Abstract:
The invention relates to a cooling strategy for an internal combustion engine ( 1 ) which has at least one cylinder head ( 2 ) and an associated cylinder block ( 3 ). A coolant flows in a coolant circuit ( 4 ), with at least one control element ( 6, 7, 8, 9 ) being assigned to the coolant circuit ( 4 ). During a warmup of the internal combustion engine, in successive phases, the coolant flow is conducted to separate cooling regions by the control elements ( 6, 7, 8, 9 ), wherein in an operating mode at operating temperature which follows the warmup, the coolant flow is conducted to separate cooling regions by the control elements ( 6, 7, 8, 9 ) taking into consideration the operating states of the internal combustion engine.

Description:
FIELD OF THE INVENTION 
   The invention relates to a cooling strategy for an internal combustion engine which has at least one cylinder head and an associated cylinder block, with a coolant flowing in a coolant circuit, and with at least one thermostat in the coolant circuit. 
   BACKGROUND OF THE INVENTION 
   EP 1 375 857 A discloses a cooling system for an internal combustion engine having a plurality of cooling cells in a cylinder head. The cooling cells are separated from one another. The cooling system also includes at least first and second control elements for regulating the throughflow quantity. The control elements are capable of regulating the quantity of cooling liquid which flows in through the first and second cooling cells. 
   It is known for the engine block and the cylinder head of the internal combustion engine to be traversed by a coolant of a coolant circuit separately from one another. In this way, it is possible for the cylinder head and the block to be cooled differently. By a split cooling circuit, during warmup, the cylinder is cooled and the block is not so that it comes to a suitable operating temperature more quickly. 
   SUMMARY OF THE INVENTION 
   A cooling system for an internal combustion engine with coolant flowing in a coolant circuit  4  is disclosed in which the engine has a cylinder head  2  and an associated cylinder block  3  with a block cooling jacket  12 . The cooling system has a pump  21  disposed in the coolant circuit  4  upstream of the internal combustion engine. There are an exhaust cooling jacket  13  and an intake cooling jacket  16  disposed in the cylinder head  2  with the exhaust and intake cooling jackets being separated. A heater is disposed in the coolant circuit  4  upstream of pump  21 . A first valve  6  is disposed in the coolant circuit  4  located between the exhaust cooling jacket  13  and the heater  17 . Coolant flows from the exhaust cooling jacket  13  to the heater when first valve  6  is open and is substantially prevents flow when the first valve  6  is closed. A second valve  7  is disposed in the coolant circuit  4  connected to receive coolant from the first valve  6  and from the intake cooling jacket  16 . When the second valve  7  is closed, flow from the intake cooling jacket  16  is prevented. A third valve  8  is disposed in the coolant circuit  4  connected to receive coolant from the second valve  7  and from the block cooling jacket  12 . When the third valve  8  is closed, flow from the block cooling jacket  12  is prevented. A fourth valve  9  is disposed in the coolant circuit  4  connected to receive coolant from the third valve  8 . A radiator  19  having a line connected to an upstream side of said pump and a line connected to said fourth valve  9  is disposed in the coolant circuit  4 . When the fourth valve is in a closed position, flow to the radiator  19  ceases. 
   In one embodiment, the first, second, and third valves are mechanical thermostats. Alternatively, the first thermostat is electrically actuated. 
   An opening temperature of the first valve  6  is lower than an opening temperature of the third valve  8 . An opening temperature of the third valve  8  is lower than an opening temperature of the second valve  7 . 
   The first valve  6  is actuated to open based on an exhaust temperature exceeding a predetermined threshold. In one embodiment that exhaust temperature is an estimate of catalytic converter temperature. 
   The engine has a coolant distributor  11 , which receives coolant flow from the pump  21  and connects to the exhaust cooling jacket  13 , the intake cooling jacket  16 , and the block cooling jacket  12 . 
   Also disclosed is a method of providing a cooling system and coolant circuit  4  for an internal combustion engine. A pump  21  is in the coolant circuit  4  upstream of the internal combustion engine. The cylinder head is provided with separated exhaust  13  and intake  16  cooling jackets. A heater, air-to-coolant heat exchanger for warming up a vehicle cabin, is disposed in the coolant circuit  4  upstream of the pump  21 . Also provided are a first valve  6 , a second valve  7 , and a third valve  8  in the coolant circuit  4 . The first valve  6  is disposed in the coolant circuit  4  between the exhaust cooling jacket  13  and the heater  17 . When the first valve is open, coolant flows from the exhaust cooling jacket  13  to the heater and flow is substantially stopped when first valve  6  is closed. The second valve  7  is disposed in the coolant circuit  4  connected to receive coolant from the first valve  6  and from the intake cooling jacket  16 . When the second valve  7  is closed, flow from the intake cooling jacket  16  ceases. The third valve  8  is disposed in the coolant circuit  4  connected to receive coolant from the second valve  7  and from the block cooling jacket  12 . When the third valve  8  is closed, flow from the block cooling jacket  12  ceases. 
