US20160032791A1

US20160032791A1 - Concentric dual independent camshaft phaser for dual overhead camshaft valve train

Info

Publication number: US20160032791A1
Application number: US14/448,420
Authority: US
Inventors: Adam C. Cecil; David M. Barnes
Original assignee: Cummins Inc
Current assignee: Cummins Inc
Priority date: 2014-07-31
Filing date: 2014-07-31
Publication date: 2016-02-04

Abstract

A variable valve timing system and methods of operation are provided. A primary valve train driver is configured to rotate about a primary axis. A primary camshaft includes a first plurality of cams positioned on the primary camshaft. The primary camshaft is coaxially coupled to the primary valve train driver. The first plurality of cams is configured to rotate about the primary axis. A primary camshaft phaser is coaxially coupled to the primary camshaft. The primary camshaft phaser is rotatably coupled to the primary valve train driver so as to rotate the primary camshaft phaser and the primary camshaft to a first phase angle. A secondary camshaft driver on the primary axis is coaxially coupled to the primary camshaft, and a secondary camshaft phaser is coaxially coupled to the primary camshaft and coupled to the secondary camshaft driver on the primary axis. The secondary camshaft phaser is rotatably coupled to the primary valve train driver so as to rotate the secondary camshaft driver on the primary axis to a second phase angle.

Description

TECHNICAL FIELD

The present disclosure relates to systems and methods for operating valve trains. The present disclosure specifically relates to variably operating dual overhead valve trains via camshaft phasing.

BACKGROUND

Variable valve timing (VVT) has been used in modern spark ignited engines to improve performance and help meet various emissions requirements. Some VVT valve train layouts comprise a single intake camshaft phaser and a single exhaust camshaft phaser within a dual overhead camshaft (DOHC) valve train. The package diameter of the camshaft phasers limits how close the intake and exhaust camshafts can be positioned relative to each other in such a valve train layout. Additionally, in four stroke engines, the camshafts are driven at half engine speed in the case of a four stroke engine, thereby warranting a camshaft drive diameter that is twice the diameter of the crankshaft drive diameter. The geometry of engine layout may make it difficult to package both an intake phaser concentric with the intake camshaft and an exhaust phaser concentric with the exhaust camshaft.

