Gyroplane rotor braking unit

For braking a gyroplane rotor, a unit is proposed which comprises a disk brake equipped with a hydraulic actuator (26), which is integrated and has force amplification, as well as a mechanical transmission (54) connecting a control member such as a handle or lever (52) to the said actuator. The amplification effect is obtained by the section difference between a control piston (34) of the actuator directly connected to the mechanical transmission and a free piston (28) of the actuator by which the braking force is exerted.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to a braking unit for use on a gyroplane in order to 
stop the rotor as soon as the aircraft has landed. 
Thus, as the rotation speed of a helicopter rotor decreases prior to its 
complete stoppage, the cyclic control making it possible to check the 
attitude of the rotor disk loses it effectiveness. 
Thus, the rotor slowing down and stopping phase should be as short as 
possible to reduce the risk of a gust of wind tilting the rotor disk 
without the pilot being able to completely oppose it by a cyclic control 
and then the blades can strike passengers leaving the aircraft or unwise 
spectators moving towards it before the rotor has completely stopped. This 
risk is particularly high in the case of lightweight aircraft, whose 
rotors are relatively close to the ground. Moreover, once stopped, the 
rotor must remain in a braked state in order to prevent rotation under the 
effect of the wind. 
The rotor brake of a helicopter is normally located on the transmission 
system mechanism driving the main rotor or the tail rotor. The control of 
the brake takes place by means of a handle generally located on the top or 
roof of the cockpit of the aircraft. The manipulation of said handle must 
make it possible for the pilot to rapidly stop the rotor without it being 
necessary to meter the braking of the latter. The pilot must be able to as 
rapidly as possible free the hand used for manipulating the handle, so as 
to maintain the rotor in a substantially horizontal plane by means of the 
cyclic pitch stick, during the stopping of the rotor, his second hand then 
being occupied by the manipulation of the collective pitch lever. 
2. DESCRIPTION OF THE RELATED ART 
In order to fulfil this function on lightweight helicopters use is made of 
an entirely mechanical braking unit by means of which friction linings 
anchored on a non-rotary support member are applied to a braking disk 
fixed to a shaft connected to the transmission system mechanism for 
rotating the helicopter rotors. This mechanism is such that the blocking 
of the rotor is maintained for as long as the control handle is not 
brought into its initial state. This mechanical braking unit 
conventionally has means making it possible to limit the braking force, so 
as to maintain it at a constant value, as well as restoring means 
constituted by a spring and by means of which the friction linings are 
automatically moved away from the disk when the handle is brought into its 
initial position. 
Although such a braking unit is generally satisfactory, it suffers from the 
disadvantage, due to its totally mechanical nature, of not being able to 
amplify or increase the force applied by the pilot to the control handle, 
so that the application force of the friction linings to the disk is low 
and the stoppage of the rotor does not take place as rapidly as would be 
wished by the pilot. 
Moreover, the use of a hydraulic control, which would make it possible to 
solve this problem, is considered inappropriate, bearing in mind the 
frequent installation of the control handle on the roof of the cockpit, 
where it is not recommended that hydraulic devices be installed due to the 
risk of oil leaks. 
The present invention specifically relates to a gyroplane rotor braking 
unit making it possible to solve the problems disclosed hereinbefore in 
connection with the existing, entirely mechanical braking units and which 
in particular amplifies the braking force applied to the control handle, 
without having recourse to complex systems such as hydraulic support and 
without introducing pressurized hydraulics in the vicinity of the control 
handle. 
SUMMARY OF THE INVENTION 
According to the invention, this result is obtained by means of a gyroplane 
rotor braking unit comprising a disk able to rotate with the rotor, at 
least one friction lining anchored on a non-rotary support member, braking 
means able to apply the friction lining to at least one face of the disk, 
a control member located in the gyroplane cockpit and transmission means 
connecting the control member to the braking means, characterized in that 
the transmission means are mechanical and that the braking means comprise 
at least one force amplification hydraulic actuator integrated into said 
support member. 
In this braking unit, the hydraulic actuator advantageously has a motor 
piston directly connected to the mechanical transmission means, a free 
piston acting on the friction lining and having a larger, section than 
that of the motor piston and a control chamber formed in the support 
member between the motor piston and the free piston. 
Preferably, at least one passage connects the control chamber to a 
hydraulic fluid tank, which can be external of the hydraulic actuator or, 
conversely, integrated into the support member. 
