Abstract:
A method for operating an internal combustion engine is provided. By taking into account a setpoint temperature T setpoint  of the internal combustion engine which depends on external and internal boundary conditions when controlling and/or regulating temperature-dependent functions of the internal combustion engine, fuel consumption and emission characteristics of the internal combustion engine are improved.

Description:
FIELD OF THE INVENTION 
   The present invention relates to a method for operating an internal combustion engine whereby the efficiency and emission characteristics are improved. 
   BACKGROUND INFORMATION 
   German Published Patent Document No. 30 24 209 and German Published Patent Document No. 41 09 498 discuss a method for the liquid-cooling of internal combustion engines in which the setpoint value of the coolant temperature is varied as a function of different parameters such as outside temperature, operating state of the engine, etc. This makes it possible to quickly attain the operating temperature after startup of the engine, while preventing the engine from overheating in all operating states. However, changing the setpoint value of the engine temperature also affects the operating performance of the engine, making it necessary to perform additional optimization. 
   SUMMARY OF THE INVENTION 
   In a method according to the present invention for controlling an internal combustion engine, boundary conditions for operating the engine are determined, a setpoint value of the engine temperature is determined as a function of the boundary conditions for operating the internal combustion engine, and the temperature-dependent functions of the internal combustion engine are controlled and/or regulated as a function of the setpoint value of the internal combustion engine temperature setpoint T setpoint  in such a manner as to make it possible to take the specified variable internal combustion engine temperature setpoint value into account even when controlling or regulating other temperature-dependent internal combustion engine functions. 
   This combination according to the present invention of determining the boundary conditions for internal combustion engine operation, determining an internal combustion engine temperature setpoint value, and controlling and/or regulating the temperature-dependent functions of the internal combustion engine makes it possible to further enhance the efficiency of the internal combustion engine, while reducing emissions. In addition, the service life and load-bearing capacity of the internal combustion engine are increased by the method according to the present invention because the internal combustion engine is always operated in a narrow temperature range. 
   In a further exemplary embodiment of the method according to the present invention, the ambient temperature, the air humidity, the load on and speed of the internal combustion engine and/or the composition of the fuel/air mixture of the internal combustion engine are determined as the boundary condition for operating the internal combustion engine. Using the above boundary conditions, which are listed as examples only, an internal combustion engine temperature setpoint value may be determined, which makes it possible to operate the internal combustion engine with optimum efficiency and emission characteristics. 
   In a further exemplary embodiment of the method according to the present invention the exhaust gas recycling rate, the injection amount, the injection point, the ignition point, the thermostat valve of the cooling circuit and/or the activation of the coolant pump is/are controlled and/or regulated as a function of the internal combustion engine temperature setpoint value. The internal combustion engine temperature affects the above-named functions in such a manner that by variably specifying an internal combustion engine temperature setpoint value and taking it into account in the above-listed exemplary functions, it is possible to optimize the operating performance as desired. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a block diagram of an internal combustion engine operated by the method according to the present invention. 
       FIG. 2  shows an exemplary embodiment of a method according to the present invention for operating an internal combustion engine. 
   

   DETAILED DESCRIPTION 
     FIG. 1  shows as a block diagram an exemplary embodiment of an internal combustion engine  1  operated by the method according to the present invention. Internal combustion engine  1  is liquid-cooled. The coolant, in particular water containing additives, is supplied to a cooler  5  via a forward line  3 . Subsequently the cooling water cooled in cooler  5  is returned to internal combustion engine  1  via a return line  7 . A coolant pump  9  is mounted in return line  7  for recirculating the coolant. Coolant pump  9  may be driven either directly by the internal combustion engine or by an electrical drive. 
   To regulate the flow rate in the cooling circuit made up of forward line  3 , cooler  5 , return line  7 , and coolant pump  9 , a bypass line  11 , via which the coolant may flow from forward line  3  to return line  7 , bypassing cooler  5 , is arranged between forward line  3  and return line  7 . A valve  13  is provided to control the distribution of coolant between the flows through cooler  5  and bypass line  11 . Valve  13  is activated by a first control unit  15  in such a manner that the internal combustion engine has a temperature T setpoint . Control unit  15  activates valve  13  as a function of temperature T actual  of forward line  3  measured by a first temperature sensor  17 . 
   To ensure that the internal combustion engine temperature is maintained over a broader range of external conditions and operating states, coolant pump  9  may be provided with a flow controller. 
