GB1424556A - Device for adjusting and maintaining valve play in internal combustion engines - Google Patents

Abstract

1424556 Hydraulic back-lash adjuster DAIMLER-BENZ AG 16 Nov 1973 [2 Dec 1972] 53373/73 Heading F2K An hydraulic back-lash adjuster pillar, forming an abutment pivot for a cam operated rocker arm of an I.C. engine valve gear, is constructed to prevent pump-up at high engine speeds and maintain valve clearance at a constant value and comprises a cylindrical housing 10 screwed into the engine cylinder head (not shown) and in which is slidingly mounted a 1st piston 12 formed with a ball head pivot 14 for the rocker arm (not shown), the 1st piston carrying a 2nd piston 21 forming a non-return valve between the usual pressure chamber 17 and reservoir 20, an oil collector groove and port 34, 35 serving to prevent oil loss by returning any oil leaking from the pressure chamber 17, past the 1st piston 12, back into the reservoir 20. A releasable clamping device 18 for clamping the 2nd piston 21 to the 1st piston 12 to maintain the 2nd piston 21, i.e. non-return valve, closed when the adjuster pillar is under compressive load, pressurizing chamber 17, comprises a resilient double conical-ended ring 26, on the 2nd piston 21, sandwiched between conically ended rings 27, 29, the clamping device 18 being retained in the 1st piston by a snapring 21 with a small axial clearance representing a predetermined amount of valve clearance. In operation, if on initial engine starting from cold an engine valve has been open and the associated hydraulic pillar has collapsed, i.e. the pressure chamber 17 has been exhausted to the reservoir 20 via the collector groove 34, 35, closing of the engine valve allows the pillar to be axially extended by a surrounding spring 16, the 2nd piston 20, i.e. non-return valve, opening at its seat 32, by vacuum, to fill the pressure chamber 17 from the reservoir 20 to restore the correct working height of the pillar. Thereafter the pillar remains at its working height, the engine valve clearance being maintained constant by the small predetermined axial clearance movement of the 2nd piston 21 clamping device 18 in the 1st piston 12 and pump-up being prevented by the clamping device 18 which clamps and prevents opening of the non-return valve piston under pressure. The reservoir 20 may be filled by dripped or sprayed oil injected from outside via a bore 14 and admission valve 36 which is notched at 38 to avoid pressurizing the reservoir 20. A push rod 43 on the valve 36 enables the non-return valve piston 21 to be opened during assembly to facilitate fitting of the 1st piston 12 in the oil filled housing 10.