Abstract:
A cooling circuit, in particular of a motor is provided that includes a drive unit with a cooling circuit, through which coolant heated in the drive unit flows, a first heat exchanger which emits heat from the coolant to the environment and a device for energy recovery with a second heat exchanger, which is switched into the cooling circuit. A line section of the cooling circuit is connectable in parallel to the second heat exchanger that includes a hydraulic element, which guides a defined coolant flow to the second heat exchanger.

Description:
[0001]    This nonprovisional application claims priority under 35 U.S.C. §119(a) to German Patent Application No. DE 10 2011 085 961.6, which was filed in Germany on Nov. 8, 2011, and which is herein incorporated by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The invention relates to a cooling circuit, in particular for a motor. 
         [0004]    2. Description of the Background Art 
         [0005]    An overall efficiency of a motor can be increased considerably by the use of previously unused waste heat. 
         [0006]    A motor with a drive unit and a device for heat recovery is known from DE 10 2008 053 066 A1. The drive unit has a cooling circuit with a first heat exchanger, which emits heat of a coolant flowing through the cooling circuit to the environment. The device for heat recovery comprises an evaporator that is flowed through by a hot exhaust gas flow. The evaporator is flowed through by a working fluid that is brought to evaporation by the heat of the exhaust gas flow. The gaseous working fluid is fed to an expansion device, from which mechanical energy can be removed. The mechanical energy can be fed directly to the drive train again, for example, or by conversion into electric energy can be used to operate ancillary components. The working fluid flowing out of the expansion device is fed to a second heat exchanger operating as a condenser, which cools the working fluid and converts it into a liquid state. The condenser is coupled to a cooling circuit of the drive unit. A pump guides the liquid working fluid to the evaporator again, in which the working fluid evaporates again and the cycle process begins again. The flow rate of the coolant flow through the condenser and the condensation performance associated therewith fluctuates due to rotational speed changes of the drive unit, for example. 
         [0007]    In addition to the embodiment described above, the condenser as is known is also cooled by a separate low-temperature circuit, which, however, requires a high expenditure due to the use of an additional pump, of additional lines and of a further heat exchanger. Furthermore, electrothermal devices for the direct conversion of heat into electric energy are known, which are cooled by an airflow. 
       SUMMARY OF THE INVENTION 
       [0008]    It is therefore an object of the present invention to cool elements of a device for heat recovery via a cooling circuit of the drive unit and to thereby ensure the most constant possible cooling capacity. 
         [0009]    In the case of the cooling circuit according to an embodiment of the invention, the second heat exchanger of the heat recovery device is integrated into the cooling circuit of the drive unit, wherein a line section of the cooling circuit connected in parallel to the second heat exchanger comprises a hydraulic element that guides a defined coolant flow to the second heat exchanger. A reliable cooling of the heat recovery device by the cooling circuit of the drive unit is thus ensured in all operating conditions. Since at the same time the pressure loss is limited by the second heat exchanger, the drive unit is also always flowed through with sufficient coolant. 
         [0010]    In an embodiment of the cooling circuit, the hydraulic element can be embodied as a pressure relief valve. With low pressure of the coolant flow, this flows entirely over the heat exchanger. If the pressure increases beyond a certain value, a partial flow flows past the heat exchanger over the line section of the cooling circuit connected in parallel. In an advantageous manner the pressure relief valve keeps the coolant flow through the heat exchanger largely constant. 
         [0011]    According to a further embodiment, the hydraulic element can be embodied as a throttle valve. The throttle valve is a cost-effective component that ensures a minimum flow rate of coolant through the second heat exchanger and the drive unit. 
         [0012]    In a further embodiment a bypass line can be provided, which, seen in the flow direction of the coolant, branches in front of the first heat exchanger and opens after it, wherein a thermostatic valve is arranged after the first heat exchanger, which thermostatic valve mixes coolant from the bypass line and the first heat exchanger to a temperature that can be determined. In an advantageous manner the arrangement in the cooling circuit makes it possible to feed coolant at a largely constant temperature to elements downstream of the thermostatic valve in a wide operating range. 
