US20040050349A1

US20040050349A1 - Variable force engine valve actuator

Info

Publication number: US20040050349A1
Application number: US10/243,901
Authority: US
Inventors: Scott Leman; Ronald Shinogle; Sean Cornell; Mingchun Dong
Original assignee: Caterpillar Inc
Current assignee: Caterpillar Inc
Priority date: 2002-09-16
Filing date: 2002-09-16
Publication date: 2004-03-18

Abstract

An engine valve actuator is provided. The engine valve actuator includes a first piston and a second piston. The second piston is moveably received within the first piston. The engine valve further includes an actuator body that has a bore defining a first stop and a second stop. The first stop is configured to engage the first piston to limit movement of the first piston at a first preselected distance of travel. The second stop is configured to engage the second piston to limit movement of the second piston at a second preselected distance. A valve element is operatively connected to the second piston to move in response to movement of the second piston.

Description

TECHNICAL FIELD

The present disclosure is directed to an engine valve actuator and more particularly to a variable force engine valve actuator.

BACKGROUND

An internal combustion engine typically includes a series of valves. These valves are configured to control the intake and exhaust of gases to and from the combustion chambers of the engine. A typical engine will include at least one intake valve and at least one exhaust valve for each chamber in the engine. The opening of each of valve is timed to occur at a certain point in the operating cycle of the engine. For example, an intake valve may be opened when a piston is moving towards a bottom dead center position within a cylinder to allow fresh air to enter the combustion chamber. An exhaust valve may be opened when the piston is moving towards a top dead center position in the cylinder to expel the exhaust gas from the combustion chamber.

The actuation, or opening and closing, of the engine valves may be controlled in a number of ways. For example, each engine valve may be operatively engaged with a cam follower that engages a cam on a cam shaft that is operatively connected to the engine crankshaft. A rotation of the crankshaft causes a corresponding rotation in the cam shaft. As the camshaft rotates, the cam moves the cam follower to actuate the engine valve. Because the rotation of the crankshaft also controls the motion of the piston, this arrangement may be used to coordinate the actuation of each engine valve with the desired movement of the respective piston.

This configuration does not, however, provide a high degree of flexibility in the timing of valve actuation. It has been found that engine efficiency may be improved by varying the timing of the valve actuation based on the operating conditions of the vehicle. With the cam and cam follower configuration, the engine valves will be actuated at the same point in the crankshaft rotation regardless of the vehicle operating conditions. Thus, these types of systems are relatively inflexible and may not be capable of maximizing the efficiency of an engine.

Another approach involves actuating the engine valves independently of the crankshaft rotation. This may be accomplished, for example, with a hydraulic system. As shown in U.S. Pat. No. 6,263,842, a hydraulically-driven piston may be used to actuate an engine valve. In this approach, each engine valve includes a piston that is connected to the engine valve and is actuated by the introduction of pressurized fluid. The valve actuation may, therefore, be controlled independently of the crankshaft rotation and may provide additional flexibility in the valve timing.

To obtain improvements in engine efficiency, the engine valves may need to be actuated when the gas within the combustion chamber is under pressure from an engine piston. A hydraulically actuated valve will need to exert a force significant enough to open the valve under these conditions. This may require either a highly pressurized fluid or a piston with a large surface area. An additional pump may be required to provide the highly pressurized fluid. A piston with a large surface area will require a substantial amount of pressurized fluid each time the valve is actuated, which may decrease the amount of fluid available to other systems within the vehicle.

In addition, a hydraulically actuated valve may not be able to control the amount of movement, i.e. “lift,” during valve actuation. In a situation where the valve is actuated when the piston is advancing within the combustion chamber, the valve lift may need to be limited to prevent a collision between the piston and the valve. Such a collision may damage the valve and prevent the valve from properly sealing the gas passageway. This damage may disrupt the operation of the engine.

The engine valve actuator of the present invention solves one or more of the problems set forth above.

