Power distribution device between an electric starter and an electric machine towards a shaft of a turbomachine

Abstract

A power distribution device between an electric starter of a turbomachine and an electric machine toward a shaft of the turbomachine, including the electric starter, the electric machine, and a controller for controlling the electric machine. An epicyclic train reducer includes a first element intended to be coupled to the shaft, a second element coupled to the electric starter, and a third element intended to be rotated by the electric machine. The controller is configured to rotate the third of the three elements so as to obtain two bearings of reduction ratios of the speeds between the first of said three elements and the second of the three elements. The controller is configured to drive the torque of the third of the three elements in accordance with a determined output torque.

Claims

1. A power distribution device between an electric starter of a turbomachine and an electric machine toward a high pressure shaft of the turbomachine, comprising: the electric starter, the electric machine, means for controlling the speed of said electric machine, an epicyclic train reducer comprising three elements, a central sun gear, an outer ring gear and a planet carrier whose planet gears mesh with said sun gear and said ring gear, said three elements being rotatable about an axis of the reducer, a first of said three elements being intended to be coupled to the high pressure shaft, a second of said three elements being coupled to the electric starter, a third of said three elements being intended to be driven in rotation by the electric machine, wherein the controlling means are configured to rotate the third of said three elements so as to obtain two bearings of reduction ratios of the speeds between the first of said three elements and the second of said three elements, and wherein the controlling means are configured to drive the torque of the third of said three elements in accordance with a determined output torque.

2. The power distribution device according to claim 1, comprising at least one inverter arranged upstream of the electric starter and the electric machine.

3. The power distribution device according to claim 1, wherein the first of said three elements is the planet carrier, the second of said three elements is the sun gear, and the third of said three elements is the ring gear.

4. The power distribution device according to claim 1, wherein the first of said three elements is the planet carrier, the second of said three elements is the ring gear, and the third of said three elements is the sun gear.

5. An aircraft turbomachine comprising a shaft and a power distribution device according to claim 1, and wherein the first of said three elements is coupled to the shaft.

6. The turbomachine according to claim 5, wherein the shaft is a high pressure shaft.

7. A method of regulating the speed of an electric machine of a power distribution device, according to claim 1, in a turbomachine of an aircraft, comprising a step of modifying the speed of the third of the three elements by driving the electric machine by controlling means so as to obtain two bearings of reduction ratios of the speeds between the first of said three elements and the second of said three elements, and a step of driving the torque of the third of said three elements as a function of a determined output torque.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) The present invention shall be better understood and other details, characteristics and advantages of the present invention shall appear more clearly on reading the description of a non-limiting example which follows, with reference to the annexed drawings on which:

(2) FIG. 1 represents very schematically a pneumatic starter of a turbomachine according to the prior art;

(3) FIG. 2 represents a graph of the speed of a high-pressure shaft of a turbomachine as a function of time for a turbomachine according to the prior art;

(4) FIG. 3 represents a graph of the torques on a high-pressure shaft as a function of the rotational speed of the high-pressure shaft during a starting for a turbomachine according to the prior art;

(5) FIG. 4 represents a very schematic representation of a part of a turbomachine comprising a power distribution device according to the invention;

(6) FIGS. 5a, 5b and 5c represent exploded views and a diagram of a epicyclic train reducer of a power distribution device according to the invention;

(7) FIGS. 6a and 6b very schematically represent a power distribution device according to a first embodiment of the invention;

(8) FIG. 7 very schematically represents a power distribution device according to a second embodiment of the invention;

(9) FIG. 8 represents a graph of the torques on a high-pressure shaft of a turbomachine as a function of the speed for a turbomachine according to the prior art;

(10) FIG. 9 represents a graph of the torques on a high pressure shaft of a turbomachine as a function of the speed for a turbomachine according to the invention; and

(11) FIGS. 10a and 10b represent very schematically a turbomachine of an aircraft in which the bowed rotor phenomenon occurs.

(12) The elements having the same functions in the different implementations have the same references in the figures.

DETAILED DESCRIPTION OF THE INVENTION

(13) FIG. 4 shows a part of a turbomachine 30 comprising a power distribution device 40.

