Associated braking method and system

Abstract

The invention relates to a method for detecting brake lining fading, and increasing the brake application force F in order to compensate for such fading.

Description

Associated braking process 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 brake efficiency, can be due in particular to a rise in 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 consequence of repetitive braking, for example on a mountain road, or of particularly long or powerful braking.

[0003] However, the use of electronic controls does not allow the vehicle driver to have full awareness of the effectiveness of their braking. Also, the electronic control generally transmits a braking instruction which assumes that the braking is not affected by a loss of effectiveness. Braking too abruptly in the absence of an actual loss of effectiveness could surprise the driver and cause an accident.

[0004] The aim 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 provision of: a speed sensor on a wheel of the vehicle; a means for measuring or calculating a temperature of a brake lining; an abacus 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; stopping the vehicle if the temperature does not conform to a criterion;

[0007] or, if the temperature is compliant: determination of the instantaneous deceleration; stopping the vehicle if the deceleration does not comply with a criterion;

[0008] or, if the deceleration is compliant, but less than the nominal value: the increase in the 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 comprise a step of notifying a driver of the vehicle if the instantaneous deceleration meets the criterion.

[0012] The chart advantageously comprises 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 instantaneous deceleration conformity criterion, 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 appended drawings in which:

[0015] is a flowchart illustrating a braking method according to the invention; and,

[0016] illustrates an abacus used in the process of.

[0017] This is a flowchart illustrating an algorithmic method 100 according to the invention; fourteen steps 101-114 are represented. According to one variant, the method is applied to a braking device for a single wheel among the wheels of the same vehicle. In another, preferred variant, it is applied to a braking device for several wheels of the same vehicle, in order to avoid a differential braking defect, which can be detrimental, in particular when it affects steered wheels.

[0018] After an initialization and start-up step 101, the algorithm 100 comprises recurring steps 102-114, which make it possible, 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 an incrementation of the time t, at each new recurrence. A third step 103 then consists of determining an instantaneous braking temperature T°(t), i.e. a temperature of a lining. The instantaneous temperature of the lining is determined from a measurement carried out by an in situ sensor and / or the instantaneous temperature is determined from a brake system temperature model (BTM: Brake System Temperature Model, in English).

[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, it is immediately stopped, in a fifth step 105.

[0021] When the temperature does not exceed the limit value TL, the algorithm continues according to Y. Thus, a sixth step 106 makes it possible to determine an instantaneous target clamping force FT(t). This clamping force corresponds to a braking instruction. This instruction corresponds to a driver instruction, for example to a degree of depression of a brake pedal; in a variant, this instruction will correspond to an electrical instruction received from an on-board computer, for example if emergency braking is engaged in automatic mode upon detection of an obstacle.

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

[0023] A seventh step 107 makes it possible to determine an instantaneous wheel rotation speed value WSS(t). This value is typically measured in situ by a sensor. An eighth step 108 makes it possible to deduce an instantaneous deceleration value D(t).

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

[0025] To make this comparison, the algorithm 100 uses an abacus 1 illustrated in . Thus, when the clamping force FT takes a given value F1, the nominal deceleration has a nominal value D1. When the instantaneous deceleration value D(t) is equal to the value D1, there is no loss of braking efficiency, in other words, there is no "fading". If the instantaneous deceleration value is lower than the nominal value D1, it means that 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 to say a low value D2 corresponding to the given force F1, the loss of efficiency is too great for this loss to be compensated for safely, particularly in the time required to stop the vehicle.

[0026] Thus, the ninth step 109 consists of verifying that for a targeted clamping force value F1, the calculated instantaneous deceleration D(t) is indeed between the two limit values ​​D1, D2 given by the abacus of the.

[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 actually 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 the clamping force proportional to the loss of braking is calculated; then, in a thirteenth step 113, the clamping force thus increased 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 at the eleventh step 111, can advantageously modify his driving and relieve the braking system, in order to lower the temperature of the brake pads. For example, instead of continuous braking, he can make repeated braking applications, thus giving the brake pads time to cool between each brake application.

[0030] Of course, the invention is not limited to the examples which have just been described. It will indeed appear to those skilled in the art that various modifications can be made to the embodiments described above, in the light of the teaching which has just been disclosed to them.

[0031] Thus, the vehicle can be any type of braked vehicle. It can be a land vehicle, for example a private car, a utility or 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 frictional force on a moving element; this element can be a brake disc, a drum or a wheel axle.

[0033] A method according to the invention makes it possible to anticipate a fading phenomenon. In particular, it makes it possible to stop the vehicle before the loss of braking becomes too great to prevent it. It makes it possible to compensate for the fading phenomenon 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 he or she can modify his or her driving and relieve the braking system, in order to lower the temperature of the brake pads.

[0034] This method is particularly advantageous because it increases safety at a low cost and is easy 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 also allows for smaller brake calipers.

[0035] References:101: algorithm initialization step102: incremental step of each loop at time t103: step of reading the lining temperature at time t104: step of choosing the action based on the temperature read105: vehicle stopping step106: step of determining the target clamping force at time t107: step of calculating and processing the wheel speed at time t108: step of calculating the deceleration at time t109: step of choosing the action based on the calculated deceleration110: vehicle stopping step111: driver warning step112: step of calculating an increase in the clamping force113: step of applying the increased clamping force114: step of taking into account the new clamping value FT(t).DN: nominal deceleration curve as a function of the target clamping forceDL: minimum permissible deceleration curveD(t): deceleration at time tF1: clamping forceD1: nominal deceleration value for clamping force F1D2: lower deceleration value for clamping force F1FT(t): target clamping force at time tT°(t): lining temperature at time tWSS(t): wheel speed at time t.

Claims

Method for optimizing braking and detecting a weakening of the effectiveness of brake linings, characterized in that it comprises a provision of: 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 chart (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) of 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) depending on an instantaneous target clamping force (F(t));then, stopping the vehicle (110) if the deceleration does not comply with said criterion; or, if the deceleration does comply, but is less than the nominal value: increasing (112, 113) the clamping force (F).; Method according to claim 1, characterized in that the instantaneous deceleration is calculated (108) from successive measurements (107) of instantaneous wheel speeds (WSS(t)). Method according to 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 complies with the criterion (DN, DL). Method according to one of claims 1 to 3, characterized in that the chart comprises a first curve (DN) giving a nominal deceleration value (D1), for a given target clamping force (F1), and a second curve (DL), giving a lower deceleration value (D2), for said given target clamping force (F1). Method according to claim 4, characterized in that the given deceleration values ​​(D1, D2) define the conformity criterion of the instantaneous deceleration (D(t)), so that said instantaneous deceleration conforms to the criterion when it is between said given values ​​(D1, D2).

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