U.S. patent number 3,731,143 [Application Number 05/229,333] was granted by the patent office on 1973-05-01 for transistorized ignition system for gas turbine engines.
This patent grant is currently assigned to The Bendix Corporation. Invention is credited to Kaushik H. Thakore.
United States Patent |
3,731,143 |
Thakore |
May 1, 1973 |
TRANSISTORIZED IGNITION SYSTEM FOR GAS TURBINE ENGINES
Abstract
An ignition system for a gas turbine engine that includes a
2-transistor oscillator which utilizes a transformer and requires
only a spark plug in the secondary of the transformer to ignite
fuel in the turbine.
Inventors: |
Thakore; Kaushik H. (Sidney,
NY) |
Assignee: |
The Bendix Corporation
(Southfield, MI)
|
Family
ID: |
26923202 |
Appl.
No.: |
05/229,333 |
Filed: |
February 25, 1972 |
Current U.S.
Class: |
315/209T;
331/111 |
Current CPC
Class: |
F02P
15/003 (20130101); H03K 3/282 (20130101); F02P
15/10 (20130101); H03K 3/2828 (20130101) |
Current International
Class: |
F02P
15/00 (20060101); H03K 3/282 (20060101); F02P
15/10 (20060101); H03K 3/00 (20060101); H03k
003/30 () |
Field of
Search: |
;315/29T ;331/111 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Kominski; John
Claims
Having described the invention, what is claimed is:
1. In combination with a gas turbine engine of the type having a
spark gap for igniting fuel in the engine and an ignition circuit
for producing an electrical discharge at the spark gap, the
improvement wherein the ignition circuit comprises:
a source of DC energy;
a transformer having a primary and a secondary winding, said
secondary winding connected across said spark gap device;
switching means connected between said DC energy source and the
primary winding of said transformer for connecting and
disconnecting said DC energy source to and from said transformer;
and
transistorized switching oscillator means connected between said
direct current source and the primary winding of said transformer
to periodically interrupt current flow from said source through
said primary winding, said transistorized switching oscillator
including:
a first transistor having collector and emitter terminals connected
in series with the primary winding of said transformer, said
transistor having alternate conductive and nonconductive intervals
to periodically interrupt the current flowing from the primary
winding of said transformer;
a first voltage divider network connected across said first
transistor and the primary winding of said transformer, said first
divider network including first and second series connected diodes
connected in series to first and second series connected
resistors;
energy storage means connected between the junction between said
diodes and the emitter of said first transistor;
diode means connected between the junction between said resistors
and the collector of said first transistor;
a resistor connected between the junction between said diodes and
the collector of said first transistor;
a second voltage divider network connected across said first
transistor and the primary winding of said transformer, said second
voltage divider network including a second transistor having a
fourth resistor connected in series with its collector, a fifth
resistor connected in series with its emitter and having its base
connected to the junction between the diodes and resistors of said
first voltage divider network; and
means for connecting the collector of said second transistor to the
base of said first transistor whereby when said switching means
connects said electrical source to said transformer, said
transistors are periodically rendered conductive, thereby
periodically causing a discharge across said spark gap connected
across the secondary winding of said transformer.
2. The electrical circuit recited in claim 1 wherein said source of
electrical energy is a battery.
3. An electrical circuit for generating a plurality of discharges
across a spark gap which comprises:
a source of DC electrical energy;
a transformer having a primary and a secondary winding, said
secondary winding connected across the spark gap;
switching means connected between said direct current source and
the primary winding of said transformer for connecting and
disconnecting said direct current source to and from said
transformer; and
transistorized switching oscillator means connected between said
direct current source and the primary winding of said transformer
to periodically interrupt current flow from said source through
said primary winding, said transistorized switching oscillator
including:
a first transistor having collector and emitter terminals connected
in series with the primary winding of said transformer, said
transistor having alternate conductive and nonconductive intervals
to periodically interrupt the current flowing from the primary
winding of said transformer;
a first voltage divider network connected across said first
transistor and the primary winding of said transformer, said first
divider network including first and second series connected diodes
connected in series to first and second series connected
resistors;
energy storage means connected between the junction between said
diodes and the emitter of said first transistor;
diode means connected between the junction between said resistors
and the collector of said first transistor;
a resistor connected between the junction between said diodes and
the collector of said transistor;
a second voltage divider network connected across said first
transistor and the primary winding of said transformer, said second
voltage divider network including a second transistor having a
fourth resistor connected in series with its collector, a fifth
resistor connected in series with its emitter and having its base
connected to the junction between the diodes and resistors of said
first voltage divider network; and
means for connecting the collector of said second transistor to the
base of said first transistor whereby when said switching means
connects said electrical source to said transformer, said
transistors are periodically rendered conductive, thereby
periodically causing a discharge across said spark gap connected
across the secondary winding of said transformer.
4. The electrical circuit recited in claim 3 wherein said source of
electrical energy is a battery.
Description
BACKGROUND OF THE INVENTION
This invention relates to an electrical spark generating apparatus
for gas turbine engines and the like.
