Method and a system for reliably starting a turbine engine

Abstract

There is provided a starting system for reliably starting a turbine engine, the system including first and second circuits connected in parallel and arranged between a battery of the engine and a DC starter of the engine, the first circuit including a DC-DC converter connected in series with a first switch and the second circuit including a second switch; a sensor configured to sense a speed of rotation of a compressor of the engine; a sensor configured to sense a temperature at an inlet to a free turbine of the engine; and a control circuit configured to control the first and second switches as a function of information supplied by the sensor configured to sense the speed of rotation of the compressor and by the sensor configured to sense the inlet temperature of the free turbine.

Claims

1. A starting system for reliably starting a turbine engine comprising a storage battery, a DC starter, an electronic regulation computer, a transmission gearbox, starting accessories for managing the distribution of fuel to injectors and for igniting the fuel during a starting stage, a gas generator comprising a compressor, a combustion chamber, a high pressure turbine, and a free turbine, the system comprising: a first circuit and a second circuit connected in parallel between said storage battery and said DC starter, wherein the first circuit comprises a DC-DC converter connected in series with a first switch, and the second circuit comprises a second switch; at least one sensor configured to sense a speed of rotation of the compressor; a sensor configured to sense a temperature at an inlet to the free turbine; and a control circuit configured to control the first and second switches as a function of information supplied by the at least one sensor configured to sense the speed of rotation of the compressor and by the sensor configured to sense the inlet temperature of the free turbine.

2. The starting system according to claim 1, further comprising a diode connected in the first circuit in series with the DC-DC converter and the first switch.

3. The starting system according to claim 1, wherein the DC starter is a starter-generator.

4. The starting system according to claim 1, further comprising a sensor configured to sense a speed of rotation of the DC starter, wherein the DC-DC converter is configured to be servo-controlled by the sensor configured to sense the speed of rotation of the DC starter when said first switch is closed.

5. The starting system according to claim 4, wherein the electronic regulation computer is configured to prepare a speed setpoint Nref corresponding to a preferred ignition window of the turbine engine and is configured to transmit the speed setpoint Nref to the DC-DC converter.

6. The starting system according to claim 1, wherein the DC-DC converter is configured to be servo-controlled by the sensor configured to sense the speed of rotation of the compressor when said first switch is closed.

7. The starting system according to claim 6, wherein the electronic regulation computer is configured to prepare a speed setpoint Nref corresponding to a preferred ignition window of the turbine engine, is configured to prepare a torque setpoint Cref, and is configured to transmit the torque setpoint Cref to the DC-DC converter.

8. The starting system according to claim 1, wherein the DC-DC converter includes an electromagnetic compatibility filter, a pre-load circuit, and a buck type chopper.

9. The starting system according to claim 1, wherein the electronic regulation computer is configured to prepare respective logic signals SL1, SL2 that are applied for actuating the first and second switches.

10. The starting system according to claim 1, wherein the electronic regulation computer is configured to detect that the speed of rotation NG of the compressor has exceeded a predetermined threshold and is configured to deactivate the first and second switches and the starting accessories.

11. The starting system according to claim 1, further comprising a control circuit for the DC-DC converter, the control circuit for the DC-DC converter comprising both a speed servo-control loop and a current servo-control loop.

12. The starting system according to claim 11, wherein said speed servo-control loop and said current servo-control loop are incorporated in an independent controller circuit configured to control the DC-DC converter.

13. The starting system according to claim 11, wherein said speed servo-control loop is incorporated in said electronic regulation computer and said current servo-control loop is incorporated in an independent controller circuit configured to control the DC-DC converter.

14. The starting system according to claim 1, wherein said system is applied to an aircraft turbine engine.

15. A starting method for reliably starting a turbine engine comprising a storage battery, a DC starter, an electronic regulation computer, a transmission gearbox, starting accessories for managing the distribution of fuel to injectors and for igniting the fuel during a starting stage, a gas generator comprising a compressor, a combustion chamber, a high pressure turbine, and a free turbine, the starting method comprising: connecting a first circuit and a second circuit in parallel and interposing said first and second circuits between said storage battery and said DC starter, the first circuit comprising a DC-DC converter connected in series with a first switch, and the second circuit comprising a second switch; measuring a speed of rotation of the compressor; measuring a temperature at an inlet of the free turbine; and controlling said first and second switches as a function of measurement information concerning the speed of rotation of the compressor and the temperature at the inlet of the free turbine.

