Fuel Distribution Control System for an Internal Combustion Engine

The invention is related to commonly assigned copending U.S. patent application Ser. No. 187,400 "Closed Loop Timing and Fuel Distribution Controls" filed Sept. 15, 1980, now U.S. Pat. No. 4,357,662, which is a continuation of U.S. patent application Ser. No. 904,131 filed May 8, 1978, now abandoned, and U.S. patent application Ser. No. 399,538 "Phase Angle Detector" filed July 19, 1982.

The invention is related to the field of internal combustion engine fuel controls and in particular to a control for correcting the quantity of fuel to be delivered to each engine cylinder to equalize the torque contribution of each cylinder to the total torque output of the engine.

Electronic ignition and fuel control systems for internal combustion engines are finding acceptance in automotive and allied industries as a result of substantial increases in fuel costs and pollution standards imposed by the government.

R. W. Randall and J. D. Powell of Stanford University in their research under a Department of Transportation sponsored project determined that for maximum efficiency of an internal combustion engine, the spark timing should be adjusted to provided a maximum cylinder pressure at a predetermined crankshaft angle past the piston's top dead center position. The results of this investigation are published in Final Report No. SUDAAR-503 entitled "Closed Loop Control of Internal Combustion Engine Efficiency and Exhaust Emission". This report contains a block diagram of a closed loop system incorporating a circuit which detects the crankshaft angle at which peak pressure occurs then compares this angle with the predetermined angle to generate an error signal. This error signal is then used to correct the ignition timing signal generated in response to other sensed engine parameters as is known in the art.

C. K. Leung and R. W. Seitz in commonly assigned pending U.S. patent application Ser. No. 187,400 filed Sept. 15, 1980 discloses an alternate closed loop engine timing control which computes the phase angle of the torque impulse applied to the engine's output shaft by the individual pistons. The method for calculating the phase angle of the torque impulse in this patent application is based on the theory that the phase angle of the torque impulse is indicative of the angle at which maximum cylinder pressure occurs. This patent application further discloses a fuel distribution system directed to equalizing the torque contribution of each cylinder to the total torque output of the engine. In the dissolved system the magnitude the torque impulses by each cylinder is computed from the instantaneous rotational velocity of the engine's crankshaft and compared with an average torque value to generate a correction signal. The correction signal is then used to correct the quantity of fuel being delivered to each cylinder.

In addition to the torque applied to the engine's crankshaft from the burning of the fuel in the individual cylinders, other factors, such as the position of the cylinder along the crankshaft and torsional vibrations will affect the instantaneous rotational velocity of the crankshaft and introduce errors into the computation of the magnitude the individual torque impulses. The prior art fuel distribution control systems provided no means for removing these errors from the computed magnitude of the torque impulses.

The invention is a fuel distribution control for an internal combustion engine having a fuel control computer generating fuel delivery signals indicative of the quantity of fuel to be delivered in response to operational parameters of the engine, means for delivering fuel to the engine in response to the fuel delivery signals and means for computing the amplitude of the torque impulse produced by the individual cylinders in response to the instantaneous rotational velocity of the engine's crankshaft. The fuel distribution control comprises means responsive to the rotational velocity of the engine and the rotational position of the engine's crankshaft for correcting the computed amplitude of the torque impulse produced by each cylinder, an averaging circuit for producing an average value for the corrected amplitudes of the torque impulses produced by each cylinder, integrator means for generating a difference signal indicative of the difference between the average amplitudes of the individual cylinder and the average amplitude of all the cylinders, means for averaging the difference signals, means for subtracting an averaged difference signal from the individual difference signals to generate a correction signal and means for summing the correction signal with the fuel deliver signal to change the quantity of fuel delivered to each cylinder tending to equalize the amplitude of the torque impulse produced by each cylinder.

The advantage of the invention is that the quantity of fuel to each cylinder is individually corrected to equalize the contribution of each cylinder to the total torque output of the engine including piston position and torque vibration. These and other advantages of the control will become apparent from reading the detailed description of the invention in conjunction with the appended drawings.

FIG. 1 is a block diagram of the fuel control system embodying the fuel distribution control.

FIG. 2 is a first embodiment of the Amplitude Correction Circuit 18.

