CN110131007B

CN110131007B - Switchable cam follower for a valve train of an internal combustion engine

Info

Publication number: CN110131007B
Application number: CN201910084536.9A
Authority: CN
Inventors: 拉雷什·卢杜桑; 安德烈·马雷什; 阿德里安·胡苏; 多鲁·格罗扎
Original assignee: Schaeffler Technologies AG and Co KG
Current assignee: Schaeffler Holding China Co Ltd
Priority date: 2018-02-08
Filing date: 2019-01-29
Publication date: 2022-09-02
Anticipated expiration: 2039-01-29
Also published as: DE102018102778B4; CN110131007A; DE102018102778A1

Abstract

A switchable cam follower of an internal combustion engine valve train, comprising an outer rocker arm with two arms, between which an inner rocker arm is mounted which can be pivoted relative to the outer rocker arm by means of a pivot shaft, at least the inner rocker arm having a cam running surface on its upper side; the cam follower has on its one end on its underside an abutment surface which cooperates with the gas exchange valve and on its other end a contact surface for the support element. The cam follower is further provided with a pot-shaped housing opposite the pivot axis on the outer rocker arm, wherein a spring-loaded locking piston is supported in a manner movable substantially perpendicular to the pivot axis, which in an unlocking position separates the inner rocker arm in terms of movement from the outer rocker arm and in a locking position connects them; the cam follower is also provided with an operating mechanism for moving the locking piston. The actuating mechanism comprises an electrically operated actuator and a control shaft which is arranged parallel to the pivot axis on the pot-shaped housing and moves the locking piston into the locking or unlocking position.

Description

Switchable cam follower for a valve train of an internal combustion engine

Technical Field

The invention relates to a switchable cam follower, in particular a rocker arm, of an internal combustion engine valve train, having an outer rocker arm with two arms, between which an inner rocker arm is mounted that can be pivoted relative to the outer rocker arm by means of a pivot axis, wherein at least the inner rocker arm has a cam running surface on its upper side for at least one cam of a camshaft, and the cam follower has an abutment surface on its lower side on one end that cooperates with a gas exchange valve and a contact surface on its other end for a support element, and further wherein the cam follower has a pot-shaped housing on the outer rocker arm opposite the pivot axis, in which a spring-loaded locking piston is mounted so as to be movable substantially perpendicular to the pivot axis, and which in an unlocking position separates the inner rocker arm from the outer rocker arm in terms of movement and connects the inner rocker arm to the outer rocker arm in a locking position, and the cam follower is also provided with an operating mechanism for moving the locking piston.

Background

In piston reciprocating internal combustion engines, rocker arms, pendulum arms or cups are usually used as cam followers for actuating gas exchange valves which, with the camshaft located above, are actuated directly by the respective cams of the same camshaft. With simple rocker arms, pendulum arms or cups, the lift of the valve controlled by them cannot be influenced.

In order to save fuel and increase the efficiency of internal combustion engines, the use of switchable cam followers has long been known. These cam followers are used in internal combustion engines to influence the lift of gas exchange valves. In the simplest case, a so-called zero lift is achieved, i.e. the associated gas exchange valve does not open even if the cam follower is actuated by the cam of the rotating camshaft. According to the design scheme of the switchable cam follower and the cam of the camshaft, the valve lift and the valve lift change curve can be changed.

Generic, switchable pendulum rockers for internal combustion engine valve trains, which are composed of an outer rocker arm and an inner rocker arm, are also known from DE 102007029465 a 1. In this case, the outer rocker arm has two arms. An inner rocker arm is disposed between the arms. Cam operation surfaces are respectively arranged on the upper sides of the two rocker arms. On the underside of the pendulum rocker arm, an abutment surface for gas exchange valves of an internal combustion engine is provided at one end. A contact surface is formed opposite the contact surface, on which the support element acts. The two rocker arms are connected to each other on one side by a common pivot shaft. A spring is mounted on the pivot shaft which presses the inner rocker arm into its upper position. Furthermore, the outer rocker arm has at its other end a cylinder housing in which a spring-loaded locking piston is guided in a sliding manner. The locking piston can connect the inner rocker arm to the outer rocker arm in terms of movement in the locking position, i.e. when the cam of the camshaft presses on the inner rocker arm, the gas exchange valve is then opened. In the unlocking position, the inner rocker arm is kinematically separated from the outer rocker arm. The inner rocker arm is thus unable to actuate the gas exchange valves that rest against the outer rocker arm. Naturally, depending on the design of the cams, the opening movement of the gas exchange valves can also be realized by cam running surfaces mounted on the outer rocker arms.

