Abstract:
A camshaft phaser for an internal combustion engine includes a driven hub attached to a camshaft, and a drive sprocket journaled to the driven hub. A locking device uses a pin receptacle having a locking bore and an engagement ramp which is contiguous with the locking bore to allow a locking pin to extend partially from its housing pin bore before the locking pin is registered with the locking bore.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    None. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a camshaft phaser having positive phase locking at one or more camshaft-to-crankshaft orientations. 
         [0004]    2. Related Art 
         [0005]    Camshaft phasers are a class of devices which allow the valve operating camshaft of a reciprocating internal combustion engine to be timed, or phased, with respect to the crankshaft of the engine. Phasers typically use locking mechanisms to maintain a selected position during engine operation. Although sliding pins have been used for this purpose in the past, the results produced by pins have generally not been amenable to desired flexibility in camshaft timing because it is difficult to drive locking pins between adjacent, relatively rotating components at high speeds, as is often the case during automotive engine operation. 
         [0006]    Various attempts have been made to at least consider, and sometimes implement, improved structures for providing high speed locking of connecting pins. For example, receiving holes have been enlarged diametrically. Although this allows latching to occur at high speed, this accommodation comes at the expense of imprecision of locating the camshaft with respect to the crankshaft. 
         [0007]    Another means for enhancing the high speed locking capability of a phaser has been to taper or chamfer the locking pin. Although this, too, promotes high speed locking, the ramp effect of the chamfering sometimes causes the pin to work its way out of the hole, thereby allowing the desired camshaft phasing to be lost. A third way of promoting lockup under high speed is to provide a hard stop or, in other words, to lock the drive sprocket with respect to the remaining portion of the device only when the sprocket has been pulled over to a position at which further rotation with respect to the camshaft is not possible. This situation is undesirable because it allows the camshaft timing to be changed with only one degree of freedom, without any chance for further timing changes. Moreover, the timing usually produced with this arrangement is often not optimal for starting the engine, which is unfortunate because start-up is an operating mode in which more control over camshaft timing is desirable. Finally, it has been proposed to increase the spring constant of a compression spring which functions to cause a locking pin to extend into its locked position. This, however, causes operational limitations of the resulting device because the hydraulic pressure needed to retract the pin is increased, thereby limiting the conditions in which re-phasing may occur. 
         [0008]    It would be desirable to provide a configuration for a camshaft phaser allowing positive pin lockup at high speed, and at different phase angles of the camshaft with respect to the crankshaft. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0009]    According to an aspect of the present invention, a camshaft phaser for an internal combustion engine includes a driven hub attached to a camshaft, and a drive sprocket journaled to the driven hub, with the drive sprocket being rotatably indexable relative to the driven hub. A locking device selectively indexes the drive sprocket to the driven hub. The locking device includes a locking pin housed reciprocably in a pin bore formed in one of the driven hub and the drive sprocket, and at least one pin receptacle formed in the other of the driven hub and the drive sprocket at a location accessible to the locking pin when the locking pin is extended from the pin bore. The pin receptacle includes a locking bore having a section configuration generally matching the section configuration of the locking pin, and an engagement ramp contiguous with the locking bore for allowing the locking pin to extend partially from the pin bore before the locking pin is registered with the locking bore. 
         [0010]    According to another aspect of the present invention, a first locking pin and first pin receptacle are available to selectively lock the drive sprocket to the driven hub when the drive sprocket is rotated in a first direction with respect to the driven hub, and a second locking pin and second pin receptacle are available for locking the drive sprocket to the driven hub when the drive sprocket is rotated in a second direction with respect to the driven hub. A camshaft timing advance resulting from the lockup of the first locking pin may be different from the camshaft timing advance produced by the lockup of the second locking pin. 
         [0011]    According to another aspect of the present invention, the engagement ramp is recessed to a depth which is less than the depth of the locking bore. The engagement ramp is provided with a hydraulic fluid which may, for example, be engine oil, which exerts pressure upon the locking pin to keep the locking pin or pins in an unlocked position until it is desired to change the camshaft phasing. 
         [0012]    According to another aspect of the present invention, the recessed engagement ramps are contiguous with the locking bores and allow locking pins to extend partially from the pin bore after the hydraulic pressure source has been deactivated but before the locking pin has become registered with the locking bore. 
         [0013]    It an advantage of a system according to the present invention that this camshaft phaser will allow rapid and highly accurate locating of a camshaft drive sprocket with respect to the camshaft. 
         [0014]    It is another advantage of a system according to the present invention that the camshaft phasing will be conducted with a minimum number of false latches. 
         [0015]    It is yet another advantage of a system according to the present invention that camshaft phasing may be accomplished in either direction, while locking the camshaft with respect to the crankshaft in a selected one of a number of different angular positions. 
         [0016]    Other advantages, as well as features of the present invention, will become apparent to the reader of this specification. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  is a perspective view of an engine crankshaft, camshaft, and camshaft drive mechanism including a phaser according to the present invention. 
           [0018]      FIG. 2  is a perspective view of a drive sprocket according to an aspect of the present invention. 
           [0019]      FIG. 3  is a plan view of a driven hub according to an aspect of the present invention. 
           [0020]      FIG. 4  is a partial sectional view of a driven hub and drive sprocket according to the present invention, showing the present locking device in an unlocked position. 
