Patent Publication Number: US-6910344-B2

Title: Compressor torque estimate device, engine controller and method of estimating compressor torque

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to a compressor torque estimate device for estimating a torque required for driving a variable displacement compressor and an engine control device. 
   For example, as a refrigerant compressor in an air conditioner for a vehicle, there is a variable displacement compressor whose displacement can be changed based on a compressor control signal from an external device. When the displacement of the variable displacement compressor is changed, a torque (a compressor torque) required for driving the compressor is also varied. 
   Therefore, conventionally, in order to appropriately operate an engine of a vehicle as a drive source of the variable displacement compressor, the compressor torque is estimated, and an output torque of the engine is controlled by considering the compressor torque (e.g. page 8 and FIG. 6 in Japanese Patent Unexamined Publication No. 2001-180261). Although there is a method in which the compressor torque is directly detected with a torque sensor, the torque sensor is relatively expensive and increases cost. Accordingly, in a technique disclosed in Japanese Patent Unexamined Publication No. 2001-180261, the compressor torque of the variable displacement compressor is estimated based on the compressor control signal. 
   In the above method for estimating the compressor torque based on the compressor control signal, when the variable displacement compressor is during a steady state, the compressor torque can be estimated with a relatively high accuracy, that is, a difference between an estimated compressor torque and an actual torque (an actual compressor torque) is relatively small. However, in a time of transition when the displacement of the variable displacement compressor is rapidly excessively changed, for example, when an air conditioner switch is turned on or off, when the rotational speed of the engine is suddenly changed, when a set temperature is changed, or when an amount of air blowing out from the air conditioner is changed, the difference between the estimated compressor torque and the actual torque becomes large due to delay (mechanical response delay) of mechanical movement in a displacement-varying operation. 
   For example, when the air conditioner switch is turned on from an OFF-state, a compressor control signal for changing to a maximum displacement is supplied from an external device to the variable displacement compressor, which is in a minimum displacement state. Therefore, the compressor torque is estimated based on the compressor control signal as an instruction for changing to the maximum displacement when the air conditioner switch is turned on. 
   However, the displacement of the variable displacement compressor becomes the maximum late from the instruction for changing to the maximum displacement due to the mechanical response delay as mentioned above. Therefore, as shown in a graph in  FIG. 4 , an extremely high torque value as the compressor torque (a solid line) is estimated almost as soon as the air conditioner switch is turned on. On the other hand, an actual torque (a dotted line) gradually increases from a low torque value. Therefore, during a certain period from a time when the air conditioner is turned on, the difference between the estimated compressor torque and the actual torque becomes large. During the certain period when the difference is large, an output torque of the engine cannot be appropriately controlled. The engine excessively rotates, and gasoline mileage and drivability of the vehicle deteriorate. 
   SUMMARY OF THE INVENTION 
   The present invention provides a compressor torque estimate device capable of estimating a compressor torque that is different from an actual torque in a relatively small degree even when a compressor control signal is rapidly excessively changed, and an engine control device. 
   In accordance with the present invention, a compressor torque estimate device is used for a variable displacement compressor whose displacement is variable based on a compressor control signal for estimating a compressor torque of the compressor. The compressor torque estimate device includes a torque calculator and a corrector. The torque calculator calculates a torque required for driving the compressor based on the compressor control signal, thereby obtaining a calculated torque. The corrector corrects the calculated torque by a procedure of first-order lag, thereby obtaining a corrected torque. The corrector also estimates the corrected torque to be the compressor torque. 
   The present invention is also applicable to an engine control device for controlling an output torque of an engine that drives a vehicle and a variable displacement compressor in an air conditioner for the vehicle. A displacement of the variable displacement compressor is variable based on a compressor control signal. The engine control device includes a compressor torque estimate device for estimating a compressor torque of the compressor, and an engine controller. The compressor torque estimate device includes a torque calculator and a corrector. The torque calculator calculates a required torque for driving the compressor based on the compressor control signal, thereby obtaining a calculated torque. The corrector corrects the calculated torque by a procedure of first-order lag, thereby obtaining a corrected torque. The corrector also estimates the corrected torque to be the compressor torque. The engine controller controls the output torque of the engine by considering the compressor torque of the compressor estimated by the corrector. 
