Method for control of idle rotations of internal combustion engines

Abstract: An addition correction term (lat) is added to a feedback control term (lfb) when an internal combustion engine is idling, a control valve (30) is under feedback control, and an auto­ matic transmission is in drive range (D range). The addition correction term (lat) is calculated by multiply­ ing a predetermined constant value (lato) by at least one of the correction coefficients which are decided based on RPM and temperature of the engine and vehicle speed. A learnt value (Pbref) is calculated based on an intake manifold (33) pressure when an internal combustion engine is in idling condition, the control valve (30) is under feedback control, and an automatic transmission is in disengagement condition, for example, neu­ tral range (N range). When the automatic transmission is turned into D range, an existing manifold pressure is detected and the addition correction term (lat) is calculated based on an difference between the learnt value and the detected manifold pressure.

Description: BACKGROUND OF THE INVENTION The present invention relates to a method for the control of the idling rotational speed of an internal combustion engine provided with a control valve adapted to control the amount of inlet air to said internal combustion engine during an idling operation thereof by allowing the degree of opening of said control valve to be controlled proportionately to the value of a control valve command (Icmd) obtained on the basis of the sum of a feedback control term (Ifb) and an addition correction term (lat) conforming to the load of an automatic transmission. Such a method is known from JP-A-6 073 026. Further prior proposals of interest are shown by EP-A-121066 and US-A-4 418 665. According to the last mentioned document a vehicle speed sensor at an output member of an automatic transmission is used. It has been customary to control the speed of idling rotations of an internal combustion engine through control of the amount of inlet air to the internal combustion engine by means of a control valve disposed in a bypass interconnecting the upstream and downstream sides of a throttle valve during a so-called idle operation or low-load operation, in which a throttle valve in an intake passage is kept in a substantially completely closed state. In an automobile provided with an automatic transmission of fluid coupling, the load of the automatic transmission is exerted on the internal combustion engine while the automatic transmission is in its in-gear state, i.e. while the position of the selector is in its drive (D) range. It has been customary, therefore, to prevent the speed of idling rotations from dropping while the automatic transmission is in the drive (D) range by adjusting the control valve in the direction of opening thereby increasing the amount of inlet air and enabling the mixture supplied into the engine to be increased. It is generally known that in an internal combustion engine of the electronically controlled fuel injection type, an increase in the amount of inlet air results in a proportional increase in the amount of fuel to be injected and, consequently, in an increase in the amount of mixture. The degree of opening of the control valve is controlled in a closed loop during an idling operation, i.e. while the throttle valve is substantially completely closed and the speed of engine rotations is in a prescribed range of idling rotations. An exciting current supplied to a solenoid proportionately controlling an opening angle of the control valve is fixed on the basis of a solenoid current command Icmd which is obtained in accordance with the following formula (1): lcmd = lfb(n) + lat wherein lfb(n) denotes a PID feedback control term (basic control term) for effecting proportional (P term), integral control term), and derivative(D term) actions based on a deviation of an actual number of engine rotations Ne from the target number of idling rotations Nrefo and lat denotes a correction term which is constant lato and applicable while the automatic transmission is in D range. As known well, the automatic transmission is provided with a pump impeller of a torque converter connected directly to the engine and a turbine runner connected directly to the output shaft and the slip rate of the automatic transmission is fixed by the ratio of the rotational speed of the impeller and runner. In other words, the ratio between the speed of engine rotations and the speed of the automobile determines the slip rate. During an idling operation, the slip rate reaches its maximum value when the automatic transmission is in the D range and the automobile is kept in a stop by putting on the brakes. When the automobile is travelling as in a creep state or in the state of engine brake, the slip rate is lower than when it is kept stopped by putting on the brakes. As the results, the external load of an engine generated by the automatic