Auxiliary drive system for a helicopter

Abstract

A drive system for a helicopter includes a main drive for driving a rotor the helicopter, a flywheel mass battery including at least one flywheel, a first transmission coupling the flywheel mass battery with the main drive such that, during operation of the main drive, output can be transferred from the main drive to the flywheel mass battery, and a second, variable transmission connecting the flywheel mass battery to the rotor of the helicopter such that a predetermined output can be transferred to the rotor through adjustment of a transmission ratio of the variable transmission.

Claims

1. A helicopter with a drive system, comprising: a main drive configured to drive a lift-generating rotor of the helicopter; a flywheel mass battery comprising at least one flywheel; a first transmission coupling the flywheel mass battery to the main drive such that, during operation of the main drive, output is transferred from the main drive to the flywheel mass battery; a second, variable transmission connecting the flywheel mass battery to the lift-generating rotor of the helicopter such that a predetermined output is transferred to the lift-generating rotor through adjustment of a transmission ratio of the variable transmission; and a main transmission between the main drive and the lift-generating rotor, wherein the main transmission comprises a first input with which the main drive is coupled, wherein the main transmission has a second input with which the flywheel mass battery is coupled via the variable transmission.

2. The helicopter with a drive system of claim 1, wherein the variable transmission is a continuously variable transmission.

3. The helicopter with a drive system of claim 1, wherein the variable transmission is electrically controlled.

4. The helicopter with a drive system of claim 1, wherein the first transmission is a transmission with a fixed transmission ratio.

5. The helicopter with a drive system of claim 1, further comprising: a freewheel unit between the first transmission and the main drive.

6. The helicopter with a drive system of claim 1, further comprising: an auxiliary drive shaft via which the variable transmission is coupled with the second input of the main transmission, wherein the auxiliary drive shaft is coupled via a freewheel unit with the main transmission.

7. The helicopter with a drive system of claim 1, further comprising: a drive shaft via which the main drive is coupled with the first input of the main transmission.

8. The helicopter with a drive system of claim 7, wherein the drive shaft is coupled via a freewheel unit with the main transmission.

9. The helicopter with a drive system of claim 7, wherein the first transmission is coupled with the drive shaft.

10. A method for operating an auxiliary drive system of a helicopter, the method comprising the steps: determining whether a main drive of the helicopter is providing a desired output; when the main drive is not providing the desired output, connecting of a flywheel mass battery to a lift-generating rotor of the helicopter via a variable transmission, the flywheel mass battery having been charged mechanically by the main drive during normal operation; controlling of a transmission ratio of the variable transmission such that a desired output is transferred to the lift-generating rotor; and separating operation of the lift-generating rotor via the main drive from operation of the lift-generating rotor via the flywheel mass battery by a first input and a second input of a main transmission, wherein the first input is coupled with the main drive and the second input is coupled via the variable transmission with the flywheel mass battery.

11. The method of claim 10, further comprising the steps: detecting whether the lift-generating rotor is being operated in autorotation; and separating of the flywheel mass battery from the lift-generating rotor when it is detected that the lift-generating rotor is being operated in autorotation.

12. The method of claim 10, further comprising the steps: detecting whether a landing procedure is being initiated; connecting of the flywheel mass battery to the lift-generating rotor when it is detected that a landing procedure is being initiated.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1 shows a schematic view of a helicopter according to an embodiment of the invention.

(2) FIG. 2 shows a schematic view of a drive system of a helicopter according to an embodiment of the invention.

(3) FIG. 3 shows a flowchart for a method for operating an auxiliary drive system of a helicopter according to an embodiment of the invention.

(4) In principle, identical or similar parts are provided with the same reference symbols.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

(5) FIG. 1 shows a helicopter 8 comprising a drive system 10 with a conventional main drive 12. The main drive 12 can comprise a combustion engine, such as a turbine or a piston engine, for example.

(6) The main drive 12 is coupled via a main transmission 14 with a rotor shaft 16 or a rotor mast 16 to the end of which a rotor 18 of the helicopter 10 is attached. In FIG. 1, the helicopter 10 is depicted as a helicopter with a main rotor 18 and a tail rotor 20. It will readily be understood that the helicopter 10 can have more than one lift-generating rotor 18 and also need not comprise a tail rotor 20.

