Abstract:
An internal combustion engine includes a variable valvetrain system for improving the range of controllability of the internal EGR technique adjusts the internal EGR lift in a more favorable window and position compared to the internal EGR window typically utilized. In particular, a combined change of lift, phase and duration of the internal EGR lift of the exhaust vale improves the controllability and stability of the desired amount of internal EGR. The present system achieves a high internal EGR capability at low loads and lower back pressure. The system also achieves controllability of internal EGR at high loads without requiring ultra low lifts. The system also allows warm-up of the exhaust after treatment system faster for higher conversion efficiency, reduced HC and NOx engine-out emissions and increased combustion stability.

Description:
FIELD 
       [0001]    The present disclosure relates to internal combustion engines and more particularly, to an internal combustion engine utilizing internal exhaust gas recirculation. 
       BACKGROUND 
       [0002]    This section provides background information related to the present disclosure which is not necessarily prior art. 
         [0003]    In the internal combustion engines in use today, it is common to use a portion of the exhaust gasses to improve the engine performance or the emissions of the combustion. A typical benefit of the use of the exhaust gas recirculation (EGR) is the reduction of the peak combustion temperature in order to avoid the creation of pollutants like NOx or the reduction of the required amount of throttling in gasoline engines. Typically, the recirculation is obtained by an external piping which brings a portion of the exhaust gasses back into the intake manifold. 
         [0004]    In recent years, an improved internal exhaust gas recirculation (internal EGR) technique has been used in order to minimize the waste of energy (waste of heat through the piping loop, waste of flow dynamic losses along the piping) of such a system bringing further benefits like the more stable combustion in cold conditions, the reduction of pollutants or an improvement of fuel efficiency. The internal EGR technique includes the opening of the exhaust gas valve during the intake stroke phase creating a so-called rebreathing lift. The control of the amount of internal EGR is obtained by applying a higher or lower lift of the exhaust valve during the intake stroke of the cylinder where the differential pressure between the exhaust manifold and the combustion chamber is in favor of filling the combustion chamber itself with exhaust gasses. 
         [0005]    Controlling the amount of internal EGR only with the usage of a higher or lower re-breathing lift brings to an edge where a small variation of such a lift corresponds to a huge variation of the gas recirculated. Such a situation limits the usage of the internal EGR technique to a restricted area of the engine map. 
       SUMMARY 
       [0006]    This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features. 
         [0007]    In order to improve the responsiveness of the variable valvetrain system and improve the range of controllability of the internal EGR technique, the present disclosure adjusts the lift in a more favorable window and position compared to the internal EGR window typically utilized. In particular, the present discourse utilizes a combined change of lift, phase and duration in order to improve the controllability and stability of the desired amount of EGR. The present system achieves a high internal EGR capability at low loads and lower back pressure. The system also achieves controllability of internal EGR at high loads without requiring ultra low lifts. The system also allows warm-up of the exhaust after treatment system faster for higher conversion efficiency, reduced HC and NOx engine-out emissions and increased combustion stability. 
         [0008]    Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
     
    
     
       DRAWINGS 
         [0009]    The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure. 
           [0010]      FIG. 1  shows a possible embodiment of an automotive system comprising an internal combustion engine; 
           [0011]      FIG. 2  is a cross-section the internal combustion engine of  FIG. 1 ; 
           [0012]      FIG. 3  is a detailed view of a possible embodiment of a cam shifting system used in an internal combustion engine according to the principles of the present disclosure, wherein two cam followers are shown; 
           [0013]      FIG. 4  is a schematic view showing a cam follower engaging a cam of the shifting unit, the shifting portion of the groove, and the driving pin; 
           [0014]      FIG. 5  is a perspective view of a possible embodiment of the shifting unit according to the present disclosure; 
           [0015]      FIG. 6  is a planar schematic view of a possible embodiment of the shifting unit according to the present disclosure; 
           [0016]      FIG. 7  is a graphic representation of the cams of a possible embodiment of the cam shifting system used in an internal combustion engine according to the present disclosure; and 
           [0017]      FIG. 8  is a graphic representation of the cam phasing of the internal EGR cam lobes according to the principles of the present disclosure. 
