CN109952416B

CN109952416B - Camshaft for internal combustion engine

Info

Publication number: CN109952416B
Application number: CN201780062263.7A
Authority: CN
Inventors: 乌伟·艾森拜斯
Original assignee: Individual
Current assignee: Individual
Priority date: 2016-10-07
Filing date: 2017-10-06
Publication date: 2021-11-16
Anticipated expiration: 2037-10-06
Also published as: CN109952416A; BR112019006860A2; DE102016119105A1; WO2018065602A1; EP3523513C0; EP3523513A1; EP3523513B1

Abstract

The invention relates to a camshaft (10) mounted at both ends for an outlet valve (70) of an internal combustion engine, having a cam (11) and a release mechanism (20). The cam (11) defines a cam profile (16) for cyclically actuating the outlet valve by rotation of the camshaft and comprises a cam body (12) and a cam profile element (40). The cam profile element (40) can be moved relative to the cam body (12) into a first cam profile position and a second cam profile position in such a way that: such that the cam profile (16) has a first cam profile shape when the cam profile element (40) is in the first cam profile position and a second cam profile shape different from the first cam profile shape when the cam profile element is in the second cam profile position. A release mechanism (20) for a cam profile element (40) is configured to hold the cam profile element in a first cam profile position at a lower first rotational speed of the camshaft and to hold the cam profile element in a second cam profile position at a higher second rotational speed.

Description

Camshaft for internal combustion engine

Technical Field

One aspect of the present disclosure relates to a camshaft for an exhaust valve of an internal combustion engine. According to one aspect, the camshaft has a movable cam profile element, by means of which a cam profile shape dependent on the rotational speed is obtained.

Background

Valve trains which generate valve strokes of intake and exhaust valves with fixed stroke heights and stroke durations by means of a camshaft are often used in internal combustion engines. However, such valve trains have disadvantages with regard to an optimum adaptation to different load ranges of the internal combustion engine. Furthermore, once the engine is started during the start phase, the camshaft actuates the valvetrain; however, the energy used to compress the gases in the combustion chamber must be applied by the starting engine, which may lead to disadvantages during starting.

To accommodate such a need, there are many valvetrains that allow for improved valve travel profiles for starting. A particularly simple but effective design is based on the following camshaft, namely: for actuating the valves, the camshaft comprises several cam tracks arranged side by side and can be displaced laterally by means of an adjusting unit. The cam path adapted to the respective requirements can then be selected by a transverse displacement of the camshaft. In the case of a camshaft for the exhaust valve, for example, one cam for the starting phase and an additional cam for normal operation can be provided as follows, namely: wherein the cam for the start phase provides an additional valve opening to reduce the gas pressure in the combustion chamber.

However, such an adjustment unit increases the space and weight requirements of the valve mechanism and requires a complex control of the adjustment unit. In addition, the stability and strength of the camshaft may be compromised.

JP 2008-82188 describes a camshaft having a pressure-reducing function and a function for phase shifting, the pressure-reducing function being dependent on the rotational speed of the camshaft. In which the control shaft 57 is rotated relative to the cam 36 by means of the centrifugal mechanism 50 so as to lift the pins 65a and 65b (see fig. 6, 7 of JP 2008-82188). This mechanism requires a tension spring 53 attached to the centrifugal mechanism along with a drive link 59 and, therefore, has a greater space requirement.

Furthermore, since the control shaft 53 is arranged on the rotational axis, at least one shaft end of the camshaft must be accessible, which leads to limitations in the mounting and placement of the camshaft.

Disclosure of Invention

The invention has the object of providing a camshaft which is adjustable on the one hand, but which, on the other hand, reduces at least some of the disadvantages described above.

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

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

Preferably, said cam profile element protrudes in a first cam profile position for actuating (opening) the exhaust valve (opposite to the surrounding cam profile), and in a second cam profile position it does not protrude or protrudes less so that the exhaust valve is not subjected to any, i.e. any substantial additional actuation (opening); thus, it does not open any further than by means of the cam profile around the cam profile element.