transmission (hereinafter referred to as "AT load") is lowered, too. The addition correction term lat of the formula (1) mentioned above is generally fixed at a prescribed value lato such as to permit correction of the AT load enough to prevent a decrease in the speed of idling rotations when the engine is kept in an idle operation after the warming of an engine has been completed and the speed of the automobile is still 0. When the AT load is small as described above, or the automobile is travelling in the creep state or in the state of engine brake, the magnitude of the addition correction term lat turns out to be too large for the actual magnitude of AT load. This trend becomes conspicuous particularly when the speed of engine rotations approaches the lower limit of the prescribed range of speed of idling rotations. As the result, the magnitude of the feedback control term Ifb(n) for adjustment to the target number of idling rotations, Nrefo, is decreased. Where the magnitude of the feedback control term lfb(n) is set at a small level as described above, a sudden application of brakes during the travel of the automobile in the creep state or in the state of engine deceleration results in a sharp increase in the AT load. There ensues a disadvantage that the decrease in the speed of engine rotations due to the increase in the AT load can no longer be corrected by the feedback control term lfb(n) and the number of engine rotations is greatly decreased or the engine is brought into a stall state. The magnitude of the feedback control term Ifb(n) is also decreased when the state of engine brake is started while the automobile is travelling on a descending slope to lower the speed of the automobile from the state of high-speed operation until the number of engine rotations falls within the range of numbers of idling rotations and the operation of the control valve is shifted to the feedback control mode. When the brakes are suddenly applied in this case as in the case mentioned above, the number of engine rotations is greatly decreased or the engine is brought to the state of stall. The PID coefficient (proportional, integral, and derivative control action gain) in the feedback control term Ifb(n) in the formula (1) is generally set at a small level. As the result, the feedback control by this term lfb(n) is generally carried out slowly. This is because the stability of the stationary idle operation is impaired when the control gain is increased to increase the magnitude of feedback control. SUMMARY OF THE INVENTION An object of this invention is to provide a method for controlling the speed of idling rotations of an internal combustion engine without heavily dropping the speed of engine rotations or inducing the state of engine stall even when the magnitude of AT load is suddenly changed (particularly suddenly increased). According to the invention, the method initially defined is characterised by said automatic transmission including a torque converter, and by obtaining said addition correction term (lat) as a continuously variable function of a parameter representing the operating state of said torque converter, wherein said parameter is the vehicle speed (V) which is a function of the rotational speed of an output member of said torque converter. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a flow chart for explaining the operation of an embodiment of the present invention. Fig. 2 is a schematic structural diagram of an apparatus for the control of number of idling rotations of an internal combustion engine, in accordance with the embodiment of this invention. Fig. 3 is a block diagram illustrating a typical detailed structure of the electronic control apparatus of Fig.2. Fig. 4 is a graph showing a typical relation between the number of engine rotations Ne and the first correction coefficient Kneat. Fig. 5 is a graph showing a typical relation between the vehicle speed V and the second correction coefficient Lat. Fig. 6 is a graph showing a typical relation between the engine temperature Tw and the third correction coefficient Ktwat. Fig. 7 is a flow chart showing the contents of the arithmetic operation in Step S1 of Fig. 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Now, the present invention will be described in detail with reference to the accompanying drawings. Fig. 2 is a schematic structural diagram of an apparatus for the control of the idling rotational speed of an internal combustion engine, in accordance with the first embodiment of this invention. With reference to the diagram, the amount of inlet air in an intake manifold 33 during an idle operation having a throttle valve 32 in a substantially completely closed state is controlled by a control valve 30 disposed in a bypass passage 31 interconnecting the upstream and downstream sides of the throttle valve 32. The degree of opening of this control valve 30 depends on the magnitude of an electric current flowing through a