       
    
    
       [0018]    Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. 
       DETAILED DESCRIPTION 
       [0019]    Example embodiments will now be described more fully with reference to the accompanying drawings. 
         [0020]    Example embodiments are provided so that this disclosure will be thorough, and will fully convey the scope to those who are skilled in the art. Numerous specific details are set forth such as examples of specific components, devices, and methods, to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, that example embodiments may be embodied in many different forms and that neither should be construed to limit the scope of the disclosure. In some example embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail. 
         [0021]    The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms “a,” “an,” and “the” may be intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms “comprises,” “comprising,” “including,” and “having,” are inclusive and therefore specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed. 
         [0022]    When an element or layer is referred to as being “on,” “engaged to,” “connected to,” or “coupled to” another element or layer, it may be directly on, engaged, connected or coupled to the other element or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly engaged to,” “directly connected to,” or “directly coupled to” another element or layer, there may be no intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.). As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
         [0023]    Although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms may be only used to distinguish one element, component, region, layer or section from another region, layer or section. Terms such as “first,” “second,” and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the example embodiments. 
         [0024]    Spatially relative terms, such as “inner,” “outer,” “beneath,” “below,” “lower,” “above,” “upper,” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. Spatially relative terms may be intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the example term “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly. 
         [0025]    With reference to  FIGS. 1 and 2 , an automotive system  10  is shown, that includes an internal combustion engine (ICE)  12  having an engine block  14  defining at least one cylinder  16  having a piston  18  coupled to rotate a crankshaft  20 . A cylinder head  22  cooperates with the piston  18  to define a combustion chamber  24 . A fuel and air mixture (not shown) is disposed in the combustion chamber  24  and ignited, resulting in hot expanding exhaust gasses causing reciprocal movement of the piston  18 . The fuel is provided by at least one fuel injector  26  and the air through at least one intake port  28 . The fuel is provided at high pressure to the fuel injector  26  from a fuel rail  30  in fluid communication with a fuel pump  32  that increase the pressure of the fuel received from a fuel source  34 . Each of the cylinders  16  has at least two cylinder valves  36   a,    36   b,  actuated by one or more camshaft  38  rotating in time with the crankshaft  20 . The intake cylinder valves  36   a  selectively allow air into the combustion chamber  24  from the port  28  and alternately the exhaust cylinder valves  36   b  allow exhaust gases to exit through a port  40 , as is known in the art. A cam phaser  42  is provided to selectively vary the timing between at least one of the camshaft(s)  38  and the crankshaft  20 . 
         [0026]    In the detailed view of an embodiment shown in  FIG. 3 , two exhaust cylinder valves  36   b,    36   b  are partially visible and are provided with a cam follower  44 ,  44   a.  The cam followers  44 ,  44   a  can be provided with a cam follower roller  46 ,  46   a  intended to contact the cams arranged on the camshaft  38 , as it will be disclosed in greater detail below. It has to be noted that different types of cam followers  44 ,  44   a  can be used, such as for example cam followers provided with a rocker arm. 
         [0027]    In the embodiments shown in  FIGS. 1, 2 and 3 , the internal combustion engine  12  is provided with at least two exhaust cylinder valves  36   b,    36   b  for each cylinder, e.g. two exhaust cylinder valves, however, the present invention can be also applied to internal combustion engines provided with one or more exhaust cylinder valves for each cylinder. The air may be distributed to the air intake port(s)  28  through an intake manifold  48 . An air intake duct  50  may provide air from the ambient environment to the intake manifold  48 . In other embodiments, a throttle body  52  may be provided to regulate the flow of air into the manifold  48 . In still other embodiments, a forced air system such as a turbocharger  54 , having a compressor  56  rotationally coupled to a turbine  58 , may be provided. Rotation of the compressor  56  increases the pressure and temperature of the air in the intake duct  50  and manifold  48 . An intercooler  60  disposed in the intake duct  50  may reduce the temperature of the air. The turbine  58  rotates by receiving exhaust gases from an exhaust manifold  62  that directs exhaust gases from the exhaust ports  40  and through a series of vanes prior to expansion through the turbine  58 . The exhaust gases exit the turbine  58  and are directed into an exhaust system  64 . 
