Abstract:
A hand drill including a housing ( 2 ), a rotary drive ( 8-15 ) arranged in the housing ( 2 ) for driving a chuck ( 6 ) provided at a front, in the drilling direction, end of the housing and in which a drill or a chisel tool is received, a compressed air-operated hammer mechanism having a pneumatic cylinder ( 22 ), a die member ( 15 ) for imparting axial blows to the drill or chisel tool, and a percussion piston ( 30 ) displaceable in the pneumatic cylinder  922 ) upon being impinged by compressed air for intermittently applying axial blows to the die member ( 15 ), and a reversing valve for connecting the hammer mechanism ( 22 ) with a source of compressed air, integrated in the percussion piston ( 30 ), and having a plurality of recesses and bores ( 46-52 ) alternatively operationally connectable with at least one inlet opening ( 23 ) and at least one discharge opening ( 24 ) of the pneumatic cylinder ( 22 ) for feeding the compressed air into the pneumatic cylinder ( 22 ) and for discharging the compressed air therefrom.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a hand drill including a housing, a chuck provided at a front, in a drilling direction, end of the housing for receiving a drill or chisel tool, a rotary drive arranged inside the housing for driving the chuck, together with the drill or chisel tool, a compressed air-operated hammer mechanism for generating axial blows to be applied to the drill or chisel tool and having a pneumatic cylinder with at least one inlet opening and at least one discharge opening, a die member for imparting the axial blows, which are generated by the hammer mechanism, to the drill or chisel tool and extending through a front limiting surface of the pneumatic cylinder, and a percussion piston displaceable in the pneumatic cylinder upon being impinged by compressed air for intermittently applying axial blows to the die member, and a reversing valve for connecting the hammer mechanism with a source of compressed air. 
     2. Description of the Prior Art 
     In addition to hand-held drills provided with electro-pneumatic hammer mechanisms or mechanical hammer mechanisms such as ratchet hammer mechanisms, spring-actuated hammer mechanisms and cushioned cam hammer mechanisms, also are used hand-held drills having a compressed air-operated or servo-pneumatic hammer mechanisms which include a pneumatic cylinder in which a percussion piston is arranged. The percussion piston is displaceable by the compressed air and periodically applies axial blows to a die member which transmits the blow to a tool secured in the chuck of the hand-held drill. In the known compressed air-operated hammer mechanisms, a reversing valve is provided between the pneumatic cylinder and the source of the compressed air, e.g., a compressor located in the drill housing. The reversing valve provides for alternating supply of the compressed air to the pneumatic cylinder and the discharge of the compressed air from the pneumatic cylinder for reciprocating the percussion piston in the pneumatic cylinder chamber. The operation of the reversing valve is controlled by end switches which are actuated in front and rear end positions of the percussion piston. The switching of the reversing valve proper is then effected by appropriate mechanical, electrical means or by communicating to the reversing valve the compressed air through control conduits. 
     The drawback of the known compressed air-operated hammer mechanisms consists in that they have a large dead volume which must be reloaded between each pressurized condition of the pneumatic cylinder and each unpressurized condition of the pneumatic cylinder. This adversely affects timely deceleration of the percussion piston and, thereby, a predetermined blow frequency. Further, the permanent reloading of the large dead volume leads to large energy losses. The known compressed-air operated hammer mechanisms have at least one reversing valve and several end switches. Such an arrangement causes a time delay in switching from one condition of the reversing valve to another condition thereof, which adversely affects the blow power. Further, the energy of a single blow and the frequency of the generated axial blows can only be controlled by the pressure acting on the hammer mechanism to a very small extent. 
     Accordingly, an object of the present invention is to eliminate the drawbacks of conventional compressed air-operated hammer mechanisms and to provide a hammer mechanism in which the time delay in switching of the pneumatic cylinder between its pressurized and unpressurized conditions is eliminated to a most possible extent. 
     Another object of the present invention is to provide a hammer mechanism in which the energy necessary for reloading of the dead volume is reduced, and the energy balance for generating axial blows is substantially improved. 
     A further object of the present invention is to provide a hammer mechanism which would provide greater possibilities for adjusting the energy of single blows and the blow frequency. 
