FIELD

[0001] The present disclosure relates to a valve actuation system providing variable valve lift. BACKGROUND

[0002] Variable valve lift systems of several configurations are known in the art. One such system utilizes a camshaft with a plurality of cam lobes that can be selectively shifted into a valve actuation path with a valve to thereby provide two or more discrete maximum valve lift settings. Another such system employs a single cam lobe but selectively places a component into the valve actuation path to vary the maximum valve lift between two or more discrete maximum valve lift settings. While such variable valve lift systems are satisfactory for their intended purposes, there remains a need in the art for an improved variable valve lift system. SUMMARY

[0003] This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features.

[0004] In one form, the present teachings provide a valve actuation system for translating a valve of an internal combustion engine along a valve axis. The valve actuation system includes an actuating element, a cam lobe and a pair of followers. The actuating element has an output portion that is movable about an output axis. The cam lobe is rotatable about a rotary axis that is transverse to the output axis. The cam lobe has a base portion and a lift portion. The cam lobe has two contact surfaces that are spaced axially apart. At least a portion of each of the contact surfaces is contoured so that a distance between the rotary axis and points on each of the contact surfaces that are spaced apart along the rotary axis is not constant. The followers are disposed between the cam lobe and the actuating element. Each of the followers is configured to engage a corresponding one of the contact surfaces. The followers are movable along a follower axis that is parallel to the rotary axis between a first position, in which the followers are spaced apart from one another by a first distance, and a second position in which the followers are spaced apart from one another by a second distance that is less than the first distance. Contact between the cam lobe, the followers and the first actuating element during rotation of the cam lobe about the rotary axis causes corresponding movement of the output portion of the first actuating element.

[0005] 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.

DRAWINGS

[0006] The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure.

[0007] Figure 1 is a section view of an exemplary valve actuation system constructed in accordance with the teachings of the present disclosure;

[0008] Figure 2 is a perspective view of a portion of the valve actuation system of Figure 1 , illustrating a cam lobe and an actuating element in more detail;

[0009] Figure 3 is a side elevation view of the cam lobe;

[0010] Figure 4 is a perspective view of the actuating element;

[0011] Figure 5 is a side elevation view of a portion of the actuating element;

[0012] Figure 6 is a top plan view of a portion of the actuating element;

[0013] Figure 7 is an enlarged view of a portion of Figure 1 , illustrating a portion of the actuating element in more detail;

[0014] Figure 8 is a top plan view of a second valve actuation system constructed in accordance with the teachings of the present disclosure;

[0015] Figure 9 is a perspective view of a portion of the valve actuation system of Figure 8; [0016] Figure 10 is an elevation view of a portion of the valve actuation system of Figure 8;

[0017] Figure 1 1 is a perspective view of a portion of the valve actuation system of Figure 8, illustrating an exemplary linear motor for selectively adjusting the effective lift of the cam lobe;

[0018] Figures 12 and 13 are alternative configurations of a rotary cam of the linear motor of Figure 1 1 that depict a step-less or infinitely variable configuration (Fig. 12) and a configuration that employs a plurality of discrete steps (Fig. 13);

[0019] Figure 14 is a perspective view of an alternately configured actuating element;

[0020] Figure 15 is a section view through a portion of the actuating element of Figure 14;

[0021] Figures 16 and 17 depict portions of valve actuation systems constructed in accordance with the teachings of the present disclosure that use further types of actuating elements; and

[0022] Figure 18 is a perspective view of the actuating element that is employed in the valve actuation system of Figure 17.

[0023] Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings.

DETAILED DESCRIPTION

[0024] With reference to Figure 1 of the drawings, a valve actuation system constructed in accordance with the teachings of the present disclosure is generally indicated by reference numeral 10. The valve actuation system 10 is configured to translate a valve 12 (Fig. 2) of an internal combustion engine (not shown) along a valve axis VA. The valve actuation system 10 can include a cam lobe 14, an actuating element 16, a pair of followers 18 and an actuation motor 20.

