Method for rotational speed spreading in an electric device, and electric device

Abstract

The present invention relates to a method of providing a wide range of rotational speeds in an electrical device having a motor. In the proposed method, the electrical device is operated in a first rotational speed range, wherein an electric current I flows through the motor. The electric current I can generate a magnetic field B. The motor of the electrical device has a first magnetic pole with a first polarity, wherein a second magnetic pole with a second polarity is generated in close proximity to the first magnetic pole as part of the method. The first polarity and the second polarity are the same. The generation and arrangement of the second magnetic pole results in a weakening of the magnetic field B, allowing the electrical device to be operated in a second rotational speed range. A second aspect of the invention relates to an electrical device for carrying out the method. The electrical device can be a machine tool or a suction device such as a vacuum cleaner.

Description

[0001] Method for speed variation in an electrical device and electrical device

[0002] The present invention relates to a method for providing a wide range of speeds in an electrical device having a motor. In the proposed method, the electrical device is operated in a first speed range, wherein an electrical current I flows through the motor. The electrical current I can generate a magnetic field B and have a flux current component l_d and a torque-generating component l_q. The motor of the electrical device has a first magnetic pole with a first polarity, wherein, within the scope of the method, a second magnetic pole with a second polarity is generated in spatial proximity to the first magnetic pole. The first polarity and the second polarity are the same. The generation and arrangement of the second magnetic pole result in a weakening of the magnetic field B, whereby the electrical device can be operated in a second speed range.The second speed range can, on average, be associated with higher speeds than the first speed range. It is particularly preferred within the meaning of the invention that the second speed range covers a wider range of speeds than the first speed range. In a second aspect, the invention relates to an electrical device for carrying out the method. The electrical device can be a power tool or a suction device, such as a vacuum cleaner.

[0003] Background of the invention:

[0004] To perform various tasks in everyday life, electrical devices should not only be able to operate at a constant motor speed, but there is often a desire for an electrical device to cover a certain, task-dependent speed range. If this speed range becomes very large, it may happen that an electrical device is not able to cover the entire desired speed range. To remedy this situation and also offer wider speed ranges, transmissions have been proposed in the prior art. Individual gear stages or "gears" can be provided that are associated with different speed ranges.

[0005] However, the inclusion of a gearbox in an electrical device can have the disadvantage that the design and manufacture of the electrical device become more complex and time-consuming, especially when a gearbox with a large number of gears or gear stages is planned. Furthermore, a gearbox can require a large amount of space or volume, making the electrical device very large and unwieldy.

[0006] There is therefore a need for alternative solutions to enable a wide speed range in electrical devices without requiring the use of a gearbox or a gearbox with a large number of gear stages or gears. Furthermore, experts would welcome an expansion of the possible speeds of an electrical device to high speeds, for example, in the range of 10,000 to 20,000 revolutions per minute. Such an expansion of the possible speeds toward particularly high speeds could provide new or enhanced functionalities for electrical devices, or enable new applications or tasks to be performed.

[0007] The object underlying the present invention is to overcome the above-described deficiencies and disadvantages of the prior art and to provide a method by which a wide range of speeds can be enabled in an electrical device. In particular, a gearbox should be dispensed with in the electrical device or, if a gearbox is present, the number of gear stages should be reduced. Furthermore, it would be desirable if the motor of the electrical device to be provided could also reach higher speeds, for example, in a range of 10,000 to 20,000 revolutions per minute.

[0008] The problem is solved by the subject matter of the independent claims. Advantageous embodiments of the subject matter of the independent claims can be found in the dependent claims.

[0009] Description of the invention:

[0010] According to the invention, a method is provided for providing a wide range of speeds in an electrical device having a motor. In the proposed method, the electrical device is operated in a first speed range, wherein an electrical current I flows through the motor. The electrical current I can generate a magnetic field B. The motor of the electrical device has a first magnetic pole with a first polarity, wherein, within the scope of the method, a second magnetic pole with a second polarity is generated in spatial proximity to the first magnetic pole. The first polarity and the second polarity are the same, e.g., both magnetic poles are south poles or both magnetic poles are north poles. The generation and arrangement of the second magnetic pole leads to a weakening of the magnetic field B, as a result of which the electrical device can be operated in a second speed range.It is preferred in the sense of the invention that the first speed range can be extended by the invention.

[0011] It may also be preferred in the sense of the invention that the second speed range covers a wider range of speeds than the first speed range.

[0012] The proposed method is characterized in particular by the following method steps: a) operation of the electrical device in a first speed range, wherein the motor is flowed through by an electrical current I, wherein the electrical current I can generate a magnetic field B, b) generation of a second magnetic pole with a second polarity in spatial proximity to a first magnetic pole with a first polarity in the motor of the electrical device, wherein the first polarity and the second polarity are the same, c) weakening of the magnetic field B by the second magnetic pole, whereby the electrical device can be operated in a second speed range.

