Method and appparatus for varying intake and exhaust valve opening and closing in a reciprocating piston engine

A modified camshaft and a modified cam follower control valve overlap and vary intake and exhaust valve opening and closing in a reciprocating piston engine. The camshaft and cam follower are modified to cause the intake valve of a piston cylinder to open at top dead center and close at bottom dead center of the intake stroke of a piston. The exhaust valve is caused to open at bottom dead center and close at top dead center to the exhaust stroke of the piston. The modification of a camshaft includes the shaping and spacing of the cam lobes to achieve, in conjunction with a modified cam follower, a desired duration and initiation of valve opening. The modification of the cam follower includes a novel shaping of the lower portion of a cam follower.

TECHNICAL FIELD OF THE INVENTION 
This invention relates to reciprocating piston engines, and more 
particularly to a method and apparatus for varying intake and exhaust 
valve opening and closing in a reciprocating piston engine. 
BACKGROUND OF THE INVENTION 
In a reciprocating four-stroke piston engine, each piston cylinder has an 
intake valve and an exhaust valve. The intake valve opens on a downstrike 
of the piston and an air-fuel mixture is drawn into the cylinder chamber. 
The mixture is compressed on the ensuing upstroke. Combustion is initiated 
at the top of that upstroke. The combustion forces the piston through a 
downstroke. The exhaust valve opens to expel gases on the final upstroke 
of the four-stroke cycle. The four-stroke cycle then begins again with the 
opening of the intake valve and a downstroke of the cylinder. A cam on a 
camshaft controls the opening and closing of each valve, respectively. In 
common engine design, there is a period during which the intake valve and 
exhaust valve are open simultaneously. This occurs during the end of the 
exhaust upstroke and the beginning of the intake downstroke when the 
intake valve opens prior to complete closing of the exhaust valve. This 
simultaneous open-valve position is called "valve overlap." In many 
instances it would be desirable to reduce or otherwise modify the duration 
or instant of occurrence of valve overlap. An important reason would be to 
increase engine efficiency by not exhausting some of the air-fuel mixture 
with gases during the exhaust upstroke or by not mixing gases which are 
combustion by-products with the air-fuel mixture. 
It can be appreciated that it would be desirable to have a means for 
controlling valve overlap in a reciprocating piston engine. It can also be 
appreciated that it would be desirable to have a means for varying intake 
and exhaust valve opening and closing in a reciprocating piston engine. 
BRIEF SUMMARY OF THE INVENTION 
It is an object of the invention to provide a means for controlling valve 
overlap in a four-stroke reciprocating piston engine. 
It is also an object of the invention to provide a means for varying intake 
and exhaust valve opening and closing in a reciprocating piston engine. 
The present invention utilizes a modified camshaft and a modified cam 
follower to control valve overlap and vary intake and exhaust valve 
opening and closing in a reciprocating piston engine. In a preferred 
embodiment, a camshaft and cam follower are modified to cause the intake 
valve of a piston cylinder to open at top dead center and close a bottom 
dead center of the intake stroke of a piston. The exhaust valve is caused 
to open at bottom dead center and close at top dead center of the exhaust 
stroke of the piston. The modification of a camshaft includes the shaping 
and spacing of the cam lobes to achieve, in conjunction with a modified 
cam follower, a desired duration and initiation of valve opening. The 
modification of the cam follower includes a novel shaping of the lower 
portion of a cam follower. 
Other aspects, objects, features, and advantages of the present invention 
will become apparent to those skilled in the art upon reading the detailed 
description of preferred embodiments in conjunction with the accompanying 
drawings and appended claims.

DETAILED DESCRIPTION OF PREFERRED EXEMPLARY EMBODIMENTS OF THE INVENTION 
While the specification concludes with claims particularly pointing out and 
distinctly claiming the subject matter which is regarded as the present 
invention, the invention will now be described with reference to the 
following description of an embodiment taken in conjunction with the 
accompanying drawings. 
