WO2019219160A1

WO2019219160A1 - A modular drive system, a load unit and a test bench comprising said modular drive system

Info

Publication number: WO2019219160A1
Application number: PCT/EP2018/062341
Authority: WO
Inventors: Axel Manøe JEPSEN; Dennis BAY; Claus Odsbjerg BECK; Claus Ørtoft POULSEN; Christian Frier Hvejsel; Daniel Bo Rønnest ANDERSEN
Original assignee: R&D A/S
Priority date: 2018-05-14
Filing date: 2018-05-14
Publication date: 2019-11-21

Abstract

The present invention relates to a modular drive system (1, 1', 1'') that comprises a plurality of drive motors (2) each arranged for providing a drive torque, and wherein the modular drive system (1, 1', 1'') is arranged for transferring the individual drive torques of the plurality of drive motors to a common drive shaft (6) of the modular drive system (1, 1', 1'') thereby providing a united drive torque. Said modular drive system (1, 1', 1'') can be incorporated in a wind turbine test bench (12, 12', 12'') e.g. together with a load application means (16, 19) or as a part of a load unit (18). In any case the modular drive system (1, 1', 1'') is arranged for reliably transmitting a driving torque to an input shaft of the device under test (14). Furthermore, since it is made of a plurality of smaller units (2), it weighs less than the conventional drive means, and accordingly cost less and is easer to repair when required.

Description

A modular drive system, a load unit and a test bench comprising said modular drive system.

The present invention relates to a modular drive system, to a load unit comprising said modular drive system and to a test bench comprising the modular drive system or the load unit.

Wind turbines are some of the largest rotating structures in the world, and due to increasing demands for higher efficiency and larger output they are increasingly becoming bigger.

Accordingly, the wind industry are not only developing larger wind turbine components, such as the gearbox, generator, braking system etc., but the interaction between said components also becomes more and more specialized and complex. This is of course advantageous regarding efficiency and output of the wind turbine, but since these large wind turbines are expensive and breakdowns are very costly, it is important to ensure that the life, durability, quality and capacity of the wind turbine and its components are tested and well documented .

Accordingly the entire process - from design to installation to operation and maintenance — have to be tested.

It is today common practice to use specialised test benches for simulating the dynamic and/or static loads acting on the wind turbine for carrying out e.g. fatigue, durability, ultimate strength, electrical, efficiency and/or function tests on the members of the wind turbines, e.g. on the nacelle, wind turbine generator etc. before said wind turbines are installed.

Testing the strength of the structural components of the wind turbine has the main purpose of reducing the use of material or optimising the design of these structural components, hereby reducing the cost and weight of the components and ensuring that they can withstand the loads that they are affected by during normal operation of the wind turbine.

Since it for obvious reasons is impossible to test the wind turbines with the turbine blades attached, it is essential to provide a test bench capable of applying equivalent rotor loads to the shaft of the turbine, and at the same time, produce the on- and off-axis loading, as it would occur in the real world, or as accelerated loads. Thus, the test system not only has to produce the loads needed to simulate blade movements and wind forces acting on said blades, but precision testing is also desired in order to be able to simulate different wind scenarios .

A number of different test benches are known in the art, see e.g. W02007144003, W02007140789, relating to test benches aiming at meeting these demands. However these known test benches have various shortcomings.

First of all, the conventional test benches incorporate a rotational drive system in the form of one or two electric motors arranged for applying a rotational torques to the shaft of the device under test, thereby simulating the rotational loads on the wind turbine. However, due to the increasing requirement for efficiency and output of the wind turbines, relatively large driving torques have to be applied to the shaft of the wind turbine, in order to mimic the conditions during operation, thus the used drive motors become larger thereby becoming more and more expensive, as well as adding to the overall size of the test bench.

Some of the known test benches furthermore incorporate a load application means which is able to apply axial and/or radial forces and moments to the device under test e.g. in order to simulate the load from the blades through the hub to the structural components of the wind turbine during operation. Such load application means normally comprises a complex mechanical system having a large number of moving parts thereby increasing the potential for mechanical failure of said load application means.

In addition, the large drive motor and the complex load application means both have to be custom made for each single test bench, further adding to the overall cost of the known test benches. This also means, that if a defect or fault occurs in one of said components, the entire test bench becomes inoperable until the defect component has been repaired or a new component installed. As an example can be mentioned, that since the drive motors are specially designed for each test bench, spare parts are normally not available and downtime until a new drive motor has been manufacture can be up to two years .

Thus, creation of improved test benches becomes an increasingly critical issue, and there is a demand for providing components for a test bench for e.g. a wind turbine which overcomes the drawbacks of the known test benches.

It is accordingly a first aspect of the present invention to provide a test bench which is arranged for applying both dynamic and/or static load to a device under test.

It is a second aspect of the present invention to providing an alternative drive system having components of a simple and relatively inexpensive character, and which is easier to repair and maintain than the conventional drive systems for test benches .

It is a third aspect of the present invention to provide a simple and compact load unit arranged for applying axial load, and/or radial loads and/or bending moments and/or driving torques to a device under test. It is a fourth aspect of the present invention to provide a drive system and/or a load unit which can be used in a test bench arranged for testing large structural components e.g. a wind turbine or its components.

It is a fifth aspect of the present invention to provide a drive system, a load unit and/or a test bench which easily can be customized and altered in relation to a new device to be tested in said test bench.

It is a sixth aspect of the present invention to provide a test bench which is more compact and weighs less than the conventional test benches for large structural components.

It is a seventh aspect of the present invention to provide a test bench which has fewer components and is easier to repair, thereby reducing any potential downtime of said test bench.

These and further aspects are achieved according to the present invention by providing a modular drive system for a test bench, said modular drive system comprises a plurality of drive motors each arranged for providing a drive torque, and wherein the modular drive system is arranged for transferring the individual drive torques of the plurality of drive motors to a common drive shaft of the modular drive system thereby providing a united drive torque, and wherein said common drive shaft is arranged for rotating an input shaft of a device under test in said test bench.

In the present invention the term "test bench" relates to a test bench arranged for testing large structural components e.g. relating to the wind industry or the aircraft industry. Accordingly, the device under test in said test bench may be a wind turbine, a nacelle, a drive train, a generator, an engine and the like, however the term is not to be construed as limiting as any structural component that is able to resist very high loads and perform under such high loads are contemplated within the scope of the present invention. Accordingly, the device under test includes, but is not limited to, any kind of drive train, generator or motor, e.g. for automobiles, trains, larger vehicles for transportation, ships, airplanes, and marine engines.

