Abstract:
A method and apparatus for restarting a locomotive engine based on the lubricating oil temperature T oil  at the time of shutdown and an average oil cool down rate R. The average cool down rate R may be a function of the ambient air temperature T AIR  at the time of shut down. The method and apparatus of this invention allows the engine to be shutdown during periods of inactivity to conserve fuel, but prevents the engine from cooling below a predetermined temperature in order to avoid excessive wear in operating limitations upon restart.

Description:
This invention relates generally to the field of the operation of internal combustion engines, and more particularly to a method and apparatus for restarting an engine prior to it cooling beyond a predetermined temperature. 
     BACKGROUND OF THE INVENTION 
     It is well known that it can be difficult to start an internal combustion engine from a cold condition, particularly during cold weather conditions. When an engine is out of service, the engine lubricating oil will achieve a temperature consistent with the ambient air temperature, and it will become highly viscous. Upon starting the engine from the cold condition, the lubricating oil will gradually warm to its normal operating temperature. However, during the warm-up period, the operation of the lubricating system is degraded due to the high viscosity of the oil. Cold starting of an internal combustion engine is made more difficult due to the increased friction caused by the high oil viscosity, and engine parts may experience accelerated wear rates during the warm-up period due to the degraded lubricating system performance. 
     Self-propelled vehicles commonly utilize an internal combustion engine as a prime mover. The assignee of the present invention is a supplier of locomotives powered by turbo-charged diesel engines, such as the General Electric model GE7FDL16 diesel engine. Such engines are subject to the disadvantages discussed above during cold starting conditions. Furthermore, the operating instructions for a locomotive may include limitations on the engine throttle settings prior to the engine achieving full operating temperature. In cold weather conditions, there may be a delay of more than one hour after starting the locomotive engine from cold conditions until the engine is capable of operating at full throttle. U.S. Pat. No. 4,592,323 issued to Vest on Jun. 3, 1986, and assigned to the assignee of the present invention, discloses a system for limiting the maximum speed of the diesel engine of a locomotive when the lubricating oil is relatively cool and hence highly viscous. The Vest patent describes the design and operation of a diesel locomotive engine system in some detail and is incorporated by reference herein. For some applications, such as when operating in a switch yard, a locomotive is used for only short periods followed by periods of inactivity. In order to avoid delays in the availability of such engines, particularly in cold weather conditions, it is common for the engine of the locomotive to be placed in the idle position during periods of inactivity. Although this approach is effective in maintaining the engine at operating temperature, it also results In the wasting of fuel during the idling periods. Alternatively, the engine may be shut down between periods of operation in order to conserve fuel, however, this increases the risk the temperature of the lubricating oil will drop below the desired operating level. 
     FIG. 1 illustrates the lubricating oil system of a prior art diesel locomotive engine  10 . An oil pump  12  draws oil from the engine  10  and delivers it to an oil cooler  14 . The oil cooler  14  functions to transfer heat from the engine oil to a cooling water supply (not shown). The oil is then pumped through a filter  16  and returned to engine  10 . For many applications, such as the GE7FDL16 diesel engine, the temperature of the oil is measured at a point in the lubricating oil system that is remote from the engine  10 . As illustrated in FIG. 1, it is common for the temperature of the oil to be measured by a temperature sensor  18  located downstream of pump  12  near the inlet of cooler  14 . Such a location is convenient for the design of the lubricating oil system, and it provides an accurate measurement of the lubricating oil temperature during the operation of the engine. However, during periods of engine shutdown, the oil becomes stagnate within the lubricating oil system and/or drains completely out of the filter  16  and cooler  14  and returns to the engine  10 . Therefore, during engine shutdown conditions, temperature measuring device  18  is ineffective for providing an indication of the lubricating oil temperature within engine  10 . Therefore, the operator of the locomotive will have no reliable indication of the actual lubricating oil temperature within engine  10  and will be unable to predict whether the operation of the engine  10  will be delayed upon startup due to lubricating oil temperature limitations. As a result, in order to assure that the locomotive will always be available for full power service, it is common practice to allow the engine to operate at idle conditions during periods of inactivity. 
