Patent Application
20100059005
The present invention relates to variable valve actuation for internal combustion engines; more particularly, to a Continuously Variable Valve Lift (CVVL) apparatus incorporating a rotatable control rod to vary the contact point of a cam follower with an engine cam lobe; and most particularly, to a method and apparatus for adjusting the lift of individual valves in a multi-valve train.
Methods and apparatus for varying the lift of combustion valves in internal combustion engines are well known. In a typical application of such apparatus, an entire multi-valve train, for example, all the intake valves on an inline engine, undergoes simultaneous and identical actuation. Such coordinated actuation is typically accomplished by providing a variable lift mechanism for each valve, and ganging these mechanisms together via a single rotatable actuator shaft controllably driven by a motor and controller. Rotation of the actuator shaft serves to vary, for each individual variable lift mechanism, the contact point of a control arm with its corresponding cam lobe, thus varying the maximum lift achievable by each valve during a full rotation of the camshaft.
A typical CVVL mechanism can vary an intake valve from a full lift position, e.g., about 10 mm, to a predetermined low lift position, e.g., about 1 mm or even completely closed (no lift).
An engine equipped with a CVVL mechanism idles typically in the low lift position, especially an engine employing valve lift as a throttling strategy, wherein it is important to have very low variation in air flow among the various cylinders. Such low variation in air flow requires very low variation in valve lift. Because of stack-ups of manufacturing tolerances among the various CVVL components and sub-assemblies, the net variation in valve lift and resulting air flow among the cylinders can be substantial in prior art engines. Such variation in lift typically is a trivial percentage at full lift but becomes highly significant at low lift.
What is needed in the art is a method and apparatus for fine-tuning the actual valve lift of each CVVL assembly at the valve actuator itself.
It is a principal object of the present invention to equalize the flow of air through all the valves in a multi-valve train.
Briefly described, an apparatus for adjusting individual valve lift in accordance with the present invention comprises a control arm assembly disposed between the cam lobes and the valve rockers for a multi-valve train. The control arm at each valve includes a driven gear. An actuator shaft driven by a motor as in the prior art includes a mating drive gear at each driven gear for rotating each control arm in a predetermined fashion to vary the overall lift of the valves. In the prior art, the mating drive gears are fixed to the actuator shaft at identical orientations. In accordance with the present invention, each mating drive gear is rotatably adjustable on the actuator shaft to permit changing of the rotational orientation of the gear with respect to the actuator shaft axis, thereby changing the contact point of the control arm assembly with its respective cam lobe. Thus, the lifts of the individual valves may be individually adjusted to provide equal air flow through all the valves in a multi-valve train.
The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:
Corresponding reference characters indicate corresponding parts throughout the several views. The exemplification set out herein illustrates one preferred embodiment of the invention, in one form, and such exemplification is not to be construed as limiting the scope of the invention in any manner.
The present invention provides a method and apparatus for adjusting cylinder-to-cylinder air flow of a CVVL system during engine assembly and calibration to produce smooth idle quality by compensating for normal build tolerances.
Referring to
Prior art CVVL mechanism 10 comprises a control arm 14 pivotably mounted on a control arm shaft 16; a cam follower 18 rotatably mounted on a follower shaft 20 on control arm 14, and having a roller 22 for following the surface of a cam lobe 24 disposed on a camshaft 26, and having a contoured shoe 28 for actuating a roller rocker 30 pivotable on a hydraulic lash adjuster 32 to open and close valve 12. The curved shoe 28 has a cam profile which has an extended base circle portion and a sloped portion up to full valve lift. An actuator shaft 134 is disposed parallel to camshaft 26. A driven gear 36 is formed on control arm 14 and is engaged by a drive gear segment 102 of adjustable drive gear assembly 100.
As is well known in the prior art, rotation of control arm 14 about shaft 16 changes both the contact point 33 of roller 22 on cam lobe 24 and the distance of follower shaft 20 from camshaft 26, thus affecting the portion of the curved shoe 28 acting on the roller rocker 30. As the control arm 14 moves in relation to the camshaft 26, the portion of the curved shoe 28 contacting the roller rocker 30 changes and varies the amount valve 12 opens.
Referring to
Referring to
The actual adjustment may be accomplished by the following procedure. First and second adjustment set screws 104 are provided, threaded into adjustment block 106 which is fastened to actuator shaft 134 as by a bolt 108 or other attachment means at a rotational location nominal for the CVVL mechanism. Because only a segment of gear 102 is required for CVVL operation, two flats 110 are provided on gear segment 102 for adjustment set screws 104 to act against. Gear segment 102 is allowed to rotate about actuator shaft 134 until the required valve lift specification is met. Gear segment 102 then is locked onto actuator shaft 134 by tightening a locker such as clamping bolt 112 that is threaded into gear segment 102 via an oversize bore 114 through actuator shaft 134. Preferably, bolt 112 is tightened on shaft 134 via a bolt shoe 116 matching the curvature of shaft 134. This procedure is repeated on each of the remaining valves so all valves have equal lift.
While the invention has been described by reference to various specific embodiments, it should be understood that numerous changes may be made within the spirit and scope of the inventive concepts described. Accordingly, it is intended that the invention not be limited to the described embodiments, but will have full scope defined by the language of the following claims.