SUMMARY OF THE INVENTION

One aspect of the present invention is directed to an engine valve actuator that includes a first piston and a second piston moveably received within the first piston. An actuator body is provided that has a bore defining a first stop and a second stop. The first stop is configured to engage the first piston to limit movement of the first piston at a first preselected distance of travel. The second stop is configured to engage the second piston to limit movement of the second piston at a second preselected distance. A valve element is operatively connected to the second piston to move in response to movement of the second piston.

In another aspect, the present invention is directed to a method of actuating a valve. A first piston having an opening is provided. A second piston is disposed within the opening. The second piston is operatively connected to a valve element. An actuator body having a bore configured to receive the first and second pistons is provided. The bore defines a first stop and a second stop. The first stop is configured to engage the first piston to limit movement of the first piston at a first preselected distance of travel. The second stop is configured to engage the second piston to limit movement of the second piston at a second preselected distance. A pressurized fluid is directed against the first and second pistons to thereby move the valve element.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate exemplary embodiments of the invention and together with the description, serve to explain the principles of the invention. In the drawings: [0012]
FIG. 1[0013] a is a cross-sectional diagrammatic view of an engine valve actuator in accordance with an exemplary embodiment of the present invention;
FIG. 1[0014] b is a top view of an engine valve actuator in accordance with an exemplary embodiment of the present invention;
FIG. 2 is a cross-sectional diagrammatic view of an engine valve actuator in accordance with another exemplary embodiment of the present invention; and [0015]
FIG. 3 is a schematic representation of an engine system having an engine valve actuator in accordance with an exemplary embodiment of the present invention.[0016]

