Abstract:
A camshaft phaser comprising a differential bevel gear arrangement to vary the phase relationship of a camshaft to a crankshaft in an internal combustion engine. In the differential gear system, a 45° beveled input gear is mounted parallel to and coaxial with a 45° beveled output gear. One or more 45° beveled spider gears is disposed in meshed relationship with the input and output gears in a gear pattern having a rectangular cross-sectional appearance. Rotation of the input gear causes an opposite rotation of the output gear. The phase relationship between the input and output gears may be varied by varying the position of the spider gear. The input gear and spider gears may be driven via a sprocket in time with the crankshaft in a plurality of arrangements.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a mechanism for varying the timing of combustion valves in internal combustion engines; more particularly, to camshaft phasers for varying the phase relationship between an engine&#39;s crankshaft and camshaft; and most particularly, to an oil-less camshaft phaser including a differential bevel gear drive. 
       BACKGROUND OF THE INVENTION 
       [0002]    Camshaft phasers (“cam phasers”) for varying the timing of combustion valves in an internal combustion engines are well known. A first element, known generally as a sprocket element, is driven by a chain, belt, or gearing from an engine&#39;s crankshaft. A second element is mounted to the end of an engine&#39;s camshaft, including intake or exhaust valve camshafts in engines having dual camshafts. 
         [0003]    In the prior art, cam phasers typically employ one of two different arrangements for achieving variable valve timing. 
         [0004]    In a first arrangement, the sprocket element is provided with a first cylinder having helical splines on its inner surface, and the camshaft element is provided with a second cylinder having helical splines on its outer surface. The first and second cylinders nest together. When one cylinder is driven axially of the other, the helical splines cause relative rotation there between, thereby changing the phase relationship. Typically, an axially-acting ram is controllably displaced by pressurized engine oil pirated from the engine oil supply system. 
         [0005]    In a second arrangement, the sprocket element is provided with a stator having a central opening and having a plurality of lobes extending radially inward into the central opening and spaced apart angularly of the stator body. The camshaft element is provided with a rotor having hub and a plurality of outwardly extending vanes. When the rotor is installed into the stator, the vanes are disposed between the lobes, thereby defining a plurality of rotor-advancing chambers on first sides of the vanes and a plurality of rotor retarding chambers on the opposite sides of the vanes. Again, pressurized oil is controllably admitted to either the advance chambers or the retard chambers to selectively alter the phase angle between the crankshaft and the camshaft, thereby varying the timing of the engine valves. 
         [0006]    While effective and relatively inexpensive, both types of prior art cam phasers suffer from several drawbacks. 
         [0007]    First, at low engine speeds engine oil pressure tends to be low, and sometimes unacceptably so; therefore, the response of a conventional cam phaser is sluggish at low engine speeds. 
         [0008]    Second, at low environmental temperatures, and especially at engine start-up, engine oil displays a relatively high viscosity and is more difficult to pump and to supply to a phaser in a rapid-response fashion. 
         [0009]    Third, using engine oil to drive a phaser is parasitic on the engine oil system and can lead to requirement for a larger oil pump. 
         [0010]    And finally, for fast actuation, a larger engine oil pump may be necessary, resulting in an additional energy drain on the engine. 
         [0011]    What is needed in the art is a camshaft phaser wherein the phaser is not actuated by pressurized oil and therefore phaser performance is not subject to variation in engine oil pressure, temperature, or viscosity. 
         [0012]    It is a principal object of the present invention to vary engine valve timing by varying camshaft phase angle without reliance on pressurized oil. 
       SUMMARY OF THE INVENTION 
       [0013]    Briefly described, a camshaft phaser in accordance with the invention comprises a differential bevel gear arrangement to vary the phase relationship of a camshaft to a crankshaft in an internal combustion engine. As is known in the art of differential gearing, a 45° beveled input ring gear is mounted parallel to and coaxial with a 45° beveled output ring gear. One or more 45° beveled spider gears is disposed in meshed relationship with the input and output gears in a gear pattern having a rectangular cross-sectional appearance. Rotation of the input gear causes an opposite rotation of the output gear. The phase relationship between the input and output gears may be varied by varying the position of the spider gear. 
