Abstract:
An improved HVAC control method immediately closes an air inlet valve to provide full cabin air recirculation when an outside air quality sensor detects polluted air, and thereafter progressively re-opens the air inlet valve at a determined rate when the air quality sensor detects unpolluted air. Preferably, the air quality sensor quantifies the pollution level of the outside air, and the opening rate of the air inlet valve is determined based on the detected pollution level. Following a high level of detected air pollution, the valve is re-opened at a relatively slow rate, and following a low level of detected air pollution, the valve is re-opened at a relatively fast rate.

Description:
TECHNICAL FIELD  
         [0001]    This invention relates to a vehicle heating, ventilation and air conditioning (HVAC) system having an air quality sensor and an inlet air control valve, and more particularly to an improved method of operating the inlet air control valve.  
         BACKGROUND OF THE INVENTION  
         [0002]    Vehicle HVAC systems commonly include an inlet air controller such as a movable valve or shutter (referred to herein simply as an inlet air valve) that is positioned to control what proportion of the inlet air is drawn from inside and outside the vehicle cabin. In a typical application, a system controller positions the air inlet valve to optimize system efficiency and occupant comfort, and the occupant is permitted to override the normal control when full cabin air recirculation or full outside air is desired. For example, cabin air recirculation may be used to limit the intrusion of polluted air when driving in congested traffic, and full outside air may be used to purge the cabin of smoke or odors. However, the average driver frequently fails to manually position the inlet air valve as recommended, and sometimes polluted air has already entered the cabin by the time the driver switches to cabin air recirculation. For these reasons, the trend is to equip vehicle HVAC systems with a filtering system and one or more air quality sensors; the filtering system filters particulates and odors from the inlet air, and the inlet air valve is automatically positioned based on the air quality sensor to minimize the amount of polluted air entering the inlet air stream. See, for example, the U.S. Pat. No. 5,725,425 to Rump et al., issued on Mar. 10, 1998, and incorporated by reference herein.  
           [0003]    A problem that occurs with automated positioning of the inlet air valve based on air quality sensing is that the HVAC system can be repeatedly cycled between the outside air and recirculation modes, particularly when the vehicle is operated in congested city traffic. Each opening and closing of the air inlet valve changes the HVAC noise level in the cabin, and the changing noise level can be annoying to the vehicle occupants. Accordingly, what is needed is an improved method of operating the air inlet valve in response to detected inlet air quality that provides the improved cabin air quality in a way that is less perceptible to the vehicle occupants.  
         SUMMARY OF THE INVENTION  
         [0004]    The present invention is directed to an improved method for controlling an inlet air valve in a vehicle HVAC system including an air quality sensor in an outside air inlet passage, wherein the air inlet valve is immediately closed to provide cabin air recirculation when the sensor detects the presence of polluted air, and is thereafter re-opened at a determined rate when the outside air is no longer polluted. In a preferred embodiment, the air quality sensor output quantifies the pollution level of the inlet air, and the opening rate of the air inlet valve is determined based on the detected level. Following a high level of detected air pollution, the valve is re-opened at a relatively slow rate, and following a low level of detected air pollution, the valve is re-opened at a relatively fast rate. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0005]    [0005]FIG. 1 is a block diagram of a vehicle HVAC system according to this invention, including an air inlet valve, an air quality sensor and a microprocessor-based control unit.  
         [0006]    [0006]FIG. 2, Graphs A-C, depict the operation of the system of FIG. 1 in a period of driving in congested traffic. Graph A depicts the output of the air quality sensor, Graph B depicts a conventional control of the air inlet valve, and Graph C depicts a control of the air inlet valve according to this invention.  
         [0007]    [0007]FIG. 3, Graphs A-C, depict the control of the air inlet valve according to this invention. Graphs A, B and C respectively depict re-opening of the inlet air valve following periods of high, medium and low air pollution levels.  
         [0008]    [0008]FIG. 4 is a state diagram depicting the functionality of a software routine executed by the microprocessor-based control unit of FIG. 1 in carrying out the control of this invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0009]    Referring to FIG. 1, the reference numeral  10  generally designates a vehicle HVAC system, including a refrigerant compressor  12  coupled to a drive pulley  14  via an electrically activated clutch  16 . In the illustrated embodiment, the compressor  12  has a fixed stroke, and the cooling capacity is controlled by cycling the clutch  16 . However, it should be understood that the compressor  12  may alternatively be a variable capacity compressor, in which case an electric or pneumatic stroke control valve is used to achieve capacity control. In any case, the drive pulley  14  is coupled to a rotary shaft of the vehicle engine (not shown) via drive belt  18 .  
