Abstract:
A method for controlling the temperature of transmission fluid in a motor vehicle includes operating in an automatic transmission fluid cooling mode, a heater priority mode entered by disabling automatic transmission fluid heating, and an automatic transmission fluid heating mode which includes sending hot engine coolant to a heat exchanger for heating the automatic transmission fluid by transferring heat from the hot engine coolant to the automatic transmission fluid. The method switches to from a heater priority mode to a transmission heating mode base on a number of sensed conditions including sensed automatic fluid transmission temperature. The method also includes an automatic transmission fluid temperature regulating mode including measuring an automatic transmission fluid temperature and switching between the cooling mode and the heating mode based measured temperature.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention pertains to the art of reducing parasitic losses in transmissions by warming up transmission fluid present in the transmission in a rapid and efficient manner thereby reducing the transmission fluid&#39;s viscosity and cooling the transmission fluid when the transmission is subject to heavy loads. 
       BACKGROUND OF INVENTION 
       [0002]    Motor vehicles are typically used to transport people from place to place. As such they often have a passenger compartment and a power source, such as an engine that drives an automatic transmission which transmits energy from the power source to a set of driven wheels to propel the vehicle. Making such motor vehicles more efficient is currently a main focus of the automobile industry. Unfortunately, most automatic transmissions typically suffer from parasitic losses on startup of the power source. Such losses are particularly acute in the presence of low ambient temperatures, such as those present in a cold start in winter or a cold start in geographic areas having cold climates. Since the automatic transmission fluid present in the transmission has a viscosity that changes based on temperature, in cold temperature the viscosity may be quite high, thereby causing unacceptable parasitic losses and reduced fuel economy at least until the power source warms up the transmission and the automatic transmission fluid. Another problem associated with controlling the temperature of automatic transmission fluid is overheating. When a motor vehicle is subject to heavy use, for example, when the motor vehicle is towing a heavy load, the automatic transmission fluid is often heated too quickly and may overcome inherent cooling present in the transmission and additional cooling systems must be employed. 
         [0003]    Also, in order to cool the engine, motor vehicles are typically provided with a cooling system that circulates a liquid coolant through the engine which heats the coolant and cools the engine. The coolant then flows through a heat exchanger or radiator to remove heat from the coolant. The coolant leaving the engine is often used as a heat source for auxiliary tasks. For example, the hot coolant leaving the engine may be sent though a heater core designed to transfer heat from the coolant to air. The hot air is then used to heat the passenger compartment. 
         [0004]    To address the problem of reduced fuel economy caused by the transmission fluid being too cold soon after engine start, many motor vehicle manufacturers are pursuing technologies that will help the automatic transmission fluid heat up more quickly. One solution has been to use an oil-to-engine coolant heat exchanger to warm the automatic transmission fluid. However, in past arrangements, additional cooling has been required and therefore the arrangements have not been cost effective. Also, such arrangements have adversely affected passenger compartment heating and even adversely affected coolant flow through associated radiators. Passenger compartment heating can be compromised if too much heat is diverted to heating the automatic transmission fluid and, in the case of a two part radiator with a low temperature loop and a high temperature loop, additional efforts are needed to ensure that engine coolant is always flowing through the low temperature loop when coolant is flowing through the high temperature loop to avoid damage to the radiator. 
         [0005]    Another solution is represented by the arrangement shown in U.S. Pat. No. 6,196,168. More specifically, a system is disclosed for preheating transmission fluid wherein part of the engine coolant is quickly heated by an internal combustion engine  17  and made available for heating of the transmission fluid as shown in  FIG. 2 . Coolant flows through an equalization tank  2  and then through an oil/water heat exchanger  5  but does not flow through radiator  4 ,  14 . However, such an arrangement still suffers from several drawbacks. For example, the arrangement employs an excessive number of parts, which form a complex system that is slow to respond to changes in temperature. Another attempt to preheat transmission fluid is represented by U.S. Pat. No. 7,267,084. As shown in  FIG. 2 , engine coolant is sent through heat exchanger/oil cooler  24  to heat transmission fluid, however the system is not designed to send only hot or cold coolant to heat exchanger/oil cooler  24  the but rather sends a mixture of the hot and cold coolant. Furthermore, in order to function properly, the arrangement in  FIG. 2  requires a relatively large number of control valves and heat exchangers yielding a relatively complicated and expensive system. 
