GB2189058A - Engine idle speed control - Google Patents

Abstract

Idle speed control is enabled by means (50-56) when the actual engine speed (RPM) becomes substantially equal to the desired engine speed (DIDLE) and disabled when the actual engine speed (RPM) becomes greater than the desired engine speed (DIDLE) by move than a set amount (v1). A speed error signal (e) generates a control signal at (40) having proportional and integral components from stems (29-31) and (32-38) respectively. When the speed control is disabled, an integrator (33) stores the last value of the integral component for immediate use when the control is next enabled. A throttle closed signal from sensor (60) may also be needed to enable the idle speed control. The control signal generated at (40) is used to control an air bypass (28). A signal (TQPOL) may be generated to control the bypass (28) and a fuel control (80) during overrun. <IMAGE>

Description

GB2189058A 1 SPECIFICATION tegral of the difference between actual speed

and desired idle speed would typically slow Engine control system including engine idle the response of the idle speed control system speed control thus lessening the desirability of the use of 70 such a system. In addition, typically the prior

Cross Reference to Related Applications idle speed control circuits are separate from

The present invention is related to the in- other engine control circuits, thus requiring ex vention described in copending International tra cost for the total engine control systems.

patent application no. PCT/US85/01195, pub- iication no. W086/00666, entitled -Engine 75 Summary of the Invention control System-, and having the same appli- An object of the present invention is to pro cant as the present application. vide an improved engine control system for controlling engine idle speed which overcomes Background of the Invention the above mentioned deficiencies of prior sys-

The present invention is related to engine 80 tems.

control systems which implement engine idle In accordance with the present invention an speed control. More specifically, the present engine control system including engine idle invention is related to engine control systems speed control apparatus, comprises means for which develop electrical control signals that providing an error signal related to the differ- are utilized to control engine idle speed. 85 ence between actual sensed engine speed and Engine control systems are known in which a desired engine idle speed; means coupled to an air bypass valve (dashpot) is provided such said error signal providing means for imple that under certain conditions, such as deceler- menting, when enabled, a closed loop engine ation, additional air is provided to the engine idle speed control in accordance with a con fuel mixture. Such systems recognize that the 90 trol signal related to at least the magnitude of idle speed of an engine bears a direct relation- said error signal; and means coupled to said ship to the amount of additional air provided engine idle speed control means for selectively by such an air bypass valve. One such sys- enabling said closed loop idle speed control tems is disclosed in US patent 4,453,514, means in response to at least the magnitude entitled, -Engine Speed Adaptive Air Bypass 95 of said actual speed being within a predeter Valve (Dashpot) Control-, which is assigned mined speed range, wherein said closed loop to the same assignee as the present inven- idle speed control means includes means for tion. positioning air-fuel mixture control apparatus in Some engine control systems have utilized accordance with said control signal, and the known relationship between the degree of 100 means for storing, until said closed loop idle air bypass valve actuation and idle speed to speed control means is enabled, the magni implement an idle speed control system in tude of a signal related to the position of said which a desired idle speed is calculated as a control apparatus at a magnitude related to function of engine coolant temperature and the the magnitude which existed when said closed degree of bypass actuation is a function of 105 loop idle speed control means was last ena the difference between actual engine speed bled, and utilizing said stored magnitude to and this desired engine idle speed. In these implement initial closed loop control of said known systems, typically the control of idle air-fuel mixture control apparatus by initially speed is implemented in direct proportion to determining said control signal when said idle the difference between actual engine speed 110 speed control means is enabled, characterized and desired idle speed. In some systems, the by said enabling means enabling said closed idle speed control is implemented by the en- loop idle control means in response to at least abling of a closed loop servo-control system the magnitude of said actual speed being sub when engine speed approaches the desired stantially equal to said desired engine idle idle speed. 115 speed, and disabling said closed loop control Typically, such engine idle speed control means whenever said actual speed is above a systems do not provide servo-control in acpredetermined speed which is greater than cordance with the integral of the difference said desired speed.

