METHOD AND APPARATUS FOR ADJUSTING THE IDLING SPEED RATE OF AN INTERNAL COMBUSTION OTTO CYCLE ENGINE

Abstract: Four speed rate (RPM) thresholds are set; if the engine revolution number at the moment is neither below the lowest threshold nor above the highest threshold and it is in the "window" between the two intermediate thresholds, the idling speed rate is varied to bring the RPM rate back in the "window".

Description: " Method and apparatus for adjusting the idling sneed rate of an inter- nal combustion Otto cycle engine " The present invention relates to an electronic device for adjusting the idling speed rate (number of revolutions per minute) setting of inter- nal combustion Otto cycle engines. The device object of the present invention, though certainly general in use, has been specially studied to comply with the new anti-pollution laws for the State of California (tJ.S.A.). According to these laws the engine idling speed rate setting device must not be touched for 50.000 miles. It is clear that with a setting adjusted in the factory and then sealed for 50.000 miles it is not possible to maintain the idling speed rate within a range acceptable for such a mileage (break-in period, seasonal change thermal differences, etc.) It is therefore necessary to utilize electronic devices with the engine revolution number (RPM) as feedback signal. This device ## indifferently operate on the air or on the mixture, when applied to systems with mixture strength correction based on an exhaust gas sensor (feedback systems). In fact, if the device is of a type acting on the air bypass, the feedback sensor automatically cor rects the mixture strength, so that it becomes rich or weak depending on the quantity of air added or subtracted by the device in order to maintain the speed rate at a specified level. Instead, if the system works with open loop on the mixture, it is ad visible the device to act on a component varying the air/fuel mixture introduced during the idle stage as in the case which will be described later, where the idle speed rate setting screw acts on a carburettor system. The object of the present invention is to provide a device of general use on systems with idling speed rate setting via idle speed rate setting screw or mixture by-pass or on systems which by-pass the inducted air. According to the invention it is provided a process for the adjust ment of the idling speed rate of internal combustion Otto cycle en gines for motor vehicles provided with: - means indicating the throttle position; - means indicating the motor vehicle is moving; - means indicating the revolution speed rate, and - means indicating when the automatic gear selector lever is in po sition D, 1, 2,2 and comprising an electronic control unit characterized in that: a. a first, a second, a third and a fourth threshold of revolution numbers (RPM) is predetermined; b. the mixture admitting throttle valve is checked to be shut; c. the motor vehicle is checked to be stationary; d. the actual engine RPM rate is checked to be not lower than the first threshold; e. the actual engine RPM rate is checked to be not higher than the fourth threshold; f. the actual RPM rate signal is compared with the window between the second and the third threshold; g. a correction of the actual RPM rate is actuated to bring it back in said window, acting on the device that varies the amount of mixture supplied to the engine. Additionally the present invention comprises a device carrying out the above mentioned process including: - first sensor means (5) for the throttle position arranged to provide at their output an electrical signal indicative the throttle is closed; - detector means (10) arranged to provide at their output an electrical signal indicative the motor vehicle is moving; - speèdgsensor means (18) arranged to provide at their output an electrical signal indicative of the revolution speed rate of the engine; - second sensor means (25) arranged to provide at their output an elec trical signal indicative the automatic gear selector lever is in position D, 1, 2, R characterized in that it further includes: a. First comparator means (28, 29, 30, 13) arranged to compare the signal indicative of the engine rotation speed rate with at least two RPM thresholds. b. Second comparator means (22) arranged to provide at their output an electrical signal when the variation of the engine rotation speed rate exceeds a fixed threshold. c. Blocking means (8) cooperating with an oscillator (9) adapted to lock this oscillator when at its inputs arrive the signals coming from the first comparator means (28, 13), the first sensor means (5), and the detector means (10). d. Controlling means(15)adapted to supply the signals coming from the second comparator means (22) for-the stepless electric motor rotation. e. Inverting means (16) for the inversion of the electric motor rotation. The invention will be further understood from the following description given by way of non-limiting example with reference to the accompanying drallings in which: Figure 1 represents, by plotting the RPM rates as abscissas and the steps of the step-by-step electric motor (which will be described lat er) as ordinates, the system correction made. Figure 2 represents, by plotting the RPM rates as abscissas and V as ordinates, the trigger diagram of the setting thresholds. Figure 3 represents, by plotting times as abscissas and the RPM rate as ordinates, the variation of the RPM rate when the engine suddenly accelerate s/decelerates. Figure 4 represents the device block diagram, according to the nven tion. The automatic