Abstract:
An improved splined cam phaser includes four assemblies: a sprocket assembly, an inner hub assembly, a cover assembly, and a piston assembly. The joined assemblies provide phaser function at reduced manufacturing cost. The component parts of the assemblies are re-configured from analogous parts in the prior art cam phaser to permit much of the improved phaser to be manufactured inexpensively by powdered metal forming or by stamping or drawing from sheet metal, in contrast with the prior art phaser wherein all parts are formed expensively either by machining from forged blanks or by investment casting. These changes reduce not only the cost of manufacture but also reduce the weight and axial length of the phaser, an important customer acceptance criterion, and improve the speed of response. Further, the proportions of some parts are altered such that all radial and axial loads are borne by a single large bearing in place of two small sequential bearings in the prior art phaser, thus reducing variability in axial alignment of the component parts.

Description:
TECHNICAL FIELD 
     The present invention relates to a cam phaser apparatus for controllably varying the phase relationship between the crankshaft and the camshaft of an internal combustion engine; more particularly, to a cam phaser having concentric splined elements counter-rotatable by a splined piston therebetween; and most particularly, to a splined cam phaser wherein the parts are optimized for ease and economy of manufacture, reduced phaser size, and improved phaser performance. 
     BACKGROUND OF THE INVENTION 
     Splined cam phasers are well known in the automotive art; see, for example, U.S. Pat. No. 5,588,404. In principle, a phaser assembly is relatively simple. A first rotatable element is fixedly mounted to the end of a camshaft of an engine and turns synchronously therewith. The first element has helical splines on its outer surface. A second rotatable element surrounds the first element concentrically and has a drive wheel, pulley, or sprocket adapted to be driven by the crankshaft of the engine. On its inner surface, the second element has helical splines opposite-handed from the splines on the first element. A generally cylindrical piston is positioned in a closed annular space between the two elements. The piston has helical splines on both its inner surface and its outer surface which mesh with the splines on the first and second elements. The piston is controllably driven axially in either direction by programmably-directed hydraulic pressure against one or the other side of the piston, causing the first and second elements to counter-rotate with respect to each other and thereby varying the relative timing of the valves with respect to the pistons by changing the rotational phase relationship between the crankshaft and the camshaft. Preferably, the first element is provided at its outer end with a sectored timing wheel, also referred to herein as a target wheel, to permit automatic monitoring of the cam position at all times. 
     The prior art cam phaser can be difficult and expensive to manufacture. Typically, all moving parts are individually machined from steel forgings. The target wheel, which carries the compressive force of the major assembly bolt, is optimally formed by investment casting, a very expensive forming method. The layout of the parts and seals does not lend itself to formation by less expensive known methods, for example, by powdered metal forming, preferably by powdered steel. Further, the internal passages in various parts, required to present hydraulic fluid to one or the other face of the piston, typically are formed labor-intensively by cutting and drilling. 
     Therefore, what is needed in the art is an improved splined cam phaser wherein the cost of manufacture is minimized by minimizing the number of machined parts. What is also needed in the art is an improved splined cam phaser wherein the alignment of first and second elements is controlled by a single axial bearing therebetween. 
     Further needed in the art is an improved splined cam phaser wherein the axial length is reduced. 
     Still further needed in the art is an improved splined cam phaser wherein the speed of response is improved. 
     Finally, what is needed in the art is an improved splined cam phaser wherein the position of the cam shaft sprocket relative to the crank shaft can be set after assembly of the splined cam shaft phaser. 