between actual engine speed and desired idle speed, as well as in proportion to the differ- 120 Brief Description of the Drawings ence between actual and desired idle speed. For a more complete understanding of the By controlling idle speed in accordance with present invention, reference should be made the integral of the difference actual speed and to the drawings in which:

desired idle speed during closed loop oper- Figure 1 comprises Figs. 1 a and 1 b which ation, an engine idle speed control system will 125 together illustrate a schematic diagram of an reduce idle speed overshoot error by prevent- engine control system which incorporates the ing the idle speed control from too rapidly present invention; responding to transient conditions. This will Figure 2 comprises a series of graphs a prevent engine stalls from occurring during through f illustrating input versus output trans transient conditions. However, providing an in- 130 fer characteristics for several of the compo- 2 GB2189058A 2 nents shown in Fig. 11; desired engine idle speed DIDLE. The terminal Figure 3 is a series of graphs a through e 26 is provided as an input to an engine idle illustrating waveforms for various signals pro- speed control means 27 shown dashed in Fig.

vided by the control system shown in Fig. 1; 1. The control means 27 effectively imple and 70 ments engine idle speed control by controlling Figure 4 comprises Figs. 4a and 4b which the degree of actuation of an air bypass valve together illustrate flowcharts showing the op- 28 which selectively adds, in accordance with eration of the components shown in Fig. 1. the magnitude of a received control signal, a and the operation of a preferred microproces- predetermined amount of air to the air fuel sor embodiment of the present invention. 75 mixture consumed by the engine 11. The air bypass valve 28 is sometimes also referred to Description of the Preferred Embodiments of as a dashpot and is typically controlled by the Invention receiving either an analog signal that controls Referring to Fig 1, an engine control system the degree of actuation of the valve or receiv- 10 is illustrated. An engine 11 is shown in 80 ing a pulse width modulated signal which ef block form and includes a body 12 coupled to fectively controls the degree of actuation of the engine crankshaft (not shown) and rotated the valve. While the present invention pro about an axis 13, corresponding to the crank- vides for having the air bypass valve 28 re shaft axis, and having an extending projection ceive a control signal, a stepper motor and air 14. Effectively coupled to the rotating body 85 valve can also be utilized as the effective equi 12 of the engine 11 is a position (speed) sen- valent of the air bypass valve 28 wherein the sor 15 which effectively senses the passage amount of air provided by the stepper motor of the rotating projection 14 and develops a and its associated air valve would be con pulse signal at an output terminal 16 wherein trolled in accordance with a received analog or the frequency of pulses at the terminal 16 is 90 digital signal.

related to engine speed. The pulses at the The idle speed control means 27 shown in terminal 16 are converted by a speed (RPM) Fig. 1 implements idle speed control in accor generator 17 into an analog RPM signal pro- dance with both a signal which varies directly vided at an output terminal 18. The generator in proportion to the idle speed error signal e 17 effectively integrates the pulses at terminal 95 and a signal related to the integral of the sig 16 to provide the RPM signal. The operation nal e. This is accomplished in the following of the components 12 through 18 is conven- manner. The terminal 26 is connected as an tional and well understood by those of aver- input to an amplifier and combined table look age skill in the art. The end result is the pro- up ROM1 29 which provides an input signal viding of an analog signal RPM at the terminal 100 to a limiter circuit 30 that provides an output 18 which has a magnitude representative of signal at a terminal 31. The combined input actual sensed engine speed. versus output transfer characteristics of the The system 10 includes an engine coolant components 29 and 30 is shown in graph b temperature sensor 20 which provides an an- of Fig. 2 wherein for small positive values of alog signal at a terminal 21 representative of 105 the signal e a linear gain relationship PRPGP engine coolant temperature. The terminal 21 is (proportional gain positive) is provided, provided as an input to a desired idle speed whereas for larger values of the signal e a generator 22 which effectively receives the maximum limit of PRPLP (proportional limit temperature signal at the terminal 21 and pro- positive) is provided. Similar relationships exist vides, in response thereto, a calculated de- 110 for negative values of the signal e. The end sired idle speed signal DIDLE at an output ter- result is that at the terminal 31 a signal is minal 23. Graph a in Fig. 2 illustrates the input provided which is proportional to the differ versus output transfer characteristic of the idle ence between actual sensed engine speed speed generator 22 wherein effectively for RPM and the calculated desired engine idle cold temperatures below T, a high idle speed 115 speed DIDLE.

