Patent Application
20130268177
The present disclosure relates to a fuel air richness estimation method, more particularly, to a fuel air richness estimation method for an internal combustion engine having a plurality of engine cylinders.
It is desirable in modern internal combustion engines to achieve high fuel economy and low engine emissions. However, the balance between high fuel economy and low, environmentally harmful, engine emissions can be a challenging task for engine designers. Part of this challenge is achieving a desired ratio between the amount of air and the amount of fuel (“fuel air ratio”) that enters an engine cylinder. This challenge is compounded by the fact that the fuel air ratio must be controlled to the desired ratio for each of a plurality of engine cylinders. A fuel air ratio imbalance between the plurality of engine cylinders will result in poor fuel economy and excessive undesirable vehicle emissions. Government regulations are beginning to require automobiles featuring internal combustion engines to maintain the fuel air ratio imbalance between the plurality of engine cylinders below a certain threshold to better control the engine's emissions.
Prior art methods teach controlling the fuel air ratio imbalance between engine cylinders by employing a wide range oxygen sensor in the individual exhaust runner of each cylinder. However, installing an individual wide range oxygen sensor in each cylinder exhaust runner is expensive and time consuming. Wide range oxygen sensors are expensive as is the labor needed to install them in each exhaust runner. Another way to estimate the fuel air ratio for each cylinder is to install an oxygen sensor at the confluence point of the exhaust runners in the exhaust manifold. The performance and complexity of this technique highly depend on the estimation methods and techniques used, the design of the manifold, and location of the sensor. Most published methods require an expensive wide range oxygen sensor installed at the confluence point of the exhaust runners and high computational resources. These methods typically fail to directly estimate the value of the fuel air ratio for each cylinder, rendering them difficult to use with vehicle on board diagnostics (“OBD”). Moreover, many prior art methods include a complicated calibration process. Further, typical prior art methods require substantial computing power to complete the estimation, but are unable to accurately estimate the fuel air ratio for each cylinder.
What is needed, therefore, is a method of measuring the fuel air ratio of each cylinder that effectively estimates the fuel air ratio of individual cylinders by utilizing a single oxygen sensor located at the confluence point of the runners. What is also needed is a method that is compatible with a wide range oxygen sensor and, generally lower cost, switching oxygen sensors. What is further needed is a method that directly estimates the value of the fuel air ratio for each cylinder, that is compatible with vehicle on board diagnostics, and includes a simplified calibration process. What is also needed is a method to more accurately estimate the fuel air ratio for each cylinder that requires reduced computing power to complete the estimation.
In one form, the present disclosure provides a method of estimating fuel richness of a plurality of engine cylinders. The method includes providing a first oxygen sensor at a confluence of a plurality of exhaust runners associated with the engine cylinders, gathering data regarding an actual fuel air ratio at the confluence of the plurality of exhaust runners using the first oxygen sensor, and forming a signal array for each of the plurality of engine cylinders using the data gathered by the first oxygen sensor. The method also includes calculating individual fuel richness for each of the plurality of engine cylinders using an individual cylinder fuel richness estimator.
In another form, the present disclosure provides a method of estimating fuel richness of an engine including providing a first oxygen sensor at a confluence of a plurality of exhaust runners associated with a plurality of engine cylinders and determining an angular position of a crankshaft of the engine. The method also includes gathering data regarding an actual fuel air ratio at the confluence of the plurality of exhaust runners using the first oxygen sensor when the crankshaft is at a predetermined rotational position. The data gathered at the predetermined rotational position corresponds to one of the plurality of engine cylinders. The method also includes forming a signal array for each of the plurality of engine cylinders using the corresponding data gathered by the first oxygen sensor, and calculating an individual fuel richness for each of the plurality of engine cylinders using an individual fuel richness estimator.
Thus, a method of measuring the fuel air ratio of each cylinder that effectively estimates the fuel air ratio of individual cylinders from the measurement of an oxygen sensor located at the confluence point of the exhaust runners is described. The method is compatible with both a wide range oxygen sensor and a switching oxygen sensor. The method directly estimates the value of the fuel air ratio for each cylinder, is compatible with vehicle on board diagnostics, and includes a simplified calibration process. Further, the method accurately estimates the fuel air ratio for each cylinder and requires reduced computing power to complete the estimation.