     FIG. 1  shows as an example the exhaust gas recycling of internal combustion engine  1  for a temperature-dependent function of internal combustion engine  1 . The method according to the present invention is, however, not limited to controlling the exhaust gas recycling as a function of temperature T setpoint  of internal combustion engine  1 . In principle, any temperature-dependent function of the internal combustion engine may be controlled or regulated by the method according to the present invention. 
   Internal combustion engine  1  is controlled by a second control unit  19 . Internal combustion engine  1  aspirates air via a suction line  21 . The exhaust gas flows from the internal combustion engine into the environment via an exhaust line  23 . An exhaust gas return line  25  is arranged between suction line  21  and exhaust line  23 . A second valve  27 , activated by second control unit  19 , is mounted in exhaust gas return line  25 . Depending on how second valve  27  is activated by second control unit  19 , a greater or smaller portion of the exhaust gas may flow from exhaust line  23  into suction line  21  via exhaust gas return line  25 . 
   When second valve  27  is closed, no exhaust gas flows from exhaust line  23  into suction line  21 . Exhaust gas recycling is used to reduce emissions, in particular NO x  emissions, of internal combustion engine  1 . 
   Exhaust gas recycling is controlled by the second control unit as a function of a temperature T actual  of forward line  3 , determined by a second temperature sensor  29 , which is a measure for temperature T setpoint  of internal combustion engine  1 . Temperature T actual  of internal combustion engine  1  may also be determined by other temperature measurements. 
   All signal links between the different components of the internal combustion engine such as first valve  13 , first temperature sensor  17 , first control unit  15 , second temperature sensor  29  and second control unit  19 , as well as second valve  27 , are shown by dashed lines in  FIG. 1 . The signal link may be either analog, digital or via a data bus. 
   It is also possible to combine first temperature sensor  17  and second temperature sensor  29  and to transmit a uniform signal to first control unit  15  and second control unit  19 . Furthermore, first control unit  15  and second control unit  19  may be combined into a single control unit. 
   In the internal combustion engine according to the present invention illustrated in  FIG. 1 , the exhaust gas recycling rate may be determined as a function of the temperature measured by second temperature sensor  29 . The first control unit may determine a setpoint temperature T setpoint  as a function of external and internal boundary conditions for operating the internal combustion engine; this setpoint temperature is also transmitted to second control unit  19 . Second control unit  19  is then able to control the exhaust gas recycling rate as a function of variable setpoint temperature T setpoint  and measured actual temperature T actual  of the internal combustion engine. As a result, the regulation of the exhaust gas recycling rate as a function of setpoint temperature T setpoint  of the internal combustion engine is further optimized, which has a positive effect on the efficiency and emission characteristics of internal combustion engine  1 . 
   An exemplary embodiment of the method according to the present invention for operating the internal combustion engine is explained below with reference to  FIG. 2 , which shows a block diagram of this exemplary embodiment. Setpoint temperature T setpoint  is determined in a determining block  91  as a function of external and internal boundary conditions, which are indicated in  FIG. 2  by an arrow. External boundary conditions include temperature and humidity of the outside air, for example. Internal boundary conditions include the load on and the operating temperature of the internal combustion engine, for example. First block  91  provides setpoint temperature T setpoint  of the internal combustion engine as an output quantity. This output quantity T setpoint  is transmitted to a first component driver  92 , for example. First component driver  92 , which may also be integrated into an actuator, outputs an actuating signal  93  to the component driven by it, as a function of setpoint temperature T setpoint  Actuating signal  93  may be the signal from first control unit  15 , illustrated in  FIG. 1 , for activating thermostat valve  13 , for example. First component driver  92  also takes into account temperature T actual  of the internal combustion engine, which is determined by first temperature sensor  17 . 
   Setpoint temperature T setpoint  of the internal combustion engine, which is output by first block  91 , is also input into a second block for determining one or more setpoint values of one or more performance parameters  111 . In second block  111 , a setpoint value of one or more performance parameters of a temperature-dependent function such as, for example, exhaust gas recycling of internal combustion engine  1 , are determined as a function of setpoint temperature T setpoint , actual temperature T actual  and further input quantities, and a setpoint value of the performance parameter(s) is output. 
   This setpoint value of the performance parameters may be used in first block  91  for calculating the setpoint temperature, as indicated by an arrow in  FIG. 2 . The setpoint value of the performance parameter(s) is also used as an input quantity of a second component driver  112  for generating a second actuating signal  113 . 
   Second actuating signal  113  may be used, for example, for controlling second valve  27  in exhaust gas return line  25 . 
   As an alternative, any other temperature-dependent function of the internal combustion engine such as injection amount, ignition point, injection point, etc., may be activated using second actuating signal  113 .