Abstract:
A control system for an internal combustion engine that utilizes an oxygen sensor signal to control at least one fuel injector while generating a false oxygen sensor signal for input to an engine control unit.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 61/590,958, filed Jan. 26, 2012, the disclosure of which is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates in general to oxygen sensors and in particular to the utilization of an oxygen sensor with an internal combustion engine. 
     Internal combustion engines can use Oxygen (O 2 ) sensors to monitor the Air to Fuel Ratio (AFR) and ensure efficient combustion. Ideally, an AFR would be utilized to provide a stoichiometric combustion in which the fuel is completely burned. Stoichiometric combustion for gasoline requires a weight ratio of 14.7 parts of air to one part of fuel. 
     Referring now to  FIG. 1 , there is shown a schematic diagram illustrating a prior art internal combustion engine control system  10 . The system  10  includes a narrow band O 2  sensor  12  that outputs a voltage indicating the presence of oxygen in the exhaust. The sensor output is sent to an Engine Control Unit (ECU)  14  that is responsive to the sensor output to modify a Pulse Width Modulated (PWM) control signal having a variable pulse width and/or duration. The PWM control signal is, in turn, sent to the engine fuel injectors  16 . Narrow band sensors used with the ECU output a voltage transitioning between 0 and 1 volts over a narrow range of AFR near 14.7, as illustrated by the graph to the left in  FIG. 2 . A rich mixture with an AFR just below 14.7 will output a voltage near 1 volt, and a lean mixture with an AFR just above 14.7 will output a voltage approaching 0 volts, as illustrated by the graph to right in  FIG. 2 . The graphs shown in  FIG. 2  illustrate the AFR output for an idealized O 2  sensor output, while the graphs shown in  FIG. 3  illustrate the AFR output for a typical O 2  actual sensor output. The ECU  14  will add fuel to the air-fuel mixture if there is a lean condition, and it will subtract fuel from the air-fuel mixture if there is a rich condition by varying the pulse width, or the duty cycle, of the PWM signal sent to the fuel injectors  16 . Therefore, the ECU continuously controls the engine fuel injectors so the AFR is maintained close to the ideal stoichiometric AFR (AFR Stoich ). 
     It will be noted that most technical books and articles discuss an “excess air factor,” or lambda (λ), instead of AFR, with λ, being the ratio of the actual AFR to the stoichiometric AFR. Thus, a λ=1.0 represents stoichiometric combustion. Lambda is used because various fuels combine differently, and a strict weight ratio of 14.7 parts of air to one part of fuel is applicable only for a specific fuel. When λ is utilized, a rich condition has λ&lt;1.0, while a lean condition has λ&gt;1.0. However, AFR is used in calculations to determine an actual quantity of fuel. For a given intake stroke, a finite quantity of air is acquired. Thus, fuel volume is utilized as the only variable to obtain a different AFR. 
     In the U.S., Europe, and Japan, catalytic after-treatment of engine exhaust gas using a catalytic converter gas has proven to be the only means of complying with the present limits for CO, NO, and HC. Catalytic converters function most effectively when λ=1. Therefore, engine controllers are designed to operate within a narrow range with λ=1.0±0.005. 
     In order to enhance engine performance, current available systems can control AFR by using a wide band O 2  sensor, while still providing a narrow band O 2  signal to the ECU, as illustrated by the engine control system  20  shown in  FIG. 4 . Components shown in  FIG. 4  that are the same as components shown in  FIG. 1  have the same numerical identifiers. As shown in  FIG. 4 , both a wide band O 2  sensor  22  and a Fuel Injector Controller (FIC)  24  have replaced the narrow band O 2  sensor  12  shown in  FIG. 1 . The FIC  24  is responsive to the output signal received from the wide band O 2  sensor  22  to generate a false narrow band signal that is sent to the ECU  14 . The false narrow band signal causes the ECU to add or subtract fuel. If a lower AFR is desired, a low narrow band O 2  signal is sent to the ECU so that fuel is added. Similarly, if a higher AFR is desired, a high narrow band O 2  signal is sent to the ECU so that fuel is subtracted. 
     The system  20  may encounter problems with newer ECUs, in which sensors are cross checked with other systems. For example, a mass air flow sensor (not shown) can calculate the amount of engine input air, which can be compared to the PWM signal being sent to the fuel injectors  16 . With the system  20  shown in  FIG. 2 , the amount of engine input air will not compare satisfactorily with the output injector pulse width, causing the ECU to generate an error signal. Accordingly, it would be desirable to be able to utilize a wide band O 2  sensor with the newer ECUs without an error signal being generated. 
     SUMMARY OF THE INVENTION 
     This invention contemplates a supplemental fuel injection controller that controls fuel delivery while providing signal/s to the ECU that correlate to stock fuel injection signals. 
