Patent Publication Number: US-8522890-B2

Title: Power tool having lubricant leakage preventing structure

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority from Japanese Patent Application No. 2009-294810 filed Dec. 25, 2009. The entire content of each of the priority application is incorporated herein by reference. 
     TECHNICAL FIELD 
     The present invention relates to a power tool having a mechanism for transmitting a rotation of an electric motor, and more particularly, to such power tool having a structure for preventing leakage of lubricant. 
     BACKGROUND 
     An electronic motor is mounted in the housing of a power tool such as a hammer drill. A cylinder driven by the electric motor is rotatably supported at the leading end of the housing, and an end tool is attached to the leading end of the cylinder. Further, a speed reduction mechanism for changing the rotary speed of the electric motor is provided in the housing. The speed reduction mechanism corresponds to a speed change mechanism. Through the speed reduction mechanism, a rotation of the electric motor is transmitted to the end tool. 
     The speed reduction mechanism is housed in a mechanism chamber defined by the housing and has a rotation transmission mechanism including a gear and an intermediate shaft. A rotation of the electric motor is transmitted to the intermediate shaft by the gear and then transmitted to the end tool. A bearing is provided within the mechanism chamber at the positions corresponding to both end portions of the intermediate shaft for rotatably supporting the intermediate shaft. 
     A lubricant is applied to the gear, intermediate shaft, and the like of the speed reduction mechanism for increase in durability and reduction in friction loss. As the lubricant, used is grease containing a metallic soap base such as Ca and Li and an oil component such as silicon oil. The grease has a high fluidity and is soft, so that the lubrication ability of the grease is not impaired even at low temperature environment. The soft grease contains a large amount of oil component. Therefore, a high temperature increases fluidity, with the result that the soap base and oil component tend to be separated from each other. Accordingly, high sealing performance is required for the mechanism chamber in order to prevent the grease from flowing out of the mechanism chamber. In order to realize the high sealing performance, a plurality of types of seal members such as an O-ring, an oil seal, a contact type sealed ball bearing are used for the mechanism chamber. The power tool having the above configuration is disclosed in, for example, laid-open Japanese Patent Application Publication No. H1-316178. 
     SUMMARY 
     In a conventional power tool, as described above, different types of seal members are used in individual portions to be sealed to realize a sealing structure of the mechanism chamber. Accordingly, sealing performance differs depending on the individual portions. When the speed reduction mechanism becomes feverish during use of such a power tool, temperature within the sealed mechanism chamber is increased to expand the air inside the mechanism chamber. In this case, if the sealing performance of only one of the above-mentioned different types of seal members is degraded, the expanded air and the grease flow outside of the mechanism chamber through the position corresponding to the seal member whose sealing performance has been degraded. The leakage of the grease may not only degrade quality and durability of the product, but also smear a working area. 
     There is an available power tool having a conversion mechanism that converts a rotary motion into a reciprocation motion and uses the conversion mechanism to reciprocate a cylindrical piston mounted in the housing. The electrical tool has, in the housing, an impacting power transmission mechanism that reciprocates a striker and intermediate member in accordance with the reciprocation motion of the cylindrical piston to transmit a striking power to the end tool. To this effect, the piston, striker, and intermediate member must be reciprocated at high speed. Therefore, relatively a large amount of grease having high fluidity needs to be put in the mechanism chamber. Further, a heat generated by the high speed reciprocation motion significantly increases pressure in the mechanism chamber. Under the circumstances, the grease whose fluidity has been increased due to the application of the heat easily flowed through the seal position to the outside of the mechanism chamber. 
     It is therefore, an object of the present invention to provide a power tool that suppresses expansion of the air in the mechanism chamber and prevents the lubricant encapsulated in the mechanism chamber from being leaked outside of the mechanism chamber to thereby increase quality and durability of the tool. 
