METHOD FOR REDUCING CLUTCH DRAG TORQUE IN A VEHICLE HYBRID TRANSMISSION SYSTEM DURING AN INTERNAL COMBUSTION ENGINE START

Abstract

The method is implemented in a vehicle having an internal combustion engine and a hybrid transmission system comprising a rotating electric machine (ME) coupled to the engine and a gearbox of the transmission system via clutch devices. According to the invention, the method comprises the steps of: A) detecting (EE) a request to start the engine with neutral engaged, and B) when the start request is detected, determining a speed gradient setpoint (GR_ME) for the machine, limiting the clutch drag torque, as a function of a difference (ER) between a speed setpoint (C_RME) and an actual speed (R_RME) of the machine, and a speed gradient (GR_AP) of a primary shaft of the gearbox. Figure 2

Description

Title of the invention: METHOD FOR REDUCING CLUTCH DRAG TORQUE IN A VEHICLE HYBRID TRANSMISSION SYSTEM DURING AN INTERNAL COMBUSTION ENGINE START

[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 reducing clutch drag torque in a vehicle hybrid transmission system during the start-up of the internal combustion engine.

[0002] It will be clear to the reader that the terms "internal combustion engine start-up" used above, as well as in the following presentation of the prior art, the following description of the invention and the attached claims, should not be interpreted restrictively and cover life situations in which the internal combustion engine is started in response to a request from the driver of the vehicle or is restarted following a request from a vehicle control strategy such as that relating to the known "stop-start" functionality integrated into the vehicle.

[0003] In hybrid vehicles, dual-clutch hybrid transmission systems, known as "eDCT" (for "electric Dual Clutch Transmission"), contribute to optimizing energy efficiency, resulting in reduced fuel consumption and pollutant emissions. "eDCT" transmission systems offer numerous advantages, particularly in terms of weight, compactness, energy management flexibility, and others. They are applicable to various known powertrain architectures, such as the mild-hybrid (MHEV) architecture, the full-hybrid ((F)HEV) architecture, and the plug-in hybrid (PHEV) architecture.

[0004] Figure 1 schematically illustrates a hybrid eGMP powertrain of a Hybrid electric vehicle. The eGMP group comprises an internal combustion engine (MT) and an "eDCT" type transmission system designated eTR. The eTR transmission system is equipped with a DCT dual-clutch automated manual transmission, a rotating electric machine (ME), and a clutch mechanism (KO).

[0005] The DCT gearbox conventionally comprises a K12 dual-clutch device and GE gear trains, as well as actuators and Synchronizers (not shown) for the automated shifting of transmission ratios. The DCT gearbox receives mechanical traction torque via its primary shaft AP to drive the rotation of the vehicle's WH wheels coupled to its output shaft AS.

[0006] The rotating electric machine ME is mechanically coupled by gears to the primary shaft AP of the DCT gearbox according to a so-called "P2" architecture. The machine ME operates in electric motor mode for electric traction of the vehicle and starting of the internal combustion engine MT, and in electric generator mode for generating electrical energy via a drive from the internal combustion engine MT and for regenerative braking.

[0007] The KO clutch device performs a coupling / decoupling function in the transmission of mechanical torque between the MT internal combustion engine and the eTR transmission system. Thus, with the KO clutch device open, the MT internal combustion engine is disconnected from the drive train, which, in electric traction mode by the ME machine, as well as in regenerative braking mode, eliminates friction losses due to the MT internal combustion engine. With the K12 dual clutch device open and the KO clutch device closed, the ME machine is essentially engaged with the MT internal combustion engine, which allows the MT internal combustion engine to start with the ME machine in motor mode and generates electrical power by driving the ME machine in generator mode with the MT internal combustion engine.

