Cam lobe profile to accommodate mechanical lash of a switchable hydraulic lash adjuster

Abstract

In an engine valve train equipped with a DHLA, the radius of the base circle of a cam lobe is decreased, relative to the radius of the base circle of a cam lobe in an engine equipped with an HLA, in proportion to the internal lash in the DHLA. The actual decrease in the base-circle radius is calculated by trigonometric relationships among the base circle portion, the length of the rocker pivot arm, and the internal lash of the DHLA. The decrease in the base circle radius is compensated by extension of the valve train lash-adjustment mechanism of the DHLA. After the internal DHLA lash is taken up during valve actuation, the coordinate position of the pivot point of the DHLA rocker arm is then identical with the coordinate position of the pivot point of an HLA rocker arm of a DHLA-equipped engine.

1 . In a valve train system for an internal combustion engine wherein the valve train system includes an HLA valve train and a DHLA valve train, said valve train system comprising:
 a DHLA in the DHLA valve train pivotably supportive of an associated rocker arm for selectively actuating an associated engine combustion valve in response to a movement of a first actuating member engaged by a contact surface of said associated rocker arm, wherein said rocker arm associated with the DHLA includes a pivot point for pivoting on the DHLA, and wherein said first actuating member includes a base contour portion, lift portion and an axis of rotation,   an HLA in the HLA valve train pivotably supportive of an associated rocker arm for selectively actuating an associated engine combustion valve in response to a movement of a second actuating member engaged by a contact surface of said associated rocker arm, wherein said rocker arm associated with the HLA includes a pivot point for pivoting on the HLA, and wherein said second actuating member includes a base contour portion, lift portion and an axis of rotation equal to the axis of rotation of said first actuating member,   the DHLA having a first length of internal axial mechanical lash that is taken up by axial compression of the DHLA during passage of the lift portion of the first actuating member past the contact surface of the associated rocker arm,   the base contour portion of the first actuating member selected to included a radius for positioning the pivot point of the rocker arm associated with the DHLA at a first coordinate position in space relative to the axis of rotation of said first actuating member, such that said pivot point is displaced by said axial compression from said first coordinate position in space to a second coordinate position in space relative to the axis of rotation of said first actuating member, for pivoting of said associated rocker arm to actuate said valve,   the pivot point of said rocker arm associated with the HLA being positioned at a third coordinate position in space relative to the axis of rotation of said second actuating member,   wherein, on a same coordinate system having its origin at said axis of rotation of said first actuating member and a y axis, the second coordinate position in space is substantially identical to the third coordinate position in space.   
   
   
       2 . The valve train system in accordance with  claim 1  wherein the base contour portion of the second actuating member further includes a radius for positioning the pivot point of the rocker arm associated with the HLA at said third coordinate position in space and wherein the base contour of the second actuating member is larger than the radius of the base contour of said first actuating member. 
   
   
       3 . The valve train system in accordance with  claim 1  wherein said rocker arm is a finger follower. 
   
   
       4 . The valve train system in accordance with  claim 3  wherein said finger follower is a roller finger follower. 
   
   
       5 . The apparatus in accordance with  claim 1  wherein said rocker arm contact surface is disposed intermediate of said rocker arm. 
   
   
       6 . An internal combustion engine comprising a valve train system including an HLA valve train and a DHLA valve train, wherein said Valve train system includes
 a DHLA,   a first rocker arm pivotably supported by said DHLA,   an engine combustion valve actuated by said first rocker arm, and   a first cam lobe engaged by a contact surface in said first rocker arm,   wherein said first cam lobe includes a base circle portion, an eccentric portion and an axis of rotation,   an HLA pivotably supportive of a second rocker arm,   an engine combustion valve actuated by said second rocker arm, and   a second cam lobe engaged by a contact surface in said second rocker arm,   wherein said second cam lobe includes a base circle portion, an eccentric portion and an axis of rotation,   wherein said DHLA has a first length of internal axial mechanical lash that is taken up by axial compression of said DHLA during passage of said eccentric portion past the contact surface of the first rocker arm,   wherein the base circle portion of the first cam lobe further includes a first radius for positioning the contact surface of said first rocker arm at a first coordinate position in space relative to the axis of rotation of said first cam lobe, such that said pivot point of said first rocker arm is displaced by said axial compression from said first coordinate position to a second coordinate position in space relative to the axis of rotation of said first cam lobe, for pivoting of said first rocker arm to actuate said valve,   wherein the pivot point of said second rocker arm associated with the HLA is positioned at a third coordinate position in space relative to the axis of rotation of the first cam lobe to actuate said valve, and   wherein, on a same coordinate system having its origin at said axis of rotation of said first cam lobe and a y axis, the second coordinate position in space is substantially identical to the third coordinate position in space.   
   
   
       7 . The engine in accordance with  claim 6  wherein the base circle portion of the second cam lobe further includes a radius for positioning the pivot point of the second rocker arm associated with the HLA at said third coordinate position in space and wherein the base circle of the second cam lobe is larger than the radius of the base circle of said first cam lobe.