METHOD FOR CONTROLLING AN AUTOMATIC TRANSMISSION IN THE CASE OF A DRIVETRAIN POWER DRIVE DRIVE

Description

technical field

[0001] The invention relates technically to the control of automatic transmission gearboxes, and in particular, the selection of the kinematic state of such gearboxes. Previous techniques

[0002] On a motor vehicle equipped with an automatic transmission, a target kinematic chain state is defined as a combination of couplers and reducers specific to the vehicle's architecture.

[0003] Choosing the target drivetrain state allows for optimal selection from among possible states, taking into account a given number of constraints. The vehicle's ability to respond to the powertrain load required by the driver via the accelerator pedal is ensured by one of the most important constraints: the performance constraint. The drivetrain state chosen as the target must be able to provide the vehicle with the acceleration demanded by the driver. In the event of a decrease in powertrain performance due to either a reduction in the maximum torque offered by the drive components (lower atmospheric pressure for the internal combustion engine, thermal protection of the battery or electric motor, etc.) or the choice of driving mode (EV or Hybrid versus Sport mode), it is necessary to adjust the performance constraints to require a level of performance that the powertrain can achieve.

[0004] From the prior art, we know of document FR2992040, which deals with the specific case of gear selection based on maximum acceleration for the current gear when a cruise control system is active. It makes no mention of taking into account a decrease in powertrain performance.

[0005] Documents FR3086362, FR3001936 and FR3048937 are also known and present methods of controlling a motor vehicle different from the invention.

[0006] Therefore, there is a need to adapt the performance constraint that a state of the powertrain must respect in order to be chosen as a target, in the case of a decrease in powertrain performance. Description of the invention

[0007] The invention relates to a control method for a motor vehicle, equipped with a powertrain and an automatic transmission, comprising the following steps: We determine the vehicle speed, the maximum static force available at the wheel for each state of the kinematic chain, the equivalent masses of each state of the vehicle's kinematic chain, and an existing acceleration constraint in nominal conditions. When we determine that a decrease in powertrain performance occurs, we perform the following steps: we determine the maximum acceleration of the vehicle as a function of the vehicle speed, the maximum static force available at the wheel for each state of the kinematic chain, and the equivalent masses of each state of the vehicle's kinematic chain; we determine the maximum acceleration of the degraded vehicle as a function of the maximum acceleration of the vehicle, the vehicle speed, and the overall typing of the function responsible for choosing the kinematic chain state.An updated acceleration constraint is determined based on the maximum acceleration of the degraded vehicle and the existing acceleration constraint under nominal conditions. A kinematic chain state is then determined based on this updated acceleration constraint, and the automatic transmission is controlled according to the determined kinematic chain state.

[0008] To determine the vehicle's maximum acceleration, the following steps can be taken: We determine a theoretical resistive force applied to the vehicle as a function of the vehicle's speed using a mapping; we determine the total theoretical force applied to the vehicle for each state of the kinematic chain as a function of the maximum static force available at the wheel for each state of the kinematic chain and the theoretical resistive force applied to the vehicle; we determine the maximum acceleration of each state of the kinematic chain as a function of the equivalent masses of each state of the vehicle's kinematic chain and the total theoretical force applied to the vehicle for each state of the kinematic chain; we determine the maximum acceleration of the vehicle as the maximum value among the maximum acceleration of each state of the kinematic chain.

[0009] To determine the maximum acceleration of the degraded vehicle, the following steps can be performed: A performance coefficient is determined based on the vehicle speed, the overall typing of the function responsible for choosing the kinematic chain state and a mapping; the maximum acceleration of the degraded vehicle is determined as the product of the maximum acceleration of the vehicle and the performance coefficient.

[0010] The updated acceleration constraint can be determined as the maximum value between the maximum degraded vehicle acceleration and the existing acceleration constraint in the nominal case.

[0011] The control method according to the invention has the advantage of adapting automatically in real time by minimizing the number of adjustment parameters, thus simplifying the fine-tuning process.

[0012] The control method can be implemented on any vehicle with a discrete-ratio automatic transmission. Brief description of the drawings

[0013] Other objects, features and advantages of the invention will become apparent from the following description, given solely by way of non-limiting example and made with reference to the accompanying drawings in which: there figure 1 illustrates the main steps of a control process according to the invention. Detailed description

[0014] The control process aims to determine and adapt the performance constraint that a drivetrain state must satisfy to be eligible as a target, in the event of a decrease in powertrain performance. Under certain conditions, such as a drop in atmospheric pressure for an internal combustion engine or battery thermal protection for an electric motor, the powertrain might not be able to provide the acceleration initially required by the driver under nominal conditions. It is therefore essential that the performance constraints be adaptable in real time, based on the maximum wheel force that the powertrain can generate.