The second rotational speed range may be substantially close to the first rotational speed range, wherein a transition between the first rotational speed range and the second rotational speed range may be defined by a threshold value or by a specific transition (transition range). The triggering mechanism is thus configured to hold the cam profile element in the first cam profile position in the event of a rotational speed below a predetermined threshold value or transition range, and to hold the cam profile element in the second cam profile position in the event of a rotational speed exceeding the predetermined threshold value or transition range. According to one aspect, the trigger mechanism is configured to bring the cam profile element from the first cam profile position to the second cam profile position during a transition from the first rotational speed to the second rotational speed (or from the first rotational speed range to the second rotational speed range).

For example, the first rotational speed may be within a typical rotational speed range for starting. According to one aspect, the first speed, which is also dependent on the engine type, is between 0rpm and 1,000rpm, and preferably between 0rpm and 500 rpm. The second rotational speed may lie within the normal operating range of the engine, in each case approximately above 500rpm, and preferably above 700rpm or 1,000rpm, relative to the rotational speed of the camshaft. Thus, the threshold value may lie, for example, in a rotational speed range between 500rpm and 1,000 rpm.

The camshaft according to the invention therefore allows a rotational speed-dependent cam profile and, consequently, a rotational speed-dependent valve travel curve of the exhaust valve. According to a particular aspect, at low rotational speeds typical for the starting phase, the cam profile element protrudes (in the first cam profile position) such that an additional valve opening is achieved (compared to a higher rotational speed or second cam profile position) such that less effort needs to be applied to the pressure starter motor in the combustion chamber.

According to one aspect of the invention, the rotational speed dependent cam profile shape can be achieved without lateral displacement of the cam. In particular, this enables the camshaft to be mounted on both sides. The mounting on both sides makes it possible to transmit power between the cam and the valve particularly advantageously, since undesired bending vibrations of the camshaft are avoided and the valve mechanism can be controlled flexibly.

The first cam profile shape may be different from the second cam profile shape, in particular in that the first cam profile shape has a protrusion for opening an exhaust valve (70) during a compression stroke of the internal combustion engine. The projection preferably occupies a rotational angle range of the camshaft of between 1 ° and 30 °. The center of this projection is preferably offset in the direction of rotation of the cam by an angle of between 90 ° and 270 °, in particular preferably by an angle of between 90 ° and 180 °, relative to the point or angle of maximum eccentricity of the cam profile (projection of the cam body).

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

In this context, "a" always means "at least one"; for example, "one cam" = "at least one cam", and the like. The first speed range may include stationary (0 speed).

Further advantageous designs are shown in the dependent claims and in the following description of the figures. Various aspects and details of the embodiments are identified herein with reference numerals of the figures; however, these reference numerals are shown for illustrative purposes only. Aspects may also be combined with other aspects, regardless of the embodiment presented.

Drawings

The drawings are as follows:

FIG. 1 shows a perspective view of a valve train for an exhaust valve according to one embodiment of the present invention;

fig. 2 shows a front view of the valve mechanism according to fig. 1;

3a-c show side views of the valve mechanism according to FIGS. 1 and 2 with the cam profile element in a first cam profile position;

4a-c show side views of the valve mechanism according to FIGS. 1 and 2 with the cam profile element in a second cam profile position;

FIG. 5 shows another side cross-sectional view of the cam of FIG. 4 b; and

fig. 6 shows a valve travel diagram of the valve mechanism according to the invention.

Detailed Description

Fig. 1 and 2 show a valve train for an exhaust valve 70 of an internal combustion engine having a camshaft 10 according to an embodiment of the invention. The camshaft 10 comprises a cam 11, which is arranged to actuate an exhaust valve 70. The camshaft 10 is rotatable about its axis. For this purpose, the camshaft 10 is supported on the cylinder head by means of

bearings

8a, 8b and is therefore supported on both sides by means of

bearings

8a, 8 b. Thus, it is an overhead camshaft. The camshaft 10 also includes a centrifugal element 21, which is described in more detail below with respect to fig. 3 and 4.

