EP1534938A2

EP1534938A2 - Improvements to latchable cam-lobe systems for poppet valve motion control

Info

Publication number: EP1534938A2
Application number: EP03740744A
Authority: EP
Inventors: Jean-Pierre Pirault
Original assignee: Powertrain Technology Ltd
Current assignee: Powertrain Technology Ltd
Priority date: 2002-06-21
Filing date: 2003-06-17
Publication date: 2005-06-01
Also published as: AU2003277971A1; GB2385888A; WO2004001199A3; GB2385888B; WO2004001199A2; GB0214361D0

Abstract

A camshaft assembly with one or several slideable camlobes, where each slideable cam (707) is capable of latching in 2 positions perpendicular to the main axis of the camshaft, so the slideable camlobe is either latched to provide the controlling valve lift, or the slideable camlobe is withdrawn within the lift curve of a pair of adjacent cams (712) and latched in this retracted position, so that these latter cams control the valve lift. The movable cam may comprise an upper cam (707) which performs the lifting of the valve, and a retaining cap or clip (708) which secures the upper cam (707) to the camshaft axle (706). The latching of the slideable cam to the cam axle can be achieved with at least one latching pin (702) which engages with holes (701 & 711) either in the slideable cam or a cam tube. The slideable cam is arranged so that the distance, on the centreline of the slideable cam, from the nose (800) of the slideable cam to the axis through the latching hole (701) for the inactive cam position, is less than the distance from the nose (801) of the fixed low lift cams to the centreline of the latching pin major axis (802).

Description

IMPROVEMENTS to LATCHABLE CAM LOBE SYSTEMS for POPPET

VALVE MOTION CONTROL

The invention relates to improvements for camshaft assemblies of internal combustion engines with switchable cam lobes that can be selectively engaged or disengaged, so that different valve timings can be achieved according to operating requirements; such camshaft assemblies are described in UK patent application GB 0106891.5.

The broadest aspect of the invention is as set out in Claim 1 and comprises a slideable cam lobe which can be selectably latched in 2 positions substantially perpendicular to the main axis of the camshaft so that the slideable cam lobe can be withdrawn and latched within the lift curve of a pair of adjacent cams, so that these adjacent cams then control the valve lift, as well as the slideable cam being latched in a second position to provide the controlling valve lift.

Figure 1 shows an isometric view of the proposed complete camshaft assembly for lifting poppet valves.

Figure 2 shows a longitudinal sectional view of a part of the proposed camshaft assembly for poppet valve actuation.

Figure 3 is an isometric view of a detachable cam lobe.

Figure 4 is an isometric view of a detachable cam lobe locking clip.

Figure 5 is shows the detail of the locking tang of the cam lobe locking clip of Fig.4.

Figure 6 shows a longitudinal elevation of one slideable cam lobe latched to the cam shaft at its lifting or active position.

Figure 7 shows the transverse cross section through one slideable cam lobe latched to the cam shaft at its full lift or active position.

Figure 8 shows the cross section through one slideable cam lobe latched to the cam shaft at its zero lift or inactive position, with the adjacent lower lift cams lifting the tappet or cam follower.

Figures 9 shows the slideable cam lobe in transition between inactive and active positions.

Figure 10 shows a transverse cross section of a second embodiment of the invention with the slideable cam at full lift, ie active.

Figure 11 shows a transverse cross section of a third embodiment of the invention with the slideable cam at full lift, ie active. Figure 12 shows a cross section of a third embodiment of the invention with the slideable cam latched to be inactive

Figure 13 shows a cross section of a fourth embodiment of the invention with the slideable cam latched to be inactive.

In the following description, the large generic elements of the assembly, according to one embodiment, are described with reference to Figs.1-6; detailed descriptions of the latching mechanisms, features and other embodiments are given with reference to the remaining figures.

With reference to Fig.l, the lifting mechanism for providing each valve with 2 possible lifts and periods comprises essentially 3 cams, ie 2 fixed outboard cams 101 and 102 of identical profiles which provide the low lift for the poppet valve, and one slideable and latchable inboard cam 103 which provides the high lift for the poppet valve. These cams, when made active by the mechanism, would bear directly against a tappet which is in contact with the poppet valve, but the tappets and the valves have been omitted for clarity. Other similar slideable cams are shown by 104-110 inclusive, ie 8 in total for this particular camshaft. Each of the slideable cams comprises 2 parts, ie the main lifting portion, ie 103-110, and a clip, eg 127, 128, 129, 130, 131, 132, 133 & 134, which holds the slideable cams to the cam axle, ie the longitudinal shaft 100. For future reference, 111, 112 and 113 are commonly referred to as the noses of the appropriate cams, ie the point of maximum lift on each cam, whilst 114, 115 and 116 are the base circle areas, ie the points of zero lift of each cam.

