Patent Publication Number: US-7216609-B2

Title: Motor vehicle cooling system

Description:
BACKGROUND AND SUMMARY 
   The present invention is a continuation of International Application PCT/SE2004/001509, filed Oct. 19, 2004, which claims priority to SE 0302834-7, filed Oct. 19, 2003, both of which are incorporated by reference. 

   The present invention relates to a cooling system for an internal combustion engine mounted in a vehicle, which cooling system comprises a flow circuit with a pump for circulating coolant via ducts in the cylinder block of the engine and a radiator, which flow circuit is separated from atmospheric pressure. 
   In conventional cooling systems for an internal combustion engine mounted in a vehicle, use is made of a relatively large expansion tank as a reserve volume for coolant and in order to compensate for the expansion of the coolant which takes place when it is heated up from cold starting to full operating temperature, around 80–90° C. The expansion tank requires space and encroaches on the cooling area. 
   The development of heavy-duty, turbocharged diesel vehicles, for example trucks, has meant an increasing demand for cooling capacity for oil coolers for engine and gearbox, charge air coolers, coolers for EGR gas and coolers for retarders. Some of these devices, for example charge air coolers, EGR coolers and transmission coolers, often require a lower temperature of the coolant inflow than that required by the internal combustion engine. 
   This demand has usually been met by increasing radiator area and coolant flow. These measures generally mean that the risk of cavitation at the coolant pump increases because the pressure drop in these cooling systems is great. 
   From U.S. Pat. No. 6,532,910, for example, it is known to pressurize a cooling system via the expansion tank by means of positive pressure from the intake side of the engine. The pressure increase means that a higher temperature can be maintained in the cooling system, at the same time as the cavitation risk decreases. One problem with this known solution is that it can take several minutes from the engine being started until the pressure in the cooling system has been built up, if the engine is run at low load. During this period of time, cavitation in the cooling system circulation pump and cylinder liners can lead to local overheating which may involve engine damage. Moreover, the system pressure can disappear in the event of minor valve leakage. 
   It is desirable therefore to produce a cooling system which makes more rapid pressure build-up possible, which can be designed in a space-saving way and with a low pressure drop and which does not lose the system pressure in the event of moderate valve leakage. 
   According to an aspect of the present invention, a cooling system for an internal combustion engine mounted in a vehicle comprises a first flow circuit with a pump for circulating coolant via ducts in a cylinder block of the engine and a radiator, the flow circuit being separated from atmospheric pressure, and a second flow circuit comprising a coolant reservoir with a normal pressure which is lower than a pressure in the first flow circuit, and a pump for circulating coolant via a pipeline between units with a cooling requirement and a second radiator, wherein the second flow circuit is connected to the first flow circuit via a one-way valve opening in a direction of the first flow circuit. 
   This design of the cooling system can allow the two flow circuits to be optimized individually for different tasks/temperature ranges with advantageous flow resistance. The flow circuit operating with a higher temperature range can be designed to be closed to the atmosphere, so that the pressure build-up in this circuit can take place rapidly. Normal pressure means the pressure which normally arises in the second flow circuit when the engine operates. 

   
     BRIEF DESCRIPTION OF FIGURES 
     The invention will be described in greater detail below with reference to illustrative embodiments shown in the accompanying drawings, in which 
       FIG. 1  is a diagrammatic sketch which shows a first flow circuit in a cooling system according to the invention, 
       FIG. 2  shows in a corresponding way a second flow circuit in the cooling system according to the invention, and 
       FIG. 3  shows in a corresponding way the two flow circuits combined so as to show the cooling system according to the invention in its entirety. 
   

