Patent Application
20050235934
Variable mechanical valve timing mechanism for adjusting the stroke of gas exchange valves in a reciprocating-piston internal combustion engine, having a plurality of cam which are fastened to a camshaft, having a plurality of gas exchange valves and valve actuating elements, having adjusting units which have a plurality of adjusting elements which are fastened to at least one rotatable adjusting shaft, having transmission apparatuses which comprise transmission elements, the transmission elements being operatively connected to the cams, to the valve actuating elements and to the adjusting elements directly or with the interconnection of transmission members (adjusting rollers, cam rollers), and having at least one adjusting device on the rotatable adjusting shaft.
Variable mechanical valve timing mechanisms of this type for adjusting the stroke of gas exchange valves in a reciprocating-piston internal combustion engine are known from DE 100 06 016 A1 and DE 100 06 018 A1.
Although these valve timing mechanisms differ in terms of the transmission elements between the cams of the camshaft, the valve actuating elements and the adjusting elements, a common feature of theirs is that the individual adjusting elements have curved paths on which the transmission elements slide or roll. Depending on the position of the rotatable adjusting shaft and thus of the curved paths of the adjusting elements, the valve actuating elements and thus the gas exchange valves are moved to a greater or lesser extent, with the result that the stroke of the gas exchange valves is adjusted, in particular the stroke of the inlet valves of the reciprocating-piston internal combustion engine. Depending on the stroke adjustment, considerable forces occur at the adjusting elements, which forces lead to torsional loading of the adjusting shaft, with the result that, depending on the spacing between the adjusting elements and the adjusting device, the stroke is adjusted incorrectly, in the, sense that the gas exchange valves are not opened sufficiently or completely. Depending on the number of cylinders of the reciprocating-piston internal combustion engine and the therefore necessary length of the adjusting shaft, in conjunction with the point of action of the adjusting device, this can lead to substantial deviations in the valve stroke.
It is therefore an object of the invention to improve a variable mechanical valve timing mechanism of the generic type having an adjusting device, in such a way that the deviations in the valve-stroke adjustment are eliminated or reduced to such a large extent that a substantially uniform cylinder filling and smooth running of the internal combustion engine are ensured.
The object of the invention is achieved in that the adjusting shaft/shafts and adjusting elements are configured and arranged in such a way and/or the number and position of the adjusting devices are selected in such a way that all of the gas exchange valves have substantially the same stroke adjustment in relation to one another.
This is initially possible as a result of the fact that the adjusting shaft/shafts is/are adapted to the torque loading accordingly by suitable selection of the section moduli of the loading, and/or as a result of the fact that the adjusting elements or their curved paths and angular positions on the adjusting shaft are selected in such a way that identical stroke adjustment takes place substantially. However, it is also possible to select the number and position of the adjusting devices in such a way that the spacing between the adjusting elements and the adjusting devices is reduced.
In one advantageous refinement of the invention, it is proposed that a plurality of adjusting devices are provided along an adjusting shaft, preferably uniformly distributed. As a result, the spacing between the respective adjusting device and the adjusting elements is shortened, with the result that the rotational angle of the adjusting elements with respect to the adjusting device is reduced accordingly.
In one preferred refinement of the invention, it is proposed that the adjusting shaft is subdivided into a plurality of sectional shafts, and each sectional shaft is assigned an adjusting device. Thus, for example, in a valve timing mechanism for a four-cylinder reciprocating-piston engine, the adjusting shaft can be divided into two sectional shafts which each have an adjusting device, with the result that, depending on the number of inlet valves per cylinder, one or two adjusting elements which are at a small distance from the adjusting device are arranged in each case on each side next to the adjusting device.
In a six-cylinder engine, for example, three sectional shafts having three adjusting devices for in each case two cylinders can be used, or else one or two sectional shafts having two adjusting devices for in each case three cylinders.
In the extreme case, each cylinder can be assigned one sectional shaft having an adjusting device. However, this then leads to costs which cannot be ignored, with the result that it is necessary to perform a cost/use analysis with regard to the number of sectional shafts having adjusting devices.
In an advantageous manner, the adjusting device is arranged centrally on the adjusting shaft or the sectional shaft or, in the case of a plurality of adjusting devices, it is to be arranged on an adjusting shaft in such a way that the load distribution is symmetrical.
The adjusting device can be of any desired configuration. An electric, hydraulic or mechanical actuator can be provided which interacts with toggle levers, gearwheels, worm gears and spindles or hydraulic cylinders
However, it is significant that the actuators or the adjusting devices are activated synchronously and with identical adjusting variables, with the result that the adjustment is identical for all the gas exchange valves.
In a further refinement of the invention, it is proposed that, starting from the adjusting device or devices, the section modulus is varied along the adjusting shaft or shafts or sectional shafts in such a way that all the adjusting devices have substantially the same adjusting angle. This can be achieved firstly in that the diameter is varied in accordance with the spacing between the adjusting elements and the adjusting devise, in order to increase the section modulus accordingly. Secondly, depending on the configuration of the adjusting shaft or the sectional shaft, if it is constructed, for example, from parts, the section modulus can likewise be adapted by suitable selection and variation of the materials.