FIG. 3 is an alternate embodiment of the Amplitude Correction Circuit 18.

FIG. 4 is an embodiment of the Averaging Circuit 20.

FIG. 5 is an embodiment of the Integrator 22.

Referring to FIG. 1, there is shown a block diagram of a fuel control system for an internal combustion engine having a fuel control computer 10 generating fuel delivery signals Q indicative of the engine's fuel requirements in response to the operational parameters of an internal combustion engine 12. A fuel delivery device 14 receiving fuel from an external source (not shown) delivers the required quantity of fuel to the engine 12 in response to the fuel delivery signals Q. The fuel delivery device 14 may be of any type known in the art, such as a separate fuel injector for each engine cylinder, a single fuel injector (unit injector) for all of the engine's cylinders, or an electronically controlled carburetor. A means, such as Digital Period Analyzer 16 generates an amplitude signal A indicative of the magnitude of each torque impulse produced by the individual engine cylinders in response to the instantaneous rotational velocity of the engine's crankshaft. An Amplitude Correction Circuit 18 responsive to the engine speed and rotational position of the engine's crankshaft and corrects on a cylinder by cylinder basis the amplitude signal A received from the Digital Period Analyzer 16. The corrected amplitude signals are then averaged for each cylinder in Averaging Circuit 20 to produce an individual average amplitude signal A for the torque impulses produced by each cylinder. An Integrator 22 integrates the average amplitude signals A generated by the Averaging Circuit 20 and outputs a difference signal .DELTA. indicative of the difference between the integrated average value A.sub.avg. of the average amplitude signals and the average amplitude signal A generated for each cylinder. The difference signal .DELTA. a is then amplified in Amplifier 24 to generate an amplified difference signal .DELTA. A. The amplified difference signal .DELTA. A is averaged in Correction Averaging Circuit 26. A Subtraction Circuit 28 subtracts the output of the Correction Averaging Circuit 26 from the amplified difference signal .DELTA. A output from Amplifier 24 to generate a correction signal .DELTA. Q. The correction signal .DELTA. Q is then summed in Addition Circuit 30 with the fuel delivery signal Q generated by Fuel Control Computer 10 to generate a corrected fuel delivery signal Q+.DELTA. Q correcting the quantity of fuel delivered to each cylinder. The corrected fuel delivery signal Q+.DELTA. Q is operative to equalize the amplitudes of the torque impulses produced by all of the cylinders.

The Digital Period Analyzer 16, such as disclosed in U.S. patent application Ser. No. 187,400 generates a phase angle signal .phi. and an amplitude signal A for each torque impulse in response to the instantaneous rotational velocity of the engine's crankshaft or other suitable rotational member of the engine. The Digital Period Analyzer first generates the functions A sin .phi. and A cos .phi. where A is the amplitude of the torque impulses and .phi. is the phase angle of the torque impulses. The Digital Period Analyzer 16 then computes the value of the phase angle .phi. and amplitude A in accordance with the equations

Preferably, the phase angle .phi. is corrected for changing engine speed engine speed as disclosed in U.S. patent application Ser. No. 399,538 entitled "Phase Angle Detector" (filed July 19, 1982.)

The details of the Amplitude Correction Circuit 18 are shown in FIG. 2. As previously discussed, the amplitude of the torque impulse imparted to the engine's crankshaft are distorted by the rotational velocity of the engine's crankshaft, the positions of the individual cylinders along the crankshaft and other torsional vibrations that may occur. Since these distortions differ as a function of engine speed as well as from cylinder to cylinder the Amplitude Correction Circuit 18 may be embodied in the form of a look-up table storing a set of correction factors for each cylinder as a function of engine speed. To reduce the number of stored correction factors for each cylinder, the engine speed may be subdivided into a plurality of discrete speed ranges and the look up table storing a single correction factor for each cylinder for each speed range. The correction factors may be empirically determined from tests or computed from known engine dynamics. Referring back to FIG. 2, a Period Counter 30 is periodically reset by a reference signal .theta..sub.REF indicative of the engine's crankshaft rotating through a predetermined angle, such as when the piston in each cylinder assumes a predetermined position. This position may be the Top Dead Center (TDC) or any other selected position. The Period Counter 30 counts the pulses generated by an Oscillator 32 and stores at the end of each rotational interval a number indicative of the time between sequential reference signals. This number is inversely proportional to the engine's rotational velocity in that interval. The frequency of Oscillator 32 is selected so that the engine speed is divided into a predetermined number of speed ranges. Preferably Counter 30 is a variable speed counter as described in U.S. patent application Ser. No. 187,400 which counts at a lower rate when the engine speed is below a predetermined value.

