Abstract:
A method for controlling a hybrid compressor system is disclosed. The hybrid compressor system includes a variable displacement hybrid compressor that is selectively driven by one of an engine and an electric motor to cool a passenger compartment of a vehicle. The method includes the steps of transmitting a demand signal to activate an electric motor drive mode of the hybrid compressor system, whereby the electric motor drives the hybrid compressor, transmitting a compressor displacement signal to the hybrid compressor to set a displacement of the compressor to a minimum level, waiting a predefined time period, activating the electric motor to drive the compressor, determining a suction pressure of a suction chamber of the hybrid compressor, determining whether the displacement of the hybrid compressor is sufficient based on the suction pressure determination, and changing the displacement of the compressor if the displacement is insufficient.

Description:
TECHNICAL FIELD 
     The present invention relates to methods for controlling a hybrid compressor system having a refrigerant compressor that is selectively driven by an engine or an electric motor, and to methods that optimize the electric motor&#39;s operation and efficiency. 
     BACKGROUND 
     Conventional automotive air conditioning systems generally include a refrigeration circuit having a refrigerant compressor. Typically, the compressor is driven by the engine via a drive belt. As the compressor is driven by the engine, the refrigerant circulates in the refrigeration circuit absorbing heat from the passenger compartment thereby providing a cooling effect. The compressor is typically coupled to the vehicle&#39;s engine via an electromagnetic clutch. Thus, when the cooling capacity of the refrigerant circuit outweighs the thermal load on the circuit, the electromagnetic clutch disengages the engine thereby halting the operation of the compressor. Furthermore, conventional automotive air conditioning systems do not operate when the engine is off, thus the passenger compartment may not be cooled when the engine is off. 
     However, an automotive hybrid air conditioning system known in the art to include a “hybrid compressor” are selectively driven by an engine or an electric motor. These hybrid air conditioning systems may be driven by the engine while the engine is running and by the electric motor when the engine is not running to effect cooling on the passenger compartment. Typically, a hybrid compressor is a refrigerant compressor having a driveshaft, wherein an electric motor is coupled to the driveshaft and an electromagnetic clutch is connected to an output shaft of the output motor. Typically the engine is connected to the output shaft through the clutch. When the clutch is turned on, engine power is transmitted to the driveshaft through the output shaft, which operates the compressor. The output shaft of the motor rotates with the driveshaft of the compressor. The rotation of the output shaft generates electromotive force in the motor. This electromotive force may be used to charge the battery. However, when the engine is turned off, the clutch is turned off and the output shaft and driveshaft are disconnected from the engine. The motor may now drive the compressor by deriving power from the battery. 
     It would be desirable to provide a control method for controlling hybrid compressors that would minimize motor stall torque and allow for a gradual ramping up of the speed of the electric motor. The control method should eliminate a large in rush current during motor start up as well as optimize motor speed and efficiency. 
    
    
     BRIEF DESCRIPTION OF THE FIGURES 
     FIG. 1 is a schematic diagram of an air conditioning system for an automobile having a hybrid compressor, in accordance with the present invention; 
     FIG. 2 is a schematic diagram of a variable displacement compressor that is selectively driven by the engine or the electric motor, in accordance with the present invention; 
     FIG. 3 a  is a flow chart illustrating a method for controlling the hybrid compressor, in accordance with the present invention; 
     FIG. 3 b  is a flow chart illustrating an alternative method for controlling the hybrid compressor, in accordance with the present invention; and 
     FIG. 3 c  is a flow chart illustrating another alternative method for controlling the hybrid compressor, in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION 
     Referring now to FIG. 1, an automotive hybrid air conditioning system  10  is schematically illustrated, in accordance with the present invention. Air conditioning system  10  includes an air conditioning duct  12  in communication with a vehicle passenger compartment (not shown), a refrigeration circuit  14 , a refrigerant compressor  16  in fluid communication with circuit  14 , an engine  18  coupled to compressor  16 , an electric motor  20  also coupled to compressor  16  and a controller  22  for controlling system  10 . Air conditioning duct  12  includes a fresh air intake vent  24  for allowing air external of the vehicle to enter the passenger compartment and an internal air recirculation vent  26  for recirculating air within the passenger compartment. An intake air door  28  is further provided to open and close vents  24  and  26  accordingly. A blower fan and motor assembly  30  is further provided to draw air into a duct  12  as well as push air through duct  12 . A plurality of passenger compartment vents  32 ,  34 ,  36  direct conditioned air into various parts of the passenger compartment. Accordingly, mode doors  38 ,  40 , and  42  open and close the passenger compartment vents, respectively. 
