FR2927601A3 - Electric control steer by wire type steering system operating method for motor vehicle, involves establishing angular position value of steering control body from mechanical action value applied on body, by using reference model - Google Patents

Abstract

The method involves establishing an angular position value of a steering control body (2) e.g. hand wheel, from a mechanical action value i.e. torque value, applied on the steering control body, by using a reference model that includes inertia term, dry friction term, viscous friction term, stiffness term, and /or mechanical action term applied on the control body by a driver. The angular position value is used for establishing a control set point of actuators (4, 7) i.e. direct current electric motors, respectively applying mechanical action on the control body and steering wheels (10). An independent claim is also included for an electric control steering system of motor vehicle, comprising hardware and software units for implementing a method for operating an electric control steering system.

Description

The invention relates to a method of operating a motor vehicle steering system of the electric control type said steer-by-wire. The invention also relates to a motor vehicle steering system of the electrically controlled type and implementing such a method.

Historically, the steering systems of motor vehicles operated exclusively through the efforts exerted by the driver on a steering wheel. These efforts on the steering wheel were transmitted to a shaft called steering column and provided at its end with a pinion meshing with a rack. The rotation of this column therefore led to a translation movement of the rack. A wheelhouse system at each end of the rack was used to orient the wheels of the motor vehicle in response to this movement of the rack.

It was then imagined, retaining the basic mechanical structure of the steering system described above, to add hydraulic assistance means to maneuver the steering wheel to improve drivability. To overcome some drawbacks including congestion and reliability, it has been imagined a power steering system in which the assistance is obtained by an electric actuator. Such a system is known as electric power steering.

To go even further in optimizing the size of the steering system, but also to allow new services in terms of man-machine interface, safety and driving pleasure, it has been imagined a steering system Steer-by-wire electrical control where the steering control is transmitted by an electrical signal emitted on electrical wires. Thus, the angular position MS \ REN061 FR.dpt of the steering wheel is translated by a control signal transmitted over electrical son and controlling an electric motor acting on the wheels to position them in the steering position corresponding to the position of the steering wheel.

This steering system allows mechanical decoupling of the steering wheel of the front axle and wheels. It has multiple benefits. An exhaustive list of these really conceivable advantages is not possible in the current state. However, some obvious benefits can be cited. In particular: the removal of the mechanical link between the steering wheel and the front axle considerably simplifies the systems. The flexibility in terms of architecture and ergonomics is improved, the assembly is simplified. Similarly, the weight and cost of the system are decreased. Finally, reliability is supposed to be improved too; the disappearance of the power steering hydraulic system is more in line with the environmental and ecological constraints; the electrical interface between the systems and controls provided to the driver facilitates the implementation of active controls (trajectory control, avoidance) and brings a gain in performance. For example, electronic throttle applications, mechanical linkage suppression has reduced fuel consumption and improved driving comfort by eliminating transmission surges.

On the other hand, if new features can be considered, a number of new problems and new difficulties emerge.

The main difficulty of the electrically controlled steering system lies in its ability to reproduce the driving sensations necessary for the good control of a vehicle. Indeed, the sensations perceived by the driver through the steering wheel have a capital part in his ability to steer the vehicle. The highly subjective nature of a conventional steering system (hydraulically or electrically assisted steering) makes the definition of a specification extremely difficult.

An electrically controlled steering system mainly comprises two actuators (typically electric motors): a feedback actuator responsible for applying a force restitution torque on the steering wheel; it is this torque that reproduces sensations that the driver would have with a conventional direction, such as a resistance to the rotation of the steering wheel and a restoring torque due in particular to the hunting of the front axle on a traditional steering system; this effort restitution torque is conventionally driven by a computer at least from the angular position information of the steering wheel; • a steering actuator to apply steering torque to the steering rack to steer the wheels at the steering angle (at a reduction factor); this steering torque is conventionally controlled by a computer implementing a fairly conventional control in which the desired magnitude is the angular position of the steering wheel and the control is the steering torque.

In fact, the two control functions provided by the two computers can of course be grouped in a single computer if it has a sufficient processing capacity. The restitution of effort at the steering wheel is conventionally carried out from three magnitudes: the angular position of the steering wheel, the speed of the vehicle and the MS \ REN061 FR.dpt moment of self-alignment of the wheels (due in particular to hunting). The difficulty arises from the fact that the system is an inter-dependent system: indeed the quality of the force feedback is influenced not only by the restitution control law but also by the steering control law.

Application US 2004 / 0039507A1 discloses an effort restitution strategy based on a reference model. However, the design uses complex automatic techniques (Hinfini): these techniques often lead to high order correctors. In addition, the structure does not clearly show the reference model. It is only present at the synthesis phase of the correctors.

