Switchable rocker arm

Abstract

A latching mechanism for variably activating an engine valve in an internal combustion engine includes a rocker arm body having a bore and a socket. A first passage leads from the socket to a first hydraulic chamber formed above a lock pin head. A second passage leads from the socket to a second hydraulic chamber formed below the lock pin head. Since both the first and the second hydraulic chamber receive pressurized oil, it is the diameter of the pin shank that determines the hydraulic force needed to axially move the locking pin to an extended position and into a locking engagement with a slider member. In an alternate embodiment of the invention the first passage connecting the first hydraulic chamber with the socket is eliminated and instead the locking pin is modified to permit flow between second hydraulic chamber and first hydraulic chamber.

Description

TECHNICAL FIELD[0001]The present invention relates to mechanisms for altering the actuation of valves in internal combustion engines; more particularly, to finger follower type rocker arm assemblies capable of changing between high and low or no valve lifts; and most particularly, to an improved oil circuit for a latching mechanism for a two-step finger follower type rocker arm assembly.BACKGROUND OF THE INVENTION[0002]Variable valve activation (VVA) mechanisms for internal combustion engines are well known. It is known to be desirable to lower the lift, or even to provide no lift at all, of one or more valves of a multiple-cylinder engine, during periods of light engine load. Such deactivation or cam profile switching can substantially improve fuel efficiency.[0003]Various approaches are known in the prior art for changing the lift of valves in a running engine. One known approach is to provide a latching mechanism in the hydraulic lash adjuster (HLA) pivot end of a rocker arm cam ...

AI Technical Summary

Benefits of technology

The invention is a rocker arm body that includes a first and a second oil passage connecting a lock pin bore with a variable oil pressure source. This allows oil to flow between the lock pin and the return spring cavity, reducing the amount of oil needed to be displaced and improving the switching response. The second oil passage also eliminates the need for a venting hole typically machined into the follower body, reducing leakage and improving the design of the return spring. The invention also allows for oil flow to both sides of the lock pin head, alleviating the concern of lock pin head jamming and reducing the chance of the lock pin head partially blocking the original passage. In an alternate embodiment, the original oil passage is eliminated and the lock pin is modified to permit oil flow between the return spring cavity and hydraulic chamber as well as from the HLA socket to and from the return spring cavity.

Problems solved by technology

First, the major diameter of the lock pin, for example, the head diameter if the lock pin includes a head and a shank, determines the magnitude of the hydraulic force generated by the oil pressure in the hydraulic chamber, which may be determined as oil pressure times pin head area, and the total volume of fluid displaced as the pin moves. The lock pin response depends, therefore, on the capacity of the system to flow the required volume of oil. Problems may occur when moving the lock pin from an extended position to a retracted position with cold oil due to the high viscosity of the oil and, thus, a lower flow rate through the HLA, at lower temperatures and at relatively low pressure. A smaller major diameter of the lock pin would reduce the required flow capacity but reduction in size is constrained by the contact stress between the lock pin and the saddle of the high lift follower.

Second, the tolerances on the diameter of the lock pin head and surrounding bore must be controlled to manage the leakage through the clearance. Consequently, manufacturing costs are increased. The axial length of the lock pin head also influences the leakage. While a longer axial length of the lock pin head would reduce the leakage, a shorter length is beneficial for packaging both the return spring and the rocker arm in the cylinder head. However, tight clearances between the lock pin head and the bore combined with shorter pin head length increases the risk of jamming the lock pin head in the bore.

Third, the return spring cavity is typically vented such that clearance between the diameter of the pin shank (minor diameter) and bore is not required to seal against oil leakage. However, tolerances on the minor diameter size cannot be increased, as the diameter must be controlled for reasons of mechanical lash.

Fourth, a passage connecting the bore with the HLA intersects the bore of some prior art two-step finger follower type rocker arm assemblies at an angle, which may limit the hole size of the passage. The lock pin head and retention plug can in some applications partially block the passage and, thus, the flow area. Further, the angled hole may be difficult to drill and may be prone to burrs in critical areas.

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