CN111075530A

CN111075530A - Variable valve gear of piston internal combustion engine

Info

Publication number: CN111075530A
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: 2020-04-28
Anticipated expiration: 2039-10-10
Also published as: DE102018125978A1; CN111075530B

Abstract

The invention relates to a variable valve gear of a piston internal combustion engine, comprising functionally identical gas exchange valves for each cylinder, the valve strokes being preset in each case by a cam of a camshaft and being able to be transmitted to the gas exchange valves by means of a switchable pressure rod, the switching of which is guided axially movably in a transverse bore in each case being connected via a connecting element to a longitudinally extending switching means, which is mounted above the pressure rod in a guide in a cylinder head and is able to be displaced longitudinally counter to the restoring force of a spring element by means of a linear actuator, the connecting element resting, engaging or being fastened above the switching means and resting, engaging or being fastened below on the end face end of the respective switching bolt. The switching means or the guide have a three-dimensionally structured surface region extending in the direction of movement at least in the lower peripheral side of the switching means or in the upper peripheral side of the guide, or the switching means and the guide have such surface regions which are complementary to one another.

Description

Variable valve gear of piston internal combustion engine

Technical Field

The invention 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 strokes of which are preset by at least one cam of a camshaft and which can be selectively transmitted to at least one associated gas exchange valve by means of a switchable pressure lever, wherein a switching bolt of the pressure lever, which is guided axially movably in a transverse bore, is connected by means of a resiliently or rigidly designed connecting element to at least one longitudinally extending switching means, which is mounted parallel to the cam axis above the pressure lever in at least one guide in the cylinder head and can be moved longitudinally by means of a linear actuator counter to a restoring force of a spring element from a rest position into a switching position, wherein the connecting element bears with its upper end against the upper end of the spring element, The at least one longitudinally extending switching means and/or the at least one guide are designed in such a way that only a linear or point contact is possible between the at least one guide and the at least one longitudinally extending switching means, as a result of which the longitudinal movement of the at least one longitudinally extending switching means in the at least one guide takes place with little friction.

Background

Variable valve transmissions 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 longitudinally extending switching means have already been proposed in the non-previously published patent applications DE 102017101792 a1, DE 102017129422 a1 and DE 102018117335.0.

The variable valve gear of a piston internal combustion engine is able to deactivate individual cylinders or groups of cylinders of the piston internal combustion engine by switching off the transferable valve strokes, and thus, in combination with switching off fuel injection to the relevant cylinder, reduce the fuel consumption and harmful substance emission of the piston internal combustion engine in partial load operation. On the other hand, the transferable stroke course of the inlet valve and/or the exhaust valve of the piston type internal combustion engine can be changed through stroke conversion, and therefore the transferable stroke course is matched with the current operation state of the piston type internal combustion engine depending on operation parameters such as engine speed and engine load. This increases the engine power and torque and reduces the specific fuel consumption of the piston internal combustion engine.

In variable valve transmissions, two components of a switchable stroke transmission element, which are movable or rotatable relative to one another, are usually provided in each case. The switchable stroke transmission element is in most cases a switchable cup tappet, roller tappet, rocker or plunger.

In a switchable valve gear, the respective stroke transmission element is connected via one component to the associated cam adjustment of the camshaft and via the other component to the valve rod of the associated gas exchange valve. The two components can be coupled to and decoupled from one another by means of a coupling device. In the coupled state, the valve strokes of the associated cam are transmitted to the respective gas exchange valve, but not in the decoupled state, so that the respective valve inlet or valve outlet of the respective cylinder remains closed. In general, the coupling element of the coupling device is held in the rest position by means of a spring element and is moved into the operating position and held there by a force that is applied to adjust the force in opposition to the restoring force of the spring element. In the case of a switchable valve gear, the rest position of the coupling element generally corresponds to the coupled state of the components of the stroke transmission element, while the operating position corresponds to the decoupled state of the components.

In the case of switchable valve drives, one component is connected to an associated primary cam adjustment of the camshaft with a specific valve stroke and to the valve rod adjustment of the associated gas exchange valve, while the other component is connected to an associated secondary cam adjustment of the camshaft with a larger valve stroke or with an additional stroke. In the decoupled or coupled state, the valve stroke of the primary cam is transmitted to the relevant gas exchange valve, while in the coupled or decoupled state the respective greater valve stroke of the primary or secondary cam is transmitted to the gas exchange valve. In the case of switchable valve gear mechanisms, the rest position of the coupling element generally corresponds to the decoupled state of the components of the stroke transmission element, while the operating position corresponds to the coupled state of the components.

