Abstract:
A motor vehicle has an engine compartment ( 123 ) and a compression ignition engine ( 100 ) disposed within engine compartment ( 123 ). Engine ( 100 ) has an air intake ( 110 ) through which combustion air enters the engine. A heater ( 120 ) heats combustion air passing through air intake ( 110 ). A sensor ( 116 ) indicates temperature in air intake ( 110 ). When temperature indicated by sensor ( 116 ) is greater than a reference temperature that demarcates a warm engine from a cold engine, a control ( 102 ) enables heater ( 120 ) to heat combustion air passing through air intake ( 110 ) upon engine starting and during a subsequent period of initial engine running whose duration is a function of temperature indicated by sensor ( 116 ) at engine starting.

Description:
TECHNICAL FIELD 
       [0001]    The technical field of this patent application concerns internal combustion engines, especially diesel engines in motor vehicles, that have intake air heaters for heating intake air during cold starts, and in particular a strategy for enabling an intake air heater to also heat intake air during a warm engine re-start in cold weather so that generation of white smoke during starting and subsequent running is minimized and ideally substantially eliminated. 
       BACKGROUND OF THE DISCLOSURE 
       [0002]    Starting a cold diesel engine in a motor vehicle is sometimes difficult, especially if the engine has been soaked for an extended time in a cold ambient condition. Various cold weather starting aids, such as glow plugs and block heaters, can facilitate engine starting. Certain diesel engines have intake air heaters that are used in cold weather to pre-heat intake air during cold engine starting and ensuing initial running until the engine warms sufficiently that further pre-heating is stopped. 
         [0003]    One type of intake air heater comprises an electric heating element that is controlled by a strategy that is embodied in an engine control system and that utilizes data indicative of intake air temperature to control the flow of electric current to the heating element. 
         [0004]    By using an intake air heater to pre-heat cold intake air, the generation of white smoke in exhaust gases leaving the engine exhaust system is minimized and ideally substantially eliminated. 
         [0005]    When ambient air that enters the engine air intake is not cold, white smoke is typically not generated, and so pre-heating by the intake air heater doesn&#39;t occur. 
         [0006]    The intake air temperature data that the strategy uses for control of the intake air heater is typically obtained from a temperature sensor that is disposed at a location in the engine air intake considered suitable for indicating intake air temperature with reasonable accuracy. 
         [0007]    When a cold engine is started in cold weather after cold soaking, the temperature sensor is also cold and gives a reasonably accurate indication of the temperature of ambient air entering the intake system. 
       SUMMARY OF THE DISCLOSURE 
       [0008]    The applicants have observed that an engine having an intake air heater may nevertheless occasionally emit white smoke during cold weather starting. The applicants have further observed that such events occur when the engine, after having been warmed in cold weather, is shut down and then re-started while the engine is still warm. When the engine is housed within a somewhat enclosed engine compartment, the extent to which the engine compartment shields the engine from the ambient surroundings contributes to the amount of time for a warm engine to cool to ambient temperature in cold weather. 
         [0009]    The applicants attribute the observed generation of white smoke to various parts of the engine remaining warm enough to cause the air intake temperature sensor to be influenced to some extent by retained heat in various parts of the engine and the engine compartment that houses the engine. 
         [0010]    If the temperature sensor is sufficiently influenced by the retained heat, it may falsely indicate sufficiently warm intake air and consequently fail to cause the intake air heater to provide sufficient heating for preventing the temporary generation of white smoke upon starting and ensuing initial running of the engine when cold ambient air is entering and passing through the air intake. 
         [0011]    The present disclosure relates to a solution for such situations. 
         [0012]    The solution is embodied in a software strategy for enabling the heater to heat intake air during a warm engine re-start in ambient temperatures that are sufficiently cold to make it likely that due to retained heat the temperature sensor is giving a false indication that intake air temperature is sufficiently warm that operation of the intake air heater should not occur. Consequently, the solution can be implemented without use of any additional sensor or sensors to perform clean-up of white exhaust smoke. 
         [0013]    A motor vehicle comprises an engine compartment and a compression ignition engine disposed within the engine compartment. The engine comprises an air intake through which combustion air enters the engine, a heater for heating combustion air passing through the air intake, and a sensor for indicating temperature in the air intake. 
         [0014]    When temperature indicated by the sensor is greater than a reference temperature that demarcates a warm engine from a cold engine, a control enables the heater to heat combustion air passing through the air intake upon engine starting and during a subsequent period of initial engine running whose duration is a function of the temperature indicated by the sensor at engine starting. 
         [0015]    A method for mitigating the generation of white smoke in exhaust gas entering atmosphere from a compression ignition engine housed within an engine compartment of a motor vehicle by enabling an intake air heater to heat combustion air passing through an air intake to the engine upon engine starting and during a subsequent period of initial engine running. 
         [0016]    The method comprises evaluating temperature indicated by a sensor disposed at a location in the air intake, and if, upon engine starting, the evaluated temperature exceeds a reference temperature that demarcates a cold engine from a warm engine, enabling the heater to heat combustion air passing through the air intake for a length of initial engine running time that is subsequent to engine starting and that is a function of the evaluated temperature. 
         [0017]    The foregoing summary, accompanied by further detail of the disclosure, will be presented in the Detailed Description below with reference to the following drawings that are part of this disclosure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]      FIG. 1  is a somewhat schematic side elevation view of a diesel engine. 
           [0019]      FIG. 2  is a diagram of a portion of an exemplary embodiment of software strategy that provides the solution described above. 
       
