Abstract
An electric drive unit for an electric handheld power tool, having an electric motor with a stator winding and a rotor winding, an actuating circuit for actuating the electric motor and a connection unit for coupling an energy source for driving the electric motor, wherein the stator winding is connected via a first node to a stator-side first half-bridge including a first semiconductor component and a second semiconductor component and is connected via a second node to the rotor winding, wherein the rotor winding is connected to a third node which is connected via a conductive component to the connection unit, and wherein the actuating circuit includes a third semiconductor component which is connected via the second node to the rotor winding and the stator winding and which is connected via a fourth node directly to the connection unit.
Claims
1-15. (canceled)
16. An electric drive unit for an electric handheld power tool, the electric drive unit comprising: an electric motor with a stator winding and a rotor winding; an actuating circuit for actuating the electric motor; and a connection unit for coupling an energy source for driving the electric motor, the stator winding being connected via a first node to a stator-side first half-bridge including a first semiconductor component and a second semiconductor component and connected via a second node to the rotor winding, the rotor winding being connected to a third node connected via a conductive component to the connection unit, the actuating circuit including a third semiconductor component connected via the second node to the rotor winding and the stator winding and connected via a fourth node directly to the connection unit.
17. The electric drive unit as recited in claim 16 wherein the actuating circuit further comprises a further semiconductor component connected via the second node to the rotor winding and the stator winding and is connected via a fifth node directly to the connection unit.
18. The electric drive unit as recited in claim 16 wherein the actuating circuit is designed to move the first semiconductor component to a non-conductive state in order to interrupt a supply current flow.
19. The electric drive unit as recited in claim 16 wherein the actuating circuit is designed to move the third semiconductor component to a conductive state in order to connect the rotor winding in parallel with the stator winding.
20. The electric drive unit as recited in claim 19 wherein the actuating circuit is designed to move the first semiconductor component to a conductive state in addition to the third semiconductor component in order to provide a magnetic flux, so that a voltage is induced at the rotor winding in the opposite direction compared to a voltage applied to the rotor winding during motor operation of the electric motor.
21. The electric drive unit as recited in claim 16 further comprising a first current measuring unit for determining a current rotor current, wherein the actuating circuit is designed to move the first semiconductor component as a function of the determined current rotor current and a predetermined threshold value of the rotor current to a non-conductive state in order to limit the rotor current.
22. The electric drive unit as recited in claim 16 wherein the conductive component includes a fourth semiconductor component and the actuating circuit further comprises a fifth semiconductor component connected via the third node to the rotor winding and connected via a fifth node directly to the connection unit.
23. The electric drive unit as recited in claim 22 wherein the actuating circuit is designed to move the fourth semiconductor component to a non-conductive state in order to interrupt a rotor current through the rotor winding.
24. The electric drive unit as recited in claim 22 wherein the drive circuit is designed to move the third semiconductor component and the fifth semiconductor component to a conductive state for reversing the polarity of an input voltage applied to the rotor winding compared to motor operation.
25. The electric drive unit as recited in claim 22 further comprising a first current measuring unit for determining a current rotor current, wherein the actuating circuit is designed to move the fifth semiconductor component and the fourth semiconductor component as a function of the determined current rotor current and a predetermined threshold value of the rotor current alternately in synchronism with opposite senses to a conductive state and to a non-conductive state in order to limit the rotor current.
26. The electric drive unit as recited in claim 25 wherein the actuating circuit is designed to move the fifth semiconductor component and the fourth semiconductor component as a function of the determined current rotor current, the predetermined threshold value of the rotor current and a current rotation speed of the electric motor alternately in synchronism with opposite senses to a conductive state and to a non-conductive state in order to limit the rotor current.
27. The electric drive unit as recited in claim 22 further comprising a stator current measuring unit for determining a current stator current, wherein the actuating circuit is designed to move the first semiconductor component alternately to a conductive state and to a non-conductive state in order to regulate a stator current through the stator winding as a function of a current rotation speed of the electric motor.
