Patent Publication Number: US-2009223469-A1

Title: Balance shaft drive system

Description:
FIELD 
     The present disclosure relates to engine assemblies including a balance shaft, and more specifically to drive arrangements for balance shafts. 
     BACKGROUND 
     The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
     Depending on the number and arrangement of cylinders, engines may exhibit inherent unbalanced forces resulting from the acceleration and deceleration of pistons. These forces may be a function of the reciprocating mass, engine stroke, connecting rod length, and crankshaft speed. The unbalanced forces, or imbalance, may produce undesirable noise and vibration. Some engines incorporate a balance shaft to counteract the imbalance. However, driving configurations for the balance shaft may be difficult to package, resulting in additional design complexity and cost. 
     SUMMARY 
     An engine assembly may include an engine structure, a crankshaft, a camshaft, a balance shaft, and first and second gears. The crankshaft, camshaft, and balance shaft may each be rotatably supported by the engine structure. The camshaft may be rotationally driven by the crankshaft and the first gear may be coupled to the camshaft. The second gear may be fixed for rotation with the balance shaft and meshingly engaged with and driven by the first gear. 
     Alternatively, an engine assembly may include an engine structure, a crankshaft, a camshaft, a cam phaser, and a balance shaft. The crankshaft, camshaft, and balance shaft may each be rotatably supported by the engine structure. The cam phaser may be coupled to the camshaft and rotationally driven by the crankshaft. The balance shaft may be rotationally driven by the cam phaser. 
     Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       DRAWINGS 
       The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
         FIG. 1  is a perspective view of an engine assembly according to the present disclosure; 
         FIG. 2  is an exploded view of a camshaft assembly of the engine assembly of  FIG. 1 ; and 
         FIG. 3  is an exploded view of a cam phaser assembly of the engine assembly of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features. 
     Referring now to  FIGS. 1-3 , an exemplary engine assembly  10  is illustrated. The engine assembly  10  may include an engine block  12 , a crankshaft assembly  14 , a camshaft assembly  16 , a cam phaser assembly  18 , a balance shaft assembly  20 , and a drive belt  22 . The crankshaft assembly  14 , camshaft assembly  16 , and balance shaft assembly  20  may each be rotatably supported by the engine block  12 . The engine block  12  may define first and second banks of cylinders  21 ,  23  including first and second sets of cylinders  25  disposed at an angle relative to one another and defining a valley  27  between the first and second banks of cylinders  21 ,  23 . 
     The crankshaft assembly  14  may include a crankshaft (not shown) and a drive hub  24  fixed to an end of the crankshaft. The drive hub  24  may include a series of teeth  26  engaged with the drive belt  22 . The drive belt  22  may include a chain belt and may be engaged with the drive hub  24  of the crankshaft and the cam phaser assembly  18  to drive rotation of the cam phaser assembly  18  based on rotation of the crankshaft, as discussed below. 
     With reference to  FIG. 2 , the camshaft assembly  16  may form a concentric camshaft. The camshaft assembly  16  may be located between the first and second banks of cylinders  21 ,  23  and may include first and second shafts  28 ,  30 , a first set of lobe members  32  and a second set of lobe members  34 . The first set of lobe members  32  may be fixed for rotation with the first shaft  28  and the second set of lobe members  34  may be fixed for rotation with the second shaft  30 . In the present example, the first set of lobe members  32  may form an intake lobe set and the second set of lobe members  34  may form an exhaust lobe set. However, it is understood that alternate arrangements may be provided where the first set of lobe members  32  may form an exhaust lobe set and the second set of lobe members  34  may form an intake lobe set. 
     With reference to  FIG. 3 , the cam phaser assembly  18  may include first, second, and third portions  36 ,  38 ,  40  and a gear  42 . The first portion  36  may form an oil chamber housing defining first and second sets of chambers  44 ,  46  and an outer hub  48  including a series of teeth  50  engaged with the drive belt  22 . The second portion  38  may form a first plate assembly fixed to the first shaft  28  of the camshaft assembly  16  and including a first plate  52  and a first series of vanes  54  fixed for rotation with the first plate  52 . The first series of vanes  54  may be located in the first set of chambers  44  of the first portion  36 . The third portion  40  may form a second plate assembly fixed to the second shaft  30  of the camshaft assembly  16  and including a second plate  56  and a second set of vanes  58  fixed for rotation with the second plate  56 . The second series of vanes  58  may be located within the second set of chambers  46  of the first portion  36 . 
     The gear  42  may be formed from powdered metal and may include an annular body  60  with helical gear teeth  62 . The gear  42  may be fixed for rotation with the first portion  36  of the cam phaser assembly  18 . For example, the gear  42  may be frictionally engaged with the first portion  36  of the cam phaser assembly  18 . 
     The drive belt  22  may be engaged with the gear  42  to drive rotation of the first portion  36  of the cam phaser assembly  18 . The rotation of the first portion  36  may be transferred to the second and third portions  38 ,  40  by pressurized fluid within the first and second sets of chambers  44 ,  46  acting on the first and second sets of vanes  54 ,  58 . As such, the camshaft assembly  16  may generally be fixed for rotation with the gear  42  as well. While the camshaft assembly  16  is illustrated as a concentric camshaft and the cam phaser assembly  18  is illustrated as a dual-independent cam phaser, it is understood that the present teachings apply equally to fixed-lobe camshafts and dual equal cam phasers. 
     As seen in  FIG. 1 , the balance shaft assembly  20  may be located between the first and second banks of cylinders  21 ,  23  and may include a balance shaft  64  and a gear  66 . The balance shaft  64  may be located within the valley  27  of the engine block  12  and may be fixed for rotation with the gear  66 . The gear  66  may be formed from powdered metal and may include a scissors gear. A scissors gear may include a gear assembly (such as gear  66 ) and a torque generating element (not shown) to reduce backlash and noise between drive and driven gears. The gear  66  may include gear teeth  68  meshingly engaged with the gear teeth  62  on the gear  42  fixed to the cam phaser assembly  18 . The gear  66 , and therefore the balance shaft  64 , may be driven by the gear  42  in a rotational direction generally opposite the rotational direction of the drive belt  22  and the gear  42 . The number of gear teeth  68  may be less than the number of gear teeth  62  to provide an increased rotational speed of the balance shaft  64  relative to the camshaft assembly  16 . For example, the number of gear teeth  68  may be less than or equal to one-half of the number of gear teeth  62  to provide a rotational speed of the balance shaft  64  that is greater than the rotational speed of the camshaft assembly  16 , and more specifically, greater than the rotational speed of the crankshaft. The gear  42  may be located between the drive hub  24  and the gear  66 . 
     During operation, rotation of the crankshaft drive hub  24  may drive the belt  22  to power rotation of the cam phaser assembly  18 , and therefore the camshaft assembly  16 . Rotation of the cam phaser assembly  18  may be transferred to the balance shaft  64  through the engagement between the gears  42 ,  66 .