Abstract:
A device for controlling engine speed of a multi-engine aircraft includes a series of components for automatically controlling the speed of the engines during the take-off, so as to avoid discrepancies in the engine speeds. To this end, as long as all engines of the aircraft do not have, at least at given intermediary moment of the take-off, a driving parameter value equal to a preset intermediate value of the parameter, the speed of all of the engines cannot exceed an intermediate speed associated with the preset intermediate value. Thus, all engines must reach the intermediate speed so that the acceleration to a higher take-off speed can continue simultaneously for all engines.

Description:
TECHNICAL FIELD 
     The present invention relates to a method and a device for controlling engine speed in a multi-engine aircraft during a take-off, as well as an aircraft provided with such a device. 
     Although the present invention is particularly adapted for airplanes provided with turbojets, it is by no way limited to such an application. It could be equally implemented on airplanes provided with turboprop engines. 
     BACKGROUND 
     It is known that such turbojets are controlled by a reliable parameter, referred to as a driving parameter, representative of the thrust level of said turbojets and that there are two kinds of driving parameters, one of them being the ratio Engine Pressure Ratio (“EPR”) between the gas pressure at the outlet and at the inlet of the turbojets and the other one being linked to the speed N 1  of the fan thereof. 
     For a determined turbojet, the nature of the driving parameter, that is the ratio EPR or the speed N 1 , is set by the manufacturer of said turbojet. 
     It is also known that, preliminarily to the take-off, the turbojets are maintained in an idling speed, with which an idling value of a driving parameter EPR or N 1  is associated. 
     Upon the initiation of the take-off, the pilots of the airplane, thru a voluntary action on the throttle lever, progressively increase the speed of the turbojets, from the idling speed, so as to reach a predefined take-off speed a take-off value of the driving parameter is associated with. 
     However, it frequently occurs, during the take-off, that the turbojets of an airplane have not all the same current value of the driving parameter at a given moment, although the corresponding throttle levers are in an identical position. Indeed, the acceleration of the fan from the idling speed is likely to vary according to the turbojets of one single airplane, for instance, because:
         the mechanical parts of the different turbojets are not lubricated identically;   some turbojets of the airplane have been changed, while the other ones are original ones, so that they do not have all the same wear;   the calibration of the idling speed is not uniform between all the turbojets;   etc.       

     This results in an outlet thrust dissymmetry of the turbojets of the airplane able to lead to a side deflection thereof, upon the take-off acceleration, that pilots must imperatively correct. Such a deflection is further even more significant as the speed of the airplane is not very high. 
     Such direction problems generate, for pilots, an additional workload and an additional vigilance upon a take-off already requiring significant attention. 
     Moreover, if the correction implemented by pilots is inappropriate or too much delayed, the take-off could be interrupted, thereby disturbing the traffic on the ground. 
     The aim of the present invention involves overcoming such drawbacks and, more specifically limiting, even removing, the above mentioned direction problems encountered during a take-off. 
     SUMMARY OF THE INVENTION 
     To this end, according to the invention, the method for controlling the engine speed of a multi-engine aircraft during a take-off, wherein a take-off speed is preliminarily determined with which a preset take-off value is associated, being common to all the engines and corresponding to a first particular value of a driving parameter of said engines, is remarkable in that:
         at least one intermediary preset value is preliminarily determined, common to all the engines and corresponding to one second particular value of the driving parameter, said intermediary preset value being strictly lower than the preset take-off value; and   the following steps are automatically carried out:   upon the initiation of the take-off, the speed of said engines increases from an idling speed to an intermediary speed corresponding to the determined intermediary preset value, so that the driving parameter associated with each one of the engines reaches said intermediary preset;   for each one of said engines, the associated current value of the driving parameter is measured;   it is detected whether, for all the engines, the difference between the current value of the driving parameter associated with each one of said engines and the determined intermediary preset value is, in absolute value, at the most equal to a predefined threshold; and   when, for all the engines, said associated difference is at the most equal to said predefined threshold, increasing the engine speed up to the determined take-off speed is continued, so that the driving parameter associated to the latter reaches the preset take-off value.       