     SUMMARY OF THE INVENTION 
     These and other objects of the present inventions, which will become apparent hereinafter, are achieved by providing a hand-held drill including a housing, a chuck provided at a front, in a drilling direction, end of the housing for receiving a drill or chisel tool, a rotary drive arranged inside the housing for driving the chuck, together with the drill or chisel tool receivable in the chuck, and a compressed air-operated hammer mechanism for generating axial blows to be applied to the drill or chisel tool. The hammer mechanism has a pneumatic cylinder with at least one inlet opening and at least one discharge opening, a die member for imparting the axial blows, which are generated by the hammer mechanism, to the drill or chisel tool and extending through a front limiting surface of the pneumatic cylinder, and a percussion piston displaceable in the pneumatic cylinder upon being impinged by compressed air for intermittently applying axial blows to the die member. A reversing valve connects the hammer mechanism with a source of compressed air. The reversing valve is integrated in the percussion piston and has a plurality of recesses and bores alternatively operationally connectable with the at least one inlet opening and the at least one discharge opening of the pneumatic cylinder for feeding the compressed air into the pneumatic cylinder and for discharging the compressed air therefrom. 
     Because the reversing valve forms an integral part of the percussion piston, the reversing valve is located within the working volume of the pneumatic cylinder. Further, a pressure is permanently applied to the inlet opening of the pneumatic cylinder. The discharge opening of the pneumatic cylinder serves only for discharging the compressed air from the pneumatic cylinder. The recesses and bores, which are formed in the reversing valve, permits to reduce the dead volume which has to be reloaded between the pressurized and unpressurized conditions of the pneumatic cylinder at each complete stroke of the percussion piston. The reduction of the reloadable dead volume permits to reduce the energy necessary for reloading and improves the general energy balance of generation of axial blows. The present invention also reduces the number of necessary conduits, connections and parts due to the fact that the valving function is now performed by the percussion piston itself instead of a separate reversing valve that was the case in the prior art hammer mechanisms. The time delay of switching is eliminated due to the fact that the percussion piston functions as its own end switch. 
     In accordance with an advantageous embodiment of the present invention, the percussion piston includes an integrated switch piston which forms the reversing valve and which is displaceable between two end pistons for alternatively directing the compressed air into the working chamber of the pneumatic cylinder and discharging the compressed air therefrom. In this embodiment, the percussion piston forms the valve housing in which a cylindrical reversing element, the switch piston, is axially displaceable. 
     Because the switch piston extends beyond the rebound surface of the percussion piston during the forward stroke of the percussion piston and beyond the rear surface of the percussion piston during the return stroke of the percussion piston, and, respectively, engages the front and rear surfaces of the pneumatic cylinder, the switch piston acts as an end switch for a respective end position of the percussion piston. Thereby, the time delay during switching is eliminated as the switch piston also functions as a reversing valve, and no time delay takes place between the actuation of the end switch and the valve, as it was the case in the prior art hammer mechanisms in which the end switches and the valve were separate elements. Because the switch piston extends beyond the end surface of the percussion piston, it engages the front or rear surface of the pneumatic cylinder before the percussion piston reaches its respective end position, so that the switching between the pressurizing and unpressurizing positions of the switch piston takes place simultaneously with the percussion piston reaching its respective end position. Thus, the reversing of the direction of movement of the percussion piston is used for simultaneous mechanical reversing of the position of the switch piston, i.e., the reversing valve. 
     Advantageously, a spring is provided in the space between the rear surface of the percussion piston and the rear wall of the pneumatic cylinder. During the rearward stroke of the percussion piston, the spring absorbs the energy of the percussion piston and thereby contributes to acceleration of the percussion piston during its forward stroke toward the die member. Upon deceleration of the percussion piston during its rearward movement, the movement energy of the percussion piston is stored in the spring which releases the stored energy during the forward stroke of the percussion piston. 
     In accordance with one embodiment of the present invention, the rear wall of the pneumatic cylinder is formed by an adjustable plate the axial position of which in the pneumatic cylinder can be changed. The changeability of the position of the rear wall-forming plate permits to easily adjust the stroke of the percussion piston. The changeability of the axial position of the adjustable plates permits to easily adjust the frequency of the generated blows and the energy of a single blow, without a need in using additional pressure. By increasing the distance between the die member and the rear wall-forming plate, the stroke of the percussion piston can be increased. The increase in stroke results in the increase of energy of a single blow and in a reduced frequency of the blows. The reduction of the stroke of the percussion piston is achieved by the reduction of the distance between the die member and the rear wall-forming plate. This, in turn, causes a reduction in the energy of a single blow and an increase of the blow frequency. 
