Method for damping torsional vibrations in a drive train, and drive train

A torsional moment acting on a component in a drive train of an aircraft may be determined using at least one sensor, where the determined torsional moment is used for adjusting at least one adjustable damping element located in or on the component and/or for regulating a torsional stiffness in the torque-conducting component. As a result, the torsional load in the component may be reduced.

RELATED APPLICATIONS

This application is a filing under 35 U.S.C. § 371 of International Patent Application PCT/EP2019/061325, filed May 3, 2019, and claiming priority to German Patent Application 10 2018 207 140.3, filed May 8, 2018. All applications listed in this paragraph are hereby incorporated by reference in their entireties.

TECHNICAL FIELD

The present disclosure relates to a method for damping torsional vibrations in a drive train in aircraft that has a torque-conducting component, and the present disclosure also relates to a drive train and a device for executing the method.

BACKGROUND

The drive train in an aircraft, e.g. a helicopter or airplane, forms a connection between the drive and a propulsion drive or ascending drive (airscrew, propeller, turbine fan) or a servo drive (e.g. landing flaps, tail unit, landing gear), via which energy is transferred through a rotational movement.

Dynamic events such as torsional vibrations, play a substantial role in aircraft drive trains. Torsional vibrations are vibrations in a torque-conducting component. In particular in a shaft/mass system with high moments of inertia and extended shafts, as is the case in particular in drive trains or drive assemblies in aircraft, there may be torsional vibrations when rotating masses are coupled to one another by means of torque-conducting components.

Torsional vibrations are fairly common in drive trains in aircraft, and are frequently disruptive or even dangerous if the machine is running at a torsionally critical rotational rate, and the vibrations are amplified through resonance. A mechanical damping of these torsional vibrations is frequently impossible in extended systems.

It is fundamentally known from the prior art to reduce the torsional vibrations in aircraft drive trains by means of torsional dampers or torsional vibration dampers.

An internal combustion engine for an airplane is described in US2003089822A. This internal combustion engine comprises a crankshaft with first and second ends, a propeller, and a transmission that is located between the first end of the crankshaft and the propeller, and functionally connects the propeller to the crankshaft. A torsion rod is located between the first end of the crankshaft and the transmission, and functionally connects the crankshaft to the transmission. A torsional vibration damper is functionally connected to one of the two ends of the crankshaft.

Torsional vibration dampers in aircraft drive shafts are known from DE 102007055336A1 and US2003089822A.

Torsional dampers for aircraft servo drives are known from GB729696A and US6290620B.

That the determination of the vibrations from the torsional moment is often imprecise, such that yield from the compensation procedure is also limited, is regarded as disadvantageous.

DETAILED DESCRIPTION

In view of the background above, an object of the present embodiments is to create a method that further reduces the torsional vibrations, and a device for executing this method. It is also the object of the invention to create a drive train with low torsional vibrations.

Certain aspects described herein are based on a method for damping torsional vibrations in aircraft drive trains that have a torque-conducting component.

A torsional moment acting on the component is determined using at least one sensor, and the determined torsional moment is used for regulating at least one adjustable damping element located in or on the torque-conducting component in the drive train, and for regulating a torsional stiffness in the torque-conducting component to reduce the torsional load in the component, and thus in the drive train.

A torque-conducting component is a solid body, in particular, supported such that it can rotate about one of its axes, e.g. a shaft. A torque-conducting component can also take the form of a transmission that converts the rotational rate and torque applied to the drive to values corresponding to the working range of the propulsion or ascending drive, or the servo drive.

First, the torsional moment that is to be damped or regulated is more precisely determined and sent directly to a computer (ECU: electronic control unit), e.g. a control unit, by means of which a greater precision is obtained than with rotational rate-stabilized damping methods.

The control unit regulates the controllable or adjustable damping element, i.e. altering the damping rate or extent of damping, and/or regulating the torsional stiffness of the torque-conducting component, resulting in an increase or decrease in the torsional stiffness, depending on the circumstances. A frequency assessment of the torsion or torque signal is used to adjust the at least one adjustable damping element, e.g. a fast Fourier transform (FFT) over a short time interval, in order to be able to identify the type of stimulation (load or drive), and to dampen at the right location. Other known mathematical processes can likewise be used.

Torsional stiffness describes the resistance of an element to elastic deformation caused by torque.

A damping element in this context is understood to be an element or unit that converts mechanical (vibrational) energy into heat or some other form of energy, thus dissipating vibrations in the vibrational system.

