Patent Application
20060218959
This patent application claims the benefit of German Application No. 10 2005 016 433.1, filed Apr. 5, 2005, the teachings and disclosure of which are hereby incorporated in its entirety by reference thereto.
The invention relates to a refrigerant compressor for refrigerating systems comprising at least one cylinder unit, which has a cylinder housing and a piston which can move in an oscillating manner in the cylinder housing, a cylinder head, with an inlet chamber, flowed through by an inlet flow of the at least one cylinder unit, and with an outlet chamber, passed through by an outlet flow of the at least one cylinder unit, and also a switching valve for interrupting the inlet flow.
Refrigerant compressors of this type are known from the prior art; with these, the switching valve provides the possibility of permanently switching off or permanently switching on one or more cylinder units.
With this solution, controlling the mass throughput is possible just on the basis of the ratio of the swept volume of the switched-off cylinder units and the swept volume of the operating cylinder units.
It is therefore an object of the invention to improve a refrigerant compressor of the generic type in such a way that it can be operated in any desired part-load ranges.
This object is achieved in the case of a refrigerant compressor of the type described at the beginning by providing a control for activating the switching valve which, for operating the refrigerant compressor in a lower part-load range, operates the switching valve in successive switching intervals, respectively comprising an opening interval and a closing interval of the switching valve, which are shorter than a shortest time period after which a temperature of an evaporator in the operating refrigerating system has risen by approximately 10% during an interruption of the inlet flow.
The advantage of the solution according to the invention can be seen in that it opens up the possibility of operating in particular a reciprocating piston compressor in a lower part-load range with any desired part load, since the mass flow to be compressed can be set steplessly and as desired by the ratio of the opening intervals and the closing intervals within each switching interval.
In this case, time periods that are adequately short are chosen for the switching intervals, so that, on account of the inertia of the reaction of the refrigerating system according to the invention to the switching intervals, only insubstantial temperature fluctuations that do not impair precise regulation of the temperature occur in the evaporator of the refrigerating systems.
As an alternative to the solution described above, a further exemplary embodiment of a refrigerant compressor of the type described at the beginning provides a control for activating the switching valve which, for operating the refrigerant compressor in a lower part-load range, operates the switching valve in successive switching intervals, respectively comprising an opening interval and a closing interval of the switching valve, which are shorter than approximately 10 seconds.
Limiting the duration of the switching intervals in such a manner likewise creates the possibility in a way according to the invention of operating the refrigerant compressor in a lower part-load range with a part load that can be set as desired, without pressure fluctuations which impair the quality of the regulation of the refrigerating system occurring in said system.
It is even more advantageous in this respect if the switching intervals are shorter than approximately 2 seconds.
To be able to operate the switching valves effectively, it is preferably provided that the switching intervals are longer than approximately 0.02 seconds.
It is even more advantageous if the switching intervals are longer than 0.05 seconds and particularly advantageous if the switching intervals are longer than 0.1 seconds.
It is particularly advantageous for switching the switching valve if the switching intervals correspond to a switching frequency which is less than an inherent or natural frequency of the switching valve.
It is even better if the switching intervals correspond to a switching frequency which is less than an inherent or natural frequency of the switching valve by a factor of 5.
In principle, with the control according to the invention it would be conceivable in the lower part-load range for example to switch off some of the cylinder units and operate only some of the cylinder units in the switching intervals.
However, a particularly suitable solution provides that, in the lower part-load range, the control operates all the cylinder units of the refrigerant compressor in the switching intervals.
Furthermore, it is conceivable also in the upper part-load range to switch off only some of the cylinder units and operate other cylinder units in the switching intervals.
It is particularly advantageous, however, if the control operates all the cylinder units in the switching intervals in the entire part-load range.
With regard to the time duration of the switching intervals, a wide variety of solution possibilities are conceivable. For instance, a variant that is particularly advantageous for reasons of simplicity provides that the control operates with switching intervals that are of a constant time.
Another advantageous solution provides that the control varies the switching intervals on the basis of a rotational drive speed of the refrigerant compressor.
