WO2011012572A2

WO2011012572A2 - Direct current electric motor, particularly for movements on motor vehicles, such as window winders, seat adjusters, windscreen wipers and the like

Info

Publication number: WO2011012572A2
Application number: PCT/EP2010/060794
Authority: WO
Inventors: Maurizio Basso; Oscar Bertuzzo; Mirko Ortoman; Antonio Surian
Original assignee: Nuova SME SpA
Current assignee: Cebi Motors SpA
Priority date: 2009-07-30
Filing date: 2010-07-26
Publication date: 2011-02-03
Anticipated expiration: 2012-01-30
Also published as: ITPD20090042U1; WO2011012572A3; DE112010003114T5

Abstract

A direct current electric motor (10), particularly for movements on motor vehicles, such as window winders, seat adjusters, windscreen wipers and the like, comprising a carcase (11) for containing a stator body with at least two poles, a rotor (12) with at least eight slots, a drive shaft (13) with commutator (14) and brushes (15), each of the brushes (15) being held in a corresponding seat (16), with radial advancement due to consumption of the brush (15), the seats (16) being formed on a brush holder body (17) to be fixed to the carcase (11). The arc of contact between the projecting end of a brush (15) and the commutator (14) has a diameter (Dl) that is equal to the diameter (D2) of the commutator (14), or which differs from it by less than 10% of the diameter (Dl) of the commutator, and each brush holder seat (16) has two lateral walls (18, 19), with positions that are parallel to each other and which are parallel to the axis of rotation of the motor, and two walls (24, 25) that are perpendicular to the previous walls, with positions that are therefore substantially perpendicular to the axis of rotation of the motor, one of these walls being shaped so as to form the stroke limit for the corresponding brush (15), so having an abutment surface (26) for the power braid (27) fixed to the brush (15).

Description

DIRECT CURRENT ELECTRIC MOTOR, PARTICULARLY FOR MOVEMENTS ON MOTOR VEHICLES, SUCH AS WINDOW WINDERS, SEAT ADJUSTERS, WINDSCREEN WIPERS AND THE LIKE

Technical field

The present invention relates to a direct current electric motor, particularly for movements on motor vehicles, such as window winders, seat adjusters, windscreen wipers and the like.

Background Art

Nowadays, reading the position, speed and acceleration of a drive shaft of a direct current electric motor, to be mounted in a motor vehicle, is generally performed by using an incremental type device, in which an electronic controller recognises a zero point (upon reaching and recognising a travel limiter) and, at such zero point, performs a first calibration so that, from such zero point, such electronic controller, by counting the impulses that it receives from a sensor installed in the motor and facing the drive shaft, can calculate and assess the movements of such shaft.

The electric motor is generally coupled to a gear reducer which, in turn, moves an actuation means to open or close a window, a door, or to move a seat or a windscreen wiper, or other similar applications.

Digital sensors, known as "Hall effect sensors", are particularly widespread in electric motors for such applications.

With the use of these sensors, the electronic controller recognises a sequence of 1/0 transitions and, from the count thereof, it obtains the information regarding position, speed and acceleration of the drive shaft and therefore of the associated actuation means.

The adoption of Hall sensors entails costs, not only in terms of components and assembly, but also in terms of control electronics and in- vehicle wiring, this last item requiring special connectors.

It is also known to detect rotation parameters of the drive shaft without resorting to Hall sensors, by setting up the electronic controller to read the analogue power signal.

In particular, the electronic controller is set up to count the so-called switching "ripples", i.e. "bounces" of voltage due to the switching between the brushes and the commutator.

In order to be usefully readable by the control electronics, an analogue signal of this sort must, however, have a low noise level which can be properly filterable by the electronics, and the impulse levels (i.e. the voltage bounces on switching) must be of sufficient energy to be properly recognised by such electronics. In this way the analogue signal is comparable to a digital signal and, as such, is computable.

To achieve this, it is necessary that the contact between brush and commutator has a stable equilibrium.

Nowadays, to favour such stable equilibrium in the contact between brush and commutator, the sector trend is to make brush holder seats that are of high precision, which do not disturb the correct radial movement of the brush held in them, and which, with such brush, define limited clearances.

Nowadays, brush holder seats are generally provided internally with box-shaped guides made of brass, which are inserted in the brush holder body made of plastics, or incorporated in a printed circuit which is a structural part of the electric motor.

Such solutions are relatively expensive, both because of the adoption of guides made of brass, and because of the costs and times for assembly that are also required.

