Method for regulating the acceleration of a turbomachine

Abstract

The invention relates to a method for regulating the acceleration of a turbine, the turbine comprising a combustion chamber, a high-pressure turbine located downstream of the combustion chamber and rotating a high-pressure shaft, and a low-pressure turbine located downstream of the high-pressure turbine and rotating a low-pressure shaft, characterized in that the method comprises the following steps: - injecting (100) mechanical power into the high-pressure shaft until the speed of the high-pressure shaft reaches a target value, and then - obtaining (200) mechanical power from the high-pressure shaft in order to keep the speed at the target value.

Description

Technical Field

[0001] The present invention relates to the general field of turbomachines for aircraft. Background Art

[0002] Typically, a turbomachine for an aircraft includes a high pressure shaft (HP shaft) driven in rotation by a high pressure (HP) turbine and a low pressure shaft (LP shaft) driven in rotation by a low pressure (LP) turbine, the low pressure shaft driving a fan of the turbomachine in rotation.

[0003] During the acceleration phase of the turbine, a delay may occur between the high pressure (HP) shaft and the low pressure (LP) shaft of the turbine in order to obtain the target speed. Indeed, the Applicant has noticed that the low pressure shaft tends not to accelerate as fast as the high pressure shaft and therefore reaches its target speed later than the high pressure shaft. The Applicant has noticed that the delay in the acceleration of the low pressure shaft is strongly increased when a reduction gear is placed between the low pressure shaft and the fan.

[0004] The delay in low pressure shaft acceleration causes a delay in fan acceleration, thereby increasing the period between the acceleration command and the moment the target thrust is achieved. Summary of the invention

[0005] Therefore, an object of the present invention is to provide a solution in response to the above-mentioned problems.

[0006] According to a first aspect, the invention relates to a method for regulating the acceleration of a turbomachine comprising a combustion chamber, a high-pressure turbine located downstream of the combustion chamber and driving a high-pressure shaft in rotation, and a low-pressure turbine located downstream of the high-pressure turbine and driving a low-pressure shaft in rotation, characterized in that the method comprises the following steps:

[0007] -Inject mechanical power into the high-pressure shaft until the speed of the high-pressure shaft reaches the target value, then

[0008] - Take mechanical power from the high pressure shaft to keep the speed at the target value.

[0009] This type of regulation method allows to reduce the delay between the acceleration of the high-pressure shaft and the low-pressure shaft. At the beginning of the acceleration phase, power is injected into the high-pressure shaft to help it accelerate, and then the acceleration of the high-pressure shaft is stopped in order to allow a strong acceleration of the low-pressure shaft: the low-pressure shaft then acquires its target speed more quickly than in the prior art. More generally, the duration of acceleration of both the high-pressure shaft and the low-pressure shaft is shorter than in the prior art.

[0010] According to a possible characteristic, the step of extracting mechanical power from the high-voltage shaft is carried out by means of the first electrical machine in generator mode.

[0011] According to a possible characteristic, the step of injecting mechanical power into the high-voltage shaft is carried out by means of the first electric machine in electric motor mode.

[0012] According to a possible characteristic, the method comprises the following step, carried out in parallel with the step of extracting mechanical power from the high-pressure shaft: injecting mechanical power into the low-pressure shaft.

[0013] According to a possible characteristic, the method comprises the following step, carried out in parallel with the step of injecting mechanical power into the high-pressure shaft: mechanical power is taken from the low-pressure shaft.

[0014] According to a possible characteristic, the step of injecting mechanical power into the low-pressure shaft is performed by the second electric machine in electric motor mode, while the step of extracting mechanical power from the low-pressure shaft is performed by the second electric machine in generator mode.

[0015] According to one possible feature, the turbine includes a high-pressure compressor, which is located upstream of the combustion chamber and is driven to rotate by a high-pressure shaft. The method includes the following steps: monitoring the high-pressure compressor by determining a surge parameter of the high-pressure compressor, and if the surge parameter of the high-pressure compressor obtains a threshold value, implementing the step of injecting mechanical power into the high-pressure shaft.

