US20070215080A1

US20070215080A1 - Variable valve actuation

Info

Publication number: US20070215080A1
Application number: US11/674,915
Authority: US
Inventors: Charles Thomas
Original assignee: Thomas Engine Co LLC
Current assignee: Thomas Engine Co LLC
Priority date: 2006-02-14
Filing date: 2007-02-14
Publication date: 2007-09-20

Abstract

A variable valve actuation mechanism actuates a valve of an internal combustion engine. The mechanism includes an actuator with a housing and a piston each moveable along a longitudinal axis in the engine. A cavity is defined between the piston and the housing. A body of fluid is disposed in the cavity and in the reservoir. A fluid passage has an open position wherein the cavity and reservoir are in fluid communication and a closed position wherein the cavity is sealed. When the passage is closed, the housing and piston move generally together. When the passage is open, fluid may pass from the cavity to the reservoir and movement of the housing relative to the piston changes the volume of the cavity.

Description

REFERENCE TO RELATED APPLICATION

This application claims priority from U.S. Provisional Patent Application Ser. No. 60/773,090, filed Feb. 14, 2006, the entire content of which is incorporated herein by reference.

FIELD OF THE INVENTION

The invention relates to internal combustion engines. More particularly, the invention relates to a variable valve actuation mechanism for internal combustion engines.

BACKGROUND OF THE INVENTION

Internal combustion (“IC”) engines are widely used for providing mechanical power to drive a variety of device. IC engines typically include a cylinder in which a fuel/air mixture is ignited, a piston movable in a reciprocating manner within the cylinder due to forces created by the ignition of the fuel/air mixture, and an output shaft driven by the reciprocating motion of the piston. IC engines also typically include a valve assembly for controlling the intake of fuel/air and exhaust of combustion products. The valve assembly is timed for appropriate intake and exhaust during the intake, compression, power and exhaust cycles of the engine. Variable valve actuation mechanisms are known for varying the timing of the valve assembly, yet it remains desirable to provide an improved variable valve actuating mechanism that provides enhanced performance, cost, and reliability over conventional designs.

SUMMARY OF THE INVENTION

A variable valve actuation mechanism is provided for actuating a valve of an internal combustion engine. The variable valve actuation mechanism includes an actuator having a housing and a piston each moveable along a longitudinal axis in the engine for actuating the valve. A cavity is defined between the piston and the housing. The mechanism also includes a reservoir and a body of fluid disposed in the cavity and in the reservoir. A fluid passage has an open position wherein the cavity and the reservoir are in fluid communication and a closed position wherein the cavity is sealed. When the passage is closed and the cavity is sealed, the housing and the piston move generally together. When the passage is opened, fluid may pass from the cavity to the reservoir and movement of the housing relative to the piston changes the volume of the cavity. Additional embodiments of the invention are also described and illustrated.

