Brush for electric motor and associated electric motor

Abstract

Brush for electric motor and associated electric motor The present invention relates to a brush (5, 5a, 5b, 5c) for a direct current electric motor (2) comprising a rotor (3), the brush (5, 5a, 5b, 5c) comprising a contact surface (SC) intended to come into contact with a commutator (7) of said rotor (1) of the electric motor (2), in which the brush (5, 5a, 5b, 5c) has a generally rectangular parallelepiped shape and comprises a single chamfer (CF) at the leading edge of the contact surface (SC).

Description

Title of the invention: Brush for electric motor and associated electric motor

[0001] The present invention falls within the field of direct current electric motors and in particular brushed electric motors in which the rotor is powered by means of brushes configured to come into contact with the rotor.

[0002] These electric motors are for example used in motor vehicle equipment.

[0003] In these electric motors, the rotation of the rotor causes friction between the rotor and the brushes, which tends to produce noise, particularly at the beginning of the brush's life. However, in the case of motor vehicle equipment, such noise can be detrimental to the comfort of passengers.

[0004] It is therefore necessary to find a solution to reduce the noise produced by the friction of the brushes on the rotor without altering the characteristics of the electric motor.

[0005] To this end, the present invention relates to a brush for a direct current electric motor comprising a rotor, the brush comprising a contact surface intended to come into contact with a commutator of said rotor of the electric motor in which the brush has a general rectangular parallelepiped shape and comprises a single chamfer at the leading edge of the contact surface.

[0006] The presence of a chamfer at the leading edge of the brush makes it possible to reduce the noise generated by the friction of the brush on the rotor at the beginning of the life of the brush while reducing the life of the brush to a minimum. In addition, the presence of a single chamfer makes it possible to reduce manufacturing costs compared to brushes having several chamfers.

[0007] According to another aspect of the present invention, the chamfer reduces the contact surface by a value of between 20% and 60%, in particular between 40% and 50% compared to a contact surface of a rectangular parallelepiped-shaped brush.

[0008] According to another aspect of the present invention, the contact surface has a height of between 1 mm and 2 mm, in particular 1.5 mm + / - 10% and the total height of the brush is between 2.5 mm and 3.5 mm, in particular 2.89 mm + / - 10%.

[0009] According to another aspect of the present invention, the ratio between the total height and the height of the contact surface is less than 1.8 or more than 2.0.

[0010] According to another aspect of the present invention, the brush comprises a combination of resin and conductive material.

[0011] Preferably, the conductive material comprises graphite, and preferably includes graphite and copper

[0012] According to another aspect of the present invention, the combination of resin and conductive material comprises a percentage of conductive material of between 50% and 70%.

[0013] The present invention also relates to a direct current electric motor comprising a stator, a brush holder element, a rotor and at least one brush according to one of the preceding claims.

[0014] According to another aspect of the present invention, the direct current electric motor comprises three brushes, a first brush associated with the mass, a second brush associated with a first rotational speed of the rotor and a third brush associated with a second rotational speed of the rotor.

[0015] According to another aspect of the present invention, the brush holder element comprises resilient means configured to urge the brushes against the rotor commutator.

[0016] Other characteristics and advantages of the invention will appear more clearly on reading the following description, given by way of illustrative and non-limiting example, and the appended drawings among which:

[0017] [Fig.l] represents a schematic perspective view of a portion of a stator of an electric motor,

[0018] [Fig-2] represents a schematic perspective view of a broom according to the present invention,

[0019] [Fig.3] represents a schematic side view of a broom according to the present invention;

[0020] In these figures, identical elements bear the same references.

[0021] The following embodiments are examples. Although the description refers to one or more embodiments, this does not necessarily mean that each reference relates to the same embodiment, or that the features apply only to a single embodiment. Single features of different embodiments may also be combined or interchanged to provide other embodiments.

[0022] [Fig.l] represents a schematic perspective view of a brush-holder element 1 of a direct current electric motor 2 as well as a portion of a rotor 3 of the electric motor arranged in the center of the brush-holder element 1. More specifically, the rotor 3 comprises a commutator 7, here shown schematically by a central ring representing a portion of the rotor 3, positioned opposite the brush-holder element 1.

[0023] The stator and the rest of the rotor are not illustrated for reasons of clarity; it may be assumed for the purposes of this document that they are configured in a conventional manner, according to the practice known to those skilled in the art in the art. field of direct current motors with brushes. The direct current motor envisaged by the present application is for example used in a motor vehicle wiping device.

[0024] The brush-holder element 1 has a generally annular or tubular shape, having a central opening configured to receive the rotor 3, in particular its commutator 7. The brush-holder element 1 comprises three brushes 5, here numbered respectively 5a, 5b and 5c configured to come into contact with the commutator 7 of the rotor 3, in the manner illustrated in [Fig.l]. In the present case, the three brushes 5a, 5b, 5c are distributed over a 180° portion of the brush-holder element 1 but other arrangements are also possible. A first brush 5a associated with the ground, a second brush 5b associated with a first rotational speed of the rotor 3 and a third brush 5b associated with a second rotational speed of the rotor 3. Thus, the second 5b and the third 5b brushes can be connected respectively to a first 9a and a second 9b power supply circuit.

[0025] However, it will be understood that the brush holder element, in other possible embodiments, could be integrated partially or entirely into the stator, the motor housing / cylinder head, or other structural element of the motor, without departing from the scope of the invention.