16. The starting method according to claim 15, wherein when initializing the starting, the starting accessories are activated and simultaneously a speed setpoint Nref is transmitted to said DC-DC converter, the speed setpoint corresponding to a preferred ignition window of the turbine, and said first switch is closed while activating the DC-DC converter to accelerate the compressor and then to regulate the voltage delivered to the starter so as to regulate the acquisition of speed by said compressor to the speed setpoint Nref, and wherein when said speed setpoint Nref is reached, the combustion chamber of the turbine engine is ignited, the temperature at the inlet of the free turbine is measured, and once a rise in temperature is detected confirming that the combustion chamber has ignited, the second switch is closed, the first switch is opened, and the DC-DC converter is deactivated, and after detecting that the speed of rotation of the compressor has exceeded an end-of-starting threshold, the starting accessories are deactivated and the second switch is opened.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Other characteristics and advantages of the invention appear from the following description of particular embodiments given as examples and with reference to the accompanying drawings, in which:

(2) FIG. 1 is a diagrammatic overall view of an embodiment of a turbine engine starter device in accordance with the invention;

(3) FIG. 2 is a more detailed view of an example of a DC-DC converter suitable for including in the device of the invention shown in FIG. 1;

(4) FIG. 3 is a diagrammatic overall view of a first embodiment of a turbine engine starter device in accordance with the invention, together with its control circuit;

(5) FIG. 4 is a diagrammatic view of a servo-control loop corresponding to the first embodiment of FIG. 3;

(6) FIG. 5 is a diagrammatic overall view of a second embodiment of a turbine engine starter device in accordance with the invention, together with its control circuits;

(7) FIG. 6 is a diagrammatic view of a servo-control loop corresponding to the second embodiment of FIG. 5;

(8) FIG. 7 is an electrical circuit diagram corresponding to a prior art starter device;

(9) FIG. 8 is a graph plotting various curves showing the appearance of maximum and minimum values for the starter torque as a function of speed of rotation for various operating conditions, suitable for guaranteeing ignition of the combustion chamber within the flying conditions;

(10) FIG. 9 is an electrical circuit diagram showing the insertion of a starter resistance in the prior art;

(11) FIGS. 10 and 11 are electrical circuit diagrams of a prior art starter device having two batteries that are connected respectively in parallel and in series as a function of a threshold speed;

(12) FIG. 12 is a graph showing a known starting sequence as controlled by a computer; and

(13) FIG. 13 is a diagram of a prior art starter device for a turboprop using an AC starter powered by a DC-AC controlled converter.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(14) FIG. 1 is a diagram showing the general configuration of a device of the invention.

(15) The reliable starter system for a turbine engine comprises a storage battery 110 that may be a single battery or a group of batteries and that may be constituted by the power supply from an on-board network of an aircraft, e.g. 28 V, but the invention is not limited to this voltage.

(16) A DC starter 120 may be constituted by a simple DC starter or by a starter generator (SG) capable of operating not only in motor mode, but also in generator mode once the starting stage has terminated, e.g. in order to power an on-board network. In the description below, the term starter is used to cover both a starter only and/or a starter-generator, unless specified to the contrary.

(17) The turbine engine starter system includes a transmission gearbox 162 including in particular stepdown gearing for transmitting motion from the starter 120 to the main axis of the engine, and also including auxiliary equipment, such as pumps associated with injectors for injecting fuel into the combustion chamber.

(18) FIG. 1 also shows the main elements of the turbine engine comprising a gas generator 160, itself comprising a compressor 164, a combustion chamber 165, and a high pressure turbine 166, together with a free turbine 167, and starting accessories 168. FIG. 1 also shows a sensor 161 for sensing the speed of rotation of the starter 120 and a sensor 163 for sensing the speed of rotation of the shaft of the compressor 164 of the engine.

(19) The starter system of the invention has first and second circuits connected in parallel and inserted between the storage battery 110 and the DC starter 120. The first circuit comprises a DC-DC converter 130 connected in series with a first switch 132 and optionally with a diode 131. The second circuit comprises a second switch 133.

(20) As described below with references to FIGS. 3 and 5, the system also has other sensors for measuring the operation of the engine, such as a sensor 151 for sensing the temperature at the inlet to the free turbine 167. The temperature T45 at the inlet to the free turbine 167 provides information representative of ignition conditions in the combustion chamber 165. It is therefore possible, instead of the sensor 151, to make use of any other type of sensor that makes it possible to observe the ignition conditions in the combustion chamber 165.