The following mechanisms, known to the person skilled in the art, are to be fundamentally considered for this:

material damping at microscopic levels through internal friction or plasticity of a solid element,

viscous damping through shearing forces at microscopic levels in viscous fluids or gases, and/or

frictional damping at microscopic levels through forces at the boundary surfaces between frictional partners moving in relation to one another.

It has proven to be the case that an adaptively or actively adjustable damping system for aircraft drive trains can be obtained by aspects discussed herein.

By reducing the peak load, it is possible to use, in particular, lighter transmissions or torque-conducting components. It has also been shown that the load to these controllable, i.e. adjustable, damping elements can be higher than in the prior art.

This is the case in particular with loads known from aviation, in which air flowing around a propeller is used for starting a motor that has stalled or been shut off (windmilling). This involves high loads and load fluctuations, which led in the past to damages in conventional torsional dampers in drive trains.

A method in which the torsional moment is determined using two sensor elements, specifically a first and second sensor element, is preferred. The first and second sensor elements preferably each detect at least one angular position and/or one rotational rate. These sensors elements are configured, therefore, as angular position sensors or rotational rate sensors. In particular, a difference in angular positions is measured in the torque-conducting component in drive train with these two sensor elements. The deformation in the torque-conducting component between the two sensor elements when a load has been applied thereto can be detected by means of the difference in angular positions. In particular, a phase shift between the first and second sensor elements is detected. The torsion in the torque-conducting component depends substantially on the stiffness of the component and the torque that is applied thereto. The load to the torque-conducting component can be derived from the difference between the angles in the two measured angular positions, wherein a torque load to the component can be determined from this. Furthermore, the rotational rate or number or rotations can likewise be generated from the sensor signals. By way of example, the temporal derivation of the angular position in relation to the selected sensor element corresponds to an angular speed.

Angular position sensors can carry out, for example, an absolute, magnetic encoded angular measurement. Alternatively, magnetic sensor elements can also be used in combination with the gearwheels in a transmission assembly, wherein this represents a cost effective and reliable measurement variation. Other sensor elements for measuring angular positions or angular speeds can likewise be used.

In an alternative embodiment, a method is preferred in which the torsional moment is determined using a single sensor element. In this case, instead of determining an absolute difference, i.e. the difference between two absolute values, as is typical with two sensors, a relative difference is determined.

Magnetoelastic or magnetoresistant sensors can preferably be use for this, i.e. an acoustic sensor or an angular position sensor, which are configured to directly measure a torsion in the component that is to be measured.

With magnetoelastic or magnetoresistant sensors, the component that is to be measured is magnetized. The sensor detects a change in the magnetic field when a change occurs in the mechanical properties, i.e. caused by a shearing load.

The function of a magnetoelastic or magnetoresistant sensor and an angular position sensor can also be obtained with an acoustic sensor, e.g. an airborne sound sensor or a structure-borne sound sensor. This can be placed on the drive train, e.g. in a transmission or on a bearing point, such that the frequencies of two elements located in the drive train are detected. Drive train elements can be elements that generate a frequency correlating to the rotational rate or load, e.g. bearings and gear teeth. The torque or loads (bends) formed in the drive train are calculated from the phase shift in the frequencies or frequency patterns of the two elements and the known stiffness between these elements.

At this point it should be noted that magnetoelastic or magnetoresistant sensors and acoustic sensors are likewise preferred, in particular, for determining the torsional moment by means of two sensor elements.

It is also preferred that the sensor elements are either mounted externally on a drive train component, e.g. the transmission, shaft, bearings, etc., or are integrated therein. Integrated means that the sensor element uses existing components in the drive train for measuring (e.g. a gearwheel as an incremental indicator) or for attachment (housings).

A method is preferred in which the determined torsional moment is used for adjusting two adjustable damping elements to reduce torsional loads in the component. The use of two damping elements has the advantage that targeted dampening can be carried out, in particular with long shafts or in a transmission. This is therefore advantageous if one damping element is placed on the input shaft, and another damping element is placed on the output shaft, of a transmission located in the drive train.

Another aspect is the provision of a drive train, specifically a drive train for aircraft, that has a component configured to conduct a torque, and which has a drive train end and a load end. The drive train comprises at least one sensor element configured to determine a torsional moment acting on the component. The drive train also comprises an adjustable damping element configured to reduce a torsional load in the component, in particular to adjust the degree of damping in the component, and to alter a torsional stiffness of the component. The drive train also comprises a control unit configured to assess the determined torsional moment, and adjust the adjustable damping element based on the torsional moment.

