EP3180498B1 - Camshaft with sliding cam packet - Google Patents

Description

The present invention relates to a camshaft to the valve train of an internal combustion engine having a fundamental and at least one sliding cam package comprising a plurality of cam profiles, wherein the fundamental shaft extends through a passage in the sliding cam package, so that it is received axially displaceably on the fundamental shaft, and means for forming a torque transmitting connection between the fundamental and the sliding cam package are provided.

Camshafts with sliding cam packs are used for variable valve train for an internal combustion engine and depending on an axial position of the sliding cam package on the fundamental shaft, a tap element for valve control with different, adjacent to each other formed on the sliding cam package cam profiles cooperate. The lifting information is stored in the specific cam profile and may include, for example, different sized valve strokes or a so-called zero stroke. For the axial adjustment of the sliding cam package, this comprises, in addition to the cam profiles, an adjusting element in which an adjusting element engages, which is arranged in a stationary manner in the receiving body for receiving the camshaft.

In a receiving body, which can be formed for example by a camshaft module in the manner of a hood, which can be applied with pre-assembled camshafts on the cylinder head of the internal combustion engine. Camshafts with a basic shaft and several sliding cam packages can also be mounted directly in the cylinder head itself.

For mounting the camshaft in the receiving body, it is possible to store the sliding cam packages themselves in associated bearing blocks of the receiving body, ie to receive rotatable, then the fundamental wave through the Pass sliding cam packages, which then drives them only rotating. For ease of assembling and handling of the components to be assembled, camshafts having a base shaft and a plurality of sliding cam packages applied to the fundamental shaft may also be preassembled, and the preassembled camshaft is then mounted in the receiving body. In this case, the camshaft is preferably mounted on the fundamental shaft, for example via corresponding bearing rings, which are applied to the fundamental shaft. The sliding cam packages are freely supported on the basic shaft, and via the means for torque-transmitting connection, the sliding cam packages rotate with the rotation of the fundamental shaft, while the sliding cam packages remain axially displaceable on the fundamental shaft.

STATE OF THE ART

For example, the shows DE 10 2008 005 639 A1 a camshaft to the valve train of an internal combustion engine with a basic shaft and with sliding cam packages, which have a plurality of cam profiles. The basic shaft extends through a passage in the sliding cam package, wherein means for forming a torque-transmitting connection between the fundamental shaft and the sliding cam package are formed, which are based on a sliding cam teeth between the outside of the basic shaft and the passage of the sliding cam package. A problem with this is that due to manufacturing tolerances of the sliding toothing and concomitant inaccuracies in the radial guidance, inadmissibly high base circle deviations of the cam profiles of the sliding cam package can occur in arrangement on the fundamental shaft. These tolerances can be reduced only by extremely accurate production of the sliding teeth in the fundamental and the counter teeth in the passage of the sliding cam package, but this requires high production times and costs. The formation of the fundamental wave as a toothed shaft and the corresponding design of the sliding cam assembly with the internal teeth also requires relatively high displacement forces when moving the sliding cam pact relative to the drive shaft.

The DE 10 2011 000 511 A1 shows for a generic type camshaft means for forming a torque transmitting connection between the fundamental shaft and the sliding cam package, which are formed as sliding blocks. Disadvantageously, while the fundamental wave must be performed as a solid shaft, otherwise the nuts can not be absorbed in the fundamental wave. In addition, there is the disadvantage of high local surface pressures between the sliding block and the corresponding recess in the passage of the sliding cam package, since it regularly comes to edge support effects.

The DE 102011 000 510 A1 shows a generic camshaft, and the means for forming a torque-transmitting connection between the basic shaft and the sliding cam package comprise a plurality of balls forming a linear roller bearing for axially displaceable receiving the sliding cam package on the fundamental shaft. Since the sliding cam package is always seated and operated in discrete positions on the basic shaft depending on the cam profiles, there may be the disadvantage that due to the high Hertzian pressure, the balls in the associated recesses can press into the surface of the recesses over a longer service life so that a rotational clearance of the sliding cam package can arise on the fundamental. Further, the balls form only a point contact with the recess in the passage of the sliding cam package or in the outer side of the fundamental shaft, whereby only small torques between the sliding cam package and the fundamental can be transmitted.

