Field of the Invention

[0001 ] The present invention refers to an electric switching system for dynamo-electric machine and, more particularly, a selective switching system of the electrical interconnections of the field coils (stator coils) of a universal electric motor, which is specially designed to transform at least one level between less two possible distinct levels of electrical voltage into mechanical force.

[0002] The present invention also refers to a power tool, preferably manual, provided with said electric switching system of dynamo-electric machine, which is specially adapted to function selectively with two possible distinct levels of electrical voltage.

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).

[0004] 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 and 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.

[0005] 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.

[0006] It occurs, however, that a universal electric motor designed to be powered with a certain level of electrical voltage may present inferior performance, or even not work, when powered with another level of electrical voltage. A universal electric motor designed to be powered with 127 Volts, for example, tends to become unusable if it is (accidentally or intentionally) powered with 220 Volts. On the other hand, a universal electric motor designed to be powered with 220 Volts, for example, tends to present unsatisfactory rotation/ torque if it is (accidentally or intentionally) powered with 127 Volts.

[0007] Considering territories (contiguous or nearby) with different power grid patterns, the incompatibility of electrical voltage levels of the power grid represents a large manufacturing and logistic problem for manufacturing companies of universal electric motors and/or manufacturing companies of products that use universal electric motors, after all, it becomes necessary to duplicate the production chain and invest a great amount of resources in specific system and routes of distribution.

[0008] These problems are, in a specially exacerbated way, observed in Brazilian territory, after all, part of the country has a residential power grid of 220 Volts by default, while another part of the country has a residential power grid of 127 Volts by default.

[0009] It is true that other types of industries suffer from this same problem. [0010] In this sense, it is common for these other types of industries to seek electro-electronic solutions to this question. Patent document PI 12724666 describes, for example, an electronic switching solution that enables an inductive motor to be powered with a level between less two possible distinct levels of electrical voltage.

[0011 ] In addition to this example, other electronic (electronic amplifiers and rectifiers) or magnetic (transformers-amplifiers or transformers-reducers) solutions capable of allowing an electric charge to be powered in one level between less two possible distinct levels of electrical voltage are also well known.

[0012] However, it is important to emphasize that there are currently no solutions that, free of electronic or magnetic resources, are capable of solving, in a simplistic way, the problems described above, and it is based on this premise that the invention in question arises.

Objects of the Invention

[0013] Thus, the fundamental purpose of the present invention is to disclose an electric switching system for dynamo-electric machine which, especially designed to make a universal electric motor a bivolt dynamo-electric machine, simplified and free of additions of purely electronic or purely magnetic resources.

[0014] Accordingly, it is one of the objects of the present invention to provide a means capable of applying the input voltage, as it originates from the residential power grid, regardless of the level of standardization, directly in a universal electric motor, making the latter to function properly.

[0015] In addition, it is also an object of the invention in question to provide an automatic means capable of reversing the connection of the coils in such a way that there is no user intervention therefor.

[0016] It is therefore one of the objects of the invention in question to disclose an power tool, preferably manual, bivolt, that is, capable of presenting a suitable operation both when powered with an electrical voltage of 220 Volts and when powered with an electrical voltage of 127 Volts.

[0017] It is also an object of the invention in question that the power tool, preferably manual, bivolt, meets the requirements of proper rotation, torque and heat dissipation, regardless of the energizing electrical voltage.

Summary of the Invention

[0018] All the previously defined objectives are fully achieved by the electric switching system for dynamo-electric machine, which comprises a universal electric motor comprising a rotor provided with an induced coil and a stator provided with two field coils, and 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.

[0019] According to the invention in question, the electric switching system for dynamo-electric machine further comprises at least one semiconductor member, which is electrically connected between the“open” electrical terminals of the electric switches of the electric switch.

[0020] In this way, the position of the reciprocal electric switches defines the topology of the electrical connection between the induced coil, the two field coils and the semiconductor member.

[0021 ] In general terms, in a topology suitable for energizing the universal electric motor with 127 Volts, the field coils are electrically connected to each other in parallel, electrically connected in series to the induced coil, and in a topology suitable for energizing the universal electric motor with 220 Volts, the field coils, the induced coil and the semiconductor member are all connected in series.

[0022] In addition, the same objects of the invention in question are also achieved by means of the power tool provided with an electric switching system for dynamo-electric machine, which comprises at least one structural shell capable of housing, in its interior, a universal electric motor comprising a rotor provided with an induced coil (11 ) and a stator provided with two field coils, at least one electric switch provided with two electric switches and at least one semiconductor member electrically connected between the“open” electrical terminals of the electric switches of the electric switching equipment. The power tool further comprises at least one external rotary shaft linked to the rotor of the universal electric motor and at least one electric cable, with an external terminal, adapted for connection to the electric distribution system.