DETAILED DESCRIPTION

An exemplary embodiment of an engine valve actuator is illustrated in FIG. 1[0017] a and is designated generally by reference number 10. As shown, engine valve actuator 10 includes an actuator body 12 having a first surface 13. Actuator body 12 is configured to be attached to a cylinder head 28 of an engine 11. Engine 11 may be any type of internal combustion engine, such as, for example, a diesel engine, a gasoline engine, or a natural gas engine.
[0018] Engine 11 includes an engine block 32 that defines a series of combustion chambers 34 (one of which is illustrated in FIG. 1a). Cylinder head 28 defines a series of passageways 30 (one of which is illustrated in FIG. 1a) that lead to and from each combustion chamber 34. The series of passageways are configured to conduct inlet gas to the combustion chamber and to release exhaust gas from the combustion chamber. For the purposes of the present disclosure, the illustrated passageway 30 may be considered as an exhaust passageway.
As illustrated in FIG. 1[0019] a, actuator body 12 defines a bore 14 that has a first stop 16 and a second stop 18. In the illustrated exemplary embodiment, first stop 16 and second stop 18 are formed in bore 14 as concentric shoulders that have different diameters and are axially spaced apart within bore 14. In other words, first stop 16 and second stop 18 may be generally circular steps that are located at different distances from first surface 13 of actuator body 12. Various alternative configurations of first and second stop 16 and 18 may be readily apparent to one skilled in the art and are considered to be within the scope of the present invention.
As also shown in FIG. 1[0020] a, a first piston 20 and a second piston 22 are disposed within bore 14. First piston 20 may be generally circular and have a first surface 42 and a second surface 46. First piston 20 may also include an opening 38 that is centrally disposed within first piston 20.
[0021] First piston 20 is disposed within bore 14 for reciprocating movement in the directions indicated by arrows 60 and 62. The movement of first piston 20 in the direction indicated by arrow 60 is limited by first stop 16. First piston 20 may move between a first position (as illustrated in FIG. 1a) until first surface 42 of first piston 20 engages first stop 16. The travel distance of first piston 20 is illustrated as distance d₁in FIG. 1a. First piston 20 may include a sealing mechanism (not shown) that is configured to create a seal with the surface of bore 14.
[0022] Second piston 22 is disposed within opening 38 of first piston 20. As illustrated in FIG. 1b, both of first and second pistons 20 and 22 may have a generally circular shape. Second piston 22 may include a sealing mechanism (not shown) that is configured to create a seal with first piston 20.
First and [0023] second pistons 20 and 22 are configured to allow for joint movement of both first and second pistons 20 and 22 relative to bore 14 and for individual movement of second piston 22 relative to first piston 20. In the exemplary embodiment illustrated in FIG. 1a, second piston 22 includes a shoulder 40 that is configured to engage first surface 42 of first piston 20. When first piston 20 moves in the direction of arrow 60, first surface 42 of first piston 20 will engage shoulder 40 of second piston so that first and second pistons 20 and 22 move together. Second piston 22 may, however, move in the direction of arrow 60 independently of first piston 20. Alternative configurations of first and second pistons 20 and 22 that provide the described joint and individual movement may be readily apparent to one skilled in the art and are considered to be within the scope of the present invention.
As also illustrated in FIG. 1[0024] a, second piston 22 includes a contact surface 46 that is configured to engage second stop 18. When second piston 22 is moving in the direction of arrow 60, second stop 18 will engage contact surface 46 to limit the movement of second piston 22. The travel distance of second piston 22 is indicated as d₂in FIG. 1a.
As further illustrated in FIG. 1[0025] a, a valve element 26 is connected to second piston 22 with a shaft 24. It should be noted that valve element 26, second piston 22, and shaft 24 may be constructed as a single unit or may be constructed as separate components that are assembled together. Valve element 26 is configured to engage a valve seat 31 in passageway 30. Valve element 26 may be any device used in an engine to selectively block an intake or exhaust passageway.
A [0026] spring 54 is disposed between cylinder head 28 and shaft 24 and acts to bias valve element 26 into engagement with valve seat 31 to block passageway 30. A locking ring 58 and a washer 56 may be connected to shaft 24. One end of spring 54 acts on washer 56 to bias shaft 24 in the direction of arrow 62 to thereby engage valve element 26 with valve seat 31.
As also shown in FIG. 1[0027] a, actuator body 12 defines a chamber 50, a fluid inlet 52, and a fluid outlet 53. Chamber 50 is configured to receive pressurized fluid through fluid inlet 52. When the pressurized fluid is introduced to chamber 50, the pressurized fluid will exert a force on second surface 44 of first piston 20 and a second surface 48 of second piston 22. The force exerted by the fluid will overcome the opposing force of spring 54 and chamber pressure to move or “lift” valve element 26 away from valve seat 31 to thereby open passageway 30 with combustion chamber 34.
The force exerted by the pressurized fluid on [0028] valve element 26 is dependent upon the contact surface area of first and second pistons 20 and 22 and the pressure of the pressurized fluid. The generated force may be increased by either increasing the pressure of the fluid or by increasing the contact surface area of first and/or second pistons 20 and 22.
The engagement of [0029] first surface 42 of first piston 20 with shoulder 40 of second piston 22 will cause first and second pistons 20 and 22 to move together until first piston 20 engages first stop 16. First stop 16 prevents further movement of first piston 20 in the direction of arrow 60. The pressurized fluid will continue to exert a force on second piston 22, which may move within opening 38 of first piston 20 in the direction of arrow 60.
The amount of movement of [0030] second piston 22 relative to first piston 20 is determined by the distance between first and second stops 16 and 18. The further the distance between first stop 16 and second stop 18, the greater the additional travel of second piston 22. The location of second stop 18 will also control the amount of lift provided to valve element 26. The maximum amount of lift provided to valve element 26 is equal to distance d₂.