[0013] The electrical device can be, for example, a machine tool or a suction device, such as a vacuum cleaner or a dust extractor. The machine tool can be a drill, rotary hammer, chisel hammer, cut-off or angle grinder, or core drilling machine, but is not limited to these. Machine tools usually have a tool with which a surface or workpiece can be processed. Typical tools are drill bits, cutting discs, core bits, or the like. If the electrical device is a suction device, a turbine of the suction device can be considered a tool of the suction device. The turbine of the suction device is preferably designed to generate a vacuum in the suction device in order to suck in dust or particles that arise, for example, when working with a machine tool.According to the invention, it is preferred that a tool of the machine tool or a turbine of the suction device is driven by the motor of the electrical device generating a rotary movement by an electric current I flowing through the motor. The electric current can have a flux current component l_d and a torque-generating component l_q. The motor of the electrical device can preferably be designed to generate a rotary movement so that an electric current I flows through the motor. The motor of the electrical device has a first magnetic pole with a first polarity, wherein, within the scope of the method, a second magnetic pole with a second polarity is generated in spatial proximity to the first magnetic pole.The motor of the electrical device can comprise a rotating rotor and a stator, wherein the rotor of the motor, in particular, can have a north pole ("rotor north pole"). This rotor north pole can represent the first magnetic pole within the meaning of the invention, wherein the first polarity of this first magnetic pole can be a north pole. If the first magnetic pole is a north pole, the second magnetic pole is also a north pole, which preferably arises directly in front of the magnetic north pole of the rotor, coming from the coils of the stator. Because the polarities of the magnetic poles are identical, repulsion occurs between the poles, and the stator north pole pushes away part of the rotor north pole. Within the meaning of the invention, this preferably means that the stator pole weakens the field of the rotor pole. This preferably results in a flux or field weakening, wherein, in particular, an opposing field is built up against the rotor pole.It is preferred in the sense of the invention that by this flux or field weakening not only the north pole but also the south pole can be weakened in an analogous manner.

[0014] This changes the magnetic behavior of the rotor north pole and, in particular, weakens the magnetic field B generated by the electric current I. A weakening of the magnetic field B, which in the sense of the invention is preferably also referred to as field weakening, means that a wider range of speeds can be achieved with the electrical device. In the sense of the invention, this preferably means that the motor of the electrical device can rotate at a wider range of speeds. In other words, the electrical device or its motor can cover a wider range of speeds. In the sense of the invention, this wider range of speeds is preferably referred to as the "second speed range", wherein the second speed range is on average associated with higher speeds than the first speed range.In the sense of the invention, this preferably means that the larger range of speeds that can be covered by the electrical device leads to higher speeds in particular being able to be achieved. Consequently, the range of speeds or its mean value can be shifted towards higher speeds. This advantage of the invention can preferably be described in that the second speed range that can be achieved after the weakening of the magnetic field B is on average associated with higher speeds than the first speed range that is reached by the motor of the electrical device before the field weakening. In the sense of the invention, it is very particularly preferred that the second speed range is "broader" than the first speed range. Thus, after the field weakening, a larger range of speeds can be covered by the electrical device.This allows the motor of the electrical device to rotate at a wider range of speeds, making the electrical device flexible and suitable for performing many applications and functions. In particular, the electrical device may be a vacuum cleaner or a device for supplying fluids on a construction site, whose turbine is often driven by comparatively high speeds. Alternatively, the electrical device may be a machine tool that can be operated at particularly high speeds for short periods of time to perform a particularly demanding task (a "boost function").

[0015] The invention advantageously makes it possible to provide a wider range of speeds than with conventional electrical devices as known from the prior art. A significant advantage of the invention is that this surprisingly wide range of speeds can be provided without having to provide two or more gear stages. In other words: the proposed electrical device requires a surprisingly small number of gear stages and is nevertheless capable of being operated over a very wide speed range. This wide speed range can preferably also be referred to as a "wide speed range" within the meaning of the invention, whereby the provision of a wide speed range in the context of the present invention is preferably also referred to as a "speed spread".This means that the invention can advantageously provide an operating method for an electrical device with which the speed range of the motor of the electrical device can be spread over a surprisingly wide range. Preferably, the method for providing a wide range of speeds in an electrical device can also be referred to as a method for speed spreading in an electrical device. The speed spread is expressed in particular in the formulation "second speed range", wherein the second speed range can, for example, be associated with higher average speeds than the first speed range. Alternatively or additionally, the second speed range can cover a wider range of speeds than the first speed range.

[0016] The invention can be used, for example, in electrical devices designed as vacuum cleaners, suction devices, or dust extractors. In such electrical devices, high speeds are particularly preferred in order to generate a strong negative pressure for sucking in dust or particles. The invention helps here by expanding the speed range of the motor of the electrical device, particularly into the range of comparatively high speeds. For example, speeds of up to 21,000 revolutions per minute can be achieved with the invention. A motor operating in such a speed range can, for example, drive the turbine of a vacuum device to generate a negative pressure.

