Abstract:
An improved control method for a dual mode compressor drive arrangement selectively operates an electric machine coupled to the compressor as a motor or a generator during operation of an engine coupled to the compressor for improved efficiency and performance. The machine is operated as a generator to increase the available power for vehicle electrical loads when compressor operation is not needed or when the engine is driving the compressor. Conversely, the machine is operated as a motor to drive the compressor under heavy engine loading or when the engine speed is outside a desired operating range defined in terms of compressor speed.

Description:
TECHNICAL FIELD  
         [0001]    This invention relates to the control of a dual mode drive arrangement for an automotive refrigerant compressor.  
         BACKGROUND OF THE INVENTION  
         [0002]    Dual mode compressor drive arrangements have been utilized to maintain continuous climate control operation in automotive powertrains, with the dual mode drive arrangement allowing a refrigerant compressor of the climate control system to be selectively driven by the powertrain internal combustion engine or an electric motor. For example, the engine may be coupled to the compressor drive shaft through an electromagnetic clutch, and the armature of the electric motor may be coupled to (or integral with) the compressor drive shaft. Typically, the drive arrangement is configured so that the compressor is driven by the engine when the engine is running, and by the electric motor when the engine is not running. For example, if the engine is turned off under idle conditions to reduce fuel consumption, the electric motor may be activated to prevent interruption of the compressor drive. Similar considerations occur in hybrid powertrain configurations where the vehicle is selectively driven by an engine or an electric drive motor, or where an engine is intermittently operated to provide supplemental electric power to an electric drive motor.  
         SUMMARY OF THE INVENTION  
         [0003]    The present invention is directed to an improved control method for a dual mode drive arrangement coupling a climate control compressor to an electric machine and an engine, where the engine is turned on and off during operation of the vehicle, and where the electric machine is selectively operated as a motor or a generator during operation of the engine for improved efficiency and performance. In a preferred embodiment, the machine is operated as a generator to increase the available power for vehicle electrical loads when compressor operation is not needed or when the engine is driving the compressor. Conversely, the machine is operated as a motor to drive the compressor under heavy engine loading or when the engine speed is outside a desired operating range defined in terms of compressor speed. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0004]    [0004]FIG. 1 is a schematic diagram of a motor vehicle powertrain including an engine, a refrigerant compressor having a dual mode drive arrangement, and a microprocessor-based control unit programmed to carry out the control of this invention.  
         [0005]    [0005]FIG. 2 is a flow diagram representative of a computer software routine executed by the control unit of FIG. 1 in carrying out the control of this invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0006]    Referring to the drawings, and particularly to FIG. 1, the control of this invention is illustrated in the context of a vehicle powertrain  10  including an engine (ENG)  12  coupled to drive a vehicle through a multiple speed ratio automatic transmission (TRANS)  14 , where the vehicle is equipped with a heating, ventilating and air conditioning (HVAC) system  16  in which engine coolant is used to heat the vehicle cabin and an air conditioning system is used to cool the vehicle cabin. However, the control of this invention is also applicable to other powertrain arrangements, including hybrid configurations where an electric motor is coupled to the vehicle drive wheels, and other HVAC systems such as a reversible cycle heat pump that is operated to selectively heat or cool the vehicle cabin.  
         [0007]    Referring to FIG. 1, the HVAC system  16  includes a refrigerant compressor  18 , a condenser (CON)  20 , an orifice tube  22 , an evaporator  24 , and an accumulator/dehydrator  26  arranged in order between the compressor discharge line  28  and the compressor suction line  30 . The condenser  20  cools the compressed refrigerant, and the orifice tube  22  allows the cooled refrigerant to expand before passing through the evaporator  24 . The accumulator/dehydrator  26  separates low pressure gaseous and liquid refrigerant, directs a gaseous portion to the compressor suction line  30 , and acts as a reservoir for the reserve refrigerant charge. In an alternative system configuration, the orifice tube  22  is replaced with a thermostatic expansion valve (TXV); in this case, the accumulator/dehydrator  26  is omitted, and a receiver/drier (R/D) is inserted upstream of the TXV to ensure that sub-cooled liquid refrigerant is supplied to the inlet of the TXV. An air intake duct  32  disposed on one side of evaporator  24  houses an inlet air blower  34  to force air past the evaporator tubes, and an air outlet duct  36  disposed on the downstream side of blower  34  and evaporator  24  houses a heater core  38  formed as an array of finned tubes that conduct engine coolant supplied from an engine coolant reservoir (R)  41  via lines  40  and  42 . The heater core  38  effectively bifurcates the outlet duct  36 , and a re-heat door  44  is adjustable as shown to control how much of the air must pass through the heater core  38 . The heated and unheated air portions are mixed in outlet duct  36  downstream of re-heat door  40 , and a pair of mode control doors  46 ,  48  direct the mixed air through one or more outlets  50 ,  52 ,  54 .  