In the JP 2008 208737 A is also shown a camshaft in which needle bearing elements are used to allow only a rotation of the cam elements of the camshaft, which, however, in comparison to DE 10 2011 000 510 A1 no rolling function for axially displaceable receiving the cam element on the fundamental meet.

From the WO 2015/176874 A1 is a camshaft to the valve train of an internal combustion engine with a fundamental and at least one sliding cam package comprising a plurality of cam profiles has become known, wherein the fundamental wave through a passage in the sliding cam package through extends so that it is received axially displaceably on the basic shaft, and wherein means for forming a torque transmitting connection between the fundamental shaft and the sliding cam package are provided, wherein the means comprise elongated needle bearing elements, which with a first part of its circular cross-section in a longitudinal groove in the passage of Insert sliding cam pack and locate with a second part of the same cross-section in a longitudinal groove in the outside of the basic shaft.

DISCLOSURE OF THE INVENTION

The object of the invention is the improved design of means for forming a torque-transmitting connection between a fundamental and a sliding cam package of a camshaft, the means should be formed as low as possible and it should also be avoided over a prolonged period of use of the camshaft a game between the sliding cam package and the fundamental become. In particular, high surface pressures in contact of the means to the passage of the sliding cam package should be avoided.

This object is achieved on the basis of a camshaft according to the preamble of claim 1 in conjunction with the characterizing features. Advantageous developments of the invention are specified in the dependent claims.

The invention includes the technical teaching that the means comprise longitudinally formed needle bearing elements which are seated with a first part of their circular cross-section in a longitudinal groove in the passage of the sliding cam package and which are located with a second part of the same cross-section in a longitudinal groove in the outside of the fundamental shaft, wherein the longitudinal groove in the passage of the sliding cam package has a deviating from a circular cross-sectional contour.

The formation of the means as a needle bearing elements leads to a wear minimum and permanent formation of a torque transmitting connection between the fundamental and the sliding cam package, and in the Substantially half the insertion of the needle bearing elements both in a longitudinal groove in the passage of the sliding cam element and in a longitudinal groove in the outside of the fundamental shaft allows a force distribution in the contact area between the needle bearing elements and the longitudinal grooves, are avoided in the high force peaks. Due to the cylindrical shape of the needle bearing elements, a curvature-curvature contact is formed in a line shape, so that the stresses of the Hertzian pressure between the needle bearing elements and the longitudinal grooves are minimized. As a result, a camshaft can be provided to the valvetrain of an internal combustion engine that does not require the use of splines between the shift cam package and the fundamental shaft, and by the use of the needle bearing members, a high force transmission between the shift cam package and the fundamental shaft is enabled, without the contact force in the circumferential direction leads to increased wear.

With particular advantage, the longitudinal groove in the outer side of the fundamental wave can have a semicircular cross section which corresponds to the circular cross section of the needle bearing elements. In particular, the circular cross-section may have the same radius as the cylindrical shape of the needle bearing elements, and sit the needle bearing elements in this semicircular cross-section, then arises over the semicircular cross-section of the needle bearing elements play-free surface contact in the surface of the longitudinal groove. In particular, the needle bearing elements can be displaced by the large contact surface wear minimum in the longitudinal groove in the outer side of the fundamental shaft when the sliding cam package is axially displaced on the fundamental shaft. The needle bearing elements can be accommodated axially fixed in the longitudinal grooves in the passage of the sliding cam package, so that they move along with the axial movement of the sliding cam package.

The longitudinal groove in the passage of the sliding cam package has a cross-sectional contour deviating from a circular arc. The deviation can take place in various ways, in particular, the deviation can be designed so that two contact areas for transmitting a contact force between the Needle bearing elements and the sliding cam package are formed in the circumferential direction, as explained in more detail below in two variants.

According to a first variant, the cross-sectional contour of the longitudinal groove in the passage of the sliding cam package may be defined by two, in particular merging radii which are larger than the diameter of the needle bearing elements, so that two opposite contact areas are formed for contact of the needle bearing element. Thus, the radius of the longitudinal groove in the passage of the sliding cam element deviates from the radius of the needle bearing elements, which serves to form the circumferentially approximately opposite defined contact areas.

