Technical Field

The present invention relates to a power tool, more particularly an electrical hammer drill, which power tool comprises a transmission switching mechanism which enables a transmission mechanism of the power tool to switch between a drilling mode, a hammering mode, a chiseling mode and a vario-lock mode. The present invention also relates to a transmission switching mechanism for the power tool.

Background Art

Power tools such as electrical hammer drills are widely used in the engineering field. In order to fulfill various processing tasks, such power tools are usually configured to be able to operate in different processing modes, such as a drilling mode, a hammering mode, a chiseling mode and the like. In order that the power tool is switchable between these modes, the power tool must be provided with a special transmission mechanism between a tool head, such as a drill bit, and a driving motor of the power tool. Usually, the transmission mechanism is connected to a transmission switching mechanism so as to enable the transmission mechanism to switch between those modes.

Chinese patent publication CN 1743138 A (Chinese patent application No. 2005/0099493) discloses a power tool which comprises a serrated sleeve, a drive bearing, a serrated shaft and a drive shaft. In this disclosed power tool, the drive shaft transmits force to the drive bearing and the serrated shaft via the serrated sleeve, such that the power tool is switchable between three modes, i.e. a drilling mode, a hammering mode and a chiseling mode. However, according to the technical solution disclosed by this reference, it is necessary to form a serrated wheel on a transmission shaft; further, all the switching actions between different modes are accomplished only by moving the transmission shaft.

Patent publication EP 1157788A2 discloses another power tool which comprises an intermediate shaft, a spindle, a pneumatic hammering arrangement and a transmission mechanism. The transmission mechanism comprises a spindle driving member, a driving sleeve and a mode change sleeve. By a driving part on the spindle driving shaft and a driving gear on an intermediate shaft cooperating with a driving part on the mode change sleeve, the power tool may be switched between three modes, i.e. a drilling mode, a hammering mode and a chiseling mode. The transmission mechanism disclosed by this reference involves in a complicated fitting between several members, which may make the assembling process more difficult and the failure rate of operation higher.

Chinese patent publication CN 2920563Y (Chinese patent application No. 200620105678.7) discloses a transmission mechanism for an electrical hammer, in which it is necessary to additionally mount a clutch to a driving shaft of the transmission mechanism so as to execute a shifting action, which may lead to a problem that excessive parts are required.

Although those conventional transmission mechanisms and transmission switching mechanisms therefor have been developed to enable the power tool to be switchable between different modes, the conventional transmission mechanisms or transmission switching mechanisms are very complex and require excessive parts. It is well-known in the mechanical field that, the fact that the transmission mechanism or transmission switching mechanism is complex and requires excessive parts, will result in a problem that the maintenance service is difficult and the failure rate is high.

Therefore, there is an urgent need for a power tool having a transmission switching mechanism which may be operated effectively and maintained conveniently.

Summary of the Invention

Therefore, one aspect of the present invention is aimed at providing a transmission switching mechanism for a power tool, comprising: a guiding rod mounted onto the power tool; a first shifting plate comprising two first shifting sections and at least one first cantilever, wherein each of the first shifting sections is provided with a through hole, the first shifting plate is mounted slidably on the guiding rod via the through holes of the two first shifting sections, and the first cantilever is able to be slid together with the first shifting plate as it is slid; a second shifting plate comprising two second shifting sections and at least one second cantilever, wherein each of the second shifting sections is provided with a through hole, the second shifting plate is mounted slidably on the guiding rod via the through holes of the two second shifting sections, the second cantilever is able to be slid together with the second shifting plate as it is slid, and the first and second shifting plates are arranged one behind the other along the longitudinal direction of the guiding rod via the through holes; and a shift member comprising a shaft which extends perpendicular to the longitudinal direction of the guiding rod and further comprising a cam having first and second arc-shaped segments, wherein the shift member is rotatable around the shaft, the shaft is stationary relative to the longitudinal direction of the guiding rod, and the radius of the first arc- shaped segment is different from that of the second arc- shaped segment, and wherein when the shift member is rotated around the shaft, the first and second shifting plates are driven to slide longitudinally on the guiding rod by the different radii of the first and second arc-shaped segments of the cam of the shift member; the transmission switching mechanism further comprises an elastic element which is configured to reset the first and second shifting plates driven by the shift member.

Preferably, the shift member is arranged between the first and second shifting plates.

Preferably, the transmission switching mechanism further comprises a connecting plate including two third shifting sections, wherein each of the two third shifting sections is provided with a through hole, the connecting plate is mounted slidably on the guiding rod via the through holes of the third shifting sections, one of the two third shifting sections of the connecting plate is arranged between the two first shifting sections of the first shifting plate and the other is arranged between the two second shifting sections of the second shifting plate.

Preferably, the first and second arc- shaped segments of the cam of the shift member are arranged between one of the first shifting sections of the shifting plate and the third shifting section of the connecting plate opposing the first shifting section.

Preferably, the first arc-shaped segment is half-circular in shape.

Preferably, the elastic element comprises a first elastic element and a second elastic element, the first elastic element is arranged to act between one of the third shifting sections of the connecting plate and the other of the first shifting sections of the shifting plate, and the second elastic element is arranged to act between the other of the third shifting sections of the connecting plate and a relevant one of the second shifting sections of the shifting plate.

Preferably, the second shifting plate comprises a serrated part, and the serrated part is distanced sufficiently from the other of the second shifting sections of the shifting plate such that, only when the transmission mechanism is in a chiseling mode, the serrated part is able to be engaged with a gear member (8) of the power tool.

Preferably, when the transmission mechanism is in a vario-lock mode, the gear member is disengaged from a rotating shaft of the power tool and the serrated part of the second shifting plate is disengaged from the gear member.