     Advantageously, the axial position of the adjustable plate, which forms the rear wall of the pneumatic cylinder, is continuously adjusted. To this end, the pneumatic cylinder can be provided, e.g., with an inner thread, with the adjustable plate being provided on its circumference with a corresponding outer thread. The stroke adjustment is effected by screwing the plate into the pneumatic cylinder a desired distance. 
     In a further advantageous embodiment of the present invention, the axial position of the plate is adjusted automatically. The adjustment of the adjustable plate can be effected dependent on predetermined criteria during the operation of the hand-held drill. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The features and objects of the present invention will become more apparent, and the invention itself will be best understood from the following detailed description of the preferred embodiments when read with reference to the accompanying drawings, wherein: 
     FIG. 1 shows a schematic view of a hand-held drill according to the present invention; 
     FIG. 2 shows an axial cross-sectional view of an air pressure-operated hammer mechanism used in a hand-held drill according to the present invention; and 
     FIGS. 3-6 show the hammer mechanism shown in FIG. 2 in different positions of the percussion piston. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A hand-held drill according to the present invention, the schematic view of which is shown in FIG. 1, is generally designated with a reference numeral  1 . The drill has a housing  2  and a handle  3  provided with a main trigger  4  for actuating the drill  1 . The feeding of an electrical current to electric components, which are arranged in the housing  2 , is effected via an electrical conductor  5 . At a side of the housing  2  opposite the handle  3 , there is provided a chuck  6  in which a drill or a chisel tool is received. The tool is designated with a reference numeral  7 . Inside the housing  2 , there is arranged an electric motor  8 . The drive shaft  9  of the electric motor  8  is connected with a drive gear mechanism  10  having two outputs. One of the outputs of the drive gear mechanism  10  serves for rotating the tool  7  received in the chuck  6 . To this end, the output drive shaft  11  of the drive mechanism  10  carries a bevel gear  12  which is engaged with a circumferential toothing  13  of a spindle  14 . A torque of the rotatable spindle  14  is transmitted, via a transmission member  15 , to the chuck  6  and the tool  7  received in the chuck  6 . 
     A second output shaft  16  of the drive gear mechanism  10  drives a compressor  17  which generates air pressure. The outlet  20  of the compressor  17  is connected with a bore  23  of a pneumatic cylinder  22  of an air pressure-operated hammer mechanism  21  which is preferably arranged within the spindle  14  coaxially therewith. The inlet  18  of the compressor  17  is connected with a bore  24  of the pneumatic cylinder  22 . For compensation of leakage, the compressor  17  is provided with a further air input  19 . The axial blows, which are generated by the hammer mechanism  21 , are transmitted to the tool  7 , which is secured in the chuck  6 , via a die member. Advantageously, the die member is formed by the transmission member  15  which in addition to the torque transmission, transmits axial blows. 
     A schematic axial cross-sectional view of the air pressure-operated hammer mechanism  21  is shown in FIG.  2 . The pneumatic cylinder  22  has a discharge bore  24  connected with a source of compressed air, e.g., a compressor. The working chamber of the pneumatic cylinder  22  is limited by front and rear limiting surfaces  25  and  26 , respectively. The die member  15  extends through the front surface  25  into the working chamber of the pneumatic cylinder  22 . As it has already discussed above, the die member  15  also functions as a torque transmission member and provides thereby for rotation of the tool  7  received in the chuck  6 . A sealing  38  seals the working chamber of the pneumatic cylinder  22  in the region of the front surface  25  in which the die member  15  extends. The rear surface  25  advantageously is formed by an adjustable plate  27  having an outer thread  28 . The end section of the pneumatic cylinder  22 , which is located remotely from the die member  15 , is provided with an inner thread  29 . The volume of the working chamber of the pneumatic cylinder  22  is changed by adjusting the position of the adjustable plate  27 . The adjustment of the position of the adjustable plate  27  can be effected, when needed, manually. In an advantageous embodiment of the invention, the adjustable plate  26  is adjusted automatically, e.g., with an adjusting motor, dependent on predetermined criteria. The adjustment of the plate  27  can be effected, e.g., during the operation of the drill to conform the impact energy of separate blows to the blow frequency of the blows generated by the hammer mechanism. 
