Internal-combustion engines – Poppet valve operating mechanism – With means for varying timing
Patent
1999-05-10
2000-09-12
Lo, Weilun
Internal-combustion engines
Poppet valve operating mechanism
With means for varying timing
123 9037, 123 9038, 74568R, 464 2, 464160, F01L 1344
Patent
active
061162000
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a system for angular adjustment of a shaft relative to a driving gear, preferably of a camshaft of an internal combustion engine, comprising a hydraulically controllable angular adjustment device rotating with the shaft and having hydraulic supply ducts in a non-rotatably fitted end cap and oil distribution ducts, associated with the supply ducts, in the angular adjustment device.
BACKGROUND OF THE INVENTION AND PRIOR ART
Such angular adjustment systems known as VCT (variable cam timing) systems, are often used in internal combustion engines to displace the position of the camshaft in relation to the crankshaft. The phase shift of the valve opening and closing times that is possible by the angular adjustment enables the valve timing to be optimised with respect to the nominal output, torque, fuel consumption and exhaust gas emission requirements of the engine.
The angular adjustment is mostly performed hydraulically by means of an internal adjusting device fitted in the camshaft driving unit. For this purpose a helical gear is fitted between the chain wheel and the camshaft, and a hydraulic piston effects an axial displacement of the helically toothed element such that an angular displacement results between the driving gear and the camshaft. The form of the adjusting device can be such that advancing or retarding of the valve timing is brought about through two alternately pressurised hydraulic ducts. The valve elements required for the control are suitably located in the non-rotating part of the system. Alternatively the control can be effected through only a single hydraulic duct through which the angular adjustment in one direction takes place, while the angular adjustment in the other direction is effected by means of a return spring.
A characteristic feature of the hydraulic adjusting devices usually used is that they are connected to the rotating camshaft. The hydraulic fluid must be supplied to the rotating adjusting device from a non-rotating hydraulic supply. For this purpose in the known systems a non-rotating end cap is provided which has a recess in it for a rotating oil distribution device. Both in the end cap and in the rotating oil distribution device at least one oil distribution duct is provided which, in the transition region between the non-rotating and the rotating elements, changes into at least one annular duct. Elastic sealing elements are provided for sealing of the annular ducts between the end cap and the rotating oil distribution device. Since the end cap is connected to the camshaft so as to rotate therewith, it is centred on the camshaft. At the same time the end cap forms a portion of the outer side wall of the engine block. The outer side wall is connected at its upper face to the cylinder head cover of the engine, and the upper edge of the outer wall must be in alignment with the cylinder head cover in order to ensure the oil-tightness of the outer wall of the engine block.
The position of the cylinder head cover relative to the axis of the camshaft is subject to quite large manufacturing tolerances arising in mass production. These tolerances affect the position of the outer side wall fitted to the cylinder head cover. For this reason in the prior art the outer side wall is made up of two parts, one being the end cap and the other the side housing. The side housing has a recess to receive the end cap, the rim of the end cap being secured on the outside of the side housing, for example by means of a screw connection, in such a way that deviations in the relative position of the side housing and the end cap can be compensated during assembly. Between the side housing and the end cap an elastic sealing element is provided in order to prevent loss of oil.
However, during the lifetime of the engine each sealing element needed on the outer housing of the engine block can become leaky, and consequently represents a possible source of problems which give rise to maintenance and repair costs. In addition the length of the engine b
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Abts Manfred
Koob Thomas
Menne Rudolf
Wildemann Roger
Drouillard Jerome R.
Ford Global Technologies Inc.
Lo Weilun
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