METHOD FOR CONTROLLING THE STARTING OF A COMBUSTION ENGINE IN A VEHICLE EQUIPPED WITH A HYBRID TRANSMISSION

Abstract

The method for controlling the start of a thermal engine (MT) is implemented in a hybrid electric vehicle having a powertrain (eGMP) comprising the thermal engine and a hybrid transmission system (eTR), the transmission system having a rotating electrical machine (ME) coupled to the engine via a clutch device (K0). According to the invention, the method comprises, during a start-up phase by the electric machine of the engine while the vehicle is running, a control (M_EB) of the clutch by means of a maximum clutch torque setpoint determined as a function of a predetermined maximum speed gradient (LGR) and a moment of inertia (Jmth) of the engine, and a control (M_MT) of the engine by means of a maximum engine torque setpoint (CM) determined as a function of a difference (EC) between the maximum gradient and a measured speed gradient (GR) and as a function of a torque (C0e) transmitted by the clutch. Figure 2

Description

Title of the invention: METHOD FOR CONTROLLING THE STARTING OF A HEAT ENGINE IN A VEHICLE EQUIPPED WITH A HYBRID TRANSMISSION

[0001] The present invention relates generally to the field of hybrid thermal-electric powertrains for motor vehicles. More particularly, the invention relates to a method for controlling the start of a thermal engine in a vehicle equipped with a hybrid transmission system.

[0002] In hybrid vehicles, dual-clutch hybrid transmission systems, known as "eDCT" for "electric Dual Clutch Transmission" in English, contribute to the optimization of energy efficiency, for a reduction in consumption and pollutant emissions. "eDCT" transmission systems provide numerous advantages, particularly in terms of weight, compactness, flexibility of energy management and others. They are applicable in various known powertrain architectures, such as the mild hybrid architecture, known as "mild-hybrid" or "MHEV" for "Mild Hybrid Electric Vehicle" in English, the complete hybrid architecture, known as "full-hybrid" or "(F)HEV" for "(Full) Hybrid Electric Vehicle" in English, and the rechargeable hybrid architecture known as "plug-in hybrid" or "PHEV" for "Plug-in Hybrid Electric Vehicle" in English.

[0003] [Fig. 1] schematically illustrates an eGMP hybrid powertrain of a hybrid electric vehicle. The vehicle considered here is of the PHEV type, for example, and integrates three traction modes, namely, a thermal traction mode, an electric traction mode and a hybrid traction mode.

[0004] The eGMP group comprises an MT thermal engine and an “eDCT” type transmission system designated eTR. The eTR transmission system is equipped with a DCT dual-clutch robotized gearbox, an ME rotating electric machine and a KO clutch device.

[0005] The DCT gearbox conventionally comprises a K12 double clutch device and GE gear trains, as well as actuators and synchronizers (not shown) for the robotized shifting of transmission ratios. The DCT gearbox receives a mechanical traction torque via its input shaft AE for the rotational drive of the WH wheels of the vehicle coupled to its output shaft AS.

[0006] The rotating electrical machine ME is mechanically coupled by gearing to the input shaft AE of the DCT gearbox according to a so-called “P2” architecture. The ME machine is connected to an electric traction storage device (not shown) of the vehicle via a reversible electric power converter (not shown). The ME machine operates in electric motor mode for electric traction of the vehicle and starting of the MT thermal engine and in electric generator mode for generating electrical energy via a drive by the MT thermal engine and for regenerative braking.

[0007] The clutch device KO fulfills a coupling / decoupling function in the transmission of mechanical torque between the thermal engine MT and the transmission system eTR. Thus, with the clutch device KO open, the thermal engine MT is disconnected from the traction chain, which makes it possible in the electric traction mode by the ME machine, as well as in the regenerative braking mode, to overcome friction losses due to the thermal engine MT, for better energy efficiency. With the double clutch device K12 open and the clutch device KO closed, the ME machine is disconnected from the transmission to the WH wheels and is only engaged with the thermal engine MT, which allows the thermal engine MT to be started with the ME machine in motor mode and the generation of electrical energy by driving the thermal engine MT of the ME machine in generator mode.

[0008] The different operating modes and life phases of the eGMP hybrid powertrain are managed by a supervisor computer ECU_S, an engine control computer ECU_E and a transmission control computer ECU_T which are connected to a BCD data communication bus, typically of the “CAN” type. The supervisor computer ECU_S is responsible for the overall management of the eGMP group, the computers ECU_E and ECU_T being responsible for the close management of the thermal engine ME and the transmission system eTR, respectively. The computers ECU_S, ECU_E and ECU_T collaborate with each other to implement different control strategies depending on the actions of the vehicle driver and life situations.

