Internal-combustion engines – Poppet valve operating mechanism – With means for varying timing
Patent
1997-09-29
1998-09-15
Lo, Weilun
Internal-combustion engines
Poppet valve operating mechanism
With means for varying timing
123 906, 123568, F01L 1300, F01L 1306, F02D 1304
Patent
active
058064761
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a valve mechanism in an internal combustion engine, comprising at least one intake valve and at least one exhaust valve in each cylinder, at least two rocker arms mounted on a rocker arm shaft for each cylinder for operating the valves, at least one cam shaft with a cam element for each rocker arm, said cam element having a first lifting ridge for actuating an associated rocker arm, and a control mechanism, by means of which the exhaust valve can be opened during the intake stroke of the engine to provide intake of exhaust into the cylinder during the intake stroke.
BACKGROUND OF THE INVENTION
SE-A-501 437 reveals a valve mechanism of the above mentioned type which permits recirculation of exhaust from the exhaust side to the cylinder during the intake stroke without requiring the gate and valve devices of the conventional recirculation system on the exhaust and intake sides. Such a valve mechanism is particularly advantageous for use in turbo-charged engines, where the pressure under certain operating conditions is higher on the intake side than on the exhaust side and where it would otherwise be necessary to use some form of pumping device to get the exhaust to the pressure side of the turbo compressor.
The known valve mechanism comprises a shaft which is rotatable and axially displaceably mounted parallel to the rocker arm shaft and which has pivot arms which are disposed to transmit a portion of the movement of the intake rocker arm to a rocker movement of the exhaust rocker arm.
SUMMARY OF THE INVENTION
The purpose of the present invention is to achieve a valve mechanism of the type described by way of introduction, which has a control mechanism which can be integrated into the cam shaft itself, so that the engine design as regards its valve system can be maintained without any modifications whatsoaver.
This is achieved according to the invention by virtue of the fact that the control mechanism comprises a slide displaceably mounted in a radial channel in the cam element for the exhaust valve and which is angularly displaced relative to the first lifting ridge, said slide having a second lifting ridge and means integrated into the cam shaft to achieve a radial displacement of the slide between a first position, in which the highest point of the second lifting ridge lies at most level with the base circle ("a") of the cam element, and a second position, in which the highest point of the second lifting ridge lies above the base circle.
The invention is based on the fact that the pressure in the cylinder during the intake stroke is low and that the second lifting ridge of the cam element only needs to overcome the force of the exhaust valve spring, which means that the surface pressure on the second lifting ridge and on the exhaust valve tappet will not be higher than what can be permitted even when the second lifting ridge is substantially shorter axially than the tappet cam follower.
BRIEF DESCRIPTION OF THE DRAWING
The invention will be described in more detail below with reference to examples shown in the accompanying drawings, where
FIG. 1 shows a partially cut away side view of a cam shaft with a control mechanism according to the invention,
FIG. 2 is a radial section through the cam shaft in FIG. 1 and a portion of an exhaust tappet,
FIG. 3 is an enlarged axial section through a portion of the cam shaft in FIG. 1, and
FIG. 4 is a schematic diagram of a control system for the mechanism according to the invention.
DETAILED DESCRIPTION OF THE INVENTION
The cam shaft generally designated 1 in FIG. 1 is intended for a six cylinder diesel engine and has for each cylinder a cam element 2 for the cylinder exhaust tappet, a cam shaft bearing 3 and a cam element 4 for its intake tappet. In the Figure, all of the cam elements 2 for the exhaust valves are shown with the same angular setting for the sake of illustration. In practice of course, they will be angularly displaced corresponding to the ignitions sequence of the engine. The cam shaf
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patent: 5404770 (1995-04-01), Kruger
patent: 5505168 (1996-04-01), Nagai et al.
patent: 5603292 (1997-02-01), Hakansson
AB Volvo
Lo Weilun
LandOfFree
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