Abstract:
A shaft mounted rotor brake ( 7 ) with at least one braking force absorption element non-rotatable connected to said shaft ( 1 ). A stationary brake actuator ( 8, 24 ) is mounted to a rotor gear box housing ( 4 ). Said stationary brake actuator ( 8, 24 ) actuates a braking force transmission element ( 17, 23 ) that is functionally coupled to the at least one braking force absorption element ( 2 ) so as to exert a braking effect. At least one rotor brake deactivation device ( 6, 9, 25 ) is provided. The at least one braking force absorption element comprises lamellas ( 2 ) interacting with stationary lamellas ( 3 ), said lamellas ( 2 ) and stationary lamellas ( 3 ) being arranged inside of the rotor gear box housing ( 4 ) with oil inside.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is related to European patent application No. EP 12 400039.9 filed Sep. 24, 2012. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention is related to a shaft mounted rotor brake with the features of the preamble of claim  1 . 
     2. Description of Related Art 
     Rotor brakes are used in helicopters and in some types of helicopters they even are a safety-relevant system. 
     The document DE 693 11 484 T2 discloses a transmission with integrated brake particularly usable for vehicles. The transmission includes, in an oil bath inside a containment and support casing, an epicyclic reduction unit which is kinematically connectable to a drive unit by means of at least two gears, of which the driven one is axially fixed, is coaxial to a sun gear of the reduction unit and is associated therewith by means of a splined coupling. A disk brake is arranged between the epicyclic reduction unit and the driven gear and has at least one first disk rigidly coupled to an internally toothed ring gear which is rigidly coupled to the containment casing and at least one second disk which is rigidly coupled so as to rotate together with the driven gear. The disk brake is associated with axially movable packing pushers. 
     The document EP 0894 712 A2 discloses a helicopter rotor brake having a disk connected angularly to a helicopter rotor. A brake caliper has friction members cooperating with the disk; and an actuating device for moving the brake caliper, parallel to the plane of the disk, between a work position engaging the disk. The brake caliper may be operated to brake the rotor, and a release position releasing the disk and wherein any possibility of the friction members interacting with the disk is prevented. 
     The document DE 103 43 055 A1 discloses a rotor shaft mounted rotor brake with a braking force absorption element non-rotatable connected to said rotor shaft; a stationary brake actuator for hydraulically or mechanically actuating a braking force transmission element that is functionally coupled to the braking force absorption element so as to exert a braking effect; and at least one rotor speed-controlled, centrifugal force-actuated rotor brake deactivation device. 
     Rotor brakes for helicopters may only be deployed on the ground and only once the (main) rotor has reached a certain speed, which is usually 40% to 50% of the rated rotor speed. Such a limitation is meaningful since, due to aerodynamic forces, the rotor speed drops relatively quickly to about 40% to 50% of the rated rotor speed, but after that, it decreases only relatively slowly. Dimensioning rotor brakes that are already effective at 70% to 100% of the rated rotor speed would entail very strong brakes, a substantial weight of the rotor brake as well as increased manufacturing costs. Therefore, especially in the civilian sector, such a design is neither desired nor, as a rule, necessary. 
     With conventional rotor brake systems, actuating the rotor brake above a value of 40% to 50% of the rated rotor speed can lead to deformation of components of the rotor brake, particularly of the brake disc, due to excessive thermal loads, in this speed range, excessive braking energy is applied to the brake system. In the extreme case, the structure of safety-relevant brake components such as, for example, the brake disk or the brake drum, can be changed and fail. As an example, mention should be made of the fact that an actuation of the rotor brake at 70% rather than at 50% of the rated rotor speed means that approximately twice as much braking energy has to be absorbed by the rotor brake system. 
     An operating error can occur with conventional rotor brakes. For example, it is possible for the pilot to accidentally actuate the rotor brake during flight, leading to overheating of the brake system components. Or the rotor brake can be actuated on the ground above the permissible speed of approximately 40% to 50% of the rated rotor speed has been reached which, as already mentioned, might lead to an overheating of the brake system components. With hydraulically activated brakes, an erroneous actuation of the braking function can also occur due to a temperature-related increase in the pressure of the hydraulic system or a malfunction of the hydraulic system. 
     BRIEF SUMMARY OF THE INVENTION 
     It is an object of the invention to provide a shaft mounted rotor brake without the disadvantages of the state of the art. 
     The solution is provided with a shaft mounted rotor brake with the features of claim  1 . 