28. The electric drive unit as recited in claim 24 wherein the actuating circuit is designed, after a predetermined period of time has elapsed after the third semiconductor component and the fifth semiconductor component have been moved to a conductive state, to move the first semiconductor component alternately to a conductive state and to a non-conductive state in order to regulate a stator current through the stator winding as a function of a current rotation speed of the electric motor.
29. The electric drive unit as recited in claim 16 wherein the electric drive unit is designed for operation from a DC voltage source, a pulsating DC voltage source or an AC voltage source with a rectifier.
30. An electric handheld power tool comprising the electric drive unit as recited in claim 16.
Description
BRIEF DESCRIPTION OF THE FIGURES
[0063] The following description explains the invention with reference to exemplary embodiments and figures, in which:
[0064] FIG. 1 shows a schematic view of an electric handheld power tool;
[0065] FIG. 2A shows a schematic view of a first embodiment of a circuit topology of an electric drive unit;
[0066] FIG. 2B shows a schematic current flow diagram during motor operation of an electric motor within the circuit topology of the electric drive unit according to FIG. 2A;
[0067] FIG. 2C shows a schematic current flow diagram during braking operation of an electric motor within the circuit topology of the electric drive unit according to FIG. 2A;
[0068] FIG. 3A shows a schematic view of a second embodiment of a circuit topology of an electric drive unit;
[0069] FIG. 3B shows a schematic current flow diagram during motor operation of an electric motor within the circuit topology of the electric drive unit according to FIG. 3A;
[0070] FIG. 3C shows a schematic current flow diagram during braking operation of an electric motor within the circuit topology of the electric drive unit according to FIG. 3A;
[0071] FIG. 4 shows a schematic view of a third embodiment of a circuit topology of an electric drive unit;
[0072] FIG. 5 shows a schematic view of a fourth embodiment of a circuit topology of an electric drive unit; and
[0073] FIG. 6 shows a schematic diagram of a sequence of a control method for braking an electric motor.
[0074] Identical or functionally identical elements are indicated by the same reference signs in the figures, unless stated otherwise.
DETAILED DESCRIPTION
[0075] FIG. 1 shows a schematic view of an electric handheld power tool 1 which is in the form of a drill by way of example. The drill 1 has a tool fitting 3 in which a drill bit is inserted as a drilling tool 5. A primary drive of the drill 1 is an electric motor 7 having a stator winding 12 and a rotor winding 14. An operator can guide the drill 1 by means of a handle 9 and put it into operation by means of a button 11. During operation, the drill 1 rotates the drill bit 5 continuously about a working axis and in so doing can drill the drill bit 5 along the working axis into a substrate.
[0076] The drill 1 has an electric drive unit 100 in FIG. 1. The electric drive unit 100 comprises the electric motor 7 and an actuating circuit 4 for actuating the electric motor 7. The electric drive unit 100 is coupled via an electrical line arrangement 13 to a connection terminal 15 which can be coupled to a power grid by means of a plug 17. As an alternative, the drill 1 can also be supplied with power via a rechargeable battery. The drive train includes, for example, a drive shaft and a transmission between the electric motor 7 and the drive shaft. The transmission can adapt, for example, a rotation speed n(t) (see FIG. 6) of the electric motor 7 to a desired rotation speed of the drill bit 5.
[0077] FIG. 2A shows a schematic view of a first specific embodiment of a circuit topology of an electric drive unit 100 which can be used, for example, in the electric handheld power tool 1 according to FIG. 1.
[0078] The electric drive unit 100 of FIG. 2A has an electric motor 7 which comprises a stator winding 12 and a rotor winding 14. The electric drive unit 100 further has an actuating circuit 4 for actuating the electric motor 7. Furthermore, the electric drive unit 100 has a connection unit 6, 8 for coupling an energy source 2 for driving the electric motor 7. In FIG. 2A, the energy source 2 is in the form of an AC voltage source with a rectifier 19 by way of an example. It is likewise possible, in particular, for the energy source 2 to be in the form of a DC voltage source or in the form of a pulsating DC voltage source.
