Abstract:
A manually operable drilling tool ( 1 ) wiht dual impacting funtion has a housing ( 2 ) containing a first striking mechanism ( 16 ) for producing axial impacts to be transferred to a drilling or chiseling tool bit ( 7 ), clamped in a chuck ( 6 ) of the tool ( 1 ). Within the housing ( 2 ), a second striking mechanism ( 20 ) is arranged for producing axial impacts, the axial impacts of which have an impact energy and an impact frequency different from the impact energy and the impact frequency of the axial impacts produced by the first striking mechanism ( 16 ). The drilling or chiseling tool bit ( 7 ), clamped in the chuck ( 6 ), can be acted upon with axial impacts produced either by the first ( 16 ) or the second striking mechanism ( 20 ) or by both striking mechanisms together. The axial impact striking, mechanisms ( 16, 20 ) can also be switched off completely for use in wood or metal.

Description:
FIELD OF THE INVENTION 
     The invention relates to a manually operable drilling tool with a striking mechanism for producing axial impacts. The drilling tool includes a housing with a chuck fitted on the housing for rotating a tool bit secured in the chuck. The striking mechanism periodically transfers axial impacts to the tool bit 
     BACKGROUND INFORMATION AND PRIOR ART 
     In fastening and excavating technology, manually operable drilling tools are known, which have a driving mechanism for imparting rotary motion to a drilling tool and are equipped with a striking mechanism for producing pulse-like impacts. The axial impacts support the excavating action of the drilling tool, especially when drilling in brittle, failing material, such as concrete, rock, brick masonry and the like. For working on very hard and compact materials, such as concrete and rock, manually operable drilling tools, equipped with an electro-pneumatic striking mechanism, prove to be very appropriate, such handheld or manually operable drilling equipment has long been known and is sold, for example, by the Assignee. The electro-pneumatic striking mechanism of such drilling equipment is designed for producing axial impacts with a high individual impact energy of, for example, about 2 J to about 8 J at a relatively low impact frequency of, for example, about 45 Hz to about 80 Hz. Because of the high energy of the individual axial impacts, manually operable drilling tools are not as suitable for working hollow brick masonry. 
     Aside from the manually operable drilling tools with an electro-pneumatic striking mechanism, other drilling tools are also known, which have a mechanical striking mechanism. These include the ratchet drills, known primarily for home owner use and the manually operable drills with a spring U-bolt striking mechanism or a spring-cam stroking mechanism employed in semi-professional and professional use. The striking mechanisms of these known handheld drilling tools produce axial impacts with a relatively low single impact energy of, for example, about 0.03 J to about 0.3 J with a relatively high impact frequency, which amounts to about 700 Hz., for example. Because of the low energy of the individual impacts, it is possible to work with impact support on hollow brick masonry with such manually operable drilling tools without destroying the hollow bricks. For working on hard materials, such as concrete or rock, such drilling tools with a mechanical striking mechanism find less use. Because of the low energy of the individual axial impacts, the user of the drilling tool must press relatively strongly against the material and the achievable drilling progress generally is too little for the professional user. 
     For working different materials, such as concrete and hollow brick masonry, two or more axial impact-supported manually operable drilling tools are required, the axial impacts of which have the single impact energy and impact frequency, suitable for the respective material, in order to work it with sufficient drilling progress, without at the same time damaging it. In general, buildings are not constructed of a continuously homogenous building material. For example, buildings have concrete load-bearing parts and the sections between these parts frequently consist of brick masonry, especially hollow brick masonry. The tool operator, who is to produce boreholes, openings or the like in these different materials in the past always had to use at least two handheld drilling tools with different stroking mechanisms having different impact energies. Since he cannot be expected to carry along two or more manually operable drilling tools at all times, the procurement of the tool, suitable for the respective material, leads to undesirable delays. 
     OBJECT OF THE INVENTION 
     Therefore, it is a primary object of the present invention to provide a remedy for these disadvantages in the state of the art. The tool operator is placed in a position to work the material, without any great delay, using the same drilling tool and working point suitable for such purpose. 
     SUMMARY OF THE INVENTION 
     This objective is accomplished in a manually operable drilling tool with a first and a second striking mechanism each arranged to transfer axial impacts to the drilling bit where the axial impacts of each have a different impact energy and impact frequency, with means for operating the striking mechanism, individually, in tandem or for rotating the tool bit without any axial impact. The manually operable drilling tool is equipped with a first striking mechanism, disposed within a housing, for producing axial impacts, which can be transferred to a rotatable drilling or chiseling tool bit, clamped in a tool chuck of the drilling tool. Within the housing, a second striking mechanism is provided for producing axial impacts, which have an impact energy and an impact frequency, different from the impact energy and the impact frequency of the axial impacts produced by the first striking mechanism. The drilling or chiseling tool bit clamped in the chuck can be acted upon by axial impact from either the first or the second striking mechanism or in tandem by using both striking mechanisms together. For special applications, the axial impact mechanisms can be switched off completely. 
