TECHNICAL FIELD

[0001] The present invention relates to an apparatus comprising an electric motor. BACKGROUND

[0002] This section is intended to provide a background or context to the invention that is recited in the claims. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, what is described in this section is not prior art to the description and claims in this application and is not admitted to be prior art by inclusion in this section.

[0003] Power tools have electric motors that generate heat during use of the power tools. The power tools may have fans that circulate ambient air for cooling the electric motors. The fan can be rotated by a rotor shaft, whereby airflow caused by the fan is dependent on the rotational speed of the motor shaft. Therefore, If a speed of rotation of the rotor shaft decreases, the speed of the fan and the airflow caused by the fan are also decreased. Eventually, when the speed of rotation of the rotor shaft is further decreased, the airflow may become insufficient for cooling the electric motor at least if the electric motor is used at a low speed for a long time. Therefore, the electric motor may be excessively heated, which can lead to degradation of the electric motor and eventually to a failure. On the other hand if the speed of rotation of the rotor shaft is increased, the airflow may become more than sufficient for cooling the electric motor, whereby power is lost in rotating the fan at a higher speed than necessary. Therefore, the rotation of the fan consumes excess power that could be used for driving a tool instead of driving the fan. The excess power consumption is of particular concern to power tools that are battery- powered, whereby operating time of the power tools is of interest.

SUMMARY

[0004] The scope of protection sought for various embodiments of the invention is set out by the independent claims. The embodiments, examples and features, if any, described in this specification that do not fall under the scope of the independent claims are to be interpreted as exampies useful for understanding various embodiments of the invention.

[0005] According to some aspects, there is provided the subject matter of the independent claims. Some further aspects are defined in the dependent claims. The embodiments that do not fall under the scope of the claims are to be interpreted as examples useful for understanding the disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006] For a more complete understanding of example embodiments of the present invention, reference is now made to the following descriptions taken in connection with the accompanying drawings in which:

Fig. 1 illustrates an example of an electric motor in accordance with at least some embodiments:

Fig. 2 illustrates a top view of the electric motor;

Fig. 3 illustrates a bottom view of the electric motor;

Fig. 4 illustrates a handheld tool in accordance with at least some embodiments Fig. 5 is a perspective view of an electric motor in accordance with at least some embodiments;

Fig. 6 is a cross-section of an electric motor in a longitudinal direction of a rotor shaft in accordance with at least some embodiments;

Fig. 7 and Fig. 8 illustrate an outer shell suitable for serving as a fan in accordance with at least some embodiments;

Fig. 9 illustrates a handheld tool equipped with a fan that is arranged co-centrically to the rotor shaft and rotatable with respect to the rotor shaft fan in accordance with at least some embodiments;

Fig. 10 illustrates an example of a crossed belt for a drive system in accordance with at least some embodiments; and

Figs. 11 , 12 and 13 illustrate examples of drive systems in accordance with at least some embodiments. DETAILED DESCRIPTON OF SOME EXAMPLE EMBODIMENTS

[0007] The foilowing embodiments are exemplary. Although the specification may refer to "an", "one", or “some” embodiment(s) in several locations, this does not necessarily mean that each such reference is to the same embodiment(s), or that the feature only applies to a single embodiment. Single features of different embodiments may also be combined to provide other embodiments.

[0008] Use of ordinal terms such as "first,” “second," “third,” etc., in the claims and description to modify a described feature does not by itself connote any priority, precedence, or order of one described feature over another or the temporal order in which acts of a method are performed, but are used merely as labels to distinguish one described feature having a certain name from another described feature having a same name (but for use of the ordinal term) to distinguish the described feature.

[0009] The verbs “to comprise” and “to include” are used In this document as open limitations that neither exclude nor require the existence of un-recited features. The features recited in dependent claims are mutually freely combinable unless otherwise explicitly stated. Furthermore, it is to be understood that the use of “a” or “an”, i.e, a singular form, throughout this document does not exclude a plurality.

[0010] Identical or corresponding functional and structural elements which appear in the different drawings are assigned the same reference numerals. When the words first and second are used to refer to different elements, it is to be understood that this does not necessarily imply or mean that the first and second elements are somehow structurally substantially different elements or that their dimensions are substantially different unless specifically stated.

[0011] In the following, it should be appreciated that a dot, is used a decimal separator in numerical values.

[0012] Fig. 1 illustrates an example of an electric motor in accordance with at least some embodiments. In Fig. 1 , the electric motor is illustrated by a cross-section of the electric motor in a longitudinal direction 113 of a rotor shaft 104 of the electric motor. Fig. 2 illustrates a top view of the electric motor and Fig. 3 illustrates a bottom view of the electric motor. The electric motor may be a brushless direct current, BLDC, electric motor 100. It shouid be noted that a brushless direct current, BLDC, electric motor may alternatively or additionally be referred to an electronically commutated motor (ECM or EC motor) or a synchronous DC motor. On the other hand, the BLDC electric motor 100, may be referred to an outrunner motor on the basis of the physical construction of the BLDC electric motor. Fig. 1 , Fig. 2 and Fig. 3 illustrate an outrunner motor that comprises a stator comprising electromagnets 110 which are arranged annular to the rotor shaft 104 and form a center (core) of the motor.

[0013] The electromagnets 110 of the outrunner motor are surrounded by an overhanging rotor that comprises permanent magnets 11 1. The overhanging rotor may comprise an outer shell 102 connected to the rotor shaft 104. In the outrunner motor, the outer shell is caused to rotate by selectively switching DC to the electromagnets, which causes a rotation of the rotor shaft. The permanent magnets 111 may be arranged annularly with respect to the electromagnets, e.g. on the inner surface of the outer shell. [0014] An example of the stator is a stator assembly, comprising a body or a stator hub 108 that is arranged annular to the rotor shaft 104. The rotor shaft 104 may extend through the stator hub and connected rotatably, e.g. by one or more bearing assemblies, to the stator hub. In accordance with at least some examples, the stator hub may comprise cooling channels 112 for cooling down the BLDC electric motor 100.

[0015] The BLDC electric motor 100 comprises cooling channels 112 that extend through the stator in the longitudinal direction 113 of the rotor shaft 104. The cooling channels comprise openings at ends that are separated from each other at least in the longitudinal direction 113 of the rotor shaft. The cooling channels provide that a fluid, i.e. a coolant fluid, for example a liquid, a gas, a mixture of gases such as air, may flow through the cooling channels via the openings of the cooling channels for cooling down the BLDC electric motor. In this way, particularly those parts of the BLDC electric motor that are operatively connected to the cooling channels for transferring heat into the coolant fluid flowing inside the cooling channels may be cooled by the coolant fluid. Examples of liquids for cooling the BLDC comprise at least water. It should be noted that for certain coolant fluids, e.g. water, sealings may be adapted and added to the BLDC electric motor for controlling flow of the coolant as needed and to avoid the coolant damaging the BLDC electric motor. In an example the heat transfer may be provided by a material of the parts of the BLDC electric motor that are in contact with the cooling channels. Since the cooling channels extend through the stator, at least the material of the stator hub, where the cooling channels 112 are located, should support efficient heat transfer from the BLDC electric motor to the coolant fluid Inside the cooling channels. An example of a material that provides efficient heat transfer is Aluminum (Al).

[0016] The cooling channels 112 may be arranged annularly with respect to the rotor shaft 104, between the rotor shaft and the electromagnets 110, whereby the electromagnets arranged around the cooling channels in a radial direction 115 of the rotor may be cooled down by the coolant fluid flowing through the cooling channels. Accordingly, the cooling channels may extend between the rotor shaft and the electromagnets 110. In an example, the cooling channels 112 may be arranged around the rotor shaft 104 at even distances, whereby an even heat transfer from the BLDC electric motor to the coolant fluid inside the cooling channels may be supported.

