Abstract:
A fuel delivery control system controls fuel delivery for an engine having a plurality of cylinders and a electronically controlled fuel injection unit for controlling fuel delivered to each cylinder in response to control signals generated by an electronic control unit. The control unit, for each cylinder, determines an engine acceleration value derived from a crank position value generated by an engine crank position sensor, compares the acceleration value to a threshold value, and terminates fuel delivery to only the cylinders for which the comparison indicates unsatisfactory combustion, up to one half of the cylinders. The control unit operates to deliver a normal amount of fuel to cylinders for which the comparison indicates satisfactory combustion, and to cylinders for which fuel delivery has been terminated for a pre-set maximum number of times.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to an engine control system, and more particularly to a control system and method for reducing white smoke from the exhaust of a compression ignition engine. 
     In compression ignition engines, if ignition fails to occur, fuel is expelled from the engine&#39;s exhaust system, as what is commonly referred to as white smoke. As a result of stricter governmental and consumer requirements for fuel economy, performance and emissions, the reduction of white smoke is desirable. 
     One system for reducing white smoke is described in U.S. Pat. No. 6,009,857, issued to Halser on Jan. 4, 2000. The Hasler patent discloses a cylinder cut-out system for a compression ignition engine having electronic unit injectors. The system includes an electronic controller which receives engine parameter sensor signals. In response to certain conditions of the sensor signals, the electronic controller deactivates a predetermined portion (half) of the electronic unit injectors. 
     U.S. Pat. No. 5,076,236, issued Dec. 31, 1991 to Yu, discloses a pressure responsive spring-biased cutoff valve for an open nozzle unit fuel injector in an internal combustion engine which allows for the selective operation of a given number of cylinders during an engine low load or idling speed condition for improved white smoke control. The 236 patent recognizes that white smoke can occur under low load or idling speed of an engine, and that “White smoke is a condition that results on engine start-up or low-load motoring conditions due to improper combustion of fuel because of insufficient compression or temperature levels”. 
     In these prior art systems, a predetermined plurality or a given number of cylinders are shut off. The problem with such systems is that they may “shut off” a group of cylinders regardless of whether some of the cylinders in that group are firing efficiently or not. This requires additional amounts of fuel to be supplied to the cylinders which have not been disabled, subjecting them to additional work for a predetermined period of time to overcome the disabled cylinders. 
     Accordingly, it would be desirable to provide a system for reducing white smoke which shuts off only cylinders which are not firing properly. 
     SUMMARY OF THE INVENTION 
     Accordingly, an object of this invention is to provide an engine control system which efficiently reduces white smoke. 
     A further object of the invention is to provide such an engine control system which shuts off only cylinders which are not firing properly. 
     These and other objects are achieved by the present invention, wherein a fuel delivery control system controls fuel delivery for an engine having a plurality of cylinders and a fuel delivery control unit which delivers fuel to each cylinder in response to control signals generated by an electronic control unit. The electronic control unit, for each cylinder, determines a cylinder firing value which is related to a quality of combustion in that cylinder, compares the cylinder firing value to a threshold value, and terminates fuel delivery to only the cylinders for which the comparison indicates unsatisfactory combustion, up to a maximum portion of the total number of cylinders. The cylinder firing value is preferably an engine acceleration value derived from a crank position value generated by an engine crank position sensor. Once a cylinder is cut out, it is shut off for a certain number of times. After this cylinder has been shut off for this certain number of times, it is then provided with a normal amount of fuel so that it can be fired normally. 
    
    
     BRIEF DESCRIPTION OF THE INVENTION 
     FIG. 1 is a simplified schematic diagram of an engine control system according to the present invention; and 
     FIGS. 2 and 3 are logic flow diagrams illustrating an algorithm executed by the engine controller of FIG.  1 . 
