CONTACTS”

Field of the Invention

[0001 ] The present invention refers to a support structure of electrical contacts for a universal electric motor and, more particularly, a support structure which, in addition to providing support for the sliding electrical contacts (or brushes) of the universal electric motor, it further comprises additional electrical contacts especially dedicated to the dynamic electrical connection with members that make part of a selective switching system of electric interconnections of the field coil (stator coils) of the universal electric motor, which is specially adapted to work with at least one level among less two possible distinct levels of electrical voltage.

[0002] The present invention also refers to the universal electric motor itself provided with the support structure of electrical contacts discussed herein.

Basis of the Invention

[0003] As known to those skilled in the art, the state of the art comprises different types of dynamo-electric machine, which are capable of transforming electric potential difference into mechanical force (electric motors) or transforming mechanical force into electric potential difference (electric generators). According to the scope of the invention in question, the universal electric motor is of particular interest, which, according to the definition widely known and abundantly documented in specialized technical literature, is composed of a stator (fixed member) and a rotor (movable member), said stator being comprised of a metal armature and at least one pair of field coils and said rotor provided with an electric collector and at least one “induced” coil. In general terms, the pair of field coils and the induced coil are electrically connected in series to each other, the electrical connection between the field coils (fixed) and the“induced” coil (movable) occurring through sliding electrical contacts, usually referred to as brushes. In its trivial electrical configuration, as mentioned above, a universal electric motor can be powered with direct current or alternating current.

[0004] Due to their versatility and high torque at low speed, universal electric motors are commonly used in electric appliances and manual power tools such as drills, electric screwdrivers and rotary cutting manual power tools. When used in these applications, it is common for universal electric motors to be configured to be powered with alternating current, after all, this type of electric current is standardized in residential power grids.

[0005] Figure 1 schematically shows the diagram of connection of a universal electric motor, the induced coil being referenced by the indication Bi1 , the field coils being referenced by the indications Bc1 and Bc2, and the sliding electrical contacts being referenced by the indication Cd1 and Cd2. In addition, the source of electrical voltage derived from the alternating current distribution system, is referenced by the indication RD. The diagram of connection of a universal electric motor demonstrated in Figure 1 is widely known to those skilled in the art.

[0006] From a constructive point of view, it is common for said sliding electrical contacts Cd1 and Cd2 to be mounted on a support structure, which is usually referred to as“brush-holder”. In general, such a support structure comprises an assembly capable of holding the sliding electrical contacts Cd1 and Cd2 in a fixed position, closely to the rotor manifold. Traditionally, support structures belonging to the present state of the art further comprise two electrical terminals through which electrical conductors are connected to the already mentioned sliding electrical contacts Cd1 and Cd2. In figure 1 , the two electrical terminals are referenced by the indications TA and TB.

[0007] Also from the constructive point of view, it is also known to those skilled in the art that the current support structures of universal electric motors, belonging to the present state of the art, further comprise a movable portion through which the direction of rotation of the rotor can be selectively defined. While it is not the merit of the invention in question to make a profound study of the constructive features of this movable portion, it should to be emphasized that it enables the invention of the poles of the induced coil Bi1 of the rotor with respect to the field coils Bc1 and Bc2 of the stator.

[0008] The diagram of connection of figure 1 makes it intuitive to understand why the current support structures of sliding electrical contacts Cd1 and Cd2 of universal electric motors have only two electrical terminals: each terminal is intended to enable the simple electrical connection between its respective sliding electrical contact, housed in the support structure, and a single electrical conductor (derived from the distribution system RD in the case of the sliding electrical contact Cd1 , and derived from the field coil Bc1 in the case of the sliding electrical contact Cd2).

[0009] However, due to the limitation of electrical terminals, the current support structures of sliding electrical contacts of universal electric motors do not allow any kind of alteration of the general topology of the diagram of connection of said motor.

[0010] Thus, it becomes impossible to rearrange the electrical connections between the induced coil and the field coils of the universal electric motor once it is assembled and the electrical connections of the sliding electrical contacts are shaped. This impossibility impairs the implementation of electrical and functional optimizations of the universal electric motor, such as integrating it into an electric switching system capable of allowing it to be powered with 127 or 220 Volts.

[001 1 ] It is based on this problem that the invention in question arises.

