Abstract:
A Start-Stop method and system for optimizing a selected set of parameters to provide an ideal balance between cabin thermal comfort and fuel economy performance is disclosed. The method and system includes several parameters to manage how long and when the engine OFF time will occur. Such parameters include, but are not limited to, outside ambient temperature, cabin temperature, cabin humidity, engine coolant temperature, and evaporator thermistor temperature. A control logic monitors inputs such as cabin humidity and, under certain conditions, sends a request for the engine to be ON. Other factors influencing engine ON time include inputs from the wiper(s), the heated windshield, the heated back light, the HVAC blower, and the temperature control setting. The disclosed system has utility in both electronic automatic temperature control (EATC) systems as well as in manual temperature control (MTC) systems.

Description:
TECHNICAL FIELD 
       [0001]    The disclosed invention relates generally to a strategy for controlling engine on and off time in a vehicle. More particularly, the disclosed invention relates to a strategy for controlling engine on and off time to optimize cabin comfort and fuel economy. Engine off time is based on variables including cabin temperature, contemporary ambient weather conditions and engine coolant temperature. Engine on time is based on variables including HVAC status, temperature control setting and various heating and cooling outputs. 
       BACKGROUND OF THE INVENTION 
       [0002]    Increased motor vehicle fuel efficiency is a long-standing objective of automobile designers and producers. Various approaches to increasing fuel efficiency have been taken including improving vehicle aerodynamics, reducing vehicle weight and improving vehicle operating efficiency. This latter approach includes devoting greater attention to drive train engineering. It also includes focusing on the vast array of peripheral devices provided with the modern automobile to improve driver and passenger comfort and looking for ways to increase efficiency in the design, use and operation of such peripheral devices. 
         [0003]    In the conventional motor vehicle, the climate control heating and cooling systems depend on the engine being on for a certain amount of time (ON time) in order to provide thermal comfort in the vehicle cabin. When not needed the vehicle&#39;s engine is turned off. According to known technology, the vehicle ON and OFF times are not managed and are subject only to the random choices of the vehicle operator without consideration of fuel economy. 
         [0004]    Accordingly, if the engine OFF time is not managed properly the balance between optimized cabin thermal comfort and fuel economy will not be achieved. As is often the case, there is room for improvement in the art of controlling vehicle operation and control to achieve maximum passenger cabin comfort for the vehicle occupants while at the same time optimizing vehicle fuel economy. 
       SUMMARY OF THE INVENTION 
       [0005]    The disclosed invention provides a Start-Stop strategy for optimizing a selected set of parameters to provide an ideal balance between cabin thermal comfort and fuel economy performance. Particularly, the disclosed Start-Stop strategy includes several defined parameters to manage how long and when the engine OFF time will occur. These parameters include, but are not limited to, outside ambient temperature (Tambient), cabin temperature (Tincar), cabin humidity, engine coolant temperature (ECT), and evaporator thermistor temperature (Tevap). 
         [0006]    More particularly, the disclosed system has utility in both electronic automatic temperature control (EATC) systems as well as in manual temperature control (MTC) systems. When used in conjunction with an EATC system, variables include Tambient, Tset point (that is, the temperature door position), engine coolant temperature (ECT), Tcabin, cabin humidity (typically as a percentage), evaporative thermistor temperature, and sunload. Similarly (but not the same), when used in conjunction with an MTC system, variables include Tambient, Tset point (that is, the temperature door position), engine coolant temperature (ECT), Tcabin, cabin humidity (typically as a percentage), and evaporative thermistor temperature. 
         [0007]    Whether an EATC system or an MTC system other inputs include, for example, the demands of the wiper(s), the heated windshield, the heated back light, the HVAC blower, the temperature control setting. Other variables are possible. 
         [0008]    The disclosed Start-Stop strategy generally includes the following steps. First, the selected cabin thermal comfort needs to be achieved before the engine can be turned OFF. The cabin thermal comfort can be based upon either the slope of Tincar/time or on Tincar at the given cabin thermal load. 