of RPM 2 is provided, for normal engine tem- The terminal 26 at which the signal e is peratures between T, and T2 a low idle speed provided is also coupled as an input to a con of RPM 1 is provided, and for excessive temtrollable gate 32 which when closed passes peratures again a high idle speed RPM 2 is this signal as an input to an intergrator 33 provided. The function of the components 20 120 that provides an output integral signal at a through 23 is conventional and well under- terminal 34. The terminal 34 is provided as an stood by those of average skill in the art. input to a controllable gate 35 which when The engine control system 10 includes an closed passes this signal as an input to a analog comparator 25 which receives at its second amplifier and table look up ROM2 36 positive input terminal the signal DIDLE and at 125 which provides an input to a limiter stage 37 its negative input terminal the signal RPM, and that provides an output signal at a terminal provides at an output terminal 26 an analog 38. When the gates 32 and 35 are closed, error signal e having a magnitude representa- the end result is that the integrator 33 will tive of the difference between the actual integrate the signal e at the terminal 26 and sensed engine speed RPM and the calculated 130 provide an integrated signal at the terminal 34 3 GB2189058A 3 as an effective input to the components 36 idle speed control apparatus 27 will maintain and 37. Typical transfer characteristics for the its previous magnitude whenever the idle components 36 and 37 are illustrated in graph speed control apparatus 27 is disabled. This c of Fig. 2 and are similar to the transfer means that during a subsequent enablement of characteristics shown in graph B of Fig. 2 for 70 the idle speed control apparatus 27, there will the components 29 and 30. The end result is be no time delay required for the integrator that at the terminal 38 a signal related to the 33 to achieve a desired output at the terminal integral of the difference between actual en- 34. This feature enables the idle speed control gine speed and calculated desired engine idle apparatus 27 to more properly respond to en- speed is provided. 75 gine transients while still providing an integral It should be noted that the transfer charac- signal as part of the idle speed control signal teristics illustrated in Fig. b and c are readily provided at the terminal 40, and this will implemented by either analog or digital circuits therefore assist the present idle speed control and do not form an essential part of the pre- apparatus 27 in preventing overshoot in con sent invention. Thus the signals at terminals 80 trolling idle speed.

31 and 38 could be either analog or digital, The manner in which the idle speed control and this is the reason for the using the an- apparatus 27 is enabled and disabled will now alog-digital terminology, -amplifier ROM---. be discussed. The error signal e at the termi The proportional signal at the terminal 31 nal 26 is connected to the negative input ter- and the integral signal at the terminal 38 are 85 minal of a digital comparator 50 which re both provided as positive inputs to a summing ceives at its positive input terminal a reference terminal 39 which provides, in response voltage V, and provides at an output terminal thereto, an idle speed control signal at an out- 51 a digital signal which is a positive (high) put terminal 40 which is provided as an input logic signal when the signal e is less than the to an electrically controllable gate 41 which, 90 reference voltage V, and a zero (low) logic when closed, provides a series connection be- signal at other times. The terminal 51 is pro tween the terminal 40 and an output terminal vided as an input to an AND gate 52 whose 42 which corresponds to a control input ter- output is directly connected to the enablement minal for the air bypass valve 28. Thus, when terminal 43 of the idle speed control appara- the gate 41 is closed, the amount of air pro- 95 tus 27. The terminal 23 at which the desired vided by the bypass valve 28 will be deter- idle speed signal DIDLE is provided is con mined by the idle speed control signal at the nected to the positive input of a digital com terminal 40. parator 53 which has its negative input di Each of the controllable gates 32, 35, and rectly connected to the terminal 18 at which 40 has a control terminal designated by prime 100 the actual engine speed signal RPM is pro notation, and each of these control terminals vided. The output of the digital comparator 53 is directly connected to an enable terminal 43 is provided at a terminal 54 that is connected of the idle speed control means 27. When a to the clock input terminal C of a flip-flop positive signal is present at the terminal 43, circuit 55. A data terminal D of the flip-flop all the gates 32,35 and 41 are closed and the 105 circuit 55 is connected to a fixed positive vol idle speed control means 27 implements en- tage B+, and a reset terminal R of the flip gine idle speed control in accordance with the flop is directly connected to the terminal 51.

difference between actual engine speed and An output terminal Q of the flip-flop provides desired engine idle speed, as well as in accor- an output at a terminal 56 which is directly dance with the integral of this difference. It is 110 connected as an input to the AND gate 52.

significant to note that when the engine idle The signal at the terminal 56 is designated speed apparatus 27 is not enabled (disabled), IDLF signifying idle flag since this signal is a low signal is present at the terminal 43 representative of both when the error signal e which results in the opening of the gates at the terminal 26 is less than an error level 32,35 and 41. This prevents the terminal 42 115 corresponding to the signal V, and when then from receiving the engine idle control signal at the actual engine speed signal RPM has fallen the terminal 40 and causes the air bypass below the calculated desired idle speed DIDLE valve to implement a minimum addition of air at the terminal 23.

