Method for varying valve timing of an internal combustion engine

Abstract

A technique is used for adjusting the valve timing of an internal combustion engine with a cam shaft and a cam lobe displaced at a rotational angle with respect to one another. Under interposition of a cam following element, such as, for example, a bucket tappet, the cam shaft and the cam lobe work together with intake or exhaust valves as well as the camshaft actuator present on the camshaft, through which the position and/or the attitude of rotation of the camshaft to the crankshaft can be changed. To decrease the valve opening time, the camshaft can be adjusted toward hate” during a valve stroke, while the camshaft is adjusted toward “early” during the immediately subsequent base circle phase of the affected camshaft. To increase the valve opening times the camshaft can be adjusted toward “early” during a valve stroke, while the camshaft is adjusted toward “late” during the immediately subsequent base circle phase of the affected camshaft. This technique permits adjustment of the angular attitude of the camshaft as well influence on the valve stroke curve.

Description

BACKGROUND AND SUMMARY OF THE INVENTION

This invention relates to a technique for changing the valve timing of an internal combustion engine.

It is commonly known that the timing of an intake or exhaust valve of an internal combustion engine can be changed by first changing the position of the intake camshaft in relation to the exhaust camshaft by means of a camshaft actuator. The opening and closing times of the intake valves are thereby adapted to a certain RPM ranges by two separate intake timings and the valve overlap, while the valve opening duration and the valve stroke remain the same (see, e.g. German document DE 38 76 762). Furthermore the prior art includes variable valve trains in which the valve opening times as well as the valve opening widths are adapted to the operating modes of the engines. German document DE 196 06 054 C2, for example, describes a variable valve train of an internal combustion engine in which the valve stroke can be adjusted between two settings with the aid of a switchable bucket tappet. The assembly is equipped with a device that adjusts the intake and exhaust times of the gas exchange valve, allowing improved filling of the cylinder over a large range of RPMs.

It is an object of this invention to expand the functional range of a camshaft actuator in such a way that, in addition to adjusting the valve timing by “shifting” the valve stroke curve toward intake or exhaust for an “early” or “late” opening, an adjustment of the valve opening time can be achieved.

This object can be achieved through the claimed features.

For decreasing the valve opening time, the invention suggests adjusting the camshaft in the direction of “late” during a valve stroke while adjusting, that is correcting the camshaft in the direction of “early,” during the immediately subsequent base circle phase of the affected camshaft. To increase the valve opening time, which is determined by the shape of the cam lobe, the invention suggests adjusting the camshaft toward “early” during a valve stroke while adjusting, that is correcting the camshaft in the direction of “late,” during the immediately subsequent base circle phase of the camshaft in question. By following these measures, the valve opening duration can be adjusted in an advantageous manner. With the use of a camshaft actuator, a range of function is thereby achieved, which is otherwise possible only with a variable valve train system.

Based on the features specified in dependent claims, additional advantageous configurations of the invention are also possible.

The technique for changing valve timing described is particularly suited for a double-rowed, 6-cylinder engine with a symmetrical ignition sequence per cylinder bank, since, in engines of this type, an even distribution of valve stroke and base circle phase on the camshaft are present.

The inventive procedure described is also suited for combination with a variable valve train, in which a valve stroke cross-over is present, because, as illustrated in the 2-setting valve cross-over exemplified in German document DE 196 06 054 C2, the base circle phase of the cam is especially long with small valve strokes.

An embodiment of the invention is described in further detail in the following description.

BRIEF DESCRIPTION OF THE DRAWING FIGURE

The drawing FIGURE is a diagram showing the valve stroke on the intake side of the internal combustion machine as well as the angular velocity of the camshaft.

