Patent Publication Number: US-9903255-B2

Title: Coolant circuit for an internal combustion engine and method of operating a coolant circuit

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application is the U.S. National Stage of International Application No. PCT/EP2012/002784, filed Jun. 30, 2012, which designated the United States and has been published as International Publication No. WO 2013/017188 and which claims the priority of German Patent Application, Serial No. 10 2011 108 953.9, filed Jul. 29, 2011, pursuant to 35 U.S.C. 119(a)-(d). 
     BACKGROUND OF THE INVENTION 
     The invention relates to a coolant circuit for an internal combustion engine, wherein the coolant can circulate between the internal combustion engine and a heat sink as a function of a switchable valve which is closed in the initial state during a cold start of the internal combustion engine, and to a method of operating a coolant circuit. 
     Such coolant circuits are used in particular in the automotive industry to cool coolant, heated by the internal combustion engine, through circulation via the heat sink. In this way, the internal combustion engine is protected from damage due to overheating. To reduce friction work of the internal combustion engine in terms of improved efficiency, a rapid heating of the internal combustion engine and thus also of the coolant is desirable, when the internal combustion engine is at a cold start. For this reason, a valve switched to a closed state can prevent a coolant circulation until a sufficient heating has been reached. 
     The determination of the point in time for opening the valve is realized in the art in dependence on when the internal combustion engine exceeds a torque or rotation speed threshold. DE 100 45 613 A1 discloses a method for controlling the coolant temperature of an engine cooling system, with the coolant temperature being controlled in dependence on a load and/or rotation speed of the internal combustion engine. This oftentimes leads to premature opening of the valve, when the coolant temperatures are too low so that efficiency losses have to be accepted. 
     DE 101 54 091 A1 describes a method and a device for controlling a cooling system of an internal combustion engine, with the capacity of a coolant pump being controllable as a function of a fuel quantity fed to the internal combustion engine. However, the fuel quality is not readily useful as a control variable for controlling a cooling system because of the absence of a stoichiometric conversion of the fuel, in particular during a cold start of the internal combustion engine. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide a coolant circuit for an internal combustion engine, and a method of operating a coolant circuit that enables an efficiency which is optimized for a cold start of the internal combustion engine. 
     According to one aspect of the invention, the object is achieved by a coolant circuit for an internal combustion engine, wherein the coolant is able to circulate between the internal combustion engine and a heat sink as a function of a switchable valve which is closed in the initial state during a cold start of the internal combustion engine, and wherein the valve is switchable into an at least partly open sequential state in response to an exhaust gas mass flow emitted from the internal combustion engine, with a control device determining an integral of the exhaust gas mass flow with respect to time and switching the valve to the sequential state when an integral threshold value is exceeded. 
     By making the opening of the valve after a cold start dependent on the emitted exhaust gas mass flow, the optimal point in time to terminate the rapid heating of the internal combustion engine can be very precisely determined. The integral value of the exhaust gas mass flow with respect to the time reflects the actual input of heat energy into the coolant. When the integral value exceeds a predefined integral threshold value, the valve is opened fully or incrementally. As a result, local overheating of the internal combustion engine (so-called “hot spots”) are effectively prevented on the one hand, and low friction work is reached as fast as possible on the other hand. A cold start can be understood in this context as a start-up of the internal combustion engine in which the coolant temperature approximately corresponds to the temperature of ambient air. A heat sink may be realized by a typical air-liquid heat exchanger which forms a circulation via a tube connection to the internal combustion engine. For forced circulation of coolant, coolant pumps, such as centrifugal pumps, are suitable. The valve is preferably configured as a heatable map-controlled thermostat or actuated by pneumatic or electric mechanics. 
     According to a preferred configuration of the coolant circuit, the control device determines the exhaust gas mass flow on the basis of an injection amount of a fuel. The control device is preferably designed hereby as a control unit for the internal combustion engine and measures in this function, inter alia, the amount of fuel to be injected. The exhaust gas mass flow being emitted after combustion and discharged through the exhaust system derives necessarily from the amount of fuel. 
     According to a preferred embodiment of the coolant circuit, the control device determines the injection amount per unit of time. Particularly advantageous is the subdivision of the injection operation into smallest possible units of time to more accurately determine the injection amount. 
     According to a preferred embodiment of the coolant circuit, the valve is part of a coolant pump or is formed by the coolant pump. The valve can be integrated into the coolant pump or formed by a switchable coolant pump. As a result, components and installation space can be saved. 
     According to another aspect of the invention, the object is achieved by a method of operating a coolant circuit for an internal combustion engine, wherein the coolant can circulate between the internal combustion engine and a heat sink as a function of a switchable valve, the method including the following steps:
         switching to a closed initial state of the valve during a cold start of the internal combustion engine;   continuously ascertaining an exhaust gas mass flow emitted by the internal combustion engine as of a cold start;   switching the valve into an at least partially open sequential state in dependence on the exhaust gas mass flow, with an integral of the exhaust gas mass flow being formed according to the time, and the sequential state being switched to when an integral threshold value is exceeded.       

     When carrying out the method according to the invention, the same advantages are attained as already mentioned for the coolant circuit. 
     BRIEF DESCRIPTION OF THE DRAWING 
     Further details and features of the invention will become apparent from the following description of a preferred exemplary embodiment with reference to the drawings. 
    
    
     
       It is shown in the drawings: 
         FIG. 1  a schematic view of a coolant circuit for an internal combustion engine; 
         FIG. 2  is a diagrammatic illustration of the exhaust gas mass flow over time. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     According to  FIG. 1 , a coolant circuit  1  for an internal combustion engine  2  has a heat sink  3 . The heat sink  3  is circulated by ambient air on one hand, and coolant on the other hand. As a result of the realized heat exchange, coolant circulating in the coolant circuit  1  cools down. The coolant circulation is implemented by a coolant pump  5 , with a switchable valve  4  being able to stop the coolant circulation. The internal combustion engine  2  has multiple combustion chambers  2   c  in which fuel is combusted so that the internal combustion engine  2  is heated. The generated heat can be dissipated by the coolant to the heat sink  3 . The fuel is injected either into the intake system  2   a  or directly into the combustion chambers  2   c  and then mixed with intake air. Spent fuel-air mixture is expelled through the exhaust system  2   b . A control device  6  ascertains the amount of injection of fuel per unit of time and determines the exhaust gas mass flow through the exhaust system  2   b . The control device  6  forms an integral of the exhaust gas mass flow over time, as shown in  FIG. 2 . During a cold start of the internal combustion engine  2 , that is, at the start at a coolant temperature which approximately corresponds to the ambient temperature, the valve  4  is in its closed starting condition and there is no coolant circulation. The control device  6  begins at the same time with a continuous computation of the integral value and causes the valve  4  to at least open in part as soon as the integral value exceeds a defined integral threshold value. 
     According to the  FIG. 2 , the integral value is formed in that the emitted exhaust gas mass flow per unit of time t x  is ascertained and integrated until the integral threshold value is exceeded.