U.S. patent number 3,792,693 [Application Number 05/179,390] was granted by the patent office on 1974-02-19 for stored temperature cold start auxiliary system.
This patent grant is currently assigned to The Bendix Corporation. Invention is credited to David G. Luchaco.
United States Patent |
3,792,693 |
Luchaco |
February 19, 1974 |
STORED TEMPERATURE COLD START AUXILIARY SYSTEM
Abstract
A cold start auxiliary circuit for use in conjunction with an
electronically controlled fuel supply system is disclosed herein.
The cold start auxiliary circuit is comprised of a first circuit
which receives and stores a signal indicative of instantaneous
engine temperature during the time period when the electrical
system energization of the vehicle is substantially stable and a
second circuit which is energized by the vehicle electrical system
and is triggered upon the initiation of engine cranking but which
is otherwise not influenced by the electrical energization
fluctuation incident to the cranking cycle. The cold start circuit
produces an output signal which is substantially proportional to
the difference between the sensed engine temperature and an
established reference upon triggering of the second circuit.
Inventors: |
Luchaco; David G. (Horseheads,
NY) |
Assignee: |
The Bendix Corporation
(Southfield, MI)
|
Family
ID: |
22656401 |
Appl.
No.: |
05/179,390 |
Filed: |
September 10, 1971 |
Current U.S.
Class: |
123/491;
123/179.15 |
Current CPC
Class: |
F02D
41/064 (20130101) |
Current International
Class: |
F02D
41/06 (20060101); F02m 051/00 (); F02b 003/00 ();
F02n 017/00 () |
Field of
Search: |
;123/32EA,179L,179G |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Goodridge; Laurence M.
Assistant Examiner: Flint; Cort
Attorney, Agent or Firm: Flagg; Gerald K.
Claims
What is claimed is:
1. In an internal combustion engine fuel control system having
means for electronically injecting fuel into the engine, and an
energizable electrical system with a three-position switch having
OFF, RUN, and CRANK positions, the improvement comprising cold
starting assist means for providing an injection signal having a
duration determined by engine temperature comprising:
temperature sensor means for providing a signal having a magnitude
inversely proportional to engine temperature;
means for receiving and storing the signal provided by said
temperature sensor means;
signal providing means responsive to the switch entering the CRANK
position for initiating an injection output signal;
means responsive to the initiation of an injection signal for
discharging said signal storing means, the time required to reduce
the stored signal to a predetermined level being determined by the
magnitude of the signal received from said temperature sensor
means; and
level detecting means for terminating said output signal when said
stored temperature indicating signal drops to a predetermined
magnitude.
2. The fuel control system as claimed in claim 1 wherein:
the fuel control system includes voltage supply means subject to
voltage fluctuations during engine start up that vary the magnitude
of the temperature indicating signal provided by said temperature
sensor means; and
the cold starting assist means further include means responsive to
the initiation of an output signal for isolating said signal
storing means from said temperature sensor means during the time
that an injection output signal is provided to thereby prevent
voltage fluctuations from altering the duration of said output
signal.
3. A circuit for generating an output pulse having a duration which
is proportional to the difference between a sensed signal and an
established reference for positive differences and which is zero
for all other relationships, said signal to be generated in
response to actuation of a control switch having at least two
active positions comprising:
a first circuit responsive to the sensed signal and to the switch
being in the first position operative to receive and store the
sensed signal; and
a second circuit responsive to said first circuit and to the switch
entering the second position operative to compare said stored
sensed signal with a preselected reference signal and to generate
an output signal having a starting point in time which coincides
with entry of the switch into the second position and a duration
proportional to the positive difference between the sensed stored
signal and the preselected reference signal.
4. The circuit as claimed in claim 3 wherein said second circuit
includes first and second serially connected bistable switches,
said switches triggerable to switch from the nonconducting state to
the conducting state and operative to thereafter remain in the
conducting state until current flow through the switch decays below
a predeterminable minimum, said first switch adapted to be
triggered by entry of the control switch into the second position
and the second switch is operative to compare the stored signal
with the preselected reference signal.
