U.S. patent number 3,858,141 [Application Number 05/420,997] was granted by the patent office on 1974-12-31 for reduced actuation time thermal relay system.
This patent grant is currently assigned to Texas Instruments Incorporated. Invention is credited to Robert P. Lackey.
United States Patent |
3,858,141 |
Lackey |
December 31, 1974 |
REDUCED ACTUATION TIME THERMAL RELAY SYSTEM
Abstract
A reduced actuation time thermal relay system for controlling
energization of a load by a power supply. The system comprises a
thermal relay having a resistive control element and a pair of
mating contacts movable between closed circuit and open circuit
positions in response to the temperature of the control element
rising above a predetermined level and falling substantially
therebelow. The system also includes means for electrically
energizing the resistive control element initially to apply a first
voltage thereby to cause rapid heating of the element and
thereafter to apply a second and reduced voltage to the element,
the reduced voltage being of sufficient magnitude to prevent the
temperature of the element from falling substantially below the
predetermined level whereby the actuation time of the thermal relay
is substantially reduced without damaging the resistive control
element.
Inventors: |
Lackey; Robert P. (North
Attleboro, MA) |
Assignee: |
Texas Instruments Incorporated
(Dallas, TX)
|
Family
ID: |
23668759 |
Appl.
No.: |
05/420,997 |
Filed: |
December 3, 1973 |
Current U.S.
Class: |
337/140;
219/492 |
Current CPC
Class: |
H01H
61/0107 (20130101) |
Current International
Class: |
H01H
61/01 (20060101); H01H 61/00 (20060101); H01h
061/013 (); H05b 001/02 () |
Field of
Search: |
;337/99,123,124,128,136,139,140 ;219/492 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Miller; J. D.
Assistant Examiner: Bell; Fred E.
Attorney, Agent or Firm: Levine; Harold Haug; John A.
McAndrews; James P.
Claims
What is claimed is:
1. A reduced actuation time thermal relay system for controlling
energization of a load by a power supply, said system
comprising:
a thermal relay having a resistive control element and a pair of
mating contacts movable between closed circuit and open circuit
positions in response to the temperature of said control element
rising above a predetermined level and falling substantially
therebelow; and
means for electrically energizing said resistive control element
initially to apply a first voltage thereby to cause rapid heating
of the element and thereafter to apply a second and reduced voltage
to said element, said reduced voltage being of sufficient magnitude
to prevent the temperature of said element from falling
substantially below said predetermined level whereby the actuation
time of said thermal relay is substantially reduced without
damaging said resistive control element.
2. A relay system as set forth in claim 1 wherein said resistive
control element comprises a wire of a martensitic memory alloy.
3. A relay system as set forth in claim 2 in which the energizing
means includes means for reducing tbe first voltage in response to
initial movement of the contacts from one position to the
other.
4. A relay system as set forth in claim 3 wherein the voltage
reducing means includes means for preventing application of said
second and reduced voltage to said control element until after
initial movement of said contacts and means for terminating
application of said first voltage to said control element after
initial movement of said contacts.
5. A relay system as set forth in claim 4 in which said means for
preventing application of the reduced voltage comprises a
diode.
6. A relay system as set forth in claim 4 wherein said terminating
means includes another contact of said relay adapted to be
disengaged after initial movement of the said pair of contacts.
7. A relay system as set forth in claim 4 in which said energizing
means further includes means for energizing said control element in
response to the presence of a control signal and for deenergizing
the control element when said control signal is absent.
8. A relay system as set forth in claim 7 wherein the means
responsive to the control signal includes a transistor having its
collector-emitter circuit serially connected with said control
element across said first voltage and the control signal is applied
to the base thereof.
9. A relay system as set forth in claim 2 in which the energization
means includes means for reducing the first voltage in response to
completion of contact movement from one position to the other.
10. A relay system as set forth in claim 9 wherein the voltage
reduction means comprises means for simultaneously terminating
application of the first voltage to the control element and
applying said second voltage thereto upon completion of contact
movement.
11. A relay system as set forth in claim 10 wherein said means
terminating application of said first voltage comprises first and
second diodes.
