Abstract
An electric portable power tool, having a housing, a shaft, a control cam, an electric drive accommodated in the housing to drive the drive shaft, and an output unit that is positively connected with the drive via a mechanical shut-off clutch to transfer torque from the drive to an insertion tool connected with the output unit. The mechanical shut-off clutch comprises a control ring that is axially mounted against the force of the return spring and at least one switch element that is run on the control cam. The control cam is delimited at one end by a first switching contour for providing a release torque of the shut-off clutch and by a boundary contour at another end. The control cam is associated with a second switching contour for providing a pre-torque which is less than the release torque.
Claims
1. An electric portable power tool comprising: a housing; a drive shaft; a control cam; an electric drive accommodated in the housing to drive the drive shaft; and an output unit that is positively connected with the electric drive via a mechanical shut-off clutch to transfer torque from the electric drive to an insertion tool connected with the output unit, wherein the mechanical shut-off clutch comprises a control ring that is axially mounted against the force of a return spring and at least one switch element that is run on the control cam, wherein the control cam is delimited at one end by a first switching contour for providing a release torque of the mechanical shut-off clutch and by a boundary contour at another end, wherein the control cam further includes a second switching contour for providing a pre-torque which is less than the release torque, wherein the first switching contour and the second switching contour are provided on a same inclined ramp of the control cam leading to a peak, and wherein, on the inclined ramp, the first switching contour is provided by a curved incline and the second switching contour is provided by a straight incline.
2. The electric portable power tool according to claim 1, wherein the first switching contour has a switching point, a tangential slope at which defines the release torque of the mechanical shut-off clutch, and wherein the second switching contour having has a pre-switching point, a tangential slope at which defines the pre-torque, which is less than the release torque.
3. The portable power tool according to claim 2, wherein the tangential slope at the switching point is greater than the tangential slope at the pre-switching point.
4. The portable power tool according to claim 2, wherein a ratio between the tangential slope at the switching point and the tangential slope at the pre-switching point is in a range from 1.2:1.
5. The portable power tool according to claim 2, wherein an angle between the tangential slope at the switching point and a plane which is oriented perpendicular to the drive shaft is in a range from 50°.
6. The portable power tool according to claim 2, wherein an angle between the tangential slope at the pre-switching point and a plane which is oriented perpendicular to the drive shaft is in a range from 20°.
7. The portable power tool according to claim 1, wherein the control cam has a constant incline in an area of the second switching contour.
8. The portable power tool according to claim 1, wherein an amount of a derivation of a profile of the control cam in an area of the first switching contour and the second switching contour is greater than 0.
9. The portable power tool according to claim 1, wherein a second derivation of a profile of the control cam in an area of the first switching contour and the second switching contour is greater than or equal to 0.
10. The portable power tool according to claim 1, wherein a plurality of the at least one switch element and the control cam are provided.
11. The portable power tool according to claim 10, wherein a boundary contour of an adjacent second control cam is formed on the first switching contour of a first control cam.
12. The portable power tool according to claim 1, wherein the mechanical shut-off clutch comprises a cam ring connected to the drive shaft in a rotationally fixed manner, on which the control cam is formed.
13. The portable power tool according to claim 1, wherein the at least one switch element is a switching ball.
14. The portable power tool according to claim 1, wherein the return spring is a compression spring, the spring force of which is adjustable.
15. The portable power tool according to claim 1, wherein the portable power tool is a cordless screwdriver.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus, are not limitive of the present invention, and wherein:
(2) FIG. 1 is a perspective view of a portable power tool,
(3) FIG. 2 shows a section of a longitudinal section through the portable power tool of FIG. 1,
(4) FIG. 3 is a side view of a first embodiment of a shut-off clutch,
(5) FIG. 4 is a perspective view of a control cam of the first embodiment of the shut-off clutch,
(6) FIG. 5 shows a first switching state of the first embodiment of the shut-off clutch,
(7) FIG. 6 shows a second switching state of the first embodiment of the shut-off clutch,
(8) FIG. 7 shows a third switching state of the first embodiment of the shut-off clutch,
(9) FIG. 8 shows a detailed view of the control cam of the first embodiment of the shut-off clutch,
(10) FIG. 9 is a perspective view of a control cam of a second embodiment of the shut-off clutch,
(11) FIG. 10 shows a first switching state of the second embodiment of the shut-off clutch, and
(12) FIG. 11 shows a second switching state of the second embodiment of the shut-off clutch.
