Abstract:
A vehicular air-conditioner includes a compressor to be driven by an engine. The vehicular air-conditioner includes a controller configured to reduce a load on the compressor in response to a braking condition of a vehicle.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
         [0001]    This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2002-368700 filed on Dec. 19, 2002; the entire contents of which are incorporated herein by reference.  
         BACKGROUND OF THE INVENTION  
         [0002]    The present invention relates to a vehicular air-conditioner which adjusts temperature environment of a vehicle interior.  
           [0003]    In order to improve temperature environment of a vehicle interior, a vehicular air-conditioner sends conditioned air whose temperature adjustment has been performed to the vehicle interior. Japanese Patent Application Laid-open No. 2001-105846A discloses that elevating of a cooling performance of a heat exchanger for cooling during vehicle deceleration recovers deceleration energy of a vehicle without giving uncomfortable feeling to a vehicle occupant, thus advantageously saving fuel consumption. According to this, a vehicle occupant great feels more uncomfortable, as a blow-off temperature of conditioned air into the vehicle interior varies greater. On the other hand, the limitation of variation range for a vehicle occupant not to feel uncomfortable is varied according to a blow-off air-flow rate into the vehicle interior. In view of this fact, a target evaporator has a decrement of blow-off temperature during vehicle deceleration. The decrement of the blow-off temperature is set to become smaller, as a target air-flow rate becomes from Low towards High. Thereby, the decrement becomes great when an air blow rate is small, thus advantageously saving fuel consumption without giving uncomfortable feeling to a vehicle occupant.  
           [0004]    A compressor in an air-conditioner is operating even during vehicle deceleration. Even when a throttle interlocked to an accelerator pedal is in a full closed state, an idle speed control valve (hereinafter, “ISC valve”) which controls engine revolutions during idling operation is opened or closed. The opening or closing permits an intake air volume to be increased, thus increasing the engine revolutions. This permits an engine to be controlled not to stop due to a load of the compressor.  
           [0005]    A passenger vehicle employs a brake apparatus. The brake apparatus utilizes a differential pressure between the atmosphere pressure and a boost pressure of the engine to amplify a pressing force of a driver on a brake pedal until the force reaches a braking force sufficient to stop a vehicle during running thereof.  
           [0006]    Accordingly, when the throttle is fully closed in a state that an air-conditioner is operating, an intake air volume into the engine is increased by the ISC valve for operating the compressor. The boost pressure is maintained due to the increase until the throttle is fully closed in a state that the air-conditioner has stopped. That is, a differential pressure between the atmospheric pressure and the boost pressure is reduced, deteriorating engine braking effect. Thus, there is a possibility that the reduction of the differential pressure deteriorates a braking performance in dependence on the structure of the brake apparatus.  
         SUMMARY OF THE INVENTION  
         [0007]    An object of the present invention is to provide a vehicular air-conditioner which reduces a load on an engine during vehicle deceleration.  
           [0008]    A first aspect of the invention is directed to a vehicular air-conditioner. The air-conditioner includes a compressor to be driven by an engine. The air-conditioner includes a controller configured to reduce a load on the compressor in response to a braking condition of a vehicle.  
           [0009]    The compressor may include a clutch configured to transmit torque from the engine to the compressor. The controller is configured to disengage the clutch to stop the compressor under the braking condition of the vehicle.  
           [0010]    The compressor may have a variable displacement compressor.  
           [0011]    The controller is configured to reduce a coolant in discharge rate from the compressor under the braking condition of the vehicle.  
           [0012]    The controller may be configured to stop reducing of a load on the compressor in response to a non-braking condition of the vehicle.  
           [0013]    The controller may include a first controller configured to control the engine and to determine the braking condition of the vehicle. The controller may include a second controller configured to reduce a load on the compressor in response to the braking condition of the vehicle.  
