EP2130651A1

EP2130651A1 - Percussion tool

Info

Publication number: EP2130651A1
Application number: EP08711844A
Authority: EP
Inventors: Yonosuke Aoki
Original assignee: Makita Corp
Current assignee: Makita Corp
Priority date: 2007-03-26
Filing date: 2008-02-22
Publication date: 2009-12-09
Anticipated expiration: 2028-02-22
Also published as: EP2130651B1; EP2130651A4; RU2477212C2; RU2009139226A; WO2008126480A1

Abstract

Vibration entailed during a striking operation of an impact tool is reduced thereby achieving improved operability and workability. In a hammer drill (1), between a reduction shaft (32) configured to transmit a rotatory motion to a tool holder (7) and an output shaft (9), an intermediate reduction shaft (31) configured to reduce a rotation speed of a rotatory motion of the output shaft (9) and transmit a speed-reduced rotatory motion to the reduction shaft (32) is disposed in a position frontward of the output shaft (9) and parallel to the output shaft (9), so that the reduction shaft (32) is disposed frontward of the intermediate reduction shaft (31), whereas a motor (8) is disposed in a position such that the output shaft (9) protrudes upward beyond a third gear (37) of the reduction shaft (32), whereby the motor (8) is positioned closer to the axis of the tool holder (7). Thus, the barycenter of the hammer drill (1) is in a position shifted frontward and upward, with the result that the moment to be produced around a tip end of a bit (20) in the hammer drill (1) during a drilling or other operation will become small.

Description

TECHNICAL FIELD

This invention relates to an impact tool such as an electric hammer, a hammer drill, and the like.

BACKGROUND ART

To give an example of a hammer drill, Patent Document 1 discloses one known type such that within a housing, a tool holder having a bit-installable front end is rotatably supported, a motor is disposed with an output shaft thereof oriented in a direction perpendicular to an axis of the tool holder, and an impact mechanism is provided which comprises a piston configured to make a reciprocating motion by means of a crank mechanism actuated according to a rotation of the output shaft and an impactor configured to move in synchronization with the piston by the action of an air spring. In this hammer drill, a shaft (reduction shaft) provided with a torque limiter which enables transmission of a rotatory motion of the motor to the tool holder within a predetermined torque is rotatably supported in a position parallel to the output shaft between the tool holder and the motor, and a switch mechanism configured to permit selection of ON and OFF of the transmission of the rotatory motion from the output shaft is provided to this shaft.
With this configuration, upon activation of the motor, the piston is caused to reciprocate by means of the crank mechanism, and the impactor synchronized with the piston strikes a bit indirectly through an interjacent element such as an impact bolt. On the other hand, the rotatory motion of the motor is transmitted to the tool holder through the shaft, and thus the rotatory motion, as well, is imparted to the bit so that the tool can be used in a hammer drill mode. When the switch mechanism is actuated to interrupt the transmission of the rotatory motion to the shaft, a striking motion only is imparted to the bit so that the tool can be used in a hammer mode.
It is often the case with this type of the impact tool that the output shaft and the impact mechanism are enclosed with an inner housing comprised of a gear housing or the like disposed inside the housing to form an impact unit which is sealed and filled with oil in order to ensure that the impactor can be moved smoothly. However, the pressure rise caused by the temperature rise inside the sealed impact unit in conjunction with the striking motion, would disadvantageously cripple an expected normal set operation of the air spring between the piston and the impactor, with the result that the impactor could not make an adequate striking operation and/or leakage of oil along with air from a sealed portion thereof might occur.
With this in view, Patent Document 2 proposes that an air chamber connected only with the outside of the impact unit and having a volume rendered variable by a diaphragm be formed in the inner housing so that reduction in volume of the air chamber can abate the increase in pressure inside the impact unit. Patent Document 3 discloses an arrangement in which a casing comprising a pressure equilibrating chamber in communication with the inside of the impact unit and a pressure equilibrating tube in communication with the ambient atmosphere while blocking the oil from flowing out is mounted to a sealed impact unit so that a differential pressure between the inside and the outside of the impact unit is cancelled by using the pressure equilibrating chamber.

