FAT STATOR COIL FOR ELECTRICAL MOTOR

Abstract

Some embodiments are directed to a coil for a stator of an electrical slotless motor), the electrical slotless motor including a rotor including at least one magnet (10), the coil including a cylindrical portion (80c) arranged to face the at least one marget, wherein a radial thickness of the cylindrical portion is greater than 28%, preferably 30% of an internal radius of the cylindrical portion.

Claims

1. A coil for a stator of an electrical slotless motor, the electrical slotless motor comprising: a rotor including at least one magnet, the coil including a cylindrical portion arranged to face the at least one magnet, wherein a radial thickness of the cylindrical portion is greater than 28%, preferably 30% of an internal radius of the cylindrical portion.

2. The coil for a stator of an electrical slotless motor according to claim 1, wherein a mass of the coil is greater than 17.5% of a total mass of the electrical slotless motor.

3. The coil according to claim 1, wherein the coil is a bell shaped coil or a U-shaped coil.

4. The coil according to claim 1, wherein the coil includes a first head section outwardly extending at a first longitudinal extremity of the coil and a second head section inwardly extending at a second longitudinal extremity of the coil.

5. The coil according to claim 4, wherein the cylindrical portion is arranged between the first head section and the second head section.

6. An electrical slotless motor including the coil according to claim 1.

7. The electrical slotless motor according to claim 6, the electrical slotless motor further including a rotor, and the rotor includes a shaft (30) presenting a longitudinal axis, and wherein the cylindrical portion presents a longitudinal axis coaxial with the longitudinal axis of the shaft.

8. The electrical slotless motor according to claim 7, wherein the coil includes a first head section outwardly extending at a first longitudinal extremity of the coil and a second head section inwardly extending at a second longitudinal extremity of the coil, and wherein each of the first head section and the second head section presents a longitudinal axis coaxial with the longitudinal axis of the shaft.

9. Use of the electrical slotless motor of claim 6, including: using during ten seconds the electrical slotless motor at a torque that is 5% of a maximum short-term allowable peak torque achieved with a current flowing through conductors of the coil generating a heat and before thermal deterioration of the coil, which is nine, preferably ten times greater that a maximum continuous allowable torque before thermal deterioration of the coil during a continuous use of the motor, using during one second the electrical slotless motor at the maximum short-term allowable peak torque, storing heat in the coil (80).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Other features and advantages of some embodiments of the presently disclosed subject matter will appear more clearly from the following detailed description of particular non-limitative examples of the invention, illustrated by the appended drawings where:

[0057] FIG. 1 represents an electrical slotless motor according to some embodiments,

[0058] FIG. 2 represents a coil for a stator of the electrical slotless motor according to some embodiments,

[0059] FIG. 3 represents a thermal limitation of a coil and motor according to some embodiments.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0060] FIG. 1 represents an electrical slotless motor according to some embodiments and a coil for a stator of the electrical slotless motor and. FIG. 2 represents the coil for the stator of the electrical slotless motor, without showing the motor.

[0061] Electrical slotless motor 2 includes a stator including a coil 80 and a rotor 1 including at least one magnet 10 mounted on a support member 40 of the motor 2, the support member 40 being mounted on a shaft 30 of the motor. The shaft 30 presents a longitudinal axis forming a rotation axis of the rotor 1. The at least one magnet 10, for example one or two or four magnets 10 form a cylindrical surface of the rotor 1, so that the magnet 10 directly faces the stator coil or coil 80 of the the electrical motor 2. Thereby an air gap 70 is formed between the magnet 10 and the coil 80. The at least one magnet 10 may be manufactured in one block, such as a monobloc. The number of magnets is not limited. The magnet 10 is mounted on the support member 40, but the shaft 30 and the support member 40 may also be manufactured in one piece, thereby forming a monobloc shaft or shaft 30.

[0062] The rotor 1 further includes two rings 20 mounted by force on the shaft 30 to be secured on the shaft 30. The two rings 20 are mounted at each longitudinal extremity of the shaft 30 and at the longitudinal extremity of magnet 10 mounted on shaft 30.

