Patent Description:
Glow plugs are commonly used to ignite a mixture of air and fuel in a combustor of gas turbine engines. However, glow plugs have drawbacks. For instance, the glow plugs have been known to achieve less than full reliability in conditions such as when the fuel and the engine are very cold or when the environment gets too hot. Cost is also a factor. There is always room for improvement.

<CIT> discloses a process and a circuit for heating up a glow plug.

<CIT> discloses a glow plug controlling method for a diesel engine of a motor vehicle.

According to an aspect of the present invention, there is provided a method for operating a glow plug in accordance with claim <NUM>.

According to another aspect of the present invention, there is provided a glow plug system in accordance with claim <NUM>.

There is described herein a glow plug system and a method for operating a glow plug. In some embodiments, the glow plug is used to ignite an engine, such as a gas turbine engine. Alternatively, the glow plug may be used for any type of application requiring such a heating element. <FIG> illustrates a gas turbine engine <NUM> of a type provided for use in subsonic flight, generally comprising in serial flow communication a fan <NUM> through which ambient air is propelled, a compressor section <NUM> for pressurizing the air, a combustor <NUM> in which the compressed air is mixed with fuel and ignited for generating an annular stream of hot combustion gases, and a turbine section <NUM> for extracting energy from the combustion gases. The fan <NUM>, the compressor section <NUM>, and the turbine section <NUM> rotate about a central axis <NUM>. The combustor <NUM> defines at least one aperture <NUM> for receiving at least one glow plug <NUM> (<FIG>) for igniting the mixture of compressed air and fuel.

Control of the operation of the engine <NUM> can be effected by one or more control systems, for example an engine controller <NUM>, which is communicatively coupled to the engine <NUM>. The engine controller <NUM> can modulate a fuel flow provided to the engine <NUM>, the position and orientation of variable geometry mechanisms within the engine <NUM>, a bleed level of the engine <NUM>, and the like, based on predetermined schedules or algorithms. In some embodiments, the engine controller <NUM> includes one or more FADEC(s), electronic engine controller(s) (EEC(s)), or the like, that are programmed to control the operation of the engine <NUM>. The operation of the engine <NUM> can be controlled by way of one or more actuators, mechanical linkages, hydraulic systems, and the like. The engine controller <NUM> can be coupled to the actuators, mechanical linkages, hydraulic systems, and the like, in any suitable fashion for effecting control of the engine <NUM>.

Although illustrated as a turbofan engine, the gas turbine engine <NUM> may alternatively be any other type of engine for which a glow plug may be used for ignition, for example a turboshaft engine or a turboprop engine. Other types of engines, such as a diesel engine or a Wankel rotary combustion engine, may also apply. The engine <NUM> may be for flight applications, industrial applications, or the like.

Referring to <FIG>, the glow plug <NUM> has a body <NUM> and a glowing end <NUM> extending from the body <NUM>. The glowing end <NUM> becomes hot during use to ignite the mixture of gas and air. The body <NUM> may define a threaded portion <NUM> to be threadingly engaged to the aperture <NUM> defined through the combustor <NUM> of the engine <NUM>. The glow plug <NUM> has a connecting end <NUM> opposite to the glowing end <NUM> for connection to a source of power.

The body <NUM> and glowing end <NUM> together form an electric heat generating member <NUM> having a resistance R. In some embodiments, the resistance R has a constant resistance component Rc that is temperature independent, and a varying resistance component Rv that is temperature dependent. The two components are connected in series such that: <MAT>.

The constant resistance component Rc is generally very low. The varying resistance component Rv varies with a resistor temperature coefficient α and a temperature T of the glow plug, such that equation (<NUM>) becomes: <MAT>.

The resistor temperature coefficient α is constant from one glow plug to another having been made with a same manufacturing process and materials, and differs from one glow plug to another having been made from different manufacturing processes and/or different materials. The constant resistance component Rc may vary between acceptable limits from one glow plug to another having been made with a same manufacturing process and materials.