         [0006]    Based on the above, there exists a need in the art for a system for heating and cooling automatic transmission fluid in a rapid and efficient manner thereby reducing the viscosity of the transmission fluid and for cooling the transmission fluid when the transmission is subject to heavy loads, while overcoming some or all of the above-mentioned shortcomings of the prior art. 
       SUMMARY OF THE INVENTION 
       [0007]    The present invention is directed to a method for controlling the temperature of transmission fluid in a motor vehicle having a radiator and an automatic transmission fluid heat exchanger. In a first embodiment, the method first includes entering a heater priority mode by having an engine thermostat prevent hot engine coolant from reaching the radiator or heat exchanger when the engine is cold. In other embodiments, a cooling mode is, optionally and briefly, entered by sending cold engine coolant to a heat exchanger for cooling the automatic transmission fluid by transferring heat from the automatic transmission fluid to the cold engine just prior to entering the heater priority mode. Additionally, the heater priority mode in the other embodiments is entered by disabling automatic transmission fluid heating using two valves that operate independently of the thermostat. 
         [0008]    In any case, the method next enters a heating mode by transferring heat from hot engine coolant to the automatic transmission fluid only when it is determined that at least one of the four following conditions is met. A first condition is met by determining if the measured engine coolant temperature is above a coolant temperature set point. A second condition is met by measuring an automatic transmission fluid temperature in the automatic transmission and determining if the measured transmission fluid temperature is above a fluid temperature set point. A third condition is met by determining if a first timer has expired. The first timer is set when a rate of change of the engine coolant temperature exceeds a rate threshold. The first timer is set to: a high timer value if the engine coolant temperature is below a low temperature set point; a variable timer value if the engine coolant temperature is between the low temperature set point and a high temperature set point; and a low timer value if the engine coolant temperature is above the high temperature set point. A fourth condition is met by determining if a second timer has expired. The second timer is set if the transmission control lever is not in the park position at which point the second timer is set to within a high variable time range if the engine coolant temperature is in a low variable temperature range; an intermediate variable time range if the engine coolant temperature is in an intermediate variable temperature range; and a low timer set point if the engine coolant temperature is above a high value temperature set point. 
         [0009]    The method then enters an automatic transmission fluid temperature regulating mode which includes measuring the temperature of the automatic transmission fluid and switching between the cooling mode and the heating mode based on the measured temperature. More specifically, the regulating mode includes measuring a sump temperature of the automatic transmission fluid and measuring a case exit temperature of the automatic transmission fluid as the fluid leaves the transmission. The cooling mode is entered when either the transmission sump temperature exceeds a first high set value or the temperature at the transmission case exit exceeds a second high set value. The heating mode is entered when both the sump temperature drops below a first low set value and the case out temperature drops below a second low set value. 
         [0010]    Each of the preferred embodiments provides a method for heating and cooling automatic transmission fluid in a rapid and efficient manner, thereby reducing the viscosity of the transmission fluid and for cooling the transmission fluid when the transmission is subjected to heavy loads. Additional objects, features and advantages of the present invention will become more readily apparent from the following detailed description of preferred embodiments when taken in conjunction with the drawings wherein like reference numerals refer to corresponding parts in the several views. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a diagram showing a vehicle incorporating a system for heating and cooling automatic transmission fluid in accordance with the invention; 
           [0012]      FIG. 2  is a schematic diagram of a first preferred embodiment of the system in  FIG. 1  in a heater priority mode using a single valve and an engine thermostat; 
           [0013]      FIG. 3  is a schematic diagram of the first preferred embodiment of the system in  FIG. 2  in an automatic transmission fluid heating mode; 
           [0014]      FIG. 4  is a schematic diagram of the first preferred embodiment of the system of  FIG. 2  in an automatic transmission fluid cooling mode; 
           [0015]      FIG. 5  is a schematic diagram of a second preferred embodiment of the system in  FIG. 1  in a heater priority mode independent of the engine thermostat using two valves; 
