Abstract:
A system and method for environmental management of a vehicle automatically operates a vehicle climate control system to defog a vehicle windshield, while still operating at or near environmental comfort guidelines determined by a vehicle occupant. The method may be executed by an HVAC control system that is configured with a preprogrammed algorithm to operate an HVAC to achieve the desired results. A number of sensors can provide inputs to the control system, which can also receive inputs from a number of manual overrides operable by an occupant of the vehicle. The preprogrammed algorithm is configured to act on the various inputs to operate the HVAC to strike an appropriate balance between occupant comfort and windshield defogging.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a division of U.S. application No. 11/668,723 filed 30 Jan. 2007, now U.S. Pat. No. 8,082,979, which is hereby incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a system and method for environmental management of a vehicle. 
     BACKGROUND 
     Automatic climate control is increasingly prevalent in vehicles today. In some vehicles, a driver merely chooses a temperature setting, and a control system operates a climate control system to achieve the desired temperature. The climate control system may control the functions of a fan—e.g., on/off and fan speed—and an air conditioning system. Such a climate control system may also control the position and movement of various air dampers, or air flow doors, to control movement of air through an evaporator core or a heater core, the recirculation of air through the vehicle, the intake of fresh air, or some combination thereof. 
     Some automatic climate control systems monitor a temperature and humidity level of the vehicle cabin to determine if a defogging operation of the windshield is desirable. When it is determined that an automatic defogging operation is desired, the air conditioning system is typically operated to provide a supply of relatively dry air to the windshield to quickly effect the defogging operation. One limitation of such systems is that operation of the air conditioning compressor uses a relatively large amount of energy. 
     In the case of a conventional vehicle, where the compressor is mechanically driven by the engine, the increased load on the engine reduces efficiency and increases fuel consumption. In the case of a hybrid electric vehicle (HEV), operation of the compressor often necessitates starting the engine to ensure that the battery is not over-discharged. One of the benefits of an HEV is the fuel savings achieved by driving the vehicle using electric motor power, while maximizing the time the engine is shut down. Thus, automatic defog operations can offset some of the benefits gained by driving an HEV. 
     Another limitation of conventional automatic defogging systems is that passenger comfort may suffer as the climate control system is operated counter to the wishes of the vehicle occupants. Conversely, if the vehicle occupants are allowed to completely override the automatic defogging operation, the windshield may not clear as quickly as desired. Thus, a need exists for a system and method for vehicle climate control that strike a balance between meeting the comfort requirements of the vehicle occupants, and quickly and efficiently defogging a windshield to provide a clear view for the driver. 
     SUMMARY 
     Embodiments of the present invention provide a system and method for environmental management of a vehicle that automatically operate a vehicle climate control system to quickly and efficiently defog a vehicle window, such as a vehicle windshield, while still operating at or near environmental comfort guidelines determined by a vehicle occupant. Embodiments of the invention provide a method for environmental management of a vehicle that includes a number of steps to balance the comfort requirements of the vehicle occupants with the goal of automatically defogging the vehicle windshield or other vehicle glass. 
     In one embodiment, the method includes determining certain environmental conditions for the vehicle, such as the temperature and humidity of the vehicle cabin. The temperature and humidity may be sensed at any location within the cabin effective to provide useful information for controlling the climate. For example, a capacitive humidity sensor may be placed near the windshield, an instrument panel, or other suitable location to determine the likelihood of the windshield becoming fogged. Certain combinations of temperature readings and humidity readings can be compared to a fog probability chart, such as commonly used in the art. 
     In one embodiment, the method may be executed by a control system for a heating, ventilating and air conditioning (HVAC) system. The HVAC control system may be configured with a preprogrammed algorithm to operate the HVAC to achieve the desired results. A number of sensors can provide inputs to the control system, and data related to fog probability may be stored in a controller, for example, in the form of a lookup table. The control system can also receive inputs from a number of manual overrides operable by an occupant of the vehicle. The preprogrammed algorithm is configured to act on the various inputs to operate the HVAC to strike an appropriate balance between occupant comfort and windshield defogging. 