SUMMARY

Various embodiments provide a variable valve timing system and methods of operating variable valve timing system for dual overhead camshaft valve trains.
In particular embodiments, a variable valve timing system is provided that includes a primary valve train driver configured to rotate about a primary axis. The variable valve timing system includes a primary camshaft including a first plurality of cams positioned on the primary camshaft. The primary camshaft is coaxially coupled to the primary valve train driver. The first plurality of cams are configured to rotate about the primary axis. The variable valve timing system also includes a primary camshaft phaser coaxially coupled to the primary camshaft. The primary camshaft phaser is rotatably coupled to the primary valve train driver so as to rotate the primary camshaft phaser and the primary camshaft to a first phase angle with respect to the primary valve train driver. The variable valve timing system includes a secondary camshaft driver on the primary axis coaxially coupled to the primary camshaft and a secondary camshaft phaser coaxially coupled to the primary camshaft and coupled to the secondary camshaft driver on the primary axis. The secondary camshaft phaser is rotatably coupled to the primary valve train driver so as to rotate the secondary camshaft driver on the primary axis to a second phase angle with respect to the primary valve train driver.
In particular embodiments, the secondary camshaft driver is a first secondary camshaft driver and the variable valve timing system further includes a secondary camshaft configured to rotate about a secondary axis. The secondary camshaft includes a second plurality of cams positioned on the secondary camshaft and a second secondary camshaft driver on the secondary axis and coupled to the first secondary driver on the primary axis by a synced drive mechanism. The secondary camshaft phaser is configured to rotate the secondary camshaft to the second phase angle with respect to the primary valve train driver. In particular embodiments, the primary valve train driver is coupled to the crankshaft via a synced drive mechanism. The primary valve train driver may include a pulley. In particular embodiments, the camshaft is a primary camshaft, and the system further comprises a secondary camshaft including a second plurality of cams positioned on the secondary camshaft. The secondary camshaft includes a secondary camshaft driver on the secondary axis coupled to the secondary camshaft driver on the primary axis via a synced drive mechanism. The secondary camshaft phaser is configured to rotate the secondary camshaft to the second phase angle with respect to the primary valve train driver. The first plurality of cams is configured to open a plurality of intake valves, in accordance with particular embodiments and the second plurality of cams is configured to open a plurality of exhaust valves. The first plurality of cams may be configured to open a plurality of exhaust valves and the second plurality of cams may be configured to open a plurality of intake valves. In particular embodiments, one or more of the primary valve train driver, the primary camshaft phaser, the secondary camshaft phaser, and the secondary camshaft driver on the primary axis are concentric with the primary camshaft. The variable valve timing system includes one or more fasteners coaxially coupling one or more of the primary valve train driver, the primary camshaft phaser, the secondary camshaft phaser and the secondary camshaft driver on the primary axis to the primary camshaft, in accordance with particular embodiments. The primary camshaft phaser may include a plurality of vanes actuatable via a change in fluid pressure to rotate the primary camshaft phaser with respect to the primary valve train driver. In particular embodiments, the secondary camshaft phaser includes a plurality of vanes actuatable via a change in fluid pressure to rotate the secondary camshaft phaser with respect to the primary valve train driver. The primary camshaft phaser includes a primary movable lock pin configured to engage and disengage the primary valve train driver and the secondary camshaft phaser includes a secondary movable lock pin configured to engage and disengage the primary valve train driver, in accordance with particular embodiments.
Particular embodiments provide a method of operating a valve train variable that includes rotating a primary camshaft phaser and a primary camshaft coaxially coupled to the primary camshaft phaser about a primary axis to a first phase angle with respect to a primary valve train driver coaxially coupled to the primary camshaft and configured to rotate about the primary axis. The primary camshaft includes a first plurality of cams positioned on the camshaft. The first plurality of cams configured to rotate about the primary axis. The method includes rotating a secondary camshaft phaser and a secondary camshaft driver on the primary axis coupled to the secondary camshaft phaser about the primary axis to a second phase angle with respect to the primary valve train driver. The secondary camshaft phaser and the secondary camshaft driver on the primary axis are coaxially coupled to the primary camshaft.
