Patent Abstract:
For the purpose of precisely controlling a power supply to the glow plug and thereby reducing unnecessary power consumption, and stopping a control logic for a time when a battery voltage is low and thereby preventing a engine stall, the present invention provides a method for dividing an engine starting step into a cranking step and an idling step, controlling power supplied to the glow plug, and operating the glow plug even after successfully entering into a running state in the case of entering into an abnormal engine state based on an amount of injected fuel, an engine speed and a coolant temperature, and thereby controlling the glow plug from before the engine starts through after it is running.

Full Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority of Korea patent Application No. 10-2000-0055108, filed on Sep. 20, 2000. 
     BACKGROUND OF THE INVENTION 
     (a) Field of the Invention 
     The present invention relates to a method for controlling a glow plug, and more particularly, to a method for controlling power supplied to the glow plug by dividing an engine starting step into a cranking step and an idling step, and operating the glow plug even after successfully entering into a running state in the case of entering into an abnormal engine state based on an amount of injected fuel, an engine speed and a coolant temperature, and thereby controlling the glow plug from before the engine starts through after it is running. 
     (b) Description of the Related Art 
     A conventional diesel engine is a compression-ignition type engine, which ignites fuel by injecting it into a combustion chamber heated to a high temperature by compressing air in a cylinder. Ignition of the conventional diesel engine may be unstable when the engine is at a low temperature in an early state of engine starting in which the engine is cold, because compression heat is not sufficient. 
     To enhance startability of a diesel engine when it is cold, a glow plug is installed in each cylinder and operated before starting the engine in order to heat air around the glow plug. 
     A conventional method for controlling a glow plug by prior art is simply to heat the glow plug for a given period of time according to coolant temperature. 
     According to the prior art, there is a problem of high power consumption. For example, the glow plug heating is continued in an unnecessary situation because the heating time is unchangeably determined by data acquired during starting. Therefore the battery may be frequently discharged because of high power consumption and the engine can be stalled in the process of starting because too much electrical power stored in the battery can be consumed by heating the glow plug. 
     SUMMARY OF THE INVENTION 
     Therefore, the present invention has been made in an effort to solve the above problem. An object of the present invention is to provide a method for controlling power supplied to a glow plug by dividing an engine starting step into a cranking step and an idling step, and operating the glow plug in the case of entering into an abnormal engine state even after successfully entering into a running state, based on an amount of injected fuel, engine speed and coolant temperature, and thereby controlling the glow plug from before the engine starts through after it is running, and stopping the process of control for a short time when a battery voltage is low. 
     Generally, a starter motor is rotated by operating a start switch, and thereby starting begins. The process of engine starting is made up of a cranking step in which the engine starts to rotate and an idling step in which the engine idles immediately after the engine is started. 
     Therefore, to achieve the above object, the method for controlling the glow plug according to the present invention controls power supplied to the glow plug by dividing the engine starting step into the cranking step and the idling step. Furthermore, the glow plug is operated even after the engine successfully starts, when the engine is in an abnormal state based on an amount of injected fuel, engine speed and coolant temperature. 
     A preheating system using a method for controlling a glow plug according to the present invention includes the glow plug being fixed on one side of a cylinder head, a battery supplying power to the glow plug, a control unit controlling power supply from the battery to the glow plug through a relay, a coolant temperature sensor measuring the temperature of the coolant, a battery voltage sensor measuring the voltage of the battery, and means for measuring an amount of injected fuel. 
     A method for controlling the glow plug of the present invention applies power to the glow plug until a power supply time exceeds a predetermined initial preheating time, or the engine is cranked, at which time the power supply to the glow plug is maintained until the power supply time exceeds a predetermined main preheating time, the engine enters into the idling state, or the coolant temperature is higher than a predetermined target value, and then the power supply to the glow plug is cut off. 
     The initial preheating time and the main preheating time are determined by tables that use the battery voltage and the coolant temperature as variables. 
     When the engine speed is greater than a predetermined speed for a predetermined time, the engine is determined to be cranking. When the engine speed reaches a predetermined speed, the engine is determined to be idling. 