The object of the invention is to provide a method of operating a steering system obviating the disadvantages mentioned above and improving the known operating methods of the prior art. In particular, the invention provides an operating method having a simple structure and easily scalable. Indeed, a designer can easily enrich the process, the order is then immediately updated. In addition, the structure is well suited to the problem of effort feedback driving. The object of the invention is still to provide a steering system implementing such a method.

According to the invention, the method of operation of a power steering system of a motor vehicle is characterized in that it comprises a step of setting a position value of a steering control member from a mechanical action value applied to the steering control member, the setting step being performed using a reference model. MS \ REN061 EN.dpt The reference model may include terms corresponding to physical phenomena.

The reference model may comprise an inertial term and / or a dry frictional term and / or a viscous friction term and / or a stiffness term and / or a mechanical action term applied to the steering control member by a driver.

The reference model may include a mechanical action term applied to steered wheels and reduced to the level of the steering control member. The term mechanical action applied on steered wheels can be reduced at the level of the steering control member by a restitution logic depending on the situation in which the vehicle is located. The reference model may vary depending on at least one parameter. The at least one parameter may include the speed of the motor vehicle.

The at least one parameter may include the position of the steering control member.

The value of the mechanical action applied to the steering control member by the driver can be estimated or measured. The position value of the steering control member can be used to establish a control set point of an actuator applying a mechanical action on the steering control member and / or the position value of the steering control member can be used. control member of MS \ REN061 FR.dpt20 direction to establish a command setpoint of an actuator applying a mechanical action on the steering wheels of the motor vehicle.

According to the invention, the electrically controlled steering system of a motor vehicle comprises hardware and software means for implementing the operating method defined above. According to the invention, the motor vehicle comprises a steering system defined above.

The appended drawing represents, by way of example, an embodiment of a steering system according to the invention.

FIG. 1 is a diagram of an embodiment of a steering system according to the invention,

FIG. 2 is a block diagram of the electronic control structure of the actuators of a steering system according to the invention.

FIG. 3 is a block diagram of a first electronic structure embodiment of a reference model used in one of the blocks (block 30) of the electronic control structure of the actuators according to FIG. 2.

FIG. 4 is a block diagram of a second embodiment of an electronic structure of a reference model used in one of the blocks (block 30) of the electronic control structure of the actuators according to FIG. 2. MS \ REN061 The steering system 1 of a motor vehicle shown in FIG. 1 mainly comprises a first device 50 called a restorer and making it possible to apply mechanical actions to a steering control member and a second device 80 called the steering system. .

The restorer comprises a steering control member 2 such as a steering wheel in mechanical connection with an actuator 4 said force restitution for example by means of a shaft 3. This actuator 4 is controlled by a calculator 5.

The steering system comprises a steering gear comprising steering wheels 10 (only one shown) in mechanical connection with a steering actuator 7, for example by means of a rack-and-pinion system 8 and a wheelhouse system 9 This actuator 7 is controlled by the computer 5.

The actuators are for example electric motors such as DC electric motors.

The computer acts on the actuators by providing them with torque setpoints represented by the arrows 11 and 12. These setpoints make it possible, for example, to determine the electrical characteristics of the signal supplying the actuators to obtain the expected torques.

The systems (governor and steering system) controlled provide the computer with various detailed information below and represented by the arrows 13 and 14, including the angular position of the steering wheel, the mechanical torque applied to the steering wheel and the angular position of the steering wheel. wheels.

MS \ REN061 EN.dpt The computer comprises software means for governing the operating method of the steering system object of the invention. These software means are described below in detail. They can in particular be implemented by computer programs contained and executed in the computer.

