Patent Publication Number: US-2021194312-A1

Title: Power tool with partition assembly between transmission and motor

Description:
RELATED APPLICATIONS 
     This application claims priority, as a continuation, of U.S. patent application Ser. No. 15/978,258, filed May 14, 2018, which is incorporated by reference. 
    
    
     TECHNICAL FIELD 
     This application generally relates to a power tool with a partition between a transmission assembly and a motor assembly to inhibit dust and grease migration between them. 
     BACKGROUND 
     Various power tools, including drills, hammer drills, screwdrivers, and impact drivers are known in the art. These power tools generally have a motor assembly that is drivingly coupled to a transmission assembly. A cover on the transmission assembly and/or the motor assembly, or a partition between the transmission assembly and/or the motor assembly, may separate the transmission assembly from the motor assembly and retain the components of these assemblies. 
     SUMMARY 
     In an aspect, a power tool includes a tool housing and a motor assembly received in the tool housing. The motor assembly has a rear end portion, a front end portion, and a motor output shaft. A transmission housing is coupled to the motor housing in which a transmission is received. A motor output shaft is drivingly coupled to the transmission. A partition assembly includes a rear cover covering a rear end portion of the transmission housing that faces the front end portion of the motor. The rear cover and the front end portion together define at least a first labyrinth path and a second labyrinth path therebetween configured to inhibit grease or dust migration between the transmission housing and the motor assembly. 
     Implementations of this aspect may include one or more of the following features. The first labyrinth path may define at least a first undulation. The second labyrinth path may define at least a second undulation. The front end portion of the motor may include a fan coupled to the output shaft for cooling the motor. The first labyrinth path may be defined by a first projection on one of the cover and the first end portion of the motor and that is received in a first recess in the other of the cover and the first end portion of the motor. The second labyrinth path may be defined by a second projection on one of the cover and the first end portion of the motor and that is received in a second recess in the other of the cover and the first end portion of the motor. The rear cover may include a first plate received over the rear end portion of the transmission housing and a second plate received over the first plate. The first plate may define the first labyrinth path and the second plate may define the second labyrinth path. The first plate may have a first central opening for receiving the motor output shaft and a first projection at least partially surrounding the first central opening and projecting rearward into a first recess in the front end portion of the motor assembly to define the first labyrinth path. The second plate may have a second central opening for receiving the first projection of the first plate, and a second projection at least partially surrounding the second central opening and projecting rearward into a second recess in the front end portion of the motor assembly to define the second labyrinth path. The cover may have at least one leg on an outer periphery of the cover that extends axially forward to snap fit onto the rear end portion of the motor housing. A seal may be disposed between a front face of the rear cover and the rear end portion of the transmission housing to further inhibit grease or dust migration between the transmission housing and the motor assembly. The seal may be integrally formed with one of the front face of the rear cover and the rear end portion of the transmission housing. A gear of a first stage of the transmission assembly may abut the rear cover to facilitate heat transfer from the transmission assembly. 
     In another aspect, a power tool includes a tool housing and a motor assembly received in the tool housing. The motor assembly has a rear end portion, a front end portion, and a motor output shaft. A transmission housing is coupled to the motor housing. A transmission is received in the transmission housing. The motor output shaft is drivingly coupled to the transmission. A partition assembly includes a rear cover covering a rear end portion of the transmission housing that faces the front end portion of the motor. The rear cover includes a first plate having a first projection defining a first central opening for receiving the motor output shaft, and a second plate having a second projection defining a second central opening for receiving the first projection, the first and second plates configured to inhibit grease or dust migration between the transmission housing and the motor assembly. 
     Implementations of this aspect may include one or more of the following features. The second plate may be layered over the first plate between the first plate and the motor assembly. The second plate may be configured to retain both the first plate and the second plate on the rear end portion of the transmission housing. The cover may have at least one leg on an outer periphery of the cover that extends axially forward to snap fit onto the rear end portion of the motor housing. The first projection may be received in a first recess in the front end portion of the motor assembly to define a first labyrinth path therebetween. The second projection may be received in a second recess in the front end portion of the motor assembly to define a second labyrinth path therebetween. The first labyrinth path may define at least a first undulation and the second labyrinth path may define at least a second undulation. The front end portion of the motor may include a fan coupled to the output shaft for cooling the motor and define a first recess that receives the first projection. The fan may define a second recess that receives the second projection. A seal may be disposed between a front face of the rear cover and the rear end portion of the transmission housing to further inhibit grease or dust migration between the transmission housing and the motor assembly. The seal may be integrally formed with one of the front face of the rear cover and the rear end portion of the transmission housing. 
