Abstract:
An improved cooling system for a turbo charged internal combustion engine is disclosed. A conduit connects a pressurizing engine air intake to the cooling system to raise the pressure in the cooling system thereby enabling an increase of the maximum temperature which coolant in the cooling system can reach. An electronically controlled valve selectively places the expansion tank in communication with the pressurizing engine air intake to maintain a desired pressure in the tank and to prevent back flow of fluid into the engine air intake.

Description:
RELATED BACK 
   This is a Continuation-in-Part application of U.S. Ser. No. 10/360,156, filed on Feb. 6, 2003, which is a divisional application of U.S. Ser. No. 09/788,874, filed Feb. 20, 2001. 

   TECHNICAL FIELD 
   This invention relates to engine cooling systems and more particularly to a novel and improved cooling system in an internal combustion engine. 
   BACKGROUND ART 
   The development of internal combustion engines for reduced exhaust emissions has resulted in significant increases in the amount of heat dissipation into engine cooling systems. 
   Traditionally, increases in the required amount of heat dissipation has been accomplished by improving the radiator cooling capacity through increasing the core size of the radiator. In addition, increased coolant and cooling air flow have been used to deal with the increase in required heat dissipation. 
   Packaging space for larger radiator cores and high energy consumption due to increased coolant and cooling air flow limit the amount of heat dissipation capacity increase that can be accomplished with these traditional approaches. 
   It is possible to improve cooling capacity by elevating the maximum permissible coolant temperature above traditional levels. The adoption of pressurized cooling systems which permitted operation with coolants up to 100° C./212° F. was a step in this direction. The addition of expansion tanks assisted in maintaining such temperature levels. However, it has become desirable to elevate coolant temperatures to even higher levels. 
   Utilization of elevated coolant temperatures requires proper pressurization under all operating, stand-still and ambient conditions in order to control cooling characteristics, secure coolant flow, prevent cavitation and cavitation erosion and to prevent unwanted boiling and overflow. 
   Temperature and pressure increase becomes more critical as the heat dissipation from the engine approaches the cooling capacity of the cooling system. A now traditional approach for pressurizing cooling systems is to rely on closed expansion or pressure tanks which depend on temperature increases of coolant and air to create and maintain desired pressures. Such a system communicates with ambient air by opening two way pressure valves thereby communicating the system with ambient air to entrain new air into the pressure tank when entrapped air and the coolant cool to create a vacuum in the system. Such systems are passive and vulnerable to leaks. Moreover, if such a system is depressurized for any reason, such as maintenance or top-off, pressure is reduced to ambient and operating time and cycles are needed to increase the pressure in the system. 
   In order to facilitate operation at higher pressure (and higher coolant temperature) some coolant systems employ an external pressure source such as the charge air system of the vehicle that is coupled to the expansion tank to boost cooling system pressure above that possible with passive systems. These systems typically use pressure relief and pressure control to the ambient atmosphere, that causes constant or frequent air flow through to the tank or pressure source resulting in oxidization of coolant and scavenging. In addition, the external pressure is constantly applied, resulting in parasitic losses at the pressure source. 
   SUMMARY OF THE INVENTION 
   According to the present invention, an internal combustion engine cooling system is pressurized by introducing air under pressure from an external pressurized source. More specifically, in the preferred and disclosed embodiment, air under pressure from an engine intake manifold is communicated into the cooling system to thereby pressurize the system and elevate the maximum available coolant temperature. In its simplest form, a conduit connects an engine intake manifold with a cooling system expansion tank via a flow control check valve. The flow control valve is in the form of a spring loaded non-return valve connected in the conduit for enabling unidirectional flow from the intake manifold to the expansion tank. 
   In an alternate embodiment, a flow control valve in the form of a spring loaded non-return valve is also used. A second spring loaded non-return valve allows decompression of the expansion tank to a threshold pressure level corresponding to the spring pressure of the second valve plus the pressure in the engine air inlet system. In order to dampen decay of pressure in the coolant system, a restrictor is interposed in series with the second non-return valve. 
   A further alternative includes a valve, such as for example a floating check valve or electronically controlled valve, between the expansion tank and the conduit that is actuated based on a level of coolant liquid in the expansion tank to block flow of coolant to the pressure source when the tank level reaches a predetermined limit. 
   A further alternative includes an electric or pneumatic switch between the restrictor and the second non-return valve. A control algorithm for this switch is based on coolant pressure, temperature, engine load parameters and duty cycles for optimizing the expansion tank pressure. 
   In a still further alternative, a two directional two way control valve is used together with pressure sensors respectively located on opposite sides of the control valve. A control algorithm for pressure control is based on selected parameters such as coolant pressure, engine load, charge air pressure, coolant temperature, ambient temperature and pressure, cooling system capacity, cooling fan speed and duty cycles. A pressure control range is calculated based on the selected parameters and the valve is actuated to maintain pressure within the control range. 