The use of a plurality of smaller drive motors in the modular drive system according to the invention wherein each drive motor has a low torque and thus also smaller dimensions makes it possible to achieve a compact modular drive system i.e. a system having both smaller dimensions as well as reduced weight , when compared to the conventional drive motors for test benches . It should in this respect be noted, that conventional test benches for e.g. wind-turbines , nacelles and the like are extremely large and heavy, e.g. weighing in the areas about 800 tons . Such test benches therefore requires very stable and very large foundations . Thus , any reduction in the weight of the structural components of the test bench, e.g. by providing a modular drive system having a lower weight, will provide an obvious advantage.

Furthermore, by dividing the drive motor into smaller components, the drive motor receive an element of redundancy. For example, when ten small motor's split the system's load a defect in a single drive motor will only reduce the drive system's capacity by 10%, allowing the system to remain active at reduced power, if desired.

Use of a plurality of drive motors instead of a single large motor, will also reduce cost to maintenance . It will for instance be possible to have spare drive motors in storage, such that it will be relatively simple to replace a defect drive motor in the modular drive system if required, ensuring that the test bench will return to its optimal efficiency in a fast and simple manner, thereby substantially eliminating any down time of the test bench .

The use of several smaller drive motors, as in the present invention, has not been contemplated in the art of test benches. This is likely due to the fact that it is generally recognized that one large motor is much more efficient than a number of smaller motors; that the use of several motors increases the number of moving parts and accordingly increases the potential for mechanical failure; and that it would be very difficult, if not impossible, to synchronize a plurality of motors and still obtain the desired low driving speed and large drive torque required to mimic the rotation of the blades which is required in e.g. wind turbine test benches.

However, the inventors of the present invention has provided a modular drive system which is arranged for both synchronizing the individual motors and transferring the individually driving torques onto a single common drive shaft, thereby creating a united, i.e. combined drive torque, which can be transferred to an input shaft on the device to be tested, e.g. a nacelle or wind turbine, and accordingly provide the desired large driving torque and low driving speed.

Within the context of the present invention the term " shaft " , is to be understood as any kind of bar, rod, pipe, tube, ring, coupling, sleeve, muff, bolt interface or other system capable of transferring a rotation . The shaft is in no way limited to being solid but could also e.g. be a hollow ring or sleeve forming or attached to the planet carrier or annulus gear of e.g. a wind turbine gearbox or generator .

The common drive shaft may transfer the obtained rotation/torque to an input shaft of e.g. a wind turbine, by means of different torque transferring elements, e.g. bearings, clutch assemblies and the like. Such torque transferring elements are well known in the art and will not be discussed in further details in the present application.

The modular drive system may be individually designed, and the number of the plurality of motors may e.g. depend on the respective drive motors used, however in a preferred embodiment the modular drive system comprises between three and fifty motors , preferably between five and thirty, and even more preferred between ten and twenty five drive motors .

There are several ways to transfer the torque load of the individual motors to the common drive shaft, e.g. through the use of suitable gear reducer units. In one embodiment the plurality of drive motors comprises a first gear that meshes with a larger centrally disposed second gear arranged for communicating with the common drive shaft. Said first gear can in one embodiment be a pinion gear mechanically connected to each drive motor, and be arranged for peripherally meshing with the larger diameter, centrally disposed, second gear, which may be in the form of a sun gear or ring gear.

The drive motors can in a simple embodiment be arranged on the same side of the second gear, however in a different embodiment the drive motors are arranged on both side of said gear, e.g. in an alternating arrangement such that the drive motors are displaced in relation to each other on each side of the second gear, thereby optimising the three-dimensional configuration of the modular drive system.

By placing the plurality of drive motors on both sides of a larger centrally disposed second gear, the modular drive system may comprise additional drive motors as said drive motors can take up space on both sides of said gear.

The first gears of the drive motors may be meshing with either the outer diameter and/or the inner diameter of the larger second gear, the only requirement of the reduction unit being that the individual drive motor can transfer their torque load to the common drive shaft.

When used in the present application the term "torque" is to be understood as the tendency of a force pair or moment to produce rotation or torsion about an axis. Torque between two components is e.g. transferred by friction or shear connection between these two components, and is thus e.g. dependent upon friction, e.g. between the common shaft of the modular drive system and the input shaft (rotor hub) of the wind turbine.

The common drive shaft has a longitudinal centre axis, and it is preferred that the plurality of drive motors are circumferentially arranged around said axis i.e. the common drive shaft is disposed in centered relationship to the circumferentially arranged drive motors. Such a solution has the advantage that it not only reduces the needed space for the mechanical parts (absence of offset shafts) , but also eliminates the need to redirect the power or relocate other components, furthermore very high reduction ratios may be achieved if desired.

In this embodiment the circumferentially arranged plurality of motors will collectively act to drive the common drive shaft and will accordingly be capable of slowing the rotation speed from the plurality of motors, while at the same time increasing the available torque. Therefore the load capability of the modular drive system can easily attain the nominal input torque of a device under test, e.g. a wind turbine generator. It is preferred within the context of the present invention that the nominal input torque of the device under test is at least about 8 MN»m and more preferably at least about 10 MN»m, but the nominal input torque may also be higher e.g. at least about 20 MN»m or at least about 35 MN»m. It is however preferred that the modular drive system is arranged for providing an overload capability of between 10% and 50% of the nominal input torque of the device under test, in order to e.g. provide stress and/or accelerated test.

Depending of the device under test, the modular drive system can easily be customised to a meet a nominal input torque or an overload torque e.g. by altering the number of drive motors, by changing the type of drive motors used, etc.

The plurality of motors and optionally their respective first gear is preferably circumferentially arranged in or at a housing. Said housing is preferably arranged to be mechanically connected to a static interface of the test bench, e.g. by bolting it directly to the test bench . This will both assist in equalizing uneven loading of the respective motors as well as counteracting rotation of the modular drive system.

It is however preferred that the modular drive system is connected to separate support structure via a torque arm system arranged for resisting the torque developed by the modular drive system, thereby preventing the counter-rotation of the modular drive system during operation.

