Abstract:
The invention relates to a compressor, particularly for air conditioners in motor vehicles, comprising a safety device for limiting high pressure, whereby the safety device is hermetically sealed until first responding, after which it slowly reduces the system pressure.

Description:
The present invention is directed to a compressor, in particular for air-conditioning systems in motor vehicles, having a safety device for limiting high pressure. 
     BACKGROUND 
     Compressors of this kind are generally known. Thus, there are compressors which discharge the entire refrigerant-oil mixture to the environment by way of rupture disks, which burst in response to the maximum pressure being exceeded. These compressors have the disadvantage that, once the rupture disk has been actuated, vehicles having a coupling-free compressor, for example, are no longer able to be driven without the risk of compressor damage occurring. 
     In addition, compressors having pressure relief valves for the refrigerant R134A are known. However, their design is not directly transferable to air-conditioning systems which use the refrigerant CO 2 , without risking considerable leakage rates already in the newly manufactured condition. In addition, the pressure relief valves currently used for the refrigerant R134A have the problem of the imperviousness being substantially degraded after a one-time actuation. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to devise a compressor which will overcome disadvantages of the prior art. 
     The present invention provides a compressor, in particular for air-conditioning systems in motor vehicles, having a safety device for limiting high pressure, the high-pressure limitation being hermetically sealed up until the first response, and the system pressure dropping slowly after that. It is thus achieved that the compressor is not damaged even during further operation. A compressor is preferred in which the safety device includes a combination of a rupture disk and a pressure relief valve. In accordance with the present invention, the rupture disk and the pressure relief valve are arranged in series. The rupture disk is pressurized on one side with the high pressure from the exhaust chamber of the compressor, while it is pressurized on the other side with atmospheric pressure. Viewed from the high-pressure side, the pressure relief valve is configured downstream of the rupture disk. 
     In addition, a compressor is preferred in which the pressure relief valve is designed for valve-opening pressure that may be clearly lower than the bursting pressure of the rupture disk. The pressure relief valve vents to the atmospheric side. In addition, a compressor is preferred in which the pressure relief valve has a defined leakage, while the rupture disk is hermetically sealed. The advantage of the pressure relief valve having a defined leakage is that no pressure is able to build up in the space between the rupture disk and valve, as long as the rupture disk is intact. Thus, the response characteristic of the rupture disk is not affected. 
     Also, a compressor is preferred, in which the defined leakage is able to be achieved by a valve seat or a valve piston of the pressure relief valve, made of porous material. In addition, a compressor is preferred, in which the defined leakage of the pressure relief valve is able to be achieved by a bypass groove or a bypass bore, or by a surface irregularity or a surface roughness in the area of the valve seat or valve piston. In addition, the defined leakage may be realized by the permeability of an elastomer seal  27  at the valve seat or valve piston. A compressor in accordance with the present invention has the distinguishing feature that, after dropping below the set pressure, the residual refrigerant contained in the system is released by the pressure relief valve only still slowly, via the leakage site. This slow, controlled discharging of the gas ensures that the system remains operational to a limited degree for a certain time, and that the user has time to drive to a service station without risking compressor damage. Such compressor damage would otherwise occur, because refrigerant that leaks out suddenly would entrain the oil and cause the compressor lubrication to fail. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention is described in greater detail below with reference to the drawing, in which: 
         FIG. 1  shows a compressor according to one embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     The figure shows a housing part  1 , which may be an integrated component of a compressor housing, for example. Embedded in housing part  1  is a rupture disk  3 , which is pressurized on its side  7  by high pressure  5  prevailing in the exhaust region of the compressor. On side  9  of the rupture disk, i.e., in region  11  of the safety device, the rupture disk is pressurized in the intact state with atmospheric pressure  15 , since pressure relief valve  13  does not close in a leak-tight manner, enabling atmospheric pressure  15  to prevail up to region  11 . As illustrated here for example, pressure relief valve  13  may be composed of a spherical valve body  17  and a conical valve seat  19 , spherical valve body  17  being pressed by a spring  21  into valve seat  19 . The preloading of spring  21 , which determines the opening pressure of pressure relief valve, may be adjusted by a suitable supporting surface  23  for spring  21 . In this context, pressure relief valve  13  is set to an opening pressure which is clearly below the bursting pressure of rupture disk  3 , so that it opens immediately in response to actuation of the rupture disk. It is intended for pressure relief valve  13  to have a defined leakage site in sealing region  25  between valve seat  19  and valve body  17 , so that it does not provide hermetic sealing action. This leakage site may be constituted of a porous material for seat  19  or for spherical valve body  17 , as well as of a bypass groove in region  25  or of a bypass bore, or of an appropriate surface condition, surface roughness and similar structures, such as elastomer seal  27 , which render possible a small amount of leakage in region  25  and thus, given an intact rupture disk, enable atmospheric pressure  15  to prevail up to valve region  11 . When the bursting pressure of rupture disk  3  is exceeded, and rupture disk  3  bursts in response to high pressure  5  toward atmospheric pressure  15  and allows the refrigerant to escape from the compressor, the effluent refrigerant will then continue to flow off under the substantially lower set pressure of pressure relief valve  13  into the atmosphere until the opening pressure of the pressure relief valve set via the spring force is also undershot within the air-conditioning system. Pressure relief valve  13  subsequently moves again into a closed position, and the refrigerant remaining in the air-conditioning circuit, including the lubricant required for lubrication is only able to still leak out slowly and thus over a longer period of time via the leakage site in region  25 . This slow, controlled discharging of the gas ensures that the system remains operational to a limited degree for a certain time, and that the user has time to drive to a service station without immediately risking compressor damage, since refrigerant and thus lubricant are still present in the system. This safety device has the further benefit of preventing the pressure prevailing inside the air-conditioning system from being suddenly relieved from maximum pressure to atmospheric pressure, so that refrigerant, which may still be in the high-pressure state within the seal material, cannot be diffused into the seals, for example, which could lead to explosive decompression and thus to destruction of the seals due to a sudden drop in pressure outside of the seal.