CONCENTRIC CAMSHAFT AXIAL POSITION CONTROL

Abstract

 A concentric camshaft for an internal combustion engine is disclosed that comprises an outer tube (12), an inner shaft (24), and two groups of cam lobes (14;22). The first group (14) is fixed for rotation with the outer tube (12) and the second group (22) is rotatably mounted on the outer tube (12) and connected for rotation with the inner shaft (24). One or more bearing rings (16,17) are mounted to the outer tube (12) providing a bearing surface for supporting the camshaft in the engine, a bearing ring (16) secured to an axial end of the outer tube (12) serving to apply drive torque to the outer tube (12). In the invention, a sleeve (30) is secured to the outer surface of the inner shaft (24) for setting the axial position of the inner shaft (24) relative to the outer tube (12), the axial length of the sleeve (30) serving to limit the axial movement of the inner shaft (24) relative to the outer tube (12); a first axial end face of the sleeve (30) serving to limit the movement of the inner shaft (24) in one axial direction, and a second axial end face of the sleeve (30) serving to limit movement of the inner shaft (24) in the opposite axial direction.

Description

FIELD OF THE INVENTION

[0001] The invention relates to a valvetrain system for an internal combustion engine, and in particular to an adjustable camshaft, known as a concentric camshaft, having two groups of cam lobes which can be phased relative to each other. When combined with a phasing system, the concentric camshaft allows the phase of one or both of the groups of lobes to be controlled independently relative to the phase of the engine crankshaft. In a single camshaft engine, for example, this could allow independent control of intake and/or exhaust valve timing.

BACKGROUND

[0002] Concentric camshafts that allow the relative timing of two sets of cam lobes to be adjusted are well known. Typically, concentric camshafts comprise an outer tube having a first set of cam lobes affixed to its outer diameter and a second set of cam lobes mounted for rotation on the outer surface of the tube. Each of the second set of cam lobes is connected via a connecting pin for rotation with an inner shaft passing through the bore of the tube. The connecting pins pass with clearance through slots in the wall of the outer tube, so as to allow rotation of the second set of cam lobes through a limited angle when the inner shaft is rotated relative to the outer tube.

[0003] In many applications, the axial location of the inner shaft with respect to the outer tube of the concentric camshaft is determined by their respective drive connections to the camshaft phaser. In such cases, no provision is made in the design of the concentric camshaft for providing an axial bearing to set the relative position of the inner shaft with respect to the outer tube.

[0004] Some designs of phasing system, however, utilise form fitting drive interfaces such as splines, driving keys or pins in the torque transmission path from the input drive to one or both sets of camshaft lobes mounted to the concentric camshaft. In these cases, it is not convenient to use the phasing system to define the axial location of the inner shaft with respect to the outer tube. It can therefore be advantageous to incorporate an axial bearing into the concentric camshaft to set the position of the inner shaft with respect to the outer tube.

[0005] The closest prior art to the invention is believed to be EP1725745, which shows a concentric camshaft having a method of maintaining both the concentricity and the axial position of an inner shaft to an outer tube using two components fitted to opposing ends of the inner shaft.

SUMMARY OF THE INVENTION

[0006] In accordance with a first aspect of the invention, there is provided a concentric camshaft as hereinafter set forth in Claim 1 of the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] The invention will now be described further, by way of example, with reference to the accompanying drawings, in which:

Figure 1A is a perspective view of a concentric camshaft connected to a camshaft phaser,

Figure 1B is a section of the camshaft and phaser of Figure 1A,

Figure 1C is a view of the end of the camshaft of Figure 1B drawn to an enlarged scale,

Figures 2A and 2B are perspective views of an inner shaft and a sleeve depicting alternative ways of providing a high friction surface,

Figure 3 is a section, similar to that of Figure 1C, of a second embodiment of a concentric camshaft connected to a drive sprocket,

Figure 4 is a similar section of a third embodiment of a concentric camshaft connected to a camshaft phaser,

Figure 5 is a perspective view of the inner shaft and the sleeve of the third embodiment,

Figure 6A is a section view of the inner shaft and the sleeve of a further embodiment,

Figure 6B is a perspective view of the embodiment of Figure 6A.

