Refrigerant compressor

The present invention relates to a hermetically encapsulated refrigerant compressor having a hermetically sealed compressor housing, in whose interior a piston-cylinder unit, which compresses a refrigerant, operates, whose cylinder is closed using a valve plate having a pressure hole and a suction hole, and a suction channel and a pressure channel are provided, via which refrigerant is suctioned via a suction valve into the suction hole and is compressed via a pressure valve from the pressure hole into the pressure channel, a suction noise damper preferably being situated in the suction channel, according to the preamble of Claim 1.

Such refrigerant compressors have been well-known for some time and predominantly are used in refrigerators or refrigerated cases. The piece count produced yearly is accordingly high.

Although the energy consumption of a single refrigerant compressor is only between 50 and 150 W, a very high energy consumption results upon consideration of all refrigerant compressors used worldwide, which is increasing continuously because of the rapidly progressing development of the so-called developing countries.

Any technical improvement which is performed on a refrigerant compressor and increases its efficiency thus conceals an enormous savings potential for energy when multiplied by the refrigerant compressors in use worldwide.

The refrigerant process per se has been known for some time. The boiling refrigerant is vaporized in the evaporator by energy absorption from the space to be cooled and finally overheats and is pumped to a higher energy level using the refrigerant compressor, where it dissipates heat via a condenser and is conveyed back into the evaporator via a throttle, in which pressure reduction and cooling of the refrigerant occurs.

The greatest and most important potential for a possible improvement of the efficiency is the reduction of the temperature of the refrigerant at the beginning of its compression procedure, i.e., upon intake into the cylinder of the piston-cylinder unit. Any reduction of this so-called suction temperature therefore causes, like the reduction of the temperature during the compression procedure and, connected thereto, the expulsion temperature, a reduction of the required work for the compression procedure.

In known hermetic refrigerant compressors according to the prior art, the refrigerant is strongly heated on its way from the evaporator (cooling space) to the intake valve of the piston-cylinder unit because of the construction.

The intake of the refrigerant occurs via a suction channel coming directly from the evaporator during an intake stroke of the piston-cylinder unit. From this suction channel, the refrigerant is suctioned via a suction noise damper and a suction valve into the interior of the cylinder, where it is compressed by the piston and expelled via a pressure valve from the interior of the cylinder into a pressure channel leading to the cooling chamber. Known refrigerant compressors have a construction in which the cylinder housing accommodating the piston is terminated by a valve plate having the suction and/or pressure holes. The valve plate is used as a seat for a cylinder cover, which is typically screwed to the valve plate and the cylinder housing. The cylinder cover has intermediate walls, which divide the cavity between cylinder cover and valve plate into chambers, which then form the suction and/or pressure channel, via which the refrigerant is suctioned into the cylinder or expelled therefrom.

The suction channel typically discharges directly into the interior of the compressor housing, which is encapsulated hermetically sealed, in proximity to the entry opening into a suction noise damper, which reduces the intake noise of the piston-cylinder unit and is typically constructed from multiple volumes which are connected to one another, as well as having the cited entry opening and an exit opening which presses against the suction hole of the valve plate to form a seal.

The known embodiment variant described has the disadvantage that the refrigerant heats up too strongly on its way from the entry into the interior of the compressor housing to the suction hole. Measurements have shown that heating by more than 20° C. occurs between a point in the suction channel shortly before the entry into the compressor housing and the first volume of the suction noise damper. The main cause of this undesired heating of the refrigerant is the fact that fresh refrigerant flowing from the suction channel into the compressor housing is mixed with refrigerant already located in the compressor housing. However, this refrigerant has a higher temperature because of the heat released by the piston-cylinder unit in operation than the refrigerant flowing from the suction channel into the compressor housing, so that a mixing temperature results upon mixing of the two refrigerant streams which is higher in any case than the temperature of the refrigerant in the suction channel before entry into the compressor housing. The cause of the mixing is the fact that the intake valve, which is seated on the valve plate and alternately closes and releases the suction hole, only releases the suction hole over a crankshaft angle range of 180° and therefore refrigerant may only be suctioned into the cylinder of the piston-cylinder unit within this time. The suction valve is closed during the other 180° crankshaft angle range, the compression cycle, but the refrigerant coming from the evaporator has a nearly constant mass flow, so that it still flows into the compressor housing even when the suction valve is closed and remains there and cools the piston-cylinder unit and heats up at the same time. In addition, due to the pressure oscillations during the compression phase, further flow procedures occur from the compressor housing to the suction noise damper and vice versa, which cause additional mixing of the refrigerant.