[0017] The cooling channels 112 provide longitudinal passages between openings of the cooling channels. The passages may have cross-sections that may be of various forms that support cooling of the parts of the BLDC electric motor, e.g. electromagnets, by a flow of coolant fluid via the cooling channels. Examples of the cross-sections comprise at least circular cross-sections, rectangular cross-sections and/or arched crosssections. It should be noted that the cooling channels may also have other shapes depending on the structure of the BLDC electric motor and implementation requirements for cooling the BLDC electric motor.

[0018] The BLDC electric motor may comprise a fan arranged at one end of the cooling channels 112 for controlling a direction of fluid flow via the cooling channels. The fan is configured to be rotated by the rotor shaft 104 for producing a pressure difference over the fan in the longitudinal direction 113 of the rotor shaft, and hence force, the fluid flow through the fan and into the cooling channels or out of the cooling channels. The outer shell 102 may serve as the fan or the BLDC electric motor comprises a separate fan connected to the rotor shaft 104. In an example, the fan may be positioned at a side of the BLDC electric motor, where the stator hub is uncovered and/or the electromagnets are uncovered. The side of the BLDC electric motor, where the stator hub is uncovered and/or the electromagnets are uncovered may be a side, where the outer shell 102 is not covering the stator hub and/or the electromagnets 110. The stator hub may be uncovered for example at least at one side of opposite sides, e.g. at a top side and at a bottom side, in the longitudinal direction 113 of the rotor shaft. In the illustrated example, the outer shell 102 is shown covering a top side of the electromagnets 110 and the stator hub 108, whereby the fan may be arranged to an opposite side of the stator hub in the longitudinal direction 113 of the rotor shaft, e.g. at a bottom side, of the BLDC electric motor. When positioned at the bottom side of the stator hub, rotation of the fan may cause a negative pressure inside the cooling channels 112. This causes coolant fluid to be drawn into the cooling channels through the openings of the cooling channels at the top side of the BLDC electric motor and out of the cooling channels via openings of the cooling channels at the bottom side the BLDC electric motor.

[0019] The electromagnets 110 may be enclosed in a sealed space 130 for preventing contamination of the electromagnets 110 by particles carried by the fluid flow. The sealed space may be formed by the stator hub, the outer shell 102 and sealing structures 118,120 between the stator hub and the outer shell. The cooling channels 112 run outside of the sealed space between the sealed space and the rotor shaft 104, whereby the electromagnets 110 are protected against particles such as dust and/or debris carried by the coolant fluid.

[0020] The sealing structures 118,120 may be configured to support a rotational movement of the stator and the outer shell 102 with respect to each other. The sealing structures may be configured to support the rotational movement of the stator and the outer shell with respect to each other at least, when a mechanical friction caused by the sealing structures to the rotational movement between the stator and the outer shell is small and/or the sealing structures do not cause mechanical friction to the rotational movement between the stator and the outer shell. Examples of sealing structures that may provide a small or a very small friction may comprise shaft sealings and bearing assemblies. Examples of sealing structures that may provide frictionless sealing comprise non-contact sealings such as labyrinth sealings. The sealed space 130 may comprise more than one type of sealing structures. For example, one of the sealing structures 118 may be a shaft sealing or a bearing assembly, and another one of the sealing structures may be a non-contact sealing such as a labyrinth sealing.

[0021] The outer shell 102 may comprise a surface 132, e.g. a top surface, that is connected to the rotor shaft 104 and configured to extend at least in the radial direction 115 of the rotor on one side of the electromagnets 110. In this way the outer shell 102 may serve for covering the electromagnets 110 on the one side, e.g. the top side. The outer shell may also comprise an annular part 122 that is arranged to extend in a direction that is parallel to a longitudinal direction of the rotor shaft. Accordingly, it should be noted that the annular part may form a part of the outer shell 102. The annular part may cover a side of the electromagnets 110 and the stator hub 108 that extends parallel to the longitudinal direction 113 of the rotor shaft. The permanent magnets 111 may be attached to the annular part at positions, where the permanent magnets surround the electromagnets. For attaching to the permanent magnets, the annular part may comprise ferromagnetic material, e.g. iron. Positioning the permanent magnets at the annular part provides that, when the electromagnets 110 are selectively activated by the DC, rotation of the outer shell may be caused at a desired speed and torque. It should be noted that in some examples, the annular part 122 of the outer shell may comprise one or more through-openings,

[0022] The outer shell 102 may be configured to provide one or more passages for the flow of the coolant fluid from outside of the BLDC electric motor into the cooling channels 112 or vice versa. For this purpose, the outer shell may be provided with one or more through-openings 116 that allow the coolant fluid to flow through the outer shell in the direction 113 of length of the rotor shaft and/or in a direction that is parallel to a radial direction 115 of the rotor. In an example, a through-opening may comprise orifices on opposite sides of the outer shell and connected by a passage through the outer shell. In an example, the through-openings may be provided on a surface, e.g, the top surface 132, of the outer shell that extends in a direction that is parallel to a radial direction 115 of the rotor and covers the electromagnets from one side, e.g, from the top or from the bottom. In another example, the through-openings may be provided on a surface, e g. surface of the annular part 122, of the outer shell 102 that is arranged to extend in a direction that is parallel to a longitudinal direction 113 of the rotor shaft and covers the electromagnets on one or more sides that may be arranged for example annular to the rotor shaft. The through-openings may be rectangular openings, circular openings and/or openings that are arched with respect to the rotor shaft. The outer shell may be at least partly of material, e.g. Al, that provides efficient heat transfer, whereby the outer shell may serve for cooling of the permanent magnets 111.

[0023] The one or more through-openings 116 of the outer shell 102 may be shaped for causing a fluid flow through the cooling channels 112, whereby the outer shell 102 may serve as a fan. In this way the outer shell may produce a pressure difference over the fan in the longitudinal direction 113 of the rotor shaft, and hence force, the fluid flow through the fan and into the cooling channels or out of the cooling channels. In this way, the fluid flow through the cooling channels may be supported even without a separate fan connected to the rotor shaft 104.

[0024] In an example, the one or more through-openings 116 may provide inlets for the coolant fluid on a top surface 132 of the outer shell 102. On an opposite side, e.g. a bottom side, of the top surface of the outer shell 102, a passage may be provided for guiding the coolant fluid into the cooling channels 112. The passage may be formed by annular structures 134, 136 of the outer shell 102. The annular structures may extend between the through-openings and the stator hub 108, and between the through- openings the rotor shaft 104. One of the annular structures 134 may form one or more outer edges of the through openings and one of the annular structures 136 may form one or more inner edges of the through openings. The outer and inner edges may be defined based on the radial direction 115 of the rotor. The annular structure 136 forming the one or more inner edges may extend between the through-openings and the rotor shaft 104, and the annular structure 134 forming the one or more outer edges may extend between the through-openings and the stator hub. Accordingly, the annular structures 136,134 may be annular to the rotor shaft and the annular structure 136 forming the one or more inner edges may be doser to the rotor shaft in the radial direction 115 than the annular structure 134 forming the one or more outer edges. In this way the cooling channels may be positioned between the annular structures 134, 136 in the radial direction of the rotor, A sealing structure may connect the annular structure 134 to the stator hub. A connection between the annular structure 136 and the rotor shaft may be an interference fit.

[0025] The stator hub 108 may comprise mounting positions 124,126 for bearing assemblies. The bearing assemblies mounted to the mounting positions connect the rotor shaft 104 rotatably with respect to the stator. In this way, the rotor shaft 104 may be rotated at a desired torque and speed with respect to the stator, when the electromagnets 110 are selectively activated by DC.

[0026] The mounting positions 124,126 for bearing assemblies may be separated in the longitudinal direction of the rotor shaft 104, for example the mounting positions may be arranged at the stator hub to positions that are separated in the longitudinal direction of the rotor shaft on the basis of a length of the cooling channels 112. Accordingly, the mounting positions may be separated by substantially, e.g. at most, by the length of the cooling channels, whereby the cooling channels may extend between the mounting positions for cooling both the bearing assemblies at the mounting positions and the electromagnets.