           [0016]      FIG. 6  is a schematic diagram of the second preferred embodiment of the system of  FIG. 5  in an automatic transmission fluid heating mode; 
           [0017]      FIG. 7  is a schematic diagram of the second preferred embodiment of the system in  FIG. 5  in an automatic transmission fluid cooling mode; 
           [0018]      FIG. 8  is a schematic diagram of a third preferred embodiment of the system in  FIG. 1  in a heater priority mode using two valves; 
           [0019]      FIG. 9  is a schematic diagram of the third preferred embodiment of the system of  FIG. 8  in an automatic transmission fluid heating mode; 
           [0020]      FIG. 10  is a schematic diagram of the third preferred embodiment of the system in  FIG. 8  in an automatic transmission fluid cooling mode; 
           [0021]      FIG. 11  is a schematic diagram of a fourth preferred embodiment of the system in  FIG. 1  in a heater priority mode using two valves; 
           [0022]      FIG. 12  is a schematic diagram of the fourth preferred embodiment of the system of  FIG. 11  in an automatic transmission fluid heating mode; 
           [0023]      FIG. 13  is a schematic diagram of the fourth preferred embodiment of the system in  FIG. 11  in an automatic transmission fluid cooling mode; 
           [0024]      FIG. 14  is a flowchart showing a control routine employed in the system of  FIG. 2  according to the first preferred embodiment of the invention; 
           [0025]      FIG. 15  is a graph showing a first timer setting versus engine coolant temperature at start-up in accordance with the invention; 
           [0026]      FIG. 16  is a graph showing a second timer setting versus engine coolant temperature at start-up in accordance with the invention; 
           [0027]      FIG. 17  is a flowchart showing a control routine employed according to the second, third and fourth preferred embodiments of the invention; and 
           [0028]      FIG. 18  is a flowchart showing details of the automatic fluid transmission temperature control routine of  FIG. 13  that applies to all four preferred embodiments. 
       
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0029]    With initial reference to  FIG. 1 , there is shown an automotive vehicle  10  having a body  11  and an internal combustion engine  12  with a radiator  14 . Within body  11  there is located a passenger compartment  15  that is heated by heat transferred from engine  12  as discussed more fully below. Power from engine  12  is transmitted to a transmission  18 , then to the other portions of a powertrain  20  and eventually to drive wheels  22 . Transmission  18  may be shifted between park, drive and reverse settings by a control lever  25 . Vehicle  10  is shown as a rear wheel drive vehicle but any type of powertrain arrangement, including front wheel, all wheel drive and hybrid systems, could be employed. A system  30  for controlling heating or cooling automatic transmission fluid flowing through transmission  18  includes a controller  35  connected to engine  12 , transmission  18 , and shift lever  25  by communication lines  37 ,  38  and  39  respectively. In accordance with the invention, system  30  functions by warming up transmission fluid present in transmission  18  in a rapid and efficient manner, thereby reducing the viscosity of the transmission fluid and cooling the transmission fluid when transmission  18  is subjected to heavy loads as more fully discussed below. 
         [0030]    Referring to  FIG. 2 , there is shown a schematic diagram of a first preferred embodiment of system  30  in a heater priority mode. An engine cooling circuit  40  is shown having a hot coolant line  42  extending from engine  12  to radiator  14 . Engine  12  is a conventional internal combustion engine having an engine block containing the usual coolant passages arranged to allow engine coolant to absorb heat generated by the operation of engine  12 . The hot engine coolant is pumped through hot coolant line  42  to radiator  14 . Radiator  14  is preferably designed to have a high temperature section  44  and a low temperature section  46 . Radiator  14  is designed to carry heat away from the hot engine coolant and transfer the heat to ambient air flowing over radiator  14  and allow the cooled engine coolant to return to engine  12  through cold engine coolant line  48  thus completing engine cooling circuit  40 . Engine cooling circuit  40  is selectively opened or closed to engine coolant flow by a thermostat  50 , preferably located between radiator  14  and engine  12  in hot coolant line  42 . Thermostat  50  closes off cooling circuit  40  upon engine startup when engine  12  is cold. Thermostat  50  opens up cooling circuit  40  when engine  12  becomes hot enough to need cooling and thus regulates the engine temperature. A return line  51  is provided with a flow restrictor device  52  or relief valve located either internally or externally to radiator  14 . Return line  51  assures proper flow through radiator  14  so that both high temperature section  44  and low temperature section  46  receive coolant flow simultaneously. 
