Direct current electric generator motor with sliding contacts

Abstract

The present invention relates to a direct current electric motor (1) with sliding contacts comprising a motor body (10), a drive shaft (15), a rotor (20), fixed to the drive shaft (15), a stator (30) coaxial to said drive shaft (15), a rotating slip ring (18), a pair of sliding electric contacts (40) cooperating with the slip ring (18), wherein the stator (30) comprises two pairs of poles each with two respective north (N1, N2) and south (S1, S2) magnetic poles and wherein with respect to two first (P1) and second (P2) planes orthogonal to each other, where the straight line of intersection of said planes coincides with the rotation axis (R) of the rotor (15), which define four quadrants (Q1, Q2, Q3, Q4) of the stator (30) of equal angular extension, said magnetic poles are each arranged on one of the four quadrants.

Description

[0001] DESCRIPTION

[0002] DIRECT CURRENT ELECTRIC GENERATOR MOTOR WITH SLIDING CONTACTS

[0003] The present invention refers in general to the field of direct current electric generator motors, in particular to a motor with sliding contacts, commonly called brushes.

[0004] As is known, an electric motor is an electric machine in which the input power is of electrical type and the output power is of mechanical type.

[0005] An electric motor can be used to move mechanical loads of different types, from small domestic appliances for everyday use to large-scale machinery, such as the processing units of industrial plants or the locomotives of trains.

[0006] Direct current electric motors are reversible machines, i.e., they can be used as electric current generators by supplying them with mechanical input power.

[0007] In the description below, the term electric motor, or simply motor, will refer to a motorgenerator, i.e. to an electric machine that, if necessary, also operates as generator.

[0008] A direct current electric motor (DC) generally comprises a rotating element or rotor, which represents the induced element of the machine and is provided with electric windings or armature windings and an inductor element or stator configured to generate a magnetic field, inside which the rotor is rotated.

[0009] Generally, the inductor magnetic field, comprising at least one north pole and one south pole, is generated through the use of permanent magnets associated with the stator and is, therefore, constant in time.

[0010] An inductor magnetic field which is constant but can be adjusted in intensity, can instead be generated using coils associated with the stator.

[0011] This direct current motor further comprises a rotary switch called commutator or slip ring, fixed to the rotating shaft of the rotor. In particular, this slip ring generally comprises elements, for example made of copper insulated from one another by sheets of mica. This slip ring is configured to cooperate with two or more (depending on the number of poles of the stator) sliding electric contacts, fixed with respect to the rotation of the slip ring and connected to respective terminals to supply current (in motor mode) or draw current (in generator mode).

[0012] As is known, the electric current that passes through the windings of the rotor, due to the fact that the latter is immersed in the magnetic field of the stator, in turn generates a magnetic field that, in motor operating mode, generates a torque that causes it to rotate. Instead, in generator operating mode, this magnetic field generates a counter torque that opposes rotation.

[0013] The magnetic field on the rotor generates two or more pairs of north-south poles fixed in space and staggered by 90° with respect to the inductor magnetic field of the stator.

[0014] Thanks to switching of the slip ring, rotation of the rotor does not modify the position of these induced poles.

[0015] In motor operating mode, the rotation speed depends on the voltage of the power supply source, on the intensity of the stator field and on the applied load (load torque).

[0016] The torque generated is generally proportional to the current passing through the windings of the rotor.

[0017] As is known, when the rotor is moving, each conductor of the windings of the rotor is subjected to a time-varying magnetic flux.

[0018] Based on the Faraday-Neumann-Lenz law, a counter-electromotive force (CEMF) that opposes the voltage supplied by the power supply is generated at the terminals of these windings. Assuming that the module of the inductor magnetic field is constant, this force depends linearly on the rotation speed of the motor.

[0019] Said CEMF, in generator operating mode, is none other than the electrical energy drawn at the terminals of the sliding contacts.

[0020] On the contrary to motor operating mode, this drawn energy at the same time generates a rotor magnetic field, which opposes the stator magnetic field and hence rotation of the rotor.

[0021] In this context, there is the need to provide an electric motor that allows a noteworthy reduction in the generation of counter-electromotive forces in the windings of the motor.

[0022] In particular, an object of the present invention is to produce a direct current electric motor, in particular with sliding contacts, having features that allow the limits and drawbacks of prior art electric machines to be overcome.

[0023] More in detail, the object of the present invention is to provide a direct current electric motor with sliding contacts that allows the counter-electromotive forces in motor operating mode and the mechanical counter torque in generator operating mode to be suppressed.

[0024] These objects are achieved by a direct current electric motor according to claim 1.