adjustment system of the engine idling speed rate or prises: - an electronic control unit receiving at¯iXts input: the discharge signal from the ignition coil; the signal of closed-throttle contact; the signal indicating the motor vehicle is moving; the signal of gear box positioned in Drive 1, 2, R (automatic transmission versions)and providing as output the order for the electric motor to rotate in the direction required by the control system. - A 12 V direct current electric motor with reducer (generally it is sufficient a reducer output speed of about 1 turn/sec.) controlled step-by-step by said central unit and with a sufficiently slow repet itivy to avoid instability. - A mechanical device for air or mixture adjustment able to receive the rotary motion from the electric motor and to vary the internal combustion engine speed rate. In case of motor vehicle with carburettor this device may be the speed rate adjusting screw itself duly modified for coupling to the electric motor. The electric motor and the engine speed variation device may be coupled rigidly or flexibly (e.g. Bowden). In this second case, permitting the location of the electric motor away from the most advantageous adjusting point, the coupling must be particularly accurate to avoid any dangerous torsional effect. Another possible engine speed rate variation device for the injection system consists of an air by-pass valve with flow section variable by means of a screw. Also in this case the electric motor/screw coupling may be rigid. Jr flexible. The system is completed by a certain number of signals often already present in the outfit. These signals are: - contact on throttle (indicating that the throttle is closed, i. e. that the accelerator pedal is released); - contact indicating the gearshift selector lever is on D, 1,2,R(au- tomatic transmission vehicles only) already present on standard versions to inhibit starting when shift lever is in any gear-engageci position; - contact indicating the motor vehicle is in movement; long since normally provided on U.S. version cars to activate the catalyst replacement interval warning-system (switch activated under the action of the odometer rotor). The function of these three contacts will be illustrated in the more detailed description of the system. An electronic control unit, which will be described later, processes the signal coming from the spark coil and generates a tachometer signal, indicating the instantaneous engine revolution number per minute which is the system feedback. The control is of "window" type, i.e. the adjustment system does not act as long as the speed rate remains within the window or it takes a corrective action by increasing or decreasing the speed rate as required whenever the RPM is not in the window. In Figure 1 it is schematically represented the way in which the sys tem operates. If at a certain instant the engine speed rate corresponds to point A and the conditions exist for the system to be operated in its adjust ment mode (the series of conditions which are to be met will be described further on) the electric motor increases step-by-step the en gine speed rate. The system action is sufficiently slow to avoid any oscillations;the correction time,e.g. in the tested prototypes, is of about a step per second (every step corresponds to an average engine speed variation of 20 to 30 RPM). A correction of about 200to00 RPM is therefore operated in about 7+ 10 seconds (7+10 steps). Still referring to Figure 1 the step-by-step system moves on of about 30 RPM to the position 3, C up to F; being F positioned within the win dow, the system stops till the engine speed rate shifts again out of the window. The above stated correction time, though slow, is satisfactory on the prototypes and avoids oscillations which arise very easily. In fact,an idling engine with open loop has slight speed rate flutterings, special ly in devices with sensor (a CO sensor) so that a more marked correction could cause oscillations. To allow a correct system operation, four tachometric thresholds have been provided, whose stepping sequence diagram is shown in Figure 2. The first threshold, Vs MIN, has been introduced to prevent the system from operating if the RPM is very low; particularly in absence of this inhibiting function the mere actuation (energising) of the ignition lock switch,without actually starting the engine, would already pre-set the control for rewing up to the maxinnun rate possible. Thresholds Vsl and Vs2 limit the adjustment window and determine the normal operation of the system, as shown in Figure 1. The threshold Vs MAX has been introduced to inhibit the system opera tion above a certain engine speed rate, surely corresponding to engine under load (in the present case about 1500 RPM). The need of such a threshold may be explained referring to Figure 3. Supposing the engine idles with motor vehicle stationary and that it is accelerated as illustrated in the Figure, between instant tO and tA the accelerator pedal is actuated and the engine quickly accelerates, at instant tA the pedal is released; should not threshold Vs ¯XVLES avoid the control system to operate, starting from t4 a corrective action, tending to rev down the idle speed would take place, proportional to the time interval in which the engine speed is above Vs 2. With enginetidling and upon accelerating to 5.000 * 6.000 RPM, such time may be of 5 or 6 seconds, so that the corrective action would last for such a time, with a consequent too low engine speed rate in the suc cessive idle speed mode. This would however not be too serious in case of