Patent Document 1: JP 9-57511 A
Patent Document 2: JP 2004-351595 A
Patent Document 3: JP 4-6506 B

DISCLOSURE OF INVENTION

Problems to be solved by the invention

The above-described conventional hammer drill has the motor, the crank mechanism and the shaft which are disposed in a rear-side space of the housing, and thus its barycenter is located off-center to a rear side thereof. As a result, the moment produced in the hammer drill around the center of the front end of the bit when a drilling or other operation is carried out becomes so great that vibration entailed during the striking operation increases, thus, making an operator uncomfortable, impairing easy operability and workability as the case may be.
On the other hand, in the arrangement as disclosed in Patent Document 2 or 3, an additional casing for forming an air chamber or a pressure equilibrating chamber should be mounted to the impact unit. This increases the number of parts, makes a tool structure complicated, and upsizes the housing to make space for mounting the casing, all of which would lead to an undesirable increase in cost.
Therefore, it is an object of the present invention to provide an impact tool in which the vibration entailed during the striking operation can be reduced to improve operability and workability, while air inside the impact unit can be released easily and reliably without causing oil leakage.

Means for solving the problems

In order to achieve the above object, the invention as set forth in claim 1 provides that a tool holder has a front end configured to hold a bit, a motor having an output shaft is disposed rearward of the tool holder with the output shaft oriented in a direction perpendicular to an axis of the tool holder, an impact mechanism comprises a piston and an impactor, the piston is configured to make a reciprocating motion by means of a crank mechanism actuated according to a rotation of the output shaft, the impactor is configured to move in synchronization with the piston by an action of an air spring, a reduction shaft is disposed in a position parallel to the output shaft between the output shaft and the tool holder, the reduction shaft comprises a driven gear and a bevel gear, the driven gear is configured to receive a rotatory motion transmitted from the output shaft, the bevel gear is configured to transmit the rotatory motion to the tool holder, an intermediate reduction shaft is disposed in a position frontward of the output shaft, rearward of the reduction shaft and parallel to the output shaft, the intermediate reduction shaft is configured to reduce a rotation speed of the rotatory motion transmitted from the output shaft and transmit a speed-reduced rotatory motion to the reduction shaft, and the motor is disposed in a position such that the output shaft protrudes upward beyond the driven gear of the reduction shaft, whereby the motor is positioned closer to the axis of the tool holder.
In order to achieve the above object, the invention as set forth in claim 8 provides that a housing has a front end configured to hold a bit, a motor having an output shaft is disposed in a rear space of the housing with the output shaft oriented in a direction perpendicular to an axis of the bit, an impact mechanism comprises a piston and an impactor, the piston is configured to make a reciprocating motion by means of a crank mechanism actuated according to a rotation of the output shaft, the impactor is configured to move in synchronization with the piston by an action of an air spring, an inner housing is provided inside the housing to define a sealed space in which an impact unit comprising the output shaft and the impact mechanism is provided, a proximity portion having an inner surface proximate to an end face of a predetermined rotation shaft provided in the impact unit is formed in the inner housing, and a vent hole affording communication between an inside of the impact unit and an outside of the impact unit is formed in a surface of the proximity portion opposed to the end face of the rotation shaft.

