EP1086306A1

EP1086306A1 - Method and device for regulating the operation of an internal combustion engine during a return to idling speed

Info

Publication number: EP1086306A1
Application number: EP99923719A
Authority: EP
Inventors: Vincent Rauch; Luis Rodrigues; Jean-Marie André TAUPIN; Edouard Franck Robert Valenciennes
Original assignee: Renault SAS
Current assignee: Renault SAS
Priority date: 1998-06-11
Filing date: 1999-06-11
Publication date: 2001-03-28
Also published as: FR2779768A1; FR2779768B1; WO1999064738A1

Abstract

According to the invention, a current torque set-point (Ccons) is determined from a set-point variable (Ncons) for said speed and from an estimate of the resistant torque (Cres) applied to the engine in order to regulate engine speed during a return to an idling speed and the idling speed that follows. The torque provided by the engine is regulated according to said variable (Ccons). The latter is determined by choosing a value therefor that causes the variable quantity ε = (N?2 - z-1N2¿) + ffrr. (N2 -N¿cons?2) to converge towards zero, where N and z-1are measured values of the engine speed, respectively at a current sampling moment and at a previous sampling moment, ffrr being a positive coefficient limited by an estimated resistant torque function threshold (C¿res?), of the current speed (N) and the set-point speed (Ncons).

Description

METHOD AND DEVICE FOR REGULATING THE OPERATION OF AN INTERNAL COMBUSTION ENGINE ON RETURN TO IDLE RPM.

The present invention relates to a method and a device for regulating the operation of a torque-controlled internal combustion engine, when this engine returns to idle speed. More particularly, the invention relates to such a method and to a device associated with an internal combustion engine propelling a motor vehicle.

As shown diagrammatically in FIG. 1 of the attached drawing, in such a vehicle 1, the operation of the engine 2 is commonly managed by a digital electronic computer 3 which receives signals from various groups of sensors 4,5 sensitive to parameters affecting the operation engine (intake pressure, engine speed, cooling water temperature, activation of an air conditioner or assistance for steering the vehicle, etc.). The computer 1 is duly programmed to develop, from signals supplied by the groups of sensors 4.5, control signals from the various actuators 6 acting on the engine, fuel miectors, spark plugs of the air / fuel mixture, etc. ..., so that the engine delivers a torque corresponding to that requested by the driver.

A position sensor of an accelerator pedal of the vehicle (not shown) delivers to the computer 3 a signal representative of this torque request. Computers are known which are also equipped with a torque regulator. Such a torque regulator makes it possible, for example, to take into account the rise of a slope by the vehicle, the activation of torque consumers such as a power steering or an air conditioner, etc. In the context of such regulation, the computer can commonly act, in addition to the opening time of the fuel collectors and the angle of advance at ignition of the air / fuel mixture, on the opening angle of the throttle valve, this throttle valve is then "motorized", and on other possible additional means making it possible to act on the quantity of air entering the engine, in particular in idle speed. When the driver lifts his foot from the accelerator pedal, a so-called "raised foot position" sensor informs the computer 3 of this situation. A strategy for returning the engine to idling speed is then executed by the computer. This strategy essentially comprises two phases, a phase of return to idling during which the rotation speed N of the engine drops from the value reached at the time of foot lift to an idle setpoint value N _cons , then a phase regulating the speed of this engine around this value N _cons , despite variations in engine load or temperature for example, or random disturbances affecting the operation of this engine (misfires, for example).

We know from patent FR-A-2 716 417 (Robert Bosch) a process for regulating the idle speed which involves the calculation of a torque setpoint. The method described does, however, only regulate the idle speed. He does not take control of the return to this regime, which then requires a different ordering process. We know from US-A-5 630 394 (Ford Motor Company) a process which successively manages the return to idle speed and then the regulation of this speed. The method described is however incompatible with the presence, in the computer 3, of a torque regulator. In addition, the management of the transition between the return phase to idle speed and the regulation phase of this speed around a setpoint must be very precise to avoid stalling the engine. This constraint increases the complexity of the process and therefore increases its development. Patent EP 0 694 121 (Siemens Automotive SA) describes a method for controlling an internal combustion engine when entering idle speed, the engine being associated with means for controlling its speed to a value of predetermined setpoint. Upon detection of an operating state of the engine calling for entry into idle speed, a decrease in the engine set point speed is controlled according to a predetermined time law, covering both the phase of return to idle speed and the speed idle proper.