         [0009]    In the event that the cabin thermal comfort is based upon the slope of Tincar/time, if the slope of Tincar/time is flat then the cabin thermal comfort has reached a steady state condition. 
         [0010]    If instead the cabin thermal comfort is based on Tincar at the given cabin thermal load, then the cabin thermal load can be determined from an established look-up table. 
         [0011]    The control logic also ensures that Tevap does not exceed a certain value since odor may occur in the event of a hot ambient temperature. In addition, if the control logic determines that the Tevap reaches a certain temperature then engine ON request will be sent. Next, the control logic monitors cabin humidity for any fogging probability risk. If the fogging probability is very high, the control logic will also send an engine ON request. 
         [0012]    Other factors for the engine ON request include the status of the wiper, the heated back light, and the heated windshield. In addition, any detected change in additional variables (such as, but not limited to, the HVAC blower, the temperature control setting, and the A/C setting) will initiate the sending of an engine ON request. 
         [0013]    The disclosed Start-Stop strategy provides an effective and efficient method of optimizing cabin thermal comfort and fuel economy performance depending on certain variables. 
         [0014]    Other advantages and features of the invention will become apparent when viewed in light of the detailed description of the preferred embodiment when taken in conjunction with the attached drawings and the appended claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    For a more complete understanding of this invention, reference should now be made to the embodiment illustrated in greater detail in the accompanying drawing and described below by way of examples of the invention wherein: 
           [0016]      FIG. 1  is a is a block diagram illustrating a Start-Stop strategy for an electronic automatic temperature control system; 
           [0017]      FIGS. 2A and 2B  represent a flow chart illustrating a Start-Stop strategy for an electronic automatic temperature control system. 
           [0018]      FIG. 3  is a block diagram illustrating a Start-Stop strategy for a manual control head temperature control system; and 
           [0019]      FIGS. 4A and 4B  represent a flow chart illustrating a Start-Stop strategy for a manual control head temperature control system according to a first embodiment of the disclosed invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0020]    In the following figures, the same reference numerals will be used to refer to the same components. In the following description, various operating parameters and components are described for different constructed embodiments. These specific parameters and components are included as examples and are not meant to be limiting. 
         [0021]    In general, the system and method for providing vehicle OFF and ON times is discussed in detail hereinafter. The disclosed Start-Stop control strategy enables the achievement of a good balance between thermal comfort control within the vehicle and maximum fuel economy. According to the disclosed system and method, users will achieve an optimum cabin thermal comfort without compromising fuel economy. Control management may be by way of either electronic automatic temperature control (EATC) or manual temperature control (MTC). Regardless of whether the control arrangement is by way of automatic temperature control or manual temperature control the system and method of the disclosed Start-Stop strategy uses a control logic which responds to various input parameters and responds with engine OFF or ON instructions. 
         [0022]    The selected cabin thermal comfort needs to be achieved before the engine can be turned OFF. The cabin thermal comfort can be based upon either on the slope of Tincar/time or on Tincar at the given cabin thermal load. In the event that the cabin thermal comfort is based upon the slope of Tincar/time, if the slope of Tincar/time is flat then it means that the cabin thermal comfort has reached a steady state condition. If instead the cabin thermal comfort is based on Tincar at the given cabin thermal load, then the cabin thermal load can be determined from an established look-up table. 
         [0023]      FIGS. 1 ,  2 A and  2 B relate to a method and system for a Start-Stop strategy using an electronic automatic temperature control system.  FIGS. 3 ,  4 A and  4 B relate to a method and system for a Start-Stop strategy for use with a manual control head temperature system. 
