EP1619362A2 - Valve train for an internal combustion engine - Google Patents

Abstract

The valve drive has a drive shaft (2) with at least one cam (3) operating a transfer element (4) acting with a second transfer element (12) acting on the stem (15) of a valve (14). The drive includes an elastic component (8), which is fitted so that the pre-tension force created by it is independent of the displacement of the first transfer element relative to the second one.

Description

The present invention relates to a valve train of an internal combustion engine according to the preamble of claim 1.

Valve trains for internal combustion engines have already become known in many embodiments. When known for a long time valve trains, it is not possible to change the valve lift, nor the valve opening time during operation of the internal combustion engine. In addition to variable valve trains in which, for example, the phase position, the valve lift, the steepness of the opening and closing edge or the opening period can be modified, the respective requirements of the thus operated internal combustion engine corresponding valve trains have become known that allow a smaller parameter variation, but constructive are formed simpler.

An example of a valve train for an internal combustion engine, with which the valve opening duration can be varied, is described in the European patent EP 0 865 566 B1. Another example of a variable valve train for an internal combustion engine is described in the unpublished German patent application 102 37 104, which is based on the applicant.

This patent application describes a valve train for an internal combustion engine, with which the height of the stroke of the gas exchange valves can be changed. The change in the lifting height can, for example, depending on the Load situation of the internal combustion engine to be modified. Thus, with the valve train described a full load control can be achieved, ie the valve lift can be maximized and take, for example, a value of about 12 mm and also a valve lift can be realized, which corresponds to the neutral position. In addition, it is also possible to set a cylinder-selective zero-stroke height, ie to realize a cylinder deactivation.

In the case of the valve drive mentioned, a first transmission element is actuated by means of a drive shaft with cam profiles such that a rotational movement of the cams leads to a pivoting movement of the first transmission element, whereby the pivoting movement of the first transmission element via a second transmission element ultimately opens the respective gas exchange valve by overcoming the spring force on the valve stem supported helical compression spring leads. About a rotation of an eccentric shaft, which acts as an actuating element, the first transmission element can now be displaced or displaced relative to the second transmission element on a control cam, so that shifts the contact point between the first and the second transmission element along the control curve. The control cam is now designed so that it has a Nullhubkurvenbereich and a Hubrampenabschnitt, so that by means of the displacement of the contact point between the first and the second transmission element at the two sections a variable valve lift is achieved, which modifies to the idling position of the engine corresponding valve lift can be.

The valve opening force generated by the drive shaft and the cam or cams disposed thereon is transmitted to the valve stem via the two transmission elements, so that it is expedient to establish a biasing force between the first transmission element and the cam to bring about a defined position of the first transmission element on the cam ,

Since, due to the relative movement between the cam and the cam follower in the form of the first transmission element, friction between the cam and the first transmission element occurs, the present invention is Invention now the object of the invention to provide a valve train of an internal combustion engine, with the one hand, a variable valve lift height can be realized and on the other hand, the requirements for the best possible friction behavior between the cam and the cam follower account is taken.

The invention now provides for solving this problem a valve train with the features of claim 1. Advantageous embodiments thereof are described in the further claims.

The invention provides a valve train of an internal combustion engine, wherein the valve drive has a rotatable drive shaft having at least one cam and a first transmission element operable therewith, which is operatively connected to a second transfer element such that this can act on a shaft of a gas exchange valve such that a displacement of the first transmission element along a control curve formed between the first and the second transmission element leads to a change in the lift height of the acted gas exchange valve and the displacement of the first transmission element by means of a rotation of a shaft and / or the actuation of an actuator and an elastic member is the first Actuates transfer element for contact with the cam and this elastic member is arranged such that the biasing force generated by the elastic member of the displacement of the first Übertr Acting element is independent relative to the second transmission element.

The invention thus provides a variable-stroke valve drive, in which the valve lift can be varied in a wide range between a full load position with maximum valve lift and a Leerlaufgasstellung with minimum valve or a Zylinderabschaltstellung Nullventilhub and thereby forming the first cam follower first transmission element of an elastic member is urged against the cam for contact with this, that the biasing force generated by the elastic member of the necessary for effecting the change of the stroke of the gas exchange valve displacement of the first transmission element is independent relative to the second transmission element.

