FR2867435A1 - Active braking system for motor vehicle, has information processing units with unit to establish braking force set point information of wheels, and another unit to process each wheel information to control braking system operation of wheels - Google Patents

Abstract

The system has information processing units (3) to calculate brake set point information of wheels of a motor vehicle. The units have a unit (7) common to all wheels to establish braking force set point information for each wheel. The units have a unit (8) processing information specific to each wheel to control in closed loop the operation of a braking system (6) corresponding to each wheel. The operation of the braking system is controlled in the closed loop using corresponding brake set point information and pneumatic force information given by sensors (4).

Description

2867435 1

  The present invention relates to active braking systems for motor vehicles.

  With the electronic systems currently embedded in the vehicles, the braking systems have evolved from a system in which the hydraulic brake actuation network is centralized and generates a force substantially equal to each wheel of the vehicle to an electrical system comprising a system centralized electronic control system which transmits brake torque setpoints to local hydraulic systems associated with each wheel.

  These new systems incorporate electronic braking distribution (REF) algorithms whose aim is to guarantee an optimal braking in terms of forces generated by classically distributing braking pressures between front and rear axles. The optimum corresponds to the case where the grip limits are reached at the same time for the front and rear wheels without locking the wheels.

  It should be noted that for safety reasons, the algorithm should prohibit a situation in which the rear wheels lock up before the front wheels. Indeed, in this situation, the vehicle is no longer stable and can start spinning.

  All other things being equal, the limits of adhesion depend on the longitudinal acceleration experienced by the vehicle and the distribution of masses thereof.

  The deceleration experienced by the vehicle is, in the current systems, interpreted according to the request of the driver on the brake pedal. It is therefore an open-loop system since there is no feedback.

  Moreover, the weight distribution is assumed to be constant which is practically false since it varies with the number of occupants of the vehicle and with its load.

  This can be explained by considering the braking equations used.

  For a vehicle, the longitudinal acceleration ax (t) of that is dictated by the equation mtax (t) = EFxi (t) where mt is the total mass of the vehicle and Fxi is the longitudinal force exerted on a wheel i, this being summed for the four wheels.

  2867435 2 Assuming the ideal situation (braking in a straight line, symmetrical grip) and the braking forces reaching their maximums at the same instant, we obtain the equation Fxi (t) = llmax E Fzi (t) where pmax is the maximum of possible adhesion depending solely on the nature of the contact between the tire and the ground and FZ; (t) is the normal force exerted on the wheel i.

  Thus, at the physical limit of the tires, one obtains pmax = 9 and thus has Fxi (t) = g.FZI (t). Conventionally, the REF uses an approximation in the distribution of the masses of the vehicle in which the mass on the front axle mav = LLr mt with L the length of the vehicle and Lar the distance from the center of gravity of the vehicle to the rear of it. Likewise, the mass on the rear axle can be written: mar Lar mt.

The

  Thus at static equilibrium, the normal force exerted on the front axle becomes Fzaavique = m av g Lar mtg and on the rear axle L Fstatique Lav zar = mars = L mg.

  In dynamics, the load then becomes approximately * static _ hma 1 / t rFzav (t \ / = zav L tx F tl F static + hma (tl zar \ I zar L x \ / where h is the height of the center of gravity of the vehicle.

  Let afreinage (t) be the coefficient of distribution of the braking as a function of the acceleration of the vehicle, that is equal to Fxar (t) = a braking (t). Fxav (t) and thus, any computation done, Lav + ax (t) hg Lar ax (t) h g to braking (ax (t! 1 and thus depends only on the longitudinal acceleration ax (t).

  The acceleration ax (t) is interpreted as the driver's demand on the brake pedal.

  Knowing that, practically, we use the three nominal parameters of mass m, ma, -nia, corresponding to a nominal change, it is easy to understand that the distribution coefficient is not optimal.

  The longitudinal setpoint forces for each set of wheels are F (t) = m roll (t) at xar \ / l + a (t) (braking. They are conventionally converted into setpoint braking torques 10 by {Cf. (t) = Radius roueav.Fxav (t C far (t) = Radius _ wheel, .Fxar (t) The approximations which are thus made lead to the design of braking systems with large margins of safety and which are therefore far from the theoretical optimum.

  Now, there are now new sensors capable of acquiring the forces exerted on a tire.

  Patent EP 0 906 206 discloses a method for regulating the driving behavior of a vehicle in which such tire force sensors are used to determine the forces acting on the wheels, these forces constituting the regulation quantity of the vehicle. process. This patent describes a possible application of this method to the electronic regulation of braking.

  If the principle of a control loop is well known, it appears that architectures of current braking systems do not allow easy implementation because they were designed in an open loop control approach.

