Displacement control device and displacement control method for variable displacement compressor

Information

  • Patent Grant
  • 6358016
  • Patent Number
    6,358,016
  • Date Filed
    Friday, July 14, 2000
    24 years ago
  • Date Issued
    Tuesday, March 19, 2002
    22 years ago
Abstract
A controller normally supplies current the magnitude of which corresponds to a required cooling performance of a refrigeration circuit to a displacement control valve. As a result the compressor displacement is adjusted in accordance with the required cooling performance (usual displacement control). When a vehicle is quickly accelerated, the controller temporarily eliminates the current value to the control valve to minimize the compressor displacement (displacement limiting control). When the control is switched from the displacement limiting control to the usual In displacement control, the controller changes the current value from zero to a target value, which corresponds to the required cooling performance, taking a predetermined restoration time. For an initial period of the restoration period, the current value is set greater than a corresponding value on a direct proportional line, which represents a constant rate of change from zero to the target value. As a result, the control is smoothly and quickly switched from the displacement limiting control to the usual displacement control.
Description




BACKGROUND OF THE INVENTION




The present invention relates to a variable displacement compressor used for vehicle air conditioners, and more specifically, to a device and a method for controlling the displacement of a compressor.




In a general variable displacement compressor used for vehicle air conditioners, the inclination angle of a swash plate provided in a crank chamber changes in accordance with the pressure in the crank chamber. The crank chamber is connected to a suction chamber through a bleed passage and also to a discharge chamber through a supply passage. In the bleed passage is provided a displacement control valve. A controller containing a computer controls a control valve to adjust the amount of refrigerant gas that flows out into the suction chamber from the crank chamber through the bleed passage. As a result, the amount of the refrigerant gas which flows out of the crank chamber changes relative to the amount of refrigerant gas which is supplied to the crank chamber from the discharge chamber through the supply passage so that the pressure in the crank chamber is adjusted.




The control valve is provided with, for example, a valve body, a pressure sensing mechanism for operating the valve body in accordance with the pressure in the suction chamber (suction pressure), and an electromagnetic actuator, which urges the valve body with a force corresponding to the value of electric current supplied from the controller. The force of the electromagnetic actuator to urge the valve body reflects the target suction pressure. The controller adjusts the value of electric current supplied to the electromagnetic actuator to change the target suction pressure.




The controller increases the value of electric current supplied to the electromagnetic actuator to decrease the target suction pressure, and decreases the value of electric current supplied to the electromagnetic actuator to increase the target suction pressure. When electric current is not supplied to the electromagnetic actuator, the target suction pressure becomes a maximum value.




When a suction pressure exceeds the target suction pressure, the pressure sensing mechanism operates the valve body so as to increase the opening size of the bleed passage. Therefore, the flow rate of refrigerant gas from the crank chamber to the suction chamber is increased and the pressure in the crank chamber is then reduced. This increases the inclination angle of the swash plate so that displacement of the compressor increases. When the displacement of the compressor increases, the cooling performance of a refrigeration circuit incorporating the compressor increases and a suction pressure decreases so that it is converged to the target suction pressure.




When the suction pressure is lower than the target suction pressure, the pressure sensing mechanism operates the valve body to decrease the opening size of the bleed passage. Therefore, the flow rate of refrigerant gas from the crank chamber to the suction chamber decreases and the pressure in the crank chamber then increases. This decreases the inclination angle of the swash plate so that the displacement of the compressor decreases. When the displacement of the compressor decreases, the cooling performance of refrigeration circuit is reduced and a suction pressure increases so that it is converged to the target suction pressure.




Thus, the pressure sensing mechanism operates the valve body in accordance with the suction pressure in order to maintain the suction pressure at the target suction pressure.




The load on a vehicle engine increases under abrupt acceleration of the vehicle. Since the compressor is driven by the vehicle engine, if the engine load is great, the displacement of the compressor is temporarily minimized to reduce the engine load. Such displacement limiting control under abrupt acceleration of the vehicle will be described with reference to time charts of FIGS.


6


(


a


) to


6


(


c


).




As shown in FIG.


6


(


a


), when a vehicle is abruptly to accelerated in a state where electric current of the predetermined value is supplied to an electromagnetic actuator of a displacement control valve, a controller sets the supplied current value for the electromagnetic actuator at zero to start the displacement limiting control. As a result, as shown in FIG.


6


(


b


), the target suction pressure Pst is set at a maximum value Pmax. Then, the pressure sensing mechanism of the displacement control valve closes the bleed passage with the valve body to bring an actual suction pressure Psa near to the maximum value Pmax. Thus, the pressure in the crank chamber increases and the inclination angle of the swash plate becomes minimum, whereby the displacement of the compressor becomes minimum as shown in FIG.


6


(


c


). In other words, the torque of the compressor becomes minimum so that the engine load is reduced.




When the target suction pressure Pst changes, some time is required for this change to be reflected in the change in the actual suction pressure Psa. Thus, when the target suction pressure Pst is rapidly changed to the maximum value Pmax as shown in FIG.


6


(


b


), the actual suction pressure Psa gradually increases toward the maximum value Pmax.




As shown in FIG.


