GB2467334A

GB2467334A - Assembled camshaft for i.c. engines

Info

Publication number: GB2467334A
Application number: GB0901486A
Authority: GB
Inventors: Ian Methley; Timothy Mark Lancefield
Original assignee: Mechadyne PLC
Current assignee: Mechadyne PLC
Priority date: 2009-01-30
Filing date: 2009-01-30
Publication date: 2010-08-04
Also published as: GB201111184D0; GB2479292B; GB2479292A; GB0901486D0; WO2010086800A1

Abstract

An assembled camshaft, eg a single camshaft phaser (SCP) camshaft 50, for mounting on an engine cylinder head, comprising a cam lobe supporting shaft 52, one or more cam lobes 56 formed separately from the shaft 52 and fitted, eg shrink-fitted, to the shaft 52 for rotation therewith, and bearing surfaces on the shaft to enable the assembled camshaft to be rotatably supported by the engine cylinder head. One-piece plain bearing components, eg bearing bushes 60, are mounted on the bearing surfaces of the shaft 52 during assembly of the camshaft. The bushes 60 may be clamped by bearing caps (112, figs. 4A,4B). A pin (115, fig.4D) may protrude from a bearing cap 112a into a drilling (64) in a bearing bush 60 to prevent the bush from rotating. Alternatively, each bearing bush (260,260', figs. 5,6A,6B) is designed as a one-piece pillar block to be secured directly to the cylinder head by threaded fasteners. The bearing bushes (260,260') may be combined into a single ladder frame (310, figs. 7A,7B) which may help maintain the correct spacing and orientation of the cam lobes during assembly.

Description

Improvements in Assembled Camshafts

Field of the invention

The present invention relates to an assembled camshaft in which individual cam lobes are assembled onto the outside of a shaft or tube.

Background of the invention

The invention is particularly, though not exclusively, applicable to an SCP (single cam phaser) camshaft which comprises an outer tube with two groups of cam lobes assembled to its outer surface, the cam lobes of the first group being permanently fixed to the outer tube whilst those of the second group of cam lobes are free to rotate on the outside of the tube and are connected for rotation with a shaft mounted within the tube, to which they are connected by pins passing through circumferentially elongated slots in the outer tube. Such a camshaft allows the timing of its two groups of cam lobes to be varied in relation to one another by relative rotation of the outer tube and the inner shaft.

An assembled camshaft is conventionally mounted on a cylinder head using two-part pillar blocks. The lower half of each pillar block is cast as part of the cylinder head and the upper half is formed as a bearing cap that is held in position by means of two bolts. Bearing surfaces which are machined on the assembled camshaft are retained within the pillar blocks.

A difficulty arises when mounting an assembled camshaft on a cylinder head if the support bearings need to be located between the cylinders of the engine rather than on the centreline of the engine cylinder. The between-cylinders bearing location would typically be used for an SCP camshaft that forms part of a cam summation system for controlling valve lift and valve opening duration, an example of which is shown in EP 1417399 (or US 6,941,910). The cylinder head bolts are typically arranged between adjacent cylinders of the engine and when the camshaft bearings are also located between adjacent cylinders, the cylinder head design can be compromised by the need to position the cylinder head bolts beneath the camshaft bearings. In particular, a hole needs to be formed in the lower half of each pillar block to allow passage of a cylinder head bolt and such a hole would prevent the lower half of the pillar block from acting directly as a bearing surface.

summary of the invention

According to the present invention, there is provided an assembled camshaft for mounting on an engine cylinder head, comprising a cam lobe supporting shaft, one or more cam lobes formed separately from the shaft and fitted to the shaft for rotation therewith, and bearing surfaces on the shaft to enable the assembled camshaft to be rotatably supported by the engine cylinder head, characterised in that plain bearing components are mounted fitted over the bearing surfaces of the shaft during assembly of the camshaft.

In one embodiment of the present invention, bearing bushes incorporated into the assembled SCP camshaft are clamped in pillar blocks each formed from two separable halves.

In an alternative embodiment of the invention, the bearing bushes may be directly bolted to a flat surface on the cylinder head in order to support the camshaft, while dispensing with the need for pillar blocks.