[0016] According to a second aspect, the invention relates to a turbomachine for an aircraft, comprising:

[0017] a high-pressure turbine located downstream of the combustion chamber and connected to the high-pressure shaft;

[0018] a low-pressure turbine, which is located downstream of the high-pressure turbine and is connected to the low-pressure shaft;

[0019] - injection device for injecting mechanical power into the high-pressure shaft;

[0020] - Extraction device for extracting mechanical power from the high-pressure shaft;

[0021] A control system connected to the injection means and to the acquisition means, the control system being configured to implement a method for regulating the acceleration of a turbomachine according to any of the preceding characteristics.

[0022] According to one possible characteristic, the injection means is a first electric machine configured to operate in electric motor mode, and the extraction means is a first electric machine configured to operate in generator mode.

[0023] According to a possible characteristic, the turbomachine comprises a second electric machine connected to the low-pressure shaft and configured to operate in electric motor mode and to inject mechanical power into the low-pressure shaft.

[0024] According to a possible characteristic, the second electric machine is configured to operate in generator mode and to draw mechanical power from the low-pressure shaft. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Other characteristics and advantages of the invention will emerge from the description given hereinafter, which refers to the accompanying drawing which illustrates a non-limiting embodiment thereof.

[0026] [ Figure 1 ] Figure 1 A turbomachine for an aircraft according to a first embodiment is schematically shown.

[0027] [ Figure 2 ] Figure 2 A turbomachine for an aircraft according to a second embodiment is schematically shown.

[0028] [ Figure 3 ] Figure 3 The steps of a method for regulating the acceleration of a turbomachine are schematically shown. DETAILED DESCRIPTION

[0029] Figure 1 A twin-rotor twin-flow aircraft turbomachine 1 is schematically shown, comprising, from upstream to downstream in the airflow direction: a fan 2 , a low-pressure (LP) compressor 3 , a high-pressure (HP) compressor 4 , a combustion chamber 5 , a high-pressure (HP) turbine 6 and a low-pressure turbine 7 .

[0030] The high-pressure turbine 6 is connected to the high-pressure compressor 4 via a high-pressure shaft 8 , while the low-pressure turbine 7 is connected to the low-pressure compressor 3 and the fan 2 via a low-pressure shaft 9 .

[0031] In addition, if Figure 1 and 2 As shown, the turbine 1 may include a reduction gear R, which connects the fan 2 to the low-pressure shaft 9, the reduction gear R thus allowing the rotational speeds of the fan 2 and the low-pressure turbine 9 to be decoupled. However, the invention can also be used for a turbine 1 in which the fan 2 is directly connected to the low-pressure shaft 3 and is therefore directly coupled to the low-pressure turbine 7. However, the invention is more advantageous when the turbine 1 includes a reduction gear R, since the Applicant has noticed that when the turbine 1 includes a reduction gear R, the inertia of the low-pressure rotor increases.

[0032] The turbomachine 1 comprises a first electrical machine 11 connected to the high-voltage shaft 8. The first electrical machine 11 is a reversible machine configured to operate, on the one hand, in generator mode, thereby obtaining mechanical power from the high-voltage shaft 8, and, on the other hand, in electric motor mode, thereby injecting mechanical power into the high-voltage shaft 8. According to another possible variant, the first electrical machine 11 is a generator and is not reversible, in which case it cannot operate as an electric motor.

[0033] like Figure 2As shown, the turbomachine 1 may comprise a second electrical machine 12 connected to the low-pressure shaft 9. The second electrical machine 12 may be an electric motor configured to inject mechanical power into the low-pressure shaft 9. The second electrical machine may be a reversible machine configured to operate, on the one hand, in generator mode, thereby obtaining mechanical power from the low-pressure shaft 9, and, on the other hand, in electric motor mode, thereby injecting mechanical power into the low-pressure shaft 9. According to another possible variant, the second electrical machine 12 is an electric motor and is not reversible, in which case the second electrical machine 12 cannot operate as a generator.

