Patent Publication Number: US-2022231577-A1

Title: Method for regulating the acceleration of a turbomachine

Description:
TECHNICAL FIELD 
     The present invention relates to the general field of turbomachines for aircraft. 
     PRIOR ART 
     Generally, a turbomachine for aircraft comprises a high-pressure shaft (HP shaft) driven in rotation by a high-pressure turbine (HP) turbine, and a low-pressure shaft (LP shaft) driven in rotation by a low-pressure (LP) turbine, the low-pressure shaft driving in rotation a fan of the turbomachine. 
     During an acceleration phase of the turbomachine, a lag can occur between the high-pressure (HP) shaft and the low-pressure (LP) shaft of the turbomachine in attaining the target rotation speed. Indeed, the applicant has noted that the low-pressure shaft tends to accelerate less quickly than the high-pressure shaft, and thus the low-pressure shaft reaches its target rotation speed later than the high-pressure shaft. The applicant has noticed that the delay in the acceleration of the low-pressure shaft increases strongly when a reduction gear is placed between the low-pressure shaft and the fan. 
     The delay in the acceleration of the low-pressure shaft causes a delay in the acceleration of the fan, thus increasing the period between the acceleration command and the moment when the target thrust is obtained. 
     DISCLOSURE OF THE INVENTION 
     The present invention therefore has as its goal to supply a solution responding the problem previously described. 
     According to a first aspect, the invention relates to a method for regulating an acceleration of a turbomachine, the turbomachine comprising a combustion chamber, a high-pressure turbine located downstream of the combustion chamber and which drives a high-pressure shaft in rotation, and a low-pressure turbine located downstream of the high-pressure turbine and which drives a low-pressure shaft in rotation, characterized in that the method comprises the following steps:
         Injecting mechanical power onto the high-pressure shaft until a speed of the high-pressure shaft attains a target value, then   Extracting mechanical power from the high-pressure shaft so as to maintain the speed at the target value.       

     A regulation method of this type allows reducing 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 onto the high-pressure shaft to help it to accelerate, then the acceleration of the high-pressure shaft is stopped so as to allow a strong acceleration of the low-pressure shaft: the low-pressure shaft then attains its target speed more rapidly than in the prior art. More generally, the duration of acceleration of the high-pressure shaft and of the low-pressure shaft are both shorter than in the prior art. 
     According to one possible feature, the step of extracting mechanical power from the high-pressure shaft is accomplished by means of a first electrical machine in the electrical generator mode. 
     According to one possible feature, the step of injecting mechanical power onto the high-pressure shaft is accomplished by the first electrical machine in the electrical motor mode. 
     According to one possible feature, the method comprises the following step, accomplished in parallel with the step of extracting mechanical power from the high-pressure shaft: injecting mechanical power onto the low-pressure shaft. 
     According to one possible feature, the method comprises the followings step, accomplished in parallel with the step of injecting mechanical power onto the high-pressure shaft: extracting mechanical power from the low-pressure shaft. 
     According to one possible feature, the step of injecting mechanical power onto the low-pressure shaft is accomplished by a second electrical machine in the electric motor mode, and the step of extracting mechanical power from the low-pressure shaft is accomplished by said second electrical machine in the electrical generator mode. 
     According to one possible feature, the turbomachine comprises a high-pressure compressor which is located upstream of the combustion chamber and which is driven in rotation by the high-pressure shaft, the method comprising the following step: monitoring the high-pressure compressor by determining a surging parameter of the high-pressure compressor, the step of injecting mechanical power onto the high-pressure shaft being accomplished if the surging parameter of the high-pressure compressor attains a threshold value. 
     According to a second aspect, the invention relates to a turbomachine for aircraft comprising:
         a high-pressure turbine which is located downstream of a combustion chamber and which is connected to a high-pressure shaft;   a low-pressure turbine which is located downstream of the high-pressure turbine and which is connected to a low-pressure shaft;   a device for injecting mechanical power onto the high-pressure shaft;   a device for extracting mechanical power from the high-pressure shaft;   a control system which is connected to the injection device and to the extraction device, the control system being configured to implement the method for regulating the acceleration of the turbomachine according to any one of the preceding features.       

