Abstract:
A dual independent phasing system (DIPS) phaser assembly for coaxial camshafts having two axially stacked, thin phasing subassemblies which are each conventional vane-cell type phaser assemblies is provided. These phasers are preassembled together as a unit to make one DIPS phaser assembly. The rotor of the rear phaser is attached to the outer camshaft of the coaxial cam, and the rotor of the front phaser is attached to the inner camshaft. The radial force from the timing chain or belt is transmitted to the outer camshaft via a chain ring or pulley connected to the stator of the rear phaser. In order to provide for ease of mounting, the DIPS phaser assembly (including the front and rear phasers) is attached to the outer camshaft via mounting bolts which are passed through openings in the rotor of the front phaser in order to attach the rear phaser rotor to the outer camshaft. A central mounting bolt is used to connect the front phaser rotor to the inner camshaft. A radially stacked DIPS phaser assembly is also provided which offers further reduced axial space requirements.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/104,037, filed Oct. 9, 2008, which is incorporated herein by reference as if fully set forth. 
     
    
     BACKGROUND 
       [0002]    The invention relates to a dual independent phasing system for independently adjusting the phase angle of both the intake and exhaust camshafts of a inner and outer camshafts of a concentric camshaft. 
         [0003]    It is known to use two axially spaced apart camshaft phasers in connection with inner and outer shafts of a concentric camshaft assembly in order to separately adjust the timing of the inner and outer camshafts. This allows the timing of the intake and exhaust valves to be adjusted to obtain improved torque/power as well as improved emissions. Further, this arrangement provides additional benefits in engine idle stability and fuel economy. 
         [0004]    Camshaft phasers that operate according to the vane-cell principle for single camshafts are known. These are described in publications by the assignee of the present invention, including U.S. Pat. No. 6,805,080, which is incorporated herein by reference as if fully set forth. 
         [0005]    One known system for adjusting the control timing of a concentric camshaft assembly is described in DE 10 2005 039 751 A1. In this publication, a camshaft phaser located at the front of the engine is connected to an outer shaft of a co-axial camshaft arrangement and a second camshaft phaser located at the rear of the engine includes an outer housing that is connected to the outer camshaft and an inner rotor that is connected to the inner camshaft. This arrangement provides separate phasers which allows for easier control; however, it involves more difficulty in accessing the rear camshaft phaser as well as more complicated assembly and engine compartment space requirements. 
         [0006]    DE 10 2006 024 793 A1 generically describes a dual phasing system for a concentric camshaft assembly which includes two camshaft phasers which are located at the front of an engine and are axially spaced adjacent to one another. The two camshaft phasers allow independent control of the outer and inner co-axial camshafts relative to the crankshaft in order to separately adjust the timing of the intake and exhaust valves of the internal combustion engine. The arrangement provides a specific spool valve control located within the inner camshaft for controlling the flow of hydraulic fluid to both the first and second camshaft phasers. 
         [0007]    DE 10 2006 028 611, also discloses two camshaft phasers located axially adjacent to one another at the front of a concentric camshaft assembly of an internal combustion engine. The first camshaft phaser is connected to a front camshaft bearing arrangement which includes oil passages for delivering hydraulic fluid to and from the camshaft phaser for the outer camshaft. Hydraulic fluid for controlling the camshaft phaser connected to the inner camshaft is delivered via internal hydraulic fluid passageways located between the outer and inner camshafts and inside the inner camshaft which are supplied with hydraulic fluid through a separate camshaft mounting bearing arrangement. 
         [0008]    These previously known dual independent phasing systems for concentric camshafts suffer from a number of drawbacks with respect to space requirements and ease of assembly to the front of a camshaft as a single assembly. Further, the prior known arrangements suffer from high external oil leakage due to the attachment method of the vanes to the covers of the camshaft phasers. Further, no system is provided for independently controlling the camshaft phasers for the inner and outer shafts so that they can be locked in base positions. Further, it would be beneficial to provide a dual independent phasing system which fits in roughly the same space within the engine assembly as a standard phaser so that additional space allocation with the engine compartment is not required. 
       SUMMARY 
       [0009]    A dual independent phasing system for concentric camshaft applications which addresses the deficiencies in the known arrangements is provided. 
