Power tool and two-speed gear assembly for a power tool

Abstract

The present invention relates to a power tool, comprising an input shaft, an output shaft and a two-speed power transmission device (T), the two-speed power transmission device (T) comprising a planetary gear (4) and a gear shift assembly, the gear shift assembly being used to pass torque through or over the planetary gear (4), the gear shift assembly comprising a driving member, a driven member (1) and an axially movable coupling sleeve (6), the axially movable coupling sleeve (6) being arranged to mutually couple the driving member (2) and the driven member (1) in a first position and to mutually couple the planetary gear (4) and the driven member (1) in a second position. A linear actuator (13, 14) is arranged to displace the coupling sleeve between the first position and the second position, wherein the linear actuator comprises a linearly movable push rod (13), the push rod (13) being arranged to displace the coupling sleeve. The present invention also relates to a method in such a power tool and a two-speed power transmission device for such a power tool.

Description

Technical Field

[0001] The present invention generally relates to a power tool, and more particularly, to a power tool including a dual-speed gear assembly. Background Art

[0002] Different types of power tools are known to be used in various industries, one common type of which is a tightening tool for tightening screws or bolts.

[0003] One problem known to give rise to various design challenges in this field is that the working conditions and the requirements for the expected output often vary greatly during use, for example with regard to the speed and torque required during different parts of a typical working operation. This is the case, for example, with the above-mentioned tightening tools, during the initial stages of tightening, during tightening the screw or nut, the so-called run-down, the required torque is low, while the speed is ideally high to reduce the time required for the operation, whereas during the actual tightening phase, i.e. during the actual tightening of the joint, the required torque is higher.

[0004] However, in order to be able to provide the desired torque levels, power tools subject to these varying requirements include one or more transmission devices, such as one or more planetary gear stages connected in series.

[0005] However, using such a transmission to achieve the higher torque levels required for actual tightening, the rotational speed provided is correspondingly reduced, resulting in an undesirably lower rotational speed also during screwing in. This becomes a significant problem, particularly in the field of power tools suitable for tightening large screws to very high torque values, where the desired high torque is often provided at very low RPMs, which in turn often makes the screwing in phase unreasonably slow.

[0006] To alleviate some of these problems, attempts have been made to use two-speed power transmissions, i.e. variators, in which the force flow through the gear unit can be varied so that a higher rotational speed can be used during screw-in, with the high torque / low speed mode being used only when required during actual tightening.

[0007] However, there are still many problems associated with such transmissions. For example, one known problem is the lack of control over the actual progress of the gearshift operation, i.e., knowing whether the gearshift actually occurred correctly. This lack of precise control over the actual current position of the gear elements may lead to damage to the gears and couplings.

[0008] Solutions have been proposed involving complex mechanisms including synchronizer rings or bulky sensors, which inherently complicate the design and generally require a large amount of space.There is therefore a need for improvement in the field of two-speed gear units for power tools. Summary of the invention

[0009] Therefore, it is desirable to provide a power tool with an improved two-speed transmission. In particular, it is desirable to provide such a transmission which provides improved possibilities for controlling the gear shifting. In order to better solve one or more of these problems, a gear unit for a tightening tool, a power tool comprising such a gear unit and a method for controlling such a power tool are provided as defined in the independent claims. Preferred embodiments are defined in the dependent claims.

[0010] According to a first aspect of the present invention, there is provided a power tool including a two-speed power transmission device, the tool including a housing, an input shaft, an output shaft and a two-speed power transmission device, the two-speed power transmission device including a planetary gear and a two-speed gear shift assembly, the two-speed gear shift assembly is used to make the torque pass through the planetary gear in a high torque / low speed driving mode or to make the torque pass over the planetary gear in a low torque / high speed driving mode. The gear shift assembly includes a driving member, a driven member, an axially movable coupling sleeve and a linear actuator, the driving member is drivingly connected to the input shaft, the driven member is drivingly connected to the output shaft, the axially movable coupling sleeve is arranged to couple the driving member and the driven member to each other in a first position, and is arranged to couple the planetary gear and the driven member to each other in a second position, the linear actuator is arranged to displace the axially movable coupling sleeve between the first position and the second position, wherein the linear actuator includes a linearly movable push rod, the push rod is arranged to displace the coupling sleeve between the first position and the second position.