[0009] Through the BCD data communication bus, the supervisor computer ECU_S receives commands from the driver, in particular through a control lever LC manipulated by the driver, information from the vehicle computers and / or information from various sensors, and transmits information and commands to the computers ECU_E and ECU_T for controlling the eGMP powertrain.

[0010] In this eGMP powertrain architecture, the starting or restarting of the thermal engine MT while the vehicle is moving is carried out using the rotating electrical machine ME, which is mechanically coupled to the thermal engine ME via the clutch device KO. It is desirable that this starting is carried out in a very short time, typically in a few hundred milliseconds, for rapid availability of the thermal engine torque and a smooth transition from traction mode, as well as for the comfort of the vehicle users. For this, the electric machine ME in motor mode and the clutch device KO must apply a significant starting torque to the thermal engine MT and this results in a very high speed gradient which can exceed 18000 rpm / s, or 18000 rpm / s ("rpm" for "revolution per minute" in English). During the start-up of the thermal engine, its lubrication is not fully operational. Too high a speed gradient generates a risk of damage to the thermal engine. In the state of the art, this life situation of starting the thermal engine MT while the vehicle is moving is not optimized.The designer has the choice between limiting the applied starting torque by taking a safety margin, at the expense of the start execution time, or violating the speed limitations, with negative consequences on the engine life.

[0011] Document DE102012009481Al describes a restart control for a heat engine in a hybrid powertrain. The restart control comprises several phases, with a progressive increase in torque in stages. The different phases of the control take into account the lubrication of the heat engine.

[0012] It is desirable to provide an optimized control solution for starting the thermal engine while a hybrid vehicle is running, making it possible to minimize the start-up time and to comply with the constraint of limiting the engine speed gradient.

[0013] According to a first aspect, the invention relates to a method for controlling the start of a heat engine implemented in a hybrid electric vehicle having a powertrain comprising the heat engine and a hybrid transmission system, the hybrid transmission system having a rotating electric machine coupled to the heat engine via a clutch device.According to the invention, the method comprises, during a starting phase by the rotating electrical machine of the thermal engine while the vehicle is running, a control of the clutch device by means of a maximum clutch torque setpoint which is determined as a function of a predetermined maximum engine speed gradient of the thermal engine and a moment of inertia of the thermal engine, and a control of the thermal engine by means of a maximum thermal engine torque setpoint which is determined as a function of a difference between the predetermined maximum engine speed gradient and a measured engine speed gradient and as a function of a torque transmitted by the clutch device.

[0014] According to a particular characteristic, the torque transmitted by the clutch device is obtained by estimation.

[0015] The invention also relates to a computer comprising a memory storing program instructions for implementing the method briefly described above. This computer is, for example, a vehicle engine control computer.

[0016] The invention also relates to a hybrid electric vehicle having a powertrain comprising a heat engine and a hybrid transmission system, the hybrid transmission system having a rotating electric machine coupled to the heat engine via a clutch device, the powertrain having a start-up phase by the rotating electric machine of the heat engine while the vehicle is running. According to the invention, the method comprises a computer as indicated above ensuring the control of the start-up phase.

[0017] According to a particular embodiment, the hybrid transmission system of the hybrid electric vehicle comprises a dual-clutch gearbox.

[0018] Other advantages and characteristics of the present invention will appear more clearly on reading the detailed description below of several particular embodiments of the invention, with reference to the appended drawings, in which:

[0019] [Fig-1] [Fig.l] is a block diagram showing schematically an architecture of a hybrid electric vehicle powertrain equipped with a dual-clutch hybrid transmission system.

[0020] [Fig.2] [Fig.2] is a functional block diagram showing an implementation of the method of the invention in the powertrain of [Fig.l].

[0021] [Fig.3] [Fig.3] represents different curves showing the benefit provided by the implementation of the method of the invention in the powertrain of [Fig.l].

[0022] With reference to [Fig.2] and [Fig.3], a particular embodiment of the method according to the invention is now described. The method is here implemented in a hybrid powertrain, such as the eGMP group of [Fig.1], comprising a thermal engine and a dual-clutch hybrid transmission system of the “eDCT” type designated respectively by their references MT and eTR.

