Anti-lock braking system module for aircraft equipped with master cylinder brake systems

A combined brake and anti-lock system for a wheeled vehicle comprising:

• an operator controlled source of pressurized hydraulic fluid having at least one master cylinder;
• a hydraulically actuated wheel rotation braking device which responds to applied hydraulic pressure to apply a braking force to a wheel of the vehicle to arrest wheel motion;
• a shuttle valve having first and second inlets and an outlet connected to the wheel rotation braking device for providing a fluid path between the inlet receiving the greatest fluid pressure and the wheel braking device;
• first and second low pressure hydraulic fluid returns;
• first and second anti-lock braking modules;
• a first normally open hold valve between the source master cylinder and the first shuttle valve inlet for selectively opening and closing a fluid flow path from the source master cylinder to the shuttle valve;
• a second normally open hold valve between the source master cylinder and the second shuttle valve inlet for selectively opening and closing a fluid flow path from the source master cylinder to the shuttle valve;
• a first normally closed decay valve between the first shuttle valve inlet and the first low pressure return for selectively opening and closing a fluid flow path from the first shuttle valve inlet to the first return;
• a second normally closed decay valve between the second shuttle valve inlet and the second low pressure return for selectively opening and closing a fluid flow path from the second shuttle valve inlet to the second return;
• a wheel speed sensing device providing an indication of the rotational, speed of the wheel;
• a valve control responsive to an indication of a skid indicative wheel speed irregularity from the sensing device to close the first and second normally open hold valves and open the first and second normally closed decay valves;
• and
• means for disabling the valve control to allow anti-lock-free braking.

A method of retrofitting an aircraft braking system of the type having two independently operable hydraulic braking circuits, each said braking circuits including a master cylinder for selectively supplying pressurized hydraulic fluid to a corresponding brake actuating mechanism, to incorporate an anti-skid feature, comprising:

• introducing two pair of valves, one pair into each of the two hydraulic braking circuits between the master cylinder and corresponding brake actuating mechanism;
• normally providing a fluid path, with the first valve of each pair, between a master cylinder and corresponding actuating mechanism and operable against spring bias to block the fluid path between the master cylinder and actuating mechanism, and the second valve of each pair normally closed and opening against spring bias to vent pressurized fluid from the corresponding actuating mechanism to a sump;
• providing a system for indicating wheel speed for at least two aircraft, wheels, one wheel controlled by one of the two braking circuits and the other wheel controlled by the other of the two braking circuits;
• electronically interconnecting the wheel speed sensing system and pairs of valves to monitor each of the two wheel speeds during aircraft operation, and to close the appropriate first valve and open the corresponding second valve upon sensing a skid indicative wheel speed irregularity of a corresponding wheel;
• and
• providing a pilot operable control for selectively disabling the electronic interconnection to fix both pairs of valves in their normal conditions directly hydraulically coupling the master cylinders to their respective brake actuating mechanisms thereby disabling the anti-skid feature.