[0011] According to a first aspect, a two-speed transmission provides an inventive solution to the above-mentioned problem by including a gear shifting mechanism designed to pass torque through the planetary gears in a high torque / low speed drive mode or to bypass the planetary gears in a low torque / high speed drive mode, wherein an improved possibility of precisely controlling the gear shift is provided by utilizing a coupling sleeve displaced by a linear actuator.

[0012] More specifically, when the linear actuator is arranged to displace the coupling sleeve, engagement (or disengagement) in each operating mode can be determined based on the position of the linear actuator. Therefore, the design cleverly provides a two-speed power transmission device that can provide accurate and precise gear shift control.

[0013] According to one embodiment, the power tool further comprises a motor and a device for monitoring the torque transmitted by the tool. The device for monitoring the torque transmitted by the tool may include, for example, a sensor, such as a torque sensor. Other examples include circuits adapted to monitor motor current or other internally provided data related to motor performance. The power tool may also form part of a system comprising a power tool and an external control unit, the external control unit operating to control the power tool.

[0014] For such a power tool, according to one embodiment, the motor is an electric motor. The tool can be, for example, a handheld power tool selected from a screwdriver, a nut runner, a drill, and a grinder. However, those skilled in the art recognize that only slight modifications to the structure are required for use with a stationary or fixed tool. In some embodiments, the power tool can be a battery-powered tool. In one embodiment, the power tool is a tool that provides a higher tightening torque, for example in the range of 2400-8000 Nm.

[0015] According to one embodiment, the gear assembly further comprises a coupling assembly arranged between the coupling sleeve and the linear actuator, the coupling assembly comprising a first element rotationally coupled to the sleeve and a second element translationally coupled to the push rod, wherein the rotation of the first element is independent of the rotation of the second element, and wherein the second element is arranged to push the first element in an axial direction. Thus, the rotation of the sleeve and the rotation of the motor do not affect the linear actuator, and the adjustment of the axial position of the sleeve can occur independently of the rotation. The second element can form part of the push rod.

[0016] In one embodiment, the gear assembly further comprises a coupling assembly arranged to couple (i.e. associate or connect) the coupling sleeve and the linear actuator, the coupling assembly comprising a first element rotationally coupled to the sleeve and a second element translationally coupled to the push rod, wherein the rotation of the first element is independent of the rotation of the second element, and wherein the second element is arranged to push the first element in an axial direction. Thus, the rotation of the sleeve and therefore the rotation of the motor does not affect the linear actuator, and adjustment of the axial position of the sleeve can occur independently of the rotation. The second element can form part of and / or be formed by the push rod.

[0017] According to one embodiment, the coupling sleeve is arranged concentrically relative to the planetary gear, wherein the second element is adapted to engage the first element at a position located in the center of the sleeve. This arrangement provides a compact space-saving design. In addition, this design further simplifies the required bearing arrangement.

[0018] According to one embodiment, the first element is a ball arranged at least partially in the sleeve, wherein the second element arranged to push the ball is formed by a push rod. Thus, the end of the push rod can abut against the rotating rod to displace the sleeve. The ball can be arranged, for example, at the end of the sleeve facing the linear actuator, for example by a press fit or the like.

[0019] According to one embodiment, the gear assembly further comprises a coupling assembly arranged between the coupling sleeve and the linear actuator, the coupling assembly comprising a first element rotationally coupled to the sleeve, wherein the rotation of the first element is independent of the rotation of the push rod, and wherein the push rod is arranged to push the first element in an axial direction. Thus, the rotation of the sleeve and therefore the rotation of the motor does not affect the linear actuator, and the adjustment of the axial position of the sleeve can occur independently of the rotation. In one embodiment, the coupling sleeve is arranged concentrically with respect to the planetary gear, and the push rod is adapted to engage the first element at a position located in the center of the sleeve. In one embodiment, the first element is a spherical object at least partially arranged in the sleeve.