     In order to attain the above and other objects, the present invention provides a power tool including a housing, an electric motor, a speed change mechanism, and a protrusion member. The housing defines therein a mechanism chamber. A lubricant is inserted in an interior of the mechanical chamber. The electric motor is accommodated in the housing. The speed change mechanism is disposed in the mechanism chamber and connected to the motor for shift-transmitting rotation of the motor. The protrusion member protrudes to the mechanism chamber from the housing in a protrusion direction. The protrusion member provides a communication passage that has one opening open at a leading end side of the protrusion member in the protrusion direction and another opening open to an exterior of the mechanical chamber. At least a part of the protrusion member provides the communication passage and is made from a resilient material. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The particular features and advantages of the invention as well as other objects will become apparent from the following description taken in connection with the accompanying drawings, in which: 
         FIG. 1  is a cross-sectional view showing an entire hammer drill according to an embodiment of the present invention; 
         FIG. 2  is a cross-sectional view taken along the line II-II in  FIG. 1 ; 
         FIG. 3  is a detailed cross-sectional view taken along the line in  FIG. 2 ; 
         FIG. 4  is a cross-sectional view of an essential portion of a hammer drill according to a first modification to the embodiment of the present invention; 
         FIG. 5  is a cross-sectional view of an essential portion of a hammer drill according to a second modification to the embodiment of the present invention; 
         FIG. 6  is a cross-sectional view of an essential portion of a hammer drill according to a third modification to the embodiment of the present invention; 
         FIG. 7  is a cross-sectional view of an essential portion of a hammer drill according to a fourth modification to the embodiment of the present invention; 
         FIG. 8  is a cross-sectional view of an essential portion of a hammer drill according to a fifth modification to the embodiment of the present invention; 
         FIG. 9  is a cross-sectional view of an essential portion of a hammer drill according to a sixth modification to the embodiment of the present invention; and 
         FIG. 10  is a cross-sectional view of an essential portion of a hammer drill according to a seventh modification to the embodiment of the present invention 
     
    
    
     DETAILED DESCRIPTION 
     A power tool according to an embodiment of the present invention will be described below with reference to  FIGS. 1 to 3 . The power tool is, as shown in  FIG. 1 , a hammer drill  1  including a handle portion  10 , a motor housing  20 , and a gear housing  30  those constituting a casing. In the following description, a direction in which the handle portion  10  extends from the motor housing  20  will be defined to as a downward direction, while the opposite direction will be defined as a upper direction, and a direction from the motor housing  20  to the gear housing  30  will be defined as a forward direction, while the opposite direction will be defined as a rear direction. 
     An electric cable  11  is attached to, and a switch mechanism (not shown) is incorporated in the handle portion  10 . To the switch mechanism, a user-operable trigger  12  is mechanically connected. The electric cable  11  connects the switch mechanism to an external power supply (not shown). A user operates the trigger  12  to thereby switch connection and disconnection between the switch mechanism and power supply. 
     The motor housing  20  is provided above the handle portion  10 . The inside of the motor housing  20  communicates with an atmosphere. The handle portion  10  and motor housing  20  are integral hard-resin molded product. An electric motor (not shown) is housed in the motor housing  20 . The motor housing  20  has an output shaft  21  for outputting a driving force. 
     The gear housing  30  is a hard-resin molded part provided in front of the motor housing  20 . A support member  30 A formed from a metal is provided inside the gear housing  30  to partition the gear housing  30  from the motor housing  20 . The gear housing  30  and support member  30 A define a speed reduction chamber  30   a  which is a mechanism chamber that houses a speed change mechanism to be described later. A portion of the gear hosing  30  and the support member  30 A which defines the mechanism chamber corresponds to a mechanism chamber forming portion. The gear housing  30  including the speed reduction chamber  30   a  contains grease serving as lubricant for reducing friction of gears to be described later. The grease is supplied to respective rubbing portions. 