The advantage of the drive train is that it can absorb peak loads using the adaptive damping element, and it can also be lighter.

It is preferred that the damping element is integrated in a clutch unit or a clutch element, which connects two sections of the torque-conducting component.

It is also preferred that two sensor elements are provided for determining the torsional moment.

It is also preferred that two damping elements are provided for reducing the torsional load.

According to another aspect, a device is to be created, in particular a control unit for aircraft, which is configured to execute the method described above.

FIG.1shows a drive train10in an aircraft in the form of an airplane. The drive train10connects a drive with a servo drive for a landing flap. It should be noted that the drive train can also be in a helicopter, by way of example, and can form a mechanical connection there between a drive and an airscrew or a propeller. The drive train10comprises a flexible shaft3, two rotational rate sensors, specifically a first rotational rate sensor4and a second rotational rate sensor5, a computer6, an adjustable damping element7, and an optional transmission9. The rotational rate sensors4,5detect the rotational rate via sensor rings4b,5bconnected to the shaft for conjoint rotation. The sensor rings are designed as incremental gearwheels in the present example. An input torque can be introduced into the drive train at the drive end1of the drive train10by means of a motor, not shown. The shaft3is configured to conduct the input torque to a load end2of the drive train10.

The measurement signals from the two sensors4,5are sent to the computer6via a suitable transmission path in the form of a radio signal transmission path4a, or5a, respectively. A hardwire transmission path could also be used. The computer6assesses the received measurement signals and actuates the adjustable damping element7via a suitable transmission path6a. The damping element7is integrated in a clutch unit11, which connects two sections, specifically section3aand section3b, of the shaft3to one another. The clutch unit11comprises two flanges11a,11b, wherein each of the two flanges is connected to a respective shaft section3a,3bfor conjoint rotation, which releasably connect the two sections3a,3bof the shaft3to one another. The sections3aand3bcould also be referred to as separate shafts that are connected by means of the clutch element11.

The two rotational rate sensors4,5are located axially between the load end2and the damping element7according to the exemplary embodiment inFIG.1. The torque measurement can fundamentally take place before, behind, or over the clutch element/torsion damping element.

FIG.2shows an axial positioning of the damping element7between the first sensor element4and the second sensor element5in another embodiment, such that the measurement of the torque takes place both in front of the adjustable damping element7, i.e. by means of the second sensor5, as well as behind the adjustable damping element7, i.e. by means of the first sensor4. The sensor4is accordingly located at the load end, while the sensor5is located at the drive end. The measurement signal obtained in front of the damping element7is sent to the computer6via the radio signal transmission path5a, and the measurement signal obtained behind the damping element7is sent to the computer6via the radio signal transmission path4a. The sensors4,5are in the form of magnetoelastic sensors in this embodiment. Rotational rate sensors for detecting a difference in angular positions could also be used. In this case, i.e. when the adjustable damping element is located in the measurement path, the damping characteristic map for all damping amounts that can be set is stored in the computer, in addition to the stiffness, in order to take into account the extent of the damping applied to the active torque, based on the difference in angular speeds. The torque transferred via the clutch11can then be derived from the stiffness and the difference in angular positions, the damping and the difference in angular speeds, and from the inertia and the difference in angular accelerations. The mathematical formula for this is:
M(t)=θ·{umlaut over (φ)}+d_var·{dot over (φ)}+c_var·φ

mass inertia is θ, the adjustable degree of damping is d_var, stiffness is c (or c_var), torque is M, rotational rate is ω(t)={dot over (φ)}, angular position is φ, and angular acceleration is {umlaut over (φ)}={dot over (ω)}.

The aim of this regulation is to reduce d_var(corresponding to d_var) to a minimum in the expression
QMW[M(t)−QMW(M(t)]

wherein QMW is the quadratic mean.

Another embodiment is shown inFIG.3, in which the drive train10is shown, comprising a transmission9with two sensors4,5, and two damping elements connected in series, specifically the first damping element7and a second damping element8. “Connected in series,” means that the damping elements are arranged successively in relation to the power flow. The second damping element8is particularly advantageous when the transmission9, which has a gear ratio i, is the component that is measured with regard to its torsional stiffness, such that one damping element, the first damping element7in this case, is configured to detect the output rotational rate of the output shaft9ain the transmission, and the other damping element, in this case the second damping element8, is configured to detect the input rotational rate of the input shaft9bin the transmission. This use of two rotational rate sensors is particularly ideal for measuring torque. According to the exemplary embodiment inFIG.3, the first sensor detects the rotational rate of the output shaft.