(21) The first and second switches 132, 133 are controlled by a control circuit 141 (FIGS. 3 and 5) as a function of information delivered by the sensor 163 for sensing the speed of rotation of the compressor 164, and by the sensor 151 for sensing the temperature at the inlet to the free turbine 167.

(22) An electronic regulation computer 142, 142, which may be constituted by a conventional electronic computer of the engine, also known as an electronic engine controller (EECU) (FIGS. 3 and 5), serves to manage the measurements supplied by the sensors 151 and 163 and to control the DC-DC converter 130 in co-operation with the control circuit 141, which may be a pre-existing electrical master box, such as a module for managing the on-board network of an aircraft.

(23) The starter device of the invention is thus constituted essentially by a DC-DC converter 130 that, when the contactor 132 is closed, powers the starter 120 at the beginning of the starting stage and supplies the power needed to keep the gas generator 160 in the ignition window.

(24) Once ignition has been confirmed, the contactor 133 is closed and the contactor 132 is opened so as to power the starter 120 without interruption directly from the battery 110, which may be incorporated in the on-board network, e.g. at 28 V, so as to enable starting to be continued in non-controlled manner.

(25) The switches 132 and 133 may form parts of the electrical master box of the helicopter. The diode 131 is not essential, however it can nevertheless be useful for the purpose of protecting the outlet from the DC-DC converter 130 during overlapping operation of the contactors 132 and 133.

(26) By way of example, the DC-DC converter 130 may comprise a simple buck chopper 136 (see FIG. 2) that takes the power supply voltage U of the network (e.g. 28 V) and delivers to the starter armature 120 the current I.sub.D needed for regulating the torque of the starter 120 and thus servo-controlling the speed of rotation NG of the shaft of the compressor 164 of the gas generator 160 on the setpoint, independently of operating conditions (voltage of the on-board network, impedances of the power supply 110 and the starter 120, opposing torque from the compressor 164, etc. . . . ).

(27) Since the electrical power needed is low, the DC-DC converter acts as a progressive starter system that limits the current drawn from the on-board network during the first instant of starting, when the back emf of the starter 120 is almost zero. This aspect makes it possible to reduce temperature constraints on the starter 120, mechanical constraints on the fluting, and the weak link of the drive from the starter 120, and, when starting on the battery 110 of the helicopter, it also makes it possible to diminish the drop in voltage observed in the on-board network when switching on the starter 120 when both speed and back emf are zero.

(28) Regulating the speed of the electrical machine requires a speed sensor 161, which may either form part of the starter 120 itself (some starter-generators come fitted therewith, in particular in order to manage defluxing), or else may be secured to the drive of the starter 120 (phonic wheel, Hall effect sensor, etc.).

(29) Since the preferred ignition window can vary as a function of the flying conditions (atmospheric pressure P0, atmospheric temperature T0), it is desirable to be able to vary the speed setpoint Nref for the DC-DC converter 130, which setpoint is prepared by the computer 142 of the turboshaft engine and is transmitted to the device over a digital or analog link 145 (e.g. as a variable duty ratio), as shown in FIG. 3.

(30) By way of example, and as shown in FIG. 2, the DC-DC converter 130 may include an electromagnetic compatibility filter 134 with coupled iron-cored inductors 101 and capacitors 102, 103 followed by a pre-loading circuit 135, having a resistor 104 that can be shunted by a switch 105, and a buck type chopper 136, with a capacitor 106, a controlled switch 107 constituted by power semiconductor components, a diode 108, and an inductor 109 for outputting a direct current (DC) I.sub.D.

(31) There follows a more detailed description of the operation of the starter system of the invention in several variant embodiments, with reference to FIGS. 3 to 6.

(32) On selecting starting, the computer (EECU) controlling the turbine engine 142 sends a logic signal SL1 to the system for managing the on-board network of the helicopter (electrical master box) 141, activates a starting solenoid valve and the spark plugs, and applies a fuel flow control relationship appropriate for starting by means of a line 149 for controlling starting accessories that are symbolically grouped together in FIGS. 1, 3, and 5 under the reference 168.

(33) Simultaneously, the EECU 142 uses various parameters that it acquires (atmospheric pressure P0, atmospheric temperature T0, residual temperature T45, i.e. the temperature of the gas at the inlet to the free turbine, etc. . . . ), in order to prepare the speed setpoint Nref corresponding to the preferred ignition window of the turboshaft engine, and it transmits this setpoint to the DC-DC converter 130.

