Abstract:
A system and method for controlling temperature within a vehicle cabin include monitoring various temperature sensors to determine current operating conditions, determining a desired temperature or temperature range based on occupant input, dynamically estimating a temperature gradient based on changes in the current operating conditions over a predetermined time, predicting when the desired temperature or temperature range will be attained based on the gradient and the current operating conditions, and controlling a heating/cooling system based on the predicted time. Controlling the heating/cooling system may include shutting off the system at a predicted time, or turning on the system at a predicted time. The process of prediction can be linear, non-linear, or empirical, i.e., based on a table.

Description:
BACKGROUND OF INVENTION 
     1. Field of the Invention 
     The present invention relates to a system and method for automatically controlling temperature in a vehicle. 
     2. Background Art 
     Current automatic temperature control (ATC) units may operate more often than required to maintain the vehicle cabin temperature at a desired level, which may result in reduced fuel economy. These ATC units oscillate back and forth around a desired temperature or temperature range with the controller operating continuously to either cool or heat the vehicle cabin in an attempt to maintain the desired temperature. 
     SUMMARY OF INVENTION 
     A system and method for controlling temperature within a vehicle cabin include monitoring various temperature sensors to determine current operating conditions, determining a desired temperature or temperature range based on occupant input, dynamically estimating a temperature gradient based on changes in the current operating conditions over a predetermined time, predicting a time when the desired temperature or temperature range will be attained based on the gradient and the current operating conditions, and controlling a heating/cooling system based on the predicted time. Controlling the heating/cooling system may include shutting off the system at the predicted time, or turning on the system at the predicted time. The process of prediction may include linear, non-linear, or empirical methods. 
     The present invention includes a number of advantages. For example, the present invention uses a predictive controller that estimates when a desired temperature setting will be reached given current conditions and current momentum of the system. This information is used to shut down the heating/cooling system so that it does not run continuously and, therefore, may result in improved fuel economy. In addition, the present invention may be used to optimize current linear heating/cooling controllers. 
    
    
     The above advantages and other advantages and features of the present invention will be readily apparent from the following detailed description of the preferred embodiments when taken in connection with the accompanying drawings. 
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a block diagram illustrating a vehicle heating/cooling system with a predictive controller according to one embodiment of the present invention; 
     FIG. 2 is an alternative representation of a vehicle heat/cooling system with a predictive controller according to one embodiment of the present invention; and 
     FIG. 3 is a flowchart illustrating operation of a system or method for controlling a vehicle heating/cooling system according to one embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION 
     In general, automatic temperature control in a vehicle is accomplished using various actuators to adjust the temperature and flow of air supplied to the cabin of the vehicle. FIG. 1 illustrates a representative air handling system of an HVAC (heating, ventilation and air conditioning) system, indicated generally by reference numeral  20 . System  20  includes various air actuators or doors  22 ,  24 ,  26 , and  28  to provide air for panel-defrost, floor-panel, temperature blend and outside recirculation, respectively. Doors  22 ,  24  and  28  are driven by vacuum motors (not shown) between their various vacuum, partial vacuum and no vacuum positions, represented by “v”, “pv”, and “nv”, respectively, in a conventional fashion. Door  26  is driven by an electric servo motor also in a conventional fashion. 
     System  20  may include a variable speed blower motor or fan  30  having a blower wheel  32 . Heating and cooling elements, such as a heater core  34  and an evaporator core  36  in a typical vehicle air conditioning plant, are also provided. Each of the above components is in communication with ducting  38  to control temperature, direction of air flow, and the ratio of fresh air to recirculated air supplied to the vehicle cabin. 
     For automatic control of the temperature and flow of air in the cabin, conditions inside and outside the cabin are monitored by appropriate sensors. Preferably, an electronic controller generates signals to control the plant actuators based on the current operating conditions indicated by the sensors and a desired temperature or temperature range for the occupant(s) of the vehicle. The desired temperature or temperature range may be indicated via a user interface that may include analog, digital, and/or voice-activated controls. The desired temperature specified by the vehicle occupant(s) may be a specific value, i.e., 70° or a range, i.e., warm, hot, cool, etc. A temperature range may be converted by the user interface or system controller to a corresponding value that may vary depending upon the current operating conditions. For example, a temperature range of “cool” may initiate air conditioning when outside ambient temperature is above a corresponding threshold, but initiate heating with low blower speed when the outside ambient temperature is below a corresponding threshold. Stated differently, for some applications, the desired or “set” temperature or temperature range may be context-sensitive based on the current operating conditions. 
