U.S. patent number 3,831,925 [Application Number 05/294,804] was granted by the patent office on 1974-08-27 for spiral spring units for pressing brushes.
This patent grant is currently assigned to Hitachi, Ltd.. Invention is credited to Sadaharu Kawai, Toshio Nakamura.
United States Patent |
3,831,925 |
Nakamura , et al. |
August 27, 1974 |
SPIRAL SPRING UNITS FOR PRESSING BRUSHES
Abstract
A spiral spring unit for pressing brushes, which consists of a
plurality of spiral spring elements bonded together at the opposite
ends thereof and which is capable of pressing the brush always with
a constant pressure.
Inventors: |
Nakamura; Toshio (Hitachi,
JA), Kawai; Sadaharu (Hitachi, JA) |
Assignee: |
Hitachi, Ltd. (Tokyo,
JA)
|
Family
ID: |
13647707 |
Appl.
No.: |
05/294,804 |
Filed: |
October 4, 1972 |
Foreign Application Priority Data
|
|
|
|
|
Oct 6, 1971 [JA] |
|
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46-77927 |
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Current U.S.
Class: |
267/156;
310/246 |
Current CPC
Class: |
F16F
1/10 (20130101) |
Current International
Class: |
F16F
1/04 (20060101); F16F 1/10 (20060101); F16f
001/12 () |
Field of
Search: |
;267/156
;310/246,247 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Marbert; James B.
Attorney, Agent or Firm: Craig & Antonelli
Claims
What is claimed is:
1. A spiral spring unit for pressing brushes, comprising: a
stationary body, a first spiral spring having one end secured to
said stationary body, the other end of said first spiral spring
pressing a brush in a predetermined direction, a second spiral
spring having a spiral configuration substantially concentric with
said first spiral spring, said second spiral spring being disposed
within the spiral space formed by said first spiral spring with a
space being provided between said first and second spiral springs,
one end of said second spiral spring being secured to the same
stationary body to which said first spiral spring is secured, the
other end of said second spiral spring being bonded to said other
end portion of said first spiral spring, said other end portions
being bonded together to cause said space between said first and
second spiral springs to decrease when said first and second
springs are wound up.
2. A spiral spring unit for pressing brushes, as defined in claim
1, wherein said first and second spiral springs have different
spring constants.
3. A spiral spring unit for pressing brushes, as defined in claim
1, wherein the spring constant of said second spiral spring is
smaller than that of said first spiral spring.
4. A spiral spring unit for pressing brushes, as defined in claim
1, wherein said second spiral spring has a plate thickness smaller
than that of said first spiral spring.
Description
This invention relates to improvements in the spiral spring unit
for pressing brushes, which is usually used at the current
collecting portions of rotary electric motors, etc., and more
particularly to improvements in the spiral spring proper
thereof.
The brush pressing spiral spring unit of the present invention can
be used at the current collecting portions of any and all rotary
electric machines, but herein it will be described as used at the
current collecting portion of an electric motor for vehicles, to
facilitate best understanding of the invention.
At the current collecting portion of a vehicle motor or the like
are generally provided conductor wires, a brush and a brush holder,
by which current is conducted between a stationary portion and a
rotating portion. However, since this type of motor is usually
arranged at a place, such as below the floor of a vehicle, where
the space is not substantially large, the motor is required to be
small in size per. se. and accordingly not a large space is
available around the current collecting portion of the motor.
For this reason, the brush and the brush holder are also required
to be small in size as a matter of course.
Should the frequency of changing the brush not be considered,
simple reduction of the brush and brush holder to meet such demand
would be possible. However, in the light of the fact that this type
of motor is usually arranged in a limited space, such as beneath
the vehicle floor, along with other parts as stated above, it is
usual that much time is required for the inspection of the motor
and frequent performance of such operation is quite cumbersome and
detrimental to the effort of saving labor. Thus, it becomes
necessary to use a brush which is low in rate of wear or has a
large height, so as to minimize the necessity of changing the
brush.
In view of the above, it will be understood that the most ideal
collector of this type is the one which is small in size and free
of maintenance, or in other words, the one which is operable for an
extended period of time without the necessity for changing the
brush used therein.
Furthermore, in this type of motor slipping of the brush or jumping
and oscillation of the brush on a rotary collector ring, such as
commutator, tends to occur due to the high rotational speed of the
motor and the vibration of the vehicle, impairing smooth conduction
of current. Therefore, means for holding the brush or a brush
holder is desired, which is capable of holding the brush against
jumping and vibration even when the motor is subjected to intense
vibrations.
Under such circumstances, a brush holder including a spiral spring
is presently being employed as the most desirable brush holding
means, which satisfies substantially all of the requirements set
forth above.
