METHOD FOR CONTROLLING THE STARTING PROCESS OF AN INTERNAL COMBUSTION ENGINE IN A HYBRID POWERTRAIN

Description

[0001] The present invention relates to the control of hybrid powertrains.

[0002] More specifically, it relates to a method for anticipating the start of a thermal engine in a powertrain (GMP) of a hybrid vehicle comprising at least one thermal engine and one electric machine, when its drive train passes from a purely electric current state to a second target state likely to require the start of the thermal engine to satisfy the driver's wheel force request. Document US9327722B1 discloses a control method for a hybrid powertrain.

[0003] Some hybrid powertrains, having a discrete ratio gearbox, have a thermal engine and at least one electric motor allowing multiple combinations of thermal torque transmission ratios and electric torque transmission ratios. Each operational combination of a " rapport thermique " and a « rapport électrique », defines a "state" of the powertrain drivetrain, such as purely electric: only the electric machine is connected to the wheels, purely thermal: only the thermal engine is connected to the wheels, or hybrid: the electric machine and the thermal engine are connected to the wheels.

[0004] Purely electric states are preferred to use the energy stored in the battery. The electric motor is then connected to the wheels, while the combustion engine is not, and is switched off (not started). In an established electric current gear, the driver, or a driving function (for example, cruise control), may increase the torque request to the GMP, to the point of switching it to a hybrid state to benefit from the power of the combustion engine in addition. Switching from an electric state to a hybrid state requires starting the combustion engine. The time required to start the combustion engine directly influences the quality of the shift. Its reduction is essential for driving pleasure, as well as for the responsiveness of the vehicle.

[0005] Publication FR 2 882 698 discloses a method for quickly taking off a hybrid vehicle from a standstill: the vehicle is taken off on the electric machine at its maximum torque by isolating the thermal engine from the thermal chain for the time necessary for starting, before introducing the torque from the thermal engine into the drive train.

[0006] Publication EP 1 970 240 describes another method of starting the thermal engine in hybrid mode. This method, like the previous one, uses cut-off clutches to temporarily isolate the thermal engine during its start-up period.

[0007] The present invention aims to reduce or eliminate the time required to start the thermal engine, when switching from an electric state to a hybrid state, by anticipating the start of the thermal engine to improve the performance of the vehicle.

[0008] To this end, it provides that: we compare the maximum force that the electrical branch of the traction chain can produce on each of the target electrical states of the GMP, to the force that each of these states must satisfy, to be chosen or maintained as a target state, and we impose an early start request on the thermal engine, if none of the target electrical states is capable of satisfying the driver's force request.

[0009] Preferably, two Booleans are created for each target electrical state, the first taking the value one if the target state is judged unable to satisfy the driver's torque demand, and the second taking the value one if the target state is judged able to satisfy this demand.

[0010] The developed strategy opportunely establishes a request for early start of the thermal engine, in order to reduce, or even cancel the effect of the thermal engine start time on the duration of the transition from an electric state to a hybrid state. This request is issued upstream of the request for a change of powertrain state, under the responsibility of another function, so that the thermal engine is already operational at the time of transition to the hybrid state.

[0011] It is mainly made from: the time required to start the thermal engine, the maximum power delivered by the electric motor, and the maximum torque delivered by the electric machine.

[0012] The main advantages of the method are the few adjustment parameters required, and the resulting memory savings. Vehicle tuning is simplified. The proposed strategy is cross-functional. It can be adapted to any hybrid vehicle with a discrete-ratio automatic transmission and at least one electric powertrain.

[0013] The present invention will be better understood from reading the following description of a non-limiting embodiment thereof, with reference to the appended drawings, in which [ Fig. 1 ] is a flowchart of the developed strategy, and [ Fig. 2 ] describes the Function F1 of the figure 1 .

[0014] The F1 function is used to determine whether an early start request for the thermal engine should be activated or deactivated, based on the physical criteria of the powertrain. It issues raw early start requests. These requests are used to anticipate the start of a thermal engine in a powertrain (GMP) of a hybrid vehicle comprising at least one thermal engine and one electric machine, when its powertrain transitions from a purely electric current state to a second target state likely to require the starting of the thermal engine to satisfy the driver's wheel force request.

