FR3103440A1 - PROCESS FOR DETERMINING THE TORQUE TRANSMITTED BY THE ENGINE TO THE DRIVE CHAIN - Google Patents

Abstract

The present invention relates to a method for determining a torque parameter transmitted by the heat engine to a powertrain traction chain further comprising a clutch. According to the invention, the method comprises the successive steps of determining (31) a torque transmissible by the clutch at each instant, the control (32) of the clutch in a controlled slip state at a slip limit value predetermined constant, and when the slip is kept constant at the slip limit value, assigning (34) the transmissible torque value to the transmitted torque parameter. The invention is applicable to any vehicle with a clutch and gearbox piloted to improve the accuracy of engine torque parameters. Figure 3

Description

METHOD FOR DETERMINING THE TORQUE TRANSMITTED BY THE ENGINE TO THE TRACTION CHAIN

The field of the invention relates to a method for determining the torque transmitted by the heat engine to the traction chain of a motor vehicle powertrain. The invention relates to the field of driving pleasure and the piloting controls of a powertrain based on the value of the torque transmitted.

Conventionally, the internal combustion engine calculates the gross engine torque it produces by measuring the flow of fuel injected and the flow of air injected into the cylinders of the engine. The gross engine torque is used to provide a first torque component to the engine accessories (air conditioning compressor, alternator, etc.), a second component is consumed by engine losses (crankshaft friction, piston friction, camshafts, cam friction, etc.), a third component is consumed by the engine to accelerate its rotational speed and finally a fourth component is transmitted by the engine shaft to the traction chain to move the vehicle, c ie to the clutch, the gearbox and finally to a vehicle wheel set. In the remainder of the description, this latter torque component will be designated by the term transmitted torque parameter.

The relation of the sum of the components forming the gross torque is exploited to calibrate under specific operating conditions the value of the loss torque which is dependent on engine aging. Furthermore, for the computer to calibrate the value of the transmitted torque parameter, it needs very specific operating conditions of the powertrain. Indeed, the engine speed must be at idle, the gearbox must be in Neutral, the air conditioning compressor must be off, and the heat engine must be at a certain temperature, because the level of engine losses is known that at certain engine oil temperature values. Finally, these conditions must be maintained for a period of approximately a few minutes. Also, in this case only, the engine computer knows that the torque transmitted is zero and therefore it can calibrate the value of the parameter to 0. In addition, the values of the loss torque are known when the engine is new, but these values are strongly dependent on aging and are calibrated under conditions of zero transmitted torque.

The problem with this method of calibrating the transmitted torque parameter and the loss torque is the rarity of the calibration conditions and therefore a risk of inaccuracy over time. This situation is likely to lead to a reduction in driving pleasure when an automated function of the powertrain is operated based on this value. A derivation of the parameter value causes, for example, inconveniences when changing gear. In fact, the torque levels at the engine output and at the gearbox input must be identical when the clutches are closed to avoid torque surges. Trajectory control functions also based on the value of the transmitted torque parameter can also be affected by an inaccuracy in the value, the impression of backing up on a slope or else residual braking holding back the progress of the vehicle when starting on a hill.

We know from the state of the art the patent document FR2943024A1 describing a method for determining the inertial torque of an internal combustion engine associated with a clutch and the engine loss torque, determined from the sum of a torque of mapped motor loss and a corrective term defined as a function of the inertial torque. We also know the patent document EP1624173A1 describing a torque calculation method for an engine connected to an automatic transmission. The document EP0904972A2 is also known describing a device intended to quantify the transmitted torque produced by an internal combustion engine from which power can be taken via a gearbox.

The invention aims to overcome the aforementioned problems and to improve the method for calibrating the value of the transmitted torque and the value of the loss torque by raising the occurrences of rolling situation compatible with a calibration operation. The aim of the invention is to reduce the drift effect of the error of the transmitted torque parameter and of the loss torque of a heat engine.

