Refrigeration – Processes – Compressing – condensing and evaporating
Reexamination Certificate
2000-04-05
2001-08-28
Tapolcai, William E. (Department: 3744)
Refrigeration
Processes
Compressing, condensing and evaporating
C062S169000, C062S228500
Reexamination Certificate
active
06279331
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method for controlling a vehicular refrigerating cycle, said refrigerating cycle comprising a variable capacity compressor, a condenser for condensing a refrigerant, an expansion valve, an evaporator for evaporating adiabatically expanded refrigerant, a by-pass line detouring said condenser, and a line switching means for either supplying the refrigerant compressed by the compressor to the condenser in a cooling mode or into the by-pass line in a heating mode, and a vehicular refrigerating cycle of the kind as disclosed above.
High efficiency engines as gasoline-injection type engines or gasoline direct injection type engines do not develop high cooling water temperatures, compared with conventional combustion engines. Using the cooling water for heating purposes does not allow to sufficiently heat the vehicle compartment.
2. Description of the Related Art
U.S. Pat. No. 4,893,748 already proposes to use a refrigerating cycle in a vehicle not only for cooling purposes, but also for heating purposes. The refrigerating cycle contains a bypass line detouring the condenser and directing high-pressure refrigerant gas discharged from the compressor directly into an evaporator arranged inside the vehicle compartment so that heat exchange may take place in the evaporator for auxiliary heating purposes. However, if the refrigerating cycle is left at rest after an operation in the cooling mode, refrigerant tends to accumulate in the condenser. If then the refrigerating cycle is operated thereafter in the heating mode, only a small amount of refrigerant is circulated deteriorating the auxiliary heating effect.
This disadvantage calls for operating the refrigerating cycle prior to an operation in the auxiliary heating mode for a short time in the cooling mode (filling operation) to collect refrigerant stored in the condenser and to transfer it to the evaporator or an accumulator.
To convey refrigerant out of the condenser in this condition it would be necessary that the evaporator pressure was lower than the condenser pressure. However, when the refrigerating cycle contains a variable capacity compressor the capacity of which automatically decreases with a decrease of its suction pressure, the condenser pressure automatically drops to about 2 atm. (absolute atmospheric pressure) if the ambient atmospheric temperature has dropped, e.g. to about −10° C. It is known from practice to use a solenoid-operated pressure regulating valve for controlling the capacity of the variable capacity compressor in a refrigerating cycle of this kind. However, even if the solenoid is supplied with a permanent maximum driving operation current of, e.g., 1 Ampere (falling within a range in which the coil of the solenoid is not burnt) the suction pressure does not decrease to more than to e.g. 2.3 atm.(absolute atmospheric pressure). Consequently, the evaporator pressure remains higher than the condenser pressure. Refrigerant stored in the condenser fails to flow out of the condenser. In case of an ambient temperature of −30° C. the condenser pressure even drops to about 1 atm. (absolute atmospheric pressure) so that it is even more difficult to collect refrigerant stored in the condenser for the heating mode and to obtain a sufficient heating effect.
EP 780 254 A discloses to provide an ejector in a heating loop to additionally obtain refrigerant from the condenser for the auxiliary heating mode operation.
DE 19 746 773 discloses a refrigerating cycle with a variable capacity compressor and a method for controlling the compressor when operating the refrigerating cycle in the heating mode. According to said method the refrigerating cycle directly starts in its heating mode. Refrigerant is sucked out of the condenser via a separate by-pass line connecting the inlet of the condenser and the inlet of the compressor. Furthermore, the capacity control mechanism of the compressor is overruled in the heating mode at least in case of low ambient temperatures such that said compressor operated with high capacity. However, this is carried out to generally increase the refrigerant pressure.
OBJECTS AND SUMMARY OF THE INVENTION
It is an object of the invention to provide a method for controlling a refrigerating cycle of the kind as disclosed as well as a vehicular refrigerating cycle allowing to achieve a sufficiently good auxiliary heating effect in the heating mode, particularly in case of low ambient temperature. The invention should allow to use a sufficient amount of refrigerant for the heating function by the evaporator which refrigerant first has been accumulated in the condenser when the refrigerating cycle was switched off and kept at rest after a cooling mode operation.
As soon as the refrigerating cycle ought to be operated in its heating mode, e.g. when being left at rest after an operation in a cooling mode, first a cooling mode setting is made and a pressure drop is adjusted declining from said condenser to said evaporator for a predetermined period of time, so that at least a part of refrigerant stored in the condenser is driven out of the condenser, e.g. into the evaporator. Then the refrigerating cycle is switched to the heating mode. A sufficiently large amount of refrigerant can be used for the heating function. The heating function can be smoothly controlled.
Even in an environment of extremely low ambient temperature, the refrigerating cycle left at rest after a cooling mode operation, expediently is operated again in the cooling mode for a short while such that the pressure in the evaporator is forced to decrease below the condenser pressure to gain refrigerant accumulated in the condenser for the heating function by the evaporator. During the heating mode a sufficiently strong and controllable heating effect can be achieved in a predetermined manner.
According to a further aspect of the method the evaporator pressure is adjusted lower than the condenser pressure for a predetermined period of time in a cooling mode setting by a compressor capacity control means. This is carried out by intentionally postponing the start of a decrease of the capacity of the compressor from a maximum until the suction pressure has dropped to a sufficiently low level.
A suction pressure value of about 2 atm. is sufficiently low to assure a useful heating effect even in case of low ambient temperatures of about −10° C. However, the suction pressure value even can be made lower, e.g. to 1 atm. or less in case of lower ambient temperatures of about −30° C.
In another embodiment of the refrigerating cycle the setting means postpones the start of the decrease of the capacity of the compressor from maximum until a suction pressure of 1 atmosphere or less has been reached. It is even possible, to adjust the setting means so that the start of the decrease of the capacity is postponed until the suction pressure has decreased to 0.3 atmospheres.
It can be advantageous to postpone the start of the decrease of the capacity from a high setting like the maximum setting to a point in time immediately prior to a state in which the refrigerant flows through the by-pass line without passing through said condenser (start of the heating mode operation of the refrigerating cycle).
Expediently the solenoid actuated pressure regulating valve normally used to control the value of a control pressure adjusting the capacity setting of the compressor also is used for this filling operation. During the filling operation the current setting means supplies an overcurrent which significantly lowers the opening response pressure of the valve to the predetermined low value of the suction pressure. Due to the overcurrent the suction pressure is able to keep the valve open and to adjust a sufficiently low control pressure maintaining a high or the maximum capacity setting of the compressor.
Said overcurrent may have a magnitude approximately double as high as a maximum magnitude of a continuous operation current supplied for a long duration heating and/or
Ali Mohammad M
Nilles & Nilles SC
Tapolcai William E.
TGK Co. Ltd.
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