Vehicle air-conditioning systems

1. An air-conditioning system for a vehicle that includes: a roof; a ceiling; a first side wall and a second side wall; and a front end and a rear end, the air-conditioning system comprising:

single air-conditioning unit mounted at the roof of the vehicle, the air-conditioning unit including an outlet portion for discharging air conditioned by the air-conditioning unit and an inlet portion for receiving air solely from the interior of the vehicle, each of the outlet portion and inlet portion of the air-conditioning unit being located between the front end and the rear end of the vehicle and between the first side wall and the second side wall of the vehicle;

a plenum chamber including a divider mounted within the plenum chamber to divide the plenum chamber into a return portion and a discharge portion, the return portion being in communication with the inlet portion of the air-conditioning unit and the discharge portion being in communication with the outlet portion of the air-conditioning unit;

at least one air-distribution duct supported between the ceiling and the roof of the vehicle in air flow communication with the outlet portion of the air-conditioning unit and the discharge portion of the plenum chamber, the at least one air-distribution duct being adapted to extend in opposite directions from the air-conditioning unit along a substantial portion of the interior of the vehicle from the outlet portion of the air-conditioning unit toward the front end of the vehicle and from the outlet portion of the air-conditioning unit toward the rear end of the vehicle and including at least one opening through which air conditioned by the air-conditioning unit can be discharged to the interior of the vehicle from the single air-distribution duct; and

at least one air-return duct supported between the ceiling and the roof of the vehicle and including at least one opening through which air from the interior of the vehicle can pass into the at least one air-return duct and be discharged from the at least one air-return duct at a discharge location, only the at least one air-return duct being in air flow communication with the return portion of the plenum chamber and the inlet portion of the air-conditioning unit at the discharge location of the at least one air-return duct whereby only air from the interior of the vehicle discharged at the discharge location is returned to the inlet portion of the single air-conditioning unit, the at least one air-return duct engaging the inlet portion of the single air-conditioning unit and extending away from engagement with the inlet portion of the single air-conditioning unit in opposite directions, one end of the at least one air-return duct terminating proximate the intersection of the ceiling of the vehicle and at least one of the first side wall and second side wall of the vehicle intermediate the front end and the rear end of the vehicle with at least one of the at least one opening in the at least one air-return duct through which air from the interior of the vehicle can pass into the at least one air-return duct being located adjacent the termination of the at least one air-return duct proximate the intersection of the ceiling of the vehicle and the at least one of the first side wall and second side wall of the vehicle intermediate the front end and the rear end of the vehicle, whereby air from the interior of the vehicle toward the front end of the vehicle returns to the inlet portion of the single air-conditioning unit in one direction and the other end of the at least one air return duct terminating proximate the intersection of the ceiling of the vehicle and the other of the first side wall and second side wall of the vehicle intermediate the front end and the rear end of the vehicle with at least one of the at least one opening in the at least one air-return duct through which air from the interior of the vehicle can pass into the at least one air-return duct being located adjacent the termination of the at least one air-return duct proximate the intersection of the ceiling of the vehicle and the other of the first side wall and the second side wall of the vehicle intermediate the front end and the rear end of the vehicle, whereby air from the interior of the vehicle toward the rear end of the vehicle returns to the inlet portion of the single air-conditioning unit in the opposite direction.

2. The air-conditioning system of claim 1 wherein the single air-return duct comprises at least two air return ducts that extend away from the inlet portion of the single air-conditioning unit toward the intersection of the ceiling of the vehicle and at least one side wall of the vehicle intermediate the front end and the rear end of the vehicle and from that location along a substantial portion of the length of the interior of the vehicle between the front end and the rear end of the vehicle, at least a respective one of the at least two air return ducts being located at each side of the inlet portion of the single air-conditioning unit.

3. The air-conditioning system of claim 1 wherein the at least one air-return duct extends away from the inlet portion of the single air-conditioning unit toward and terminates proximate the intersection of the ceiling of the vehicle intermediate the front end and the rear end of the vehicle and the first side wall of the vehicle and away from the inlet portion of the single air-conditioning unit and toward and terminates proximate the intersection of the ceiling of the vehicle and the second side wall of the vehicle intermediate the front end and the rear end of the vehicle.

4. The air-conditioning system of claim 3 wherein at least one of the at least one opening in the at least one air-return duct is located adjacent the termination of the at least one air-return duct proximate the intersection of the ceiling of the vehicle and the first side wall of the vehicle and at least one of the at least one opening in the at least one air-return duct is located adjacent the termination of the at least one air-return duct proximate the intersection of the ceiling of the vehicle and the second side wall of the vehicle.

5. The air-conditioning system of claim 1 wherein the at least one air-return duct is adapted to extend substantially linearly along a substantial portion of the length of the interior of the vehicle between the front end and the rear end of the vehicle.

6. The air-conditioning system of claim 1 wherein the at least one air- distribution duct comprises: a pair of air-distribution ducts, each of which is of a length adapted to extend from a first end located toward the front end of the vehicle to a second end located toward the rear end of the vehicle; and an air-distribution cross duct between the pair of air-distribution ducts located intermediate the length of each air-distribution duct, the air-distribution cross duct being in air flow communication with each of the pair of air-distribution ducts and the outlet portion of the air-conditioning unit, whereby air conditioned by the air-conditioning unit can flow through the air-distribution cross duct to the pair of air-distribution ducts.

7. The air-conditioning system of claim 6 wherein openings in the pair of air-return ducts are located at each of the first end and second end of each of the pair of air-return ducts.

8. The air-conditioning system of claim 1 wherein each of the outlet portion and the inlet portion of the air-conditioning unit are located nearer the center than either the front end or the rear end of the vehicle and nearer the center than either the first side wall or the second side wall of the vehicle.