     According to one possible feature, the injection device is a first electrical machine configured to operate in the electric motor mode, and the extraction device is the first electrical machine configured to operate in the electrical generator mode. 
     According to one possible feature, the turbomachine comprises a second electrical machine which is connected to the low-pressure shaft and which is configured to operate in the electric motor mode and to inject mechanical power onto the low-pressure shaft. 
     According to one possible feature, the second electrical machine is configured to operate in the electrical generator mode and to extract mechanical power from the low-pressure shaft. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other features and advantages of the present invention will be revealed by the description given below, with reference to the appended drawings which illustrate one embodiment of it devoid of any limiting character. 
         FIG. 1  shows schematically a turbomachine for aircraft according to a first embodiment. 
         FIG. 2  shows schematically a turbomachine for aircraft according to a second embodiment. 
         FIG. 3  shows schematically the steps of a method for regulating the acceleration of a turbomachine. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
       FIG. 1  illustrates schematically an aircraft two spool, double flow turbomachine  1  comprising, from upstream to downstream in the flow direction of the air flow, 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 (LP) turbine  7 . 
     The high-pressure turbine  6  is connected to the high-pressure compressor  4  by a high-pressure shaft  8 , and the low-pressure turbine  7  is connected to the low-pressure turbine  3  and to the fan  2  by a low-pressure shaft  9 . 
     In addition, as illustrated in  FIGS. 1 and 2 , the turbomachine  1  can comprise a reduction gear R which connects the fan  2  to the low-pressure shaft  9 , the reduction gear R thus allowing decoupling the rotation speeds of the fan  2  and of the low-pressure turbine  9 . However, the invention can also be used for a turbomachine  1  in which the fan  2  is directly connected to the low-pressure shaft  3 , and is thus directly coupled to the low-pressure turbine  7 . The invention is however more advantageous when the turbomachine  1  comprises a reduction gear R, the Applicant having noted that the inertia of the low-pressure spool is increased when the turbomachine  1  comprises a reduction gear R. 
     The turbomachine  1  comprises a first electrical machine  11  which is connected to the high-pressure shaft  8 . The first electrical machine  11  is a reversible machine which is configured to, on the one hand, operate in the electrical generator mode and thus extract mechanical power from the high-pressure shaft  8 , and on the other hand to operate in the electric motor mode and thus inject mechanical power onto the high-pressure shaft  8 . According to another possible variant, the first electrical machine  11  is an electrical generator and is not reversible, said first electrical machine  11  not being able to operate as an electric motor in this variant. 
     As illustrated in  FIG. 2 , the turbomachine  1  can comprise a second electrical machine  12  which is connected to the low-pressure shaft  9 . The second electrical machine  12  can be an electric motor which is configured to inject mechanical power onto the low-pressure shaft  9 . The second electrical machine can be a reversible machine which is configured, on the one hand, to operate in the electrical generator mode and thus extract mechanical power from the low-pressure shaft  9 , and on the other hand to operate in the electric motor mode and thus inject mechanical power onto the low-pressure shaft  9 . According to another possible variant, the second electrical machine  12  is an electric motor and is not reversible, said second electrical machine  12  not being able to operate as an electrical generator in this variant. 
     The turbomachine  1  comprises a control system  13  which is connected to the first electrical machine  11  and to the second electrical machine  12 . The control system  13  is configured to implement a method for regulating the acceleration of the turbomachine  1  in order to reduce the time taken by said turbomachine  1  to accelerate. In other words, the method implemented by the control system  13  allows reducing the delay between the acceleration command and the moment when the turbomachine  1  generates the target thrust. The method allows in particular reducing the delay in attaining takeoff thrust. 
     The method of regulating the acceleration of the turbomachine  1  implemented by the control system  13  comprises the following steps:
         Injecting  100  mechanical power onto the high-pressure shaft  8  until a speed of the high-pressure shaft  8  reaches a target value, then   Extracting  200  mechanical power from the high-pressure shaft  8  so as to maintain the speed at the target value by the same electrical machine  11 .       

