Method of determining the fluid temperature of an electronic automatic transmission system
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an automatic transmission primarily intended for motor vehicle use, and more particularly, to a method of determining the fluid temperature of a transmission that is controlled electronically and hydraulically. 
     2. Description of Related Art 
     Generally speaking, land vehicles require three basic components. These components comprise a power plant (such as an internal combustion engine) a power train and wheels. The internal combustion engine produces force by the conversion of the chemical energy in a liquid fuel into the mechanical energy of motion (kinetic energy). The function of the power train is to transmit this resultant force to the wheels to provide movement of the vehicle. 
     The power train&#39;s main component is typically referred to as the &#34;transmission&#34;. Engine torque and speed are converted in the transmission in accordance with the tractive-power demand of the vehicle. The vehicle&#39;s transmission is also capable of controlling the direction of rotation being applied to the wheels, so that the vehicle may be driven both forward and backward. 
     A conventional transmission includes a hydrodynamic torque converter to transfer engine torque from the engine crankshaft to a rotatable input member of the transmission through fluid-flow forces. The transmission also includes frictional units which couple the rotating input member to one or more members of a planetary gearset. Other frictional units, typically referred to as brakes, hold members of the planetary gearset stationary during flow of power. These frictional units are usually brake clutch assemblies or band brakes. The drive clutch assemblies can couple the rotating input member of the transmission to the desired elements of the planetary gearsets, while the brakes hold elements of these gearsets stationary. Such transmission systems also typically provide for one or more planetary gearsets in order to provide various ratios of torque and to ensure that the available torque and the respective tractive power demand are matched to each other. 
     Transmissions are generally referred to as manually actuated or automatic transmissions. Manual transmissions generally include mechanical mechanisms for coupling rotating gears to produce different ratio outputs to the drive wheels. 
     Automatic transmissions are designed to take automatic control of the frictional units, gear ratio selection and gear shifting. A thorough description of general automatic transmission design principals may be found in &#34;Fundamentals of Automatic Transmissions and Transaxles,&#34; Chrysler Corporation Training Manual No. TM-508A, which is hereby incorporated by reference. Additional descriptions of automatic transmissions may be found in U.S. Pat. No. 3,631,744, entitled &#34;Hydromatic Transmission,&#34; issued Jan. 4, 1972 to Blomquist, et al., and U.S. Pat. No. 4,289,048, entitled &#34;Lock-up System for Torque Converter,&#34; issued on Sept. 15, 1981 to Mikel, et al. Each of these patents is hereby incorporated by reference. 
     In general, the major components featured in such an automatic transmission are: a torque converter as above-mentioned; fluid pressure-operated multi-plate drive or brake clutches and/or brake bands which are connected to the individual elements of the planetary gearsets in order to perform gear shifts without interrupting the tractive power; one-way clutches in conjunction with the frictional units for optimization of power shifts; and transmission controls such as valves for applying and releasing elements to shift the gears (instant of shifting), for enabling power shifting, and for choosing the proper gear (shift point control), dependent on shift-program selection by the driver (selector lever), accelerator position, the engine condition and vehicle speed. 
     The control system of the automatic transmission is typically hydraulically operated through the use of several valves to direct and regulate the supply of pressure. This hydraulic pressure control will cause either the actuation or deactuation of the respective frictional units for effecting gear changes in the transmission. The valves used in the hydraulic control circuit typically comprise spring-biased spool valves, spring-biased accumulators and ball check valves. Since many of these valves rely upon springs to provide a predetermined amount of force, it will be appreciated that each transmission design represents a finely tuned arrangement of interdependent valve components. While this type of transmission control system has worked well over the years, it does have its limitations. For example, such hydraulically controlled transmissions are generally limited to one or a very small number of engines and vehicle designs. Therefore, considerable cost is incurred by an automobile manufacturer to design, test, build, inventory and repair several different transmission units in order to provide an acceptable broad model line for consumers. 
     Additionally, it should be appreciated that such hydraulically controlled transmission systems cannot readily adjust themselves in the field to compensate for varying conditions such as normal wear on the components, temperature swings and changes in engine performance over time. While each transmission is designed to operate most efficiently within certain specific tolerances, typical hydraulic control systems are incapable of taking self-corrective action on their own to maintain operation of the transmission at peak efficiency. 
