Abstract:
Air conditioning system controls are optimized for an air conditioning system having a compressor in IC engine vehicles and in hybrid or fuel cell vehicles having electric drive motors by first determining the operating temperature of at least one of the following vehicle components: engine coolant and transmission oil for all types of vehicles, and for hybrid or fuel cell vehicles also determining the operating temperature of inverter coolant and the electric drive motors. At least one operating temperature is then compared to lower and upper temperature limits. If the operating temperature is outside of the temperature limits air conditioner heat load is reduced by at least one of the following steps: increasing cabin air recirculation, reducing cabin blower speed and reducing air conditioner compressor capacity. Subsequent to reducing air conditioner heat load, selected operating temperature or temperatures are monitored to determine if the operating temperature exceeds the upper temperature limit or limits. If the operating temperature or temperatures exceed the upper limit or limits the compressor is shut off.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention is directed to methods of optimizing vehicular air conditioning control systems. More particularly, the present invention is directed to such methods which result in reduced propulsion cooling system size in non-hybrid vehicles and lower operating temperature for coolant loops in hybrid and fuel cell vehicles. 
       BACKGROUND OF THE INVENTION 
       [0002]    Conventional vehicle propulsion cooling systems include heat exchangers and fans, the size of which is based on propulsion system losses. Losses are absorbed by engine coolant, engine oil and transmission oil. Those losses typically are momentarily exacerbated when the vehicle operates on a steep gradient and/or is towing a trailer, especially when the ambient air temperature is high. With respect to hybrid and fuel cell vehicles, propulsion cooling loops require lower operating temperatures than conventional power train vehicles. 
         [0003]    Air conditioning condensers are typically the first heat exchangers in the CRFM (Condenser Radiator Fan Module) air stream. Propulsion cooling system heat exchangers typically include engine radiators and transmission oil coolers. Hybrid and fuel cell vehicles also include inverter radiators and electric motor radiators. These heat exchangers are typically disposed downstream of the A/C (Air Conditioning) condenser, and are therefore affected by A/C condenser heat load. 
         [0004]    In current production vehicles having power train controls, when propulsion cooling systems approach maximum temperature limits, A/C system control is typically limited to A/C compressor interrupt. A/C compressor interrupt results in a complete loss of cabin cooling because the A/C system simply shuts off when propulsion system thermal limits are reached. 
       SUMMARY OF THE INVENTION 
       [0005]    In view of the aforementioned considerations, the present invention optimizes air conditioning systems for vehicles by momentarily reducing A/C condenser heat load during transient, high ambient temperature/high propulsion system load events, thereby allowing an overall reduction in propulsion cooling system size. 
         [0006]    Reducing the required propulsion cooling system size includes at least one of the following possibilities: 
         [0007]    1) reducing radiator cooling size, e.g., by core thickness reduction, fin density reduction, and/or core face area reduction; 
         [0008]    2) reducing electric cooling fan size, e.g., by reduced fan motor power; 
         [0009]    3) for hybrid and fuel cell vehicles the possibilities also include:
       3a) reducing power electronics radiator size, e.g., by core thickness reduction, fin density reduction, and/or by reducing core face area reduction, and/or   3b) reducing electric motor cooler size, e.g., by reduced core thickness, fin density reduction, and/or core face area reduction.       
 
         [0012]    In another aspect, there is a reduction of mass and cost of propulsion cooling systems for the following vehicles: hybrid vehicles that have either an electric A/C compressor or an external capacity control A/C compressor; fuel cell vehicles that have either an electric A/C compressor or an external capacity control A/C compressor; and conventional power train vehicles that have an external capacity control A/C compressor; as well as conventional power train vehicles that have a fixed displacement A/C compressor. 
         [0013]    In a further aspect, the realization of cabin air conditioning is maintained during propulsion system thermal excursions and improved fuel economy is realized due to, for example, reduced CRFM (Condenser Radiator Fan Module) electric fan power and CRFM mass. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    Various other features and attendant advantages of the present invention will be more fully appreciated as the same becomes better understood when considered in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the several views, and wherein: 
           [0015]      FIG. 1  is a perspective view of a controller according to the invention in combination with an automotive vehicle, wherein in the illustrated example the vehicle is a hybrid vehicle; 
           [0016]      FIG. 2  is a flow chart outlining operation of the controller of  FIG. 1 ; 
           [0017]      FIG. 3  is a diagrammatical illustration of the controller used with a strong-hybrid arrangement; 
           [0018]      FIG. 4  is a diagram illustrating results for a specific simulation in a hybrid or non-hybrid vehicle; 
           [0019]      FIG. 5  is a graph of theoretical eThermal simulation results for an A/C system optimization of a propulsion cooling system of reduced size in a non-hybrid vehicle; 
           [0020]      FIG. 6  is a graph of eThermal simulation results for a model of an A/C system optimization in a propulsion cooling system of reduced size used in a non-hybrid vehicle; 
           [0021]      FIG. 7  is a tabulation of results for examples of amounts of condenser heat load reduction showing positive impacts to the vehicles, and 
           [0022]      FIG. 8  is a graph of eThermal simulation results for an A/C system optimization of reduced propulsion cooling system size in a non-hybrid example. 
       