5. The circuit as claimed in claim 4 including amplifier means
having a control electrode, said control electrode coupled to the
interconnection of said serially connected switches, said amplifier
responsive to the conductive condition of the first switch to
initiate an output control pulse and further responsive to the
conductive condition of the second switch to terminate the output
control pulse.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the field of electronically
controlled fuel supply systems for internal combustion engines, and
more particularly to that portion of the above-noted field which is
concerned with auxiliary circuits to control the provision of fuel
to the engine for transient operating conditions which is in
addition to that provided by the main electronic fuel control
system. In particular, the present invention is directed toward
cold starting auxiliary circuits which provide additional fuel to
assist in rapid and efficient starting of the engine.
2. Summary of the Prior Art
It is well known within the prior art to provide additional charges
of fuel to an engine residing at a comparatively low ambient
temperature in order to facilitate the starting of that engine. In
addition, it is also known within the art to provide such
additional fuel charges in the form of injector valve energizing
pulses generated by circuitry which operates in cooperative
association with an electronic fuel control system. Circuitry such
as is illustrated in pending applications Ser. Nos. 46,681, 46,705,
and 46,706, and in U.S. Pat. Nos. 3,504,657 and 3,533,381,
represent several of the techniques of generating the additional
fuel providing pulses. However, the circuitry for accomplishing
this function has a common failing. The prior art circuitry makes
use of the engine temperature sensor which is typically an
electrically powered thermistor deriving its energy from the
vehicle electrical system. The output characteristics of such
thermistors are a function of the temperature of their environment
and of the voltage level energization which they receive. In
operating the starting cycle of an automotive engine, the vehicle
electrical system is subject to large fluctuations in battery
voltage which occur as the starter system of that engine is
energized. This occurs because of the large amounts of electrical
current required to energize the starting motor and the starting
shift solenoid. As a consequence, the prior art cold starting
assist systems are subject to the generation of erroneous output
signals which occur primarily as a result of the above-noted
fluctuations of the battery voltage. It is therefore an object of
the present invention to provide a cold starting assist circuit
which is substantially free from erroneous signals caused by
battery voltage variations during operation. It is a further object
of the present invention to provide such a system in which the
temperature signal to be used by the cold starting assist circuit
is derived prior to energization of the starting motor and the
starting shift solenoid. It is a further object of the present
invention to provide such a circuit in which the temperature
information is received and stored prior to energization of the
starter motor and starter shift solenoid and which stored
information is later used to control the duration, in time, of the
cold start assist signal. It is a still further object of the
present invention to provide such a cold start assist system which
makes use of successively triggered bistable switches to control
the initiation and termination of an injector valve means control
pulse in response to a time base signal derived from an electrical
storage device which has been charged to a value representative of
engine temperature independently of the starting motor and starting
shift solenoid of the associated engine.
The prior art systems also were arranged to initiate fuel delivery
in a timed relation with energization of the vehicle electrical
system. However, I have determined that best results (minimum
emissions and most reliable rapid starting) occur when the delivery
of the additional cold starting charge occurred in relationship to
the initiation of cranking. It is therefore a still further object
of the present invention to provide a cold starting assist circuit
which initiates delivery of the additional fuel charge in a timed
relationship with engine cranking and which is thereafter
substantially free from cold starting assist signal variations
caused by fluctuations in the supply voltage.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates, in a schematic diagram form, an electronic fuel
control system for a reciprocating piston internal combustion
engine.
FIG. 2 illustrates one form of an electronic control unit for use
in a fuel control system according to FIG. 1.
FIG. 3 shows the preferred embodiment of a circuit according to the
present invention for use in a fuel control system according to
FIG. 1.
FIG. 4 shows a modification which may be applied to the circuit of
FIG. 3 in order to permit that circuit to accept an unstable input
temperature signal.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to FIG. 1, an electronic fuel control system is shown
in schematic form. The system is comprised of a computing means 10,
a manifold pressure sensor 12, a temperature sensor 14, an input
timing means 16 and various other sensors denoted as 18. The
manifold pressure sensor 12 and the assorted other sensors 18 are
mounted on throttle body 20. The output of the computing means 10
is coupled to an electromagnetic injector valve member 22 mounted
in intake manifold 24 and arranged to provide fuel from tank 26 via
pumping means 28 and suitable fuel conduits 30 for delivery to a
combustion cylinder 32 of an internal combustion engine, otherwise
not shown. While the injector valve member 22 is illustrated as
delivering a spray of fuel toward an open intake valve 34, it will
be understood that this representation is merely illustrative and
that other delivery arrangements are known and utilized.