Preferably, the serrated part of the second shifting plate is connected to the other of the second shifting sections of the shifting plate by a connecting section which extends parallel to the guiding rod.

Another aspect of the present invention is aimed at providing a power tool comprising a transmission mechanism and the above-mentioned transmission switching mechanism.

Brief Description of the Drawings

Exemplary embodiments of the present invention will be explained in details on the basis of the drawings, in which:

Figure 1 schematically shows a perspective view of main components of a power tool, especially an electrical hammer drill, according to a preferred embodiment of the present invention;

Figure 2a schematically shows a perspective view of a transmission mechanism and a transmission switching mechanism of the power tool according to the preferred embodiment of the present invention wherein the transmission mechanism and the transmission switching mechanism are in a hammering mode; Figure 2b schematically shows a sectional perspective view of the transmission mechanism shown in figure 2a;

Figure 2c schematically shows a sectional perspective view of the transmission switching mechanism shown in figure 2a;

Figure 3a schematically shows a perspective view of the transmission mechanism and the transmission switching mechanism of the power tool according to the preferred embodiment of the present invention wherein the transmission mechanism and the transmission switching mechanism are in a chiseling mode;

Figure 3b schematically shows a sectional perspective view of the transmission mechanism shown in figure 3a;

Figure 3c schematically shows a sectional perspective view of the transmission switching mechanism shown in figure 3a;

Figure 4a schematically shows a perspective view of the transmission mechanism and the transmission switching mechanism of the power tool according to the preferred embodiment of the present invention wherein the transmission mechanism and the transmission switching mechanism are in a drilling mode;

Figure 4b schematically shows a sectional perspective view of the transmission mechanism shown in figure 4a;

Figure 4c schematically shows a sectional perspective view of the transmission switching mechanism shown in figure 4a;

Figure 5a schematically shows a perspective view of the transmission mechanism and the transmission switching mechanism according to the preferred embodiment of the present invention wherein they are in a vario-lock mode; and

Figure 5b schematically shows a perspective view of the transmission switching mechanism shown in figure 5a.

Detailed Description of Preferred Embodiments

A transmission switching mechanism of a power tool, in particular an electrical hammer drill, according to a preferred embodiment of the present invention will be explained with reference to the drawings. It is noted that like reference numerals represent elements which have like or similar functions throughout the drawings.

First, it should be noted that the transmission switching mechanism according to the present invention is not limited to be applied in electrical hammer drills. That is, any kinds of power tools, for example an electrical saw which is switchable between a pure rotating mode, a pure reciprocating mode and a combination mode, can adopt the transmission switching mechanism according to the present invention.

Now a power tool according to the present invention and a transmission switching mechanism thereof will be explained with an electrical hammer drill as an illustrative but not restrictive example.

As shown in figure 1, the power tool generally comprises a hammer tube 1, a gear 2 which is mounted in a fixed manner relative to the hammer tube 1, a cylinder assembly 3 which is set in the hammer tube 1, a transmission mechanism 4 and a transmission switching mechanism 10. The transmission mechanism 4 comprises a wobble bearing 5, a rotation drive element 6, a shaft 7 and a gear member (pinion) 8. The drive element 6 of the transmission mechanism 4 is driven by a motor (not shown) of the power tool to rotate. The shaft 7 is mounted such that it cannot be rotated with respect to the drive element 6. In this way, when the drive element 6 is rotated, the shaft 7 is also rotated correspondingly. The gear member (pinion) 8 of the transmission mechanism 4 is mounted on the shaft 7, more particularly on a first axial portion of the shaft 7, such that the gear member is slidable longitudinally. The transmission switching mechanism 10 is configured to act on the transmission mechanism 4 such that the transmission mechanism 4 is switchable between different modes. The configuration of the transmission switching mechanism 10 will be explained in details below.

In a normal state, the gear member 8 is free rotatable on the shaft 7 around its central axis. Only when a key 8a of the gear member 8 is mated with a slot 7a of the shaft 7 (as shown in figure 1), the gear member 8 is rotatable by the shaft 7. Since the gear member 8 is engaged with the gear 2, the gear 2 is rotated by the gear member 8 such that the hammer tube 1 is rotated. In this way, when a corresponding tool head or a tool bit for example a drill bit is mounted on the power tool, an operator may accomplish an operation such as a drilling operation using the rotating tool head or the tool bit of the power tool. This can be called as a drilling mode.

As shown in figure 1, the wobble bearing 5 of the transmission mechanism 4 comprises an inner ring (i.e. a bearing sleeve 5c) and an outer ring. A railway is provided between the inner ring and the outer ring. For example, balls are provided in the railway The railway is provided obliquely relative to the shaft 7. A swing arm of the wobble bearing 5 is, at one end thereof, pivotally connected to the cylinder assembly 3 in the hammer tube 1. The bearing sleeve 5c of the wobble bearing 5 is mounded such that it is rotatable around the center longitudinal axis of the shaft 7, more particularly the bearing sleeve is mounded on a second axial portion of the shaft 7 in said manner.

In the normal state, the bearing sleeve 5c is rotatable around the longitudinal axis of the shaft 7. The rotation of the shaft 7 can be transferred to the wobble bearing 5 only when a key 5a of the wobble bearing 5 is mated with a slot 7b of the shaft 7 (as shown in figure 2). Because the railway of the wobble bearing 5 is provided obliquely relative to the shaft 7, the swing arm integrally formed with the outer ring of the wobble bearing can be swung along the longitudinal axis of the shaft 7 when the shaft 7 drives the bearing sleeve 5c to rotate. Thereby, a piston in the cylinder assembly 3 can reciprocate along the longitudinal axis of the hammer tube 1, such that the tool head or the tool bit can be driven to reciprocate along the longitudinal axis of the hammer tube 1. Thus when a corresponding tool heat such as a plow bit is mounted on the power tool, the operator may accomplish an operation such as a chiseling operation. This can be called as a chiseling mode.

