WO2012146361A1

WO2012146361A1 - Valve drive for gas exchange valves of an internal combustion engine having a main camshaft and cam carriers which can be displaced between rotary bearings of the main camshaft into two or more discrete displacement positions

Info

Publication number: WO2012146361A1
Application number: PCT/EP2012/001711
Authority: WO
Inventors: Michael Gross; Stefan Dengler
Original assignee: Audi Ag
Priority date: 2011-04-23
Filing date: 2012-04-20
Publication date: 2012-11-01
Also published as: EP2702253B1; JP2014512486A; DE102011018503A1; EP2702253A1; JP5901742B2

Abstract

The invention relates to a valve drive (1) for gas exchange valves (2) of an internal combustion engine, having at least one main camshaft (4), having at least one cam carrier (5) which is axially displaceable on the main camshaft (4) and which comprises at least one cam group (6, 7) with at least three cams (13, 14, 15) with different cam profiles, having devices (21, 22, 23, 24, 25) for the axial displacement of the cam carrier (5) on the main camshaft (4) into a number of discrete displacement positions corresponding to the number of cams (13, 14, 15) of the cam group (6, 7), and having a locking device (26) with a spring-loaded ball (28) for locking the cam carrier (5) in the discrete displacement positions. In order inter alia to reduce the required installation space, it is proposed according to the invention that the main camshaft (4) is mounted at both sides of the cam carrier (5) in a positionally fixed rotary bearing (3), and that the spring-loaded ball (28) of the locking device (26) is arranged in a recess (27) of the main camshaft (4) and pushes the cam carrier (5), in two outer displacement positions, in each case against a positionally fixed axial stop (3, 18).

Description

Valve gear for gas exchange valves of an internal combustion engine with a basic camshaft and between pivot bearings of the basic camshaft in two or more discrete shift positions displaceable cam carriers

The invention relates to a valve train for gas exchange valves of an internal combustion engine according to the preamble of claim 1, and an internal combustion engine with such a valve train.

To improve the thermodynamic properties of internal combustion engines mechanical devices are known which influence the working cycle of the valve train and, for example, allow a speed-dependent change in the opening times and / or the stroke of gas exchange valves of cylinders of the internal combustion engine.

A valve train is already known from EP 1 608 849 B1, in which a plurality of cam carriers are arranged in a rotationally fixed and axially displaceable manner on a base camshaft. For actuating two gas exchange valves of a cylinder of the internal combustion engine, two axially offset cam groups are provided on each cam carrier, each of which has two cams with different cam profiles. By axial displacement of the cam carrier on the base camshaft between two discrete shift positions, one of the two cams of each cam group can be brought into abutting contact with a drag lever of one of the two gas exchange valves, whereby the stroke and / or the opening times of the gas exchange valves can be adjusted. The axial displacement of the cam carrier on the base camshaft is carried out by means of two worm gears, which are arranged at an axial distance from each other. Each worm drive comprises an actuator mounted in the cylinder head housing of the internal combustion engine with an extendable driver pin engageable with an opposing cam or gate on the cam carrier. The cam or shift gate has a left-handed helical groove in one of the two worm gears and a right-handed helical groove in the other of the two worm gears, so that the cam carrier can be moved back and forth between the two discrete shift positions by actuating the corresponding actuator. In each of the two displacement positions of the cam carrier is pressed from one side against a arranged between the cam groups stationary pivot bearing in which the cam carrier rotatably charged is gert. The cam carrier is held in each of the two displacement positions by a ball inserted into a bore of the base camshaft locking device which is pressed by a spring against an inclined edge on the inner circumference of the cam carrier and thereby presses one of the cam groups from one side against the pivot bearing.

