Abstract:
A motor vehicle has an electric power supply that includes a battery bank ( 122 ), a compression ignition engine ( 100 ), different types of cold start aids ( 118, 120 ) that draw electric current from the power supply for aiding engine starting in cold ambient temperature, and a control ( 124 ) for monitoring voltage of the power supply while the cold start aids are drawing current from the battery bank and for interrupting the current to a lower priority one of the cold start aids, but not a higher priority one of the cold start aids, when monitored voltage falls below a threshold voltage.

Description:
REFERENCE TO RELATED APPLICATION AND PRIORITY CLAIM 
       [0001]    This application claims the priority of Provisional Patent Application No. 61/078,126, filed on 3 Jul. 2008, the entire content of which is incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    This disclosure relates to internal combustion engines, especially diesel engines that have cold start aids, electrically operated glow plugs and intake air heaters in particular, for facilitating cold engine starting in cold weather. More specifically, the disclosure relates to a strategy that is effective when several cold start aids are being concurrently used for disabling a first cold start aid, but not a second one, should battery bank voltage in a vehicle that contains the engine drop enough to impair effectiveness of second cold start aid, thereby allowing the latter to continue operating at a somewhat higher voltage due to reduced current draw on the battery bank. 
       BACKGROUND OF THE DISCLOSURE 
       [0003]    Starting a cold diesel engine in a motor vehicle is difficult in some environmental conditions, such as when the engine has been soaked for an extended time in a cold ambient temperature. Various cold weather starting aids, such as glow plugs and block heaters, can facilitate engine starting. 
         [0004]    A block heater typically is not operated by vehicle battery power, but rather by commercial AC electricity when plugged into a domestic or commercial AC receptacle. 
         [0005]    A glow plug start aid system typically comprises one or more glow plugs associated with each combustion chamber, and some form of controller or control system that controls the delivery of electric current to the glow plugs from the vehicle battery bank. Glow plugs typically operate after the ignition switch has been turned on but before the engine is cranked, and they stay on only for a limited amount of time. 
         [0006]    A glow plug lamp in an instrument panel typically serves as a wait-to-start indicator to inform the driver that the glow plugs have been turned on and that he/she should wait to crank the engine to allow the glow plugs time to be effective. Because the engine is not running as the glow plugs are starting to heat the engine cylinders, the engine-driven alternator is not keeping the battery bank recharged, and therefore the electricity for operating the glow plugs is being supplied exclusively by the battery bank. The glow plugs may continue to be energized for some amount of time after the engine has been cranked and commences running under its own power. 
         [0007]    Certain diesel engines also have intake air heaters that are used in cold weather to pre-heat intake air during cold engine starting and ensuing initial running. An intake air heater serves to mitigate the generation of white smoke in engine exhaust until the engine becomes warmer and ceases exhausting white smoke. One type of intake air heater comprises an electric heating element that is controlled by a strategy that is embodied in the engine control system and utilizes data indicative of intake air temperature to control the flow of electric current to the heating element. 
       SUMMARY OF THE DISCLOSURE 
       [0008]    The applicants have observed that when starting a diesel engine in a motor vehicle is attempted under certain conditions, especially cold weather conditions, the engine may not start even though several different types of electric-operated cold start aids are being concurrently used. The applicants have identified a cause of such “no starts” as a weakened condition of the vehicle&#39;s battery bank on which multiple cold start aids are imposing a heavy current draw. 
         [0009]    The simultaneous use of an intake air heater and glow plugs in a cold-soaked engine can create sufficiently large drain on a weakened battery bank that battery bank voltage drops to a level that noticeably impairs the effectiveness of one or both of these cold start aids and/or the ability of the engine cranking motor to develop enough torque for accelerating the engine to a high enough cranking speed (rpm) for enabling the engine to start and commence running under its own power. 
         [0010]    This disclosure provides for priority of operation to be given to a first of two cold start aids over a second in such a situation so that increased battery bank voltage that results from discontinuance of battery bank current to the second cold start aid can increase the effectiveness of the first. Specifically, the applicants have determined that priority should be given to continuance of glow plug operation over continuance of operation of an intake air heater in such a situation. 