         [0031]    A passenger compartment heating circuit  60  is shown as starting at engine  12 , extending through heater core supply line  62  to a heater core  64  and then back to engine  12  through a heater core return line  66 . Engine coolant always flows through heating circuit  60  when engine  12  is running, however the amount of heat carried by the engine coolant may vary as described more fully below. Regardless, excess heat from engine  12  is transferred to hot engine coolant that passes through heater core supply line  62  to heater core  64 . In heater core  64 , heat is then transferred from the hot engine coolant to air that is used to heat passenger compartment  15 . An automatic transmission temperature regulation circuit  68  includes a transmission temperature regulation fluid line  69  that guides transmission fluid from transmission  18  to a heat exchanger  70  and back to transmission  18 . Heat exchanger  70  preferably transmits heat either to or from the transmission fluid flowing through temperature regulation circuit  68  in a manner discussed in more detail below. 
         [0032]    A transmission preheating circuit  74  receives hot engine coolant from passenger compartment heating circuit  60 . Preferably, transmission preheating circuit  74  connects to supply line  62  of heating circuit  60  just up stream of heater core  64  through a main preheating supply line  76 . Alternatively, transmission preheating circuit  74  receives hot engine coolant from heater core return line  66  through an optional preheating supply line  78 , which connects to main preheating supply line  76 . In either case, preheating supply line  76  is connected to a first valve  80  which in turn is connected to a shunt line  82  extending between first valve  80  and heat exchanger  70 . Preheating circuit  74  also includes a preheating return line  84  for returning engine coolant to passenger compartment heating circuit  60 . A transmission cooling circuit  89  includes a cold engine coolant supply line  90  that extends from radiator  14  to first valve  80 . Cooling circuit  89  provides relatively cool engine coolant to first valve  80 . 
         [0033]    In  FIG. 2 , system  30  is shown in a heater priority mode. Since thermostat  50  also will prevent coolant flow to first valve  80  when engine  12  is cold, no coolant travels from radiator  14  to exchanger  70  even though first valve  80  is positioned to allow such flow. The heater priority mode only lasts a short time until engine  12  warms up and then thermostat  50  will switch positions to that shown in  FIGS. 3 and 4 . In  FIG. 3 , first valve  80  is positioned to allow a flow  94  of hot engine coolant through optional supply line  78  or a flow  96  of hot engine coolant through supply line  76  to heat exchanger  70  thus placing system  30  in an automatic transmission fluid heating mode. Heat from engine  12  is transferred in engine  12  to hot engine coolant flow  96  that flows through supply line  62  and then preheating supply line  76  to first valve  80  and shunt line  82 . The heat then transfers from the hot engine coolant to the relatively cool automatic transmission fluid. The heat then travels through transmission temperature regulation circuit  68  to preheat the transmission fluid in transmission  18  when system  30  is operating in cold ambient temperatures. By contrast, in  FIG. 4 , system  30  is shown in an automatic transmission fluid-cooling mode. In the fluid-cooling mode, first valve  80  is positioned to allow a flow  97  of relatively cool engine coolant through engine coolant supply line  90  to first valve  80 . The cool engine coolant travels through shunt line  82  to heat exchanger  70  and functions to cool the automatic transmission fluid flowing through temperature regulation circuit  68 . 
         [0034]    Controller  35  is connected several temperature sensors in order to determine a starting temperature that is indicative of the temperature of the automatic transmission fluid when engine  12  is started. For example, controller  35  is connected to a temperature sensor  101  through communication line  37  to allow controller  35  to read the temperature of engine  12  or the engine coolant in engine  12 . Controller  35  is also connected to temperature sensors  103  and  105  through communication line  38  and  39  so that controller  35  is allowed to read the temperature of the transmission fluid in the sump or a transmission case exit. Alternatively, the case exit temperature is inferred from the sump fluid temperature and other signals available to controller  35 . Additionally, ambient temperature is measured from any location such as the air intake to engine  12  or the air flowing in passenger compartment  15 . Preferably, any one of these temperatures, or other measured temperatures indicative of the automatic transmission fluid when engine  12  is started, constitute the starting temperature. Controller  35  also includes a first timer T 1  and a second timer T 2 . With this configuration, controller  35  is able to control the position of valve  80  through control line  110  depending on the sensed temperatures and based on certain timing to switch system  30  between the automatic transmission heating mode of  FIG. 2  and the automatic transmission cooling mode of  FIG. 3  as discussed more fully with respect to  FIG. 10 . 
