Patent Publication Number: US-2016237863-A1

Title: Arrangement for axially shifting a cam assembly on a cam shaft

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a U.S. national stage application under 35 U.S.C. §371 of International Application No. PCT/EP2014/071460, filed on Oct. 7, 2014, and claims benefit to British Patent Application No. 1317871.0, filed on Oct. 9, 2013. The International Application was published in English on Apr. 16, 2015, as WO 2015/052197 A1 under PCT Article 21(2). 
    
    
     FIELD 
     The present invention relates to an arrangement for axially shifting a cam assembly on a cam shaft. 
     BACKGROUND 
     Variable valve lifting (VVL) and Variable valve timing (VVT) systems are used alone or in combination to vary the opening height and/or opening timing of intake and/or exhaust valves of internal combustion engine cylinders in order to improve one or more of performance, fuel economy and emissions levels. One known type of VVL and/or VVT system uses axial cam shifting. In such a system, a cam piece is arranged on a camshaft so that it can be moved axially along the cam shaft between at least two positions and the opening height and/or timing of a cylinder valve controlled by the cam piece depends upon which of the axial positions the cam piece is in. For example, the cam piece may comprise a first lift lobe for controlling a valve when the cam piece is at a first axial position on a camshaft and a second lift lobe for controlling that valve differently when the cam piece is at a second axial position on a camshaft. In a known system, one of the axial positions of the cam piece corresponds to a ‘cylinder deactivation position’ and in this position a cam follower remains continuously on a base circle of the cam piece so that the valve remains closed throughout a cylinder cycle. 
     One known actuator arrangement for shifting one or more cam pieces axially on a cam shaft is described in US2010/0251982. In this arrangement, each cam piece is provided with axial connecting paths in the form of spiral grooves running in the opposite sense to each other. The shifting of a given cam piece is realized according to the construction of the connecting paths by an electro-magnetically controlled activation element that is coupled selectively in the spiral grooves. The axial profile of the spiral groove engaged with the activation element has the result that, during the common (lobe-free) base-circle phase of a cam of the cam piece, the cam piece is shifted in a self-controlled way from one axial position to the next. A separate electro-magnetically controlled activation element is required for each cam piece to be shifted and so the actuator arrangement comprises a relatively large number of components. 
     SUMMARY 
     An aspect of the invention provides a cam shifting arrangement for shifting at least a first cam piece axially along a cam shaft of a valve train assembly of an internal combustion engine to selectively position the first cam piece in at least a first axial position or a second axial position on the cam shaft, the shifting arrangement comprising: a shifting member arranged substantially parallel with the cam shaft, wherein the shift member is moveable to cause the first cam piece to be moved between the first axial position and the second axial position. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be described in even greater detail below based on the exemplary figures. The invention is not limited to the exemplary embodiments. All features described and/or illustrated herein can be used alone or combined in different combinations in embodiments of the invention. The features and advantages of various embodiments of the present invention will become apparent by reading the following detailed description with reference to the attached drawings which illustrate the following: 
         FIG. 1  is a schematic perspective view of components of an internal combustion engine including a valve train assembly; 
         FIG. 2  illustrates a cam arrangement; 
         FIG. 3  is a schematic side view of the internal combustion engine of  FIG. 1  with the valve train assembly in a first configuration; 
         FIG. 4  is a schematic side view of the internal combustion engine of  FIG. 1  with the valve train assembly in a second configuration; 
         FIG. 5  is a schematic illustration of a firing sequence of three engine cylinders of an internal combustion engine; 
         FIG. 6  is a schematic perspective sectional view the internal combustion engine of  FIG. 1 ; 
         FIG. 7  illustrates a retention pin; 
         FIG. 8  is a schematic side sectional view of a camshaft; 
         FIG. 9  is a perspective view of an actuator rod; 
         FIG. 10  is a side sectional view of the actuator rod of  FIG. 9 ; 
         FIG. 11  is a schematic side sectional view of a valve train assembly in a first configuration; 
         FIG. 12  is a schematic side sectional view of the valve train assembly in a second configuration; 
         FIG. 13  is a schematic perspective view of part of a valve train assembly; 
         FIG. 14  is a schematic perspective view of part of an engine; 
         FIG. 15  is a schematic perspective view of the part of the valve train assembly of  FIG. 13 ; 
         FIG. 16  is a schematic perspective view of a shifting rod; 
         FIG. 17  is a schematic perspective view of part of a another valve train assembly; 
         FIG. 18  is a schematic side view of the part of a valve train assembly of  FIG. 17 ; and 
         FIG. 19  is a schematic perspective view of a component of the valve train assembly of  FIGS. 17 and 18 . 
     
    
    
     DETAILED DESCRIPTION 
     It is desirable to provide an alternative arrangement for axially shifting a cam assembly on a cam shaft. 
     According to an aspect of the invention, there is provided a cam shifting arrangement for shifting at least a first cam piece axially along a camshaft of a valve train assembly of an internal combustion engine to selectively position the cam piece in at least a first axial position or a second axial position on the cam shaft, the shifting arrangement comprising; a shifting member arranged substantially parallel with the cam shaft and moveable to cause the first cam piece to be moved between the first axial position and the second axial position. 
