MACHINE TOOL WITH A MOTOR SHAFT AND A FAN WHEEL, WHICH HAS A MAGNETIC COUPLING BETWEEN THE MOTOR SHAFT AND THE FAN WHEEL

Description

[0001] The present invention relates to a machine tool comprising a motor and a motor shaft, wherein a fan wheel in the machine tool is configured to generate an airflow for cooling the motor. The machine tool is characterized in that the coupling between the fan wheel and the motor shaft is magnetic, such that the motor shaft drives the fan wheel to a rotational movement at a speed lower than the speed of the motor shaft. Due to the magnetic coupling of the fan wheel and the motor shaft, the movements of the two components can advantageously be decoupled from one another, so that an increase in the rotational speed of the motor shaft does not automatically lead to an increase in the speed of the fan wheel. This allows fan losses to be significantly reduced and the efficiency of the machine tool's motor to be substantially improved.In a second aspect, the invention relates to a method for cooling a motor of a machine tool, wherein there is a magnetic coupling between a fan wheel and a motor shaft of the machine tool. Background of the invention:

[0002] In the prior art, machine tools are known that can be used to perform heavy-duty work, for example, on construction sites. Examples include core drilling machines or grinding and cutting machines. These machines typically use a motor to drive a tool, such as a drill bit or a disc-shaped grinding or cutting tool. The motor can generate heat, which can be dissipated from the motor area of ​​the machine tool by means of cooling devices. Fan wheels are known in the prior art, but these are usually mounted on the motor shaft of the machine tool. In other words, there is a rigid mechanical connection between the fan wheel and the motor shaft or the motor itself. This rigid mechanical connection results in the fan wheel and the motor rotating at essentially the same speed.

[0003] As a consequence of the fan's fixed mounting, the airflow generated by the fan to cool the machine tool's motor ("cooling airflow") cannot be adjusted independently of the motor's speed. In conventional machine tools, as known from the prior art, the cooling airflow increases with the speed of the fan and motor shaft unit. The resulting fan losses even increase with the cube of this unit's speed. This increase is, unfortunately, inversely proportional to the motor's cooling demand. It has been shown that this undesirable discrepancy between motor speed and available cooling capacity from the cooling airflow can be exacerbated when using brushless drives.This amplification is observed particularly in brushless motors with a high speed spread, i.e., in brushless motors where the minimum and maximum speeds of the drive motor differ significantly from each other.

[0004] To overcome the undesirable discrepancy between engine speed and cooling capacity, or the high cooling capacity losses, prior art has proposed using ventilation units with their own motors to adjust the cooling capacity independently of the engine speed. However, such ventilation units are often very bulky and heavy, making machine tools cumbersome and unwieldy, which can be particularly tiring during long working hours on construction sites.

[0005] A machine tool known from the prior art is described in EP 3 598 613 A1. A cooling unit with magnetic coupling is known from FR 2 819 119 A1.

[0006] The object of the present invention is therefore to overcome the disadvantages of the prior art described above and to provide a machine tool in which the cooling capacity can be adjusted independently of the speed of the machine tool's motor, without the need for a separate ventilation unit with its own motor. The aim of the invention is, in particular, to provide compact and portable machine tools in which, moreover, fan losses, especially at high motor speeds, can be significantly reduced.

[0007] The problem is solved by the subject matter of the independent claims. Advantageous embodiments relating to the subject matter of the independent claims are found in the dependent claims. Description of the invention:

[0008] The invention provides a machine tool with a motor and a motor shaft according to claim 1, wherein a fan wheel in the machine tool is configured to generate an airflow for cooling the motor. The machine tool is characterized in that the coupling between the fan wheel and the motor shaft is magnetic, such that the motor shaft drives the fan wheel to a rotational movement at a speed that is lower than the speed of the motor shaft. It has been shown that the dependence of the rotational speeds can be significantly reduced by providing the magnetic coupling. Thus, a higher speed of the motor shaft does not necessarily lead to a higher speed of the fan wheel. Although the motor shaft is still configured to drive the fan wheel, i.e., to cause a rotational movement of the fan wheel, even with the magnetic coupling in place.However, due to the magnetic coupling of the components according to the invention, the motor shaft and the fan wheel do not rotate at the same speed; rather, the speed of the fan wheel is always lower than the speed of the motor shaft. Therefore, in accordance with the invention, it is preferably also referred to as a decoupling of the speeds of the motor shaft and the fan wheel.

