Patent Publication Number: US-6035831-A

Title: Fuel dosage control process for internal combustion engines

Description:
FIELD OF THE INVENTION 
     The present invention is directed to a method for influencing fuel metering in an internal combustion engine. 
     BACKGROUND INFORMATION 
     The German Patent No. 41 15 211 discloses an electronic control system for metering fuel in an internal combustion engine. In the known system, a basic injection quantity signal is gated with a transition-compensation signal to adapt the metered fuel quantity in response to acceleration and deceleration. In determining the transition-compensation signal, inter alia a wall-film quantity signal, as well as a series of correction signals are considered. 
     An object of the present invention is to further improve the known system. In particular, the present invention should make it possible to observe a desired air/fuel ratio with the greatest possible accuracy and in the greatest possible number of operating states of the internal combustion engine. 
     SUMMARY OF THE INVENTION 
     The present invention has the advantage of enabling an optimal fuel metering in the dynamic operation of the internal combustion engine. 
     This is achieved by taking one or a plurality of signals into consideration which describe the heat flow toward or away from the intake section. 
     In known methods heretofore, setting parameters for the fuel metering entailed finding a compromise between various operating states, e.g., high/low ambient temperature or high/average vehicular speed level. By taking these influences on the wall-film characteristics into consideration, an optimal air/fuel mixture can be achieved for these states in transient operation. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a schematic representation of an internal combustion engine comprising essential components for controlling the fuel metering. 
     FIG. 2 shows a block diagram for clarifying how the fuel metering is influenced using the method according an embodiment of the present invention. 
     FIG. 3 shows a variant of the block diagram shown in FIG. 2. 
     FIG. 4 shows a flow chart of the an embodiment of method according to the present invention. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 is a schematic representation of an internal combustion engine 100 and essential components for controlling fuel metering in an open or closed loop. By way of an intake section 102, an air/fuel mixture is supplied to internal combustion engine 100, and the exhaust gases are released into an exhaust duct 104. Viewed in the flow direction of the intake air, mounted in intake section 102 are an air-flow sensor or mass air-flow sensor 106, for example a hot-film air-mass meter, a temperature sensor 108 for detecting intake-air temperature, a throttle valve 110 with a sensor 111 for detecting the opening angle of throttle valve 110, a pressure sensor 112 for detecting the pressure in intake section 102, and at least one injection nozzle 114. As a rule, air-flow sensor or mass air-flow sensor 106, and pressure sensor 112 are alternatively provided. Mounted in exhaust duct 104 is an oxygen probe 116. Mounted on internal combustion engine 100 are an engine speed sensor 118 and a sensor 119 for detecting the temperature of the internal combustion engine. Internal combustion engine 100 has, for example, four spark plugs 120 for igniting the air/fuel mixture in the cylinders. Also shown in FIG. 1 are a sensor 122 for detecting vehicular speed and an electromotor 124, which drives a fan arranged in the engine compartment. 
     The output signals from the described sensors are transmitted in a central control unit 126. In particular, the signals are: a signal m from air-flow sensor or mass air-flow sensor 106, a signal TAn from temperature sensor 108 for detecting the intake-air temperature, a signal α from sensor 111 for detecting the opening angle of throttle valve 110, a signal PS from pressure sensor 112 downstream from throttle valve 110, a signal λ from oxygen sensor 116, a signal n from speed sensor 118, a signal TMot from sensor 119 for detecting the temperature of internal combustion engine 100, and a signal v from sensor 122 for detecting vehicular speed. Control unit 126 evaluates the sensor signals and drives injection nozzle(s) 114 and spark plugs 120. In addition, control unit 126 drives electromotor 124. 
     As a rule, the device for implementing the method according to the present invention is integrated in control unit 126. with the aid of the method according to the invention, the influence that the wall temperature of the intake section 102 has on the actually metered fuel quantity can be taken into consideration when metering the fuel. There is no need in the method of the present invention for a sensor for detecting wall temperature downstream from injection nozzle(s) 114. Instead--depending on the degree of accuracy required--one or more variables that influence wall temperature are taken into consideration. Using these influence variables as a point of departure, a correction signal fTW or kTW is generated. Correction signal fTW or kTW influences a transition-compensation signal UK, which, in turn, influences a basic injection-quantity signal tp. The transition-compensation signal UK has the property of increasing the metered fuel quantity in response to acceleration and of lowering the metered fuel quantity in response to deceleration. 
     In accordance with the method of the present invention, correction signal fTW or kTW can either be determined directly from the corresponding influence variables or on the basis of an intermediate variable TW, which represents the wall temperature of intake section 102 and is determined from the influence variables. Considered relevant as influence variables are a heat flow QK generated by the fuel vaporization, a heat flow QAn between the air flowing through intake section 102 and the wall of intake section 102, a heat flow QMot between the engine block and the wall of intake section 102, and a heat flow QU between the ambient air flowing past the outer wall of intake section 102 and the wall of intake section 102. The relation between influence variable TW for the wall temperature of intake section 102 and influence variables QK, QAn, QMot and QU can be represented by the following differential equation: 
     