[0023] Generally speaking, the method according to the invention uses the known relationships below (1) and (2) to link the engine speed gradient (expressed in rpm.s') to the thermal engine torque (expressed in Nm), knowing the moment of inertia (expressed in kg.m2) of the thermal engine, namely:

[0024] (1) Co=(J.dco / dt), in which Co is the torque (in Nm), J is the moment of inertia (in kg.m2), co is the angular velocity (in rd.s ') and dco / dt is the angular acceleration (in rd.s2); and

[0025] (2) 1 rpm=120irrd.s'.

[0026] The method according to the invention comprises a preliminary test phase on the engine MT thermal engine and a process operating phase for starting the MT thermal engine while the vehicle is running.

[0027] The objective of the preliminary test phase is to determine, with a command in open loop, a maximum engine speed gradient LGR, that is to say, an engine speed gradient close to an organic limit of the thermal engine MT, but which remains lower than it. The determined maximum engine speed gradient LGR is stored in memory, for example here in the engine control computer ECU_E, to be used subsequently for controlling the start of the thermal engine MT while the vehicle is moving.

[0028] In the operating phase of the method, for starting the thermal engine MT, the rotating electrical machine ME supplies the clutch device KO with an electric motor torque Cme. Typically, the electric motor torque Cme has a constant value for the duration of the start. According to the invention, the clutch device KO is controlled with a maximum clutch torque setpoint COc which is determined by the maximum engine speed gradient LGR and the moment of inertia of the thermal engine and the thermal engine MT is controlled with a maximum engine torque setpoint CM which is a function of a difference EC between the maximum engine speed gradient LGR and a measured engine speed gradient and of a clutch torque COe which is an estimate of the torque CO actually transmitted by the clutch device KO.

[0029] With particular reference to [Fig.2], an embedded software system for controlling the thermal engine SWEN is typically hosted in the engine control computer ECU_E dedicated to managing the thermal engine MT.

[0030] The embedded software system for controlling the thermal engine SWEN is installed in a memory MEM of the computer ECU_E. The software system SWEN comprises several software modules dedicated to the implementation of different control strategies for the thermal engine MT which are activated according to the life situations of the vehicle. The software system SWEN comprises in particular a software module M_CD responsible for managing the starting of the thermal engine MT in accordance with the invention.

[0031] The software module M_CD authorizes the implementation of the method according to the invention by the execution of program code instructions by a processor (not shown) of the computer ECU_E. The computer ECU_E, under the supervision of the software module M_CD, cooperates in particular with the supervisor computer ECU_S and the transmission control computer ECU_T for the implementation of the method according to the invention.

[0032] As visible in [Fig.2], the M_CD software module notably comprises two functional blocks M_EB and M_MT.

[0033] The M_EB functional block is responsible for determining the torque setpoint maximum clutch torque COc for controlling the clutch device KO and essentially comprises a CE function. The CE function is a calculation function which determines the maximum clutch torque setpoint COc to be supplied to the clutch device KO from the aforementioned maximum engine speed gradient LGR and the moment of inertia Jmth of the thermal engine. The CE function uses in particular the general relations (1) and (2) mentioned above to determine the maximum clutch torque setpoint COc.

[0034] The maximum clutch torque setpoint COc is supplied to the transmission control computer ECU_T for controlling the clutch device KO. The computer ECU_T hosts in memory a functional block M_K0 responsible for controlling the clutch device KO and comprising in particular a control function M_CC0 and an estimation function M_C0e. The function M_CC0 receives as input the maximum clutch torque setpoint COc and a torque estimate COe supplied by the estimation function M_C0e. The torque COe is an estimate of the actual clutch torque CO supplied to the thermal engine MT by the clutch device KO. The function M_CC0 delivers as output a controlled command C_C0. The controlled command C_C0 controls the clutch device KO for supplying the desired torque CO.

[0035] The functional block M_MT of the software module M_CD is responsible for determining the maximum thermal engine torque setpoint CM for controlling the thermal engine MT. The functional block M_MT includes in particular functions S0, CT and SL

[0036] The function S0 is a subtraction operator that provides a deviation EC between the maximum engine speed gradient LGR and a measured engine speed gradient GR. The measured engine speed gradient GR is typically obtained by deriving the current engine speed. The gradient deviation EC is provided as input to the function CT.