[0009] In a further aspect, the invention relates to a cooling unit for a machine tool motor according to claim 9, wherein the cooling unit comprises a motor shaft and a fan wheel for generating an airflow to cool the machine tool motor. In the proposed cooling unit, the coupling between the fan wheel and the motor shaft is magnetic, so that the dependence of the rotational speed of the fan wheel and the motor shaft can be significantly reduced.

[0010] It is preferred in accordance with the invention that the fan wheel is arranged on the motor shaft. A significant advantage of the present invention is that there is no rigid, mechanical connection between the motor shaft and the fan wheel, but rather a magnetic coupling. By providing a magnetic coupling between the fan wheel and the motor shaft, the simultaneous, uniform movement of the fan wheel and motor shaft, known from the prior art and which can lead to an insufficient supply of cooling air to the motor, can be avoided. Instead, the movements of the fan wheel and the motor shaft are decoupled from each other, so that the amount of air supplied for cooling the motor of the proposed machine tool can be better regulated or adjusted. Due to the magnetic coupling between the fan wheel and the motor shaft, the decoupling of the movements preferably occurs at high motor speeds.

[0011] It is preferred, according to the invention, that the speed of movement of the fan wheel or the motor shaft is specified using the rotational speed n of the respective component. The magnetic coupling between the fan wheel and the motor shaft thus advantageously ensures that the rotational speed of the fan wheel no longer increases to the same extent as the rotational speed of the motor shaft or the motor. This effectively avoids the cooling losses that increase with the cube of the rotational speed. Furthermore, improved motor cooling can be provided with a better-adapted cooling airflow. The cooling airflow can also be used, in particular, to cool the power electronics of the machine tool.In accordance with the invention, it is preferred that the fan wheel of the machine tool is configured to generate a cooling airflow with which the motor and / or the power electronics of the machine tool can be cooled.

[0012] A further significant advantage of the invention is that it provides a cost-reduced cooling solution for a machine tool, which is also characterized by its small footprint. This allows for the development of particularly compact machine tools. In particular, the inventors have recognized that the fan losses known to occur in conventional machine tools at increasing motor speeds can be significantly reduced by replacing the rigid connection between the fan wheel and the motor shaft with a magnetic coupling. This also advantageously leads to an improvement in the overall efficiency of the motor and / or the machine tool.

[0013] The fan wheel preferably has a substantially circular base. Guide elements for directing and transporting the airflow for cooling the machine tool motor can be arranged on the upper surface of the fan wheel. The fan wheel can also have a central opening, which preferably also has a substantially circular base. The opening is preferably located centrally in the fan wheel. The opening can be configured to accommodate the motor shaft. In other words, the motor shaft can pass through the opening of the fan wheel, and according to the present invention, there is no rigid mechanical connection between the motor shaft and the fan wheel, but rather a magnetic coupling.

[0014] It is preferred, according to the invention, that the fan wheel comprises magnetic areas for generating the magnetic coupling between the fan wheel and the motor shaft. It is particularly preferred, according to the invention, that the magnetic areas are permanent magnets. For example, a number of permanent magnets can be integrated into the fan wheel.

[0015] The integration of the permanent magnets into the fan wheel can be achieved, for example, by injecting the permanent magnets into the fan wheel material during manufacturing. This design is particularly advantageous if the fan wheel is made of or comprises plastic. The permanent magnets can advantageously form the magnetic areas provided for generating the magnetic coupling between the fan wheel and the motor shaft. For example, in the context of the present invention, 2 to 20, preferably 4 to 14, more preferably 6 to 10, and most preferably 8 permanent magnets can be used or integrated into the fan wheel.

