WO2001036240A1

WO2001036240A1 - Electronic braking device

Info

Publication number: WO2001036240A1
Application number: PCT/CA2000/001361
Authority: WO
Inventors: Yvon Rancourt; Christian Menard
Original assignee: Newtech Mecatronic Inc.
Priority date: 1999-11-15
Filing date: 2000-11-15
Publication date: 2001-05-25
Also published as: AU1682901A

Abstract

The invention concerns a braking control device whereby maximum braking control is obtained by measuring and controlling the drag torque measured on the brake by means of a sensor measuring said torque (43). Advantageously, the drag torque is controlled by the pilot's brake pedal (31). It enables to control the braking force whatever be the actuating member for the mechanical mobile parts of the hydraulic, pneumatic or electromagnetic brake (39).

Description

ELECTRONIC BRAKING DEVICE

FIELD OF THE INVENTION

The present invention relates to a brake control device in which the control of the maximum braking efficiency is obtained by measuring and controlling the drag torque measured on the brake using a sensor for measuring this torque. . Advantageously, the drag torque is controlled by the pilot's brake pedal.

PRIOR ART

Electronic braking systems were introduced to the market at the end of the 1960s. It was the aeronautics sector which first used these devices, in order to solve the technical problems caused by the use of anti - mechanical, electromechanical and electro-hydraulic blockers. Examples of these include the "max-stop" from Dunlop, the "mini modulator" from Messier in Europe, the "anti-skid" from Bendix and Hydro Air in the United States. All these devices are generally called "anti-skid".

Anti-skid or anti-blockers, as their name suggests, aim to prevent the locking of a wheel or several wheels of a mobile such as an automobile, a train, an airplane etc. that we want to stop. The operation consists, during the moments of braking when the pressure is applied to the brakes, to measure by mechanical means such as the weights, or electric such as a deceleration or speed variation sensor, the deceleration of the wheel which equips the mobile, and cut, as a function of a certain deceleration, the hydraulic supply applied to the wheel brake, in order to release the rotational movement of the wheel and allow it to regain speed by function of grip on the ground. This action then allows the moving vehicle to avoid blocking the wheel, i.e. stopping the wheel and, consequently, destroying the coating. wheel (tires, tires, etc.) which could cause loss of directional control of the mobile.

For airplanes, the initial objective was not to destroy the tires and to avoid flat spots on the tread, bursts and all types of deterioration, for example, the slip of the tire bead in the rim, which could have endangered the safety of the airplane during braking on the ground, both during landing and during the taxiing.

For trains, the objective has been to avoid the flats on the steel tread, and therefore not to create facets on the wheels, these facets causing premature wear of the wheels and rails, jolts and random noises at each revolution of the wheel during the rolling, thus causing the activation of mechanical natural frequencies and destruction by bursting of the wheel.

Originally, these systems were developed for security purposes. However, it is necessary to locate the mobiles in time and to take into consideration an important factor which is the increase in the speed and the weight of the latter, as well as the increase in the number of vehicles in circulation. These parameters, combined with technological progress, have contributed to the evolution of anti-blockers.

In the case of airplanes, the landing speed is generally between 100 and 360 km / h, and their mass varies between 8 and 100 tonnes. For a train, the speed is of the same order of magnitude, but the mass is greater and varies greatly depending on the number of wagons making up the train.

In the 1960s, the mere fact of avoiding the locking of the wheels did not optimally solve the problem posed by braking, this problem being to stop the mobile for the optimal distance allowed by the grip ground. The laws of physics indicate that to achieve this objective, it is necessary to apply to the brakes a braking force in accordance with the maximum allowed by the law of adhesion to which the wheel is subjected, and that consequently, the wheel will never be blocked if at all times the laws of physics are respected.

A device commonly known as the Advanced Anti-Skid System (SPAD), currently in service on aircraft of the company Dassault and the Airbus Industries Consortium, has recently been developed. The SPAD is an electronic system which exploits the principle of wheel slip control. In theory, the slip is related to the grip, and therefore the control of the slip is a good method to maintain a wheel at a desired slip, slip which can be adjusted for a value where the wheel evolves at the maximum of the curve d grip, therefore maximum braking efficiency. However, the difficulty is that the slip, which is also the result of the equation g = (V- v) / V in which V is the linear speed of the mobile to stop, and v is the speed of the wheel to brake , is not very easy to calculate with precision for the following reasons. Indeed, the calculation of the linear speed V of the mobile is not easy to obtain, either from the point of view of precision or economically. Indeed, the greater the precision, for example of the order of 2 to 3%, the higher the costs associated with obtaining such precision. There are several techniques for obtaining the linear speed V. The best known are the following:

The first consists in obtaining the speed of the mobile relative to the ground by measuring, using a tachometer mounted on a device in contact with the ground (unbraked wheel), the speed of the mobile.

The second measures the deceleration of the vehicle using a sensor such as an accelerometer, then integrates this deceleration to calculate the speed. This way of proceeding supposes a precise calibration of the accelerometer and consideration of the change in the position of the accelerometer, in the positive or negative direction, depending on the movements of the mobile.