     The HVAC control system operates to perform a number of functions, including controlling operation of: a fan system for generating an airflow, an air conditioning system for cooling the airflow, a recirculation system for controlling the amount of fresh and recirculated air introduced into the HVAC system, a mode system for controlling the direction of the airflow, and a heating system for heating the airflow. In many vehicles, the heating system will include a heater core, and heating the airflow is effected by diverting at least a portion of the airflow through the heater core. At least some of the functions are automatically controllable to effect automatic defogging of the windshield, and at least some of the automatically controllable functions are subject to manual overrides by a vehicle occupant. 
     Based on the inputs from the sensors, which indicate the relevant environmental conditions, it is determined whether it is desirable to defog the windshield. The status of the manual overrides is then determined, and the HVAC system is automatically controlled to effect defogging of the windshield when it is determined that none of the manual overrides have been selected. 
     In some embodiments of the present invention, if any of the manual overrides are selected, the automatic defog operation is ended or not allowed to run. This provides maximum control to the vehicle occupants. In other embodiments, the automatic defog operation is prohibited only when an air conditioning override or a recirculation override is selected. Thus, if a fan system override is selected, the automatic defog operation will be allowed to operate. In the latter instance, it may be desirable to limit the automatic control of the fan system such that only small speed adjustments are allowed. This allows the automatic defog system to effectively operate the fan outside the range selected by the vehicle occupant, but close enough to the occupant selection that the deviation is not noticeable. 
     In other embodiments of the present invention, a limited automatic defog operation is allowed regardless of the manual override chosen. For example, if a fan override is selected, automatic defog operation is allowed, but with limited air conditioning adjustments. Thus, the air conditioning system may be operated intermittently even when the occupant has requested that the air conditioning system be shut down. Conversely, if the fan override is not selected, but either of the air conditioning override or the recirculation override is selected, the automatic defog operation is allowed, but with limited operation of both the air conditioning system and the fan system. As explained below, other embodiments are contemplated within the scope of the present invention such that a balance is achieved between the environmental conditions desired by the vehicle occupants and the goal of automatically defogging the windshield. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram illustrating a system for environmental management of a vehicle in accordance with an embodiment of the present invention; 
         FIG. 2  is a block diagram illustrating a control system of the environmental management system shown in  FIG. 1 ; 
         FIG. 3  is a chart illustrating embodiments of a method of the present invention; and 
         FIG. 4  is a front plan view of a control head illustrated schematically in  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION 
     As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention that may be embodied in various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention. 
     In general, control of temperature and defogging of the windshield within an automobile is accomplished using various actuators to adjust the temperature and flow of air supplied to the cabin of the vehicle.  FIG. 1  schematically shows a system  10  for environmental management of a vehicle in accordance with an embodiment of the present invention. The vehicle includes a heating, ventilating and air conditioning (HVAC) system, generally indicated at  20 . The HVAC system  20  includes the arrangement of air flow doors, including panel-defrost, floor-panel, and outside recirculated air actuators or doors  22 ,  24 , and  28 , respectively. 
     The doors are part of an air distribution system for directing the flow of conditioned air to various locations within a passenger cabin in a vehicle, such as to the windshield, floor, or instrument panel as is commonly known. The doors  22 ,  24  and  28  may be driven by vacuum motors (not shown) between their various vacuum, partial vacuum and no vacuum positions in a conventional fashion as indicated in  FIG. 1 , or may be driven by an electric servo motor. A temperature control blend door  26  is also provided, and may be driven by an electric servo motor (not shown). 
     The HVAC system  20  also includes a variable speed fan system  30  including a blower wheel  32  for generating an airflow. The HVAC system  20  further includes a heating system, shown in  FIG. 1  as a heater core  34 , and an air conditioning system  35 , including an evaporator core  36  and a compressor  37 . The compressor  37  may be an electric compressor rather than one that is mechanically driven by an engine. This provides greater control of the operation of the HVAC  20 , in that electric compressors can be configured for variable speed operation, unlike their mechanical counterparts whose speed is inextricably linked with the speed of the engine. 