   The first valve  6  is, in one embodiment, electronically actuated based on an estimate of exhaust temperature. It is caused to open when the exhaust temperature exceeds a threshold. The exhaust temperature can be a catalytic converter temperature. 
   A fourth valve  9  is disposed in the coolant circuit  4  connected to receive coolant from the third valve  8 . Also, a radiator  19  having a line connected to an upstream side of the pump  21  and to the fourth valve  9  is provided. When the fourth valve is in a closed position, flow to radiator  19  ceases. In one embodiment, the second, third, and fourth valves  7 ,  8 ,  9  are mechanical thermostats and an opening preset temperature of the fourth valve  9  is higher than opening present temperatures of the second and third valves  7 ,  8 . 
   The invention is based on the knowledge that cooling water jackets have the main function of dissipating the heat generated as a result of the combustion, wherein the cooling water jackets should be designed such that the temperature distribution is homogeneous. It is therefore predominantly provided that the cooling water jacket is designed for full-load operation, in which a maximum temperature is generated. However, by the invention, which provides integrated engine cooling management or a cooling strategy, it is possible to obtain both the advantages of good oil warm-up, exhaust gas warm-up, engine warm-up and passenger compartment warm-up already in the warm-running phase of the internal combustion engine, and also good cooling of the engine at operating temperature. 
   It is therefore advantageously provided that, in a first phase of warmup, the coolant has a flow value of zero, with the corresponding, first control element (valve  6 ) being closed. The control element can for example be an electromechanical valve or electrically-heated thermostat controlled based on exhaust gas temperature. Directly after the internal combustion engine is started, the exhaust gas temperature has not yet reached the desired temperature value, so that the valve is initially closed, preferably for a number of seconds, so that a coolant flow is initially interrupted. In first phase of warmup, this leads to significantly improved catalytic converter warm-up and also to a faster structure warm-up and, therefore, oil warmup. The desired temperature on which to base opening temperature can be operating temperature of the catalytic converter, and can have, in one example, a value of about 500° C. (catalytic converter lightoff temperature) of the exhaust gas temperature. 
   Once the exhaust gas temperature has reached the lightoff temperature of the catalytic converter, the firat valve  6  opens, as the second phase of warmup begins. The exhaust ducts and exhaust gas manifold are provided coolant, so that coolant flows through an exhaust gas side of the cylinder head to a heater  17 . In this way, the thermally highly loaded regions of the internal combustion engine, in particular the exhaust gas side, are cooled, with the coolant absorbing the generated heat and the coolant then flowing into the heater  17 , so that the passenger compartment can be warmed up more quickly by the heater  17  as a result of the lower thermal masses. 
   It is also provided within the context of the invention that, in a third phase of the warmup, the exhaust ports and exhaust gas manifold and the cylinder block are cooled, with the exhaust gas control element or the valve  8 , or a block thermostat, being opened, so that the coolant flows through the exhaust gas side  13  of the cylinder head and the cylinder block  12  to the heater. It is provided, in a fourth phase of the warm-up, that the entire internal combustion engine is cooled, with the exhaust gas control element or valve  7 , a second control element or a thermostat, and the third control element (valve  8 ) or the block thermostat, being opened, so that the coolant flows through an exhaust gas side of the cylinder head and through the inlet side of the latter and also through the cylinder block to the heater. 
   When the engine is at operating temperature (phase  5 ), it is provided that, in addition to the coolant flow through the heater  17  described in phase  4 , the coolant flows through a radiator  19  and an overflow tank  18 . For this purpose, it is possible to provide a conventional thermostat or a characteristic-map-controlled valve (characteristic map thermostat) as a fourth control element (valve  9 ). 
   The four control elements specified by way of example are preferably arranged in series, with successive control elements being connected to one another by means of connecting lines. 
   After the internal combustion engine has reached its operating temperature, it is advantageously provided that different cooling strategies can be used depending on the operating state of the internal combustion engine. It is favorably provided, in a part-load operating mode of the internal combustion engine, that the outlet side of the cylinder head and the cylinder block are cooled, with the coolant flowing through the exhaust gas side of the cylinder head and through the cylinder block to the heating heat exchanger. In a full-load operating mode of the internal combustion engine, it is advantageously provided that the entire internal combustion engine is cooled, with the coolant flowing through the exhaust gas side of the cylinder head and through the inlet side of the latter and also through the cylinder block to the heating heat exchanger, to the radiator and also to a compensating tank. 