only one acceleration or deceleration, as the system would restore the speed at the nominal value as soon as the tachometer signal falls below Vs 1. In case of repeated accelerations and decelerations the adjustment sys tern keeps reducing, Gradually accumulating the effects of revving down to the lowest possible rate. In this situation it is very likely that, leaving the engine with closed throttle, the adjustment control would not have sufficient time to make up for the previously activated speed rate reduction and the engine would stall. From Figure 3 it can be also noted that the above described malfunction is not avoided simply introducing the threshold Vs MAX which inhibits beyond it the control system operation. In fact this would avoid the malfunction only in the interval tA-tB, while it would be still possible in the interval t3-tC. For this reason the electronic module controlling the system is provid ed with delay control time at about 2 seconds after the instant at which passage below the Vs MAX threshold occurs and during which time the adjustment continues to be inhibited. Furthermore, in the electronic module is provided a consent controlled by the throttle position, which operates as follows: as soon as the throttle moves from the closure position, the idle speed control system is inhibited, but it does not operate instantaneously when the throttle is closed, but only after a delay of about 2 seconds. This delay avoids the previously described malfunction as a result of slight accelerations in neutral (i.e. such as will not exceed Vs MAX) of a repetitive type. In fact in this case the accelerations would be followed by decelera tions at closed throttle with dwelling of the RPM above Vs 2 for about 0,4 + 0,7 seconds with a consequent order for a speed rate reduction. The above said timing control avoids a cumulative speed reduction. The electronic module takes the moving vehicle signal input;this signal is only a switch activated by the odometer rotor and is usually part of the U.S. version vehicle instrumentation as it is used for the catalyst replacement interval warning system. This signal, duly processed, supplies a further inhibiting condition of the idle speed rate control system, corresponding to a vehicle speed of about V 1 ms. If such inhibiting control were not provided, following malfunction could arise: assuming a gear is engaged and the accelerator pedal is released, the motor vehicle being in motion at low speed and RPM below Vs 1, the adjustment system would operate by way of increasing the RPM speed rate, but, a gear being engaged, this would lead to a vehicle speed increase which could be moderate if the road is slightly climb ing and the relative speed rate could therefore fail to fall within the control window. It is possible that in particular situations the system could operate the max. speed rate increase, thus causing an excessive power at the road wheels, certainly not intentional on part of the driver. The opposite effect would be on slight downgrades with gear engaged and vehicle moving. If the engine speed is out of the window above threshold Vs 2,the sys tern would reduce the RPMspeed rate to the maximum possible limit, so that most likely the engine would falter and stop the moment the clutch were released. In case of a motor vehicle with automatic transmission, there would be a malfunction on downgrades when the engine speed rate is above the window due to the "driving" effect of the torque converter, the automatic control could order a complete speed reduction with the engine turning off the moment the motor vehicle is suddenly braked (spike stops). In motor vehicles with automatic transmission it has been verified that it is convenient, even if not essential, to reduce the window value of about 100 RPM when transmission is in D, 1, 2, R in order to avoid a rather notable "motoring over" of the motor vehicle. For such a scope it has been utilized the existing contact system, avoiding the starting with the selector lever in any position other than N or P. When transmission selector lever is in these positions, the contact is closed to earth, the signal reaches the electronic-control unit and pre-sets the window to its nominal value, this being applicable to the basic version with manual transmission. When the gearshift lever is in any other position, the contact is no more to earth and this pre-sets a reduction of about 100 RPM to said window value. We are now going to describe in detail the electronic circuit according to the present invention, referring to Figure 4. The battery voltage is applied, through diode 1 for protection against the polarity reversals, to block 2, which provides stabilized voltage supply VO to the integrated circuits and the thresholds. The non-stabilized voltage output from block 2 upstream of the stabilizing section reaches. block 3 which, through the four transistors TR1, TR2, TR3, TR4, controls the electric motor (indicated as M), previously mentioned, and establishes the rotation of its drive shaft in either directions. If the transistors TELl and TR4 are conducting, the electric motor X turns in one direction, while the conduction of transistors TR2 and TR3 causes rotation in the opposite direction. If the two transistor couples are out off, there is obviously no drive from the electric motor. A resistor R5 is connected between the emitters of transistors TR2 and TR4 and the earth and such emitters are connected to block 4 limiting the current for motor M. The voltage of resistor R5, which is directly proportional to the cur rent flowing through the four transistors