POWER TOOL AND METHOD OF OPERATING A POWER TOOL

Abstract

The present invention relates to a power tool having a motor, the motor including a rotor and a stator, the stator including a first winding and a second winding, the windings being designed to allow operation of the motor of the power tool at substantially full speed but at substantially half power compared to a comparative motor, in which the stator coil is substantially fully wound with a continuous wire layer. In a further aspect, the present invention relates to a method of operating such a power tool and a method of performing charge balancing between two accumulators in the power tool. The dual-winding stator may be used in conjunction with a bridge circuit consisting of a motor inverter and a stator coil to allow charge balancing between two accumulators in the power tool.

Description

[Technical field]

[0001] The present invention relates to a power tool having a motor, the motor including a rotor and a stator, the stator including a first winding and a second winding, the windings being designed to allow operation of the motor of the power tool at substantially full speed but at substantially half power compared to a comparative motor, in which the stator coil is substantially fully wound with a continuous wire layer. In a further aspect, the present invention relates to a method of operating such a power tool and a method of performing charge balancing between two accumulators in the power tool. The dual-winding stator may be used in conjunction with a bridge circuit consisting of a motor inverter and a stator coil to allow charge balancing between two accumulators in the power tool. [Background technology]

[0002] In the prior art, power tools are known that are able to carry out different types of operations, such as hammer drills, chisels, cut or angle grinders, screwdrivers or core drills, in each of which the tool is driven by a motor. The power supply can be provided via a mains connection or by means of a battery or accumulator.

[0003] A large number of applications of such power tools are known, in which high power is required to perform the corresponding tasks. In the case of power tools in which the power source is formed by an accumulator, it may happen that the power required for the task exceeds the maximum possible output of the accumulator. To meet this challenge, such power tools are often equipped with an interface for two accumulators, so as to be able to provide the desired power with two accumulators, which may be connected in series or in parallel.

[0004] However, when using a power tool with two accumulators, the following problems may arise: if one of the accumulators is fully or partially discharged, it is not possible to provide full power to the power tool for the entire working period; if one of the accumulators is fully discharged, no further power can be drawn from it; therefore, it may be necessary to stop working with the power tool, even though there is still a charge remaining in one of the two accumulators.

[0005] In the prior art, methods are known that may enable charge balancing between electrical components in a power tool. For example, US Patent No. 5,631,534A discloses an arrangement of electronic components that allows charge balancing between batteries connected in series. If such a balancing method is implemented at the device or accumulator level, such an arrangement requires a large number of components, such as various switches, drivers, inductances and current measuring devices. Such an arrangement is complex to manufacture and prone to errors.

[0006] Additionally, a problem is known from the prior art that with known balancing methods, charge balancing can only be performed when the power tool is stopped. Summary of the Invention [Problem to be solved by the invention]

[0007] Therefore, the object of the present invention is to overcome the above-mentioned deficiencies and drawbacks of the prior art and to provide an improved power tool having at least two accumulators and a method of operating the power tool, which allows charge balancing between the accumulators. It is of particular interest of the present invention that the charge balancing is also performed in both directions. Those skilled in the art will also understand that technical solutions can be provided whereby charge balancing between the accumulators of a power tool can be performed at least during operation or even during work with the power tool. [Means for solving the problem]

[0008] This object is achieved by the subject matter of the independent claims. Advantageous embodiments of the subject matter according to the invention are set forth in the dependent claims.

[0009] In a first aspect, this object is achieved by a power tool having a motor, the motor including a rotor and a stator. The stator includes a first winding and a second winding, the windings being designed to allow operation of the motor of the power tool at a speed within the range of the comparative motor, but at substantially half the power compared to the comparative motor, the stator coil of the comparative motor being substantially fully wound with a continuous winding. One possible embodiment of such a dual-winding stator is shown in FIG. 1. Separate stator coil pairs are shown in FIG. 2.

[0010] In the proposed construction of the electric motor, the rotor is arranged inside the motor and the stator is arranged around the rotor. The stator may, for example, include three stator coil pairs, each of which may consist of a first stator coil and a second stator coil. The stator coils may in particular be arranged in a circular manner around the rotor of the motor of the power tool. In the sense of the present invention, it is preferred that the stator coils of the stator coil pairs are substantially opposite each other in the stator. Thus, the arrangement of the stator coils may, for example, be configured such that the first coil of the first coil pair is followed by the first coil of the second coil pair, then the first coil of the third coil pair, then the second coil of the first coil pair, then the second coil of the second coil pair, and then the second coil of the third coil pair.

