Abstract:
An electric starter motor for an internal combustion engine includes a rotatable output axle, a driving member mounted around the output axle, an output gear rotatably mounted around the output axle, and a friction member sandwiched between the output gear and the driving portion of the driving member. The output gear is slidable along the output axle. The hub of the driving member extends through the friction member and into the output gear.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This non-provisional patent application claims priority under 35 U.S.C. §119(a) from Patent Application No. 201010250323.8 filed in The People&#39;s Republic of China on Aug. 2, 2010. 
       FIELD OF THE INVENTION 
       [0002]    This invention relates to an electric starter motor used for starting an internal combustion engine, such as a gasoline engine, a diesel engine and the like. 
       BACKGROUND OF THE INVENTION 
       [0003]    A starter for an engine typically includes an output axle driven by an electric motor, an output gear, a driving plate, and an elastic friction member all directly mounted on the output axle. The driving plate is movable along the output axle. The friction member is located between the driving plate and the output gear. The driving plate defines screw threads in mesh with screw threads defined on the output axle, such that the driving plate moves along the output axle when the output axle rotates, and the driving plate thus urges the friction member and transmit the torque to the output gear via the friction member. However, lubrication oil filled in the gap between the driving plate and the output axle is liable to leak to the friction member, impairing performance of the friction member. As a result, the torque of the output axle can not be transmitted to the output gear efficiently. 
         [0004]    Therefore, there is a need in the art to provide an improved starter for engine which can overcome the above described shortcomings. 
       SUMMARY OF THE INVENTION 
       [0005]    Accordingly, in one aspect thereof, the present invention provides a starter motor for an engine, the starter motor comprising a rotatable output axle; a driving member mounted around the output axle, the driving member comprising a hub mounted around the output axle with screw threads, and a driving portion extending radially from the hub; an output gear rotatably mounted around the output axle, the output gear being movable along the output axle; and a friction member sandwiched between the output gear and the driving portion of the driving member, wherein the hub of the driving member extends through the friction member and into the output gear. 
         [0006]    Preferably, the starter motor further comprises a pressure spring abutting the output gear and urging the output gear against the friction member. 
         [0007]    Preferably, the hub of the driving member extends into a first central hole of the output gear and supports the output gear. 
         [0008]    Preferably, the first central hole is defined in one end of the output gear, the output gear further defines a second central hole in an opposite end, the first central hole communicates with the second central hole, and the first central hole has a diameter larger than that of the second central hole. 
         [0009]    Preferably, the hub of the driving member contacts an inner surface of the output gear corresponding to the first central hole, and the output axle contacts an inner surface of the output gear corresponding to the second central hole. 
         [0010]    Preferably, the hub defines a plurality of screw threads along all the length of the inner surface in mesh with screw threads defined on an outer surface of the output axle. 
         [0011]    Preferably, the friction member is annular. 
         [0012]    Preferably, the driving portion of the driving member, the friction member and the output gear have a substantially same maximal overall diameter. 
         [0013]    According to a second aspect, the present invention also provides a starter motor, comprising a rotatable output axle with a plurality of first screw threads defined on an outer periphery; a driving member mounted around the output axle, the driving member comprising a hub defining a plurality of second screw threads on an inner surface, and a driving portion, wherein the second screw threads are in mesh with the first screw threads of the output axle; an output gear rotatably mounted around the output axle, the output gear being movable along the output axle; and a friction member mounted around the hub of the driving member and in friction contact with the output gear and the driving portion of the driving member, wherein the hub of the driving member extends through the friction member and into the output gear. 
         [0014]    Preferably, the starter motor further comprises a pressure spring abutting the output gear and urging the output gear against the friction member. 
         [0015]    Preferably, the hub of the driving member extends into a first central hole of the output gear and supports the output gear. 
         [0016]    Preferably, the first central hole is defined in one end of the output gear, the output gear further defines a second central hole in an opposite end, the first central hole communicates with the second central hole, and the first central hole has a diameter larger than that of the second central hole. 
         [0017]    Preferably, the hub of the driving member contacts an inner surface of the output gear corresponding to the first central hole, and the output axle contacts an inner surface of the output gear corresponding to the second central hole. 