It is appreciated that in the case that the gear 2 on the hammer tube 1 and the cylinder assembly 3 are driven simultaneously by the shaft 7 (as shown in figure 1) to rotate, a hammering operation can be accomplished when a corresponding tool bit is mounted on the power tool. This can be called as a hammering mode.

Specifically, the transmission switching mechanism 10 according to the preferred embodiment of the present invention will be explained on the basis of figures 2 to 5. The transmission switching mechanism 10 according to the present invention can be used to adjust the power tool such that the power tool is able to be in different modes, such as hammering, chiseling, drilling and vario-lock modes.

Figures 2a and 2b show the transmission mechanism 4 according to the preferred embodiment of the present invention which is in the hammering mode. As shown in these figures, the transmission mechanism 4 comprises the wobble bearing 5, the rotation drive element 6, the shaft 7 and the gear member 8, wherein a sleeve tube 9 is mounted in a central hole of the drive element 6 such that this sleeve tube is stationary relative to the drive element 6. Although in this embodiment the sleeve tube 9 is mounted such that it is stationary relative to the drive element 6, it is also conceived that in an alternative embodiment the sleeve tube 9 is integrally formed with the drive element 6.

As to the construction and the operation principle of the wobble bearing 5, please refer to technical materials of the prior art. Therefore, the explanations about them are omitted here.

In this embodiment, the bearing sleeve 5c of the wobble bearing 5 is rotatably mounted around an outer surface of the sleeve tube 9. In order to prevent the bearing sleeve 5c from moving along the axis of the sleeve tube 9, a protrusion 5d, which protrudes radially from the inner surface of the central hole of the bearing sleeve 5c, is able to be engaged into a circumferential groove 9a which is provided circumferentially in the outer surface of the sleeve tube 9. Therefore, when the transmission mechanism 4 is operated, the bearing sleeve 5c of the wobble bearing 5 is stationary axially relative to the sleeve tube 9 but the bearing sleeve 5c may rotate around the sleeve tube 9. However, the present invention is not limited to the mentioned manner. For example, it is also possible that a groove is recessed radially on the inner surface of the central opening of the bearing sleeve 5c and a protrusion is protruded from the outer surface of the sleeve tube 9, such that the groove is engaged with the protrusion so as to prevent the bearing sleeve 5c from moving axially relative to the sleeve tube 9.

In order to reduce the friction occurred when the bearing sleeve 5c rotates, any suitable bearing arrangement, such as a needle bearing, may optionally be provided between the inner surface of the central hole of the bearing sleeve 5c and the outer surface of the sleeve tube 9.

A portion of the shaft 7 is inserted slidably in the sleeve tube 9. In order that the rotation of the sleeve tube 9 can be transferred to the shaft 7, key-slot arrangements, which are matable with each other, are respectively provided on the outer surface of the shaft 7 and the inner surface of the sleeve tube 9 along the longitudinal axes of the shaft 7 and the sleeve tube 9. By cooperation of these key-slot arrangements, any rotation of the sleeve tube 9 is able to be transferred to the shaft 7.

For example, in this embodiment, one end of the shaft 7 which is inserted in the sleeve tube 9 is formed in a triangle or square shape. The central hole of the sleeve tube 9 for receiving the shaft 7 has a shape which is complementary to the shape of the end of the shaft 7. That is, the central hole is able to be formed in a complementary triangle or square shape. Therefore, the shaft 7 is slidable along the longitudinal axis of the sleeve tube 9, and the shaft 7 may be driven by the sleeve tube 9 to rotate.

It is appreciated that he present invention is not limited to the mentioned case. Any suitable arrangement, by which the rotation of the drive element 6 may be transferred to the shaft 7 meanwhile the shaft 7 is slidably longitudinally, may be provided on the shaft 7. The suitable arrangement includes, but not limited to, a friction clutch arrangement or the like.

As shown in figure 2b, a radially protruding boss 7d is provided circumferentially on the shaft 7 at a substantially longitudinal intermediate position thereof. In this embodiment, the wobble bearing 5 is mounted between the boss 7d and the drive element 6. One end of the boss 7d facing towards the drive element 6 is provided with the slot 7b, which is matable with the key 5a provided at one end of the bearing sleeve 5c of the wobble bearing 5 far away from the drive element 6. Preferably, a plurality of slots 7b are provided circumferentially at the end of the boss 7d. In order to transfer a rotational movement from the shaft 7 to the wobble bearing 5c, the plurality of slots 7b are alignable respectively with a plurality of keys 5a provided at the end of the bearing sleeve 5c of the wobble bearing 5 far away from the drive element 6 such that these slots 7b may receive the keys 5a as the shaft 7 is slid towards the drive element 6.

In order to transfer the rotational movement, it is also appreciated that a converse configuration is possible, that is, the keys are provided on the shaft 7 and the slots are provided on the bearing sleeve of the wobble bearing 5 respectively. In this embodiment, rotation is transferred between the shaft 7 and the wobble bearing 5 by means of the key- slot arrangements. However, the present invention is not limited by this. Any suitable arrangement, which can be used to transfer a rotational movement between two parts, may be adopted. For example, a friction clutch, an electromagnetic clutch or the like may be provided between the shaft 7 and the bearing sleeve 5c of the wobble bearing 5 for transferring the rotational movement.

The gear member 8 is mounted around a portion of the shaft 7 which is opposite to the drive element 6, such that the gear member 8 is rotatable around the longitudinal central axis of the shaft 7 and is slidable back and forth along the longitudinal axis of the shaft 7. Similarly, at one end face of the boss 7d of the shaft 7 opposite to the slot 7b, a slot 7a is provided which is matable with a key 8a provided at one end of the gear member 8 facing towards the slot 7a.