The third uses an inertial unit which provides information on the speed of the mobile.

The fourth calculates the average speed of all the braked wheels, and this information is transmitted to an electronic calculation operator who calibrates the speed.

The fifth calculates, relative to a target, the speed using a radar, a laser or a telemetric device.

Each of these techniques has significant disadvantages.

For techniques 2 and 4, the accuracy of the speed measurement varies between 3 to 15%, which is hardly acceptable. The implementation of technique 1 assumes that at least one of the wheels or an additional wheel is equipped with a tachometer independent of the wheels subjected to braking. Technique 5 includes, in principle, uncertainties when the target is lost, for example as a function of the density of the fog, the size of the puddles, the orientation of the antennas and targets, the effect of echoes and interference of any kind, etc. Furthermore, the cost of implementing techniques 1 to 3 and 5 is relatively high, and therefore hardly acceptable for a braking system which controls the sliding of the wheels for application sectors such as the automobile and land transport.

It is understood that the cost and imprecision of measuring the speed limits the possibilities of the systems which control the sliding of the wheels and that, by the same fact, it is difficult to keep the wheels to brake at optimal glide, therefore at an optimal grip, and thus obtain an optimal stopping distance.

IN THE DRAWINGS Figure 1 illustrates the theoretical appearance of a so-called "natural" grip-slip curve established at the start of braking with a strong deceleration of the axle;

Figure 2 illustrates a characteristic grip-slip curve established at the start of braking (idealized course); Figure 3 illustrates a characteristic curve τ as a function of the slip;

Figure 4 illustrates different grip-slip curves established experimentally at a speed V _τ of 120 km / h;

Figure 5 illustrates the influence of the deceleration of the axle on the position of the apex B;

Figure 6 illustrates the deformations of the curves τ = F (sliding) with very high and prolonged sliding;

Figure 7 illustrates the evolution of the relation μ., As a function of energy; Figure 8 illustrates the modification of the grip by the maintained slip;

Figure 9 illustrates a braking curve during a stop from 180 km / h with controlled permanent slip;

Figures 10a and 10b illustrate a sensor used in the device of the present invention; Figure 11 illustrates an electronic module used in the device of the present invention;

Figure 12 shows the sensor output voltage (V) vs. displacement (μm);

Figures 13a, 13b, 14a and 14b illustrate a brake comprising a sensor according to the present invention;

Figure 15 illustrates a detail of Figure 14; Figure 16 illustrates a force curve (N) as a function of the air gap (mm);

Figures 17a and 17b illustrate the position of the sensor on a brake pedal; FIG. 18 illustrates a situation where a sensor has been put in the brake at a pressure capable of maintaining a constant torque on the wheel, and where the initial speed Vref of this wheel decreases linearly from Vref towards a zero speed;

Figure 19 illustrates the organization of control loops; Figure 20 illustrates the principle of brake regulation according to the present invention with a pedal setpoint controller;

Figure 21 illustrates the so-called torque setpoint law C _c = F (U1) which the brake must follow;

Figure 22 illustrates the law of measurement of the drag torque, or braking torque, on the brake Cf by the torque sensor;

Figure 23 illustrates the general reference equation of the pole which is related to the mathematical equations of the tire of the wheel and the suspension;

Figures 24a and 24b illustrate a grip curve as a function of the wheel slip rate, and different pedal setpoint control curves;

Figures 25a and 25b illustrate examples of the regulator transfer function (gain and phase);

Figure 26 illustrates the composition of the electronic device according to the present invention;

Figures 27 and 28 illustrate the calculation of the longitudinal speed V _L from the wheel speed information, braking torque, distance traveled and mass of the vehicle; and

Figure 29 illustrates the variation of the system elements during braking. DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a new braking system designated under the name IBS (Intelligent Braking System), which makes it possible to maintain the braking torque to the maximum allowed by the grip to which the wheel is subjected, and therefore to be able to obtain efficiency. maximum braking.

To properly situate the object of the invention, the basic equations which govern braking are provided below, as well as the conventional definition of grip as well as the parameters which influence grip. The basic parameters and equations are as follows.

P is the load on the ground of the axle in the dynamic state;

M is the mass on the ground of the vehicle; g is the sliding of the wheel relative to the ground;

Fe is the braking force of an axle brought back to the rim and relative to the brakes using ground-wheel grip;

F is the sum of Fe for the vehicle; r is the radius of the wheel;

I is the moment of polar inertia of the axle; m is the sum of l / r ² for the vehicle; Re is the reaction of the road on the axle or drag;

R is the sum of Re for the vehicle; v is the circumferential speed of the wheel;

Vt is the vehicle translation speed;

Yv is the deceleration of the vehicle, or dVt / dt; Yr is the deceleration of the wheel, or dv / dt; and

Ra is the resistance to the advancement of the vehicle;

The basic braking equation is

Re = Fe ± (l / r ² ) dv / dt

In a braking phase, when the axle does not slip, the equation is Re = Fe - (l / r ² ) dv / dt

For vehicle M * Yv = R + Ra

In a non-braking phase,

Re = (l / r ² ) dv / dt

The conventional definition of grip makes it possible to write that in the presence of a maximum braking force (Fmax), reduced to the rim, it is possible to exert a force on an axle without the latter slipping. The maximum reaction Rmax of the wheel corresponding to the force Fmax the available grip. This is expressed by the relation τ = Rmax / P = μ since by definition the axle does not slip, the inertia term (l / r ² ) dv / dt is weak compared to Fe in the case of a car, and if we neglect this term we then obtain τ = Fmax / P = μ which shows that the braking force is in direct relation with the grip.