     BRIEF SUMMARY OF THE INVENTION 
     Thus, there is a particular need for a method and apparatus for operating an engine in a manner that prevents cold starts and that improves the fuel efficiency of the engine. A method of operating a locomotive engine is provided comprising the steps of: obtaining an average cool down rate of the engine oil after shutdown of the engine; shutting down the engine; obtaining the oil temperature at the time of engine shutdown; calculating a maximum shutdown time for the engine by subtracting a predetermined minimum oil temperature from the oil temperature at the time of engine shutdown and dividing that difference by the average cool down rate; and restarting the engine before exceeding the maximum shutdown time. In addition, an apparatus for operating a locomotive engine is provided comprising: a means for storing an average engine cool down rate; a means for measuring the ambient temperature at the time of engine shutdown; a means for measuring the oil temperature at the time of engine shutdown; a controller connected to the means for storing, means for measuring the ambient temperature, and means for measuring the oil temperature, the controller comprising a means for calculating a maximum shutdown time as a function of the average oil cool down rate, the ambient temperature at the time of engine shutdown, and oil temperature at the time of engine shutdown; a means for measuring time elapsed after engine shutdown connected to the controller; and a means for starting the engine connected to the controller and operable to start the engine when the time elapsed after engine shutdown equals or exceeds the maximum shutdown time. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The feature and advantages of the present invention will become apparent from the following detailed description of the invention when read with the accompanying drawings in which: 
     FIG. 1 is a schematic illustration of a prior art internal combustion engine lubricating oil system. 
     FIG. 2 is a flow chart illustrating a method of operating an engine wherein the engine is restarted within a calculated maximum shutdown time period. 
     FIG. 3 is a schematic illustration of an engine and lubricating oil system used for implementing the method of FIG.  2 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In order to prevent the cold startup of an engine, it would be helpful to have available a measurement of the actual lubricating oil temperature within the engine. Unfortunately, many applications of large self-propelled traction vehicles such as locomotives do not include a temperature sensor in an appropriate location within the primary mover engine. While it is possible to add a temperature measuring device at an appropriate position within the engine, such additional instrumentation would be costly to install and would increase the maintenance cost for the vehicle. In lieu of adding such sensors to every vehicle, the inventor has developed a method of operation and apparatus for ensuring that the engine is restarted prior to cooling below a predetermined oil temperature limit. 
     In one embodiment of the present invention, the inventor has taken representative data from a GE7FDL16 diesel locomotive engine. The temperature of the lubricating oil T OIL  was measured as a function of the time period after engine shutdown at a variety of different ambient air temperatures T AIR . By obtaining a large and representative sampling of such data, as illustrated in step  20  in FIG. 2, the inventor was able to calculate an average rate of cool down R for the engine, as illustrated in step  22  of FIG.  2 . Since the average cool down rate may change as a function of ambient air temperature, a plurality of cool down rates R may be calculated for a plurality of ambient air temperature ranges. For the GE7FDL16 engine, it was determined that when the temperature of the ambient air T AIR  is greater than 39 degrees Fahrenheit and less than or equal to 55 degrees Fahrenheit, the cool down rate R is 0.15 degrees Fahrenheit/minute. For the same engine, the average cool down rate R when the ambient air temperature T AIR  is greater than 55 degrees Fahrenheit but less than 110 degrees Fahrenheit is 0.10 degrees Fahrenheit/minute. 
     Based upon the average cool down rate R, a maximum shutdown time period SDT MAX  may be calculated, as in step  24  of FIG.  2 . The maximum shutdown time SDT MAX  is selected to prevent the lubricating oil temperature from dropping below a predetermined minimum temperature T MIN  as may be defined by the engine designer. For the GE7FDL16 engine, the minimum lubricating oil temperature T MIN  may be 140 degrees Fahrenheit. By subtracting the minimum lubricating oil temperature T MIN  from the temperature of the oil T OIL  at the time of shutdown, and dividing that difference by the average cool down rate R, the maximum shutdown time SDT MAX  may be calculated in step  24 . 
     When the engine is shutdown in step  26  of FIG. 2, a timer is activated to provide the elapsed time ET after engine shutdown. In step  28  of FIG. 2, the elapsed time ET is compared to the maximum shutdown time SDT MAX . If the elapsed time ET equals or exceeds the maximum shutdown time SDT MAX , a decision is made to restart the engine in step  30 . 