[0015] First, we calculate an anticipated speed corresponding to the vehicle speed at which the engine would be started if a start request were issued at that moment. It is called VEH_SPD_ANT. The anticipated speed of the vehicle when the combustion engine starts is a function of the vehicle speed, the starting time of the combustion engine, and the longitudinal acceleration of the vehicle. It is calculated as follows: VEH _ SPD _ ANT = VEH _ SPD + ENG _ START _ DLY * VEH _ LONG _ ACCEL .

[0016] In this calculation, VEH_SPD is the current vehicle speed, ENG_START_DLY is the starting time of the thermal engine, a calibrated parameter, which can depend on the water temperature of the thermal engine, and VEH_LONG_ACCEL is the current longitudinal acceleration of the vehicle.

[0017] A maximum wheel force value is then calculated for each state of the electric powertrain. The maximum wheel force is equal to the minimum between the maximum power that the electric machine can provide in its isopower zone, at the anticipated speed of the vehicle when the thermal engine starts, and the product of the maximum torque that the electric machine of the GMP can provide in its isotorque zone by the overall transmission ratio allowing the maximum torque of the electric machine to be transformed into the equivalent of wheel force. It is called EV_DLS_X_FORC_MAX, and is calculated as follows: EV_DLS_X_FORC_MAX = MIN (POW_EV_MAX / VEH_SPD_ANT, TQ_EV_MAX*DLS_RAT_X), avec POW_EV_MAX for the maximum power that the electric machine can provide in its iso power zone (this data can be configured or provided by a third-party function), TQ_EV_MAX for the maximum torque that the electric machine can provide in its iso torque zone (this data can be configured or provided by a third-party function), VEH_SPD_ANT for the anticipated speed calculated previously, DLS_RAT_X for the overall transmission ratio allowing the maximum torque of the electric machine to be transformed into the equivalent force at the wheel (parameterized data).

[0018] For each of the states of the electric traction chain, the force EV_DLS_X_FORC_MAX is then compared to a force query FORC_DLS_TGT, which is the wheel force that an electric drivetrain state must satisfy to be chosen or maintained as the current target state of the gearbox. This comparison makes it possible to define a ratio for each of the electrical states. This ratio is called RAT_EV_PERF_DLS_X. It represents the capacity of the target state to satisfy the force request to the wheel FORC_DLS_TGT, compared to the maximum possible performance EV_DLS_X_FORC_MAX of the state concerned, at the anticipated speed calculated upstream of the strategy.

[0019] The ratio RAT_EV_PERF_DLS_X is calculated as follows: RAT_EV_PERF_DLS_X = FORC_DLS_TGT / EV_DLS_X_FORC_MAX. The ratio RAT_EV_PERF_DLS_X is less than 1, if the target state is capable of providing more force than required by the force request to the wheel, and greater than 1 otherwise. It is compared to a first threshold RAT_EV_PERF_DLS_SET_THD, above which it is considered that the state of the electric powertrain concerned will not ensure the desired performance, so much so that it risks implying the choice of a hybrid target state.

[0020] The ratio RAT_EV_PERF_DLS_X is also compared to a second threshold RAT_EV_PERF_DLS_RST_THD, lower than the first, below which it is considered that the electric powertrain state concerned will ensure sufficient performance, which means that it will be kept as the target state, whereas otherwise it would be discarded.

[0021] From this ratio, we create two booleans for each target electrical state, LOW_EV_PERF_DLS_X_SET And LOW_EV_PERF_DLS_X_RST : if RAT_EV_PERF_DLS_X is greater than or equal to the first threshold RAT_EV_PERF_DLS_SET_THD, SO LOW_EV_PERF_DLS_X_SET = 1 if RAT_EV_PERF_DLS_X is lower than the second threshold, RAT_EV_PERF_DLS_RST_THD, SO LOW_EV_PERF_DLS_X_RST = 1

[0022] Under these conditions: the first boolean, LOW_EV_PERF_DLS_X_SET takes the value one if the ratio of the force required to satisfy the driver's wheel force request to the maximum potential force on the targeted electrical state is greater than the first threshold, because the target state is then deemed incapable of satisfying the driver's torque request, and the second boolean LOW_EV_PERF_DLS_X_RST takes the value one if the ratio of the force required to satisfy the driver's wheel force request to the maximum potential force on the targeted electrical state is less than or equal to the second threshold, because the target state is then deemed capable of satisfying this request.