With reference to Fig.2, the fixed low lift cams 201 & 202, 205 & 206, 207 & 208, 209 & 210, 211 & 212, 213 & 214, 215 & 216, 217 & 218 are shown grouped in pairs and integral with the cam axle 204, the slideable and latchable cams, which are not shown, occupying the spaces, referred to as axle slots, between the pairs of fixed cams, ie 228, 229, 230, 231, 232, 233, 234 and 235. An oil feed gallery 219 receives oil from the engine oil circuit and this oil can access the latching mechanisms of the slideable cams via drillings 220, 221, 222, 223, 224, 225, 226 and 227, the exact shape, number and dispostions of these drillings depending upon the particular embodiment of this invention. The cam axle, which can be a single piece, and its fixed cams can be of cast iron, chill cast iron, spheroidal graphite nodular iron, steel, or forged steel, or forged metal matrix composites such as steel alloys reinforced with dispersed ceramic particles, eg titanium diboride particles, or forged aluminium alloys reinforced with ceramics, eg dispersed silicon carbide particles, which ideally have a particle size equal or smaller than 3 microns. In the case of metal matrix composites cam axles, the fixed cams could be coated, in one embodiment, with a fusable tungsten steel coating.

With reference to Fig.3, one embodiment of the latchable and slideable lobe 300 has a cam profile 303 around a substantial periphery of the cam lobe, holes 301 & 302 to receive latching means, a formed slot 308, the parallel sides of which engage with the parallel sides of the axle slots, and means for fixing a retaining mechanism for the cam lobe onto the cam axle. In the embodiment of Fig.3, the fixing means are slots 304, 305, 306 and 307 which accommodate tongues and locking tangs of a clip, which will be described with reference to Figure 4. The major 2 sides of the formed slot of the slideable cam lobe, of which only 309 is visible in Fig.3, are substantially parallel to each other and to the corresponding sides of the axle slot to which they are fitted. The other sides of the slideable cam are also substantially parallel to the major planes of the 2 lower lift cams adjacent to the axle slot, and are therefore substantially orthogonal to major axis of the cam axle.

The slideable cam lobe may be of a sintered material, cast, chill cast material, forged material, or a metal matrix composite material which is either forged or cast. The material can be cast iron, chill cast iron, a steel, forged aluminium alloys, forged aluminium alloys reinforced with dispersed ceramic silicon carbide particles which may be smaller than 3 microns, cast aluminium alloys reinforced with structured and/or woven ceramic fibres, such as alumina. The material can also be a steel reinforced with dispersed ceramic particles, eg titanium diboride. The profiled functional surface of slideable cam can be coated with a hard fusable material, such as a tool steel, or a tungsten steel alloy coating.

With reference to Fig.4, this retaining clip 400 secures the slideable cam 309, shown in Fig.3, to the camshaft axle 204 shown in Fig.2. one embodiment of the clip, the clip is manufactured from a steel or a spring steel pressing which has rails 401, 402, 403 & 404 which engage in corresponding slots (304-307 inclusive) in the slideable cam shown in Fig.3. The clip is automatically locked in position by the tangs 405 and another on the B side which is not visible; these tangs can be released with a tool to allow clip removal. The side rails are part of 2 side members 407 and 408 which bridge the open end of the slideable cam, thus retaining the slideable cam to the cam axle. In another embodiment, the bridging, retention and locking functions can be achieved from stiff steel wire, or the slideable cam can be secured by a cross rivet which has a head at one end and a means for locking the rivet at the other end. Such locking may include a riveting head, a circlip or a deformable or cripping washer. In another embodiment, the slideable cam lobe can be retained by crimping, swaging or bending relatively flexible portions of the slideable lobe in the non lifting area of the slideable cam lobe, so that the bent portions overlap the cam axle slot and limit the maximum travel of the slideable cam on the cam axle in one direction. In order for the slideable cam to function satisfactorily in both active and inactive modes, the retaining clip, or any other retention embodiment, must have a maximum effective radius in the areas A & B, about the rotational axis of the cam axle, which is less than the base circle radius of the adjacent low lift cams, and the maximum effective height of the clip, in the area around C, must be shorter than the effective radius across A or B by an amount which is substantially the difference in maximum lift between the high and low lift cams. This ensures that the high lift slideable cam can be parked in the inactive position without the retaining means or clip fouling the tappet. A consequence of this base circle geometry of the slideable cam is that the slideable cam profile has to be generated from a smaller base circle radius than the profile for the fixed cams.