[0017] The electrical device can, however, also be designed as a machine tool. Examples of machine tools include drills, hammer drills, chisel hammers, cutting or angle grinders, or core drilling machines, but are not limited to these. It has been shown that the invention can provide a boost function with which, for example, reinforcing bars or pipes in a concrete substrate to be processed can be severed. Within the scope of the boost function, the machine tool or its motor can be operated at a particularly high speed for a short period of time. This particularly high speed then makes it possible to cut through metal components that may be contained in a concrete substrate as so-called iron strikes. Within the meaning of the invention, it is preferred that the speed spread enables a boost function to cut through possible metal components in a concrete substrate to be processed.In this embodiment of the invention, the electrical device can be designed as a machine tool, in particular as a core drilling device. The tool of the machine tool can then preferably be a core bit. Advantageously, the invention enables the provision of comparatively high speeds, especially in the short term. In this way, various applications that rely on high speeds can be handled particularly well by the proposed electrical device.

[0018] The invention advantageously makes it possible to provide an electrical device with a maximum of one gear stage, which is nevertheless capable of covering a wide range of speeds. Within the meaning of the invention, it is preferred that the electrical device has no gear or a gear stage with a maximum of one gear stage. With the aid of so-called field weakening, speed ranges can be achieved that are not achievable with conventional commutation of the motor of the electrical device when the electrical device is operated in the control regime of the optimal MTPA angle (MTPA = Maximum Torque Per Ampere). Within the meaning of the invention, it is preferred that the angle beta can be adjusted by the current components l_d and l_q. The MTPA angle is preferably the optimal angle beta at which a maximum torque is delivered at a current x.Within the meaning of the invention, it is preferred that there is an optimal angle beta, i.e., an MTPA angle, for each stator current. The wide range of speeds can be provided in particular by electronics of the electrical device, with which the electrical current I in a rotor magnetization axis can be manipulated such that the magnetic field B is weakened, thereby enabling higher speeds. In other words, the electronics of the electrical device can be configured to influence, in particular, the current component along the d-axis ("flux current component l_d") in a space vector representation, so that this influence weakens the magnetic field B of the rotor of the motor of the electrical device and a wider range of speeds can be provided. The "d-axis" in a space vector representation can preferably also be referred to as the "rotor magnetization axis" within the meaning of the invention.Conventional electrical devices are typically operated at their maximum torque per ampere (MTPA) range, where the electrical devices achieve maximum torque per ampere (MTPA). However, it has been shown that when an electrical device is operated according to the MTPA control scheme, only a narrow range of speeds is accessible. The invention overcomes this disadvantage by generating the second magnetic pole in close proximity to the first magnetic pole and thereby weakening the magnetic field B.

[0019] The weakening of the magnetic field B of the motor of the electrical device is preferably referred to as "field weakening" or "flux weakening" within the meaning of the invention. In the context of the present invention, the field weakening is preferably created by constructing the second magnetic pole in direct spatial proximity to the first pole, with the polarities of the two poles being the same. The provision of the second magnetic pole in the motor of the electrical device is comparable to replacing a magnetic material in a permanent magnet. If such a permanent magnet with—for example—a weaker magnetic material—with the same motor geometry and the same control and voltage—is used to operate an electric motor, the idle speed of such a motor will generally increase. Such a replacement of the magnetic material is obviously not possible during operation of an electrical device.Here, the invention now offers an alternative possibility for weakening the magnetic field B within the motor of the electrical device during operation of the electrical device in order to increase the range of possible speeds for the user of the electrical device. In other words, the invention can provide an alternative method for performing field weakening in an electrical device or an operating method for an electrical device in which the range of available speeds can be increased by field weakening. The proposed method makes it possible, in particular, to provide a wide range of speeds in an electrical device having an electric motor; thus, the invention represents a method for providing a wider range of speeds or speed ranges.This eliminates the need for a gearbox when covering a wide speed range, or eliminates the need for additional gear stages when a gearbox is already installed. This makes it possible to create a compact, handy, and easy-to-handle machine tool or a compact and easily transportable vacuum cleaner.

[0020] According to the invention, it is preferred that the motor of the electrical device comprises a rotating rotor and a stator. Preferably, a portion of the magnetic field of the stator of the motor of the electrical device can be adjusted so that a north pole is created exactly in front of the magnetic north pole of the rotor of the motor of the electrical device, wherein this north pole comes from the coils of the stator, i.e. is arranged on the stator side. Due to the identical polarity of the first and second magnetic poles, there is a repulsion between the two poles, so that the stator north pole "pushes away" part of the rotor north pole. In this way, the rotor north pole is weakened - analogous to exchanging the magnetic material of a permanent magnet from a stronger to a weaker magnetic material. The weakening of the rotor north pole leads to a weakening of the magnetic field B of the motor of the electrical device, so that higher speeds ora wider range of speeds can be achieved with the engine.