   The present invention also provides a method of estimating a compressor torque of a displacement variable compressor whose displacement is variable based on a compressor control signal. The method includes the steps of calculating a torque required for driving the compressor based on the compressor control signal to obtain a calculated torque, correcting the calculated torque by a procedure of first-order lag to obtain a corrected torque, and estimating the corrected torque to be the compressor torque. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The features of the present invention that are believed to be novel are set forth with particularity in the appended claims. Aspect of the invention may best be understood by reference to the following description of the presently preferred embodiments together with the accompanying drawings in which: 
       FIG. 1  is a longitudinal cross-sectional view of a compressor according to a preferred embodiment; 
       FIG. 2  is a cross-sectional view of a control valve according to the preferred embodiment; 
       FIG. 3  is a graph showing changes in a compressor torque and an actual torque after an air conditioner switch is turned on in the preferred embodiment; and 
       FIG. 4  is a graph showing changes in a compressor torque and an actual torque after an air conditioner switch is turned on in a prior art. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   A preferred embodiment according to the present invention will be described. The present invention is applied to an air conditioner for a vehicle. 
   As shown in  FIG. 1 , a variable displacement compressor includes a housing  11 . A crank chamber  12  as a control chamber is defined in the housing  11 . A drive shaft  13  is rotatably arranged in the crank chamber  12 . The drive shaft  13  is operatively connected to an engine E (internal combustion engine) as a drive source for a vehicle. The drive shaft  13  is rotatably driven by supplying power from the engine E. 
   A lug plate  14  is integrally rotatably mounted on the drive shaft  13  in the crank chamber  12 . A swash plate  15  as a cam plate is accommodated in the crank chamber  12 . The swash plate  15  is slidably inclinably supported by the drive shaft  13 . A hinge mechanism  16  is interposed between the lug plate  14  and the swash plate  15 . Therefore, the swash plate  15  is rotatable synchronously with the lug plate  14  and the drive shaft  13  and inclinable with respect to the axis of the drive shaft  13  through the hinge mechanism  16 . 
   A plurality of cylinder bores  11   a  is formed in the housing  11 . Only one cylinder bore  11   a  is shown in  FIG. 1. A  single-headed piston  17  is accommodated in each of the cylinder bores  11   a  so as to reciprocate therein. Each of the pistons  17  is coupled to the swash plate  15  through a pair of shoes  18 . Therefore, the rotational movement of the swash plate  15  in accordance with the rotation of the drive shaft  13  is converted into the reciprocating movement of the piston  7  through the pair of shoes  18 . 
   A valve plate assembly  19  is arranged in the housing  11 . A compression chamber  20  is defined by the piston  17  and the valve assembly  19  on the back side (the right side in  FIG. 1 ) in the cylinder bore  11   a.  A suction chamber  21  and a discharge chamber  22  are defined in the housing  11  on the back side of the valve plate assembly  19 . 
   As the piston  17  moves from its top dead center to its top bottom dead center, refrigerant gas in the suction chamber  21  is introduced into the compression chamber  20  through a suction port  23  and a suction valve  24  that are formed in the valve plate assembly  19 . As the piston  17  moves from its bottom dead center to its top dead center, the refrigerant gas introduced into the compression chamber  20  is compressed to a predetermined pressure and is discharged into the discharge chamber  22  through a discharge port  25  and a discharge valve  26  that are formed in the valve plate assembly  19 . 
   A bleed passage  27  and a supply passage  28  are provided in the housing  11 . The bleed passage  27  interconnects the crank chamber  12  with the suction chamber  21 . The supply passage  28  interconnects the discharge chamber  22  with the crank chamber  12 . A control valve CV is arranged on the supply passage  28  in the housing  11 . 
   A balance between a quantity of high-pressure discharged gas introduced from the discharge chamber  22  through the supply passage  28  into the crank chamber  12  and a quantity of the gas discharged from the crank chamber  12  through the bleed passage  27  into the suction chamber  21  is controlled by adjusting the opening degree of the control valve CV. And then, the pressure in the crank chamber  12  is determined. A pressure differential between the crank chamber  12  and the compression chamber  20  is varied in accordance with a change in the pressure in the crank chamber  12 , and an inclination angle of the swash plate  15  is varied. As a result, the stroke of the piston  17 , that is, the displacement of the compressor is adjusted. The inclination angle of the swash plate  15  is an angle between the swash plate  15  and a hypothetical plane perpendicular to the axis of the drive shaft  13 . 