Further areas of applicability of the present disclosure will become apparent from the detailed description and claims provided hereinafter. It should be understood that the detailed description, including disclosed embodiments and drawings, are merely exemplary in nature intended for purposes of illustration only and are not intended to limit the scope of the invention, its application or use. Thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention.
In one embodiment, the confluence 17 of the exhaust runners is the point at which all of the individual exhaust runners 11, 12, 13, 14 are joined together. In one embodiment, one or more of the individual exhaust runners 11, 12, 13, 14 may join with a second of the individual exhaust runners 11, 12, 13, 14 separately from the other individual exhaust runners 11, 12, 13, 14. In this embodiment, the confluence of the individual exhaust runners 11, 12, 13, 14 is the point at which the exhaust gas flow from all of the individual exhaust runners 11, 12, 13, 14 flows through a single exhaust pipe. In one embodiment, the oxygen sensor 10 is installed at or downstream of the confluence 17 of the exhaust runners but upstream of a catalytic converter. In one embodiment, an engine having multiple banks of engine cylinders includes one exhaust manifold 20, one confluence 17 of the exhaust runners, and one oxygen sensor 10 per bank of engine cylinders. In one embodiment, an engine having multiple banks of engine cylinders includes more than one exhaust manifold 20, more than one confluence 17 of the exhaust runners, and one oxygen sensor 10 per confluence 17.
The oxygen sensors 1, 2, 3, 4, 10 are connected to an on board electronic system (“electronic system”) 100. The electronic system 100 may be an engine electronic control unit or any other control unit or computer onboard the vehicle. The electronic system 100 is in communication with vehicle sensors 180 that provide data to the electronic system 100 regarding the operating conditions of the engine and the vehicle. The vehicle sensors 180 may include, but are not limited to, engine RPM, intake manifold air pressure, crankshaft position, cam position, coil packs, temperature, and any other sensors known to one of skill in the art. The electronic system 100 is also in communication with select vehicle control parameters 190 that may be adjusted and controlled by the electronic system 100. The vehicle control parameters 190 may include, but are not limited to, fuel injectors, coil packs, throttle body, and any other adjustable or controllable parameters one of skill in the art may adjust or control in association with an engine or vehicle.
In the method of
After imbalance detection (step S30), the electronic system 100 records the presence of any imbalance (step S40). In one embodiment, the electronic system 100 may keep a running record of the fuel air ratio of the individual cylinders and/or any imbalance between the cylinders. In the event the fuel air ratio exceeds a predetermined threshold, a vehicle operator may be notified of the imbalance by a warning light, chime, or any other method (step S50). In one embodiment, a vehicle operator is warned of the fuel air ratio imbalance if the imbalance exceeds one of the predetermined thresholds. In one embodiment, the vehicle operator is warned if one of the predetermined thresholds is exceeded on a single run cycle of the engine. In one embodiment, the vehicle operator is warned only after one of the predetermined thresholds is exceeded on more than one run cycles of the engine. In one embodiment, the warning light may be triggered only for the duration of the imbalance.
In discussing the fuel air ratio, a normalized fuel air ratio is more convenient to use than the fuel air ratio itself. The normalized fuel ratio may be calculated by multiplying the measured fuel air ratio by 14.64. A normalized fuel air ratio of one indicates the fuel air ratio is at the stoichiometric value. A normalized fuel ratio greater than one indicates there is a greater percentage of fuel to air than the stoichiometric ratio. A normalized fuel ratio less than one indicates there is a greater percentage of air to fuel than the stoichiometric ratio. A fuel richness estimation is used to estimate the deviation of the normalized fuel air ratio from the stoichiometric value. The fuel richness estimation may be calculated by use of the following equation:
Fuel Richness(%)=ΔΦ=(Φ−1)×100=[14.64×(F/A)−1]×100 (Eq. 1)
In Equation 1, 14.64×(F/A) is the normalized fuel air ratio, where “F/A” is the fuel air ratio. When ΔΦ=0, the fuel air ratio is balanced at the stoichiometric ratio. When, ΔΦ>0, the fuel air ratio contains a higher proportion of fuel to air than the stoichiometric ratio (“rich”). Where ΔΦ<0, the fuel air ratio contains a higher proportion of air to fuel than the stoichiometric ratio (“lean”).
