U.S. patent number 3,812,378 [Application Number 05/233,196] was granted by the patent office on 1974-05-21 for aircraft starter control system.
This patent grant is currently assigned to The Bendix Corporation. Invention is credited to William E. Coman.
United States Patent |
3,812,378 |
Coman |
May 21, 1974 |
AIRCRAFT STARTER CONTROL SYSTEM
Abstract
A control system for automatically closing a solenoid-operated
air valve that supplies pressurized air to rotate an air turbine
starter motor of an aircraft engine when the starter rotor reaches
a predetermined rotational speed. The control system senses
rotation of the starter rotor and produces a pulse train wherein
each of the pulses generated has a duration which is a function of
the rotational speed of the starter rotor and compares each pulse
duration to a reference pulse which corresponds to a predetermined
rotational speed of the starter rotor. When the duration of the
rotor pulses decreases to a point where they are shorter in
duration than a reference pulse, the supply of pressurized air is
removed from the starter, thereby removing power from the starter
at the predetermined speed.
Inventors: |
Coman; William E. (Newport,
NY) |
Assignee: |
The Bendix Corporation
(Teterboro, NJ)
|
Family
ID: |
22876289 |
Appl.
No.: |
05/233,196 |
Filed: |
March 9, 1972 |
Current U.S.
Class: |
290/38R; 290/37R;
123/179.31 |
Current CPC
Class: |
B64D
41/00 (20130101); F02N 11/0848 (20130101) |
Current International
Class: |
B64D
41/00 (20060101); F02N 11/08 (20060101); F02n
017/00 () |
Field of
Search: |
;290/37,38
;123/199A,179 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Simmons; G. R.
Attorney, Agent or Firm: Cuoco; Anthony F. Hartz; S. H.
Claims
1. A starter control system for automatically de-energizing a
circuit, which supplies power to said starter, when the starter
rotor reaches a predetermined rotational speed, said control system
comprising:
means for generating a first pulse train wherein each of said
pulses generated has a duration D.sub.1 which is a function of the
rotational speed of said starter rotor, said pulses decreasing in
duration as the rotational speed of said rotor increases, said
means for generating a first pulse train comprising:
a permanent magnet generator; and
a bistable circuit that initiates a pulse upon receiving a first
impulse from said permanent magnet generator and terminates said
pulse upon a second impulse from said permanent magnet
generator;
means for generating a second pulse train wherein each of said
pulses generated has a constant time duration D.sub.2 that
corresponds to said predetermined rotational speed of said starter
rotor at which said motor is to be de-energized; and
switching means for de-energizing the circuit that supplies power
to said starter when the duration D.sub.1 of a pulse of said first
pulse train is shorter than the duration D.sub.2 of a pulse of said
second pulse train whereby the starter is automatically
de-energized when said starter rotor reaches said predetermined
rotational speed, said switching means comprising:
a first comparator circuit for receiving the pulses from said first
pulse generator and said second pulse generator, said first
comparator producing a first signal when the duration of a pulse
from said first pulse generator is shorter in duration than a pulse
from said second pulse generator; and
a transistorized switching circuit operable to remove electrical
energy to said starter upon receipt of said first signal from said
first comparator,
2. The starter control system recited in claim 1 wherein said
permanent magnet generator also includes means for rectifying the
pulses generated
3. The starter control system recited in claim 1 wherein said
switching means for de-energizing the circuit that supplies
electrical energy to said starter further comprises:
a second comparator having means for receiving a signal from said
first comparator and means for receiving a signal from said
permanent magnet generator, said second comparator operative to
produce an output signal when it receives said first signal from
said first comparator and a signal from said generator; and wherein
said
transistorized switching circuit conducts to apply electrical
energy to said starter upon receipt of said output signal from said
second comparator and is nonconductive to de-energize the circuit
which supplies electrical energy to said starter in the absence of
a first signal from
4. The starter control system recited in claim 3 wherein said
second comparator comprises:
a first transistor having its base in electrical circuit
relationship with the output of said first comparator;
a zener diode in circuit relationship with one other electrode of
said first transistor and circuit relationship with the rectifying
means of said permanent magnet generator; and
a silicon-controlled rectifier having its gate in electrical
circuit relationship with said zener diode and one of its other
electrodes in circuit relationship with the remaining electrode of
said first transistor, said SCR being conductive when said first
transistor is nonconductive and said zener diode is conductive,
whereby said second comparator produces an output signal to turn
off the transistorized switch
5. In combination with an electric starting system for cranking an
engine of the type having a source of electrical power, a starter
motor, a solenoid and a mechanical switch for connecting the
electrical power in circuit relationship with the solenoid, which,