[0020] In one embodiment, the connecting member further includes a second element that is translationally connected to the push rod, and the second element is adapted to engage the first element, wherein the rotation of the first element is independent of the rotation of the push rod, and wherein the push rod is arranged to push the first element in an axial direction by pushing the second element.

[0021] According to one embodiment, the first axially acting spring means is arranged for biasing the coupling sleeve towards the first position of said coupling sleeve.Examples include a compression spring arranged against a suitable part of, for example, the housing and acting on the second end of the sleeve.

[0022] According to one embodiment, the first position and the second position are respectively a first end position and a second end position, wherein the coupling sleeve is continuously movable between them and can be positioned at any position between the first end position and the second end position. Or, in other words, the push rod of the linear actuator can be positioned at any position between the first end position and the second end position. Preferably, the position of the push rod can be monitored over the entire interval.

[0023] According to one embodiment, the driven member comprises a first engagement portion adapted to engage a corresponding congruent first portion of the coupling sleeve, and wherein the planet gear comprises a planet carrier comprising a second engagement portion adapted to engage a corresponding congruent second portion of the coupling sleeve. For example, according to one embodiment, at least one of the first engagement portion and the second engagement portion has a polygonal shape, with examples including a square or hexagonal cross-section.

[0024] According to one embodiment, the planetary gear is a first planetary gear stage. According to one embodiment, the power tool further comprises a front gear unit or a second stage gear unit. In such an embodiment, the transmission of the present invention can be arranged between the motor and the front or second stage gear unit, so that the driven member of the transmission engages the front gear, i.e. is drivingly connected to the output shaft via the front gear. This is advantageous because the front gear unit for such a tool can be a replaceable front gear unit, so that the front gear unit can be replaced according to the desired torque while the two-speed transmission remains in or on the tool.

[0025] According to one embodiment, the power tool further comprises a bevel gear arranged between the input shaft and the drive member, so that the drive member is connected to the input shaft via the bevel gear. This may be advantageous because due to the change of direction of the power transmission system at the bevel gear, the above-mentioned design of the centered push rod can be achieved more easily.

[0026] According to one embodiment, the linear actuator is a linear motor, for example, a DC servo motor including a solid stator housing, a coil assembly, and a multi-pole magnetic push rod.

[0027] According to one embodiment, the linear motor includes at least one internal position sensor configured to sense the position of the push rod. Examples include internal Hall sensors. Thus, the position of the push rod can be continuously determined and monitored. In one embodiment, the linear motor further includes a control unit configured to, for example, monitor and control the movement of the push rod and communicate with, for example, an external control unit configured to control the power tool.

[0028] According to a second aspect of the present invention, a two-speed power transmission device is provided, which is used for a power tool according to any one of the above embodiments, the transmission device includes a planetary gear and a two-speed gear shift assembly, the two-speed gear shift assembly is used to make the torque pass through the planetary gear in a high torque / low speed driving mode or to make the torque pass over the planetary gear in a low torque / high speed driving mode. The gear shift assembly includes a driving member, a driven member, a coupling sleeve and a linear actuator, the driving member is drivingly connected to the input shaft, the driven member is drivingly connected to the output shaft, the coupling sleeve is arranged to mutually couple the driving member and the driven member in a first position, and is arranged to mutually couple the planetary wheel carrier and the driven member in a second position, and the linear actuator is arranged to displace the coupling sleeve between the first position and the second position, wherein the linear actuator is a linear actuator including a linearly movable push rod, the push rod is arranged to displace the coupling sleeve between the first position and the second position.

[0029] The objects, advantages and features of a transmission conceivable within the scope of the second aspect of the present invention may be readily appreciated by reference to the foregoing discussion of the first aspect of the present invention.