The

mountings

8a, 8b on both sides allow an advantageous power transmission between the cam and the valve, since undesired bending vibrations of the camshaft are avoided. The mountings on both sides also enable flexible control of the valve mechanism; according to a preferred aspect, the transmission gear or chain drive sprocket connected to the crankshaft of the internal combustion engine is located on one side 7a of the camshaft and the output gear connected to the intake valve drive shaft is located on the other side 7b of the camshaft 10. This allows the camshaft to be used in a valve drive, as described, for example, in DE 102005057127.

The valve mechanism also includes a mechanism for actuating the exhaust valve 70 by the cam 11. In the embodiment shown in fig. 1 and 2, the mechanism includes a rocker arm 60 and a shim 72 disposed between the cam 11 and the outlet valve 70 such that the outlet valve is actuated by the cam 11 via the rocker arm 60 and the tappet 72. Fig. 2 also shows a valve spring 74 that biases the valve 70 against the cam 11 (at least in stages, e.g., where the valve is actuated) and, as a result, creates a force lock between the valve 70 and the cam 11. In the phase in which the valve is not actuated, the valve spring presses the valve into the valve seat, which exerts a corresponding reaction force.

As can be seen in fig. 2, the cam 11 comprises a cam body 12 and a cam profile element 40 (see fig. 3b, 4 b; in fig. 2 only one end of the cam profile element can be seen as relief surface 44), which cam body 12 and cam profile element 40 together define the cam profile 16 of the cam 11. More precisely, the cam profile 16 is formed by a relief surface 44 of the cam profile element 40 (also designated as cam profile surface of the cam profile element) and the remaining cam profile surface 14 of the cam body 12. The cam profile 16 is a profile of the cam 11 which actuates the exhaust valve 70 when the camshaft 10 rotates and therefore has a decisive influence on the valve travel curve of the exhaust valve 70.

The cam profile element 40 is designed as a pin which can be retracted into the cam body 12 and extended out of the cam body 12 (see also fig. 3b, 4 b).

In the extended position (first cam profile position shown in fig. 3 b), the cam profile surface 44 of the cam profile element 40 protrudes with respect to the remaining cam profile surface 14. As a result, the outlet valve 70 undergoes additional actuation (opening) by the cam profile surface 44 of the cam profile element 40. In the retracted position (second cam profile position shown in fig. 4 b), the cam profile surface 44 is arranged flush (substantially non-protruding) with the remaining cam profile surface 14, so that the outlet valve is not subjected to any additional actuation (opening), which means that there is no substantial actuation (opening). Thus, the cam profile 16 has a variable cam profile shape depending on whether the cam profile element 40 is in the first cam profile position or the second cam profile position.

The cam contour surface 44 of the cam contour element 40 is thereby arranged on the following sections of the cam contour 16, namely: in this section, the outlet valve 70 is closed at least in the second cam profile position or on the remaining cam profile surface 14 of this section surrounding the cam profile element 40.

Thus, the cam profile surface 44 of the cam profile element 40 acts as relief surface 44; at low speeds of rotation in a typical cranking phase, the additional valve opening (in the first cam profile position) allows the pressure in the combustion chamber to be relieved, so that less effort needs to be applied to the pressure-starting motor in the combustion chamber. At higher rotational speeds typical for normal operation, additional valve openings are prevented so that a loss of engine efficiency does not have to be accepted.

As shown in fig. 2, a cam profile element 40 (with respect to the axial direction of the camshaft) is mounted centrally in the cam 11. This central mounting, in particular in combination with the valve train with the rocker arm 60, ensures a uniform and low-loss transmission of force from the cam 11 to the valve 70. According to a general aspect, the center of the cam profile element 40 is offset from the center of the cam (relative to the axial direction) by less than 20% of the cam width.

Fig. 3 and 4 show in more detail the triggering mechanism 20 of the valve mechanism as shown in fig. 1 and 2, by means of which triggering mechanism 20 the cam profile element 40 is moved (retracted and extended) as a function of the rotational speed. Thus, the triggering mechanism 20 ensures that the cam profile element 40 or its cam profile surface 44 is extended at low rotational speeds (first cam profile position) and retracted at higher rotational speeds (second cam profile position).