         [0024]    Referring first to the Start-Stop strategy using an electronic automatic temperature control system of the disclosed invention, and with reference to  FIG. 1 , a block diagram illustrating a representative Start-Stop strategy for an electronic automatic temperature control (EATC) system is shown, generally illustrated as  10 . The system  10  includes various sensors that provide signals representative of ambient (outside) air temperature (Tambient)  12 , engine coolant temperature (ECT)  14 , the vehicle cabin temperature (Tcabin)  16 , the vehicle cabin humidity (as a percentage)  18 , the evaporator thermistor temperature  20 , and the sunload  22 . In addition, an occupant interface allows the occupant to provide a desired temperature or temperature range (Tset Point)  24 . The sensor and interface signals are provided to the electronic automatic temperature control (EATC)  26  which is operatively associated with the engine  28 . 
         [0025]    The inputs provided to the EATC  26  from the ambient air temperature  12 , the engine coolant temperature  14 , the cabin temperature  16 , the vehicle cabin humidity  18 , the evaporator thermistor temperature  20 , the sunload  22 , and the temperature or temperature range 24 in general enable the EATC  26  to establish engine ON and OFF times as required for desired cabin thermal comfort and maximum fuel economy. However, other inputs may provide information to the control logic of the EATC  26 . These include, without limitation, the windshield wiper(s)  30 , the heated windshield  32 , the heated back light  34 , the HVAC blower  36 , the temperature control setting  38 , and the A/C request  40 . 
         [0026]    With respect to  FIGS. 2A and 2B , a flow chart illustrating a Start-Stop strategy for an electronic automatic temperature control system according to an embodiment of the disclosed invention is set forth. According to the illustrated flow chart, the engine is first confirmed to be in its OFF condition. An initial inquiry is made as to system status. Specifically, one or more of the following queries may be made: Is the blower voltage (“Blower V”) up? OR has the blend door position been changed (“Blend Door [position] changed”)? OR is the air conditioning turned on (“AC Request=ON) coupled with the outside ambient temperature (“OAT”) being greater than a predetermined value? If any one of these events has occurred then the vehicle engine is turned to its ON condition. 
         [0027]    If, on the other hand, none of these events has occurred an inquiry is made as to whether or not the HVAC system is in the defrost mode. If the system is in the defrost mode, then reference is made to a look up table the engine will be turned to its ON condition. In addition, an engine ON request may also be initiated depending on the status of the AC which is dependent upon the choice of the user or, if the system is in the “auto” mode, then the request is ON. 
         [0028]    If the system is not in the defrost mode, then one or more of the ambient air temperature  12 , the engine coolant temperature  14 , the cabin temperature  16 , the vehicle cabin humidity  18 , the evaporator thermistor temperature  20 , the sunload  22 , and the temperature or temperature range 24 will be evaluated to determine engine pull up or pull down (“EPUD”). The EPUD may be based on the Tcabin according to the outside ambient temperature versus the Tset point (whether there is low/no sunload or whether there is high sunload). As an alternative, the EPUD may be based on the slope of Tincar/time according to the outside ambient temperature versus the Tset point for high sunload. As a further alternative, the EPUD may be based on engine coolant temperature according to the outside ambient temperature versus the Tset point. As yet a further alternative, the EPUD may be based on the evaporator thermistor temperature according to the outside ambient temperature versus the Tincar. 
         [0029]    Once the EPUD is determined based upon one or more of the inquiries set forth above, the following query is made: Is the engine coolant temperature less than a temperature specified in a look-up table? Is the Tincar less than the Tcabin (based on the look up table in the heating mode) or is the Tincar greater than the Tcabin (based on the look up table in the cooling mode)? Is the Tincar/time slope less than an absolute temperature (to be determined)? If the determination of any of these is found to be “yes,” then an engine ON request is made. 