     SUMMARY OF THE INVENTION 
     Briefly described, an improved splined cam phaser in accordance with the invention comprises four assemblies: a sprocket assembly, an inner hub assembly, a cover assembly, and a piston assembly. The joined assemblies provide an improved phaser function over that of the prior art phaser. The component parts of the assemblies are re-configured from the analogous parts of the prior art phaser to permit much of the improved phaser to be manufactured inexpensively by powdered metal forming or by stamping from sheet metal, in contrast with a prior art cam phaser wherein all parts are formed expensively either by machining from forged blanks or by investment casting. These changes reduce the cost of manufacture, reduce the weight and axial length, and improve the speed of response, all of which are important customer acceptance criteria. In addition, the irregularly shaped and larger capacity oil passages of the present invention, which require no machining after forming, permit further improvement in speed of response time of the phaser assembly. Further, the proportions of some parts are altered such that all radial and axial loads are borne by a single bearing, rather than the two bearings as in the prior art phaser, thereby reducing variability in axial alignment of the component parts. 
     The present invention overcomes the problems of the prior art by providing a cam phaser with a lighter, less expensive sheet metal cover. The invention uses a sheet metal cover to replace the conventional cast and machined cover by rearranging the load distribution of the cam phaser. Instead of the cover bearing the load, the invention places the load on an inner hub. With the load redistributed, the cover is made with less expensive materials and processes. In the preferred embodiment, the cover is made of sheet metal or net casting. The cover, while providing a seal for the pressure chamber that actuates the piston, no longer bears the load of the camshaft. A target wheel, also of sheet metal, is an optional component that is be mounted on the outside of the cover. The target wheel has indicia for generating signals representative of the angular position of the cam phaser. Those signals are used to control the setting of the angle of the cam phaser. 
     With the present invention all the components of the cover and the inner hub are net shaped as originally manufactured thereby eliminating the cost of additional machining. The added machining of o-ring grooves is also eliminated. Likewise, targets are net cast into the sheet metal cover or are easily stamped rather than machined into a cast cover. 
     Further, with the present invention the manufacturing of the piston is simplified and the cost reduced by eliminating the need to machine grooves for the seals in the piston skirt. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing and other objects, features, and advantages of the invention, as well as presently preferred embodiments thereof, will become more apparent from a reading of the following description in connection with the accompanying drawings in which: 
     FIG. 1 is a cross-sectional view of a prior art spline-type cam phaser substantially as disclosed in U.S. Pat. No. 5,588,404; 
     FIG. 2 is a cross-sectional view of an improved spline-type cam phaser in accordance with the invention; 
     FIG. 3 is an exploded cross-sectional view of the sprocket assembly of the cam phaser shown in FIG. 2; 
     FIG. 4 is an assembled cross-sectional view of the exploded sprocket assembly shown in FIG. 3; 
     FIG. 5 is an exploded cross-sectional view of the inner hub assembly of the cam phaser shown in FIG. 2; 
     FIG. 6 is an assembled cross-sectional view of the exploded inner hub assembly shown in FIG. 5; 
     FIG. 7 is an exploded cross-sectional view of the cover assembly of the cam phaser shown in FIG. 2; 
     FIG. 8 is an assembled cross-sectional view of the exploded cover assembly shown in FIG. 7; 
     FIG. 9 is an exploded cross-sectional view of the cam phaser shown in FIG. 2, showing the combining of the assemblies shown in FIGS. 4,  6 , and  8  with a piston assembly; 
     FIG. 10 is an assembled cross-sectional view of the exploded assemblies shown in FIG. 9, FIG. 10 being substantially identical with FIG. 2; 
     FIG. 11 is a plan view of a sprocket wheel shown in FIG. 3; 
     FIG. 12 is a plan view of a target wheel shown in FIG. 7; 
     FIG. 13 is a cross-sectional view of an alternative embodiment of a phase control piston wherein a non-load-bearing portion of the piston is formed from a plastic polymer; and 
     FIG. 14 is an elevational view of the phase control piston shown in FIG.  13 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The improvements and benefits conferred by a cam phaser in accordance with the invention may be best understood by first considering a prior art cam phaser. 
