Method for dynamically controlling four-wheel-drive motor vehicle wheelsets, control means, vehicle and program based on such a method

Abstract

The invention relates to a method for controlling the wheelsets (12, 17) of a powertrain in a four-wheel-drive motor vehicle, the method comprising the following steps: determining: – a driver torque setpoint; – a distribution ratio for the torque setpoint between the wheelsets (12, 17); – a derivative of the distribution ratio; – whether the motor vehicle is in sled mode; – derivatives of torque gradients to be applied to the wheelsets (12, 17) depending on whether the vehicle is in sled mode or not; filtering the torque gradient derivatives to avoid oscillations in the wheelsets (12, 17); and controlling the torques applied to the wheelsets (12, 17) according to the filtered torque gradient derivatives. The invention also relates to a program, a control means and a vehicle based on such a method.

Description

[0001] DESCRIPTION TITLE OF THE INVENTION: METHOD FOR DYNAMIC CONTROL OF FOUR-WHEEL DRIVE MOTOR VEHICLE AXLES, CONTROL MEANS, VEHICLE AND PROGRAM BASED ON SUCH A METHOD

[0001] The present invention claims priority from French application No. 2308946 filed on 08 / 25 / 2023, the content of which (text, drawings and claims) is incorporated herein by reference.

[0002] The invention relates to the field of electric vehicles and hybrid vehicles, with four-wheel drive, having a front axle and a rear axle. The invention relates in particular to the dynamic control of the front and rear axles in various cases of use of these vehicles, in particular in "sled mode". "Sled mode" is defined for such a vehicle in that the front axle produces a positive torque in the direction of travel so as to move the vehicle forward, while the rear axle produces a negative torque in the opposite direction to the positive torque causing the vehicle to move backward, but the negative torque having a value lower than that of the positive torque, the vehicle moves forward.

[0003] The preventive comfort filter function is a function that filters the raw driver torque setpoint in order to significantly reduce oscillations of the powertrain when passing through mechanical clearances. It therefore has a preventive correction action on the oscillations generated by this passage of mechanical clearances. This therefore significantly improves the longitudinal comfort of the vehicle and also typifies its longitudinal dynamics.

[0004] On a 4x4 type vehicle, the choice of architecture for the preventive approval filter function is very important since the location of the application of the distribution calculated by the operating points function can simplify or complicate the calculations of the preventive approval filter.

[0005] In the case of the continuous approval filter described in patent application FR2202362, the distribution is applied downstream of a global powertrain filter. In this case, the synchronization of the passage of games as well as the dynamics of the torques is perfectly controlled.

[0006] However, in the case of choosing a preventive pleasure filter with an application of the distribution which is done upstream of the filter, some questions concerning the control of the torque dynamics on a variable distribution, may arise. For this reason, the applicant filed a patent application FR2304176 concerning the antagonistic control of the torque dynamics of the vehicle's axles on a variable distribution in order to have a single torque dynamics while the vehicle has two axles. This makes it possible to achieve a variable distribution without the driver feeling the slightest loss of pleasure and performance. Figure 2 shows a preventive pleasure filter solution with a distribution and antagonistic distribution control of the aforementioned patent application FR2304176. The torque of the powertrain, a distribution ratio ^ ^^^^ and its derivative ^ ^^̇^^allow to determine a torque setpoint gradient before ^ ^ ^ ^ ^̇^^ and a rear torque setpoint gradient ^ ^ ^ ^ ^̇^^ . The IVC reference in Figure 2 relates to an overall torque command corresponding to the driver's acceleration.

[0007] These gradients are filtered by respective positive approval filters FAV, FAR to obtain filtered instructions. BT designates the activation or not of the sled mode.

[0008] The method according to the invention begins by detecting the sled mode on the 4x4 vehicle, that is to say that the front axle generates a positive torque in the direction of travel while the rear axle produces a lower negative torque forward so that the vehicle continues to move forward. This allows the rear axle to recharge the battery while driving.

[0009] However, the torque dynamics between the front and rear axles are very rarely the same. This different torque dynamic is felt from a user perspective in that the vehicle may accelerate or slow down unintentionally.

[0010] The applicant filed the aforementioned patent application FR2304176 concerning the antagonistic distribution control, however this invention can only be applied over a positive torque range. However, in sled mode, by definition, the front axle torque is positive and the rear axle torque is negative.