[0079] Furthermore, in FIG. 2A, the stator winding 12 is connected via a first node 10 to a stator-side first half-bridge which comprises a first semiconductor component T1 and a second semiconductor component T2. In addition, the stator winding 12 is connected via a second node 16 to the rotor winding 14. The rotor winding 14 is connected to a third node 18 which is connected via a conductive component T4 to a second connection 8 of the connection unit 6, 8. The energy source 2 has, in particular, a first pole, preferably a positive pole, which is connected to a first connection 6 of the connection unit 6, 8. The energy source 2 further comprises a second pole, in particular a negative pole, which is connected to the second connection 8 of the connection unit 6, 8. The actuating circuit 4 comprises a third semiconductor component T3 which is connected via the second node 16 to the rotor winding 14 and the stator winding 12 and which is connected via a fourth node 20 directly to the second connection 8 of the connection unit 6, 8. In addition, the first semiconductor component T1 and the third semiconductor component T3 have a respective freewheeling diode T1D, T3D connected in parallel. In FIG. 2A, the second semiconductor component T2 is in the form of a diode. An anode connection of the diode is connected to the second connection 8 of the connection unit 6, 8. The diode is therefore arranged in particular in the reverse direction with respect to a supply current of the energy source 2. Furthermore, in FIG. 2A, the first semiconductor component T1 and the third semiconductor component T3 are each in the form of an IGBT by way of example.
[0080] FIG. 2B shows a schematic current flow diagram of a supply current which is generated in the energy source 2 during motor operation of an electric motor 7 within the circuit topology of the electric drive unit 100 according to FIG. 2A. During motor operation (drive situation), the conductive component T4 is permanently in a conductive state and the third semiconductor component T3 is permanently in a non-conductive state, so that the stator winding 12 is connected in series with the rotor winding 14. The electric motor 7 is operated as a series-wound machine here. The level of the supply current through the stator winding 12 and the rotor winding 14 and thus also the current rotation speed n(t) (see FIG. 6) of the electric motor 7 are regulated in particular by moving the first semiconductor component T1 alternately to a conductive state and to a non-conductive state.
[0081] In FIG. 2B, when the electric motor 7 is being driven, the supply current flows, as shown in FIG. 2B by the arrows A, from the energy source 2 via a first connection 6 of the connection unit 6, 8 and via a fifth node 22 through the first semiconductor component T1, from the first semiconductor component T1 via a first node 10 through the stator winding 12, from the stator winding 12 via a second node 16 through the rotor winding 14 to a third node 18, from the third node 18 through the conductive component T4 via a fourth node 20 and via a second connection 8 of the connection unit 6, 8 back to the energy source 2.
[0082] FIG. 2C shows a schematic current flow diagram during braking operation of an electric motor 7 within the circuit topology of the electric drive unit 100 according to FIG. 2A. During braking operation, the respective semiconductor components are actuated as follows:
[0083] In a first step, the first semiconductor component T1 is moved to a non-conductive state in order to switch the electric motor 7 from motor operation to braking operation. The supply current flow is interrupted by moving the first semiconductor component T1 to a non-conductive state. In a second step, the third semiconductor component T3 is moved to a conductive state in order to connect the rotor winding 14 in parallel with the stator winding 12. In a third step, the first semiconductor component T1 is moved to a conductive state in order to provide a magnetic flux, so that a voltage is induced at the rotor winding 14 in the opposite direction compared to a voltage applied to the rotor winding 14 during motor operation of the electric motor 7. In a fourth step, the first semiconductor component T1 is moved to a non-conductive state as a function of a predetermined threshold value I.sub.L (see FIG. 6) for a rotor current I.sub.R(t) (see FIG. 6) through the rotor winding 14 in order to limit the rotor current I.sub.R(t). The rotor current I.sub.R(t) is preferably limited to a predetermined threshold value. For example, a current measuring unit RCMU is provided for this purpose, which is designed in order to monitor the rotor current I.sub.R(t). In a fifth step, the first semiconductor component T1 is alternately moved to a conductive state and to a non-conductive state in order to regulate a stator current Is(t) (see FIG. 6) through the stator winding 12 as a function of a current rotation speed n(t) (see FIG. 6) of the electric motor 7. The stator current Is(t) is preferably regulated to a rotation speed-dependent value. For example, a further current measuring unit SCMU is provided for this purpose, which is designed in order to monitor the stator current I.sub.R(t). When the rotation speed n(t) of the electric motor 7 has reached a predetermined threshold value, the electric motor 7 is preferably completely disconnected from the energy source 2. This concludes the braking process.