To improve the effect on the working cycle of the valve train, it is desirable to expand the or each cam group by at least one additional cam. Such an extension of the cam group (s) by an additional cam with a further cam profile, however, makes it necessary to move the cam carrier back and forth between at least three different displacement positions to selectively bring all the cam with the cam follower in abutting contact. In order to make this possible, DE 10 2007 010 150 A1 has already proposed a valve drive of the type mentioned in the introduction, in which each cam carrier has two cam groups each having three cams and is displaceable between three discrete displacement positions. The cam carrier is held in the three displacement positions by a stationary mounted in the housing of the internal combustion engine locking device which acts on a together with the cam carrier axially displaceable pivot bearing. In this case, the spring-loaded ball of the locking device engages in the three displacement positions in three recesses of a mounted on the outside of the rotary bearing locking bar, which are separated by two projections. In the two outer displacement positions, the ball is pressed in each case against an outer edge of one of the two projections in order to press the cam carrier against a stationary stop of the cylinder head housing. In the middle displacement position, the ball engages in a complementary shaped recess of the locking bar between the two projections. In this solution is considered disadvantageous that the pivot bearing must be axially slidably guided in the cylinder head housing, which complicates the lubrication of the pivot bearing that the locking device in the cylinder head housing in the radial direction of the basic cam requires relatively much space, and that below the basic camshaft in the vicinity of the Towing lever two additional stops for the sliding pivot bearing must be provided, although there is little free space available.

Proceeding from this, the invention has the object to improve a valve train of the type mentioned in that a movable pivot bearing is unnecessary and less space is needed. This object is achieved in that the basic camshaft is mounted on both sides of the cam carrier in a stationary pivot bearing and that arranged in a bore of the basic camshaft spring-loaded ball of the locking device presses the cam carrier in two opposite outer displacement positions of the cam carrier against a stationary axial stop.

The invention is based on the idea, the stationary pivot bearing for rotatably supporting the camshaft and serving to define the two outer discrete shift positions stops not in the region of the cam carrier, but beyond the front ends of the cam carrier, i. between adjacent cam carriers to arrange. In this way, the ball of the locking device as in the valve gear from EP 1 608 849 B1 accommodated in a transverse bore of the base camshaft and be pressed by the spring from the inside against an oblique edge of a recess on the inner circumference of the cam carrier to the cam carrier in the two outer displacement positions against one of the fixed axial stops to be pressed, which is preferably formed by one of the two adjacent to the cam carrier pivot bearing o- a bearing block of this pivot bearing. As a result, the required space can be considerably reduced.

In order to hold the cam carrier in one or more inner displacement positions, the spring-loaded ball in these displacement positions expediently engages in an opposite recess on the inner circumference of the cam carrier, which is arranged between the two recesses with the oblique flanks. In other words, the cam carrier has on its inner circumference at least three axially successively arranged recesses, of which at least the two outer are each delimited by an oblique flank and are separated by projections of at least one interposed recess. When the cam carrier is displaced from one outer shift position to the other outer shift position, the spring-loaded ball successively moves over the projections and through the inner recess (s). For manufacturing reasons, all recesses are preferably formed as grooves which rotate around the inner circumference of the cam carrier, wherein the axial center distance of the recesses corresponds to the axial center distance of the associated cam or cam profiles. As in the prior art according to EP 1 608 849 B1 or DE 10 2007 010 150 A1, the means for axially displacing the cam carrier preferably comprise a worm drive with at least one stationary actuator from which at least one driver extends and into an opposite helical groove of a curve - Or switching gate of the cam carrier can eintrack. Depending on whether the driver is meshed in a right-handed or left-handed groove, the cam carrier is moved accordingly on the base camshaft to the left or to the right.

In order to be able to change the stroke and / or the opening times of both valves simultaneously in internal combustion engines with two intake or exhaust valves per cylinder, the or each cam carrier expediently has two cam groups, which are arranged at an axial distance corresponding to the distance between the valves. Since due to the storage of the basic camshaft between adjacent cam carriers in the area between the two cam groups of each cam carrier not a pivot bearing must be provided as in the prior art according to EP 1 608 849 B1 or DE 10 2007 010 150 A1, the cam or shift gate can be arrange the worm drive according to a further preferred embodiment of the invention between the two cam groups of each cam carrier, which allows a significant reduction in the length of each cam carrier. In addition, unlike in this prior art, a single worm gear with a continuous curve or shift gate for displacement of the cam carrier is sufficient.

In addition, the curve or shift gate and the at least one actuator of the means for axially displacing the cam carrier in their execution can be arbitrarily adapted to the axial distance of the valves or to the available space. Preferably, the cam carrier is pressed in the two outer displacement positions below the base camshaft against the pivot bearing or against a bearing block of the pivot bearing, which above the camshaft sufficient space for the at least one actuator is provided.

A further advantageous embodiment of the invention provides that the central cam of each cam group is slightly wider than the two outer cam of each cam group, since the caused by thermal expansion of the cylinder head and the basic cam shaft tolerances of the displacement there are greater than in the outer cam. In the following the invention will be explained in more detail with reference to an embodiment shown in the drawing.