         [0013]    In an embodiment, the second heat exchanger can be arranged after the first heat exchanger seen in the flow direction of the coolant. The second heat exchanger is flowed through by coolant in an advantageous manner, which has the lowest temperature in the cooling circuit. In the cold-start phase, heat inserted into the second heat exchanger helps to bring the drive unit quickly to operating temperature. 
         [0014]    According to a further embodiment of the invention, it is provided to arrange the second heat exchanger after the thermostatic valve seen in the flow direction of the coolant. The coolant exiting from the thermostatic valve has a uniformly low temperature level and is particularly suitable for cooling the second heat exchanger. Furthermore, the arrangement has the advantage that in a cold-start phase of the drive unit the coolant heats via the second heat exchanger, whereby the operating temperature can be reached more quickly. Due to the uniform level of the coolant, moreover a marked overcooling in the second heat exchanger is avoided. 
         [0015]    According to a further embodiment, the second heat exchanger can be arranged after the drive unit and before the first heat exchanger seen in the flow direction of the coolant. This arrangement renders possible the supply of the second heat exchanger with a coolant flow of the highest possible temperature. This arrangement is advantageous when the necessary cooling temperature in the second heat exchanger is high or at the level of the temperature of the coolant upon exit from the drive unit. 
         [0016]    In a further embodiment, a further thermostatic valve interacts with the bypass line such that below a temperature that can be determined the predominant proportion of the coolant circumvents the first heat exchanger. A quick heating up of the drive unit can be achieved with this device. 
         [0017]    In a further embodiment a further bypass line can be provided, which branches in the cooling circuit before the first heat exchanger and opens after the second heat exchanger, seen in the flow direction of the coolant. A further thermostatic valve is arranged in the further bypass line. The quantity of heat that is to be dissipated via the second heat exchanger can fluctuate greatly in unsteady vehicle operation. Since the exit temperature of the coolant at the second heat exchanger depends on the quantity of heat to be dissipated, the coolant exit temperature of the drive unit can fluctuate thereby. The arrangement renders possible in an advantageous manner a thermostatic valve-controlled admixture of coolant from the coolant outlet into the coolant inlet of the drive unit, whereby the coolant inlet temperature is to be kept at a largely constant level over a wide operating range. 
         [0018]    According to a further embodiment, the further thermostatic valve holds the main branch through the first heat exchanger partially open. A continuous flow through of the main branch renders possible a mixture of hot and colder coolant in the thermostatic valve so that the coolant temperature after the thermostatic valve is largely constant. For example, a one-plate thermostat with open main branch can be used for the further thermostatic valve. 
         [0019]    In a further embodiment of the invention the further thermostatic valve has a higher switching temperature than the thermostatic valve. The temperature in the thermostatic valve can be adjusted by mixing coolant before the first heat exchanger and coolant after the first heat exchanger. The switching temperature of the thermostatic valve is lower than that of the further thermostatic valve, which determines the maximum temperature in the main branch before the first heat exchanger. The temperature after the thermostatic valve can thus be derived by admixing cooled coolant after the first heat exchanger from the temperature level of the coolant before the first heat exchanger and thus can be adjusted to a constant level over a wide operating range. 
         [0020]    In a further embodiment a pump is arranged directly after the thermostatic valve seen in the flow direction of the coolant. With this arrangement the pump is flowed through by uniformly tempered coolant, whereby a good pump efficiency can be achieved. 
         [0021]    In a further embodiment of the invention, the pump is arranged in the cooling circuit before the drive unit. This arrangement has the advantage that the outlet side of the pump can be connected to the drive unit in a manner optimized in terms of installation space, i.e., without piping. The arrangement of the pump can thereby take place at the inlet or outlet side of the coolant. 
         [0022]    In an embodiment, manner the second heat exchanger is embodied as a condenser of the device for heat recovery. The condenser is cooled by the cooling circuit of the drive unit. A working fluid of a cycle process, for example, of a Clausius Rankine process, condenses through cooling in the condenser. A condensation device of a a cycle process can be operated in an advantaegeous manner without major additional expenditure with the above-described arrangement, which process permanently improves the overall efficiency of a motor. 