[0084] During braking operation, the third semiconductor component T3 in particular is permanently in a conductive state. As a result, the stator winding 12 and the rotor winding 14 are no longer connected in series. The electric motor 7 is therefore operated as a shunt-wound machine and no longer as a series-wound machine (see FIG. 2B). The voltage induced at the rotor winding 14, in particular during braking operation, is preferably caused by a rotor current I.sub.R(t) induced according to Lenz's law in the rotor winding 14. Since this flow of current is directed in such a way that the magnetic field caused by it counteracts its cause, a braking torque is produced, which counteracts the rotation of the rotor. Thus, the electric motor 7 is braked.
[0085] During braking operation, a supply current flows, as shown by the arrows A in FIG. 2C, from the energy source 2 via a first connection 6 of the connection unit 6, 8 and via a fifth node 22 through the first semiconductor component T1, from the first semiconductor component T1 via a first node 10 through the stator winding 12, from the stator winding 12 via a second node 16 through the third semiconductor component T3, from the third semiconductor component T3 via a fourth node 20 and via a second connection 8 of the connection unit 6, 8 back to the energy source 2. At the same time, an induced current flows in the rotor winding 14, which induced current is shown by the arrows B in FIG. 2C. The induced current is directed opposite to the supply current. This oppositely directed current flows from the second node 16 through the third semiconductor component T3 to a fourth node 20, from the fourth node 20 through the conductive component T4 to a third node 18, and from the third node 18 through the rotor winding 14 back to the second node 16.
[0086] FIG. 3A shows a schematic view of a second embodiment of a circuit topology of an electric drive unit 100 which can be used, for example, in the electric handheld power tool 1 according to FIG. 1.
[0087] The electric drive unit 100 of FIG. 3A has a similar structure to the electric drive unit 100 of FIG. 2A. Only the differences from the electric drive unit 100 of FIG. 2A are explained below. In addition to FIG. 2A, the electric drive unit 100 of FIG. 3A has a fifth semiconductor component T5. By way of example, said fifth semiconductor component is in the form of an IGBT with a freewheeling diode T5D connected in parallel with it. The fifth semiconductor component T5 is connected via a third node 18 to the rotor winding 14 and is connected via a fifth node 22 directly to a first connection 6 of the connection unit 6, 8. Furthermore, the conductive component T4 in FIG. 3A is in the form of a fourth semiconductor component T4 and likewise, by way of example, in the form of an IGBT with a freewheeling diode T4D connected in parallel with it. The second semiconductor component T2 in FIG. 3 is also in the form of an IGBT with a freewheeling diode T2D connected in parallel with it.
[0088] FIG. 3B shows a schematic current flow diagram of a supply current during motor operation of an electric motor 7 within the circuit topology of the electric drive unit 100 according to FIG. 3A. The feed current flow during motor operation in FIG. 3B is identical to the feed current flow during motor operation in FIG. 2B, for which reason an explanation is omitted here. It should be noted that the semiconductor component T4 is permanently in a conductive state in this case. Furthermore, the second semiconductor component T2 and the fifth semiconductor component T5 are permanently in a non-conductive state during motor operation.
