EP0579592A1 - Internal combustion engine comprising a camshaft with axial moving device - Google Patents

Abstract

The camshaft has several switchable cams with different axial offset, per valve. It is moved by a control device. The device consists of a shift link (10) with two or more helical opposite guide grooves (10'), and a catch (11), which is moved into the grooves by a trigger (12). The guide grooves end in release grooves (10"), and engagement of the catch in one of these defines various operational positions of the camshaft (3). The guide grooves are worked into the camshaft. The catch is secured against turning about the camshaft axis (3a), pref. is connected to the cylinder head via a housing (13) of the control device. The catch is formed by a spring ring around the camshaft.

Description

The invention relates to an internal combustion engine with at least one camshaft axially displaceable by an adjusting device with a plurality of switchable cams having different axial offsets per valve.

In order to vary the valve lift curve during the operation of the engine and thus to be able to adapt the optimal opening and closing times to the respective engine operating state, it is desirable to switch between several cam shapes per valve during operation. This can be done expediently by an axially displaceable camshaft with different cams per valve.

From DE-OS 35 03 740 an internal combustion engine of the type mentioned is known, in which the camshaft is axially displaced by a hydraulic adjusting device. The cams used to actuate a valve each have identical, rising cam tracks for the valve opening. The different control times required for different speed ranges are achieved by a relative rotation of the camshaft by means of a helical toothing of the camshaft gear. Switching between two cams is made possible by the fact that the rising part of adjacent cams assigned to a valve forms a common surface. The blocking of the axial movement during the shifting process by the stages is avoided by the end faces of the cam stages being offset by a certain amount in the sequence of the valve actuation compared to the immediately preceding ones. Switching is triggered by a mechanical or electrical speed pulse, which is, however, independent of the respective camshaft angle. Due to the lack of a relationship between camshaft displacement and camshaft angle, the bucket tappet or transmission lever strikes the end faces of the selected cams at the beginning of the shifting process until the tappet or transmission lever reaches the transition surface between the cams on the base circle or the rising cam track can reach and switch. This causes additional noise and increasing wear on the valve actuation, but can also lead to pinching damage.

The object of the invention is to avoid these disadvantages and to provide an adjusting device for camshafts with which a controlled and stop-free axial displacement of the camshaft is made possible.

According to the invention, this is achieved in that the adjusting device consists of a sliding link with at least two helical guide grooves arranged in opposite directions, which end in ring-shaped clearance grooves, and a driver that can be steered into the guide grooves by a trigger element, by stepping the driver into one of the Clearance grooves different operating positions of the camshaft can be defined. The slope and the position of the helical guide grooves and the position of the individual cams on the camshaft is chosen so that switching between two cams of a valve takes place while the bucket tappet or transmission lever faces a common tangential plane of both cams. This avoids shear stress on the end faces of the cams. During a changeover process, the camshaft automatically pushes itself from the first operating position in the axial direction into the second operating position by the driver engaging in the guide grooves, the two operating positions being specified by annular release grooves. No additional force is therefore required to displace the camshaft, so that the release element, which only brings the driver into an initial position, can be dimensioned relatively small.

It is preferably provided that the two guide grooves, which are helical in the opposite direction of rotation, are machined into the camshaft, and the driver is secured against rotation about the camshaft axis, preferably connected to the cylinder head via a housing of the adjusting device. This space-saving arrangement is characterized by simple and inexpensive manufacture. However, it is also conceivable for the driver to be rigid with the camshaft train, and to arrange the sliding link in the cylinder head.

In a preferred embodiment of the invention it is provided that the driver is designed as an open spring ring arranged concentrically around the camshaft, which is secured against rotation with the camshaft and in an area, preferably diametrically opposite the free ends of the spring ring, in the area of the cylinder head or in the housing Adjustment device is mounted securely in the axial direction, one of the two free ends being bendable in the direction of the camshaft axis by the release member. At the beginning of each switching operation, one end of the spring ring is bent into an initial position by the release element, as a result of which the spring ring is deflected into the guide groove which moves relative to the spring ring.