     According to the invention a shaft mounted rotor brake comprises at least one braking force absorption element non-rotatable connected to said shaft. A stationary brake actuator is mounted to a rotor gear box housing, said stationary brake actuator actuating a braking force transmission element that is functionally coupled to the at least one braking force absorption element so as to exert a braking effect. At least one rotor speed-controlled rotor brake deactivation device is provided for supervision of said stationary brake actuator. The at least one braking force absorption element comprises lamellas connected to said shaft and stationary lamellas non-rotatable connected to said housing, said lamellas interacting with the stationary lamellas. Said lamellas and stationary lamellas are arranged inside of the rotor gear box housing with oil inside. 
     A first advantage of the invention is that the inventive shaft mounted rotor brake is lubricated by gear box oil. A further advantage of the invention is that the gear box oil system is capable to absorb any additional heat due to any friction in the inventive shaft mounted rotor brake and to filter wear particles from the lamellas. The inventive shaft mounted rotor brake allows a durable rotor brake at reduced maintenance, reduced pilots workload and reduced misuse possibilities by a crew/pilot. 
     According to a preferred embodiment of the invention the shaft is a drive shaft of the main gearbox. By using an already existing drive shaft the amount of additional parts required for the rotor brake system is minimized, leading to a simple and cost-efficient design. 
     According to a further preferred embodiment of the invention the shaft is an additional shaft coupled to the drive shaft of the main gearbox for more constructive flexibility. 
     According to a further preferred embodiment of the invention the rotor speed-controlled rotor brake deactivation device comprises a ring shoulder integral with the shaft, counter springs, centrifugal slides and a ring slide with conical shape. At nominal rotations per minute (rpm) of the shaft the centrifugal slides are pressed against the counter springs in their outer position distal to the shaft. Due to its conical shape the ring slide cannot engage with the centrifugal slide to counter act as an abutment. In case the drive shaft speed is reduced, the centrifugal slides are pushed back by the counter springs to the inner position. If now the rotor brake is actuated, the ring slide engages with the centrifugal slides and the rotor brake is engaged. In case of unintended actuation of the rotor brake above the allowed rpm of the main rotor, the centrifugal slides are not at their inner position and the rotor brake cannot engage. 
     According to a further preferred embodiment of the invention the rotor speed-controlled rotor brake deactivation device is a rotational speed depending brake actuator, actuated by the centrifugal force of rotating masses installed on the rotating shaft. Below the critical main rotor rpm, the actuator allows the actuation of the rotor brake by the pilot, above the critical main rotor rpm, it is not possible to actuate the rotor brake. 
     According to a further preferred embodiment of the invention the rotor brake deactivation device is dependent of the pressure of the gear box oil using the dependency between the pressure of the gear box oil and the rotational speed of a main rotor head to prevent the brake from unintended engagement. This has the advantage, that the oil pressure available in the main gearbox can be used for both the brake actuation as well as the brake control. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       A preferred embodiment of the invention is presented with reference to the following description and the attached drawings. 
         FIG. 1  shows a radial half cross section of a shaft mounted rotor brake according to the invention; 
         FIG. 2  shows a schematic view of a preferred embodiment of a shaft mounted rotor brake according to the invention; 
         FIG. 3  shows a cross section of a further preferred embodiment of a shaft mounted rotor brake according to the invention; 
         FIG. 4  shows a cross section of a first operating condition of the further preferred embodiment of  FIG. 3 ; 
         FIG. 5  shows a cross section of a second operating condition of the further preferred embodiment of  FIG. 3 ; and 
         FIG. 6  shows a cross section of a third operating condition of the further preferred embodiment of  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     According to  FIG. 1  rotating lamellas  2  mounted on a drive shaft  1  of a rotor (not shown) of a helicopter are integrated in a gear box (not shown) with a fix housing  4  encompassing said drive shaft  1 . The rotational speed of the drive shaft  1  correlates with the speed of the rotor of the helicopter. The drive shaft  1  is either part of a drive train or part of an additional train dedicated for a rotor brake  7 . The drive shaft  1  is supported in bearings  19 . The fix housing  4  and the rotor brake  7  are closed around said drive shaft  1  with oil inside. 
     Several lamellas  2  of the rotor brake  7  are integrated as braking force absorption element and connected via a spline connection to the drive shaft  1 . Stationary lamellas  3  as braking force absorption element are mounted in between said lamellas  2  to the housing  4  of the gear box. The brake system  7  is lubricated by the gear box oil capable to absorb the additional heat and to filter any wear particles from the lamellas  2  and stationary lamellas  3 . 
