Displacement control device and displacement control method...

Details Displacement control device and displacement control method... Displacement control device and displacement control method...

2000-07-14

2002-03-19

Koczo, Michael (Department: 3746)

Pumps

Condition responsive control of drive transmission or pump...

Adjustable cam or linkage

C062S228500

Reexamination Certificate

active

06358016

ABSTRACT:

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 press

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