Referring to <FIG>, there is illustrated an example embodiment of a glow plug system <NUM>. The glow plug <NUM> is powered by a glow plug power source <NUM>, which may be a power supply, a battery, or any other device capable of providing at least two fixed voltage levels to the glow plug <NUM>. A glow plug controller <NUM> is coupled to the glow plug power source <NUM> and applies a glow plug temperature control strategy that uses the glow plug current IGPL flowing into the glow plug <NUM> as a temperature detection mechanism and adapts the glow plug voltage VGPL applied to the glow plug <NUM> by the glow plug power source <NUM> accordingly.

Since the constant resistance component Rc and the resistor temperature coefficient α are constant, the total glow plug resistance R will be constant for a given temperature T. If the glow plug <NUM> is powered with a first, nominal constant voltage VN, then the glow plug current IGPL at the minimum threshold temperature T1, will be a first value Ix. Threshold I<NUM> should be set at a value that corresponds to Ix, to account for effects that might decrease the resistance and thereby increase current, such as plug to plug variation and external cooling effects. Similarly, if the glow plug <NUM> is powered with VN at a maximum threshold temperature T2 (which can be higher than T1), then the glow plug current IGPL will be a second value ly. Threshold I<NUM> should be set at a value that corresponds to ly, to account for effects that might increase the resistance and thereby decrease current, such as plug to plug variation and external heating effects. As long as the glow plug current IGPL is kept within I<NUM> and I<NUM>, the glow plug temperature T will be protected from overheating.

Generally, the glow plug controller <NUM> is configured to monitor the glow plug current IGPL and to make a control decision based on the glow plug current IGPL. There are three possible actions, depending on the value of the glow plug current IGPL. When the glow plug current is between an upper threshold I<NUM> and a lower threshold I<NUM>, a nominal voltage VN is applied to the glow plug <NUM> by the glow plug power source <NUM>. If the nominal voltage VN is already applied to the glow plug <NUM>, then VN is maintained.

When the glow plug current exceeds the upper threshold I<NUM>, a voltage VH > VN is applied to the glow plug <NUM>. Indeed, when IGPL exceeds I<NUM>, this is indicative that the glow plug temperature T is low (for a constant voltage) and the temperature should be increased. The higher voltage VH causes the temperature T of the glow plug to increase, based on: <MAT> where R can be replaced with equation (<NUM>) to get: <MAT>.

Therefore, if V increases, T will also increase. When the glow plug current falls below the lower threshold I<NUM>, substantially no voltage is applied to the glow plug <NUM>. Indeed, the low IGPL is indicative that the glow plug temperature T is high (for a constant voltage) and the temperature should be decreased. Applying substantially zero volts (or removing any voltage application) causes the temperature T of the glow plug to decrease, based on equations (<NUM>) and (<NUM>) above. It will be understood that the expression "substantially no voltage" encompasses applying a very low voltage, such as <NUM> V or another low value having a substantially same effect as applying zero volts.

In some embodiments, the difference between the upper threshold I<NUM> and the lower threshold I<NUM> is less than or equal to a given percentage of the current I<NUM>, such as <NUM>%. For example, the upper threshold I<NUM> is set to <NUM> A and the lower threshold I<NUM> is set to <NUM> A, such that the difference is <NUM> A, which is <NUM>% of I<NUM>. In some embodiments, the upper and lower thresholds are set so as to have a given difference, such as <NUM> A, <NUM> A, <NUM> A, <NUM> A, <NUM> A, <NUM> A, or <NUM> A. Other embodiments may also apply depending on practical implementations, according to the enclosed claims.

In some embodiments, the upper and lower current thresholds I<NUM>, I<NUM> are selected based on a predicted resistance of the glow plug <NUM> at a desired threshold temperature T1, T2, respectively. In some other embodiments, the upper and lower current thresholds I<NUM>, I<NUM> are selected based on a predicted current at target temperatures (which may differ from the threshold temperatures T1, T2), for example this might be used if some margin relative to the maximum and minimum temperature limits is desired.