In a preferred embodiment the torque arm system comprises a pair of interconnected hydraulic actuators connecting the modular drive system and e.g. the test bench. The pair of actuators are in fluid communication such that they may operate in response to each other in a cross-arrangement i.e. if one actuator is extended the other actuator will extend accordingly. Such a construction will in a simple and effective way counteract rotation of the modular drive system, while allowing translational movement with the load application means . A person skilled in the art will understand that the specific construction in order to transfer the torque from the plurality of drive motors to the common drive shaft , as well as preventing counter-rotation of the modular drive system and obtaining a suitable gear reduction, may vary depending on the components used . For instance, the sun gear or ring gear may on one embodiment be part of the main bearing, whereas they in an alternative embodiment are separated into a bearing and ring gear . Furthermore, the main bearing is preferably a moment bearing as this is capable of constraining both radial axial and bending movements , but could in an alternative embodiment be separated into two single non-moment bearings .

Since wind turbines only operate at relatively low speeds it is preferred that the plurality of motors are gear reduced to provide output of between 0 to 25 RPM of the input shaft of the device under test, preferably between 5 - 20 RPM.

The plurality of drive motors are preferably hydraulic motors or electric motors, and may be selected from the group consisting of AC (alternating current) motors, including both synchronous and asynchronous motors, DC (direct current) motors, PM (permanent magnet) motors, and the like.

In a simple embodiment the plurality of drive motors are connected in parallel and preferably to an electric drive, e.g. an AC or DC drive, which is arranged for splitting the output current equally so that each drive motor delivers the same torque. This provides a very simple and inexpensive embodiment of the modular drive system according to the invention.

In an alternative embodiment at least one of the pinion gears may be driven by a plurality of drive motors, i.e. several motors coupled serially in tandem to a common pinion shaft. If the plurality of motors are identical it will not only be easier to synchronise the individual motors, but use of identical motors also ensures that spare drive motors can be stocked and replaced quickly if a failure occurs in one of said drive motors. However, a person skilled in the art would understand that one or more of the plurality of motors could be different, and that e.g. different rotational speeds of the respective motors can be matched through a gear reduction. The only requirement being when selecting the individual drive motors, is that the modular drive system is arranged for transferring the individual drive torques of the plurality of drive motors to a common drive shaft of the modular drive system thereby providing a united drive torque.

The modular drive system according to the invention is arranged for providing a drive torque to the input shaft of the device under test, thereby mimicking the rotation of the rotor and drive train. However, during normal operation the structural components of e.g. a wind turbine are also subjected to dynamic loads caused e.g. by the wind loads on the blades. In order to provide realistic tests, such loads, vibrations and deformations have to be taken into account. It is therefore preferred that the modular drive system is connected to a load application means arranged for creating axial forces and/or radial forces and/or bending moments about the centre axis of the input shaft of the device under test, or to a point where the longitudinal axes of the three blades of a wind turbine would intersect .

In a preferred embodiment the load application means is arranged for providing five degrees of freedom (DOF), that e.g. can be described in the blade and hub coordinate systems. The respective loads are axial and radial forces around and along the X-, y-, and z-axes (F_x, F_Y, F_z) , and bending moments about the y- and z-axes (M_Y, M_z) , however the load application means may also be arranged for providing fewer degrees of freedom if desired and/or it may be arranged for also providing a torque.

In one embodiment the load application means may comprise an axially mounted rotating disc and a number of hydraulic actuators that can act on the disc and thus create axial and radial forces and bending moments about the centre axis of the input shaft of the device to be tested. Such a load application means is e.g. known from W02007144003.

An alternative load application means is known from WO2013135246, which relates to a hexapod system of three angularly distributed pairs of independently controllable linear actuators selected to move the moveable load application means and the device under test.

However, due to the stiffness of the device under test and/or the structure supporting said device, the load application means will need to translate and rotate in all directions in space when it applies load to the device to be tested. As the modular drive system is a substantially stationary unit, there will be a relative movement between the modular drive system and the load application means, and it is accordingly preferred to insert a coupling element between the modular drive system and the load application means arranged for absorbing the relative movements between the two elements. However, due to the large relative movements that need to be handled, a relatively long coupling element is required, adding not only to the overall dimensions of the test bench but also to the weight and costs of said test bench.

Accordingly, the present invention also relates to a load unit in which the modular drive system according to the invention is integrated with a load application means. Such a load unit will provide a combined structure that will negate the requirement for a coupling element arranged for absorbing the relative movements between the two components.

Since the modular drive system and load application means is combined into an integrated load unit, said load unit has a more compact structure than the individual components, and accordingly the dimensions and weight of a test bench incorporating such a load unit will be reduced.

The load application means is preferably arranged for providing six degrees of freedom. The five degrees of freedom (F_x, F_Y, F_z, M_y, M_z) are provided by the load application means and the sixth degree of freedom, the driving torque (M_x) for rotation the input shaft of the device under test, is transferred to the device under test by means of the modular driving system according to the invention. If the load application means is also arranged for providing a torque, said torque may be combined with the driving torque from the modular driving system.

By using the load unit according to the invention, which is arranged for subjecting the device under test for loads in all six degrees of freedom, it is possible to simulate the load acting on the device under test both during normal operation as under extreme situations , hereby making it possible to compare different devices , e.g. wind turbines under the same normal load conditions as well as performing accelerated life tests . This is advantageous , in that it hereby is possible to perform a more efficient test of the device under test , which enables that the load types and sizes can be dynamically adjusted e.g. to be substantially realistic if needed or to inflict overload if desired .

In a preferred embodiment the load application means of the load unit comprises a moveable structure, e.g. consisting of one or more cylinders, suspended from a support e.g. a test bench, by means of at least four radial load applying means. Said radial load applying means are arranged for applying radial forces on the moveable structure, and are preferably connected to both the distal end and to the proximal end of the moveable structure via load transferring flanges arranged at each end of the moveable structure. The radial load applying means are preferably attached to the flanges at a predetermined radial distance in a longitudinal centre plane of the moveable structure. The predetermined radial distance may be selected in order to ensure that the optimal load/force can be transferred from the radial load applying means to the moveable structure.

It is furthermore preferred that the load application means comprises at least one axial load applying means arranged for providing an axial load and/or a bending moment to the movable structure. In a preferred embodiment there are two axial load applying means, but additional axial load applying means may be used if desired. Said axial load applying means are preferably connected to the distal end of the movable structure by means of load transferring elements arranged on either side of the moveable structure, e.g. below a plane passing though the longitudinal centre axis of the moveable structure.