           [0014]    The braking condition may include a first condition of a predetermined vehicle speed or more or predetermined engine revolutions or more. The braking condition may include a second condition of pressing-down of a brake pedal, lighting of a tail lamp or increase of a brake hydraulic pressure. The braking condition may include a third condition of release of an accelerator pedal.  
           [0015]    A second aspect of the invention is directed to a method of controlling a vehicular air-conditioner. The control method includes the step of determining a braking condition of a vehicle. The control method includes the step of reducing a load on a compressor in response to the braking condition of the vehicle.  
           [0016]    The determining of the braking condition of the vehicle may include the step of determining a predetermined vehicle speed or more or predetermined engine revolutions or more. The determining of the braking condition may include the step of determining pressing-down of a brake pedal, lighting of tail lamp or increase of a brake hydraulic pressure. The determining of the braking condition may include the step of determining release of an accelerator pedal. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]    [0017]FIG. 1 is a block diagram illustrating a vehicular air-conditioner of an embodiment according to the present invention;  
         [0018]    [0018]FIG. 2 is a flowchart illustrating control of the air-conditioner indicated in FIG. 1;  
         [0019]    [0019]FIG. 3 is a flowchart illustrating a normal control in an A/C computer;  
         [0020]    [0020]FIG. 4 is a flowchart illustrating a load reduction control of a vehicle braking condition in the A/C computer;  
         [0021]    [0021]FIG. 5 is a diagram illustrating a logic circuit about conditions of the braking condition;  
         [0022]    [0022]FIG. 6 is a graph illustrating variation of a boost pressure during baking, while the air condition indicated in FIG. 1 is operating;  
         [0023]    [0023]FIG. 7 is a graph illustrating variation of the boost pressure during baking, while a comparative air-conditioner is operating; and  
         [0024]    [0024]FIG. 8 is a schematic diagram illustrating a structure of a brake apparatus. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0025]    Embodiments of the present invention are described with reference to the drawings.  
         [0026]    A vehicular air-conditioner  1  according to an embodiment utilizes an engine driving force as a power source, as indicated in FIG. 1. The air-conditioner  1  includes a variable displacement compressor  10  which can change a discharge rate of coolant according to a set temperature in a vehicle interior. The air-conditioner  1  includes an electromagnetic control valve (ECV)  11 . The air-conditioner  1  includes a clutch  14  which transmits torque from an engine to the compressor. The air-conditioner  1  includes an air-conditioner computer (A/C computer)  12  which controls the compressor  10  under an operating condition. The A/C computer  12  is electrically connected to the ECV  11  and the clutch  14 . The air-conditioner  1  includes a Tint sensor  13  which measures an air temperature to be introduced into the air-conditioner  1 .  
         [0027]    The compressor  10  compresses or discharges coolant supplied inside of a cylinder when a piston reciprocates inside the cylinder provided inside a main body of the compressor. Variation of an internal pressure in a crank chamber can cause a stroke amount of the reciprocating piston to change a discharge rate of the coolant.  
         [0028]    The ECV  11  introduces a high pressure in a discharge chamber into the crank chamber and is controlled by an external signal.  
         [0029]    The A/C computer  12  calculates and determines a target evaporator passing-through air temperature on the basis of a vehicle interior temperature sensor, an outside air temperature sensor output, a solar radiation sensor, and respective set values (blower temperature). The A/C computer  12  outputs a signal to the ECV  11  so as to establish the target value.  
         [0030]    The A/C computer  12  transmits or receives signals to or from an engine computer  51  which performs engine control by a vehicle body equipment  50 . The engine computer  51  has signals to be inputted from various sensors. That is, the engine computer receives sensor signals about a brake pedal  52 , a tail lamp  53 , a brake hydraulic pressure  54 , engine revolutions  55 , a boost pressure  56 , a vehicle speed  57  and an accelerator  58  in order to determine a running condition of a vehicle.  
         [0031]    The A/C computer  12  acquires sensor signals through the engine computer  51 . The A/C computer  12  determines “braking condition” of a vehicle on the basis of these sensor signals to control the ECV  11 . Such a constitution may be employed that the engine computer  51  determines the “braking condition” of the vehicle on the basis of the sensor signals to transmit the results to the A/C computer  12 .  