     In another aspect, a power tool includes a tool housing and a motor assembly received in the tool housing. The motor assembly has a rear end portion, a front end portion, a motor output shaft, and a fan coupled to the front end portion and rotatably driven by the motor output shaft. A transmission housing is coupled to the motor housing with a transmission received in the transmission housing to which the motor output shaft is drivingly coupled. A partition assembly includes a rear cover covering a rear end portion of the transmission housing that faces the fan. The rear cover includes a first plate having a first projection defining a first central opening that receives the motor output shaft and that is received in a first recess in the fan to define a first labyrinth path therebetween, and a second plate having a second projection defining a second central opening that receives the first projection and that is received in a second recess in the fan to define a second labyrinth path therebetween to inhibit grease or dust migration between the transmission housing and the motor assembly. 
     In another aspect, a power tool includes a tool housing and a motor assembly received in the tool housing. The motor assembly has a rear end portion, a front end portion, and a motor output shaft. A transmission housing is coupled to the motor housing with a transmission received in the transmission housing. A partition assembly includes a sealing ring and a rear cover covering a rear end portion of the transmission housing that faces the front end portion of the motor. The rear cover of the transmission housing and the front end portion of the motor together define a first labyrinth path. The partition assembly is configured to inhibit grease or dust migration between the transmission housing and the motor assembly. 
     Implementations of this aspect may include one or more of the following features. The front end portion of the motor may include a fan coupled to the output shaft for cooling the motor. The first labyrinth path may be defined by a first annular projection on the cover that is received in a first annular recess in the fan. The first annular recess may define an undercut configured to further inhibit grease or dust migration. The first labyrinth path may define at least a first undulation. A second labyrinth path may be defined between the rear cover of the transmission housing and the front end portion of the motor to inhibit grease or dust migration between the transmission housing and the motor assembly. The second labyrinth path may define at least a second undulation. The rear cover may include a first plate received over the rear end portion of the transmission housing and a second plate received over the first plate. The first plate may define the first labyrinth path and the second plate may define the second labyrinth path. The first plate may include a first central opening for receiving the motor output shaft and a first projection at least partially surrounding the first central opening and projecting rearward into a first recess in the front end portion of the motor assembly to define the first labyrinth path. The second plate may include a second central opening for receiving the first projection of the first plate, and a second projection at least partially surrounding the second central opening and projecting rearward into a second recess in the front end portion of the motor assembly to define the second labyrinth path. The transmission assembly may include an input sun gear to which the motor output shaft is drivingly coupled. The sealing ring may be disposed on the input sun gear. The cover may include a first annular projection and the sealing ring may be coupled to the first annular projection. A seal may be disposed between a front face of the rear cover and the rear end portion of the transmission housing to further inhibit grease or dust migration between the transmission housing and the motor assembly. The seal may be integrally formed with one of the front face of the rear cover and the rear end portion of the transmission housing. 
     In another aspect, a power tool includes a tool housing and a motor assembly received in the tool housing. The motor assembly has a rear end portion, a front end portion, a motor output shaft, and a fan coupled to the motor output shaft adjacent the front end portion. A transmission housing is coupled to the motor housing with a transmission having a plurality of gears received in the transmission housing and to which the motor output shaft is drivingly coupled. A partition assembly includes a rear cover covering a rear end portion of the transmission housing that faces and is adjacent the fan of the motor and that is configured to abut against at least one of the gears of the transmission assembly to facilitate heat transfer from the transmission assembly. 
     Implementations of this aspect may include one or more of the following features. The rear cover and the fan together may define a first labyrinth path therebetween configured to inhibit grease or dust migration between the transmission housing and the motor assembly. The first labyrinth path may be defined by a first projection on one of the cover and the fan and that is received in a first recess in the other of the cover and the fan. The rear cover and the fan together may define a second labyrinth path therebetween configured to inhibit grease or dust migration between the transmission housing and the motor assembly. The second labyrinth path may be defined by a second projection on one of the cover and the fan and that is received in a second recess in the other of the cover and the fan. The rear cover may include a first plate received over the rear end portion of the transmission housing and a second plate received over the first plate. The first plate may be configured to abut the gear. The first plate may have a first central opening for receiving the motor output shaft and a first projection at least partially surrounding the first central opening and projecting rearward into a first recess in the fan to define a first labyrinth path. The second plate may have a second central opening for receiving the first projection of the first plate, and a second projection at least partially surrounding the second central opening and projecting rearward into a second recess in the fan. The cover may have at least one leg on an outer periphery of the cover that extends axially forward to snap fit onto the rear end portion of the motor housing. A seal may be disposed between a front face of the rear cover and the rear end portion of the transmission housing to further inhibit grease or dust migration between the transmission housing and the motor assembly. The seal may be integrally formed with one of the front face of the rear cover and the rear end portion of the transmission housing. 
