CAMSHAFT FOR THE VALVE DRIVE OF AN INTERNAL COMBUSTION ENGINE WITH A VARIABLE VALVE OPENING DURATION

Abstract

A camshaft for a valve drive of an internal combustion engine having a variable valve opening time may include an outer shaft and an inner shaft that extends through the outer shaft, with the inner shaft being held rotatably with respect to the outer shaft. The camshaft may further include a cam having a multiple-piece configuration, comprising a first part cam and a second part cam. Either the first part cam or the second part cam may be connected fixedly to the outer shaft so as to rotate with it, and the other part cam may be connected fixedly to the inner shaft so as to rotate with it. The camshaft may also include a bearing inner ring of a shaft bearing that is held on the outer shaft, with one of two second part cams comprising an axial attachment that forms at least one part of the bearing inner ring.

Claims

1.-5. (canceled)

6. A camshaft for a valve drive of an internal combustion engine having a variable valve opening time, the camshaft comprising: an outer shaft; an inner shaft that extends through the outer shaft, with the inner shaft being held rotatably with respect to the outer shaft; a cam having a multiple-piece configuration and comprising a first part cam and a second part cam, wherein either the first part cam or the second part cam is connected fixedly to the outer shaft so as to rotate with the outer shaft, wherein the part cam that is not connected fixedly to the outer shaft so as to rotate with the outer shaft is connected fixedly to the inner shaft so as to rotate with the inner shaft; and a bearing inner ring of a shaft bearing being held on the outer shaft, wherein the second part cam comprises an axial attachment that forms at least one part of the bearing inner ring.

7. The camshaft of claim 6 wherein the cam is a first cam, the camshaft further comprising a second cam that is adjacent to the first cam and comprises a first part cam and a second part cam, wherein the bearing inner ring has a multiple-piece configuration and a part of the bearing inner ring is configured by way of the second part cam of the second cam.

8. The camshaft of claim 7 wherein a gap is formed between the two second part cams, which together form the bearing inner ring, wherein the gap is oriented axially with a radial bore in the outer shaft.

9. The camshaft of claim 6 wherein the cam comprises the first part cam, the second part cam, and an additional second part cam, wherein the first part cam is arranged axially between the two second part cams, wherein one of the two second part cams forms the at least one part of the bearing inner ring.

10. The camshaft of claim 6 wherein the cam comprises the first part cam, the second part cam, and an additional second part cam, wherein the first part cam is a fixed part cam.

11. The camshaft of claim 6 wherein the cam comprises precisely one of the first part cam and precisely one of the second part cam, the first part cam being positioned axially next to the second part cam, wherein the second part cam forms the at least one part of the bearing inner ring.

12. The camshaft of claim 6 wherein the inner shaft can rotate 20-30 with respect to the outer shaft.

13. The camshaft of claim 6 wherein a relative rotational position between the inner and outer shafts controls an orientation of an outer contour of the first part cam with respect to an outer contour of the second part cam.

14. The camshaft of claim 6 wherein a cross section of the first part cam increases conically radially to an inside so as to form a shoulder.

15. The camshaft of claim 6 further comprising a bearing bush with one or more lubricant bores disposed between the inner and outer shafts.

Description

[0021] FIG. 1 shows details of a camshaft 1 according to the invention for an internal combustion engine in cross section. The camshaft 1 comprises a hollow outer shaft 2 and an inner shaft 3 which is arranged such that it is mounted concentrically within the outer shaft 2 such that it can be rotated about a rotational angle of, in particular, at most 35, preferably from 20 to 30. The camshaft 1 comprises two cams 6, 6 which comprise a plurality of part cams 4, 5 which can be rotated with respect to one another. Here, the first part cam 4 is connected fixedly to the inner shaft 4 so as to rotate with it and is arranged rotatably on the outer shaft 2, whereas the second part cams 5 are held on the outer shaft 2 such that they are fixed against rotation and displacement. Here, the arrangement of the first part cam 4 such that it is fixed against rotation and displacement can be realized via conventional methods by means of a non-positive and/or a positively locking and/or integrally joined connection. The second part cam 5 is connected fixedly to the inner shaft 3 so as to rotate with it via a pin 12. Said pin 12 cannot be seen in the sectional illustration according to FIG. 1; it can still be seen in one of the following figures, however.

