DE102019110715A1 - Valve train of an internal combustion engine and method for avoiding incorrect switching on a switchable valve train - Google Patents

Abstract

A valve train of an internal combustion engine with gas exchange valves, which are actuated via at least one camshaft with the interposition of at least one switchable lever-like cam follower, has switchable cam followers which can be switched between a first switch position and a second switch position position by a slide bar (5) moved by an actuator (6) are. In order to avoid unwanted switching operations of the slide bar and the actuator when the actuator is in the idle state, which can be caused by vibrations, the actuator (6) should be positively connected to the slide bar (5), a locking unit (8) being provided to hold the slide bar ( 5) in its rest position, in which the cam follower is actuated in its second switching position, prevents movement.

Description

Field of invention

The invention relates to a valve drive of an internal combustion engine with gas exchange valves, which are actuated via at least one camshaft with the interposition of at least one switchable lever-like cam follower, the switchable cam follower being switchable between a first switch position and a second switch position position by a slide bar moved by an actuator. The invention also relates to a method for avoiding incorrect switching on a switchable valve drive.

State of the art

From the DE 10 2013 210 871 A1 an actuator is known which consists of an electromagnet and a pressure pin actuated by this and can serve to be used in a sliding cam system of an internal combustion engine. There is also the possibility of using this actuator to switch a switchable lever-like cam follower, which is used in a valve train of an internal combustion engine, directly or indirectly via push bars from a rest position to a switching position.

Cam followers of reciprocating internal combustion engines, which are used to actuate the gas exchange valves, are usually designed as rocker arms, rocker arms or rocker arms and as cups and preferably interact with cams of an overhead camshaft arranged in the cylinder head. The lift of the gas exchange valve controlled by it cannot be influenced with a simple, i.e. non-switchable, cam follower.

To save fuel and increase the efficiency of the internal combustion engine, it has been known for a long time to use switchable cam followers or sliding cams. These are used to influence the stroke of the gas exchange valves. In the simplest case, a so-called zero stroke is implemented, i. H. the associated gas exchange valve remains in its closed position, although the cam of the rotating camshaft actuates the cam follower. Depending on the design of the switchable cam follower and the cams of the camshaft, changes in the valve lift can also be implemented.

From the DE 10 2017 101 792 A1 a generic valve drive is known in which a slide bar can be displaced via an actuator, which can switch switchable rocker arms from a first switching position designed as a rest position to a second switching position via connecting arms designed as leaf springs. In this case, two functionally identical gas exchange valves are provided per cylinder, of which at least one gas exchange valve is actuated via the switchable rocker arm by a camshaft mounted in the cylinder head. Each switchable rocker arm has a locking piston for switching. To actuate the locking piston, a sliding switch pin is provided, which protrudes laterally from the rocker arm.

The slide bar is mounted in the cylinder head so that it can be longitudinally displaced parallel to the camshaft in such a way that the connecting arms can move each switching pin into one of its two switching positions. The first switching position is reached by means of return springs arranged on the switching bolt and / or on the slide bar. The slide bar is moved by an actuator which has an electromagnet and which is usually attached to the outside of the cylinder head. The electromagnet has a stationary ring coil and an armature which is axially displaceable in its center and which interacts with a switching pin protruding from the housing of the actuator. At its free end facing the actuator, the slide bar is provided with a tab with which the switch pin is connected in a non-positive manner.

A disadvantage of this arrangement is its sensitivity to vibrations in the direction of movement of the push bar, which has been proven through tests. If the switching device vibrates, for example during its operation in a motor vehicle, the movable masses of the slide bar and the actuator are excited and shifted against the force of the return springs of the system. This can trigger an unwanted switching process of the switchable rocker arm via the connecting arms on the push bar, so that malfunctions occur.

Disclosure of the invention

The object of the present invention is to propose a device and a method with which undesired switching operations of the slide bar and of the actuator can be avoided when the actuator is in the idle state.

This object is achieved by the features of the characterizing part of the independent patent claim 1 solved. Advantageous refinements are reproduced in the patent claims which are dependent on them and which can represent an aspect of the invention either individually or in various combinations with one another.

According to this, the invention is based on a valve drive of an internal combustion engine with gas exchange valves which have at least one camshaft be actuated with the interposition of at least one switchable lever-like cam follower. The switchable cam follower can be switched between a first switch position and a second switch position position by a slide bar moved by an actuator.

According to the invention it is provided that the actuator is positively connected to the slide bar and that a locking unit is provided which prevents the slide bar from moving in its rest position in which the cam follower is actuated in its second switching position.

