CN111075530B

CN111075530B - Variable valve gear for piston internal combustion engine

Info

Publication number: CN111075530B
Application number: CN201910958079.1A
Authority: CN
Inventors: 阿德里安·比兰; 弗兰克·希姆塞尔; 阿尔诺·贝希施泰特
Original assignee: Schaeffler Technologies AG and Co KG
Current assignee: Schaeffler Holding China Co Ltd
Priority date: 2018-10-19
Filing date: 2019-10-10
Publication date: 2023-10-20
Anticipated expiration: 2039-10-10
Also published as: DE102018125978A1; CN111075530A

Abstract

The invention relates to a variable valve gear of a piston internal combustion engine, which has a ventilation valve with the same function for each cylinder, the valve stroke is preset by a cam of a cam shaft and can be transmitted to the ventilation valve by means of a switchable pressure lever, the switching of the pressure lever, which is guided in an axially movable manner in a transverse bore, is connected to a longitudinally extending switching device via a connecting element, which is supported above the pressure lever in a guide in a cylinder head and can be moved longitudinally by means of a linear actuator in opposition to the restoring force of a spring element, the connecting element being pressed against, embedded or fastened on the switching device at the top and on the end of the corresponding switching pin at the end. The switching means or guide has a three-dimensionally structured surface region which extends in the direction of movement at least over a section of the lower peripheral side of the switching means or of the upper peripheral side of the guide, or the switching means and guide have such surface regions which are complementary to one another.

Description

Variable valve gear for piston internal combustion engine

Technical Field

The invention relates to a variable valve gear of a piston internal combustion engine, comprising at least one gas exchange valve of identical function for each cylinder in a cylinder head of the piston internal combustion engine, the valve stroke of which is preset by at least one cam of a camshaft and can be selectively transmitted to at least one associated gas exchange valve by means of a switchable pressure lever, wherein a switching pin, which is guided in each case in an axially movable manner in a transverse bore, is connected to at least one longitudinally extending switching means via a connecting element of elastic or rigid design, which is supported parallel to the camshaft above the pressure lever in at least one guide in the cylinder head and can be displaced longitudinally from a rest position into a switching position by means of a linear actuator in opposition to the restoring force of the spring element, wherein the connecting element is in each case in contact with, engages or fastened at its lower end to an end of the respective switching pin, and wherein the at least one switching means and/or at least one guide part extending in each case in the longitudinal direction is designed such that at least one switching means can be displaced only in a low-friction manner in at least one contact with the at least one guide part extending longitudinally.

Background

Variable valve drives of the type in which the valve strokes of a plurality of functionally identical gas exchange valves can be switched off or switched by means of a common switching element extending in longitudinal direction have been proposed in the non-previously published patent applications DE 10 2017 101 792A1, DE 10 2017 129 422A1 and DE 10 2018 117 335.0.

The variable valve gear of a piston internal combustion engine enables individual cylinders or groups of cylinders of the piston internal combustion engine to be deactivated by switching off the transmittable valve strokes, and thus reduces the fuel consumption and the pollutant emissions of the piston internal combustion engine in partial-load operation in combination with switching off the fuel injection to the associated cylinders. On the other hand, the transmittable stroke course of the inlet valves and/or the outlet valves of a piston internal combustion engine can be changed by means of a stroke change and is thus adapted to the current operating state of the piston internal combustion engine as a function of operating parameters, such as the engine speed and the engine load. This allows an increase in engine power and torque and a reduction in the specific fuel consumption of the piston internal combustion engine.

In general, in a variable valve drive, two components of a switchable stroke transmission element are each provided, which components can be moved or rotated relative to one another. The switchable stroke transmission element is mostly a switchable cup tappet, roller tappet, rocker arm or plunger.

In a valve drive that can be switched off, the respective stroke transmission element is connected via one component to an associated cam adjustment of the camshaft and via the other component to a valve stem adjustment of the associated gas exchange valve. The two components can be coupled to each other or decoupled by means of a coupling device. In the coupled state, the valve stroke of the associated cam is transmitted to the associated gas exchange valve, while in the decoupled state, the associated valve inlet or valve outlet of the respective cylinder is kept closed. The coupling element of the coupling device is usually held in the rest position by means of a spring element and is moved by the application of a control force into the actuating position counter to the restoring force of the spring element and held there. In a valve drive which can be switched off, the rest position of the coupling element corresponds largely to the coupled state of the components of the stroke transmission element, while the actuating position corresponds to the uncoupled state of the components.