[0022] The two part cams 4, 5 can comprise outer contours which are identical or different from one another. The relative orientation of the outer contours of the two part cams 4, 5 with respect to one another can be set in a targeted manner using the relative rotational position between the inner shaft 3 and the outer shaft 2. If the radially elevated regions of the outer contours of the two part cams are superimposed on one another in the circumferential direction of the camshaft, the opening duration of the associated valve is reduced. If the radially elevated regions of the outer contours of the two part cams are arranged offset with respect to one another in the circumferential direction of the camshaft, the opening duration of the associated valve is increased.

[0023] The camshaft 1 is held in a housing (not shown) by means of a plain bearing 9. The plain bearing comprises a bearing outer ring 8 and a bearing inner ring 7 (multiple-piece in the case of FIG. 1).

[0024] FIG. 1 indicates a drag lever 13 using dashed lines. For interaction of the drag lever 13 with the cam 6, the drag lever always has to lie against the cam 6 on a predefined minimum contact length l.sub.1. (measured parallel to the camshaft axis A), in order to limit the surface pressure to a permissible maximum value. On account of the multiple-piece configuration of the cam, however, it is possible that the drag lever 13 is in contact with only one of the part cams 4, 5. FIG. 1 shows said operating state, only the first part cam 4 being in contact with the drag lever 13 here. The maximum permissible surface pressure may not be exceeded even in a case like this. As a result, both the first part cam and the second part cams 5 together have to have in each case a minimum length l.sub.1on the outer contour. Therefore, the multiple-piece cam 6 of a variable camshaft of this type requires fundamentally considerably more axial installation space than a single-piece cam. The dimension x in FIG. 1 shows the axial free travel between the cams.

[0025] It can be seen, furthermore, that the cross section of the first part cam 4 increases conically radially to the inside, that is to say forms a type of shoulder 16. This is necessary, since each part cam requires a minimum contact area on the outer shaft and/or a certain axial length for receiving the pin 12. As a result, the space requirement on the outer shaft for contact of the part cams is increased by each part cam. Thus, each part cam requires a certain connecting length l.sub.2 on the outer shaft 2, l.sub.2 in this case being greater than l.sub.1. Therefore, the regions of the outer part cams 5 which are in contact with the outer shaft 2 also migrate axially to the outside. In addition, the plain bearing requires a predefined plain bearing length l.sub.3.

[0026] According to the invention, one of the two second part cams 5 is then configured in one piece with the bearing inner ring 7 of the plain bearing 9. It can be seen in FIG. 1 that the regions of the required contact l.sub.2 of the part cam on the outer shaft 2 thus overlap with the length l.sub.3 of the plain bearing 9. This results according to the invention in a space-saving arrangement in the axial direction.

[0027] In one variant, the first part cam 4 can also be the fixed part cam instead of the second part cams 5. Then, the second part cams 5 are connected fixedly to the inner shaft 4 so as to rotate with it and are arranged rotatably on the outer shaft 2, whereas the first part cam 4 is connected to the outer shaft 2 fixedly against rotation and displacement. The camshaft is then mounted via one of the adjustable part cams 5.

[0028] Furthermore, a radial bore 10 is provided in the outer shaft 2, which radial bore 10 is oriented axially with a gap 11 which results between two part cams 5 or bearing inner ring parts 7 which are arranged adjacently. By way of the bore 10 and the gap 11, a lubricant channel is formed between the plain bearing 8 and the intermediate space, radially between the outer shaft 2 and the inner shaft 3.

[0029] FIG. 2 shows an alternative refinement which largely corresponds to the refinement according to FIG. 1. Therefore, only the differences will be discussed in the following text. The cams 6 comprise merely one second part cam 5. If, however, the drag lever 13 bears only against one of the two part cams 4, 5, tilting moments can act disadvantageously on the drag lever 13. Therefore, a refinement according to FIG. 1 is preferred, since the drag lever 13 is loaded by the cam 6 in a constantly centered manner there.