[0011] In this case, the equations defined in patent application FR2304176 concerning antagonistic distribution control are no longer valid and the invention proposes to add this specific case. Indeed, as the distribution factor is defined between 0 and 1, when there is a positive front axle torque and a negative rear axle torque, there is in this case a distribution greater than 1 which calls into question our equations.

[0012] Figure 3 illustrates the problem that can be encountered on a 4x4 vehicle if the torque dynamics of each axle are not controlled when sled mode is activated.

[0013] The equations which define the antagonistic distribution control (co-pending application FR2304176 referred to above) are as follows: C ^^^^ is the powertrain setpoint; C ^ ^^ ^ ̇^^is the torque gradient to be applied to the front axle; is the torque gradient to be applied to the rear axle; ^ ^^^^ is the distribution ratio defined as follows with Te a so-called sampling time):

[0014] The sampling time is the computation time of the C function ^ ^^ ^ ̇^^ ou depending on the case. For example, a time Te of 10ms means that every 10ms the function is calculated and therefore the value is updated.

[0015] We note that the antagonistic distribution control which is defined by the equations above is not valid in this case of sled mode.

[0016] Indeed, the distribution ratio is bounded between 0 and 1 and this is to robustify the antagonistic distribution control since otherwise the torque gradient would be greater than what the front axle actually does. However, in the case of sled mode the distribution ratio is greater than 1. Thus, the equation is not valid in this specific case since the torque gradients and therefore the torque balance will be erroneous.

[0017] This is what is highlighted in the graphs in Figure 3. The torque gradient of the rear axle is 0 Nm / s. As the distribution ratio is limited to 1 while the torque gradient of the front axle is not limited. Here we can clearly see the problem generated by the limitation of the distribution ratio.

[0018] An objective of the present invention is to remedy the defects of the prior art, and in particular to propose a solution for antagonistic control of a four-wheel drive electric or hybrid vehicle, in particular in sled mode, that is to say when the front axle produces a positive torque in the direction of travel while the rear axle produces a lower negative torque forward so that the vehicle continues to move forward.

[0019] To achieve this objective, the invention proposes a method for controlling a front wheel set and a rear wheel set of a powertrain of a motor vehicle having four-wheel drive comprising the following steps: – determining a torque setpoint from the driver; – determining a distribution ratio of the driver's torque setpoint between the front wheel set and the rear wheel set; the method being characterized in that it comprises the following steps: – determining a derivative of the distribution ratio; - determining whether the motor vehicle is in sled mode;– determining a torque gradient to be applied to the front wheel set and a torque gradient to be applied to the rear wheel set, the torque gradient to be applied to the front wheel set and the torque gradient to be applied to the rear wheel set being a function of the driver's torque setpoint, the distribution ratio and the derivative of the distribution ratio determined in the case where the motor vehicle is in sled mode; and in the opposite case, the torque gradient to be applied to the rear wheel set is rather a function of the torque gradient to be applied to the front wheel set; – filtering the torque gradient to be applied to the front wheel set and the torque gradient to be applied to the rear wheel set to avoid oscillations on said front and rear wheel sets;– control a torque applied to the front wheel set according to the torque gradient to be applied to the filtered front wheel set and a torque applied to the rear wheel set according to the torque gradient to be applied to the filtered rear wheel set.;

[0020] Advantageously, the invention makes the realization of the driver torque request robust even in sled mode. It makes it possible to secure the entire torque dynamics of each train when there is a change in distribution, an activation of the sled mode, and therefore the stability of the vehicle.

[0021] In addition, the invention contributes to improving the vehicle's longitudinal ride quality. It improves the energy efficiency of the powertrain since the sled mode allows the battery to be recharged using the rear axle while driving without the driver noticing it.

[0022] According to a variant, the torque gradient to be applied to the front wheel set is determined using the formula: C ^^^^ is the powertrain setpoint; C ^ ^^ ^ ̇^^ is the torque gradient to be applied to the front axle; C ^ ^^ ^ ̇^^ is the torque gradient to be applied to the rear axle; ^ ^^^^ is a distribution ratio defined as follows: Te is a calculation time of the function C ^ ^^ ^ ̇^^ .

[0023] This allows you to obtain a precise value of the torque gradient to be applied to the front axle.