Advantageous effects of the invention

According to the invention as set forth in claim 1, the reduction shaft is disposed frontward of the intermediate reduction shaft, and the motor is positioned closer to the axis of the tool holder, so that the impact tool has its barycenter shifted frontward and upward and thus attains an improved weight balance as a whole. As a result, the moment to be produced in the impact tool around a front end of the bit during a drilling or other operation will become small, and vibration entailed during a striking operation thereof is reduced thereby achieving improved operability and workability. Moreover, since the motor is in a position shifted closer to the axis of the tool holder, the tool may be rendered compact in its height direction.
Furthermore, if the intermediate reduction shaft optionally comprises a switch mechanism configured to permit selection of ON and OFF of transmission of the rotatory motion to the reduction shaft, then the switching operation can be performed easily at the switch mechanism as the switch mechanism is provided at the intermediate reduction shaft of which the torque applied thereto is smaller. In particular, if the reduction shaft optionally comprises a torque limiter, the switching operation can be performed prior to the application of impact (load) by the striking operation as the intermediate reduction shaft is located upstream of the reduction shaft, so that a good operability can be maintained.
According to the invention as set forth in claim 8, air inside the impact unit can be released reliably without causing oil leakage from the vent hole, and thus adequate lubrication can be maintained. Moreover, separation of air and oil is achieved by means of the rotation shaft, which provides a reasonable design utilizing the existing configurations; therefore, a fabrication step for providing means for releasing air can be minimized so that increase in cost and required space can be minimized, too.
In a particular embodiment that the rotation shaft is the output shaft of the motor, leakage of oil can more effectively be prevented as the most rapidly rotating output shaft is utilized.
Furthermore, if a protrusion and a recess are optionally provided at the end face of the rotation shaft and the surface of the proximity portion in which the vent hole is formed, the labyrinth seal formed by the protrusion and the recess can serve to more effectively prevent the leakage of oil.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be described hereinafter with reference to the accompanying drawings.
In FIG. 1, which shows a partial vertical section of a hammer drill as one example of an impact tool, a hammer drill 1 comprises an outer housing 2 and components housed therein which includes a rotation and impact unit 3 disposed in an upper space thereof and a motor 8 disposed rearward of the rotation and impact unit 3 in a lower space thereof, wherein the rotation and impact unit 3 has a tool holder 7 protruding frontward (leftward in the drawing), and the motor 8 has an output shaft 9 thereof oriented upward. The rotation and impact unit 3 is enclosed in, and defined by, an inner housing inside the outer housing 2, wherein the inner housing comprises a holder housing 4 in which the tool holder 7 is rotatably supported, a crank housing 5 which is disposed rearward of and coupled to the holder housing 4, and a gear housing 6 which is disposed below and coupled to the crank housing 5. The output shaft 9 of the motor 8 is rotatably supported by ball bearings 10 held at the bottom of the gear housing 6 and is inserted in the rotation and impact unit 3. Denoted by reference numerals 11 and 12 are seal rings which seal a protruded portion of the tool holder 7 and an inserted portion of the output shaft 9, respectively.
In a portion of the crank housing 5 right above the output shaft 9, as shown also in FIG. 2, a tubular proximity portion 14 is formed which has a through hole 13 extending laterally and tunneling through the rotation and impact unit 3 and of which an underside facing to an inside of the rotation and impact unit 3 is proximate to an end face of the output shaft 9. In a surface of the proximity portion 14 opposed to the end face of the output shaft 9, a vent hole 15 coaxial with the output shaft 9 is formed so that the through hole 13 connecting to an outside of the rotation and impact unit 3 is in communication with an inside of the rotation and impact unit 3. At a portion of the proximity portion 14 in which the vent hole 15 is formed, a protrusion 16 having a shape of a circular cone tapering toward the end face of the output shaft 9 is provided coaxially with the vent hole 15. At the end face of the output shaft 9, a recess 17 having a circular shape with an inverted tapered surface 18 provided at an open side thereof, contoured to fit the shape of the tapering of the protrusion 16 is provided. In this way, a labyrinth seal 19 is formed from around the output shaft 9 to the vent hole 15 in the rotation and impact unit 3.
On the other hand, the tool holder 7 has a front end configured to be able to hold a bit 20 fitted and installed therein, and incorporates an impact bolt 21 as an interjacent element which is disposed rearward of the bit 20 and configured to be movable frontward and rearward in a predetermined stroke. Denoted by reference numeral 22 is a bevel gear coupled to a rear end of the tool holder 7.