The disadvantages of this design are: the locking piston is activated by oil pressure in the internal combustion engine. When the oil pressure is high, the locking piston is switched over, and when the oil pressure drops, the spring of the locking piston moves the locking piston into another position again. During activation of the locking piston, the oil pressure must be constant. This requires a higher pump power of the oil hydraulic pump than would be provided for a valve train without the switchable pendulum arm. Due to other consumers in the oil circuit, a strong pressure drop can occur, which leads to an undesired switching of the locking piston. In the case where there is a start-stop automatic control apparatus for an internal combustion engine, the switching state cannot be stored until shut down. When activated, the locking piston is always in its unlocking position.

It is known from WO 2016/197088A 1: in the case of a switchable cam follower, instead of a hydraulic actuation of the locking piston, an electromagnetically operated actuator in the form of a coil is provided, which in the energized state holds the locking piston in its unlocking position against the pressure of a compression spring. In the event of no current flow in the coil, the compression spring moves the locking piston into the locking position. The arrangement is constructed such that a part of the locking piston cooperates directly with the coil. This arrangement therefore requires the coil to be energized as long as the locking piston should remain in its unlocking position.

Disclosure of Invention

The task of the invention is that: the described disadvantages are avoided and an actuating mechanism for a switchable cam follower, in particular a pendulum rocker, is proposed, which in the switching position does not depend on the maintenance of the oil pressure/actuating force.

The starting point of the invention is then a switchable cam follower, in particular a pendulum rocker arm, of an internal combustion engine valve train. The cam follower is provided with an outer rocker arm having two arms between which an inner rocker arm is supported for pivotal movement relative to the outer rocker arm via a pivot shaft. At least the inner rocker arm has on its upper side a cam running surface for at least one cam of a camshaft of the internal combustion engine. The cam follower has an abutment surface on its underside at one end and a contact surface at its other end. Gas exchange valves of an internal combustion engine cooperate with the contact surfaces, while support elements are arranged on the contact surfaces. The cam follower has, on its outer rocker arm, a pot-shaped housing opposite the pivot axis, in which a spring-loaded locking piston is mounted so as to be movable substantially perpendicularly to the pivot axis and which, in the unlocked position, separates the inner rocker arm from the outer rocker arm in terms of movement and, in the lockable position, connects the inner rocker arm to the outer rocker arm. Furthermore, an actuating mechanism is provided for displacing the locking piston.

According to the invention: the actuating mechanism comprises an electrically operated actuator and a control shaft, wherein the control shaft is mounted on the pot-shaped housing parallel to the pivot axis and moves the locking piston into the locking or unlocking position.

The arrangement according to the invention makes it possible to create electrically operating actuating devices of very small construction, wherein only slight constructional changes are required in the existing cam followers, without increasing the installation space of these cam followers. This applies in particular to the two necessary return springs (lost motion torsion springs) which always keep the inner rocker arm in its uppermost position in the unlocked state, which can advantageously be arranged coaxially around the housing of the control shaft. In the case of the invention, the control shaft can be screwed or moved in order to reach these two stations. For this purpose, only a small adjustment stroke is required.

An electromagnet may be provided as an electrically operated actuator. It is equally well conceivable to use an electric motor, which may have an additional transmission. In the case of internal combustion engines with a plurality of cylinders and/or lift valves and thus a plurality of switchable cam followers, the individual actuators can be specifically actuated by electrically operated actuators in order to achieve a common starting position for all switchable cam followers.

In order to move the locking piston into its two positions, the control shaft can be equipped with a closed control curve which ensures that the locking piston can reach its locked and unlocked positions. For this purpose, the control curves can be distributed over the circumference of the control shaft, so that the two positions of the locking piston can be reached by screwing the control shaft. For this purpose, the control curve itself can be varied in its depth analogously to the cams of the camshaft.

