Patent Application
20070000461
The invention relates to a device for variable actuation of gas exchange valves of internal combustion engines of the introductory portion of claim 1.
Such devices are used to control gas exchange valves in such a way as to make it possible to operate reciprocating engines without the throttle valve that would otherwise be necessary.
Such a device is disclosed in DE 101 23 186 A1, for example. In this device, a rotating cam first drives a connecting link, which executes a pure oscillating rotary motion and carries a radial cam, which is composed of a rest area and a lift area. The radial cam transfers the lifting curve necessary for actuation of the valve to the roller of a driven element similar to a cam follower which in turn actuates the valve. The desired different valve lifting curves are produced by the fact that the center of rotation of the connecting link is displaced on an arc-shaped path which is concentric to the roller of the driven element when it is in the position that it assumes when the valve is closed. The center of rotation is formed by a roller which is provided on the connecting link and which is supported in a non-positive manner on an arc-shaped track in the housing; this track is also concentric to the roller of the driven element, that is, it forms an equidistant to the path of the center of rotation and is designated as the coulisse. In addition, the roller on the connecting link is supported against a cam disk, whose angular position determines the position of the center of rotation on its arc-shaped path.
DE 101 00 173 describes a completely variable valve train which has driving means, for example a cam and, arranged between the driving means and the gas exchange valve, a connecting link, which acts indirectly on the gas exchange valve; the valve stroke can be changed by adjusting an adjustable guide element.
Other devices of this type have been disclosed in which the center of rotation of the connecting link driven by the cam is supposed to be adjusted on a circular path (OS 195 32 334 A1; EP 0 717 174 A1; DE 101 64 493). However, the previous publications do not contain any teaching about how to construct the devices to realize such adjustment.
However, the prior art device has some disadvantages. All known devices have the common disadvantage that due to manufacturing tolerances the more the valve strokes of the individual cylinders are reduced for the purpose of controlling the load, the greater their differences relative to one another. Moreover, the valve strokes of the gas exchange valves of the same cylinder cannot be changed independently. Completely shutting off the gas exchange valves, that is keeping them closed constantly, and the possibility of turning off a cylinder by completely turning off all intake and/or exhaust valves of individual cylinders, has also not previously been known. Another disadvantage results from the fact that the adjustment of the valve lifting curve occurs during the valve stroke of at least individual gas exchange valves. This requires a high adjusting force, that is, a high adjustment torque with high adjusting power.
It is an object of the invention to create a device which avoids the disadvantages of the prior art and allows additional variability for valve actuation that is entirely mechanical.
This accomplished with the distinguishing features of claims 1 or 2. Advantageous embodiments and further developments are described in claims 2 through 10. Claims 11 and 12 describe processes for operating the inventive device. The displacement of the transmission elements, which causes the change in the valve lifting curve, is performed in separate units for each gas exchange valve or in separate units for several gas exchange valves, each of which is adjacent, and this is done in such a way that these units are adjusted independently of one another, at least some of the time.
In one embodiment of the invention, the position of the changeable transmission element on the respective adjustment curve preferably is determined by direct or indirect contact with one or more cam disks, which are put on one or more adjusting shafts that are connected in a torsionally rigid manner. In another embodiment, the cam disks are put on an axially displaceable adjusting axle. The adjusting shaft or the adjusting axle can in turn be rotated or displaced through a suitable transmission or a connecting element by an adjusting motor. Of course the adjustment can also be accomplished by hydraulic elements. If the units are guided by a linearly adjustable slide, the adjustment can also be accomplished directly from the adjusting motor through a spindle which has a movement thread.
All embodiments also share the fact that the connecting links or their cam rollers have to be held in contact with the cams by special springs. This is immediately seen from the situation at zero lift, when there is cylinder cutout.
The inventive device, including an adjusting motor or an adjusting device, can be separately provided for every valve of an engine, so that any combination of valve strokes or opening angles of the individual valves of an engine is possible, including the turning off of individual cylinders. However, as a rule common adjustment of several valves is provided. This applies especially for intake and exhaust valves of a cylinder in multiple-valve engines. For example, two intake valves can be actuated by a cam through a connecting link which has a radial cam for each valve. Since only one connecting link and only one guide of the units are present, both valves are adjusted together and in the same way. However, the inventive device also allows the common connecting link to have two different radial cams on it with the result of two different lifting curves on the two valves, despite the fact that they are adjusted together. This variant makes it possible, especially in the lowest load range, to open only one of the two valves. The special advantage of this possibility is that in the lowest load range it is only necessary to expose very small cross sections which can be more precisely observed, if they are only exposed by one valve. In addition, opening only one of the intake valves makes it possible to produce swirl in the cylinder charge. The inventive device further expands the possibilities for producing different valve lifting curves for two intake or exhaust valves of a cylinder by the fact that two different cams and two connecting links are used with different radial cams. Nevertheless, the two valves can be adjusted together, since the two connecting links can be mounted on a common unit.
It is also possible to adjust the displacement of transmission elements which cause a change in the valve lifting curve of a larger number of parallel valves together by an adjusting motor or mechanism, especially when it is mounted on a common unit.
Since it is of great significance for the acceptance of variable valve actuation, that is also the inventive device, to keep the adjusting power small, and since it is higher when the device or its slip joints and links are in loaded condition than when they are in the load-free state that is present to a great extent when the valve is closed, the inventive device provides adjustment essentially during the common rest phases of all valves to be adjusted in common. These rest phases are derived from the signals of [sensors on] the crankshaft and the camshaft, and become shorter and shorter the more valves are adjusted together. Thus, the number of valves adjusted together is limited.
The common adjustment of the intake and exhaust valves only of one cylinder in every case produces long rest phases that are “friendly” to adjustment. However, it also makes possible individual load control of the individual cylinders with an inventive adjustment strategy that involves controlling the torques of the individual cylinders for each load state of the entire engine. This is essential for engine smoothness, especially in the lower load range, since manufacturing tolerances mean that the valve strokes do not sufficiently coincide. The signals necessary for this adjustment strategy are also supplied by the rotational angle sensor of the crankshaft and assigned to the individual cylinders by the rotational angle sensor of the camshaft.
In a variant of the inventive design, the displacement of transmission elements, which causes the change in the valve lifting curve, is implemented by means of a common, rotatable adjusting shaft with cam disks. If the adjustment of all or at lease some of the intake and exhaust valves is largely independent, this offers the possibility of turning off selected valves by means of the continuous adjusting shaft, that is no longer opening them or at least adjusting a smaller valve stroke. To accomplish this, sections of the described cam disks of the adjusting shaft are formed as a rest for the valves that are not turned off. The rest area is a contour which is formed from an arc that is concentric to the center of rotation of the adjusting shaft. Rotation of the adjusting shaft does not change the valve stroke of the displacement units controlled by the cam disks with rest within the active area of the rest, while the valve stroke of the displacement units controlled by the cam disks without rest is changed. This change can be carried out until the valve(s) is/are held completely closed. If all intake valves or/and the exhaust valves of the same cylinder are triggered in this way, the change in load is turned off for selected cylinders. Of course the same function is achieved by using a straight guided draw key with a corresponding cam contour. The rest area is then a contour which is formed from a line parallel to the sliding direction of the draw key.
The invention is explained in greater detail below by means of drawings of a few sample embodiments. In the associated drawings,
N Sector
| Number | Date | Country | Kind |
|---|---|---|---|
| 103 12 958.8 | Mar 2003 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP04/02740 | 3/17/2004 | WO | 9/14/2005 |