Objects of the Invention

[0012] Thus, the fundamental purpose of the present invention is to disclose a support structure of electrical contacts for a universal electric motor capable of enabling the change of the electrical connection topology of the inductive motor elements even after the manufacture thereof.

[0013] In addition, it is also an object of the invention in question that the support structure of electrical contacts for a universal electric motor enables the integration of said motor into an electric switching system capable of enabling said motor to be powered with 127 or 220 Volts.

Summary of the Invention

[0014] All the previously defined objects are fully achieved by the support structure of electrical contacts disclosed herein, which comprises at least one body comprising at least two housing seats each dedicated to the support of at least one sliding electrical contact, and at least one base comprising at least two support regions adapted for securing electrical terminals electrically connected to the sliding electrical contacts and, in addition, at least three support regions, each adapted for securing an electrical terminal, which are electrically insulated from each other and electrically insulated from the sliding electrical contacts.

[0015] The tangible benefits to the creation of the support structure of electrical contacts disclosed herein are particularly optimized by a universal electric motor provided with an support structure of electrical contacts which, in addition to a rotor equipped with an induced coil and a stator equipped with two field coils, it is integrated to the at least one electric switch provided with two reciprocal electric switches, each capable of establishing a selective electrical connection between a “common” electrical terminal and a“closed” electrical terminal or an“open” electrical terminal, and it is further provided at least one semiconductor member electrically connected between the“open” electrical terminals of the electric switch.

[0016] Said support structure is also composed of at least one body comprising at least two housing seats each dedicated to the support of at least one sliding electrical contact, and at least one base comprising at least two support regions adapted for securing electrical terminals electrically connected to the sliding electrical contacts and other at least three support regions each adapted for securing an electrical terminal, which are electrically insulated from each other and electrically insulated from the sliding electrical contacts.

[0017] In this application, the electrical terminal T1 of the base of the support structure of electrical contacts is connected to the electric distribution system and the sliding electrical contact, the electrical terminal T2 of the base of the support structure of electrical contacts is connected to the sliding electrical contact, the field coil and the“closed” electrical terminal of the electric switch, the electrical terminal T3 of the base of the support structure of electrical contacts is connected to the“common” electrical terminal of the electric switch and to the field coil, the electrical terminal T4 of the base of the support structure of electrical contacts is connected to the“closed” terminal of the electric switch, the field coil and the electric distribution system, and the electrical terminal T5 of the base of the support structure of electrical contacts is connected to the field coil and to the“common” electrical terminal of the electric switch. The references T 1 , T2, T3, T4 and T5 can be verified in figure 5.

Description of the Drawings

[0018] The invention in question is described in detail with the aid of the merely exemplary illustrative figures, listed below, which:

[0019] Figure 1 shows, as previously mentioned, the diagram of connection of a universal electric motor belonging to the current state of the art;

[0020] Figure 2 shows, in a schematic and simplified way, the diagram of connection of a universal electric motor integrated to an exemplary electric switching system;

[0021 ] Figure 3 shows, in exploded perspective, a preferred embodiment of the support structure of electrical contacts for a universal electric motor, according to the invention in question; [0022] Figures 4A and 4B illustrate the preferred embodiment of the support structure of electrical contacts for a universal electric motor, according to the present invention, in a bottom view;

[0023] Figure 5 shows, from the diagram of Figure 2, the scheme of interaction between the members of the universal electric motor and the members of the electric switching system and the electrical terminals of the support structure of electrical contacts for a universal electric motor, according to the invention in question;

[0024] Figure 6 shows, in exploded detailed perspective, the electrical terminals existing in the preferred embodiment of the support structure of electrical contacts for a universal electric motor, according to the present invention; and

[0025] Figure 7 shows, in partial exploded perspective, the base and the selector integrating the support structure of electrical contacts for a universal electric motor, according to the invention in question.

Detailed Description of the Invention

[0026] In accordance with the central objects of the invention in question, it is proposed a support structure of electrical contacts for a universal electric motor which allows changing the topology of electrical connections of the inductive members of the motor even after the end of manufacture thereof.

[0027] Next, and based on figure 2, there is described a situation in which there is a need to change the topology of electrical connections of the inductive members of a universal electric motor. More particularly, said situation refers to manual power tools (drill, electric screwdriver, circular saw), or any other related tool whose operation is based on mechanical work generated by a universal electric motor, which can be powered with 127 or 220 Volts.