         [0028]    The exhaust system  64  may include an exhaust pipe  66  having one or more exhaust after treatment devices  68 . The after treatment devices  68  may be any device configured to change the composition of the exhaust gases. Some examples of after treatment devices  68  include, but are not limited to, catalytic converters (two and three way), oxidation catalysts, lean NO x  traps, hydrocarbon adsorbers, selective catalytic reduction (SCR) systems, and particulate filters. Other embodiments may include an exhaust gas recirculation (EGR) system  70  coupled between the exhaust manifold  62  and the intake manifold  48 . The EGR system  70  may include an EGR cooler  72  to reduce the temperature of the exhaust gases in the EGR system  70 . An EGR valve  74  regulates a flow of exhaust gases in the EGR system  70 . 
         [0029]    The automotive system  10  may further include an electronic control unit (ECU)  80  in communication with one or more sensors and/or devices associated with the internal combustion engine  12 . The ECU  80  may receive input signals from various sensors configured to generate the signals in proportion to various physical parameters associated with the internal combustion engine  12 . The sensors include, but are not limited to, a mass airflow and temperature sensor  84 , a manifold pressure and temperature sensor  86 , a combustion pressure sensor  88 , coolant and oil temperature and level sensors  90 , a fuel rail pressure sensor  92 , a cam position sensor  94 , a crank position sensor  96 , exhaust pressure and temperature sensors  98 , an EGR temperature sensor  100 , and an accelerator pedal position sensor  102 . Furthermore, the ECU  80  may generate output signals to various control devices that are arranged to control the operation of the ICE  12 , including, but not limited to, fuel injectors  26 , the throttle body  52 , the EGR valve  74 , and the cam phaser  42 . Dashed lines are used to indicate communication between the ECU  80  and the various sensors and devices, but some are omitted for clarity. 
         [0030]    Turning now to the ECU  80 , this apparatus may include a digital central processing unit (CPU) in communication with a memory system, or data carrier, and an interface bus. The CPU is configured to execute instructions stored as a program in the memory system, and send and receive signals to/from the interface bus. The memory system may include various storage types including optical storage, magnetic storage, solid state storage, and other non-volatile memory. The interface bus may be configured to send, receive, and modulate analog and/or digital signals to/from the various sensors and control devices. 
         [0031]    With reference to  FIGS. 3-7 , according to a possible embodiment, the internal combustion engine  12  comprises a cam shifting system  110  comprising a shifting unit  112 . According to a possible embodiment, as for the example shown in the figures, the shifting unit  112  is a hollow element, preferably having a cylindrical shape. The shifting unit  112  is coupled rotatably fixed to the camshaft  38 . In other words, when the camshaft  38  rotates around a camshaft rotation axis R, the shifting unit  112  rotates together with the camshaft  38 . Furthermore, the shifting unit  112  is movable, with respect to the camshaft  38 , preferably it is axially moveable along the camshaft rotation axis R. As mentioned, this axial movement is known as “shifting movement” of the shifting unit  112 . 
         [0032]    The shifting unit  112  is coupled to the camshaft  38  to be rotatably fixed and axially moveable by means known in the art. In the shown embodiments, the shifting unit  112  is provided with an internal splines  114 , that meshes with an external splines  114 ′ of the camshaft  38 . Thanks to the splined engagement  114 ,  114 ′, the rotational movement of the camshaft  38  is transmitted to the shifting unit  112 ; furthermore, the shifting unit  112  can slide on the camshaft  38  along the camshaft rotation axis R. The shifting unit  112  is provided with two or more cams  116 ,  118 ,  120  for a cam follower  44 ,  44   a.    
         [0033]    According to a possible embodiment, the shifting unit  112  comprises a first cam  116  provided with a first cam base circle  116   a  with an exhaust cam lobe  116   b  and an EGR cam lobe  116   c  extending from the base circle  116   a,  a second cam  118  provided with a second cam base circle  118   a  and with an exhaust cam lobe  118   b  and an EGR cam lobe  118   c  extending from the base circle  118   a  and a third cam  120  provided with a third base circle  120   a  and with an exhaust cam lobe  120   b  and an EGR cam lobe  120   c  extending from the third base circle  120   a.  The shifting unit  112  can also comprise additional cams. According to a possible embodiment, the additional cams can include exhaust cam lobes and EGR cam lobes of different height and/or different circumferential length than the first through third cams  116 ,  118 ,  120 , or can be provided with only a cam base circle to form a deactivation cam of the shifting unit  112 , or can be provided with a cam base circle and with just an exhaust cam lobe and no EGR cam lobe so that the internal EGR can be disabled. 