[0021] In the field-oriented control regime, the stator field, i.e., the magnetic field of the stator of the motor of the electrical device, typically consists of three individual fields, which preferably correspond to the three motor phases. In the context of the present invention, this stator field can be converted such that two virtual coils form directly in front of the north pole (d-axis) and offset by 90° in front of the north pole. The d-axis is preferably defined such that it runs through the center of the north pole of the rotor. The position and arrangement of these two virtual coils is illustrated in Figure 1, which shows a motor in a rotor-fixed or rotating dq coordinate system.

[0022] In this rotating dq-coordinate system, two fields can advantageously be controlled: The D-field can be used to manipulate or influence the magnetic flux linkage between the north pole of the rotor and the stator coil. The Q-field can be used to manipulate or change the torque of the motor of the electrical device. The change in torque is based on the idea that a south pole on the stator coil leads to an attraction of the north pole of the rotor. The current that thus flows through the stator coil can advantageously be used to variably adjust the motor torque as needed. The D-field is preferably linked to the flux current component l_d, while the Q-field is linked to the torque-generating component l_q of the electric current. An overview of the quantities and relationships used can be found in Figures 1 and 2.

[0023] When using field-oriented control of the electrical device or its motor, the stator field, i.e., the magnetic field of the stator of the motor of the electrical device, the electric current can have a flux current component l_d and a torque-generating component l_q, wherein the weakening of the magnetic field B is preferably achieved by a flux current component l_d shifted in a negative direction. The field orientation is preferably configured to convert the various relevant variables into a preferably rotating coordinate system, wherein the coordinate system is oriented in particular to the flux or field of the rotor of the motor of the machine tool.

[0024] The flux current component l_d can preferably also be referred to as "d-current" within the meaning of the invention, while the torque-generating component l_q can be referred to as "q-current" within the scope of the invention. It is preferred within the meaning of the invention that the proposed method is carried out in particular with negative d-currents or that the weakening of the magnetic field B is made possible by a negative flux current component l_d. If, during operation of the electrical device, the optimal MTPA range, in which the electrical device is operated with a maximum torque per supplied current, is left and, in addition, a negative flux current component l_d weakens the magnets in the motor of the electrical device (=> field weakening), the speed of the motor can increase considerably. This can advantageously lead to speeds or speed ranges being able to be achieved without the need for a gearbox on the electrical device.The speeds or speed ranges that can be achieved in this way preferably correspond to the second speed range that can be reached by the motor of the electrical device after field weakening, whereby the speeds of the second speed range are on average greater than the speeds of the first speed range that the motor of the electrical device reaches before field weakening. If a gearbox is already present on the electrical device, the number of gear stages can be reduced with the invention, so that the gearbox can be constructed more simply or can comprise fewer parts and components. This can, for example, simplify the manufacture or repair of the electrical device. In the sense of the invention, it is preferred that the electrical device is not operated at an operating point with a maximum torque when the electrical device is operating in the second speed range.The term "operating point" in the sense of the invention can preferably be understood as the so-called "MTPA point", in which the electrical device is controlled or operated in such a way that the lowest possible current leads to the greatest possible resulting torque (MTPA = maximum torque per ampere). In the sense of the invention, it is particularly preferred that the electrical device is not operated at an MTPA point with a maximum torque when the electrical device is operating in the second speed range. The invention thus differs precisely from conventional electrical devices as described in the prior art. Conventional electrical devices are generally operated precisely at their MTPA point, in which the electrical devices or their motors achieve a maximum torque per ampere (Maximum Torque Per Ampere = MTPA).However, it has been shown that when an electrical device is operated according to the MTPA control scheme, only a narrow range of speeds is accessible. To still offer the user a wider range of speeds, gear stages are often used in the current technology.

[0025] However, the provision of multiple gear stages often comes with the disadvantage of increasing the weight of the machine tool and requiring increased complexity in setting up and assembling the device. Furthermore, control elements must usually be provided to make adjustments to the gear system. For example, selector switches may be required to select a gear stage or "gear" so that the machine tool user can use the transmission.

[0026] In the field of electrical devices, standard commutation methods such as block commutation or field-oriented control are usually used to control the motor of the electrical device. The motor of the electrical device is generally operated at the optimum MTPA angle, whereby the optimum MTPA angle in the sense of the invention is the angle that generates the greatest torque with the smallest supplied current. The present invention departs from this conventional control concept for the electric motor, in which the aim is to generate the greatest possible torque with the smallest possible electrical current, in order to be able to achieve a wider range of speeds with the electrical device. A further advantage that can be made possible with the invention is that the provision of a gearbox in the electrical device can be dispensed with.If the electrical device already has a transmission, the invention can advantageously reduce the number of required transmission stages while still covering a wide range of speeds. In other words, the invention can cover a particularly wide speed range without requiring a complex transmission or a large number of transmission stages on the electrical device.