         cW*mW*dTW/dt=QK+QAn+QMot+QU 
    
     In this case, cW represents the specific heat and mW the mass of the wall of intake section 102. The influence variables QK, QAn, QMot and QU are determined from operating parameters and material parameters. 
     Heat flow QK produced by the fuel vaporization is determined in accordance with the following equation: 
     
         QK=-qKE*hK*x 
    
     In this case, qKE represents the fuel quantity metered per unit of time. This variable is, thus, defined by control unit 126. hK represents the specific evaporation heat of the fuel and is a known material constant. x represents the proportion of fuel being deposited on the wall of intake section 102, which fuel subsequently cools the wall of intake section 102 through evaporation. Variable x is stored in an engine characteristics map as a function of speed n and pressure PS in intake section 102. 
     The heat flow QAn between the air flowing through intake section 102 and the wall of intake section 102 is determined in accordance with the following equation: 
     
         QAn=αN(m)*(TAn-TW) 
    
     Here, αN(m) represents the heat transfer coefficient between the air flowing past and the wall of intake section 102 as a function of air-mass flow m. 
     The heat flow QMot between the engine block and the wall of intake section 102 is determined in accordance with the following equation: 
     
         QMot=aMot*(TMot-TW) 
    
     αMot describes the heat transfer coefficient between the engine block and the wall of intake section 102 and is a material constant. 
     The heat flow QU between the ambient air flowing past on the outside of intake section 102 and the wall of intake section 102 is a function of the air-mass flow of the ambient air flowing past and of the temperature difference between the ambient air and the wall of intake section 102. The air-mass flow can be determined on the basis of signal v for the vehicular speed and, optionally, of a signal for the operating state of electromotor 124, which drives the fan in the engine compartment. The temperature of the ambient air can be determined using an ambient-temperature sensor (not shown in FIG. 1) or using sensor 108 for intake-air temperature. 
     The differential equation indicated above can be solved by replacing the time derivation of the wall temperature of intake section 102 by a corresponding difference quotient, i.e., the term dTW/dt is replaced by the term (TWNew-TWOld)/dt. Rearranging according to TWNew, yields the following equation: 
     
         TWNew=TWOld+(dt/(cW*mW))*(QK+QAn+QMot+QU) 
    
