EP1980371B1

EP1980371B1 - Impact tool

Info

Publication number: EP1980371B1
Application number: EP07707646.1A
Authority: EP
Inventors: Masanori Furusawa
Original assignee: Makita Corp
Current assignee: Makita Corp
Priority date: 2006-01-31
Filing date: 2007-01-29
Publication date: 2014-03-19
Anticipated expiration: 2027-01-29
Also published as: WO2007088821A1; EP1980371A1; EP1980371A4; JP2007203388A

Description

FIELD OF THE INVENTION

The present invention relates to an impact tool according to the preamble of claim 1, in which a tool bit performs a predetermined operation by striking movement in its axial direction. Such an impact tool is known from DE 830 332 C1 .

BACKGROUND OF THE INVENTION

JP 45-14236 A and DE 967 868 A describe impact tools, respectively.
An impact tool in the form of an electric hammer is known in which a tool bit is driven by a motor and performs a predetermined operation by striking movement in its axial direction. Such an electric hammer is disclosed, for example, in Japanese non-examined laid-open Patent Publication No. 2005-335046 . In this electric hammer, a crank mechanism converts the rotating output of a motor into linear motion of a piston, and a striking element is caused to reciprocate by the action of an air spring or pressure fluctuations of air within an air chamber as a result of reciprocating movement of a piston and thereby strikes the tool bit.
In the above-described known impact tool, in order to increase working efficiency, the number of revolutions of the motor must be increased to drive the tool bit at high speed. However, the crank mechanism which is driven by the motor and a mechanical movement part such as a striking mechanism which is used for driving the tool bit are limited in following capability, for example, with respect to the rotational speed of the motor. Therefore, higher working efficiency cannot be realized by increasing the motor speed. In this point, further improvement is required.

DISCLOSURE OF THE INVENTION

OBJECT OF THE INVENTION

It is, accordingly, an object of the present invention to provide an effective technique for improving the working efficiency of an impact tool.

