WO2009098497A1

WO2009098497A1 - Oil feed arrangement for an scp camshaft

Info

Publication number: WO2009098497A1
Application number: PCT/GB2009/050079
Authority: WO
Inventors: Timothy Mark Lancefield; Owen Richard Alwyn
Original assignee: Mechadyne Plc
Priority date: 2008-02-05
Filing date: 2009-01-28
Publication date: 2009-08-13
Also published as: GB2457228A; GB0802006D0

Abstract

A camshaft is formed of an inner shaft (12), an outer tube (14) surrounding and rotatable relative to the inner shaft. Two groups of cam lobes (16, 18) are mounted on the outer tube. The cam lobes (16) of the first group being fast in rotation with the outer tube and the cam lobes (18) of the second group are rotatable relative to the outer tube (14) In the invention, one end of the camshaft (10) communicates with a cavity (31) in the engine to which a lubricant is supplied under pressure. The lubricant enters into the camshaft in an axial direction and serves to pressurise an annular passage between the inner shaft (12) and the outer tube (14) via which the lubricant is applied to the interface between the outer tube (14) and the cam lobes (18) of the second group.

Description

OIL FEED ARRANGEMENT FOR AN SCP CAMSHAFT

Field of the invention

This invention relates to a lubrication arrangement for a single cam phaser (SCP) camshaft.

Background of the invention

To enable the relative timing of valves to be adjusted in engines having a single camshaft, it has previously been proposed to use SCP camshafts. Such a camshaft is an assembly comprising an inner shaft, an outer tube surrounding and rotatable relative to the inner shaft, and two groups of cam lobes mounted on the outer tube. The first group of cam lobes is fast in rotation with the outer tube and the second group is rotatable relative to the outer tube and connected for rotation with the inner shaft by means of drive members passing through circumferentially elongated slots in the outer tube. By using a camshaft phaser to rotate the inner shaft relative to the outer tube, the relative phase of the valves operated by the different cam lobes can be adjusted.

Because the different components of an SCP camshaft can move relative to one another, they need to be lubricated. In particular, a lubricant needs to be applied to any interface between the inner shaft and the outer tube and to the interface between the outer tube and each of the cams lobes of the second group which rotates with the inner shaft.

Conventionally, the oil supply to lubricate the relatively movable components of an SCP camshaft is supplied via the camshaft bearings. The cylinder block or cylinder head into which the camshaft is mounted would normally have an oil supply to each bearing block, and this supply would be used to feed oil to the inside of the camshaft via a set of grooves and drillings in the camshaft bearings.

Figure 1 in the accompanying drawings is a section through the end of an SCP camshaft and the rear end of an engine block in which it is mounted showing a known design for lubricating the camshaft. The part of Figure 1 within the marked dotted square is shown to an enlarged scale in Figure Ia. Figure 2 is a perspective view showing the camshaft of Figure 1 separated from the inner shaft support bush and the end bearing.

Figures 1 and 2, show an SCP camshaft 10 having an inner shaft 12 and an outer tube 14. The outer tube is fast in rotation with some cam lobes, such as the cam lobe 16, while other cam lobes 18 can rotate on the outer tube 14 and are connected to the inner shaft 12 by drive pins 20. In the case of the SCP camshaft in Figures 1 and 2, the inner shaft 12 is supported in the outer tube 14 by means of support bushes 22 while the outer tube 14 is supported in bearing blocks in the engine by means of bearings 24.

It can be seen from Figures 1 and Ia that oil is supplied to the rear bearing 24 of the SCP camshaft 10 via a drilling 26 from a crankshaft bearing, and that any leakage from the rear bearing into a cavity 31 defined by the rear cover 28 may return to the sump via an oil drain passage 29.

It is seen in Figure 2 that the camshaft bearings 24 have a groove 30 in their outer surface to ensure a constant oil supply from the camshaft bearing feed 26. The oil is transferred to a second groove 32 in the bore of the bearing 24 via a pair of drillings 34. The inner groove 32 is necessary to ensure a constant oil supply to a further hole 36 through the camshaft outer tube 14, regardless of the angular alignment of the bearing 24 on the tube 14. In the case of the rear camshaft bearing 24, the oil hole 36 through the camshaft tube supplies oil to the bush 22 supporting the inner drive shaft 12. It can be seen from Figure 2 that there is a similar arrangement of grooves 38 and drillings 40 for the bush 22, which is assembled into the bore of the camshaft outer tube 14.

In the case of the intermediate camshaft bearings, the oil hole 36 through the camshaft outer tube 14 feeds oil into the clearance between the bore of the outer tube 14 and the inner drive shaft 12, and this lubricates the moving cam lobes 18 via connecting pin holes in the tube.

A disadvantage of this design is that the various grooves and drillings add a significant cost to the machining of the bearing 24 and the inner bush 22. Whilst some simplification of the design would be possible if the assembly angle of the bearings on to the camshaft tube could be guaranteed, this in itself would add significant complexity to the assembly operation.