6


(


a


), a displacement limiting control due to abrupt acceleration of a vehicle is completed after the lapse of the predetermined time S from its start. After that, the displacement limiting control is shifted to a usual displacement control in accordance with a cooling performance required for the refrigeration circuit. Specifically, the controller resumes the supply of current to the electromagnetic actuator after the lapse of the predetermined time S after setting the supplied current value for the electromagnetic actuator at zero. At this time, the controller obtains the target current value A


3


according to the cooling performance required for the refrigeration circuit, and gradually increases the supplied current value for the electromagnetic actuator from zero to the target current value A


3


for the predetermined time T (refer to the straight line H in FIG.


6


(


a


)). According to this increase, the target suction pressure Pst gradually decreases from the it maximum value Pmax to the value P


3


corresponding to the target current value A


3


for the predetermined time T as shown in FIG.


6


(


b


).




If the target suction pressure Pst rapidly decreases from the maximum value Pmax to the value P


3


, the actual suction pressure Psa, which is gradually increasing toward the maximum value Pmax, significantly exceeds the value P


3


temporarily. Then, the pressure sensing mechanism of the displacement control valve causes the valve body to abruptly open the bleed passage to decrease the actual suction pressure Psa to the value P


3


. This leads to an abrupt decrease in the pressure in the crank chamber and rapidly increases the displacement of the compressor. As a result, the torque of the compressor rapidly increases and the engine load rapidly increases, whereby the vehicle drivability is deteriorated. To avoid such problems, the target suction pressure Pst gradually decreases from the maximum value Pmax to the value P


3


for the predetermined time T.




As shown in FIG.


6


(


b


), the actual suction pressure Psa is always lower than the target suction pressure Pst set at the maximum value Pmax through the predetermined time S when the displacement limiting control is being executed. Further, since the target suction pressure Pst gradually decreases at the completion of the displacement limiting control, the actual suction pressure Psa is still lower than the target suction pressure Pst between the completion of the displacement limiting control and the end of time Ta. When the time Ta elapses after the completion of the displacement limiting control, the actual suction pressure Psa substantially becomes equal to the target suction pressure Pst. After that, the actual suction pressure Psa is gradually reduced to the value P


3


as the target suction pressure Pst is gradually reduced to the value P


3


.




When the actual suction pressure Psa is lower than the target suction pressure Pst, the pressure sensing mechanism of the displacement control valve causes the valve body to control the opening size of the bleed passage to increase the actual suction pressure Psa so as to bring it near the target suction pressure Pst. In other words, even if the displacement limiting control is completed, the pressure sensing mechanism does not execute an operation for decreasing the actual suction pressure Psa, that is an operation for increasing displacement of a compressor from the minimum state until the time Ta elapses after the completion.




In addition, the displacement control valve completely closes the bleed passage during execution of the displacement limiting control and the pressure in the crank chamber is excessively increased due to the high pressure gas supplied through the supply passage. Therefore, even if the control valve increases the opening size of the bleed passage to increase the displacement of the compressor after the lapse of the time Ta after the completion of the displacement limiting control, it takes much time to lower the pressure in the crank chamber to pressure by which the displacement of the compressor can shift from the minimum state to an increased state. Thus, as shown in FIG.


6


(


c


), the displacement of the compressor shifts from the minimum state to the increased state with a delay of a considerably long time Tb after the completion of the displacement limiting control. That is, the displacement of the compressor is maintained in the minimum state for a time longer than the execution time S of the displacement limiting control. This means that a cooling performance of the refrigeration circuit unnecessarily decreases for a long time. As a result, the passenger compartment temperature further becomes higher than before execution of the displacement limiting control, which gives discomfort to passengers in the vehicle.




SUMMARY OF THE INVENTION




Accordingly, it is an objective of the present invention to provide a displacement control device and a displacement control method for a variable displacement compressor which smoothly and rapidly shift a displacement limiting control to a usual displacement control.




To attain the above-mentioned object, the present invention provides a displacement control device for a compressor that changes the displacement in accordance with the pressure in a control pressure chamber. The control device includes a control valve, a detector and a controller. The control valve controls the pressure in the control pressure chamber. The control valve has a valve body and an electromagnetic actuator for actuating the valve body. The actuator urges the valve body by a force the magnitude of which corresponds to the value of current supplied to the actuator. The detector detects external conditions that are necessary for controlling the compressor displacement. The controller controls the value of current supplied to the actuator. The controller selects a control mode to be executed from a usual displacement control and a displacement limiting control based on the detected external conditions. When the usual displacement control is selected, the controller sets the current value to a target value, which corresponds to the detected external conditions. When the displacement limiting control is selected, the controller temporarily sets the current value to a specific value to minimize the compressor displacement. When the control mode is switched from the displacement limiting control to the usual displacement control, the controller changes the current value from the specific value to the target value taking a predetermined restoration period. For at least part of the restoration period, the controller sets the current value to a value that is closer to the target value than a corresponding value on a direct proportional line, which represents a constant rate of change from the specific value to the target value.




The present invention also provides a method for controlling the displacement of a compressor that changes the displacement in accordance with the pressure in a control pressure chamber. The method includes: controlling the pressure in the control pressure chamber by a control valve, wherein the control valve has a valve body and an electromagnetic actuator for actuating the valve body, wherein the actuator urges the valve body by a force the magnitude of which corresponds to the value of current supplied to the actuator; detecting external conditions that are necessary for controlling the compressor displacement; selecting a control mode to be executed from a usual displacement control and a displacement limiting control based on the detected external conditions; setting the current value to a target value, which corresponds to the detected external conditions, when the usual displacement control is selected; temporarily setting the current value to a specific value to minimize the compressor displacement when the displacement limiting control is selected; and changing the current value from the specific value to the target value taking a predetermined restoration period when the control mode is switched from the displacement limiting control to the usual displacement control. For at least part of the restoration period, the current value is set to a value that is closer to the target value than a corresponding value on a direct proportional line, which represents a constant rate of change from the specific value to the target value.




Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.











BRIEF DESCRIPTION OF THE DRAWINGS




The invention, together with objects and advantages thereof, 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 cross-sectional view of a variable displacement compressor in one of the embodiments of the present invention;





FIG. 2

is a partially enlarged cross-sectional view showing the compressor of

FIG. 1

when it is being operated in the maximum displacement;





FIG. 3

is a partially enlarged cross-sectional view showing the compressor of

FIG. 1

when it is being operated in the minimum displacement;




FIGS.


4


(


a


) to


4


(


c


) are time charts showing operations during the displacement limiting control in the compressor of

FIG. 1

;





FIG. 5

is a time chart showing operations during a displacement limiting control in another embodiment; and




FIGS.


6


(


a


) to


6


(


c


) are time charts showing operations during a displacement limiting control in a conventional compressor.











DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS




One embodiment according to the present invention will be described with reference to FIG.


1


through FIG.


4


(


c


). First, the structure of a variable displacement compressor will be described. As shown in

FIG. 1

, a front housing member


11


is joined by the front end of a cylinder block


12


. A rear housing


13


is joined by the rear end of the cylinder block


12


through a valve plate assembly


14


. A control pressure chamber, which is a crank chamber


15


in this embodiment, is defined by the front housing member


11


and the cylinder block


12


.




A drive shaft


16


is rotatably supported by the front housing member


11


and the cylinder block


12


to extend through the crank chamber


15


. The drive shaft


16


is connected to a vehicle engine Eg, which functions as an external driving force, through a clutch mechanism C such as an electromagnetic clutch. The clutch mechanism C selectively transmits the driving force of the engine Eg to the drive shaft


16


.




A rotary support


17


is fixed to the drive shaft


16


in the crank chamber


15


. A drive plate, which is a swash plate


18


in this embodiment, is supported on the drive shaft


16


. The swash plate


18


slides along and inclines relative to the axis L. A hinge mechanism


19


is located between the rotary support


17


and the swash plate


18


. The swash plate


18


is connected to the rotary support


17


through the hinge mechanism


19


. The hinge mechanism


19


causes the swash plate


18


to rotate integrally with the rotary support


17


. Further, the hinge mechanism


19


guides the sliding and the inclination of the swash plate


18


with respect to the drive shaft


16


.




As the center portion of the swash plate


18


is moved toward the rotary shaft


17


, the inclination angle of the swash By plate


18


increases. On the other hand, as the center portion of the swash plate


18


is moved toward the cylinder block


12


, the inclination angle of the swash plate


18


decreases. A limit ring


20


is mounted on the drive shaft


16


between the swash plate


18


and the cylinder block


12


. As shown in

FIG. 1

, when the swash plate


18


contacts the rotary support


17


, the inclination angle of the swash plate


18


becomes maximum. As shown in

FIG. 3

, when the swash plate


18


contacts the limit ring


20


the inclination angle of the swash plate


18


becomes minimum.




Cylinder bores


21


(only one is shown in

FIG. 1

) extend through the cylinder block


12


to surround the drive shaft


16


. A single-headed piston


22


is accommodated in each cylinder bore


21


. Each piston


22


is coupled to the periphery of the swash plate


18


through a pair of shoes


23


. The swash plate


18


converts rotation of the drive shaft


16


to reciprocation of each piston


22


in the corresponding cylinder bore


21


.




A suction chamber


24


, which is a suction pressure zone, and a discharge chamber


25


, which is a discharge pressure zone, are formed in the rear housing member


13


. A suction port


26


, a suction valve flap


27


, a discharge port


28


and a discharge valve flap


29


are formed in the valve plate assembly


14


to correspond to each of the cylinder bores


21


.




When each piston


22


is moved from the top dead center position to the bottom dead center position, refrigerant gas is sucked to the corresponding cylinder bores


21


from the suction chamber


24


through the suction port


26


and the suction valve flap


27


. When each piston


22


is moved from the bottom dead center position to the top dead center position, the refrigerant gas is compressed to a predetermined pressure in the corresponding cylinder bore


21


and is then discharged to the discharge chamber


25


through the discharge port


28


and the discharge valve flap


29


. When the piston


22


compresses the refrigerant gas, a high pressure refrigerant gas escapes from the inside of the cylinder bore


21


to the crank chamber


15


through a slight gap between the piston


22


and the cylinder bore


21


. Such gas is referred to as blowby gas.




An external refrigerant circuit


61


connects the suction chamber


24


to the discharge chamber


25


. The external refrigerant circuit


61


includes a condenser


62


, an expansion valve


63


and an evaporator


64


. The compressor and the external refrigerant circuit


61


form a refrigeration circuit for a vehicle air-conditioner.