[0015] The existing performance constraint is expressed in the form of an acceleration (m / s²< ) which is easily quantifiable in terms of passenger perception and vehicle performance.

[0016] The process of controlling an automatic transmission comprises three steps 1, 2, 3, illustrated by the figure 1 This allows for the determination of an appropriate acceleration constraint, FINAL_ACCEL_CST_SAT, in the event of a decrease in powertrain performance. This appropriate acceleration constraint must be met by a specific drivetrain state to be eligible to become a target for execution by the automatic transmission.

[0017] The first step 1 allows us to determine the maximum acceleration of the vehicle MAX_VEH_ACCEL as a function of the speed of the vehicle VEH_SPD, the maximum static force available at the wheel for each state of the kinematic chain MAX_WHL_FORC_DLS and the equivalent masses of each state of the kinematic chain of the vehicle VEH_EQ_WGHT_DLS.

[0018] The second step 2 allows the maximum acceleration of the vehicle MAX_VEH_ACCEL_CST degraded (in other words, after taking into account a possible decrease in powertrain performance) to be determined as a function of the maximum acceleration of the vehicle MAX_VEH_ACCEL, the speed of the vehicle VEH_SPD and the global typing of the function responsible for choosing the kinematic chain state DLS_TGT_FCT_TYP.

[0019] The third step 3 allows the updated acceleration constraint FINAL_ACCEL_CST_SAT to be determined as a function of the maximum acceleration of the vehicle MAX_VEH_ACCEL_CST degraded and the existing acceleration constraint in nominal case FINAL_ACCEL_CST.

[0020] We will now describe the different steps in more detail.

[0021] The first step 1 comprises four sub-steps labeled 11, 12, 13, 14.

[0022] The first substep 11 allows the theoretical resistive force applied to the vehicle RES_FORC to be determined as a function of the vehicle speed VEH_SPD using a map, for example an interpolation table. This can also be provisioned by a third-party function. RES _ FORC = f VEH _ SPD

[0023] The second sub-step 12 allows us to determine the total theoretical force applied to the vehicle TOT_VEH_FORC_DLS for each state of the kinematic chain as a function of the maximum static force available at the wheel for each state of the kinematic chain MAX_WHL_FORC_DLS and the theoretical resistive force applied to the vehicle RES_FORC TOT _ VEH _ FORC _ DLS = MAX _ WHL _ FORC _ DLS − RES _ FORC

[0024] MAX_WHL_FORC_DLS and TOT_VEH_FORC_DLS are X-dimensional vectors (X being the number of kinematic chain states present in the powertrain).

[0025] The third sub-step 13 allows the maximum acceleration of each state of the kinematic chain MAX_VEH_ACCEL_DLS to be determined as a function of the equivalent masses of each state of the vehicle kinematic chain VEH_EQ_WGHT_DLS and the total theoretical force applied to the vehicle TOT_VEH_FORC_DLS for each state of the kinematic chain. MAX _ VEH _ ACCEL _ DLS = TOT _ VEH _ FORC _ DLS / VEH _ EQ _ WGHT _ DLS

[0026] The maximum acceleration of each state of the kinematic chain MAX_VEH_ACCEL_DLS and the equivalent masses of each state of the vehicle kinematic chain VEH_EQ_WGHT_DLS are each contained in a vector of dimension X.

[0027] The fourth substep, 14, determines the maximum vehicle acceleration, MAX_VEH_ACCEL, based on the maximum acceleration of each state in the kinematic chain, MAX_VEH_ACCEL_DLS.

[0028] The maximum vehicle acceleration MAX_VEH_ACCEL is defined as the maximum value among the maximum acceleration of each state of the kinematic chain MAX_VEH_ACCEL_DLS. MAX _ VEH _ ACCEL = max MAX _ VEH _ ACCEL _ DLS

[0029] The second step, 2, comprises two sub-steps, labeled 21 and 22, and aims to estimate the vehicle's maximum acceleration, MAX_VEH_ACCEL_CST, in a degraded state. In the event of a decrease in powertrain performance due to either a reduction in maximum torque offered by the drive components or the selection of a mode (EV or Hybrid versus Sport mode), the vehicle's maximum acceleration, MAX_VEH_ACCEL_CST, in a degraded state, evolves in real time, each time providing the maximum static force available at the wheel, taking into account the performance reduction.