         [0034]    The contour of the EGR cam lobes  116   c,    118   c,    120   c,  as well as the exhaust cam lobes  116   b,    118   b,    120   b  are visible in  FIG. 7 , that is a graphical illustration showing the shape of the cams along their extension around the camshaft rotation axis R. More in detail,  FIG. 7  shows the lift provided by the cams  116 ,  118  and  120  (on the y-axis (ordinate)) and the extension in 360 degrees about the camshaft rotation axis R (on the x-axis (abscissa)). Cam followers  44 ,  44   a  are part of relevant cylinder valves  36   b,    36   b.  As known, the coupling between the cams  116 ,  118 ,  120  and the cam followers  44 ,  44   a  transforms the rotational movement of the camshaft into a reciprocating movement of the cylinder valves  36   b,    36   b.  Part of the cams  116 ,  118 ,  120  are arranged one next to the other. In the shown embodiments, cam  116  is arranged next to cam  118 , and cam  120  is arranged next to cam  118 . It has to be noted that the cams intended to contact the cam followers  44 ,  44   a,  are shown in the attached figures with the same reference numbers  116 ,  118  and  120 . 
         [0035]    It has to be noted that in the following, reference will be made to only one cam follower  44  of a cylinder valve  36   b  intended to contact the cams  116 ,  118 ,  120  of the shifting unit  112 . What is disclosed in connection to the cam follower  44  can be applied to the other cam followers of the engine, such as for example to the cam follower  44   a  shown in  FIG. 3 . 
         [0036]    According to a possible embodiment, as for example shown in  FIG. 3 , the same shifting unit  112  can be provided with two or more cams  116 ,  118 ,  120  for two or more cam followers. For example, in the embodiment shown in  FIG. 3 , a single shifting unit  112  is provided with two or more cams for the two cam followers  44 ,  44   a.  However, according to different possible embodiments, two shifting units can be provided, having two or more cams  116 ,  118 ,  120 , to engage respectively the cam follower  44  and the cam follower  44   a.  Cams  116  and  118  can engage cylinder valve  36   b,  and in particular the cam follower  44 . As mentioned above, the following description applies also to cams  116 ,  118  and  120  intended to be engaged by cam follower  44   a  of the cylinder valve  36   b.    
         [0037]    Cams  116 ,  118  and  120  are each provided with a base circle  116   a ,  118   a  and  120   a.  Additionally cams  116  and  118  are also each provided with exhaust lobes  116   b,    118   b,    120   b  and EGR lobes  116   c,    118   c,    120   c  that each protrude from the base circle  116   a,    118   a,    120   a,  respectively. As mentioned above, an additional cam can be a deactivation cam, i.e. cam not providing lift of the cylinder valve, and therefore it is provided only with the base circle. 
         [0038]    As shown in  FIGS. 6 and 7 , the cams  116 ,  118  and  120  can be provided with EGR cam lobes  116   c,    118   c,    120   c  having different heights relative to the camshaft rotation axis R. In addition, the EGR cam lobes  116   c,    118   c,    120   c  can have different circumferential lengths. The EGR cam lobes  116   c,    118   c  and  120   c  can each also include different rotational starting locations so that the phase of each of the EGR cam lobes also differs relative to one another. Therefore, each of the cam lobes  116   c,    118   c,    120   c  provides a different actuation of the cylinder valve  36 , and in particular a different lift height, phase and duration of the cylinder valve for tuning the internal EGR activation for different engine operating conditions. More in detail, an EGR cam lobe  116   c  of the first cam  116  can comprise a rear ramp portion  126  arranged at the same distance from the camshaft rotation axis R, of a portion  126  of the EGR cam lobe  118   c  of the second cam  118  and of a portion  126  of the EGR cam lobe  120   c  of the third cam  120 , to provide the same return of the cam follower  44 ,  44   a.  These portions  126  of cam lobes of different cams  116 ,  118 ,  120  can be seen for example in the graphic representation of  FIG. 7 , wherein the return portion  126  of the cam lobes  116   c,    118   c,  and  120   c  of cams  116 ,  118 ,  120  are partially overlapped, i.e. are arranged at the same distance from the camshaft rotation axis to provide the same lift of the cam follower. In other words, the adjacent cams  116 ,  118 ,  120  are provided with a portion  126  of a cam lobe that is arranged at the same distance from the camshaft rotation axis R, so as to provide the same lift of the cam follower  44  as it returns toward the base circle. 
