Abstract:
An axially-compact camshaft phaser wherein the phaser bearing flange on the camshaft, connected to a timing chain sprocket or cam drive gear, is axially inverted in comparison to prior art cam phasers so that the bearing flange extends axially and inwardly of the phaser stator and rotor such that radial drive load on the phaser is sustained within the hydraulic portion of the phaser rather than externally thereof. The overall axial length of the phaser may be reduced thereby by about 25% relative to some prior art phasers and the Phaser Envelop volume may be reduced by 15% while maintaining an equivalent torque capacity.

Description:
TECHNICAL FIELD 
     The present invention relates to cam phasers for reciprocating internal combustion engines for altering the phase relationship between valve motion and piston motion; more particularly, to cam phasers having a vaned rotor disposed in an internally-lobed stator to form actuation chambers therebetween; and most particularly to an axially-compact cam phaser wherein an inverted sprocket or pulley hub bearing permits a large reduction in the axial length of the phaser compared with that of prior art phasers, while providing substantially equivalent torque capacity. 
     BACKGROUND OF THE INVENTION 
     Cam phasers are well known in the automotive art as elements of systems for reducing combustion formation of nitrogen oxides (NOX), reducing emission of unburned hydrocarbons, improving fuel economy, and improving engine torque at various speeds. As is known, under some operating conditions it is desirable to delay or advance the closing and opening of either the intake valves or the exhaust valves or both, relative to the valving in a similar engine having a fixed relationship between the crankshaft and the camshaft. 
     Cam phasers employ a first element driven in fixed relationship to the crankshaft and a second element adjacent to the first element and mounted to the end of the camshaft in either the engine head or block. The first element is typically a cylindrical stator mounted coaxially to a crankshaft-driven gear or pulley and having a plurality of radially-disposed chambers separated by inwardly-extending radial lobes and the second element is a vaned rotor mounted to the end of the camshaft through an axial bore in the stator and having a vane disposed in each of the stator chambers such that limited relative rotational motion is possible between the stator and the rotor. The chambers are sealed typically by front and rear face seals of the stator. The apparatus is provided with suitable porting so that hydraulic fluid, for example, engine oil under engine oil pump pressure, can be brought to bear controllably on opposite sides of the vanes in the chambers. Control circuitry and valving, commonly a multiport spool valve, permits the programmable control of the volume of oil on opposite sides of each vane to cause a change in rotational phase between the stator and the rotor, in either the rotationally forward or backwards direction, to either advance or retard the opening of the valves with respect to the position of the pistons in the cylinders. 
     Cam phaser designs heretofore have faced two powerful and antithetical needs: compact size and high torque capacity. 
     Regarding small size, many engine applications require the addition of a cam phaser unit within the envelope of an existing engine design which may have been in production for several years and which gives no special consideration to space for such a unit in the vicinity of the camshaft end. Thus, to be useful with as many engine designs as possible, a cam phaser should occupy as little volume as possible. 
     Regarding high torque capacity, a cam phaser must be capable of generating sufficient rotational torque between the stator and rotor to drive the advancing and retarding of valve opening and closing, which average torque for representative engines can be about 3 Nm. The rotational torque that a cam phaser is capable of generating depends on several variables including the operating temperature of the engine, the operating age of the engine, the viscosity of the oil, and numerous other known engine factors. Therefore, for smooth engine operation and rapid response under all anticipated oil pressure and use conditions, the torque capacity of a cam phaser should be substantially greater than the average torque of 3 Nm for representative engines. 
     Torque capacity is the product of force applied at a distance from an axis of rotation. The torque capacity (T 1 ) of a specific cam phaser can be expressed in terms of available oil pressure (P) and volume displacement per radian (V) as follows: 
     
       
           T   1   =PV   (Eq. 1) 
       
     
     A volume parameter, referred to herein as the Phaser Envelope (PHE), is defined herein as pi times the square of the stator diameter D times the axial length L of the phaser, divided by 4, and represents the cylindrical volume required to contain the phaser: 
     
       
           PHE =(π D   2   L )/4  (Eq. 2) 
       