[0030] The final acceleration constraint must adapt to this performance reduction and remain consistently less than or equal to the acceleration the powertrain is capable of providing. Depending on the selected mode (EV, Sport, etc.), the difference between the acceleration available from the powertrain and the acceleration required by the driver may vary. Estimating a coefficient of performance (COEFF_PERF) is therefore essential to account for this difference.

[0031] The first sub-step 21 of the second step 2 allows the coefficient of performance COEFF_PERF to be determined as a function of the speed of the vehicle VEH_SPD and the global typing of the function responsible for choosing the state of the kinematic chain DLS_TGT_FCT_TYP with the help of a mapping, for example an interpolation table.

[0032] The overall typing of the function responsible for choosing the kinematic chain state DLS_TGT_FCT_TYP includes several typings whose value is developed according to the driver's driving mode (Economy, Neutral, Dynamic, etc.) and according to pollution control constraints (Catalyzer heating phase in progress, etc.) or other needs.

[0033] The second sub-step 22 of the second step 2 allows the maximum acceleration of the degraded vehicle MAX_VEH_ACCEL_CST to be determined as a function of the coefficient of performance COEFF_PERF and the maximum acceleration of the vehicle MAX_VEH_ACCEL.

[0034] The maximum acceleration that the vehicle can achieve MAX_VEH_ACCEL_CST degraded is defined as the product of the maximum acceleration of the vehicle MAX_VEH_ACCEL and the coefficient of performance COEFF_PERF. MAX _ VEH _ ACCEL _ CST = COEFF _ PERF ⋅ MAX _ VEH _ ACCEL

[0035] Substep 31 of step 3 aims to ensure that this adaptation strategy is only activated if a performance degradation occurs. To achieve this, the updated acceleration constraint FINAL_ACCEL_CST_SAT is determined to be the minimum between the degraded maximum acceleration MAX_VEH_ACCEL_CST and the existing acceleration constraint in the nominal case FINAL_ACCEL_CST. FINAL _ ACCEL _ CST . FINAL _ ACCEL _ CST _ SAT = min MAX _ VEH _ ACCEL _ CST , FINAL _ ACCEL _ CST

[0036] The updated acceleration constraint, named FINAL_ACCEL_CST_SAT, which takes into account the decrease in powertrain performance, is then used at the end to define the kinematic chain states that can be chosen as a target for the automatic transmission.

Claims

1. Control method for a motor vehicle, provided with a powertrain and with an automatic transmission, comprising the following steps: • determining the speed of the vehicle, the maximum static force available at the wheel for each state of the drive train, the equivalent masses of each state of the drive train of the vehicle and an existing acceleration constraint in a nominal case, • when it is determined that a drop in performance of the powertrain takes place, the following steps are carried out: • determining (1) the maximum acceleration of the vehicle as a function of the speed of the vehicle, of the maximum static force available at the wheel for each state of the drive train and of the equivalent masses of each state of the drive train of the vehicle, • determining (2) a degraded maximum acceleration of the vehicle as a function of the maximum acceleration of the vehicle, of the speed of the vehicle and of a global typing of the function responsible for the choice of the drive train state, • determining (3) an updated acceleration constraint as a function of the degraded maximum acceleration of the vehicle and of the existing acceleration constraint in a nominal case, • determining a drive train state as a function of the updated acceleration constraint, and controlling the automatic transmission as a function of the determined drive train state.

2. Control method according to Claim 1, wherein, to determine the maximum acceleration of the vehicle, the following steps are carried out: • determining (11) a theoretical resistive force applied to the vehicle as a function of the speed of the vehicle with the aid of a map, • determining (12) the theoretical total force applied to the vehicle for each state of the drive train as a function of the maximum static force available at the wheel for each state of the drive train and of the theoretical resistive force applied to the vehicle, • determining (13) the maximum acceleration of each state of the drive train as a function of the equivalent masses of each state of the drive train of the vehicle and of the theoretical total force applied to the vehicle for each state of the drive train, • determining the maximum acceleration of the vehicle as the maximum value among the maximum acceleration of each state of the drive train.

3. Control method according to either one of the preceding claims, wherein, to determine the degraded maximum acceleration of the vehicle, the following steps are carried out: • determining (21) a performance coefficient as a function of the speed of the vehicle, of the global typing of the function responsible for the choice of the drive train state and of a map, • determining (22) the degraded maximum acceleration of the vehicle as the product of the maximum acceleration of the vehicle and of the performance coefficient.

4. Control method according to any one of the preceding claims, wherein the updated acceleration constraint is determined as the maximum value among the degraded maximum acceleration of the vehicle and the existing acceleration constraint in a nominal case.