     The invention includes a control system for an internal combustion engine that includes at least one fuel injector for the internal combustion engine and an engine control unit that is operable to generate a pulse width modulated control signal for the at least one fuel injector that may be a function of an O 2  sensor input signal. The system also includes an O 2  sensor that is operable to generate an output signal that is a function of the amount of oxygen present at the sensor. The system further includes an enhanced fuel injection controller connected to the O 2  sensor, the engine controller, and the at least one fuel injector. The enhanced fuel injection controller is responsive to the O 2  sensor output signal to generate and send a false O 2  sensor signal to the ECU. The enhanced fuel injection controller also may be operative to send a desired PWM control signal to the at least one fuel injector, with the desired PWM control signal being a function of the wide band oxygen sensor output signal. Alternately, the system may operate in an open loop mode, in which the signal received from the O 2  sensor is not utilized. 
     The enhanced fuel injection controller also is operative to receive the PWM control signal from the engine control unit and to generate the false O 2  sensor signal as a function of the PWM control signal received from the engine control unit. 
     The invention also includes a method for controlling an internal combustion engine that includes providing an enhanced fuel injection controller having a first input port that is connected to an O 2  sensor and a second input port that is connected to the output of an engine control unit. The enhanced fuel injection controller also has an output port that is connected to at least one fuel injector. The method also includes the steps of receiving an output signal from the O 2  sensor at the input port of the enhanced fuel injection controller and generating a desired control signal for the at least one fuel injector with the enhanced fuel injection controller that is a function of the O 2  sensor output signal and the ECU output signal. 
     The method further contemplates that the enhanced fuel injection controller also generates a false O 2  sensor signal, which is sent to an oxygen sensor input port on the ECU. 
     Various objects and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram illustrating a prior art internal combustion engine control system. 
         FIG. 2  illustrates a pair of graphs, wherein the left graph shows the ideal relationship between AFR and a narrow band O 2  sensor output voltage, and the right graph shows the sensor output signal as a function of time. 
         FIG. 3  illustrates a pair of graphs, wherein the left graph shows the typical relationship between AFR and a narrow band O 2  sensor output voltage, and the right graph shows the sensor output signal as a function of time. 
         FIG. 4  a schematic diagram illustrating another prior art internal combustion engine control system. 
         FIG. 5  is a schematic diagram illustrating an internal combustion engine control system that is in accordance with the present invention. 
         FIG. 6  illustrates the amount of fuel delivered by an injector as a function of time. 
         FIG. 7  is a flow chart for an algorithm for the operation of the internal combustion engine control system shown in  FIG. 3 . 
         FIG. 8  is a flow chart for an alternate embodiment of the algorithm shown in  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawings, there is illustrated in  FIG. 5  a schematic diagram illustrating an internal combustion engine control system  30  that is in accordance with the present invention. Components shown in  FIG. 5  that are similar to components shown in  FIGS. 1 and 4  have the same numerical identifiers. As shown in  FIG. 5 , the control system  30  includes an O 2  sensor  22 , which may be either a wide band O 2  sensor or a narrow band O 2  sensor. The system  30  also includes an Enhanced Fuel Injector Controller (EFIC)  32  that both sends and receives signals from the ECU  14 . The EFIC  32  includes a conditioning circuit  34  and a microprocessor  36 , with the conditioning circuit  34  conditioning the output signal from the O 2  sensor  22 . The O 2  sensor  22  output signal AFR sensor  is then supplied to an O 2  sensor input port of the EFIC  32 . As will be described below, the EFIC  32  generates a computed, or false, AFR signal (AFR computed ) that is supplied to the ECU  14 . The ECU is responsive to the AFR computed  signal to generate a PWM output (PWM ECU ) that is sent to the EFIC  32 . Other sensors (which are shown as a single block  38  in  FIG. 5 ) are connected to the ECU. Such other sensors  38  may be utilized to crosscheck with the AFR determined by the stock systems narrow band O 2  sensor reading. The EFIC then generates a PWM output (PWM EFIC ) that is used to control the fuel injectors  16 . The PWM signal controlling the fuel injectors  16  may either be open loop or closed loop. 
     It is noted that the engine control system  30  shown in  FIG. 5  is operated in a closed loop mode of operation. Closed loop control modifies the injector pulse width dependent upon the wide band O 2  signal to maintain a specified AFR. The closed loop method may vary. A conventional closed loop control feedback method using Proportional, Integral, Derivative (PID) control modifies the PWM dependent upon the relationship of a target AFR to a sensor AFR as determined by the O 2  sensor  22  according to conventional methods. A computed closed loop method calculates a new PW signal with the EFIC  32  by utilizing the target AFR and sensor AFR values to directly calculate a new injector pulse width. For a finite quantity of air, the operation of the system  30  can be described by the following equation:
 
