Central tire inflation system

A central tire inflation system for sensing and maintaining selected pressures in tire chambers of tire assemblies mounted for rotation at opposite ends of at least one axle assembly supporting a chassis of a vehicle controlled by an operator;

• the system comprising:
• an air source for providing pressurized air at pressure at least equal to normally maximum tire chamber air pressure;
• selector means including means selectively activated by the operator for preselecting one of several desired tire chamber air pressures;
• a control circuit including means automatically operative several times per hour to activate a pressure check mode to compare tire pressure signals form a sensing means with a preselected tire pressure, and automatically operative to activate inflation, deflation and steady-state modes respectively in response to the sensed tire pressure being less than or greater than or within limits of the preselected tire pressure;
• an air circuit for connecting the air source to each tire chamber, the air circuit including rotary seal means connecting non-rotatably mounted parts of the air circuit with rotatably mounted parts of the air circuit for communicating air therebetween;
• a control valve secured to each tire assembly, each control valve having a first port connected to one of the rotatably mounted parts of the air circuit, a second port connected to the tire chamber of the associated tire assembly, and valving means movable to a position blocking the second ports in response to air pressure at the first port being substantially atmospheric pressure and movable to a position unblocking the second ports in response to a non-atmospheric pressure at the first port;
• valve means operative in response to the automatic activation of the steady-state mode by the control circuit means to vent the air circuit to atmosphere for moving the valving means of the control valves to the blocking positions and for unpressurized operation of the rotary seal means;
• the valving means operative in response to the automatic activation of the check, inflate and deflate modes to apply the non-atmospheric pressure to the first ports for moving the valving means to the unblocking positions;
• and the valve means operative in response to:
• activation of the check mode to momentarily apply the non-atmospheric pressure for establishing an air pressure in the air circuit at the sensing means representive of tire pressure, activation of the inflate mode to connect the air source to the first ports for increasing the tire pressure, and activation of the deflate mode to connect the second ports to vent means for decreasing the tire pressure;
• characterized by:
• switch means manually activated by an operator during vehicle operation in hazard zones for automatically increasing the frequency of activating the check modes by the control conduit means from several times per hour to several times per minute for automatically more quickly detecting low tire pressure conditions, and for automatically more quickly activating the inflation modes to prevent flat tire conditions within the air capacity of the air supply.