         [0030]    If no “yes” determination is made, then the engine remains OFF and an assessment of fogging probability is made. If the risk of fogging probability is determined to be very high, then the control logic of the EATC  26  will send an engine ON request. On the other hand, if the risk of fogging probability is determined not to be very high, then the following inquiry is made: Is K1 (a calibratable value) greater than the ambient temperature and is the ambient temperature greater than the freezing point? If this inquiry is answered “yes,” then a further determination is made. Specifically, if fogging probability (“Fog Prob”) is determined to be greater than a certain predetermined value or if the wiper(s)  30 , heated windshield  32 , or heated back light  34  are “on” coupled with the AC request being “on” (depending on the user&#39;s choice or the auto mode being set to “on” as described above), then an engine ON request is made. 
         [0031]    On the other hand, if the answer is “no” to the inquiry “Is K1 greater than the ambient temperature and is the ambient temperature greater than the freezing point?”, then an additional inquiry is made: Is K2 (a calibratable value) less than the outside ambient temperature? If the answer to this inquiry is “yes,” then a further determination is made. Specifically, if the percentage of relative humidity (“% RH”) is found to be greater than a determined level or if the temperature of evaporation (“Tevap”) is found to be greater than an evaporator thermistor temperature table (“Tevap Table”) or if the wiper(s)  30 , the heated windshield  32 , or the heated back light  34  are “on” coupled with the AC request being “on” (again depending on the user&#39;s choice or the auto mode being set to “on” as described above), then an engine ON request is made. 
         [0032]    If the answer is “no” to the inquiry “Is K2 (a calibratable value) less than the outside ambient temperature?”, then the control logic finishes its inquiries and no further requests for either engine ON or engine Off are made. 
         [0033]    The above discussion related to  FIGS. 1 ,  2 A and  2 B relate to a method and system for a Start-Stop strategy using an electronic automatic temperature control system. As an alternative to this approach, the method and system for a Start-Stop strategy according to the disclosed invention may also employ a manual control head system as set forth in  FIGS. 3 ,  4 A and  4 B. 
         [0034]    Referring Start-Stop strategy using a manual control head system of the disclosed invention, and with reference to  FIG. 3 , a block diagram illustrating a representative Start-Stop strategy for a manual temperature control system (MTC) is shown, generally illustrated as  50 . The system  50  includes various sensors that provide signals representative of ambient (outside) air temperature (Tambient)  52 , engine coolant temperature (ECT)  54 , the vehicle cabin temperature (Tcabin)  56 , the vehicle cabin humidity (as a percentage)  58 , and the evaporator thermistor temperature  60 . (No sunload sensor is provided with the manual temperature control system.) In addition, an occupant interface allows the occupant to provide a desired temperature or temperature range (Tset Point)  62 . The sensor and interface signals are provided to the manual temperature control (MTC)  64  which is operatively associated with the engine  66 . 
         [0035]    The inputs provided to the MTC  64  by the ambient air temperature  52 , the engine coolant temperature  54 , the cabin temperature  56 , the vehicle cabin humidity  58 , the evaporator thermistor temperature  60 , and the temperature or temperature range (Tset Point)  62  in general enable the MTC  64  to establish engine ON and OFF times as required for desired cabin thermal comfort and maximum fuel economy. However, as with the EATC system set forth above, other inputs may provide information to the control logic of the MTC  64 . These include, without limitation, the windshield wiper(s)  68 , the heated windshield  70 , the heated back light  72 , the HVAC blower  74 , the temperature control setting  76 , and the A/C request  78 . 
         [0036]    With respect to  FIGS. 4A and 4B , a flow chart illustrating a Start-Stop strategy for a manual temperature control system according to an embodiment of the disclosed invention is set forth. According to the illustrated flow chart, the engine is first confirmed to be in its OFF condition. An initial inquiry is made as to system status. Specifically, one or more of the following queries may be made: Is the blower voltage (“Blower V”) up? OR has the blend door position been changed (“Blend Door [position] changed”)? OR is the air conditioning turned on (“AC Request=ON) coupled with the outside ambient temperature (“OAT”) being greater than a predetermined value? If any one of these events has occurred then the vehicle engine is turned to its ON condition. 