to the air fuel mixture. This also causes the Essentially, until the error signal e fails be integrator 33 to maintain, at its output termi- 120 low the reference level V, the flip-flop 55 nal 34, the magnitude of the integral signal remains reset such that a 0 logic level is pro provided at this terminal when the integrator vided at the terminal 56. When the signal e is 33 was last enabled. This is because the below the reference level V,, then it is pos gates 32 and 35 prevent the integrator 33 sible to set the flip-flop output high. When from receiving any additional input signals, and 125 actual engine speed then first fails below the prevent the output of the integrator from de- calculated desired idle speed, the flip-flop 55 caying because of any current drain provided will be clocked by a rising signal transition at by the components 36 and 37. This is signifi- terminal C and provide a high signal at the cant since a major aspect of the engine con- terminal 56 representative of a clocked idle trol system 10 is that the integrator 33 of the 130 speed enablement flag. This high signal will be 4 GB2189058A 4 maintained until the signal e exceeds the level the table 73 is essentially to compensate the V, causing the flip-flop to be reset. The high pressure signal MAP at the terminal 71 for idle flag signal at terminal 56 will provide for expected variations in no load engine pressure enabling the idle speed control apparatus 27 which occur as a function of engine speed, in the event of a closed throttle position, 70 wherein the effects of load have been essen since throttle position is a third input to the tially ignored. Thus the signal at the terminal AND gate 52 shown in Fig. 1. 75 is representative of a manifold air pressure In Fig. 1, a throttle position sensor 60 is signal which has been effectively normalized illustrated in block form as providing an analog as a function of engine speed.

throttle position signal THR at a terminal 61. 75 It has been determined that since no load The terminal 61 is connected to the positive manifold air pressure appears to vary as a input of a digital comparator 62 which has its function of engine speed as a parabola, effec negative input terminal connected to a refer- tively subtracting a parabolic speed compen ence voltage V, The digital comparator 62 sating signal, such as the signal provided at provides an output at a terminal 63 which is 80 terminal 74, can provide an engine speed nor coupled through an inverter 64 as an input to malized pressure signal at the terminal 75.

the AND gate 52. Essentially, for a closed The transfer characteristic relationship imple throttle (foot off the accelerator pedal) the mented by the table 73 is determined by the magnitude of the throttle position signal THR type of engine utilized. The end result is that will be less than the reference voltage V2. 85 a manifold pressure signal is provided at the This will result in 0 logic magnitude at the terminal 75 which is representative of speed terminal 63 and therefore result in a positive compensated actual sensed engine manifold (high) logic input to the AND gate 52 being pressure.

provided by the inverter 64. The end result is It should be noted that the actual sensed that in the event of a high idle flag signal at 90 engine manifold pressure is directly related to the terminal 56 and a closed throttle position, engine fuel consumption since it forms a relia the AND gate 52 will provide a high output at ble measure of the air-fuel mixture consumed the terminal 43 resulting in enabling the idle by the engine 11. In connection with this, it speed control apparatus 27. Disabling of the should be noted that the terminal 71 at which idle speed apparatus 27 occurs in response to 95 the signal MAP is provided is also provided as either a non-closed throttle position or the a direct input to a fuel control apparatus 80 magnitude of the signal e being outside the which provides, as its output, a desired predetermined range defined by the voltage amount fuel to the engine 11. The fuel control V, apparatus 80 effectively provides fuel to the An additional significant aspect of the en- 100 engine 11 in accordance with the magnitude gine control system 10 relates to developing of the MAP signal at the terminal 71 multi an engine torque polarity signal TQPOL repre- plied by any deceleration factor corresponding sentative of the difference between actual en- to the magnitude of a signal received at an gine fuel consumption and engine fuel con- additional input terminal 81 of the fuel control sumption which occurs during engine idle 105 apparatus. Implementing fuel control in this speed. Preferably the magnitude of the engine manner is within the skill of those in the art fuel consumption at engine idle speed is not a since it amounts merely to providing fuel to present fixed magnitude, but is continuously the engine in accordance with the magnitude recalculated each time the engine 11 is oper- of the analog signal at the terminal 71 multi ated at engine idle speed. This is accom- 110 plied by some additional correction factor plished in the following manner. represented by the signal at the terminal 81 The engine control system 10 includes an which is contemplated as having a magnitude engine manifold air pressure sensor 70 which ranging from 0 to 1.