[0037] The CT function is a regulation function which determines a thermal engine torque pre-setpoint CP as a function of the gradient difference EC. The CT regulation function determines the pre-setpoint CP by exploiting in particular the general relations (1) and (2) mentioned above, taking into account the moment of inertia Jmth of the thermal engine, and by applying, if necessary, gain adjustment and phase correction processing. The function S1 is a subtraction operator which produces the maximum thermal engine torque setpoint CM=CP-C0e, by subtracting the estimated clutch torque COe from the thermal engine torque pre-setpoint CP.

[0038] The contribution of the method of the invention, compared to the prior art, for starting the MT thermal engine while driving is illustrated by the curves in [Fig.3].

[0039] The start-up comprises different phases, for the thermal engine MT and for the clutch device KO, which are designated M1 to M3 and E1 and E2. The phases M1, M2 and M3 correspond respectively to a start-up launch phase, a rev-up phase and a torque transfer phase. The phases E1 and E2 correspond respectively to a clutch slip phase and a clutch closing phase.

[0040] Curves C1, C2 and C3 show changes in torques (C) during starting, namely, the constant torque Cme supplied by the rotating electrical machine ME and the torque C0 transmitted via the clutch device KO. Curves C2 and C3 show the torques C0 for a start according to the prior art and a start according to the invention, respectively. Curves C4 and C5 show changes in rotational speeds (VR) during starting, namely, the rotational speed of the rotating electrical machine ME and the rotational speed of the primary transmission shaft, respectively. Curves C6 and C7 show changes in the speeds RM of the heat engine for a start according to the prior art and for a start according to the invention, respectively.Curves C8 and C9 show engine speed gradient (GRD) developments during starting, namely, engine speed gradients for a start according to the prior art and for a start according to the invention, respectively. The line CIO represents the limit corresponding to the maximum engine speed gradient LGR.

[0041] The action of the method of the invention on the engine speed gradient and on the evolution C7 of the engine speed RM is represented schematically by the arrows F1 and F2. With the method of the invention, the corresponding gradient curve C9 remains below the fixed limit of maximum engine speed gradient LGR. Compared to the prior art (curve C6) which accepts an engine speed gradient much higher than LGR to obtain a short starting time DD, the method according to the invention (curve C7) makes it possible to obtain a substantially equivalent starting time while respecting the limit LGR.

[0042] The present invention provides a low-cost, software-based solution for optimizing the start-up of the thermal engine in a hybrid vehicle while driving. The proposed solution is suitable for different types of hybrid electric vehicles.

[0043] The invention is not limited to the particular embodiments which have been described here by way of example. Those skilled in the art, depending on the applications of the invention, will be able to make various modifications and variants falling within the scope of protection of the invention.

Claims

Claims

1. Method for controlling the start of a thermal engine (MT) implemented in a hybrid electric vehicle having a powertrain (eGMP) comprising said thermal engine (MT) and a hybrid transmission system (eTR), said hybrid transmission system (eTR) having a rotating electrical machine (ME) coupled to said thermal engine (MT) via a clutch device (KO), characterized in that it comprises, during a start-up phase by said rotating electrical machine (ME) of said thermal engine (MT) during the running of said vehicle, a control (M_EB) of said clutch device (KO) by means of a maximum clutch torque setpoint (COc) which is determined as a function of a predetermined maximum engine speed gradient (LGR) of said thermal engine (MT) and a moment of inertia (Jmth) of said thermal engine (MT),and a control (M_MT) of said thermal engine (MT) by means of a maximum thermal engine torque setpoint (CM) which is determined as a function of a difference (EC) between said predetermined maximum engine speed gradient (LGR) and a measured engine speed gradient (GR) and as a function of a torque (COe) transmitted by said clutch device (KO).,

2. Method according to claim 1, characterized in that said torque transmitted by said clutch device (KO) is obtained by estimation (COe).

3. Computer comprising a memory (MEM) storing program instructions (M_CD) for implementing the method according to claim 1 or 2.

4. Calculator according to claim 3, characterized in that said calculator is an engine control calculator (ECU_E).

5. Hybrid electric vehicle having a powertrain (eGMP) comprising a heat engine (MT) and a hybrid transmission system (eTR), said hybrid transmission system (eTR) having a rotating electrical machine (ME) coupled to said heat engine (MT) via a clutch device (KO), said powertrain (eGMP) having a start-up phase by said rotating electrical machine (ME) of said heat engine (MT) during the running of said vehicle, characterized in that it comprises a computer (ECU_E) according to claim 3 or 4 ensuring the control of said start-up phase startup.

6. An electric hybrid vehicle according to claim 5, characterized in that said hybrid transmission system (eTR) comprises a dual clutch gearbox (DCT).

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