         [0010]    The system  10  further includes a condenser  20 , an orifice tube  22 , an evaporator  24 , and an accumulator/dehydrator  26  arranged in order between the compressor discharge port  28  and suction port  30 . A cooling fan  32 , operated by an electric drive motor  34 , is controlled to provide supplemental air flow through the condenser  20  for removing heat from condenser  20 . The orifice tube  22  allows the cooled high pressure refrigerant in line  38  to expand in an isenthalpic process before passing through the evaporator  24 . The accumulator/dehydrator  26  separates low pressure gaseous and liquid refrigerant, directs a gaseous portion to the compressor suction port  30 , and acts as a reservoir for the reserve refrigerant charge. In an alternative system configuration, the orifice tube  22  is replaced with a thermostatic expansion valve (TXV); in this case, the accumulator/dehydrator  26  is omitted, and a receiver/drier (R/D) is inserted in line  38  upstream of the TXV to ensure that sub-cooled liquid refrigerant is supplied to the inlet of the TXV.  
         [0011]    The evaporator  24  is formed as an array of finned refrigerant conducting tubes, and an air intake duct  40  disposed on one side of evaporator  24  houses an air filter  41  and an inlet air blower  42  driven by an electric blower motor  43  to force the inlet air past the filter  41  and evaporator  24 . The air intake duct  40  is bifurcated upstream of the filter  41  and blower  42 , and an inlet air valve  44  is adjustable as shown by the servo motor (SM)  46  to control inlet air mixing. Depending on the position of inlet air valve  44 , outside air may enter air intake duct  40  through duct leg  44   a  as indicated by arrow  48 , and passenger compartment air may enter air intake duct  40  through duct leg  44   b  as indicated by arrow  50 . For purposes of this disclosure, the air inlet valve  44  is considered to be closed when the leg  44   a  is fully restricted, and the inlet air consists essentially of cabin air from the leg  44   b ; conversely, the air inlet valve  44  is considered to be open when the leg  44   b  is fully restricted, and the inlet air consists essentially of outside air from the leg  44   a.    
         [0012]    An air outlet duct  52  disposed on the downstream side of blower  42  and evaporator  24  houses a heater core  54  formed as an array of finned tubes that conduct engine coolant. The heater core  54  effectively bifurcates the outlet duct  52 , and a re-heat valve  56  is adjustable as shown to control how much of the air must pass through the heater core  54 . The heated and un-heated air portions are mixed in a plenum portion  62  of outlet duct  52  downstream of re-heat valve  56 , and a pair of mode control valves  64 ,  66  direct the mixed air through one or more outlets, including a defrost outlet  68 , a panel outlet  70 , and a heater outlet  72 . The mode control valve  64  is adjustable as shown to switch the outlet air between the defrost and panel outlets  68 ,  70 , and the mode control valve  66  is adjustable as shown to control airflow through the heater outlet  72 .  
         [0013]    The system  10  is controlled by the microprocessor-based control unit  90  based on various inputs. In the illustrated embodiment, such inputs include: cabin air temperature CAT, the outside air temperature OAT, outside air quality level OAQL, and the usual operator demand inputs, such as the desired temperature, and override controls for the inlet air valve  44 . The CAT and OAT signals are obtained with conventional temperature sensors (not shown), and the OAQL signal is provided by the air quality sensor  92 . The air quality sensor  92  is mounted on the outside air inlet leg  44   a  as indicated, and its OAQL output signal on line  94  provides an indication of the level of pollutants in the inlet leg  44   a . In the illustrated embodiment, the sensor  92  may be a Paragon MK IV air quality sensor, available from Paragon AG, in which case the output OAQL assumes one of four possible voltage levels following an initial warm-up period: a first voltage level for clean (i.e., unpolluted) air, and second, third and fourth levels for increasingly polluted air. See, for example, the trace of Graph A, FIG. 2, which represents a typical OAQL signal vs. time during driving in congested traffic; in Graph A, the level C designates clean air, and the levels I, II and III designate increasingly polluted air.  
         [0014]    In response to the above mentioned and other inputs, the control unit  90  develops output signals for controlling the compressor clutch  16 , the cooling blower motor  34 , the blower motor  43 , and the air control valves  44 ,  56 ,  64  and  66 . In FIG. 1, the output signal CL for the clutch  16  appears on line  96 , and the output signal FC for the condenser fan control appears on line  98 . The output signal IAV for positioning the inlet air valve  44  appears on line  99 , and is applied as an input to the servo motor  46 , which in turn, is mechanically coupled to inlet air valve  44  as mentioned above. For simplicity, output signals and actuators for the blower motor  43  and the air control valves  56 ,  64 ,  66  have been omitted in FIG. 1.  