         [0023]    Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]    The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus, are not limitive of the present invention, and wherein: 
           [0025]      FIG. 1  illustrates a motor with a cooling circuit and with a drive unit with a device for heat recovery from an exhaust gas flow, 
           [0026]      FIG. 2  illustrates an alternative cooling circuit of the drive unit from  FIG. 1 , 
           [0027]      FIG. 3  illustrates a further alternative of the cooling circuit of the drive unit from  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0028]    Identical components and components with identical action in  FIGS. 1 through 3  are labeled below with the same reference numbers. 
         [0029]    The motor shown in  FIG. 1  comprises a device for heat recovery  10  and a drive unit  2  embodied as an internal combustion engine with an engine block  4 , an exhaust system  6  and a coolant circuit  8 . 
         [0030]    The coolant circuit  8  comprises a first heat exchanger  11 , which is connected via a feed line and return line  12 ,  14  to the engine block  4  of the drive unit  2 . A second heat exchanger  16  operating as a condenser is connected in parallel to a second section  17  of the return line  14 . A pressure relief valve  18  is arranged in the section  17  running parallel to the condenser  16 . 
         [0031]    A bypass line  20  branches out of the feed line  12  before the first heat exchanger  11  and opens before the condenser  16  into a thermostatic valve  21  arranged in the return line  14 . 
         [0032]    A further bypass line  22  likewise branches out of the feed line  12 , it opens into a further thermostatic valve  24  arranged after the condenser  16  in the return line  14 . A pump  26  is arranged between the further thermostatic valve  24  and the engine block  4 . 
         [0033]    The device for heat recovery  10  comprises a closed steam cycle  30  with an evaporator  28 , an expander  32 , the condenser  16  incorporated in the cooling circuit  8  and a further pump  36 . Mechanical work can be removed from the expander  32  on the shaft  34 . 
         [0034]    The function of the motor is described below. 
         [0035]    Hot exhaust gas from the exhaust system  6  flows through the evaporator  28 , which is flowed through by a working fluid conveyed by the further pump  36 . The working fluid of the device for heat recovery  10  evaporates, flows in the steam cycle  30  to the expander  32  and does mechanical work, which can be used via the shaft  34  and a device (not shown) in the drive train of a motor vehicle as propulsive force. In the condenser  16  cooled by the cooling circuit  8  the working fluid liquefies and the further pump  36  guides the working fluid again to the evaporator  28 . 
         [0036]    In the cooling circuit  8  the pump  26  conveys coolant through the engine block  4  and the cooling circuit  8 . In order to achieve the quickest possible warming up of the internal combustion engine  2 , the further thermostatic valve  24  in the further bypass line  22  is largely opened up to a temperature of, for example, 85° C., so that the coolant, circumventing the first heat exchanger  11 , heats up quickly. The further thermostatic valve  24  thereby guides and the bypass line  20  further guides a partial quantity of the coolant flow to the first heat exchanger  11 . The thermostatic valve  21  mixes hot coolant flowing through the bypass line  20  and coolant cooled by the first heat exchanger  11  to a temperature of 70° C., for example. If the temperature of 85° C. is exceeded, the further thermostatic valve  24  closes and the predominant part of the coolant flows to cool the internal combustion engine  2  through the first heat exchanger  11 . Nevertheless, even in this operating state the thermostatic valve  21  mixes hot coolant flowing through the bypass line  20  and coolant cooled by the first heat exchanger  11 . The condenser  16  is thus flowed through over a wide operating range of the internal combustion engine  2  by coolant at a largely constant temperature of 70° C., for example, an overcooling of the working fluid of the device for heat recovery  10  is avoided. 
         [0037]    The tempered coolant flowing out of the thermostatic valve  21  flows into the condenser  16 , wherein, once a pressure that can be determined is exceeded, the pressure relief valve  18  opens and a partial quantity flows over the section  17  of the return line  14  connected in parallel to the condenser  16 . The arrangement secures a largely constant flow through or a minimum flow through of the coolant through the condenser  16  and a constant condensation performance associated therewith. 