In particular embodiments, the method includes rotating a secondary camshaft to the second phase angle, via the secondary camshaft driver on the primary axis coupled to the secondary camshaft by a synced drive mechanism coupling the secondary camshaft driver on the primary axis to the secondary camshaft The method includes rotating the primary camshaft phaser and the primary camshaft to the first phase angle with respect to the primary valve train driver includes actuating the primary camshaft phaser via a change in a fluid pressure, in accordance with particular embodiments. The method may include rotating the primary valve train driver via a crankshaft coupled to a plurality of pistons. In particular embodiments, the primary valve train driver is configured to rotate at ½ the speed of the crankshaft. The method includes actuating a plurality of intake valves via the first plurality of cams, in accordance with particular embodiments. The method may include actuating a plurality of exhaust valves via the first plurality of cams.
Particular embodiments provide an engine assembly that includes an engine block housing a plurality of cylinders. The plurality of cylinders includes a plurality of pistons positioned therein. The plurality of pistons is coupled to a crankshaft. The engine assembly includes a cylinder head coupled to the engine block, a plurality of intake valves positioned in the cylinder head, a plurality of exhaust valve positioned in the cylinder head, a primary valve train driver coupled to the crankshaft, the camshaft driver configured to rotate about a primary axis, and an intake camshaft including a first plurality of cams configured to cause actuation of the intake valves. The intake camshaft is coaxially coupled to the primary valve train driver. The first plurality of cams is configured to rotate about the primary axis. The engine assembly includes an intake camshaft phaser coaxially coupled to the intake camshaft. The intake camshaft phaser is rotatably coupled to the primary valve train driver so as to rotate the intake camshaft phaser and the intake camshaft to a first phase angle with respect to the camshaft driver. The engine assembly includes a secondary camshaft driver on the primary axis coaxially coupled to the intake camshaft and an exhaust camshaft phaser coaxial coupled to the intake camshaft and coupled to the secondary camshaft driver on the primary axis. The exhaust camshaft phaser is rotatably coupled to the primary valve train driver so as to rotate the exhaust camshaft phaser and the secondary camshaft driver on the primary axis to a second phase angle with respect to the primary valve train driver.
In particular embodiments, the engine assembly includes an exhaust camshaft including a second plurality of cams configured to cause actuation of the exhaust valves. The exhaust camshaft may include a secondary sprocket coupled to the drive sprocket by a chain drive, wherein the exhaust camshaft phaser is configured to rotate the exhaust camshaft to the second phase angle with respect to the primary valve train driver. The primary valve train driver includes a camshaft pulley coupled to the crankshaft via a belt, in accordance with particular embodiments. The camshaft driver may be configured to rotate at ½ the speed of the crankshaft. In particular embodiments, one or more of the primary valve train driver, the intake camshaft phaser, the exhaust camshaft phaser, and the drive sprocket are concentric with the intake camshaft. The engine assembly includes one or more fasteners coaxially coupling one or more of the primary valve train driver, the intake camshaft phaser, the exhaust camshaft phaser and the drive sprocket to the intake camshaft, in accordance with particular embodiments. The intake camshaft phaser may include a first plurality of vanes actuatable via a change in a first fluid pressure to rotate the primary camshaft phaser with respect to the primary valve train driver and the secondary camshaft phaser may include a second plurality of vanes actuatable via a change in second fluid pressure to rotate the secondary camshaft phaser with respect to the primary valve train driver. In particular embodiments, the intake camshaft phaser includes a primary movable lock pin configured to engage and disengage the primary valve train driver and the exhaust camshaft phaser includes a secondary movable lock pin configured to engage and disengage the primary valve train driver.
It should be appreciated that all combinations of the foregoing concepts and additional concepts discussed in greater detail below (provided such concepts are not mutually inconsistent) are contemplated as being part of the inventive subject matter disclosed herein. In particular, all combinations of claimed subject matter appearing at the end of this disclosure are contemplated as being part of the inventive subject matter disclosed herein.