     
     The radial dynamic load imposed by the engine on the timing sprocket or pulley of the cam phaser is quite large and requires a substantial axial length of bearing between the sprocket and the camshaft to sustain the load. In prior art cam phasers, such a bearing is provided adjacent to, and axially displaced from, the stator/rotor hydraulic components of the phaser, thereby extending substantially the overall axial length of the phaser, the space required in the engine envelope to accommodate the phaser and, most significantly, the cylindrical volume or phaser envelop (PHE) required to contain the phaser. The PHE, in cm 3 , for prior art cam phasers having axially displaced bearings is typically in the range of 250 to 300. In a newer compact cam phaser design, disclosed in U.S. Patent to Lichti, et al titled “Diametrically Compact Cam Phaser”, assigned to the assignee hereof, bearing Ser. No. 09/388,103, the cam phaser has a PHE of 190 cm 3  while still maintaining a torque capacity (T 1 ) of 4.8 Nm at 20 psi oil pressure. However, in the Diametrically Compact Cam Phaser, because the bearing is displaced axially away from the stator/rotor hydraulic components, approximately 36% of the unit&#39;s total PHE is used up in providing support for the radial load of the chain drive. 
     What is needed is a compact cam phaser having an axial length significantly less than that of prior art cam phasers such that the Phaser Envelope can be substantially smaller at no significant sacrifice in bearing load capability or torque capacity. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to an axially-compact camshaft phaser wherein the bearing on the camshaft is axially inverted, in comparison to prior art cam phasers, so that the bearing extends inwardly of the phaser stator and rotor such that the bearing function is carried out over an axial length primarily within the hydraulic portion of the phaser rather than externally thereof. The overall axial length L and phaser envelop PHE of the phaser may be thereby significantly reduced without sacrificing torque capacity. 
    
