US20120055426A1

US20120055426A1 - Engine including variable valve lift mechanism

Info

Publication number: US20120055426A1
Application number: US12/877,550
Authority: US
Inventors: Clyde A. Bulloch
Original assignee: GM Global Technology Operations LLC
Current assignee: GM Global Technology Operations LLC
Priority date: 2010-09-08
Filing date: 2010-09-08
Publication date: 2012-03-08
Also published as: CN102400725A; DE102011111675A1

Abstract

An engine assembly may include an engine structure, an engine valve, a valve lift mechanism, and first and second camshafts. The engine structure may define a combustion chamber and a port in communication with the combustion chamber. The engine valve may be supported by the engine structure and displaceable between an open position where the port is in communication with the combustion chamber and a closed position to isolate the port from communication with the combustion chamber. The valve lift mechanism may be engaged with the engine valve. The first camshaft may be rotationally supported by the engine structure and may include a first cam lobe engaged with the valve lift mechanism. The second camshaft may be rotationally supported by the engine structure and may include a second cam lobe engaged with the valve lift mechanism.

Description

FIELD

The present disclosure relates to engine valvetrain assemblies.

BACKGROUND

This section provides background information related to the present disclosure which is not necessarily prior art.
Engines typically include a camshaft to actuate intake and/or exhaust valves. The camshaft may include cam lobes engaged with a valve lift mechanism to open and the close the valves. The timing of valve opening and/or closing may be varied by a cam phaser coupled to the camshaft.

SUMMARY

An engine assembly may include an engine structure, an engine valve, a valve lift mechanism, and first and second camshafts. The engine structure may define a combustion chamber and a port in communication with the combustion chamber. The engine valve may be supported by the engine structure and displaceable between an open position where the port is in communication with the combustion chamber and a closed position to isolate the port from communication with the combustion chamber. The valve lift mechanism may be engaged with the engine valve. The first camshaft may be rotationally supported by the engine structure and may include a first cam lobe engaged with the valve lift mechanism. The second camshaft may be rotationally supported by the engine structure and may include a second cam lobe engaged with the valve lift mechanism.
A method of actuating an engine valve may include displacing the engine valve from a closed position to an open position at a first valve lift profile to provide communication between an engine port and an engine combustion chamber. The displacing may include a first cam lobe on a first camshaft and a second cam lobe on a second camshaft engaging a valve lift mechanism engaged with the engine valve. The first camshaft may be rotated relative to the second camshaft. The engine valve may be displaced from the closed position to the open position at a second valve lift profile different than the first valve lift profile after the first camshaft is rotated relative to the second camshaft via engagement between the first and second cam lobes and the valve lift mechanism.
Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings described herein are for illustrative purposes only and are not intended to limit the scope of the present disclosure in any way.

FIG. 1 is a schematic fragmentary section view of an engine assembly including first and second camshafts engaged with a valve lift mechanism in a first position according to the present disclosure;

FIG. 2 is a schematic illustration of the first and second camshafts and the valve lift mechanism shown FIG. 1 in a second position;

FIG. 3 is a schematic illustration of the first and second camshafts and the valve lift mechanism shown FIG. 1 in a third position;

FIG. 4 is a schematic illustration of the first and second camshafts and the valve lift mechanism shown FIG. 1 in a fourth position; and

FIG. 5 is a graphical illustration of the range of lift profiles provided by the present disclosure.

Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings.