Instead of the spring ring, it can also be provided in a favorable embodiment with respect to the friction losses that the driver is formed by a first cylindrical pin and a second cylindrical pin, the geometrical longitudinal axes of which are approximately normal to the camshaft axis, and both pins, preferably rotatable, in the cylinder head or are mounted in a housing of the adjusting device, wherein the second pin is also displaceably mounted in the direction of the camshaft axis and can be deflected in the direction of the camshaft axis by the release element.

In the context of the invention it is provided that the trigger member is actuated hydraulically. The hydraulic release element itself can be dimensioned very small, since the axial displacement forces of the camshaft are provided by the camshaft drive.

In an embodiment of the invention with several valves of one valve type per cylinder, the cams belonging to different operating positions of the camshaft are designed for different valve lift curves. This means that the optimal valve lift and timing can be used for different engine operating states.

In an embodiment of the invention it is provided that those activated in at least one operating position of the camshaft Cams of valves of the same type of valve per cylinder are designed for different valve lift curves. This is particularly favorable in the partial load range if, for example, one of two intake valves per cylinder follows a valve lift curve with a small stroke and short opening time, while the second inlet valve is actuated with an even smaller stroke and shorter opening time. However, the second inlet valve can also remain completely closed in the partial load range, as a result of which the opening force necessary to overcome the spring force and the friction can be saved.

It is preferably provided that an activated cam, preferably via a forked rocker arm, actuates a plurality of valves in at least one operating position of the camshaft. As a result, the number of cams on a camshaft can be reduced, which has a favorable effect on the size and the manufacturing costs.

• a) bei Vollast und hoher Drehzahl ein oder mehrere für eine Ventilerhebungskurve mit großem Hub und langer Öffnungszeit ausgelegte(r) Nocken,
• b) bei Vollast und niedriger Drehzahl ein oder mehrere für eine Ventilerhebungskurve kurzer Öffnungszeit ausgelegte(r) Nocken und
• c) bei Teillast zumindest zwei für unterschiedlichen Ventilerhebungskurven mit kleinem Hub und kurzer Öffnungszeit ausgelegte Nocken aktiviert werden, wobei die Verstellung der Nockenwelle in Abhängigkeit vom Motorbetriebszustand erfolgt. Damit wird die für den jeweiligen Betriebsbereich des Motors optimale Ventilerhubungskurve nachgefahren.

The method for changing the valve lift in an internal combustion engine according to the invention provides that for actuating valves of the same type of valve per cylinder

• a) at full load and high speed, one or more cams designed for a valve lift curve with a large stroke and long opening time,
• b) at full load and low speed, one or more cams designed for a valve lift curve with a short opening time and
• c) at partial load, at least two cams designed for different valve lift curves with a small stroke and a short opening time are activated, the camshaft being adjusted as a function of the engine operating state. This traces the valve lift curve that is optimal for the respective operating range of the engine.

The invention is explained in more detail below on the basis of exemplary embodiments illustrated in the drawings.

Fig. 1

eine Längsansicht einer Nockenwelle mit Verstellvorrichtung gemäß der Erfindung,

Fig. 2

eine Detailansicht der Verstellvorrichtung nach Linie II-II in Fig. 1,

Fig. 3

ein Detail der Verstellvorrichtung,

Fig. 3a

eine Schrägansicht eines schematisch dargestellten Auslöseorganes,

Fig. 3b

eine Ausführungsvariante der Verstellvorrichtung nach der Erfindung,

Fig. 3c

einen Schnitt durch die Verstellvorrichtung nach der Linie III-III in Fig. 3b,

Fig. 4

eine Längsansicht des antriebsseitigen Endes der Nockenwelle,

Fig. 5

eine Längsansicht einer anderen Ausführungsform der Erfindung mit teilweise weggeschnittener Nockenwelle,

Fig. 6

einen Schnitt einer Ventilbetätigung nach der Linie VI-VI in Fig. 5,

Fig. 7

einen weiteren Längsschnitt dieser Ausführungsform,

Fig. 8

einen Längsschnitt einer weiteren Ausführungsform der Erfindung.