   The alternate embodiments using electronic control units enable diagnosis of the systems actual functioning condition. The system compares actual pressure levels, time temperatures and valve positions with expected critical pressures under given conditions in the setting and design parameters for the system and components used in it. Diagnostic information is available for drivers and service information. It also can be used for actively changing the functioning of the system to enable continued use of the engine vehicle in a so-called limp home mode in case of system malfunction. 
   Accordingly, the objects of this invention are to provide a novel and improved engine coolant system and a method of engine cooling. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
       FIG. 1  is a schematic view of a turbo charged engine and cooling system for an over the highway heavy duty truck or tractor made in accordance with the present invention; 
       FIG. 2  is a schematic view of one embodiment of the novel portions of the cooling system of the present invention; 
       FIG. 3  is a schematic showing of an alternate flow control valve arrangement for the system of  FIG. 2 ; 
       FIG. 4  is a further alternate arrangement of the flow control valving for the system of  FIG. 2 ; 
       FIG. 5  is a schematic view of yet another alternate flow control valving arrangement for the system of  FIG. 2 ; 
       FIG. 6  is a schematic view of yet another alternate flow control valving arrangement for the system of  FIG. 2 ; and 
       FIG. 7  is a flowchart depicting a control method according to one embodiment of the present invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring to the drawings and  FIG. 1  in particular, a schematic of an engine and cooling system for an over the highway truck or tractor is shown generally at  10 . The truck is equipped with a turbo charged engine  12 . As shown somewhat schematically in  FIG. 2  the engine  12  is equipped with a cylinder head  14  having an air intake manifold  15 . The engine  12  is equipped with a turbo charger pressurizing the intake manifold  15  as shown schematically at  16  in  FIG. 2 . 
   The engine  12  is equipped with a cooling system which includes an expansion tank  18 ,  FIG. 2 . The expansion tank  18  is a standard tank including an outlet  20  connected to an inlet of a water or coolant pump. The tank  18  includes a fill opening equipped with a pressure cap  22 . In the disclosed embodiment, the cap  22  includes a tank pressure relief and coolant overflow valve  24  and a vacuum relief valve  25  as is now conventional in coolant systems. 
   A conduit  26  connects the intake manifold  15  to the expansion tank  18 . The conduit  26  communicates with the expansion tank  18  through an inlet  28 . A floating check valve  30  functions to control unidirectional fluid flow through the inlet  28  when a level of coolant  32  in the tank  18  rises to a higher level than that depicted in  FIG. 2 . Thus, the check valve  30  functions to prevent coolant  32  from entering the conduit  26 . 
   A flow control valve  34  is interposed in the conduit  26 . In its simplest form, the flow control valve is a simple spring loaded non-return valve which allows pressurized flow from the manifold  15  to the tank  18 , but prevents reverse flow of pressurized fluid from the tank  18  to the manifold  15 . 
   With the embodiment of  FIG. 2 , the tank pressure relief valve  24  will control the pressure in the cooling system. So long as the pressure level at which the tank pressure relief valve operates is higher than the pressure in the system, the operating pressure in the system will always be above the opening pressure of the flow control valve and below the tank pressure relief valve&#39;s opening pressure due to the one way functioning of the flow control valve  34 . 
   In the embodiment of  FIG. 3 , a second valve in the form of another spring loaded non-return valve  35  is provided. The valve  35  allows decompression of the expansion tank pressure down to a threshold pressure level corresponding to the spring pressure of the valve  35  plus the pressure of the engine air inlet system. In order to dampen the pressure decay in the cooling system, a restrictor  36  is in series with the second flow control valve  35 . In  FIG. 3 , the restrictor is shown on the coolant side of the valve but it could be on the engine side. 
   With the embodiment of  FIG. 4 , a directional control flow valve  38  is added to the system in series with the restrictor  36  and the second or decompression control valve  35 . The directional control valve  38  functions to prevent automatic pressure decay in the expansion tank by maintaining a higher pressure when the engine load and the pressure in the engine intake system is reduced. 
   An electronic control unit  40  controls the positioning of the directional control valve. The control algorithm for this function is based on coolant pressure, temperature, engine load parameters, and duty cycles relevant for optimizing the expansion tank pressure. Alternatively, a pneumatic switch may be substituted for the electrically controlled directional control valve that has been described. 
     FIG. 5  discloses an alternative which offers full flexibility in building up and maintaining pressure in the expansion tank  18  and therefore in the coolant system. The alternate of  FIG. 5  includes control of pressure variations and amplitudes. The system of  FIG. 5  utilizes a two directional, two way control valve  42 . Pressure sensors  44 , 45  are respectively positioned between the one way valve  42  and the expansion tank  18  and between the one way valve and the engine intake manifold  15 . A restrictor  46  is interposed in series with the direction control valve  42  and the pressure sensor  45 . 