12. A relay system as set forth in claim 9 in which said energizing
means further includes means for energizing said control element in
response to the presence of a control signal and for deenergizing
the control element in the absence thereof.
13. A relay system as set forth in claim 12 wherein the means
responsive to the control signal includes a transistor having its
collector-emitter circuit serially connected with said control
element and the control signal is applied to the base thereof.
14. In a thermal relay system for controlling energization of a
load by a power supply, said system including a thermal relay
having a resistive control element and a pair of mating contacts
movable between closed circuit and open circuit positions in
response to the temperature of said control element rising above a
predetermined level and falling substantially therebelow; the
improvement comprising means for electrically energizing said
resistive control element initially to apply a first voltage
thereby to cause rapid heating of the element and thereafter to
apply a second and reduced voltage to said element, said reduced
voltage being of sufficient magnitude to prevent the temperature of
said element from falling substantially below said predetermined
level whereby the actuation time of said thermal relay is
substantially reduced without damaging said resistive control
element.
Description
BACKGROUND OF THE INVENTION
This invention relates generally to relay systems and more
particularly to a reduced actuation time thermal relay system.
The use of conventional electromagnetic relays as an interface
between integrated circuit controls and relatively high current
electrical loads has not been generally satisfactory and practical.
A recently developed thermal actuator appears to be quite useful as
an interface between the low power outputs of such integrated
circuit controls and electrical loads having substantial current
requirements. Such a thermal actuator utilizes a wire of a
martensitic memory alloy which will, when heated to a transition
temperature by the passage of electric current, change its length
and actuate electrical contacts capable of handling substantial
currents. Thus these thermal actuators have a very high gain so
that they may be energized by low power sources such as integrated
circuits and control the energization of substantial loads.
However, the time required between the initiation of energization
of the control wire of such actuators and the actual actuation of
the contacts is in some applications, e.g., the operation of the
brakelights and horn in automotive vehicle applications, greater
than desired. This inherent time delay of such thermal actuators,
which involves a "thermal wind-up" from ambient temperatures to the
transition temperature of the wire, is typically in the order of
0.1 to 0.5 seconds.
SUMMARY OF THE INVENTION
Among the several objects of the invention may be noted the
provision of an improved thermal relay system; the provision of
such a system which will greatly reduce the actuation time of the
thermal relay without damage to the relay; the provision of such a
system which has a decreased transfer time of the contacts between
their open circuit and closed circuit positions and greatly reduce
the possibility of contact welds; and the provision of such a
system which is reliable in operation and is simple and economical
to manufacture. Other objects and features will be in part apparent
and in part pointed out hereinafter.
Briefly, a reduced actuation time thermal relay system of this
invention comprises a thermal relay having a resistive control
element and a pair of mating contacts movable between closed
circuit and open circuit positions in response to the temperature
of the control element rising above a predetermined level and
falling substantially therebelow. The system also includes means
for electrically energizing the resistive control element initially
to apply a first voltage thereby to cause rapid heating of the
element and thereafter to apply a second and reduced voltage to the
element. The reduced voltage is of sufficient magnitude to prevent
the temperature of the element from falling substantially below the
predetermined level whereby the actuation time of the thermal relay
is substantially reduced without damaging the resistive control
element.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a plan of a thermal actuator such as is utilized in a
thermal relay system of this invention;
FIG. 2 is a section generally on line 2--2 of FIG. 1 with certain
components shown in elevation;
FIG. 3 is a schematic diagram of a reduced actuation time thermal
relay system of the present invention;
FIG. 4 is a graph illustrating the reduction in actuation time of a
system of the present invention as compared to that of a thermal
actuator such as shown in FIGS. 1 and 2;
FIG. 5 is a schematic diagram of an alternate embodiment of the
present invention which reduces contact transfer time as well as
thermal windup time; and
FIG. 6 is a graph illustrating the improved response time of the
alternate embodiment as compared to that of a thermal actuator such
as shown in FIGS. 1 and 2.