In addition to the fact that the process described is suitable for a servo-controlled motor in speed and not in torque, it should be noted that the law of decrease is fixed and does not take account of possible variations in the load of the motor or other operating conditions of this engine, which directly influence the natural dynamics of declining speed. On the one hand, this can cause inconvenience in driving the vehicle. On the other hand, when the regulation of regime includes an integral term, as it is for example the case of a regulation PI, PID or LQI, it also results from it the important risk that this term is charged during the decrease of the regime then discharges by inducing an under-speed when the idle setpoint is stabilized. The object of the present invention is to provide a method for regulating the operation of an internal combustion engine, when returning to idle speed, which does not have any of the drawbacks of the methods described above and which is well suited to a torque-controlled motor.

The present invention also aims to provide such a method which ensures the phase of return to idle speed and the regulation phase of this speed without it being necessary to distinguish these two phases during engine operation. Another object of the present invention is to provide a device for implementing this method.

These objects of the invention are achieved, as well as others which will appear on reading the description which follows, with a method of regulating the operation of an internal combustion engine controlled in torque, during a return to idle speed, this process comprising the following steps: a) it is determined whether a state calling for a return to the idle speed is present, b) if so, a current torque setpoint is determined from a setpoint value for said idle speed and an estimate of the resistive torque applied to the engine, so as to continuously regulate the engine speed when returning to idle speed and during the subsequent idle speed, and c) the torque delivered by the motor from said current torque setpoint.

According to a preferred implementation of the method according to the invention, the current torque setpoint is determined by choosing for it a value which causes the variable quantity ε defined by the expression to converge to zero:

ε = (N ² - z ^~ V) + ffrr- (N ² -N _cons ² ) where:

- N and z ^~ N are the values of the engine speed measured, respectively, at the current sampling instant and the previous sampling instant, - ffrr is a positive coefficient bounded by a threshold function of the estimated resistive torque C _res , of the current speed N and of the reference speed N _cons .

As will be seen later in detail, the regulation of the engine through the quantity ε makes it possible to merge the return to idling and the regulation of idling with all the flexibility required, this regulation being perfectly suited to a torque-controlled motor.

For the implementation of this method, the invention provides a device comprising a) means for detecting the appearance of a state calling for a return to idle speed, b) means for then determining a set value for this regime, c) means for estimating the resistive torque then applied to the engine, d) means for calculating a current reference value for the torque which the engine must deliver, from said current regime reference value of idling and of said resistive torque, to continuously bring the engine speed to said setpoint and regulate it, and e) means for regulating the engine torque to said current setpoint.

Other characteristics and advantages of the present invention will appear on reading the description which follows and on examining the appended drawing in which:

- Figure 1 shows the architecture of the regulation device according to the invention, already partially described in the preamble to this description, and - Figure 2 is a flow diagram of a program for implementing the regulation method according to invention.

Referring to Figure 1 of the accompanying drawing where it appears that the computer 3 of the device according to the invention essentially comprises an estimator 7 of the resisting torque C _res applied to the engine 2, a speed regulator 8 characteristic of the present invention and comprising , as will be seen below, means for calculating a current setpoint value C _cons for the torque which the motor 2 must deliver, from a current setpoint N _cons of the idle speed and the resistive torque C _re3 estimated by the estimator 1, and a regulator 9 of the engine torque at the current setpoint C _COns / this latter regulator being known in itself, all like the estimator 7.