         [0038]      FIG. 2  shows an alternative cooling circuit  8  to that shown in  FIG. 1 . The steam cycle, not shown, corresponds to that from  FIG. 1 , the condenser  16  is hereby connected to the steam cycle  30  of the device for heat recovery  10  in the same manner as in  FIG. 1 . 
         [0039]    In the cooling circuit  8  according to the representation in  FIG. 1  the first heat exchanger  1  is connected via the feed line and return line  12 ,  14  to the engine block  4 . The return line  14  is connected in parallel to the condenser  16 . The pressure relief valve  18  is likewise arranged in the section  17  of the return line  14  running parallel to the condenser  16 . The bypass line  20  branches before the first heat exchanger  11  from the feed line  12  and opens after the first heat exchanger  11  via the thermostatic valve  21  into the return line  14 . The further thermostatic valve  24  is here provided in the branch from the feed line  12 . The coolant pump  26  is arranged between the thermostatic valve  21  and the condenser  16 . 
         [0040]    In the warm-up phase of the internal combustion engine  2 , up to a switching temperature that can be predetermined of 95° C., for example, the further thermostatic valve  24  adopts a switching position such that for the rapid heating of the internal combustion engine  2  a main flow of the coolant, largely circumventing the first heat exchanger  11 , flows from the feed line into the return line  12 ,  14  and a partial flow flows via the first heat exchanger  11 . The main flow and partial flow of the coolant is mixed in the thermostatic valve  21 . The thermostatic valve  21  is adjusted, for example, such that from a coolant temperature of approx. 70° C. it mixes cooled coolant from the first heat exchanger  11  with the coolant from the bypass line  20 . 
         [0041]    After the switching temperature of the further thermostatic valve  24  has been exceeded, the preponderant part of the coolant flows via the first heat exchanger  11 . As long as the coolant from the first heat exchanger  11  does not exceed the temperature of 70° C., the thermostatic valve  21  feeds coolant tempered to 70° C. to the pump  26  or to the condenser  16 . The arrangement makes it possible to provide tempered coolant to the condenser  16  and to the pump  26  over a wide operating range. 
         [0042]    The condenser  16  and the pressure relief valve  18  connected in parallel interact in the same way as already described in  FIG. 1 . 
         [0043]    The structure of the cooling circuit  8  from  FIG. 3  corresponds essentially to that of  FIG. 2 . In contrast to  FIG. 2 , the condenser  18  with the pressure relief valve  18  connected in parallel is arranged in the feed line  12  between the internal combustion engine  2  and the first heat exchanger  11 . 
         [0044]    The pump  26  arranged before the engine block  4  in the return line  14  conveys coolant in the cooling circuit  8 . Hot coolant flows out of the internal combustion engine  2  through the condenser  16 . Up to a defined pressure in the feed line  12 , the entire coolant quantity flows through the condenser  16 , when the pressure is exceeded, the pressure relief valve  18  opens and a partial quantity of the coolant flows past the condenser  16  directly to the first heat exchanger  11 . The condenser  16  is thereby flowed through by a largely constant coolant flow at high temperature. A thermostatic valve  21  mixes cooled-down coolant flowing out of the first heat exchanger  11  and uncooled hot coolant flowing via a bypass line  20  to a defined temperature. 
         [0045]    The pump  26  guides the coolant tempered by mixing in the thermostatic valve  21  to the engine block  4  again. A further thermostatic valve  24  guides up to a certain temperature the coolant flow via the bypass line  20  largely past the first heat exchanger  11  so that the internal combustion engine  2  warms up as quickly as possible. According to the embodiment in  FIG. 2 , a partial flow always flows via the first heat exchanger  11 , so that a mixing of coolant of different temperature level is possible in the thermostatic valve and the pump  26  as well s the drive unit are supplied with tempered coolant. 
         [0046]    In further exemplary embodiments, not shown, in  FIG. 1  through  FIG. 3  a throttle valve instead of the pressure relief valve  18  is connected in parallel to the condenser  16 . The throttle valve ensures a fixed division of the coolant flow through the condenser  16  and the bypass line  17  connected in parallel. 
         [0047]    The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are to be included within the scope of the following claims.