EP3523513B1 - Camshaft for internal combustion engine - Google Patents

Description

One aspect of the invention relates to a camshaft for an exhaust valve of an internal combustion engine. According to one aspect, the camshaft has a movable cam contour element, by means of which a speed-dependent cam contour shape is obtained.

In combustion engines, valve trains are usually used that use a camshaft to generate a valve lift of the intake and exhaust valves with a fixed lift height and lift duration. However, such a valve train has disadvantages in terms of optimal adaptation to different load ranges of the internal combustion engine. In addition, the camshaft actuates the valve train when the engine is started during the starting phase; However, the energy to compress the gas in the combustion chamber must be applied by the starter motor, which can lead to disadvantages during starting.

To adapt to these requirements, there are numerous valve trains that allow a different valve lift curve for starting. A particularly simple but effective design is based on a camshaft, which comprises several cam tracks arranged laterally next to one another to actuate a valve and which can be moved laterally by means of an adjusting unit. A cam track adapted to the respective requirements can then be selected by moving the camshaft laterally. In the case of a camshaft for an exhaust valve, one cam can be provided for the starting phase and another cam for normal operation, with the cam for the starting phase providing an additional valve opening to reduce the pressure of the gas in the combustion chamber.

However, such an adjustment unit increases the space and weight requirements of the valve train and requires complex control of the adjustment unit. In addition, the stability and strength of the camshaft can be impaired.

The JP 2008-82188 describes a camshaft with a decompression function that depends on the rotation speed of the camshaft and a phase shift function. A control shaft 57 is rotated relative to the cam 36 by means of a centrifugal mechanism 50 in order to raise pins 65a and 65b (see Fig. 6 , 7 of JP 2008-82188 ). This mechanism requires a tension spring 53 attached to the centrifugal mechanism and a transmission member 59, and therefore requires increased space. In addition, because of the control shaft 53 arranged on the rotation axis, at least one shaft end of the camshaft must be accessible, which results in restrictions on the storage and placement of the camshaft.

In the EP 3 061 930 A1 A camshaft with a decompression device for reducing pressure in the cylinder when starting the engine is described. Here, a centrifugal element is provided directly adjacent to a drive pinion of the camshaft.

The aim of the present invention is to provide a camshaft which, on the one hand, is adjustable but, on the other hand, reduces at least some of the disadvantages mentioned above.

The invention is described in the attached set of claims.

According to one aspect of the present invention, a camshaft specifically for an exhaust valve of an internal combustion engine is provided. The camshaft includes a cam and a trigger mechanism for its cam contour element. The cam defines a cam contour for cyclically actuating the exhaust valve by rotating the camshaft. The cam includes a cam body and the cam contour element. The cam contour element is movable relative to the cam body into a first cam contour position and into a second cam contour position, such that the cam contour has a first cam contour shape when the cam contour element is in the first cam contour position, and has a second cam contour shape different from the first cam contour shape when the cam contour element is in the second cam contour position. The triggering mechanism is configured to hold the cam contour element in the first cam contour position at a first, lower speed of the camshaft (in particular at a first speed range), and to hold the cam contour element at a second, higher speed of the camshaft (in particular at a second speed range that is opposite to the first speed or the first speed range is higher) in the second cam contour position.

The camshaft is mounted on both sides, that is, it has a first bearing and a second bearing for rotatably supporting the camshaft about its camshaft axis, the cam being arranged axially between these bearings. According to the invention, the trigger mechanism is also arranged between these bearings.

According to the invention, the cam contour element is designed as a pin that can be inserted and extended into the cam body. According to the invention, the trigger mechanism comprises a centrifugal element. The centrifugal element is arranged directly adjacent to the cams.

Preferably, the cam contour element protrudes in the first cam contour position for actuating (opening) the exhaust valve (relative to the surrounding cam contour), and does not protrude or protrudes less in the second cam contour position, so that the exhaust valve does not require any - that is, no significant - additional actuation (opening). experienced, so not is opened significantly further than by means of the cam contour surrounding the cam contour element.

The second speed range can essentially adjoin the first speed range, wherein the transition between the first and second speed ranges can be defined either with a threshold value or with a certain transition (transition range). Thus, the triggering mechanism is configured to hold the cam contour element in the first cam contour position when the speed falls below a predetermined threshold or transition range, and to maintain the cam contour element in the second cam contour position when the speed exceeds the predetermined threshold or transition range. According to one aspect, the triggering mechanism is configured to bring the cam contour element from the first cam contour position to the second cam contour position during the transition from the first speed to the second speed range (or from the first speed range to the second speed range).