         [0037]    If, on the other hand, none of these events has occurred an inquiry is made as to whether or not the HVAC system is in the defrost mode. If the system is in the defrost mode, then reference is made to a look up table the engine will be turned to its ON condition. In addition, an engine ON request may also be initiated depending on the status of the AC which is dependent upon the choice of the user or, if the system is in the “auto” mode, then the request is ON. 
         [0038]    If the system is not in the defrost or max defrost mode, then one or more of the ambient air temperature  52 , the engine coolant temperature  54 , the cabin temperature  56 , the vehicle cabin humidity  58 , the evaporator thermistor temperature  60 , and the temperature or temperature range (Tset Point)  62  will be evaluated to determine engine pull up or pull down (“EPUD”). The EPUD may be based on the Tcabin according to the outside ambient temperature versus the temperature door position being between, for example, 0% closed (full cold) and 100% open (full hot). As an alternative, the EPUD may be based on engine coolant temperature according to the outside ambient temperature versus the temperature door position being between, for example, 0% and 100% of full heat. As a further alternative, the EPUD may be based on the slope of Tincar/time according to the outside ambient temperature versus the temperature door position being between, for example, 0% and 100% of full heat. As yet a further alternative, the EPUD may be based on the evaporator thermistor temperature according to the outside ambient temperature versus the Tincar. 
         [0039]    Once the EPUD is determined based upon one or more of the inquiries set forth above, the following query is made: Is the engine coolant temperature less than a temperature specified in a look-up table? Is the Tincar less than the Tcabin (in heating mode) or is the Tincar greater than the Tcabin (in cooling mode)? Is the Tincar/time slope less than an absolute temperature (to be determined)? If the determination of any of these is found to be “yes,” then an engine ON request is made. 
         [0040]    If no “yes” determination is made, then the engine remains OFF and an assessment of fogging probability is made. The following inquiry is made: Is K1 (a calibratable value) greater than the ambient temperature and is the ambient temperature greater than the freezing point? If this inquiry is answered “yes,” then a further determination is made. Specifically, if fogging probability (“Fog Prob”) is determined to be greater than a certain predetermined value or if the wiper(s)  68 , heated windshield  70 , or heated back light  72  are “on” coupled with the AC request being “on” (based on the user&#39;s choice or the auto mode being set to “on” as described above), then an engine ON request is made. 
         [0041]    On the other hand, if the answer is “no” to the inquiry “Is K1 (a calibratable value) greater than the ambient temperature and is the ambient temperature greater than the freezing point?”, then an additional inquiry is made: Is K2 (another calibratable value) less than the outside ambient temperature? If the answer to this inquiry is “yes,” then a further determination is made. Specifically, if the percentage of relative humidity (“% RH”) is found to be greater than a determined level or if the temperature of evaporation (“Tevap”) is found to be greater than an evaporator thermistor temperature table (“Tevap Table”) or if the wiper(s)  68 , the heated windshield  70 , or the heated back light  72  are “on” coupled with the AC request being “on” (again depending on the user&#39;s choice or the auto mode being set to “on” as described above), then an engine ON request is made. 
         [0042]    If the answer is “no” to the inquiry “Is K2 (another calibratable value) less than the outside ambient temperature?”, then the control logic finishes its inquiries and no further requests for either engine ON or engine Off are made. 
         [0043]    The above-described logic is only exemplary and it is to be understood that many variations may be made without deviating from the invention as disclosed and described. For example, the climate load demand values can be modified as required. 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. 
         [0044]    The above-described control logics are only exemplary and it is to be understood that many variations may be made without deviating from the invention as disclosed and described. For example, the climate load demand values can be modified as required. 
         [0045]    In addition, the control logic set forth above generally represents control logic for the described embodiments of a system or method according to the disclosed invention. As will be appreciated by one of ordinary skill in the art, the diagrams 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. 
         [0046]    While the best mode for carrying out the invention has been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention as defined by the following claims.