[0008] The various operating modes and life phases of the eGMP hybrid powertrain are managed by a supervisory control unit ECU_S, an engine control unit ECU_E, and a transmission control unit ECU_T, which are connected to a BCD data communication bus, typically of the CAN type. The supervisory control unit ECU_S is responsible for the overall management of the eGMP, while the ECU_E and ECU_T control units are responsible for the detailed management of the internal combustion engine MT and the eTR transmission system, respectively. The ECU_S, ECU_E, and ECU_T control units collaborate to implement different control strategies depending on the driver's actions and driving conditions.Through the BCD bus, the ECU_S receives commands from the driver, information from the vehicle's control units, and / or information from various sensors, and transmits information and commands to the ECU_E and ECU_T control units for the eGMP powertrain control. Specifically, the ECU_S receives PP position information from a control lever (LC) operated by the driver and A_PA information indicating that a vehicle's accelerator pedal (PDA) is pressed, in order to control the vehicle's movement. Typically, the lever positions... LC control includes at least two driving positions, namely, forward D and reverse R, a neutral N position and a parking P position, as well as a (not shown) manual transmission gear shifting position.

[0009] When starting the internal combustion engine MT, with the lever LC in the neutral (N) position, the inventive entity observed an unpleasant sensation in the driver's experience. Specifically, the driver experiences a brief, unpleasant jolt of acceleration. This negative driving experience is related to the architecture of the hybrid transmission system and the control of the rotating electric machine ME in this particular driving situation.

[0010] When the vehicle is stationary, in "vehicle started" mode with the ignition on, and the LC lever is in neutral (N), the first or second gear is already engaged in the DCT transmission. The functionality of the neutral (N) position is achieved by keeping the dual-clutch device K12 open to prevent torque transmission to the wheel when the machine ME is started to start the internal combustion engine MT. The aforementioned inconvenience experienced by the driver when starting the internal combustion engine MT is due to the fact that a frictional torque, known as "clutch drag," is transmitted by the dual-clutch device K12 when it is open. This clutch drag torque depends, in particular, on the amount of oil present between the discs of the device K12 and its temperature.The problem is more noticeable when the engine is cold, as the oil viscosity is higher. The clutch drag torque is then greater and can induce a wheel torque exceeding 300 Nm, with an acceleration close to 0.7 m / s².

[0011] Document EP2641800A1 describes a device for controlling the drive torque transmitted to a transmission system of a hybrid vehicle. The device includes means designed to correct a torque transmitted by a clutch device in order to compensate for variations in engine torque, thus providing a more precise and reliable response to driving commands.

[0012] The present invention aims to provide a solution to the aforementioned drawback of the prior art.

[0013] According to a first aspect, the invention relates to a method for reducing clutch drag torque implemented in a hybrid electric vehicle having a powertrain comprising an internal combustion engine and a hybrid transmission system, the hybrid transmission system having a rotating electric machine coupled to the internal combustion engine via a first clutch device and a gearbox coupled to the rotating electric machine via a second clutch device capable of transmitting clutch drag torque.According to the invention, the method comprises the steps of A) detecting a request to start the internal combustion engine by the rotating electric machine occurring when a control lever of the hybrid transmission system is placed in a neutral position, and B) when the start request is detected in step A) determining a speed gradient setpoint to be applied in an ongoing control of the rotating electric machine as a function of several pieces of information including information representing a difference between a current speed setpoint applied in the control of the rotating electric machine and a current effective speed of the rotating electric machine, and information representing a current speed gradient of a primary shaft of the gearbox, the speed gradient setpoint being determined so as to obtain a reduction in the clutch drag torque.

[0014] According to a particular embodiment, said information also includes information representing a press on a vehicle accelerator pedal, this information inducing a limitation of the reduction of the clutch drag torque when the press on the accelerator pedal exceeds a predetermined threshold.

[0015] According to a particular feature, in step B) of the process, the regime gradient setpoint is determined using a mapping.

[0016] The invention also relates to a computer comprising a memory storing program instructions for the implementation of the process briefly described above when these instructions are executed by a processor of the computer.

[0017] According to a particular embodiment, the computer is a transmission control computer responsible for managing the hybrid transmission system.