     The manually operable drilling tool of the present invention combines in one tool several drilling tools with striking mechanisms for different single impact energies and impact frequencies. Since such a manually operable drilling tool can be operated with the first striking mechanism providing axial impacts of high energy and low frequency or with the additional striking mechanism offering individual axial impacts of low energy and high frequency, or with both striking mechanisms operating together, the impact output can be adapted very easily to different materials. It is no longer necessary to provide several drilling tools with striking mechanisms for providing axial impacts with different individual impact energies and impact frequencies. The impact parameters of the striking mechanism of the manually operable drilling tool can be adapted at the work site for the materials to be worked. It is self-evident that such a drilling tool can be operated without axial impact support, since both stroking mechanisms can be switched off. This type of operation is desirable, for example, for drilling at a high rpm and without axial impact in wood and metal. 
     For flexibility in the use of the manually operable drilling tool on a large number of different solid materials, it is advantageous if the individual impact energies of the axial impacts produced by the first and second striking mechanisms have a ratio in the range of about 6: to about 250:1, and preferably in the range of about 10:1 to about 40:1, and if their impact frequencies have a ratio in a range of about 1:1.1 to about 1:15. 
     It has proven to be advantageous if the first striking mechanism is an electro-pneumatic striking mechanism with an exciter piston disposed within a guiding tube, a free piston and a snap element acting on the drilling or chiseling tool bit disposed forwardly in axial alignment with the guiding tube. Preferably, the second striking mechanism is a mechanical striking mechanism, which interacts with the snap element. The differences in the energies of the individual parts and in the impact frequencies of the striking mechanisms can be achieved, for example, because impacts are produced completely differently by electro-pneumatic and mechanical striking mechanisms. 
     The mechanical striking mechanism can be constructed as a single ratchet striking mechanism or as a spring U-bolt striking mechanism. From a structural point of view and in order to achieve satisfactory drilling progress in spite of the low impact power, a spring-cam striking mechanism has proven to be advantageous. 
     In order to cover the largest possible area of use for different, solid materials, it is advantageous if the electro-pneumatic striking mechanism for producing axial impacts is constructed with a large individual impact energy of about 2 J to about 8 J and a low impact frequency of about 45 Hz to about 80 Hz and if the spring-cam striking mechanism for producing axial impacts is constructed with a small individual impact energy of about 0.03 J to about 0.3 J and a high impact frequency of about 50 Hz to about 700 Hz. 
     For a construction requiring as little space as possible, it is proven advantageous if the spring-cam striking mechanism is disposed coaxially to the guiding tube of the electro-pneumatic striking mechanism and penetrated axially by the snap element. Moreover, the spring-cam striking mechanism has a cam ring, which is disposed non-rotatably in the housing, and has a spring-loaded percussion piston. The percussion piston is disposed so that it can rotate relative to the cam ring and has cams that interact with the cams of the cam ring for producing axial impacts. 
     Advisably, the percussion piston interacts with a sleeve, which is connected non-rotatably with the machine spindle, and can be driven rotationally. At the same time, the machine spindle forms the guiding tube for the electro-pneumatic striking mechanism. The torque, transmitted to the sleeve by the machine spindle, can be transferred, preferably over a spherical torque transfer element, to the percussion piston. When its cams slide off those of the cam ring, the percussion piston is moved against the restoring force of a cylinder spring, penetrated by the snap element, translatorily from the cams of the cam ring. After passing through the largest stroke, it is disengaged and accelerated back into the starting position by a cylinder spring. At the same time, it strikes against a collar, which is provided at the snap element and mounted ahead of the cam ring. By these means, it is prevented that the axial impact is introduced into the housing over the cam ring. 
     The striking mechanism of the manually operable drilling tool can be connected or disconnected. For this purpose, for example, in addition to being able to switch the electro-pneumatic striking mechanism, a switching element is provided for the mechanical striking mechanism, by means of which the cams of the percussion piston can be disengaged from the cams of the cam ring. In a particularly advantageous embodiment of the drilling tool, the two striking mechanisms can be actuated automatically, preferably during the operation, as a function of specific criteria, in order to adapt the impact energy and frequency of the axial impacts to the material being worked to set the optimum operating point in this matter. 