In addition to the cited discharge of the suction pipe into the compressor housing in proximity to the entry opening into the suction noise damper, embodiment variations are also known, for example, from WO 03/038280, in which the suction channel is conducted directly into the suction noise damper without a bypass via the interior of the compressor housing. In this way, the mixing of the refrigerant flows resulting in heating of the refrigerant at beginning of the compression procedure may not occur. However, this achievement of the object has the disadvantage that there is usually a greater pressure drop during the suctioning, which reduces the volumetric efficiency and thus the energy efficiency to varying degrees.

All known refrigerant compressors have an identical construction of the piston-cylinder unit, however, in particular of the cylinder housing, which is closed using a valve plate and a cylinder cover adjoining thereto. The cylinder cover preferably covers the entire valve plate, which also has the suction hole and the pressure hole. The suction valve temporarily closing the suction hole and the pressure valve temporarily closing the pressure hole are also situated on the valve plate. The cylinder cover is typically provided with a recess for the suction channel, and/or for the end section of the suction noise damper, which discharges into the suction hole.

The refrigerant heated by the compression procedure is pressed via the pressure valve and the pressure hole out of the cylinder into the cylinder cover, where, because of the design of the cylinder cover, it fills up the cylinder cover completely at least in the section forming a pressure channel and thus also comes into contact with the valve plate forming a part of this pressure channel. Because of this, the temperature of the valve plate essentially corresponds to the temperature of the compressed refrigerant. Because the gas in the interior of the cylinder is colder than the valve plate over more than 300° crank angle, a heat flow occurs directly from the valve plate or indirectly from the valve plate to the cylinder wall and from there to the gas in the interior of the cylinder, which has a negative effect on the energy efficiency.

Furthermore, the high temperature existing in the cylinder cover also causes a heat flow in the direction of the end section of the suction noise damper, which is enclosed by the cylinder cover, but by which the refrigerant coming from the suction noise damper, which is still to be compressed, is also undesirably heated. In summary, it may thus be stated that the known refrigerant compressor designs act contrary to the object cited at the beginning, namely a reduction of the suction temperature and the expulsion temperature, because of their cylinder cover design.

A hermetically encapsulated compressor having a suction housing situated on a base plate on the cylinder head and a pressure housing separated therefrom is known from U.S. Pat. No. 5,288,212. The same base plate forms the shared floor of suction and pressure housings and presses flat against the cylinder head configuration.

It is therefore the object of the present invention to avoid the described disadvantages and provide a refrigerant compressor of the type cited at the beginning, which allows a significant reduction of the suction temperature and the expulsion temperature.

This is achieved according to the present invention by the characterizing features of Claim 1.

By providing an independent component, which forms the pressure channel and completely envelops it, and connecting this component directly to the pressure hole, the pressure channel is completely thermally separated from the valve plate. The components according to the present invention allow the direct exit of the hot, compressed refrigerant via the pressure hole into the pressure channel without having to flow out along a section of the valve plate. Only the area of the valve plate directly enclosing the pressure hole comes into contact with the hot refrigerant on its side facing away from the piston. The heat transfer from the hot, already compressed refrigerant to the valve plate may thus be drastically reduced in relation to typical cylinder heads in refrigerant compressors. The valve plate and the cylinder wall remain cooler and thus allow dissipation of the heat from the interior of the cylinder housing, and/or prevent the flow of heat into the gas in the cylinder. Furthermore, in this way, the heat transfer from the valve plate to the suction hole and thus into the suction channel may be reduced, by which the intake temperature may be decreased.

The area of the pressure channel which is incident on the valve plate, i.e., the area which lies inside the pressure contact edge, may be dimensioned precisely and optimized in regard to heat transfer by the characterizing features of Claim 2. It is necessary on one hand for the pressure hole to lie inside this area and on the other hand for the transition between pressure channel and pressure flow to be implemented for favorable flow and nonetheless allow a tight connection. Because according to the present invention the pressure channel or more precisely the last section of this channel is incident on the pressure hole and thus on the valve plate essentially perpendicularly to prevent heat transfer from the valve plate to the pressure channel and/or vice versa, the shape of the pressure contact edge may be selected in such a way that the refrigerant only flows around the valve plate along a small area.

According to the present invention, the ratio of the cross-sectional area of the pressure hole to the area enclosed by the pressure contact edge is greater than 1/12.