As shown in

FIG. 1

, a control passage, which is a bleed passage


30


, connects the crank chamber


15


to the suction chamber


24


. A displacement control valve


31


is accommodated in the rear housing


13


to regulate the bleed passage


30


. A supply passage


32


connects the discharge chamber


25


to the crank chamber


15


. The high pressure refrigerant gas in the discharge chamber


25


is supplied to the crank chamber


15


through the supply passage


32


.




A temperature adjuster


33


for setting the target value of a passenger compartment temperature, a passenger compartment temperature sensor


34


, a pedal position sensor


35


, the clutch mechanism C and the control valve


31


are connected to a controller X. The pedal position sensor


35


detects a degree of depression of the vehicle gas pedal, that is the position of the gas pedal. The degree of pedal depression represents the load on the engine Eg. The controller X contains a computer. Further, the controller X is connected to the control valve


31


through a drive circuit


36


. The temperature adjuster


33


, the temperature sensor


34


and the pedal position sensor


35


form an external state detecting means or an external state detector.




The control valve


31


will now be described. As shown in

FIGS. 2 and 3

, the control valve


31


has a valve housing


41


and a solenoid unit


42


, which are coupled to each other. A valve chamber


43


, which also serves as a pressure sensing chamber, is formed in the valve housing


41


. A valve body


44


is located in the valve chamber


43


. A valve hole


45


extends axially in the valve housing


41


. The valve hole


45


opens in the valve chamber


43


to face the valve body


44


. The valve chamber


43


is connected to the suction chamber


24


through the downstream portion of the bleed passage


30


.




A pressure sensing member, which is a bellows


46


in this embodiment, is housed in the valve chamber


43


. The top end of the bellows


46


is fixed to the ceiling wall of the valve chamber


43


and the lower end of the bellows


46


is connected to the valve body


44


. A setting spring


47


is located in the bellows


46


. The setting spring


47


sets the initial length of the bellows


46


. The valve chamber


43


, the bellows


46


and the setting spring


47


form a pressure sensing mechanism.




The solenoid unit


42


, or the electromagnetic actuator, has a plunger chamber


48


. To the upper opening of the plunger chamber


48


is fitted a fixed core


49


. A plunger


50


is housed in the plunger chamber


48


. A cylindrical coil


51


is located around the fixed core


49


and the plunger


50


. The drive circuit


36


is connected to the coil


51


. A follower spring


52


is located between the plunger


50


and the bottom wall of the plunger chamber


48


and urges the plunger


50


toward the fixed core


49


.




A guide hole


53


extends through the fixed core


49


to be coaxial with the valve hole


45


. A transmission rod


54


extends in the guide hole


53


and the valve hole


45


. The proximal end of the transmission rod


54


is fixed to the plunger


50


. The follower spring


52


urges the transmission rod


54


through the plunger


50


toward the valve body


44


, which causes the distal end of the transmission rod


54


to contact the valve body


44


. In other words, the plunger


50


and the valve body


44


are coupled to each other by the transmission rod


54


. The valve body


44


is urged in a direction to open the valve hole


45


by the follower spring


52


.




A port


55


is formed in the valve housing


41


between the valve chamber


43


and the plunger chamber


48


. The valve hole


45


is connected to the crank chamber


15


through the port


55


and the upstream portion of the bleed passage


30


. The valve chamber


43


, the valve hole


45


and the port


55


form a part of the bleed passage


30


.




Under operating conditions of the engine Eg, when an air-conditioner operating switch (not shown) is turned on and the passenger compartment temperature detected by the temperature sensor


34


exceeds the target temperature set by the temperature adjuster


33


, the controller X actuates the clutch mechanism C to drive the compressor.




The controller X normally determines a cooling performance required for the refrigeration circuit based on signals from the temperature adjuster


33


and the temperature sensor


34


. Accordingly, the controller X determines the value of current supplied to the coil


51


. The controller X supplies the current of the determined value to the coil


51


through the drive circuit


36


. Then, between the fixed core


49


and the plunger


50


is generated electromagnetic attraction force according to the supplied current value. The magnitude of the attraction force represents the target value of the pressure in the suction chamber


24


(target suction pressure) and urges the valve body


44


through the transmission rod in a direction increasing the opening size of the valve hole


45


.




On the other hand, the bellows


46


of the control valve


31


expands and contracts in accordance with the pressure in the valve chamber


43


. In other words, the bellows


46


applies a force the magnitude of which corresponds to the pressure in the valve chamber


43


to the valve body


44


. In this case the pressure (suction pressure) in the suction chamber


24


is introduced into the valve chamber


43


through the downstream portion of the bleed passage


30


. Therefore, the valve chamber


43


is exposed to the suction pressure.




The suction pressure in the valve chamber


43


urges the valve body


44


toward the valve hole


45


. Further, the valve body


44


is exposed to the pressure (crank pressure) in the crank chamber


15


through the upstream portion of the bleed passage


30


, the port


55


and the valve hole


45


. The crank. pressure urges the valve body,


44


away from the valve hole


45


. The crank pressure is than the suction pressure. Therefore, the valve body


44


is urged away from the valve hole


45


by the force corresponding to the difference between the crank pressure and the suction pressure.




Each of the forces that act on the valve body


44


determines the position of the valve body


44


with respect to the valve hole


45


, that is the degree of the opening of the valve hole


45


.




