other motions. It is also desirable to be able to switch between events part way through an event, typically after a given amount of lift. Within the rocker itself, there is no way to determine the relative motion (valve lift). T
Collier Shannon Scott PLLC
Dahbour Fadi H.
Diesel Engine Retarders, Inc.
Walberg Teresa
Yohannan David R.
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