With reference to Figure 5, 505 is a side member of the retaining clip of Fig.4, 502 being the base of the clip; the retaining rails are not visible in this section. The locking tang 503 can be seen engaging in a corner relief 504 of the slideable cam 501, effectively retaining the slideable cam 501 to the cam axle 500. The tang 503 is bendable about the base 502 of the clip so that the clip can be inserted and removed from the slideable cam by elastically bending the tangs. Fig.5 shows the clip and slideable cam in the effective zero lift position, the peripheral extremity of the clip 502 having a radius which is less than the base circle radius of the adjacent low lift cams, as depicted in part by 510.

With reference to Fig.6, the high lift (inboard) slideable cam 601 is seen between the 2 fixed outer lower lift cams 602 & 603, latched in its high lift position and lifting the tappet 606. The retaining clip 604 is visible, as is one latching pin hole 605, of this particular embodiment. There is clearance 607 and 608 betweeen the slideable cam and the fixed cams, and hence it is possible to see portions 609 & 610 of the cam axle 611.

With reference to Figs.7, 8 and 9, this embodiment uses a single cross pin 702 to perform the latching of the high lift slideable cam 707 to the cam axle 706, in both full lift and effective no lift positions. For achievement of the full lift condition (Fig.7), a high level oil pressure in the oil gallery 709 acts on the collar of the spring carrier 702c with adequate force to compress the spring 703 and move the pin 702 into the hole 711, thus locking the high lift cam 707 to the cam axle 706. Alternative embodiments can have springs which are in tension. The latching of the slideable cam in its high lift position takes place whilst the cam assembly for the particular valve is in its base circle period, ie the only force acting on the slideable cam is a the centrifugal force which pulls the cam 707 radially outwards from the cam axle 706 along the cam axis YY. This outward motion of the slideable cam, during the base circle period, will occur when the cam is rotated 90-270 degrees relative to the position shown in Fig.7; there is adequate time, during the base circle period and up to engine speeds of about 4000-5000rpm, for the centrifugal force to accelerate the slideable cam from its inactive position to its latched active position, and be in position for the immediate valve lift event.

The slideable cam is usually arranged so that its cam profile has at least one matching lift point, relative to the fixed low lift cams, during the opening phase of the valve lift, and one matching lift point, relative to the fixed low lift cams, during the closing phase of the valve lift. These matching lifts may be in the opening and closing ramp phases of the valve lift profiles.

For the effective zero lift condition of the slideable cam 707, the spring force from the spring 703 is adequate to overcome a lower level oil pressure in the oil gallery 709, moving the pin 702 towards the face 707a of the cam 707. The higher and lower oil pressures in the galleries are achieved by some switching device in the engine oil circuit, such as an electrical solenoid valve. When the pin end 702a is retracted from the cam hole 711 and the pin end 702b is in contact with the face 707a, the cam 707 can be displaced along the axis of the cam axle 713 when there is adequate reaction force from the valve spring and tappet to overcome the inertia forces acting on the cam 707. The hole 701 in the slideable cam is then moved progressively by the action of the tappet forces on the cam until the hole 701 aligns with the pin end 702b. The pin 702 can now engage the hole 701 to lock the cam 707 in its effective zero lift position, ie the cam 707 is now masked by the two lower lift side cams 712 (only one of these side cams is visible in this view, Fig.8). The retaining clip 708, described with reference to Fig.6, acts as a second level safety device to ensure that the cam 707 cannot leave contact with the cam axle 706.

Another feature of the embodiment shown in Fig. 7 are the support rings 704 and 705 that are fitted to the cam axle holes 716 and 717. The support ring 704 acts as a reaction stop to the spring 703 and prevents excessive bending of the pin 702 when engaged in the cam hole 711. The support ring 705 acts prevents excessive bending of the pin 702 when engaged in the cam hole 701.