[0089] FIG. 3C shows a schematic current flow diagram during braking operation of an electric motor 7 within the circuit topology of the electric drive unit 100 according to FIG. 3A. During braking operation, the respective semiconductor components are actuated as follows:
[0090] In a first step, the fourth semiconductor component T4 is moved to a non-conductive state in order to switch the electric motor 7 from motor operation to braking operation. In a second step, the third semiconductor component T3 and the fifth semiconductor component T5 are moved to a conductive state in order to reverse the polarity of an input voltage applied to the rotor winding 14 compared to motor operation. In a third step, the fourth semiconductor component T4 and the fifth semiconductor component T5 are moved as a function of a predetermined threshold value I.sub.L (see FIG. 6) for a rotor current I.sub.R(t) (see FIG. 6) through the rotor winding 14 alternately in synchronism with opposite senses to a conductive state and to a non-conductive state in order to limit the rotor current I.sub.R(t). The rotor current I.sub.R(t) is preferably limited to a predetermined threshold value. For example, a current measuring unit (not shown) is provided for this purpose, which is designed in order to monitor the rotor current I.sub.R(t). The fourth semiconductor component T4 and the fifth semiconductor component T5 form, in particular, a rotor-side second half-bridge. In a fourth step, the first semiconductor component T1 is alternately moved to a conductive state and to a non-conductive state in order to regulate a stator current Is(t) (see FIG. 6) through the stator winding 12 as a function of a current rotation speed n(t) (see FIG. 6) of the electric motor 7. The stator current Is(t) is preferably regulated to a rotation speed-dependent value. For example, a further current measuring unit (not shown) is provided for this purpose, which is designed in order to monitor the stator current I.sub.R(t). When the rotation speed n(t) of the electric motor 7 has reached a predetermined threshold value, the electric motor 7 is preferably completely disconnected from the energy source 2. This concludes the braking process.
[0091] During braking operation, the third semiconductor component T3 in particular is permanently in a conductive state. As a result, the stator winding 12 and the rotor winding 14 are no longer connected in series. The electric motor 7 is therefore operated as a shunt-wound machine and no longer as a series-wound machine (see FIG. 3B). The stator current Is(t) through the stator winding 12 (as in the drive situation) is regulated in particular by the stator-side first half-bridge comprising the first semiconductor component T1 and the second semiconductor component T2. The rotor current I.sub.R(t) through the rotor winding 14 is regulated by the rotor-side second half-bridge comprising the fourth semiconductor component T4 and the fifth semiconductor component T5. A voltage induced at the rotor winding 14 is preferably caused by a rotor current I.sub.R(t) induced according to Lenz's law during braking operation in the rotor winding 14. The induced rotor current I.sub.R(t) in the rotor winding 14 is caused in particular by the polarity reversal (see above, second step) of the input voltage at the rotor winding 14. Since this flow of current is directed in such a way that the magnetic field caused by it counteracts its cause, a braking torque is produced, which counteracts the rotation of the rotor. Thus, the electric motor 7 is braked.
[0092] During braking operation of the electric motor 7, a supply current flows, as shown by the arrows A in FIG. 3C, from the energy source 2 via a first connection 6 of the connection unit 6, 8 and via a fifth node 22 through the first semiconductor component T1, from the first semiconductor component T1 via a first node 10 through the stator winding 12, from the stator winding 12 via a second node 16 through the third semiconductor component T3, from the third semiconductor component T3 via a fourth node 20 and via a second connection 8 of the connection unit 6, 8 back to the energy source 2. In addition, the feed current flows from the energy source 2 via the first connection 6 of the connection unit 6, 8 via the fifth node 22 through the fifth semiconductor component T5 to a third node 18. Due to the polarity reversal of the input voltage (see above, second step) at the rotor winding 14, the supply current now flows through the rotor winding in the opposite direction (compared to motor operation). At the same time, a current is induced in the rotor winding 14, which current flows in the same direction, so that the two currents are added up in terms of absolute value. As shown by arrow B in FIG. 3C, the induced current flows from the third node 18 through the rotor winding 14 to the second node 16.
[0093] The following applies in particular to FIGS. 3A-3C: if, for example, the supply current through the stator-side first half-bridge becomes too high, the first semiconductor component T1 is moved to a non-conductive state and the second semiconductor component T2 is moved to a conductive state, so that the supply current can decay across the latter. If, on the other hand, in particular the current through the rotor-side second half-bridge, which current is composed in particular of the supply current and the induced current, becomes too high, the fifth semiconductor component T5 is moved to a non-conductive state and the fourth semiconductor component T4 is moved to a conductive state, so that the current can decay across the latter.
[0094] FIG. 4 shows a schematic view of a third embodiment of a circuit topology of an electric drive unit 100.
