Internal-combustion engines – Poppet valve operating mechanism – Valve driven closed
Reexamination Certificate
2002-02-12
2004-03-16
Lo, Weilun (Department: 3761)
Internal-combustion engines
Poppet valve operating mechanism
Valve driven closed
C123S090240, C123S090340, C123S090600, C123S090520, C074S567000, C251S251000
Reexamination Certificate
active
06705262
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a valve mechanism, in particular for internal combustion engines of motor vehicles, with a driven cam element and with a valve actuator displaceable or pivotable by the cam element.
Valve mechanisms for the valve control of internal combustion engines, in particular for motor vehicles, conventionally have a device (spring, hydraulic element, etc.), by means of which the valve is acted upon in the closing position. At least during the open phase, therefore, the valve actuator (valve tappet, drag lever, rocker arm or the like) is pressed against part of a closed valve control surface, said part being eccentric to the shaft axis. During the closing of the valve, care must be taken to ensure that the valve disk does not strike the valve seat too quickly, since it otherwise rebounds. This requires relatively complicated coordination between the masses to be moved, the forces arising, the material properties, etc.
There has therefore been no lack of proposals for guiding the valve actuator positively on the cam element, various embodiments having been developed, which are each based on two eccentric valve control surfaces instead of the return spring. Actual versions may be gathered, for example, from GB patent specification 19,193 (1913) and GB patent specification 434,247, wherein the cam element has, on at least one end face, a groove, the two side walls of which form the valve control surfaces. A roller or the like arranged at the end of the valve actuator engages into the groove from the side. A cam element having a surrounding web is known, for example, from European patent publication EP 429,277.
Further examples of positive guides make use, instead of valve control surfaces parallel to the axis of rotation of the camshaft, of two valve control surfaces which are arranged axially one behind the other and are formed on two differently shaped camshaft elements, for example European patent publications EP 355 659 B, and EP 384 361 A, etc.
Both the first version of the positive guides with end-face grooves and the lateral engagement of the sensing element and the second version with two cam elements and two sensing elements for each valve have, as compared with the first-mentioned valve mechanism with a return spring, an increased axial extent and a greater number of components which present either structural, spatial or economic problems.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a desmodromic valve mechanism of the type mentioned above, which overcomes the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and which appreciably reduces the prior art problems and constitutes a space-saving, lightweight and cost-effective design.
With the foregoing and other objects in view there is provided, in accordance with the invention, a valve mechanism, comprising:
at least one driven cam element and a valve actuator driven by said cam element;
a flexible surround element, said cam element being rotatably disposed in said flexible surround element about an axis of rotation;
a bearing pin inserted in an insertion orifice formed in said surround element, said bearing pin movably connecting said valve actuator to said flexible surround element for movement of said valve actuator in a plane perpendicular to the axis of rotation of said cam element.
In other words, the objects of the invention are achieved, according to the invention, in that the cam element is arranged rotatably in a flexible surround element which is connected movably to the valve actuator in a plane perpendicular to the axis of rotation of the cam element.
The surround element surrounds the circumference of the cam element without appreciable play, so that it is matched to the cam shape, and, because of the nature of the surround element, the cam element can rotate in the latter. Since the surround element connected to the valve actuator cannot corotate with the cam element, the travel of the cam region about the axis of rotation of the cam element is converted into a lifting or to-and-fro movement of the valve actuator mounted displaceably or pivotably in the cylinder head. The valve actuator does not execute any movement as long as the region of connection of the surround element to the valve actuator comes to bear against the base-circle region of the rotating cam element, is then moved radially away from the axis of rotation of the cam element and is finally led back again, while the cam region of the cam element passes the region of connection of the surround element to the valve actuator.
Since the surround element comes to bear, essentially free of play, against the circumferential surface of the cam element, a valve actuator freely projecting from the surround element would always be oriented perpendicularly to the tangent to the circumferential surface of the cam element and at the same time deviate from radial orientation to the axis of rotation of the cam element, on the one hand, in the rising cam region and, on the other hand, in the falling cam region. The movable connection of the surround element to the valve actuator permits the pivoting or tilting movement of the surround element in the cam region, so that the necessary freedom of movement of the valve actuator in its sliding or pivot bearing remains preserved. The surround element is therefore arranged, in particular, pivotably about an axis on the valve actuator or on a holder for the valve actuator.
Preferably, the valve actuator has a holder, to which the surround element is connected, in particular movably, and on which a part guided in the sliding or pivot bearing of the valve actuator is held preferably adjustably.
In a first version there is provision for the surround element to have an open loop, the two ends of which are fixed to a holder for the actuator. When the two ends of the open loop pass through one another or, touching one another, project from the cam element, then, because of the flexibility of the material of the surround element, a physical axis may be unnecessary, since the two ends can be jointly bent on both sides to the required extent. For connection to the valve actuator, there is preferably provision for the two ends of the open loop to have insertion orifices for a connecting element. The insertion orifices may be formed by folding round and, depending on the material of the loop, stitching, adhesive bonding, welding or the like of the folded-round end. In a particularly advantageous version, the open loop consists of a band closed on itself which is led to and fro around the cam element and the reversals of which form the insertion orifices.
In a further version, the flexible surround element is designed as a closed loop and is provided with a holder for the valve actuator. The tying of the holder into the loop can in this case be achieved in a simple way by means of a protuberance wherein the holder is arranged. The protuberance is achieved, in particular, by constricting a region of the surround element which forms an excess length, said constriction being, for example, pinched off, stitched or the like.
A closed flexible loop may be formed, for example, by a deformable ring. If the ring consists of plastic, it may also be fiber-reinforced or reinforced on the inside and/or outside with a steel or fabric band. Particularly in this version, an elastomeric plastic could also be used, which is vulcanized onto the band. For the movable connection, there is preferably provision for the ring to have a recess, wherein a bearing pin of the valve actuator is provided, the axis of said pin being parallel to the axis of rotation of the cam element.
Both and open and closed loops can be achieved when the surround element is a rope which, in particular, is inserted into a circumferential groove of the cam element, a roller chain, wherein a joint pin forms the holder of the valve actuator, a strip or band consisting of a sheetlike material, wherein threads or fibers are provided
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