The first speed can, for example, be in a speed range typical for starting. According to one aspect, the first speed - also depending on the engine type - is between 0 rpm and 1000 rpm, preferably between 0 rpm and 500 rpm. The second speed can be in a normal operating range of the engine, for example above 500 rpm, preferably above 700 rpm or 1000 rpm, in each case based on the speed of the camshaft. The threshold value can therefore be, for example, in a speed range between 500 rpm and 1000 rpm.

The camshaft according to the invention thus allows a speed-dependent cam contour shape and consequently a speed-dependent valve lift curve of the exhaust valve. According to a special aspect, at low speeds, which are typical for the starting phase, the cam contour element protrudes (in the first cam contour position), so that an additional valve opening (compared to higher speeds or the second cam contour position) is achieved, so that the starter does less work against the Pressure must be applied in the combustion chamber.

According to one aspect of the invention, this speed-dependent cam contour shape can be achieved without a lateral displacement of the cam. This enables the camshaft to be mounted on both sides in particular. The storage on both sides allows particularly favorable power transmission between the cam and valve, as undesirable Bending vibrations of the camshaft are avoided and a flexible control of the valve train.

The first cam contour shape can differ from the second cam contour shape in particular in that the first cam contour shape has a highlight in order to open the exhaust valve (70) during a compression stroke of the internal combustion engine. The highlighting preferably occupies a rotation angle range of the camshaft between 1° and 30°. A center of the highlight is preferably offset by an angle of between 90° and 270°, particularly preferably between 90° and 180°, in the direction of rotation of the cam relative to a point or angle of maximum eccentricity of the cam contour (projection of the cam body).

The cam contour element is preferably mounted (in the axial direction) centrally in the cam.

Here, "on" always means "at least on", e.g. "one cam" = "at least one cam", etc. The first speed range can include standstill (speed 0).

Further advantageous embodiments are shown in the dependent claims and in the following description of the figures. Individual aspects and details of the embodiments are shown with reference numbers in the figures; however, these reference numbers are provided for illustration purposes only. Aspects can also be combined with other aspects independently of the embodiment shown.

• Fig. 1 zeigt eine perspektivische Ansicht eines Ventiltriebs für ein Auslassventil gemäß einer Ausführungsform der Erfindung;
• Fig. 2 zeigt eine Frontalansicht des Ventiltriebs gemäß Fig. 1;
• Fig. 3a-c zeigen seitliche Ansichten des Ventiltriebs gemäß Fig. 1 und 2 mit dem Nockenkonturelement in der ersten Nockenkonturstellung;
• Fig. 4a-c zeigen seitliche Ansichten des Ventiltriebs gemäß Fig. 1 und 2 mit dem Nockenkonturelement in der zweiten Nockenkonturstellung;
• Fig. 5 zeigt eine weitere seitliche Querschnittsansicht des Nocken von Fig. 4b; und
• Fig. 6 zeigt ein Ventilhubdiagramm für den erfindungsgemäßen Ventiltrieb.

Show in the figures:

• Fig. 1 shows a perspective view of a valve train for an exhaust valve according to an embodiment of the invention;
• Fig. 2 shows a front view of the valve train according to Fig. 1 ;
• Fig. 3a-c show side views of the valve train according to Fig. 1 and 2 with the cam contour element in the first cam contour position;
• Fig. 4a-c show side views of the valve train according to Fig. 1 and 2 with the cam contour element in the second cam contour position;
• Fig. 5 shows another side cross-sectional view of the cam of Fig. 4b ; and
• Fig. 6 shows a valve lift diagram for the valve train according to the invention.

Fig. 1 and 2 show a valve train for an exhaust valve 70 of an internal combustion engine with the camshaft 10 according to an embodiment of the invention. The camshaft 10 includes a cam 11 arranged to actuate the exhaust valve 70. The camshaft 10 can be rotated about its axis. For this purpose, the camshaft 10 is mounted on the cylinder head by bearings 8a, 8b - i.e. on both sides. It is therefore an overhead camshaft. The camshaft 10 further comprises a centrifugal element 21, which is described below in relation to Figures 3 and 4 is described in more detail.

The storage on both sides by the bearings 8a, 8b allows a favorable power transmission between the cam and the valve, since undesirable bending vibrations of the camshaft are avoided. The storage on both sides also allows flexible control of the valve train: According to a preferred aspect, a drive gear or sprocket connected to a crankshaft of the internal combustion engine is located on the side 7a of the camshaft, and an output gear connected to an intake valve drive shaft is located on the other side 7b the camshaft 10. This means that the camshaft can, for example, in the DE 102005057127 The valve train described can be used.