[0018] The invention also relates to a hybrid electric vehicle having a powertrain comprising an internal combustion engine and a hybrid transmission system, the hybrid transmission system having a rotating electric machine coupled to the internal combustion engine via a first clutch device and a gearbox coupled to the rotating electric machine via a second clutch device, and also comprising a control unit as indicated above. The gearbox of the hybrid transmission system may be a dual-clutch gearbox incorporating the aforementioned second clutch device.

[0019] Other advantages and features of the present invention will become more apparent upon reading the detailed description below of a particular embodiment of the invention, with reference to the accompanying drawings, in which:

[0020] Fig. 1 is a block diagram schematically showing an architecture of a hybrid electric vehicle powertrain equipped with a dual-clutch hybrid transmission system.

[0021] The [Fig.2] is a functional block diagram showing an implementation of the method of the invention in the powertrain of the [Fig.1].

[0022] Fig. 3 represents different curves showing the benefit provided by the implementation of the process of the invention in the powertrain of Fig. 1.

[0023] With reference to the aforementioned figures, a particular embodiment of the method according to the invention is now described. The method is implemented here in a hybrid powertrain of an electric hybrid vehicle, such as the eGMP group of [Fig. 1], comprising an internal combustion engine and a hybrid dual-clutch transmission system of the "eDCT" type, designated respectively by their reference numbers MT and eTR.

[0024] In general, the method according to the invention achieves a reduction in clutch drag torque during the starting phases of the internal combustion engine with neutral (N) engaged, by reducing the speed gradient of the rotating electrical machine during these phases. The reduction in clutch drag torque mitigates the negative sensation of a brief acceleration experienced by the driver, as described above. The method of the invention provides a speed gradient setpoint to be applied for the rotational control of the rotating electrical machine during the aforementioned phases.

[0025] With particular reference to [Fig. 2], an embedded software system M_CME for controlling the rotating electric machine ME is typically hosted in the transmission control unit ECU_T, which is responsible for controlling the eTR hybrid transmission system. Generally, the ECU_T hosts several control strategies for the eTR hybrid transmission system, which are activated depending on the vehicle's operating conditions. The M_CME software system for controlling the ME machine outputs a torque setpoint CP_ME for torque control of the ME machine.

[0026] The M_CME software system is implemented in a MEM memory of the ECU_T computer and includes in particular a REG_RME control software module whose function is to determine the aforementioned torque setpoint CP_ME and an M_RTE software module whose function is to determine, in accordance with the process of the invention, a speed gradient setpoint GR_ME which is used by the REG_RME control software module to control the ME machine.

[0027] The REG_RME control software module implements an algorithm that determines the CP_ME torque setpoint based, in particular, on a setpoint of C_RME regime for the ME machine and the GR_ME regime gradient setpoint provided by the M_RTE software module.

[0028] The M_RTE software module enables the implementation of the method according to the invention by the execution of program code instructions by a processor (not shown) of the ECU_T computer.

[0029] In the invention, the M_RTE software module is activated to perform a processing procedure inducing the reduction of the clutch drag torque when the start-up life phase of the internal combustion engine with the neutral position N engaged is detected.

[0030] An EE signal, visible in [Fig. 2], informs the M_RTE software module of the detection of the aforementioned life phase and activates the processing performed by it. When activated by the EE signal, the M_RTE software module determines the GR_ME engine speed gradient setpoint from information that is generally already available in the ECU_T control unit or collected via the BCD data communication bus.

[0031] As shown in [Fig.2], in the embodiment considered here, the software module M_RTE determines the speed gradient setpoint GR_ME from the aforementioned speed setpoint C_RME provided by a control strategy during the start-up of the internal combustion engine MT, an information R_RME indicating the actual speed (measured or evaluated by calculation) of the machine ME, an information GR_AP indicating the speed gradient (measured or evaluated by calculation) of the primary shaft AP of the DCT gearbox and the information A_PA of the driver's press on the accelerator pedal PDA of the vehicle.