   For example, when the pressure in the crank chamber  12  is decreased, the inclination angle of the swash plate  15  is increased, and the displacement of the compressor is increased. On the other hand, when the pressure in the crank chamber  12  is increased, the inclination angle of the swash plate  15  is decreased, and the displacement of the compressor is decreased. As shown by a solid line in  FIG. 1 , a minimum inclination angle of the swash plate  15 , that is, a minimum displacement of the compressor is substantially set at zero. Accordingly, when the compressor is in a minimum displacement state, a load for driving the compressor that is applied to the engine E is considered substantially zero. 
   As shown in  FIG. 1 , a refrigerant circulation circuit in an air conditioner for the vehicle includes the above-mentioned compressor and an external refrigerant circuit  30 . The external refrigerant circuit  30  includes a condenser  31 , an expansion valve  32  as a pressure reducing device and an evaporator  33 . 
   A first pressure monitoring point P 1  is set in the discharge chamber  22 . A second pressure monitoring point P 2  is set in a refrigerant passage at a predetermined distance from the first pressure monitoring point P 1  toward the condenser  31 . The first pressure monitoring point P 1  is interconnected with the control valve CV through a first pressure introducing passage  35 . The second monitoring point P 2  is interconnected with the control valve CV through a second pressure introducing passage  36 . A fixed throttle  37  is formed in the refrigerant passage between the first and second pressure monitoring points P 1  and P 2 . 
   As shown in  FIG. 2 , a valve chamber  42 , a communication passage  43  and a pressure sensing chamber  44  are formed in a valve housing  41  of the control valve CV. A rod  45  is movably arranged in the valve chamber  42  and the communication passage  43  in an axial direction (in a vertical direction in FIG.  2 ). The upper end portion of the rod  45  is interposed into the communication passage  43  and blocks the pressure sensing chamber  44  from the communication passage  43 . The valve chamber  42  is interconnected with the crank chamber  12  through the downstream part of the supply passage  28 . The communication passage  43  is interconnected with the discharge chamber  22  through the upstream part of the supply passage  28 . The valve chamber  42  and the communication passage  43  institutes a part of the supply passage  28 . 
   The rod  45  includes a valve body  46  in the intermediate part of the rod  45 . The valve body  46  is arranged in the valve chamber  42 . A step located between the valve chamber  42  and the communication passage  43  forms a valve seat  47 . The communication passage  43  forms a valve hole. When the rod  45  moves upward from the position (a lowest position) in  FIG. 2  to a top position (a highest position) where the valve body  46  of the rod  45  contacts the valve seat  47 , the communication passage  43  is blocked. Namely, the valve body  46  of the rod  45  functions as a valve body capable of adjusting the opening degree of the supply passage  28 . 
   A pressure sensing member  48  constituted of a bellows is accommodated in the pressure sensing chamber  44 . The upper end portion of the pressure sensing member  48  is fixed to the valve housing  41 . The upper end portion of the rod  45  is interposed into the lower end portion (a movable end) of the pressure sensing member  48 . A first pressure chamber  49  that is the inside of the pressure sensing member  48  and a second pressure chamber  50  that is the outside of the pressure sensing member  48  are defined in the pressure sensing chamber  44  by the pressure sensing member  48  forming a cylinder with a bottom in shape. A pressure Pd H at the first pressure monitoring point P 1  is introduced into the first pressure chamber  49  through the first pressure introducing passage  35 . A pressure Pd L at the second pressure monitoring point P 2  is introduced into the second pressure chamber  50  through the second pressure introducing passage  36 . Namely, the pressure sensing chamber  44  and the pressure sensing member  48  constitute a pressure differential detector and detect a pressure differential between the first and second pressure monitoring points P 1  and P 2 . 
   An electromagnetic actuator  51  as a set pressure differential changing means is provided on the lower side of the valve housing  41 . The electromagnetic actuator  51  includes an accommodation cylinder  52  forming a cylinder with a bottom in shape in an intermediate part in the valve housing  41 . A center post (a fixed iron core)  53  forming a column in shape is fixedly interposed into the accommodation cylinder  52  at the opening of the upper side of the accommodation cylinder  52 . Therefore, a plunger chamber  54  is defined on a lower side in the accommodation cylinder  52 . 
   A plunger (a movable iron core)  56  forming a cylinder with a cover in shape is movably accommodated in the plunger chamber  54  in the axial direction. A guide hole  57  is formed in the center of the center post  53  so as to extend therethrough in the axial direction. The lower end portion of the rod  45  is movably arranged in the guide hole  57  in the axial direction. The lower end surface of the rod  45  contacts the upper end surface of the plunger  56  in the plunger chamber  54 . 