The simpler structure is: the control curve is generated by varying its diameter over a portion of the axial length of the control shaft, wherein the control curve has regions of smaller and larger diameter, i.e. a minimum and a maximum. The minimum and maximum portions of the control curve are dimensioned such that, by an axial displacement of the control shaft, the locking piston can each reach one of its two positions.

In order to prevent the control shaft from being screwed about its longitudinal axis in this case, the locking piston has a rib with a sliding surface in its region facing forward of the control curve, wherein the rib corresponds in terms of its length to the width of the control curve.

In order to eliminate the need for a holding force caused by an electrically operated actuator in both positions of the locking piston, it is proposed in a development of the invention that: locking devices are provided at the minimum and maximum of the lift curve, which hold the locking piston in this position. Thereby also ensuring that: when starting an internal combustion engine, the cam follower and thus the lift valve controlled thereby always have the position they occupy when they are switched off.

The locking device of simple construction is provided with one locking groove at each of the smallest and largest portions of the control curve, into which the end of the locking piston facing the control curve can be locked by the force of its spring. The electrically operated actuator must then be designed such that it can move the control shaft against the force of the spring locking the piston.

Due to their structural dimensions, electric toroidal coils have proven to be advantageous as electrically operated actuators. What makes sense in this case is: the above-mentioned locking means are provided at the respective minimum and maximum portions of the control curve. The ring coil can thus be kept currentless while the control shaft is held in the locking or unlocking position of the locking piston.

Alternatively to this, it may be expedient to provide an electric toroidal coil with a magnet in the form of a circular bar in its center. The magnet is used for: the control shaft is held in its position when the ring coil is currentless. A separate locking device can thereby be dispensed with. A permanent magnet or an electromagnet may be used as the magnet. The permanent magnet has the following advantages: it does not require energy to hold the control shaft.

It is advantageous that: an electrically operated actuator is provided at each end of the control shaft. Of course, it is also possible to provide only one actuator when the control shaft is held in the minimum or maximum by other means, for example a compression spring. The electrically operated actuator must then be designed such that it can adjust the control shaft into another position against the force of the compression spring.

In order to support the magnetic force exerted by the electrically operated actuator, it is advantageous that: the control shaft has compression springs on both end sides thereof. In order to keep the installation space small, the spring ends of the compression springs surround the respective electrically operated actuator.

A leaf spring, which is arranged perpendicularly to the path of movement of the locking piston, has proven to be a space-saving solution for the spring of the locking piston. In this case, the leaf spring is supported on the one hand on the shoulder of the locking piston and on the other hand on the pot-shaped housing. By means of the spring it is ensured that: the locking piston always bears against the control curve of the control shaft and can follow this.

It is expedient for the electrically operated actuator to be actuated by an engine control unit of the internal combustion engine.

Drawings

For further elucidation of the invention reference is made to the accompanying drawings in which a number of embodiments are shown simplified. Wherein:

FIG. 1 shows a perspective view of a switchable pendulum rocker arm;

fig. 2 shows a longitudinal section of the pendulum rocker arm according to fig. 1 with a locking piston and a control shaft according to the invention in an unlocked position, as a side view;

fig. 3a shows a cross section of the pendulum rocker arm according to fig. 2 with one electrical coil as an electrically operated actuator at each end of the control shaft and a locking piston in the unlocked position as a top view;

FIG. 3b shows a perspective view of the pendulum rocker arm with coil and compression spring according to FIG. 3a, wherein the pot housing is shown in cross-section;

FIG. 4a shows a top view of the pendulum arm as in FIG. 3a, with the locking piston and control shaft in the locking position;

FIG. 4b shows a perspective view of the pendulum arm as in FIG. 3b, with the locking piston and control shaft in the locking position;

FIG. 5a shows a schematic view of a first embodiment of a lift curve on a control shaft;

fig. 5b shows a schematic diagram of a second embodiment of a lift curve on a control shaft.