         [0010]    In a first embodiment of the invention, the dual independent phasing system (DIPS) for coaxial camshafts comprises two axially stacked, thin phasing subassemblies which are each individually similar to a conventional vane-cell type phaser assembly of the assignee such as disclosed in U.S. Pat. No. 6,805,080. These phasers are assembled together as a unit to make one DIPS phaser assembly. The rotor of the rear phaser is attached to the outer camshaft of the coaxial cam, and the rotor of the front phaser is attached to the inner camshaft. The axial force from the timing chain or belt is transmitted to the outer camshaft via a chain ring connected to the stator of the rear phaser. In order to provide for ease of mounting, the DIPS phaser assembly (including the front and rear phasers) is attached to the outer camshaft via mounting bolts which are passed through openings in the rotor of the front phaser in order to attach the rotor of the rear phaser to the outer camshaft. A central mounting bolt is used to connect the rotor of the front phaser to the inner camshaft. 
         [0011]    Preferably, in order to provide separate locking of the phase position of both the inner and outer camshafts, while maintaining the spacing requirements for the DIPS phaser assembly, radially oriented locking pins are located within the rotors of the front and rear phasers which are engagable in matching recesses in the respective stators of the front and rear phasers. Preferably the phaser associated with the intake camshaft is held in an advanced position and the phaser associated with the exhaust camshaft is held in a retarded position by the respective locking pins when the hydraulic fluid pressure drops below a certain level, such as during initial starting of the internal combustion engine. However, either the front or rear phaser can have a base (locked) position in either an advanced or retarded position, allowing combinations such as advance-advance, advance-retard, retard-advance, or retard-retard. 
         [0012]    In a second embodiment of the invention, the DIPS phaser assembly includes a radially stacked phaser arrangement including an inner phaser and an outer phaser arranged concentrically over the inner phaser. The outer phaser includes an outer stator that is connected to the timing chain ring or timing belt pulley. The rotor of the outer camshaft phaser is connected to the outer camshaft and includes vanes which extend into spaces defined by inwardly directed projections of the outer stator, defining separate chambers on each side of the vanes. Extending radially inwardly from the rotor of the outer camshaft phaser is the stator of the inner camshaft phaser which includes radially inwardly directed projections. Vanes from the inner rotor of the inner camshaft phaser extend between the radially inwardly directed projections to define, in conjunction with the inwardly directed projections, separate chamber on each side of the inner rotor vanes. The rotor of the inner camshaft phaser is attached to the inner camshaft. In this arrangement, the outer camshaft can be advanced or retarded relative to the crankshaft by supplying pressurized hydraulic fluid to the first or second sets of chambers of the outer camshaft phaser causing vanes in the chambers to either advance or retard the outer camshaft phaser rotor and thereby adjust the timing position of the outer camshaft. The phase position of the inner camshaft is similarly adjusted by providing pressurized hydraulic fluid to the first or second sets of chambers of the inner camshaft phaser to rotate the vanes which separate the chambers in order to adjust the position of the inner camshaft relative to the position of the outer camshaft. The engine control module for his embodiment is programmed to compensate for the compound movement of the inner rotor created by movement of the outer rotor, such that if the outer phaser is to be advanced 10° while maintaining the position of the inner phaser, the engine controller would need to advance the outer phaser the desired 10° while retarding the inner phaser 10° to keep it statically timed. 