         [0014]    In a series of embodiments, a plurality of spider gears are arranged on a spider gear carrier which is driven rotationally by an electric motor between the input and output gears to vary the relative angular positions of the spider gears and thus to vary the phase relationship of the input gear to the output gear. The driving means may be disposed outside the spider carrier or within the spider carrier. A preferred system for driving the spider gear carrier employs a worm gear drive to eliminate backlash from camshaft torque variations. 
         [0015]    In a third embodiment, the sprocket wheel is a part of the spider gear carrier such that the crankshaft drives the spider gears, which are now input gears, and the phase of the previous input gear is changed by either a motor or a braking system to change the phase of the output gear. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: 
           [0017]      FIG. 1  is a schematic cross-sectional view of a bevel gear system; 
           [0018]      FIG. 2  is a schematic cross-sectional view of a differential bevel gear camshaft phaser in accordance with the invention; 
           [0019]      FIG. 3  is a schematic cross-sectional view taken along line  3 - 3  in  FIG. 2 ; 
           [0020]      FIG. 4  is a schematic cross-sectional view of another embodiment of a camshaft phaser in accordance with the invention, showing provision for easy bolting of the phaser onto an engine camshaft; 
           [0021]      FIG. 5  is a schematic isometric view of a spur gear drive for actuating a camshaft phaser in accordance with the invention; 
           [0022]      FIG. 6  is a schematic isometric view of a worm gear drive for actuating a camshaft phaser in accordance with the invention; 
           [0023]      FIG. 7  is a schematic elevational cross-sectional view of an external spur gear drive and full-circle spider gear carrier suitable for use in, for example, the embodiment shown in  FIG. 4 ; 
           [0024]      FIG. 8  is a drawing like that shown in  FIG. 7 , showing that only a limited arc of the spider gear carrier is needed for a single spider gear embodiment; 
           [0025]      FIGS. 9 through 12  are schematic cross-sectional views of four additional embodiments showing four different exemplary arrangements for driving a spider gear carrier internally of the carrier; 
           [0026]      FIG. 13  is a schematic cross-sectional view of an another embodiment showing a sprocket wheel mounted for driving a spider gear carrier directly with a motor for altering the phase of a first ring gear; and 
           [0027]      FIG. 14  is a schematic cross-sectional view of yet another embodiment like the embodiment shown in  FIG. 13  but having a brake mounted on the first ring gear for altering the phase of the first ring gear. 
       
    
    
       [0028]    The exemplifications set out herein illustrate currently preferred embodiments of the invention. Such exemplifications are not to be construed as limiting the scope of the invention in any manner. 
       DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0029]    To help understand the various embodiments of the present invention, referring to  FIG. 1 , gear mechanism  100  describes the general operation of a bevel gear system. The main components of this differential bevel gear system are first bevel (or ring) gear  104 , second bevel (or ring) gear  106 , spider bevel gear  108 , control gear  110 , and optional spur gears  112 , 114 . First gear  104  is an input bevel gear fixed to an input drive mechanism  116 . First input bevel gear  104  is connected to second bevel gear  106  via spider gear  108 . Spider gear  108  rotates on its own axis  118 . Second bevel gear  106  is an output gear linked to a driven output shaft  120  through spur gears  112 , 114 . Control gear  110 , which is linked to both input and output bevel gears  104 , 106  via gearmesh, is attached to a rotary driving source  122  as described below. Differential bevel gear drive system  102  has an input member to output shaft ratio of 1:1. 
         [0030]    Input bevel gear  104  transmits the torque/speed at right angles to output bevel gear  106  via spider gear  108 . Input and output bevel gears  104 , 106  are identical, i.e. they have the same number of teeth, module, and geometry and are mounted symmetrically on their own axis  123  transverse of axis  118  of spider gear  108  and control gear  110 . Spur gear  112  is mounted on shaft  126  of output bevel gear  106  and rotates at the same speed as output bevel gear  106 . Spur gear  112  further drives spur gear  114 , which is rigidly fixed to output shaft  120 , through gearmesh. The gear ratio between the spur gears is 1:1. This arrangement allows output shaft  120  to rotate in the same direction and at the same rotational speed as input drive member  116 . Alternatively, gears  112  and  114  could be omitted, and the output shaft would rotate in a direction opposite that of the input member. Also, the gear ratios mentioned above are only exemplary. Any gear ratio can be chosen for any of these gears. 