Different designs are known for adjusting the coupling element of the switchable stroke transmission element. The hydraulic control is usually effected via a solenoid-operated switching pressure line, as described, for example, in DE 102006057894 a1 for stroke blocking and in DE 102006023772 a1 for stroke switching of the switching valve. For selective stroke switching or stroke switching in groups, separate switching pressure lines each with an associated switching valve are required, as described, for example, in DE 10212327 a 1. The supply of switching pressure oil from the respective switching pressure line to the switchable stroke transmission element is usually effected via a multi-flow hydraulic support element, as is also known, for example, from DE 10330510 a 1. The electromagnetic adjustment of the coupling element of the switchable stroke transmission element is usually carried out by means of an electromagnet, which is indirectly or directly operatively connected to the coupling element, as described, for example, in US 5544626 a or in DE 102016220859 a 1.

The arrangement of the individual hydraulic switching pressure lines and the associated valves or the individual electric switching lines and the associated electromagnets for each coupling element in or on the cylinder head of the piston internal combustion engine is often based on narrow space conditions and is relatively difficult and costly.

This disadvantage in valve transmissions of the type mentioned at the outset is eliminated by the use of an elongated switching means which can switch off or switch over a plurality of functionally identical gas exchange valves.

In such a valve gear, the coupling element of the switchable pressure lever can be moved into the coupling or decoupling position of the primary and secondary levers in each case by means of a switching bolt, which is mounted so as to be axially movable in a transverse bore of the secondary lever, counter to the restoring force of the spring element. Each shift pin projects with its outer end from the secondary lever and is connected at this end via an upwardly directed, elastic connecting element, for example in the form of a leaf spring or a rigidly designed connecting element, for example in the form of a cross bar, to an elongated shifting means, for example in the form of a shift lever, a push bar, a flat bar or a rail. The longitudinally extending shift element is arranged above the pressure rod parallel to the associated camshaft and is mounted in at least one guide in the cylinder head and can be moved by means of an actuator linearly in opposition to the restoring force of the spring element in the axial direction of the shift element from a rest position into a shift position.

During the longitudinal displacement of such a switching means in an associated guide in the cylinder head of a piston internal combustion engine, frictional resistance is formed on the basis of sliding, sticking and/or viscous friction, which may lead to a change in the switching times of an electromechanical switching system consisting of a linear actuator, a longitudinally extending switching means and a switchable pressure rod. The usable operating range of the system, in which the valve stroke can be switched or shut off when the piston internal combustion engine is running, can thus be significantly limited.

In order to avoid the friction-related stick-slip effect, i.e., chattering slip, of such a valve gear mechanism in the guide of the cylinder head, it is proposed in DE 102018117335.0 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 design change of the switching means, for example by deformation of the basic body of the switching means with radially extending beads, ridges, circumferential ribs or by such measures at the guides, for example radial projections.

Disadvantageously, all these measures lead to a significant increase in the radial diameter of the switching system or to an increase in the dimension in the direction perpendicular to the direction of movement of the switching means and thus to a higher demand for construction space. This is not necessarily allowed in the cylinder heads provided. In addition, stable and precisely adapted guidance in the cylinder head groove over the entire length of the switching means is thereby made difficult. The linear guidance of the switching means by means of the rolling bearing, which is alternatively proposed for this purpose, likewise increases the required installation space (significantly increases the production costs) and, in addition, disadvantageously limits the actuating travel of the switching means.

In the case of an elongated switching means designed as a sliding bar, which is advantageously guided in a groove in the cylinder head and is mounted in a sliding manner therein by means of oil lubrication, the viscous friction effect has proven to be particularly problematic. The lubrication of the contact area between the sliding strip and the cylinder head channel is achieved by means of oil mist or splashes of oil from the surroundings of the cylinder head. The resulting oil film between the sliding strip and the surface of the cylinder head groove leads to internal friction forces, the so-called viscous friction, in the longitudinal movement of the sliding strip. 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 large correlation with temperature. Lubricating oils have a high viscosity, in particular at low ambient temperatures, for example during 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. Furthermore, 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 means cannot be precisely determined and the viscosity is likewise subject to fluctuations influenced by operation and tolerances, the degree and in particular the non-continuity of the viscous friction leads to a corresponding discontinuity in the regulating speed of the switching means and thus in the switching time of the valve gear and the mentioned disadvantageous consequences. There is therefore a need to further develop switching devices that support such switching systems.