The higher the passenger compartment temperature is with respect to the target temperature, in other words, the greater the cooling performance required for the refrigeration circuit is, the controller X makes the supplied current value for the coil


51


greater. Accordingly, the attraction force between the fixed core


49


and the plunger


50


becomes stronger and the force which urges the valve body


44


away from the valve hole


45


increases. This means that the target suction pressure is set at a lower value. The bellows


46


causes the valve body


44


to adjust the opening size of the valve hole


45


such that the actual suction pressure is maintained to the lower target suction pressure. That is, the greatr the supplied current value to the coil


51


is, the control valve


31


adjusts the displacement of the compressor to maintain the lower suction pressure.




If the actual suction pressure is higher than the target suction pressure, the bellows


46


causes the valve body


44


to increase the opening size of the valve hole


45


. Then, the flow rate of the refrigerant gas discharged to the suction chamber


24


from the crank chamber


15


through the bleed passage


30


increases, and the pressure in the crank chamber


15


decreases. Thus, the inclination angle of the swash plate


18


increases and the displacement of the compressor increases. The increase in the compressor displacement increases the cooling performance of the refrigeration circuit and decreases the actual suction pressure so that the actual suction pressure is converged to the target suction pressure.




When the valve body


44


fully opens the valve hole


45


, a great amount of the refrigerant gas is discharged from the crank chamber


15


to the suction chamber


24


, whereby the pressure in the crank chamber


15


significantly decreases. Accordingly, the inclination angle of the swash plate


18


becomes maximum and the displacement of the compressor becomes maximum (see FIG.


2


).




The smaller the difference between the passenger compartment temperature and the target temperature is, in other words, the smaller the cooling performance required for the refrigeration circuit is, the controller X makes the supplied current value for the coil


51


smaller. Accordingly, the attraction force between the fixed core


49


and the plunger


50


becomes weaker and the force which urges the valve body


44


in a direction distant from the valve hole


45


decreases. This means that the target suction pressure is set at a higher value. The bellows


46


causes the valve body


44


to adjust the opening size of the valve hole


45


so that the actual suction pressure is maintained at the higher target suction pressure. That is, the smaller the supplied current value for the coil


51


is, the control valve


31


adjusts the displacement of the compressor to maintain the higher suction pressure.




If the actual suction pressure is lower than the target suction pressure, the bellows


46


causes the valve body


44


to decrease the opening size of the valve hole


45


. Then, the flow rate of the refrigerant gas discharged to the suction chamber


24


from the crank chamber


15


through the bleed passage


30


decreases, and the pressure in the crank chamber


15


increases. Thus, the inclination angle of the swash plate


18


becomes smaller and the displacement of the compressor decreases. The decrease in the compressor displacement decreases the cooling performance of the refrigeration circuit and increases an actual suction pressure so that the actual suction pressure may be converged to the target suction pressure.




When the valve body


44


fully closes the valve hole


45


, no refrigerant gas is discharged from the crank chamber


15


to the suction chamber


24


, which significantly increases the pressure in the crank chamber


15


. Accordingly, the inclination angle of the swash plate


18


becomes minimum and the displacement of the compressor becomes minimum (see FIG.


3


).




As described above, the displacement of the compressor is usually adjusted according to the cooling performance required for the refrigeration circuit. However, when the load on the engine Eg abruptly increases under an abrupt acceleration of the vehicle, a displacement limiting control for reducing the engine load is performed. The displacement limiting control temporarily minimizes the displacement of the compressor.




To reduce the engine load under abrupt acceleration of a vehicle, a clutch mechanism C may be turned off and the compressor may be temporarily separated from the engine Eg. However, to ensure the minimum cooling performance even under abrupt acceleration of the vehicle and to avoid shock that accompanies the turning on/off of the clutch mechanism, turning the clutch mechanism C off temporarily is not preferable.




Next, a displacement limiting control under abrupt acceleration of the vehicle will be described with reference to time charts of FIG.


4


(


a


) to FIG.


4


(


c


). As shown in FIG.


4


(


a


), when the degree of pedal depression detected by the pedal position sensor


35


reaches the predetermined value or greater under a state where the predetermined value of current was supplied to the coil


51


of the control valve


31


, the controller X determines the start of abrupt acceleration of a vehicle and starts the displacement limiting control. That is, the controller X commands the drive circuit


36


to make the supplied current value for the coil


51


change from a value corresponding to the required cooling performance to a specific value, or zero.




As a result, as shown in FIG.


4


(


b


), the target suction pressure Pst changes over from the value corresponding to the required cooling performance to the maximum value Pmax. Then, the bellows


46


causes the valve body


44


to close the valve hole


45


so that an actual suction pressure Psa approximates the maximum value Pmax. Therefore, the pressure in the crank chamber


15


increases and the displacement of the compressor becomes minimum as shown in FIG.


4


(


c


). In other words, the torque of the compressor becomes minimum, whereby the engine load is reduced. Thus, the vehicle is faborably abruptly accelerated.




As shown in FIG.


4


(


a


), after the predetermined time S (for-example one second) has passed from the start of the displacement limiting control, the controller X completes the displacement limiting control and shifts the displacement limiting control to a usual displacement control according to the cooling performance required for the refrigeration circuit. Specifically, the controller X increases the supplied current value for the coil


51


from zero to the target current value A


3


according to the required cooling performance for the predetermined time T. Accordingly, as shown in FIG.


4


(


b


), the target suction pressure Pst decreases from the maximum value Pmax to a value P


3


corresponding to the target current value A


3


for the predetermined time T.




