Abstract:
The present invention provides a method of inferring the engine coolant temperature in cylinder head temperature sensor equipped vehicles including the steps of measuring the cylinder head temperature, calculating the engine coolant temperature from the measured cylinder head temperature as a function of at least one vehicle operational state, generating a signal for the calculated engine coolant temperature, and sending the generated signal to a display.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to an automotive engine coolant temperature determination method. More particularly, the present invention relates to a method using a cylinder head temperature sensor to infer such a temperature. 
     2. Disclosure Information 
     It is well known that malfunctions of engine cooling systems, such as a leak, will generally cause damage to the engine due to excessive engine overheating. To indicate such an event, a temperature sensing system for an internal combustion engine may include an engine coolant temperature (ECT) sensor, a cylinder head temperature (CHT) sensor, or a combination of the two. The temperature sensors record a temperature and relay the information to an electronic engine controller, which, in turn, relays the information to an operator, typically via an instrument display panel. 
     In ECT sensor equipped vehicles the sensor typically communicates with a coolant passage in a cylinder head. The problem with ECT sensor equipped vehicles is that an accurate reading of the CHT can not be obtained. Having an accurate CHT reading is important with respect to fuel economy and emissions. 
     In CHT sensor equipped vehicles the sensor typically communicates with the cylinder head at a location adjacent the combustion chamber of the engine. A problem with CHT sensor equipped vehicles is that the ECT can not be accurately calculated. For example, the CHT can be up to 70 degrees Fahrenheit hotter than the ECT and the temperature gauge would read hot when the system is really operating within a normal temperature range, thereby giving a “false reading”. 
     To combat these problems many vehicles are equipped with both ECT and CHT sensors. A problem with a two sensor system is that it is more costly than the single sensor systems. A further problem is that the algorithm programmed into the engine controller is more complex because of the need to receive information from two sensors. 
     It would therefore be desirable to provide a method of accurately inferring ECT in CHT sensor equipped vehicles that overcomes the deficiencies associated with previous systems. 
     SUMMARY OF THE INVENTION 
     The present invention overcomes the disadvantages of the prior art approaches by providing a method of inferring ECT in CHT sensor equipped vehicles including the steps of measuring the CHT, calculating the ECT from the measured CHT as a function of at least one vehicle operational state, generating a signal for the calculated ECT, and sending the generated signal to a display. 
     It is an object and advantage of the present invention to calculate ECT as a function of the vehicle operational state. Calculation in this fashion prevents “false readings” which may arise when CHT is running hotter then ECT, but still within an acceptable operational range. 
     A feature of the present invention is to filter the calculated ECT to prevent inaccurate display readings resulting from sudden changes in vehicle operational states, the filter step being performed prior to the step of generating a signal. 
     These and other advantages, features and objects of he invention will become apparent from the drawings, detailed description and claims which follow. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an automotive vehicle according to the present invention; 
         FIG. 2  is a partial cross-sectional view of an internal combustion engine having a temperature sensing system according to the present invention; and 
         FIG. 3  is a flow chart showing a method for inferring ECT in CHT sensor equipped vehicles according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawings,  FIG. 1  shows an automotive vehicle  10  having an internal combustion engine  12  and a dashboard  14  housing an instrument display panel  16 . As known in the art, the display panel  16  has a variety of gauges which communicate various vehicle operational states such as vehicle speed, engine revolutions per minute, and engine temperature for example. 
     A temperature sensing system  11 , shown in  FIG. 2 , infers ECT from a measured CHT. The engine  12  includes a cylinder block  18  having a cylinder  20  formed therein and a piston  22  reciprocally housed within the cylinder  20 . A cylinder head  24  is mounted to the cylinder block  18 , with a cylinder head gasket  26  disposed therebetween, such that the cylinder head  24  closes the outer end of the cylinder  20 , thereby defining a combustion chamber  28  between the top of the piston  22  and an insulation deck  30  of the cylinder head  24 . A sparkplug  32  is fastened to the cylinder head  24  to communicate with the combustion chamber  28 . A cooling system  34  of the engine  12  is generally provided by a coolant passage  36  formed in the cylinder head  24 . A coolant  38  circulates in coolant passage  36  to cool the engine  12 . 