As in the case of existing braking units, force limiting means are 
advantageously provided between the control member and the friction 
lining. 
In a first embodiment of the invention, these force limiting means are 
located in the mechanical transmission means and the passage connecting 
the tank to the control chamber is sealed by the motor piston when the 
latter is not in the brake release position. 
According to a second embodiment of the invention, the force limiting means 
are integrated into the hydraulic actuator. The passage by which the tank 
is linked with the control chamber then has a pressure relief valve, whose 
opening takes place automatically when the pressure in the control chamber 
reaches a value above an actuating pressure of the force limiting means. 
In this case, the force limiting means advantageously have a third piston 
exposed to the opposing actions of the pressure prevailing in the control 
chamber and elastic means. 
Moreover, in this second embodiment of the invention, the control chamber 
is also linked with the tank by a second passage normally closed by a 
check valve allowing a hydraulic fluid passage from the tank into the 
control chamber when the pressure in the latter drops below a threshold 
below a predetermined vacuum. 
According to a preferred embodiment, the support member is constituted by a 
fixed bracket over-lapping the disk and the latter is mounted so as to 
slide along its axis. The bracket then supports a hydraulic actuator, 
which acts directly on a first friction lining adjacent to a first face of 
the disk and, via the sliding disk, on a second friction lining adjacent 
to the second face of the disk.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
In FIG. 1, reference 10 designates a brake disk, which is mounted on 
splines 12 formed on a driving flange 14 integral with the shaft 16 
forming part of the transmission system mechanism rotating the rotors of a 
helicopter, e.g. the shaft ensuring the transmission between the main 
gearbox and the rear rotor of the aircraft. The fitting of the disk 10 on 
the driving flange 14 by splines 12 has the effect of rendering the disk 
10 integral in rotation with the shaft 16 and consequently the helicopter 
rotors, whilst still allowing a displacement of the disk 10 parallel to 
the axis of the shaft 16. 
Besides the braking disk 10, the braking unit shown in FIG. 1 comprises a 
support member 18 constituted by a bracket overlapping the disk 10 and 
fixed to a fixed structure of the helicopter (not shown), e.g. by means of 
bolts. 
In its part located beyond the peripheral edge of the disk, the support 
member 18 is traversed parallel to the axis of the disk by two pins 20, 
which support and anchor two friction linings 22a, 22b positioned facing 
each of the faces of the disk 10. More specifically, each of the friction 
linings 22a, 22b is carried by a plate 24a, 24b respectively and the pins 
20 traverse portions of said plates 24a, 24b located beyond the peripheral 
edge of the disk 10. 
The fixing of the support member 18 to a fixed portion of the helicopter 
takes place from the side of said member adjacent to the friction lining 
22a and a force amplification hydraulic actuator 26 is integrated into the 
support member 18 from the side adjacent to the friction lining 22b. 
More specifically the hydraulic actuator 26 incorporates a free piston 28, 
which is received in sliding manner in a bore 30 made in the support 
member 18, along an axis parallel to the axis of the disk 10 and in front 
of the friction lining 22b. This bore 30 issues on the side of the 
friction lining 22b, so that the free piston 28 bears on the plate 24b by 
means of an element 32 made from a thermally insulating material. 
The hydraulic actuator 26 also incorporates a motor piston 34, which is 
received in sliding manner in a second bore 36 made in the support member 
18 and linked with the bore 30 in order to form with the latter a control 
chamber 38. In the embodiment shown in FIG. 1, the bore 36 is oriented 
according to a direction perpendicular to the axis of the disk 10. 
However, this orientation is not imperative and the axis of the bore 36 
could also be differently oriented, e.g. coaxially to the axis of the bore 
30. The section of the motor piston 34 is smaller than that of the free 
piston 28, so that when the control chamber 38 is filled with hydraulic 
fluid, any force transmitted to the motor piston 34 is amplified, when it 
is applied by the hydraulic fluid to the free piston 28. 
On its outer surface the free piston has a groove in which is received an 
annular gasket 40. In a comparable manner, on the outer surface of the 
motor piston there are two grooves in which are received annular gaskets 
42. The gaskets 40 and 42 ensure the insulation of the control chamber 38 
with respect to the exterior. 