The hole 711 can have an enlarged eccentric diameter relative to the locking pin 702 , such that there is clearance between the pin side and the unloaded side of the slideable cam 707 holes, ie 71 la. In one embodiment of this feature, the eccentricity of the full lift latching pin hole in the slideable cam is towards the base circle diameter direction of the cam.

The latching pin 702 also has means for providing a reaction surface 702c to the spring 703, and this reaction surface 702c also forms a collar, and partial seal, for the oil pressure in gallery 709, ie the collar is a sliding fit with the latching pin hole 716 in the cam axle, h the embodiment of Figs.7-9, the collar 702c also has a sleeve portion 702d which helps reduce oil loss from the pressurised supply in gallery 709. Other embodiments of this collar are a crimped washer, or a ring fitted with interference to the pin 702.

The rate and preload of the spring 703 in Figs.7-9 is such that it can be substantially compressed by the higher oil pressure in the gallery 709, allowing the pin to be moved towards the surface 715 of the cam 707, whilst there is adequate spring force to overcome the lower oil pressure and move the pin towards the surface 707a of the cam 707.

The ends of the pin 702a and 702b may be bevelled or chamfered to allow a more progressive entry into the holes 701 and 711.

Another optional feature of this embodiment is a transverse hole 799 through the slideable cam 707 which may be of any desired profile. This transverse hole could have a substantial cross section of material between it and the cam slot in the slideable cam.

With reference to Figs.6-9, in combination with Fig.l, it can be seen that the latchable high lift cam 707 (Fig.8) does not need a no lift or "base circle" cam portion, as the base circle portion of the latchable cam is effectively provided by the base circle diameters of the 2 adjacent cams (Fig.6, 602 and 603, also Fig.8, 712).

With reference to Fig.8, when latched in the inactive position, the profile of the high lift cam is encompassed within the profile of the adjacent low lift cams 813. The broad geometrical requirements for achieving this in the base circle radius portions of the cams are explained with reference to Fig.4. Fig.8 additionally shows that for the latchable higher lift cam profile to be totally inactive, allowing for tolerances in the mechanism, then the latching geometry of the high lift cam is arranged so that the distance, on the centreline of the slideable cam, from the nose 800 of the slideable cam to the axis through the latching hole(s) 701 in the slideable cam, used to keep the cam in its inactive position, is less than the distance from the nose 801 of the fixed low lift cams to the centreline of the major axes of the latching pins 802. For reference, this distance difference is called the retraction offset.

With reference to Fig.9, the latching pin 702 has exited from the high lift latching hole 711 of the cam 707, and this allows the slideable cam to be displaced by the reaction force in the tappet such that the slideable cam moves towards its effective zero lift latched position, which is fully achieved when the latching pin 702 reaches the centreline of the hole 701. As the cam nose 902 of the slideable cam 707 reaches the same height as the cam nose of the adjacent low lift cams, the chamfered pin end 727 engages a transverse groove 901 in the sliding face 707a of the cam 707; the aperture of the zero lift latching pin hole is contained within the width of this groove. The width of the transverse groove, from the centreline of the latching tube hole to the edge of the groove furthest from the cam nose, is such that it at least equals the retraction offset. The force from the spring 703 on the latching pin 711, acts on the inclined surface of the transverse groove 901, forcing the chamfered pin end to slide outwards from the centreline XX of the cam and thus pulling the slideable cam so that the nose of the slideable cam 902 is forced below the noses of the 2 adjacent low lift cams. This ensures that the nose of the high lift cam is clearly inactive, and is necessary to accommodate tolerance accumulations in the mechanisms and camshaft assembly. The magnitude of the additional retraction of the slideable cam relative to the cam noses of the fixed cams is defined in the section with reference to Fig.8, and is applied also to the entry chamfer 901.

With reference to Fig.10, this embodiment incorporates an additional, or redundant, safety latch pin 1001 fitted to the slideable cam 707, and acted upon by the spring 1002. In this arrangement, the support collar 1005 is set back from the face 1007 of the cam axle so that there exists a recess 1004, which is slightly larger in size than the profile of the additional latch pin 1001. This allows the slideable cam to be latched simultaneously on both sides of the cam axle, thus reducing any tipping of the cam 707 relative to the cam axle 706. The spring 1002 reacts against an abutment 1003, which in this embodiment is a plug or cap 1003 fitted with interference into the hole 1008.