     The working chamber of the pneumatic cylinder  22  is separated by a percussion piston  30  into a front pressure chamber  35  and a rear pressure chamber  36 . The front pressure chamber  35  extends between a front rebounding surface  33  of the percussion piston  30  and the front surface  25  of the pneumatic cylinder  22 . The rear pressure chamber  36  is limited axially by a rear surface  34  of the percussion piston  30  and the rear surface  26  defined by the adjustable plate  27 . The percussion piston  30  has a symmetrical outer contour. Two recesses, which are provided on the circumference of the percussion piston  30  define, together with the cylindrical wall of the housing of the pneumatic cylinder  22 , front and rear annular grooves  31  and  32 , respectively. Sealing rings  37 , which are provided in the circumferential surface of the percussion piston  30 , seal the grooves  31  and  32  relative to each other and relative to the front and rear pressure chambers  35  and  36 , respectively. A helical spring  40  is provided in the rear pressure chamber  36 . In the embodiment shown in the drawings, the spring  40  is supported against the adjustable plate  27 . The spring  40  is compressed between the adjustable plate  27  and the rear surface  34  of the percussion piston  30 . 
     A switch piston  41  is arranged in an axial stepped core  39  formed in the percussion piston  30 . The switch piston  41  is axially displaceable and has an axial length greater than the axial length of the percussion piston  30 . The switch piston  41  is formed as a symmetrical body and has a middle section  42  having an increased diameter. The axial displacement of the switch piston  41  is limited by stop shoulders defined by the middle section  42 . The front stop shoulder  43  is formed by a shoulder of the stepped core  39  of the percussion piston  30 . The rear stop shoulder  45  is formed by a surface of a sleeve  44  which surrounds the rear section of the switch piston  41  and which is secured in the stepped bore  39  by being screwed-in or by being press-fit in the bore  39 . The axial distance between the stop shoulders  43  and  45  is greater than the axial extent of the middle section  42 , and the stop shoulder  43  and  45  limit the axial displacement of the switch piston  41  arranged inside of the percussion piston  30 . The switch piston  41  is provided with bores and annular grooves which, together with the annual grooves  31 ,  32  and control bores formed in the percussion piston  30 , perform an integrated ventilation function and an end point change-over. 
     The arrangement of the bores and annual grooves in the switch piston  41 , together with commutation of the delivery and discharge bores  23  and  24  of the pneumatic cylinder  22  with the control bores in the percussion piston  30 , and their respective functions will now be explained in detail with reference to FIGS. 3-6. FIGS. 3-4 show the percussion piston  30  in its for stroke position in a direction toward the die member  15 . The switch piston  41  is provided with axial blind bores  46  and  48  the mouths of which open into the front and rear pressure chambers  35  and  36 , respectively. The axial blind holes  46  and  48  communicate with valve chambers  47  and  51  which are formed as recesses on the circumference of the increased diameter, middle section  42 . A connection bore  50  connects the front annular groove  31  of the percussion piston  30  with the stepped bore  39 . The compressed air, which is fed through the feed opening  23  of the pneumatic cylinder  22 , is permanently fed to the annular groove  31 , and the rear annular groove  32  is permanently connected with the discharge bore  24 . 
     As shown in FIG. 3, the compressed air, which is delivered to the front annular groove  31 , is fed to the rear pressure chamber  36  via the connection bore  50  in the valve chamber  51  and via the blind bore  48 . Thereby, the percussion piston  30  is accelerated in a direction toward the die member  15 . The front pressure chamber  35  is deaerated via the blind bore  46 , the valve chamber  47 , a control bore  52  formed in the percussion piston  30 , and the discharge opening  24  of the pneumatic cylinder  22 . FIG. 3 shows the percussion piston  30  in a position in which the rebound surface  33  of the piston  30  is rebound against the die member  15 . The switch piston  41 , which has a greater length than the percussion piston  30 , has its end projecting beyond the rebound surface  33  of the piston  30  and engaging the front surface  25  of the pneumatic cylinder  22 . Upon further forward movement of the percussion piston  30 , an axial displacement of the switch piston  41  and reversing of the integrated valve takes place. 
