Method and apparatus for controlling ignition timing for an internal combustion engine

Abstract: An ignition timing control method and apparatus for a vehicle which provides an engine torque output waveform for canceling vibrational disturbances caused by sudden throttle plate (22) movement resulting in engine accelerations and decelerations. The ignition timing is variably advanced and retarded in accordance with a phase-shifted derivative of engine speed to produce an appropriate engine torque output waveform for optimally canceling the vehicle vibrational disturbances. The phase shift is accomplished by applying a time delay to the engine speed derivative. A negative bias is added to the ignition timing for retarding ignition timing by a predetermined amount to permit a full sinusoidal canceling waveform. A blend multiplier is utilized to gradually remove the effects of the canceling waveform and bias, thereby gradually returning the ignition timing to its original setting.

Description: This invention relates to a method and apparatus for controlling ignition timing for an internal combustion engine. BACKGROUND OF THE INVENTION Rapid throttle plate maneuvers resulting in sudden engine acceleration or deceleration generate powertrain torque disturbances which may produce objectionable vehicle vibrational disturbances to occupants. The vibrational disturbances are comprised of transient, generally sinusoidal, longitudinal vibrations of the vehicle which gradually dampen out. These vibrational disturbances result in engine speed variations. Prior art methods for minimizing the vibrational disturbances include publication EU 0 315 171 A2, which describes an engine control that detects transient induced longitudinal accelerations of a vehicle, derives the derivative of that acceleration and applies the differentiated signal as a correction to the normal engine ignition timing. The derived signal, being a second derivative of sinusoidal vehicle velocity variations, tends to at least partially cancel and thereby reduce these variations. The described method of detecting such acceleration is a chassis mounted accelerometer; but the reference states that the acceleration signal may alternatively be derived from the change rate of engine speed. Publication GB 2 191 539 describes the application of an engine retard correction derived from the derivative of engine speed, the correction being initiated in response to a change in throttle position, air intake quantity or basic fuel injector pulse width indicative of vehicle acceleration. The period of application of the correction may vary with the gear of the transmission as well as other factors. The prior art references described above take effective advantage of the sinusoidal nature of the transient induced velocity variations to derive a canceling ignition timing control correction from the velocity variations themselves. However, they overlook the following important consideration. As shown in FIG. 3 of this document, the torque output of a typical spark ignited, internal combustion engine varies with ignition timing so as to produce maximum output torque at a predetermined timing 45, with output torque decreasing as the timing is either advanced or retarded from this predetermined timing. For greatest engine efficiency, the engine ignition timing is normally calibrated for near maximum torque, slightly retarded from this predetermined timing of maximum torque. The application of a sinusoidal ignition timing correction could, during the advance peaks of the correction, shift the actual ignition timing past the point of maximum timing into an area where torque decreases with advancing timing and could thus render the system uncontrollable and ineffective. SUMMARY OF THE INVENTION The present invention is directed to an ignition timing control method (claim 5) and apparatus or controller (claim 1) for a vehicle which provides an engine torque output waveform for canceling vibrational disturbances caused by sudden accelerations and decelerations. According to the present invention, an engine ignition timing control applies a bias ignition timing retard correction to a determined ignition timing in addition to the sinusoidal ignition timing retard correction of the prior art to ensure that the variations of the sinusoidal ignition timing correction do not advance engine ignition timing beyond a predetermined