(14) The turbomachine 30 comprises an accessory gear box 32 which is configured to be driven by an engine shaft. The accessory gear box 32 may comprise multiple gear trains connected to output shafts to drive various equipment.

(15) The turbomachine 30 also comprises an engine 36 with a high-pressure shaft 34.

(16) The power distribution device 40 comprises an electric starter 42. An electric starter is a device intended to assist in starting the turbomachine. The electric starter provides electrical energy to drive the turbomachine during the starting phases. The operation of an electric starter is self-sustaining, but the electric starter generally cannot start itself, unlike an electric motor.

(17) The electric starter 42 has a mass, noted M, and is characterized by a maximum torque, noted Cmax.

(18) The shaft 44 of the electric starter 42 is connected to the high-pressure shaft 34 of the engine 36 of the turbomachine 30 via the accessory gear box 32, and in particular via gears 38 of the accessory gear box 32. The electric starter 42 comprises a clutch 45 configured to disengage the shaft 44 of the starter from the engine 36 of the turbomachine 30 beyond a certain high-pressure rpm.

(19) The accessory gear box 32 generally makes the connection between the engine shaft and the electric starter 42, which can be used to drive the turbomachine during starting phases or to generate an electric current when the turbomachine is started.

(20) Turbomachine 30 also comprises an electric machine 46. The electric machine 46 can be an electric motor. An electric motor is a device for converting an electrical energy into mechanical energy. The electric machine 46 can be of low power.

(21) The input power, represented by the arrow P, is divided between the electric machine 46 and the starter 42.

(22) The turbomachine 30 may comprises at least one power electronics element, e.g. an inverter, arranged upstream of the electric starter 42 and the electric machine 46. For example, in FIG. 4, an inverter 48a receives part of the input power P and transfers it to the electric machine 46, and an inverter 48b receives the other part of the input power P and transfers it to the electric starter 42.

(23) The turbomachine 30 may comprise an electrical source 60 configured to supply power to the power electronics element, e.g. inverters 48a, 48b, and thus the electric machine 46 and the electric starter 42. The electric source 60 may be the aircraft electrical system or a dedicated battery.

(24) The turbomachine 30 also comprises means for controlling the speed of the electric machine.

(25) The turbomachine 30 also comprises an epicyclic gear train reducer 50. The properties of the epicyclic train reducer 50 are used to adapt the torque between the starter 42 and the high pressure shaft 34.

(26) The FIGS. 5a, 5b and 5c show an epicyclic gear train reducer 50.

(27) The epicyclic train reducer 50 comprises a sun gear 52A, also called an internal sun gear, arranged to rotate about the axis of the reducer at a rotational speed, noted ωA, and a planet carrier 52U arranged to rotate about the axis of the reducer at a rotational speed, noted ωU.

(28) The epicyclic train reducer 50 also comprises planet gears 52S which mesh with the central sun gear 52A and are carried by a planet carrier 52U.

(29) The epicyclic train reducer 50 also comprises an outer ring gear 52B, also known as an outer sun gear, which is arranged to rotate about the axis of the reducer at a rotational speed, noted ωB, and with which the planet gears 52S also mesh.

(30) In the epicyclic train reducer 50, the three elements, namely the central sun gear 52A, the planet carrier 52U and the ring gear 52B, are rotatable about the axis of the reducer. For example, the ring gear 52B is free to rotate inside a fixed housing 52C which is configured to protect the reducer 50.

(31) The operation of epicyclic train reducer 50 is governed by the Willis formula. It is a two-degree-of-freedom mechanism, in which the knowledge of the rotational speeds of two elements among the central sun gear 52A, the planet carrier 52U and the ring gear 52B, allows the calculation of the rotational speed of the third element.

