METHOD FOR DETERMINING A TAKEOFF ENGINE SPEED FOR IMPROVING ACOUSTIC AND VIBRATIONAL PERFORMANCE IN VEHICLES

Abstract

The process determines a takeoff engine speed setpoint (RC) which is intended to be supplied to the internal combustion engine of a vehicle equipped with an automatic type gearbox during takeoff, the takeoff engine speed setpoint being determined prior to its recording in memory (E3) in a computer of the vehicle.According to the invention, the method comprises an estimation (E1) of a maximum engine torque (CMmax) that the internal combustion engine must deliver during takeoff in various vehicle operating conditions, and a determination (E2) of the takeoff engine speed setpoint from the maximum engine torque and a curve (CRC) giving permissible engine speed values ​​as a function of the engine torque delivered by the internal combustion engine, the permissible engine speed values ​​having been calculated beforehand so as to exclude engine speeds likely to cause amplification of the internal combustion engine's vibrational excitations in the vehicle. Fig. 4.

Description

Title of the invention: METHOD FOR DETERMINING A TAKE-OFF ENGINE SPEED FOR IMPROVING ACOUSTIC AND VIBRATION PERFORMANCE IN VEHICLES

[0001] The invention generally relates to reducing the vibration and acoustic level in the passenger compartment of a vehicle when it takes off, with a view to improving the comfort and driving pleasure of the vehicle. By "takeoff" is meant a life situation in which the vehicle starts moving to go from a zero speed to a non-zero speed. More particularly, the invention relates to a method for determining a takeoff engine speed setpoint which is supplied to the thermal engine of a vehicle when it takes off, with a view to improving the acoustic and vibration performance in the passenger compartment of the vehicle.

[0002] Generally speaking, the invention is applicable in vehicles equipped with an automatic gearbox. The terminology “automatic gearbox” must here be interpreted broadly and covers in particular piloted or robotized manual gearboxes, dual-clutch gearboxes and torque converter gearboxes, but not exclusively. The gearboxes may be associated with different types of coupling member, typically a dry clutch in a piloted manual gearbox and a dry or wet clutch in a dual-clutch gearbox.

[0003] With powertrains equipped with an automatic gearbox, the take-off procedure is initiated when the vehicle is stationary with the combustion engine running, the gearbox lever is in the forward position, called "Drive" or "D", the brake pedal is released and the coupling member, typically a dry or wet clutch, is open. The take-off procedure begins by bringing the combustion engine speed to a target take-off engine speed that has been predefined. Once the target take-off engine speed is reached, with the first gear of the gearbox engaged, the coupling member begins to close and transmit torque from the combustion engine to the gearbox and to the wheel. The coupling member slips until the vehicle speed reaches a certain speed determined on the first gear of the gearbox, and then closes.The take-off procedure is then stopped and the engine speed moves from the target take-off engine speed to a speed value corresponding to the driver's depressing of the accelerator pedal and the gearbox ratio changing according to the depressing of the accelerator pedal.

[0004] The target take-off engine speed is set to a single value, this same value being used to carry out the various take-offs of the vehicle. The target take-off engine speed is recorded once and for all in the engine control computer during its calibration. The target take-off engine speed is defined according to the engine torque available at this engine speed, as well as the noise level and fuel consumption of the engine at this speed. It is necessary to have a sufficiently high engine torque to ensure the various types of take-offs, according to the different depressions of the accelerator pedal by the driver. It is also necessary during take-off to limit fuel consumption and maintain an acceptable noise level in the passenger compartment, fuel consumption and noise level which increase with the engine speed.

[0005] The curves shown in [Fig.l] represent, as an illustration for a medium power thermal engine, the evolution of the engine torque as a function of time for different engine speeds. As visible in these curves, the torque supplied by the thermal engine at idle speed (of the order of 750 rpm) is less than 80 Nm, while that available at 2000 rpm is greater than 150 Nm.

[0006] The thermal engine must be brought to a high speed to have torque available quickly and to be able to ensure take-off for all vehicle life situations, while the desired reductions in fuel consumption and noise require the lowest possible engine speed, ideally close to idle. Thus, the target take-off engine speed is set at a compromise value which is usually around 1600 rpm.

[0007] As illustrated in [Fig.2], the powertrain 1 is mounted on elastic suspension shims 2 in the vehicle. Normally, the frequency excitation of the heat engine is filtered by the elastic suspension shims before being transmitted to the vehicle structure. However, depending on the preload level of the shims, vibrations may be transmitted into the vehicle structure and be highly perceptible to the driver and passengers.