when energized, couples the starter motor to the engine and
connects the electrical power to the starter motor to crank the
engine, wherein the improvement comprises:
switching means for automatically de-energizing said solenoid when
said starter rotor has reached a predetermined rotational speed,
said means for de-energizing said solenoid further including:
means for generating a first pulse train wherein each of said
pulses generated has a duration D.sub.1 which is a function of the
rotational speed of said starter rotor;
means for generating a second pulse train wherein each of said
pulses generated has a constant time duration D.sub.2 that
corresponds to said predetermined speed of said starter rotor;
and
means for de-energizing said solenoid when the duration D.sub.1 of
a pulse of said first pulse train is shorter than the duration
D.sub.2 of a pulse of said second pulse train whereby said starter
motor is automatically decoupled from said engine when said starter
rotor reaches said
6. The control system as recited in claim 5 wherein said means for
de-energizing said solenoid includes a transistor switch, in series
electrical relationship with said solenoid, that is conducting ON
when D.sub.1 is greater than D.sub.2 and is nonconducting OFF when
D.sub.1 is
7. The control system as recited in claim 5 wherein said means for
generating said first pulse train includes a permanent magnet
generator
8. The control system as recited in claim 6 wherein said means for
generating said first pulse train includes a permanent magnet
generator
9. The control system as recited in claim 6 including a full wave
rectifier bridge having its output terminals connected to the
collector and emitter electrodes of said transistor switch and its
input terminals connected in series with said source of electrical
power so that said transistor switch is operable regardless of the
direction that current flows through said
10. A control system for automatically closing a solenoid operated
air valve that supplies pressurized air to rotate an air turbine
starter motor of an engine, when the starter rotor reaches a
predetermined rotational speed, said control system comprising:
means for sensing the rotational speed of said starter rotor and
generating a first pulse train wherein each of said pulses
generated has a duration D.sub.1 which is a function of the
rotational speed of said starter rotor;
means for generating a second pulse train wherein each of said
pulses generated has a constant time duration D.sub.2 that
corresponds to said predetermined rotational speed of said starter
rotor; and
means for closing the solenoid operated air valve when the duration
D.sub.1 of a pulse of said first pulse train is shorter than the
duration D.sub.2 of a pulse of said second pulse train whereby said
supply of presusrized air is removed from said starter when said
starter rotor reaches said
11. The control system as recited in claim 10 including a d-c power
supply for supplying power to said solenoid and wherein said means
for closing the solenoid operated air valve includes a transistor
switch and a full wave rectifier bridge in circuit relationship
with said power supply to control the power applied to said
solenoid, said transistor switch having its emitter and collector
terminals connected to the output of said bridge, said rectifier
bridge having two input leads connectable in series to said d-c
power supply whereby said transistor switch is operable to permit
current to flow into said solenoid from said d-c supply when either
lead of said bridge is connected to the positive side of said d-c
power supply and the remaining lead of said bridge is connected to
said negative
12. A control system as recited in claim 10 wherein the means
for
13. The control system as recited in claim 10 wherein said means
for generating a first pulse train includes a bistable circuit that
initiates a pulse upon receiving a first impulse from said
permanent magnet generator and terminates said pulse upon a second
impulse from said
14. The control system as recited in claim 12 wherein said means
for generating a first pulse train includes a bistable circuit that
initiates a pulse upon receiving a first impulse from said
permanent magnet generator and terminates said pulse upon receiving
a second impulse from
15. The control system as recited in claim 13 wherein said means
for closing the solenoid operated air valve includes a comparator
that compares the duration of a pulse from said bistable to the
duration of a pulse from said second pulse train generator and
provides an output signal when the duration of the pulse from said
bistable is shorter than the
16. The control system as recited in claim 14 wherein said means
for closing the solenoid operated air valve includes a comparator
that compares the duration of a pulse from said bistable to the
duration of a pulse from said second pulse train generator and
provides an output signal when the duration of the pulse from said
bistable is shorter than the
17. The control system as recited in claim 10 wherein said means
for closing the solenoid operated air valve includes a
transistorized switch in series electrical relationship with said
solenoid and the power supplied to the solenoid so that when said
transistorized switch is open, said solenoid is de-energized
whereby said valve is closed thereby removing the supply of
pressurized air that rotates said starter motor.