timing of maximum torque. The bias ignition timing retard correction is initiated a bias delay time after the detected predetermined change in throttle plate position that also initiates the sinusoidal ignition timing retard, the bias delay time thus preventing the additional retard until it is needed and thereby reducing undesirable effects such as engine torque loss. The bias ignition timing retard correction is initiated with a bias value sufficient to accommodate the maximum advance in the initial cycle of the sinusoidal ignition timing retard correction without advancing the ignition timing of the engine beyond the point of maximum torque, and is thereafter decreased gradually to zero. Both the bias value and the bias delay time are derived from an engine operating parameter, which may preferably be a transmission operational state, values of which may be calibrated during vehicle design for optimal system operation and stored in an electronic lookup table. Alternative values of the transmission operational state may differ for automatic or manual transmissions. In a manual transmission, the possible states are preferably defined by the gear arrangements, including neutral. For an automatic transmission including a torque converter clutch the states include some at least partially defined by whether the clutch is locked or unlocked. Brief Description of the Drawings The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: FIG. 1 illustrates a schematic view of an ignition timing control system for an internal combustion engine in accordance with the present invention; FIGS. 2A-2D illustrate graphs of an uncorrected engine speed, a derivative of the uncorrected engine speed, an engine torque output canceling waveform and a corrected engine speed, respectively; FIG. 3 illustrates a graph of engine torque output versus spark timing; and FIG. 4 illustrates a control logic flow chart for executing an ignition timing control system in accordance with the present invention. Detailed Description of the Preferred Embodiment Referring to the drawings, FIG. 1 illustrates a schematic view of an ignition timing control system for an internal combustion engine in accordance with the present invention. A vehicle on-board microprocessor-based control unit 10 receives input signals from an engine rotational speed sensor 12, throttle plate position sensor 14, vehicle speed sensor 18 and, if the vehicle is equipped with an electronically-controlled automatic transmission, a transmission gear sensor 16. The engine speed sensor 12 typically comprises a crankshaft sensing device which outputs a signal every predetermined angle of crankshaft 20 rotation. The throttle plate position sensor 14 outputs a signal corresponding to the position of the throttle plate 22 in the engine intake airway 24. The throttle plate 22 controls the rate of air flow into the engine. For vehicles equipped with electronically-controlled automatic transmissions, the transmission gear sensor 16 detects the current transmission gear being electronically commanded (i.e., engaged and transmitting engine torque), or, if no gear is commanded, an idle condition. The commanded gear and idle condition identify the current operating condition of the transmission, which will hereinafter be referred to as the transmission state. Automatic transmissions are also equipped with a torque converter clutch which can be in one of a locked or unlocked position. Operation of the clutch is controlled by the control unit 10. As such, the control unit 10 does not require a sensor for detecting the position of the torque converter clutch, the position being a known parameter. For vehicles equipped with manual or hydraulically-controlled transmissions, the gear engaged is determined by a calculation based upon the sensed engine speed and vehicle speed. In response to the input signals received, as well as the known and calculated parameters, the control unit 10 outputs ignition timing control signals via signal line 28 to a vehicle on-board ignition control module 30 for firing the engine spark plugs 32 at varied times. The ignition timing control signals are calculated in accordance with a control logic executed by the control unit 10. The control logic will be described in more detail with reference to FIG. 4. Vehicle accelerations and decelerations are initiated by the vehicle driver's movement of an accelerator pedal