Abstract
Percussion unit, especially for a rotary hammer and/or percussion hammer, comprising a control unit which is designed for open-loop and/or closed loop control of a pneumatic percussion mechanism, and at least one operating condition sensor unit. According to the disclosure, the control unit is designed to detect at least one percussion mechanism parameter depending on measurement values of the operating condition sensor unit.
Claims
1. A percussion mechanism unit for at least one of a rotary hammer and a percussion hammer comprising: a pneumatic percussion mechanism configured to generate percussive impulses; and a control unit having at least one operating-condition sensor configured to sense at least one of a temperature and an ambient air pressure, the control unit being configured to: determine a maximum frequency of the pneumatic percussion mechanism based on the at least one of the temperature and the ambient air pressure, the maximum frequency being a frequency at which a kinetic energy of the percussive impulses stops increasing with increased frequency of the percussive impulses; determine at least one operating parameter of the pneumatic percussion mechanism based on the determined maximum frequency; and operate the pneumatic percussion mechanism with the at least one operating parameter.
2. The percussion mechanism unit as claimed in claim 1, wherein: the operating-condition sensor unit is configured to sense the temperature and the ambient air pressure; and the control unit is configured to determine the maximum frequency of the pneumatic percussion mechanism based on the temperature and the ambient air pressure.
3. The percussion mechanism unit as claimed in claim 1, wherein the control unit is configured to determine a limit frequency of the pneumatic percussion mechanism, the limit frequency being a frequency below which a starting of the pneumatic percussion mechanism to generate the percussive impulses is ensured.
4. The percussion mechanism unit as claimed in claim 1, wherein the at least one operating parameter is a throttle characteristic quantity of a venting unit.
5. The percussion mechanism unit at claimed in claim 1, wherein the at least one operating parameter is at least one of a percussion frequency and a percussion-mechanism rotational speed.
6. The percussion mechanism unit as claimed in claim 1, wherein the control unit is configured to determine the at least one operating parameter using a computing unit.
7. The percussion mechanism unit as claimed in claim 1, wherein the control unit is configured to determine the maximum frequency with reference to at least one of a characteristic curve and a family of characteristics stored in a memory unit.
8. The percussion mechanism unit as claimed in claim 1, wherein the control unit is configured to take account of at least one of positional information, an operating mode, and an application case in determining at least one of the maximum frequency and the at least one operating parameter.
9. The percussion mechanism unit as claimed in claim 1, wherein the control unit is configured to take account of at least one wear parameter in determining at least one of the maximum frequency and the at least one operating parameter.
10. The percussion mechanism unit as claimed in claim 1, wherein the control unit is configured, in at least one operating state, to set the at least one operating parameter temporarily to a starting value to change from an idling operating state to a percussive operating state.
11. The percussion mechanism unit as claimed in claim 1, wherein the control unit is configured, in at least one operating state, to set the at least one operating parameter to an above-critical working value in a percussive operating state.
12. The percussion mechanism unit as claimed in claim 1, wherein the control unit is configured, in at least one operating state, to set the at least one operating parameter directly to a working value, to change from an idling operating state to an percussive operating state.
13. The percussion mechanism unit as claimed in claim 1, further comprising: an operation change sensor configured to signal a change of the operating mode.
14. The percussion mechanism unit as claimed in claim 1, wherein the control unit has at least one delay parameter, which is configured to influence a time period for a change between two values of the at least one operating parameter.
15. The percussion mechanism unit as claimed in claim 1, wherein a hand power tool comprises the percussion mechanism unit.