   As already stated above, in the first phase of warmup, the exhaust gas control element is preferably controlled by the exhaust gas temperature. Here, the valve (valve  6 ) preferably opens when an operating temperature of the catalytic converter is reached, which can be the case already after a few seconds after the internal combustion engine is started. From the second phase of warmup, the corresponding control elements are controlled by the coolant temperature, as a result of which the corresponding control elements are designed as a thermostat, preferably as a single-acting thermostat. To actuate the respective control element or thermostat, the coolant temperature is preferably less than 50° C. in the second phase, wherein the coolant temperature can have a value between 50 and 80° C. in the third phase, and wherein a coolant temperature of between 80 and 110° C. can be present in the fourth phase. In the fifth phase which follows the fourth phase of warmup, the engine has reached its operating temperature. The coolant temperature is regulated between 80° C. (full load) and 110° C. (part load) as a function of the engine operating point. The temperatures or temperature ranges which are specified are of course not intended to be limiting, but are provided for purposes of illustration. 
   To carry out the method according to an aspect of the present invention, one control element is assigned to an exhaust gas side of the cylinder head, to an inlet side of the cylinder head and to the cylinder block, with it being possible for a further control element or thermostat to be controlled by a characteristic map (characteristic map thermostat), with the control elements being separately actuable, so that in a warmup phase of the internal combustion engine and in a following operating mode at operating temperature, separately selectable cooling regions can be traversed by the coolant. 
   It is favorable, within the context of the invention, if the coolant circuit has a cylinder block water jacket and a cylinder head water jacket which is divided into an inlet-side water jacket and an exhaust-gas-side water jacket, a so-called “split cooling system” (split cooling circuit, cylinder head), with it being possible for a coolant distributor to be assigned to the coolant circuit. 
   Provided overall, therefore, is an integrated and flexible heat management system for an internal combustion engine, in which a energy is transferred from a source to a sink within the engine and the motor vehicle, or any other application, as a function of the operating states of the internal combustion engine and the respective demands of the vehicle occupants. This advantageously provides for avoiding heat transfer in specific regions as long as the internal combustion engine is cold. This corresponds for example to the first phase of the warm-running phase of the internal combustion engine, in which no coolant flows. At the same time, it is advantageously obtained that a heat flow directly into the passenger compartment is obtained as quickly and effectively as possible. The cooling regions can of course themselves be divided up, with in particular the “split cooling system” (split cooling circuit, cylinder head) being considered here. 
   A faster warm-up of the internal combustion engine is advantageously obtained by the strategy according to the invention and the special design of the internal combustion engine, with harmful emissions to the environment being simultaneously reduced. In addition, friction losses are minimized because the engine oil is brought to its operating temperature more rapidly, and fuel consumption is therefore improved. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIGS. 1-5  show a schematic of a thermal management system of an internal combustion engine, at a range of phases during warmup; and 
       FIG. 6  is a table identifying the features of the phases. 
   

   In the figures, identical parts are provided with the same reference symbols, and parts are generally also described only once. 
   DETAILED DESCRIPTION 
     FIGS. 1-5  show a cooling system for an internal combustion engine  1  which has at least one cylinder head  2  and an associated cylinder block  3 . A coolant flows in a coolant circuit  4  having four control elements  6 ,  7 ,  8 , and  9 . 
   The internal combustion engine  1  has a coolant distributor  11  supplying a cylinder block water jacket  12  and a cylinder head water jacket which is divided into an exhaust gas side  13  and an inlet side  16 . 
   The coolant circuit  4  also has a heater  17  (e.g., an air to coolant heat exchanger used for heating the vehicle cabin, the large arrow above  41  an below  40  heater  17  indicating air flow across heater  17 ), an overflow reservoir  18 , a radiator  19  and a pump  21 . Radiator  19  is an air to coolant heat exchanger with the large arrows shown above  43  and below  42  radiator  19  indicating air flow across radiator  19 . In  FIG. 5 , the piping and connections between the various elements are shown; while, in  FIGS. 1-4 , much of it is not shown to aid in simplifying the discussion of those phases of operation. Of course, the piping and connections exist in all configurations whether or not there is flow through the various regions of coolant circuit  4 . 
   The exhaust gas side  13  of the cylinder head water jacket is coupled to a first control element  6 . The inlet side  16  of cylinder head water jacket  13  is coupled to a second control element  7 . The cylinder block water jacket  12  is coupled to a third control element which is embodied as a thermostat (block thermostat). In addition, fourth control element, valve  9 , control element is arranged in the internal combustion engine  1 . Control elements  7 ,  8 , and  9  may alternatively be electrically operable valves or thermostats. 
     FIG. 1  illustrates the condition in the coolant circuit  4  just after startup of a cold engine (phase  1 ). All control elements  6 ,  7 ,  8 , and  9  are closed, so that no coolant flows in coolant circuit  4 . In one embodiment, opening of valve  6  is based on exhaust gas temperature. Faster warm-up of a catalytic converter and engine oil is obtained by interrupting flow in the coolant circulation. The interruption in the coolant flow in coolant circuit  4  is illustrated by the connecting lines being elements shown as dashed lines; the coolant flow is substantially zero. 