[0063] The coil 80 includes electrical wires or electrical wire conductors made out of copper or any other metallic material or material adapted to conduct electricity. The wires are wound to form the coil 80 and are substantially included in a plan including the longitudinal axis of the shaft 30 when coil 80 is installed on the motor 2, to enhance magnetic compactness and the filling factor of coil 80, that is to say to reach a maximum content of wound wire in a determined volume of the coil 80. As represented in FIG. 2, the coil 80 includes a winding radius 80z. The stator further includes a lamination stack 81 mounted over the coil 80 and axially maintained by two plastic or steel rings 91 of the stator.

[0064] The electric motor 2 further includes a set of phase wires or live wires 83 connected to the coil 80 and an incremental coder 85, that may be a Hall effect sensor as an example, arranged to monitor the rotating speed or rotating displacement of the rotor 1, with the help of sensing magnet 86 and magnet support 87 mounted on the ring 20 or directly on shaft 30.

[0065] The electric motor 2 further includes a set of bearings, such as ball bearings 88 and main flanges 89, made out of aluminium or steel, and mounted at each of its extremities, and a spring 90 arranged to preload the ball bearings 88. The electric motor 2 further includes an electric motor tube or external tube 82 and the main flanges 89. The lamination stack 81 is maintained into the external tube 82 by the two plastic or steel rings 91, and the coil 80 is glued in the external tube 82 and lamination stack 81.

[0066] As an alternative, the electric motor 2 can be sensorless, that is to say with only phase cable.

[0067] Motor 2 presents an outer surface defining a smallest external dimension 101 of motor 2. The outer surface defining the smallest external dimension is the external dimension of external tube 82. In other words, the external tube 82 is a steel cylinder having the smallest external dimension 101 that is a radial thickness or motor radial thickness 101, and external tube 82 is coaxially mounted with the shaft 30, in case of full assembly of motor 2.

[0068] Considering FIG. 1 and FIG. 2 together, the coil 80 for the stator includes a cylindrical portion 80c arranged to be in regards of or to face the at least one magnet 10, a first head section 80a outwardly extending at a first longitudinal extremity of the coil 80 and a second head section 80b inwardly extending at a second longitudinal extremity of the coil 80. The cylindrical portion 80c is arranged between the first head section 80a and the second head section 80b. In other words, the coil 80 is bell-shaped or U-shaped.

[0069] The coil 80 and/or the cylindrical portion 80c present a longitudinal axis too, that is coaxial with the longitudinal axis of the shaft 30 when the shaft 30 and the coil 80 are mounted on the electrical motor 2. For this mounting and to allow passage to the shaft 30, the coil 80 includes a first opening 80e on the side of the live wires 83 and a second opening 80d at the opposite side. The winding radius 80z is located close to the second head section 80d, linking the cylindrical portion 80c and the second head section 80b.

[0070] The cylindrical portion 80c has a radial thickness or coil radial thickness 100, an internal radius 102 and an external radius 103.

[0071] The coil 80 is considered as being fat or having the capacity to allow the motor 2 to reach high rotation speed typically up to 40 000 rpm, high peak torques and high continuous torques on user requests when the radial thickness 100 of the cylindrical portion 80c is greater than 28%, preferably 30% of the internal radius 12 or when the radial thickness 100 of the cylindrical portion 80c is greater than 22%, preferably 25% of the external radius 103 of the cylindrical portion 80c, or when the radial thickness 100 of the cylindrical portion 80c is greater than 25%, preferably 28% of the average radius of the cylindrical portion 80c, the average radius being the average of the internal radius and the external radius along the cylindrical portion 80c of the coil 80 arranged to facing the magnet 10.

[0072] When the radial thickness 100 is greater than 17.5% of the smallest external dimension 101 of the motor 2, preferably 18%, and more preferably 20%, the coil is also able to reach such high peak torques and high continuous torques before thermal destruction or limitations

[0073] In other words, the coil 80 is considered as fat if the mass of the coil 80 is greater than 17.5% of the mass of the electrical motor 2, preferably 18%, and more preferably 20%.

[0074] The total mass of the electrical motor 2 is considered as a relevant mass of the motor 2 to participate in the functioning of motor 2. That is to say that the relevant total mass of motor 2 could be defined as the sum mass of the external tube 82, of the coil 80, of the shaft 30, the support member 40, of the at least one magnet 10, of the bearings 88, of the lamination stack 81, of the rings 20, the flanges 89, the lives wires 83, the spring 90, the incremental coder 85, sensing magnet 86 and magnet support 87.

