Abstract:
The inventive stress test rig for helicopter transmission comprises a first test rig transmission ( 16 ) which is driven by a motor ( 38 ) and forms a closed stress circuit via shafts ( 4, 14, 54 ), connecting couplings ( 12 ) a stress mechanism ( 40, 42 ), a second test rig transmission ( 52 ) and a test transmission ( 2 ) having a rotor shaft ( 4 ) on the output side. To house the test transmission ( 2 ), it has a clamping plate ( 23 ) which by means of at least one actuator ( 22 ) can be rotated about the rotor shaft axis of the test transmission to compensate load-induced displacements at the connecting couplings ( 12 ) of the test transmission.

Description:
FIELD OF THE INVENTION 
     The invention relates to a stress test rig for helicopter transmissions. 
     BACKGROUND OF THE INVENTION 
     In DE 196 16 729 A1, a generic stress test rig has been disclosed. One test rig transmission, driven by a motor, is operatively connected via shafts and connecting couplings with a helicopter transmission to be tested which has a rotor shaft on the output side. Situated above the rotor shaft of the test transmission, a second test rig transmission is operatively connected with the rotor shaft. A combination of shafts connecting to the first test rig transmission completes the stress circuit. A stress mechanism is provided for predetermining the stress torque in the stress circuit. By the feedback of power from the test transmission output to the test transmission input, high testing powers are made possible without a correspondingly high expenditure of energy, since only power losses must be applied by the motor in the stress test rig. 
     During rotation speed reductions, helicopter transmissions branch input powers from one to three prime movers to different outputs like main rotor, rear rotor and auxiliary outputs. The specifically highly stressed transmissions are small and light in design according to the requirements in air travel. The housing are mainly made of aluminum and magnesium alloys. The elasticity modules of the materials are from one half to one third of the elasticity module of steel alloys, i.e. the elastic deformations are accordingly larger under load. A torsion of the transmission housing around the rotor shaft axis particularly occurs. 
     The consequence of this is that inputs or outputs which are disposed on the transmission at a radial distance from the rotor shaft axis, shift from an initial position. Opposite to the axes of attachable shafts, which lead to the prime movers or to the rear rotor output, the axes of the inputs and outputs of the transmission gearings and radial displacements occur. 
     In the helicopter, part of this displacements is compensated by non-torsional, angularly movable discs or diaphragm couplings. But a considerable part of the displacements are compensated by the connecting shafts, very long as a rule, leading to the prime movers or to the rear rotor output. 
     When the transmission is installed in such a stress test rig, the installation situation of the transmission is extensively simulated in the helicopter cell. For reasons of technical economy and space, however, substantially shorter input and output shafts are being used. 
     On account of the short shafts, a large part of the displacements must be compensated by the coupling elements. Together with substantially high load of the coupling elements due to the large angles, there also appear on the input and output shafts of the helicopter transmission substantially high bearing loads in a radial direction. The heavy loads simultaneously with very high rotational speeds of up to about 25,000 1/min (revolutions per minute) can result in destruction of the coupling elements and damage to the supporting range of the input and output points and on the highly sensitive free wheels of the helicopter transmission. But the stresses in the test rig must not exceed the operating loads on the helicopter or, in the worst case, cause damage to the transmission. 
     U.S. Pat. No. 5,207,676 has disclosed a gear cutting test machine having devices for position changes of the individual gear wheels geared with each other. 
     The problem on which the invention is based is to further develop a generic stress test rig so that, as exact as possible, a simulation of the loads appearing on the helicopter is made possible in a small space. The stress test rig must be flexibly adaptable to different types of helicopter transmissions and load profiles, and operate safely within admissible loads or damages. 
     SUMMARY OF INVENTION 
     The problem is solved by the fact that a clamping plate, rotatable by at least one actuator around the rotor shaft axis of the test transmission, is provided for supporting the test transmission. The arrangement makes it possible, wholly or partly, to compensate for the displacements appearing under load on the connecting couplings of the test transmission. 
     In an advantageous development of the invention, the rotatable clamping plate and the actuators are situated on an assembly truck which accommodates the test transmission and all necessary adaptation devices, e.g. adaptative transmissions. In connection with this invention, the use of an assembly truck offers the advantage that with simple means an individual adaptation for different types of helicopter transmission is possible. The connecting points for transmission bottoms or bottom flange of the test transmission are situated in the clamping plate so that the axis of rotation of the clamping plate coincides at least approximately with the rotor shaft axis. The arrangement of the clamping plate of the actuators and, if needed, the required adaptation transmission on the assembly truck makes possible a standardized connecting point of assembly truck to test rig. 