     However, in recent years, a more advanced form of transmission control system has been proposed, which would offer the possibility of enabling the transmission to adapt itself to changing conditions. In this regard, U.S. Pat. No. 3,956,947, issued on May 18, 1976 to Leising, et al., which is hereby incorporated by reference, sets forth a fundamental development in this field. Specifically, this patent discloses an automatic transmission design which features an &#34;adaptive&#34; control system that includes electrically operated solenoid-actuated valves for controlling certain fluid pressures. In accordance with this electric/hydraulic control system, the automatic transmission would be &#34;responsive&#34; to an acceleration factor for controlling the output torque of the transmission during a shift from one ratio of rotation (between the input and output shafts of the transmission) to another. Specifically, the operation of the solenoid-actuated valves would cause a rotational speed versus time curve of a sensed rotational component of the transmission to substantially follow along a predetermined path during shifting. 
     3. Objects of the Present Invention 
     It is one of the principal objects of the present invention to provide a significantly advanced electronically controlled transmission which is fully adaptive. By fully adaptive, it is meant that substantially all shifts are made using closed-loop control. In particular, the control is closed loop on speed, speed ratio, or slip speed of either N t  (turbine) and N e  (engine) or a combination of N t  and N o  (output) which will provide the speed ratio or slip speed. This transmission control is also capable of &#34;learning&#34; from past experience and making appropriate adjustments on that basis. 
     Another object of the present invention is to provide an automatic transmission in which the shift quality is maintained uniform regardless of the engine size, within engine performance variations or component condition (i.e. the transmission control system will adapt to changes in engine performance or in the condition of the various frictional units of the transmission). 
     It is a more specific object of the present invention to provide a method of determining the fluid temperature of an automatic transmission. 
     This application is one of several applications filed on the same date, all commonly assigned and having similar Specification and Drawings, these applications being identified below. 
     
         __________________________________________________________________________
U.S. Ser. No.                                                             
          Title                                                           
__________________________________________________________________________
187,772   AN ELECTRONICALLY-CONTROLLED,                                   
          ADAPTIVE AUTOMATIC TRANSMISSION                                 
          SYSTEM                                                          
187,751   AUTOMATIC FOUR-SPEED TRANSMISSION                               
189,493   PUSH/PULL CLUTCH APPLY PISTON OF AN                             
          AUTOMATIC TRANSMISSION                                          
189,781   SHARED REACTION PLATES BETWEEN                                  
          CLUTCH ASSEMBLIES IN AN AUTOMATIC                               
          TRANSMISSION                                                    
189,492   CLUTCH REACTION AND PRESSURE PLATES                             
          IN AN AUTOMATIC TRANSMISSION                                    
188,602   BLEEDER BALL CHECK VALVES IN AN                                 
          AUTOMATIC TRANSMISSION                                          
188,610   PRESSURE BALANCED PISTONS IN AN                                 
          AUTOMATIC TRANSMISSION                                          
189,494   DOUBLE-ACTING SPRING IN AN                                      
          AUTOMATIC TRANSMISSION                                          
188,613   PARK LOCKING MECHANISM FOR AN                                   
          AUTOMATIC TRANSMISSION                                          
187,770   SOLENOID-ACTUATED VALVE ARRANGEMENT                             
          OF AN AUTOMATIC TRANSMISSION SYSTEM                             
187,796   RECIPROCATING VALVES IN A FLUID                                 
          SYSTEM OF AN AUTOMATIC TRANSMISSION                             
187,705   VENT RESERVOIR IN A FLUID SYSTEM OF                             
          AN AUTOMATIC TRANSMISSION                                       
188,592   FLUID ACTUATED SWITCH VALVE IN AN                               
          AUTOMATIC TRANSMISSION                                          
188,598   DIRECT-ACTING, NON-CLOSE CLEARANCE                              
          SOLENOID-ACTUATED VALVES                                        
188,618   NOISE CONTROL DEVICE FOR A                                      