Disclosure of the Invention

The aim of the present invention is to provide a direct current electric motor, particularly for movements on motor vehicles, such as window winders, seat adjusters, windscreen wipers and the like, that is capable of overcoming the above mentioned drawbacks of known types of direct current electric motors, at low cost. Within this aim, an object of the invention is to provide an electric motor that improves the stable equilibrium of the regions of contact between the brushes and the commutator.

Another object of the invention is to provide an electric motor that is simple to assemble by the same standards of electric motors of the known type.

A further object of the invention is to devise an electric motor that can be associated with known gear reducers without requiring special modifications to said gear reducers.

Another object of the invention is to provide a direct current electric motor that can be controlled also without the onboard installation of Hall effect sensors or of other similar sensors.

A further object of the invention is to provide a direct current electric motor, particularly for movements on motor vehicles such as window winders, seat adjusters, windscreen wipers and the like, that is easy to make using known systems and techniques.

This aim, as well as these and other objects which will become better apparent hereinafter, are achieved by a direct current electric motor, particularly for movements on motor vehicles, such as window winders, seat adjusters, windscreen wipers and the like, that comprises a carcase for containing a stator body with at least two poles, a rotor with at least eight slots, a drive shaft with commutator and brushes, each of said brushes being held in a corresponding seat, for radial advancement due to consumption of said brush, said seats being formed on a brush holder body to be fixed to said carcase, characterised in that

- the contact arc between the projecting end of a brush and the commutator has a diameter that is equal to the diameter of the commutator, or which differs from it by less than 10% of the same diameter of the commutator, and in that

- each brush holder seat has two lateral walls, with positions that are parallel to each other and which are parallel to the axis of rotation of the motor, and two walls that are perpendicular to the previous ones, with positions that are therefore substantially perpendicular to the axis of rotation of the motor, one of said walls being shaped so as to form the stroke limit for the corresponding brush, so having an abutment surface for the braid fixed to the brush.

Brief description of the drawings

Further characteristics and advantages of the invention will become better apparent from the following detailed description of two preferred, but not exclusive, embodiments of the direct current electric motor according to the invention, illustrated by way of non-limiting example in the accompanying drawings, wherein:

Figure 1 is a perspective view, with the rotor partially extracted from the carcase, of an electric motor according to the invention in a first embodiment thereof;

Figure 2 is a perspective view of the brush holder body;

Figure 3 is a sectional view perpendicular to the axis of the electric motor of the brush holder body;

Figure 4 is a further sectional view perpendicular to the axis of the electric motor of the brush holder body;

Figure 5 is a diagram of the thrust force of a brush;

Figure 6 is a longitudinal sectional view of a detail of the electric motor according to the invention;

Figure 7 is a perspective view of a portion of a brush holder body of an electric motor according to the invention in a second embodiment thereof;

Figure 8 is a transverse sectional view of the brush holder body of Figure 6.

Ways of carrying out the Invention

With reference to the figures, a direct current electric motor according to the invention is generally designated, in Figure 1, by the reference numeral 10.

The structure 10 comprises a carcase 11, a rotor 12, a drive shaft 13 with commutator 14 and brushes 15.

The brushes 15 are held in a corresponding seat 16, with advancement due to consumption.

The seats 16 are formed on a brush holder body 17, to be fixed to the carcase 11.

The Figures from 2 to 4 show an electric motor of the type that comprises a stator body with four poles and a rotor with nine slots, such elements not being shown for the sake of simplicity, with the brushes 15 that are placed to operate in two radial directions that are angularly distant from each other by an angle P of 80°.

The seats 16 each have two lateral walls 18 and 19, with positions that are parallel to each other and which are parallel to the axis of rotation of the motor.

From the lateral walls 18 and 19 ridges 20 protrude for containing the clearances between such lateral walls and the corresponding facing surfaces of the respective brush 15.

Specifically, the fitting clearance between the width A of the brush 15 and the minimum distance B between the opposing ridges of the inner faces of the lateral walls of the brush seat is comprised between 2% and 12% of the minimum distance B.

The contact arc between the projecting end 21 of one brush 15 and the commutator 14 has a diameter Dl that is equal to the diameter D2 of the commutator 14, as in Figure 4, or which differs from it by less than 10% of the diameter Dl .

Each seat 16 for a brush 15 also comprises two walls 24 and 25 that are perpendicular to the lateral walls 17 and 18, with positions that are thus substantially perpendicular to the axis of rotation of the motor.

Similarly, the perpendicular walls 24 and 25 also have ridges 20a that run along the lower perpendicular wall 25 in a direction that is parallel to the radial direction of advancement of the brush 15, and along the upper perpendicular wall 24 in a tangential direction; the ridges 20a are also for containing the clearances between the walls 24 and 25 and the corresponding facing surfaces of the respective brush 15.

