Internal-combustion engines – Engine speed regulator – Responsive to deceleration mode
Reexamination Certificate
2001-12-17
2004-04-06
Gimie, Mahmoud (Department: 3747)
Internal-combustion engines
Engine speed regulator
Responsive to deceleration mode
C123S090110, C123S090120
Reexamination Certificate
active
06715466
ABSTRACT:
TECHNICAL FIELD
This invention relates generally to valve actuators and, more particularly, to an apparatus and method for accurately controlling movement of an internal combustion engine exhaust valve in a compression braking cycle.
BACKGROUND
Internal combustion engines, both two cycle and four cycle, utilize reciprocating intake valves to supply a combustible gas to a combustion chamber. Reciprocating exhaust valves are used to exhaust gasses of combustion from the combustion chamber. For many years, a camshaft driven by the main crankshaft of the engine exclusively controlled the operation of the intake and engine valves. With ever increasing demands for improved engine performance over the years, this fixed and inflexible operation of the intake and engine valves with respect to the combustion cycle of the engine proved to be a disadvantage. For example, it is often desirable to adjust the valve timing for different engine operating conditions and/or engine speeds.
In one such application, it is often desirable to use engine compression braking to provide supplemental braking for vehicles traveling down hills. With engine compression braking, the engine is used as an energy absorbing air compressor, and it is necessary to operate the exhaust valves independently of their normal power generating combustion cycle. Thus, the exhaust valves are operated by actuators independent of the rocker arms or other devices operating the exhaust valves during a power generation mode.
More specifically, in a known normal engine compression braking mode, the fuel system is turned off; and the exhaust valve is closed during the compression stroke in the normal manner. However, when the piston is close to the top-dead-center position, the exhaust valve is opened; and the compressed air is vented out of the exhaust system. Thus, energy is absorbed in the compression of the air, but the compressed air is released before the energy can be recovered by the engine.
In another known engine compression braking mode, the exhaust valve is opened near the end of a prior intake stroke, that is, around the bottom-dead-center position. After some crankshaft rotation, such as about 30° for example, the exhaust valve is again closed. Opening the exhaust valve at the end of the intake stroke admits a pulse of high pressure exhaust gases into the combustion chamber for a supercharging effect. The higher initial combustion chamber density then results in greater compression and greater braking power generated during the compression breaking event. As with the normal engine compression braking, the exhaust valve is again opened around the top-dead-center position to vent the compressed gases.
As will be appreciated, the operation of an exhaust valve during a compression braking operation is different than the exhaust valve operation during normal engine operation. In order to provide this varied valve operation, it is known to open and close the exhaust valves by electronically operated hydraulic actuators. The flow of hydraulic fluid to a hydraulic actuator is normally controlled by an electromagnetic solenoid. While such solenoids provide large forces and have long strokes, solenoids do have certain drawbacks. For example, first, during actuation, current must be continuously supplied to the solenoid in order to maintain the solenoid in its energized position. Further, to overcome the inertia of the armature and provide faster response times, a solenoid is driven by a stepped current waveform. A very large current is initially provided to switch the solenoid; and after the solenoid has changed state, the drive current is stepped down to a minimum value required to hold the solenoid in that state. Thus, a relatively complex and high power current driver is required.
In addition to requiring a relatively complex and high current power source, the requirement of continuous current flow to maintain the solenoid at its energized position leads to heating of the solenoid. The existence of such a heat source, as well as the ability to properly dissipate the heat, often is of concern depending on the environment in which the solenoid is used.
Second, the force produced by a solenoid is dependent on the air gap between the armature and stator and is not easily controlled by the input signal. This makes the solenoid difficult to use as a proportional actuator. Large proportional solenoids are common, but they operate near or at the saturation point and are very inefficient.
Third, small, relatively fast acting nonproportional solenoids may have response times defined by the armature displacement as fast as 350 microseconds. However, this response time can be a significant limitation in applications that require high repetition rates or closely spaced events. Further, it is known that there is a substantial delay between the start of the current signal and the start of the armature motion. This is due to the inductive delay between the voltage and magnetic flux required to exert force on the armature. In control systems, such delays lead to variability.
SUMMARY OF THE INVENTION
In accordance with the principles of the present invention, an electrohydraulic actuator for operating an exhaust valve of an internal combustion engine to provide engine compression braking is disclosed. A thermally prestressed electroactive bender actuator has at least two operating states and switches between those states in response to a command signal. An exhaust valve actuator system is coupled with the thermally prestressed electroactive bender actuator and the exhaust valve. The exhaust valve actuator system operates the exhaust valve as a function of the at least two operating states of the thermally prestressed electroactive bender actuator. The thermally prestressed electroactive bender actuator and the exhaust valve actuator system operate the exhaust valve to effect engine compression braking.
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Cotton III Clifford E.
Holtman Richard H.
Waterfield Larry G.
Caterpillar Inc
Gimie Mahmoud
Lundquist Steve D
Wood Herron & Evans LLP
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