         [0039]    These portions  126  of the EGR cam lobes  116   c,    118   c,    120   c  can be placed next to one another, and they are arranged at the same distance from the camshaft rotation axis R. In other words, these portions form a common surface of the cams because they provide the same lift of the cylinder valve. As it will be explained subsequently, during the shifting movement of the shifting unit  112 , the cam follower  44  engages at least a portion of a cam lobe, and preferably a portion of a cam lobe arranged at the same distance from the camshaft rotation axis of a portion of a cam lobe of another cam. 
         [0040]    As known, when the cam follower  44  of a cylinder valve  36  engages the base circle  116   a,    118   a    120   a  of a cam, the cylinder valve is not actuated (not lifted) and preferably maintained in a closed position. On the contrary, when the cam follower  44  engages a cam lobe of a cam, the cylinder valve is lifted and thus opened. The height of the lobe determines the height or distance of the lift of the valve from the closed to the open position. 
         [0041]    As for example shown in  FIG. 7 , the base circle  116   a,    118   a,    120   a  corresponds to the portion of the lines not providing a lift, while the cam lobes correspond to the portion of the lines providing a lift of the cam follower. According to an embodiment, the base circle  116   a  of cam  116  can have the same diameter of the base circle  118   a  of cam  118 . Also, the base circle  120   a  of the further cam  120  can have the same diameter of the other base circles of the other cams  116 ,  118 . The term diameter is used herein to indicate that the base circles  116   a,    118   a  and  120   a  have the same distance from the camshaft rotation axis R. Preferably the distance is measured along a radial line passing through the camshaft rotation axis R. According to an embodiment, the cams  116 ,  118 ,  120  are provided with the exhaust cam lobes  116   b,    118   b,    120   b  each having the same shape, although the shapes (height and duration) of the exhaust cam lobes  116   b,    118   b,    120   b  can be different. 
         [0042]    According to an embodiment, the shifting unit  112  can be provided with at least one groove  128 . In particular, as for example in the shown embodiment, the internal combustion engine  12  is provided with at least one driving pin  130  that can be selectively engaged and disengaged from the groove  128 . In the shown embodiments, see for example  FIG. 3 , two driving pins  130  are provided. The at least one driving pin  130  is actuated by a suitable device, such as for example an actuator controlled by the ECU  80  of the internal combustion engine, so as to be moved from at least a position in which it engages the groove  128  and at least a position in which it is disengaged from the groove  128 . According to a possible embodiment, at least one driving pin  130  can be selectively extracted and retracted from a body of a suitable actuator, in order to engage/disengage the groove  128 . The groove  128  comprises a shifting portion  128   a,  and the driving pin  130  is operable to be selectively engaged with and disengaged from the shifting portion  128   a  of the groove  128 . The engagement between the driving pin  130  and the shifting portion  128   a  of the groove  128  causes the movement of the shifting unit  112  along the camshaft, i.e. causes the shifting movement of the shifting unit  112 . 
         [0043]    The shifting portion  128   a  can be shaped as a helical portion, i.e. as a curved path extending between two points, or portions, arranged at different distances from each other along the extension of the camshaft rotation axis. In other words, the shifting portion  128   a  is extending to connect points of the shifting unit external surface that are lying on different planes perpendicular to the camshaft rotation axis R. The shifting portion can be left-handed or right handed so that the shifting unit  112  can be moved during the rotation of the camshaft while the driving pin is engaged in the shifting portion  128   a  of the groove. 