Detailed Description

Fig. 1 shows a switchable pendulum rocker arm 1 as a cam follower for an internal combustion engine in a perspective view. The swing arm includes an outer rocker arm 2, the middle portion of which extends into two arms 3. Between these arms 3, an inner rocker arm 4 extends in a manner allowing a swinging movement relative to the outer rocker arm. The inner rocker arm has a roller 6 in its middle section 5, which serves as a running surface for a cam, not shown in detail, of a camshaft, not shown in detail. Depending on the design of the camshaft, it is also possible to provide a cam which cooperates with a cam running surface on one or both arms 3 of the outer rocker arm 2 when the inner rocker arm 4 is unlocked from the outer rocker arm 2.

The inner rocker arm 4 has a cross member 16 at the end, which is coupled to a box-like open middle section 5, which is delimited by two rod-like arms 17. The arms 17 merge strongly towards one another towards the end 15 opposite the transverse beam into a meandering web 7, which is approximately orthogonal to the longitudinal middle plane of the pendulum rocker arm 1. In this end region, a pivot shaft 10 is arranged in the outer rocker arm 2, which pivot shaft also traverses the inner rocker arm 4, so that the inner rocker arm 4 is connected to the outer rocker arm 2 in a pivotable manner. On the underside 8 of the outer rocker arm 2, an abutment surface 9 (fig. 2) for a likewise not shown gas exchange valve of the internal combustion engine is provided at this end 15. The outer rocker arm 2 encloses the inner rocker arm 4 as much as possible, so that a very compact pendulum rocker arm 1 is formed. The pendulum rocker arm thus also has a small moment of inertia.

At the end 18 adjacent to the transverse member 16, the outer rocker arm 2 is provided with a pot-shaped housing 13, in which a locking piston 20 and its actuating mechanism 19, which will be described below, are arranged. At this end, the pot-shaped housing 13 has a dome-shaped contact surface 14 (fig. 2) on its underside 8 for a support element, not shown in detail.

Cylinder bolts 11 are respectively mounted on the opposite outer sides of the pot-shaped housing 13 in a manner projecting at right angles and surrounded by a respective torsion spring 12. A torsion spring 12 (also referred to as a lost motion spring) is supported on the outer rocker arm 2 on one side and on the inner rocker arm 4 on the other side. Thereby ensuring that: when the inner rocker arm is not cam-operated, the inner rocker arm 4 with its roller 6 is always in its uppermost end position.

In the illustration according to fig. 2, the locking piston 20 and a part of the actuating mechanism 19 can be seen further. The locking piston 20 is in its unlocking position, i.e., the inner rocker arm 4 is not connected to the outer rocker arm 2. The locking piston 20 is mounted in an axially movable manner in a bore 21 in the pot-shaped housing 13. The locking piston has a rib with a sliding surface 23 in the region 22 at the front. At the end facing away from the sliding surface 23, the locking piston 20 has a stepped shoulder 24. A leaf spring 25 is arranged on the shoulder 24, which leaf spring holds the locking piston 20 in its unlocking position. At the same time, the leaf spring 25 serves to keep the locking piston in contact with the control shaft 27 with its sliding surface 23 at all times, as is shown in the following fig. 3 and 4. The leaf spring 25 extends with its longitudinal extent perpendicular to the travel direction of the locking piston 20. The shoulder 24 is also arranged in such a way that it can engage the underside of the cross member 16 from below when the shoulder is moved axially in the direction of the cross member 16. This is always possible when the roller 6 is not cam-operated, since the torsion spring 12 will then bring the inner rocker arm to its highest position, so that the shoulder 24 of the locking piston can engage the cross member 16 from below.

The sliding surface 23 of the locking piston 20 bears linearly against a control cam 26, which is formed in the circumference of a control shaft 27. The control shaft 27 is of cylindrical design and is mounted in the two pins 11, as will be described below.

The entire structure of the actuating mechanism 19 can be seen in the plan view of the cross section in fig. 3a, which actuating mechanism has a control shaft 27 with a control curve 26 and an electrically operated actuator, which is described below. The control shaft 27 is mounted in two pins 11, which are formed on the free end of the pot-shaped housing 13 in a laterally projecting manner. Around the periphery of these pins 11, two torsion springs 12 are arranged, which keep the non-actuated inner rocker arm 4 in its uppermost position at all times. Here, too, the bearing pin of the roller 6 is seen, which is arranged only in the inner rocker arm 4 in order to ensure a swiveling movement in the unlocking position of the locking piston 20. The roller 6 is not shown for a good overview.