         [0031]    When phasing in the advance or retard direction between the input drive member and the output shaft is desired, rotary driving source  122 , such as an electric motor, applies torque on control gear  110  depending on the phasing adjustment. Thus, control gear  110  rotates output bevel gear  106  in either advance or retard direction with respect to input bevel gear  104 , which ultimately changes the phase of output shaft  120  relative to input shaft  116 . The phase adjustment, whether in the advance or retard position, is controlled by an algorithm in an electronic control module (ECM) (not shown). To avoid any backdrive from torque fluctuations in the output shaft, the electric motor should be sized to the maximum required torque. The electric motor may work as a generator in one of the retard or advance directions. 
         [0032]    Differential gear system  102  may have straight or spiral bevel gear teeth. Spiral teeth will have two or more teeth in contact at all times, which transmits motion more smoothly and quietly than with straight bevel gears. On the other hand, straight bevel gears are simpler to manufacture and cost less. The gears preferably are of AGMA quality class  8  or  9 . 
         [0033]      FIGS. 2-3 , in accordance with the invention, omit for clarity of presentation the various obvious bearings and housing needed for proper operation of the device, except for spider gear bearings  219 . Also not shown for clarity are lubrication conduits. 
         [0034]    The present invention described below has the following advantages over a conventional oil driven camshaft phaser:
       a) the phaser works independently of the engine oil, and issues such as oil temperature, viscosity, low pressure, and the like are avoided.   b) the phaser is compact, and the overall package can be manufactured within a 130 mm×30 mm envelope.   c) high performance requirements such as high phase rate (250 crank°/sec) and high authority (100 crank°) can be achieved.       
 
         [0038]    Referring to  FIGS. 2 and 3 , a first embodiment  200  of a camshaft phaser in accordance with the invention includes a differential bevel gear system  202  which differs slightly from system  102 . The main components of differential bevel gear system  202  are an input bevel gear  204 , an output bevel gear  206 , a spider bevel gear or gears  208 , a spider gear carrier  209 , and control mechanism  211 . Input bevel gear  204  is fixed to sprocket  216  for being driven in time with the crankshaft of an internal combustion engine (not shown) and is connected to output bevel gear  206  via spider gears  208 . Output bevel gear  206  drives camshaft  120  of the internal combustion engine, directly. Spider gears  208  rotate on their own axes  218  within bearings  219 . When the phase angle between the crankshaft and the camshaft is fixed, control mechanism  211  does not rotate, and spider gear carrier  209  is stationary. The sprocket rotation thus drives the camshaft directly via the bevel gears. The differential allows the input torque to be split between the two spider gears  208 . This equal load sharing reduces the stress on the teeth. 
         [0039]    When the phase angle between the crankshaft and the camshaft needs to be changed, upon the appropriate command from an ECM the control mechanism driving source  222  (an electric motor is proposed in this embodiment, although other forms of rotational activation are embraced by the invention) rotates the spider gear carrier  209  about axis  123  via an optional gear  223 . Rotation of motor  222  in one direction will advance the relative phase angle, and rotation of motor  222  in the opposite direction will retard the relative phase angle between the crankshaft and the camshaft. 
         [0040]    Referring to  FIGS. 2 through 6 , in a presently preferred drive embodiment the drive control mechanism consists of a motor  222  driving a worm gear  223 . This gearing arrangement is preferred because of the self-locking properties of worm gears, that is, the driving mechanism is not back drivable, under normal conditions. This is a very important design factor because camshaft load torques have very large oscillations, on the order of for instance +/− 12 Nm compared to an average friction torque of 1.0 to 1.5 Nm. These large oscillations of load can cause oscillations of the camshaft position if they not prevented by the self-locking nature of the worm gear. 
