Abstract:
The invention pertains to a stationary vehicle air conditioning system with a refrigerant circuit, in which at least one compressor circulates the refrigerant to at least two condensers. The at least one compressor may be powered by the vehicle&#39;s mechanical power, by an electrical source, or by a combination of these driving forces. Depending on desired operating characteristics, the condensers may be arranged in a series or parallel configuration. A second compressor also may be added, which second compressor may be powered by a source other than the mechanical energy of the vehicle&#39;s engine.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This patent application claims the benefit of German Patent Application No. DE 10 2004 042 691.0, filed Sep. 1, 2004, which is hereby incorporated by reference. 
   FIELD OF THE INVENTION 
   The invention pertains to a vehicle air conditioning system and method, and more particularly, to an air conditioning system that is particularly advantageous for use with a vehicle in which the engine is not running (a “stationary vehicle”). The invention may be employed, for example, with a truck having a first air conditioner in the driver&#39;s compartment and a second air conditioner in a sleeping compartment. The air conditioning system and method includes a plurality of components that may be operated in a first mode while the engine is running and in a second mode while the engine is not running. 
   BACKGROUND OF THE INVENTION 
   German patent application DE 44 14 547 A1 describes a stationary vehicle air conditioning system in which the vehicle engine mechanically drives a first compressor and a DC electric motor powered by auxiliary vehicle batteries electrically drives a second compressor connected in parallel thereto. In normal operation, i.e., with the engine running, the first compressor circulates the refrigerant in the refrigerant circuit without the assistance of the second compressor, and, in stationary operation, i.e., with the engine off, the second compressor circulates the refrigerant without the assistance of the first compressor. The cooling of the refrigerant in each case takes place in a condenser arranged downstream of the junction of the two branches. This arrangement of components does not permit the systems to operate in an optimal manner. 
   Other types of stationary air conditioning systems with a cold storage unit are also known in the art, but such cooling systems typically require an undesirable charging time. There is thus a need for a stationary air conditioning system that permits the components to operate in a more optimal manner and without an undesirable charging time. 
   BRIEF SUMMARY OF THE INVENTION 
   A stationary vehicle air conditioning system with a refrigerant circuit is provided. The circuit includes at least one electrical or mechanical compressor that circulates refrigerant in the refrigerant circuit. The circuit further includes first and seconds condensers. In one embodiment, the first condenser is air cooled by a fan that is mechanically driven by the engine, e.g., through a belt connected to a rotating engine part, and the second condenser is cooled by an electrically driven fan, which is powered by a source other than the mechanical action of the engine. In this embodiment, the second condenser is thus cooled independently of the operation of the vehicle engine. 
   In a preferred embodiment of the invention, the second condenser may be connected in series or in parallel to the first condenser. The second condenser can be arranged in such a manner that is it constantly present in the refrigerant circuit, or, in the alternative, an appropriate arrangement of valves may selectively place or switch the second condenser into a series arrangement with the first condenser when the engine is not running. The provision of a second condenser connected in series with the first condenser permits an improved design of the two condensers for operation when the vehicle is operating in one of two modes, i.e., the engine is stopped or running. The first condenser with associated fan is designed, for instance, for normal operation with the engine running, and the second condenser with associated fan is designed, for instance, for stationary operation with the engine stopped, thereby permitting optimization of performance. 
   In a preferred embodiment, an electrically driven fan generates an air stream that passes through the second condenser. The fan is also preferably inactive during normal operation, so that cooling of the refrigerant is accomplished primarily by the first condenser. The second condenser may be bypassed, so that refrigerant does not flow through the second condenser in normal operation, whereby the required power for the compressor (and thus the power diverted from engine) can be reduced somewhat and/or the second condenser does not act as a refrigerant accumulator. 
   In an alternative embodiment, as described in more detail below, the refrigerant circuit includes a bypass around the first condenser, so that in stationary operation the flow can be directed around the first condenser, whereby the required drive power of the electric compressor can be reduced and/or the first condenser does not act as a refrigerant accumulator. 
   As an alternative to the series connection, the condensers may be arranged in parallel. Depending on the operating mode (normal or stationary operation) refrigerant is preferentially caused to flow through one of the condensers and the fan arranged there is driven mechanically or electrically. 
   Preferably a receiver is arranged downstream of each of the condensers. Excess liquid coolant can be collected in these receivers and is quickly available when needed. 