In some embodiments, all voltage levels, i.e. VN, VH and substantially zero volts are applied through the glow plug power source <NUM>. For example, the glow plug controller <NUM> may instruct the glow plug power source <NUM> to apply VN, VH or <NUM> volts (i.e. no voltage) as a function of the monitored glow plug current IGPL.

In some embodiments, and as illustrated in <FIG>, the glow plug power source <NUM> is operable only at VN and another power source <NUM> is operable at VH. In this case, the glow plug power source <NUM> may be an on/off type power source that toggles between VN and substantially zero volts, and the glow plug power source <NUM> may be an on/off type power source that toggles between VH and substantially zero volts.

In some embodiments, the glow plug power source <NUM> remains on even when the glow plug power source <NUM> is turned on, such that toggling the glow plug power source <NUM> on/off causes the glow plug voltage VGPL to toggle between VH and VN.

In some embodiments, applying the higher voltage VH to increase the glow plug temperature T comprises toggling between the voltage VH and the voltage VN in order to ensure that the current observed at VN can be periodically compared to thresholds I1 and I2 and the glow plug temperature T increases in a controlled manner and remains under control. Toggling may be done pseudo-randomly or at a given rate with a fixed pulse duration until the monitored glow plug current IGPL measured at VN falls below the upper threshold I<NUM>. Using the embodiment of <FIG>, toggling between VH and VN comprises instructing the glow plug power source <NUM> to alternatively apply VH and VN. Using the embodiment of <FIG>, toggling between VH and VN comprises turning the glow plug power source <NUM> on/off repeatedly while maintaining the glow plug power source <NUM> on. Other embodiments may also apply.

In some embodiments, substantially zero volts (or no voltage) is applied to the glow plug <NUM> for a pre-determined or estimated amount of time in order to cause the temperature T to decrease. However, when there is no voltage applied to the glow plug <NUM> there is also no current to monitor. Therefore, applying substantially no voltage to the glow plug <NUM> may, in some embodiments, comprise toggling between substantially no voltage and VN in order to periodically compare the current at VN with thresholds I<NUM> and I<NUM>, to ensure that the glow plug temperature decreases in a controlled manner and does not get too hot. This helps to ensure that the glow plug life exceeds an expected minimum number of cycles and expected minimum total duration of operation. This also helps to ensure that the glow plug does not get too cold before VN is once again applied, which can improve the ability of the system to successfully ignite the engine. Toggling may be performed pseudo-randomly or using a given rate with a fixed pulse duration until the monitored glow plug current IGPL exceeds the lower threshold I<NUM> when VN is applied. Using the embodiment of <FIG>, toggling between substantially zero volts and VN comprises instructing the glow plug power source <NUM> to alternately apply no voltage and VN. Using the embodiment of <FIG>, toggling between substantially zero volts and VN comprises turning the power source <NUM> on/off repeatedly while maintaining the glow plug power source <NUM> off. Other embodiments may also apply.

Referring to <FIG>, there is illustrated a specific and non-limiting example for implementation of the glow plug system <NUM>. A glow plug <NUM> is operatively coupled to a glow plug power supply <NUM>. An on/off external control turns the power supply <NUM> on and off. Three resistors R1, R2, R3 are connected in series between the glow plug power supply <NUM> and ground, and are used to set the output voltage Vout of the power supply <NUM>, where <MAT>.

As shown in the <FIG>, RA = R2 + R3 and RB = R1. Depending on the position of switch <NUM>, Vout may be set to VN or VH. When switch <NUM> is on (i.e. closed), Vout = VH; when switch <NUM> is off (i.e. open), Vout = VN. When switch <NUM> is on (i.e. closed), VGPL =Vout. When switch <NUM> is off (i.e. opened), VGPL = <NUM>. Therefore, the various configurations of switches <NUM>, <NUM> cause VGPL to be set to any one of VN, VH, and substantially zero V.