         [0018]    Preferably, the second screw threads are defined along all the length of the inner surface of the hub. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    Preferred embodiments of the invention will now be described, by way of example only, with reference to figures of the accompanying drawings. In the figures, identical structures, elements or parts that appear in more than one figure are generally labeled with a same reference numeral in all the figures in which they appear. Dimensions of components and features shown in the figures are generally chosen for convenience and clarity of presentation and are not necessarily shown to scale. The figures are listed below. 
           [0020]      FIG. 1  is an assembled, isometric view of a starter in accordance with an exemplary embodiment of the present invention; 
           [0021]      FIG. 2  is an isometric view of an output axle of the starter of  FIG. 1 ; 
           [0022]      FIG. 3  shows a relationship of the output axle and a driving member of the starter of  FIG. 1 ; 
           [0023]      FIG. 4  shows a relationship of the output axle, the driving member and a friction member of the starter of  FIG. 1 ; 
           [0024]      FIG. 5  shows a relationship of the output axle, the driving member, the friction member and an output&#39;gear of the starter of  FIG. 1 ; 
           [0025]      FIG. 6  shows a relationship of the output axle, the driving member, the friction member, the output gear, and a pressure spring of the starter of  FIG. 1 ; and 
           [0026]      FIG. 7  is a cross section of an assembly of the driving member, the friction member, and the output gear of the starter of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0027]    Referring to  FIG. 1 , the starter for an engine includes an output axle  13  driven by a motor  11 , a driving member  21  mounted around the output axle  13 , an output gear  26  movably mounted around the output axle  13 , a friction member  24  located between the driving member  21  and the output gear  26 , a pressure spring  32  abutting against the output gear  26  so as to urge the output gear  26  against the friction member  24 . The friction member  24  is pressed between and in friction contact with the driving member  21  and the output gear  26 . 
         [0028]    When the starter starts to rotate, the driving member  21  driven by the rotating output axle  13  moves along the output axle  13 , and pushes against the friction member  24 . The friction member  24 , in turn, presses against the output gear  26 , to move the output gear  26  to a working position, where the output gear  26  engages with a flywheel of the engine. After the output gear  26  has engaged the flywheel, the output gear  26  stops moving along the output axle  13 . As the output axle  13  continues rotating, the driving member  21  which has a tendency to move towards the output gear  26  continues to press against the friction member  24 , increasing friction forces between the friction member  24  and both the driving member  21  and the output gear  26 . When the friction forces reach a certain value, the friction member  24  and the output gear  26  rotate with the driving member  21 . Therefore, the torque of the output axle  13  is transmitted to the output gear  26  via the driving member  21  and the friction member  24 , to thereby drive the engine. 
         [0029]    Referring to  FIG. 2 , the output axle  13  includes a thin portion  12  at an axial end. The thin portion  12  has a smaller diameter than the other portion of the output axle  13 , for mounting the driving member  21 , the friction member  24 , the output gear  26 , and the pressure spring  32  thereon. More specifically, the thin portion  12  of the output axle  13  defines a plurality of male screw threads  14  at one fixed end for mounting the driving member  21  thereon. An opposite free end of the thin portion  12  defines a plurality of fine screw threads  15  for mounting a nut  31  thereon (see  FIG. 6 ). One end of the pressure spring  32  urges the nut  31  via a washer, and the other end of the pressure spring  32  abuts against and urges the output gear  26 . The output axle  13  can be a shaft of a motor, or an output shaft of a gear driven by a motor. 
         [0030]    Referring to  FIG. 3 , the driving member  21  includes a hub  23  and a driving portion  22  extending radially from the hub  23 . The hub  23  is cylindrical, and the driving portion  22  is disc-shaped. The hub  23  defines a central hole  230  there through for allowing the output axle  13  to extend through. A plurality of female screw threads  232  (see  FIG. 7 ) meshing with the male screw threads  14  of the output axle  13  is defined in an inner surface of the hub  23  surrounding the central hole  230 . Alternatively, the female screw threads  232  can be defined on the output axle  13 , and correspondingly, the male screw threads  14  are defined in the hub  23  of the driving member  21 . The driving member  21  is mounted around the output axle  13 , with the output axle  13  extending through and in mesh with the hub  23 . Lubricant oil is filled in a gap between the output axle  13  and the hub  23  of the driving member  21 , so as to facilitate the movement of the driving member  21  along the output axle  13 . 
