Title:
Desmodromic valve system including single cam surface for closing and opening the valve
Kind Code:
A1


Abstract:
A desmodromic valve and cam system is provided. The system may comprise a cam lobe mounted to a cam shaft and defining an effective cam surface. The system may also comprise a rocker mounted to a valve wherein the rocker pivots up and down in response to an input of the cam lobe to close and open the valve. More particularly, the effective cam surface of the cam lobe pushes up on the rocker follower surface to close the valve and pushes down on the rocker follower surface to open the valve.



Inventors:
Decuir, Julian A. (Pinon Hills, CA, US)
Application Number:
11/899668
Publication Date:
03/13/2008
Filing Date:
09/07/2007
Primary Class:
International Classes:
F01L1/047
View Patent Images:
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Primary Examiner:
DENION, THOMAS E
Attorney, Agent or Firm:
STETINA BRUNDA GARRED & BRUCKER (ALISO VIEJO, CA, US)
Claims:
What is claimed is:

1. A desmodromic valve and cam system for an internal combustion engine comprising an engine block and at least one head which utilizes at least one intake and one exhaust valve per cylinder, the system comprising: a main camshaft assembly adapted to be received within a plurality of journals disposed internally within the engine block, the camshaft assembly including one cam lobe for each intake valve and exhaust valve, each cam lobe having an effective cam surface facing radially outward; a rocker pivotable about a rocker pivot axis, the rocker having a valve movement end adapted to be mechanically linked to a valve head such that the rocker can either push down or pull up the valve head as the rocker is respectively pivoted down or up about the rocker pivot axis to respectively open or close the valve, the rocker having closing and opening follower surfaces which are arranged and configured to radially face inward to a central portion of the rocker, the closing and opening follower surfaces being representative of desired valve performance characteristics, wherein the rocker is pivoted upward when the effective cam surface of the cam contacts the closing follower surface and pivoted downward when the effective cam surface of the cam contacts the opening follower surface; wherein the cam lobes rotate such that the effective cam surface reciprocally contacts the closing follower surface and the opening follower surface to respectively close and open the valve without the need to use valve springs to close the valves.

2. The desmodromic valve and cam system of claim 1 wherein the closing and opening follower surfaces have an oblong circular configuration.

3. The desmodromic valve and cam system of claim 1 wherein the cam lobe has a circular configuration.

4. The desmodromic valve and cam system of claim 1 wherein the cam lobe defines an effective cam surface which is about one half of the outer periphery of the cam lobe.

5. The desmodromic valve and cam system of claim 1 wherein a rotating axis of the cam lobe is offset with a center of the cam lobe.

6. The desmodromic valve and cam system of claim 1 wherein the rocker comprises a first part and a second part which is removeably securable to each other to form the rocker.

7. The desmodromic valve and cam system of claim 1 wherein the closing and opening follower surfaces define a box shaped configuration.

8. The desmodromic valve and cam system of claim 1 wherein the rocker has a groove and the cam lobe has a mating protrusion for aligning the cam lobe to the rocker as the cam lobe rotates.

9. The desmodromic valve and cam system of claim 8 wherein a groove depth varies about a periphery of the rocker to control an amount of time that the valve stays closed, stays opened or both.

10. The desmodromic valve and cam system of claim 9 wherein a height of the protrusion varies about a periphery of the cam lobe to control the amount of time that the valve stays closed, stays opened, or both.

11. A desmodromic valve and cam system for an internal combustion engine comprising an engine block and at least one head which utilizes at least one intake and one exhaust valve per cylinder, the system comprising: a main camshaft assembly adapted to be received within a plurality of journals disposed internally within the engine block, the camshaft assembly including one cam lobe for each intake valve and exhaust valve, each cam lobe having an effective cam surface facing radially outward; a rocker pivotable about a rocker pivot axis, the rocker having a valve movement end adapted to be mechanically linked to a valve head such that the rocker can either push down or pull up the valve head as the rocker is respectively pivoted down or up about the rocker pivot axis to respectively open or close the valve, the rocker having a central aperture, the central aperture defining a travel path; a slider sized and configured to slid up and down along the travel path within the central aperture of the rocker, the slider having opening and closing follower surfaces mateable with the effective cam surface of the cam lob, the opening and closing follower surfaces being arranged to face radially inward; wherein the cam lobes rotate such that the effective cam surface reciprocally contacts the closing follower surface and the opening follower surface to respectively close and open the valve without the need to use valve springs to close the valves, and an angle of the travel path is representative of desired valve performance characteristics.

12. The desmodromic valve and cam system of claim 11 wherein a position of the rocker pivot axis in a horizontal direction and vertical direction is representative of desired valve performance characteristics.

13. The desmodromic valve and cam system of claim 11 further comprising a spring disposed between the rocker and slider to bias the slider to one side of the rocker.

14. The desmodromic valve and cam system of claim 13 wherein a spring force exerted on the slider by the spring is representative of desired valve performance characteristics.

15. The desmodromic valve and cam system of claim 11 wherein the opening and closing follower surfaces form a circular configuration.