Disclosure of Invention

Against this background, the object of the present invention is to provide a variable valve gear mechanism of a piston internal combustion engine of the type mentioned at the outset with switchable pressure struts, in which the longitudinally extending switching means are mounted and guided in a space-saving manner and with little frictional resistance influenced by operation, in which, in particular, the switching times of the pressure struts are as little as possible dependent on the operating conditions, and in which the valve gear mechanism is furthermore inexpensive to produce.

The solution of this object is achieved with a valve gear having the features of independent claim 1, while advantageous embodiments and refinements of the invention are defined in the appended dependent claims.

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 strokes of which are each preset by at least one cam of a camshaft and which can be selectively transmitted to at least one associated gas exchange valve by means of a switchable pressure lever, wherein a switching bolt of the pressure lever, which is guided axially movably in a transverse bore, is connected by means of an elastically or rigidly configured connecting element to at least one longitudinally extending switching means, which is mounted parallel to the cam axis above the pressure lever in at least one guide in the cylinder head and can be moved longitudinally by means of a linear actuator against a restoring force of a spring element from a rest position into a switching position, the connecting element is in each case in contact with, embedded in or fastened with its upper end on the longitudinally extending switching means and in contact with, embedded in or fastened with its lower end on the end side of the switching bolt of the respective plunger, and the at least one longitudinally extending switching means and/or the at least one guide are designed in such a way that only a linear or point contact can be obtained between the at least one guide and the at least one longitudinally extending switching means, so that a longitudinal movement of the at least one longitudinally extending switching means in the at least one guide takes place with little friction.

In order to solve the stated problem, it is provided according to the invention in the valve drive that the at least one longitudinally extending switching means or the at least one guide has a three-dimensionally structured surface region extending in the direction of movement at least in a section of the lower peripheral side of the base body of the switching means or the upper peripheral side of the base body of the guide, or that the at least one longitudinally extending switching means and the at least one guide have two such surface regions which are complementary to one another.

Thus, according to the invention, provision is made for the design to be made only with regard to the surface of the switching means or the surface of the guide which runs lengthwise, but not with regard to the actual shape of the base body of the component itself. The dimensions of the switching means and the guide, in particular their thickness or radial diameter, are therefore not changed, or only slightly changed. The switching means can thus be supported in the guide with a precisely matched and stable surface.

According to an embodiment of the invention, it can be provided that at least one longitudinally extending switching means is mounted in a plain bearing of at least one guide, wherein an oil film is formed between the switching means and the guide.

The oil film between the switching means running lengthwise and the guide of the switching means in the cylinder head leads, during the longitudinal movement of the switching means, to an internal friction force F determined by the actuating speed v of the switching means, the effective contact surface a between the switching means and the guide, the temperature-dependent viscosity η of the oil and the thickness d of the oil film_RAs long as there is always a continuous oil film of sufficient fluid, the sliding and sticking friction of the switching device will play a secondary role in this thinking, so that the viscous friction essentially causes frictional resistance when the switching device is moved.

It has surprisingly been found that, in comparison with a non-structured contact surface, the three-dimensional surface structure on the switching means and/or the guide advantageously modifies the contact surface between the switching means and the guide in such a way that the frictional resistance is reduced under all operating conditions and manufacturing tolerances and the operationally influenced fluctuations of the frictional resistance are also reduced due to the lower frictional resistance. In particular, the effect of the strong temperature dependence of the viscosity of the lubricant on the frictional resistance is reduced. Thereby extending 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 component of the at least one switching element or of the at least one guide. The switching device extending lengthwise can thus be manufactured, for example, as an inexpensive casting, which has the desired surface structure. The guide in the cylinder head, which is thus formed, can be provided with a suitable surface structure, for example, by milling.

In a further development of the valve gear, it is provided that the three-dimensionally structured surface region is arranged as an additional component on the at least one switching means or the at least one guide and is fixedly connected thereto. Thus, for example, a structured coating can be applied to the switching means or the guide. Also possible are housings with structured sleeves, bushings, etc. In this case, the receptacle in the base body or guide of the switching means can be configured to be 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 means or the guide can advantageously consist of other materials, in particular of particularly slidable materials.