   In place of a mechanically driven fan at the first condenser, an electrically driven one can be provided, so that a control of fan power independent of the engine is possible, whereby the cooing performance can be optimized. Alternatively, an electrically drivable fan can also be provided in addition to the mechanical fan. 
   In stationary operation, power is preferably supplied to the compressor and the fan or fans via batteries, an external power source such as a line power terminal and/or an auxiliary power unit (“APU”). 
   Preferably, particularly in case of a series connection, refrigerant can be caused to flow through both condensers at least in part, with only one of the condensers being cooled by an air stream. The other condenser in this case is cooled only during normal operation by a mechanically driven fan. This allows a simpler configuration of the refrigerant circuit and a simpler regulation thereof. Moreover, a certain cooling power is provided even if air does not flow through the first condenser. 
   The condenser through which there is only a partial flow in stationary operation can be set up, especially in a series connection, to act as an additional receiver for refrigerant. In this arrangement, the excess refrigerant that is not required for the lower cooling power required in stationary operation may be collected for future use. The condenser is appropriately constructed for this purpose. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     While the appended claims set forth the features of the present invention with particularity, the invention and its advantages are best understood from the following detailed description taken in conjunction with the accompanying drawings, of which: 
       FIG. 1 , a simplified representation of a refrigerant circuit according to a first embodiment; 
       FIG. 2 , a simplified representation of a refrigerant circuit according to a second embodiment; 
       FIG. 3 , a simplified representation of a refrigerant circuit according to a third embodiment; 
       FIG. 4 , a simplified representation of a refrigerant circuit according to a fourth embodiment; 
       FIG. 5 , a simplified representation of a refrigerant circuit according to a fifth embodiment; 
       FIG. 6 , a simplified representation of a refrigerant circuit according to a sixth embodiment; 
       FIG. 7 , a simplified representation of a refrigerant circuit according to a seventh embodiment; 
       FIG. 8 , a simplified representation of a refrigerant circuit according to a eighth embodiment; and 
       FIG. 9 , a simplified representation of a refrigerant circuit according to a ninth embodiment. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  illustrates a vehicle air conditioning system  1  with a front air conditioner  2  and a rear air conditioner  3  includes a refrigerant circuit  4 . A vehicle air conditioning system  1  according to the invention as in one of the embodiments described below can preferably be used in a truck with an area such as a sleeping compartment that is separate from the driver&#39;s compartment, with front air conditioner  2  being located in the driver&#39;s compartment and a rear air conditioner  3  in a separate area of the vehicle. 
   A belt driven first compressor  5 , which is powered with the aid of the vehicle engine, circulates refrigerant through circuit  4  in normal operation while the engine is running. In stationary operation, i.e., with the motor stopped, the first compressor likewise is stopped, and a second compressor  6  is driven electrically by means of batteries or an external (AC) power source or an auxiliary power unit (APU). The electric power source is indicated in all figures with dashed lines. 
   In a first embodiment of the invention, as illustrated in  FIG. 1 , two compressors  5  and  6  are arranged in parallel branches of refrigerant circuit  4 . In order to prevent backflow when second compressor  6  is not running, a check valve (not shown) is arranged in the corresponding branch of refrigerant circuit  4 , downstream of second compressor  6  in the direction of refrigerant flow. A matching check valve can also be provided in the other branch downstream of first compressor  5 . 
   The flow of refrigerant through circuit  4  in “normal” operation, i.e., with the vehicle&#39;s engine running, will be described first. Compressor  5  drives refrigerant, which is hot as a result of compression, through a first condenser  7  that is cooled by air via a first vehicle-engine driven fan  8 . Condenser  7  may be further cooled by wind or by an air stream generated through the motion of the vehicle. Downstream of condenser  7 , a first receiver  9  is arranged to collect and temporarily store excess liquid refrigerant. Downstream of this receiver, the circuit splits into two branches: a first branch  11  that can be closed off by a valve  10  and a second branch  13  that can be closed off by a valve  12 . The arrangement of these branches creates a bypass around a second condenser  14  depending on the respective operation of values  10  and  12 . An electrically driven fan  15  supplies cooling air through a second condenser  14 . Similar to the first condenser, second condenser  14  includes a receiver  16 . 