This is achieved in an advantageous manner that regardless of the position of the first transmission element relative to the second transmission element applied by the elastic component biasing force applied over the cam angle assumes the same values and is not changed by a relative movement of the first transmission element relative to the second transmission element, so that at Comparable cam angles a same biasing force and thus surface pressure between the cam and the first transmission element as a cam follower component, without this being introduced by a displacement of the first transmission element relative to the second transmission element, a dependence in the course of the biasing force. Since thus the biasing force does not depend on the displacement of the first transmission element relative to the second transmission element, this displacement also does not lead to a displacement-dependent friction between the Wälzpartnern cam and follower cam component, so the first transmission element.

According to an advantageous embodiment of the invention, it is provided that the elastic member is rotatably mounted on the drive shaft relative to this and that this can be achieved by means of a rotatably mounted on the drive shaft holder, which receives and holds the elastic member.

In a further development of the invention it is provided that the first transmission element is a pivot lever, on which a rolling body is rotatably mounted, which is in rolling contact with the cam of the rotatable drive shaft. Thus, a rolling condition is realized between the rolling elements of the pivot lever and the cam, which contributes positively to the goal of reducing the friction power.

According to an advantageous embodiment according to the invention, the elastic member may be a torsion spring which is received by the holder rotatably mounted on the drive shaft and having a spring arm, which in a bore engages the pivot lever and thus keeps the rolling elements on the pivot lever in contact with the cam.

Now, when the cam with its cam lobe profile comes into contact with the rolling element, the arranged between the drive shaft and the pivot lever torsion spring is stretched, so that the torsion spring ensures that after the turning away of the cam lobe profile from the contact with the rolling elements of the rolling elements against the cam base circle is pressed and thus the rolling element remains in contact with the cam.

According to a development of the invention, it is provided that the above-mentioned control cam is formed on the pivot lever and has a Nullhubkurve and has a Hubrampenabschnitt and the pivoting lever thus formed along the control cam on a second transmission element rotatably arranged rolling elements is displaced. In other words, this means that the pivoting lever can be displaced along the control cam on the rolling body of the second transmission element, so that the contact point between the pivoting lever or the control cam formed on the pivot lever and the rolling element is in the region between the zero-stroke curve and the lifting ramp section so that, when the contact point is in the zero-stroke curve, a cylinder-selective valve deactivation and thereby cylinder deactivation can be realized, and when the contact point is in the range of the lift ramp portion of the control cam, a change in the lift of the gas exchange valve can be realized, as appropriate the position of the contact point along the Hubrampenabschnitts or its geometric design.

According to a development of the invention, it is provided that the shaft for displacing the first transmission element relative to the second Übertragungsüngselement is an eccentric shaft and displacement of the pivot lever on the rolling elements of the second transmission element along the control cam by a predetermined distance is possible by means of a rotation of the eccentric shaft. Thus, by a rotation of the eccentric shaft, for example, a cylinder bank selective Basic tuning of the lifting height of the gas exchange valve of this cylinder bank can be achieved.

By means of an actuation of an eccentric shaft downstream actuator in the form of a piston / cylinder unit, a displacement of the pivot lever on the rolling elements of the second transmission element along the control curve can take place by a predetermined distance, which can be superimposed additively the displacement induced by the eccentric shaft. In other words, this means that depending on the position of the actuator, the displacement caused by the eccentric shaft can be compensated, for example, or by the actuation of the actuator in the direction of displacement of the pivot lever on the second transmission element with the same direction additive superimposed extended displacement of the pivot lever on the rolling elements of the second transmission element can be realized with the example, a shift of the contact point of the control cam on the pivot lever to the rolling elements of the second transmission element can be realized in the range of Nullhubkurve the cam itself and thus a cylinder-selective cylinder shutdown by the valve gear according to the invention.

According to an advantageous embodiment, it is provided that the above-mentioned holder is made of a plastic material, on which the torsion spring can be releasably fixed, for example by means of a latching connection. By a rotatable arrangement of the torsion spring holding holder on the drive shaft is achieved so that the torsion spring is clamped between the drive shaft and the rolling elements of the pivot lever, that the spring force generated by the torsion spring is independent of a displacement of the pivot lever relative to the second transmission element.

Thus, the biasing force with which the rolling elements of the pivot lever is pressed against the cam of the drive shaft, regardless of the displacement of the pivot lever relative to the second transmission element. The geometric relationship between the center of the camshaft, a pivot point of the spring arm The torsion spring and the center of the rolling element of the pivot lever thus remains independent of the position of the pivot lever always the same and thus the biasing force or to be overcome friction.