[0027] To weaken the magnetic field B, a voltage V_s is required. This voltage V_s can be greater than the voltage V_s_max available in the electrical device. The voltage V_s required for field weakening cannot usually be generated by conventional control methods such as block commutation or field-oriented control if the MTPA control principle attempts to achieve maximum torque with the lowest possible consumption of electrical current. The block diagram describing the control of the electrical device according to the present invention can therefore preferably be expanded to include additional blocks and components in order to provide the voltage V_s for field weakening that exceeds the voltage limit V_s_max.The correspondingly supplemented block diagram is shown in Figure 3, wherein the block diagram shown in Figure 3 shows a possible embodiment of the invention. The additional voltage A required for the field weakening preferably results from the difference between the available voltage V_s_max and the voltage V_s required for the weakening of the magnetic field, ie

[0028] A = V_s - V_s_max

[0029] Field weakening can be implemented, for example, as follows: If more voltage A is required to weaken the magnetic field B, a certain degree of excess voltage can be diverted from the d-current and pushed further into the negative range. The d-current preferably ensures that the magnetic field B of the rotor of the electrical device's motor is reduced or weakened. This allows the motor to be operated with more voltage than before, enabling higher speeds or a wider range of speeds. Of course, other options are also conceivable and preferred for implementing field weakening.

[0030] According to the invention, it is preferred that rotational speeds in a range from 4,000 to 21,000 revolutions per minute are achieved, preferably rotational speeds in a range from 4,200 to 15,000 revolutions per minute, particularly preferably rotational speeds in a range from 4,500 to 10,000 revolutions per minute, and most preferably rotational speeds in a range from 5,000 to 8,000 revolutions per minute. In one embodiment of the invention, the flux current component l_d of the electric current can generate a north pole in front of the north pole of the rotor of the motor of the machine tool, so that the magnetic field B is weakened by the identical polarity of the magnetic poles, allowing the motor of the electrical device to rotate at a wider range of rotational speeds.Within the meaning of the invention, it is particularly preferred that the flux current component l_d of the electric current creates the second north pole in front of the rotor north pole on the stator side of the motor of the machine tool. The formulation that the second north pole creates in front of the rotor north pole on the stator side of the motor of the machine tool can preferably be described in the context of the present invention as the north pole, as an example of a second magnetic pole, being created in spatial proximity to the rotor north pole, as an example of a first magnetic pole. In other words, the first magnetic pole can be formed by a north pole, while the second magnetic pole is also formed by a north pole, i.e., a pole of the same polarity.Preferably, the flux current component l_d of the electric current creates a magnetic pole with a second polarity in the region of a rotor pole with a first polarity, wherein the polarities of the rotor pole and the magnetic pole are the same. According to the invention, it is particularly preferred that the flux current component l_d of the electric current creates a magnetic pole with a second polarity in front of the rotor pole with the first polarity, wherein the polarities of the rotor pole and the magnetic pole are the same. Preferably, the magnetic pole with the second polarity forms on the stator side of the motor of the machine tool. According to the invention, it is preferred that the flux current component l_d of the excess current does not generate any torque, while the current component l_q can be referred to as a "torque-generating component of the electric current."

[0031] In a second aspect, the invention relates to an electrical device for carrying out the proposed method. The terms, definitions, and technical advantages introduced for the method preferably apply analogously to the electrical device. The motor of the electrical device is a brushless motor. It is particularly preferred within the meaning of the invention for the motor of the electrical device to be a BLDC motor, i.e. a brushless direct current motor. The field weakening capability of the motor of the electrical device is preferably achieved via a suitable geometry of the motor, with a design with buried magnets being particularly preferred. Buried magnets advantageously ensure particularly good field weakening capability, so that they can be used to provide an increased speed range of the electrical device particularly easily. The invention can advantageously be used with motors with different numbers of poles.This means, in the context of the invention, that the use of the invention is not limited to individual motor designs with a specific number of poles. For example, the invention can be used in electric motors with two, three, four, six, eight, ten, twelve, or more poles.

[0032] According to the invention, it is preferred that the motor of the electrical device be controllable using field-oriented control or block commutation, with Figure 3 particularly showing field weakening with field orientation or for a motor controlled with field orientation. Preferably, the motor of the electrical device is electronically commutated or electronically commutable.

[0033] Within the meaning of the invention, it is particularly preferred that the electrical device is not operated at a maximum torque at an operating point or MTPA point. Instead, it is preferable that the degree of overvoltage is diverted from the d-current or the flux current component l_d of the electrical current and shifted further into the negative range. The d-current or the flux current component l_d of the electrical current then preferably ensures that the magnetic field B of the rotor of the motor of the electrical device is weakened, so that the achievable speed range can be expanded (=> speed spread).

[0034] It is preferred within the meaning of the invention that the electrical device has electronics configured to manipulate an electric current I in a rotor magnetization axis such that the magnetic field B of the rotor of the motor of the electrical device is weakened, thereby enabling higher speeds. It is particularly preferred within the meaning of the invention that the motor of the electrical device commutates with electronics using field-oriented control (FOC). Preferably, the field-oriented control used in the context of the present invention can be configured to enable a speed spread by adjusting or changing the angle beta. In the context of the present invention, the speed spread can advantageously be brought about without a voltage increase, as is necessary in conventional electrical devices.As already explained above, the angle beta is the angle that can be adjusted by the current components l_d and l_q. Preferably, in the context of the invention, the angle beta can be varied, while the MTPA angle, as the optimal angle beta, characterized by maximum torque at minimum electrical current, is fixed for each motor or stator current.

