associated braking method and system

Abstract

The invention relates to a method for detecting a decrease in the effectiveness of brake linings, and increasing the brake clamping force F to compensate for this decrease. Figure for the abstract: Figure 1.

Description

Title of the invention: Associated braking method and system

[0001] The invention relates to a braking method, in particular to a method for limiting or compensating for a loss of efficiency, in particular known by the English term "fading".

[0002] This weakening of braking, this loss of braking efficiency, can notably be due to a rise in the temperature of the brake linings beyond an optimal operating temperature, that is to say, a loss of friction when the lining reaches and exceeds this temperature. This can be the result of repeated braking, for example on a mountain road, or of particularly long or heavy braking.

[0003] However, the use of electrical controls does not allow the vehicle driver to be fully aware of the effectiveness of their braking. Therefore, the electrical control generally transmits a braking command that assumes the braking is not affected by any loss of effectiveness. Excessive braking in the absence of any actual loss of effectiveness could surprise the driver and cause an accident.

[0004] The object of the invention is to propose a braking system and / or method which makes it possible to limit or compensate for a loss of efficiency of the "fading" type.

[0005] According to a first object of the invention, a braking method for a vehicle comprises a supply: - a speed sensor on one wheel of the vehicle; - a means of measuring or calculating the temperature of a lining brake; - a nomogram giving, for a target clamping force, a nominal deceleration value and a lower deceleration value; - a braking algorithm;

[0006] the algorithm comprising the following recurring steps: - a determination of said instantaneous temperature; - the vehicle will stop if the temperature does not meet a criterion;

[0007] or, if the temperature is compliant: - the determination of instantaneous deceleration; - the vehicle will stop if the deceleration does not conform to a criterion;

[0008] or, if the deceleration is compliant, but less than the nominal value: - the increase in clamping force.

[0009] The lower deceleration value is a value below which the deceleration is insufficient and can no longer be compensated.

[0010] Instantaneous deceleration is advantageously calculated from successive measurements of instantaneous wheel speeds.

[0011] The method may further include a step to warn a driver of the vehicle if the instantaneous deceleration meets the criterion.

[0012] The nomogram advantageously includes a first curve giving a nominal deceleration value, for a given target clamping force, and a second curve, giving a lower deceleration value, for the given target clamping force.

[0013] The given deceleration values ​​advantageously define the criterion for conformity of the instantaneous deceleration, so that the instantaneous deceleration conforms to the criterion when it is between these given values.

[0014] Several embodiments of the invention will be described below, by way of non-limiting examples, with reference to the accompanying drawings in which:

[0015] [Fig.1] is a logic diagram illustrating a braking method according to the invention; and,

[0016] [Fig.2] illustrates a nomogram used in the method of [Fig.1].

[0017] Figure 1 is a flowchart illustrating an algorithmic process 100 according to the invention; fourteen steps 101-114 are shown. In one embodiment, the process is applied to a braking device for a single wheel among the wheels of the same vehicle. In another, preferred embodiment, it is applied to a braking device for several wheels of the same vehicle, in order to avoid a differential braking failure, which can be detrimental, particularly when it affects steering wheels.

[0018] After an initialization and start-up step 101, the algorithm 100 includes recurrent steps 102-114, which allow, at successive times t, t+1, to check the braking conditions and to compensate for any loss of efficiency, when possible.

[0019] A second step 102 consists of incrementing the time t at each new recurrence. A third step 103 then consists of determining an instantaneous braking temperature T°(t), that is, a temperature of a brake pad. The instantaneous temperature of the brake pad is determined from a measurement taken by an in-situ sensor and / or the instantaneous temperature is determined from a brake system temperature model (BTM).

[0020] In a fourth step 104, the instantaneous temperature is compared to a limit value TL. When the temperature exceeds this limit value TL, typically five hundred degrees Celsius (500°C), to ensure the safety of the vehicle, its shutdown is initiated immediately, in a fifth step 105.

[0021] When the temperature does not exceed the limit value TL, the algorithm continues along Y. Thus, a sixth step 106 determines an instantaneous target clamping force FT(t). This clamping force corresponds to a braking command. This command corresponds to a driver instruction, for example, the degree to which a brake pedal is depressed; in a variant, this command will correspond to an electrical command received from an on-board computer, for example, if emergency braking is initiated automatically upon detection of an obstacle.

[0022] In the illustrated example, the third and sixth steps are carried out in parallel.

[0023] A seventh step 107 allows for the determination of an instantaneous wheel rotational speed value WSS(t). This value is typically measured in situ by a sensor. An eighth step 108 allows for the deduction of an instantaneous deceleration value D(t).

[0024] In a ninth step 109, the instantaneous deceleration value is compared to limit value curves DN, DL, where the DN curve is that which brings together the nominal deceleration values ​​expected for each of a set of target clamping forces FT, and, where the DL curve is the curve of lower deceleration values, from which braking is no longer ensured correctly for each of these target clamping forces.

[0025] To perform this comparison, algorithm 100 uses a nomogram 1 illustrated in [Fig. 2]. Thus, when the clamping force FT takes a given value Fl, the nominal deceleration has a nominal value DL. When the instantaneous deceleration value D(t) is equal to the value Dl, there is no loss of braking efficiency, in other words, there is no fading. If the instantaneous deceleration value is less than the nominal value Dl, there is a loss of braking efficiency, in other words, there is fading. When the loss of efficiency exceeds the limit formed by the lower curve DL, that is, a low value D2 corresponding to the given force Fl, the loss of efficiency is too great to be safely compensated for, particularly in the time required to bring the vehicle to a stop.

