U.S. patent number 3,590,262 [Application Number 04/820,124] was granted by the patent office on 1971-06-29 for brush-operating gear for electrical machines.
This patent grant is currently assigned to The Plessey Company Limited. Invention is credited to Frederick R. Jones, Bernard R. Sheffield.
United States Patent |
3,590,262 |
Sheffield , et al. |
June 29, 1971 |
BRUSH-OPERATING GEAR FOR ELECTRICAL MACHINES
Abstract
The commutator brushes required for the starter operation of a
combined starter-generator are lifted through cam action on
completion of the starting operation by a spring-urged ring member
which, at the beginning of the starter operation is turned against
the spring bias by a rotary solenoid to disengage the brush holders
thus allowing the brushes to be applied by application springs. The
rotary solenoid is preferably of the type having inner and outer
stator poles between which the pole pieces of an annular rotor
penetrate, the resulting gaps, or at least one of them, being wedge
shaped to maintain throughout the stroke a torque sufficiently high
to overcome the progressively loaded return springs, sufficient
initial torque being ensured by asymmetric location of the solenoid
rotor pole pieces relative to the solenoid stator pole pairs in the
deenergized position.
Inventors: |
Sheffield; Bernard R. (Ilford,
Essex, EN), Jones; Frederick R. (Ilford, Essex,
EN) |
Assignee: |
The Plessey Company Limited
(Ilford, Essex, EN)
|
Family
ID: |
10147665 |
Appl.
No.: |
04/820,124 |
Filed: |
April 29, 1969 |
Foreign Application Priority Data
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|
|
|
|
May 1, 1968 [GB] |
|
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20545/68 |
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Current U.S.
Class: |
290/46;
310/240 |
Current CPC
Class: |
H02K
23/52 (20130101) |
Current International
Class: |
H02K
23/52 (20060101); H02k 023/52 () |
Field of
Search: |
;310/240,246
;290/38,46 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Duggan; D. F.
Claims
What we claim is:
1. An electromagnetic device for lifting from the commutator of an
electric machine brushes which are normally applied to the
commutator by brush-loading spring means, the device comprising
lifting means including a brush-lifter ring operable by rotation
about the axis of the commutator to withdraw the brushes from
contact with the commutator against the action of said
brush-loading spring means, lifting spring means associated with
said brush-lifter ring and urging said ring in the direction of
such brush-lifting operation with a torque sufficient to move the
ring from an inoperative position allowing the brushes to engage
the commutator to an operative position in which the brushes are
lifted off the commutator, and a rotary solenoid operative when
energized to return said brush-lifter ring from its operative
position to its inoperative position against the action of said
lifting-spring means, said rotary solenoid including an annular
yoke and a magnetizing coil, both coaxial with the commutator, and
an armature member coaxially rotatable relative to the yoke and
mechanically connected to said brush-lifter ring, said yoke having
circumferentially spaced pole pieces projecting at one side of the
coil to form, when the coil is energized, magnetic poles of one
polarity, and said armature member including armature elements
spaced circumferentially for respective cooperation with said pole
pieces and each having two surface portions extending approximately
in the direction of movement of the element about the common axis
of the commutator and armature member and facing respectively one
of said pole pieces and a surface portion of said yoke at the
opposite side of the coil, the mutually facing surface portions of
said armature element and pole piece being inclined relative to the
direction of their relative movements over at least part of their
length in such manner as to cause the effective airgap between the
armature element and yoke to decrease as the armature member moves,
when the coil is energized, the brush-lifting ring from its
inoperative position towards its operative position.
2. Device as claimed in claim 1, wherein the yoke has a set of
outer pole pieces spaced circumferentially, a set of inner pole
pieces similarly spaced and arranged to face the outer pole pieces
across a radial gap, with the coil arranged to produce a magnetic
field in which the inner and outer pole pieces are respectively
magnetized with opposite polarity, the armature member having a set
of magnetizable armature pole pieces which are angularly spaced
similarly to the pole pieces of the yoke and are so arranged so as
to be able, by rotation of the armature member, to enter each gap
between an inner and outer pole piece of the yoke, leaving residual
radial gaps at their inner and outer surfaces, at least one of
these residual gaps varying in radial width from a maximum
operative when the armature pole piece is substantially withdrawn
rotationally from the gap between two coordinated pole pieces of
the yoke, to a minimum operative when the armature pole piece has
entered the gap between the two coordinated pole pieces of the yoke
to the maximum extent.
3. A device as claimed in claim 1 for use with an engine starter,
wherein the solenoid is arranged to be energized automatically
prior to the energization of the circuit including the commutator
brushes and the starter-field winding in series with the starter
armature the solenoid-energizing circuit including a switch opening
the circuit when and as long as the speed of the machine exceeds a
predetermined value.
