Patent GB-999135-A (GB)
Title: Automatic brake control device
Inventor: FARR GLYN PHILLIP REGINALD
IPC: B60T8/17
Filed: 1961-04-25
Abstract: 999,135. Fluid-pressure braking systems. DUNLOP RUBBER CO. Ltd. April 13, 1962 [April 25, 1961], No. 14842/61. Heading F2F. [Also in Division G1] In order to provide controlled braking of an aircraft in dependence upon aircraft speed during landing, a fluid-pressure braking system comprises means responsive to the speed of an unbraked wheel on the aircraft for selectively energizing electromagnetic means adapted to modify the pole strength of a permanent magnet 26a so as to cause pivoting of a member 12 adapted to control the pressure of fluid applied to the brakes. In the hydraulic braking system shown a solenoid-operated inlet valve 5 is controlled by a switch 2 on the pilot's pedal 1 via a relay 3, and a valve assembly 16 operable to connect the hydraulic source to the brake cylinders or the brake cylinders to an exhaust conduit 21 is controlled in accordance with aircraft speed and also by a skid-preventing device 35 which is connected via a valve 36 having a restricted passage 37 to a skid-sensing unit responsive to the difference in speed of a braked wheel and an unbraked wheel. The speed-responsive control for the valve assembly 16 comprises a coil 9a which is fed with a variable current from a generator 28 associated with an unbraked datum wheel. An amplified current is supplied by an amplifier 29 via a non-linear resistor 33 and a rectifier 31 so as to set up a correspondingly varying voltage. An opposing fixed voltage from a stabilizer 32 determines a threshold speed below which, because of the rectifier 31, no current flows through the coil 9a. Above this speed the current through coil 9a depends on the speed of the generator 28, rising non- linearly as determined by resistor 33. This current acts in opposition to a second current in a coil 9 which is determined partly by the manual setting of a potentiometer 27 and partly by a skid-sensing means comprising a variable resistor 43, a slider 42 of which is moved to the right when, owing to a skid, pressures on opposite sides of a piston 39 become unbalanced. These two currents are arranged to modify the pole strength of permanent magnet 26a, so that at higher aircraft speeds the pressure in the brake cylinders is reduced, following a desired characteristic which depends upon the current flowing through coil 9 as set by the potentiometer 27. The current through coil 9 can be increased at any time by the pilot depressing pedal 1 beyond the position necessary to close the switch 2. The pivoted member 12 is urged against the resilience of a sealing member 25 with a force proportional to the pole strength of magnet 26a as modified by the currents in coils 9 and 9a to cause its end 12a to block to a greater or lesser extent an orifice 13 leading from a chamber 11 which is connected to the hydraulic supply via a restriction 10. The fluid passing through the orifice 13 is led to exhaust via passage 22. The pressure thus built up in chamber 11 acts on piston 14, so that, in the absence of a skid and when the speed of the aircraft is decreasing, exhaust valve 15 is closed to seal off exhaust passage 20 and hence cut-off the brake cylinders from exhaust, and valve assembly 16 is moved to the left to lift the valve portion 16c off its seat, so that fluid passes from the supply into the brake cylinders until the brake cylinder pressure equals the pressure in chamber 11, the area of valve 15 exposed to brake cylinder pressure being equal to the area of piston 14 acted on by pressure in chamber 11. Consequently, any change of pressure in chamber 11 causes a corresponding change in brake cylinder pressure. When a skid occurs and the current in coil 9 is reduced, the resulting reduction of pressure in chamber 11 caused by reduced force acting on the member 12 partially releases the brakes.