BRIEF DESCRIPTION OF THE DRAWINGS

The skilled artisan will understand that the drawings primarily are for illustrative purposes and are not intended to limit the scope of the subject matter described herein. The drawings are not necessarily to scale; in some instances, various aspects of the subject matter disclosed herein may be shown exaggerated or enlarged in the drawings to facilitate an understanding of different features. In the drawings, like reference characters generally refer to like features (e.g., functionally similar and/or structurally similar elements).

FIG. 1A is a schematic diagram representing a front view of a camshaft assembly constructed according to example embodiments; and FIG. 1B is a schematic diagram representing a side view of the camshaft assembly of FIG. 1A.

FIG. 2 is a side view of a camshaft assembly, in accordance with example embodiments.

FIG. 3 is a perspective view of the camshaft assembly of FIG. 2.

FIG. 4 is a graph illustrating a phase angle shift provided by a camshaft assembly, in accordance with example embodiments.

FIG. 5 is a flow diagram showing a method of operating a camshaft assembly, in accordance with example embodiments.

The features and advantages of the inventive concepts disclosed herein will become more apparent from the detailed description set forth below when taken in conjunction with the drawings.

DETAILED DESCRIPTION

Following below are more detailed descriptions of various concepts related to, and embodiments of, inventive variable valve timing systems and methods of operating variable valve timing system for internal combustion engines. It should be appreciated that various concepts introduced above and discussed in greater detail below may be implemented in any of numerous ways, as the disclosed concepts are not limited to any particular manner of implementation. Examples of specific implementations and applications are provided primarily for illustrative purposes.
FIGS. 1A and 1B are schematics of a camshaft assembly, in accordance with example embodiments. FIG. 1A shows a front view of a schematic of a camshaft assembly 100. FIG. 1B shows a side view of the schematic of the camshaft assembly 100. As depicted in FIG. 1A, the camshaft assembly 100 includes a primary valve train driver 19, which in the illustrated embodiment includes a camshaft drive pulley 1 that rotates around a fixed axis, primary axis 14. The primary valve train driver 19 is actuated by crankshaft drive 13 configured to actuate the primary valve train driver in synchronization with the crankshaft of an engine to which the camshaft assembly 100 is coupled. The primary axis 14 is concentric with a primary camshaft 12. In particular embodiments, the primary camshaft 12 is an intake camshaft including cams configured to actuate intake valves and in other embodiments the primary camshaft 12 is an exhaust camshaft including cams configured to actuate exhaust intake valves. The primary camshaft 12 is coaxial with the primary valve train driver 19 so as to rotate about primary axis 14. The primary camshaft 12 includes plurality of cams positioned on the primary camshaft 12. The cams are configured to rotate about the primary axis 14 with the primary camshaft 12 and are configured to actuate valves, such as intake valves positioned at intake ports in a cylinder head coupled to an engine block. The engine block houses a plurality of cylinders coupled to a crankshaft. In accordance with example embodiments, the primary valve train driver 19 is configured as a pulley and is coupled to the crankshaft via crankshaft drive 13 configured as a belt drive.
The crankshaft rotates the primary valve train driver 19 at half the speed of the crankshaft of the engine, in accordance with particular embodiments. The primary valve train driver 19 is maintained at a fixed sync with respect to the crankshaft. The camshaft timing, for example for the primary camshaft 2, can be adjusted through primary cam phaser 2 coupled to the primary camshaft 12. The primary cam phaser 2 includes primary vanes 3, whose phase angle relative to the primary valve train driver 19 is adjustable. In particular embodiments, the primary vanes 3 may be adjusted by changing the pressure of a working fluid, such as engine oil, on either side 4 or 5 of the primary vanes 3. A secondary camshaft 6 rotates around a fixed secondary axis 15 and is driven by a secondary camshaft drive assembly including a first secondary camshaft driver 18 configured to rotate about primary axis 14 and coupled to a second, secondary camshaft driver 16 configured to rotate about secondary axis 15. In example embodiments the first secondary camshaft driver 18 and the second secondary camshaft driver 16 include sprockets coupled by a chain 7. A secondary cam phaser 8 concentrically coupled to the primary camshaft 12 to rotate about primary axis 14 includes secondary vanes 9 that are configured to adjust the camshaft timing for the secondary camshaft 6 relative to the primary valve train driver 19, by changing a phase angle of the secondary vanes 9 with respect to the primary valve train driver 19. The vanes 9 are typically adjusted by changing the pressure of a working fluid (typically engine oil) on either side 10 and 11 of the secondary vanes 9. The camshaft timing for both the primary camshaft 12 and the secondary camshaft 6 can be adjusted independent of one another relative to the primary valve train driver 19.