Description
This invention relates to brush-operating gear for electrical
machines and has for an object to provide improved brush-operating
gear which is particularly suitable for application to electric
engine-starter motors which are intended to continue running after
starting of an engine, for example because their armature is
arranged thereafter to perform another operation such as the
generation of electric current. In such cases it is desirable for
the starter brushes to be lifted off the commutator when the
starting operation has been completed and to be maintained in the
lifted condition during the normal running of the engine which has
been started, thus considerably reducing wear of the commutator and
brushes.
The present invention provides for this purpose brush-operating
gear including a brush-lifting element which is biased by spring
means to a position of engagement with the brush mechanism in which
the brushes are lifted off the commutator against the action of
brush-application springs, and a solenoid operable to move the
brush-lifting element against the action of the bias spring means,
thus allowing the brushes to be placed into contact with the
commutator by the application spring and withdrawing the
brush-lifting element from operative engagement with the brush
mechanism.
One object of the invention is to provide a brush-operating gear of
the kind set forth which can be accommodated in a commutator-type
electric machine with minimum increase of the dimensions of the
machine. With this object in view, the solenoid is preferably of
the rotary type and preferably has a stator provided with a set of
outer pole pieces spaced circumferentially of the solenoid, a set
of inner pole pieces similarly spaced and arranged to face the
outer pole pieces across a radial gap, a magnetizing member,
preferably a magnetizing winding, arranged to produce a magnetic
field in which the inner and outer pole pieces are respectively
magnetized with opposite polarity, and a rotor member having a set
of magnetizable pole pieces which are angularly spaced similarly to
the stator pole pieces and are so arranged so as to be able, by
rotation of the rotor, to each enter the gap between an inner and
outer stator pole piece, leaving residual radial gaps at their
inner and outer surfaces, at least one of these residual gaps
varying in radial width from a maximum operative when the rotor
pole piece is substantially withdrawn rotationally from the gap
between two coordinated stator pole pieces, to a minimum operative
when the rotor pole piece has entered the gap between the two
coordinated stator pole pieces to the maximum extent.
This permits the achievement of a torque characteristic of the
rotary solenoid corresponding to the torque required at each
position, thus minimizing the necessary dimensions of the solenoid
system.
The accompanying drawings illustrate one embodiment of the
invention applied to a combined alternator-generator and
starter-exciter unit as described and claimed in our copending
British Pat. application No. 18,692 of 19th Apr. 1963 (Inventors
S.S. Hall, R. Miller, P. Riley) and corresponding applications in
other countries.
FIG. 1 is an elevation in axial section of the complete unit,
FIG. 2 is a cross section on line 2-2 of FIG. 1, the sector A being
shown in the brush-engaged position and the remainder of the figure
being shown in the brush-lifted position, and
FIG. 3 is a cross section substantially on line 3-3 of FIG. 1.
Referring now to the drawing, the arrangement comprises a two-part
housing 1, 2 in which two rotor systems 9 and 17, carried by a
common shaft 7, are rotatable within a stator-iron structure 11 and
a field structure 18 respectively. The winding 19 on the rotor 17
has connections to a commutator 20 which, when the rotor is running
as a motor armature for starting an engine coupled to the shaft 7
by a stud shaft 23, cooperates with a set of brushes 21, only one
of which is shown, and brush-operating gear 30 is provided for
lifting the brushes 21 off the commutator except when the motor 17,
18 is energized for starting an associated engine and its rotor
speed is below a predetermined value lying between the speeds
respectively corresponding to the self-sustaining speed and the
normal running speed of the engine to be started. The construction
so far mentioned is described in more detail in our said copending
application, but the brush-operating gear will now be described in
more detail with particular reference to the accompanying
drawings.
The brush-operating gear comprises a rotary solenoid having a
stator-core structure 33 formed as a ring whose profile is
substantially a U-section the open side of which faces the armature
17, and which accommodates, at the bottom of the U, a magnetizing
winding 34 coaxial with the shaft 7. At the open end of the U its
outer wall is subdivided to form a number of uniformly spaced outer
pole pieces 35 each of which is faced in radially spaced relation
by an inner pole piece 36 connected to the radially inner wall of
the U-section annular body 33. This stator-core structure is
supported at 37 in a stationary housing body 38 attached to the
outer end of the starter housing 2, and has a central bore 39 whose
wall is radially spaced from the shaft 7. Supported in this bore 39
by needle rollers 40 is a sleeve 41 from which extends an annular
flange 42 which is thus mounted for rotation about the axis of the
core structure 33, and which carries magnetizable armature
pole-piece plates 43 which project from the flange into the annular
space defined by the radially inner surface of the outer pole
pieces 35 and the radially outer surface of the inner pole pieces
36, the radial thickness of the armature pole pieces 43 being
somewhat less than the minimum radial distance between the said
surfaces so as to leave an airgap both at the radially inner and at
the radially outer side of each armature pole piece when pole piece
has moved to its maximum depth into the space between said inner
and outer stationary pole pieces 35, 36.