(34) On activation of the logic signal SL1, the electrical master box 141 closes the contactor 132 (activation via the line 147) and sends the activation setpoint to the DC-DC converter 130 (activates the ON/OFF signal via the line 144).

(35) The DC-DC converter 130 powered by the on-board network 110 begins to operate, accelerates rotation of the shaft of the compressor 164 of the gas generator 160, and then regulates the current I.sub.D delivered to the starter 120 so as to regulate the acquisition of speed NG by the rotary machine on the speed setpoint Nref.

(36) Once the EECU 142 observes that the speed of rotation NG of the shaft of the compressor 164 of the gas generator 160, as measured by the sensor 163 and supplied to the EECU by the line 148, has reached the speed setpoint Nref and has become stabilized thereat, the electronic regulation computer 142 proceeds to ignite the turbine engine by sending the required control information over the line 149 for controlling the starting accessory.

(37) When the EECU 142 detects and confirms ignition of the combustion chamber, e.g. by measuring the rise in T45 via the line 151, it sends a logic signal SL2 to the system 141 for managing the on-board network of the helicopter, and then deactivates the logic signal SL1.

(38) On activation of the logic signal SL2, the electrical master box 141 closes the contactor 133 (activation via the line 143): the starter 120, powered directly from the on-board network 110, continues accelerating and starting the turbine engine in conventional manner. Simultaneously, the diode 131 becomes blocked against reverse current, thus serving to avoid short-circuiting the outlet from the DC-DC converter 130.

(39) It should be observed that overlap in the control of the contactors 132 and 133, as made possible by the diode 131, serves to guarantee that there is no discontinuity in the electrical power supply to the starter 120.

(40) On deactivation of the logic signal SL1, the electrical master box 141 opens the contactor 132 (deactivation of the signal transmitted via the line 147), thereby isolating the outlet from the DC-DC converter 130 of the starter 120, and sending the deactivation setpoint for the DC-DC converter 130 (deactivation of the ON/OFF signal on the line 144).

(41) When the EECU 142 detects that the speed NG of the shaft of the compressor 164 of the gas generator 160 exceeds an end-of-starting threshold (threshold from which the turboshaft engine operates independently), it deactivates the starting accessories 168 via the line 149, and also the logic signal SL2.

(42) On deactivation of the logic signal SL2, the electrical master box 141 opens the contactor 133 (deactivation of the control signal via the line 143), thereby switching off the electrical power supply to the starter 120.

(43) Above a speed threshold, the starter-generator 120 can be switched into generator mode so as to power the on-board network 110, however this operation cannot be performed if the starter is a starter only.

(44) From the point of view of controlling the DC-DC converter 130, there are to be found in conventional manner two interleaved regulation loops: speed servo-control followed by torque or current servo-control (see FIGS. 4 and 6).

(45) The speed setpoint Nref corresponding to the ideal ignition window for the turbine engine, as delivered by the line 172, is prepared by the EECU 170 of the turbine engine in the block 171 as a function of parameters that are acquired by the EECU 170 (for example and in non-exhaustive manner, atmospheric pressure P0, air temperature T0 at the inlet to the compressor, . . . ), and is then transmitted to the control system 180 of the DC-DC converter 130 in digital or analog manner.

(46) The speed ND of the rotary machine as measured by the sensor 161 and as transmitted by the line 146 (FIG. 3) or 181 (FIG. 4) is compared with the speed setpoint Nref in the comparator 182 in order to give a speed error N, which is processed by the corrector 183 in order to give a torque setpoint Cref. This torque setpoint Cref is processed by the block 184, which transforms it into a current setpoint Iref. The measured current I.sub.D at the outlet from the DC-DC converter 130 is compared with the reference Iref in the comparator 186 to give an error I, which is processed by the corrector 187 to give a setpoint 188 for the conduction duty ratio , which is used for controlling the power semiconductor(s) 189 (FIG. 4) or 107 (FIG. 2) of the chopper of the DC-DC converter 130.