which, in turn, controls the positioning of a throttle plate 22 in the engine intake airway 24 for regulating the amount of air entering the engine. Vehicle accelerations and decelerations are anticipated by the control unit 10 via changes in the position of the throttle plate 22 as sensed by the throttle plate position sensor 14. The faster the throttle plate movement, the greater the anticipated acceleration or deceleration. Referring to FIG. 2A there is illustrated a graph of uncorrected engine speed (RPM) variations occurring during a sudden vehicle acceleration initiated by movement of the throttle plate 22 at time t 0 . Vehicle vibrational disturbances relating to gear lash and driveline component torsional characteristics result in these engine speed variations. The engine speed variations, which are generally sinusoidal in nature, decrease in amplitude (dampen) as the engine traverses from a lower to higher speed, the first amplitude 40 being the largest. FIG. 2B illustrates a graph of the derivative of the engine speed signal of FIG. 2A. As a derivative, it corresponds to the change in engine speed over time. The graph of FIG. 2B, hereinafter referred to as ΔRPM, is (i) at a maximum positive value at points along the graph of FIG. 2A of greatest positive slope, (ii) at a maximum negative value at points along the graph of FIG. 2A of greatest negative slope, and (iii) at zero at points along the graph of FIG. 2A with zero slope. FIG. 2C illustrates an ignition timing correction signal 44, otherwise known as the engine torque output canceling waveform, which corresponds to a negative or inverse of the ΔRPM graph of FIG. 2B (i.e., a mirror-image) which is phase shifted and multiplied by a gain factor. The gain factor (GAIN1-14) is determined by means of a look-up table, as illustrated in TABLE 1 below, as a function of the sign (+/-) of ΔRPM and the current transmission state which, in the case of an automatic transmission, includes the throttle plate position and torque converter clutch condition. ΔRPM MANUAL TRANSMISSION STATE AUTOMATIC TRANSMISSION STATE GAIN FACTOR negative 1 1 GAIN1 negative 2 2 GAIN2 negative 3 Throttle Open Clutch Unlocked GAIN3 negative 4 Throttle Open Clutch Locked GAIN4 negative 5 Throttle Closed Clutch Unlocked GAIN5 negative 6 Throttle Closed Clutch Locked GAIN6 negative Idle Idle GAIN7 positive 1 1 GAIN8 positive 2 2 GAIN9 positive 3 Throttle Open Clutch Unlocked GAIN10 positive 4 Throttle Open Clutch Locked GAIN11 positive 5 Throttle Closed Clutch Unlocked GAIN12 positive 6 Throttle Closed Clutch Locked GAIN13 positive Idle Idle GAIN14 As mentioned above, vehicle vibrational disturbances result in engine speed variations. This makes the derivative of engine speed a good measure of the vehicle disturbances. When engine speed is not varying, ΔRPM is zero. When engine speed begins to vary, it shows up in ΔRPM. For optimal cancellation, the engine speed variations, as represented by the signal of FIG. 2A, and the engine output torque canceling waveform, represented by signal 44 of FIG. 2C, should be aligned 180° out-of-phase such that the maximum negative amplitude 42 of FIG. 2C occurs simultaneously with the maximum positive amplitude 40 of FIG. 2A. As noted by comparing the ΔRPM waveform of FIG. 2B with the engine speed waveform of FIG. 2A, a phase shift is required for alignment. This is graphically represented in FIG. 2C as the time delay between t 2 and t 3 , which effectively shifts the canceling waveform 44 of FIG. 2C to the right. The amount of phase shift (PHASE1-7) is determined by means of a look-up table, as illustrated in TABLE 2 below, as a function of the current transmission state which, in the case of an automatic transmission, includes the throttle plate position and torque converter clutch condition. The phase shift can be predetermined because the frequency of engine speed oscillation is typically 2-4Hz, depending upon the above noted factors. The exact values are determined during vehicle design. Once the frequency of oscillations are known, the amount of phase shift can be calculated and the required time delay determined to produce the desired phase delay. MANUAL TRANSMISSION STATE AUTOMATIC TRANSMISSION STATE PHASE SHIFT 1 1 PHASE1 2 2 PHASE2 3 Throttle Open Clutch Unlocked PHASE3 4 Throttle Open Clutch Locked PHASE4 5 Throttle Closed Clutch Unlocked PHASE5 6 Throttle Closed Clutch Locked PHASE6 