   A spring  60  for urging the plunger  56  is accommodated between the inner bottom surface of the accommodation cylinder  52  and the plunger  56  in the plunger chamber  54 . The spring  60  urges the plunger  56  toward the side of the rod  45 . The rod  45  is urged toward the side of the plunger  56  based on spring characteristics of the pressure sensing member  48  (hereinafter called a bellows spring  48 ). Therefore, the plunger  56  and the rod  45  continuously integrally move upward and downward. The bellows spring  48  whose spring force is larger than that of the spring  60  is utilized. 
   A coil  61  is formed around the accommodation cylinder  52  on the outer circumferential side of the accommodation cylinder  32  in a range crossing the center post  53  and the plunger  56 . Electric power is supplied from a drive circuit  71  to the coil  61 . A magnitude of electromagnetic force (electromagnetic attraction) in accordance with a supply amount of the electric power generates between the plunger  56  and the center post  53  by supplying the electric power from the drive circuit  71  to the coil  61 . The electromagnetic force is transmitted through the plunger  56  to the rod  45 . Energization control to the coil  61  is performed by adjusting applied voltage. Pulse width modulation control is utilized for adjusting the applied voltage. 
   In the control valve CV, the position of the rod  45  (the valve body  46 ), that is, the opening degree of the supply passage  28  is determined as follows. 
   As shown in  FIG. 2 , when the coil  61  is not energized (a duty ratio Dt is equal to zero %), the downward urging force of the bellows spring  48  is dominant for positioning the rod  45 . Therefore, the rod  45  is positioned at the lowest position of the rod  45 , and the valve body  46  fully opens the communication passage  43 . The pressure in the crank chamber  12  becomes the possible maximum pressure under the conditions at the time. The pressure differential between the crank chamber  12  and the compression chamber  20  through the piston  17  is relatively large. As a result, the inclination angle of the swash plate  15  becomes the minimum, and the displacement of the compressor becomes the minimum. 
   In the control valve CV, when the coil  61  is energized at more than a minimum duty ratio (more than 0%) in a duty ratio variable range, the sum of the spring force of the spring  60  and the upward electromagnetic force is larger than the downward urging force by the bellows spring  48 , and the rod  45  begins to move upward. In this state, the spring force of the spring  60  and the upward electromagnetic force acts against the downward urging force of the bellows spring  48  and a downward pressing force based on pressure differential ΔPd (=Pd H−Pd L) between the first and second pressure monitoring points P 1  and P 2 . The valve body  46  of the rod  45  is positioned with respect to the valve seat  47  at a position where these upward and downward urging forces reach balance. 
   For example, when the rotational speed of the engine E decreases and flow rate of the refrigerant gas in the refrigerant circulation circuit decreases, the downward pressing force based on the pressure differential ΔPd between the first and second pressure monitoring points P 1  and P 2  decreases. The upward and downward urging forces applied to the rod  45  cannot maintain the balance by the electromagnetic force at the time. Therefore, the rod  45  (the valve body  46 ) moves upward, the opening degree of the communication passage  43  decreases, and the pressure in the crank chamber  12  tends to fall. Consequently, the swash plate  15  is inclined in a direction in which the inclination angle of the swash plate  15  increases, and the displacement of the compressor is increased. As the displacement of the compressor is increased, the flow rate of the refrigerant gas in the refrigerant circulation circuit increases, and the pressure differential ΔPd between the first and second pressure monitoring points P 1  and P 2  increases. 
   On the other hand, when the rotational speed of the engine E increases and the flow rate of the refrigerant gas in the refrigerant circulation circuit increases, the downward pressing force based on the pressure differential ΔPd between the first and second pressure monitoring points P 1  and P 2  increases. The upward and downward urging forces applied to the rod  45  cannot maintain the balance by the electromagnetic force at the time. Therefore, the rod  45  (the valve body  46 ) moves downward, the opening degree of the communication passage  43  increases, and the pressure in the crank chamber  12  tends to increase. Consequently, the swash plate  15  is inclined in a direction in which the inclination angle of the swash plate  15  decreases, and the displacement of the compressor is decreased. As the displacement of the compressor is decreased, the flow rate of the refrigerant gas in the refrigerant circulation circuit decreases, and the pressure differential ΔPd between the first and second pressure monitoring points P 1  and P 2  decreases. 