With reference to Fig.l 1, this embodiment uses 2 latching pins 11001 and 11002 which engage holes 11016 and 11017 for the active operation of the high lift cam, whilst the inactive position is achieved with the pins 11001 and 11002 latched into holes 11011 and 11012 which are in the latching tube 11010 which is rigidly attached to the moveable cam 11009. The operational sequence between high lift and effective zero lift modes is now described. A valve in the engine's oil circuit controls the oil pressure to the gallery 11013 to "low" or "high" pressure levels. At high pressure levels, as would exist in the condition shown in Fig.l 1, the resultant oil pressure hydraulic force acting on the pin 11001 and 11002 areas in direct contact with the oil, ie faces 11014, 11015, forces the pins radially outwards from the centreline of rotation of the camshaft into the locking holes 11016, 11017, the pin travel being limited by the springs 11005, 11006. The spring reacts against end stop 11003 and 11004. There is also centrifugal force acting on the pins 11001 and 11002 which help to keep the pins in the holes 11016 & 11017. At the lower oil pressure level, the spring forces exerted by the springs 11005 and 11006 are adequate to overcome the oil pressure force acting on the pin areas 11014 & 11015 in direct contact with the oil and the pins are forced inwards so that the pin ends 11025 & 11026 protrude into the line of travel of the latching tube 11010, unlatching the upper slideable cam from the axle 11027. As the cam turns against the contacting tappet, with the valve spring underneath, the reaction of the tappet forces the slideable cam to move along the surfaces 11028 and 11029 until the end of the cam tube 11030 comes into contact the pin ends 11025 and 11026. The cam tube 11030 has a bevelled or radiused end 11031 which encourages the pins 11001 and 11002 to be displaced outwards whilst the cam tube slides further into the body of the cam axle 11027. The pins ends 11025 & 11026 then engage into the holes 11011 & 11012 of the latching tube, effectively locking the upper cam into its "zero lift" position, as shown in Fig.12. The holes in the latching tube can have chamfers.

As can be seen, the slideable cam in its active position uses the base circle diameter 11025 of the adjacent low lift cams.

Other optional features of this embodiment include a seal 11008 fitted to either the cam tube 11010 or the cam axle 11027 and support collars 11003 and 11004 to guide the latching pins 11001 and 11002. In this embodiment, the seal could be an elastomeric type O-ring which fits into a groove in the cam tube 11010 or alternatively fits into a groove in the cam axle 11027.

The slideable cam can be retained to the cam axle by fixing clip 11040 which can be of same types as described with reference to previous sections describing Figs. 4 and 5.

With reference to Fig.12, this shows the slideable cam 11009 latched to the cam axle 11027 in the effective zero lift position; the proportions, profile and dimensions of the slideable cam, relative to the adjacent low lift cam, are such to ensure that that the slideable cam, when in its inactive position, can be nested within the profile of the adjacent low lift cams. In particular, allowing for tolerances in the mechanism, the latching geometry of the slideable high lift cam is arranged so that the distance, on the centreline of the slideable cam, from the nose of the slideable cam 12003 to the axis through the latching holes in the slideable cam tube (11041, Fig.l 1), used to keep the cam in its inactive position, is less than the distance from the nose of the fixed low lift cams 12002 to the centreline of the major axes of the latching pins 12004.

A further feature of the embodiment, shown in Figs. 11 & 12, is the use of conical ended latching pins 12055 and 12056 (Fig.12) to engage with the holes 12057 and 12058 in the cam tube 12052. This conical engagement feature enables the slideable cam to be latched below the surfaces of the adjacent fixed cam 12002.

The latching tube may have a chamfered transverse groove, larger in width than the diameter of the latching hole, and orthogonal to the latching hole for the inactive cam position, the groove extending mainly on the side of the latching hole furthest from the cam nose. The groove width, extending from the centreline of the latching hole(s) in the latching tube towards the retaining clip portion of the slideable cam lobe, is equal to or greater than the difference between the distances, on the centreline of the slideable cam, from the nose of the slideable cam to the axis through the latching holes in the cam tube, used to keep the cam in its inactive position, and the distance from the nose of the fixed low lift cams to the centreline of the major axes of the latching pins

In the embodiment shown in Figs.11 & 12, the cam tube 11010, which is rigidly joined to the slideable cam 11009, may be realized in alternative forms, eg a hollow tube pressed into the slideable cam, or a tube which is sintered as part of a sintered slideable cam, or a hollow cam tube may be secured (Fig.12) by having a swaged portion in the hollow cam tube with enlarged diameter 12022, relative to the main body of the tube 12021 , on one side of one of a substantially horizontal surface 12050 of the slideable cam, with a fixing circlip 12051, on the other side of the same horizontal surface of the slideable, or alternatively the tube is joined to the slideable cam by swages in the cam tube above and below the said horizontal surface. In cam tube fixing arrangements using swages and/or circlips, some clearance may be provided between the outer diameter of the cam tube 12052 and the diameter of the hole 12053 in the slideable cam, thus allowing some compliance, to compensate for tolerance stacks, between the axes of the hole in the cam axle 12054 and the cam tube 12052.