         [0041]    Other gear types can be envisioned, such as a spur gear  225  as shown in  FIG. 5 . If a spur gear is used, the system needs to be designed so as to avoid or minimize position oscillations due to camshaft torque variations. One solution consists of using motor  222  to constantly provide a torque to carrier  209 , so as to hold it in position. The torque profile and magnitude must be adjusted to provide sufficient resistance to camshaft torque oscillations without inducing motion of spider gear carrier  209 . 
         [0042]    It is desirable for a cam phaser to be preassembled e.g. at the supplier&#39;s factory, then assembled as a unit directly onto an engine. This is by far preferable to sending the phaser in two or more subassemblies to the engine plant, and requiring assembly of the various phaser parts to the engine. Referring now to  FIG. 4 , embodiment  300  lends itself to being pre-assembled. A central bore  330  is created in various components of the phaser, including sprocket  316 , input gear  304 , and carrier assembly  309 , making possible the use of a central bolt  332  to mount phaser  300  via output gear  306  onto camshaft assembly  320 . Alternatively, a flanged output gear (not shown) may be slipped over the end of the camshaft and bolted radially thereto. 
         [0043]    In most engines, it is desirable for the intake camshaft to be in the full retard position and for the exhaust camshaft to be in the full advance position during engine cranking. It may also be envisioned for some engines that an intermediary position (not quite full retard and/or not quite full advance, respectively) may be preferable, especially for cold starts. The ECM can use motor  222 , 322  to drive the system to any desired position before or during engine cranking. Preferably, this is accomplished during engine shut down, although a position adjustment may otherwise be performed just prior to or during cranking proper, for instance, if temperature conditions have changed since engine shut down. 
         [0044]    In case of phaser failure, e.g., power failure to the motor, however, there may be a loss of phasing control, that is, the camshaft may be left in whatever phasing position it was when the failure occurred. Depending on what that position is, this could lead to starting difficulties or failure. Of course, if an impeding fault is detected, the phaser could be driven to a desirable fall-back position before the fault is so severe as to make further phasing impossible. However, failures may not always be detected in time. Therefore, a bias spring (not shown) may be included in the mechanism to bias the phaser towards either full retard (intake) or full advance (exhaust). 
         [0045]    There must be at least one, and preferably are several, spider gears in the differential bevel gear drive system of the present invention. In a preferred embodiment, there are three spider gears  208  as shown in  FIG. 7 , disposed symmetrically around a circular (full circle) carrier  209 . (Note:  FIG. 2  as drawn implies an even number of spider gears; however, this is only for simplicity of drawing and explanation). The advantage of three is balance and symmetry. A larger number of spider gears would be unnecessarily expensive and cumbersome. However, any number of spider gears is possible, including just a single one as shown in  FIG. 8 . Generally, the load and pitch diameter define the number of spiders. Size is determined by the load bearing capacity of the teeth. 
         [0046]    Referring to  FIG. 8 , in an alternative embodiment, carrier  209 ′ encompasses only a partial circle (arc of span α). Such an arrangement is possible because the range of phase shifting is limited (35 cam degrees is typical of current engines, 50 cam degrees is expected in future engines). Therefore, the control mechanism needs to rotate by only the desired range of phase shifting (35°, 50°, etc.). Carrier  209 ′ need therefore encompass only the desired phasing range, plus some tolerance, for a total span a as shown in  FIG. 8 . However, the configuration of  FIG. 7  has the advantage of a more compact packaging and of distributing the load over several symmetrically placed spider gears. Of course, the size of carrier  209  or  209 ′ is not limited to either full circle or span α, and other span values in between are possible within the scope of the invention. 
         [0047]    Referring now to  FIGS. 9 through 12 , other arrangements of a differential bevel gear cam phaser in accordance with the invention can be considered. For instance, the spider gears may be mounted on the outer periphery of the carrier ring and extend radially outwards therefrom, instead of on the inside of the carrier ring as shown thus far. 