BRIEF DESCRIPTION OF THE DRAWINGS

Advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:
FIG. 1 is a cross-sectional view of portions of a variable valve actuation mechanism according to the present invention in a first position;
FIG. 2 is a cross-sectional view of the mechanism of FIG. 1 moved into a second position;
FIG. 3 is a cross-sectional view of the mechanism of FIGS. 1 and 2 shifted into a third position;
FIG. 4 is a cross-sectional view of portions of a variable valve actuation mechanism according to a second embodiment of the present invention with a cam lobe in a first position;
FIG. 5 is a view similar to FIG. 4 with the cam rotated to a second position;
FIG. 6 is a view similar to FIGS. 4 and 5 with the cam rotated to a third position;
FIG. 7 is a view similar to FIGS. 4-6 with the cam rotated to a fourth position;
FIG. 8 is a view similar to FIGS. 4-7 with the cam rotated to a fifth position;
FIG. 9 is a view similar to FIGS. 4-8 with the cam rotated to a sixth position;
FIG. 10 is a view similar to FIGS. 4-9 with the cam rotated to a seventh position;
FIG. 11 is a view similar to FIGS. 4-10 with the cam rotated to a eighth position;
FIG. 12 is a view similar to FIGS. 4-11 with the cam rotated to a ninth position;
FIG. 13 is a view similar to FIGS. 4-12 with the cam rotated to a tenth position;
FIG. 14 is a cross-sectional view of portions of a variable valve actuation mechanism according to the a third embodiment of the present invention;
FIG. 15 is a view similar to FIG. 14, with the fluid removed from the illustration;
FIG. 16 is a view similar to the view of FIGS. 14 and 15 wherein the housing is not cut away;
FIG. 17 is a view similar to FIGS. 14-16 wherein the housing is removed from the support;
FIG. 18 is a cross-sectional view of portions of a variable valve actuation mechanism according to a fourth embodiment of the present invention;
FIG. 19 is a view similar to FIG. 18 with the fluid removed;
FIG. 20 is a view similar to FIGS. 18 and 19 wherein the housing is not cut away;
FIG. 21 is a view similar to FIGS. 18-20 with the housing removed from the support; and
FIG. 22 is a view of a variable valve actuation system.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides various embodiments of a mechanism for actuating the valves of an internal combustion engine. The mechanism may take the place of a typical mechanical or roller tappet or lifter, or may be used in other ways. The illustrated embodiments, discussed below, are in the form of a roller lifter. Generally, the various embodiments of the present invention include an actuator with a housing and a piston that define a first input end and a second output end of the actuator. A fluid cavity is defined between the piston and the housing, with the cavity being filled with a generally incompressible fluid. Depending on the embodiment and the method of operation, the amount of fluid in the cavity may be increased, thereby increasing the size of the cavity and the distance between the input and output ends of the actuator, may be decreased, thereby reducing the size of the cavity and the distance between the ends, or the fluid may be trapped thereby forcing the housing and piston to move as a unit Addition of fluid to the cavity may be accomplished through the supply of pressurized fluid, such as engine oil. The amount of fluid in the cavity may be decreased by allowing the fluid to pass out of the cavity while a load is applied to the actuator, or the fluid may be pumped out. The cavity may be closed off such that fluid is trapped such as by closing or blocking fluid passages that would otherwise be in fluid communication with the cavity.
By positioning the variable actuator between an input device, such as an eccentric lobe on a cam, and an output device such as a pushrod in a valve train, the actuator may be used to vary how much of the input motion is provided to the output device. One application of this actuator is to vary the valve lift of engine intake and/or exhaust valves.
FIGS. 1-3 illustrate a first embodiment of an actuator according to the present invention. These Figures illustrate an eccentric cam lobe 10 which serves as in input device. The cam lobe is rotatable about a rotational axis 12. Unlike a typical cam, the rotational axis 10 of the cam shaft 14 supporting the lobe 10 can be displaced in an off-axis or lateral direction to vary the midpoint of travel of the actuators 20 and 22 that are in mechanical communication with the cam lobe 10. Each of FIGS. 1-3 illustrate a different position of the rotational axis 12 and a resulting starting position of the cam lobe 10 and actuators 20 and 22. The present invention may be used in a variety of applications. The embodiment shown in FIGS. 1-3 is a design for use in a barrel engine with a central drive shaft and cam shaft, which actuates tappets that extend generally radially outwardly therefrom. An exemplary engine and valve train is shown in pending PCT application serial number PCT/US2006/024591, the entire contents of which is incorporated herein by reference. Actuators 20 and 22 illustrate just two of the multiple actuators or tappets that may extend radially outwardly from a single cam. In alternative embodiments, tappets or actuators may only extend in one direction from a cam.
