CONCENTRIC CAMSHAFT ARRANGEMENT

A concentric camshaft arrangement comprises an inner shaft, an outer tube concentrically arranged around the inner shaft and rotatably supported in a cylinder head. A first set of lobes is fixed for rotation with the outer tube and a second set of lobes is rotatably supported by bearing journals on the outer tube and connected for rotation with the inner shaft. The outer tube is supported in the cylinder head by means of a roller bearing and an oil feed is provided for supplying oil for lubricating the bearing journals of the second set of cam lobes. At least part of the oil feed is defined by a radial clearance between the outer surface and an inner surface of the cylinder head that is sealed at its axial ends, the radial clearance being larger than any radial clearance at the roller bearing so that loads on the camshaft are supported at least predominantly by the roller bearing.

FIELD OF THE INVENTION

The present invention relates to concentric camshaft arrangements and particularly to concentric camshaft arrangements that use roller bearings to support the loads of the camshaft.

BACKGROUND OF THE INVENTION

Known concentric camshafts have an inner shaft and an outer tube that are rotatable relative to one another. A first set of cams is fixed for rotation with the outer tube and a second set of cams is mounted on bearing journals on the outer tube and connected for rotation with the inner shaft by means of pins that extend through circumferentially elongated slots in the outer tube.

Such known concentric camshafts are typically supported in the engine using hydrodynamic bearings to allow the camshaft to rotate within the engine. JP2010196488 describes an example of a concentric camshaft supported in a cylinder head in this manner.

It is desirable in the automotive industry to minimise frictional losses for improved fuel consumption and reduced CO2 emissions. It is therefore attractive to use roller bearings, that exhibit lower friction, to support the loads of concentric camshafts, rather than traditional hydrodynamic bearings. WO2012/014069 discloses the use of a roller bearing to support the loads of a camshaft. The term “roller bearing” is used herein to refer to an anti-friction bearing that employs any form of rolling elements, such as balls, cylindrical rollers or needle rollers.

As well as offering significant benefits in term of lower friction, especially at lower engine speeds, roller bearings require very little in the way of an oil supply. Therefore, the oil pump can be reduced in size, potentially reducing losses further.

However, the use of roller bearings presents a problem in that the bearing journals supporting the movable cam lobes of the second set on the outer tube of a concentric camshaft require an oil feed to reduce friction and prevent wear between the moving cam lobes and the camshaft outer tube. If roller bearings are used to support the loads of known concentric camshafts, providing an oil feed via one or more of the hydrodynamic bearing journals of the concentric camshaft is no longer possible and an alternative oil feed is required to lubricate the journal bearings of the second set of cam lobes.

SUMMARY OF THE INVENTION

It is therefore desirable in the automotive industry for there to be an improved concentric camshaft arrangement which overcomes the problems associated with known arrangements.

According to the present invention there is provided a concentric camshaft arrangement comprising an inner shaft, an outer tube concentrically arranged around the inner shaft and rotatably supported in a cylinder head, a first set of lobes fixed for rotation with the outer tube, a second set of lobes rotatably supported by bearing journals on the outer tube and connected for rotation with the inner shaft, a roller bearing mounted between the outer tube and the cylinder head, and an oil feed for supplying oil for lubricating the bearing journals of the second set of cam lobes, wherein at least part of the oil feed is defined by a radial clearance between the outer surface of the outer tube and an inner surface of the cylinder head that is sealed at its axial ends, the radial clearance being larger than any radial clearance at the roller bearing so that loads on the camshaft are supported at least predominantly by the roller bearing.

The sealing means advantageously comprises a first and second seal ring each providing a seal between the outer surface of the outer tube and the inner surface of the cylinder head.

In one embodiment, the outer tube includes a separately formed oil feed ring fixed securely to the outer surface of the outer tube for rotation therewith, the outer surface of the oil feed ring being the surface that is spaced from the inner surface of the cylinder head by the radial clearance forming the oil feed.

The diameter of the outer surface of the oil feed ring_may be substantially equal to the outer diameter of the roller bearing.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Referring toFIG. 1, a known concentric camshaft10has an inner shaft12and an outer tube14. A first set of cams16is fixed for rotation with the outer tube14and a second set of cams18is rotatably mounted on bearing journals on the outer tube14and connected for rotation with the inner shaft12by means of pins19that pass through circumferentially elongated slots30in the outer tube14.