The oblique line H shown by the two dotted and dash lines and the solid line in FIG.


4


(


a


) is a direct proportional increase line showing that the supplied current value for the coil


51


increases from zero to the target current value A


3


at a constant rate. During a period (the first term t


1


and the second term t


2


) in the predetermined time T, the values of current supplied to the coil


51


are set at values A


1


and A


2


, which are greatr than values in the corresponding period on the direct proportional increase line H.




Specifically, at the same time when the displacement limiting control has been completed, the supplied current value for the coil


51


is abruptly increased to the value A


1


from zero and the current value A


1


is maintained only during the first term t


1


. Subsequently, the supplied current value is abruptly lowered to the value A


2


, which is lower than the value A


1


, and the current value A


2


is maintained only during the second term t


2


. The second term t


2


is completed when the is current value A


2


agrees with a value on the direct proportional increase line H. In the subsequent third term t


3


, the supplied current value is gradually increased to the target current value A


3


in accordance with the direct proportional increase line H.




An oblique line H′ shown by two dotted and dash lines and a solid line in FIG.


4


(


b


) is a line corresponding to the direct proportional increase line H in FIG.


4


(


a


), which is a direct proportional decrease line showing that the target suction pressure Pst decreases from the maximum value Pmax to a value P


3


at a constant rate. During the first term t


1


and the second term t


2


, the target suction pressure Pst is set at values P


1


and P


2


. The values P


1


and P


2


correspond to the current values A


1


and A


2


and lower than values in the corresponding period on the direct proportional decrease line H′.




At the completion of the displacement limiting control, the current value A


1


in the first term t


1


sets the target suction pressure Pst to the value P


1


, which is significantly lower than the actual suction pressure Psa. Therefore, as shown in FIG.


4


(


b


), the actual suction pressure Psa is significantly higher than the value P


1


of the target suction pressure Pst immediately after the completion of the displacement limiting control. Then, the bellows


46


causes the valve body


44


to widely open the valve hole


45


to decrease the actual suction pressure Psa to the value P


1


immediately after the completion of the displacement limiting control. As a result, the pressure in the crank chamber


15


abruptly decreases so that the displacement of the compressor changes from the minimum state to an increased state with no substantial delay after the completion of the displacement limiting control, as shown in FIG.


4


(


c


).




As shown in FIG.


4


(


b


), in the second term t


2


, the target suction pressure Pst is set at a value P


2


, which is higher than the value P


1


and lower than the actual suction pressure Psa, when the supplied current value is changed to a value A


2


. In other words, in the second term t


2


, the target suction pressure Pst further increases to near the actual suction pressure Psa as compared with the case in the first term t


1


. Accordingly, the bellows


46


causes the valve body


44


to operate such that the opening size of the valve hole


45


is further reduced as compared with the case in the first term t


1


. As a result, an abrupt and excessive decrease in the pressure in the crank chamber


15


is prevented, which prevents an abrupt increase in the displacement and the torque of the compressor as shown in FIG.


4


(


c


).




As shown in FIG.


4


(


b


), the actual suction pressure Psa is substantially converged to the value P


2


of the target suction pressure Pst at the completion of the second term t


2


. In the subsequent third term t


3


, the target suction pressure Pst gradually decreases to the value P


3


in accordance with the direct proportional decrease line H′ as the supplied current value gradually increases in accordance with the direct proportional increase line H. The actual suction pressure Psa lowers in accordance with a gradual decrease of the target suction pressure Pst without deviating from the line showing the decrease in the target suction pressure Pst. Therefore, no abrupt change in the pressure in the crank chamber


15


occurs and the displacement and the torque of the compressor smoothly increase.




The present embodiment described above has the following advantages.




In returning to the usual displacement control from the displacement limiting control, the supplied current value for the coil


51


is changed to the target current value A


3


according to the required cooling performance from zero for the predetermined time T. Thus, the displacement of the compressor, in other words, the torque of the compressor gradually increases and an abrupt increase in the engine load is prevented, which improves the vehicle drivability.




In terms t


1


and t


2


just after the completion of the displacement limiting control, the supplied current values for the coil


51


are set at values A


1


and A


2


, which are nearer to the target current value A


3


than values in the corresponding period on the direct proportional increase line H shown in FIG.


4


(


a


). As a result, the pressure in the crank chamber


15


rapidly decreases and the displacement of the compressor changes from the minimum state to an increased state without substantial delay from the completion of the displacement limiting control. Thus, the compressor is operated at the minimum displacement only for a term substantially equal to the execution time S for the displacement limiting control, in other words, only for a necessary minimum time. Thus, the displacement limiting control does not significantly lower the cooling performance of the refrigeration circuit, and the passengers are not disturbed.




The supplied current value A


2


in the second term t


2


subsequent to the first term t


1


is made smaller than the supplied current value A


1


in the first term t


1


. As a result, the displacement of the compressor immediately increases after the completion of the displacement limiting control. However, an abrupt increase in displacement, which is accompanied with shock, is prevented. Therefore, the displacement limiting control is smoothly and rapidly changed to a usual displacement control.




