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Dokumentenidentifikation EP1852947 20.12.2007
EP-Veröffentlichungsnummer 0001852947
Titel Bürstenhalter für Gleichstrommotor und Bürstenhalteranordnung und Verbesserungen davon
Anmelder Faz Elektrik Motor Makina Sanayi ve Ticaret A.S., Izmir, TR
Erfinder Taner, Osman, Doganlar Mah, Bornova, 35050, Izmir, TR
Vertreter derzeit kein Vertreter bestellt
Vertragsstaaten AT, BE, BG, CH, CY, CZ, DE, DK, EE, ES, FI, FR, GB, GR, HU, IE, IS, IT, LI, LT, LU, LV, MC, NL, PL, PT, RO, SE, SI, SK, TR
Sprache des Dokument EN
EP-Anmeldetag 05.05.2006
EP-Aktenzeichen 061136016
EP-Offenlegungsdatum 07.11.2007
Veröffentlichungstag im Patentblatt 20.12.2007
IPC-Hauptklasse H01R 39/38(2006.01)A, F, I, 20071009, B, H, EP

Beschreibung[en]
Technical Field of the Invention

The present invention relates to a brush-brush holder assembly for a direct current electrical machine.

Background of the Invention

The direct current (DC) machine is one of the first machines devised to convert electrical power into mechanical power. Electric current flows through a wire loop located in a magnetic field and presence of the two fields result in a torque which tends to rotate the rotor. As already known, stationary parts of the motor are referred to as the stator; moving parts, including the wire loop, are referred to as the rotor or armature.

As the rotor turns, the current in the armature windings is commutated to produce a continuous torque output. The electric current is fed to the wire loop using carbon brushes that make contact with an extension of the armature known as the commutator. Together, the brush and commutator act as a switch that changes the direction of the electric current, causing the loop to continually rotate in a single direction.

The commutator is made of conductive segments representing the termination of individual coils of wire distributed around the armature. The carbon brushes are usually held in place with a brush holder, securing the brushes in the appropriate position relative to the commutator contact surface. The disadvantage of commutator motors are that sparking tends to occur between commutator segments and brushes, which eats away the metal of the segment. Even without sparks the rubbing of brush on segments wears away both and more maintenance is required than in the case of brushless machines.

There are quite a large number of patents/patent applications directed at dc machine armature current switching systems. Among others, one such system is disclosed in EP 1 489 727 . Among the most prominent drawbacks thereof, one such lies in that the brush basically consists of two separate parts, namely the holder portion and the portion that actually provides electrical contact with the commutator; from among those parts however, only the second part is used in conduction switching. The first part only serves to the purpose of supporting the operational part in general terms and transferring force to brush ends to keep electrical contact with the commutator.

The importance of the discussion of brush usability along its entire length stems from the well-know fact that frequent maintenance requirement is a major unpleasant factor for a DC machine, this machine although having convenient operational characteristics such as for instance unsophisticated speed control.

Referring back to EP 1 489 727 , the disclosure therein proposes three different embodiments, all of which making use of a support shaft onto which brush portions are mounted through suitable slots located on their bodies, eventually leading to a two-part non-monolithic design utilizing a limited length portion of the brushes. More specifically, it is not anymore possible to benefit from the carbon brush base portions after the brush end portions are worn away. Over time, it is inevitable that the carbon brushes wear away and require replacement; this naturally requiring periodic shutdown and maintenance.

The operational design suggested by the present invention ensures practical use of the carbon brushes along their entire length instead of a limited portion thereof, as well as providing a reliable electrical contact with the commutator. The brushes according to the present invention are directly connected to support means, which are secured to the brush holder, to apply required contact force on the brushes in order for holding them against the commutator. The contact surface between the brush and the commutator is enhanced and a more reliable contact is established.