     Such an arrangement provides for a straightforward and reliable means of axially shifting a cam piece along a camshaft. When used in respect of valve trains that comprises a plurality of cam pieces that need to be axially shifted along a cam shaft, the arrangement negates the requirement of having a separate actuator for each cam piece. 
       FIG. 1  is a schematic illustration of part of an internal combustion engine  1 . In this example the engine  1  is a three cylinder engine comprising three cylinders  3 . A valve train assembly  5  of the Overhead Camshaft (OHC) type comprises a camshaft  7  for operating three pairs of valves  9  wherein each of the pairs of valves  9  is for a respective one of the three cylinders  3 . The valves  9  are either all intake valves or all exhaust valves. Each valve comprises a return spring biased to return that valve to a closed positions after it has been opened. It will be appreciated that whatever type of valves the valves  9  are (i.e. intake or exhaust), the engine  1  will comprise a second camshaft, similar to the camshaft  7 , for operating three corresponding pairs of the other type valves, one pair of valves for each cylinder  3 . Accordingly, each cylinder  3  comprises a pair of intake valves and a pair of exhaust valves. The camshaft  7  comprises a camshaft pulley  8  at one end connected by gearing to an engine crankshaft so that in use crankshaft rotation causes rotation of the camshaft  7 . 
     The camshaft  7  comprises three cam assemblies  11  mutually spaced apart along a longitudinal axis of the camshaft  7 . Each cam assembly  11  is for controlling a respective one of the three pairs of valves  9 . To this end, each valve comprises at its upper end a lifting pad  9   a  arranged to be in sliding engagement with a cam assembly  11  as the camshaft  7  rotates. As will explained in greater detail below each cam assembly  11  is rotationally locked with respect to the camshaft  7  (i.e. when the camshaft  7  and hence each cam assembly  11  rotate, there is no relative rotation between the camshaft  7  and each cam assembly  11 ) but the cam assemblies  11  are shift-able, along the longitudinal axis of the camshaft  7  between a first position that provides for a normal engine combustion mode and a second position that provides for a cyclical cylinder deactivation mode. 
     Referring now to  FIG. 2  in particular, each cam assembly  11  defines first and second cam sections  13 , one at each respective end of the cam assembly  11 , separated by a central section  14 . Each cam assembly  11  defines a central bore  14   a  extending along its longitudinal axis and through which, when the valve train assembly  3  is assembled, the cam shaft  7  extends. 
     Each cam section  13  further defines first  15  and second  17  cams arranged side-by-side along the axis of cam assembly  11 . Each first cam  15  comprises a base circle  15   a  and a pair of lift lobes  15   b . In this example, the lift lobes  15   b  are identical and have an angular separation of 180 degrees. Each second cam  17  defines a base circle  17   a  and a single lift lobe  17   b . The lift lobe  17   b  may have a different profile to the lift lobes  15   b.    
     When the cam assemblies  11  are in the first position that provides for normal engine combustion mode each first cam  15  is positioned so that it is in sliding contact with its respective one of the lifting pads  9   a  of a valve  9  and each second cam  17  is positioned so that it is not in contact that respective one of the lifting pads  9   a . In contrast, when the cam assemblies  11  are in the second position that provides for cylinder deactivation mode, it is each second cam  17 , rather than each first cam  15 , that is positioned so that it is in sliding contact with its respective one of the lifting pads  9   a  of a valve  9 . 
     It will be appreciated that in standard internal combustion engines comprising camshaft systems, a complete four stroke engine cycle of a cylinder comprises two complete rotations (i.e. 720 degrees) of the engine&#39;s crankshaft and one rotation (i.e. 360 degrees) of the camshaft (and thus the crankshaft is connected to drive a camshaft at half its own rate of rotation). Typically, each cam comprises a single main lift lobe so that the engine valve controlled by that cam is actuated once per engine cycle. 
     In contrast, in this example, the engine crankshaft is connected to the cam pulley  8  by gearing, for example a planetary gear system, so as to drive the camshaft  7  at one quarter of the crankshaft&#39;s own rate of rotation so that a complete four stroke engine cylinder cycle comprises two complete rotations of the engine&#39;s crankshaft (as per normal) but only one half of a rotation (i.e. 180 degrees) of the camshaft  7 . 
     Accordingly, when the cam assemblies  11  are in the first position that provides for a normal engine combustion mode ( FIG. 3 ), even though the camshaft  7  is rotating at half the normal rate of a camshaft, each valve  9  is still operated once per engine cycle by virtue of each first cam  15  having two first lift lobes  15   b  at 180 degrees separation. However, for a given first cam  15  of a cam assembly  11 , the particular one of the two first lift lobes  15   b  that activates a valve  9  in a given engine cycle of a cylinder  3  alternates from cycle to cycle. 
     When the cam assemblies  11  are in the second position ( FIG. 4 ), the two second cams  17  of the cam assembly  11  of a given cylinder  3  activate the two valves  9  of that cylinder only once every other cylinder engine cycle because the camshaft  7  is rotating at a ¼ the rate of the crankshaft and each second cam  17  comprises only a single lobe  17   b , but do not activate the valves  9  in each cycle that falls between successive active cycles. During those engine cycles in which the cylinder  3  is de-activated, the base circles  17   a  of the second cams  17  remain in sliding contact with their respective valves  9  for the whole of the engine cycle and hence the valves  9  remain closed. 
