Modern internal combustion engines may incorporate advanced throttle control systems, such as, for example, intake valve throttle control systems, to improve fuel economy and performance. Generally, intake valve throttle control systems control the flow of gas and air into and out of the engine cylinders by varying the timing and/or lift (i.e., the valve lift profile) of the cylinder valves in response to engine operating parameters, such as engine load, speed, and driver input. For example, the valve lift profile is varied from a relatively high-lift profile under high-load engine operating conditions to a reduced/lower low-lift profile under engine operating conditions of moderate and low loads.
Intake valve throttle control systems vary the valve lift profile through the use of various mechanical and/or electromechanical configurations, collectively referred to herein as variable valve actuation (VVA) mechanisms. Several examples of particular VVA mechanisms are detailed in commonly-assigned U.S. Pat. No. 5,937,809, the disclosure of which is incorporated herein by reference. Generally, a conventional VVA mechanism includes a rocker arm that is displaced in a generally radial direction by an input cam of a rotating input shaft, such as the engine camshaft. A pair of link arms transfers the displacement of the rocker arm to pivotal oscillation of a pair of output cams relative to the input shaft or camshaft. Each of the output cams is associated with a respective valve. The pivotal oscillation of the output cams is transferred to actuation of the valves by cam followers, such as, for example, direct acting cam followers or roller finger followers.
A desired valve lift profile is obtained by orienting the output cams in a starting or base angular orientation relative to the cam followers and/or the central axis of the input shaft. The starting or base angular orientation of the output cams determines the portion of the lift profile thereof that engages the cam followers as the output cams are pivotally oscillated, and thereby determines the valve lift profile. The starting or base angular orientation of the output cams is set via a control shaft that pivots a pair of frame members which, via the rocker arm and link arms, pivot the output cams to the desired base angular orientation.
The frame members in a conventional VVA mechanism are pivoted relative to a fixed pivot point, typically the centerline of the frame to control shaft coupling. The frame members also establish a fixed pivot length. The fixed pivot length, referred to herein as the ground link, is represented by the linear distance between the input shaft or camshaft central axis and the frame to rocker arm coupling. Since the pivot length or ground link is fixed, pivotal movement of the control shaft results in pure pivotal movement of the frame to rocker arm coupling, i.e., the frame to rocker arm coupling does not move in a direction toward or away from the central axis of the camshaft. The pure pivotal nature of the movement of the frame to rocker arm coupling provides for variation of the amount of lift imparted by the mechanism to the associated valves. However, the pure pivotal nature of the movement of the frame to rocker arm coupling precludes significant control over the timing or phasing of the valve opening event.
The frame members are typically pivotally disposed upon the input shaft, and thus there is a certain amount of friction between the rotating input shaft and the non-rotating frame members pivotally disposed thereon. This friction between the frame members and input shaft reduces the efficiency of the mechanism as well as the engine upon which it is installed, and requires a bearing surface be formed on the engine camshaft or input shaft. Further, the frame members occupy the limited space between the valves of a cylinder. The placement of the frame members within the space between the valves creates size constraints on other engine components which must also be disposed within that space.
Therefore, what is needed in the art is a VVA mechanism that enables control over the timing or phasing of the valve opening event.
Furthermore, what is needed in the art is a VVA mechanism that consumes or occupies substantially less space between the cylinder valves.
Even further, what is needed in the art is a VVA mechanism that substantially reduces and/or eliminates friction between the frame members and the engine camshaft or input shaft.
Moreover, what is needed in the art is a VVA mechanism that eliminates the need for a conventional frame member or members.