Moreover, the control chamber 38 is linked with a pressurized fluid tank 44 
located outside the support member 18 by a passage 46, which issues into 
the bore 36 at a location in the vicinity of the gasket 42 closest to the 
control chamber 38, when the motor piston 34 occupies its brake release 
position illustrated in FIG. 2. Under these conditions, the tank 44 is 
consequently linked with the control chamber 38. Conversely, any 
displacement of the motor piston 34 resulting from an actuation of the 
braking unit has the effect of interrupting the link between the passage 
46 and the control chamber 38. The gasket 42 furthest from the control 
chamber 38 then maintains the seal of the tank 44 with respect to the 
exterior. 
The hydraulic tank 44, whose function is to compensate hydraulic fluid 
volume variations in the control chamber 38 under the effect of thermal 
expansion, possible leaks or wear to the friction linings 22a, 22b, can in 
particular be constituted by the tank of the helicopter hydraulic 
installation. 
In the embodiment illustrated in FIG. 1, a return or restoring spring 48 is 
mounted on at least one of the pins 20, between the plates 24a and 24b, so 
as to act on the friction linings 22a, 22b moving them away from one 
another. Thus, the friction linings 22a, 22b are automatically moved away 
from the disk 10, when the braking force is released. However, an 
automatic taking up of the wear of the linings 22a and 22b is then ensured 
by a means of a locking ring 50 mounted with a certain axial clearance in 
a groove formed on the outer surface of the free piston 28. This locking 
ring 50 is in engagement with the inner surface of the bore 30 and has a 
shape such that it authorizes the displacement of the free piston 28 
towards the disk 10, whilst opposing the displacement of the piston 28 in 
the reverse direction with a force greater than the return force exerted 
by the spring 48, when the aforementioned axial clearance has been taken 
up. 
In another, not shown embodiment, the return spring 48 and the locking ring 
50 are eliminated. In this case, the automatic moving apart of the 
friction linings 22a, 22b with respect to the disk 10 is obtained as a 
result of the natural warp of the latter. Thus, there is no need for an 
automatic taking up of the wear of the friction linings. 
The braking unit illustrated in FIG. 1 also comprises a control handle or 
lever 52 located in the cockpit of a helicopter, usually on its roof, 
together with completely mechanical transmission means 54 by which a 
movement of the handle 52 is directly transmitted to the motor piston 34. 
More specifically, the control handle 52 is articulated on a spindle 56, so 
as to be able to pivot by approximately 45.degree. between an inoperative 
position illustrated in FIG. 1 and a braking unit actuating position. 
During its tilting, the control handle 52 rotates a pinion 58 meshed on a 
rack 60 forming one of the ends of the transmission means 54. 
The rack 60 is connected to the end of a flexible control member 62, such 
as a flexible, stainless steel plate, by means of force limiting means 64 
constituted by an elastic rod. The flexible control member 62 then travels 
within a sheath 66 fixed to the helicopter structure, e.g. between two 
rows of balls according to a known procedure. The opposite end of the 
flexible control member 62 is fixed directly to the motor piston 34. 
The operation of the braking unit described hereinbefore with reference to 
FIG. 1 will now be explained. In the inoperative state, the different 
elements constituting the braking unit occupy the positions illustrated in 
FIG. 1. In particular, the control handle 52 occupies its inoperative 
position, the two friction linings 22a, 22b are slightly detached from the 
disk 10 and the control chamber 38 is linked with the tank 44 by the 
passage 46. 
When the pilot operates the control handle 52 to bring it into its braking 
position, indicated in dotted line form in FIG. 1, the rack 60 drives the 
flexible control member 62 via force limiting means 64, in such a way that 
the motor piston 34 moves downwards in the bore 36 with reference to FIG. 
1. Under the effect of this displacement the braking force is transmitted 
to the free piston 28 by the hydraulic fluid contained in the control 
chamber 38, which is then insulated from the tank 44 by the closing of the 
passage 46. An effect of amplifying the force exerted on the motor piston 
34 is obtained by the section difference between the pistons 34 and 28. 
Therefore the control handle 52 can be more easily manipulated with a 
limited force. 
The force exerted on the free piston 28 has the effect of applying the 
friction lining 22b to the facing face of the disk 10 and to make the 
latter slide along its axis in order to apply its opposite face to the 
friction lining 22a. Therefore a braking force is obtained, whose value is 
limited to a given braking torque and force by the force limiting means 64 
placed in the mechanical transmission means 54. The locking of the brake 
leading to the immobilization of the helicopter rotor is maintained for as 
long as the control handle 52 is in its actuating position. 