In a switchable valve drive, one component is connected to an associated primary cam adjustment of a camshaft with a specific valve stroke and to a valve stem adjustment of an associated gas exchange valve, while the other component is connected to an associated secondary cam adjustment of the camshaft with a greater valve stroke or with an additional stroke. In the uncoupled or coupled state, the valve stroke of the primary cam is transmitted to the associated gas exchange valve, while in the coupled or uncoupled state, the respective greater valve stroke of the primary or secondary cam is transmitted to the gas exchange valve. In a switchable valve drive, the rest position of the coupling element corresponds largely to the uncoupled state of the components of the stroke transmission element, while the actuating position corresponds to the coupled state of the components.

Different designs of coupling elements are known for adjusting the switchable stroke transmitting element. The hydraulic control is usually effected via a switching pressure line controlled by a solenoid valve, as described for example in DE 10 2006 057 894 A1 for a stroke cut-off and in DE 10 2006 023 772 A1 for a stroke change of the gas exchange valve. For selective switching off or switching of the strokes in groups, separate switching pressure lines are required, each having an associated switching valve, as described, for example, in DE 102 12 a 1. The transfer of the switching pressure oil from the respective switching pressure line into the switchable stroke transmission element is usually effected via a multi-flow hydraulic support element, as is known, for example, from DE 103 30 510A1. The electromagnetic actuation of the coupling element of the switchable stroke transmission element is generally carried out by means of an electromagnet, which is connected in an operative manner to the coupling element indirectly or directly, as is described, for example, in US 5 544 626A or in DE 10 2016 220 859A1.

The arrangement of individual hydraulic switching pressure lines and associated valves or individual electrical switching lines and associated electromagnets for each coupling element in or on the cylinder head of a piston internal combustion engine is generally relatively difficult and costly due to the small space.

This disadvantage in the valve gear of the initially mentioned type of construction is eliminated by the use of a switching device which extends lengthwise and which can switch off or switch over a plurality of functionally identical gas exchange valves.

In this valve drive, the coupling element of the switchable lever can be moved into the coupling position or the decoupling position of the primary and secondary lever in each case by means of a switching pin which is mounted in an axially movable manner in a transverse bore of the secondary lever, counter to the restoring force of the spring element. Each switching pin protrudes with its outer end from the secondary lever and is connected at this end via an upwardly directed, elastic, e.g. leaf spring-like or rigidly embodied connecting element, e.g. in the form of a transverse lever, to a longitudinally extending switching element, e.g. in the form of a switching lever, a push bar, a flat bar or a rail. The switching element, which extends in a longitudinal direction, is arranged above the pressure lever parallel to the associated camshaft and is supported in at least one guide in the cylinder head and can be displaced by the actuator linearly counter to the restoring force of the spring element in the axial direction of the switching element from the rest position into the switching position.

In the case of a longitudinal displacement of such a switching element in an associated guide in the cylinder head of a piston internal combustion engine, frictional resistance is formed on the basis of sliding, adhesion and/or viscous friction, which may lead to a change in the switching time of an electromechanical switching system consisting of a linear actuator, a longitudinally extending switching element and a switchable pressure lever. The available operating range of the system in which the valve stroke can be switched or shut off during operation of the piston internal combustion engine is thus significantly limited.

In order to avoid the friction-dependent stick-slip effect, i.e. jerky sliding, of the switching means of such a valve gear in the guide of the cylinder head, it is proposed in DE 10 2018 117 335.0 mentioned at the beginning to design the switching lever and/or the guide in such a way that only a linear or point contact is obtained between the guide and the switching lever. This is to be achieved by a structural change of the switching element, for example by deforming the base body of the switching element with radially extending pressure channels, bulges, circumferential flanges, or by such measures taking place at guides, for example radial projections.

All these measures disadvantageously lead to a significant increase in the radial diameter of the switching system or to an increase in the gauge size in a direction perpendicular to the direction of movement of the switching device and thus to a higher demand for structural space. This is not necessarily allowed in the cylinder head provided. In addition, a stable and exactly adapted guidance in the head groove over the entire length of the switching device is thereby made difficult. The linear guidance of the switching device by means of the rolling bearing proposed for this purpose likewise increases the necessary installation space (significantly increases the production costs) and, in addition, can disadvantageously limit the actuating travel of the switching device.