(32) The Willis formula is expressed by the following equations:

(33) $\begin{array}{cc}\frac{\omega B-\omega U}{\omega A-\omega U}=k& \left[\mathrm{Math}2\right]\end{array}$
with ωA the rotational speed of the central sun gear 52A, ωU the rotational speed of the planet carrier 52U, ωB the rotational speed of the ring gear 52B, and the factor k, also called the ratio, a constant determined by the geometry of the gears.
For the reducer in FIG. 5, the factor k complies with the following equation:

(34) $\begin{array}{cc}k={\left(-1\right)}^p\frac{{\Pi }_i{Z}_i}{{.Math.}_j{Z}_j}& \left[\mathrm{Math}3\right]\end{array}$
where p is the number of external contacts with the gears, .sub.iZ.sub.i is the product of the number of teeth of the gears that drive, .sub.jZ.sub.j is the product of the number of teeth of the gears that are driven, Z.sub.i is the number of teeth of the gears that drive and Z.sub.j is the number of teeth of the gears that are driven. The factor k is therefore negative with a modulus of less than 1.

(35) The high pressure shaft 34 is coupled to one of the three elements of the reducer 50, the starter 42 is coupled to a second element of the reducer 50, and the electric machine 46 is coupled to the third element of the reducer 50 to drive the rotational speed of the latter.

(36) The accessory gear box 12 can be coupled to the first of the three elements of reduction box 50, the accessory gear box 12 being connected to the high pressure shaft 34.

(37) In order to obtain a variation of the rotation speed of the reduction ratio of the torque between the starter and the high pressure shaft, at a constant input power between the starter and the electric machine, the rotation speed of the third element of the reducer 50 can be varied.

(38) According to the invention, the controlling means are configured to rotate the third of said three elements so as to change the speed reduction ratio between the first of said three elements and the second of said three elements, i.e. to obtain two reduction ratio bearings of the speeds between the first of said three elements and the second of said three elements.

(39) In other words, the controlling means are configured to drive the electric machine 46 so as to obtain two reduction ratio bearings of the speeds between the starter 42 and the high pressure shaft 34.

(40) For example, the controlling means can be configured to drive the electric machine 46 so as to obtain two reduction ratio bearings of the speeds between the starter 42 and the accessory gear box 12, the latter being connected to the high pressure shaft 34.

(41) Six kinematic combinations are possible for positioning the three pieces of equipment, namely the high pressure shaft 34, the electric machine 46 and the starter 42, in relation to the three elements of the epicyclic train reducer 50.

(42) The combinations are listed in the table below. This table also shows the gear train ratio k as a function of rotation speeds ωA, ωB, ωU of the corresponding elements of the epicyclic train reducer 50 in the configuration.

(43) TABLE-US-00001 TABLE 1 Ratio of the epicyclic gear Starter 42 connected to the planet carrier 52U 1A Electric machine 46 connected to the ring gear 52B High pressure shaft 34 connected to the sun gear 52A $\frac{\omega A}{\omega U}=1-k$ 1B Electric machine 46 connected to the sun gear 52A High pressure shaft 34 connected to the ring gear 52B $\frac{\omega B}{\omega U}=\frac{k-1}{k}$ Starter 42 connected to the ring gear 52B 2A Electric machine 46 connected to the planet carrier 52U High pressure shaft 34 connected to sun gear 52A $\frac{\omega A}{\omega B}=k$ 2B Electric machine 46 connected to the sun gear 52A High pressure shaft 34 connected to the planet carrier 52U $\frac{\omega U}{\omega B}=-\frac{k}{1-k}$ Starter 42 connected to the sun gear 52A 3A Electric machine 46 connected to the ring gear 52B High pressure shaft 34 connected to the planet carrier 52U $\frac{\omega U}{\omega A}=\frac{-1}{k-1}$ 3B Electric machine 46 connected to the planet carrier 52U High pressure shaft 34 connected to the ring gear 52B $\frac{\omega B}{\omega A}=\frac{1}{k}$

(44) The torques delivered by the high-pressure shaft 34, the electric machine 46 and the starter 42 are connected by a balance expression of the gear.

(45) In particular, a study of the reducer 50 gives the following balance relationship of the train and power balance relationship:
CA+CB+CU=0  [Math 4]
ωA×CA+ωB×CB+ωU×CU=0  [Math 5]
with CA the torque acting on the sun gear 52A, CB the torque acting on the ring gear 52B, CU the torque acting on the planet carrier 52U, ωA the rotational speed of the central sun gear 52A, ωB the rotational speed of the ring gear 52B and ωU the rotational speed of the planet carrier 52U.

