FR3077098A1 - METHOD FOR CONTROLLING A THERMAL MOTOR OF A MOTOR VEHICLE - Google Patents

Abstract

The invention relates mainly to a method for controlling a motor vehicle engine (1), characterized in that, to follow a speed profile (P_cy) defining a plurality of set speeds as a function of time, said method comprises the following steps: - a step of modeling a delay of execution of a torque (tr) linked to a capacity of the heat engine to provide a torque, - a step of calculating an acceleration (a) allowing to reach a target speed, said acceleration taking account of the torque execution delay (tr), a step of calculating a torque applied by driving wheels to obtain the previously calculated acceleration (a), a step of determining a corresponding motor torque (Cm), and - a step of activating a control member (P) of the vehicle to obtain the motor torque previously determined.

Description

* 54) METHOD OF DRIVING A HEAT ENGINE OF A MOTOR VEHICLE.

FR 3 077 098 - A1

@) The invention relates mainly to a method for controlling a heat engine of a motor vehicle (1), characterized in that, to follow a speed profile (P_cy) defining a plurality of set speeds as a function of time, said method comprises the following steps:

a step of modeling a delay in the execution of a torque (tr) linked to a capacity of the heat engine to supply a torque,

a step of calculating an acceleration (a) making it possible to reach a target speed, said acceleration taking into account the delay in execution of the torque (tr),

a step of calculating a torque applied by driving wheels to obtain the previously calculated acceleration (a),

a step of determining a corresponding engine torque (Cm), and

- A step of activating a control member (P) of the vehicle to obtain the previously determined engine torque.

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The present invention relates to a method for controlling a heat engine of a motor vehicle. The invention finds a particularly advantageous application in the management of the control of petrol and / or diesel type engines.

Recent changes in regulations on the emission of pollutants into the atmosphere have called into question the approval cycles of motor vehicles.

Thus, the predominantly urban homologation cycle to which is added an extraurban cycle (EUDC or Extra-Urban Driving Cycle in English) is replaced by the WLTC type approval cycle (or Worldwide harmonized Light vehicles Test Cycle in English or harmonized world test cycle for passenger cars and light commercial vehicles in French) which is 50% longer, going from 1200 seconds to 1800 seconds. Furthermore, the cycle monitoring tolerances are less restrictive, in order to ensure wider coverage around the certification cycle in terms of pollution control and to take into account different ways of driving more representative of a panel of drivers.

The time required to complete the WLTC type approval cycle requires the operator of the dynamometer to work much longer at his station without cutting off activity, which is likely to cause a loss of concentration. and therefore errors invalidating the test carried out. In addition, this phenomenon is problematic when we want to compare settings since it generates the resumption of tests.

The speed profile monitoring tolerances being at low constraint, it is necessary to develop tuning methods which make it possible to take into account all the ways of driving, and for this to develop new calibration methods. statistical. Under these conditions, there is a need to compare settings with good repeatability of the test and to be able to perform representative tests of the conductors to take into account the robustness of the settings.

The invention aims to meet these needs by providing a method of controlling a thermal engine of a motor vehicle, characterized in that, to follow a speed profile defining a plurality of set speeds as a function of time, said process includes the following steps:

a step of modeling a delay in the execution of a torque linked to a capacity of the heat engine to provide a torque,

- a step of calculating an acceleration making it possible to reach a target speed, said acceleration taking into account the delay in execution of the torque,

a step for calculating a torque applied by driving wheels to obtain the previously calculated acceleration,

a step of determining a corresponding engine torque, and

- A step of activating a vehicle control member to obtain the previously determined engine torque.

The invention thus allows the driver to be replaced by a model for controlling the heat engine. This model makes it possible to follow the certification cycle to be carried out while being flexible enough to simulate different types of drivers. In addition, taking into account the delay in executing the torque requested from the engine, the cycle monitoring model is very representative of reality.

According to one implementation, the delay in the execution of the torque corresponds to:

- an atmospheric phase corresponding to an operating phase of the engine at atmospheric pressure;

- a lag phase corresponding to the time necessary for a speed of a turbocharger to reach an effective operating range,

- a supercharged phase in which the turbocharger operates within its effective operating range.

According to one implementation, a temporal evolution of the couple during the atmospheric phase and the latency phase is modeled by a straight line and in that a temporal evolution of the couple during the supercharged phase is modeled by a polynomial .