[0008] The preload level on the shims of the powertrain is a function of the torque at the wheel which itself depends on the slope and / or the mass on board the vehicle. The mechanical stresses applied to the shims induce a modification of their stiffness. This modification of stiffness causes natural resonance modes of the powertrain to rise on the shims which can approach or cross the frequency excitation of the heat engine, such as the harmonic H1.5 for a three-cylinder engine, or even H1 if the engine is poorly balanced, and the harmonic H2 for four-cylinder engines. When the natural vibration mode of the powertrain on its shims corresponding to the main excitation frequency of the heat engine has a frequency sufficiently close to that of the harmonic of the heat engine, there is then a phenomenon of amplification of the excitation of the main harmonic of the engine by the natural mode of resonance of the powertrain on its blocks. Such a vibration phenomenon propagates in the structure of the vehicle. It can occur in different life situations of the vehicle, but its effects are more critical during takeoff because this is the life situation presenting the strongest torques at relatively low engine speeds. In a vehicle equipped with a manual gearbox, when this vibration phenomenon appears during takeoff, the driver naturally corrects it by operating the clutch pedal and the accelerator pedal of the vehicle.On the other hand, in state-of-the-art vehicles equipped with an automatic gearbox, such a vibration phenomenon can occur during the take-off procedure and degrade the acoustic and vibration performance in the vehicle's passenger compartment.

[0009] Document FR2879526A1 discloses a method for assisting the take-off of a motor vehicle in which an engine speed setpoint is first calculated from a parameter capable of detecting the driver's wishes. A take-off assistance torque is then calculated from the engine speed setpoint to take into account an inertial torque necessary for the acceleration of the rotating parts of the powertrain and is used when the vehicle takes off.

[0010] It is desirable to provide a solution to the aforementioned drawbacks of the state of the art by proposing a method for determining the speed setpoint to be supplied to the vehicle's thermal engine during take-off, with a view to improving the acoustic and vibration performance.

[0011] According to a first aspect, the invention relates to a method for determining a take-off engine speed setpoint which is intended to be supplied to the thermal engine of a vehicle equipped with an automatic gearbox during take-off thereof, the take-off engine speed setpoint being determined prior to its recording in memory in a computer of the vehicle.According to the invention, the method comprises an estimation of a maximum engine torque that the thermal engine must deliver during take-off in different life situations of the vehicle, and a determination of the take-off engine speed setpoint from the maximum engine torque and a curve giving authorized engine speed values ​​as a function of the engine torque delivered by the thermal engine, the authorized engine speed values ​​having been calculated beforehand so as to exclude engine speeds likely to cause an amplification of the vibration excitations of the thermal engine in the vehicle.

[0012] According to a particular characteristic, the maximum engine torque is estimated from an engine torque necessary to take off the vehicle when it is at its total authorized laden weight.

[0013] According to another particular characteristic, the maximum engine torque is estimated from the engine torque necessary to take off the vehicle when it is at its total authorized laden weight and on a slope of ten percent (10%).

[0014] According to another aspect, the invention also relates to a computer in a vehicle equipped with an automatic gearbox, this computer comprising a memory in which is recorded a take-off engine speed setpoint determined by the implementation of the method briefly described above.

[0015] According to a particular characteristic, the calculator is a vehicle engine control calculator.

[0016] The invention also relates to a vehicle comprising a computer as indicated above.

[0017] 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:

[0018] [Fig. 1] [Fig. 1] is a curve showing the evolution of the engine torque as a function of time, for several thermal engine speeds.

[0019] [Fig.2] [Fig.2] is a perspective view showing a powertrain mounted on its elastic suspension shims.

[0020] [Fig.3] [Fig.3] is a block diagram of a vehicle powertrain and an engine control computer in which a take-off engine speed setpoint determined by implementing the method according to the invention is recorded in memory.

[0021] [Fig.4] [Fig.4] shows different steps included in the method according to the invention.

[0022] [Fig.5] [Fig.5] shows a curve of the highest resonant frequencies of the natural modes of the powertrain on its elastic suspension shims as a function of the wheel torque.

[0023] [Fig.6] [Fig.6] shows a curve of forbidden frequencies and a curve of limit frequencies as a function of the wheel torque.

[0024] [Fig.7] [Fig.7] shows a curve of forbidden frequencies and a curve of limit frequencies as a function of the engine torque.