(46) The FIGS. 6a and 6b show the configuration 3A in which the high pressure shaft 34, and thus the accessory gear box 32, is connected to the planet carrier 52U, the electric starter 42 is connected to the sun gear 52A, and the electric machine 46 is connected to the ring gear 52B.

(47) The FIG. 7 shows the configuration 2B in which the high pressure shaft 34 is connected to the planet carrier 52U, the electric starter 42 is connected to the ring gear 52B, and the electric machine is connected to the sun gear 52A.

(48) The configuration 3A allows to minimize the maximum torque of the electric machine 46, but requires the electric machine 46 to operate at a higher maximum speed than with the configuration 2B.

(49) According to the prior art, i.e. without a power distribution device, with a reduction ratio K, for example equal to 2.8, between the starter and the high-pressure shaft of the turbomachine, a starter of mass M and torque Cdnnax with an input power, noted Pmax, is capable of developing at the high-pressure shaft of the turbomachine a maximum torque, noted Co, equal to Cdnnax*K, with the torque profile as a function of speed shown in FIG. 8.

(50) The FIG. 8 shows a graph of the torques on a high pressure shaft, noted CHP, of a turbomachine as a function of the speed of the high pressure shaft, noted v. On this graph, curves a and e represent the resistive torque, i.e. the sum of the Cmot and Caccess torques, respectively at ambient temperature, e.g. 20° C., and at low temperature, e.g. −40° C.; the curve c represents the inertial torque, i.e. the torque unbalance; the curves b and d represent the torque to be delivered by the starter, respectively at ambient temperature and low temperature. On this graph, the point P1 indicates ignition of the engine, the point P2 indicates the autonomy of the turbomachine, the point P3 indicates the starter cut-off and the point P4 indicates engine rpm at idle. In the FIG. 8, the area A corresponds to the period of time when only the starter is running; and the area B corresponds to the period of time when the starter and the engine are running at the same time.

(51) With this profile, the input power, represented by the curve b, is increasing and becomes constant from the ignition, i.e. after the point P1. This profile corresponds to the requirements of the turbomachine at ambient temperature. The low-temperature torque profile, represented by the curve d, requires a higher maximum torque at the beginning of the starting which is Cdnnax*K*1.45 up to approx. 10% of the maximum speed of the turbomachine.

(52) With the power distribution device according to the invention, for each speed of the output shaft of the turbomachine, the electrical power is distributed between the electric starter and the electric machine in order to develop the maximum torque at the shaft of the turbomachine.

(53) The FIG. 9 shows a graph of the torque on the high-pressure shaft, noted CHP, of the turbomachine as a function of the speed of the high-pressure shaft, noted v. On this graph, the curve d represents the torque to be delivered by the starter at low temperature; the curve f represents the power of the engine; the curve g represents the starter power; the curve h represents the resulting power curve; the curve i represents the curve of the resulting torque; and the lines j1 and j2 represent the reduction ratio K between the high-pressure shaft and the starter. In the FIG. 9, the area C corresponds to a phase where the starter is active and the engine is passive with a power of 0 kW. The zone D corresponds to a phase where the starter is active with a power less than 62 kW and where the engine is active with a power less than 10 kW. The zone E corresponds to a phase where the starter is active with a power less than 50 kW and where the engine is active with a power less than 15 kW to 20 kW. In this graph the maximum power Pmax is equal to 72 kW.

(54) The torque ratio passes from a value K1 equal to 2.8 (line j1) at high speed to a value K2 equal to 4 (line j2) at low speed from the ignition, i.e. at 20% of the maximum speed of the turbomachine.

(55) This increase in the torque ratio K2/K1 of 1.4 at low rpm makes it possible to reach the maximum torque required at low temperature at the beginning of the starting. This maximum torque can be maintained up to about 15% of the maximum speed of the turbomachine. The maximum power is therefore taken from 15% of the maximum speed of the turbomachine. This maximum power is then distributed between the starter and the electric machine from this speed of 15% to 100% of the speed of the turbomachine in order to maintain the reduction ratio K1 so as not to exceed the maximum speed of the starter.

