Motor-fan assembly and combustion-type power tool employing the same

MOTOR-FAN ASSEMBLY AND COMBUSTION-TYPE POWER TOOL EMPLOYING THE SAME

BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention

[0002] The present invention relates to a motor-fan assembly and a combustion-type power tool, such as nail gun, employing the same.

[0003] 2. Description of the Related Art

[0004] A fan for agitating a gaseous matter or mixing two or more kinds of gaseous matters has been used in a variety of situations. Typically, a motor is a source for driving the fan. Attachment of the motor shaft to the fan has conventionally been made as shown in FIG. 1.

[0005] FIG. 1 is a partial cross-sectional view showing a conventional motor-fan assembly. A motor 9a is accommodated in a casing 9c. The casing 9c is formed with a hole 9d for allowing the motor shaft 9b to pass therethrough. The motor shaft 9b protrudes outward from the casing 9c through the hole 9d. A fan 8 is fixedly attached to the tip end portion 9e of the shaft 9b. The tip end portion 9e of the shaft 9b has a D-shaped cross-section. Specifically, a flat portion 9/ is formed on the outer periphery of the shaft 9b to extend in a longitudinal direction of the shaft 9b.

[0006] As best shown in FIG. 8, the fan 8 has a hub

portion 8b and a plurality of blades 8a (four in the illustrated example) extending radially outwardly from the hub portion 8b and also equally angularly spaced apart from one another around the hub portion 8b. A center hole 8c is formed in the hub portion 8b.

[0007] A connection block 11 is used to connect the motor shaft 9b and the fan 8. FIGS. 2 through 5 show the connection block 11, in which FIG. 2 is a top view, FIG. 3 is a cross-sectional view cut along the line III-III in FIG. 2, FIG. 4 is a side view, and FIG. 5 is a bottom view. The connection block 11 is an intermediate member disposed between the motor shaft 9b and the fan 8. Specifically, the motor shaft 9b is secured to the connection block 11 and the fan 8 is fixed to the connection block 11.

[0008] As shown in FIGS. 2 and 3, a through-hole 11a is formed in the connection block 11 for allowing the motor shaft 9b to be inserted thereinto. A lateral hole lid is also formed in the connection block 11. The lateral hole lid is open to the outer periphery of the connection block 11 and extends perpendicular to the direction in which the throughhole 11a extends. The lateral hole lid extends to reach the through-hole 11a. A female screw lib is threaded in the inner periphery of the hole lid so that a male screw 12 can threadingly engage the female screw lib as shown in FIG. 1.

[0009] To assemble the motor 9 and the fan 8 using the connection block 11, the fan 8 is firstly attached to the connection block 11 by caulking. FIG. 6 shows the fan 8 and the connection block 11 before caulking, FIG. 7 shows the fan 8 and the connection block 11 after caulking. FIG. 8 is a bottom view showing the fan 8 caulked to the connection block 11. As shown in FIGS. 3 and 8, the connection block 11 is provided with a plurality of caulking pieces 11c (eight in the illustrated example) at the lower peripheral portion of

the connection block 11. The caulking pieces 11c are equally angularly spaced apart from one another around the lower periphery of the connection block 11. As shown in FIG. 6, to place the connection block 11 and the fan 8 in an assembling state, the caulking pieces 11c are slided down along the inner wall of the center hole 8c of the hub portion 8b until the caulking pieces 11c protrude outwardly from the center hole 8c. Then, the caulking pieces 11 are bended radially outwardly, whereby the fan 8 is attached to to the connection block 11.

[0010] To attach the motor shaft 9b to the connection block 11 with the fan 8 attached thereto, the motor shaft 9b is inserted into the through-hole 11a of the connection block 11 while directing the flat portion 9/ of the motor shaft 9b toward the lateral hole lid. The male screw 12 is threadingly engaged with the female screw lib formed in the lateral hole lid. The male screw 12 is advanced deeper until the tip end thereof is brought into abutment with the flat portion 9/ of the shaft 9b. Abuttment of the male screw 12 with the flat portion 9/ fixedly attaches the motor shaft 9b to the connection block 11 and prevents the motor shaft 9b from detaching from the connection block 11 during rotation.

[0011] One problem with the above-described conventional motor-fan assembly is that formation of the flat portion 9/ on the motor shaft 9b requires a special machining, which causes an increase of cost in manufacturing the assembly. Another problem is that the male screw 12 and the lateral hole lid for accepting the male screw 12 are unsymmetrical elements in the assembly, causing rotational balance of the fan 8 to degrade When vibrations of the motor shaft 9b occur as a result of the rotational imbalance of the fan 8, the motor shaft 9b may contact the hole 9d of the motor casing 9c during rotation As a result, the service life of the motor 9a is shortened.

SUMMARY OF THE INVENTION

[0012] The present invention has been made to solve the aforementioned problems, and accordingly it is an object of the invention to provide a stably operable motor-fan assembly.

[0013] Another object of the invention is to provide a motor-fan assembly having a prolonged service life.

[0014] Still another object of the invention is to provide a motor-fan assembly that can be manufactured at a low cost.

[0015] To achieve the above and other objects, there is provided a motor-fan assembly that includes a motor, a fan, and a connection rod. The motor has a shaft that extends in a first direction and outputs rotational force. The connection rod connects the shaft of the motor to the fan. A cross-section of the shaft of the motor and the connection rod cut along the imaginary longitudinal axis is symmetrical in shape with respect to the imaginary longitudinal axis.

