DE102013010330B4 - Camshaft and method for assembling such a camshaft - Google Patents

Abstract

Camshaft (14, 16) with a base shaft (22) and a sleeve which can be moved axially on the base shaft (22), the sleeve being fixable in an axial position on the base shaft (22) by means of a locking device, the locking device comprising a locking element which is loaded by a spring element (36) and which is arranged in an opening in the base shaft (22) and engages in a locking recess (46) in the sleeve, characterized in that the sleeve has a mounting opening (32) which is dimensioned and arranged such that the spring element (36) and the locking element can be introduced through this into the opening in the base shaft (22).

Description

The invention relates to a camshaft for the valve train of an internal combustion engine, in particular a camshaft with a so-called sliding cam system. The invention also relates to a method for assembling such a camshaft.

Sliding cam systems are used to adapt the valve lift of one or more of the intake and/or exhaust valves to the respective operating state of the internal combustion engine by axially displacing a sleeve-shaped cam carrier having several cam contours on a base shaft of the camshaft.

A valve train with a sliding cam system is, for example, known from EN 10 2007 010 148 A1 known. The sliding cam system comprises a cam carrier as part of the camshaft, which is arranged on a base shaft of the camshaft in a rotationally fixed manner but can be moved in the axial direction. The cam carrier has two cam groups, each with two cams arranged next to one another (in the axial direction) with different cam contours.

The stroke of the valves assigned to these cam groups can be adjusted by moving the cam carrier into one of a total of three defined axial positions, whereby a contact element of a rocker arm, with which the valves are actuated, is brought into contact either with one of the two cams or with a "zero cam", which is essentially a section of the cam carrier that has no cam elevation. When the rocker arm comes into contact with one of the two cams, the respective valve is actuated with a stroke defined by the respective cam elevation and also dependent on the transmission ratio of the rocker arm. When the rocker arm comes into contact with the "zero cam", the stroke of the valve is zero in accordance with the missing cam elevation. Valve shutdown is therefore implemented via the "zero cam".

The individual cam carriers are adjusted in the axial direction of the camshaft using a link integrated into the cam carrier, which forms a Y-shaped groove running in the circumferential direction. This groove therefore has two diverging partial grooves in one section. The actual adjustment is achieved using an adjusting device that has a total of three extendable adjusting pins, one of which is extended and engages in a section of the groove depending on the respective position of the cam carrier on the base shaft and the desired adjusting device. If one of the adjusting pins engages in one of the diverging partial grooves, this leads to an axial displacement of the cam carrier on the base shaft as a result of the relative rotation of the link wheel to the pin.

The respective axial position of the cam carriers is ensured by a locking device which has a spring-loaded locking ball which engages in a corresponding recess of the cam carrier on the outside in the individual axial positions.

A functionally similar valve train with a sliding cam system is known from the EN 10 2011 011 803 A1 known. The sliding cam system there also includes a locking device with a spring-loaded locking ball for each cam carrier. There, however, the locking balls and their springs are arranged in through-holes in the base shaft and engage in the defined axial positions on the inside in recesses in the sleeve-shaped cam carriers.

A montage of the EN 10 2011 011 803 A1 known valve train is particularly difficult when the fixed, i.e. non-adjustable cams are connected to the base shaft by means of a press fit. The cam sleeves are heated and the base shaft cooled significantly (e.g. -180°C) and then joined by pushing the base shaft into the cam sleeves and the cam carriers of the sliding cam system and by adjusting the component temperatures. When the fixed cams are thermally joined to the base shaft in this way, the locking balls with their springs must already be inserted into the openings in the base shaft, where they also cool down significantly in a short time. Compressing the locking balls, as is necessary for pushing on the cam carriers, is then usually no longer possible without damaging the springs.

Furthermore, the EN 10 2011 000 511 A1 a camshaft with a sliding cam system is known, in which the axially movable and rotationally fixed mounting of a cam carrier on a base shaft of the camshaft is achieved by two sliding blocks, which are arranged in longitudinal grooves offset by 180° in both the base shaft and the sliding cam sleeve. In a through-opening connecting the two longitudinal grooves of the base shaft, a receiving sleeve is arranged, which accommodates a coil spring and a ball at each end. The coil spring loads the two balls against the inside of the two sliding blocks. The balls each engage in one of several recesses formed on the inside of the corresponding sliding block in order to To ensure that the cam carrier is fixed in defined axial positions on the base shaft. The sliding cam system is installed by sliding the cam carrier onto the base shaft with the sliding blocks pressed together and thus sunk into the longitudinal grooves of the base shaft.

