Patent Publication Number: US-2020284296-A1

Title: Gear train of an actuator

Description:
BACKGROUND OF THE INVENTION 
     The present disclosure relates to an actuator having a gear train, and more particularly, to a gear assembly of the gear train. 
     Motorized actuators utilized, for example, in the automotive industry have a wide range of applications, and may be applied to any mechanical device requiring a specific motion. For example, motorized actuators are utilized in EGR valves, throttle bodies, variable vane turbocharges, and other applications. Such actuators are often small with packaging and cost restraints, while needing to be robust and reliable in design. Unfortunately, known actuators use ball bearings to provide friction free rotation of internal gear shafts. Various load and vibration forces may wear upon such bearing and other components limiting the actuators useful life. 
     For example, known ball bearing assemblies used in such actuators have an outer periphery, or race, that is press fitted to an actuator housing, and an inner periphery, or race, of the ball bearing assembly is press fitted to the gear shaft. Consequently, axial movement of the shaft is limited by the ball bearing assembly, which must absorb axial forces. This axial absorption may reduce the useful life of the ball bearing assembly. 
     Accordingly, it is desirable to provide more robust actuator designs within packaging and cost restraints. 
     SUMMARY OF THE INVENTION 
     According to one, non-limiting, exemplary embodiment of the present disclosure, a gear train includes a housing, a gear, a shaft, a needle bearing, and a stop shim. The housing includes an end face traversing an axis and a cylindrical surface centered to the axis. The face and the surface defines a bore. The gear is disposed in the housing, and is adapted to rotate about the axis. The shaft is engaged to, and projects axially from, the gear. The shaft includes an end portion disposed in the bore. The needle bearing is seated in the bore, and is disposed radially between the surface and the end portion. The stop shim is disposed axially between the end face and the end portion for limiting axial displacement of the gear shaft. The stop shim is made of a material that is harder than a material of the housing. 
     In accordance with another embodiment, a gear train includes a housing, a gear, a gear shaft, and a bearing assembly. The housing includes an end face traversing an axis and a cylindrical surface centered to the axis. The end face and the cylindrical surface define a bore. The gear is disposed in the housing, and is adapted to rotate about the axis. The gear shaft is engaged to, and projecting axially from, the gear. The gear shaft includes an end portion disposed in the bore. The bearing assembly includes a cylindrical bearing race seated in a bore, and a plurality of needle bearing elements disposed radially between the cylindrical bearing race and the end portion. 
     In accordance with another embodiment, a motorized actuator includes a housing, an intermediate gear assembly, and first and second play reduction assemblies. The intermediate gear assembly is mounted in the housing for rotation about an axis. The intermediate gear assembly includes a shaft, a driving gear, and a driven gear. The shaft has opposite first and second end portions. The driving gear is engaged to the shaft, and is axially disposed between the opposite first and second end portions. The driven gear is engaged to the shaft, and is axially disposed between the driving gear and one of the second end portion. The first and second play reduction assemblies are mounted to the respective first and second end portions, and are seated to the housing. The first and second play reduction assemblies each include a stop shim adapted to axially abut the first and second end portions, respectively, and a needle bearing adapted to rotationally support the shaft. 
     These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is a cross section of an actuator utilizing a gear train as one exemplary embodiment of the present disclosure; 
         FIG. 2  is a disassembled perspective view of a gear assembly of the gear train; and 
         FIG. 3  is a perspective cross section of a second embodiment of a bearing assembly of the gear assembly. 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to the Figures, where the invention will be described with reference to specific embodiments, without limiting same, an actuator  20 , which may be motorized, is illustrated in  FIG. 1 . Non-limiting applications of the actuator  20  may include actuation of automotive combustion engine throttle plates, actuation of variable vanes in a turbocharger, actuation of EGR valves, and others. 
     The actuator  20  may include a gear train  22 , an electric motor  24 , a controller  26  (e.g., electronic circuit board), an electrical connector  28 , and a housing  30 . The electrical connector  28  may facilitate the communication of control signals to the controller  26 , and the routing of electric power to the controller  26  and the motor  24 . In operation, the motor  24  is adapted to drive the gear train  22  within the housing, and the gear train drives the application (i.e., throttle plates, EGR valves, etc.). 
     In one embodiment, the gear train  22  includes an input shaft  32  (i.e., motor rotor), an intermediate shaft  34 , an output shaft  36 , an input gear  38 , at least one intermediate gear (i.e., two illustrated as  40 ,  42 ), and an output gear  44 . The input shaft  32  is adapted to rotate about a motor axis  46 , the intermediate shaft  34  is adapted to rotate about an axis  48 , and the output shaft  36  is adapted to rotate about an axis  50 . The axes  46 ,  48 ,  50  are spaced from, and substantially parallel to, one-another. In other embodiments, additional gears may be part of the gear train  22  and mounted for rotation within the housing  30 . Moreover, gear architecture may facilitate the axes  46 ,  48 ,  50  not being parallel to one-another in order to meet a packaging requirements and/or the needs of a specific application. 