AFR sensor *FUEL EEIC =AFR target *FUEL computed ; where
         AFR sensor  is the AFR as read by the O 2  sensor,   FUEL EFIC  is the fuel quantity controlled by the EFIC, which is a function of PWM EFIC ,   FUEL computed  is a new fuel quantity calculated by the ECU, which is a function of PWM ECU , and   AFR target  is the desired AFR.       

     The above equation may be solved for the new fuel quantity, FUEL computed , as:
 
FUEL computed =(AFR sensor *FUEL EEIC )/AFR target , or
 
 fn (PWM new )=(AFR sensor   *fn (PWM EFIC ))/AFR target .
 
     The EFIC  32  uses an algorithm to characterize a relationship between FUEL EFIC  and PWM target . The algorithm may include either an equation and/or a lookup table. 
     The quantity of fuel delivered by a fuel injector is not directly proportional to the time that the injector is powered, as illustrated in  FIG. 6 . An equation or a second lookup table may be used to correlate fuel delivered by an injector to the time the injector is on. A common approximation is to define the difference between the time an injector is powered and the time fuel flows. This constant is called the injector turn-on, lag, or dead time. Fuel quantity with respect to injector pulse width may be defined using the injector turn-on time approximation as:
 
FUEL=RATE inj *( PW−C ); where
         FUEL is the fuel quantity delivered by an injector,   RATE inj  is the flow rate for the injector,   PW is the duration the injector is powered, and   C is the injector turn-on time.       

     Combining the aforementioned equations, the computed AFR received by the ECU may be calculated relative to the time the injector is powered as follows:
 
 PW   computed =[AFR sensor *( PW   EFIC   −C )]/( PW   ECU   −C ); where
         PW EFIC  is the previous pulse width from the EFIC powering the injector which resulted in the measured AFR, AFR sensor , and   PW computed  is a new pulse width from the ECU to the EFIC.       

