Patent GB-1128058-A (GB)
Title: Self regulating braking system for aircraft wheels
IPC: B64C25/46
Filed: 1965-11-12
Abstract: 1,128,058. Aircraft anti-skid braking systems. RECHERCHES - ETUDES - PRODUCTION. 12 Nov., 1965 [12 Nov., 1964], No. 48148/65. Heading F2F. [Also in Divisions G3 and H1] In an anti-skid system for the braking of aircraft wheels, an inertia-operated braking control device C is housed in the journal 3 of a wheel 1 and controls an electrically-operated valve 12 interposed in the hydraulic braking circuit to prevent wheel locking taking place, an electrically-controlled delay device T being provided in the electrical circuit to control the braking on surfaces with low co-efficients of friction. The hydraulic braking circuit consists of a piston and cylinder device 6, 7, controlled  by a brake pedal (not shown), which in turn controls a distributer valve arrangement 9 controlling fluid to the brakes 2 of wheel 1 when the electrically controlled valve 12 is open via hydraulic conduits 11 and 13 and closing the connection when electrically-controlled valve 12 is closed due to energization of the coil 21 when a skidding condition has been sensed. The inertia-operated braking control device C is provided with an inertia fly-wheel 44 (Fig. 2) which controls operation of two electrical switches 59, 60, a first switch 60 closing when the wheel skids along the ground, a second switch 59 closing when a deceleration of the wheel greater than that produced by closing the first switch. A third switch 22 is mounted in parallel in the circuit of the electrically controlled valve and is controlled by the positions of the shock absorbing system of the undercarriage of the aircraft, the third switch 22 being opened when the shock absorber is compressed and closed when the shock absorber is relaxed. The delay means T is controlled electrically by the second switch 59 and comprises a resistancecapacitance system, with relays, which actuates the electrically-controlled valve for aperiod determined by the resistance-capacitance system. In operation, while the aircraft is still on the ground, the shock absorber 5 is depressed and the contact switch 22 is open. When the pilot depresses the brake pedal the piston and cylinder device 7 is actuated to operate the hydraulic distributor valve 9 and braking pressure is transmitted to the brake actuating cylinder 14 so long as the deceleration does not bring the projection 55 (Fig. 4) on the inertia fly-wheel 44 into contact with the first switch or contact 60, braking is permitted, however, if the braking is too great and contact is established between the projection 55 and the contact 60 (Fig. 3) with the circuit closed, current can flow and supply the electrically-operated valve 12 by way of the lead 98. The valve 12 then connects the hydraulic conduit 13 to the return conduit 15 and closes the inlet conduit 11 to relieve the brakes. As soon as excessive deceleration ceases the contact between the projection 55 and the contact 60 no longer exists and the electrically operated valve is no longer supplied with electricity and braking being permitted if the pilot continues to depress the brake pedal. When the wheel 1 encounters slippery ground conditions the deceleration will be even more excessive and there will be contacts not only between the projection 55 and the contact 60 but also between a projection 54 (Fig. 4) and the contact 59. The delay box T will be controlled by means of the contact 59 and the lead 96 to energize the electrically operated valve 12 and cause the brake to be relieved. By this time the debraking period will no longer be linked to the time of contact between the contact 59 and the projection 54 (Figs. 3 and 4) and will depend solely on the time taken to discharge the capacitor in the delay box T. This longer time enables the wheel to restart more easily on ground having a low coefficient of friction and prevents any locking of the wheels. This delay also occurs if the aircraft should rebound and the shock absorbing contact comes into play and if the wheel enters a hollow in the ground the same condition will apply. The invention may also be applied to a system wherein the electrically operated valves associated with each of the wheels are controlled by one delay box T only.