16. A desmodromic valve and cam system retrofit kit for an engine, the kit comprising: at least one cam lobe attachable to a stock cam shaft of the engine, the cam lobe defining an effective cam surface facing radially outward; a corresponding rocker defining opening and closing follower surfaces facing radially inward, the opening and closing follower surfaces being representative of desired valve performance characteristics, the effective cam surface being mateable with the opening and closing follower surfaces in a reciprocal manner as the cam lobe rotates to pivot the rocker down and up about a rocker pivot axis to respectively open and close a valve of the engine, the rocker defining a valve moveable end and a lifter end; a valve joint pivotally connected to the valve moveable end of the rocker and connectable to a stem of the valve; a lifter joint pivotally connected to the lifter moveable end of the rocker and connectable to the lifter which is sized and configured to fit within a lifter aperture of the engine.

Description:

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefits of U.S. Provisional Patent Application Ser. No. 60/843,074, filed on Sep. 8, 2006, the entire contents of which are expressly incorporated herein by reference.

STATEMENT RE: FEDERALLY SPONSORED RESEARCH/DEVELOPMENT

Not Applicable

BACKGROUND

The present invention relates to desmodromic valve and cam systems for internal combustion engines with intake and exhaust valves, and more particularly, to a rocker which regulates the opening as well as the closing of the valve.

Most conventional internal combustion piston driven engines utilize valve trains to induct an air/fuel mixture into the cylinders and to expel the burned air/fuel mixture from the cylinders. Typically, each cylinder is assigned at least one intake valve and at least one exhaust valve. The valves are typically pushed down by rockers thereby opening the valve and pushed upwardly by springs thereby closing the valve. In a conventional pushrod engine, the other end of the rocker is in contact with one end of a pushrod. Further, the other end of the pushrod is typically in contact with a lifter which is in contact with a camshaft lobe. In overhead cam configurations, the other end of the rocker typically is in direct contact with the camshaft lobe, thereby eliminating the need for pushrods. When the valve stem is pushed down by the rocker to open the valve, the spring is compressed. The valve is closed when the spring decompresses thereby pulling the valve stem up through the valve guides until the head of the valve is seated in the valve seat.

For example, in a typical four-stroke engine, an intake valve is opened by an intake rocker which receives an input force from an intake cam lobe while the piston goes down inducting an air/fuel mixture into the cylinder. This is known as the induction stroke. While the intake valve stem is being pushed down through an intake valve guide, an intake spring concentrically positioned around the intake valve stem is compressed. Next, the cam lobe continues to rotate allowing the intake spring to decompress and push the intake valve back up through the intake valve guide until the intake valve is seated in the intake valve seat. The piston also moves back up the cylinder. At this point in the combustion process, the air/fuel mixture is compressed. This stage is known as the compression stroke. With both the intake and exhaust valves closed so that the combustion chamber is sealed tight, a spark is then produced by a spark plug which ignites the air/fuel mixture wherein the rapidly expanding hot gases force the piston downward with great energy creating power. This is known as the power stroke. The exhaust valve then opens by an exhaust rocker receiving input from an exhaust cam lobe. The piston moves up the cylinder and the exhaust valve expels the burned air/fuel mixture, also known as the exhaust stroke. The exhaust cam lobe continues to rotate and allows an exhaust spring to push the exhaust valve back to the closed position.

The aforementioned conventionally configured valve train systems for opening and closing the valves have proven to be highly effective and reliable in the past. However, closing the valve by the force of the spring does have some disadvantages. Most notably, pushing the valves open against the force of the springs consumes engine power. The springs in the engine induce considerable tension into the valve train because they continuously force the valve mechanism against the rocker as the camshaft rotates. In other words, the valve springs are continuously pushing the valves closed and additional work must be performed to overcome such spring tension wasting energy that could be used to create output power. Another disadvantage is that because the cam mechanism cannot afford to have any “bounce” from the springs, the cam profile has to be somewhat gentle, i.e., it must gently push the valve, but never shove it. This means the valve must open slowly like a water faucet—not quickly like a light switch, for example. Another disadvantage is that when the motor is turned at high RPM's, the valves can “float” and hit the piston. In other words, the spring does not traverse the valve back to the closed position fast enough such that the piston hits the valve. Valve float happens when the speed of the engine is too great for the valve springs to handle. As a result, the valves will often stay open and/or “bounce” on their seats.

To overcome these disadvantages, innovative desmodromic valve trains have evolved over about the last century; however, in a very slow technological pace and in most applications with little or limited success. The term “desmodromic” arises from the two Greek words: “desmos” (controlled or linked), and “dromos” (course or track). A desmodromic system is also known as a system that provides “positive valve actuation” wherein both strokes are “controlled”. In other words, desmodromic valves are those which are positively closed by a leverage system or follower, rather than relying on the more conventional springs to close the valves. Typically, a desmodromic valve operating system utilizes a camshaft that controls both the opening and closing of the valve.

Desmodromic valve trains have several advantages over conventional spring closed valves trains. A first major advantage is that in a desmodromic valve system there is almost no wasted energy in driving the valve train. The reason is that the constant force that the springs exert on the valve train is removed. Another advantage is that there is no possibility of “bounce” in the desmodromic system because the speed of the valve to be traversed from the opened position to the closed position is not dependent on the spring but the cam profiles can be as steep as the engine designer wishes them to be. This desirable aspect allows the engine to be more powerful and more flexible. Thus, the manufacturer can use more radical cam grinds or profiles for better performance. Another advantage is that when the motor is turned at high RPM's or even over-revved, the valves are still controlled, whereas when the valves are returned by springs the valves sometimes can “float” and hit the piston.