[0035] In accordance with the invention, it is preferred that the control device of the electrical device be able to detect that a higher voltage is required. This higher voltage, or the additional voltage compared to the existing voltage, is represented in Figure 3 as "delta." To deliver this voltage to the motor, the d-current, or the d-current component, is advantageously manipulated. This change in the d-current component results in a changed beta angle. In other words, a change in the d-current component leads to a change in the beta angle, so that a higher voltage can be provided in the motor of the electrical device. Alternatively, in the context of the present invention, it may be preferable to change the beta angle.

[0036] According to the invention, it is preferred that the geometry of the motor improves its field weakening capability, so that the motor's magnetic field B is weakened and the speed range is expanded. According to the invention, it is preferred that the electrical device has a human-machine interface for entering a desired speed range.

[0037] The motor of the machine tool is a brushless motor, which can preferably deliver a power of more than 1.8 kilowatts (kW). The machine tool can preferably be a brushless electrical device with a braking function. For example, the machine tool can be designed as an electrically operated cut-off grinder. Within the meaning of the invention, it is particularly preferred that the machine tool is a battery-operated cut-off grinder with a cutting disc as the tool. The machine tool can be connected to at least one energy supply device in order to be supplied with electrical energy from the energy supply device. The at least one energy supply device of the machine tool can, for example, deliver a voltage of more than 20 volts (V). A voltage between 21 and 22 V is particularly preferred.The machine tool may also have two or more energy supply devices. If the machine tool has more than one energy supply device, the electrical energy released during deceleration of the machine tool may be fed back into the first and / or second energy supply device. This recuperation may occur substantially simultaneously, sequentially, or according to a specially designed algorithm.

[0038] The cutting disc is a disc-shaped tool of the cut-off machine. The cutting disc can have a diameter that is, for example, greater than 230 millimeters (mm). For example, the cutting disc can have diameters of 300 mm, 250 mm or 400 mm, but is not limited to these. The weight of the cutting disc can, for example, be in a range between 200 and 2,500 grams, i.e. between 0.2 and 2.5 kilograms (kg). For example, the weight of the cutting disc can assume values ​​of 210 grams, 530 grams, 550 grams, 930 grams, 1,270 grams, 1,280 grams, 1,720 grams or 2,450 grams, but is not limited to these. For example, the cutting disc can be a diamond cutting disc or an abrasive cutting disc with bonded abrasive grains. A diamond cutting disc is preferably characterized in that it has a steel core with diamond segments.

[0039] Further advantages emerge from the following description of the figures. The figures, the description, and the claims contain numerous features in combination. Those skilled in the art will expediently consider the features individually and combine them into further meaningful combinations. In the figures, identical and similar components are numbered with the same reference numerals.

[0040] They show:

[0041] Fig. 1 schematic representation of the motor of a preferred embodiment of the electrical device in a rotor-fixed, rotating dq coordinate system

[0042] Fig. 2 Overview of quantities and terms in the rotor-fixed, rotating dq-coordinate system

[0043] Fig. 3 Block diagram of a possible embodiment of the method or representation of a possible functioning of the electronics of the electrical device

[0044] Fig. 4 schematic representation of a preferred embodiment of the proposed machine tool

[0045] Implementation examples and figure descriptions:

[0046] Figure 1 shows a schematic representation of the motor 12 of a preferred embodiment of the electrical device in a rotor-fixed, rotating dq coordinate system, which can preferably also be referred to as a space vector representation. The coordinate system shown in Figure 1 preferably represents the motor 12 of the electrical device 100 in a stator-fixed coordinate system. Figure 1 shows, in particular, the rotor 20 of the motor 12 of the electrical device 100. The d and q axes of the space vector representation and a control of the electrical device 100 in a field-oriented control system can be seen. As can be seen in Figure 1, two virtual coils (black blocks) are formed, each of which forms directly in front of the north pole on the d-axis and 90° in front of the north pole.The basic idea underlying the present invention, illustrated in Figure 1, is that the electrical currents and voltages, which are typically impressed on the fixed stator, are mathematically converted into a preferably rotating coordinate system on the rotor. This has the advantage that alternating quantities, which, for example, have a sinusoidal shape, become equal quantities.

[0047] Figure 2 shows an overview of quantities and terms in the rotor-fixed dq coordinate system and in the space vector representation. Shown are the d-axis and the q-axis, as well as an exemplary electrical current l_ex, which is represented as a point in the space vector diagram. According to the invention, it is preferred that the axes of the rotor-fixed coordinate system be designated by the letters "q" and "d". The physical quantities, such as current I, voltage v, or inductance L along these axes, are then each represented by the letter q or d as an index: l_d, l_q, vq, vd, Lq, or Ld. An underscore may or may not be used to separate the physical quantities and the index.