There is a complementary approach which is that of the requested adhesion. It can be expressed as a function of the braking force F or of the vehicle deceleration Yv. The equation is τ = R / Mg = (M * Yv - Ra) / Mg knowing that (M + m) Yv = F + Ra and that M ^* Yv = R + RA, we deduce then that τ = F / g (m + m)

We can also establish the relation which takes into account the rearing effects by introducing the term P. In this case, the equation is τ = (Fe -l / r ² - Yv) / P the natural law of grip has the expression τ = Re / P, and the available grip depends on the variable g which determines the relative slip of the wheel with respect to the ground. One expresses the slip by the relation of the absolute speed of the slip and the speed of the vehicle, relation which one can express in the form Slip = WΛ t with W = Vt -v, which is the absolute speed of the slip.

Generally speaking, the available grip depends on a variable which is the relative slip of the wheel with respect to the ground. There is, for each wheel-ground contact state defined by the Coulomb coefficient μ and for each speed, an available grip curve similar to that of Figure 1 and Figure 2.

It can be seen that the adhesion passes through a very sharp maximum point if the slip is very low, for example in the case of steel-on-steel friction, and through a less sharp maximum point for a much greater slip, for example in rubber friction on asphalt (see Figure 3).

The analysis of the adhesion curves makes it possible to note that beyond point B, the adhesion decreases and, at each point, the curve satisfies the equation τP = Re = Fe - (l / r ^ dv / dt If Fe is kept constant, that is to say if the braking torque is constant, then the equation becomes dτ / dv * dv / dt * P = (-l / r ² ) d ² v / dt ² On sees that in this case dτ / dv is canceled at the same time as the second derivative of the speed v. The grip-slip curves vary with grip (Figure 4), which themselves depend on atmospheric conditions, as well as parameters such as speed, pressure of the wheel on the ground and slip energy developed in wheel-ground contact. There are therefore an infinite number of grip curves and, during braking, we pass from one curve to another.

The equation of the sliding energy has for expression t E = JPzWdt

The parameters which influence the grip are the macrogeometric state of the wheel-ground surfaces in contact, the soil pollution, the atmospheric conditions, the running speed, the dynamic vertical load P of the axle. The geometrical parameters of the wheel and the ground have their influence on the specific contact pressure wheel-ground. On this last point, it is interesting to note that this parameter is very influenced by the dynamics of the vehicle and in particular by the suspension. On the theoretical level, the influence of the specific pressure Ps on the adhesion can only be considered in the field of pseudo-sliding thanks to the theories of Hertz: Ps = K1 * Q ^1/3 and of Kalker: τ = K2 * Q ^"1/3 , K1 and K2 being constants and Q designating the dynamic load on the wheel.

It is deduced from the above that Δτ / τ = ΔPs / Ps, which determines that any increase in the specific pressure leads to a proportional decrease in adhesion.

It is mentioned above that the sliding energy has an influence on the adhesion, and therefore on the sliding power. By definition, the sliding energy of an axle evaluated between the start of braking and any instant is expressed according to the above definition, and this energy moves the vertex (see Figure 5). As illustrated, a strong deceleration reduces the time required to reach point B as well as the grip at this point. However, this is offset by a stronger slip. Consequently, the sliding energy is the same in both cases. The more the deceleration increases, the more the vertex B is rejected towards the right of the curve. The contact of a steel wheel with a steel rail is a typical example. If we consider the contact of a rubber wheel on an asphalt floor, the point B also moves, but the grip does not decrease. Rather, it increases due to the regeneration of the tire surface and the increase in temperature of the contact surface.

The trend of the changes in the position of B is linked to

A) the deformation of the characteristics τ = f (slip) (see Figure 6)

B) the evolution of the curves μ = f (optimal slip) at isoenergy (see Figure 7)

The regeneration of the grip during controlled braking, which maintains the slip in the vicinity of the optimum, makes it possible to observe a progressive rise in the grip which seems to be in relation with the development of the energy of the slip. In certain cases, for a given energy, the adhesion can double, or even triple in the space of 10 seconds, which illustrates, to a certain extent, Figure 8. For the same sliding at any point, the adhesion increases with time t of sliding maintenance. During the time τ, we progressively pass from the adhesion curve C1 (point M) to the adhesion curve C2 (point N). The new adhesion in N is greater than that in M, it can if necessary reach and exceed the adhesion μ., Which one had at time t = 0 at the point B corresponding to the optimal slip.