The brush holder having a spiral spring has many advantages, such
as that since the spring does not have a rotating or sliding
portion, there is no fear of the relative rotation or sliding of
the brush holder being impaired by the brush powder or dusts in air
attaching to the contacting portion; that it is relatively small in
size and can be used with a brush having a large height; and that
it can absorb the vibrations of the brush because the spring is
small in inertia per. se.
Because of such advantages, the brush holder having a spiral spring
has been widely used as the most effective one, at least to the
present time.
However, with the demand for increasing the speeds of vehicles more
and more, which is expected to become greater in the future, and
with the demand for rendering vehicles maintenance-free for a
longer period of time, the conventional brush holder including a
simple spiral spring very recently has become unsatisfactory to
meet such demands.
The reason why the brush holder, having heretofore being considered
as ideal, has reached the limitation of its use will be explained
hereunder with reference to an example thereof shown in FIG. 5 of
the drawings.
In FIG. 5 there is shown a spiral spring 10 having a relatively
large number of turns. The spring is subjected to a displacement as
indicated by the chain line when set in a brush pressing position.
Each turn of the coiled portion of the spring is also subjected to
a slight displacement in this case but such displacement is not
shown.
In the Figure, the displacement of the spring from the position Q
to the position P, namely the angle of torsion of the spring, is
indicated by symbol .alpha. and it will be obvious that the larger
the angle of torsion .alpha. is, the more advantageous, when it is
desired to use a brush of larger height.
The angle of torsion .alpha. and the stress .sigma. occurring in
the spring are generally expressed by the following formulae
respectively:
.alpha. = 687.sup.. P.sup.. a.sup.. l/E.sup.. b.sup.. t.sup.3
.sigma. = 6.sup.. P.sup.. a/b.sup.. t.sup.2
wherein:
P = the pressure
l = the effective length
E = the Young's modulus
t = the thickness
b = the width of the spring plate.
It will be understood from the above formulae that in order to make
the pressure change of the spring smaller with respect to the
margin of wear of the brush, it becomes necessary to reduce the
spring constant by making the effective length l of the spring
large and increasing the number of turns of the same. However, this
will result in such disadvantages that the stress in the spring
increases and the turns of the spring get so close to each other as
to interfere with each other, and that the diameter of the spring
becomes large.
In general, the brush portion of a rotary electric machine rises in
temperature during operation of said machine. Therefore, an
increase of stress in a brush holding spring tends to result in a
lowering of the spring pressure due to the creeping phenomenon and
the interturn interference of the coiled portion of the spring
causes an abnormal vibration of the spring, all of which provide
causes of unsatisfactory commutation.
Furthermore, a motor for vehicles is normally used in a wide range
of speed from zero to 500 r.p.m. but a spiral spring consisting of
a single spring plate has its resonance point in the neighbourhood
of 1,000 - 6,000 C.P.m., so that such a spring during operation
tends to become defective in both the pressure characteristic and
vibration characteristic, due to occurrence of resonance of the
turns of the spring.
The present invention has been achieved under the circumstances
described above. It is, therefore, the object of the invention to
provide a spring unit of the type described, which is small in
size, capable of pressing a brush with a minimum pressure change
and with a minimum stress, and has a large resonance suppressing
and damping effect.
According to one aspect of the invention, there is provided a
spring unit of a small size, a low stress and a small pressure
change, which is composed of a first spiral spring having one end
secured to a stationary body for pressing a brush at the other end
thereof and a second spiral spring coiled into a configuration
substantially concentric with and disposed within the spiral space
of said first spiral spring, one end of said second spiral spring
being secured to the same stationary body to which the first spiral
spring is secured, and the other end thereof being bonded to the
other end portion of said first spiral spring.
According to another aspect of the invention, there is provided a
spring unit of the character described, in which said first and
second spiral springs have different spring constants thereby to
enhance the resonance suppressing and damping effect of the spring
unit, and further said second spiral spring is smaller in width
than said first spiral spring and arranged in close contact with
the side of said first spiral spring closer to the axis thereof
thereby to facilitate the fabrication of the spring unit.
FIG. 1 is a perspective view of a brush holder comprising the
spring unit of the present invention;
FIG. 2 is a side elevational view of the spring unit only of the
brush holder shown in FIG. 1;
FIGS. 3 and 4 are side elevational views respectively showing other
embodiments of the spring unit of the invention; and
FIG. 5 is a side elevational view of a conventional spring
unit.
The present invention will be described in detail with reference to
the embodiments thereof shown in the drawings.
In FIG. 1 there is shown in perspective a brush holder 3 comprising
a brush 1 and a spring unit 2.