An oil feed20is provided in one or more of the camshaft hydrodynamic journal bearings21and formed from radial holes24in the outer tube14, in conjunction with annular grooves26in the inner bore22of the journal bearing21.

Pressurised oil is fed into the concentric camshaft10and flows along an oil feed path28, defined between the inner shaft12and the outer tube14, to exit through slots30formed in the outer tube14directly under the bearing journals of the second set of cams18.

In the description of the embodiments of the invention that now follows, like components have been allocated reference numerals with the same least significant digits, but in the 100, 200, 300 or 400 series, depending on the embodiment. In the appended claims, the most significant digit of reference numerals that refer to components found in several embodiments has been replaced by a prime (′).

Referring toFIG. 2, a concentric camshaft arrangement100, according to a first embodiment of the present invention, comprises a concentric camshaft110having an inner shaft112and an outer tube114. A first set of cams116is fixed for rotation with the outer tube114and a second set of cams118is rotatably mounted on bearing journals on the outer tube114and connected to the inner shaft112, by pins119, for rotation therewith.

The concentric camshaft110is co-axially arranged within a bore122of the cylinder head121, such that a predefined clearance exists between the bore122and the external surface of the outer tube114.

A camshaft oil feed120is formed in a portion of the cylinder head121. The camshaft oil feed120extends into a groove126, which is formed in and extends around the circumference of the outer surface of the outer tube114. A plurality of circumferentially spaced apart radial holes124extend radially inwards from the groove126through the wall of the outer tube114.

The radial holes124extend into a tubular lubricating cavity128which forms an oil feed path extending axially between the outer surface of the inner shaft112and the inner surface of the outer tube114. The lubricating cavity128extends past the pins119.

The lubricating cavity128is formed by a predetermined clearance between the outer surface of the inner shaft112and the inner surface of the outer tube114.

In use, pressurised oil is fed into the concentric camshaft110and flows through the lubrication cavity128to exit through pin slots130, formed in the outer tube114, directly under the bearing journals of the second set of cams118.

Accordingly, the interface between the inner shaft112and the outer tube114and the bearing journals of the second set of cams118are all adequately lubricated.

The camshaft arrangement100further comprises a drive flange132having a flange portion134and a tubular portion136. The tubular portion136has an internal diameter to correspond to the external diameter of the outer tube114such that the drive flange132is fixed to an end portion138of the outer tube114for rotation therewith.

A portion of the cylinder head121is machined to provide a region of increased internal diameter140, which serves to define two sides of a cavity for accommodating a roller bearing142. The two other sides of the bearing cavity are defined by the outer surface of the tubular portion136and a radial surface of the flange portion134. The roller bearing142, which comprises rolling bearing elements144retained within a bearing housing146, is pressed into the bearing cavity and fixed to the surface of the increased internal diameter140.

The roller bearing elements144have a radial clearance which is less than the predetermined radial clearance between the bore122and the external surface of the outer tube114. This ensures that all the camshaft loads are at least predominantly supported by the bearings, instead of being partially shared by the oil feed.

The concentric camshaft arrangement100further comprises a first seal148and a second seal150serving to provide an oil seal between the outer surface of the outer tube114and the bore122of the cylinder head portion121.

The first and second seals,148and150, are ring-type or O-ring type seals which are disposed in sealing grooves formed one on each side of the oil groove126around the circumference of the external surface of the outer tube114such as to prevent undesirable escape of the oil from the clearance formed at the interface of the outer surface of the outer tube114and the bore122. This ensures that the oil from the groove126passes into the radial holes124.

Third and fourth seals152,154are disposed at opposite ends of the lubrication cavity128, and between the outer surface of the inner shaft112and the inner surface of the outer tube114. The third and fourth seals152,154are ring-type or O-ring type seals which are positioned in seal grooves formed around the circumference of the outer surface of the inner shaft112and maintain the oil within the lubricating cavity128.

A second set of rolling bearings156is disposed around the outer tube114at the opposite end of the concentric camshaft110relative to the cylinder head portion121.

The embodiment shown inFIG. 3differs from that ofFIG. 2in that, instead of having an oil groove (126inFIG. 2) disposed around the circumference of the outer tube (114inFIG. 2), the second embodiment has a separately formed oil feed sleeve256that is fixed to, so as to rotate with and effectively form part of the outer tube214. An oil groove226is disposed around the external circumference of the oil feed sleeve256and is arranged to receive oil from an oil feed220, disposed in a portion of the cylinder head221. The oil groove226communicates with a plurality of circumferentially spaced apart radial holes258, which extend through the wall of the oil feed sleeve256.