18. The control system as recited in claim 11 wherein said means
for closing the solenoid operated air valve includes a
transistorized switch in series electrical relationship with said
solenoid and the power supplied to the solenoid so that when said
transistorized switch is open, said solenoid is de-energized
whereby said valve is closed thereby removing the supply of
pressurized air that rotates said starter motor.
19. The control system as recited in claim 12 wherein said means
for closing the solenoid operated air valve includes a
transistorized switch in series electrical relationship with said
solenoid and the power supplied to the solenoid so that when said
transistorized switch is open, said solenoid is de-energized
whereby said valve is closed thereby removing the supply of
pressurized air that rotates said starter motor.
20. The control system as recited in claim 14 wherein said means
for closing the solenoid operated air valve includes a
transistorized switch in series electrical relationship with said
solenoid and the power supplied to the solenoid so that when said
transistorized switch is open, said solenoid is de-energized
whereby said valve is closed thereby removing the supply of
pressurized air that rotates said starter motor.
21. The control system as recited in claim 15 wherein said means
for closing the solenoid operated air valve includes a
transistorized switch in series electrical relationship with said
solenoid and the power supplied to the solenoid so that when said
transistorized switch is open, said solenoid is de-energized
whereby said valve is closed thereby removing the supply of
pressurized air that rotates said starter motor.
22. A control system for de-energizing a circuit, said control
system comprising:
a first circuit which includes:
a first source of electrical energy;
a reactive circuit element in series circuit relationship with said
first source of electrical energy;
a first switch connected in series circuit relationship with said
source of electrical energy and said reactive circuit element, said
switch operable upon closing to apply electrical energy to said
reactive circuit element; and
a transistor switch in series circuit relationship with said
reactive circuit element, said transistor switch operable upon
closing of said first switch to permit electrical energy to be
supplied to said reactive circuit element, said transistor switch
including a passive circuit element in circuit relationship with
said transistor and having a voltage applied thereto from said
first source upon closing of said first switch which forward biases
said transistor so that said transistor is conductive (ON);
a second circuit which includes:
an electromagnetic source of electrical energy separate from said
first source of electrical energy for producing pulses which vary
in duration as a function of a determinable parameter of said
electromagnetic device, and including a permanent magnet generator
having a rotor and stator element, said generator generating
electrical energy levels which are proportional to the rotational
speed of the generator;
the reactive circuit element being the winding of an
electromechanical device that controls power to a starter motor and
said permanent magnet generator being mechanically linked to said
starter motor; and
a second solid state switching circuit in circuit relationship with
said passive circuit element of said first circuit and said
electromagnetic source of electrical energy, said second switch
operable to apply a reverse voltage across said passive circuit
element when said electromagnetic source of electrical energy
produces a pulse having a predetermined duration whereby said first
transistor switch is reverse biased rendering said first transistor
switch nonconductive, thereby
23. A control system as recited in claim 22 wherein the reactive
circuit element is the winding of an electromechanical device and
wherein said electromagnetic source of electrical energy is
mechanically linked to said
24. A starter control system for automatically de-energizing a
circuit, which supplies power to said starter, when the starter
rotor reaches a predetermined rotational speed, said control system
comprising:
means for generating a first pulse train wherein each of said
pulses generates has a duration D.sub.1 which is a function of the
rotational speed of said starter rotor, said pulses decreasing in
duration as the rotational speed of said rotor increases, said
means for generating a first pulse train including: a permanent
magnet generator;
means for generating a second pulse train wherein each of said
pulses generated has a constant time duration D.sub.2 that
corresponds to said predetermined rotational speed of said starter
rotor at which said motor is to be de-energized; and
switching means for de-energizing the circuit that supplies power
to said starter when the duration D.sub.1 of a pulse of said first
pulse train is shorter than the duration D.sub.2 of a pulse of said
second pulse train whereby the starter is automatically
de-energized when said starter rotor reaches said predetermined
rotational speed, said switching means for de-energizing the
circuit that supplies electrical energy to said starter
comprising:
a transistorized switching circuit that includes at least one
transistor, said transistor allowing electrical energy to be
supplied to said starter in the conducting state and preventing
electrical energy from being supplied to said starter in the
nonconducting state; and
a comparator means for receiving pulses from said first pulse
generator, pulses from said second pulse generator, and a voltage
signal from said permanent magnet generator, said comparator means
operable to produce an output signal upon receipt of a voltage
signal of predetermined magnitude from said generator and a pulse
from said first pulse generating means having a duration greater
than a pulse from said second pulse generating means, said output
signal coupled to said transistor switch to render said transistor
conductive, whereby electrical energy is supplied to said starter
when said transistor conducts and when said signal from said
comparator means is removed, said transistor switch is
nonconductive and said starter is de-energized.
