Title: Method and apparatus to suppress electrical noise in a rotor assembly for an electrical machine
Abstract: A dynamoelectric machine includes a rotor having a rotor shaft; two flux carrying segments rotatably disposed on the rotor shaft; a field coil disposed between the two flux carrying segments, the field coil having a pair of coil leads; an insulative member disposed at one end of the shaft; a pair of slip rings longitudinally spaced on the insulative member and having respective coupling terminals; and a diode having a pair of diode leads, each diode lead electrically connected to one of the pair of coil leads of the field coil and to one of the respective coupling terminals, the diode configured to suppress electrical noise as a result of an interface between the pair of slip rings and respective brushes.
Patent Number: 7,015,608 Issued on 03/21/2006 to Hartman, et al.
| Inventors:
|
Hartman; Roger A. (Indianapolis, IN);
Bradfield; Michael D. (Anderson, IN)
|
| Assignee:
|
Delco Remy International, Inc. (Anderson, IN)
|
| Appl. No.:
|
899739 |
| Filed:
|
July 27, 2004 |
| Current U.S. Class: |
310/68R; 310/51 |
| Current Intern'l Class: |
H02K 11/00 (20060101) |
| Field of Search: |
310/51,68R,232,234,216,254,261
|
References Cited [Referenced By]
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| 5306974 | Apr., 1994 | Bates.
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| 5424594 | Jun., 1995 | Saito et al.
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| 5717270 | Feb., 1998 | Lau et al.
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| 5905319 | May., 1999 | McLendon.
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| 6271607 | Aug., 2001 | Vandenbossche.
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| 6396175 | May., 2002 | Fujita et al.
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| 6400058 | Jun., 2002 | Liau.
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| 6476535 | Nov., 2002 | Oohashi et al.
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| 6580194 | Jun., 2003 | Mizutani et al.
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| 2002/0047366 | Apr., 2002 | Allendorf et al.
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| 2002/0079751 | Jun., 2002 | Janisiewicz et al.
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| 2002/0140301 | Oct., 2002 | Kershaw et al.
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| 2002/0149276 | Oct., 2002 | Borden et al.
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| 2003/0075997 | Apr., 2003 | Keim et al.
| |
Primary Examiner: Lam; Thanh
Attorney, Agent or Firm: Cantor Colburn LLP
Claims
What is claimed is:
1. A slip ring assembly for an automotive alternator comprising:
a pair of slip rings longitudinally spaced on an automotive alternator rotor
shaft along a longitudinal axis, said pair of slip rings having respective coupling
terminals extending therefrom; and
a diode having a pair of diode leads, each diode lead configured to be electrically
connected to one of a pair of coil leads of a field coil disposed on said rotor
shaft and to one of said respective coupling terminals, said diode configured to
suppress electrical noise as a result of an interface between said pair of slip
rings and respective brushes, said diode disposed on a rotor shaft side of said
slip ring/brush interface.
2. The assembly of claim 1, wherein said pair of slip rings is longitudinally
spaced on said rotor shaft via an insulative member operably coupled to said shaft.
3. The assembly of claim 1, wherein said diode is rotatable with said rotor shaft.
4. The assembly of claim 1, wherein said insulative member is a molded cylinder
having a cavity to receive said shaft, said exposed end of said cylinder includes
a diode receptacle configured to retain said diode and allow rotation thereof relative
to said cylindrical member.
5. The assembly of claim 4, wherein said diode receptacle includes a block assembly
extending from said exposed end defining said cylinder, said block assembly defining
a cavity to retain said diode therein and slots configured in opposing walls defining
said block assembly to allow ingress and egress of said diode leads for connection
with one of said pair of coil leads.
6. The assembly of claim 5, wherein said pair of slip rings is insert molded
with said cylinder.
7. The assembly of claim 6, wherein said cylinder is molded plastic.
8. The assembly of claim 5, wherein each of said respective coupling terminals
and said pair of coil leads extending from said exposed end extend from one of
two opposing apertures configured in said exposed end to align with said pair of
diode leads for connection therewith.
9. A rotor far an automotive alternator comprising:
an automotive alternator rotor shaft;
two flux carrying segments rotatably disposed on said rotor shaft;
a field coil disposed between said two flux carrying segments, said field coil
having a pair of coil leads;
an insulative member disposed at one end of said shaft;
a pair of slip rings longitudinally spaced on said insulative member and having
respective coupling terminals; and
a diode having a pair of diode leads, each diode lead electrically connected
to one of said pair of coil leads of said field coil and to one of said respective
coupling terminals, said diode configured to suppress electrical noise as a result
of an interface between said pair of slip rings and respective brushes, said diode
disposed on a rotor shaft side of said slip ring/brush interface.