[0011] In the context of the present invention, an odd number of stator coils may also be provided. The stator of the proposed power tool may, for example, be designed to include nine stator coils or to have nine slots. In the context of the present invention, the topology of the motor of the proposed power tool corresponds to the topology of a conventional motor, the stator coils of which are preferably, for example, "half the size" of a standard motor. Preferably, the term "half the size" means, in the context of the present invention relating to the stator coil, that the wire on which the stator coil is wound has substantially half the diameter of the wire on which the stator coil of a conventional standard motor is wound. In other words, the wire on which the stator coil of the motor of the proposed power tool is wound is half as thick as the wire on which the stator coil of a conventional comparison motor is wound. To compensate for the resulting smaller amount of metal or inductive material, in the context of the present invention, it is preferred that the stator coil of the proposed motor is double wound. For the purposes of the present invention, this means, for example, that each tooth of the stator is wound twice as much or with twice as many turns compared to a conventional standard motor.

[0012] In the sense of the present invention, the stator coils of the stator are wound identically or substantially identically in the sense that their windings comprise a first and a second wire layer, the wire layers being preferably formed in such a way that they allow operation of the motor of the power tool at a speed within the range of the speed of the comparative motor, but at substantially half the power compared to the comparative motor. Operation of the motor at half the power compared to the comparative motor is made possible in particular by the provision of two wire layers present in the stator coils and forming the first and second windings of the stator of the motor of the power tool.

[0013] In the sense of the present invention, the stator coil preferably comprises a first wire layer and a second wire layer, the first wire layer being preferably an inner wire layer and the second wire layer being preferably an outer wire layer. The wires may preferably consist of copper or a copper alloy. The bifilar winding of the stator coil of the proposed motor represents the basic idea of ​​the present invention. The two windings preferably represent two coils, electrically or galvanically insulated from one another, which together form the stator coil of the proposed power tool motor. The two windings, electrically or galvanically insulated from one another, are preferably arranged around the teeth of the stator.

[0014] In the sense of the present invention, it is preferred that the first wire layers of two stator coils arranged adjacent to each other in the stator are electrically conductively connected to each other. In other words, there is a conductive connection between the first wire layers of two adjacent stator coils. For example, the first wire layer of the stator coil of the second stator coil pair can be connected on one side to the first wire layer of the stator coil of the first stator coil pair, and this first wire layer of the stator coil of the second stator coil pair is connected on the other side to the first wire layer of the stator coil of the third stator coil pair. In addition, there can be an electrical connection between each of the first wire layers of the stator.

[0015] In the sense of the present invention, it is preferred that the stator is wound twice in a substantially identical manner. In the sense of the present invention, the provision of a stator with two windings is preferably referred to as a "double-wound stator". The "double winding" is in particular achieved by a first winding and a second winding of the stator, each of which comprises a wire layer. The winding with the first wire layer forms the first winding of the stator coil, and the winding with the second wire layer forms the second winding of the stator coil. Preferably, each of the windings is designed such that the winding allows the power tool motor to operate at full speed and at half power. In this way, the double-wound stator acts like two separate motors, but arranged or wound on the stator. In the sense of the present invention, it is preferred that the partial power of the two windings substantially adds up to the total power of the comparative motor, and that the stator coil of the comparative motor is substantially completely wound with a continuous wire layer. In other words, this last subclause preferably means that in connection with the present invention relating to a comparative motor, full or half power or speed is specified, the comparative motor envisaged being characterised by being substantially completely wound with a continuous wire layer.

[0016] In the sense of the present invention, it is preferred that the first winding of the stator coil is energized by a first inverter, while the second winding of the stator coil is energized by a second inverter, so that the sum of the two windings allows the motor of the power tool to provide a power within the range of the comparative motor. In other words, when the windings of the stator are each energized by an inverter, it is possible to approach substantially the full power of the comparative motor. Preferably, each winding contributes substantially half of the total output of the comparative motor. In other words, the contribution of each of the two winding layers is about 50% of the power of the comparative motor.