As can be seen particularly well here, a control curve 26 extending in the axial direction of the control shaft 27 is machined at its circumference. The control curve has a minimum portion 28 and a maximum portion 29, wherein the diameter of the control shaft 27 is smallest at the minimum portion 28 and approximately corresponds to the outer diameter of the control shaft at the maximum portion 29.

At each end of the control shaft 27, an electric toroidal coil 30, 30' is arranged as an electrically operated actuator. Inside each annular coil is a round bar-shaped magnet 31, 31', which is preferably designed as a permanent magnet. In each plug 11, both are held by an annular plug 32, 32', which also closes the plug 11 at the same time. A compression spring 33, 33 'is supported on one side on the end face of the control shaft 27 facing the annular coil and on the other side on the plug 32, 32'. In order to save installation space, the compression spring 33 concentrically surrounds the annular coil 30 and the magnet 31, while the compression spring 33' surrounds the annular coil 30' and the magnet 31 '. In this exemplary embodiment, the control shaft 27 with its annular coils 30 and 30' and the magnets 31 and 31' and the compression springs 33 and 33' forms the actuating element 19.

The uncoupled position of the locking piston 20 is shown in fig. 3 a. In order for the locking piston 20 to occupy this position, its rib must be located with its sliding surface 23 at the smallest part 28 of the control curve 26. This means that: a free end face of the control shaft 27 bears against the magnet 31'. The compression spring 33' is then pressed strongly together, the compression spring 33 having its maximum length. Due to the magnet 31', the coil 30' can be kept currentless.

In fig. 3a, the orientation and arrangement of the leaf springs 25 can also be seen. The leaf spring is designed as a w-shaped bent leaf spring, the middle part 34 of which is supported on the stepped shoulder 24. The two free ends of which are supported at opposite openings in the pot-shaped housing 13 by means of holders 35.

Fig. 3b again shows the arrangement of the control shaft 27 in the two pins 11 or the orientation of the locking pistons 20 in the pot-shaped housing 13 and the orientation of the leaf springs 25. Identical components are provided with the same reference numerals, wherein for a better overview not all components are provided with reference numerals. Here, it is particularly evident that: the stepped shoulder 24 is not located below the underside of the cross member 16, i.e. the locking piston 20 is in its unlocked position.

In fig. 4a and 4b the same views as in fig. 3a and 3b are shown, the only difference being: the inner rocker arm 4 is coupled to the outer rocker arm 2 by means of a locking piston 20, i.e. a shoulder 24 of the locking piston 20 engages underneath the cross member 16 of the inner rocker arm 4. Here, the same members are also provided with the same reference numerals.

In order to reach the locking position, the locking piston 20 must be moved against the force of its leaf spring 25. This can be achieved by: the control shaft 27 is moved relative to its station shown in fig. 3a and 3b to its other end station. The sliding surface 23 is thereby moved along the control curve 26 to the maximum 29. The movement of the control shaft 27 is realized by: by applying a voltage to the toroidal coil 30', a magnetic field is generated which opposes the magnetic field of the magnet 31'. Thereby, the control shaft 27 can be moved towards the annular coil 30 due to the force of the compression spring 33'. This movement is supported by the magnetic field of the magnet 31 and by applying a voltage to the ring coil 30, so that the ring coil generates a magnetic field by which the control shaft 27 is pulled against the force of the compression spring 33 and of the leaf spring 25. Once the control shaft 27 abuts the magnet 32, the ring coils 30 and 30' can be switched to no voltage.

In fig. 5a, the control curve 26 and the two ring coils 30 and 30 'and the compression springs 33 and 33' are again shown in a strongly simplified manner, together with the roughly depicted locking piston 20 with its leaf springs 25. Here, it is very clearly seen that: the sliding surface 23 of the rib of the locking piston can move from the largest part 29 to the smallest part 28 of the control curve 26 and vice versa. Here also: no locking mechanism is arranged on the control curve 26. The two magnets 31 and 31 'thus serve to hold the control shaft 27 in its two end positions in the absence of voltage to the ring coil 30 or 30'.