DETAILED DESCRIPTION
(13) FIG. 1 shows a perspective view of an electrical portable power tool 1 which, in the exemplary embodiment shown, is formed as an industrial cordless screwdriver 2 with high precision, more precisely as an angle screwdriver 3, which is usually used in industrial series screw fastenings. This angle screwdriver 3 has a drive 5 accommodated in a housing 4, the direction of rotation of which can be adjusted by means of an adjusting switch 6 in order to give the user the option of loosening a screw fastening again. The electric energy required to supply the drive 5 with power is provided in the shown embodiment by a rechargeable battery 7, which is removably mounted on the angle screwdriver 3. At the end of the angle screwdriver 3 facing away from the battery 7, a receptacle 8 is formed by means of which different attachments or insertion tools can be connected. In the exemplary embodiment shown, this is an angle head 9, for example.
(14) The detail of a longitudinal section through the angle screwdriver 3 displayed in FIG. 2 shows that the drive 5 drives a drive shaft 11 via a gearbox 10. The drive shaft 11 is positively connected via a mechanical shut-off clutch 12 with an output unit 13. This output unit 13 ends in the receptacle 8, to which the various attachments or tools can be attached.
(15) As can also be seen in particular from FIG. 3, which shows a first embodiment of the shut-off clutch 12, the latter comprises a control ring 15 mounted axially against the force of a return spring 14, which is essentially designed to be rotationally fixed to a switch element 16, which in the embodiment is shown as a switching ball 17. The switching ball 17 runs on a control cam 18 which is formed on a cam ring 19 that is non-rotatably connected to the drive shaft 11. The torque applied by the drive 5, coming from the gearbox 10, is introduced in the shut-off clutch 12 on the cam ring 19 and, with a closed shut-off clutch 12, is ultimately transferred to the output unit 13. In this case, the torque is transferred via the switch element 16 from the control cam 18, which is formed on the cam ring 19, to the control ring 15, which is provided in triplicate in the exemplary embodiment shown. The switch elements 16 are each captively received on the control ring 15 in a ball pocket 20, though they have some degree of freedom of motion. As already mentioned above, the control ring 15 is axially mounted on the output unit 13 against the force of the pretensioned return spring 14, which is mounted between the control ring 15 and a pressure ring 21. The axial position of the pressure ring 21 in the direction of the receptacle 8 is limited by means of an adjusting ring 22, which is adjustably mounted on the output unit 13 via a threaded connection 23. The axial position of the pressure ring 21 and therefore the spring tension of the return spring 14 can thus be changed by the adjusting ring 22. In this way, the tensioned length of the return spring 14, and thus the axial pretensioning force of the return spring 14 onto the control ring 15, can be adjusted. This allows for the release torque and thus the screwing torque to be set. The cam ring 19 is rotatably mounted against the output unit 13 to allow for the relative rotation required for releasing the shut-off clutch 12. The control cam 18 is delimited at one end by a first switching contour 24 and by a boundary contour 25 at the other end. The release torque of the shut-off clutch 12, which corresponds to the screwing torque, is ultimately provided by the first switching contour 24. In addition to the first switching contour 24 and the boundary contour 25, the control cam 18 includes a second switching contour 26, the function of which in particular will be explained in more detail below with reference to FIGS. 4 to 8.
(16) FIG. 4 shows, in particular, the second switching contour 26, which is formed between the boundary contour 25 and the first switching contour 24. This second switching contour 26 provides a pre-torque that is less than the release torque. Whereas the control cam 18 in the area of the first switching contour 24 has a profile with a curvature or radius adapted to the switch element 16, the control cam 18 in the area of the second switching contour 26 has a constant incline, and is therefore ultimately formed as a straight line. The amount of the derivation of the profile of the control cam 18 in the area of the first switching contour 24 and the second switching contour 26 is thereby consistently greater than 0, and the second derivation of the profile of the control cam 18 in the area of the first switching contour 24 and the second switching contour 26 is greater than or equal 0. It can also be seen from FIG. 4 that the boundary contour 25 of an adjacent second control cam 18 is formed on the first switching contour 24 of a first control cam 18.