The measurement signals delivered by the groups of sensors 4 and 5 are selectively delivered to the torque estimator 7, to the speed regulator 8 and to the torque regulator 9 according to the known needs of the estimator 7 and of the regulator 9. As regards the regulator 8, the signals received will be specified below.

Among the sensors for operating parameters of the vehicle, there is conventionally a sensor for depressing the accelerator pedal (not shown) and a sensor sensitive to the arrival of said pedal in the "raised foot" position. It is this latter sensor which signals to the computer 3 that the vehicle is in a state calling for a return to idling speed. Other optional conditions can be posed to trigger such a return such as, for example, the passage of the speed of rotation of the motor below a threshold.

The torque estimator 7 is constituted by software stored in the computer 3. The software inputs are digital measurement values supplied by sensors of groups 4 and 5, allowing this software to calculate or evaluate the various resistant couples, the sum of which opposes the torque delivered by the engine 2. These resistant couples are essentially those consumed in the engine, in particular by friction, and by accessories of the energy-consuming vehicle such as an alternator, a air conditioner compressor, steering pump assisted, etc. The resistive torque C _res thus calculated is supplied to the speed regulator 8.

The speed regulator 8 comprises means for determining a reference speed value N _id s of idling, a function of one or more engine operating parameters such as, for example, the engine water temperature, the operating condition of the air conditioner, the operating status of the power steering, etc. This value is taken from a "map" of N _cons whose inputs are constituted by these parameters, said map being recorded in the memory of the calculator 3.

The speed regulator 8 also comprises software means designed to calculate, from the speed N of the engine, the idle speed setpoint N _cons and the resistive torque C _res supplied by the estimator 7, the value C _c o _ns of the current torque setpoint that the engine must supply to correct the variations in speed so that they cause the speed value N of the engine to converge to the idle setpoint N _cons .

These software means execute the calculation program illustrated in FIG. 2, to which we now refer.

The calculation program is executed cyclically as soon as an entry into idle speed is triggered by a signal from the "foot raised" position sensor of the accelerator pedal, and by any other optional signals, as shown. saw above.

In step 100, the speed regulator 8 receives the values of the operating parameters of the engine 2 supplied by the groups of sensors 4,5, in particular the speed value N of this engine, and the value of the resistive torque C _res calculated by the estimator 7. In step 110, the speed regulator 8 draws from a map the value of the idle speed setpoint N _cons , as seen above.

In step 120, according to a characteristic of the present invention, the regulator 8 calculates a coefficient ffrr chosen so as to respect the following relation:

ffdyn-C _rp „

0 <ffrr <- _{2 2} - ^£ ^ ^L (1)

N -N _cons

where ffdyn is a constant function of the characteristics of the engine. For an internal combustion engine with four

7200 times, for example, ffdyn = with n _cv ι = number of engine cylinders, J _{word /} engine inertia. We show that respect for double inequality

(1) above ensures that the value of the torque setpoint C _cons calculated by the regulator 8 according to the procedure explained below remains, as it should, positive. Respecting the double inequality (1) we can choose for ffrr, for example:

ffdyn-C _res ffrr = (2)

2N ²

or :

ffdyn-C _rp -, ffrr = —- ¹ ≈ ^ (3)

N (N + N _cons )

In step 130, according to another characteristic of the present invention, the regulator 8 calculates a variable quantity ε, from the squares of the regime N, of the measurement preceding this regime z N stored in memory of the previous calculation cycle, and of the value of the setpoint N _con3 of the idling speed, this variable ε taking the form: ε = (N ² - z ^~ V) + ffrr- (N ² -N _con3 ² ) (4 ) ε is the variable regulated by the speed regulator 8. To do this, the regulator calculates, in step 140, the value of the torque setpoint C _COn s to be transmitted to the torque regulator 9, which converges ε towards zero. In step 150, the current measured value of the speed N is stored, where it replaces the previous value z N. The torque setpoint C _con s is finally addressed, in step 160, to the torque regulator 9 which regulates engine 2 both when the engine is running in idle speed and in normal speed. This regulator can also, for this purpose, receive torque instructions from other devices, outside of the return to idle or subsequent idle speed. The calculation of the setpoint value C _cons gui causes ε to converge to zero can be performed using one of several regulation algorithms well known to those skilled in the art.