The actuators 20 and 22 are substantially identical, and therefore only actuator 22 will be described in detail. The actuator 22 is disposed and supported in hole 24 in a tappet carrier, engine block, or other support 26, which may or may not form part of the actuator itself. The hole 24 is preferably generally cylindrical. The actuator includes a housing 28 and a piston 30 that are spaced apart so as to define a fluid cavity 32 therebetween. The housing 28 has a first end 34 including a roller 36 that serves as a bearing member for contacting the cam lobe 10. The housing has an opposite second end 38 with a generally cylindrical body 40 extending therebetween. The cylindrical body is slidably received in the cylindrical support hole 24 for movement along a longitudinal axis of the hole. The piston 30 is also generally cylindrical and slidably received in the hole 24 for movement along the longitudinal axis. The actuator 22 may be said to have a first input end defined by the roller 36 and a second output end defined by the piston 30.
A biasing member 42 is preferably disposed in the cavity 32 and biases the housing 28 and the piston 30 away from each other. The cavity 32 between the housing 28 and piston 30 is filled with an incompressible fluid, such as engine oil. At least one outlet 44 is provided in the support 26 for allowing fluid to enter or exit the cavity between the housing 28 and piston 30.
Three movement zones for the actuator 22 are labeled as a slosh area, between lines C and A, a squish area between lines A and B, and a lift area between lines B and D. Referring to FIG. 1, the cam shaft 14 is illustrated in a position most distant from the support 26. The cam lobe has a lift portion 11 wherein the surface of the lobe is most distant from the axis of rotation 12. As will be clear to those of skill in the art, rotation of the cam lobe 10 in the position shown in FIG. 1 will result in movement of the housing 28 in the “slosh” area defined between points C and A. Movement of the housing 28 in this region results in substantially no movement of the piston 30, as fluid in the cavity 32 is displaced and replaced through the outlet 44. As the housing 28 is moved in the slosh area towards the piston 30, the fluid leaks or is squeezed out through the outlet 44. As the housing moves away from the piston, in the slosh area, fluid is preferably provided through the outlet 44. If the fluid in the outlet 44 is pressurized, fluid will flow from the cavity into the outlet when the pressure in the cavity exceeds the pressure in the outlet 44, such as when the cam lobe is forcing the housing 28 toward the piston. When the force of the lobe is removed, when it rotates to a lower lift position, the biasing member will bias the housing toward the cam and the pressure in the cavity will fall below the pressure in the outlet, and fluid will again fill the cavity. In this situation, the valve being driven by the actuator 22 will be mostly or completely deactivated. The outlet 44 may be considered to be part of or in fluid communication with a reservoir of fluid and/or a pressurized supply of oil in an engine.
In FIG. 2, the cam shaft 14 and cam lobe 10 are shifted transversely toward the support 26 and actuator 22 relative to the position shown in FIG. 1. In this position, rotation of the cam shaft 14 about the axis 12 causes reciprocal movement of the housing 28 within the slosh, squish and “lift” areas. There is substantially no movement of the piston 30 until the housing 28 is moved beyond the end of the squish area at line B and into the lift area. Once the second end 38 of the housing passes line B, the cavity is sealed or cut off from the outlet 44 and therefore the piston 30 and housing 28 move together. The outlet may be considered part of a passage that may be open, as shown in FIG. 1, or closed, as in FIGS. 2 and 3. In the open position, there is fluid communication between the cavity and a reservoir of fluid, and in the closed position the reservoir is sealed off.
In the lift area, displacement of the housing 28 toward the piston 30 causes compression of the fluid therebetween, thereby causing displacement of the piston 30 with the housing 28. It should be noted that the fluid is preferably substantially incompressible. As such, compression of the fluid does not cause a reduction in the volume of the cavity but instead merely transfers force from the housing to the piston. Shifting the cam shaft 14 and cam lobe 10 in this manner changes the midpoint of travel for the housing 28 and consequently the motion profile for the piston 30 and valve train. Shifting the midpoint of travel toward the actuator 22 shortens the maximum distance between the second end 38 of the housing 28 and line B. Thus, shifting the midpoint of travel toward the actuator 22 minimizes the delay associated with the displacement of fluid through the outlet 44.