[0095] The electric drive unit 100 of FIG. 4 has a similar structure to the electric drive unit 100 of FIG. 2A. Only the differences from the electric drive unit 100 of FIG. 2A are explained below. The actuating circuit 4 of FIG. 4 has a further semiconductor component T6. The further semiconductor component T6 is connected via the second node 16 to the rotor winding 14 and the stator winding 12 and is connected via a fifth node 22 directly to a first connection 6 of the connection unit 6, 8. The further semiconductor component T6 is, in particular, in the form of a diode in FIG. 4. A cathode connection of the diode is connected to the fifth node 22 while an anode connection of the diode is connected to the second node 16. The further semiconductor component T6 in the form of a diode is therefore arranged in particular in the reverse direction with respect to the feed current of the energy source 2. As in FIG. 2A, the second semiconductor component T2 of FIG. 4 is, in particular, in the form of a diode and is interconnected, as explained in FIG. 2A.
[0096] FIG. 5 shows a schematic view of a fourth embodiment of a circuit topology of an electric drive unit 100.
[0097] The electric drive unit 100 of FIG. 5 has a similar structure to the electric drive unit 100 of FIG. 3A. Only the differences from the electric drive unit 100 of FIG. 3A are explained below. As in FIG. 2A, the second semiconductor component T2 of FIG. 5 is, in particular, in the form of a diode and is interconnected, as explained in FIG. 2A.
[0098] FIG. 6 shows a schematic diagram of a sequence of a control method for braking an electric motor 7 (see FIGS. 1, 2A, 2B, 2C, 3A, 3B, 3C, 4, 5), for example an electric motor 7 of the electric handheld power tool 1 according to FIG. 1. The schematic diagram of FIG. 6 comprises three graphs 51, 52 and 53. A first graph 51 shows the profile of the current rotation speed n of the electric motor 7 (vertical axis) as a function of time t (horizontal axis). A second graph 52 shows the profile of the rotor current I.sub.R in the electric motor 7 (vertical axis) as a function of time t (horizontal axis). A third graph 53 shows the profile of the stator current Is in the electric motor 7 (vertical axis) as a function of time t (horizontal axis).
[0099] Initially, the electric handheld power tool 1 is in motor operation (time interval between t.sub.0 and t.sub.1). In particular, a rotor current I.sub.R(t) (see second graph 52, time interval between t.sub.0 and t.sub.1) flows through a rotor winding 14 (see FIGS. 1, 2A, 2B, 2C, 3A, 3B, 3C, 4, 5) as a function of a target rotation speed of the electric motor 7 and a stator current Is(t) (see third graph 53, time interval between t.sub.0 and t.sub.1) flows through a stator winding 12 (see FIGS. 1, 2A, 2B, 2C, 3A, 3B, 3C, 4, 5) as a function of the target rotation speed of the electric motor 7.
[0100] If, for example, the drilling tool 5 (see FIG. 1) of the electric handheld power tool 1 becomes wedged in a rebar during motor operation when working with the electric handheld power tool 1, this is detected by a sensor, such as a gyro sensor, as an operation interruption state of the electric handheld power tool 1.
[0101] The operation interruption state is detected at time t.sub.1, in the case of which the electric motor 7 is switched over from motor operation to braking operation. For this purpose, for example, a supply current flow through the stator winding 12 and/or the rotor winding 14 is interrupted. After the switching over, the system waits for the rotor current I.sub.R(t) to decay, this taking place, for example, in a few milliseconds. The rotor current I.sub.R(t) is considered to have decayed when it reaches or falls below a predetermined switching threshold value. In the present case, the predetermined switching threshold value is 0 A, which is reached at time t.sub.2 (see second graph 52).
[0102] Then, for example, the polarity of an input voltage at the rotor winding 14 is reversed. As a result, the rotor current I.sub.R(t) flows in the opposite direction (compared to the time interval between t.sub.0 and t.sub.1) and rises. The rotor current I.sub.R(t) of the rotor winding 14 is then limited as a function of a predetermined threshold value I.sub.L (see second graph 52). In particular, the rotor current is limited or regulated to a constant value or a value which is variable over time, in particular a value which is dependent on the rotation speed. In FIG. 6, the second graph 52 shows, starting from time t.sub.2, that the rotor current I.sub.R(t) rises to ?20 A after the polarity reversal (corresponds in particular to the predetermined threshold value I.sub.L) and is limited there. For example, in the embodiment shown in FIG. 3A, the limiting is carried out by means of moving a fourth semiconductor component T4 (see FIGS. 3A, 3B, 3C, 5) and a fifth semiconductor component T5 (see FIGS. 3A, 3B, 3C, 5) alternately in synchronism with opposite senses to a conductive state and to a non-conductive state as a function of the predetermined threshold value I.sub.L for the rotor current I.sub.R(t).