     According to the present invention, a temperature sensor  42  having a threaded portion,  40 , communicates with the insulation deck  30  in the cylinder head  24  adjacent the combustion chamber  28 . Preferably, the temperature sensor  42  is a thermistor as is known in the art. The temperature sensor  42  senses the cylinder head  24  temperature and relays the information to an electronic engine controller (EEC)  44  having a keep alive memory (KAM) storage device  46 . 
     Referring now to  FIG. 3 , according to the present invention, a method of inferring ECT from a CHT sensor is described. At step  50 , the process is initiated. At step  52 , it is determined whether a CHT is available from the EEC. If not, then at step  54  the engine temperature signal generated and sent to the display  16  (ECT DISPLAY) is set equal to a failure mode value of ECT (ECT FMEM). Generally, the engine temperature signal generated and sent to the display  16  at step  54  equals the combustion chamber air charge temperature during a cold start, and ramps to a calibratible constant whose value is typical for a warm engine. 
     If a valid CHT is available, then at step  56 , it is determined whether the initial pass through this process has been completed (INIT FLG). The initial pass completed is indicated by a 1 as discussed below. 
     If the initial pass was completed, then at step  58 , a temporary ECT value is determine. This temporary value is equal to the CHT value minus a first function (F1(RPM, LOAD)) plus a second function (F2(CHT)). The first function is derived from a calibratible look up table showing the deviation of ECT from CHT as a function of revolutions per minute (RPM) and cylinder air charge temperature (LOAD). Both RPM and LOAD values may be derived from the EEC. The second function is to account for the difference between ECT and CHT increases for very high values of CHT. 
     At step  60 , the engine temperature signal generated and sent to the display  16  (ECT DISPLAY) is set equal to a rolling average function (ROLAV) used to filter out noise. The rolling average function is determined as a function of the temporary ECT value and a calibratible time constant (RUN TC) and takes into consideration the fact that CHT heats faster than the engine coolant. 
     At step  62 , the temperature difference (DELTA) is determined and stored. The DELTA is the difference between the CHT and the engine temperature signal generated. The DELTA is sent to the display  16  and is stored in KAM, so that the DELTA at power-down is available during the next power-up. At step  64 , the process ends. 
     If the pass at step  56  was not completed, then the process flow moves to step  66 , where DELTA is determined as a function of the last DELTA stored in KAM multiplied by an exponential decay function (EXP). The EXP is a function of the number of minutes the engine  12  has been powered down (SOAKTIME) divided by a calibratible time constant (SOAK TC), which determines the rate at which DELTA decays during a soak. This information is available from the EEC  44 . The EXP is equal to 1 if SOAKTIME equals zero and decays to zero as SOAKTIME approaches infinity. At step  68 , the engine temperature signal generated and sent to the display  16  is equal to the difference between the CHT and the DELTA from step  66 . At step  70 , INIT FLG is registered as 1 indicating that the initial pass has been completed. At step  64 , the process ends. 
     The present invention is advantageous for a number of reasons. First, because ECT is calculated as a function of the vehicle operational state “false readings” are avoided. For example, “false readings” which may arise when CHT is running hotter than ECT, but still within an acceptable operational range. Further, filtering the calculated ECT prevents inaccurate display readings resulting from sudden changes in vehicle operational states. More specifically, because ECT is being inferred by CHT as a function of RPM and LOAD, anomalous readings for RPM and LOAD need to be taken out of the calculation as they tend to change faster than actual CHT and ECT. In other words, if ECT is being inferred at a time when there is a sudden spike in RPM, with the RPM then returning to normal running, without filtering, the ECT calculation would indicate being out of control limits when that is not actually the case. It is an important aspect of the invention, therefore, that not only is ECT inferred from CHT as a function of vehicle operational states, but also that the ECT sent to the display is filtered to eliminate noise resulting from the various operational states. 
     Various other modifications to the present invention will, no doubt, occur to those skilled in the art to which the present invention pertains. It is the following claims, including all equivalents, which define the scope of the present invention.