This invention relates to a small mass transit vehicle having an air conditioning unit mounted upon the rear wall of the vehicle and, in particular, to apparatus for attenuating the sound generated by the unit.
In many small buses of the type used to shuttle people about airports or the like, the air conditioning unit that is used to provide cooling to the passenger compartment is generally mounted upon the outside of the buses rear wall. An opening is provided in the rear wall through which return air from the passenger compartment is drawn into the evaporator section of the air conditioning unit. Conditioned supply air from the evaporator is distributed throughout the bus through a system of ducts. The opening in the rear wall is typically situated directly over a row of seats located along the rear wall of the bus. As a consequence, passengers that are seated in the rear of the bus are subjected to a good deal of noise produced by the evaporator fans and the return air flow that is being drawn through the opening. The noise levels throughout the bus can, under certain conditions, be high enough so that passengers cannot effectively communicate verbally with the bus driver. Failure to communicate leads to a good deal of confusion within the bus and the failure of passengers to debus at the desired locations. This, in turn, produces missed connections and other unwanted travel delays.
It is therefore a primary object of the present invention to reduce the noise level in the passenger compartment generated by the air conditioning system of a small bus such as an airport shuttle bus or the like.
A still further object of the present invention is to improve the ability of passengers in a small bus to communicate effectively with the operator of the bus.
Another object of the present invention is to break the sound path of air that is returning from the passenger compartment of a small bus to the air conditioning unit of the bus without adversely effecting the efficiency of the unit.
These and other objects of the present invention are attained in a small mass transit vehicle that contains an air conditioned passenger compartment. The air conditioning unit is secured to the outside of the bus""s rear wall. An opening is located centrally in the rear wall through which return air from the passengers compartment is drawn into the evaporator of the air conditioner. A housing is mounted over the central opening which has a front wall that extends laterally beyond either side of the opening. Apertures are mounted in the extended sections of the front wall so that the return air is forced to move over a tortuous path of travel between the apertures and the central opening thereby attenuating the noise associated with the return air flow. The interior surfaces of the housing are covered with an open celled foam which further attenuates the sound produced by the air conditioning unit.