          SOLENOID-ACTUATED VALVE                                         
188,605, now U.S.                                                         
          FLUID ACTUATED PRESSURE SWITCH FOR                              
Pat. No. 4,871,887                                                        
          AN AUTOMATIC TRANSMISSION                                       
filed April 29, 1988.                                                     
187,210   METHOD OF APPLYING REVERSE GEAR OF                              
          AN AUTOMATIC TRANSMISSION                                       
187,672   TORQUE CONVERTER CONTROL VALVE IN A                             
          FLUID SYSTEM OF AN AUTOMATIC                                    
          TRANSMISSION                                                    
187,120   CAM-CONTROLLED MANUAL VALVE IN AN                               
          AUTOMATIC TRANSMISSION                                          
187,181   FLUID SWITCHING MANUALLY BETWEEN                                
          VALVES IN AN AUTOMATIC TRANSMISSION                             
187,704   METHOD OF OPERATING AN ELECTRONIC                               
          AUTOMATIC TRANSMISSION SYSTEM                                   
188,020   METHOD OF SHIFT SELECTION IN AN                                 
          ELECTRONIC AUTOMATIC TRANSMISSION                               
          SYSTEM                                                          
187,991   METHOD OF UNIVERSALLY ORGANIZING                                
          SHIFTS FOR AN ELECTRONIC AUTOMATIC                              
          TRANSMISSION SYSTEM                                             
188,603   METHOD OF DETERMINING AND                                       
          CONTROLLING THE LOCK-UP OF A TORQUE                             
          CONVERTER IN AN ELECTRONIC                                      
          AUTOMATIC TRANSMISSION SYSTEM                                   
188,617   METHOD OF ADAPTIVELY IDLING AN                                  
          ELECTRONIC AUTOMATIC TRANSMISSION                               
          SYSTEM                                                          
189,553   METHOD OF DETERMINING THE DRIVER                                
          SELECTED OPERATING MODE OF AN                                   
          AUTOMATIC TRANSMISSION SYSTEM                                   
188,615   METHOD OF DETERMINING THE SHIFT                                 
          LEVER POSITION OF AN ELECTRONIC                                 
          AUTOMATIC TRANSMISSION SYSTEM                                   
188,594   METHOD OF DETERMINING THE                                       
          ACCELERATION OF A TURBINE IN AN                                 
          AUTOMATIC TRANSMISSION                                          
188,607   METHOD OF DETERMINING THE                                       
          CONTINUITY OF SOLENOIDS IN AN                                   
          ELECTRONIC AUTOMATIC TRANSMISSION                               
          SYSTEM                                                          
189,574   METHOD OF DETERMINING THE THROTTLE                              
          ANGLE POSITION FOR AN ELECTRONIC                                
          AUTOMATIC TRANSMISSION SYSTEM                                   
188,604   METHOD OF CONTROLLING THE SPEED                                 
          CHANGE OF A KICKDOWN SHIFT FOR AN                               
          ELECTRONIC AUTOMATIC TRANSMISSION                               
          SYSTEM                                                          
188,591   METHOD OF CONTROLLING THE APPLY                                 
          ELEMENT DURING A KICKDOWN SHIFT FOR                             
          ELECTRONIC AUTOMATIC TRANSMISSION                               
          SYSTEM                                                          
188,608   METHOD OF CALCULATING TORQUE FOR AN                             
          ELECTRONIC AUTOMATIC TRANSMISSION                               
          SYSTEM                                                          
187,150   METHOD OF LEARNING FOR ADAPTIVELY                               
          CONTROLLING AN ELECTRONIC AUTOMATIC                             
          TRANSMISSION SYSTEM                                             
188,595   METHOD OF ACCUMULATOR CONTROL FOR A                             
          FRICTION ELEMENT IN AN ELECTRONIC                               
          AUTOMATIC TRANSMISSION SYSTEM                                   
188,599   METHOD OF ADAPTIVELY SCHEDULING A                               
          SHIFT FOR AN ELECTRONIC AUTOMATIC                               
          TRANSMISSION SYSTEM                                             
188,601   METHOD OF SHIFT CONTROL DURING A                                
          COASTDOWN SHIFT FOR AN ELECTRONIC                               
          AUTOMATIC TRANSMISSION SYSTEM                                   
