Internal-combustion engines – Valve – Reciprocating valve
Reexamination Certificate
2002-12-04
2003-07-29
Kamen, Noah P. (Department: 3747)
Internal-combustion engines
Valve
Reciprocating valve
C123S07900R
Reexamination Certificate
active
06598577
ABSTRACT:
BACKGROUND
1. Field of the Invention
The present invention relates to intake valves for internal combustion engines. More particularly, this invention pertains to an intake valve that includes a floating valve seat.
2. Description of the Prior Art
Among the most critical elements of an internal combustion engine are the valves that regulate the gas flow into and out of the combustion chambers. Each chamber houses a reciprocating piston. Thus, for example, an eight cylinder engine has eight pistons requiring the careful regulation of sixteen valves (assuming two valves per cylinder).
The output of the engine consists of rotation of a crankshaft. This is distributed to the wheels by means of a differential engaged to an axle. Rotation of the crankshaft is produced through successive, phased inputs of angular motion via connecting rods pivotally engaged at one end to pistons, and, at the other, to rod journals which are often offset from the main journals that lie along the axis of rotation of the crankshaft. The application of successive, phased forces to the offset journals results in crankshaft rotation.
The axis of rotation of the crankshaft is aligned with that of a drive shaft that can be engaged and disengaged from the crankshaft by means of a clutch. The output of the drive shaft is, in turn, employed, to drive the wheels of the vehicle through the differential.
Thus, an internal combustion engine translates the reciprocating motions of the pistons into rotation of a shaft. The generation of the reciprocating movements of the pistons is accomplished through the well-understood four-stroke process of internal combustion known as the Otto cycle. The four elements of this process include an “intake stroke” during which a mixture of air and fuel is received at the top of the combustion chamber (i.e. above the piston) from a carburetor or fuel injectors. The piston travels downwardly (pulled by the rotating crankshaft via the connecting rod), creating a vacuum that sucks in the air-fuel mixture. After the intake stroke, the portion of the combustion chamber above the piston is sealed by the closure of an intake valve and a “compression stroke” is commenced during which the connecting rod pushes the piston upwardly, compressing the air-fuel mixture. Once the compression stroke has been completed, a high-voltage spark is emitted by a spark plug, igniting the air-fuel mixture within the sealed combustion chamber. The resulting combustion of the mixture causes an expansion of gaseous volume, generating a force that acts downwardly upon the top of the piston during a “power stroke”. This drives the piston down to impart rotation to the crankshaft. The amount of angular motion imparted is, in part, dependent upon the number of engine cylinders. Once this motion has been completed, the gases within the combustion chamber are vented during an “-exhaust stroke” as the piston is again driven upwardly within the cylinder by the rotation of the crankshaft and the exhaust valve that regulates the passage of gases through an exhaust port is opened. Another four-stroke cycle then begins with another intake stroke in which air-fuel mixture is admitted through a reopened intake valve and the exhaust valve is closed. At a typical freeway engine speed of 2200 r.p.m., the entire four-stroke process is completed at a rate of eighteen times per second in each cylinder.
Intake and exhaust ports communicate with the portion of the cylinder that lies above top dead center of the piston (i.e., the combustion chamber). The intake and exhaust valves seal the head ports. The motions of the valves are derived from the crankshaft of the engine through a valve train linkage that includes the valve itself.
The valves include elongated stems and terminate in generally-circular broadened heads that include angled faces cut to match an angle formed by a head seat formed within the engine head. The head seats and poppet-type valves interact whereby the combustion chamber is opened to communicate with the intake and/or exhaust ports by the action of the valve train pushing down on the valves and then closed by a spring, a side component of the valve train. The spring returns the valve (stem protruding from the combustion chamber of the head to the rocker assembly side of the head) until its enlarged head abuts the head seat adjacent the top of the combustion chamber. A seal is formed between the circumferential face of the valve and the circular head seat. Conversely, an intake valve admits a gaseous mixture when driven downwardly to disengage the valve face from the head seat located in the combustion chamber of the engine head.
The cam of the valve linkage that defines the relationship between rotation of the crankshaft (and, thus travel of the piston within the cylinder) and the opening and closing of the intake and exhaust valves is of static design. Since the cam possesses a static, fixed shape, the relative timing of the opening and closing of the valves with respect to the travel of the piston within its cylinder is correspondingly limited or static.
The mass, and resulting momentum and inertia, of the valve train constrains the ability of the engine to operate in an idealized manner insofar as the coordination of valve operation and piston movements within the combustion chamber. For example, a typical profile of the intake stroke might consist of the cam gear gradually opening the inlet valve by one-eighth inch upon the piston having.traveled downwardly by two inches, then increasing to one quarter inch when piston travel has increased to three inches, then continuing to be held open by one-quarter inch during the fourth inch of travel of the piston. The valve might then begin to close during the interval between the fourth and fifth or final inches of downward travel of the piston. This would occur in anticipation of its imminent closure for the subsequent compression stroke.
Such “preparation” of the valve for closure during the transition from the intake to the compression stroke, built into the shape of the cam, is an acknowledgment of the inability of the valve train to reverse direction instantaneously in view of its mass. The non-idealized operation of the valve with respect to the movement of the piston within the combustion chamber has the effect of either forcing some amount of the fresh air-fuel mixture out of the chamber through the intake port (in the event that the point of closure of the intake valve occurs after the direction of the piston has reversed) or the admission of a less-than-maximum amount of air-fuel mixture into the chamber (in the event that the point of closure occurs somewhat prior to completion of downward travel of the piston). In either event, the torque generated by the engine is reduced below that theoretically possible with a valve linkage of zero mass.
An additional practical limitation upon valve operation is crankshaft rotation rate (in r.p.m.). Practical cam design requires more gradual transitions between valve openings and closings at a high r.p.m. engine output to prevent risk of valve train element disengagements. The resultant gradual reversals of valve direction further reduce the torque that may be generated by an internal combustion engine through reduction and/or contamination of intake of fresh air-fuel mixture and loss of compression.
Like issues pertain to the transition from the exhaust to the intake strokes. The exhaust valve, symmetrically located at the top of the combustion chamber with respect to the intake valve, undergoes closure during this transition. In the event that the intake valve, making a transition from a closed to an open attitude as the piston rises to the top of its travel, opens “early” (before the exhaust valve has closed and the piston reached the top of the chamber, a condition known as “overlap”), exhaust gases can escape from the chamber through the slightly open intake valve and into the intake port (a condition known as “reversion”). This will contaminate the fresh air-fuel mixture admitted during the intake stroke. Convers
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