As shown more clearly in FIG. 2, a number of spiral-strip springs
44 each have their center fixed in the stationary housing body 38
and their outer end attached to a block 45 which is secured to the
flange 42 so that when, due to energization of the winding 34, the
armature pole pieces have moved to the position 43a shown in sector
A of FIG. 2, the spiral springs 44 are tensioned due to the
extension of their outer end portions 46 so that upon cessation of
the energization of winding 34, the springs 44 will return the
flange plate 42 to the angular position in which its armature pole
pieces are in the position shown at 43 in the remainder of the same
FIG. 2 outside the sector A. The commutator brushes 21 are mounted
in brush-holder arms 47 which, as shown in FIG. 3, are pivotally
mounted at 48 in the stationary structure, and the arms 47 are
urged by springs 49 to apply the brushes 21 to the commutator 20.
Each brush-holder arm 47 is equipped with a cam block 50 having
suitably inclined lifting-cam surface 51, and four lifting rollers
52 are carried on the flange plate 42 in such relation that when,
at the end of a starting operation, the plate 42 moves to displace
its pole pieces from the position 43a, shown in sector A of FIG. 2,
to the position 43 shown outside sector A in FIG. 2, each
brush-holder arm 47 is engaged by one of the rollers 52. After
engaging the surface 51, this roller cooperates with the surface 51
to lift, by means of the cam block 50, the brush-holder arm 47 and
thus to lift the brush 21 from the armature 20. The winding 34 may
be connected in parallel with the circuit including the brushes,
and armature winding 19, and series field winding 22 so that, when
the engine is to be started, and before a voltage is applied to the
starter motor via brushes 21, the winding 34 is energized, and the
resulting magnetic flux will cause the flange 42 to be rotated to
move the solenoid armature pole pieces 43 from their normal
position illustrated in FIG. 2 outside Sector A to the position 43a
illustrated in sector A, causing the flange 42 to rotate in the
direction of the arrow X, thereby moving the rollers 52 along the
cam surfaces 51 against the action of the spiral-strip springs 44
so as to allow the brush-pressure springs 49 to apply the brushes
21 to the commutator 20. When as a result of this starter
operation, the engine has begun to fire and the engine speed has
reached a value intermediate between the self-sustaining speed and
the minimum normal running speed of the engine, a speed-responsive
switch 53, controlled for example by the appearance of an output
voltage in the terminals 14 or 16 of the alternator-generator part
of the unit, cuts off the starter current and at the same time the
energization of the winding 34, thus allowing the springs 44 to
return the flange 42 to its position shown outside sector A, and
during this movement the rollers 52 cooperate with the cam surfaces
51 of the blocks 50 to raise the brush-holder arms 47 against the
action of the brush-pressure springs 49 and thus lift the brushes
21 clear of the commutator 20.
In one example, in which the unit is intended for application to a
power takeoff pad of an aircraft gas-turbine engine whose normal
running speed is 12,000 r.p.m., the brush-lifting mechanism was
arranged to lift the starter brushes at a speed corresponding to
7,000 r.p.m. of the engine, which, although only seven-twelfths of
the full running speed of the engine, was about twice the
self-sustaining speed, thus on the one hand minimizing the risk of
starting failure and on the other ensuring that the brushes will
never be in contact with the commutator at anything like the full
engine speed, a feature which greatly assists in obtaining a long
service life of the commutator and brushes between overhauls.
Since the torque opposed by the spiral-strip springs 44 to the
angular displacement of the flange plate 42 increases with
progressive movement of the plate from the brushes-lifted position
to the brushes-applied position, it is desireable to ensure that
the torque of the rotary solenoid follows a somewhat similar law
and at least does not unduly decrease during the progress of the
brush-application movement. In order to approximate such condition,
the mutually facing surfaces of the solenoid-armature pole pieces
43 and of the pole pieces of the annular body 33 are, in the
illustrated preferred form of the invention, angularly displaced in
the circumferential direction in such a manner that the gap at
least at one of the radially inner and outer surfaces of the pole
pieces 43 becomes narrower as these pole pieces enter, due to the
rotation of flange plate 42, into the space between the inner and
outer pole pieces 35 and 36 of the solenoid stator body 33. This
feature can be clearly seen in FIG. 2 at the radially outer surface
36a of the pole pieces 36.
Suitable stop means, not shown, are preferably provided for
limiting the movement of the flange plate 42 in the direction of
the arrow X under the action of the solenoid winding 34 and also to
limit its movement in the opposite direction under the action of
the spiral-strip springs 44; the latter limit is so chosen that
that end of each armature pole piece 43 which is leading during
movement in the direction X, is much closer to the nearest pair of
pole pieces 35 and 36 than the opposite end of the same pole pieces
is to its next adjacent pair of pole pieces 35 and 36. This will
ensure that a large torque in the desired direction is produced
when the winding 34 is first energized.
* * * * *