[0025] In Figures 1 through 3, the cam lobe 14 is mounted to a structure (not shown) that can be mounted to a cylinder head (not shown) of an internal combustion engine (not shown) for rotation about a rotary axis 30. The cam lobe 14 has a base portion 32 and a lift portion 34. As will be appreciated, the base portion 32 is formed about a base circle 38 and is configured to interact with the remainder of the valve actuation system 10 in a manner that permits the valve 12 to be maintained in a closed position. As will also be appreciated, the lift portion 34 extends radially outward from the base circle 38 and is configured to interact with the remainder of the valve actuation system 10 in a manner that permits the valve 12 to be translated along the valve axis VA from a first or closed position to a second position, such as a fully open position, and then back to the first position. The cam lobe 14 can include first and second contact surfaces 40 and 42, respectively, that can be spaced axially apart. At least a portion 44 of each of the first and second contact surfaces 40 and 42 is contoured in a manner in which at any given angular location on the lift portion 34, the dimension between the rotary axis 30 and points on the contoured portion 44 of each of the first and second contact surfaces 40 and 42 that are spaced axially apart along the rotary axis 30 different. For example, the dimension between the rotary axis 30 and points on the contoured portion 44 of each of the first and second contact surfaces 40 and 42 can increase with increasing distance from an associated axial end of the cam lobe 14 (i.e., the dimension increases with decreasing distance toward the other one of the first and second contact surfaces 40 and 42). In the particular example provided, the rate of change of the contoured portion 44 across the width of each of the first and second contact surfaces 40 and 42 on the lift portion 34 of the cam lobe 14 at a given rotational position varies in a constant manner (i.e., a manner that is proportional to a distance between two points on one of the first and second contact surfaces 40 and 42). Alternatively, the rate of change could vary in a non-constant manner, such as exponentially, quadratically or geometrically.

[0026] In Figures 1 , 4 and 5, the actuating element 16 can be any type of structure that is employed to transmit movement between the cam lobe 14 and the valve 12. For example, the actuating element 16 could be a rocker arm (not shown) or a bucket tappet (not shown). In the particular example provided, the actuating element 16 is a finger follower 50 having a lifter mount 52, which is configured to engage a hydraulic lifter 54 (Fig. 2), and an output portion 56 that is configured to engage the valve 12 and drive the valve 12 about an output axis, which is coincident with the valve axis VA. In the example provided, the output portion 56 comprises a valve mount. The finger follower 50 further comprises a follower holder 60 into which the followers 18 are received. In the example provided, the followers 18 are hardened, spherical balls and the follower holder 60 is a trough or well 62. The well 62 can matingly conform to the spherical surfaces of the followers 18 in a manner that permits movement of the followers 18 along a follower axis FA in a direction that is parallel to the rotary axis 30.

[0027] The followers 18 can be retained in the well 62 in any desired manner. For example, a clip 64 can be fixedly coupled to the actuating element 16 to retain the followers 18 in the well 62. With specific reference to Figures 4 through 6, the actuating element 16 can include a pair of ribs 66 that can border opposite sides of the well 62, the clip 64 can include a clip body 68 and a pair of flanges 70 that can extend generally perpendicular to the clip body 68, and the clip 64 can be secured to the ribs 66 in any desired manner, such as staking or welding the flanges 70 of the clip 64 to the ribs 66. The clip body 68 can define a slotted follower aperture 72 that can extend along an axis that can be parallel to the rotary axis 30. The follower aperture 72 can be sized smaller in width than the diameter of the followers 18. Configuration in this manner retains the followers 18 between the actuating element 16 and the clip 64 while permitting the followers 18 to extend through the clip 64 and roll in the well 62 in directions that are parallel to the rotary axis 30.

[0028] With reference to Figures 1 , 4 and 7, the actuating element 16 can include one or more elements that can be employed to bias one or more of the followers 18 in a predetermined direction in the well 62. In the particular example provided, the actuating element 16 includes a spring 80 and a contact member 82. The spring 80 is received in a bore 86 that is formed in the well 62. The contact member 82 can be received in the bore 86 and can include one or more exterior surfaces that can engage the followers 18. In the example provided, the contact member 82 is a spherical ball that is driven into engagement with the followers 18 to thereby drive the followers 18 apart from one another. It will be appreciated that the contact member 82 could be formed as an elongated pin and that the portion of the exterior surface of the contact member 82 that contacts the followers 18 could be defined in whole or in part by a spherical radius or a frusto-conically shaped surface.

