Method and apparatus for controlling a switchable cam follower

Abstract

An internal combustion engine is equipped to supply the camshaft bearings with pressurized oil via a first dedicated oil gallery independently of the hydraulic lash adjusters (HLAs) and any valve deactivation devices which are supplied from a second dedicated oil gallery. The galleries may be connected at their downstream ends and a flow restriction is placed in a connecting passage or within each HLA. An improved HLA is similar to a prior art HLA except that the prior art annular oil distribution groove in the outer surface of the HLA body is eliminated to prevent communication of the primary engine oil gallery with the HLA. The secondary gallery is formed remotely from the first oil gallery in the HLA residence bore in the engine, and the HLA is prevented from rotating within the residence bore.

Description

TECHNICAL FIELD[0001]The present invention relates to variable valve activation mechanisms for combustion valves of internal combustion engines; more particularly, to methods and apparatus for controllably supplying activating engine oil to such variable valve activation mechanisms including switchable cam followers; and most particularly, to an improved hydraulic lash adjuster and control scheme for such controllable valve actuation.BACKGROUND OF THE INVENTION[0002]Mechanisms for varying the valve timing and / or lift of combustion valves in internal combustion engines are well known. A typical prior art selective valve deactivation mechanism includes a switchable cam follower such as an articulated two-step deactivation roller finger follower (DRFF) disposed between an engine camshaft lobe and a valve stem. The DRFF includes a hydraulically-actuated lock pin to engage or disengage the articulated members. In one example of a DRFF, the lock pin is engaged between the articulated memb...

AI Technical Summary

Benefits of technology

[0010]Briefly described, an internal combustion engine is equipped to supply the camshaft bearings with pressurized oil via a first dedicated oil gallery independently of the hydraulic lash adjusters and any valve deactivation devices which are supplied from a second dedicated oil gallery. To improve air purging of both galleries, the galleries are connected and a small-orifice flow restriction is placed either in a connecting passage between the first and second galleries or within the HLAs themselves. In an aspect of the present invention, the primary engine oil gallery is as in the prior art, to minimize required retooling of engine molds. An improved hydraulic lash adjuster, formed in accordance with the invention, is identical with a prior art HLA except that the prior art annular oil distribution groove in the outer surface of the body is eliminated to prevent communication of the primary engine oil gallery with the HLA. The secondary gallery is formed remotely from the first oil gallery in the HLA residence bore in the engine, and the HLA is prevented from rotating within the residence bore. Thus, the HLA can communicate for actuation with only the new, second oil gallery. Forming the improved HLA requires only the omission of the prior art annular oil groove in the HLA body and provision for non-rotation of the improved HLA.

Problems solved by technology

A problem arises in using a single oil gallery in such a dual mode in that the pressure logic of a deactivation application mandates that oil pressure in the gallery be low (lock pin engaged, valves actuated) at the highest engine speeds and load conditions.

Under these conditions, the camshaft bearings, which are oiled from the same gallery, are subjected to highest load and lowest oil flow which can result in premature bearing wear or outright failure.

This approach avoids the necessity for an ROCV, which is both bulky and expensive, but it requires significant changes in the prior art HLA design to provide independent oil feeds for the lash adjustment and switching functions.

Such designs significantly reduce the volume of the HLA low-pressure chamber, raising concerns for potential noise upon cold start of the engine.

Further, it can be difficult and expensive to provide two adjacent galleries so close together within the engine block; and further, significant leakage can occur between the two galleries along the wall of the HLA residence bore.

However, this approach can be difficult to package on existing engine block or head arrangements because of the common oil gallery shared by the HLAs and the cam bearings.

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