If also the longitudinal groove formed in the passage of the sliding cam element with the same radius as the passage in the outside of the fundamental shaft and would have the longitudinal groove thus a radius corresponding to the radius of the needle bearing elements, so highly stressed areas would be at the Längsnutkanten the longitudinal grooves in the passage of the sliding cam package and arise in the outside of the fundamental wave. These material stresses on the groove edges, which are very high due to edge-bearing effects, can be avoided by the two radii which define the cross-sectional contour of the longitudinal groove in the passage of the sliding cam package. In particular, taking into account high torque requirements between the sliding cam package and the fundamental and taking into account given material specifications would be expected to increase wear of the highly loaded groove edges, if the radii of both longitudinal grooves would correspond to the radius of the needle bearing elements. However, if the semicircular shape of the longitudinal grooves in the passage of the sliding cam package is formed by two partial circles with larger but mutually equal radii whose center points are shifted relative to one another, defined contact areas are created for the needle bearing element without creating highly stressed areas on the groove edges. The respective radius of the pitch circle is greater than the radius of the needle bearing elements. This geometry changes the direction of the contact normal forces on the needle bearing elements. Due to radius differences between the longitudinal grooves and the needle bearing elements arise Hertzian contact areas, and since the direction of the load engagement is changed by the changed geometry between the fundamental shaft and the sliding cam package, it is sufficient to form only one of the two longitudinal grooves other than a radius contour corresponding to the radius of the needle bearing members. The edge load is minimized in both components, ie in the fundamental and also in the sliding cam package.

The occurring Hertzian pressure decreases as the radii of the contact partners approach each other as well as possible. Since the sliding cam package is preferably made of hardened bearing steel, the special geometry is formed there. In the fundamental wave, the semicircular shape is preferred, which is adapted to the geometry of the needle bearing elements, in order to achieve as far as possible no differences in radii. As a result, the load in the fundamental wave is reduced and the shaft material can meet lower requirements.

According to a second variant, the cross-sectional contour of the longitudinal groove in the passage of the sliding cam package may have a trapezoidal shape, so that two opposite contact areas are also formed for the contact of the needle bearing element. As an alternative to the dome shape so that the cross section of the longitudinal groove in the passage of the sliding cam package can be performed according to a trapezoidal shape, and the direction of the load attack can thus also be selectively changed. The shape can be reproduced more easily in terms of manufacturing technology than the dome shape and the influence of the manufacturing tolerances on the resulting load direction is lower. The trapezoidal shape has two obliquely arranged trapezoidal flanks, which are connected by a trapezoidal base. Although the maximum occurring Hertzian pressure between the longitudinal groove in the passage of the sliding cam package and the needle bearing elements increase, as instead of a cylinder-cylinder mating a cylinder-level pairing arises, but it can also be avoided with this contact surface pairing sufficiently large stress peaks in the material of the sliding cam package especially as there is line contact.

Advantageously, the longitudinal groove in the outer side of the fundamental shaft can be formed axially parallel to the extension of the fundamental shaft and / or one and preferably at least two needle bearing elements can be accommodated in a longitudinal groove. A plurality of longitudinal grooves can be provided on the circumference of the basic shaft, distributed equally or unequally, for example two, preferably three and particularly preferably four or more than four longitudinal grooves. A preferably corresponding number of longitudinal grooves can be provided in the passage of the sliding cam package.

If at least two needle bearing elements are accommodated in a longitudinal groove, jamming of the sliding cam package on the fundamental shaft can be avoided since the fundamental can experience a torsion which can lead to an axial clamping of the sliding cam package in the case of very long needle bearing elements. However, if two or, for example, more needle bearing elements are accommodated in a single longitudinal groove, then the individual needle bearing elements are correspondingly shorter and the risk of an axial jamming of the sliding cam package on the fundamental shaft is minimized. Consequently, even with a stronger torsion of the fundamental wave, a shift of the sliding cam package take place.

A spacer element may be present between two needle bearing elements accommodated in a longitudinal groove, wherein the spacer element may in particular be designed as a sheet metal element which at least partially surrounds the fundamental shaft, wherein the spacer element may also comprise a plastic material or another material. The sheet metal element may have a width corresponding to a substantial part of the length of the sliding cam package, and a wide spacer element causes, for example, two needle bearing elements are received in a longitudinal groove only in the outer regions of the sliding cam package.

