Patent Publication Number: US-6668764-B1

Title: Cooling system for a diesel engine

Description:
BACKGROUND OF INVENTION 
     The present invention relates to a cooling system and method for thermal management of an engine in a vehicle, and more particularly to a diesel engine in a vehicle. 
     Conventionally, a cooling system for a diesel engine in a vehicle includes a water pump, for pumping a liquid coolant through the system, a radiator for cooling the coolant, and an oil cooler for cooling oil used by the engine. A fan is also typically provided to draw air through the radiator in order to enhance the cooling effect of the radiator. The coolant is also typically routed through a heater core in order to provide heat for the vehicle passenger compartment, when needed, as well as being routed through an exhaust gas recirculation (EGR) cooler. 
     The water pump and the fan are typically driven off of the engine crankshaft, so their speed is strictly a function of the engine speed. Consequently, when the engine is started cold, a pair of thermostats, one upstream of the radiator and one upstream of the oil cooler, are needed to block the flow through the radiator and oil cooler, respectively, in order to maintain as much heat in the system as possible until the coolant and oil have heated up to their respective operating temperatures. As each comes up to temperature, its thermostat opens and the flow continues strictly as a function of engine speed. But the routing of the coolant and the amount of coolant flow are not a function of any other vehicle or engine parameters that are important to maintaining the desired engine temperature. Moreover, there is a relatively large number of components employed to create this cooling system with limited ability to accurately control the engine temperature. 
     Thus, it is desirable to have a diesel engine cooling system that overcomes the drawbacks of conventional engine cooling systems. In particular, it is desirable to have a system with the ability to more accurately provide the desired engine coolant and oil cooling, while minimizing the number of components required for the system. 
     SUMMARY OF INVENTION 
     In its embodiments, the present invention contemplates a cooling system for a diesel engine, having a coolant inlet and a coolant outlet, in a vehicle. The cooling system has a coolant circuit adapted to operatively engage the coolant inlet and coolant outlet, and a pump operatively engaging the coolant circuit to pump a coolant therethrough. The cooling system also includes a radiator operatively engaging the coolant circuit, an oil cooler operatively engaging the coolant circuit, and a heater operatively engaging the coolant circuit. A valve has a first valve port adapted for receiving coolant from the engine, a second valve port for selectively receiving coolant from the oil cooler, a third valve port for selectively routing coolant to the radiator, and a fourth valve port for selectively routing coolant to the heater, and with the valve being controllable to selectively control the routing of the coolant through the valve ports. The cooling system also has a control module electrically coupled to the valve for electronically controlling the valve to thereby control the routing of the coolant through the valve ports. 
     The present invention further contemplates a method of controlling an engine temperature of a diesel engine in a vehicle, with the diesel engine having a coolant circuit including a water pump, a flow control valve, and a radiator, an oil cooler, and a heater each operatively connected to the flow control valve, the method comprising the steps of: detecting a plurality of operating conditions; determining if the operating conditions are within a first mode, a second mode, a third mode, a fourth mode, a fifth mode, or a sixth mode of operation; adjusting the flow control valve to substantially prevent routing of coolant through the radiator and allow for routing of coolant through the heater and the oil cooler if the operating conditions are in the first mode; adjusting the flow control valve to substantially prevent routing of coolant through the radiator and the oil cooler and allow for routing of coolant through the heater if the operating conditions are in the second mode; adjusting the flow control valve to allow for routing of coolant through the radiator, the heater and the oil cooler if the operating conditions are in the third mode; adjusting the flow control valve to substantially prevent routing of coolant through the heater and allow for routing of coolant through the radiator and the oil cooler if the operating conditions are in the fourth mode; adjusting the flow control valve to substantially prevent routing of coolant through the radiator and the heater and allow for routing of coolant through the oil cooler if the operating conditions are in the fifth mode; and adjusting the flow control valve to substantially prevent routing of coolant through the radiator, the heater and the oil cooler if the operating conditions are in the sixth mode. 
     An advantage of the present invention is that there is a smaller number of components used in the diesel engine cooling system as compared to a conventional system. A single valve selectively controls the amount of coolant flow if any through the radiator, oil cooler and other heat exchangers. 
     Another advantage of the present invention is that the amount of coolant flowing through the radiator can be more precisely controlled, thus allowing for more accurate control of the coolant temperature, and hence, engine temperature. 