[0027] In accordance with at least some embodiments, the BLDC electric motor comprises a rotor 102 comprising a rotor shaft 104 and a stator arranged around the rotor shaft. The stator comprises a stator hub 108 comprising electromagnets 110, and cooling channels 112 extending in a direction that is paralie! to a longitudinal direction 113 of the rotor shaft and the cooling channels 112 are positioned between the rotor shaft 104 and the electromagnets 110. The positioning of the cooling channels provides that the stator may be cooled by a coolant fluid flowing through the cooling channels.

[0028] In accordance with at least some embodiments, the rotor, comprises an outer shell 102 connected to the rotor shaft 104 and the outer shell is configured to extend in a direction that Is parallel to a radial direction 115 of the rotor on one side of the electromagnets 110 for covering the electromagnets 110. The outer shell comprises one or more through-openings 116 for passage of fluid between surroundings of the BLDC electric motor and the cooling channels 112. In this way the outer shell allows a coolant fluid to pass through the outer shell, while also covering the electromagnets and the permanent magnets 111 against particles carried by the coolant fluid.

[0029] In accordance with at least some embodiments, the one or more through- openings 116 are positioned between the electromagnets 110 and the rotor shaft 104 in a radial direction of the rotor. The positioning of the through-openings provides that the electromagnets may be covered by a surface of the outer shell that extends in a direction that is parallel to the radial direction 115 of the rotor, while a coolant fluid may be passed through the outer shell.

[0030] In accordance with at least some embodiments, the one or more through- openings 116 are arranged annularly with respect to the rotor shaft 104. In this way a flow of coolant fluid may be supported to cooling channels that are arranged annularly with respect to the rotor shaft. Provided the cooling channels are also arranged annularly with respect to the rotor shaft 104 the annular arrangement of the through-openings 116 provides that the coolant fluid may enter the cooling channels 112 via the through- openings 116 the shortest way.

[0031] In accordance with at least some embodiments, the one or more through- openings 116 are rectangular openings, circular openings and/or openings that are arched with respect to the rotor shaft 104. The shapes of the openings may be selected to support guiding a coolant fluid to the cooling channels.

[0032] In accordance with at least some embodiments, the BLDC electric motor comprises sealing structures 118,120 between the stator hub 108 and the outer shell, and the electromagnets 110 are enclosed within a space 130 formed by the outer shell and the stator hub 108 and the sealing structures 118,120. In this way contamination of the electromagnets 110 and the permanent magnets 111 by particles carried by a fluid flow may be prevented.

[0033] In accordance with at least some embodiments, the sealing structures 118,120 comprise one or more shaft sealings, one or more non-contact-sealings, for example one or more labyrinth sealings, and/or one or more bearing assemblies. The sealing structures provide that a mechanical friction to a rotational movement of the stator hub and the outer shell is small or the mechanical friction may be prevented. It should be noted that the sealing structures of the BLDC electric motor may comprise different types of sealing structures, for example a non-contact sealing structure, for example a labyrinth seal, and a contact sealing structure, for example a shaft sealing or a bearing assembly.

[0034] In accordance with at least some embodiments, the sealing structures 118,120 comprise a first sealing structure 118 and a second sealing structure 120, and the first sealing structure 118 is arranged at first positions, at the stator hub 108 and at the outer shell, radially outwards from the cooling channels 112 and the second sealing structure 120 is arranged at second positions, at the stator hub 108 and at the outer shell, separated in the longitudinal direction 113 of the rotor shaft 104 and/or in a direction that is transverse to the longitudinal direction 113 of the rotor shaft 104 from the first positions. At least some positions of the sealing structures provide that at least one of the sealing structures may be positioned away radially away from the cooling channels, whereby exposure of the sealing structure to particles of the coolant fluid may be reduced. On the other hand at least some positions of the sealing structures provide that the outer shell may cover the electromagnets 110 on opposite sides in the longitudinal direction 113 of the rotor shaft,

[0035] In accordance with at least some embodiments, the outer shell comprises an annular part 122 arranged to extend in a direction that is parallel to the longitudinal direction 113 of the rotor shaft 104 for annularly covering at least a part of the stator and at least one of the second positions comprise a position at the annular part 122 of the outer shell. Sealing structure at the annular part provides that exposure of the sealing structure to particles of the coolant fluid may be reduced due to the location of the sealing structure being away from the cooling channels in a radial direction 115 of the rotor.

[0036] In accordance with at least some embodiments , the cooling channels 1 12 extend through the stator hub 108 in the longitudinal direction 113 of the rotor shaft 104.

I n this way the cooling channels do not need space from around the electromagnets and structure of the BLDC electric motor may be compact,

[0037] In accordance with at least some embodiments, wherein the cooling channels 112 have circular cross-sections, rectangular cross-sections and/or arched crosssections. The cross-sections of the cooling channels provide efficient cooling depending on implementation of the BLDC electric motor.

[0038] In accordance with at least some embodiments, the cooling channels 112 are arranged annularly with respect to the rotor shaft 104, In this way efficient heat transfer from the electromagnets 110 into a coolant fluid flowing through the cooling channels may be supported.

[0039] In accordance with at least some embodiments, the stator hub 108 comprises mounting positions 124,126 for bearing assemblies and the cooling channels 112 extend between the mounting positions 124,126 and the electromagnets 110. In this way the position of the cooling channels support cooling of the bearing assemblies,

[0040] In accordance with at least some embodiments, the BLDC electric motor comprises a heat sink 128 arranged on a surface of the stator hub 108. The heat sink provides additional cooling, which may be needed depending on implementation of the BLDC electric motor.

[0041] In accordance with at least some embodiments, the BLDC electric motor comprises a fan arranged at one end of the cooling channels 112. The fan provides controlling movement of the coolant fluid through the cooling channels.

[0042] In an example, the outer shell 102 may serve as the fan or a separate fan may be connected to the rotor shaft 104. The one or more through-openings 116 of the outer shell 102 are inclined with respect to at least one of: the direction that is parallel to a longitudinal direction 113 of the rotor shaft; the direction that is parallel to a radial direction 115 of the rotor; and a direction of rotation of the rotor shaft 104, In this way the through-openings 116 may be shaped for causing a fluid flow through the cooling channels 112, whereby the outer shell 102 may serve as a fan. The cross-sections of the through-openings may be rectangular openings, circular openings and/or openings that are arched with respect to the rotor shaft. In an example, an inclination of a through- opening 116 may be achieved by deflecting a position of one end of the through-opening at one side of the outer shell with respect to a position of an opposite end of the through- opening 116 at the opposite side of the outer shell. Accordingly, the opposite ends of the through-opening may be deflected with respect to each other in at least one of the longitudinal direction 113 of the rotor shaft, the radial direction 115 of the rotor and the direction of rotation of the rotor shaft. In an example, the deflection may be achieved by drilling the though-opening through the outer shell at an inclined angle with respect to at least one of the longitudinal direction 113 of the rotor shaft and the radial direction 115 of the rotor.

[0043] Fig. 4 illustrates a handheld tool in accordance with at least some embodiments. The handheld tool 200 comprises a BLDG electric motor 100 In accordance with at least some of the embodiments described with Fig. 1 , Fig. 2 and Fig. 3. In the following the handheld tool is described with reference to Fig. 4 and the items described with Figs. 1 to 3. The handheld tool is illustrated by a cross-section of the handheld tool in a longitudinal direction 113 of a rotor shaft of the BLDC electric motor 100. Accordingly , the handheld tool and the BLDG electric motor therein may be powered by DC electricity. The DC may be obtained from controller that controls switching of DC current, e.g. from an inverter, to the electromagnets 110. The DC fed by the controller to each of the electromagnets may be Pulse Width Modulated (PWM) DC. In this way the controller may control the speed and torque of the rotor shaft 104. The controller may be implemented in software using a microcontroller or microprocessor computer, or may alternatively be implemented using analog or digital circuits.