[0030] According to a third aspect of the present invention, a method for controlling a power tool, the power tool includes a planetary gear and a two-speed gear switching assembly, the two-speed gear switching assembly is used to allow torque to pass through the planetary gear in a high torque / low speed drive mode or to allow torque to pass over the planetary gear in a low torque / high speed drive mode by means of a connecting sleeve and a linear actuator, the linear actuator is arranged to move the connecting sleeve, the method includes the following steps: operating the tool in a low torque / high speed drive operation mode, wherein the connecting sleeve is arranged in a first position so that the torque passes over the planetary gear; confirming that a tight fit position has been reached; displacing the connecting sleeve forward to reach a second position by axially moving the linear actuator in a first direction; and operating the tool in a high torque / low speed drive operation mode, wherein the connecting sleeve is arranged in a second position so that the torque passes through the planetary gear.

[0031] According to one embodiment, the method is a method in a power tool comprising a dual-speed transmission according to any of the preceding embodiments, the method comprising the steps of: operating the tool in a low torque / high speed drive operating mode, wherein the coupling sleeve is arranged in the first position in which the drive member and the driven member are coupled to each other; confirming that the snug position has been reached; displacing the coupling sleeve forwardly to reach the second position by axial movement in a first direction by means of a linear actuator; and operating the tool in a high torque / low speed drive operating mode, wherein the coupling sleeve is arranged in the second position in which the planetary wheel carrier and the driven member are coupled to each other. Forwardly is understood to be a direction towards the end of the output shaft, at which end a socket or the like will engage.

[0032] That is, in other words, when screwing in (i.e. low torque / high speed mode) begins, the push rod and therefore the coupling sleeve are in the first position, i.e. the rear position, in which the coupling sleeve connects the drive member to the output shaft. When the tight fit position is reached, the screwing in ends, which can be identified, for example, by exceeding the current limiting threshold. For the sake of completeness, the tight fit position is the point at which the screwing in phase enters the actual tightening phase. For example, these tightening conditions can be monitored by an external control unit. This is followed by sending a signal to the linear motor that the screwing in is complete, and the displacement of the push rod and therefore the displacement of the coupling sleeve forward toward the second position begins. When the coupling sleeve engages the planetary gear, i.e. the coupling sleeve is positioned in the second position, a signal can be sent, for example, to an external control unit, indicating that the low speed gear is in place. Now, the final and actual tightening phase (i.e. high torque / low speed) can begin.

[0033] According to one embodiment, the step of reaching the second position further includes, if the coupling sleeve fails to engage the planetary gear, achieving rearward displacement by axial rearward movement of the linear actuator in a second opposite direction; achieving rotation of the planetary gear; and moving the coupling sleeve forward by axial movement in the first direction by means of the linear actuator to reach the second position.

[0034] According to one embodiment, the method is a method in a power tool including a dual-speed transmission device according to any one of the aforementioned embodiments, and the step of reaching the second position further includes: if the connecting sleeve fails to engage the planetary wheel carrier, a rearward displacement is achieved by an axial rearward movement of the linear actuator in a second opposite direction; a rotation of the drive member is achieved; and the connecting sleeve is moved forward by an axial movement in a first direction by means of a linear motor to reach the second position.

[0035] That is, if the push rod fails to reach the front or first position due to, for example, a rotational mismatch between the cross section of the sleeve and the corresponding surface of the planet gear to be engaged, the direction of axial movement is reversed and the push rod is moved back a short distance, possibly simultaneously with the motor rotating the planet carrier, thereby allowing the coupling sleeve to provide a new position to engage. Thus, changes between drive modes of the transmission can be facilitated.

[0036] In one embodiment, the method may further include the steps of recognizing that the target torque has been reached and displacing the coupling sleeve backward to return to the first position by axial movement of the linear motor in the second direction. That is, the torque may be monitored by, for example, a torque sensor, and when the desired torque is reached, the linear motor receives a signal and returns to re-enter the high speed / low torque mode. This movement of the coupling sleeve may be followed by or combined with simultaneous rotation of the motor to help the coupling sleeve properly engage as described above.

[0037] The objects, advantages and features of the method contemplated within the scope of the third aspect of the present invention may be readily appreciated by reference to the foregoing discussion of the second aspect of the present invention.