  The object of the invention is therefore to overcome this drawback, namely to define a braking system architecture which uses pneumatic sensors to generate an effective braking and in particular an optimal electronic braking distribution. so

  Fxav (t) = Mt r} ax (t) 1 + a braking \ t! The object of the invention is therefore an active braking system for a motor vehicle comprising driver-controlled vehicle braking control means connected to appropriate information processing means for calculating braking command information for each wheel of the vehicle from the brake control information and other information relating to the dynamic behavior of the vehicle and regulate in a closed loop braking means of each wheel of the vehicle from the corresponding braking instruction information and pneumatic force information delivered by corresponding pneumatic force acquisition means installed on each wheel, characterized in that the information processing means comprise, on the one hand, a first information processing unit common to each wheel; all the wheels of the vehicle to establish the braking force instructions information for ch one of them and, secondly, second information processing units specific to each wheel to regulate closed loop operation of the corresponding braking means specific to each wheel of the vehicle.

  According to other characteristics of the invention: the information relating to the dynamic behavior of the vehicle comprises the pneumatic force information of each wheel; the information processing means comprise means for optimizing the braking instruction information; the optimization means use the normal pneumatic force information from the pneumatic force acquisition means, so that the wheel adhesion limits are reached simultaneously; the optimization means comprise determination means; the total mass of the vehicle, the height of the center of gravity of the vehicle, and the respective distances separating the center of gravity of the front and rear axles from the information of normal pneumatic forces, in order to determine the optimum ratio between the front and rear braking forces, - the optimization means use the information of pneumatic forces lo nitudinal signals from the pneumatic force acquisition means, so that the wheel adhesion limits are reached simultaneously, each second information processing unit enslaves, by a closed-loop control, each force instruction from the first information processing unit by the acquisition means comprising longitudinal pneumatic force sensors for each wheel, the braking means are controlled by a local electro-hydraulic braking device (EHB ), electro-mechanical (EMB) or hydraulic (ABS).

  the information processing means are integrated in a single computer, or the information processing means are integrated in several computers, the second processing units then being installed in computers corresponding to each wheel.

  The invention will be better understood on reading the description which follows, given solely by way of example, and with reference to the appended drawings, and in which: FIG. 1 is an overall diagram of the invention; ; FIG. 2 is a diagram of the functional architecture of the invention; - Figure 3 is a diagram of the central control of the vehicle; FIG. 4 is a diagram of the local braking regulation according to the invention; FIG. 5 is a diagram of a first embodiment of the invention; and - Figure 6 is a diagram of a second embodiment of the invention.

  Referring to Figure 1, the active braking system for a motor vehicle 1 according to the invention comprises brake control means 2 controlled by the driver. They correspond classically to the brake pedal associated with the master cylinder.

  The control means 2 are conventionally connected to information processing means 3 such as automobile computers.

  These information processing means 3 are, moreover, connected to sensors 4 installed on each wheel 5 so as to transmit to the information processing means 3 the pneumatic forces experienced by the wheel.

  The pneumatic forces can conventionally be broken down into three orthogonal forces: a longitudinal force, axis x, in the direction of movement of the vehicle, a normal force, axis z, perpendicular to the roadway and a transverse force, axis y, perpendicular horizontally to the displacement.

  Each wheel comprises a brake system 6 which, conventionally in the active braking systems, comprise a hydraulic braking system which receives, from the information processing means, electric braking torque controls to be applied. The hydraulic system then actuates the pads of the disc brakes to cause the requested braking.

  In order to allow precise control of the braking, the information processing means 3 comprise two units: a first unit 7 is in charge of the overall behavior of the vehicle under braking and a second unit 8 is responsible for the local regulation of the braking on each wheel.

  The operation of the system, Figure 2, is as follows.

  The first unit 7 receives the braking command 2 as well as general information 9 on the dynamic behavior of the vehicle such as its speed, its acceleration, the position of the steering wheel, and in particular information from the pneumatic force sensors. .

  From this information and pre-established behavioral models stored in the unit, this first unit 7 deduces a distribution of braking torques between the wheels, in particular between the nose gear and the rear axle, in order to obtain optimum braking.

  By taking up the equations previously described, it is now possible to replace the nominal and approximate values, mav, mar and h by their values calculated from the real conditions.

  Thus, the front and rear masses can be deduced from the normal forces on the front and rear trains as detected by the pneumatic force sensors = Fzav mav Fg tzar mar g braking 2867435 It is conceivable that the accuracy of the masses is no longer dependent than the accuracy of the sensors.

  It is also possible to calculate the height h of the center of gravity of the vehicle by a simple modeling thereof, modeling whose main parameter is the travel of the suspension and tires, which travel depends on the masses supported.

  Thus h becomes a function of masses: h = f (mav, mar).

  By repeating the calculations presented previously with these new values, we obtain

The

The

  Lav + ax (t) with braking (ax (t = hg () t Lar ax (t) hg Fxav (t) = Mt (t) ax (t) 1 + a braking Fxar (t) = mt braking (t) Atl + a (t) The values being updated according to the actual load of the vehicle 15 are therefore much more accurate.