[0016] According to the invention, the fan wheel has a toothed ring, the toothed ring comprising magnetic areas for generating the magnetic coupling between the fan wheel and the motor shaft. The toothed ring of the fan wheel is therefore preferably also referred to as a "magnetic toothed ring" within the meaning of the invention. The toothed ring has teeth that are preferably arranged uniformly around a central region of the toothed ring. The toothed ring of the fan wheel is also referred to as the first toothed ring within the meaning of the invention.

[0017] Furthermore, according to the invention, the motor shaft also has a toothed ring, which, for the purposes of the invention, is also referred to as a second toothed ring. This second toothed ring is also a magnetic toothed ring within the meaning of the invention. This means that it has magnetic areas. The second toothed ring of the motor shaft preferably rotates at the same speed, i.e., preferably at the same rotational speed n, as the motor of the machine tool. Thus, according to the invention, the fan wheel has a first toothed ring and the motor shaft has a second toothed ring, wherein the magnetic coupling between the motor shaft and the fan wheel is effected by the magnetic toothed rings. In other words, the toothed rings of the fan wheel and the motor shaft are configured to generate the magnetic coupling between the motor shaft and the fan wheel.

[0018] In accordance with the invention, it is preferred that the permanent magnets or magnetic areas are preferably arranged in a uniformly distributed manner in an outer region of the fan wheel or the gear rings. Non-magnetic areas are preferably located between the permanent magnets or magnetic areas. In other words, the magnetic areas or permanent magnets can be separated from each other by non-magnetic areas. The permanent magnets or magnetic areas can each have a substantially rectangular or trapezoidal base. An inner side of the preferably rectangular or trapezoidal base can be shorter than an outer side of the base of the permanent magnets or magnetic areas. The inner sides of the permanent magnets or magnetic areas preferably face the motor shaft.In accordance with the invention, it is preferred that the magnetic areas or the permanent magnets are arranged in a base plate of the fan wheel. However, it may also be preferred that the magnetic areas or the permanent magnets are arranged in the guide elements of the fan wheel or coincide with them.

[0019] It is preferred, according to the invention, that the magnetic areas or permanent magnets are arranged in the fan wheel in such a way that a north pole and a south pole of the permanent magnet or magnetic areas are opposite each other. Preferably, the poles of the magnetic areas or permanent magnets are located in the circumferential direction of the fan wheel, i.e., along an imaginary concentric ring, which may be provided in an outer region of the fan wheel. Tests have shown that the integration of the permanent magnets in the fan wheel results in particularly good robustness against dust.

[0020] It is preferred, according to the invention, that the number of teeth of the second gear ring corresponds to the number of magnetic areas or the number of permanent magnets of the first gear ring or the fan wheel. This preferably means, according to the invention, that the second gear ring can have, for example, 2 to 20, preferably 4 to 14, more preferably 6 to 10, and most preferably 8 teeth. The provision of the magnetic areas in the gear ring can be achieved, for example, by incorporating permanent magnets or ferromagnetic inserts into the teeth of the gear ring. This can be particularly advantageous if the gear ring is made of plastic. The use of plastic allows for particularly lightweight gear rings. It is also preferred, according to the invention, that the gear ring is made of or comprises a permanent magnetic material.For example, ferromagnetic iron can be used as a material and starting material for manufacturing the gear ring. It has been shown that iron gear rings can be manufactured particularly easily as simple stamped parts. Alternatively, iron gear rings can be pressed directly and thus easily installed.