(17) FIGS. 5 to 7 show the sequence of the releasing behavior of the portable power tool 1 according to the invention, which is realized by the control cam 18. FIG. 5 shows the state of the shut-off clutch 12 during the screw fastening. In this case, the switch element 16 rests on the second switching contour 26, which defines the pre-torque, and the torque is transferred from the drive 5 via the gearbox 10 and the closed shut-off clutch 12 to the output unit 13. The torque of the drive 5 introduced on cam ring 19 is transferred to the control ring 15 until the pre-torque is exceeded. The switch element 16 then slides onto the second switching contour 26, as shown in FIG. 6. In this case, the control ring 15 is axially adjusted against the force of the return spring 14. This axial displacement of the control ring 15 can now be detected, for example by means of a magnet and a corresponding Hall sensor, and be used to already prepare or initiate the shutdown and the braking of the drive 5 at this early stage by means of corresponding drive electronics. When the actual release moment is then reached, i.e. when the switch element 16 slides beyond the first switching contour 24, the control ring 15 is further axially adjusted against the force of the return spring 14. This can be seen in particular in FIG. 7. This displacement is now also detected, for example, by the above-mentioned magnet and the Hall sensor, and the shutdown and braking of the drive 5 is completed and the screw fastening is thus ended. The force of the return spring 14 then pushes the control ring 15 with the switch element 16 back onto the control cam 18 of the cam ring 19. The second switching contour 26 thereby ensures that a signal earlier in time for the braking of the drive shaft 11 takes place early enough so that the repeated release of the shut-off clutch 12 is avoided. The drive 5 continues to rotate the cam ring 19 at a very low speed until the second switching contour 26 of the switch element 16 is reached. There it comes to a standstill. The shut-off clutch 12 is now in its starting position for the next screw fastening in which the switch element 16 rests against the second switching contour 26.
(18) It can be seen from FIG. 8 that the first switching contour 24 has a switching point 31, the tangential slope of which defines the release torque of the cut-off clutch 12. The pre-torque is thereby defined by the tangential slope of a pre-switching point 32, which is associated with the second switching contour 26. The tangential slope of the switching point 31 is greater than the tangential slope of the pre-switching point 32, which ultimately results in the pre-torque being less than the release torque, which is determined by the tangential slope in the switching point 31 of the first switching contour 24. In the exemplary embodiment shown, the ratio between the tangential slope of the switching point 31 and the tangential slope of the pre-switching point 32 is approximately 2:1. In this case, the angle between the tangential slope of the switching point 31 and a plane 33 that is oriented perpendicular to the drive shaft 11 is between 60° and 70°. The angle between the tangential slope of the pre-switching point 32 and the plane 33, however, is between 30° and 35°.
(19) FIG. 9 shows a perspective view of a control cam 18 of a second embodiment of the shut-off clutch 12. Here, the control cam 18 has a first maximum 34, which forms the first switching contour 24 and defines the release torque, and a second maximum 35, which forms the second switching contour 26 and defines the pre-torque. The first maximum 34 is greater than the second maximum 35 and the ratio between the height of the first maximum 34 and the height of the second maximum 35 is 5:1. In addition, the slope of the flank of the first maximum 34 is greater than the slope of the flank of the second maximum 35.
(20) In a partially sectioned view, FIG. 10 and FIG. 11 show the axial adjustment of the control ring 15 when the applied torque exceeds the pre-torque. In this case, the switch element 16, which is formed as a switching ball 17, is adjusted by the height of the second maximum 35, which forms the pre-torque. Due to the lower height of the second maximum 35 as compared to the first maximum 34, there is also a lesser axial displacement of the control ring 15 than if the switch element 16 is adjusted by the height of the first maximum 34, which occurs when the shut-off clutch 12 is released. This difference in the axial adjustment can thus be used again in order to be able to differentiate whether the axial adjustment of the control ring 15 was carried out by the pre-torque or by the release torque.
(21) The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are to be included within the scope of the following claims.
