Hand-held power screwdriver with a low-noise torque clutch

[0001] 1. Field of Invention

[0002] The present invention relates to a hand-held power screwdriver with a low-noise torque clutch.

[0003] 2. Description of the Prior Art

[0004] In the hand-held power screwdrivers used for screwing in of screws, in order to prevent overrotation of a screw, force flow from the drive motor to the screw-driving tool is interrupted upon the torque reaching a predetermined threshold. As a torque clutch, usually, a conventional ratchet clutch with two, preloaded against each other, ratchet members issued. The ratchet members have respective, circumferentially arranged, oblique cams. The drawback of a conventional ratchet clutch consists in disturbing loud grating which in addition to noise, leads to a significant wear of the ratchet clutch.

[0005] European Patent EP990488B1 discloses a hand-held power screwdriver with a low-noise torque clutch which is formed as a combination of a ratchet clutches. To this end, oblique cams are formed on opposite sides of an axially displaceable ratchet member and are associated with two axially spaced ratchet clutches. The combination torque clutch is unnecessary very complex and, with two ratchet clutches, the wear of the power screwdriver is unnecessarily high.

[0006] Accordingly, an object of the present invention is a hand-held power screwdriver with a low-noise torque clutch having a low wear.

[0007] This and other objects of the present invention, which will become apparent hereinafter, are achieved by providing a hand-held power screwdriver having a support sleeve, a tool spindle axially displaceable in the support sleeve, a spindle spring for axially resiliently preloading the tool spindle and a low-noise torque clutch for transmitting torque to the tool spindle. The torque clutch is formed of combined claw clutch and ratchet clutch. The ratchet clutch has a ratchet clutch spring for axially resiliently preloading the ratchet clutch, a rotatably driven first ratchet member and a second ratchet member both having, respectively, oppositely oriented, circumferentially arranged oblique cams. The claw clutch has a claw clutch spring for axially resiliently preloading the claw clutch, a first claw member and a second claw member both having, respectively, oppositely oriented claws. The first claw member of the claw clutch is fixedly connected with the second ratchet member of the ratchet clutch for joint rotation therewith. The second claw member is connected with the tool spindle by at least one engagement member for joint rotation with the tool spindle and for being disconnected from the tool spindle. A retaining element secures the second claw member of the claw clutch to the tool spindle in the free-running position of the screwdriver.

[0008] The provision of an engagement member for connecting the second claw member with the tool spindle for joint rotation therewith, and of retaining element for securing the second claw member with the tool spindle in the free-running position permitted to provide a technologically simple, low-noise torque clutch. Because only one ratchet clutch is used, the wear of the torque clutch is noticeably reduced.

[0009] Advantageously, the spring rigidity of the ratchet clutch spring is greater than a spring rigidity of the spindle spring, a spring rigidity of which is greater than a spring rigidity of the claw clutch spring. As a result, upon axial rearward displacement of the tool spindle in the screwdriver over a set switching path, first the claw spring, then the spindle spring, and finally the ratchet spring become compressed and vice versa.

[0010] Advantageously, the second ratchet member and the claw member are formed by a ratchet sleeve freely rotatable about the tool spindle and axially displaceable therealong, with a rear end side of the ratchet sleeve forming the circumferentially arranged, oblique cams and with a front, drive end side forming the straight claws. Thereby, a technologically simple combination of a ratchet clutch with a claw clutch is achieved.

[0011] Advantageously, the second claw member is formed by a rear end side of a claw sleeve axially displaceable over the tool spindle, with the at least one engagement member connecting the claw sleeve with the tool spindle for joint rotation therewith. Thereby, a technologically simple switching of the claw clutch by an axial displacement of the claw sleeve is achieved.

[0012] Advantageously, the claw sleeve has, at its rear side, at least one, extending radially inwardly, entrain web cooperating with the at least one engagement member and has, at its front, drive side, a free-running region formed as an annular inner groove. Thereby, upon an axial displacement of the claw sleeve, it becomes formlockingly connected with the engagement member.

[0013] Advantageously, the retaining element is formed as an annular O-ring securable on the tool spindle and becoming pinched between the tool spindle and the claw sleeve in the free-running position, frictionally securing the claw sleeve against the resiliently preloaded claw spring. Thereby, a technologically simple retention of the claw sleeve against the biasing force of the claw spring is achieved.

[0014] Advantageously, the engagement member is formed as a cylinder oriented parallel to the tool spindle and arranged radially inside and outside of tool spindle, with a cylinder axis coinciding with a circumferential surface of the tool spindle. Such an engagement member is capable of transmitting high torques.

[0015] Advantageously, there are provided several engagement members, preferably, three engagement members. With several, in particular with three engagement members, the tool spindle is not subjected to bending torques and is capable of transmitting high torques.

[0016] The novel features of the present invention, which are considered as characteristic for the invention, are set forth in the appended claims. The invention itself, however, both as to its construction and its mode of operation, together with additional advantages and objects thereof, will be best understood from the following detailed description of preferred embodiment, when read with reference to the accompanying drawings.