[0025] [Fig.8] [Fig.8] shows a curve of prohibited engine speeds and a curve of limit engine speeds as a function of engine torque.

[0026] With reference to [Fig. 3], a vehicle comprising a GMP powertrain is considered. The GMP powertrain comprises a thermal engine MT and an automatic gearbox BV. A coupling member OC, for example a dry clutch, ensures the function of transmitting the engine torque, supplied by the thermal engine MT, to the gearbox BV.

[0027] In the vehicle, an engine control computer CTRL controls the powertrain GMP by applying control strategies capable of responding to the different life situations of the vehicle. The engine control computer CTRL implements the control strategies according to the actions of the driver on different control members of the vehicle, such as the accelerator pedal and the gearbox lever, and information from different sensors. The information from sensors and other members, necessary for the control strategies, is read by the engine control computer CTRL typically on the vehicle's data communication network, for example of the "CAN" bus type.

[0028] The vehicle take-off procedure is managed by a DEC software module which is hosted and executed in a computer. It is considered here that this DEC software module is hosted in the CTRL engine control computer. The DEC software module is implemented in a MEM memory of the CTRL engine control computer. The take-off procedure is managed by the DEC software module by the execution of program code instructions in a processor (not shown) of the CTRL engine control computer.

[0029] The DEC software module uses an engine speed setpoint RC which must be applied during takeoff of the vehicle. This engine speed setpoint RC, also called hereinafter “target takeoff engine speed RC”, has been previously determined in accordance with the method of the invention and stored in the engine control computer CTRL, typically during the calibration thereof. The engine control computer CTRL adjusts various PAR control parameters of the thermal engine MT to obtain this desired target takeoff engine speed RC during takeoff.

[0030] With reference now more particularly to Figs. 4 to 8, the method according to the invention implemented to determine the target take-off engine speed RC which is stored in the engine control computer CTRL is described in detail above.

[0031] The natural resonance frequencies of the GMP powertrain on its shims are linked to the stiffness of the shims. The stiffness of the shims varies with the level of mechanical stress applied to them. The mechanical stress applied to the shims is dependent on the engine torque, referred to as CM hereinafter, delivered by the MT thermal engine. The natural resonance frequencies of the GMP powertrain on its shims therefore depend on the engine torque CM.

[0032] In accordance with the method of the invention, a curve, designated CRC hereinafter, is established which makes it possible to determine authorized engine speed values ​​as a function of the engine torque CM delivered by the thermal engine, for a vehicle considered. These permissible engine speed values ​​are values ​​that will generate frequency excitation beyond the natural resonance frequencies of the GMP powertrain on its shims. The CRC curve thus provides filtering of critical speeds that would produce vibrations in the vehicle structure.

[0033] [Fig.4] shows the main steps E1 to E3 and S1 to S4 included in the method according to the invention.

[0034] In step E1, the maximum engine torque CMmax that can be achieved during takeoff in the various life situations of the vehicle is determined. For example, it is the engine torque necessary to take off the vehicle at its maximum authorized load, or in other words, at its total authorized laden weight, and on a slope of 10% which will be retained as being the maximum engine torque CMmax.

[0035] In step E2, the target take-off engine speed RC corresponding to the maximum engine torque CMmax determined in step El is read on the CRC curve.

[0036] In step E3, the target takeoff engine speed RC determined in step E2 is recorded in memory in the computer of the vehicle managing the takeoff procedure. Typically, this computer is the engine control computer (CTRL in [Fig. 3]) of the vehicle and the target takeoff engine speed RC is recorded during the calibration thereof.

[0037] Steps S1 to S4 shown in [Fig.4] relate to the ME method used in accordance with the method of the invention to determine the CRC curve. This ME method is detailed below with reference also to Figs.5 to 8.

[0038] In step SI, as visible in [Fig.5] for the example of a powertrain with a three-cylinder thermal engine, a CFR curve is determined giving the highest resonance frequency FR of the resonance natural modes of the powertrain on its shims as a function of the torque at the wheel CR.

[0039] In step S2, as seen in [Fig.6] with the same example as in [Fig.5], a forbidden frequency curve CF1 and a limit frequency curve CFL are calculated. The forbidden frequency curve CF1 gives a forbidden frequency FI as a function of the torque at the wheel CR. The limit frequency curve CFL gives a limit frequency FL as a function of the torque at the wheel CR.