The load unit is preferably arranged for being directly coupled to the input shaft of the device under test, thereby providing a simpler and more compact structure than hitherto known. During use the radially and axial load applying means will apply loads to the moveable structure, said movable structure will function as a moment arm and transfer the applied load directly to the device under test.

Applying the load to the device under test via the moveable structure provides the advantage that it is possible to more accurately simulate the real load situations or to perform accelerated life tests e.g. by establishing a permanent overload situation or providing varying load situations, thereby increasing the efficiency and/or realism of a test using the load unit according to the invention.

In a preferred embodiment the axial and/or radial load applying means are linear actuators, e.g. hydraulic actuators, arranged for extending and retracting in order to apply forces to the moveable structure. A person skilled in the art will be able to calculate the required forces for each hydraulic actuator e.g. by using a transformation matrix based on a geometric model, thereby determining the mutual interaction between the respective actuators, and accordingly control and/or adjust the forces applied by the respective actuators to the movable structure .

It is preferred that the radial and axial load applying means are arranged for independently applying forces to the movable structure, thereby ensuring that load application means can transfer one to five degrees of freedom to the device under test, depending on the number of activated actuators. The load application unit can therefore simulate any wind condition the device under test may be subjected to both during normal and extreme wind conditions. It is in this respect preferred that the hydraulic actuators are connected individually to e.g. proportional valves or servo controlled valves making it possible to control the load inflicted by each of the actuators individually .

The hydraulic actuators are preferably rigidly connected to a substantially rigid structure of the test bench ensuring that when the hydraulic actuators are extending or retracting their full load is transferred substantially to the movable structure to which the hydraulic actuator is mounted or connected to. However, suitable bearings and/or connector element may be used in order to ensure that the loads from the actuators can be transferred to the moveable structure. It is preferred that the plurality of motors of the modular drive system are uniformly arranged along a radial circumference of the cylindrical movable structure, preferably such that a longitudinal centre axis of the moveable structure coincides with a longitudinal centre axis of the common drive shaft. Using this unique construction both provides a very compact structure, in which the load application means and modular drive system is overlapping, but also that said two components easily can be operatively connected to each other, such that the load unit may transfer load in six degrees of freedom to an input shaft of a device to be tested.

The modular drive system of the load unit may be connected to the test bench via a torque arm system arranged for resisting the torque developed by the modular drive system, thereby preventing the counter-rotation of the modular drive system during operation. However, in a simple embodiment of the load unit according to the invention, the modular drive system is directly connected to the load application means, such that it is the non-rotating part of the load application means that prevents counter-rotation of the modular drive system during operation .

The unique construction of the load unit enables said unit to create the axial and radial forces, bending moments and drive torque in order to simulate the effects of for example wind load on a wind turbine or one of its structural component. For instance, the load unit of the present invention enables application of shaft rotation, torque, bending moments and shear forces similar to those encountered by e.g. a nacelle during normal operation. Thus the invention may e.g. serve to simulate real time wind loads in order to analyze the dynamic operation behavior of wind turbines. The novel load unit has up to six degrees of freedom for application of load and it is possible to apply load to almost all large structural components such as wind turbines and airplane engines, including but not limited to, coupled dynamic dependencies, such as those relating to main shaft, main shaft support bearings, bearing housings, gearbox, yaw drive system, and brake assembly.

In one embodiment the load application means and modular drive system of the load unit are connected by means of a drive shaft coupling which connects the common shaft of the modular drive system with a main shaft of the load application means. However, drive shaft couplings are expensive and in a preferred embodiment a drive shaft coupling is not be required as the main shaft of the modular drive system can be used also for the load application means, such that the rotational parts of the modular drive system is directly connected to a rotational part of the load application means.

However, the specific arrangement for transferring the loads from the load unit to the input shaft of the device under test, depends on the specific constructions of said load unit, it is however preferred that the load unit is arranged for applying loads in six degrees of freedom to the input shaft of the device under test.

The present invention also relates to a test bench, e.g. a wind turbine test bench. Said test bench may in one embodiment comprise a modular drive system according to the invention, in a another embodiment a modular drive system and a load application means connected by means of a connecting element, and in a third embodiment comprise a load unit according to the invention .

Using a test bench that comprises the modular drive system according to the invention, irrespectively of whether or not said modular drive system is connected to a load application means or incorporated into a load unit, provides a number of advantages compared to the prior art. First of all, the modular drive system is arranged for reliably transmitting a driving torque to an input shaft of the device to be tested. Furthermore, since it is made of a plurality of smaller units, it weighs less than the conventional drive means, and accordingly cost less and is easer to repair when required.

A test bench incorporating the load unit according to the invention further has the advantage that such a test bench is able to stress the device under test with loads (e.g. wind loads) in all six degrees of freedom. The load application means of said load unit contains at least six hydraulic actuators which are located on different parts of a suspended movable structure in order to provide five degrees of axial forces, radial forces, and bending moments. The sixth degree of freedom, i.e. the driving torque is provided by the modular driving system, and the assembled test bench provides a full size ground test bench which is arranged for both applying realistic wind loads to a device under test, e.g. a wind turbine, as well as being more compact and having a lower weight than hitherto known.

Even though the driving torque is delivering by the modular drive system according to the invention, the load application means may be arranged for at least partly also providing a drive torque if desired.

In order to maximize the power output from a wind turbine the rotor on a conventional wind turbine is angled, i.e. the rotor plane and the drive train are positioned in an angle which is not parallel with the horizontal plane of the ground. Since the drive train and the drive train components are very essential component of a wind turbine it is advantageous to test these components at the correct tilt angle.

Depending on the type of wind turbine, different tilt-angles exists. The most common are 5° for geared turbines and 6° for DD turbines, however both larger and smaller tilt-angels exist. In order to meet these requirements the conventional test benches are arranged for accommodating a wind turbine with a predetermined tilt angle. However, such conventional test benches are not capable of changing the tilt angle after the test bench has been constructed, and it is accordingly not possible to test a wind turbine with a different tilt angle under optimal conditions which is unacceptable from a manufacturing point of view. Thus, a new test bench normally has to be constructed.