[0028] Thus, Figure 2 illustrates an electric switching system capable of transforming a traditional universal electric motor into a bivolt universal electric motor (able to operate when fed with 127 or 220 Volts), said electric switch being capable of changing the general topology of the universal electric motor so that each of the possible topologies obtained is specially adapted to be powered with a specific electrical voltage range.

[0029] To this end, the system shown in figure 2 comprises a universal electric motor comprising a rotor equipped with an induced coil Bi1 and a stator equipped with two field coils Bc1 and Bc2, an electric switch 1 provided with two reciprocal electric switches each of which is capable of establishing selective electrical connection between a“common” electrical terminal 1 1 , 14 and a“closed” electrical terminal 12, 15 or an“open” electrical terminal 13, 16 and a semiconductor member 3.

[0030] For the sake of illustration and sufficiency of disclosure, the following is highlighted:

[0031 ] · The universal electric motor may comprise a fundamentally traditional universal electric motor and already integrated to the current state of the art (at least as regards its necessary basic members). Thus, all the basic details of universal electric motors - the fact that sliding electrical contacts 11 1 are provided which, via a collector (not shown), connect the induced coil 11 to the other members of the motor, for example - are present in the universal electric motor of the present invention. It is worth noting, however, that the“electromagnetic recipe” of the induced coil Bi1 and the“electromagnetic recipe” of the field coils Bc1 and Bc2 can vary according to the torque and rotation requirements of each motor. Anyway, it is emphasized, the electric switching system is applicable in any and all universal electric motor.

[0032] · The electric switch 1 is nothing more than the joining of two traditional relays belonging to the current state of the art, with the proviso that these two relays, although electrically independent, are actuated in a reciprocal manner, that is, they are actuated together. The terminals of the electric switch 1 have been arbitrarily referred to as:“common” electrical terminal 1 1 that can cooperate with the “closed” electrical terminal 12 or with the“open” electrical terminal 13, and“common” electrical terminal 14 that can cooperate with the“closed” electrical terminal 15 or with the“open” electrical terminal 16. Thus, said electric switch 1 has two reciprocal electric switches 2 (electrically independent, but linked to a single activation/ deactivation mechanism) that, selectively cooperating, are able to establish electrical connection between a pair of terminals (1 1/12 and 14/15, for example) and, consequently, to de-establish electrical connection to another terminal (13 and 16, in the same example).

[0033] · The semiconductor member 3 comprises, according to the simplest embodiment of the invention in question, a diode (semiconductor member widely known to those skilled in the art and fully described in specialized technical literature) whose main function in the electric switching system for dynamo-electric machine consists of rectifying (or removing part) of the sine signal of electrical voltage that energizes the universal electric motor. The semiconductor member 3 is electrically connected between the“open” electrical terminals 13 and 16 of the electric switch 1.

[0034] As can be seen, the diagram of connection of the universal electric motor integrated to an exemplary electric switching system, as shown in figure 2, is expressively more complex than the traditional diagram of connection of figure 1.

[0035] In general terms, the diagram of connection of the universal electric motor integrated to an exemplary electric switching system of Figure 2 comprises at least five electrical connection points (P1 , P2, P3, P4, P5) to be carried out in the support structure of electrical contacts for a universal electric motor. Consequently, it is noteworthy to note that a trivial support structure of electrical contacts for a universal electric motor does not support the diagram of connection of the universal electric motor integrated to an exemplary electric switching system of Figure 2. [0036] To this end, in order to meet this need, a new support structure of electrical contacts is disclosed, which is fundamentally composed of a body S and a base B, as shown in Figures 3 and 7.

[0037] According to the preferred embodiment of the invention in question, the body S, or rotation direction selecting body, comprises two housing seats S1 , S2 each dedicated to the support of at least one sliding electrical contact Cd1 , Cd2. It should be pointed out that it is not the object of the present invention to provide excessive explanations on typical details of said body S, after all it can be a rotation direction selecting body which comprises the already known support structures of electrical contacts for universal electric motors.

[0038] Also according to the preferred embodiment of the invention in question, the base B comprises two support regions B1 , B2 adapted for securing electrical terminals T1 , T2 electrically connected to the sliding electrical contacts Cd1 , Cd2 and three support regions B3 , B4, B5, each adapted for securing an electrical terminal T3, T4, T5. Accordingly, the support structure of electrical contacts disclosed herein differs from the other related structures by the fact that said electrical terminals T3, T4, T5 are electrically insulated from each other and electrically insulated from the sliding electrical contacts Cd1 , Cd2.

