Abstract:
Backlash is controlled in an opposed-piston engine that includes two crankshafts disposed in a parallel, spaced-apart relationship and a gear train coupling the first and second crankshafts, the gear train including a driving gear coupled to the first crankshaft and a split gear assembly engaged with the driving gear to transfer rotation from the driving gear to the split gear assembly. The split gear assembly includes first and second gears, a spring mechanism that acts to angularly offset the first gear relative to the second gear in a first direction, and a one-way clutch mechanism that prevents relative angular movement of the first gear relative to the second gear in a second direction opposite the first direction.

Description:
RELATED APPLICATIONS 
       [0001]    This application contains subject matter related to the subject matter of commonly-owned U.S. application Ser. No. 13/944,787, “Gear Noise Reduction In Opposed-Piston Engines” and commonly-owned U.S. application Ser. No. 14/074,618, “Gear Noise Reduction In Opposed-Piston Engines”, which is a continuation-in-part of U.S. application Ser. No. 13/944,787. 
     
    
     BACKGROUND 
       [0002]    The field is reduction of noise, vibration, and harshness (NVH) in an opposed-piston engine. More specifically, the field covers controlling backlash in the gear train of an opposed-piston engine with a split gear construction. 
         [0003]    Gear vibration and clash in an internal combustion engine of a vehicle lead to intense whining and/or sharp impulse noise which can cause operator and passenger discomfort. Engine whine and rattle also add to the constant cacophony that makes proximity to transportation routes and industrial sites very unpleasant. Consequently, performance standards and environmental regulations relating to engines increasingly include NVH limits. 
         [0004]    When gears interface with each other, there are usually gaps between the interfacing gear teeth. As the gears rotate, these gaps are closed when the teeth move to make contact, which can result in gear rattle. In some instances, the space is called backlash; in other instances the movement made to close the gaps is called backlash. In either case, it is desirable to control, reduce, or eliminate backlash. 
         [0005]    The gear train of an opposed-piston engine with dual crankshafts inherently experiences torque reversals. In the case where a phase difference is provided between the crankshafts in order to differentiate port opening and closing times, the gear train is subjected to multiple torque reversals during every cycle of engine operation. With backlash, the engine&#39;s operation is afflicted with audible clatter and hammering as instantaneous accelerations caused by the reversals cascade through the gear train. Even without an inter-crankshaft phase difference, momentary inter-gear torque reversals result from idler bounce and/or gear/shaft rotational distortion. 
         [0006]    The well-known split gear construction provides an underpinning for various solutions to gear train backlash. In a split gear construction, two or more gears are arranged in an abutting, face-to-face relationship on a common shaft or post so as to act as a single gear. Various means are employed to impose and maintain a rotational offset between the gears by a distance amounting to some fraction of a gear tooth. The relative movement effectively increases the width of the split gear&#39;s teeth, thereby closing interstitial space between meshed gear teeth. Some of these split gear constructions use bias members such as springs that continuously act between the gears so as to maintain a rotational offset that varies in response to rotation of the gear and to sporadic accelerations caused by torque reversals, etc. The rotational offset automatically moves the gears to maintain closure of the gaps between meshed gear teeth. See, for example, U.S. Pat. No. 2,607,238 and U.S. Pat. No. 3,174,356. Because the resulting back-and-forth movements of the split gear teeth resemble the opening and closing actions of scissor blades, these gears may also be called “scissor gears”. In this regard, see US publication 20110030489. 
         [0007]    In related U.S. application Ser. Nos. 13/944,787 and 14/074,618 split gear constructions include combinations of compliant and stiff gears. The compliant gears receive the torque load first and slightly deform as the stiff gears begin to absorb the gear loads. As a compliant gear deforms, a stiff gear increasingly absorbs torque loads, which are transmitted via friction between compliant and stiff gears. Consequently, only a compliant gear transfers the total torque load to a hub thereby reducing or eliminating gear backlash. 
         [0008]    The spring-biased split gear constructions are intended to automatically eliminate backlash by relative rotation between the two gears in opposing directions. Thus, as a succession of torque reversals occurs, slack is taken up by a succession of rotational adjustments of the split gears. This results in a continuous back-and-forth movement of the gears that causes wear of the gear parts and consumes energy. The split gear constructions of the related applications depend on the availability of compliant materials which may be in short supply, or, if available, unsuited to particular applications. Therefore, it is desirable to have spring-biased gear constructions with anti-backlash capability available that reduce wear, conserve energy, and operate well in a broad range of applications. 