     In the gear housing  30 , an intermediate shaft  32  extending parallel to the output shaft  21  is supported by the gear housing  30  and support member  30 A through bearings  32 B and  32 C so as to be rotatable about the axis of the intermediate shaft  32 . The bearings  32 B and  32 C that support the intermediate shaft  32 , each of which is a ball bearing with seal (non-contact type), are provided at both end portions of the intermediate shaft  32  and held by a part of the gear housing  30  and support member  30 A. Further, a side handle  13  is provided near a tool holder  35  (to be described later) of the gear housing  30 . 
     A motor pinion gear  22  is provided at the leading end of the output shaft  21 . A first gear  31  meshingly engaged with the motor pinion gear  22  is coaxially fixed to the intermediate shaft  32  at the electric motor side. A gear section  32 A is formed at the leading end side of the intermediate shaft  32  and is meshingly engaged with a second gear  33  (described later). The support member  30 A and the casing constituted by the handle portion  10 , motor housing  20 , and gear housing  30  define in combination a housing. 
     A cylinder  34  is provided in the gear housing  30  at the portion above the intermediate shaft  32 . The cylinder  34  extends parallel to the intermediate shaft  32  and is rotatably supported by the support member  30 A. The second gear  33  is fixed to the outer circumference of the cylinder  34 . The meshing engagement between the second gear  33  and gear section  32 A allows the cylinder  34  to be rotated about an axis of the cylinder  34 . 
     The above-mentioned tool holder  35  is provided at the leading end side of the cylinder  34  for detachably holding an end tool  60 . The support member  30 A thus supports the motor pinion gear  22 , intermediate shaft  32 , and cylinder  34 , so that a higher mechanical strength is required for the support member  30 A as compared to the gear housing  30  and motor housing  20 . Therefore, the support member  30 A is made from a metal. 
     A clutch  36  that is biased by a spring in the direction toward the electric motor is splined to the middle portion of the intermediate shaft  32 . The clutch  36  can be switched, by a change lever  37  provided at the lower portion of the gear housing  30 , between hammer drill mode (position shown in  FIG. 1 ) and drill mode (the clutch  36  is moved to the position on the leading end side of the intermediate shaft  32 ). A motion conversion section  40  that converts a rotary motion into a reciprocation motion is rotatably disposed over the intermediate shaft  32  at the portion on the electric motor side of the clutch  36 . The motion conversion section  40  corresponds to the speed change mechanism. The motion conversion section  40  has an arm portion  40 A reciprocally movable in the longitudinal direction of the hammer drill  1  by the rotation of the intermediate shaft  32 . 
     At the time when the clutch  36  is positioned at the hammer drill mode through the change lever  37 , the clutch  36  connects the intermediate shaft  32  to the motion conversion section  40 . The motion conversion section  40  is connected to a piston  42  provided in the cylinder  34  through a piston pin  41  so as to operate simultaneously with the piston  42 . The piston  42  is reciprocally movably disposed within the cylinder  34  in the direction parallel to the intermediate shaft  32  in a sliding manner with respect to the cylinder  34 . A striker  43  is installed in the piston  42 , and an air chamber  44  is defined in the cylinder  34  and between the piston  42  and striker  34 . An intermediate member  45  is supported in the cylinder  34  at the portion on the opposite of the air chamber with respect to the striker  43  so as to be slidable in the moving direction of the piston  42 . The end tool  60  is located at the portion on the opposite side of the striker with respect to the intermediate member  45 . The striker  43  therefore strikes the end tool  60  through the intermediate member  45 . 
     A rotation output of the motor is transmitted from the motor pinion gear  22  to the intermediate shaft  32  through the first gear  31 . The rotation of the intermediate shaft  32  is then transmitted to the cylinder  34  through the meshing engagement between the gear section  32 A and second gear  33  disposed over the cylinder  34 . Thus, the end tool  60  is rotated. When the clutch  36  is shifted to the hammer drill mode through the change lever  37 , the clutch  36  is connected to the motion conversion section  40  to transmit the rotation of the intermediate shaft  32  to the motion conversion section  40 . The motion conversion section  40  allows the piston pin  41  to convert the rotation into a reciprocation motion of the piston  42 . The reciprocation motion of the piston  42  causes the air in the air chamber  44  defined between the striker  43  and piston  42  to be repeatedly compressed and expanded, thereby imparting a striking force to the striker  43 . The striker  43  then moves forward to butt the rear end surface of the intermediate member  45  and the striking force is transmitted to the end tool  60  through the intermediate member  45 . As described above, in the hammer drill mode, the rotation force and striking force are simultaneously imparted to the end tool  60 . 