[0023] According to the invention in question, the position of the reciprocal electric switches defines the topology of electrical connection between the induced coil, the two field coils and the semiconductor member, wherein in a topology suitable for energizing the universal electric motor with 127 Volts, the field coils are electrically connected to each other in parallel, electrically connected in series to the induced coil, and wherein in a topology suitable for energizing the universal electric motor with 220 Volts, the field coils, the induced coil and the semiconductor member are all connected in series.

Description of the Drawings

[0024] The invention in question is described in detail with the aid of the merely exemplary illustrative figures, listed below, which:

[0025] Figures 1 and 2 schematically illustrate the electric switching system for dynamo-electric machine according to the invention in question; in figure 1 , the switching allows the universal electric motor to operate if powered with 127 Volts; in figure 2, the switching allows the universal electric motor to operate if powered with 220 Volts;

[0026] Figure 3 illustrates, for reference purposes, the electric switch which make part of the electric switching system for dynamo-electric machine according to the invention in question; [0027] Figures 4 and 5 show, respectively, the topology of the coils of the universal electric motor adapted for energizing with 127 Volts and 220 Volts;

[0028] Figure 6 schematically illustrates a preferred embodiment of the electric switching system for dynamo-electric machine;

[0029] Figures 7A and 7B respectively illustrate the waveform of the voltage drop under the“induced” coil and under any of the field coils when the universal electric motor is, in the suitable topology, powered with 127 Volts; and

[0030] Figures 8A and 8B respectively illustrate the waveform of the voltage drop under the“induced” coil and under any of the field coils when the universal electric motor is, in the suitable topology, powered with 220 Volts.

Detailed Description of the Invention

[0031 ] In accordance with the central objects of the invention in question, a solution is proposed by means of which a manual power tool (drill, electric screwdriver, circular saw), or any other related tool whose operation is based on mechanical work generated by a universal electric motor, can be powered with 127 or 220 Volts.

[0032] That is, in accordance with the invention in question, there is disclosed a 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).

[0033] In general terms, the inventive core of the present invention concerns the possibility, from a simple electric switch, 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 range of electrical voltage.

[0034] Thus, according to the invention in question, the electric switching system presently disclosed configures the electrical connections between the members that make part of the universal electric motor so that a certain arrangement of electrical connections allows the universal electric motor to operate when powered with 127 Volts and certain arrangement of electrical connections allows the universal electric motor to operate when powered with 220 Volts.

[0035] In addition to said switch, it is indispensable that the semiconductor member is present in at least one of the two possible topologies of the motor, as detailed below.

[0036] To this end, as shown in Figures 1 and 2, the electric switching system for dynamo-electric machine, disclosed herein, comprises a universal electric motor comprised of a rotor provided with an induced coil 11 and a stator provided with two field coils E1 and E2, an electric switch 1 provided with two reciprocal electric switches 2, each capable of establishing a selective electrical connection between a “common” electrical terminal 11 , 14 and an“closed” electrical terminal, 12, 15 or an “open” electrical terminal 13, 16 and a semiconductor member 3.

[0037] In general terms, said 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.

[0038] It is worth noting, however, that the“electromagnetic recipe” of the induced coil 11 and the“electromagnetic recipe” of the field coils E1 and E2 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.

[0039] In general terms, the electric switch 1 , better illustrated in figure 3, 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.

[0040] In order to better understand the invention in question, the terminals of the electric switch 1 have been arbitrarily named as follows:“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.

[0041 ] In any case, this arbitrary designation should not be interpreted in a definitive manner, after all, the invention in question may be embodied with one or more switches or changeover switches analogous to the electric switch 1 defined herein.

[0042] Thus, what becomes relevant and indispensable to the invention in question is that 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, in figure 3) and, consequently, to de-establish electrical connection to another terminal (13 and 16, in figure 3).

[0043] The existence of said electric switch 1 therefore comprises one of the main inventive features of the invention in question, after all, as will be described below, it is by means of this member that the universal electric motor can assume one of two possible topologies, each suitable for energizing by a specific range of electrical voltage.

[0044] Also in general terms, the semiconductor member 3 comprises, in accordance with 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.

[0045] As shown in Figures 1 and 2, referring to certain numerical indications existing only in figure 3, it is verified that the semiconductor member 3 is electrically connected between the“open” electrical terminals 13 and 16 of the electric switch 1. Thus, as will be shown below, although the semiconductor component 3 is always present (at least physically) in the electric switching system disclosed herein, its “electrical functionality” is observed in only one of two possible topologies that the universal electric motor can assume. This is another of the great merits of the invention in question.

[0046] Also as shown in figures 1 and 2, also referring to certain numerical indications existing only in figure 3, it is noticed the following:

[0047] · The induced coil 11 has one of its terminals (one of its sliding contacts 11 1 ) directly connected to the electrical voltage source; its other terminal (its other sliding contact 11 1 ) is simultaneously connected to the field coil E1 and to the “closed” terminal 12 of the electric switch 1.