188,620   METHOD OF TORQUE PHASE SHIFT                                    
          CONTROL FOR AN ELECTRONIC AUTOMATIC                             
          TRANSMISSION                                                    
188,596   METHOD OF DIAGNOSTIC PROTECTION FOR                             
          AN ELECTRONIC AUTOMATIC                                         
          TRANSMISSION SYSTEM                                             
188,597   METHOD OF STALL TORQUE MANAGEMENT                               
          FOR AN ELECTRONIC AUTOMATIC                                     
          TRANSMISSION SYSTEM                                             
188,606   METHOD OF SHIFT TORQUE MANAGEMENT                               
          FOR AN ELECTRONIC AUTOMATIC                                     
          TRANSMISSION SYSTEM                                             
188,616   ELECTRONIC CONTROLLER FOR AN                                    
          AUTOMATIC TRANSMISSION                                          
188,600   DUAL REGULATOR FOR REDUCING SYSTEM                              
          CURRENT DURING AT LEAST ONE MODE OF                             
          OPERATION                                                       
188,619   UTILIZATION OF A RESET OUTPUT OF A                              
          REGULATOR AS A SYSTEM LOW-VOLTAGE                               
          INHIBIT                                                         
188,593   THE USE OF DIODES IN AN INPUT                                   
          CIRCUIT TO TAKE ADVANTAGE OF AN                                 
          ACTIVE PULL-DOWN NETWORK PROVIDED                               
          IN A DUAL REGULATOR                                             
188,609   SHUTDOWN RELAY DRIVER CIRCUIT                                   
188,614   CIRCUIT FOR DETERMINING THE CRANK                               
          POSITION OF AN IGNITION SWITCH BY                               
          SENSING THE VOLTAGE ACROSS THE                                  
          STARTER RELAY CONTROL AND HOLDING                               
          AN ELECTRONIC DEVICE IN A RESET                                 
          CONDITION IN RESPONSE THERETO                                   
188,612   THROTTLE POSITION SENSOR DATA                                   
          SHARED BETWEEN CONTROLLER WITH                                  
          DISSIMILAR GROUNDS                                              
188,611   NEUTRAL START SWITCH TO SENSE SHIFT                             
          LEVER POSITION                                                  
188,981   OPEN LOOP CONTROL OF SOLENOID COIL                              
          DRIVER                                                          
__________________________________________________________________________
 
    
     Commonly assigned application Ser. No. 07/187,772, filed Apr. 29, 1988 now U.S. Pat. No. 4,875,391 will be printed in its entirety. The Figures and the entire Specification of that application are specifically incorporated by reference. For a description of the above copending applications, reference is made to the above mentioned U.S. Pat. No. 4,875,391. 
     SUMMARY OF THE INVENTION 
     To achieve the foregoing objects, the present invention provides a comprehensive four-speed automatic transmission system. While this transmission system particularly features a fully adaptive electronic control system, numerous other important advances are incorporated into this unique transmission system, as will be described below in detail. 
     The transmission control system includes a microcomputer-based controller which receives input signals indicative of engine speed, turbine speed, output speed (vehicle speed), throttle angle position, brake application, predetermined hydraulic pressure, the drive selected gear or operating condition (PRNODDL), engine coolant temperature, and/or ambient temperature. This controller generates command or control signals for causing the actuation of a plurality of solenoid-actuated valves which regulate the application and release of pressure to and from the frictional units of the transmission system. Accordingly, the controller will execute predetermined shift schedules stored in the memory of the controller through appropriate command signals to the solenoid-actuated valves and the feedback which is provided by various input signals. 
     Another primary feature of the present invention is to provide an adaptive system based on closed-loop control. In other words, the adaptive control system performs its functions based on real-time feedback sensor information, i.e., the system takes an action which affects the output, reads the effect, and adjusts the action continuously in real-time. This is particularly advantageous because the control actuations can be corrected as opposed to an open loop control in which signals to various elements are processed in accordance with a predetermined program. 