     Referring to FIG. 1, numeral  10  generally indicates a portion of the valve gear of an internal combustion engine including a camshaft  12  conventionally carrying a plurality of valve-actuating cams (not shown) and mounted for rotation in the cylinder head or other portion of a multi-camshaft engine (not shown). Camshaft  12  includes at one end an enlarged cylindrical journal  14 , which may be a bearing journal, on the end of which is fixedly mounted a prior art variable cam phaser  16  formed in accordance with the prior art, substantially as disclosed in U.S. Pat. No. 5,588,404 issued Dec. 31, 1996 to Lichti et al., the relevant disclosure of which is hereby incorporated by reference. 
     Cam phaser  16  includes an outer drive member in the form of a pulley  18  (although a chain sprocket, gear, or other suitable drive device could equally well be used). The pulley  18  includes an outer rim  20 , adapted to be driven by a toothed timing belt (not shown). As the belt drives pulley  18 , the cam phaser  16  transfers its rotary motion to the camshaft  12 . The angular position of the cam phaser  16  with respect to the camshaft is adjusted to vary the opening and closing of the valves. That adjustment is made to increase or reduce horsepower and/or fuel efficiency. Rim  20  is connected by a web  22  with a tubular portion  24  extending axially to one side of the web and having at an outer end a cylindrical external bearing surface  26 . Within the portion  24  and extending from the outer end adjacent bearing surface  26  are internal right hand helical splines  28 . 
     Pulley  18  is supported for relative rotation upon a coaxial driven hub assembly comprising an assembly of a hub flange  30  and a hub  32 . The hub flange includes an end having a circular recess  34  in which the end of the camshaft journal  14  is received. A flange  36  extends outwardly from the recess  34  and terminates outwardly in an enlarged cylindrical journal  38  that slidably engages an internal bearing surface  40  of tubular portion  24 . Adjacent to the flange  36  and opening away from the camshaft  12 , the hub flange  30  includes a recess  42  adjacent an external guiding surface  44  containing a piston seal ring  46 . Adjacent the guiding surface  44 , a shoulder  48  extends inwardly to a smaller diameter tubular portion  50  on which the hub  32  is supported. 
     Hub  32  comprises a tubular body provided, on an outer diameter, with external left hand helical splines  52 . On its inner diameter, hub  32  includes a raised portion  54  carried by tubular portion  50 , an end face  56  engaging the shoulder  48 , and an annular shoulder  58  that is engaged by an outwardly flared flange  60  formed by a thin wall end of the tubular portion  50  of the hub flange. Further outward, in the direction away from the camshaft, the hub  32  inner diameter forms a slightly enlarged internal locating surface  62  having a retaining groove  64  toward its inner end. 
     An annular cover  66  having a central opening and a generally U-shaped annular cross-section is mounted on the outer ends of the hub  32  and tubular portion  24 . The cover includes an outer wall  68  with an inner surface engaging the bearing surface  26  of the tubular portion  24  and an inner wall  70  having an outer surface engaging the internal locating surface  62  of the hub. An inward extension of the inner wall forms a shoulder  72  against which is clamped the head  74  of a central fastener in the form of an attaching bolt  76 . The bolt extends through openings in the cover  66  and the hub flange  30  into a hollow center  78  of the camshaft  12  wherein it is threadably engaged in a manner not shown. An annular end wall  80  of the cover extends between the outer and inner walls  68 , 70  and encloses an annular space within the cam phaser. Within this space are located a first annular phase control piston  82  and a second annular lash control piston  84 . 
     The first piston  82  divides the annular space into an annular pressure chamber  86  adjacent the cover  66  and an annular return chamber  88  between the flange  36  and the piston  82 . Piston  82  includes a ring of external right hand helical splines  90  engaging the internal splines  28  within the tubular portion  24  of the pulley. 
     Additionally, there is a ring of internal left hand helical splines  92  that engage the external helical splines  52  of the hub  32 . Accordingly, axial motion of the piston  82  causes a change in the angular orientation or phase relation between pulley  18  and the hub  32 , as well as the associated camshaft  12  to which the hub is attached. Changing the phase relationship produces a corresponding change in the time when the valves open and close. 