     As the engine starts idling, the amount of injected fuel and the engine speed are measured. When the amount of injected fuel is greater than a predetermined fuel injection reference amount, or the engine speed is greater than a predetermined reference speed, the glow plug is preheated until the amount of fuel being injected and the engine speed become respectively lower than the fuel injection reference amount and the reference speed. 
     After engine starting is complete, when the coolant temperature is lower than a determined critical temperature, or the amount of injected fuel is less than a determined critical amount of injected fuel, or the engine speed is lower than a determined critical speed, the glow plug is again preheated until the coolant temperature, the amount of injected fuel and the engine speed are respectively greater than the critical values. 
     In each control step, when the battery voltage being measured is lower than a predetermined critical voltage, the power supply to the glow plug and the execution of the detailed steps are stopped. The power supply to the glow plug and the execution of the detailed steps remain stopped until the battery voltage is higher than the critical voltage, and then the power supply to the glow plug and the execution of the detailed steps are resumed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic view of a glow plug system in which a method for controlling glow plugs by an embodiment of the present invention is used. 
     FIG. 2 is a flowchart showing an embodiment of a method for controlling a glow plug of the present invention. 
     FIG.  3  and FIG. 4 are flowcharts showing respectively a detailed step of a starting glow plug control step and a running glow plug control step. 
     FIG.  5  and FIG. 6 are flowcharts showing respectively a detailed step of a post-preheating step and an instantaneous preheating step. 
     FIG.  7  and FIG. 8 are drawings showing respectively an example of a table that determines an initial preheating time and an example of a table that determines a main preheating time. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings. 
     FIG. 1 is a schematic view of a glow plug system in which a method for controlling glow plugs by an embodiment of the present invention is used. 
     As shown in FIG. 1, the glow plug system according to the embodiment of the preset invention includes a glow plug  110  being fixed on one side of a cylinder head  150 , a battery  135  supplying power to the glow plug, a relay  115  being connected to the glow plug  110  and switching a power supply from the battery  135  to the glow plug  110 , a glow plug control unit  120  being connected to the relay  115  and controlling an operation of the relay  115 , a coolant temperature sensor  125  inputting a variable with which the glow plug control unit  120  controls an operation of the relay  115 , a battery voltage sensor  130 , and a fuel volume sensor  145  for measuring an amount of injected fuel, and it further comprises a start switch  140  controlling the power supply to the glow plug control unit  120 . 
     The glow plug  110  can be an arbitrary heating device that transforms electrical energy into thermal energy, and the fuel volume sensor  145  for measuring the amount of injected fuel can be any arbitrary device that performs the function. 
     The start switch  140  includes an ‘on’ position for supplying power to sensors attached to the engine and a ‘start’ position for supplying power to a starter motor and thereby rotating the starter motor. 
     Though the control unit  120  can be a singular control unit controlling the relay  115  by signal inputs from the above sensors  125 ,  130  and  145 , it is preferable that the control unit is an electronic control unit (ECU) also controlling actuators of the engine. 
     FIG. 2 is a flowchart showing an embodiment of a method for controlling a glow plug of the present invention. 
     As shown in FIG. 2, a method for controlling the glow plug of the present invention comprises a starting glow plug control step S 210  controlling the glow plug for engine starting, and a running glow plug control step S 220  controlling the glow plug after engine starting. 
     Generally, the starter motor is rotated by operating the start switch of the engine, and thereby starting begins. In the starting glow plug control step S 210 , the engine-starting step is divided into a cranking step in which the engine rotates and an idling step in which the engine starts to idle after the engine is started, and power supplied to the glow plug is controlled from the point of operating the start switch to the point of entering into the idling state. Furthermore, it is determined whether the engine is stable when entering the idling state, and when the engine is determined to be unstable, the glow plug is again actuated. 
     In the running glow plug control step S 220 , when the engine is unstable based on the amount of injected fuel, the engine speed and the coolant temperature even after the engine starts idling, the glow plug is operated, and thereby the glow plug can be controlled after engine starting. 
     While the engine normally operates, running glow plug control step S 220  is executed continuously. When the engine start switch  140  is turned off, the running control step S 220  ends. 