     The first electrical machine  11 , operating in the electric motor mode, is thus commanded by the control system  13  to accelerate the high-pressure shaft  8  until it attains the target speed. Then the first electrical machine  11 , operating in the electrical generator mode, is commanded by the control system  13  to extract mechanical power from the high-pressure shaft  8  when the high-pressure shaft  8  has attained the target speed. 
     The Applicant has taken notice of the fact that curbing the rotation speed of the high-pressure shaft  8  when the high-pressure spool of the turbomachine  1  has attained the target speed (by extracting mechanical power from the high-pressure shaft) allows accelerating the speed increase of the low-pressure spool of the turbomachine  1  and thus allows obtaining the target thrust more rapidly. In fact, the rotation speed of the high-pressure shaft  6  being curbed, additional energy is transmitted to the low-pressure shaft  7 . 
     The control system  13  can regulate the acceleration of the turbomachine by using the corrected speed of the high-pressure shaft  8 . The corrected speed of the high-pressure shaft  8  corresponds to the temperature-weighted rotation speed of the high-pressure shaft  8 . 
     According to one advantageous variant allowing further reducing the duration of acceleration of the low-pressure spool of the turbomachine  1 , when said high-pressure shaft  8  has attained the target speed, the mechanical power extracted from the high-pressure  8  is injected onto the low-pressure shaft  9  (step  250 ). 
     This variant can be implemented by the control system  13  which controls the first electrical machine  11  so that it operates in the electrical generator mode and supplies the second electrical machine  12 , which operates in the electric motor mode, with electricity. A transformer can be located between the first electrical machine  11  and the second electrical machine  12  in order to adapt the electrical current. 
     According to one possible solution, the first electrical machine  11  is supplied with electricity by a battery  14  when it operates in the electric motor mode. 
     According to another possible solution, the first electrical machine  11  is supplied with electricity when it operates in the electric motor mode by the second electrical machine  12  which operates in the electrical generator mode  12 , the second electrical machine  12  generating electricity by extracting mechanical power from the low-pressure shaft  9  (step  150 ). The Applicant has in fact taken notice of the fact that it is advantageous to first ensure rapid acceleration of the high-pressure spool, then of the low-pressure spool. A transformer can be positioned between the first electrical machine  11  and the second electrical machine  12  in order to adapt the electrical current. 
     According to one possible variant allowing reducing the risk of surging 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 accomplished by determining a surging parameter of the high-pressure compressor and by injecting mechanical power onto the high-pressure shaft  8  when said pumping parameter of the high-pressure compressor  4  attains a threshold value. Pumping is the phenomenon by which a reversal of the direction of the flow of air occurs due to too high a pressure difference between the inlet of the compressor and the outlet of the compressor. 
     The surging parameter of the high-pressure compressor  4  can be determined based on the pressure ratio of said high-pressure compressor  4 , i.e. the ratio between the outlet pressure of the high-pressure compressor  4  and the inlet pressure of said high-pressure compressor  4 , and on the flow rate of said high-pressure compressor  4 . The turbomachine  1  can therefore comprise a first pressure sensor which is configured to measure the pressure at the inlet of the high-pressure compressor  4 , as well as a second pressure sensor which is 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 can also comprise a flow rate meter which is configured to measure the flow rate of air in the high-pressure compressor  4 , said flow rate meter being connected to the control system  13 . 
     Thus, the fact that the control system  13  is configured to monitor the evolution of the surge parameter and control the injection of mechanical power into the high-pressure compressor  4  when the value of the parameter indicates that a surge phenomenon is likely to occur, allows reducing the risk of surging. 
     This step of monitoring the high-pressure compressor  4  is accomplished throughout the method and simultaneously with the other steps. When mechanical power is injected into the high-pressure compressor  4  because the surge parameter of said high-pressure compressor  4  has attained the threshold value, the curbing of the speed of the high-pressure shaft  8  is temporarily stopped until the surge parameter again passes below the threshold value.