     A large helical coil compression spring  94  is seated against the flange  36  of the hub flange and is received in a recess  96  of the piston  82  for biasing the piston in a direction toward the annular cover  66 , tending to return the camshaft to a predetermined position, such as a retarded or advanced position for valve actuation. The spring  94  lies within the return chamber  88  formed on the camshaft side of the piston. A piston seal ring  100  seated in a groove in a guiding surface  102  of the piston  82  engages a cylinder surface  104  within the tubular portion  24  of the pulley  18 . Piston seal ring  100  and piston seal ring  46  in the guiding surface  44  of flange  60 , which engages a cylindrical surface of the piston, limit the leakage of oil between the pressure chamber  86  and the return chamber  88 . 
     Piston  82  alters the phase of the camshaft. When piston  82  moves in a direction against the bias of spring  94 , it retards the camshaft timing, by forcing pressurized engine oil (or hydraulic fluid) through passages  108  in the camshaft and  110  in the hub flange which communicate with drain passage  114  in the camshaft. Passage  112  is connected to a pressurized oil supply for forcing piston  82  in an advance direction. Suitable seals are provided to prevent the leakage of pressure and drain oil from the interior of the cam phaser to external surfaces of pulley  18 . 
     The annular lash control piston  84  is located in the pressure chamber  86  between the piston  82  and cover  66 . This piston includes external and internal helical splines like those of piston  82  and also engaging the corresponding splines  28 , 52  of the pulley and hub respectively. The splines of the two pistons are preferably formed with machined end surfaces of the pistons in engagement with one another so that the helices of the splines are continuous when the pistons are engaged. An annular groove  120  in the phase control piston  82 , opening toward the facing surface of the lash control piston  84 , receives a cylindrical compression spring, preferably in the form of a wave spring  122 . Spring  122  urges the lash control piston  84  away from the phase control piston  82  and takes up the lash in the splines between the associated pulley and hub. In this lash control action, the pistons  82 , 84  function in the same manner as known split gears used for lash control in gear drives. 
     Prior to assembly of the cam phaser, the hub flange  30  has its tubular portion  50  extending axially. This component is then assembled together with the hub  32 , pistons  82 , 84 , and pulley  18 . Hub  32  is not fixed to the hub flange but is rotatable on the tubular portion  50 , so that the pulley  18  with splined pistons and hub may be rotated relative to the hub flange  30  in order to properly time the pulley to the hub flange with the compression spring  94  fully extended. The outer end of the tubular portion  50  is then deformed, such as by staking or rolling, to form the flange  60  shown in FIG.  1 . Flange  60  engages shoulder  58  of the hub, locking the components in their desired orientations. The cover  66  may then be installed and is retained by a retaining ring  124  until assembly of the unit to an engine camshaft. 
     Thereafter, the pre-timed mechanism is installed on a camshaft  12  as in FIG. 1. A conventional pin (not shown) may be used to orient the hub flange  30  to the camshaft for proper timing. Bolt  76  is threaded through the openings into the camshaft and tightened so as to lock the cover, hub, hub flange, and camshaft elements into fixed relation. This manner of assembly permits the manufacture and assembly of the splined components to be carried out without regard to any requirement for orientation or fixed relation of the internal and external splines other than the splines on the two pistons which are formed together. This allows timing of the elements to be conducted only after assembly of the mechanism components in the manner just described. 