The control valve


31


in the present embodiment has the solenoid unit


42


and the bellows


46


. The solenoid unit


42


sets the target suction pressure, which is used as the reference of operations of the bellows


46


, according to the supplied current value. The bellows


46


actuates the valve body


44


according to the actual suction pressure. As described in the background section, a change of the displacement of a compressor from the minimum state to an increased state delays after the displacement limiting control is completed. This problem is particularly likely to occur in the control valve


31


, which has the above described structure. Therefore, the application of the control system of the present embodiment to the control valve


31


is the most effective in overcoming the problem.




It should be apparent to those skilled in the art that the present invention may be embodied in many other specific forms without departing from the spirit or scope of the invention. Particularly, it should be understood that the invention may be embodied in the following forms.




A current supply system for the coil


51


in the predetermined time T is not limited to the system shown in FIG.


4


(


a


). For example, as shown in

FIG. 5

, a supplied current value for the coil


51


may be immediately increased to the predetermined value (which is lower than the target current value A


3


) from zero immediately after the completion of the displacement limiting control and the value may be gradually increased to the target current value A


3


from the predetermined value at a constant ratio. In this case, the supplied current values for the coil


51


become greater than values in the corresponding period on the direct proportional increase line H in the entire predetermined time T.




Further, the supplied current values for the coil


51


may be maintained between the first term t


1


and the second term t


2


. Specifically, the supplied current value may be increased to the predetermined value (which is lower than the target current value A


3


) from zero after the completion of the displacement limiting control and the predetermined value may be then maintained until the required value agrees with a value on the direct proportional increase line H.




The periods of time in which the supplied current values for the coil


51


are made greater than the values on the direct proportional increase line H are not limited to the terms t


1


and t


2


shown in FIG.


4


(


a


). For example, the supplied current values may be greater than the values on the line H during a period after some time from the completion of the displacement limiting control.




The control valve to which the present invention is applied is not limited to that shown in

FIGS. 2 and 3

. For example, unlike the control valve


31


of

FIGS. 2 and 3

, the present invention may be applied to a control valve in which the target suction pressure is raised as the supplied current value to the coil is increased. As a pressure sensing member, a diaphragm may be used in place of the bellows


46


. Further, the pressure sensing member may be omitted, and the valve body


44


may be operated only by the solenoid unit


42


. Further, the present invention may be applied to a control valve located in the supply passage


32


.




The displacement limiting control may be started when the rate of change per unit time for a degree of pedal depression detected by the pedal position sensor


35


becomes the predetermined value or more.




Therefore, 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 and equivalence of the appended claims.



