Internal-combustion engines – Poppet valve operating mechanism – Tappet
Reexamination Certificate
2001-01-31
2002-03-19
Lo, Weilun (Department: 3748)
Internal-combustion engines
Poppet valve operating mechanism
Tappet
Reexamination Certificate
active
06357407
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a roller valve lifter having a roller at one end thereof that cooperates with a lobe of a camshaft in an internal combustion engine. More specifically, the invention relates to improving the lubrication of the valve lifter and preventing rotation of the lifter.
BACKGROUND OF THE INVENTION
Conventional camshaft or “cam”, internal combustion engines typically utilize valve lifters, push rods, and valve springs along with rocker arms to open and close the valves of the engine to allow air and fuel to enter and exhaust to exit the cylinders of the engine during combustion. These components are collectively referred to as the “valve train.”
In conventional cam engines as opposed to those of over-head design, a valve lifter with a pushrod rides on the lobes of the camshaft which is rotated by the crankshaft. As the lifter reciprocates up and down, the push rod seated in the lifter also reciprocates and communicates this up and down motion via a rocker arm to either an intake or exhaust valve. A high tension spring ranging from approximately 200 to 1000 ft·lbs, surrounds the stem of the valve and when the spring is compressed, the valve is pushed into the cylinder.
During the up stroke of the piston in the cylinder, the intake valve opens to allow fuel and air to enter the combustion chamber. Somewhere near the very top of the up stroke, both the intake and the exhaust valves close and the spark plug creates a spark to ignite the air-fuel mixture which is under compression by the piston. This results in a high temperature explosion which forces the piston downward, called the “power stroke,” thereby translating this movement via a connection rod to rotate the crankshaft which, in turn, translates this angular motion to the wheels of the vehicle via a set of gears. Near the bottom of the compression stroke, the exhaust valve opens to expel the burnt fuel mixture out of the cylinder. After the piston changes directions and begins the up stroke, the exhaust valve continues to remain open thereby forcing any remaining the spent gases out of the cylinder. However, during this same time, the intake valve begins to open to recharge the cylinder with fuel. It is not until the piston has started to travel upward that the exhaust valve closes. Thus, at various times during the compression cycle, both the intake and exhaust valves will be open and closed at the same time. The timing of the opening and closing of the valves is controlled by the physical design of the oval shaped lobes on the camshaft. As the valve lifter is pushed upward by the lobe of the camshaft, the valve lifter pushes the pushrod up which drives the rocker arm downward, causing the valve to open. Likewise, as the lifter and pushrod travel downward, the rocker arm raises and the valve closes due to the biasing action of the valve spring.
In high speed engines, measured as revolutions per minute (RPM), the valve train components are under extreme stress and high temperatures. To increase engine performance and decrease component wear which may eventually lead to failure, various valve lifter configurations have been designed. Solid and hydraulic valve lifters are the most common designs used in conventional cam engines. Hydraulic lifters are typically used in relatively low RPM engines, up to 6,500, whereas solid valve lifter designs are preferred in high RPM applications such as racing and high performance applications. Conventional hydraulic and solid lifters have a flat surface that is fixed or integral with the body of the lifter and is adapted to engage and ride on the lobes of the camshaft. The engagement between the fixed surface of the lifter body and the camshaft lobe creates high frictional forces causing the surfaces of the lobes to wear. Therefore, the higher the RPM of the engine, the greater the wear and the likelihood of material being removed. As material is removed from the surface of the lobe, the timing of the opening and closing of the valve also changes. This change in timing may hamper engine performance such as by allowing excess air-fuel mixture to enter the cylinder causing a rich condition. Conversely, improper timing may permit the air-fuel mixture to escape through the exhaust valve which results in a lean condition. Either of these conditions will affect cylinder pressure and decrease performance and may cause misfiring of the cylinder and engine damage. Furthermore, if this improper timing allows a valve to remain open when the piston is near the top of the compression stroke, the piston will strike the valve resulting in bent pushrods and valves, broken valve springs and lifters and will eventually lead to catastrophic engine failure.
To decrease lobe wear in high performance engines, a roller has been added to the body of the valve lifter for riding on the cam. The roller allows the use of a camshaft with lobes of steeper ramp angles to provide faster valve opening and closing for accommodating high RPM engines. The roller engagement between the roller and rotating cam lobe reduces the frictional forces generated therebetween. Not only does the presence of the roller decrease cam lobe and valve lifter wear, it also provides smoother transitions as the roller travels over the peak of the lobe thereby decreasing valve train noise. Likewise, various bearing and sleeve configurations have been utilized to decrease friction and wear of the shaft rotatably mounting the roller to the valve lifter. For high performance engines, needle bearings have replaced solid rollers, bushing and conventional ball bearings to decrease wear and more evening spread the load over the surface of the shaft. However, these bearings and bushings also rely upon oil to function properly.
Although the addition of the roller increases camshaft and valve train life, overall roller wear is a function of engine speed (RPM). High performance engines such as those used in drag racing applications produce extremely high engine speeds (6,000 to 13,000 RPM) over a short duration of time (i.e. less than 5 to 12 seconds). Conversely, stockcar racing engines produce relatively high engine speeds of typically 5,000 to 8,000 RPM and under racing conditions, maintain those speeds for long periods of time (2 to 3 hours). At these high engine speeds, it becomes difficult to provide oil to the valve lifter, roller and bearing assembly as well as adequate lubrication of the camshaft.
From the ground up, a typical engine is configured with an oil pan for holding oil and an oil pump which feeds the oil to various locations in the engine. Above the oil pan sits the engine block and the crankshaft, such that a portion of the crank rotates in the oil. In a typical “V”-style engine, that is, one having cylinders at an angle to the left and right sides of the block in a “V” pattern with the crankshaft positioned at the apex of the “V”, the camshaft is typically located directly above and in parallel with the crank. In straight cylinder configuration engines wherein all cylinders are aligned in a row, the crankshaft and cylinders are located in the same plane and camshaft is positioned to one side so not to interfere with the travel of the connecting rods.
The valve lifters, in an “V” style engine, are located in a lifter galley. The lifters are lubricated by oil in the engine block and receive direct lubrication from a transverse oil passageway in the engine block that intersect the bores in which the valve lifters are positioned and indirectly from oil that is sprayed into the lifter galley from the rotation of the crankshaft and connecting rods. Various methods have been employed to increase the lubrication of the valve lifters and camshaft.
One method used to increase the movement of oil to the valve lifters and camshaft is the addition of small holes to the crankshaft and the dynamic balance weights of the crank. These holes, or oil squirters, pickup oil from the pan and any oil on the surface of the crank and throw the oil to the camshaft and valve lifter as the crankshaft and rotates. Thi
Banner & Witcoff , Ltd.
Competition Cams
Lo Weilun
LandOfFree
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