     The heater core  34  and the evaporator core  36  respectively heat and cool the airflow generated by the fan system  30 . The generated airflow is distributed through an airflow distribution system and associated ducting  38 . The HVAC system  20  controls the temperature, the direction of the airflow, and the ratio of fresh air to recirculated air. The HVAC system  20  further includes a low pressure cycle switch  39  which communicates with the compressor  37 . The low pressure switch  39  is operable to deactivate the compressor  37  under certain conditions. In addition, the compressor  37  can be deactivated when the evaporator core temperature drops below a predetermined value; this helps to prevent freezing of the evaporator core  36 . 
     As described in more detail below, operation of the HVAC system  20  is controlled by a control system  40 .  FIG. 2  shows the control system  40 , including an electronic controller  42 . The controller  42  generates signals to control the HVAC system  20  according to a variety of inputs. For example, the controller  42  receives inputs from a passenger cabin temperature sensor  44 , an ambient temperature sensor  46 , an engine coolant temperature sensor  48 , an evaporator temperature sensor  50 , a humidity sensor  52 , and a discharge air temperature sensor  54 . The sensors  44 - 54  respectively provide signals that are representative of interior cabin temperature, ambient (outside) air temperature, evaporator temperature, engine coolant temperature (ECT), relative humidity of the passenger cabin, and discharge air temperature—i.e., the temperature of the air being discharged from the HVAC system  20  into the vehicle cabin. 
     In addition to receiving inputs from the sensors  44 - 54 , the controller  42  may also receive inputs from a vehicle occupant via an input device  56 . The input device  56  may be a control head as commonly used in vehicle instrument panels and illustrated in  FIG. 4 . As explained more fully below, the input device  56  allows a vehicle occupant to manually control the HVAC functions, and in some cases, override an automatic operation of the HVAC system  20 . The controller  42  controls operation of the compressor  37 , as well as the doors  22 - 28  to regulate the temperature and flow of air, and ultimately to maintain the comfort of driver and passengers in the vehicle. In addition, the controller  42  is programmed with an algorithm to effect automatic defogging of the vehicle windshield. 
     Turning to  FIG. 3 , a chart  58  illustrates a number of embodiments of the present invention. For this description, the HVAC system  20  and its control system  40 , shown in  FIGS. 1 and 2 , will be used for reference. In each of Options  1 - 5  illustrated in  FIG. 3 , the method examines manual overrides of certain HVAC functions. In particular, three manual overrides are used. They are the manual overrides of: the fan system  30 , the air conditioning system  35 , and the recirculation system—i.e., the recirculation door  28 . These manual overrides can be selected by actuating one or more of the selector switches shown in  FIG. 4 . 
       FIG. 4  illustrates in detail the control head  56 , schematically shown in  FIG. 2 . The control head  56  acts as an input device for the vehicle occupants, allowing manual selection of various climate control functions. A mode selector switch  60  allows an occupant to choose where airflow will be directed. A temperature selector switch  62  provides air temperature control, and a fan selector switch  64  provides on-off and fan speed control. The recirculation switch  66  allows for full recirculation of cabin air, all fresh air, or some combination thereof. The A/C switch  68  allows an occupant to manually select air conditioning. The control head  56  is just one example of a control head that can be used with the present invention. Other control heads, including other analog or digital control heads may also be used. 
     Embodiments of the present invention can automatically control any of the five climate control options that are manually controllable as shown in FIG.  4 —i.e., mode, temperature, fan, recirculation, and air conditioning. It is contemplated that each of the options  1 - 5  illustrated in  FIG. 3  are mutually exclusive. That is, a control system, such as the control system  40  shown in  FIG. 2 , will be configured to operate an automatic defog operation in accordance with only one of the five options at any one time. The decision as to which option to use may be made by vehicle manufacturers based on considerations such as, for example, how much climate control to allocate to the vehicle occupants, how much automatic climate control to allow, when to allow automatic climate control, and what level of functionality of automatic climate control should be allowed. 