[0044] The handheld tool 200 may comprise openings 204 arranged on a housing of the handheld tool for allowing an air flow to enter the housing for cooling the BLDC electric motor. The air flow may include particles such as dust and debris, and therefore the BLDC electric motor should be protected against the particles such that accumulation of the particles into the BLDC electric motor and overheating caused by the accumulated particles and eventual failures of the BLDC electric motor caused by excess heating could be prevented. In an example, the housing of the handheld tool 200 may comprise openings at one or more surfaces of the housing. The housing may comprise handie portion 208 that may be dimensioned for allowing the handie to be manually gripped by a smgie hand power grip. The housing may further comprise a body portion 210 that houses the BLDC electric motor. The openings may be provided at both the body portion and the handle portion. Both the handle portion and the body portion may comprise a surface at which one or more openings 204 may be provided for allowing an air flow to enter the housing. Having openings at both the handle portion and body portion support airflow in situations, where one of them is blocked, which may temporarily happen during use of the handheld tool .

[0045] The air flow is illustrated by thick arrows in Fig. 4. The air flow enters the housing via the openings 204. Inside the housing, the airflow is guided to the BLDC electric motor 100 and particularly to the through-openings at the outer shell 102. At the BLDC electrio motor, the air flow may enter the cooling channels 112 and cool down the BLDC electric motor. The air flow that exits the cooling channels is exhaust air. The exhaust air may be guided to an exhaust outlet 206 for removing the exhaust air from the housing. In this way the air that has warmed up by the BLDC electric motor may be removed and fresh air may be drawn inside the handheld tool for cooling the BLDC motor. The BLDC electric motor 100 may comprise a fan 207 for drawing fresh air into the cooling channels 112 and removing the used air out via the exhaust outlet.

[0046] In accordance with at least some embodiments, wherein the BLDC motor 100 is configured for driving tools and/or accessories of the handheld tool. Examples of the tools and accessories comprise at least a backing pad, polishing pad, sanding pad, a grinding disc, a drill bit, a screwdriver bit, a chisel and a circular saw blade. In an example, a rotor shaft 104 of the BLDC electric motor may comprise a thread for attaching tools and/or accessories to the rotor shaft 104.

[0047] In accordance with at least some embodiments, the handheld tool 200 is a polisher, a sander, a grinder, a screwdriver, an impact driver, a drill, a circular saw, chain saw or jack hammer.

[0048] Fig. 5 and Fig. 6 illustrate examples for a passage of fluid between surroundings and cooling channels of an electric motor and a fan arranged to control a direction of the fluid via the cooling channels in accordance with at least some embodiments. Fig. 5 is a perspective view of the electric motor 500 and Fig. 6 is a cross-section of the electric motor in a longitudinal direction 113 of a rotor shaft 104 of the electric motor. The electric motor may be at least partly in accordance with the electric motor described with Fig. 1, Fig. 2 and Fig. 3. The electric motor 500 comprises a stator arranged around a rotor shaft 104, an outer shell connected to the rotor shaft 104 and cooling channels 112 positioned between the rotor shaft 104 and electromagnets 110 of the stator.

[0049] A passage for fluid may be provided by one or more through-openings 524 arranged to the outer shel! in a radial direction 115 of the rotor. In this way a flow of fluid in the radial direction 115 through the outer shell may be provided. More particularly, the through-openings may serve for passages of fluid into the cooling channels 112 inside the outer shell and/or for passages of fluid from the cooling channels 112 out of the outer shell.

[0050] In an example, a through-opening 524 may comprise orifices on opposite sides of the outer shell and connected by a passage through the outer shell One of the orifices may be provided on an outer surface of the outer shell arranged to extend in a direction that is parallel to the longitudinal direction 113 of the rotor shaft, and one of the orifices may be provided on an inner surface of the outer shell, whereby the passage of the through-opening may provide a flow of fluid in the radial direction 115 through the outer shell.

[0051] In an example, the passage of the through-opening 524 may be a radial passage inside the outer shell. The radial passage may extend between a stator hub 108 of the stator and a top surface 532 of the outer shell and between a surface of the annular part 522 and the cooling channels 112. The radial passage may have a top wall 526 and a bottom wall 528 that are separated in the longitudinal direction 113 of the rotor shaft. The top wall may be formed by the top surface 532 of the outer shell and the bottom wall may be formed by a radial surface of the outer shell, located below the top surface In the longitudinal direction of the rotor shaft and separated by a distance from the top surface in the longitudinal direction 113 of the rotor shaft. The bottom wall is configured to separate the electromagnets 110 from the fluid flowing inside the radial passage. The top wall may extend in one or more sections between the surface of the annular part 522 and the rotor shaft 104. The bottom wall may extend in one or more sections between the surface of the annular part 522 and the stator hub.

[0052] Orifices of the one or more through-openings may comprise annular structures 534, 536 for connecting the radial passages to the stator hub and the rotor shaft. The annular structures 534, 536 may be annular to the rotor shaft and the annular structure 536 may be closer to the rotor shaft in the radial direction 115 than the annular structure 534. In this way the cooling channels may be positioned between the annular structures 534, 536 in the radial direction of the rotor. A sealing structure 118 may connect the annular structure 534 to the stator hub. A connection between the annular structure and the rotor shaft may be an interference fit.

[0053] A fan 502 may be arranged at one end of the cooling channels 112 for controlling a direction of fluid flow via the cooling channels. The fan 502 may be located at a bottom end of the cooling channels, below the stator hub 108, In the longitudinal direction 113 of the rotor shaft. The fan may be configured to be rotated by the rotor shaft 104 for producing a pressure difference over the fan in the longitudinal direction 113 of the rotor shaft, and hence force, the fluid flow through the fan and into the cooling channels or out of the cooling channels.

[0054] In an example, the fan 502 may be connected to the rotor shaft 104 or an output shaft driven by the rotor shaft, whereby the fan may be rotated directly or indirectly by the rotor shaft.

[0055] Fig. 7 and Fig. 8 illustrate an outer shell suitable for serving as a fan in accordance with at least some embodiments. Fig. 7 is a perspective view of the outer shell and Fig.8 is a cross-section of a part of the outer shell. The outer shell 702 may be used in a BLDC electric motor described at least in some embodiments described herein. In the following the outer shell is described with reference to at least some of the items described with Fig. 1.

[0056] The outer shell comprises a surface 732, e.g. a top surface or outer surface, that may be connected to a rotor shaft 104. When connected to the rotor shaft 104, the surface 732 may extend at least in the radial direction 115 of the rotor on one side of the electromagnets 110. The outer shell comprises through-openings 716 that are inclined with respect to at least one of: the direction that is parallel to a longitudinal direction 113 of the rotor shaft; the direction that is parallel to a radial direction 115 of the rotor; and a direction 706 of rotation of the rotor shaft 104. In this way the through-openings 716 may be shaped for causing a fluid flow through the cooling channels 112, whereby the outer shell 102 may serve as a fan.

[0057] In an example, the Inclination of the through-openings 716 causes that positions of opposite ends of the through openings are deflected with respect to each other in the radial direction 115 and/or the longitudinal direction 113, In an example, an inclination of a through-opening 716 may be achieved by deflecting a position of one end of the through-opening at one side of the outer shell, e.g. at the outer surface 732, with respect to a position of an opposite end of the through-opening 716 at the opposite side of the outer shell, e.g. at an inner surface 734 of the outer shell. Accordingly, the through- opening may comprise an orifice at one end at a position “POST’ on the outer surface 732 and the through -opening may comprise another orifice at the other end at a position “POST on the inner surface 734 that is on the opposite side of the of the outer shell than the outer surface 732. Examples of the inclination are illustrated by angles a, p, 6 and y at different sides of the through-opening in the direction 706 of rotation of the rotor shaft. The angles a and p are angles with respect to the longitudinal direction 113 and the angles 6 and y are angles with respect to the radial direction 115. It should be noted that the inclination of the through-opening may be defined further with respect to the direction 706 of rotation of the rotor shaft. In an example, angles a and p of the through-opening with respect to the longitudinal direction may be different at different sides of the through- opening in the direction 706 of rotation. Similarly, angles 6 and y of the through-opening with respect to the radial direction may be different at different sides of the through- opening in the direction 706 of rotation.