         [0048]    In embodiment  400 , spider carrier  409  includes an axial shaft  470  extending through input gear  404  and sprocket  416 . A reduction drive gear  472  is mounted on shaft  470  and is driven by a spur gear  425  and motor  422 . As the rotational position of carrier  409  is changed by rotation of shaft  470 , the phase is changed between input gear  404  and output gear  406 , thus changing the phase of camshaft  423 . 
         [0049]    In embodiment  500 , drive motor  522  is mounted directly on the carrier shaft  570  for driving carrier  509 . Obviously, direct drive motor  522  has very different characteristics from drive motor  422 . 
         [0050]    Referring to  FIGS. 11 and 12 , the drive motor may be recessed within the envelope of the mechanics. In embodiment  600 , carrier shaft  670  is actually the motor rotor, surrounded by the motor stator  680 . In embodiment  700 , an “inside-out” motor configuration is used wherein the carrier shaft is omitted and the motor stator  780  is surrounded by the motor rotor  782  which forms a part of the spider carrier  709 . 
         [0051]    Referring to  FIGS. 13 and 14 , another differential gear system arrangement in accordance with the invention consists in having a sprocket drive the spider carrier rather than the first bevel ring gear. Phasing is then achieved by adjusting the rotational position of the first bevel ring gear. 
         [0052]    In embodiment  800 , a motor  822  mounted onto first bevel ring gear  804  (defining thereby gear  804  as a control gear for this embodiment) acts as a brake on shaft  823  in balancing camshaft friction during operation with constant camshaft angular position (no phasing). The spiders do not spin on their axes and the entire assembly  800  (that is, shaft  823 , control gear  804 , output gear  806 , spider gears  808 , gear carrier  809 ) all rotate together at the same speed, driven by sprocket  816 . When phasing is desired, the motor torque on shaft  823  is either decreased or increased thus causing rotation of spider gears  808  either clockwise or counterclockwise. 
         [0053]    Another operating mode for embodiment  800  consists in having motor  822  hold control gear  804  steady during operation with constant camshaft angular position. In this mode, spider gears  808  spin on their axes and transfer the drive torque to output gear  806  and camshaft  820 . Phasing is achieved by rotating shaft  823  of the motor  822  in either direction. 
         [0054]    Referring to  FIG. 14 , in embodiment  900 , motor  822  is replaced by a spring/brake system  922  mounted on control gear  904 . In this alternative, a torsional spring rotates the system in one direction, and a brake acts against the spring. By adjusting the brake torque, various phaser positions can be achieved. The brake is preferably electromagnetic, and preferably of the hysteresis type. Brakes, especially their controllers, are less expensive than motors and motor controllers, but brake torque can be applied only to slow the motion of a rotating body, and cannot accelerate it. In some configurations, the camshaft friction may be sufficient to counter-balance the brake torque, and the torsional spring can be less stiff or even omitted altogether. In such a configuration, when the phaser is not adjusting the camshaft phasing, the brake torque (like the motor torque in embodiment  800 ) is set at a level equal to the camshaft friction torque, so that spider gears  908  do not spin on their axes. The entire assembly  900  (that is, control gear  904 , output gear  906 , spider gears  908 , gear carrier  909 ) all rotate together at the same speed, driven by sprocket  916 . When phasing is desired, the brake torque on control gear  904  is either decreased or increased thus causing rotation of spider gears  908  either clockwise or counterclockwise. 
         [0055]    An aspect of the invention includes the use of a differential bevel gear with an input gear, an output gear, and spider gears and carrier. The engine sprocket, the camshaft, and the controlling elements (motor, spring and brake, etc.) are each operationally connected to one or the other of the differential bevel gears. It is understood that there are various permutations possible concerning which gear or carrier is connected to the sprocket, camshaft, and controlling element, all embodying the general principles of the present invention. 
         [0056]    While the invention has been described by reference to various specific embodiments, it should be understood that numerous changes may be made within the spirit and scope of the inventive concepts described. Accordingly, it is intended that the invention not be limited to the described embodiments, but will have full scope defined by the language of the following claims.