     FIG.  3  and FIG. 4 are flowcharts showing respectively a detailed step of a starting glow plug control step and a running glow plug control step. 
     FIG. 3 is a flowchart showing detailed steps of the starting control step in an embodiment of a method for controlling the glow plug of the present invention. 
     If the start switch is turned to an ‘on’ or a ‘start’ state, the starting glow plug control step S 210  is initiated. 
     If the starting glow plug control step S 210  starts, the control unit  120  determines whether the coolant temperature sensor is working properly, in step S 310 . The determination is made by ordinary logic of an electronic control unit (ECU). 
     If the coolant temperature sensor is determined to be working properly in step S 310 , the temperature detected from the coolant temperature sensor  125  is fixed as the coolant temperature (S 320 ). If the coolant temperature sensor is determined to be malfunctioning in step S 310 , a default temperature is fixed as the coolant temperature (S 315 ). The default temperature can be fixed as a sufficiently low temperature with reference to an ordinary cold starting situation of the engine. For example, the default temperature can be fixed as −25° C. 
     The control unit  120 , after fixing the coolant temperature, operates the relay  115  such that power is applied to the glow plug  110  from the battery  135  (S 325 ). 
     After applying power to the glow plug  110 , the control unit  120  measures an elapsed time of power application, and then the control unit  120  determines whether the measured time exceeds a predetermined preheating time (hereinafter called an initial preheating time) (S 330 ). 
     The initial preheating time is determined by a table that uses the battery voltage and the coolant temperature as variables. 
     FIG. 7 is a drawing showing an example of a table that determines the initial preheating time. The initial preheating time is determined according to the coolant temperature and the battery voltage as shown in FIG.  7 . The initial preheating time for a coolant temperature and a battery voltage not given in FIG. 7 can be determined by linear approximation based on the coolant temperatures and battery voltages given in FIG.  7 . 
     As shown in FIG. 3, when the control unit  120  determines that the elapsed time for the power application is not greater than the initial preheating time, the control unit  120  determines whether the engine is being cranked (S 335 ). 
     In step S 335 , the engine is determined to be cranking when the engine speed is greater than a predetermined speed for more than a predetermined time. The predetermined time and the predetermined speed can be set respectively as an elapsed time in which the starter motor rotates normally and an arbitrary RPM (Revolutions per Minute). By way of example, the predetermined time can be 0.5 seconds, and the predetermined speed can be 450 RPM. 
     If the engine is determined to be not cranking in step S 335 , step S 330  is executed again. 
     If the measured time is determined to be greater than the initial preheating time in step S 330 , or if the engine is determined to be cranking in step S 335 , the initial preheating in the cranking step ends, and the preheating in the idling entrance step (hereinafter called main preheating) starts. 
     If the main preheating starts, the control unit  120  determines whether the measured time from power-apply start time exceeds the main preheating time (S 340 ). 
     The main preheating time is determined by using a table with the coolant temperature and the battery voltage as variables, as shown in FIG.  8 . The main preheating time for a coolant temperature and a battery voltage not given in FIG. 8 can be determined by linear approximation based on the coolant temperatures and the battery voltages given in FIG.  8 . 
     As shown in FIG. 3, if, in the step of determining whether the measured time from the power-apply start time is greater than the main preheating time, the measured time is determined to be not greater than the main preheating time, the control unit  120  determines whether the engine has started idling (S 345 ). 
     In the determination of entrance to the idling state (S 345 ), if the engine speed becomes a predetermined speed, it is determined to be idling. The predetermined engine speed can be an arbitrary speed of the engine at which the electronic control unit (ECU) recognizes that starting is completed, and by way of example, the predetermined engine speed can be 800 RPM. 
     If the engine is determined to have not entered the idling state in step S 345 , the control unit  120  measures the coolant temperature and determines whether the coolant temperature is higher than a predetermined target value (S 350 ). 
     The predetermined target value can be an arbitrary coolant temperature, and for example it can be 50° C. 
     If the coolant temperature is determined to be not higher than the predetermined target value, the step determining whether the measured time is greater than the main preheating time (S 340 ) is executed again. 