With regard to the form of the switching valve, so far no further details have been provided.
So it would be conceivable to form the switching valve in such a way that it acts on the inlet flow directly, for example under magnetic control.
For reasons of the required high valve forces, however, it has proven to be advantageous if the switching valve is a servo valve.
In particular, it is advantageous in this respect if the servo valve comprises a valve body which can be actuated by a pressure associated with the pressure in the outlet chamber.
In order to ensure that the valve body does not automatically assume the end position brought about by the pressure in the outlet chamber, it is preferably provided that the valve body is acted upon by an elastic force accumulator acting counter to the effect of the pressure on the valve body.
With regard to the actuation of the valve body by the pressure in the outlet chamber, a wide variety of structural solutions are conceivable. For example, solutions with membranes acted upon by the pressure in the outlet chamber or the like would be conceivable.
A particularly suitable solution provides that the valve body is coupled to a switching piston which can be acted upon by a pressure associated with the pressure in the outlet chamber and is guided in a switching cylinder housing, and which then actuates the valve body.
With regard to acting upon the switching piston, it has proven to be advantageous if the switching piston and the switching cylinder housing enclose a switching cylinder chamber and if the pressure in the switching cylinder chamber is controllable.
Furthermore, it is favorable for structural reasons if the valve body and the switching piston form a unit which is guided in the switching cylinder housing.
Furthermore, it is advantageous in the case of a servo valve of this type if it comprises a control valve which can be activated by the control.
A control valve of this type is formed for example as a rapidly responding, electrically activatable solenoid valve or similarly constructed valve.
For operating the servo valve, it is provided in the case of an advantageous exemplary embodiment that the control valve opens or closes a connecting channel between the control cylinder chamber and the outlet chamber, so that, in a simple manner, there is the possibility of acting upon the switching piston with medium under the pressure in the outlet chamber.
In the case of a servo valve of this type, to achieve an inherent frequency that is as high as possible, and consequently a short switching time, it is preferably provided that the inherent frequency of the unit comprising the switching piston, valve body and elastic force accumulator corresponds at least to the inherent frequency of the switching valve.
A high inherent frequency of this type of the switching valve can be achieved in particular if the switching piston is produced from a lightweight structural material.
A lightweight structural material of this type may be, for example, a lightweight metal or else a plastics material, for example also a fiber-reinforced plastics material.
A further advantageous form of the switching piston provides that it is formed as a hollow body, so that a high inherent frequency of the unit comprising the switching piston, valve body and elastic force accumulator can also be achieved in this way.
Further features and advantages of the invention are the subject of the description which follows and the representation of some exemplary embodiments in the drawing.
An exemplary embodiment of a refrigerating system according to the invention, designated as a whole by 10, comprises a refrigerant compressor 12, from the high-pressure connection 14 of which a line 16 leads to a condenser, designated as a whole by 18, in which the compressed refrigerant is condensed by removal of heat.
From the condenser 18, liquid refrigerant flows in a line 20 to a collector 22, in which the liquid refrigerant collects and from which the latter then flows via a line 28 to an expansion valve 30 for an evaporator 32.
After flowing through the evaporator 32, the evaporated refrigerant flows via a line 34 to a low-pressure connection 36 of the refrigerant compressor 12.
As represented in
Each of the cylinder units 44 is formed by a cylinder housing 46, in which a piston 48 can be moved in an oscillating manner by the piston 48 being able to be driven by a connecting rod 50, which for its part is mounted on an eccentric 52 of an eccentric shaft 54, which is driven for example by an electric motor 55.
The cylinder housing 46 of each of the cylinder units 44 is closed off by a valve plate 56, on which a cylinder head 58 is disposed.
In this case, the valve plate 56 preferably covers not only one cylinder housing 46 of a bank of cylinders 42, but all the cylinder housings 46 of the respective bank of cylinders 42, and in the same way the cylinder head 58 likewise reaches over all the cylinder housings 46 of the respective bank of cylinders 42.
The compressor housing 40 also comprises an inlet channel 60, which is in connection with the low-pressure connection 36 and is, for example, integrated in the compressor housing 40.
