FR3101667A1 - Method of controlling a gearbox for a diagnostic measurement in a predetermined engine speed range - Google Patents

Abstract

The present invention relates to a method of controlling a gear ratio for performing exhaust line diagnostics to improve diagnostic accuracy. The method consists in authorizing a diagnostic function of a pollution control unit only in a predetermined range of the engine speed of the heat engine, said range being defined by a low limit (RG_min) and an upper limit (RG_max) of engine speed. According to the invention, the method comprises, in the event of detection of a diagnostic execution request (AUTH_osc), the steps of determining the instantaneous speed of the vehicle, the determination of at least one compatible speed ratio (RP ) of said speed imposing the control of the motor in said range and the control of the automatic engagement of said compatible speed ratio (RP). Figure for the abstract: figure 1

Description

Method of controlling a gearbox for a diagnostic measurement in a predetermined engine speed range

The field of the invention relates to a method for controlling a powertrain for measuring a diagnostic function, in particular for diagnosing a pollution control member of an exhaust line for the combustion gases of an engine. thermal motor. The invention relates more generally to the field of monitoring and purifying the exhaust gases of a motor vehicle.

Motor vehicles powered by an internal combustion engine are fitted with an exhaust line fitted with one or more pollution control devices, such as three-way catalysts. The depollution performance depends on the efficiency of these organs. For a catalyst, the state of efficiency can be evaluated from a diagnostic function whose objective is to measure a parameter specific to the catalyst, possibly the oxygen storage capacity, generally designated by the acronym OSC for " Oxygen Storage Capacity ”.

Patent documents US20110120095A1 and DE102016124427A1 are known from the state of the art, describing known techniques for measuring OSC parameters. As those skilled in the art know, the measurement of an OSC parameter is carried out using oxygen probes upstream and downstream of the catalyst. The measurements must be carried out under suitable engine operating conditions to guarantee a sufficient level of reliability. In particular, it is necessary to avoid too low engine temperatures, or even situations of strong dynamics in torque and speed. It is essential that the measurements of the OSC parameter be consistent because they are used by the engine control functions to define settings for the pollution control functions. However, these measurements are not always carried out under optimal conditions affecting the efficiency of the exhaust line depollution function.

The following documents are also known describing the powertrain control strategies intended for the preconditioning of pollution control units. Document EP1151216A1 describes, for example, a strategy for preheating the catalyst consisting in regulating the flow of the exhaust gases when this strategy is activated. Document US2008161156A1 proposes a powertrain control strategy aimed at forcing a neutral position of the gearbox to trigger regeneration of the particle filter. EP1574707A1 provides an engine idle speed control strategy to activate catalytic conversion immediately following starting an engine. The strategy is applied as soon as a change of position from the "Neutral" position to the "Drive" position is detected. Finally, we know the document EP0415024A1 describing a method of starting a heat engine aimed at controlling the gearbox according to a determination law specifically configured to increase the air flow at start-up relative to the automatic determination law calibrated for optimize fuel consumption.

While the vehicle is moving, the engine speed and engine torque vary according to the driver's wishes. This situation can lead to measurement errors during a diagnosis. There is therefore a need to improve the precision of the measurements and to guarantee the measurement conditions favorable to the execution of a diagnosis. The objective of the invention is to guarantee the best measurement conditions for an OSC diagnosis.

More precisely, the invention relates to a method for controlling a motor vehicle powertrain for measuring a diagnostic function, the powertrain comprising a heat engine, an exhaust line for combustion gases from the heat engine comprising a pollution control unit and a controlled gearbox, which method consists in authorizing a diagnostic function of the pollution control unit only in a predetermined range of the engine speed of the heat engine, said range being defined by a low limit and an upper limit engine speed. According to the invention, the method further comprises the following successive steps in the event of detection of a request to perform the diagnosis:

- Determination of the instantaneous speed of the vehicle,

- The determination of at least one speed ratio compatible with said speed imposing control of the motor in said range,

- The control of the automatic engagement of said compatible gear ratio.