Fig. 1 shows a side view of a part of a valve train for pairs of intake valves of cylinders of an internal combustion engine, which comprises a portion of a basic camshaft mounted in pivot bearings with an axially displaceable cam carrier;

Fig. 2 shows a longitudinal sectional view of a slightly longer portion of the basic camshaft with three cam carriers and locking means for locking the cam carrier;

FIG. 3 shows an enlarged view of the section III in FIG. 2.

With the only partially shown in the drawing valve train 1 for pairs of intake valves 2 of cylinders (not shown) of an internal combustion engine with an overhead, in rotary bearings 3 of a cylinder head housing (not shown) of the engine rotatably mounted camshaft base 4, as well as several, on the base camshaft 4 axially displaceable cam carriers 5, the stroke and / or the opening times of the intake valves 2 of each cylinder can be adjusted independently of the stroke and / or the opening times of the intake valves 2 of the remaining cylinders.

For this purpose, the valve drive 1 for each pair of inlet valves 2 comprises one of the displaceable cam carrier 5, which is non-rotatably connected to the Grundnockenweile 4 and two axially spaced cam groups 6, 7 has. Each of the two cam groups 6, 7 interacts with a roller 8 of a pivotally mounted roller cam follower 9 of one of the valves 2. About the roller 8 a shown in Fig. 1, at the lower end with a valve plate 10 'provided valve member 10 is actuated, press against the force of a valve spring 1 1 (Fig. 2) in the cylinder head down to open the respective valve 2 leaves. The valve drive 1 furthermore comprises, for each of the valves 2, a hydraulic valve clearance compensation element 12 likewise shown in FIG. 1.

Each of the two cam groups 6, 7 of each cam carrier 5 has three cams 13, 14, 15 which project beyond the outer circumference of the cam carrier 5 on one side and have different cam profiles or cam contours. On the cam 3, 4, 15 diametrically opposite side of the cam carrier 5, the No- groups 6, 7 a base circle portion 16 which extends with a constant outer diameter over the entire axial length of the cam groups 6, 7 and over a circumferential angle of about 180 degrees. The degree of projection of the cams 13, 14, 15 over the base circle portion 16 varies according to the desired lift height of the valve member 10, while the angular position of a vertex of the cams 13, 14, 15 in the direction of rotation of the base camshaft 4 corresponding to the desired time of maximum opening of the valve 2 varies. The cam profiles or cam contours of the cams 13, 14, 15 of the two cam groups 6, 7 can each be shaped and / or dimensioned differently. In both cam groups 6, 7, the central cam 14 is slightly wider than the two outer cams 13 and 15, as will be explained later.

The three cams 13, 14, 15 of both cam groups 6, 7 can be brought by axial displacement of the cam carrier 5 on the base camshaft 4 between three discrete shift positions either with the roller 8 of the finger lever 9 of the cam group 6 and 7 associated valve 2 in abutting contact ,

The three displacement positions are shown in FIG. 2 using the example of three cam carriers 5. The left cam carrier 5 is located there in its right outer displacement position in which it rests with its right front end 17 from the left against a bearing block 18 of the adjacent pivot bearing 3, which is arranged between the left and the central cam carrier 5, and in which Rolls 8 of the drag lever 9 of the two valves 2 each with the left outer cam 13 of the cam groups 6, 7 come into abutting contact. The cam carrier 5 shown in the middle is in its middle displacement position, in which its two front ends 17 each have an axial distance from the bearing chairs 18 of the two adjacent, both sides of the cam carrier 5 arranged pivot bearing 3 and in which the rollers 8 of the cam followers 9 of two valves 2 with the central cam 14 of the two cam groups 6, 7 come into abutting contact. The right cam carrier 5 is in its left outer displacement position in which he rests with his left front end 16 from the right against the bearing block 18 of the adjacent pivot bearing 3 between the middle and the right cam carrier 5 and in which the rollers 8 of the drag lever 9 of two valves 2 in each case with the right outer cam 15 of the cam groups 6, 7 come into abutting contact. In contrast, Fig. 1 shows only a cam carrier 5, which is in its middle displacement position. In order to non-rotatably connect the cam carrier 5 to the base camshaft 4, but to allow their axial displacement along the base camshaft 4, the hollow cylindrical cam carrier 5 along a part of its inner circumference on an inner longitudinal teeth 19 (Fig. 2), which with a complementary External longitudinal toothing 20 (FIG. 1) on a part of the base camshaft 4 meshes.