FIG. 2 is a side sectional view of a camshaft assembly, in accordance with example embodiments. FIG. 3 illustrates a perspective view of the camshaft assembly of FIG. 2. A camshaft assembly 100 includes a camshaft 102 having a plurality of cams 103 positioned thereon. The cams 103 are configured to rotate about the longitudinal axis of the camshaft 102. The camshaft assembly 100 also includes a camshaft drive pulley 101 coaxially coupled to the camshaft 102. A primary camshaft phaser 104 is coaxially coupled to the camshaft 102. In particular embodiments, the primary camshaft phaser 104 is concentric with camshaft 102. The primary camshaft phaser 104 is coupled to the camshaft 102 via a fastener 113, in accordance with particular embodiments. The camshaft 102 includes a camshaft bearing 114. The primary camshaft phaser 104 may include an intake camshaft phaser or an exhaust camshaft phaser. The primary camshaft phaser 104 is rotatably coupled to the camshaft drive pulley 101 to rotate the primary camshaft phaser 104 and the camshaft 102 with respect to the camshaft drive pulley 101.
In accordance with particular embodiments, the primary camshaft phaser 104 includes a plurality of vanes 105. The plurality of vanes 105 may be configured to adjust the timing of the camshaft 102. Specifically, the plurality of vanes 105 may, pursuant to a change in an oil pressure, from the oil pressure supply line 106, cause the primary camshaft phaser 104 to rotate with respect to the camshaft drive pulley 101. In particular embodiments, the change in oil pressure may cause lock pins 107 to disengage permitting the primary camshaft phaser 104 to rotate with respect to the camshaft drive pulley 101.
A secondary camshaft phaser 109 is also coaxially coupled to the camshaft 102 and a drive sprocket 108 is coaxially coupled to the camshaft shaft 102. The drive sprocket 108 is fixed with respect the secondary camshaft phaser 109, in the illustrated embodiment, via one or more fasteners 112. The secondary camshaft phaser 109 is rotatably coupled to the camshaft drive pulley 101 to rotate the secondary camshaft phaser 109 and the drive sprocket 108 to a phase angle with respect to the camshaft drive pulley 101 independent of the phase angle of the primary camshaft phaser 104. In particular embodiments, a secondary camshaft 202 is coupled to the drive sprocket 108 via a secondary sprocket 208 and a chain drive 203. Accordingly, secondary camshaft phaser 109 is configured to shift the valve timing, by changing the phase angle of the secondary camshaft 202 with respect to the camshaft drive pulley 101 via rotating of the secondary camshaft phaser 109 and the secondary sprocket 208 with respect to the camshaft drive pulley 101. In particular embodiments, the secondary camshaft phaser 109 is rotated with respect to the camshaft drive pulley 101 via changes in pressure of a fluid such as oil supplied via oil supply line 206 actuating the vanes 110 of the secondary camshaft phaser 109 and disengagement of lock pins 207.
FIG. 4 is a graph illustrating a phase shift provided by a camshaft assembly, in accordance with example embodiments. As demonstrated in FIG. 4, a primary camshaft phaser and a coaxial secondary camshaft phaser may be adjusted to various phase angles with respect to an angular position of a camshaft driver, such as a camshaft drive pulley. Varying the phase angle of each of the primary camshaft phaser and secondary camshaft phaser changes the timing of the cams of an intake camshaft and an exhaust camshaft shaft independently to change the intake valve timing and the exhaust valve timing and thereby vary engine performance. In particular embodiments, the phase angle of the primary camshaft phaser or secondary camshaft phaser may be varied by a phase angle, including but not limited to, up to 55 degrees. In particular embodiments, the phase angle of the primary camshaft phaser or secondary camshaft phaser may be varied by a phase angle, including but not limited to, up to 70 degrees. The phase angle of the primary camshaft phaser and secondary camshaft phaser may be independently varied and the change in the angle may be distinct for different cycles.
FIG. 5 is a flow diagram showing a method of operating a camshaft assembly, in accordance with example embodiments. The process 500 may be controlled by one or more engine controllers in accordance with example embodiments to control the valve time of one or more intake valves and exhaust valves in response to varying engine conditions or to vary engine performance. The valve timing adjustments may be altered during engine operation. At 501, a primary camshaft phaser and primary camshaft coaxially coupled to the primary camshaft phaser is rotated to a first phase angle or by a first phase angle quantity with respect to a camshaft drive pulley coaxially coupled to the primary camshaft about the coaxial axis of the camshaft, primary camshaft phaser and camshaft drive pulley. At 502, a secondary camshaft phaser and a drive sprocket coaxially coupled to the secondary camshaft phaser are rotated with respect to the camshaft drive pulley to a second phase angle. The second process 502 may be independently initiated during the first process 501 and may occur during rotation of the camshaft drive pulley via the crankshaft. In particular embodiments, the process 500 may also include , at 503, a secondary camshaft being rotated to the second phase angle via the drive sprocket, a secondary sprocket coupled to the secondary camshaft, and a chain drive coupling the drive sprocket to the secondary sprocket.