[0029] Returning to Figure 1 , the actuation motor 20 is configured to control the position of the followers 18 relative to the first and second contact surfaces 40 and 42 on the cam lobe 14. In the particular example illustrated, the actuation motor 20 comprises a pair of linear motors 100, each of which having a rotary input member 102, a rotary (adjustment) cam 104, an adjustment or cam follower 106 and an output member 108. The rotary input members 102 can be rotatably disposed about axes that are parallel to the rotary axis 30 of the cam lobe 14 but which are offset from a longitudinal axis of the well 62. In the example provided, the rotary cam 104 has an axial end face 1 10 that is conforms to a plane that intersects the rotational axis of the rotary cam 104 at a non-perpendicular angle (as when a plane cuts through a right circular cylinder to form an ellipse).

[0030] Each rotary cam 104 can be fixedly coupled to its associated rotary input member 102 for common rotation. The output members 108 can be cup-shaped structures having an axial wall 1 14 and a circumferentially extending wall 1 16 that cooperate to define an internal cavity 1 18 into which the cam follower 106 is received. The output members 108 can optionally be installed into a structure 120 to which the valve actuation system 10 is coupled, so as to be guided for sliding movement along an axis that is coincident with or parallel to the longitudinal axis of the well 62. In the example provided, a through bore 124 is formed in the structure 120 and is sized to slidably receive the circumferentially extending wall 1 16 therein. The output members 108 can extend through the through bore 124 and can be disposed on opposite sides of the actuating element 16 such that a corresponding one of the followers 18 is disposed in abutment with an exterior side of the axial wall 1 14. An associated one of the cam followers 18 can be received in the internal cavity 1 18 and can abut an interior side of the axial wall 1 14 (in addition to abutting the axial end face 1 10 of the rotary cam 104).

[0031] It will be appreciated that rotation of each of the rotary cams 104 (via the rotary input members 102) through a predetermined angle in a first direction can cause corresponding movement of an associated one of the output members 108 in direction toward the other one of the output members 108 to thereby overcome the force that is applied to the followers 18 by the spring 80 and the contact member 82 to urge an associated one of the followers 18 toward the other one of the followers 18. It will also be appreciated that further rotation of each rotary cam 104 in the first direction within predefined limits, or in a second, opposite direction through the predetermined angle can permit the output member 108 and the associated one of the followers 18 to be driven away from the other one of the output members 108 by the force that is applied to the followers 18 via the spring 80 and the contact member 82.

[0032] During operation, the cam lobe 14 will rotate about the rotary axis 30 with the first and second contact surfaces 40 and 42 in contact with the followers 18 such that each of the followers 18 contacts an associated one of the first and second contact surfaces 40 and 42 over a path or line of contact that circumscribes the cam lobe 14. The actuation motor 20 can be operated to alter the points at which the followers 18 contact the first and second contact surfaces 40 and 42 (i.e., to move the lines of contact along the rotary axis 30) to thereby vary the amount by which the output portion 56 of the actuating element 16 moves along the valve axis VA. For example, the actuation motor 20 can be operated to position the output members 108 in a location that permits the followers 18 to be moved into the first position (which is depicted in phantom line) or in another location that permits the followers 18 to be moved into the second position (which is depicted in solid line).

[0033] When the followers 18 are positioned in the first position, the lines of contact 150a are axially outboard of the lines of contact 150b when the followers 18 are positioned in the second position. Due to the contoured configuration of the first and second contact surfaces 40 and 42 on the lift portion 34, the distance between the rotary axis 30 and the contoured portion of the first and second contact surfaces 40 and 42 at all points on the outer lines of contact 150a that are on the lift portion 34 of the cam lobe 14 is different (e.g., smaller) than the distance between the rotary axis 30 and the tapered portion of the first and second contact surfaces 40 and 42 on the inner lines of contact 150b that are on the lift portion 34 of the cam lobe 14. Accordingly, the maximum "valve lift" produced by the cam lobe 14 (which corresponds to the maximum amount by which the output portion 56 of the actuating element 16 is moved along the valve axis VA) grows relatively larger as the followers 18 are moved from the first position toward the second position. It will be appreciated that the length of the line of contact 150a about the perimeter of the cam lobe 14 is different (i.e., smaller in the example provided) than the length of the line of contact 150b about the perimeter of the cam lobe 14.