One disadvantage of prior art desmodromic valve train systems is that they have not been adapted to be installed or “retrofitted” into existing modern conventional engines. That is to say, the aforementioned prior art desmodromic systems appear to utilize specialized designs which require unique heads, valve trains and/or engine blocks. Thus, to use the aforementioned desmodromic systems, entirely new engine platforms have to be designed and built. Unfortunately, however, most manufacturers are not willing to invest the sizeable amounts of capital to build such desmodromic engines, or much less, market vehicles with engine platforms which have not been proven or which have had a past history for reliability problems.

Therefore, it would be advantageous to provide a desmodromic valve and cam system which utilizes hydraulic lifters or the like that may be either integrated into a new engine design or of which may be retrofit onto an existing engine head design without requiring the head or valves to be replaced. Such a springless system would operate more efficiently than conventional valvetrains since the spring tension is reduced or eliminated from the valvetrain resulting in greater horsepower and fuel economy; while the incorporation of hydraulic lifters or the like will make the desmodromic system more reliable. By providing a retrofit desmodromic system, the cost of the upgrade could be maintained lower than that of a system which requires the entire head to be replaced. It would further be advantageous to provide a desmodromic valve and cam system which is simple to manufacture, inexpensive and of which may be easily retrofitted into existing head designs which may have already been manufactured and of which are being currently sold. Furthermore, it would be desirable to provide a desmodromic valve and cam system wherein the cam duration/lift could be adjusted. Such features would provide a wide array of adjustability in regards to being able to tune the engine's performance characteristics.

BRIEF SUMMARY

The present desmodromic cam and valve system addresses the deficiencies discussed above, discussed below, and those that are known in the art. The present desmodromic cam and valve system may be retrofittable onto conventional engines. The present desmodromic cam and valve system may comprise a rocker defining an opening follower surface and a closing follower surface. The opening and closing follower surfaces may be formed within the rocker. Also, the opening and closing follower surfaces may be arranged and configured to face inwardly and toward each other. The opening and closing follower surfaces define the desired valve performance characteristics in regard to the timing of the opening and closing of the valve as well as the duration/lift of the valve.

A cam lobe attached to the cam shaft and rotatable via rotation of the cam shaft may be disposed within the rocker. The cam lobe may define an effective cam surface. The effective cam surface contacts the opening and closing follower surfaces as the cam lobe rotates in a to reciprocally pivot the rocker upwards and downwards. In particular, the effective cam surface contacts the closing follower surface to traverse the valve to the closed position. Subsequently, the effective cam surface contacts the opening follower surface to traverse the valve to the opened position. The opening follower surface may be located generally at the lower portion of the rocker. Also, the closing follower surface may be located generally at the upper portion of the rocker.

The opening and closing follower surfaces may have different configurations. For example, the opening and closing follower surfaces may be configured to form an oblong circular configuration. Alternatively, the opening and closing follower surfaces may be arranged to form a box configuration.

In an aspect of the desmodromic valve and cam system, the rocker may be a split rocker having first and second parts that are removeably attachable to each other such that the cam shaft does not have to be disassembled to install the rocker.

In an aspect of the desmodromic valve and cam system, a plurality of rockers may be provided to a mechanic or user. Each of the rockers may have a unique opening and closing follower surface corresponding to different timing for closing and opening the valve and the lift/duration of the valve. The mechanic or user may install the rocker with the desired valve performance characteristics. For example, if the automobile is to be used on the local streets, then the rocker for street driving may be installed on the automobile engine. Alternatively, if the same automobile is to be used in a race, then the rocker for racing may be installed on the automobile engine. Accordingly, merely by switching out the rocker the performance of the automobile engine may be adapted to the current use of the automobile. To simplify the disassembly and installation of the rockers, each of the rockers may be a split rocker as discussed above.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the various embodiments disclosed herein will be better understood with respect to the following description and drawings, in which like numbers refer to like parts throughout, and in which:

FIG. 1 is a front perspective view of an intake valve and an exhaust valve of an engine;

FIG. 1A is a cross sectional view of the exhaust valve shown in FIG. 1 illustrating a cam lobe at a bottom dead center position and the exhaust valve fully opened;

FIG. 1B illustrates the exhaust valve after the cam lobe has been rotated counter clockwise ninety degrees with respect to the cam lobe position shown in FIG. 1A;

FIG. 1C illustrates the exhaust valve after the cam lobe has been rotated counter clockwise ninety degrees with respect to the cam lobe position shown in FIG. 1B;

FIG. 1D illustrates the exhaust valve after the cam lobe has been rotated counter clockwise ninety degrees with respect to the cam lobe position shown in FIG. 1C.

FIG. 1E is a side view of a rocker illustrating (1) an angle of a rocker follower surface to a line defined by a rocker pivot axis and a valve moveable end of the rocker and (2) a length of the rocker follower surface, the timing of closing and opening the valve being alterable by altering the angle and length;

FIG. 2 is a rear perspective view of lifters for the intake valve and the exhaust valve shown in FIG. 1;

FIG. 3 is a side view of a split rocker;

FIG. 4 is a perspective view of a split rocker having a protrusion formed about an outer periphery of a cam lobe and a mating groove formed about an inner periphery of the rocker;

FIG. 5 is a side view of a rocker including a spring loaded nub for mitigating against harmonics in the desmodromic valve and cam system;

FIG. 6 is an alternate embodiment of a rocker compared to the rocker shown in FIG. 1;

FIG. 7 is a cross sectional view of an alternate embodiment for controlling the opening and closing of the valve;

FIG. 8 is a side view of a cam lobe with a protrusion and a rocker with a varying groove depth for controlling the amount of time that the valve stays closed; and

FIG. 9 is a side view of a cam lobe with a varying height protrusion and a rocker with a varying groove depth for controlling the amount of time that the valve stays closed.

