Note: Descriptions are shown in the official language in which they were submitted.
Back~round of the Inventlon
In the contact spring arrangement disclosed in German
patent specification No. 1 213 917, an essential portion of
. the pull exerted by the armature is stored in a double contact
spring. Accordingly, practically no excitation energy is
required to provide the contact force. In the known arrange-
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ment, an actuating nipple is disposed between the free ends
of a bifurcated spring which has the same flexibility in both
directions of its actuation. It is necessary that the contact
clearance is smaller than the travellina distance of the
armature by the path of travel required by the spring in
either direction of actuation. It is furthermore dis-
advantageous that the bifurcated spring ends exhibit the same
flexibility at the opening as at the closing of the contact
couple.
In view of this problem, German Auslegeschrift 2 454 967
suggests an arrangement in which the contact couple is posi-
tively and forcibly opened, whereas the closing of the contact
couple is done solely by pre-tensioning the contact spring.
However, this arrangement allows only a small proportion
of the pull provided by the armature to be stored in the
contact spring.
It is an object of the present invention to provide a
contact spring arrangement for a polarized relay which not
only stores an essential portion of the permanent-magnetic
pull exerted by the armature in a contact sprin~ as the
contact force, but also ensures a positive and forced opening
of the contact couple with a contact clearance which is not
reduced by any contact spring bending.
It is a further object of the present invention to
provide a contact arrangement as set forth above, which is
easy to manufacture and assemble from a minimum of structural
components.
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Summary of the Invention
To this end the invention provides a relay including:
a stationary contact; a first contact spring having a
movable contact mounted thereon, said first cotact spring
being movable between a first position wherein said
movable contact contacts said stationary contact, and a
second position wherein said movable contact is spaced
from said stationary contact; a second contact spring
disposed adjacent said first contact spring; said second
contact spring containing a portion touching said first
contact spring when said first contact spring is in said
first position; armature means for moving said first
contact spring between said first and second positions;
said armature means including first actuator means for
operatively engaging said second contact spring at a
predetermined area and biasing said second contact spring
against said first contact spring at said portion; and
second actuator means for engaging said first contact
spring at a predetermined area and moving said first
contact spring to said second position; and
wherein h C h' ; L1 is the length measured along
said second contact spring between said area of operative
engagement of said second contact spring with said first
actuator means and said portion of said second contact
spring; L3 is the length measured along said first
contact spring between said area of engagement of said
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first contact spring with said second actuator means and
said movable contact; h is the thickness of said first
contact spring, and h' is the thickness of said second
contact spring.
Such an arrangement permits the storing of an
essential portion of the permanent-magnetic pull provided
by the armature in the contact springs and guarantees a
forced c~ntact opening even in case the contact couple
should have become stuck together, with a clearance
unaffected by any spring bending. Moreover, the presence
of two contact springs permits a greater current load.
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Brief Description of the Drawings
Fig. 1 is a cross-sectional view showing a contact
spring arrangement for a polarized electromagnetic relay
according to a first embodiment of this invention;
E~ig. 2 is a view similar to Fig. 1 of a second
embodiment;
Figs. 3 and 4 show a contact spring arrangement
according to a third embodiment of the invention in two
different switching positions;
Fig. 5 illustrates a fourth embodiment of this
invention;
Figs. 6 and 7 are a cross-sectional and, respectively,
a perspective view of a fifth embodiment of the invention
and of a variation thereof;
Fig. 8 is a graph used for explaining the above
embodiment, in which graph various forces are plotted
against the travelling distance; and
Fig. 9 is a schematic diagram showing a c-circuit
which may be used with the present invention,
Detailed Description of Preferred Embodiments
In the arrangement shown in Fig. 1, a permanent-
magnetic armature 8 of a polarized relay having a magnet M
is pivoted about an axis passing through its center of
gravity A between pole shoes 9, 9' and is depicted in one
of two rest positions. The magnet M is partially embedded
and thus fixed in a manner known per se by the synthetic
material of an actuator 12. The
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at~ature 8 and the actuator 12 form a unit with actuator
portions 6, 7, 6' and 7' integrally formed on the actuator.