SUMMARY OF THE INVENTION

The above-described problem can be solved by the features of independent claim 1.
The present invention provides an impact tool including a motor, a first motion converting mechanism, a first striking mechanism, a second motion converting mechanism, a second striking mechanism and a tool bit. The first motion converting mechanism converts a rotating output of the motor into linear motion, and the first striking mechanism is driven by the first motion converting mechanism and thereby performs linear motion. The second motion converting mechanism converts a rotating output of the motor into linear motion, and the second striking mechanism is driven by the second motion converting mechanism and thereby performs linear motion. The tool bit is struck by the first and second striking mechanisms and thereby reciprocates and performs a predetermined operation on a workpiece. The tool bit is struck alternately by the striking mechanisms. The impact tool according to the invention further comprises an intermediate element adapted to transmit striking force of the first and second striking elements to the tool bit. The "impact tool" in this invention typically represents an electric hammer in which a tool bit performs a hammering operation on a workpiece solely by linear striking movement in the axial direction, or an electric hammer drill in which a tool bit performs a hammer drill operation on a workpiece by striking movement in the axial direction and rotation around its axis.
The "first motion converting mechanism" and the "second motion converting mechanism" typically represent a mechanism that converts the rotating output of the motor into linear motion of a piston by a crank mechanism, but they are not limited to this. The first and second motion converting mechanisms also suitably include a mechanism that converts rotation of a rotating body rotated by the motor, into swinging motion of a swinging member and thereafter converts the swinging motion of the swinging member into linear motion of the piston, and a mechanism that converts rotation of the motor into linear motion of the piston by using a swash plate which is rotated by the motor. Further, the "first striking mechanism" and the "second striking mechanism" typically represent a construction that includes a striking element which is caused to reciprocate by pressure fluctuations of air within an air chamber as a result of reciprocating movement of a piston, and an intermediate element which transmits the reciprocating movement of the striking element to the tool bit, but they also suitably includes a construction without the intermediate element.
In the present invention, the impact tool includes the "first and second motion converting mechanisms". This means that the impact tool has at least two motion converting mechanisms. In addition to the first and second motion converting mechanisms, it may suitably include a third motion converting mechanism and further a fourth converting mechanism. Similarly, the impact tool includes the "first and second striking mechanisms" in this invention, which means that the impact tool has at least two striking mechanisms. In addition to the first and second striking mechanisms, it may suitably include a third striking mechanism and further a fourth striking mechanism.
According to this invention, the tool bit is struck by the first motion converting mechanism which is driven by the motor and the first striking mechanism and by the second motion converting mechanism which is driven by the motor and the second striking mechanism, and thereby performs a predetermined operation. Therefore, compared with a known impact tool in which a single motion converting mechanism and a single striking mechanism are used to drive the tool bit, the operating efficiency is improved. In other words, if the number of strokes of the tool bit per unit time is set to be equal to that of the known impact tool, the rotational speed of the motor and the driving speeds of the motion converting mechanisms and the striking mechanisms can be decreased. As a result, wear of a sliding part can be reduced and thus the durability can be improved without a decrease in operating efficiency.
In the impact tool, the first and second striking mechanisms are configured to perform linear motion in a direction opposite to each other. Therefore, when one striking mechanism strikes the tool bit member, the other striking mechanism linearly moves in a direction opposite to the one striking mechanism. Thus, the first and second striking mechanisms function as a counter weight with respect to each other. With such a construction, vibration which is caused in the axial direction of the tool bit member during operation can be reduced in a rational manner. Thus, such a construction is effective in reducing vibration of the impact tool.
For example, preferably, the first striking mechanism has a cylindrical first striking element that performs linear motion so as to drive the tool bit. The second striking mechanism has a cylindrical second striking element that performs linear motion so as to drive the tool bit, and the second striking element has generally the same mass as the first striking element. The first and second striking elements are configured to perform linear motion in a direction opposite to each other. With this construction, the tool bit is struck alternately by the first and second striking elements and reciprocates, so that the number of strokes of the tool bit per unit time is increased and the first and second striking elements can further enhance the function as a counter weight with respect to each other.
Further, in the impact tool, preferably, the first and second striking mechanisms are disposed one above the other in parallel. With this construction, the driving balance of the impact tool can be further improved.

EFFECT OF THE INVENTION

According to this invention, an effective technique for improving the working efficiency of an impact tool is provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional side view schematically showing an entire electric hammer according to a first embodiment of the invention.
FIG. 2 is a sectional side view showing an essential part of the hammer.
FIG. 3 is a sectional view taken along line A-A in FIG. 2.
FIG. 4 is a sectional side view showing an entire electric hammer according to a second embodiment, which is not part of the invention.
FIG. 5 is a sectional side view showing an essential part of the hammer.
FIG. 6 is a sectional view taken along line B-B in FIG. 5.
FIG. 7 is a sectional view taken along line C-C in FIG. 5.

REPRESENTATIVE EMBODIMENT OF THE INVENTION

(First Embodiment)