     As air is drawn into duct  12  through vents  24  or  26 , the air is conditioned by an evaporator  44 , which acts as a heat exchanger to effectuate cooling of the air passing through the duct  12 . A heater core  46  is further provided to effectuate heating of the air circulating through duct  12  when a heater core  48  allows intake air to pass through heater core  46 . 
     The refrigerant circuit  14  of air conditioning system  10  further includes a condenser or a radiator  50 , an expansion valve  52  and an accumulator  54 . In operation, the refrigerant circuit  14  in communication with compressor  16  compresses a coolant. The compressed coolant is then cooled by condenser  50 . A The cooled coolant then undergoes adiabatic expansion through the expansion valve  52  and then the coolant evaporates in evaporator  44  providing the desired cooling effect of the passenger compartment. Accumulator  54  provides gas/liquid separation of the coolant and adjusts the quality of the coolant. 
     The control unit  22  controls the operation of the aforementioned automotive air conditioning system. Various sensors and switches (not shown) are in communication with control unit  22  to provide information regarding heat loading on the passenger compartment, as well as desired cooling level indicated by a vehicle occupant. Further, control unit  22  includes control logic, which may be implemented through hardware or software or a combination thereof. 
     In an embodiment of the present invention, executable code is stored in memory of control unit  22 . Such memory may include for example, random access memory, read only memory, and/or non-volatile memory. The specifics of the executable code for controlling the operation of air conditioning system  10  will be described in subsequent paragraphs. Control unit  22  at appropriate conditions will output control signals to operate various actuators and drives to control the operation of motors such as the fan motor, vent doors and intake doors as needed. Further, control unit  22  controls the operation of an electromagnetic clutch, which engages and disengages the compressor  16  from engine  18 . 
     Compressor  16  is preferably a hybrid compressor having two drive sources, for example engine  18  and electric motor  20 . Electromagnetic clutch  28  is further provided to engage and disengage compressor  16  from engine  18 , for example when engine  18  is not running or when there is no cooling demand. Further, compressor  16  is interconnected through driveshafts  60 ,  62 , and  64  to electric motor  20 . 
     In an embodiment of the present invention, a second electromagnetic clutch  66  is provided to disengage electric motor  20  from compressor  16  when engine  18  is driving the compressor. Thus, the present invention operates more efficiently than prior art methods and systems by disengaging the motor, thereby reducing the load on the engine. Further, a gear box  68  may be provided to change the rotational speed of the transmission shafts  62  and  64 . In this way, the present invention allows a variety of electric motors having different rotational speed and torque specifications to be utilized. 
     Referring now to FIG. 2, a schematic diagram of variable displacement compressor  16  is shown in greater detail, in accordance with the present invention. Compressor  16  includes a driveshaft  140  that is operatively coupled to an external drive source such as vehicle engine  18  by electromagnetic clutch  28  and to electric motor  20 . A swashplate  142  is rotatably secured to shaft  140  and is pivotable about the driveshaft. A pair of guide arms  161  and  162  are attached to swashplate  142  at a first end and to pistons  150  and  151  at a second end. The engagement between guide arms  161 ,  162  and the associated pistons guides the inclination of the swashplate  142  and rotates the swashplate with respect to the driveshaft  140 . Driveshaft  140  and swashplate  142  are positioned within a crankcase chamber  147 . The pressure in crankcase chamber  147  controls the angle of inclination of the swashplate. 
     Generally, compressor  16  further includes a cylinder housing  148  having cylindrical bores  144  and  145  extending therethrough. Each bore  144  and  145  accommodates one piston  150 ,  151 . Each piston and bore define compression chambers  153 ,  155 . Alternatively, each piston may be coupled to the swashplate by a pair of shoes (not shown). Rotation of the swashplate is converted into reciprocation of pistons  150 ,  151  in bores  144 ,  145  by means of the shoes, as well known in the art. 