Furthermore, it is well known in the art of electronic fuel control
systems that computing means 10 may control an injector valve means
comprised of one or more injector valve members 22 arranged to be
actuated singly or in groups of varying numbers in a sequential
fashion as well as simultaneously.
The computing means 10 is illustrated here as being energized by
battery 36 through the switching means 38. Switching means 38 is
illustrative of the typical automotive ignition switch having OFF,
RUN, and CRANK positions. The switching means 38 has contacts 40,
42, 44, which correspond to the three positions, respectively, and
a rotatable slider member 46 which is coupled to battery 36 and
which is arranged to contact various of the contacts 40, 42, 44
upon rotation. Contact 40 is electricaly isolated and corresponds
to the OFF position while contacts 42 and 44 are the electrically
active contacts and are coupled to various operating circuitry of
the associated engine and vehicle. Slider 46 is adapted to have
stable positions in contact with contacts 40 and 42 and to be
biased out of contact with contact 44. Slider 46 is further adapted
to have the bias controllably overcome and to thereafter contact
both contacts 42 and 44. Contact 42 is coupled to the ignition
circuitry, not shown, and to the computing means 10. Contact 44 is
coupled to the engine starter system illustrated as coil 48. This
is intended to be illustrative of the starting system of an engine
which may include starter motor, starter shift solenoid, and
various relay and contact mechanisms. Contact 44 is also coupled to
circuit location C and the significance of this will be explained
hereinbelow.
Referring now to FIGS. 1 and 2 and particularly to FIG. 2, an
illustrative electronic fuel control system main computation
circuit 110 is shown. The circuit is shown as being energized by a
voltage supply designated as B+ at the various locations noted. In
the application of this system to an automotive engine fuel control
system, the voltage supply could be the battery 36 and/or battery
charging system conventionally used as the vehicle's electric power
source, and would be transmitted to the circuit 110 through
contacts 42, 46 of switch means 38. For convenience, switch means
38 has been omitted. The man skilled in the art will recognize that
the electrical polarity of the voltage supply could readily be
reversed.
The circuuit 110 receives, along with the voltage supply, various
sensory inputs, in the form of voltage signals in this instance,
indicative of various operating parameters of the associatd engine.
Intake manifold pressure sensor 12 supplies a voltage indicative of
manifold pressure, temperature sensor 14 is operative to vary the
voltage across the parallel resistance associated therewith to
provide a voltage signal indicative of engine temperature and
voltage signals indicative of engine speed are received from input
timing means 16 at circuit input port 116. This signal may be
derived from any source indicative of engine crank angle, but is
preferably from the engine's ignition distributor.
The circuit 110 is operative to provide two consecutive pulses, of
variable duration, through sequential networks to circuit location
118 to thereby control the ON time of transistor 120. The first
pulse is provided via resistor 122 from that portion of circuit 110
having inputs indicative of engine crank angle and intake manifold
pressure. The termination of this pulse initiates a second pulse
which is provided via resistor 124 from that portion of the circuit
110 having an input from the temperature sensor 14. These pulses,
received sequentially at circuit location 118, serve to turn
transistor 120 ON (that is, transistor 120 is triggered into the
conduction state) and a relatively low voltage signal is present at
circuit output port 126. This port may be connected, through
suitable inverters and/or amplifiers to the injector valve means
(shown in FIG. 1) such that the selected injector valve means are
energized whenever the transistor 120 is ON. It is the current
practice to use switching means to control which of the injector
valve means are coupled to circuit location 126 when the system is
used for actuation of less than all injector valve means at any one
time. Because the injector valve means are relatively slow acting,
compared with the speed of electronic devices, the successive
pulses at circuit point 118 will result in the injector valve means
remaining open until after the termination of the second pulse.