16. A method for operating a percussion mechanism unit for at least one of a rotary hammer and a percussion hammer, the percussion mechanism unit having (i) a pneumatic percussion mechanism configured to generate percussive impulses and (ii) a control unit having at least one operating-condition sensor configured to sense at least one of a temperature and an ambient air pressure, the method comprising: sensing, with the at least one operating-condition sensor, the at least one of the temperature and the ambient air pressure; determining, with the control unit, a maximum frequency of the pneumatic percussion mechanism based on the at least one of the temperature and the ambient air pressure, the maximum frequency being a frequency at which a kinetic energy of the percussive impulses stops increasing with increased frequency of the percussive impulses; and determining, with the control unit, at least one operating parameter of the pneumatic percussion mechanism based on the determined maximum frequency; and operating, with the control unit, the pneumatic percussion mechanism with the at least one operating parameter.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) Further advantages are given by the following description of the drawings. The drawings show three exemplary embodiments of the disclosure. The drawings, the description and the claims contain numerous features in combination. Persons skilled in the art will also expediently consider the features individually and combine them to create appropriate further combinations.
(2) There are shown in the drawing:
(3) FIG. 1 shows a schematic representation of a rotary and percussion hammer having a percussion mechanism unit according to the disclosure, in a first exemplary embodiment, in an idling mode,
(4) FIG. 2 shows a schematic representation of the rotary and percussion hammer in a percussion mode,
(5) FIG. 3 shows a schematic representation of a simulated amplitude-frequency response of a non-linear oscillatory system,
(6) FIG. 4 shows a schematic representation of a further simulated amplitude-frequency response of the non-linear oscillatory system,
(7) FIG. 5 shows a schematic representation of a simulated percussion energy of the percussion mechanism unit in the case of a starting of the percussion mechanism with a falling and with a rising percussion frequency,
(8) FIG. 6 shows a schematic representation of a possible definition of a starting value, a limit value, a working value and a maximum value,
(9) FIG. 7 shows a schematic representation of the simulated percussion of the percussion mechanism unit in the case of a starting of the percussion mechanism in differing ambient air pressure conditions,
(10) FIG. 8 shows a block diagram of an algorithm of the percussion mechanism unit,
(11) FIG. 9 shows a linear family of characteristics of a percussion mechanism having a percussion mechanism unit, in a second exemplary embodiment,
(12) FIG. 10 shows a bilinear family of characteristics,
(13) FIG. 11 shows a schematic representation of a venting unit of a percussion mechanism of a rotary and percussion hammer having a percussion mechanism unit, in a third exemplary embodiment, and
(14) FIG. 12 shows a further schematic representation of the venting unit.
DETAILED DESCRIPTION
(15) FIG. 1 and FIG. 2 show a rotary and percussion hammer 12a, having a percussion mechanism unit 10a, and having a control unit 14a, which is provided to control a pneumatic percussion mechanism 16a by open-loop and closed-loop control. The percussion mechanism unit 10a comprises a motor 36a, having a transmission unit 38a that drives a hammer tube 42a in rotation via a first gear wheel 40a and drives an eccentric gear mechanism 46a via a second gear wheel 44a. The hammer tube 42a is connected in a rotationally fixed manner to a tool holder 48a, in which a tool 50a can be clamped. For a drilling operation, the tool holder 48a and the tool 50a can be driven with a rotary working motion 52a, via the hammer tube 42a. If, in a percussive operating state, a striker 54a is accelerated in a percussion direction 56a, in the direction of the tool holder 48a, upon impacting upon a striking pin 58a that is disposed between the striker 54a and the tool 50a it exerts a percussive impulse that is transmitted from the striking pin 58a to the tool 50a. As a result of the percussive impulse, the tool 50a exerts a percussive working motion 60a. A piston 62a is likewise movably mounted in the hammer tube 42a, on the side of the striker 54a that faces away from the percussion direction 56a. Via a connecting rod 64a, the piston 62a can be moved periodically in the percussion direction 56a and back again in the hammer tube 42a, by the eccentric gear mechanism 46a driven with a percussion-mechanism rotational speed. The piston 62a compresses an air cushion 66a enclosed, between the piston 62a