In the tool holder 7, a cylinder 23 held by the crank housing 5 is loosely inserted from rearward; inside the cylinder 23, a striker 24 as an impactor disposed frontward and a piston 26 disposed rearward of the striker 24 with an air chamber 25 interposed therebetween are housed, in a manner that renders them movable frontward and rearward, respectively. The piston 26 is connected via a connecting rod 27 to an eccentric pin 29 provided protrusively on an upper surface of the crank shaft 28. The crank shaft 28 is disposed rearward of the output shaft 9 and rotatably supported by the crank housing 5 and the gear housing 6 in a position parallel to the output shaft 9. A gear 30 provided at a lower portion of the crank shaft 28 is in mesh with the output shaft 9. In this way, a crank mechanism comprised of the connecting rod 27 and the crank shaft 28 can convert a rotatory motion of the output shaft 9 to a reciprocating motion of the piston 26.
An intermediate reduction shaft 31 is disposed below the tool holder 7 and frontward of the output shaft 9, and is rotatably supported in a position parallel to the output shaft 9, whereas a reduction shaft 32 is disposed frontward of the intermediate reduction shaft 31, and rotatably supported in a position parallel to the intermediate reduction shaft 31. At the outset, our discussion focuses on the intermediate reduction shaft 31, of which an upper end portion and a lower end portion are rotatably supported by ball bearings 33 held in the crank housing 5 and by needle bearings 34 held in the gear housing 6, respectively, and on which a first gear 35 is provided above and a second gear 36 is provided below so that the first gear 35 is in mesh with the output shaft 9 and the second gear 36 is in mesh with a third gear 37 which serves as a driven gear of the reduction shaft 32.
As described above, in this embodiment, a pinion of the output shaft 9 is in mesh with the first gear 35 provided on an upper portion of the intermediate reduction shaft 31, and the motor 8 is disposed in such a position that the output shaft 9 protrudes upward beyond the third gear 37 of the reduction shaft 32. In other words, the motor 8 is positioned closer to the axis of the tool holder 7.
It is however to be noted that the first gear 35 is fitted on the intermediate reduction shaft 31, rotatably relative to the intermediate reduction shaft 31, and a switch plate 39 having engageable teeth 40, 40, .. provided protrusively on an underside thereof and configured to be engageable with engageable recesses 38, 38, .. provided on an upper surface of the first gear 35 is provided in a position above the first gear 35 on, and coupled with splines of, the intermediate reduction shaft 31 so that the switch plate 39 is movable in an axial direction and rotatable integrally with the intermediate reduction shaft 31. The switch plate 39 is biased by a coil spring 41 toward a position in which the switch plate 39 engages with the first gear 35, and can be operated by manipulation of a switch member (not shown) provided at the outer housing 2 to slide to a position (right-hand position in FIG. 1) in which the switch plate 39 engages with the first gear 35 and to a position (left-hand position in FIG. 1) in which the switch plate 39 disengages from the first gear 35. In this way, a switch mechanism configured to permit selection of ON and OFF of transmission of the rotatory motion to the reduction shaft 32 is implemented.
Next, our discussion is directed to the reduction shaft 32, of which an upper end portion and a lower end portion are rotatably supported by ball bearings 42 held in the crank housing 3 and by ball bearings 43 held in the gear housing 6, respectively, and on which a bevel gear 44 is provided at an upper end thereof and meshed with the bevel gear 22 of the tool holder 7. The third gear 37 is fitted on, and configured to be rotatable independently from, the reduction shaft 32, and divided into an upper plate 45 meshed with the second gear 36 of the intermediate reduction shaft 31 and a lower plate 46 configured to rotate integrally with the reduction shaft 32. An engageable member 48 configured to be biased toward a radial direction of protrusion thereof by a coil spring 47 is provided on the lower plate 46, and engages with an engageable portion 49 provided on an inner side surface of the upper plate 45. In this way, a torque limiter is configured to transmit a rotatory motion of the second gear 36 to the reduction shaft 32 when the torque is not greater than such a magnitude that the engageable member 48 can be kept in engagement with the engageable portion 49 by the pressing force of the coil spring 47, and to cause the engageable member 48 to move away from the engageable portion 49 against the pressing force of the coil spring 47 to cause the upper plate 45 alone to rotate at idle, thereby interrupting transmission of torque from the second gear 36 toward the reduction shaft 32, when a torque exceeding the magnitude as mentioned above is produced at a tool holder 7 side.