    
    
     DETAILED DESCRIPTION 
     A fuel delivery control system  10  controls fuel delivery to an engine  12  having a plurality of fuel injectors  14 - 24  supplying fuel to a corresponding plurality of cylinders  26 - 36 . Fuel is supplied to the injectors  14 - 24  by a fuel delivery unit or injection pump  38 , such as an electronically controlled rotary injection pump, such as made by Bosch, which permits individual control of the injectors and cylinders. Alternatively, the fuel delivery unit could be a high pressure common rail unit, unit injectors or a hydraulic electronic unit injectors. Although FIG. 1 shows an engine with six cylinders, the present invention is applicable to any engines having more than one cylinder. 
     A microprocessor-based engine control unit (ECU)  40  supplies control signals to the injection pump  38 . The ECU  40  cooperates with the injection pump  38  and injectors  14 - 24  to control fuel delivery to the cylinders  26 - 36  of the engine  12  as a function of various sensed parameters and operator inputs, such as does the Focus™ controller which has been used on production John Deere engines. Like the Focus™ controller, the ECU calculates the amount of fuel to be delivered to the next cylinder to be fired, and causes the injection pump  38  to deliver that amount of fuel to the cylinder to be fired. 
     The ECU  40  generates control signals in response to a coolant temperature signal from coolant temperature sensor  42 , a engine crank position signal from crank position sensor  44 , a manifold air temperature signal from manifold air temperature sensor  46 , and a fuel temperature signal from fuel temperature sensor  48 . As did prior production John Deere Focus 
     controllers, the ECU  40  includes a “motoring” mode or function  115 , which shuts off fuel delivery to all cylinders during certain conditions, such as deceleration. 
     According to the present invention, the ECU  40  also continuously updates a cylinder index value, N, representing the particular cylinder which is in the process of firing. The ECU  40  also repetitively executes the algorithms  100  and  200 , represented by the flow charts shown in FIGS. 2 and 3, respectively, once for each cylinder to be fired. The conversion of these flow charts into a standard language for implementing the algorithms described by the flow charts in a digital computer or microprocessor, will be evident to one with ordinary skill in the art. 
     Preferably, the amount of fuel to be delivered is calculated by ECU  40  as a function of a cylinder factor, CF(N), determined by algorithms  100  and  200  for each cylinder, N, as described below. For example, when CF(N)=0, no fuel will be delivered to the Nth cylinder, and when CF(N)=1, a normal amount of fuel will be delivered to the Nth cylinder. The cylinder index value, N, is set outside of algorithms  100  and  200 , by the ECU  40  as a function of the crank position signal from sensor  44 . 
     Referring now to FIG. 2, algorithm  100  determines whether or not the cylinder cut-out algorithm  200  will be executed. After starting at step  102 , steps  104 - 110  direct the algorithm to step  116  and enables the cylinder cut-out algorithm  200  if all the following conditions are present: ( 104 ) coolant temperature is less than a maximum coolant temperature threshold, CT, (such as 50 degrees C), ( 106 ) the engine  12  is operating in a normal governor or “run mode”, ( 108 ) a run timer value is less than a maximum operating time, TT, such as 5 minutes, and ( 110 ) engine speed (derived from crank position) is less than a maximum engine speed, ST, such as 1900 rpm. The normal governor or “run mode” can be defined as preferably the normal governor-controlled operating condition of the engine  12 , and is an operating condition other than conditions such as a start-up condition, a fuel limiting or torque curve operating mode, and a stopped mode. 
     If any one of these conditions is not present, then step  112  sets an index value for the number of cylinders being cut-out, NC, to zero, since no cylinders will be cut out when the engine  12  is operating normally. Step  112  also sets the number of injection events to be cut-out, NF, for all cylinders, to zero, and sets the cylinder factor, CF, for all cylinders, equal to 1, and step  114  enables a normal operational mode (disables cylinder cut-out). The normal operational mode includes various conventional engine operating modes, including a motoring mode  115 , wherein fuel supply is terminated to all cylinders, such as during deceleration of the engine  12 . Preferably, as a result of steps  106  and  110 , the cylinder cut-out algorithm  200  is enabled when the engine speed is within a range of approximately  700  to 1900 rpm, but these speeds are merely exemplary and could be varied without departing from the invention. 