[0040] The forbidden frequency curve CF1 is obtained directly from the curve C FR calculated in step SI by adding to the frequencies FR of the curve CFR a margin MG between +2 Hz and +5 Hz. Thus, the forbidden frequencies FI of the curve CF1 are given by the equality: FI=MG.FR.

[0041] The MG margin is a function of the excited mode. The MP margin is a minimum margin to be placed between the frequency excitation of the thermal engine and the highest resonant frequency FR of the powertrain on its blocks to avoid an amplification of the excitation frequency of the main harmonic of the engine. thermal by the natural resonance mode of the powertrain on its shims.

[0042] The CFL limit frequency curve is obtained by applying a maximum function MAX between the CF1 curve and the CFR curve weighted by a coefficient Racine (2), i.e. Racine (2) = 1.414 in rounded value. Thus, the limit frequencies FL of the CFL curve are given by the equality: FL=MAX (FI; 1.414.FR), the MAX function determining the limit frequency FL as being the highest frequency between FI and 1.414.FR.

[0043] In step S3, as seen in [Fig.7] with the same example as in Figs.5 and 6, a forbidden frequency curve CF12 and a limit frequency curve CFL2 are calculated giving a forbidden frequency FI2 and a limit frequency FL2, respectively, as a function of the engine torque CM. The curves CF12 and CFL2 are obtained from the curves CF1 and CFL by calculating the engine torque CM corresponding to the torque at the wheel CR when the coupling member OC is closed.

[0044] The engine torque CM is obtained by dividing the wheel torque CR by the gear ratio RD of the gearbox and adding the inertia torque CI, i.e. CM=(CR / RD)+CI. The inertia torque CI is obtained by the product of the inertia of the gearbox shaft lines and the angular acceleration of the rotating parts.

[0045] In step S4, as seen in [Fig.8] with the same example as in Figs.5 to 7, a curve of prohibited engine speeds Crmi and a curve of limit engine speeds CRML are calculated giving a prohibited engine speed RMI and a limit engine speed RML, respectively, as a function of the engine torque CM. The curves Cj^ and C RML are obtained from the curves CF12 and CFL2 by calculating the prohibited engine speed RMI and the limit engine speed RML corresponding to the prohibited frequency FI2 and the limit frequency FL2, respectively.

[0046] The engine speeds RMI and RML are deduced from the frequencies FI2 and FL2, respectively, using the following equality: RM=F.60 / HP, in which RM is the engine speed in revolutions per minute, F is the frequency and HP is the main harmonic of the heat engine. The main harmonic of the four-stroke heat engine is determined essentially by the number of cylinders thereof. Thus, the main harmonic HP of a four-stroke heat engine is:

[0047] - H 1.5 for a three-cylinder engine (H1 for a non-three-cylinder engine balance),

[0048] - H2 for a four-cylinder engine,

[0049] - H3 for a six-cylinder engine,

[0050] -etc...

[0051] In the case of the example considered here of a three-cylinder thermal engine, considering that this engine is balanced, the equality RM=F.60 / l.5 is used for calculate the RMI and RML engine speeds.

[0052] Either of the Crm and CRML curves may be used by the method of the invention as the CRC curve. The choice will depend on the powertrain control strategy. Thus, for example, if reductions in fuel consumption and noise are preferred, the Cr^ curve may be chosen for the CRC curve. Otherwise, the CRML curve may be chosen for the C RC curve and will offer a stronger guarantee against the occurrence of the vibration phenomenon described above.

[0053] 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 take-off of a vehicle equipped with an automatic gearbox (BV) comprising a supply to a computer (CTRL) of said vehicle of a take-off engine speed setpoint (RC) to a thermal engine (MT) of said vehicle, said take-off engine speed setpoint (RC) being determined from an estimate (El) of a maximum engine torque (CMmax) delivered by said thermal engine (MT) during a take-off in different life situations of said vehicle and from a curve (CRC) giving authorized engine speed values ​​as a function of the engine torque (CM) delivered by said thermal engine (MT), characterized in that said maximum engine torque (CMmax) is estimated from the engine torque necessary to take off said vehicle when it is at its total authorized laden weight and on a slope of ten percent (10%).

2. Calculator (CTRL) in a vehicle equipped with an automatic gearbox (BV), characterized in that it comprises a memory (MEM) in which a take-off engine speed setpoint (RC) is recorded for implementing the method according to claim i

3. 1. Calculator according to claim 2, characterized in that said calculator is an engine control calculator (CTRL) of said vehicle.

4. Vehicle comprising a computer (CTRL) according to claim 2 or 3.

Images