provides an analog signal MAP, at a terminal As stated previously, a major aspect of the 71, which is representative of the sensed en- 115 engine control system 10 concerns developing gine manifold pressure. The terminal 71 is an engine torque polarity signal TGPOL which connected as a positive input to a summing is related to the difference between actual en terminal 72. The engine speed signal RPM at gine fuel consumption and the engine fuel the terminal 18 is connected as an input to a consumption which exists during no load en MAP adjustment table look up 73 which, in 120 gine idle speed conditions. If less fuel is being response thereto, provides an output signal at consumed at any time than the fuel which is a terminal 74 which is connected as a nega- required during engine idle speed, then clearly tive input to the summing terminal 72. The the momentum of the engine dominates and difference output of the summing terminal 72 there is negative torque polarity indicating that is provided at an output terminal 75 at which 125 the engine momentum is driving the engine an adjusted MAP signal ADJIVIAP is provided. rather than having to supply fuel to the engine The input versus output transfer characteristic to have the engine overcome its own inertia.

of the MAP adjustment table 73 is illustrated When a condition of negative torque polarity in graph d of Fig. 2 and is shown to have a has been detected, typically it is desirable to somewhat parabolic shape. The function of 130 reduce the fuel to the engine so as to con- GB2189058A 5 serve fuel and to increase the amount of air fold pressure. When the gate 82 is opened being supplied to the engine to insure com- because the engine is no longer in an idle plete combustion of fuel supplied to the en- condition, the output of the integrator at the gine. Both of these functions will result in the terminal 85 is maintained constant such that enleanment of the air-fuel mixture to the en- 70 the summing terminal 86, which has a high gine during conditions of negative torque po- input impedance, will still provide at the termi larity, and this saves fuel and insures more nal 87 a signal related to the difference be complete combustion of the fuel supplied to tween actual manifold pressure and the mani the engine thus reducing engine exhaust polu- fold pressure which exists at engine idle 10.tion. Thus a key aspect of the engine control 75 speed. In this manner an engine torque polar system 10 resides in accurately providing a ity signal MPOL at the terminal 87 is pro torque polarity signal which can be utilized to vided.

develop the proper fuel mixture enleanment It should be noted that the pressure adjust functions which are desired. This is accom- ment table look up 73 has been added to the plished in the following manner. 80 control system 10 to merely provide a more The speed adjusted pressure signal accurate indication of torque polarity at the AWMAP at the terminal 75 is connected as terminal 87, but that even if the table look up an input to a controllable gate 82 which when 73 were replaced by a direct connection be closed provides for directly connecting the ter- tween the terminals 18 and 74, the signal at minal 75 to an output terminal 83 which is 85 the terminal 87 will still be substantially repre connected as an input to an integrator circuit sentative of the actual torque polarity of the 84. The integrator 84 provides an average idle engine 11. It should be noted that the dis speed pressure signal PIDLE at an output ter- closed configuration for providing the torque minal 85 which is connected as a positive polarity signal at the terminal 87 provides for input to a summing terminal 86. The actual 90 continuously monitoring and averaging the speed adjusted pressure signal at the terminal amount of engine fuel consumption, as mea is connected as a negative input to the sured by engine manifold pressure, at engine summing terminal 86 which provides at a ter- idle conditions and comparing this to the ac minal 87 a difference signal MPOL represen- tual manifold pressure which exists at other tative of engine torque polarity. 95 times. When actual manifold pressure is less Essentially, the gate 82, when closed, al- than the idle speed manifold pressure, this in lows the integrator 84 to average the speed dicates a negative torque polarity condition in adjusted pressure signal at the terminal 75 dicative of engine momentum driving the en and provides this average signal to the output gine rather than the utilization of fuel to over- terminal 85. Since the signal at the terminal 100 come the engine inertia. In this situation it is is representative of the pressure at idle typically desirable to reduce engine fuel and speed, the gate 82 should be closed only dur- increase the amount of air in the engine air ing idle speed conditions. This is accom- fuel mixture. This is accomplished in the fol plished in the following manner. lowing manner.