   Also, for example, when the duty ratio Dt upon energizing the coil  61  becomes large and the upward electromagnetic force becomes large, the upward and downward urging forces cannot maintain the balance by the downward pressing force based on the pressure differential ΔPd between the first and second pressure monitoring points P 1  and P 2  at the time. Consequently, the rod  45  (the valve body  46 ) moves upward, the opening degree of the communication passage  43  decreases, and the displacement of the compressor is increased. As a result, the flow rate of the refrigerant gas in the refrigerant circulation circuit increases, and the pressure differential ΔPd between the first and second pressure monitoring points P 1  and P 2  increases. 
   On the other hand, when the duty ratio Dt upon energizing the coil  61  becomes small and the upward electromagnetic force becomes small, the upward and downward urging forces cannot maintain the balance by the downward pressing force based on the pressure differential ΔPd between the first and second pressure monitoring points P 1  and P 2  at the time. Consequently, the rod  45  (the valve body  46 ) moves downward, the opening degree of the communication passage  43  increases, and the displacement of the compressor is decreased. As a result, the flow rate of the refrigerant gas in the refrigerant circulation circuit decreases, and the pressure differential ΔPd between the first and second pressure monitoring points P 1  and P 2  decreases. 
   Namely, the control valve CV is formed so as to internally autonomously position the rod  45  (the valve body  46 ) in accordance with the change of the pressure differential ΔPd between the first and second pressure monitoring points P 1  and P 2 . The rod  45  is positioned in such a manner that a control target (a set pressure differential) of the pressure differential ΔPd determined by the duty ratio Dt (a compressor control signal) upon energizing the coil  61  is maintained. Also, the set pressure differential can be changed from an external device by adjusting the duty ratio Dt upon energizing the coil  61 . In other words, the electromagnetic actuator  51 , the pressure sensing chamber  44  and the bellows spring  48  constitute a compressor controller, determine the set pressure differential based on the duty ratio Dt, and adjust the displacement of the compressor in such a manner that the pressure differential detected by the pressure differential detector approaches the set pressure differential. 
   As shown in  FIG. 2 , an air conditioner ECU  81  that generally conducts control of the air conditioner and an engine ECU  82  that generally conducts control of the engine E are installed in the vehicle. Each of the air conditioner ECU  81  and the engine ECU  82  is an electronic control unit that includes a CPU, a ROM, a RAM and an I/O interface and that is similar to a computer. The air conditioner ECU  81  is communicably connected to the engine ECU  82 . 
   An air conditioner switch  83 , a temperature setting device  84 , a temperature sensor  85 , a Pd sensor  86  and a Ps sensor  87  are connected to the air conditioner ECU  81 . The air conditioner switch  83  is an on-off switch for the air conditioner operated by an occupant. The temperature setting device  84  is a device for an occupant to set a set temperature in a vehicle compartment. The temperature sensor  85  detects a temperature in the vehicle compartment. In the refrigerant circulation circuit, the Pd sensor  86  detects a pressure Pd in a discharge pressure region including the refrigerant passage between the discharge chamber  22  in the compressor and the condenser  31 , the discharge chamber  22  and the condenser  31 . In the refrigerant circulation circuit, the Ps sensor  87  detects a pressure Ps in a suction pressure region including a refrigerant passage between the evaporator  33  and the suction chamber  21  in the compressor, the evaporator  33  and the suction chamber  21 . Also, the drive circuit  71 , or the control valve CV (the coil  61 ) as a control element is connected to the air conditioner ECU  81 . 
   An accelerator position sensor  88  for detecting an accelerator position (a degree of an accelerator pushed down) and a rotational speed sensor  89  for detecting a rotational speed Ne of the engine E are connected to the engine ECU  82 . Also, an electronically controlled throttle valve device  75  provided in the engine E is connected as a control element to the engine ECU  82 . 
   The air conditioner ECU  81  calculates the duty ratio Dt based on information (e.g. information on the on-off state of the air conditioner switch  83 , the temperature in the vehicle compartment and the set temperature) from information detecting means for air conditioning, that is, from the air conditioner switch  83 , the temperature setting device  84  and the temperature sensor  85 . The air conditioner ECU  81  instructs the drive circuit  71  to energize the coil  61  at a calculated duty ratio Dt. 