With reference to Fig.13, this embodiment is a variation of that proposed with reference to Fig.12, in that the cam tube 13001 is attached to the slideable cam 13009 by means of the retaining clip 13004. The cam tube, in this embodiment, can be attached orthogonally to the retaining clip by several means, eg by having a swaged portion in the hollow cam tube with enlarged diameter 13002, relative to the main body of the tube 13001, on one side of one of the substantially horizontal surfaces of the clip, with a fixing circlip 13003 on the other side of the same horizontal surface 13004 of the clip, or alternatively the tube is joined to the retaining clip by swages in the cam tube above and below the said horizontal surface. In these cam tube fixing arrangements using swages and/or circlips, some clearance may be provided between the outer diameter of the cam tube 13001 and the diameter of the hole 13010 in the cam axle, thus allowing some compliance, to compensate for tolerance stacks, between the axes of the hole in the cam axle 13001 and the cam tube 13001.

The previously described assemblies may be used in any type of internal combustion engine which uses camshafts to open poppet valves. The poppet valve actuation may be through bucket tappets, or finger or roller followers.

Claims

1) A camshaft assembly having slideable cams which can be selectably latched in 2 positions substantially perpendicular to the main axis of the camshaft.

2) A camshaft assembly, according to Claim 1, in which the slideable cam can be withdrawn and latched within the lift curve of a pair of adjacent cams, so that the adjacent cams control the valve lift.

3) A camshaft assembly, accordmg to Claims 1-2, in which the slideable cam can be latched in a second position to provide the controlling valve lift.

4) A camshaft assembly, according to Claims 1-3, having at least one latching pin which can be used to latch the slideable cam in 2 positions.

5) A camshaft assembly, according to Claims 1-4, in which the latching pins are controlled by springs.

6) A camshaft assembly, as in Claim 5, in which the springs are in compression.

7) A camshaft assembly, as in Claim 5, in which the springs are in tension.

8) A camshaft assembly, as claimed in Claims 4-7, in which each latching pin has a rigidly attached collar which engages with a sliding fit in the hole containing the latching pin.

9) A camshaft assembly, as in Claim 8, in which the latching pin collar also serves as a reaction member for the spring that controls the latching pin.

10) A camshaft assembly, as in Claims 4-9, in which the latching pin or pins have chamfered ends.

11) A camshaft assembly, as in any previous claim, in which the slideable cam is arranged so that the distance, on the centreline of the slideable cam, from the nose of the slideable cam to the axis through the latching hole, used to keep the cam in its inactive position, is less than the distance from the nose of the fixed low lift cams to the centreline of the latching pin major axis.

12) A camshaft assembly, as claimed in any previous claim, in which the slideable cam has a chamfered transverse groove in the sliding face of the main camslot in the cam axle, larger in width than the diameter of the latching hole, and orthogonal to the latching hole for the inactive cam position, the groove extending mainly on the side of the latching hole furthest from the cam nose. 13) A camshaft assembly, as claimed in Claim 12, in which the groove width, extending from the centreline of the latching hole towards the retaining clip end of the slideable cam, is equal to or greater than the difference between the distances, on the centreline of the slideable cam, from the nose of the slideable cam to the axis through the latching holes in the slideable cam, used to keep the cam in its inactive position, and the distance from the nose of the fixed low lift cams to the centreline of the major axes of the latching pins.

14) A camshaft assembly, as claimed in all previous claims, in which the opening and closing lift profiles of the slideable cam match at least one lift point on the opening lift, and at least one lift point on the closing lift of the 2 fixed cams either side of the slideable cam.

15) A camshaft assembly, as claimed in previous Claim, which has a tube rigidly attached to the slideable cam, this tube engaging with the cam axle.

16) A camshaft assembly, as claimed in Claim 15, in which the tube has chamfered holes for the latching pin engagement.