According to one variant, the determination step consists in calculating an estimated theoretical speed as a function of said instantaneous speed and of a predetermined transmission factor specific to each report indicating a vehicle speed value for a predetermined speed, and in selecting the report compatible speed for which the theoretical speed is within said range.

According to one variant, the transmission factor specific to each report indicates a vehicle speed value for an engine speed of 1000 rpm.

According to a variant, if two or more compatible speed ratios are detected, during the step of determining compatible speed ratios, the method further comprises the following successive steps:

- Determining the gear ratio engaged at the instant of detection of the request to perform the diagnostic,

- The control of the automatic engagement of the gear ratio, among said two or more compatible gears, which is closest to the gear ratio engaged.

According to a variant, the request to perform the diagnostic is activated only if the temperature of the engine is greater than a first predetermined minimum temperature threshold and if the temperature outside the vehicle is greater than a second predetermined minimum temperature threshold.

According to a variant, the request to perform the diagnosis is activated only if a parameter representative of the distance traveled by the vehicle since the previous execution of the diagnosis is greater than a predetermined distance threshold.

According to one variant, the diagnosis consists in estimating the operation of a three-way catalyst of the exhaust line and in that it comprises measuring the oxygen storage capacity of said catalyst.

According to the invention, there is provided a control unit for a motor vehicle powertrain also comprising a heat engine and an exhaust line for the combustion gases of the heat engine comprising a pollution control member, which method consists of authorizing a function diagnostic of the pollution control unit only in a predetermined range of the engine speed of the heat engine, said range being defined by a low limit and a high limit of engine speed, the control unit being configured to implement the method of control according to any one of the preceding embodiments.

The invention also provides a motor vehicle comprising a powertrain comprising a heat engine, an exhaust line for combustion gases from the heat engine comprising a pollution control member and a gearbox controlled by said control unit.

The invention also relates to a program-computer product comprising instructions which, when the program is executed by a control unit of the powertrain, lead the latter to implement any one of the embodiments of the control method. 'a gear ratio according to the invention for measuring a diagnostic function in a predetermined engine speed range.

The control method improves the accuracy of diagnostic measurements of exhaust line depollution components. The invention does not require any architectural modification of the powertrain because the solution is a software modification interfacing between the diagnostic module and the transmission control module. In particular, the invention allows an improvement in the learning of the OSC diagnosis of the three-way catalyst, and by extension, the improvement of the engine control strategies which depend on the state of the catalyst as well as the improvement of the level of emissions. at the outlet of the line, the exhaust.

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

schematically shows a powertrain control unit configured to implement the method according to the invention.

is a graph illustrating a speed range favorable to performing the diagnostic making it possible to determine the gear ratio to be engaged.

The control method according to the invention relates to motor vehicles with thermal or partially thermal engines, called hybrids. Such a powertrain comprises a heat engine equipped with an exhaust line comprising a pollution control unit, possibly a catalyst. The invention is aimed at powertrains comprising a controlled gearbox, also called robotic. This type of gearbox is controlled by a computer continuously determining the best gear ratio according to one or more determination laws and controlling this ratio automatically by means of electromechanical actuators. The computer issues the commands to said actuators to engage the best gear.

To ensure optimum performance of the emission control unit, the powertrain continuously performs diagnostic functions, such as the OSC diagnostic function of a three-way catalyst. Other diagnostic functions of a catalyst may be concerned by the control method, or more generally the diagnostic functions inherent in the operation of the engine or of any pollution control member of an exhaust line, such as a particulate filter.

FIG. 1 represents a powertrain control unit 100 comprising a control module 10 of a diagnostic function of a pollution control member of an exhaust line of a motor vehicle and a control module 11 of the torque transmission, in particular the control of the gearbox and the transmission ratio. The function of the control module 10 is to trigger the diagnostic function under optimum operating conditions of the powertrain.