           [0021]      FIG. 5  is similar to  FIG. 4 , but shows the locking device of  FIG. 4  after hydraulic pressure has been lowered and a locking pin is partially extended from a pin bore. 
           [0022]      FIG. 6  is similar to  FIGS. 4 and 5 , but shows a locking pin fully seated in a locking bore so as to establish phasing between a crankshaft and a camshaft or, in other words, between a crankshaft and a camshaft via a phaser which locks the driving sprocket to the driven hub of the camshaft. 
           [0023]      FIG. 7  is similar to  FIG. 3 , but shows another embodiment having locking bores and engagement ramps located at different radii from the axially directed center line of a camshaft. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0024]    As shown in  FIG. 1 , crankshaft  32 , having a crankshaft sprocket  28 , powers a chain,  26 , which rotates drive sprocket  24 . Drive sprocket  24  operates a camshaft,  18 , which has a plurality of cam lobes,  20 . The torque necessary for driving sprocket  24  to power camshaft  18  is a direct result of the force transmitted by one or more locking pins  36 , which are driven between sprocket  24  and driven hub  14 . It should be clear from this description that driven hub  14  cannot rotate with respect to camshaft  18 . In other words, driven hub  14  is rotationally locked to camshaft  18 . 
         [0025]      FIG. 2  illustrates drive sprocket  24  as having pin bores,  38 , which house locking pins  36 . Pins  36  serve to selectively index drive sprocket  24  to driven hub  14 . As noted above, each of locking pins  36  is housed in one of pin bores  38 . Each of pins  36  is urged into the locking position by a compression spring,  40 . Pin bores  38  also have a bleed orifice,  44 , which prevents fugitive oil from building up behind locking pins  36  and thereby hydrostatically preventing locking pins  36  from moving to an unlocked position. 
         [0026]      FIG. 3  shows first details of pin receptacles formed in driven hub  14  at locations accessible to locking pins  36  when locking pins  36  are extended from pin bores  38 . Each of the pin receptacles includes an engagement ramp,  48 , which is recessed to a depth which is less than the depth of the contiguous locking bore  52  associated with each engagement ramp. Ramps  48  preferably have an invariant depth, which facilitates manufacturing of the present system. 
         [0027]      FIG. 3 , and also,  FIG. 1 , show that locking bores  52  and, for that matter, engagement ramps  48 , are furnished with high pressure oil which originates within an axial cam bore  56  and which flows outwardly through radial camshaft bores  60  and into radial hub bores  64 . When high pressure oil, most likely lubricant oil, is furnished to locking bore  52  and engagement ramps  48 , the result is that, as shown in  FIG. 4 , locking pins  36  are maintained in their retracted position against the urging force of compression springs  40 . This allows the phasing of drive sprocket  24  and, hence, crankshaft  32 , to change with respect to driven hub  40  and, accordingly, camshaft  18 . 
         [0028]    As seen in  FIG. 4 , locking pin  36  provides no impediment to the relative movement of drive sprocket  24  with respect to driven hub  14  when locking pin  36  has been pushed into its retracted position by hydraulic pressure acting through passages  56 ,  60 , and  64 . However, at  FIG. 5 , hydraulic pressure has been lessened through passages  56 ,  60 , and  64  to the extent that pin  36  is available to extend axially from pin bore  38 . This brings another advantage to mind, inasmuch as it is not required to have a very powerful spring  40  to extend locking pin  36 . As noted above, this is indeed fortunate, because a more powerful spring will require higher hydraulic pressure, thereby limiting the capabilities of the system. 
         [0029]    It is notable in  FIG. 5  that pin  36  is now enmeshed with engagement ramp  48  and has begun sliding along engagement ramp  48  toward locking bore  52 . When locking pin  36  reaches abutment  52   a  on the far side of locking bore  52 , the relative rotation of sprocket  24  with respect to driven hub  14  will be arrested, and pin  36  will extend fully into bore  52 , thereby locking drive sprocket  24  with driven hub  14  ( FIG. 6 ). 
         [0030]      FIG. 3  illustrates two pin bores  52 , with the pin bores being available to provide different phasings of camshaft  18  with respect to crankshaft  32 . Notice, too, that engagement ramps  48  are on opposite sides of their respective locking bores  52 , which allow the engagement ramps to be used when the driving sprocket  24  is rotating in either direction with respect to camshaft  18 . 
         [0031]    Engagement ramps  48  are arcuately shaped and have a radius of curvature matching the radius of revolution of the locking pins. This is particularly apparent from the separate embodiment shown in  FIG. 7 , which illustrates two locking bores,  66 , and two engagement ramps,  68 , set at different radial distances from the axially directed centerline, C, of camshaft  18 . Because each of the locking pins  68  is fed from a separate axially directed bore,  72 , or  74 , locking pins  68  may be engaged independently. 
         [0032]    Those skilled in the art will appreciate in view of this disclosure that the forces necessary to displace driven hub  14  and camshaft  18  rotationally with respect to sprocket  24  may be provided either by the forces acting upon the camshaft as a result of the energy stored in the valve springs, or by a hydraulically or electrically driven device. Such devices are known in the art and are not part of the present invention. 
         [0033]    The foregoing invention has been described in accordance with the relevant legal standards, thus the description is exemplary rather than limiting in nature. Variations and modifications to the disclosed embodiment may become apparent lo those skilled in the art and fall within the scope of the invention. Accordingly the scope of legal protection afforded this invention can only be determined by studying the following claims.