         [0013]    Further aspects of the invention, which can be used alone or in combination, are described in detail below. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    The foregoing Summary and the following detailed description will be better understood when read in conjunction with the appended drawings, which illustrate preferred embodiments of the invention. In the drawings: 
           [0015]      FIG. 1  is a side view of a dual independent phasing system (DIPS) phaser assembly in accordance with the first preferred embodiment of the invention; 
           [0016]      FIG. 2  is a side elevational view of a front phaser prior to assembly with the rear phaser of the DIPS phaser assembly of  FIG. 1 ; 
           [0017]      FIG. 2A  is a front elevational view of the front phaser taken along line  2 A- 2 A in  FIG. 2 ; 
           [0018]      FIG. 2B  is a rear elevational view of the front phaser taken along line  2 B- 2 B in  FIG. 2 ; 
           [0019]      FIG. 3  is a side elevational view of the rear phaser of  FIG. 1  prior to assembly to form the DIPS phaser assembly; 
           [0020]      FIG. 3A  is a front elevational view of the rear phaser taken along line  3 A- 3 A in  FIG. 3 ; 
           [0021]      FIG. 3B  is a rear elevational view of the rear phaser taken along line  3 B- 3 B in  FIG. 3 ; 
           [0022]      FIG. 4  is a front elevational view of the DIPS phaser assembly of  FIG. 1  taken along lines  4 - 4  in  FIG. 1 ; 
           [0023]      FIG. 5  is a rear elevational view of the DIPS phaser assembly of  FIG. 1  taken along lines  5 - 5  in  FIG. 1 ; 
           [0024]      FIG. 6  is an isometric cross-sectional view taken along line  6 - 6  in  FIG. 4 ; 
           [0025]      FIG. 7  is a cross-sectional view through the DIPS phaser assembly taken along line  7 - 7  in  FIG. 6 ; 
           [0026]      FIG. 8  is a cross-sectional view through the DIPS phaser assembly taken along line  8 - 8  in  FIG. 6 ; 
           [0027]      FIG. 9  is a rear elevational view of the front phaser illustrating the oil passages in conjunction with  FIGS. 7 and 8 ; 
           [0028]      FIG. 10  is a cross-sectional view of the DIPS phaser assembly taken along line  10 - 10  in  FIG. 6 ; 
           [0029]      FIG. 11  is a rear elevational view of the rear phaser which, in conjunction with  FIG. 10 , shows the oil passages for advancing and retarding the rear phaser; 
           [0030]      FIG. 12  is a front prospective view of the second embodiment of the DIPS phaser assembly in accordance with the present invention; and 
           [0031]      FIG. 13  is a cross-sectional view taken along lines  13 - 13  in  FIG. 12 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0032]    Certain terminology is used in the following description for convenience only and is not limiting. The words “front,” “rear,” “upper” and “lower” designate directions in the drawings to which reference is made. The words “inwardly” and “outwardly” refer to directions toward and away from the parts referenced in the drawings. A reference to a list of items that are cited as “at least one of a, b, or c” (where a, b and c represent the items being listed) means any single one of the items a, b or c, or combinations thereof. The terminology includes the words specifically noted above, derivatives thereof and words of similar import. 
         [0033]    Referring now to  FIGS. 1 and 6 , a DIPS camshaft phasing system having a preassembled DIPS phaser assembly  10  in accordance with the present invention is shown. The DIPS camshaft phaser assembly  10  is used in conjunction with a concentric camshaft arrangement for transferring torque from the crankshaft of an internal combustion engine to both inner and outer camshafts  12 ,  14 , respectively (shown in  FIG. 6 ), in order to control the intake and exhaust valves of the internal combustion engine. As concentric camshaft systems are known, the inner and outer concentric camshafts  12 ,  14  are not described in further detail and would be understood by a person of ordinary skill in the art. Activation of intake and exhaust gas exchange valves using camshafts and associated rocker arms, finger levers, cup tappets and other types of actuators are also known, and are therefore not described herein. 
         [0034]    The DIPS camshaft phaser  10  is provided as a unitized assembly which can be connected to the inner and outer camshafts  12 ,  14  when the engine is being assembled. The unitized DIPS phaser assembly  10  includes a front phaser  20  and a rear phaser  70 , which can be separately assembled and then joined together. The front phaser  20  is shown in detail in  FIGS. 2 ,  2 A,  2 B and  6 - 9 . The rear phaser  70  is shown in detail in  FIGS. 3A ,  3 B,  6  and  10 - 11 .  FIGS. 4 and 5  show front and rear views respectively of the assembled DIPS phaser assembly  10 . 
         [0035]    Referring to  FIGS. 2 ,  2 A,  2 B and  6 - 9 , the front phaser  20  is a camshaft phaser which operates in accordance with the vane-cell principle and is connected to the inner camshaft  12 . The front phaser  20  includes a rotor  22  having vanes  24  extending therefrom into spaces formed between inwardly directed projections  30  of the stator  28 . The vanes  24  are preferably spring biased outwardly to provide a tight seal against the mating surface of the stator  28 . The vanes  24  divide the spaces between the inwardly directed projections  30  of the stator  28  into first chambers  32  and second chambers  34 . A front cover  38  and a rear cover  40  are located on both sides of the rotor  22  and stator  28  and are fastened to the stator  28  in order to create a sub-assembly of the front phaser  20 , and to define the front and rear walls of the chambers  32 ,  34 . 