    
    
     DETAILED DESCRIPTION 
       [0020]    A diesel engine  100 , like the one shown in  FIG. 1 , comprises an engine control system (ECS)  102  that comprises one or more processors that control various systems and devices, one of which is a fuel injection system  104  controlled by a fuel control strategy. Fuel injection system  104  comprises fuel injectors  106  that inject fuel into engine cylinders  108  where the injected fuel combusts to power the engine. Charge air enters cylinders  108  through an air intake system  110  to support combustion. 
         [0021]    Measurement of various temperatures related to operation of engine  100  are performed by various sensors such as a coolant temperature sensor  112  associated with the coolant system at a suitable location and an oil temperature sensor  114  associated with the lubrication system at a suitable location. In the case of air intake system  110 , an intake air temperature sensor  116  is disposed at a suitable location in the intake system to measure temperature. The three sensors provide coolant temperature data, oil temperature data, and intake air temperature data respectively to ECS  102 . 
         [0022]    Because pre-heating of a cold diesel engine should occur, especially if the engine has been soaked in cold ambient conditions,  FIG. 1  shows both a glow plug heater system  118  and an intake air heater  120 . The latter is associated with intake system  110  and is enabled by a strategy embodied in control system  102 . Actual operation of heater  120 , when enabled, occurs when a relay  121  is operated closed by ECS  102  to connect an electric power supply  122  in the vehicle to the heater so that electricity can flow through heater  120  and create heat that is transferred to air in intake system  110 . 
         [0023]    Engine  100  is housed within an engine compartment  123 , shown only schematically in  FIG. 1 , of a vehicle. Engine compartment  123  provides some degree of sheltering of engine  100  from the ambient environment. 
         [0024]      FIG. 2  shows a strategy  124  that is embodied in ECS  102  for enabling operation of heater  120 . 
         [0025]    The strategy is activated when the engine is placed in an engine running mode by the driver of the vehicle operating the usual switch, commonly called the ignition switch, when starting the engine. The engine running mode is one of several possible modes and is indicated in ECS  102  by the numeral “2”. When the engine is in its running mode, the value of a parameter OMS_MODE assumes a value “2”. 
         [0026]    The strategy comprises a logic function  126  that provides a logic “0” output when the value of OMS_MODE is other than “2”, but provides a logic “1” output when the value of OMS_MODE is “2”. 
         [0027]    When the output of function  126  changes from a logic “0” to a logic “1”, a timing function (timer)  128  starts to nm. Elapsed time is given by the value of a parameter IAH_RUN_TMR, and that parameter is one input to a logic function  130  that compares the value of IAH_RUN_TMR and the value of a parameter IAH_HS_ON_TM. 
         [0028]    Logic function  130  provides a logic “1” output when the value of the parameter IAH_HS_ON_TM is greater than the value of the parameter IAH_RUN_TMR, and otherwise provides a logic “0” output. 
         [0029]    Intake air temperature sensor  116  provides an electric signal correlated with its temperature, and that signal is evaluated by ECS  102  to create a value for a parameter IAT_Signal corresponding to the sensor temperature. 
         [0030]    The strategy comprises a look-up table, or map,  132  that is populated with various values for the parameter IAH_HS_ON_TM, each such value being correlated with a respective range of values for IAT_Signal. The value for IAT_Signal that is presented to look-up table  132  when the strategy is activated at the commencement of the engine running mode to cause the corresponding value for IAH_HS_ON_TM to be presented to function  130  for comparison with the running time provided by timing function  128 . 
         [0031]    The values for IAH_HS_ON_TM in look-up table  132  are correlated with values for IAT_Signal such that the greater the evaluated temperature above a reference temperature that demarcates a warm engine from a cold engine, the lesser the value for IAH_HS_ON_TM. 
         [0032]    With engine  100  running, the “1” logic output of function  126  is also supplied to one input of a two-input AND logic function  134 . The other input of function  134  is the output of function  130 . With the engine running and with the temperature indicated by sensor  116  at engine starting being sufficiently high to cause the output of function  130  to be a logic “1”, the output of AND logic function  134  is a logic “1”, enabling heater  120 . Assuming that engine  100  continues running, the timer will time out after the amount of time obtained from look-up table  132  at engine starting on the basis of engine temperature has elapsed. Should engine  100  be shut down before the timer times out, the output of function  126  would change from logic “1” to logic “0” at shut down, and consequently change the output of function  134  to unenable heater  120 . 
         [0033]    The strategy addresses the following situation. 
         [0034]    If engine  100  is shut down after having been warmed and re-started shortly thereafter in cold ambient temperature, the engine and associated components will not have had time to cool to ambient temperature. The time for retained heat to dissipate is affected to some extent by engine  100  and associated components being housed inside engine compartment  123  where they are somewhat sheltered even though the usual engine compartment isn&#39;t completely sealed off from the outside. In such a situation engine sensor  116  can still be significantly warmer than ambient upon engine starting, and therefore fail to accurately disclose intake air temperature until after it has been sufficiently cooled by intake air flow through air intake system  110 . The extent of the inaccuracy depends on various factors but will in general have an inverse correlation with the length of time between engine shut down and re-start. 
         [0035]    If function  132  presents a relatively smaller non-zero value for IAH_HS_ON_TM to function  130 , a longer elapsed time on timing function  128  will be needed before the output of function  130  switches from a logic “1” to a logic “0” to unenable intake air heater  120 , provided that engine  100  is not shut down sooner. 
         [0036]    If function  132  presents a relatively larger non-zero value for IAH_HS_ON_TM to function  130 , a shorter elapsed time on timing function  128  will be needed before the output of function  130  switches from a logic “1” to a logic “0” to unenable intake air heater  120 , provided that engine  100  is not shut down sooner.