Idle Idle PHASE7 FIG. 2C also illustrates a negative bias term 46 which is added to the basic ignition timing for retarding ignition timing upon the occurrence of a rapid accelerator pedal maneuver. The purpose of adding the negative bias is illustrated in FIG. 3. Referring to FIG. 3, ignition timing is generally set to provide near maximum torque (e.g., at point 45). Recall that the torque canceling waveform 44 illustrated in FIG. 2C is produced by advancing and retarding ignition timing to provide for increasing and decreasing torque, respectively. However, if the ignition timing is already near maximum torque, advancing ignition timing too much (e.g., to point 48) could ultimately result in reduced torque, rendering the system uncontrollable and ineffective. By using the negative bias to temporarily reduce the output torque of the engine (e.g., to point 47), sufficient room for developing a full sinusoidal torque canceling waveform is available. Referring back to FIG. 2C, adding the negative bias 46 at the moment of initial accelerator pedal maneuver t 0 would result in retarded ignition timing prior to actual vehicle acceleration t 1 , thereby inducing significant engine torque loss, sluggish acceleration and possible misfire. For this reason, the bias 46 is not immediately added upon the occurrence of a rapid accelerator pedal maneuver. Rather, it is delayed by an amount referred to as the bias delay, graphically represented in FIG. 2C as the time between t 0 and t 1 . The amount of bias (BIAS1-7) and bias delay (DELAY1-7) are preselected during design of the vehicle and determined during vehicle operation by means of a look-up table, as illustrated in TABLE 3 below, as a function of the current transmission state which, in the case of an automatic transmission, includes the throttle plate position and torque converter clutch condition. The bias delay is designed such that its value results in the addition of the negative bias term 46 coincident with engine acceleration at time t 1 . MANUAL TRANSMISSION STATE AUTOMATIC TRANSMISSION STATE BIAS BIAS DELAY 1 1 BIAS1 DELAY1 2 2 BIAS2 DELAY2 3 Throttle Open Clutch Unlocked BIAS3 DELAY3 4 Throttle Open Clutch Locked BIAS4 DELAY4 5 Throttle Closed Clutch Unlocked BIAS5 DELAY5 6 Throttle Closed Clutch Locked BIAS6 DELAY6 Idle Idle BIAS7 DELAY7 The ignition timing is retarded by the bias amount 46 until time t 4 , corresponding to the maximum engine rotational disturbance 40 of FIG. 2A, at which point the bias amount is gradually decreased until completely removed. Failure to gradually remove the bias would result in overcompensation as the engine speed variations decreased, and sluggish acceleration followed by a sudden engine power surge as the bias was suddenly removed. FIG. 2D illustrates a graph of the corrected engine speed, defined as the sum of the uncorrected engine speed of FIG. 2A, the canceling waveform 44 of FIG. 2C and the negative bias term 46 of FIG. 2C. Notice that the speed variations of the corrected engine speed of FIG. 2D is much reduced from the speed variations of the uncorrected engine speed of FIG. 2A. By enabling the control unit 10 of FIG. 1 to advance and retard the basic ignition timing to produce the engine torque output waveform illustrated in FIG. 2C, the present invention is capable of producing a waveform for canceling the sinusoidal vibrational disturbances of the vehicle. FIG. 4 illustrates a computer logic flow chart executed by the control unit 10 of FIG. 1 for performing ignition timing control in accordance with the present invention. Referring to FIG. 4, the algorithm begins at step 50 by setting the current ignition timing value (TIME) to the basic, uncorrected ignition timing value (BASIC) of the vehicle, a known parameter within the control unit 10. The engine RPM sensor 12, engine throttle plate position sensor 14, transmission gear sensor 16 and vehicle speed sensor 18 are next read in step 52. In step 53, changes in engine RPM (ΔRPM) and throttle plate position occurring since the last sensor reading are calculated. Step 53 also determines a transmission state based upon (i) the current transmission gear being commanded, as sensed by the transmission gear sensor 16, if the vehicle is equipped with an electronically-controlled automatic transmission, or (ii) engine RPM and vehicle speed, if the vehicle is equipped with a manual or hydraulically-controlled