     Advantages may include one or more of the following. The partition between the transmission assembly and the motor assembly may reduce or inhibit grease migration and dust contamination between the transmission assembly and the motor assembly. The partition also may help facilitate alignment between the motor assembly and the transmission assembly. In addition, the partition may facilitate heat transfer from the hottest portion of the transmission. These and other advantages and features will be apparent from the description, the drawings, and the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side plan view of an embodiment of a power tool. 
         FIG. 2  is a side cross-sectional view of the power tool of  FIG. 1 . 
         FIG. 3A  is a close-up side cross-sectional view of the power tool of  FIG. 1  showing a motor assembly, a transmission assembly, and an embodiment of a partition assembly between the motor assembly and the transmission assembly. 
         FIG. 3B  is a close-up side cross-sectional view similar to  FIG. 3B , showing a ring gear of the transmission assembly abutting the partition assembly. 
         FIG. 4  is a close-up side cross-sectional view of a motor fan and the partition assembly of  FIG. 3 . 
         FIG. 5  is a close up side cross-sectional view of a portion of the motor fan and the partition assembly of  FIG. 3 . 
         FIG. 6  is a perspective view of the motor fan of  FIG. 3 . 
         FIG. 7  is an exploded perspective view of the partition assembly and transmission housing of  FIG. 3 . 
         FIG. 8  is an exploded perspective view of the motor assembly, transmission assembly, and partition assembly of  FIG. 3 . 
         FIG. 9  is an alternative embodiment of a partition assembly usable with the motor assembly and transmission assembly of  FIG. 3 . 
         FIG. 10  is a side cross-sectional view of the cover of  FIG. 9 . 
         FIG. 11  is a perspective view of another alternative embodiment of a partition assembly usable with the motor assembly and transmission assembly of  FIG. 3 . 
         FIG. 12  is a perspective view of the motor assembly and transmission assembly of  FIG. 3  with yet another alternative embodiment of the cover of the transmission assembly. 
         FIG. 13  is a side cross-sectional view of an alternative embodiment of a power tool having a motor assembly, a transmission assembly, and a partition assembly between the motor assembly and the transmission assembly. 
         FIG. 14  is a close-up side cross-sectional view showing the cover  FIG. 13 . 
         FIG. 15  is a side cross-sectional view of an alternative embodiment of a partition assembly with a seal usable with the motor assembly and transmission assembly of  FIG. 3 . 
         FIG. 16  is an exploded view of another alternative embodiment of a sun gear and O-ring seal of a partition assembly. 
         FIG. 17  is a side cross-sectional view of an alternative embodiment of a partition assembly usable with the motor assembly and transmission assembly of  FIG. 3 . 
         FIG. 18  is a front view of an embodiment of a cover and a seal of the partition assembly of  FIG. 17 . 
         FIG. 19  is a perspective view of another embodiment of a transmission housing and a seal of the partition assembly of  FIG. 17 . 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIGS. 1 and 2 , in an embodiment, a power tool  10  includes a housing assembly  12 , a motor assembly  14 , a trigger assembly  16 , a transmission assembly  18 , a clutch assembly  20 , and an output spindle  22  extending along a longitudinal axis X. The housing assembly  12  comprises a pair of handle housing shells  23  that together form a tool housing  22 . The tool housing  22  defines a handle  36  and a motor cavity  40  into which the motor assembly  14  is received. The motor assembly  14  includes a rear end portion  200 , a front end portion  204 , an outer stator  15 , an inner rotor  17 , and an output shaft  92  coupled to the rotor  17  and extending along the longitudinal axis X to provide a rotary input torque to the transmission assembly  18 . The transmission assembly  18  includes a generally tubular transmission housing  32  that can be removably coupled to the tool housing  22 , e.g., via a plurality of threaded fasteners (not shown). The transmission housing  32  contains a speed reduction gearset  106  configured to transmit rotary power from the motor output shaft  92  to the output spindle  22 . The transmission housing  32  has a generally tubular front wall portion  102  and a generally tubular rear wall portion  104 , which may be removably attached to each other, e.g., by threaded fasteners, or which may be integral. At least part of the front wall portion  104  forms a portion of the exterior of the power tool  10 . 