According to one implementation, characteristic coefficients of the different phases are obtained by tests of the motor vehicle carried out on a dynamometer.

According to one implementation, the acceleration is calculated from a difference between a set speed at the end of an acceleration period and the actual speed at the end of the torque execution delay, divided by an acceleration time.

According to one implementation, said torque applied by the drive wheels is determined from a wheel radius, a force opposing a movement of said motor vehicle dependent on a speed of said motor vehicle, d 'a mass of said motor vehicle, and said acceleration of said motor vehicle.

According to one implementation, said engine torque is determined from a gearbox ratio and said torque applied by the drive wheels.

According to one implementation, said speed profile corresponds to an approval cycle to be followed.

According to one implementation, said speed profile is defined by a computer of said motor vehicle following a detection of a change of speed setpoint.

The invention also relates to an engine computer comprising a memory storing software instructions for the implementation of the method for controlling a heat engine as defined above.

The invention will be better understood on reading the description which follows and on examining the figures which accompany it. These figures are given only by way of illustration but in no way limit the invention.

Figure 1 is a schematic representation of a motor vehicle installed on an engine test bench for the implementation of the combustion engine control method according to the invention;

FIG. 2a is a graphical representation of the time as a function of the torque, at iso-regime, representing the three phases of the delay in the execution of the engine torque;

Figure 2b is a schematic representation of the logic modules on board the computer for determining the execution delay of the engine torque;

Figure 3 is a schematic representation of the logic modules on board the computer for the implementation of the combustion engine control method according to the invention.

Figure 1 is a schematic representation of a vehicle 1 installed on an engine test bench 2 in order to follow an approval cycle, for example of the WLTC type (or Worldwide harmonized Light vehicles Test Cycle in English). To this end, a computer 3 is able to control the depressing of the accelerator pedal 5 of the vehicle 1 via a corresponding actuator. The accelerator pedal 5 is depressed on the basis of inputs applied to the computer 3, namely in particular an instantaneous actual speed V (t), a gearbox ratio RB, and a speed profile P_cy corresponding to the homologation cycle of interest. This speed profile P_cy defines a plurality of setpoint speeds as a function of time.

The invention provides a control method for following as precisely as possible the speed profile P_cy. To this end, corresponding logic modules can be implemented in software in a data memory 4 of the computer 3 which can be the engine computer of the vehicle 1 or an independent computer, as shown in FIGS. 2b and 3.

More specifically, we model the delay in the execution of the torque tr requested from the engine. This delay tr is due to the inertia of the engine and the entire transmission. This delay tr is not constant but depends on several parameters defined below.

To determine this delay, so-called Torque Ascent Slopes (PMC) curves are determined on a roller bench. To this end, the driver switches the accelerator pedal from 0% to 100% at once, starting from a selected speed. This acceleration is counteracted by the dynamometer to keep the engine speed constant in order to analyze the behavior of the engine torque. This procedure is carried out at different speeds, which makes it possible to characterize the torque obtained as a function of time under full load (change from 0% to 100% of the accelerator pedal at once).

The curve shown in FIG. 2a obtained for a given speed, here of 1500 revolutions / min, shows that the delay tr execution in torque corresponds to:

an atmospheric phase tr 1 corresponding to an operating phase of the engine at atmospheric pressure;

- a latency phase tr2 corresponding to the time necessary for a speed of a turbocharger to reach an effective operating range,

- a supercharged phase tr3 in which the turbocharger operates within its effective operating range. The duration of these phases is of course variable depending on the starting speed of the engine which can be for example between 800 rpm and 2500 rpm.

The time evolution of the engine torque C during the atmospheric tri phase and the latency phase tr2 can be modeled by a straight line; while the time evolution of the engine torque C during the supercharged phase can be modeled by a polynomial. The overall torque execution delay tr is equal to the sum of the durations of the different phases tr 1, tr2, and tr3.

Figure 2b highlights that the delay tr execution of the engine torque depends on characteristic coefficients a1, b1, a2, b2, c2, a3, b3, c3 which were obtained during the tests carried out on a dynamometer . In an example of implementation with a particular heat engine, the characteristic coefficients are constant and are respectively worth a1 = -0.0002, b1 = 0.5717, a2 = 8.10 ^-7 , b2 = -0.0036, c2 = 4.0736, a3 = 3.10 ^-5 , b3 = 0.1097, c3 = 119.69.