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 the at least one lengthways extending switching means and/or the at least one guide. The switching means can therefore have a longitudinal rib, which is arranged, for example, on the underside of the switching means, which is designed as a push bar, facing the bearing web in the cylinder head, wherein an oil film is formed between the profile of the longitudinal rib and the surface of the bearing web. A lubricant reserve can accumulate 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 formed continuously over the entire length of the switching means 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 grain profile extending in the direction of movement of the switching means on at least one longitudinally extending switching means. Such a convex grain profile can be inexpensively impressed over a desired length from the peripheral side of the switching element with little effort.

Drawings

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

fig. 1 shows a simplified, sectioned illustration of a cylinder head of a piston internal combustion engine and a variable valve gear and a guide of an elongated switching means in the cylinder head, seen from obliquely above;

FIG. 2 shows a diagrammatic representation of a switchable pressure lever of the variable valve gear according to FIG. 1;

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

fig. 4 shows a schematic illustration of a known longitudinally extending switching device and its guide in a cylinder head in longitudinal section;

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

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

Some structural elements in the drawings are identical, and therefore they are labeled with the same reference numerals. Structural elements which are structurally identical in a multiple repetition in a six-cylinder piston internal combustion engine are labeled with the same reference numerals.

Detailed Description

The cylinder head 1 of an exemplary assumed six-cylinder piston internal combustion engine shown in fig. 1, which has twelve inlet valves and twelve exhaust valves, respectively, therefore has a variable valve gear 2. The exhaust camshaft 3 is mounted in the cylinder head 1 in a plurality of, for example, seven camshaft half-bearing blocks 6. Furthermore, a plurality of, for example seven, associated upper camshaft half bearing caps 5 are also screwed onto the separating plane 4, which is also designed on the cylinder head 1 for receiving the valve covers, not shown. Fig. 1 shows two camshaft half-bearing blocks 6 and two camshaft half-bearing covers 5, which are each associated with a camshaft half-bearing block 6, by way of example and in a simplified schematic manner.

The upper camshaft half-bearing caps 5 each overlap a guide 8, which is arranged in the partition plane 4 and is designed as a recess in the camshaft half-bearing block 6, wherein the guides 8, which are designed as recesses, are arranged flush with one another. The guide 8 serves to accommodate a switching means 9 which is configured as an elongate extension of the push bar. The switching means 9 is thereby guided in a sliding bearing formed between the camshaft half bearing block 6 and the camshaft half bearing cover 5.

The illustrated switching means 9, which is embodied as a sliding bar, is in switching connection at one end with the linear actuator 10 and extends as far as the last axially opposite end of the exhaust camshaft 3. The longitudinally extending switching means 9 serves for actuating six switchable pressure levers 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 designed as leaf springs, for each of the last three cylinders are fastened to the shifting device 9 in a force-fitting manner. The connecting element 16, which is designed as a leaf spring, serves to switch the switchable pressure lever 14 of the valve gear 4 by acting on one of the six switching pins 17.

The exhaust valves 15 of each cylinder can be shut off via the associated switchable pressure lever 14 with regard to the stroke processes that can be transmitted. The structure of this switchable plunger 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 plunger 14 has on its underside at one end a hemispherical profile 12 for a ball head of a support element 20 mounted on the housing side, which has an integrated hydraulic valve play compensation element. At the other end of the pressure rod 14, an abutment surface 7 is formed, on which the valve rod 13 of the associated exhaust valve 15 is supported.

The inner rod 18 is in operative contact on its upper side with an associated exhaust cam 22, the so-called primary cam, of the camshaft 3 via an active element 21, which is in the present case designed as a cam roller rotatably mounted by the rolling bearing 11. The outer rod 19 has a frame shape that fits around the inner rod 18, and it is pivotably supported on the inner rod 18 via a hinge pin 23 arranged on the valve side.