The invention is based on the knowledge that the slide bar is positively connected to the moving components of the actuator that moves it to form an overall system, and that a locking device is provided in this overall system that allows the overall system to move, i.e. the slide bar with the movable components of the actuator, prevents. It does not matter where the locking device engages. It can attack the slide bar or components of the actuator as long as there is a positive connection between the components of the overall system that can be excited to vibrate. The locking device prevents vibrations that occur from influencing the adjustment functions of the overall system in its idle state and thus causing unintentional switching of the switchable rocker arms. Therefore, irregularities in the running of the engine, which result from incorrect switching, can be prevented. The specific design of the actuator is irrelevant here. It does not matter whether the actuator works pneumatically, hydraulically or electrically.

A preferred development of the invention provides that the actuator is designed as an electromagnet, the armature of which is directly connected to the slide bar and that the locking device engages the armature. Since the actuator is usually arranged on the outside of the cylinder head or on the cylinder head cover of the internal combustion engine, it can be structurally simpler to expand it with a locking device. Their arrangement on the slide bar is partly not possible for reasons of space, since it is located inside the valve housing that accommodates the valve drive. The aforementioned solution also makes it structurally simple to ensure that the locking device is switched off when the electromagnet is energized.

The locking device can be in force-fit or, alternatively, form-fit contact with the armature of the electromagnet. A positive connection is preferred, since this prevents incorrect switching of the overall system in a simple and reliable manner when vibrations occur.

In order to unlock the locking device in a simple manner, it is proposed according to a further development of the invention to have the unlocking performed by the magnetic flux of the energized electromagnet by arranging the locking components of the locking device in the magnetic flux in such a way that they are released by the Magnetic force get into their unlocking function. This reduces the construction cost, because no further device is required to release the locking device.

If, as is known with some actuators, a switch pin is provided between the armature and the slide bar, it may be sufficient to let the locking device engage the switch pin, since the mass of the armature in the overall system is negligible on the one hand and the armature is also in its idle state on the other is frictionally in contact with the switch pin, so it is quasi clamped.

The locking device preferably consists of a displaceable locking pin made of magnetic material, and the armature or switching pin has a recess aligned with this, into which the locking pin can be moved. It is sensible to press the locking pin from an energy storage device, in particular a compression spring, into the recess and, when energized by the magnetic force, pull it out of the recess against the force of the compression spring. The depression can also be designed as a circumferential groove, which is easier to manufacture than a depression in terms of manufacturing technology. More than one locking pin can also be provided; two opposing locking pins are preferably provided which, when the actuator is in the idle state, snap into the groove or respective recess.

As an alternative to the locking pin, an eccentrically mounted ring can also be used, which can also be swiveled into the recess or groove by an energy storage device, in particular a compression spring, in the rest state.

In a method for avoiding incorrect switching on a switchable valve train with gas exchange valves that are actuated via at least one camshaft with the interposition of at least one switchable lever-like cam follower, the switchable cam follower is moved by a sliding bar between a first position and a second position. To do this, an armature of an actuator designed as an electromagnet acts on the slide bar. It is provided according to the invention that the magnetic field of the energized electromagnet moves the locking device in such a way that it is out of the operative connection with the Anchor is released. Thus, no separately controlled device is required to release the locking device and keep it released until the sliding bar has returned to its rest position. Then the energization of the electromagnet is switched off again so that the locking device can block the armature again. If a switch pin is interposed, the process works in the same way with the switch pin.

The invention is not limited to the specified combination of the features of the independent patent claim 1 and the claims dependent thereon. Furthermore, there are further possibilities for combining individual features with one another, in particular when they result from the patent claims, the following description of the exemplary embodiments or directly from the figures. In addition, the reference of the claims to the figures through the use of reference signs should in no way limit the scope of protection of the claims to the illustrated embodiment examples.

Figure list

• 1 eine perspektivische Ansicht einer Schubleiste mit acht schaltbaren Nockenfolgern und einem Aktuator zur Steuerung der Schubleiste,
• 2 einen Längsschnitt durch den als Elektromagneten ausgebildeten Aktuator nach 1 mit einer Arretiereinrichtung.

To further explain the invention, reference is made to the drawings, in which an exemplary embodiment is shown in simplified form. Show it:

• 1 a perspective view of a slide bar with eight switchable cam followers and an actuator for controlling the slide bar,
• 2 a longitudinal section through the actuator designed as an electromagnet 1 with a locking device.