    
    
     DETAILED DESCRIPTION 
       [0023]    Referring now to  FIG. 1 , a controller  10  in a hybrid vehicle  11  selectively connects an IC engine  13  or an electric traction motor  14  to the drive wheels  15  of the hybrid vehicle. The controller  10  is mounted at any convenient location in the vehicle  11 , but typically is mounted in an engine compartment  16 . Controllers such as cabin temperature controllers and controllers for HVAC systems including a compressor  17  and a condenser  18  are preferably installed in the cabin, for example, within the instrument panel, or under the seats, or maybe installed in the trunk. 
         [0024]      FIG. 2  is a flow chart outlining the step-by-step operation of a controller  10  according to the invention. In the “initial step,” the controller  10  checks a first truth table  21  to determine if any of the following conditions are true:
       1) whether the operating temperature of the engine coolant is higher than a temperature limit T 1 A and lower than a temperature limit T 2 A, or   2) whether the operating temperature of the transmission oil is higher than a temperature limit T 1 B and lower than a temperature limit T 2 B, or   3) whether the operating temperature of the inverter coolant is higher than a temperature limit T 1 C and lower than a temperature limit T 2 C, or   4) whether the operating temperature of the electric motor is higher than a temperature limit T 1 D and lower than a temperature limit T 2 D.         
         [0029]    Information on various other parameters applicable to a given system may also be checked by the controller in its decision making process. The temperature limits T 1 A, T 2 A, T 1 B, T 2 B, T 1 C, T 2 C, T 1 D and T 2 D, are predetermined based on design choices for a given vehicle  12 . Temperature limits T 1 C, T 2 C, T 1 D and T 2 D apply only to hybrid and fuel cell vehicles. 
         [0030]    If the answer to all of the parameters checked in the initial step by the truth table  21  is “YES,” then the A/C system operation is within normal ranges and the controller  10  periodically repeats the same initial step of checking the parameters. 
         [0031]    If the answer to any of the parameters in the initial step  21  is “NO,” then the controller  10  responds in step  22  by: 
         [0032]    1) increasing cabin recirculation of air by X %, 
         [0033]    2) reducing cabin blower speed by Y %, and/or 
         [0034]    3) reducing compressor capacity by Z %. 
         [0000]    These adjustments achieve a reduction of A/C condenser heat load. Preferably, all three, i.e., increasing cabin recirculation of air by X %, reducing cabin blower speed Y %, and reducing compressor capacity Z % are performed to achieve optimization according to the invention. Alternatively, any one or more, or preferably two of the three procedures in step  22  are performed. The percent values for X, Y, Z are predetermined based on design choices for a given vehicle  12 . Alternatively, the X, Y, Z values are based on a calculation in the controller  10  based on various data, such as vehicle operating parameters/conditions. 
         [0035]    Following the above steps  21  and  22  which achieve a reduction of A/C condenser heat load, the controller  10  checks a second truth table  23  to determine whether any of the following conditions are true: 
         [0000]    1) the operating temperature of the engine coolant is higher than the high temperature limit T 2 A, or
 
2) the operating temperature of the transmission oil is higher than the high temperature limit T 2 B, or
 
3) the operating temperature of the inverter coolant is higher than the high temperature limit T 2 C, or
 
4) the operating temperature of the electric motor is higher than the high temperature limit T 2 D.
 
The controller  10  may also check information on various other parameters not in the illustrated truth table  23  applicable to a given system. The values the high temperature limits T 2 A-T 2 D can be the same as the temperature limits in pre-corresponding order listed in the initial step  21  of the controller  10 , or alternatively the values can be different. For example, the temperature values of the first predetermined values T 2 A-T 2 D, other than the values in the first step  21 , can be a function of the temperature values of the first step.
 