Description
BACKGROUND OF THE INVENTION
The present invention relates to an aircraft starter control system
of the type having a control circuit to de-energize the aircraft
starter motor when the starter rotor has reached a predetermined
speed.
Basically, the control system for an aircraft starter includes a
device for sensing the rotational speed of the starter rotor and a
control circuit that removes power to the starter solenoid once the
aircraft engine has started, thereby preventing the starter rotor
from being rotated at excessive speeds that would adversely affect
the starter motor.
Present starter control systems sense the rotation of the starter
rotor by inducing an electric potential in a winding of a magnetic
pickup and passing the signal produced to a filter circuit. The
filter circuit blocks all signals below a predetermined frequency.
The output of the filter circuit is connected to a transistor
switch which is turned OFF when the frequency of the input signal
exceeds a predetermined value. The transistor switch is connected
in series to an electrical power source and when the transistor
switch is OFF, power to the starter is removed. The disadvantage of
this type of circuit is the filter network associated therewith,
which is both bulky and expensive. Further, the response time of
the control circuit is limited by the fact that it is responsive to
a frequency, which is a plurality of pulses, rather than a pulse.
An example of the aforementioned prior art control system can be
found in U.S. Pat. No. 3,440,433 to W. E. Coman, entitled "Aircraft
Starter Control" issued Apr. 22, 1969.
SUMMARY OF THE INVENTION
This invention provides an aircraft starter control system that is
smaller in size, less expensive and has a faster response time than
prior art control systems.
The invention is an airraft starter control system characterized by
a control circuit which is responsive to each revolution of the
starter rotor and de-energizes the starter circuit when the starter
rotor reaches a predetermined rate.
In one embodiment of the invention the control circuit comprises: a
permanent magnet generator for generating a first pulse train
wherein each of the pulses generated has a duration which is a
function of the rotational speed of the starter rotor; a second
pulse generator for generating a second pulse train wherein each of
the pulses generated has a constant time duration that corresponds
to a predetermined rotational speed of the starter rotor, at which
the starter is to be de-energized; a comparator circuit for
receiving the pulses from the first and second pulse generator and
producing a first output signal when the duration of a pulse from
the first pulse generator is shorter in duration than a pulse from
the second pulse generator; and a transistorized switching circuit
in combination with the power supplied to the starter, the
transistorized circuit including a transistor switch which upon
receipt of said first signal from said comparator becomes
nonconductive to de-energize the circuit which supplies power to
the starter.
Accordingly, it is an object of this invention to provide an
improved control circuit for a control system for an aircraft
starter motor.
It is another object of this invention to provide an automatic
control circuit that de-energizes a starter motor of an aircraft
engine from the engine when it reaches a predetermined rotational
speed.
It is another object of this invention to provide a control circuit
that includes a transistor switch that is polarity insensitive
whereby the transistor switch operates regardless of how the
transistor is connected to a power supply.
It is still another object of this invention to provide an improved
aircraft starter control system that is more compact than prior
control systems, and less expensive than prior control systems.
It is a further object of this invention to provide an aircraft
starter control system which does not require bulky and expensive
high pass signal filters.
It is still a further object of this invention to provide an
aircraft starter control system that utilizes integrated circuits
and is vibration resistant.
Yet another object of this invention is to provide an aircraft
starter control circuit that has a faster response time and better
accuracy than previous aircraft control systems.
The above and other objects and features of the invention will
become apparent from the following detailed description taken in
conjunction with the accompanying drawings and claims which form a
part of the specification.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of an aircraft starter control
system.
FIG. 2 is a block diagram of a control circuit for an aircraft
starter control system that utilizes the principles of this
invention.
FIG. 3 is an alternate block diagram of a control circuit for an
aircraft starter control system that utilizes the principles of
this invention.
FIG. 4 is a schematic diagram of a control circuit shown in FIG.