     Thus, thanks to this invention, as long as the engines of the aircraft do not have, at least at a given moment of a take-off, a roughly identical driving parameter value (that is the predetermined intermediary preset value), the engine speed cannot exceed the intermediary speed associated with said intermediary preset value. Before resuming the speed increase for reaching the take-off speed, the value of the driving parameter of each one of the engines should be roughly equal to the intermediary preset value. This allows to automatically remove an optional discrepancy of the value of the driving parameter between the engines, able to generate a speed dissymmetry between the engines, before resuming the speed increase. Thereby any risk of a significant side deflection of the aircraft (generated by such a speed dissymmetry) able to require pilots to interfere in order to be corrected, is thus prevented. The pilots&#39; workload is reduced, on the one hand, because controlling the engine speed is carried out automatically upon the take-off and, on the other hand, because this invention nearly completely precludes the risk of a side deflection of the aircraft upon the take-off. 
     In a particular embodiment according to this invention:
         a time-delay with a predefined duration is triggered upon the initiation of the take-off; and   a warning is emitted to the pilots of the aircraft when said difference associated with at least one of the engines remains higher than said threshold after said time-delay has expired.       

     Thus, the pilots can decide to interrupt the take-off if they consider this is necessary, after having been warned. 
     Alternatively or additionally, it is indeed obvious that the take-off could be automatically interrupted, in the case where said difference associated with at least one of the engines would remain higher than said threshold after a time-delay has expired. 
     Furthermore, when the engines are turbojets, the driving parameter associated with the engines could be either the ratio EPR between the gas pressures at the outlet and at the inlet of the engines, or the rotation speed N 1  of the fan of the engines. 
     However, instead of the driving parameter N 1  or EPR, this invention could be similarly implemented using a thrust parameter defined from N 1  and/or from EPR. 
     Preferably, the take-off is initiated when the throttle levers respectively associated with the engines are brought in a position corresponding to the determined take-off speed. 
     Thus, once the controlling levers are in a take-off position, the pilots are normally exempted from any additional handling of the latter, at least until take-off is completed. 
     Advantageously, the detection step could be carried out in a continuous mode during the whole take-off. Any other appropriate detection mode could however be implemented, for instance a detection at predetermined regular intervals. 
     Furthermore, the present invention further relates to a device for controlling the engine speed of a multi-engine aircraft during a take-off including:
         means for receiving at least one preset value, common to all the engines and corresponding to a particular value of the driving parameter;   parameter measurement sensors that measure, for each one of the engines, the associated value of the driving parameter; and   engine speed controllers that control the engine speed, is remarkable in that:   the preset value is an intermediary preset value strictly lower than a take-off preset value corresponding to a predetermined take-off speed;   the device also includes means for detecting whether, for all the engines, the difference between the current value of the driving parameter associated with each one of the engines and the intermediary preset value is, in absolute value, at the most equal to a predefined threshold; and   the engine speed controllers for controlling the engine speed are configured so as to:
           receive an order representative of the predetermined take-off speed;   after the initiation of the take-off, increase the speed of the engines from an idling speed to an intermediary speed corresponding to the determined intermediary preset value, so that the driving parameter associated with each one of the engines reaches the intermediary preset value;   continue the increase of the engine speed up to the predetermined take-off speed, when, for all the engines, the associated difference is at the most equal to the predefined threshold, so that the driving parameter associated therewith reaches the take-off preset value.   
               

     In an embodiment according to this invention, the device also comprises:
         a time-delay device able to trigger, upon the initiation of the take-off, a time-delay of a predefined duration; and   a warning device that emits a warning to the pilots of the aircraft when the difference associated with at least one of the engines remains higher than the threshold after the time-delay has expired.       

     Moreover, the present invention also relates to an aircraft including a controlling device such as described hereinabove. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The FIGS. of the appended drawing will better explain how this invention could be implemented. In these FIGS., like reference numerals relate to like components. 
         FIG. 1  is a block diagram of a device, according to the invention, for controlling the engine speed of a four-engine airplane, shown from the top, during a take-off. 
         FIG. 2  is a graph showing the time evolution of the rotation speed N 1  in the two external engines of the airplane of  FIG. 1 , according to the engine speed applied to the latter during a take-off. 
     