Thus, in a preferred embodiment of the test bench according to the invention, the load unit is arranged for being tilted in dependence of the device to be tested. The tilting may e.g. be obtained by adjusting the height of the four radial load applying means of the load unit or by tilting the entire load unit. In this way the test bench according to the invention can be used to accommodate all kind of wind turbines irrespectively of the tilting angle of said wind turbine, as the tilting angle of the load unit easily can be adjusted, among others due to the fact that it is independent of other stationary components of the test bench.

The invention also relates to a method of applying a load to a device under test. Said method comprises the following steps: providing a load unit according to the present invention providing a device under test in operative coupling with the load unit,

operating said load unit via the hydraulic actuators and/or the common shaft of said load unit, and

measuring data representing the applied load.

The steps of operating the hydraulic actuators and/or the common shaft of the load unit may advantageously comprise applying translation and/or rotational load, such as one or more of axial force, radial force, axial displacement, lateral displacement, vertical displacement, drive torque, bending torque and radial displacements.

It may be convenient to provide the load unit at an angle to horizontal to get the test set-up as close to natural conditions as possible.

The method may further comprises a calculation step, including subtracting the load contributions representing the friction loss, rolling resistance and weight of the load application unit from the measurement data to obtain true data for the load applied to the device under test.

A preferred use of any or all of the modular drive system, load unit, the test bench, and the method according to the invention is for testing a wind turbine or a structural component of a wind turbine such as a nacelle, a generator, a drive train and the like.

The inventions will be described in further details below with references to the accompanying drawing in which,

Fig. 1 is a schematic view of a first embodiment of a modular drive system according to the invention in an assembled state,

Fig. 2 is an exploded view of the modular drive system shown in fig. 1,

Fig. 3 is a schematic view of a second embodiment of a modular drive system according to the invention,

Fig. 4 is a schematic view of a third embodiment of a modular drive system according to the invention,

Fig. 5 is a first embodiment of a wind turbine test bench according to the invention, Fig. 6 is a second embodiment of a wind turbine test bench according to the invention,

Fig. 7 is a load unit according to the invention in an assembled state,

Fig. 8 is a load application means of the load application unit shown in fig. 7,

Fig. 9 shows a proximal section of the load application means of fig. 8,

Fig. 10 shows a distal section of the load application means of fig. 8,

Fig. 11 is a partly exploded view of the load unit of fig. 7,

Fig. 12 is a third embodiment of a wind turbine test bench according to the invention,

Fig. 13 shown in perspective and more details, the embodiment of fig. 11, and

Fig. 14 is a side perspective of the embodiment shown in fig. 13.

The invention will be described below with the assumption that the test bench is used for testing a wind turbine, however this assumption is not to be construed as limiting, and the test bench can just as easily be used to test other large structural components, e.g. a nacelle, a drive train, or other non wind- related components such as an airplane engine.

Fig. 1 shows a first embodiment of the modular drive system 1 according to the invention in an assembled state, and fig. 2 shows the same but in a partly exploded view. Said modular drive system comprises ten drive motors 2 each arranged for providing a drive torque. Each of the drive motors 2 has a drive shaft 3 that is mechanically connected to a pinion gear 4 peripherally engaging the teeth of a ring gear 5 for rotating a common drive shaft 6 of the modular drive system 1 thereby providing a united drive torque. In fig. 2 one of the motors 2a, has been withdrawn from the pinion gear 4 and ring gear 5 in order to illustrate the components in further details.

The plurality of motors 2, their respective pinion gears 4 and the ring gear 5 is connected to each other by means of a housing 7 which can be mechanically connected to a static interface of a test bench e.g. by means of an anchoring assembly or torque arm system (see fig . 11 for further details ) and side plates 8 mounted on said housing 7. The ring gear 5 and pinion gears 4 are arranged inside the housing 7, and the drive shaft 3 of each motor 2 engages the pinion gears 4 though a guiding assembly 9 having a guide disc 10 , for guiding and controlling the movement of the motor 2, and an opening 11 such that the drive shaft 3 can engage the pinion gear 4.

The common drive shaft 6 has a longitudinal centre axis X_com and the respective drive motors 2 are circumferentially and evenly distributed in relation to said axis, i.e. the common drive shaft 6 is disposed in centred relationship to the circumferentially arranged drive motors 2.

In the embodiment shown in fig. 1 and 2 the drive motors are identical electric motors connected in parallel to an electric drive (not shown) which is arranged for splitting the output current equally so that each drive motor 2 delivers the same torque. This provides a very simple and inexpensive embodiment of the modular drive system 1 according to the invention, however a person skilled in the art will understand that the respective drive motors 2 in different embodiments could be different from each other, be arranged in a different manner, or be powered differently.

In the embodiment of fig. 1 the ten circumferentially spaced drive motors 2 will collectively act to drive a common drive shaft 6 and will by means of the pinion gears 4 and ring gear 5 obtain a desired gear reduction and accordingly slow the rotation speed from the plurality of drive motors 2, while at the same time increasing the available torque. In a preferred embodiment the load capability of the modular drive system 1 can attain the nominal input torque of a device under test e.g. a wind turbine generator i.e. at least 8 MN»m, however it is preferred that the modular drive system can provide an overload torque which is between 10% and 50% of the nominal input torque of a device under test.

The common drive shaft 6 of the modular drive system may then, by means of different torque transferring elements (not shown) , e.g. bearings, clutch assemblies and the like, transfer the obtained rotation/torque to an input shaft of the wind turbine.

By means of the torque transferring elements, the modular drive system 1 according to the invention can in a simple and effective way transfer a driving torque to an input shaft of a device under test. Furthermore, since the modular drive system 2 is made of a plurality (ten) smaller drive motors, the modular drive system weighs less than the conventional drive means for wind turbine test benches, and accordingly cost less and is easier to repair when required.

In the embodiment shown in fig. 1 and fig. 2, the drive motors 2 are all arranged on the same side of the ring gear 5. Fig. 3 shows a second embodiment of the modular drive system 1 ' according to the invention in which the modular drive system comprises twenty drive motors 2, ten on each side of the ring gear 5. The second embodiment of the modular drive system 1 ' corresponds in principle to the first embodiment, and for like parts the same reference number is used, the main difference being that the housing 7 ' is modified such that each side of the housing 7 ' comprises ten guiding assemblies 9 for accommodating the respective drive motors 2.