     It will be appreciated that preferably, if each single lobe  17   b  is shaped differently from each lobe  15   b  and/or angularly offset from the lobe  17   b  that it is closest to, the valve lift for each cylinder that is provided in the deactivation mode will be different (in height and/or timing) from the valve lift for each cylinder that is provided in the normal combustion mode and can be made more suitable for the lower engine speeds and loads associated with the deactivation mode. 
     In this example, the cylinders  3  have a known so called 1-2-3 firing order (i.e. a sequence of power delivery of the cylinders). Accordingly, the lift lobes of each cam arrangement  11  are angularly offset with respect to the corresponding lift lobes of the other two cam arrangements  11  so that the timing of the various valve events is appropriate for the cylinder firing order. 
       FIG. 5  illustrates schematically a firing sequence for the three cylinders (individually labelled  1 ,  2  and  3  in  FIG. 5 ) and further indicates for each of the three cylinders which of its engine cycles is active and which is in-active when the valve train assembly  5  is the second configuration. Each active cycle is indicated by two full line curves (one representing the valve lift of an intake valve, the other the valve lift of an exhaust valve) and each in-active cycle is indicated by two broken line curves. Looked at individually, it can be seen that, as described above, for a given cylinder, every other engine cycle is active with successive active cycles being separated by an inactive cycle. For cylinders  1  and  3  (as labelled in the Figure) odd numbered cycles are active and even numbered cycles are inactive and vice versa for the cylinder labelled  2 . As the cylinders are fired in the repeating sequence 1-2-3, the net overall repeating sequence for the three cylinders in combination is 1(active)-2(inactive)-3(active)-1(inactive)-2(active)-3(inactive) with the result that engine torque remains well balanced because every active cycle in the firing sequence is followed by an inactive cycle and vice versa. Moreover, in contrast with cam-less cylinder deactivation systems, this result is achieved in a straightforward manner simply by placing the valve train assembly into the second configuration. There is no requirement for a solenoid (or other such control system) for each valve (or pair of valves) for repeatedly activating and deactivating the valve(s) from cycle to cycle. 
     It will be appreciated that within two cam revolutions each cylinder is activated once and deactivated once and in effect the 3 cylinder engine is running in a 1.5 cylinder mode. 
     Referring now primarily to  FIGS. 6 to 12  there is described an example actuation system for axially shifting the cam assemblies  11  so as to configure the valve train assembly  5  between the first configuration and the second configuration. 
     In this example, each cam assembly  11  comprises first  20  and second  22  retention pins which prevent relative rotation between that cam assembly  11  and the camshaft  7  but allow that cam assembly  11  to move axially along the camshaft  11  between the first and second positions. 
     As seen in  FIG. 7 , the first retention pin  20  comprises a first cylindrical portion  23  defining towards a first end surface  25  a pair of cut out shoulder sections  27  (only one is visible in the view of  FIG. 7 ). Each cut out section  27  comprises a first planar contact surface  29  and a second planar contact surface  31 . The first planar contact surface  29  is perpendicular to and intersects the first end surface  25  and the second planar contact surface  31  is parallel to the first end surface  25  and intersects the first planar contact surface  29 . The first retention pin  20  further comprises a second cylindrical portion  33  which is coaxial with the first cylindrical portion  23  and extends from the first end surface  25 . The second cylindrical portion  33  has a smaller diameter and a smaller length than the first cylindrical portion  23 . 
     The second retention pin  22  is similar to the first retention pin  20  but does not comprise a second cylindrical portion  33 . 
     In each cam assembly  11 , the first retention pin  20  is received within a first aperture  35  defined by the cam assembly  11  and the second retention pin  22  is received within a second aperture  37  also defined by the cam assembly  11 . The first retention pin  20  fits tightly in the first aperture  35  with the second planar contact surfaces  31  resting on an outer surface  39  of the camshaft  7  and the first planar contact surfaces  27  in contact with the side walls of a first guide slot  41  defined in the cam shaft  7 . The end surface  25  of the first retention pin  20  is flush with the inner surface  43  of the camshaft  7  and the second cylindrical portion  33  extends into the hollow interior of the camshaft  7 . 
     Similarly, the second retention pin  22  fits tightly in the second aperture  37  with the second planar contact surfaces  31  resting on the outer surface  39  of the camshaft  7  and the first planar contact surfaces  27  in contact with the side walls of a second guide slot  45  defined in the cam shaft  7 . The end surface  25  of the second retention pin  22  is flush with the inner surface  43  of the camshaft  7  but, as there is no second cylindrical portion  33 , no part extends into the hollow interior of the camshaft  7 . 
     Thus, the rotational position of a cam assembly  11  relative to the camshaft  7  is fixed (to be non-rotatable) while a degree of axial sliding movement of the cam assembly  11  relative to the camshaft  7  is permitted. 
