Patent Publication Number: US-2016230643-A1

Title: Engine cooling system

Description:
TECHNICAL FIELD 
     The present invention relates to an engine cooling system, and more specifically relates to an engine cooling system including a Rankine cycle with an improved performance while suppressing an increase in vehicle weight caused by employing the Rankine cycle. 
     BACKGROUND ART 
     Conventionally, there has been a proposal to employ a Rankine cycle in a vehicle in order to recover waste heat from an engine and thereby improve the fuel economy, as described in, for example, Japanese patent application Kokai publication No. 11-51582 (Patent Literature 1). For example, engine-main-body cooling water heated by an engine main body is used as a heating source of a Rankine cycle while intercooler cooling water cooled by a sub-radiator is used as a cooling source, so that a temperature difference between these flows of cooling water can be recovered as a power energy in a compressor (turbine). 
     However, when such a Rankine cycle is employed on a vehicle, the vehicle weight is increased. This may counterbalance the effect of improving the fuel economy. 
     Moreover, since the temperature of the engine-main-body cooling water is merely around 100° C., it is only possible to obtain a relatively small temperature difference between the flows of cooling water. Hence, it is difficult to have the Rankine cycle exhibit a sufficient performance to further improve the fuel economy. 
     PRIOR ART DOCUMENT 
     Patent Document 
     Patent Document 1: Japanese patent application Kokai publication No. 11-51582 
     SUMMARY OF THE INVENTION 
     Problem to be Solved by the Invention 
     An object of the present invention is to provide an engine cooling system capable of suppressing an increase in vehicle weight caused by employing a Rankine cycle and capable of improving the Rankine cycle performance. 
     Means for Solving the Problem 
     In order to achieve the above object, an engine cooling system of the present invention is an engine cooling system including: a Rankine cycle configured such that a coolant circulates through a cooling pump, an evaporator, an expander, and a condenser in this order; an engine main body in which a supercharger is arranged in an intake passage; and a radiator through which cooling water for the engine main body circulates. The engine cooling system is characterized in that a sub-radiator is installed parallel to the radiator, compressed air compressed by the supercharger is used as a heating source for the evaporator, and outlet-side cooling water of the sub-radiator is used as a cooling source for the condenser. 
     Effects of the Invention 
     According to the engine cooling system of the present invention, the heating source used for the evaporator in the Rankine cycle is compressed air having a higher temperature than that of conventional engine-main-body cooling water. This makes it possible to improve the performance of the Rankine cycle, thereby improving the fuel economy. 
     Moreover, since compressed air is cooled using the evaporator of the Rankine cycle, this eliminates the need for an existing intercooler. Hence, it is possible to suppress an increase in vehicle weight. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         FIG. 1  is a configuration diagram of an engine cooling system according to an embodiment of the present invention. 
     
    
    