The control structure of the restorer and of the steering system, represented in FIG. 2, comprises different blocks: A first block called Reference Model 30 determines an angular position value of the flywheel called Angle_volant_ref as a function of a torque value applied to the steering wheel called Couple_conducteur; this value of angular position of the steering wheel constitutes the desired behavior for the steering system. It is therefore in this block that is modeled all the desired dynamic behavior for the vehicle. A second block 40 called Corrector de_position_restitution determines a torque setpoint value for the restituer called torque_receater as a function of the angular position of the flywheel Angle_volant_ref and a function of a measured angular position of the steering wheel called Angle_volant; this set value is supplied to the restorer; this block realizes the enslavement of the angular position of the steering wheel. It may be a conventional servocontrol of an electromechanical system and different strategies may be used. The simplest to achieve is undoubtedly a structure with nested loops: speed loop included in a position loop. Other strategies can also be used. This block outputs the control signal of the rendering motor: it is therefore thanks to this servo that the driver gets the force feedback (or torque) during maneuvers on the vehicle. MS \ REN061 FR.dpt A third block 60 called TrajectoryControlControls determines a wheel steering position value called Angle_run_ref as a function of the angular position value of the flywheel Angle_flying_ref; This block realizes the development of the position setpoint for the wheel steering system. In nominal mode the realized function is described by the equation: Angle_rules_ref = Demul (V) x Angle_volant_ref (Eq. 1) in which, Demul (V) corresponds to the desired gear ratio. To obtain a manageable vehicle, it may be advantageous to vary this ratio depending on the speed of the vehicle (denoted V). A fourth block 70 called Corrector_de_position_braquage determines a torque setpoint value for the steering system called torque_braquage as a function of the angular position of steering of the wheels Angle_roues_ref and as a function of a measured angular position of wheel-turning position called Angle_roues; this set value is supplied to the steering system; this block realizes the control of the angular position of steering wheels. It may be a conventional servocontrol of an electromechanical system and different strategies may be used. The simplest to achieve is undoubtedly a structure with nested loops: speed loop included in a position loop. Other strategies can also be used. It outputs the control signal of the steering system motor.

Thus, the restatractor receives a torque applied by the driver 20 on the steering wheel and torque torque setpoint torque from block 40. At the output, two sensors can provide two measurements: the position MS \ REN061 FR.dpt measured angular steering wheel Angle_volant and the measurement of the torque applied by the driver on the steering wheel Couple_conducteur. Alternatively, the values of one or more of these parameters can be estimated. The steering system receives meanwhile the setpoint of steering wheel torque Couple_braquage. At the output, a sensor makes it possible to provide the measured angular position of steering of the wheels. Alternatively, the value of this parameter can be estimated. A first embodiment of the first block 30 is described hereinafter with reference to FIG.

The purpose of this block is to perform a behavior similar to that found on a conventional vehicle (with a steering column and power steering). The following dynamic is then imposed on the steering system: Jref s2 0 + Kv (V) s 0 + Kp (V, 0) A + Csec (V, 8) sgn (s0) = Ccond (Eq.2) where: Ccond is the torque applied to the steering wheel by the driver 20 Driving torque, s is the Laplace operator, 0 is the flying angle Angle_volant_ref, sgn (x) is the sign function (returns 1 if x> _0, returns -1 if x <0). The various terms of the model correspond to physical phenomena actually occurring in the steering system and are as follows: ## EQU1 ## corresponds to the inertial term that one feels on a conventional steering wheel. The modification of this term makes it possible to have a feel of steering wheel either heavier or lighter regardless of its real inertia. Kv (V) s 0: corresponds to a viscous friction. This term varies with the speed of the vehicle.

Kp (V, 0) 0: corresponds to a torque of the stiffness type: the felt torque is proportional to the flying angle. The coefficient of stiffness Kp (V, 0) varies with the vehicle speed and with the flying angle itself. This term is important because it defines directly the mode of the vehicle's pendulum and the restoring torque that is exerted on the steering wheel during and after cornering. This reaction torque is low for the low speeds of the vehicle so as to facilitate maneuvers for the driver. On the other hand, when the speed is important, the reaction torque increases so as to harden the steering wheel.

Csec (V, 0) sgn (s0): corresponds to an adjustable dry friction. This term is also variable with the speed of the vehicle and with the angle of the steering wheel itself.

A first operator 100 makes it possible to perform a balance of pairs reflecting the equation Eq. 2 described above. An amplifier 110 makes it possible to involve the inertia Jref mentioned above. The signal obtained is then integrated at a first integrator 120 and a second integrator 130. The signals from the first integrator and the second integrator are used in an operator 140, in particular with a vehicle speed information to establish the term Csec (V, 0) sgn (s0) which is used in the operator 100. The signal from the first integrator is used in an operator 150, in particular with a vehicle speed information to establish the term Kv (V) s 0 which is used in the operator 100. The signal from the second integrator is used in an operator 160, in particular with information from MS \ REN061 FR.dpt vehicle speed to establish the term Kp (V, 0) e which is used in the operator 100.

The signal from the second integrator is the reference angular position value 5 of the steering wheel Angle_flight_ref.

The four operators 110, 140, 150 and 160 can be modified to adjust the behavior of the steering system according to the feeling desired by the driver. Each operator can be modified independently of the others to adjust the different components of the steering system, respectively, the inertia component, the dry friction component, the viscous friction component and the stiffness component.

A second embodiment of the first block 30 is described hereinafter with reference to FIG. 4.