The viscous friction effect has proved to be particularly problematic in switching devices which are embodied as elongated push rails, which are advantageously guided in grooves in the cylinder head and in which they are slidingly supported by means of oil lubrication. Lubrication of the contact points between the pusher shoes and the head grooves is achieved by oil mist or splash oil from the surroundings of the head. The oil film thus produced between the pusher shoe and the surface of the cylinder head groove causes internal friction, the so-called viscous friction, in the longitudinal movement of the pusher shoe. The viscous friction of the oil film determines in this arrangement a frictional resistance which acts against the actuating force of the linear actuator in the longitudinal movement of the switching means and is overcome by the actuating force.

However, the viscosity of oil as a lubricant has a great correlation with temperature. Lubricating oils have a high viscosity, especially at low ambient temperatures, for example in the cold start phase of a piston internal combustion engine, which leads to a significant increase in the frictional resistance until a stick-slip effect is caused. In addition, viscous friction is also related to the thickness of the oil film. However, since the thickness of the oil film and the distribution of the oil film along the switching device cannot be precisely determined and the viscosity likewise suffers from fluctuations that are influenced by operation and tolerances, the degree of viscous friction and in particular the discontinuity lead to corresponding discontinuities in the adjustment speed of the switching device and thus in the switching time of the valve drive and the adverse consequences mentioned. There is therefore a need to further develop switching devices supporting such switching systems.

Disclosure of Invention

Against this background, the object of the present invention is to provide a variable valve gear with a switchable pressure lever of a piston internal combustion engine of the initially mentioned type, in which the switching element extending lengthwise is supported and guided in a space-saving manner and with little frictional resistance and with little fluctuation of the frictional resistance which is influenced by operation, in which the switching time of the pressure lever is as little as possible dependent on the operating conditions, and in which the valve gear is furthermore inexpensive to produce.

The invention therefore relates to a variable valve gear of a piston internal combustion engine, which has at least one functionally identical gas exchange valve for each cylinder in a cylinder head of the piston internal combustion engine, the valve stroke of which is preset by at least one cam of a camshaft and can be selectively transmitted to at least one associated gas exchange valve by means of a switchable pressure rod, wherein a switching pin, which is guided in each case in an axially movable manner in a transverse bore, is connected to at least one longitudinally extending switching means via an elastically or rigidly designed connecting element, which is supported parallel to the camshaft in at least one guide in the cylinder head above the pressure rod and can be displaced longitudinally from a rest position to a switching position by means of a linear actuator in opposition to the restoring force of a spring element, wherein the connecting element is respectively abutted, embedded or fastened with its lower end to the end of the respective switching pin, and wherein at least one switching means is designed such that at least one of the switching means can be displaced only in a linear contact or at least one of the at least one guide is able to be displaced longitudinally or at least one of the at least one guide means.

In order to solve the above-mentioned object, the invention provides in the valve drive that at least one elongated switching element or at least one guide has a three-dimensionally structured surface region extending in the direction of movement at least over a section of the lower peripheral side of the base body of the switching element or of the upper peripheral side of the base body of the guide, or that at least one elongated switching element and at least one guide have two such surface regions that are complementary to one another.

According to the invention, provision is therefore made for the design measures to be taken which relate only to the surface of the switching element or the surface of the guide which extends lengthwise, but not to the actual shape of the base body of the component itself. The gauge dimensions of the switching means and the guide, in particular its thickness or radial diameter, are therefore unchanged or only slightly changed. The switching means can thus be supported in the guide with a structured surface in an exactly matched and stable manner.

According to an embodiment of the invention, it can be provided that at least one switching element extending in the longitudinal direction is supported in a sliding bearing of at least one guide, wherein an oil film is formed between the switching element and the guide.

The oil film between the elongated switching element and the guide of the switching element in the cylinder head causes an internal friction force F in the longitudinal movement of the switching element, which is determined by the adjusting speed v of the switching element, the effective contact surface a between the switching element and the guide, the temperature-dependent viscosity η of the oil and the thickness d of the oil film _R =η·a·v/d. As long as there is always a continuous oil film of sufficient fluid, the sliding friction and the sticking friction of the switching device will play a secondary role in this consideration, so that viscous friction basically results in frictional resistance when the switching device is moved.