Both [0031] first piston 20 and second piston 22 are moved for the first portion of the lift of valve element 26. When first piston 20 engages first stop 16, the fluid required to continue movement of valve element 26 is decreased as only second piston 22 continues to move. Thus, the amount of fluid required to continue movement of valve element 26 is decreased in comparison to the amount of fluid require to initiate movement of first and second pistons 20 and 22.
The combined contact surface area of first and [0032] second pistons 20 and 22 may provide the force required to actuate the valve when, for example, the piston is at or near a top dead center position. Referring to FIG. 1a, when pressurized fluid is introduced to chamber 50, the pressurized fluid will act on the surfaces of both first and second pistons 20 and 22 and will exert a first force on valve element 26. The first force may be great enough to lift valve element 26 under any condition, including when a piston 36 is advancing in combustion chamber 34. After first piston 20 engages first stop 16, the pressurized fluid will act only on second piston 22 to exert a second force on valve element 26. The second force may be great enough to continue to move valve element 26 through the remainder of the lift height.
[0033] Passageway 30 may be closed by releasing the pressurized fluid from chamber 50 through fluid outlet 53. When the pressure in chamber 50 is reduced the force of spring 54 will act on shaft 24 to move first and second pistons 20 and 22 in the direction of arrow 62 until valve element 26 engages valve seat 31.
Another exemplary embodiment of [0034] engine valve actuator 10 is illustrated in FIG. 2. In this alternative exemplary embodiment, actuator body 12 defines a second chamber 64 having a fluid inlet 66 and a fluid exit 68. Second chamber 64 is configured to receive a pressurized fluid through fluid inlet 66. Second chamber 64 is disposed adjacent first piston 20 so that a pressurized fluid introduced to second chamber 64 will exert a force on first piston 20. In addition, chamber 50 is configured so that pressurized fluid introduced to chamber 50 will exert a force on second piston 22.
The configuration illustrated in FIG. 2 may also provide for a variable force valve actuation using fluid having a constant pressure. Pressurized fluid may be introduced to one or both of [0035] chamber 50 and second chamber 64 to create different forces on valve element 26. For example, fluid at a predetermined pressure may be introduced into chamber 50 to act on second piston 22 and exert a first force on valve element 26. Fluid at the same pressure may also be introduced into second chamber 64 to act on first piston 20 and exert a second force on valve element 26. In addition, the pressurized fluid may be introduced into both chamber 50 and second chamber 64 to act on both first and second pistons 20 and 22 to exert a third force on valve element 26. This configuration allows pressurized fluid to selectively act on either first or second pistons 20 and 22 or both first and second pistons 20 and 22. Thus, the magnitude of the force exerted on valve element 26 may be controlled by selectively directing pressurized fluid into one or both of chamber 50 and second chamber 64.
The embodiment illustrated in FIG. 2 may also provide for variable lift heights of [0036] valve element 26. A first preselected lift height may be obtained by introducing pressurized fluid into second chamber 64. The pressurized fluid will act to move first piston 20 into engagement with first stop 16. As no fluid is introduced into chamber 50, second piston 22 will not move relative to first piston 20. Thus, the lift height of valve element 26 will be equivalent to distance d₁. Alternatively, to obtain a second preselected lift height, pressurized fluid may be introduced into chamber 50. The pressurized fluid will act on second piston 22 to move second piston 22 into engagement with second stop 18. Thus, the lift height of valve element 26,will be equivalent to distance d₂. In this manner, different lift heights of valve element 26 may be achieved.
As illustrated in FIG. 3, [0037] engine valve actuator 10 may be connected to a fluid rail 74. Fluid rail 74 may be connected to any pressurized fluid system included in a vehicle. For example, fluid rail 74 may be part of the engine lubrication system, the fuel injection system, or a hydraulic lift system.
As shown, a source of [0038] pressurized fluid 70 draws fluid from a tank 72 and provides pressurized fluid to fluid rail 74. The flow of pressurized fluid to engine valve actuator 10 is governed by a first inlet valve 76 and, for the exemplary embodiment illustrated in FIG. 2, a second inlet valve 80. In addition, a first outlet valve 78 and, for the exemplary embodiment illustrated in FIG. 2, a second outlet valve 82 control the flow of fluid from engine valve actuator 10 to tank 72.
First and [0039] second pistons 20 and 22 may be configured based on the pressure of the fluid within fluid rail 74. For example, if the pressure of the fluid within fluid rail 74 is expected to be relatively low, first and second pistons 20 and 22 may have a large contact surface area. Alternatively, if the pressure of the fluid within fluid rail 74 is expected to be higher, the contact surface area of first and second pistons 20 and 22 may be reduced.
[0040] Engine valve actuator 10 may be used to independently actuate valve element 26. Alternatively, as shown in FIG. 3, engine valve actuator 10 may be used to supplement a cam and cam follower system. As shown, a cam 86 may be affixed to a cam shaft 84, which is, in turn, connected to the engine crankshaft. A cam follower 88 is disposed between cam 86 and a lever 90. Lever 90 is configured to pivot about a pivot point 92. Lever 90 is connected to shaft 24.
When [0041] cam shaft 84 rotates, cam 86 will also rotate, thereby causing cam follower 88 to move in a reciprocal fashion. As cam follower 88 moves up, lever 90 will pivot about pivot point 92 and move shaft 24 of engine valve actuator 10. The movement of shaft 24 causes valve element 26 to lift and open the passageway to the combustion chamber.
If it is desired to open the passageway to the combustion chamber at a time other than the standard timing governed by the crankshaft rotation, pressurized fluid may be introduced to [0042] chamber 50 and/or second chamber 64. In this manner, the engine valve of the present invention may be coupled with a conventional cam and cam follower arrangement.