     In accordance with one aspect of the present invention, the controller is programmed to determine the transmission temperature based on ambient and/or engine coolant temperatures and on observed transmission and engine warmup rates. Alternatively, the controller may be programmed to determine the transmission temperature based on the response of the pressure sensors. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects, features and advantages of the present invention will become more fully apparent from the following detailed description of the preferred embodiment, the appended claims and in the accompanying drawings in which: 
     FIGS. 21A-D illustrate the transmission temperature determination methodology according to the present invention; FIGS. 21A through 21C are flow charts of the pressure switch test and transmission temperature methodology; FIG. 21D is a graph of a predicted transmission temperature methodology. 
    
    
     PRESSURE SWITCH TEST AND TRANSMISSION TEMPERATURE DETERMINATION METHOD 
     The purpose of the pressure switch test method is to verify that &#34;OFF&#34; element or clutch pressure switches will read high if a failure should occur. The purpose of the transmission temperature determination method is to determine when the transmission 100 has warmed up sufficiently to impose normal response requirements when the transmission controller 3010 sets the initial transmission temperature range (r) to either &#34;warm&#34; or &#34;cold&#34;. 
     Referring to FIGS. 21A through 21C, the methodology for the pressure switch test and transmission temperature determination is shown at 1900. At the beginning or start in block 1902, the methodology advances to diamond 1904 and determines whether the transmission 100 is presently operating in first, second or third gear by performing speed calculations. If the transmission 100 is not presently operating in first, second or third gear, the methodology advances to diamond 1905 and determines whether the shift lever position (SLP) 606 is reverse R or neutral N by either the SLP or PRNODDL methods previously described. If SLP 606 is reverse or neutral, the methodology advances to block 1906 and clears a retest flag. The methodology then advances to block 1907 and turns OFF or terminates the pressure switch test. If SLP is not reverse or neutral, the methodology also advances to block 1907. The methodology then advances to block 1908. At block 1908, the transmission controller 3010 resets a timer to a predetermined value such as zero and sets a default value of time corresponding with three seconds if a pressure switch test flag (PSTF) has been set or eleven seconds with the transmission fluid temperature cold; five second with the transmission temperature fluid warm; and two seconds with the transmission fluid temperature hot. Once this has been accomplished, the methodology returns. 
     At diamond 1904, if the transmission 100 is operating in either first, second or third gear, the methodology advances to diamond 1910 and determines whether the shift lever position (SLP) method or test, previously described, is ON or in progress by looking for a flag. If the SLP test is ON, or in progress, the methodology advances to block 1907 previously described to terminate the pressure switch test. If the SLP test is not ON, the methodology advances to diamond 1912 and determines whether engine speed N e  is less than a predetermined speed, S, i.e. 650 r.p.m. when the transmission fluid temperature is cold, or less than 1000 r.p.m. when the transmission fluid temperature is warm or hot. Also, the transmission controller 3010 determines whether a N o  /N t  speed check fault count (SCF) is greater than a predetermined value or a pressure switch fault count (PSF) is greater than another predetermined value. If any of the above criteria is met in diamond 1912, the methodology advances to block 1907 previously described to terminate the pressure switch test. If all of the criteria is not met in diamond 1912, the methodology advances to block 1914 and starts or continues a timer. The methodology then advances to diamond 1916 and determines whether the pressure switch test is ON or in progress by looking for a flag. If the pressure switch test is not ON, the methodology advances to diamond 1918 and determines whether the time on the timer is greater than a predetermined time period. If the time on the timer is not greater than the predetermined time period, the methodology returns. If the time on the timer is greater than the predetermined time period, the methodology advances to diamond 1921 and determines whether SCF is less than a predetermined value such as 60 and the PSF equals zero. If that criteria is not true, the methodology advances to block 1908 previously described. If that criteria is true, the methodology advances to diamond 1922 and determines whether a solenoid continuity test, to be described under section heading &#34;SOLENOID CONTINUITY TEST METHOD&#34;, has been inactive for a predetermined time period, i.e. greater than 400 ms, by looking for a flag. If the solenoid continuity test has not been inactive for the predetermined time period, the methodology returns. If the solenoid continuity test has been inactive for more or greater than the predetermined time period, the methodology advances to block 1924. At block 1924, the transmission controller 3010 turns ON or activates the pressure switch test, sets count n on the counter equal to a predetermined value such as zero, and turns ON both the two/four shift 634 and overdrive 632 solenoid-actuated valves. The methodology then advances to block 1926 and resets the timer equal to zero and sets a default value corresponding to ten seconds with the transmission fluid temperature cold; four seconds with the transmission fluid temperature warm; and sixty seconds with the transmission fluid temperature hot. The methodology then returns. 
