BRUSHLESS DC MOTOR OF A HAND TOOL MACHINE

Description

State of the art

[0001] The invention relates to a brushless DC motor—also called a BLDC (brushless direct current) or EC (electronically commutated) motor—of an electrical processing device according to the preamble of independent claim 1. The brushless DC motor has a stator, a rotor, a fan, and a flywheel. The rotor, the fan, and the flywheel are arranged in a rotationally fixed manner on a motor shaft of the brushless DC motor, and the flywheel is at least partially enclosed by the fan axially along the motor shaft. The invention further relates to an electric power tool with a brushless DC motor.

[0002] By design, the rotors of brushless DC motors have a very low moment of inertia. Unlike a brushed DC motor, there are no windings on the rotor. Furthermore, the rotor diameter of a brushless DC motor is generally smaller than that of a brushed DC motor. This means that the rotational energy stored in idle mode by a BLDC motor is at least an order of magnitude lower. However, in the application of many electrical processing devices, especially power tools, high levels of stored rotational energy can be very advantageous, making machining processes more comfortable and efficient.

[0003] DE 10 2012 216 496 A1 discloses a handheld power tool, in particular a hammer drill, drill driver, or impact wrench, with an electronically commutated drive motor. The drive motor is provided with a disc-shaped rotor and a stator. A flywheel is formed on the rotor, which, according to one embodiment, is designed as a flywheel that is at least partially disc-shaped. An optional fan wheel for cooling is provided on a motor shaft of the brushless DC motor or on the flywheel. The fan wheel can, for example, be a component made from a plastic material using an injection molding process or from a metal sheet using a stamping and bending process, which is glued and / or integrally connected to the flywheel.

[0004] EP 2 845 689 A2 discloses an electric power tool in which a flywheel can be driven by a drive unit to supply kinetic energy to a tool body through a power transmission section of the flywheel. Furthermore, a ventilation unit is mounted in such a way that it generates cooling air together with the flywheel.

[0005] Further examples of fan and flywheel configurations of brushless and brushed electric motors can be found in EP 3 035 508 A2, CN 206 673 729 U, US 3 906 266 A, US 5 375 637 A and JP S53 16114 U.

[0006] The object of the invention is to provide a brushless DC motor for an electrical processing device compared to the prior art, which, despite its relatively low weight and high power density, meets the requirements of a high mass moment of inertia while at the same time providing sufficient cooling and a compact size of the electrical processing device. Advantages of the invention

[0007] To achieve the stated object, the flywheel is provided with a groove at one axial end running around its radially outer circumference, into which groove a radially inwardly projecting collar of the fan engages.

[0008] This allows for a particularly short design combined with a high maximum torque of the BLDC motor and a secure axial fit of the fan on the flywheel. At the same time, the proposed solution is very robust and reliable in operation.

[0009] In the context of the invention, electrical processing devices are understood to include, among other things, battery-operated or mains-powered power tools for processing workpieces using an electrically driven tool. The electrical processing device can be designed either as a hand-held power tool or as a stationary power tool. Typical power tools in this context are hand-held or pillar drills, screwdrivers, impact drills, planers, angle grinders, orbital sanders, polishers, or the like. Motor-driven garden tools such as lawn mowers, grass trimmers, pruning saws, or the like can also be considered as electrical processing devices. Furthermore, the invention is applicable to brushless DC motors in household appliances such as vacuum cleaners, mixers, etc.

[0010] In a further embodiment of the invention, the flywheel has a very high mass inertia, a very high shaft pressure, and a very high homogeneous density. This makes the proposed solution simple and cost-effective to manufacture without balancing. In addition, a very good form and / or material connection with the motor shaft is ensured. The flywheel is particularly advantageously made of brass or iron as a single piece. Brass is a particularly well-suited material for the production of a fast-rotating flywheel because its density of typically 8.5 g / cm³< results in a very high mass inertia with a small size, and brass's modulus of elasticity of up to 120 GPa allows for very high shaft pressure. This reliably prevents the flywheel from potentially spinning during operation. Due to the high homogeneous density of brass, the flywheel can be installed directly without a complex and expensive balancing process.The assembly consisting of the rotor, fan, and flywheel can thus meet the requirements for the maximum permissible rotor imbalance without additional machining processes. Corresponding advantages arise from the use of iron instead of brass. However, it is also conceivable to manufacture the flywheel from ceramic, artificial stone, or other materials, especially plastics, that have comparable properties to those of brass mentioned above.

