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.

Description:
TECHNICAL FIELD 
     This invention relates to engine cooling systems and more particularly to a novel and improved cooling system in a turbo charged 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 has 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 at 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 to 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. 
     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 thereby to 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 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. 
     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 an over the highway heavy duty truck or tractor equipped with a turbo charged engine and cooling system 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; and 
     FIG. 5 is a schematic view of yet another alternate flow control valving arrangement for the system of FIG.  2 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the drawings and FIG. 1 in particular, 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 now 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  28  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 control 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 only to 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 FIGS. 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. 
     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.