[0021] The arrangement or orientation of the magnetic areas or permanent magnets in the second gear ring preferably corresponds to the arrangement or orientation of the magnetic areas or permanent magnets within the fan wheel or within the first gear ring of the fan wheel. In the context of the invention, this preferably means that the magnetic areas or permanent magnets of the second gear ring are arranged in an outer region of the gear ring, this outer region preferably being formed by the teeth of the gear ring. The magnetic areas or permanent magnets are preferably arranged or aligned with each other such that a north pole and a south pole are opposite each other. In other words, the north pole of a first tooth and the south pole of a second tooth of the gear ring can be arranged opposite each other.It is preferred, according to the invention, that the teeth of the gear ring form yoke-like magnetic bridges to the permanent magnets or the magnetic areas in the fan wheel or its gear ring. The gear rings can be exposed or, for example, injection-molded in plastic. According to the invention, the gear rings with their magnetic areas, which are located particularly in the teeth of the gear ring, can preferably be referred to as a permanent or ferromagnetic perforated mask. It is preferred, according to the invention, that the gear rings of the fan wheel and the motor shaft constitute magnetic coupling rings with which the magnetic coupling between the fan wheel and the motor shaft can be established. The magnetic coupling is achieved in particular through the interaction of the magnetic areas of the gear rings of the fan wheel and the motor shaft.

[0022] According to the invention, the fan wheel has a first toothed ring as a first magnetic coupling ring, and the motor shaft has a second toothed ring as a second magnetic coupling ring, with the magnetic coupling occurring between the toothed rings of the components "fan wheel" and "motor shaft." According to the invention, the first toothed ring and the second toothed ring are magnetically corresponding to each other. This preferably means that the toothed rings are similar or identical to each other with respect to the distribution of magnetic and non-magnetic areas. It is particularly preferred that the toothed rings are designed as magnetic shadow masks.

[0023] In a second embodiment, the machine tool comprises an electromagnet that provides the magnetic coupling between the fan wheel and the motor shaft. The electromagnet can have a base body and a coil for generating a magnetic field. The base body can, in particular, comprise a ferromagnetic material. For the purposes of the invention, this preferably means that the base body can be made of a ferromagnetic material, such as iron. It is also preferred for the purposes of the invention that the base body comprises at least a portion of a ferromagnetic material, such as iron. Preferably, the base body comprises a first region surrounded by the coil and a second region having an opening in which a first toothed ring of the fan wheel and a second toothed ring of the motor shaft are rotatably arranged relative to each other.

[0024] It is preferred within the scope of the invention that the dependence of the movements of the fan wheel's gear rings and the motor shaft can be significantly reduced by the invention, in particular the magnetic coupling, compared to a rigid connection between the fan wheel and the motor shaft. This preferably means, within the scope of the invention, that the coupling between the movements of the fan wheel and the motor shaft is considerably less pronounced due to the magnetic coupling between the two components than with a rigid connection, as is known in conventional machine tools. The motor shaft's gear ring preferably moves at the rotational speed of the machine tool's motor. The magnetic coupling between the two gear rings advantageously decouples the movement of the fan wheel's gear ring, and thus preferably also the movement of the fan wheel itself, from the movement of the motor shaft.This significantly reduces the dependence of the fan wheel's movement on the motor shaft's movement and effectively avoids an increase in the fan wheel's rotational speed at higher motor speeds, which is associated with increased fan losses.

[0025] It is preferred, according to the invention, that the coil can be energized to generate a magnetic field. This magnetic field can be transmitted from the preferably ferromagnetic base body in the areas of the gear rings of the fan wheel and motor shaft, thus creating magnetic coupling between the gear rings. Tests have shown that the embodiment of the invention with an electromagnet offers the advantage that the cooling airflow can be controlled and adjusted by the electronics of the machine tool. The cooling airflow can advantageously be regulated, in particular, according to requirements. For example, in the context of the present invention, the temperature of the machine tool motor and / or the temperature of the electronics can be determined and used as a basis for regulating or adjusting the cooling airflow.Furthermore, the ambient temperature of the machine tool can be taken into account to adjust the cooling airflow for the machine tool's motor. The adjustability of the cooling airflow represents a significant advantage of the invention's design, which uses an electromagnet to establish a magnetic coupling between the fan wheel and the motor shaft.