         [0011]    The solution is embodied in a software strategy that monitors battery bank voltage and interrupts current to a lower priority cold start aid while allowing current to continue to a higher priority cold start aid when monitored voltage falls below some threshold voltage. The strategy also comprises a hysteresis function that after the strategy has interrupted the current to the lower priority cold start aid, is effective to terminate the interruption of current only if the monitored voltage rises above a voltage that is greater than the threshold voltage. 
         [0012]    The claimed subject matter relates to a motor vehicle comprising an electric power supply that includes a battery bank, a compression ignition engine disposed within the engine compartment, and two different types of cold start aid that draw electric current from the power supply for aiding engine starting in cold ambient temperature. 
         [0013]    A control monitors voltage of the power supply while both start aids are drawing current from the battery bank and interrupts the current to a lower priority one of the two different types of cold start aids, but not the higher priority one, when monitored voltage falls below some threshold voltage. 
         [0014]    The claimed subject matter also relates to a method for mitigating battery bank voltage drop when different types of cold start aid are operating to aid starting of a compression ignition engine in cold ambient temperature by drawing electric current from the battery bank when battery bank voltage drops below some threshold. 
         [0015]    The method comprises monitoring voltage of the battery bank and interrupting current to a lower priority one of the cold start aids, but not a higher priority one, when monitored voltage falls below the threshold voltage. 
         [0016]    The claimed subject matter further relates to a motor vehicle comprising a battery bank, a compression ignition engine, an electric cranking motor that operates to crank the engine by drawing electric current from the battery bank, multiple cold start aids that operate by drawing electric current from the battery bank to pre-heat the engine in cold ambient temperature prior to operation of the cranking motor, and a control for monitoring voltage of the battery bank while the cold start aids are drawing current from the battery bank prior to operation of the cranking motor and for interrupting current to a cold start aid when the monitored voltage falls to some voltage that is greater than that at which the ability of the cranking motor to accelerate the engine to a cranking speed high enough to enable the engine to start and commence running under its own power would begin to become impaired. 
         [0017]    The claimed subject matter still further relates to a method for preventing state-of-charge of a battery bank in a motor vehicle from being depleted by cold start aids that concurrently draw electric current from the battery bank to pre-heat a compression ignition engine in cold ambient temperature prior to engine cranking by an electric cranking motor that, when operated also draws electric current from the battery bank, to an extent that would begin to impair the ability of the cranking motor to accelerate the engine to a cranking speed high enough to enable the engine to start and commence running under its own power. 
         [0018]    The method comprises monitoring voltage of the battery bank and interrupting current to a cold start aid when the monitored voltage falls to some voltage that is greater than that at which the ability of the cranking motor to accelerate the engine to a cranking speed high enough to enable the engine to start and commence running under its own power would begin to become impaired. 
         [0019]    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 
         [0020]      FIG. 1  is a somewhat schematic side elevation view of a diesel engine showing elements relevant to the present disclosure. 
           [0021]      FIG. 2  is a diagram of a portion of an exemplary embodiment of software strategy in a control associated with the engine. 
       
    
    
     DETAILED DESCRIPTION 
       [0022]    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. 
         [0023]    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 . 
         [0024]    Because a cold diesel engine is typically pre-heated to facilitate starting, 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 a battery bank  122  in the vehicle&#39;s electrical system to the heater so that electricity can flow through heater  120  and create heat that is transferred to air in intake system  110 . After pre-heating, engine  100  is cranked by operating an electric cranking motor  123  that also draws current from battery bank  122 . 
         [0025]      FIG. 2  shows an example of a strategy  124  that is embodied in ECS  102  for mitigating the effect of decreased battery bank voltage on one or more electrically operated cold start aids and/or the ability of cranking motor  123  to develop sufficient torque for accelerating engine  100  to a cranking speed high enough for enabling it to start and commence running under its own power when battery bank  122 , for whatever reason, is in a weakened condition. 