More precisely, the control module 10 defines a predetermined range of the speed setpoint expressed in revolutions / minute of the drive shaft of the heat engine for which the execution of the diagnostic function is only authorized and in which the speed engine is limited when performing the OSC diagnostic function. More precisely, said engine speed range is defined by a low limit RG_min and a high limit RG_max. The engine speed is controlled by the control unit (computer) of the heat engine according to various operating parameters of the powertrain, for example the torque setpoint, the speed / transmission ratio of the gearbox, the pedal position accelerator, speed control setpoint, vehicle speed setpoint.

The parameters defining RG_min and RG_max are communicated to the control module 11 of the powertrain gearbox in order to determine the speed ratio compatible with the instantaneous speed making it possible to impose the control of the heat engine in the favorable speed range RG_min, RG_max.

In addition, the control module 10 controls an activation signal AUTH_osc of the diagnostic function OSC authorizing in a first state the measurement of the OSC parameter specific to the catalyst when the operating conditions of the heat engine are optimal and prohibiting the measurement when the conditions are not met. This signal depends on parameters monitored at the input of module 10 which will be described below.

More precisely, the module 10 receives as input various operating parameters of the powertrain. A first parameter is a value representative of a distance traveled DST by the vehicle since the last execution of the diagnostic function. The DST distance is measured from a value representative of the variation in the odometer, for example. A second parameter T_mth is the temperature of the heat engine (for example the engine cooling circuit), and a third parameter T_ext is the exterior temperature of the vehicle measured by a sensor of the vehicle. Indeed, these temperatures also condition the activation of the diagnostic function. It is therefore understood that the activation signal AUTH_OSC is activated under optimum temperature conditions, that is to say after the temperature triggering of the catalyst once the vehicle is rolling.

The control module 11 is a computer control unit in charge of the automatic gear shift strategy of the controlled gearbox. This strategy consists in engaging the best gear ratio, this gear ratio being determined autonomously by the control module 11, thanks to the interpretation of the parameters P_GMP of the powertrain such as the torque and the engine speed, the Depression of the accelerator pedal, the acceleration setpoint, the speed setpoint, the vehicle speed, the operating mode of the gearbox, the resistive torque of the vehicle, or even the driving profile which can be selected manually or automatically (economy mode, sport mode for example). The control module 11 automatically controls the actuators of the gearbox but also the actuators of the clutch device coupling the drive shaft of the heat engine and the primary shaft of the gearbox for changing gears. The controls determine the speed and ease of shifting. At high gradient and high load, the driving style is sporty and at low gradient and low load rather a style that is comfortable and economical in consumption.

In the context of the invention, the law for determining the speed ratios stored by the control module 11 determines the speed ratio (s) compatible with the instantaneous speed of the vehicle RP and moreover is configured to force the combustion engine to be controlled in the favorable speed range RG_min, RG_max.

More precisely, said determination law stores, for each report, a transmission factor V1000 (Rn), where Rn is one of the speed ratios among the n ratios of the gearbox. The factor V1000 (Rn) associates a vehicle speed value for a rotation speed of 1000 rpm on each report Rn. The law for determining the RP compatible ratio is constrained by a regulation criterion in the CR regime so that the following relationship is respected:

Where RGth is the theoretical speed value for the instantaneous speed, V is the instantaneous speed of the vehicle, V1000 (RP) the transmission factor of the compatible ratio RP, RG_min and RG_max are the lower and upper limits respectively of the favorable speed range at diagnosis. When several RP gear ratios are compatible with the instantaneous speed of the vehicle, the control unit controls the gear ratio closest to the gear ratio during engagement, the gear immediately rising or falling.

The control unit 100 is provided with an integrated circuit computer and electronic memories, the computer and the memories being configured to perform the control method according to the invention. But it doesn't have to be. Indeed, the computer could be external to the control unit 100, while being coupled to the latter 100. In the latter case, it can itself be arranged in the form of a dedicated computer comprising a possible dedicated program. , for example. Consequently, the control unit, according to the invention, can be produced in the form of software (or computer (or even “software”) modules, or else of electronic circuits (or “hardware”), or else of electronic circuits (or “hardware”). 'a combination of electronic circuits and software modules.