A current sensor <NUM> monitors the glow plug current IGPL flowing into the glow plug <NUM>. In an example embodiment, the current sensor <NUM> is a resistor, but any device that detects electric current in a wire and generates a signal proportional to that current may be used. The generated signal may be analog or digital. If the sensed current is greater than the upper threshold I<NUM>, switch <NUM> is closed (i.e. turned on) via switch controller <NUM> so that VGPL = Vout = VH in order to cause the temperature T of the glow plug <NUM> to increase. If, when VN is applied, the sensed current is not greater than the upper threshold I<NUM> and is not lower than the lower threshold I<NUM>, switch <NUM> is held open via switch controller <NUM> so that VGPL = Vout = VN. If the sensed current is not greater than the upper threshold I<NUM> and is lower than the lower threshold I<NUM>, switch <NUM> is opened (i.e. turned off) via switch controller <NUM> such that VGPL = <NUM>.

It will be understood that the glow plug assembly <NUM> may be implemented in various ways and that the example of <FIG> is one such way. In some embodiments, the glow plug controller <NUM> is implemented in one or more computing device <NUM>, as illustrated in <FIG>. For simplicity only one computing device <NUM> is shown but the system may include more computing devices <NUM> operable to exchange data. The computing devices <NUM> may be the same or different types of devices. Note that the controller <NUM> can be implemented as part of a full-authority digital engine controls (FADEC) or other similar device, including electronic engine control (EEC), engine control unit (ECU), avionics or cockpit equipment, electronic propeller control, propeller control unit, and the like. In some embodiments, the controller <NUM> is implemented as part of the engine controller <NUM>, in part or in whole. In this manner, operation of the glow plug may be managed by an engine control system. Other embodiments may also apply.

The processing unit <NUM> may comprise any suitable devices configured to implement the method XX such that instructions <NUM>, when executed by the computing device <NUM> or other programmable apparatus, may cause the functions/acts/steps performed as part of a method <NUM> as described in <FIG> to be executed.

Referring to <FIG>, a method <NUM> of operating a glow plug is described. At step <NUM>, the glow plug current IGPL is monitored. When the glow plug current IGPL at VN < I<NUM> and > I<NUM>, a nominal voltage VN is continuously applied to the glow plug at step <NUM>. When the glow plug current at VN, IGPL > I<NUM>, a voltage VH > VN is applied to the glow plug at step <NUM>. When the glow plug current at VN, IGPL < I<NUM>, no voltage (or substantially zero volts) is applied to the glow plug at step <NUM>. After each one of steps <NUM>, <NUM>, <NUM>, the method <NUM> loops back to step <NUM> to continue monitoring the glow plug current and apply the proper voltage in order to manage the temperature of the glow plug.

In some embodiments, applying the voltage VH > VN to the glow plug at step <NUM> comprises toggling between the voltage VH and the voltage VN until the monitored glow plug current at VN falls below the upper threshold I<NUM>. In some embodiments, applying substantially no voltage to the glow plug at step <NUM> comprises toggling between substantially no voltage and the voltage VN until the monitored glow plug current at VN rises above the lower threshold I<NUM>. In some embodiments, monitoring of the glow plug current IGPL at step <NUM> is only done while VN is applied.

Although the method <NUM> refers to "applying a voltage" to the glow plug, it will be understood that this expression includes applying the voltage via one or more power source as well as causing one or more power source to apply the voltage. The expression also includes causing one or more switches, such as the one illustrated in <FIG>, to open and close in order to set the glow plug voltage VGPL to substantially zero or to Vout as defined by a glow plug power supply The method <NUM> may be performed by the glow plug controller <NUM> using an embodiment as illustrated in <FIG>, <FIG>, <FIG>, <FIG>, a combination thereof, according to the enclosed claims.