DETAILED DESCRIPTION

The particulars shown herein are by way of example and for the purposes of illustrative discussion of the embodiments of the present invention only and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the present invention.

The present invention is a desmodromic valve and cam system 10 which eliminates use of springs normally used to close the intake and exhaust valves. The present invention is designed such that it may be incorporated into modern engine designs yet to be manufactured, or may be retrofit to existing head designs, such as used in conventional V-8's, V-6's, V-10's, inline 4's, inline 6's and the like. The desmodromic valve and cam system 10 may be utilized with gasoline type engines or diesel engines. Moreover, the various aspects of the desmodromic valve and cam system 10 may be utilized in various engine designs which use poppet valves. It is appreciated that the desmodromic valve and cam system 10 may be installed and/or retrofitted to fit on many other conventional heads that have been previously manufactured or which are currently being manufactured from numerous engine manufacturers. Additionally, it is recognized that the desmodromic valve and cam system 10 may be integrated into specially designed heads. Thus, the scope of the desmodromic valve and cam system 10 should not be limited to the exemplary embodiment disclosed herein. Rather, the exemplary embodiments of the desmodromic valve and cam system 10 disclosed herein should be viewed as merely as one embodiment of numerous embodiments which may utilize the fundamental concepts taught and disclosed herein.

FIG. 1 illustrates a perspective view of a head of a conventional engine block 12 with the desmodromic valve and cam system 10 installed thereon. The head may be of any design known in the art used for typical internal combustion engines. FIG. 1 shows an intake valve assembly 14, an exhaust valve assembly 16, and a camshaft 18. The intake valves and the exhaust valves open and close to allow air and fuel to enter a cylinder of the piston and burned fuel to escape out of the cylinder. FIG. 2 is a rear view of the engine block 12 and desmodromic valve and cam system 10 shown in FIG. 1 illustrating a lifter hold down assembly 20, lifter connector assemblies 22 and lifters 24 for the exhaust valve assembly 16 (See FIG. 1) and the intake valve assembly 14 (See FIG. 1).

FIGS. 1 and 1A-D illustrate one revolution of the camshaft 18 illustratively showing a cam lobe 26 opening and closing a valve 28. In particular, as shown in FIG. 1A, the cam lobe 26 defines an effective cam surface 30 which generally pushes upward and downward on the rocker follower surface 34 (i.e., opening and closing follower surfaces) as the camshaft 18 is rotated. The effective cam surface 30 extends about one half of the cam surface as shown by arrow 31. For example, FIGS. 1 and 1A-1D illustrate the effective cam surface 30 as the camshaft 18 is rotated in the counterclockwise direction 32. FIGS. 1 and 1A illustrate the cam lobe 26 at bottom dead center. At this position, the cam lobe 26 pushes down on the lower portion of the rocker follower surface 34 to fully open the valve 28. As the camshaft 18 rotates counterclockwise 32 a quarter turn (see FIG. 1B), the valve 28 traverses toward the closed position. The effective cam surface 30 of the cam lobe 26 pushes up on the upper portion of the rocker follower surface 34. At 180° from the bottom dead center (see FIG. 1C), the cam lobe 26 reaches the top dead center position. At this position, the valve 28 is fully closed. The effective cam surface 30 transitions from pushing upward on the upper portion of the rocker follower surface 34 to pushing downward on the lower portion of the rocker follower surface 34. As the cam shaft 18 rotates counter clockwise 32 another quarter turn (see FIG. 1D), the valve 28 travels toward the open position. The effective cam surface 30 pushes downward on the lower portion of the rocker follower surface 34. After one complete revolution of the camshaft 18 and cam lobe 26, the valve is fully opened again and positioned as shown in FIG. 1A.

More particularly, the rocker 36 may have a valve moveable end 38 (see FIGS. 1 and 1A) and a lifter moveable end 40 (see FIG. 1A). As shown in FIG. 1A, the proximal distal end 42 of the valve stem 44 may be attached to the valve moveable end 38 of the rocker 36 via the valve connector assembly 46. The valve connector assembly 46 may comprise a valve keeper 48. The valve keeper 48 may have a base portion 50 with an aperture 52. The proximal distal end 42 of the valve stem 44 may be inserted through the aperture 52 of the base portion 50. A spring 54 may be disposed around the proximal distal portion/end of the valve stem 44 and a retainer 56 threaded onto the proximal end 42 of the valve stem 44. The compressibility of the spring 54 allows the valve 28 to adjust such that the valve 28 may be seated onto the valve seat 58 as the valve 28 is being closed. The valve keeper 48 may also have two tines 60, which are sized and configured to fit adjacent opposed sides of the rocker 36. The two tines 60 may have aligned holes 62 which allow a pin 64 to be inserted therethrough. The valve moveable end 38 of the rocker 36 may have a slotted hole 66 in the general horizontal direction (i.e., aligned to rocker pivot axis 90). The aligned holes 62 may be aligned to the slotted hole 66. A pin 64 may be inserted through the slotted hole 66 and fixedly engaged (e.g., via a set screw) in the aligned holes 62. The slotted hole 66 at the valve moveable end 38 of the rocker 36 allows the rocker 36 to pivot about the rocker pivot axis 90 without applying a detrimental bending force to the valve stem.

