Air mixing system for auxiliary vehicle HVAC units

[00002] 1. Field of the Invention

[00003] The present invention relates to motor vehicle cabin climate control and more particularly to a system for mixing outside and recirculated inside air for secondary climate control zones in vehicles having multiple zones for heating, ventilation and air conditioning (HVAC) control.

[00004] 2. Description of the Problem

[00005] Motor vehicles having relatively large passenger cabins, such as extended cab trucks and recreational vehicles, often provide zonal heating and cooling for different sections of the cabin. Separating heating and cooling functions by zone allows heating and cooling to be limited to those zones that are in use, reducing the load on the heating and cooling plants, particularly the compressor for air conditioning. Typically the zones are arranged from front to back of the vehicle. Each zone will have an independent HVAC unit, located in its own merged heating and cooling air circulation system to reduce the quantity and cost of duct work. HVAC units comprise a blower, an evaporator and a heater core. One air conditioning compressor typically serves all of the evaporators.

[00006] The forward operator area is typically provided with an HVAC unit which has vent controls allowing air to be drawn from within the cabin (recirculation air), which can be heated or cooled more quickly, or allowing air to be drawn from outside the vehicle to freshen the air within the cabin. Rapid cooling of a zone is obtained by recirculating cabin air rather than drawing in outside air. When freshening of the air in the operator area is desired, outside air can usually be conveniently drawn through a grill placed just ahead of and under the front windshield of the vehicle. Zones located toward the rear of the cabin have typically drawn only inside air, in part due to the concern for the load being place on the air conditioning compressor and in part due the lack of a convenient access to outside air. However, it is desirable to provide fresh air mixing for all zones as an enhancement to passenger comfort, if it can be done without placing an excessive load on the air conditioning compressor.

[00007] According to the invention there is provided a zonal climate control system for a vehicle passenger compartment. Each zone is independently controlled. The zones rely on the same engine driven heat source, usually the engine cooling system and one engine driven heat pump or air conditioning compressor. The zones are arranged longitudinally with a forward zone climate unit corresponding to the operator area of the vehicle. The forward zone climate unit comprises, an air circulation system having an outlet to the vehicle passenger compartment, an inlet from the vehicle passenger compartment, an inlet communicating with an outside environment, a heater core coupled to the engine driven heat source and an evaporator coupled to the engine driven compressor. The passenger compartment further includes a rearward zone climate unit, comprising, an air circulation system having an outlet to the vehicle passenger compartment, an inlet from the vehicle passenger compartment, an inlet communicating with the outside environment through the exterior skin of the vehicle, a heater core coupled to the engine driven heat source and an evaporator coupled to the engine driven compressor. An actuable door provides for closing and opening the inlet of the rearward zone climate unit communicating with the outside environment. Positioning of the door is under the control of a temperature sensor for the rearward zone. A pressure sensitive check valve is positioned in the inlet of the rearward zone climate unit from the passenger compartment.

[00008] Additional effects, features and advantages will be apparent in the written description that follows.

[00014] Referring now to the figures and particularly to FIG. 1, a truck 10 is shown on which the heating, ventilation and air conditioning system of the invention is advantageously installed. Truck 10 comprises a cab 11 which rests on a frame 12. An engine compartment 14 is separated from a passenger compartment 15 by a dash panel 16. Supported on dash panel 16 is a forward zone HVAC unit 18. Located in engine compartment 14 is an engine driven air conditioning compressor 20 and a engine cooling system 22. Compressor 20 pumps out heat drawn from passenger compartment 15. Engine cooling system 22 may be tapped to transfer excess heat from a vehicle engine to passenger compartment 15.

[00015] HVAC unit 18 communicates with passenger compartment 15 through dash panel 16. Unit 18 includes an evaporator coupled with compressor 20 for the circulation of refrigerant and an heater core coupled with cooling system 22 for the circulation of engine coolant. Air may be drawn into the unit from an outside air duct 24 or from an inside, recirculation duct 28. Treated air is exhausted into passenger compartment through a number of ducts including vent 26. HVAC unit 18 provides heating, ventilation and cooling to the forward zone 42 of passenger compartment 15.

[00016] A secondary HVAC unit is located within a rear storage compartment or bunk 30 located in a rearward zone 44 of passenger compartment 15. The secondary HVAC unit has a recirculation inlet 32 drawing air from the lower part of rearward zone 44 and an outlet 34 into the upper part of the rearward zone.

[00017] Referring now to FIGS. 2 and 3, a rear zone air intake duck system 51 is illustrated positioned in a stripped down cab 11, located toward the rear of the cab and primarily on a floor 52 of the cab. A rear zone circulation duct system 151 includes a riser section 54 in the back wall 19. Intake duct duck system 51 includes two inlets. Rear zone circulation duct system 151 has one outlet 34. Inlet 36 is positioned to draw air from inside the vehicle, and inlet 36 is located through the exterior skin 38 of cab 11. Inlet 36 is a NACA (National Advisory Committee for Aeronautics) type ram duct, which may be variably opened or closed by positioning of door 56. Air is forced or drawn through duct system 51 in the direction indicated by the arrows from the inlets 36 and 32 through a blower 58 into an evaporator 60 and a heater core 62. Blower 58, evaporator 60 and heater core 62 form a rear zone or secondary HVAC unit 61.

[00018] FIG. 4 illustrates schematically a climate control system 100 for a two zone vehicle passenger compartment utilizing front and rear HVAC units 18 and. The prime mover for climate control system is the vehicle engine, which supplies excess heat to an engine cooling system 22 and which drives an air conditioning compressor 20 on demand. The cooling system 22 supplies heated engine coolant through a pipe 78 to front and rear HVAC units 18 and 61. Compressor 20 supplies refrigerant through pipe 80 to front and rear HVAC units 18 and 61. Rear HVAC unit 61 draws air from inlet ducts which are controlled by valves. Door 56 provides the valve which controls the quantity of air drawn through inlet 36, while a check valve 132 is positioned in inlet 32. Check valve 132 only passes air when the pressure deficit in duct 50 falls sufficiently below the ambient pressure to pull the valve open against gravity. All things being equal, check valve 132 will admit progressively more air to channel 50 as door 56 is progressively closed, other conditions being equal.

[00019] The position of door 56 is set by a controller 72 in response to temperature sensed by temperature sensor 74. Controller 72 operates to open door 56 progressively during air conditioning as cabin temperature decreases toward a thermostat set point. In effect, as less and less work required to cool the outside air to the desired degree, the greater the amount of outside air is mixed with the inside air. The greater the degree to which door 56 is open, the less the pressure drop inside duct 50 and the greater the degree to which check valve 132 is closed.

[00020] The invention provides a truck HVAC system, which provides fresh air mixing for all zones of a motor vehicle climate control system. While the invention is shown in only one of its forms, it is not thus limited but is susceptible to various changes and modifications without departing from the spirit and scope of the invention.