     Each cam assembly  11  further comprises an axial position positioning pin  46  received within a third aperture  47  defined by the cam assembly  11 . Each positioning pin  46  comprises a tip portion  46   a , a head portion  46   b  and a biasing member  46   c  disposed between the two. For each cam assembly  11 , the camshaft  7  is provided with first  48  and second  49  formations on its outer surface  39  which respectfully precisely define the first and second axial positions of the cam assembly  11 . The tip portion  46   a  of each positioning pin  46  is complimentary in shape to the first  48  and second  49  formations so that when a cam assembly  11  is in the first position its positioning pin  46  engages the first formation  47  and when the cam assembly  11  is in the second position its positioning pin  46  engages the second formation  49 . The biasing member  46   c  of each positioning pin  46  is arranged to bias its tip  46   c  towards the outer surface  39  of the camshaft  7  so that the positioning pin  46  functions to retain its cam assembly  11  in its axial position when in either the first position or the second position. In this way, a positioning pin  46  inhibits a cam assembly  11  from being accidently moved out of the first or second positions. 
     In this example, for a given cam assembly  11 , the first retention pin  20 , the second retention pin  22  and the positioning pin  46  are held in position in that cam assembly  11  by means of a clip  50  that is attached around the central section  14  of the cam assembly. 
     It will be appreciated that for a given cam assembly  11 , the first guide slot  41 , the second guide slot  45 , the first formation  48  and the second formation  49  formed in the cam shaft  7  for that assembly  11  are angularly offset around the circumference of the cam shaft  11  with respect to those corresponding slots and formation for the other cam assemblies  11 . This enables the cam assemblies  11  to be fitted to the cam shaft  11  with the required angular offset of the corresponding lift lobes of the cam arrangements  11  required to provide the various valve events appropriate for the cylinder firing order. 
     An actuation rod  51  which is co-axial with and fitted inside the camshaft  7  is provided for moving the cam assemblies  11  between the first and second positions and to this end is driven by an actuator  52  (See  FIG. 1 ). As best illustrated in  FIGS. 9 and 10 , the actuation rod  51  comprises three pairs of raised portions  53   a ,  53   b  spaced apart axially on its outer surface  55 , each pair comprising a first raised portion  53   a  and a second raised portion  53   b . Each first raised portion  53   a  and second raised portion  53   b  of a pair comprises respective first  53   c  and second  53   d  push surfaces. The pairs of raised portions  53   a  and  53   b  are positioned along the actuation rod  51  so that each corresponding pair of first  53   c  and second  53   d  push surfaces define a region through which the second cylindrical portion  33  of a first retention pin  20  of a cam assembly  11  is free to move through as the cam shaft  11  rotates (the actuation rod  51  itself does not rotate). The first  53   c  and second  53   d  contact surfaces each tapers in height along its length and for a given pair of opposing first  53   c  and second  53   d  contact surfaces, the first  53   c  and second  53   d  contact surfaces are angled across the surface of the actuation rod  51  in opposite senses so that at one end the first  53   c  and second  53   d  contact surfaces are closer together than they are at the other end. It will be appreciated that as the cam shaft  11  rotates, each portion  33  enters the region at the end were the first  53   c  and second  53   d  contact surfaces are furthest apart and leaves the region at the end where the first  53   c  and second  53   d  contact surfaces are closest together. 
     As illustrated, each first raised portion  53   a  and each second raised portion  53   b  may be non-integral with the actuation rod  51  and may be fixed to the actuation rod  51  by some suitable means (e.g. snap-fitted). Alternatively, each first raised portion  53   a  and each second raised portion  53   b  may be formed integrally the actuation rod  51 . 
     As illustrated in  FIG. 11 , when in the first non-deactivating position, the positioning pin  46  of each cam assembly  11  engages a first formation  48  to help retain that cam assembly  11  in position as the cam shaft  7  (and cam assemblies  11 ) rotates about it axis. In order to shift the cam assemblies  11  from the first position to the second position, the actuator  52  shifts the actuation rod  51  axially (to the right as viewed in the plane of  FIG. 11 ) by a fixed amount which brings each first  53   c  surface into contact with a second cylindrical portion  33  of a first retention pin  20  so that the actuation rod  51  exerts a pushing force on the cam assemblies  11  causing the positioning pins  46  to disengage from the first formations  48  and the cam assemblies  11  to slide axially across the cam shaft  7  until the cam assemblies  11  are in the second position and under the action of the biasing members  45   c  the positioning pins  45  have engaged the second formations  49 . 
     Similarly, in order to shift the cam assemblies  11  from the second position to the first position, the actuator shifts the actuation rod  51  axially in the reverse direction (to the left as viewed in the plane of  FIG. 12 ) by the fixed amount which brings each second  53   d  surface into contact with a second cylindrical portion  33  of a first retention pin  20  so that the actuation rod exerts a pushing force on the cam assemblies  11  causing the positioning pins  46  to disengage from the second formations  49  and the cam assemblies  11  to slide axially across the cam shaft until the cam assemblies  11  are in the first position and under the action of the biasing members the positioning pins  46  have engaged the first formations  48 . 
     Accordingly, the actuation system provides a simple and reliable system for configuring the valve train assembly in the first and second configurations. 
     Referring now first to  FIG. 13  there is a schematic illustration of a part of another valve train assembly  150  of the Overhead Camshaft (OHC) type comprising a camshaft  157  (of which only a central section is illustrated) for operating gas exchange valves of the cylinders of an internal combustion engine  158 . The valves operated by the camshaft  157  are either all intake valves or all exhaust valves and, accordingly, whichever the type of valves controlled by the camshaft  157  (i.e. intake or exhaust), the engine comprises a second valve train assembly  151 , similar to the valve train assembly  150  for operating the other type of valves. 