The physical connection between said support means and the brushes is arranged such that the force exerted on the non-linear brushes is delivered to the brush ends and therefrom to the commutator lateral surface in the manner that the intensity and the direction of the force applied consecutively from one component to another component is constant for a given length of the non-linear brush, ensuring both usability of a longer brush due to the operational and effective design thereof and reliable contact force independent of how much of the brushes have actually been worn away or left.

Objects of the Invention

The primary object of the present invention is to provide a DC electric motor brush-brush holder assembly having a longer brush life and therefore an improved practical usability for the motor.

Summary of the Invention

The present invention proposes an improved design allowing use of longer brushes in order for extending brush life in which the intensity and the direction of the contact force required for ensuring electrical conduction in between the commutator and the brush end is devised in the manner to adapt a brush body superimposed on an arc portion the center of which is used for pivoting support means to apply required contact force on the brush body. The support means contacts the brushes by a single point-connection provided on the longitudinal axis of the non-linear brush body.

Brief Description of the Figures

Accompanying drawings are given solely for the purpose of exemplifying a direct current motor brush card assembly whose advantages over prior art were outlined above and will be explained in detail hereinafter:

  • Fig. 1 demonstrates a side view of the brush card assembly taken along the cross-section A-A depicted in Fig. 2.
  • Fig. 2 demonstrates an upper view of the brush card assembly.
  • Fig. 3 demonstrates a brush body according to the present invention.
  • Fig. 4 demonstrates a brush holder assembly along with torsional spring element and the brush.
  • Fig. 5 demonstrates a brush holder assembly alone.
  • Fig. 6 demonstrates a torsional spring element.

Detailed Description of the Invention

Referring now to the figures outlined above, under the motor cover extend the brush card assembly along with the commutator (11), the brushes (12) and the metal bars (13) connected to electrical elements (17) for filtering the noise caused by the commutation of the brushes (12). Since the topology of the filtering circuit is of no importance in regard to the scope of the present invmention, and characteristics of a LC low pass filter, which can for instance be used to address the noise issue, is known to those skilled in the art, no further details will be given herein in regard to this filtering circuit.

The brush base (14) of Fig. 1 is made of a thermoplastic material having a high heat deflection temperature. It is a single-piece monolithic block manufactured along with the brush holders by a single moulding operation. The thermoplastic material proves to remain solid up to 215° C under 8 MPa pressure. It is a strong material in terms of mechanical properties (165 MPa tensile strength and tensile modulus 14400 MPa). Said brush base (14) is fixedly mounted in between the cover and the motor body by means of flaps (15).

The present invention enables use of longer brushes (12). The length of a brush (12) is basically the key factor in determining brush life. According to the present invention, the brushes (12) are conventionally held in position and supported to push against the commutator by means of support means in the form of torsional spring elements (16). Fig. 2 shows a 4-pole dc motor with 4 brushes (12). The non-linear brushes (12) contact the commutator (11) segments in a manner to provide an optimized commutator-brush-brush holder relationship enabling accommodation of longer brushes due to the way the contact force that is required for switching the polarization is formed, delivered and applied as will be hereinafter explained in detail.

The intensity and the direction of the contact force required for ensuring electrical conduction between the commutator (11) and the brush (12) end is devised in the manner to adapt a brush (12) body superimposed on an arc portion, the center of which is used for pivoting said torsional spring element (16) to apply required contact force on the brush body. The torsional spring element (16) pushes the brush (12) by a single-point contact force which is tangential to the non-linear longitudinal axis of the non-linear brush (12) body.

The single-point contact between the brush body (12) and the torsional element (16) is provided by adapting said torsional element (16) to have a hook-shape ending (18) along a point on which said brush (12) is pushed against the lateral surface of the commutator (11). The hook-shape endings (18) of the torsional spring elements (16) are suitable for engaging in an indentation (19) formed on the brush (12) body. Said indentation (19) is suitable for receiving said hook-shaped ending (18) in the manner that the largest diameter of the tubular body of said hook-shaped ending (18) on the horizontal axis fits on the height of said indentation (19). The indentation (19) is set parallel to the horizontal axis.