The damping elements7,8are again configured as clutch elements11with adjustable damping in this exemplary embodiment, wherein the clutch element11connects the output shaft9ato a shaft section9d, which leads to the load end2, and the clutch element12connects the input shaft9bto a shaft section9c, which leads to the drive end1of the drive train.

Starting from the drive end1, the components are arranged in the following axial series: second damping element8, second sensor5, transmission9, first sensor4, first damping element7, and load end2.

The measurement values obtained by means of the sensors4,5are sent to the computer unit6via radio signal transmission paths4a,5a. This evaluates the measurement values and controls the first damping element via a first radio signal transmission path6aand the second damping element via a second radio signal transmission path6bin order to dampen and alter the torsional stiffness. As such, both damping elements can be actuated simultaneously. It may also be the case that only one of the two damping elements is actuated, if this is more advantageous according to the control algorithm. Hardwire transmission paths can also be used instead of the radio signal transmission paths in this embodiment.

FIGS.4and5show sections of a drive train, as described above, in which the clutch unit is disengaged.

It has be shown that the measurement point(s) for the functional mechanical elements in the drive train, specifically

damping: d, also including the components of the clutch element,

can “cut free” or disengage at arbitrary points. The sequence of the functional elements (damping, stiffness, inertia) can be varied in the drive train, or distributed, e.g. in the form of a series connection (cf.FIG.3), or in the form of a parallel connection (not shown). With a parallel connection, numerous elements can be located in the clutch unit, or the torque can be distributed, e.g., to different parallel conductor paths.

With angular position sensors or rotational rate sensors, it is assumed there are two measuring points, in order to obtain a difference.FIG.4ashows two measuring points for a disengaged clutch unit.FIG.5shows a first measuring point, and optional, alternative, or additional measuring points A, B, C, D, E, F.

There are numerous ways to obtain the difference in angular positions, which measure the distance at a tangent to, or along the elastic element.

FIGS.6to8show different damping elements for use in the drive train. A frequency assessment of the torque signal (FFT over a short time interval) is used to actuate the adjustable damping elements, to be able to identify the type of stimulation, i.e. load-side, (e.g. through a propeller or airscrew), or drive-side (e.g. rotational asymmetry in the internal combustion engine), and to dampen at the right point.

The adjustment of the damping in the damping element takes place through ERF, MRF, or by flowing through a choke through hydraulic valves in the case of a shearing of a hydraulic medium.

InFIG.6, the clutch unit11has two flanges11aand11b. Both flanges11a,11bhave surfaces71,72facing one another. Thin cylindrical ribs are provided on the sides71,72of the flanges11a,11b, which intermesh in a meandering pattern without coming in contact with the opposite flange.

The ribs form a space75, closed radially inward and outward, over an insulating seal, which is filled with an electrorheological fluid (ERF). The cylindrical ribs form a capacitor in which the ERF acts as a dielectric medium. When a voltage U is applied, an electrical field is formed, by means of which the particles in the ERF align and alter the shear rate. The change to the shear rate in the viscous ERF results in an adjustable damping in the clutch element.

An adjustable eddy current brake is shown inFIG.7. The coil generates a magnetic field based on the current source, and this results in a damping torque, based on the field strength and the rotational speed.

Furthermore, a hydraulic piston with two working chambers can be formed between the two shafts or shaft sections, or on the flange on the clutch unit. When the clutch unit is twisted, the fluid is conveyed through a choke from one working chamber to the other. The damping is altered through an adjustable valve or a magnetorheological fluid (MRF), on which a magnetic field acts.

FIG.8shows possible embodiments for integrating a hydraulic damper in an elastic clutch unit. The working chambers in the damper are large enough to cover the angular range of the elastic clutch unit.

A known planetary gearing composed of dual-weighted flywheels is illustrated in images a) and b) inFIG.8, which uses the planet gears for actuating the damper (rotational damper or linear damper). Image c) shows a tangential linear piston damper.

FIG.9shows the use of the drive train10, powered by a shaft turbine22for driving a rotor21in a helicopter20.

FIG.10shows the use of the drive train10according to the invention powered by a hydraulic motor32for a leading edge flap31in an airplane.