     If the pressure switch test is ON or activated at diamond 1916, the methodology advances to block 1927 and adds a value of 1 to the count n on the counter such that n equals n plus 1. The methodology then advances to diamond 1928 (FIG. 21B) and determines whether the transmission 100 is presently operating in first or second gear by performing speed calculations and the OD pressure switch 646 is ON or pressurized. If that criteria is true, the methodology advances to block 1930 and turns OFF the overdrive solenoid-actuated valve 632. The methodology then advances to diamond 1932. If that criteria is not true, the methodology advances to diamond 1932 and determines whether the transmission 100 is operating in first or third gear as previously described and the two/four shift pressure switch 648 is ON or pressurized. If that criteria is true, the methodology advances to block 1934 and turns OFF the two/four shift solenoid-actuated valve 634. The methodology then advances to diamond 1936. If that criteria is not true, the methodology advances to diamond 1936 and determines whether the transmission temperature range is hot or the count n is greater than a predetermined value such as 7. 
     At diamond 1936, if the transmission fluid temperature is not hot or the count n is not greater than 7, the methodology advances to diamond 1938 and determines whether the two/four shift solenoid-actuated valve 634 has been turned OFF. If the two/four shift solenoid-actuated valve 634 is not OFF, the methodology returns. If the two/four solenoid-actuated valve 634 is OFF, the methodology advances to diamond 1940 and determines whether the engine temperature is greater than a predetermined temperature such as 75 degrees F. (Fahrenheit). If the engine temperature is greater than the predetermined temperature, the methodology advances to block 1942 and determines or concludes that the transmission temperature range is warm. If the engine temperature is not greater than the predetermined temperature, the methodology determines or concludes that the transmission temperature range is still cold. The methodology advances from block 1942 and diamond 1940 to diamond 1943 and determines whether the count n is less than or equal to a predetermined value such as 5. If n is greater than 5, the methodology advances to diamond 1948 to be described. If n is less than or equal to 5,  the methodology advances to diamond 1944, which is initially set to zero, and determines whether a count x on a counter is greater than or equal to a predetermined value such as 8. If x is less than 8, the methodology advances to block 1945 and adds a predetermined value of 1 to x such that x equals x plus 1. The methodology then advances to diamond 1948. If x is equal to or greater than the predetermined value, the methodology advances to diamond 1946 and determines if the engine temperature is greater than a second predetermined temperature such as 145 degrees F. If the engine temperature is greater than the second predetermined temperature, the methodology advances to block 1947 and determines or concludes that the transmission fluid temperature is hot and advances to diamond 1948. If the engine temperature is not greater than the second predetermined temperature, the transmission controller 3010 maintains that the transmission fluid temperature is warm and advances to diamond 1948. 