   While the vehicle&#39;s engine is running, first valve  10  is open and second valve  12  is closed, so that refrigerant flows through first branch  11 . Second fan  15  is inactive in normal operation. Refrigerant circuit  4  further splits into two branches downstream of the second condenser: branches  17  and  18  are associated with air conditioners  2  and  3 , respectively, with a valve  19  in branch  17  associated with front air conditioner  2  being capable of cutting off the flow of refrigerant. Before reaching a respective evaporator  20  or  21 , refrigerant flows through an expansion member  22  or  23 , respectively, in which refrigerant is expanded and thereby cooled. Associated with each evaporator  20  and  21  is an electrically driven fan  24  and  25 , respectively, which forces air through evaporators  20  and  21 , respectively, and into the respective climate control zone. After flowing through evaporators  20  and  21  the refrigerant streams are reunited and returned to first compressor  5  in normal operation. 
   In stationary operation, i.e., with the vehicle engine stopped, circulation of the refrigerant is accomplished primarily through the second and electrically driven compressor  6 . Refrigerant flows through first condenser  7 , as when the vehicle engine is running. Because the engine is stopped, however, fan  8  does not supply an air stream to cool condenser  7 . Nevertheless, due to possibly lower cooling requirements in stationary mode, this arrangement may be acceptable. Based on appropriate sensors, mechanical switches, and/or electromechanical switches, valve  10  is closed, and refrigerant flows through a now correspondingly open valve  12  and condenser  14 . A fan  15 , which is driven with the aid of the electric power source, supplies air to cool condenser  14 . Excess liquid refrigerant thereafter collects in downstream second receiver  16 . Corresponding to normal operation, the refrigerant circuit splits into two branches  17  and  18 , and the refrigerant flows through these branches in the manner previously described. Coolant thereafter returns to second compressor  6  due to the inactive compressor  5 . 
   Refrigerant flowing through parallel connected evaporators and different compressors tends to accumulate in certain components during stationary operation. In particular, a parallel connected and inoperative compressor can accumulate an undesirably high amount of excess refrigerant, which can in turn lead to a drop in cooling power and, under certain circumstances, to a failure of the compressors. This failure mode may be caused, at least in part, by the fact that the same amount of refrigerant exists in both the stationary and engine-running modes of operation. Because a smaller amount of refrigerant is typically required in stationary mode, due to the lower cooling needs, it may be necessary to take further appropriate measures to reduce the amount of refrigerant during stationary operation. This may be accomplished, for example, by drawing off a predetermined amount of refrigerant via a bypass (not shown) and temporarily storing this refrigerant in an accumulator (not shown) during stationary operation. After normal operation is resumed, the stored refrigerant may be pumped back into the refrigerant circuit. 
   In an alternative to the foregoing embodiment, the second compressor  6  may be operated intermittently rather than continuously. According to another alternative, a refrigerant receiver with variable capacity is provided, and an expansion member may be integrated into a receiver and dryer unit, so that corresponding combinations are provided in place of the two expansion members of the first embodiment. As yet an additional alternative, the refrigerant circuit includes a bypass with an ice accumulator into which the excess (cold) refrigerant is directed, thereby permitting the refrigerant to be cooled and stored during stationary operation. In addition, at least part of the condenser through which cooling air does not flow in stationary operation can provide interim storage of the excess refrigerant. 
     FIG. 2  illustrates a second embodiment. In this embodiment, only a single electrically driven compressor  106  circulates coolant both in normal operation and as needed in stationary operation. This single compressor replaces the parallel branches with mechanically driven compressor  5  and electrically driven compressor  6  of  FIG. 1 . The circuit thereafter operates as described above. 
     FIG. 3  illustrates yet another embodiment in which a hybrid compressor  205 / 206 , which can be driven both mechanically by the engine and electrically, may be substituted for the single electrical compressor of  FIG. 2 . In normal operation, the running vehicle engine drives hybrid compressor  205 / 206 , and, in stationary operation, an electrical source (such as batteries, an external power source or an APU) supplies power to compressor  205 / 206 . In other respects, this embodiment is similar to the prior embodiments. 
   A fourth embodiment of the invention is illustrated in  FIG. 4 . In this embodiment, the circuit  4  splits into two branches downstream of the junction of compressors  5  and  6 . A first branch  411  can be closed off by a first valve  410 , thereby forming a bypass to the second branch  413 , which can be closed off by a second valve  412 . In normal operation, first valve  410  is closed and second valve  412  is open, so that refrigerant flows through second branch  413  and thus through condenser  7 , and, subsequently, through condenser  14 . 