  Thus, the first information processing unit 7, FIG. 3, receives the braking setpoint ax as well as the front and rear pneumatic forces Fzav, Fzar for calculating the setpoints in braking torques Fxcav, FxcarÉ. The braking torque information is received by the second unit 8 which, for each wheel, establishes a closed-loop control / command system, FIG. 4. For each wheel, this second unit 8 receives, on the one hand, the brake torque setpoint Fxc originating from the first 7 and on the other hand, the longitudinal force Fxm experienced by the wheel and provided by the force sensors and therefore pneumatic 4. This second unit deduces a new braking torque which is transmitted at 11 to the local device. braking of the corresponding wheel.

  The local braking device 11 is composed of, for example, an electro-hydraulic braking system (EHB), an electromechanical braking system (EMB) or a hydraulic system (ABS).

  The local braking device 11 is thus able to translate the new braking torque into pressure or current so as to apply a braking torque to the wheel whose value is measured by the pneumatic force sensor 4.

  In the physical implementation of the invention described above, FIG. 5, the first 7 and second 8 units are separated between a central computer which contains the first unit 7 and decentralized computers with each wheel 5 and containing the second unit. 8, which is thus duplicated. The communication between the central computer and the decentralized computers is performed via a data link, such as, for example, a CAN bus.

  Another physical implementation of the invention, FIG. 6, consists in grouping together in a single central computer the first and second units 7, 8.

  These then behave, conventionally, as tasks managed by the operating system of this computer, the coordination between these tasks being carried out conventionally by semaphore and mailbox.

  In the implementation of the invention described, the pneumatic force sensors make it possible to detect the longitudinal and normal forces that apply to the wheel.

  A low cost implementation of the invention is implemented by the use of pneumatic force sensors which generate only information on the longitudinal force experienced by the wheel.

  The first unit then calculates the optimum distribution to the four wheels 30 using only these longitudinal forces.

  As indicated, the normal forces are used to determine the distribution of the masses mt, mav, mar. Consequently, the absence of sensors making it possible to detect the normal forces necessitates the use of the approximations of these masses as explained in the description of the prior art.

  This approximation can, however, be reduced by using information accessible on the vehicle control network in a conventional manner such as the state of the clutch, the torque delivered by the engine to the wheels and the use of the brake pedal.

  It is thus possible to estimate the total mass of the vehicle by knowing the traction force of the engine when no braking is applied and the transmission engaged. However this traction force can be deduced without difficulty from the longitudinal forces and the engine torque.

  Knowing then the total mass, it is possible to make the assumption that the difference of this one with the nominal mass corresponds to a loading of the trunk and thus to an increase of the rear mass only.

  The invention thus makes it particularly advantageous to use pneumatic force sensors to regulate an electronic braking distribution.

2867435 10

Claims (10)

  An active braking system for a motor vehicle (1) comprising driver-controlled vehicle braking control means (2) connected to information processing means (3) adapted for calculating braking command information. for each wheel of the vehicle from the braking control information and other information relating to the dynamic behavior of the vehicle and regulating in a closed loop braking means (6) of each wheel of the vehicle from the setpoint information of corresponding braking and pneumatic force information delivered by means of acquisition (4) of corresponding pneumatic forces installed on each wheel, characterized in that the information processing means (3) comprise, on the one hand, a first information processing unit (7) common to all the wheels of the vehicle for setting the braking force setting information for each e of them and, secondly, second processing units (8) of information specific to each wheel to regulate closed loop operation of the braking means (6) corresponding to each specific wheel of the vehicle.   2. Active braking system according to claim 1, characterized in that the information relating to the dynamic behavior of the vehicle comprises the information of pneumatic forces of each wheel.   3. Active braking system according to claim 2, characterized in that the information processing means (3) comprise means for optimizing the braking command information.   4. Active braking system according to claim 3, characterized in that the optimization means use the normal pneumatic force information from the acquisition means (4) of pneumatic forces, so that the limits of adhesion of wheels are reached simultaneously.   Active braking system according to claim 4, characterized in that the optimization means comprise means for determining the total mass of the vehicle, the height of the center of gravity of the vehicle, and the respective distances separating the center of the vehicle. gravity of the front and rear axles from the information of normal pneumatic forces, in order to determine the optimum ratio between the forward and reverse braking forces.   6. Active braking system according to claim 3, characterized in that the optimization means use the longitudinal pneumatic force information from the acquisition means (4) of pneumatic forces, so that the limits of adhesion wheels are reached simultaneously.   7. Active braking system according to any one of the preceding claims, characterized in that each second information processing unit (8) enslaves, by a closed-loop control, each braking effort setpoint coming from the first information processing unit (7) using the acquisition means (4) comprising longitudinal pneumatic force sensors for each wheel.   8. Active braking system according to claim 7, characterized in that the braking means 6 are controlled by a local braking device 11 of electro-hydraulic (EHB), electro-mechanical (EMB) or hydraulic (ABS).   9. Active braking system according to any one of the preceding claims, characterized in that the information processing means (3) are integrated in a single computer.   Active braking system according to one of Claims 1 to 8, characterized in that the information processing means (3) are integrated in a plurality of computers, the second processing units (8) being then installed in respective calculators at each wheel.