The present invention relates to portable hairdryer devices and, in particular, refers to an electric motor for a portable hairdryer device.

The known portable hairdryers, intended for both professional and home use, are devices equipped with an outer casing typically made of a plastic material provided with a handle and defining a cavity inside which an electric motor, a fan of the centrifugal or axial type, connected and rotated by the electric motor, and one or more electric heating elements, especially electric resistors, for air heating are housed.

When the hairdryer is in use, i.e., when the electric motor and the heating element are powered by electric current, the fan is rotatably driven by the electric motor and generates inside the casing, more precisely in an air duct formed therefrom, a flow of air which is sucked into the rear part of the hairdryer through an intake opening, flows into the duct and outflows from a front delivery opening of the casing. The air flow passes through the heating element (electric resistor) which, when it is supplied by electric current, generates heat by Joule effect. Then the air flow heats up and outflows, heated, from the delivery opening of the hairdryer.

The hairdryer electric motor is generally of the commutator type and includes a stator integral with the casing and equipped with stator windings powered with direct or single phase alternating electric current, a rotor equipped with rotor or armature windings and placed inside the stator and in axis with it and a commutator or switch fixed to the rotor and engaged by a couple of brushes for supplying the rotor windings with direct or single-phase alternating electric current. The rotor and stator are made of ferromagnetic material and the greater the power required to operate the fan to generate an air flow suitable for drying hair in a reasonably short time, the larger the dimensions.

The brushes are fixed and therefore slide on the commutator formed by a plurality of overlapping copper strips. The brushes are typically made up of elongated elements, having a cylindrical or prismatic shape, made of carbon or graphite - and, for this reason, commonly called "carbon brushes" - i.e., of a material that ensures excellent electrical conductivity and, at the same time, a reduced friction coefficient.

Since they abut with the strip commutator, the brushes are subject to progressive wear and therefore have a limited lifetime. Therefore the electric motor and, thus, the hairdryer must be periodically serviced to replace the worn brushes with new ones.

To ensure an optimal current transmission and a regular and constant consumption or wear for an adequate lifetime, the brushes must be kept in abutment with the rotating commutator with an appropriate thrust or compression force.

For this purpose, helical compression springs are typically used which exert an axial force on the bearing end of the brush opposite to the abutment end of the commutator so as to thrust and keep the latter in abutment with the rotating element.

Alternatively, helical torsion springs are used, i.e. helical bending stressed springs which exert a thrust on the brushes through one of the two ends. More precisely, the spring body, made up of metal wire coils wrapped in a helix, is mounted on a pin of a supporting frame of the electric motor, with one end locked to the aforementioned frame and the remaining active end that acts elastically on the brush.

In both types of spring, the force exerted, which is proportional to the linear lengthening of the spring body (in the case of a helical compression spring) or to the rotation angle of the active end (in the case of a helical bending spring), it is not constant for the entire lifetime of the brush but decreases with its wear i.e. with length decreasing.

Consequently, the known electric motors have the disadvantage of comprising supplying and reversing brushes having a limited lifetime, with wear which progressively increases and conductivity performances which decay at the same time.

GB 1128810 describes a housing for brushes comprising an insulating casing which houses a brush biased by two opposite torsional springs, each of which comprises a given number of coaxial turns and is equipped with a free end. The other ends of the two opposite torsional springs are secured together and arranged so that the free ends are aligned with the axis of the brush.

EP0087190 describes a commutator motor designed to be incorporated in portable tool devices, preferably in hand tools. Such motor includes a stator with windings or a permanent magnet and a rotor with a commutator. The electric connection between the commutator and the current supply is ensured by a couple of diametrically opposed brushes of different polarity, the brushes being displaceable with respect to the commutator axis to vary the field angle between the stator and rotor.

An object of the present invention is to improve the known electric motors for portable hairdryers, in particular the electric commutator motors provided with supplying and reversing brushes made of carbon or graphite.

Another object is to provide an electric commutator motor for portable hairdryers provided with supplying and reversing brushes having long lifetime and high performance in terms of electrical conductivity.

These and other purposes are achieved by an electric heating element for portable hairdryers according to claim 1.