   For example, when the air conditioner switch  83  is in an ON-state, the air conditioner ECU  81  compares the set temperature of the temperature setting device  84  with a detected temperature of the temperature sensor  85 . The air conditioner ECU  81  changes the duty ratio Dt in such a manner that the detected temperature approaches the set temperature. Namely, when the detected temperature is higher than the set temperature, the duty ratio Dt is increased. Accordingly, the displacement of the compressor is increased. On the other hand, when the detected temperature is lower than the set temperature, the duty ratio Dt is decreased. Accordingly, the displacement of the compressor is decreased. 
   Also, the air conditioner ECU  81  forms a compressor torque estimate device. The air conditioner ECU  81  estimates a compressor torque Tr′ required for driving the compressor based on the duty ratio Dt upon energizing that is sent as an instruction for the control valve CV from the air conditioner ECU  81  to the drive circuit  71 . The air conditioner ECU  81  transmits information on the compressor torque Tr′ to the engine ECU  82 . 
   The air conditioner ECU  81  functions as a torque calculator and calculates a torque Tr(n) required for driving the compressor under the conditions (Pd, Ps, Ne and Dt) based on information (Pd, Ps, Ne and Dt) from information detecting means for calculating torque, that is, from the Pd sensor  86 , the Ps sensor  87  and the rotational speed sensor  89 . The air conditioner ECU  81  calculates the torque Tr(n) with a pre-stored equation (1) as follows:
 
 Tr ( n )=(theoretical torque)/(operating efficiency)=60/2π Nc·[m/ ( m −1)· Pd·Qd·{ 1−( Pd/Ps ) (1−m)/m   }]/ηad   (1)
 
wherein m denotes a ratio of specific heat (1.03 when the refrigerant gas is R134a), Nc denotes a rotational speed (rpm) of the compressor (the drive shaft  13 ), Qd denotes a flow rate of the refrigerant gas, Pd denotes a discharge pressure, and Ps denotes a suction pressure. Also, “n” is a counted value whose initial value is “two”. “One” is added to “n” every time a compressor torque estimate routine is repeated. When the air conditioner switch  83  is turned off, the counted value n is reset to the initial value. Torque Tr(1) is pre-stored as zero. A calculated torque Tr(n) is temporarily stored in a RAM of the air conditioner ECU  81  until a next compressor torque estimate routine finishes.
 
   A rotational speed Nc of the drive shaft  13  is calculated by considering a pre-stored pulley ratio (change gear ratio) in a power transmission path between the engine E and the drive shaft  13  into information on the rotational speed Ne of the engine E received from the engine ECU  82 . Namely, the rotational speed sensor  89  functions as a rotational speed detecting means for detecting a physical quantity or the rotational speed Ne of the engine E having correlation with the rotational speed Nc of the drive shaft  13 . 
   The flow rate Qd of the refrigerant gas is expressed by “(a flow coefficient)·(an area of the fixed throttle  37 )·√{square root over ( )}(2ΔPd/ρd)”. The pressure differential ΔPd is determined by a function of an input electric current value to the coil  61  of the control valve CV and valve characteristics of the control valve CV. The input electric current is determined from the duty ratio Dt and a voltage of a power supply (a battery). The specific gravity ρd of the discharged gas can approach the discharge pressure Pd. Namely, the air conditioner ECU  81 , which determines the pressure differential ΔPd, functions as a refrigerant flow rate detecting means. The air conditioner ECU  81  is capable of obtaining the flow rate Qd of the refrigerant gas from the duty ratio Dt, which is sent as the instruction from the air conditioner ECU  81  to the drive circuit  71 . 
   The operating efficiency ηad of the compressor is calculated by the following equation (2):
 
 ηad= 1− A·Nc/{ ( B·Qd ) c   +A·Nc}   (2)
 
wherein “A”, “B” and “C” are constants that are predetermined by an experiment.
 
   The air conditioner ECU  81  functions as a corrector. The air conditioner ECU  81  corrects the calculated Torque Tr(n) by a procedure of first-order lag and a procedure of delay and estimates a corrected torque to be a compressor torque Tr′. 
   Namely, the air conditioner ECU  81  functions as a corrector for the procedure of the first-order lag and calculates a candidate torque Tr′(n) with the following equation (3) from a torque Tr(n−1) calculated at the last routine and a candidate torque Tr′(n−1) of the compressor torque Tr′ calculated at the last routine:
 
 Tr′ ( n )=(1− e   −at )· Tr′ ( n− 1)+ e   −at   ·Tr ( n− 1)  (3)
 
wherein “a” is a time constant, and “t” is a sampling time of the air conditioner ECU  81 .