[0026] The brush-holder element 1 also comprises elastic means such as springs (not visible in [Fig.l]) configured to constrain the brushes 5 against the commutator 7 of the rotor 3 during the lifetime of the brush 5, in particular during the operation of the electric motor 2.

[0027] As shown in Figures 2 and 3, the brushes 5 have a general rectangular parallelepiped shape. The face of the parallelepiped configured to come into contact with the commutator 7 of the rotor 3 is called the contact surface and denoted SC.

[0028] Furthermore, at least one of the brushes 5, all the brushes 5a, 5b and 5c in the present example, comprise a single chamfer denoted CF arranged at the leading edge of the brush 5, that is to say the edge of the contact surface SC that a portion of the commutator 7 of the rotor 3 reaches first during rotation of the rotor.

[0029] The size of the chamfer CF is chosen to reduce the contact surface SC by a value of between 20% and 60%, in particular between 40% and 50% (compared to a brush having a rectangular parallelepiped shape (without chamfer)).

[0030] The brush 5 has for example a total height H of between 2.5 mm and 3.5 mm, in particular 2.89 mm + / - 10% and the height h of the contact surface SC is for example between 1 mm and 2 mm, in particular 1.5 mm + / - 10%. Preferably, the ratio H / h between the total height H and the height of the contact surface h is less than 1.8 or more than 2.0.

[0031] The chamfer forms for example an angle between 50° and 70° with the surface of SC contact. The total length L of the brush is for example between 7mm and 9mm, in particular 8mm+ / -10% and the length 1 of the chamfer is for example between 2.5mm and 3.5mm, in particular 2.8mm+ / -10%.

[0032] A chamfer CF provided on a reduced portion of the length L of the brush 5 makes it possible to hold the brush 5 effectively in its support and not to reduce the service life of the brush 5 too much.

[0033] The brush 5 comprises, for example, a combination of resin and conductive material. The conductive material is normally a composition of carbon and / or graphite, the latter being particularly interesting for its lubricating properties. However, the conductive material may further comprise other electrically conductive substances, in particular powdered metals. Copper and silver are particularly interesting, because of their high conductivity.

[0034] Thus, the use of brushes 5 comprising a single chamfer CF at the leading edge of the contact surface of the brush 5 makes it possible to reduce the noise produced by the friction of the brush 5 on the commutator 7 at the start of the life of the brush due to the reduced contact surface SC. This noise decreases after a period of use of the brush corresponding to a running-in period of the brush 5. The contact surface SC is therefore increasingly larger as the brush 5 wears, which makes it possible to limit the wear rate of the brush 5 and thus ensure a long service life while minimizing the noise produced at the start of the life of the brush 5.

[0035] Furthermore, the fact that the brushes 5 are asymmetrical makes them easier to manufacture, and more stable during operation because they are less likely to oscillate or vibrate in the brush-holder element after a certain degree of wear, than symmetrical chamfered brushes.

Claims

Claims

1. Brush (5, 5a, 5b, 5c) for a direct current electric motor (2) comprising a rotor (3), the brush (5, 5a, 5b, 5c) comprising a contact surface (SC) intended to come into contact with a commutator (7) of said rotor (3) of the electric motor (2), characterized in that the brush (5, 5a, 5b, 5c) has a generally rectangular parallelepiped shape and comprises a single chamfer (CF) at the leading edge of the contact surface (SC).

2. Brush (5, 5a, 5b, 5c) for electric motor (2) according to claim 1 in which the chamfer (CF) reduces the contact surface (SC) by a value of between 20% and 60%, in particular between 40% and 50% compared to the contact surface obtained with a brush of rectangular parallelepiped shape.

3. Brush (5, 5a, 5b, 5c) for electric motor (2) according to the preceding claim in which the contact surface (SC) has a height (h) between 1mm and 2mm, in particular 1.5mm+ / -10% and the total height (H) of the brush (5) is between 2.5mm and 3.5mm, in particular 2.89mm+ / -10%.

4. Brush (5, 5a, 5b, 5c) for electric motor (2) according to the preceding claim, in which the ratio (H / h) between the total height (H) and the height of the contact surface (h) is less than 1.8 or more than 2.

0.

5. Brush (5, 5a, 5b, 5c) for an electric motor (2) according to one of the preceding claims in which the brush (5, 5a, 5b, 5c) comprises a combination of resin and conductive material.

6. A brush (5, 5a, 5b, 5c) according to the preceding claim, wherein the conductive material comprises graphite, and preferably comprises graphite and copper.

7. Brush (5, 5a, 5b, 5c) for electric motor (2) according to one of claims 5 and 6, in which the combination of resin and conductive material comprises a percentage of conductive material of between 50% and 70%.

8. Direct current electric motor (2) comprising a stator, a brush holder element (1), a rotor (3) and at least one brush (5, 5a, 5b, 5c) according to one of the preceding claims.

9. Direct current electric motor (2) according to the preceding claim comprising three brushes (5, 5a, 5b, 5c), a first brush (5a) associated with the ground, a second brush (5b) associated with a first rotation speed of the rotor (3) and a third brush (5c) associated with a second rotation speed of the rotor (3).

10. Direct current electric motor (2) according to one of claims 8 or 9 wherein the brush holder element (1) comprises elastic means configured to constrain the brushes (5, 5a, 5b, 5c) against the commutator (7) of the rotor (3).

Images