The sliding power benefits from the sliding energy, but this sliding is not conservative, because the grip gain ceases when cancels the sliding, and therefore the sliding power. This explains why a braking system which tolerates sliding cyclically, therefore without maintaining it, poorly regenerates grip, and therefore cannot achieve optimal performance.

A study by finite elements has shown that the sliding wheel maintained on the ground undergoes, in the contact zone, a fugitive rise in temperature directly linked to the sliding and therefore to the sliding power. Figure 9 illustrates the variations of the optimum of adhesion as a function of speed V for a steel on steel contact. The same is true for rubber / asphalt contact, except that the speeds must be multiplied by a factor of approximately 1.5.

Given the above, it is clear that the search for an optimal slip is very complex given the large number of variables which are otherwise difficult to control.

The object of the invention is to show that by considering the equations of the physics of an axle and wheel-ground system, therefore by acquiring means for permanently measuring the braking force which develops in a brake, we obtains the image of the grip, and by that very fact that of the drag Re which is the basic parameter. All modern braking systems require knowledge of Re or its calculation. Indeed, knowing Re at each instant, and in particular its maximum value, makes it possible to control the optimal braking efficiency since it is the values of Re which determine the conditions of the slip to which each wheel will be subjected.

The invention does not seek to impose a slip value, but rather an optimal braking force which balances the optimal drag, which will determine the optimal braking efficiency corresponding to the physical parameters to which the wheel or wheels are subjected, as well as the axle. The present invention consists in measuring the braking force developed in the brake, using an extensiometry sensor. Such a sensor is illustrated in Figures 10a and 10b, and is designed to measure the deformation of the structure on which it is fixed. It therefore makes it possible to measure the forces, torques and accelerations applied to this structure. The sensitive element of the sensor works only in bending. The stresses are therefore very low on the fixing points whatever the type of stress on the structure. Operation is based on a mechanical extensometer method, with integrated conditioning electronics. It delivers, for information only, an electrical signal which comes from an electronic module (see Figure 11) between 0.5 volts and 4.5 volts for a displacement of the anchor points variable from 0 to 40 μm in accordance with Figure 12. As an example, Figures 13a and 13b illustrate such a sensor placed on a brake. Such a sensor mounted on a brake caliper also produces an electrical signal directly related to the braking force developed by the brake.

The sensor is used regardless of the brake activation systems, that is to say, whether these systems are hydraulic, pneumatic or electromagnetic. Figures 14a, 14b and 15 give an embodiment of a brake equipped with a magnetic ring and an armature. The armature is in relation to the friction plates of the brake. The magnetic field produced by the passage of current in the magnetic ring closes in the armature and the force (in Newton) produced is given in Figure 16 as an indication for a ring supplied by a voltage of 12 volts.

Knowledge of the actual braking torques makes it possible to measure the drag torques and to give control signals using electronics which places the value of the torque which must be applied in the brakes at the optimum values which correspond to the optimum adhesion. The control action of the IBS system is determined by the pilot who imposes a torque setpoint on the brakes, that is to say which imposes a braking torque on all the brakes through the use of a sensor associated with the action on the brake control pedal, the sensor being called torque setpoint

The value of the torque in each brake is controlled by a sensor, the signal of which is compared at all times to the torque setpoint.

The computer which measures and carries out the weights as a function of the drag torques adapts the torque setpoints as a function of the optimum of the admissible adhesions for each wheel, which makes it possible to apply the torque adapted to the optimal braking conditions in the brakes.

The system is controlled in the same way as a pilot would, who would adapt his action on the pedal according to grips so as to obtain maximum braking efficiency and the shortest stopping distance possible.

The I B S system calculates the adhesions with precision and makes it possible to place the regulation of the torques of the brakes to the maximum of the adhesions allowed by the physical laws which govern braking.

The IBS system modifies the driver's request (automatic reduction of the torque setpoints) if the requested couples are unacceptable (too high) for the grip conditions to which the vehicle is subjected. It always leaves it to the driver to freely control the braking (increase in torque settings) if the requested torques are acceptable for the grip conditions to which the vehicle is subjected. The sensor operates as follows. When the electromagnetic pressure or force is applied in the brake and the wheel turns, the part of metal on which the sensor is fixed is subjected to forces which determine elongations in the structure of the brake and the sensor. An example of installation of the sensor on a brake pedal is illustrated in Figures 17a and 17b. These elongations are of the order of several tens of microns. The sensor therefore makes it possible to have an image of the drag, but above all it makes it possible to know the exact position of the maximum of the grip curve when the wheel is braked and that it is driven by a rotational movement (see Figure 18). In this figure, we note that when it is put in the brake at a pressure capable of maintaining a constant torque on the wheel and that this causes a linear decrease in the speed of the braked wheel from an initial speed Vref from a given value to zero speed, the slip of this wheel at the reference speed corresponds to a value of 0% slip, and under the effect of the braking force, the speed decreases and the wheel reaches 100 % slip.