[0034] It will be appreciated from this disclosure that the valve actuation system 10 can be configured to vary maximum valve lift between two or more values. Moreover, it will be appreciated that the valve actuation system 10 can be configured to cause no valve lift (i.e., the maximum valve lift is zero) during rotation of the cam lobe 14 to effectively de-activate an associated engine cylinder.

[0035] With reference to Figures 8 through 12, a second valve actuation system 10a constructed in accordance with the teachings of the present disclosure is shown. The valve actuation system 10a is generally similar to the valve actuation system 10 (Fig. 1 ) except that a different actuation motor is employed. In the example illustrated, the actuation motor 20a comprises a single linear motor 100a having a rotary input member 102a, a pair of rotary cams 104a, a pair of cam followers 106 and a pair of output members 108. The rotary input member 102a can include a shaft that can be mounted to a structure (which can be mounted to a cylinder head) for rotation about an axis that can be parallel to the rotary axis 30 (Fig. 1 ). The rotary input member 102a can be coupled to a source of rotary power, such as a stepper motor (now shown) or can be coupled to an input lever 200 that permits the rotational position of the rotary input member 102a to be controlled via a linear motor 100. The rotary cams 104a are coupled to the rotary input member 102a for rotation therewith. An axial end face 1 10 of each of the rotary cams 104a can be contoured in a desired manner (e.g., tapered in the particular example illustrated) to cause/permit corresponding translation of the cam followers 18 (to thereby cause/permit corresponding translation of the output members 108 and followers 18).

[0036] While the valve actuation systems 10 and 10a of Figures 1 and 8, respectively, have been illustrated and described as being capable of providing a maximum valve lift that is infinitely variable between a first maximum value (which could be zero) and a second maximum value, it will be appreciated that in the alternative, the actuation motors could be employed to provide a plurality of discrete (but different) maximum valve lift values. In the example of Figure 13, the axial end face -b of the rotary cam 104b is similar to that of the rotary cam 104a in Figures 1 1 and 12, stepped so as to have three distinct widths, with each width being associated with a different, discrete maximum valve lift value.

[0037] With reference to Figures 14 and 15, a portion of another valve actuation system is illustrated. In this example, the actuating element 16c is a roller finger follower having a follower body 300, an axle 302, a pair of followers or rollers 304 and one or more biasing springs 306. The axle 302 is non-rotatably coupled to the follower body 300. Each of the rollers 304 can be received on the axle 302. If desired, a bearing 310 can be disposed between each of the rollers 304 and the axle 302. Each of the rollers 304 can have a desired edge profile 320, such as an edge profile that is at least partly defined by a radius. The biasing spring(s) 306 can bias the rollers 304 in a direction away from one another. In the example provided, two biasing spring 306 are provided and each biasing spring 306 is disposed between the follower body 300 and a thrust washer 324 that is disposed in abutment with an associated one of the rollers 304. Each of the rollers 304 can optionally be retained on the axle 302 by any desired means, such as a thrust washer 328 that is fixedly coupled to the axle 302. An actuation motor, such as the actuation motor 20 of Figure 1 or the actuation motor 20a of Figure 8, can be employed to control the position of the rollers 304 on the first and second contact surfaces 40 and 42 (Fig. 1 ).

[0038] Figure 16 and Figures 17 and 18 depict two other valve actuation systems constructed in accordance with the teachings of the present disclosure. In Figure 16, the valve actuation system 10e has an actuating element 16e that is a rocker arm, whereas in Figures 17 and 18, the valve actuation system 10f has an actuating element 16f that is a bucket tappet.

[0039] The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.