Patent Application
20120055426
The present disclosure relates to engine valvetrain assemblies.
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.
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.
The drawings described herein are for illustrative purposes only and are not intended to limit the scope of the present disclosure in any way.
Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings.
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
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 (
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.
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 (
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.