DETAILED DESCRIPTION

Examples of the present disclosure will now be described more fully with reference to the accompanying drawings. The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses.
Example embodiments are provided so that this disclosure will be thorough, and will fully convey the scope to those who are skilled in the art. Numerous specific details are set forth such as examples of specific components, devices, and methods, to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, that example embodiments may be embodied in many different forms and that neither should be construed to limit the scope of the disclosure. In some example embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail.
When an element or layer is referred to as being “on,” “engaged to,” “connected to” or “coupled to” another element or layer, it may be directly on, engaged, connected or coupled to the other element or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly engaged to,” “directly connected to” or “directly coupled to” another element or layer, there may be no intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.). As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.
Although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms may be only used to distinguish one element, component, region, layer or section from another region, layer or section. Terms such as “first,” “second,” and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the example embodiments.
An exemplary engine assembly 10 is schematically illustrated in FIG. 1 and may include an engine structure 12, first and second camshafts 14, 16 rotationally supported on the engine structure 12, a first cam phaser 18 coupled to the first camshaft 14, a second cam phaser 20 coupled to the second camshaft 16, an engine valve 22 and a valve lift mechanism 24 engaged with the first and second camshafts 14, 16 and the engine valve 22. In the present non-limiting example, the engine assembly 10 is illustrated as an overhead camshaft engine where the engine structure 12 is a cylinder head. However, it is understood that the present disclosure is not limited to overhead camshaft arrangements and applies equally to a variety of other engine configurations as well, such as cam-in-block (or pushrod) engines. It is also understood that the engine valve 22 may be an exhaust valve or an intake valve.
The first camshaft 14 may include a first cam lobe 26 engaged with the valve lift mechanism 24 and the second camshaft 16 may include a second cam lobe 28 engaged with the valve lift mechanism 24. The first cam lobe 26 may include a first base circle region 30 and a first peak region 32 defining a first peak 34. Similarly, the second cam lobe 28 may include a second base circle region 36 and a second peak region 38 defining a second peak 40.
The first and second camshafts 14, 16 may be laterally offset from one another (non-coaxial) and may extend generally parallel to one another. The first and second cam lobes 26, 28 may be laterally offset from one another and longitudinally aligned to one another. More specifically, the second cam lobe 28 may be radially spaced from an outer periphery of the first cam lobe 26.
The valve lift mechanism 24 may include a pivot arm 42 defining a first end 44 engaged with the first cam lobe 26, a second end 46 engaged with the second cam lobe 28 and a pivot 50 located between the first and second ends 44, 46. The valve lift mechanism 24 may define a body extending laterally between the first and second ends 44, 46. Therefore, the first and second ends 44, 46 may form lateral ends of the valve lift mechanism 24. The first end 44 may include a first roller member 52 engaged with the first cam lobe 26 and the second end 46 may include a second roller member 54 engaged with the second cam lobe 28. The engine valve 22 may be pivotally coupled to the valve lift mechanism 24 at the pivot 50 and may be displaced from a closed position (not shown) to an open position (FIG. 1) against the force of a valve spring 58 by the first and second cam lobes 26, 28 to provide communication between an engine port 60 defined in the engine structure 12 and an engine combustion chamber 62.
FIGS. 1-4 illustrate four lift conditions (lift profiles) provided by the engine valve 22 and FIG. 5 graphically illustrates each of the lift profiles. In FIG. 5, the Y-axis illustrates valve lift and the X-axis illustrates crank angle. The lift duration and height of the engine valve 22 may be controlled by advancing and retarding the first and second cam lobes 26, 28 via the first and second cam phasers 18, 20. The first and second camshafts 14, 16, and therefore first and second cam lobes 26, 28, may be rotated relative to one another. More specifically, the first camshaft 14 may be rotated from a first position (fully retarded) to a second position (fully advanced) in a first rotational direction (R1) of the first camshaft 14. The first camshaft 14 may additionally be displaced to any position between the first and second positions.
Similarly, the second camshaft 16 may be rotated from a third position (fully retarded) to a fourth position (fully advanced) in a second rotational direction (R2) of the second camshaft 16. The second camshaft 16 may additionally be displaced to any position between the third and fourth positions. While the first and second rotational directions (R1, R2) are illustrated as being opposite one another, it is understood that the first and second camshafts 14, 16 may alternatively rotate in the same direction.
FIG. 1 illustrates a maximum valve lift height condition, graphically illustrated by curve (C1) in FIG. 5. The maximum valve lift height condition may correspond to a minimum valve lift duration condition. The first peak 34 of the first cam lobe 26 may be engaged with the valve lift mechanism 24 when the second peak 40 of the second cam lobe 28 is engaged with valve lift mechanism 24 when the first camshaft 14 is in the first position and the second camshaft 16 is in the fourth position. As discussed above, the first position of the first camshaft 14 may provide a fully retarded position for the first cam lobe 26 and the fourth position of the second camshaft 16 may provide a fully advanced position for the second cam lobe 28. Therefore, the lift profile (curve (C1)) may define the maximum valve lift height of the engine valve 22 when the first cam lobe 26 is in the fully retarded position and the second cam lobe 28 is in the fully advanced position.