In a four-stroke reciprocating piston engine, each piston reciprocates in a 
cylinder. The topmost position of the piston is referred to as "top dead 
center," and abbreviated "TDC." The bottommost position of the piston is 
referred to as "bottom dead center," and is abbreviated "BDC." The 
reciprocating, translational motion of each piston directly relates to the 
rotation of a crankshaft. One-half revolution of the crankshaft equates to 
movement of a piston from TDC to BDC. An additional one-half revolution 
brings the piston back to TDC. Piston movement either from TDC to BDC or 
from BDC to TDC is one "stroke" of the four-stroke engine. The four 
strokes are the intake stroke, the compression stroke, the power stroke 
and the exhaust stroke. Using the intake stroke as a starting point, the 
piston moves from TDC to BDC. An air-fuel mixture is taken into the piston 
cylinder during this stroke. The mixture is compressed on the upstroke 
from BDC to TDC. At TDC the compressed mixture is ignited causing 
expansion of gases in the cylinder. The expansion of gases forces the 
piston through a down stroke wherein power is delivered to the crankshaft. 
On the final stroke of the four-stroke cycle the piston moves from BDC to 
TDC forcing the gases tot he top of the cylinder. The four-stroke cycle 
immediately begins again. A camshaft controls the opening and closing of 
the intake valves and exhaust valves. The opening and closing of each 
valve is controlled by the rotation of a cam on the camshaft. The rotation 
of the camshaft is directly related to the rotation of the crankshaft. One 
complete rotation of the crankshaft equates to one-half rotation of the 
camshaft. And, in turn, each stroke of a piston is one-half turn of the 
crankshaft (180 degrees) and one-quarter turn of the camshaft (90 
degrees). 
Valve overlap is a condition that occurs when the exhaust valve and intake 
valve are open at the same time. The overlap may be due to the exhaust 
valve remaining open late, that is, after the piston starts its intake 
stroke, or it may be due to the intake valve opening early, that is, 
before the piston completes its exhaust stroke, or it may be due to a 
combination of the two. A common engine design causes a valve to remain 
open for 120 degrees of camshaft rotation. This exceeds by 30 cam-degrees 
the 90 cam-degrees (which equates to 180 crankshaft-degrees), the duration 
of a complete intake downstroke or a complete exhaust upstroke. The 
invention enables a valve to stay open for a shorter duration than that 
found in an engine of traditional design and, further, enables that open 
duration to be equal to the 90 cam-degrees that equates to 180 
crankshaft-degrees for a complete intake or exhaust stroke. The invention 
uses two features to vary the opening and closing of intake and exhaust 
valves, namely, (1) modification of a camshaft and (2 ) modification of 
the cam followers which are translated by the cam lobes of the camshaft. 
The preferred embodiment illustrated completely eliminates valve overlap by 
opening and closing the exhaust valve during the exhaust upstroke (which 
equates to a 180-degree rotation of the crankshaft and a 90-degree 
rotation of the camshaft) and opening the intake valve at the end of the 
exhaust stroke (which is the beginning of the intake stroke) and closing 
the intake valve at the end of the intake stroke (which also equates to a 
180-degree rotation of the crankshaft and a 90-degree rotation of the 
camshaft). In the illustrated preferred embodiment, a camshaft in which 
each intake cam lobe and each exhaust cam lobe is designed (in conjunction 
with the design of the cam follower) to open and close within a 90-degree 
rotation of the camshaft. In addition, each set of intake and exhaust cam 
lobes is spaced to allow the exhaust valve to fully open and fully close 
before the intake valve opens. This equates to the 90-degree spacing 
between the exhaust and intake cam lobes. Cam followers, in general, have 
either a dome-like bottom portion which engages the cam, a flat bottom 
portion which engages the cam or a roller which protrudes from the bottom 
portion which engage the cam. In the illustrated preferred embodiment, 
FIGS. 2 and 3, the cam follower is modified to provide a trailing edge 
which causes the cam follower to become disengaged from the cam lobe 
sooner than it would be in the case of a cam follower which is not 
modified. 
Reference will now be made to FIGS. 1-3 in which the same numbers are 
indicative of the same elements throughout the figures. In FIG. 1, therein 
is illustrated a frontal view of a section of a camshaft 10 embodying 
teachings of the present invention. Cams 14 and 16 with cam lobes 20 and 
60, respectively, rotate about the axis 12 of the camshaft 10. The intake 
valve cam lobe 20 is designed to open an intake valve when the lifting 
ramp 22 of the intake valve cam lobe 20 lifts an intake valve cam follower 
and close that intake valve when the closing ramp 26 of the intake valve 
cam lobe 20 lowers the intake valve cam follower. Likewise, the exhaust 
valve cam lobe 60 is designed to open an exhaust valve when the lifting 
ramp 62 of the exhaust valve cam lobe 60 engages an exhaust valve cam 
follower and close that exhaust valve when the closing ramp 66 of the 
exhaust valve cam lobe 60 engages the exhaust valve cam follower. The cam 
lobes 20 and 60 are designed so that the respective intake and exhaust 
valves are open and closed during a rotation of 90 degrees of the 
camshaft. There is also a 90-degree spacing between the exhaust valve cam 
lobe 60 and the intake valve cam lobe 20. This spacing is illustrated by 
noting the angle between the nose 24 of the intake valve cam lobe 20 and 
the nose 64 of the exhaust valve cam lobe 60. The 90-degree spacing allows 
the exhaust valve to fully open and close before the intake valve opens, 
as discussed above. 