The invention can be better understood and implemented with reference to the attached drawings which illustrate exemplifying and non-limiting embodiments thereof, wherein:

Figure 1 is a side view of the electric motor of the invention associated with a fan and mounted in a portable hairdryer, the latter illustrated in dashed lines;

Figure 2 is a section according to the plane II-II in Figure 1 which illustrates, in particular, a commutator and supplying brushes;

Figure 3 is an enlarged partial detail of the electric motor of Figure 2, wherein some parts have been removed for greater clarity, and illustrates a supplying brush and a related thrusting elastic element in an initial operating configuration;

Figure 4 is a partial side view of the electric motor of Figure 3;

Figure 5 is a view similar to that of Figure 3, which illustrates the supplying brush and the related elastic thrust element in a final operating configuration;

Figure 6 is a partial side view of the electric motor of Figure 5.

With reference to Figures 1 to 6, an electric motor 1 according to the invention is shown, arranged to be mounted on a portable hairdryer 50 to rotate a fan 51 around a main axis X. In particular, the electric motor 1 is mounted inside a casing 52 of the hairdryer 50 and is fixed to the latter by means of a supporting frame 8.

The electric motor 1 comprises a stator 2 provided with stator windings 22 adapted to be supplied by direct or single-phase alternating electric current, and a rotor 3 provided with rotor windings 23 and rotating inside the stator 2 about the main axis X. The electric motor 1 also comprises a commutator or switch 4 fixed to, and rotating with, the rotor 3 and electrically connected to the rotor windings 23, and a couple of brushes 5 which can be supplied by direct or single-phase alternating electric current, and housed in containment means 7 connected to the supporting frame 8 of the electric motor 1. Each brush 5 has an elongated shape and is provided with a first end 5a arranged to abut against the commutator 4 so as to reverse an electric supply of the rotor windings 23. The brush 5, of a known type, has, e.g., a parallelepiped shape with a square cross section and is made of graphite or carbon powder or a graphite and copper mixture, so as to present a high electrical conductivity and a reduced friction coefficient.

The electric motor 1 has also a couple of thrusting elastic elements 6, each of which acting on a second end 5b opposite to the first end 5a of the respective brush 5 so as to exert a force F along an operative direction T in cooperation with the containment means 7, which is adapted to maintain the first end 5a abutting the commutator 4, in particular when a distance between the first end 5a and the second end 5b of said brush 5 decreases because of the wear, i.e. when the length of the brush 5 decreases.

The two brushes 5 are arranged on opposite sides of the commutator 4.

The containment means comprises a couple of containment elements 7 connected to the supporting frame 8 of the stator 2 and provided with respective seats 17 elongated and arranged to slidably housing respective brushes 5. Each seat 17 has four walls which block transverse movements of the respective brush 5 allowing the latter to slide only along the operative direction T, thrust by the respective thrusting elastic element 6 against the commutator 4 with force F.

Each thrusting elastic element comprises a helical torsion spring 6, also called a helical bending spring, provided with a central body 10 free to move and formed by a plurality of metal wire coils that forms the spring, a first branch 11, rotatably connected to the containment means 7, and a second branch 12 acting on the second end 5b of the respective brush 5. Thanks to the central body 10 free to move, the second branch 12 of the helical torsion spring 6 is able to exert on the second end 5b of the respective brush 5 a substantially constant force F along the direction T, as better explained in the following description. The first branch 11 and the second branch 12 form an angle b (greater than 180°) which varies with the variation of the distance between the first end 5a and the second end 5b of the brush 5, in particular it decreases with the reduction of this distance due to wear.

Each torsion coil spring 6 is connected to the respective brush 5 and the related containment element 7 so that a longitudinal winding axis Y of the coils of the central body 10 is almost parallel to the main axis X. A side wall of each containment element 7 has an elongated slot 7b that allows the passage of the branches 11, 12 of the helical torsion spring 6, whose body 10 is positioned externally to the aforementioned containment element 7.