Thus, fig. 3a and 4a are side views as viewed from the right side in fig. 2; FIGS. 3b and 4b are side sectional views taken along the plane A-A of FIG. 2; and fig. 3c, 4c are side sectional views along the plane B-B of fig. 2. Fig. 3a-c show the cam profile element in a first cam profile position, and fig. 4a-c show the cam profile element in a second cam profile position.

Fig. 3a, 3c show a side view or a sectional view of the centrifugal element 21 of the triggering mechanism 20. The centrifugal element 21 is designed as a lever having a first lever arm 27 and a second lever arm 28 on both sides, and the centrifugal element 21 is rotatably mounted on the camshaft 10 about the axis 22 (i.e. on a suspension rotating with the camshaft 10, here on a cam body 12, which cam body 12 is rigidly connected to the camshaft 10). Fig. 3a, 3c show the centrifugal element 21 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 around the axis 22 relative to the first centrifugal position.

The biasing element 30 shown in fig. 3c, 4c biases the centrifugal element 21 towards the first centrifugal position (in the view of fig. 3a, 4a, counter-clockwise). The biasing element 30 is arranged in an opening of the camshaft 10 extending transversely through the camshaft such that the longitudinal axis of the biasing element 30 extends at right angles through the rotational axis of the camshaft. The biasing can be achieved by a return spring which is arranged approximately concentrically to the longitudinal axis of the biasing element 30 in the camshaft 10 and clamps (presses) the biasing element 30 against the centrifugal element 21. The return spring may be a compression spring sandwiched between (a stop in) the opening of the camshaft and (a stop on) the biasing element 30.

In one aspect, the length of the section of the biasing element 30 protruding from the camshaft 10 towards the centrifugal element 21 is shorter than the camshaft radius of the camshaft 10 at that location. This applies to the first and/or second centrifugation position. This allows a particularly compact arrangement of the biasing element 30.

In the first centrifugal position the centrifugal element 21 is clamped (pressed) against the first stop by the biasing element 30. Here, the first stop is formed at the first lever arm, for example, by the intermediate piece 26 of the first lever arm and the camshaft 10. The first stop is arranged on a lever side of the centrifugal element 21 different from 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 the maximum compression of the return spring of the biasing element 30 or by an additional stop between the second lever arm 28 and the camshaft 10.

In one aspect, the biasing element 30 is connected to the centrifugal element 21 in a force-fitting manner; in particular, it is pressed against the centrifugal element 21.

The bias applied by the biasing element 30 towards the first centrifugal position brings the centrifugal element 21 in a rest position or, at low rotational speeds of the camshaft (first rotational speed), in the first centrifugal position, as shown in fig. 3 a.

In the embodiment shown, the centrifugal element is designed as a lever. The lever 21, and in particular the

lever arms

27, 28 thereof, is dimensioned such that the centrifugal force acting when the camshaft is rotated acts more strongly on the first lever arm 27 than on the second lever arm 28, and therefore a torque directed towards the second centrifugal position (i.e. clockwise oriented in the view of fig. 3a, 4 a) is exerted on the centrifugal element 21 as a whole. If the rotational speed exceeds a certain threshold value (e.g. at a second, higher rotational speed), the torque exceeds the bias of the biasing element 30 and as a result the centrifugal element 21 is subsequently in the second centrifugal position, as shown in fig. 4 a.

According to one aspect, the lever extends along a partial section around the camshaft 10. According to one aspect, the center of gravity of the first lever arm 27 is offset by more than 90 °, preferably more than 120 °, or even more than 135 °, relative to the center of gravity of the second lever arm 28. According to one aspect, the center of gravity and/or the lever end of the first lever arm 27 is offset by more than 90 °, preferably more than 120 °, or even more than 135 °, relative to the pivot axis 22 (relative to the rotational axis of the camshaft 10 and in the direction of spatial extension 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 with respect to the pivot axis 22 by less than 90 °, preferably by less than 45 °, or even by less than 30 °. According to one aspect, the center of gravity and/or lever end of the first lever arm 27 is offset with respect to the pivot axis 22 by more than two times, three times or even four times the angle of the center of gravity or lever end of the second lever arm 28. In this context, the angle is always defined around the axis of rotation of the camshaft 10 and in the direction of the spatial extension of the centrifugal element 21. These aspects allow a lever with a sufficiently large lever arm and at the same time a low space requirement 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 parallel to the camshaft axis. According to one aspect, the lever axis is arranged eccentrically with respect to the camshaft axis; preferably, it is radially away from the camshaft axis in the direction of the protruding portion of the cam body 12. The projecting portion is an angular range radially from the camshaft axis, which has an angular deviation of less than 30 ° in the direction of projection (maximum eccentric point) of the cam body 12.