In one embodiment of the method, the oxygen sensor 10 is a wide range oxygen sensor. In another embodiment, the oxygen sensor 10 is a switching oxygen sensor. Because of its inherent characteristics, a linearization process (step S11) is applied to the signal from the oxygen sensor 10 to improve estimation performance when a switching oxygen sensor is utilized. The linearization process (step S11) need not be applied to the signal from the oxygen sensor 10 when a wide range oxygen sensor is utilized. Where a wide range oxygen sensor is used, the individual cylinder fuel richness estimation step S10 begins with signal array formation (step S12).
In the linearization process (step S11), the inverse of the switching oxygen sensor's transfer function, a nonlinear function, is first obtained. Typically, this would be obtained from data from the manufacturer of the switching oxygen sensor showing the output voltage of the switching oxygen sensor versus the actual fuel air ratio. Alternatively, the function may be obtained by recording the actual output voltages of the switching oxygen sensor in response to known fuel air ratios and fitting a function to the resulting curve. In one embodiment, the function, i.e., linearized switching oxygen sensor signal, is expressed as:
x(n)=p(O2(n))=a0+a1(O2(n)−c)+ . . . +ax(O2(n)−c)Y (Eq. 2)
In the above polynomial equation, “O2(n)” is the raw O2 signal, “n” is the sampling index, and “c” is a constant. The constant “c” represents the bias used for shifting the raw signal of the oxygen sensor 10 as would be understood by one of skill in the art. In one embodiment, the constant “c” equals −0.5. Further, “ai”, where “i” is zero through X. X and Y are coefficients of the polynomial of Y degrees. Generating the polynomial as described above reduces the negative impact of the switching oxygen sensor's nonlinear characteristics on the fuel air ratio estimation.
After the linearization process (step S11) is complete, the linearized switching oxygen sensor voltage enters a signal array formation step S12. Where a wide range oxygen sensor is used, the linearization process (step S11) is skipped and the oxygen sensor voltage is directly passed into the signal array formation step S12. As discussed above, an imbalance in the fuel air ratio between multiple cylinders distorts the voltage signal from the oxygen sensor 10. This distortion is the result of high frequency signal components in the output signal of the oxygen sensor 10. The imbalance signal frequency ranges about from 5 to 60 Hz, depending on the number of engine cylinders the engine includes and the operating RPM of the engine. Also as discussed above, the severity of the distortion depends upon the degree of the imbalance between the fuel air ratio of the individual cylinders. The distorted/imbalance oxygen sensor 10 signal contains the information utilized by the method to estimate individual cylinder fuel richness. After the signal array is formed (step S12), the signal array enters the individual fuel richness estimator step S13.
X(nk)=[x(nk)x(nk−1) . . . x(nk−N+1) 1] (Eq. 3)
In the above equation, x(nk−j), where j=0, 1, . . . N−1, are the linearized oxygen sensor signals if a switching oxygen sensor is used or the wide range oxygen sensor signals if a wide range oxygen sensor is used. The oxygen sensor signals are sampled at predetermined and constant angular positions of the engine's crankshaft, as discussed above. A total of “N” samples are taken, where “N” is an integer as described above. In one embodiment, “N” is equal to the number of engine cylinders. In the above equation, x(nk) (i.e., where j=0) is the signal sampled from the oxygen sensor 10 at cylinder k's sampling period. In one embodiment, the sampling period for cylinder k is when it is at TDC. The terms x(nk−j), where j=1, . . . N−1, represent previous sample points of the wide range or switching oxygen sensor's 10 output from cylinder k. In the vector, the constant “1” is included as a bias for better estimation performance. Thus, x(nk) is the current sample of the wide range or switching oxygen sensor's 10 output for cylinder k, x(nk−1) is the previous sample of the wide range or switching oxygen sensor's 10 output for cylinder k, and x(nk−J) is the j previous samples ago of the wide range or switching oxygen sensor's 10 output for cylinder k. In one embodiment, the constant “1” may be omitted. Further, “z−1” is a unit delayer that delays the input one sample period. As described above, the current array vector of cylinder “k” is (X(nk)). The previous array vector of cylinder “k” is X(nk−mNcyl) rather than X(nk−1), where Ncyl is the number of engine cylinders of the engine and “m” is the number of sampling points for each cylinder.
