Patent Description:
Aircraft are frequently powered by turbine engines. Turbine engines (also referred to as gas turbines) are a type of internal combustion engine that have an upstream rotating compressor coupled with a downstream turbine and a combustion chamber in-between where fuel is injected and combusted to create pressurized exhaust having a high velocity. As air enters the turbine engine, fuel is added and ignited using a suitable ignition system, such as a capacitive discharge ignition (CDI) system. The capacitive discharge system includes an exciter that generates a spark discharge at an igniter in the combustion chamber to ignite the fuel. Typically, the exciter portion of the capacitive discharge ignition system creates this spark discharge using a spark-gap gas-discharge tube (SGT). The SGT includes two electrodes that are spaced apart by an air or spark gap in the presence of an inert gas. The SGT is electrically connected between an igniter and a storage capacitor receiving a charge from a power source. When the voltage of the storage capacitor exceeds the trigger voltage of the SGT, the SGT starts to conduct thus delivering the stored energy from the capacitor ultimately causing the igniter to spark.

In a typical SGT construction, both of the electrodes of the SGT are enclosed and sealed from the atmosphere within a glass housing, which also includes a gas that facilitates a stable voltage level to release energy thereby creating a spark at the igniter. Many SGTs use a radioactive inert gas to maintain ionization within the SGT. The use of a glass SGT with radioactive gas fill may present risks due to glass component breakage and gas leakage, thereby affecting the CDI system operation.

<CIT> describes an interesting apparatus for providing ignition to a turbine engine.

Accordingly, it would be desirable to provide an alternative component that provides the functionality of a SGT without the associated risks of breakage and leakage. Further, it would be desirable to provide an alternative component that provides consistent sparking voltages supplied to the igniter.

There is provided a solid state spark device according to claim <NUM>.

For at least some embodiments, this construction allows the solid state spark device to be placed in circuit in an exciter for an ignition system of a turbine engine so as to supply sparking power from a storage capacitor or other capacitive storage element to an igniter. The device may be placed in series between the storage capacitor and igniter such that it can be implemented as a two terminal device that operates from charging current received from the storage capacitor as the capacitor charges up to a desired sparking voltage for the igniter.

In accordance with various different embodiments, the solid state spark device may include any one or more of the following features in any technically-feasible combination.

In one aspect of the invention there is provided a solid state spark device that operates as a two terminal spark gap in a CDI exciter of an aircraft ignition system connectable in series between an igniter and a capacitive storage element that charges up to a sparking voltage sufficient to create a spark on the igniter. The device includes a triggering transformer, a triggering circuit, and a control circuit. The triggering circuit is electrically connected to a first coil of the transformer and includes circuit elements including a capacitor charged via one of the terminals of the solid state spark device, wherein the circuit element supply current to the first coil by discharging the capacitor via the first coil when the voltage on the capacitor reaches a predefined triggering voltage. This current through the first coil of the triggering transformer induces an output in a second coil of the transformer. The control circuit is electrically connected to the second coil and includes a first switch controlled by the output from the second coil to discharge the capacitive storage element to the igniter by connecting the two terminals of the solid state spark device. The switch, when activated by the triggering circuit, discharges energy from the exciter into an igniter of the aircraft ignition system.

Preferred exemplary embodiments of the invention will hereinafter be described in conjunction with the appended drawings, wherein like designations denote like elements, and wherein:.

<FIG> depicts a generalized block diagram showing an exemplary implementation of a turbine engine ignition system <NUM> that includes a solid state device that provides sparking energy for an igniter without the need for spark-gap gas-discharge tube (SGT). The system <NUM> includes a power source <NUM>, a capacitive storage element <NUM>, an igniter <NUM>, and a solid state spark device <NUM>. Generally speaking, the power source <NUM> can apply a charge to the capacitive storage element which, as shown, may be a capacitor <NUM>. When the capacitor <NUM> accumulates sufficient charge it causes the igniter <NUM> to discharge, thereby creating a combustion-initiating spark. The capacitor <NUM> and solid state spark device <NUM> together form an exciter with the spark device <NUM> operating as a switch regulating the discharge of the capacitor <NUM> across the igniter <NUM> in order to permit discharge only when sufficient energy exists in capacitor <NUM>, thereby ensuring a sufficiently powerful spark.