Interposed between the valve moveable end 38 and the lifter moveable end 40 is the internal rocker follower surface 34. The internal rocker follower surface 34 may further be defined by an opening portion of the rocker follower surface 34 (i.e., opening follower surface) and a closing portion of the rocker follower surface 34 (i.e., closing follower surface). The opening portion of the rocker follower surface 34 may be generally disposed at the lower portion of the rocker follower surface 34, whereas the closing portion of the rocker follower surface 34 may be generally disposed at the upper portion of the rocker follower surface 34. The opening portion and the closing portion of the rocker follower surface 34 may collectively form an oblong circular configuration as best shown in FIG. 1E. The oblong circular configured rocker follower surface 34 may define a length 68 as well as an angle 70. The opening and closing characteristics of the valve 28 may be altered by adjusting the length 68 of the oblong configured follower surface and the angle 70 of the rocker follower surface 34. In particular, the closer the oblong configured follower surface 34 of the rocker 36 is tilted toward the valve 28, as shown by phantom lines 71, the longer the valve 28 remains closed. Conversely, the further away the oblong configured follower surface of the rocker 36 tilts away from the valve 28, as shown by phantom lines 71, the longer the valve 28 stays open. Additionally, the closer the right side 75 of the rocker follower surface 34 is to the center of the rocker 36, the sooner the valve 28 is traversed to the opened position thereby resulting in a longer period of time that the valve 28 stays open, and vice versa. Also, the closer the left side 77 of the rocker follower surface 34 is to the center of the rocker 36, the sooner the valve 28 is traversed to the closed position thereby resulting in a longer period of time that the valve 28 stays closed, and vice versa.

Referring to FIG. 1B, the lifter moveable end 40 may be secured to the lifter 24 via a lifter connector assembly 22. In particular, the lifter connector assembly 22 may comprise a lifter keeper 72 having an L shaped configuration. The lifter keeper 72 may have a base portion 74 and two tines 76. The base portion 74 may be fixedly engaged to the lifter 24. For example, the base portion 72 may have an aperture 78 for receiving a bolt therethrough. The lifter 24 may have a cylindrical configuration. A threaded aperture 82 may be formed through the top surface of the lifter 24. The threaded aperture 82 of the lifter 24 may be aligned to the aperture 78 of the base portion 74 of the lifter keeper 72. A bolt 80 may be inserted through the aperture 78 of the base portion 74 of the lifter keeper 72 and threadingly engaged to the threaded aperture 82 of the lifter 24 to fixedly engage the lifter 24 to the lifter connector assembly 22. The lifter 24 may be sized and configured to fit within the lifter aperture 84 of engine block 12.

The two tines 76 of the lifter keeper 72 may be sized and configured to fit on opposed sides of the rocker 36 at the lifter moveable end 40 of the rocker 36. The lifter moveable end 40 and the two tines 76 may have aligned holes 86. A pin 88 may be inserted through the aligned holes 86. However, the hole 86 of the rocker 36 at the lifter moveable end 40 may be slightly larger than the aligned holes 86 of the two tines 76. The pin 88 may frictionally engage the holes 86 of the two tines 76 and may be fixedly engaged thereto with a set screw. The pin 88 may freely slide within the hole 86 of the rocker 36 at the lifter moveable end 40 such that the rocker 36 may pivot about such pin. The central axis of the pin may define the rocker pivot axis 90.

In operation, the oil may be flowed through the lifter aperture 84 of the engine block 12 via an oil supply line 92. The oil flowed into the lifter aperture 84 of the engine block 12 urges the lifter 24 up (i.e., out of the lifter aperture 84 of the engine block 12). The lifter hold down assembly 20 holds the lifter keeper 72 and the lifter down (i.e., in the lifter aperture 84 of the engine block 12). In particular, as shown in FIG. 2, the lifter hold down assembly 20 may be bolted to the bolt holes 94 for the journal brackets 96. A base 98 of the lifter hold down assembly 20 may have a post 100 with a spring receiving aperture on its lower end. A spring 102 may be received therein and when the lifter hold down assembly 20 is secured to the engine block 12, the spring 102 may apply a downward force on the base portion 74 (See FIG. 1B) of the lifter keeper 72 which opposes the upward force created by the oil flowing through the lifter aperture 84.