The error signal e at the terminal 26 which 105 The terminal 87 at which the torque polarity is representative of the difference between ac- signal MPOL is provided is connected as an tual engine speed and the desired calculated input to a controllable gate 95 which when engine idle speed is coupled as an input to a closed provides a direct connection between terminal 88 which is provided as the negative the terminal 87 and a first deceleration loop input to a digital comparator 89 and the posi- 110 up table 96 and a second deceleration look up tive input to a digital comparator 90. The table 97, each of which providing output sig positive input of the comparator 89 is con- nals at terminals 98 and 99, respectively. A nected to a high reference level V, and the control terminal 95' of the gate 95 receives negative input of the comparator 90 is con- its input from a connection to the terminal 43 nected to a low reference level V, The out- 115 through an inverter 100. The connection of puts of the comparators 89 and 90 are pro- the components 95 through 100 results in vided as inputs to an AND gate 91 which having the gate 95 block any implementation provides, in response thereto, an output signal of fuel control or air bypass control in accor directly connected to a control terminal 82' of dance with the torque polarity signal MPOL the controllable gate 82. This configuration re- 120 when the idle speed control apparatus 27 is sults in closing the gate 82 when the engine enabled. This is because during enablement of speed error signal e is within the voltage level idle speed control the gate 95 is open and V3 and V, which are contemplated as forming provides a zero input to the look up tables 96 a guard band about 0 magnitude for the error and 97. However, at other times the gate 95 signal e. Thus when actual engine speed is 125 will be closed resulting in the torque polarity approximately the desired calculated engine signal MPOL being provided as an input to idle speed, the AND gate 91 will close the the look up tables 96 and 97. Transfer char gate 82 resulting in the integrator 84 provid- acteristics for these tables are illustrated in ing at the terminal 85 a manifold pressure graphs e and f in Fig. 2 wherein for positive signal PIDLE representativeof idle speed mani- 130 values of the signal MPOL above some mini- 6 GB2189058A 6 mum threshold, the signal at the terminal 98 mately equal to the desired engine idle speed will implement, but by virtue of a direct con- DIDLE, at which time the idle speed control nection of this terminal to the terminal 42, apparatus 27 will be enabled and maintain en providing of additional air to the air-fuel mix- gine speed at this level by virtue of the oper ture via the air bypass apparatus 28 in accor- 70 ation of the air bypass apparatus 28.

dance with the magnitude of the signal Graph c in Fig. 3 illustrates a signal 103 TWOL. representative of the manifold air pressure sig It should be remembered that negative tor- nal MAP at the terminal 7 1. Prior to the time que polarity is indicated by the signal TWOL t, a first level of manifold pressure is main- exceeding 0 magnitude. Thus for negative tor75 tained, and subsequently this level will de que polarity at other than idle speeds, this is crease to a minimum level of MAP and then indicative of a deceleration condition which subsequently increase such that at approxi will result in additional air being provided to mately the time t, the idle speed pressure the air fuel mixture of the engine 11. Similarly, level PIDLE will be obtained. It should be for a magnitude of the torque polarity signal 80 noted that at a time t, after t, the manifold TWOL above some minimum positive thresh- pressure signal 103 will decrease below the old, the amount of fuel provided by the fuel idle speed pressure reference level PIDLE.

control 80 will be reduced due to the direct Graph d in Fig. 3 illustrates a signal 104 connection of the terminal 99 to the terminal representative of the engine torque polarity 81. This results in a fuel reduction multiplica- 85 signal TWOL. Prior to the time tl, this signal tion factor caused by engine deceleration indi- is negative indicating that a higher manifold cated by a positive magnitude of the signal pressure exists than at no load idle speed TWOL. It should be noted that the transfer condition and this is indicative of the engine characteristics illustrated in graphs e and f of utilizing fuel to overcome its own inertia. At Fig. 2 are characteristic of a particular engine 90 the time tl, the torque polarity signal 104 and would have to be recalculated for differ- starts to increase and will change polarity at ent engines, but that in general the increase of the time t, and maintain a positive polarity air to the engine fuel mixture and the decrease until approximately the time t, Between the of fuel to the engine fuel mixture is desired times h and tO the signal 104 is positive for sufficiently large magnitudes of negative 95 which is indicative of negative torque polarity torque polarity which are indicated by a sub- meaning that the engine momentum, rather stantial positive magnitude of the signal than engine fuel, is causing engine operation.

TWOL. Graph e in Fig. 3 illustrates a signal 105 The operation of the engine control system representative of the engine speed error signal 10 will now be explained in conjunction with 100 e at the terminal 26. Prior to the time t, a the signal waveforms illustrated in Fig. 3 substantial positive difference exists between wherein the vertical axis of each of these wa- engine speed and calculated engine idle speed.

veforms is representative of magnitude and At the time tl, the signal e starts to decrease, the horizontal axis is representative of time and will eventually decrease below the refer- with the time axes being illustrated on an 105 ence level V, corresponding to the reference identical scale for all of the waveforms in Fig. voltage applied to the digital comparator 50.