Preferably, a plurality of slots 7a are provided on the boss 7d of the shaft 7 such that these slots are matable with a plurality of keys 8a provided at the end of the gear member 8 facing towards the slots 7a. Therefore, when the gear member 8 is slid along the longitudinal axis of the shaft 7 in such a way that the keys 8a of the gear member are engaged into the slots 7a of the boss 7d of the shaft 7, the gear member 8 may be driven by the shaft 7 to rotate. That is, in this case, the gear member 8 is rotated along with the shaft 7. Therefore, by the gear member 8 engaging with the gear 2, the shaft 7 finally drives the gear 2 to rotate such that the hammer tube 1 is rotated. It can be conceived that, in order to eliminate the friction between the inner surface of the central hole of the gear member 8 and the outer surface of the shaft 7, a ball bearing, a needle bearing or the like may be suitably provided between them.

In order that the shaft 7 is slidable back and forth along the longitudinal axis of the sleeve tube 9, a groove 7c is provided circumferentially on the shaft 7 or on the boss 7d of the shaft 7, more particularly between the slots 7a and 7b. The groove 7c may be engaged with a shift plate of a switching mechanism not shown in the figures, such that the shaft 7 may be moved back and forth relative to the drive element 6 and the sleeve tube 9 in a direction of the longitudinal axis of the shaft 7. Therefore, the shaft 7 is slidable.

Similarly, a groove 8b is also provided on a periphery of the gear member 8. The groove 8b may also be engaged with the shift plate of the switching mechanism not shown in the figures, such that the gear member 8 may be moved back and forth relative to the shaft 7 in the direction of the longitudinal axis. Therefore, the gear member 8 is slidable.

Although the shaft 7 and the gear member 8 are slidable along the longitudinal axis of the shaft 7 due to their grooves, it can be conceived that any other suitable arrangement, which may be used to drive the shaft 7 and the gear member 8 to move longitudinally, is possible. For example, as an alternative, a radially protruding flange is provided circumferentially on each of the shaft 7 and the gear member 8, such that the flange may be driven by the corresponding shift plate of the switching mechanism to slide the shaft and the gear member.

Although in the exemplary embodiment of the present invention the gear member 8 and the bearing sleeve 5c are driven to rotate by the boss 7d provided on the shaft 7, it should be understood that the present invention is not limited by this. For example, as an alternative, at the position of the shaft 7 shown in figures 2a and 2b, a circumferential groove is provided on the outer surface of the shaft 7; and a plurality of space-apart key, which protrude radially and inwardly from the inner surface of the central hole of the gear member 8 and the inner surface of the central hole of the bearing sleeve 5c of the wobble bearing 5, are engaged in the circumferential groove, such that each of the bearing sleeve 5c and the gear member 8 is rotatable around the shaft 7. In order that the gear member 8 and the bearing sleeve 5c are rotated by the rotating shaft 7, a plurality of longitudinal grooves are provided on the shaft 7 along its longitudinal axis, which are communicated with the circumferential groove. The plurality of the longitudinal grooves are alignable circumferentially with a plurality of keys of the bearing sleeve 5c and a plurality of keys of the gear member 8. When the bearing sleeve 5c and/or the gear member 8 are/is slid longitudinally such that the keys are engaged into the longitudinal grooves respectively, the shaft 7 may drive the wobble bearing 5 and/or the gear member 8 to rotate.

Figure 2c only shows the transmission switching mechanism 10 according to the preferred embodiment of the present invention. The transmission switching mechanism 10 comprises a guiding rod 11, two shifting plates 12 and 13, a connecting plate 14, a shift member 17 and springs 16a and 16b. The shifting plates 12 and 13 as well as the connecting plate 14 are mounted such that they are passed by the guiding rod 11. Therefore, the shifting plates 12 and 13 as well as the connecting plate 14 are slidable along the longitudinal axial of the guiding rod 11. The guiding rod 11 is substantially parallel to the shaft 7.

Specifically, as shown in figure 2c, shifting sections 12c and 12d of the shifting plate 12, shifting sections 14a and 14c of the connecting plate 14 as well as shifting sections 13c and 13d of the shifting plate 13 are provided with through holes, such that the guiding rod 11 is passed through these through holes so as to enable the shifting plates 12 and 13 and the connecting plate 14 to be slidable on the guiding rod 11.

In the embodiment of the present invention, the connecting plate 14 is U-shaped in a cross section which is along the guiding rod 11 and perpendicular to the horizontal plane. The connecting plate 14 comprises the two shifting sections 14a and 14c as well as a connecting section 14b of which both ends are connected to the shifting sections 14a and 14c respectively. The shifting sections 14a and 14c are folded downwardly from the ends of the connecting section 14d respectively and are formed vertically. The shifting sections 14a and 14c are perpendicular to the connecting section 14b and the shifting sections are parallel with each other.

The shifting plate 12 comprises the two shifting sections 12c and 12d as well as a connecting section 12b of which both ends are connected to the shifting sections 12c and 12d. The shifting sections 12c and 12d are folded upwardly from the ends of the connecting section 12b and are formed vertically. The shifting sections 12c and 12d are perpendicular to the connecting section 12b and the shifting sections are parallel with each other. A cantilever 12e protrudes from a side of the shifting section 12d. The plane where the cantilever 12e is located is substantially perpendicular to the connecting section 12b. Similarly, the shifting plate 12 is U-shaped in a cross section which is along the guiding rod 11 and perpendicular to the horizontal plane.