and the striker 54a, in the hammer tube 42a. Upon a movement of the piston 62a in the percussion direction 56a, the striker 54a is accelerated in the percussion direction 56a. The striker 54a can be moved back again, against the percussion direction 56a, by a rebound on the striking pin 58a and/or by a negative pressure that is produced between the piston 62a and the striker 54a as a result of a return movement of the piston 62a, against the percussion direction 56a, and/or by a counter-pressure in a percussion space 100a between the striker 54a and the striking pin 58a, and can then be accelerated for a subsequent percussive impulse back in the percussion direction 56a. Venting openings 68a are disposed in the hammer tube 42a, in a region between the striker 54a and the striking pin 58a, such that the air enclosed between the striker 54a and the striking pin 58a in the percussion space 100a can escape. Idling openings 70a are disposed in the hammer tube 42a, in a region between the striker 54a and the piston 62a. The tool holder 48a is mounted so as to be displaceable in the percussion direction 56a, and is supported on a control sleeve 72a. A spring element 74a exerts a force upon the control sleeve 72a, in the percussion direction 56a. In a percussion mode 76a, in which the tool 50a is pressed against a workpiece by a user, the tool holder 48a displaces the control sleeve 72a against the force of the spring element 74a such that it covers the idling openings 70a. If the tool 50a is taken off the workpiece, the tool holder 48a and the control sleeve 72a, in an idling mode 80a, are displaced by the spring element 74a in the percussion direction 56a, such that the control sleeve 72a releases the idling openings 70a. A pressure in the air cushion 66a between the piston 62a and the striker 54a can escape through the idling openings 70a. In the idling mode 80a, the striker 54a is not accelerated, or is accelerated only slightly, by the air cushion 66a (FIG. 1). In the idling operating state, the striker 54a does not exert any percussion impulses, or exerts only slight percussion impulses, upon the striking pin 58a. The rotary and percussion hammer 12a has a hand power-tool housing 82a, having a handle 84a and an ancillary handle 86a, by which it is guided by the user.
(16) Starting of a percussive operating state upon switching over the percussion mechanism unit 10a from the idling mode 80a to the percussion mode 76a by closing the idling openings 70a is dependent on percussion-mechanism parameters, in particular on the percussion-mechanism rotational speed and an ambient air pressure. Owing to the air cushion 66a enclosed between the piston 62a and the striker 54a, the piston 62a is subjected to a periodic excitation, at a percussion frequency that corresponds to the percussion-mechanism rotational speed of the eccentric gear mechanism 46a.
(17) The percussion mechanism 16a constitutes a non-linear oscillatory system. To aid comprehension, FIG. 3 shows a schematic representation of a simulated amplitude-frequency response of a general, non-linear oscillatory system, in relation to a frequency f. The amplitude A in this case corresponds to the amplitude of an oscillating body of the system, corresponding to the striker 54a and not represented in greater detail here, in the case of an external excitation, as effected by the piston 62a in the case of the percussion mechanism 16a. The amplitude-frequency response is non-linear, the amplitude-frequency response having a plurality of solutions at high frequencies. Which amplitude ensues in this range depends, inter alia, on the direction in which the frequency f is varied. If, starting from a higher frequency f, the frequency goes below a minimum frequency 124a of the range of the amplitude-frequency response having a plurality of solutions, the amplitude A jumps from a vertex 126a with an infinite slope to an admissible solution of the amplitude-frequency response having a higher level. If a maximum frequency 128a of the range of the amplitude-frequency response having a plurality of solutions is exceeded from a lower frequency f, the amplitude A jumps from a vertex 130a with an infinite slope to an admissible solution of the amplitude-frequency response having a lower level. In FIG. 3, this behavior is indicated by arrows. FIG. 4 shows a further simulated amplitude-frequency response of the non-linear oscillatory system in the case of different conditions. Instead of having a maximum frequency 128a, the amplitude-frequency response has a gap 132a. This case occurs, for example, if the maximum frequency 128a is higher than a possible excitation frequency with which the oscillatory system can be excited. In the case of the percussion mechanism 16a, the excitation frequency can be limited, for example, by a maximum rotational speed of the eccentric gear mechanism 46a.