[0048] The electric current l_ex has a flux current component l_d and a torque-generating component l_q, which correspond to the q and d coordinates of the electric current l_ex in the space vector diagram, respectively. Furthermore, Figure 2 shows the MTPA line L and the MTPA angle W. If the electrical device 100 were operated according to the MTPA control scheme, so that the greatest possible torque is to be achieved with the least possible expenditure of electric current, the point symbolizing the electric current l_ex would lie on the MTPA curve K. In order to optimally utilize the available electric current I, it is preferred according to the MTPA control scheme that the electric current I lies on the MTPA curve K. However, within the meaning of the invention, it is preferred that the electric current I or an operating point of the electrical device 100 does not lie on the MTPA curve K, but rather away from it.In other words, in the context of the present invention, a deliberate deviation from the MTPA control scheme is made in order not to maximize torque in the electrical device 100, but rather to provide the widest possible range of speeds. By deviating from the MTPA control scheme, the electrical device 100 is not controlled to maximize torque, but rather to provide the widest possible range of speeds.

[0049] The electric current l_ex, which is shown as an example in Figure 2, has a flux current component l_d and a torque-generating component l_q, wherein the torque-generating component l_q assumes a positive value, while the flux current component l_d assumes a negative value. A larger range of speeds or a shift in the speeds towards larger values ​​can be achieved by weakening the magnetic field B, wherein Figure 2 shows that a field weakening B occurs particularly at negative values ​​of the flux current component l_d of the electric current l_ex. In contrast, positive flux current components l_d of the electric current l_ex generally have a field-strengthening effect, i.e. they cause a field strengthening. According to the invention, it is preferred that the magnetic field B can be manipulated along the d-axis of the space vector representation.As shown in Figure 2, a shift of the flux current component l_d of the electric current l_ex in a negative direction (to the left) can lead to a field weakening FW-, while a shift of the flux current component l_d of the electric current l_ex in a positive direction (to the right) can lead to a field strengthening FW+. It is particularly preferred in the context of the present invention that the magnetic flux coupling from the rotor into the stator is weakened.

[0050] In addition, Figure 2 shows the angle ß enclosed by the flux current component l_d and the moment-forming component l_q of the electric current I. The following relation applies: tan(ß) = l_d / l_q.

[0051] Furthermore, Figure 2 shows that the torque can be manipulated or influenced along the q-axis of the space vector diagram. This possibility of influencing the torque is symbolized in Figure 2 by the reference symbol "M," which preferably also stands for "torque-generating" or for the torque. Figure 3 shows a block diagram of a possible embodiment of the method or a representation of a possible mode of operation of the electronics 18 of the electrical device 100. The block diagram shows how the electronics 18 controls the electrical device 100.

[0052] The input value of the control is a request for the speed of the motor 12 of the electrical device 100, where this request is referred to as l_s*. A superscript asterisk preferably denotes a target value within the meaning of the invention. For example, the angle ß enclosed by the flux current component l_d and the torque-generating component l_q of the electrical current I can be 30° in the context of the present invention. The angle ß can be used via the relationships depicted in Figure 3 to calculate the flux current component l_d and the torque-generating component l_q of the electrical current I.

[0053] The proposed method is implemented in the block diagram shown in Figure 3, particularly by those blocks that are surrounded by a dashed rectangle in the lower right-hand area of ​​the block diagram. In these blocks, the current stator voltage V_s and a voltage limit V_s_max are used as input variables to calculate a theoretically required overvoltage A. The overvoltage A preferably results from the difference between the available voltage V_s_max and the voltage V_s required to weaken the magnetic field B, i.e.

[0054] A = V_s - V_s_max.

[0055] If, for example, the electrical device 100 is a battery-operated electrical device 100 that is supplied with electrical energy via a power supply device 14, a voltage limit can be, for example, V_dc = 18-25 volts (V). The parameters for the field weakening B- determined in this way are then incorporated into the further calculations performed by the electronics 18 of the electrical device 100 in order to control the motor 12 of the electrical device 100, so that the widest possible range of motor speeds or motor speeds can be provided. The electronics 18 of the electrical device 100 can comprise controllers or control devices at various locations, which are designated by the reference symbol "PI". The PI controllers can in particular be designed as so-called PI controllers.

[0056] Figure 4 shows a schematic representation of a preferred embodiment of the proposed electrical device 100, wherein the electrical device 100 shown in Figure 4 is, in particular, a machine tool 10. A suction device 50 is not shown in the figures. However, those skilled in the art will know what a suction device 50, which may be, for example, an industrial or workshop vacuum cleaner, looks like and is typically designed. The machine tool 10, shown in Figure 4, has a motor 12, which is, in particular, designed as a brushless motor. The machine tool 10 can have a tool 16, which can be designed, for example, as a disk-shaped cutting tool. The machine tool 10 shown in Figure 4 is preferably a cut-off machine, with which cuts can be made in a substrate, such as concrete.The tool 16 of the machine tool 10 can be surrounded by a blade guard (no reference symbol) to protect the user of the machine tool 10 from flying chips and sparks. The machine tool 10 can be connected to at least one power supply device 14 to supply the machine tool 10 with electrical power. Of course, the machine tool 10 can also draw electrical power via a mains connection from a public or construction site network. The machine tool 10 can also have one or more handles (no reference symbol) with which the user of the machine tool 10 can transport the machine tool 10 or guide it during work.