[0058] Fig. 9 illustrates a handheld tool equipped with a fan that is arranged co- centrically to the rotor shaft and rotatable with respect to the rotor shaft fan in accordance with at least some embodiments. The handheld tool 290 may be in accordance with the handheld tool 200 described with Fig. 4 with a difference that the handheld tool 290 comprises a drive system 902 for the fan 207. Accordingly, thanks to the drive system, instead of the fan being fixed to be directly driven by the rotor shaft 104, the drive system provides that the fan may be driven indirectly by the rotor shaft. In this way the fan may be rotated at different speed than the rotor shaft, whereby a sufficient cooling for the electric motor may be provided even at low speeds of the rotor shaft.

[0059] The handheld tool 290 comprises an electric motor, for example a brushless direct current, BLDC, electric motor 100, described with Fig. T The electric motor comprises a rotor and a stator and a fan 207. The rotor comprises an outer shell 102 arranged annular to the stator and said outer shell is connected to a rotor shaft 104, whereby the outer shell may be rotated at the same speed with the rotor shaft. The fan 207 is arranged co-centrically to the rotor shaft and rotatable with respect to the rotor shaft, in this way the fan and the rotor shaft may have a common axis of rotation but the fan and the rotor shaft may be rotated at different speeds.

[0060] The handheld tooi 290 comprises the drive system 902 for the fan 207, the drive system comprising means for driving the drive system by a rotation of the outer shell and means for driving the fan by the drive system, and the drive system is configured to transform the rotation of the outer shell 102 to a rotation of the fan 207 with a drive ratio of 1 :F, where F is higher than 1. The drive ratio 1:F, where F is higher than 1 , provides that the fan may be rotated at a speed that is higher than a rotational speed of the rotor shaft. Examples of the means comprise at least drive surfaces, belts, gears, pulleys, wheels and one or more transmission shafts that may be operatively connected with the outer shell and the fan for transforming the rotation of the outer shell 102 to a rotation of the fan 207. Therefore, the drive system provides that the outer shell 102, fan 207 and the rotor shaft 104 are operatively connected, or linked, so that if any of the outer shell 102, fan 207 and the rotor shaft 104 is rotated manually the other components will move and not be stationary.

[0061] In an example, the drive ratio 1 :F may be provided by the fan 207 comprising a drive surface 916, a gear connected to the fan or a wheel connected to the fan for engaging with the drive system 902 and transferring a rotation of the outer shell 102 via the drive system to a rotation of the fan. The drive surface, the gear or the wheel may have a diameter, or radius, in a radial direction 115 of the rotor, e.g. the outer shell 102, and the diameter may be smaller than a diameter of the outer shell 102 in the radial direction 115 of the rotor. In this way the rotation of the outer shell 102 may be transformed to the rotation of the fan 207 with the drive ratio 1 :F.

[0062] In an example in accordance with at least some embodiments, the drive surface 916 of the fan 207 is provided at a sleeve that extends in a longitudinal direction 113 of the rotor shaft 104 around the rotor shaft 104.

[0063] In an example, the means for driving the drive system by a rotation of the outer shell 102 may be configured to operatively connect the outer shell and the drive system for transforming the rotation of the outer shell to a rotational movement at the drive system.

[0064] In an example, the means for driving the fan 207 by the drive system may be configured to operatively connect the drive system and the fan for transforming the rotational movement at the drive system to the rotation of the fan. [0065] In an example, the fan 207 is arranged co-centrically to the rotor shaft 104 and rotatable with respect to the rotor shaft by a bearing arrangement. The fan may be attached to the rotor shaft by the bearing arrangement that is arranged at a mounting position provided at the fan. Accordingly, the bearing arrangement at the mounting position provides that the fan may be supported rotatable with respect to the rotor shaft. In this way the fan is rotatable around the rotor shaft even if the rotor shaft is not rotated. The fan is co~centric with respect to the rotor shaft, whereby the center points of rotation of the rotor shaft and the fan are aligned. In other words the fan and the rotor shaft are rotated around a common axis of rotation.

[0066] For example, the drive system may comprise the gears, pulleys and/or wheels connected to the one or more transmission shafts 910 that extend in a direction 123 parallel to the longitudinal direction 113 of the rotor shaft for operatively connecting with the outer shell and the fan and for transforming the rotation of the outer shell 102 to a rotation of the fan 207. In an example, the one or more transmission shafts 910 may be rotatable about axes defined by their respective longitudinal directions and operatively connected by belts to a drive surface at the fan and a drive surface at the outer shell, whereby the rotation of the outer shell 102 may be transferred to a rotation of the fan 207. For example, a pulley connected to a transmission shaft 910 may be connected to the drive surface provided at the outer shell or at the fan by a belt for transferring a rotational movement. It should be noted that instead of connecting the drive surfaces at the outer shell and at the fan by belts to the one or more transmission shafts, a separate gear or a wheel may be connected to the outer shell and/or the fan for transferring the rotational movement. For example, a gear or a wheel connected to a transmission shaft 910 may be connected directly to the gear or a wheel at the outer shell or to the gear or a wheel at the fan, for transferring the rotational movement.

[0067] In an example, the drive system may be provided with a single transmission shaft 910, whereby at least one gear, pulley 912 and/or wheel may be connected to the transmission shaft for transferring a rotational movement of the outer shell 102 to the transmission shaft 910, and at least one further gear, pulley 914 and/or wheel may be connected to the transmission shaft 910 for transferring a rotational movement of the transmission shaft to the fan 207. In an example, the drive system may comprise one or more intermediary gears between the transmission shaft 910 and the outer shell 102 of the rotor and/or one or more intermediary gears between the fan 207 and the transmission shaft 910. The one or more intermediary gears and/or wheels may provide that a direction of rotation transferred from the outer shell to the transmission shaft 910 and from the transmission shaft to the fan may be controlled. For example, the number and arrangement of the intermediary gears and/or wheels may cause that the direction of rotation of the fan 207 is reversed with respect to the direction of rotation of the rotor. The intermediary gears and wheels may be connected to one or more respective transmission shafts that may be arranged to extend in a direction 123 parallel to the longitudinal direction 113 of the rotor shaft and between the transmission shaft 910 and the rotor shaft 104 in the radial direction 115 of the rotor shaft 104.

[0068] In an example, the fan extends in the radial direction 115 of the rotor shaft 104 away from the rotor shaft. The fan may comprise e.g. one or more blades that extend radially away from the rotor shaft, whereby a rotation of the fan may cause a fluid flow, e.g. airflow, for cooling the electric motor. The amount of the fluid flow is dependent on the dimensions of the blades in the radial direction 115 and in the longitudinal direction 113, a rotational speed of the fan and a number of the blades.

[0069] In an example in accordance with at least some embodiments, the drive system comprises at least one transmission shaft 910 and

- one or more belts 904, gears, pulleys 912 and/or wheels for driving the at least one transmission shaft by the outer shell of the rotor, and/or

- one or more belts 908, gears, pulleys 914 and/or wheels for driving the fan by the at least one transmission shaft.

[0070] In an example the at feast one transmission shaft 910 may be supported to a position inside the body portion 210 that houses the electric motor 100. Accordingly, the at least one transmission shaft may be connected by a first arrangement of one or more belts 904, gears, pulleys 912 and/or wheels to the outer shell 102 and by a second arrangement of one or more belts 908, gears, pulleys 914 and/or wheels to the fan 207, whereby the fan may be driven indirectly by the rotor shaft.