In the hammer drill 1 configured as described above, with a bit 20 installed and held in the tool holder 7, when a switch lever (not shown) provided at the outer housing 2 is manipulated to activate the motor 8, the rotatory motion of the output shaft 9 is transmitted to the crank shaft 28, and the rotatory motion of the crank shaft 28 is converted to the reciprocating motion of the piston 26 actuated via the connecting rod 27. The striker 24 is moved via the air chamber 25 in synchronization with the reciprocating motion of the piston 26, and strikes the rear end of the impact bolt 21 that has been pushed by the rear end of the bit 20 and protruded into the cylinder 23. In this way, the striking motion by the striker 24 is imparted indirectly to the bit 20.
On the other hand, at the side of the intermediate reduction shaft 31, the rotatory motion of the output shaft 9 is, first, transmitted to the first gear 35. Hereupon, if the switch plate 39 has been operated to switch to the position in which it engages with the first gear 35, then the first gear 35 and the intermediate reduction shaft 31 integrally rotate together, and thus the rotatory motion of the intermediate reduction shaft 31 is transmitted from the second gear 36 through the third gear 37 to the reduction shaft 32. Accordingly, the tool holder 7 to which the rotatory motion is transmitted from the bevel gear 44 of the reduction shaft 32 rotates, so that the bit 20 operates in a hammer drill mode in which a rotatory motion as well as a striking motion is made. Contrariwise, if the switch plate 39 has been operated to the position in which it disengages from the first gear 35, then the rotatory motion of the first gear 35 is not transmitted to the intermediate reduction shaft 31. Accordingly, the tool holder 7 fails to make a rotatory motion, so that the bit 20 operates in the hammer mode in which the striking motion only is imparted thereto.
It is to be noted that with a configuration of the intermediate reduction shaft 31 being interposed between the reduction shaft 32 and the output shaft 9, the reduction shaft 32 is located in a position shifted significantly frontward in comparison with the position of a reduction shaft in a tool designed under the conventional scheme. Moreover, the output shaft 9 can be configured to mesh with the first gear 35 located on an upper portion of the intermediate reduction shaft 31, unlike a conventional arrangement in which the output shaft is configured to mesh with the third gear 37 located on a lower portion of the reduction gear 32, and thus the position of the motor 8 is shifted upward closer to the axis of the tool holder 7. In this way, the position of the reduction shaft 32 that is provided with the bevel gear 44 and the torque limiter and is thus of a relatively heavy weight is shifted, and the motor 8 comes closer to the axis of the tool holder 7; therefore, the barycenter of the hammer drill 1 is shifted frontward, so that the weight balance of the tool including the motor 8 may be improved. Accordingly, the moment to be produced around the tip end of the bit 20 is reduced, and the vibration which would occur during the drilling or other operation may adequately be reduced.
Even if heat produced by the striking operation in the impact mechanism including the tool holder 7 raises the temperature of air hermetically sealed in the rotation and impact unit 3, the pressure rise in the rotation and impact unit 3 is prevented because the inside of the rotation and impact unit 3 is in communication with the through hole 13 that is the outside of the rotation and impact unit 3, via the vent hole 15 which opens near the end face of the output shaft 9 so that air is released through the vent hole 15. Meanwhile, around the opening of the vent hole 15 facing to the inside of the rotation and impact unit 3, the output shaft 9 is rapidly rotating, and oil filled in the rotation and impact unit 3 is blocked from entering the vent hole 15 through the labyrinth seal 19, so that only the air separated from oil is securely released out through the vent hole 15. Consequently, adequate lubrication with oil can be maintained.
Thus, according to the hammer drill 1 configured as described above, the intermediate reduction shaft 31 configured to reduce the rotation speed of the output shaft 9 and transmit the speed-reduced rotatory motion to the reduction shaft 32 is disposed in a position parallel to the output shaft 9, frontward of the output shaft 9 between the reduction shaft 32 and the output shaft 9, so that the reduction shaft 32 is disposed frontward of the intermediate reduction shaft 31, while the motor 8 is disposed in a position such that the output shaft 9 protrudes upward beyond the third gear 37 of the reduction shaft 32 so that the motor 8 is positioned closer to the axis of the tool holder 7. Therefore, the hammer drill 1 has its barycenter shifted frontward and upward and thus attains an improved weight balance as a whole. Accordingly, the moment to be produced in the hammer drill 1 around the front end of the bit 20 during the drilling or other operation will become small, and vibration entailed during the striking operation is reduced whereby improved operability and workability can be achieved. Furthermore, since the motor 8 is in a position shifted closer to the axis of the tool holder 7, the hammer drill 1 may be rendered compact in its height direction.