DETAILED DESCRIPTION OF THE INVENTION

The inventive procedure is described based on a 6-cylinder boxer engine, both camshafts of which are equipped with camshaft actuator as well as a two-setting valve stroke change-over on the intake side. Internal combustion engines of this type are made by the Porsche Corporation under the model series 996 “VarioCamPlus-System.” The construction and function of this variable valve train therefore does not need to be described in further detail. With the aid of a hydraulically-activated camshaft actuator, the valve timing can be continuously adjusted on the intake side, while, because of the 2-setting valve cross-over, valve stroke curve A can be adjusted with a small cam lobe and valve stroke curve B can be adjusted with a large cam lobe as the diagram illustrates. The valve timing as well as the valve stroke are controlled as a function of the operating parameters of the internal combustion engine such as load or RPM. A possible field of the valve train in which the various operating modes of the valve train are plotted as a function of RPM and load of the internal combustion engine is described and illustrated in German document DE 196 06 054 C2. As long as a continuous adjustment of the angle of rotation of the intake camshaft to the exhaust camshaft and to the crankshaft of the internal combustion engine is present, only valve stroke is shifted toward “early” or “late.” The angular velocity of the camshaft is, up to the actual adjustment process, constant, as shown by the dashed line C in the diagram.

Below the inventive procedure for decreasing or increasing the valve opening duration with the aid of a camshaft actuator is described in further detail. The technique is particularly useful, when the internal combustion engine is driven by small valve strokes, because the base circle phase of the “small cam lobe” is particularly long.

1. Decreasing the Valve Stroke Curve.

During a valve stroke, the intake camshaft is adjusted toward “late” in the amount Δφ, while the attitude of rotational angle of the camshaft is reset, that is, corrected toward “early” during the immediately subsequent base circle, preferably in the amount Δφ. This process is repeated, provided that the valve opening duration for the current operating mode of the internal combustion engine is reduced relative to the “normal” valve opening duration, which is determined by the valve cam lobes. The valve opening, curve D, illustrated in the diagram is thereby provided. Corresponding to valve opening, curve D, is the angular velocity of the camshaft, curve E, whereby it is evident that, during the valve stroke, a positive acceleration of the camshaft toward “late” occurs, while a negative acceleration of the camshaft toward “early” occurs due to the resetting during the base circle phase of the affected cam lobe.

2. Increasing the Valve Stroke Curve.

In this case, the camshaft is adjusted toward “early” in the amount Δφ during the valve stroke, while the camshaft is corrected toward “late” during the base circle, preferably in the amount of Δφ.

The proposed procedure makes it possible to implement further valve stroke geometry with the same cam lobe shape. An influence of the valve stroke curve is then particularly important if a high adjustment velocity can be implemented with the camshaft actuator. An electrically controlled camshaft actuator of the prior art is particularly advantageous in this respect. The previously described procedure is, as has already been mentioned, especially suited for double-rowed 6-cylinder engines, without any restrictions to this configuration, because, in the case of the 1-6-2-4-3-5 ignition sequence used in the Porsche boxer engine, a symmetrical ignition sequence per cylinder bank can be produced, thereby ensuring even distribution of valve stroke and base circle phase on the camshaft. The procedure can also be used on the exhaust side of the internal combustion engine, wherein the exhaust camshaft is also equipped with the necessary camshaft actuator in this case.

Claims

1-3. (canceled)

4. A method for changing a valve timing of an internal combustion engine with a camshaft and a cam lobe displaced at a rotational angle with respect to each other, the camshaft and the cam lobe, under interposition of at least one appropriate cam following element, acting together with intake or exhaust valves of the internal combustion engine as well as with a camshaft actuator situated on the camshaft, through which at least one of a position and a rotational attitude of the camshaft can be adjusted for a crankshaft, comprising: (a) adjusting the camshaft toward “late” during a valve stroke and toward “early” during an immediately subsequent base circle phase of the camshaft to decrease a valve opening time, and (b) adjusting the camshaft toward “early” during a valve stroke and toward “late” during an immediately subsequent base circle phase of the camshaft to increase the valve opening time.

5. The method as claimed in claim 4, wherein the internal combustion engine is a double-rowed, 6-cylinder engine with symmetrical ignition sequence for each cylinder bank.

6. The method as claimed in claim 4, wherein the internal combustion engine is equipped with a device for valve stroke change-over.

7. The method as claimed in claim 4, wherein the cam following element is a bucket tappet.

8. The method as claimed in claim 5, wherein the internal combustion engine is equipped with a device for valve stroke change-over.

9. The method as claimed in claim 7, wherein the internal combustion engine is a double-rowed, 6-cylinder engine with symmetrical ignition sequence for each cylinder bank.

10. The method as claimed in claim 7, wherein the internal combustion engine is equipped with a device for valve stroke change-over.

11. The method as claimed in claim 9, wherein the internal combustion engine is equipped with a device for valve stroke change-over.