In FIG. 3, the cam shaft 14 is shifted more toward the actuator 22 resulting in the housing 120 moving within only the lift or in the squish and lift areas. Thus, movement of the housing 28 results in substantially full actuation of the piston 30 and valve train. The cam shaft 14 and cam lobe 10 can be shifted by any suitable mechanisms known by those having ordinary skill in the art, such as by hydraulic or electric motorized actuators. It should also be appreciated by those skilled in the art that the transverse movement of the cam shaft 14 shown in FIGS. 1-3 is applicable to the other embodiments described herein.
While the piston 28 and housing 30 are illustrated as being spaced apart and not in mechanical contact, an alternative embodiment provides a housing that has a bore defined therein and the piston is received in the bore. The fluid filled cavity is defined in the bore between the piston and the housing. A passage similar to passage 44 may be selectively in fluid communication with the cavity depending on the position of the housing relative to a support. The housing may provide a travel limit for the piston such that the piston cannot be move out of the bore.
Referring to FIGS. 4-13, another alternative actuation mechanism for actuating a valve of an internal combustion engine is generally indicated at 110. The mechanism 110 includes a tappet housing 120, a piston 140, a biasing member 150 and a bearing member 160.
The tappet sleeve or housing 120 is slidably supported in a cylindrical hole 122 formed in a roller tappet carrier supported in an engine block or formed in the engine block itself. The housing 120 is cylindrically shaped. A bore 124 is formed in one end of the housing 120 for slidably receiving the piston 140 therein. A fluid cavity is formed in the housing 120. A portion of the fluid cavity is defined by an annular slot 126 and a center bore 128. Both the annular slot 126 and center bore 128 are formed in an end wall of the housing 120. The center bore 28 is generally concentric with the slot 126. A middle section 130 of the housing 120 has a reduced outer diameter relative to the ends. An annular space 132 is defined between the middle section 130 and the walls defining the hole 122 due to the reduced diameter of the middle section 130. A reservoir 134 is continuous with the annular space 132, slot 126 and bore 128 so that fluid can pass freely therebetween. A generally incompressible fluid is disposed in the slot 126, bore 128, annular space 132 and reservoir 134. The reservoir may take the form of a pressurized supply of fluid, such as an oil supply in an engine or may be in fluid communication therewith.
Preferably, each of the systems illustrated herein has a fluid reservoir in fluid communication with the cavity such that fluid may pass quickly back and forth between the cavity and reservoir. As will be clear to those of skill in the art, energy loss may be minimized by positioning the reservoir nearby and/or provided a large passage between the cavity and reservoir. It is also preferred that the reservoir have an air or gas chamber therein, as illustrated, with the gas chamber serving as an air or gas spring. It is preferred that the cavity and reservoir also be in fluid communication with a lubrication system such as a pressurized oiling system.
The piston 140 includes a head 142 slidably supported in the bore 124 of the housing 120. The head 142 is cylindrically shaped. The head 142 includes an annular groove 144 for receiving and supporting a lubricant for minimizing friction between the piston 140 and the housing 120. Optionally, the annular groove 144 supports an annular gasket. A rod 146 extends outwardly from one end of the head 142 toward the end wall of the bore 124. The rod 146 is axially aligned with the center bore 128. A valve or valve actuation mechanism in the form of a pushrod and/or rocker arm is operatively coupled with the opposite end of the head 142, so that the valve is actuated by movement of the piston 140.
A recess 131 is formed in the opposite end of the housing 120 for receiving the bearing member 160 therein. The bearing member 160 is provided in the form of a roller. The bearing member 160 is pivotally coupled to the housing 120 and received in the recess 131. A portion of the bearing member 160 protrudes outwardly from the recess 131 for rollingly engaging an eccentric cam lobe 170. The cam lobe 170 is rotatably driven by a cam shaft 180 for rotation about an axis 182 of the cam shaft 180. It should be appreciated that the components shown in the figures may not be to scale and the profile of the cam lobe 170 may be different than shown.
The biasing member 150 is provided in the form of a helical spring, which maintains the bearing member 160 in contact with the cam lobe 170. Optionally, the biasing member 150 includes a plurality of springs for biasing the bearing member 160 toward the cam lobe 170.