   DETAILED DESCRIPTION 
   The cooling system according to the invention will be described in connection with  FIGS. 1 and 2  as two separate flow circuits, which are shown combined in  FIG. 3 . 
   The main task of the first flow circuit shown in  FIG. 1  is to regulate the temperature of an internal combustion engine  10 . For this purpose, the flow circuit comprises a circulation pump  11  which on the pressure side feeds coolant in through ducts in the cylinder block of the engine  10  for cooling cylinder liners and cylinder head. The coolant also passes through an oil cooler  12  and an EGR cooler  13  arranged in conjunction with the cylinder head. 
   The coolant leaves the cylinder head via a thermostat valve  14  which can in a known way conduct the flow either, at low temperature, via a return line  15  directly back to the inlet of the pump  11  or, at higher temperatures, via the pipeline  16  through a radiator  17 . This is connected to the suction side of the pump, which is also connected via a pipeline  18  to a filling/venting vessel  19   a , which is connected to the radiator  17  via a pipeline  19   b  and is provided with a pressure-tolerant filling cover and a pressure control valve  20 . An outlet from this valve  20  is connected to a coolant reservoir  21  shown in  FIGS. 2 and 3 . A pipeline  22   a  extends from a point upstream of the thermostat valve  14 , via a heater  23  for heating the cab of the vehicle, to a point downstream of the radiator  17 . A venting line  22   b  extends from the same part of the circuit to the filling/venting vessel  19   a . A further branch line  24  forms a connection to the second flow circuit, which connection is limited by means of a compression-spring-loaded non-return valve  25 . This first flow circuit is therefore separated from atmospheric pressure by means of the pressure control valve  20  and the non-return valve  25 . 
   The main task of the second flow circuit shown in  FIG. 2  is to regulate the temperature of one or more heat exchanger(s)  26  for charge air and EGR and also for gearbox cooling  27 . For this purpose, the flow circuit comprises a circulation pump  28  which on the pressure side feeds coolant through a pipeline  29 . After passing through the heat exchanger(s) mentioned above, the coolant is cooled by means of a radiator  30  which is positioned upstream of the radiator  17  in relation to an air flow which passes these radiators. A branch line  31  for venting is connected to the pipeline  29  upstream of the radiator  30  and connects the latter to the coolant reservoir  21  via a choke  32 . The branch line  24  is connected to the pipeline  29  of the second flow circuit on the pressure side of the circulation pump  28 . This second flow circuit suitably operates with a lower temperature and a lower pressure than the first flow circuit. 
     FIG. 3  shows the two flow circuits combined to form the cooling system according to the invention. By dividing the cooling system into two separate flow circuits, the pressure drop can be kept low. When the engine is started, the first flow circuit is pressurized with coolant which is fed from the coolant reservoir  21  to the suction side of the circulation pump  11  with the aid of the circulation pump  28  and the branch line  24 . During pressure build-up, venting of the cooling system takes place to the coolant reservoir  21  via the pressure control valve  20  in the first circuit and the choke  32  in the second circuit. On cooling, coolant can be drawn from the tank  21  to the first flow circuit via the non-return valve  25  and the branch line  24 . 
     FIG. 3  shows a variant of the invention where the second flow circuit has been provided with a variable choke  33  downstream of the branch line  24  and upstream of the heat exchanger  27 . This choke  33  can be used actively in order to increase the pressure drop in the second flow circuit momentarily when the engine is started, which speeds up the pressure build-up in the first flow circuit and thus reduces the risk of cavitation damage. Moreover, the choke can be used in order to feed coolant from the second flow circuit (the low temperature circuit) to the first flow circuit (the high temperature circuit) in order to increase the cooling performance momentarily, for example in the case of retarder braking. In this connection, coolant with a lower temperature is fed to the first flow circuit through the non-return valve  25 , and a corresponding quantity of coolant is fed out through the pressure valve  20  to the coolant reservoir  21 . 
   A further variant of the invention is shown in  FIG. 3 . In the event of a large pressure drop over the second flow circuit, the feed pressure from this circuit to the first flow circuit may become too high. In this connection, the feed pressure can be limited by the reducing valve  25 . According to  FIG. 3 , the cooling system has a line with a non-return valve  35  which makes it possible for coolant to flow into the first flow circuit from the coolant reservoir  21  when the cooling system undergoes cooling. 
   In the present application, the use of terms such as “including” is open-ended and is intended to have the same meaning as terms such as “comprising” and not preclude the presence of other structure, material, or acts. Similarly, though the use of terms such as “can” or “may” is intended to be open-ended and to reflect that structure, material, or acts are not necessary, the failure to use such terms is not intended to reflect that structure, material, or acts are essential. To the extent that structure, material, or acts are presently considered to be essential, they are identified as such. 
   The invention is not to be regarded as being limited to the illustrative embodiments described above, but a number of further variants and modifications are conceivable within the scope of the patent claims which follow. For example, the filling/venting vessel  19   a  can be combined with the radiator  17 . The pressure control valve  20  does not have to be integrated with the filling/venting vessel  19   a  but can instead be positioned at the inlet to the coolant reservoir  21  or on the line between the latter and the vessel  19   a . Various components with a cooling requirement, for example an EGR cooler and an oil cooler, can be connected optionally to one or other flow circuit according to requirement and optimization and are therefore not tied to the illustrative embodiment shown.