It can then be seen that the signal produced by the sensor mounted on the brake describes a curve which shows an increase in the value of the signal for wheel slip values from 0% to around 18%, then a decrease in the value of the signal large enough for slip values of about 18% to about 28%, and then a moderate decrease in the value of the signal for slip values of about 28% to about 84%, then large about 84% to 100%.

The sensor delivers an image of the drag, therefore of Re. It thus makes it possible to locate the level of grip, as well as its maximum. Indeed, the same recording for an increased load P on the wheel and carried out under the same conditions gives the same maximum at 18% with a higher maximum level. The time taken for the wheel to travel from 0% to 100% is in the range of 0.5 to 0.6 seconds. The slip value is not maintained, so the slip energy does not evolve the position of maximum grip towards increasing sliding in this case.

Knowledge of the maximum of the curve is one of the main elements used in the implementation of the invention. The maximum grip curve is traversed when the wheel is subjected to a constant torque Cf and the speed of the wheel tends towards increasing slip. It is therefore necessary to impose a torque setpoint Ce on the wheel. Figure 19 gives the organization of the control loops, a command of the invention which is based on the agreement between a torque setpoint Ce requested by the pilot and the resulting torque Cf in the brake thanks to the implementation by means explained below.

The sensor mounted on the brake pedal, according to Figures 17a and 17b, delivers an electrical signal the level of which is in direct or indirect relation to the mechanical force which opposes the movement of the pedal and which determines the function U1 = F (fp) (see Figure 20) in which U1 is expressed in volts and fp in mdeca Newton units and which can translate several pedal forces: fpa, fpb, fpc for example. The operator 32 determines a so-called pedal force instruction law which is related to the sensations desired by the driver as a function of the type of vehicle or of the vehicle itself.

The pedal law therefore receives the function F (fp) and modifies the function to develop a so-called torque setpoint law Ce = F (U1) (see Figure 18) which the brake must follow. It is understood that the operator 32 is capable of calculating laws Ce (a, b, c.) As a function of the set point that one wishes to give to different brakes. For the invention to be better understood, we will focus on a single wheel and a single setpoint law, for example the law

Cc (a) = F (U1)

Still in Figure 19, the torque setpoint law is directed to three summing operators connected in cascade 33, 34 and 35, which each have the ability to perform several functions. The first 33 compares the setpoint Ce requested with the result from a calculation operator 37 which is a controller of the setpoint of the pedal and which we will consider at this stage without action on the law of the pedal. The second 34 compares the requested setpoint Ce with the result from a calculation operator 36 which is a slip controller in which the system operates, and which delivers a corrective function greater or less than the torque setpoint Cc (a). In the case where the operator 36 is deactivated, that is to say when the system does not integrate the knowledge of the slip, then the operator 36 does not intervene and the operator 34 is without action. Therefore, it is the operator 35 which compares the setpoint Ce requested with the result from the calculation operator 33. The drag torque or braking torque is measured on the brake Cf by the torque sensor 43 whose the law is a function of U2 = F (Cf) (see Figure 22). U2 is expressed in volts and Cf in mdeca Newton units, which translates the torque of the brake Cf (a) for example. The function U2 = F (Cf) enters a torque regulation operator 38 which provides the processing necessary for the stability of the torque control control loop, and which will be explained below. The results of the treatments of 38 go into 35 which performs the comparison of the information in order to deduce therefrom a signal on a proportional actuator which determines the pressure in the brake 40 and consequently ensures the closing of the control-command loop.

Balance is then obtained between the requested setpoint and the torque in the brake. The operation of the control loop is as follows. If the value of the torque measured on the brake Cf is increasing, this means that the wheel is moving in the stable zone of the grip curve. This is the case Cc-Cf = - E1. If the value of the drag torque is decreasing, and the setpoint is increasing or constant, then the wheel moves in the unstable zone of the grip curve. This is the case Cc-Cf = + E1. At the maximum of the adhesion curve, Ce -Cf = 0.

In other words, there are three possibilities: 1) the braking torque Cf, which can be applied to the brake and to the wheel, is always greater than the torque setpoint Ce requested by the pilot.

2) the braking torque Cf, which can be applied to the brake and to the wheel, is always smaller than the torque setpoint Ce requested by the pilot. 3) the maximum braking torque Cf applied to the brake and to the wheel is the maximum applicable taking account of the grip.

We then understand that it suffices to compare the torque setpoint requested and the drag torque. If the variations of the two pieces of information are of the same sign, it is because the wheel is moving in the stable zone of the grip curve. If the two pieces of information are of opposite sign, then the wheel moves in the unstable zone of the grip curve. Between the two zones is the maximum, i.e. the value at which the torque setpoint must be maintained to obtain optimal braking efficiency. The device must therefore continuously increase the torque setpoint as long as the 2 pieces of information are of the same sign, and decrease as a function of time the torque setpoint when the information items are of the opposite sign. To this is added an operation which consists in measuring the derivative of the signal produced by the dCf / dt sensor, and the result of this operation is used to check the consistency of the orders and to confirm the direction of the orders of increase and decrease of the torque setpoint. The speed of correction of the torque setpoint will be all the slower as the difference Ce - Cf = + E1 will be large (unstable zone) and all the more rapid as Cc-Cf = - E1 will be large (stable zone) .