When the pilot brings the handle 52 into its inoperative position, the 
motor piston 34 returns to its initial position illustrated in FIG. 1. 
Thus, a suction effect is brought about in the control chamber 38, which 
leads to a recoil of the free piston 28 by a value corresponding to the 
clearance existing between the locking ring 50 and the groove in which 
said ring is received on the piston 28. The joint spacing of the friction 
linings 22a, 22b is ensured by the spring 48. Under these inoperative 
conditions, the connection of the tank 44 to the control chamber 38 makes 
it possible to automatically compensate any volume variation of the 
latter. 
It should be noted that the manipulation of the control handle 52 is 
facilitated by the amplification effect obtained as a result of the 
hydraulic actuator, without any hydraulic fluid being located above the 
helicopter cockpit. Therefore there are no hydraulic fluid leakage risks 
in said area. 
A second embodiment of the invention will now be described relative to 
FIGS. 2 and 3. In this second embodiment, identical or comparable elements 
to those of the first embodiment are designated by the same references, 
increased by 100. 
As in the first embodiment, the braking unit illustrated in FIG. 2 and 3 
comprises a disk 110, rotatably connected to a shaft, which is itself 
integral in rotation with the transmission system mechanism rotating the 
helicopter rotors, whilst being free to move parallel to its axis. A 
support member 118 in the form of a bracket is joined to a fixed part of 
the helicopter and overlaps the disk 110. This support member 118 supports 
and anchors two friction linings 122a, 122b in front of each of the faces 
of the disk 110 by means of two pins 120. 
In this second embodiment of the invention there is also a force 
amplification hydraulic actuator 126 integrated into the support member 
118 and mainly having a free piston 128 mounted in a bore 130 so as to 
directly press the friction lining 122b against the adjacent face of the 
disk 110 and a motor piston 134 received in a bore 136 oriented, as 
hereinbefore, in a direction perpendicular to that of the bore 130. As is 
more specifically illustrated in FIG. 3, the bores 130 and 136 are 
tangential to one another and define between the pistons 128 and 134 a 
control chamber 138 filled with hydraulic fluid. As in the first 
embodiment, the section of the free piston 128 is larger than that of the 
motor piston 134, so as to give the hydraulic actuator 126 an effect of 
amplifying the force applied to the motor piston 134. The recoil of the 
free piston 128 is also controlled by a locking ring 150 received with a 
clearance in a groove formed on said piston. 
In FIGS. 2 and 3, the control handle and the mechanical transmission means 
between the latter and the motor piston 134 are not shown. However, these 
two elements are identical to those described relative to FIG. 1, with the 
exception of the force limiting means 164, which are no longer placed on 
the mechanical transmission means and are instead integrated into the 
support member 114, like the hydraulic actuator 126. 
More specifically, these force limiting means 164 in this case comprise an 
annular piston 168, received in sliding manner in a bore 170 formed in the 
support member 118 coaxial to the bore 136. A stack of elastic washers 172 
also located in the bore 170 bears both on the annular piston 168 and on 
the opposite end of the bore 170, in order to normally apply the piston 
168 to the end of the bore 170 closest to the control chamber 138, as 
illustrated in FIGS. 2 and 3. 
The sealing of the sliding of the annular piston 168 in the bore 170 is 
ensured by an annular gasket 174 received in a groove formed on the outer 
surface of the piston 168. As in also illustrated in FIG. 3, the end of 
the motor piston 134 turned towards the control chamber 138 is slidingly 
received in the annular piston 168, no matter what the positions 
respectively occupied by the pistons 134 and 168. The sealing of this 
sliding action is ensured by an annular gasket 176 located in a groove 
formed in the inner surface of the annular piston 168. 
The embodiment of FIGS. 2 and 3 also differs from that of FIG. 1 by the 
fact that the tank 144 is also integrated into the support member 118. In 
this case, the passage 146 connecting the tank 144 to the control chamber 
138 is machined directly in the support member 118 and issues into the 
bore 130, as illustrated in FIG. 3. The link between the tank 144 and the 
chamber 138 is controlled by a pressure relief valve 178 located in the 
passage 146. The opening of said valve 178 intervenes when the pressure in 
the control chamber 138 exceeds a predetermined value above the pressure 
causing the recoil of the annular piston 168 in opposition to the action 
of the elastic washers 172. 