10. The machine of claim 9, wherein said diode is rotatable with said rotor shaft.
11. The machine of claim 9, wherein said insulative member is a molded cylinder
having a cavity to receive said shaft, said exposed end of said cylinder includes
a diode receptacle configured to retain said diode and allow rotation thereof relative
to said cylindrical member.
12. The machine of claim 11, wherein said diode receptacle includes a block assembly
extending from said exposed end defining said cylinder, said block assembly defining
a cavity to retain said diode therein and slots configured in opposing walls defining
said block assembly to allow ingress and egress of said diode leads for connection
with one of said pair of coil leads.
13. The machine of claim 12, wherein said pair of slip rings is insert molded
with said cylinder.
14. The machine of claim 13, wherein said cylinder is molded plastic.
15. The machine of claim 12, wherein each of said respective coupling terminals
and said pair of coil leads extending from said exposed end extend from one of
two opposing apertures configured in said exposed end to align with said pair of
diode leads for connection therewith.
16. An automotive alternator comprising:
a housing defining a drive end and an opposite slip ring end;
a stator;
an automotive alternator rotor shaft;
two flux carrying segments rotatably disposed on said rotor shaft rotatable within
said stator;
a field coil disposed between said two flux carrying segments, said field coil
having a pair of coil leads;
an insulative member disposed at one end of said shaft;
a pair of slip rings longitudinally spaced on said insulative member and having
respective coupling terminals; and
a diode having a pair of diode leads, each diode lead configured to be electrically
connected to one of said pair of coil leads of said field coil and to one of said
respective coupling terminals, said diode configured to suppress electrical noise
as a result of an interface between said pair of slip rings and respective brushes,
said diode disposed on a rotor shaft side of said slip ring/brush interface.
17. The generator of claim 16, wherein said diode is rotatable with said rotor shaft.
18. The generator of claim 16, wherein said insulative member is a molded cylinder
having a cavity to receive said shaft, said exposed end of said cylinder includes
a diode receptacle configured to retain said diode and allow rotation thereof relative
to said cylindrical member.
19. The generator of claim 18, wherein said diode receptacle includes a block
assembly extending from said exposed end defining said cylinder, said block assembly
defining a cavity to retain said diode therein and slots configured in opposing
walls defining said block assembly to allow ingress and egress of said diode leads
for connection with one of said pair of coil leads.
20. The generator of claim 19, wherein said pair of slip rings is insert molded
with said cylinder.
21. The generator of claim 20, wherein said cylinder is molded plastic.
22. The generator of claim 19, wherein each of said respective coupling terminals
and said pair of coil leads extending from said exposed end extend from one of
two opposing apertures configured in said exposed end to align with said pair of
diode leads for connection therewith.
23. A method to suppress electrical noise generated in a brush type rotor of
a wound-field automotive alternator, the method comprising:
connecting a diode in parallel with a field coil on a rotor shaft side of a slip
ring/brush interface; and,
disposing said diode on an exposed end of a slip ring assembly rotable with an
automotive alternator rotor shaft.
24. The method of claim 23, further comprising:
connecting leads extending from said diode with a corresponding field coil lead
of said field coil and a respective coupling terminal extending from a corresponding
slip ring.
25. The method of claim 24, wherein said connecting leads includes crimping each
said respective coupling terminal around a corresponding field coil lead and diode lead.
Description
TECHNICAL FIELD
This application relates generally to an electrical apparatus. More specifically,
this application relates to a method and apparatus to suppress electrical noise
in a rotor assembly for an electrical machine.
BACKGROUND
Lundell alternators are used almost exclusively for passenger vehicle on-board
electrical generation. A Lundell alternator includes a wound-field claw pole rotor
that has the characteristic of satisfying most functional demands such as power
output, size, and reliability in a cost effective manner. In a dynamoelectric machine
having such a rotor, it is necessary to apply a voltage across the rotating field
coil winding to produce a time varying magnetic field. A slip ring and brush arrangement
is used to complete an electrical circuit between the rotating field coil winding
and the stationary electronics of the alternator, particularly the voltage regulator.