     In determining the active value TWNew for the wall temperature, a starting value TWStart is initially specified for the wall temperature and the active value TWNew is then determined iteratively from the preceding value TWOld. Relevant details are shown in the flow chart of FIG. 4 and described in the corresponding text. 
     FIG. 2 shows a block diagram for clarifying how the fuel metering is influenced by the method according to the present invention. A load signal L and a signal n for the speed of internal combustion engine 100 are each fed into one input of a block 200. Load signal L can be determined in a well known manner on the basis of one of the signals m, PS or α. A basic injection-quantity signal tp is held ready at the output of block 200. It is generally known from the related art how to determine the basic injection-quantity signal tp from signals L and n. The output of block 200 is linked to a first input of a node 202. The second input of node 202 is linked to the output of a node 204. A first input of node 204 is linked to the output of a block 206 for transition compensation. The second input of node 204 is linked to the output of a block 208, which carries out the method according to the present invention. As a rule, a series of input signals is injected into block 208. What signals these are, in particular, depends upon which of the influence variables QK, QAn, QMot and QU are to be considered. The double arrow pointing at block 208 is representative of all input signals. 
     Signals L and n for load and speed of internal combustion engine 100 are applied to both inputs of block 206. From these signals, block 206 determines a transition-compensation signal UK for influencing basic injection-quantity signal tp and holds ready signal UK at its output. Signal UK is gated at node 204 with a correction signal fTW, which is output from block 208. The signal generated by the gating at node 204 is gated at node 202 with the basic injection-quantity signal tp to form an injection signal te. Injection signal te is fed to a block 210, where, if indicated, other corrections are made, for example as a function of signal TMot for the temperature of internal combustion engine 100 or of signal λ of oxygen sensor 116, and which, in the end, generates a signal for triggering injection nozzle(s) 114. 
     As illustrated in FIG. 2, the method according to the present invention makes it possible to produce a correction signal fTW, which influences signal UK and, thus, also the basic injection-quantity signal tp. In other words, in the end, correction signal fTW influences the fuel metering. It is already known how to determine signal UK by means of block 206. A corresponding method is described, for example, in German Patent No. 41 15 211. 
     The block diagram shown in FIG. 2 relates to one of several possible ways of using correction signal fTW, which is produced according to the method of the present invention, to influence the fuel metering. An alternative possibility is depicted in FIG. 3. 
     FIG. 3 depicts a variant of the block diagram shown in FIG. 2. FIG. 3 illustrates how signal UK is influenced by a correction signal kTW produced using the method of the present invention. The further processing of signal UK follows analogously to FIG. 2 and is not shown in detail in FIG. 3. However, node 204 depicted in FIG. 2 is omitted. Taking the place of block 206 in FIG. 2, are blocks 300 and 302 in FIG. 3 and a node 304 connected therebetween. From signals L and n for the load and for the speed of internal combustion engine 100, which are fed into its two inputs, block 300 determines a signal for altering the wall film of fuel in intake section 102. The thus produced signal is gated at node 304 with a correction signal kTW, which is generated by block 208 using the method according to the present invention. In the final analysis, correction signal kTW has the same effect on the transition-compensation signal UK as correction signal fTW described above, i.e., in both cases, the fuel metering is influenced in the same manner. However, since correction signals fTW and kTW have different kinds of effects on signal UK, as a rule, the correction signals themselves are not identical. 
     The signal produced from node 304 is fed into the input of block 302, which generates signal UK using a method known from German Patent No. 41 15 211. 
     FIG. 4 depicts a flow chart of the method according to the present invention. In a first step 400, signal TwOld is set to a starting value TWStart. In the subsequent step 402, all input variables required for the method are input. Step 402 is followed by a step 404. Depending on the exemplary embodiment, one or more input variables QK, QAn, QMot and QU are determined in step 404. The equations described further above are used for the particular heat flow. Step 404 is followed by a step 406, in which signal TWNew is determined for the prevailing wall temperature in accordance with the equation already named further above. Depending on the exemplary embodiment, this equation contains one or more of the influence variables QK, QAn, QMot and QU, which represent the individual heat flows. Step 406 is followed by a step 408, where signal TWOld for the preceding wall temperature is set to the value TWNew of the prevailing wall temperature. Step 408 is followed by a step 410. In step 410, from signal TWNew for the prevailing wall temperature, correction signal fTW or kTW is determined for influencing the fuel metering. In this case, correction signal fTW or kTW is read out, for example, as a function of signal TW from a characteristic. The flow chart completes its cycle at step 410 and begins anew at step 402.