With particular advantage, the fundamental wave can be formed from a tubular body. A hollow base shaft has a low weight, and since by the inventively designed means a spline can be omitted, and no nuts must be included in the fundamental wave, The wall of the hollow running basic wave can be made thin. This saves further weight of the camshaft.

With further advantage, the outer diameter of the fundamental shaft with the diameter of the passage in the sliding cam package form a fit, so that a substantially play-free sliding fit of the sliding cam package is formed on the fundamental shaft. The advantage over a sliding toothing arises in the simple manufacturability of the sliding seat of the sliding cam package on the basic shaft, and the fundamental wave must be adjusted in diameter only the diameter of the passage in the sliding cam package. For example, a minimum excess of the diameter of the passage relative to the outer diameter of the fundamental wave can be generated in order to achieve a blockade-free displacement of the sliding cam package on the fundamental, which can still work when a heat distortion occurs. On the other hand, optimum guidance of a tapping element over the cam profiles of the sliding cam package is achieved by minimizing or avoiding radial bearing play of the sliding cam package on the fundamental shaft, which protects the valve train of the internal combustion engine. In particular, no oil can foam in the oil volume of the hydraulic valve clearance compensation elements of the valve train, which serve for the play-free guidance of the pick-off elements on the cam profiles.

Finally, for further improvements of the camshaft according to the invention still retaining rings may be provided which are arranged on at least one and preferably on both end sides of the sliding cam package, so that the needle bearing elements are secured axially in the longitudinal grooves by the retaining rings. The needle bearing elements are consequently fixed in the axial direction in the longitudinal groove on the inside by the spacer element and on the outside by the retaining rings. The retaining rings can be introduced into provided circumferential grooves in the end sides of the sliding cam package, for example non-positively, positively, force-positively or cohesively. For example, the retaining rings can be soldered or welded to the side surfaces of the sliding cam package, in particular by electron beam welding, by laser welding or by a Friction welding. Alternatively, the retaining rings can also be arranged by a screw or adhesive connection on the side surfaces of the sliding cam package. The circlips have an inner diameter that is slightly larger than the outer diameter of the fundamental.

The inventive design of the camshaft with further advantage results in a simple assembly of the sliding cam packages on the fundamental shaft. First, the spacer element in the form of a spring plate and the needle bearing elements in the passage of the sliding cam element can be joined, and with the needle roller elements used in the longitudinal grooves in the passage of the sliding cam package this can be pushed onto the basic shaft. The needle bearing elements also engage in the longitudinal grooves in the outside of the fundamental shaft. Finally, the retaining rings can be attached to the end sides of the sliding cam package. Thus, a simple, cost-effective production of the camshaft is achieved and it can be generated on the fundamental shaft, a very good radial centering of the sliding cam packages. In particular, short needle bearing elements can be used, and the fundamental wave can be made hollow.

PREFERRED EMBODIMENT OF THE INVENTION

Figur 1

eine perspektivische Ansicht einer Nockenwelle mit einer Grundwelle und einem aufgebrochenen Schiebenockenpaket, wobei erfindungsgemäße Mittel zur Übertragung eines Drehmomentes zwischen dem Schiebenockenpaket und der Grundwelle gezeigt sind,

Figur 2

eine perspektivische, aufgeschnittene Ansicht eines Schiebenockenpaketes mit eingesetzten Nadellagerelementen und mit einem Distanzelement in Form eines Bleches,

Figur 3

eine quergeschnittene Ansicht eines zylindrischen Nadellagerelementes, das mit einem ersten Teil in einer Längsnut im Durchgang des Schiebenockenpaketes und mit einem zweiten Teil in einer Längsnut in der Außenseite der Grundwelle einsitzt und

Figur 4

eine Querschnittsansicht eines Nadellagerelementes, wobei in Abwandlung des Ausführungsbeispiels gemäß Figur 3 die Längsnut im Durchgang des Schiebenockenelementes eine Trapezform aufweist.