The sleeve radial holes258are axially aligned with the radial holes224disposed in the outer tube214, which, as previously described, provide oil into the lubrication cavity228. The oil then exits the lubrication cavity228through pin slots230, formed in the outer tube214, directly under the bearing journals of the second set of cams218.

The diameter of the cylinder head bore222also differs from that of the first embodiment in that it is equal to the external diameter of the bearing housing246. This arrangement has the advantage of reducing costs during manufacture by avoiding the need to machine a bearing cavity.

A predefined clearance exists between the bore222and the external surface of the sleeve256. This ensures that all the camshaft loads are properly supported by the bearings rather than being partially shared by the oil feed.

The arrangement according to the second embodiment also allows for camshaft axial thrust control. A flanged portion260projecting from the axial end of the oil feed sleeve256abuts an axial surface of the cylinder head221to limit axial displacement of the camshaft.

The oil feed sleeve also provides a control feature262to control the end float of the roller bearing242.

First and second seals248,250seal between the outer surface of the sleeve256and the bore222of the cylinder head portion221.

The first and second seals248,250are ring-type or O-ring type seals which are disposed in seal grooves formed each side of the oil groove226around the circumference of the external surface of the sleeve256such as to prevent undesirable escape of oil from the clearance formed at the interface of the outer surface of the sleeve256and the bore222. This ensures the passage of oil from the groove226into the radial holes258.

Having the first and second seals248,250disposed in the sleeve256eliminates the need for there to be grooves formed in the outer tube214and therefore advantageously allows the camshaft to maintain its integral strength.

Third and fourth seals252,254serve the same purpose as the seals152and154in the first embodiment.

The third embodiment of the invention, as shown inFIG. 4, comprises a second oil feed364disposed in a portion of the cylinder head321. The second oil feed364serves to provide a pressurised oil supply to a camshaft phaser oil supply cavity366for use with a phaser having an integral spool valve for controlling the phase of the camshaft.

A second oil groove368is disposed around the external circumference of the oil feed sleeve356and arranged to receive oil from the second oil feed364. The second oil groove368communicates with a plurality of circumferentially spaced apart second radial holes370, which extend through the wall of the oil feed sleeve356.

The second sleeve radial holes370are aligned with a plurality of circumferentially spaced apart second outer tube radial holes373, which are in fluid communication with the phaser oil supply cavity366to provide pressurised oil from the second oil feed364thereto.

A fifth seal372is disposed in a seal groove extending circumferentially around the external circumference of the sleeve356, such that the second oil groove368is disposed between the first seal350and the fifth seal372. The fifth seal372is, once again, a ring-type or O-ring type seal.

It will be appreciated that a greater number of oil feeds may be provided in the same camshaft arrangement to accommodate either a standard camshaft phaser, which requires two feeds/returns, or a twin camshaft phaser, which requires four feeds/returns.

FIGS. 5 and 6show a fourth embodiment of a concentric camshaft arrangement400having similar features to the embodiments described above.FIGS. 5 and 6additionally show a hydraulic cam phaser474installed in the cylinder head421. In this embodiment, instead of using two separate oil feeds, as described in relation to the third embodiment, a single oil feed420is used to feed oil into both the concentric camshaft410and the phaser474.

As described with reference to previous embodiments, the oil feed420extends into a sleeve oil groove426from which a plurality of radial holes458extend through the sleeve456and align with radial holes424which extend radially through the outer tube414.

The outer tube radial holes424extend in fluid communication into an oil distributor480which comprises a camshaft oil distributor482and a phaser oil distributor484.

The camshaft oil distributor482has a plurality of camshaft oil supply channels486which are in fluid communication with lubrication cavity428for supplying oil thereto. As previously described, the lubrication cavity428supplies oil through pin slots430for lubrication of the bearing journals of the second set of cams418.

The phaser oil distributor484has a plurality of phaser oil supply channels488which are in fluid communication with phaser oil supply cavities466to supply pressurised oil thereto.

The camshaft oil distributor482additionally comprises a camshaft oil restrictor490in the drive shaft (or alternatively this may be a small drilling) to control and balance the relative flow of oil into the camshaft and the phaser.

A one-way valve492can be positioned in either the feed to the phaser or camshaft to control oil flow and prevent oil drainage from the phaser when the engine is stopped.

FIG. 6provides an alternative section view showing oil feed drillings494for the integral spool valve496.