     A further advantage of the present invention is that the amount of coolant provided to the oil cooler can be controlled, thus allowing for more accurate control of the oil temperature. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a schematic drawing of a diesel engine and engine cooling system in accordance with the present invention; 
     FIG. 2 is a table illustrating operating conditions and corresponding opening/closing of different valve ports that occur after engine warm-up; 
     FIG. 3 is a table illustrating operating conditions and corresponding opening/closing of different valve ports that occur during engine warm-up; 
     FIG. 4 is a table illustrating coolant flow paths for six modes of valve operation; and 
     FIG. 5 is a graphic illustration of the valve port opening characteristics and order of the valve modes for a multi-port valve employed in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 illustrates a diesel engine  10  connected to an engine cooling circuit  12 . The engine  10  includes a coolant inlet  14  and a coolant outlet  16 . The coolant flow paths are illustrated in FIG. 1 with thick lines, and arrow heads indicating the direction of coolant flow in the lines. The coolant outlet  16  connects to a first inlet  18  on a multi-port valve  20 , and to an exhaust gas recirculation (EGR) cooler inlet  22  on an EGR cooler  24 . A first outlet  26  from the valve  20  leads to an inlet  28  on an auxiliary heater  30 , which has an outlet  32  that leads to an inlet  34  on a heater  36 , which, in turn, has an outlet  38  that leads to an inlet  40  on a water pump  42 . An outlet  44  of the water pump  42  then connects to the coolant inlet  14  of the engine  10 . The outlet  44  of the water pump  42  also connects to an inlet  46  of an oil cooler  48 . The oil cooler  48  includes an outlet  50  that connects to a second inlet  52  on the valve  20 . The multi-port valve  20  also has a second outlet  54  that leads to both an inlet  56  on a degas bottle  58  and an inlet  60  on a radiator  62 . An outlet  64  on the degas bottle  58  and an outlet  66  on the radiator  62  connect to the inlet  40  to the water pump  42 . 
     An electric motor  70  is connected to and drives an input shaft  72  of an engine fan  74 . This motor  70  is electrically connected to and driven by a control module  76 . The electrical connections between components are illustrated in FIG. 1 by dashed lines. The Control module  76  also electrically connects to and controls the position of the valve  20 . A second electric motor  78  connects to an input shaft  80  of the water pump  42 . This second motor  78  is also electrically connected to and driven by the control module  76 . The control module  76  is electrically connected to the cooling circuit  12  and engine  10  in order to monitor and control the engine cooling process. The control module  76  communicates with various subsystems and sensors on the engine  10  through various electrical connections  82 , such as an ambient temperature sensor  84 , a coolant temperature sensor  86 , an engine speed monitor  88 , and an engine load demand monitor  90 . While the engine fan  74  and the water pump  42  are illustrated as being driven by electric motors, either one or both may also be driven in a more conventional fashion, such as a pulley and belt assembly or a gear set connected to the engine crankshaft. 
     FIGS. 2-3 illustrate the operation logic of the system of FIG.  1 . For FIGS. 2 and 3, the term “cold” in the table for the coolant indicates a temperature that is below the desired operating level, while “hot” indicates a coolant temperature that is above the desired operating level. The term “cold” for ambient air temperature means a temperature that is below the vehicle occupant&#39;s set temperature, and the term “hot” means a temperature that is above the occupant&#39;s set temperature. The term “low” for engine speed indicates an engine speed (typically measured in revolutions per minute (RPM)) that is less than a predetermined engine speed, while the term “high” for engine speed indicates an engine speed that is greater than this predetermined engine speed. The term “low” for engine load indicates an engine load demand (typically measured by the throttle position) that is less than a predetermined engine load demand, while the term “high” for engine load indicates an engine load demand that is greater than this predetermined engine load demand. The particular predetermined engine speed threshold and predetermined engine load threshold may be different depending upon the particular engine/vehicle combination being employed. 
     The operating conditions—ambient temperature, coolant temperature, engine speed, and engine load—can all be determined by sensors on or associated with the engine  10  and communicated to the control module  76 . The control module  76  will then use the particular operating conditions to determine the valve position needed for the desired coolant flow through the various components. The control module  76  communicates with the valve  20  to cause it to move to the desired position. 