(18) FIG. 5 shows the effect of the non-linear amplitude-frequency response upon the percussive operating state of the percussion mechanism 16a. FIG. 5 shows a simulated percussion energy E of the percussion mechanism 16a in the case of a starting of the percussion mechanism with a falling percussion frequency 92a, and with a rising percussion frequency 94a. If the striker 54a is excited with a rising percussion-mechanism rotational speed, or percussion frequency 94a, the percussion energy E rises with the rise in the percussion frequency 94a. If the striker 66a is excited with a falling percussion-mechanism rotational speed, or percussion frequency 92a, starting from an idling operating state, from a high percussion-mechanism rotational speed, the percussive operating state commences only at a certain percussion-mechanism rotational speed. This percussion-mechanism rotational speed constitutes a limit frequency 20a. Above this percussion frequency, in the case of a falling percussion frequency 92a the striker 54a does not begin to move, or begins to move only with a low amplitude and/or speed, even if the idling openings 70a are closed in the case of a switchover from the idling mode 80a (FIG. 1) to the percussion mode 76a (FIG. 2). No percussive impulses, or only very slight percussive impulses, are exerted upon the striking pin 58a by the striker 54a. Above a maximum value 90a, the percussion energy E drops sharply. In this case, the striker 54a does not execute any movement in the percussion direction 56a, or executes movements of small amplitude in the percussion direction 56a, such that no percussive impulses, or only slight percussive impulses having a low percussion energy E, are delivered to the striking pin 58a. Depending on ambient conditions and the design of the percussion mechanism 16a, the limit frequency 20a lies in a range of from 20-70 Hz. The maximum value 90a is greater than the limit frequency 20a and, depending on ambient conditions and the design of the percussion mechanism 16a, lies in a range of from 40-400 Hz. Depending on ambient conditions and the design of the percussion mechanism 16a, the percussion energy E reaches 1-200 joules at the limit frequency 20a, and 2-400 joules at the maximum value 90a.
(19) FIG. 6 shows a schematic representation of a possible definition of operating parameters, in particular of a starting value 28a, the limit frequency 20a, a working value 30a and the maximum value 90a. The limit frequency 20a is preferably selected in the case of a percussion-mechanism rotational speed n at which the amplitude-frequency response has a single-valued solution and a reliable starting of the percussion mechanism is possible. The starting value 28a is less than or equal to the limit frequency 20a. A reliable starting of the percussion mechanism can be ensured, irrespective of the direction from which the starting value 28a is approached. The limit frequency 20a represents the transition to a multi-valued amplitude-frequency response and the maximum starting value 28a. The starting value 28a is preferably selected at an interval from the limit frequency 20a, for example with a 10% lower percussion-mechanism rotational speed. Once the percussive operating state has been assured, the percussion mechanism 16a can be operated with a higher output in the case of an above-critical working value 30a. A reliable starting of the percussion mechanism is not guaranteed in the case of the above-critical working value 30a. Above the maximum value 90a, the percussion energy E drops sharply. The working value 30a is therefore selected so as to be lower than the maximum value 90a. The working value 30a may be defined by the control unit 14a or may be set by the user, for example via a selector switch, not represented in greater detail here. The working values 30a are defined in dependence on, inter alia, a case of performing work and/or a type of material and/or a tool type. Working values 30a are assigned to various settable work operations. A working value 30a above the limit frequency 20a is an above-critical working value 30a; a working value 30a below the limit frequency 20a and/or below the starting value 28a is a stable working value 30a. Besides the starting value 28a and the limit frequency 20a, an idling value 140a may optionally be defined. The idling value 140a is set, in particular, in the idling mode 80a. Advantageously, the idling value 140a is set so as to be higher than the starting value 28a. A ventilation unit, driven by the motor 36a and not represented here, can be operated with a higher rotational speed than in the case of operation with the starting value 28a. The cooling of the percussion mechanism 16a in the idling mode 80a is improved. The user perceives an operating noise of the rotary and percussion hammer 12a to be louder than in the case of the starting value 28a. Further, advantageously, the idling value 140a is set so as to be lower than the working value 30a. Sound emissions and/or vibrations can be reduced in comparison with operation with the working value 30a. Upon changing from the idling mode 80a to the percussion mode 76a, the starting value 28a can be attained more rapidly than from the working value 30a.