Surprisingly, it has been found that, compared to a contact surface without structure, the three-dimensional surface structure on the switching element and/or the guide advantageously changes the contact surface between the switching element and the guide in such a way that the frictional resistance is reduced under all operating conditions and manufacturing tolerances and that, due to the lower frictional resistance, the fluctuations of the frictional resistance that are affected by the operation are also reduced. In particular, the invention reduces the effect of the strong temperature dependence of the viscosity of the lubricant on the frictional resistance. Thereby expanding the usable operating range of the switching system.

According to an embodiment of the invention, it can be provided that the three-dimensionally structured surface region is formed as an integral part of the at least one switching device or of the at least one guide. The switching device extending lengthwise can thus be produced, for example, as an inexpensive cast part, which has the desired surface structure. The guide thus constructed in the cylinder head can be provided with a suitable surface structure, for example by milling.

A further development of the valve drive provides that the three-dimensionally structured surface region is arranged as an additional component on and fixedly connected to the at least one switching device or the at least one guide. Thus, for example, a structured coating can be applied to the switching device or the guide. Housings with structured sleeves, bushings, etc. are also possible. In this case, the receptacle in the base body or guide of the switching device can be configured correspondingly smaller in diameter, so that no increase in installation space is required. The additional component or the coating arranged on the base body of the switching device or the guide can advantageously be made of other materials, in particular of a particularly slidable material.

According to an embodiment of the invention, it can be provided that the three-dimensionally structured first surface region is formed as a rib profile extending in the direction of movement of the switching means on at least one switching means and/or at least one guide extending in the longitudinal direction. The shifting device can therefore have a longitudinal rib, which is arranged, for example, on the underside of the shifting device configured as a push rail facing the bearing webs in the cylinder head, wherein an oil film is formed between the longitudinal rib profile and the surface of the bearing webs. A lubricant reserve can be accumulated between the longitudinal ribs, so that a continuous and safe supply of lubricant to the sliding bearing is ensured. Such a rib profile can be arranged or configured continuously over the entire length of the switching device or only in the region of the guide.

According to a further embodiment of the invention, it can be provided that the three-dimensionally structured second surface region is formed as a convex particle profile extending in the direction of movement of the switching means on at least one switching means extending in a longitudinal direction. Such a convex particle profile can be embossed inexpensively from the peripheral side of the switching element over the desired length with little effort.

Drawings

The invention is explained in detail below with the aid of an embodiment shown in the drawings. Wherein:

fig. 1 shows a simplified sectional illustration of a cylinder head and a variable valve gear of a piston internal combustion engine and a guide of a longitudinally extending switching device in the cylinder head, seen obliquely from above;

fig. 2 shows a schematic representation of a switchable lever of the variable valve gear according to fig. 1;

fig. 3 shows a longitudinal section through the switchable lever according to fig. 1 and 2, through the valve rod, through the hydraulic support element and through the cam acting on the lever;

fig. 4 shows a schematic view of a known switching element extending lengthwise and its guide in the cylinder head in a longitudinal section;

fig. 5a shows a schematic view of a switching device according to the invention and its guide in a cylinder head in a longitudinal section according to a first embodiment;

fig. 5b shows a top view of the switching device according to fig. 5a from below;

fig. 6a shows a schematic view of a switching device according to the invention and its guide in a cylinder head in a longitudinal section according to a second embodiment;

fig. 6b shows a top view of the switching device according to fig. 6a from below.

Some of the structural elements in the drawings are identical, and thus are labeled with the same reference numerals. In a six-cylinder piston internal combustion engine, structural elements which are identical in structure and repeated several times are in particular denoted by identical reference numerals.

Detailed Description

The cylinder head 1 of the exemplary assumed six-cylinder piston internal combustion engine shown in fig. 1, which has twelve inlet valves and twelve outlet valves each, therefore has a variable valve gear 2. The exhaust camshaft 3 is supported in the cylinder head 1 in a plurality of, for example seven, camshaft half bearing blocks 6. Furthermore, several, for example seven, associated upper camshaft half-bearing caps 5 are also fastened to the cylinder head 1 on the separating plane 4, which is also designed to receive a valve cap, not shown. Two camshaft half bearing blocks 6 and two camshaft half bearing caps 5, which are each assigned to a camshaft half bearing block 6, are shown in fig. 1 by way of example and in a schematic simplified manner.