A fork part 12a is provided at a free end of the cantilever 12e. In the embodiment of the present invention, the guiding rod 11 is provided such that it is parallel to the shaft 7. For example, the guiding rod 11 is separated from the shaft 7 such that the fork part 12a may be engaged with the groove 8b of the gear member 8. Therefore, if the shifting plate 12 is slid along the guiding rod 11, the gear member 8 is also slid on the shaft 7. In this way, it enables the gear member 8 to be slidable along the shaft 7.

The shifting plate 13 of the transmission switching mechanism 10 also comprises a cantilever 13e. Similar to the shifting plate 12, the shifting plate 13 is U-shaped in a cross section which is along the guiding rod 11 and perpendicular to the horizontal plane. The shifting plate 13 comprises the two shifting sections 13c and 13d as well as a connecting section 13b of which both ends are connected to the shifting sections 13c and 13d respectively. The shifting sections 13c and 13d are folded upwardly from the ends of the connecting section 13b and are formed vertically. The shifting sections 13c and 13d are perpendicular to the connecting section 13b and the shifting sections are parallel with each other. The cantilever 13e protrudes from a side of the shifting section 13d. The plane where the cantilever 13e is located is substantially perpendicular to the connecting section 13b.

Optionally, in the embodiment of the present invention, rounded portions are provided between the connecting section 13b and the shifting sections 13c and 13d of the shifting plate 13. Similarly, rounded portions are also provided between the connecting section 12b and the shifting sections 12c and 12d of the shifting plate 12 as well as between the connecting section 14b and the shifting sections 14a and 14c of the shifting plate 14.

A fork part 13a is provided at a free end of the cantilever 13e. For example, the fork part 13a may be engaged with the groove 7c of the shaft 7. Therefore, if the shifting plate 13 is slid along the guiding rod 11, the shaft 7 can be driven to slide along the sleeve tube 9. In this way, it enables the shaft 7 to be slidable along the sleeve tube 9.

The shifting plate 13 also comprises a connecting section 13f which extends laterally from the fork part 13a. The connecting section 13f extends in such a way that it is parallel to the guiding rod 11, that is, to the connecting section 13b. One end of the connecting section 13f is provided with a serrated part 13g. The serrated part 13g is folded upwardly from the connecting section 13f and is formed vertically. Teeth of the serrated part 13g are configured to engage with the teeth of the gear member 8.

In the embodiment of the present invention, the connecting plate 14 is arranged across the shifting section 12d of the shifting plate 12 and the shifting section 13d of the shifting plate 13. That is, the shifting section 12d of the shifting plate 12 and the shifting section 13d of the shifting plate 13 are located between the two shifting sections 14a and 14c of the connecting plate 14.

The shift member 17 is located between one of the shifting plates and the connecting plate 14. In the exemplary embodiment, the shift member 17 is located between the shifting section 12c of the shifting plate 12 and the shifting section 14c of the connecting plate 14. In the embodiment of the present invention, the shift member 17 is embodied as a cam. The cam is comprised of a circular arc- shaped segment having a smaller radius and a flat arc- shaped segment having a larger radius. The cam has a thickness. The circular arc- shaped segment, of which the radius is smaller, of the cam has a center in the cam. A driving shaft 15 is mounted at the center. The driving shaft 15 is for example mounted in a housing of the power tool such that this shaft can be driven by motor of by hand so as to rotate the cam 17. In the exemplary embodiment, the flat arc- shaped segment of the cam 17 is embodied in a flat manner such that the radius of the flat arc- shaped segment is greatly larger than the radius of the circular arc-shaped segment. The edge of the flat arc-shaped segment is tangent to the periphery of the driving shaft 5. However, it is appreciated that the flat arc- shaped segment of the cam 17 can be replaced by a flat shaped or flat rectangle-shaped segment as soon as the thickness of the segment or the distance of the edge of the segment apart from the center of the shaft 15 is less than the radius R of the circular arc-shaped segment.

In the exemplary embodiment, the springs 16a and 16b are mounted between the shifting plates 12 and 13 and the connecting plate 14 respectively. Specifically, as shown in figure 2c, the spring 16a is mounted between the shifting section 14c of the connecting plate 14 and the shifting section 12d of the shifting plate 12. Both ends of the spring 16a are attached against the shifting section 14c of the connecting plate 14 and the shifting section 12d of the shifting plate 12 respectively, such that, under tension of the spring 16a, the outer surface of the cam 17 is always contacted with the shifting section 12c of the shifting plate 12 and the shifting section 14c of the connecting plate 14. As shown in figure 2c, the shifting section 12d is pressed against the shifting section 13d by the spring 16a.

In the exemplary embodiment, the shifting section 13d of the shifting plate 13 is arranged between the shifting section 12d of the shifting plate 12 and the shifting section 14a of the shifting plate 14. The spring 16b is mounted between the shifting section 13c of the shifting plate 13 and the shifting section 14a of the connecting plate 14. Both ends of the spring 16b are attached against the shifting section 13d of the shifting plate 13 and the shifting section 14a of the connecting plate 14 respectively, such that, under tension of the spring 16b, the shifting section 13d of the shifting plate 13 is contacted with the shifting section 14a of the connecting plate 14. By means of the two springs 16a and 16b, the shifting section 12d of the shifting plate 12, the shifting section 13d of the shifting plate 13 and the shifting section 14a of the connecting plate 14 are pushed together. It should be noted that, although the springs 16a and 16b are adopted in the preferred embodiment of the present invention, any other suitable elastic element can be adopted in the transmission switching mechanism 10 according to the present invention.