A first embodiment of the present invention is now described with reference to FIGS. 1 to 3. In this embodiment, an electric hammer is explained as a representative example of an impact tool according to the present invention. FIG. 1 is a sectional side view schematically showing an entire electric hammer 101 as a first embodiment of the impact tool according to the present invention. As shown in FIG. 1, the electric hammer 101 of this embodiment mainly includes a body 103 that forms an outer shell of the electric hammer 101, a single hammer bit 163 detachably coupled to the tip end region (on the left side as viewed in FIG. 1) of the body 103 via a hollow tool holder 161, and a handgrip 109 that is connected to the other end of the body 103 on the side opposite to the hammer bit 163 and designed to be held by a user. The hammer bit 163 is a feature that corresponds to the "tool bit" according to the present invention. For the sake of convenience of explanation, the side of the hammer bit 163 is taken as the front side and the side of the handgrip 109 as the rear side.
The body 103 mainly includes a motor housing 105 that houses a driving motor 111, and a gear housing 107 that houses first and second crank mechanisms 113, 115 and first and second striking mechanisms 117, 119. The rotating output of the driving motor 111 is appropriately converted into linear motion via the first and second crank mechanisms 113, 115 and transmitted to the striking mechanisms 117, 119. Then, an impact force is generated in the axial direction of the hammer bit 163 via the striking mechanisms 117, 119. The driving motor 111 is a feature that corresponds to the "motor" according to this invention. The first and second crank mechanisms 113 and 115 are features that correspond to the "first motion converting mechanism" and the "second motion converting mechanism", respectively, according to this invention. Further, the first and second striking mechanisms 117 and 119 are features that correspond to the "first striking mechanism" and the "second striking mechanism", respectively, according to this invention. The driving motor 111 is driven when a trigger 109a on the handgrip 109 is depressed.
FIG. 2 shows an essential part of the hammer 101 in enlarged sectional view, and FIG. 3 is a sectional view taken along line A-A in FIG. 2. As shown in FIG. 2, the first and second crank mechanisms 113 and 115 are disposed one above the other in parallel within the gear housing 107. The first crank mechanism 113 includes a first crank plate 125 that can rotate in a horizontal plane, a first eccentric shaft 127 that is disposed in a position displaced from the center of rotation of the first crank plate 125, and a first crank arm 129 loosely connected at one end to the first eccentric shaft 127, and a first driving element in the form of a first piston 133 mounted to the other end of the first crank arm 129 via a first connecting shaft 131. The first crank plate 122 is circular and has a driven gear 125a on the outer peripheral surface. The driven gear 125a engages with a driving gear 121 that is rotationally driven by the driving motor 111. The first piston 133 is slidably disposed within a first bore 151 a of a cylinder 151, and when the driving motor 111 is driven, the first piston 133 reciprocates in the axial direction of the cylinder 151 (in the axial direction of the hammer bit).
The second crank mechanism 113 includes a second crank plate 137 that can rotate in a horizontal plane, a second eccentric shaft 139 that is disposed in a position displaced from the center of rotation of the second crank plate 137, and a second crank arm 141 loosely connected at one end to the second eccentric shaft 139, and a second driving element in the form of a second piston 145 mounted to the other end of the second crank arm 141 via a second connecting shaft 143. The second piston 145 is slidably disposed within a second bore 151 b of the cylinder 151.
The axis of rotation of the first crank plate 125 coincides with the axis of rotation of the second crank plate 137. Further, the amount of displacement of the first eccentric shaft 127 from the center of rotation of the first crank plate 125 is equal to the amount of displacement of the second eccentric shaft 139 from the center of rotation of the second crank plate 137. Further, the first eccentric shaft 127 is connected to the second eccentric shaft 139 by a connecting member 147 with a phase difference of about 180° in the direction of rotation of the first crank plate 125. Specifically, the second crank mechanism 115 is driven via the connecting member 147 by the first crank mechanism 113 that is driven by the driving motor 111. The second piston 145 then reciprocates in a direction opposite to the first piston 133 with a delay of about 180° crank angle with respect to the first piston 133.
The first and second striking mechanisms 117 and 119 are disposed one above the other in parallel. The first striking mechanism 117 includes a first striking element in the form of a first striker 153 that is slidably disposed within the first bore 151 a of the cylinder 151 and reciprocates in the axial direction of the cylinder 151, and an intermediate element in the form of an impact bolt 157 that is slidably disposed within the cylindrical tool holder 161 and transmits the kinetic energy of the first striker 153 to the hammer bit 163. The first striker 153 is driven via the action of an air spring or pressure fluctuations of air within a first air chamber 151 c as a result of sliding movement of the first piston 133. The first striker 153 then collides with (strikes) the impact bolt 157 and transmits the striking force to the hammer bit 163 held by the tool holder 161, via the impact bolt 157. Specifically, the first striking mechanism 117 is driven by the first crank mechanism 113.