The valve 28 may operate in the following manner. The lifter moveable end 40 of the rocker 36 is urged upward due to the oil flowing through the lifter aperture 84. As a result, the rocker pivot axis 90 (See FIG. 1B) is also urged upward. The lifter hold down assembly 20 holds the lifter 24 in place via the spring 102 and balances the upward force caused by the flowing oil. The rocker 36 reciprocally pivots up and down, as shown by arrow 103, about the rocker pivot axis 90. The timing of the rocker 36 pivoting up and down and the duration/lift of the valve 28 are determined by the effective cam surface 30 of the cam lobe 26 and the rocker follower surface 34 (i.e., opening and closing follower surfaces). In particular, when the cam lobe's thickest portion contacts the lower portion of the rocker follower surface 34 (See FIG. 1A), the cam lobe 26 is at the bottom dead center position. The valve 28 is also fully opened at this position. The cam shaft 18 may rotate counter clockwise which also rotates the cam lobe 26 counter clockwise. As the cam shaft 18 rotates in the counter clockwise direction, the effective cam surface 30 of the cam lobe 26 pushes upward on the upper portion of the rocker follower surface 34. The distance between the rotating center of the cam lobe 26 and the point of contact between the effective cam surface 30 and the upper portion of the rocker follower surface 34 begins to increase thereby pushing the rocker 36 upward. The rocker 36 is pushed upward until the cam lobe 26 reaches the top dead center. When the cam lobe 26 is at the top dead center (See FIG. 1C), the rocker 36 is pivoted fully upward and the valve 28 is fully closed. At this point, the spring loaded valve stem 44 assists in seating the valve 28 in the valve seat 58. As the cam shaft 18 and the cam lobe 26 continues to rotate in the counter clockwise direction, the effective cam surface 30 begins to push downward on the lower portion of the rocker follower surface 34 thereby pivoting the rocker 36 downward and traversing the valve 28 to the opened position.

The cam lobe 26 may be fixedly attached to the cam shaft 18 such that the cam lobe 26 rotates as the cam shaft 18 is rotated. The cam lobe 26 may be fixedly attached to the cam shaft 18 via any method known in the art such as a pinned connection, keyway connection, splined connection, etc.

In an aspect of the desmodromic valve, the rocker 36 may be a split rocker such that the cam shaft 18 does not have to be disassembled to mount the rocker 36 about the cam lobe 26, as shown in FIG. 3. The first part 104 of the rocker 36 may be attached to the second part 106 of the rocker 36. In particular, the first part 104 of the rocker may have two threaded holes 108 sized and configured to receive a bolt 110. The second part 106 of the rocker 36 may have two through holes 112 aligned to the two threaded holes 108 of the first part 104 and sized such that the bolts 110 may slide therethrough 112. To mount the split rocker 36 on the camshaft 18 of an engine, the first part 104 and the second part 106 of the rocker 36 may be placed around the cam lobe 26 with the threaded holes 104 aligned to the through holes 112 of the second part. Bolts may be inserted through the through holes 112 and threadingly engaged to the threaded holes 108. The bolts may be tightened so as to attach the first part 104 and the second part 106 together. The lifter moveable end 40 of the rocker 36 may be attached to the lifter 24 via the lifter connector assembly 22. Also, the valve moveable end 38 of the rocker 36 may be attached to the valve 28 via the valve connector assembly 46.

One advantage of the split rocker is that the cam shaft 18 does not have to be removed or disassembled to mount the rocker 36. Instead, the rocker 36 may be placed over the cam lobe 26 and installed with a minimal amount of time. Another advantage of the split rocker 36 is that a mechanic or user may be provided with a plurality of different split rockers 36. Each of the rockers 36 may have different valve performance characteristics. For example, a first rocker 36 may have a valve performance characteristic for racing. A second rocker may have a valve performance characteristic for normal street driving. The user or mechanic may interchange the appropriate rocker 36 depending on the current use of the automobile. If the automobile is being used to race, then the first split rocker 36 may be installed on the cam lobe 26. If the automobile is being used to drive on the streets, then the second split rocker 36 may be installed on the cam lobe 26. Hence, the split rocker 36 provides additional flexibility to the user such that the automobile may be used for varying purposes.

In another aspect of the desmodromic valve and cam system 10, the cam lobe 26 may be aligned to the rocker 36 via a groove 114 and mating cam lobe protrusion 116, as shown in FIG. 4. In particular, the opening and closing follower surfaces 34 of the rocker 36 may be formed with a groove 114 about an inner periphery thereof. The cam lobe 26 defining an outer surface (which includes the effective cam surface 30) may additionally be formed with a protrusion 116 about the periphery of the cam lobe 26. Preferably, the protrusion 116 is formed about the entire outer periphery of the cam lobe 26, although the protrusion 116 may be intermittently formed about the periphery of the cam lobe 26. The protrusion 116 may be sized and configured to slide within the groove 114 of the rocker 36 to center the cam lobe 26 and the rocker 36. As the cam lobe 26 rotates, the effective cam surface 30 slides against the opening and closing follower surfaces. At least some part of the protrusion 116 remains in the groove 114 such that the cam lobe 26 stays centered within the rocker 36 as the cam lobe 26 rotates. Alternatively, it is also contemplated that the protrusion 116 may be formed on the inner periphery of the rocker 36 and the groove 114 formed about the outer periphery of the cam lobe 26.