 
   The air conditioner ECU  81  stores a calculated candidate torque Tr′(n) as a latest value in a candidate torque storage region of the RAM of the air conditioner ECU  81 . The candidate torque storage region is capable of storing a plurality of candidate torques Tr′(n) in order of calculation. The plurality is a predetermined number (Tr′(n), Tr′(n−1), Tr′(n−2) . . . ). In the plurality of candidate torques stored in the candidate torque storage region, an oldest value is deleted every time a new candidate torque Tr′(n) is calculated. The value calculated at the next routine relative to a routine where the oldest value is calculated is considered a new oldest value. 
   The air conditioner ECU  81  functions as a corrector for the procedure of the delay. The air conditioner ECU  81  reads out the oldest value stored in the candidate torque storage region of the RAM, estimates the compressor Torque Tr′ to be the oldest value, and sends the compressor torque Tr′ to the engine ECU  82 . A period that the routine is repeated until the latest value in the candidate torque storage region is changed into the oldest value, that is, a delay time as a predetermined time in a correction by the procedure of the delay can be predetermined by a number of the candidate torque Tr′(n) stored in the candidate torque storage region. 
   When the air conditioner switch  83  is turned off, all values of the candidate torques Tr′(n) including the latest value and the oldest value are reset to zero in the candidate torque storage region of the RAM. Also, a candidate torque Tr′(1) is pre-stored as zero. Therefore, the compressor torque Tr′ is estimated to be zero during the predetermined delay time from a time when the air conditioner switch  83  is turned on. 
   The engine ECU  82  as an engine controller calculates a target engine output torque from information on the accelerator position from the accelerator position sensor  88  and the rotational speed Ne from the rotational speed sensor  89  and information on the compressor torque Tr′ received from the air conditioner ECU  81 . The engine ECU  82  actuates the throttle valve device  75  based on a calculated target engine output torque and adjusts an intake air quantity of engine E. 
   According to the preferred embodiment, the following advantageous effects are obtained. 
   (1) The air conditioner ECU  81  calculates the torque Tr(n) required for driving the compressor based on information such as the duty ratio Dt, which is sent as the instruction from the air conditioner ECU  81  to the drive circuit  71 . And then, the air conditioner ECU  81  corrects the calculated torque Tr(n) by the procedure of the first-order lag and estimates the compressor torque Tr′ from the corrected candidate torque Tr′(n). Therefore, even during a time of transition when the displacement of the compressor is rapidly excessively changed, the estimated compressor torque Tr′ can be gradually changed in accordance with mechanical response delay of the compressor. Accordingly, even during the time of transition, the difference between the estimated compressor torque Tr′ and an actual torque can be relatively small. 
   (2) The air conditioner ECU  81  corrects the torque Tr(n) by the procedure of the delay in addition to the procedure of the first-order lag. Therefore, the procedure of the delay can cover an area that cannot be covered by the procedure of the first-order lag, that is, an area in which it is hard to reduce the difference between the estimated compressor torque Tr′ and the actual torque. Even in the above area, the difference between the estimated compressor torque Tr′ and the actual torque can be relatively small. 
   Namely, for example, when the air conditioner switch  83  is turned on from an OFF-state, the air conditioner ECU  81  rapidly changes the duty ratio Dt, which is sent as the instruction from the air conditioner ECU  81  to the drive circuit  71 , from zero substantially to a maximum value based on a relatively large difference between the detected temperature and the set temperature. Therefore, the duty ratio Dt sent as the instruction to the drive circuit  71  is rapidly increased from zero substantially to the maximum value, and the opening degree of the control valve CV is rapidly decreased. However, as shown by the dotted line in  FIG. 3 , due to the mechanical response delay of the variable displacement compressor including the swash plate  15 , there is a slight delay (a dead area X) until the displacement of the compressor begins to increase from the minimum displacement, that is, until the actual torque begins to increase from zero. 
   The procedure of the first-order lag can appropriately deal with only a response delay until the displacement of the compressor reaches a desired displacement corresponding to the duty ratio Dt from the start of change in the displacement of the compressor (change of the inclination angle of the swash plate  15 ). Therefore, as shown by a two-dot line in  FIG. 3 , when the compressor torque Tr(n) is corrected only by the procedure of the first-order lag, the difference between the estimated compressor torque Tr′ and the actual torque is large to some extent. 