The signal array vector formed in step S12 is then input into the individual cylinder fuel richness estimator step S13. In the embodiment of
In one embodiment, the neural network fuel richness estimator is configured to have one hidden layer. In one embodiment, one or more tan-sigmoid neurons are used. In one embodiment, any type and number of neurons may be used. In one embodiment, a MATLAB® provided Levenberg-Marquardt algorithm may be used for training the neural network. In one embodiment, any type of algorithm may be used for training the neural network.
One disadvantage of neural networks is that they typically require large computational resources. Moreover, the learning process for the network is time consuming. The large computational power demands and learning process may, but need not necessarily, limit the use of neural networks in production vehicles. Thus, while neural networks may be utilized in the method of the present invention, an alternative method for performing the individual cylinder fuel richness estimation (step S13) is also disclosed.
Ψk(nk)=wkox(nk−1)+ . . . +wk(N−1)x(nk−N+1)+WkN (Eq. 4)
In the above equation, x(nk−j), where x(nk) is taken from Equation 3. Further, wkj, where j=0, 1, . . . , N, denotes the estimator's weighs. “N” is an integer of the same value as in Equation 3. The coefficients or weights of the individual cylinder linear fuel richness estimator may be determined using the least squares method. Alternatively, the coefficients or weights of the individual cylinder linear fuel richness estimator may be determined using any other curve fitting or equation generating method desired. To determine the coefficients, the exhaust system of
The sum of Equation 4 is sent to a signal filter for smoothing and noise removal. In one embodiment, the signal filtering is performed by a low pass filter. In one embodiment, any type of signal filter may be used. In one embodiment, the low pass filtering is performed by an exponential filter using the following equation:
ΔΦk(nk)=(1−α)ΔΦk(nk−1)+αΨk(nk) (Eq. 5)
In the above equation, α is the filter coefficient of the exponential filter and Ψk(nk) is the output from Equation 4. In one embodiment, α= 1/32. In one embodiment, α> 1/32 or α< 1/32. In one embodiment, any type of low pass filtering may be performed.
The algorithm of the individual cylinder linear fuel richness estimator (step S13″) requires (N+2) multipliers and (N+1) additions for each cylinder of the engine per engine cycle. If one data point is taken in each engine cycle, i.e., m=1, and N=Ncyl, where Ncyl is equal to the number of engine cylinders, then the individual cylinder linear fuel richness estimator (step S13″) requires only (Ncyl+2) multipliers and (Ncyl+1) additions. For example, a v6 (Le., six cylinder) engine would require 8 multipliers and 7 additions for each cylinder (k) per engine cycle. If a 5 degree polynomial is used, each new added data point requires 9 multipliers and 6 additions.
In one embodiment, any number of engine cylinders may be included with the engine. Moreover, the engine cylinders and exhaust runners may be configured in any desired arrangement. It should be appreciated that the present disclosure is not limited to the particular mechanical configuration described herein. In one embodiment, the individual cylinder neural network fuel richness estimator (step S13′) offers better training performance but worse evaluation (i.e., actual estimation performance) than the individual cylinder linear fuel richness estimator (step S13″). However, when an individual cylinder neural network fuel richness estimator (step S13′) having a single linear neuron is used, the performance between the individual cylinder neural network fuel richness estimator (step S13′) and the individual cylinder linear fuel richness estimator (step S13″) is similar.
In one embodiment, because of the presence of the oxygen sensors 1, 2, 3, 4, the exhaust system of
Thus, a method of measuring the fuel air ratio of each cylinder that effectively estimates the fuel air ratio of individual cylinders from the measurement of an oxygen sensor located at the confluence point of the runners is described. The method is compatible with both a wide range oxygen sensor and a switching oxygen sensor. The method directly estimates the value of the fuel air ratio for each cylinder, is compatible with vehicle on board diagnostics, and includes a simplified calibration process. The method accurately estimates the fuel air ratio for each cylinder and requires reduced computing power to complete the estimation, rendering the method simpler and more effective than prior art methods. The method is capable of adjusting the fuel air ratio for individual engine cylinders and of individual cylinder fuel air ratio imbalance control.