     At the time when the clutch  36  is shifted to the drill mode, the clutch  36  disconnects the connection between the intermediate shaft  32  and motion conversion section  40  to allow the rotation of the intermediate shaft  32  to be transmitted to the cylinder  34  through the gear section  32 A and second gar  33 . Accordingly, in the drill mode, only the rotation is imparted to the end tool  60 . 
     The speed reduction chamber  30   a  that is defined by the gear housing  30  and houses the rotation transmission mechanism is sealed by a plurality of types of seal members. These seal members prevent the grease from being leaked outside the gear housing  30 . 
     More specifically, an oil seal  71  is provided between an outer peripheral surface of the cylinder  34  and gear housing  30 , an O-ring  72  is mounted to an inner peripheral surface of the cylinder  34  that supports the intermediate member  45 , and an O-ring  73  is mounted at the connection portion between the change lever  37  and gear housing  30 . Further, an O-ring  74  is mounted at the connection portion between the support member  30 A and gear housing  30 . A bearing (not shown) that supports the motor pinion gear  22  is formed by a sealed ball bearing (contact type) and contributes to the sealing of the speed reduction chamber  30   a.    
     As shown in  FIG. 1 , a pressure adjusting mechanism  50  is provided on the support member  30 A. The pressure adjusting mechanism  50  is located in substantially the middle portion between the intermediate shaft  32  and cylinder  34  and is located on the right side of the support member  30 A as viewed from the end tool  60  side toward the support member  30 A as shown in  FIG. 2 . The pressure adjusting mechanism  50  corresponds to a protrusion member. 
     As shown in  FIG. 3 , the pressure adjusting mechanism  50  mainly includes a first passage forming component  51 , a second passage forming component  52 , and a filter  53  and extends frontward in the speed reduction chamber  30   a . The pressure adjusting mechanism  50  is in a cantilever shape and adjusts a pressure in the speed reduction chamber  30   a.    
     The first passage forming component  51  is located at the leading end side of the pressure adjusting mechanism  50  and is made from rubber material. The rubber material is used as one example of a resilient material. The first passage forming component includes a mounted section  51 A and an extending section  51 B. The mounted section  51 A is in a cylindrical shape and is formed with a holding space  51   a . An inner diameter of the holding space  51   a  is substantially equal to or slightly smaller than an outer diameter of the second passage forming component  52 . The leading end portion of the second passage forming component  52  is inserted into the holding space  51   a . Since the inner diameter of the holding space  51   a  is substantially equal to or slightly smaller than the outer diameter of the second passage forming component  52 , the second passage forming component  52  inserted in the holding space  51   a  is attached firmly to the inner surface of the mounted section  51 A that forms the holding space  51   a , thereby preventing the second passage forming component  52  from disengaging from the holding space  51   a . Since the second passage forming component  52  is attached firmly to the mounted section  51 A, leakage of the grease and the air to the outside from between the second passage forming component  52  and the mounted section  51 A can be prevented. A click portion  51 C protruding toward the holding space  51   a  is provided on the mounted section  51 A at the rear end thereof. 