[0034] The turbomachine 1 comprises a control system 13 connected to the first electric machine 11 and the second electric machine 12. The control system 13 is configured to implement a method for regulating the acceleration of the turbomachine 1 so as to reduce the time required for the acceleration of said turbomachine 1. In other words, the method implemented by the control system 13 allows to reduce the delay between the acceleration command and the moment when the turbomachine 1 generates the target thrust. In particular, the method reduces the delay in obtaining the take-off thrust.

[0035] The method for regulating the acceleration of the turbine 1 implemented by the control system 13 comprises the following steps:

[0036] -Inject mechanical power 100 into the high pressure shaft 8 until the speed of the high pressure shaft 8 reaches the target value, then

[0037] - Extracting 200 mechanical power from the high-pressure shaft 8 in order to maintain the speed at the target value by means of the first electric machine 11 .

[0038] Therefore, the first electric machine 11 operating in electric motor mode is commanded by the control system 13 to accelerate the high-voltage shaft 8 until it obtains the target speed. Then, the first electric machine 11 operating in generator mode is commanded by the control system 13 to extract mechanical power from the high-voltage shaft 8 when the high-voltage shaft 8 has obtained the target speed.

[0039] The Applicant has noted the fact that, when the high-pressure rotor of the turbomachine 1 has already achieved the target speed, suppressing the rotation speed of the high-pressure shaft 8 (by extracting mechanical power from the high-pressure shaft) allows the speed increase of the low-pressure rotor of the turbomachine 1 to be accelerated, thus allowing the target thrust to be achieved more quickly. In fact, the rotation speed of the high-pressure shaft 6 is suppressed and additional energy is transferred to the low-pressure shaft 7.

[0040] The control system 13 may use the modified speed of the high pressure shaft 8 to regulate the acceleration of the turbine. The modified speed of the high pressure shaft 8 corresponds to the temperature-weighted rotational speed of the high pressure shaft 8.

[0041] According to an advantageous variant, when said high-pressure shaft 8 has reached the target speed, it also allows reducing the acceleration duration of the low-pressure rotor of the turbine 1 , the mechanical power extracted from the high-pressure shaft 8 being injected into the low-pressure shaft 9 (step 250 ).

[0042] This variation can be achieved by the control system 13 controlling the first motor 11 so that it operates in generator mode and supplies power to the second motor 12, which operates in electric motor mode. A transformer can be located between the first motor 11 and the second motor 12 to adapt the current.

[0043] According to one possible solution, the first electric machine 11 is powered by the battery 14 when it operates in electric motor mode.

[0044] According to another possible solution, the first electric machine 11 is powered by the second electric machine 12 when it operates in electric motor mode, the second electric machine 12 operating in generator mode 12, the second electric machine 12 generating electricity by taking mechanical power from the low-voltage shaft 9 (step 150). The applicant has in fact noted the fact that it is advantageous to ensure first a rapid acceleration of the high-voltage rotor and then of the low-voltage rotor. A transformer can be positioned between the first electric machine 11 and the second electric machine 12 to adapt the current.

[0045] According to one possible variant, allowing to reduce the risk of surges of the high-pressure compressor 4, the control system 13 is configured to implement a step of monitoring the high-pressure compressor 4. This step of monitoring the high-pressure compressor 4 is achieved by determining a surge parameter of the high-pressure compressor and by injecting mechanical power into the high-pressure shaft 8 when said surge parameter of the high-pressure compressor 4 obtains a threshold value. Pumping is a phenomenon by which the direction of the gas flow is reversed due to an excessively high pressure difference between the compressor inlet and the compressor outlet.