   The direction control valve  42  is controlled by an electronic control unit  48 . A control algorithm for the control unit  48  is based on selected parameters such as coolant pressure, engine load, charge pressure, coolant temperature, ambient temperature, ambient pressure, cooling system capacity, cooling fan speed, and duty cycles. The pressure in the expansion tank is optimized by actively pressurizing to satisfy coolant system function. While the pressure is optimized, it is raised to no higher than necessary pressure levels and with pressure variations and amplitudes which match the properties of materials used in the coolant system. 
   A passive pressure build-up in the expansion tank will take place naturally and in parallel with the active pressure control systems that have been described. How the passive pressure build-up will interact depends on which of the embodiments is employed. 
   The embodiments of  FIGS. 4 and 5  make it possible to diagnose a system&#39;s actual functioning condition and to identify problems. Such a system compares actual pressure levels, time, temperatures and valve positions with expected critical pressures under given conditions and the setting of design parameters for the system as well as components used in it. 
   Diagnostic information derived when either the embodiment of  FIG. 4  or  5  is in use, can be used for driver and service information. It can also be used for actively changing the functioning of the system to enable continued use of the vehicle in a so-called limp home mode in case of an identified system malfunction. Examples of changing functions are modifying valve functions, shutting off the active system pressurizing by the turbo charger, reduction of available engine power and heat dissipation, and altered cooling fan, speed and fan-clutch engagement. 
   Operation 
   In operation from cold engine start up, operation of the turbo charger will transmit air under pressure through the conduit  26  to the expansion tank  18 . Assuming the pressure relief setting of the cap pressure relief valve  24  is high enough, air under pressure will flow through the flow control valve  34  until pressure in the expansion tank  18  is approaching the relief valve opening pressure (but not higher). Should the pressure of air from the turbo charger  16  drop, the one way flow control valve  34  will prevent a pressure drop in the expansion tank  18 . 
   With the embodiment of  FIG. 3 , the second non-return flow valve  35  functions to reduce the pressure in the coolant system when outlet pressure from the turbo charger is reduced, but not lower than the pre-set opening pressure of the second flow control valve  35 . 
   With the embodiment of  FIG. 4 , the directional control valve  38  functions to prevent automatic pressure decay in the expansion tank to maintain higher pressure when the engine load and the pressure of the engine intake system is reduced. The electronic control unit  40  of the  FIG. 4  embodiment, will function based on the parameters that have been selected to control pressure decay in the coolant system. 
   With the embodiment of  FIG. 4 , pressure in the coolant system in relation to pressure in the engine air inlet  15  is totally controlled by the one way directional control valve  42  which in turn is controlled by the electronic control unit  46 . This functioning is in accordance with the parameters that have been described. 
   The embodiment of  FIG. 5  is effective to control coolant system pressure appropriate for operating parameters and as such to maximize performance benefits of a pressurized cooling system. 
   Electronic Controlled Coolant System with Modulated Pressurization 
     FIG. 6  is a schematic diagram of coolant pressure control system that includes a tank pressure sensor  51 , electronically controlled bidirectional flow control valve  42 , and an electronic control unit (ECU)  50  for controlling the flow control valve. The pressure cap  22  operates as discussed above and maintains pressure between two absolute limits P 0 −C 2  and P 0 +C 1 , where P 0  is an estimated optimal pressure that is based on nominal operating conditions, and C 1  and C 2  are the calibration levels of the vacuum valve  25  and the pressure relief valve  24 , respectively. The conduit and tank inlet are shown schematically in  FIG. 6 , but are similar in appearance and operation to that shown in  FIG. 2 . A pressure source  60 , such as the manifold  15  shown in  FIG. 2 , is connected to the bidirectional valve  42 . In the embodiment shown in  FIG. 6 , the floating check valve assembly  30  ( FIG. 2 ) has been suitably replaced with an electronic tank level sensor  53  that sends signals indicative of tank level to the ECU  50 . 
   The pressure sensor  51  measures the system pressure, P e , within the tank. This tank pressure is input to the ECU  50 . The ECU also receives signals indicative of pressure source pressure level, P s , from pressure sensor  61 . The ECU continually calculates a real time optimal pressure, P 0rt , for the system based on present vehicle operating conditions. A control range that is a function of the calculated P 0rt  is stored in the ECU. The control range is an amount of allowed deviation from any given P 0rt . The control range is suitably selected to maintain the system pressure within the absolute limits P 0 −C 2  and P 0 +C 1  dictated by the components of the pressure cap  22 . Using the control range and the calculated P 0rt , the ECU determines a target pressure range. When the system pressure, P e , is outside the target range, the ECU controls the valve  42  to supply or bleed pressure by allowing flow between the pressure source  60  to the tank. In addition, the ECU controls the valve to prevent flow from the tank to the pressure source when the level sensor  53  indicates a high tank level. Of course, if at any time the pressure of the system falls outside the absolute limits of the pressure cap, the pressure cap will operate to connect the coolant system to the ambient atmosphere. 