         [0035]    Turning to  FIGS. 5-7 , there is shown a second preferred embodiment of the invention. Most of the parts of the second preferred embodiment are the same as the first preferred embodiment and like reference numerals are used for like parts. Only the differences between the two embodiments will be discussed here. In the second preferred embodiment, a system  130  has a transmission cooling circuit  189  with a second valve  190  not found in the first preferred embodiment. Second valve  190  is connected to an engine coolant supply line  192 . Second valve  190  is controlled by controller  35  through communication line  195  and is adapted to switch flow between a cold-coolant return conduit  198  and coolant line  192 . Second valve  190  is positioned to selectively send cold engine coolant flow  199  back to engine  12  as in  FIGS. 5 and 6 , or to send cold engine coolant to valve  80  as in  FIG. 7  to place system  130  in a transmission cooling mode. When second valve  190  sends fluid back to engine  12 , system  130  is placed in a heater priority mode when valve  80  is in a position as shown in  FIG. 5 , or an automatic transmission fluid heating mode when valve  80  is in a position as shown in  FIG. 6 . In the heater priority mode, system  130  does not provide any flow through heat exchanger  70 . In the transmission heating mode, a flow  196  of hot engine coolant is sent to heat exchanger  70  from engine  12  and in the automatic transmission fluid cooling mode, a flow  197  of cold engine coolant is sent to heat exchanger  70  from radiator  14 . In the second embodiment, thermostat  50  is preferably located in coolant line  48  and does not affect switching system  130  between modes. 
         [0036]    Turning now to  FIGS. 8-10 , there is shown a third preferred embodiment of the invention. Most of the parts of the third preferred embodiment are the same as the second preferred embodiment and like reference numerals are used for like parts. Only the differences between the two embodiments will be discussed here. Specifically, valve  80  of the second preferred embodiment which receives flow from both line  76  and line  192 , has been replaced with a valve  280  that only receives coolant flow from line  76 . Line  192  has been replaced with line  292  that directly connects second valve  190  to line  82 . In  FIG. 8 , system  230  is in a heater priority mode with no coolant flowing through heat exchanger  70  because first valve  280  is closed preventing the flow of hot engine coolant from engine  12  through line  76 , while valve  190  is set to return cold engine coolant back to engine  12  and prevents cold engine coolant from reaching heat exchanger  70 . In  FIG. 9 , system  230  is in an automatic transmission fluid heating mode with a hot engine coolant flow passing through heat exchanger  70  because first valve  280  is open allowing the flow of hot engine coolant from engine  12  through line  76 , while valve  190  is set to return cold engine coolant back to engine  12  and prevents cold engine coolant from reaching heat exchanger  70 . In  FIG. 10 , system  230  is in an automatic transmission fluid cooling mode with a cold engine coolant flow passing through heat exchanger  70  because first valve  280  is closed preventing the flow of hot engine coolant from engine  12  through line  76 , while valve  190  is set to supply cold engine coolant to heat exchanger  70  through line  292 . 
         [0037]    Turning now to  FIGS. 11-13 , there is shown a fourth preferred embodiment of the invention. Most of the parts of the fourth preferred embodiment are the same as the third preferred embodiment and like reference numerals are used for like parts. Only the differences between the two embodiments will be discussed here. Specifically, valve  190  of the third preferred embodiment has been replaced with valve  290  which is set to either allow or not allow flow from radiator  14  to heat exchanger  70 . Additionally, return conduit  198  is not used but rather return line  51  and restriction device  52  from the first embodiment are used. Valves  280  and  290  are closed in  FIG. 11  thus placing a system  330  into a heater priority mode. In  FIG. 12 , system  330  is in an automatic transmission fluid heating mode with a hot engine coolant flow passing through heat exchanger  70  because first valve  280  is open allowing the flow of hot engine coolant from engine  12  through line  76 , while valve  290  is set to return cold engine coolant back to engine  12  and prevents cold engine coolant from reaching heat exchanger  70 . In  FIG. 13 , system  330  is in an automatic transmission fluid cooling mode with a cold engine coolant flow passing through heat exchanger  70  because first valve  280  is closed preventing the flow of hot engine coolant from engine  12  through line  76 , while valve  290  is set to supply cold engine coolant to heat exchanger  70  through line  292 . 
