FR2852647A1 - Wear maintaining method for hydraulic braking system of motor vehicle, involves wheel lock system pretensioning brake calipers to maintain braking pads in light touch with braking disc after acceleration and braking phases - Google Patents

Abstract

The method involves braking one wheel when instability of a vehicle is detected by a wheel lock system (8) cooperating with a hydraulic braking system (1), where the lock system can independently lock wheels. Brake calipers (5) are pretensed by the wheel lock system in a manner that braking pads are continuously in light touch with a braking disc (44) after acceleration and braking phases.

Description

Method for maintaining a substantially

  equivalent between the brake pads and their associated disc.

  The invention relates to a allowing the maintenance of a substantially equivalent play between the brake pads and their associated disc and in particular to such a method used for a braking system of a motor vehicle.

  Manufacturers are constantly striving to improve the safety of their vehicles. In particular in the field of braking systems, the qualities of the braking system must be constantly improved in order to make the vehicle safer.

  The common technique currently used is that of disc brakes. The latter is based on the use of friction phenomena comprising destructive elements 15 (the pads) which each pinch a disc secured to a wheel of the vehicle in order to slow the latter. Consequently, as the braking progresses, the thickness of the pads decreases, inducing a variation in the clearance between the disc and said pads which is detrimental to the quality of the braking.

  The object of the present invention is to overcome all or part of the drawbacks mentioned above by providing an inexpensive method adapting to current braking systems and allowing the latter to maintain a constant clearance between each disc and its pads even when these last have lost thickness.

  To this end, the invention relates to a method making it possible to keep a substantially equivalent clearance between a braking disc and its pads of a motor vehicle 30 comprising the steps consisting in: braking at least one wheel from the activation of the control of a braking system; -accelerate at least one wheel from the activation of the control of a motor system; braking at least one wheel from the detection of an instability of said vehicle by a locking system of the 5 wheels cooperating with said braking device but being able to lock each wheel independently of the latter; characterized in that it further comprises the step consisting in prestressing each brake caliper to a threshold value io by virtue of said wheel locking system so that each of the pads is continuously substantially touched by its braking disc outside the acceleration and braking phases. This makes it possible to use an existing system already on the vehicle to compensate in particular for the wear of the pads.

  Advantageously, the prestressing, according to a first variant, comprises the steps consisting in: - detecting the deactivation of the engine system control to initiate the actuation of each brake caliper up to its said threshold value; - Maintain this actuation as long as none of said commands is activated so that the braking system has a minimum play that is substantially constant to overcome before effectively braking said vehicle.

  The method according to the invention is active by default when the driver does not brake and does not accelerate so that the brakes are ready to operate optimally.

  According to this same variant, the method further comprises the steps consisting in: - detecting the activation of the braking system control in order to complete actuating each caliper by the braking system alone and thus releasing the wheel locking system from its actuation function to allow the vehicle to be braked; - detect the deactivation of the brake system control; -determine the threshold value for which each pad leaves contact with its brake disc; - maintain the brake preload at this threshold value as long as none of the said commands is activated allowing the braking system to be prepared.

  After each braking, this allows each caliper to determine its threshold value and thus to individually compensate for the play between the disc and its pads.

  According to a second variant of the invention, the prestressing advantageously comprises the steps consisting in: - determining the deactivation of the control of the engine system to release at least one accumulator charged as a function of said threshold value and included in said blocking system wheels so as to actuate in a defined manner each brake caliper; - Maintain this actuation as long as none of said commands is activated so that the braking system has a substantially constant minimum play to overcome before effectively braking said vehicle.

  This avoids having to overcome the inertia of the wheel lock system pump and being able to immediately activate the brake calipers.

  Advantageously, the method, according to this same variant, further comprises the steps consisting in: detecting the activation of the braking system control in order to complete actuating each caliper by the braking system alone and thus releasing the wheel locking system of its actuation function to allow the vehicle to be braked; -detect the deactivation of the brake system control; -determine the threshold value for which each pad leaves contact with its brake disc; - Maintain the brake preload at this threshold value as long as none of said commands is activated while recharging said accumulators to allow the braking system to be prepared and said preload to be reset.

  According to the invention, the determination of the threshold value is advantageously carried out on the basis of measurements of at least one pressure sensor of the wheel locking system. This makes it possible to use an already existing architecture to control the process. This makes it possible to control, for example from a single pressure sensor of said wheel locking system, to estimate, for example by means of a computer, the control of the brake calipers.

  The measurements of each sensor are carried out, advantageously according to the invention, upstream of each brake caliper to allow independent control of the touch of the pads around each disc. This allows optimum control of the play of the brake pads with respect to their associated disc depending in particular on their respective wear.

  Advantageously according to the invention, the compensation method is initialized when the engine system control is activated.

  Other particularities and advantages will emerge clearly from the description given below, by way of indication and in no way limiting, with reference to the appended drawings, in which: - Figure 1 is a schematic representation of the means used by the method according to a first variant of the invention; - Figure 2 is a diagram of the method according to the first variant of the invention; - Figure 3 is a schematic representation of the means used by the method according to a second variant of the invention; - Figure 4 is a diagram of the method according to the second variant of the invention.