It will be noted that the variable ε comprises a first term (N 2 - z — 1N2) which gives rise to two successive samples z N and N of the speed, or speed, of the engine, this term being therefore sensitive to the current variation of this

2 speed. The second term of ε, ie ffrr (N - N _cons 2) is itself sensitive to the deviation from the current speed N to the reference speed N _cons .

Thus, when the engine speed is high, and therefore far from the idle speed N _cons , it is the first term which is predominant in ε because ffrr is small, whereas, when the speed is close to idle, it is the second term which predominates because ffrr is large. It is as well as the regulation of the motor through the variable ε allows regulation to be ensured both during the idling phase and during the idling phase proper, and this without discontinuity and therefore with flexibility and simplification of the development , in accordance with one of the aims of the present invention.

Claims

1. Method for regulating the operation of a torque-controlled internal combustion engine, during a return to idle speed, characterized in that: a) it is determined whether a state calling for a return to idle speed is present, b) in the affirmative, a current torque setpoint (C _cons ) is determined from a setpoint value (N _con3 ) for said idle speed and an estimate of the resistive torque (C _res ) applied to the engine , so as to continuously regulate the engine speed when returning to the idle speed and during the subsequent idle speed, and c) the torque delivered by the engine is regulated from said current torque setpoint.

2. Method according to claim 1, characterized in that the current torque setpoint (C _Co n _s ) is determined by choosing a value for the latter which converges the variable quantity (ε) defined by the to zero. expression: ε = (N ² - z ^" V) + ffrr- (N ² - N _cons ² ), where

- N and z ^" N are values of the engine speed measured, respectively, at the current sampling instant and the previous sampling instant,

- ffrr is a positive coefficient bounded by a threshold which is a function of the estimated resistive torque (C _res ) _r of the current regime (N) and of the reference regime (N _cons ).

3. Method according to claim 2, in which the coefficient (ffrr) is such that:

7200 where ffdyn =, n _cy ι and J _mot being respectively ^{π 'n} cyl ^{' J} mot the number of cylinders of the engine and the moment of inertia of its output shaft.

4. Method according to claim 3, in which the coefficient (ffrr) is such that:

ffdy -C _res ffrr = -

2W

5. Method according to claim 3, in which the coefficient (ffrr) is such that:

ffdyn-C _res ffrr =

N (N + N _cons )

6. Device for implementing the method according to claim 1, characterized in that it comprises: a) means for detecting the appearance of a state calling for a return to idling speed, b) means to then determine a setpoint value (N _cons ) for this regime, c) means for estimating the resistive torque (C _res ) then applied to the engine, d) means for calculating a current setpoint value (C _con s) for the torque which the engine must deliver, from said current idle speed reference value (N _cons ) and from said resistive torque (C _res ) _ι to continuously reduce the engine speed (N) to said value of setpoint (N _cons ) and regulate it, and e) means for regulating the engine torque at said current setpoint value (C _con s) •

7. Device according to claim 6, characterized in that said means for calculating and regulating the engine speed comprise a) means for calculation of the expression ε = (N - z N) + ffrr (N - N _cons ) where N and z N are the values of the engine speed measured, respectively, at a current sampling instant and at the instant d '' previous sampling, ffrr a positive coefficient bounded by a threshold function of the estimated resistive torque (C _res ), the current speed (N) of the motor and the set speed (N _cons ) determined, and) means for determining the current set point of torque (C _C ons) ^by choosing for this the value which makes converge (ε) towards zero.

8. Device according to any one of claims 6 and 7, characterized in that it is integrated into an engine operation management computer.

9. Motor vehicle powered by an internal combustion engine associated with a device according to any one of claims 6 to 8.