More specifically, the invention relates to a method for determining a torque parameter transmitted by the internal combustion engine to a powertrain traction chain further comprising a clutch. According to the invention, the method comprises the following successive steps:

• The determination of a torque transmissible by the clutch at each instant,
• The control of the clutch in a controlled slip state at a predetermined constant slip limit value,
• When the slip is held constant at the slip limit value, assigning the transmittable torque value to the transmittorque parameter.

According to a variant, the transmissible torque is calculated from the following relationship: Ctr2=Femb*µemb*Remb, where:

- Femb is the force exerted on the clutch discs,

- µemb is the friction coefficient level of the clutch discs determined from a predetermined table according to the measured temperature of the clutch oil,

- Remb is the value of the average radius of the contact area of the discs.

According to a variant, the force exerted is calculated from the product of the value of a pressure parameter measured by a pressure sensor of the clutch and a parameter of the contact surface of the clutch discs.

According to a variant, the control of the clutch in a controlled slip state consists in enslaving the slip value according to the measurement of a difference between the speed of the engine shaft of the heat engine and the speed of the primary shaft. of the clutch.

According to a variant, the slip limit value is between 5 rpm and 20 rpm, preferably 10 rpm.

According to a variant, the torque that can be transmitted by the clutch is determined by a first clutch control module and the transmitted torque parameter is a parameter shared with second control modules of the powertrain, for example the control module of the heat engine, and communicated through a shared communication bus.

The invention also relates to a method for calibrating the torque parameter transmitted by the heat engine to the traction chain of a powertrain in which the value of the torque parameter transmitted is determined from a value calculated by the module for controlling the clutch of the powertrain in accordance with the method according to the invention.

The invention also relates to a method for calibrating the loss torque parameter of a heat engine of a powertrain also comprising a clutch, consisting in calibrating the loss torque of the engine by controlling a controlled slip state of the clutch and in calculating the loss torque as a function of a transmitted torque parameter value calculated in accordance with the method according to the invention.

The invention relates to a motor vehicle comprising a powertrain comprising a heat engine controlled by a first control module and a clutch controlled by a second control module, in which the first control module is configured to request the second control module to determination of the torque value transmitted to the traction chain at the engine output.

The invention also provides a program-computer product comprising instructions which, when the program is executed by a control unit of the heat engine, lead the latter to implement any one of the embodiments of the method for determining the transmitted torque.

The invention makes it possible to determine with improved precision the value of the torque transmitted without having to wait for the specific conditions that cancel the action of the torque components taken by the accessories, of engine loss torque. The method thus increases the recurrence of the engine parameter calibration phases and significantly increases the precision of the torque control of any autopilot function based on the value of the torque transmitted by the engine.

Other characteristics and advantages of the present invention will appear more clearly on reading the following detailed description comprising embodiments of the invention given by way of non-limiting examples and illustrated by the appended drawings, in which:

schematically represents a motor vehicle powertrain capable of implementing the method according to the invention.

represents the functional architecture of calculation modules configured to communicate to each other the value of the torque parameter transmitted through a communication bus of the powertrain.

represents an algorithm of the method for determining a parameter of the torque transmitted by the heat engine of a powertrain according to the invention.

The invention applies to vehicle powertrains comprising a thermal engine, of the conventional and hybrid type, and more particularly to the methods for determining and calibrating engine torque parameters established conventionally from predetermined maps in new condition and dependent on engine aging. In particular, the transmitted torque parameter of the motor which is calculated from the following relationship: Ctr1= Cmot – Cacc – Cpert – Crot, where Cmot is the gross torque generated by the motor, Cacc is the drive torque of the accessories , Cpert the pert torque and Crot the inertial torque used to increase the rotational speed of the rotating parts of the engine. Cpert varies over time due to engine aging, which is why this component is generally calibrated on an ad hoc basis under operating conditions that cancel out the transmitted torque component.

Figure 1 shows a vehicle powertrain comprising a heat engine 10, a clutch device 11 and a gearbox 12 whose output shaft is mechanically connected to a wheel set, in this example front. The clutch 11 connects in torque transmission the output shaft of the engine and the primary shaft of the gearbox, and can be a multi-disc wet clutch, with single or double clutch, or any type of clutch pilot. In this example the clutch 11 is of the hydraulically actuated double clutch type for which it is necessary to provide hydraulic pressure to close the clutches and therefore transmit the engine torque from the engine shaft to the rest of the traction chain. Other types of clutch are able to implement the method according to the invention as long as their control can be automated to command a controlled slip state.