     The speed reduction gearset  106  may be a multi-speed gearset, and in the illustrated example, comprises a three-stage, two-speed planetary transmission  108 . The transmission  110  has a first stage  130 , a second stage  132  and a third stage  134 , with the first and second stages  130  and  132  disposed in the rear wall portion  104 , and the third stage  134  disposed in the front wall portion  102 . Each stage  130 ,  132 ,  134  includes a sun gear meshed with a plurality of planet gears and a ring gear surrounding and meshed with the planet gears. For example, the first stage  130  includes a sun gear  280  mounted on the output shaft  92 , a plurality of planet gears  282  meshed with the sun gear  280 , and a ring gear  283  surrounding and meshed with the planet gears  282 . The transmission assembly  18  may also include a speed selector mechanism  108  configured to change the speed reduction ratio of the speed reduction gearset  106 . Further details regarding the housing assembly  12 , motor assembly  14 , trigger assembly  16 , transmission assembly  18 , clutch assembly  20 , and output spindle  22  may be found in U.S. Pat. No. 9,481,080, which is incorporated by reference. 
     Referring also to  FIGS. 3A-8 , in an embodiment, a partition assembly  5  between the motor assembly  14  and the transmission assembly  18  comprises a fan  206  on a front end portion of the motor assembly  14  and a rear cover  240  on a rear end  242  of the transmission assembly  18 . The fan  206  is rotatably driven by the motor output shaft  92  in order to cool the motor assembly  14 . The fan  206  has a generally disk shaped body  205  with a central hub  214  that is keyed to the output shaft  92  via a keyway  216 , a front face portion  208  that faces toward the transmission assembly  18 , and a rear face portion  210  that faces toward the remainder of the motor assembly  14 . The rear face portion  210  carries a plurality of fan blades  212  configured to blow cooling air over the motor assembly  14  when the output shaft  92  rotates. The front face portion  208  has a generally flat annular wall  218  with a first annular recess  220  located radially outward from the hub  214  at a first radial distance R 1  from the longitudinal axis X and a second annular recess  222  located radially outward from the hub  214  at a second radial distance R 2  from the longitudinal axis X is greater than the first radial distance R 1 . The first annular recess  220  is bounded by a first inner radial wall  224 , a first outer radial wall  226 , and a first annular wall  228 , and has a first height H 1  and a first depth D 1 . The second annular recess  222  is bounded by a second inner radial wall  230 , a second outer radial wall  232 , and a second annular wall  234 , and has a second height H 2  that is less than the first height H 1 , and a second depth D 2  that is greater than the first depth D 1 . In other embodiments, the first height H 1  may be less than or equal to the second height H 2  and the first depth D 1  may be greater than or equal to the second depth D 2 . 
     The rear cover  240  covers the rear end  242  of the generally tubular rear portion  104  of the transmission housing  32 . The cover  240  is generally disk shaped and has a central aperture  248  that receives the motor output shaft  92 , a front face  244  that faces the reduction gearset  110 , a rear face  246  that faces the fan  206 , and a peripheral edge portion  250  that couples the rear cover  240  to the tubular rear portion  104  of the transmission housing  32 . The rear face  246  includes a first annular projection  252  and a second annular projection  254  extending rearward from the rear face  246 . The first annular projection  252  defines the central aperture  248  and is configured to be received in the first annular recess  220  of the fan  204 . The second annular projection  254  is configured to be received in the second annular recess  222  of the fan  204 . 
     In the illustrated embodiment, the rear cover  240  is formed in two parts that comprise a first cover plate  260  and a second or outer cover plate  270 . The first cover plate  260  is disk-shaped with the first annular projection  252  on its inner periphery that surrounds the central aperture  248 . The first cover plate  260  also has a plurality of first legs  262  extending axially forward from an outer peripheral edge  264  of the first cover plate  260 . The first legs  262  are configured to be received in corresponding grooves  266  in an outer surface  268  of the rear wall portion  104  of the transmission housing  32  to inhibit relative rotation between the first cover plate  260  and the transmission housing  32 . The second cover plate  270  is disk-shaped with the second annular projection  254  on its inner periphery surrounding a central opening  272  that is larger than the central aperture  248 . The second cover plate  270  also has a plurality of second legs  274  extending axially forward from the outer peripheral edge portion  250  of the second cover plate  270 . Each of the second legs  274  defines an enclosed slot  276  that is configured to receive a ramped protrusion  278  on the outer surface  268  of the rear wall portion  104  of the transmission housing  32  in a snap-fit connection to rotationally and axially secures the second cover plate  270  to the transmission housing  32 . In the illustrated embodiment, the cover  240  is composed of separate first and second cover plates  260 ,  270  as it is less costly to manufacture the plates individually out of individual pieces of sheet metal. However, as described below, in other embodiments, the cover  240  may be formed of a single integral piece of material. In addition, the cover  240  may be attached to the transmission housing  32  by other types of connections such as by a bayonet-type connection, by threaded fasteners, by being welded, or by using an adhesive. Also, the cover plates  260 ,  270  may be affixed to one another, e.g., by threaded fasteners, welding, or adhesive. 