TR1, TR2, TR3, TR4, is applied to block 4, and controls the block, which will be described lat er, which controls the above mentioned four transistor set, reducing the extent of monitoring if the voltage drop at R5 should exceed a given value. Block 4 has a double function; if, for any reason, transistor pair TRI and TR2 (or TR3 and TR4) is conducting, what could cause a short circuit, block 4 would limit the current value to a non-dangerous lev el; furthermore, as the electric motor is controlled by pulses, the current must be limited at a fixed value, otherwise the electric motor could operate with different steps, varying with the battery voltage, thus influencing the adjustment speed rate. The closed-throttle signal fed to block 5 is filtered and formed by block 6 and transmitted to a delay circuit 7 delaying of about 2 seo- onds the throttle closing signal which, after such a delay, reaches an inhibiting block 8 which "locks" the oscillator 9 when the throttle is opened. The signal of motor vehicle in movement (drive contact from block 10) is filtered and converted from frequency into voltage by block 11whose output reaches a threshold circuit 12, whose output reaches block 8, constituting a further inhibiting signal for oscillator 9, so that, if the vehicle road speed exceeds a determined speed (about 1 m/sec.),the oscillator will lock. Furthermore the oscillator circuit 9 may be "locked" by the signals Vs MIN and Vs SILGX, coming respectively from comparators 13 and 14 described later); the first comparator 13 avoids the adjustment system to be activated when the engine speed is too low or the engine is inoperative, the second comparator 14 avoids the malfunction already described illustrat ing Figure 3. The oscillator circuit 9 generates frequency pulses of about 1 Hz controlling the step-by-step electric motor operation. This control may be prevented when any blocking signal reaches circuit 8. At oscillator circuit 9 arrives the signal coming from a continuous run ning block 15 when to it are transmitted logic signals of a convenient level coming from a derivator and threshold circuit, which will be de scribed later. The oscillator circuit 9 is connected to circuit 16 selecting the con trol signals for motor clockwise or anticlockwise rotation. The selected control signals are supplied to a monitoring circuit 17 of the four transistors ml, TR2, TR3, TR4. The signal from the ignition coil arrives at a divider and filter cir cuit 18, whose output is fed to a trigger circuit 19, generating a rect angular pulse with the same frequency of the signal from the coil. Circuit 19 is connected to a monostable circuit 20 whose output filtered by circuit 21 constitutes the voltage signal Vn directly proportional to the engine RPM. This signal Vn is fed to the derivative circuit with threshold 22 processing the Vn signal and generates two logic signals if Vn increases or decreases at a rate exceeding the prefixed threshold; when this occurs the. electric motor runs continuously and not step-by-step. Circuit 22 actually determines a rapid correction in the presence of a sudden variation of the speed rate, which could occur when the air cooler is switched on or off or when shifting the gear selector lever from N to D in motor vehicles with automatic transmission. Circuit 22 supplies two logic signals "at' and "b" to circuit 15 con necked to oscillator 9 which, in this case, as already said,will cause the motor to run steplessly. Circuit 231 consisting of an adjustable potentiometer associated with a resistive distribution network, allows fixing the tachometer thresh olds at the desired value. In the described embodiment, it has been preferred only one adjustment instead of four independent adjustments for saving reasons, considering that a greater precision is required for the window adjustment, while Vs MIN and Vs MAX may also be less accurate and therefore can be obtained after a convenient choice of the distribution network. In the present case by means of the potentiometer 23 are fixed only thresholds Vs 1 and Vs 2; all remaining thresholds are consequently fixed at values depending upon the voltage divider, with an accuracy depending solely upon the precision of the voltage divider. This value is correct for motor vehicles with manual transmission. J In case of motor vehicles with automatic transmission all thresholds decrease of about 100 RPM and this is obtained through circuit 24, which, by connecting in parallel to potentiometer circuit 23 the resis tor R6, causes the above mentioned decrease. Circuit 24 is monitored by the contact on gearshift lever 25(for automatics)after filtering and forming (circuit 26) of the signal suppliea by the contact; it has also been included a delay circuit 27 avoiding undesired corrections during abrupt shifts from S to D and vice versa. For motor vehicles with manual transmission the cable transmitting the alternate current signal is directly connected to earth. In case of motor vehicle with automatic transmission, when gearshift lever is in position N or P, the contact is closed and therefore the thresholds are the same as for the manual transmission; when the lever is in positions D, 1, 2, R the contact is open, and the circuit involved operates the above mentioned decrease. Blocks 28, 29, 30, 13 are four comparators for the definition of the four tachometric thresholds utilized for the system control. Circuit 28, representing the maximum threshold (Vs MAX) is connected to the delay circuit 14 that memorises the threshold for about 2 seconds after the downstepping takes place, as already explained.