The gearbox 12 and the clutch 11 form a robotic torque transmission member with automatic piloting, that is to say that the gear changes, the opening and the closing of the clutch can be triggered and automatically controlled by a control module dedicated to the gearshift function.

Similarly, control functions of the thermal engine 10 are controlled automatically by a specific control module in particular to continuously determine the value of operating engine parameters, such as the parameters Cmot, Ctr1, Cacc, Cpert and Crot. The value of these parameters depends on the control functions of the robotic clutch and the robotic gearbox.

In FIG. 2, a flowchart represents a first functional module 20 dedicated to controlling the heat engine and calculating the engine parameters and the torque parameters Cmot, Ctr1, Cacc, Cpert and Crot mentioned above. A second functional module 21 is dedicated to controlling the gearbox and the clutch. A third functional module 22 is dedicated to an automatic vehicle trajectory control function, possibly.

The functional modules 20, 21, 22 can be made in the form of software modules (or computer modules (or “software”)), or electronic circuits (or “hardware”), or even a combination of electronic circuits and software modules.

More precisely, the engine control module 20 saves in a memory the transfer function between the gross engine torque Cmot created and the quantity of fuel injected, the quantity of air injected, and the temperature of the engine. These latter values are measured by means of on-board sensors. Learning for the calculation of the Cmot parameter is done at idle speed and over a period generally of the order of a few tens of seconds in order to average the air flow and the fuel flow, and therefore the average torque in order to minimize the error in the estimation of the torque Cmot.

In addition, the engine control module 20 calculates the torque Cacc, from torque correspondence tables stored in the memory of the control module 20. The torque Crot is calculated by the engine computer from the engine rotation speed parameter. engine shaft "engine speed" measured by the speed sensor which informs of the level of acceleration of the parts of the mobile coupling of the engine and the inertia parameter of the parts of the mobile coupling calibrated (recorded) in the engine computer during the engine calibration phase in design. And the control module 20 obtains the value of Crot thanks to the product of these last two parameters.

The invention proposes a method for determining the torque Ctr1 transmitted by the control module 20 of the thermal engine judiciously determined according to the value of the torque Ctr2 transmitted from the clutch, and more precisely when it is controlled in a slipping state. controlled to a slip limit value.

More specifically, by transmissible torque is meant the value of the maximum torque that can be transmitted by the clutch, in this case from the output shaft of the engine to the primary shaft of the gearbox, without generating a state of clutch slippage.

Indeed, in this precise state of sliding the transmitted torque value is equal to the transmissible torque value. This method of determination has the advantage of increasing the calculation opportunities for carrying out the periodic calibration of the transmitted torque parameter and of the motor loss torque parameter.

As seen in Figure 2, other operating parameters P20, P21 of the powertrain can be calculated according to the value of the transmitted torque Ctr1 when it is obtained from the transmissible torque Ctr2, such as the loss torque Cpert of the thermal engine by the module 20, or control parameters of other powertrain control modules, such as modules 22 for trajectory control and automatic braking. The value of the transmitted torque Ctr1 can be read through an information communication bus 23 multiplexed and shared between several computers, for example a CAN bus commonly used in motor vehicles (“Controller Area Network” in English).

The transmissible torque Ctr2 is a function of the axial pressure exerted on the disks of the clutch or clutches and on the friction surface and is known precisely at all times. The transmittable torque is calculated according to the type of clutch used in the powertrain and the calculation function to determine the axial pressure or force is adapted according to the technology of the clutch actuator exerting the pressure.

Thus, it is understood that the module 21 is capable of determining the transmissible torque Ctr2 of the clutch at each instant and the control modules 20, 21, 22 are configured so as to be able to control the clutch in a controlled slip state at a predetermined constant slip limit value, and when the slip is held constant at the slip limit value, assigning the transmittable torque value Ctr2 through the clutch to the transmittable torque parameter Ctr1.

