Device for controlling the steering of a vehicle

Abstract

A device for controlling the steering (10) of a motor vehicle comprises at least one steered actuator (4) associated with a system for steering the wheels of the vehicle and / or steered actuators (6) associated with an isolated braking system at the wheels of the vehicle, the control device comprising at least one control unit (12) configured to retrieve at least one value characteristic of the movement of the vehicle and to issue control commands (13) to the at least one steered actuator (4, 6) according to said retrieved value. According to the invention, the control unit (12) comprises a calculation module (14) in which a model of the lateral dynamic behavior of the vehicle frame (16) is implemented, and at least one specific physical quantity of the lateral dynamic behavior is calculated based on a specific drift (δ) of each set of front and rear wheels of the vehicle. s1 ,δ s2 ) is expressed according to

Description

[Technical Field]

[0001] The present invention relates to a device for controlling the steering of a motor vehicle, in particular to a control device implemented with a dynamic behavior model, which makes it possible, on the one hand, to adjust the drive of the vehicle before the vehicle starts to move, and, on the other hand, to control the steering when the vehicle is moving. [Background technology]

[0002] The majority of vehicles are currently fitted with controlled chassis, i.e. chassis having at least one controlled actuator. By way of non-limiting example, a vehicle may be fitted with assisted steering, configured to adapt the steering angle of the wheels to the vehicle's driving conditions, or with separated braking systems, in which each wheel is associated with an independently controlled braking system so that a braking force specific to each wheel can be generated.

[0003] These controlled actuators are generally controlled by a control unit of the vehicle using a vehicle model that represents a target behavior that the actual vehicle must follow. During development testing of the vehicle, the vehicle model is adjusted by trial and error until it represents the behavior desired by those responsible for developing the chassis. When the vehicle is running, the control unit references this vehicle model, adjusted by trial and error, to control the operation of the controlled actuators.

[0004] The lateral dynamics models conventionally used to model the behavior of a vehicle chassis are built around a model known as the bicycle model, which is well known to development engineers and is based on equations for yaw dynamics and equations for chassis drift dynamics.

[0005] In this bicycle model, the behavior is adjusted via the parameters of the modeled vehicle, these parameters being the front weight, rear weight, equivalent cornering stiffness of the axle set, or yaw inertia.

[0006] It may be noted that the parameters considered in this model are static parameters that are not directly connected to the dynamic behavior of the vehicle whose trajectory is to be controlled. Summary of the Invention

[0007] In this context, the present invention proposes an alternative to existing control devices, in particular by taking into account parameters other than those conventionally used and by using different models, for example, for the single bicycle model mentioned above. The present invention therefore proposes a steering control device for a motor vehicle, comprising at least one controlled actuator associated with the steering system of the wheels of the vehicle and / or controlled actuators associated with separate braking systems at the wheels of the vehicle, said control device comprising at least one control unit adapted to obtain at least one value characteristic of the vehicle's travel and to send a command to the at least one controlled actuator as a function of this obtained value or of these obtained values. According to the present invention, the control unit comprises a calculation module implementing a vehicle chassis lateral dynamic behavior model, wherein at least one specific physical variable of the lateral dynamic behavior is expressed as a function of specific derivatives of each front and rear wheel set of the vehicle.

[0008] A separated braking system fitted to a vehicle equipped with a steering control device according to the invention activates differential braking of each wheel of the vehicle, one wheel at a time where appropriate, through specific control of controlled actuators.

[0009] In this case, the chassis behavior model is special in that it takes into account the specific drift of each wheel set of the vehicle, as compared to what was previously possible, so as to take into account the lateral dynamic behavior of the car and its chassis. The behavior model is therefore expressed in a much more effective way for chassis development by generating a specific drift concept.

[0010] This is because the specific drift of an axle set, compared to merely the kinematic drift, takes into account the parameters on which the drift angle is based, namely the tire cornering stiffness, the axle set rotation induced by lateral forces, and the axle set steering (toe-in or toe-out) induced by steering (toe-in or toe-out). Since the specific drift is determined as a function of the latter, it also takes into account the normal load. This makes it possible to generalize the equivalent cornering stiffness under a given normal load.

[0011] It has been found that this lateral dynamic behavior is primarily induced by several physical variables, including the vehicle wheelbase, the vehicle weight distribution, i.e., the ratio of the weight at the front axle set to the overall weight, the inertia distribution, i.e., the ratio of the equivalent inertia of the point weight as seen at the axle set to the yaw inertia, and the specific drift of the drivetrain, i.e., the angle of drift of the axle set under lateral acceleration.

[0012] The inventors have identified the fundamental role played by the specific drifts of the axle sets in the lateral dynamic behavior of the vehicle, noting that they characterize the performance of the drivetrain in terms of guidance, which directly affects the speed of response and the lateral stability of the vehicle. As the vehicle follows a trajectory at a given speed, the development of these specific drifts is measured by evaluating the vehicle's understeering gradient, which in particular takes into account the additional steering wheel angle to be added. Each specific drift implicitly takes into account the weight of the axle set and therefore the distribution of the load between the front and rear of the vehicle.