[0016] It is desirable that the connection rod have a circular cross-section anywhere along an entire length of the connection rod. The circular cross-section appears when the connection rod is cut along a line extending in a second direction perpendicular to the first direction.

[0017] It is also desirable that the connection rod be formed with a hole in coaxial with the imaginary longitudinal axis, and the shaft of the motor is force-fitted into the hole of the connection rod to thereby secure the shaft of the motor to the connection rod. Alternatively, the shaft of the motor may be loosely inserted into the hole of the connection rod and secured to the connection rod with an adhesive material.

[0018] First and second tightening members both engageable with the connection rod may further be provided to secure the fan to the connection rod. In a state where the shaft of the motor is inserted into the center hole formed in the hub portion of the fan, the first tightening member engaged with the connection rod at one side of the hub portion and the second tightening member engaged with the connection rod at another side of the hub portion are moved toward each other with the hub portion interposed therebetween, thereby securing the fan to the connection rod.

[0019] The connection rod, the first tightening member, and the second tightening member are made from the same material which may be steel.

[0020] According to another aspect of the invention, there is provided a connector for connecting a motor shaft to a fan. The connector includes a connection rod, and first and second tightening members. The connection rod has an imaginary longitudinal axis extending in a first direction, and a circular cross-section anywhere along an entire length of the connection rod. The circular cross-section appears when the connection rod is cut along a line extending in a second direction perpendicular to the first direction. The connection rod includes a first part formed with a hole in coaxial with the imaginary longitudinal axis for receiving the motor shaft, and a second part formed at least partially with an engaging portion. The first tightening member is engageable with the engaging portion of the second part, and the second tightening member also engageable with the engaging portion of the second part, wherein the first tightening member and the second tightening member are used to attach the fan to the connection rod.

[0021] The motor-fan assembly and connector as described above are particularly advantageous when used in a combustion-type power tool.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] 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:

[0023] FIG. 1 is a partial cross-sectional view showing a conventional motor-fan asseembly;

[0024] FIG. 2 is a top view showing a connection block used in the assembly shown in FIG. 1;

[0025] FIG. 3 is a cross-sectional view cut along the line III-III in FIG. 2;

[0026] FIG. 4 is a side view showing the connection block shown in FIG. 2;

[0027] FIG. 5 is a bottom view showing the connection block shown in FIG. 2;

[0028] FIG. 6 is a cross-sectioanl view showing a fan unit and a connection block that are used in the assembly shown in FIG. 1;

[0029] FIG. 7 is a cross-sectional view showing an assembled fan unit and connection block;

[0030] FIG. 8 is a bottom view showing the assembled fan unit and connection block shown in FIG. 7;

[0031] FIG. 9 is a cross-sectional view cut along the line IX-IX in FIG. 1;

[0032] FIG. 10 is a cross-sectional view showing a motorfan assembly according to an embodiment of the invention;

[0033] FIG. 11 is a side view showing a motor employed in the assembly shown in FIG. 10;

[0034] FIG. 12 is a partial cross-sectional view showing a connection rod used in the assembly shown in FIG. 10;

[0035] FIG. 13 is a front view showing a nut used in the assembly shown in FIG. 10;

[0036] FIG. 14 is a front view showing a fan used in the assembly shown in FIG. 10;

[0037] FIG. 15 is a cross-sectional view cut along the line XV-XV in FIG. 14 and

[0038] FIG. 16 is a cross-sectioan view showing an essential portion of a combustion-type nail gun.

DETAILED DESCRIPTION OF THE
PREFERRED EMBODIMENTS

[0039] A motor-fan assembly according to a preferred embodiment of the invention will be described with reference to FIGS. 10 through 15.

[0040] As shown in FIG. 10, the motor-fan assembly according to the embodiment of the invention includes a motor 9a, a fan 15, a connection rod 13, a first nut 14a serving as a tightening member, and a second nut 14b serving as the tightening member in cooperation with the first nut 14a. In the illustrated embodiment, a casing 9c accommodates the motor 9a. As shown in FIG. 11, the motor 9a has a rotating shaft 9b for outputting a rotational force of the motor 9a. Unlike the conventional shaft shown in FIG. 1, the shaft 9b according to this embodiment is not formed with a flat portion that extends in the longitudinal direction but a rod-like member having a circular crosssection anywhere along the entire length of the shaft 9b. The casing 9c is formed with a hole 9d from which the shaft 9b penetrates out to the casing 9c.

[0041] The connection rod 13 has a circular cross-section anywhere along the entire length thereof. The circular crosssection appears when the connection rod 13 is cut along a line extending in a direction perpendicular to the axial direction of the connection rod 13. As shown in FIG. 12, the connection rod 13 includes a first part "A" formed with a hole 13fc in coaxial with the longitudinal axis of the rod 13, and a second part "B" formed at least partially with a male screw portion 13a.

[0042] As shown in FIG. 13, first and second nuts 14a , 14fc are used in conjunction with the connection rod 13 to connect the motor shaft 9b to the fan 15. Both the first and second nuts 14a , 14fc are formed with female screw portions that are threadingly engageable with the male screw portion formed in the second part "B" of the connection rod 13 shown in FIG. 12.