[0046] The surge parameter of the high-pressure compressor 4 may be determined based on the pressure ratio of the high-pressure compressor 4, i.e., the ratio between the outlet pressure of the high-pressure compressor 4 and the inlet pressure of the high-pressure compressor 4, and the flow rate of the high-pressure compressor 4. Therefore, the turbomachine 1 may include a first pressure sensor configured to measure the pressure at the inlet of the high-pressure compressor 4, and a second pressure sensor configured to measure the outlet pressure of the high-pressure compressor 4, the first pressure sensor and the second pressure sensor being connected to the control system 13. The turbomachine may also include a flow meter configured to measure the air flow rate in the high-pressure compressor 4, the flow meter being connected to the control system 13.

[0047] Therefore, the fact that the control system 13 is configured to monitor the evolution of the surge parameter and to control the injection of mechanical power into the high-pressure compressor 4 when the parameter value indicates that a surge phenomenon may occur allows reducing the risk of surge.

[0048] This step of monitoring the high-pressure compressor 4 is performed in the whole method and is performed simultaneously with the other steps. When mechanical power is injected into the high-pressure compressor 4, because the surge parameter of the high-pressure compressor 4 has obtained the threshold value, the speed suppression of the high-pressure shaft 8 is temporarily stopped until the surge parameter passes below the threshold value again.

Claims

1. A method for regulating the acceleration of a turbine (1), the turbine (1) comprising a combustion chamber (5), a high-pressure turbine (6) located downstream of the combustion chamber (5) and driving a high-pressure shaft (8) in rotation, and a low-pressure turbine (7) located downstream of the high-pressure turbine (6) and driving a low-pressure shaft (9) in rotation, characterized in that: The method comprises the following steps: - injecting (100) mechanical power into the high pressure shaft (8) until the speed of the high pressure shaft (8) reaches a target value, and then - extracting (200) mechanical power from the high pressure shaft (8) in order to keep the speed at the target value, The steps of extracting mechanical power from the high-voltage shaft and injecting mechanical power into the high-voltage shaft are achieved by using the first electric machine in generator mode for the extracting step and switching the first electric machine to electric motor mode for the injecting step, The method also includes a step of injecting mechanical power into the low-pressure shaft by the second motor (12) in electric motor mode in parallel with the step of acquiring mechanical power from the high-pressure shaft, and also includes a step of switching the second motor to generator mode and acquiring mechanical power from the low-pressure shaft by the second motor in generator mode in parallel with the step of injecting mechanical power into the high-pressure shaft.

2. The method according to claim 1, characterized in that The turbine (1) comprises a high-pressure compressor (4), which is located upstream of the combustion chamber (5) and is driven to rotate by the high-pressure shaft (8). The method comprises the following steps: monitoring the high-pressure compressor (4) by determining a surge parameter of the high-pressure compressor (4), and if the surge parameter of the high-pressure compressor (4) obtains a threshold value, injecting mechanical power into the high-pressure shaft (8).

3. A turbine (1) for an aircraft, comprising: - a high-pressure turbine (6) located downstream of the combustion chamber (5) and connected to a high-pressure shaft (8); - a low-pressure turbine (7) located downstream of the high-pressure turbine (6) and connected to a low-pressure shaft (9); - an injection device (11) for injecting mechanical power into the high-pressure shaft (8); - an acquisition device (11) for acquiring mechanical power from the high-pressure shaft (8); a control system (13) connected to the injection device (11) and to the acquisition device (11), the control system (13) being configured to implement the method for regulating the acceleration of a turbomachine according to claim 1, the injection device is a first electric machine configured to operate in electric motor mode, and the extraction device is the first electric machine configured to operate in generator mode, The turbine also includes a second electric machine connected to the low-pressure shaft and configured to operate in an electric motor mode and inject mechanical power into the low-pressure shaft, and to operate in a generator mode and extract mechanical power from the low-pressure shaft.

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