         [0036]    If the answer to any of the parameters is “YES in the second truth table  23 , the A/C compressor is shut off and a Flag AA is set in step  24 . Then the controller  10  repeats checking the parameters discussed above. If the answer to all of the parameters that have been checked is “NO,” then the controller  10  checks as to whether Flag AA in an A/C restart mode. 
         [0037]    If the Flag AA is present, the A/C system is restarted by the A/C restart step  24  to perform cabin recirculation at limited cabin blower speed and reduced compressor capacity. Preferably, all three, i.e., cabin recirculation plus limited cabin blower speed and reduced compressor capacity are performed to achieve optimization according to the invention. Alternatively, any one or more preferably two of the three may be performed. The cabin recirculation, limited cabin blower speed and reduced compressor capacity is limited and/or reduced by predetermined amounts, or alternatively are a function of full capacity values, e.g., a percentage of the same or are based on various changing vehicle performance parameters/conditions, for example, a calculation based on data provided to the controller  10 . Following the check of the Flag AA  25 , the controller  10  rechecks the truth table  21 . 
         [0038]      FIG. 3  depicts a hybrid air conditioning system, in which an air stream  30  enters the system from the front end of the vehicle  12  and passes through an A/C condenser  31 . Downstream of the A/C condenser  31 , the air stream  30  passes through a transmission oil cooler  32  and a power electronics heat exchanger  33 . Transmission oil  35  circulates between the transmission oil cooler  32  and transmission  36 . Fluid  39  circulates from the power electronics heat exchanger  33  to a power train power electronics and/or electric traction motor  40  followed by vehicle power electronics  41 . Further downstream, the air stream  30  passes through an engine radiator  43  positioned in front of an electric fan package  44 , which engine radiator cools coolant fluid from the IC engine  13  of  FIG. 1 . 
         [0039]      FIG. 4  illustrates a hybrid simulation in which the air conditioning load is decreased according to the previously discussed arrangement illustrated in  FIG. 2 . In  FIG. 4 , there is heat rejection in front of the engine radiator  43  due to the conditioned air  30  passing through both the auxiliary transmission oil cooler  32  and the AC condenser  31 . When the load on the AC condenser  31  is reduced using the method of  FIG. 2 , there is a reduction of less than 10% in the air available to cool coolant in the engine radiator  43  due to heat rejection by both the AC condenser  31  and the auxiliary transmission oil cooler  32 . This results in approximately 10% reduction in the temperature of the coolant from the internal combustion engine  13  ( FIG. 1 ) to the engine radiator  43 , which reduces power train cooling content, i.e., the mass, dimensions and thus cost of the heat exchanger (the engine radiator  43 ) and the cooling fan package  44  ( FIG. 2 ). This feature is available for both hybrid and non-hybrid vehicles as well as fuel cell vehicles in which the internal combustion engine  13  is replaced by a fuel cell. 
         [0040]      FIG. 5  is a graph of results using data for an A/C system optimization for a propulsion cooling system of reduced size in a non-hybrid vehicle. Conditioned air results in KW and Temperature T (C) are graphed as a function of time and include condenser outside air (OSA)  51  introduced into the cabin; condenser recirculated air  52 ; condenser air out temperature  53 ; conditioner recirculated air out temperature  54  and engine rpm/100  55 . As is seen in  FIG. 5 , by using the method of  FIG. 2 , there is an approximately 50% reduction in conditioner heat load  51  from heat load of the cabin OSA  51  compared with the heat load of cabin recirculation air  52 . There is also about a 10% reduction in conditioner air out temperature  54  when using the method of  FIG. 2 . 
         [0041]      FIG. 6  is a graph similar to  FIG. 5 , but also plotting the temperature  57  of coolant into the engine radiator  43  during cooling of outside air, as well as the temperature  59  of coolant into the engine radiator  43  during cooling of recirculating air from the cabin of the vehicle. It is seen from  FIG. 6  that by employing the method of  FIG. 2 , wherein cabin recirculation air is increased, while cabin blower speed and compressor capacity are reduced during recirculation, the temperature  59  of coolant into the engine radiator  43  is substantially lower than the temperature  57  of coolant into the engine radiator when outside air is being cooled. This difference allows for a smaller radiator size, as well as fan package size in non-hybrid vehicles. In hybrid or fuel cell powered vehicles, condensers run by electric motors consume less power by increasing cabin recirculation while reducing cabin blower speed and compressor capacity. 
         [0042]      FIG. 7  is a chart tabulating examples of condenser heat load reduction resulting improvements to the vehicle efficiency. The chart shows that for hybrid/fuel cell vehicles with electric A/C compressor, the average A/C condenser heat load reduction by forcing cabin recirculation and having reduced compressor capacity is about 11%, which impacts the vehicle by a reduction in transmission sump temperature and a reduction in engine radiator inlet coolant temperature. 
         [0043]    For non-hybrid vehicles with a belt driven compressor, where cycling is fixed if using a displacement compressor, displacement can be reduced if using a variable capacity compressor. There are also improvements in efficiency. As is set forth in the chart of  FIG. 7 , the average A/C condenser heat load reduction by forcing cabin recirculation and having reduced compressor capacity is about 50%. This results in a reduction in engine radiator inlet coolant temperature or a reduction in Engine Radiator Core Thickness. This provides a potential production cost option in designing and/or manufacturing an automotive vehicle. 
         [0044]      FIG. 8  illustrates results in a graph for an A/C system optimization for reduced propulsion cooling system size in a non-hybrid example. Condenser heat load  81  in watts (w) and engine rpm  82 , as well as vehicle speed  83  in kph and condenser air out temperature  84  in ° C. are plotted as a function of time with cabin HVAC in a recirculation mode  92  versus an outside air (OSA) mode  94  with the vehicle on 0% grade. The data shows that when the system is in a cabin recirculation mode, the condenser load  92  is lower than when the system is in cabin in OSA mode  94 . The method of  FIG. 8  is carried out by a controller operated in accordance with the method of  FIG. 2 . While the data plotted is for a non-hybrid vehicle, the same principles apply for hybrid and fuel cell vehicles. 
         [0045]    From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention, and without departing form the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions.