Abstract:
In a portable electric tool, a switch arrangement comprises a trigger on/off switch having a depressable trigger and a reversing switch having an actuating lever. An interlocking arrangement, operative between the lever and the trigger, prevents actuation of the reversing switch when the trigger is depressed. The lever comprises a pivoted bell crank, one of the legs of which carries part of the interlocking arrangement, and the other leg of which extends transversely to the trigger and engages with a slide manually slidable in an orifice in a side wall of the tool&#39;s housing to effect pivoting of the lever.

Description:
FIELD OF THE INVENTION 
     This invention relates to a switch arrangement for an electric tool, particularly for portable electric tools such as, for example, drills, percussion drills, screwdrivers, etc. It particularly relates to the arrangement of a reversing switch in conjunction with the main on/off switch. 
     BACKGROUND OF THE INVENTION 
     It is known in reversible portable power drills to incorporate a pivoted actuating lever for the reversing switch above and adjacent the trigger of the trigger on/off switch, a retention pin on the acutating lever entering either of two retention slots in the trigger upon depression of the latter. In this way, the direction of the reversing switch has to be selected before the trigger is depressed to energise the tool, and while the trigger is depressed the actuating lever is prevented from being further actuated. 
     In such switch arrangements, conventionally the acutating lever for the reversing switch is located between the lower housing wall of the motor compartment and the upper part of the trigger. The trigger is accommodated adjacent the top of a pistol grip handle, so that the actuating lever is, therefore, arranged in the region of the transition between the pistol grip handle and the motor compartment housing, see for example U.S. Pat. No. 4,342,931. The actuating lever is long and extends forwardly beyond the trigger, the freely accessible forward end of the lever being manipulated by the fingers of the operator to pivot the lever. 
     In the above switch arrangement, there is a danger that the user will inadvertently pivot the actuating lever as he or she grips the tool&#39;s handle and moves the index finger into position to squeeze the trigger. Furthermore, there is a risk of the acutating lever being broken off during operation because of its relatively long pivoted length, particularly as it is made of electrically insulating plastic material. 
     SUMMARY OF THE INVENTION 
     The object of the invention is to provide an improved switch arrangement for reversing an electric tool. 
     A feature by which this object is achieved is the provision of a bell crank type lever for actuating the reversing switch and interlocking with the trigger of a trigger on/off switch. This has the advantage that the operation point for the reversing switch is located at one side of the tool&#39;s housing, preferably at the top of one side of a pistol grip handle, so minimizing the possibility of inadvertent operation. 
     Another preferred feature is the provision of a slide in the side wall of the tool&#39;s housing,and engaging an end of the bell crank therewith. This has the advantage that the reversing switch is operated by the slide which cannot be subjected by the user to such a load that the actuating lever can be inadvertently broken or damaged. 
     A further optional feature of the invention is the provision of slots of different depth in the trigger. This has the advantage that the depth through which the trigger can be depressed in one selected position of the reversing switch is limited, so enabling the speed of the tool to be limited in one direction of drive more than in the other direction of drive. 
     Accordingly, there is provided by the present invention a switch arrangement for an electric tool comprising a trigger-switch for energizing the electric tool and having a depressable trigger with two retention slots therein, a reversing switch, a pivoted bell crank lever having two legs, the lever being connected to the reversing switch for actuation thereof by pivoting of the lever, a retention projection adjacent an end of one of the legs, the retention projection engaging in a respective one of the retention slots upon actuation of the trigger depending upon the pivotal position of the lever, and the other of the legs extending transversely to the trigger for manual actuation to effect pivoting of the lever. 
     Preferably, the other leg engages with a manually operable slide displaceable along an orifice in a side wall of the tool&#39;s housing. The free end of this other leg may be formed with an enlarged head which engages in a cavity in the slide. The head preferably has a crowned peripheral surface to aid rotation thereof in the cavity. 