Much difficulty has been experienced in providing a simple ignition
system of small size, weight and with a minimum of components which
will function satisfactorily to ignite so-called jet and gas
turbine engines under all operating conditions. One example of a
previous ignition system for a turbine engine is disclosed in U.S.
Pat. No. 2,651,005 entitled "Electrical Apparatus" to T. Tognola,
issued Sept. 1, 1953. However, this type of device utilizes a
vibrator to create the oscillations that cause an electrical
discharge across a spark gap to ignite fuel in a turbine engine.
The disadvantages of such a system are (1) the short mechanical
life of a vibrator, (2) the short life of the battery used to drive
the vibrator because the vibrator uses so much power, and (3) the
cost of the entire circuit.
SUMMARY OF THE INVENTION
This invention provides a simple and reliable transistorized
ignition system for an automobile gas turbine engine.
The ignition system is characterized by a 2-transistor oscillator
circuit that receives power from an automobile battery and applies
it to a step-up transformer that has its secondary winding
connected to a spark gap discharge device that sparks at the
frequency rate of the oscillator to ignite fuel in the turbine
engine.
In one embodiment of the invention the ignition system for an
automobile gas turbine engine comprises: a battery for supplying a
DC voltage; a transformer having a primary winding and a secondary
winding, with the secondary winding connected across a spark gap
discharge device for igniting fuel in the engine; and a
transistorized oscillator circuit that is connected to the battery
and the primary winding of the transformer to periodically
interrupt current from the battery to the primary winding whereby
the oscillating current causes periodic electrical discharges
across the spark gap device to ignite the fuel in the turbine
engine. The circuit described provides high energy output pulses at
the spark discharge device while requiring a low input voltage
equal to the automobile battery voltage. The circuit is further
capable of operating under short or open circuit conditions at the
secondary winding of the step-up transformer.
Accordingly, it is an object of this invention to provide a
battery-powered transistorized ignition system for an automobile
gas turbine engine.
It is another object of this invention to provide a transistorized
ignition system for a gas turbine engine that requires only a spark
gap discharge device in the secondary winding circuit of a step-up
transformer.
It is still another object of this invention to provide a
transistorized ignition system for a gas turbine engine that has a
minimum amount of components and preferably no more than two
transistors.
It is still another object of this invention to provide a
relatively inexpensive ignition system for a gas turbine
engine.
A still further object of this invention is to provide a novel
simplified ignition or spark-producing system which is useful for
igniting automobile gas turbine engines.
Another object of this invention is to provide an electrical
apparatus for creating electrical sparks or arcs that are adapted
for igniting combustible materials.
Yet another object of this invention is to provide a transistorized
ignition system for a gas turbine engine that is capable of
operating under open circuit and short circuit conditions in the
secondary circuit of the step-up transformer without damage to the
remaining components of the ignition circuit.
It is yet another object of this invention to provide a constant
power ignition system whereby regardless of variations of input
voltages within a predetermined range of 8-24 volts the output
power remains constant.
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 this specification.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of an ignition system for an automobile
turbine engine.
FIG. 2 is a schematic diagram of a battery-powered transistorized
ignition circuit that accomplishes the objects of this
invention.
DETAILED DESCRIPTION OF THE DRAWINGS
Referring now to FIG. 1, there is shown a block diagram of an
ignition system for an automobile turbine engine which includes an
ignition circuit 1 and a turbine engine 2 that includes a spark gap
40 therein for igniting the fuel fed to the engine.
FIG. 2 is a schematic diagram of a preferred embodiment of the
ignition circuit 1 shown in FIG. 1. The source of electrical energy
for the circuit is a battery 3 which is an ordinary automobile
battery or a DC power supply having a voltage between 8 and 24
volts. The switch 5 is operable to connect and disconnect the
battery to the circuit and is preferably a part of or associated
with the ignition switch of an automobile. The spark gap discharge
device 40 is a spark plug or the like which receives energy
generated by the transistorized circuit and transformer. This
causes a plurality of electrical discharges across spark gap 40
which occur at the same frequency rate as the oscillations in the
primary portion of the transformer 30.
The first portion of the oscillator circuit includes a resistor 11
in series with the emitter of transistor 10 which has its collector
in series with resistor 12 and its base in series with resistor 15
and diode 23. Blocking diode 23 is connected to the collector of
transistor 20. The collector of transistor 10 is connected to the
base of transistor 20 through lead 21 to provide a base current
(drive) to transistor 20 when transistor 10 is conducting.
The resistor 11, the transistor 10 and the diodes 13, 14 are
connected in the configuration shown to form a constant current
regulator. This provides a constant current during increasing input
voltages. The constant current output of this configuration
provides the base current drive through lead 21 for transistor 20.