A camshaft with a sliding cam system is still available from the EN 10 2011 109 256 A1 known. In this camshaft, the cam carrier is designed in several parts, with a connecting element being arranged between a base element on the one hand and cam elements and a switching gate on the other hand in order to connect these components to one another in a rotationally fixed manner. The connecting element is partially arranged in a holding opening in the base element. The connecting element forms locking recesses that interact with a locking element of a base camshaft in order to fix the cam carrier in one of several defined axial positions on the base camshaft.

Based on this prior art, the invention was based on the object of specifying an easy-to-assemble camshaft with a sliding cam system for the valve train of an internal combustion engine.

This object is achieved by a camshaft according to independent patent claim 1 and by a method for assembling such a camshaft according to patent claim 8. Advantageous embodiments of the camshaft according to the invention are the subject of the further patent claims and emerge from the following description of the invention.

A generic camshaft with a base shaft and (at least) one sleeve that can be moved axially on the base shaft, wherein the sleeve can be fixed in an axial position on the base shaft by means of (at least) one locking device, wherein the locking device comprises (at least) one locking element, in particular a locking ball, loaded by (at least) one spring element, which is arranged in an opening of the base shaft and engages in one of several locking recesses of the sleeve, is further developed according to the invention in that the sleeve has (at least) one assembly opening that is dimensioned and arranged such that the locking element and the spring element can be introduced into the opening of the base shaft through this.

The sleeve can in particular be a cam carrier or a part (in particular the part forming the sliding gate) of such a cam carrier of a sliding cam system. It can preferably be provided that the (part of the) cam carrier(s) is arranged on the base shaft in a rotationally fixed manner (but axially displaceable).

The locking element and the spring element can be inserted into the opening of the base shaft through the assembly opening during assembly of the camshaft. This can be done in particular after the sleeve (e.g. the cam carrier) has been pushed onto the base shaft. The locking element and the spring element, which are designed with regard to the sliding cam system according to the EN 10 2011 000 511 A1 This avoids the problem described when thermally joining the fixed cams. In addition, the assembly method is particularly suitable when space is limited.

In order to prevent the spring element and the locking ball from being lost through the mounting opening and to achieve a support of the spring element at the end facing away from the locking element, in a preferred embodiment of the camshaft according to the invention it can be provided that the spring element is supported on a holding element fastened in the opening of the base shaft.

The holding element can advantageously be designed in such a way that it can be inserted through the assembly opening into the opening of the base shaft. The holding element can thus be inserted at the same time as or subsequently to the insertion of the locking element and the spring element, which can be associated with easy assembly.

In particular, the holding element can be designed as an elastically deformable retaining ring or retaining disk, the outer circumference of which can be reduced in size and which can engage in a groove in the wall of the opening of the base shaft.

In a further preferred embodiment of the camshaft according to the invention, it can be provided that the base shaft has a receiving sleeve that forms the opening and is arranged in (at least) one receiving opening of a base body of the base shaft. Such a design of the base shaft can be particularly advantageous if the base body of the base shaft is tubular, which can have weight-related advantages. Hardening of the base shaft can advantageously be omitted. Only a small bore is required.

In such a camshaft, it can also preferably be provided that the spring element loads the receiving sleeve against a shoulder in the receiving opening (e.g. the bottom of the receiving opening). This easily creates a Losing the receiving sleeve from the receiving opening of the base body is avoided.

In particular, the receiving opening of the base body of the base shaft on the side on which the ball protrudes a little way from the base shaft under spring load in order to engage in the locking recess of the sleeve (e.g. the cam carrier) can have a diameter that is large enough for the receiving sleeve to be inserted into the receiving opening. On the opposite side, adjacent to the mounting opening in the sleeve, the receiving opening can, however, have a diameter that is smaller than the outer diameter of the receiving sleeve but larger than the diameter of the locking element and the spring element.

In particular, in order to avoid contamination of the locking device, it can further be provided that the mounting opening can be closed by means of a plug.

• 1: einen Ventiltrieb mit zwei erfindungsgemäßen Nockenwellen;
• 2: einen Längsschnitt durch einen Teil einer der Nockenwellen;
• 3: einen Schritt bei der Montage des Ventiltriebs;
• 4: einen nachfolgenden Schritt bei der Montage des Ventiltriebs;
• 5: eine erste alternative Ausgestaltung einer erfindungsgemäßen Nockenwelle; und
• 6: eine zweite alternative Ausgestaltung einer erfindungsgemäßen Nockenwelle.

The invention is explained in more detail below using an embodiment shown in the drawings. In the drawings,

• 1 : a valve train with two camshafts according to the invention;
• 2 : a longitudinal section through part of one of the camshafts;
• 3 : a step in the assembly of the valve train;
• 4 : a subsequent step in the assembly of the valve train;
• 5 : a first alternative embodiment of a camshaft according to the invention; and
• 6 : a second alternative embodiment of a camshaft according to the invention.