     The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiment when read in connection with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a schematic representation of a manually operable drilling tool embodying the present invention; 
     FIG. 2 is an axial section of two striking mechanisms used in the drilling tool in FIG. 1; and 
     FIG. 3 is an axial section of the mechanical striking mechanism in FIG. 2, shown on an enlarged scale. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 is a schematic drawing of a manually operable drilling tool  1  embodying the present invention. The tool has a housing  2  with a handle  3 , containing a main switch  4  for activating the drilling tool  1 . Electrical components, disposed within the housing  2 , are supplied with energy over an electric supply lead  5 . At the opposite end of the housing  2  from the handle  3 , a chuck  6  is provided, in which a drilling or chiseling tool bit  7  can be clamped, the bit is shown only in part. The drilling tool  1  has an axis of rotation A extending through the chuck  6   b  for the tool bit. An electric driving motor  8  is disposed within the housing  2 . A drive shaft  9  of the driving motor  8  is connected with a transmission or drive unit  10  having two outputs. One output of the transmission unit  10  drives or rotates the tool bit  7 , clamped in the chuck  6 . For this purpose, a drive shaft  11  on the output side of the transmission unit  10  is provided with a tapered spur wheel  12 , which engages the peripheral teeth  13  on a machine spindle  14 , connected non-rotationally with the chuck  6 . A second shaft  15  at the output of the transmission unit  10  drives an electro-pneumatic first striking mechanism  16 , disposed within the machine spindle  14 . The axial impacts, produced by the electro-pneumatic striking mechanism  16 , can be transferred to the tool bit  7 , clamped in the  6 . To this extent, the construction of the drilling tool  1  corresponds to the known, axial impact-supported hammer drills, as sold, for example, by the assignee. 
     Contrary to known hammer drills, the hand drilling tool  1  includes a second striking mechanism  20 . The axial impacts produced by the second striking mechanism  20  are transferable to the tool bit  7 , clamped in the chuck  6 , and have an individual impact energy and an impact frequency different from the individual impact energy and impact frequency of the axial impacts produced by the electro-pneumatic first striking mechanism  16 . Preferably the second striking mechanism  20  is a mechanical striking mechanism, such as a ratchet striking mechanism, a spring U-bolt striking mechanism or a spring-cam striking mechanism. 
     FIG. 2 is an axial section of the two striking mechanisms  16  and  20 . The description is limited to the details required for an understanding of the invention. The second shaft  15  at the output side of the transmission unit  10  drives an eccentrically mounted exciter piston  17 , shown in phantom, of the electro-pneumatic striking mechanism  16 . The exciter piston  17  is guided in the interior of the machine spindle  14 , which functions as a guiding tube  14  and can be rotated via its outer teeth  13 , which interacts rotationally with the tapered spur wheel  12 , driven by the drive shaft  11 . Due to the eccentric arrangement of the exciter piston  17 , the rotational movement of the shaft  15  is converted into a translation of the exciter piston  17  within the guiding tube  14 . FIG. 2 shows the exciter piston  17  at its rearward dead center, before it is moved axially in the direction of the chuck  6 . An air cushion within the machine spindle or guiding tube  14  transfers the axial motion of the exciter piston  17  to a free piston  18 . As a result, the latter carries out a periodic axially reciprocating motion. The forward motion of the free piston  18  in the direction of the tool holding fixture  6  is limited by a snap element  19 , which transfers the axial impact from the free piston  18  to the tool bit  7 , clamped in the chuck  6 . The air cushion between the free piston  18  and the exciter piston  17  prevents the rebounding free piston  18  from striking the exciter piston  17 . Electro-pneumatic striking mechanisms are adequately known from the state of the art and are components of the hammerdrills provided by the Assignee. It is self-evident that implement-specific modifications can be provided at the striking mechanism  16 , without deviating from the basic principle described. The axial impacts produced by such electro-pneumatic striking mechanisms, have an individual impact energy in the range of about 2 J to about 8 J and are produced with impact frequencies in the range of about 45 Hz to about 80 Hz. 
     The second striking mechanism  20  is disposed coaxially with the first electro-pneumatic striking mechanism  16 . In particular, it is constructed as a spring cam striking mechanism and comprises a cam ring  21 , which is held non-rotatably in the interior of the housing  2 , and a percussion piston  22 , which can be rotated relative to the cam ring  21  and shifted against the restoring force of a spring  23 . The cam ring  21  and the percussion piston  22  are penetrated axially by the snap element  19 . The spring  23  is supported, on the one hand, at the percussion piston  22  and, on the other, at a sleeve  24 , which is rotationally coupled with the machine spindle  14 , which forms the guiding tube for the electro-pneumatic striking mechanism  16 . The torque of the machine spindle or guiding tube  14 , rotated by the driving motor  8 , is transferred, on the one hand, over the snap element  19  to the drilling tool  7  clamped in the tool holding fixture  6 . On the other hand, the torque is also introduced into the sleeve  24  and transferred over a preferably spherical torque transfer element  25  to the percussion piston  22 . A switching clement  31 , accessible on the outside of the housing  2 , enables the spring-cam striking mechanism to be switched off. 