     The extending section  51 B is located at the front side of the mounted section  51 A and has an outer diameter that is smaller than that of the mounted section  51 A such that the extending section  51 B is in a constriction shape with respect to the mounted section  51 A. The extending section  51 B includes a constriction portion  51 D extending from the front end of the mounted section  51 A, and a head portion  51 E located on the front end of the constriction portion  51 D. The head portion  51 E has an outer diameter larger than that of the constriction portion  51 D. A first passage  51   b  is formed on both of the constriction portion  51 D and the head portion  51 E. The first passage  51   b  includes a front opening formed on the peripheral wall part of the head portion  51 E to permit the first passage  51   b  to communicate with the speed reduction chamber  30   a , and a rear opening to permit the first passage  51   b  to communicate with the holding space  51   a . An area of the first passage  51   b  between the front opening and the rear opening extends in the front-to-rear direction. Hence, the first passage  51   b  has a bending section at a region between the front opening that opens to the speed reduction chamber  30   a  and a position where the first passage  51   b  enters the constriction portion  51 D. 
     The second passage forming component  52  is in a cylindrical shape and is integrally provided on the gear housing  30  to protrude toward the speed reduction chamber  30   a . A second passage  52   a  is formed on the second passage forming component  52 . The second passage  52   a  includes a front opening that is located at the front end of the second passage  52   a  and opens frontward, and a rear opening that opens to the inside of the motor housing  20 . Since the mounted section  51 A is mounted on the front end portion of the second passage forming component  52 , the second passage  52   a  communicates with the holding space  51   a . Further, since the inside of the motor hosing  20  communicates with the atmosphere, the second passage  52   a  also communicates with the atmosphere. A depressed portion  52   b  with which the click portion  51 C is engaged is provided on an outer circumferential surface of the cylindrical portion of the second passage forming component  52 . The click portion  51 C and the depressed portion  52   b  provide an engagement portion. The disengagement of the first passage forming component  51  from the second passage forming component  52  can be restrained by the engagement portion. 
     The filter  53  made from a felt having air permeability is located on the holding space  51   a  in a state where the first passage forming component  51  is mounted on the second passage forming component  52 . The filter  53  separates the first passage  51   b  and the second passage  52   a  from each other. Accordingly, an air flowing between the first passage  51   b  and the second passage  52   a  can be filtered by the filter  53 . The first passage  51   b , the second passage  52   a , and the filter  53  define a communication passage  50   a.    
     Drilling operation using the hammer drill  1  will be described. When performing drilling using the hammer drill  1 , a user firstly holds the side handle  13  and handle portion  10  with both hands and pulls the trigger  12 . Thus, an electrical power is supplied to the motor to drive the motor. The motive energy of the motor is transmitted by the rotation transmission mechanism including the motor pinion gear  22 , first gear  31 , intermediate shaft  32 , gear section  32 A, second gear  33 , and the like to the end tool  60  as a rotation force. Although the friction loss of the driving force is reduced since the grease is supplied to the respective gears, a slight friction occurs and the friction is converted into heat energy to generate heat. Further, the rotation force is converted into a reciprocation force through the motion conversion section  40  to allow the piston  42  and intermediate member  45  to generate striking force. In this case, the air is compressed in the air chamber  44  in the piston  42  to generate heat of compression, and a part of kinetic energy by the impact of the striker  43  against the intermediate member  45  is converted into heat energy to generate heat. 
     These heat generation factors heats the inside of the gear housing  30 , with the result that the encapsulated grease becomes feverish. The grease becomes feverish, thereby increasing its fluidity. Further, since the air exists in the gear housing  30 , the volume of the air is expanded when the gear housing  30  is heated. Air-tightness is secured at the respective seal portions, so that the heated and expanded air is discharged to the atmosphere through the communication passage  50   a  permitting communication between the speed reduction chamber  30   a  and the atmosphere. 