Detailed description of the drawing

In the 1 Figure 3 is a side view of a camshaft 1 with a total of eight cams 2 an otherwise not shown cylinder head of a four-cylinder internal combustion engine. Below each cam 2 there are switchable rocker arms 3 , each with a gas exchange valve 4th is operated. In 1 there are two functionally identical gas exchange valves for each cylinder unit 4th shown, i.e. two gas exchange valves serving as outlet valves or inlet valves 4th . Thus, not all gas exchange valves of the cylinder head are visible in this illustration.

Parallel to the camshaft 1 runs a push bar 5 from which fasteners 5a , which are designed as leaf springs, on switching elements, not shown, switchable rocker arms 3 attack. The push bar 5 is mounted in the cylinder head so that it can be moved lengthways and is controlled by an actuator 6 moved to a second switch position. To do this, she points to the actuator 6 facing end has a tab angled by 90 ° 7th on. The actuator 6 is attached to the front of the cylinder head. He has a locking device 8th , whose structure is based on the following 2 emerges, and a drive device 9 on that with the tab 7th cooperates and the push bar 5 shifts in its longitudinal direction. This is where the push bar 5 from the actuator 6 into its second switching position against the force of a return spring 5b postponed. The return spring 5b moves the slide bar 5 into a first switching position, also referred to as the rest position. There, as already explained, the one from the push bar 5 outgoing connecting elements are designed as leaf springs, their spring force also acts on the push bar 5 . For the explanation of the present invention, the structure of the valve control will not be discussed in detail. As an example of such a valve control and the switching elements used in this regard, refer to the DE 10 2017 101 792 B4 referenced.

In the 2 , which is explained below, is the one with the locking device according to the invention 8th provided actuator 6 shown. The 2 a longitudinal section through the actuator 6 , which uses an electromagnet as the drive device 10 having. The electromagnet 10 consists of a fixed in an actuator housing 6.1 attached ring coil 10.1 and one in the center of the ring coil 10.1 located anchor 10.2 . In the in 2 The illustration shown is the electromagnet 10 not energized. The armature is therefore in its retracted position, ie in the rest position in which it is as far as possible into the actuator housing 6.1 has retracted.

The anchor is as a cylindrical pin 11 formed, the length of which is such that it is with its free end 12 from the actuator housing 6.1 protrudes. At this free end he has a recording 13 on which the tab 7th the sliding bar 5 attacks positively. This form-fitting connection is designed in such a way that it is practically free of play, at least in the direction of movement of the slide bar. The opposite end of the pen 11 is in the actuator housing 6.1 of a ring made of a magnetic material 14th surround.

In the present case, the anchor is 10.2 directly with the push bar 5 connected. But it is just as well conceivable within the scope of the invention that the anchor 10.2 acts on a separate switch pin, which is in a on the armature housing 6.1 attached switch housing is housed. Then the switch pin is directly with the slide bar 5 form-fitting and with the anchor 10.2 positively connected.

Inside the actuator housing 6.1 the anchor points 10.2 two wells 15th and 16 on the can also be designed overall as a circumferential groove. Perpendicular to the longitudinal axis of the anchor 10.2 and, the two wells 15th and 16 Opposite in the radial direction, there is a locking pin each 17th assigned, this being on a stop 18th prop up. The attack 18th can also be the inside of a base plate of the actuator housing 6.1 be. The recess and the locking pin thus form the locking device 8th for the anchor 10.2 and therefore also for those with the anchor 10.2 connected sliding bar 5 . Preferably the locking pins are 17th at the stop 18th via guide elements 18a guided in the longitudinal direction.

Each locking pin is made of a magnetizable material and designed in cross-section so that it can move into its associated recess with almost no play when it is aligned with it. A compression spring acting on each locking pin is used for this purpose 19th who have each locking pin 17th pushes into its assigned recess. Any locking pin 17th is so in the actuator housing 6.1 arranged that when the electromagnet is energized 10 some of the magnetic flux also passes through the locking pins 17th flows. So that a magnetic force is exerted on them, which the locking pins 17th against the force of their compression springs 19th back from their hollows 15th and 16 pulls and holds on there. This becomes the anchor 10.2 free and can move the slide bar 5 move into their switching position.