DETAILED DESCRIPTION OF THE DRAWINGS

[0008] Figures 1A, 1B and 1C illustrate the construction of a concentric camshaft 10 in a first embodiment, having an outer tube 12 with a first set of cam lobes 14 non-rotatably fitted to its outer surface together with additional bearing rings 16, 17 that support the camshaft 10 in the engine (not shown). Drive torque is transmitted to the outer tube 12 by a camshaft phaser 18 secured via four bolts 20 to the first bearing ring 16 secured to the end of the outer tube 12. A second set of cam lobes 22 mounted to the outer tube 12 are free to rotate about the outer tube 12, and are connected to an inner shaft 24 via connecting pins 26 that pass through arcuate slots in the outer tube 12, such that the second set of cam lobes 22 are able to rotate relative to the first set 14 through an angular range defined by the circumferential length of the slots.

[0009] The phaser 18, the internal construction of which is well known and therefore not shown in detail in the drawings, may for example be a hydraulic phaser having a stator driven by the engine crankshaft and two output driving connections of which at least one is rotated with a phase that is adjustable relative to the phase of the stator.

[0010] In the first embodiment, the drive connection between the camshaft phaser 18 and the inner shaft 24 is via a splined interface 28 and so the drive connection itself is unable to set the axial position of the inner shaft 24. A sleeve 30 is secured to the outer surface of the inner shaft 24 to control its axial position, the sleeve 30 being positioned inside the first bearing ring 16 with a clearance around its outer surface, its axial location being defined by the axial end face of the outer tube 12 and the adjacent face of the camshaft phaser 18. The axial clearance of the sleeve 30 is defined by the length of the sleeve 30 and the assembled distance of the outer tube 12 from the end face of the first bearing ring 16 against which the camshaft phaser 18 is secured.

[0011] A plug 32 is fitted the opposite end of the bore of the outer tube 12 from the camshaft phaser 18 in order to define a closed volume between the inner shaft 24 and the outer tube 12 that can be used to provide oil, either for lubrication of the camshaft 10 and phaser 18, or for actuating the camshaft phaser 18. Oil can be supplied to this cavity from the camshaft bearings of the engine via drillings in one or more of the bearing rings 17. Oil pressure in the cavity will exert an axial force on the inner shaft 24 in the direction of the camshaft phaser 18, hence generating an axial force between the sleeve 30 mounted to the inner shaft 24 and its mating face on the camshaft phaser 18. Thus, the sleeve 30 also acts as a seal to prevent leakage of oil from the cavity between the inner shaft 24 and outer tube 12.

[0012] To increase the axial load capacity in the joint between the inner shaft 24 and the sleeve 30, a high friction surface texture can be used rather than a high interference fit. A high friction texture 34 could be applied to either the outer surface of the inner shaft 24, as depicted in Figure 2A, or could be applied to the bore of the sleeve 30 prior to assembly, as designated 35 in Figure 2B.

[0013] A second embodiment of the invention is shown in Figure 3. The second embodiment is identical in function to the first, however a sealing ring 136 is used to retain oil in the cavity between the outer tube 112 and the inner shaft 124, the seal 136 being located between the end face of the outer tube 112 and the adjacent end face of the sleeve 130 fitted to the inner shaft 124. Instead of a phaser 18, a drive sprocket 138 may be fitted to the first bearing 116. In this case, a phasing system (not shown) to control the phasing of the inner shaft 124 relative to the tube 112 could be fitted to the opposite end of the camshaft 110. The additional seal 136 of the second embodiment could, however, equally be used with the phasing system location of the first embodiment.

[0014] The sealing ring 136 also acts to define the axial position of the inner shaft 124 if it is forced in the direction away from the input drive sprocket 138.

[0015] In a third embodiment of the invention, shown in Figure 4, the drive connection between a first output of the camshaft phaser 218 and the outer tube 212 is via a splined interface 220 between the phaser 218 and the first bearing ring 216, whilst a second output of the phaser 218 is connected to the inner shaft 224 via a bolt 235. As in other embodiments, the connections to the cam phaser 218 are unable to set the relative axial positions of the inner shaft 224 and the outer tube 212. The sleeve 230 is secured to the outer surface of the inner shaft 224 to control its axial position, which in this case is defined by the end face of the outer tube 212 and an additional retaining ring 238 pressed into the bore of the first bearing ring 216. Whilst in principle the same result could be achieved by using a stepped bore in the first bearing ring 216, it would hinder assembly of the first bearing ring 216 to the outer tube 212 to the correct axial position when the inner shaft 224 is already in place.