For the purpose of this disclosure, the term “coupled” means the joining of two members directly or indirectly to one another. Such joining may be stationary or moveable in nature. Such joining may be achieved with the two members or the two members and any additional intermediate members being integrally formed as a single unitary body with one another or with the two members or the two members and any additional intermediate members being attached to one another. Such joining may be permanent in nature or may be removable or releasable in nature.
It should be noted that the orientation of various elements may differ according to other exemplary embodiments, and that such variations are intended to be encompassed by the present disclosure. It is recognized that features of the disclosed embodiments can be incorporated into other disclosed embodiments.
It is important to note that the constructions and arrangements of apparatuses or the components thereof as shown in the various exemplary embodiments are illustrative only. Although only a few embodiments have been described in detail in this disclosure, those skilled in the art who review this disclosure will readily appreciate that many modifications are possible (e.g., variations in sizes, dimensions, structures, shapes and proportions of the various elements, values of parameters, mounting arrangements, use of materials, colors, orientations, etc.) without materially departing from the novel teachings and advantages of the subject matter disclosed. For example, elements shown as integrally formed may be constructed of multiple parts or elements, the position of elements may be reversed or otherwise varied, and the nature or number of discrete elements or positions may be altered or varied. The order or sequence of any process or method steps may be varied or re-sequenced according to alternative embodiments. Other substitutions, modifications, changes and omissions may also be made in the design, operating conditions and arrangement of the various exemplary embodiments without departing from the scope of the present disclosure.
While various inventive embodiments have been described and illustrated herein, those of ordinary skill in the art will readily envision a variety of other mechanisms and/or structures for performing the function and/or obtaining the results and/or one or more of the advantages described herein, and each of such variations and/or modifications is deemed to be within the scope of the inventive embodiments described herein. More generally, those skilled in the art will readily appreciate that, unless otherwise noted, any parameters, dimensions, materials, and configurations described herein are meant to be exemplary and that the actual parameters, dimensions, materials, and/or configurations will depend upon the specific application or applications for which the inventive teachings is/are used. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific inventive embodiments described herein. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that, within the scope of the appended claims and equivalents thereto, inventive embodiments may be practiced otherwise than as specifically described and claimed. Inventive embodiments of the present disclosure are directed to each individual feature, system, article, material, kit, and/or method described herein. In addition, any combination of two or more such features, systems, articles, materials, kits, and/or methods, if such features, systems, articles, materials, kits, and/or methods are not mutually inconsistent, is included within the inventive scope of the present disclosure.
Also, the technology described herein may be embodied as a method, of which at least one example has been provided. The acts performed as part of the method may be ordered in any suitable way unless otherwise specifically noted. Accordingly, embodiments may be constructed in which acts are performed in an order different than illustrated, which may include performing some acts simultaneously, even though shown as sequential acts in illustrative embodiments.
The indefinite articles “a” and “an,” as used herein in the specification and in the claims, unless clearly indicated to the contrary, should be understood to mean “at least one.”
In the claims, as well as in the specification above, all transitional phrases such as “comprising,” “including,” “having,” “involving,” and the like are to be understood to be open-ended, i.e., to mean including but not limited to.
The claims should not be read as limited to the described order or elements unless stated to that effect. It should be understood that various changes in form and detail may be made by one of ordinary skill in the art without departing from the spirit and scope of the appended claims. All embodiments that come within the spirit and scope of the following claims and equivalents thereto are claimed.