[0038] Further objectives, features and advantages of the present invention will become apparent when studying the following detailed disclosure, the drawings and the appended claims.Those skilled in the art will appreciate that different features of the present invention can be combined to create embodiments other than those described in the following. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] The invention will be described in the following illustrative and non-limiting detailed description of exemplary embodiments with reference to the accompanying drawings, in which

[0040] Figure 1is a cross-sectional view of an exemplary power tool including a dual-speed power transmission according to one embodiment.

[0041] Figure 2 is a first perspective view of some components of an exemplary transmission according to one embodiment.

[0042] All the figures are schematic, not necessarily to scale, and generally show only parts which are necessary in order to elucidate the invention, wherein other parts may be omitted or merely mentioned. DETAILED DESCRIPTION

[0043] Figure 1 is a cross-sectional view of a portion of an exemplary power tool according to an embodiment, in this case a hand-held tightening tool. The tool comprises a housing H, an input shaft IS, a motor connected to a drive member 2 via a bevel gear 20, an output shaft 1, and a two-speed transmission T arranged between the input shaft and the output shaft. Further, the tool is connected to an external control unit, which operates to control the rotation speed of the motor, which will be described in more detail below when describing the function of the tool.

[0044] Figure 1 The two-speed power transmission device 1 of the embodiment shown in the figure includes a planetary gear 4 and a gear shift assembly, wherein the gear shift assembly is used to make the torque from the input shaft IS to the output shaft 1 through the planetary gear 4 in the high torque / low speed driving mode or to make the torque from the input shaft IS to the output shaft 1 across the planetary gear 4 in the low torque / high speed driving mode. The transmission device in the low torque / high speed driving mode is as follows Figure 1 as shown in .

[0045] The planetary gear 4 comprises a ring gear (or gear ring) fixed in the housing H and a planetary carrier 41. The transmission assembly comprises a drive member 2, which in the embodiment shown forms part of a bevel gear 20, and a driven member 1 drivingly connected to an output shaft 1.

[0046] The coupling sleeve 6 is axially movable between a first position, in which the sleeve couples the drive member 2 and the driven member 1 to each other, and a second position, i.e. Figure 1 In the low torque / high speed mode shown in , in the second position the sleeve couples the planetary gear 4 (more specifically the planet carrier 4 a ) and the driven member 1 to each other.

[0047] The linear actuator 13, 14 is used to move the coupling sleeve between the first and second positions, more specifically, in the illustrated embodiment, a linear DC servo motor comprising a solid stator housing 14, a coil assembly and a linearly movable multi-pole magnetic push rod 13 is arranged to push the coupling sleeve from the first position to the second position. The linear motor further comprises an internal Hall sensor configured to sense the position of the rod 13 and an internal control unit or controller board 15. The compression spring 3 is arranged to bias the coupling sleeve 6 towards the first position.

[0048] In the embodiment shown, the push rod engages with a second element 12 of a coupling assembly arranged between the coupling sleeve 6 and the linear motors 13, 14. However, the second element 12 in the embodiment shown forms part of the push rod. The coupling assembly further comprises a first element 8 in the form of a ball 8, which is arranged in the sleeve 6 at a first end 6a of the sleeve 6 and thus rotates with the coupling sleeve 6. The rotation of the sleeve 6 is independent of the rotation of the push rod 13 of the linear motor (and therefore independent of the rotation of the second element 12 forming part of the push rod 13). The ball 8 has a suitable size to fit the end 6a of the coupling sleeve 6, and the push rod 13 is arranged to engage (i.e. push) the ball at a position located in the center of the sleeve (i.e. via the second element 12).

[0049] Now refer to Figure 2 Describing the engagement between the coupling sleeve 6 and the driven member 1 in the first mode and with the planet carrier 41 in the second mode, Figure 2 The sleeve 6 , the planet carrier 41 , the drive component 2 and the driven component 1 are shown in the perspective view.

