Abstract:
A cam phaser ( 10 ) for dynamically adjusting a rotational relationship of a camshaft ( 24 ) of an internal combustion engine with respect to an engine crank shaft can include a planetary gear system ( 12 ) having a split ring gear ( 18 ) including a drive-side ring gear ( 18   a ) to be driven by the engine crank shaft through an endless loop power transmission member and an output-side ring gear ( 18   b ) connectable for rotation with the camshaft ( 24 ). A sun gear ( 14 ) can be located concentric with the split ring gear ( 18 ), and a number of planetary gears ( 16   a,   16   b,    16   c ) can be in meshing engagement between the sun gear ( 14 ) and the split ring gear ( 18 ). The output-side ring gear ( 18   b ) can have a different  number of teeth (greater or lesser) than compared with the drive-side ring gear ( 18   a ) by a value corresponding to a multiple of the number of planetary gears to provide tooth alignment at an engagement position of each of the planetary gears ( 16   a,    16   b,    16   c ).

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to a planetary gear assembly for dynamically adjusting a phase angle or rotational relationship of a camshaft with respect to an engine crankshaft to improve fuel efficiency of an internal combustion engine. 
       BACKGROUND 
       [0002]    There are many different devices currently in production to achieve this phasing of the engine camshaft. For example, see U.S. Patent Application Publication No. 2010/0064997; U.S. Patent Application Publication No. 2004/0206322; U.S. Pa. No. 7,506,623; U.S. Pat. No. 7,047,923; U.S. Pat. No. 6,971,352; U.S. Pat. No. 6,138,622; U.S. Pat. No. 6,129,061; U.S. Pat. No. 5,680,836; U.S. Pat. No. 5,361,736; U.S. Pat. No. 5,327,859; U.S. Pat. No. 4,850,427; and German Patent No. DE4110195. While each of these devices appear suitable to perform the intended function, it has been found that the devices have high overall cost and/or high frictional losses. It would desirable to provide a cam phaser with lower frictional losses and at a lower overall cost. 
       SUMMARY 
       [0003]    A cam phaser is disclosed for dynamically adjusting a rotational relationship of a camshaft of an internal combustion engine with respect to an engine crank shaft. The cam phaser can include a planetary gear system having a drive-side ring gear driven by the engine crank shaft through sprocket and an endless loop power transmission member, a number of planetary gears, and a centrally located sun gear. The cam phaser further includes an output-side ring gear concentric with the sun gear and connected to the camshaft. The output-side ring gear can have a different number of teeth (greater or lesser) than compared with the drive-side ring gear by a value corresponding to a multiple of the number of planetary gears to provide tooth alignment at an engagement position of each of the planetary gears. 
         [0004]    The drive-side ring gear can be piloted radially by the output-side ring gear. An electric motor can be connected to the sun gear for driving the sun gear in relation to the planetary gears. The electric motor can rotate at a speed equal to the drive-side ring gear to maintain a constant phase position, and variance of the electric motor speed from an equal value can cause a cam phase change function to occur. The drive-side ring gear, the output-side ring gear, the number of planetary gears, and the sun gear define an epicyclic gear drive connection having a high numerical gear ratio allowing accurate phasing angle adjustment with a relatively low driving torque requirement for the electric motor. The drive-side ring gear and output-side ring gear define a split ring gear. The planetary gears can be supported by first and second carrier plates axially piloted by the drive-side ring gear and the output-side ring gear for securing the number of planetary gears in an axial direction. 
         [0005]    A cam phaser for dynamically adjusting a rotational relationship of a camshaft of an internal combustion engine with respect to an engine crank shaft can include a planetary gear system having a split ring gear including a drive-side ring gear to be driven by the engine crank shaft through a sprocket and an endless loop power transmission member and an output-side ring gear connectable for rotation with the camshaft. The planetary gear system can have a sun gear located concentric with the split ring gear, and a number of planetary gears in meshing engagement between the sun gear and the split ring gear. 
         [0006]    The output-side ring gear can have a different number of teeth (greater or lesser) than compared with the drive-side ring gear by a value corresponding to a multiple of the number of planetary gears to provide tooth alignment at an engagement position of each of the planetary gears. The drive-side ring gear piloted radially by the output-side ring gear. An electric motor can be connected to the sun gear for driving the sun gear in relation to the planetary gears. The electric motor can rotate at a speed equal to the drive-side ring gear to maintain a constant phase position, wherein variance of the electric motor speed from an equal value can cause a cam phase change function to occur. The drive-side ring gear, the output-side ring gear, the number of planetary gears, and the sun gear define an epicyclic gear drive connection having a high numerical gear ratio allowing accurate phasing angle adjustment with a relatively low driving torque requirement of the electric motor. The planetary gears can be supported by first and second carrier plates axially piloted by the drive-side ring gear and the output-side ring gear for securing the number of planetary gears in an axial direction. 