    
    
     DETAILED DESCRIPTION 
     The four-engine airplane AC, schematically shown from the top on  FIG. 1 , comprises a fuselage F and two wings W 1  and W 2 , being symmetrical with respect to said fuselage F. The wing W 1  carries an external engine M 1  and an internal engine M 2 . Similarly, the wing W 2  carries an internal engine M 3  and an external engine M 4 . 
     Each engine M 1  to M 4  is of the double flux turbojet type, but this invention is by no way limited to this example, as explained previously. 
     As is schematically shown on  FIG. 1 , the speed of each engine M 1  to M 4  of the airplane AC could be controlled by means of a specific throttle lever J 1  to J 4  able to occupy any position between a maximum speed position (shown in dashed lines) and an idling position (shown in a full line). 
     Usually, preliminarily to the take-off, the pilots of the airplane AC determine the take-off parameters, and including the take-off speed to be applied (that is the usual speeds FLEX or TOGA), as a function of characteristics of the airplane AC (design, bulk in the empty state, load, etc.), the dimensions and the state of the runway, the meteorological information, etc. 
     With the determined take-off speed there is associated a take-off preset value N 1   d  common to all the engines M 1  to M 4  and corresponding to a particular value of a driving parameter of said engines M 1  to M 4 . 
     As also known, the driving parameter of each one of said engines M 1  to M 4 —such a parameter being representative of the thrust level of the corresponding engine—is either the one known in the aeronautical field as EPR (Engine Pressure Ratio) and being equal to the ratio between the gas pressure at the outlet of the turbine and the gas pressure in the air inlet cowl, or the one known as N 1  and corresponding to the rotation speed of the fan of said engines M 1  to M 4 . 
     In the remainder of the description, only the driving parameter N 1  will be considered. It is obvious that the invention could be implemented similarly with the parameter EPR. 
     In addition, the speed of each one of the engines M 1  to M 4  is controlled, as known, by a controlling electronic calculator EEC 1  to EEC 4  (Electronic Engine Control). Such calculators EEC 1  to EEC 4  associated with the engines M 1  to M 4  each receive an order representative of the engine speed to be applied, transmitted by the associated throttle levers J 1  to J 4  and corresponding to the respective position thereof. The calculators EEC 1  to EEC 4  calculate, more specifically from such received order, the fuel flow rate to be addressed to the engines M 1  to M 4 , respectively. 
     On  FIG. 1 , the throttle levers J 1  to J 4  of the engines M 1  to M 4  and the calculators EEC 1  to EEC 4  are shown outside the airplane AC, while they actually are mounted on board the latter. 
     According to this invention, a device  1  for automatically controlling the engines speed M 1  to M 4  of the airplane AC during a take-off is embedded on board the latter. It is also shown outside the airplane AC for clarity reasons. 
     The controlling device  1  of this invention comprises:
         means  2  for receiving a preliminarily determined intermediary preset value N 1 x (via the link L 1 ), common to all the engines M 1  to M 4  and corresponding to a particular value of the driving parameter N 1 . The intermediary preset value N 1 x is strictly lower than the take-off preset value N 1 d (namely N 1 x&lt;N 1 d). For instance, N 1 x could be equal to 50% of N 1 d;   parameter measurement sensors  3  for continuously measuring, for each one of the engines M 1  to M 4 , the current value of N 1 . For instance, the parameter measurement sensors  3  could comprise one or more rotation speed sensors so as to give the measurement N 1 c 1  to N 1 c 4  of the current rotation speed of the fan of each one of the engines M 1  to M 4 , respectively. Such current values N 1 c 1  to N 1 c 4  could be displayed on screens embedded in the cockpit of the airplane AC, so as to be viewed by the pilots; and   means  4  for detecting whether, for all the engines M 1  to M 4 , the difference d 1  to d 4  between the current value N 1 c 1  to N 1 c 4  associated with each one of the engines and the intermediary preset value N 1 x is, in absolute value, at the most equal to a predefined threshold Th (for instance 1% of N 1 x) (namely |N 1 cj−N 1 x|=dj with j= 1 ,  2 ,  3  or  4 , so that dj&lt;Th). Such means  4  is able to receive the current values N 1 c 1  to N 1 c 4  and the intermediary preset value N 1 x, thru the links L 1  and L 2 ;       

     In addition, the controlling device  1  comprises engine speed controllers  5  for controlling the engine speed M 1  to M 4 , respectively. Such engine speed controllers  5  are able to:
         receive the order representative of the predetermined take-off speed transmitted by the corresponding throttle levers J 1  to J 4  to the engines M 1  to M 4 , via the links L 3 ;   increase, after the take-off has been initiated, the engine speed M 1  to M 4  from an idling speed up to an intermediary speed corresponding to the intermediary preset value N 1 x, so that the driving parameter N 1  associated with each one of the engines M 1  to M 4  reaches N 1 x;   continue increasing the engine speed M 1  to M 4  up to the determined take-off speed, when, for all the engines M 1  to M 4 , the associated difference d 1  to d 4  is at the most equal to the predefined threshold Th, so that the driving parameter N 1  associated with the latter reaches N 1 d.       

