Abstract:
A method for controlling power consumption of a compressor of an automotive vehicle climate system may include identifying an energy source providing energy to power the compressor and selecting an operating parameter of the climate system based on the identified energy source to control power consumption of the compressor.

Description:
BACKGROUND 
     An automotive climate control system may include a compressor that pressurizes and moves refrigerant through an evaporator. Such compressors operate to accommodate vehicle cabin cooling demands. Some compressors operate either at a full-on or full-off mode. That is, the speed of the compressor cannot be varied. Other compressors, such as electric air conditioning compressors, may operate at varied speeds. 
     SUMMARY 
     Power consumption of a vehicle climate control system&#39;s variable capacity compressor may be controlled by altering and/or selecting operating parameters for the climate system based on an energy source providing energy to power the compressor. The energy source may be an electrical power storage unit, a regenerative braking system, and/or an engine. The operating parameters may include a target evaporator temperature, maximum compressor speed, maximum compressor power, and/or controller response time. 
     While example embodiments in accordance with the invention are illustrated and disclosed, such disclosure should not be construed to limit the invention. It is anticipated that various modifications, alternative designs, and control methods including equivalents thereof may be made without departing from the scope of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of an embodiment of an automotive vehicle. 
         FIG. 2  is a flow chart depicting an example algorithm for controlling power consumption of the compressor of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to  FIG. 1 , an automotive vehicle  10  may include a cabin  12 , engine  14 , power storage unit  16  (e.g., traction battery, ultra capacitor, etc.), regenerative braking system  18 , climate system  20  and one or more controllers  22 . The engine  14  and traction battery  16  may provide energy to move the vehicle  10 . The regenerative braking system  18  may capture energy from vehicle braking (active or coasting) for storage by the traction battery  16  and/or use by electrical devices within the vehicle  10 . In other embodiments, the vehicle  10  may be a plug-in battery electric vehicle, fuel cell vehicle, etc. 
     The climate control system  20  may include a condenser  24 , variable capacity compressor  26  (e.g., variable speed, variable displacement, belt driven electrically variable displacement, etc.), and evaporator  28 . Coolant may be circulated through the loop (shown in dark line) fluidly connecting the condenser  24 , compressor  26  and evaporator  28 . The coolant cools air (indicated by arrows) passing over the evaporator  28 . This air may be used to cool the cabin  12 . 
     The vehicle  10  further includes one or more sensors  30   n  (e.g.,  30   a - 30   e ). In the embodiment of  FIG. 1 , the sensor  30   a  senses the pressure in the loop between the condenser  24  and compressor  26 . The sensor  30   b  senses the temperature of the evaporator  28 . The sensors  30   c - 30   e  sense the temperature, humidity and sun load respectively in the cabin  12 . Other and or different sensors may also be used. Information from the sensors  30   n  is communicated to the one or more controllers  22 . 
     Cabin temperature is related to evaporator temperature:
 
cabin temp.= f (evaporator temp.).  (1)
 
Additionally, evaporator temperature is related to compressor speed:
 
evaporator temp.= f (compressor speed).  (2)
 
Hence, cabin temperature is related to compressor speed:
 
cabin temp.= f (compressor speed).  (3)
 
     To achieve a desired cabin temperature (input by an occupant of the vehicle), a target evaporator temperature (and thus a corresponding compressor speed) may be selected by the one or more controllers  22 . Such targets may be established through testing, simulation, etc. The one or more controllers  22  may use a proportional-integral (PI) control scheme (or any other suitable control scheme) that determines the compressor speed based on a difference between the actual and target evaporator temperatures. The one or more controllers  22  may also limit compressor speed and compressor power, as known in the art. 
     Table 1 illustrates potential sources of energy to power the compressor  26 . The “cheapest” energy (the energy having the least impact on fuel economy) is listed at the top. The most “expensive” energy (the energy having the greatest negative impact on fuel economy) is listed at the bottom. 
                               TABLE 1               Source                                    Regenerative Braking           Compression Braking           Engine, Low BSFC           Engine, High BSFC           Battery                        
Energy generated during regenerative braking is less expensive compared with energy generated during compression braking. Energy generated during compression braking is less expensive than energy generated by the engine  14  illustrated in  FIG. 1 . Energy generated by the engine  14  running with low brake specific fuel consumption is less expensive than energy generated by the engine  14  running with high brake specific fuel consumption, etc. Hence, powering the compressor  26  with energy generated during regenerative braking will have the least impact on fuel economy. Powering the compressor  26  with energy taken from the traction battery  16  will have the greatest impact on fuel economy. (Assuming that energy stored in the traction battery  16  was generated, for example, by the engine  14  or through regenerative braking, and that losses occur while storing energy to and retrieving energy from the traction battery  16 .)
 