[0017] The proposed power tool can preferably also have more than two inverters, for example the power tool can have 3, 4, ... or n inverters, in which case the contribution to the motor power of the proposed power tool is 33%, 25% or 1 / n·100%.

[0018] In the sense of the present invention, the comparative motor does not include two windings or two layers of wire, but preferably includes only one winding and one layer of wire forming the winding. In the sense of the present invention, the stator preferably includes three stator coil pairs. The motor of the power tool preferably has at least two motor phases.

[0019] In the sense of the present invention, the motor is preferably a brushless motor. In the sense of the present invention, it is preferably an electronically commutated motor, which is also preferably called an "EC motor" in the sense of the present invention. The rotor of the motor of the proposed power tool may have an armature field, for example, via brushes. For example, in the sense of the present invention, n individual accumulator electronics of a known power tool having only one accumulator can be connected to each other via a brushless motor having an n-fold-wound stator according to the present invention. In an exemplary embodiment of the present invention, two individual accumulator electronics can be connected to each other via an EC motor having a double-winding stator in order to double the power of the motor. As a result, a new cost-optimized power tool electronics can be obtained, since such individual accumulator electronics are available at low cost due to their large volume. In the sense of the present invention, it is preferred that a subsystem consisting of a sub-motor, a respective one accumulator, an inverter and electronics share the magnetic flux in the sheet metal of the stator of the entire motor. The power tool may preferably include n subsystems, the subsystems including accumulators, electronics and windings in the motor. As a result, a power tool having n subsystems will include n accumulators, n electronics and n windings in the motor. In other words, the number of subsystems, accumulators, electronics and windings in the motor of a power tool correspond to the subsystems or their components that share the magnetic flux in the stator iron.

[0020] In a second aspect, the present invention relates to a method for operating a power tool, in which a first winding of a stator coil is energized by a first inverter, while a second winding of the stator coil is energized by a second inverter, whereby a power in the range of a comparative motor is provided to the motor of the power tool. The definitions, technical effects and advantages explained for the proposed power tool apply equally to the proposed method for operating. In the sense of the present invention, it is particularly preferred that the total power of the motor can be provided by energizing the windings via two inverters, which total power preferably corresponds to the total power of the comparative motor. In addition to the first and second inverters, further inverters, for example three or four inverters, can be provided.

[0021] In one embodiment of the present invention, two stand-alone or independent inverters are connected in series with each other via the motor of the power tool. The inverter is preferably arranged between the motor and one of the two separate accumulators in each case. In other words, in this preferred embodiment of the present invention, the first accumulator, the first inverter, the motor, the second inverter and the second accumulator may be connected in series with each other. In particular, when the accumulators have different voltage levels or charge states, charge balancing is provided in the context of the present invention. Usually, the accumulator with a lower charge level also has a lower voltage level. As a result, charge or electrical balancing current may flow from a fully charged accumulator with a higher voltage level in the direction of the other accumulator with, for example, a lower charge state and a lower voltage level.

[0022] In the sense of the present invention, the power tool preferably comprises a first accumulator and a second accumulator. More than two accumulators can also be provided, and in this specification, two accumulators are usually assumed for clarity. The double-winding stator proposed in the context of the present invention allows charge balancing between the accumulators of the power tool to be carried out in a particularly simple manner. In particular, it is possible for charge balancing to take place in both directions. In the sense of the present invention, it is preferred to increase the charge of the empty accumulator to the charge level of the fully charged accumulator. This can be done, for example, by asymmetrically withdrawing charge from the accumulator. Preferably, in the sense of the present invention, an asymmetric withdrawal of charge means, for example, that the fully charged accumulator has a share of 70% of the total power provided, while the empty accumulator has a share of 30% of the total power. During this process, both accumulators continue to empty, but to different extents. As a result, after a certain period of time, a uniform charge level of at least two accumulators can be achieved.

[0023] In the sense of the present invention, it may also be preferred that one of the accumulators is charged by one of the part motors, i.e. the motor whose stator coil is formed by one of the two windings, and operates against the other part motor. In other words, in this exemplary embodiment of the present invention, one of the part motors is slightly braked, since one inverter side operates against the other inverter side. This preferably means that the first part motor is in generator mode, so that its accumulator can be charged.