As shown enlarged in
If the switching valve 70 is open, the inlet flow 74 has the possibility of entering via an inlet opening 76, provided in the valve plate 56, and an inlet valve 78, provided on the valve plate 56, into a cylinder chamber 80, delimited by the respective piston 48 and the respective cylinder housing 46 as well as the valve plate 56, in order to be compressed in said chamber by the oscillating movement of the piston 48, so that an outlet flow 86 leaves the cylinder chamber 80 via an outlet opening 82 and an outlet valve 84 and enters into an outlet chamber 88 of the cylinder head 58.
The switching valve 70 is formed as a servo valve which is integrated in the cylinder head 58 and has a valve body 90, with which an inflow opening 92, provided in the valve plate 56, of the inlet chamber 72 can be closed.
The valve body 90 is also disposed on a switching piston 94, which is guided in a switching cylinder housing 96, so that the switching piston 94 can be moved in the direction of the valve plate 56 by pressure prevailing in a switching cylinder chamber 98, to close the inflow opening 92 in said valve plate.
A switching cylinder unit 100, which is formed by the switching cylinder housing 96, the switching piston 94 and the switching cylinder chamber 98 and is integrated in the cylinder head 58, is in this case controllable by means of a control valve 110, which comprises an electromagnetically movable control piston 112, with which a control valve seat 114 can be closed, the control piston 112 and the control valve seat 114 being provided for the purpose of interrupting or clearing a connection between a pressure channel 116, leading to the outlet chamber 88, and a pressure feed channel 118, leading to the switching cylinder chamber 98, for the switching cylinder 100.
If the connection between the high-pressure channel 116 and the pressure feed channel 118 is cleared, the switching cylinder chamber 98 is under the high pressure prevailing in the outlet chamber 88 and, consequently, the switching piston 94 moves in the direction of the valve plate 56 and presses the valve body 90 against the latter, in order to close the inflow opening 92 in the valve plate 56.
In this case, the force acting on the switching piston 94 as a result of the high pressure in the switching cylinder chamber 98 opposes the force of an elastic force accumulator 120, which on the one hand is supported on the switching cylinder housing 96 and on the other hand acts on the switching piston 94 in such a way that the latter moves away from the valve plate 56, and consequently moves the valve body 90 into a position clearing the inflow opening 92.
In particular, the switching piston 94 is provided with a pressure relieving channel 122, which leads from an opening facing the switching cylinder chamber 98 to an outlet opening 124, which is represented in
The switching valve 70 can be activated by a control 130, represented in
Within the duration of the respective switching interval SI, the time period of the opening interval O and of the closing interval S can then be set variably in relation to each other in all part-load ranges, so that either the opening interval O is greater than the closing interval or vice versa.
In the extreme case, the opening interval O may extend substantially over the entire duration of the switching interval SI, while the closing interval S becomes as small as desired, or, conversely, the closing interval S may extend substantially over the entire duration of the switching interval SI, so that the opening interval O is as small as desired.
Since, in the refrigerating system 10 according to the invention, evaporation of liquid refrigerant generally takes place constantly via the expansion valve 30, an interruption of the compression of refrigerant by the refrigerant compressor 12 leads to a rise of the temperature T in the evaporator 32.
However, the system is provided with a reaction inertia, so that, when there is an interruption of the suction removal of refrigerant from the evaporator 32, the temperature T of the evaporator 32 does not rise immediately but instead, as represented in
As long as the value D lies around values less than 10% of an initial temperature TA of the evaporator, these fluctuations are irrelevant to the function of the refrigerating system according to the invention.
For this reason, the switching interval SI is chosen such that it is shorter than the time period Z that elapses before the temperature T of the evaporator 32 has risen from a temperature TA of the evaporator 32 by a value D of approximately 10%, even better approximately 5%, when there is a sudden interruption in the suction removal of refrigerant from the evaporator 32 and the feeding of medium under high pressure takes place at the high-pressure connection 14.
This ensures that the opening intervals O and the closing intervals S within the respective switching interval SI have no significant effect on the function of the refrigerating system and merely lead to slight temperature fluctuations of the evaporator 32 of the refrigerating system according to the invention.