Corresponding reference characters indicate corresponding parts
throughout the several views of the drawings.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to FIGS. 1 and 2, a thermal relay or actuator is
indicated generally by 1. This relay comprises a frame, preferably
molded from a thermosetting synthetic resin material, having a pair
of spaced parallel sidewalls 2 with three bridging support portions
3, 4 and 5. Bridging portion 3 has a threaded bore 6 receiving a
machine screw 7 to secure thereto one end of a switch arm 8 and a
terminal lug 9. Bridging support 4 is provided with a doubly
counterbored bore 10 which receives a shank of a machine screw 11,
the tip of which is threaded into a terminal lug 12 carrying a
contact 13 on an inner end thereof while the outer end serves as a
normally closed (NC) terminal for the actuator or relay. Another
terminal lug 14 is secured to the undersurface of support 4 by a
retainer 4a against which the head of screw 11 bears. The inner
cantilevered end of lug 14 carries another fixed contact 15 and the
outer end of lug 14 constitutes a normally open (NO) terminal for
relay 1. A double-faced contact 16 is mounted on the free end of
switch arm 8 which is biased upwardly into engagement with contact
13 by a coil spring 17 seated in a well 18 of bridging support
5.
A bell crank 19 of electrical insulation material is mounted for
pivotal movement about a pin 20 within the recess formed between
sidewalls 2. A nose 21 constituting one end of the bell crank bears
against the switch arm 8 on the surface opposite that against which
the end of spring 17 acts. The other end of crank 19 has two
integrally formed spaced tongues 22 projecting therefrom, while a
similar tongue 23 is formed on the upper surface of support 3.
Mounted on support 3 are two similar spaced terminal members 24 and
25 having upper arms, the outer end of which serve as terminal
posts 26 and 27, and legs 24a and 25a extending downwardly and
secured to support 3. Members 24 and 25 have outwardly projecting
ends 29 and 29a forming terminals for connection to a low level
power source.
A thin wire 28 of a martensitic memory alloy, such as that formed
of a selected nickel-titanium alloy referred to as Nitinol, has its
opposite ends secured to terminal posts 26 and 27 and is trained
around tongues 22 and 23 and four reaches. This wire, tensioned by
spring 17 acting against the nose of crank 19 to rotate it
counterclockwise, is a resistive control element, which when heated
above a transition temperature by the passage of low level current,
will quickly shorten because of a sudden change in its modulus of
elasticity and overcome the biasing action of spring 17 to move
switch arm 8 and cause contact 16 to engage contact 15. When the
actuator or terminal relay wire 28 is electrically deenergized, it
cools below its transition temperature and will revert to its
original modulus of elasticity and thereby lengthen so as to permit
contact 16 to disengage contact 15 and return to engagement with
contact 13.
This thermal actuator is particularly useful in that it has a high
gain and can be directly operated by the very low power level
provided by integrated circuit chips. However, the time required
for actuation of the relay to move contact 16 from one to the other
of its positions, although typically in the order of 0.1 to 0.5
seconds, is too long for some applications of this actuator.
A reduced actuation time thermal relay system of this invention is
shown in FIG. 3. In addition to thermal actuator 1 the system
includes means for electrically energizing resistive control
element 28 initially to apply a first voltage corresponding to V1
(hereafter referred to as V1) to cause rapid heating of the element
and thereafter to apply a second and reduced voltage corresponding
to V2 (hereafter referred to as V2) to the element to prevent the
temperature of the control element from falling substantially below
its transition temperature. An electrical load 30 is connected to
the NO relay terminal carrying contact 15 while the NC terminal and
its contact 13 are interconnected to V2 via a diode D1 and terminal
29 of control wire 28. The other terminal 29a of control element 28
is connected to ground through the collector-emitter circuit of a
transistor Q1. The base of Q1 is connected through a current
limiting resistor R1 to an input terminal 31.
With no control signal applied to input terminal 31 and the base of
transistor Q1, Q1 does not conduct and control element 28 remains
at ambient temperatures with the relay contacts as shown in FIG. 3.