solenoid 16. The amount of the fuel injected through an injection nozzle 34 is fixed by the conventional means in accordance with the amount of inlet air in the intake manifold 33. A piston 38 inside a cylinder 35 repeats a reciprocating motion to rotate a crank shaft 36. A TDC sensor 5 generates a pulse each time the piston in each cylinder reaches 90 degrees before the top dead center. In other words, the TDC censor 5 issues the same number of pulses (hereinafter referred to as "TDC pulses") as the number of cylinders each time the crank shaft 36 makes two rotations and feeds them to an electronic control unit 40. An engine rotation (RPM) counter 2 senses the number of engine rotations by clocking the intervals in the TDC pulses fed out by the TDC sensor 5, issues a corresponding RPM digital signal, and feeds it to the electronic control unit 40. An engine temperature sensor 4 detects the temperature of engine cooling water, issues a corresponding engine temperature signal in the form of a digital signal, and feeds it to the electronic control unit 40. An AT position indicator 7 feeds to the electronic control unit 40 a D range detection signal when the selector position of the automatic transmission is in the drive range or an N range detection signal when the selector position is in the neutral range. A speed sensor 9 detects a vehicle speed and feeds a corresponding digital speed signal to the electronic control unit 40. The electronic control unit 40 controls the electric current flowing through the solenoid 16 in the manner to be described afterward. Fig. 3 is a block diagram illustrating a typical detailed structure of the electronic control unit 40 of Fig. 2. The electronic control unit 40 comprises a micro-computer 53 composed of a central processing unit (CPU) 50, a memory 51, and an interface 52 and a control valve driving circuit 54 for controlling the electric current flowing through the solenoid 16 in compliance with a command (value of solenoid current command Icmd) from the micro-computer 53. The control valve driving circuit 54 issues a control signal for controlling the electric current flowing through the solenoid 16 in accordance with the command Icmd. As the result, the degree of opening of the control valve 30 (Fig. 2) is controlled in accordance with the command Icmd and, consequently, the speed of idling rotations is controlled in accordance with the command Icmd. Fig. 1 is a flow chart for explaining the operation of one preferred embodiment of this invention. The operation illustrated by this flow chart is started by the interruption of a TDC pulse. The processing (which directly bears on the present embodiment) will be described hereinbelow solely on the assumption that the throttle valve is in a substantially completely closed state, the speed of rotations is in the prescribed range of speed of idling rotations, and the engine is operating in the feedback control mode. Step S1 --- This step calculates the value of lfb(n) based on the arithmetic operation in the feedback control as explained afterward with respect to Fig. 7. Step S2 --- This step determines whether the automatic transmission is in the D range or in the N range, in accordance with the output of the AT position indicator 7. The processing proceeds to Step S4 when the D range is indicated or to Step S3 when the N range is indicated. Step S3 --- This step sets the addition correction term lat in the formula (1) at 0. Then, the processing proceeds to Step S8. Step S4 -- This step detects the current rotational speed Ne from the input signal to the RPM counter 2 and, based on the RPM, Ne, looks up the Ne ∼ Kneat table stored in advance in the memory 51. As the result, the first correction coefficient Kneat is fixed. Fig. 4 is a graph showing the relation between the number of rotations Ne and the first correction coefficient Kneat. As noted from Fig. 4, this coefficient Kneat is "1.0" when the number of rotations equals the target number of idling rotations Nrefo proportionately decreases as the speed of rotations decreases from the number Nrefo, and proportionately increases as the number of rotations increases from the number Nrefo. The coefficient Kneat is an empirical value of correction for the constant value lato required in preventing the value of the feedback control term lfb(n) from being varied even when the speed of idling rotations is raised or lowered with reference to the value of the feedback control term lfb(n) existing when the engine is in a braked state, namely the vehicle speed is 0, the engine warming has been completed and the hydraulic oil of the automatic transmission has reached a stabilized state, and the speed of rotations equals the target number of idling rotations Nrefo. Step S5 --- This step detects the existing vehicle speed, V, from the input signal to the speed sensor 9 and, based on the vehicle speed V, looks up the V ∼ Lat table stored in advance in the memory 51. As the result, the