The upper camshaft half bearing caps 5 each overlap the guide portions 8 arranged in the partition plane 4 in the form of recesses in the camshaft half bearing blocks 6, wherein the guide portions 8 in the form of recesses are arranged flush with one another. The guide 8 serves to accommodate a switching element 9 which is embodied as a longitudinal extension of the pusher strip. The switching means 9 are thereby guided in a sliding bearing formed between the camshaft half bearing housing 6 and the camshaft half bearing cap 5.

The switching means 9 shown, which is embodied as a push strip, is in switching connection with the linear actuator 10 at one end and extends up to the last axially opposite end of the exhaust camshaft 3. The switching means 9 extending in length are used for actuating six switchable struts 14 of six exhaust valves 15 of the last three cylinders of a piston internal combustion engine having six cylinders.

As is shown in particular in fig. 2, six connecting elements 16, which are embodied as leaf springs, are fastened to the switching means 9 in a force-locking manner for each of the last three cylinders. The connecting element 16 embodied as a leaf spring serves to switch the switchable pressure lever 14 of the valve actuating device 4 by acting on one of the six switching pins 17.

The exhaust valve 15 of each cylinder can be cut off by means of the associated switchable lever 14 with respect to the course of the stroke that it can transmit. The construction of this switchable lever 14 is shown in detail in fig. 2 and 3. The pressure lever 14 thus has an inner lever 18 (so-called primary lever) and an outer lever 19 (so-called secondary lever), respectively. The pressure lever 14 has a hemispherical profiling 12 on its lower side at one end for a ball head of a housing-side support element 20 with an integrated hydraulic valve play compensation element. At the other end of the pressure lever 14, an abutment 7 is formed, on which the valve rod 13 of the associated outlet valve 15 is supported.

The inner lever 18 is in operative contact on its upper side via an actuating element 21, which is currently configured as a cam roller rotatably mounted by means of a rolling bearing 11, with an associated exhaust cam 22, the so-called primary cam, of the camshaft 3. The outer lever 19 has a frame shape surrounding the inner lever 18, and is pivotably supported on the inner lever 18 via a hinge pin 23 arranged on the valve side.

Coaxially with respect to the longitudinal axis of the switching pin 17, a pair of torsion springs 24a, 24b, so-called no-load springs, are arranged on the outer lever 19, which serve to hold the inner lever 18 in the pivoted-in rest position against the outer lever 19 and to guide the inner lever 18 back against the outer lever 19 by means of the spring force after the inner lever 18 has been deflected out. As already mentioned, the switchable lever 14 is in this example configured for the shut-off valve stroke. Alternatively to this, the pressure lever 14 can be configured for switching between a large stroke and a small stroke. For this purpose, the outer lever 19 can have, as a further active element, on both sides in the longitudinal direction thereof, respectively widened web sections each having an outer sliding surface, which, on the basis of the spring force of the torsion springs 24a, 24b, are each in active contact with an associated secondary cam of the exhaust camshaft 3.

For the form-locking connection of the outer rod 19 and the inner rod 18, a locking device 25 shown in fig. 3 is provided, which can be actuated against the force of a restoring spring, not shown, via a switching pin 17 which is mounted in an axially movable manner in a transverse bore of the outer rod 19. The type of construction and the embodiment of the locking device 25 are not important here and are not the subject of the invention. It is important only that by means of the axial movement of the switching pin 17, the guide pin 25a is moved in the longitudinal direction of the pressure lever 14 by the locking pin 25b, which can be moved in a guide groove extending obliquely to the axis of rotation of the pressure lever 14 and is positively guided, whereby the locking pin 25b engages with the coupling element 25c on the inner lever 18 and whereby the inner lever 18 is locked with the outer lever 19.

The switching means 9, which are embodied as elongated push strips, can be moved longitudinally from the rest position into the switching position by means of a linear actuator 10, which is embodied, for example, as an electromagnetic actuating drive. In the rest position, the switching means 9 is moved in, so that the connecting element 16 embodied as a leaf spring releases the respectively associated switching pin 17 of the pressure lever 14. Thereby, the lock pin 25b is moved back, and thereby the coupling between the inner rod 18 and the outer rod 19 is eliminated. Thus, when the exhaust cam 22 acts on the inner lever 18 via the acting element 21 of the pressure lever 14, which is configured as a cam roller, the inner lever 18 of the outer lever 19, which is pivotally mounted on one side, can be pivoted away freely downward. The associated exhaust valve 15 is thus not opened by the outer lever 19 of the pressure lever 14.