         [0044]    As visible for example in the schematic view of  FIG. 4 , when the driving pin  130  is operated to engage the shifting portion  128   a,  the shifting unit  112  is moved along the camshaft. Due to the shifting movement of the shifting unit  112 , the cam follower  44  engages at least two different cams. In other words, before starting the shifting movement of the shifting unit the cam follower  44  engages a first cam  116 , while at the end of the shifting movement, the cam follower engages a different cam  118 . It has to be noted that the shifting portion  128   a  is shown in a schematic manner and its extension has been reduced to allow a clear representation. The shifting portion  128   a,  i.e. the helical portion, extends between two rectilinear portions  128   b  of the groove  128  which are extending on two planes perpendicular to the camshaft rotation axis, so that when the driving pin  130  engages said rectilinear portions  128   b  of the groove  128 , the shifting unit  112  is not moved along the camshaft rotation axis. 
         [0045]    It has to be noted that the shifting unit  112  can be moved along the camshaft, by means of the shifting portion  128   a  of the groove  128  between at least two positions, corresponding to positions in which the cam follower  44 ,  44   a  engages respectively two different cams  116 ,  118 ,  120  of the shifting unit  112 . 
         [0046]    It has to be noted that the cam shifting system  110  of the internal combustion engine may comprise two or more driving pins  130 , as for example shown in  FIG. 3 , so as when different driving pins  130  engage the shifting portion  128   a,  different movement of the shifting unit  112  along the camshaft rotation axis can be obtained, corresponding to different positions in which the cam follower  44  engages different cams  116 ,  118 ,  120 . During the movement of the shifting unit along the camshaft rotation axis, i.e. during the shifting movement caused by the engagement of the driving pin  130  with the shifting portion  128   a,  the cam follower  44 , and in particular the cam follower roller  46  engages (contacts) at least two cams  116 ,  118 ,  120 . 
         [0047]    The cam shifting system  110  according to the present disclosure and in particular the shifting portion  128   a  is configured such that during the shifting movement of the shifting unit  112  along said camshaft rotation axis R, the cam follower  44  engages at least a portion of at least one cam lobe  116   b,    118   b.  In other words, the cam follower engages also the cam lobe of the cam in addition to the cam base circle used in the known cam shifting systems, when the shifting unit is moved along the camshaft to provide the engagement of the cam follower from a first cam to at least one different cam  116 ,  118 ,  120 . More in detail, the shifting portion  128   a  of the groove  128  is extending on an arc A of the external surface of the shifting unit  112 , providing a cam follower shifting path FSP (see for example  FIG. 7 ) between at least two cams  116 ,  118 ,  120 , and the cam follower shifting path comprises at least a portion of at least one cam lobe  116   b,    118   b.  In other words, when the shifting unit is moved along the camshaft, the cam follower  44  is moved between at least two cams  116 ,  118 , 120  i.e. it is moved from a position in which it engages a first cam  116  into a position in which it engages a different cam  118 . 
         [0048]    According to a possible embodiment, as for example shown in  FIG. 4 , the shifting portion  128   a  of the groove  128  is extending on an arc A that is greater than the arc B on which the base circle  116   a,    118   a,    120   a  is extending. The arcs A and B cover angles measured from the camshaft rotation axis R. Advantageously, the shifting portion  128   a  is extending along the surface of the shifting unit, thus corresponding to an arc of the rotation of the camshaft, that is greater than the extension of the base circle of a cam of the shifting unit. It follows that when the shifting unit is shifted along the camshaft, due to the engagement of the driving pin with the shifting portion  128   a,  the cam follower engages the base circle and also at least a portion of the cam lobe  116   b,    118   b,    120   b.  According to a possible embodiment, the arc B on which the base circle  116   a,    118   a,    120   a  extends, is defined by the longest base circle  116   a,    118   a,    120   a  of said at least two cams  116 ,  118 ,  120 . 