     Further, compressor  16  includes a rear housing  170  having a suction chamber  172  and  173  and a discharge chamber  174 . Suction ports  176  and  177  and discharge ports  178  and  179  are also provided at each chamber. A suction valve (not shown) is provided at each suction port for opening and closing the suction port. A discharge valve (not shown) is provided at each discharge port for opening and closing the discharge port. Further, a bypass port or orifice  175  is provided between crankcase chamber  147  and suction chamber  172 . 
     As each piston  150 ,  151  moves from a fully extended position to a fully retracted position refrigerant is drawn into the corresponding suction port from the suction chamber to enter the associated compression chamber. Conversely, when each piston moves from a fully retracted position to a fully extended position, the refrigerant is compressed in compression chambers  153 ,  155  and the discharge valve opens allowing refrigerant to flow into discharge chamber  174  through associated discharge ports  178 ,  179 . The inclination of swashplate  148  varies in accordance with the difference between the pressure in crankcase chamber  147  and the pressure in compression chambers  153 ,  155 . More specifically, the difference between the pressure in crankcase chamber  147  (PC) and the pressure in the suction chambers  172 ,  173  (PS) or the pressure difference “PC−PS” determines the inclination of the swashplate. PC is maintained at a pressure value that is higher than the suction pressure PS (PC&gt;PS). An increase in the pressure difference PC−PS decreases the inclination of the swashplate. This shortens the stroke of each piston  150 , 151  and decreases the displacement of compressor  16 . On the other hand, a decrease in pressure difference PC−PS increases the inclination of swashplate  142 . This lengthens the stroke of each piston  150 , 151  and increases the displacement of compressor  16 . 
     In FIG. 2 swashplate  142  is indicated by solid-lines (a) in a first position (position a). When the swashplate is in position (a) the pistons  150 ,  151  do not reciprocate within chambers  153 ,  155 . Compressor  16  is at its minimum displacement. As indicated by dashed-lines (b) the swashplate may be disposed in a second position (position b). Position (b) illustrates the maximum angle of inclination the swashplate can achieve. This is also the position in which compressor  16  achieves its maximum displacement. Depending on the pressures in crankcase chamber  147 , suction chamber  172  and discharge chamber  174  the swashplate may be inclined at any angle between position (a) and (b) achieving variable displacement. 
     An electronic control valve  200  is in communication with the discharge chamber  174 , through a refrigerant/oil separator  202 , and with the crankcase chamber. Electronic control valve  200  regulates the pressure in crankcase chamber  147 , suction chamber  172  and discharge chamber  174 , by selectively opening and closing communication ports connecting the crankcase chamber to the discharge chamber. A control strategy for actuating valve  200  will be described hereinafter. 
     In a preferred embodiment of the present invention, a control strategy for controlling the operation of compressor  16  and electromagnetic control valve  200  is implemented in software, or in hardware or in both software and hardware. For example, control logic for controlling the operation of control valves  200  in one embodiment, is stored in the read only memory of the controller  22 . 
     Referring now to FIG. 3 a , a variable displacement compressor and control valve strategy or method  300  is illustrated, in accordance with the present invention. Method  300  is activated when engine  18  is not operating or not driving compressor  16 . Advantageously, method  300  improves the efficiency of electric motor  20  and provides optimal operation of system  10 . 
     Method  300  is initiated at block  302  when controller  22  receives an A/C demand signal indicating that air conditioning of the passenger compartment is desired. Since the engine is not operating, controller  22  initiates an electric motor A/C mode, wherein the electric motor becomes the power source to drive compressor  16 . At block  304 , the controller sends a compressor displacement signal to control valve  200  to reduce the capacity of the variable displacement compressor  16  to a minimum displacement. The compressor displacement signal is set to a maximum level. At block  306 , the controller waits a programmable amount of time before it starts electric motor  20 , this allows for movement of swashplate  142 . Electric motor  20  is then energized by controller  22 , as represented by block  308 . 
     At block  310 , the suction pressure of suction chamber  172  is determined from reading a low-pressure transducer, in communication with suction chamber  172 , and an evaporator thermister. The capacity or displacement sufficiency of compressor  16  is checked at block  312  by evaluating the suction pressure. If the capacity of compressor  16  is sufficient, then at block  314  method  300  determines whether there is excess capacity. If there is not excess capacity then the method returns to block  310  where the suction pressure is again monitored. However, if the controller determines that there is excess capacity in compressor  16  after evaluating the suction pressure, then the compressor displacement signal is increased to decrease the capacity of compressor  16 , as represented by block  316 . 