Show it:

Fig. 1

2 shows a longitudinal view of a camshaft with an adjusting device according to the invention,

Fig. 2

2 shows a detailed view of the adjusting device according to line II-II in FIG. 1,

Fig. 3

a detail of the adjustment device,

Fig. 3a

2 shows an oblique view of a schematically illustrated trigger element,

Fig. 3b

a variant of the adjustment device according to the invention,

Fig. 3c

3b shows a section through the adjusting device along the line III-III in FIG.

Fig. 4

2 shows a longitudinal view of the drive-side end of the camshaft,

Fig. 5

2 shows a longitudinal view of another embodiment of the invention with the camshaft partially cut away,

Fig. 6

5 shows a section of a valve actuation along the line VI-VI in FIG. 5,

Fig. 7

another longitudinal section of this embodiment,

Fig. 8

a longitudinal section of a further embodiment of the invention.

Parts with the same function have the same reference symbols.

The exemplary embodiments relate to an internal combustion engine with four cylinders arranged in series. 1 shows a part of a cylinder head 1 of this internal combustion engine with partially removed camshaft bearing brackets 5a. The camshaft 3 has two cams 4a, 4b per valve 6a, 6b. The cams 4a are for a valve lift curve with a large stroke and a long opening time of the valves 6a, 6b for use at full load and high speed, the nockers 4b are for a short stroke and a short opening time of the valves 6a, 6b designed for partial load operation and / or low speed. In the position of the camshaft 3 shown, the cams 4b are activated and actuate the valves 6a, 6b via beads 7 on the tappets 8. The laterally released beads 7 provide the neighboring deactivated cams 4a with the necessary scope for free rotation. The tappets 8 themselves are secured against rotation about the valve axis.

The adjusting device 9 is provided at one end of the camshaft 3. This consists of the sliding link 10 formed as part of the camshaft 3, the driver 11 and the trigger element 12.

As can be seen in FIG. 2, the sliding link 10 has two guide grooves 10 ′, which are machined into the camshaft 3 in a helical manner in the opposite direction of rotation. Both guide grooves 10 'end in the clearance grooves 10' 'machined into the camshaft in a ring. The driver 11 designed as a spring ring 11 'is connected to the housing 13 or the cylinder head 1 in a body-fixed and rotationally secure manner in a region 14c diametrically opposite the free ends 14a, 14b, as can be seen from FIG. 3a. At the free end 14a of the spring ring 11 ', the pistons 16 of the triggering element 12 engage, which trigger the camshaft displacement. The movement of the pistons 16 is indicated by the arrows 16 ', the displacement of the camshaft 3 triggered thereby by the arrow 3'. In order to ensure reliable triggering of the axial camshaft displacement, the free ends 14a, 14b of the spring ring 11 'in the direction of the camshaft axis 3a in the housing 13 or cylinder head 1 must have sufficient scope 14'. The maxiamle displacement length of the camshaft corresponds. the width of the sliding link 10 and is marked with 20.

The camshaft displacement is triggered by the hydraulically actuated trigger element 12 shown in FIG. 3. The oil supply is designated 18, the oil return 19. Pistons 16 preloaded by springs 15 are displaceably mounted in the housing 13. Apart from the triggering process for the camshaft movement, the spring ring 11 'and the trigger member 12 remain in the rest position. At a certain speed, the electrically operated valve 17 opens the oil supply 18 one of the two release pistons 16, whereby a bending moment is exerted on the spring ring 11 '. As soon as the free end 14a of the spring ring 11 'reaches the beginning of the guide groove 10', the spring ring 11 'automatically slides along the guide groove 10' of the rotating camshaft 3, while the camshaft 3 moves in the direction of the camshaft axis 3a. The change between the cams 4a and 4b takes place when the relevant tappets face a common tangential plane 4 'spanned by the flanks of two adjacent cams 4a, 4b (FIG. 1). As soon as the spring ring 11 'reaches the release groove 10'', the camshaft displacement ends. Analog, functionally identical parts are provided for the displacement movement in the opposite direction, the spring ring 11 'being pressed in the opposite direction.