         [0036]    By applying pressurized hydraulic fluid in either the first chambers  32  or the second chambers  34  or both the first and second chambers  32  and  34 , the rotor  22  and the inner camshaft  12  connected thereto can be rotated into an advanced or retarded position relative to the stator  28 , or can be hydraulically locked in a generally fixed position relative to the stator  28 . 
         [0037]    The stator  28  is fastened via bolts  52  which extend through openings  53  to the stator  78  of the rear phaser  70  which is connected to the timing chain gear  86  or alternately a timing belt pulley. 
         [0038]    A hollow attachment bolt  48 , shown in  FIG. 6 , is used to connect the rotor  22  of the front phaser assembly to the inner camshaft  12 . As shown in detail in  FIGS. 6-9 , pressurized hydraulic fluid passageways  102 ,  104  are provided in a bearing surface  100  on the outer camshaft  14  for supplying pressurized hydraulic fluid to the first and second chambers  32 ,  34  of the front phaser  20 . The pressurized hydraulic fluid passages designated as a whole as  102  provide pressurized hydraulic fluid to the chambers  34  in order to rotate the rotor  22  in a direction to retard the timing of the inner camshaft  12 . The pressurized hydraulic fluid passages designated as a whole as  104 , provide pressurized hydraulic fluid to the first chambers  32  in order to rotate the rotor  22  in a direction to advance the inner camshaft  12  timing. The pressurized hydraulic fluid is provided to the outer cam bearing surface  100  shown in  FIG. 6  through a hydraulic valving system (not shown) so that either or both hydraulic fluid passages  102  and  104  can be connected to a source of pressurized hydraulic fluid or a drain in order to selectively advance or retard the timing of the inner camshaft ( 12 ), or hydraulically lock the position of the rotor  22  with the stator  28 . 
         [0039]    As shown in  FIG. 2A , the front and rear covers  38 ,  40  of the front phaser  20  are connected together with the stator  28  via bolts  50 . Clearance holes are provided through the outer cover  54  as well as through the front and rear cover plates  38 ,  40  and the stator  28  for assembly bolts for joining the front phaser  20  to the rear phaser  70 . 
         [0040]    Referring to  FIGS. 8 and 9 , a radially extending locking pin  56  is provided in the rotor  22  which can engage in a corresponding recess  58  in the stator  28  that can be used to hold the stator  28  and rotor  22  in a fixed base position relative to one another. This is required during startup of the engine and at other times when the pressure of the pressurized hydraulic fluid is insufficient to provide for stable adjustment or holding of the rotor  22  relative to the stator  28 . The radial locking pin  56  is released preferably via pressurized hydraulic fluid being supplied to the recess  58  in order to depress the locking pin  56  inwardly into the rotor  22 . 
         [0041]    In the first preferred embodiment, the front phaser  20  is used to control the inner camshaft  12  which has cam lobes that control the intake valves, and thus the preferred base position for engaging the axial locking pin  56  is in the advanced position. 
         [0042]    Referring now to  FIGS. 3 ,  3 A,  3 B,  6  and  10 - 11 , the rear phaser  70  will be explained in further detail. The rear phaser  70  also operates according to the vane-cell principal, and includes a rotor  72  having a plurality of vanes  74  extending outwardly therefrom. The vanes  74  are preferably spring biased and extend into spaces located between inwardly directly projections  80  on a stator  78 . The vanes  74  divide the spaces into first and second chambers  82 ,  84 , respectively, which are located on either side of each vane  74 . Front and rear covers  88 ,  90  from the front and rear walls of the chambers  82 ,  84  and allow the rear phaser  70  to be separately preassembled. 
         [0043]    The stator  78  is preferably connected to a timing chain gear  86 , or alternatively to a timing belt pulley, that is connected via a timing chain or belt to the crankshaft of an internal combustion engine in order to transfer torque from the crankshaft to the inner and outer camshafts  12 ,  14  of the concentric camshaft. The timing gear  86  or pulley can be connected directly to the stator  78 , or to the front or rear covers  88 ,  90 , or can be formed integrally with any of these components. 