    
     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 an axial cross-sectional view of the Diametrically Compact Cam Phaser taken along line  1 — 1  in FIG. 2, showing an axially displaced bearing of the prior art; 
     FIG. 2 is an axial-transverse cross-sectional view of the cam phaser shown in FIG. 1, taken along line  2 — 2  in FIG. 1; 
     FIG. 3 is an axial cross-sectional view of an axially-compact cam phaser in accordance with the invention, taken along line  3 — 3  in FIG. 4, showing an inverted bearing extending into a well in the rotor; and 
     FIG. 4 is an axial-transverse cross-sectional view of the cam phaser shown in FIG. 3, taken along line  4 — 4  in FIG.  3 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The benefits of the present invention can be more fully appreciated by first examining Diametrically Compact Cam Phaser  10  having its bearing displaced away from its stator/rotor components, as in the prior art, as shown in FIGS.  1 - 2 . Cam phaser  10  includes well-known generic components: a stator-drive element  14  (in this case, a chain drive sprocket); a stator  16  having a plurality of inwardly extending lobes  17 ; a rotor  18  having a cylindrical hub  20  and a plurality of outwardly-extending vanes  22 ; and a plurality of timing-advancing chambers  24  and timing-retarding chambers  26  being formed between the rotor vanes and the stator. 
     Chambers  24  and  26  are axially closed on a first side by a cover plate  28 , which can be integral with stator  16 , and on a second side by an axial face  30  of a bearing  32 , which may be integral with stator-drive element  14 . Oil for actuating the rotor with respect to the stator, by expanding the volume of chambers on first sides of the vanes and contracting the volume of chambers on second sides of the vanes, is distributed to the chambers via passages  34 . 
     Bearing  32  has a cylindrical bore  35  which is rotatably disposed against journal  36  of camshaft  38 , as shown in FIG. 1, to sustain the radial load imposed by the timing chain or belt in creating torque T 1 . Journal  36  defines a portion of camshaft  38  which is axially separated from end portion  40  of camshaft  38 , which may extend a distance into hub  20 , as in FIG.  1 . Thus, the load is borne on bearing elements  32  and  36  which are axially additional in length to the hydraulic elements  16 ,  18 , and  28 . Hence, the use of volumetric space in the vicinity of the end of the camshaft is rather inefficient. In some engines, the outermost camshaft bearing (not shown) is near enough to the end of the camshaft that phasers designed in accordance with the prior, art bearing design cannot be fitted thereto. 
     Referring to FIGS.  3 - 4 , an axially-compact camshaft phaser  42  in accordance with the invention includes the above-listed generic parts. Phaser  42  exhibits torque performance at least equivalent to prior art phasers within a much smaller Phaser Envelope (PHE). 
     Unlike the prior art stator drive elements, drive element  14  of phaser  42  is preferably of the minimum axial thickness required structurally to sustain the sprocket working load. Further, element  14  does not extend axially away from the hydraulic elements of the phaser, as in the prior art. Instead, preferably drive element  14  is substantially smooth on its outer axial face  44  and is provided with a cylindrical bearing flange  46  extending axially inwards of phaser  42  such that the journal portion  36  of camshaft extension  48  is included within stator drive element  14  and rotor  18 . In the embodiment shown in FIGS. 3 and 4, camshaft  38  is a pre-existing camshaft which is provided with a press-fit extension  48 , although, obviously, the end of camshaft  38  itself can be formed in the shape of extension  48  within the scope of the invention. 
     Phasers driven by dry timing belts typically require a cylindrical “snout” (not shown) extending rearwards of drive element  14  for cooperation with a rotating oil seal to prevent engine oil from reaching the timing belt. Therefore, phasers having oil-lubricated timing chains and gears can obtain the greatest measure of axial compactness from the invention, as the snout is obviated thereby. 
     Extension  48  preferably is provided with an axial face  49  and a cylindrical axial extension  50 , onto which rotor  18  is pressed via central bore  52  therein such that rotor  18  is both centered on and rotationally fixed to extension  48  and hence to camshaft  38 . Kidney shaped oil grooves  54  formed in axial face  56  of rotor  18  is sealed against face  49  to form passages which communicates with radial passages  34  in hub  20  and with feed passages  33  in camshaft  38  and extension  48  to supply oil to chambers  24 . Similar radial passages  37  supply oil to chambers  26  from a supply via bore  52 . Rotor face  56  extends radially beyond the inner end of bearing flange  46  and is recessed within rotor  18  by the length I of wall  57  substantially equal to the axial length of flange  46 , face  56  and wall  57  forming thereby a well  58 , as shown in FIG.  3 . 
     Recessing the bearing up into the rotor/stator while maintaining the same torque capacity requires either an increase in stator axial height (H) or an increase in overall diameter (D) over the prior art. The embodiment shown in FIGS.  3 - 4  maintains the stator axial height (H) while increasing overall diameter (D). This slight diameter increase moderately increases the volume occupied by the rotor/stator hydraulic components but dramatically reduces the volume required for the bearing support. The total improvement by this invention is a 25% reduction of the overall length (L) of the cam phaser and a reduction of the PHE by 15%. 
     A cam phaser in accordance with the invention, having radial bearing surfaces recessed within a well in the rotor, has a phaser envelope PHE less than 190 cm 3 , a stator diameter D less than 80 mm, a stator axial height H less than 23 mm, an overall axial length L less than 40 mm, a hydraulic capacity of at least 16 ml, and a phase operating range of at least 250°, provides a torque T 1  of at least 5.0 Nm at 20 psi oil pressure. A preferred embodiment thereof, providing 5.0 Nm of torque T 1  at 20 psi has a phaser envelope PHE of 162 cm 3 , a stator diameter D of 79 mm, a stator axial height H of 22 mm, an overall axial length L of 33 mm, a hydraulic capacity of 16 ml, and a phase operating range of 30°. 
     The foregoing description of the invention, including a preferred embodiment thereof, has been presented for the purpose of illustration and description. It is not intended to be exhaustive nor is it intended to limit the invention to the precise form disclosed. It will be apparent to those skilled in the art that the disclosed embodiments may be modified in light of the above teachings. The embodiments described are chosen to provide an illustration of principles of the invention and its practical application to enable thereby one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. Therefore, the foregoing description is to be considered exemplary, rather than limiting, and the true scope of the invention is that described in the following claims.