         [0038]      FIG. 14  is a flowchart showing a control routine  300  employed in system  30  of  FIGS. 2-4  according to the first preferred embodiment of the invention. Control routine  300  starts when a key is turned, as in step  310 , to start engine  12 . Controller  35  then switches valve  80  to the position shown in  FIG. 2  while engine thermostat  50  is closed to place system  30  in the automatic transmission fluid heater priority mode. Also, controller  35  calculates settings for first and second timers T 1 , T 2  at step  312  as discussed more fully with respect to  FIGS. 15 and 16 . While the graphs of  FIGS. 15 and 16  show settings for timers T 1  and T 2  being set by measured engine coolant temperature, the settings for timers T 1  and T 2  are optionally set by any measured temperature indicative of the automatic transmission fluid when engine  12  is started that constitutes the starting temperature as discussed more fully above. Loop  315  simply represents a logical flow node. Controller  35  keeps valve  80  activated until one of four events occurs. At step  320  the engine coolant temperature is measured and if the engine coolant temperature is not greater than a threshold of preheat 190 degrees Fahrenheit (88° C.) control routine  300  continues. At step  325 , the transmission fluid&#39;s temperature in the sump is checked, and if the temperature is not above 200 degrees Fahrenheit (93° C.), control routine  300  continues. At step  330 , timer T 1  is checked. If timer T 1  is not on at step  330 , then the rate of change of the transmission temperature is checked at  332 . If the rate of change is less than a rate threshold of preferably one degree Fahrenheit (5/9° C.), per minute, then the timer is set at step  334 . While timer T 1  is running at step  336 , the routine continues. At step  340 , timer T 2  is checked. If timer T 2  is not running at step  340 , then control lever  25  is checked to determine if transmission  18  is in park. If transmission  18  is moved from park into reverse, drive or any other position, then timer T 2  is set. While timer T 2  is running, control routine  300  continues. If the engine coolant temperature drops below 190 degrees Fahrenheit (88° C.), or the temperature of the automatic transmission fluid in the sump drops below 200 degrees Fahrenheit (93° C.), or either timer T 1 , T 2  runs out, then control routine  300  switches valve  80  at step  350  and at step  360  the automatic transmission fluid regulation mode is entered. While the listed temperatures are preferable, other temperatures may be used in step  320  and  325  to determine when the control routine enters step  350 . For example, a lower temperature of 160 degrees Fahrenheit (71° C.) may be used in step  320 . Preferably, the temperature setting in step  320  should be below a setting present for thermostat  50  to ensure proper operation of routine  300 . 
         [0039]      FIG. 15  is a graph  370  showing a first timer setting  372  verses the starting temperature, in this case engine coolant temperature (ECT)  374  at engine start up. At very cold engine coolant temperatures below a low temperature set point, preferably 0 degrees Fahrenheit (−18° C.), the timer T 1  is set to a high timer value, preferably 10 minutes, as shown by line  376 . Between the low temperature set point and a high temperature set point, preferably 0 (−18° C.), and 15 degrees Fahrenheit (−9° C.) respectively, timer T 1  setting changes as shown by line  377  as a variable timer value, preferably between 10 and 0 minutes. Intermediate points on the graph are preferably derived by interpolation. Above the high temperature set point, timer T 1  is set to a low timer value, preferably 0 minutes as shown by line  378 . Alternatively, more set points are used to define the relationship between timer T 1  and the starting temperature. 