3.
DETAILED DESCRIPTION OF THE DRAWINGS
Referring now to the drawings, FIG. 1 illustrates an aircraft
starter control system. In this system the control circuit senses
the rotational speed of the starter rotor and transmits a signal to
deenergize the power to the starter motor and/or starter solenoid
when the rotational speed of the starter rotor has reached a
predetermined speed. For purposes of this invention a signal may be
either the presence of a current (voltage) or the absence of a
current (voltage), depending on how one wishes to operate the
circuit.
FIG. 2 illustrates how the control circuit reacts to pulses
generated by rotation of the starter rotor. In this embodiment a
permanent magnet generator 1 supplies impulses to a bistable 2 and
an AND gate 9. The bistable device 2 initiates a pulse upon receipt
of a first impulse from the permanent magnet generator 1 and
terminates the pulse upon a second impulse from the permanent
magnet generator 1. The output of the bistable or flipflop device 2
is applied to a comparator 5 and to a pulse generator 3. The pulse
generator 3 produces a pulse of fixed duration upon receipt of a
pulse from the bistable 2. The duration of the pulse from the pulse
generator 3 may be adjusted to correspond to any one of a plurality
of speeds at which de-energization of the starter is desired. The
comparator 5 receives pulses from the pulse generator 3 and from
the bistable 2. The comparator then compares the two signals and
provides an output signal to the AND gate 9 when the duration of a
pulse from the bistable device 2 is greater than the duration of a
pulse from the pulse generator 3. The AND gate 9, upon receipt of a
signal D.sub.3 from the permanent magnet generator 1 and the
absence of an output current from the comparator 5 (D.sub.1 greater
than D.sub.2), supplies a signal to power switch 6 to permit power
to be supplied to the starter 8 from a power supply 7. As the speed
of the starter rotor increases, the pulse duration from the
bistable 2 will decrease. When there is a signal D.sub.3 from the
permanent magnet generator 1 and the duration of a pulse from the
pulse D.sub.2 generator 3 is greater than the duration of a pulse
D.sub.1 from the bistable 2, the comparator 5 will not supply a
signal to the AND gate 9 and no power will be supplied to the
starter.
Noted on the block diagram shown in FIG. 2 are the symbols D.sub.1
and D.sub.2 which correspond to the duration of a pulse from the
bistable device 2 and pulse generator 3 respectively. D.sub.3
corresponds to a signal (voltage) supplied from the permanent
magnet generator circuit 1. From FIG. 2 and the notations it can be
seen that power will be supplied to the starter 8 when the duration
of a pulse from the bistable 2 is greater than a pulse from the
pulse generator 3 and a signal D.sub.3 is present at the AND gate
9. This condition is indicated by the solid line which indicates
that the power switch 6 is ON when D.sub.1 is greater than D.sub.2
and signal D.sub.3 is present at the AND gate 9. Conversely, the
starter 8 will be de-energized when the duration of a pulse D.sub.2
from the pulse generator 3 is greater than the duration of a pulse
D.sub.1 from the bistable 2. This condition is indicated by the
dotted line which indicates that the power switch is OFF when
D.sub.2 is greater than D.sub.1.
FIG. 3 is also a block diagram of a control system that
incorporates the principles of this invention. The symbols used on
the lines connecting the blocks correspond to the following
information: D.sub.1 is the duration of a pulse from the bistable
2; D.sub.2 is the duration of a pulse from the pulse generator 3;
D.sub.3 is the signal from the permanent magnet generator circuit
which is preferably a voltage signal rather than a pulse signal.
The numbers associated with the lines connecting blocks can be used
together with the circuit shown in FIG. 4 to identify the signal
connecting leads between each circuit.
When the starter rotor is rotating, the permanent magnet generator
1 supplies pulses to the bistable device 2 which in turn supplies
pulses to the comparator 4 and pulses to trigger pulse generator 3.
Comparator 4 compares the duration of the pulses from the pulse
generator 3 to the duration of a pulse from the bistable 2 and
produces an output signal when the duration of a pulse D.sub.1 from
the bistable has a duration greater than a pulse D.sub.2 from the
pulse generator 3. Comparator 5, upon receiving a signal from the
comparator 4 and a signal from the permanent magnet generator 1,
supplies an output signal to transistor switch 6, allowing
transistor switch 6 to remain ON, thereby supplying power to the
starter and starter solenoid. The absence of a signal from
comparator 5, indicated by dotted line 501, causes transistor
switch 6 to turn OFF, thereby de-energizing the starter and/or
starter solenoid. The conditions necessary to de-energize the
starter are indicated at the output of comparator 5, that is, that
the duration of a pulse D.sub.2 from the pulse generator 3 be
greater in duration than a pulse D.sub.1 from the bistable 2 and
there must be a signal from permanent magnet generator 1.