Fig. 4 shows a third embodiment of the modular drive system 1 ' ' . Said embodiment is a variant of the embodiment shown in fig. 1 and 2, but where the pinion gears 4 in the embodiment of fig. 1 and 2, are meshing with the outer periphery of the ring gear 5, the pinion gears 4 are in the third embodiment meshing with an inner diameter of the ring gear 5. However, said pinion gears 4 could also be meshing with both the inner and outer diameter of said ring gear 5 if desired, the only requirement being that the individual drive motor 2 can transfer their torque load to the common drive shaft 7 via a suitable gear reduction unit.

Fig. 5 shows schematically a first embodiment 12 of a test bench according to the invention in which the modular drive system 1 of fig. 1 and 2 via a first coupling element 13 is connected to a wind turbine 14. The respective components is supported by suitable support structures 15. Even though fig. 5 shows a coupling element 13, the modular drive system 1 may in an alternative and preferred embodiment be directly coupled to the wind turbine 14.

In the embodiment shown in fig. 5 the modular drive system 1 provides a drive torque to the input shaft of the wind turbine 14, thereby mimicking the rotation of the rotor/blades . However, during normal operation the structural components of a wind turbine are also subjected to dynamic loads caused among others by the wind load on the blades. Thus, in order to provide realistic tests when using the wind turbine test bench according to the invention the wind turbine has to be subjected to among others similar loads, vibrations and deformations as it would during normal and extreme conditions.

A second embodiment 12 ' of a test bench according to the invention is shown in fig. 6. This embodiment corresponds to the embodiment of fig. 5 and for like parts the same reference number is used. In the second embodiment 12' the device under test 14 is connected to a load application means 16 arranged for creating axial forces and/or radial forces and/or bending moments about a longitudinal centre axis X_test of the input shaft of the device under test, thereby providing between one and five degrees of freedom, i.e. axial and radial forces along the X-, y-, and z-axes axis (F_x, F_Y, F_z) , and bending moments about the y- and z-axes (M_Y, M_z) . The device under test is further connected to the modular drive system 1 shown in fig. 1 and 2 in order to provide a drive torque to an input shaft of the device under test 14.

However, in order for the load application means 16 to transfer the desired loads to the device under test 14, said load application means have to move in all directions in space and since the modular drive system 1 is a substantially stationary unit, there will be a relative movement between the modular drive system 1 and the load application means 16. A second coupling element 17 arranged for absorbing the relative movements between the modular drive system 1 and the load application means 16 is therefore inserted between said two components 1, 16.

Due to the relative high loads, a relative long second coupling element 17 is required, adding not only to the overall dimensions of the wind turbine test bench 12 ' but also to the weight and costs of said test bench 12 ' . Fig. 7 shows a load unit 18 arranged for providing between two to six degrees of freedom to an input shaft of a device under test. Said load unit 18 is arranged for integrating the modular drive system 1 and a load application means 19 arranged for providing one to five degrees of freedom of load.

Said load application means 19 may in principle be any kind of load application means that can be integrated with the modular drive system 1 according to the invention, but the load application means shown in fig. 7 is a preferred embodiment of said load application means.

The load application means 19 which is shown in a partly exploded view in fig. 8 comprises a cylindrical moveable structure 20 suspended from the support (not shown) e.g. a test bench, by means of four radial load applying means 21 (21a, 21b, 21c, 21d) . In order to fully support the moveable structure, the four radial load applying means 21a, 21b, 21c, 21d are distributed evenly, such that two radial load applying means 21a, 21b are arranged at the distal end 22a of the moveable structure 20 and two radial load applying means 21c, 21d at the proximal end 22b of said structure 20.

Each of the radial load applying means 21 consist of a linear hydraulic actuator 23 connected to a first connection unit 24 arranged for anchoring the actuator 23 to the test bench (not shown) and a second connection unit 25 arranged for connecting the hydraulic actuator 23 to the movable structure 20. Said first and second connection units 24,25 comprises a suitable bearing assembly or non-rigid joint 26 that will allow the moveable structure to move in relation to the loads applied by the hydraulic actuators 23.

The radial load applying means 21 are individually connected to the distal end 22a and proximal 22b end of the cylindrical moveable structure 20 via a distal load transferring flanges 27a, and a proximal load transferring flange 27b, arranged at the ends of said moveable structure.

The radial load applying means 21 are attached to said load transferring flanges 27a, 27b at an attachment point 29, arranged at predetermined radial distance R_f from a longitudinal centre axis X_m of the moveable structure 20. This is illustrated in fig. 9, which shows a proximal section 28 of the load application means 19 from its proximal end 22b. In order to provide sufficient movement and loads to the moveable structure 20, the radial distance R_f from the attachment point 29 of the radial load applying means 21 to the load transferring flange 27, is larger than the radius of the cylindrical moveable structure R_m. In the embodiment shown the predetermined radial distance R_f is about twice the inner radius of the moveable structure R_m, however said distance may be larger or shorter, depending on e.g. the dimensions of the load application means 19. In the embodiment shown, the attachment point 29 between the second connection unit 25 and the load transferring flange 27 is furthermore placed below the centre axis X_m in order to provide a more stable structure, however said attachment point can be placed above or at the centre axis X_m in different embodiments.

In order to provide further loads to the cylindrical moveable structure 20 one radial load applying means 21b, 21d at each end of the cylindrical moveable structure 20, is double connected to the load transferring flange 27, via a double connection unit 30, comprising a support plate 31 and a link shaft unit 32.

Two axial load applying means 33 (33a, 33b), one on each side of the moveable structure 20, are connected to the distal load transferring flange 27a by means of curved thrust plates 34, as also shown in fig. 10, which shows the inner side of a distal section 35 of the load application means 19. Said curved thrust plates 34 has a larger radius of curvature than the cylindrical moveable structure 20.

Each of the axial load applying means consist of a linear hydraulic actuator 36 connected to a third connection unit 37 arranged for anchoring the axial actuator to the test bench (not shown) and a fourth connection unit 38 arranged for connecting the hydraulic actuator 36 to the movable structure 30 via the thrust plate 34. In the embodiment shown the third connection unit 37 comprises a tripod structure for additional support. As the first and connection units 24,25, the third and fourth connection units 37,38 also comprises suitable bearing assemblies or non-rigid joints 39 that will allow the moveable structure 20 to move in relation to the loads and forces applied by the hydraulic actuators 23,36.