[0032] It will be noted that in other embodiments of the method of the invention, the software module M_RTE will be able to determine the regime gradient setpoint GR_ME without taking into account the information A_PA of pressing on the accelerator pedal PDA.

[0033] As seen in [Fig.2], the M_RTE software module essentially uses three functions designated SI, LIM_GRD and S2 to determine the regime gradient setpoint GR_ME.

[0034] The function S1 is a subtraction operator receiving as input the operating regime setpoint C_RME and the actual operating regime R_RME of the machine ME and delivering as output the operating regime difference ER = (C_RME - R_RME) existing between these two incoming operating regime information.

[0035] The LIM_GRD function is typically implemented using a CAT mapping. The LIM_GRD function receives as input the engine speed deviation information ER and the accelerator pedal depress information A_PA and provides as output a gradient deviation setpoint GRD, also called the differential gradient setpoint GRD, between the engine speed gradient GR_ME of the ME machine and the engine speed gradient GR_AP of the primary shaft AP. The gradient deviation setpoint GRD is a function of the input variables ER and PDA (accelerator pedal position A_PA), namely, GRD = f(ER, A_PA). The different values ​​assigned to the gradient deviation setpoint GRD, depending on the values ​​of the input variables ER and A_PA, are determined to achieve the desired feel for the driver. Typically, these values ​​assigned to the gradient deviation setpoint GRD and stored in the CAT map are determined through testing and simulations.

[0036] In the function implemented by the CAT mapping, namely GRD=f(ER, A_PA), the input variable A_PA, representing the pressure on the accelerator pedal PDA, acts to significantly increase the value of the gradient deviation setpoint GRD when the pressure on the accelerator pedal PDA exceeds a predetermined threshold. When this predetermined threshold is exceeded, the input variable A_PA induces a lesser limitation on the engine speed gradient GR_ME of the ME engine, which, consequently, controls a limitation on the reduction of the clutch drag torque. This functionality, introduced by taking into account the input variable A_PA, allows the driver to experience a sensation of acceleration (due to the clutch drag torque) that is then consistent with their acceleration demand.

[0037] The function S2 is a summation operator that receives as input the gradient deviation setpoint GRD and the operating gradient GR_AP of the primary shaft AP and outputs the operating gradient setpoint GR_ME. The sum of the GRD information set by the CAT mapping and the GR_AP information (measured or evaluated by calculation) gives the operating gradient setpoint GR_ME for the machine ME, as shown by the following equality: GRD + GR_AP = (GR_ME - GR_AP) + GR_AP = GR_ME.

[0038] The contribution of the process of the invention, compared to the prior art, is illustrated by the curves in [Fig.3].

[0039] Three functional phases T_AR, T_MV and T_DM occur successively during the start-up of the internal combustion engine MT and are shown in [Fig.3]. The phases T_AR, T_MV and T_DM correspond respectively to a shutdown phase of the MT engine which precedes a start-up command occurring at a time D_MT, a ramp-up phase of the internal combustion engine MT set in rotation by the machine ME and a start-up phase of the internal combustion engine MT with an actual start occurring at a time MT_0N.

[0040] Curves C1, C2, and C3 in [Fig. 3] show the evolution of the operating speed (SP in rpm) during these three functional phases T_AR, T_MV, and T_DM. Curves C1, C2, and C3 respectively show the evolution of the operating speed S_ME1 of the ME machine according to the prior art, and the evolution of the operating speed S_ME2 of the ME machine obtained with the limitation of the regime gradient implemented in the process of the invention and the evolution of the S_MT regime of the MT thermal engine.

[0041] Considering more particularly the illustrative curves Cl and C2, it follows from the comparison of these curves that the process of the invention makes it possible to obtain a speed gradient GRL of the ME machine, resulting from the GR_ME setpoint delivered by the M_RTE software module, which is lower than a speed gradient GRI which would be obtained with the prior art, until reaching a SP_D speed close to the speed at which the MT motor starts.