         [0026]    The strategy comprises two comparison functions  126 ,  128  and a latch function  130 . ESC  102  monitors the output voltage of battery bank  122  in any suitably appropriate way such as by reading it on a data link in the vehicle electrical system as a parameter designated in  FIG. 2  as IVP_Signal. 
         [0027]    Parameter IVP_Signal is one of two inputs to each comparison function  126 ,  128 . The other input to comparison function  128  is a parameter IAH_IVP_ON. The other input to comparison function  126  is a parameter IAH_IVP_OFF. 
         [0028]    The output of comparison function  126  is an input to a reset input of latch function  130 . The output of comparison function  128  is an input to a set input of latch function  130 . When latch function  130  is latched in the set state, the value of a parameter provided at its output and designated IAH Enabled, enables current flow to intake air heater  120 . When latch function  130  is latched in the reset state, the value of parameter IAH Enabled unenables current flow to intake air heater  120 . 
         [0029]    When intake air heater  120  has been commanded to operate in aid of engine starting by a command input, the state of latch function  130  determines whether or not current is allowed to flow to the heater. 
         [0030]    The value for parameter IAH_IVP_OFF corresponds to a battery bank voltage below which it has been determined that current to intake air heater  120  should be discontinued. The value for parameter IAH_IVP_ON corresponds to a battery bank voltage above which it has been determined that current to intake air heater  120  should be restored. 
         [0031]    As long as the voltage of battery bank  122  exceeds the value corresponding to parameter IAH_IVP_ON, a typical value being approximately  10  volts in a nominal  12  volt electrical system, then comparison function  128  keeps latch function  130  in the reset state, allowing current to flow to intake air heater  120 . 
         [0032]    Should the voltage of battery bank  122  begin dropping and fall below the value corresponding to parameter IAH_IVP_ON, the output of comparison function  128  that had been applying a set signal to the set input of latch function  130  disappears. Latch function  130  will continue latched in the set state until a reset signal is applied to its reset input. Consequently, as long as battery bank voltage remains greater than the value corresponding to parameter IAH_IVP_OFF, latch function  130  remains latched, allowing current flow to intake air heater  120  to continue. 
         [0033]    Should the voltage of battery bank  122  drop further and fall below the value corresponding to parameter IAH_IVP_OFF, the output of comparison function  126  applies a reset signal to the reset input of latch function  130 , causing IAH Enabled to now unenable current flow to intake air heater  120 . 
         [0034]    With both intake air heater  120  and glow plug heater system  118  drawing current from battery bank  122  at the time that latch function is reset, the unenabling of the intake air heater causes current flow to the intake air heater to stop. The reduced current drain on the battery bank allows battery bank voltage to rise and consequently increase the power input to the glow plug heater system at least temporarily depending on the condition of the battery bank and on when the engine is actually cranked in an attempt to start it. 
         [0035]    Depending on the particular engine and electrical system, operation of the glow plugs may also be interrupted while the engine is being cranked. Once the engine starts and begins to operate the alternator, recharging of the battery bank would be expected to begin restoring battery bank voltage toward nominal system voltage, such as  12  volts for example. Once parameter IVP_Signal rises above the value of parameter IAH_IVP_ON, comparison function  128  sets latch function  130  to once again enable the intake air heater. If the command to operate the intake air heater is still in effect, the intake air heater will begin to once again draw current from the battery bank. 
         [0036]    The voltage differential represented by the difference between the voltage represented by parameter IAH_IVP_ON and the voltage represented by parameter IAH_IVP_OFF, as applied to the disclosed strategy, is sufficiently large (about one volt in the disclosed example) to provide a hysteresis function in the ON-OFF characteristic of the strategy that precludes the likelihood of frequent switching between on and off that might impose extra stress on the electrical system. The voltage/heating characteristic of the glow plugs and/or operating characteristic of cranking motor  123  may be factors for selecting a suitable value for parameter IAH_IVP_OFF. One example could be selecting a value for parameter IAH_IVP_OFF greater than that at which the ability of cranking motor  123  to accelerate engine  100  to a cranking speed high enough to enable the engine to start and commence running under its own power would begin to become impaired.