         [0007]    A method for assembling and dynamically adjusting a rotational relationship of a camshaft of an internal combustion engine with respect to an engine crank shaft can include assembling a planetary gear system having a split ring gear including a drive-side ring gear to be driven by the engine crank shaft through a sprocket engaging an endless loop power transmission member and an output-side ring gear connectable for rotation with the camshaft, locating a sun gear of the planetary gear system concentric with the split ring gear, engaging a number of planetary gear in meshing engagement between the sun gear and the split ring gear, and providing the output-side ring gear with a different number of teeth (greater or lesser) than compared with the drive-side ring gear by a value corresponding to a multiple of the number of planetary gears to provide tooth alignment at an engagement position of each of the planetary gears. 
         [0008]    The planetary gear system assembly can be rotated as a unit with the sprocket to minimize frictional losses. An electric motor connected to the sun gear can be driven at the same speed as the drive-side ring gear to maintain a constant phase position, or can be driven at a speed not equal to the drive-side ring gear to cause a phase change function. 
         [0009]    Other applications of the present invention will become apparent to those skilled in the art when the following description of the best mode contemplated for practicing the invention is read in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The description herein makes reference to the accompanying drawings wherein like reference numerals refer to like parts throughout the several views, and wherein: 
           [0011]      FIG. 1  is a perspective view of a cam phaser with one end plate removed showing an internally located planetary gear set having a split ring gear, a concentrically located sun gear and a number of planetary gears in meshing engagement between the sun gear and the split ring gear; and 
           [0012]      FIG. 2  is a cross sectional view of the cam phaser of  FIG. 1 , where the output-side ring gear has a different number of teeth (greater or lesser) than compared with the drive-side ring gear by a value corresponding to a multiple of the number of planetary gears to provide tooth alignment at an engagement position of each of the planetary gears. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    Referring now to  FIGS. 1-2 , a split ring gear planetary cam phaser  10  is illustrated. The cam phaser  10  can include a planetary gearset  12  with a centrally located sun gear  14 , a number of identical planetary gears  16   a,    16   b,    16   c,  and a split ring gear  18  defined by two ring gears (i.e. a drive-side ring gear  18   a  and an output-side ring gear  18   b ). Each of the two ring gears  18   a,    18   b  has a different number of teeth with respect to the other ring gear, where the difference in the number of teeth equals a multiple of the number of planetary gears  16   a,    16   b,    16   c  in the planetary gearset  12 . The gear teeth of the two ring gears  18   a,    18   b  can have modified profiles to allow the ring gears  18   a,    18   b  to mesh properly with the planetary gears  16   a,    16   b ,  16   c.  The planetary gears  16   a,    16   b,    16   c  can be maintained in a fixed relationship to each other by a planetary carrier  20   a,    20   b.  An engine crankshaft (not shown) can be rotationally engaged through a timing chain (not shown) to one of the two ring gears  18   a  through a sprocket  22 , and the engine camshaft  24  can be rotationally engaged to the other of the two ring gears  18   b.  An electric motor  26  can be rotationally engaged with the sun gear  14  of the planetary gearset  12 . When the sun gear  14  can be rotated by the electric motor  26  at the same speed as either of the ring gears  18   a,    18   b,  since both ring gears  18   a,    18   b  rotate in unison, to maintain a constant cam phase position. When the sun gear  14  is driven at a different speed from the ring gears  18   a,    18   b  by the electric motor  26 , a slightly different speed of one ring gear to the other ring gear causes a cam phase shift function. In this way a very high numerical ratio can be obtained and the camshaft can be phased either plus or minus from the nominal rotational relationship of the crankshaft to the camshaft  24 . 
         [0014]    The cam phaser  10  can be used for dynamically adjusting the rotational relationship of the camshaft  24  to the engine crankshaft to improve the fuel efficiency of the engine. The cam phaser  10  achieves this cam phasing function with lower frictional losses and at a lower overall cost than previously known devices. The adjustment of the cam phasing angle is done with the planetary gearset  12 , which provides a high numerical ratio (by way of example and not limitation, such as approximately 57:1 in the illustrated configuration), so that the cam phasing angle can be adjusted accurately with a relatively low driving torque of the adjusting electric motor  26 . 