Industrial Applicability

As will be apparent from the foregoing description, the present disclosure provides a variable force [0043] engine valve actuator 10. The disclosed engine valve actuator 10 creates a variable force to lift a valve element 26 based on the input of pressurized fluid. In addition, the engine valve actuator 10 may provide for variable lift heights of the valve element 26. Thus, the present disclosure provides a valve actuation system that has a high degree of flexibility in valve timing that allows for precise movement of the valve element 26. These benefits are accomplished without the addition of significant costly modifications and/or parts.
The disclosed [0044] engine valve actuator 10 may be implemented into any type of internal combustion engine 11. Incorporation of the disclosed engine valve actuator 10 into an internal combustion engine 11 may allow for an increase in the efficiency of the engine 11. As will be recognized by one skilled in the art, the efficiency of an engine 11 may be improved by actuating one of more of the engine valves 26 at different points in the operating cycle of the engine 11 based on the vehicle operating conditions.
However, achieving these efficiency gains may require that an [0045] engine valve 26 be actuated when the respective combustion chamber 34 is under compression. For example, a properly timed valve actuation during the braking, or slowing, process of the vehicle may improve the efficiency of the engine 11. This efficiency gain may be realized by actuating an engine exhaust valve at the end of the compression stroke of the engine 11 to exhaust the compressed gas instead of inducing combustion. This results in the engine 11 expending energy to compress the gas in the combustion chamber 34, instead of generating energy during combustion. Thus, the compression of the gas in the combustion chamber 34 may be used to help slow the vehicle. One skilled in the art may recognize additional opportunities, such as, for example, the Miller cycle, where engine efficiency gains may be realized by actuating the engine valves at various points during the operation cycle of an internal combustion engine.
The disclosed [0046] engine valve actuator 10 may generate an initial actuation force that is great enough to overcome the force of the compression within the combustion chamber 34. Once the valve has moved through a first portion of the lift distance, the force on the valve element 26, and the pressurized fluid requirements of the engine valve actuator 10, may be reduced. This provides the flexibility required to actuate the valve under a variety of engine operating conditions. Thus, incorporation of the engine valve actuator 10 into an internal combustion engine may allow the performance of the engine to be optimized.
It will be apparent to those skilled in the art that various modifications and variations can be made in the disclosed engine valve actuator. Other embodiments may be apparent to those skilled in the art from consideration of the specification and practice of the engine valve actuator disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope being indicated by the following claims and their equivalents. [0047]

Claims

What is claimed is:

1. An engine valve actuator, comprising:

a first piston;

a second piston moveably received within the first piston;

an actuator body having a bore defining a first stop and a second stop, the first stop configured to engage the first piston to limit movement of the first piston at a first preselected distance of travel, the second stop configured to engage the second piston to limit movement of the second piston at a second preselected distance; and

a valve element operatively connected to the second piston to move in response to movement of the second piston.