[0026] Thus, the ninth step 109 consists of verifying that for a targeted clamping force value Fl, the calculated instantaneous deceleration D(t) is indeed between the two limit values ​​Dl, D2 given by the nomogram of [Fig.2].

[0027] A tenth step 110 consists of stopping the vehicle if the instantaneous deceleration value is too low to be compensated.

[0028] If the value of the instantaneous deceleration D(t) is indeed between the limit values ​​D1, D2: - in an eleventh step 111, the driver is warned of the malfunction of the braking system; then, - in a twelfth step 112, an increase in clamping force proportional to the braking loss is calculated; then, - in a thirteenth step 113, the increased clamping force is applied; and, - in a fourteenth step (114), the increased force is taken into account as the target clamping force F(t).

[0029] The driver, warned in step eleven 111, can advantageously modify their driving and reduce the load on the braking system in order to lower the temperature of the brake pads. For example, instead of continuous braking, they can perform repeated braking maneuvers, thus allowing the pads time to cool between each application of the brakes.

[0030] Of course, the invention is not limited to the examples just described. It will indeed appear to a person skilled in the art that various modifications can be made to the embodiments described above, in light of the teaching just disclosed to him.

[0031] Thus, the vehicle can be any type of braked vehicle. It can be a land vehicle, for example a private car, a utility vehicle or a heavy goods vehicle or their trailer; it can also be a rail or air vehicle.

[0032] Furthermore, the term lining should be understood in a broad sense; it applies to any type of friction element applying a friction force to a moving element; this element may be a brake disc, a drum or a wheel axle.

[0033] A method according to the invention makes it possible to anticipate brake fade. In particular, it makes it possible to stop the vehicle before the loss of braking power becomes too great to prevent. It makes it possible to compensate for brake fade as much as possible so that the deceleration corresponds to that expected by the driver. It also makes it possible to warn the driver so that they can modify their driving and reduce the load on the braking system, in order to lower the temperature of the brake pads.

[0034] Such a method is particularly advantageous because it allows for increased safety at a low cost and is simple to implement. It uses data from the wheel speed sensor (WSS) and a brake system temperature model (BTM). It reduces the force required to ensure sufficient braking; it therefore also allows for a reduction in the size of the brake calipers. List of documents cited

[0035] 101: algorithm initialization step

[0036] 102: incremental step of each loop at time t

[0037] 103: step of reading the lining temperature at time t

[0038] 104: Action selection step based on the temperature reading

[0039] 105: Vehicle stopping step

[0040] 106: step of determining the target clamping force at time t

[0041] 107: step of calculating and processing the wheel speed at time t

[0042] 108: step of calculating the deceleration at time t

[0043] 109: step of choosing the action based on the calculated deceleration

[0044] 110: Vehicle stopping step

[0045] 111: Driver warning stage

[0046] 112: Calculation step for an increase in clamping force

[0047] 113: step of applying the increased clamping force

[0048] 114: step of taking into account the new clamping value FT(t).

[0049] DN: Nominal deceleration curve as a function of the target clamping force

[0050] DL: curve of minimum permissible decelerations

[0051] D(t): deceleration at time t

[0052] Fl: clamping force

[0053] DI: nominal deceleration value for clamping force Fl

[0054] D2: lower value of the deceleration for the clamping force Fl

[0055] FT(t): target clamping force at time t

[0056] T°(t): packing temperature at time t

[0057] WSS(t): wheel speed at time t

Claims

Demands

1. A method for optimizing braking and detecting a decrease in the effectiveness of brake linings, characterized in that it comprises providing: - a speed sensor (WSS) on a wheel of the vehicle; - a means for measuring or calculating an instantaneous temperature (T°(t)) of a brake lining; - a nomogram (1) giving, for an instantaneous target clamping force FT(t), a nominal deceleration value (DN, D1) and a lower deceleration value (DL, D2); - a braking algorithm (100); the algorithm comprising the following recurring steps: - determination (103) of said instantaneous temperature; - stopping (104, 105) the vehicle if said instantaneous temperature does not conform to a criterion (TL); or, if the temperature conforms: - determination (107, 108) of an instantaneous deceleration (D(t));then, - comparison (109) of the instantaneous deceleration according to a criterion (DN, DL) as a function of an instantaneous target clamping force (F(t)); then, - stopping of the vehicle (110) if the deceleration does not conform to said criterion; or, if the deceleration conforms, but is less than the nominal value: - increase (112, 113) of the clamping force (F).;

2. Method according to claim 1, characterized in that the instantaneous deceleration is calculated (108) from successive measurements (107) of instantaneous wheel speeds (WSS(t)).

3. A method according to any one of claims 1 and 2, characterized in that it further comprises a step (111) for warning a driver of the vehicle if the instantaneous deceleration conforms to the criterion (DN, DL).

4. Method according to any one of claims 1 to 3, characterized in that the nomogram has a first curve (DN) giving a nominal deceleration value (Dl), for a given target clamping force (Fl), and, a second curve (DL), giving a lower deceleration value (Dl), for said given target clamping force (Fl).

5. A method according to claim 4, characterized in that the given deceleration values ​​(D1, D2) define the conformity criterion of the instantaneous deceleration (D(t)), such that said instantaneous deceleration conforms to the criterion when it is between said given values ​​(D1,D2).

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