The duration of the first pulse is controlled by the monostable
multivibrator network associated with transistors 128 and 130. The
presence of a pulse received via input port 116 will trigger the
multivibrator into its unstable state with transistor 128 in the
conducting state and transistor 130 blocked (or in the
nonconducting state). The period of time during which transistor
128 is conducting will be controlled by the voltage signal from
manifold pressure sensor 12. Conduction of transistor 128 will
cause the collector 128c thereof to assume a relatively low voltage
close to the ground or common voltage. This low voltage will cause
the base 134b of transistor 134 to assume a low voltage below that
required for transistor 134 to be triggered into the conduction
state, thus causing transistor 134 to be turned off. The voltage at
the collector 134c will, therefore, rise toward the B+ value and
will be communicated via resistor 122 to circuit location 118 where
it will trigger transistor 120 into the ON or conduction state thus
imposing a relatively low voltage at circuit port 126. As
hereinbefore stated, the presence of a low voltage signal at
circuit port 126 will cause the selected injector valve means to
open. When the voltage signal from the manifold pressure sensor 12
has decayed to the value necessary for the multivibrator to relax
or return to its stable condition, transistor 130 will be triggered
ON and transistor 128 will be turned OFF. This will, in turn, cause
transistor 134 to turn ON, transistor 120 to turn OFF and thereby
remove the injector control signal from circuit port 126.
During the period of time that transistor 134 has been held in the
nonconducting, or OFF state, the relatively high voltage at
collector 134c has been applied to the base of transistor 136,
triggering the transistor 136 ON. The resistor network 138,
connected to the voltage supply, acts with transistor 136 as a
current source and current flows through the conducting transistor
136 and begins to charge capacitor 140. Simultaneously, transistor
142 has been biased ON and, with the resistor network 144,
constitutes a second current source. Currents from both sources
flow into the base of transistor 146, thereby holding this
transistor ON which results in a low voltage at the collector
146c.
When transistor 128 turns OFF signaling termination of the first
pulse, transistor 134 turns ON and the potential at the collector
134c falls to a low value. The current from the current source
comprised of transistor 136 and resistor network 138 now flows
through the base of transistor 136 and the capacitor 140 ceases to
charge. The capacitor will then have been charged, with the
polarity shown in FIG. 2, to a value representative of the duration
of the first pulse. However, at the end of the first pulse when
transistor 134 is turned ON, the collector-base junction of
transistor 136 is forward biased, thus making the positive side of
capacitor 140 only slightly positive with respect to ground as a
result of being separated from ground by only a few pn junctions.
This will impose a negative voltage on circuit location 148 which
will reverse bias diode 150 and transistor 146 will be turned OFF.
This will initiate a high voltage signal from the collector of
transistor 120 ON and a second injector valve means control pulse
will appear at circuit port 126. The time duration between the
first and second pulses will be sufficiently short so that the
injector valve means will not respond to the brief lack of
signal.
While the diode 150 is reverse biased, the current from the current
source comprised of transistor 142 and resistor network 144 will be
flowing through circuit location 148 and into the capacitor 140 to
charge the capacitor to the point that circuit location 148 will
again be positive. This will then forward bias diode 150 and
transistor 146 will turn back on. This will terminate the second
pulse and the injector valve means will subsequently close.
The duration of the second pulse will be a function of the time
required for circuit location 148 to become sufficiently positive
for diode 150 to be forward biased. This in turn is a function of
the charge on capacitor 140 and the magnitude of the charging
current supplied by the current source comprised of transistor 142
and resistor network 144. The charge on capacitor 140 is, of
course, a function of the duration of the first pulse. However, the
rate of charge (i.e., magnitude of the charging current) is a
function of the base voltage at transistor 142. This value is
controlled by the voltage divider networks 152 and 154 with the
effect of network 154 being variably controlled by the engine
temperature sensor 14.
Referring now to FIGS. 2 and 3, and in particular to FIG. 3, the
cold start auxiliary circuit 200 of the present invention is
illustrated. Circuit 200 is illustrated as being energized by B+
and this energization is derived through contacts 42, 46 of switch
38. For convenience, this connection has not been illustrated.
Circuit 200 also receives inputs at input terminals A and C. These
terminals correspond to the similarly designated terminals A (in
FIG. 2) and C (in FIG. 1). Input terminal A is connected to the
base 202b of input transistor 202 through resistor 204. The emitter
202e of transistor 202 is connected to one side of capacitor 206
while the collector 202c of transistor 202 is connected to B+.
Registor. 208 interconnects the base 202b with the other side of
capacitor 206.