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 1A is a plan view from above of a typical DOHC (dual overhead camshaft) cylinder head with the camshafts fitted, Figure lB is a plan view of the same cylinder head as in Figure 1A with the camshafts removed, Figure 2 is a perspective view of a valve train of the type described in EP 1417399, which requires the camshaft bearings to be located between cylinder centre lines, Figure 3 is a perspective view of an assembled SCP camshaft of the invention, Figure 3A is a perspective view of a bearing bush which forms part of the camshaft of Figure 3, Figure 4A is a plan view of a DOHC cylinder head with camshafts supported by bearings located between cylinder centre lines and overlying the cylinder head bolts, Figure 4B is a section in the plane A-A of Figure 4A, Figures 4C and 4D are details of Figure 4B drawn to an enlarged scale, Figure 5 is a perspective view of an assembled camshaft of a second embodiment of the invention, Figures 6A and 6B are longitudinal and transverse sections, respectively, of a cylinder head fitted with two camshafts as shown in Figure 5, Figure 7A shows a one-piece ladder frame composed of ten bearing supports, Figure 7B shows a single unit comprising two assembled camshafts using the ladder frame of Figure 7A, and Figure 8A is a perspective view from beneath of a ladder frame, similar to that of Figure 7A integrated into an engine cover, Figure 8B is a view similar to that of Figure 8A with two assembled camshafts in place, Figure BC is a plan view from above of the cover of Figures BA and 8B, and Figure 8D is a section on the line A-A in Figure BC.

Detailed description of the preferred embodiment(s) Figure 1A shows a typical design for a DOHC cylinder head 10 with the camshaft bearing journals 12 positioned on the cylinder centrelines between each pair of cam lobes 14.

Figure lB shows the same cylinder head 10 with the camshafts 18 removed in order to show clearly the position of the cylinder head bolts 16 that are located between the engine cylinders.

Figure 2 shows a valve train, as described in EP 1417399, which is designed to provide control over the duration of each valve event by summing the action of two cam lobes which can varied in phase relative to one another.

The valve 80 in Figure 2 is operated by a rocker 84 of which one end rests on a fixed lash adjuster 86. A central pivot 88 of the rocker 84 is mounted on a summation lever 90 having a first pair of cam followers 92 in contact with a pair of cam lobes and a single cam follower 94 in contact with a further cam lobe that can be varied in phase relative to the first pair. By virtue of this summation mechanism, the displacement of the valve 80 is determined by the sum of the instantaneous lifts of the cam lobes.

An important point to note about this design of valve train is that the cam follower 94 lies on the centreline of the cylinder. Accordingly, this type of rocker system precludes the use of camshaft bearings that are located on the cylinder centreline. Conventionally this might be achieved by using a more complex cylinder head design with removable split bearing shells fitted in pillar blocks located above the cylinder head bolts that have to be machined in conjunction with the rest of the cylinder head.

Figure 3 shows an assembled camshaft in accordance with a first embodiment of the invention for operating the valve train of Figure 2 and Figures 4A to 4D show two such camshafts mounted in a cylinder head.

Referring to Figure 3, the SCP camshaft 50 shown therein is composed of an outer tube 52 and an inner shaft 54. Cam lobes 56 for acting on the cam followers 92 are shrink fitted on to the outer tube 52 and rotate with it. A cam lobe 58 for operating the follower 94 is placed over the outer tube 52 in between each pair of cam lobes 56 on the cylinder centreline. The cam lobe 58 is free to rotate relative to the outer tube 52 and is connected for rotation with the inner shaft 54 by a pin (not shown) that passes with clearance through an arcuate slot in the outer tube 52.

Bearing bushes 60 are assembled as part of the camshaft between each group of cam lobes 56,58 on the centrelines between adjacent cylinders. A modified bearing bush 60' is arranged at the end of the camshaft 50 as will be described below.

A bearing bush 60 is shown separately in Figure 3A. The outer surface of the bush 60 as a central region 61 of reduced diameter separated by shoulders 62 from two outer regions 63 of larger diameter. The inner surface of the bearing bush 60 likewise has a central region of reduced diameter 65 separated by shoulders 66 with two end regions of larger diameter. In addition, the bush 60 has two drillings 64 and 68 one serving as a locating feature and the other as an oil passage.