         [0032]    One example of a control method of the air-conditioner  1  is described with reference to FIG. 2.  
         [0033]    First, when a switch of the air-conditioner  1  is turned on, control starts (S 1 ). Next, the engine computer  51  transmits sensor signals to the A/C computer  12 . The A/C computer  12  determines whether or not the vehicle is under a braking condition on the basis of the sensor signals (S 2 ).  
         [0034]    In case of the vehicle under a “non-braking condition”, the A/C computer  12  controls the ECV  11  according to a normal control (S 3 ). On the other hand, when the vehicle is under a braking condition during running, the A/C computer  12  confirms an upper limit value of the Tint (S 4 ) to perform a load reduction control to the ECV  11  (S 5 ).  
         [0035]    With reference to FIG. 5, the “braking condition” in step S 2  is determined according to an AND with the following first, second and third conditions. The first condition is a vehicle speed equal to or more than X (km/h) or engine revolutions equal to or more than Y (rpm). The second condition is a pressing-down of the brake pedal  52 , a lighting of the tail lamp  53  or increase of the brake hydraulic pressure  54 . The third condition is a state that the accelerator pedal has not been pressed, or release of the accelerator pedal.  
         [0036]    Control of the steps S 2 , S 3 , S 4  and S 5  is repeated until the switch in the air-conditioner  1  is turned off.  
         [0037]    With reference to a flowchart indicated in FIG. 3, the normal control S 3  under the “non-braking condition” is described.  
         [0038]    The Tint sensor  13  detects an air temperature introduced into the air-conditioner  1  (S 31 ).  
         [0039]    Next, the A/C computer  12  calculates a difference between an output temperature of the Tint sensor  13  and a set target temperature of a vehicle interior. The A/C computer  12  calculates DUTY ratio of PWM control from the temperature difference (S 32 ). The A/C computer  12  outputs the DUTY ratio to the ECV  11  to control opening or closing of the ECV 11  (S 33 ).  
         [0040]    A control method in the “braking condition” is described on the basis of a flowchart indicated in FIGS. 2 and 4.  
         [0041]    In FIG. 2, the A/C computer  12  determines whether or not a temperature Tint of air introduced into the air-conditioner  1  exceeds a predetermined upper limit value (S 4 ).  
         [0042]    Here, there is a possibility that the Tint over the upper limit value increases a vehicle interior temperature to give uncomfortable feeling to a vehicle occupant. Accordingly, the A/C computer  12  performs the normal control S 3 . On the other hand, when the Tint is equal to or less than the upper limit value, the control of the A/C computer  12  performs the load reduction control S 5 .  
         [0043]    In FIG. 4, the A/C computer  12  under the load reduction control S 5  outputs a required DUTY ratio to the EVC  11  (S 51 ). That is, reducing of the DUTY ratio of the ECV 11  reduces an opening degree of the ECV 11 . This establishes the stroke amount of the compressor  10  at substantially zero, thus reducing an engine load. On the other hand, the A/C computer  12  may disconnect the clutch  14  to stop the compressor  10 . Further, the A/C computer  12  may reduce a discharge rate of coolant of the compressor  10 .  
         [0044]    With reference to FIGS. 6 and 7, variations of boost pressures in the air-conditioner  1  and a comparative air-conditioner during operation is described. A vehicle is under an accelerating condition before at time t1. The vehicle is under a constant running condition between times t1 and t2. The vehicle is under a braking condition between times t2 and t3. The vehicle is put in an idling condition on time t3 and thereafter. The air-conditioner  1  is put in an operating condition for the whole period of time.  
         [0045]    From comparison of FIGS. 6 and 7 to each other, the air-conditioner  1  has small variation of the boost pressure B during the braking condition of the vehicle (times t2 to t3) as compared with the comparative air-conditioner. Accordingly, the boost pressure due to the air-conditioner  1  is sufficiently lowered as compared with that in the comparative air-conditioner.  