     Referring to FIGS. 2-14, an improved splined cam phaser  126  embodying the invention includes a generally tubular inner hub assembly  128  comprising a generally cylindrical inner hub  130  and a hub flange  132 . See FIGS. 5 and 6. The hub flange  132  includes a recess  134  for receiving the flat end of a camshaft  12  having advance and retard oil passages  136 , 138  formed therein and a central threaded bore  140  for receiving bolt  76  to mount the inner hub assembly  128  onto the camshaft  12 . The hub flange  132  has an oversize central bore  142  for passage of the bolt  76  and first and second passages  144 , 146  mating with the advance and retard oil passages  136 , 138 , respectively in the camshaft  12  to admit oil to the advance and retard oil galleries of phaser  126 . The hub flange  132  has a cylindrical outer wall portion  148  having an axially extensive outer guide surface  150  and an axially extensive inner piston guide surface  152 . The oversize bore  142  in the hub flange is sized to receive in interference fit a boss  154  on the inner hub  130 , the boss sealably mating with the end of the camshaft  12  to prevent leakage between the oil supply passages  136  and  138 . A portion of the inner hub  130  distal from the camshaft comprises a longitudinal gear  156  having external left hand helical splines  52 . A shouldered step  158  in the inner hub adjacent the gear  156  receives a formed ring  160  for retaining an inner piston seal  162 . The axial bore  164  in inner hub  130  is assymetrically enlarged through its distal portion to provide an oil passage  166  to the pressure chamber, as discussed below. The inner hub  130  and hub flange  132  are press fit together to define an annular return chamber  88  therebetween, as shown in FIGS. 5 and 6. The hub flange  132  is configured so that it may be easily formed inexpensively by powdered metal forming in known fashion, such forming including net shaping of the oil passages  144 , 146 . The inner hub  130  is preferably formed by machining of a forged blank and can be alternately formed from powdered metal. 
     In the present invention, the several functions of prior art annular cover  66  are divided among several inexpensively formed new components which are assemblable into a cover assembly  168  which is less expensive to manufacture than investment-cast cover  66 . Cover assembly  168  comprises an outer hub  170  and cover  218 , and an optional timing wheel  172  as shown in FIGS. 7 and 8. The outer hub  170  has an axial bore  174  for accommodating bolt  76  and is supported concentrically within a wider-diameter outer portion  176  of the inner hub  130 , to which it is attached for joint rotation by a pin  178 . An annular space  180  between the inner hub  130  and the outer hub  170  defines an annular passage for pressurized oil from the assymetric axial bore  164  in the inner hub to the pressure chamber. The outer hub  170  is provided with an axial outer recess  182  for receiving the head  74  of the bolt  76  and with a short axial boss  184  having parallel sides surrounding the recess for receiving timing wheel  172  which is preferably stamped from sheet steel. Timing wheel  172  permits continuous measurement of the phase of the camshaft relative to the crankshaft by an external sensor (not shown). The timing wheel  172  has a non-circular central opening  186  having parallel sides  188 , as shown in FIG. 12, which is matable with the boss  184  on the outer hub  170 . The timing wheel  172  may have both radial and axial flange portions  190 , 192  as desired, and is readily and inexpensively formed by stamping or deep drawing from sheet metal. The outer hub  170  is also configured for inexpensive and reliable forming by powdered metal techniques. The cover  218  is provided with a central recess  220  which surrounds the outer hub  170  and which has a lip  222  for engaging a step  224  on the outer hub  170 . Preferably, an O-ring  226  is captured between lip  222  and step  224  to provide a rotating seal of the pressure chamber  86 . The cover  218  is readily and inexpensively formed by stamping or deep drawing from sheet metal. 
     An advantage of the present cam phaser configuration is that the juncture of the cover with the sprocket flange is no longer a rotary bearing which can adversely affect axial alignment. Prior art cover  66  is fixed to the camshaft by bolt  76  and rotates therewith against hub flange  24  (surface  26  in FIG.  1 ). Cover  66  serves also as a timing wheel. In the present invention, cover  218  is fixed to the sprocket flange  200  and instead rotates with the sprocket and crankshaft, there being a new rotary seal  226 , such as an o-ring, between cover  218  and outer hub  170 . Outer hub  170  bears the axial load formerly borne by cover  66 . This improvement, and the associated reduction in fabrication costs of the improved timing wheel assembly, is possible because there is no secondary axial guiding surface  26  as in prior art phaser  16 , due to the axially longer primary guiding surface  150 / 210  formed in inner hub assembly  128  and sprocket assembly  194 , respectively, as discussed in more detail below. 
