Note: Descriptions are shown in the official language in which they were submitted.
)6956
This invention relates to timed switch apparatus for elcctric loads.
Timed switches find particular application in the control of heavy
direct current applied to window heaters in vehicles, particularly backlite
heaters in automobiles and truc!:s.
It has become increasingly apparent over the ]ast Eew years that
sources of energy are not inexhaustible, that fuels for motor vehicles
continue to increase in price, and that all possible savinqs in operation costs
of the vehicle are to advantage. ~urther, backlite heaters intended for
defrosting purposes draw heavy currents, in some instances, of the order of
40 amps, or even more where the trend is to larger glass areas, from a 12-volt
car battery supply. At those times when headlights and in-car heaters are
also switched on there is heavy competition for the available output from the
battery and alternator. If the backlite has merely a simple on-off switch and
the heater is used continuously in such conditions, particularly when the car
is in stop-and-go traffic, the battery can be run flat.
I have disclosed a backlite timer in my prior Canadian Patent 868,629
issued 13 April, 1971 directed to a long interval timing device to which
reference may be made for background. The corresponding U.S. Patent is 3,571,665
issued 23 March, 1971.
That timer ensures that the heater is not on continuously by providing
an interval of operation for defrosting and which can vary to some extent with
environmental temperature conditions.
To conform with the laws requiring continued improvina gasoline
consumption efficiency there is also a steady accent in the automobile manufact-
uring trade on the need to reduce weight. Apparatus here disclosed may replace
a switch, pilot-light, wiring harness, connectors relay and timing circuitry
currently employed in timed defrost arrangements, by a single package having
typically one-third the weight of the assemblies now employed in the industry.
1~695~
Considerable cost savings per car can flow from lower initial cost and weight
and space savings.
Another feature of one embodiment of inventive apparatus here
described takes account of the fact that where initial defrosting may require
the application of current for an interval of the order of 10 to 15 minutes
before switch-off, subsequently the backlite heater may need to be reactivated
one or more times for demisting purposes. The subsequent periods may usefully
be less than that of the first. With single period timers the interval chosen
has to be a compromise.
In this present disclosure, an electrical time switching device is
described which allows not only an initia~ period of operatiol~, but al50
provides the opportunity of having shorter periods of operation for the second
and subsequent actuations of the device, such as is beneficial for demisting
purposes after initial defrost action.
It is also to advantage, and a device is so described, which in a
multiple period timer, includes an automatic reset after the automobile has
been stopped, so that the next time the backlite heater is required the full
initial timing period of operation can be provided. A typica] period of
operation would initially be 10 minutes with a 5-minute period in each
subsequent operation. In some applications, second and subsequent periods of
2.5 minutes would be satisfactory.
As will be further described herein, an energy efficient auto-
matic simplified timing device can be constructed with manual actuation
and override providing a positive "feel" to the operator and including a
pilot-light indicator of essentially infinite life, all in a single
package. Prototypes of specific embodiments here described have been
delivering currents of 50 amperes both reliably and without any excessive
contact heating. It will be understood that the apparatus disclosed is
not limited to operation of automobile backlite heaters but may be used
9S6
in a wide variety of applications both in automobiles and elsewhere where
single or multiple timed operations may be required. Those skilled in
the art will appreciate that the timer circuitry may be used with or with-
out conjunction of electric load switching or as an independent timing
mechanism when timing functions are required.
In accordance with one aspect of the invention there is provided,
a timed switch for an electric load which comprises in combin- .
ation,
a pair of contacts for connection with and actuation of said
0 load,
a timer circuit,
manually actuable means for effecting operation of said contacts,
said timer circuit being activated in response to operation of said
contacts,
holding means associated with said contacts for holding said
contacts in operated condition, and for releasing said contacts to
unoperated condition,
means interconnecting said timer circuit and said holding means
for releasing said contacts upon expiry of a predetermined time period
0 measured by said timer circuit,
said manually actuable means also including means for effecting
said contacts to unoperated condition upon manual actuation thereof.