Claims: CLAIMS: 1. A process for adjusting the idle speed rate setting of internal combustion Otto cycle engines on motor vehicles provided with: - means indicating the throttle position; - means indicating the motor vehicle is moving; - means indicating the revolution speed rate, and - means indicating when the automatic gear selector lever is in position D, 1, 2, R and comprising an electronic control unit characterized In that: a. a first, a second, a third and a fourth threshold of revolution numbers (RPM) is predetermined; b. the mixture admitting throttle valve is checked to be shut; c. the motor vehicle is checked to be stationary; d. the actual engine RPM rate is checked to be not lower than the first threshold; e. the actual engine RPM rate is checked to be not higher than the fourth threshold; f. the actual EPM rate signal is compared with the window between the second and the third threshold; g. a correction of the actual RPM rate is actuated to bring it back in said window, acting on the device that varies the amount of mixture supplied to the engine. 2. A process, according to Claim 1, characterized in that the sig nal indicating the throttle is closed is accepted with a pre-established time delay. 3. A process, according to Claims 1 and 2, characterized in that the signal indicating the rewing down below the fourth threshold is accepted with a pre-established time delay. 4. A process according to Claims 1, 2 and 3 characterized in that in motor vehicles with automatic transmission the system provides shift ing of said second and third RP9l threshold value to a prefixed lower speed rate by stepping down the RPM. 5. A process according to Claim 4 characterized in that the shifting of said window is dependent upon the automatic transmission gear selector lever position. 6. A process according to Claim 1.5 characterized in that the correction is made by means of a step-by-step electric motor adapted to act on devices capable of varying the amount of the fuel/air mixture. 7. A process according to Claims 1 + 6 characterized in that the monitoring frequency of the electric motor avoids engine speed rate oscillations (hunting). o. A process according to Claims 1 + 7 characterized in that in case of sudden speed rate variation due to sudden load application or release the electric motor is controlled in stepless manner as a function of a derivative signal representing the engine speed rate variation. 9. Device carrying out the process according to any of Claims 1 to 8 including: - first sensor means (5) for the throttle position arranged to provide at their output an electrical signal indicative the throttle is closed; - detector means (10) arranged to provide at their output an electrical signal indicative the motor vehicle is moving; - speed sensor means (lib) arranged to provide at their output an electrical signal indicative of the revolution speed rate of the engine; - second sensor means (25) arranged to provide at their output an elec trical signal indicative the automatic gear selector lever is in position D, 1, 2, R characterized in that it further includes: a. first comparator means (2d, 29, 30, 13) arranged to compare the signal indicative of the engine rotation speed rate with at least two RPM thresholds; b. second comparator means (22) arranged to provide at their output an electrical signal when the variation of the engine rotation speed rate exceeds a fixed threshold; c. blocking means (8) cooperating with an oscillator (9) adapted to lock this oscillator when at its inputs arrive the signals coming from the first comparator means (28, 13), the first sensor means (5) and the detector means (10); d. controlling means adapted to supply the signals coming from the second comparator means (22) for the stepless electric motor rotation; e. inverting means (16) for the inversion of the electric motor rotation. 10. A device according to Claim 9 characterized in that it comprises a stabilizer (2) connected to a control circuit (3) connected to a mon itoring circuit (17), in turn connected to a selector (16) to which are conveyed the signals coming from an oscillator (9) connected to a block circuit (b) and to a stepless working circuit (15), a throttle contact sensor (5) connected to a forming circuit t6) conveying its signal to a delay circuit (7) connected to said block circuit (tri), a sensor indicating that the motor vehicle is moving (10) connected to a threshold circuit t12); ; a voltage divider filter circuit (18) receiv ing the signals from the ignition coil connected to a trigger circuit (19) connected to a monostable circuit (20) connected to a filter circuit (21) in turn connected to a threshold derivator circuit (22) con nectedtotbsstepless working circuit (15); a potentiometer (23) being connected to a first (2it), a second (29), a third (30) and a fourth(13) threshold circuit, all connected in turn to the filter circuit (21 )and to the threshold derivator circuit (22); this first threshold circuit being connected to a delay circuit (14) connected to the block circuit tom), said second and third threshold circuit (29 and 30) being connected to said selector circuit (16); said fourth threshold circuit (13) being connected to said block circuit (#).

Inventors: DI NUNZIO, VITTORIO
Applicants: FIAT AUTO S.P.A.
Application year: 1981
Main classification: F02D31
IPC codes: F02M3, F02B1, F02D41, G01P1, F02D31