Internal-combustion engines – Poppet valve operating mechanism – Hydraulic system
Reexamination Certificate
2000-12-29
2003-01-28
Lo, Wellun (Department: 3748)
Internal-combustion engines
Poppet valve operating mechanism
Hydraulic system
C123S090160, C123S090410, C123S321000, C123S586000
Reexamination Certificate
active
06510824
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to methods and apparatus for intake and exhaust valve actuation in internal combustion engines.
BACKGROUND OF THE INVENTION
Valve actuation in an internal combustion engine is required in order for the engine to produce positive power, as well as to produce engine braking. During positive power, intake valves may be opened to admit fuel and air into a cylinder for combustion. The exhaust valves may be opened to allow combustion gas to escape from the cylinder.
During engine braking, the exhaust valves may be selectively opened to convert, at least temporarily, an internal combustion engine into an air compressor. This air compressor effect may be accomplished by partially opening one or more exhaust valves near piston top dead center position for compression-release type braking, or by maintaining one or more exhaust valves in a partially open position for much or all of the piston motion for bleeder type braking. 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 engine brake can develop retarding horsepower that is a substantial portion of the operating horsepower developed by the engine in positive power.
The braking power of an engine brake may be increased by selectively opening the exhaust and/or intake valves to carry out exhaust gas recirculation (EGR) in combination with engine braking. Exhaust gas recirculation denotes the process of channeling exhaust gas back into the engine cylinder after it is exhausted out of the cylinder. The recirculation may take place through the intake valve or the exhaust valve. When the exhaust valve is used, for example, the exhaust valve may be opened briefly near bottom dead center on the intake stroke of the piston. Opening of the exhaust valve at this time permits higher pressure exhaust gas from the exhaust manifold to recirculate back into the cylinder. The recirculation of exhaust gas increases the total gas mass in the cylinder at the time of the subsequent engine braking event, thereby increasing the braking effect realized.
For both positive power and engine braking applications, the engine cylinder intake and exhaust valves may be opened and closed by fixed profile cams in the engine, and more specifically by one or more fixed lobes which may be an integral part of each of the cams. The use of fixed profile cams makes it difficult to adjust the timings and/or amounts of engine valve lift needed to optimize valve opening times and lift for various engine operating conditions, such as different engine speeds.
One method of adjusting valve timing and lift, given a fixed cam profile, has been to incorporate a “lost motion” device in the valve train linkage between the valve and the cam. Lost motion is the term applied to a class of technical solutions for modifying the valve motion dictated by a cam profile with a variable length mechanical, hydraulic, or other linkage means. In a variable valve actuation lost motion system, a cam lobe may provide the “maximum” (longest dwell and greatest lift) motion needed for a full range of engine operating conditions. A variable length system may then be included in the valve train linkage, intermediate of the valve to be opened and the cam providing the maximum motion, to subtract or lose part or all of the motion imparted by the cam to the valve.
This variable length system (or lost motion system) may, when expanded fully, transmit all of the cam motion to the valve, and when contracted fully, transmit none or a partial amount of the cam motion to the valve. An example of such a system and method is provided in Vorih et al., U.S. Pat. No. 5,829,397 (Nov. 3, 1998), Hu, U.S. Pat. No. 6,125,828, and Hu U.S. Pat. No. 5,537,976, which are assigned to the same assignee as the present application, and which are incorporated herein by reference.
In some lost motion systems, an engine cam shaft may actuate a master piston which displaces fluid from its hydraulic chamber into a hydraulic chamber of a slave piston. The slave piston in turn acts on the engine valve to open it. The lost motion system may include a solenoid valve and a check valve in communication with a hydraulic circuit connected to the chambers of the master and slave pistons. The solenoid valve may be maintained in an open or closed position in order to retain hydraulic fluid in the circuit. As long as the hydraulic fluid is retained, the slave piston and the engine valve respond directly to the motion of the master piston, which in turn displaces hydraulic fluid in direct response to the motion of a cam. When the solenoid position is changed temporarily, the circuit may partially drain, and part or all of the hydraulic pressure generated by the master piston may be absorbed by the circuit rather than be applied to displace the slave piston.
Historically, lost motion systems, while beneficial in many aspects, have also been subject to many drawbacks. For example, the provision of hydraulic passages in various engine components, as is required in lost motion systems, may decrease the structural stiffness, and thus the effectiveness, accuracy, and lifespan of such components. The need for added components or components of increased size in order to accommodate a lost motion system may also increase valve train inertia to the point that it becomes problematic at high engine speeds. The use of hydraulics may also result in initial starting difficulties as the result of a lack of hydraulic fluid in the system. It may be particularly difficult to charge the system with hydraulic fluid when the fluid is cold and has a higher viscosity. Lost motion systems may also add complexity, cost, and space challenges due to the number of parts required. Furthermore, the need for rapid and repeated hydraulic fluid flow in prior art systems has also resulted in undesirable levels of parasitic loss and overheating of hydraulic fluid in the system.
Thus there is a need for, and the various embodiments of the present invention provide: improved structural stiffness compared to other lost motion systems that depend on displaced oil volumes to transmit motion; increased maximum valve closing velocities as compared to other lost motion systems; reduced cost and complexity due to the reduced number of high speed trigger valves and check valves required for the system; improved performance at initial start-up and decreased susceptibility to cold hydraulic fluid; decreased size and improved capability for integration into the cylinder head; reduced parasitic loss as compared with other lost motion systems; and improved hydraulic fluid temperature control.
The complexity of, and challenges posed by, lost motion systems may be increased by the need to incorporate an adequate fail-safe or “limp home” capability into such systems. In previous lost motion systems, a leaky hydraulic circuit could disable the master piston's ability to open its associated valve(s). If a large enough number of valves cannot be opened at all, the engine cannot be operated. Therefore, one valuable feature of various embodiments of the invention arises from the ability to provide a lost motion system which enables the engine to operate at some minimum level (i.e. at a limp home level) should the hydraulic circuit of such a system develop a leak. A limp home mode of operation may be provided by using a lost motion system which still transmits a portion of the cam motion to the valve after the hydraulic circuit associated with the cam leaks or the control thereof is lost. In this manner the most extreme portions of a cam profile still can be used to get some valve actuation after control over the variable length of the lost motion system is lost and the system has contracted to a reduced length. The foregoing assumes, of course, that the lost motion system is constructed such that it will assume a contracted position should con
Ernest Steven
Leitkowski Edward T.
Mossberg Jeffrey
Paterson Guy
Schwoerer John A.
Collier Shannon Scott PLLC
Diesel Engine Retarders, Inc.
Lo Wellun
Yohannan David R.
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