   In contrast to the first embodiment, the refrigerant circuit in  FIG. 4  does not include a bypass for second condenser  14 . Furthermore, receiver  16  is only arranged downstream of second condenser  14 . Electrically driven fan  15  supplies cooling air receiver  16 , but no air is needed nor supplied to a second receiver, such as receiver  9  in the embodiment of  FIG. 1 . 
   By reference to  FIG. 4 , the flow of refrigerant during normal operation will now be described. First compressor  5  supplies refrigerant, which is hot due to compression, through a first condenser  7  that is air-cooled. The open position of second valve  412  and closed position of first valve  410  forces refrigerant through branch  413 . A first fan  8  supplies cooling air to condenser  7  with the aid of the vehicle engine. Cooling also takes place due to relative wind or air flows generated through the movement of the vehicle. Subsequently, the cooled refrigerant flows through second condenser  14 , with electrically driven fan  15  inactive, and through receiver  16 . 
   In stationary operation, electrically driven compressor  6  causes refrigerant to flow through the circuit  4 . Due to the opened first valve  410  and closed second valve  412 , refrigerant flows through the bypass branch  411  and around first condenser  7 . First fan  8  is shut off due to the inactive engine, and therefore supplies no cooling air stream. Refrigerant thereafter flows through second condenser  14  in which the refrigerant is cooled via second fan  15 , which is driven with the aid of the electric power supply. Excess refrigerant accumulates in downstream receiver  16 . Corresponding to normal operation, there is subsequently a distribution of the refrigerant to the two branches  17  and  18 . 
     FIG. 5  illustrates a fifth embodiment in which only one electrically driven compressor  106  circulates refrigerant both in normal operation and, as needed, in stationary operation. This embodiment is thus similar in certain respects to the embodiment of  FIG. 2  in that a single compressor and branch replaces mechanically driven compressor  5  and electrically driven compressor  6 . Likewise,  FIG. 6  illustrates a similar embodiment in which a hybrid compressor  205 / 206 , which can be driven both mechanically by the engine and electrically, replaces the single electrically driven compressor  106  of  FIG. 5 . In regard to normal and standard operation in other respects, the reader is referred to the description of the prior embodiments. 
     FIG. 7  illustrates yet another embodiment. In this embodiment, electrical compressor  106  circulates refrigerant to the two condensers  7  and  14  that are connected to the refrigerant circuit in parallel. A first valve  726  arranged upstream of the first condenser  7  and a second valve  727  arranged upstream of the second condenser permit the selective operation of one or both of condensers  7  and  14 . A receiver  16  is positioned downstream of the junction of parallel branches  728  and  729 . The remaining configuration of refrigerant circuit  4  corresponds to that of the previously described embodiments. 
   In normal operation, the refrigerant in the embodiment illustrated in  FIG. 7  is circulated by electrical compressor  106  and, because of open first valve  726  and closed second valve  727 , it flows through first branch  728 , in which first condenser  7  is arranged. Fan  8 , driven by the running engine, supplies cooling air to condenser  7 , whereas electrically driven fan  15  for second condenser  14  remains inactive. Subsequently the refrigerant flows through a receiver  16 . In stationary operation, first valve  726  is closed and second valve  727  is opened such that refrigerant flows only through second condenser  14 . In this case, electrically driven fan  15  supplies air to flow through the second condenser  14 , while mechanically drivable first fan  8  is inactive. The refrigerant subsequently flows through receiver  16 .  FIG. 8  operates similarly to  FIG. 7 , with the exception of a hybrid compressor  205 / 206  that is provided in place of electrical compressor  106  of the seventh embodiment. 
     FIG. 9  illustrates a ninth embodiment of the invention. As in the first embodiment, a parallel connection of a mechanically driven compressor  5  and an electrically driven compressor  6  is provided in place of electrical compressor  106  of the seventh embodiment. Otherwise, the ninth embodiment agrees with the seventh embodiment. 
   While this invention has been described with an emphasis upon particular embodiments, it should be understood that the foregoing description has been limited to the presently contemplated best modes for practicing the invention. It will be apparent that further modifications may be made to the invention, and that some or all of the advantages of the invention may be obtained. Also, the invention is not intended to require each of the above-described features and aspects or combinations thereof. In many instances, certain features and aspects are not essential for practicing other features and aspects. The invention should only be limited by the appended claims and equivalents thereof, since the claims are intended to cover other variations and modifications even though not within their literal scope.