[0071] In an example the outer shell 102 may have a drive surface 903 and a belt 904 is arranged to run around the outer shell on the drive surface and around a pulley 912 connected to the at least one transmission shaft 910. Also the pulley may have a drive surface. In this way the belt may transform the rotation of the outer shell to a rotational movement of the at least one transmission shaft 910. [0072] In an example a belt 908 is arranged to run around a pulley 914 connected to the at least one transmission shaft 910 and a drive surface 916 of the fan 207. In this way the fan may transform the rotational movement of the at least one transmission shaft to a rotation of the fan. The drive surface of the fan may be provided at a sleeve that extends in a longitudinal direction 113 of the rotor shaft around the rotor shaft. The drive surface may be located below the stator hub 108 and above one or more blades of the fan. The sleeve may be integrated to the fan or the sleeve may be a separate part that is fixed to the fan. The fan comprising an integrated sleeve may be manufactured by e.g. 3D~ printing. The sleeve may comprise a mounting position for a bearing arrangement, whereby the fan may be supported rotatable with respect to the rotor shaft by the bearing arrangement.

[0073] In an example a pulley 912,914, a fan 207 and/or an outer shell 102 may have a drive surface. Drive surfaces of the outer shell and the pulley 912 connected by a belt 904 may be adapted to have a sufficient friction or to interlock with the belt 904 arranged on the drive surfaces such that a rotational movement may be transferred by the belt between the pulley and the outer shell. Similarly, drive surfaces of the fan and the pulley 914 connected by a belt 908 may be adapted to have a sufficient friction or to interlock with the belt 908 arranged on the drive surfaces such that a rotational movement may be transferred by the belt between the pulley and outer shell. At the outer shell the drive surface 903 may be at the annular part 122 and at the at least one transmission shaft 910 the drive surface may be at the pulley 912, whereby the belt 904 arranged on the drive surfaces of the outer shell and the at least one transmission shaft may efficiently transfer the rotation of the rotor shaft 104 to the at least one transmission shaft. At the fan, the drive surface 916 may be at the sleeve that extends in the longitudinal direction 113 of the rotor shaft around the rotor shaft and at the at least one transmission shaft the drive surface may be at the pulley 914, whereby the belt 908 arranged on the drive surfaces of the fan and the at least one transmission shaft may efficiently transfer the rotation of the at least one transmission shaft to the fan for causing a fluid flow for cooling the electric motor. Examples of the drive surfaces comprise knurled surfaces, surfaces with toothing and/or surfaces made of material that provides sufficient friction for preventing slippage of the drive surface. An example of the material is rubber.

[0074] In an example the belt 904,908 may be a rubber belt that has a reinforced structure based on fiberglass. Alternatively or additionally, the belt may be a grooved belt, e.g. a multi-grooved belt. Accordingly, the belt may have one more grooves that extend in a running direction of the belt, whereby travelling of the belt in a direction that is parallel to the longitudinal direction of the rotor shaft may be prevented. Preferably, the pulleys used in connection with the belts have matching profiles with the belts, e.g. matching with the groove structure of the belts.

[0075] In an example of the drive system, the transmission shaft comprises two pulleys 912,914, e.g. an upper pulley and a lower pulley, that are separated in a direction 123 that is parallel to the longitudinal direction 113 of the rotor shaft. Accordingly, the transmission shaft extends in the direction 123 that is parallel to the longitudinal direction 113 of the rotor shaft and the pulleys are separated in the longitudinal direction of the rotor shaft 113. The upper pulley is connected by a drive belt to the outer shell 102 and the lower pulley is connected by a belt 908 to the fan, whereby the fan may be indirectly driven by the rotor shaft.

[0076] In an example, instead of connecting the transmission shaft 910 by pulleys and belts to the outer shell and the fan, the pulleys and belts may be at least partially replaced by wheels and/or gears at the transmission shaft 910, rotor and the fan. For example, the transmission shaft 910 may have a wheel or gear, e.g. an upper wheel or upper gear, that is configured to engage a drive surface at the rotor, e.g, at the outer shell 102, whereby the rotation of the rotor shaft may be communicated to a rotation of the transmission shaft. For example, the transmission shaft 910 may have a wheel or gear, e.g, a lower wheel or lower gear, that is configured to be rotated with the transmission shaft and to engage a drive surface 916 at the fan 207, whereby the rotation of the transmission shaft may be communicated to a rotation of the fan. The drive surface at the fan may be provided e.g. at a side of the fan towards the stator hub 108. The upper wheel/gear and lower wheel/gear may be separated in a direction 123 that is parallel to the longitudinal direction 113 of the rotor shaft. Accordingly, the transmission shaft extends in the longitudinal direction of the rotor shaft 113 and the upper and lower wheels/gears are separated in the longitudinal direction of the rotor shaft 113. Drive surface of the fan 207 configured to engage a gear may comprise e.g. toothing for transferring a rotational movement from the transmission shaft to the fan. Drive surface of the outer shell 102 configured to engage a gear may comprise e.g. toothing for transferring a rotational movement from the outer shell to the transmission shaft. Drive surface of the fan 207 configured to engage a wheel connected to the transmission shaft may comprise material, e.g. rubber, that provides sufficient friction for preventing slippage of the wheel on the drive surface for transferring a rotationai movement from the transmission shaft to the fan. Drive surface of the outer shell 102 configured to engage a wheel connected to the transmission shaft may comprise material, e,g. rubber, that provides sufficient friction for preventing slippage of the wheel on the drive surface for transferring a rotational movement from the outer shell to the transmission shaft. Instead of the drive surface, the fan and/or the outer shell may be connected a separate wheel or gear for engaging with a wheel or gear at the transmission shaft for transferring a rotational movement to the transmission shaft or from the transmission shaft.

[0077] In an example, the drive ratio may refer to a ratio of rotational speeds of the outer shell 102 and the fan 207, The drive ratio may be formed based on a transmission of the rotation of the outer shell by the one or more belts, gears, pulleys and/or wheels to a rotation of the transmission shaft 910, and a transmission of the rotation of the transmission shaft by the one or more belts, gears, pulleys and/or wheels, to a rotation of the fan 207.

[0078] In an example in accordance with at least some embodiments, the drive system comprises a first pulley 912 configured to be driven by a first belt 904 connecting the first pulley 912 and the outer shell, and a second pulley 914 configured to drive a second belt 908 connecting the second pulley 914 and the fan 207, The first pulley and the second pulley may be connected to a transmission shaft of the drive system, whereby the rotational speed T of the outer shell may be transformed to a rotational speed of the transmission shaft ‘E’ and the rotational speed of the transmission shaft ‘E’ may be transformed to the rotation speed T' of the fan,

[0079] In an example, diameters of the first pulley 912 and the second pulley 914 may the same. In another example, the diameters of the first pulley 912 and the second pulley 914 may be different. The different diameters of the first pulley and the second pulley provide adjusting the drive ratio 1 :F of transforming a rotation of the outer shell 102 to a rotation of the fan 207, Therefore, different sizes of pulleys give a different ratio 1:F.