A first wall 24 of such walls is shaped so as to form the travel limit for the corresponding brush 15, so having an abutment surface 26 for the power braid 27 fixed to the brush 15 .

The brush holder body 17 with the seats 16 as described can be made by injection moulding of plastics, using moulds that are structurally simple and which lack the complex radial trolleys that are generally used for making seats for the brushes of such brush holder bodies.

Indeed, as can be seen from the detail in Figure 6, the first perpendicular wall 24, which is shaped so as to form the travel limit abutment 26 for the brush 15, is provided by a flap that extends from a side wall 19, at which a counter-shaped hole 24a is formed on the opposite perpendicular wall 25, and is made by a corresponding relief of one of the two dies of the mould with which the brush holder body 17 is made.

This structural distinctive characteristic makes it possible to make the brush holder body 17 by means of a simple mould composed of two dies, and the omission of using complex trolleys to make undercuts makes it possible, even more advantageously, to develop eight impressions for each mould instead of four, for the same overall dimensions of the mould, so doubling production rates and halving production times.

The overall length L of the brush 15 is at least double, and preferably triple, with respect to the useful travel C of the same brush 15, measured as the distance between the braid 27 and the travel limit abutment 26.

Each brush 15 is pushed radially towards the commutator 14 by an end arm 29 of a helicoid spring, which acts on the rear face of the brush 15.

The arm 29 of the brush pushing spring is arranged so as to act on a plane that is perpendicular to the axis of the motor, and touches the brush 15 at a point T that is at a distance K from the meridian plane Pm of the brush 15 which is less than or equal to 35% of the width A of the brush 15 measured on the same plane of action of the arm 29. This is shown in the diagram of Figure 5.

The width A of a brush 15 on a plane that is perpendicular to the axis of rotation of the motor is comprised between 80% and 97% of the width G of a reed 14a of the commutator 14.

It should be understood that such electric motor according to the invention can also be made with a stator body with permanent magnets that is composed of two poles and a rotor with eight polar slots, and in which the sliding directions of the two brushes are radial with respect to the rotor and are spaced by an angle of 180° with respect to the axis of the commutator.

It should be understood that such electric motor according to the invention can also be made with nine pole shoes and a stator with permanent magnets that is composed of four poles, with the seats of the brushes which are distant by an angle of 80° from each other, as in Figures 2 to 4, or of 120°, or of 160° with respect to the axis of the commutator.

It should be understood that such electric motor according to the invention can also be made with a rotor provided with ten pole shoes and a stator body with permanent magnets that is composed of two or four poles, in which the sliding directions of the two brushes are radial with respect to the rotor, and are distant by an angle of 72°, or 108°, or 144° or 180° with respect to the axis of the commutator.

It should be understood that such electric motor according to the invention can also be made with a rotor with twelve pole shoes and a stator body with permanent magnets that is composed of two or four poles, in which the sliding directions of the two brushes form an angle of 90° or 180° between them and geometric with respect to the axis of the commutator.

With the distinctive structural characteristics described above of the brushes 15, of the brush pushing springs, and of the position and shape of the seat 16 in which the brushes slide, a stable and constant contact is obtained between the commutator 14 and the brushes 15, on a surface that has an arc of circumference with a radius that is equal to that of the commutator except for a modest deviation.

Such contact surface can be cylindrical, or cylindrical except for a series of circumferential grooves or, alternatively, can have a conical surface but with the maximum radial encumbrance of the brush.

Thanks to these distinctive structural characteristics, the sum of the forces acting on the brush 15 is substantially equal to zero, and the sum of the moments of the forces acting on the brush with respect to any point on the surface of the brush resting on the commutator is very close to zero.

With the electric motor 10 according to the invention, during operation, in both directions of rotation of the commutator 14, no significant parting or movement can be detected between the brush 15 and the commutator 14.

This makes it possible to obtain a voltage signal that can be read at the two ends of the power line, which is adapted to be effectively read and converted into information about the position, speed and acceleration of the rotor, and therefore into information about the position, speed and force expressed by the motor to be controlled.

Figures 7 and 8 show an electric motor according to the invention in a second embodiment thereof.

In Figure 7 two brushes 115 are shown that are radially arranged at 180° from each other.

The braids 127, the travel limiters 126, the lateral walls 118 and 119 of the seats of the brushes with the ridges 120 and 120a, can all be seen.