More specifically, the control module 21 is able to calculate the transmissible torque value Ctr2 from the relationship below where the parameters are measured by sensors, or relate to dimensional physical parameters of the clutch components very little subject to change over time and known to be new. This mode of calculation from the clutch parameters guarantees the accuracy of the value of the transmissible torque parameter Ctr2 at all times.

More precisely, Ctr2=Femb*µemb*Remb, where:

• Femb is the force exerted on the clutch discs,
• µemb is the friction coefficient level of the clutch discs determined from a predetermined table as a function of the measured temperature of the clutch oil,
• Remb is the value of the average radius of the contact area of the discs.

The value μemb is a value which changes with the temperature, but the predetermined table recorded in the memory of the module 21 makes it possible to correct the value μemb as a function of the measured temperature.

Remb is a distance that does not change over time and is known and precise.

In addition, according to a variant making it possible to guarantee the precision of the calculation of the force exerted Femb, Femb = Pemb*Semb, where Pemb is the pressure parameter measured by a pressure sensor of the clutch and Semb is a parameter of the surface of contact Sembe of the clutch discs. Semb is a surface that does not evolve over time and is known in design and precise. In another variant, the force is evaluated as a function of the position of the disc actuator, for example.

In figure 3, we now describe an example of the algorithm of the process for determining the torque parameter Ctr1 transmitted by a heat engine motor shaft. In this situation, it is assumed that a request for calibration of the transmitted torque is requested by the thermal engine module, or more generally that a parameter of the powertrain requests the calibration or the determination of the value of the torque transmitted Ctr1. During a first step 31, the clutch control unit determines the torque Ctr2 that can be transmitted by the clutch at each instant. The transmissible torque Ctr2 is calculated from the following relationship: Ctr2=Femb*µemb*Remb.

Then, in a second step 32, the clutch control unit controls a controlled slip state at a predetermined constant slip limit value so as to be able to assign the value of the transmissible torque to the parameter of the torque transmitted by the engine .

More precisely, the control of the clutch in a controlled slip state consists in enslaving the slip value according to the measurement of a difference between the speed of the engine shaft of the heat engine and the speed of the primary shaft of the clutch. The speed difference is preferably low to avoid excessive slip or a closed state without slip, indicating in these two situations significant differences between the transmitted torque and the transmissible torque.

According to a variant, the slip limit value is between 5 rpm and 20 rpm, preferably 10 rpm.

More precisely, to control the enslavement to the slip limit value, the engine module measures the engine speed by means of the engine shaft rotation speed sensor, this value is transmitted via the vehicle communication bus to the module clutch control for the implementation of the controlled slip function. At the same time, the clutch control module measures the primary shaft speed of the clutch and gearbox by means of the primary clutch shaft speed sensor. The "controlled slip" function constantly regulates a difference in speed, for example 10 rpm between the engine speed and the primary shaft speed.

Several servo situations are possible and taken into account by the clutch control module when performing the “controlled slip function”. If the engine drives the gearbox (positive transmitted torque):

• When the primary shaft speed difference is less than 10 rpm in relation to the engine speed, the "controlled slip" function detects that the clutch is transmitting too much torque and therefore reduces the pressure in the clutch.
• When the primary shaft speed difference is greater than 10 rpm in relation to the engine speed, the "controlled slip" function detects that the clutch is not transmitting enough torque and therefore increases the pressure in the clutch.

And in the case where it is the gearbox that drives the motor (torque transmitted is negative):

• When the primary shaft speed difference is less than 10 rpm in relation to the engine speed, the "controlled slip" function detects that the clutch is transmitting too much torque and therefore reduces the pressure in the clutch.
• When the primary shaft speed difference is greater than 10 rpm compared to the engine speed, the "controlled slip" function detects that the clutch is not transmitting enough torque and therefore increases the pressure in the clutch .

Then, in accordance with the method according to the invention, the clutch control unit continuously checks in a step 33 whether the slip state is maintained at the slip limit value for a sufficient predetermined duration.