     If the transmission fluid temperature is hot at diamond 1936, the methodology advances to diamond 1948 and determines whether the transmission 100 is operating in third gear and that the two/four solenoid-actuated valve 634 has been turned OFF (i.e. at block 1934). If that criteria is true, the methodology advances to block 1950 and clears the retest flag (RTF). The methodology then advances to block 1951 and turns OFF or terminates the pressure switch test and returns. If the criteria in diamond 1948 is not true, the methodology advances to diamond 1952 and determines whether the transmission 100 is operating in second gear and the overdrive solenoid-actuated valve 630 has been turned OFF. If the above criteria is met or true at diamond 1952, the methodology advances to block 1950 previously described. If the above criteria is not met at diamond 1952, the methodology advances to diamond 1954 and determines whether the transmission 100 is operating in first gear and the two/four 634 and overdrive 630 solenoid-actuated valves have been turned OFF. If that criteria is true, the methodology advances to block 1950 previously described. If that criteria is not true, the methodology advances to diamond 1955 and determines whether the value of n is greater than or equal to the value of Z. If n is less than Z, the methodology returns. If n is greater than or equal to Z, the methodology advances to diamond 1956 and determines whether the transmission fluid temperature is cold. If the transmission fluid temperature is cold, the methodology advances to block 1951 previously described to terminate the pressure switch test. If the transmission fluid temperature is not cold, the methodology advances to diamond 1958 and determines whether the retest flag (RTF) has been set. If the RTF has been set, the methodology advances to block 1960 and reports a pressure switch test failure to the diagnostics to be described under section heading &#34;ON-BOARD DIAGNOSTICS&#34;. The methodology then advances to bubble 1962 and goes to shutdown mode. If the RTF is not set, the methodology advances to block 1964 and sets the RTF and the time on the timer equal to a predetermined value such as 5. The methodology then advances to block 1951 previously described to terminate the pressure switch test and returns. 
     The preferred method of determining the fluid temperature of the transmission 100 is an &#34;accumulated run time&#34; method. This method predicts T o , transmission fluid temperature. It bases the prediction on ambient and/or engine coolant temperatures and on observed transmission and engine warm-up rates. By using ambient temperature, the engine block heaters use is accommodated. If engine temperature is lower than ambient, it will be used since it is more accurate. In the absence of any temperature sensor data, -3° F. is used for ambient. The sensor data is received via the CCD link from the engine controller 3020. 
     This method includes measuring the time spent in a non-neutral gear condition which represents effectively torque converter slippage. When the torque converter 110 is slipping while transmitting torque from the engine to the transmission 100, heat is generated by energy conversion. This heat elevates the temperature of the transmission fluid. The transmission controller 3010 monitors time (T R ) (FIG. 21D) and approximates with acceptable accuracy, the quantity of heat generated, and thereby the elevation of transmission fluid temperature. Testing can be conducted to determine the relationship between the &#34;run time&#34; T R  and the quantity of temperature use (ΔT) in the transmission sump as illustrated in FIG. 21D. 
     The method includes reading the temperature of the engine by an input sensor and multiplying the engine temperature by a predetermined value such as 0.1. The method also includes reading the temperature of the ambient air by an input sensor and multiplying the ambient temperature (T A ) by a predetermined value such as 0.9. These values are added together to obtain the temperature point on the T o  ordinate. The transmission controller 3010 monitors or resumes the run time period (T R ) once the SLP 606 does not equal neutral N and N e  is greater than a predetermined speed such as 800 r.p.m. The measured run time is multiplied by a predetermined slope value such as 10 and is added to the summed value of the multiplied engine and ambient temperature. Thus, the equation of the curve T o  in FIG. 21D may be defined as follows: 
     
         T.sub.o =(0.9T.sub.A +0.1 Σ)+10*T.sub.R 
    
     Accordingly, if T o  is less than 40° Fahrenheit (F), the transmission fluid temperature will be predicted or set to cold. If T o  is greater than 80° F., the transmission fluid temperature will be predicted or set to hot. Otherwise, the transmission fluid temperature is predicted as or set to warm. 
     Additionally, a transmission temperature flag β o  (super cold) allows for near-normal operation under sub-zero conditions. This flag is set when T o  is less than 0° F. and cleared when T o  is greater than 10° F. The super cold flag β o  is used by the transmission controller 3010 to extend shift times and inhibit a third to first (3-1) shift by setting a flag. Other uses are also available. 
     Accordingly, this alternative, but preferred method allows the transmission controller 3010 to determine the transmission fluid temperature without a dedicated temperature sensor immersed in the transmission fluid. 
     The present invention has been described in an illustrative manner. It is to be understood that the terminology which has been used is intended to be in the nature of words of description rather than of limitation. 
     Obviously, many modifications and variations are possible in light of the above teachings. Therefore, the subject invention may be practiced otherwise than as specifically described.