Referring now to FIG. 8, a groove depth 158 of the groove 114 may be varied about the rocker periphery to control the amount of time that the valve stays open, stays closed or both. By way of example and not limitation, the groove depth 158 at the lifter side 160 of the rocker 36 may be less than a protrusion height 162 but greater than the protrusion height 162 about the rest of the rocker periphery. In operation, the effective cam surface 30 lifts the rocker 36 up to close the valve and pushes the rocker 36 down to open the valve. To increase the amount of time that the valve stays closed, the groove depth 158 at the lifter side 160 of the rocker 36 is made shallower compared to the protrusion height 162. When the cam lobe 26 is at the top dead center (see FIG. 8), the protrusion 116 does not contact the bottom 164 of the groove 114. As the cam lobe 26 continues to rotate in the counter clockwise direction, the protrusion 114 begins to contact the bottom 164 of the groove 114 at the lifter side 160 of the rocker 36 because the groove depth 158 at the lifter side 160 of the rocker 36 is less than the protrusion height 162. The contact between the protrusion 116 and the bottom 164 of the groove 114 at the lifter side 160 of the rocker 36 keeps the valve closed for a longer duration of time. The amount of time that the valve stays closed may be increased or decreased by making the groove depth 158 at the lifter side 160 of the rocker 36 shallower or deeper. The same principle may be applied to keep the valve open for a longer or shorter duration of time by changing the groove depth 158 at the valve side 166 of the rocker 36.

Additionally, referring to FIG. 9, to further control the amount of time that the valve stays closed and/or opened, the protrusion height 162 may be varied about the periphery of the cam lobe 26 and the groove depth 158 may be varied about the periphery of the rocker 36. As shown in FIG. 9, the height 162 of the protrusion 116 may be enlarged at the thickest portion of the cam lobe 26. The groove depth 158 of the groove 114 at the lifter side 160 of the rocker 36 may be made shallower compared to the rest of the groove 114 and the protrusion height 162 such that the protrusion 116 can contact the bottom 164 of the groove at the lifter side 160 of the rocker 36. This will maintain the valve in the closed position longer. In operation, the effective cam surface 30 opens and closes the valve by lifting the rocker 36 up and pushing the rocker 36 down. When the cam lobe 26 reaches top dead center (see FIG. 9), the enlarged portion of the protrusion 116 does not contact the bottom 164 of the groove 114. As the cam lobe 26 continues to rotate in the counter clockwise direction, the protrusion 116 begins to contact the bottom surface 164 of the groove 114 at the lifter side 160 of the rocker 36. This contact keeps the valve closed for a longer duration of time. The amount of time that the valve stays open may also be increased by making the groove depth 158 on the valve side 166 of the rocker 36 shallower such that the enlarged portion of the protrusion 116 does contact the bottom 164 of the groove 114 at the valve side 166 of the rocker 36 as the cam lobe 26 rotates.

In another aspect of the desmodromic valve and cam system 10, the harmonics of the desmodromic valve and cam system 10 may be reduced or eliminated by a spring loaded nub 118 installed within the cam lobe 26 and pressing against the rocker follower surface 34 (i.e., opening and closing following surfaces) as shown in FIG. 5. In particular, the cam lobe 26 may have a through hole 120 which extends between the cam surface 122 and the aperture 124 of the cam lobe 26. Preferably, the through hole 120 is formed in the cam surface 122 at a position other than the effective cam surface 30. When the cam lobe 26 is mounted to the cam shaft 18, the through hole 120 may receive a spring 126. The spring 126 may rest on the exterior surface of the cam shaft 18. Alternatively, the through hole 120 may be formed only partially through the cam lobe 26 so as to not extend to the aperture 124 of the cam lobe 26. After the spring 126 is disposed within the through hole 120, a nub 118 sized and configured to slide within the through hole 120 may be placed within the through hole 120. The spring 126 is sufficiently long such that a distal tip 128 of the nub 118 may extend beyond the cam surface 122 of the cam lobe 26. As the cam lobe 26 rotates within the rocker 36 and the effective cam surface 30 pushes against the opening and closing follower surfaces, the nub 118 also pushes against the opening and closing follower surfaces to reduce or mitigate against harmonics.

FIG. 6 is an alternate embodiment of the opening and closing follower surfaces of the rocker 36. In particular, the rocker follower surfaces 34 may have a box configuration in that certain portions of the rocker follower surfaces 34 are flat. By way of example and not limitation, the rocker follower surfaces 34 shown in FIG. 6 has upper 130 and lower surfaces 132 which are flat. The upper 130 and lower surfaces 132 are additionally parallel with respect to each other. Additionally, the rocker follower surfaces 34 may also have flat upper and lower diagonal surfaces 143, 136. Lastly, the rocker follower surfaces 34 may also define left and right vertical surfaces 138, 140. The cam lobe 26 may be disposed within rocker 36 such that the rocker follower surfaces 34 circumscribe the cam lobe 26. As the cam lobe 26 rotates within the rocker 36, the effective cam surface 30 contacts the flat upper 134 and lower diagonal surfaces 136, and flat left 138 and right vertical surfaces 140 to pivot 103 the rocker 36 up and down and respectively close and open the valve 28. When the rocker 36 has a box configured follower surface, the effective cam surface 30 contacts only certain portions of the inner periphery of the rocker 36 as the cam lobe 26 rotates.

FIG. 7 illustrates another embodiment of the desmodromic valve and cam system 10. The desmodromic valve may comprise a rocker 36, slider 142, cam lobe 26, a lifter connector assembly 22, lifter 24, lifter connector assembly 22, and a valve connector assembly 46. The cam lobe 26 may be fixedly attached (e.g., via a keyway) to the camshaft 18 such that the cam lobe 26 rotates in conjunction with the camshaft 18. The cam lobe 26 may have a circular outer periphery. The cam lobe 26 may have an aperture 124 for receiving the cam shaft 18. The cam lobe aperture 124 may be offset from a center of the cam lobe 26. In this manner, the cam lobe 26 rotates about a rotating axis 153 which is offset from its center.