Further, the compound improving measures will be described in more detail below together with the description of a preferred embodiment of the invention with reference to FIGS. It shows:

FIG. 1

a perspective view of a camshaft having a basic shaft and a broken sliding cam package, wherein means according to the invention for transmitting a torque between the sliding cam package and the fundamental are shown,

FIG. 2

a perspective, cutaway view of a sliding cam package with inserted needle bearing elements and with a spacer element in the form of a sheet,

FIG. 3

a cross-sectional view of a cylindrical needle bearing element which is seated with a first part in a longitudinal groove in the passage of the sliding cam package and with a second part in a longitudinal groove in the outside of the fundamental shaft and

FIG. 4

a cross-sectional view of a needle bearing element, wherein in a modification of the embodiment according to FIG. 3 the longitudinal groove has a trapezoidal shape in the passage of the sliding cam element.

FIG. 1 shows a perspective view of a camshaft 1 with a basic shaft 10 shown in sections, and on the basic shaft 10 is an example of a sliding cam package 11 is added, which is shown in a half-section and axially slidably seated on the fundamental shaft 10.

The sliding cam package 11 can be moved back and forth on the basic shaft 10 in the axial direction, and the sliding cam package 11 has a plurality of mutually different cam profiles 12 which, depending on the adjusted axial position on the basic shaft 10, pass on different lifting information to a picking element.

For transmitting torque between the basic shaft 10 and the sliding cam package 11 are used means 14, and the means 14 comprise according to the invention elongated needle bearing elements 15th

In synopsis with FIG. 2 It is shown that in the passage 13 of the sliding cam package 11, through which the fundamental shaft 10 extends, longitudinal grooves 16 are introduced. The longitudinal grooves 16 are distributed over the circumference at equal distances from each other and extend with constant cross section in the axial direction in the inner wall of the passage 13. The longitudinal grooves 16 correspond with their number and with their position with longitudinal grooves 17 in the outer side of the fundamental 10 are introduced.

The needle bearing elements 15 are seated with a first part of their circular cross section in the longitudinal grooves 16 in the passage 13 of the sliding cam package 11 and with a second part of the same circular cross section sit in the longitudinal grooves 17 in the outside of the fundamental shaft 10, wherein the parts of the circular cross section of the needle bearing elements 15 preferably each half in the longitudinal grooves 16, 17 are seated.

In a respective longitudinal groove 16, 17, two needle elements 15 are seated, which are held at a distance from each other via a spacer element 18 designed as sheet metal elements. The spacer element 18 encloses the fundamental shaft 10 substantially completely and is seated in a correspondingly rotated centrally arranged recess in the passage 13 of the sliding cam package 11. As a result, the needle bearing elements 15, which each sit laterally to the spacer element 18 in the longitudinal grooves 16, 17, are held at a distance from each other.

The needle bearing elements 15 are prevented from axially slipping out of the longitudinal grooves 16, 17 by securing rings 19 on the side surfaces of the sliding cam package 11, by which the needle bearing elements 15 are secured axially.

The exemplary embodiment shows a hollow basic shaft 10, wherein the camshaft 1 can be mounted via the basic shaft 10 in a receiving body, for example in a hood module or in a cylinder head.

FIG. 3 shows a first embodiment for receiving a needle bearing element 15 in the longitudinal grooves 16 and 17, wherein the longitudinal groove 16 is inserted in the passage 13 of the sliding cam package 11 and the longitudinal groove 17 is introduced into the outside of the fundamental shaft 10. The illustration shows the needle bearing element 15, which is half seated in the longitudinal groove 17, wherein the longitudinal groove 17 has a contour with a radius which corresponds approximately to the radius of the cylindrical needle bearing element 15. Deviating from the radius of the needle bearing element 15, the longitudinal groove 16 has two radii and through the two radii are defined two areas for the introduction of a contact force F, and in the areas touched the needle bearing element 15, the surface in the longitudinal groove 16. The slight deviation from the radius of the needle bearing element 15 prevents the Längsnutkanten 22 form highly stressed areas, as the Contact force F on the larger areas spaced from the Längsnutkanten 22 is distributed.