Figures 2a and 2b show that the transmission mechanism 4 according to the preferred embodiment of the present invention is in the hammering mode. In this hammering mode, the key 8a of the gear member 8 and the key 5a of the bearing sleeve 5c are simultaneously engaged in the slots 7a and 7b of the shaft 7. Therefore, the gear member 8 and the bearing sleeve 5c are rotated simultaneously by the shaft 7. In this case, the gear 2 is driven to rotate by the gear member 8 such that the hammer tube 1 is rotated. Therefore, the swing arm 5b is swung back and forth due to the rotating bearing sleeve 5c such that the piston is reciprocated in the cylinder assembly 3. In this mode, the operator may accomplish an operation such as a hammering operation using the power tool mounted with the tool head, for example, the tool bit.

In the present invention, no serrated wheel is formed directly on the shaft 7 of the transmission mechanism 4. In fact, the pre-formed gear member 8 is assembled around the shaft. This will greatly reduce the difficulty of manufacturing the shaft 7, that is, will greatly reduce the cost of manufacturing the transmission mechanism according to the present invention.

Additionally, figure 2a shows that the transmission switching mechanism 10 according to the present invention is assembled to the transmission mechanism 4. Figure 2c shows a perspective view of only the transmission switching mechanism 10 according to the present invention.

As shown in figures 2a, 2b and 2c, the fork parts 12a and 13a of the transmission switching mechanism 10 are inserted into the groove 8b of the gear member 8 and the groove 7c of the shaft 7 respectively. Specifically, the shifting plate 12 of the transmission switching mechanism 10 is configured to control the sliding of the gear member 8 on the shaft 7, and the shifting plate 13 of the transmission switching mechanism 10 is configured to control the sliding of the shaft 7 along the sleeve tube 9. In the exemplary embodiment of the present invention, the length of the connecting section 13f of the shifting plate 13, i.e. the longitudinal distance between the fork part 13a and the serrated part 13g is provided such that, when the key 8a of the gear member 8 is engaged in the slot 7a of the boss 7d of the shaft 7, the length of the connecting section 13f is larger than the distance which is measured from the groove 7c of the boss 7d of the shaft 7 to a free end of the gear member 8 opposite to the key 8a. That is, when the key 8a of the gear member 8 is engaged in the slot 7a of the boss 7d, the serrated part 13g of the shifting plate 13 of the transmission switching mechanism 10 is separated from the free end of the gear member 8 opposite to the key 8a by a distance, i.e. they are disengaged from each other.

As shown in figure 2a, the transmission mechanism 4 is in the hammering mode. In this mode, the serrated part 13g of the shifting plate 13 is substantially flush with the shifting section 12c of the shifting plate 12, such that the serrated part 13g is separated from the free end of the gear member 8. In this case, because the serrated part 13g is not engaged with the gear member 8, the gear member 8 and the bearing sleeve 5c are simultaneously rotated by the shaft 7 such that the gear 2 and the cylinder assembly 3 are operated simultaneously.

As shown in figure 2c, in the hammering mode, the shift member of the transmission switching mechanism 10, i.e. the circular arc-shaped segment, of which the radius is smaller, of the cam 17 is pressed against the shifting section 14c of the connecting plate 14 by the spring 16a and the flat arc-shaped segment of the cam 17 is pressed against the shifting section 12c of the shifting plate 12. The cam 17 is installed onto the housing of the power tool via the shaft 15 and the guiding rod 11 is secured to the power tool, such that the shaft 15 is fixed relative to the longitudinal axis of the guiding rod 11. In this operating mode, the distance between the fork parts 12a and 13a enables them to be engaged into the grooves 8b and 7c and enables the gear member 8 and the bearing sleeve 5 to be simultaneously engaged with the shaft 7, such that the gear member 8 and the bearing sleeve 5c can be driven to rotate.

It is emphasized that, when the gear member 8 and the bearing sleeve 5c are engaged with the shaft 7, the serrated part 13g is separated from the gear member 8 and disengaged from it such that the rotational movement of the gear member 8 is not hampered.

In the exemplary embodiment of the present invention, the center of the shaft 15 coincides with the center of the circular arc- shaped segment, of which the radius is smaller. The normal distance from the center of the shaft 15 of the shift member 17 to the shifting section 14c of the connecting plate 14 is defined as x. The normal distance from the center of the shaft 15 of the shift member 17 to the shifting section 12c of the shifting plate 12 is defined as y. In the hammering mode shown by figures 2a to 2c, y is obviously less than x.

Figures 3a and 3b show that the transmission mechanism 4 according to the exemplary embodiment of the present invention is in the chiseling mode.

As shown in figure 3b, the shift member 17 is rotated by driving the shaft 15. Therefore, the shifting plate 12 is slid relative to the guiding rod 11 far away from the boss 7d of the shaft 7. In the meantime, the fork part 12a of the shifting plate 12 is moved such that the gear member 8 is slid longitudinally far away from the boss 7d of the shaft 7 until the key 8a of the gear member 8 is disengaged from the slot 7a of the boss 7d. Although the shaft 7 is now still driven to rotate by the drive element 6, the shaft 7 is only free rotatable in the hole of the gear member 8 and the gear member 8 is not driven to rotate. Therefore, in this case, the gear 2 of the power tool is not driven to rotate and thus the hammer tube 1 is not rotated. Because only the key 5a of the bearing sleeve 5c is engaged in the slot 7b of the shaft 7, the tool head of the power tool can only be reciprocated along the longitudinal axis of the cylinder assembly 3. Now, the operator may accomplish the chiseling operation using the power tool.

According to the present invention, the mode switching, for example from the hammering mode to the chiseling mode, of the transmission mechanism may be accomplished only by moving the gear member 8 without moving the whole shaft 7. Therefore, any possible worn region between parts is reduced, such that the serviceability of the transmission mechanism is enhanced. Furthermore, it is obviously easier to move the gear member 8 than to move the whole shaft 7, such that the transmission mechanism may be operated more conveniently.