In such an arrangement, two copper slip rings are mounted on a rotating shaft
extending from the rotor and are electrically insulated from the shaft and each
other through plastic material that supports the rings. Each ring is connected
to one end of the field coil winding. The rings are cylindrical in shape and roughly
about 5 to about 10 mm in axial length. An electrical brush rides, or more appropriately,
slides, on a respective rotating slip ring. The two brushes are secured to a stationary
frame of the alternator via a brush holder or similar structure, and are forced
into direct, sliding contact with an exposed surface of a corresponding slip ring.
A biasing member, such as a spring, is used to bias each brush in contact with
a corresponding slip ring.
The two brushes are commonly solid carbon, or carbon-copper pieces that are typically
rectangular in shape. The brushes are electrically connected to the rest of the
alternator to provide the voltage across the field coil. During use, the slip rings
rotate with the rotor shaft and the two brushes slide across the exposed surface
of a corresponding slip ring to complete the electrical field circuit between the
field coil winding and the alternator.
The electrical interface between the brush and respective slip ring, however,
is not perfect. The brushes do not always make continuous, low-impedance contact
with the slip rings due to vibration, surface roughness and roundness of the slip
rings coupled with the rotational speeds of the rotor. Furthermore, the inductance
of the field coil winding can lead to negative voltage spikes within the field
circuit. Consequently, localized arcing and sparking occur between the slip rings
and corresponding brushes. This in turn produces electrical noise that can be disruptive
to other on-board vehicle electronics, such as the radio.
Accordingly, it is desired to suppress the electrical noise generated
due to the aforementioned voltage spikes that occur as a result of the imperfect
slip ring/brush interface.
BRIEF SUMMARY OF THE INVENTION
The above discussed and other drawbacks and deficiencies are overcome or alleviated
by a dynamoelectric machine including a rotor composed of a rotor shaft; two flux
carrying segments rotatably disposed on the rotor shaft; a field coil disposed
between the two flux carrying segments, the field coil having a pair of coil leads;
an insulative member disposed at one end of the shaft; a pair of slip rings longitudinally
spaced on the insulative member and having respective coupling terminals; and a
diode having a pair of diode leads, each diode lead electrically connected to one
of the pair of coil leads of the field coil and to one of the respective coupling
terminals, the diode configured to suppress electrical noise as a result of an
interface between the pair of slip rings and respective brushes.
In an exemplary embodiment, a slip ring assembly for a dynamoelectric machine
is disclosed. The slip ring assembly includes a pair of slip rings longitudinally
spaced on a rotatable shaft along a longitudinal axis, the pair of slip rings have
respective coupling terminals extending therefrom; and a diode having a pair of
diode leads. Each diode lead is configured to be electrically connected to one
of a pair of coil leads of a field coil and to one of the respective coupling terminals.
The diode is configured to suppress electrical noise as a result of an interface
between the pair of slip rings and respective brushes.
In another embodiment, an alternating current (AC) generator for a motor vehicle
is disclosed. The generator includes a housing defining a drive end and an opposite
slip ring end; a stator; a rotor shaft; two flux carrying segments rotatably disposed
on the rotor shaft rotatable within the stator; a field coil disposed between the
two flux carrying segments, the field coil having a pair of coil leads; an insulative
member disposed at one end of the shaft; a pair of slip rings longitudinally spaced
on the insulative member and having respective coupling terminals; and a diode
having a pair of diode leads. Each diode lead is configured to be electrically
connected to one of a pair of coil leads of a field coil and to one of the respective
coupling terminals. The diode is configured to suppress electrical noise as a result
of an interface between the pair of slip rings and respective brushes.
In yet another embodiment, a method to suppress electrical noise generated in
a brush type rotor of a wound-field electrical machine is disclosed. The method
includes connecting a diode in parallel with a field coil on a rotor side of a
slip ring/brush interface.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a partial sectional view through a Lundell alternator illustrating
a noise suppression diode operably coupled to a slip ring assembly in accordance
with an exemplary embodiment;
FIG. 2 is a partial sectional view of a rotor assembly of the alternator of
FIG. 1 incorporating a noise suppression diode electrically connected in parallel
to a corresponding slip ring of the slip ring assembly and field coil winding lead
wire in accordance with an exemplary embodiment;
FIG. 3 is a circuit diagram of an exemplary embodiment of the rotor assembly
of FIGS. 1-2 in electrical communication with a stator assembly, rectifier bridge,
voltage regulator, vehicle loads and a battery in accordance with an exemplary
embodiment; and
FIG. 4 is an enlarged perspective view of a right hand side of the rotor assembly
of FIG. 2 illustrating connection of the noise suppression diode and respective
leads extending therefrom in accordance with an exemplary embodiment.