[0026] It is preferred according to the invention that the magnetic field generated by the electromagnet can be switched on and off in a binary manner. This can preferably be achieved by switching the current flowing through the coil of the electromagnet on or off. It is particularly preferred according to the invention that this current can be regulated, i.e., set to any value between 0 and 100%. This preferably also allows the strength of the generated magnetic field to be adjusted. The strength of the generated magnetic field preferably influences the strength of the magnetic coupling between the fan wheel and the motor shaft, so that by adjusting the current or the magnetic field, the strength of this magnetic coupling can advantageously also be adjusted. Tests have shown that the strength of the magnetic coupling determines how strongly the motor shaft drives the fan wheel.In other words, the strength of the magnetic coupling can determine the degree of dependence between the rotational speeds of the fan wheel and the motor shaft. A strong magnetic field preferably leads to a strong magnetic coupling between the fan wheel and the motor shaft. This results in the fan wheel being driven more strongly by the motor shaft, and its rotational speed being only slightly lower than that of the motor shaft. A weak magnetic field preferably leads to a weak magnetic coupling between the fan wheel and the motor shaft. This results in the fan wheel being driven less strongly by the motor shaft, and its rotational speed being significantly lower than that of the motor shaft.

[0027] The invention makes it possible, in particular, to ensure that the machine tool is only cooled when necessary. This significantly reduces the use of the fan, which is especially advantageous in regions with inconsistent or unreliable energy or voltage supplies and considerably simplifies the operation of the machine tool.

[0028] In a second aspect, the invention relates to a method for cooling the motor of a machine tool, wherein a magnetic coupling exists between a fan wheel and a motor shaft of the machine tool. The magnetic coupling preferably leads to a decoupling of the movements of the fan wheel and the motor shaft from one another, which, in the context of the invention, preferably means that the fan wheel is less strongly affected by the movement of the motor shaft than if there were a rigid connection between the components "fan wheel" and "motor shaft". This ensures, in particular, that the fan wheel does not experience a rapid increase in the speed of the motor, but rather that the rotational speed and / or velocity of the fan wheel can remain at lower speeds despite the high rotational speeds of the motor and motor shaft. The terms, definitions, and technical advantages introduced for the machine tool apply analogously to the cooling method.

[0029] Further advantages arise from the following description of the figures. The figures, the description, and the claims contain numerous features in combination. A person skilled in the art will expediently consider the features individually and combine them into meaningful further combinations.

[0030] However, the scope of protection of the invention is determined exclusively by the following claims.

[0031] In the figures, identical and similar components are numbered with the same reference symbols. They show: Fig. 1 Side view of a cooling unit with motor shaft and fan wheel. Fig. 2 View of a possible arrangement of magnetic areas. Fig. 3 View of a possible design of a gear ring. Fig. 4 Side view of a cooling unit with motor shaft, fan wheel and electromagnet. Examples of implementation and description of figures:

[0032] Figure 1Figure 1 shows a side view of a motor shaft 2 and a fan wheel 3, which together form a cooling unit for a machine tool (not shown). The motor shaft 2 is connected to the motor 1 (not shown) and, when the machine tool is in operation, preferably rotates at the same speed, i.e., rotational speed, as the motor 1 itself. A magnetic coupling exists between the fan wheel 3 and the motor shaft 2, which, according to a first embodiment of the invention ( Figs. 1 to 3 ) can be generated by magnetic areas 4 or permanent magnets 5. According to a second embodiment of the invention ( Fig. 4 The magnetic coupling can be generated by an electromagnet 8. In this embodiment of the invention, the proposed cooling unit also includes the electromagnet 8, which is provided for generating the magnetic coupling between the fan wheel 3 and the motor shaft 2.