         [0046]    This causes the load reduction control to reduce the strove amount of the compressor  1  during the braking condition of the vehicle, thus reducing an engine load. Thereby, the opening degree of the ISC valve can be reduced in the full closed state of the throttle. Therefore, decrease in the intake air volume into the engine allows the boost pressure is lowered.  
         [0047]    With reference to FIG. 8, a brake apparatus  70  is used in a passenger vehicle. The brake apparatus  70  has a brake pedal  52  to be pressed down by a driver. The brake apparatus  70  includes a master back  71  boosting a pressing force of the brake pedal  52 . The brake apparatus  70  includes a master cylinder  72  which converts the boosted pressing force to a hydraulic pressure. The brake apparatus  70  includes hydraulic pressure pipes  73  which transfer the converted hydraulic pressure to respective wheels. The brake apparatus  70  has brake discs  74  to rotate together with the respective wheels. According to the brake apparatus  70 , pressing-down of the brake pedal  52  performed by a driver permits a piston in the master cylinder  72  to push brake pads against the brake discs  74 . Frictions between the brake pads and the brake discs  74  obtains a braking force.  
         [0048]    The master back  71  has an internal space separated into an atmospheric pressure chamber  75  and a boost pressure chamber  76 . The master back  71  includes a piston  77  provided slidably so as to change volumes of the atmospheric pressure chamber  75  and the boost pressure chamber  76 . The master back  71  includes a boost pressure pipe  78  for supplying a boost pressure to the boost pressure chamber  76 . The master back  71  includes an atmospheric pressure pipe  80  provided with an atmospheric pressure ECV 79  for controlling an air volume introduced into the atmospheric pressure chamber  75 .  
         [0049]    When the brake pedal  52  is pressed down, the master back  71  opens the atmospheric pressure ECV  79  according to the pressing force. Thereby, the piston  77  is pulled from the atmospheric pressure chamber  75  towards the boost pressure chamber  76  so that the pressing force is amplified. The amplified pressing force is transferred to the master cylinder  72 .  
         [0050]    Accordingly, by causing the boost pressure during braking condition to approach to the boost pressure put in a state where the air-conditioner is not operating. This enlarges the amplifying ratio of the pressing force conducted by the master back  71 , thus stabilizing the braking force.  
         [0051]    As described above, the control apparatus of the compressor determines the current state as the “braking condition” to perform the load reduction control. The control reduces an intake air volume required for decreasing the engine load to maintain the engine revolutions. Thereby, the opening degree of the ISC valve can be narrowed, which lowers the boost pressure of the engine in the vicinity of the stopped condition of the air-conditioner. Accordingly, a stable braking performance is obtained even while the interior air conditioning is being performed.  
         [0052]    In case that the control apparatus determines that the vehicle is under the “non-braking condition”, the load reduction control is terminated. Thereby, the load reduction control is performed during the braking condition of the vehicle, which reduces the engine load without giving uncomfortable feeling to a vehicle occupant.  
         [0053]    This control permits the boost pressure to be lowered down to about the stopped condition of the air-conditioner for vehicle. Thereby, the engine brake acts in the identical manner to the stopped condition of the vehicular air-conditioner, thus achieving a further strong braking force.  
         [0054]    In this embodiment, the compressor  10  is employed to change the stroke amount of the piston, thus reducing the engine load. On the other hand, a compressor with a clutch  14  for transmission of torque from the engine may be employed to disconnect the clutch  14  during braking condition of the vehicle to stop operation of the compressor. Thereby, a similarly advantageous effect can be obtained even if the engine load is reduced.  
         [0055]    Although the invention has been described above by reference to certain embodiments of the invention, the invention is not limited to the embodiments described above. Modifications and variations of the embodiments described above will occur to those skilled in the art, in light of the above teachings. The scope of the invention is defined with reference to the following claims.