More particularly, figure 3a is a perspective view, showing the power tool having the transmission mechanism 4 assembled with the transmission switching mechanism 10 in the chiseling mode. Figure 3c shows a perspective view of only the transmission switching mechanism 10 in the chiseling mode.

During switching from the hammering mode to the chiseling mode, the shift member 17 is, from a position shown in figure 2c, rotated clockwisely by 90 degrees to a position shown in figure 3c. By comparing figures 2a and 2c with figures 3a and 3c, it is found that, during the shift member 17 is rotated, the shift member 17 is always pressed against the shifting section 12c of the shifting plate 12 and the shifting section 14c of the connecting plate 14 by the spring 16a. During the cam is rotated, the normal distance x from the center of the shaft 15 of the shift member 17 to the shifting section 14c of the connecting plate 14 is unchanged and is always equal to the radius R of the circular arc-shaped segment because the circular arc-shaped segment, of which the radius is small, of the cam 17 is slid over the shifting section 14c and the center of the shaft 15 is stationary relative to the longitudinal axis of the guiding rod 11. Furthermore, during the cam is rotated by 90 degrees as above, the normal distance y from the center of the shaft 15 of the shift member 17 to the shifting section 12c of the shifting plate 12 is continuously increased because the contacting between the flat arc-shaped segment of the shift member 17 and the shifting section 12c of the shifting plate 12 is converted into the contacting between the circular arc-shaped segment and the shifting section 12c. When the cam 17 is in the position shown by figure 3c, the normal distance y is kept maximally as the radius R of the circular arc-shaped segment.

During the above process, because the shaft 15 of the shift member 17 remains stationary relative to the shifting and connecting plates along the longitudinal axis of the guiding rod 11, the connecting plate 14 and the shifting plate 13 remain stationary but the shifting plate 12 is moved to the left along the longitudinal axis of the guiding rod 11, as shown in figure 3c. In this case, as shown in figure 3a, the gear member 8 is driven to move to the left by the shifting plate 12, such that the key 8a of the gear member 8 is disengaged from the slot 7a of the shaft 7. Therefore, the gear member 8 is not driven to rotate by the shaft 7. Additionally, during this process, the gear member 8 is moved towards the serrated part 13g of the shifting plate 13 such that the gear member 8 is engaged with the serrated part 13g and thus the gear member 8 is prevented from rotating.

It should be noted that although in the chiseling mode the key 8a of the gear member 8 is disengaged from the slot 7a of the shaft 7, the gear member 8 is engaged with the serrated part 13g of the transmission switching mechanism 10 so as to prevent the gear member 8 from rotating.

Figures 4a and 4b show that the transmission mechanism 4 according to the exemplary embodiment of the present invention is in the drilling mode.

As shown in figures 4a and 4b, the shaft 15 is driven to rotate the shift member 17. Therefore, the shifting plate 13 is slid relative to the guiding rod 11 far away from the boss 7d of the shaft 7. During the shifting plate 13 is slid, the fork part 13a is correspondingly moved such that the boss 7d of the shaft 7 is moved far away from the wobble bearing 5 and thus the slot 7b of the boss 7d is disengaged from the key 5a of the bearing sleeve 5c while the gear member 8 is moved along with the shaft 7, that is, the gear member 8 is still kept rotating by the shaft 7. Therefore, in this case, although the drive element 6 drives the sleeve tube 9 and the shaft 7 to rotate, the sleeve tube 9 only rotates freely in the central hole of the wobble bearing 5 and the bearing sleeve 5c of the wobble bearing 5 is not rotated, such that the piston is not reciprocated in the cylinder assembly 3. Because the gear member 8 drives only the gear 2 to rotate, the tool head of the power tool is rotated only around the central axis of the hammer tube 1. In this case, the operator may accomplish a drilling operation using the power tool.

More particularly, figure 4a is a perspective view, showing the power tool having the transmission mechanism 4 assembled with the transmission switching mechanism 10 in the drilling mode. Figure 4c shows a perspective view of only the transmission switching mechanism 10 in the drilling mode. During switching from the hammering mode to the chiseling mode, the shift member 17 is, from the position shown by figures 3a and 3c, rotated clockwisely by 90 degrees to a position shown by figure 4a. By comparing figures 3a and 3c with figures 4a and 4c, it is found that, during the shift member 17 is rotated, the segments of the shift member 17 are always pressed against the shifting sections 12c and 14c by the spring 16a. Therefore, the normal distance x is decreased and the normal distance y is unchanged, that is, the normal distance y is always equal to the radius R of the circular arc- shaped segment. In this case, because the shaft 15 is relatively stationary along the longitudinal axis of the guiding rod 11, the shifting plate 12 of the transmission switching mechanism 10 remains stationary while the connecting plate 14 and the shifting plate 13 are simultaneously moved to the left by the springs 16a and 16b. In this mode, the shifting sections 13d and 14a are pressed together by the spring 16a, and the connecting plate 14 and the shifting plate 13 are displaced to the left along the guiding rod 11 by the springs 16a and 16b. Therefore, the shaft 7 is driven by the fork part 13g of the shifting plate 13 to displace to the left along the longitudinal axis of the sleeve tube 9 such that the slot 7b of the shaft 7 is disengaged from the key 5a of the wobble bearing 5.

As clearly shown in figure 4c, in this drilling mode, the serrated part 13g of the shifting plate 13 is displaced to the left along the guiding rod 11 such that the serrated part 13g is disengaged from the gear member 8 and is separated from it. Again, the serrated part 13g of the shifting plate 13 is substantially flush with the shifting section 12c of the shifting plate 12.