As shown in Figures 4A to 4D, this design allows the cylinder head to be constructed in a conventional manner using bearing caps 112a to retain the camshaft 50 in position and having a cylindrical bore machined through the cylinder head and bearing caps into which the camshaft is mounted. In this case, however, the cylinder head bolts 116 are contained in counter-bores 112e that are machined directly into the lower half 112b of the pillar block 112.

The bearing bushes 60 fitted to the camshaft serve to cover the bolt 116 counter-bores and provide an uninterrupted bearing surface.

The clamping surfaces 63 on the outside of the bush 60 correspond with the enlarged portions of the bore such that any distortion of the bush resulting from the clamping forces will not distort the camshaft bearing surface 65. The reduced outer diameter in the central region 61 of the bush is not suitable for clamping because it lies directly over the counter-bore of the adjacent cylinder head bolt 116. This reduced diameter section provides an effective means for distributing oil around the outside of the bush 60 to supply the bearing surface via a drilling 68.

In order to ensure that the bush is located correctly in the cylinder head and is prevented from rotating under all conditions, a location feature is advantageous. Whilst this may be achieved in a variety of different ways, the detail view of Figure 4D shows a simple pin 115 that is fitted to the bearing cap 112a and protrudes into the drilling 64 in the bearing bush 60.

The front bearing bush 60' on the camshaft is of a different design to the others, having a collar 72 at one end for controlling the axial position of the camshaft in the cylinder head. The front bearing bush also includes oil drillings 73 for providing a control oil supply to the camshaft phaser that is fitted to the front of the SCP camshaft.

The second embodiment of the invention, shown in Figure 5, 6A and 6B uses a different design of bearing bush 260, 260' from shown in Figure 3. In this case, each bearing bush 260, 260' is designed to be secured directly to the cylinder head by threaded fasteners, and acts as a one-piece pillar block, thereby dispensing with the need for pillar blocks to be provided in the cylinder head.

This design of bearing bush 260 removes the requirement for the cylinder head to be line-bored as an assembly with its bearing caps. Instead, a flat face needs to be machined for the bearing bushes to be secured to. It is important for the bearing bushes 260, 260' to be accurately machined such that the camshaft bearing bores all lie the same distance above the mating face within a close manufacturing tolerance.

The direct clamping of the bearing bushes 260, 260' to the top of the cylinder head removes the need for any features to avoid distortion of the bearing bore or features to position the bushes axially or rotationally. One or more of the bearing bushes could be doweled in position on the cylinder head to guarantee that the installed camshafts are accurately located.

As with the previous design, the bearing bushes may be used to supply oil to the camshaft journals, to supply the control oil feeds to a camshaft phaser 416, and to control the axial position of the camshaft in the cylinder head.

The embodiment of the invention shown in Figures 7A and 7B is essentially the same as that of Figures 5 and 6, save that the individual bearing bushes 260, 260' have been connected to one another to form a ladder frame 310.

Combining all of the individual bearing bushes 260, 260' into a single ladder frame structure 310 is advantageous because it allows all of the camshaft bearing bores for a single camshaft to be machined in a single operation. It therefore follows that the axis of all the bearing bores will be aligned correctly to each other without the need for a tight positional tolerance of the camshaft bores relative to the clamping face.

In order to produce the assembly of the camshafts in the ladder frame 310, the camshaft outer tube 52 needs to be assembled through the bearing bores and the individual cam lobes at the same time. This could be achieved with a manufacturing fixture or jig into which the ladder frame and the cam lobes are located before the camshaft tube is inserted, the cam lobes being heated and/or the camshaft tube being cooled in order to generate a shrink fit.

Alternatively, the ladder frame 310 may itself form the basis of the assembly jig because the bearings are spaced correctly to locate the groups of cam lobes whilst the camshaft tube is inserted. In order to assemble the camshaft correctly in this way, the groups of cam lobes need to be held in a small fixture that may be located angularly with respect to the ladder frame. This can be achieved by machining a small reference feature into each section of the ladder frame -as indicated at 312 in Figure 7A.

A ladder frame 310 as shown in Figure 7A would typically lie underneath an engine cover bolted to the top of the cylinder head. The embodiment of the invention shown in Figures BA to 8D further simplifies assembly by integrating the ladder frame 310 into the engine cover 410.