The four radial load applying means 21 are arranged for providing a larger load to the moveable structure 20 than the two axial load applying means 33, but in another embodiments the used actuators could be sized differently. In further embodiment the linear actuators 23,36 could also be motor driven spindles, pneumatic cylinders or other, and the load application means 19 could comprise another number of hydraulic actuators such as two, three or seven or eight, or another suitable number, and the actuators could be placed and spaced differently .

Fig. 11 shows a partly exploded view of the load unit 18 in fig. 7, and as can be seen the housing 7 of the modular drive unit 1 is inserted in the cylindrical moveable structure 20 at connection point 40 via suitable connection units 41. In this way the plurality of motors 2 will be uniformly arranged along a radial circumference of the cylindrical movable structure 20, in such a way that the longitudinal centre axis X_m of the moveable structure coincides with the longitudinal centre axis X_com of the common drive shaft . The modular drive system 1 is connected to the test bench via a torque arm system 42 arranged for both counteracting rotation of the modular drive system and absorbing any relative movements as well as shocks and measuring forces.

Said torque arm system 42 comprises a pair of interconnected hydraulic actuators 45a, 45b arranged in fluid communication such that they may operate in response to each other i.e. if one actuator 45a extend the other actuator 45b will equally extend etc. Such a construction will in a simple and effective way counteracting any rotation of the modular drive system, while allowing translational movement with the load application means .

The thereby provided load unit 18 is a very compact structure, in which the load application means 19 and modular drive system 1 is overlapping and therefore takes up very little space. Said load unit 18 may further transfer load to a device under test in two to six degrees of freedom, depending on how many actuators 23,36 are activated. The five degrees of freedom (F_x, F_Y, F_z, M_Y, M_z) are provided by the load application means 19 and the sixth degree of freedom, the driving torque (M_x) for rotation the input shaft of the device under test, is transferred to the device under test by means of the modular driving system 1.

The respective radial and axial hydraulic actuators 23,36 are operatively connected to one or more hydraulic power units (not shown) , and comprises proportional valves or servo controlled valves (not shown) making it possible to control the load inflicted by each of the actuators 23,36 individually, such that the load application means 19 can transfer five degrees of freedom to the device under test. Accordingly, the load unit 18 is arranged for creating the axial and radial forces in order to simulate the effects of for example wind load on a wind turbines or one of its structural component. For instance, the load unit 18 enables application of shaft rotation, torque, bending moments and shear forces similar to those encountered by a wind turbine during normal operation. Thus the invention may e.g. serve to simulate real time wind loads in order to analyze the dynamic operation behavior of wind turbines.

Fig. 12 shows schematically a third embodiment 12 ' ' of a test bench according to the invention, in which the load unit 18 of fig. 7 is directly connected to a device under test 14.

As is evident from this figure, the second coupling element 17 of fig. 6 is no longer required, and the test bench 12' ' therefore becomes more compact, lighter and less expensive than the test bench 12' of fig. 6.

Fig. 13 and 14 shows the embodiment of fig. 11 in more details, where a wind turbine generator 43 is directly connected to the load unit 18 shown in e.g. fig. 7. The test bench is placed on a foundation 44 and the load unit 18 has been placed at an angle a corresponding to the tilt angle of the rotor of the wind turbine. Since the load unit 18 is an integrated structure, which is independently of other stationary components in the driveline of the test bench 12 ' ' the tilt- angle a of said load unit may easily be adjusted. This can e.g. be obtained by adjusting the height of the four radial load applying means 21 of the load unit 18 or by tilting the entire load unit 18 e.g. by changing the slope of the foundation 44. However, in any case, the test bench 12' ' may be modified in dependence of the optimal tilt angle of the device to be tested. The inventors of the present invention has found that the required length of a wind turbine test bench as shown in e.g. fig. 13 and accordingly the foundation 44 for said test bench may be reduced from about 20% to about 35% compared to the test bench 12' as shown in fig. 6 in which the modular drive system 1 and the load application means 19 are separated by a second coupling element 17. Furthermore, since such a coupling element 17 depending on the circumstances, may have a weight about 100 tons and e.g. costs between 1 and 2 million euros, significant reductions in the weight and cost may be obtained using the load unit 18 according to the invention.

Irrespectively of the embodiment, the test bench may be dimensioned to accommodate any kind of relevant device under test, e.g. wind turbine or its structural elements or an airplane engine, and may accordingly be arranged for operating at any desirable power range e.g. in a range between 1 MW and 10 MW, preferably with an overload capacity of between 10% and 50%. However devices under test having larger and smaller power ratings are also contemplated within the scope of the present invention. Since the modular drive system 1 , 1 ' , 1 ' ' and/or load unit 18 easily and individually can be adjusted to meet the required drive torques, e.g. by altering the use of the plurality of motors 2, by using different motors or by using additional or fewer motors. Accordingly, it will be possible to apply high torque dynamics as calculated by the real time aerodynamic load simulation or given by field data to e.g. a given wind turbine or its structural components. Further wind loads may be delivered by the load application means 19 which may either be a stand alone construction or integrated into the load unit 18. In this respect, the test benches according to the invention is able to stress the wind turbine with wind loads in all six degrees of freedom.

Modifications and combinations of the above principles and designs are foreseen within the scope of the present invention.

Claims

1. A modular drive system (I,I',I'¹) for a test bench ( 12 , 12 ' , 12 ' ' ) , said modular drive system (1) comprises a plurality of drive motors (2) each arranged for providing a drive torque and wherein the modular drive system (1) is arranged for transferring the individual drive torques of the plurality of drive motors (2) to a common drive shaft (6) of the modular drive system (1) thereby providing a united drive torque, and wherein said common drive shaft (6) is arranged for rotating an input shaft of a device under test ( 14 ) .

2. A modular drive system (I,I',I'¹) according to claim 1, wherein the torque load of the plurality of drive motors (2) are transferred to the common drive shaft (6) by means of one or more gear reducing units (4,5) .

3. A modular drive system ( 1 , 1 ' , 1 ' ' ) according to claim 1 or 2, wherein each of the plurality of drive motors (2) are connected to first gear, e.g. a pinion gear (4), and wherein each first gear (4) is peripherally meshing with a larger diameter, centrally disposed second gear (5), e.g. a sun gear or ring gear, and wherein the second gear is arranged for communicating with the common drive shaft (6) .