     An advantageous arrangement of the actuators results when two symmetrically opposite actuators are provided, each of which is situated tangentially to the direction of rotation of the clamping plate between a connecting point on the clamping plate and a connecting point on the assembly truck. By virtue of this arrangement, the support of the rotatable clamping plate on the assembly truck remains at least approximately free of radial forces. 
     Stresses can be avoided by an axially movable support of the clamping plate in a direction along the axis of rotation. 
     In an advantageous development of the invention, the stress mechanism has a stress motor with an electric stress torque regulator unit controlled by a microprocessor and an overlay transmission. The stress-torque dependent control of the actuators is simplified, especially when an electronic actuator-control regulator unit with a signal input for theoretical stress torque value and at least one signal output for a theoretical position value of an actuator or of the clamping plate is provided. 
     On account of the short shafts, a large part of the displacements must be compensated by the coupling elements. Together with substantially high load of the coupling elements due to the large angles, there also appear on the input and output shafts of the helicopter transmission substantially high bearing loads in a radial direction. The heavy loads simultaneously with very high rotational speeds of up to about 25,000 1/min (revolutions per minute) can result in destruction of the coupling elements and damage to the supporting range of the input and output points and on the highly sensitive free wheels of the helicopter transmission. But the stresses in the test rig must not exceed the operating loads on the helicopter or, in the worst case, cause damage to the transmission. 
     Great security can be obtained when in the stress circuit at least one torque sensor is situated and the electronic actuator-control regulator unit has at least one signal input for an actual value of the stress torque of the torque sensor or when at least one sensor is provided for the actual position value of an actuator or of the clamping plate. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is shown in detail with reference to the drawings wherein: 
     FIG. 1 is a diagrammatic top view on one part of a stress test rig known already; 
     FIG. 2 is a diagrammatic top view of one part of an inventive stress test; 
     FIG. 3 is a diagrammatic side view of one part of an inventive stress test rig; and 
     FIG. 4 is a diagrammatic representation of the control of the stress test rig. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The well known test transmission  2 , shown in FIG. 1, has a rotor shaft  4  extending perpendicular to the drawing plane. The rotor shaft is operatively connected with an upper test rig transmission  52  (not shown). Situated on the side of the test transmission  2  are two inputs  6 ,  8  and one output  10  leading to the rear rotor. They are operatively connected by means of connecting couplings  12  and shafts  14 A,  14 B,  14 C with corresponding outputs and inputs of the lower test rig transmission  16 . The test transmission  2  is fixed by means of four struts  18  upon an assembly truck  20  that can be fastened in the test rig. Occurring under load, a reaction torque of the test transmission  2  occurs and is transmitted essentially by means of transmission bottoms, bottom flanges or horizontal struts (not shown) to the assembly truck  20 . The reaction torque, which results in a housing deformation of the test transmission  2 , acts under load between the connecting points and the rotor shaft. 
     As consequence of the deformation of the housing, the laterally situated inputs and outputs  6 ,  8 ,  10  are bent relative to the connecting shafts  14 A,  14 B,  14 C connecting to the test rig transmission  16  by the angles β 1 , β 2 , β 3 . Designed as discs or diaphragm couplings, the connecting couplings  12  can compensate, to a certain extent, for the displacement. But as result of the shorter connecting shafts  14 A,  14 B,  14 C relative to the installation in a helicopter and of the high rotational speeds of up to 25,000 1/min (revolutions per minute), the loads on the connecting couplings  12  are considerable, which can lead to damage in the connecting couplings. The radial forces on the inputs and outputs  6 ,  8 ,  10  are also substantially stronger than in the helicopter installation. 
     FIG. 2 diagrammatically shows one part of an inventive stress test rig in top view. The displacement occurring under load on the connecting couplings  12  are compensated by a clamping plate  23  rotatable around the axis of the rotor shaft  4 . The clamping plate rotates, relative to the assembly truck  20 , by virtue of two hydraulically or electrically operated actuators  22 , which, symmetrically opposite each other, and are situated tangentially to the direction of rotation of the clamping plate between one connecting point  24  of the clamping plate and one connecting point  26  of the assembly truck. 