[0103] After the polarity of the input voltage at the rotor winding 14 has been reversed (see above), the system waits, for example, for a predetermined period of time to elapse (time interval between t.sub.2 and t.sub.3). The predetermined period of time is, in particular, up to 2 ms or up to 3 ms. It should be noted that waiting for this period of time is not absolutely necessary. During this predetermined period of time, the first semiconductor component T1 (see FIGS. 2A, 2B, 2C, 3A, 3B, 3C, 4, 5) is preferably in a non-conductive state in the embodiment of FIGS. 2A, 2B and 2C, in the embodiment of FIGS. 3A, 3B and 3C, in the embodiment of FIG. 4 and in the embodiment of FIG. 5. After the predetermined period of time has elapsed, at time t.sub.3, the stator current Is(t) through the stator winding 12 is increased as a function of the current rotation speed n(t) of the electric motor 7, in particular with a drop in the current rotation speed n(t). This occurs in the time interval between times t.sub.3 and t.sub.4 in the third graph 53 of FIG. 6. This advantageously results in an increase in the braking torque with which the rotor is braked.
[0104] In other words, for example in the first moment after the polarity reversal of the input voltage at the rotor winding 14 has been carried out, the first semiconductor component T1 remains in a non-conductive state. This results in the stator winding 12 remaining unenergized and therefore the stator current Is(t) is, because of the stator winding 12, not rising with the rotor current I.sub.R(t) which rises after the polarity reversal (see the interval between t.sub.2 and t.sub.3). After the predetermined period of time, which is up to 2 ms or up to 3 ms for example, has elapsed, the first semiconductor component T1 is moved to a conductive state. As a result, the stator winding 12 is energized and the stator current through the stator winding 12 can, for example, be increased in a controlled manner with a drop in the current rotation speed n(t) of the electric motor 7 (see the time interval between times t.sub.3 and t.sub.4 in the third graph 53 of FIG. 6). Owing to this measure, the rotor current I.sub.R(t) and the stator current Is(t) of the electric motor 7 can be set independently of one another.
LIST OF REFERENCE SIGNS
[0105] 1 Electric handheld power tool [0106] 2 Energy source [0107] 3 Tool fitting [0108] 4 Actuating circuit [0109] 5 Drilling tool [0110] 6 Connection unit [0111] 7 Electric motor [0112] 8 Connection unit [0113] 9 Handle [0114] 10 Nodes [0115] 11 Button [0116] 12 Stator winding [0117] 13 Line arrangement [0118] 14 Rotor winding [0119] 15 Connection terminal [0120] 16 Nodes [0121] 17 Plug [0122] 18 Nodes [0123] 19 Rectifier [0124] 20 Nodes [0125] 22 Nodes [0126] 51 Graph [0127] 52 Graph [0128] 53 Graph [0129] 100 Electric drive unit [0130] A Arrow [0131] B Arrow [0132] I.sub.L Threshold value [0133] I.sub.R(t) Rotor current [0134] I.sub.s(t) Stator current [0135] n(t) Rotation speed [0136] t Time [0137] t.sub.0 Time [0138] t.sub.1 Time [0139] t.sub.2 Time [0140] t.sub.3 Time [0141] t.sub.4 Time [0142] T1 Semiconductor component [0143] T1D Freewheeling diode [0144] T2 Semiconductor component [0145] T2D Freewheeling diode [0146] T3 Semiconductor component [0147] T3D Freewheeling diode [0148] T4 Conductive component [0149] T4D Freewheeling diode [0150] T5 Semiconductor component [0151] T5D Freewheeling diode [0152] T6 Semiconductor component