[0013] The bicycle models used up to now do not explicitly mention the specific drift of the drivetrain, since this is a concept specific to chassis development, not to physical and scientific modeling in particular. In this sense, the inventors assume that the concept of specific drift forms the basis for the timing of the dynamic response of the chassis, and propose that in a device for controlling the steering of a vehicle, a control unit implements a parameterization in its modeling that takes this specific drift into account. The specific drift makes it possible to build a model by simply measuring the lateral acceleration and vertical load on each axle set, as opposed to the concept of drift angle, which requires measuring the tires, deflections and elastic-plastic kinematic characteristics (or bushings).

[0014] More specifically, the implemented modeling makes it possible to link system variables, such as response time, bandwidth or static-dynamic behavior, to specific drifts that further represent the quality of the lateral guidance of the drive unit and to the quality of the response of the chassis' lateral dynamics.

[0015] According to an optional feature of the invention, it is possible to provide that the chassis lateral dynamic behavior model implemented in the calculation module is configured to express at least one yaw velocity as a function of the specific drift of each of the front and rear wheel sets of the vehicle.

[0016] Where appropriate, the drift in the center of gravity of the vehicle and the lateral acceleration of the vehicle are also expressed as a function of the specific drift of each of the front and rear wheel sets of the vehicle.

[0017] It is thus possible to express each of the specific physical variables of the lateral dynamic behavior as a function of the specific drift of each drive unit, and the yaw velocity is more specifically modeled in order to subsequently be able to calculate the reference yaw moment and the effective yaw moment.

[0018] According to an optional feature of the invention, the chassis lateral dynamic behavior model is configured to represent the transfer function between the yaw velocity and the steering system of the front wheel set or the steering of the rear wheel set, or the yaw moment due to actuators associated with the decoupled braking system, as a function of static-to-dynamic gains defined as a function of the specific drift of the front and rear wheel sets of the vehicle.

[0019] In this regard, the control unit may be configured to transmit priority command instructions directed to controlled actuators associated with the steering system before, if appropriate, transmitting command instructions directed to controlled actuators associated with the separated brake system.

[0020] The expression of the transfer function as a function of the specific drift, as allowed by the lateral dynamic behavior model shown, makes it possible to demonstrate, in particular, that the longitudinal deceleration for the vehicle wheels is too great to obtain a gain equivalent to that obtained by the maximum deflection allowed by the mechanical structure of the wheelset.

[0021] According to an optional feature of the invention, the static-to-dynamic gains associated with each of the steering systems of the front and rear wheelsets may be a function of the understeering gradient, i.e., the difference between the specific drift of the front axle set and the specific drift of the rear axle set.

[0022] Specifically, the static-dynamic gain is the difference between the specific front and rear drifts that determines the sharpness of the vehicle's lateral turns. This difference is also referred to as the understeering gradient, and as previously mentioned, takes into account the additional steering wheel angle that will be added to make the vehicle follow a trajectory at a given speed.

[0023] In this regard, the control unit is configured to transmit priority command instructions directed to the controlled actuators associated with the rear wheel set steering system before transmitting, where appropriate, command instructions directed to the controlled actuators associated with the front wheel set steering system.

[0024] The representation of the transfer function as a function of the specific drift, as allowed by the lateral dynamic behavior model shown, makes it possible to demonstrate, from a dynamics point of view, that in particular a speed of response is undoubtedly advantageous for steering inputs of the wheels of the rear axle set, i.e. for steering control by acting first on the steering of the rear wheel set and then on the steering of the front wheel set.

[0025] In other words, if a vehicle is fitted with at least one controlled actuator configured to perform decoupled braking of one wheel of the vehicle, a controlled actuator configured to steer rear wheels of the vehicle and a controlled actuator configured to steer front wheels of the vehicle, the command instructions generated by the control unit, e.g. command instructions for corrective actions, consist primarily of command instructions for the steering angle actuator of the rear wheels of the vehicle.

[0026] According to an optional feature of the invention, it is possible to provide a control unit configured to receive input parameters and dynamic driving parameters, and configured to firstly compare reference data calculated by applying a chassis lateral dynamic behavior model based on values ​​of the input parameters and reference values ​​of the dynamic driving parameters with valid data calculated by applying a chassis lateral dynamic behavior model based on values ​​of the same input parameters and valid values ​​of the dynamic driving parameters, and secondly generate corrective action commands when a significant difference between the reference data and the valid data occurs.

[0027] The valid values ​​of the dynamic driving parameters can come from measurements performed in real time via appropriate sensors while the vehicle is running, or can come from test data implemented by the operator when the chassis is being developed.