The valve train further includes a mechanism for actuating the exhaust valve 70 through the cam 11. In the Fig Fig. 1 and 2 In the embodiment shown, this mechanism includes a rocker arm 60 and a shim (valve adjustment plate) 72, which are arranged between the cam 11 and the exhaust valve 70, so that the exhaust valve is actuated by the cam 11 via the rocker arm 60 and the tappet 72. Next is in Figure 2 a valve spring 74 is shown, which biases the valve 70 (at least in phases, for example when the valve is actuated) against the cam 11 and thus creates a frictional connection between the valve 70 and the cam 11. In a phase in which the valve is not actuated, the valve spring presses the valve into the valve seat, which applies the corresponding counterforce.

As in Fig. 2 can be seen, the cam 11 includes a cam body 12 and a cam contour element 40 (see Fig. 3b , 4b ; in Fig. 2 only one end of the cam contour element acting as a decompression surface 44 can be seen), which together define the cam contour 16 of the cam 11. More specifically, the cam contour 16 is formed by the decompression surface 44 of the cam contour element 40 (also referred to as the cam contour surface of the cam contour element) and by a remaining cam contour surface 14 of the cam body 12. The cam contour 16 is the cross-sectional profile of the cam 11, which actuates the exhaust valve 70 when the camshaft 10 rotates and which therefore significantly influences the valve lift curve of the exhaust valve 70.

The cam contour element 40 is designed as a pin that can be moved in and out of the cam body 12 (see also Fig. 3b , 4b ).

In the extended position (first cam contour position, in Fig. 3b shown), the cam contour surface 44 of the cam contour element 40 protrudes from the remaining cam contour surface 14. The result of this is that the exhaust valve 70 experiences additional actuation (opening) through the cam contour surface 44 of the cam contour element 40. In the retracted position (second cam contour position, in Fig. 4b shown), the cam contour surface 44 is arranged flush with the remaining cam contour surface 14 (does not protrude significantly), so that the exhaust valve does not experience any - meaning no significant - additional actuation (opening). Thus, the cam contour 16 has a variable cam contour shape that depends on whether the cam contour element 40 is in the first or second cam contour position.

The cam contour surface 44 of the cam contour element 40 is arranged on a section of the cam contour 16 in which the exhaust valve 70 - at least in the second cam contour position or in the remaining cam contour surface 14 of this section surrounding the cam contour element 40 - is closed.

The cam contour surface 44 of the cam contour element 40 thus acts as a decompression surface 44: At low speeds, which are typical for the starting phase, the additional valve opening (in the first cam contour position) allows pressure in the combustion chamber to be released, so that the starter does less work against the pressure in the combustion chamber must apply. At higher speeds, which are typical for normal operation, the additional valve opening is prevented, so that no losses in terms of engine efficiency have to be accepted.

As in Fig. 2 can be seen, the cam contour element 40 is mounted centrally in the cam 11 (with respect to the axial direction of the camshaft). This central mounting, in particular in conjunction with the valve drive having a rocker arm 60, causes a uniform and low-wear force transmission from the cam 11 to the valve 70. According to a general aspect, a center of the cam contour element 40 deviates from a center (with respect to the axial direction). of the cam by less than 20% of the width of the cam.

In the Figures 3 and 4 is the trigger mechanism 20 of the valve train according to Fig. 1 and 2 shown in greater detail, by means of which the cam contour element 40 is speed-dependent is moved (retracted and extended). The triggering mechanism 20 thus ensures that the cam contour element 40 or its cam contour surface 44 is extended at low speeds (first cam contour position) and is retracted at higher speeds (second cam contour position).

Here are Fig. 3a , 4a lateral views, from the right side in Fig. 2 seen; Fig. 3b , 4b lateral cross-sectional views in plane AA of Fig. 2 ; and Fig. 3c , 4c lateral cross-sectional views in plane BB of Fig. 2 . In Fig. 3a-c is the cam contour element in the first cam contour position, and in Fig. 4a-c the cam contour element is shown in the second cam contour position.

The side view or cross-sectional view of the Fig. 3a, 3c show the centrifugal element 21 of the trigger mechanism 20. The centrifugal element 21 is designed as a double-sided lever with a first lever arm 27 and a second lever arm 28 and is rotatable about an axis 22 on the camshaft 10 (ie on a suspension that rotates with the camshaft 10, here on the cam body 12) rigidly connected to the camshaft 10. In Fig. 3a, 3c the centrifugal element 21 is shown in a first centrifugal position; in Fig. 4a, 4c it is shown in a second centrifugal position, in which the centrifugal element 21 is rotated clockwise about the axis 22 compared to the first centrifugal position.