Claims
  • 1. A displacement control device for a compressor that changes the displacement in accordance with the pressure in a control pressure chamber, comprising:a control valve for controlling the pressure in the control pressure chamber, the control valve having a valve body and an electromagnetic actuator for actuating the valve body, wherein the actuator urges the valve body by a force the magnitude of which corresponds to the value of current supplied to the actuator; a detector for detecting external conditions that are necessary for controlling the compressor displacement; and a controller for controlling the value of current supplied to the actuator, wherein the controller selects a control mode to be executed from a usual displacement control and a displacement limiting control based on the detected external conditions, wherein, when the usual displacement control is selected, the controller sets the current value to a target value, which corresponds to the detected external conditions, wherein, when the displacement limiting control is selected, the controller temporarily sets the current value to a specific value to minimize the compressor displacement, wherein, when the control mode is switched from the displacement limiting control to the usual displacement control, the controller changes the current value from the specific value to the target value taking a predetermined restoration period, and wherein, for at least part of the restoration period, the controller sets the current value to a value that is closer to the target value than a corresponding value on a direct proportional line, which represents a constant rate of change from the specific value to the target value.
  • 2. The control device according to claim 1, wherein the control valve includes a pressure sensing mechanism, and wherein the pressure sensing mechanism moves the valve body in accordance with a suction pressure, which is the pressure of refrigerant gas drawn into the compressor.
  • 3. The control device according to claim 2, wherein the pressure sensing mechanism moves the valve body such that the suction pressure is maintained at a target suction pressure, and wherein the target suction pressure is determined by the current value supplied to the electromagnetic actuator.
  • 4. The control device according to claim 1, wherein the part of the restoration period includes an initial period of the restoration period.
  • 5. The control device according to claim 4, wherein, at substantially the same time as the displacement limiting control is finished, the controller instantaneously changes the current value to a first value, the first value being between the specific value and the target value.
  • 6. The control device according to claim 5, wherein the controller maintains the current value to the first value for a predetermine first period after the displacement limiting control is finished, wherein, for a subsequent second period, the controller maintains the current value to a second value, which is closer to the specific value than the first value, and then gradually changes the current value from the second value to the target value along the direct proportional line.
  • 7. The control device according to claim 5, wherein, during the restoration period, the controller gradually changes the current value at a constant rate from the first value to the target value.
  • 8. The control device according to claim 1, wherein the specific value is zero.
  • 9. The control device according to claim 1, wherein the compressor is installed in a refrigeration circuit and is driven by an external drive source, wherein the detector includes a first detector for detecting an external condition that represents the load on the external drive source and a second detector for detecting an external condition that represents a required cooling performance of the refrigeration circuit, wherein the controller selects the control mode to be executed based on the external condition detected by the first detector, and wherein, when the usual displacement control is selected, the controller determines the current value in accordance with the external condition detected by the second detector.
  • 10. The control device according to claim 9, wherein the external drive source is a vehicle engine, and the first detector detects a depression degree of an acceleration pedal of the vehicle.
  • 11. The control device according to claim 9, wherein the compressor is installed in a vehicle, wherein the second detector includes a temperature sensor for detecting the temperature of a passenger compartment and a temperature adjuster for setting a target value of the passenger compartment temperature, wherein, when the usual displacement control is selected, the controller determines the current value in accordance with the difference between the detected compartment temperature and the set target temperature.
  • 12. A displacement control device for a compressor installed in a refrigeration circuit, wherein the compressor is driven by an external drive source and changes the displacement in accordance with the pressure in a control pressure chamber, the control device comprising:a control valve for controlling the pressure in the control pressure chamber, the control valve including: a valve body; a pressure sensing mechanism, wherein the pressure sensing mechanism moves the valve body in accordance with a suction pressure, which is the pressure of refrigerant gas drawn into the compressor, such that the suction pressure is maintained at a predetermined target suction pressure; and an electromagnetic actuator for urging the valve body by a force the magnitude of which corresponds to the value of current supplied to the actuator, wherein the current value determines the target suction pressure; a first detector for detecting an external condition that represents the load on the external drive source; a second detector for detecting an external condition that represents a required cooling performance of the refrigeration circuit; and a controller for controlling the value of current supplied to the actuator, wherein the controller selects a control mode to be executed from a usual displacement control and a displacement limiting control based on the external condition detected by the first detector, wherein, when the usual displacement control is selected, the controller sets the current value to a target value, which corresponds to the external condition detected by the second detector, wherein, when the displacement limiting control is selected, the controller temporarily sets the current value to a specific value to minimize the compressor displacement, wherein, when the control mode is switched from the displacement limiting control to the usual displacement control, the controller changes the current value from the specific value to the target value taking a predetermined restoration period, and wherein, for at least an initial period of the restoration period, the controller sets the current value to a value that is closer to the target value than a corresponding value on a direct proportional line, which represents a constant rate of change from the specific value to the target value.
  • 13. The control device according to claim 12, wherein, at substantially the same time as the displacement limiting control is finished, the controller instantaneously changes the current value to a first value, the first value being between the specific value and the target value.
  • 14. The control device according to claim 13, wherein the controller maintains the current value to the first value for a predetermine first period after the displacement limiting control is finished, wherein, for a subsequent second period, the controller maintains the current value to a second value, which is closer to the specific value than the first value, and then gradually changes the current value from the second value to the target value along the direct proportional line.
  • 15. The control device according to claim 13, wherein, during the restoration period, the controller gradually changes the current value at a constant rate from the first value to the target value.
  • 16. The control device according to claim 12, wherein the external drive source is a vehicle engine, and the first detector detects a depression degree of an acceleration pedal of the vehicle.
  • 17. The control device according to claim 12, wherein the compressor is installed in a vehicle, wherein the second detector includes a temperature sensor for detecting the temperature of a passenger compartment and a temperature adjuster for setting a target value of the passenger compartment temperature, wherein, when the usual displacement control is selected, the controller determines the current value in accordance with the difference between the detected compartment temperature and the set target temperature.
  • 18. A method for controlling the displacement of a compressor that changes the displacement in accordance with the pressure in a control pressure chamber, comprising:controlling the pressure in the control pressure chamber by a control valve, wherein the control valve has a valve body and an electromagnetic actuator for actuating the valve body, wherein the actuator urges the valve body by a force the magnitude of which corresponds to the value of current supplied to the actuator; detecting external conditions that are necessary for controlling the compressor displacement; selecting a control mode to be executed from a usual displacement control and a displacement limiting control based on the detected external conditions; setting the current value to a target value, which corresponds to the detected external conditions, when the usual displacement control is selected; temporarily setting the current value to a specific value to minimize the compressor displacement when the displacement limiting control is selected; and changing the current value from the specific value to the target value taking a predetermined restoration period when the control mode is switched from the displacement limiting control to the usual displacement control, wherein, for at least part of the restoration period, the current value is set to a value that is closer to the target value than a corresponding value on a direct proportional line, which represents a constant rate of change from the specific value to the target value.
  • 19. The method according to claim 18, wherein the step changing the current value from the specific value to the target value includes instantaneously changing the current value to a first value at substantially the same time as the displacement limiting control is finished, wherein the first value is between the specific value and the target value.
  • 20. The method according to claim 19, wherein the step of changing the current value from the specific value to the target value further includes:maintaining the current value to the first value for a predetermine first period after the displacement limiting control is finished; maintaining the current value to a second value, which is closer to the specific value than the first value, for a second period, which is subsequent to the first period; and gradually changing the current value from the second value to the target value along the direct proportional line after the second period.
Priority Claims (1)
Number Date Country Kind
11-209357 Jul 1999 JP
US Referenced Citations (9)
Number Name Date Kind
4796438 Sato Jan 1989 A
4848101 Suzuki Jul 1989 A
4862700 Suzuki Sep 1989 A
4894999 Kaiju et al. Jan 1990 A
5022232 Sakamoto et al. Jun 1991 A
5823000 Takai Oct 1998 A
6102668 Kawaguchi et al. Aug 2000 A
6224348 Fukanuma et al. May 2001 B1
6244159 Kimura et al. Jun 2001 B1
Foreign Referenced Citations (1)
Number Date Country
0 814 262 Dec 1997 EP