Referring now to FIG. 2, therein is illustrated one of the cams shown in 
FIG. 1, a corresponding cam follower 40 configured in accordance with the 
teachings of a preferred embodiment of the invention, and the interaction 
between the cam lobe 20 and the cam follower 40. For reference and 
identification purposes the cam 14 with lobe 20 illustrated and discussed 
is referred to as an intake cam, however, the description of the structure 
and operation of this cam 14 and lobe 20 would be equally applicable to an 
exhaust cam 16 and lobe 60. The cam 14 rotates counterclockwise. The solid 
representation of the cam 14 illustrates the cam 14 in a position at which 
the cam lobe 20 initially lifts, or translates, the cam follower 40. The 
phantom (dotted line) representation illustrates the cam 14 with lobe 20 
(20') in a position at which the lobe 20 (20') has just completed lowering 
the cam follower 40. The cam lobe 20 is configured to work in conjunction 
with the cam follower 40 to cause opening and closing of the corresponding 
valve within a 90 degree rotation of the cam 14. The cam lobe 20 has a 
lifting ramp 22, a nose 24 and a lowering ramp 26. During the 90-degree 
rotation of the cam 14 that opens and closes a valve, a point on the lower 
portion of the cam follower 40 is engaged by the lifting ramp 22, nose 24 
and lowering ramp 26 of the cam lobe 20. The intake and exhaust valve 
typically consists of a valve head and a valve stem. Translational motion 
is imparted to the valve either by direct action upon the valve stem or by 
movement of a push rod which in turn imparts motion to the valve through a 
linkage. In typical engine use, the cam follower 40, engages either the 
valve stem or a valve push rod. The cam follower 40 has a top portion 
which receives either a valve stem or valve push rod 15 and translates the 
valve stem or push rod 15 as the cam follower 40 is translated. The valve 
stem or push rod 15 is shown being received within a hollow center portion 
of the cam follower 40. The interaction between the cam follower 40 and a 
valve stem or the cam follower and the push rod would be the same, 
therefore, the valve stem and push rod 15 are referred to interchangeably 
with respect to the cam follower 40. The lower portion of the cam follower 
40 is configured to work in conjunction with the cam lobe 20 to provide 
the desired amount and duration of lift. The cam follower 40 has a 
generally cylindrical shape and translates within a cylindrical opening in 
the engine block 15. The lower portion has a leading edge 44 which is the 
part of the cam follower 40 that is engaged by and is in contact with the 
cam lobe 20 during lifting and lowering of the cam follower 40. The cam 
follower 40 has a trailing edge 46 that is configured so that the cam lobe 
20 does not engage the trailing edge as the cam 14 rotates. The trailing 
edge 46 in the embodiment illustrated is shown as a plane which obliquely 
cuts through the lower portion of the cam follower 40. On the lower 
portion of the cam follower 40, at the intersection of the trailing edge 
46 and the leading edge 44 is a curved surface, or shoulder, 42 that 
serves as the contact point for the initial lifting of the cam follower by 
the lifting ramp 22 of the cam lobe 20 and the final engagement point for 
the lowering ramp 26 of the cam lobe 20. The contact between the contact 
curve 42 and the beginning of the lifting ramp 22 of the cam lobe 20 is 
shown in the solid line illustration of the cam lobe 20. The phantom 
depiction of the cam lobe 20' shows the cam lobe 20' in a position at 
which the cam follower 40 has been lowered. The lowering ramp 26 of the 
cam lobe 20 is shown engaging the contact curve 42 of the cam follower 40 
at the same point at which the lifting ramp 22 initially made contact with 
the contact curve 42. The cam lobe 20 does not make contact with the 
trailing edge of the cam follower 40 because the trailing edge is cut away 
at an angle to prevent contact with the lower portion of the cam follower 
40 beyond the contact curve 42. This enables the cam follower 40 to be 
completely lowered faster than one which has not been modified in 
accordance with teachings of the invention. The contact curve 42 is shown 
as being slightly to the right of the center line of the cam follower 40 
and cam 14 to achieve the 90 degree opening and closing desired in this 
embodiment. Movement of the contact curve 42 to the left or right of the 
position shown varies the lifting duration of the cam follower 40. This 
