Handheld power tool, in particular a power drill or screwdriver

A handheld power tool, in particular a power drill or power screwdriver, has a tool holder, which is displaceably received in a housing and which can be driven via a drive unit; a microswitch that can switch the drive unit on and off is provided, which is switchable upon an axial displacement motion of the tool holder via an actuating element. The actuating element is joined axially solidly to the tool holder, so that the axial displacement motion of the tool holder at the same time acts as the displacement motion of the actuating element, which motion actuates the microswitch.

This application is based on German Patent Application DE 10 2007 019 434.1 filed Apr. 25, 2007, upon which priority is claimed under 35 U.S.C. 119(a)-(d).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a handheld power tool, in particular to a power drill or power screwdriver, such as a battery-operated drill or screwdriver.

2. Description of the Prior Art

U.S. Pat. No. 5,557,990 discloses a battery-operated screwdriver which includes a tool holder, received displaceably in a housing, for receiving a tool; the tool holder is driven by an electric drive motor. The battery-operated screwdriver is provided with a push-start mechanism, which enables automatic starting of the drive motor as soon as the tool in the tool holder is placed with pressure on the screw to be screwed in or unscrewed and the tool holder has been displaced axially backward some distance into the housing, whereupon a switching mechanism is actuated that switches on the electric motor. A radially projecting actuating element is axially displaced by the tool holder and pressed against a microswitch by way of which the electric motor is to be switched on and off; with the aid of a spring element, the tool holder is displaced backward to its original position as soon as the screwdriver is moved away from the screw. The actuating element, which is acted upon by the tool holder and switches the microswitch on and off, is located in the housing of the power tool on the axial face end of the tool holder and is pressed by the spring element against the face end of the tool holder.

OBJECT AND SUMMARY OF THE INVENTION

With this prior art as the point of departure, the object of the invention is to equip a handheld power tool, in particular a power drill or power screwdriver, with an improved, structurally simply constructed push-start mechanism which functions reliably even over a long service life of the power tool.

The handheld power tool of the invention, which in particular is a power drill or power screwdriver or a battery-operated screwdriver, has a tool holder that is received displaceably in a housing and which is embodied for instance for receiving a screwdriver; the tool holder can be driven by means of a drive unit. The drive unit is switched on and off by a microswitch, which upon an axial displacement motion of the tool holder can be switched via an actuating element. This actuating element is axially solidly joined to the tool holder and executes the same displacement motion as the tool holder, so that its displacement motion at the same time represents the switching motion that acts on the microswitch.

This embodiment has the advantage that only relatively few components are needed to realize the push-start mechanism of the handheld power tool. The actuating element, by way of which the microswitch is switched on and/or off, is unable to execute any relative motion with respect to the tool holder, at least in the axial direction but expediently in the circumferential direction as well; instead, it is solidly joined to the tool holder, so that the adjusting motion of the tool holder is converted directly into the switching motion of the microswitch. As a result, additional spring elements for the actuating element can be dispensed with. Both the switching-on motion and the switching-off motion are executed with a high degree of safety and reliability.

In a practical refinement, the tool holder is in rotary engagement with a driven shaft and is retained axially adjustably relative to the driven shaft. The driven shaft is advantageously driven by the drive shaft of the drive unit and in particular is rotationally connected to the drive shaft via a coupling member; the coupling member allows a shutoff of the drive unit in the event that the tightening moment or torque that is transmitted by the tool holder reaches or exceeds the value of the coupling torque. This shutoff mechanism for the coupling member, in addition to the shutoff mechanics, is embodied via the push-start mechanism, so that shutoff of the drive unit occurs when the preset torque is reached, both in the event of a returning axial motion of the tool holder and with the tool holder pushed into place while the power tool is in operation.

The driven shaft, by way of which the driving motion of the drive unit is transmitted to the tool holder, advantageously has a face-end recess, in which a spring element, in particular a compression spring with which the tool holder cooperates, is received. For that purpose, the face end of the tool holder remote from the tool rests on the spring element in the recess in the driven shaft, and an axial displacement motion of the tool holder into the housing of the handheld power tool takes place counter to the force of the spring element. As soon as the handheld power tool is taken away from the workpiece being machined, the tool holder, under the influence of the spring element, can axially resume its outset position, whereupon the actuating element on the tool holder is likewise axially restored, and the microswitch that switches the drive unit is shifted into the off position.

The actuating element is expediently embodied structurally as an actuation ring joined axially solidly to the tool holder and seated on the outer jacket face of the tool holder. A radially projecting actuation tab is embodied preferably in one piece on the actuating element; it cooperates with the microswitch and adjusts it between the ON and OFF positions.

It may also be practical to provide a lighting means on the handheld power tool that is switched on and/or off by the displacement motion of the tool holder. Switching the lighting means on and off is expediently likewise effected via the microswitch. As the lighting means, a light-emitting diode or LED is preferably considered.

The drive unit is embodied in particular as an electric drive motor, whose rotor shaft forms the drive shaft that is connected via the coupling member to the driven shaft that drives the tool holder. Optionally, a gear is disposed in the transmission path between the drive motor and the tool holder.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In the drawings, identical components are identified by the same reference numerals.

AsFIG. 1and the enlarged view inFIG. 4show, the screwdriver1has a housing2, in which an electric drive motor3is received. The rotor shaft4of the electric drive motor3acts as the drive shaft, which via a planet carrier5is connected by the gear to a coupling member6in a manner fixed against relative rotation; for transmitting a preset maximum torque, the coupling member6is seated on a driven shaft7. The driven shaft7is connected in a manner fixed against relative rotation to a tool holder8for receiving a tool, in particular a screwdriver or screwdriver bit, and the tool holder8, for receiving the tool, has a face-end recess11in a portion located outside the housing2.

