Piston compressor for refrigerant, with thermal insulation

Details Piston compressor for refrigerant, with thermal insulation Piston compressor for refrigerant, with thermal insulation

2000-04-06

2002-10-01

Freay, Charles G. (Department: 3746)

Pumps

Three or more cylinders arranged in parallel, radial, or...

C417S319000, C417SDIG001, C092S071000, C192S056500

Reexamination Certificate

active

06457947

ABSTRACT:

BACKGROUND OF THE INVENTION
The invention relates to a compressor, in particular for the air conditioning system of an automobile, with a housing and a compressor unit accommodated in the housing for taking in and compressing a refrigerant, the refrigerant flowing from an intake area preferably formed in a front-end housing cover through the compressor unit into a discharge area preferably likewise formed in the housing cover.
In most cases, compressors of the kind under discussion are named air-conditioning compressors, and are known from practice in a large variety of types of construction. Such compressors comprise a housing, which encloses an externally operated compressor or pump unit. The pump unit that is designed and constructed, for example, as an axial piston pump, comprises in turn at least one piston that is adapted for reciprocal movement in a cylinder block. Normally, such a compressor is equipped with a plurality of pistons and operates by the swash plate or pivot disk principle. When rotating a swash plate, the pistons will reciprocate in the direction of their longitudinal axis, with a receiving disk being nonrotatably supported in the housing.
Air-conditioning compressors of a large variety of types operate with a refrigerant. Besides conventional refrigerants, whose use appears to become more and more critical in the light of an increasing awareness of the environment, it is possible to use as a refrigerant an inert gas, such as, for example, CO
2
, which is noncritical under environmental aspects. However, the use of such a refrigerant leads to higher pressures within the compressor, thereby necessitating quite special constructional measures, for example, with respect to the selection of material and wall thickness of the housing.
The use of a high-strength material for the housing of the compressor makes it easy to absorb as early as in the intake state the high pressures necessary or occurring in the case of a refrigerant having a high density. For example, it is thus necessary to withstand bursting pressures of up to 30 MPa at discharge temperatures of up to about 160° C. to 170° C.
As aforesaid, compressors of the kind under discussion comprise an intake area and a discharge area. Whereas on the suction side, in the intake area, the refrigerant flows in at a temperature mostly ranging from 30° C. to 400, the temperatures on the pressure side, i.e., discharge area, are in a range from 80° C. to about 170° C.
Normally, compressor housings are made of metal, for example, aluminum, of high-quality steel, or of a high-tensile steel. Consequently, the high temperature in the discharge area is bound to become effective on the intake area to the extent that same is heated via the housing material coming into contact with the refrigerant, as well as the interiors of the compressor. As a result, the gaseous refrigerant is heated on the intake side, whereby its density decreases. This again leads to a loss in delivery or a reduction of the mass flow of the refrigerant and, thus, to a loss in output of the compressor. Because of the temperature influence by the discharge area on the intake area, the efficiency of a conventional compressor is considerably reduced.
A further concept of the invention relates to a compressor, in particular for the air conditioning system of an automobile, wherein a belt drives the compressor unit via a drive wheel coupled with the drive shaft, and wherein the drive wheel comprises a belt pulley body engaging the belt, the belt pulley body being coupled via a coupling device directly or indirectly with the drive shaft.
The compressors under discussion are driven via a belt, which is guided over a belt pulley hereafter drive wheel. The belt in turn is driven via the crank shaft of the internal combustion engine of an automobile.
Malfunctions may occur in the operation of the compressor. Thus, for example, the compressor unit or the drive shaft may block. If the belt loops about the drive wheel at a very small angle, the belt is expected to slip on the drive wheel or the belt pulley. In this instance, the drive wheel will heat up very considerably. This leads after a short time to damage and finally to destruction of the belt, so that even the subassemblies that are driven by the belt, for example the water pump or alternator, can no longer be operated. As a result, the automobile is no longer operable.
If the belt loops about the drive wheel or belt pulley at a larger angle, for example, more than 180°, it is hardly possible that the belt slips on the drive wheel or belt pulley. This leads either to a tearing of the belt or to a choking of the engine. Likewise, in such an instance, the automobile is no longer operable.
To avoid the above-described problems, an electromagnetic clutch has already been integrated in the drive wheel of the compressor. Should the belt slip or should the clutch halves slip, the clutch will undergo a very considerable heating. If a predetermined temperature is reached, a safety fuse will interrupt the coil current, and the clutch disengages the compressor, so that the belt can continue to move with the belt pulley body of the drive wheel. This ensures the operation of safety-relevant components of the automobile, for example the water pump and/or the alternator, which are likewise driven by this belt.
However, the electromagnetic clutch as known from practice, is problematic, inasmuch as it is constructed relatively large, expensive with respect to its individual components, and represents a quite considerable cost factor. Primarily, due to its complexity, such an electromagnetic clutch causes an extraordinary weight load, which is diametrically opposite to a weight reduction as is constantly sought in the current automobile construction. Because of its enormous overall size, the compressor is not suitable for installation in small engine compartments.
From the practice alone, it is already known to provide an overload clutch with a disk-shaped rubber body having an external gear tooth system, whose gear teeth shear in the event of excessive stress. In this case, the clutch is a purely mechanical overload clutch, whose disengagement behavior can be defined only in a certain bandwidth. At any rate, such an overload clutch is barely reliable.
It is the object of the present invention to improve and further develop a compressor of the initially described kind such that its efficiency becomes more favorable in comparison with conventional compressors, that the compressor is constructed smaller, that its weight is reduced, and that accordingly it is easier and less expensive to manufacture the compressor. Furthermore, it is an object to increase output and to ensure at a lesser expense at least the same safety, in particular a protection of the belt drive and the internal combustion engine, as in the case of compressors known until now.
SUMMARY OF THE INVENTION
The above and other objects and advantages of the present invention are achieved by the provision of a compressor of the described type wherein the components coming into contact with the refrigerant, and specifically the interior walls of the intake area and the discharge area, are thermally insulated against the refrigerant at least partially and in areas of contact.
To begin with, it has been recognized by the present invention that the high temperature difference between the discharge area and intake area of a conventional compressor of the kind under discussion leads to a decrease of efficiency, due to a heating of the intake area and the refrigerant because of the thermal conductivity of the compressor components.
Furthermore, it has been recognized by the present invention that the here-analyzed problems can be lessened, in that components coming into contact with the refrigerant are thermally insulated to a certain degree, so that the heating of the refrigerant is at least reduced. To this end, the walls forming the flow path between the intake area and the discharge area are thermally insulated against the refrigerant at least slightly in areas of

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