The brush holder 3 has at one end thereof a brush receiving box 4
in which the brush 1 is slidably received.
The brush holder 3 also has a fixed pin 5 which has the inner end 6
of the spring unit 2 secured thereto and thus supports the entire
spring unit 2.
The outer end 7 of the spring unit 2 is placed on the top of the
brush 1, and the brush is normally urged into pressure contact with
a collector ring (not shown) as indicated by the arrow, under the
biasing force of the spring unit. The brush holder 3 comprising the
spring unit 2 and the brush 1 is fixed to a predetermined
stationary portion (not shown) through an insulation rod 8.
The spring unit 2, as shown in FIG. 2, is composed of a first
spiral spring 2a secured to the fixed pin 5 of the brush holder at
one or inner end and having a brush pressing portion at the other
or outer end thereof, and a second spiral spring 2b disposed within
the spiral space of said first spiral spring. The second spiral
spring 2b, similar to the first spiral spring 2a, is secured to the
fixed pin 5 at the inner end thereof, and the outer end thereof is
bonded integrally with the outer end of the first spiral spring
2a.
In this case, while the outer ends of both springs are bonded
together, it is not essential that the outer ends are always
aligned with each other, it being only necessary that the outer end
of the second spiral spring is bonded to the first spiral spring
near the outer end extremity thereof.
Alternatively, the spring unit 2 may be fabricated in the form
shown in FIG. 3.
In this form of the spring unit, the thickness t of a first spiral
spring 2c is differentiated from the thickness T of a second spiral
spring 2d.
Differentiating the thicknesses means to differentiate the natural
vibrations of the springs and has the effect of suppressing the
vibration of the spring unit as a whole, though will be described
in greater detail later, and thus makes it possible to use the
spring unit with machines and equipments which are subjected to
intense vibrations. Besides differentiating the thicknesses, many
other methods may of course be considered to differentiate the
natural vibrations of both springs, such as differentiating the
materials or widths of the springs.
In FIG. 4 is shown a spring unit in which the first and second
spiral springs of different thicknesses mentioned above are bonded
together over substantially the entire lengths thereof and
especially the second spiral spring 2d having a relatively small
thickness is bonded to that side of the first spiral spring 2c
having a relatively large thickness which is closer to the axis of
the springs. The function and effect of this spring unit will not
be described here as they will be described in detail later.
Now, the functions of the various forms of spring unit described
hereinbefore will be explained hereunder: As may be apparent from
the formulae given previously, a stress .sigma. occurring in a
spiral spring is in inverse proportion to the square of the plate
thickness and the angle of torsion .alpha. thereof is in inverse
proportion to the cube of the plate thickness, for the same output.
Therefore, by forming the spiral spring unit by laminating the
first and second spiral springs of smaller thicknesses (than the
conventional one) as described herein, it becomes possible, for the
same output, to reduce the effective length of the spring unit and
hence to reduce the number of turns and to make the angle of
torsion large, or in other words, to minimize a change in pressure
of the spring occurring incident to wear of the brush and to reduce
the stress.
Further, where the first and second springs are respectively made
of materials which have different spring constants, they have
different natural frequencies, so that the energy loss occurring at
the time of vibration due to mutual inteference of the laminated
spring plates, i.e., the vibration damping effect, becomes very
large and thus a spiral spring unit can be obtained which is
excellent in its effect of suppressing resonance or abnormal
vibration.
The production of a prototype spiral spring unit of the invention
has revealed that it is extremely difficult to assemble two spiral
springs into a unitary spring unit, with the circular
configurations of their innermost turns matching with each other,
and the assembly work is quite time-consuming. However, when spiral
springs of different thicknesses are used and especially the spiral
spring of smaller thickness is to be disposed inwardly of the other
spring with respect to the axis of the springs, the smaller
thickness spring leans backward slightly more than the other spring
in the case when both springs are formed concurrently by a cold
working, with one ends thereof fixed. Therefore, the coiled portion
of the inner spring can be easily bonded to the coiled portion of
the outer spring without requiring any additional effort.
The spring unit of the invention, as described herein, is composed
of the first and second spiral springs bonded with each other at
the opposite ends thereof and, therefore, is small in size, low in
stress and small in pressure change, owing to the inherent
properties of the springs. Further, the springs are made of
material having different spring constants and the plate
thicknesses of the springs are differentiated, and further the
spring of smaller thickness is disposed inside of the spring of
larger thickness with respect to the axis of the springs, so that
the spring unit has a large effect for suppressing or damping
resonances and can be easily produced, in addition to the
advantageous features set forth above.
Although the present invention has been described herein with
reference to spring units having first and second springs, it is to
be understood that the spring units of the invention may be
composed of three or more springs .
* * * * *