[0039] Thus, again referring to figure 3, it is verified that:

[0040] · The sliding electrical contact Cd1 of the induced coil Bi1 is connected to the electric distribution system RD through the electrical terminal T1 of the base B of the support structure of electrical contacts.

[0041 ] · The sliding electrical contact Cd2 of the induced coil Bi1 is simultaneously connected to the field coil Bc1 and to the“closed” terminal 12 of the electric switch 1 by means of the electrical terminal T2 of the base B of the support structure of electrical contacts.

[0042] · The field coil Bc2 has one of its terminals connected to the “common” terminal 1 1 of the electric switch 1 by means of the electrical terminal T3 of the base B of the support structure of electrical contacts.

[0043] · The field coil Bc2 has its other terminal connected simultaneously to the electric distribution system RD and to the“closed” terminal 15 of the electric switch 1 by means of the electrical terminal T4 of the base B of the support structure of electrical contacts.

[0044] · The field coil Bc1 has its other terminal connected to the“common” terminal 14 of the electric switch 1 by means of the electrical terminal T5 of the base B of the support structure of electrical contacts.

[0045] Based on this arrangement, it is observed that it is the position of the reciprocal electric switches 2 that defines the topology of electrical connection between the induced coil Bi1 , the two field coils Bc1 , Bc2 and the semiconductor member 3, wherein in a suitable topology for energizing the universal electric motor with 127 Volts, the field coils Bc1 , Bc2 are electrically connected to each other in parallel, and electrically connected in series to the induced coil Bi1 and in a topology suitable for energizing the universal electric motor with 220 Volts, the field coils Bc1 , Bc2, the induced coil Bi 1 and the semiconductor member 3 are all connected in series.

[0046] Although it is not merit of the invention in question to detail the functional nuances of such arrangement, it remains only to mention that in the topology suitable for energizing the universal electric motor with 127 Volts (field coils electrically connected to each other in parallel, and electrically connected in series to the induced coil, without connection to the semiconductor) it is verified that the equivalent inductance and equivalent inductive reactance are smaller than the individual inductive inductances and reactances, which allows the universal electric motor to function properly at a lower voltage. In turn, in the topology suitable for energizing the universal electric motor with 220 Volts (field coils, induced coil and semiconductor member connected in series) the existence of the semiconductor member causes the effective voltage on each of the members has a decrease of about 30% in relation to the grid voltage range, and this allows the universal electric motor to operate properly with a higher voltage.

[0047] From the constructive point of view, as shown in Figures 3, 4, 6 and 7, considering the preferred embodiment of the support structure of electrical contacts, the following is highlighted:

[0048] · The body S and the base B are made of polymeric material, preferably by thermoforming process.

[0049] · The terminals T1 , T2, T3, T4 and T5 are made of ferrous metal alloy, preferably by a stamping process.

[0050] · The housing seats S1 , S2 of the body S comprise recesses provided with circumferential walls sized in accordance with the measurements of the sliding electrical contacts Cd1 , Cd2.

[0051 ] · The support regions B1 , B2 are provided on the upper face of the base B, and comprise recesses molded from the shape of the terminals T1 , T2.

[0052] · The support regions B3, B4 and B5 are provided on the lower face of the base B, and comprise recesses or holes molded from the shape of the terminals T3, T4 and T5.

[0053] · The electrical terminals T3, T4, T5 extend in the opposite direction to the electrical terminal T 1.

[0054] · The electrical terminal T2 comprises a projection extending in an analogous direction to the electrical terminals T3, T4, T5, and a projection extends in an analogous direction to the electrical terminal T1.

[0055] · The electrical terminals T1 , T2 optionally comprise electric tracks for moving the body S and reversing the polarity of the sliding electrical contacts Cd1 , Cd2, this embodiment being trivial in support structures of electrical contacts belonging to the current state of the art.

[0056] It is important to highlight that the above description is for the sole purpose of describing in an exemplifying manner the particular embodiment of the patent of invention in question. It is therefore clear that modifications, variations and constructive combinations of the elements performing the same function in substantially the same manner to achieve the same results, remain within the scope of protection delimited by the appended claims.