[0050] from Figure 1 and Figure 2 It can be seen that the driven member 1 is supported by a bearing 50 at a first end 1a and comprises a first engagement portion 1b at a second end 1b. The planetary carrier 41 similarly comprises a second engagement portion 41b. These engagement portions 1b and 41b are adapted to engage the corresponding first and second portions 6a, 6b of the coupling sleeve 6, the corresponding interaction surfaces having a matching shape, which in both cases is hexagonal in the embodiment shown.

[0051] In operation, the power tool of the illustrated embodiment forms part of a system including an external control unit (not shown) operative to control the tool.

[0052] The coupling sleeve 6 is initially biased towards the first position to perform screwing in, i.e. the low torque / high speed mode. Therefore, the push rod 13 is also in the rear position where the coupling sleeve 6 connects the drive member with the output shaft 1. Figure 1 .

[0053] The screwing in is finished when the tight fit position is reached, which in the embodiment shown is recognized by the external control unit when the current limiting threshold is exceeded. When the linear motor receives the signal that the screwing in is finished, the displacement of the push rod 13 forwards towards the second position begins, and thus the displacement of the coupling sleeve 6 forwards towards the second position begins.

[0054] The position of the push rod 13 and therefore the position of the coupling sleeve 6 is monitored by an internal Hall sensor, so that it can be determined when the coupling sleeve engages the planetary gear, i.e. the second position has been reached. A signal is sent to an external control unit and the final and actual tightening phase (i.e. high torque / low speed mode) begins. However, if the corresponding hexagonal matching section 6a of the coupling sleeve 6 is not aligned with the planet carrier and the sleeve 6 fails to engage the planet wheel carrier 41, the linear motor achieves a linear movement in the opposite direction (i.e. backwards). The forward movement is then repeated, but in combination with a simultaneous slow rotation of the motor and therefore the carrier 41 allows a new position to facilitate engagement. Those skilled in the art will appreciate that the forward movement and rotation can also be performed as consecutive steps.

[0055] During final tightening, the torque is monitored by a torque sensor (not shown), and when the desired torque is reached, the linear motors 13, 14 receive a signal and the push rod 13 moves back to allow the sleeve 6 to perform the high speed / low torque mode again. This movement of the coupling sleeve 6 can be combined with the simultaneous rotation of the motor to help the coupling sleeve engage correctly as described above.

[0056] Although the present invention has been shown and described in detail in the drawings and the foregoing description, such showing and description should be considered illustrative or exemplary rather than restrictive; the present invention is not limited to the disclosed embodiments. It is understood by those skilled in the art that many modifications, variations and changes are conceivable within the scope defined by the appended claims. In addition, in practicing the claimed invention, those skilled in the art can understand and implement variations of the disclosed embodiments after studying the drawings, the disclosure and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "one" or "an" does not exclude a plurality. The fact that certain measures are recorded in mutually different dependent claims does not mean that a combination of these measures cannot be used to advantage. Any figure mark in the claims should not be interpreted as limiting the scope of the claims.

Claims

1. A power tool comprising: Housing (H); Input shaft (IS); Output shaft; as well as Two-speed power transmission (T), The two-speed power transmission device comprises a planetary gear assembly (4) and a two-speed gear shift assembly, wherein the two-speed gear shift assembly is used to allow torque to pass through the planetary gear assembly (4) in a high torque / low speed driving mode or to allow torque to pass over the planetary gear assembly (4) in a low torque / high speed driving mode; The gear switching assembly includes a drive member (2) drivingly connected to the input shaft, a driven member (1) drivingly connected to the output shaft, an axially movable coupling sleeve (6) arranged to couple the drive member (2) and the driven member (1) to each other in a first position and arranged to couple the planetary gear assembly (4) and the driven member (1) to each other in a second position, and a linear actuator (13, 14) arranged to displace the coupling sleeve between the first position and the second position, wherein the linear actuator comprises a linearly movable push rod, the push rod being arranged to displace the coupling sleeve between the first position and the second position, wherein the planetary gear assembly further comprises a coupling assembly arranged between the coupling sleeve and the linear actuator, the coupling assembly comprising a first element (8) which is rotationally coupled to the coupling sleeve, wherein the rotation of the first element is independent of the rotation of the push rod, and wherein the push rod is arranged to push the first element in an axial direction, wherein the coupling sleeve is arranged concentrically with respect to the planetary gear assembly, and wherein the push rod is adapted to engage the first element at a position located in the center of the coupling sleeve.