As shown in FIG. 3, a second passage 180 is formed parallel to the passage 
146 between the tank 144 and the control chamber 138. This passage 180, 
which also issues into the bore 130, is internally equipped with a check 
valve 182 for authorizing fluid passage from the tank 144 to the chamber 
138, when a vacuum in the latter reaches a predetermined threshold. 
Moreover, FIG. 3 shows that the tank 144 is permanently linked by a 
passage 181 with that portion of the bore 170, which contains the stack of 
elastic washers 172. 
To complete the description of the braking unit illustrated in FIGS. 2 and 
3, FIG. 3 shows that the control chamber 138 can be linked with the 
exterior by a passage 184, which is normally sealed by a needle valve 186. 
In addition, the tank 144 can be linked with the exterior by a bleed screw 
188 (FIG. 2), which is normally closed. 
The operation of the braking unit described hereinbefore will now be 
explained. As in the first embodiment of the invention, an actuation of 
the control handle placed in the helicopter cockpit has the effect of 
displacing the motor piston 134 in its bore 136 in a downwards direction 
relative to FIGS. 2 and 3. This displacement is transmitted to the free 
piston 128 by the hydraulic fluid contained in the chamber 138, so that 
the friction linings 122a and 122b are applied against the two faces of 
the disk 110 and brake the rotor. 
During this actuating phase, the downward movement of the motor piston 134 
continues whilst the braking force is already exerted on the disk 110. 
Consequently, the pressure in the chamber 138 increases and the annular 
piston 168 moves upwards in opposition to the action exerted by the spring 
washers 172. 
When the downward travel of the piston 134 continues, whereas the annular 
piston 168 abuts, the pressure relief valve 178 opens and the excess 
hydraulic fluid escapes from the control chamber 138 into the tank 144. 
The braking unit remains in this state whilst the control handle is 
maintained in its braking position. Thus, the locking of the rotor is 
ensured, particularly in the case of wind. 
When the control handle is brought into its inoperative position, the motor 
piston 134 returns to its position illustrated in FIGS. 2 and 3. The 
annular piston 168, pushed by the spring washers 172, then returns into an 
abutment position, as illustrated in FIGS. 2 and 3. This movement is 
accompanied by a recoil of the free piston 128 by the value authorized by 
the locking ring 150, whose function is comparable to the locking ring 50 
in the first embodiment of the invention. 
In the final recoil phase of the motor piston 134, the check valve 182 
opens and enables the control chamber 138 to fill with hydraulic fluid 
from the tank 144, in order to compensate the vacuum which then tends to 
form in the chamber 138. 
As has been shown by the previous description, the taking up of the wear of 
the friction linings 122a and 122b is automatic. Thus, during each braking 
operation, the total displacement of the free piston 128 is equal to the 
displacement due to the taking up of the clearance between the disk 110 
and the linings 122a and 122b, increased by the displacement corresponding 
to the wear of the linings and the disk. When the brake is released, the 
free piston 128 only recoils by the constant clearance between the disk 
and the linings determined by the locking ring 150. The piston 128 
gradually advances during each braking action and the hydraulic fluid 
volume necessary is supplied by the tank 144 through the check valve 182. 
In the first embodiment of the invention, the thermal protection of the 
hydraulic actuator 26 was ensured by the element 32 interposed between the 
free piston 28 and the friction lining 22b. A comparable solution could be 
adopted in the second embodiment. However, in the case illustrated in 
FIGS. 2 and 3, it is the free piston 128 which is directly made from a 
thermally insulating material such as a ceramic material. 
In order to replace the friction linings 122a and 122b, the brake is 
removed and the valve 186 is opened so as to permit the recoil of the free 
piston 128. This operation enables the hydraulic fluid located in the 
control chamber 138 to return to the tank 144 with a minimum force. 
After fitting new linings, the brake is filled with hydraulic fluid by 
gravity through the hole of the valve 186 after having removed the latter. 
The bleed screw 188 then enables the air contained in the circuit to 
escape. 
Obviously, the invention is not limited to the embodiments described in 
exemplified manner hereinbefore and covers all variants thereof. Thus, 
instead of being supported in mobile manner parallel to its axis, the 
brake disk can be directly fixed to a shaft connected to the main gearbox 
of the helicopter. The support member can then either be mounted so as to 
slide parallel to said axis, or is also fixed, but equipped with two 
opposite hydraulic actuators located on either side of the disk. In 
comparable manner, the supporting and anchoring of the friction linings to 
the support member can be carried out differently.