[0011] In a further embodiment, the flywheel merges flush with the fan at least on one side in the radial direction of the motor shaft. This effectively prevents unwanted noise that could occur during operation of the BLDC motor or the electrical processing device. Furthermore, the available cross-sectional area for the motor's cooling air flow is not restricted.

[0012] Furthermore, it is provided that, in the radial direction of the motor shaft, an outer contour of the flywheel essentially corresponds to an outer contour of the fan over at least 50% of its axial extension along the motor shaft. In this way, a simple and cost-effective overmolding of the flywheel with the fan can be achieved while simultaneously achieving a good form and / or material connection. Furthermore, it is advantageous if the flywheel tapers, in particular conically, over at least 50% of its axial extension along the motor shaft. This enables, on the one hand, easier overmolding of the flywheel from one side, but on the other hand also allows for easier sliding of the fan onto the flywheel or easier insertion of the flywheel into the fan. This can be supported by the flywheel having a convex shape on at least one side that approximates the course or shape of the cooling air flow of the engine.

[0013] The invention also relates to a hand-held power tool with a brushless DC motor according to the invention. Examples of implementation drawing

[0014] The invention is described below with reference to Figures 1 and 2 explained by way of example, whereby the same reference numerals in the figures indicate the same components with the same functionality.

[0015] It shows Fig. 1: a schematic representation of an electrical processing device designed as a handheld power tool with a brushless or electronically commutated DC motor, Fig. 2: a schematic representation of a BLDC or EC motor according to the invention with a flywheel in a first exemplary embodiment, Fig. 3: a schematic representation of a BLDC or EC motor according to the invention with a flywheel in a second exemplary embodiment and Fig. 4: a schematic representation of a BLDC or EC motor according to the invention with a flywheel in a third exemplary embodiment. Description of the embodiments

[0016] Fig. 1shows, by way of example, an electrical processing device designed as a handheld power tool 10 with an electronically commutated DC motor 12. The handheld power tool 10 illustratively has a housing 14 with a handle 16 and a tool holder 18 and can be mechanically and electrically connected to a battery pack 20 for an off-grip power supply. In the present example, the battery pack 20 has a supply voltage of 10.8 V. However, the invention can also be applied without restriction to electrical processing devices with battery packs of other voltage and power classes.

[0017] The handheld power tool 10 is embodied here, by way of example, as a cordless impact wrench. However, it should be noted that the present invention is neither limited to cordless impact wrenches nor to handheld power tools in general, but rather can be applied to various electrical processing devices in which a BLDC or EC motor 12 is used, e.g., in handheld or pillar drills, screwdrivers, hammer drills, planers, angle grinders, orbital sanders, polishing machines, or the like, but also in motor-driven garden tools, such as lawn mowers, grass trimmers, pruning saws, or the like, or household appliances, such as vacuum cleaners, mixers, etc., regardless of whether the electrical processing device can be operated independently of the mains using the battery pack 20 or connected to the mains.

[0018] The housing 14 houses, by way of example, the BLDC motor 12, which is supplied with power by the battery pack 20, a gear 22, and a percussion mechanism 24. According to one embodiment, the motor 12 is designed in the manner of a disk motor and can be actuated, i.e. switched on and off, for example, via a manual switch 26. For the sake of simplicity, the term “motor” will occasionally be used below, even if this always refers to a BLDC or EC motor. The motor 12 can preferably be electronically controlled or regulated in such a way that both reversing operation and specifications regarding a desired rotational speed and / or torque can be implemented. The functioning and structure of the motor 12 are generally known to those skilled in the art and will therefore not be further described.

[0019] Illustratively, the motor 12 is connected to the gear 22 via an associated motor shaft 28, which converts rotation of the motor shaft 28 into rotation of a drive member 30, e.g., a drive shaft, provided between the gear 22 and the striking mechanism 24. This conversion preferably occurs such that the drive member 30 rotates relative to the motor shaft 28 with increased torque but reduced rotational speed. The motor 20 and the gear 22 are arranged, for example, in the housing 14, but can alternatively also be arranged in a housing associated with them or in separate motor and gear housings, which in turn are arranged in the housing 14.