17) A camshaft assembly, as claimed in Claims 15-16, in which the tube has a chamfered, bevelled or radiused end.

18) A camshaft assembly, according to Claims 15-17, in which the slideable cam is arranged so that the distance, on the centreline of the slideable cam, from the nose of the slideable cam to the axis through the latching holes in the slideable cam latching tube, used to keep the cam in its inactive position, is less than the distance from the nose of the fixed low lift cams to the centreline of the major axes of the latching pins.

19) A camshaft assembly, according to Claims 15-18, in which the latching tube has a chamfered transverse groove, larger in width than the diameter of the latching hole, and orthogonal to the latching hole for the inactive cam position, the groove extending mainly on the side of the latching hole furthest from the cam nose.

20) A camshaft assembly, as claimed in Claim 19, in which the groove width, extending from the centreline of the latching hole(s) in the slideable cam latching tube, towards the retaining clip part of the slideable cam, is equal to or greater than the difference between the distances, on the centreline of the slideable cam, from the nose of the slideable cam to the axis through the latching holes in the cam tube, used to keep the cam in its inactive position, and the distance from the nose of the fixed low lift cams to the centreline of the major axes of the latching pins in the cam axle.

21) A camshaft assembly, as claimed in Claims 15-20, in which the latching pins engage in the tube. 22) A camshaft assembly, as claimed in Claim 21, in which the latching pins have conical ends for engagement in the latching tube.

23) A camshaft assembly, as claimed in Claims 15-22, in which the latching tube has means for sealing with the cam axle.

24) A camshaft assembly, as claimed in Claims 15-22, in which the cam axle has means for sealing with the latching cam tube.

25) A camshaft assembly, as claimed in Claims 23-24, in which the seal means is an elastomeric O-ring type seal.

26) A camshaft assembly, as claimed in Claim 15, in which the latching cam tube is secured to the slideable cam by a press fit between the hollow tube and the mating hole in the slideable cam.

27) A camshaft assembly, as claimed in Claim 15, in which the latching cam tube and the slideable cam are a single sintered part.

28) A camshaft assembly, as claimed in Claims 15-25, in which a hollow latching cam tube is a clearance fit in a mating hole in the slideable cam, the cam tube being retained to the slideable cam by a circlip engaging in a groove in the hollow cam tube on one side of a substantial cross member of the sliding cam, with another circlip being on the other side of the same substantial cross member of the sliding cam

29) A camshaft assembly, as claimed in Claims 15-25, in which a hollow latching cam tube is a clearance fit in a mating hole in the slideable cam, the cam tube being retained to the slideable cam by a circlip engaging in a groove in the hollow cam tube on one side of a substantial cross member of the sliding cam, with a swage in the tube on the other side of the same substantial cross member of the sliding cam

30) A camshaft assembly, as claimed in any previous claim, in which the slideable cam lobe is a cast material.

31) A camshaft assembly, as claimed in Claims 1-29, in which the slideable cam lobe is a chill cast material.

32) A camshaft assembly, as claimed in Claims 1-29, in which the slideable cam lobe is a chill cast iron material.

33) A camshaft assembly, as claimed in Claims 1-29, in which the slideable cam lobe is a sintered material.

34) A camshaft assembly, as claimed in Claims 1-29, in which the slideable cam lobe is a forged material. 35) A camshaft assembly, as claimed in Claims 1-29, in which the slideable cam lobe is a metal matrix composite material.

36) A camshaft assembly, as claimed in Claims 1-29, in which the slideable cam lobe has a hard fusable coating deposited on a metallic core.

37) A camshaft assembly, as in Claims 1-29, in which the slideable cam lobe is a hard fusable coating deposited on a cast iron core.

38) A camshaft assembly, as claimed in Claims 1-29, in which the slideable cam lobe is a hard fusable coating deposited on a steel core.

39) A camshaft assembly, as claimed in Claims 1-29, in which the slideable cam lobe is a hard fusable coating deposited on an aluminium core reinforced with ceramic.

40) A camshaft assembly, as claimed in Claims 1-29, in which the slideable cam lobe is a hard fusable coating deposited on a forged aluminium alloy core reinforced with dispersed ceramic particles.

41) A camshaft assembly, as claimed in Claims 1-29, in which the slideableable cam lobe is a hard fuseable coating deposited on a forged aluminium core reinforced with dispersed silicon carbide particles.

42) A camshaft assembly, as claimed in Claim 41, in which the dispersed silicon carbide particles are smaller than 3 microns in diameter.