second correction coefficient Lat is fixed. Fig. 5 is a graph showing the relation between the vehicle speed V and the second correction coefficient Lat. This coefficient Lat as noted from Fig. 5, is "10" when the vehicle speed is 0 and approaches "0" in proportion as the vehicle speed rises. The coefficient Lat is an empirical value of correction for the constant value lato required in preventing the value of the feedback control term lfb(n) from being varied even when the vehicle speed V is raised with reference to the value of the feedback control term, lfb(n) existing when the number of rotations equals the target number of idling rotations, the engine warming has been completed and the hydraulic oil of the automatic transmission has reached a stabilized state, and the vehicle speed is 0. Step S6 --- This step detects the existing temperature Tw from the output signal of the temperature sensor 4 and, based on the temperature Tw, looks up the Tw ∼ Ktwat table stored In advance in the memory 51. As the result, the third correction coefficient Ktwat is fixed. Fig. 6 is a graph showing the relation between the temperature Tw and the third correction coefficient Ktwat. This coefficient Ktwat, as noted from Fig. 6, is "1.0" when the temperature exceeds the temperature Tw1 after completion of the engine warming and increases in proportion as the temperature falls below the temperature Tw1. This coefficient Ktwat is an empirical value of correction for the constant value lato required in preventing the value of the feedback control term lfb(n) from being varied even when the temperature Tw is lowered from the temperature Tw1 after completion of the engine warming with reference to the value of the feedback control term lfb(n) existing when the vehicle speed is 0, the number of rotations is set at the target number of idling rotations, the engine warming has been completed, and the hydraulic oil of the automatic transmission has reached a stabilized state. Step S7 --- This step calculates the addition correction coefficient lat of the formula (1), based on the following formula (2). lat = lato x Kneat x Lat x Ktwat It is noted from the formula (2), the present embodiment corrects the constant correction term lato existing so far when the automatic transmission is in the D range by multiplying this term by the coefficients Kneat, Lat and Ktwat, and adopts the product of the formula (2) as a new correction term lat. The value of lato is a constant stored in advance in the memory 51. The processing has been described as effecting the correction with the multiplication of the constant value lato by all the correction coefficients Kneat, Lat, and Ktwat. This invention does not require the correction to be made invariably in this manner. For example, by multiplying the constant value lato by one or two of the three correction coefficients Kneat, Lat, and Ktwat, the value of lat can be approximated to an adequate value conforming to the actual AT load. Step S8 --- This step adds the value of lat set in Step S3 or Step S7 to the value of lfb(n) calculated in Step S1 and issues the sum as a solenoid current command Icmd to the control valve driving circuit 54. Then, the processing returns to the main program. As the result, the control valve 30 (Fig. 2) has the degree of its opening controlled by the control valve driving circuit 54 and the solenoid 16 in accordance with the command Icmd. Fig. 7 is a flow chart showing the detail of the arithmetic operation performed in Step S1 of Fig. 1. Step S41 --- This step reads in the reciprocal (period) of the number of rotations detected by the RPM counter 2 or an equivalent value, Me(n) (wherein n denotes the current speed of detection). Step S42 --- This step calculates the deviation ΔMef of the value Me(n) read in as described above from the reciprocal or period of the target number Nrefo of idling rotations or an equivalent value Mrefo set in advance. Step S43 --- This step calculates the difference between the value Me(n) mentioned above and the value Me measured in the previous cycle in the same cylinder as the value Me(n) was detected [Me(n-6) where the engine is a 6-cylinder engine], i.e. the rate of change ΔMe of the period. Step S44 --- This step calculates the integration term li, the proportional term lp, and the derivative term Id by using the values ΔMe and ΔMef mentioned above, and the integration term control gain Kim, the proportional term control gain Kpm, and the derivative term gain Kdm, in accordance with the formulas of arithmetic operation shown in the diagrams. The various control gains mentioned above have been stored in the memory 51 in advance. Step S45 --- This step effects the calculation of the value lai(n) by adding the integral term Ii obtained in Step S44 to the value lai (value in the previous cycle: n-1). To be used as the value lai(n-1) in the next cycle, the value lai(n) obtained in this step is put to temporary storage in the memory 