     A rotor brake actuator  8  as stationary brake actuator is actuated hydraulically via a supply line  15  to a hydraulic assembly  5  as a braking force transmission element with a pressure chamber  16  closed by a piston head  17  of said rotor brake actuator  8 . A spring  18  pushes the rotor brake actuator  8  away from the rotor brake  7  against the pressure p on the piston head  17  supplied via the supply line  15 . 
     A rotor speed-controlled rotor brake deactivation device  6  is mounted on the shaft  1  to counteract any brake forces from the rotor brake actuator  8  at rotational speeds of the shaft  1  below nominal speed. 
     The rotor speed-controlled rotor brake deactivation device  6  comprises a ring shoulder  6   a , counter springs  6   b , conical centrifugal slides  6   c  radial movable relative to drive shaft  1  and a conical ring slide  6   d  axially movable on drive shaft  1 . The ring shoulder  6   a , the counter springs  6   b , the conical centrifugal slides  6   c  and the conical ring slide  6   d  are concentrically arranged relative to drive shaft  1 . The conical centrifugal slides  6   c  are adjacent to the conical ring slide  6   d  with the conical centrifugal slides  6   c  narrowing towards the drive shaft  1  being complementary to the conical ring slide  6   d  widening towards the drive shaft  1 . The conical ring slide  6   d  is provided with an abutment plate  12  towards the rotor brake  7 . 
     At nominal speed of the drive shaft  1  the centrifugal slides  6   c  press against the counter springs  6   a , said centrifugal slides  6   c  then being located in an outer position distal to the drive shaft  1 . Thus the conical centrifugal slide  6   b  is removed from the complementary conical ring slide  6   d  and conical ring slide  6   d  free to slide axially on drive shaft  1  does not counter act any pressure resulting from brake forces exerted from the rotor brake actuator  8  via the lamellas  2  and stationary lamellas  3 . In case of unintended actuation of the rotor brake  7  the slides  6   d  cannot return to an inner position and the rotor brake  7  cannot engage as the abutment plate  12 . 
     In case the speed of the drive shaft  1  is sufficiently reduced, the conical centrifugal slides  6   b  are pushed back towards the shaft  1  by the counter springs  6   b  into the inner position. If now the rotor brake  7  is actuated by the rotor brake actuator  8 , the conical ring slide  6   d  engages with the conical centrifugal slides  6   b  and the rotor speed-controlled rotor brake deactivation device  6  allows engagement of the rotor brake  7 . 
     According to  FIG. 2  the same references are applied for corresponding features of  FIG. 1 . An alternative rotor speed-controlled rotor brake deactivation device  9  comprises a mass  10  attached by a retaining spring  13  to the drive shaft  1 . The mass  10  rotates with the drive shaft  1 . The mass  10  is fixed to an end of a lever  14 , rotating with the drive shaft  1 . Said lever  14  is pivotable around a point  11  to allow radial displacement of mass  10  relative to the drive shaft  1 . A connecting lever  14   a  is mounted angularly stiff to lever  14  at point  11  and extends with an articulated rod  14   b  through a linear bearing  40  in a bearing support  41  rotating with the drive shaft  1 . The articulated rod  14   b  is articulated to the connecting lever  14   a  and to the abutment plate  12 , said abutment plate  12  being adjacent to a lateral lamella  2  of the rotor brake  7  mounted to the drive shaft  1 . The articulation of the articulated rod  14   b  serves to compensate length variations during any brake operations. 
     If the mass  10  is moved outside away from the shaft  1 —due to centrifugal forces from the shaft  1  at nominal rotational speed—the lever  14  is pivoted radial outside. The movement of the lever  14  is transmitted by means of the stiff connection at point  11  to the connecting lever  14   a  to withdraw the abutment plate  12  via the articulated rod  14   b  from the lamellas  2 ,  3  to open the rotor brake  7  at a predetermined rotational speed of the drive shaft  1  related to the spring rate of the retaining spring  13  and the weight of mass  10 . 
     An automatic engagement of the rotor brake  7  is achieved either with pilot activated rotor brake actuator  8  or without pilot activated rotor brake actuator  8 . 
     Independently from the pilot actuator  8  the rotor brake  7  will automatically disengage above a certain speed during start and slow down. The transmission system must cover the produced heat. 