(20) FIG. 7 shows the simulated percussion energies E of the percussion mechanism 16a in the case of a starting of the percussion mechanism with a falling and a rising percussion frequency, in differing ambient conditions. In this example, the curve 134a shows the percussion energy E in the case of a first ambient air pressure, and the curve 136a shows the percussion energy E in the case of a second ambient air pressure that is lower than the first ambient air pressure. A limit frequency 138a in the case of the second ambient air pressure occurs at a lesser percussion frequency than the limit frequency 20a in the case of the first ambient air pressure. If the second ambient air pressure is 10% lower than the first ambient air pressure, the limit frequency 138a is 1-25% lower than in the case of the first ambient air pressure, depending on other influencing factors. A temperature of the percussion mechanism 16a, in particular of the hammer tube 42a, likewise influences the limit frequency 20a. At a lower ambient temperature, there is an increased friction of the striker 54a in the hammer tube 42a, in particular as a result of an increasing viscosity of lubricants. If the temperature of the hammer tube 42a falls by 10K, the limit frequency 20a is reduced by 1-30%, depending on other influencing factors. The limit frequency 20a may also vary by +/20% because of influences caused by the tool. The tool may affect a rebound of the striker 54a from the striking pin 58a, and thus influence the limit frequency 20a of the percussion frequency.
(21) The control unit 14a is provided to determine the percussion-mechanism parameters in dependence on measurement values of an operating-condition sensor unit 18a. In particular, the control unit 14a is provided to determine the limit frequency 20a of the amplitude-frequency response for a reliable starting of the percussion mechanism. The operating-condition sensor unit 18a is provided to sense a temperature and the ambient air pressure. The operating-condition sensor unit 18a is integrated as a module on a circuit board of the control unit 14a. The operating-condition sensor unit 18a senses an ambient temperature. The temperature affects a viscosity of lubricants and a friction of the striker 54a with the hammer tube 42a. The ambient air pressure affects, in particular, the return movement of the striker 54a, and the limit frequency 20a of the amplitude-frequency response for a reliable starting of the percussion mechanism. In addition, the operating-condition sensor unit 18a has a radio interface, not represented in greater detail here, by means of which it can obtain temperature and ambient air pressure data from an external device, likewise not represented in greater detail here, such as a smartphone and/or from the Internet. The control unit 14a is further provided to define operating parameters of the percussion mechanism 16a. The operating parameter is determined by means of a computing unit 24a for calculating a formula. A possible formula for definition of a pressure-dependent maximum value 90a of the setpoint percussion-mechanism rotational speed in dependence on the ambient air pressure is:
f.sub.setpoint,max=f.sub.0+C.sub.lin,p*P
wherein f.sub.0 represents a base frequency and/or base rotational speed, C.sub.lin,p represents an application-dependent constant of the pressure term, and P represents the ambient air pressure. In the present example, f.sub.0 has the value of 10 Hz, and C.sub.lin,p has a value of 0.05 Hz/mbar. In the case of an ambient air pressure of 1000 mbar, f.sub.setpoint,max is 60 Hz. Persons skilled in the art will adapt these parameters as appropriate. In the case of different base rotational speeds and/or different pressure-dependent and application-dependent constants C.sub.lin,p, pressure-dependent values can be defined accordingly for the starting value 28a, the working value 30a and the limit frequency 20a. If the working value 30a and/or the maximum value 90a of the setpoint percussion-mechanism rotational speed is defined below the limit frequency 20a, the starting value 28a can be omitted, and the percussion mechanism 16a can be started with the working value 30a.