2. The engine valve actuator of claim 1, wherein the first piston has a first contact surface area and the second piston has a second contact surface area that is smaller than the first contact surface area.

3. The engine valve actuator of claim 1, wherein the actuator body defines a first chamber operatively associated with the first piston and a second chamber operatively associated with the second piston, each of the first and second chambers configured to receive a pressurized fluid.

4. The engine valve actuator of claim 1, wherein the first piston includes an opening and the second piston is slidably disposed within the opening.

5. The engine valve actuator of claim 4, wherein the second piston includes a shoulder configured to selectively engage the first piston adjacent the opening.

6. The engine valve actuator of claim 5, wherein the actuator body defines a chamber configured to receive a pressurized fluid such that the pressurized fluid acts on the first piston and the second piston.

7. The engine valve actuator of claim 1, wherein the first preselected distance is less than the second preselected distance.

8. A method of actuating a valve, comprising:

providing a first piston having an opening;

disposing a second piston within the opening, the second piston operatively connected to a valve element;

providing an actuator body having a bore configured to receive the first and second pistons and defining a first stop and a second stop, the first stop configured to engage the first piston to limit movement of the first piston at a first preselected distance of travel, the second stop configured to engage the second piston to limit movement of the second piston at a second preselected distance; and

directing a pressurized fluid against at least one of the first and second pistons to thereby move the valve element.

9. The method of claim 8, wherein the first piston and second piston move together until the first piston engages the first stop.

10. The method of claim 8, wherein the second piston moves independently of the first piston.

11. An engine, comprising:

an engine block defining at least one chamber;

a cylinder head defining at least one passageway leading to the at least one chamber;

at least one valve actuator having a first piston;

a second piston slidably received within the first piston; and

a valve element operatively connected to the second piston and disposed adjacent the at least one opening in the cylinder head, the valve element moveable between an open position and a closed position where the valve element blocks the opening in the cylinder head.

12. The engine of claim 11, wherein the actuator body defines a chamber operatively associated with the first and second pistons and the engine further includes a source of pressurized fluid operable to supply a pressurized fluid to the chamber to move the first and second pistons together until the first piston engages the first stop.

13. The engine of claim 12, further including a valve configured to control the rate of fluid flow into the chamber.

14. The engine of claim 11, wherein the actuator body defines a first chamber operatively associated with the first piston and a second chamber operatively associated with the second piston and the engine further includes a source of pressurized fluid operable to selectively supply a pressurized fluid to at least one of the first and second chambers.

15. The engine of claim 14, further including a first valve configured to control the rate of fluid flow from the source of pressurized fluid into the first chamber and a second valve configured to control the rate of fluid flow from the source of pressurized fluid into the second chamber.

16. The engine of claim 11, further including a spring acting to bias the valve element into the closed position.

17. The engine of claim 11, wherein the first piston has a first contact surface area and the second piston has a second contact surface area, the second contact surface area being less than the first surface area.

18. The engine of claim 11, wherein the first piston includes an opening and the second piston is disposed within the opening, the second piston including a shoulder configured to engage the first piston adjacent the opening.

19. The engine of claim 11, wherein the first preselected distance is less than the second preselected distance.

20. The engine of claim 11, further including a cam shaft having a cam affixed thereto and a cam follower operatively engaged with the valve element to actuate the valve element as the cam shaft rotates.

21. A method of actuating a valve, comprising:

providing a first piston having an opening;

directing pressurized fluid against the first piston to engage the first piston with the second piston and move the valve element a first preselected distance; and

directing pressurized fluid against the second piston to move the valve element a second preselected distance.