[0025] According to the present invention, said electric motor comprises a motor body and a drive shaft.

[0026] The drive shaft rotates around a rotation axis and has a first end connectable to a mechanical load or to a user (as a function of its use as motor or generator), and a second opposite end.

[0027] The motor body comprises a stator, coaxial to said drive shaft, and a rotor, coaxially fixed to the drive shaft to rotate jointly therewith.

[0028] The stator comprises pole expansions to generate a inductor magnetic field along a constant direction.

[0029] The rotor comprises electric windings.

[0030] The motor further comprises a rotating slip ring, firmly fixed to the second end of the drive shaft, provided with conductive elements, each connected to one of the electric windings of the rotor.

[0031] Said conductive elements of the slip ring are configured to cooperate with the sliding electric contacts of the motor, fixed with respect to rotation of the slip ring. In motor operating mode, said electric contacts supply the electric windings of the rotor with a direct current supply voltage, adapted to generate a torque to start rotation of the rotor.

[0032] Instead, in generator operating mode, it is possible to draw direct current or voltage from said electric contacts.

[0033] The electric motor according to the present invention is characterized in that the stator comprises two pairs of north N and south S magnetic poles.

[0034] Said magnetic poles can comprise electrically powered permanent magnets or coils.

[0035] With respect to two planes Pl and P2 orthogonal to each other, where the straight line of intersection of said planes coincides with the rotation axis of the rotor, which define four quadrants of the stator of equal angular extension (of 90°), said magnetic poles are each arranged on one of the four quadrants.

[0036] The plane Pl separates the first and the second quadrant from the third and from the fourth quadrant, while the plane P2 separates the first and the fourth quadrant from the second and from the third quadrant.

[0037] More in detail,

[0038] - a first north pole N and a second north pole N are arranged respectively in the first and in the second quadrant of the stator, and a third south pole S and a fourth south pole S are arranged respectively in the third and in the fourth quadrant of the stator.

[0039] Preferably, said magnetic poles are arranged close to the plane Pl.

[0040] The angular extension of the magnetic poles, i.e., the arc of the body of the stator occupied by the permanent magnet or by the windings of the coil, is preferably of around 45° or less.

[0041] This means that between the two north N and south S poles there is a free area of the stator of at least 90°.

[0042] According to the present invention, in motor operating mode, the magnetic field generated by the pairs of north and south poles of the first and of the third quadrant must be identical to the magnetic field generated by the pairs of north and south poles of the second and of the fourth quadrant.

[0043] Instead, in generator operating mode the magnetic field of one of the aforesaid two pairs of poles must be greater than the magnetic field generated by the other pair, as a function of the direction of rotation applied to the rotor.

[0044] Thanks to the aforesaid configuration of the magnetic poles, it is possible to significantly reduce, or even eliminate, the effects of the magnetic fields that generate the aforesaid counter-electromotive force in motor operating mode.

[0045] These effects have as a result a significantly high gain of the output of the electric motor which requires a much smaller supply voltage, and hence current, for the same amount of power output.

[0046] Likewise, in generator operating mode, said motor requires a lower mechanical input power for the same amount of electrical energy generated.

[0047] Preferably, according to an aspect of the invention, the two sliding contacts are arranged along a straight line Xc, said straight line lying on a plane orthogonal to the rotation axis of the rotor and being rotated by an angle a with respect to the plane Pl.

[0048] In motor operating mode, said angle a is preferably between 15° and 45°, more preferably between 30° and 45°.

[0049] As will be better explained below, this arrangement of the contacts allows generation of the torque that causes the rotation of the rotor in motor mode, and generation of a voltage at the terminals of the contacts in generator mode.

[0050] Further features and advantages of the present invention will be more apparent from the description of an example of embodiment as illustrated in the accompanying Fig. 1 which schematically shows a cross-sectional view of the electric motor according to the present invention. With reference to the accompanying figure, there is illustrated a direct current electric motor provided with sliding contacts or brushes, indicated as a whole with 1.

[0051] The motor 1 comprises a body 10 and a drive shaft 15, rotating around an axis R with respect to the body of the motor 10.

[0052] The shaft 15 has a first end (not shown in the figure) connectable, for example, to a mechanical load to be rotated (in the case of motor operating mode) or to a mechanical power source (in the case of generator operating mode).

[0053] The body 10 of the motor comprises a rotor 20 and a stator 30.

[0054] The rotor 20 is fixed to the drive shaft 15. Said rotor 20 comprises electric windings (not illustrated in the figure).

[0055] The drive shaft 15 also has a second opposite end 16 on which a slip ring 18 is mounted. Said slip ring 18 is provided with a plurality of conductive elements 19, each electrically connected to one of the windings of the rotor 20.