In accordance with a second aspect of the invention there is
provided;
a timed switch for an electric load which comprises,
a housing,
relay means mounted within said housing, said relay means
including a pair of relay contacts for series connection with said load
and relay holding means for holding said contacts in a closed condition
-- 3 --
11~6956
and for releasing said contacts to an opened condition,
a timer circuit mounted within said housing,
manually actuable means carried by said housing for mechanically
moving said contacts to the closed condition, said timer circuit being
activated in response to the closing of said contacts by said manually
actuable means, said relay holding means being activated in response to the
closing of said contacts by said manually actuable means to hold said
contacts in the closed condition,
means interconnecting said timer circuit and said relay holding
means for deactivating said relay holding means to release said contacts
to the opened condition upon expiry of a predetermined time period
measured by said ~ r, tir~r c;r~;t~
said manually actuable means also including means for mechanical-
ly moving said contacts to the opened condition upon manual actuation
thereof.
In accordance with a third aspect of the invention there is
provided;
a timed switch for an electric load which comprises,
a housing,
a pair of contacts in said housing for connection with and
actuation of said load,
a timer circuit mounted within said housing,
manually actuable means carried by said housing for effecting
operation of said contacts, said timer circuit being activated in response
to operation of said contacts,
holding means associated with said contacts for holding said
contacts in operated condition, and for releasing said contacts to
unoperated condition,
means interconnecting said timer circuit and said holding means
-- 4 --
;956
for releasing said contacts upon expiry of a predetermined time period
measured by said timer circuit,
said manually actuable means also including means for effecting
said contacts to unoperated condition upon manual actuation thereof.
The timer circuit may include a timer circuit board with means
mounting the board on a rigid support with the housing. Illumination means
may be within the housing connected to illuminate upon operation of the
contacts and may be visible exteriorly of the housing adjacent the manually
actuable means. Terminals may be provided on the housing for electrical
load and power supply connection. The timer circuit may include means for
measuring of first and a second predetermined time period upon a first
and subsequent operation of the timer circuit with a potential sensitive
means for modifying at least the second predetermined period.
Specific embodiments of the invention will now be described
having reference to the accompanying drawings in which;
Figure 1 shows a side sectioned view of one embodiment of a
complete timing switch package;
Figure 2 is a plan view of the device from above, and Figure 3 a
plan view from the device of figure l; and
Figure 4 is a schematic circuit diagram of electronic circuitry
associated with the timing function and employing a digital integrated
circuit.
~ith reference first to figures 1 to 3, a casing 1 of a suitable
plastic material, such as A.B.S., has pivoted to one end of it on projecting
stubs 2 (Figure 3), a manually rockable actuating cover 3. At the other
end of the housing 1 extending from a mounting plate 4 are electrical
contact spades 5 for connection to wiring harness or other socket terminals
(not shown). Spring ears 6 on the case 1 in conjunction with stop flanges
7 enable the package assembly to be snap mounted for instance in an
- 4a -
6956
automobile dashboard. Received in socket 9 of cover 3 is a stub 8 of an
actuating arm 10. The arm 10 is pivoted on short shafts 8' caaxial with
stubs 2 received in the housing 1, and is constructed as two downward
depending sections 10' one behind the other in figure 1, straddled by a ~-
web 10". A spring 11 engages extsnsions on .he a = 10 to ettsot
.:
. !
,`<
., . ' '
. I
- 4b -
9S6
a restoring action whenever the rockable cover 3 is displaced from
the central position shown in figure 1. A second spring (not
shown) behind spring 11 engages the arm 10 only when the cover 3
is rocked to displace the arm anti-clockwise, thereby providing a
greater resilient resistance to the cover 3 when the arm is
rotated anti-clockwise. This improves the balanced "feel" of the
device as will be explained later.
Mounted on the plate 4 is a relay yoke, coil and core
assembly 15, a timing circuit board 16 and a spring,beryllium
copper or phosphor bronze output contact post 17 connected to out-
put spade contact 18. Beryllium copper alloys are preferred for
the post material.
The relay assembly comprises yoke 20 containing coil and
former assembly 21, moveable core 22 with an armature or "obturator"
23 of a suitable conductive spring material such as spring
beryllium copper or phosphor bronze. The obturator carries a
contact 25. By virtue of the fact that the obturator 23 is fasten-
ed at its bottom end by retention between yoke 20 and a magnetical-
ly permeable end plate 26, downward movement of the core 22 causes
contact 25 to move both in an outward and a downward direction and
thus effects very efficient contact wiping action with the contact
30 mounted on post 17. The particular way in which this kind of
wiping action and relay obturator structure produces very
efficient contacting is described in my U.S. patents 4,003,011
issued 11 January, 1977 and 4,064,470 issued 20 December, 1977.
Further details of this particular structure will not be elaborated
here.