     MODES FOR CARRYING OUT THE INVENTION 
     Hereinafter an embodiment of the present invention will be described with reference to the drawing.  FIG. 1  shows an engine cooling system according to the embodiment of the present invention. 
     This engine cooling system includes a sub-radiator  2  and a radiator  3  disposed in this order from a front surface of a vehicle  1 . The sub-radiator  2  and the radiator  3  are configured to perform air-cooling by utilizing vehicle-speed wind and cooling wind of a cooling fan (not shown) when the vehicle  1  is running or idling. 
     In a diesel engine  4 , which is a cooling target of the engine cooling system, air A is drawn to an intake passage  5 , passes through an air cleaner not shown, and is compressed by a compressor  7  of a turbocharger  6 . Then, compressed air  8  thus obtained is supplied to an engine main body  10  via an intake manifold  9 . 
     The compressed air  8  supplied to the engine main body  10  is mixed with a fuel and burned, thereby generating a thermal energy. Then, a burned gas  11  thus obtained is discharged from an exhaust manifold  12  to an exhaust passage  13 . Some of the burned gas  11  is diverted as an EGR gas  15  into an EGR passage  14 , which is located in front of the intake manifold  9  and connected to the intake passage  5 . To the EGR passage  14 , a water-cooled EGR cooler  16  and an EGR valve  17  configured to adjust a flow amount of the EGR gas  15  are disposed in this order from the exhaust passage  13  side. 
     Flow amounts of engine-main-body cooling water  18  for cooling the engine main body  10  and EGR-cooler cooling water  19  used for cooling in the EGR cooler  15  are regulated by a thermostat  20 . The engine-main-body cooling water  10  and the EGR-cooler cooling water  19  are forced to circulate between the radiator  3  and corresponding one of the engine main body  10  and the EGR cooler  15  by the water pump  13 . 
     On the other hand, cooling water  22  diverted from the thermostat  19  during warming-up time of the engine main body  10  circulates without passing through the radiator  3 . Note that some of the engine-main-body cooling water  18  normally flows as the EGR-cooler cooling water  19 . 
     A portion of the burned gas  11  which is not diverted to the EGR passage  15  is released as an exhaust gas G into the atmosphere after an exhaust gas purification device  24  including DPF, SCR, and the like purifies harmful substances by driving the rotation of a turbine  23  of the turbocharger  6 . 
     The engine cooling system as described above is provided with a Rankine cycle  31  configured such that a coolant  30  circulates through a cooling pump  25 , an evaporator  26 , an expander  28  linked to an electric power generator  27 , and a condenser  29  in this order. 
     A cooling side of the condenser  29  in this Rankine cycle  31  links an inlet side of the water pump  21  to an outlet side of the sub-radiator  2 . Outlet-side cooling water  32  of the sub-radiator  2  (some of the engine-main-body cooling water  18  and the EGR-cooler cooling water  19  after cooling) flows into the cooling side. 
     Moreover, a heating side of the evaporator  26  of the Rankine cycle  31  is arranged in the intake passage  5  between the compressor  7  and the EGR passage  14 . The compressed air  8  compressed to high temperature (for example, approximately 160° C.) by the compressor  7  flows to the heating side. 
     The coolant  30  which circulates through the Rankine cycle  31  is compressed by the cooling pump  25 , and heated at a constant pressure by the high-temperature compressed air  8  in the evaporator  26 , so that the coolant  30  is turned into an over-heated vapor at high pressure. While the coolant  30  is subjected to an adiabatic expansion in the expander  28 , an electric power is generated by driving the rotation of the electric power generator  27 . Then, the coolant  30  is cooled at a constant pressure by the outlet-side cooling water  32  of the sub-radiator  2  in the condenser  29 , and is returned to a liquid. The electric power generated by the electric power generator  27  is charged in a battery (not shown) and serves as a power source for electronic parts of the vehicle  1 . 
     As described above, unlike a conventional case, the engine-main-body cooling water  18  is not used as the heating source for the evaporator  26  in the Rankine cycle  31 , but the compressed air  8  having a higher temperature is used instead. This makes it possible to improve the power recovering performance of the Rankine cycle  31 , thereby improving the fuel economy. 
     For example, the power generation by an alternator is reduced because of an increased amount of electric power generated in the electric power generator  27  whose rotation is driven by the expander  28  in the Rankine cycle  31 . Thus, a load to the engine main body  10  is reduced, improving the fuel economy. 
     Moreover, since the compressed air  8  is cooled using the evaporator  26  of the Rankine cycle  31 , this eliminates the need for an existing intercooler. Hence, it is possible to suppress an increase in vehicle weight. 
     Note that it is needless to say that the cooling target of the engine cooling system of the present invention is not limited to the diesel engine  4  as described above, and includes a gasoline engine, as well. 
     EXPLANATION OF REFERENCE NUMERALS 
     
         
           1  vehicle 
           2  sub-radiator 
           3  radiator 
           4  diesel engine 
           8  compressed air 
           10  engine main body 
           18  engine-main-body cooling water 
           25  cooling pump 
           26  evaporator 
           27  electric power generator 
           28  expander 
           29  condenser 
           30  coolant 
           31  Rankine cycle 
           32  outlet-side cooling water (of sub-radiator)