     As shown in  FIG. 3B , the rear cover  240  is metal and is mounted to the transmission housing  32  so that the first stage ring gear  283  can abut against the rear cover  240 , with the rear cover very close to the fan  206 . This facilitates superior heat dissipation from the first stage  130  of the transmission assembly, which tends to be the hottest portion of the transmission assembly during operation. 
     To assemble the motor assembly  14  and the transmission assembly  18 , the first cover plate  260  is non-rotationally coupled to the rear end  242  of the transmission housing  32  by inserting the first legs  262  into the grooves  266 . Next, the second cover plate  270  is placed over and abutting the first cover plate  260  and the second legs  274  are rotationally and axially secured to the rear end  242  of the transmission housing  32  by snap-fitting the second legs  274  over the ramped protrusions  278 . After the rear cover  240  is secured to the transmission housing  32 , the output shaft  92  of the motor assembly  14  is inserted through the central aperture  248  of the cover  240  so that the sun gear  280  on the output shaft  92  meshes with planet gears  282  in the first stage  130  of the reduction gearset  106 . At the same time, the first annular projection  252  on the cover  240  is received in the first annular recess  220  in the fan  206 , and the second annular projection  254  is received in the second annular recess  222  in the fan  206 . A first space  255  between the first projection  252  and the walls  224 ,  226 ,  228  that bound the first annular recess  220  defines a first labyrinth path A having a first generally U-shaped undulation. A second space  256  between the second projection  254  and the walls  230 ,  232 ,  234  that bound the second annular recess  222  defines a second labyrinth path B having a second generally U-shaped undulation. 
     Together, the first labyrinth path A and the second labyrinth path B of the partition assembly  5  reduce or inhibit migration of grease and dust contamination between the transmission assembly  18  and the motor assembly  14  by trapping grease and/or dust. The multiple labyrinth path is significantly more effective in trapping the grease than is a single labyrinth path. In alternate embodiments, there may be more than two labyrinth paths. In addition, one or more of the labyrinth paths may have a different configuration such as crenellated, bustrophedonic, wave-like, S-shaped, Z-shaped, and/or sinusoidal. 
     Referring to  FIGS. 9 and 10 , in another embodiment, a power tool  310  similar to power tool  10  may include a partition assembly  305  that includes the fan  206 , described above, together with a one-piece or unitary cover  340  that covers the rear end  242  of the generally tubular rear portion  104  of the transmission housing  32 . The cover  340  is generally disk shaped and has a central aperture  348  that receives the motor output shaft  92 , a front face  344  that faces the reduction gearset  110 , a rear face  346  that faces the fan  206 , and a peripheral edge portion  350  that couples the cover  340  to the tubular rear portion  104  of the transmission housing  32 . The rear face  346  includes a first annular projection  352  and a second annular projection  354  extending rearward from the rear face  346 . The first annular projection  352  surrounds the central aperture  348  and is configured to be received in the first annular recess  220  of the fan  204 . The second annular projection  354  is configured to be received in the second annular recess  222  of the fan  204 . The cover  340  has one or more first legs  362  extending radially outward from an outer peripheral edge  364  of the cover  340 . The legs  362  are configured to be received in corresponding grooves in the rear wall portion  104  of the transmission housing  32  to inhibit relative rotation between cover  340  and the transmission housing  32 . The cover  340  also has a plurality of second legs  374  extending radially outward from the first annular projection  352  and axially rearward from the rear face  346 . Each of the second legs  374  is configured to be received in corresponding grooves in the tool housing  22  (not shown) to rotationally and/or axially retain the cover  340  in the tool housing  22 . 