     The above equation shows that the AFR, as determined by the wide band O 2  sensor, is not coincident to the fuel currently being delivered by the injectors as controlled by the EFIC. This is due to the fact that a finite time elapses between when the fuel is delivered, the combustion occurs, and the exhaust travels to, and is measured by, the O 2  sensor. Some method must be used to match the AFR as measured by the wide band O 2  sensor to the PW output by the EFIC. The preferred method is to synchronize the measurement of the O 2  value relative to the engine rotation and, thus, to the time the PW was output by the EFIC, and also to maintain a recorded history of those PW durations. The PW which caused the current AFR value may then be obtained from that history, which provides a fixed index. 
     If the computed AFR is less than the stoichiometric AFR, then a rich condition exists, and a false low signal O 2  is output from the EFIC  32  to the ECU  14 . If the computed AFR is greater than the stoichiometric AFR, then a lean condition exists, and a false high O 2  signal is output from the EFIC  32  to the ECU  14 . These relationships are illustrated by the following equations: 
     if AFR computed &gt;AFR Stoich , a false low O 2  signal is sent to the ECU  14 , and; 
     if AFR computed &lt;AFR Stoich , a false high O 2  signal is sent to the ECU  14 . 
     Thus, the ECU  14  continues to operate in a normal manner as in prior art devices, and the output signal PWM ECU  from the ECU will be compared within other vehicle sensors  38  to other sensor signals without triggering an error signal. Accordingly, the present invention will not have the problem described above involving mismatched sensor output signals since the output pulse width PWM ECU  from the ECU would be ideal for a stoichiometric AFR, while the EFIC output pulse width PW EFIC  is actually being supplied to the fuel injectors  16 . 
     As noted above, it is also possible to utilize the EFIC  32  and the ECU  14  in an open loop mode of operation in which the O 2  sensor  22  is not utilized. Open loop control modifies the PWM signal independent of the wide band O 2  signal. The duration of the injector pulse supplied by the EFIC  32  to the fuel injectors may be either fixed or variable relative to the pulse width output by the ECU. 
     The present invention also contemplates an algorithm for controlling the operation of an internal combustion engine that is illustrated by the flow chart shown in  FIG. 7 . The algorithm is entered through block  40  and proceeds to decision block  42  where it is determined whether the engine is running. If the engine is not running, the algorithm exits through block  43 . If the engine is running, the algorithm transfers to functional block  44  where the output of the O 2  sensor is checked for AFR sensor . The algorithm then continues to functional block  45  where a target AFR, AFR des , is selected for the required engine performance. The target AFR may be a function of the O 2  sensor signal, AFR sensor , or a function of another engine parameter, such as, for example, throttle position. The algorithm then advances to functional block  46  where the EFIC  32  calculates desired pulse width, PW r , that can be a function of the target AFR. The algorithm then continues to functional block  48  where the ECU  14  generates an ECU output pulse width, PW ecu , which is needed by the EFIC  32  to calculate the computed AFR, AFR computed , that is sent to the EFIC  32 . Accordingly, the algorithm advances to functional block  50 , where AFR computed  is determined. The algorithm then continues to decision block  54 . 
     If, in decision block  54 , AFR computed  is less than AFR Stoich , a rich condition exists, and the algorithm transfers to functional block  56 , where a rich condition false O 2  high signal is sent to the ECU  14 . The algorithm then transfers back to functional block  42  for another iteration. If, in decision block  54 , it is determined that AFR computed  is not less than AFR Stoich , the algorithm transfers to decision block  58 . 
     If, in decision block  58 , AFR computed  is greater than AFR Stoich , a lean condition exists and the algorithm transfers to functional block  60  where a lean condition false O 2  low signal is sent to the ECU  14 . The algorithm then transfers back to functional block  42  for another iteration. However, if, in decision block  58 , AFR computed  is not greater than AFR Stoich , the algorithm transfers to functional block  62  where the O 2  signal from the previous iteration is sent to the ECU  14 . The algorithm then transfers back to functional block  42  for another iteration. 