Instead of the spring ring 11 ', two pins 22, 23 rotatable about their longitudinal axes 22a, 23a can be used, the longitudinal axes 22a, 23a being normal to the camshaft axis 3. In the embodiment shown in Fig. 3b and 3c, the two pins 22, 23 are diametrically opposed. The switching process is initiated by moving the pin 23 through one of the two pistons 16 of the triggering element 12 in the direction of the camshaft axis 3a.

The camshaft 3 is driven on the opposite end face of the cylinder head 1, as can be seen in FIG. 4, via a sliding element 21 rotatably mounted in the cylinder head 1, in which the camshaft 3 is accommodated in a longitudinally displaceable manner and to which a camshaft drive wheel (not shown) is flanged can.

In one embodiment of the variants described above, the displacement length 20 of the camshaft 3 is 18 mm. Because of the phase shift of the individual cams 4a, 4b, not all cams can be switched over at the same time. The camshaft shift gradually triggers the following processes: the lateral play is overcome between 0 and 2 mm; according to the firing sequence ACDB, the cam 4a of cylinder A is activated after 2 mm, the cam 4a of cylinder C after 4 mm, the cam 4a of cylinder D after 6 mm and the cam 4a of cylinder B after 8 mm. During the remaining displacement length of 8 to 18 mm, the full width of the cams 4a over the Beaded 7 of the tappets 8 effective. During this displacement movement, the camshaft 3 makes two and a quarter revolutions.

Instead of providing separate pairs of cams for each valve, three switchable cams 4a, 4b, 4c are provided in the embodiment shown in FIGS. 5 to 7 for controlling two valves 6a, 6b of the same type of valve per cylinder. The valves 6a, 6b are actuated via rocker arms 24, 25, each of which has a roller 24 'or 25' for reducing friction. Using the forked rocker arm 25, the actuation of both valves 6a, 6b is possible by overcoming the force of the valve springs 6 'by means of a single cam 4a, 4b or 4c. The forked rocker arm acts directly on a valve 6a and indirectly on the second valve 6b by deflecting the smaller rocker arm 24.

With the three differently designed cams 4a, 4b and 4c, three different engine operating areas can be covered. These are: Range B1 - full load at high speed, requires synchronous actuation of valves 6a, 6b by cams 4a with a large stroke and long opening time; Range B2 - full load at low speed, requires synchronous actuation of the valves 6a, 6b by a cam 4b with a small stroke and a short opening time; Area B3 - partial load, requires asynchronous actuation of the valves 6a and 6b, one valve 6a being actuated by the cam 4b with a small stroke and a short opening time, the other valve 6b being actuated by the cam 4c with a very small stroke.

In the middle operating position shown in FIGS. 5 and 7, the cam 4c designed for a flat valve lift curve with a very short stroke and short opening time opens both valves 6a and 6b via the forked rocker arm 25. The resulting stroke movement of the valve 6a is, however, superimposed by the deflection transmitted from the cam 6b via the rocker arm 24 to the valve 6a, so that the opening of the valve 6a is significantly larger than the opening of the valve 6b. If the camshaft 3 is shifted to the right by the adjusting device 9 in FIG. 5 or 7, the cam 4b assumes a position above the forked rocker arm 25 and can synchronize both valves 6a and 6b, Act according to area B2. The deflection of the camshaft from the middle operating position in the opposite direction positions the cam 4a above the forked rocker arm 25, as a result of which the valves 6a and 6b can be opened synchronously with a large stroke - corresponding to the range B1. The outermost deflection positions of the cams are indicated by dashed lines in FIG. 7.