The axial displacement of the cam carrier 5 on the base camshaft 4 for adjusting the stroke or opening times of the intake valves 2 takes place as needed and is always carried out when the base circle portion 16 of the cam groups 6, 7 during a rotation angle of the base camshaft 4 of about 180 degrees rolls 8 of the cam follower 9 is opposite. The extent of the axial displacement of a cam carrier 5 between two adjacent displacement positions corresponds to the center distance of adjacent cams 13, 14 and 14, 15 of the cam groups 6, 7.

Thus, the cam carrier 5 can be moved as needed in any of the three displacement positions, a single worm gear 21 is provided for each cam carrier 5. The worm drive 21 comprises a single cam or switching gate 22, which is arranged approximately in the axial center of the cam carrier 5 between the two cam groups 6, 7 or between the two valves 2, and a stationary mounted in the cylinder head housing actuator 23, the in Fig 1 is shown only schematically. Depending on the design of the actuator 23 may have one or more driving pins 24 which extend either from the actuator 23 and can be brought with its free end with an opposite groove 25 of the cam or switching gate 22 into engagement with the cam carrier 5 each to the Center distance between two adjacent cams 13, 14 and 14, 15 to move in one of the three discrete shift positions.

The outer diameter of the cam or gate 22 is dimensioned so that the cam or gate 22 at a displacement of the cam carrier 5 from the middle displacement position in one of the two outer displacement positions in the axial direction with one of two brackets 37 (FIG. overlaps, of which the roller 8 of the Rollenschlepphebels 9 is rotatably supported.

In order to hold each cam carrier 5 in the respectively desired displacement position, a locking device 26 is provided for each cam carrier 5. As best shown in FIG. 2, each locking device 26 comprises a ball 28 inserted into a blind blind bore 27 of the base camshaft 4 and spaced from one between the blind hole 27 and the ball 28 arranged prestressed helical compression spring 29 is pressed radially against an opposite inner circumference of the cam carrier 5. Within the region of the cam carrier 5, which is opposite the ball 28 when moving between the three displacement positions, the inner circumference of the cam carrier 5 is not provided with the inner longitudinal teeth 19, but with three circumferential grooves 30, 31, 32 arranged in the axial direction one behind the other are.

The central groove 31 has a concave rounded groove cross-section adapted to the shape of the ball and is separated from the adjacent outer grooves 30, 32 on both sides by a projection 33, 34 rounded in cross-section. As shown in Fig. 2 for the central cam carrier 5, the ball 28 is pressed in the middle displacement position of the cam carrier 5 of the spring 29 in the central groove 31, so that the cam carrier 5 alone by the latching engagement of the ball 29 in as a catch - recess groove 31 is held in this middle displacement position. If in this displacement position of the worm gear 21, an axial displacement force is exerted on the cam carrier 5, the ball 28 is pressed to the left or right against one of the two projections 33, 34 and of this projection 33, 34 against the force of the spring 29 in the Blind hole 27 pushed back so that the ball 28 on the projection 33, 34 can move away into the adjacent groove 30, 32. The movement of the ball 28 ends when the cam carrier strikes 5 with its front end 16 in the direction of movement against the bearing block 18 of the adjacent pivot bearing 3, as shown in Fig. 2 for the left and right cam carrier 5.

The two outer grooves 30, 32 are bounded on their side facing the middle groove 31 each by an oblique edge 35, 36. Against this edge 35 or 36, the ball 28 is pressed by the helical compression spring 29 when the cam carrier 5 abuts with a front end 16 in the direction of movement against the bearing block 18 of the adjacent pivot bearing 3, which limits the axial displacement of the cam carrier 5 in the respective outer displacement position , By the contact pressure of the ball 28 against the inclined edge 35, 36 is exerted by the ball 28, an axial force component on the cam carrier 5, as shown in Fig. 2 by arrows. This axial force component ensures that the cam carrier 5 is pressed in each of the two outer displacement positions with one of its front ends 16 against the bearing seat 18 of the adjacent pivot bearing 3 in the direction of movement and thereby in one defined position is held, in which the cam profile of one of the two outer cam 13, 15 of the roller 8 of the roller cam follower 9 exactly opposite. For this reason, the width of the two outer cams 13, 15 can each be made slightly narrower than the width of the middle cam 14.