         [0031]    Referring to  FIG. 4 , the friction member  24  is annular, and mounted around the hub  23  of the driving member  21 . The friction member  24  has two opposite contact surfaces  25  for contacting the driving portion  22  of the driving member  21  and the output gear  26  (see  FIG. 5 ), respectively. The hub  23  of the driving member  21  extends through the contact surfaces  25 , such that the lubricant oil between the hub  23  of the driving member  21  and the output axle  13  is prevented from leaking to the friction member  24 . Accordingly, the friction member  24  is protected from contamination. Preferably, the friction member  24  is made of rubber, such as nitrile butadiene rubber and the like. 
         [0032]    Referring to  FIGS. 5-7 , the output gear  26  is mounted around the output axle  13 , with the friction member  24  sandwiched between the output gear  26  and the driving portion  22  of the driving member  21 . The output gear  26  has a plurality of teeth  27  circumferentially spaced at an outer periphery for engaging with the flywheel of the engine. The output gear  26  defines a first central hole  28  at one end adjacent to the friction member  24 , and a second central hole  29  at an opposite end. The second central hole  29  communicates with the first central hole  28 . The first central hole  28  has a diameter larger than that of the second hole  29 . The diameter of the first central hole  28  is substantially the same as an outer diameter of the hub  23  of the driving member  21 . The diameter of the second hole  29  is substantially the same as an outer diameter of the thin portion  12  of the output axle  13 . 
         [0033]    The thin portion  12  of the output axle  13  is fittingly received in the second central hole  29  of the output gear  26 , contacting an inner surface of the output gear  26  corresponding to the second central hole  29 . A free end of the hub  23  of the driving member  21  extends into the first central hole  28  of the output gear  26 , and the hub  23  of the driving member  21  contacts an inner surface of the output gear  26  corresponding to the first central hole  28 . As the hub  23  of the driving member extends into the first central hole  28  of the output gear  26 , the lubricant oil is prevented from leaking to the friction member  24 . In addition, the output gear  26  is supported by both the hub  23  and the output axle  13 , avoiding an offset between an axis of the output gear  26  and the output axle  13 , which may result in disengagement of the output gear  26  and the flywheel of the engine. Furthermore, the output gear  26  supported by both the hub  23  of the driving member  21  and the output axle  13  can rotate smoothly. 
         [0034]    Preferably, the female screw threads are defined along all the length of the inner surface of the hub  23 , so as to ensure a coaxiality of the hub  23  of the driving member  21  and the output axle  13 , and accordingly a coaxiality of the output gear  26  and the output axle  13  is ensured. 
         [0035]    Referring to  FIGS. 6 and 7 , the pressure spring  32  is located between the nut  31  and the output gear  26 . One end of the pressure spring  32  bears against the nut  31  via a washer, and the other end of the pressure spring  32  bears against the output gear  26  via a spring seat  33  and urges the output gear against the friction member  24 . Thus, the friction member  24  is always pressed between the driving member  21  and the output gear  26 . 
         [0036]    In this embodiment, the driving member  21 , the friction member  24  and the output gear  26  are independent components, and the driving portion  22  of the driving member  21 , the friction member  24  and the output gear  26  have a substantially same maximal overall diameter. Alternatively, the driving portion of the driving member  21  may be received in the friction member  24 . Further, the friction member  24  may be integrally formed with one of the driving member  21  and the output gear  26 , for example, by insert molding. 
         [0037]    Although the invention is described with reference to one or more preferred embodiments, it should be appreciated by those skilled in the art that various modifications are possible. Therefore, the scope of the invention is to be determined by reference to the claims that follow. 
         [0038]    In the description and claims of the present application, each of the verbs “comprise”, “include”, “contain” and “have”, and variations thereof, are used in an inclusive sense, to specify the presence of the stated item but not to exclude the presence of additional items.