         [0009]    According to this disclosure the technological problem of backlash in the gear train of an opposed-piston engine is solved with a split gear construction that achieves wear reduction, energy conservation, and good operation in a broad range of applications. In this construction, relative rotation between two gears of a split gear assembly is allowed in a first direction, but constrained in the second direction. A first gear of the split gear is automatically rotated with respect to the second gear in the first direction until it contacts one flank of a tooth groove in a mating gear. At this point the second gear is in contact with the opposite flank of the tooth groove and backlash is reduced, if not eliminated, as the split gear rotates. When torque reversal occurs, the counter-rotation constraint keeps the two gears locked in their previously-rotated positions and no backlash is available. 
       SUMMARY 
       [0010]    A split gear assembly includes first and second gears, a spring mechanism that acts to rotate the first gear relative to the second gear in a first direction, and a one-way clutch mechanism that prevents rotation of the first gear relative to the second gear in a second direction opposite the first direction. 
         [0011]    A gear train assembly coupling two crankshafts of an opposed-piston engine that are disposed in a parallel, spaced-apart relationship includes a driving gear coupled to a first crankshaft and a split gear assembly engaged with the driving gear to transfer rotation from the driving gear to the split gear assembly. The split gear assembly includes first and second gears, a spring mechanism that acts to rotate the first gear relative to the second gear in a first direction, and a one-way clutch mechanism that prevents rotation of the first gear relative to the second gear in a second direction opposite the first direction. 
         [0012]    Backlash is controlled in an opposed-piston engine that includes two crankshafts disposed in a parallel, spaced-apart relationship and a gear train coupling the first and second crankshafts. The gear train includes a driving gear coupled to the first crankshaft and a split gear assembly engaged with the driving gear to transfer rotation from the driving gear to the split gear assembly. A method of controlling the backlash includes driving rotation of the first and second crankshafts, angularly offsetting a first gear of the split gear assembly relative to a second gear in a first direction, and preventing relative angular movement of the first gear relative to the second gear in a second direction opposite the first direction. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is a side view of a gear train in an opposed-piston engine equipped with two crankshafts. 
           [0014]      FIG. 2  is an end view of the same gear train with a gear box cover removed. 
           [0015]      FIG. 3  is front view of a split gear assembly for an opposed-piston gear train according to this disclosure. 
           [0016]      FIG. 4  is an isometric view of a portion of the split gear assembly of this disclosure. 
           [0017]      FIG. 5  is a partial elevation view showing a split gear according to this disclosure in meshed engagement with a mating gear. 
           [0018]      FIG. 6  is an exploded view of the split gear assembly of this disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    Constructions and methods of operation directed to the control of backlash in opposed-piston engines are described in detail with reference to the drawings.  FIGS. 1 and 2  show a gear train  10  for an opposed-piston engine equipped with two crankshafts  12  and  14 . The crankshafts  12  and  14  are disposed in parallel, in a spaced-apart arrangement. The precise opposed-piston configuration by which the crankshafts  12  and  14  are driven for rotation is a matter of design choice; one example is seen in  FIG. 1C  of commonly-owned U.S. Ser. No. 13/858,943 and PCT/US2014/033066. The gear train  10  includes a plurality of gear assemblies, two of which (indicated by reference numeral  16 ) are fixed to respective ends of the crankshafts  12  and  14  for rotation thereby, and one of which (indicated by reference numeral  15 ) is fixed to the end of a power take-off shaft  18 . In this configuration, two idler gear assemblies  19  are provided; each idler gear assembly is mounted for rotation on a fixed shaft or post. As a result of the configuration of the gear train  10 , the crankshafts  12  and  14  are co-rotating, that is to say, they rotate in the same direction. However, this is not meant to so limit the scope of this disclosure. In fact, the gear assembly construction disclosed in this specification can be incorporated into gear trains with fewer, or more, gear assemblies, and with counter-rotating crankshafts. Thus, although these figures show five gears for the gear train it should be understood that the number and types of gears required is dictated only by the particular engine configuration. Also, the output drive shaft can be connected to any one of the gears. In any case, these gear train assemblies often experience backlash that causes vibration, noise and gear tooth wear during torque reversal events or other normal gear operation that occur during each cycle of engine operation. 
