Internal-combustion engines – Poppet valve operating mechanism – Hydraulic system
Reexamination Certificate
2000-05-08
2001-01-30
Lo, Weilun (Department: 3748)
Internal-combustion engines
Poppet valve operating mechanism
Hydraulic system
C123S188900
Reexamination Certificate
active
06178935
ABSTRACT:
PRIOR ART
The invention is based on a valve control device for an internal combustion engine. In a valve control device of this kind, which has been disclosed by DE 195 11 320 A1, a piston-shaped valve member of a gas exchange valve controls the opening and closing of an inlet and outlet cross section on the combustion chamber of the engine to be fed. The gas exchange valve, which is embodied as a disk valve, has an axially movable valve member whose valve member shaft is coupled by way of a piston rod to an adjusting piston (differential piston) that can be hydraulically actuated, by which the individual gas exchange valve can be directly actuated independently of the other gas exchange valves. The hydraulic adjusting piston in the known valve control device is thereby disposed directly on the valve member shaft or the piston rod of the gas exchange valve and thereby constitutes a part of the gas exchange valve member itself. With a lower annular end face, the adjusting piston defines a first hydraulic working chamber and with its upper piston end face, defines a second hydraulic working chamber, and these working chambers can be filled with a highly pressurized pressure fluid and emptied by way of corresponding pressure fluid lines. The hydraulic working pressure in the lower working chamber acts on the adjusting piston in the closing direction of the gas exchange valve and the upper working chamber acts on the adjusting piston in the opening direction of the valve member of the gas exchange valve. It is then possible, through the alternating filling of the working chambers with high pressure, to hydraulically actuate the adjusting piston and to thus move the valve member of the gas exchange valve rigidly connected to it in the opening or closing direction.
The known valve control device, however, has the disadvantage that a static redundancy occurs on the adjusting piston, which is caused by a double centering of the adjusting piston. Since the hydraulic adjusting piston is guided directly on its outer circumference surface and is also guided on its inner surface by way of the piston rod firmly connected to the adjusting piston, along a second guide surface of the valve member, which even with extremely small tolerance deviations can cause the hydraulic adjusting piston to stick and can result in a jamming of the gas exchange valve.
Valve control devices have also been disclosed in which the hydraulic adjusting piston is fastened to the valve member shaft of the gas exchange valve by means of a screw thread. This has the further disadvantage that the transmission of force from the hydraulic adjusting piston to the valve member shaft occurs by way of the screw thread, which results in a high dynamic alternating tension/pressure stress in a zone with a concentration of stress, which can cause fatigue fractures there.
ADVANTAGES OF THE INVENTION
The valve control device has the advantage over the prior art that the hydraulic differential piston actuating the gas exchange valve has a radial play between its two guide surfaces, or in relation to the guide surface of the gas exchange valve.
This is achieved in a structurally advantageous manner by virtue of the fact that the piston of a hydraulic valve actuation device, which is preferably embodied as a differential piston, has two parts, wherein the two piston parts are guided so that they can slide axially, are operatively connected to each other, and have a radial play in relation to each other. Consequently, the two piston parts can execute a relative motion in the radial direction in relation to each other, which in the event of tolerance deviations, reliably prevents a jamming of the differential piston and thus reduces the manufacturing costs with regard to tolerance sensitivity. In order to nevertheless assure a reliable sealing of the two hydraulic working chambers defined by the differential piston, the two-part differential piston is embodied so that a first piston part slides in a sealed fashion with a large diameter on its radial outer circumference surface against a cylinder guide surface, wherein it has a radial play in relation to the piston rod of the gas exchange valve that passes through it axially. The second, smaller diameter piston part is guided in a sealed fashion with its radial inner wall surface against the piston rod and has a radial play in relation to the cylinder guide wall. The two piston parts can now move radially in relation to each other during operation, wherein the axial piston end faces that are oriented toward each other rest against each other in a sealed fashion. Alternatively, however, it is also possible to provide an axial sealing element, e.g. a sealing disk, between the end faces of the piston parts of the differential piston. Furthermore, it is possible to embody one of the two piston end faces as ball-shaped in order to produce a reliable seal between the end faces.
The two piston parts are also operatively connected to the piston rod in the axial direction by way of axial stop faces and have a slight axial play that permits a radial compensation movement in relation to each other. The valve member shaft of the gas exchange valve is advantageously embodied as being of one piece with the piston rod of the differential piston and is advantageously guided axially in a guide bush whose end wall surface simultaneously defines a lower hydraulic working chamber. On the one end, the stop face on the piston rod is advantageously embodied as an annular stop face which comes into direct contact with the one end face of the differential piston. The second stop is advantageously constituted by a separate component, which is press-fitted onto the shaft of the piston rod, is embodied as a valve wedge, and can be placed around the piston rod as a result of having a multi-part form.
On its outer circumference, this wedge-shaped component has a conical cross sectional expansion in the direction of the differential piston and a corresponding cone ring is slid axially against this expansion. The clamping force directed radially inward is exerted by means of a clamping nut that is screwed onto the piston rod and thereby clamps the cone ring through the radial clamping of the wedge-shaped stop components. A lower end face of the wedge-shaped stop components thus constitutes a stop face, which cooperates with an upper annular end face of the differential piston. In order to define the position of the wedge-shaped stop components on the shaft of the piston rod, it is also advantageous to provide the valve wedges with ribs that protrude radially inward and engage in a corresponding groove on the shaft of the piston rod.
In order to prevent a loss of the clamping force exerted by the clamping nut, and in order to also permit an axial compensation of play, it is also advantageous to provide a spring element between the nut and the cone ring, which spring element is preferably embodied as a spring disk or spring ring and can have a U-shaped contour.
With the above-described disposition and fastening of the upper stop to the piston rod, it is possible to guide the larger diameter differential piston part with radial play in relation to the shaft of the piston rod and in a sealed fashion inside the cylinder housing and to guide the smaller diameter differential piston part with radial play in relation to the cylinder housing wall and in a sealed fashion against the piston rod, wherein the working chambers axially adjoining the differential piston are completely sealed off from one another by the axial seal between the differential piston parts. Consequently, the two piston parts of the differential piston can be axially guided independently of one another against the guide surfaces, with very tight fits or tolerances. As a result, the elastic sealing elements required in known valve control devices are no longer necessary.
Alternatively, it is also possible to replace the piston rod completely by means of the valve member shaft of the gas exchange valve.
Furthermore, the currently separate guidance of the indi
Beuche Volker
Diehl Udo
Franzl Stefan
Kappenstein Ulrich
Mischker Karsten
Greigg Edwin E.
Greigg Ronald E.
Lo Weilun
Robert & Bosch GmbH
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