[0024] In the sense of the present invention, it is preferred that the charge balancing between the first and second accumulators of the power tool can be performed in both directions, in particular when the power tool is at a standstill.

[0025] The two-sidedness of the charge exchange or its bidirectionality is achieved in particular by the two windings of the stator forming a complete H-bridge or bridge circuit together with the inverter assigned to them. In the context of the present invention, the fact is exploited that this bridge circuit behaves like a bidirectional direct current / direct current converter (DC-DC converter), in particular a step-down / step-up DC-DC converter, and that such a DC-DC converter is able to "pump", i.e. transfer, current or electrical energy in both directions. In the sense of the present invention, the inductance required for charge balancing is preferably provided by the stator coil of the motor of the power tool. As in a transformer, electrical energy is transferred from one winding to the other. In this way, charge differences or different charge states of the accumulators of the power tool can be balanced. In particular by using the motor of the power tool as a direct current / direct current converter (DC-DC converter), the charge balancing described may be possible when the power tool is at a standstill.

[0026] In the sense of the present invention, the first accumulator has a first charge state and the second accumulator has a second charge state, and when the power tool is stopped, the charge states can be balanced by the above-mentioned charge balancing means, in particular by means of a bridge circuit. For example, if the first accumulator has a first charge state of 75% and the second accumulator has a second charge state of 25%, the present invention allows a charge balancing to be carried out such that at the end of the operation both accumulators have a charge state of about 50%. In particular, the charge balancing carried out in this way allows a longer and more effective use of the power tool, since the charge is better distributed in the accumulators and can thus be utilized. In particular, it avoids a situation in which the work with the power tool has to be terminated, even though one of the accumulators is still fully charged.

[0027] In the sense of the present invention, each accumulator is preferably assigned an inverter, and charge balancing between an accumulator with a higher charge state and an accumulator with a lower charge state is preferably performed in that the accumulator with the lower charge state is transferred from the operating mode to the generator mode by the inverter assigned to it, so that the capacity of the accumulator with the higher charge state can be advantageously utilized, resulting in charge balancing. The transfer from the operating mode to the generator mode of the accumulator with the lower charge state can be performed by applying a small braking torque, in particular to the inverter of the accumulator with the lower charge state. This method of performing charge balancing between accumulators of a power tool can advantageously also be performed during operation, i.e. while working with the power tool, for which no technically satisfactory solution existed in the prior art.

[0028] 3 shows a preferred embodiment of the present invention, for example, a first winding is connected to a first accumulator through a first inverter, while a second winding is connected to a second accumulator through a second inverter. The circuit shown in FIG. 3 can advantageously allow charge balancing both during operation and when the power tool is stopped.

[0029] The advantage of the proposed invention is that the two inverters can be designed for a simple accumulator voltage, which is especially advantageous when working with small voltages.

[0030] Another important advantage of the present invention is that if one side of the power tool fails or an accumulator becomes depleted, it can continue to work with half the torque compared to an intact power tool with two at least partially charged accumulators.

[0031] In a third aspect, the present invention relates to a method for performing charge balancing between two accumulators in a power tool, the power tool comprising a first inverter for energizing a first stator coil and a second inverter for energizing a second stator coil, the inverter forming a bridge circuit with the stator coil, which is set up to perform charge balancing between the accumulators of the power tool. The above definitions, technical effects and advantages apply equally to the proposed balancing or charge balancing method. In the sense of the present invention, the stator coil forms a stator with a first winding and a second winding, and the charge balancing is preferably achieved by transferring electrical energy from the first winding to the second winding of the stator or vice versa.

[0032] Further advantages will become apparent from the following description of the figures. Exemplary embodiments of the invention are illustrated in the figures. The figures, description and claims include a number of feature combinations. Those skilled in the art will also consider features individually and combine them as appropriate to generate further useful combinations.

