Patent GB-1018548-A (GB)
Title: Automatic wheel brake system
Inventor: SMITH HAROLD RICHARD
IPC: B60T8/17
Filed: 1964-04-30
Abstract: 1,018,548. Fluid pressure; brakes. NORTH AMERICAN AVIATION Inc. April 30, 1964, No. 18062/64. Heading F2F. [Also in Division G3] An automatic wheel brake system comprises means for actuating a brake to apply braking torque to the wheel during normal braking, brake release means adapted to effect release of the brake, means for determining actual slippage of the wheel resulting from actuation of the brake and automatic means operable to actuate the brake release means in response to a predetermined amount of slippage of the wheel being attained. In the embodiment disclosed in Fig. 1 the main landing wheel 1 of an aircraft is adapted to be braked by means of a multidisc brake 2 adapted to be actuated by means  of fluid pressure actuator 3, 33 when fluid is supplied to the left-hand side of pistons 27 via conduit 31 from an inlet connection 25 from a source of pressure fluid when the brake pedal 8 is depressed. When this occurs a potentiometer circuit 7 feeds a signal Tc through an amplifier 10 through mixers 23, 34 and a coil 5 to actuate a valve spool 26 in a downward direction. When the brake pedal is released the valve spool moves upwardly to shut off the supply of fluid to the conduit 31 and fluid pressure is supplied through conduit 32 leading to the right-hand side of the pistons 27 in the actuators 3, 33 to release the brakes. The braking torque applied to the brake is measured by a torque sensor 11 which provides a signal which is fed into the mixer 34 to perform a limiting function. The signal from the torque sensor 11 TB is also supplied to a computer circuit 13. A signal VB is supplied from a signal generator 12 which may be used to determine the rotational speed of the wheel 1 and this signal is fed into a differentiating circuit comprising a slip computer 14. A reference wheel 17 is provided with a signal generator 18 which supplies a signal VR to the computer 14. A further signal FN is supplied from a transducer 30 which responds to the air pressure in a shock-absorbing strut 20, this signal being applied to a trigger amplifier 60 in the computer 13. The resulting output signal from the computer 13 and its associated quotient computer 50 furnishes an output signal proportional to the braking coefficient (i. The output signals from the computers 13 and 14 U and S respectively are both fed into a computer 16 which computes the slope of the derivative of U with the derivative of S each with respective time. The output from the computer 16 is conducted into a slope limiter 98 which also receives a signal from a slope reference signal source 77 and a signal is supplied to a mixer 35 through a conductor 135. A third loop of the system disclosed above comprises signal generators 12 and 18, computer 14, slip limiter 90, mixers 23 and 35 and the hydraulic system component shown in Fig. 1. This third or slip loop system is normally for emergency or for protective brake control use and does not affect brake operation except when the second loop described above fails to function properly such as the non-functioning of the computers 13 or 16. Thus the amount of torque applied by the brake 2 depends in part upon the intensity of the originating signal Tc depending on the amount of displacement of the pedal 8 and in part by the modified signals supplied from mixers 35, 23, 34 to the coil 5 dependent upon an excessive torque sensed by the generator 11 and modified by the computing circuits 13-16 inclusive so that the brake release means is actuated in response to a condition of incipient skidding. In an alternative embodiment disclosed in Fig. 3 (not shown) the valve 4 of Fig. 1 is replaced by a modulating valve 103 which contains a valve spool 114, 126 and 127 which controls the passage of fluid from a pressure circuit via conduit 25, a conduit 31 leading to the brake actuators 3, 33 and a conduit 24 leading to a drain. The valve 103 also contains a magnet 112 in the field of which operates a flapper member 109 to control the flow of fluid emanating from an opening 119 in a nozzle 110 supplied from the conduit 25. The slip signal outputs S from computer 14 is fed to a mixer 35 instead of through a slip limiter 90 as shown in Fig. 1 and the output from a mixer 23 is applied to the valve 103 such that automatic brake release is achieved by moving the flapper member 109 to the position resulting in maximum flow from the nozzle 110 in the event of an incipient skid occurring. Other embodiments are disclosed in the Specification including one (Fig. 4, not shown) in which the potentiometer circuit 7 is replaced by a pilot-operated valve 132 which normally applies pressure to the brake actuators except when the valve 103 is actuated to interrupt communication between the pilotoperated valve and the brake actuator so that mixers 23 and 34 are eliminated.