DESCRIPTION OF THE PREFERRED EMBODIMENT
This disclosure relates to a diode mounted on the rotor of a wound-field electrical
machine and connected in parallel with the field coil to suppress electrical noise
as a result of negative voltage spikes. The invention significantly reduces electrical
noise generated from the voltage spikes due to an imperfect slip ring/brush interface.
In particular, the invention discloses the diode connected in parallel between
the slip ring leads and the field leads, as well as being rotatable with a slip
ring assembly to which it is attached.
Referring now to FIG. 1, an alternator
10 has a rotor assembly generally
designated by the reference numeral
20 and stator assembly generally designated
by the reference numeral
15. The rotor assembly
20 includes a shaft
21 supporting all rotating magnetic circuit structures thereof including
conventional pole-members or segments
16A and
16B, rotor core
17
and field coil
18 wound upon bobbin
12. Each segment
16A and
16B has P/2 claw poles where P is an even number and representative of the
total number of poles. Additionally, all other non-magnetic circuit rotating structures
are carried thereby, including air circulation fans
19 (only one shown)
located at axially opposite sides of the pole-members, and a slip ring assembly
30 located at one extreme end of the shaft. One fan (not shown) is formed
from sheet metal stock and spot welded to pole-member
16B while fan
19
is formed from an appropriate thermoplastic material and heat staked to tower extensions
(not shown) from the field coil bobbin
12. The shaft
21 in turn is
rotatably supported within a housing
26 by a pair of bearings
22
(only one shown). Bearing
22 (shown) is located between the slip ring assembly
30 and the fan
19.
Still referring to FIG. 1 and with the aid of reference to FIG. 2, which shows
a sectional view of the slip ring assembly
30 in accordance with the present
invention assembled to the rotor shaft
21, certain features of the invention
are abundantly more clear. Coil leads
18A of field coil
18 are wrapped
about respective posts
12A of bobbin
12 and pass through holes configured
in fan
19. Slip ring assembly
30 is made of a pair of copper rings
31, each having a slip ring lead
32 joined such as by welding thereto.
The copper rings and wires are molded into a an insulative member
80, such
as a molded cylinder of thermoset material, to complete the slip ring assembly.
Slip ring assembly
30 is pressed onto the end of rotor shaft
21 and
the slip ring leads
32 are routed into channels generally indicated at
34
in FIG. 2 along the shaft
21 where they are joined such as by soldering
to the coil leads
18A of field coil
18.
Still referring to FIGS. 1 and 2 with the aid of FIG. 3, slip rings
31
are configured for supplying an electric current to the rotor assembly
20
via a pair of brushes
36 being housed in a brush holder
38 disposed
inside housing
26 so as to slide in contact with these slip rings
31.
A voltage regulator
39 (FIG. 3) for adjusting the magnitude of an alternating
voltage generated in a stator winding
40 of stator assembly
15 is
operably coupled with the brush holder
38. Slip ring assembly
30
includes a noise suppression diode
100 operably mounted to an exposed end
or one end
101 defining assembly
30. Leads
102 and
104
extending from diode
100 are electrically connected in parallel with coil
leads
18a at a location where coil leads
18a are electrically
connected with slip ring leads
32 extending from end
101 of slip
ring assembly
30. In an exemplary embodiment, noise suppression diode has
an axial lead configuration and is capable of handling voltages up to about thirty
volts (30V).
A rectifier
42 for converting alternating current generated in the stator
40 into direct current is mounted inside housing
26, the rectifier
42 being constituted by a three-phase full-wave rectifier in which three
diode pairs, respectively, are connected in parallel, each diode pair being composed
of a positive-side diode d
1 and a negative-side diode d
2 connected
in series (see FIG. 3). Output from the rectifier
42 can be supplied to
a storage battery
44 and an electric load
46.
As described above, the rotor assembly
20 is constituted by: the field
winding
18 for generating a magnetic flux on passage of an electric current;
and pole cores or segments
16A and
16B disposed so as to cover the
field winding
18, magnetic poles being formed in the segments
16A
and
16B by the magnetic flux generated by the field winding
18. The
segments
16A and
16B are preferably made of iron, having two first
and second claw-shaped magnetic poles
50 and
52, respectively, disposed
on an outer circumferential edge and offsetly aligned with each other in a circumferential
direction so as to project axially, and the end segment pole cores
5 and
52 are fixed to the shaft
21 facing each other such that the claw
pole of one core is aligned with a gap defined between contiguous claw poles of
the other core and intermesh with the opposing magnetic poles of the other core
as is well known in the art of Lundell rotor assemblies.
