Associated braking process and system

Abstract

The invention relates to a method for detecting a weakening of brake lining efficiency, and increasing the brake application force F to compensate for this weakening. Figure for 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 effectiveness of the brakes, may in particular be due 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 may be the consequence of repetitive braking, for example on a mountain road, or of particularly long or powerful braking.

[0003] However, the use of electric controls does not allow the driver of the vehicle to have full awareness of the effectiveness of his braking. Also, the electric 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: - a speed sensor on a wheel of the vehicle; - a means of measuring or calculating the temperature of a lining of brake; - 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 meet a criterion;

[0007] or, if the temperature is correct: - determination of 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] The instantaneous deceleration is advantageously calculated from successive measurements of instantaneous wheel speeds.

[0011] The method may further comprise a step for warning a driver of the vehicle if the instantaneous deceleration complies with 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] [Fig.l] is a flowchart illustrating a braking method according to the invention; and,

[0016] [Fig.2] illustrates an abacus used in the method of [Fig.l].

[0017] [Fig.l] 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 carried out 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 carry out this comparison, the algorithm 100 uses an abacus 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 lower than the nominal value Dl, this 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 Fl, the loss of efficiency is too great for this loss to be able to be compensated 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 Fl, the calculated instantaneous deceleration D(t) is indeed between the two limit values ​​Dl, D2 given by the chart in [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 actually between the limit values ​​Dl, 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 tightening 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 in the eleventh step 111, can advantageously modify his driving and relieve the braking system, in order to lower the temperature of the linings. For example, instead of continuous braking, he can make repeated braking applications, thus allowing time for the linings 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 the 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 as much as possible to compensate for the fading phenomenon so that the deceleration corresponds to that expected by the driver. It also makes it possible to warn the driver so that he modifies his driving and relieves the braking system, in order to lower the temperature of the linings.

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

[0035] 101: algorithm initialization step

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

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

[0038] 104: step of choosing action according to the temperature read

[0039] 105: vehicle stopping step

[0040] 106: step of determining the targeted 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 according to the calculated deceleration

[0044] 110: vehicle stopping step

[0045] 111: Driver warning step

[0046] 112: step of calculating an increase in the clamping force

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

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

[0049] DN: curve of nominal decelerations as a function of the target clamping force

[0050] DL: curve of minimum admissible decelerations

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

[0052] Fl: clamping force

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

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

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

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

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

Claims

Claims

1. 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, Dl) 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 comply with a criterion (TL); or, if the temperature does comply: - 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 is not in accordance with said criterion; or, if the deceleration is in accordance, but 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. 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).

4. Method according to one of claims 1 to 3, characterized in that the abacus shows 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. Method according to claim 4, characterized in that the given deceleration values ​​(D1, D2) define the instantaneous deceleration conformity criterion (D(t)), so that said instantaneous deceleration conforms to the criterion when it is between said given values ​​(D1, D2).

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