[0028] According to an optional feature of the invention, it is possible to implement that the reference data is a reference yaw moment and the effective data is an effective yaw moment, and the control unit is configured to calculate, for one part, the reference yaw moment by using a chassis lateral dynamic behavior model having a reference value, and to calculate, for the other part, the effective yaw moment by using a chassis lateral dynamic behavior model having an effective value.

[0029] Here too, the velocity of the vehicle can be obtained by the control unit from a velocity sensor mounted on the vehicle or following the implementation of test data by the operator.

[0030] According to an optional feature of the invention, it may be provided that the control unit is configured to simultaneously calculate the reference yaw moment and the effective yaw moment.

[0031] The specific rear drift also determines the reaction time constant between the front and rear axle sets when the vehicle is cornering. The greater the specific rear drift, the longer the reaction time between the operation of the rear axle set and the operation of the front axle set. A well-timed vehicle is one in which the response of the rear axle set is faster than that of the front axle set. This timing should allow for transitions that are not easily noticed by the driver, especially when transferring weight. Implementation of the device according to the invention with a chassis behavior model that takes the specific drift into account makes it possible to optimize this performance. In this regard, the device may make it possible to realize control of the yaw moment, which can be generated by one of a controlled system, in particular a four-steered wheel system with controlled actuators that allow the steering of each wheel to be managed individually, and a separated braking system with controlled actuators that allow the braking action for each wheel to be managed individually.

[0032] According to an optional feature of the invention, it is possible to provide that the at least one controlled actuator is an actuator of the steering angle of the rear wheels of the vehicle, the steering angle of the rear wheels being determined with respect to the determined front axle set angle of the chassis and for balancing the calculated effective yaw moment with the calculated reference yaw moment.

[0033] According to an optional feature of the invention, it may be provided that the at least one controlled actuator is an actuator of an isolated brake of a wheel of the vehicle, the yaw moment generated by the brake of this wheel being determined with respect to the determined front axle set angle of the chassis and for balancing the calculated effective yaw moment with the calculated reference yaw moment.

[0034] According to an optional feature of the invention, it may be provided that the input parameters consist of at least a specific drift of the front axle set and a specific drift of the rear axle set.

[0035] According to an optional feature of the invention, the specific drift of the front axle set is between 0.3 and 1 deg / (m / s 2 ) reference value.

[0036] According to an optional feature of the invention, the specific drift of the rear axle set is between 0.1 and 0.6 deg / (m / s 2 ) reference value.

[0037] It should be noted that the specific values ​​implicitly take into account the deflection and elastic-plastic kinematic phenomena of the axle set. Therefore, it is not useful to estimate the cornering stiffness of the axle set, but taking into account the specific drift in the form of a range of values ​​makes it possible to generalize uncertainties and, for example, changes in the normal load on the tires induced by changes in longitudinal and lateral acceleration.

[0038] According to an optional feature of the invention, it is possible to provide that the specific drift of the rear axle set is fixed and determined as a function of the driving style type identified by the control unit.

[0039] Depending on the vehicle velocity and the type of desired driving behavior, for example, sporty or economical, the invention provides for modifying a reference value for a specific drift of the rear axle set. In this connection, the control unit may have a table of data in which specific drift values ​​are associated with velocity values. The reference data, for example the calculation of the reference yaw moment, is modified accordingly, and the command, for example the steering angle of the rear wheel set, which is a function of the comparison of this reference data with the corresponding valid data, is modified accordingly.

[0040] According to an optional feature of the invention, it may be provided that the input parameters consist of at least the weight distribution and the inertia distribution of the vehicle.

[0041] It is therefore worth noting that the lateral dynamic behavior model according to the invention in the first case takes into account the dynamic parameters of the vehicle, for example their distribution, and that the static parameters, in particular the weight and inertia of the vehicle, are not taken into account as reference parameters, but, where appropriate, through the calculation of gains taken into account during the dynamic parameterization of the vehicle.

[0042] According to an optional feature of the invention, it may be provided that the input parameters further consist of a coefficient of the vehicle weight and vehicle wheelbase, and a steering step-down ratio.

[0043] According to an optional feature of the invention, it can be realized that the chassis lateral dynamic behavior model is described around a modal decomposition of the relationship between vehicle yaw and drift, at least one decomposition being related to the steering angle actuator of the front wheel set and at least one other decomposition being related to the steering angle actuator of the rear wheel set or to the controlled actuator of a separated braking system.

[0044] According to an optional feature of the invention, it may be provided that the chassis lateral dynamic behavior model is configured to express yaw velocity as a function of each of said decompositions.

[0045] According to an optional feature of the invention, it may be provided that the values ​​obtained by the control unit consist of the vehicle velocity, the steering angle of the front wheel set, and the steering angle of the rear wheel set.

[0046] According to an optional feature of the invention, it may be provided that the control unit is configured to communicate with a plurality of sensors that are capable of measuring values ​​that are subsequently obtained by the control unit when the vehicle is running.