The second striking mechanism 119 includes a second striking element in the form of a second striker 155 that is slidably disposed within the second bore 151b of the cylinder 151 and reciprocates in the axial direction of the cylinder 151, and the above-described impact bolt 157. The second striker 155 is driven via the action of an air spring within a second air chamber 151 d as a result of sliding movement of the second piston 145. The second striker 155 then collides with (strikes) the impact bolt 157 and transmits the striking force to the hammer bit 163 held by the tool holder 161, via the impact bolt 157. Specifically, the second striking mechanism 119 is driven by the second crank mechanism 115.
The impact bolt 157 has an axial rear end having a strike surface 157a that is large enough to receive the striking movement of the first striker 153 on its radially lower region and to receive the striking movement of the second striker 155 on its radially upper region.
The cylinder 151 includes the circular first bore 151a in which the first piston 133 and the first striker 153 are slidably disposed, and the circular second bore 151b in which the second piston 145 and the second striker 155 are slidably disposed. The cylinder 151 is mounted to the gear housing 107 such that it is locked against movement in its axial and circumferential directions. The cross section structure of the cylinder 151 is shown in FIG. 3. The tool holder 161 is mounted to the front end of the gear housing 107 such that it is locked against movement in its axial and circumferential directions. The hammer bit 163 is held by the tool holder 161 such that it is allowed to move in the axial direction with respect to the tool holder 161.
Operation of the electric hammer 101 constructed as described above is now explained. When the driving motor 111 (shown in FIG. 1) is driven, the driving gear 121 is caused to rotate by the rotating output of the driving motor 111. When the driving gear 121 rotates, the first crank plate 125 is caused to rotate via the driven gear 123 that engages with the driving gear 121. Then, the first eccentric shaft 127 on the first crank plate 125 is caused to revolve. As a result, the first crank arm 129 is caused to swing, and the first piston 133 mounted on the front end of the first crank arm 129 is caused to linearly slide within the cylinder 151. When the first piston 133 slides from the non-compressing side (the right side as viewed in FIGS. 1 and 2) to the hammer bit 163 side, the first striker 153 is caused to reciprocate within the cylinder 151 by pressure fluctuations of air or the action of the air spring within the first air chamber 151 c. The first striker 153 then collides with the impact bolt 157 and thereby transmits the kinetic energy (striking force) to the hammer bit 163. Thus, the hammer bit 163 slides within the tool holder 161 and performs a hammering operation on the workpiece.
Meanwhile, in the second crank mechanism 115, when the first eccentric shaft 127 is caused to revolve by rotation of the first crank plate 125, the second eccentric shaft 139 is caused to revolve on the rotation axis of the second crank plate 137 via the connecting member 147. As a result, the second crank arm 141 is caused to swing, and the second piston 145 is caused to slide within the second bore 151 b of the cylinder 151. In this embodiment, a phase difference of about 180° crank angle is provided between the first eccentric shaft 127 and the second eccentric shaft 139. Therefore, the second piston 145 is caused to linearly slide within the second bore 151b of the cylinder 151 with a delay of about 180° crank angle with respect to the first piston 133. When the second piston 145 slides from the non-compressing side to the hammer bit 163 side, the second striker 155 is caused to reciprocate within the cylinder 151 by the action of the air spring within the second air chamber 151d which is caused by the sliding movement of the second piston 145. The second striker 155 then collides with the impact bolt 157 and thereby transmits the kinetic energy (striking force) to the hammer bit 163. Thus, the hammer bit 163 slides within the tool holder 161 and performs a hammering operation on the workpiece..
As described above, according to this embodiment, the single hammer bit 163 can perform two strokes of striking movement in one turn of the crank. Therefore, compared with a known electric hammer which provides one stroke of striking movement in one crank turn, the number of strokes of the hammer bit 163 is doubled if the number of revolutions of the driving motor 111 is set to be identical to that of the known hammer. Therefore, the operating efficiency is improved. From an alternative point of view, if the number of strokes of the hammer bit 163 per unit time is set to be equal to that of the known hammer, the rotational speed of the driving motor 111 and the driving speeds of the first and second crank mechanisms 113, 115 and the first and second striking mechanisms 117, 119 can be decreased. As a result, wear of a sliding member or a sliding part such as an O-ring can be reduced and thus the durability can be improved without a decrease in operating efficiency.
Further, in this embodiment, the first piston 133 and the second piston 145 are driven with a phase difference of about 180° crank angle. Thus, the first striker 153 and the second striker 155 reciprocates in a direction opposite to each other. Therefore, when one striker or, for example, the first striker 153 linearly moves toward the hammer bit 163 (forward), the other striker or, for example, the second striker 155 linearly moves away from the hammer bit 163 (rearward). Thus, the first and second strikers 153, 155 function as a counter weight with respect to each other. With such a construction, vibration which is caused in the axial direction of the hammer bit during hammering operation can be reduced in a rational manner. Thus, such a construction is effective in reducing vibration of the electric hammer 101.