transmission. After determining a logic timer (LOGIC) value is zero in step 58, predetermined vehicle triggering conditions are monitored in step 54. If they are detected, the LOGIC timer is initiated in step 56. Vehicle triggering conditions may comprise changes in the engine throttle plate position greater than a predetermined change or changes in the transmission torque converter clutch condition (locked versus unlocked). Step 58 thereafter monitors the value of the LOGIC timer to determine when it has timed-out. As long as the LOGIC timer has been initiated and not yet timed-out, step 60 sets a blend multiplier value (BLEND) to "1". A bias delay timer (DELAY) is also initiated in step 56. The value of the bias delay timer is determined by means of a look-up table, as illustrated in TABLE 3, as a function of the current transmission state which, in the case of an automatic transmission, includes the throttle plate position and torque converter clutch condition. In step 61, the value of a phase delay (PHASE) is determined by means of a look-up table, as illustrated in TABLE 2, as a function of the current transmission state which, in the case of an automatic transmission, includes the throttle plate position and torque converter clutch condition. The function of the PHASE delay will be discussed below with reference to step 70. In step 62, the value of a gain factor (GAIN) is determined by means of a look-up table, as illustrated in TABLE 1, as a function of ΔRPM and the current transmission state which, in the case of an automatic transmission, includes the throttle plate position and torque converter clutch condition. Further, the GAIN factor is multiplied by the ΔRPM value of step 52 to arrive at an ignition timing correction signal term, referred to as the RDSC ( R PM D erivative S park C ontrol) Spark term. The RDSC Spark term can be either a positive or negative number for advancing or retarding, respectively, the ignition timing of the vehicle. In step 66, all positive values of the RDSC Spark term, as determined by step 64, are multiplied by the current BLEND multiplier value. In step 68, the RDSC Spark term is stored in a shift register (SHIFT) for delayed delivery to the Ignition Timing Module 30 of FIG. 1, the delayed delivery resulting in a phase shift of the RDSC Spark term. Use of a blend multiplier keeps the vehicle ignition timing from being advanced too far (e.g., to point 48 in FIG. 3), resulting in a reduced torque and an uncontrollable and ineffective system. Recall that in step 61, the amount of required PHASE delay was determined. The value of PHASE represents the number of shifts within the shift register the RDSC Spark term must encounter before exiting the register. In step 70, the RDSC Spark term is shifted out of the SHIFT register and is added to the current ignition TIME value, updating its value. The bias DELAY timer, initiated in step 56, is continuously monitored at step 74. Once the bias DELAY timer has timed out, step 76 proceeds to (i) determine a bias value (BIAS) by means of a look-up table, as illustrated in TABLE 3, as a function of the current transmission state which, in the case of an automatic transmission, includes the throttle plate position and the torque converter clutch condition, (ii) updates the BIAS value by multiplying it by the current BLEND multiplier value, and (iii) add the updated BIAS value to the current ignition TIME value. In step 84, the current ignition TIME value, which may include RSDC and BIAS adjustments from step 70 and/or step 76, is sent to the Ignition Control Module (ICM) 30 of FIG. 1 by the control unit 10 via signal line 28. Referring back to step 58, if the LOGIC timer times-out and no new triggering conditions are detected in step 54, the BLEND multiplier which was initially set to "1" in step 60 is gradually reduced to zero in step 80 by incrementally subtracting a constant value K during each operation of the logic algorithm. This results in a simultaneous reduction of the BIAS value (in step 76) and the RDSC Spark term (in step 66) to zero. Once the BLEND multiplier has reached zero, as determined in step 82, step 84 sends the current ignition TIME value to the Ignition Control Module (ICM) 30 of FIG. 1, whereupon the program exits. The value of TIME, with the BLEND multiplier equal to zero, is equivalent to the BASIC ignition timing of the vehicle in accordance with step 50.