Hence the base current of transistor 20 is fairly constant over the
entire input voltage range. Since the collector current of
transistor 10 is relatively constant, the "ON" time of the
transistor 20 will decrease as the input voltage increases. Since
the "ON" time of transistor 20 decreases as the input voltage
increases, the input average current will also decrease if the
"OFF" time of the transistor 20 is constant. In this system the
"OFF" time of transistor 20 is a function of the ratio of the
inductance of the secondary winding 32 of the transformer 30 to the
resistance of the secondary winding 32 and voltage drop across the
spark discharge device 40. The "OFF" time (T) may then be expressed
by the following equation:
T.sub.off = L.sub.s /R.sub. s Ln (1 + I.sub.o .sup.. R.sub.s
/V.sub.s)
where:
L.sub.s = Inductance of the secondary winding 32
R.sub.s = Resistance of the secondary winding 32
Ln = Natural log
I.sub.o = Initial current in the secondary winding 32 when the
energy in the transformer 31 begins to discharge through the spark
gap device 40
Since these parameters are fixed for a particular transformer and a
particular spark plug, the turnoff time will be constant. Similarly
the "ON" time may be expressed by the following equation:
T.sub.on = L.sub.p I.sub.p /E
where:
L.sub.p = Inductance of primary
I.sub.p = Peak input current
E = Battery voltage
OPERATION
When switch 5 is closed the battery 3 applies electrical power to
the circuitry causing capacitor 7 to charge through diode 13. The
capacitor eventually attains the voltage equal to the battery
voltage less the forward voltage drop of the diode 13. A current
flows from the base of transistor 10 through resistors 11, 15 and
16 to ground 4. This turns transistor 10 "ON" which permits a
collector current to flow to ground through resistor 12 and through
lead 21 to provide a base current to transistor 20, thereby turning
transistor 20 "ON." When transistor 20 is "ON," current from the
battery 3 flows through the primary winding 31 of transformer 30
and through the collector and emitter of transistor 20. With
transistor 20 "ON" a linearly rising current begins to flow through
the primary winding 31 of the transformer 30. Due to the inductance
of the primary winding this current develops a constant voltage
(approximately equal to the input voltage) across the primary
winding 31 of the transformer 30. This voltage across the primary
31 causes diode 23 to conduct "ON" and causes more current to flow
through resistor 11 and the emitter-base junction of transistor 10.
This causes transistor 20 to saturate quickly. A linearly rising
current flows through the primary winding 31 and transistor 20
until the current reaches a peak value equal to the current through
the base of transistor 20 times the gain of the transistor, at
which time the transistor 20 comes out of saturation. When
transistor 20 comes out of saturation the voltage across the
transistor 20 increases and the voltage across the primary winding
31 will drop toward zero. As the voltage across the transistor 20
increases, it charges capacitor 7 through resistor 22. When the
capacitor 7 charges to a voltage that overcomes the base voltage on
transistor 10, the transistor 10 will stop conducting. This removes
the current flowing in lead 21 to the base of transistor 20,
turning transistor 20 "OFF." Transistor 10 stays "OFF" as long as
the voltage across the transistor 20 is high. During the "OFF" time
the voltage across the transistor 20 is approximately equal to the
voltage across the spark gap divided by the turns ratio of the
transformer 30 plus the voltage of the battery 3. Turning
transistor 20 "OFF" results in a sudden decrease of the current
flowing through the primary winding 31 and collector of transistor
20. During this time the rate of change of current (di/dt) becomes
sharply negative, the high voltage induced in the secondary winding
32 of the transformer 30 also reverses, and the secondary winding
32 becomes a current source. The high voltage produced by the
secondary winding causes an electrical discharge across the spark
gap device 40 and the energy stored in the transformer 30 is
dissipated in the electrical discharge in the spark gap discharge
device 40.
When the energy stored in the transformer 30 is delivered to the
spark discharge device 40, the current in the secondary winding 32
goes to zero. Simultaneously, a current starts to flow through
resistor 11, emitter-base junction of transistor 10, resistor 15
and resistor 16, turning transistor 20 "ON." The capacitor 7
discharges through resistor 22 and collector emitter junction of
transistor 20 until the voltage of the capacitor 7 reaches the
battery voltage 3 minus the voltage drop across diode 13. The
circuit is now in a state to repeat the above-described cycle.
In one satisfactorily operable system the ignition system described
in FIG. 2 had the values or were of the types indicated below:
battery 3 8-24 volts DC capacitor 7 .15 microfarads - 50 volts
diodes 13, 14, 23 1N645 resistor 11 8.5 ohms - 1 watt resistor 12
82 ohms -0.5 watt resistor 15 1.5 K ohms -0.5 watt resistor 16 10 K
ohms - 0.5 watt resistor 22 1.5 K ohms -0.5 watt transistor 20
(NPN) TIP 3055 transistor 10 (PNP) TIP 30A transformer 30 primary
180 turns--No.18 secondary 18,000 turns--No.40 Bendix Part No.
10-372561-1 switch 5 single pole 2-contact
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 inventions 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 semiconductors or solid state control devices
may be substituted for the types illustrated. Accordingly, it is
intended that the illustrative and descriptive materials herein be
used to illustrate the principles of the invention and not to limit
the scope thereof.
* * * * *