More specifically, the delay linked to the sorting atmospheric phase depends on the coefficients a1 and b1, the engine torque C and the engine speed N. It is obtained from the logic operating modules M1, M2, and M3.

The delay of the latency phase tr2 depends on the coefficients a2, b2, and c2, the engine speed N and the engine speed squared (cf. squaring module M4). It is obtained from the logic operation modules M5, M6, and M7.

The delay of the supercharged phase tr3 depends on the coefficients a3, b3, and c3, the torque C, the engine speed N, and the engine speed squared. It is obtained from logic operation modules M8, M9, M10, and M11.

The module M12 makes it possible to sum the delays linked to the different phases tri, tr2, and tr3 in order to deduce the delay in the execution of the torque tr.

The computer 3 can then determine the acceleration necessary for the vehicle 1 to reach the set speed from the speed profile P_cy associated with the approval cycle. This acceleration takes into account the delay in execution of the torque tr previously calculated.

In this case, the acceleration a of the vehicle 1 is calculated from a difference between the set speed at the end of an acceleration period v (t + tr + ta) and the actual speed at the end of an execution delay of the couple v (t + tr), divided by the acceleration time ta. Thus, the acceleration a of vehicle 1 is obtained from the following relation:

V (t + tr + ta) - V (t + tr) a = -------------------- ta with:

- a being the acceleration of the vehicle;

- tr being a delay in the execution of a requested torque linked to the capacity of the engine to supply torque;

- ta being an acceleration time of the vehicle;

- V (t + tr + ta) being a set speed of the speed profile;

- V (t + tr) being a real speed at the end of the execution delay.

The engine computer 3 determines this relationship via the logic operation modules M2 'and M3'.

It is noted that the shorter the acceleration time of the vehicle ta, defined in the computer 3, the more precise the monitoring of the speed profile P_cy and the lower the acceleration a of the vehicle 1. Consequently, this makes it possible to follow the increasingly smooth speed profile P_cy. The vehicle acceleration time ta has a minimum measurement step tp minimum of the actual speed.

The determination of the actual speed at the end of the torque execution delay v (t + tr) is linked to the capacity of the heat engine to supply torque. We determine at each instant t, the parameters of the tangent in to: v (t) _r ieiie = pt + b.

[0038] In choosing a pitch tp measurement, determining a slope of a line p = ζρ ^tP ^ ^{'and a value} b = K (t) (1- ^) + V (t -tp) - ^. The real speed v (t + tr) is therefore obtained from the following relation:

v (t ₊ tr) = ----------- (t + tr) + v (t) (1--) + v (t - t _P ) with:

- tr being the delay in execution of the torque of the requested torque;

- tp being a measurement step;

- V (t + tr) being the actual speed at the end of the execution delay;

- v (t) being the actual instantaneous speed;

- v (t - tp) being the actual speed at the end of the previous measurement step.

The engine computer 3 determines this relationship by means of the logic operation modules M4 'to M13'. It is also noted that the module M13 makes it possible to introduce into the determination of the real speed v (t + tr) the concept of delay by introducing the measurement step tp.

The torque applied by the driving wheels Cr necessary for the advancement of the vehicle 1 is obtained via the determination of a propulsion force Fp. By applying Newton's second law, we arrive at the following equation:

Σ F = M. a A Fp- f (Vr) = M.a

Which leads to the following formula:

Fp = / (Fr) + M.a This formula is not vector, because all the vectors are on the same basic vector. Here the acceleration a represents the differential of speed with respect to time. The acceleration a is therefore an algebraic value. Therefore, the acceleration a can be as positive as negative. Indeed, during the acceleration phase of vehicle 1, the value of a is positive, and during the deceleration phase, the value of a is negative.

From the above formula, the torque Cr is obtained by calculation from the acceleration a of the vehicle 1 previously calculated. More specifically, the torque Cr is determined from a wheel radius R, a force f (V) opposing a movement of the vehicle depending on the actual speed Vr of the vehicle 1, the force f (V) being named road law, of a mass M of vehicle 1, and of the acceleration a of vehicle 1, according to the following relation:

Cr = R. (f (Vr) + Ma) with:

- Cr being the torque applied by the driving wheels;

- R being a wheel radius;

- Vr being a real speed of the vehicle;

- M being a mass of the vehicle;

- a being the acceleration of the vehicle;

- f (Vr) being a force opposing a movement of the vehicle, called the road law, depending on the actual speed of the vehicle Vr.