(7) The helicopter 10 has a mechanical auxiliary drive system 22 designed to feed output to the main transmission 14 in the event the main drive 12 fails. For this purpose, the helicopter 10 has a controller 24 designed to detect a failure of the main drive 12 and to control the auxiliary drive system 22 appropriately.

(8) FIG. 2 shows a section from FIG. 1 with the drive system 10 and shows, in particular, the auxiliary drive system 22 in more detail.

(9) The main drive 12, for example a turbine 12, is coupled via a shaft 30 with a first input 32 of the main transmission 14. Located between the input 32 and the shaft 30 is a freewheel unit 34, which can transfer torque from the turbine 12 or the shaft 30 to the main transmission 14 but, conversely, prevents torque from being transferred from the transmission to the main drive 12.

(10) The auxiliary drive system 22 comprises a flywheel mass battery 36, which is coupled via a shaft 30 with an auxiliary transmission 38 that is coupled at its other end with the shaft 30 and hence with the main drive 12. The auxiliary transmission 38 can be a transmission with a fixed transmission ratio and comprise two pinions 40, for example.

(11) A freewheel unit 42 is arranged between the auxiliary transmission 38 and the shaft 30, the freewheel unit 42 is designed to transfer torque from the shaft 30 or the main drive 12 to the auxiliary transmission 38 and hence to the flywheel mass battery 36 but, conversely, prevents torque from being transferred from the flywheel mass battery 36 to the main drive 12.

(12) In this way, output can be transferred from the main drive 12 to the flywheel mass battery 36 when the main drive 12 is running. During normal operation of the helicopter 10, a first portion of the output generated by the main drive 12 is transferred via the freewheel unit 34 to the main transmission 14 and used to drive the rotor 18 of the helicopter 10. Another, second portion of the output (which is usually smaller than the first portion) is transferred via the auxiliary transmission 38 to the flywheel mass battery 36 in order to cause the flywheel masses to rotate, that is, to charge the flywheel mass battery 36, and also to compensate for frictional losses in the flywheel mass battery 36.

(13) If the main drive 12 fails, the flywheel mass battery 36 can continue to rotate without output being transferred back to the main drive 12.

(14) To store the energy, the flywheel mass battery 36 can have one or more flywheels 44. It is possible for the flywheel mass battery 36 to merely comprise one flywheel 44, but several and/or counter-rotating flywheels 44 are also possible.

(15) The auxiliary drive system 22 further comprises a variable transmission 46 by means of which the flywheel mass battery 36 is coupled with the second input 48 of the main transmission 14. An input of the variable transmission 46 is connected to the shaft 30, which is rigidly connected to the flywheel mass battery 36. The other input of the transmission 46 is connected to a shaft 50, which is coupled via a freewheel unit 52 with the second input 48 of the main transmission.

(16) The freewheel unit 52 is designed to transfer torque from the variable transmission 46 to the main transmission 14 but to prevent torque from being transferred from the main transmission 14 to the variable transmission 46 and hence to the flywheel mass battery 36.

(17) By virtue of the two freewheel units 34 and 52, either the main drive 12 or the fly-wheel mass battery 36 (or both) can input torque into the main transmission 14. Conversely, through the freewheel units 34 and 52 the main drive 12 and the fly-wheel mass battery 36 are prevented from mutually impeding each other, for example if the main drive 12 has failed.

(18) The variable transmission 46 can be a continuously variable transmission 46 comprising cone pulleys 56 mechanically connected by means of a chain 54 or belt 54, for example. By changing the spacing of the cone pulleys 56, the transmission and transfer ratio of the transmission 46 can be adjusted in a stepless manner.

(19) The adjustment of the transmission ratio of the transmission can be done by means of the controller 24, which, controls corresponding actuators of the variable transmission 46, for example. This controller can also be designed to detect the current rotational speed of the flywheels 44 and the operating mode (defect/normal operation) of the main drive 12.

(20) FIG. 3 shows a method for controlling the auxiliary drive system 22 which can be carried out from the controller 24.

(21) In step 100, the controller 24 detects a failure or a defect of the main drive 12. A corresponding signal can be provided by a main drive controller of the drive 12, for example.