The Indian 1 The valve train of an internal combustion engine shown is arranged in a cylinder head housing 10 of a reciprocating piston internal combustion engine, not shown. The cylinder head housing 10 forms two bearing tunnels 12, in each of which a camshaft 14, 16 according to the invention is mounted. The two camshafts 14, 16 are driven by a crankshaft (not shown) of the internal combustion engine by means of a toothed belt, for which purpose a first of the camshafts 14 is connected to a drive wheel 18.

Each of the two camshafts 14, 16 comprises a base shaft 22, on which four individual cams 24 and two cam carriers 26 are arranged. The individual cams 24 are connected to the base shafts 22 in an axially and rotationally secured manner, while the sleeve-shaped cam carriers 26 are also mounted on the base shafts 22 in a rotationally secured manner but are axially displaceable within limits.

The individual cams 24 are fixed by means of press fits, while the cam carriers 26 are secured against rotation by means of longitudinal teeth on an inner surface of each of the cam carriers 26 in conjunction with a corresponding longitudinal toothing on the outer surface of each of the base shafts 22. The longitudinal toothing ensures that the cam carriers 26 can be displaced in the longitudinal direction of the camshafts 14, 16, whereby a stroke switch of the valves (not shown) of the internal combustion engine actuated by cams of the cam carriers 26 can be realized.

Each of the cam carriers 26 comprises two cam sections 28, each of which forms two cams arranged next to one another and having different cam contours.

By means of the camshafts 14, a two-stage valve lift circuit can be implemented for the valves of the internal combustion engine actuated by the cams of the cam carriers 26. This valve lift circuit is achieved by an axial displacement of the cam carriers 26, whereby an actuating element (not shown), such as a roller cam follower, which is assigned to a valve of the internal combustion engine, is brought into contact with one of the cams of each of the cam sections 28, whereby the valve is actuated according to the respective cam contour.

The displacement of each of the cam carriers 26 takes place via a link section 30, in whose otherwise cylindrical outer surface a V-shaped control groove is introduced. The link section 30 of each of the cam carriers 26 is assigned an actuator (not visible) connected to the cylinder head housing 10, which has two control pins (not visible) that can be individually controlled to engage in the control groove of the associated link section 30 as required and to displace the respective cam carrier 26 in one direction on the base shaft 22 as a result of the relative movement between the rotating link section 30 and the stationary control pin of the actuator. This creates two axial positions for each of the cam carriers 26.

By means of a locking device, the two axial positions of each cam carrier 26 can be secured against unintentional axial displacement.

Each of the locking devices comprises a locking element in the form of a locking ball 34 and a spring element 36, both of which are housed in a receiving sleeve 38 are arranged. The receiving sleeve 38 is arranged in two collinear (with respect to its longitudinal axis) aligned, i.e. overlapping receiving openings 40, 42 of a tubular base body 44 of the associated base shaft 22. In the assembled state, the locking ball 34 of each locking device engages in one of two locking recesses 46 that are formed on the inside of the associated cam carrier 26. The spring element 36 loading the locking ball 34 is supported on the side facing away from the locking ball 34 on a retaining disk 48. The retaining disk 48 is fixed in a retaining groove on the inside of the receiving sleeve 38.

The (first) receiving opening 40 on that side of the base body 44 of the base shaft 22 on which the locking ball 34 engages in the locking recesses 46 has (before mounting the receiving sleeve 38) a diameter that is slightly larger, equal to, or only slightly smaller than the outer diameter of the receiving sleeve 38. The second receiving opening 42 has a stepped diameter. A first section of the receiving opening adjacent to the inside of the base body 44 has a diameter that is (before mounting the receiving sleeve 38) slightly larger, equal to, or only slightly smaller than the outer diameter of the receiving sleeve 38. A second section of the second receiving opening 42 adjacent to the outside of the base body 44, on the other hand, has a diameter that is significantly smaller than the outer diameter of the receiving sleeve 38 and in particular corresponds to the inner diameter of the receiving sleeve 38. This forms an annular shoulder within the second receiving opening 42, on which the corresponding end of the receiving sleeve 38 is supported at the front, wherein it is guided in the first section of the second receiving opening 42. The preload of the spring element 36 causes the receiving sleeve 38 to be pressed against this shoulder. This reliably prevents the receiving sleeve 38 from being lost from the receiving openings 40, 42. In addition, the receiving sleeve 38 can also be clamped in the first receiving opening 40 and/or the first section of the second receiving opening 42 if the associated diameters are designed accordingly.