Coaxially with respect to the longitudinal axis of the shift bolt 17, a pair of

torsion springs

24a, 24b, so-called Lost Motion springs, are arranged on the outer lever 19, which serve to hold the inner lever 18 in the inwardly pivoted rest position against the outer lever 19 and to guide the inner lever 18 back by means of the spring force after it has been deflected out, in order to abut against the outer lever 19. As already mentioned, the switchable pressure lever 14 is in this example configured for closing the valve stroke. Alternatively to this, the plunger 14 can be configured for switching between a large stroke and a small stroke. For this purpose, the outer lever 19 can have, as further active elements, widened web sections on both sides in its longitudinal direction, each with an outer sliding surface, which, due to the spring force of the torsion springs 24a, 24b, are in active contact with the 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 via a switching bolt 17, which is mounted so as to be axially movable in a transverse bore of the outer rod 19, against the force of a return spring, not shown. The type of construction and the embodiment of the locking device 25 are not important here and are not subject of the invention. It is only important that the guide pin 25a is displaced in the longitudinal direction of the pressure rod 14 by the axial movement of the switch bolt 17 by the locking pin 25b, which can be moved in a guide groove extending obliquely to the axis of rotation of the pressure rod 14 and is guided by force, whereby the locking pin 25b engages with the coupling element 25c on the inner rod 18 and thereby locks the inner rod 18 with the outer rod 19.

The switching means 9, which is designed to displace the longitudinal extension of the slats, can be moved longitudinally from the rest position into the switching position by means of a linear actuator 10, which is designed, for example, as an electromagnetic actuating drive. In the rest position, the switching means 9 is moved in, so that the connecting element 16, which is designed as a leaf spring, releases the respectively associated switching pin 17 of the pressure lever 14. Thereby, the lock pin 25b is moved back, whereby the coupling between the inner lever 18 and the outer lever 19 is eliminated. As a result, when the exhaust cam 22 acts on the inner lever 18 via the actuating element 21 of the pressure lever 14, which is designed as a cam roller, the inner lever 18, which is pivotably supported on one side, of the outer levers 19 can be freely pivoted away downward. The associated exhaust valve 15 is therefore not opened by the outer lever 19 of the pressure lever 14.

In order to assume the switching position, the switching means 9, which is designed as a push bar, can be moved laterally by means of the linear actuator 10, as mentioned, so that the respective connecting element 16, which is designed as a leaf spring, presses the associated switching pin 17 inward into the switchable pressure lever 14, as a result of which the coupling between the outer lever 19 and the inner lever 18 is brought about. 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 pivot away from each other and open the associated exhaust valve.

As already mentioned, an elongated switching means 9, which is designed as a sliding bar, is mounted in the guide 8 between the camshaft half bearing block 6 and the camshaft half bearing cover 5 and is guided in a sliding manner therein. The guides of the switching device 9 according to the invention are schematically shown in two examples in fig. 5a, 5b and 6, 6 b. A conventional guide of a switching device 9 according to the prior art, which is likewise schematically illustrated in fig. 4, is first explained.

The switching means 9 shown in fig. 4, which is designed as a longitudinal extension of a sliding bar according to the prior art, is therefore placed over the entire surface on the guide 8, which is here in the present case designed as a groove, in the cam half bearing seat 6 designed as a web in the cylinder head 1, wherein an oil film 26 for lubricating the guide 8 is formed between the unstructured flat lower circumferential side 27 of the switching means 9 and the likewise unstructured flat upper circumferential side 28 of the guide 8. For the sake of clarity, the thickness d of the oil film 26 is shown too high in fig. 4 to 6 b. During the longitudinal movement 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 upper circumferential side 28, in which the orientation of the guide 8 is fixed, and the lower circumferential side 27 of the switching means 9, which moves relative thereto. The frictional resistance that results therefrom is largely dependent on the thickness d of the oil film 26 and, with regard to its viscosity, on the temperature. The switching time at the switching of the pressure lever 14 accordingly changes to a large extent depending on the frictional resistance acting when the switching means 9 is moved.

Fig. 5a and 5b show a longitudinally extending switching means 30, which is configured as a push bar, according to a first embodiment of the invention, the circumferential 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 designed as a rib profile made up of a plurality of, in this case, five longitudinal ribs 32a which are arranged parallel to one another and extend in the direction of movement 29 of the switching means 30. The rib profile is embossed from the lower peripheral side 31 of the switching device 30. Alternatively, the rib profile can be fastened as an additional component to the switching means 30, and the base body of the switching means 30 is correspondingly thinner. In any case, the dimensions of the switching means 30 differ from conventional generic switching means 9 of the plain bearing type only slightly or not.