     Concentrically surrounding the inner hub assembly  128  is a sprocket assembly  194  comprising a generally flat toothed sprocket wheel  196  for receiving a timing chain (not shown). The sprocket assembly has a central opening  198  and a generally cylindrical sprocket flange  200  having a shouldered portion  202 , as shown in FIG.  3 . The portion  202  is fit into the sprocket wheel opening  198  to form the sprocket assembly  194 , as shown in FIG.  4 . The sprocket wheel  196  is provided with a plurality of holes  204  for bolting the wheel to the flange via matching holes  206  in flange  200 . Preferably, the holes in the sprocket wheel are radially slotted to permit precise timing adjustment of the phaser by slight rotation of the sprocket wheel past the sprocket flange during final assembly. As shown in FIG. 9, during assembly, the sprocket flange  200  is disposed radially apart from the inner hub assembly  128  to form an annular space  208  therebetween, as discussed further below. The sprocket flange  200  is preferably formed by machining of a forged blank. The sprocket wheel  196  is readily formed inexpensively by known powdered metal forming techniques, wherein powdered metal is compressed and solidified in a mold to yield a rigid, durable part. 
     A portion of the inner wall of the sprocket flange proximal to the camshaft is a smooth cylindrical guiding surface  210  for rotatably mating with the cylindrical outer surface  150  of the hub flange  132  to form an axially-extensive single bearing for carrying all imposed radial loads and for maintaining axial alignment of the hub assembly and the sprocket assembly. The portion of the inner wall of the sprocket flange distal from the camshaft is provided with internal right hand helical splines  28 . 
     In the annular space  208  between the sprocket flange and the hub assembly is disposed a piston assembly  211  comprising an annular phase control piston  82  and an annular lash control piston  84 . The pistons are provided on their outer and inner surfaces, respectively, with external right hand helical splines  90  and internal left hand helical splines  92  for meshingly engaging the corresponding splines  28 , 52  on the sprocket flange and the hub assembly, respectively. An intermediate annular chamber  120  between the pistons holds a wave spring  122  for urging the pistons apart to take up lash in the splines. The pistons divide the annular space  208  into an annular pressure chamber  86  and an annular return chamber  88 . The phase control piston  82  has an inner skirt  212  which is slidably sealed against the piston seal  162  in the seal ring  160 , and an outer seal ring  214  and outer piston seal  216  which is slidably disposed against the inner guide surface  152  of the outer wall portion  148 . The pressure chamber  86  is closed by the inverted cup-shaped cover  218  which is an element of the cover assembly  168  which is sealingly attached as by crimping to the outer end of the sprocket flange  200 . 
     Referring to FIGS. 13 and 14, the cost and weight of annular phase control piston  82  may be reduced by substituting a moldable plastic polymer, for example, Nylon 6/6 available from E.I. DuPont de Nemours, Wilmington, Del. USA, for a non-load-bearing portion of the piston. In alternative embodiment  82   a , the load-bearing splined portion  82   b  is machined from a forged metal blank, as in piston  82 , but without the skirt portion. A flange  83  is provided as a lock for plastic skirt  85  which is conveniently overmolded onto piston  82   b  in known insert molding fashion to yield embodiment  82   a.    
     Within the return chamber  88  is disposed a helical coil compression spring  94  for biasing the pistons to a full advance position. The spring  94  is seated at its proximal end in an annular recess  42  in the hub flange and at its distal end in an annular recess  96  in the phase control piston. 
     To complete fabrication of the improved phaser  126 , as shown in FIG. 9, the piston assembly  211  and compression spring  94  are installed onto the inner hub assembly  128  and the two assemblies are inserted into the sprocket assembly  194  through the central opening  228  in the sprocket flange  200 . A snap ring  230  is installed in the groove  232  formed between the sprocket flange  200  and the hub flange  132  to retain the inner hub assembly  128  in the sprocket assembly  194 . The cover assembly  168  including the O-ring  226  and cover  218  is inserted into the recess  176  (FIG. 5) in the inner hub assembly  128 , the two assemblies being rotationally aligned to permit a pin  178  to be inserted therebetween. The radial flange  234  on the cover  218  is then sealed to the sprocket flange  200  as by roll crimping or welding. The cover  168  is retained in the phaser by bolt  76 . 