When a control signal is applied to the base of transistor Q1, it
conducts and control element 28 is energized by V1 via normally
closed contacts 13, 16. Since the cathode of diode D1 is at a
higher potential than its anode, D1 is back biased preventing
energization of element 28 by voltage source V2. The potential of
V1 is so high that it causes very rapid heating of resistance
control wire 28 to its transition temperature whereupon contact arm
8 will start to move contact 16 away from contact 13. V1 is of such
a magnitude that if it were applied to control wire 28 for a
substantial period of time the wire could be damaged. However, as
soon as contact 16 disengages contact 13, the circuit from V1 to
wire 28 is broken and diode D1 becomes forward biased so that wire
28 is then energized by the lower potential voltage source V2. The
magnitude of V2 is sufficient to maintain the temperature of
element 28 preferably somewhat above the predetermined transition
temperature of wire 28 or in any event to prevent this temperature
from falling substantially below transition temperature. The
application of V1 and then V2 voltage to wire 28 thus reduces the
actuation time of contact arm 8 in moving contact 16 into
engagement with contact 15 thereby to energize load 30. Diode D1
serves as a means for preventing application of the second and
reduced voltage to the control element until after initial contact
movement and contact 13 in conjunction with contact 16 constitutes
means for terminating application of the first voltage to the
control element after initial contact movement.
When the control signal to the base of transistor Q1 is removed, Q1
ceases to conduct and control element 28 is thus deenergized. As
the temperature of element 28 falls substantially below its
transition temperature, the contact 16 will move away from contact
15 and deenergize load 30.
If the desired control function of the relay system is to maintain
the load 30 energized while the control wire 28 remains deenergized
and to deenergize the load in response to heating of element 28
above its transition temperature, this is accomplished by a simple
modification of the circuit of FIG. 3. Load 30 is simply
disconnected from contact 13 and connected to contact 15, with no
other circuit changes necessary. The load continues to be energized
by V1 and control element 28 remains unheated as long as no signal
is applied to the base of Q1 which therefore remains nonconducting.
When a signal is applied to the base of Q1, it will conduct thereby
simultaneously applying the overdriving V1 voltage to control wire
28 to effect accelerated heating thereof and causing contact arm 8
to move contact 16 away from contact 13 thereby deenergizing load
30. After this accelerated opening of contacts 16 and 13, control
wire 28 is energized at the lower voltage level of V2 and it
remains so until the control signal is removed.
FIG. 4 illustrates the reduction in the actuation time of thermal
actuator 1 as effected by the system of this invention shown in
FIG. 3. Actuation time is plotted along the abscissa and the
ordinate represents the distance the contact 16 of contact arm 8
moves during actuation of the relay or actuator. Actuation time is
the sum of the thermal windup time (tw) and the contact transfer
time (tt). The former is the time required for the control element
to heat to its transition temperature from ambient from the instant
of electrical energization thereof. The latter is the time required
to move the contact from its normal or rest position to its contact
make or alternate actuated position after the transition
temperature is reached. Curve B illustrates both the thermal windup
and transfer times of relay 1 energized by a voltage source of the
usual potential applied to relay 1, i.e., typically the voltage
level V2. Curve A illustrates the reduced actuation time of the
relay system of FIG. 3, wherein the thermal windup time (tw) is
greatly reduced by the application of the overvoltage V1 during
initial energization. The transfer times are essentially the same
for relay 1 and the system of FIG. 3 inasmuch as the same voltage,
V2, is applied to the control element during the transfer periods.
The short dashed extensions of curves A and B following contact
make represent the overtravel of the contact arm between initial
contact make and the contact's final actuated position, and
indicate increasing contact pressures. With this system of FIG. 3,
the advantageous reduced thermal windup time is accomplished
without risk of damage to the control element due to extended
application of an overvoltage because the system utilizes the
separation of contacts 13 and 16 to terminate the overvoltage. In
other words, the system is self-protecting.
A reduced actuation time thermal relay system is shown in FIG. 5
which provides not only reduced thermal windup time but also
substantially reduced contact transfer time. While similar to the
FIG. 3 system, it differs in several respects. In FIG. 5 one side
of thermal element 28 is connected directly to the positive
polarity terminal of V1 and the other terminal thereof is connected
via the collector-emitter circuit of Q1 to the junction between two
diode anodes D2 and D3 connected back-to-back. The cathode of D2 is
connected to contact 15 and output load 30. The cathode of D3 is
connected to the positive polarity terminal of a voltage source V3,
the negative terminal of which is grounded. The potential of V3 is
considerably lower than that of V1.