     In this example, the engine  158  is a four cylinder engine and there are a pair of intake valves and a pair of exhaust valves per cylinder) and the illustrated section of the cam shaft  157  is for operating one of the valve types (i.e. intake valves or exhaust valves) of the second and third cylinders of the engine  158 . To that end, the camshaft  157  comprises four separate first  160   a , second  160   b , third  161   a  and fourth  161   b  cam assemblies mutually spaced apart along a longitudinal axis of the camshaft  157  with the first cam assembly  160   a  and the second cam assembly  160   b  for operating first and second valves respectively of the second cylinder and the third cam assembly  161   a  and the fourth cam assembly  161   b  for operating first and second valves respectively of the third cylinder. In this example, the engine  158  is of the type where supports  152  are provided that support the camshaft between the cam assemblies of each given cylinder (e.g. a support  152  is located between the cam assembly  160   a  and the cam assembly  160   b  of the second cylinder and another support  152  is located between the cam assembly  161   a  and the cam assembly  161   b  of the third cylinder). The cam shaft comprises a camshaft pulley at one end connected by gearing to an engine crankshaft so that in use crankshaft rotation causes rotation of the camshaft  157  but in this example the gearing is such that the camshaft  157  rotates at the standard half the rate of rotation of the crankshaft. 
     Again, as with the example described above with respect to  FIGS. 1 to 12 , each cam assembly  160   a ,  160   b ,  161   a  and  161   b  is rotationally locked with respect to the camshaft  157  but the cam assemblies  160   a ,  160   b ,  161   a  and  161   b  are shift-able along the longitudinal axis of the camshaft  157  between a first position that provides for a normal engine combustion mode and a second position that provides for a cylinder deactivation mode. In this example, the cylinder deactivation mode is a standard cylinder deactivation mode for a four cylinder engine in that the second and third cylinders (remain deactivated in every engine cycle because a cam follower of each valve is always on a base circle of a cam assembly  160   a ,  160   b ,  161   a  and  161   b  while the first and fourth cylinders remain active in every engine cycle with the valves of those cylinders being controlled by respective other cam assemblies for those valves. 
     Referring again to  FIG. 13  in particular, each cam assembly  160   a ,  160   b ,  161   a  and  161   b  defines a respective cam section  163  at one of its ends and each cam section  163  further defines first  165  and second  167  cams arranged side-by-side along the axis of the respective cam assembly  160   a ,  160   b ,  161   a  and  161   b . Each first cam  165  comprises a base circle  165   a  and a lift lobe  165   b . In contrast, each second cam  167  defines a base circle  167  only (i.e. it does not define a lift lobe). 
     Accordingly, when the cam assemblies  160   a ,  160   b ,  161   a  and  161   b  are in the first position that provides for normal engine combustion mode each first cam  165  is positioned so that it is in sliding contact with a cam follower of a valve so that that cam&#39;s lift lobe  165   b  activates the valve ever cylinder cycle. However, when the cam assemblies  160   a ,  160   b ,  161   a  and  161   b  are in the second position that provides for cylinder deactivation mode, it is each second cam  167 , rather than each first cam  165 , that is positioned so that it is in sliding contact with a cam follower of a valve and because each second cam  167  comprises a base circle only, each valve remains inactive in each cylinder cycle. 
     Referring now to all of  FIGS. 13 to 16 , an actuation system for axially shifting the cam assemblies  160   a ,  160   b ,  161   a  and  161   b  between the first and second positions comprises an electro-magnetic actuator  170  comprising an actuation pin  172 , and an actuation or shifting rod  174  which is co-axial with and fitted inside the camshaft  157 . The actuation pin  172  is for selectively engaging either one of a pair of spiral grooves  175  (only one is illustrated in the Figure) formed in the first cam assembly  160   a , to shift the first cam assembly  160   a  between its first and second positions. In order to shift the first cam assembly  160   a  from the first position to the second position the actuation pin  172  engages a first one of the pair of spiral grooves  175  and to shift the first cam assembly  160   a  from the second position to the first position the actuation pin  172  engages the second one of the pair of spiral grooves  175 . The use of such a pin  172  and grooves  175  for axially shifting a cam assembly on a cam shaft is known in the art and so this particular aspect of the actuation system will not be described in any further detail. However, advantageously in this example, the cam assemblies  160   a ,  160   b ,  161   a  and  161   b  and the shifting rod  174  are arranged so that when the first cam assembly  160   a  is axially shifted from its first position to its second position (or vice versa) by the actuator  170 , the first cam assembly  160   a  causes the shifting rod  174  to be axially shifted in the same direction as the first cam assembly  160   a  so that in turn the shifting rod  174  causes each of the cam assemblies  160   b ,  161   a  and  161   b  to be axially shifted from its first position to its second position (or vice versa). 