Claims: An ignition timing controller for an internal combustion engine having a throttle plate (22) for controlling the rate of flow of air into the engine, a throttle plate position sensor (14), and an engine speed sensor (18), the ignition timing control being responsive to the engine speed sensor and the throttle plate position sensor to derive therefrom an ignition timing (10) and being further responsive thereto, when the output of the engine throttle plate position sensor indicates a predetermined change in throttle plate position sufficient to create a sinusoidal variation in engine speed, to provide a sinusoidal ignition timing retard correction (61,62,66,68) derived from, and phase shifted so as to reduce, the sinusoidal variation in engine speed, the ignition control being characterized in that it further provides a bias ignition timing retard correction (76) in addition to the sinusoidal ignition timing retard correction to ensure that the variations of the latter do not advance engine ignition timing beyond a predetermined timing of maximum torque, the bias ignition timing retard correction being initiated a bias delay time after the detected predetermined change in throttle plate position, the bias ignition timing retard correction having initially a bias value sufficient to accommodate the maximum advance in the initial cycle of the sinusoidal ignition timing retard correction without advancing ignition timing of the engine past the point of maximum torque and being thereafter decreased gradually to zero (80), the bias delay time and bias value both being derived from a vehicle operational parameter. An ignition timing controller according to claim 1 further characterized in that the engine includes a transmission having a plurality of alternative operational states and that the ignition timing control includes an apparatus (16,53) for sensing a current transmission operational state from the plurality of alternative operational states and deriving at least one of the bias delay time and bias value from a plurality of predetermined values stored in an electronic lookup table (10) as a function of the current transmission operational state. An ignition timing controller according to claim 2 further characterized in that certain ones of the plurality of alternative transmission operational states distinguish between different transmission gears being engaged and transmitting engine torque, or idle if no transmission gears are engaged. An ignition timing controller according to claim 2 further characterized in that the transmission is an automatic transmission having a torque converter clutch and that certain ones of the alternative transmission operational states distinguish between the torque converter being locked or unlocked. A method of controlling ignition timing of an internal combustion engine for a vehicle, the engine having a throttle plate (22) for controlling the rate of air flow into the engine, the method minimizing vehicle vibrations during engine accelerations and comprising the steps of: sensing an engine rotational speed (18,52); sensing an engine throttle plate position (14,52); determining an ignition timing for the engine (10); calculating a change in the sensed engine throttle plate position (53) over a first predetermined time period; calculating a change in the sensed engine rotational speed over a second predetermined time period (53) when the change in the sensed engine throttle plate exceeds a predetermined value, the change in the sensed engine rotational speed having a generally sinusoidal waveform with decreasing amplitudes over time, representative of vehicle vibration during engine acceleration; providing a sinusoidal ignition timing retard correction (61,62,66,68) to the determined ignition timing when the change in the sensed engine throttle plate position exceeds the predetermined value, the sinusoidal ignition timing retard correction being derived from, and phase shifted so as to reduce, the sinusoidal variation in engine speed and thus decreasing over time along with the sinusoidal variation in engine speed; deriving a bias value (76) and a bias delay time (60) from an engine operating parameter; initiating a bias ignition timing retard correction (76) to the determined ignition timing at a time delayed for a bias delay time after the change in sensed engine throttle plate position exceeds the predetermined value, the bias ignition timing retard correction comprising the bias value, the bias value being sufficient to accommodate the maximum advance in the initial cycle of the sinusoidal ignition timing retard correction without advancing ignition timing of the engine beyond the point of maximum torque; and thereafter gradually reducing the bias ignition timing retard correction to zero (80). A method of controlling ignition timing of an internal combustion engine according to claim 5, the engine having a transmission, the method further comprising the steps of: sensing a current transmission operational state (16,53), the current transmission operational state distinguishing between a plurality of transmission gears being engaged and transmitting engine torque, or idle if no transmission gears are engaged; and determining the bias value (76) and the bias delay time (60) as a function of at least the current transmission operational state. A method of controlling ignition timing of an internal combustion engine according to claim 5, the engine having an automatic transmission with a torque converter clutch, the method further comprising the steps of: sensing a current transmission operational state (16,53), the current transmission operational state distinguishing between the torque converter clutch being locked or unlocked; and determining the bias value (76) and the bias delay time (60) as a function of at least the current transmission operational state.

Inventors: BAUERLE PAUL ALAN, CUBR ANTHONY EDWARD, GARRETT DAVID PARKE, MARSH RICHARD ALLAN, MATHEWS DAVID STEWART, VANEK MICHAEL JOHN, BAUERLE, PAUL ALAN, CUBR, ANTHONY EDWARD, GARRETT, DAVID PARKE, MARSH, RICHARD ALLAN, MATHEWS, DAVID STEWART, VANEK, MICHAEL JOHN
Applicants: GEN MOTORS CORP, GENERAL MOTORS CORPORATION
Application year: 1995
Main classification: F02P5
IPC codes: F02P5, F02D41