According to an additional aspect, the centrifugal element 21 is arranged directly adjacent to the cam 12, i.e. without another functional part in between, such as a bearing for the cam or the like. According to one aspect, the axial distance (side-to-side) between the centrifugal element 21 and the cam 12 is less than 0.5 cm. According to one aspect, the axial distance between the central plane of the centrifugal element 21 and the central plane of the cam 12 is less than twice the axial width of the cam or less than 1.5 times, or even less than the axial width of the cam. According to one aspect, the camshaft is supported on both sides, and the centrifugal element 21 is arranged between the two

bearings

8a, 8 b. This enables a compact design in the axial direction as well.

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

This coupling is realized such that the cam profile element (40) is held in the first cam profile position if the centrifugal element (21) assumes the first centrifugal position (as shown in fig. 3 b) and the cam profile element (40) is held in the second cam profile position if the centrifugal element (21) assumes the second centrifugal position (as shown in fig. 4 b).

The cam profile element 40 is designed as a pin which is arranged at least partially in a blind hole of the cam body 12 along the pin axis and can be retracted into the blind hole. The surface of the cam profile element 40 facing outwardly from the blind bore forms a cam profile surface 44. In a first cam profile position (fig. 3 b) the pin at least partially protrudes from the blind hole, and in a second cam profile position (fig. 4 b) the pin is substantially retracted into the blind hole such that the cam profile surface 44 is flush with the surrounding surface.

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

According to one aspect, the stop body 24 is connected to the centrifugal element 21 in a positive-locking, in particular rigid, manner. According to one aspect, the connection between the centrifugal element 21 and the stop body 24 is arranged eccentrically with respect to the camshaft axis, preferably radially offset from the projection or nose of the cam body 12 (angular range +/-30 ° around the projection).

According to one aspect, the stop body can be rotated 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 stop body axis is arranged eccentrically with respect to the camshaft axis, preferably in a protruding portion of the cam body 12. According to one aspect, the stopper body axis corresponds to the lever axis of the centrifugal element (lever) 21, and the stopper body 24 can rotate together with the centrifugal element 21.

The cam profile element 40 is biased against the stop body 24. This biasing is not shown and can be achieved, for example, by a return spring which is arranged concentrically to the axis of the cam profile element 40 and clamps (presses) the cam profile element 40 against the stop body 24. The return spring may be a compression spring sandwiched between the blind hole or (a stop in) the cam body 12 and (a stop on) the cam profile element 40. According to one aspect, the cam profile element 40 is connected to the stop body 24 in a force-fitting manner (pressed against it). According to one aspect, the contact portion between the stop body 24 and the cam profile element 40 is arranged in the cam body 12, preferably in a protruding portion of the cam body 12.

According to one aspect, the stop body 24 is non-circular in the portion of the cam profile element 40 clamped against the stop body 24.

If the centrifugal element 21 is in the first centrifugal position, the stop body 24 is in the first stop position and provides the cam profile element 40 with a first stop defining a first cam profile position for the cam profile element 40. If the centrifugal element 21 is in the second centrifugal position, the stop body 24 is in the second stop position and provides the cam profile element 40 with a second stop defining a second cam profile position for the cam profile element 40. According to one aspect, the first stop and the second stop are different. Preferably, the second stop is recessed relative to the first stop.

In the embodiment of fig. 3b, 4b, the stop body is realized by a shaft 24, which shaft 24 rotates about an axis 22 (fig. 3c, 4 c) and is rigidly connected to the centrifugal element 21. Thus, depending on the centrifugal position of the centrifugal element 21, the shaft 24 rotates into a first stop position (fig. 3 b) or into a second stop position (fig. 4 b).