     Referring now to FIG. 3, algorithm  200  is entered at step  202 , whenever algorithm  100  executes step  116  and enables cylinder cut-out. The first time algorithm  200  is executed, the values NF( 1 - 6 )=0, NC=0 and CF( 1 - 6 )=1 are what was established by a previous operation of step  112  of algorithm  100 . In subsequent operations of algorithm  200 , these values are set, decremented or increment within algorithm  200 , and those modified values will continue to be set and used by algorithm  200  until algorithm  100  once again disables cylinder cut-out and the values are re-initialized by step  112 . 
     Step  204  compares NF(N) to zero, and if NF(N) is not equal to zero (this means that cylinder N has been cut-out), then step  210  decrements the counter value NF(N) by 1, and step  212  sets CF(N) equal to zero (to cause the Nth cylinder to be cut-out). 
     Then, in step  214 , if NF(N) is not equal to zero, it means that the Nth cylinder has been cut-out less than CO or 50 times, for example, and step  214  directs the subroutine to step  222  so that the Nth cylinder will be cut-out due the step  212 . If in step  214 , NF(N) is equal to zero, it means that the Nth cylinder has been cut-out the maximum allowed number of times, CO, and step  214  directs the subroutine to step  216  which decrements NC by 1 (to indicate that the number of cylinders being cut-out is being reduced) and sets CF(N) equal to 1 so that the Nth cylinder will be fired (not cut-out) during the next series of cylinder firings, and then directs the subroutine to return via step  222 . 
     Referring back again to step  204 , if NF(N) equals zero, (this means that the Nth cylinder is not going to be cut-out), then step  206  sets EA equal to a calculated engine acceleration, and step  208  compares EA to an acceleration threshold, AT. Preferably, the control unit  40  calculates or derives, from the crank angle or position signal, for each cylinder, the engine acceleration resulting from operation of a particular cylinder, such as by determining the derivative of the engine speed signal which is derived from the crank position signal. 
     Then, if in step  208  EA is greater than an acceleration threshold, AT, it means that cylinder N fired normally and the subroutine returns at step  222  with CF(N)=1 for the Nth cylinder. If, in step  208  EA is not greater than AT, it means that cylinder N has misfired and the subroutine proceeds to step  218 . 
     Step  218  compares the number of cylinders currently being cut-out, NC, to a maximum number, MNC, such as half of the total number of cylinders in the engine  12 . If, in step  218 , NC is not less than MNC, it means that no additional cylinders are to be cut-out, and the algorithm is directed to step  222 . If, in step  218 , NC is less than MNC, it means that additional cylinders can be cut-out and the algorithm is directed to step  220 . Step  220  sets the index value NF(N) equal to CO, the number of times (such as  50 ) a cylinder should be cut-out after a misfire is detected. Step  220  also increments NC by 1 (to indicate that an additional cylinder will be cut-out) and sets CF(N) equal to zero so that cylinder N will be cut-out during the next series of cylinder firings. 
     Thus, the ECU  40  determines if a particular cylinder or cylinders are misfiring, and cut-outs only the cylinders which are misfiring, while disabling at most only half of the cylinders. Thus, this system does not automatically shut off a predetermined, selected group of cylinders, but instead, detects which cylinder(s) are actually misfiring by measuring the amount acceleration of the crankshaft, and shuts off the fuel supply only to the misfiring cylinders. Acceleration and cylinder misfiring is detected by using an engine crank position sensor, and measuring the time period between pulses from the crank position sensor. Once it is determined that a particular cylinder is not firing, that cylinder is shut off for a certain number of engine cycles. After that number of engine cycles, that cylinder is injected with the normal amount of fuel (steps  214 ,  216  and  222 ). 
     While the present invention has been described in conjunction with a specific embodiment, it is understood that many alternatives, modifications and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, this invention is intended to embrace all such alternatives, modifications and variations which fall within the spirit and scope of the appended claims.