[0048] · The field coil E1 , in addition to having one of its terminals simultaneously connected to the induced coil 11 and to the“closed” terminal 12 of the electric switch 1 , has its other terminal connected to the“common” terminal 14 of the electric switch 1.

[0049] · The field coil E2 has one of its terminals connected to the“common” terminal 1 1 of the electric switch 1 , and its other terminal is simultaneously connected to the electrical voltage source and to the“closed” terminal 15 of the electric switch 1.

[0050] · The semiconductor member 3, as described above, has one of its terminals connected to the “open” terminal 13 of the electric switch 1 , its other terminal being connected to the“open” terminal 16 of the electric switch 1. It should be emphasized that the“polarization” of the semiconductor member 3 is irrelevant since the electrical voltage source is of the alternating type. [0051 ] In this way, considering that, in one way or another, all coils and the semiconductor member 3 are connected to the electric switch 1 , it should be noticed that it is the position of the reciprocal electric switches 2 of the electric switch 1 which defines the topology of electrical connection between the induced coil 11 , the two field coils E1 , E2 and the semiconductor member 3.

[0052] Thus, in a topology suitable for energizing the universal electric motor with 127 Volts, the field coils E1 , E2 are electrically connected to each other in parallel, electrically connected in series to the induced coil 11 , as shown in figure 1 and in particular in figure 4. It is important to notice that in this topology the semiconductor member 3 is disconnected from the circuit defined herein and, therefore, it is as if the same did not exist in the present topology.

[0053] On the other hand, as shown in figure 2 and in particular in figure 5, in a topology suitable for energizing the universal electric motor with 220 Volts, the field coils E1 , E2, the induced coil 11 and the semiconductor member 3 are all connected in series.

[0054] Therefore, it is indispensable to observe:

[0055] · The “127 Volt topology” is unprecedented when considered in a universal electric motor. In this topology, considering that the field coils E1 and E2 are in parallel, 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 this case 127 Volts. Figures 7A and 7B respectively illustrate the waveform of the voltage drop under the“induced” coil 11 and the waveform of the voltage drop under any of the field coils E1 or E2.

[0056] · The “220 Volt topology”, similar to the traditional topology of a universal electric motor, is unprecedented considering the existence of a semiconductor member 3 connected in series with the other members. In this topology, considering the existence of the semiconductor member 3, which acts as a half wave rectifier, it is verified that the effective voltage on each of the members (induced coil 11 and field coils E1 , E2) 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, in this case, 220 Volts. Figures 8A and 8B respectively illustrate the waveform of the voltage drop under the “induced” coil 11 and the waveform of the voltage drop under any one of the field coils E1 or E2.

[0057] According to the invention in question, the assembly of the electric switch 1 and, consequently, the change of the position of the reciprocal electric switches 2 can occur in different ways.

[0058] In a simpler embodiment, the electric switch 1 may be integrally mechanical and, in this way, the change of the position of the reciprocal electric switches 2 occurs as a result of external force performed by any user.

[0059] In a more sophisticated embodiment, the electric switch 1 may be electronic (or microprocessed) and, in this way, the change of the position of the reciprocal electric switches 2 occurs as a result of microprocessed control.

[0060] In an intermediate embodiment (and preferred, at least for power tools in general), the electric switch 1 may be electromechanical and, in this way, the change of the position of the reciprocal electric switches 2 occurs as a result of electromagnetic actuation.

[0061 ] This preferred embodiment is schematically illustrated in Figure 6.

[0062] According to this preferred embodiment, the electric switch 1 is electromechanical and comprises a coil 21 whose actuation is able to generate electromagnetic effect capable of changing the positioning of the reciprocal electric switches 2.

[0063] Optionally, said coil 21 , assembled to change the positioning of the reciprocal electric switches 2, may be replaced by an electric or electronic circuit (with two simultaneous drive coils, for example) specifically adapted for promote the same function.

[0064] In particular, said coil 21 is directly connected to the power grid, which energizes the universal electric motor and, in this way, such a coil is specially designed to generate electromagnetic effect capable of changing the positioning of the reciprocal electric switches 2 only when powered with 220 Volts. This means that when powered at 127 Volts, said coil 21 is unable to change the positioning of the reciprocal electric switches 2.

[0065] Thus, according to this preferred embodiment, the electric switch 1 comprising the coil 21 acts as a kind of electromechanical input voltage detector, changing the positioning of the reciprocal electric switches 2 (and the topology of the universal electric motor) only in specific and previously“programmed” situations.

[0066] In general terms, it is the“electric recipe” of coil 21 that, configured to generate relevant magnetic field only when powered at 220 Volts, allows this type of implementation.

[0067] The invention in question also provides for the application of the whole of the above-described concept in embodiments of manual power tools provided with elec tric cable, with an external terminal, adapted for connection to the electric distribution system, such as drills, electric screwdrivers, circular saws, and other equivalent manual power tools.

[0068] 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.