With reference to <FIG>, there is shown a schematic of an exemplary solid state spark device <NUM> that is used with the turbine engine ignition system <NUM>. The spark device <NUM> includes a triggering circuit <NUM>, a control circuit <NUM>, and a triggering transformer <NUM>. The spark device <NUM> can be electrically connected to the capacitor <NUM> that ultimately provides voltage/current to the igniter <NUM> causing spark. The triggering circuit <NUM> of system <NUM> can be electrically connected to the input from capacitor <NUM> as well as a primary coil <NUM> of the triggering transformer <NUM>. The triggering circuit <NUM> includes a number of circuit elements to carry out its functions; these include a voltage divider <NUM>, a capacitor <NUM>, and a switch <NUM>. Both the voltage divider <NUM> and the capacitor <NUM> are electrically connected to the switch <NUM>. In this implementation, the switch <NUM> can be implemented using a diode for alternating current (DIAC); however, other types of switches could be substituted.

The voltage divider <NUM> can comprise two resistors <NUM> and <NUM>; the resistor <NUM> can be wired in parallel with the capacitor <NUM>. Resistor <NUM> can have a resistance value large enough to withstand the voltage amounts applied across it and reduce leakage current across the capacitor <NUM>. The switch <NUM> and resistors <NUM> and <NUM> of the triggering circuit <NUM> can be selected such that the output voltage from the triggering circuit <NUM> at the primary coil <NUM> is zero until the capacitor <NUM> is charged to a sparking voltage sufficient to provide the desired spark energy at igniter <NUM>. Once the capacitor <NUM> reaches the sparking voltage (e.g., <NUM>,<NUM> volts), the triggering circuit <NUM> will then output current to the primary coil <NUM> causing the spark device <NUM> to discharge the stored energy on capacitor <NUM> into igniter <NUM>, as will be described below.

The values of resistors <NUM> and <NUM> can be selected based on the desired sparking voltage for capacitor <NUM> and on the breakdown voltage of the DIAC switch <NUM>. Thus, the resistors <NUM>, <NUM> of voltage divider <NUM> have resistance values that allow capacitor <NUM> to charge up to a triggering voltage dependent on or equal to the breakdown voltage of the switch <NUM> when the capacitive storage element <NUM> reaches the sparking voltage. The quantity and resistance value of the resistors used in the triggering circuit <NUM> can depend on desired sparking voltage being delivered to the igniter <NUM>. In one embodiment, the sparking voltage can be <NUM>,<NUM> volts (V) with the sparking device configured to discharge capacitor <NUM> into igniter <NUM> once the capacitor <NUM> reaches that sparking voltage. In this embodiment, the switch <NUM> may be a DIAC having a breakdown voltage of about <NUM> volts, which is the point at which the switch becomes conductive, thereby supplying current to the coil <NUM> and thereby energizing transformer <NUM>. To achieve triggering at this voltage, the resistors <NUM> and <NUM> can be implemented using a <NUM> MΩ resistor and a <NUM> KS2 resistor, respectively.

In other embodiments, different sparking voltages for capacitor <NUM> and triggering voltages for switch <NUM> may be used; for example, the sparking voltage may be <NUM>,<NUM> volts or may range up to, for example, <NUM>,<NUM> volts (V); and the triggering circuit <NUM> may be implemented with different resistance values or numbers of resistors as desired or necessary to achieve the desired voltage trigger point.

