Automotive air-conditioning system and apparatus
BACKGROUND OF THE INVENTION 
     The invention relates to an apparatus for the air-conditioning of the interior of automobiles, with a refrigerant circuit which consists of a low-pressure part and a high-pressure part and in which the vaporous refrigerant is drawn off from an evaporator by a compressor and, while experiencing an increase in pressure, is fed to a condenser for cooling and condensation, and the condensed refrigerant is collected in a collecting vessel, from which it can be diverted via an expansion valve into the evaporator, while experiencing a pressure drop and cooling, a pressure-release valve with a blow-off outlet being provided between the compressor and the condenser in the high-pressure part of the refrigerant circuit. 
     To allow such apparatuses to have as light-weight a construction as possible, the maximum pressure in the refrigerant circuit is limited by the pressure-release valve. In accordance with SAE standard J 639 applicable at the present time, the refrigerant pressure in an air-conditioning system of a vehicle may not exceed 35.5 bar for a refrigerant R12 and 44.4 bar for a refrigerant R22. When these pressures are exceeded, the refrigerant is blown off into the environment. According to the standard named, the high-pressure part of the refrigerant circuit must have a bursting pressure of at least 2.5 times the maximum pressure. 
     Under particularly adverse operating conditions, especially very high outside temperatures and the lack of any head wind and consequently a considerable break-down in the removal of heat, the maximum pressure can be exceeded and a blow-off of the refrigerant can occur. According to recent findings, the refrigerants conventionally used are harmful to the environment. Futhermore, the blownoff refrigerant is then lacking later when the apparatus is operating normally. 
     SUMMARY OF THE INVENTION 
     To avoid the disadvantages described, the object on which the invention is based is to find an apparatus, by means of which a specific pressure can be prevented from being exceeded without a blow-off of the refrigerant into the open, there being no need to make the constructional parts more pressure-resistant. 
     In accomplishing the foregoing object, there has been provided according to one aspect of the present invention a blow-off outlet of the pressure-release valve connected to an intermediate reservoir for the escaping refrigerant. When the permissible pressure is exceeded, refrigerant can blow off into the intermediate reservoir in order to reduce the pressure in the high-pressure part of the refrigerant circuit, so that, even when there is a further increase in temperature, no further rise in pressure can occur any longer in the high-pressure part. The refrigerant intercepted in the intermediate reservoir can be returned into the refrigerant circuit later and reused, and harm to the environment caused by escaping refrigerant is prevented. 
     The size of the intermediate reservoir depends on the refrigerant used, on the volume of the apparatus, on the maximum possible outside temperature to which the vehicle can be exposed, and on the set maximum pressure in the high-pressure part of the apparatus. 
     To ensure a particularly simple return of the refrigerant into the refrigerant circuit, there can be parallel to the pressure-release valve a return valve which takes effect on one side and by means of which the intermediate reservoir can be emptied again at least partially when the pressure in the high-pressure part fails. The pressure-release valve and the return valve can be integrated in a space-saving way as a structural unit, for example if the return valve is built into the valve body of the pressure-release valve. 
     Another possibility for the return of the refrigerant is for the intermediate reservoir to be connected to the suction line of the compressor, preferably via a temperature-controlled and/or pressure-controlled discharge valve. 
     An especially simple adaptation to different operating conditions can be achieved if the receiving volume of the intermediate reservoir is variable. If appropriate, here the intermediate reservoir can be connected to the high-pressure part of the refrigerant circuit directly without a pressure-release valve. 
     The intermediate reservoir can be designed as a gas reservoir, with a storage chamber for the refrigerant and with a hemetically sealed gas chamber, the two chambers being separated from one another by means of an elastic diaphragm. Such gas-reservoir constructions are used in hydraulic systems or as pressure-compensating vessels in hot-water heating systems. 
     In another embodiment, the intermediate reservoir can be designed in a concertina-like manner such as a bellows. At the same time, the longitudinal extension of the bellows can be influenced by at least one spring, prestressed if appropriate, and the prestress of the spring can be adjustable for adaptation to different operating conditions and types of apparatus. 
    
    
     The foregoing and other aspects will become apparent from the following detailed descriptions of the invention when considered in conjunction with the accompanying drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The FIGURE illustrates the automotive air-conditioning system and apparatus of this invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The vehicle air-conditioning system illustrated diagrammatically has a compressor 1 which pumps gaseous refrigerant, while increasing its pressure, into a condenser 2. The refrigerant condenses and at the same time cools and flows into a collecting vessel 3. After filtration and water removal, the condensed refrigerant can, via an expansion valve 4, expand in an evaporator 5, while experiencing a pressure drop, at the same time absorbing ambient heat. The evaporated refrigerant is sucked out of the evaporator 5 through a suction line 6 by the compressor 1, compressed and returned to the circuit in the condenser 2. 
     A low-pressure part 7 of the refrigerant circuit comprises the evaporator 5 and the suction line 6 up to the compressor, while a high pressure part 8 comprises the condenser and the collecting vessel 3. The compressor 1 can be cut in and cut out via a temperature switch 9, for example via a magnetic coupling 10. 
     In order to limit the pressure in the highpressure part 8 at an especially high ambient temperature, which does not normally occur, an intermediate reservoir 11 for the compressed, but not yet condensed refrigerant is connected to the delivery line 12 of the compressor 1, specifically via a pressure-release valve 13 which makes the connection between the delivery line 12 and the intermediate reservoir 11 when a predetermined maximum pressure is exceeded. So that the intermediate reservoir 11 can be emptied again at least partially, there is, as represented by broken lines, a return valve 14 which can be combined with the pressure-release safety valve 13. 
     As also shown, instead of the return valve 14 there can be a discharge valve 15 which can connect the intermediate reservoir 11 to the suction line 6. This can take place in a temperature-controlled manner, when the ambient temperature falls again or when a sufficiently low pressure prevails in the low-pressure part 7. At all events, it is necessary to prevent the pressure from rising undesirably in the low-pressure part 7 in the critical operating situation. The intermediate reservoir 11 can be a normal gas-holding vessel, the volume of which is calculated according to the size of the system, the expected maximum temperature and the refrigerant used. The intermediate reservoir 11 can also be provided as a gas reservoir known per se, with a pressure-compensating chamber closed off by means of a diaphragm. 
     Instead of the intermediate reservoir 11, there can alternately be provided a variable-volume intermediate reservoir 11&#39; the wall of which can be provided, for example, in a concertina-like manner such as a bellow 16. The vessel 11&#39; then has to be installed so as to be of variable length, the change in length also being limited by a spring 17, the prestress of which is, where appropriate, adjustable.