FIG. 4 is a schematic diagram of the block diagram shown in FIG. 3.
For clarity, portions of the circuitry have been outlined by dotted
lines and identified as corresponding to the circuitry associated
with the particular block shown in FIG. 3.
The permanent magnet generator circuit 1 includes a permanent
magnet 101 which may be attached to the rotor shaft of the starter
(not shown) to induce a voltage pulse in winding 102. Pulses from
winding 102 are applied to a full wave rectifier bridge having
diodes 11. The output of the bridge is attached to a circuit that
includes capacitors 12 and 14, zener diode 13 and resistor 15 for
smoothing out and regulating the rectified current from the bridge
10. The rectified current produced by the bridge 10 is supplied to
zener diode 52 of comparator 5 through lead 101. The output of the
bridge 10 that is smoothed by capacitors 12 and 14 is also supplied
to a bistable device through resistors 19, 21 and lead 100.
Transistor 17, in circuit relationship with capacitor 18 and
resistor 16, is connected to one input of the bridge 10 and the
negative output of the bridge 10. The transistor 17 shorts out the
signal that flows through resistor 19 on every half-cycle so that
only one pulse is supplied to the bistable 2 for every revolution
of the starter rotor. Therefore, in this arrangement the bistable
will produce one pulse for every two revolutions of the starter
rotor.
The bistable device 2 shown within the dotted lines is a solid
state integrated circuit 22 that is capable of operating over a
temperature range of -65.degree.F to 250.degree.F. The bistable 22
receives its input power from lead 23 and its input signals through
lead 100 from the permanent magnet generator circuit 1. The
bistable 2 is a flipflop circuit that initiates a pulse upon
receiving a first impulse from the permanent magnet generator
circuit 1 and terminates such pulse on a second impulse from the
permanent magnet generator 1. The bistable or flipflop device 22
supplies a trigger pulse to pulse generating circuit 3 through lead
200 and a complementary pulse to comparator 4 through lead 201.
The pulse generator circuit 3 includes resistors 31 and 32 and
capacitor 33 which determine the duration of the pulses generated
by the multivibrator circuit 30 which is an integrated circuit
capable of operating over a temperature range of -65.degree. F to
250.degree.F. The resistors 31, 32 or capacitor 33 may be manually
adjustable so that the duration of the pulses generated by the
multivibrator circuit 30 can be adjusted to correspond to any fixed
duration which further corresponds to a particular rotor speed.
Each time the multivibrator circuit 30 receives a pulse through
lead 200 from the flipflop device 22, it produces an output pulse
having a fixed duration determined by resistors 31 and 32 and
capacitor 33. These pulses of the multivibrators circuit having
constant duration are supplied through lead 300 to comparator
circuit 4.
The comparator 4 includes an integrated circuit 40 that is capable
of operating over a temperature range of -65.degree.F to
250.degree.F. The integrated circuit 40 produces an output signal
through lead 400 and diode 42 to comparator circuit 5 upon receipt
of a pulse from the flipflop device 22 that is greater in duration
than a pulse supplied to the comparator 40 from the multivibrator
30. In the event that the duration of a pulse from the
multivibrator 30 is greater than the duration of a pulse from the
flipflop circuit 22, the comparator 40 does not provide an output
signal through lead 400 and diode 42.
The second comparator 5 or AND gate includes a transistor switch 54
that is conductive upon receipt of a signal from the first
comparator 4 through lead 400 and diode 42; a zener diode 52 which
does not allow current to flow through the collector-emitter
terminals of transistor 54 until there is a sufficient drive
current available at the output of the bridge 10 in the permanent
magnet generator circuit; and a silicon-controlled rectifier 57
which has a signal supplied to the gate 59 thereof when transistor
54 is OFF, thereby allowing a current to flow through lead 501,
diode 68, silicon-controlled rectifier 57 and lead 500 which is the
return to the negative side of the rectifier bridge 10. With
current flowing through diode 68 a positive potential is developed
between points B and A, with B being the positive terminal.