   The ECU calculates P 0rt  for the system based on a number of factors. These factors include present engine operating conditions such as engine load and speed as sensed by the engine control module, or ECM,  65 ; coolant temperature as sensed by temperature probe  63  which is suitably positioned in an area through which coolant flows; ambient conditions as sensed by various sensors indicated generally as  67 ; vehicle operating parameters such as road speed as sensed by the vehicle control module, or VCM,  75 ; and cooling system parameters  69  such as coolant type, and/or specific properties of materials used in the cooling system. The cooling system parameters may be stored in the ECU at vehicle assembly and changed during subsequent vehicle service as necessary. These parameters included cooling fan speed, duty cycle, and system capacity. P 0rt  and its associated target range are calculated to provide stable engine and cooling system performance such that, for example, unwanted coolant boiling and coolant discharge at elevated coolant temperatures and pump cavitation are prevented at a wide range of temperatures. The ECU  50  controls the valve  42  to modulate the tank pressure to provide sufficient pressure to the system with a minimum of scavenging of air through the valve  42 . If tank pressure is higher than the target range, the ECU  50  may open the valve to relieve the pressure to reduce material stresses in the system. The pressure differential between the pressure at the pressure source P s  and the pressure within the cooling system P e  determines the direction of flow through the valve. 
   Referring now to  FIG. 7 , one possible method  700  for controlling the operation of the valve  42  is illustrated in flowchart form. In general, the optimum pressure, P 0rt , is periodically calculated as conditions change. The optimum pressure P 0rt  and the associated control range are selected to provide stable engine and cooling system function under a wide range of operating conditions and to prevent or limit coolant boiling and discharge at elevated coolant temperatures, pump cavitation, and cavitation erosion. A control range (C.R. in  FIG. 7 ) for pressure that varies as a function of the calculated P 0rt  is stored in the ECU. The control range can be a continuous or step-wise function, or a set of discrete control points, or any other function that results in a target pressure range that controls stability and minimizes scavenging of air through the enclosure. For example, at certain optimum pressures, it will be possible to maintain a “looser” control over the system pressure to minimize valve operation and potential scavenging of air. At other optimum pressures, it may be desirable to specify a “tighter” control range to more closely regulate pressure even if it results in some scavenging of air. 
   The method  700  will now be described in greater detail. The valve is normally closed as indicated in  710 . At  720  a real time optimal pressure P 0rt  is calculated based on the parameters discussed above. At  730 , the system pressure Pe is compared to the lower point of the target range at the optimal pressure (P 0rt −C.R./2). If the system pressure is not below this point, it is compared to the upper limit (P 0rt +C.R./2) at  760 . If the system pressure is within the lower and upper points of the target range, the method returns and the valve is at the closed position ( 710 ). If, however, the system pressure P e  is below the target range at  730 , the method checks the system pressure P e  at  740  to determine if it is at a lower pressure than the pressure source pressure P s . If P e  is less than P s , then the valve is opened at  750  to raise the system pressure P e . The method loops through  720 – 750  until P e  is raised into the target range. At  740 , if P e  is not less than P s , then opening the valve will not raise P e  and the valve is not opened. In this case the method returns to  720  where a new P 0rt  is calculated and if P e  falls below the absolute limit of the pressure cap, the pressure cap will vent from atmosphere. 
   Likewise, if the system pressure P e  is higher than the upper control limit at  760 , the system pressure P e  is compared to the pressure source pressure PS at  770  to determine if P e  is higher than P s . If P e  is higher than the system pressure P s , the valve is opened at  780  to vent to the pressure source. The method loops until P e  is lowered into the target range. At  770  if P e  is already lower than P s  opening the valve will not lower P e , so the method returns to  720 . If P e  increases to a level above the absolute limit of the pressure cap, the pressure cap will vent to atmosphere. The method described above is but a single example of suitable control algorithms for implementing the inventive cooling system and other possible algorithms will be apparent to those of skill in the art. 
   Although the invention has been described in its preferred form with a certain degree of particularity, it is understood that the present disclosure of the preferred form has been made only by way of example and that numerous changes in the details of construction, operation and the combination and arrangement of parts may be resorted to without departing from the spirit and scope of the invention as hereinafter claimed.