This in Fig. 3c , 4c The biasing element 30 shown tensions the centrifugal element 21 towards the first centrifugal position (in the view of Fig. 3a , 4a counterclockwise). The biasing element 30 is arranged in an opening of the camshaft 10 that runs transversely through the camshaft, so that the longitudinal axis of the biasing element 30 runs at right angles through the axis of rotation of the camshaft. The preload can be carried out by a return spring, which is arranged approximately concentrically to the longitudinal axis of the preload element 30 in the camshaft 10 and tensions (presses) the preload element 30 against the centrifugal element 21. The return spring can be a compression spring clamped between (a stop in) the opening of the camshaft and (a stop on) the biasing element 30.

In one aspect, the length of the portion of the biasing element 30 protruding from the camshaft 10 toward the centrifugal element 21 is shorter than the camshaft radius of the camshaft 10 at this point. This applies in the first and/or the second Centrifugal position. This makes a particularly compact arrangement of the prestressing element 30 possible.

In the first centrifugal position, the centrifugal element 21 is tensioned (pressed) against a first stop by the biasing element 30. Here the first stop is formed on the first lever arm, for example by a center piece 26 of the first lever arm, and the camshaft 10. The first stop is arranged on a different lever side of the centrifugal element 21 than the biasing element 30. The first stop limits the pivoting of the centrifugal element 21 in the direction in which the biasing element 30 biases the centrifugal element 21. The pivoting of the centrifugal element 21 in the opposite direction is limited by a maximum compression of the return spring of the biasing element 30, or by a further stop between the second lever arm 28 and the camshaft 10.

In one aspect, the biasing element 30 is non-positively connected to the centrifugal element 21, in particular pressed against the centrifugal element 21.

The bias towards the first centrifugal position exerted by the biasing element 30 causes the centrifugal element 21 to be in the rest position or in the first centrifugal position at low speeds (at a first speed) of the camshaft, as shown in Fig. 3a shown.

In the embodiment shown, the centrifugal element is made of a lever. The lever 21 and in particular its lever arms 27, 28 are dimensioned such that the centrifugal force acting when the camshaft rotates acts more strongly on the first lever arm 27 than on the second lever arm 28 and thus on the centrifugal element 21 overall a force directed towards the second centrifugal position (ie in the view of Fig. 3a , 4a clockwise) torque. If the speed exceeds a certain threshold value (for example at a second, higher speed), this torque outweighs the preload through the preload element 30, and as a result the centrifugal element 21 is then in the second centrifugal position, as in Fig. 4a shown.

In one aspect, the lever extends along a sub-segment around the camshaft 10. According to one aspect, the center of gravity of the first lever arm 27 is offset from the center of gravity of the second lever arm 28 by more than 90°, preferably more than 120° or even by more than 135°. According to one aspect, the center of gravity and/or the lever end of the first lever arm 27 is more than 90° relative to the pivot axis 22, preferably offset by more than 120° or even by more than 135° (with respect to the axis of rotation of the camshaft 10 and in the direction of the spatial extent of the centrifugal element 21). According to one aspect, the center of gravity and/or the lever end of the second lever arm 28 is offset from the pivot axis 22 by less than 90°, preferably less than 45° or even by less than 30°. According to one aspect, the center of gravity and/or the lever end of the first lever arm 27 is offset from the pivot axis 22 by more than twice, three or even four times the angle than the center of gravity or the lever end of the second lever arm 28. Here, the angle is always defined around the axis of rotation of the camshaft 10 and in the direction of the spatial extent of the centrifugal element 21. These aspects allow a lever with a sufficiently large lever arm and at the same time low space requirements in the radial direction, so that a compact design is possible.

According to one aspect, the centrifugal element (lever) 21 is pivotable about a lever axis running parallel to the camshaft axis. According to one aspect, the lever axis is arranged eccentrically to the camshaft axis, preferably spaced radially in the direction of a projection region of the cam body 12 from the camshaft axis. The projection area is the angular area extending radially from the camshaft axis with an angular deviation of less than 30° in the direction of the projection (point of maximum eccentricity) of the cam body 12.