[0033] In the figures, identical and similar components are designated with the same reference numerals. [Brief description of the drawings]

[0034] [Figure 1] 1 illustrates an exemplary embodiment of a dual-winding stator in accordance with a preferred embodiment of the present invention. [Diagram 2] 3 shows a possible embodiment of a stator having three stator coil pairs. [Diagram 3] 1 shows an example circuit of a dual-winding stator with two accumulators. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0035] FIG. 1 shows an exemplary embodiment of the proposed motor 12 of a power tool 10 (the power tool 10 is not shown). In FIG. 1, the rotor 14 and the stator 16 of the motor 12 of the power tool 10, which is preferably a brushless electric motor, can be seen. The stator 16 comprises a series of stator coils 20, 30, which can be arranged, for example, in pairs or form a stator coil pair 18. In each case, one group of stator coils can preferably be called the first stator coil 20 and the other group of stator coils can preferably be called the second stator coil 30. The stator 16 of the motor 12 of the power tool 10 comprises a first winding 70 and a second winding 80, the windings 70, 80 comprising wire layers 22, 32, respectively. In the sense of the present invention, the first winding 70 preferably comprises the first wire layer 22 and the second winding 80 preferably comprises the second wire layer 32. Each stator coil 20, 30 preferably includes a first wire layer 22 and a second wire layer 32, with the first wire layer 22 of the stator coils 20, 30 forming a first winding 70 of the stator 16, while the second wire layer 32 of the stator coils 20, 30 forming a second winding 80 of the stator 16. Each of the two windings 70, 80 allows the power tool 10 to be operated at full speed but with only half the power compared to the operation of the comparative motor, which corresponds substantially to the proposed motor, but the stator of the comparative motor has only one winding, i.e. one wire layer. Preferably, each of the two windings 70, 80 of the proposed dual-winding stator 16 is energized by an inverter 24, 34, with the first winding 70 of the stator 16 of the motor 12 of the power tool 10 being energized by the first inverter 24, while the second winding 80 of the stator 16 of the motor 12 of the power tool 10 being energized by the second inverter 34. As a result, advantageously, the total power of the motor 12 can be approached, with each winding layer 70, 80 contributing approximately 50% to the power of the motor 12.

[0036] In addition, FIG. 1 shows electrical lines 60 that may be present between the first wire layers 22 of adjacent stator coils 20, 30 in each case. The electrical lines may be arranged on the inside of the stator 16 and connect the first wire layers 22 in the stator coils 20, 30 in each case to each other. The rotor 14 of the motor 12 of the power tool 10 is arranged inside the motor 12 of the power tool 10, so that the inside of the stator 16 preferably faces the rotor 14 of the motor 12 of the power tool 10. The interconnection shown in FIG. 1 is only one exemplary embodiment of the invention among many other possibilities. The lines coming from the windings 70, 80 go one by one to each of the inverters 24, 34. The motor 12 of the power tool 10 can also be an external rotor motor.

[0037] Figure 2 shows a possible embodiment of the stator 16 of the motor 12 of the power tool 10 having three stator coil pairs 18. Each stator coil pair 18 preferably includes a first stator coil 22 and a second stator coil 32 that together form the stator coil pair 18 and are preferably located opposite each other in the stator 16 of the motor 12 of the power tool 10. The three stator coil pairs 18 are designated as stator coil pairs 18a, 18b and 18c in Figure 2 and sub-figures 2a, 2b and 2c.

[0038] FIG. 3 shows a circuit diagram of a preferred embodiment of the proposed double-winding stator 16 with two inverters 24, 34. The stator 16 of the motor 12 of the power tool 10 is shown in the center of FIG. 3. The letters A, B, C represent the three stator coil pairs 18a, 18b, 18c, while the numbers 1, 2 indicate either the first stator coil 22 or the second stator coil 32 of the stator coil pair 18. In other words, the stator coils A1, B1, C1 form the first stator coil 22 of the stator coil pair 18, while the stator coils A2, B2, C2 form the second stator coil 32 of the stator coil pair 18. The first stator coils A1, B1, C1 are preferably connected to the first inverter 24, while the second stator coils A2, B2, C2 are preferably connected to the second inverter 34. In the sense of the present invention, it is preferred that the inverter 24, 34 and the stator coils 20, 30 form a bridge circuit 90 or an H-bridge, via which bridge circuit 90 a charge balancing between the accumulators 40, 50 of the power tool 10 may be possible. The accumulators 40, 50 are not shown. This is possible in particular because the motor 12 of the power tool 10 is used as a DC / DC converter. This makes it possible to transfer electrical energy from the first winding 70 of the stator 16 to the second winding 80 of the stator 16 or vice versa. By being able to transfer electrical energy from one winding 70 of the stator 16 to the other winding 80, energy can also be transferred from one accumulator 40 to the other accumulator 50, so that the charge differences can be balanced. This charge balancing method can be carried out in particular when the power tool 10 is at a standstill. Its particular advantage is that electrical energy can be transferred in both directions.