         [0008]    The compressor  18  is mechanically driven by a dual mode drive arrangement including an electric machine (M)  60  and a clutched belt drive mechanism  62 . The belt drive mechanism  62  includes a drive pulley  64 , a belt  66  coupling the drive pulley  64  to an engine crank pulley  68 , and an electromagnetic clutch  70  that is selectively activated via line  72  to couple the drive pulley  64  to a drive shaft of compressor  18 . When the engine  12  is turned off to conserve fuel or to reduce exhaust emissions, the clutch  70  is disengaged, and continued operation of the HVAC system  16  can be maintained by activating the electric machine  60  in a motoring mode via line  74  to drive the compressor  18 . When the engine  12  is running, the electric machine  60  is ordinarily deactivated, and the clutch  70  is activated as required to allow the engine  12  to drive compressor  18  through pulley mechanism  62 . Under certain conditions, however, the compressor  18  may be driven by electric machine  60  during operation of engine  12 ; this ensures that the compressor  18  is driven at an appropriate speed and reduces engine loading. Under certain other conditions, the electric machine  60  may be activated in a generating mode during engine operation; this generates supplemental electrical power that can be used to operate vehicle electrical loads  76  and/or to charge the vehicle storage battery  78 .  
         [0009]    The above-described control is carried out by a microprocessor-based control unit  80  programmed to execute a software routine based on the flow diagram of FIG. 2. Thus, the control unit  80  is coupled to storage battery  78 , and controls the electric machine  60  and electromagnetic clutch  70  via lines  74  and  72 , respectively. Additionally, the control unit  80  is coupled to transmission  14  via line  82  to influence transmission shifting, as explained below.  
         [0010]    Referring to the flow diagram of FIG. 2, the control unit  80  first executes block  90  to determine if cabin heating or cooling by the HVAC system  16  is requested. If not, the motoring mode of machine  60  is discontinued by block  92 , and block  94  is executed to determine if the engine  12  is running and the electric load demand exceeds the available power being produced by an engine-driven generator (not shown). Block  96  deactivates the generating mode of machine  60  if block  92  is answered in the negative, while block  98  engages the compressor clutch  70  and activates the generating mode to produce supplemental electric power for the loads  76  if block  92  is answered in the affirmative. It is noted that engaging the clutch  70  also drives compressor  18 , even though HVAC operation has not been requested; in this case, the re-heat door  44  can be adjusted to maintain the vehicle cabin temperature, and the capacity of compressor  18  can be minimized through the use of a bypass mechanism (not shown) or by adjusting its capacity directly if compressor  18  is a variable stroke compressor.  
         [0011]    If the control unit  80  determines at block  90  that HVAC operation is requested, the blocks  100 - 120  are executed to engage the best compressor drive mode, and to activate the machine  60  in either motoring or generating mode. If the engine  12  is not running, as determined at block  100 , the block  102  disengages the compressor clutch  70  and activates the motoring mode of machine  60  to provide the requested HVAC operation. The blocks  104 ,  106  and  108  also direct the execution of block  102  when the engine  12  is running if: (1) there is heavy engine loading, (2) the compressor  18  is being driven at an excessive speed, or (3) the engine speed is too low to provide adequate HVAC performance and transmission downshifting will not alleviate the problem. If transmission downshifting is available and will increase the compressor speed, as determined at block  108 , the block  110  provides a downshift signal to transmission  14  via line  82 . If the above-mentioned conditions are not detected or the transmission is downshifted to provide adequate compressor speed, the block  112  engages the compressor clutch  70 , and the blocks  114 - 120  determine if machine  60  should be operated in the generating mode to develop supplemental electric power. If block  114  determines that the electric load demand exceeds the available power being produced by the engine-driven generator, the generating mode is activated by block  116  until the combined power produced by machine  60  and the engine driven generator exceeds the electric load demand by at least a hysteresis amount HYST, whereupon block  120  deactivates the generating mode.  
         [0012]    In summary, the control of this invention takes full advantage of the dual mode drive system  62 , allowing both the HVAC system  16  and powertrain  10  to operate as efficiently as possible, with excellent temperature control of the vehicle cabin. While described in reference to the illustrated embodiment, it is expected that various control modifications will occur to those skilled in the art, particularly when the control is applied to different powertrain and HVAC configurations. For example, it is possible that the machine  60  may also be used for engine cranking, if desired. Accordingly, it will be understood that the scope of this invention is not limited to the illustrated embodiment, and that control methods incorporating such modifications may fall within the scope of this invention, which is defined by the appended claims.