In the dynamoelectric machine
10 constructed in this manner, an electric
current is supplied to the field winding
18 during start up from the storage
battery
44 through the brushes
36 and the slip rings
31, generating
a magnetic flux. After the alternator turns on and begins to produce power, the
alternator internally provides the field current. The first claw-shaped magnetic
poles
50 of segment
16A are magnetized into a fixed polarity by this
magnetic flux (such as North seeking (N) poles), and the second claw-shaped magnetic
poles
52 of segment
16B are magnetized into the opposite polarity
(such as South-seeking (S) poles). At the same time, rotational torque from the
engine is transmitted to the shaft
21, by means of the belt (not shown)
and the pulley (not shown), rotating the rotor assembly
20. Thus, a rotating
magnetic field is imparted to the armature winding
40 of stator assembly
15, inducing a voltage across the armature winding
40. An alternating-current
electromotive force from induced voltage across armature winding
40 passes
through rectifier
42 and is converted into direct current, the magnitude
thereof is adjusted by the voltage regulator
39, storage battery
44
is charged, and the current is supplied to the electrical load
46.
Referring now to FIG. 4, slip ring assembly
30 of FIGS. 1-3 may
include insulative member
80 molded from plastic, including Polyphenylene
Sulfide, having the desired creep and dimensional characteristics for molding a
net dimensioned assembly and also having appropriate tensile and impact characteristics.
The slip rings
31 may be manufactured using a conventional cold forming
process, each slip ring
31 being continuous about its respective circumference
and having an appropriate length terminal
32 extending therefrom. The slip
rings
31 are insert molded into the slip ring assembly
30, the slip
ring terminals
32 serving as a first locating feature, and the outside diameter
of the slip rings
31 serving as second locating feature. A conventional
straight pull mold may be used to produce the slip ring assembly.
In an exemplary embodiment as depicted in FIG. 4, slip ring assembly
30
includes a molded support wall
110 extending from end
101 for supporting
diode
100. Support wall
110 includes a molded block assembly
112
having a cavity
114 configured therein to receive a body portion of diode
100 and includes slots
116 disposed at opposing ends of block assembly
112 to allow corresponding diode leads
102 and
104 to extend
therefrom and allow ingress and egress of the diode leads
102 and
104
from block assembly
112. Support wall
110 is configured to retain
diode
100 while shaft
21 rotates slip ring assembly
30 mounted thereto.
End
101 of assembly
30 includes opposing apertures
120 configured
to allow corresponding slip ring lead terminals
32 and a respective field
lead
18A to extend therethrough for electrical connection with a respective
diode lead
102,
104 generally indicated at
122.
If necessary, excess insulating material may be stripped where the coil leads
18A exit the end of the slip ring assembly through apertures
120
and each coil lead is secured to a respective one of the slip ring terminals
32
at
122. Preferably, the slip ring terminals
32 are crimped around
the diameter of the coil leads and diode leads
102,
104 and then
welded or soldered. This electrical connection connects the diode in parallel with
the field coil and suppresses the voltage spikes that occur as a result of an imperfect
slip ring/brush interface.
Significant alternator assembly advantages are realized with a slip ring
assembly as described. The disclosed invention solves the technical problem at
minimal cost versus the alternatives. It also allows use of a brush type construction
that has significant performance and size advantages over a brushless construction.
Disposing a diode connected across the field coil winding allows for dissipation
of voltage spikes that may be generated as a conductive state of the interface
between the brushes and corresponding slip rings varies during operation of the generator.
While incorporation of the exemplary noise suppression diode with a slip ring
assembly has been described for use with generators associated with vehicles, the
same may also be used and incorporated in applications other than generators for
a vehicle where suppression or reduction of electrical noise is desired.
While the invention has been described with reference to an exemplary embodiment,
it will be understood by those skilled in the art that various changes may be made
and equivalents may be substituted for elements thereof without departing from
the scope of the invention. In addition, many modifications may be made to adapt
a particular situation or material to the teachings of the invention without departing
from the essential scope thereof. Therefore, it is intended that the invention
not be limited to the particular embodiment disclosed as the best mode contemplated
for carrying out this invention, but that the invention will include all embodiments
falling within the scope of the claims.
*