     An H-shaped adaptor may hold the reversing switch in the upper part thereof and the trigger-switch in the lower part thereof with the lever disposed between the reversing switch and the trigger-switch. The other leg of the lever may extend outwardly through an orifice in one side of the adaptor. By means of such an adaptor, the housing of the trigger-switch, the bell crank lever, and the housing of the reversing switch can be combined in a simple way into a single sub-assembly which can be inserted as such into the tool&#39;s housing. 
     Other objects, features and advantages of the present invention will become more fully apparent from the following detailed description of the preferred embodiment, the appended claims and the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS; 
     In the accompanying drawings: 
     FIG. 1 is a side elevational view of the rear and handle portion of a portable electric drill incorporating a reversing switch and triggerswitch arrangement according to the invention; 
     FIG. 2 is a similar view to FIG. 1 of the other side of the rear and handle portion of the drill, but with one clam-shell half of the housing removed to expose the reversing switch and trigger-switch arrangement; and with an upper portion of the trigger of the triggerswitch broken away and partially in section. 
     FIG. 3 is a section on the line III--III in FIG. 2; 
     FIG. 4 is an end view in the direction of the arrow IV in FIG. 2 of an adaptor for mounting the reversing switch and trigger-switch arrangement in the handle of the drill; 
     FIG. 5 is a side view of the adaptor of FIG. 4 in the direction of the arrow V in FIG. 4; 
     FIG. 6 is a plan view of the reversing switch actuating lever as shown in FIG. 3; and 
     FIG. 7 is an end view of the actuating lever in the direction of the arrow VII in FIG. 6. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The preferred embodiment of the invention is shown in a portable electric drill in FIGS. 1, 2 and 3, with particular components shown in FIGS. 4 to 7. To the front of the rear and handle portion shown in FIG. 1 is attached a front housing (not shown) from which extends a chuck (not shown) driven by the tool&#39;s electric motor M which is shown diagrammatically in FIG. 2. 
     The housing of the portion of the tool illustrated consists of two half-shells 1, 1&#39; which form the pistol grip handle and motor housing of the portable power drill. As is customary in electronically controlled drills equipped for reversal of the direction of rotation, the main on/off switch, accommodated in a housing 35, and the reversing switch, accommodated in a housing 36, are located in the region of transition between the pistol grip handle and the motor housing. The wiring of the switches and the associated circuits are not shown in the Figures, but are of conventional design. 
     An H-shaped adaptor 15 (FIGS. 4 and 5), which can be made of plastic, serves for mounting the housings 35, 36 of the two switches. The housing 35 of the on/off trigger-switch is pushed in between two legs 17 of the adaptor 15 which extend downwards, so that projections on this housing penetrate into engagement with cut-outs 18 (FIGS. 2 and 5) in the adpator, and thus remains connected to the adaptor. a bell crank actuating lever 25 (FIGS. 6 and 7), to be described in greater detail later, is placed on the cross piece 16 of the adaptor 15, so that one of the legs 27 of the lever 25 extends through lateral orifices 22, 23 in a side 21% the adaptor 15 as shown in FIG. 3. The reversing switch housing 36 is then guided between the upper legs 19 of the adaptor 15 and pressed down therebetween until hooks 20 at the upper ends of the legs 19 engage with cut-outs in the reversing switch housing 36. 
     The actuating bell crank lever 25 is essentially L-shaped and carries at the free end of its leg 27 a head 28 with a crowned peripheral surface (FIGS. 3, 6 and 7). A retention pin 29 is formed on the free end of the other leg 26 and extends therefrom perpendicularly to the plane of the lever in which the two legs 26, 27 lie. The leg 26 is provided with a bore 30 and also with an aperture or cut-out 31. The centers of the retention pin 29, the bore 30, and the cut-out 31 are in line, with the cut-out 31 being on the side of the bore 30 opposite to the retention pin 29. When the housing 36 of the reversing switch is mounted on the adaptor 15 a pin 40 (indicated in broken lines in FIG. 3) provided on the underside of the housing 36 engages with the bore 30. An actuating element (not shown) projecting from the housing 36 for directly actuating the reversing switch, extends into the cut-out 31. Consequently, pivoting the actuating lever 25 about the pin engaged in the bore 30 results in actuation of the reversing switch. 
