Technical Field

The present invention relates to a transmission mechanism for a power tool, especially for an electrical hammer drill.

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, for example a drill bit, and a driving motor of the power tool.

CN 1743138A (Chinese patent application No. 200510099493.X) 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, which may substantially increase the difficulty of manufacturing the shaft. Furthermore, all the switching actions between different modes are accomplished only by moving the transmission shaft, which may increase difficulty in the assembling process.

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 the 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.

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

Summary of the Invention

To this end, one aspect of the present invention is aimed at providing a transmission mechanism for a power tool, which transmission mechanism comprises: a shaft driven by a drive mechanism of the power tool, the shaft comprising a first axial portion, a second axial portion and a driving portion provided between the first and second axial portions; a gear mounted to the first axial portion, the gear being slidable relative to the first axial portion in an extension direction of the shaft, wherein the gear and the driving portion of the shaft are provided therebetween with driving parts which are matable with each other; and a wobble bearing mounted to the second axial portion, the wobble bearing comprising an inner ring, an outer ring and a railway provided between the inner ring and the outer ring in an orientation oblique relative to the second axial portion, the inner ring and the driving portion being provided therebetween with driving parts which are matable with each other, and the outer ring being provided thereon with a swing arm which extends in an oblique plane defined by the railway.

Preferably, the driving portion of the shaft is integrally formed on the shaft. Preferably, the driving portion of the shaft is a boss on the shaft, and the corresponding driving part of the driving portion of the shaft is a slot or key provided on the boss of the shaft for being engaged with a corresponding key or slot of the inner ring of the wobble bearing and/or a corresponding key or slot of the gear.

Preferably, the wobble bearing is mounted to the second axial portion via a sleeve tube in which the second axial portion is slidable.

Preferably, the driving part of the driving portion of the shaft is a component mounted on the shaft.

Preferably, a bearing is mounted between the first axial portion of the shaft and the gear and/or another bearing is mounted between the second axial portion of the shaft and the inner ring of the wobble bearing.

Preferably, the sleeve tube is provided on its periphery with a locking arrangement, which locking arrangement is matable with a corresponding locking arrangement on the inner ring of the wobble bearing such that the inner ring is rotatable only around a central axis of the sleeve tube.

Preferably, the driving portion is located between the gear and the wobble bearing.

Preferably, the sleeve tube is integrated with a drive element of the drive mechanism.

Another aspect of the present invention is aimed at providing a power tool comprising the above-mentioned transmission 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 of the power tool according to the preferred embodiment of the present invention wherein the transmission mechanism is in a hammering mode;

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

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

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

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

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

Detailed Description of Preferred Embodiments

A transmission 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 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 mechanism according to the present invention.

Now a power tool according to the present invention and a transmission 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 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, and a transmission mechanism 4. 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.

In a normal state, the gear member 8 is free rotatable on the shaft 7around 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 for example 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 such that the wobble bearing 5 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.

Normally, 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 5 a of the wobble bearing 5 is mated with a slot 7b of the shaft 7 (as shown in figure 2). Because the rollway of the wobble bearing 5 is provided obliquely relative to the shaft 7, especially relative to the second axial portion of the shaft 7, the swing arm integrated 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 for example a plow bit is mounted on the power tool, the operator may accomplish an operation for example 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 rotating shaft 7 (as shown in figure 1), 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 mechanism according to the preferred embodiment of the present invention will be explained on the basis of figures 2 to 5. The transmission mechanism according to the present invention can be used to adjust the power tool such that the power tool may be in different modes, such as hammering, chiseling and drilling 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 appreciated that in an alternative embodiment the sleeve tube 9 is integrated with the drive element 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, may 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, for example 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, i.e. the second axial portion, is slidably inserted 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 may 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 may 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 the 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. In this embodiment, the wobble bearing 5 is mounted between the boss 7d and the drive element 6. At one end of the boss 7d facing towards the drive element 6 are 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. 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 a 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 rotation.

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 is appreciated 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 is appreciated 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.

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 both engaged in the slots 7a and 7b of the shaft 7, such that the gear member 8 and the wobble bearing 5 may be driven to rotate by the rotating shaft 7. In this case, the gear member 8 drives the gear 2 to rotate, such that the hammer tube 1 is rotated; at the same time, the swing arm 5b is swung back and forth by the rotating bearing sleeve 5c, such that the piston is reciprocated in the cylinder assembly 3. In this mode, a tool head mounted on the power tool can carry out a rotation movement and a reciprocating movement for chiseling. In this way, the operator may accomplish a hammering operation using the power tool mounted with the tool head for example a drill bit.

No serrated wheel part is formed directly on the shaft 7 of the transmission mechanism 4 according to the present invention, and indeed the pre-formed gear member 8 is mounted around the shaft. Therefore, this greatly decreases the difficulty of manufacturing the shaft. That is, the cost for manufacturing the transmission mechanism according to the present invention is reduced. Furthermore, when either the gear member or the shaft is impaired, the impaired one may be easily replaced, which reduces the cost of maintenance.

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 3a, in this mode, the gear member 8 is slid longitudinally far away from the boss 7d of the shaft 7, such that the key 8a of the gear member 8 is disengaged from the slot 7a of the boss 7d. Although the shaft 7 is rotated, it only rotates freely in the central hole of the gear member 8 and does not drive the gear member 8 to rotate. Therefore, in this case, the gear 2 of the power tool is not rotated, and the hammer tube 1 is not rotated. Since only the key 5a of the wobble bearing 5 is engaged in the slot 7b of the shaft 7, the tool head of the power tool can be reciprocated only along the longitudinal axis of the cylinder assembly 3. At this time, the operator can accomplish a chiseling operation using the power tool.

Using the technical means of 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.

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, in this mode, the shaft 7 is slid longitudinally such that the boss 7d of the shaft 7 is moved 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 still kept rotating by the shaft 7. In this case, although the drive element 6 drives 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.

The transmission mechanism according to the present invention and its three operating modes are explained illustratively above. However, the transmission mechanism according to the present invention may optionally be in other operating 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 7d may be simultaneously disengaged from the key 8a of the gear member 8 and the key 5 a of the bearing sleeve 5c. In this way, the power tool may be in an idle or resting for maintenance mode so that replacement, maintenance 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.