  In the examples of Figures 1 and 3, it can be seen that the invention uses a hydraulic braking system 1 for a motor vehicle (not shown) comprising a pedal 2, a braking amplifier 3, a master cylinder 4a io comprising a reservoir 4b, discs 44 and stirrups 5 which each control at least two plates (not shown). Thus in a very known manner, the actuation of the pedal 2 moves at least one piston 6 in the master cylinder 4a. This displacement generates a displacement of fluid in the hydraulic circuit 7 of the braking system 1 which forces the pads (not shown) to come into contact with its disc 44 in order to brake the vehicle. This configuration being very well known, it will not be further detailed below.

  In these Figures 1 and 3, the braking system 1 further comprises a wheel locking system 8 which, included in the hydraulic circuit 7, makes it possible to brake one or more wheels independently of the braking system 1, that is that is to say without pedal 2 having been activated. This system 25 for locking the wheels 8 can for example be a system of the "trajectory corrector" type, well known under the brand "E.S. P.0".

  Thus in the example of FIG. 1, it can be seen that the braking system 1 comprises two hydraulic circuits 7a 30 and 7b. Each is used to control a pair of brake calipers 5, for example those on the left and right or those in front and behind. Each hydraulic circuit 7 comprises valves, for example of the electrical type, which can selectively open or close to, for example, isolate areas of the hydraulic circuit 7 and a pump 9 allowing the wheel locking system 8 to send pressurized fluid into the hydraulic circuit 7 without having to press the pedal 2.

  In the example of FIG. 1, each hydraulic circuit 7 comprises an isolation valve 10, a first intake valve 5 and, for each stirrup 5, a second intake valve 12 and an exhaust valve 13 Finally, to monitor the hydraulic circuits 7a and 7b, a single pressure sensor 15 is placed inside or preferably upstream of each stirrup (cf. in FIG. 1). The explanations below are based on a configuration of a sensor 15 for each stirrup 5.

  In FIG. 2, an example of a diagram of the different steps of the method according to the invention can be seen. A phase 20 consists in detecting the release of the accelerator pedal (not shown) using, for example, a position detector (not shown) of the accelerator pedal. This detection is used because it is likely that if the driver stops accelerating, it is, in most cases, to brake.

  If this detection 20 is positive, the method goes to step 21, namely filling the stirrups 5 with the pumps 9 of the wheel locking system 8. In order for the stirrups 5 to be actuated, the valves 10 and 13 are closed and the valves 11 and 12 open. In fact, the pumps 9 will suck the fluid contained in the reservoir 4b and send it to the stirrups 5.

  Phase 22 consists of using the sensors 15 to detect each pressure upstream of the stirrups 5 and to compare it with a touch pressure corresponding to said touch of the pads (not shown) with its associated disc. For the first use, this pressure depends on the construction of the stirrups 5 and the desired clearance. For the following uses, it is determined by the method which is explained below.

  A loop is thus created because if the pressure measured is less than the touch pressure, the process returns from phase 22 to step 21 to continue filling. When the measured pressure becomes equal to or greater than the touching pressure 5, the process goes from phase 22 to step 23 which is maintaining the actuation of the calipers 5 at the touching position of the brake pads around of the disc. This is achieved, for example, by closing the valves 12 or by stopping the pumps 9. However, preferably, it is more advantageous to close each valve 12 as a function of its associated sensor 15 to allow improved and individualized precision of the stirrups 5 as to at their respective touch position of each disc 44. (For obvious reasons of economy, it is in any case preferable to stop the pumps 9 when the valves 12 are closed). The calipers 5 are therefore in step 23 actuated in order to optimize future braking of the vehicle.

  The next two phases 24 and 28 relate respectively to the detection of the depressing of the brake pedal 2 and that of the acceleration pedal (not shown).

  Thus in the case where neither one nor the other is actuated, the method returns to step 23, thereby creating a loop which makes it possible to maintain the ideal clearance between the pads and their associated disc 44 to promote the possible braking of the driver and leave said clearance as long as no command from the driver has been issued. On the other hand, if during phase 28, acceleration is requested, the process is initialized until phase 20 and step 29 obliges the wheel locking system 8 to return to its "normal" state. ie 30 the valves 10 and 12 open, the valves 11 and 13 closed and the pumps 9 off.

  If phase 24 detects that the brake pedal 2 has been depressed, step 25 is identical to step 29 above. Indeed, the pre-actuation of the calipers 5 by the wheel locking system 8 is "replaced" by the "usual" braking system, that is to say that the pressure generated by the master cylinder 4a is sent in the stirrups 5. This first (8) therefore no longer needs to be used.

  Phase 26 detects the release of the brake pedal 2.

  When said release is carried out, step 27 detects by means of the 5 measurements of the sensors 15 when the pressure drops to a minimum corresponding to the touch position. Consequently for each stirrup, a touch value can therefore be measured and "recorded" by maintaining the pressure in step 30 by closing its associated valve 12 10. Indeed, the driver can choose to brake again after having released the brake pedal 2. Thus after step 30 of maintaining the touch position of each caliper 5, the process returns to phase 24 and 28 for respectively possible braking or acceleration. The touch value thus measured for each stirrup 5 is then used when the method returns to step 21.