     If however, at block  312  the capacity of the compressor  16  is determined to be insufficient then the head pressure is checked at block  318 . The head pressure is determined based on input from the high-pressure transducer to ensure that the head pressure is within a specified range. If the head pressure is not within the specified range, then the compressor displacement signal to actuate control valve  200  is increased to decrease the capacity of compressor  16 , as represented by block  316 . However, if at block  318  the head pressure is determined to be within the allowable range after the high pressure transducer is read, the compressor displacement signal is decreased to increase the capacity of compressor  16 , as represented by block  320 . 
     In an alternative embodiment of the present invention, an alternative method  400  for controlling variable displacement compressor  16  and control valve  200  when engine  18  is not driving compressor  16  is illustrated in flowchart form in FIG. 3 b . Method  400  is initiated at block  402  when controller  22  receives an A/C demand signal. The A/C demand signal indicates that the air conditioning of the passenger compartment is desired. Since the engine is not operating, controller  22  initiates an electric A/C mode wherein the electric motor becomes the power source to drive compressor  16 . At block  404 , the controller sends a compressor displacement signal to control valve  200  to reduce the capacity of the variable displacement compressor  16  to a minimum displacement. The compressor displacement signal is set to a maximum. At block  406 , the controller waits a programmable amount of time before it starts electric motor  20  to allow for movement of the swashplate  142 . Electric motor  20  is energized after a voltage is switched by controller  22 , as represented by block  408 . At block  410 , the low pressure transducer is read. The capacity sufficiency of compressor  16  is checked at block  412 . If the capacity of compressor  16  is sufficient, then at block  414  the method determines whether there is excess capacity in compressor  16 . If there is not excess capacity then the method returns to block  410  where the low pressure transducer is monitored. However, if the controller determines that there is excess capacity in compressor  16  after evaluating the low pressure transducer, then the compressor displacement signal is increased to decrease the capacity of compressor  16 , as represented by block  416 . 
     If however, at block  412  the capacity of the compressor  16  is determined to be insufficient, after reading the low pressure transducer, the compressor displacement control signal is sent to the control valve to increase the capacity of compressor  16 , as represented by block  420 . 
     In still another alternative embodiment of the present invention, an alternative method  500  for controlling variable displacement compressor  16  and control valve  200  when engine  18  is not driving compressor  16  is illustrated in flowchart form in FIG. 3 c . Method  500  is initiated at block  502  when controller  22  receives an A/C demand signal. The A/C demand signal indicates that the air conditioning of the passenger compartment is desired. Since the engine is not operating, controller  22  initiates an electric A/C mode wherein the electric motor becomes the power source to drive compressor  16 . At block  504 , the controller sends a compressor displacement signal to control valve  200  to reduce the capacity of the variable displacement compressor  16  to a minimum displacement. The compressor displacement signal is set to a maximum. At block  506 , the controller waits a programmable amount of time before it starts electric motor  20  to allow for movement of swashplate  142 . Electric motor  20  is energized after a voltage is switched by controller  22 , as represented by block  508 . At block  510 , the evaporator core thermister is read. The capacity sufficiency of compressor  16  is checked at block  512 . If the capacity of compressor  16  is sufficient, then at block  514  the method determines whether there is excess capacity in compressor  16 . If there is not excess capacity then the method returns to block  510  where the evaporator temperature is monitored. However, if the controller determines that there is excess capacity in compressor  16  after evaluating the evaporator core temperature, then the compressor displacement signal is increased to decrease the capacity of compressor  16 , as represented by block  516 . 
     If however, at block  512  the capacity of the compressor  16  is determined to be insufficient, after reading the evaporator core temperature using the evaporator thermister, the compressor displacement control signal is sent to the control valve to increase the capacity of compressor  16 , as represented by block  520 . 
     As any person skilled in the art of hybrid compressors will recognize from the previous detailed description and from the figures and claims, modifications and changes can be made to the preferred embodiments of the invention without departing from the scope of this invention defined in the following claims.