In Figure 8 an arm 129 for pushing the brush 115 is clearly visible, as well as the commutator 114 with eight pole shoes.

In practice it has been found that the invention fully achieves the intended aim and objects.

In particular, with the invention an electric motor has been devised that improves the stable equilibrium of the regions of contact between the brushes and the commutator, making it possible to obtain a reading signal of the power supply voltage that is clean and which can be interpreted as information about the position, speed and acceleration of the motor.

Moreover, with the present invention an electric motor has been provided that is simple to assemble by the same standards of electric motors of known types.

Therefore, with the invention a direct current electric motor has been provided that can be controlled also without the onboard installation of Hall effect sensors or of other similar sensors.

Moreover, with the invention an electric motor has been provided that can be associated with known gear reducers without requiring special modifications to such gear reducers.

Further, with the present invention a direct current electric motor has been provided, particularly for movements on motor vehicles, such as window winders, seat adjusters, windscreen wipers and the like, that is easy to make using known systems and techniques.

The invention thus conceived is susceptible of numerous modifications and variations, all of which are within the scope of the appended claims. Moreover, all the details may be substituted by other, technically equivalent elements.

In practice the materials employed, as well as the dimensions and the contingent shapes, may be any according to requirements and to the state of the art.

The disclosures in Italian Utility Model Application No. PD2009U000042 from which this application claims priority are incorporated herein by reference.

Where technical features mentioned in any claim are followed by reference signs, such reference signs have been inserted for the sole purpose of increasing the intelligibility of the claims and accordingly such reference signs do not have any limiting effect on the interpretation of each element identified by way of example by such reference signs.

Claims

1. A direct current electric motor (10), particularly for movements on motor vehicles, such as window winders, seat adjusters, windscreen wipers and the like, that comprises a carcase (11) for containing a stator body with at least two poles, a rotor (12) with at least eight slots, a drive shaft (13) with commutator (14) and brushes (15), each of said brushes (15) being held in a corresponding seat (16), for radial advancement due to the consumption of said brush (15), said seats (16) being formed on a brush holder body (17) to be fixed to said carcase (11), which is characterised in that

— the contact arc between the projecting end of a brush (15) and the commutator (14) has a diameter (Dl) that is equal to a diameter (D2) of the commutator (14), or which differs from it by less than 10% of said diameter (Dl) of the commutator, and in that

- each brush holder seat (16) has two lateral walls (18, 19), with positions that are parallel to each other and which are parallel to the axis of rotation of the motor, and two walls (24, 25) that are perpendicular to the previous walls, with positions that are therefore substantially perpendicular to the axis of rotation of the motor, one of said walls being shaped so as to form the stroke limit for the corresponding brush (15), so having an abutment surface (26) for the power braid (27) fixed to the brush (15).

2. The structure according to claim 1, characterised in that each of said seats (16) has two lateral walls (18, 19) from which ridges (20) protrude to contain the clearances between said lateral walls (18, 19) and the corresponding facing surfaces of the respective brush (15).

3. The structure according to the preceding claims, characterised in that said perpendicular walls (24, 25) have ridges (20a) for containing the clearances between said walls and the corresponding facing surfaces of the respective brush (15).

4. The structure according to the preceding claims, characterised in that the overall length (L) of the brush (15) is at least double with respect to the useful travel (C) of said brush (15), measured as the distance between said braid (27) and said travel limit abutment (26).

5. The structure according to claim 1, characterised in that the fitting clearance between the width (A) of the brush (15) and the minimum distance (B) between the opposing ridges (20) of the inner faces of the lateral walls of the brush seat is comprised between 2% and 12% of said minimum distance (B).

6. The structure according to one or more of the preceding claims, characterised in that the arm (29) of the brush pushing spring is arranged so as to act on a plane that is perpendicular to the axis of the motor and touches the brush (15) at a point (T) that is at a distance (K) from the meridian plane (Pm) of the brush which is less than or equal to 35% of the width (A) of the brush when measured on the same plane on which the arm acts.

7. The structure according to the preceding claims, characterised in that the width (A) of a brush on a plane that is perpendicular to the axis of rotation of the motor is comprised between 80% and 97% of the width (G) of a reed of the commutator.

8. The structure according to the preceding claims, characterised in that it comprises a stator body with two poles, and a rotor with eight slots, the brushes being arranged to act in radial directions that are diametrically opposed to each other.

9. The structure according to claims from 1 to 6, characterised in that it comprises a stator body with four poles and a rotor with nine slots, the brushes being arranged to act in radial directions that are angularly distant from each other by an angle selected between 80°, 120°, 160°.