The function of zener diode 52 is to inhibit the action of
silicon-controlled rectifier 57 by preventing current flow to gate
59 when the rotational speed of rotor 101 is very low. Under this
condition the voltage available at lead 23 is insufficient to
properly operate the logic elements and can cause a false shutdown
signal from first comparator 4.
From the description of the second comparator 5 it is evident that
the second comparator operates as a signal inverter. In other
words, when a signal is supplied to the second comparator 5 from
the first comparator 4, no potential is developed across diode 68.
However, when the input signal from the first comparator 4 through
lead 400 and diode 42 is removed, the second comparator 5 produces
an output signal in the form of a voltage developed across diode
68.
The transistor switch 6 is a transistorized switching network that
includes a main switching transistor 66; signal amplifying
transistors 62 and 64; zener diode 67; and a full wave rectifier
bridge 60 that includes rectifiers 61 and 72. The input leads 68
and 69 to the bridge 60 also function as the output leads of the
transistor switch 6.
The transistor switch does not require a rectifier bridge 60.
However, the bridge 60 makes the transistor switch 66 polarity
insensitive. In other words, regardless of the polarity of the
signal applied to leads 68 and 69, transistor 66 will function.
When transistor 66 is ON there is a current path from lead 68,
diode 61, transistor 66, diode 72 and lead 69, and coil 81 is
energized by battery 82. When transistor 66 is OFF, current cannot
flow between leads 68 and 69 and coil 81 is de-energized.
The transistors 62, 64 and 66 are arranged in combination with a
bridge rectifier 60 so that when the current flows through the
bridge from battery 82, transistor 66 is forward biased ON and
transistors 62 and 64 are also conducting ON. Transistors 62, 64
and 66 remain ON when transistor 54 is ON which allows current to
bypass diode 68 through lead 500 where it returns to the negative
terminal of bridge rectifier 10. However, when transistor 54 is
OFF, silicon-controlled rectifier 57 is gated ON generating a
voltage across diode 68 that reverse biases transistor 62 which in
turn turns OFF transistors 64 and 66.
The starter circuit 8 includes a source of d-c power, such as a
battery 82, in series with a starter motor and/or solenoid winding
81 which is in series with transistor 66 of the transistor switch
6. Therefore, when transistor 66 is conducting (ON), power is
supplied to the coil 81 and when transistor switch 66 is
nonconducting (OFF), power is removed from winding 81.
OPERATION
In operation the aircraft starter control system operates as
follows: certain aircraft engines have air turbine starter motors
which are driven by a supply of pressurized air when a
solenoid-operated control valve is opened. Consider now FIG. 4
which shows a winding 81 which corresponds to the solenoid valve.
To supply pressurized air to a turbine starter motor, electrical
energy, applied to the solenoid valve 81, operates to open the
valve and supply pressurized air to rotate a turbine starter motor
to start the engine (not shown). Current flowing through the coil
81 also flows through lead 68, diode 61, transistor 66, diode 72
and lead 69 to ground. Simultaneously, as the starter rotor begins
to rotate, the permanent magnet 101 rotating past the coil 102
induces electrical impulses in the coil 102 that are rectified by
bridge rectifier 10. During the initial stages of starting (low
speeds) the duration of the pulses D.sub.1 generated by the
flipflop 22 is longer than the duration of the pulses D.sub.2
generated by the monostable multivibrator circuit 30 and therefore
comparator 40 produces an output signal to keep transistor 54 ON.
With transistor 54 ON, current from the output of the bridge 10
flows through lead 101, zener diode 52, the emitter-collector
electrodes of transistor 54, and back through lead 500 to the
negative end of the bridge rectifier 10. With transistor 54 ON, no
current flows through leads 501 and 502 and therefore no current
flows through the silicon-controlled rectifier 57 or diode 68.