[0047] The invention also relates to a method for controlling the steering of a vehicle fitted with a control device as claimed in one of the above claims, in the course of which the following steps are carried out: first a calculation step, in which a module calculates, for one part, an effective yaw rotation moment and a reference yaw rotation moment, then a comparison step, in which the calculation module balances the two calculated yaw rotation moments to subsequently deduce in a deduction step from thereon at least one value that must be met by the rear angle and / or the brake yaw moment as a function of the steering angle of the front wheel set.

[0048] The invention will be better understood from reading the following description and from examining the accompanying figures, which are given purely by way of example and do not in any way limit the invention. [Brief explanation of the drawings]

[0049] [Figure 1] 1 is a schematic representation of a vehicle and of a steering control device according to the invention that can be mounted on such a vehicle, the control unit forming part of the control device being shown in outline, in particular to a scale that makes it possible to understand the components. [Figure 2] 1 is a diagram of the wheels of a vehicle in the process of cornering, making it possible to illustrate the concept of a particular drift of an axle set; [Figure 3] 2 is a flow diagram illustrating the operating modes of the control unit shown schematically in FIG. 1; DETAILED DESCRIPTION OF THE INVENTION

[0050] It will be recalled that the present invention consists of a device for controlling the steering of a motor vehicle, capable of generating command instructions for actuators controlled via a calculation module implemented with a vehicle chassis lateral dynamic behavior model that takes into account in particular the specific drift of each of the front and rear wheel sets of the vehicle.

[0051] The vehicle 1 shown in Figure 1 has, inter alia, a steering control device 10 whose function is to affect the steering of the vehicle, for example by using steering action on one or other of the wheel sets 2 of the vehicle 1 to keep the vehicle on a target trajectory while cornering at high or low velocities.

[0052] The steering control device 10 more particularly comprises a control unit 12 configured to send command instructions 13 to controlled actuators each associated with one of the wheels 2 .

[0053] In the example shown in Figure 1, the controlled actuators consist more particularly of a first controlled actuator 3 associated with the steering system of the front wheel set and a second controlled actuator 4 associated with the steering system of the rear wheel set, the vehicle having a system of four steered wheels.

[0054] These controlled actuators in turn consist of third controlled actuators 6 associated with the decoupled braking system, each third controlled actuator 6 being associated with one of the wheels 2 of the vehicle in order to generate a yaw moment specific to each wheel, or at least to each wheel set, front or rear, when decoupled braking is required.

[0055] The vehicle also has at least one sensor 8, which in this case may take the form of a velocity sensor located on one of the wheels. Other sensors 8 may be provided to take into account changes in dynamic parameters as the vehicle is moving.

[0056] A more detailed description of the steering control device 10, and in particular the control unit 12, will now be provided.

[0057] The control unit comprises in particular a calculation module 14 in which a chassis lateral dynamic behavior model 16 is implemented, which expresses physical variables specific to the lateral dynamics of the chassis as a function of the specific drift δs1 and the drift δs2 of each wheelset, as described above, where one specific drift is associated with one wheelset.

[0058] The control unit 12 is configured to obtain input parameters 18 intended to be loaded into the calculation module 14 and dynamic driving parameters 19 forming the characteristic values ​​of the vehicle's driving. This control unit 12 is configured to operate the calculation module 14 by applying a chassis lateral dynamic behavior model 16 having these various parameters 18, 19 and to generate, as a function thereof, command instructions 13 aimed at one or other of the various controlled actuators 3, 4, 6.

[0059] More particularly, the input parameters 18 include at least one specific drift of the drive train of the vehicle, more particularly both the specific drift δs1 of the front axle set and the specific drift δs2 of the rear axle set. The parameters may further include a weight distribution α, which may consist of the ratio of the weight of the front axle set to the weight of the vehicle, and an inertia distribution λ of the vehicle, for example in the form of an inertia ratio, and also the vehicle weight M, the vehicle wheelbase L, and a steering step-down ratio coefficient η.

[0060] The vehicle weight M considered here as input parameter 18 is the kerb weight, which, in addition to having a fixed value implemented in the control unit, makes it possible to ensure that any corrective actions to be taken on one or the other of the axle sets do not risk stopping the wheels turning.

[0061] Each input parameter 18 is implemented in a calculation module with a value that is determined, in particular, when the vehicle is being designed and / or when the vehicle is being developed.

[0062] As a non-limiting example, the specific drift δs1 of the front axle set may be between 0.3 and 1 deg / (m / s 2 ) The specific drift δs2 of the rear axle set has a value of 0.1 to 0.6 deg / (m / s 2 ) values.

[0063] The value of the specific drift of the rear axle set δs2 can be modified as a function of the vehicle velocity V and the desired type of behavior. For that purpose, the control unit can have a memory 20 in which a table of values ​​is stored relating velocities or driving behaviors, including, for example, economical or sporty driving, to the specific drift value of the rear axle set δs2. More specifically, if there is a desire to have good lateral guidance performance at high velocities and thereby the most economical and safest possible lateral dynamic behavior, it is necessary to make provision for reducing the value of the specific drift of the rear axle set.