As a voltage level at the capacitive storage element <NUM> increases or ramps up, the voltage at the voltage divider <NUM> and capacitor <NUM> can increase at the same or similar rate. Once the voltage across the capacitor <NUM> reaches the triggering voltage, the breakdown voltage of the switch <NUM> has been met and current flows from capacitor <NUM> through the primary coil <NUM>. This current from the switch <NUM> flows through the primary coil <NUM> and induces current flow in a secondary coil <NUM> of the triggering transformer <NUM> through a steering diode <NUM> of the control circuit <NUM>.

The control circuit <NUM> can be electrically connected to the secondary coil <NUM> of the triggering transformer <NUM> and includes the steering diode <NUM> and a resistor <NUM> that provide electrical input to a gate <NUM> of switch <NUM>. The induced current flow in the secondary coil <NUM> can pass through the steering diode <NUM> to the gate <NUM>. The current from the secondary coil <NUM> reaching the gate <NUM> closes the switch <NUM> thereby making it conductive. As a result, charge from the capacitor <NUM> can pass through the switch <NUM> to the igniter <NUM> thereby creating a spark. When the current induced in the secondary coil <NUM> decays, the current to the gate <NUM> stops and the switch <NUM> opens after the energy of the capacitor has been exhausted. This process can be repeated for subsequent sparks by subsequent charging of the capacitor <NUM>, and the spark rate may be controlled based in part on the resistance values for resistors <NUM> and <NUM>, as well as using other techniques that will be known or will be apparent to those skilled in the art.

The switch <NUM> can be implemented using a thyristor or silicon-controlled rectifier (SCR), such as a MOS-controlled semi-conductor switch. In one particular implementation, the switch <NUM> used in the solid state spark device <NUM> can be the switch assembly described in <CIT>.

The resistor <NUM> may be used to provide a low impedance at the gate <NUM> of switch <NUM> making it less susceptible to electromagnetic interference (EMI) or other switching noise.

It is to be understood that the foregoing description is not a description of the invention itself, but of one or more preferred exemplary embodiments of the invention. The invention is not limited to the particular embodiment(s) disclosed herein, but rather is defined solely by the claims below. It should be appreciated that the resistors and switches identified above can be generically be identified by the term "circuit element," which includes resistors or switches. Furthermore, the statements contained in the foregoing description relate to particular embodiments and are not to be construed as limitations on the scope of the invention or on the definition of terms used in the claims, except where a term or phrase is expressly defined above. Various other embodiments and various changes and modifications to the disclosed embodiment(s) will become apparent to those skilled in the art. All such other embodiments, changes, and modifications are intended to come within the scope of the appended claims.

Claim 1:
A solid state spark device (<NUM>) for use in an aircraft ignition system (<NUM>), wherein the solid state spark device (<NUM>) is a two terminal device connectable in series between an igniter (<NUM>) and a capacitive storage element (<NUM>) that charges up to a sparking voltage sufficient to create a spark on the igniter (<NUM>), wherein the solid state spark device (<NUM>) comprises:
a triggering transformer (<NUM>) having first and second coils (<NUM>, <NUM>);
a triggering circuit (<NUM>) electrically connected to the first coil (<NUM>) and configured to trigger the discharge of the capacitive storage element (<NUM>), the triggering circuit (<NUM>) including circuit elements that include a capacitor (<NUM>) charged via one of the terminals of the solid state spark device (<NUM>) when the solid state spark device is connected in series between the capacitive storage element (<NUM>) and igniter (<NUM>), wherein the circuit elements of the triggering circuit (<NUM>) supply current to the first coil (<NUM>) by discharging the capacitor (<NUM>) via the first coil (<NUM>) when the voltage on the capacitor reaches a predefined triggering voltage, wherein the current through the first coil (<NUM>) of the triggering transformer (<NUM>) induces an output in the second coil (<NUM>); and
a control circuit (<NUM>) that is electrically connected to the second coil (<NUM>) and includes a first switch (<NUM>) controlled by the output from the second coil (<NUM>) to discharge the capacitive storage element (<NUM>) to the igniter (<NUM>) by connecting the two terminals of the solid state spark device (<NUM>).