[0033] The magnetic areas 4 or the permanent magnets 5 can, for example, be arranged in the fan wheel 3. However, according to the invention, it is generally provided that the magnetic areas 4 or the permanent magnets 5 are arranged in a toothed ring 6, wherein the toothed ring 6 is connected to the fan wheel 3. It is provided, according to the invention, that the fan wheel 3 has a first toothed ring 6, wherein the first toothed ring 6 comprises magnetic areas 4 and / or permanent magnets 5 that can cause magnetic coupling with the motor shaft 2. The motor shaft 2 comprises a toothed ring 7, which, according to the invention, is referred to as the second toothed ring 7. It is provided, according to the invention, that the second toothed ring 7 of the motor shaft 2 is magnetically corresponding to the first toothed ring 6 of the fan wheel 3. This means, according to the invention, that the arrangement of the magnetic areas 4 or the permanent magnets 5 is such that the magnetic areas 4 and / or permanent magnets 5 are arranged in a toothed ring 6.The permanent magnets 5 on the second gear ring 7 are configured similarly or identically to the arrangement of the magnetic areas 4 or the permanent magnets 5 on the first gear ring 6. The gear rings 6, 7, or their magnetic areas 4 and / or their permanent magnets 5, interact with each other in such a way that movement of the motor shaft 2 is transmitted to the fan wheel 3. The inventors have recognized that by providing a magnetic coupling between the fan wheel 3 and the motor shaft 2, a direct transmission of movement between the components 2, 3 can be prevented. Instead, a movement of the motor shaft 2 at high speeds is preferably converted into a movement of the fan wheel 3 at a lower speed. This significantly reduces losses in cooling performance, such as those that can occur with a rigid connection between the fan wheel 3 and the motor shaft 2.

[0034] Fig. 2Figure 1 shows a possible arrangement of magnetic areas 4 on the fan wheel 3 or on the first toothed ring 6 of the fan wheel. The magnetic areas 4 can be formed by small permanent magnets 5, which can, for example, be embedded in the material of the fan wheel 3 or the first toothed ring 6. The magnetic areas 4 or the permanent magnets 5 can be arranged in an outer region of the fan wheel 3 or its first toothed ring 6, with a south pole and a north pole of each pair of permanent magnets 5 facing each other. In other words, the magnetic areas 4 or the permanent magnets 5 are arranged such that a north pole and a south pole are aligned with each other.

[0035] Fig. 3Figure 1 shows a possible embodiment of a gear ring 6, 7. The gear ring can be either the first gear ring 6 of the fan wheel 3 or the second gear ring 7 of the motor shaft 2. The gear rings 6, 7 have teeth 14, wherein, in particular, the teeth 14 of the second gear ring 7 preferably form yoke-like magnetic bridges to the permanent magnets 5 or the magnetic areas 4 in the fan wheel 3 or its gear ring 6.

[0036] Fig. 4 Figure 1 shows a second embodiment of the invention in which the magnetic coupling is generated using an electromagnet 8. In particular, Figure 2 shows Fig. 4A proposed cooling unit with electromagnet 8. The electromagnet 8 comprises a base body 9 and a coil 10, the coil 10 being configured to generate a magnetic field. The coil 10 is preferably wound around a first region 11 of the base body, while a second region 12 of the base body 9 has an opening 13 in which the gear rings 6, 7 of the fan wheel 3 and the motor shaft 2 can be arranged. In particular, the figure shows Fig. 4 a motor shaft 2 with fan wheel 3 and electromagnet 8.

[0037] According to the invention, the coupling between the fan wheel 3 and the motor shaft 2 is magnetic, so that the dependence of the movement of the fan wheel 3 on the movement of the motor shaft 2 can be significantly reduced. In a second embodiment of the invention, the cooling unit comprises an electromagnet 8, which can effect the magnetic coupling between the fan wheel 3 and the motor shaft 2. For this purpose, the electromagnet 8 comprises a base body 9 and a coil 10 for generating a magnetic field, wherein the base body 9 can comprise a ferromagnetic material. The base body 9 has a first region 11, which is surrounded by the coil 10, and a second region 12, which has an opening 13 in which a first toothed ring 6 of the fan wheel 3 and a second toothed ring 7 of the motor shaft 2 are rotatably arranged relative to each other. Reference symbol list