  In the example illustrated in FIGS. 3 and 4, we can see a second possible variant of the invention. This second variant consists in adding, with respect to the first variant, 20 accumulators of fluid at a touch pressure in the wheel locking system 8 corresponding to that of the explanation above in FIG. 2. It is possible to therefore see, in FIG. 3, a filling valve 16 giving access to the accumulator 17 on each hydraulic circuit 7. This second variant is in fact thought to overcome the inertia of the pumps 9 by sending fluid under pressure more quickly in the stirrups 5.

  In the example illustrated in FIG. 4, it can be seen that step 21 and phase 22 of the first variant consisting in filling the stirrups 5 with fluid up to said touch position are replaced by step 31 consisting in releasing fluid from the accumulators 17 in the stirrups 5. It suffices to open the valves 16 and 12 and to close the valve 10.

  As in the first variant, as soon as the pressure detected by each sensor 15 is substantially equal to the touch pressure of its caliper 5, the associated valve 12 is closed in accordance with step 23 to maintain the 5 plates of the caliper 5 when its brake disc 44 is touched.

  The second difference with the first variant relates to step 30, consisting in maintaining the touch pressure following braking, which is replaced by step 40 which not only maintains said pressure but also recharges the accumulators 17. This filling is carried out using the pumps 9 of the wheel locking system 8. For this, the valves 10, 12 must be closed (the latter already being closed for maintaining the pressure 15 in the stirrups 5) and open the valves 11 and 16. This makes it possible to suck the fluid from the reservoir 4b towards the pumps 9 to force the filling of the accumulators 17.

  In the same way, step 29 of the first variant, consisting in initializing the method and the locking system of the wheels 8, is replaced by step 39 which takes the same actions but also fills the accumulators 17, the filling being carried out in the same manner as in step 40.

  Of course, the present invention is not limited to the example illustrated but is susceptible to various variants and modifications which will appear to those skilled in the art. In particular, an accumulator 17 can be provided for each caliper 5. Also, if there is no single sensor 15 in the hydraulic circuit 7, a computer can be installed to estimate said touch pressure and the value of the pressure in stirrups 5.

Claims (8)

R E V E N D I C A T I O N S   1. Method for keeping a substantially equivalent clearance between a brake disc (44) and its pads of a motor vehicle comprising the steps consisting in -braking at least one wheel from the activation of the control (2) d 'a braking system (1); -accelerate at least one wheel from the activation of the control of a motor system; braking at least one wheel from the detection of instability of said vehicle by a wheel locking system (8) cooperating with said braking device but being able to lock each wheel independently of the latter; characterized in that it further comprises the step of prestressing each brake caliper (5) to a threshold value by virtue of said wheel locking system so that each of the pads is continuously substantially at touch of its braking disc (44) outside the acceleration and braking phases.   2. Method according to claim 1, characterized in that said prestressing comprises the steps consisting in: -detecting the deactivation of the engine system control to initiate the actuation of each brake caliper (5) up to its said threshold value ; -maintain this actuation as long as none of said commands is activated so that the braking system has a minimum play that is substantially constant to overcome before effectively braking said vehicle. i1   3. Method according to claim 2, characterized in that it further comprises the steps consisting in: -detecting the activation of the control (2) of the braking system (1) to finish actuating each caliper (5) by 5 the braking system (1) alone and thus release the wheel locking system (8) from its actuation function to allow the vehicle to be braked; -detect the deactivation of the control system (2) of the braking system (1); -determining the threshold value for which each pad leaves contact with its brake disc (44); - maintain the brake preload at this threshold value as long as none of the said commands is activated allowing the braking system to be prepared.   4. Method according to claim 1, characterized in that the prestressing comprises the steps consisting in: -determining the deactivation of the engine system control to release at least one accumulator (17) charged according to said threshold value and included in said 20 wheel locking system (8) to thereby actuate in a defined manner each brake caliper (5); - maintain this actuation as long as none of said commands is activated so that the braking system (1) has a substantially constant minimum play to be overcome before effectively braking said vehicle.   5. Compensation method according to claim 4, characterized in that it further comprises the steps consisting in: -detecting the activation of the control (2) of the braking system (1) to finish actuating each caliper (5) by the braking system (1) alone and thus release the wheel locking system (8) from its actuation function to allow the vehicle to be braked; -detecting the deactivation of the control (2) of the braking system (1); -determining the threshold value for which each pad leaves contact with its brake disc (44); - Maintain the preload of the brakes at this threshold value as long as none of said commands is activated while recharging said accumulators to enable the braking system to be prepared and to reset said preload.   6. Method according to claim 3 or 5, characterized in that the determination of the threshold value is carried out from measurements of at least one pressure sensor (15) included in the wheel locking system (8).   7. Method according to claim 6, characterized in that the measurements of each sensor (15) are made upstream of each brake caliper (5) to allow i5 to be controlled independently of the touch of the pads around each disc (44) .   8. Method according to one of the preceding claims, characterized in that it is initialized when the engine system control is activated.