The arrangement of Fig. 1 is mirror-symmetric with respect
to both the X axis and the Y axis, but not shown completely
for simplicity. The armature 8 is shown in one of its end
positions in which the pole shoes 9' have travelled through
a distance s and bear against the pole ends 10, 10' of a coil
core (not shown) with a force F4. Fixed contacts 5, 5' are
disposed laterally of the X axis of the armature 8, and
a contact terminal 3 to which contact springs 1, 2' are
fixedly connected with their centers is disposed in the
middle between the fixed contacts. The free ends of the contact
spring 1 are provided with portions forming movable contacts
4, 4' opposite the fixed contacts 5, 5'. The contact spring
2' extends at the side of the contact spring 1, which functions
as a double-throw contact. Both springs 1, 2' are provided
with a small bias force FK (Fig. 8) with respect to the actuator
portions 6, 7 and 6, 7' which are disposed in close proximity
of the fixed contacts 5, 5' and the movable contacts 4, 4'.
At the moment of contact closure, the movable contact, e.g.
4', engages the fixed contact 5' with the bias force FK. The
actuator portion 6' then releases the contact spring 1, and
the actuator portion 7' presses with a force F on the spring
2' which, with its length L1 exerts a force Fl on the loca-
tion K at which it touches the contact spring 1. This force
F1 is thus transmitted by the contact spring 1 through its
length L2 on the contact 4', 5' and added to the bias contact
force FK. 'rhis type of contact closure surpresses any contact
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chattering because the force F1 cancels already at the
moment o contact closure any oscillations that may be
produced by the movable contact ~' hitting the fixed contact
5'.
A further advantage of the double contact spring according
to the present invention resides in the branching of the contact
- current. One portion of this current flows from the contact
couple 4', 5' through the contact spring 1 to the contact
terminal 3, as usual, while the rest of the current flows
from the contact spring 1 in the opposite direction through
the touching point K and the spring 2' to the contact terminal
3. Still a further advantage will be recognized by considering
the formula for calculating the bending, which includes the
ratio L : h3. For instance, if the spring length L equals 1
and the thickness h equals 0.1, the ratio L : h equals 1000.
If the single thickness of 0.1 is replaced by twice the thick-
ness of 0.05, the same cross-sectional area will result in a
ratio L3 : 2 x h3 = 13 : 2 x 0.053 = 4000. If twice a thickness
of 0~075 is selected, the ratio L3 : h becomes 1135, which
means 50 per cent more cross-sectional area and an accordingly
higher allowable current load with approximately equal spring
properties. In practice, however, the permissible current
load of the double contact spring according to the invention
is even higher because the entire surface is about twice as
large as with a single spring of similar resilient properties
This improves the dissipation of heat and at the same time
reduces the resistance for high-frequency currents due to
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skin effect
For realizing the respective desired spring properties
and sti~fness of the contact sprin~s used, the widths of the
springs may also be varied. In contrast to a variation in
S the spring length and thickness, however, a variation in
widths affects the bending of the contact springs only
linearly.
During contact closure, the spring constant should be
very small within the range x of sprinq excursion (compare
Fig. 4) and should increase with an average gradient in the
subsequent range of contact closure movement, in order to
achieve proper storing~of permanent-magnetic pull for the
contact force and for obtaining stable pull-in and drop-out
values of the relay. The same properties should be guaranteed
even in case the contact clearance increases due to contact
burn-off. On the other hand, inthe forced contact opening,
the spring constant should increase with a very large gradient,
which means that the spring section then effective must be
stiff. For this reason, the spring length L2 between the
contacting position of the movable and fixed contacts 4', 5'
and the actuator portion 6' is made as short as possible.