However, it is also possible for the adjusting cams of the adjusting elements and/or the angular position of the adjusting elements on the adjusting shaft or shafts or sectional shafts to be modified in order to attain an identical stroke adjustment of the gas exchange valves. The concept of the invention can namely also be realized in that, taking into consideration the rotation of the adjusting shaft, the adjusting elements are mounted at the respective location in a leading angular position, with the result that the stroke adjustment is corrected accordingly. For this purpose, it can be necessary to adapt the curved profile accordingly, as the adjustment would be excessively pronounced in the event of relatively small stroke adjustment and thus relatively low forces on the adjusting elements or relatively low torque on the adjusting shaft.
In order to explain the invention further, reference is made to the drawings, in which exemplary embodiments of the invention are shown in simplified form, and in which:
In FIGS. 1 to 6, unless shown in detail, gas exchange valves are denoted by 1, which gas exchange valves are installed in the cylinder head of a reciprocating-piston internal combustion engine. The gas exchange valves are inlet valves which control the inlet flow of air or an air/fuel mixture. The reciprocating-piston internal combustion engine shown is an engine with a row of four cylinders which each have two inlet valves. Each gas exchange valve 1 is operatively connected to a valve actuating element 2 which is configured as a drag lever which is supported on a hydraulic tappet at that end which faces away from the gas exchange valve 1.
Furthermore, 4 denotes a camshaft which is mounted in the cylinder head of the internal combustion engine and to which cams 5 are fastened. An adjusting shaft 6 is arranged parallel to the camshaft 4, which adjusting shaft 6 (likewise in a manner not shown) is mounted rotatably in the cylinder head of the internal combustion engine. Adjusting elements 7 are arranged fixedly on the adjusting shaft 6 so as to rotate with it, each gas exchange valve 1 or each valve element 2 being assigned an adjusting element 7.
Furthermore, transmission elements 8 are arranged between the cams 5 of the camshaft 4, the adjusting shaft 6, the adjusting elements 7 and the valve actuating elements 2, which transmission elements 8 have a rocker arm which is actuated by the cams 5, is supported on the adjusting shaft 6 and displaces guide members which roll on an adjusting cam 9 of the adjusting elements 7; in the process, the valve actuating element 2 is pivoted and the gas exchange valve 1 is opened. The stroke of the gas exchange valves is adjusted from a zero or minimum adjustment to the maximum stroke adjustment as a function of the rotational position of the adjusting shaft 6 and thus of the adjusting elements 7 and the adjusting cam 9. A spring element 11 which ensures restoring of the rocker arms and thus contact of the rocker arms with the cams 5 is in operative contact with each end of the rocker arms which faces away from the cams 5.
An adjusting device which can have various configurations, as explained in the general description, is operatively connected to the adjusting shaft 6. For the sake of simplicity, it is configured as an adjusting lever 10 in FIGS. 1 to 6.
As can be seen easily, large forces are produced on the adjusting elements 7 and adjusting shaft 6 as a result of the high rotational speed of the camshaft 4 and the large accelerations of the cams 5 onto the transmission elements, as the transmission elements also come into contact with the adjusting cam 9 with high acceleration. If only one adjusting unit or one adjusting lever 10 is then attached at the end or in the middle of an adjusting shaft 6 for a four-cylinder engine or even a six-cylinder engine, high rotational deformations occur in the adjusting shaft 6, which lead to incorrect stroke adjustment of the gas exchange valves 1.
If, therefore, according to the invention, in each case one adjusting device or one adjusting lever 10 is attached between the cylinders 1 and 2 and the cylinders 3 and 4 in a four-cylinder engine, the rotational angle of the adjusting elements 7 is reduced considerably in relation to the adjusting lever 10, on account of the shortening of the path.
In FIGS. 4 to 6, the adjusting shaft 6 is divided into two sectional shafts 12, and each sectional shaft 12 is assigned an adjusting device, distinguished by the adjusting lever 10, with the result that each sectional shaft 12 is adjusted appropriately, without the adjusting devices being influenced relative to one another.
Both in the exemplary embodiment according to FIGS. 1 to 3 and also according to FIGS. 4 to 6, it mast of course be ensured that the adjusting devices rotate the adjusting shafts 6 or the sectional shafts 12 at the same adjusting angle and synchronously, in order that the stroke of all the gas exchange valves 1 is adjusted uniformly.
The optimum case for the stroke adjustment accuracy and naturally also for the costs would exist if each cylinder were assigned a dedicated sectional shaft with dedicated adjusting unit (adjusting lever 10). However, this would also lead to high costs. For this reason, a compromise between adjusting accuracy and costs has to be made.
As defined in the general description and the patent claims, the section modulus of the adjusting shaft or of the sectional shafts can be adapted appropriately to the forces which act on the adjusting elements by different material selection or by different diameters of the adjusting shaft or of the sectional shafts.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2004 020 623.6 | Apr 2004 | DE | national |