would also equate to a change in the angular distance between the intake 
lobe 20 and the phantom representation of the intake lobe 20'. The manner 
of cooperation between the cam and cam follower may also be achieved by 
utilizing cams of a larger, smaller or different configuration. For 
example, by using a cam lobe 20 of a larger size, it is possible to fully 
lift the cam follower 40 quicker and hold it in the lifted position longer 
and then lower it faster without changing the total lifting duration (that 
is, period during which the valve is "open"). As previously stated, in the 
embodiment illustrated, the cam follower 40 is cylindrical and is thus 
likely to rotate within the engine block 13 in which it is seated. If the 
cam follower 40 rotates, the cam lobe 20 will not properly engage the cam 
follower 40. Therefore, it is necessary to prevent rotation of the cam 
follower 40. In the embodiment shown, this is done by creating a flat 
notch 48 in the cam follower 40 which is a plane surface separated from 
the other portion of the cam follower 40 by a shoulder. In conjunction 
with the creation of the flat notch 48, a pin 50 is installed in the 
engine block for engaging the notched portion 48 of the cam follower 40. 
The cam follower 40 is able to translate in to-and-fro reciprocating 
motion but does not rotate. The exact points of contact between the cam 
follower 40 and cam lobe 20 must be maintained once established. To aid in 
this regard, a retaining ring 54 is placed around the cam follower 40 to 
prevent the cam follower 40 from moving downward below the point of 
attachment of the retaining ring 54 to the cam follower 40. A method of 
attaching a retaining ring 54 is to place a groove around the cam follower 
40 and insert a snap ring 54 is to place a groove. In order to maintain 
optimum operation, the cam follower 40 must normally be kept in close 
contact with members that connect the cam follower to the valve (that is, 
the valve stem or push rod 15 and any linkage associated therewith). To 
help keep the cam follower 40 in contact with these connecting members a 
slight upward force is applied to the cam follower 40 when it is in its 
lowermost position. This is accomplished by insertion of a spring washer 
52 between the retaining ring 54 and the engine block 13 as shown. 
Referring now to FIG. 3, therein is shown a preferred embodiment of the 
invention as illustrated in FIG. 2 except that the cam follower 40 uses a 
roller 42' as its contact point rather than the contact curve 42 which is 
shown in FIG. 2. 
The preferred embodiment of the invention discussed above completely 
eliminates valve overlap. However, the invention may be practiced to 
provide valve overlap as desired but without being limited to the amount 
of valve overlap inherent in the original engine design. For example in 
the case of an engine which has a "supercharger" which forces air into a 
cylinder to enhance air intake, in order to purge expended combustion 
gases from the cylinder it may be desirable to allow the exhaust valve to 
remain open during a part of the time that the intake valve is open. This 
may be accomplished by causing the intake valve to open prior to the end 
(TDC) of the exhaust upstroke of the piston. In that instance, the intake 
valve remains open for greater than a 90-degree rotation of the intake 
valve cam. The intake valve cam follower would then be configured to cause 
lifting and lowering of the cam follower 40 over a rotational period of 
greater than 90 degrees, for example, 100 degrees. The intake valve cam 
and exhaust valve cam would then be positioned on the cam shaft to allow 
the additional 10 degrees of intake valve opening to occur prior to 
completed lowering of the cam follower for the exhaust valve. This would 
equate to a valve overlap of 10 cam-degrees, or 20 crankshaft-degrees. 
Modification of the camshaft alone controls only the point of valve 
opening, and modification of the cam follower alone controls only the 
duration of valve opening and closing. The preferred embodiment of the 
invention utilizes both in combination as explained above. 
As should be apparent from the foregoing specification, the invention is 
susceptible of being modified with various alterations and modifications 
which may differ from those which have been described in the preceding 
specification and description. Accordingly, the following claims are 
intended to cover all alterations and modifications which do not depart 
from the spirit and scope of the invention.