         [0049]    The cam follower shifting path FSP, also called cam follower shifting window, i.e. the portion of the cams  116 ,  118 ,  120  engaged by the cam follower  44  when the shifting unit is moved along the camshaft rotation axis R while it is rotated together with the camshaft, comprises the cam lobes  116   b,    118   b,    120   b  as well as the base circle portions  116   a,    118   a,    120   a  (see for example  FIG. 7 ). In other words, the cam follower shifting path FSP represents the surface of the cams contacted by the cam follower during the rotation of the camshaft while the shifting unit is moved along the camshaft due to the engagement of the driving pin  130  with the shifting portion  128   a  of the groove  128 . The cam follower shifting path FSP can be also seen as the arc of the cams contacted by the cam follower, during the rotation of the camshaft while the shifting unit is moved along the camshaft. 
         [0050]    As already mentioned above, the contact of the cam follower  44  with a cam lobe of the cam advantageously allows to increase the cam follower shifting path FSP, so that the shifting movement of the shifting unit can be performed in an increased rotation angle of the camshaft, thus increasing the time available to carry out the shifting movement and thus reducing the accelerations involved. Advantageously, according to a possible embodiment, during the shifting movement of the shifting unit  112  along the camshaft  38 , the cam follower  44  can therefore engage at least a portion of the base circle  116   a  of a first cam  116  and at least a portion of the cam lobe  118   b  of a second cam  118 . According to a possible embodiment, during the shifting movement of the shifting unit  112 , the cam follower  44  engages two cam lobes of at least two different cams. 
         [0051]    According to a possible embodiment, a portion  126  of a cam lobe  116   b  of a cam  116  is arranged at the same distance from the camshaft rotation axis R, of a portion  126  of a cam lobe  118   b  of a different cam  118 , so as to provide the same lift of the cam follower  44 . In other words, portions  126  of cam lobes  116   b ,  118   b,  belonging to two different cams  116 ,  118 , preferably belonging to two adjacent cams, are arranged at the same distance from the camshaft rotation axis R. More in detail, the cams  116 ,  118  have a common surface, on a portion of their cam lobes, arranged at the same distance from the camshaft rotation axis R, so as the same lift of the cam follower, and thus of the cylinder valve  36 , can be provided. 
         [0052]    Advantageously, according to an embodiment of the invention, during the shifting movement of the shifting unit  112  along the camshaft rotation axis R, the cam follower  44  engages a portion  126  of the cam lobe that is arranged at the same distance with respect to the camshaft rotation axis of a portion  126  of the cam lobe of another cam. According to a possible embodiment, during the shifting movement of the shifting unit  112  along the camshaft rotation axis R, the cam follower  44  engages the portions  126  of two cam lobes that are arranged at the same distance with respect to the camshaft rotation axis. 
         [0053]    According to a possible embodiment, the portion  126  arranged at the same distance from the camshaft rotation axis R axis to provide the same lift of the cam follower, comprises at least part of an opening ramp of the EGR cam lobes  116   c,    118   c,    120   c.  In other words, according to a possible embodiment of the invention, at least a portion of the opening ramp  126  of at least one cam lobe  116   c ,  118   c,    120   c  is contacted (engaged) by the cam follower  44  during the shifting movement of the shifting unit along the camshaft. 
         [0054]    According to a possible embodiment, as for example shown in  FIG. 3 , the shifting unit  10  can be provided with two or more cams  116 ,  118 ,  120  for each cam follower and a single groove  128  provided there between. However, other possible embodiments can be provided, for example by using a single shifting unit having two or more cams and a groove and a relative driving pin, intended to control the movement of the shifting unit, for a single cam follower of the internal combustion engine. 
         [0055]    The present invention also relates to a method of controlling the cylinder valve actuation of an internal combustion engine  12  provided with a cam shifting system  110  according to the invention. What is disclosed above in connection to the internal combustion engine can be applied to the method and vice versa. The method comprises the steps of operating the internal combustion engine to rotate the camshaft  38  in order to actuate the at least one exhaust cylinder valve  36   b.  The method further comprises the step of actuating the driving pin  130  to engage the shifting portion  128   a  of the groove  128  to move the shifting unit  112  with respect to the camshaft  38  along the camshaft rotation axis R. As already mentioned above, during the movement of the shifting unit  112  along the camshaft rotation axis R, the cam follower  44 ,  44   a  engages a portion  126  of an EGR cam lobe  116   c,    118   c ,  120   c  of a first cam  116 ,  118 ,  120  arranged at the same distance from the camshaft rotation axis R, of a portion  126  of an EGR cam lobe  116   c,    118   c,    120   c,  of a different cam  116 ,  118 ,  120  to provide the same lift of the cam follower  44 ,  44   a.    