     An alternate algorithm that includes interpolation is shown in  FIG. 8 , where blocks that are similar to blocks shown in  FIG. 4  have the same numerical designators. A narrow band O 2  sensor, such as a Nernst cell, indicates the existence or absence of oxygen and yields two stable conditions: rich or lean. However, within a narrow λ, range of perhaps 0.995 to 1.005, the signal transitions between the two extremes. Creating just a high or low signal (a square wave) is the roughest approximation to a narrow band sensor. The alternate algorithm shown in  FIG. 8  interpolates a voltage between the two extremes while within the very narrow band close to λ=1.0. 
     The alternate algorithm proceeds as described above through functional block  50  after which the difference, DELTA, between AFR computed  and AFR sensor  is determined in functional block  64 . The algorithm then continues as described above except that decision blocks  66  and  68  have been added after decision blocks  54  and  58 , respectively. In decision blocks  66  and  68 , DELTA is compared to a high threshold T H  and a low threshold T L , respectively. The threshold values T H  and T L  are just above and below the stoichiometric AFR, with typical values being 14.72 and 14.68, respectively, but also depending upon the specific fuel being used. Alternately, a lambda λ of 1.0±0.005 may be utilized. The present invention also contemplates that the threshold values T H  and T L  may be a variable function of a engine parameter, such as, for example, throttle opening, and/or a vehicle parameter, such as, for example, vehicle speed. If in either decision block  66  or  68 , it is determined that DELTA falls between T H  and T L , the algorithm transfers to functional block  70 . 
     In functional block  70  an interpolated false narrow band O 2  signal is determined and sent to the ECU  14 . Within the band between T H  and T L , the ECU makes smaller changes in the PWM than provided in decision blocks  56  and  62 . It is also contemplated that the change may be made proportional to the magnitude of DELTA and that the changes may have different magnitudes depending upon which threshold triggers the interpolation step. The algorithm then continues to functional block  72  where the fuel condition is adjusted in either a rich or lean direction and in an amount determined by the interpolation that occurs in functional block  70 . 
     The interpolation described above is an improved approximation but is still just that, an approximation. The present invention also contemplates using more complex methods to improve the approximation (not shown). It is also contemplated that the ECU corrects the fuel by a lessening amount as λ approaches 1.0. This makes the improved approximation perform better. Following functional block  70 , the algorithm transfers back to decision block  42  for the next iteration. 
     The high and low threshold values, T H  and T L  are determined for the specific engine being controlled and/or the expected service environment. Typically, the threshold values would be just above and below the stoichiometric AFR for the engine. For example, the invention contemplates that T H  may be set at 1.2, while T L  may be set at 0.8; however, other values may be used for the threshold values. 
     It will be appreciated that the algorithms shown in  FIGS. 7 and 8  are meant to be exemplary and that the invention may also be practiced with algorithms that differ from the ones shown. 
     While the invention has been described and illustrated for both narrow and wide band O 2  sensors, the invention contemplates that a wide band O 2  sensor is used for improved engine performance. A wide band O 2  sensor outputs a signal based on the AFR over a wide range. This allows the ECU to maintain the AFR at any value. The present invention contemplates that Stoichiometric AFR is used to create the cleanest emissions from the engine. However, the invention can also be practiced with an AFR other than the Stoichiometric AFR in order to produce more power and/or better efficiency. When a wide band O 2  sensor is used to determine the AFR sensor  for improved engine performance, the EFIC  32  will provide an apparent AFR, AFR computed , to the ECU  14  while also providing PW EFIC  to the fuel injectors  16  that provides the desired enhanced engine performance. The use of the apparent AFR, AFR computed , sent to the ECU  14  assures that any cross checking with other vehicle sensors by the ECU  14  will not trigger any alarm signals. 
     In accordance with the provisions of the patent statutes, the principle and mode of operation of this invention have been explained and illustrated in its preferred embodiment. However, it must be understood that this invention may be practiced otherwise than as specifically explained and illustrated without departing from its spirit or scope. Thus, while the preferred embodiment has been described and illustrated as utilizing O 2  sensors, it will be appreciated that the invention also may be used with other type of sensors, such as, for example, mass flow sensors.