[0020] The impact mechanism 24 connected to the drive member 30 is, for example, a rotary or rotating impact mechanism that generates sudden, high-intensity rotational impulses and transmits them to an output shaft 32, e.g., an output spindle. The tool holder 18 is provided on the output shaft 32 and is preferably designed to accommodate insert tools and, according to one embodiment, can be connected both to an insert tool with an external coupling, e.g., a screwdriver bit, and to an insert tool with an internal coupling, e.g., a socket wrench. Illustratively, the tool holder 18 can be connected to an insert tool 34 with an external polygon coupling 36 or to an insert tool with an internal polygon coupling. The insert tool 34 is, for example, designed as a screwdriver bit with the external polygon coupling 36, illustratively designed as a hexagon coupling, which is arranged in the tool holder 18.Such a screwdriver bit is sufficiently known from the prior art, so that a detailed description is omitted here for the sake of brevity.

[0021] Figure 2 shows the motor 12 designed according to a first embodiment, wherein the stator having the drive windings is not shown (compare Figure 4). The brushless DC motor 12 has a rotor 38 mounted on the motor shaft 28 in a rotationally fixed manner, which, due to its design, has a relatively low moment of inertia compared to brushed DC motors. This is due, on the one hand, to the fact that the rotor 38 does not have to support any windings, and, on the other hand, because it can have a significantly smaller diameter than the rotor of a brushed DC motor. This results in the problem that certain machining processes to be performed with the electrical machining device in conjunction with a BLDC motor can no longer be carried out as efficiently and evenly due to the relatively low stored rotational energy.

[0022] The motor shaft 28 is rotatably mounted in the housing 14 of the handheld power tool 10 via two ball bearings 40. Instead of the ball bearings 40, other types of bearings, such as roller or plain bearings, can also be used without limiting the invention. To cool the motor 12 and, if applicable, any power electronics controlling it (not shown), a fan 40 is arranged on the motor shaft 28 in a rotationally fixed manner. This fan is generally manufactured as a plastic injection-molded part. In the exemplary embodiment shown, the plastic injection-molded part 40 supports the rotor 38 over its entire length. However, it is also possible for the fan 40 to be designed as a separate injection-molded part from the rotor 38.

[0023] According to the invention, a flywheel 44 is arranged on the motor shaft 28 in a rotationally fixed manner and is at least partially enclosed by the fan 42 axially along the motor shaft 28. This enables a particularly short design of the BLDC motor 12 in conjunction with a high maximum torque. Furthermore, the solution is very robust and reliable in operation. The fan 42 completely encloses the flywheel 44 in the radial direction 46 of the motor shaft 28 in order to achieve a particularly good form-fitting and / or material-locking connection between the fan 42 and the flywheel 44 and to prevent axial projections of the flywheel 44 relative to the fan 12.

[0024] The flywheel 44 exhibits a very high mass inertia, a very high shaft pressure, and a very high homogeneous density. For this purpose, the flywheel 44 is preferably manufactured in one piece from brass or iron. Brass is a particularly suitable material because its density of typically 8.5 g / cm³< results in a very high mass inertia with a small size, and the elastic modulus of brass of up to 120 GPa allows for very high shaft pressure. This effectively prevents the flywheel 44 from spinning on the motor shaft 28 during operation. Due to the high homogeneous density of brass, the flywheel 44 can be installed directly without a complex and expensive balancing process. The assembly consisting of rotor 38, fan 42, and flywheel 44 can thus meet the requirements for the maximum permissible rotor imbalance without additional machining processes.Instead of brass or iron, it is also conceivable to manufacture the flywheel 44 from ceramic, artificial stone or other materials, in particular plastics, which have comparable properties.