The first branch 11 of each helical torsion spring 6 comprises a first middle section 11a connected to the central body 10 and a first terminal section l ib rotatably connected to the respective containment element 7. The first middle section 11a and the first terminal section l ib are respectively almost orthogonal and almost parallel to said main axis X, i.e. substantially orthogonal to each other to form a first branch 11 bent at 90°, upwards with reference to the side views of Figures 4 and 6. The first terminal section 1 lb is inserted with play in a hole 17 of an upper wall 7a of the respective containment element 7, so as to rotate around an axis parallel to the winding axis Y and the main axis X.

The second branch 12 of the helical torsion spring 6 comprises a second middle section 12a connected to the central body 10 and a second terminal section 12b that abuts an outer face of the second end 5b of the respective brush 5. The second middle section 12a and the second terminal section 12b are respectively almost orthogonal and almost parallel to the main axis X, i.e. substantially orthogonal to each other to form a second branch 12 bent at 90°, downwards with reference to the side views of Figures 4 and 6.

The helical torsion springs 6 are springs which are shaped in such a way that the branches or the ends are able to exert a torque M or couple of axis substantially coinciding with the winding axis or spring axis. The torque M translates into a tangential force F exerted by each branch according to the formula

M = F R

wherein:

M is the torque (Nm);

F is the force (N);

R is the length of each branch (m).

As known, the torque M is proportional to an angle b formed by the two arms of the spring according to the formula

M = K· b

where K is the stiffness of the spring and is defined by the formula:

d ⁴

K = E—

64D _n

wherein:

E is Young's modulus of the spring material;

d is the diameter of the spring wire;

D the diameter of the coils of the body 10.

Force F is also proportional to the angle b according to the formula

F = K· b/R

Therefore, as it happens in the known applications, by rigidly fixing one of the arms of the spring to the supporting frame and thus blocking also the whole body 10, the remaining branch exerts a force that is proportional to the angle b i.e., variable according to the position of the branch and, in the specific case, to the length of the brush 5 on which said branch acts. With the assembly of the helical torsion spring 6 of the electric motor 1 of the invention, which provides for the rotatable fixing of the first branch 11 to the supporting element 7 and the second branch 12 acting in thrust on the second end 5b of the brush 5, the body 10 is advantageously free to move with the progressive consumption of the brush 5.

As a consequence, as the angle b formed by the two branches 11, 12 varies, in addition to the variation of the torque M, proportionally according to the formula M = K- b, also an arm R of the force F exerted by the second branch 12 varies, said arm R corresponding to the distance of the application point of the force F (at the second terminal section 12b of the second branch 12) from the winding axis Y orthogonally to the operative direction T.

Since the force F is directly proportional to the torque M and inversely proportional to the arm R (according to the formula F = M/R) and since both the torque M and the arm R vary, in particular almost proportionally, with the variation of the angle b, as a consequence, the force F remains almost constant during the variation of said angle b i.e. when the distance between the first end 5a and the second end 5b of the brush 5 varies.

In an initial configuration (Figures 3 and 4), the initial length of the brush 5, i.e. an initial distance do between the two ends 5a, 5b of the brush 5, an initial angle bo formed by the two branches 11, 12, an initial torque Mo exerted by the helical torsion spring 6 and an initial arm Ro of the force F take the respective maximum values.

Differently, in a final configuration (Figures 5 and 6), of consumption or advanced wear of the brush 5, the final length of the brush 5, i.e. a final distance d _f between the two ends 5a, 5b of the brush 5, a final comer bi formed by the two branches 11, 12, a final torque M _f and a final force arm R _f of force F take the respective minimum values. Since as mentioned above the force F is a function of both the torque M and the arm R according to the formula F = M/R, it is found that such force F remains substantially constant in use for the different angular positions of the second branch 12, since both the values of the torque M and of the arm R increase or rise proportionally to the increase or decrease of the angle b between the branches 11, 12 of the helical torsion spring 6. Each brush 5 is then thrust and kept in abutment with the commutator 4 along the operative direction T by the respective helical torsion spring 6 with an almost constant force F, as detected by the tests carried out by the applicant, for each length of the brush 5, i.e., regardless of consumption or wear of the latter during the operation of the electric motor 1.

The hairdryer electric motor 1 of the invention therefore allows the supplying brushes 5 to have a lifetime and performances in terms of electrical conductivity greater than those of the brushes of similar known commutator electric motors.