Since the intermediate reduction shaft 31 includes a switch mechanism configured to permit selection of ON and OFF of transmission of the rotatory motion to the reduction shaft 32, the switching operation can be performed easily at the switch mechanism in that the switch mechanism is provided at the intermediate reduction shaft 31 of which the torque applied thereto is smaller. In particular, the intermediate reduction shaft 31 is located upstream of the reduction shaft 32 that includes the torque limiter, and thus, the switching operation can be performed prior to the application of impact (load) by the striking operation, so that a good operability can be maintained.
On the other hand, since the proximity portion 14 having an inner surface proximate to an end face of the output shaft 9 provided in the rotation and impact unit 3 is formed in the crank housing 5, and the vent hole 15 affording communication between the inside of the rotation and impact unit 3 and the outside of the rotation and impact unit 3 is formed in a surface of the proximity portion 14 opposed to the end face of the output shaft 9. Thus, air inside the rotation and impact unit 3 can be released reliably without causing oil leakage through the vent hole 15, and therefore adequate lubrication can be maintained. Moreover, separation of air and oil is achieved by means of the output shaft 9, which provides a reasonable design utilizing the existing configurations; therefore, a fabrication step for providing means for releasing air can be minimized so that increase in cost and required space can be minimized, too.
In particular, since the rotation shaft is the output shaft 9 of the motor 8, the output shaft 9 that rotates at the highest speeds can be utilized to more effectively prevent the oil leakage.
Further in this embodiment, the protrusion 16 located coaxially with the vent hole 15 is formed at the surface of the proximity portion in which the vent hole 15 is formed, and the recess 17 in which the protrusion 16 is inserted in a noncontact manner is formed at the end face of the output shaft 9, and thus the labyrinth seal 19 formed with the protrusion 16 and the recess 17 may serve to more effectively prevent the oil leakage.
In the above-described embodiment, the switch mechanism comprising a switch plate and other components is used, but the switch mechanism is not limited to this configuration. A slide key configured to engage with and disengage from the first gear may be provided in the intermediate reduction shaft, or the first gear may be slid in the axial direction to engage with and disengage from spline teeth or keys at the side of the intermediate reduction shaft; likewise, the specific configurations may be modified where appropriate. The switch mechanism may alternatively be provided in the reduction shaft, and the switch mechanism may be omitted.
Moreover, the torque limiter is provided in the reduction shaft in the above-described embodiment, but the configurations of the torque limiter may be designed differently where appropriate, and the torque limiter may be omitted.
Besides, the types of bearings for each reduction shaft, configurations of the gears, etc. may be changed where appropriate. The arrangement of the intermediate reduction shaft, the reduction shaft and the output shaft may not be limited to such that they are aligned in a straight line extending in the front-rear direction. As long as the front-rear arrangement such that the reduction shaft is in a position shifted frontward in comparison with a conventional arrangement can be maintained, the shafts may be arranged in such a manner that they are staggered laterally.
On the other hand, in the above-described embodiment, the tubular proximity portion having a through hole tunneling through the rotation and impact unit is formed, but the configuration thereof is not limited to this tunneling configuration, and may be a hole which has a bottom and extends to the end face of the rotation shaft such as the output shaft.
Although the protrusion and the recess are formed at the surface of the proximity portion in which the vent hole is formed and at the end face of the rotation shaft, respectively, the positions at which they are formed may be interchanged. The recess may be formed, other than by the receding of a surface, by providing an annular ridge rising from a surface to make a space in which the protrusion can loosely be inserted. The labyrinth seal may be formed by providing two such annular ridges which are coaxially provided in a manner that permits them to be loosely fitted together. Rather, it is to be understood that the oil leakage can be prevented without the protrusion and the recess by simply arranging the end face of the rotation shaft in a position close to the vent hole.
In the above-described embodiment, the output shaft is adopted as the rotation shaft, but the present invention may be applied to an end face of any other rotation shaft such as the intermediate reduction shaft, the reduction shaft and the crank shaft, as long as the proximity portion and the vent hole can be formed. Accordingly, the proximity portion may be formed in any housing other than the crank housing provided that it is an inner housing defining the impact unit. The present invention may be applicable not only to a hammer drill but also to a hammer in which a striking motion only is imparted to the bit by the crank mechanism.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partially illustrated vertical section of a hammer drill.
FIG. 2 is an enlarged view of an output shaft and a portion around it.