43) A camshaft assembly, as claimed in Claims 1-29, in which the slideable cam lobe comprises a hard fusable coating deposited on a cast aluminium core reinforced with a structured ceramic matrix.

44) A camshaft assembly, as claimed in Claim 43, in which alumina is used for the structured ceramic matrix.

45) A camshaft assembly, as in any previous claims, in which the slideable cam lobes have a transverse hollow portion, or a hole through the body of the cam.

46) A camshaft assembly, as claimed in Claim 45, in which there is a substantial cross member in the sliding cam, formed by the material between the through hole in the sliding cam and the main central aperture of the sliding cam.

47) A camshaft assembly, as claimed in all previous Claims, which has eccentric clearance holes for the latching pin engagement in the slideable cam, the clearance holes having an eccentric centre to the axes that correspond to the latching pin axes, when engaged in those holes.

48) A camshaft assembly, as claimed in Claim 47, in which the eccentricity of the full lift latching pin hole(s) in the slideable cam is towards the base circle diameter direction of the cam. 49) A camshaft assembly, as claimed in any previous claim, which has a cam axle is made of some type of cast iron material.

50) A cam axle of a camshaft assembly, as claimed in Claim 49, which is of chill cast iron.

51) A cam axle of a camshaft assembly, as claimed in Claim 49, which is of spheroidal graphite nodular cast iron.

52) A cam axle of a camshaft assembly as claimed in Claims 1-48, which is of forged steel.

53) A cam axle of a camshaft assembly as claimed in Claims 1-48, which is of a metal matrix composite.

54) A cam axle of a camshaft assembly as claimed in Claim 53, which is of forged aluminium alloy reinforced with dispersed silicon carbide particles.

55) A cam axle of a camshaft assembly, as claimed in Claim 54, which has silicon carbide particles with a diameter of less than 3 microns.

56) A cam axle of a camshaft assembly as claimed in Claim 53, which is of forged steel alloy reinforced with dispersed titanium diboride particles.

57) A camshaft assembly, as claimed in previous claims, which has an additional latch pin fitted to the slideable cam, and acted upon by a spring which can engage with the end of the latch pin hole in the cam axle when the latchpin is already engaged in the main hole in the sliding cam, which secures the sliding cam in the high lift position.

58) A camshaft assembly, as claimed in Claim 57, in which the support collar in the cam axle, on one side of the cam axle, is recessed from the face of the cam axle so that there exists a recess, which is slightly larger in size than the profile of the additional safety latch pin.

59) A camshaft assembly, as claimed in Claim 57-58, in which there is a spring acting on the additional latch pin.

60) A camshaft assembly, as claimed in Claim 57-59, which has a fixed abutment against which the spring, which actuates the additional latching pin, can react.

61) A camshaft assembly, as claimed in Claim 60, in which the fixed abutment is a plug or cap fitted with interference into a hole in the sliding cam.

62) A camshaft assembly, as claimed in any previous Claim, in which the slideable cam has a slot with sides that are substantially parallel to each other and to the sides of the mating cam axle portion. 63) A camshaft assembly, as claimed in any previous Claim, with support collars in the cam axle to guide the latching pin(s).

64) A camshaft assembly, as claimed in Claims 1-14 & 30-63, in which the slideable cam tube has a chamfered transverse groove in the sliding face of the cam tube, larger in width than the diameter of the latching hole, and orthogonal to the latching hole for the inactive cam position, the groove extending mainly on the side of the latching hole furthest from the cam nose.

65) A camshaft assembly, substantially as described in Fig.l

66) A camshaft assembly, substantially as described in Fig.2.

67) A camshaft assembly, substantially as described in Fig.3.

68) A camshaft assembly, substantially as described in Fig.4.

69) A camshaft assembly, substantially as described in Fig.5.

70) A camshaft assembly, substantially as described in Fig.6.

71) A camshaft assembly, substantially as described in Fig.7.

72) A camshaft assembly, substantially as described in Fig.8.

73) A camshaft assembly, substantially as described in Fig.9.

74) A camshaft assembly, substantially as described in Fig.10.

75) A camshaft assembly, substantially as described in Fig.11.

76) A camshaft assembly, substantially as described in Fig.12.

77) A camshaft assembly, substantially as described in Fig.13.

78) A camshaft assembly, as described in any preceding claim, when used in conjunction with an internal combustion engine.