A shoulder flange 31 extends from the upper end of core
22 where it is engageable by the web 10" ~ocking of the arm 10
in the clockwise direction shown in figure 1 causes the web
to depress shoulder 31 pushing the core 22 into the former assembly
21 and causing con~act 25 to engage contact 30. When the core 22
is depressed fully into the former its lower end strikes
--5--
6'9~i~
the end plate 26 to complete the magnetic circuit through the
yoke 20, core 22 and end plate 26. Since the winding 19 on
former 21 has become energized by closing of contacts ~5 and
30 (in a r~nner which will be explained later) the core snaps
against the plate 26 and is held in that position after release
of rockable cover 3 and return o:E the arm 10 to the position
shown in figure 1. The closing of the magnetic circuit ensures
solid holding of the relay core even in the presence of strong
vibration.
When the core is to be released, rocking of cover 3
and arm 10 in a counterclockwise direction causes the arm to
engage the upper leg 35 on post 17. This action breaks contact
between 25 and 30, removing current from the coil 19 on former
21, and allowing collapse of the f 1UY. in the yoke, core and
end plate circuit (assisted by incidental air gaps between
the yoke and the core at the upper end, and between the
core and the end plate at the lower end) so that the core moves
rapidly out of the former back to the position shown in
figure 1 striking the web 10" on arm 10.
It can be seen that this arrangement produces a snap
action sensible by the operator both upon actuation of the
device and closing of the relay when core 22 strikes plate 26,
and also upon manual release of the relay. by the hammering
action of the shoulder 31 against the web 10'. In
order to balance the "feel" of the device generally, since the
resilient resistance encountered by the arm 10 when moved in a
clockwise direction to force core 22 into former 21 is somewhat
greater than that encountered when the arm 10 is rocked against
leg 35 to open contacts 25 and 30, the clockwise rotating
action of the second spring 11 has been provided (as previously
detailed). This results in essentially all of the mallually
--6--
95~
applied rocking effort being applied to t,he shoulder 31 when
switching the device "ON" but in the manually applied effort
being resisted by the springs 11 (and leg 35) when the device is
manually switched "OFF".
An indicator light 40, preferably a light emitting
diode,is provided in the upper end of casing 1, directed to
cause its light to fall on a window or lens 41 mounted in the
rockable cover 3, to provide an indication to the operator
whenever the device has been actuated and contacts 25 and 30 are
in closed position.
The schematic diagram of figure 4 illustrates the
contacts 25 and 30, the light emitting diode 40, coil 19 fo.r core-
22, and the terminal 50 connected to the backlite load. Input
terminal 18 provides input battery +ve 53 to contact 30, and to
ignition switch 80, which is.in turn connected to input terminal
51. Battery -ve (not shown) is connected to ground which is
applied to input terminal 52.
Referring in more detail to figure 4, there is included
an integrated circuit package 55 which embodies a power supply
~ 56, an oscillator 57, a counter 58, an output logic control 59
.and an output stage 60. Terminals provided on this package 55
are ground 61, oscillator input terminals 62 and 63, power
supply input 64, initiating input 65, output logic time select
66 and coil activate terminal 67. Battery input at terminal 18
is applied to contact 30, and when the device is m~nually
actuated to close contact 25 against contact 30, the battery is
then applied to terminal 50 and the backlite load 70. Connected
to the lead from contact 25 to terminal 50 are one side of
resistor 75, one side of relay coil 19, and a series connected
resistor 76 and light emitting diode 40, whose other side is
returned to ground. Thus the application of the battery
potential to contact 25 also applies an initiating voltage to
--7--
fi956
input 65, and also illuminate~ the diode 40. The voltage
applied to relay coil 19 causes a current to flow through this
coil v~a te~minal 67 and thence to ground through output stage
60 and terminals 61 and 52. This
current provides sufficient magnetic flux in the relay yoke
assembly, core and end plate to hold the core at its inner
position, although the current is not sufficient itself to
pull in the core in the absence of the manual actuation
provided by the engagement of arm 10 on the shoulder 31.
Because only a small current is needed for holding purposes
the winding 19 is constructed with the characteristics of a
holding coil, rather than the much heavier characteristics
needed for a pull-in winding.
It can be seen that the closing of the car ignition
switch 80 has also applied battery potential to terminal 51
which is fed through resistor 81 to power supply input 64.