• Fig. 1 einen Ventiltrieb gemäß einer Ausführungsform nach der vorliegenden Erfindung in Volllaststellung mit einer Drehfeder in Grundstellung;
• Fig. 2 eine Volllaststellung ähnlich Fig. 1 mit aufgrund der Drehung der Nocke gespannter Drehfeder und betätigtem Gaswechselventil;
• Fig. 3 dem Ventiltrieb in einer Leerlaufstellung mit Drehfeder in Grundstellung und unbetätigtem Gaswechselventil;
• Fig. 4 eine Abbildung ähnlich Fig. 3 mit Ventiltrieb in Leerlaufstellung mit aufgrund der Drehung der Nocke gespannter Drehfeder und betätigtem Gaswechselventil;
• Fig. 5 einen Ventiltrieb in einer Stellung zur Herbeiführung einer Zylinderabschaltung mit Drehfeder in Grundstellung; und
• Fig. 6 eine Darstellung ähnlich Fig. 5 mit aufgrund der Drehung der Nocke gespannter Drehfeder und unbetätigtem Gaswechselventil.

The invention will be explained in more detail below with reference to the drawing. This shows in:

• 1 shows a valve train according to an embodiment of the present invention in full load position with a torsion spring in basic position.
• Fig. 2 is a full load position similar to Figure 1 with due to the rotation of the cam tensioned torsion spring and actuated gas exchange valve.
• 3 shows the valve drive in an idle position with torsion spring in the basic position and unconfirmed gas exchange valve.
• 4 is an illustration similar to Figure 3 with valve train in neutral position with due to the rotation of the cam tensioned torsion spring and actuated gas exchange valve.
• 5 shows a valve drive in a position for bringing about a cylinder deactivation with a torsion spring in the basic position; and
• Fig. 6 is a view similar to Fig. 5 with due to the rotation of the cam tensioned torsion spring and unactuated gas exchange valve.

Below follows a description of the valve train with reference to Fig. 1 of the drawing, wherein the reference numbers introduced here apply to the other figures.

1 of the drawings now shows a valve train 1 according to an embodiment of the present invention in a schematic view for ease of understanding in a plan view.

The valve drive 1 has a drive shaft 2, which is rotated by the base engine, not shown, via a drive in the form of a chain or a toothed belt or the like in rotation. In the figures, the drive shaft 2 is shown with only one cam 3, but may be the drive shaft with cams of a multi-cylinder internal combustion engine, so that it is readily apparent that the drive shaft 2 may have a plurality of cams 3. The valve drive 1 shown can thus serve for the inlet control of a multi-cylinder multi-valve internal combustion engine.

The cam 3 now follows a cam follower component or first transmission element 4 in the form of a pivoting lever.

At the cam 3 facing the end of the pivot lever 4, a rolling element 5 is rotatably arranged in the form of a roller on the pivot lever 4, so that it comes between the cam 3 and the roller 5 to a rolling operation. The pivot lever 4 has in the region of the bearing of the roller 5 a bore or receptacle 6, in which a spring arm 7 of a torsion spring 8 engages. The torsion spring 8 is received in a made of a plastic material holder 9, wherein for receiving the torsion spring 8, the holder 9 is formed in two parts and by latching the two housing halves of the holder 9, the torsion spring 8 is fixed in the holder 9. The thus created unit of torsion spring 8 and holder 9 can now be rotatably mounted on a bearing portion of the drive shaft or camshaft 2.

The pivot lever 4 can be displaced by 180 degrees from the full-load basic position of the valve drive shown in FIGS. 1 and 2 of the drawing into a neutral basic position shown in FIGS. 3 to 6 by means of a rotation of an eccentric shaft 10, wherein the in FIGS. 1 and 2 of FIG Drawing shown full load position of the idle position shown in Fig. 3 and 4 in particular differs in that the point of contact between a formed on the pivot lever 4 and a control cam arranged on a second transmission element 12 roller 13 from the designated with HR Hubrampenabschnitt the control curve 11 migrates to the NH designated Nullhubabschnitt the cam 11.

The second transmission element 12 in the form of a finger lever can press on a valve stem 15 for actuation of a gas exchange valve 14 and is supported at its end 16 opposite the valve stem 15 at, for example, a hydraulically operating valve clearance compensation element 17.

The gas exchange valve 14 is axially guided with its valve stem 15 in a valve stem guide 18 which may be pressed into a cylinder head, not shown, and is kept closed in an unopened state by means of a coil spring 19, so that the valve disc 20 against a in the cylinder head of Internal combustion engine arranged valve seat presses.