We now describe the control method for setting the engine speed in the range favorable to performing the diagnosis. In order to guarantee the best diagnostic measurement conditions, the method performs the diagnostic function of the pollution control unit only in the predetermined range of engine speed defined by the low limit RG_min and the high limit RG_max.

In FIG. 2, there is shown schematically an example of the optimum predetermined speed range Z1 delimited by the low limit RG_min and the high limit RG_max. The graph represents the optimum speed range expressed in rpm for an OSC measurement on the abscissa and the torque value at full load Lmax, expressed in N.m, as a function of the engine speed. The torque band delimited by the dotted lines represents the optimum torque range for the same diagnosis.

If a request to run the AUTH_osc diagnostic is detected, the method determines the instantaneous speed of the vehicle V at the instant of activation of the AUTH_osc signal from the parameters P_GMP, then determines which speed ratio RP is compatible with instantaneous speed and which is configured to force the motor to be controlled in said range. Then, the method comprises controlling the automatic engagement of the RP compatible gear ratio so as to control the engine speed in the optimum range Z1.

To this end, the method determines the compatible speed ratio RP from the theoretical speed value RGth, which is calculated from the instantaneous speed V and from the transmission factor V1000 (RP) specific to each report, and from the criterion regulation in CR engine speed according to which it is recalled that:

[Math 2]:

The theoretical RGth speed is calculated for each gear ratio. In addition, the method here exploits the transmission factor V1000 (Rn) for each report indicating a speed value at a speed of 1000 rpm. It is of course understood, however, that it is not excluded to exploit other transmission factors which are capable of associating a predetermined speed value with a vehicle speed in order to determine the compatible speed of the range imposed by the diagnosis. without departing from the scope of the invention.

To illustrate the determination of the ratio RP, let us take as a non-limiting example that each transmission factor V1000 (Rn) of the gearbox is configured according to the following parameters stored in the memory of the gearbox control unit :

• V1000 (1st) = 7.2
• V1000 (2nd) = 13.5
• V1000 (3rd) = 18.3
• V1000 (4th) = 22.3
• V1000 (5th) = 26.1

For V1000 in first gear, the transmission factor means that at 1000 rpm the vehicle is traveling 7.2 km / h, and so on in each gear. Now consider that the vehicle is traveling at 70km / h and the gearbox is engaged in fourth gear. In this example, the diagnostic module sets the low limit RG_min to the value of 3500 rpm and the high limit RG_max to the value of 4500 rpm. The theoretical RGth speed for the fourth gear at 70km / h according to the previous configuration takes the following value:

[Math 3]:

This value does not respect the value of the regulation criterion CR, because the theoretical RGth speed is lower than the low limit RG_min. The conditions for performing the diagnostic are not optimal in terms of engine operating speed. The diagnosis is therefore not carried out.

In this example, the regulation criterion CR indicates that the 3rd gear is the compatible ratio RP because the theoretical speed RGth for this ratio has a value of 3825 rpm. This value is in the Z1 range.

In summary, the process takes place as described below. Assuming that the gear ratio being engaged is the selected ratio RP compatible with the speed range Z1 for performing the diagnostic, the control unit maintains this same gear ratio as long as the signal from activation AUTH_osc is active.

If the gear ratio being engaged differs from the ratio RP, or if the actual measured speed differs from the optimum speed range, then the gearbox and clutch control unit performs the shift procedure. from gear to gear RP selected for performing the diagnostic so as to drive the heat engine at an engine speed favorable to the diagnostic included in the predetermined range Z1. The control module 11 then controls the appropriate actuator commands for the clutch and the gearbox. The RP gear ratio imposing the engine speed in the predetermined range Z1 is kept engaged as long as the activation signal AUTH_osc is active.

