Patent Publication Number: US-8122863-B2

Title: Camshaft phaser for the inner camshaft of a concentric camshaft assembly

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 61/104,051, filed Oct. 9, 2008, which is incorporated herein by reference as if fully set forth. 
    
    
     BACKGROUND 
     The invention relates to a camshaft phaser or adjuster for the inner camshaft of a concentric camshaft assembly, and in particular to a camshaft phaser or adjuster for adjusting the relative rotational angle position of an inner camshaft of a concentric camshaft assembly relative to the phase position of the outer camshaft and the crankshaft of an internal combustion engine. 
     Camshaft phasers that operate according to the vane-cell principle for use on 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. These work well in connection with DOHC engines where all the intake or exhaust cam lobes are located on separately located intake and exhaust camshafts. 
     It has also been known to use camshaft phasers in connection with concentric camshaft assemblies for controlling the phase position of the inner camshaft, the outer camshaft or both. One such arrangement is described in DE 10 2006 024 793 A1. This publication discloses a dual phasing system for a concentric camshaft assembly which includes two camshaft phasers which are located at the front of an engine that are axially spaced adjacent to one another. These two camshaft phasers allow independent control the rotation angle of the outer and inner co-axial camshafts relative to the crankshaft in order to allow separate adjustment of the timing of the intake and the exhaust valves of the internal combustion engine. However, this arrangement provides additional complexity which is often not required to obtain many of the benefits of adjusting either the inner or the outer camshafts of a concentric camshaft assembly without the need for adjusting both. 
     A problem with the known camshaft phasers for use with either or both the inner and outer camshafts of a concentric camshaft assembly is that the chain or belt loads from the timing chain or belt are transmitted to the inner camshaft. This can cause bending and binding of the inner camshaft relative to the tubular outer camshaft. Additionally, in the prior known systems, the phaser is formed with opposing vanes extending from the front and rear covers of the phaser, toward one another, with one of the covers being attached to the inner shaft and the other cover being attached to the outer shaft. This arrangement has been shown to lack durability and includes basic design flaws which affect the functionality of such proposed systems. 
     It would be desirable to provide a camshaft phaser for a concentric camshaft assembly that allows for phasing of either the intake or exhaust lobes of a camshaft in which the drive load from the timing chain or belt extending from the crankshaft to the timing gear or timing belt pulley of the concentric camshaft arrangement is transmitted to the outer shaft of the concentric camshaft. Additionally, it would be desirable to provide the phaser as a preassembled unit which can be installed in a simple manner during assembly of the engine, minimizing the complexity of the assembly steps required. Further, the phaser should be removable as a single unit for service so that it can be easily removed and installed in the field. 
     SUMMARY 
     The present invention provides a camshaft phaser for the inner camshaft of a concentric camshaft assembly in an internal combustion engine which addresses the deficiencies in the known arrangements. 
     In the preferred embodiment of the invention, the camshaft phaser or adjuster for the inner camshaft of a concentric camshaft assembly comprises a vane-cell type phaser assembly of the type disclosed in the assignee&#39;s U.S. Pat. No. 6,805,080 for use in connection with single camshafts. The phaser assembly of the present invention includes an inner rotor with radially outwardly extending vanes which is attached to the inner camshaft. The rotor is surrounded by a stator having radially inwardly directed projections which contact the outer surface of the rotor and form working spaces into which the vanes extend. The vanes divide the working spaces into first and second sets of pressure chambers which can be pressurized with a hydraulic medium in order to rotate the rotor in an advancing or retarding direction relative to the stator. Front and rear covers are attached to the stator and define the front and rear sides of the pressure chambers. The timing gear or timing belt pulley is also attached to the stator. In order to transfer the loads caused by the timing chain or belt directly into the outer camshaft, the rear cover includes a splined opening. The front end of the outer camshaft includes a splined connection complementary to the splined opening in order to provide a positive fit connection between the outer camshaft and the rear cover for direct transfer of the timing chain or belt loads into the outer camshaft. In a preferred embodiment, the first camshaft journal of the outer camshaft is located directly adjacent to the splined connection. 
     Preferably, the rotor is connected to the inner camshaft via a central bolt assembly that includes a central bore in which a valve assembly is located for controlling the flow of pressurized hydraulic medium to the pressure chambers used to rotate the inner rotor relative to the stator. In a preferred embodiment, the valve assembly is a solenoid driven spool valve which directs pressurized hydraulic medium to either or both sets of pressure chambers between the stator and the rotor to either advance or retard the rotor with the attached inner camshaft relative to the stator (which is connected to the outer camshaft and the crankshaft) and/or to hydraulically fix the position of the rotor relative to the stator. 