According to the present invention, the torsional elements (16) are fixedly attached to locking slots (20) provided on the brush holder assembly. Those locking slots (20) are cylindrical elevations along the periphery of the lateral surfaces of which are encircled by a circular groove to receive the torsional spring elements (16).

The brushes (12) according to the present invention are designed to lie on arc portions on the center of which the torsional elements (16) are present. The fact that the brush (12) bodies shaped in the form of a proper arc of a circle whose center is occupied by the torsional elements (16) ensures that the longitudinal body of the torsional element (16) substantially coincides onto one of the outermost radiuses of the arc in question. Since the hook-shaped ending (18) of the torsional element (16) is designed to exert the pushing force in the direction of the surface normal of the contact surface, the torsional element (16) precisely lying on the radius and exerting the pushing force in the direction of the longitudinal axis of the brush (12) body results in a very effective design n terms of the optimization and maximization of the contact force delivered to the brush body (12).

As the brushes (12) wear away over time, they get shorter and shorter and this will eventually lead to a significant change in the original operation layout of the torsional element (16), brush (12) and commutator (11) trio. On the other hand, since the original direction of the force exerted by the torsional element (16) will remain intact due to the geometrical shape of the brush (12) body, sound operation will go on independent of the brush (12) length. Since the originally set operation conditions will remain unchanged until the brush (12) body is fully consumed, the full length of the body will then be functional in terms of usability. In sum, longer brush usability is ensured due to the operational design of the present invention.

According to the present invention, the point onto which the contact force is applied within the indentation (19) is exactly on the brush (12) body longitudinal axis line, which is also joining the contact point to the center of gravity of the actual brush (12) body. This is due to the fact that the center of gravity of the brush body for any given length lies on the longitudinal axis of the brush (12).

Referring now to Fig. 5, the brush holder assembly therein comprises a set of special arrangements to support the operational design defined above. The brush holder comprises a set of curvilinear projections (21) designed to receive the brushes (12) from below. Those are given a corresponding arc form adapted to the brushes (12) in order for keeping them on the trajectory as long as they are sufficient in length for motor operation. The projections (21) contact the brush (12) bottom surface from below by a contact connection extending along a line. In other words, the points to which the projections (21) make contact with the brush (12) form a linear contact line. The linear contact line extending longitudinally along the peak points of the projections (21) basically eliminates unnecessary friction caused by a two-dimensional contact area.

Again in Fig. 5, it can be seen delimiting elements 22 and 23, which surround the brush (12) of Fig. 4 in the manner to restrict its movement from both sides. The delimiting element 22 is designed to occupy only a limited space, in the form of a vertical support extension with a substantially narrow portion that reaches over the brush (12) upper surface, allowing air flow through to enable natural cooling by convection.

To evacuate heat occurring with friction and to enable effective heat transfer, an evacuation window (24) so as to extend longitudinally along a bottom line of the brush (12) lateral surface is arranged. Such an opening (25) is also embedded in the middle of the brush (12) holder assembly to reinforce convection currents.

The brush card assembly of Fig. 2 is designed for a 4-pole dc motor. The operational design of the present invention so as to incorporate a 4-brush brush cart assembly comprising brush-brush holder assemblies as is explained so far can accommodate longer brushes and therefore extend brush life in a 4-pole motor.

According to the present invention, the brush (12) end that makes contact with the commutator (11) is set eccentric to the commutator (11) in the sense that the mediator of the line that passes from the two edge points of the brush (12) arc that makes contact with the commutator (11) do not pass from the geometrical center of said commutator (11). Therefore a more reliable contact is established by increasing the contact surface between the brush (12) and the commutator (11). It is apparent from Fig. 7 that the contact surface along a line I2 is greater than that along I1.