[0056] The stator 30, i.e., the fixed part of the electric machine, has the task of generating a magnetic flux required for operation of the machine.

[0057] The active sides LI, L2 of the rotor 20, which are immersed in the respective magnetic fields of the stator, are represented schematically in Fig. 1.

[0058] This stator 30 is coaxial to the drive shaft 15 and comprises two pairs of poles, each with two respective north Nl, N2 and south SI, S2 magnetic poles.

[0059] Said magnetic poles can comprise permanent magnets or electrically powered coils.

[0060] In Fig. 1 two planes Pl, P2 are represented, orthogonal to each other, the straight line of intersection of which coincides with the rotation axis R of the rotor, which define four quadrants Q1-Q4 of the stator of equal angular extension of 90°. As can be seen in the figure, the plane Pl separates the first and the second quadrant QI, Q2 from the third and from the fourth quadrant Q3, Q4, while the plane P2 separates the first and the fourth quadrant QI, Q4 from the second and from the third quadrant Q2, Q3. The magnetic poles of the two pairs of poles are each arranged in one of the four quadrants.

[0061] More in detail, a first north pole N 1 and a second north pole N2 are arranged respectively in the first and in the second quadrant of the stator, while a first south pole S 1 and a second south pole S2 are arranged respectively in the third and in the fourth quadrant of the stator.

[0062] Free areas 35, i.e., areas not affected by magnetic poles, are present between the first north pole N1 and the second north pole N2 and between the first south pole SI and the second south pole S2.

[0063] In the embodiment illustrated in the figure, said free areas 35 have an angular extension of around 90°, while the magnetic poles Nl, N2, SI, S2 each have an angular extension of around 45°.

[0064] A pair of sliding contacts 40, or brushes, are arranged aligned along a straight line Xc rotated by an angle a with respect to the plane Pl.

[0065] The angle of inclination a of this straight line Xc is such that said straight line passes through the free areas 35 of the stator.

[0066] Preferably, said straight line Xc is arranged close to the boundary areas between a north or south magnetic pole and a respective free area.

[0067] The present invention, as described and illustrated, is susceptible to numerous modifications and variations, all falling within the scope of the inventive concept; moreover, all details may be replaced with other technically equivalent elements.

Claims

Claims

1. A direct current electric motor (1) with sliding contacts, comprising:- a motor body (10)- a drive shaft (15), said drive shaft having a first end connectable to a load or to a mechanical power source and a second opposite end (16);- the motor body (10) comprising:- a rotor (20), fixed to the drive shaft (15) and which can rotate jointly therewith around a rotation axis (R), said rotor (20) comprising electric windings;- a stator (30) coaxial to said drive shaft (15); the electric motor (1) further comprising:- a slip ring (18) firmly fixed to the second end (16) of the drive shaft (15) and provided with conductive elements (19) connected to respective electric windings of the rotor (20);- a pair of sliding electric contacts (40) aligned along a straight line (Xc) fixed with respect to the body (10) of the motor, said sliding contacts (40) being configured to cooperate with the conductive elements (19) of the slip ring to supply the electric windings of the rotor with a direct current supply voltage adapted to generate a torque to start rotation of the rotor or to draw a current, when the drive shaft is connected to a mechanical power source; characterized in that the stator (30) comprises two pairs of poles with two respective north (N 1 , N2) and south (S 1 , S2) magnetic poles, wherein with respect to two first (Pl) and second (P2) planes orthogonal to each other, where the straight line of intersection of said planes coincides with the rotation axis (R) of the rotor (15), which define four quadrants (QI, Q2, Q3, Q4) of the stator (30) of equal angular extension said magnetic poles are each arranged on one of the four quadrants.

2. The electric motor according to claim 1, wherein a first north pole(Nl) and a second north pole (N2) are arranged respectively in the first and in the second quadrant (QI, Q2) of the stator (30) and a first south pole (SI) and a second south pole (S2) arc arranged respectively in the third and in the fourth quadrant (Q3, Q4) of the stator (30).

3. The electric motor according to claim 1 or 2, wherein said magnetic poles (Nl, N2, SI, S2) are arranged close to the first plane (Pl) and have an angular extension of 45° or less.

4. The electric motor according to any one of the preceding claims, wherein the straight line (Xc) along which the sliding contacts (40) lie is rotated with respect to the plane (Pl) by an angle a between 15° and 45°.

5. The electric motor according to any one of the preceding claims, wherein said magnetic poles (Nl, N2, SI, S2) comprise permanent magnets or coils supplied with a direct current with a constant or variable intensity.

Images