Summary of the invention

According to the present invention, there is provided an engine having an assembled camshaft formed of an inner shaft, an outer tube surrounding and rotatable relative to the inner shaft, and two groups of cam lobes mounted on the outer tube, the cam lobes of the first group being fast in rotation with the outer tube and the cam lobes of the second group being rotatable relative to the outer tube and connected for rotation with the inner shaft by means of drive members passing through circumferentially elongated slots in the outer tube, characterised in that one end of the camshaft communicates with a cavity in the engine to which a lubricant is supplied under pressure, the lubricant entering into the camshaft in an axial direction and serving to pressurise an annular passage between the inner shaft and the outer tube via which the lubricant is applied to the interface between the outer tube and the cam lobes of the second group.

In the invention, lubricant enters axially into the end of the camshaft, thereby avoiding the need for grooves and drillings in the support bearings of the camshaft.

The invention utilises the fact that oil is already present inside the rear cover of the engine adjacent to the rear camshaft bearing in order to provide an oil supply to all the components of the SCP camshaft. This allows significant simplification of the SCP camshaft design and hence reduced manufacturing costs.

Brief description of the drawings

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

Figures 1, Ia and 2 are, as previously described, a section, an enlarged detail, and a perspective view of a known SCP camshaft, and

Figures 3 and 4 are sections similar to the detail of Figure Ia, showing two different embodiments of the invention .

Detailed description of the preferred embodiment (s)

To avoid repetition, components that have already been described have been allocated the same reference numerals and the ensuing description will concentrate on the modifications that have been made in order to implement the invention . The first embodiment of the invention is shown in Figure 3. From a comparison of this drawing with Figure Ia, it will be seen that the camshaft bearings 24 are of a much simpler design, having no oil grooves 30 nor drillings 34. The drive shaft support bush 22 is also simplified and requires no grooves 38 nor drillings 40. There is instead an additional drilling 26a branching from the drilling 26 that supplies oil to the camshaft bearing 24 from the crankshaft. This additional drilling 26a supplies oil into the cavity 31 enclosed by the rear cover 28 from the oil. In place of the additional drilling 26a, it may be sufficient to rely on oil leakage from the rear bearing, more particularly because camshaft bearings on some engines can be designed with large clearances .

The oil passes from the rear cover cavity 31 through an axial bore 12a in the inner drive shaft 12 and feeds oil both to the rear support bush 22 through a drilling 12b, and through a cross bore 12c to the narrow annular passage between the outer tube 14 and the inner shaft 12. Oil flowing through this latter passage then lubricates all of the parts of the SCP camshaft assembly.

In order to prevent the possibility of any oil leaks from the rear cover 28, or excessive axial force on the camshaft thrust bearing, it is advantageous to include a pressure relief mechanism 42 that will vent oil back to the sump should the oil pressure rise above a predetermined level. Alternatively, a vent hole (not shown) may be added formed in the outer tube 14 at some point along its length, preferably towards the front. So long as the vent hole diameter is below that of the oil feed, some oil pressure will be maintained inside the camshaft, but the vent will reduce the pressure some way below the supply pressure.

The second embodiment, shown in Figure 4, uses a different design of SCP camshaft that does not require support bushes to locate the inner shaft within the outer tube. Instead, the drive pins 20 of different cam lobes of the second group are arranged in different planes to centre the inner shaft 12 within the outer tube. An example of such a camshaft design is described in WO2007/052075.

This design of camshaft allows a further simplification of the design because, in the absence of any support bushes 22 to obstruct the oil flow, the oil in the rear cover cavity 31 will feed directly into the annular passage between the inner shaft and the outer tube of the camshaft.

Claims

1. An engine having an assembled camshaft formed of an inner shaft, an outer tube surrounding and rotatable relative to the inner shaft, and two groups of cam lobes mounted on the outer tube, the cam lobes of the first group being fast in rotation with the outer tube and the cam lobes of the second group being rotatable relative to the outer tube and connected for rotation with the inner shaft by means of drive members passing through circumferentially elongated slots in the outer tube, characterised in that one end of the camshaft communicates with a cavity in the engine to which a lubricant is supplied under pressure, the lubricant entering into the camshaft in an axial direction and serving to pressurise an annular passage between the inner shaft and the outer tube via which the lubricant is applied to the interface between the outer tube and the cam lobes of the second group.

2. An engine as claimed in claim 1, wherein the camshaft is connected at its front end to a phaser operative to drive the inner shaft and the outer tube of the camshaft in synchronism with rotation of a crankshaft of the engine, and wherein a removable cover mounted on the engine to enclose the rear end of the camshaft defines the cavity supplying lubricant under pressure to the camshaft.

3. An engine as claimed in claim 1 or 2, wherein means are provided for limiting the pressure of the lubricant in the cavity.

4. An engine as claimed in any preceding claim, wherein the inner shaft is supported in the outer tube by means of support bushes and lubricant is supplied to the annular passage between the inner shaft and the outer tube of the camshaft by way of an axial drilling formed in the end of the inner shaft.

5. An engine as claimed in claim 4, wherein the axial drilling communicates with a radial drilling in the inner shaft serving to lubricate one of the support bushes.

6. An engine as claimed in any one of claims 1 to 3, wherein the axis of the inner shaft is held in position relative to that of the outer tube by the drive members connecting the inner shaft to the cam lobes of the second group, and lubricant from the pressurised cavity enters directly into the annular passage between the inner shaft and the outer tube.

7. An engine as claimed in any preceding claim wherein the outer tube of the camshaft is provided with a bleed hole at the end of the annular passage remote from the pressurised cavity to ensure a constant flow of lubricant and to limit the pressure of the lubricant supply.