         [0056]    It has to be noted that the shifting movement of the shifting unit  112  can be performed in order to obtain the desired actuation (lift) of the at least one cylinder valve. Therefore, the engagement/disengagement of the driving pin  130  with the shifting portion  128   a  of the groove  128  of the shifting unit  112  can be performed, according to the present method, in order to provide the engagement of the at least one cam follower  44 ,  44   a  with the desired cam  116 ,  118 ,  120  having the desired profile to provide desired cylinder valve lift. The shifting movement of the shifting unit can be performed by means of the ECU  80  of the internal combustion engine controlling the engagement/disengagement of the driving pin  130  with/from the shifting portion  128   a.    
         [0057]    According to an embodiment, the method comprise a step of monitoring at least one value of at least one operating parameter of the internal combustion engine  12  during its operation. The at least one operating parameter can comprise an engine load correlated parameter, measured and/or evaluated by means at least one sensor, not shown, eventually in combination with stored data. The method step of actuating the driving pin  130  to engage the shifting portion  128   a  of the groove  128 , to move the shifting unit  112  with respect to the camshaft  38 , is carried out as a function of the monitored value of the at least one operating parameter. 
         [0058]    According to a possible embodiment, the contact of the cam follower with at least two cams of the shifting unit is carried out by contacting a portion of at least two cam lobes of two cams having the same distance from the camshaft rotation axis to provide the same lift of the cylinder valve. During the movement of the shifting unit  112  along the camshaft rotation axis R, the cam follower  44 ,  44   a  engages a portion  126  of a cam lobe  116   b,    118   b  of a first cam  116 ,  118 ,  120  arranged at the same distance from the camshaft rotation axis R, of a portion  126  of a cam lobe of a different cam, to provide the same lift of the cam follower  44 ,  44   a.    
         [0059]    As discussed above in connection to the internal combustion engine, at least a part of an opening ramp  126  of a cam lobe can be engaged by the cam follower during the shifting movement of the shifting unit. 
         [0060]    The system of the present disclosure provides a secondary valve opening event with variable phasing, lift and duration for internal EGR quantity control from the light to high load engine operation. In particular, the system provides high internal EGR capability at low loads and controllability of internal EGR at high loads without requiring ultra-low lifts. This results in warm-up of the after-treatment exhaust components faster for higher conversion efficiency resulting in reduced HC and NOx engine-out emissions and increased combustion stability. 
         [0061]    In particular, with reference to  FIG. 8 , at engine light load, a higher lift and duration EGR cam lobe  120   c  can be selected with the cam lobe being phased toward the intake opening position “A”, as illustrated in  FIG. 8 , while at high engine load a lower lift and duration EGR cam lobe  116   c  can be selected with the cam lobe being phased toward the intake closing at, for example position “B”, as illustrated in  FIG. 8 . At medium load or during transition from high load to low load, it may be desirable to utilize a mid-range lift and duration EGR cam lobe  118   c  that is phased at a mid-range position C, as illustrated in  FIG. 8 . The relative phasing of the EGR cam lobes  120   c,    118   c,    116   c  can be implemented on the cam lobes based upon the optimal phase position for the engine operating conditions corresponding to each cam lobe. Alternatively, the ECU  80  can control the operation of the cam phaser  42  and shifting unit  112  according to a predetermined schedule depending upon the engine load so as to provide improved control from low engine load to high engine load internal EGR requirements. The internal EGR can provide faster control response of charge dilution during transient operation; efficient heating of the in-cylinder charge by recycling energy and species from previous cycle to intake charge; enhance the cold start warm-up of the engine partially replacing fuel-based warm-up strategies; and enable a higher after-treatment efficiency with lower emissions during the warm-up process of diesel engines. 
         [0062]    Transitions from internal EGR to low-pressure EGR favor reductions of emissions spikes and increase the engine operating range applicability of low pressure EGR. 
         [0063]    The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.