In use, the cam lobe 170 is driven by the engine via the cam shaft 80. The bearing member 160 rolls along the outer eccentric surface of the cam lobe 170, thereby causing reciprocating movement of the housing 120 relative to the hole 122. As shown by the sequence of FIGS. 4-9, counterclockwise rotation of the cam lobe 170 causes axial displacement of the housing 120 toward the piston 140. The rod 146 moves toward the center bore 128. Fluid is displaced into the reservoir 134. Movement of the housing 120 does not cause displacement of the piston 140 until fluid becomes trapped between the rod 146 and the bore 128, which occurs starting with FIG. 7. Due to the incompressible nature of the fluid, continued axial displacement of the housing 120 in the up direction in FIG. 9 causes movement of the piston 140 therewith. While FIGS. 7-11 illustrate the lower end of the rod 146 stopping at the top of the bore 128, in practice the rod may protrude somewhat into the bore depending on the clearances and the time that the rod is adjacent the bore. In FIGS. 10-13, the bearing member 160 rolls beyond the high point of the cam lobe 170, so that the housing 120 moves downwardly in the direction of the cam shaft 180. The piston 140 follows the housing 120 downwardly until FIGS. 12-13, wherein the valve is closed. At this point, the biasing member 150 biases the housing 120 and the piston 140 apart from each other, thereby maintaining the bearing member 160 in contact with the cam lobe 170. Fluid is drawn from the reservoir to fill the bore 128 as the rod 146 is withdrawn from the bore 128.
Thus, rotation of the cam lobe 170 about the axis of the cam shaft 180 causes reciprocal movement of the housing 120 along the axis of the hole 122. The piston 140 reciprocates with the housing 120, although initial movement of the housing 120 is lost relative to the piston 140 due to the need to first displace fluid from and compress the remaining fluid between the bore 128 with the rod 146. The reciprocal movement of the piston 140 causes actuation of the valve via engagement between the piston head 140 with the valve directly, or the rod or rocker arm mechanically coupled therebetween.
A third embodiment of the invention is shown in FIGS. 14-17, wherein the slot and the bore of the prior embodiment are replaced by a single fluid cavity 228 formed in the housing 220. This third embodiment may operate like the first embodiment, wherein an outlet 244 is provided which is in selective fluid communication with the cavity 228, depending on the position of the housing 220. The outlet 244 may be part of or in fluid communication with a reservoir of fluid, such as a pressurized supply of oil in an engine. FIG. 14 shows fluid filling the cavity 28, an annular area 230 around the housing 220 and the outlet 244. FIG. 15 illustrates the actuator without fluid. FIG. 16 illustrates the actuator wherein the housing 220 is not cut away, and FIG. 17 shows the housing removed from the hole or support in the engine block. In the position illustrated in FIGS. 14 and 15, the reservoir 228 is cut off from the outlet 244 due to the position of the housing relative to the outlet.
A fourth embodiment of the invention is shown in FIGS. 18-21, wherein a portion of the housing from the third embodiment is removed leaving only an end portion 320. The biasing member 350 is compressed between the piston 340 and the end portion 320. The piston 340 is slidably supported in the hole 322 in the engine block as in the first embodiment, rather than the bore of the housing as in the second embodiment. FIG. 18 illustrates the actuator with fluid in the cavity 328 and outlet 344. In the position shown, the passage between the cavity 328 and outlet 344 is closed. FIG. 19 illustrates the actuator with the fluid removed. FIG. 20 illustrates the actuator wherein the end portion 320 is not cut away, and FIG. 21 illustrates the actuator by itself, without being in a hole of support.
Referring to FIG. 22, a variable valve actuation system is generally illustrated at 400. The system includes a cam shaft 402 that is rotatable about a rotational axis. The cam shaft includes at least one lobe 404. A tappet carrier or other support 406 has a receiving area 422 defined therein and receives a variable actuator according to any embodiment of the present invention. The illustrated version includes a housing 420, piston 440 and biasing member 450. One end of the actuator is in mechanical communication with the cam lobe 404 and the other is in mechanical communication with a valve 460 via a valve train including a rocker arm 462 and a pushrod 464. An opening 470 is defined in the inner surface of the support 406 and is in fluid communication with a reservoir and/or fluid supply as discussed previously. The actuator has an opening that is in fluid communication with the opening 470 in some positions of the actuator. In the illustrated embodiment, the opening in the actuator is the entire gap between the housing and piston, which is the side of the cavity 480.
The invention has been described in an illustrative manner. It is, therefore, to be understood that the terminology used is intended to be in the nature of words of description rather than of limitation. Many modifications and variations of the invention are possible in light of the above teachings. Thus, within the scope of the appended claims, the invention may be practiced other than as specifically described.