According to a further aspect, the centrifugal element 21 is arranged directly adjacent to the cam 12, i.e. without any other functional part in between, such as a bearing for the cam. According to one aspect, the axial distance between the centrifugal element 21 and the cam 12 (side surface to side surface) is less than 0.5 cm. According to one aspect, the axial distance between a center plane of the centrifugal element 21 and a center plane of the cam 12 is less than twice or less than 1.5 times the axial width of the cam, or even less than the axial width of the cam. According to one aspect, the camshaft is mounted on both sides, and the centrifugal element 21 is arranged between the two bearings 8a, 8b. This enables a compact design even in the axial direction.

Fig. 3b , 4b show the cam contour element 40 and a coupling mechanism which couples the centrifugal element 21 to the cam contour element 40.

This coupling takes place in such a way that the cam contour element (40) is held in the first cam contour position when the centrifugal element 21 assumes the first centrifugal position (as in Fig. 3b shown), and that the cam contour element 40 is held in the second cam contour position when the centrifugal element 21 assumes the second centrifugal position (as in Fig. 4b shown).

The cam contour element 40 is designed as a pin, which is at least partially arranged in a blind hole of the cam body 12 along a pin axis and can be inserted into it. The surface of the cam contour element 40 directed outwards from the blind hole forms the cam contour surface 44. In the first cam contour position ( Fig. 3b ), the pin is at least partially extended out of the blind hole, and in the second cam contour position ( Fig. 4b ), the pin is essentially retracted into the blind hole so that the cam contour surface 44 is flush with the surrounding surfaces.

The coupling mechanism between the centrifugal element 21 and the cam contour element 40 is realized by a movable stop body 24, which is in a first or second stop position depending on the centrifugal position of the centrifugal element 21. The stop body is realized as a pin that is rigidly connected to the centrifugal element 21 and can be rotated about an axis parallel to the camshaft axis.

According to one aspect, the stop body 24 is positively, in particular rigidly, connected to the centrifugal element 21. According to one aspect, the connection between the centrifugal element 21 and the stop body 24 is arranged eccentrically to the camshaft axis, preferably offset radially to a projection or projection region (angular range of +/- 30 ° around the projection) of the cam body 12.

According to one aspect, the stop body is rotatable about a stop body axis parallel to the camshaft axis by moving the centrifugal element 21 between the first and second centrifugal positions. According to one aspect, the stop body 24 or the stop body axis is arranged eccentrically to the camshaft axis, preferably arranged in a projection region of the cam body 12. According to one aspect, the stop body axis is equal to a lever axis of the centrifugal member (lever) 21, and the stop body 24 is rotatable together with the centrifugal member 21.

The cam contour element 40 is biased against the stop body 24. The preload is not shown and can be carried out, for example, by a return spring which is arranged approximately concentrically to the axis of the cam contour element 40 and tensions (presses) the cam contour element 40 against the stop body 24. The return spring can be a compression spring clamped between (a stop in) the blind hole or cam body 12 and (a stop on) the cam contour element 40. According to one aspect, the cam contour element 40 is non-positively connected to (pressed against) the stop body 24. According to one aspect, the contact area between the stop body 24 and the cam contour element 40 is arranged in the cam body 12, preferably in a projection area of the cam body 12.

According to one aspect, the stop body 24 is out of round in the area in which the cam contour element 40 tensions against the stop body 24.

When the centrifugal element 21 is in the first centrifugal position, the stop body 24 is in the first stop position and provides a first stop for the cam contour element 40, which defines the first cam contour position for the cam contour element 40. When the centrifugal element 21 is in the second centrifugal position, the stop body 24 is in the second stop position and provides a second stop for the cam contour element 40, which defines the second cam contour position for the cam contour element 40. In one aspect, the first and second stops are different. The second stop is preferably set back compared to the first stop.

In the embodiment of Fig. 3b , 4b This stop body is realized by a shaft 24 which rotates around the axis 22 ( Fig. 3c , 4c ) is rotatable and rigidly connected to the centrifugal element 21. Depending on the centrifugal position of the centrifugal element 21, the shaft 24 is moved into the first stop position ( Fig. 3b ) or in the second stop position ( Fig. 4b ) rotates.

The cam contour element 40 is a pin displaceably mounted in the cam 11 along a cam contour element axis, and is biased against the shaft (stop body) 24 (i.e. biased towards the cam body 12 or toward the second cam contour position).

Due to this preload, the cam contour element 40 therefore assumes the position that is specified by the stop with the shaft 24. In the first stop position the Wave 24 ( Fig. 3b ), the stop is produced by a comparatively more protruding section of the shaft 24. This blocks movement of the cam contour element 40 into the cam body 12 (toward the second cam contour position), so that the cam contour element 40 is in the first cam contour position, that is, its cam contour surface 44 protrudes from the remaining cam contour surface 14.