FIG. 4 shows in a modification of the embodiment FIG. 3 a longitudinal groove 16 in the passage 13 of the sliding cam package 11 with a trapezoidal shape, while, as in connection with FIG. 3 already described, the longitudinal groove 17 in the outer side of the fundamental shaft 10 has a radius corresponding to the radius of the cylindrical needle bearing element 15. The trapezoidal longitudinal groove 16 has two obliquely arranged, opposite trapezoidal flanks 20, and as a groove bottom extends between the trapezoidal flanks 20 a trapezoidal base side 21st

The contact areas between the needle bearing element 15 and the longitudinal groove 16 formed on the trapezoidal flanks 20, as indicated by the two contact forces F. Even by a trapezoidally shaped longitudinal groove 16 highly stressed areas are avoided at the Längsnutkanten 22.

The invention is not limited in its execution to the above-mentioned, preferred embodiments. Rather, a number of variants is conceivable, which makes use of the illustrated solution even with fundamentally different types of use. All of the claims, the description or the drawings resulting features and / or advantages, including constructive details or spatial arrangement, can be essential to the invention both in itself and in various combinations.

LIST OF REFERENCE NUMBERS

1

camshaft

10

fundamental wave

11

Sliding cam package

12

cam profile

13

passage

14

medium

15

Needle bearing element

16

longitudinal groove

17

longitudinal groove

18

spacer

19

circlip

20

trapezoid side

21

Trapezoid base side

22

Längsnutkante

F

contact force

Claims (9)

1. Camshaft (1) for the valve train of an internal combustion engine having a basic shaft (10) and having at least one sliding cam pack (11) comprising a plurality of cam profiles (12), the basic shaft (10) extending through a passage (13) in the sliding cam pack (11), with the result that the latter is received on the basic shaft (10) such that it can be displaced axially, and means (14) for forming a torque-transmitting connection between the basic shaft (10) and the sliding cam pack (11) being provided, the means (14) comprising needle bearing elements (15) of elongate configuration which are seated with a first part of their circular cross section in a longitudinal groove (16) in the passage (13) of the sliding cam pack (11) and which are seated with a second part of the same cross section in a longitudinal groove (17) in the outer side of the basic shaft (10), characterized in that the longitudinal groove (16) in the passage (13) of the sliding cam pack (11) has a cross-sectional contour which differs from a circular arc.
2. Camshaft (1) according to Claim 1, characterized in that the longitudinal groove (17) has a semi-circular cross section in the outer side of the basic shaft (10), which semi-circular cross section corresponds with the circular cross section of the needle bearing elements (15) .
3. Camshaft (1) according to either of Claims 1 and 2, characterized in that the cross-sectional contour of the longitudinal groove (16) in the passage (13) of the sliding cam pack (11) is defined by way of two radii which are greater than the diameter of the needle bearing elements (15), with the result that two contact regions which lie opposite one another are formed for the contact of the needle bearing element (15).
4. Camshaft (1) according to either of Claims 1 and 2, characterized in that the cross-sectional contour of the longitudinal groove (16) in the passage (13) of the sliding cam pack (11) has a trapezoidal shape, with the result that two contact regions which lie opposite one another are formed for the contact of the needle bearing element (15).
5. Camshaft (1) according to one of the preceding claims, characterized in that the longitudinal groove (17) is configured in the outer side of the basic shaft (10) axially parallel to the extent of the basic shaft (10), and/or one and preferably at least two needle bearing elements (15) being received in a longitudinal groove (17).
6. Camshaft (1) according to one of the preceding claims, characterized in that there is a spacer element (18) between two needle bearing elements (15) which are received in a longitudinal groove (17), the spacer element (18) being configured, in particular, as a sheet metal element which encloses the basic shaft (10) at least partially.
7. Camshaft (1) according to one of the preceding claims, characterized in that the basic shaft (10) is formed from a tubular body.
8. Camshaft (1) according to one of the preceding claims, characterized in that the external diameter of the basic shaft (10) forms, with the diameter of the passage (13) in the sliding cam pack (11), a fit size with respect to one another, with the result that a substantially play-free sliding fit of the sliding cam pack (11) on the basic shaft (10) is formed.
9. Camshaft (1) according to one of the preceding claims, characterized in that locking rings (19) are provided which are arranged on at least one and preferably on the two end sides of the sliding cam pack (11), with the result that the needle bearing elements (15) are secured axially.

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