FIG. 2 illustrates a maximum advanced condition for engine valve opening, graphically illustrated by curve (C2) in FIG. 5. During the maximum advanced condition, the first camshaft 14 may be in the second position and the second camshaft 16 may be in the third position. Therefore, the lift profile (curve (C2)) may define a maximum advanced condition for opening of the engine valve 22 when the first cam lobe 26 is in a fully advanced position and the second cam lobe 28 is in a fully advanced position. The second peak 40 of the second cam lobe 28 may be rotationally offset from the valve lift mechanism 24 when the first peak 34 of the first cam lobe 26 is engaged with the valve lift mechanism 24 when the first camshaft 14 is in the first position and the second camshaft 16 is in the third position. The maximum advanced condition may generally provide an earlier valve opening event relative to nominal operating conditions. The peak engine valve lift during the maximum advanced condition may occur earlier than a peak engine valve lift occurring during the maximum valve lift height condition discussed above.
FIG. 3 illustrates a maximum retarded condition for engine valve opening, graphically illustrated by curve (C3) in FIG. 5. During the maximum retarded condition, the first camshaft 14 may be in the second position and the second camshaft 16 may be in the third position. Therefore, the lift profile (curve (C3)) may define a maximum retarded condition for opening the engine valve 22 when the first cam lobe 26 is in the fully retarded position and the second cam lobe 28 is in the fully retarded position. The first peak 34 of the first cam lobe 26 may be rotationally offset from the valve lift mechanism 24 when the second peak 40 of the second cam lobe 28 is engaged with the valve lift mechanism 24 when the first camshaft 14 is in the second position and the second camshaft 16 is in the fourth position. The maximum retarded condition may generally provide delayed valve opening event relative to nominal operating conditions. The peak engine valve lift during the maximum retarded condition may occur later than a peak engine valve lift occurring during the maximum valve lift height condition discussed above.
FIG. 4 illustrates a maximum valve lift duration condition, graphically illustrated by curve (C4) in FIG. 5 (minimum height). The maximum valve lift duration condition may correspond to a minimum valve lift height condition. The first peak 34 of the first cam lobe 26 and the second peak 40 of the second cam lobe 28 may be rotationally out of phase with one another during the maximum valve lift duration condition. More specifically, the first camshaft 14 may be in the second position and the second camshaft 16 may be in the third position during the maximum valve lift duration condition. As discussed above, the second position of the first camshaft 14 may provide a fully advanced position for the first cam lobe 26 and the third position of the second camshaft 16 may provide a fully retarded position for the second cam lobe 28. Therefore, the lift profile (curve (C4)) may define the maximum opening duration of the engine valve 22 when the first cam lobe 26 is in the fully advanced position and the second cam lobe 28 is in the fully retarded position.
The valve lift mechanism 24 provides for variation of engine valve lift height, duration and timing of engine valve opening by adjusting the phase of the first and second cam lobes 26, 28 relative to one another without the use of a hydraulically actuated lift mechanism. During operation, the engine valve 22 may be displaced from the closed position (not shown) to the open position (FIG. 1) at a first valve lift profile to provide communication between the engine port 60 and the engine combustion chamber 62. The displacing may include the first cam lobe 26 on the first camshaft 14 and the second cam lobe 28 on the second camshaft 16 engaging the valve lift mechanism 24 engaged with the engine valve 22.
The engine valve 22 may be displaced from the closed position to the open position at a second valve lift profile different than the first valve lift profile after rotating the first camshaft 14 relative to the second camshaft 16 via engagement between the first and second cam lobes 26, 28 and the valve lift mechanism 24. Rotating the first camshaft 14 relative to the second camshaft 16 may include actuating the first cam phaser 18 coupled to the first camshaft 14. The second camshaft 16 may also be rotated relative to the first camshaft 14 via the second cam phaser 20 coupled to the second camshaft 16.
The first valve lift profile may include the first peak 34 of the first cam lobe 26 being engaged with the valve lift mechanism 24 when the second peak 40 of the second cam lobe 28 is engaged with the valve lift mechanism 24. The second valve lift profile may include the first peak 34 of the first cam lobe 26 being rotationally offset from the valve lift mechanism 24 when the second peak 40 of the second cam lobe 28 is engaged with the valve lift mechanism 24.
The engine valve 22 may be displaced to a maximum valve lift height when the first cam lobe 26 is in a fully retarded position and the second cam lobe 28 is in a fully advanced position. A maximum retarded condition for displacement of the engine valve 22 may be defined when the first cam lobe 26 is in a fully retarded position and the second cam lobe 28 is in a fully retarded position. A maximum advanced condition for displacement of the engine valve 22 may be defined when the first cam lobe 26 is in a fully advanced position and the second cam lobe 28 is in a fully advanced position. A maximum opening duration of the engine valve 22 may be defined when the first cam lobe 26 is in a fully advanced position and the second cam lobe 28 is in a fully retarded position.
Displacing the engine valve 22 from the closed position to the open position at the second valve lift profile may include the first cam lobe 26 being engaged with the first end 44 of the valve lift mechanism 24 and the second cam lobe 28 being engaged with the second end 46 of the valve lift mechanism 24. The engagement between the first and second cam lobes 26, 28 and the valve lift mechanism 24 may rotationally displace the valve lift mechanism 24 about the pivot 50 located between the first and second ends 44, 46 of the valve lift mechanism 24 to provide the second valve lift profile.