Operation of the FIG. 5 system is as follows:
With no control signal applied to the base of transistor Q1, it
does not conduct and control element 28 remains deenergized and at
ambient temperatures. Load 30 is also not energized because contact
16 is not in engagement with contact 15 and diode D3 prevents
energization of the load from V3. When a control signal, preferably
from an integrated circuit or solid state control, is applied to
the base of the transistor, it conducts so that current will flow
from power source V1 to control element 28 and load 30. Since
substantially the entire voltage drop is across the control
element, it will rapidly heat to its predetermined transition
temperature. When element 28 reaches that temperature, contact 16
will move away from contact 13 toward contact 15.
In contrast to the previous embodiment, however, the higher voltage
is applied until contact 16 engages contact 15. When these contacts
close, load 30 becomes fully energized since it is directly
connected across V1. Also since the cathode of diode D2 is at a
higher potential than its anode, the diode is back biased isolating
control element 28 from load 30. A second and reduced voltage is
applied to control element 28 as it, the collector-emitter circuit
of transistor Q1, and diode D3 are series connected from the
positive side of V1 to the positive side of the lower potential
voltage source V3. The magnitude of this reduced voltage applied to
the control element is equal to the d.c. level of V1 minus the d.c.
level of V3. Thus diodes D2, D3 comprise means responsive to
completion of contact movement to simultaneously terminate
application of the first voltage (V1) to the control element and to
apply a second and reduced voltage (V1-V3) thereto. This second
reduced voltage is again of sufficient magnitude to prevent the
temperature of control element 28 from falling substantially below
its predetermined transition temperature thereby maintaining the
contacts 15, 16 in their closed position. The system of FIG. 5 is
now in its steady state operating condition.
When the control signal is removed from the base of transistor Q1,
it stops conducting causing deenergization of control element 28
and permits the temperature of the element to fall substantially
below its predetermined transition temperature thereby to open
contacts 16,15 and deenergize load 30.
FIG. 6 compares the actuation time of the FIG. 5 system with that
of thermal relay 1 used alone. Curve C represents the former while
dashed curve B again represents the latter. As is indicated, both
the thermal windup time (tw) and the transfer time (tt) of the
system of FIG. 5 are greatly reduced because the overvoltage is
applied to the control element from the moment of initial
energization of the element until contact 16 has substantially
completed its movement from its initial position engaging contact
13 to its actuated position engaging contact 15. Again, the system
is self protecting in that damage to control element 28 because of
prolonged overvoltage energization thereof is avoided because
closure of contact 16 against contact 15 automatically effects
reduction of the voltage applied across element 28 by V1-V3. It is
also to be noted that because of the reduced transfer time of this
system contact sticking or welds is minimized.
The degree of reduction of actuation time of the reduced actuation
time thermal relay system is a function of the magnitude and
duration of the overvoltage applied to the control element. Thermal
relay 1, when energized at normal rated voltage has a typical
actuation time of 100 milliseconds (ms) comprising a 70 ms thermal
windup time and a 30 ms contact transfer time. The reduced
actuation time thermal relay system of FIG. 3 by reducing the
thermal windup time to an exemplary 7 ms reduces the total
actuation time to 37 ms. By also reducing the transfer time to an
exemplary 3 ms, the system of FIG. 5 reduces the total actuation
time of relay 1 from 100 ms to 10 ms, i.e., by a whole order of
magnitude. An actuation time of 10 ms is comparable to that of a
conventional electromagnetic-type high current relay.
It is to be noted that both of the previously described embodiments
are well suited to inclusion in an integrated circuit control since
resistor R1, transistor Q1, and the various diodes can be included
within an integrated circuit chip.
In view of the above, it will be seen that the several objects of
the invention are achieved and other advantageous results
attained.
As various changes could be made in the above constructions without
departing from the scope of the invention, it is intended that all
matter contained in the above description or shown in the
accompanying drawings shall be interpreted as illustrative and not
in a limiting sense.
* * * * *