     If the measured time is determined to be greater than the main preheating time in step S 340 , or if the engine is determined to be idling, or if the coolant temperature is determined to be higher than the predetermined target value in the step determining the coolant temperature, the control unit  120  cuts off power supplied to the relay  115  such that the power supply from the battery  135  to the glow plug  110  is cut off (S 355 ). 
     After the power supply to the glow plug  110  is cut off, the control unit  120  determines whether the amount of injected fuel from an injector is greater than a predetermined fuel injection reference amount (S 360 ). 
     The fuel injection reference amount can be set as a maximum amount of fuel that can be injected in a normal engine speed range, and it can be set using a fuel control device of the engine. By way of example, in an engine in which the amount of injected fuel is less than 70 mm 3  in all normal driving circumstances, the fuel injection reference amount can be set as 75 mm 3 . 
     Generally, the amount of fuel that can normally be injected into an engine has a maximum value. Therefore, if the amount of injected fuel is determined to be greater than the fuel injection reference amount, it can be determined that the engine is cranking or it is malfunctioning. 
     If the amount of injected fuel is determined to be not greater than the fuel injection reference amount in step S 360 , it is determined whether the engine speed is greater than a predetermined reference engine speed (S 365 ). 
     The reference engine speed can be set as a maximum engine speed at which the engine operates normally, and it can be set at a fuel cutoff RPM in which the electronic control unit (ECU) cuts off the fuel supply. By way of example, generally in diesel engines the reference engine speed is set at 4500 RPM. 
     If the engine speed is determined to be not higher than the reference engine speed in step S 365 , the starting control step (S 210 ) ends. 
     If the amount of injected fuel is determined to be greater than the fuel injection reference amount in step S 360 , or if the engine speed is determined to be greater than the reference engine speed in step S 365 , a post-preheating step (S 370 ) is executed. 
     FIG. 5 is a flowchart showing detailed steps of the post-preheating step (S 370 ). 
     As shown in FIG. 5, if the post-preheating step (S 370 ) starts, the control unit  120  operates the relay  115  such that power is applied to the glow plug  110  from the battery  135  (S 510 ). 
     After power is applied to the glow plug  110 , the control unit  120  determines whether the amount of injected fuel from the injector is greater than the predetermined fuel injection reference amount (S 515 ). 
     If the amount of injected fuel is determined to be not greater than the fuel injection reference amount in step S 515 , the control unit  120  determines whether the engine speed is greater than the predetermined reference engine speed (S 520 ). 
     If the amount of injected fuel is determined to be greater than the fuel injection reference amount in step S 515 , or if the engine speed is determined to be greater than the reference engine speed in step S 520 , the step determining if the amount of injected fuel is greater than the fuel injection reference amount (S 515 ) is executed again. 
     If the engine speed is determined to be not greater than the reference engine speed in the step S 520 , the control unit  120  cuts off power supplied to the relay  115  such that the power supply from the battery  135  to the glow plug  110  is cut off. 
     After the power supply to the glow plug  110  is cut off, the post-preheating step (S 370 ) ends, at which point the starting control step (S 210 ) ends, and if the starting glow plug control step (S 210 ) ends, the running glow plug control step (S 220 ) is executed as shown in FIG.  2 . 
     FIG. 4 is a flowchart showing detailed steps of the running glow plug control step (S 220 ) in an embodiment of the present invention. 
     If the running glow plug control step (S 220 ) starts, the control unit  120  detects the coolant temperature and determines whether the coolant temperature is lower than a predetermined critical coolant temperature (S 410 ). 
     The predetermined critical coolant temperature can be set as an arbitrary temperature by which the engine is determined to be abnormally cool. By way of example, the predetermined critical temperature can be set as −20° C. 
     If the coolant temperature is determined to be not lower than the critical coolant temperature in step S 410 , the amount of injected fuel is measured and the control unit  120  determines whether the amount of injected fuel is less than the fuel injection critical amount (S 415 ). 