(Second Embodiment)

A second embodiment which is not part of the present invention is now described with reference to FIGS. 4 to 7. The electric hammer 101 according to the second embodiment has two tool bits, or a first hammer bit 173 and a second hammer bit 175, as a tool bit member, and in the other points, it has the same construction as the first embodiment. Components or elements in the second embodiment which are substantially identical to those in the first embodiment are given like numerals as in the first embodiment and are not described or briefly described.
FIG. 4 shows the entire electric hammer 101, and FIG. 5 shows an essential part of the hammer 101. FIGS. 6 and 7 are sectional views taken along line B-B and line C-C, respectively, in FIG. 5. As shown in FIGS. 4 and 5, a tool holder 171 in the second embodiment has two bores for the first hammer bit 173 and the second hammer bit 175. The tool holder 171 is mounted to the front end of the gear housing 107 such that it is locked against movement in its axial and circumferential directions. The first and second hammer bits 173 and 175 are held by the tool holder 171 such that it is allowed to move in the axial direction with respect to the tool holder 171.
The first striking mechanism 117 includes a first striking element in the form of the first striker 153 that reciprocates within the first bore 151 a of the cylinder 151 in the axial direction of the hammer bit, and a first intermediate element in the form of a first impact bolt 177 that is slidably disposed within the tool holder 171 and transmits the kinetic energy of the first striker 153 to the first hammer bit 173. The first striker 153 is driven via the action of an air spring of the first air chamber 151c of the cylinder 151 as a result of sliding movement of the first piston 133. The first striker 153 then collides with (strikes) the first impact bolt 177 and transmits the striking force to the first hammer bit 173 held by the tool holder 171, via the first impact bolt 177.
The second striking mechanism 119 includes a second striking element in the form of the second striker 155 that reciprocates within the second bore 151b of the cylinder 151 in the axial direction of the hammer bit, and a second intermediate element in the form of a second impact bolt 179 that is slidably disposed within the tool holder 171 and transmits the kinetic energy of the second striker 155 to the second hammer bit 175. The second striker 155 is driven via the action of an air spring within the second air chamber 151 d of the cylinder 151 as a result of sliding movement of the second piston 145. The second striker 155 then collides with (strikes) the second impact bolt 179 and transmits the striking force to the second hammer bit 175 held by the tool holder 171, via the second impact bolt 179.
The first crank mechanism 113 for driving the first striking mechanism 117 and the second crank mechanism 115 for driving the second striking mechanism 119 have the same construction as in the first embodiment. Therefore, when the driving motor 111 is driven, the first striking mechanism 117 is driven by the first crank mechanism 113, and the second striking mechanism 119 is driven by the second crank mechanism 115. As a result, the first and second hammer bits 173 and 175 each perform one stroke of striking movement in one crank turn. In other words, a total of two strokes of striking movement are performed by the first and second hammer bits 173 and 175 in one crank turn. Therefore, like in the first embodiment, the operating efficiency can be improved. On the other hand, if the total number of strokes of striking movement of the first and second hammer bits 173 and 175 are set to be equal to that of the known hammer, the rotational speed of the driving motor 111 and the driving speeds of the first and second crank mechanisms 113, 115 and the first and second striking mechanisms 117, 119 can be decreased. As a result, wear of a sliding member or a sliding part such as an O-ring can be reduced and thus the durability can be improved without a decrease in operating efficiency
Further, the first piston 133 of the first crank mechanism 113 and the second piston 145 of the second crank mechanism 115 reciprocates within the cylinder 151 with a phase difference of about 180° crank angle. Therefore, like in the first embodiment, vibration which is caused in the axial direction of the hammer bit during hammering operation can be reduced in a rational manner. Thus, such a construction is also effective in reducing vibration of the electric hammer 101. Further, in this embodiment, with the construction using the two hammer bits 173, 175, a hammering operation can be performed on a wider area at the same time, compared with a construction using one hammer bit.
In the above-described embodiments, the crank mechanisms 113, 115 are used as a means for converting the rotating output of the driving motor 111 into linear motion of the pistons 133, 145. However, such means is not limited to them, but other mechanisms may also be used, including a mechanism that converts rotation of a rotating body rotated by the driving motor 111, into swinging motion of a swinging member and thereafter converts the swinging motion of the swinging member into linear motion of the pistons 133, 145, and a mechanism that converts rotation of the driving motor 111 into linear motion of the pistons 133, 145 by using a swash plate which is rotated by the driving motor 111. Further, in the above-described embodiments, the two crank mechanisms 113, 115 and the two striking mechanisms 117, 119 are provided. However, these mechanisms may be further increased in number.
Further, in the above-described embodiments, the electric hammer 101 is described as a representative example of the impact tool. However, the present invention can also be applied to a hammer drill according to the first embodiment in which the hammer bit 163 perform not only the striking movement in the axial direction but rotation around its axis.