     Referring to  FIG. 11 , in another embodiment, a power tool  410  similar to the power tool  10  may include a partition assembly  405  that includes the fan  206  described above and a rear cover  440 , similar to the rear cover  240  of  FIGS. 3-8 . The rear cover  440  may comprise a first cover plate (not shown) similar to the first cover plate  260 , and a second cover plate  470  similar to the second cover plate  270 . The rear cover  440  differs from the rear cover  240  in that the second cover plate  470  has a plurality of second legs  474  extending radially outward from an outer peripheral edge portion  450  of the second cover plate  470 . Each of the second legs  474  defines an enclosed screwhole  476  that is configured to receive a threaded fastener  478  that is also received in a screw boss  480  on the outer surface  268  of the rear wall portion  104  of the transmission housing  32  to rotationally and axially secures the second cover plate  470  to the transmission housing  32 . 
     Referring to  FIG. 12 , in another embodiment, a power tool  510  similar to the power tool  10  may include a partition assembly  505  that includes the fan  206  described above and a rear cover  540 , similar to the rear cover  240  of  FIGS. 3-8 . The rear cover  540  may comprise a first cover plate (not shown) similar to the first cover plate  260 , and a second cover plate  570  similar to the second cover plate  270 . The rear cover  540  differs from the rear cover  240  in that the second cover plate  570  has a plurality of L-shaped legs  574  extending axially forward from an outer peripheral edge portion  550  of the second cover plate  570 . Each of the L-shaped legs  574  is configured to receive one of the ramped protrusions  278  that on the outer surface  268  of the rear wall portion  104  of the transmission housing  32  to rotationally and axially secure the second cover plate  570  to the transmission housing  32 . 
     Referring to  FIGS. 13 and 14 , in another embodiment, a power tool  610 , different from the power tool  10 , includes a housing assembly  612 , a motor assembly  614 , a transmission assembly  618 , a rotary impact assembly  620  (including a cam carrier  621 , a hammer being driven by the cam carrier  623 , and an anvil  625  that can be struck by the hammer  623 , and a spring  627  biasing the hammer away from the cam carrier  623 ), and an output spindle  622  extending along a longitudinal axis X and coupled to the anvil  625 . The housing assembly  612  comprises a pair of handle housing shells  623  that together form a tool housing  622  and a handle (not shown, but similar to the handle  36  in  FIGS. 1 and 2 ). The tool housing  622  defines a motor cavity  640  into which the motor assembly  614  is received. The motor assembly  614  includes a rear end portion  600 , a front end portion  604 , an outer stator  615 , an inner rotor  617 , and an output shaft  692  coupled to the rotor  617  and extending along the longitudinal axis X to provide a rotary input torque to the transmission assembly  618 . The transmission assembly  618  includes a generally tubular transmission housing  632  that can be removably coupled to the tool housing  622 , e.g., via a plurality of threaded fasteners (not shown). The transmission housing  632  contains the rotary impact assembly  620  and a speed reduction gearset  606  configured to transmit rotary power from the motor output shaft  692  to the rotary impact assembly  620 . The transmission housing  632  has a generally tubular wall portion  607 , at least part of which forms a portion of the exterior of the power tool  610 . The speed reduction gearset  606  may be a planetary gearset  609  having an input sun gear  611 , a plurality of planet gears  613  driven by the sun gear  611  and carried by the cam carrier  621  of the rotary impact assembly  620 , and a stationary ring gear  619  that meshes with the planet gears  613 . The speed reduction gearset  606  reduces the output speed of the motor shaft  692  and transmits rotary motion to the rotary impact assembly  621 , which transmits rotational motion to the output spindle  622 , for example, as described in U.S. Patent Application Publication No. 2016/0250738, which is incorporated by reference. 
     A partition assembly  605  between the motor assembly  614  and the transmission assembly  618  comprises a front motor end plate  642  on a front end portion  604  of the motor assembly  614  and a rear cover  670  on a rear end of the transmission assembly  18 . The rear end portion  600  of the motor assembly  614  includes a fan  640  for cooling the motor assembly  614  coupled to and rotatably driven by the motor output shaft  692 . The front motor end plate  642  has a central opening  644  through which the motor output shaft  692  extends. The motor end plate  642  has a generally disk shaped body  646  with a front face portion  648  that faces toward the transmission assembly  618 , and a rear face portion  650  that faces toward the remainder of the motor assembly  614 . The front face portion  648  has a generally flat annular wall  654  with a first annular recess  654  located radially outward from longitudinal axis X at a first radial distance R 1  and a first annular projection  656  located radially outward from the longitudinal axis X at a second radial distance R 2  that is greater than the first radial distance R 1 . The first annular recess  654  is bounded by a first inner radial wall  658 , a first outer radial wall  660 , and a first annular wall  662 , and has a first height H 1  and a first depth D 1 . 