[0075] FIG. 3 represents a thermal limitation of a coil and motor according to some embodiments.

[0076] The thermal limitation of the coil 80 is presented as an elevation of temperature 203 of the coil 80 due to the high peak torques and/or high continuous torques requested by a user, in particular in the field of industrial power tools. A typical use is a high peak torque or maximum short-term allowable peak torque before thermal deterioration of one second preceded and/or followed by a ten second use at a continuous torque of 5% of the maximum short-term allowable peak torque before thermal deterioration, for a duration of a shift of four hours or a shift of eight hours, but the shift of use can be longer such as one day or two days thereby limited by the use of tool on which the motor 2 is connected. The continuous torque can be at medium speed (10 000 to 20 000 rpm) or higher speed up to 40 000 rpm. Typically, the maximum short-term allowable peak torque is greater than nine, preferably ten times a maximum allowable continuous torque, at a medium speed of 10 000 to 20 000 rpm or higher speed up to 40 000 rpm. In the case of a peak torque request, the elevation of temperature 202 of the coil 80 is adiabatic, that is to say there is not enough time to evacuate temperature to the environment of the motor 2. In other words, the coil temperature 202 increases too quickly to allow for evacuation and the coil 80 is deteriorated if the coil temperature 202 reaches 150 C. or more, which is a usual thermal limit 205 of a coil and motor manufacturing. That is to say that the coil 80 is considered as an adiabatic fuse, and thermal limitation before deterioration of the coil 80 is set at 150 C. Thermal limit for destruction is deemed to be above the thermal limitation before deterioration. Typically, the maximum short-term allowable peak torque is up to around 3 N.m.

[0077] FIG. 3 is a graphic where the abscissa represents temperature, preferably in Celsius degrees and the ordinate represents time, preferably in seconds, and shows different temperatures in the case of use presented above, with typical use of high peak torque and continuous torque, with peak torque during one second. A stator temperature 200 is represented as a flat line as the coil is considered as an adiabatic fuse, and motor 2 and its body is considered at room temperature, e.g. 25 C. Theoretical impact of thermal resistance on coil 204 is represented as a dashed flat line of theoretical coil temperature due to low continuous torque 201.

[0078] FIG. 3 clearly shows the elevation of temperature of coil temperature 202, and in particular the quick and high elevation of temperature 203 due to the high peak torque. The high elevation of temperature 203 drives the coil temperature 202 near or close to the usual thermal limit 205 of the coil and motor manufacturing.

[0079] In other words, a coil difference of temperature in adiabatic conditions T where temperature can not be evacuated from coil 80 is

[00001]$.Math..Math.T=\frac{R.Math.I^2}{\mathrm{Cp}.Math.m}.Math.t$

[0080] where T is in C., R is a total resistance of coil 80 in ohms, I is an current intensity traversing coil 80 in Amperes during a short time t in seconds (typically one second, or a time for which adiabatic conditions are reached for high peak torques), Cp is a heat capacity of coil material in J.kg.sup.1.K.sup.1 and m is the coil mass in kg.

[0081] In addition, torque is usually defined as C=k.I.

[0082] where C is torque in N.m, k is a torque constant for a given coil 80 in N.m/A and I is the current intensity traversing coil 80 in Amperes. Thereby, the maximum short-term allowable peak torque before thermal deterioration of the coil 80 is clearly linked to the root square of the elevation of temperature 203 due to high peak torque.

[0083] Finally, a coil difference temperature in non adiabatic conditions T where temperature can be evacuated from coil 80 is

T=R.I.sup.2 Rth

[0084] where T is in C., R is the total resistance of coil 80 in ohms previously defined, I is the current intensity traversing coil 80 in Amperes during continuous torque, and Rth is a thermal resistance in Kelvin per Watt between the external tube 82 of motor 2 in contact with ambient air and the coil 80. Thereby, the maximum continuous allowable torque is defined and not linked to time duration as maximum short-term allowable peak torque does.

[0085] It is of course understood that obvious improvements and/or modifications for one of ordinary skill in the art may be implemented, still being under the scope of some embodiments of the presently disclosed subject matter as it is defined by the appended claims.