     In this example as best seen in  FIG. 15 , the cam assembly  160   a  and the cam assembly  160   b  both comprise a pair of retention pins  176  and the cam assembly  161   a  and the cam assembly  161   b  both comprise a retention pin  176  which retention pins  176  are all similar in design to the first retention pins  20  described above. Each retention pin  176  is received within its own aperture defined by its cam assembly  160   a ,  160   b ,  161   a  and  161   b  and extends into its own respective guide slot  178  formed through the cam shaft  157 . Each retention pin  176  comprises a cylindrical main portion  176   a  and a smaller diameter cylindrical end portion  176   b  which end portion  176   b  extends into the hollow interior of the cam shaft  157 . The cam assembly  161   a  and the cam assembly  161   b  both further comprise a retention pin  179  also received within its own aperture defined by the respective cam assembly  161   a ,  161   b . Each retention pin  179  is shorter than the retention pins  176  and comprises a cylindrical portion that extends into its own respective guide slot  180  formed through the cam shaft  157  but does not comprise any portion that extends into the hollow interior of the cam shaft  157 . 
     Each cam assembly  160   a ,  160   b ,  161   a  and  161   b  further comprises an axial positioning pin  181 , similar to the axial positioning pin  46  described above, received within its own aperture defined by the respective cam assembly  160   a ,  160   b ,  161   a  and  161   b . Again, each positioning pin  181  engages a first formation in the cam shaft  157  when its cam assembly  160   a ,  160   b ,  161   a  and  161   b  is in the first position and engages a second formation in the cam shaft  157  when its cam assembly  160   a ,  160   b ,  161   a  and  161   b  is in the second position. 
     For a given cam assembly  160   a ,  160   b , the pair of retention pins  176 , and the positioning pin  181  and, for a given cam assembly  161   a  and  161   b  the retention pin  176 , the retention pin  179  and the positioning pin  180 , are held in position in their respective cam assembly  160   a ,  160   b ,  161   a  and  161   b  by means of a respective clip  182  that is attached around that cam assembly  160   a ,  160   b ,  161   a  and  161   b.    
     The shifting rod  174  comprises two pairs of opposing circumferential ridges  190   a  and  190   b . Each pair of circumferential ridges  190   a  and  190   b  is associated with a respective one of the cam assemblies  160   a  and  160   b  and the ridges  190   a  and  190   b  of a pair have respective contact surfaces  190   c  and  190   d  that define a space into which the end portions  176   b  of the retention pins  176  of that pair&#39;s cam assembly extend and are free to move through as the cam shaft  157  rotates. 
     The shifting rod  174  further comprises two pairs of raised portions  193   a ,  193   b , which are similar to the pairs of raised portions  53   a  and  53   b  described above. Each pair of raised portions  193   a  and  193   b  is associated with a respective one of the cam assemblies  161   a  and  161   b  and comprises a first raised portion  193   a  and a second raised portion  193   b  and each first raised portion  193   a  and second raised portion  193   b  of a pair comprises respective first  193   c  and second  193   d  push surfaces. Each pair of first  193   c  and second  193   d  push surfaces define a space through which the end portion  176   b  of the retention pin  176  of that pair&#39;s cam assembly  161   a  and  161   b  is able to move as the cam shaft  158  rotates. 
     In order to shift the cam assemblies  160   a ,  160   b ,  161   a  and  161   b  from the first position to the second position (or vice versa), the electromagnetic actuator  170 , under the control of an engine control system, causes the actuation pin  172  to engage the spiral groove  175  to drive the cam assembly  160   a  from the first position to the second position (or vice versa). Immediately the cam assembly  160   a  begins to move, its retention pins&#39;  176  end portions  176   b  contact, depending upon the axial direction of the cam assembly&#39;s  160   a  movement, either the contact surface  190   c  or the contact surface  190   d  of the pair of circumferential ridges  190   a  and  190   b  associated with cam assembly  160  causing the shifting rod  174  move in the same axial direction as the cam assembly  160   a . The movement of the shifting rod  174  brings, depending upon the direction of movement, either the contact surface  190   c  or the contact surface  190   d  of the pair of circumferential ridges  190   a  and  190   b  associated with the cam assembly  160   b  into contact with the end portions  176   b  of that cam assembly&#39;s  160  retention pins  176  to drive the cam assembly  160   b  from the first position to the second position (or vice versa). 
     Additionally, the movement of the shifting rod  174  brings, depending upon the direction of movement, either the contact surface  193   c  or the contact surface  193   d  of each pair of raised portions  193   a ,  194   b  into contact with the end portion  176   b  of the retention pin  176  of the cam assembly  161   a ,  161   b  associated with that pair of raised portions  193   a ,  194   b  to drive the cam assemblies  161   a  and  161   b  from the first position to the second position (or vice versa). The arrangement is such that first cam assembly  160   a  and the second cam assembly  160   b  (i.e. the cam assemblies for cylinder  2 ) move immediately with the shifting rod  174  whereas the cam assemblies  161   a  and  161   b  (i.e. the cam assemblies for cylinder  3 ) move later (i.e. the time taken for 180 degrees rotation of the cam shaft) as a result of the raised portions  193   a  and  194   b . It will be appreciated that the shifting rod  174  may have moved but be stationary again before the cam assemblies  161   a  and  161   b  are caused to be moved. 
     It will be appreciated that the retention pins  176  participate in transmitting torque from the cam shaft to the cam assemblies and in the axial shifting of the cam assemblies whereas the retention pins participate only in transmitting torque from the cam shaft to the cam assemblies. 
