Abstract:
In a DC power source unit that can selectively charge a battery pack and supply DC power to a cordless power tool through an adaptor shaped like the battery pack, a battery pack insertion space, into which the battery pack is inserted to charge, is substantially sealed or closed so as not to be in fluid communication with the inner space in which the circuit components are disposed. Cooling air for cooling the circuit components are not disturbed by disturbing air flow which may otherwise be created if the battery pack insertion space is not sealed.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a DC power source unit that can selectively charge a battery pack, which is used as a power source for a cordless power tool, and supply DC power to the cordless power tool through an adaptor shaped like the battery pack. 
     2. Description of the Related Art 
     Cordless power tools are convenient because they can be used anywhere without being restricted by the length of a power cable. However, because the capacity of the battery is limited, the length of time that the power tool can be used is also limited. U.S. Pat. No. 6,172,860 (corresponding to DE-OS 19844426 A1) and Japanese Patent Publication (A) No. 11-101836 (corresponding to a co-pending U.S. application Ser. No. 09/478,798) disclose DC power source units that can be used for cordless power tools, in which DC power is continuously supplied to the power tool via an adapter. The DC power source unit can be used along with the battery pack. 
     Japanese Patent Publication (A) No. 2000-184614discloses a DC power source unit with a battery pack charging function, which will be described in more detail while referring to FIG. 1. A power tool  20  is operable with a battery pack  19  that has a shape insertable into a handgrip of the power tool  20 . The power tool  20  is also operable with an adapter  18  that has a substantially same shape as the battery pack  19 . The adapter  18  is connected to a DC power source unit  17  via a cord  22 , and the DC power source unit  17  is connected, while in use, to a commercial AC power source via a cord  15  and a plug  14 . The DC power source unit  17  supplies DC power to the power tool  20  when the adapter  18  is used instead of the battery pack  19 . 
     The DC power source unit  17  is accommodated in a rectangular box having a top wall, side walls, and a bottom wall. The top wall is formed with a battery pack insertion hole  8 , into which the battery pack  19  is inserted for charging. 
     The DC power source unit  17  is being operated not only during charging the battery pack  19  but also during supplying DC power to the power tool  20 . Accordingly, a large amount of heat is generated from the circuit components contained in the DC power source unit  17 , however, no proposal has ever been made for dissipating the heat. 
     SUMMARY OF THE INVENTION 
     The most conceivable solution for dissipating the heat and cooling the circuit components in the DC power source unit would be providing a cooling system. If, as shown in FIG. 2, cooling air inlet holes  3  are formed in one side wall of the rectangular box  7 , air outlet holes  21  in the opposite side wall, and a cooling fan  1  is fixed to the inner surface of the side wall in which the air outlet holes  21  are formed, then circuit components  25  mounted on fins  2  would be cooled by air introduced from the air inlet holes  3   
     However, the air flows through the box  7  in different patterns depending upon whether or not the battery pack  19  is inserted into the insertion hole  81  because terminal holes  4  are formed in positions below the battery pack insertion hole  8 . When the battery pack  19  is not inserted into the insertion hole  8 , the air Introduced through the battery pack insertion hole  8  and the terminal holes  4  flows in patterns  6  out through the air outlet holes  21  in addition to the air introduced through the air inlet holes  3  and flows in pattern  5 . 
     On the other hand, insertion of the battery pack  19  into the insertion hole  8  closes the terminal holes  4 , thereby interrupting air flowing in patterns  6 . In this condition, air flowing in patterns  5  effectively cools down the circuit components  25 . The air flowing in patterns  6  disturbs the air flowing in patterns  5  and thus lowers the cooling effect attained by the air flowing in patterns  5 . 
     In view of the foregoing, it is an object of the invention to assure cooling of circuit components contained in a DC power source unit regardless of whether or not a battery pack is inserted into an insertion hole. 
     To achieve the above and other objects, there is provided a DC power source unit that is capable of maintaining air flow generated by a cooling fan unchanged regardless of whether or not the battery pack is accommodated in the battery pack insertion hole. The housing is formed with an air inlet portion and an air outlet portion, preferably in a confronting relation. The housing is further formed with a battery pack insertion hole. There is provided means for defining a battery pack accommodating space for accommodating a battery pack inserted from the battery pack insertion hole. A substrate is disposed inside the housing. Circuit components are mounted on the substrate and disposed in the main inner space of the housing that is different from the battery pack accommodating space. The circuit components are mutually connected together to generate charging power to be supplied to the battery pack and DC power to be supplied via an adapter to the power tool for driving. The battery pack is used as an alternative power source of the power tool and charged by the charging power when inserted from the battery pack insertion hole and accommodated in the battery pack insertion space. Air flow generating means, such as a cooling fan, is disposed in the main space for generating air flow to cool down the circuit components. Air flow maintaining means is provided for maintaining the air flow at substantially constant regardless of whether or not the battery pack is accommodated in the battery pack accommodating space. The air flow maintaining means maintains a speed of the air flow at substantially constant and also maintains a volume of air per a unit time at substantially constant. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects, features and advantages of the invention will become more apparent from reading the following description of the embodiment taken in connection with the accompanying drawings in which: 
     FIG. 1 is a perspective view showing a power tool, a battery pack, and a conventional DC power source unit with a charging function; 
     FIG. 2 is a cross-sectional top view showing the inner arrangement of the DC power source unit shown in FIG.  1  and illustrating patterns in which cooling air flows; 
     FIG. 3 is a vertical cross-sectional view showing the inner arrangement of the DC power source unit according to a first embodiment of the invention; and 
     FIG. 4 is a vertical cross-sectional view showing the inner arrangement of the DC power source unit according to a second embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A first preferred embodiment of the invention will now be described with reference to FIG.  3 . 