The time base or the gain of the increase or decrease of the torque setpoint is therefore variable depending on the sign and the difference between the values of Ce and Cf. The Laplace equation for the control loop of torque is as follows

Cc - Cf = ^ k (El). ^{(1 + p3H1 + 4H1 +)}

(l - pl) - (l -p2) in which e ^τp is the pure delay that exists between the moment when the electromagnetic pressure or force is put in the brake and the moment when the torque is actually active on the brake. This delay is a mechanical characteristic of the brake design. It is generally at best 10 milliseconds for so-called "full contact" brakes with a friction surface of 360 °, and at most 50 to 100 milliseconds for caliper brakes.

(1 - p1) the pole of the 45 ° phase shift point for the proportional solenoid valve or of the electromagnetic actuator (1 - p2) the pole of the 90 ° phase shift point for the proportional solenoid valve or the electromagnetic actuator

(1 + p3) the pole of the 45 ° phase advance point corrector of the proportional solenoid valve or of the electromagnetic actuator (1 + p4) the pole of the 90 ° phase advance point corrector the proportional solenoid valve or the electromagnetic actuator (1 + p5) the pole of the 45 ° phase advance point corrector of the signal delivered by the brake torque sensor. k (E1) is the result of the comparison of the torque setpoint and the braking torque.

The pole p5 is a pole which is related to the mathematical equations of the tire of the wheel 41 and of the suspension 42 whose general equation of reference with respect to Figure 23 is as follows

_{D1 ^} Mg - (Kp + Ks) Kp - Ks in which

D1: displacement of the suspended mass,

M: Suspended mass, m: unsprung mass,

Ks: Suspension stiffness, Cs: suspension damping, Kp: Pneumatic stiffness,

Cp: pneumatic damping,

Z2: body travel,

Z1: wheel travel,

Z0: ground clearance, and in which the natural frequency has two natural modes which are the body frequency mode and the wheel beat mode expressed by

fcaisse

The pole p5 is linked to the natural frequency of the assembly and its setting determines the stability of the wheel when the torque control is carried out. The torque control loop and the timing of this pole eliminate the dynamic and frequency reactions due to the suspended assembly, and attenuates the frequencies contained in the spectrum of the natural frequencies of the suspended masses under the effect of an impact on wheel contact -ground. The ground is the generator of the grip curve in the device.

Figures 24a and 24b explain more precisely the operation of the invention. The pilot presses at time t1 until time t2 on the brake pedal and imposes an increasing brake torque setpoint up to the value P1. During this time interval, on the curve μ = F (g), the slip changes from point 0% to point P1% of slip. The braking torque follows and is consistent with the requested setpoint. The device evolves in the stable zone of the sliding curve.

If the pilot stabilizes his action on the brake pedal from time t2 to time t3, the brake torque setpoint is stable at the value P1. During this time interval, on the curve μ = F (g) of sliding, the sliding point P1 is preserved. The device evolves in the stable zone of the sliding curve. It retains the setpoint P1 and the braking torque remains stable at times from t2 to t3.

The pilot applies more pressure on the brake pedal at time t3 until time t4 and imposes a setpoint of increasing torque on the brake up to the value P2. During this time interval, on the curve μ = F (g), the slip changes from point P1 to point P2. The braking torque follows and is consistent with the requested setpoint. The device evolves in the maximum zone of the sliding curve.

The pilot presses at time t4 until time t5 on the brake pedal and imposes an increasing torque setpoint on the brake up to the maximum value Px. During this time interval, on the curve μ = F (g), the slip changes from point P2 to point P4. The braking torque, taking account of the grip, is no longer consistent with the requested setpoint. Indeed, the device evolves and passes from the stable zone to the unstable zone of the sliding curve. The braking torque or drag torque is then no longer consistent with the setpoint and no longer follows the setpoint of the pedal. Then the operator 37 intervenes to reduce the setpoint of the operator 33, which delivers a modified pedal setpoint law so that the consistency between the setpoint torque and the braking torque is found, and therefore requires the reduction of the torque up to to obtain a point which is situated in the zone of the maximum of the grip curve, that is point P3 in the example given.

Without operator intervention, the device would have reached point P5 and the uncontrolled drag torque would have been much lower. Figures 24a and 24b also show the behavior of the wheel with the correction of the braking torque and without the correction. However, in the device, it is necessary to take into consideration the relation which exists between the speed of the wheel and the sliding zone in which the wheel moves. It is necessary to know in which direction this curve is traversed, so that the operator 37, that is to say, the pedal setpoint controller, gives the orders adapted to the expected behavior. For this purpose, the operator 37 performs another calculation in order to detect the state of the behavior of the wheel beyond the maximum grip. The operator receives information about the speed of the wheel and then calculates the second derivative dv ² / dt ² , which makes it possible to know if the wheel, beyond the maximum, loses speed in the direction of increasing slippage , therefore towards blocking or if the wheel picks up speed in the direction of decreasing sliding.