     Referring now to  FIGS. 17 to 19 , there is illustrated a valve train assembly  205  comprising a camshaft  207  for operating three pairs of valves each pair of valves for a respective one of three engine cylinders not shown. Similar to the embodiment described above with respect to  FIGS. 1 to 12 , in this embodiment the valve train assembly  205  is configurable in a first configuration that provides for a normal engine combustion mode and a second configuration that provides for a cyclical cylinder deactivation mode. 
     To that end, the camshaft  207  comprises a first cam assembly  260 , a second cam assembly  261   a  and a third cam assembly  261   b  each for operating a respective one of the three pairs of valves. Again, each of the cam assemblies  260 ,  261   a  and  261   b  is rotationally locked with respect to the camshaft  207  but is shift-able along the longitudinal axis of the camshaft  207  between a first position for the normal engine combustion mode and a second position for the cyclical cylinder deactivation mode. 
     Furthermore, each of the cam assemblies  260 ,  261   a  and  261   b  defines first and second cam sections  270  (for clarity labelled only on the third cam assembly  261   b ) for respectively controlling a first valve and a second valve of a respective one of the pairs of valves. Similar to the arrangement in the first embodiment, each cam section  270  defines first  272  and second  274  cams (for clarity labelled only on the left hand side of the first cam assembly  260 ), each first cam  272  defining a base circle  272   a  and a pair of lift lobes  272   b  having an angular separation of 180 degrees and each second cam  274  defining a base circle  274   a  and a single lift lobe  274   b  (for clarity labelled only on the left hand side of the second cam assembly  261   a ). 
     Again similar to the first described embodiment, the engine crank shaft is connected by a gearing system to drive the camshaft  207  at ¼ the rate of rotation of the crankshaft. Accordingly, when the cam assemblies  260 ,  261   a  and  261   b  are in the first position, each valve is operated once per engine cycle in response to a pair of lift lobes  272   b  and when the cam assemblies  260 ,  261   a  and  261   b  are in the second position, each valve is operated once every engine cycle in response to a single lift lobe  274   b.    
     An actuation system for axially shifting the cam assemblies  260 ,  261   a  and  261   b  comprises an electro-magnetic actuator comprising an actuation pin, a shifting barrel  276  and a shifting rod arrangement  278 . 
     The shifting barrel  276 , like the cam assemblies  260 ,  261   a  and  261   b , is mounted on the cam shaft  257  so as to be rotationally fixed with respect there to, but is axially moveable along the cam shaft between first and second positions corresponding to the normal engine combustion mode and the cyclical cylinder deactivation mode. The shifting barrel  276  comprises a pair of grooves  278  and the electro-magnetic actuator causes an actuation pin to engage one of the pair of grooves  280  to move the shifting barrel  276  from its first position to its second position and to engage the other one of the pair of grooves  280  to move the shifting barrel  276  from its second position its first position. 
     In this embodiment, the shifting rod arrangement  278  is arranged and supported parallel to the cam shaft  257 , but unlike the shifting rods described in the above embodiments it is external to the cam shaft  257 . 
     In some respects similar to the example described above with respect to Figures, in this example, the shifting rod arrangement  278 , the shifting barrel  276  and the cam assemblies  260 ,  261   a  and  261   b  are arranged so that when the actuator moves the shifting barrel  276  from its first position to its second position (or vice versa), the shifting barrel  276  causes the shifting rod arrangement  278  to be axially shifted in the same direction as the shifting barrel  276  so that the shifting rod arrangement  278  causes each of the first cam assembly  260 , the second cam assembly  261   a  and the second cam assembly  261   b  to be shifted from its first position to its second position (or vice versa). 
     The shifting rod arrangement  278  comprises first  278   a  and second  278   b  parallel sub rods which are supported by first  282 , second  284 , third  286  and fourth  288  support members axially spaced apart along the longitudinal axis of shifting rod arrangement  278 . 
     The first support member  282  comprises a generally ‘U’ shaped member  290  having a pair of arms  290   a  extending transversely from the shifting rod arrangement  278  towards the cam shaft  257  and the second support member  284  comprises a similar ‘U’ shaped member  291  also having a pair of arms  291   a  extending transversely from the shifting rod arrangement  278  towards the cam shaft  257 . 
     At one end, the shifting barrel  276  defines a first circumferential groove  294  into which extend end portions of the pair of arms  290   a  of the first support member  282 . At roughly its midpoint, the first cam assembly  260  defines a second circumferential groove  295  into which extend end portions of the pair of arms  291   a  of the second support member  284 . 
     The third support member  286  supports a first contact platform  295  and the fourth support member  288  supports a similar second contact platform  297 . 
     As illustrated in  FIG. 19 , each of the first  295  and second  297  contact platforms comprises a face  300  defining a recessed portion  302  comprising a first side contact surface  304  and an opposing second side contact surface  306 . The first side contact surface  304  and the second side contact surface  306  each tapers in height in both directions along its length (i.e. it is higher along it middle portion than at its ends) are curved and are divergent so that they are closer to each other at one end than they are at the other end. 
     At roughly its midpoint, the second cam assembly  261   a  defines a circumferential collar  310   a  from which extends a first cylindrical contact member  312   a . Likewise, at roughly its midpoint, the third cam assembly  261   b  defines a circumferential collar  310   b  from which extends a second cylindrical contact member  312   b.    