[0030] The second part cams 5 are connected fixedly to the outer shaft 2; the first part cams 4 are connected fixedly to the inner shaft 3 so as to rotate with it. For fixed connection of the inner shaft 3 to the corresponding part cam 4 so as to rotate with it, the above-addressed pin construction for fixed connection of one of the part cams to the inner shaft so as to rotate with it can be seen in FIG. 2. A pin 12 is guided in each case through a slot-shaped recess 14 which runs transversely with respect to the camshaft rotational axis A in the hollow outer shaft 2, and is connected fixedly to the inner shaft 3, in particular in a non-positive or positively locking manner. Furthermore, the pin 12 engages in a positively locking manner into that part cam which is connected fixedly to the inner shaft so as to rotate with it, in this case the part cam 4.

[0031] FIG. 3 shows an alternative refinement which corresponds largely to the refinement according to FIG. 2. Therefore, only the differences will be discussed in the following text. The first part cams 4 are connected fixedly to the outer shaft 2; the second part cams 5 are connected fixedly to the inner shaft 3 so as to rotate with it via in each case one pin 12 in the way which has been described above.

[0032] In the refinement of FIG. 3, a separate bearing bush 15 with one or more lubricant bores is provided radially between the inner shaft 3 and the outer shaft 2. A bearing bush 15 of this type can readily also be used in the refinements according to the other figures.

[0033] FIG. 4 shows an alternative refinement which corresponds largely to the refinement according to FIG. 2. The bearing inner ring 7 is formed firstly by a part cam 5, as is also the case in FIG. 1. Secondly, the inner ring is formed by a bearing ring 17 which is separate from the part cam 5 and is not a constituent part of a cam. The gap 11 is formed between the part cam 5 and the bearing ring 17.

[0034] FIG. 5 shows an alternative which is not claimed. Two single-piece cams 6, 6 are shown, which are always in interaction with in each case one drag lever 13, 13 in all operating states. The two cams 6 form parts of the bearing inner ring 7. The right-hand cam 6 is an adjustable cam which is connected fixedly to the inner shaft 3 so as to rotate with it by way of the pin 12, and is held rotatably with respect to the outer shaft 2. The left-hand cam 6 is a fixed cam which is connected fixedly to the outer shaft 2 so as to rotate with it.

[0035] FIG. 6 shows an alternative which is not claimed. Two single-piece cams 6, 6 are shown which are always in interaction with in each case one drag lever 13, 13 in all operating states. The right-hand cam 6 is an adjustable cam which is connected fixedly to the inner shaft 3 so as to rotate with it by way of the pin 12, and is held rotatably with respect to the outer shaft 2. Said cam completely forms the bearing inner ring 7. The left-hand cam 6 is a fixed cam which is connected fixedly to the outer shaft 2 so as to rotate with it and does not assume any function at all of the bearing 8.

[0036] A plain bearing has been shown exclusively as a bearing in the exemplary embodiments. The invention is likewise applicable in the case of anti-friction bearings. In the embodiments according to the invention in accordance with FIGS. 1 to 4, a part cam forms in each case only one part of the bearing inner ring. It is also possible, however, that a part cam completely forms the bearing inner ring.

LIST OF DESIGNATIONS

[0037] 1 Camshaft [0038] 2 Outer shaft [0039] 3 Inner shaft [0040] 4 First part cam [0041] 5 Second part cam [0042] 6 Cam [0043] 7 Bearing inner ring [0044] 8 Bearing outer ring [0045] 9 Plain bearing [0046] 10 Radial bore in the outer shaft [0047] 11 Gap in the bearing inner ring [0048] 12 Pin [0049] 13 Drag lever [0050] 14 Slot-shaped recess [0051] 15 Bearing sleeve [0052] 16 Shoulder [0053] 17 Bearing ring [0054] l.sub.1Contact length between drag lever and cam [0055] l.sub.2Connecting length between part cam and outer shaft [0056] l.sub.3Plain bearing length