A Cylinder Counter 34 is reset by a reference signal .theta..sub.o indicative of the beginning of each engine cycle. The Cylinder Counter 34 counts the reference signals .theta..sub.REF and generates a sequential set of numbers one for each engine cylinder. Each number generated in Cylinder Counter 34 uniquely identifies one of the engine's cylinders.

At the end of each period, signified by the occurrence of the reference signal .theta..sub.REF the numbers stored in Period Counter 30 and Cylinder Counter 34 are input to Multiplexer 36 which generates an address identifying a specific storage location in a Look-Up-Table 38. The Look-Up-Table 38 may be a conventional read-only-memory (ROM) or any comparable type memory storing a set of correction factors "c.sub.i " for each engine cylinder as a function of engine speed. The address generated by the Multiplexer 36 identifies the cylinder in response to number received from the Cylinder Counter 34 and identifies the specific speed related correction factor for the cylinder in response to the number received from the Period Counter 30.

The correction factor "c.sub.i " output from the Look-Up Table 38 is multiplied with the amplitude A generated by the Digital Period Analyzer 16 in a multiplier circuit 40 to produce a correction increment having a value equal to c.sub.i A. The amplitude correction is then summed with the amplitude signal A in a sum amplifier 42 to generate a corrected amplitude signal A+c.sub.i A corrected for both engine speed and other errors that may have been caused by the particular location of that particular cylinder along the engine's crankshaft. Alternatively the correction factor stored in Look-Up Table 38 may be (1+c.sub.i) eliminating the need for sum amplifier 42 as would be obvious to one skilled in the art.

An alternate embodiment of the amplitude correction circuit is shown on FIG. 3. In this embodiment the phase angle signal .phi. is used to correct the amplitude signal A prior to the correction for engine speed and position of the cylinder along the engine's crankshaft. As disclosed Randall and Powell, previously cited, maximum engine efficiency is obtained when the cylinder pressure occurs at a predetermined angle of the crankshaft past the top dead center (TDC) position. Additionally, C. K. Leung and R. W. Seitz in U.S. patent application Ser. No. 187,400 filed on Sept. 15, 1980 have disclosed that the phase angle of the torque impulse is a measure of the angle at which maximum cylinder pressure occurs. Therefore when the phase angle of the torque impulse is different from the phase angle desired to produce maximum efficiency of the engine the amplitude of the torque impulse is less than it would have been had the phase angle been correct. Based on the assumption that the ignition or injection timing is being corrected independently to produce the desired phase angle, the amplitude should be first corrected for the phase angle error.

Referring now to FIG. 3, the phase angle .phi. of the torque impulse generated by the Digital Period Analyzer 16 is first compared with a desired or reference phase angle .phi..sub.REF in a difference Amplifier 44 to generate a phase angle error signal .DELTA. .phi.. The phase angle error signal is then amplified in Amplifier 46 to generate an amplitude correction signal .DELTA. .phi.. The amplitude correction signal .DELTA. .phi. is summed in Sum Amplifier 46 with the amplitude signal A output from the Digital Period Analyzer 16 to generate a phase angle corrected amplitude signal A.sub..phi..

Instead of a single Look-Up Table 38 of the embodiment discussed relative to FIG. 2, the alternate embodiment comprises a plurality of Look-Up Tables 50 through 56, each Look-Up Table storing a correction factor c.sub.i or (1+c.sub.i) for engine speed and the position of the cylinder along the engine's crankshaft for a particular engine cylinder. The illustrated embodiment is for a 4 cylinder engine therefore there are 4 separate Look-Up-Tables. For a 6 cylinder engine, there would be 6 Look-Up-Tables etc.