     As illustrated in the block diagram of FIG. 2, a representative application includes various sensors for the heating/cooling system that provide signals representative of vehicle cabin temperature  40 , ambient (outside) air temperature  42 , engine coolant temperature (ECT)  44 , discharge air temperature  46  and sun load  48 , for example. In addition, an occupant interface allows the occupant to provide a desired temperature or temperature range  50  as described above. The sensor and interface signals are conditioned by associated conditioning circuitry  52  before being provided to an electronic controller  54  via inputs  56 . Controller  54  preferably includes a microprocessor  58  in communication with one or more computer readable storage media represented by random access memory (RAM)  60  and read-only memory (ROM)  62 . As will be appreciated by one of ordinary skill in the art, the computer-readable storage media may include various types of physical devices for temporary and/or persistent storage of data which include solid state, magnetic, optical, and combination devices. For example, the computer readable storage media may be implemented using one or more physical devices such as DRAM, PROMS, EPROMS, EEPROMS, flash memory, and the like. Depending upon the particular application, the computer-readable storage media may also include floppy disks, CD ROM, and the like. As explained in greater detail with reference to FIG. 3, controller  54  executes instructions stored in the computer readable media to process inputs  56  and generate outputs  64  for use by a hardware controller  44  which, in turn, controls doors  22 - 28  to regulate the temperature and flow of air to achieve the desired temperature or temperature range. 
     The diagram of FIG. 3 generally represents control logic for one embodiment of a system or method according to the present invention. As will be appreciated by one of ordinary skill in the art, the diagram may represent any one or more of a number of known processing strategies such as event-driven, interrupt-driven, multi-tasking, multi-threading, and the like. As such, various steps or functions illustrated may be performed in the sequence illustrated, in parallel, or in some cases omitted. Likewise, the order of processing is not necessarily required to achieve the features and advantages of the invention, but is provided for ease of illustration and description. Although not explicitly illustrated, one of ordinary skill in the art will recognize that one or more of the illustrated steps or functions may be repeatedly performed depending upon the particular processing strategy being used. 
     Preferably, the control logic is implemented primarily in software executed by a microprocessor-based controller. Of course, some or all of the control logic may be implemented in software, hardware, or a combination of software and hardware depending upon the particular application. When implemented in software, the control logic is preferably provided in a computer-readable storage medium having stored data representing instructions executed by a computer to control the heating/cooling of the vehicle cabin. The computer-readable storage medium or media may be any of a number of known physical devices which utilize electric, magnetic, and/or optical devices to temporarily or persistently store executable instructions and associated calibration information, operating variables, and the like. 
     As represented by block  100  of FIG. 3, various vehicle sensors are monitored to provide an indication of the current operating conditions. Sensor data is preferably periodically sampled and stored in a computer readable storage medium for future processing by the controller as described below. Signals from an occupant interface, which may include an analog, digital, or voice-activated interface, for example, are processed to determine a desired temperature or temperature range as represented by block  110 . The desired temperature or temperature range is compared to one or more current temperatures as indicated by the vehicle sensors to determine a difference or error between the desired and actual temperature. In the case of a desired temperature range, the minimum, maximum, or average temperature may be used as the desired depending upon whether the system is currently operating and whether the system most recently was used for heating or cooling. 
     Using the stored sensor data, a system momentum or gradient is determined as represented by block  120 . The system momentum or gradient provides an indication of how quickly the actual temperature is changing toward the desired temperature or temperature range. The system momentum or gradient is used in combination with the current operating conditions to predict when (time wise) the desired temperature will be attained as represented by block  130 . The process of predicting when to start (and stop) the system may be lined as represented by block  132 , non-linear as represented by block  134 , or even empirically based, i.e., using one or more lookup tables stored in memory and indexed by the current temperature and/or system gradient as represented by block  136 . Similarly, a Kalman filter could be used to predict the timing characteristics as represented by block  138 . Those of ordinary skill in the art will recognize various other methods for predicting the start and stop time in accordance with the present invention. 
     An estimate of when the system (cooling or heating) should be turned off is determined based on the predicted time that the desired temperature will be attained as represented by block  140 . These steps are preferably repeated until the desired temperature is attained, i.e., the error or difference between the actual and desired temperatures is near zero or below a corresponding threshold at which time the heating/cooling is controlled (turned off) as represented by block  150 . Alternatively, the system may purposely overshoot the desired temperature (predicted time) by running (or remaining off) for a predetermined or adaptable time in addition to the time required to reach or maintain the desired temperature. This feature allows the system to remain off with the temperature staying within an acceptable error range. The particular environmental conditions as well as the desired set point and system momentum will influence the amount of time that the temperature will remain within a desired range with the system off. These factors are preferably considered when determining the amount of overshoot. 
     Once the heating/cooling source has been shut off, the current operating conditions continue to be monitored and the system momentum or gradient determined to predict when the heating/cooling system should be restarted based on how quickly the actual temperature is deviating from the desired value, i.e., based on the difference and the rate of change of the difference. 
     Thus, the present invention provides a predictive controller that predicts or estimates when a desired temperature setting will be reached given current conditions and current momentum of the system. This information is then used to shut down the heating/cooling system so that it does not run continuously and, therefore, may result in improved fuel economy. In addition, the present invention may be used to optimize current linear heating/cooling controllers. 
     While embodiments of the invention have been illustrated and described, it is not intended that these embodiments illustrate and 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.