   However, in the present preferred embodiment, the procedure of the delay is utilized in combination with the procedure of the first-order lag. As shown by a solid line in  FIG. 3 , the estimated compressor torque Tr′ begins to change after the delay time from the time when the duty ratio Dt is changed. Therefore, in the dead area X, the difference between the estimated compressor torque Tr′ and the actual torque can be relatively small. 
   (3) The air conditioner ECU  81  continuously corrects the calculated Tr(n). It is assumed that the air conditioner ECU  81  is formed so as to correct the calculated Tr(n) only during the time of transition when the displacement of the compressor is rapidly excessively changed and not during the steady state. Compared to this case, a program can be simple in the present preferred embodiment, and a computing load on the air conditioner ECU  81  can be reduced. 
   (4) The engine ECU  82  adjusts the intake air quantity of the engine E by considering the compressor torque Tr′, which is estimated by the air conditioner ECU  81 . Therefore, for example, when the air conditioner switch  83  is turned on from the OFF-state, the intake air quantity of the engine E can be appropriately adjusted even during the time of transition when the displacement of the compressor is rapidly excessively changed. Accordingly, the engine E appropriately rotates, and gasoline mileage and drivability of the vehicle can be improved. 
   According to the present invention, following alternative embodiments may be practiced. 
   In the above-mentioned preferred embodiment, the air conditioner ECU  81  corrects the calculated torque Tr(n) by both the procedure of the first-order lag and the procedure of the delay. However, the air conditioner ECU  81  may be formed so as to correct the calculated torque Tr(n) only by the procedure of the first-order lag and so as to estimate a corrected torque to be the compressor torque Tr′. In this formation, for example, as shown by the two-dot line in  FIG. 3 , the difference between the estimated compressor torque Tr′ and the actual torque can be smaller than that in a prior art as shown by a solid line in FIG.  4 . 
   In the above-mentioned preferred embodiment, the air conditioner ECU  81  continuously corrects the calculated torque Tr(n). However, the air conditioner ECU  81  may corrects the calculated torque Tr(n) only during the time of transition when the variable displacement of the compressor is rapidly excessively changed. During the other time, that is, During the steady state, the air conditioner ECU  81  may not correct the calculated torque Tr(n) and may estimate the calculated torque Tr(n) to be the compressor torque Tr′. Namely, for example, when a varying rate of the duty ratio Dt is equal to, or more than a predetermined rate, the air conditioner ECU  81  corrects the calculated torque Tr(n). When the varying rate of the duty ratio Dt is less than the predetermined rate, the air conditioner ECU  81  does not correct the calculated torque Tr(n). In this manner, accuracy of the estimation of the compressor torque Tr′ during the steady state can be improved. 
   The engine ECU  82  may estimate the compressor torque Tr′. In this case, the engine ECU  82  may receive operational information (the discharge pressure Pd, the suction pressure Ps and the duty ratio Dt sent as the instruction from the air conditioner ECU  81  to the drive circuit  71 ) from the air conditioner ECU  81 , or may detects the operational information on its own. Also, the air conditioner ECU  81  may be removed, and the engine ECU  82  may serve as the air conditioner ECU  81  for air conditioning control and compressor torque estimation. 
   The engine ECU  82  may control an ISCV (an idle speed control valve) based on the compressor torque Tr′ from the air conditioner ECU  81 . This manner stabilizes idling of the engine E. 
   The engine ECU  82  may control a fuel injection system based on the compressor torque Tr′ from the air conditioner ECU  81 . In this case, the engine ECU  82  adjusts an injection quantity of the engine E by considering the compressor torque Tr′ estimated by the air conditioner ECU  81 . 
   The control valve CV may be changed to a variable set suction pressure type, or a variable set discharge pressure type. The control valve CV internally mechanically detects the suction pressure or the discharge pressure. The control valve CV internally autonomously moves a valve body in such a manner that the displacement of the compressor is changed. The displacement of the compressor is changed so as to cancel change of a detected pressure. A set suction pressure or a set discharge pressure as a standard for positioning the valve body can be adjustable by a compressor control signal from an external device. 
   The control valve CV may be changed to a bleed control valve that controls an opening degree of the bleed passage  27 , not the opening degree of the supply passage  28 , so as to adjust the pressure in the crank chamber  12 . 
   The present invention may be applied to a wobble plate type variable displacement compressor. 
   The present examples and embodiments are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein but may be modified within the scope of the appended claims.