     The rear cover  670  covers a rear end  672  of the generally tubular wall  607  of the transmission housing  632 . The cover  670  is generally disk shaped and has a central aperture  674  that receives the motor output shaft  692 , a front face  674  that faces the reduction gearset  609 , a rear face  676  that faces the motor assembly  614 , and a peripheral edge portion  678  that couples the rear cover  670  to the transmission housing  632 . The rear face  246  includes a second annular recess  680  and a second annular projection  682  extending rearward from the rear face  676 . The second annular recess  680  is bounded by a second inner radial wall  684 , a second outer radial wall  686 , and a second annular wall  688 , and has a second height H 2  that is greater than the first height H 1 , and a second depth D 2  that is greater than the first depth D 1 . In other embodiments, the first height H 1  may be less than or equal to the second height H 2  and the first depth D 1  may be less than or equal to the second depth D 2 . 
     To assemble the motor assembly  614  and the transmission assembly  618 , the cover  670  is non-rotationally coupled to the rear end  672  of the transmission housing  632  and the output shaft  692  of the motor assembly  614  is inserted through the central aperture  674  of the cover  670  so that a sun gear  611  meshes with planet gears  613  of the reduction gearset  609 . At the same time, the first annular projection  656  on the motor end plate  642  is received in the second annular recess  680  in the cover  670 , and the second annular projection  682  on the cover  670  is received in the first annular recess  654  in the motor end plate  642 . A first space  655  between the second projection  682  and the walls  658 ,  660 ,  662  that bound the first annular recess  654  defines a first labyrinth path A having a first generally U-shaped undulation. A second space  657  between the first projection  656  and the walls  684 ,  686 ,  688  that bound the second annular recess  680  defines a second labyrinth path B having a second generally U-shaped undulation. Together, the first labyrinth path A and the second labyrinth path B of the partition assembly  605  reduce or inhibit migration of grease and dust contamination between the transmission housing  32  and the motor assembly  14  by trapping grease and/or dust. The multiple labyrinth path is significantly more effective in trapping the grease than is a single labyrinth path. In alternate embodiments, there may be more than two labyrinth paths. In addition, one or more of the labyrinth paths may have a different configuration such as crenellated, bustrophedonic, wave-like, S-shaped, Z-shaped, and/or sinusoidal. 
     Referring to  FIGS. 15 and 16 , in another embodiment, a power tool  710  similar to the power tool  10  may include a partition assembly  705  between a motor assembly  714  and a transmission assembly  718 , similar to the motor assembly  14  and transmission assembly  18 , described above. The partition assembly  705  includes a fan  706  similar to the fan  206 , described above, and a one-piece or unitary cover  740  that covers the rear end  742  of a generally tubular rear portion  704  of the transmission housing  732 . The fan  706  is rotatably driven by a motor output shaft  792  in order to cool the motor assembly  714 . The fan  706  has a generally disk shaped body  705  with a central hub  715  that is keyed to the output shaft  792 , a front face portion  708  that faces toward the transmission assembly  718 , and a rear face portion  711  that faces toward the remainder of the motor assembly  714 . The rear face portion  711  carries a plurality of fan blades  712  configured to blow cooling air over the motor assembly  714  when the output shaft  792  rotates. The front face portion  708  has a generally flat annular wall with an annular recess  720  located radially outward from the hub  214  at a first radial distance R from the longitudinal axis X. The annular recess  720  is bounded by an inner radial wall  724 , an outer radial wall  726 , and an annular wall  728 , and has a height H and a depth D. 
     The cover  740  is generally disk shaped and has a central aperture  748  that receives a motor output shaft  792 , a front face  744  that faces the reduction gearset  110 , a rear face  746  that faces the fan  706 , and a peripheral edge portion  750  that couples the cover  740  to the tubular rear portion  704  of the transmission housing  732 . The rear face  746  includes an annular projection  752  extending rearward from the rear face  746 . The annular projection  752  surrounds the central aperture  748  and is configured to be received in the annular recess  720  of the fan  704 . The cover  740  is retained on the transmission housing  732  similar to one of the covers shown in  FIGS. 7, 11, and 12 . 