     FIG. 3 shows the spring-cam second striking mechanism  20  of FIG. 2 on an enlarged scale. The cam ring  21  and the percussion piston  22  are penetrated axially by the snap element  19 . The cam ring  21  is connected non-rotationally with the housing  2 , for example, by screws  32 . The cam ring  21  has cams  27  which, in the switched-on state of the spring-cam second striking mechanism  20 , are in engagement with cams  28 , which are provided at the side of the percussion piston  22  facing the cam ring  21 . The torque of the rotating machine spindle  14  is introduced into the non-rotatably coupled sleeve  24 . The spherical torque transfer element  25 , disposed between the sleeve  24  and the percussion piston  22  in an axial groove  26 , transfers the torque to the percussion piston  22 . While the percussion piston  22  is rotating relative to the cam ring  21 , the cams  27  and  28  slide over one another and the rotational movement of the percussion piston  22  is converted into a translational movement. At the same time, the percussion piston  22  is moved rearward against the restoring force of the spring  23 , which is supported, on the one hand, at the percussion piston  22  and, on the other, at the sleeve  24 . Spring  23 , which is already pre-tensioned, is tensioned additionally by the stroke, which arises from the height of the cams  27  and  28 . As the percussion piston  22  is rotated further relative to the cam ring  21 , the largest stroke is exceeded, the edges of the cams  27 ,  28  slide over one another and the translatory forward motion of the percussion piston is released once again. The tensioned spring  23  accelerates the percussion piston  22  axially in the direction of the cam disk  21 , until a collar  29  at the percussion piston  22  strikes against a ring collar  30  on the snap element  19 . The ring collar  30  is mounted in front of the cam ring  21  in such a manner, that the axial impact energy of the percussion piston  22  is transferred to the snap element  19  and not introduced into the cam ring  21 . The snap element  19  transfers the axial impact, produced by the spring-cam second striking mechanism  20 , once again onto the tool bit clamped in the chuck  6 . 
     The individual impact energy of the axial impacts, produced by the second striking mechanism  20 , depends on the pretension on the spring  23  and on the height of the cams  27 ,  28 , which is fixed by the stroke. Preferably, the second striking mechanism for producing axial impacts is designed for an individual impact energy of about 0.03 J to about 0.3 J. The impact frequency of the axial impacts depends on the number of cams  27 ,  28  at the cam disk  21  or at the percussion piston  22 , interacting in the peripheral direction. Preferably, the axial impacts can be produced with an impact frequency in the range of about 50 Hz to about 700 Hz. 
     It can be noted in FIG. 3, that the cams  27 ,  28  can be disengaged over the switching element  31 , in order to switch off the spring-cam second striking mechanism  20 . In FIG. 3, the switching element  31  is shown as a twisting and sliding element, which can be actuated manually from outside of the housing  2 . It is self-evident that the switching element  31  can also be engaged and disengaged automatically between the cams  27 ,  28  and activated as a function of specific criteria. For known hammer drills with an electro-pneumatic striking mechanism, this final control element can usually be switched on or off. In conjunction with the spring-cam second striking mechanism  20 , which can be switched on or off, there arc many possible variations for operating the inventive manually operable drilling tool. In a first operational variation, the drilling tool  1  can be operated without axial impact support. This may be required, for example, for producing boreholes in steel or wood, which are drilled only at a high rpm without axial impact support. Further operational variations arise out of the alternate activation of the first or the second striking mechanism, as a result of which the axial impact support takes place either with a high individual impact energy and a relatively low frequency, as is required, for example, in concrete, or the axial impacts can be produced with a low individual impact energy and a high impact frequency, for drilling in hollow brick masonry without, at the same time, destroying the bricks. For special applications, the simultaneous activation of both striking mechanisms is also possible. 
     The invention has been explained using a manually operable drilling tool with an electro-pneumatic first striking mechanism and a spring-cam second striking mechanism as an example. Within the inventive concept, alternative variations of the construction can also provide different combinations of striking mechanisms. For example, an electro-pneumatic striking mechanism can be combined with a ratchet striking mechanism or a spring U-bolt striking mechanism. Manually operable drilling tools, which have two mechanical striking mechanisms with different individual impact energies and impact frequencies, can also be realized. In a further variation, two electro-pneumatic striking mechanisms can also be provided in one manually operable drilling tool, with which axial impacts with individual impact energies of different magnitudes and frequencies can be produced. 
     While specific embodiments of the invention have been shown and described in detail to illustrate the application of the inventive principles, it will be understood that the invention may be embodied otherwise without departing from such principles.