3. Subsequently, the magnitude of the signal e In graph a in Fig. 3, a signal 101 represen- will oscillate around 0 magnitude and be tative of the throttle position signal THR is within the guard band represented by the illustrated. Prior to a time t, the throttle posi- 110 levelsV3 and V, At this time, the gate 82 tion is at a first level THR1. At the time t, will be opened such that the integrator 84 will the accelerator pedal is fully released resulting sample the manifold pressure and in response in a decrease in throttle position until at a thereto provide an updated average idle speed time t2 a final closed throttle position indicated manifold pressure signal PIDLE at the terminal by the level THR2 is arrived at. It should be 115 85.

noted that this level THR2 is less than the Preferably the present invention will be im reference leveIV2which means that the digital plemented by microprocessor control of an comparator 62 will now produce a low logic engine. However, this will substantially corre level at the terminal 63 whereas previously a spond to the operation of the engine control high logic level had been produced. The effect 120 system 10 shown in Fig. 1. Flowcharts are of this is to permit the AND gate 52 to enaillustrated in Fig. 4 which describe the pre ble the idle speed control means 27 after the ferred microprocessor implementation of the time t2 if other conditions have been met. present invention and also correlate to the op Graph b in Fig. 3 illustrates a signal 102 eration of the hardware embodiment shown in representative of the signal RPM indicative of 125 Fig. 1. The flowcharts in Fig. 4 will now be engine speed. Prior to the time tl, engine discussed in detail.

speed is at a level RPM 1. At the time t, A main flowchart program 200 (Fig. 4b) is slightly after the time t, engine speed will effectively executed periodically. This start to decrease until substantially at a subse- flowchart is entered at an initial point 201 and quent time t, engine speed will be approxi- 130 is designated the main fuel control program.

7 GB2189058A 7 From 201 control passes to a process block to a terminal 314 and then on to a process 202 which calculates fuel as a function of block 315 which effectively calculates the er manifold air pressure. This is implemented by ror signal e as the difference between actual the fuel control apparatus 80 in Fig. 1. Then engine speed and the desired calculated idle control passes to a process block 203 which 70 speed. If the idle loop flag has not been set implements the multiplication of the calculated as determined by the decision block 313, con fuel by any deceleration factors. This repre- troi passes to a decision block 316 which sents in effectively multiplying the fuel which determines if engine speed is equal to or less was calculated as a function of manifold presthan the desired idle speed. If not, control sure by any deceleration factors provided at 75 returns to the terminal 304. If engine speed is the terminals 98 and 99 in Fig. 1. Control less than the desired idle speed, then the idle then passes to an implement fuel control pro- speed loop flag is set by a process block 317 cess block which represents the actual supply- and control passes to the terminal 314 for ing of fuel to the engine by the fuel control calculation of the signal e. The blocks 316 apparatus 80. This is readily implemented by 80 and 317 represent the setting of the flip-flop having the degree of opening of a fuel valve 55 and then the resultant enabling of idle controlled by the magnitude of a calculated speed control by the AND gate 52.

analog or digital signal. Control then passes to From the process block 315, control passes a return step 205 indicative of the multiple to a decision block 318 which determines if periodic execution of the flowchart 200. 85 the error signal e is between the guard band During the periodic execution of the V3 and V, If it is, then the speed adjustment flowchart 200, a flowchart 300 in Fig. 4a may for manifold pressure is calculated by a pro also be periodically executed or enterred as cess block 319, and the adjusted MAP signal part of an interrupt subroutine. This flowchart ADJIVIAP is integrated (by the integrator 84) is entered at an initial point 301 and then the 90 to get a new average idle speed manifold desired idle speed is calculated by a process pressure by a process block 320. Control then block 302. Control then passes to a decision passes to a summing terminal 321. If the sig block 303 which decides if actual sensed en- nal e is not between the guard band V, and gine speed is above the calculated desired en- V, control passes from the decision block 18 gine idle speed plus 300 RPM. The 300 RPM 95 directly to the terminal 321. From the terminal represents a reference level corresponding to 321 control passes to a series of process the voltage V, If this is the case, then idle blocs 322, 323, 324, 325 and 326, and speed control will not be implemented and then to the summing terminal 310. The pro control passes to a summing terminal 304. cess blocks 322 through 326 essentially calFrom this terminal control then passes to a 100 culate the proportional error control signal at process block 305 wherein the speed adjust- the terminal 31, enable the error signal inte ment factor provided by the look up table 73 grator 33 by closing the gates 32 and 35, is calculated. Control then continues to a pro- calculate the integral error control signal at the cess block 306 where the signal TQPOL is terminal 38, sum the proportional and integral calculated by comparing the idle speed pres105 signals to provide the composite idle speed sure signal at the terminal 85 with the speed control signal at the terminal 40, and imple adjusted pressure signal at the terminal 75. ment idle speed control by providing a control Control then passes to process blocks 307 signal through the gate 41 to the air bypass and 308 wherein the deceleration factors pro- apparatus 28.

