Internal-combustion engines – Engine speed regulator – Responsive to deceleration mode
Reexamination Certificate
1999-09-22
2001-09-25
Yuen, Henry C. (Department: 3747)
Internal-combustion engines
Engine speed regulator
Responsive to deceleration mode
Reexamination Certificate
active
06293248
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the field of engine compression braking.
2. Description of the Background Art
Engine braking is an engine operating mode wherein the engine is reconfigured during operation to provide a braking effect to an associated vehicle. This may be desirable or necessary when regular wheel brakes are inadequate to provide complete braking. An example is a need for powerful and prolonged braking operations on steep grades, such as on mountain roads. Engine braking finds particular applicability on large vehicles having high wheel weights and correspondingly high momentum, and where conventional wheel brakes may fade or fail under high loading conditions or under prolonged use.
A compression type engine brake works by opening intake valves during an intake stroke and by opening exhaust valves at or near the end of the compression stroke of an associated cylinder. During the compression stroke of an engine, the air in a cylinder is compressed, requiring a work input by the engine. In normal engine operation the combustion stroke follows the compression stroke and recoups the work expended during the compression stroke. However, during compression braking, the opening of the exhaust valve near the end of the compression stroke means that no expansion of the compressed air occurs. Instead, the air is simply exhausted from the engine. The net result is that during engine braking operation the engine is not generating power but instead is absorbing power. The engine compression brake is therefore an efficient braking system that can be used as a supplement to or a substitute for conventional wheel brakes, and may be used for repeated and extended braking operations.
Related art compression brakes generally work as four-cycle compression brakes, with one exhaust valve opening event and one intake valve opening event per two crankshaft revolutions. Four-cycle braking is usually done because most large engines are four-cycle in nature, with the valve train designed for one opening event per cycle. However,
FIG. 1
shows a graph illustrating the increased braking power available in a two-cycle braking system over a four-cycle braking system. Related art compression braking is therefore much less efficient than it could be.
Related art compression brakes typically rely on a mechanical linkage of some sort to activate the compression brake and to transmit compression braking events to one or more valves. While such linkages are durable, they do not allow for variations. Mechanical linkages are designed for a particular engine and application. Mechanical linkages therefore do not readily accommodate variations such as different timings between engines and different engine timings based on ambient characteristics such as intake air temperature, pressure, or humidity. An additional drawback is that related art compression brakes often require that the normal valve operation be disabled for braking operations. Further, related art compression brakes often rely on additional linkages or devices that exist apart from a valvetrain mechanism, requiring additional expense and modification of an engine in order to function.
Therefore, there remains a need in the art for improvements in engine braking systems.
SUMMARY OF THE INVENTION
A two-cycle compression braking apparatus is provided according to a first aspect of the invention. The two-cycle compression braking apparatus comprises a positive power hydraulic lash adjuster positioned in a travel path of a power rocker arm and being capable of opening an associated at least one valve when a hydraulic fluid is held in the positive power hydraulic lash adjuster, and a compression brake hydraulic lash adjuster positioned on a compression brake rocker arm and positioned over the associated at least one engine valve and being capable of opening the associated at least one valve when the hydraulic fluid is held in the compression brake hydraulic lash adjuster, wherein in a positive power mode the hydraulic fluid is held in the positive power hydraulic lash adjuster to actuate the at least one associated valve while the compression brake hydraulic lash adjuster does not actuate the at least one associated valve, and in a compression braking mode the hydraulic fluid is held in the compression brake hydraulic lash adjuster to actuate the at least one associated valve while the positive power hydraulic lash adjuster does not actuate the at least one associated valve so that at least one exhaust valve is opened near a top dead center position of an associated piston while at least one intake valve is opened near a bottom dead center position of the associated piston to perform the two-cycle engine compression braking.
A method of two-cycle compression braking on a four stroke engine using a hydraulic lash adjustment is provided according to a second aspect of the invention. The method comprises the steps of releasing a hydraulic fluid in a positive power hydraulic lash adjuster, and holding a hydraulic fluid in a compression brake hydraulic lash adjuster, wherein a rocker arm motion is transmitted to at least one exhaust valve and to at least one intake valve to perform two-cycle engine compression braking.
A method of two-cycle compression braking on a four stroke engine using a hydraulic lash adjuster positioned on a rocker arm is provided according to a third aspect of the invention. The method comprises the steps of releasing a hydraulic fluid in a positive power hydraulic lash adjuster, transferring the hydraulic fluid from the positive power hydraulic lash adjuster to a compression brake hydraulic lash adjuster, and holding the hydraulic fluid in the compression brake hydraulic lash adjuster, wherein an exhaust rocker arm motion is transmitted to at least one exhaust valve near a top dead center position of an associated cylinder and an intake rocker arm motion is transmitted to at least one intake valve near a bottom dead center position of said associated cylinder to perform said two-cycle engine compression braking.
The above and other features and advantages of the present invention will be further understood from the following description of the preferred embodiment thereof, taken in conjunction with the accompanying drawings.
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Bartel John B.
Schmidt Joseph H.
Zsoldos Jeffrey S.
Mack Trucks, Inc.
Rothwell Figg Ernst & Manbeck
Vo Hieu T
Yuen Henry C.
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