Claims

1. A variable valve timing system, comprising:

a primary valve train driver configured to rotate about a primary axis;

a primary camshaft including a first plurality of cams positioned on the primary camshaft, the primary camshaft coaxially coupled to the primary valve train driver, the first plurality of cams configured to rotate about the primary axis;

a primary camshaft phaser coaxially coupled to the primary camshaft, the primary camshaft phaser rotatably coupled to the primary valve train driver so as to rotate the primary camshaft phaser and the primary camshaft to a first phase angle with respect to the primary valve train driver;

a secondary camshaft driver on the primary axis coaxially coupled to the primary camshaft; and

a secondary camshaft phaser coaxially coupled to the primary camshaft and coupled to the secondary camshaft driver on the primary axis , the secondary camshaft phaser rotatably coupled to the primary valve train driver so as to rotate the secondary camshaft driver on the primary axis to a second phase angle with respect to the primary valve train driver.

2. The variable valve timing system of claim 1, wherein the secondary camshaft driver is a first secondary camshaft driver, and further comprising a secondary camshaft configured to rotate about a secondary axis, the secondary camshaft including a second plurality of cams positioned on the secondary camshaft and a second secondary camshaft driver on the secondary axis coupled to the first secondary camshaft driver on the primary axis by a synced drive mechanism, wherein the secondary camshaft phaser is configured to rotate the secondary camshaft to the second phase angle with respect to the primary valve train driver.

3. The variable valve timing system of claim 1, wherein the primary valve train driver includes a primary valve train driver coupled to the crankshaft via a synced drive mechanism.

4. The variable valve timing system of claim 1, wherein the primary valve train driver includes a pulley.

5. The variable valve timing system of claim 2, wherein the first plurality of cams is configured to open a plurality of intake valves.

6. The variable valve timing system of claim 5, wherein the second plurality of cams is configured to open a plurality of exhaust valves.

7. The variable valve timing system of claim 2, wherein the first plurality of cams is configured to open a plurality of exhaust valves.

8. The variable valve timing system of claim 7, wherein the second plurality of cams is configured to open a plurality of intake valves.

9. The variable valve timing system of claim 2, wherein one or more of the primary valve train driver, the primary camshaft phaser, the secondary camshaft phaser, and the secondary camshaft driver on the primary axis are concentric with the primary camshaft.

10. The variable valve timing system of claim 2, further comprising one or more fasteners coaxially coupling one or more of the primary valve train driver, the primary camshaft phaser, the secondary camshaft phaser and the secondary camshaft driver on the primary axis to the primary camshaft.

11. The variable valve timing system of claim 1, wherein the primary camshaft phaser includes a plurality of vanes actuatable via a change in fluid pressure to rotate the primary camshaft phaser with respect to the primary valve train driver.

12. The variable valve timing system of claim 1, wherein the secondary camshaft phaser includes a plurality of vanes actuatable via a change in fluid pressure to rotate the secondary camshaft phaser with respect to the primary valve train driver.

13. The variable valve timing system of claim 1, wherein the primary camshaft phaser includes a primary movable lock pin configured to engage and disengage the primary valve train driver, and wherein the secondary camshaft phaser includes a secondary movable lock pin configured to engage and disengage the primary valve train driver.

14. A method of operating a valve train variable comprising:

rotating a primary camshaft phaser and a primary camshaft coaxially coupled to the primary camshaft phaser about a primary axis to a first phase angle with respect to a primary valve train driver coaxially coupled to the primary camshaft and configured to rotate about the primary axis, the primary camshaft including a first plurality of cams positioned on the camshaft, the first plurality of camshaft configured to rotate about the primary axis; and

rotating a secondary camshaft phaser and a secondary camshaft driver on the primary axis coupled to the secondary camshaft phaser about the primary axis to a second phase angle with respect to the primary valve train driver, the secondary camshaft phaser and the secondary camshaft driver on the primary axis coaxially coupled to the primary camshaft.