     In other words, as long as there is at least one of the differences d 1  to d 4  strictly higher than the threshold Th, the engine speed controllers  5  maintain the speed of the other engines (difference d 1  to d 4  is at the most equal to the threshold Th) in the intermediary speed. There is no increase of the speed for reaching the take-off speed for these engines. 
     In a particular embodiment of this invention shown on  FIG. 1 , the means  2  and engine speed controller  5  associated with each of the engines M 1  to M 4  of the device  1  could be integrated into the electronic controlling calculators EEC  1  to EEC 4 , respectively. 
     According to this invention, the controlling device  1  is activated as soon as the take-off is initiated, that is when the throttle levers J 1  to J 4  associated with the engines M 1  to M 4  are brought in a position corresponding to the determined take-off speed. Thus, once the levers J 1  to J 4  are in a take-off position, it is then no longer required to handle them (except, optionally in the case of an emergency situation) until the end of the take-off (the device  1  automatically managing the engines speed M 1  to M 4 ). 
     Nevertheless, a deactivation device (not shown on the FIGS.) of the controlling device  1  could be provided, so that the pilots are able to manually control the take-off of the airplane AC, in a usual way. 
     Furthermore, according to this invention, the intermediary preset value N 1 x is obtained, preliminarily to the take-off, using the determination device  6 , able to have the form, for instance, of a laptop or of a digital simulator on the ground, whether handled or not by the pilots. The determination device  6  could determine N 1 x from data relative to the characteristics of the airplane AC (design, bulk in the empty state, load, etc.), to the dimensions of the runway, to meteorological information, etc. 
     Although the determination device  6  is shown outside the controlling device  1 , it is obvious that it could, alternatively, be integrated into the latter. Automatically implementing the determination device  6  also remains possible. 
     Furthermore, the controlling device  1  could also comprise:
         a time-delay device  7  able to trigger, upon the initiation of the take-off, a time-delay T of a predefined duration; and   a warning device  8  for emitting a warning to the pilots of the airplane AC, when the difference d 1  to d 4  associated with at least one of the engines M 1  to M 4  remains higher than the threshold Th until the time-delay T has expired. The warning could be visual and/or sound and be spread, for instance, inside the cockpit of the airplane AC.       

     Furthermore,  FIG. 2  illustrates, by way of an example, a diagram showing the time evolution of the parameter N 1  associated with each one of the two external engines M 1  (in solid line) and M 4  (in a dashed line) of the airplane AC (see  FIG. 1 ) depending on the speed engine applied upon a take-off. 
     As shown on  FIG. 2 , although the engines M 1  and M 4  have, in idling speed, different respective rotation speeds N 1   o   1  and N 1   o   4  (as a result, for instance, of a different calibration of the idling speed), namely N 1   o   1 &gt;N 1   o   4 , these converge, thanks to this invention, to a same intermediary value Nix (moment ti). 
     Indeed, the fan of M 1 , having a rotation speed N 1   o   1  higher than that N 1   o   4  of the fan of M 4 , more rapidly reaches the speed N 1   x . However, thanks to this invention, it remains maintained at this speed N 1   x  (the speed of M 1  is stabilized at the intermediary speed associated with N 1   x ) whereas the speed of the fan of M 4  continues its acceleration so as to reach Nix. Once the latter has also reached Nix (moment ti), the fans of M 1  and M 4  roughly have the speed (namely N 1   x ) and increasing the speed of M 1  and M 4  could then be continued so as to achieve the take-off speed. 
     As illustrated on  FIG. 2 , after continuing to increase the speed of M 1  to M 4  (moment ti) beyond the intermediary speed, the speeds of the fans of the latter roughly remain identical until they reach the value N 1   d . The speed difference between M 1  and M 4 , existing preliminarily to the moment ti, has thus completely disappeared after this moment (without pilots being involved), eliminating any risk of thrust dissymmetry at the outlet of the engines M 1  and M 4 . 
     Furthermore, the present invention could also implement, not a single one, but two or more intermediary preset values N 1   x . In such a case, increasing the engine speed occurs through successive levels (there are as many intermediary levels as intermediary preset values being implemented). 
     In addition, this invention could also be implemented so that it only applies to external engines of a four-engine airplane.