     Since the fluidity of the grease in the gear housing  30  is increased, it is likely that the grease is adhered to the first passage forming component  51  and enters into the communication passage  50   a  through the front opening of the first passage forming component  51 . However, since the first passage forming component  51  is made from rubber material and has the constriction shape, the first passage forming component  51  vibrates like a pendulum by vibrations generated from the driving of the gears and the like and the reciprocation motion of the piston  42 . A position where the first passage forming component  51  is mounted on the second passage forming component  52  is served as a fulcrum for the vibration of the first passage forming component  51 . The front opening of the communication passage  50   a  (the first passage forming component  51 ) that opens to the speed reduction chamber  30   a  is formed on the leading end section of the first passage forming component  51  having the constriction shape. The position at which the front opening is formed is the most vibrating position in the first passage forming component  51 . Hence, even if the grease is adhered to near the front opening of the first passage forming component  51  by increasing the fluidity of the grease due to the application of the heat in the drilling operation, the adhered grease is shook off from the first passage forming component  51  due to the vibration of the first passage forming component  51  caused by the vibration in the drilling operation. Accordingly, the entering of the grease from the front opening of the communication passage  50   a  to inside thereof can be avoided. 
     The heated air in the gear housing  30  contains grease component. Since the filter  53  is provided on the communication passage  50   a , the grease component is trapped by the filter  53  when the air containing grease component is entered into the filter  53 . Therefore, the leakage of the grease component to the atmosphere can be avoided 
     After stopping operation of the hammer drill  1 , the speed reduction chamber  30   a  and the like are subjected to natural cooling to cool the internal air, resulting in the reduction in the volume of the air. As a result, the speed reduction chamber  30   a  assumes a negative pressure to allow the outside air to flow into the speed reduction chamber  30   a  through the filter  53  and communication passage  50   a . At this time, the grease component adhered to the filter  53  can be given back into the speed reduction chamber  30   a  together with the outside air. As a result, clogging of the filter  53  hardly occurs and, therefore, the filtration capability of the filter  53  can be maintained over prolonged period of time. 
     While the invention has been described in detail and with reference to specific embodiments thereof, it would be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit and scope of the invention. For example, as shown in  FIG. 4 , an extending section  151 B may be in a substantially conical shape. That is, a cross-section perpendicular to a direction in which the extending section  151 B extends from the mounted section  51 A, of the extending section  151 B has an outer diameter that gradually increases toward the leading end side (front side) of the extending section  151 B. 
     With this structure, a fulcrum portion for the vibration in the first passage forming component  51  becomes thinner than the leading end portion of the first passage forming component  51  and a weight of the leading end portion of the first passage forming component  51  is increased. Hence, the grease adhered to the first passage forming component  51  can be shook off in more certainty. Further, the extending section  151 B may be in a pyramidal shape, instead of the conical shape. If the extending section  151 B is in the pyramidal shape, a vibration direction of the extending section  151 B can be defined. 
     As shown in  FIG. 5 , the first passage forming component  51  has a first inner wall surface  51 F that defines the first passage  51   b . The first inner wall surface  51 F may be configured such that the inner diameter of the first passage  51  gradually increases toward the leading end side (front side) in a protruding direction of the pressure adjusting mechanism  50 . 
     With this structure, the first inner wall surface  51 F has an ascending slope section from the front side to the second passage forming component  52  side (rear side). Accordingly, if the grease enters the communication passage  50  and is adhered to the inner wall surface  51 F, the movement of the grease from the first passage  51   b  to the second passage  52   a  can be restrained. 
     As another configuration of the first inner wall surface having the rising slope, as shown in  FIG. 6 , a first inner wall surface  151 F may have a stepped portion rising from the first passage forming component  51  side to the second passage forming component  52  side. With this structure, the grease that moves toward the second passage  52   a  on the first inner wall surface  151 F is blocked by the stepped portion of the first inner wall surface  151 F, thereby preventing the grease from moving from the first passage  51   b  to the second passage  52   a  more certainly. 
     As shown in  FIG. 7 , the first inner wall surface  251 F may have a concave/convex portion having annular projections and annular recesses alternately arrayed from the front opening to rear opening of the first passage  51   b.    