As already mentioned above, the holder 9 is rotatably mounted at a bearing point of the drive shaft or camshaft 2, so that a rotation of the camshaft 2 does not lead to a deflection of the spring arm 7 with respect to the center axis 21 of the torsion spring 8, as long as the cam 3 rolls with its base circle on the roller 5. Since the torsion spring 8 exerts a biasing force in the basic position shown in FIG. 1, the roller 5 is pressed against the cam 3 by this pretensioning force.

As it is readily apparent, this position of the valve train 1 was achieved in that the cam 3 come into contact with the cam 5 with its cam elevation curve 22 is and thus has acted upon the pivot lever 4 in the direction of the gas exchange valve 14 out. The pivoting movement of the pivoting lever 4 leads to a shift of the contact point between the Hubrampenabschnitt HR of the control cam 11 and the roller 13, so that the valve play compensating element 17 supporting cam followers 12 directed towards the valve stem 15 of the gas exchange valve 14 is directed downward and thus the gas exchange valve 14th in an open position presses (in Fig. 2 is the sake of simplicity, the coil spring 19th has been omitted), so that the gas exchange valve 14 is open with maximum lift height for gas exchange operation. By the rotational movement of the cam 3, the spring arm 7 of the torsion spring 8 is biased and keeps the roller 5 in contact with the cam third

Fig. 3 of the drawing shows now the valve gear 1 in the neutral position corresponding to a basic position with the torsion spring 8 in basic position. To bring about the idling position, the eccentric shaft 10 has been rotated by 180 degrees, which leads to a displacement of the pivot lever 4 along the control cam 11 in the designated zero NH range. As is readily apparent from FIG. 3 in comparison to FIG. 1, the included between the center axis 21 and a along the center axis of the spring arm 7 reference axis 23 included angle α by the displacement of the pivot lever 4 along the control cam 11 in the area of the zero stroke section of the control cam 11 is not changed. Thus, the base of the torsion spring 8 corresponding biasing force is maintained, so that no change in the friction conditions in the valve train 1 has resulted from the displacement of the pivot lever 4.

Fig. 4 of the drawings now shows a representation similar to FIG. 3 with a rotated cam, so that the gas exchange valve 14 performs a valve lift, which is sufficient to maintain the idle speed of the internal combustion engine. As an example, when the valve lift of the gas exchange valve in the full load position is 12 mm, for example, the valve lift in the idling position may be reduced to a value of, for example, 1.5 mm. The biasing force generated in the deflected by the rotation of the cam 3 and tensioned position of the torsion spring 8 corresponds to the biasing force of the torsion spring 8 in the illustrated in Fig. 2 deflected position in full load operation.

Finally, Fig. 5 of the drawings shows the valve train 1 in a position to effect selective cylinder deactivation. This position was realized by a further displacement of the pivot lever 4 along the zero lift curve NH of the control cam 11 by means of the application of a piston / cylinder unit 24 with, for example, pressure oil from the engine lubricating oil circuit. The application of the piston / cylinder unit 24 now leads to a displacement brought about by the displacement of the pivoting lever 4 due to the rotation of the eccentric shaft 10, which is additively superimposed on a further displacement of the pivoting lever 4 brought about by the piston / cylinder unit 24 such that the point of contact between the Control cam 11 and the roller 13 has been moved to the end of the zero lift NH. In this position, the valve train 1, in which the biasing force of the torsion spring 8 in the unactuated initial position of the biasing force of the torsion spring 8 in the unactuated basic position in the full load position of the valve train 1 and in the idle position of the valve train 1 corresponds (the angle α has not changed) , A rotation of the cam 3 (see Fig. 6 of the drawing) to a rolling of the contact point between the roller 13 and the control cam 11 in the zero-turn NH, so that it no longer comes to an opening of the valve stem 15 by the cam follower 12 , the gas exchange valve 14 remains closed, the associated cylinder of the internal combustion engine is excluded from the gas exchange process, the cylinder is selectively switched off.

Also in the position shown in Fig. 6, actuated by the cam 3 and thus deflected and cocked position of the torsion spring 8, the biasing force generated by the torsion spring 8 corresponds to those of the torsion spring 8 in the tensioned state in idle position of the valve gear 1 and in tensioned state in full load position of the valve train 1 is generated. Thus, the biasing force of the torsion spring 8 changes in each of the cam 3 not actuated basic position or actuated by the cam 3 deflected biased position not in response to the displacement of the pivot lever 4 and thus not in response to the desired or realized valve lift ,

With regard to features of the invention which are not explained in greater detail above, reference is expressly made to the claims and the drawings, moreover.