[0042] Curves C4 and C5 in [Fig. 3] show the evolution of clutch drag torque (TQ in Nm) during the three aforementioned phases T_AR, T_MV, and T_DM. Curves C4 and C5 respectively show the evolution of the clutch drag torque CTI of the ME machine according to the prior art and the evolution of the clutch drag torque CT2 of the ME machine obtained with the limitation of the speed gradient implemented in the method of the invention.

[0043] Comparing the illustrative curves C4 and C5, it is clear that the method of the invention makes it possible to obtain a significant reduction in clutch drag torque. With the invention, a clutch drag torque CTI having a peak value of approximately 300 Nm can be reduced to a clutch drag torque CT2 having a peak value of approximately 50 Nm.

[0044] The present invention provides a low-cost, software-based solution for improving driver feedback during engine start-up from neutral in vehicles equipped with a dual-clutch hybrid transmission system known as "eDCT". The proposed solution is particularly suitable for hybrid electric vehicles (MHEVs).

[0045] The invention is not limited to the particular embodiment described herein by way of example. A person skilled in the art may, depending on the applications of the invention, make various modifications and variations falling within the scope of the invention's protection.

Claims

Demands

1. A method for reducing clutch drag torque implemented in an electric hybrid vehicle having a powertrain (eGMP) comprising an internal combustion engine (MT) and a hybrid transmission system (eTR), said hybrid transmission system (eTR) having a rotating electric machine (ME) coupled to said internal combustion engine (MT) via a first clutch device (KO) and a gearbox (DCT) coupled to said rotating electric machine (ME) via a second clutch device (K 12) capable of transmitting said clutch drag torque, characterized in that it comprises the steps of A) detecting (EE) a start request of said internal combustion engine (CD) by said rotating electric machine (ME) occurring when a control lever (LC) of said hybrid transmission system (eTR) is placed in a neutral (N) position,and B) when said start request is detected in step A) determine a speed gradient setpoint (GR_ME) to be applied in an ongoing control of said rotating electrical machine (ME) as a function of several pieces of information including information representing a deviation (ER) between a current speed setpoint (C_RME) applied in said control of said rotating electrical machine (ME) and a current effective speed (R_RME) of said rotating electrical machine (ME), and information representing a current speed gradient (GR_AP) of a primary shaft (AP) of said gearbox (DCT), said speed gradient setpoint (GR_ME) being determined so as to obtain a reduction of said clutch drag torque.

2. Method according to claim 1, characterized in that said several pieces of information also include a piece of information (A_PA) representing a press on an accelerator pedal (PDA) of said vehicle, said information (A_PA) inducing a limitation of said reduction of said clutch drag torque when said press on said accelerator pedal (PDA) exceeds a predetermined threshold.

3. Method according to claim 1 or 2, characterized in that, in step B), said regime gradient setpoint (GR_ME) is determined using a mapping (CAT).

4. Computer comprising a memory (MEM) storing program instructions (M_RTE) for the implementation of the method according to any one of claims 1 to 3 when said instructions are executed by a processor of said computer.

5. Calculator according to claim 4, characterized in that said calculator is a transmission control computer (ECU_T) responsible for managing said hybrid transmission system (eTR).

6. Electric hybrid vehicle having a powertrain (eGMP) comprising an internal combustion engine (MT) and a hybrid transmission system (eTR), said hybrid transmission system (eTR) having a rotating electric machine (ME) coupled to said internal combustion engine (MT) via a first clutch device (KO) and a gearbox (DCT) coupled to said rotating electric machine (ME) via a second clutch device (K12), characterized in that it comprises a computer (ECU_T) according to claim 4 or 5.

7. Electric hybrid vehicle according to claim 6, characterized in that said gearbox of said hybrid transmission system (eTR) is a dual clutch gearbox (DCT) incorporating said second clutch device (K12).

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