Method for controlling the wear on a brake pad of a disk braking device of a motor vehicle

Abstract

The invention relates to a method for controlling the wear on a braking device (F) acting on at least one wheel of a motor vehicle, the braking device (F) comprising: a caliper (E) comprising two brake pads, wherein one (P1) is referred to as fixed relative to the caliper (E), and the other (P2) is referred to as movable relative to the caliper (E), wherein the brake pad referred to as the movable brake pad is drivable so as to bear against the brake disk (D), which rotates as one with the wheel and is positioned between the brake pads (P1, P2), and wherein the braking device comprises an electrically controlled parking brake comprising an electric motor (M) for actuating a screw / nut mechanism (2) intended to exert a bearing force against a brake piston (1) bearing against the brake pad referred to as the movable brake pad (P2), and thereby to drive the brake pad referred to as the movable brake pad (P2) into a clamping position against the disk (D) and the brake pad referred to as the fixed brake pad (P1), in the parking braking position. The method comprises: a phase 1 comprising driving the nut (21) of the screw / nut mechanism (2) from an initial position to a reference position; a phase 2 comprising driving the nut (21) of the screw / nut mechanism (2) from the reference position (PREF) to a bearing position, wherein the brake pad referred to as the movable brake pad (P2) bears against the disk (D), and wherein the bearing position (PA) precedes the parking braking position (PS), in which the parking brake is engaged, wherein the method comprises determining the distance (d) travelled by the nut (21) of the screw / nut mechanism (2) between the reference position and the bearing position, comparing the determined distance with a predetermined reference distance, and calculating a difference between the two distances in order to determine the wear on the braking device associated with the loss of thickness of the brake pad referred to as the movable brake pad (P2), of the disk (D), and / or of the brake pad referred to as the fixed brake pad (P1).

Description

Description Title of the invention: method for monitoring the wear of a brake pad of a motor vehicle disc braking device

[0001] The invention relates to a method for monitoring the wear of a braking device acting on at least one wheel of a motor vehicle, the braking device comprising: a caliper comprising two brake pads, one said to be fixed relative to the caliper and the other said to be movable relative to said caliper being drivable in bearing against the brake disc integral in rotation with the wheel and positioned between the brake pads, the braking device comprising an electrically controlled parking brake comprising an electric motor for actuating a screw / nut mechanism intended to exert a bearing against a brake piston which is in bearing against the so-called movable brake pad, thus causing the said brake pad to be clamped against the disc in the parking braking position; the invention also relates to a device for monitoring brake pad wear.

[0002] Motor vehicles have a braking device. Such a braking device comprises, at the wheel, a brake disc installed to rotate with the rim of the vehicle wheel and two brake pads which are installed on opposite sides of the brake disc using a caliper. At least one of the two brake pads is "movable" relative to the caliper to clamp against the brake disc.

[0003] The brake disc is generally harder than the brake pads, so the brake pads wear down and become thinner over time. To generate sufficient friction braking, it is therefore necessary to replace worn brake pads with new ones when their thickness falls below a certain value. It is therefore important to be able to monitor the wear condition of a vehicle's brake pads.

[0004] State of the art

[0005] In document EP-A-4 091 891, a system and a method for monitoring the wear of brake pads of a motor vehicle are proposed. The motor vehicle comprises a braking device acting on a wheel of the vehicle, which comprises a brake pad fixed in rotation relative to the wheel of the vehicle and movable linearly parallel to an axis of rotation of the wheel of the vehicle.

[0006] The braking device comprises a brake piston configured to drive the brake pad against the disc and an electric parking brake which has a drive motor and a piston drive portion actuated by said drive motor, said piston drive portion driving the brake pad against the disc when the motor vehicle brakes.

[0007] The wear monitoring method comprises operating, after parking the motor vehicle, the drive motor to cause the driving portion of the piston to move to a predetermined reference position; moving the driving portion of the piston from the reference position to a stop position corresponding to the parking brake position of the brake piston; determining a distance between the reference position and the stop position; and calculating a difference between the determined distance and a predetermined reference distance to determine the thickness loss of the monitored brake pad.

[0008] The vehicle also includes a control system associated with this process.

[0009] This reference distance is therefore a displacement distance of the piston drive part moving from the reference position to the stop position, said displacement distance is determined when the brake pad to be checked has a known thickness or the brake pad is new and the motor vehicle is in parking brake.