In the second stop position ( Fig. 4b ), the stop is produced by a comparatively less protruding or flattened section of the shaft 24. This enables movement of the cam contour element 40 into the cam body 12 (towards the second cam contour position), and due to the preload, the cam contour element 40 is consequently in the second cam contour position, that is, with its cam contour surface 44 not protruding.

In this way it is achieved that at low speeds (first speed) the cam contour surface 44 protrudes and thus causes additional actuation of the exhaust valve 70, as in Figs. 3a-3c depicted; and that at higher speeds (second speed) the cam contour surface 44 is flush with the remaining cam contour surface 14 and thus the additional actuation of the exhaust valve 70 is prevented.

Regarding Fig. 5 the position of the cam contour element 40 is described in more detail.

As already mentioned, the cam contour surface - more precisely its center 44 ' - of the cam contour element 40 is preferably arranged on a section of the cam contour 16 in which the exhaust valve - at least in the second cam contour position or in the remaining cam contour surface of this section - is closed.

The cam contour surface of the cam contour element 40 is preferably arranged in a section of the cam contour 16 which is assigned to a compression stroke of the internal combustion engine.

Preferably, an angle α between the point 16a of maximum eccentricity of the cam contour 16 and the center 44' of the cam contour surface is less than 180° (measured in the direction of rotation as in Fig. 5 shown, with the direction of rotation being clockwise, as shown in Fig. 3b and 4b rocker arm 60 shown is visible). For example, the angle α can be between 90° and 180°, particularly preferably between 105° and 180° or even between 125° and 180°. This ensures that the cam contour surface can act efficiently as a decompression surface and allow pressure to be released in the combustion chamber during cranking.

The point 16a of maximum eccentricity of the cam contour 16 is generally independent of the cam contour position, and is defined with respect to the second cam contour position to avoid ambiguity.

The cam contour element 40 is a pin displaceably mounted in the cam 11 along a cam contour element axis. The axis of this pin 40 deviates by an angle of less than 45°, preferably less than 30°, from the radial direction of the camshaft through the center 44' of the cam contour surface.

The entire cam contour surface of the cam contour element 40 only occupies a limited angular range of the cam contour 16, preferably less than 45°, particularly preferably less than 30°, and most preferably less than 15°. The cam contour surface of the cam contour element 40 preferably occupies an angular range of at least 2°.

Regarding Fig. 6 a valve lift diagram of a four-stroke engine is described, which is operated by means of the valve train according to the invention. The valve lift diagram shows schematically the valve opening V of an intake valve (dashed curve labeled I) and the exhaust valve driven by the valve train according to the invention (solid curve labeled E and E`) as a function of a phase angle α of the engine cycle, approximately half the angle of the crankshaft. BDC denotes the bottom dead center (at phase angle α = 0° and α = 180°) and TDC denotes the top dead center of the crankshaft (at phase angle α = 90° and α = 270°). The diagram shows the following cycles of the four-stroke engine in this order: Eject; suction; compacting; Work.

Curves E and I represent common valve lift curves of the four-stroke engine. Curve E' represents the additional actuation by the cam contour element 40 in the first cam contour position. This additional actuation is not present in the second cam contour position, i.e. curve E' is characterized by a flat one Curve (no valve lift replaced). This additional actuation occurs in the compression stroke before top dead center. As already described, this additional actuation E` allows gas to escape from the combustion chamber and thus pressure can be reduced, so that the work to be done by the starter motor against the pressure is reduced.

Figure 6 also illustrates some general aspects of the arrangement of the cam contour element 40 in relation to the engine phase, which are described below and optionally for any embodiments apply. Here, the motor phase angle α is defined so that it runs through the interval from 0° to 360° during an engine cycle. In one aspect, the engine is a four-stroke engine and the engine phase angle α is half the valve crank angle.

According to one aspect, the cam contour surface of the cam contour element 40 is arranged for valve actuation during a compression stroke of the internal combustion engine. According to a further aspect, the cam contour surface of the cam contour element 40 is arranged such that a phase angle α _P of a maximum valve lift of this cam contour surface is by a phase difference in the range of 70 ° - 30 °, preferably in the range of 65 ° - 45 ° before top dead center UDC am end of the compression cycle. According to a further aspect, the valve opening caused by the cam contour surface of the cam contour element 40 covers a phase interval (α _O - α _C ) of the engine cycle of more than 2 ° or more than 3 ° or even more than 5 °, and or of less than 20 °, less than 15° or even less than 10°, for example between 3° and 15°, preferably between 5° and 10°. Here α _O is defined as the phase in which the valve opening exceeds the value of 10% of the maximum valve opening at α _P , and α _C is defined as the phase in which the valve opening falls below this value again. In other words, the phase interval (α _O - α _C ) is the range at which the valve opening is greater than 10% of the maximum valve opening at α _P.