     The unit composed of the two switches and the actuating lever 25, and which is coupled together by the adaptor 15, is mounted in the housing in a manner now to be described. 
     In the housing shell 1 there is a lateral orifice 8, into which is inserted a slide 9 having a gripping surface 10 and lengthwise extending regions 11 which engage behind the sides of the orifice 8. The slide 9 can be moved to and fro in the sectional plane of FIG. 3. 
     The slide 9 is first introduced into the half-shell 1, so that it is in the position shown in FIG. 3. The unit coupled together by the adaptor 15 is then mounted in spaced apart seating locations in the half-shell 1. The other half-shell 1&#39; has correponding seating locations. A felt layer 13 for tolerance compensation is arranged between the adaptor 15 and the extending regions 11 of the slide 9. A spring (not shown) with engagement lugs may be employed for additional retention if desired. In the mounted state, the head 28 of the actuating lever 25 extends into a cylindrical cavity 12 in the slide 9 (FIG. 3), the cavity 12 extending inside the raised button-like grip portion 10 of the slide 9. 
     In the further course of assembly, the trigger 2 for actuating the on/off trigger-switch is inserted. The trigger has two retention slots 3, 4 separated by a center wall 5 (FIG. 3). A transverse wall 6, partly across the trigger 2, causes the retention slot 4 to have less depth (or length) than the retention slot 3. 
     When the portable electric drill is in operation, the direction of rotation is set as a result of the displacement of the slide 9 into one of its two end positions. The actuating lever 25 is pivoted about the center axis of the bore 30, and the head 28 is able to rotate within the cavity 12 due to the crowned peripheral surface of the head. This pivoting of the actuating lever 25 displaces the retention pin 29 into a position aligned either in front of the retention slot 3 or in front of the retention slot 4. When the trigger 2 is pressed into the main switch housing 35 and the on/off switch is thus actuated, the retention pin 29 penetrates into the associated retention slot 3 or 5. In this actuated position of the trigger-switch, the position of the actuating lever is thus locked, and the user can no longer move the actuating lever 25 into another position by displacement of the slide 9. Thus, the position of the reversing switch cannot be changed while the trigger-switch is depressed. 
     The rotational speed of the drill is electronically controlled in known manner so that it increases with the increasing displacement or depression of the trigger 2 into the tool&#39;s housing. Consequently, higher rotational speed can be achieved when the retention pin 29 engages in the full length retention slot 3 than when the retention pin 29 engages in the retention slot 4 of less depth. The position for engagement of the retention pin 29 with the retention slot 4 is, therefore, arranged for the direction of rotation serving for the removal or loosening of screws and the like, while engagement with the retention slot 3 is assigned to the direction of rotation for normal drilling. That is, the difference in depth of the slots 3 and 4 enables the maximum reverse speed to be limited to less than the maximum forward speed. 
     As can be seen from FIG. 3, the leg 26 extends in the same direction as the trigger 2 and is adjacent to the trigger, while the other leg 27 extends transversely to the trigger and terminates adjacent the orifice 8 in the side wall of the handle. 
     It will be appreciated that by having the reversing control 9 in the side of the pistol grip handle, the trigger 2 can be located right up against the lower side of the motor compartment without the need for any gap therebetween. This has been found to be the most convenient position for easy operation of the trigger with the index finger. However, the bell crank lever 25 still enables the reversing control 9 to be located adjacent the trigger 2, and in such a position that it can readily be operated by the thumb of the hand grasping the pistol grip handle. 
     It should also be noted that by engaging one leg of the bell crank lever in the slide 9, the possibility of ingress of dirt and the like into the interior of the tool&#39;s housing at the location of the reversing control is prevented or minimized. 
     The above described embodiments, of course, are not to be construed as limiting the breadth of the present invention. Modifications, and other alternative constructions, will be apparent which are within the spirit and scope of the invention as defined in the appended claims.