     A first space  755  between the projection  752  and the walls  724 ,  726 ,  728  that bound the annular recess  720  define a first labyrinth path A having a first generally U-shaped undulation to reduce or inhibit migration of grease and dust contamination between the transmission assembly  718  and the motor assembly  714  by trapping grease and/or dust. To further reduce or inhibit migration of grease and dust contamination, the radial outer wall  726  of the annular recess  720  in the fan  706  is provided with an undercut  725 , while the inner hub  715  has its front face  727  trimmed back. To even further reduce or inhibit migration of grease and dust contamination, a first annular seal  782  (e.g., an elastomeric or plastic O-ring) is received on the input sun gear  780  that is driven by the motor output shaft  792  (as shown in the implementation of  FIGS. 16A and 16B ), and/or a second annular seal  788  (e.g., an elastomeric or plastic O-ring) is formed on an inner diameter of the annular projection  752  of the cover  740  (as shown in the implementation of  FIG. 15 ). Together these features reduce or inhibit migration of grease and dust contamination more than the labyrinth path A by itself. These features may be combined with multiple labyrinth paths, as described above. 
     Referring to  FIGS. 17-19 , in another embodiment, a power tool  810  similar to the power tool  10  may include a partition assembly  805  between a motor assembly (not shown) and a transmission assembly  818 , similar to the motor assembly  14  and transmission assembly  18 , described above. The partition assembly  805  includes a fan (not shown) similar to the fan  206 , described above, and a one-piece or unitary cover  840  that covers the rear end  842  of a generally tubular rear portion  804  of the transmission housing  832 . The cover  840  is generally disk shaped and has a central aperture  848  that receives the motor output shaft, a front face  844  that faces the reduction gearset  110 , a rear face  846  that faces the fan, and a peripheral edge portion  850  that couples the cover  840  to the rear portion  842  of the transmission housing  832 . The rear face  846  includes an annular projection  852  extending rearward from the rear face  846 . The annular projection  852  surrounds the central aperture  848  and is configured to be received in the annular recess of the fan. The cover  840  is retained on the transmission housing  832  similar to one of the covers shown in  FIGS. 7, 11, and 12 . 
     A seal  860  is disposed between a peripheral portion  862  of the front face  844  of the cap  840  and the rear end portion  842  of the transmission housing  832 . The seal  860  may be annular, ring shaped, or semi-circular, and may be formed of a metal, plastic, or elastomeric (e.g., rubber) material. As shown in  FIG. 18 , the seal  860  may be integrally formed (e.g., overmolded) with front face  844  of the cap  840 . Alternatively, as shown in  FIG. 19 , the seal  860  may be integrally formed (e.g., overmolded) with the rear end portion  842  of the transmission housing  832 . In other embodiments, the seal  860  may not be integrally formed with either the transmission housing  832  or the cap  840 , and may instead be sandwiched between them. The seal  860  is configured to reduce or inhibit migration of grease and dust contamination between the transmission assembly  810  and the motor assembly. The seal  860  may be combined with one or more of the multiple labyrinth paths, as shown in  FIGS. 3-8 , and/or the features of  FIGS. 15-16  to further reduce or inhibit migration of grease and dust contamination between the transmission assembly and the motor assembly. 
     Example embodiments have been provided so that this disclosure will be thorough, and to fully convey the scope to those who are skilled in the art. Numerous specific details are set forth such as examples of specific components, devices, and methods, to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, that example embodiments may be embodied in many different forms and that neither should be construed to limit the scope of the disclosure. In some example embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail. 
     The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms “a,” “an,” and “the” may be intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms “comprises,” “comprising,” “including,” and “having,” are inclusive and therefore specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed. 
     When an element or layer is referred to as being “on,” “engaged to,” “connected to,” or “coupled to” another element or layer, it may be directly on, engaged, connected or coupled to the other element or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly engaged to,” “directly connected to,” or “directly coupled to” another element or layer, there may be no intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.). As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
     Although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms may be only used to distinguish one element, component, region, layer or section from another region, layer or section. Terms such as “first,” “second,” and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the example embodiments. 
     Terms of degree such as “generally,” “substantially,” “approximately,” and “about” may be used herein when describing the relative positions, sizes, dimensions, or values of various elements, components, regions, layers and/or sections. These terms mean that such relative positions, sizes, dimensions, or values are within the defined range or comparison (e.g., equal or close to equal) with sufficient precision as would be understood by one of ordinary skill in the art in the context of the various elements, components, regions, layers and/or sections being described. 
     Numerous modifications may be made to the exemplary implementations described above. These and other implementations are within the scope of the following claims.