It should be noted that although in the hammering or drilling mode the serrated part 13g of the shifting plate 13 is shown substantially flush with the shifting section 12c of the shifting plate 12, it is possible that they are not flush with each other as soon as they may achieve the same function.

Now the vario-lock mode of the transmission mechanism 4 which is realized by the transmission switching mechanism 10 according to the present invention will be explained below. Figures 5a and 5b show that the transmission mechanism 4 and its transmission switching mechanism according to the exemplary embodiment of the present invention are in the vario-lock mode.

It should be noted that in both the vario-lock mode according to the present invention and the chiseling mode according to the invention, only the gear member 8 is disengaged from the shaft 7. However, the two modes are distinguished in mainly that in the vario-lock mode, the serrated part 13g of the transmission switching mechanism 10 is not engaged with the gear member 8. Therefore, in the vario-lock mode, although the gear 2 of the hammer tube 1 is engaged with the gear member 8, the hammer tube 1 is free rotatable. The vario-lock mode is characterized in that although the power tool is operated in a mode similar to the chiseling mode, the tool head may be freely rotated around the longitudinal central axis of the cylinder assembly 3 such that this may facilitate accomplishing some special processing task.

In the vario-lock mode, the normal distance y from the central axis of the shaft 15 of the shift member 17 to the shifting section 12c of the shifting plate 12 is less than the normal distance x from the central axis of the shaft 15 of the shift member 17 to the shifting section 14c of the connecting plate 14, and the normal distance x is kept to be equal to the radius of the circular arc-shaped segment of the shift member 17. Now the operation principle of the hammering mode switching into the vario-lock mode will explained as an illustrative but not restrictive example.

As shown in figure 2c, in the hammering mode, the normal distance y reaches a minimum value and the normal distance x is equal to the radius R of the circular arc-shaped segment. As shown in figure 5b, the cam 17 is rotated clockwisely by an angle, for example, of 45 degrees such that the normal distance y is increased but is less than the radius R. Because the shaft 15 is stationary longitudinally, the connecting plate 14 and the shifting plate 13 are kept stationary longitudinally and the shifting plate 12 is moved to the left as shown. Because the fork part 12a is engaged in the groove 8b of the gear member 8, the gear member 8 is driven to move to the left by the shifting plate 12 such that the gear member is disengaged from the shaft 7. However, the distance that the shifting plate 12 moves is insufficient to enable the serrated part 13g of the shifting plate 13 to engage with the gear member 8.

The case that the hammering mode is switched into the vario-lock mode is only illustratively explained above. However, according to the present invention, it is also possible that the drilling or chiseling mode is switched directly into the vario-lock mode in a similar principle.

In the embodiment of the present invention, the shift member 17 is embodied as the cam as shown. However, the present invention is not limited by this. For example, the flat arc-shaped segment of the shift member 17 can be replaced by a flat segment and/or the circular arc- shaped segment, of which the radius is small, of the shift member 17 can be replaced by an elliptic segment or a triangular segment with chamfer. That is, the shift member 17 can be comprised of two contacting portions which can be contacted with the shifting sections 12c and 14c respectively. The distance from the edge of one of the contacting portions to the central axis of the shaft 15 is always larger than the distance from the edge of the other of the contacting portions to the central axis of the shaft 15. The shapes and sizes of the contacting portions are designed such that they enable the shift member 17 to be in the positions shown by figures 2c, 3c, 4c and 5b. In the technical solution of the present invention, the connecting plate 14 may be optionally omitted. In this case, for example, the shift member 17 may be located between the shifting plates 12 and 13, while the springs 16a and 16b are arranged to act on the shifting plates 12 and 13 such that the plates can be returned to their original positions. For example, the springs 16a and 16b are arranged to act on the sections of the shifting plates 12 and 13 opposite to the shift member 17 respectively. In this way, by rotating the shift member 17, the transmission mechanism can also achieve the above mode.

Optionally, according to the present invention, in the case that the connecting plate 14 is provided, the shift member 17 may also be located between the shifting plates 12 and 13. In this case, by the springs acting between the connecting and shifting plates, the shifting plates 12 and 13 may also be driven by rotating the shift member 17. It is appreciated that the present description non-restrictively explains the preferred embodiment of the present invention. Any structure which can enable the shift member 17 to drive the shifting plates 12 and 13 falls into the scope of the present invention.

The inventive transmission mechanism and its four modes are only illustratively explained above. However, optionally, the transmission mechanism according to the present invention can be in other modes. For example, the gear member 8 and the shaft 7 may be moved longitudinally such that the slots 7a and 7b of the boss 7 may be disengaged from the key 8a of the gear member 8 and the key 5a of the bearing sleeve 5c. In this way, the power tool can be in a resting for maintenance mode so that replacement, repairmen or other operations can be performed to the tool head.

Furthermore, in the exemplary embodiment of the present invention, the shaft 7 is inserted in the sleeve tube 9 such that the shaft 7 may be driven by the drive element 6 to rotate in any case. However, it is also appreciated that a suitable clutch arrangement is provided between the shaft 7 and the sleeve tube 9. Therefore, although the shaft 7 is slidable longitudinally in the sleeve tube 9, the shaft 7 may be driven by the drive element 6 to rotate only when the clutch arrangement is put into function (activated). This clutch arrangement may be of any existing type of clutch known by those skilled in the art and may comprises, but not limited to, a friction clutch or the like. Therefore, when the shaft 7 is slid in such a way that the clutch arrangement is not put into function, neither the gear member 8 nor the bearing sleeve 5c can be rotated. In this case, it is safe to replace the tool head for the power tool and to perform maintenance or service to it.

Any modifications, changes or combinations to the embodiments described here which can be made by those skilled in the art after reading the present specification without departing from the spirit of the present invention fall within the scope of the present invention.