Claims

1. A variable valve actuation mechanism for actuating a valve of an internal combustion engine, the variable valve actuation mechanism comprising:

an actuator including a housing and a piston each movable along a longitudinal axis in the engine for actuating the valve, a cavity being defined between the piston and the housing;

a reservoir;

a body of fluid disposed in the cavity and in the reservoir;

a fluid passage having an open position wherein the cavity and the reservoir are in fluid communication and a closed position wherein the cavity is sealed;

wherein when the passage is closed and the cavity is sealed, the housing and the piston move generally together; and

wherein when the passage is open, fluid may pass from the cavity to the reservoir, and movement of the housing relative to the piston changes the volume of the cavity.

2. A variable valve actuation mechanism according to claim 1, further including a biasing member disposed between the housing and the piston, the biasing member biasing the housing and piston away from each other.

3. A variable valve actuation mechanism according to claim 1, wherein the reservoir comprises a pressurized supply of engine oil.

4. A variable valve actuation mechanism according to claim 1, wherein the reservoir is in fluid communication with a pressurized supply of engine oil.

5. A variable valve actuation mechanism according to claim 1, wherein the reservoir is at least partially filled with a gas that serves as a gas spring.

6. A variable valve actuation mechanism according to claim 1, wherein the housing and the piston are both generally cylindrical.

7. A variable valve actuation mechanism according to claim 1, wherein the housing includes a roller for interaction with a cam lobe.

8. A variable valve actuation mechanism according to claim 1, wherein the housing has a bore defined therein, the piston being slidably received in the bore.

9. A variable valve actuation mechanism according to claim 1, wherein the bore in the housing and the piston are both generally cylindrical.

10. A variable valve actuation mechanism according to claim 1, further including a cam shaft with a cam lobe rotatable about a rotational axis, the cam lobe being in mechanical communication with the housing for actuating the housing in a reciprocating manner along the longitudinal axis, the cam being movable in a direction transverse to the rotational axis to cause a corresponding shift in the midpoint of travel of the housing.

11. A variable valve actuation system comprising:

a cam shaft with a cam lobe, the shaft being rotatable about a rotational axis;

a tappet support with a receiving area defined therein, the receiving area having an inner surface with a fluid supply opening defined therein;

a fluid supply in fluid communication with the supply opening;

a valve movable between an open and a closed position;

a variable valve actuator having a first and a second end, the actuator comprising;

a housing defining the first end of the actuator;

a piston defining the second end of the actuator;

a cavity defined between the housing and piston;

the actuator having an outer surface with an opening defined therein, the opening being in fluid communication with the cavity, the actuator being received in the receiving area with the outer surface of the actuator adjacent the inner surface of the receiving area;

one of the ends of the actuator being in mechanical communication with the cam lobe and the other of the ends being in mechanical communication with the valve;

the variable valve actuator having a first position wherein the opening in the outer surface is in fluid communication with the opening in the inner surface of the receiving area such that the cavity is in fluid communication with the fluid supply, wherein when the actuator is in the first position fluid may pass between the cavity and the supply such that movement of the housing relative to the piston changes the volume of the cavity; and

the variable valve actuator having a second position wherein the opening in the outer surface is not in fluid communication with the opening in the inner surface of the receiving area such that the cavity is sealed and the housing and piston move generally together

12. A variable valve actuation system according to claim 11, further including a biasing member disposed between the housing and the piston of the actuator, the biasing member biasing the housing and piston away from each other.

13. A variable valve actuation system according to claim 11, wherein the fluid supply comprises a pressurized supply of engine oil.

14. A variable valve actuation system according to claim 11, wherein the fluid supply includes a reservoir.

15. A variable valve actuation system according to claim 14, wherein the reservoir is at least partially filled with a gas that serves as a gas spring.

16. A variable valve actuation system according to claim 11, wherein the housing and the piston are both generally cylindrical.

17. A variable valve actuation system according to claim 11, wherein the housing includes a roller for interaction with the cam lobe.

18. A variable valve actuation system according to claim 11, wherein the housing has a bore defined therein, the piston being slidably received in the bore.

19. A variable valve actuation system according to claim 11, wherein the bore in the housing and the piston are both generally cylindrical.