Refrigeration – With indicator or tester – Condition sensing
Reexamination Certificate
2000-01-21
2001-06-05
McDermott, Corrine (Department: 3744)
Refrigeration
With indicator or tester
Condition sensing
C062S149000, C062S292000
Reexamination Certificate
active
06240733
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method for the diagnosis of an air conditioning system, in particular a vehicle air conditioning system having a condenser, an evaporator, an expansion device and a compressor, the stroke of which can be set via a valve.
BACKGROUND OF THE INVENTION
The above named air conditioning systems are known in principle and are used in particular in vehicles for the cooling of the vehicle cabin. The refrigerant circuit of these air conditioning systems is filled with a refrigerant, for example with R 134a (previously also R 12).
In air conditioning systems of this kind there is the problem that refrigerant must be added from time to time, since there is the danger when the level is low that the compressor housing heats up so much that the compressor is damaged or that the lifetime of the compressor is reduced respectively.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method for the diagnosis of an air conditioning system by means of which a statement about the degree of filling of the refrigerant circuit can be made.
A method for the diagnosis of an air conditioning system having a condenser, an evaporator, an expansion device (either an orifice or a thermal expansion valve) and a compressor, the stroke of which can be set via a valve, is characterized in that a maximum compressor stroke is set abruptly when the air conditioning system is running, whereupon a pressure impulse arising in the high pressure side of the refrigerant circuit is measured in order to determine the degree of filling of the refrigerant circuit.
The invention is based on the finding that as the refrigerant level decreases (or drops below a critical charge limit), there is a corresponding reduction in the high side pressure peak after a rapid upstroke. This phenomenon is used to define a critical charge-peak pressure curve which can be stored in the form of a look-up table. The method according to the present invention involves rapidly upstroking a variable displacement compressor, measuring the associated peak in high side pressure and comparing the value to the stored values in the look-up table.
According to the method of the present invention, the compressor lifetime can be extended by detecting refrigerant levels below critical charge which can cause overheating of the compressor. Thus, the present invention serves as a diagnostic aid for servicing the air-conditioning system. The present invention also provides a method for the diagnosis of an air conditioning system which can be realized with simple technical means. The present invention further provides a method for the diagnosis of an air conditioning system which can be carried out in an automated manner.
According to the present invention, there is no need for an evaporator outlet refrigerant temperature or pressure sensor. The low charge detection can be performed using just a high side pressure sensor in the air-conditioning system. This is advantageous since many air-conditioning systems only have a high side pressure sensor available.
Advantageous embodiments of the invention are described in the subordinate claims.
It is particularly advantageous when the maximum compressor stroke is set starting from a minimum compressor stroke, i.e. when the stroke of the compressor is changed within the shortest time from a minimum stroke to a maximum stroke. In this case the pressure impulse arising in the high pressure side of the refrigerant circuit is a maximum, which facilitates the evaluation.
It is advantageous when the measured pressure impulse is compared to predetermined pressure values and a diagnosis report is issued or not in dependence on this comparison. A diagnosis report of this kind can be an optical and/or an acoustical signal; or a corresponding warning can be shown on a display.
Through the comparison with predetermined pressure values, which can be established in test experiments, it can be determined whether the measured pressure impulse lies above or below a threshold value, which allows a conclusion to be drawn about an insufficient filling with refrigerant. In this it is advantageous when the measured pressure impulse is compared with pressure values which are stored in a look-up table and which in each case are associated with a specific degree of filling. Through this it is for example possible to issue a warning when a critical degree of filling is being approached and/or to block the air conditioning system when this critical degree of filling is reached or exceeded so that the driver is obliged to replenish the refrigerant.
It is particularly advantageous when the measured pressure impulse is compared with pressure values which are stored in a look-up table and which are associated in each case with a specific degree of filling in dependence on the ambient temperature. Through this procedure the influence of the ambient temperature can be taken into account.
In order to establish a critical degree of filling it can be determined in test experiments at which respective degree of filling a predetermined critical temperature of the compressor housing and/or of the refrigerant emerging from the compressor is reached. Through this a critical degree of filling can be defined which must not be dropped below in order that the critical maximum temperature is not exceeded.
It is particularly advantageous when the method in accordance with the invention is automatically carried out at predetermined time intervals, which can be done by an electronic control system. Through this the driver of the motor vehicle can be warned in time when the degree of filling is too low.
An electric valve is preferably used for the valve, for example a solenoid actuated valve, with the control of the valve preferably being done through a pulse width modulation. Through this it is for example possible to rapidly upstroke the compressor by stepping down the PWM valve duty cycle from 100% to 0%.
The pressure impulse which arises at the high pressure side of the refrigerant circuit can in principle be measured at an arbitrary location at the high pressure side. The outlet of the compressor or the outlet of the condenser is preferably used for the pressure measurement, with it being possible to use pressure sensors which in this case are already present so that no additional components are required.
The carrying out of the method in accordance with the invention is preferably done using an electronic control system, which on the one hand controls the valve of the compressor, and is connected on the other hand to a pressure sensor on the high pressure side. The corresponding comparison pressure values can also be stored in this control system.
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patent: 3302421 (1967-02-01), Karnes
patent: 3303663 (1967-02-01), Miller et al.
patent: 3400552 (1968-09-01), Johnson et al.
patent: 4114448 (1978-09-01), Merritt
patent: 5758506 (1998-06-01), Hancock et al.
patent: 63-17258 (1988-01-01), None
patent: 1-193567A (1989-08-01), None
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Archibald Charles Andrew
Brandon Giles M.
Kachur Christopher M.
Delphi Technologies Inc.
Griffin Patrick M.
Jones Melvin
McDermott Corrine
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