4. A modular drive system ( 1 , 1 ' , 1 ' ' ) according to any of the claims 1, 2 or 3, wherein the common drive shaft (6) has a longitudinal center axis (X_com) and wherein the plurality of drive motors (2) are circumferentially arranged, and preferably evenly spaced, around said axis (X_com) .

5. A modular drive system ( 1 , 1 ' , 1 ' ' ) according to any of the preceding claims, wherein the plurality of drive motors (2) are circumferentially arranged in or at a housing (7) which is arranged to be mechanically connected to a static interface of a support .

6. A modular drive system (I,I',I'¹) according to any of the claims 3 to 5, wherein the plurality of drive motors (2) are arranged on the same side of the second gear (5) or on both sides of the second gear.

7. A modular drive system (I,I',I'¹) according to any of the preceding claims, wherein the modular drive system (I,I',I'¹) comprises between three and fifty drive motors (2), preferably between five and thirty drive motors (2), and even more preferred between ten and twenty five drive motors (2 ) .

8. A modular drive system (I,I',I'¹) according to any of the preceding claims, wherein the modular drive system is arranged for delivering a nominal input torque of at least about 8 MN»m and more preferably at least about 10 MN»m.

9. A modular drive system ( 1 , 1 ' , 1 ' ' ) according to claim 8, wherein the modular drive system is arranged for providing an overload capability of between 10% and 50% of the nominal input torque of the device under test.

10. A modular drive system ( 1 , 1 ' , 1 ' ' ) according to any of the preceding claims , wherein the plurality of drive motors (2 ) are identical , or wherein at least one of the plurality of drive motors (2a) are different from the other motors (2 ) .

11. A modular drive system ( 1 , 1 ' , 1 ' ' ) according to any of the preceding claims, wherein the modular drive system ( 1 , 1 ' , 1 ' ' ) is arranged for being combined with a load application means (16,19) arranged for providing at least one to five degrees of freedom to an input shaft of a device under test (14) .

12. A modular drive system (I,I',I'¹) according to any of the preceding claims, wherein a coupling element (17) is inserted between the modular drive system (I,I',I'¹) and the load application means (16,19), said coupling element being arranged for absorbing the relative movement between the modular drive system ( 1 , 1 ' , 1 ' ' ) and the load application means (16,19).

13. A load unit (18) arranged for providing between two to six degrees of freedom to an input shaft of a device under test (14), wherein said load unit (18) comprises the modular drive system ( 1 , 1 ' , 1 ' ' ) according to any of the claims 1 to 12, and a load application means (16,19) arranged for providing at least between one to five degrees of freedom.

14. A load unit (18) according to claims 13, wherein the modular drive system ( 1 , 1 ' , 1 ' ' ) is directly connected to a separate support structure via a torque arm system (42) arranged for resisting the torque developed by the modular drive system (I,I',I' '), thereby preventing the counter rotation of the modular drive system during operation.

15. A load unit (18) according to claims 13, wherein the modular drive system ( 1 , 1 ' , 1 ' ' ) is directly connected to the load application means (16,19), such that said load application means (16,19) prevent counter-rotation of the modular drive system ( 1 , 1 ' , 1 ' ' ) during operation.

16. A load unit (18) according to any of the claims 13 to 15, wherein the load unit (18) is an integrated unit and the load application means (16,19) is operatively connected to the modular drive system (I,I',I' ') .

17. A load unit (18) according to any of the claims 13 to 16, wherein the load application means (19) comprises a cylindrical moveable structure (20) suspended from the test bench by means of at least four radial load applying means (21) .

18. A load unit (18) according to claim 17, wherein the at least four radial load applying means (21) are connected to the distal end (22a) and the proximal end (22b) of the moveable structure (20) via distal and proximal load transferring flanges (27a, 27b) arranged at the respective ends of the moveable structure (20) .

19. A load unit (18) according to any of the claims 13 to 18, wherein the load application means (19) further comprises at least one axial load applying means (33) arranged for providing an axial force and/or a bending moment to the moveable structure (20).

20. A load unit (18) according to any of the claims 13 to 19, wherein each axial load applying means (33) are connected to the distal end (22a) of the moveable structure (20) by means of load transferring elements, e.g. in the form of two curved thrust plates (34) connected to the distal load transferring flange (27a) .

21. A load unit (18) according to any of the claims 13 to 20, wherein the load unit (18) is arranged for being directly coupled to the device under test (14), e.g. to the input shaft of said device.

22. A load unit (18) according to any of the claims 13 to 21, wherein the axial and/or radial load applying means (21,33) are linear actuators (23,36), e.g. hydraulic actuators, arranged for extending and retracting in order to apply loads to the moveable structure (20) .

23. A load unit (18) according to any of the claims 13 to 22, wherein load unit (18) is arranged for independently controlling the radial and axial load applying means (21,33) .

24. A load unit (18) according to any of the claims 17 to 23, wherein the plurality of motors (2) of the modular drive system ( 1 , 1 ' , 1 ' ' ) are uniformly arranged along a radial circumference of the cylindrical moveable structure (20), preferably such that a longitudinal centre axis (X_m) of the moveable structure (20) coincides with the longitudinal centre axis of the common drive shaft (X_com) .

25. A test bench ( 12 , 12 ' , 12 ' ' ) comprising the modular drive system ( 1 , 1 ' , 1 ' ' ) according to any of the claim 1 - 12 or a load unit (18) according to any of the claims claim 13 - 24.

26. A test bench ( 12 , 12 ' , 12 ' ' ) according to claim 25, wherein the test bench ( 12 , 12 ' , 12 ' ' ) comprises means for tilting the load unit (18) .

27. A method of providing two to six degrees of freedom to a device under test (14), said method comprises the following steps :

- providing a load unit (18) according to any of the claims 13 - 24,

- providing a device under test (14) in operative coupling with said load unit (18),

- operating said load unit (18) via radial and axial load applying means (21,33) and/or the common drive shaft (6) of said load unit (18), and

- measuring data.

28. Use of a modular drive system (1) according to any of the claims 1 - 12, a load unit (18) according to any of the claims 13 - 24, a test bench according to any of the claims 25 - 26, or the method according to claim 27, for testing a wind turbine, a structural component of a wind turbine, a generator or a motor for automobiles, trains, larger vehicles for transportation, ships, and airplanes.