(22) In step 102 output is introduced from the auxiliary drive system 22 in a transition phase between the detection of the defect and the beginning of autorotation. For this purpose, the controller 24 adjusts the transmission ratio of the variable transmission 46 such that the desired output is transferred from the flywheel mass battery 36 to the rotor. For this purpose, the controller 24 can determine the current rotational speed of the flywheel mass battery 36.

(23) If the main drive is not rotating or not rotating with sufficient speed, the main drive 12 is uncoupled by means of the freewheel unit 34 from the main transmission 14 and by means of the freewheel unit 42 from the flywheel mass battery 36. Continuing to step 102, the flywheel mass battery 36 is coupled via the variable transmission 46 with the main transmission 14 and is adjusted by the controller 24 such that the desired output is introduced into the second input 48 of the main transmission 48.

(24) In step 104, the rotor 18 transitions to autorotation and the auxiliary drive system 22 is adjusted so as not to introduce any output. For this purpose, the pilot sets the rotor 18 to autorotation, which is detected by the controller 24, for example by means of a corresponding signal from a control system of the helicopter 8. Upon detection of the signal, the controller 24 adjusts the variable transmission 46 such that no more output is transferred to the rotor 18.

(25) In step 106, the landing procedure of the helicopter 8 is initiated and the auxiliary drive system 22 is set so as to introduce output again. The landing procedure is initiated by the pilot by moving the rotor 18 out of the autorotation position into a landing position in which the energy stored in the rotor and transmission is used to brake the helicopter 8. This switchover can be detected by the controller 24, for example through a corresponding signal from the control system of the helicopter 8. After that, the controller 24 sets the variable transmission 46 (analogously to step 102) again such that the desired output is introduced into the second input 48 of the main transmission 14 in order to additionally drive the rotor 18.

(26) To enable estimation of how a flywheel mass battery and its flywheel could be dimensioned, the following formulas can be used:

(27) TABLE-US-00001 Kinetic rotational energy $W_{\mathrm{rot}}=\frac{1}{2}.Math.J.Math.{}^2$ Torque of a flywheel as a massive cylinder (a cylindrical shell has twice the torque.) $J=\frac{1}{2}.Math.m.Math.R^2$ Energy density of the flywheel $\frac{W_{\mathrm{rot}}}{m}=\frac{R^2.Math.{}^2}{4}={\left(\frac{R.Math.}{2}\right)}^2$ Circumferential speed v.sub.u = R .Math. Energy density $\frac{W_{\mathrm{rot}}}{m}=\frac{v_u^2}{4}$

(28) This results in the following values for various materials.

(29) TABLE-US-00002 Specific Maximum Density strength energy density Strength (MPa) (kg/m.sup.3) (MPa/kg) (MJ/kg) Steel 1700 7800 0.22 0.11 Aluminum 600 2700 0.22 0.11 Titanium 1200 4500 0.27 0.13 CFRP 3200 2000 1.6 0.8

(30) Despite their low mass density, high-strength materials such as CFRP (carbon fiber-reinforced plastics), for instance, can be used as the material for the flywheel. Metals and metal alloys are also suitable materials.

(31) By comparison, lithium batteries have an energy density of 200 Wh/kg, which corresponds to 0.72 MJ/kg.

(32) An EC120-type helicopter has a power input of about 100 kW. For 30 s, this corresponds to an energy requirement of 3 MJ. The energy density of CFRP is 800 kJ/kg, which yields a flywheel weight of 3.75 kg.

(33) Assuming a factor of 4 for additional components (bearings, housing), one obtains a mass for the flywheel mass battery of about 15 kg. For the other components of the auxiliary drive system as well (first transmission, variable transmission, actuators, control, etc.), a weight of 15 kg can be assumed. For the auxiliary drive system, this results in a total weight of 30 kg.

(34) In addition, it should be pointed out that comprising does not exclude any other elements or steps, and one or a does not exclude the plural. Furthermore, it should be noted that features or steps that have been described with reference to one of the above exemplary embodiments can also be used in combination with other features or steps of other exemplary embodiments described above. Reference symbols in the claims are not to be regarded as a restriction.

(35) The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.