It is specified that the road law f (V) is defined according to the following relation:

f (V) = FO + Fl.V + F2.V ⁿ with:

- FO, Fl, F2 being resistance values applied to a given speed of the vehicle;

- n being a factor for example equal to 2.

The engine torque Cm is determined from a gearbox ratio RB and the torque applied by the drive wheels Cr. Note that the RB gearbox ratio represents the gear chain between the engine output and the wheels. The two couples Cm and Cr are linked by the following relation:

Cm = RB. Cr or Cm = RB. R. (f (Vr) + Ma) with:

- Cm being the engine torque;

- RB being the gearbox ratio;

- Cr being the torque applied by the driving wheels;

- Vr being a real speed of the vehicle;

- M being a mass of the vehicle;

- a being the acceleration.

The engine computer 3 determines this relationship by means of the logic operation modules M14 'to M17'.

From the engine torque Cm previously determined, a depression value P of the acceleration pedal 5 of the vehicle 1 is determined. This depression value P is determined from a Cart_1 mapping establishing a correspondence between the determined engine torque Cm and a depressing value P of the acceleration pedal 5. When the depressing value P is determined, the acceleration pedal 5 is depressed by this depressing value P.

Alternatively, we can calculate the corresponding displacement of another type of control member to obtain the desired torque.

In the present case, the speed profile P_cy corresponds to an approval cycle. As a variant, the speed profile could be defined by the computer 3 of the vehicle 1, following a detection of a change of speed setpoint. The change in speed setting may for example be detected by a geolocation system 5 by satellite, for example of the GPS type (or Global Positioning System in English) or by an optical reading of a traffic sign.

Claims (10)

1. Method for controlling a heat engine of a motor vehicle (1), characterized in that, in order to follow a speed profile (P_cy) defining a plurality of set speeds as a function of time, said method comprises the following steps: a step of modeling a delay in the execution of a torque (tr) linked to a capacity of the heat engine to supply a torque, - a step of calculating an acceleration (a) making it possible to reach a target speed, said acceleration taking into account the delay in execution of the torque (tr), a step of calculating a torque applied by driving wheels (Cr) to obtain the previously calculated acceleration (a), a step of determining a corresponding engine torque (Cm), and - A step of activating a control member (P) of the vehicle to obtain the previously determined engine torque. 2. Method according to claim 1, characterized in that the delay in the execution of the torque (tr) corresponds to: - an atmospheric phase (sorting) corresponding to an operating phase of the engine at atmospheric pressure; - a lag phase (tr2) corresponding to the time necessary for a speed of a turbocharger to reach an effective operating range, - a supercharged phase (tr3) in which the turbocharger operates within its effective operating range. 3. Method according to claim 2, characterized in that a temporal evolution of the couple during the atmospheric phase (tri) and the latency phase (tr2) is modeled by a straight line and in that a temporal evolution of the torque during the supercharged phase (tr3) is modeled by a polynomial. 4. Method according to claim 3, characterized in that coefficients characteristic of the different phases (tri, tr2, tr3) are obtained by tests of the motor vehicle carried out on a dynamometer. 5. Method according to any one of claims 1 to 4, characterized in that the acceleration (a) is calculated from a difference between a set speed at the end of an acceleration period (v ( t + tr + ta)) and the actual speed at the end of the torque execution delay (V (t + tr)), divided by an acceleration time (ta). 6. Method according to any one of claims 1 to 5, characterized in that said torque applied by the drive wheels (Cr) is determined from a wheel radius 5 (R), of a force opposing a movement of said motor vehicle (/ (Vr)) dependent on a speed (Vr) of said motor vehicle (1), of a mass (M) of said motor vehicle ( 1), and said acceleration (a) of said motor vehicle (1). 7. Method according to any one of claims 1 to 6, characterized in that said engine torque (Cm) is determined from a gearbox ratio (RB) and said 10 torque applied by the drive wheels (Cr). 8. Method according to any one of claims 1 to 7, characterized in that said speed profile (P_cy) corresponds to an approval cycle to be followed. 9. Method according to any one of claims 1 to 7, characterized in that said speed profile (P_cy) is defined by a computer (3) of said motor vehicle (1) 15 following a detection of a speed setpoint change. 10. Engine computer (3) comprising a memory (4) storing software instructions for implementing the method for controlling a heat engine (1) as defined in any one of the preceding claims. 1/3