Summarily, the present invention proposes a DC machine brush cart assembly comprising a brush base (14), a commutator (11), an electrical filtering circuit for filtering the noise caused by commutation, a plurality of brush holders each of which with a non-linear brush (12) body and a support means (15) for exerting required contact force on said brush (12) to push it against said commutator (11) wherein said brush (12) body is superimposed on an arc portion, in the center of which is pivoted said support means (16) so as to substantially coincide onto one of the outermost radiuses of said arc portion and to exert contact force on said brush (12) by a single-point contact force in the direction of the surface normal of the contact surface, the contact force also being tangential to the longitudinal axis of said brush (12) body.


Anspruch[en]
A DC machine brush cart assembly comprising a brush base (14), a commutator (11), an electrical filtering circuit for filtering the noise caused by commutation, a plurality of brush holders each of which with a non-linear brush (12) body and a support means (15) for exerting required contact force on said brush (12) to push it against said commutator (11) characterized in that;

said brush (12) body is superimposed on an arc, in the center of which said support means (16) is pivoted so as to coincide onto the outermost radius of said arc and so as to exert force on said brush (12) from a point which corresponds primary axis of said arc and in a direction normal to corresponding contact surface of said brush (12), whereby said contact force always applies parallel to the primary axis of said arc throughout entire service life of the brush body.
A DC machine brush cart assembly according to Claim 1 wherein said brush (12) end making contact with said commutator (11) is set eccentric to the commutator (11) in the manner that the mediator of the line that passes from the two edge points of the brush (12) arc that makes contact with the commutator (11) do not pass from the geometrical center of said commutator (11) whereby an increased contact surface is maintained in between the commutator and the brush. A DC machine brush cart assembly according to Claim 2 wherein said support means (16) is formed to be a torsional spring element (16) having a hook-shape ending (18) along a point on which said brush (12) is pushed against the lateral surface of the commutator (11) A DC machine brush cart assembly according to Claim 3 wherein said hook-shape endings (18) of the torsional spring elements (16) engage in a horizontal indentation (19) formed on the brush (12) surface. A DC machine brush cart assembly according to Claim 2 wherein the brush holder comprises a plurality of curvilinear projections (21) corresponding to the brush (12) bodies for contacting the same from below. A DC machine brush cart assembly according to Claim 5 wherein the points to which the projections (21) contact the brush (12) form a linear contact line. A DC machine brush cart assembly according to Claim 5 wherein the brush holder comprises delimiting elements (22, 23) surrounding the brush (12) in the manner to restrict its movement from both sides. A DC machine brush cart assembly according to Claim 7 wherein the delimiting element 22 is provided in the form of a limited-width vertical support extension with a substantially narrow portion that reaches over the brush (12) upper surface, allowing air flow through to enable natural cooling by convection. A DC machine brush cart assembly according to Claim 7 wherein the brush holder comprises an evacuation window (24) extending longitudinally along a bottom line of the brush (12) lateral surface whereby heat occurring with friction is evacuated and effective heat transfer is enabled. DC machine brush cart assembly according to Claim 7 wherein the brush holder comprises an opening (25) embedded in the middle of the brush (12) holder assembly to reinforce convection currents. A DC machine brush cart assembly according to Claim 2 wherein said brush base (14) is a single-piece monolithic thermoplastic block manufactured along with the brush holders by a single moulding operation. A DC machine brush cart assembly according to Claim 2 wherein said torsional elements (16) are fixedly attached to cylindrical elevations along the periphery of the lateral surfaces of which are encircled by a circular groove to receive said torsional spring elements (16). A DC electrical machine comprising the DC machine brush cart assembly of Claim 2.






IPC
A Täglicher Lebensbedarf
B Arbeitsverfahren; Transportieren
C Chemie; Hüttenwesen
D Textilien; Papier
E Bauwesen; Erdbohren; Bergbau
F Maschinenbau; Beleuchtung; Heizung; Waffen; Sprengen
G Physik
H Elektrotechnik

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