         [0044]    Third and fourth pressurized hydraulic fluid passages  106 ,  108  extend from the outer cam bearing surface  100 . The third passages, designated as a whole as  106 , are connected to the second chambers  84  such that pressurized hydraulic fluid introduced into these chambers  84  cause the rotor  72  to rotate in a direction to retard the timing of the outer camshaft  14 . Pressurized fluid introduced through the fourth hydraulic fluid passages, designed as a whole as  108 , which are connected to the first chambers  82  cause the rotor  72  to rotate in an advancing direction relative to the stator  78 . Applying pressurized hydraulic fluid through both the third and fourth passages  106 ,  108  causes both the first and second chambers  82 ,  84  of the rear phaser  70  to be pressurized, hydraulically locking the rotor  72  into a fixed position relative to the stator  78 . 
         [0045]    In the preferred embodiment, a hydraulic control valve is utilized to connect either or both of the third and fourth pressurized hydraulic fluid passages  106 ,  108  to either a source of pressurized hydraulic fluid or a drain so that pressurized hydraulic fluid can be selectively supplied to either or both of the first and second chambers  82 ,  84  of the rear phasers  70 . 
         [0046]    As shown in  FIGS. 10 and 11 , preferably holes  76  are provided in the rotor  72  of the rear phaser  70  for bolts that can be used to connect the rear phaser rotor  72  to the outer camshaft  14 . 
         [0047]    In order to allow assembly of the unitized DIPS phaser assembly  10  to the inner and outer camshaft  12 ,  14 , clearance holes  26  are provided through the inner rotor  22  shown in  FIG. 7 , so that bolts  98 , also shown in  FIG. 7 , can be installed through the front phaser  20  and into the rotor  72  of the rear phaser  70  in order to form the connection between the rear rotor  72  and the outer camshaft  14 . As previously noted, the front phaser rotor  22  can be connected to the inner camshaft  12  via a central attachment bolt  48 , which is preferably provided with portions of the first oil passages  102  as shown in  FIG. 6 . 
         [0048]    Referring again to  FIG. 10 , the rear phaser  70  includes a radial locking pin  110  located in the rotor  72  which engages in a recess  112  in the rear phaser stator  78  in order to lock the rotor  72  into a fixed, base position relative to the stator  78 . This is important during startups when there is insufficient oil pressure to provide reliable adjustment of the rotor  72  relative to the stator  78 . The radial locking pin  110  is released when sufficient hydraulic fluid pressure is supplied to the recess  112  in order to press the spring biased locking pin  110  back into the rotor  72 . 
         [0049]    Referring now to  FIG. 3A , a helical equalizing spring  96  is connected between the rear phaser stator  78  and rotor  72 . This spring  96  is used to equalize the force required to advance the rear phaser rotor  72  relative to the stator  78 . Depending on the particular design, an equalizing spring could be provided for the front phaser  20 , both the front phaser  20  and the rear phaser  70 , or neither phaser. 
         [0050]    In use, the DIPS phaser assembly  10  allows easier assembly of a DIPS phaser assembly for concentric camshafts that allows timing adjustments to both the inner and outer camshafts  12 ,  14  due to the fact that it can be preassembled and then attached to the concentric camshaft during assembly of the engine. This reduces the number of parts and the time required during assembly of the engine and allows the DIPS phaser assembly  10  to be completely assembled offsite, preferably at a separate manufacturing facility. Additionally, the arrangement of the timing chain gear  86  or alternatively the timing belt pulley on or connected to the stator  78  allow direct axial transfer of loads via the supporting surfaces formed by the inwardly directed projections  80  of the stator  78  against the rotor  72 , which rests directly on the outer camshaft  14 . This prevents any bending loads from being introduced into the inner camshaft  12  as the axial loads are directly transferred to the outer camshaft  14 . This arrangement further provides a reduced axial length in comparison to other known arrangements due to the radial locking pin arrangement for locking the inner and outer camshafts  12 ,  14  into a base position. This advantageously allows the DIPS phaser assembly  10  to fit roughly into the same engine packaging space as a standard camshaft phasing system. 
         [0051]    Referring now to  FIGS. 12 and 13 , the second embodiment of the DIPS phaser assembly  120  is shown. The DIPS phaser assembly  120  includes two radially stacked phasers for separately phasing the inner and outer camshafts  160 ,  162  of a concentric camshaft arrangement. 