vided by the look up tables 97 and 96 are 110 While specific embodiments of the present calculated. Control then passes to a process invention have been shown and described, fur block 309 which implements these decelerather modifications and improvements will oc tion factors by virtue of the fuel control appa- cur to those skilled in the art.

ratus 80 and the air bypass apparatus 28.

Claims (7)

1. -50 Then control passes to a final summing termi- 115 CLAIMS nal 3 10 and

   from there execution of the 1. An engine control system including en flowchart 300 may be periodically repeated as gine idle speed control apparatus, comprising:

   indicated by a recycle step 311. means for providing an error signal related If the decision block 303 determines that to the difference between actual sensed en- engine speed is below the calculated idle 120 gine speed and a desired engine idle speed; speed plus 300 RPM, then control passes to means coupled to said error signal providing a decision block 312 which determines if means for implementing, when enabled, a throttle position is closed, and if not control closed loop engine idle speed control in accor will pass to the terminal 304. 1f the throttle dance with a control signal related to at least position is closed, control passes to a de- 125 the magnitude of said error signal; and cision block 313 which determines if the idle means coupled to said engine idle speed closed loop flag (IDLF) has been set. This cor- control means for selectively enabling said responds to determining whether a positive or closed loop idle speed control means in re 0 logic state is present at the terminal 56. If sponse to at least the magnitude of said ac the idle loop flag has been set, control passes 130 tual speed being within a predetermined speed 8 GB2189058A 8 range, wherein said closed loop idle speed control means includes means for positioning air-fuel mixture control apparatus in accordance with said control signal, and means for storing, until said closed loop idle speed control means is enabled, the magnitude of a signal related to the position of said control apparatus at a magnitude related to the magnitude which existed when said closed loop idle speed control means was last enabled, and utilizing said stored magnitude to implement initial closed loop control of said air-fuel mixture control apparatus by initially determining said control signal when said idle speed control means is enabled, characterized by said enabling means enabling said closed loop idle control means in response to at least the magnitude of said actual speed being substantially equal to said desired engine idle speed, and disabling said closed loop control means whenever said actual speed is above a predetermined speed which is greater than said desired speed.
2. 2. An engine control system according to claim 1 wherein said enabling means includes means for enabling said closed loop engine idle speed control means in reponse to a throttle position sensor signal having a magnitude indicative of a closed throttle position, in addition to said actual speed being substantially equal to said desired idle speed.
3. 3. An engine control system according to claim 2 wherein said enabling means includes means for disabling said closed loop engine speed control means in response to any one of said error signal being outside of a predetermined range about zero magnitude and said throttle position signal indicating other than a closed throttle position.
4. 4. An engine control system according to claim 1 wherein said enabling and disabling means includes a flip-flop means providing an output signal controlling the enabling and disabling of said closed loop control means.
5. 5. An engine control system according to claim 4 wherein said flip-flop means includes a reset terminal coupled to an output of a comparator which receives, as one input, said error signal and which receives, as another in- put, a reference potential.
6. 6. An engine control system according to claim 5 wherein said flip-flop means has a clock terminal coupled to an output terminal of a comparator which receives, as its inputs, a signal related to said actual engine speed and a signal related to said desired engine speed, and wherein said comparator provides a digital output signal to said flip-flop clock terminal.
7. 7. An engine control system substantially as hereinbefore described with reference to the accompanying drawings.

   Printed in the United Kingdom for Her Majesty's Stationery Office, Dd 8991685, 1987, 4235. Published at The Patent Office, 25 Southampton Buildings, London, WC2A lAY, from which copies may be obtained.