[0025] The flywheel 44 merges flush into the fan 42 at least on one side at its axial end 45 in the radial direction 46 of the motor shaft 28 in order to effectively avoid, for example, unfavorable noises that could arise during operation of the motor 12 or the electrical processing device 10. In order to realize a simple and cost-effective overmolding of the flywheel 44 with the fan 42 while at the same time achieving a good form and / or material connection, an outer contour 48 of the flywheel 44 in the radial direction 46 of the motor shaft 28 over at least 50% of the axial extent 50 of the flywheel 44 essentially corresponds to an outer contour 52 of the fan 42. In addition, the flywheel 44 tapers, in particular conically, over at least 50% of its axial extent 50 along the motor shaft 28 in order to, on the one hand, simplify overmolding of the flywheel 44 from one side and, on the other hand, also simplify sliding the fan 42 onto the flywheel 44 orto facilitate easier insertion of the flywheel 44 into the fan 42. This can be supported by the flywheel having a convex shape at least on one side of its axial end 45. This additionally ensures that the flywheel 44 does not negatively influence the airflow of the fan 42.

[0026] The connection between rotor 38, flywheel 44, fan 42, and motor shaft 28 can be created in various ways. For example, it is possible to first overmold the flywheel 44 with a fan 42 and then press this component onto the motor shaft 28 of the brushless DC motor 12. Alternatively, the rotor 38 can be overmolded with the fan 42 and then the flywheel 44 can be inserted into the fan 42 and pressed onto the motor shaft 28. Furthermore, it is conceivable to manufacture the fan 42, flywheel 44, and rotor 38 as individual parts and then press them individually onto the motor shaft 28. The flywheel 44 can either be inserted into the fan 42 or the fan 42 can be pushed onto the flywheel 44.

[0027] The Figures 3 and 4each show a schematic representation of a second and third embodiment of the flywheel 44 of the BLDC or EC motor 12 according to the invention. In Figure 3 the flywheel 44 tapers in contrast to Figure 2 not conical, but non-linear with a radius 54 over approximately 50% of its axial extension 50 along the motor shaft 28, and then tapering slightly conically towards the rotor (not shown) over the remaining 30%. Figure 4The flywheel 44 has, at one axial end 45, a groove 60 running around its radially outer periphery 58, into which a radially inwardly projecting collar 62 of the fan 42 engages. In this way, the fan 42 has a secure axial fit on the flywheel 44. In addition, assembly can be simplified, since the fan 42, as a finished injection-molded part, only needs to be pushed onto the flywheel 44, which is already pressed onto the motor shaft 28, in order to then press the rotor 38 onto the motor shaft 28. Figure 4 is also the one in the Figures 2 and 3 Stator 64 (not shown) with its drive windings 66 can be seen.

[0028] Finally, it should be noted that the illustrated embodiments do not refer to the Figures 1 to 4shown size relationships between stator and flywheel or fan is not limited to the arrangement and number of bearing points of the motor shaft, the drive windings or other features not directly related to the invention.

Claims

1. Brushless DC motor (12) of an electric machining device (10), having a stator (64), a rotor (38), a fan (42) and a flywheel (44), wherein the rotor (38), the fan (42) and the flywheel (44) are arranged for conjoint rotation on a motor shaft (28) of the brushless DC motor (12), and wherein the flywheel (44) is enclosed at least partially by the fan (42) axially along the motor shaft (28), wherein the flywheel (44) has, at one axial end (45), a groove (60) extending around its radially outer periphery (58), in which a radially inwardly protruding collar (62) of the fan (42) engages.

2. Brushless DC motor (12) according to Claim 1, characterized in that the flywheel (44) has very high inertia, a very high shaft pressure and a very high homogeneous density.

3. Brushless DC motor (12) according to either of the preceding claims, characterized in that the flywheel (44) consists integrally of brass or of iron.

4. Brushless DC motor (12) according to one of the preceding claims, characterized in that the flywheel (44) transitions into the fan (42) in a flush manner at least on one side (45) in the radial direction (46) of the motor shaft (28).

5. Brushless DC motor (12) according to one of the preceding claims, characterized in that, in the radial direction (46) of the motor shaft (28), an external contour (48) of the flywheel (44), along at least 50% of its axial extent (50) along the motor shaft (28), corresponds substantially to an external contour (52) of the fan (42).

6. Brushless DC motor (12) according to one of the preceding claims, characterized in that the flywheel (44) tapers, in particular in a conical manner, along at least 50% of its axial extent (50) along the motor shaft (28).

7. Brushless DC motor (12) according to one of the preceding claims, characterized in that the flywheel (44) has a convex shape at least on one side (45).

8. Hand-held power tool (10) having a brushless DC motor (12) and a flywheel (44) according to one of the preceding claims.