Protection against transients is provided by capacitor 78
between terminal 65 and ground, and by capacitor 82 between
terminal 64 and ground. The application of the initiating
2n voltage at 65 switches on the oscillatorand tllc output stage
G0. lhc oscillator is basically a rclaxation circuit whose
timing is effected by resistor 83 between terminals 62 and 63
and capacitor 84 between terminal 63 and ground. A typical
frequency of oscillation is 3.4 hertz and this frequency is
applied to the counter 58. Typically the counter would allow
counting to 2,048 (which corresponds to a 10-minute period).
The counter is read by the output logic 59, and when the total
of 2,048 is achieved, the logic 59 triggers the output stage 60,
which cuts off, interrupting the current throuc~h coil 19 and
causing the core 22 to drop out. The zener diode 77 limits
the voltac,e impulse appearing on terminal 67 due to the
inductive effect of coil 19. The drop out of the core opens
--8--
6~S6
the contacts 30, 25 removing the power supply to the backlite
load, to the light emitting diode 40, and to the input 65.
The ignition swi-tch 80 remains closed however, so that the
power supply 56 is still actuated, thereby retaining output
logic 59 in a condition sensitive to the fact that it has
produced an output following an initial count by counter 58.
If now the timer is actuated a second time by an
operator again closing con-tacts 30, 25, applying a new
initiating input to terminal 65, the oscillator will once again
be switched on and the counter 58 set in action. This time
however as the output logic 59 reads the counter, it produces
a signal to the output stage 60 after a count of only 1,024
is reached. This time corresponds to 5 minutes, and therefore
the contacts 30, 25 are opened after a 5-minute period. As
theoutput logic control 59 continues to be sensitive to the
fact that an output has been produced, subsequent initiations
of the device by closing contacts 30 and 25 will each time
result in the 5-minute timing period. I~hen ignition switch 80
is opened,the input to power supply terminal 64 is removed and
the output logic 59 will also be deactivated. Any subsequent
closing of ignition switch 80 will return the logic 59 to its
initial state and will result in an initial timing output only
after a count of 2,048 has been achieved.
The output logic 59 is provided with the time select
terminal 66, which allows for different functions of the output
logic control 59 dependent upon the voltage applied to terminal
66. If pin 66 is connected to ground 61 as illustrated in
figure 4, then, a~ previously described,the first -timing interval
will allow for a count of 2,048 (lO minutes) whereas the
subsequent counts will be 1,024 (5 minutes). If however pin 66
is connected to the positive voltage on pin 64, the initial
i956
count will, as before, be 2,048, but subsequent counts will be
512 (or 2.5 minutes). If terminal 66 is left unconnected,
there is no change in response to the counter between the first
and any subsequent timer actuations.
It can be seen therefore that considerable
flexibility is provided for variations in timing period between
an initial time out and subsequent timings, as may be desired.
Thls kind of flexibility is not possible in an analog type of
timer in which a capacitor is allowed to charge only once
during the timing cycle. By using digital logic with a counter,
much higher oscillation frequences are permissible resulting
in very, very much smaller capacitors with much higher
tolerance and lower temperature sensitivity. Such changes`
result in a much smaller unit, lower cost, higher accuracy
and improved flexibility and performance.
With the new device, testing is greatly facilitated
because the oscillator runs at a constant speed and it can be
checked for accurate frequency in a period of a few seconds.
Using the electrolytic analog processes, matching of resistors
to capacitors is necessary and testing requires the full run
through of the timing period. Typically, using an analog
device, the timing capacitor had to be of the order of 220 ~fd
with tolerances of -50~ to +100~. Using the much lower value
charging capacitor 84 of the present disclosure (approximately
.01 ~ufd) and readily available at close tolerance, individual
matching is no longer required.
By the particular structure shown, manual cancellation
or override can be effected to switch the circuit off any time
before its automatic time out since removal oE potential from
--1 0--
l~U69~
input 65, by manual opening of contacts 30, 25 will switch off
the output stage 60. The removal of input at 65 also deactivates
the oscillator 57, and subsequent reapplying and starting of the
oscillator will cause the counter to start from zero. The count
necessary for actuating output from logic 59 will depend upon
whether or not the logic had already produced a first output,
before the manual cancellation was effected.
Details of the counter 58 and the output loyic
control 59 and the way in which the output logic can read the
counter 58 differently between an initial and subsequent
operation will be apparent to those skilled in the art as well
as the alteration of the reading dependent upon the application
of ground, high voltage or open circuit to the terminal 66.
I2L integrated circuit logic techniques are particularly
suitable for the construction of the counter and output logic
control.