     A splined cam phaser in accordance with the invention has several important advantages over the prior art cam phaser. First, an inner hub assembly  128  that includes a separate hub flange  132  and an inner hub  130  replaces the complex conventional hub flange  30 . The prior art hub flange  30  is entirely machined from a complex forged blank and is very expensive to fabricate. The present inner hub  130  is also machined from a forging, but the forging is much less complex and the machining is much less expensive. The inner hub  130  is configured to permit powdered metal forming, at significant savings in fabrication cost. 
     Second, the axially short external guiding surface  44  on the prior art hub flange  30  is reconfigured as an axially extensive external guiding surface  150  on hub flange  132 . The axial length is sufficient that all radial loads may be borne on this one bearing surface, eliminating the need for a second external bearing surface  26  as on the prior art hub flange  30 . In the prior art phaser  16 , variances in the first and second bearings are additive, whereas in the improved phaser all variance is contained in a single bearing. Thus, total bearing variance is reduced and axial alignment of the component parts is significantly improved. 
     Third, the hub flange  132  is conveniently configured such that the oil passages  144 , 146  are net formed in the flange during powdered metal fabrication thereof, thus eliminating the complex and expensive drilling and machining of oil passages required by the prior art hub flange. As the oil passage are net formed, no secondary or finish machining is required, thus reducing cost. 
     Fourth, eliminating the second bearing removes the need for great structural strength and rigidity in annular cover  66 , which is also needed to support the axial load imposed by the bolt head  74  without being deformed. Cover  66  is formed very expensively by investment casting. In phaser  126 , cover  66  is reconfigured as cover assembly  168  having three separate parts: the outer hub  170 , the cover  218 , and the optional timing wheel  172 . The cover and timing wheel are readily stamped, punched, or deep drawn by a shaped ram or form from sheet metal in known fashion, and the outer hub is readily formed by powdered metal forming, all at a great reduction in cost over prior art cover  66 . Axial length of the phaser is also reduced by obviating the need for a thick cover. Reduction in mass of the cover also reduces inertia and thus improves speed of response of the phaser. 
     Fifth, the inner piston seal is provided by a separate grooved ring  160 , for supporting seal  162 , the ring being pressed into a shouldered step  158  in inner hub  130 . This permits easy machining of the inner hub to form the hub splines  52  before installation of the ring with no required allowance in length of the inner hub to accommodate a machining transition zone between the splines and the seal groove. This improvement reduces the minimum axial length of the phaser. 
     Sixth, an integral O-ring groove to accommodate an O-ring  226  as an inner seal to the annular pressure chamber  86  is formed between a step  224  on the outer hub and the lip  222  on the cover. Thus, the need to machine an o-ring groove to seal the the annular pressure chamber is eliminated. 
     Seventh, timing of the phaser can be performed after assembly by relative rotation of the sprocket wheel  196  and sprocket flange  200  as described above. Thus, no post assembly staking of the outer hub to the inner hub, as in the prior art phaser, is required. 
     Eighth, the annular phase control piston is formed partially of a plastic polymer to reduce cost and weight. 
     It will be seen from the above that, in contrast with the prior art cam phaser, only the splined components of the improved cam phaser are formed by machining from forged blanks (the inner hub, the sprocket flange, and the two pistons). All other structural parts are be formed by other inexpensive processes from inexpensive starting materials, thus reducing the cost of manufacture, improving ease of assembly, reducing size and weight, and improving response performance. 
     From the foregoing description, it will be apparent that there has been provided an improved splined cam phaser, wherein the cost and ease of fabrication is very significantly reduced, size is reduced, and speed of response is improved. Variations and modifications of the herein described cam phaser, in accordance with the invention, will undoubtedly suggest themselves to those skilled in this art. Accordingly, the foregoing description should be taken as illustrative and not in a limiting sense.