     In these connecting shafts  14 A,  14 B,  14 C between the upper and lower test rig transmissions  16 ,  52  and inputs and outputs of the test transmission  2 , sensors  28 ,  30 ,  32 ,  34  are disposed for determining the actual value of the stress torque (FIG.  4 ). This can be determined from the sum of the signal values of the torque sensors  28 ,  30  and  32  or from the signal value of the torque sensor  34  disposed on the rotor shaft. The actuator-control regulator unit  36 , shown in FIG. 2, has a signal input for the actual value of the torque of the stress torque and signal outputs for theoretical values of the position of the actuators  22 . Depending on the signal input, the signal outputs are measured, e.g. by a linear interrelation with the signal input so as to compensate for the displacement on the connecting couplings  12 . Other methods are described with reference to FIG.  4 . 
     FIG. 3 shows a diagrammatic side view representation of one part of an inventive stress test rig. Parts corresponding to each other are provided with the same reference numerals. The test transmission transmits the reaction torque originating in the ratio via bottom flanges (not shown) to the clamping plate  23  rotatable around the axis of the rotor shaft. The struts  18 , additionally placed between test transmission and assembly truck, transmit to the helicopter in essence the vertical forces appearing between rotor and helicopter cell; the same forces developed by pitching and rolling torques. The clamping plate  23  is axially movably supported with the bearing  56  in the assembly truck  20  relative to the torsion axis or the rotor shaft axis. Hereby stresses are prevented. The rotor shaft  4  is connected via a coupling  58  with the upper test rig transmission  52 . A torque sensor  34  is located between rotor shaft  4  and upper test rig transmission  52 . The upper test rig transmission  52  is coupled by shaft connections (not shown in FIG. 3) with the lower test rig transmission  16  whereby the stress circuit is completed. 
     FIG. 4 diagrammatically shows a test rig construction and the control devices. The motor  38  drives the lower test rig transmission  16  and compensates for any power losses occurring in the stress circuit. The stress circuit between lower test rig transmission  16  and upper test rig transmission  52  is closed by the shaft  54  and the overlay transmission  40 . The overlay transmission  40  has an input from a stress motor with an electric stress-torque regulator unit  42  controlled by microprocessor. The stress mechanism  40 ,  42  produces, depending on the stress-torque theoretical value  44 , the stress torque in the stress circuit. Construction and mode of operation of the stress mechanism are not an object of this invention. 
     The electronic actuator-control regulator unit  36  receives the signal of the stress-torque nominal value  44  and issues a theoretical position value  48  for the actuator  22 . In the simplest case, there is a linear interrelation between the two signals. Since the theoretical stress-torque nominal value  44  is a control variable, a time characteristic caused by a feedback is prevented. In principle, it is also possible to use an actual stress-torque value  46  of a torque sensor  34  for producing the theoretical position value  48 . If the actuator-control regulator unit  36  has a signal input for the stress-torque nominal value  44  and a signal input for the theoretical stress-torque value  35 , by comparing the signals, an erroneous operation of the test rig can be diagnosed, if needed, in order to disconnect the test rig to prevent damages. Besides, if the actuator-regulator control unit  36  evaluates a signal  50  of a sensor for the actual position value, an erroneous operation of the actuator can also be determined. If the actual position value falls back by a certain amount from the theoretical position value, it is, likewise, possible to assume an erroneous operation or react accordingly. When the actual stress-torque value  46  suddenly drops as result of an operation failure, the actuators  22  are immediately moved to an accelerated emergency operation in a neutral normal position. 
     REFERENCE NUMERALS 
       2  test transmission 
       4  rotor shaft 
       6  input 
       8  input 
       10  output 
       12  connecting coupling 
       14 A, B, C 
       16  lower test rig transmission 
       18  strut 
       20  assembly truck 
       22  actuator 
       23  clamping plate 
       24  connecting point 
       26  connecting point 
       28  torque sensor 
       30  torque sensor 
       32  torque sensor 
       34  torque sensor 
       36  actuator-control regulation unit 
       38  motor 
       40  overlay transmission 
       42  stress motor with microprocessor-shafts control regulator unit 
       44  theoretical stress-torque value 
       48  theoretical position value 
       50  actual position value 
       52  upper test rig transmission 
       54  shaft 
       56  bearing 
       58  coupling 
     β 1 ,  2 ,  3  angle