The cam lobe 26 may be disposed within the slider 142. The slider 142 may have a central cavity 144 which corresponds with the outer periphery of the cam lobe 26. For example, the central cavity 144 may have a circular configuration and be sized and configured such that the cam lobe 26 can slidingly rotate within the slider 142. As the cam lobe 26 rotates, the offset rotation of the cam lobe 26 may push the slider 142 up along travel path A and down along travel path B.

The slider 142 may be disposed within a central cavity 146 of the rocker 36. The central cavity 146 of the rocker 36 may have a rectangular configuration. The central cavity 146 of the rocker 36 may also define the travel path A, B of the slider 142. The slider 142 may travel along the travel path A, B. Springs 148 may be disposed above the slider 142. The springs 148 may be adjusted via the set screws 150 to increase or decrease the amount of spring force to be applied to the slider 142 during operation of the desmodromic valve and cam system 10. The spring force adjusts the timing of the valve closing and opening as well as eliminates or mitigates against harmonics in the desmodromic valve and cam system 10. The springs 148 placed above the slider 142 may be adjusted so as to apply an appropriate amount of force to the slider 142 based on the desired opening and closing characteristics of the valve 28 and the desired lift/duration of the valve. In particular, the greater the spring force, the longer the valve 28 remains closed, and vice versa. Additionally, the opening and closing characteristics of the valve 28 may be altered by changing the angle of the slider 142 travel paths A, B as shown by phantom line C. Additionally, the opening and closing characteristics of the valve 28 may be altered by adjusting the location of the rocker pivot axis 90 closer to or further away from the valve 28 in the horizontal direction. The opening and closing characteristics of the valve 28 may be altered or adjusted by raising or lowering the rocker pivot axis 90 also in the vertical direction.

The rocker 36 may define a valve moveable end 38 and a lifter moveable end 40. The rocker 36 may be secured to the valve stem 44 of the valve 28, as discussed above via a valve 28 connector assembly 46. The lifter moveable end 40 may be attached to a lifter 24, as discussed above via a lifter connector assembly 22. The lifter 24 attached to the valve moveable end 38 of the rocker 36 may replace the conventional lifter and be inserted into the lifter aperture 84.

In operation, the rotation of the cam lobe 26 slides the slider 142 within the rocker 36 and lifts or pushes down the valve moveable end 38 of the rocker 36 to close or open the valve 28. To lift the valve moveable end 38 upward so as to close the valve 28, the cam lobe 26 applies a force to the slider 142 and also to the left inside surface 152 of the rocker 36. Conversely, as the cam lobe 26 rotates, the effective cam surface 30 of the cam lobe 26 pushes against the inner surface of the slider adjacent the right inside surface 154 of the rocker 36. Such movement also applies a pressure on the right inside surface 154 of the rocker 36 thereby traversing the valve 28 to the opened position.

In an aspect of the desmodromic valve and cam systems discussed above, an optional spring 156 may be disposed within the lifter aperture 84 under the lifter 24. The spring 156 supports the lifter 24 in the event that oil is not flowing through the oil supply line 92. For example, when the engine is turned on, the oil flows through the oil supply line 92 and urges the lifter 24 upward. However, when the engine is turned off, the oil stops flowing through the oil supply line 92. Without the spring 156, the lifter 24 drops downward and the rocker pivot axis 90 also drops downward. To maintain the rocker pivot axis 90 at the proper position for starting the engine, the optional spring 156 supports the lifter 24 and maintains the rocker pivot axis 90 at the proper position. Accordingly, when the engine is initially started, the spring 156 supports the lifter 24 and maintains the rocker pivot axis 90 at the proper position. Once the engine is started and the oil is flowing through the lifter aperture 84, oil flowing through the oil supply line 92 and the lifter aperture 84 lifts the lifter 24 and brings the rocker pivot axis 90 to the optimal position.

In an aspect of the desmodromic valve and cam system, referring back to FIG. 8, the spring 54 may be replaced or used in conjunction with a spring 168 disposed between the cam shaft 18 and the cam lobe 26. As discussed above, the spring 54 serves to seat to valve in the valve seat in the event that the valve contacts the valve seat before the cam lobe 26 reaches top dead center. The spring 168 disposed between the cam lobe 26 and the cam shaft 18 may serve the same purpose as spring 54. In particular, the cam lobe 26 may have a hole 170 at the square aperture 124 of the cam lobe 26. The spring 168 urges the cam lobe 26 to one side of the cam shaft 18, as shown in FIG. 8, but also allows the cam lobe 26 to be pushed downward if the valve is seated in the valve seat before the cam lobe 26 reaches top dead center. The cam shaft 18 shown in FIG. 8 is square. The cam shaft 18 may be slideable within the square aperture 124 of the cam lobe 26 along the direction of the spring 168 provided by the gap 172 between the cam lobe 26 and the cam shaft 18. It is also contemplated that the spring 168 disposed between the cam shaft 18 and cam lobe 26 may be employed in round shafts, splined shafts and various other types of shaft.

The above description is given by way of example, and not limitation. Given the above disclosure, one skilled in the art could devise variations that are within the scope and spirit of the invention disclosed herein. Further, the various features of the embodiments disclosed herein can be used alone, or in varying combinations with each other and are not intended to be limited to the specific combination described herein. Thus, the scope of the claims is not to be limited by the illustrated embodiments.