[0038] 1 Motor 2 Motor shaft 3 Fan wheel 4 Magnetic areas 5 Permanent magnets 6 First tooth of the fan wheel 7 Second tooth of the motor shaft 8 Electromagnet 9 Base body 10 Coil 11 First area of ​​the base body 12 Second area of ​​the base body 13 Opening of the base body 14 Teeth of the toothed rings

Claims

1. Power tool having a motor (1) and a motor shaft (2), wherein a fan wheel (3) in the power tool is designed to generate an air flow for cooling the motor (1), wherein a coupling is formed magnetically between the fan wheel (3) and the motor shaft (2) such that the motor shaft (2) drives the fan wheel (3) in a rotary movement with a speed that is less than a speed of the motor shaft (2), characterized in that the fan wheel (3) has a first sprocket (6), wherein the first sprocket (6) comprises magnetic regions (4) for creating the magnetic coupling between the fan wheel (3) and the motor shaft (2), and in that the motor shaft (2) has a second sprocket (7), wherein the second sprocket (7) is magnetic in a manner corresponding to the first sprocket (6) of the fan wheel (3) or to the fan wheel (3).

2. Power tool according to Claim 1, characterized in that the fan wheel (3) comprises magnetic regions (4) for creating the magnetic coupling between the fan wheel (3) and the motor shaft (2).

3. Power tool according to Claim 1 or 2, characterized in that a number of permanent magnets (5) are integrated in the fan wheel (3).

4. Power tool according to Claim 1, characterized in that the power tool comprises an electromagnet (8) that brings about the magnetic coupling between the fan wheel (3) and motor shaft (2).

5. Power tool according to Claim 4, characterized in that the electromagnet (8) has a basic body (9) and a coil (10) for generating a magnetic field.

6. Power tool according to Claim 5, characterized in that the basic body (9) comprises a ferromagnetic material.

7. Power tool according to either of Claims 5 and 6, characterized in that the basic body (9) comprises a first region (11), which is surrounded by the coil (10), and a second region (12), which has an opening (13) in which a first sprocket (6) of the fan wheel (3) and a second sprocket (7) of the motor shaft (2) are arranged so as to be rotatable with respect to one another.

8. Method for cooling a motor (1) of a power tool according to one of the preceding claims, characterized in that there is a magnetic coupling between a fan wheel (3) and a motor shaft (2) of the power tool.

9. Cooling unit for a motor (1) of a power tool, wherein the cooling unit comprises a motor shaft (2) and a fan wheel (3) for generating an air flow for cooling the motor (1) of the power tool, wherein a coupling is formed magnetically between the fan wheel (3) and the motor shaft (2) such that the motor shaft (2) drives the fan wheel (3) in a rotary movement with a speed that is less than a speed of the motor shaft (2), characterized in that the fan wheel (3) has a first sprocket (6), wherein the first sprocket (6) comprises magnetic regions (4) for creating the magnetic coupling between the fan wheel (3) and the motor shaft (2), and in that the motor shaft (2) has a second sprocket (7), wherein the second sprocket (7) is magnetic in a manner corresponding to the first sprocket (6) of the fan wheel (3) or to the fan wheel (3).

10. Cooling unit according to Claim 9, characterized in that the cooling unit comprises an electromagnet (8) that brings about the magnetic coupling between the fan wheel (3) and motor shaft (2).

11. Cooling unit according to Claim 10, characterized in that the electromagnet (8) has a basic body (9) and a coil (10) for generating a magnetic field.

12. Cooling unit according to Claim 11, characterized in that the basic body (9) comprises a ferromagnetic material.

13. Cooling unit according to either of Claims 11 and 12, characterized in that the basic body (9) comprises a first region (11), which is surrounded by the coil (10), and a second region (12), which has an opening (13) in which a first sprocket (6) of the fan wheel (3) and a second sprocket (7) of the motor shaft (2) are arranged so as to be rotatable with respect to one another.