         [0020]      FIG. 3  is a front view of a split gear assembly  30  for a gear train coupling two crankshafts of an opposed-piston engine according to this disclosure. At least one of the gear assemblies in the gear train  10  of  FIGS. 1 and 2  may include the split gear assembly  30 ; in some instances, some or all of the gear assemblies  15 ,  16 , and  19  may include the split gear assembly  30 . Preferably, at least one of the idler gear assemblies  19  includes the split gear assembly. Referring to  FIGS. 3 and 6 , the split gear assembly  30  includes a first gear  31  (the “anti-backlash gear”), a second gear  40  (the “power gear”), a spring mechanism  50 , and a one-way clutch mechanism  60 . 
         [0021]    As per  FIGS. 3 ,  4  and  6 , the anti-backlash gear  31  has an annular structure  32  with a plurality of gear teeth  33  extending radially outwardly therefrom. The annular structure  32  transitions to an axially-extending annular flange  34 . Wedge-shaped indentations  35  are formed in an inner annular wall of the flange  34 . Each indentation  35  has a ramped wall portion  37  extending tangentially to the center of the anti-backlash gear between opposing end wall portions  38  and  39 . The ramped wall portions  37  are angled in the same direction with respect to the center of the split gear assembly. The power gear  40  has an annular structure  41  with a plurality of gear teeth  42  extending radially outwardly therefrom. The annular structure  41  transitions to a circular floor  43  that extends radially inwardly of the power gear  40  to an axially-extending annular flange  45 . The flange  45  has a smooth outer annular wall  46 . The peripheries on the gears  31  and  40  where the gear teeth are located have identical diameters; preferably, but not necessarily, the teeth  33  and  42  are identically shaped in the radial direction of the split gear  30 . When the gears  31  and  40  are aligned for assembly as per  FIGS. 3 and 4 , with the teeth  33  and  42  registered, they present and operate as a single gear. 
         [0022]    As per  FIGS. 4 and 6 , the spring mechanism  50  includes a plurality of springs  51 . In the exemplary embodiment of the figures, there are three coiled springs  51 , although this is not meant to limit either the number or type of springs in the spring assembly. The one-way clutch mechanism  60  includes a plurality of coiled springs  61  and cylindrical rollers  62 . Each of the springs  61  is associated with a respective one of the rollers  62  to form a clutch unit. In the exemplary embodiment of the figures, there are six clutch units, although this is not meant to limit the number of clutch units. Further, although the one-way clutch mechanism is illustrated as being constituted of roller/spring units, this is not meant to be limiting; other clutch units may include, for example, sprag devices. 
         [0023]    The power gear  40  may be formed from a hardened steel material or other material suitable for handling the load stresses demands of a gear train. The anti-backlash gear  31  may be of a softer material that has been either hardened or coated to ensure uniform wear. The springs  51  and  61  may be helical devices, formed from hardened steel. The rollers  62  may be solid cylindrical devices formed from hardened steel. 
         [0024]    As per  FIGS. 3 ,  4 , and  6 , the anti-backlash gear  31  and the power gear  40 , with their teeth registered, are assembled into a close abutting relationship in which the flange  34  is received in space defined by the annular structure  41 , the floor  43 , and the flange  45 . With the gears  31  and  40  thus positioned, a circular array of wedge-shaped spaces is defined between the wedge-shaped indentations  35  of the anti-backlash gear  31  and the outer flange wall  46  of the power gear  40 . 
         [0025]    As per  FIGS. 4 and 5 , the springs  51  of the spring mechanism are distributed in a circumferential array in the split gear assembly  30 , each being received in a respective one of the shaped spaces  35 . Each spring  51  is compressed, having a first end fixed relative to the anti-backlash gear by a wall portion  38  of the anti-backlash gear  31  a second end fixed relative to the power gear  40  by a pin  64  fixed to the floor  43  of the power gear  40 . The compressed conditions of the springs  51  act between the backlash and power gears  31  and  40  by exerting a bias that causes relative rotation between the gears  31  and  40 . In the example shown the direction of relative movement of the anti-backlash gear with respect to the power gear is clockwise (CW); but this is not meant to be limiting since rearrangement of parts can make the bias direction counter-clockwise (CCW). 