If so, the one-step method 34 includes a step of assigning the transmittable torque value Ctr2 to the transmitted torque parameter Ctr1. More precisely, the clutch control unit informs via the communication bus to the other modules, including the engine control module, the value of the torque transmitted Ctr1=Ctr2.

Otherwise, if the speed difference is not maintained at the limit slip value, the method keeps step 32 active for controlling the controlled slip function.

The method according to the invention is judiciously used to respond to engine parameter calibration requests, for example of the transmitted torque parameter, as well as to calibration requests of the loss torque parameter calculated as a function of a value of transmitted torque parameter. More generally, any control module, computer or function of the powertrain, external to the clutch control module, is capable of requesting the value of the torque transmitted from the clutch module, by triggering a slip phase at the value of slip limit, for a given duration sufficient for the determination of the torque.

Mention may be made of the following functions using the method according to the invention to improve driving pleasure:

• The "gear change" service is improved in terms of gear change pleasure, because during a gear change, the gearbox computer gives the torque instructions to the engine computer to ensure that the driver and passengers do not feel any torque surge.
• The hill assist function uses the transmitted torque information broadcast over the vehicle's communication bus to know when the function must release the vehicle's braking system for the cleanest possible take-off of the vehicle without giving the driver the impression of backing up on a slope or the impression that the brakes are holding the vehicle forward.
• The trajectory control computer also uses the torque information transmitted for the quality of cornering and the management of torque distribution on the drive wheels to maintain the vehicle trajectory desired by the driver.

Claims (9)

Method for determining a torque parameter transmitted (Ctr1) by the internal combustion engine to a powertrain traction chain further comprising a clutch, the method being characterized in that it comprises the following successive steps:

• The determination (31) of a transmittable torque (Ctr2) by the clutch at each instant,
• The clutch control (32) in a controlled slip state at a predetermined constant slip limit value,
• When the slip is held constant at the slip limit value, assigning (34) the transmittable torque value to the transmittorque parameter (Ctr1).

Determination method according to Claim 1, characterized in that the transmissible torque (Ctr2) is calculated from the following relationship: Ctr2=Femb*µemb*Remb, where:

• Femb is the force exerted on the clutch discs,
• µemb is the friction coefficient level of the clutch discs determined from a predetermined table as a function of the measured clutch oil temperature,
• Remb is the value of the average radius of the contact area of the discs.

Determination method according to Claim 2, characterized in that the force exerted (Femb) is calculated from the product of the value of a pressure parameter measured by a pressure sensor of the clutch and a parameter of the contact surface (Semb) of the clutch discs. Determination method according to any one of Claims 1 to 3, characterized in that the control of the clutch in a controlled slip state consists in enslaving the slip value as a function of the measurement of a difference between the speed of the drive shaft of the internal combustion engine and the speed of the primary clutch shaft. Determination method according to any one of Claims 1 to 4, characterized in that the slip limit value is between 5 rpm and 20 rpm, preferably 10 rpm. Determination method according to any one of Claims 1 to 5, characterized in that the torque transmissible (Ctr2) by the clutch is determined by a first control module (21) of the clutch and in that the parameter of transmitted torque (Ctr1) is a parameter shared with second powertrain control modules (20,22), for example the thermal engine control module, communicated through a shared communication bus (23). Process for calibrating the torque parameter transmitted (Ctr1) by the combustion engine to the traction chain of a powertrain in which the value of the torque parameter transmitted (Ctr1) is determined from a value calculated by the module for controlling the clutch of the power train in accordance with the method according to any one of claims 1 to 6. Method for calibrating the loss torque parameter of a heat engine of a powertrain also comprising a clutch, characterized in that it consists in calibrating the loss torque of the engine by controlling a controlled slip state of the clutch and calculating the loss torque as a function of a transmitted torque parameter value (Ctr1) according to the method of claim 7. Motor vehicle comprising a powertrain comprising a heat engine (10) controlled by a first control module (20) and a clutch (11) controlled by a second control module (21), characterized in that the first control module ( 20) is configured to request the second control module (21) to determine the torque value transmitted (Ctr1) to the traction chain at the engine output.