EXPLANATION OF REFERENCE NUMERALS

1 -- HAMMER DRILL, 2 -- OUTER HOUSING, 3 -- ROTATION AND IMPACT UNIT, 4 -- HOLDER HOUSING, 5 -- CRANK HOUSING, 6 -- GEAR HOUSING, 7 -- TOOL HOLDER, 8 -- MOTOR, 9 -- OUTPUT SHAFT, 13THROUGH HOLE, 14 -- PROXIMITY PORTION, 15 -- VENT HOLE, 16PROTRUSION, 17 -- RECESS, 18 -- INVERTED TAPERED SURFACE, 19LABYRINTH SEAL, 20 -- BIT, 21 -- IMPACT BOLT, 23 -- CYLINDER, 24STRIKER, 25 -- AIR CHAMBER; 26 -- PISTON, 27 -- CONNECTING ROD, 28CRANK SHAFT, 31 -- INTERMEDIATE REDUCTION SHAFT, 32 -- REDUCTION SHAFT, 35 -- FIRST GEAR, 36 -- SECOND GEAR, 37 -- THIRD GEAR, 39SWITCH PLATE, 44 -- BEVEL GEAR.

Claims

An impact tool comprising:
a tool holder having a front end configured to hold a bit;

a motor having an output shaft, the motor being disposed rearward of the tool holder with the output shaft oriented in a direction perpendicular to an axis of the tool holder;

an impact mechanism comprising a piston and an impactor, the piston being configured to make a reciprocating motion by means of a crank mechanism actuated according to a rotation of the output shaft, and the impactor being configured to move in synchronization with the piston by an action of an air spring;

a reduction shaft disposed in a position parallel to the output shaft between the output shaft and the tool holder, the reduction shaft comprising a driven gear and a bevel gear, the driven gear being configured to receive a rotatory motion transmitted from the output shaft, and the bevel gear being configured to transmit the rotatory motion to the tool holder; and