As soon as the AUTH_osc activation signal is deactivated, indicating the end of the diagnosis, the control module determines the gear ratio configured in the law of determination for the instantaneous vehicle speed, but this time without imposing the engine speed. The law of determination is that effective before the activation of the AUTH_osc signal. The normal shift law operates normally in accordance with the planned control mode without action of the regulation criterion in diagnostic mode, for example “DRIVE” position and eco mode activated.

Furthermore, the method optimally provides for the purpose of reducing the shifting time between gear ratios and improving driveability, only in the event of detection of two or more compatible gear ratios, during the step of determining the compatible gear ratio, the method further comprises a step of determining the gear ratio engaged at the instant of activation of the signal AUTH_osc, then the control of the automatic engagement of the compatible gear ratio, which is closest to the gear ratio engaged at that moment for performing the diagnostic.

Claims (9)

Method for controlling a motor vehicle powertrain for measuring a diagnostic function, the powertrain comprising a heat engine, an exhaust line for combustion gases from the heat engine comprising a pollution control member and a gearbox. controlled speeds, which method consists in authorizing a diagnostic function of the pollution control unit only in a predetermined range (Z1) of the engine speed of the heat engine, said range being defined by a low limit (RG_min) and an upper limit (RG_max ) engine speed, the method being characterized in that it further comprises the following successive steps in the event of detection of a diagnostic execution request (AUTH_osc):

• Determining the instantaneous speed (V) of the vehicle,
• The determination of at least one compatible speed ratio (RP) of said speed (V) imposing control of the motor in said range (Z1),
• Control of the automatic engagement of said compatible gear ratio (RP).

Method according to Claim 1, characterized in that the determining step consists in calculating a theoretical speed (RGth) estimated as a function of said instantaneous speed (V) and of a predetermined transmission factor (V1000 (Rn)) specific to each report indicating a vehicle speed value for a predetermined speed, and in selecting the compatible speed ratio (RP) for which the theoretical speed (RGth) is included in said range (Z1). Method according to Claim 2, characterized in that the transmission factor (V1000 (Rn)) specific to each report indicates a vehicle speed value for an engine speed of 1000 rpm. Method according to any one of claims 1 to 3, characterized in that in the event of detection of two or more compatible speed ratios, during the step of determining compatible speed ratios (RP), the method further comprises the following successive steps:

• Determining the gear ratio engaged at the instant of detection of the diagnostic execution request (AUTH_osc),
• The control of the automatic engagement of the gear ratio, among said two compatible ratios or more, which is closest to the gear ratio engaged.

Method according to any one of Claims 1 to 4, characterized in that the request for carrying out the diagnostic (AUTH_osc) is activated only if the engine temperature (T_mth) is greater than a first predetermined minimum temperature threshold and if the temperature outside the vehicle (T_ext) is greater than a second predetermined minimum temperature threshold. Method according to any one of claims 1 to 5, characterized in that the diagnostic execution request (AUTH_soc) is activated only if a parameter representative of the distance traveled (DST) by the vehicle since the previous diagnostic execution is greater than a predetermined distance threshold. Process according to any one of Claims 1 to 6, characterized in that the diagnosis consists in estimating the operation of a three-way catalyst of the exhaust line and in that it comprises the measurement of the storage capacity in oxygen of said catalyst. Control unit (100) of a motor vehicle powertrain also comprising a heat engine and an exhaust line for combustion gases from the heat engine comprising a pollution control unit, which method consists of authorizing a diagnostic function of the engine. pollution control unit only in a predetermined range of the engine speed of the heat engine, said range being defined by a low limit (RG_min) and an upper limit (RG_max) of engine speed, characterized in that it is configured to implement the Control method according to any one of claims 1 to 7. Motor vehicle comprising a powertrain comprising a heat engine, an exhaust line for combustion gases from the heat engine comprising a pollution control member and a gearbox controlled by a control unit (100), characterized in that the unit control (100) is according to claim 8.