In this embodiment, the camshafts are assembled in place in the engine cover and then the whole assembly can be fitted to the top of the cylinder head as a single unit.

Figures BA and 8B also show how the oil supply to each of the camshaft bearings can be achieved using drillings 412 in the ladder frame 310 Figure 8C also shows how control valves 414 for the phasing systems 416 might be integrated into the assembly.

It would of course be possible to include these features in the ladder frame 310 of Figure 7A and 7B if desired.

Advantages of the Invention The described preferred embodiments of the invention offer the following advantages when compared to existing designs: * Camshaft bearings can to be positioned directly above cylinder head bolts, without the need for complex cylinder head design.

* Camshafts can be integrated into a sub-assembly that can be fitted to the cylinder head in a single operation.

* Positioning of the camshaft lobes during the camshaft assembly operation is simplified.

* Camshaft and variable valve actuating systems can be combined into a single sub-assembly.

Claims

-10 -CLAIMS1. An assembled camshaft for mounting on an engine cylinder head, comprising a cam lobe supporting shaft, one or more cam lobes formed separately from the shaft and fitted to the shaft for rotation therewith, and bearing surfaces on the shaft to enable the assembled camshaft to be rotatably supported by the engine cylinder head, characterised in that one-piece plain bearing components are mounted on the bearing surfaces of the shaft during assembly of the camshaft.
2. A camshaft assembly as claimed in claim 1, wherein the shaft the cam lobe supporting shaft is formed of an outer tube and an inner shaft located within the outer tube and rotatable relative thereto, the camshaft having a first set of cam lobes fast in rotation with the outer tube and a second set of cam lobes rotatably mounted on the outer tube and connected for rotation with the inner shaft by means of pins passing with clearance through circumferentially extending slots in the outer tube, whereby the relative phase of the two sets of cam lobes may be varied by rotating the inner shaft relative to the outer tube.
3. A camshaft as claimed in claim 1 or 2, wherein the plain bearing components have a cylindrical outer locating surface for engaging in a mating bore in the engine cylinder head to locate the camshaft relative to the cylinder head.
4. A camshaft as claimed in claim 3, wherein the locating surfaces of the plain bearing components are axially offset from the inner surfaces of the bearing components in contact with the bearing surfaces on the cam lobe supporting shaft.
5. A camshaft as claimed in claims 3 or 4, wherein each plain bearing component includes an alignment feature -11 -to ensure correct axial and/or rotational positioning of the bearing component in the cylinder head.
6. A camshaft as claimed in claim 1 or 2, wherein the plain bearing components are capable of being directly mounted on a flat face of the cylinder head by means of threaded fasteners.
7. A camshaft as claimed in claim 6 wherein a plurality of bearing components that engage a number of bearing surfaces on at least one camshaft are connected to one another to form a ladder frame, the camshaft and ladder frame being capable of mounting on the cylinder head in a single operation.
8. A camshaft as claimed in claim 7, wherein the ladder frame is integrated with an engine cover, whereby the camshaft(s) and engine cover are capable of being fitted to the cylinder head in a single operation.
9. A camshaft as claimed in claim 7 or 8, wherein the ladder frame serves as a fixture to maintain the correct spacing between cam lobes during assembly of the camshaft (s)
10. A camshaft as claimed in claim 8, wherein the ladder frame has tooling features to ensure the correct orientation of the cam lobes during assembly.
11. A camshaft as claimed in any one of claims 7 to 10, wherein the ladder frame contains oil passages for supplying lubricating oil to the camshaft bearings.
12. A camshaft as claimed in any preceding claim wherein a camshaft phaser is fitted to the camshaft.-12 -
13. A camshaft as claimed in claim 12 wherein the oil feeds for controlling the phaser pass through one or more plain bearing components.
14. A camshaft as claimed in claim 13 wherein a phaser control valve is integrated with the camshaft and bearing assembly.
15. A camshaft as claimed in any preceding claim wherein one or more of the plain bearing components are used to control the axial position of the camshaft in the cylinder head.
16. A camshaft system substantially as herein described with reference to and as illustrated in the accompanying drawings.