A modification of the control curve 26 is very schematically shown in fig. 5 b. Here, the locking grooves configured as the concave portions 36 and 37 are at the minimum portion 28 and the maximum portion 29, respectively. The contour of which corresponds to the sliding surface 23 on the rib of the locking piston 20. The locking piston 20 can thus be locked in its two positions without having to use a magnet in the form of a circular rod on the annular coil. In this way a simple bistable arrangement is provided.

List of reference numerals

1 pendulum type rocking arm

2 outer rocker arm

32 arm

4 inner rocker arm

54 middle section

6 roller

7 contact piece

81 lower side

9 contact surface

10 shaft

11 bolt

12 torsion spring

13 cylinder type shell

14 domed contact surface

15 opposite to 18

16 crossbeam

174 of the arm

End of 182 opposite to 15

19 operating mechanism

20 locking piston

2113 of the hole

2220 front area

23 sliding surface

Stepped shoulder at 2420

25 leaf spring

26 control curve

27 control shaft

28 smallest part

29 maximum part

30. 30' toroidal coil

31. 31' round bar magnet

32. 32' ring plug

33. 33' compression spring

3425 middle part

35 holder

36 recess

37 recess

Claims

1. Switchable cam follower for a valve train of an internal combustion engine, comprising an outer rocker arm (2) with two arms (3), between which arms (3) an inner rocker arm (4) is mounted that is pivotally movable relative to the outer rocker arm by means of a pivot axis (10), wherein at least the inner rocker arm (4) has on its upper side a cam running surface for at least one cam of a camshaft, and the cam follower has on its lower side (8) on one end (15) an abutment surface (9) that cooperates with a gas exchange valve and on its other end (18) a contact surface (14) for a support element, and comprising a pot-shaped housing (13) on the outer rocker arm (2) opposite the pivot axis (10), in which a spring-loaded locking piston (20) is mounted so as to be displaceable substantially perpendicularly to the pivot axis (10), and which in an unlocking position kinematically separates the inner rocker arm (4) from the outer rocker arm (2) and in a locking position connects the inner rocker arm (4) with the outer rocker arm (2), and which is further provided with an operating mechanism (19) for moving the locking piston (20), characterized in that the operating mechanism (19) comprises an electrically operated actuator and a control shaft (27), wherein the control shaft (27) is arranged on the pot-shaped housing (13) parallel to the pivot axis (10) and moves the locking piston into a locking position or an unlocking position.

2. Switchable cam follower according to claim 1, characterized in that the control shaft (27) is supported in a bearing housing arranged on the pot-shaped housing (13) and has a control curve (26) with a maximum portion (29) and a minimum portion (28).

3. Switchable cam follower according to claim 2, characterized in that the locking piston (20) has a rib with a curved sliding surface (23) at its forward region (22) facing the control curve (26).

4. Switchable cam follower according to claim 2, characterized in that the control curve (26) has locking means at the maximum (29) and minimum (28) sections, respectively.

5. The switchable cam follower according to any of the preceding claims, characterized in that the electrically operated actuator is provided with an annular coil (30, 30').

6. Switchable cam follower according to claim 5, characterized in that the ring coil has a magnet (31, 31') in the shape of a circular bar arranged in its center.

7. Switchable cam follower according to claim 5, characterized in that one electrically operated actuator each is arranged at both end sides of the control shaft (27).

8. The switchable cam follower as claimed in claim 7, characterized in that a compression spring (33, 33') is supported at both end sides of the control shaft (27) in each case, the free end of the compression spring concentrically surrounding the electrically operated actuator.

9. Switchable cam follower according to claim 2, characterized in that the locking piston (20) has a shoulder (24) on which a leaf spring (25) is arranged for moving the locking piston (20) towards the control curve (26), the free end of the leaf spring being supported on the pot-shaped housing (13).

10. The switchable cam follower of claim 1, wherein the electromagnetic actuator is operated by an engine control of an internal combustion engine.