[0039] Due to the proposed invention of the double-wound stator 16, charge balancing can also be performed during operation of the power tool 10. For this purpose, an inverter (e.g. 24) connected to the accumulator to be charged can be switched from motor operation to generator operation. As a result, the capacity of a fully charged accumulator (e.g. 50) can be used to recharge the accumulator with a lower charge state (e.g. 40). This method can be made possible by applying a particularly small braking torque. This braking action can be used to generate electrical energy, which can then preferably be used to charge the accumulator with the lower charge state. In particular, the generated electrical energy can be used to charge its capacity. This double feed means that the two motors can in effect be controlled independently of each other, one part motor can act on the other part motor to brake it. As a result, one part motor can advantageously go into generator mode and charge its accumulator. In the sense of the invention, in FIG. 3, each of the two coil triangles preferably represents a part motor. In other words, one of the coil triangles represents the first part motor 20 , 24 , 70 of the proposed power tool 10 , and the other coil triangle represents the second part motor 30 , 34 , 80 of the proposed power tool 10 . [Explanation of symbols]

[0040] 10 Power tools 12 Power tool motors 14 Rotor 16 Stator 18 Stator coil pair 20 First stator coil 22 1st wire layer 24 First inverter 30 Second stator coil 32 Second Wire Layer 34 Second inverter 40 First Accumulator 50 Second Accumulator 60 Electric Line 70 First Winding 80 Second Winding 90 H-bridge or bridge circuit

Claims

1. A power tool (10) having a motor (12), the motor including a rotor (14) and a stator (16), the stator (16) including a first winding (70) and a second winding (80), The first winding (70) includes a first layer of wires (22) energized by a first inverter (24) from a first accumulator (40); The second winding (80) includes a second layer of wires (32) energized by a second inverter (34) from a second accumulator (50); The first wire layer (22) and the second wire layer (32) form a double winding; the inverter (24 or 34) assigned to the accumulator (40 or 50) having a lower charge state among the first accumulator (40) and the second accumulator (50) is transitioned from an operating mode to a generator mode; A power tool (10).

2. 2. The power tool (10) of claim 1, wherein the stator (16) includes several stator coil pairs (18), each stator coil pair (18) including a first stator coil (20) and a second stator coil (30).

3. A power tool (10) as described in claim 2, characterized in that the stator coils (20, 30) face each other within the stator (16).

4. A power tool (10) according to claim 2 or 3, characterized in that the stator (16) includes three stator coil pairs (18).

5. A power tool (10) as described in claim 2, characterized in that the first inverter (24) and the second inverter (34) form a bridge circuit (90) with the stator coil (20, 30).

6. The power tool (10) according to claim 1 or 2, characterized in that the motor (12) is a brushless motor.

7. A method of operating a power tool (10) according to claim 1 or 2, comprising: The method of claim 1, wherein charge balancing between the first accumulator (40) and the second accumulator (50) can be performed in both directions.

8. A method for performing charge balancing between two accumulators (40, 50) in a power tool (10), comprising the steps of: the inverter (24, 34) forms a bridge circuit (90) with the stator coils (20, 30) that is set up to perform charge balancing between the accumulators (40, 50) of the power tool (10); The power tool (10) has a motor (12), the motor including a rotor (14) and a stator (16), the stator (16) including a first winding (70) and a second winding (80); The first winding (70) includes a first layer of wires (22) energized by a first inverter (24) from a first accumulator (40); The second winding (80) includes a second layer of wires (32) energized by a second inverter (34) from a second accumulator (50); The first wire layer (22) and the second wire layer (32) form a double winding; the inverter (24 or 34) assigned to the accumulator (40 or 50) having a lower state of charge among the first accumulator (40) and the second accumulator (50) is transitioned from an operating mode to a generator mode.

9. The method described in claim 8, characterized in that the charge balancing is achieved by transferring electrical energy from the first winding (70) of the stator (16) to the second winding (80) or vice versa.

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