[0064] Dynamic driving parameters 19 are acquired by the control unit 12 and may consist in particular of the vehicle velocity, the steering angle of the front wheel set and the steering angle of the rear wheel set. The calculation module 14, via the chassis lateral dynamic behavior model 16, is able to define what effective values ​​of the dynamic driving parameters entail changing the calculated data and generates corrective actions for the chassis via controlled actuators.

[0065] The lateral dynamic behavior model 16 can be implemented during the development process and when the vehicle is running, when reference and effective values ​​of the various parameters 18, 19 are entered by the operator into the control unit 12 to test the behavior of the chassis when a given difference is observed between reference data calculated based on the reference values ​​and effective data calculated based on the effective values, in order to implement corrective actions on the steering in real time.

[0066] In the latter case, the control device 10 is configured to communicate with a plurality of sensors and a sensor 8 configured to determine, for example, the velocity of the vehicle, whether this is the vehicle's longitudinal velocity or its lateral velocity.

[0067] It should be noted that these sensors 8 are configured to measure various dynamic parameters when the vehicle is running, and that these sensors may be specifically dedicated to the operation of the steering control device or may be used in other ways for other functions implemented in the vehicle, without departing from the context of the present invention, provided that the control unit of the control device according to the present invention is able to obtain these data on demand or continuously.

[0068] The control unit is configured firstly to compare valid data, calculated by applying the same model 16 based on values ​​of the same input parameters 18 and valid values ​​of the dynamic driving parameters 19 measured on the vehicle in real time, with reference data, calculated by applying the chassis lateral dynamic behavior model 16 based on values ​​of the input parameters 18 and reference values ​​of the dynamic driving parameters 19. The control unit is further configured secondly to generate corrective action commands in case of significant differences between the reference data and the valid data.

[0069] The chassis lateral dynamic behavior model 16 and how it represents physical variables specific to lateral dynamics as a function of the specific drift of a wheel set, as shown in Figure 2 for the rear wheels as an example, will now be described in more detail.

[0070] The chassis lateral dynamic behavior model 16 is described particularly by focusing on the mode decomposition of the yaw drift pair mode.

[0071] Each decomposition is associated with a respective actuator capable of generating a yaw moment, i.e. with each of the controlled actuators mentioned above, more specifically with the steering angle actuator of the front wheels 3, the steering angle actuator of the rear wheels 4 and the separate brake actuator 6.

[0072] The first mode decomposition for the first controlled actuator 3 associated with the steering system of the front wheel set is as follows: TIFF0007727668000001.tif16170The second mode decomposition for the second actuator 4 associated with the steering system of the rear wheel set is as follows: TIFF0007727668000002.tif15170 The third mode decomposition for the third controlled actuator 6 associated with the decoupled brake system is as follows: TIFF0007727668000003.tif19170For each of these mode decompositions, the following applies: δ f : steering angle of the wheels of the front set in radians δ r : steering angle of the rear set of wheels in radians M vdc : Brake system yaw moment in Nm Wheelbase in L:m Vm = Vm1 + Vm2 + Vm3: modal vector of yaw / drift pair modes α: Weight distribution, su G0:sec -1 In the yaw gain δ s1 :rad / (m / s 2 ) specific frontal drift δ s2 :rad / (m / s 2 ) specific rear drift τ Ψ : Time constant of the yaw / drift pair mode in seconds ξ Ψ Damping of yaw / drift pair modes in :su

[0073] With such a decomposition, the physical variables, specifically yaw velocity, lateral acceleration, and drift angle, can be expressed as linear combinations of the components of the modal vector.

[0074] Yovelocity is then expressed as: TIFF0007727668000004.tif14170

[0075] Furthermore, the drift at the center of gravity can be expressed as: TIFF0007727668000005.tif17170Then, the lateral acceleration is expressed by a linear combination of the two previous variables, i.e., TIFF0007727668000006.tif11170

[0076] Here, all parameters are expressed as a function of a particular drift.

[0077] Thus, the time constant τ of the yaw / drift pair mode Ψ can be written as: TIFF0007727668000007.tif25170Thus, the reduced damping ξ of the yaw / drift pair mode Ψ can be written as: TIFF0007727668000008.tif31170Thus, the yaw gain G0 can be written as: TIFF0007727668000009.tif18170

[0078] Furthermore, the corresponding transmission zeros are again determined by a specific drift δ s1 , δ s2 , expressed as a function of one and / or the other of

[0079] The yaw velocity transmission zero for the steering command of the wheels of the rear axle set can be written as: (10)τ1=Vδs1 The yaw velocity transmission zero for the steering command of the wheels of the front axle set can be written as: (11)τ2=Vδs2 The drift angle transmission zero for the steering command of the wheels of the rear axle set can be written as: TIFF0007727668000010.tif13170The drift angle transmission zero with respect to the steering command of the wheels of the front axle set can be written as: The yaw velocity transmission zero for the yaw moment generated by the braking system can be written as: TIFF0007727668000012.tif12170

[0080] It is then possible to express the transfer functions commonly used in relating vehicle dynamics, in particular yaw velocity, lateral acceleration and lateral force, as a function of the specific drift, thereby making it possible to then quantify the transient lateral dynamics of the vehicle.