[0010] The piston drive part consists of the nut of a screw / nut mechanism, the nut being fixed in rotation and driven in translation along the screw which, kept fixed in translation, is driven in rotation by the drive motor. In order to have a certain reference position, the screw has a stop, which, when the nut is in abutment against it, constitutes the reference position. Thus, when the motor vehicle is stationary, the control method can be triggered by actuating the motor which brings the nut to its reference position, for example in abutment against a stop element carried by the screw, then subsequently triggering the driving of said nut to drive it and the piston towards the brake pad and a brake application position in which said nut is in the stop position.

[0011] A distance is then defined between the reference position and the parking brake position. This distance is stored as a reference distance, for example when the brake pad is new. Then, during the vehicle's operating time, this control process is repeated and allows new values ​​to be established for the distance between the reference position and the parking brake position which, compared with the reference distance, allow the brake pad wear to be assessed over time and thus warn the driver of excessive wear, for example, requiring the brake pads to be changed.

[0012] However, it has been observed that when the piston is tightened in the parking brake position, a deformation of the caliper can occur which depends on the force exerted by the piston and its position which also depends on the wear of the brake pad. The measurement carried out thus disturbs the measured value and this disturbance is dependent on each type of caliper.

[0013] Statement of the invention

[0014] The present invention aims to provide an improved method for controlling a brake aimed at remedying this drawback.

[0015] The invention thus relates to a method for monitoring the wear of a braking device acting on at least one wheel of a motor vehicle, the braking device comprising: a caliper comprising two brake pads, one said to be fixed relative to the caliper and the other said to be movable relative to said drivable caliper bearing against the brake disc integral in rotation with the wheel and positioned between the brake pads, the braking device comprising an electrically controlled parking brake comprising an electric motor for actuating a screw / nut mechanism intended to exert pressure against a brake piston bearing against the so-called movable brake pad and to drive said so-called movable brake pad into clamping against the disc and the fixed brake pad, in the parking braking position;the method comprising: a phase 1 comprising driving the nut of the screw / nut mechanism to move from an initial position to a reference position;a phase 2 comprising the driving in movement of the nut of the screw / nut mechanism from the reference position to a support position in which the so-called mobile brake pad is supported against the brake disc, said support position being a position before the parking braking position in which the parking brake is applied, said method comprising the determination of the distance traveled by the nut of the screw / nut mechanism between the reference position and said support position, the comparison of the determined distance and a predetermined reference distance, and the calculation of a difference between the two distances to determine the wear of the braking device linked to the loss of thickness of the so-called mobile brake pad, of the disc and of the so-called fixed brake pad.;

[0016] The method according to the invention thus makes it possible to determine with greater certainty the value of the wear of the braking device and in particular of the so-called mobile brake pad, of the disc and of the so-called fixed brake pad, by choosing along the travel of the nut of the screw / nut mechanism to a parking braking position, a support position corresponding to a position in which the nut and the piston have driven the so-called mobile brake pad into contact with the brake disc, this support position being upstream of the parking braking position of the nut and downstream of the contact position in which the so-called mobile brake pad is in contact with the disc.

[0017] Advantageously, the support position being located upstream of the parking braking position, a risk of measurement error linked to the deformation of the caliper in the parking braking position is avoided, while the support position located after a so-called contact position avoids risks of measurement inaccuracy linked to clearances which may result from wear or deformation of the braking device over time and thus disrupt the contact position. The contact position is a position in which the piston begins to exert pressure on the brake pad. The support position is therefore a position located between the contact position and the parking braking position of the brake pad with the disc.

[0018] Preferably, the reference position is predetermined and corresponds to a position in which the nut of the screw / nut mechanism is spaced from the piston and is in rear abutment against a stop element provided on the screw, for example at the end of the screw of said screw / nut mechanism opposite the end engaged with the piston. In particular, the predetermined reference position is distinct from the position of the nut in the non-activated position of the parking brake.

[0019] The initial position is the position of the nut along the screw when the control method is implemented, this initial position being able to be the parking brake position of the nut when the parking brake is activated (clamping of the disc) or an inactive position of the nut when the parking brake is not activated.

[0020] The method further comprises a phase 3 comprising driving the nut of the screw / nut mechanism from the support position to a final position which may be the initial position or another position such as the braking position.