(22) In an operating mode, the control unit 14a, as well as taking account of the ambient air pressure, can take account of the temperature; in this case, the functional equation is expanded as follows:
f.sub.setpoint,max=f.sub.0+C.sub.lin,p*P+C.sub.lin,T*T
C.sub.lin,T represents an application-dependent constant of the temperature term. The other operating parameters are defined in a similar manner. In the present example, f.sub.0 has the value of 5 Hz, and C.sub.lin,p has a value of 0.05 Hz/mbar, and C.sub.lin,T has a value of 0.25 Hz/ C., wherein the temperature in C. is to be inserted. In the case of an ambient air pressure of 1000 mbar and a temperature of 20 C., f.sub.setpoint,max is 60 Hz. Persons skilled in the art will adapt these parameters as appropriate. As well as the ambient air pressure and temperature, further terms can be introduced, such as a term dependent on an operating hours count, which takes account of an alteration of the percussion mechanism caused by wear. A position sensor of the operating-condition sensor unit 18a, not represented here, senses a position of the rotary and percussion hammer 12a; in the definition of the operating parameters, the positional information can be taken into account in a further term. The term for the working position is selected such that f.sub.setpoint,max is reduced in the case of an upwardly directed working position, and is increased in the case of a downwardly directed working position. Persons skilled in the art can define appropriate factors for this term by experiments.
(23) In a further operating mode, the user can use a rotary wheel, not represented in greater detail here, to set a rotational speed factor (X.sub.rotation) 88a, which is then multiplied by a pressure-dependent and/or temperature-dependent setpoint percussion number for the percussive operating state f.sub.setpoint,max:
f.sub.setpoint=X.sub.rotation*f.sub.setpoint,max
The rotational speed f.sub.setpoint is set by the control unit 14a in the percussive operating state. Thus, starting from the optimum working value 30a for the respective operating conditions, the user can lower the percussion-mechanism rotational speed as required.
(24) FIG. 8 shows a block diagram of an algorithm of the percussion mechanism unit 10a. In a first step 142a, the maximum value 90a of the setpoint percussion number is set in dependence on the ambient air pressure P and temperature T. In a second step 144a, the rotational speed factor 88a is multiplied by the maximum value 90a, in order to determine the working value 30a of the setpoint percussion number. A feedback control unit 96a controls the motor 36a by means of a power electronics unit 146a. In the determination of rotational speed of the motor 36a, required for a setpoint percussion number, the percussion mechanism unit 10a takes account of a transmission ratio of the transmission unit 38a. A rotational-speed actual value 148a, for controlling the motor 36a by closed-loop control, is fed back by the motor 36a to the feedback control unit 96a.
(25) If an above-critical working value 30a is selected as a setpoint percussion number, the control unit 14a is provided to set the setpoint percussion number temporarily to the starting value 28a for the purpose of changing from the idling operating state to the percussive operating state. After a defined timespan, in which a starting of the percussion mechanism has occurred in the case of operation of the percussion mechanism 16a with the starting value 28a, the setpoint percussion number is increased to the working value 30a. The timespan during which the percussion mechanism unit 10a sets the starting value 28a in the case of a starting of the percussion mechanism is defined by a delay parameter. The delay parameter is defined by persons skilled in the art or, advantageously, can be set by the user.
(26) An operation change sensor 32a is provided to signal a change of the operating mode to the percussion mechanism unit 10a. The operation change sensor 32a is disposed such that it senses a control sleeve position, and signals when the control sleeve 72a is displaced from the idling mode 80a to the percussion mode 76a. The percussion mechanism unit 10a then sets the setpoint percussion number temporarily to the starting value 28a if an above-critical working value 30a has been selected.
(27) The following description and the drawings of further exemplary embodiments are limited substantially to the differences between the exemplary embodiments and, in principle, reference may also be made to the drawings and/or the description of the other exemplary embodiments in respect of components having the same designation, in particular in respect of components having the same reference numerals. To differentiate the exemplary embodiments, the letters b and c have been appended to the references of the further exemplary embodiments, instead of the letter a of the first exemplary embodiment.