     When in the first configuration or the second configuration, as the cam shaft  257  rotates (and hence as the shifting barrel  276 , and the cam assemblies  260 ,  261   a  and  261   b  rotate) the shifting barrel  276  rotates without contacting the pair of arms  290   a , the first cam assembly  260  rotates without contacting the pair of arms  291 , the second cam assembly  261   a  rotates with the first cylindrical contact member  312  passing freely through the recessed portion  302  of the first contact platform  295  and the third cam assembly  261   b  rotates with the second cylindrical contact member  312   b  passing freely through the recessed portion  302  of the second contact platform  297 . 
     In order to shift the cam assemblies  260 ,  261   a  and  261   b  from the first position to the second position (or vice versa), the electromagnetic actuator under the control of an engine control system, causes an actuation pin to engage one or other (depending on the required direction) of the grooves  280  to drive the shifting barrel  276  from its first position to its second position (or vice versa). 
     Immediately the shifting barrel  276  begins to move, one or other (depending upon the direction of motion) of a pair of side walls of the first circumferential groove  294  contacts the end portions of the pair of arms  290   a  causing the shifting rod arrangement  278  to move in the same axial direction as the shifting barrel  276 . 
     The movement of the shifting rod arrangement  278  brings the end portions of the pair of arms  291   a  into contact with (depending upon the direction of movement) one or other of the pair of side walls of the second circumferential groove  295  causing the first cam assembly  260  to move in the same axial direction as the shifting barrel  276  so that the first cam assembly  260  moves between its first and second positions (or vice versa). 
     Additionally, the movement of the shifting rod arrangement  278  brings, (depending upon the direction of movement) either the first contact surface  304  or the second contact surface  306  of the first contact platform  295  into contact with the first cylindrical contact member  312   a  causing the second cam assembly  261  to move in the same direction as the shifting barrel  276  so that the third cam assembly  261   a  moves between its first and second positions (or vice versa). 
     Similarly, the movement of the shifting rod arrangement  278  brings, (depending upon the direction of movement) either the first contact surface  304  or the second contact surface  306  of the second contact platform  297  into contact with the second cylindrical contact member  312   b  causing the third cam assembly  261   b  to move in the same direction as the shifting barrel  276  so that the third cam assembly  261   b  moves between its first and second positions (or vice versa). 
     It will be appreciated that the arrangement is such that first cam assembly  260  starts to move immediately with the shifting rod arrangement  278 , whereas the angular positions of first cylindrical contact member  312   a  and the second cylindrical contact member  312   b  cause the second cam assembly  261   a  and the third cam assembly  261   b  to move later. In general, the cam assemblies are arranged to move in a sequence that matches the firing sequence of the cylinders associated with the cam assemblies. Accordingly, as the cylinders of the cam assemblies  260 ,  261   a ,  261   b  having a firing sequence of 1-2, -3, the cam assembly  260  moves first, the cam assembly  261   a  second, and the cam assembly  261   a  third. It will be appreciated, that the shifting rod arrangement  278 , having moved, may be stationary when contact between the first contact surface  304  or the second contact surface  306  of the first contact platform  295  and the first cylindrical contact member  312   a  causes the second cam assembly  261  to move and contact between the first contact surface  304  or the second contact surface  306  of the second contact platform  297  and the second cylindrical contact member  312   b  causes the third cam assembly  261   b  to move. 
     Although in this embodiment, both sub rods  278   a  and  278   b  of the shifting rod arrangement  278  move when the shifting barrel  276  moves, as an alternative, only one of them may move, say rod  278   b , the other rod serving as a sliding support for the components  282 ,  284 ,  286  and  288 . 
     The above embodiments are to be understood as illustrative examples of the invention only. Further embodiments of the invention are envisaged. 
     It is to be understood that any feature described in relation to any one embodiment may be used alone, or in combination with other features described, and may also be used in combination with one or more features of any other of the embodiments, or any combination of any other of the embodiments. Furthermore, equivalents and modifications not described above may also be employed without departing from the scope of the invention, which is defined in the accompanying claims. 
     While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive. It will be understood that changes and modifications may be made by those of ordinary skill within the scope of the following claims. In particular, the present invention covers further embodiments with any combination of features from different embodiments described above and below. Additionally, statements made herein characterizing the invention refer to an embodiment of the invention and not necessarily all embodiments. 
     The terms used in the claims should be construed to have the broadest reasonable interpretation consistent with the foregoing description. For example, the use of the article “a” or “the” in introducing an element should not be interpreted as being exclusive of a plurality of elements. Likewise, the recitation of “or” should be interpreted as being inclusive, such that the recitation of “A or B” is not exclusive of “A and B,” unless it is clear from the context or the foregoing description that only one of A and B is intended. Further, the recitation of “at least one of A, B, and C” should be interpreted as one or more of a group of elements consisting of A, B, and C, and should not be interpreted as requiring at least one of each of the listed elements A, B, and C, regardless of whether A, B, and C are related as categories or otherwise. Moreover, the recitation of “A, B, and/or C” or “at least one of A, B, or C” should be interpreted as including any singular entity from the listed elements, e.g., A, any subset from the listed elements, e.g., A and B, or the entire list of elements A, B, and C.