The operator 37 will also perform another calculation based on the equation g = V-v / V. This calculation is based on the derivative of the slip dg / dt, derivative which makes it possible to know, for each speed, in which zone the wheel evolves compared to the maximum of the grip curve. The parameter g is delivered by the slip calculation operator 45 which receives the speed information from all the wheels which are fitted to the vehicle and are a part of the vehicle parameters. In this case, a calculation of the longitudinal speed of the vehicle which is based on the knowledge of the braking torques applied on each wheel and the speed of each wheel can be performed (see Figure 27). This calculation takes into account the physical equations of the device and allows, from the measured couples, to calculate in the following software operators, the braking forces 53, then the deceleration 54 and the linear speed of the vehicle 55. A number of software operators complementary allow verification of the accuracy thanks to the use of calculations based on braking torques, wheel speeds, distances and kinetic energies. These operators provide security redundancy in the event of failure of the main calculation chain described above.

The operators implemented are: An operator 64 which exploits the speeds of the wheels and performs a calculation of the average of these maximum or minimum speeds and of combinations of the maximum and minimum values. This operator delivers the estimated speed of the vehicle when the driver acts on the brake pedal. The exact vehicle speed is delivered when the brake pedal is not activated by the driver.

An operator 57 who exploits the speeds of the wheels in order to determine the distance traveled.

An operator 59 which exploits the pulses delivered by a sensor indicating the pulses emitted by the gearbox and this in order to determine the distance traveled.

A distance weighting operator 58 in order to correct the information delivered by the distance traveled operators 57 and 59.

An operator 61 which exploits the braking torques of the wheels in order to determine the braking work.

An operator 63 which uses the braking work information as well as the information delivered by an operator 62 which calculates the initial kinetic energy of the vehicle. This operator 63 equates the conservation of the kinetic energy linked to the vehicle and delivers the linear speed of the vehicle at each instant as a function of the kinetic energies used.

An operator 65 ensures the comparisons and weights which make it possible to obtain the calculated linear speed of the vehicle.

Vehicle mass is either provided by a sensor, displayed by the driver or calculated. If the mass is calculated, the mass of the vehicle is calculated as follows:

The operators allow to know the deceleration and, from the start of braking, the initial speed VO (1) of the vehicle is known, the operators 56, 57, 58, 59 calculate the distance traveled so it is possible to carry out the deceleration equation (1) = VO * VO / 2D.

When the pilot acts on the brakes, the operator 64 calculates the deceleration (2) resulting from the knowledge of the torques and the estimated mass of the vehicle. When the driver stops the action on the brakes, a comparison is made between the two decelerations, the common factor being the mass (the physical value), it is then possible to calculate the real mass of the vehicle, we also measure of the new speed VO (2) of the vehicle and, knowing the differences between the speeds VO (1) - VO (2), and the time, the actual deceleration (3) of the vehicle is calculated in a given time. The comparison and the weighting of the 3 decelerations makes it possible to know, between 2 braking actions, the total mass of the vehicle and to deduce therefrom the mass per axle if an operator 54 for calculating the deceleration per axle has been chosen. It is also possible to deduce therefrom the mass per wheel if an operator 54 has been chosen for calculating the deceleration per wheel. These calculations are consistent for a vehicle moving on flat ground. In the case where the vehicle is traveling on a positive or negative slope, (hill or descent) a correction operator is introduced which then calculates the equation M = Mo. g COS (angle of the slope on which the vehicle is moving), equation in which Mo is the mass of the vehicle on flat ground and M, the result of the mass of the vehicle when it is on a positive or negative slope.

FIG. 28 gives a simplified partial embodiment of the calculation of the linear speed and the average precision obtained for a vehicle which operates on flat or semi-flat ground is of the order of 2 to 3%. This precision is sufficient, since the real value of the slip is not important, because it is the signs of changes beyond the maximum that interest the process and the work of the operator 37. Figure 29 is an example which illustrates the variation of the different elements during braking. The vehicle's initial speed is 150 km / h. A first curve illustrates the speed of the vehicle versus time (seconds). A second curve illustrates the speed of a vehicle wheel. A third curve illustrates the braking torque and its optimal values. A fourth curve illustrates the force exerted on the brake. A fifth curve illustrates the force exerted by the driver on the pedal. Finally, the sixth curve illustrates the force corrected by the IB S system. As can be seen in this graph, when the driver exerts a certain pressure on the pedal, the speed of the vehicle and the wheel decreases until the wheel locks. At this point, the vehicle continues to slow down, but the braking torque and the force exerted on the brake peak. In a vehicle without the IBS system, the driver continues to exert a force on the pedal and the vehicle continues to slow down while potentially being less stable laterally. With the IBS system, the pressure exerted on the pedal is corrected to prevent the wheel from locking up, the optimal braking torque is reached and braking takes place gently.