[0016] The inner shaft 224 has a uniform outer diameter in the region of the sleeve 230, and the inner shaft 224 passes completely through the sleeve 230 such that the fixed connection to the sleeve 230 and the concentric location between the inner shaft 224 and the phasing system 218 can utilise predominantly the same shaft diameter.

[0017] The third embodiment also illustrates how the outer surface of the sleeve 230 can be used to provide a bearing surface to maintain concentricity between the inner shaft 224 and the first bearing ring 216. Figures 4 and 5 illustrate the sleeve 230 with an exaggerated outer profile form 237 to avoid any jamming of the shaft in the case where there is a slight misalignment of the sleeve 230 in the first bearing ring 216. The use of the sleeve 230 as a support bearing would equally be possible in the previous embodiments.

[0018] Figure 5 additionally illustrates a method of transmitting oil past the sleeve 230 to lubricate the phaser 218 or to provide actuation pressure. In this case, the sleeve 230 has a profiled inner surface that defines oil passages when the sleeve is fitted to the inner shaft 224. Figures 6A and 6B show that a similar result could also be achieved in the first embodiment by allowing the splines of the inner shaft 24 to pass under the sleeve 30.

Claims

1. A concentric camshaft for an internal combustion engine comprising:

an outer tube (12);

an inner shaft (24);

two groups of cam lobes (14;22), the first group (14) being fixed for rotation with the outer tube (12) and the second group (22) being rotatably mounted on the outer tube (12) and connected for rotation with the inner shaft (24); and

one or more bearing rings (16,17) mounted to the outer tube (12) providing a bearing surface for supporting the camshaft in the engine, a bearing ring (16) secured to an axial end of the outer tube (12) serving to apply drive torque to the outer tube (12);

characterised in that

a sleeve (30) is secured to the outer surface of the inner shaft (24) for setting the axial position of the inner shaft (24) relative to the outer tube (12), the axial length of the sleeve (30) serving to limit the axial movement of the inner shaft (24) relative to the outer tube (12);

a first axial end face (31) of the sleeve (30) serving to limit the movement of the inner shaft (24) in one axial direction, and

a second axial end face (33) of the sleeve (30) serving to limit movement of the inner shaft (24) in the opposite axial direction.

2. A concentric camshaft according to claim 1, wherein the second axial end face of the sleeve (230) is located by a component (238) secured to the bearing ring (216) that drives the outer tube.

3. A concentric camshaft according to claim 2, wherein a drive sprocket (138) is mounted to the bearing ring (116) driving the outer tube (112) and serves to locate the second axial end face of the sleeve (130).

4. A concentric camshaft according to claim 2, wherein a phasing system (18; 218) is mounted to the bearing ring (16,216) driving the outer tube and serves to locate the second axial end face of the sleeve (30,230).

5. A concentric camshaft according to any preceding claim, wherein the sleeve (30) provides a sealing face to retain oil in the cavity between the inner shaft and the outer tube.

6. A concentric camshaft according to claim 5, wherein a sealing ring (136) is located between the first axial end face of the sleeve (130) and the end face of the outer tube (112) to retain oil in a cavity between the inner shaft and the outer tube.

7. A concentric camshaft according to any of claims 1 to 5, wherein the first axial end face of the sleeve (30) is located by the end face of the outer tube (12).

8. A concentric camshaft according to any of claims 1 to 4, wherein features are provided in the bore of the sleeve (30,230) and/or the outer surface of the inner shaft (24,224) to allow oil from a cavity between the inner shaft and the outer tube to pass from one side of the sleeve (30,230) to the other.

9. A concentric camshaft according to any preceding claim, wherein the outer surface of the sleeve (30) provides a bearing face to transmit radial force from the inner shaft (24) to the bearing ring (16) that drives the outer tube.

10. A concentric camshaft according to claim 9 , wherein the outer surface of the sleeve is profiled to compensate for small amounts of misalignment of the sleeve (30) within the bore of the bearing ring (16).

11. A concentric camshaft according to any preceding claim, wherein the inner shaft (24) has a constant outer diameter in the region where the sleeve (30) is mounted which region passes entirely through the sleeve (30) and provides a concentric location face for mounting a driving component (218) to the inner shaft (224).

12. A concentric camshaft according to any preceding claim, wherein a high friction surface (34,35) is provided between the inner shaft (24) of the camshaft and the sleeve (30).

Drawing