Claims

What is claimed is:

1. An engine assembly comprising:

an engine structure defining a combustion chamber and a port in communication with the combustion chamber;

an engine valve supported by the engine structure and displaceable between an open position where the port is in communication with the combustion chamber and a closed position to isolate the port from communication with the combustion chamber;

a valve lift mechanism engaged with the engine valve;

a first camshaft rotationally supported by the engine structure and including a first cam lobe engaged with the valve lift mechanism; and

a second camshaft rotationally supported by the engine structure and including a second cam lobe engaged with the valve lift mechanism.

2. The engine assembly of claim 1, further comprising a first cam phaser coupled to the first camshaft and operable to rotate the first camshaft between first and second positions relative to the second camshaft to vary a lift profile of the engine valve.

3. The engine assembly of claim 2, wherein a first peak of the first cam lobe is engaged with the valve lift mechanism when a second peak of the second cam lobe is engaged with valve lift mechanism when the first camshaft is in the first position.

4. The engine assembly of claim 3, wherein the first peak of the first cam lobe is rotationally offset from the valve lift mechanism when the second peak of the second cam lobe is engaged with valve lift mechanism when the first camshaft is in the second position.

5. The engine assembly of claim 2, further comprising a second cam phaser coupled to the second camshaft and operable to rotate the second camshaft relative to the first camshaft.

6. The engine assembly of claim 5, wherein the lift profile defines a maximum valve lift height of the engine valve when the first cam lobe is in a fully retarded position and the second cam lobe is in a fully advanced position.

7. The engine assembly of claim 6, wherein the lift profile defines a maximum retard condition for opening of the engine valve when the first cam lobe is in a fully retarded position and the second cam lobe is in a fully retarded position.

8. The engine assembly of claim 6, wherein the lift profile defines a maximum advanced condition for opening of the engine valve when the first cam lobe is in a fully advanced position and the second cam lobe is in a fully advanced position.

9. The engine assembly of claim 6, wherein the lift profile defines a maximum opening duration of the engine valve when the first cam lobe is in a fully advanced position and the second cam lobe is in a fully retarded position.

10. The engine assembly of claim 2, wherein the valve lift mechanism includes a pivot arm defining a first end engaged with the first cam lobe, a second end engaged with the second cam lobe and a pivot located between the first and second ends, the valve lift profile being varied by the first and second cam lobes adjusting a rotational orientation of the valve lift mechanism about the pivot.

11. A method comprising:

displacing an engine valve from a closed position to an open position at a first valve lift profile to provide communication between an engine port and an engine combustion chamber, the displacing including a first cam lobe on a first camshaft and a second cam lobe on a second camshaft engaging a valve lift mechanism engaged with the engine valve;

rotating the first camshaft relative to the second camshaft; and

displacing the engine valve from the closed position to the open position at a second valve lift profile different than the first valve lift profile after the rotating via engagement between the first and second cam lobes and the valve lift mechanism.

12. The method of claim 11, wherein the rotating includes actuating a cam phaser coupled to the first camshaft.

13. The method of claim 12, wherein the first valve lift profile includes a peak of the first cam lobe being engaged with the valve lift mechanism when a peak of the second cam lobe is engaged with the valve lift mechanism.

14. The method of claim 13, wherein the second valve lift profile includes the peak of the first cam lobe being rotationally offset from the valve lift mechanism when the peak of the second cam lobe is engaged with the valve lift mechanism.

15. The method of claim 12, further comprising rotating the second camshaft relative to the first camshaft via a second cam phaser coupled to the second camshaft.

16. The method of claim 15, wherein the engine valve is displaced to a maximum valve lift height when the first cam lobe is in a fully retarded position and the second cam lobe is in a fully advanced position.

17. The method of claim 16, wherein a maximum retard condition for displacement of the engine valve is defined when the first cam lobe is in a fully retarded position and the second cam lobe is in a fully retarded position.

18. The method of claim 16, wherein a maximum advanced condition for displacement of the engine valve is defined when the first cam lobe is in a fully advanced position and the second cam lobe is in a fully advanced position.

19. The method of claim 16, wherein a maximum opening duration of the engine valve is defined when the first cam lobe is in a fully advanced position and the second cam lobe is in a fully retarded position.

20. The method of claim 11, wherein the displacing the engine valve from the closed position to the open position at the second valve lift profile includes the first cam lobe being engaged with a first end of the valve lift mechanism and the second cam lobe being engaged with a second end of the valve lift mechanism, the engagement between the first and second cam lobes and the valve lift mechanism rotationally displacing the valve lift mechanism about a pivot located between the first and second ends of the valve lift mechanism to provide the second valve lift profile.