     Although the five options illustrated in  FIG. 3  have some differences in implementation, there are similarities as well, For example, in each of the Options  1 - 5  illustrated in  FIG. 3 , the automatic defog operation (“Auto Defog Actions”) is run if none of the three manual overrides is selected. The first option, which has seven states, can be succinctly summarized as two states, since six of the seven states are the same. In sum, if any of the three manual overrides are chosen in Option  1 , then the automatic defog operation is ended or not run—i.e., it is prohibited. Conversely, in Option  2 , there are four states, although the first state is common to Option  1  and the other three options. In Option  2 , if either the air conditioning override or the recirculation override is chosen, the automatic defog operation is ended or not run. If the fan system override is selected, however, the automatic defog operation is allowed to run. 
     Although the automatic defog operation is operable in State  4 , it is run in a limited mode—i.e., only small and incremental adjustments of the fan operation are allowed. For example, if the fan system  30  is being supplied with a 4 volt potential, it may be automatically increased to 5 volts to increase its speed, while still operating near the occupant selected level. As discussed above, such limited operation of the HVAC system components helps to make the automatic defog operation transparent to the vehicle occupants. In addition to the functions shown in the chart  58 , automatic operation of the mode and temperature functions are allowed in States  1 ,  2 , and  4 . 
     In Option  3 , a limited function of the automatic defog operation is allowed regardless of which of the three overrides is selected by the vehicle occupant. Automatic operation of mode and temperature functions are allowed in all eight states, but states  3 ,  5 , and  7  limit some of the automatic functions. For example, just as in state  4  of Option  2 , each of states  3 ,  5 , and  7  in Option  3  allow only limited automatic control of the fan system  30 . In addition, in states  2 - 8 , automatic operation of the air conditioning system  35  is limited. This may include intermittent and/or short term use of the compressor  37  even if the manual A/C switch  70 —see FIG.  4 —is in the “off” position. It is worth noting here that automatic control of the air conditioning system  35  is further limited by ambient temperature. For example, a predetermined temperature such as 30° F. may be chosen as a minimum temperature below which the compressor  37  will not be allowed to operate. 
     If the fan override is selected in Option  3 , the automatic defog operation is allowed to run, but with limited operation of the air conditioning system  35 . This may involve intermittent operation of the compressor  37 , or varying its speed. If, in Option  3 , the fan override is not selected, but either of the air conditioning override or the recirculation override is selected, the automatic defog operation is allowed with limited operation of both the fan system  30  and the air conditioning system  35 . 
     As with the first three options, Option  4  allows full automatic defog operation when none of the three manual overrides are selected. Conversely, Option  4  gives precedence to a manual override of the recirculation function, prohibiting the automatic defog operation if the recirculation override is chosen—regardless of the other two manual override selections. In Option  4 , automatic operation of mode and temperature functions are only allowed in States  1 - 4 . 
     In states  2 - 4 , either or both of the fan override and the air conditioning override are selected, but not the recirculation override. In these three states, the automatic defog operation is allowed to run, but with limited operation of fan system  30 , the air conditioning system  35 , and the recirculation door  28 . The limitations on automatic operation of the fan system  30  and air conditioning system  35  may be as described above, while limiting the automatic operation of recirculation may include limiting the automatic control to only slight changes in the recirculation setting. 
     Option  5  provides full functionality of the automatic defog operation in the first four states—i.e., as long as the recirculation override is not selected, all automatic operations of the HVAC system  20  are allowed. If, however, the manual recirculation override is selected, the automatic defog operation is still allowed to operate, but only in a limited manner, as in states  2 - 4  in Option  4 . Also, similar to Option  3 , automatic operation of mode and temperature functions is allowed in all states. It is worth noting that other embodiments of the present invention may use different combinations of automatic and manual climate control operation to achieve the desired result of balancing vehicle occupant comfort with automatic, efficient implementation of a windshield defogging operation. 
     While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention. Additionally, the features of various implementing embodiments may be combined to form further embodiments of the invention.