The tool holder8is retained axially displaceably relative to the driven shaft7but is joined positively to the driven shaft in the rotary direction, so that the rotary motion of the driven shaft7is also transmitted to the tool holder8. A recess12(FIG. 4) is made in the face end of the driven shaft7, and a spring element13embodied as a compression spring is inserted into this recess. The spring element13is acted upon by a peg of tapered cross section of the tool holder8that protrudes into the recess12. As long as no forces are acting on the tip, which receives the tool, of the tool holder8, the tool holder8is maximally forced out of the housing2of the battery-operated screwdriver1in the axial direction because of the spring force of the spring element13.

Because of the axial displaceability of the tool holder8, the tool holder can be shifted axially inward counter to the force of the spring element13, as soon as the tool, received in the recess11in the tool holder8, is pressed against a screw or the like. The actuating element9, located solidly on the jacket face of the tool holder8, thereupon comes into contact with the microswitch10and puts it in the ON state, whereupon the microswitch10, which is connected to the electronics of the drive motor3, switches this motor on. The actuating element9comprises an actuation ring14, which surrounds the jacket face of the tool holder8and is expediently axially retained by two securing rings, and an actuation tab15, which is embodied in one piece with the actuation ring14and is embodied as a radially projecting portion that extends in the direction of the microswitch10and is embodied for actuating the microswitch10.

As soon as the tool received in the tool holder8is force-free, the tool holder8, under the influence of the spring element13, is axially displaced back into its outset position, in which the tool holder protrudes maximally far out of the housing2. The actuating element9thereupon becomes disengaged from the microswitch10, so that the microswitch10is converted from the ON to the OFF state, and the electric drive motor3is switched off.

The actuating element9is solidly joined in the axial direction to the tool holder8, but the actuating element9does not execute the rotary motion of the tool holder8; instead, it is solidly joined in the rotary direction to the housing2of the screwdriver1.

In the lower, front part of the housing2, there is a lighting means16, embodied in particular as a light-emitting diode (LED), which illuminates the work field of the handheld power tool. For that purpose, the lighting means16is located at an oblique angle to the longitudinal axis17of the handheld power tool, in such a way that the free face end of the tool holder8and the areas in front of the face end are all illuminated. The lighting means16is received in a bulging portion18of the housing2.

The lighting means16is switched on and off via the axial displacement motion of the tool holder8. This is done in particular in such a way that the switching state of the lighting means16is controlled via the microswitch10, which thus has the task not only of switching the electric drive motor3on and off but also of switching the lighting means16on and off. Switching the lighting means16on and off is thus done in the same way as the switching on and off of the electric drive motor. Optionally, however, only switching on is done via the microswitch and hence via the electronics27of the drive motor, while switching off is conversely done in a timed manner via the electronics.

Switching the lighting means16on and optionally also off can also be done via a rotation-direction setting switch19(FIG. 2), by way of which the direction of rotation of the tool holder8can be fixed or reversed. In the exemplary embodiment, the rotation-direction setting switch19is located in the lateral area of the housing and is embodied as a spring-loaded push button, which presses on a further microswitch28which is located inside the screwdriver. The shutoff of the lighting means is typically done in timed fashion via the electronics27of the drive motor.

As further shown inFIGS. 4 and 5, the shutoff of the electric drive motor can also be done via a torque shutoff device. The torque shutoff device includes a switching element23, which is subjected to force by a compression spring24and is kept by the compression spring in contact with a shutoff microswitch25; in the contact position of the switching element23, the shutoff microswitch25is on. The switching element23is retained axially adjustably in the housing2and can be put into the out-of-contact position with the shutoff microswitch25by a bearing disk21, which is seated on the jacket face of the driven shaft7and is located axially displaceably on the driven shaft. The bearing disk21is located on the side of the driven shaft facing toward the coupling member6and defines one end of a compression spring20that is embodied as a spiral spring and that on the other end is fixed on the driven shaft7by a second bearing disk22. The bearing disk21moves axially away from the coupling member6as soon as the tightening torque of the tool holder8, or of the tool received in it, matches the torque of the coupling member6. In this axial motion—to the left in terms of FIGS.4and5—the switching element23is displaced out of the contact position with the shutoff microswitch25into the out-of-contact position, counter to the force of the compression spring24, whereupon the shutoff microswitch25, via the electronics, shuts off the electric drive motor3. As already noted, the shutoff may, however, also be done in timed fashion via the electronics27.

As soon as the bearing disk21, by the force of the compression spring20, is displaced back into its outset position, in which the bearing disk21rests axially on an annular shoulder26of the driven shaft7, the switching element23also, by the force of the compression spring24, again moves toward the shutoff microswitch25, whereupon this shutoff microswitch is displaced into the ON position that switches the electric drive motor on.

Advantageously, the lighting means16is shut off automatically, as soon as the shutoff microswitch25switches the electric drive motor3off.

It may also be practical for the lighting means16not to be switched off until a preset length of time has elapsed, via a time switch after the completion of the work step or in other words after the shutoff of the electric drive motor. In that case, the shutoff of the lighting means16occurs only with a time lag after the shutoff of the electric drive motor.

The foregoing relates to a preferred exemplary embodiment of the invention, it being understood that other variants and embodiments thereof are possible within the spirit and scope of the invention, the latter being defined by the appended claims.