     Referring now to  FIGS. 1 and 2 , the operation of the compressor  26  may be controlled so as to influence the impact on fuel economy. At operation  32 , the one or more controllers  22  may receive a desired temperature input from an occupant of the vehicle  10 . The occupant, for example, may select 75° F. via a signal input device on an instrument panel of the vehicle  10 . 
     At operation  34 , the one or more controllers  22  may set default operating parameters for the climate system  20 . These parameters may include one or more of target evaporator temperature, maximum compressor speed, maximum compressor power, response time of the one or more controllers  22 , etc. In some embodiments, the default operating parameter values may be set based on the desired temperature and the assumption that the source of power for the compressor  26  is compression braking. The target evaporator temperature, maximum compressor speed or displacement, etc. may be set aggressively (resulting in faster performance of the climate system  20 ) as energy to power the compressor  26  is assumed to be relatively cheap. 
     In other embodiments, the default operating parameter values may be set based on the desired temperature and the assumption that the source of power for the compressor  26  is relatively expensive (resulting in slower performance of the climate system  20 ). Generally speaking, lower target evaporator temperatures and shorter controller response times, as well as higher maximum compressor speeds and compressor power improve performance of climate systems. (Certain compressors, however, may be less efficient at high or low speeds.) 
     At operation  36 , the one or more controllers  22  may determine, in a known fashion, the actual power source for the compressor  26 . For example, the one or more controllers  22  may determine whether the energy to power the compressor is being generated by the engine  14 , traction battery  16  or regenerative braking system  18 . 
     At operation  38 , the one or more controllers  22  may determine whether the actual power source is different than the assumed power source. That is, the one or more controllers  22  may determine if the assumption regarding the cost of energy to power the compressor  26  is accurate given current vehicle circumstances. For example, the one or more controllers  22  may determine, in a known fashion, whether energy generated from compression braking is the actual source of power for the compressor  26  (in the case where compression braking is the assumed source of power). If no, the algorithm may end. 
     If the actual power source is different than the assumed power source, the one or more controllers  22  may determine, at operation  40 , whether energy from the actual power source is more expensive than energy from the assumed power source. For example, the one or more controllers  22  may determine, in a known fashion, that the engine  12  is generating energy to power the compressor  26  and that the engine  12  is running with high brake specific fuel consumption. As such, the relative cost of the energy to power the compressor  26  is more expensive than the assumed relative cost used to set the default operating parameter values (assuming that the default operating parameters were set with an assumption of relatively cheap energy, such as energy from compression braking, to power the compressor  26 ). If no, the algorithm may end. 
     If energy from the actual power source is more expensive than energy from the assumed power source, the one or more controllers  22  may, at operation  42 , alter the operating parameter(s) of the climate system  20  to reduce the power consumption of the compressor  26  (at the expense of performance). Continuing with the example above, the one or more controllers  22  may raise the target evaporator temperature, increase its response time, decrease the limit on compressor speed and/or decrease the limit on compressor power. The amount by which the operating parameters are altered may be determined via testing, simulation, etc. and, in some embodiments, balance the desire to reduce power consumption with the performance expected/tolerated by vehicle occupants. 
     Returning to operation  40 , the one or more controllers  22 , if the energy from the actual power source is not more expensive (i.e., is less expensive) than energy from the assumed power source, may alter the operating parameter(s) of the climate system  20  to increase the power consumption of the compressor  26  (to improve performance). The one or more controllers  22 , for example, may lower the target evaporator temperature, decrease its response time, increase the limit on compressor speed and/or increase the limit on compressor power. Again, the amount by which the operating parameters are altered may be determined via testing, simulation, etc. and balance power consumption with performance. 
     In other embodiments, the one or more controllers  22  may access a look-up table having values for the climate system operating parameters mapped with the potential sources of energy for the compressor  26 . Before selecting the operating parameters for the climate system  20 , the one or more controllers  22  may determine, in a known fashion, the energy source for the compressor  26  and retrieve one or more operating parameters associated with that source from the look-up table. In such embodiments, default operating parameters may not be necessary. The one or more controllers  22  may periodically determine the energy source for the compressor  26  and retrieve/alter the appropriate operating parameters, etc. Other scenarios are also possible. 
     As apparent to those of ordinary skill, the algorithms disclosed herein may be deliverable to a processing device in many forms including, but not limited to, (i) information permanently stored on non-writable storage media such as ROM devices and (ii) information alterably stored on writeable storage media such as floppy disks, magnetic tapes, CDs, RAM devices, and other magnetic and optical media. The algorithms may also be implemented in a software executable object. Alternatively, the algorithms may be embodied in whole or in part using suitable hardware components, such as Application Specific Integrated Circuits (ASICs), state machines, controllers or other hardware components or devices, or a combination of hardware, software and firmware components. 
     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 various changes may be made without departing from the spirit and scope of the invention.