POWER TOOL AND TWO-SPEED GEAR ASSEMBLY FOR A POWER TOOL

Abstract

The present specification relates to a power tool comprising an input shaft and an output shaft and a two-speed power transmission comprising a planetary gear and a gear shift assembly for directing torque through or past the planetary gear comprising a driving member, a driven member and an axially movable coupling sleeve arranged to intercouple in a first position the driving member and the driven member and to intercouple in a second position the planetary gear and the driven member. A linear actuator is arranged to displace the coupling sleeve between the first and second position, wherein the linear actuator comprises a linearly movable push bar arranged for displacing the coupling sleeve. The present specification also relates to a method in and a two-speed power transmission for such a power tool.

Claims

1. Power tool comprising: a housing (H); an input shaft (IS); an output shaft; and a two-speed power transmission (T), said two-speed power transmission comprising a planetary gear (4) and a two speed gear shift assembly for directing torque through said planetary gear (4) in a high torque/low speed drive mode or past said planetary gear (4) in a low torque/high speed drive mode; said gear shift assembly comprising a driving member (2) drivingly connected to said input shaft, a driven member (1) drivingly connected to said output shaft, an axially movable coupling sleeve (6) arranged to intercouple in a first position said driving member (2) and said driven member (1) and to intercouple in a second position said planetary gear (4) and said driven member (1), and a linear actuator (13, 14) arranged to displace said coupling sleeve between said first and second position, wherein said linear actuator comprises a linearly movable push bar (13) arranged to for displacing said coupling sleeve between said first and second position.

2. Power tool according to claim 1, wherein said gear assembly further comprises a coupling assembly arranged between said coupling sleeve and said linear actuator, said coupling assembly comprising a first element (8) rotationally coupled to said sleeve, wherein a rotation of said first element is independent of a rotation of said push bar and wherein said push bar is arranged to push said first element in an axial direction.

3. Power tool according to claim 2, wherein said coupling sleeve is concentrically arranged with respect to said planetary gear and wherein said push bar is adapted to engage said first element in a position lying in a center of said sleeve.

4. Power tool according to claim 3, wherein said first element is a ball arranged at least partly in said sleeve.

5. Power tool according to any of the preceding claims, wherein a first axially acting spring means (3) is arranged for biasing said coupling sleeve toward said first position of said coupling sleeve.

6. Power tool according to any of the preceding claims, wherein said first and second position is a first and second end position and wherein said coupling sleeve is continuously movable there between and may be positioned at any position between said first and second end position.

7. Power tool according to any of the preceding claims, wherein said driven member comprises a first engaging portion (1b) adapted to engage a corresponding congruent first portion of said coupling sleeve, and wherein said planetary gear comprises a planet wheel carrier (41) comprising a second engaging portion (41b) adapted to engage a corresponding congruent second portion of said coupling sleeve.

8. Power tool according to claim 7, wherein at least one of said first and second engaging portion have a polygonal cross section.

9. Power tool according to any of the preceding claims, further comprising a bevel gear arranged between said input shaft and said driving member, such that said driving member is connected to said input shaft via said bevel gear.

10. Power tool according to any of the preceding claims, wherein said linear actuator is a linear DC servo motor comprising a solid stator housing, a coil assembly, and a multi-pole magnetic push rod.

11. Power tool according to any of the preceding claims, wherein said linear actuator comprises at least one internal position sensor configure to sense a position of said push bar.

12. Power tool according to any of the preceding claims, wherein said planetary gear is a first planetary gear step.

13. Two-speed power transmission for a power tool according to any of the preceding claims, said transmission comprising a planetary gear and a two speed gear shift assembly for directing torque through said planetary gear in a high torque/low speed drive mode or past said planetary gear in a low torque/high speed drive mode; said gear shift assembly comprising a driving member drivingly connected to said input shaft, a driven member drivingly connected to said output shaft, a coupling sleeve arranged to intercouple in a first position said driving member and said driven member and to intercouple in a second position said planet wheel carrier and said driven member, and a linear actuator arranged to displace said coupling sleeve between said first and second position, wherein said linear actuator is a linear actuator comprising a linearly movable push bar (13) arranged to displace said coupling sleeve between said first and second position.

14. Method for controlling a power tool comprising a planetary gear (4) and a two speed gear shift assembly for directing torque through said planetary gear (4) in a high torque/low speed drive mode or past said planetary gear (4) in a low torque/high speed drive mode by means of a coupling sleeve and a linear actuator arranged to displace said coupling sleeve], said method comprising the steps of: running the tool in the low torque/high speed drive mode of operation in which the coupling sleeve is arranged in a first position directing torque past said planetary gear; identifying that snug has been reached; displacing said coupling sleeve forwards by an axial movement in a first direction by means of said linear actuator to arrive at said second position; and running the tool in the high torque/low speed drive mode of operation in which the coupling sleeve is arranged in the second position directing torque through said planetary gear.

15. Method according to claim 14, wherein the step of arriving at said second position further comprises, if said coupling sleeve fails to engage said planetary gear, effecting a displacement of said coupling sleeve backwards by an axial movement in a second opposite direction of said linear actuator; effecting a rotation of said planetary gear; and effecting a displacement of said coupling sleeve forwards by an axial movement in said first direction of said linear actuator to arrive at said second position.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The invention will be described in the following illustrative and non-limiting detailed description of exemplary embodiments, with reference to the appended drawing, on which

[0041] FIG. 1 is a cross sectional view of an exemplary power tool comprising a two-speed power transmission according to one embodiment.

[0042] FIG. 2 is a first perspective view of some of the components of an exemplary transmission according to one embodiment.

[0043] All figures are schematic, not necessarily to scale and generally only show parts which are necessary in order to elucidate the invention, wherein other parts may be omitted or merely suggested.

DETAILED DESCRIPTION

[0044] FIG. 1 is a cross sectional view of a portion of an exemplary power tool according to one embodiment, in this case a handheld tightening tool. The tool comprises a housing H, an input shaft IS, a motor connected to the driving 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 operative to control the rotational speed of the motor which will be described in greater detail below when describing the functionality of the tool.

[0045] The two-speed power transmission 1 of the embodiment shown in FIG. 1 comprises a planetary gear 4 and a gear shift assembly for directing torque from the input shaft IS to the output shaft 1 through the planetary gear 4 in a high torque/low speed drive mode or past the planetary gear 4 in a low torque/high speed drive mode. The transmission is shown in FIG. 1 in the low torque/high speed drive mode.

[0046] The planetary gear 4 comprises a ring gear (or gear rim) secured in the housing H and a planet wheel carrier 41. The transmission assembly comprises a driving member 2, in the illustrated embodiment forming part of the bevel gear 20, and a driven member 1 drivingly connected to the output shaft 1.

[0047] A coupling sleeve 6 is axially movable between a first position where the sleeve intercouples the driving member 2 and the driven member 1, i.e. the low torque/high speed mode illustrated in FIG. 1, and a second position intercoupling the planetary gear 4—more particularly the planet carrier 4a the driven member 1.

[0048] A linear actuator 13,14 is used to displace the coupling sleeve between said first and second position more particularly, 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 arranged to push the coupling sleeve from the first to the second position. The linear motor further comprises an internal hall sensor configured to sense a position of the bar 13 and an internal control unit or controller board 15. A compression spring 3 is arranged to bias the coupling sleeve 6 toward the first position.

[0049] In the illustrated embodiment, the push bar engages a second element 12 of a coupling assembly arranged between the coupling sleeve 6 and the linear motor 13, 14. The second element 12 in the illustrated embodiment however forms part of the pushed bar. This coupling assembly further comprises a first element 8 in the form of a ball 8 arranged in the sleeve 6 at a first end 6a thereof and hence rotating along with the coupling sleeve 6. The rotation of the sleeve 6 is independent from the rotation of the push bar 13 of the linear motor (and hence that of the second element 12 forming part of the push bar 13). The ball 8 has a suitable size to fit the end 6a of the coupling sleeve 6 and the push bar 13 is arranged to engage the ball (i.e. push) in a position lying in the center of said sleeve (i.e. via the second element 12).

[0050] The engagement between the coupling sleeve 6 and, as in the first mode, the driven member 1 and in the second mode the planet carrier 41 will now be described with reference to FIG. 2 showing the sleeve 6, the planet carrier 41, driving member 2 and the driven member 1 in a perspective view.

[0051] A may be seen from FIGS. 1 and 2, the driven member 1 is supported at a first end 1a by a bearing 50 and at a second end 1b comprises a first engaging portion 1b. The planet wheel carrier 41 similarly comprises a second engaging portion 41b. These engaging portions 1b and 41b adapted to engage a corresponding first 6a and second 6b portion of the coupling sleeve 6, the respective interacting surfaces have a congruent shape, in the illustrated embodiment a hex-shape in both instances.

[0052] In operation, the power tool of the illustrated embodiment forms part of a system comprising an external control unit (not shown) operative to control the tool.

[0053] The coupling sleeve 6 is initially biased towards the first position to perform run down—i.e. low torque/high speed mode. It follows that the push bar 13 as well is in a back position where the coupling sleeve 6 connects the driving member with the output shaft 1, FIG. 1.

[0054] Run down ends when snug is reached, in the illustrated embodiment this is identified by the external control unit when a current limit threshold is passed. As the linear motor receives a signal that run down is complete, displacement of the push bar 13 and hence the coupling sleeve 6 forwards towards the second position starts.

[0055] The position of the push bar 13 and hence the position of the coupling sleeve 6 is monitored by the internal hall sensor such that it may be determined when the coupling sleeve engages the planetary gear, i.e. has reached the second position. A signal is sent to the external control unit and the final and actual tightening phase (i.e. high torque/low speed mode) starts. If however, the respective hex-shaped congruent cross sections 6a of the coupling sleeve 6 and the planet carrier misalign and the sleeve 6 fails to engage the planet wheel carrier 41, the linear motor effects a linear motion in a reverse direction (i.e. backwards). The forward movement is then repeated but combined with a simultaneous slow rotation of the motor and hence the carrier 41 to allow for a new position to facilitate engagement. The skilled person realizes that the forward movement and the rotation may be executed as consecutive steps as well.

[0056] During final tightening, the torque is monitored by a torque transducer (not shown) and when the desired torque is reached the linear motor 13,14 receives a signal and the push bar 13 moves backwards to allow the sleeve 6 to engage high speed/low torque mode again. This movement of the coupling sleeve 6 may be combined with a simultaneous rotation of the motor to help the coupling sleeve to engage properly as described above.

[0057] While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiment. The skilled person understands that many modifications, variations and alterations are conceivable within the scope as defined in the appended claims. Additionally, variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, form a study of 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 “a” or “an” does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope of the claims.