[0017] The drawings show:

[0018] FIG. 1 a longitudinal cross-sectional partial view of a hand-held power screwdriver according to the present invention;

[0019] FIG. 2 a cross-sectional view of a detail of the power screw-driver shown in FIG. 1 in its screwdriving position;

[0020] FIG. 3 a cross-sectional view of the detail shown in FIG. 2 in a free-running position of the power screwdriver; and

[0021] FIG. 4 a cross-sectional view along line IV-IV in FIG. 3.

[0022] A hand-held power screwdriver according to the present invention, a portion of which is shown in FIG. 1, includes a rotatably driven, working tool spindle 4 axially displaceable in a support sleeve 3, a semi-rigid spring 2 for axially preloading the tool spindle 4, and a low-noise torque clutch 5 for transmitting torque to the tool spindle 4. The torque clutch 5 is formed of a claw clutch 6 and a ratchet clutch 7. The ratchet clutch 7, which is axially resiliently preloaded with a rigid spring 8, has a first ratchet member 7a rotatably driven by an electric motor (not shown), and a second ratchet member 7b. The first and second ratchet members 7a and 7b are provided, respectively with oppositely oriented, circumferentially arranged, oblique cams 9. The claw coupling 6, which is axially resiliently preloaded with a weak spring 10, has a first clutch member 6, which is connected with the second ratchet member 7b of the ratchet clutch 7 for joint rotation therewith, and a second claw member 6b. The claw members 6a and 6b are provided, respectively, with oppositely oriented, circumferentially arranged, straight claws 11. As it is graphically illustrated by the thickness of the spring wire, the springing rigidity of the ratchet clutch spring 8, which is formed as a compression spiral spring, is greater than the rigidity of the tool spindle spring 2 the rigidity of which is, however, greater than the rigidity of the claw spring 10. In the completely unloaded idle position, which is shown in the drawing, the ratchet clutch 7 is clutched by the biasing force of the spring 8, the tool spindle 4 is located in its completely driven position as a result of application thereto of the biasing force of the spring 2, and the claw clutch is clutched by the biasing force of the claw spring 10. An engagement member 12, which is secured on the tool spindle 4, is located in a circumferentially free idle region 16 of the second claw member 6b, which is formed as an inner annular groove, whereby the tool spindle 4 is freely rotatable, without an application a load thereto.

[0023] In the screwdriving position of the power screwdriver according to the present invention, which is shown in FIG. 2, with the tool spindle 4 being axially offset, at its rear side, against the biasing force of the semi-rigid spring 2, the engagement member 12, which is axially displaced together with the tool spindle 4, connects the second claw member 6b of the claw clutch 6 with the tool spindle 4 for joint rotation therewith. The second ratchet member 7b is provided, together with the first claw member 6a, on a ratchet sleeve 13. The ratchet sleeve 13 is mounted on the tool spindle 4 for rotation thereabout and for axial displacement relative thereto. The circumferentially arranged, oblique cams 9 are provided on the rear end side of the ratchet sleeve 13, and the straight claws 11 are provided on the front or drive end side of the ratchet sleeve 13. The second claw member 7b is formed on the rear end side of the claw sleeve 14, which is axially displaceable on the tool spindle 4 but which is connected with the tool spindle 4 for joint rotation therewith by the engagement member 12 in the screwdriving position shown in FIG. 2. To this end, the claw sleeve 14 has, at its rear side, an extending radially inward entrain web 15 that cooperates with the engagement member 12, with the idle region 16 being formed at the drive side of the claw clutch sleeve 14.

[0024] In the free-running position of the power screwdriver according to the present invention, which is shown in FIG. 3, the first claw member 6a and the second claw member 6b are spaced from each other and are, thus, disconnected. A retaining member 17 is formed as an annular O-ring which is secured on the tool spindle 4. The retaining member 17 is displaced into the free-running position from the screwdriving position, which is shown in FIG. 2, upon a torque exceeding a predetermined threshold, as a result of disengagement of the ratchet sleeve 13 which is caused by rotation in opposite directions of the cams 9, and thereby of the claw sleeve 14. The retaining member 17 becomes coaxially deformed between the tool spindle 4 and the claw sleeve 14 and the claw sleeve 14 become frictionally secured in the free-running position against the biasing force of the weak preloaded claw spring 10 until the tool spindle 4 is axially released. The semi-rigid spindle spring 2 biases the tool spindle 4 in the screwdriving direction, whereby the claw sleeve 14 disengages from the retaining member 17, the O-ring, and occupies the idle position shown in FIG. 1.

[0025] Generally, as shown in FIG. 4, there are provided three engagement members 12 which are formed as cylinders and are oriented parallel to the tool spindle 4. The engagement cylinders are arranged radially inside and outside of the tool spindle 4, with respective axes coinciding with the circumferential surface of the tool spindle 4. The engagement cylinders are circumferentially arranged about the tool spindle 4 and are secured thereon. The claw sleeve 14 has three entrain webs 15 associated with respective engagement members 12. The weak claw spring 10 is located inside of the rigid ratchet clutch spring 8, with both springs 8 and 10 being located within the support sleeve 3.

[0026] Though the present invention was shown and described with references to the preferred embodiment, such is merely illustrative of the present invention and is not to be construed as a limitation thereof and various modifications of the present invention will be apparent to those skilled in the art. It is therefore not intended that the present invention be limited to the disclosed embodiment or details thereof, and the present invention includes all variations and/or alternative embodiments within the spirit and scope of the present invention as defined by the appended claims.