(47) In another embodiment that is slightly different and shown in FIGS. 5 and 6, the speed servo-control loop is calculated by the EECU 270. The speed setpoint Nref supplied as input 272 to a comparator 274 is prepared by the EECU 270 in the same manner as above, in a block 271 that is analogous to the block 171 of FIG. 4, but it is compared with the measured speed of rotation NG of the shaft of the compressor 164 of the gas generator 160 (which is proportional to the speed of rotation ND of the starter 120), as supplied on the input 273 of the comparator 274 so as to prepare the torque setpoint Cref, which is transmitted by the EECU 270 to the control circuit 280 of the DC-DC converter 130. This torque setpoint Cref is processed by the control circuit 280 of the DC-DC converter 130 in the same manner as in the above-described embodiment of FIG. 4, the elements 281 to 286 of FIG. 6 corresponding to the elements 184 to 189 of FIG. 4 respectively and not being described again, so as to end up with controlling the semiconductors 286 of the chopper.

(48) It can be seen that one of the advantages of this embodiment is that it makes it possible to omit the speed sensor 161 on the starter 120, the speed loop being processed directly in the turboshaft engine computer by acquiring the speed NG of the gas generator using the sensor 163.

(49) In general manner, the invention relates both to a system and to a method for reliably starting a turbine engine.

(50) The method for reliably starting a turbine engine having a storage battery 110, a DC starter 120, an electronic regulation computer 142, 142, a transmission gearbox 162, starting accessories 168 for managing the distribution of fuel to injectors and for igniting the fuel during a starting stage, a gas generator 160 itself comprising a compressor 164, a combustion chamber 165, and a high pressure turbine 166, together with a free turbine 167, comprises the following steps: connecting first and second circuits in parallel and interposing them between said storage battery 110 and said DC starter 120, the first circuit comprising a DC-DC converter 130 connected in series with a first switch 132 and the second circuit comprising a second switch 133; measuring the speed of rotation of the compressor 164; measuring the temperature at the inlet of the free turbine 167; and controlling said first and second switches 132, 133 as a function of measurement information concerning the speed of rotation of the compressor 164 and the temperature at the inlet of the free turbine 167.

(51) More particularly, when initializing starting, the starting accessories 168 are activated and simultaneously a speed setpoint Nref is transmitted to said DC-DC converter 130, the speed setpoint corresponding to a preferred ignition window of the turbine, and said first switch 132 is closed while activating the DC-DC converter 130 to accelerate the compressor 164 and then regulate the voltage delivered to the starter 120 so as to regulate the acquisition of speed by said compressor 164 to the speed setpoint Nref, and when said speed setpoint Nref is reached, the combustion chamber 165 of the turbine engine is ignited, the temperature at the inlet of the free turbine 167 is measured, and once a rise in temperature is detected confirming that the combustion chamber 165 has ignited, the second switch 133 is closed, the first switch 132 is opened, and the DC-DC converter 130 is deactivated, and that after detecting that the speed of rotation of the compressor has exceeded an end-of-starting threshold, the starting accessories 168 are deactivated and the second switch 133 is opened.

(52) The method and the system of the invention for reliable starting present numerous advantages.

(53) They make it possible to reduce the number of abortive starts as a result of failure to ignite or of flameout in the combustion chamber of the gas generator of the turbine engine.

(54) They make it possible for starting to be more robust relative to starting conditions (flying conditions, oil temperature, power supply voltage for the starter, etc. . . . ).

(55) They make it possible to minimize dispersions on the duration of starts.

(56) They therefore make it possible to avoid ventilation between an abortive start and a new attempt, and consequently they make it possible to reduce the size and the weight of the on-board battery.

(57) They simplify the work of the manufacturer in designing the electrical power supply for the starter, in order to comply with the required maximum starting torque template.

(58) They make it possible to limit inrush current when starting at zero speed, thereby making it possible to minimize wear on the brushes of the starter-generator, to minimize stresses on the coupling (fluting, weak link), to reduce the voltage drop in the on-board network, and to optimize dimensioning of the battery.

(59) This leads to better availability for helicopters, given the lower rate of abortive starts.

(60) By reducing the power of the device, its weight and cost are also reduced compared with a static converter dimensioned for full starting power (about 15% of the maximum starting power).

(61) The system of the invention is compatible with most 28 V starter-generators and starters with brushes presently in use on helicopters.

(62) The invention is not limited to the embodiments described, but extends to any variant coming within the ambit of the claims.

(63) Thus, by way of example, the device including the controlled DC-DC converter 130 may be installed by a manufacturer directly in the electrical master box 141, provided the specifications of the engine are known, which specifications comprise firstly requirements in terms of performance (torque, speed), and secondly the interfaces used (format for transmitting the speed setpoint to the device).