As fig. 5a shows, the individual longitudinal ribs 32a are semicircular in cross section, so that the switching means 30 are placed in a linear manner on the guide 8, which is configured as a groove, in the cam bearing half 6. The oil film 26 formed between the surface region 32 of the switching means 30 and the circumferential side 28 above the guide 8 is distributed in the recesses of the rib profile. The viscous friction during the longitudinal movement of the switching means 30 is significantly reduced due to the surface structure. Neither a stick-slip effect at low oil temperatures nor a strong change in the viscous friction at the longitudinal movement of the switching means 30 will occur thereby. The switching time at which the plunger 14 is switched changes correspondingly little.

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

List of reference numerals

1 Cylinder cover

2-valve transmission device

3 camshaft, exhaust camshaft

4 planes of separation

5 camshaft half bearing cover

6 cam half bearing seat

7 contact surface on pressure lever for gas exchange valve

8 guide of switching device in cylinder head

9 elongated switching device, pusher bar (prior art)

10 linear actuator

11 rolling bearing for supporting a reaction element

12 hemispherical profile on a plunger for supporting an element

13 valve rod

14 switchable pressure lever

15 scavenging air valve

16 connecting element, leaf spring

17 switching bolt on pressure lever

18 inner rod and primary rod

19 outer pole, secondary pole

20 support element

21 acting element on a pressure lever, cam roller

22 cam and exhaust cam

23 hinge bolt on pressure lever

24a first torsion spring, no-load spring

24b second torsion spring, no-load spring

25 locking device on a press rod

25a guide pin on a locking device

25b locking pin on locking device

25c coupling element on locking device

26 oil film

27 lower peripheral side on the elongated switching device (prior art)

28 upper peripheral side surface on the guide portion

29 switching the direction of motion of the device

30 longitudinally extending switching device, pusher bar (first embodiment)

31 lower peripheral side surface on the longitudinally extending switching device (first embodiment)

32 three-dimensionally structured surface region (first embodiment)

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

33 longitudinally extending switching device, pusher bar (second embodiment)

34 lower peripheral side of the longitudinally extending switching device (second embodiment)

35 three-dimensionally structured surface region (second embodiment)

35a convex particles of a 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) for each cylinder in a cylinder head (1) of the piston internal combustion engine, the valve strokes of which are each preset by at least one cam (22) of a camshaft (3) and which can be selectively transmitted to at least one associated gas exchange valve (15) by means of a switchable pressure rod (14), wherein a switching bolt (17) of the pressure rod (14), which is each axially movably guided in a transverse bore, is connected via a resiliently or rigidly designed connecting element (16) to at least one longitudinally extending switching means (30, 33), which is mounted parallel to the camshaft (3) above the pressure rod (14) in at least one guide (8) in the cylinder head (1), and can be moved longitudinally by means of a linear actuator (10) against the restoring force of a spring element from a rest position into a switching position, wherein the connecting element (16) is in each case placed, fitted or fastened with its upper end against a longitudinally extending switching means (30, 33) and with its lower end against an end face of a switching bolt (17) of the respective pressure lever (14), and wherein the at least one longitudinally extending switching means (30, 33) and/or the at least one guide (8) are designed in such a way that only a linear or point contact can be obtained 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) or the at least one guide (8) has a three-dimensionally structured surface area (32, 35) extending in the direction of movement (29) at least on a peripheral side (31, 34) below the base body of the switching means (30, 33) or on a section of the peripheral side (28) above the base body of the guide (8), or the at least one longitudinally extending switching means (30, 33) and the at least one guide (8) have two such surface areas (32, 35) which are complementary.

2. Variable valve gear according to claim 1, characterized in that the at least one lengthways extending switching means (30, 33) is supported in a sliding bearing of at least one guide (8), wherein an oil film is configured 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 region (32, 35) is designed as an integral component of the at least one switching means (30, 33) or of the at least one guide (8).

4. The variable valve gear according to one of claims 1 to 3, 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 on the at least one guide (8) and is fixedly connected thereto.

5. The variable valve gear according to one of claims 1 to 4, characterized in that the three-dimensionally structured first surface region (32) is formed as a rib profile extending in the direction of movement (29) of the switching means (30) on the at least one longitudinally extending switching means (30) and/or on the at least one guide (8).

6. The variable valve gear according to one of claims 1 to 4, characterized in that the three-dimensionally structured second surface region (35) is formed as a convex grain profile extending in the direction of movement (29) of the switching means (33) on the at least one longitudinally extending switching means (33) and/or the at least one guide (8).