         [0015]    According to the present invention, the control unit  90  regulates the position of inlet air valve  44  in response to the outside air quality level signal OAQL so as to minimize the admission of polluted air into the inlet air stream. When the OAQL signal indicates the presence of polluted air in inlet leg  44   a , the control unit  90  quickly closes the air inlet valve  46  to provide full cabin air recirculation. When the polluted air is no longer present, the control unit  90  reopens the inlet air valve  46  at a determined rate. The re-opening rate is determined based on the indicated pollution level prior to the indication of clean air. The different rates for the air quality sensor  46  of the illustrated embodiment are graphically depicted in FIG. 3. Each of the Graphs A-C depict an inlet air valve control signal IAV developed by control unit  90  as a function of time. Graph A depicts a situation in which the OAQL signal indicates level I air pollution in the time interval t 0 -t 1 ; Graph B depicts a situation in which the OAQL signal indicates level II air pollution in the interval t 0 -t 1 ; and Graph C depicts a situation in which the OAQL signal indicates level III air pollution in the interval t 0 -t 1 . So long as the OAQL signal indicates the presence of polluted air, the inlet air valve  44  is maintained closed for full cabin air recirculation (RECIRC) as indicated. When the OAQL signal returns to C (clean air) at time t 1 , the inlet air valve  44  is re-opened (i.e., to full outside air OSA) at a determined rate. In the situation depicted by Graph A, the indicated pollution level was low (level I), and the control unit  90  re-opens the inlet air valve  44  at a relatively fast rate A that will fully open the valve  44  at time t 2 , which may be approximately  12  seconds after time t 1 . In the situation depicted by Graph B, the indicated pollution level was medium (level II), and the control unit  90  re-opens the inlet air valve  44  at a medium rate B that will fully open the valve  44  at time t 3 , which may be approximately 30 seconds after time t 1 . In the situation depicted by Graph C, the indicated pollution level was high (level III), and the control unit  90  re-opens the inlet air valve  44  at a relatively slow rate C that will fully open the valve  44  at time t 4 , which may be approximately 60 seconds after time t 1 . Alternatively, the rate of re-opening may be non-linear (exponential, for example) instead of linear, as designated by the broken traces A′, B′ and C′ in Graphs A, B and C, respectively.  
         [0016]    Graphs A and C of FIG. 2 illustrate the effect of the above-described control (with linear re-opening rates A, B and C) for a period of driving in stop-and-go city traffic. The inlet air valve  44  is re-opened at a rate (A, B or C) corresponding to the indicated pollution level (I, II or III) just prior to receipt of the clean air indication. In contrast, Graph B illustrates a conventional or known control in which the air inlet valve  44  is quickly re-opened each time the OAQL signal indicates the presence of clean air. Comparing Graphs B and C, it is easily seen that the control of the present invention results in significantly less movement of the inlet air valve  44 , and testing has shown that the cabin noise level fluctuation under such driving conditions is significantly reduced.  
         [0017]    The state diagram of FIG. 4 represents the functionality of a software routine executed by the control unit  90  for carrying out the control of this invention. The diagram depicts three states or modes of operation: a Clean Air state  100  in which OAQL=C, a Close Inlet Air Valve state  102  that is entered whenever OAQL transitions from C to I, II or III, and a Re-Open Inlet Air Valve state  104  that is entered whenever OAQL transitions from levels I, II or III to C. In state  100 , the control unit  90  sets the inlet air valve signal IAV at a minimum value MIN for full outside air (OSA). In state  102 , the control unit  90  sets the inlet air valve signal IAV at a maximum value MAX for full cabin air recirculation (RECIRC), and updates a variable OAQL_LAST to store the most recent level of the air quality signal OAQL prior to a transition to the C level. In state  104 , the control unit  90  sets the inlet air valve signal IAV according to: 
           IAV=MAX −( RATE*T ) 
         [0018]    where RATE is a rate determined as a function of OAQL_LAST, and T is the elapsed time in state  104 . Thus, state  104  serves to re-open the inlet air valve  44  at a determined rate as described above in respect to FIGS.  2 - 3 , and the control unit  90  transitions to the state  106  when IAV has been reduced to the minimum value MIN (for fall OSA), provided that OAQL remains at level C. If OAQL transitions from level C to levels I, II or III while the state  104  is active, the control unit  90  will re-enter state  102  as indicated in FIG. 4.  
         [0019]    In summary, tie control of this invention provides a novel and advantageous way of operating an inlet air valve in response to sensed air quality that achieves the objective of minimizing intrusion of polluted air into the vehicle cabin while also minimizing the associated noise level in the cabin. Since the noise fluctuation introduced by the control is less perceptible to the occupants, the driver is less likely to override the control in a way that provides less effective filtering of the cabin air. While described in reference to the illustrated embodiment, it is expected that various modifications in addition to those mentioned above will occur to those skilled in the art. Thus, the control of this invention may be applied to air conditioning systems configured differently than shown in FIG. 1, or to air quality sensors that provide an output that is different than described herein. For instance, if the air quality sensor  46  is configured to provide an output that varies continuously (linear or non-linear) with the detected level of pollution, the re-opening rate may be calibrated as a function of the sensor output level to achieve essentially the same operation as depicted in FIGS.  2 - 3 . Accordingly, it will be understood that methods incorporating these and other modifications may fall within the scope of this invention, which is defined by the appended claims.