This second embodiment makes it possible to take into account the actual forces (or torques) applied to the wheels by the steering actuator. It is indeed possible to wish in certain situations to restore all or part of these efforts to the driver. (This makes it possible to reproduce the behavior of a traditional variable-assistance steering system). The control structure of the reference model type also makes it possible to perform this function. Thus, the operators 210, 220, 230, 240, 250 and 260 of the control structure are identical to the operators 110, 120, 130, 140, 150 and 160 of the structure of FIG. 3. On the other hand, the operator 200 comprises, with respect to the operator 100, an additional entry to take account of the steering torque of the wheels brought to the level of the torque-resistant steering wheel. MS \ REN061 EN.dpt To do this, an amplifier 270 and a reproduction logic 280 process the steering-resistant torque signal at the level of the wheels_resistant_rocks to bring it back to a torque at the level of the steering wheel torque_resistant. The steering-resistant torque at the wheels can be measured or estimated.

The torque signal at the torque_resistant steering wheel may be the result of a situation logic and a possible filtering calculation. For example, it is possible in this way to warn the driver of an arrival in abutment on a sidewalk (in particular by a sharp increase in the resisting torque), or conversely to warn the driver during a turn on a weak grip (notably by a fall resistant torque). These strategies not detailed here are represented by the logic of restitution.

Thus, the proposed invention is based on a reference model strategy making it possible, from a measurement or estimation of the driving torque, to develop the angular position signal of the steering wheel Angle_volant_ref, which constitutes a base of desired behavior. for the steering system. It is therefore in this reference model that all the desired dynamic behavior for the vehicle and, in particular, for the steering system is modeled. Indeed, this magnitude Angle_volant_ref once obtained, is sent to the two correctors 40 and 70 responsible for carrying out the steering torque setpoints of the actuators of the steering system.

As seen above, the main advantages of the invention lie in the following facts: the invention can easily be realized on an onboard computer and, since the equations are simple, the computing capacity required for this function is very low, MS \ REN061 EN.dpt the setting parameters for the feeling are simple, they allow to act on terms of the reference model, the adjustment parameters may vary depending on the speed of the vehicle and, possibly, depending on other parameters As the angular position of the steering wheel, the reference model can easily be enriched or simplified according to the specifications retained on a given vehicle, the settings parameters correspond to physical quantities determining physical phenomena actually occurring in the systems. of direction: these parameters are therefore natural for a person skilled in the art, the invention makes it possible to whether or not additional effort measures are taken at the wheel level.

MS \ REN061 FR.dpt

Claims (12)

claims : A method of operating a system (1) electrically controlled steering of a motor vehicle, characterized in that it comprises a step of establishing a position value (Angle_volant_ref) of an organ ( 2) from a mechanical action value (driver torque) applied to the steering control member, the setting step being performed using a reference model. 2. Operating method according to claim 1, characterized in that the reference model comprises terms corresponding to physical phenomena. 3. Operating method according to claim 1 or 2, characterized in that the reference model comprises an inertial term (Jfef s2 0) and / or a dry friction term (Csec (V, 8) sgn (s0)) and or a viscous friction term (Kv (V) s 8) and / or a stiffness term (Kp (V, O) 8) and / or a mechanical action term applied to the steering control member by a driver (Ccond). 4. Operating method according to one of the preceding claims, characterized in that the reference model comprises a mechanical action term applied to the steering wheels and brought to the level of the steering control member (torque_resistant). 5. Operating method according to the preceding claim, characterized in that the term mechanical action applied on the steering wheels is brought to the MS \ REN061 EN.dptcommand direction member by a return logic dependent on the situation in which the vehicle is located. 6. Operating method according to one of the preceding claims, characterized in that the reference model varies according to at least one parameter. 7. Operating method according to claim 6, characterized in that the at least one parameter comprises the speed of the motor vehicle. 8. Operating method according to claim 6 or 7, characterized in that the at least one parameter comprises the position of the steering control member. 9. Operating method according to one of the preceding claims, characterized in that the value of the mechanical action (torque_conducteur) applied to the steering control member by the driver is estimated or measured. 20 10. Operating method according to one of the preceding claims, characterized in that the position value (Angle_volant_ref) of the steering control member (2) is used to establish a control setpoint (Torque_resistor) of a Actuator (4) applying a mechanical action on the steering control member and / or in that the position value (Angle_volant_ref) of the steering control member (2) is used to establish a control setpoint (Torque_braking) an actuator (7) applying a mechanical action on the steering wheels of the motor vehicle. MS \ REN061 EN.dpt1517 11. Electrically operated steering system of a motor vehicle comprising hardware means (4, 5, 7) and software (30, 40, 60, 70) for implementing the operating method according to one of the preceding claims. . 12. Motor vehicle comprising a steering system according to claim 11. MS \ REN061 FR.dpt