(56) In the FIG. 9, there is a phase at ratio K2 with zero electric power to the electric machine at zero speed and electric power powering the starter; and a phase at ratio K1 with maximum power distributed between the starter and the electric machine.

(57) For the device in the FIG. 6, at 10% of the speed, i.e. at 2000 rpm, with a torque of 248 Nm, the input power is 52 kW. The reduction ratio K2 is equal to 4.

(58) The power received by the electric machine 46 is 0 kW. The torque transmitted by electric machine 46 is 27 Nm, and its speed is therefore 0 rpm.

(59) The power transmitted by the ring gear 52B is 0 kW. The reduction ratio KB of the ring gear 52B is 7. The torque transmitted by the ring gear 52B is 187 Nm, so its speed is 0 rpm.

(60) The power received by the electric starter 42 is 52 kW. The torque transmitted by the electric starter 42 is 62 Nm, and its rotational speed is 8000 rpm.

(61) The power transmitted to the high-pressure shaft 34 is 52 kW. The torque transmitted to the high-pressure shaft 34 is 248 Nm, and its rotational speed is 2000 rpm.

(62) For the device in the FIG. 6, at 35% of the speed, i.e. at 7000 rpm, with a torque of 98 Nm, the input power is 72 kW. The reduction ratio K2 is equal to 2.8.

(63) The power received by the electric machine 46 is 8 kW. The torque transmitted by the electric machine 46 is 10 Nm, and its rotational speed is 7000 rpm.

(64) The power transmitted by the ring gear 52B is 8 kW. The reduction ratio KB of the ring gear 52B is 7. The torque transmitted by the ring gear 52B is 74 Nm, and its rotational speed is 1000 rpm.

(65) The power received by the electric starter 42 is 64 kW. The torque transmitted by the electric starter 42 is 24 Nm, and its rotational speed is 25000 rpm.

(66) The power transmitted to the high pressure shaft 34 is 72 kW. The torque transmitted to the high-pressure shaft 34 is 98 Nm, and its rotational speed is 7000 rpm.

(67) For the device in the FIG. 7, at 10% of the speed, i.e. at 2000 rpm, with a torque of 241 Nm, the input power is 50 kW. The reduction ratio K1 is equal to 2.2 and the reduction ratio K2 is equal to 2.8.

(68) The power received by the electric machine 46 is 0 kW. The torque transmitted by the electric machine 46 is 31 Nm, so its speed is 0 rpm.

(69) The power transmitted by the planetary gear 52A is 0 kW. The torque transmitted by the planetary gear 52A is 68 Nm, so its rotational speed is 0 rpm.

(70) The power received by the electric starter 42 is 50 kW. The torque transmitted by electric starter 42 is 62 Nm, and its rotational speed is 7753 rpm.

(71) The power transmitted by the ring gear 52B is 50 kW. The torque transmitted by ring gear 52B is 173 Nm, and its rotational speed is 2770 rpm.

(72) The power transmitted to high-pressure shaft 34 is 50 kW. The torque transmitted to the high-pressure shaft 34 is 241 Nm, and its rotational speed is 2000 rpm.

(73) The invention also relates to a method of regulating the speed of an electric machine 46 of a turbomachine 30 as described above.

(74) The method comprises a step of changing the speed of the third of the three elements by driving the electric machine 46 by means of the controlling means so as to modulate the speed reduction ratio between the first of said three elements and the second of said three elements in a discontinuous manner. Specifically, the method comprises a step of changing the speed of the third of the three elements by driving the electric machine 46 by means of the controlling means so as to obtain two bearings of reduction ratios of the speeds between the first of said three elements and the second of said three elements.

(75) In particular, the speed of the electric machine 46 is adapted so that the speed reduction ratio between the starter 42 and the high pressure shaft 34 varies in a discontinuous manner. Preferably, the speed of the electric machine 46 is adapted so that the speed reduction ratio between the starter 42 and the high-pressure shaft 34 is high at low rpm and is low at high rpm of the turbomachine 30.

(76) The method comprises a step of driving the torque of the third of said three elements as a function of a determined output torque, i.e. the output torque to be achieved.