[0023] We create a third boolean ICE_START_ANT_REQ_SET which takes the value one if all the first booleans LOW_EV_PERF_DLS_X_SET are set to one. Under these conditions, no electric target state is capable of satisfying the wheel force request, so a hybrid state will be chosen. The planned state change is preceded by the anticipated start of the thermal engine.

[0024] We create a fourth boolean ICE_START_ANT_REQ_RST, which takes the value one, if one of the booleans LOW_EV_PERF_DLS_RST is set to one. Under these conditions, at least one electrical target state is capable of satisfying the wheel force request. The target state will remain electric. Anticipating a possible start of the thermal engine is not necessary.

[0025] In summary, we compare the maximum force that the electrical branch of the traction chain can produce on each of the target electrical states of the GMP, to the force that each of them must satisfy to be chosen or maintained as a target state, and we impose an early start request on the thermal engine, if none of the target electrical states is capable of satisfying the driver's force request.

[0026] The purpose of function F2 is to consolidate the raw requests for anticipation of the start of the thermal engine ICE_START_ANT_REQ_SET And ICE_START_ANT_REQ_RST. During this step, a request for early start of the thermal engine, called ICE_START_ANT_REQ, becomes effective, if all of the following parameters are met: the boolean ICE_START_ANT_REQ_SET is at one, no purely electric vehicle operating mode of the vehicle or the GMP is required by the driver, and the thermal engine is neither started nor in the process of starting.

[0027] It becomes ineffective if one of the following conditions is true: the boolean ICE_START_ANT_REQ_RST is at 1, a purely electric vehicle operating mode which effectively prohibits the starting of the thermal engine, is required by the driver, the thermal engine is started.

[0028] The anticipated start request for the thermal engine thus developed and applied allows the thermal engine to be started at the moment when a hybrid state is chosen as a target. The time required for start-up is therefore eliminated from the overall time taken to achieve the new state. This anticipation significantly improves the vehicle's responsiveness to driver requests.

Claims

1. Method for anticipating the starting of a thermal engine in a powertrain (GMP) of a hybrid vehicle comprising at least one thermal engine and one electric machine, when its drivechain goes from a current purely electric state to a second target state likely to require the starting of the thermal engine in order to satisfy the request for force at the wheel from the driver, according to which - the maximum force that can be produced by the electric branch of the drivechain on each of the target electric states of the GMP is compared with the force that each of them must satisfy in order to be chosen or maintained as target state, and - a request for anticipated starting is imposed on the thermal engine if none of the target electric states is capable of satisfying the force request from the driver, - two Booleans are created for each target electric state, the first taking the value one if the target state is judged incapable of satisfying the torque demand from the driver, and the second Boolean taking the value one, if the target state is judged capable of satisfying this demand, - a third Boolean is created which takes the value one if all the first Booleans are equal to one, and - a fourth Boolean is created which takes the value one if at least one of the second Booleans is at one, characterized in that - the request for anticipated starting becomes effective, if the third Boolean is at one, no purely electric mode of operation of the GMP is requested by the driver, and the thermal engine is neither started nor is in the process of being started, and in that - the request for anticipated starting becomes ineffective if one of the following conditions is true: - the fourth Boolean is equal to one, - a purely electric mode of operation of the GMP is requested by the driver, - the thermal engine is started.

2. Anticipation method according to Claim 1, characterized in that the first Boolean takes the value one if the ratio of the force needed in order to satisfy the request for force at the wheel from the driver over the maximum potential force in the targeted electric state is greater than one.

3. Anticipation method according to Claim 1 or 2, characterized in that the second Boolean takes the value one if the ratio of the force needed in order to satisfy the request for force at the wheel from the driver over the maximum potential force in the targeted electric state is less than or equal to a second threshold.

4. Anticipation method according to Claim 3, characterized in that the maximum force at the wheel is equal to the minimum between the maximum power that the electric machine can supply within its iso power region over the anticipated speed of the vehicle at the starting of the thermal engine, and the product of the maximum torque that the electric machine of the GMP can supply within its iso torque region times the overall transmission ratio allowing the maximum torque of the electric machine to be transformed into an equivalent of force at the wheel.

5. Anticipation method according to Claim 4, characterized in that the anticipated speed of the vehicle at the starting of the thermal engine is a function of the speed of the vehicle, of the time for starting the thermal engine, and of the longitudinal acceleration of the vehicle.