     There may also exist an overall maximum shutdown period MAX defined by the engine designers. For example, it is desirable to limit the maximum shutdown period MAX for a GE7FDL16 engine to a period of four hours in order to maintain an adequate lubricating oil film on the engine bearings. If the elapsed time has not exceeded the calculated maximum shutdown time SDT MAX  in step  28 , there may be a further decision in step  32  wherein the elapsed time ET is compared to the predetermined maximum time MAX. If the elapsed time ET equals or exceeds the predetermined maximum value MAX, a decision is made to restart the engine in step  30 . 
     After restart, the engine is then permitted to run for a defined period of time in order to increase the temperature of the lubricating oil, as illustrated in step  32  of FIG.  2 . This time period may be a fixed period, or it may be a function of the ambient temperature T AIR  or oil temperature Toil. After the defined running period, the engine may again be shut down as in step  26 , and the entire process repeated as necessary to maintain the engine in a state of readiness. 
     The method illustrated in FIG. 2 will assure that the engine is not subjected to a cold starting condition, while allowing the engine to be shut down when not in use in order to minimize the fuel consumption. The particular values utilized for the cool down rate R may be empirically determined, calculated by computer modeling, or arbitrarily assigned based on operating experience. Similarly, the particular calculation performed to determine the maximum shutdown time SDT MAX  in step  24  may take into account other variables or constants that are appropriate for a particular engine application. For example, the altitude or wind velocity may significantly affect the cool down rate R, or the probability of the need for further use of the engine may be considered when calculating the maximum shutdown time SDT MAX . 
     FIG. 3 illustrates an apparatus for implementing the method of FIG.  2 . Components in FIG. 3 that are similar to those in the prior art device of FIG. 1 are consistently numbered between the two figures. Specifically, an engine  10  having a lubricating oil system including a pump  12 , cooler  14 , filter  16 , and temperature measuring instrument  18  are included in the apparatus of FIG. 3. A means  34  for automatically starting the engine  10  is provided to accomplish the restart of the engine  10  in step  30  of FIG.  2 . Such means  34  for starting the engine may include components that provide a similar function for other purposes as may be available on prior art engines. For example, the engine starter, fuel injection system and governor may be part of the means  34  for starting the engine. A controller  36  is provided having an output signal  38  for activating the means  34  for starting the engine. The controller has as inputs signals for the oil temperature T OIL , elapsed time ET after engine shutdown, and ambient air temperature T AIR . In addition, the controller  36  is attached to a means  40  for storing an average engine lubricating cool down rate R. Thus, the controller  36  has available the necessary inputs for performing the steps of calculating the maximum shutdown time SDT MAX  and for comparing that shutdown time to the elapsed time ET, as illustrated in steps  24 ,  28  of FIG.  2 . Controller  36  may also perform the function of step  32  of comparing the elapsed time ET to a predetermined maximum value MAX, as illustrated in step  32  of FIG.  2 . Should the decision of step  28  or  32  be favorable for restarting the engine  10 , a signal  38  is passed to the means  34  for starting the engine to accomplish step  30  of FIG.  2 . Controller  36  may also perform the decisional steps necessary to determine the run time of the engine  10  as illustrated in step  32  of FIG.  2 . 
     Controller  36  may be embodied as any hardware, software, and/or firmware device as may be known in the art. For example, most modern locomotives contain a centralized computer control system that may be modified to include the functions described herein. The means  40  for storing the cool down rate R may be a memory function in a solid state electronic device or may be a programmed value in software or firmware. The functions of controller  36  may be performed manually by an operator, however, a preferred embodiment would permit the unattended operation of such a system. Other components of the apparatus of FIG. 2 are available as standard items, such as an air temperature measurement instrument  42  and the timing device  44  operable to generate the elapsed time ET signal in response to a shutdown signal SD. 
     While the preferred embodiment of the present invention has been shown and described herein, it will be obvious that such embodiments are provided by way of example only. Numerous variations, changes and substitutions will occur to those of skill in the art without departing from the invention herein. Accordingly, it is intended that the invention be limited only by the spirit and scope of the appended claims.