While in the embodiment variant shown in FIGS. 5 to 7 the same cams 4b designed for short stroke and short opening time are used for motor operating areas B2 and B3, the arrangement of an additional cam 4b ', as can be seen in FIG. 8, offers the possibility a better adaptation to engine operating areas B2 and B3. Compared to the previously described embodiment, the positions of the cams 4c and 4b are interchanged. The drawn operating position of the camshaft 3 corresponds to the engine operating range B3, the valves 6a and 6b being opened asynchronously. By moving the camshaft 3 from the position shown to the left, the cam 4b comes to rest on the forked rocker arm 28. A synchronous actuation of the two valves 6a and 6b by the cam 4b in the engine operating area B2 is thus possible. A further displacement of the camshaft 3 to the left positions the cam 4a over the forked rocker arm 28 and the cam 4b over the rocker arm 27. The deflection of the cam 4a is superimposed on the deflection of the cam 4b, so that both valves 6a and 6b are opened synchronously with a large stroke become, which corresponds to the engine operating range B1. With 5 'tunnel bearings for the camshaft are designated, which are moved when the camshaft is moved. The maximum deflection of the cam 4b 'and the tunnel bearing 5' is indicated by dashed lines.

The proposed adjustment device can be used both in valve controls with bucket tappets and in valve controls with rocker arms or rocker arms.

Claims (9)

Internal combustion engine with at least one camshaft axially displaceable by an adjusting device with several switchable and different axial offsets per valve, characterized in that the adjusting device (9) consists of a shifting link (10) with at least two helical guide grooves (10) arranged in opposite directions to each other '), which end in annular release grooves (10''), and a driver (11) which can be deflected into the guide grooves (10') by a trigger element (12), whereby by deflecting the driver (11) into one of the release grooves (10 '') different operating positions of the camshaft (3) can be defined. Internal combustion engine according to claim 1, characterized in that the two guide grooves each helically formed in the opposite rotational sense, are incorporated into the camshaft (3) (10 ') and the driver (11) secured against rotation about the camshaft axis (3a), preferably via a Housing (13) of the adjusting device (9) is connected to the cylinder head (1). Internal combustion engine according to claim 1 or 2, characterized in that the driver (11) (11 ') designed as an open around the camshaft (3) concentrically arranged spring ring which is secured against co-rotation with the camshaft and in one, preferably the free ends ( 14a, 14b) of the spring ring (11 ') diametrically opposite, area (14c) in the cylinder head (1) or in the housing (13) of the adjusting device (9) is mounted so that it cannot move in the axial direction, one of the two free ends (14a, 14b ) is bendable by the release member in the direction of the camshaft axis (3a). Internal combustion engine according to claim 1 or 2, characterized in that the driver (11) is formed by a first cylindrical pin (22) and a second cylindrical pin (23) whose geometrical longitudinal axes (22a, 23a) approximately normal to the camshaft axis (3a) lie, and both pins (22, 23) preferably rotatable in the cylinder head (1) or in a housing (13 ') of the adjusting device (9'), the second pin (23) also being displaceably mounted in the direction of the camshaft axis (3a) and by the release member (12) in the direction of the camshaft axis (3a ) can be deflected. Internal combustion engine according to one of claims 1 to 4, characterized in that the triggering member (12) is actuated hydraulically. Internal combustion engine according to claim 1 with several valves of one valve type per cylinder, characterized in that the cams (4a, 4b, 4c) belonging to different operating positions of the camshaft (3) are designed for different valve lift curves. Internal combustion engine according to claim 1 or 6, characterized in that the activated in at least one operating position of the camshaft (3), cams (4a, 4b, 4c) by valves (6a, 6b) of the same type of valve per cylinder (A, B, C, D ) are designed for different valve lift curves. Internal combustion engine according to one of claims 1, 6 or 7, characterized in that in at least one operating position of the camshaft (3) an activated cam (4a, 4b, 4c), preferably via a forked rocker arm (25), a plurality of valves (6a, 6b ) operated. A process for changing the valve lift in an internal combustion engine according to one of claims 1 to 8, comprising more than two switchable and designed for different valve lift curves cam per valve, characterized in that for actuating valves (6a, 6b) of the same type of valve per cylinder (A , B, C, D) a) at full load and high speed, one or more cams (4a) designed for a valve lift curve with a rough stroke and long opening time, b) at full load and low speed, one or more cams (4b) designed for a valve lift curve with a short opening time and c) at part load, at least two cams (4b, 4c) designed for different valve lift curves with a small stroke and short opening time are activated, the camshaft (3) being adjusted as a function of the engine operating state.

Images