51. When the memory 51 has not stored any data as lai, it suffices to have a numerical value resembling lai stored in advance in the memory and have this numerical value read out as lai(n-1). Step S46 --- This step defines the value of lfb-(n) by adding the values of lp and Id calculated in Step S44 to the value of lai(n) calculated in Step S45. As is clear from the foregoing description, the present embodiment, when the internal combustion engine is in the process of an idle operation under feedback control and the automatic transmission is in the D range, determines the correction coefficients based on the vehicle speed, the rotational speed of the engine, and the engine temperature and then fixes the addition correction term tat in the formula (1), by multiplying the prescribed value lato required to be added when the automatic transmission is in the D range, by at least one of the correction coefficients mentioned above. As the result, the addition correction term lat is made an adequate value and the value of the feedback control term lfb(n) of the formula (1) is stabilized and is relieved of the possibility of decreasing to an excessive extent. (Effect of the Invention) As is clear from the description above, a particularly important embodiment of this invention brings about the following effects. (1)The feedback control term lfb(n) which defines the value Icmd of the solenoid current command is not allowed to assume an excessively small value even when the internal combustion engine in process of idle operation under feedback control is placed in a loaded state. When the load is suddenly increased, therefore, this increase in the load can be corrected by the term lfb(n). As the result, the possibility of the number of rotations being decreased to a great extent or the possibi!ity of the engine being brought into the state of stall can be prevented. (2) The feedback control term lfb(n) which defines the value Icmd of the solenoid current command is stabilized and is not allowed to assume a excessively small value even when the internal combustion engine is in process of idle operation under feedback control and the automatic transmission is in the D range, when the AT load is suddenly increased, the increase in the load can be corrected by the term lfb(n). As the result, the possibility of the number of rotations being decreased to a great extent or the possibility of the engine assuming the state of stall is precluded.

Claims: A method for the control of the idling rotational speed of an internal combustion engine provided with a control valve (30) adapted to control the amount of inlet air to said internal combustion engine during an idling operation thereof by allowing the degree of opening of said control valve (30) to be controlled proportionately to the value of a control valve command (Icmd) obtained on the basis of the sum of a feedback control term (lfb) and an addition correction term (lat) conforming to the load of an automatic transmission, characterized by said automatic transmission including a torque converter, and by obtaining said addition correction term (lat) as a continuously variable function of a parameter representing the operating state of said torque converter wherein said parameter is the vehicle speed (V) which is a function of the rotational speed of an output member of said torque converter. A method according to Claim 1, wherein said addition correction term (lat) is obtained by correcting a prescribed constant number (lato)-based on a first correction coefficient (Kneat) corresponding to the engine rotational speed (Ne). A method according to claim 2, wherein said addition correction term (lat) is obtained by correcting the prescribed constant number (lato) based on a second correction coefficient (Lat) corresponding to the vehicle speed (V). A method according to claim 2 or 3, wherein said addition correction term (lat) is obtained by correcting the prescribed constant number (lato) based on the product of the second correction coefficient (Lat) and a first correction coefficient (Kneat) corresponding to the engine rotational speed. A method according to Claim 1, wherein said addition correction term (lat) is obtained by correcting a prescribed constant number (lato) based on a third correction coefficient (Ktwat) corresponding to the engine temperature. A method according to Claim 5, wherein said addition correction term (lat) is obtained by correcting the prescribed constant number (lato) based on the product of said third correction coefficient (Ktwat), a first correction coefficient (Kneat) corresponding to the engine rotational speed and a second correction coefficient (Lat) corresponding to the vehicle speed.

Inventors: IWATA TAKAHIRO, KIUCHI TAKEO, YASUOKA AKIMASA, IWATA, TAKAHIRO, KIUCHI, TAKEO, YASUOKA, AKIMASA
Applicants: HONDA MOTOR CO LTD, HONDA GIKEN KOGYO KABUSHIKI KAISHA
Application year: 1986
Main classification: F02D41
IPC codes: F02D31, F02D41