The time periods of the switching intervals SI usually lie around time periods which are shorter than approximately 10 seconds, even better shorter than approximately 2 seconds.
On the other hand, in order to ensure adequate opening intervals O, the switching intervals are longer than approximately 0.02 seconds, even better longer than 0.05 seconds and preferably longer than 0.1 seconds.
A preferred operating range provides switching intervals SI of a duration that lies between 0.1 and 10 seconds.
To ensure such shorter time intervals SI, it is preferably provided that the switching pistons 94 together with the valve bodies 90 and the elastic force accumulators 120 altogether have an inherent frequency which is higher than the frequency corresponding to the maximum switching intervals SI, so that the switching pistons 94 are capable of realizing the opening intervals O and the closing intervals S substantially without delay within the switching intervals SI.
The inherent frequencies of the systems comprising the switching piston 94, valve body 90 and elastic force accumulator 120 are preferably higher than the frequencies corresponding to the switching intervals SI by a factor of at least 5 or even better at least 10.
To realize this, it is suitably provided that the switching pistons 94 are made of a lightweight structural material, for example lightweight metal or plastics material, in order that small masses have to be moved.
In the case of a second exemplary embodiment of a refrigerant compressor according to the invention, represented in
The solution according to the invention provides, for example, a switching valve 70 of this type for each bank of cylinders, so that there is the possibility of correspondingly switching off the inlet flow for all the cylinder units 44 of a bank of cylinders 42.
However, it is also conceivable to dispose a switching valve 70 of this type in such a way that it controls the inlet flow 74 to all the cylinder units 44 of the entire refrigerant compressor.
In the case of an advantageous solution, at least in a lower part-load range, that is to say in a range between approximately 1% and approximately 30% of the maximum mass flow, the control 130 controls all the cylinder units 44 with the same switching intervals.
However, even in higher part-load ranges, for example in an upper part-load range between approximately 30% and 100% of the maximum mass flow, it is advantageous to operate all the cylinder units 44 with the same switching intervals in order to avoid balancing problems of the reciprocating piston compressor that occur if cylinder units 44 are completely switched off.
The control 130 is then capable when the refrigerant compressor 12 is operated in the full-load range of activating the switching valve 70 in such a way that the valve body 90 is constantly in the position clearing the inflow opening 92, so that the inlet flow 74 can flow to all the cylinder units 44 of the respective bank of cylinders 42.
In this case, the maximum mass flow of refrigerant is compressed to high pressure H.
There is also the possibility of activating the switching valve 70 in a zero-load range in such a way that the valve body 90 is constantly in its position closing the inflow opening 92. In this case, substantially no mass flow of refrigerant is compressed. Only the mass flow flowing through the pressure channel 116 and the pressure of the channel 118 and also the pressure relieving channel 122 is compressed.
In the part-load range, the control 130 is capable of continuously setting any desired part load, to be precise in such a way that the time period of the opening interval O and the time period of the closing interval S, which add together to give the time period of the switching interval SI, are set variably in the desired ratio.
In this case, the switching interval SI may be equal in all part-load ranges.
However, it is also conceivable to vary the switching interval SI either proportionally or in individual steps dependent on the rotational speed of the eccentric shaft 54, and consequently of the electric motor 55.
For example, the variation of the switching interval SI takes place in such a way that, at low rotational speed of the electric motor, the switching intervals SI are long and at high rotational speed of the electric motor the switching intervals are shorter.
The advantage of the solution according to the invention can be seen in that, in the case of the reciprocating piston compressor, the power consumption is proportional to the mass throughput, and consequently, when there is a reduction in the mass throughput through successive opening intervals O and closing intervals S in the part-load range, there is the possibility of also reducing the power consumption of the reciprocating piston compressor.
Furthermore, the solution according to the invention provides the possibility of controlling the mass throughput to implement the starting process of the refrigerant compressor 12 in such a way as to minimize the risks of boiling-out refrigerant.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2005 016 433.1 | Apr 2005 | DE | national |