         [0052]    The radially stacked DIPS phaser assembly  120  includes an inner rotor  122  that is connected to the inner camshaft  162 . The inner rotor  122  includes outwardly biased, radially extending vanes  124  which extend into spaces formed between inwardly directed projections  130  of an inner stator/outer rotor ring  128 . The vanes  124  divide the spaces into first and second chambers  132 ,  134 , respectively. The inner stator/outer rotor ring  128  further includes outwardly directed vanes  136  having radially, outwardly directed seals  138  on the ends thereof. These vanes  136  of the inner stator/outer rotor ring  138  extend into spaces located between inwardly directed projections  144  of an outer stator  142 . These outer vanes  136  divide the spaces into third and fourth chambers  146 ,  148 . A timing chain gear  150 , or alternatively, a timing belt pulley, is fixed to the outer stator  142 . The first, second, third and fourth chambers  132 ,  134 ,  146 ,  148  are bounded on the front and rear sides via a front cover  152  and a rear cover  154 . An oil passage plate  153  is located between the front cover  152  and the inner rotor  122 , inner stator/outer rotor ring  128  and outer stator  142 , and is used in order to provide pressurized hydraulic fluid passages that extend to the third and fourth chambers  146 ,  148 . Pressurized hydraulic fluid passages to the first and second chambers  132 ,  134  are provided via a central hydraulic fluid distributor  156  through openings (not shown) in the inner rotor  122  in a known manner. The inner rotor  122  is preferably connected to the inner camshaft  162  in a known manner by a central bolt. 
         [0053]    The inner stator/outer rotor ring  128  is connected via and adaptor  140  to the outer camshaft  162 . As shown in  FIG. 13 , one or more pins  164  can be utilized to ensure a locked rotational connection between the connection part  140  and the outer camshaft  162 . 
         [0054]    The radial loads from the timing chain or belt are carried via the bearing surfaces of the outer stator  142  to the inner stator/outer rotor ring  128 , and into the outer camshaft  162 . 
         [0055]    In operation, the DIPS radially stacked phaser assembly  120  is operated in a similar manner to the first embodiment of the DIPS axially stacked phaser assembly  10 . The position of the outer camshaft  162  relative to the timing chain gear  150  or alternatively the timing belt pulley which is in a fixed phase relationship with the crankshaft via a traction element, such as a timing chain or belt, is adjusted by supplying hydraulic fluid to either or both of the third and fourth chambers  146 ,  148  in order to cause the inner stator/outer rotor ring  128  to rotate relative to the outer stator  142 . By supplying pressurized hydraulic fluid to either of the third and fourth chambers  146 ,  148 , the timing of the outer camshaft  162  can be either advanced or retarded, and supplying pressurized hydraulic fluid to both the third and fourth chambers  146 ,  148  locks the outer rotor  128  in position relative to the outer stator  142 . Preferably, a base position locking pin arrangement is provided in order to hold the inner stator/outer rotor ring  128  in a fixed position relative to the outer stator  142  during periods of low hydraulic fluid pressure, such as during the startup. 
         [0056]    In order to adjust the timing of the inner camshaft  160 , pressurized hydraulic fluid is provided to either of the first and second chambers  132 ,  134  in order to rotate the inner rotor  122  relative to the inner stator/outer ring  128 . Supplying pressurized hydraulic fluid to both the first and second chambers  132 .  134  locks the inner rotor  122  in position relative to the inner stator  128 . A second locking mechanism is preferably also provided for locking the inner rotor  122  to the inner stator/outer rotor ring  128  in order to hold the inner rotor in a base position during engine startup or at times of insufficient pressurized hydraulic fluid being delivered to either or both of the first and second chambers  132 ,  134 . 
         [0057]    Due to the radially stacked arrangement of the phasers for the inner and outer camshafts  160 ,  162 , a more complex control system is required by the engine control module (not shown). For example, in order to advance the outer phaser while maintaining the position of the inner phaser, the engine controller is required to advance the outer phaser to the desired angle, for example 10° advanced, while retarding the inner phaser an equal amount, in this example of 10° in the retarded direction, in order to keep the inner phaser statically timed. 
         [0058]    The radially stacked DIPS phaser assembly  120  provides all of the advantages noted above in connection with the first preferred embodiment with respect to the ability to preassemble a unitized DIPS phaser separate and apart from an engine and allow for easy attachment to the engine during assembly. This also allows for easier maintenance of the DIPS phaser assembly  120  as it can be removed and replaced as a unitized assembly in a straight forward manner. Additionally, the radially stacked DIPS phaser  120  provides further advantages in reduced axial space requirements in comparison to the known systems.