In order to take up the switching position, the switching means 9 embodied as a push bar can be moved laterally by means of the linear actuator 10, as mentioned, so that the respective connecting element 16 embodied as a leaf spring presses the associated switching pin 17 inwardly into the switchable lever 14, thereby causing a coupling between the outer lever 19 and the inner lever 18. The inner lever 18 can thus transmit the actuating force from the exhaust cam 22 to the outer lever 19, so that the two levers 18, 19 are pivoted jointly away and the associated exhaust valve is opened.

As already mentioned, the switching means 9, which are embodied as longitudinally extending push strips, are mounted in the guide 8 between the camshaft half bearing housing 6 and the camshaft half bearing cap 5 and are guided in a sliding manner therein. The guiding of the switching device 9 according to the invention is schematically shown in two examples in fig. 5a, 5b and 6, 6 b. A conventional guide of the switching device 9 according to the prior art, which is also shown schematically in fig. 4, is explained first.

The switching element 9, which is shown in fig. 4 and is configured as a longitudinal extension of the push rail according to the prior art, is thus placed over the guide 8, which is now configured as a groove, in the cam half bearing block 6, which is configured as a lug in the cylinder head 1, wherein an oil film 26 for lubricating the guide 8 is formed between the unstructured flat lower peripheral side 27 of the switching element 9 and the likewise unstructured flat upper peripheral side 28 of the guide 8. For clarity of illustration, the thickness d of the oil film 26 is shown too high in fig. 4 to 6 b. Upon a longitudinal displacement of the switching means 9 in the direction of movement 29, viscous friction occurs with shear forces, which lead to a reduction in the speed of the oil film between the azimuthally fixed upper peripheral side 28 of the guide 8 and the lower peripheral side 27 of the switching means 9 relative to this. The frictional resistance thus produced is largely dependent on the thickness d of the oil film 26 and on its viscosity on temperature. The switching time during the switching of the pressure lever 14 is accordingly largely dependent on the frictional resistance acting during the displacement of the switching device 9.

Fig. 5a and 5b show a switching device 30 according to a first embodiment of the invention, which is embodied as a push strip and extends lengthwise, the peripheral side 31 of which has a three-dimensionally structured surface area 32. As is shown in particular in fig. 5b, the surface region 32 is formed as a rib profile consisting of a plurality of, in this case five longitudinal ribs 32a arranged parallel to one another and extending in the direction of movement 29 of the switching device 30. The rib profile is embossed from the lower circumferential side 31 of the switching device 30. Alternatively, the rib profile can be fastened as an additional component to the switching device 30, and the base body of the switching device 30 is correspondingly thinner. In any case, the dimensions of the switching device 30 are not or only slightly different from those of the conventional switching device 9 of the plain bearing type.

As shown in fig. 5a, the individual longitudinal ribs 32a are configured in a semicircular manner in cross section, so that the switching means 30 are placed in a linear manner on the guide 8 in the form of a groove in the cam half bearing block 6. The oil film 26 formed between the surface region 32 of the switching device 30 and the upper circumferential side 28 of the guide 8 is distributed in the recesses of the rib profile. The viscous friction upon longitudinal movement of the switching device 30 is significantly reduced based on the surface structure. Thus, neither the stick-slip effect at low oil temperatures nor the strong change in the viscous friction at the longitudinal movement of the switching device 30 occurs. The switching time when switching the pressure lever 14 changes correspondingly little.

Fig. 6a and 6b show a longitudinally extending switching element 33 according to a second embodiment of the invention, which is configured as a push bar, the lower circumferential surface 34 of which has a three-dimensionally structured surface area 35. As is shown in particular in fig. 6b, the surface region 35 is configured as a convex particle profile made up of a plurality of convex particles 35 a. The convex particle profile is embossed from the lower peripheral side 34 of the switching device 33. The convex particle 35a has the shape of a cylindrical section, the cross section of which can be regarded as a dot shape, so that the switching means 33 are placed in a dot shape on the guide 8 in the cam half bearing seat 6, which is configured as a groove. Alternatively, particularly advantageous embodiments with convex particles in the form of spherical segments are possible for this purpose. As in the rib profile according to fig. 5a and 5b, the adhesive friction is significantly reduced by the convex particle profile according to fig. 6a and 6b compared to a full-face abutment.