The cam profile element 40 is a pin which is mounted in the cam 11, is displaceable along the cam profile element axis and is biased against the shaft (stop body) 24 (i.e. in the direction of the cam body 12 or towards the second cam profile position).

Based on this offset, the cam profile element 40 thus assumes the position that the stop specifies with the shaft 24. In the first stop position of the shaft 24 (fig. 3 b), the stop is produced by a relatively more protruding section of the shaft 24. This prevents the cam profile element 40 from moving into the cam body 12 (towards the second cam profile position) such that the cam profile element 40 is in the first cam profile position, i.e. its cam profile surface 44 protrudes with respect to the remaining cam profile surface 14.

In the second stop position (fig. 4 b), the stop is produced by a relatively less protruding or flattened section 25 of the shaft 24. This releases the cam profile element 40 from moving into the cam body 12 (towards the second cam profile position) and, due to said biasing, the cam profile element 40 is thus in the second cam profile position, i.e. it does not protrude with its cam profile surface 44.

In this way, it is achieved that at low rotational speeds (first rotational speed) the cam profile surface 44 protrudes and, thus, causes an additional actuation of the exhaust valve 70, as shown in fig. 3a-3c, and at higher rotational speeds (second rotational speed) the cam profile surface 44 is flush with the remaining cam profile surface 14 and, thus, prevents an additional actuation of the exhaust valve 70.

With reference to fig. 5, the position of the cam profile element 40 will be described more precisely. As already mentioned, the cam profile surface of the cam profile element 40, more precisely the center 44a thereof, is preferably arranged at the following sections of the cam profile 16, namely: at this section, the outlet valve is closed at least in the second cam profile position or in the remaining cam profile surface of the section.

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 the compression stroke of the internal combustion engine.

The angle a between the point of maximum eccentricity 16a of the cam profile 16 and the centre 44a of the cam profile surface is preferably less than 180 ° (measured in the direction of rotation as shown in fig. 5, wherein the direction of rotation is clockwise, as can be seen on the basis of the rocker arm 60 shown in fig. 3b and 4 b). For example, the angle α may be between 90 ° and 180 °, preferably between 105 ° and 180 °, or even between 125 ° and 180 °. This ensures that the cam profile surface effectively acts as a relief surface and that pressure can be released from the combustion chamber during start-up.

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

The cam profile element 40 is a pin which is mounted in the cam 11 and is displaceable along the cam profile element axis. The axis of the pin 40 deviates from the radial direction of the camshaft through the centre 44a of the cam profile surface by an angle of less than 45 °, preferably less than 30 °.

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

Referring to FIG. 6, a valve stroke diagram for a four stroke engine operated using a valvetrain according to the present invention is depicted. The valve travel diagram schematically shows the valve opening V of the inlet valve (curve in dashed lines and marked I) and the exhaust valve (curves in solid lines and marked E and E') driven by the valve mechanism according to the invention, according to the phase angle a of the engine cycle, which is approximately half the crankshaft angle. BDC denotes a bottom dead center (at phase angles α = 0 ° and α = 180 °), and TDC denotes a top dead center of the crankshaft (at phase angles α = 90 ° and α = 270 °). The diagram shows the following cycles of a four stroke engine in this order, namely: ejecting; air intake; compressing; and (6) working.

Curves E and I represent typical valve stroke curves for a four-stroke engine. Curve E' represents the additional actuation of the cam profile element 40 in the first cam profile position. In the second cam profile position, there is no such additional actuation, i.e. curve E' is replaced by a flat curve (no valve travel). This additional actuation occurs during the compression stroke before top dead center. As already described, this additional actuation E' allows the gases to escape from the combustion chamber and thus reduces the pressure, so that the work to be performed on the pressure by the starter motor is reduced.

Fig. 6 also illustrates some general aspects of the arrangement of the cam profile element 40 relative to the motor phase, which are described below and optionally applicable to any of the embodiments. The motor phase angle α is thus defined in such a way that: it passes through an interval from 0 ° to 360 ° during the motor cycle. According to one aspect, the engine is a four stroke engine and the engine phase angle α is one half of the valve crank angle.