Although not shown in the drawing, the central groove 31 does not necessarily have a matched to the shape of the ball 28 concave rounded groove cross-section, but may for example also have a limited by two flat oblique edges triangular groove cross-section, in which case the located in the central groove 31 ball 28 is pressed by the spring 29 at two points against the two flanks.

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LIST OF REFERENCE NUMBERS

valve train

intake valves

pivot bearing

base camshaft

cam support

cam group

role

Roller cam

valve member

valve disc

valve spring

Lash adjuster

cam

Base circle portion

Frontal cam carrier

Bearing swivel bearing

Internal spline cam carrier

External longitudinal toothing Basic camshaft

worm drive

curve backdrop

actuator

Carrier pin

groove

locking

Blind hole

Bullet

Helical compression spring

groove

groove groove

Lead ledge flank

flank

Retainer roll

Claims

P AT EN TA NSPR O CHE

1. Valve drive for gas exchange valves of an internal combustion engine having at least one base camshaft, at least one on the base camshaft axially displaceable cam carrier comprising at least one cam group with at least three cams with different cam profiles, means for axially displacing the cam carrier on the base camshaft in one of the number of cams Cam group corresponding number of discrete displacement positions, and a locking device with a spring-loaded ball for locking the cam carrier in the discrete shift positions, characterized in that the base camshaft (4) on both sides of the cam carrier (5) in stationary pivot bearings (3) is mounted and that the spring-loaded Ball (28) of the locking device (26) in a recess (27) of the base camshaft (4) is arranged and the cam carrier (5) in two outer displacement positions each against a stationary axial stop (3, 18) press t.

2. Valve drive according to claim 1, characterized in that the spring-loaded ball (28) of the locking device (26) engages in at least one located between the outer displacement positions inner displacement position in an opposite recess (31) on the inner circumference of the cam carrier (5).

3. Valve drive according to claim 2, characterized in that the spring-loaded ball (28) of the locking device (26) in the inner displacement position with the opposite recess (31) is in latching engagement.

4. Valve drive according to one of the preceding claims, characterized in that the cam carrier (5) at its inner periphery at least three in the axial direction successively arranged recesses (30, 31, 32), of which the two outer recesses (30, 32) are each separated by projections (33, 34) of at least one interposed recess (31).

5. Valve drive according to claim 4, characterized in that the axial center distance of the recesses (30, 31, 32) corresponds to the axial center distance of adjacent cams (13, 14, 15) of the cam groups (6, 7).

6. Valve drive according to claim 4 or 5, characterized in that at least the two outer recesses (30, 32) each bounded by an oblique edge (35, 36).

7. Valve drive according to claim 4, 5 or 6, characterized in that the recesses are circumferential grooves (30, 31, 32) in the inner circumference of the cam carrier (5).

8. Valve drive according to one of the preceding claims, characterized in that the cam carrier (5) has two cam groups (6, 7), which are arranged at an axial distance from each other, and that the means (21, 22, 23, 24, 25) for axial displacement of the cam carrier (5) comprise a worm drive (21) with a single cam or shift gate (22) arranged between the two cam groups (6, 7).

9. Valve drive according to claim 8, characterized in that the worm drive (21) comprises at least one stationary actuator (23) with at least one extendable driver (24) extending into a helical groove (25) of the cam or shift gate (22). eintrack.

10. Valve drive according to claim 8 or 9, characterized in that the cam or shift gate (22) of the worm drive (21) in the two outer displacement positions with a holder (37) of a roller (8) of a drag lever (9) of a the gas exchange valves (2) overlaps.

11. Valve gear according to one of the preceding claims, characterized in that the central cam (14) of each cam group (6, 7) is slightly wider than the outer cam (13, 15) of each cam group (6, 7).

12. Valve drive according to one of the preceding claims, characterized in that the spring-loaded ball (28) of the locking device (26) in each of the two outer displacement positions a front end (16) of the cam carrier (5) against the axial stop (3, 18) presses ,

13. A vent drive according to one of the preceding claims, characterized in that the axial stop (3, 18) of one of the stationary pivot bearing (3) or of a bearing block (18) of the stationary pivot bearing (3) is formed.

14. Internal combustion engine, characterized by at least one valve gear (1) according to one of the preceding claims.