Since ther is no current flow through diode 68 in the forward
direction, transistors 62, 64 and 66 of the transistorized switch
circuit are forward biased ON. As the rotational speed of the rotor
increases, the duration of the pulses D.sub.1 generated by the
flipflop 22 decreases until D.sub.1 is less than D.sub.2 and the
solenoid air valve 81 is de-energized. More specifically, the
de-energization of the solenoid 81 is accomplished as follows: as
the speed of the starter rotor increases, the pulse rate of the
permanent magnet alternator 1 increases, thereby shortening the
duration of the pulses produced by the flipflop 22. When the
duration of a pulse D.sub.1 becomes shorter than the duration
D.sub.2 of a pulse from the multivibrator circuit 30, comparator 40
ceases to produce an output signal to transistor 54. When the
comparator 40 ceases to provide an output signal to the transistor
54, transistor 54 turns OFF. This action allows current D.sub.3 to
flow through lead 502, diode 55 and the gate electrode 59 of the
silicon-controlled rectifier 57, turning the silicon-controlled
rectifier ON. Once the silicon-controlled rectifier 57 is ON, a
current flows from a bridge rectifier 10 through lead 101 out
through lead 501, up through diode 68, through silicon-controlled
rectifier 57, and then through the lead 500 to the negative end of
the bridge 10. The current flowing through diode 68 acts to reverse
bias transistor 62, turning transistor 62, 64 and 66 OFF. With
transistor 66 OFF, current can no longer flow through winding 81 of
the solenoid. With the winding of the solenoid de-energized, the
source of pressurized air is isolated from the starter and the
starter rotor which no longer has power applied to it to cause it
to rotate. Silicon-controlled rectifier 57 remains latched ON as
long as current flows from generator coil 102, preventing
re-energization of the circuit until the starter has slowed to a
relatively low speed.
The following table summarizes the conditions which permit or
prevent a current to flow through winding 81:
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Coil 81 Energized Coil 81 De-energized Starter ON Starter OFF
__________________________________________________________________________
1. Pulse duration D.sub.1 greater than pulse duration D.sub.2 Pulse
duration D.sub.2 greater than pulse duration D.sub.1 and current
signal D.sub.3 2. Output signal from comparator 4 No output signal
from comparator 4 3. Transistor 54 ON Transistor 54 OFF 4. Zener
diode 52 ON Zener diode 52 ON 5. SCR 57 OFF SCR 57 ON 6. Diode 68
reverse biased OFF Diode 68 forward biased ON 7. Transistors 62,
64, 66 ON Transistors 62, 64, 66 OFF
__________________________________________________________________________
in one satisfactorily operable system, the circuit shown in FIG. 4
included the following circuit elements which had the values or
were of the types indicated as follows:
Rectifier bridge 10 1 ampere, 50 volt Diode 11 1 ampere, 50 volt
Capacitor 12 47 MFD, 35 volt Zener diode 13 1N5338A Capacitor 14
220 MFD, 20 volt Resistor 15 100 ohms, 5 watt Resistor 16 5600
ohms, 1/4 watt Transistor 17 2N1613 Capacitor 18 0.01 MFD, 50 volt
Resistor 19 220 ohms, 1/4 watt Resistor 21 560 ohms, 1/4 watt Pulse
generator 30 54121 Resistor 31 18000 ohms, 1/4 watt, 1% Resistor 32
24 ohms to 2000 ohms (select for precise speed setting, 1/4 watt
Capacitor 33 0.10 MFD, 50 volt Flipflop 22 5473 (1/2) (J-K)
Comparator 40 5473 (other 1/2) Diode 42 1N4001 Zener diode 52
1N4741A Resistor 53 470 ohms, 1/4 watt Transistor 54 1N1613 Diode
55 1N4001 Resistor 56 1000 ohms, 1/4 watt Silicon-controlled
rectifier 57 2N4212 Resistor 58 1000 ohms, 1/4 watt Rectifier
bridge 60 25 ampere, 100 volt Rectifier 61 25 ampere, 100 volt
Transistor 62 2N1613 Resistor 63 15,000 ohms, 1/4 watt Transistor
64 2N3251A Resistor 65 24 ohm, 1/4 watt Transistor 66 2N3716 Zener
diode 67 1N4754 Solenoid valve 81 Bendix Model 38E45 Storage
battery 82 28 volt d-c
While a preferred embodiment of the invention has been disclosed,
it will be apparent to those skilled in the art that changes may be
made to the invention as set forth in the appended claims, and in
some cases certain features of the invention may be used to
advantage without corresponding use of other features. For example,
different types of semi-conductors or solid state control devices
may be substituted for the types illustrated. Further, a signal
from a comparator may be considered as being either the presence or
the absence of a voltage (current) which has an effect on another
stage of the circuit. Accordingly, it is intended that the
illustrative and descriptive materials herein be used to illustrate
the principles and not to limit the scope thereof.
* * * * *