     The gears  38 ,  40 ,  42 ,  44  may each include a plurality of gear teeth (not shown) for coupling with the teeth of adjacent gears as is known by one having skill in the art. Gear  38  is centered and fixed to an end portion of input shaft  32 , gears  40 ,  42  are centered and fixed to a mid-portion  52  of intermediate shaft  34  (see  FIG. 2 ), and output gear  44  is centered and fixed to output shaft  36  within the housing  30 . In operation, gear  38  is coupled to and drives the gear  40  and gear  42  is coupled to and drives the output gear  44 . In other embodiments additional gears (not shown) may be mounted between the gears shown to establish required torques, rotation speeds, packaging, and/or shaft orientations. It is contemplated and understood that the various gear to shaft engagements may be accomplished via a press fit, manufactured as a single piece, and/or other means. 
     In one embodiment, actuator  20  may further include a lip seal  54  seated to the housing  30 , and adapted to seal about the rotating output shaft  36 . Various bearings  56  may also be seated within, and to, the housing  30  for supporting and facilitating relatively friction free rotation of the output shaft  36 . 
     Referring to  FIGS. 1 and 2 , the actuator  20  may include a gear assembly  58  housed by, and located within, the housing  30 . In one example, gear assembly  58  includes the intermediate shaft  34 , gears  40 ,  42 , and at least one bearing assembly (i.e., two illustrated as  60 ,  62  in  FIG. 2 ). Each bearing assembly  60 ,  62  includes a needle bearing  64  and a stop shim  66 . The intermediate shaft  34  includes the mid-portion  52  and opposite end portions  68 ,  70 . The mid-portion  52  extends axially between the end portions  68 ,  70  with respect to axis  48 , with end portion  68  projecting axially outward from gear  40  and end portion  70  projecting axially outward from gear  42 . 
     In one embodiment, the housing  30  includes two housing segments  72 ,  74  adapted to be fastened together during assembly. The first housing segment  72  includes a cylindrical surface  76  and an end face  78  that may be circular. The cylindrical surface  76  and the end face  78  define the boundaries of a blind bore  80  in the housing segment  72 . The second housing segment  74  includes a cylindrical surface  82  and an end face  84  that may be circular. The cylindrical surface  82  and the end face  84  define the boundaries of a blind bore  86  in the housing segment  74 . 
     When the actuator  20  is fully assembled, the end portions  68 ,  70  of the intermediate shaft  34  and the respective bearing assemblies  60 ,  62  are disposed in the respective blind bores  80 ,  86 . More specifically, the needle bearings  64  of the bearing assemblies  60 ,  62  are seated against the respective cylindrical surfaces  76 ,  82 , and the stop shims  66  of the bearing assemblies  60 ,  62  are placed against the respective end faces  78 ,  84 . The intermediate shaft  34  is not constrained axially by needle bearings  64 , and is thus capable of moving axially within the needle bearings. 
     In one embodiment, the stop shims  66  are disc-shaped each having a cylindrical side  88  that opposes, and is press fitted or close proximity to, the respective cylindrical surfaces  76 ,  82  carried by the respective housing segments  72 ,  74 . The stop shims  66  are adapted to limit axial displacement of the intermediate shaft  34 , and are made of a material that is harder than the material of the housing  30 . For example, the stop shims  66  may be metallic while the housing may be made of a softer material (e.g., plastic). In another embodiment, the stop shims  66  may be made of steel and the housing  30  may be made of cast aluminum. To minimize friction, between the rotating intermediate shaft  34  and the stop shims  66 , the shims may be coated with a friction reducing material such as graphite, Teflon, or others. In another embodiment, the stop shims may be a unitary part of the housing, or the housing may be made, at least partially, of a hardened material such that separate stop shims are not needed. 
     In one example, the axial displacement of the intermediate shaft  34  may be limited to a minimum displacement of greater than about 0.111 millimeters and a maximum axial displacement of about 0.289 millimeters (i.e., the maximum axial play). In one example, a diameter (see arrow  90  in  FIG. 2 ) of the needle bearings  64  is within a range of about four (4) millimeters to eight (8) millimeters. 
     Referring to  FIG. 3 , a second embodiment of a bearing assembly is illustrated wherein like elements to the first embodiment have like identifying numerals except with the addition of a prime symbol suffix. A bearing assembly  60 ′ includes a plurality cylindrical elements  92  (i.e., needle bearings, or rolling elements) spaced circumferentially from one another and disposed in a housing  94 . The housing  94  includes a bearing race  96  that may be substantially cylindrical, and a stop shim  66 ′. In one example, the bearing race  96  and the stop shim  66 ′ are one unitary piece that may be homogeneous. When assembled, the bearing race  96  seats against the cylindrical surface  76  of the housing segment  72 , and the stop shim  66 ′ of the housing  94  axially bears upon (or intermittently bears upon) the end face  78  (also see  FIG. 2 ). 
     Advantage and benefits of the present disclosure include an intermediate shaft whose axial displacement is not constrained by bearings, and is thus allowed to freely move axially for improved distribution of axial forces. Other advantages include an alternative to the use of ball bearings that may break during axial loading. Yet further, the present disclosure provide a relatively simple, robust, and optimized packaging design. 
     While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description.