In case any arcing that may occur should require a larger
clearance between the contact to the actuator portion 6',
which consists of synthetic material, a forced contact opening
may be achieved by providing the contact spring 1 either with
a stiffening embossed profile 13 (Fig. 6) or, as an equivalent
measure, with a thickness h which is larger than the thickness
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h' of the more flexible contact spring 2. This is un-
problematic because the relatively great spring length L5
is effective with a very small spring constant upon openinq
of the contact couple.
In the embodiment shown in Fig. 2, two normally
open contact couples are disposed again laterally of the X
axis of an armature (not shown) which contact couples are
closed when the armature is pivoted about its axis A in the
direction of the arrows as described above. The present
1Q embodiment includes a further possibility to make the spring
2' even more flexible with respect to the contact spring 1
by varying the length ratio L6 : L7 in addition to the ratio
of the spring thicknesses h : h'. This may be done by mounting
the two contact springs 1, 2' on differently positioned contact
terminals 3, 3' which may be connected externally or remain
separate. An electric separation, however, is useful only
for high switching voltages and low switching currents because
the additional air gap g will increase the breakdown voltage.
Moreover, the second contact terminal 3' provides for a better
adjustment, which is available also in case the two contact
terminals 3, 3' are bifurcated and joined in a carrier portion
consisting of synthetic material (as known per se) to form
one single terminal pin extending from the base of the relay~
In order to obtain the symmetry of forces shown in Fig. 8,
two normally closed contact couples may be provided on the
other side of the X axis, or the second contact couple disposed
on the same side may be designed with corresponding geometry to
provide an analogous force dependency on the travellin~-distance.
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In the arrangement of Figs. 3 and 4, a double-throw
contact is disposed at an end of the armature 8. Fig. 3
represents the contact arrangement in its central position,
while Fig. 4 represents the arrangement in one of its end
positions. In this embodiment, the two contact spring
members 1, 2 are formed from one resilient strip which is
provided with two movable contacts 4, 4' opposite the fixed
contacts 5, 5' and is centrally connected to a contact ter-
minal 3. The two contact members 1, 2 are symmetrical with
respect to the X axis. In close proximity to the contacts
4, 5 and 4', 5', the two spring members of this double contact
spring bear with a small bias force FK against actuator
portions 6, 7 which consist of synthetic material and are
formed integrally with the armature 8. The free ends of the
spring members extend beyond the movable contacts 4, 4' and
are bent to~ards each other in such a manner that a small
air gap g is formed at a distance L2 from the mo~able
contacts, the size of the air gap g being determined in
accordance with the requirements of a proper storage of
permanent-magnetic pull. It is also possible to omit the
air gap g so that the spring members touch each other in
all positions of the armature.
In actuation, as shown in Fig. 4, the actuation force F
acts on the spring 2 and is distributed to the contact ter-
minal 3 at the ratio (F L) : L6 = F2 and to the touchinglocation K at the ratio ~F . L4) : L6 = F1 which latter force
correspondingly increases the contact force F3~ The thus
1~39807
caused bending of the spring 2 increases the geometrically
determined contact clearance x by the width f of spring
excursion during the switch-over process. The contact
clearance available in the final condition of contact
closure is a = x + f ~ g', where the gap g' = g(L3 + L4) : L6
As may be understood, the contact clearance a in the final
switching condition may be larger than the travelling distance
s of the armature, if the ratio (L3 + L4) : L6 is ~roperly
selected. In this case, however, the contact force F3 is
reduced.
The embodiment of Fig. 5 operates onthe same principle
as that of Figs. 3 and 4 but has two pairs of double-throw
contact systems disposed at the side of each other and at
an end of the relay. The opposite end of the relay may be
provided with the same contact arrangement or with the
one shown in Fig. 3, thereby providing a polarized relay
having the double contact spring of the present invention
and two, three or four pairs of double-throw contacts, in
which all contacts 4, 5, 4', 5' are positioned in close
pro~imity to the axis X, thereby rendering the wear of the
actuator portions 6, 7 with respect to the contacts to be
actuated very small.