According to a further aspect, the cam contour element is arranged in a non-actuation region of the cam, so that the valve is not actuated in an area around the cam contour element. According to a further aspect, the (maximum) valve lift through the cam contour element (in the first cam contour position) is less than 30%, less than 20% or even less than 10% of the (maximum) valve lift through the cam as a whole (i.e. through point 16a of the Cam contour, see Fig. 5 ).

The operation - in particular the starting process - of an internal combustion engine with the valve train described herein can therefore be described as follows, with the reference numbers referring to all figures:
First, approximately at the beginning of starting, the camshaft 10 rotates at a low (first) speed and cyclically actuates the exhaust valve 70 through the cam 11. Due to the low (first) speed, the cam contour element is located 40 in the first cam contour position, in which its cam contour surface 44 protrudes, so that the exhaust valve 70 is actuated by the cam contour surface 44 during a compression stroke of the internal combustion engine. The first cam contour position is achieved as described above by the trigger mechanism 20 holding the cam contour element 40 in the first cam contour position, as shown in FIG Figs. 3a-3c shown and described in relation to these figures. The protruding cam contour surface 44 opens the valve so that the pressure of the gas in the combustion chamber can be reduced.

As the process progresses, the rotation of the camshaft is accelerated to a second, higher speed. Due to the higher speed, the cam contour element 40 becomes the second cam contour position ( Figs. 4a-4c ) moves in which the cam contour surface 44 does not protrude or protrudes less. The movement towards the second cam contour position is achieved, as described above, by the trigger mechanism 20 holding the cam contour element 40 in the second cam contour position, as in Figs. 4a-4c shown and described in relation to these figures. As a result, the exhaust valve 70 is no longer actuated by the cam contour surface 44 of the cam contour element 40, ie there is no significant additional valve opening. This enables normal operation of the internal combustion engine and in particular normal compression of the air-fuel mixture in the combustion chamber.

Even if individual exemplary embodiments are described above and shown in the figures, the scope of protection results solely from the claims. Furthermore, details of the embodiment described above are described for illustrative purposes only with respect to this embodiment.

Claims (10)

1. Camshaft (10) for an exhaust valve (70) of an internal combustion engine, wherein the camshaft comprises:

   - a first bearing (8a) and a second bearing (8b) for rotatably supporting the camshaft (10) about its camshaft axis;

   - a cam (11), wherein the cam (11) defines a cam contour (16) for cyclically actuating the exhaust valve by rotating the camshaft, and wherein the cam (11) comprises a cam body (12) and a cam contour element (40),
   wherein the cam contour element (40) is movable, relative to the cam body (12), into a first cam contour position and into a second cam contour position, such that the cam contour (16) has a first cam contour shape if the cam contour element (40) is in the first cam contour position, and has a second cam contour shape, which is different from the first cam contour shape, if the cam contour element is in the second cam contour position; and

   - a trigger mechanism (20) for the cam contour element (40), wherein the trigger mechanism (20) is configured to hold the cam contour element at a first, lower rotation speed of the camshaft in the first cam contour position, and to hold the cam contour element at a second, higher rotation speed of the camshaft in the second cam contour position,

   wherein the cam (11) and the trigger mechanism (20) are arranged axially between the first bearing (8a) and the second bearing (8b), and wherein

   the cam contour element (40) is designed as a pin, which can be retracted into and extended from the cam body (12), and wherein

   the trigger mechanism (20) comprises a centrifugal element (21), wherein the centrifugal element (21) is arranged directly adjacent to the cam (12).
2. Camshaft according to any of the preceding claims, wherein
   the cam contour element (40) for actuating the exhaust valve (70) protrudes if the cam contour element (40) is in the first cam contour position, and the cam contour element (40) does not protrude or protrudes less if the cam contour element is in the second cam contour position.
3. Camshaft according to any of the preceding claims, wherein the trigger mechanism (20) comprises the centrifugal element (21) and a coupling mechanism (24), wherein

   the centrifugal element (21) is mounted to take a first centrifugal position at the first, lower rotation speed of the camshaft, and to take a second centrifugal position by the action of centrifugal force at the second, higher rotation speed of the camshaft, and wherein

   the coupling mechanism (24) couples the centrifugal element (21) to the cam contour element (40), in order to hold the cam contour element (40) in the first cam contour position if the centrifugal element (21) takes the first centrifugal position, and to hold the cam contour element (40) in the second cam contour position if the centrifugal element (21) takes the second centrifugal position.
4. Camshaft according to claim 3, wherein at least one of (a) through (c):