an intermediate reduction shaft disposed in a position frontward of the output shaft, rearward of the reduction shaft and parallel to the output shaft, the intermediate reduction shaft being configured to reduce a rotation speed of the rotatory motion transmitted from the output shaft and transmit a speed-reduced rotatory motion to the reduction shaft,
wherein the motor is disposed in a position such that the output shaft protrudes upward beyond the driven gear of the reduction shaft, whereby the motor is positioned closer to the axis of the tool holder.
The impact tool according to claim 1, wherein the intermediate reduction shaft comprises a first gear disposed in an upper position and a second gear disposed in a lower position, the first gear being in mesh with the output shaft, and the second gear being in mesh with the driven gear.
The impact tool according to claim 1 or 2, wherein the intermediate reduction shaft comprises a switch mechanism configured to permit selection of ON and OFF of transmission of the rotatory motion to the reduction shaft.
The impact tool according to claim 3, wherein the switch mechanism is comprised of the first gear provided rotatably relative to the intermediate reduction shaft, a switch plate configured to be rotatable integrally with the intermediate reduction shaft and movable in an axial direction of the intermediate reduction shaft thereby engage with or disengage from the first gear, a coil spring configured to bias the switch plate toward a position in which the switch plate engages with the first gear, and a switch member configured to be externally operable to move the switch plate to a position in which the switch plate engages with the first gear and to a position in which the switch plate disengages from the first gear.
The impact tool according to claim 2, wherein the reduction shaft comprises a torque limiter configured to interrupt transmission of torque from the second gear of the intermediate reduction shaft toward the reduction shaft when a predetermined magnitude of torque is produced at a tool holder side.
The impact tool according to claim 5, wherein the torque limiter comprises:
two parts which are configured by dividing the driven gear of the reduction shaft and of which one is an upper plate provided rotatably relative to the reduction shaft and meshed with the second gear of the intermediate reduction shaft and the other is a lower plate configured to rotate integrally with the reduction shaft; an engageable member provided on the lower plate and configured to be biased toward a radial direction of protrusion thereof by a coil spring; and an engageable portion provided on an inner side of the upper plate and configured to be engageable with the engageable member, wherein the engageable member is caused to engage with the engageable portion by a pressing force of the coil spring when the torque is within the predetermined magnitude, while the engageable member is caused to move away from the engageable portion against the pressing force of the coil spring to cause the upper plate alone to rotate at idle when the torque is out of the predetermined magnitude.
The impact tool according to claim 1, comprising an inner housing provided inside the housing to define a sealed space in which an impact unit comprising the output shaft and the impact mechanism is provided, wherein a proximity portion having an inner surface proximate to an end face of a predetermined rotation shaft provided in the impact unit is formed in the inner housing, a vent hole affording communication between an inside of the impact unit and an outside of the impact unit is formed in a surface of the proximity portion opposed to the end face of the rotation shaft.
An impact tool comprising:
a housing having a front end configured to hold a bit;

a motor having an output shaft, the motor being disposed in a rear space of the housing with the output shaft oriented in a direction perpendicular to an axis of the bit;

an impact mechanism comprising a piston and an impactor, the piston being configured to make a reciprocating motion by means of a crank mechanism actuated according to a rotation of the output shaft, and the impactor being configured to move in synchronization with the piston by an action of an air spring; and

an inner housing provided inside the housing to define a sealed space in which an impact unit comprising the output shaft and the impact mechanism is provided,
wherein a proximity portion having an inner surface proximate to an end face of a predetermined rotation shaft provided in the impact unit is formed in the inner housing, a vent hole affording communication between an inside of the impact unit and an outside of the impact unit is formed in a surface of the proximity portion opposed to the end face of the rotation shaft.
The impact tool according to claim 8, wherein the rotation shaft is the output shaft of the motor.
The impact tool according to claim 8 or 9, wherein a protrusion located coaxially with the vent hole is formed at one of the end face of the rotation shaft and the surface of the proximity portion in which the vent hole is formed, and a recess in which the protrusion is inserted in a noncontact manner is formed at the other of the end face of the rotation shaft and the surface of the proximity portion in which the vent hole is formed.
The impact tool according to claim 10, wherein the protrusion has a shape of a tapering circular cone, and the recess has a circular shape with an inverted tapered surface provided at an open side thereof, contoured to fit the shape of the circular cone of the protrusion.
The impact tool according to claim 8, wherein the proximity portion has a tubular shape with a through hole extending laterally and an underside thereof facing to an inside of the impact unit is proximate to the end face of the output shaft.