         [0015]    When the engine is running and the cam phase is not being adjusted, the entire cam phaser  10  assembly rotates as a unit which minimizes frictional losses. When the engine is running and the cam phase is not being adjusted, the adjusting electric motor  26  can be driven at the same speed as the camshaft to maintain a constant cam phase position. When the engine is running and the cam phase needs to be adjusted, the adjusting electric motor  26  can be driven at a speed not equal to the rotational speed of the split ring gear  18  to cause a cam phase shift function to occur in either the advancing or retarding directions. 
         [0016]    The timing chain which is driven by the engine crankshaft can be engaged with teeth of a sprocket  22 . By way of example and not limitation, in the illustrated and described configuration, the number of teeth on the engine crank sprocket can be nineteen (19) and the number of teeth on sprocket  22  can be thirty-eight (38), which yields a ratio such that the sprocket  22  can be driven at half the speed of the engine crank. The planetary gearset  12  assembly as illustrated can have a single sun gear  14 , and three planetary gears  16   a,    16   b,    16   c,  which can be in a driving meshing relationship with the sun gear  14 . There can be two separate ring gears  18   a,    18   b  concentric with the sun gear  14 . The sprocket  22  can have the ring gear teeth of the drive-side ring gear  18   a  formed on an inner diameter and can be piloted radially by the output-side ring gear  18   b.  The number of teeth on the drive-side  ring gear  18   a  can be either greater or less than the number of teeth on the output-side ring gear  18   b,  where the difference in number of teeth is a multiple of the number of planetary gears  16   a,    16   b,    16   c.  In this way, there is tooth alignment at the engagement position of each of the three planetary gears  16   a,    16   b,    16   c.    
         [0017]    By way of example and not limitation, in the illustrated and described configuration, the drive-side ring gear  18   a  can have seventy (70) internal teeth and the output-side ring gear  18   b  can have sixty-seven (67) teeth. By way of example and not limitation, the sun gear can have twenty-six (26) teeth in the illustrated and described configuration, while each of the planetary gears  16   a,    16   b,    16   c  can have twenty-one (21) teeth. This arrangement results in a very high gear ratio of one ring gear to the other ring gear. If the drive-side ring gear  18   a  is held stationary, the sun gear  14  can turn 57.55 times to cause one revolution of the output-side ring gear  18   b . Therefore, one degree of cam phase change can require almost sixty (60) degrees of relative rotation of the sun gear  14  to the sprocket  22 . It should be recognized by those skilled in the art that different gear ratios can be achievable with the disclosed invention and therefore the invention is not limited to the specific configuration illustrated and discussed herein. 
         [0018]    The output-side ring gear  18   b  can be rotationally secured to an end plate  28  which can be secured, by way of example and not limitation, by a bolt  36  to the camshaft  24 . In this way the output-side ring gear  18   b  and the end plate  28  can be joined to one another and act as one with the camshaft  24  which can be securely piloted for rotation to the engine block without needing additional piloting features. The relative speed of sprocket  22  and connected drive-side ring gear  18   a  to the output-side ring gear  18   b  is low and a simple steel-on-steel or bushing is sufficient to properly radially locate the parts relative to one another. Another end plate (not shown in  FIGS. 1-2 ) can be provided to axially locate sprocket  22  and the connected drive-side ring gear  18   a.    
         [0019]    The three planetary gears  16   a,    16   b,    16   c  can be circumferentially and radially located in position by the two carrier halves  20   a,    20   b,  which by way of example and not limitation, can be secured to each other by three bolts  30   a  ,  30   b,    30   c . It is believed that the planetary gears  16   a,    16   b,    16   c  can be located radially and circumferentially by the intermeshing gear teeth, which would further reduce the cost of the assembly by eliminating the two carrier halves. It is further believed that the planetary gears  16   a,    16   b,    16   c  can be axially located by being interposed between two spaced apart end plates, similar to the illustrated end plate  28 , if the carrier halves  20   a,    20   b  are not present. Since all of the gears  14 ,  16   a,    16   b,    16   c,    18   a,    18   b  only rotate relative to each other during the phasing of the camshaft, noise should not be a problem. The gears  14 ,  16   a,    16   b,    16   c,    18   a,    18   b  can all be spur gears which produce no axial loading components. 
         [0020]    An indexing electric motor  26  can be attached to the device housing (not shown) with an output shaft  38  of the electric motor  26  secured to the sun gear  14 . As long as the motor  26  runs at the same speed as the sprocket  22  cam phasing does not occur. Increasing or decreasing the speed of the motor  26  will cause the indexing or phasing function of the planetary gearset  12 . A sensor  32  can be used as feedback to a motor controller  34  to measure a current position of the sprocket  22  to the camshaft  24  to determine what adjustment, if any, is desired at any point in time to achieve optimal engine efficiency. 
         [0021]    While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiments but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims, which scope is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures as is permitted under the law.