Figs. 6 and 7 represent a contact spring arrangement
in which the touching point K between the contact springs
1, 2' is defined by a dent formed in the sprin~ 2'. The
actuator portions 6, 7 of an a~lature (not shown) engage
the outermost portions of the free ends of the contact
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springs 1, 2', while the touching point K is in the
area of the contacts 4, 5, and 4', 5' so that the contact
current is branched into both springs 1 and 2'.
In detail, Fig. 6 shows a normally open contact in
which the springs 1, 2' have their one ends mounted on a
terminal-3 and electrically connected to each other. For
contact closure, the actuator portion 7 presses the contact
spri~g 2' to the left in Fig. 6 until the movable contact 4
provided on the spring 1 engages the fixed contact 5. If
the springs 1, 2' are biassed against the actuator portions
6, 7, the contact couple is closed with an according bias
co~tact force FK. In the further movement, the spring
force F1 (Fig. 8) trans~itted from the spring 2' through the
dent on the touching point is added to this bias contact
force FK. It is mainly the spring length L1 of the contact
spring 2' which determines the amount of permanent-magnetic
pull M' stored as the contact force F3.
In the opposite actuation, i.e. in the opening of the
contact couple 4, 5, the actuator portion 6 moves to the right
in Fig. 6 and - due to the stiffness of the spring length L3 -
forcibly withdraws the movable contact 4 from the fixed con-
tact 5. In case the required spring characteristic of the
length L1 or the stiffness of the length L3 cannot be realized
by their ratio alone, the contact sprinq 1 may be provided with
a thickness h which is greater than the thickness h' of the
spring 2'. The same may be achieved by selecting different
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spring widths, although the spring charaeteristie varies
only linearly in response to the width.
The arrangement of Fig. 7 is formed as a double-
throw eontaet, the actuation of both eontaet eouples 4, 5
ancl 4', 5' being performed in the same manner as shown in
Fig. 6. Other than in Fig. 6, the contact springs 1, 2'
are integrally formed and fixed eentrally to the eontaet
terminal 3, with two resilient seetions extending to each
side. The sections extending somewhat parallel to eaeh other
~n both sides of the terminal 3 are eonneeted by webs 11.
The eontaet springs 1, 2' thus form one single punehed
and bent pieee of sheet metal whieh is positioned on the
terminal 3 by the two webs 11 prior to being finally
secured by spot welding or the like.
Fig. 8 finally represents the force-travelling distance
eharacteristic of the embodiments described above in connection
with Figs. 1 to 7~ The broken curve M' which rises progres-
sively from the center O represents the permanent-magnetie
pull acting on the pole shoes 9, 9' of the armature 8 during
the path of travel s in the absence of excitation. The
represented characteristic of the permanent-magnetie pull M'
which is symmetrieal with respect to the æ axis i5 useful
when a bistable switching behavior, i.e. an arran~ement with
rest positions on both sides, is desired. The Z axis may
be offset from the center of the armature travelling distanee,
for instanee when an asymmetrie rest position on one side
resulting in one normally-elosed contaet is intended. This
may be aehieved for instanee by pole surfaces 9, 9' of
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different size.
In the present case, the forces of the contact spring
members 1, 2, 2' individually and in combination counter~
act the permanent-magnetic pull M' according to the dotted
lines D. In accordance with the geometry shown, the force
F applied by the actuator portions 6, 7, on the springs 1,
2, 2' is divided so.that a smaller proportion F2 acts on the
contact terminal 3, 3' and a larger proportion F3 acts through
the touching point K of the springs 1, 2, 2' on the contacts
4, S or 4', 5', respectively. Within the distance x of
contact travel, the counter forces exerted by the springs
are insignificant. In t~he moment of contact closure, biassed
springs create a bend or step in the characteristic which
marks the bias contact force FK. Since the contact force
thus neither starts at zero nor corresponds to the relatively
high final contact force, the danger of the contact couple
to become welded together is substantially diminished.
Similarly, the danger of contact chattering is reduced by
the comparatively smooth engagement between the fixed and
movable contacts. Safety and life of the contacts are con-
siderably increased by this measure.