         [0026]    The clutch units  61 ,  62  of the one-way clutch mechanism are distributed in a circumferential array in the split gear assembly  30 , where they are interspersed with the springs  51  of the spring mechanism. Each clutch unit is received in a respective one of the shaped spaces  35 . Each spring  61  is compressed between a wall portion  39  of the anti-backlash gear  31  and a roller  62 . The compressed condition of the spring  61  acts between the wall portion  39  of the anti-backlash gear  31  and the roller  62  by forcing the roller  62  into increasingly smaller wedge-shaped space between the angled wall portion  37  of the anti-backlash gear  31  and the smooth outer wall  46  of the power gear flange  45 . In the example shown this locks the anti-backlash gear  31  against rotation relative to the power gear  40  in a direction opposite to the direction of relative movement resulting from the bias action of the spring mechanism  50 . In the example shown in the figures, the one-way clutch mechanism  60  locks the anti-backlash gear  31  against counter-clockwise (CCW) movement relative to the power gear  40 ; but this is not meant to be limiting since rearrangement of parts can make the locked direction clockwise (CW). 
         [0027]    Referring now to  FIGS. 3 ,  4 , and  5 , the split gear  30  operates as a single gear with means to control backlash in the meshing interface with a mating gear  70 . In the meshing interface, the teeth  42  of the power gear  40  are in normal contact with the teeth  72  of the mating gear  70 . The anti-backlash gear  31  is spring loaded by the three weak springs  51 , which angularly offsets the anti-backlash gear  31  relative to the power gear  40  in a first direction (CW in the example) so that it moves slightly ahead of the power gear  40 . As best seen in  FIG. 5 , this ensures that the leading flank of the anti-backlash gear  31  is always in contact with the trailing flank of the mating gear  70  whenever the trailing flank of the power gear  41  is in contact with the leading flank of the mating gear  70 . That is to say, the leading and trailing edges of the split gear  30  are always in contact with the leading and trailing flanks of the mating gear  70  whenever in driving force contact, (two to three gear teeth at any one time). 
         [0028]    Still referring to  FIG. 5 , a clutch unit  61 ,  62  is shown located within a wedge-shaped space  35  of the anti-backlash gear  31 . The spring  61  keeps the roller  62  lodged in the wedge-shaped space  31 . If, during a torque reversal, pressures are exerted on the anti-backlash gear  31  in a CCW direction the roller  62  is forced toward the wall portion  38 , thereby locking the anti-backlash gear  31  from CCW movement. The combination of continuous trailing and leading flank contacts of the meshing gear teeth produced by the spring mechanism  50  with the directional locking of the clutch mechanism  60  guarantees anti-backlash control during torque reversals. 
         [0029]    It is preferred that the springs  51  of the spring mechanism  50  be no stronger than required to ensure that the anti-backlash gear  31  is always in an advanced state in relation to the power gear  40 . However, it is also possible that normal engine vibrations, caused by other than gear backlash conditions, could cause the same effect, which might eliminate the need for the springs  51 . In contrast, the springs  61  of the one-way clutch mechanism  60  should have strength sufficient to withstand the high forces encountered during high-power operation. Under these conditions, it will be the case that the strength of the clutch springs  61  exceeds the strength of the biasing springs  51 . 
         [0030]    It is preferred that in a five-gear engine configuration at least the two idler gears  19  have the split gear configuration with anti-backlash capability as described above. Regardless of the number of gears in the gearbox, one or more idler gears preferably would be split gears with anti-backlash capability as described above. The split gear  30  may be mounted for rotation in a gear train using conventional arrangements. For example, with reference to  FIGS. 1 ,  3 , and  6 , when used as an idler gear  19 , a split gear assembly  30  according to this specification may be assembled as described, received on a hub  80 , and rotatably mounted on a stationary post  85  in a gear box  86 . 
         [0031]    It will be understood that the scope of the invention as described and illustrated herein is not limited to the described embodiments. Those of skill will appreciate that various modifications, additions, known equivalents, and substitutions can be made to the split gear assembly without departing from the scope and spirit of the invention as set forth in the following claims.