Another safety function based on the calculation of the deceleration of the speed of the wheel makes it possible to immediately change the torque setpoint set to zero and to impose a zero electromagnetic pressure or force in the brake. say a total brake release and reapply the pressure or an electromagnetic force when the value of the re-acceleration of the wheel allows it. The values of the intervention level of this acceleration or deceleration safety is variable depending on the slip or the speed of the vehicle.

The invention can advantageously have an additional level of control which is the slip control of the wheel. This control keeps the wheel at an imposed or variable slip. It is then necessary to calculate the vehicle speed with acceptable accuracy. The operation of such a control is included in the diagram of Figure 19, which includes an optional module. The latter processes and determines the slip control that the device wants to impose on the wheel. This module receives measurements and parameters related to the vehicle, the elements of which will be explained below. It includes an operator for calculating the speed of the vehicle 45, an operator for calculating the slip 46, a comparator 48 which determines the sign of the commands which results from the comparison of the slip which it is desired to impose and deliver by the operator 49 and that of the actual slip at which the wheel is maintained. The signals from the comparator 47 are used by a slip regulation operator 49 whose action will be to issue to the operator 34 orders for increasing or decreasing the torque setpoint to maintain the wheel at the requested slip.

The equation for the slip control loop is as follows

where, for information, W _! = 0.15 rads w ₅ = 120 rads w ₂ = 4.15 rads w ₆ = 600 rads w ₃ = 43 rads w ₇ = 1700 rads w ₄ = 60 rads w ₈ = 1800 rads

what the graphs in Figures 25a and 25b represent.

This equation takes into account the calculation elements which are linked to the main mechanical, hydraulic, electrical, electronic components and the sensors, which constitute the slip command control loop. The invention shows that it is possible to control the braking efficiency on each wheel, and subsequently to impose on each wheel a predetermined or pre-calculated drag torque. The composition of the electronic device (see Figure 26) consists of an electronic control unit which receives information from different sensors and which controls the actuators.

Since the force applied to the brakes will vary depending on the vehicle load, an alternative to further improve braking efficiency is to provide the vehicle with a sensor on the suspension so that the vehicle load is taken into account during braking optimization calculations. For example, for a vehicle comprising a hydraulic suspension at the front and an air suspension at the rear, a gauge placed on the rear suspension of each wheel and connected to the device of the invention could very well fulfill this task. .

The electronic circuit box is preferably made up of a 16-bit microcontroller with a base clock frequency of 20 MHz, a 256 kB flash memory, a CAN converter with 16 10-bit coded inputs , and 4 PWM outputs.

The input parameters are:

1 brake pedal setpoint; 4 tachometric wheel speed sensor inputs;

4 brake torque sensor inputs;

4 on / off contact signal inputs;

4 outputs for controlling proportional solenoid valves or electromagnetic actuators; and 1 output for a relay. Although the present invention has been described using specific implementations, it is understood that several variations and modifications can be grafted onto said implementations, and the present application aims to cover such modifications, uses or adaptations of the present invention following, in general, the principles of the invention and including any variation of the present description which will become known or conventional in the field of activity in which the present invention is found, and which can be applied to the essential elements mentioned above, in accordance with the scope of the following claims.

Claims

The realizations for which an exclusive right of property or privilege is claimed are defined as follows:

1. Braking control device in which the control of the maximum braking efficiency is obtained by measuring and controlling the drag torque measured using a sensor measuring this torque.

2. Device according to claim 1 wherein the drag torque is controlled by the pilot's brake pedal.

3. Device according to claim 2 in which the pedal imposes a setpoint for the drag torque, and said torque is controlled by a command control loop receiving the setpoint and measurement information.

4. Device according to claim 3 wherein the loop comprises a corrector capable of controlling and stabilizing the frequency changes to which the wheel is subjected.

5. Device according to claim 3 wherein the setpoint and the torque are maintained equal to the requested value as long as the drag torque is equal to the setpoint torque, and adapted as a reduction when the setpoint torque is greater than the drag torque.

6. Device according to claim 1 in which the calculation of the second derivative of the speed of the wheel and / or of the first derivative of the slip makes it possible to obtain the direction of the evolution of the increase or the decrease of the torque setpoint.

7. Device according to claim 1 further comprising a sliding module determining the direction of the evolution of an increase or decrease in the torque setpoint.

8. Device according to claim 7, in which the slip module imposes a slip value setpoint, and in which the module is controlled by a command control loop receiving the setpoint and speed measurement information.

9. Device according to claim 8 wherein the loop is provided with a corrector capable of controlling and stabilizing the sliding of the wheel, the loop being also superimposed on the torque reference loop.

10. Device according to claim 1, wherein the brake activation means is at least one of the hydraulic, pneumatic and electromagnetic activation means.

11. Device according to claim 1, in which the sensor is located on the pilot's brake pedal.

12. Device according to claim 1, in which the sensor is located on the brake.

13. Device according to claim 1, further comprising a module for verifying the calculation of longitudinal speed from a wheel speed, a braking torque, a distance traveled and a mass of the vehicle.