(28) FIG. 9 and FIG. 10 show a characteristic curve and a family of characteristics of a percussion mechanism unit in a further exemplary embodiment. The percussion mechanism unit of the second exemplary embodiment differs from the previous one in that an operating parameter is determined by means of a memory unit for storing a characteristic curve and a family of characteristics. The characteristic curve (FIG. 9) and the family of characteristics (FIG. 10) serve, as described, to define a maximum value 90b of a setpoint percussion number f.sub.setpoint,max. The characteristic curve defines the maximum value 90b in dependence on an ambient air pressure P; the family of characteristics serves to define the maximum value 90b in dependence on the ambient air pressure P and a temperature T. Intermediate values of the family of characteristics are interpolated as appropriate by the percussion mechanism unit.
(29) FIG. 11 and FIG. 12 show a percussion mechanism unit 10c in a further exemplary embodiment. The percussion mechanism unit 10c differs from the previous percussion mechanism unit in that an operating parameter defined by a control unit 14c is a throttle characteristic quantity of a venting unit 22c. A percussion space in a hammer tube 42c is delimited by a striking pin and a striker. The venting unit 22c has venting openings in the hammer tube 42c, for venting the percussion space. The venting unit 22c serves to equalize the pressure of the percussion space with that of an environment of a percussion mechanism 16c. The venting unit 22c has a setting unit 102c. The setting unit 102c is provided to influence a venting of the percussion space disposed in front of the striker in a percussion direction 56c, during a percussion operation. The hammer tube 42c of the percussion mechanism 16c is disposed in a transmission housing 104c of a rotary and percussion hammer 12c. The transmission housing 104c has ribs 106c, disposed in a star configuration, that face toward an outside of the hammer tube 42c. Pressed in between the hammer tube 42c and the transmission housing 104c, in an end region 110c that faces toward an eccentric gear mechanism, there is a bearing bush 108c, which supports the hammer tube 42c on the transmission housing 104c. The bearing bush 108c, together with the ribs 106c of the transmission housing 104c, forms air channels 112c, which are connected to the venting openings in the hammer tube 42c. The air channels 112c constitute a part of the venting unit 22c. The percussion space is connected, via the air channels 112c, to a transmission space 114c disposed behind the hammer tube 42c, against the percussion direction 56c. The air channels 112c constitute throttle points 116c, which influence a flow cross section of the connection of the percussion space to the transmission space 114c. The setting unit 102c is provided to set the flow cross section of the throttle points 116c. The air channels 112c constituting the throttle points 116c constitute a transition between the percussion space and the transmission space 114c. A setting ring 149c has inwardly directed valve extensions 120c disposed in a star configuration. Depending on a rotary position of the setting ring 149c, the valve extensions 120c can fully or partially overlap the air channels 112c. The flow cross section can be set by adjustment of the setting ring 149c. The control unit 14c adjusts the setting ring 149c of the setting unit 102c by rotating the setting ring 149c by means of a servo drive 122c. If the venting unit 22c is partially closed, the pressure in the percussion space that is produced upon a movement of the striker in the percussion direction 56c can escape only slowly. A counter-pressure forms, directed against the movement of the striker in the percussion direction 56c. This counter-pressure assists a return movement of the striker, against the percussion direction 56c, and thereby assists a starting of the percussion mechanism. If the value selected for the percussion-mechanism rotational speed is an above-critical working value at which reliable starting of the percussion mechanism is not possible with the venting unit 22c open, the control unit 14c partially closes the venting unit 22c, for the purpose of changing from an idling operating state to a percussive operating state. Starting of the percussive operating state is assisted by the counter-pressure in the percussion space. After the percussion mechanism has been started, the control unit 14c opens the venting unit 22c again. The control unit 14c can also use the operating parameter of the throttle characteristic quantity of the venting unit 22c for the purpose of regulating output.