As previously discussed relative to FIG. 2 a Cylinder Counter 34 generates a number indicative of the cylinder which is producing the torque impulse being analyzed in response to the signals .theta..sub.o indicative of the beginning of each engine cycle and .theta..sub.REF indicative of the beginning of the torque impulse produced by each successive cylinder. At the beginning of each torque impulse, the number stored in Cylinder Counter 34 indicative of the cylinder which produced the torque impulse is input to a Decoder 58 which produces a signal on one of 4 output lines corresponding to the number received from the Cylinder Counter 34. Each of the four output lines of Decoder 58 are connected to the enable input of one of the four Look-Up-Tables 50 through 56.

Simultaneously the Period Counter 30 generates a number which is inversely proportional to the engine speed in response to the number of pulses generated by Oscillator 32 during sequentially received reference signals .theta..sub.REF as previously discussed. The output of Period Counter 30 is used to address all four of the look up tables simultaneously.

The Look-Up-Table enabled by the output from Decoder 58 will output the appropriate correction factor to Multiplier Circuit 40 through OR gate 60. The phase angle corrected amplitude A.sub..phi. is multiplied by the received correction factor in Multiplier Circuit 40, and summed with the phase angle corrected signal A.sub..phi. in Sum Amplifier 42 to generate the corrected amplitude signal having a value:

where the phase angle corrected amplitude A.sub..phi. is equal to:

As noted in the discussion of the first embodiment of the Amplitude Correction Circuit, if the correction factor has the value (1+c.sub.i) Sum Amplifier 42 is not required.

It will be recognized by those skilled in the art that the phase angle correction circuit illustrated with reference to FIG. 3 may also be incorporated in the Amplitude Correction Circuit of FIG. 2.

The details of the Averaging Circuit 20 are shown in FIG. 4. As previously discussed the Decoder 58 outputs a signal on four separate lines, one at a time in response to the number stored in Cylinder Counter 34. The Cylinder Counter 34 and Decoder 58 may be the same decoder discussed relative to FIG. 3 or may be separate elements. The output lines of the Decoder 58 are connected to one input of a set of AND gates 62 through 68 which are enabled in a sequential order in response to the output signals of Decoder 58.

The corrected amplitude signal A (1+c.sub.i) generated by the Amplitude Correction Circuit 18 is received at the other inputs to AND gates 62 through 68. The outputs of the AND gates are individually connected to the input of an associated averaging circuit 70 through 78, one for each engine cylinder. As the AND gates 62 through 68 are sequentially enabled by the signals from Decoder 58, the corrected amplitude signals are sequentially input into the associated averaging circuit and averaged with the prior corrected amplitude signals received from the same engine cylinder. The averaging circuits 70 through 76 average the corrected amplitude signals in accordance with the equation: ##EQU1## where the subscript "i" designates the particular cylinder. The averaging circuits may be of any type known in the art including the averaging circuit discussed in detail in U.S. patent application Ser. No. 187,400.

The outputs from Decoder 58 along with the outputs from the Averaging Circuits 70 through 76 are connected to a Switch 78 which outputs the averaged amplitude signal A from the appropriate averaging circuit in a corresponding sequential order in response to the output of Decoder 58.

The details of the Integrator 22 are shown on FIG. 5. Referring to FIG. 5, the average amplitude signals A.sub.i generated in averaging circuits 70 through 78 of FIG. 4 are sequentially received by an integrator 80 which generates an integrated average signal A.sub.avg. having the value: ##EQU2##

The average signal A.sub.i is then compared with the integrated average signal in difference amplifier 82 to generate the amplitude error signal .DELTA. A. The integrator circuit may be an averaging circuit similar to averaging circuits 70 through 76 or any other circuit known in the art capable of producing an integrated average amplitude signal.

Although the fuel distribution control has been described with reference to specific hard wired circuits, it is recognized that a person skilled in the art is well capable of writing a program for a microprocessor or minicomputer operative to perform the same functions. It is not intended that the invention be limited to the hardwired circuits disclosed. On the contrary the invention may be embodied in any conceivable alternate form including programmed microprocessors or minicomputers without departing from the spirit of the invention as described above and set forth in the appended claims.