     The component flows are illustrated in FIG. 2 that correspond to the operating conditions. While the component flows shown in the tables of FIGS. 2 and 3 are shown as two state—either on or off—the valve  20  can of course be adjusted to allow for partial flows. So the term “off” means little or no coolant flow through that particular component, while the term “on” means the valve is mostly or fully open to allow coolant flow through that particular component. 
     The multi-port valve preferably has six modes—that is, six different positions that will control whether the coolant flows to the radiator, heater and/or oil cooler. FIG. 4 shows the coolant flow paths for the six modes. By having these six modes, the control module  76  can transition from the current mode to a new desired mode, when one or more of the operating conditions changes. Mode  1  represents a valve position where coolant will generally flow through the heater  36  and oil cooler  48 , but not the radiator  62 . Mode  2  represents a valve position where coolant will generally flow through the heater  36 , but not through the radiator  62  or oil cooler  48 . Mode  3  represents a valve position where coolant will generally flow through the heater  36 , oil cooler  48  and the radiator  62 . Mode  4  represents a valve position where coolant will generally flow through the radiator  62  and the oil cooler  48 , but not the heater  36 . Mode  5  represents a valve position where coolant will generally flow through the oil cooler  48 , but not the radiator  62  or the heater  36 . And finally, mode  6  represents a valve position where coolant will generally be blocked from flowing through the radiator  62 , the heater  36 , and the oil cooler  48 . 
     FIG. 5 is a graph illustrating the preferred arrangement of the valve modes about the valve  20  in order to smoothly transition from one mode to other modes, depending upon changing engine operating conditions. The amount of valve opening for coolant flow to a particular component is illustrated on the vertical axis while the valve angle is illustrated on the horizontal axis. Also, the particular mode that the valve  20  is in based upon the valve angle is noted on the horizontal axis as well. Line  94  represents the valve opening to the second valve outlet (see FIG. 1) for coolant flow through the radiator  62 , line  96  represents the valve opening to the second valve inlet  52  for coolant flow through the oil cooler  48 , and line  98  represents the valve opening to the first valve outlet  26  for coolant flow through the heater  36 . 
     FIG. 2 illustrates the operational logic of the engine cooling circuit  12  after the diesel engine  10  is warmed up. For most of the  8  different combinations of operating conditions shown, there is one valve mode (and hence the coolant routing) corresponding to the particular set of operating conditions. But for two sets of operating conditions, there are two valve modes each. For the operating condition where the ambient and coolant temperatures are cold, while the engine speed and load are low, the initial preferred valve position is mode  2  since the radiator is not needed to draw heat from the coolant, but the heater is needed to heat the passenger compartment. In this initial mode, the oil cooler is off, but after a preset time or when the oil reaches a predetermined temperature, the control module  76  will signal the valve  20  to switch into a mode  1  position, which will allow for coolant flow through the oil cooler  48  while still blocking flow through the radiator  62 . Also, for the operating condition where the ambient temperature is cold, the coolant temperature is hot, and the engine speed and load are low, the initial preferred valve position is mode  3 , so that the coolant will flow through the radiator to be cooled. But with a cold ambient temperature and if the engine speed and load remain low, it may be that the coolant temperature drops sufficiently that the coolant will not need to be cooled further by the radiator. The control module  76  will then signal the valve  20  to switch to mode  1 , which will block flow through the radiator. As stated above, the valve can also be moved within a mode to increase or decrease slightly the flow through a particular coolant circuit element in order to more precisely manage the thermal characteristics of the engine. 
     Moreover, in addition to the control module  76  adjusting the valve  20 , the control module may also vary the speed of the water pump  42  and the engine fan  70  (if equipped with other than conventional crankshaft driven components) in order to more precisely manage the thermal characteristics of the diesel engine operation. 
     FIG. 3 illustrates the operational logic of the engine cooling circuit  12  before the engine has warmed up. In this table the operating conditions where oil warming may be needed are considered. Under these operating conditions, when oil warming is needed, the valve  20  is set to a mode where there will be coolant flow through the oil cooler  48 , but not flow through the radiator  62 . While if no oil warming is needed, then the coolant flow is blocked through both the radiator  62  and the oil cooler  48 . 
     While certain embodiments of the present invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention as defined by the following claims.