The locking ball 34, the spring element 36 and the retaining disk 48 are mounted - in this order - through a sufficiently large mounting opening 32 in the cam carrier 26 (cf. 3 and 4 ). The mounting opening 32 is aligned collinearly with the receiving openings 40, 42 and thus with the receiving sleeve 38. To insert the retaining disk 48, it must be deformed in such a way that its outer diameter, which in the unloaded state is larger than the inner diameter of the second section of the second receiving opening 42 and the receiving sleeve 38, is sufficiently reduced. For this purpose, the retaining disk is radially slit several times, forming spring tabs that can be elastically deflected. As soon as the retaining disk 48 in the receiving sleeve 38 reaches the retaining groove, the spring tabs engage in it and the retaining disk 48 is fixed within the receiving sleeve 38.

The 5 The camshaft 14, 16 according to the invention shown differs from that of the 2 to 4 in that the base shaft 22 is designed in the form of a solid shaft, whereby a receiving sleeve 38 can be dispensed with. The base shaft 22 itself forms a receiving opening 40 in which the locking ball 34, the spring element 36 and the retaining disk 48 are arranged, wherein the retaining disk 48 engages in a circumferential retaining groove in the wall of the receiving opening 40.

The 6 The camshaft 14, 16 according to the invention shown differs from that of the 2 to 4 in that the retaining disk 48 is integrated into the receiving sleeve 38, which thereby forms an H-shaped longitudinal section surface. To assemble this camshaft 14, 16, it can be provided that the locking ball 34 and the spring element 36 are first inserted into the corresponding section of the receiving sleeve 38 and the unit is then inserted into the base body 44 of the base shaft 22 via the assembly opening 32 in the cam carrier 26 and a sufficiently large second receiving opening 42. The receiving sleeve 38 can then be fixed in the base body 44, for example, via a press fit in the receiving openings 40, 42.

The inventive design of the camshafts 14, 16 enables an advantageous assembly of a valve train in the cylinder head housing 10 provided with one-piece bearing bridges 20 for the camshafts 14, 16 according to the 1 . For this purpose, the individual cams 24 and the cam supports 26 are positioned at the respective positions within the bearing tunnels 12 using holding devices and the base shafts 22 are pushed from one of the front sides of the cylinder head housing 10 through the bearing openings formed in the bearing bridges 20, the individual cams 24 and the cam supports 26. The base shafts 22 were previously cooled down considerably and, if necessary, the individual cams 24 were also heated in order to produce the intended press fit between these elements after a temperature adjustment. The spring elements 36, locking balls 34 and, if necessary, the receiving sleeves 38 and/or retaining disks are then 48 through the mounting openings 32 of the cam carrier 26. This takes place after the temperature of the base shafts 22 has reached a value which excludes damage to the spring elements 36 in particular during assembly as a result of strong cooling of the spring elements 36 by the base shafts 22 and subsequent deformation in the cold state.

List of reference symbols

10

Cylinder head housing

12

Storage tunnel

14

camshaft

16

camshaft

18

drive wheel

20

Bearing bridge

22

Fundamental wave

24

Single cam

26

Cam carrier

28

Cam section

30

Scenery section

32

Mounting opening

34

Locking ball

36

Spring element

38

Mounting sleeve

40

Receiving opening

42

Receiving opening

44

Base body

46

Recessed recess

48

Retaining disc

Claims (8)

Camshaft (14, 16) with a base shaft (22) and a sleeve which can be moved axially on the base shaft (22), the sleeve being fixable in an axial position on the base shaft (22) by means of a locking device, the locking device comprising a locking element which is loaded by a spring element (36) and which is arranged in an opening in the base shaft (22) and engages in a locking recess (46) in the sleeve, characterized in that the sleeve has a mounting opening (32) which is dimensioned and arranged in such a way that the spring element (36) and the locking element can be introduced through this into the opening in the base shaft (22). Camshaft (14, 16) according to Claim 1 , characterized in that the spring element (36) is supported on a holding element fastened in the opening of the base shaft (22). Camshaft (14, 16) according to Claim 2 , characterized in that the holding element is designed such that it can be introduced through the mounting opening (32) into the opening of the base shaft (22). Camshaft (14, 16) according to Claim 2 or 3 , characterized in that the holding element is designed as an elastically deformable retaining ring or retaining disk (48) which engages in a groove in the wall of the opening. Camshaft (14, 16) according to one of the preceding claims, characterized in that the base shaft (22) has a receiving sleeve (38) forming the opening, which is arranged in a receiving opening (40, 42) of a base body (44) of the base shaft (22). Camshaft (14, 16) according to Claim 5 , characterized in that the spring element (36) loads the receiving sleeve (38) against a shoulder in the receiving opening (42). Camshaft (14, 16) according to one of the preceding claims, characterized in that the mounting opening (32) can be closed by means of a plug. Method for assembling a camshaft (14, 16) according to one of the preceding claims, characterized in that the locking element and the spring element (36) are introduced through the assembly opening (32) of the sleeve into the opening of the base shaft (22).

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