It will be understood by those skilled in the art that the method <NUM> allows the temperature of the glow plug to be managed without any independent temperature feedback and without complex micro-processors to measure glow plug voltage. The glow plug assembly <NUM> may thus have lower costs, lower weight, and be more reliable due to lower component count and higher power supply efficiency. As stated above, glow plug management may also be integrated into an engine controller <NUM> of an engine <NUM>, for example via a solenoid driver interface. In some embodiments, an internal processor of the engine controller <NUM> may also be used to provide gradually varying glow plug voltages to the glow plug. The method <NUM> does not require any calculations, such as resistance calculations or others, to manage the glow plug temperature. The method <NUM> does not require any feedback or input related to environmental and engine operating conditions to manage the glow plug temperature. The method <NUM> does not rely on any data to be provided by the engine controller <NUM> or any other device to manage the glow plug temperature.

In some embodiments, the upper threshold I<NUM> is associated with a maximum value for the resistance of the glow plug that limits the temperature T of the glow plug to a maximum temperature for the nominal voltage VN, and the lower threshold I<NUM> is associated with a minimum value for the resistance of the glow plug that limits the temperature T of the glow plug to a minimum temperature for the nominal voltage VN. As such, the upper and lower current thresholds may be set as a function of the value of the resistance of the glow plug.

For example, the glow plug temperature T may be centered at <NUM>, with the upper and lower temperature limits set above and below this value to <NUM> and <NUM>, respectively. In some embodiments the maximum temperature is less than <NUM> and the minimum temperature is greater than <NUM>. In some embodiments, the maximum temperature corresponds to a temperature that permits a cycle life of at least <NUM> cycles for the glow plug. Upper and lower glow plug current values may be associated with the upper and lower temperature values, for example <NUM> amps and <NUM> amps, respectively. These values are exemplary only and may differ, depending on practical implementations. In some embodiments, the lower temperature threshold is set to be high enough to initiate fuel air mixture ignition in the engine <NUM>.

The method <NUM> for operating a glow plug and glow plug system <NUM> described herein may be implemented in a high level procedural or object oriented programming or scripting language, or a combination thereof, to communicate with or assist in the operation of a computer system, for example the computing device <NUM>. Alternatively, the method <NUM> and system <NUM> may be implemented in assembly or machine language. The language may be a compiled or interpreted language. Program code for implementing the method <NUM> and system <NUM> may be stored on a storage media or a device, for example a ROM, a magnetic disk, an optical disc, a flash drive, or any other suitable storage media or device. The program code may be readable by a general or special-purpose programmable computer for configuring and operating the computer when the storage media or device is read by the computer to perform the procedures described herein. Embodiments of the method <NUM> and system <NUM> may also be considered to be implemented by way of a non-transitory computer-readable storage medium having a computer program stored thereon. The computer program may comprise computer-readable instructions which cause a computer, or more specifically the processing unit <NUM> of the computing device <NUM>, to operate in a specific and predefined manner to perform the functions described herein, for example those described in the method <NUM>.

Claim 1:
A method (<NUM>) for operating a glow plug (<NUM>), the method comprising:
monitoring a glow plug current (IGPL) flowing into the glow plug (<NUM>) when a glow plug voltage (VGPL) applied to the glow plug (<NUM>) is equal to a nominal voltage (VN);
comparing the glow plug current (IGPL) to an upper threshold (I<NUM>) and a lower threshold (I<NUM>) that is less than the upper threshold (I<NUM>);
maintaining the glow plug voltage (VGPL) applied to the glow plug (<NUM>) at the nominal voltage (VN) when the glow plug current (IGPL) is between the upper threshold (I<NUM>) and the lower threshold (I<NUM>);
increasing the glow plug voltage (VGPL) applied to the glow plug (<NUM>) to a second voltage (VH) that is greater than the nominal voltage (VN) when the glow plug current (IGPL) exceeds the upper threshold (I<NUM>); and
decreasing the glow plug voltage (VGPL) applied to the glow plug (<NUM>) to substantially no voltage when the glow plug current (IGPL) falls below the lower threshold (I<NUM>).