     In a preferred embodiment, a locking pin is provided in the rotor to engage the front cover, rear cover or stator in a base position of the inner camshaft when insufficient pressurized hydraulic medium is available for maintaining sufficient control of the position of the rotor relative to the stator. 
     It is further preferred if a helical spring is connected between the rotor and the stator to balance the force required for rotating the rotor in an advancing direction relative to the stator in comparison to the force required for retarding the position of the rotor relative to the stator. 
     Further aspects of the invention, which can be used alone or in combination, are described in detail below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing summary and the following detailed description will be better understood when read in conjunction with the appended drawings, which illustrate a preferred embodiment of the invention. In the drawings: 
         FIG. 1  is a front elevational view of a camshaft phaser assembly according to the present invention; 
         FIG. 2  is a top view of the camshaft phaser assembly shown in  FIG. 1 ; 
         FIG. 3  is a rear elevational view of the camshaft phaser assembly of  FIG. 1 ; 
         FIG. 4  is a front perspective view of the concentric camshaft assembly showing the inner camshaft and the outer camshaft; 
         FIG. 5  is a cross-sectional view through the camshaft phaser of  FIG. 1  and the front of the concentric camshaft assembly taken along lines  5 - 5  in  FIG. 1 ; and 
         FIG. 6  is a cross-sectional view through the camshaft phaser taken along line  6 - 6  in  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     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 the 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 terms camshaft “phaser” and “adjuster” are used interchangeably. The terminology includes the words specifically noted above, derivatives thereof and words of similar import. 
     Referring to  FIG. 1-6 , a camshaft phaser  10  for a concentric camshaft assembly  12  is shown. The concentric camshaft assembly  12 , which is shown in detail in  FIG. 4 , preferably includes the inner shaft  14  having a front end, with a central bolt receiving hole  16 , oil feed passages  18  and a timing pin bore  19 , that protrudes from the front end of the outer tubular shaft  22 , which has a splined connection  24  located at the front end adjacent to the first bearing journal  26 . Those skilled in the art will understand that both the inner and outer camshafts include cam lobes, with the cam lobes of the inner camshaft protruding through openings in the outer tubular camshaft. One of the inner camshaft or the outer camshaft is used to control the opening of the intake valves of an internal combustion engine, and the other is used to control the opening of the exhaust valves. 
     As shown in detail in  FIGS. 5 and 6 , the camshaft phaser  10  includes a rotor  30  having radially outwardly directed vanes  32 . The rotor  30  is located inside a stator  40  which includes radially inwardly directed projections  42 . These projections  42  include bearing surfaces  48  which slidingly engage the outer surface of the rotor  30  at positions between the vanes  32 . The vanes  32  extend into working spaces  43  defined between the projections  42  to divide the working spaces  43  into a first set of chambers  44  and a second set of chambers  46 . The front and rear walls of these chambers are defined by a front cover  50  and a rear cover  52 . The front and rear covers  50 ,  52  are connected to the stator  40  via bolts  51 . 
     Preferably, a locking pin  58  is located within the rotor  30  and is of the type described in U.S. Pat. No. 6,805,080, and is spring biased into a position in which it engages in a corresponding recess located in the front cover  50 . The recess is connected to a source of pressurized hydraulic medium such that when sufficient pressurized hydraulic medium is available for stable operation of the phaser  10 , the locking pin  58  is disengaged from the recess  59  allowing the rotor  30  to move from the base position in order to advance or retard the timing of the inner camshaft  14  relative to the outer camshaft  22  and the crankshaft (not shown) of the internal combustion engine. 
     As shown in the Figures, a timing gear  54  is located on or connected to the stator and is connected to the crankshaft of the internal combustion engine via a timing chain (not shown). Alternatively, instead of a timing gear  54 , a timing belt pulley could also be provided or any other suitable drive could be utilized for transferring the rotating motion of the crankshaft to the camshaft phaser  10 . The timing gear  54  could alternatively be formed on or connected to the front or rear covers  50 ,  52 . 
     As shown in detail in  FIGS. 3 and 4 , the rear cover  52  shown in  FIG. 3  includes a splined opening  53  in which the splined end  24  at the front of the outer camshaft  22  engages. This splined connection provides for a direction transfer of the radial loads created by the timing chain or timing belt acting on the timing gear  54  or pulley located on the stator  40  to the outer camshaft  22 . This arrangement prevents these radial loads from being introduced into the inner camshaft  14  in order to prevent bending and/or binding of the inner camshaft  14 . 