     With this structure, if the grease enters the communication passage  50  (the first passage  51   b ) and is adhered to the inner wall surface  51 F, the movement of the grease to the second passage forming component  52  can be prevented by the concave/convex portion. Further, the grease adhered to the inner wall surface  51 F mostly remains in the concave portion. Hence, even if the grease is adhered to the inner wall surface  51 F, the reduction of the cross-sectional area of the first passage  51   b  can be avoided. Accordingly, the reduction of the air passage section of the communication passage  50   a  can be restrained, thereby stabilizing the pressure in the pressure reduction chamber  30   a . Note that, the concave/convex portion may be formed on an inner wall (second inner wall surface) that defines the second passage  52   a , instead of or in addition to the first inner wall surface  51 F. 
     As shown in  FIG. 8 , the second passage  52   a  may includes a bending passage  52   c  at the open portion of the second passage  52   a  that communicates with the first passage  51   b . The bending passage  52   c  opens to a direction perpendicular to a direction from the first passage  51   b  to the second passage  52   a . The bending passage  52   c  opens to a downside at the side surface part and the vicinity of the leading end of the second passage forming component  52 . A gap is formed between the vicinity of the leading end of the second passage forming component  52  and the inner surface of the mounted section  51 A that defines the holding space  51   a.    
     With this structure, the communication passage  50   a  has a bending section at a boundary between the filter  53  and the second passage  52   a . Even if the grease absorbed in the filter  53  flows to the second passage  52   a  side due to grease saturating in the filter  53 , the grease collides against the bending section of the bending passage  52   c  and flows on the surface of the bending section. Hence, the leakage of the grease to the outside can be delayed. The delay effect can be improved by increasing the number of bending times. The bending section may be formed on the first passage  51   b.    
     As shown in  FIG. 9 , a second passage forming component  152  may be provided independently of the gear housing  30 . In this case, the gear housing  30  is formed with a mounting hole  30   b  for mounting a second passage forming component  152 . The mounted portion  152 A of the second passage forming component  152  is mounted on the mounting hole  30   b  to fix the second passage forming component  152  to the gear housing  30 . Since a second passage  152   a  opens at the mounted portion  152 A, the insertion and fixing of the mounted portion  152 A to the mounting hole  30   b  allows the second passage  152   a  to communicate with the atmosphere. The second passage forming component  152  is configured to gradually enlarge its external dimension toward the leading end of the second passage forming component  152 . On the other hand, the mounted section  151 A of the first passage forming component  151  has an inner diameter of the holding space  151   a  that is gradually decreasing toward the rear end of the mounted section  151 A. With this structure, the mounted section  151 A is firmly engaged with the second passage forming component  152 , thereby restraining the disengagement of the first passage forming component  151  from the second passage forming component  152 . Since the second passage forming component  152  is provided independently of the gear housing  30 , the manufacture of the gear housing  30  can be simplified. For example, if the gear housing  30  is produced by a casting, a casting die can be simplified. The second passage forming component  152  can be mounted on the gear housing  30  by forming the mounting hole  30   b  on a conventional gear housing. 
     A shown in  FIG. 10 , a bending passage  152   c  may be formed on the second passage forming component  152  in the same manner as the second passage forming component  52  shown in  FIG. 8 . With this structure, since the second passage forming component  152  is provided independently of the gear housing  30 , the second passage  152   a  and the bending passage  152   c  can be easily formed. 
     Note that, the second passage forming component  152  shown in  FIGS. 9 and 10  needs not to be made from metal similar to the support member  30 A. For example, the second passage forming component  152  may be made from rubber material similar to the first passage forming component  51 . Since the second passage forming component  152  is made from rubber material, the base section of the second passage forming component  152  is served as a fulcrum for the vibration of the pressure adjusting mechanism  50 . Hence, the whole pressure adjusting mechanism  50  can be vibrated in the drilling operation. Accordingly, the grease adhered to the opening of the communication passage  50   a  that is located at the speed reduction chamber  30   a  side can be shook off more appropriately in comparison with a case where only the first passage forming component  51  vibrates. Further, if the second passage forming component  152  is made from rubber material, the first passage forming component  51  does not necessarily have to be made from rubber material. Further in the above embodiments, the power tool is the hammer drill  1 . However, the present invention can be applied to the power tool having a structure that encloses the grease.