[0081] The chassis lateral dynamic behavior model 16 implemented in the control unit 12 is configured in particular to express yaw velocity as a function of a respective modal decomposition of the relationship between vehicle yaw and drift, and the calculation will now be described taking into more particular consideration this expression of yaw velocity, in particular the yaw velocity transfer function.

[0082] The transfer function between front wheel yaw velocity and steering can be read as: TIFF0007727668000013.tif23170The transfer function between rear wheel velocity and steering can be read as follows: TIFF0007727668000014.tif25170The transfer function between yaw velocity and yaw moment due to the braking system can be read as follows: TIFF0007727668000015.tif24170

[0083] The chassis lateral dynamic behavior model 16 is therefore configured to represent the transfer function between yaw velocity and the respective systems associated with the controlled actuators as a function of static-to-dynamic gains defined as a function of the specific drift of the front and rear wheel sets of the vehicle.

[0084] Taking into account the various representations of the lateral dynamic behavior model as described above, the computational actions performed by the control unit 12, and more particularly by the computation module 14, will now be described.

[0085] As mentioned above, the calculation module 14 is configured to make it possible to control the chassis behavior by calculating data, more particularly in this case the yaw rotation moment, for both the reference values ​​and the effective values ​​of the various parameters used to calculate this data, whether these effective values ​​are introduced by the operator or obtained in real time by a control device while the vehicle is running.

[0086] The yaw rotational moment of a vehicle is given by the product of yaw inertia and yaw acceleration according to the following equation: (18)M yaw =I zz s 2 Ψ

[0087] The calculation module 14 takes into account the chassis lateral dynamic behavior model 16 and the transfer function formulations previously described in equations (15), (16) and (17) and calculates the yaw moment based on the specific drift using the following equation: At the same time, the calculation module 14 calculates a reference to this yaw rotation moment, which can be written as follows: (20)M yaw =I zz s 2 Ψ ref

[0088] Since the assumption is that the reference yaw velocity is given by a reference vehicle having only two steered wheels, or in other words, since the assumption is that the reference yaw velocity comes only from the steering angle applied by the driver, the reference yaw velocity must be a function of the steering wheel angle only, i.e., here only the steering of the front wheels.

[0089] Therefore, the reference velocity can be expressed as follows by considering only the transfer function stated in equation (15): TIFF0007727668000017.tif25170The reference yaw moment is therefore expressed as a function of the two previous equations as follows: TIFF0007727668000018.tif14170

[0090] The calculation module 14, via the chassis lateral dynamic behavior model 16, is configured to firstly carry out a calculation step E1, as can be seen in FIG.

[0091] During the calculation step E1, the module calculates for one part the effective yaw rotation moment M yaw eff , i.e., the calculation of the yaw moment expressed in equation (19) with the values ​​of the input parameters 18 and the effective values ​​of the dynamic driving parameters 19, and for the other part, the reference yaw rotation moment Myaw ref , i.e., the calculation of the yaw moment expressed in equation (22) with the values ​​of the input parameters 18 and the reference values ​​of the dynamic driving parameters 19.

[0092] The control unit 12 is parameterized so that the calculation module can simultaneously calculate the reference yaw rotation moment and the effective yaw rotation moment.

[0093] Secondly, as shown in FIG. 3, during the comparison step E2, the calculation module balances the effective yaw moment with the reference yaw moment according to the following equation: TIFF0007727668000019.tif17170

[0094] Then, thirdly, as shown in FIG. 3, during a deduction step E3, the calculation module deduces from the equilibrium relation (23) the values ​​that the rear angle and / or braking yaw moment must satisfy as a function of the steering angle of the front wheel set.

[0095] If the vehicle has a system of four steered wheels without a separate braking system, the calculation module applies a yaw moment of the braking system equal to zero (Mvdc=0) to equation (23), thereby obtaining a direct relationship giving the steering angle of the rear wheel set as a function of the steering angle of the front wheel set, which can be written as follows: TIFF0007727668000020.tif27170

[0096] In this regard, a selection is made to control the steering angle of the rear wheel set solely as a function of the steering angle of the front wheel set, i.e., the steering angle of the rear wheels, or of the rear wheel set, is determined for the determined steering angle of the front wheel set and for balancing the calculated effective yaw moment with the calculated reference yaw moment.

[0097] In addition, in particular as a function of the analysis carried out by the inventors based on a chassis lateral dynamic behavior model and described below, the control unit is configured to send priority command instructions to the controlled actuators associated with the steering system of the rear wheel set before sending command instructions, if appropriate, to the controlled actuators associated with the steering system of the front wheel set.