According to one aspect, the cam profile surface of the cam profile element 40 is arranged for valve actuation during a compression stroke of the internal combustion engine. According to an additional aspect, the cam profile surface of the cam profile element 40 is arranged in such a way that: so that the phase angle alpha of the maximum valve stroke of the cam profile surface_PA phase difference lying in the range of approximately 70 ° to 30 °, preferably in the range of 65 ° to 45 °, before the top dead center UDC at the end of the compression stroke. According to an additional aspect, the valve opening caused by the cam profile surface of the cam profile element 40 covers the following phase interval (α) of the engine cycle_O - α_C) Namely: more than 2 ° or more than 3 °, or even more than 5 °, and/or less than 20 °, less than 15 ° or even less than 10 °, for example between 3 ° and 15 °, and preferably between 5 ° and 10 °. Thereby, α_OIs defined as the valve opening exceeding alpha_PA phase of 10% of the maximum valve opening, and a_CIs defined as the phase at which the valve opening is again lower than this value. In other words, the phase interval (α)_O - α_C) The valve opening is greater than alpha_PMaximum valve opening degree ofIn the range of 10%.

According to an additional aspect, the cam profile element is arranged in a non-actuated part of the cam, such that no valve actuation takes place in a part around the cam profile element. According to an additional aspect, the (maximum) valve travel through the cam profile element (in the first cam profile position) is less than 30%, less than 20%, or even less than 10% of the (maximum) valve travel through the cam as a whole (i.e. through point 16a of the cam profile; see fig. 5).

Thus, the operation of an internal combustion engine, in particular the starting sequence, with a valve mechanism as described herein may be described as follows, wherein the reference numbers refer to all figures:

initially, for example, at the start of cranking, the camshaft 10 rotates at a low (first) speed, and thereby the exhaust valve 70 is periodically actuated by means of the cam 11. Due to this low (first) speed, the cam profile element 40 is in a first cam profile position, in which its cam profile surface 44 protrudes, so that the exhaust valve 70 is actuated by the cam profile surface 44 during the compression stroke of the internal combustion engine. As mentioned above, the first cam profile position is achieved by the trigger mechanism 20 holding the cam profile element 40 in the first cam profile position, as shown in and described with respect to fig. 3a-3 c. By means of the protruding cam profile 44, the valve is opened, so that the gas pressure in the combustion chamber can be reduced.

In the further course, the rotation of the camshaft is accelerated to a second, higher speed. With this higher speed, the cam profile element 40 moves to a second cam profile position (fig. 4a-4 c) where the cam profile surface 44 does not protrude or protrudes less. As mentioned above, the movement towards the second cam profile position is achieved by the triggering mechanism 20 holding the cam profile element 40 in the second cam profile position, as shown in and described in relation to fig. 4a-4 c. As a result, the outlet valve 70 is no longer actuated by the cam profile surface 44 of the cam profile element 40, i.e. there is no significant additional valve opening. This allows for normal operation of the internal combustion engine and, in particular, normal compression of the air-fuel mixture in the combustion chamber.

Although various embodiments are described above and depicted in the drawings, the scope of protection only derives from the claims. Furthermore, the details of the above embodiments are described for illustrative purposes only with respect to this embodiment, but it is intended that they should not be associated with the embodiment in question; rather, they may also be used and combined in association with any of the more general aspects.

Claims

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

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

-a cam (11), wherein the cam (11) defines a cam profile (16) for periodically actuating the exhaust valve by rotating the camshaft, and wherein the cam (11) comprises a cam body (12) and a cam profile element (40),

wherein the cam profile element (40) is movable relative to the cam body (12) into a first cam profile position and a second cam profile position, such that the cam profile (16) has a first cam profile shape if the cam profile element (40) is in the first cam profile position and the cam profile (16) has a second cam profile shape different from the first cam profile shape if the cam profile element is in the second cam profile position; and

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

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

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

the trigger mechanism (20) comprises a centrifugal element (21), the centrifugal element (21) being arranged directly adjacent to the cam (11).