[0024] Alternatively, if the vehicle is not in sled mode, then the torque gradient to be applied to the rear wheel set is determined using the formula: where C ^^^^ is the powertrain setpoint; C ^ ^^ ^ ̇^^is the torque gradient to be applied to the front axle; C ^ ^^ ^ ̇^^ is the torque gradient to be applied to the rear axle; ^ ^^^^ is a distribution ratio defined as follows: Te is a calculation time of the function C ^ ^^ ^ ̇^^ .

[0025] This allows to obtain a precise value of the torque gradient to be applied to the rear axle in the specific case where the vehicle is not in sled mode.

[0026] Alternatively, if the vehicle is in sled mode, then the torque gradient to be applied to the rear wheel set is determined using the formula: where C ^ ^^ ^ ̇^^ is the torque gradient to be applied to the front axle; and C ^ ^^ ^ ̇^^ is the torque gradient to be applied to the rear axle.

[0027] This allows to obtain a precise value of the torque gradient to be applied to the rear axle in the specific case where the vehicle is in sled mode.

[0028] According to a variant, the step of filtering the torque gradient to be applied to the front wheel set and the torque gradient to be applied to the rear wheel set is carried out respectively by means of a first filtering means and a second filtering means.

[0029] This allows the driver torque setpoint to be filtered to best limit oscillations of the drive train caused by crossing mechanical clearances.

[0030] Alternatively, the steps are implemented by a control means.

[0031] This allows control to be carried out by the control means which is part of the powertrain.

[0032] The invention further relates to a control means implementing the control method according to the invention.

[0033] Another subject of the invention relates to a motor vehicle implementing the control method according to the invention.

[0034] The invention further relates to a computer program comprising program code instructions for executing the steps of the control method according to the invention, when said program operates on a computer.

[0035] The invention will be further detailed by the description of non-limiting embodiments, and on the basis of the appended figures illustrating variants of the invention, in which: - [Fig. 1] schematically illustrates a powertrain of a four-wheel drive motor vehicle, suitable for implementing the method according to the prior art and the method according to the invention; - [Fig. 2] schematically illustrates a distribution of torque setpoints suitable for implementing the method according to the prior art and the method according to the invention; - [Fig. 3] schematically illustrates changes over time of antagonistic control parameters of the front and rear axles in the context of a method according to the prior art; and - [Fig. 4] schematically illustrates changes over time of antagonistic control parameters of the front and rear axles in the context of a method according to the invention.

[0036] The applicant designed a sled mode case detection with the aim of activating a specific strategy for antagonistic control in sled mode.

[0037] In particular, it is planned to add to the antagonistic control strategy of the co-pending patent application FR2304176, a strategy that makes it possible to detect the sled mode. This makes it possible to control the torque dynamics of each train in this specific case; and to respect the torque balance and thus realize the driver torque request and the request for recharging the battery by the rear train.

[0038] A vehicle suitable for the invention is illustrated in Figure 1. It comprises: - control means 11 comprising for example at least one processor and at least one memory storing software instructions for implementing the method according to the invention; - a hybrid type powertrain 10, comprising a front wheel set 12 comprising a heat engine 13 and a first electric traction motor 14; and a rear wheel set 17 provided with a second electric traction motor 18 associated with a speed reducer 19 and a device 20 for coupling and decoupling the second electric traction motor 18 with the rear wheels of the powertrain 10;- a coupling and decoupling device 15 making it possible to selectively couple and decouple the thermal engine 13 and / or the first electric traction motor 14 with the front wheel set 12, the coupling and decoupling device 15 taking the form of a gearbox in order to be able to isolate the first electric traction motor 14 from the thermal engine 13 during a pure electric driving mode, a clutch 16 being interposed between the thermal engine 13 and the first electric traction motor 14.;

[0039] The coupling and decoupling device 20 may consist of a dog clutch device, a clutch or a gearbox.

[0040] In the context of the invention, firstly it is detected that the powertrain 10 is in sled mode. The sign of the torque of the front axle and the rear axle is observed while checking whether the rear axle is declared below the clearances.

[0041] The reference B generally designates a state. The determination of the sign can be done by the following formulas: B ^^^_^^^^^^^ = sign ^C ^^^^_^^^ ^ ; B ^^^_^é^^^^^ = sign ^C ^^^^_^^^ ^ ; If sign ^C ^^^^^^^ ^ = "+" then B ^^^_^^^^^^^ = otherwise B ^^^_^^^^^^^ = 0 ; If sign ^C ^^^^^^^ ^ = "+" then B ^^^_^é^^^^^ = 1, otherwise B ^^^_^é^^^^^ = 0, where B ^^^_^^^^^^^ denotes a positive state of the front axle; B ^^^_^é^^^^^ denotes a negative state of the rear axle; B ^^^_^^^^^^^^ denotes a sled mode state; and B ^^^^_^^^_^^^^ denotes a state under the games.