2. The power tool according to claim 1, wherein: The first element is a ball arranged at least partially in the coupling sleeve.

3. A power tool according to any one of the preceding claims, wherein: First axially acting spring means (3) are arranged for biasing the coupling sleeve towards the first position of the coupling sleeve.

4. The power tool according to claim 1, wherein: The first position and the second position are a first end position and a second end position, and wherein the coupling sleeve is continuously movable therebetween and positionable at any position between the first end position and the second end position.

5. The power tool according to claim 1, wherein: The driven member comprises a first engagement portion (1b) adapted to engage a corresponding conforming first portion of the coupling sleeve, and The planetary gear assembly comprises a planet wheel carrier (41), the planet wheel carrier (41) comprising a second engagement portion (41b), the second engagement portion (41b) being adapted to engage a corresponding mating second portion of the coupling sleeve.

6. The power tool according to claim 5, wherein: At least one of the first engaging portion and the second engaging portion has a polygonal cross-section. 7 . The power tool according to claim 1 , further comprising a bevel gear disposed between the input shaft and the drive member, such that the drive member is connected to the input shaft via the bevel gear.

8. The power tool according to claim 1, wherein: The linear actuator is a linear DC servo motor including a solid stator housing, a coil assembly, and a multi-pole magnetic push rod.

9. The power tool according to claim 1, wherein: The linear actuator includes at least one internal position sensor configured to sense a position of the push rod.

10. The power tool according to claim 1, wherein: The planetary gear assembly is a first planetary gear stage.

11. A two-speed power transmission device for use with a power tool according to any one of the preceding claims, the transmission device comprising a planetary gear assembly and a two-speed gear shift assembly, the two-speed gear shift assembly being used to allow torque to pass through the planetary gear assembly in a high torque / low speed driving mode or to bypass the planetary gear assembly in a low torque / high speed driving mode; The gear switching assembly includes a drive member drivingly connected to the input shaft, a driven member drivingly connected to the output shaft, a coupling sleeve arranged to couple the driving member and the driven member to each other in a first position and arranged to couple the planetary gear assembly and the driven member to each other in a second position, and a linear actuator arranged to displace the coupling sleeve between the first position and the second position, in, The linear actuator is a linear actuator comprising a linearly movable push rod, the push rod being arranged to displace the coupling sleeve between the first position and the second position, The planetary gear assembly further includes a coupling assembly disposed between the coupling sleeve and the linear actuator, the coupling assembly including a first element (8) which is rotationally coupled to the coupling sleeve, wherein the rotation of the first element is independent of the rotation of the push rod, and wherein the push rod is arranged to push the first element in an axial direction, wherein the coupling sleeve is arranged concentrically with respect to the planetary gear assembly, and wherein the push rod is adapted to engage the first element at a position located in the center of the coupling sleeve.

12. A method for a power tool according to any one of claims 1 to 10, the method comprising the following steps: operating the tool in a low torque / high speed drive mode of operation wherein the coupling sleeve is arranged in a first position to allow torque to be bypassed by the planetary gear assembly; Confirm that the tight fit position has been reached; displacing the coupling sleeve forwardly to the second position by axial movement of the linear actuator in a first direction; as well as The tool is operated in a high torque / low speed drive mode of operation with the coupling sleeve disposed in the second position such that torque is passed through the planetary gear assembly.

13. The method according to claim 12, wherein: The step of reaching the second position further comprises, if the coupling sleeve fails to engage the planetary gear assembly, A rearward displacement of the coupling sleeve is achieved by axial movement of the linear actuator in a second opposite direction; Achieving rotation of the planetary gear assembly; as well as The forward displacement of the coupling sleeve to reach the second position is achieved by axial movement of the linear actuator in the first direction.

Images