The invention relates to a brake actuator for an aircraft wheel hydraulic brake.
The hydraulic brakes used for braking the wheels of aircraft generally comprise a ring having multiple cavities in which brake actuators are housed removably. Each of the actuators comprises a liner which is sealingly added to one of the cavities of the ring and in which a piston is mounted to slide sealingly along an axis of sliding. The ring distributes hydraulic fluid under pressure to all its cavities, which fluid acts on the piston in order to cause it to deploy and apply a braking force to friction pads extending opposite the ring, rotors of which rotate with the wheels and stators of which are prevented from rotating.
In general, the piston has an operational travel that it covers when a braking force is applied. This operational travel, of the order of a few millimetres, is enough to allow the braking force to be applied to the friction pads and to cause the push-rod to retreat to allow the rotors to rotate freely. To this end, a spring extending inside the piston ensures that the push-rod retreats into a retracted position when the braking force is no longer applied.
However, the friction pads gradually become worn as a result of repeated application of braking forces so it is important to ensure that the piston is always near the friction pads. In order to achieve this it is known practice to fit the brake actuators with a wear compensation device that extends inside the piston. The wear compensation device comprises a mobile stop which is mounted to slide with friction along the axis of sliding on a central rod extending into the piston and which defines the position to which the piston retreats.
When a braking force is applied, the piston is pushed towards the friction pads and, if necessary, carries the mobile stop along with it, overcoming the friction between the rod and the stop, thereby causing the mobile stop to move forward along the central rod. When the force is released, the spring, which extends between the mobile stop and the piston, causes the piston to retreat as far as the new retracted position, which has moved forward because the mobile stop has moved forward.
There is known, from FR2820794, a brake actuator which is illustrated in
It is an object of the invention to propose a brake actuator for an aircraft hydraulic brake that has a simplified structure.
In order to achieve this goal, there is proposed a brake actuator for an aircraft hydraulic brake, which is intended to be added into one of the cavities of a brake ring, the actuator comprising
Thus, the mobile stop is reduced to its simplest form, the friction member forming on one hand the mobile stop which arrests the piston in the retracted position, and on the other hand a support for the elastic return member which thus acts directly on the friction member. The actuator of the invention thus has a greatly simplified structure.
Any type of elastic member can be used, provided that it has, when compressed, a sufficient increase in force in order to be able to push back the mobile stop in the event that the piston is not in contact with the friction pads while its useful travel is already exhausted. In particular, and according to a particular aspect of the invention, the elastic member is an elastic spring whose coils can meet under the force applied by the fluid under pressure. Thus compacted, the helical spring behaves like a non-deformable solid able to push the mobile stop.
The invention will be better understood in the light of the following description given with reference to the figures of the attached drawings, among which:
With reference to
The actuator 100 first of all comprises a generally cylindrical liner 1 which is housed sealingly inside the cavity 200 of the ring. For that purpose, a seal 2 collaborates with an external face of the liner to contain the hydraulic fluid within the cavity.
A piston 3 is mounted to slide in the liner 1 along an axis of sliding X. To that end, the piston 3 comprises a protrusion 11 that is shaped like a bearing which fits closely against an internal face of the liner 1 and which receives a seal 6. The distal end 5 of the liner 1 is shaped as a bearing to guide the piston 3. The distal end 5 of the liner 1 is fitted with a scraper 7.
It will be noted that the proximal end 4 of the piston 3 is in this instance closed by a wall 8 formed as an integral part of the piston, so as to confine the hydraulic fluid in a zone distant from the discs 300. The distal end of the piston 3 accommodates a shoe 9 to apply pressure to the discs 300.
The actuator 100 is provided with a wear compensation device, which, according to the invention, extends between the liner 1 and the piston 3. The wear compensation device 10 is in this case reduced to a friction ring 13 which rubs against the internal face of the liner 1.
One of the faces of the friction ring 13 (oriented towards the distal end 5 of the liner 1) serves as a stop to define the retracted position of the piston 3. The retracted position is defined by the protrusion 11 coming into contact against the friction ring 13. The other of the faces of the friction ring 13 (oriented towards the proximal end 4 of the piston 3) serves as a support for a return spring 16 returning the piston 3 towards the retracted position. The spring 16 thus acts directly on the friction ring 13.
The way in which the brake actuator of the invention works is as follows. Starting from the retracted position illustrated in
However, it may be that the distance between the shoe 9 and the discs is greater than the operational travel of the piston 3. In this situation, and as illustrated in
Then, when the braking force is released, the piston 3 moves back under the effect of the spring 16 until the piston 3 abuts against the opposing face of the friction ring 13, as illustrated in
The invention is not restricted to that which has just been described but on the contrary encompasses any variant that falls within the scope defined by the claims. In particular, although the friction member which constitutes on its own the mobile stop is in this case a friction ring, it is possible to use other types of friction member such as a spiral friction segment, or furthermore a succession of friction washers. Although the elastic return member is in this case a helical spring, any other elastic member can be used, provided that it has, when compressed, a sufficient increase in force in order to be able to push back the mobile stop in the event that the piston is not in contact with the friction pads while its operational travel is already exhausted.
Number | Date | Country | Kind |
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14 62376 | Dec 2014 | FR | national |