         [0040]      FIG. 16  is a graph  380  showing a second timer setting  382  verses the starting temperature, in this case engine coolant temperature (ECT)  384  at engine start up. At very cold engine coolant temperatures in a low variable temperature range, preferably between −40 and 0 degrees Fahrenheit (−18° C. and −4° C.), timer T 2  is set within a high variable time range as shown by line  386 . The high variable time range is preferably between 45-30 minutes. When the temperature is in an intermediate temperature range, preferably between 0 and 20 degrees Fahrenheit (−18° C. and −9° C.), timer T 2  is set to a variable amount as shown by line  387 . Again, in an intermediate variable time range, preferably between 30 to 0 minutes, intermediate points on the graph are derived by interpolation. Above a high value temperature set point, preferably 20 degrees Fahrenheit (−7° C.), timer T 2  is set to a low timer set point, preferably 0 degrees Fahrenheit (−18° C.) as shown by line  388 . Alternatively, more set points are used to define the relationship between timer T 2  setting and starting temperature. 
         [0041]      FIG. 17  is a flowchart showing a control routine  400  employed in systems  130 ,  230  and  330  according to the second, third and fourth preferred embodiments of the invention. Control routine  400  starts when a key is turned as in step  410  to start engine  12 . At step  412 , first valve  80 ,  280  and second valve  190 ,  290  are switched to the position shown in  FIGS. 7 ,  10  and  13  so that systems  130 ,  230 , and  330  enter the automatic transmission-cooling mode. Also, controller  35  calculates settings for first and second timers T 1 , T 2  at step  412  based on one of the initial starting temperature of the engine coolant, ambient air or automatic transmission fluid. Preferably, less than two seconds later, control routine  400  then proceeds to step  415  and switches second valve  190 ,  290 . At this point, systems  130 ,  230 , and  330  are in the heater priority mode wherein no engine coolant flow is passing through heat exchanger  70 . Control routine  400  then essentially incorporates all the steps of control routine  300  of  FIG. 10  and therefore the description of routine  300  will not be repeated. Control routine  400  will then switch first valve  80 ,  280  if any one of the four conditions described above occur to enter the heating mode. Preferably, second valve  190 ,  290  will also switch. 
         [0042]    After control routine  300  has completed, control routine  400  enters automatic transmission fluid regulation mode at step  460  as can best be seen in  FIG. 18 . Systems  130 ,  230  and  330  are in automatic transmission warming mode when first entering step  461  and then the routine proceeds to loop  462 . Preferably, systems  130 ,  230  and  330  switch to automatic transmission cooling mode if either of the following two conditions are met, i.e., sump temperature exceeds a set value, preferably 220 degrees Fahrenheit (104° C.) as seen at step  463 , or transmission case output temperature exceeds a set value, preferably 260 degrees Fahrenheit (127° C.) as seen at step  464 . Essentially, these conditions indicate that the automatic transmission fluid needs cooling, thus first and second valve are switched to enter the cooling mode as shown at step  465 . Of course, it is possible that these conditions may not be met when transmission  18  is subject to a light duty cycle. Systems  130 ,  230  and  330  then switch back to automatic transmission heating mode as shown in steps  466 ,  467 ,  468  and  469  if both the following conditions are met, i.e., sump temperature drops below a set value (TOT), preferably 200 degrees Fahrenheit (93° C.) as shown in step  467 , and transmission case out temperature drops below a set value, preferably 220 degrees Fahrenheit (104° C.) as shown in step  468 . At step  469 , systems  130 ,  230  and  330  then proceed to switch back and forth between the warming mode and the cooling mode based on the same criteria as shown by loops  462  and  466 . While described with respect to systems  130 ,  230  and  330  of  FIGS. 5-13 , the automatic transmission temperature regulation is also employed by the first preferred embodiment by switching valve  80  between the warming mode of  FIG. 3  to the cooling mode of  FIG. 4  based on the temperature criteria described above. 
         [0043]    Each of the four preferred embodiments provides a system for heating and cooling automatic transmission fluid in a rapid and efficient manner thereby reducing the transmission fluid&#39;s viscosity and cooling the transmission fluid when the transmission is subjected to heavy loads. Although described with reference to preferred embodiments of the invention, it should be readily understood that various changes and/or modifications can be made to the invention without departing from the spirit thereof. For example, the optional preheating supply line  78  shown in  FIGS. 2-4  could be used in any of the embodiments shown in  FIGS. 5-13 . In general, the invention is only intended to be limited by the scope of the following claims.