[0080] In an example in accordance with at least some embodiments, the at least one of the first belt 904 and the second belt 904,908 of the drive system is crossed. The crossed belt provides that a direction of rotation can be changed. For example, if the first belt 904 is crossed, directions of rotation of the outer shell 102 and the transmission shaft 910 are opposite. Consequently, the rotation of the transmission shaft 910 is transferred by the second belt to the fan 207 without changing the direction of rotation, whereby directions of rotation of the fan 207 and the transmission shaft 910 are the same. Similarly, if the second belt 908 is crossed, directions of rotation of the transmission shaft 910 and the fan 207 are opposite. Accordingly, the rotation of the outer shell 102 is transferred by the first belt 904 to the transmission shaft 910 without changing the direction of rotation, whereby directions of rotation of the transmission shaft 910 and the outer shell 102 are the same. With crossing the belt(s) one can get contact surface of the belt(s) on the pulley(s) may be increased and thus it is more unlikely that the belt(s) slips. It is also possible to reduce gyroscopic forces by having two bodies, e.g. two of the outer shell, the transmission shaft and the fan, of the system rotating in opposite directions. [0081] In an example of reducing the gyroscopic forces by crossing a belt, let us consider that the electric motor 100 has an inertia, h. When the outer shell 102 is rotating with an angular velocity cm it produces angular momentum, b, according to

The direction of b is perpendicular to the radius of the rotor shaft and longitudinal direction 113 of the rotor shaft 104. Similarly, the fan 207 has an angular momentum, 12 which takes the form (2), where F is the drive ratio, i.e. gearing ratio. If the fan and the outer shell 102 are rotating in opposite directions the value of F is negative and the net angular momentum L is achieved by a sum of the Li and U, or a subtraction of absolute values of Li and Ls. Determining the net angular momentum by subtraction as follows

The net angular L momentum and the gyroscopic forces are reduced which stabilizes the electric motor 100. Therefore, maneuverability of a handheld tool comprising the electrio motor is improved.

[0082] In an example in accordance with at least some embodiments, a speed of the rotor shaft is 700 to 2500 revolutions per minute (rpm) and the drive ratio is for example 1 :3,25. In this way the speed of the fan may be higher than the speed of the rotor shaft. It should be noted that the torque of the rotor shaft transferred to the fan is also scaled, apart from transmission losses, based on the drive ratio 1:F.

[0083] Fig. 10 illustrates an example of a crossed belt for a drive system in accordance with at least some embodiments. The example is illustrated utilizing the context of a handheld tool comprising an electric motor 100 and a fan 207 described with Fig, 9. In Fig. 10 the crossed belt is the belt 904 that connects an outer shell 102 and a pulley 912 of a transmission shaft 910, The belt 904 is crossed in a longitudinal direction 113 of the rotor shaft and in a radial direction 115 of the rotor, whereby a direction of rotation 1008 of the pulley may be opposite with respect to a direction of rotation 1006 of the outer shell 102. Additionally, crossing of the belt 904 provides that a contact surface of the belt with a drive surface 903 of the outer shell and a contact surface of the belt with a drive surface of the pulley is increased which reduces the likelihood that the belt slips during operation. It should be noted that the examples may be applied also to the belt 908 that connects the fan to the pulley 914 at the transmission shaft,

[0084] In the first view 1002 of Fig. 10, the crossed belt is illustrated as a sideview, where a viewing plane extends substantially parallel to the longitudinal direction 113 of the rotor shaft. In the second view 1004 of Fig. TO, the crossed belt is illustrated as a top view, where a viewing plane extends substantially transversely to the longitudinal direction 113 of the rotor shaft. In the first view and the second view the belt 904 is arranged around the outer shell 102 and the pulley 912. Referring to the first view, the belt extends in a running direction (illustrated by arrow on the belt) of the belt from a front side of the outer shell towards the pulley 912, to the back side of the pulley. Following the belt in the running direction of the belt, at the pulley, the belt goes around the pulley from the back side of the pulley to the front side of the pulley and further to the outer shell 102, to the back side of the outer shell. Accordingly, the front side refers here to the side of the outer sheil/pulley seen in the sideview and the back side of the refers here to the side of the outer sheil/pulley that cannot be seen in the sideview. Referring to the second view 1004, the belt extends in the running direction (illustrated by arrow extending parallel to the belt) of the belt from a lower side of the outer shell towards the pulley 912, to an upper side of the pulley. Following the belt in the running direction of the belt, at the pulley, the belt goes around the pulley from the upper side of the pulley to the lower side of the pulley and further to the outer shell 102, to the upper side of the outer shell. Accordingly, the lower side and upper side refer here to opposite the sides of the outer sheil/pulley in the direction of the orientation the drawing.

[0085] Figs, 11 , 12 and 13 illustrate examples of drive systems in accordance with at least some embodiments. The drive systems are described with reference to items described in Fig. 9, where applicable, and comprise one or more gears, pulleys 912 and/or wheels for driving the transmission shaft 910 by the outer shell 102 of the rotor, and/or one or more gears, pulleys 914 and/or wheels for driving the fan 207 by the transmission shaft 910.

[0086] The examples 1102, 1104, 1106, 1108, 1110, 1140 of drive systems are illustrated by views that illustrate parts of the drive systems as seen from a top or from a bottom, where the viewing direction is parallel to the longitudinal direction 113 of the rotor shaft and perpendicular to the radial direction 115 of the rotor. Each of the examples is illustrated by two views ‘A ^! and ‘B’, where the ‘A’ illustrates means for driving the drive system by a rotation of the outer shell and the ‘B’ illustrates means for driving the fan 207 by the drive system. It should be noted that the views ‘A’ and ^! B’ are shown side-by-side for illustrative purposes only and in practice the parts shown in each view are arranged on the rotor shaft and the transmission shaft 910, whereby they are stacked similar to the example of a drive system for the fan described in Fig. 9, where the fan 207 is arranged co-centrica I ly to the rotor shaft 104 and rotatable with respect to the rotor shaft 104, and the drive system comprises a first pulley 912 configured to be driven by a first belt 904 connecting the first pulley 912 and the outer shell 102, and a second pulley 914 configured to drive a second belt 908 connecting the second pulley 914 and the fan 207. [0087] In views ‘A’ in the examples 1102,1106. the outer shell 102 is configured to operate as a gear. The outer shell may comprise e.g. toothing on a surface 1103, e.g, a drive surface, towards the transmission shaft 910. Alternatively a separate gear is arranged co-centrically with the rotor shaft and connected to the outer shell. The transmission shaft may comprise a gear 1112 that is in contact with the outer shell, e.g. at the surface that comprises the toothing, or the separate gear, whereby a rotation of the outer shell is transferred to a rotation of the transmission shaft. Therefore, a direction of rotation 1118 of the gear, and the transmission shaft, is opposite with respect to a direction of rotation 1116 of the outer shell 102, whereby gyroscopic forces are reduced which stabilizes the electric motor 100 and improves maneuverability of a handheld tool comprising the electric motor.

[0088] In view ‘B’ of the example 1102, the fan 207 may comprise e.g. toothing on a surface 1105, e.g. a drive surface, towards the transmission shaft 910, or a separate gear may be arranged co-centrically to the rotor shaft and connected to the fan. The transmission shaft may comprise a gear 1114 that is in contact with the fan, e.g. at the surface that comprises the toothing, or the separate gear, whereby a rotation of the gear 1114, and the transmission shaft, is transferred to a rotation of the fan. Therefore, a direction of rotation 1 128 of the gear is opposite with respect to a direction of rotation 1126 of the fan. Referring to both views ‘A’ and ‘B’ of the exampie 1102; the gears 1112, 1114 are both connected to the transmission shaft, whereby the gear 1114 is rotated with the gear 1112. Therefore, the direction of rotation of the fan 207 is the same as the direction of rotation of the outer shell 102.

[0089] In view ‘B ^! of the example 1106, the transmission shaft 910 may comprise a pulley 914 and the fan 207 may be connected to the pulley by a belt 908. Therefore, a direction of rotation 1130 of the pulley 914, and the transmission shaft, is the same with respect to a direction of rotation 1126 of the fan. Referring to both views ‘A’ and ^l B ^! of the example 1106, the gear 1112 and the pulley 914 are both connected to the transmission shaft, whereby the pulley 914 is rotated with the gear 1112. Therefore, the direction of rotation of the fan 207 is the same as the direction of rotation of the pulley 914. However, since the direction of rotation 1118 of the gear 1112 is opposite with respect to the outer shell also the direction of rotation of the fan is opposite with respect to the outer shell, whereby gyroscopic forces are reduced which stabilizes the electric motor 100 and improves maneuverability of a handheld tool comprising the electric motor.