[0042] Once the sled mode is detected, the specific torque dynamic control strategy of each train is applied.

[0043] The front axle maintains its torque dynamics since the distribution ratio is saturated at 1 in sled mode. On the rear axle, we also take this torque dynamics value from the front axle where we apply the "-" sign to obtain an antagonistic torque dynamics, and thus make it transparent for the user (no degradation of performance and pleasure).

[0044] When then sled mode detected.

[0045] SO So the distribution rate for sled mode is 1.

[0046] The formula can be used as an equation for the front axle torque dynamics in sled mode (because the front axle has a positive torque range).

[0047] The formula cannot be used as an equation for the torque dynamics of the rear axle in sled mode since a negative torque is required.

[0048] So, in case of sled mode ^^^^_^^^^^^^^= 1, the torque dynamics of the rear axle is: C ^^^ ^ ^^ ^ ̇^^ = −(C^^ ̇ ^ )

[0049] With the addition of this latter formula to the antagonistic distribution control strategy, the process is robust and suitable for all powertrain life situations.

[0050] From the graphs in Figure 4, we can see that this strategy for antagonistic torque control during sled mode solves the problem mentioned above well.

[0051] The maximum and minimum gradients of the powertrain are determined from calibratable tables (the same maps as for the antagonistic distribution control strategy). This allows to always calibrate on the dynamics of the slowest axis so that the antagonistic dynamics are the same and the driver does not perceive it while driving.

[0052] Vehicle speed variations and even user discomfort are no longer present.

[0053] The process of calculating the antagonistic distribution control with the integration of the addition for the sled mode is carried out according to the scheme in Figure 2.

Claims

CLAIMS 1. Method for controlling a front wheel set (12) and a rear wheel set (17) of a powertrain of a motor vehicle having four-wheel drive comprising the following steps: – determining a torque setpoint from the driver; – determining a distribution ratio of the driver's torque setpoint between the front wheel set (12) and the rear wheel set (17); the method being characterized in that it comprises the following steps: – determining a derivative of the distribution ratio; – determining whether the motor vehicle is in sled mode; – determining a torque gradient to be applied to the front wheel set (12) and a torque gradient to be applied to the rear wheel set (17); – filtering the torque gradient to be applied to the front wheel set (12) and the torque gradient to be applied to the rear wheel set (17) to avoid oscillations on said front (12) and rear (17) wheel sets;– controlling a torque applied to the front wheel set (12) as a function of the torque gradient to be applied to the filtered front wheel set (12) and a torque applied to the rear wheel set (17) as a function of the torque gradient to be applied to the filtered rear wheel set (17), characterized in that the torque gradient to be applied to the front wheel set (12) is determined by means of the formula:; where C ^^^^ is the powertrain setpoint; C ^ ^^ ^ ̇^^ is the torque gradient to be applied to the front axle; C ^ ^^ ^ ̇^^ is the torque gradient to be applied to the rear axle; ^ ^^^^ is a distribution ratio defined as follows: Te is a calculation time of the function C ^ ^^ ^ ̇^^ , in that if the vehicle is not in sled mode, then the torque gradient to be applied to the rear wheel set (17) is determined by means of the formula: where Te is also a calculation time of the function C ^ ^^ ^ ̇^^ , and in that if the vehicle is in sled mode, then the torque gradient to be applied to the rear wheel set (17) is determined by means of the formula: C ^ ^ ^^ ^ ̇^^ = −(C ^^ ^ ^ ̇ ^ ) .

2. Control method according to claim 1, characterized in that the step of filtering the torque gradient to be applied to the front wheel set (12) and the torque gradient to be applied to the rear wheel set (17) is carried out respectively by means of a first filtering means (F AV ), and a second filtering means (F AR).

3. Control method according to any one of claims 1 to 2, characterized in that the steps are implemented by a control means (11).

4. Control means (11) implementing the control method according to claim 3.

5. Motor vehicle implementing the control method according to any one of claims 1 to 3.

6. Computer program comprising program code instructions for executing the steps of the control method according to any one of claims 1 to 3, when said program operates on a computer.

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