[0098] If the vehicle does not have a four steered wheel system and has a separate braking system, a choice is made to control the yaw moment generated by the braking system as a function of the steering angle of the front wheel set, and equation (23) can be written as: TIFF0007727668000021.tif40170

[0099] In other words, the yaw rotation moment generated by the wheel brakes is determined for the determined steering angle of the front wheel set of the chassis and for the balance between the calculated effective yaw moment and the calculated reference yaw moment.

[0100] If the vehicle has a separated braking system and a system of four steered wheels, the calculation module can determine pairs of values ​​of the steering angle of the rear wheel set and of the yaw moment generated by the controlled actuator associated with the corresponding wheel set as a function of the steering angle of the front wheel set. Alternatively, and in particular as a function of the analysis carried out by the inventors based on a chassis lateral dynamic behavior model and described below, the control unit is configured to send priority command instructions to the controlled actuators associated with the steering system of the wheels, in particular of the rear wheel set, before sending command instructions, if appropriate, to the controlled actuators associated with the separated braking system.

[0101] For example, as mentioned, a chassis lateral dynamic behavior model and its qualitative analysis to define which controlled actuators should be implemented as a priority is described herein.

[0102] As mentioned above, the appearance of the transfer function is the same for three inputs, specifically the yaw moment generated by the front wheel set steering, the rear wheel set steering, and the decoupled braking system, each of which is a function of the static-dynamic gain G0.

[0103] As an example, examination of the static-dynamic gain in yaw velocity as a function of drivetrain braking input, i.e., by examining equations (15) and (16) above, makes it possible to say whether the drivetrain is the front or rear axle set, for steering input, that the gain is then given by: TIFF0007727668000022.tif12170

[0104] This gain explicitly gives rise to two basic variables: the first, L, characterizes the wheelbase of the vehicle, and the second, (δs1-δs2), characterizes the difference between the specific front and rear drifts, also called the understeering gradient.

[0105] The gain is at most the characteristic velocity given by: TIFF0007727668000023.tif15170

[0106] The calculation module takes this relationship into account to determine the specific drift of the rear set of wheels to be applied as a function of the specific drift of the front set of wheels.

[0107] Examination of the dynamic behavior of the transfer functions, and more particularly the zeros of these various transfer functions, likewise allows a qualitative analysis to be undertaken.

[0108] For steering of the wheels of the front axle set, the zero time constant is proportional to the specific rear drift at a given speed: (28)τ2=Vδs2 If steering is performed by the rear set of wheels, the zero time constant is proportional to the specific front drift at a given speed: (29)τ1=Vδs1 Finally, if the yaw moment is generated by a decoupled braking system, the zero time constant can be expressed as a function of the specific drift of the two axle sets: TIFF0007727668000024.tif12170

[0109] The inventors have found that from a dynamics point of view, the speed of response is undoubtedly advantageous for steering inputs of the wheels of the rear axle set, then for steering inputs of the wheels of the front axle set, and then for yaw rotation moments generated by the separated braking system, with a response of 0.3° / (m / s 2 ) can be demonstrated.

[0110] From the detailed description given, it follows that the present invention very well achieves the established objective of proposing a modification of existing control devices that allows the vehicle to be reliably and quickly given various configurations according to the target of a reference model. This objective is achieved by implementing in the control unit a chassis lateral dynamic behavior model that is simply expressed as a function of the chassis' system characteristics, specifically the specific drifts of the front and rear wheel sets. The selection of the specific drifts therefore makes it possible to modify, among other things, the desired understeering gradient and the guidance performance of the rear axle set. Another advantage of this model is that it differentiates the evolution of the yaw gain, which is implemented by changing the wheelbase or by changing the understeering gradient (difference in the specific drift).

Claims

1. A steering control device (10) for a motor vehicle (1) having at least one controlled actuator (3, 4) associated with a steering system of wheels (2) of the vehicle and / or a controlled actuator (6) associated with a separate braking system at the wheels (2) of the vehicle, the steering control device (10) having at least one control unit (12) configured to acquire at least one value characteristic of the driving of the vehicle and to send a command instruction (13) to the at least one controlled actuator (3, 4, 6) as a function of the acquired value or of the acquired values, The control unit (12) comprises a calculation module (14) implemented with a vehicle chassis lateral dynamic behavior model (16), wherein at least one specific physical variable of the vehicle chassis lateral dynamic behavior model is determined by a specific drift (δ ) of each of the front and rear wheel sets of the vehicle. ｓ１ , δ ｓ２ ) as a function of steering control device.