   (a): the centrifugal element (21) is a lever that is mounted on the camshaft (10) in such a manner that the centrifugal force acting during rotation of the camshaft exerts on the lever (21) a torque directed towards the second centrifugal position, and the trigger mechanism (20) has a biasing element (30) that biases the lever (21) towards the first centrifugal position, wherein the biasing element (30) is connected in a force-fitting manner to the centrifugal element (21) - in particular, is pressed against the centrifugal element (21) by means of a compression spring;

   (b): the centrifugal element (21) is a lever pivotable about a lever axis extending parallel to the camshaft axis, wherein the lever axis is preferably arranged eccentrically to the camshaft axis, wherein the lever axis is particularly preferably spaced apart from the camshaft axis in the direction of a protrusion portion of the cam body (12).
5. Camshaft according to any of claims 3 and 4, wherein preferably at least one of (d) and (e):

   (d): the coupling mechanism (24) is connected to the centrifugal element (21) for blocking a movement of the cam contour element (40) towards the second cam contour position if the centrifugal element (21) is in the first centrifugal position, and for releasing the movement of the cam contour element (40) towards the second cam contour position if the centrifugal element (21) is in the second centrifugal position, wherein
   the cam contour element (40) is biased towards the second cam contour position;

   (e): the coupling mechanism comprises a stop body (24) against which the cam contour element (40) is biased, and the stop body (24) is connected in a positive-locking - in particular, rigid - manner to the centrifugal element (21) in order to take, together with the centrifugal element (21), the first or second centrifugal position, respectively, e.g., in order to be rotatable, together with the centrifugal element 21, about the lever axis described in (b), wherein the stop body (24) in the first centrifugal position provides a first stop for the cam contour element (40), and, in the second centrifugal position, provides a second stop, which is different from the first stop, for the cam contour element (40), wherein the stop body (24) is preferably arranged eccentrically to the camshaft axis.
6. Camshaft according to any of the preceding claims, wherein the cam contour element (40) is a pin being mounted in the cam (11) displaceably along a cam contour element axis, and being biased towards the second cam contour position.
7. Valve train for an internal combustion engine having a camshaft according to any of the preceding claims, wherein the camshaft (10) is connected axially outside the first bearing (8a) to a drive gear for driving by a crankshaft of the internal combustion engine, and is connected axially outside the second bearing (8b) to an output gear for driving an intake valve actuating unit.
8. Internal combustion engine having a valve train according to claim 7, wherein the drive gear is connected to the crankshaft, and wherein the output gear is connected to an intake valve actuating unit.
9. Method for actuating an exhaust valve (70) of an internal combustion engine, wherein the internal combustion engine has a camshaft (10) with a cam (11), wherein the cam (11) has a cam body (12) and a cam contour element (40) movable relative to the cam body (12), wherein the cam contour element (40) is designed as a pin, which can be retracted into and extended from the cam body (12), and wherein

   the camshaft (10) is rotatably mounted about its camshaft axis by means of a first bearing (8a) and a second bearing (8b) such that the cam (11) and a trigger mechanism (20) are arranged axially between the first bearing (8a) and the second bearing (8b), and wherein the trigger mechanism (20) comprises a centrifugal element (21), wherein the centrifugal element (21) is arranged directly adjacent to the cam (12);

   wherein the method comprises:

   - rotating the camshaft (10) at a first speed for cyclically actuating the exhaust valve by the cam (11), wherein the cam contour element (40) is in a first cam contour position, at which a cam contour surface (44) of the cam contour element (40) protrudes such that the exhaust valve (70) is actuated by the cam contour surface (44) during a compression stroke of the internal combustion engine;

   - accelerating the rotation of the camshaft to a second speed that is higher than the first speed,

   - moving the cam contour element (40) by means of the trigger mechanism (20) to a second cam contour position, at which the cam contour surface (44) does not protrude or protrudes less, such that the exhaust valve (70) is no longer actuated by the cam contour surface (44) of the cam contour element (40).
10. Use of the camshaft according to any of the claims 1 to 7 or the valve train according to claim 8 for actuating an exhaust valve of an internal combustion engine, in particular according to the method according to claim 9.

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