In case a gap y exists between the free ends of the
sprinys 1, 2 or 2' during the deflection, the force counter-
acting F increases duxing the closing of this gap g by the
actuation of the spring 2 or 2'. The contact force, however,
is not increased thereby, hecause no force is transmitted
from the spring 2 on the spring 1. Since the increase of
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force counteracting F during the closure of the gap g is
negligible, it is not shown in the graph of Fig. 8. When
the springs 1, 2 touch each other in the closed condition
of the air gap g, the transmission of spring force
increases the contact force by Fl to F3, by which the
positioning force of the armature is reduced. In the
final condition, the excitation energy need only be
sufficient to overcome the relatively small final
positioning force of the armature 8 in order to change the
switching state of the relay. On the other hand,
practically no excitation energy is re~uired for the
relative large contact force F3, which is of particular
importance in view of the fact that the contact clearance
_ is relatively large with respect to the travelling
distance s of the armature, and in view of the positive
and forced contact opening. These advantages are achieved
by properly adjusting the contact springs for the two
different purposes of contact closure and contact opening,
which contact springs additionally share the load of the
contact current.
The invention thus promotes the compensation of
temperature influence for achieving a constant pull-in
voltage as disclosed in U.S. patent specification No.
3,634,793 as well as the application of the so-called
C-circuit in modern relay technology. A C-circuit by
which bistable relays may be operated in mono-stable
fashion, is known for instance from H. Sauer "Relais
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1~398C~7
Lexikon", 1975, page 12, (shown in Fig. 9) and from
"Elektronik", vol. 60, issue 24 of December 27, 1978, page
43.
The circuit shown in Fig. 9 comprises input terminals
20 and 22 which provide supply voltage to the series
combination of a relay coil 24 and capacitor 26. When the
relay is to be activated, switch 28 is closed. Positive
curent passes through zener diode 30, diode 32, coil 24,
capacitor 26 and diode 34 to excite coil 24. Positive
current continues to flow until capacitor 26 becomes fully
charged.
A circuit co~prising transistor 36 and 28 has an
output circuit including terminals 40 and 42 connected in
parallel across the series combination of coil 24 and
capacitor 26. When switch 28 is opened, a negative
current path is established for the base of transistor 36
through zener diode 30 and resistor 40, thus rendering
transistor 36 conductive. Conduction of transistor 36
produces a positive current at the base of transistor 38
rendering that transistor conductive. Transistor 38
latches transistor 36 in the conductive state and
terminals 40 and 42 effectively become shorted to provide
a negative exciting current from capacitor 26 through coil
24, thereby resetting the relay to its rest position.
As indicated above, the invention achieves a
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satisfactory storage of permanent-magnetic pull as the
contact force in addition to the often required forced
contact opening. It is therefore only necessary to determine
the final positioning force F4 of the armature 8 in considera-
tion of the temperature coefficient of a BaOFe or similarpermanent magnet M in such a manner that the centrally
pivoted and therefore balanced armature 8 is safely maintained
in its desired position over the entire range of operating
temperatures even under shock influences. A small final
positioning force F4 is useful in the C-circuit, because
the pull-in power for which the storage capacitor controlling
the function of the C-circuit depends on this final positioning
force~ The smaller the pull-in power of the relay is, the
smaller is the capacity which the capacitor connected in
series with the coil may have. The capacitor is charged when
the power is switched on and blocks the flow of current through
the coil until it is discharged in the other direction through
the coil and a multivibrator, thereby resetting the relay
armature to its rest position, when the power is switched
off. This is of particular significance in safety circuits
for which a forced guidance of the movable contacts is pre-
scribed, because it is not only impossible to over-excite
the relay in case of an over voltage in the excitation clrcuit,
but the relay is also prevented from being re-excited due to
the blocking of the current flow upon the switch-on process
which takes only a few milliseconds. Therefore, no heat will
be generated any more. The reliability and life of the relay
and any structural elements existing in the vicinity of the
relay are thus substantially increased.