[0057] The machine tool 10, shown in Figure 4, has electronics 18 connected to the motor 12 and the power supply device 14 via lines (without reference numerals). Data, electrical signals, or electrical energy can be exchanged between the electronics 18, the motor 12, and / or the power supply device 14 of the machine tool 10 using the lines.

[0058] The motor 12 of the machine tool 10, shown in Figure 4, comprises a stator 22 and a rotor 20. In the exemplary embodiment of the invention shown in Figure 4, the rotor 20 is arranged inside the stator 22 of the motor 12. Of course, many other motor geometries are also conceivable and preferred within the meaning of the invention. Furthermore, the machine tool 10, shown in Figure 4, can have a human-machine interface 24 via which a user of the electrical device 100 can make inputs. The human-machine interface 24 can have actuating elements, such as switches or buttons (not shown), that can be actuated by a user to make inputs. Alternatively or additionally, the human-machine interface 24 can have a display device, such as a screen or monitor (not shown), via which the electrical device 100 can display information to the user.The inputs or information may, for example, relate to a desired speed range or an actual speed range of the electrical device 100. List of reference symbols.

[0059] 10 Machine tool

[0060] 12 Engine

[0061] 14 Power supply device

[0062] 16 tools

[0063] 18 Electronics

[0064] 20 rotors

[0065] 22 Stator

[0066] 24 Human-machine interface

[0067] 50 suction device

[0068] 100 electrical devices

[0069] PI controllers, especially PI controllers

[0070] S South Pole

[0071] N North Pole

[0072] B Magnetic field

[0073] FW+ field strengthening

[0074] FW field weakening

[0075] M moment-forming, torque

[0076] I electric current l_ex exemplary current l_q moment-forming component of the electric current l_d flux current component ß angle enclosed by the moment-forming component l_q and the flux current component l_d K MTPA curve

[0077] W MTPA angle for the current l_s a, b, c: real 3-phase system q: q-axis of the rotor-fixed coordinate system orthogonal to the magnetic flux vq: voltage in q-direction p0: angle between d-axis and the phase ad: d-axis of the rotor-fixed coordinate system along the magnetic flux vd: voltage in d-direction

[0078] CD: Angular velocity

Claims

Patent claims 1. Method for providing a wide range of speeds in an electrical device (100) having a motor (12), characterized by the following method steps: a) operating the electrical device (100) in a first speed range, wherein an electrical current I flows through the motor (12), wherein the electrical current I can generate a magnetic field B, b) generating a second magnetic pole with a second polarity in spatial proximity to a first magnetic pole with a first polarity in the motor (12) of the electrical device (100), wherein the first polarity and the second polarity are the same, c) weakening the magnetic field B by the second magnetic pole, whereby the electrical device (100) can be operated in a second speed range.

2. Method according to claim 1, characterized in that the second speed range is associated on average with higher speeds than the first speed range.

3. Method according to claim 1 or 2, characterized in that the electric current I can have a flux current component l_d and a moment-forming component l_q, wherein the weakening of the magnetic field B is achieved by a negative flux current component l_d.

4. Method according to one of the preceding claims, characterized in that the electrical device (100) is not operated at a maximum torque in an MTPA point when the electrical device (100) operates in the second speed range.

5. Method according to one of the preceding claims, characterized in that Speeds in a range of 4,000 to 21,000 revolutions per minute are achieved, preferably speeds in a range of 4,200 to 15,000 revolutions per minute, particularly preferably speeds in a range of 4,500 to 10,000 revolutions per minute and most preferably speeds in a range of 5,000 to 8,000 revolutions per minute.

6. Electrical device (100) for carrying out the method according to one of the preceding claims, characterized in that a motor (12) of the electrical device (100) is a brushless motor.

7. Electrical device (100) according to claim 6, characterized in that the electrical device (100) is a machine tool (10) or a suction device (50).

8. Electrical device (100) according to one of claims 6 or 7, characterized in that the motor (12) of the electrical device (100) can be controlled by means of a field-oriented control or a block commutation.

9. Electrical device (100) according to one of claims 6 to 8, characterized in that the electrical device (100) has electronics (18) which are designed to manipulate an electrical current I in a rotor magnetization axis in such a way that a magnetic field B is weakened, thereby enabling higher rotational speeds.

10. Electrical device (100) according to one of claims 6 to 9, characterized in that the electrical device (100) has a human-machine interface (24) for inputting a desired speed range.

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