     According to  FIG. 3  the same references are applied for corresponding features of  FIGS. 1 and 2 . Actuation of the shaft mounted rotor brake  7  is performed by the gear box oil and an actuation piston  26 . The dependency on the rotational speed of the pressure p of the gear box oil is used within the actuator  8  to prevent the rotor brake  7  from unintended engagement. 
     The rotor brake  7  comprises the concentric lamellas  2  on shaft  1  and the concentric stationary lamellas  3  arranged at the housing  4  of the gear box. A concentric brake piston  23  operates the engagement of the interacting lamellas  2 ,  3 . A pressure p in a chamber  24  of the housing  4  pushes the brake piston  23  towards the rotor brake  7  to operate the engagement of the lamellas  2 ,  3 . The chamber  24  is discharged by an outlet  21 . 
     An oil pressure-controlled rotor brake deactivation device  25  comprises an actuator piston  26  and an actuation spring  27  interacting with a control piston  28  in a control casing  30 . The operating range of the control piston  28  is limited by an abutment ring  29  in the control casing  30 . An oil supply line provides oil pressure to a control piston chamber  31 . An oil pressure line  20  to chamber  24  is controlled by the control piston  28  and a non-return valve  22  is supported by a non-return spring  32 . 
     According to  FIG. 4  the shaft mounted rotor brake  7  of  FIG. 3  is shown in a first operating condition. The actuator piston  26  is actuated at nominal speed of the rotor, e. g. unintentionally by the pilot. Oil pressure p is supplied into the control piston chamber  31  pressing the control piston  28  against the abutment ring  29  in its initial position. Thus the outlet  21  to chamber  24  remains open, no pressure is exerted to brake piston  23  and the rotor brake  7  is not engaged. 
     According to  FIG. 5  the shaft mounted rotor brake  7  of  FIG. 3  is shown in a further operating condition. The speed of the rotor is decreased and consequently the oil pressure supplied to the control piston chamber  31  is reduced. Actuation of the actuator piston  26  lifts the control piston  28  off the abutment ring  29  towards its alternative abutment position blocking the outlet  21  and opening a passage from the oil pressure line  20  to chamber  24  by pushing open the non-return valve  22  against the action from the non-return spring  32 . The pressure from the oil pressure line  20  in chamber  24  is exerted to brake piston  23  and the rotor brake  7  is engaged. 
     According to  FIG. 6  the shaft mounted rotor brake  7  of  FIG. 3  is shown in a still further operating condition. The speed of the rotor is still decreased and there is no more any oil pressure supplied to the control piston chamber  31 . On-going actuation of the actuator piston  26  keeps the control piston  28  off the abutment ring  29  at its alternative abutment position still blocking the outlet  21  and keeping open the passage from the oil pressure line  20  to chamber  24 . Once the chamber  24  is filled with gear box oil the non-return valve  22  is set back on its seat by the action from the non-return spring  32  to block the oil pressure line  20 . The pressure in chamber  24  is maintained and the rotor brake  7  remains engaged to prevent the rotor from turning. 
     To start the rotor the actuator piston  26  is released and the control piston  28  is reset against the abutment ring  29  by the increasing oil pressure, counteracting the actuation spring  27 . Thus the control piston  28  opens the outlet  21  and closes the passage from the oil pressure line  20  relieving any pressure in chamber  24 . The rotor brake  7  opens and the rotor is prepared for start. 
     REFERENCE LIST 
     
         
           1  driven shaft 
           2  lamellas 
           3  stationary lamellas 
           4  fix housing 
           5  hydraulic assembly 
           6  rotor speed-controlled rotor brake deactivation device 
           6   a  ring shoulder 
           6   b  counter spring 
           6   c  conical centrifugal slides 
           6   d  conical ring slide 
           7  rotor brake 
           8  rotor brake actuator 
           9  rotor speed-controlled rotor brake deactivation device 
           10  mass 
           11  point 
           12  abutment plate 
           13  retaining spring 
           14  lever 
           15  supply line 
           16  pressure chamber 
           17  piston head 
           18  spring 
           19  bearings 
           20  oil pressure line 
           21  outlet 
           22  non return valve 
           23  brake piston 
           24  chamber 
           25  oil pressure-controlled rotor brake deactivation device 
           26  actuation piston 
           27  actuation spring 
           28  control piston 
           29  abutment ring 
           30  control casing 
           31  control piston chamber 
           32  non return spring 
           14   a  connecting lever 
           14   b  articulated lever 
           40  linear bearing 
           41  bearing support