     Referring again to  FIG. 5 , the rotor  30  is connected to the inner camshaft  14  via central bolt assembly  60  which clamps the rotor  30  to the inner camshaft  14 . Preferably, a timing pin is placed in the timing pin bore  19  of the inner camshaft  14  and is received in a corresponding bore in the rotor  30  in order to set a desired fixed position between the inner camshaft  14  and the rotor  30 . Alternatively, the timing between the outer camshaft  22  and the inner camshaft  14  can be controlled within the camshaft assembly, or it can be established when assembling the engine, for example by engaging a tool at the rear of the camshaft assembly in alignment slots on the inner and outer camshafts  14 ,  22 . 
     As shown in detail in  FIG. 5 , the central bolt assembly  60  includes a valve assembly  63  for directing pressurized hydraulic fluid to the first set of chamber  44  for rotating the rotor  30  in an advancing direction relative to the stator  40  in order to advance the timing of the inner camshaft  14 , or to the second set of chambers  46  in order to rotate the rotor  30  in a direction to retard the timing of the inner camshaft  14 . Hydraulic fluid can be applied to both the first and second sets of chambers  44 ,  46  in order to hydraulically lock the rotor  30  in a generally fixed position relative to the stator  40 . An electromagnetic solenoid (not shown) is used in order to adjust the position of the valve spool  64  within the inner bore  62  to direct pressurized hydraulic fluid to the passages  82 ,  84  as required. The valve spool  64  is biased to an initial position via a spring  68  which rests on a shoulder within the central bolt assembly  60 . Preferably, pressurized hydraulic fluid is provided to the central bolt assembly  60  via pressurized hydraulic fluid being delivered in the space between the inner camshaft  14  and the outer camshaft  22  of the concentric camshaft assembly  12 . This travels past a check valve  22  and through a filter  70  of the central bolt assembly  60  prior to reaching the valve spool  64  which directs the pressurized hydraulic fluid to the passages  82 ,  84  or to a drain back to the engine oil reservoir. 
     As shown in  FIG. 5 , a helical spring  55  acts between the stator  40 , via two of the five assembly bolts  51  (see  FIG. 5 ) that engage the spring  55 , and the rotor  30 , via a spring cover  56  that is attached to the spring  55  and extends through a clearance hole in the front cover  50  and is clamped to the rotor  30  using the bolt assembly  60 . The spring  55  balances the hydraulic force required to rotate the rotor  30  in a direction to advance the timing of the inner camshaft  14  in comparison to the force required to rotate the rotor  30  in a direction to retard the timing of the inner camshaft  14 . 
     As shown in  FIGS. 1 and 5 , a timing sensor plate  80  is connected to the front of the camshaft phaser  10  and, by the use of a position sensor (not shown) allows the position of the rotor  30  to be determined so that the timing position of the rotor  30  and the inner camshaft  14  can be accurately controlled using an engine control module (not shown) which controls the valve assembly  63 . 
     The camshaft phaser  10  is preassembled as a unit that can be installed in one piece of the front end of the concentric camshaft assembly  12  by aligning the rotor  30  with the inner camshaft  14  so that the timing bin bore  19  and timing pin located therein align with the corresponding timing pin bore  34  in the rotor  30 , and sliding the splined end  24  of the outer camshaft  22  into the splined opening  53  in the rear cover  52  attached to the stator. The central bolt assembly  60  is then used to clamp the rotor  30  to the inner camshaft  14  and holds the entire phaser  10  in position axially on the front end of the concentric camshaft assembly  12 . 
     The camshaft phaser  10  for the inner camshaft  14  of the concentric camshaft assembly  12  provides all the advantages of the known phasers for single camshafts and addresses the drawbacks of the known camshaft phasers which have been suggested for use in connection with the inner camshaft of a concentric camshaft assembly. Specifically, by providing a splined connection between the outer camshaft and the timing gear or timing belt pulley, the loads from the timing belt or chain are transferred directly via the stator  40  and the rear cover plate  52  into the outer camshaft  22  thus preventing potential binding of the inner camshaft  14  which can occur in the known prior art arrangements. Thus all the advantages of a conventional vane-cell type camshaft phaser which was known for use in connection with single camshafts can now be utilized to control the inner camshaft  14  of a concentric camshaft assembly  12  in a stable and reliable manner. Additionally, by providing the camshaft phaser  10  as a unitized assembly which is attached using the central bolt  60  to the inner camshaft and via the splined connection between the outer camshaft  22  and the rear cover  52 , the camshaft phaser  10  according to the invention can be easily installed and removed during assembly and for service of the engine and/or camshaft phaser  10 .