Refrigeration – Automatic control – Of external fluid or means
Reexamination Certificate
1998-07-29
2001-03-20
Tanner, Harry B. (Department: 3744)
Refrigeration
Automatic control
Of external fluid or means
C062S159000, C062SDIG001
Reexamination Certificate
active
06202430
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a method of detecting excessive pressure in a refrigerant fluid in a condenser of an air conditioning loop in the fluid circuit of a dual-mode air conditioning and heating installation, during discharges of the fluid to the condenser from a heating loop of the same circuit, a compressor being provided for driving the fluid in the circuit.
BACKGROUND OF THE INVENTION
In a conventional dual-mode (heating and air conditioning) circuit, when the pressure of the refrigerant fluid in the condenser reaches the same value as the pressure of the fluid at the outlet of the compressor, the momentary discharges of fluid from the heating loop, intended to control pressure in the loop, are no longer effective to reduce the compressor outlet pressure. As a result, the pressures prevailing at the suction and delivery sides of the compressor will increase without it being possible to reduce them. This leads to a runaway situation such that the maximum safe pressures in the loop of the circuit are quickly reached.
Such a situation can be found in particular in a circuit of a heating and air conditioning apparatus for the cabin of a vehicle, of the general kind described in French patent specifications FR 2 717 126A and 2 731 952A. These circuits comprise a first branch containing an evaporator followed by the compressor, a second branch containing the condenser and a third branch containing no condenser. The second and third branches are arranged in parallel with each other so as to constitute, with the first branch, a cooling loop and a heating loop respectively. Switching means are provided for sending the fluid leaving the first branch selectively into the second branch or into the third branch. The heating and air conditioning apparatus further includes means for passing into the cabin air which has undergone heat exchange with the evaporator.
When the fluid is flowing in the cooling loop, the dual-mode circuit operates as a conventional air conditioning circuit. When the fluid is flowing in the heating loop, the evaporator is used as a heat exchanger for heating the cabin, with the fluid normally remaining in the gaseous state: this is the heating mode.
In a circuit of the above type, switching means are provided, typically comprising one or more discharge valves, for discharging fluid to the condenser from the heating loop. This enables the circuit to pass momentarily from the configuration of the heating loop to the configuration of the air conditioning loop so that the compressor can discharge fluid into the condenser, thereby reducing the mass of fluid in circulation once the configuration corresponding to the heating loop has been restored.
In such discharges, the pressure of the refrigerant fluid in the condenser can exceed safety limits, or other limits appropriate to correct operation in the loop.
DISCUSSION OF THE INVENTION
An object of the invention is to detect excessive pressure in the refrigerant fluid in the condenser, without calling for special sensors which would increase the cost of the circuit.
The invention arises from the realisation that the increase in pressure in the refrigerant fluid in the condenser can be detected from information which is available in relation to the frequency of occurrence of the discharges and the outlet pressure of the compressor.
According to the invention in a first aspect, a method of detecting excessive pressure in a refrigerant fluid in a condenser of an air conditioning loop of a circuit, during discharges of the fluid to the condenser from a heating loop of the said circuit, a compressor being provided for driving the fluid in the circuit, is characterised by the following operations:
(a) the frequency of the discharges is continuously determined, and an evaluation is made as to whether the measured frequency exceeds a threshold frequency; and
(b) the outlet pressure of the compressor is continuously determined, and an evaluation is made as to whether the measured pressure exceeds a regulation or demand pressure by a given excess value over a given period of time, whereby an excessive frequency in operation (a) and an excess pressure in operation (b) indicates that the pressure of the refrigerant fluid in the condenser is excessive.
The threshold frequency is preferably about 1 Hz.
Preferably, the excess value is about 3% and the period of time is about 20 seconds.
The value of the frequency of occurrence of the discharges is typically obtained by means of a control module which governs the discharges themselves.
Preferably, the pressure at the outlet of the compressor is determined by means of a pressure sensor which serves to regulate the pressure of the fluid in the heating mode.
According to a preferred feature of the invention, in the event of an excess pressure in the refrigerant fluid in the condenser, the condenser is ventilated by forced air ventilation for a period of time sufficient to reduce the pressure of the refrigerant fluid in the condenser. This ventilating time is preferably a function of the temperature of the outside air. The ventilation of the condenser is preferably obtained by control of a motorised fan unit associated with the condenser.
According to another preferred feature of the invention, where the circuit is that of an air conditioning apparatus for the cabin of a motor vehicle, the circuit including a first branch containing an evaporator followed by the said compressor, a second branch containing the said condenser, and a third branch containing no condenser, with the second and third branches being connected in parallel with each other in such a way as to constitute, with the first branch, a cooling loop and a heating loop respectively, switching means being provided for transmitting the fluid leaving the first branch selectively into the second branch or into the third branch, and the apparatus further including means for delivering into the cabin air which has undergone heat exchange with the evaporator, the condenser is ventilated when excessive pressure is detected in the refrigerant fluid in the condenser.
According to the invention in a second aspect, an apparatus for performing the method of the first aspect of the invention is characterised in that it includes: control means adapted to act on at least one discharge valve; a frequency sensor connected to the discharge valve or valves for detecting the frequencies of occurrences of the discharges; and a pressure sensor connected to the output of the compressor.
Preferably, the control means comprise a computer connected to the frequency sensor and the pressure sensor, and adapted to deliver a control signal to open the discharge valve or valves in the event of the threshold frequency and the demand pressure being exceeded.
The computer is preferably connected to a motorised fan unit associated with the condenser, for ventilating the latter.
REFERENCES:
patent: 4582124 (1986-04-01), Yoshimi et al.
patent: 5291941 (1994-03-01), Enomoto et al.
patent: 5316074 (1994-05-01), Isaji et al.
patent: 5483805 (1996-01-01), Fujii et al.
patent: 5537831 (1996-07-01), Isaji et al.
patent: 5706664 (1998-01-01), Hara
patent: 2 717 126 (1995-09-01), None
patent: 2 731 952 (1996-09-01), None
Morgan & Finnegan L.L.P.
Tanner Harry B.
Valeo Climatisation
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