List of reference numerals

1. Cylinder cover

2. Valve drive

3 camshaft, exhaust camshaft

4. Separation plane

5. Half bearing cover of camshaft

6. Cam half bearing seat

Contact surface for air exchange valve on 7 pressure lever

Guide for a switching device in an 8-cylinder head

9 switching means extending lengthwise, pusher shoes (prior art)

10 linear actuator

11 Rolling bearing for supporting an active element

Hemispherical molding for a support element on a 12-bar

13. Valve rod

14. Switchable pressure lever

15. Scavenging valve

16 connecting element, leaf spring

Switching bolt on 17 pressure lever

18 inner rod, primary rod

19 outer rod, secondary rod

20 support element

Action element on 21 compression bar, cam roller

22 cam, exhaust cam

Hinge bolt on 23 compression bar

24a first torsion spring, no-load spring

24b second torsion spring, no-load spring

25. Locking device on a compression bar

Guide needle on 25a locking device

25b locking pin on locking device

Coupling element on 25c locking device

26. Oil film

27 lengthwise-extending lower peripheral side surfaces of the switching device (Prior Art)

Upper peripheral side surface on 28 guide portion

29 direction of movement of switching device

30 elongated switching device, pusher slat (first embodiment)

31 lower peripheral side face of the vertically elongated switching device (first embodiment)

32 three-dimensionally structured surface region (first embodiment)

32a longitudinal ribs of structured surface region (first embodiment)

33, a push-on slat (second embodiment)

34 lower peripheral side face of the vertically elongated switching device (second embodiment)

35 three-dimensionally structured surface region (second embodiment)

35a structured surface region (second embodiment)

d thickness of oil film

Claims

1. A variable valve gear (2) of a piston internal combustion engine, which has at least one functionally identical gas exchange valve (15) per cylinder in a cylinder head (1) of the piston internal combustion engine, the valve stroke of which is preset in each case by at least one cam (22) of a camshaft (3) and can be selectively transferred by means of a switchable pressure lever (14) to at least one associated gas exchange valve (15), wherein a switching pin (17) of the pressure lever (14), which is guided in each case axially in a transverse bore, is connected via a connecting element (16) of elastic or rigid design to at least one switching means (30, 33) extending longitudinally above the pressure lever (14) and supported parallel to the camshaft (3) in at least one guide (8) in the cylinder head (1), and can be moved longitudinally from a rest position to a switching position by means of a linear actuator (10) counter to the restoring force of a spring element, wherein the connecting element (16) engages at least one of its ends (30, 33) on the respective ends, which ends (16) are fastened and at least one of the switching pins (30, 33) is fastened against the respective ends (16, respectively 33 And/or at least one guide (8) is designed in such a way that only linear or point contact is possible between the at least one guide (8) and the at least one longitudinally extending switching means (30, 33), so that a longitudinal movement of the at least one longitudinally extending switching means (30, 33) in the at least one guide (8) takes place with little friction, characterized in that the at least one longitudinally extending switching means (30, 33) has a three-dimensionally structured surface region (32, 35) extending in the direction of movement (29) at least over a section of the peripheral side (31, 34) of the base body of the switching means (30, 33), or the at least one guide (8) has a three-dimensionally structured surface region (32, 35) extending in the direction of movement (29) at least over a section of the peripheral side (28) of the base body of the guide (8), or the at least one switching means (30, 33) and the at least one guide (8) have two such longitudinal surface regions (32, 35).

2. Variable valve gear according to claim 1, characterized in that the at least one switching means (30, 33) extending lengthwise is supported in a sliding support of at least one guide (8), wherein an oil film is constructed between the switching means (30, 33) and the guide (8).

3. Variable valve gear according to claim 1 or 2, characterized in that the three-dimensionally structured surface area (32, 35) is configured as an integral component of the at least one switching means (30, 33) or of the at least one guide (8).

4. Variable valve gear according to claim 1 or 2, characterized in that a three-dimensionally structured surface region (32, 35) is arranged as an additional component on the at least one switching means (30, 33) or the at least one guide (8) and is fixedly connected thereto.

5. Variable valve gear according to claim 1 or 2, characterized in that the three-dimensionally structured first surface area is configured as a rib profile extending in the direction of movement (29) of the switching means (30) on the at least one lengthwise-extending switching means (30) and/or the at least one guide (8).

6. Variable valve gear according to claim 1 or 2, characterized in that the three-dimensionally structured second surface area is configured as a convex particle profile extending in the direction of movement (29) of the switching means (33) on the at least one lengthwise extending switching means (33) and/or the at least one guide (8).