Patent ID: 6039018
Filing Date: 2000-03-21
Classification: F01L

Abstract:
A hydraulic lash adjuster capable of use in an engine valve train connecting a cam and a valve, said adjuster comprising:a cup-shaped body with a peripheral outer wall defining an internal cylinder formed around an axis and having closed and open ends;hydraulic means in the body including a plunger reciprocable along the cylinder axis and having a cylindrical side wall with an open end operatively engagable with a cooperating member of the valve train to take up lash in the associated valve train, the plunger defining a low pressure chamber for receiving hydraulic fluid supplied from the engine, the plunger being spaced from the closed end of the cylinder and defining therewith a high pressure chamber connected through a non-return check valve with the low pressure chamber for delivering fluid to the high pressure chamber,a plunger spring acting between the closed end of the cylinder and the plunger and urging the plunger toward engagement with said cooperating member of the valve train; anda control ring mounted within the plunger cylindrical side wall and having a thermal expansion rate greater than that of the cylindrical side wall, the control ring cooperating with the cylindrical side wall to control leakdown of hydraulic fluid through a leakdown path from the high pressure chamber during valve opening events of the valve gear;wherein said leakdown path is formed by a secondary clearance between the control ring and the cylindrical wall of the plunger and means for communicating the secondary clearance with the high pressure chamber the control ring directly reducing the secondary clearance upon increasing temperature of the hydraulic fluid to thereby control the increase in fluid leakdown from the high pressure chamber due to reducing of fluid viscosity upon increasing fluid temperature.