     The fuel injection critical amount can be set as a minimum value of the amount of fuel that can be injected at a normal engine speed range, and it can be set using a fuel control device of the engine. By way of example, the critical amount of injected fuel can be set as 10 mm 3 . 
     If the amount of injected fuel is determined to be not less than the critical amount of injected fuel in step S 415 , the control unit  120  determines whether the engine speed is less than the critical engine speed (S 420 ). 
     The critical engine speed can be set as a minimum engine speed at which the engine operates normally. By way of example, the critical engine speed can be set at 800 RPM. 
     If the engine speed is determined to be not less than the critical engine speed in step S 420 , the step determining if the coolant temperature is less than the critical coolant temperature (S 410 ) is executed again. 
     If the coolant temperature is determined to be less than the critical coolant temperature in step S 410 , or if the amount of injected fuel is determined to be less than the fuel injection critical amount in step S 415 , or if the engine speed is determined to be less than the critical engine speed in the step S 420 , an instantaneous preheating step (S 425 ) is executed. 
     FIG. 6 is a flowchart showing detailed steps of the instantaneous preheating step (S 425 ). 
     As shown in FIG. 6, if the instantaneous preheating step (S 425 ) starts, the control unit  120  applies power to the relay  115  such that power is supplied to the glow plug  110  from the battery  135 . 
     After power is applied to the glow plug  110 , the control unit  120  measures the coolant temperature and determines whether the coolant temperature is less than the predetermined critical coolant temperature (S 615 ). 
     If the coolant temperature is determined to be not lower than the critical coolant temperature in step S 615 , the control unit  120  determines whether the amount of injected fuel is less than the fuel injection critical amount (S 620 ). 
     If the amount of injected fuel is determined to be not less than the critical amount of injected fuel in step S 620 , the control unit  120  determines whether the engine speed is less than the predetermined critical engine speed (S 625 ). 
     If the coolant temperature is determined to be lower than the critical coolant temperature in step S 615 , or if the amount of injected fuel is determined to be less than the fuel injection critical amount (S 620 ), or if the engine speed is determined to be less than the predetermined critical engine speed (S 625 ), the step of evaluating the coolant temperature (S 615 ) is executed again. 
     If the engine speed is determined to be not less than the predetermined critical engine speed in step S 625 , the control unit  120  cuts off the power supplied to the relay  115  such that the power supply from the battery  135  to the glow plug  110  is cut off, at which point the instantaneous preheating step (S 425 ) ends. 
     If the instantaneous preheating step (S 425 ) ends, the step of evaluating the coolant temperature (S 410 ) is executed again as shown in FIG.  4 . 
     Therefore, while the engine operates, continuous detection of whether instantaneous preheating is needed is performed, and in the case when instantaneous preheating is needed the instantaneous preheating can be executed. 
     In the detailed steps S 330 ˜S 350 , S 410 ˜S 420 , S 515 ˜S 520  and S 615 ˜S 625 , being executed while power is supplied to the glow plug  110  in the starting glow plug control step (S 210 ) and the running glow plug control step (S 220 ), if the battery voltage being measured is lower than a predetermined critical voltage it is preferable that the control unit  120  stops both the power supply to the glow plug and execution of the detailed steps, and stands by until the battery voltage is higher than the critical voltage. Once it is, the control unit can resume the power supply to the glow plug and execution of the detailed steps, and it thereby allows the battery to charge when it is becomes low due to operation of the glow plug. 
     The critical voltage can be set as a minimum value of the battery voltage in which the starter motor of the engine can be rotated stably. By way of example, the critical voltage can be set as 8V. 
     The above-described preferable embodiments of the present invention are to be considered in all respects to be illustrative and not restrictive. Thus, various improvements and modifications to this invention may occur to those skilled in the art, and such improvements and modifications will fall within the scope of the present invention. 
     According to the embodiment of the present invention, during cold starting of an engine, the control unit divides the starting of the engine into several steps and then precisely controls starting of the engine. In addition, the control unit precisely controls the power supply to the glow plug, and thereby unnecessary power consumption can be decreased. Furthermore, if the charge of the battery is low, the control logic stops for a short time and thereby prevents an engine stall.

Technology Classification (CPC): 5