   Although engine oil and the engine structure are rapidly warmed up during phase  1  ( FIG. 1 ), there is no flow to the heater  17 . Thus, there is no appreciable warming of the passenger compartment. 
   Once the exhaust gas temperature reaches, for example, the operating temperature of the catalytic converter, valve  6  opens, as illustrated in  FIG. 2 , (phase  2 ). The coolant flows through the exhaust gas side  13  of the cylinder head water jacket to the heater  17 . In this second phase, the exhaust ports and exhaust manifold are provided coolant through their coolant jacket. As illustrated in  FIG. 2 , valve  6  is connected to thermostat  7  via a connecting line  22 , with thermostat  7  connected by a connecting line  23  to block thermostat  8 , which is connected by a connecting line  24  to valve  9  (characteristic map thermostat). Valve  9  is connected by connecting line  26  to heater  17 , which is connected to line  27  to pump  21 , which transports the coolant via connecting line  28  to the coolant distributor  11 . The exhaust gas side  13  of the cylinder head water jacket is connected by line  29  to valve  6 . 
   In the second phase of the warmup, coolant is provided to the exhaust ports and exhaust manifold. The coolant flows through heater  17  to heat the passenger cabin. Because the exhaust ports and the exhaust side of the cylinder head tend to operate at a higher temperature than other components, by transported coolant from the exhaust into heater  17 , the cabin of the vehicle is rapidly heated. 
     FIG. 3  illustrates a third phase of the warmup, with valve  6  and block thermostat  8  both open so that coolant flows through the exhaust gas side  13  of the cylinder head and through the cylinder block  3  or through the cylinder head water jacket to the heater  17 . The cylinder block water jacket  12 , connected by line  31  directly to block thermostat  8 , is provided coolant flow in this configuration. Hereby, the thermally critical regions are cooled, with the transport of energy into the coolant taking place precisely where heat is generated. The two cooling regions, exhaust gas side  13  and cylinder block water jacket  12 , are connected in parallel. 
     FIG. 4  illustrates a fourth phase of the warmup, in which the entire internal combustion engine  1  is cooled. Valves  6 ,  7 , and  8  are open so that coolant flows through the exhaust gas side  13  and the intake side  16  of the cylinder head water jacket and through the cylinder block water jacket  12  to heater  17  (valve  9  remains closed). The intake side  16  of the cylinder head water jacket is connected by line  32  to thermostat  7 . 
   In the fourth phase, a homogenization of the engine temperature distribution is obtained, with low thermal losses in the combustion chamber being obtained. At the same time, an increased transfer of energy into the oil is obtained on account of the higher temperature level. The three cooling regions, exhaust gas side  13 , intake side  16 , and cylinder block water jacket  12 , are connected in parallel. 
   In a fifth phase, the engine is at operating temperature. Valves  6 ,  7 ,  8 , and  9  are open, valve  9  allowing flow to radiator  29  via line  33  with return flow to line  27 , which is the input to pump  21 , provided by line  34 . It is additionally provided that the coolant flows to overflow reservoir  18  which, in one embodiment, connects to valve  9  via line  36 . Overflow reservoir  18  returns to line  27  via line  37 . 
     FIG. 5  illustrates the cooling strategy for the internal combustion engine  1  at operating temperature under full load. Here, the entire internal combustion engine  1  is cooled, with the coolant flowing through the exhaust gas side  13  of the cylinder head water jacket and through the inlet side  16  of the latter and also through the cylinder block or the cylinder block water jacket  12  to the heater  17 , to the radiator  19  and to a compensating tank  18 . Valve  9  is connected by a connecting line  33  to the radiator  19 , which itself opens out via a connecting line  34  into the connecting line  27  from the heater  17  to the pump  21 . From the connecting line  33 , a connecting line  36  branches off to the compensating tank  18 , which itself is connected by a connecting line  37  to the connecting line  27  from the heater  17  to the pump  21 . 
     FIG. 6  is a table outlining the various phases encountered in the warmup procedure and shows the various attributes and advantages during the phases according to aspects of the present invention. 
   It is possible for the valve  6  to be dispensed with if the pump  21  or the coolant pump in the coolant circuit  4  is replaced by a regulatable coolant pump with a zero feed option. 
   Not illustrated is a cooling strategy for a part-load operating mode of the internal combustion engine at operating temperature, in which the exhaust gas side  13  of the cylinder head water jacket and the cylinder block  3  or the cylinder block water jacket  12  is cooled, with the coolant flowing through the exhaust gas side  13  of the cylinder head water jacket and through the cylinder block  3  or through the cylinder block water jacket  12  to the heater  17 .