15. The method of claim 14, further comprising rotating a secondary camshaft to the second phase angle, via the secondary camshaft driver on the primary axis, coupled to the secondary camshaft by a synced drive mechanism coupling the secondary camshaft driver on the primary axis to the secondary camshaft .

16. The method of claim 14, wherein rotating the primary camshaft phaser and the primary camshaft to the first phase angle with respect to the primary valve train driver includes actuating the primary camshaft phaser via a change in a fluid pressure.

17. The method of claim 14, further comprising rotating the primary valve train driver via a crankshaft coupled to a plurality of pistons.

18. The method of claim 17, wherein the primary valve train driver is configured to rotate at ½ the speed of the crankshaft.

19. The method of claim 14, further comprising actuating a plurality of intake valves via the first plurality of cams.

20. The method of claim 14, further comprising actuating a plurality of exhaust valves via the first plurality of cams.

21. An engine assembly including:

an engine block housing a plurality of cylinders, the plurality of cylinders including a plurality of pistons positioned therein, the plurality of pistons coupled to a crankshaft;

a cylinder head coupled to the engine block;

a plurality of intake valves positioned in the cylinder head a plurality of exhaust valve positioned in the cylinder head a primary valve train driver coupled to the crankshaft, the primary valve train driver configured to rotate about a primary axis;

an intake camshaft including a first plurality of cams configured to cause actuation of the intake valves, the intake camshaft coaxial coupled to the primary valve train driver, the first plurality of cams configured to rotate about the primary axis;

an intake camshaft phaser coaxially coupled to the intake camshaft, the intake camshaft phaser rotatably coupled to the primary valve train driver so as to rotate the intake camshaft phaser and the intake camshaft to a first phase angle with respect to the primary valve train driver;

a drive sprocket coaxially coupled to the intake camshaft; and

an exhaust camshaft phaser coaxial coupled to the intake camshaft and coupled to the drive sprocket, the exhaust camshaft phaser rotatably coupled to the primary valve train driver so as to rotate the exhaust camshaft phaser and the drive sprocket to a second phase angle with respect to the primary valve train driver.

22. The engine assembly of claim 21 further comprising an exhaust camshaft including a second plurality of cams configured to cause actuation of the exhaust valves and, the exhaust camshaft including a secondary sprocket coupled to the drive sprocket by a chain drive, wherein the exhaust camshaft phaser is configured to rotate the exhaust camshaft to the second phase angle with respect to the primary valve train driver.

23. The engine assembly of claim 21, wherein the primary valve train driver includes a camshaft pulley and is coupled to the crankshaft via a belt.

24. The engine assembly of claim 21, wherein the primary valve train driver is configured to rotate at ½ the speed of the crankshaft.

25. The engine assembly of claim 21, wherein one or more of the primary valve train driver, the intake camshaft phaser, the exhaust camshaft phaser, and the drive sprocket are concentric with the intake camshaft.

26. The engine assembly of claim 21, further comprising one or more fasteners coaxially coupling one or more of the primary valve train driver, the intake camshaft phaser, the exhaust camshaft phaser and the drive sprocket to the intake camshaft.

27. The engine assembly of claim 21, wherein the intake camshaft phaser includes a first plurality of vanes actuatable via a change in a first fluid pressure to rotate the intake camshaft phaser with respect to the primary valve train driver and wherein the exhaust camshaft phaser includes a second plurality of vanes actuatable via a change in second fluid pressure to rotate the exhaust camshaft phaser with respect to the primary valve train driver.

28. The engine assembly of claim 21, wherein the intake camshaft phaser includes a primary movable lock pin configured to engage and disengage the primary valve train driver and wherein the exhaust camshaft phaser includes a secondary movable lock pin configured to engage and disengage the primary valve train driver.