[0090] In view B’ of the example 1104, the fan 207 may comprise e.g. toothing on a surface 1105 towards the transmission shaft 910, or a separate gear may be arranged co-centrically to the rotor shaft and connected to the fan, for driving the fan. The transmission shaft may comprise a gear 1114 that is in contact with the fan, e.g. at the surface that comprises the toothing, or the separate gear, whereby a rotation of the gear 1114. and the transmission shaft, is transferred to a rotation of the fan. Therefore, a direction of rotation 1128 of the gear 1114, and the transmission shaft, is opposite with respect to a direction of rotation 1126 of the fan. Referring to both views 'A' and ^! B’ of the example 1104, the gears 1112,1114 are both connected to the transmission shaft, whereby the gear 1114 is rotated with the gear 1112. Since the direction of rotation 11 18 of the gear 1112 is the same with the direction of rotation 1116 of the outer shell 102, the direction of rotation 1126 of the fan 207 is opposite with respect to the direction of rotation of the outer shell, whereby gyroscopic forces are reduced which stabilizes the electric motor TOO and improves maneuverability of a handheld tool comprising the electric motor. [0091] In view ‘B* of the example 1108, the transmission shaft 910 may comprise a pulley 914 and the fan 207 may be connected to the pulley by a belt 908. Therefore, a direction of rotation 1130 of the pulley, and the transmission shaft, is the same with a direction of rotation 1126 of the fan. Referring to both views ‘A' and ’B’ of the example 1108, the gear 1112 and the puliey 914 are both connected to the transmission shaft, whereby the pulley 914 is rotated with the gear 1112, Therefore, the direction of rotation of the fan 207 is the same as the direction of rotation of the pulley 914. However, since the direction of rotation 1118 of the gear 1112 is the same with the direction of rotation 1116 of the outer shell also the direction of rotation of the fan is the same as the direction of rotation of the outer shell.

[0092] In views ‘A’ in the examples 1104,1108,1110 the outer shell 102 is configured to operate as a gear, or a separate gear is connected to the outer shell, similar to the examples 1102,1106. However, as a difference to the examples 1102,1106, in the examples 1104,1108,1110 the drive system comprises an intermediary gear 1120 that is in contact with the outer shell and the gear at the transmission shaft and configured to transfer a rotation of the outer shell to the gear at the transmission shaft. Accordingly, the outer shell, or the separate gear connected to the outer shell, and the gear at the transmission shaft are not directly in contact, but the rotation of the outer shell is transferred to a rotation of the transmission shaft via the intermediary gear. Therefore, a direction of rotation 1138 of the intermediary gear is opposite with respect to a direction of rotation 1116 of the outer shell 102, but the direction of rotation 1118 of the gear, and the transmission shaft, is the same as the direction of rotation of the outer shell,

[0093] In view ‘B’ of the example 1110, the transmission shaft 910 may comprise a pulley 914 and the fan 207 may be connected to the pulley by a belt 908 that is crossed. Therefore, a direction of rotation 1130 of the pulley, and the transmission shaft, is the opposite with respect to a direction of rotation 1126 of the fan. Referring to both views ‘A ^! and ‘B ^: of the example 1110, the gear 1112 and the pulley 914 are both connected to the transmission shaft, whereby the pulley 914 is rotated with the gear 1112. The direction of rotation 1118 of the gear 1112 is the same with the direction of rotation 1116 of the outer shell. However, since the belt 908 is crossed, the direction of rotation of the fan is the opposite to the direction of rotation of the outer shell, whereby gyroscopic forces are reduced which stabilizes the electric motor TOO and improves maneuverability of a handheld tool comprising the electric motor.

[0094] In view ‘A* of the example 1140, the transmission shaft 910 may comprise a pulley 912 and the outer shell 102 may be connected to the pulley by a belt 904 that Is crossed. Therefore, a direction of rotation 1158 of the pulley, and the transmission shaft, is the opposite with respect to a direction of rotation 1116 of the outer shell.

[0095] In view ‘B’ in the example 1140 the fan 207 is configured to operate as a gear, or a separate gear is connected to the outer she!!, similar to the examples 1102,1104. However, as a difference to the examples 1102,1104, in the example 1140 the drive system comprises an intermediary gear 1122 that is in contact with the fan, or a separate gear connected to the fan, and the gear 1142 at the transmission shaft and the intermediary gear is configured to transfer a rotation of the transmission shaft to the fan. Accordingly, the fan. or the separate gear connected to the fan. and the gear at the transmission shaft are not directly in contact, but the rotation of the transmission shaft is transferred to a rotation of the fan via the intermediary gear 1122. Therefore, a direction of rotation 1148 of the intermediary gear is opposite with respect to a direction of rotation 1116 of the fan 207.

[0096] Referring to both views ‘A’ and 'B’ of the example 1140, the gear 1142 and the pulley 912 are both connected to the transmission shaft, whereby the pulley 912 is rotated with the gear 1142. Since the belt 904 is crossed, the direction of rotation 1131 of the gear 1142 is opposite with respect to the direction of rotation 1116 of the outer shell. The intermediary gear 1122 provides that the direction of rotation 1126 of the fan is opposite with respect to the direction of rotation of the outer shell, whereby gyroscopic forces are reduced which stabilizes the electric motor 100 and improves maneuverability of a handheld tool comprising the electric motor.

[0097] It shouid be noted that although at least part of the foregoing examples described with reference to Figs. 11 ,12 and 13 use for transferring a rotational movement, wheels may be used instead of the gears for transferring the rotational movement. Accordingly, a wheel may be connected to the transmission shaft instead of the gear 1112 and/or a wheel may be connected to the transmission shaft instead of the gear 1114,1142. Drive surface 1105 of the fan 207 configured to engage a wheel connected to the transmission shaft may comprise material, e.g. rubber, that provides sufficient friction for preventing slippage of the wheel on the drive surface for transferring a rotational movement from the transmission shaft to the fan. Drive surface 1103 of the outer shell 102 configured to engage a wheel connected to the transmission shaft may comprise material, e.g. rubber, that provides sufficient friction for preventing slippage of the wheel on the drive surface for transferring a rotational movement from the outer shell to the transmission shaft, in the exampies of Fig. 12 and 13 the intermediary gears 1120,1122 may be replaced with wheels, when wheels are used instead of the gears.

[0098] It should be note that in the foregoing any direction in a radia! direction may be a direction that is parallel to the radial direction and or any direction in a longitudinal direction may be a direction that is paralie! to the longitudinal direction. A direction that is parallel with the radial direction or the longitudinal direction may be determined on the basis of a comparison of the direction with the radiai direction or the longitudinal direction. In an exampie, the direction may be evaluated to determine whether the direction is parailel with the radiai direction or the longitudinal direction. The direction may be divided into components of a coordinate system, such as a cartesian coordinate system spanned in X, Y and Z-dimension, whereby one of the X, Y and Z-dimensions may be aligned with the radiai direction or the longitudinal direction. Then a length of the components of the evaluated direction may be compared with each other and if the component with the highest value is in the direction of the dimension that is aligned with the radia! direction or the longitudinal direction, the direction may be determined to be parallel with the radial direction or the longitudinal direction. In a simple example, if an evaluated direction has only a component in the X-direction, that is aligned with the radiai direction, the evaluated direction may be determined to be parallel with the radial direction, in another example, if an evaluated direction has X, Y and Z~ components such that the X-component has the highest vaiue, X>Y>Z, then if the X-direction is aligned with the radial direction, the evaluated direction may be determined to be parailel with the radial direction.

[0099] The examples described herein are applicable to an electric motor, a handheld tool comprising an electric motor and any other apparatus that comprises an electric motor that is cooled by a fan.

[0100] The foregoing description has provided by way of exemplary and non-limiting exampies a full and informative description of the exemplary embodiment of this invention. However, various modifications and adaptations may become apparent to those skilled in the relevant arts in view of the foregoing description, when read in conjunction with the accompanying drawings and the appended claims. However, all such and similar modifications of the teachings of this invention will still fall within the scope of this invention.