2. The camshaft of claim 1,

the cam profile element (40) for actuating the exhaust valve (70) protrudes if the cam profile element (40) is in the first cam profile position, and the cam profile element (40) does not protrude or protrudes less if the cam profile element is in the second cam profile position.

3. A camshaft as claimed in claim 1, characterized in that the triggering mechanism (20) comprises a centrifugal element (21) and a coupling mechanism, wherein,

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

the coupling mechanism couples the centrifugal element (21) to the cam profile element (40) in order to hold the cam profile element (40) in the first cam profile position if the centrifugal element (21) assumes the first centrifugal position and to hold the cam profile element (40) in the second cam profile position if the centrifugal element (21) assumes the second centrifugal position.

4. The camshaft of claim 3, wherein at least one of the following (a) to (c):

(a) the method comprises the following steps The centrifugal element (21) is a lever which is mounted on the camshaft (10) in such a way that the centrifugal force acting during rotation of the camshaft exerts a torque on the lever (21) towards the second centrifugal position, and the trigger mechanism (20) has a biasing element (30), which biasing element (30) biases the lever (21) towards the first centrifugal position, wherein the biasing element (30) is connected to the centrifugal element (21) in a force-fitting manner;

(b) the method comprises the following steps The centrifugal element (21) is a lever which is pivotable about a lever axis which extends parallel to the camshaft axis, wherein the lever axis is arranged eccentrically with respect to the camshaft axis.

5. The camshaft of claim 3, wherein at least one of the following (d) and (e):

(d) the method comprises the following steps The coupling mechanism is connected to the centrifugal element (21) for preventing the cam profile element (40) from moving towards the second cam profile position if the centrifugal element (21) is in the first centrifugal position and for releasing the cam profile element (40) from moving towards the second cam profile position if the centrifugal element (21) is in the second centrifugal position, wherein

The cam profile element (40) is biased towards the second cam profile position;

(e) the method comprises the following steps The coupling mechanism comprises a stop body (24), against which the cam profile element (40) is biased, and which stop body (24) is connected to the centrifugal element (21) in a positively locking manner in order to take the first centrifugal position or the second centrifugal position, respectively, together with the centrifugal element (21), wherein the stop body (24) provides the cam profile element (40) with a first stop in the first centrifugal position and a second stop, different from the first stop, in the second centrifugal position.

6. A camshaft as claimed in claim 1, characterized in that the cam profile element (40) is a pin which is mounted displaceably in the cam (11) along a cam profile element axis and is biased towards the second cam profile position.

7. Valve train for an internal combustion engine, with a camshaft according to one of the preceding claims, wherein the camshaft (10) is connected axially outside a first bearing (8 a) to a transmission gear for driving by a crankshaft of the internal combustion engine and axially outside a second bearing (8 b) to an output gear for driving an intake valve actuation unit.

8. An internal combustion engine having a valve mechanism according to claim 7, wherein the transmission gear is connected to a crankshaft, and wherein the output gear is connected to the intake valve actuation unit.

9. Method for actuating an exhaust valve (70) of an internal combustion engine, wherein the internal combustion engine has a camshaft (10), wherein the camshaft (10) has a cam (11), wherein the cam (11) has a cam body (12) and a cam profile element (40) which is movable relative to the cam body (12),

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

wherein the camshaft (10) is rotatably mounted about a camshaft axis of the camshaft (10) by means of a first bearing (8 a) and a second bearing (8 b) such that the cam (11) and the triggering mechanism (20) are arranged axially between the first bearing (8 a) and the second bearing (8 b), and wherein,

the trigger mechanism (20) comprises a centrifugal element (21), the centrifugal element (21) being arranged directly adjacent to the cam (11);

wherein the method comprises the following steps:

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

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

-moving the cam profile element (40) by means of the triggering mechanism (20) to a second cam profile position, in which the cam profile element (40) is retracted and the cam profile surface (44) is not or less protruding, so that the exhaust valve (70) is no longer actuated by the cam profile surface (44) of the cam profile element (40).