Will energize the electromagnet 10 switched off again, so the push bar pushes 5 about the return spring acting on it 5b also the anchor firmly attached to it 10.2 back into the actuator housing 6.1 inside. Since at the same time the compression springs 19th the locking pins again due to the lack of magnetic force 17th against the anchor 10.2 can slide the locking pins 17th when the armature reaches the rest position 10.2 back into their then aligned depressions 15th and 16 snap into place and so a longitudinal movement of the anchor 10.2 and the sliding bar 5 and thus prevent their vibrations.

Within the scope of the invention, the locking pin can also have a specially designed tip with a congruent contour in the recess 15th or. 16 corresponds, for example, a conical tip which cooperates with a conical recess. Then the extension movement of the locking pin generated by the magnetic force 17th are supported by the conical surfaces on the recess and the tip of the locking pin. However, when designing the recess and the tip of the locking pin, it must be ensured that the locking pins are prevented from moving out and thus avoiding free movement and swinging of the slide bar in its rest position.

It is also conceivable for the anchor 10.2 an additional return spring to be provided when the drive device is not activated 9 the anchor and its positive coupling with the slide bar 5 also move this back to the rest position.

Furthermore, the drive device must 9 not be an electromagnet. Other drive devices can also be used, such as, for example, hydraulically or pneumatically operating drive devices or also a rotating or linearly operating electric motor. It must then be ensured that the locking device is also released simultaneously with the activation of the drive device.

The present embodiment describes an electromagnet with an armature in a housing. However, it is irrelevant for the invention whether one, two or more electromagnets with their components are arranged in the housing and accordingly a locking device is provided for each armature. It is also irrelevant for understanding the invention how the electromagnet is controlled.

List of reference symbols

1

camshaft

2

cam

3

switchable rocker arm

4th

Gas exchange valve

5

Push bar

5a

Connecting element

5b

Return spring

6th

Actuator

6.1

Housing from 6

7th

Tab on 5

8th

Locking device

9

Drive device

10

Electromagnet

10.1

Ring coil of 10

10.2

Anchor from 10

11

cylindrical pin

12

free end of 11

13th

admission

14th

ring

15th

deepening

16

deepening

17th

Locking pin

18th

attack

18a

Guide elements

19th

Compression spring

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• DE 102013210871 A1 [0002]
• DE 102017101792 A1 [0005]
• DE 102017101792 B4 [0023]

Claims (10)

Valve drive of an internal combustion engine with gas exchange valves (4) which are actuated via at least one camshaft (1) with the interposition of at least one switchable lever-like cam follower (3), the switchable cam follower (3) being actuated by a slide bar (5) moved by an actuator (6) is switchable between a first switch position and a second switch position, characterized in that the actuator (6) is positively connected to the slide bar (5) and that a locking unit (8) is provided which holds the slide bar (5) in its rest position which the cam follower (3) is actuated in its second switching position, prevents it from moving. Actuator after Claim 1 , characterized in that the actuator (6) consists of an electromagnet (10), the armature (10.2) of which is directly connected to the slide bar (5), and that the locking unit (8) engages the armature (10.2). Actuator after Claim 1 or 2 , characterized in that the locking unit (8) is in a force-locking manner with the armature (10.2). Actuator after Claim 1 or 2 , characterized in that the locking unit (8) is positively connected to the armature (10.2). Actuator according to at least one of the preceding Claims 2 to 4th , characterized in that the locking device (8) is arranged in the actuator (6) in such a way that it can be moved into an unlocking position by the magnetic flux. Actuator according to at least one of the preceding claims, characterized in that the locking device (8) consists of at least one movable locking pin (17) and of a magnetic material, and that the armature (10.2) / switching pin on its periphery has at least one recess (15 or . 16), which is arranged such that the locking pin (17) can be moved into the recess (15 or 16). Actuator after Claim 6 , characterized in that the locking pin (17) can be moved into the recess (15 or 16) by an energy store. Actuator according to at least one of the preceding Claims 1 to 5 , characterized in that the locking device (8) consists of an eccentrically mounted ring which can be pivoted into the recess by an energy storage device. Actuator according to at least one of the preceding claims, characterized in that the energy storage device is a compression spring (19). Method for avoiding incorrect switching on a switchable valve train with gas exchange valves (4) which are actuated via at least one camshaft (1) with the interposition of at least one switchable lever-like cam follower, the switchable cam follower from a sliding strip (5) between a first position and a second Position is moved, for which purpose an armature of an actuator (6) designed as an electromagnet engages the slide bar, the actuator (6) and the slide bar (5) being designed according to at least one of the preceding claims, characterized in that the magnetic field of the energized electromagnet (10) moves the locking device (8) in such a way that it is released from the operative connection with the armature (10.2).

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