2. The vehicle chassis lateral dynamic behavior model (16) implemented in the calculation module (14) calculates the specific drift (δ) of each of the front and rear wheel sets of the vehicle. ｓ１ , δ ｓ２ 2. The steering control device of claim 1, configured to express at least one yaw velocity as a function of

3. The vehicle chassis lateral dynamic behavior model (16) calculates a transfer function between the yaw velocity and the steering system of the front wheel set and / or the rear wheel set, and a transfer function between the yaw moment due to the actuator associated with the decoupled brake system, in accordance with the specific drift (δ) of the front wheel set and the rear wheel set of the vehicle. ｓ１ , δ ｓ２ 3. The steering control device of claim 2, wherein the steering control device is configured to express the static-dynamic gain as a function of the static-dynamic gain defined as a function of the dynamic gain.

4. 4. A steering control device according to claim 3, wherein the control unit (12) is configured to transmit priority command instructions (13) directed to the controlled actuators (3, 4) associated with the steering system before transmitting, where appropriate, command instructions (13) directed to the controlled actuators (6) associated with the separated brake system.

5. The static-dynamic gains associated with each of the steering systems of the front and rear wheel sets are a function of understeering gradient, i.e., the specific drift δ of the front axle set. ｓ１ and the specific drift δ of the rear axle set ｓ２ 5. The steering control device according to claim 3, wherein the difference between

6. 6. A steering control device according to claim 5, wherein the control unit (12) is configured to transmit priority command instructions (13) directed to the controlled actuators (4) associated with the steering systems of the rear wheel set before transmitting, where appropriate, command instructions (13) directed to the controlled actuators (3) associated with the steering systems of the wheels.

7. 7. The steering control device according to claim 1, wherein the control unit is configured to receive input parameters and dynamic driving parameters, the control unit being configured to firstly compare reference data calculated by applying the vehicle chassis lateral dynamic behavior model based on values ​​of the input parameters and reference values ​​of the dynamic driving parameters with valid data calculated by applying the vehicle chassis lateral dynamic behavior model based on values ​​of the same input parameters and valid values ​​of the dynamic driving parameters, and secondly generate corrective action commands when a significant difference between the reference data and the valid data occurs.

8. The reference data is the reference yaw moment (M ｙａｗ ｒｅｆ ), and the effective data is the effective yaw moment (M ｙａｗ ｅｆｆ ), and the control unit, on the one hand, calculates the reference yaw moment (M ｙａｗ ｒｅｆ ) and, on the other hand, by using the vehicle chassis lateral dynamic behavior model (16) with the effective values, the effective yaw moment (M ｙａｗ ｅｆｆ 8. The steering control device of claim 7, configured to calculate

9. The control unit (12) determines the reference yaw moment (M ｙａｗ ｒｅｆ ) and the effective yaw moment (M ｙａｗ ｅｆｆ 9. The steering control device of claim 8, configured to simultaneously calculate:

10. The at least one controlled actuator (4) is an actuator of the steering angle of the rear wheels of the vehicle, and the steering angle (δ ｒ ) is the determined front axle set angle (δ ｆ ) and the calculated effective yaw moment (M ｙａｗ ｅｆｆ ) and the calculated reference yaw moment (M ｙａｗ ｒｅｆ 10. The steering control device according to claim 8, wherein the steering angle is determined for balance with the steering angle.

11. The at least one controlled actuator (6) is an actuator of the isolated brake of a wheel of the vehicle, and the yaw moment generated by the brake of this wheel is determined by the determined front axle set angle (δ) of the chassis. ｆ ) and the calculated effective yaw moment (M ｙａｗ ｅｆｆ ) and the calculated reference yaw moment (M ｙａｗ ｒｅｆ 10. The steering control device according to claim 8, wherein the steering angle is determined for balance with the steering angle.

12. The input parameters include the specific drift (δ ｓ１ ) and the specific drift (δ) of the rear axle set ｓ２ 12. A steering control device according to any one of claims 7 to 11 when dependent on claim 5, comprising:

13. The specific drift (δ ｓ２ 13. The steering control device of claim 12, wherein the driving style type is fixed and determined as a function of the driving style type identified by the control unit (12).

14. A steering control device according to any one of claims 8 to 13, wherein the input parameters (18) consist of at least the weight distribution and the inertia distribution of the vehicle.

15. 15. A steering control device according to any one of claims 1 to 14, wherein the control unit (12) is configured to communicate with a plurality of sensors (8) having the ability to measure values ​​that are subsequently obtained by the control unit when the vehicle is moving.

16. 16. A method for controlling the steering of a vehicle fitted with a control device according to any one of claims 1 to 15, characterized in that firstly the calculation module calculates on the one hand the effective yaw rotation moment (M ｙａｗ ｅｆｆ ) and reference yaw rotation moment (M ｙａｗ ｒｅｆ ) and then a comparison step (E2) in which the calculation module balances the calculated effective yaw rotation moment (M yaw eff ) and the reference yaw rotation moment (M yaw ref ), and a deduction step (E3) in which the comparison step (E2) deduces at least one value that must be satisfied by the rear angle and / or the braking yaw moment as a function of the steering angle of the front wheel set.

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