1.

Ventiltrieb

2.

Antriebswelle

3.

Nocke

4.

Schwenkhebel

5.

Laufrolle

6.

Bohrung

7.

Federarm

8.

Drehfeder

9.

Halter

10.

Exzenterwelle

11.

Steuerkurve

12.

2. Übertragungselement, Schlepphebel

13.

Laufrolle

14.

Gaswechselventil

15.

Ventilschaft

16.

Schlepphebelende

17.

Ventilspielausgleichselement

18.

Ventilschaftführung

19.

Schraubenfeder

20.

Ventilteller

21.

Mittenachse

22.

Nockenerhebungskurve

23.

Bezugsachse

24.

Kolben/Zylindereinheit

LIST OF REFERENCE NUMBERS

1.

valve train

Second

drive shaft

Third

cam

4th

pivoting lever

5th

caster

6th

drilling

7th

spring arm

8th.

torsion spring

9th

holder

10th

eccentric shaft

11th

cam

12th

2. Transmission element, drag lever

13th

caster

14th

Gas exchange valve

15th

valve stem

16th

Drag lever end

17th

Lash adjuster

18th

Valve stem guide

19th

coil spring

20th

valve disc

21st

mid-axis

22nd

Cam elevation curve

23rd

reference axis

24th

Piston / cylinder unit

Claims (12)

Valve gear of an internal combustion engine, comprising a rotatable drive shaft (2) with at least one cam (3) and a first transmission element (4) actuatable therewith, with a second transmission element (12) acting on a shaft (15) of a gas exchange valve (14) An operative connection is such that a displacement of the first transmission element (4) along a control curve (11) formed between the first (4) and second (12) transmission element leads to a change in the lift height of the gas exchange valve (14) being acted upon, and the displacement of the first transmission element (4) by means of a rotation of a shaft (10) and / or the actuation of an actuator (24), and an elastic member (8) acts on the first transmission element (4) for contact with the cam (3), characterized in that the elastic component (8) is arranged in such a way that the prestressing force generated by the elastic component (8) is dependent on the displacement ng of the first transmission element (4) relative to the second transmission element (12) is independent. Valve gear according to claim 1, characterized in that the elastic member (8) on the drive shaft (2) is arranged rotatable relative thereto. Valve gear according to claim 1 or 2, characterized in that the elastic member (8) by means of a relative to the drive shaft (2) rotatable holder (9) on the drive shaft (2) is arranged. Valve gear according to one of the preceding claims, characterized in that the first transmission element (4) is a pivot lever on which a rolling body (5) is rotatably mounted, which is in rolling contact with the cam (3). Valve gear according to claim 4, characterized in that the elastic Component (8) is a torsion spring which engages with a spring arm (7) in a bore (6) of the pivot lever (4) and holds the rolling elements (5) in contact with the cam (3). Valve gear according to claim 4 or 5, characterized in that the control cam (11) on the pivot lever (4) is formed and a zero stroke (NH) and a Hubrampenabschnitt (HR) has and the pivot lever (4) along the control cam (11) on a on the second transmission element (12) rotatably arranged rolling elements (13) is displaceable. Valve drive according to one of claims 4 to 6, characterized in that the shaft (10) is an eccentric shaft and by means of the rotation of the eccentric shaft (10) a displacement of the pivot lever (4) on the rolling body (13) of the second transmission element (12) along the Control cam (11) takes place by a predetermined distance. Valve drive according to one of claims 4 to 7, characterized in that the actuator (24) is a piston / cylinder unit, by means of whose actuation a displacement of the pivot lever (4) on the rolling body (13) of the second transmission element (12) along the control cam (11 ) takes place by a predetermined distance, which is additive superimposed by the eccentric shaft (10) induced displacement. Valve gear according to one of claims 3 to 8, characterized in that the holder (9) is preferably made of a plastic material. Valve gear according to claim 9, characterized in that the torsion spring (8) on the holder (9) by means of a latching connection is releasably fixed. Valve gear according to claim 9 or 10, characterized in that the holder (9) together with the torsion spring (8) releasably on the drive shaft (2) is rotatably fixed. Valve gear according to one of claims 5 to 11, characterized in that the torsion spring (8) by means of the holder (9) between the drive shaft (2) and the rolling body (5) of the pivot lever (4) is clamped that of the torsion spring (8) spring force generated by a displacement of the pivot lever (4) relative to the second transmission element (12) is independent.

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