Input terminal C is coupled to the base 210b of control transistor
210 through base resistor 212. The collector of transistor 210 is
coupled to the B+ supply voltage by resistor 214 and is also
coupled to the base 202b of transistor 202 by way of resistor 216
and diode 218. The interconnection of diode 218 and resistor 216 is
coupled to the B+ supply voltage by way of resistor 220 and is also
coupled to the control electrode of bistable switch 222. A
capacitor 224 interconnects the control electrode of bistable
switch 222 with the anode thereof. A resistor 226 connects the
anode of the bistable switch 222 with the B+ supply voltage. The
cathode of bistable switch 222 is connected to ground by way of
zener diode 228, resistor 230, diode 232, and zener diode 234. A
transistor 236 is connected with its base or control electrode 236b
connected to the junction of zener diode 228 and resistor 230 with
its base-emitter junction in parallel with resistor 230.
A second bistable switch 238 is connected in parallel with zener
diode 234 so that the anode of switch 238 is connected to the
cathode of zener diode 234 while the cathode of bistable switch 238
is connected to the anode of zener diode 234. A capacitor discharge
transistor 240 is connected so that its base 240b is connected to
the cathode of zener diode 234 by way of resistor 242 and with its
collector 240c connected to the one side of capacitor 206 while its
emitter 240e is connected through resistor 244 to the other side of
capacitor 206. The control electrode of bistable switch 238 is
connected to the collector 240c by way of resistor 246. The base
240b of transistor 240 is also connected to ground through resistor
248 and diode means 250.
The power output stage of the circuit 220 is comprised of a pair of
transistors 252, 254. The base 252b of transistor 252 is connected
to the collector of transistor 254 and both are connected to the
source of electrical supply by resistor 260. The base 252b is also
connected to the collector of transistor 236 by way of resistor 262
and to the base 202b of transistor 202 by way of diode 264. The
collector of transistor 252 is connected to the base of transistor
254 and to output terminal 266 by way of resistor 268. The emitter
of transistor 254 is connected directly to output terminal 266. The
cathode of zener diode 234 is connected to output terminal 266 by
way of resistor 268.
OPERATION
In the operation of a vehicle having an internal combustion engine
with a fuel control system which incorporates the present
invention, the turning of switch 38 from the OFF position through
the RUN position to the CRANK position will result in the
application of electrical energy through contacts 46, 42 to the
circuit 200 and to the circuit 110 in such a manner that an
electrical signal appears at terminal A prior to the application of
any signal to terminal C. The signal received in terminal A willl
be an electrical voltage which is substantially inversely
proportional to the temperature of the engine at the moment slide
46 contacts contact member 42. The presence of this voltage signal
at terminal A coupled with the application of B+ supply voltage
through switch means 38 to circuit 200 will result in the
conduction of transistor 202 so that capacitor 206 will receive and
store an electrical signal which is equivalent to the signal
received at A reduced by one emitter-base junction voltage drop so
that the signal received and stored by capacitor 206 will be
indicative of the engine temperature. The remaining portion of the
circuit will be substantially inactive due to the fact that
transistor 210 requires receipt of a signal at terminal C before it
can become active and all other active devices within circuit 200
depend upon the conduction of transistor 210 following circuit
energization to become active. By suitably arranging the electrical
values of resistors 204 and 208 and capacitor 206, the circuit can
be adapted to charge capacitor 206 up to the level permitted by the
signal received at terminal A in the amount of time it will take
the normal operator to rotate switch 38 through the RUN to the
CRANK position. Upon entry of the switch into the CRANK position, a
high-voltage signal will appear at terminal C and this signal will
be applied to the base 210b of transistor 210 by way of resistor
212. Receipt of this high-voltage signal will cause transistor 210
to go into conduction. The effect of conduction of transistor 210
will be to cause the voltage appearing between resistors 214 and
216 to drop. This will cause current to flow through resistors 220
and 216 to ground through transistor 210 and thereby causing the
voltage appearing at the gate electrode of bistable switch 222 to
drop. Bistable switch 222 is selected such that it will be
nonconducting following energization of circuit 200. Until such
time as the voltage applied to the gate electrode of bistable
switch 222 drops to a value 1 diode voltage drop below that applied
to the anode the switch 222 will be open. Upon initial energization
of circuit 200, the voltage applied to both the gate and anode
electrodes of device 222 will be substantially B+ value since no
current will be flowing through the various associated electrical
elements. However, application of a reduced voltage to the gate
electrode by way of current flow through resistor 220 and resistor
216 will cause bistable switching device 222 to go into conduction.
Device 222 is further selected to remain conductive for all values
of voltage applied to the gate electrode thereafter so long as a
minimal value of current is flowing through the device. The device
illustrated is known as a programmable unijunction transistor
(PUT). However, an SCR would also be suitable for the purpose and
other devices well known in the industry may also be utilized.