     FIG. 4 shows a condition in which the percussion piston  30  reaches its forward end position, and the switch piston has been completely axially displaced. In this position, the rear end of the switch piston  41  extends beyond the rear surface  34  of the percussion piston  30 , and the compressed air can flow through the bore  23 , the front annular groove  31 , the connection bore  50 , the valve chamber  47  and the front blind bore  46  of the switch piston  41 . Through the mouth of the blind bore  46 , the compressed air is discharged from the front pressure chamber  35  which is formed between the front surface  25  of the pneumatic cylinder  22  and the rebound surface  33  of the percussion piston  30 . In a condition shown in FIG. 4, the front pressure chamber  35  is completely closed. The kinetic energy of the percussion piston  30  is transmitted to the die member  15 . Upon engaging the die member  15 , the percussion piston  30  immediately rebounds therefrom, and the front pressure chamber  35  again opens and can be filled with the compressed air. As a result, the percussion piston  30  is displaced toward the adjustable plate  27  against a biasing force of the helical spring  40 , which is located in the rear pressure chamber  46 . The air from the rear pressure chamber  36  is discharge through the rear blind bore  48 , the valve chamber  51 , the control bore  52 , the rear annular groove  32  and the discharge opening  24  of the pneumatic cylinder  22 . 
     FIG. 5 shows the position of the percussion piston  30  during its rearward stroke just before the piston  30  reaches its rear end position. The rear pressure chamber  36  is almost completely closed. The spring  40  is compressed between the rear surface  34  of the percussion piston  30  and the adjustable plate  27 . The spring  40  functions as an energy accumulator during the rearward movement of the percussion piston  30 . The front pressure chamber  35  is almost completely open. The filling and the discharge of the front and rear pressure chambers  35  and  36  is effected according to the sequence which was explained on the basis of FIG.  4 . In the position shown in FIG. 5, the rear end of the switch piston  41  extends beyond the rear surface  34  of the percussion piston  30  and engages the rear surface  26  of the pneumatic cylinder  22 . The switching of the valve takes place automatically upon the percussion piston having reached its dead point position. 
     FIG. 6 shows the percussion piston  30  in its rear dead point position. The switching process is completed by axial displacement of the switch piston  41 , and the valve is automatically reversed. The helical spring  40  is in a condition of its maximum compression. Upon being released, the spring  40  contributes to the acceleration of the percussion piston  40  in a direction toward the die member  15 , releasing its accumulated energy. As a result of the axial displacement of the switch piston  41 , the compressed air, is fed through the inlet bore  23 , the front annular groove  31 , the connection bore  50 , and the blind bore  48  into the rear pressure chamber  36 , causing acceleration of the percussion piston  30  in the direction of the die member  15 . The front pressure chamber  35  is again deaerated via the blind bore  46 , the valve chamber  47 , the control bore  52 , the rear annular space  32 , and the discharge opening  24  of the pneumatic cylinder  22 . 
     The advantage of the integration of the reversing valve into the percussion piston consists in that the valving function and the displacement reversing function are effected by one member. The occurrence of the end position and switching take place simultaneously. As a result, retardation of the switching action is eliminated. In the embodiment of the hand-held drill according to the present invention which is shown in the drawings, the energy accumulation during the rearward displacement of the percussion piston is effected by using a spring, in particular a helical spring. Thereby, a continuous supply of energy from a compressor can take place during both the forward stroke and the return stroke of the percussion piston. Additional pressure accumulators are not needed. The energy accumulation can also be effected due to air cushion provided between the rear surface of the percussion piston and the rear surface of the pneumatic cylinder. To this end, it is sufficient when the rear surface of the pneumatic cylinder has, in the region of the mouth of a respective blind bore formed in the switch piston, appropriate recesses. The recesses enable filling of the rear pressure chamber with compressed air during the switching of the percussion piston movement, thus preventing a complete closure of the rear pressure chamber at the rear dead point. As it has already been explained above, that compressed air can be produced using an electrical drive and a compressor. It is to be pointed out that the hammer mechanism according to the present invention can be used in hand-held drills provided with a compressed air accumulator for driving the percussion piston. In accordance with another embodiment of the present invention, the entire hand drill can be operated with a source of compressed air. In his case, both the rotational drive of the tool and operation of the hammer mechanism is effected by using the compressed air source, e.g., a compressed air conduit. 
     Though the present invention has been shown and described with reference to a preferred embodiment, such is merely illustrative of the present invention and is not to be construed as to be limited to the disclosed embodiment and/or details thereof, and the present invention includes all modifications, variations and/or alternate embodiments within the sprint and scope of the present invention as defined by the appended claims.