     The DC power source unit has a battery charging function and a DC power generating function. The battery pack  19  as shown in FIG. 1 is used as a power source of the cordless power tool and charged by the DC power source unit. The DC power source unit can also supply DC power to the power tool through an adapter as described with reference to FIG.  1 . 
     The outer appearance of the DC power source unit according to the first embodiment is substantially the same as that of the conventional DC power source unit shown in FIG.  1 . That is, the housing  7  of the DC power source unit of the first embodiment is also substantially in a rectangular box shape. The upper wall of the housing  7  is formed with a battery pack insertion hole  5 . Although not shown in FIG. 3, the side wall of the housing  7  is formed with air inlet holes and air outlet holes in a confronting relation similar to that shown in FIG. 1. A substrate  10  is disposed on the bottom wall of the housing  7 . 
     The battery pack insertion hole  8  is substantially an elongated circular shape slightly larger than and similar to the cross-sectional shape of the leg portion of the battery pack  19 . The battery pack  19  can only be inserted into the insertion hole  8  when oriented in a predetermined direction. That is, the shape of the battery pack insertion hole  8  does not allow the battery pack  19  to insert with different orientation. 
     A compartment wall  9  extends vertically downwardly from the battery pack insertion hole  8 . A compartment bottom wall  26 , which extends horizontally from the lower end of the compartment wall  9 , is formed integral with the compartment wall  9 . The compartment wall  9  and the compartment bottom wall  26  define a battery pack accommodating space which occupies a part of the inner space of the housing  7 . Thus, the vertical length of the compartment wall  9  is substantially equal to the length of the leg portion of the battery pack  19 . 
     Typically, four electrode engagement holes  4  are formed in the lower portions of the battery pack accommodating space. A recess formed in the lower portion of the compartment wall  9  and a cut-away portion in the bottom wall  26  form each electrode engagement hole  4 . The electrode engagement holes  4  allow terminals  11  derived from the substrate  10  to pass through and penetrate into the battery pack accommodating space. The electrodes of the battery pack inserted into the battery pack insertion hole  8  are brought into contact with the corresponding terminals  11  in the battery pack accommodating space. The electrodes on the battery pack include positive and negative electrodes of the battery and electrodes of thermistor and thermostat. The thermistor and thermostat provide information about the temperature of the battery, based on which whether the battery pack is fully charged or not is determined. 
     A cylindrical-shape shielding wall  12  joins the lower portion of the compartment wall  9  and further extends vertically downwardly to a position just above the substrate  10 . The housing  7 , the compartment wall  9 , and the shielding wall  12  are integrally formed. 
     The terminals  11  derived from the substrate  10  penetrate into the battery pack accommodating space through the electrode engagement holes  4 . The terminals  11  protrude horizontally inward and are exposed in the battery pack accommodating space to enable connection with the corresponding electrodes of the battery pack  19 . 
     A cooling fan  1  is disposed in the inner space of the housing  7  and generates air flow to most effectively cool down circuit components  25  mounted on the substrate  10  and a cooling fin  2 . The shielding wall  12  and the substrate  10  interrupt the air flow patterns which would otherwise be created in the space between the electrode engagement hole  4  and the cooling fan  1 . 
     The circuit components  25  are mutually connected together to generate charging power to be supplied to the battery pack and DC power to be supplied to the cordless power tool via a cord  22  and the adapter. 
     With the internal structure of the DC power supply unit, air flow generated by the cooling fan  1  remains substantially unchanged regardless of whether or not the battery pack is accommodated in the battery pack insertion space. More specifically, a speed of the air flowing in the internal space of the housing  7  is maintained at substantially constant. Also, the volume of air per a unit time is maintained at substantially constant. Accordingly, a small-size cooling fan  1  suffices to cool the circuit components. As a result, the DC power source unit per se can be compact in size and manufactured at low cost. 
     Next, a second embodiment of the invention will be described with reference to FIG.  4 . The second embodiment differs from the first embodiment in that a cylindrical flow shielding member  13  is force-fitted to the lower end and outer periphery of the compartment wall  9 . The flow shielding member  13  has a vertical length longer than the distance from the upper surface of the substrate  10  and the lower end of the compartment wall  9 . Desiccating agent is coated on the surface of the substrate  10  to maintain a dry condition. The overall thickness of the substrate  10 , including the thickness of the desiccating agent coating layer, varies at the time of manufacturing. However, this variation in the thickness of the substrate  10  can be compensated for by the flow shield member  13 . 
     Although the present invention has been described with respect to specific embodiments, it will be appreciated by one skilled in the art that a variety of changes may be made without departing from the scope of the invention. For example, the flow shield  13  as employed in the second embodiment of the invention can be in the form of bellows with soft resiliency. By urging such flow shield against the substrate  10 , the air flowing through the terminal holes  4  can be completely closed. Further, the substrate  10  has been described to be placed on the bottom wall of the housing  7 , it can be placed anywhere as far as the mounting place is inside the housing  7 . The place where the cooling fan  1  is set is not restricted either. 
     As described, the terminal holes formed in the lower portions of the battery pack insertion space are shielded or closed, cooling air introduced from the air inlet holes into the housing  7  and discharged out to the housing  7  through the air outlet holes is not affected regardless of whether or not the battery pack is inserted Into the insertion hole  8 . That is, the speed of the cooling air is not lowered and the amount of cooling air is not reduced as a result of shielding effects. Accordingly, cooling the circuit components is assured with the cooling system.