Capacitor 224 operates to prevent an instantaneous voltage change
between the gate electrode and the anode electrode so as to prevent
transient voltage spikes or differentials from inadvertently
triggering the switching device 222 and also prevents turn on by
the "rate effect" following circuit energization. The presence of
the low voltage signal applied to the gate of switching device 222
will cause the voltage appearing at base 202b to drop to a
relatively low value, thereby switching off transistor 202. This is
operative to thereafter isolate memory device 206 from the source
of temperature input signal and hence end variations resulting from
battery voltage variations.
When switching device 222 goes into conduction, a current will flow
through zener diode 228, resistor 230, conventional diode 232, and
zener diode 234. The two zener diodes will operate to provide
selected voltage drops thereacross so as to provide suitable
voltage signals to the transistors whose bases are connected to the
zener diodes. The application of the proper voltage signal to the
base of transistor 236 will cause it to go into conduction so that
current will flow down through resistors 256 and 262. The voltage
drop appearing across resistor 256 will be sufficient to trigger
resistor 252 into conduction and this in turn will trigger
transistor 254 into conduction so that an output current signal
will appear at output terminal 266. Again, by suitable selection of
the resistive values of resistors 260 and 268, the amount of
current appearing at terminal 266 can be calculated to be
sufficient to controllably energize a selected injector valve
means.
The voltage appearing at the cathode of zener diode 234 will be
applied to the base of transistor 240 by way of resistor 242, and
due to the action of resistor 248 and diode means 250, will be of
sufficient value to cause transistor 240 to go into conduction.
Conduction of transistor 240 will operate to drain electrical
energy from capacitor 206 in the normal capacitor discharge
fashion, and the voltage appearing at the collector of transistor
240 will decay. This voltage value is communicated by resistor 246
to the gate electrode of second bistable switching device 238. In
this instance, the device is illustrated as being of the same type
as the previously described bistable switching device 222. It may
also be dissimilar so long as the operational characteristics are
substantially as described with reference to device 222. When the
voltage received by the gate electrode of bistable switch 238 drops
to a value which is one diode drop below the regulated value
established by zener diode 234, bistable switch 238 will go into
conduction and current will flow therethrough. Since the combined
resistance of diode 232 and bistable switch 238, in conduction, can
be readily arranged to be substantially lower than that of zener
diode 228 combined with resistor 230, the amount of current flowing
into the base of transistor 236 can be substantially reduced to a
value less than that required to maintain transistor 236 in
conduction and this device will turn off. The turning off of
transistor 236 will be operative to turn off transistors 252 and
254 in cascade fashion and the current signal appearing in terminal
266 will cease. During the time that transistor 236 is in
conduction the low voltage signal appearing at the collector
thereof will be operative, through diode 264, to maintain the base
202b of transistor 202 at a low value of voltage further insuring
isolation of the storage element 206 and eliminating the
possibility that charging of capacitor 224 could inadvertently
terminate the isolation provided by diode 218. Resistor 268 is
operative to provide a current flow path between the power output
stage and zener diode 234 to provide additional current for that
zener diode to insure that it operates well into its regulation
range without drawing excess current through switch 222.
Referring now to FIG. 4, an input stage for interconnecting the
input terminal A with the memory and storage device 206 is
illustrated. This figure illustrates a second transistor 280 whose
emitter is coupled to the base 202b of transistor 202 and whose
base is connected to resistor 204. An additional resistor 282
connects the emitter of transistor 280 to the B+ supply which is,
for the purposes intended herein, the same B+ supply as is
illustrated and commented on with regard to FIG. 3. The base of
transistor 280 is coupled through resistor 284 to the collector
which is grounded. Terminal A of the FIG. 3 embodiment may be
coupled directly to the temperature responsive element which is
herein illustrated in FIG. 2 as thermistor 14. However, where
convenience has dictated that terminal A be remote from the
temperature sensor element by one or more diode junctions as, for
instance, when a transistor is interposed therebetween, a
transistor 280, as illustrated in FIG. 4, may be coupled into the
input stage. Such additional transistor should be selected to be a
pnp transistor if the intervening transistor is an npn transistor
so that the temperature effects of the respective base-emitter pn
junctions will be mutually self-compensating.
* * * * *