Description of Numerals

101 electric hammer (impact tool)
103 body
105 motor housing
107 gear housing
109 handgrip
109a trigger
111 driving motor
113 first crank mechanism
115 second crank mechanism
117 first striking mechanism
119 second striking mechanism
121 driving gear
125 first crank plate
125a driven gear
127 first eccentric shaft
129 first crank arm
131 first connecting shaft
133 first piston
137 second crank plate
139 second eccentric shaft
141 second crank arm
143 second connecting shaft
145 second piston
147 connecting member
151 cylinder
151a first bore
151b second bore
151c first air chamber
151d second air chamber
153 first striker
155 second striker
157 impact bolt
157a strike surface
161 tool holder
163 hammer bit (tool bit member, tool bit)
171 tool holder
173 first hammer bit (tool bit member, first tool bit)
175 second hammer bit (tool bit member, second tool bit)
177 first impact bolt
179 second impact bolt

Claims

An impact tool comprising:
a motor (111),

a first motion converting mechanism (113) that converts a rotating output of the motor (111) into linear motion,

a first striking mechanism (117) that is driven by the first motion converting mechanism (113) and thereby performs linear motion,

a second motion converting mechanism (115) that converts a rotating output of the motor into linear motion,

a second striking mechanism (119) that is driven by the second motion converting mechanism and thereby performs linear motion, and

a tool bit (163) that is detachably held by a cylindrical tool holder (161) and that performs a predetermined operation on a workpiece, wherein

the first striking mechanism (117) has a first striking element (153) that performs linear motion so as to drive the tool bit (163),

the second striking mechanism (119) has a second striking element (155) that performs linear motion so as to drive the tool bit (163), the second striking element (155) having generally the same mass as the first striking element (153),

the first and second striking elements (153, 155) are configured to perform linear motion in a direction opposite to each other,

the tool bit (163) is struck alternately by the first and second striking elements (153, 155) and reciprocates, whereby the number of strokes of the tool bit (163) per unit time is increased and the first and second striking elements (153, 155) serve as a counter weight with respect to each other,

characterized in that the impact tool further comprises an intermediate element (157) in the form of an impact bolt (157) that is slidably disposed within the cylindrical tool holder (161) and adapted to transmit striking force of the first and second striking elements (153, 155) to the tool bit (163).
The impact tool as defined in claim 1, wherein the first and second striking elements (153, 155) are cylindrically shaped having generally the same diameter.
The power tool as defined in claim 1 or 2, wherein the first and second striking mechanisms (117, 119) are disposed one above the other in parallel.