[0021] The invention also relates to a device for monitoring the wear of a braking device acting on at least one wheel of a motor vehicle, the braking device comprising a caliper comprising two brake pads, one said to be fixed relative to the caliper and the other said to be movable relative to said caliper, being drivable in bearing against the brake disc integral in rotation with the wheel and positioned between the brake pads, the braking device comprising an electrically controlled parking brake comprising an electric motor for actuating a screw / nut mechanism intended to exert a bearing against a brake piston bearing against the movable brake pad and thus drive said movable brake pad in clamping against the disc and the brake pad fixed, in the parking braking position, the control device comprising an electronic control unit for the parking brake, said unit comprising: a first control module configured to actuate the screw / nut mechanism from an initial position of the nut to a predetermined reference position of said nut; a second module configured to actuate the screw / nut mechanism from the reference position of the nut to a support position of the nut in which the nut and the piston have driven the so-called mobile brake pad to bear against the disc; a third module configured to determine a distance between the reference position and the support position;a fourth module configured to compare the determined distance and a predetermined reference distance and to calculate a difference between the two distances corresponding to wear of the braking device linked to the loss of thickness of the movable brake pad, the disc and / or the fixed brake pad.;

[0022] In the braking device, the screw / nut mechanism is actuated by an electric motor, the nut constituting the drive part of the piston moving along the screw to enable the so-called mobile brake pad to be driven under the effect of the piston and the nut, to achieve the clamping of the brake disc by the pads as well as the release of the brake pad to stop the braking.

[0023] During operation of the electric parking brake, the motor operating current varies during the actuation of the screw / nut mechanism. Thus, when parking braking is required, the motor is activated to start the screw / nut mechanism and a higher starting current occurs. After the peak current at motor start, the operating current drops rapidly and the screw / nut mechanism is actuated with a stable motor operating current throughout the "free" travel of the nut along the screw.

[0024] When the nut presses on the piston, the so-called movable brake pad is also pressed towards the brake disc to come into contact with the latter, the intensity of the operating current again undergoes a variation linked to this pressing force on the piston. Once the brake pad is in contact with the disc, the intensity of the current increases rapidly until the parking braking position, where a peak in the intensity of the operating current is again observed then a drop, and the actuation of the screw / nut mechanism is then stopped. The so-called movable brake pad is thus held in the parking braking position using the screw / nut mechanism acting on the piston.

[0025] When the parking brake is deactivated, the electric motor actuating the screw / nut mechanism drives the nut in translation in the opposite direction along the screw to an inactive position of the parking brake, in which it ceases to hold the so-called mobile brake pad against the disc, and therefore the clamping of the disc by the two brake pads.

[0026] In order to estimate the tightening force and the displacement of the nut of the screw / nut mechanism, the useful information is therefore the current consumed by the electric actuating motor insofar as the current consumed is proportional to the force generated by the actuating motor, the voltage applied to the terminals of said actuating motor, as well as the speed of the actuating motor.

[0027] Thus, according to the control method according to the invention, the intensity of the current of the electric actuating motor of the screw / nut mechanism is measured, and in particular variations in the intensity of the current, to estimate the different positions of the nut along its travel on the screw such as the reference stop position, the contact position, the support position and the tightening position. This support position is thus defined at a minimum by a current support intensity of the actuating motor reaching an intensity value corresponding to the intensity of the operating current during its “free” travel to which is added a predefined intensity constant at least equal to 0.5 amps, and less than 23 amps, for example at least equal to 2 amps and preferably between 2 and 4 amps.

[0028] In phase 1, the nut of the screw / nut mechanism is driven from the initial position to the reference position in backstop against the screw stop element, then in phase 2, from the reference position to the support position identified by reaching the support intensity measurement, then from the support position to a final position.

[0029] From this current intensity value, the third module estimates the distance between the predetermined reference position and the support position and the fourth module compares said estimated distance and a predetermined reference distance to determine the wear of the braking device.

[0030] Thus, when fitting the brake pads, the control method according to the invention is implemented to establish the initial distance of the travel of the nut of said screw / nut mechanism between the predetermined reference position and the support position, this initial distance then serves as a reference distance, and is stored. Then during the use of the parking braking device over time, the control method according to the invention is implemented at different times, preferably predefined, to determine the distance between the predetermined reference position and the support position at that time and compare it to the reference distance to assess the wear of the brake pads and its evolution.

[0031] The reference distance is therefore the distance by which the nut moves from the reference position to the parking brake position, said reference distance being determined when the brake pads have a known lining thickness or when the brake pads are new.

[0032] Based on the observed deviation, the method determines whether or not the brake pads need to be changed. Thus, if this deviation exceeds a predetermined threshold value, the vehicle control system includes a module configured to emit a warning signal to the vehicle driver via a human-machine interface, of the need to change the brake pads. Several threshold values ​​can be envisaged, generating progressive warning messages.

[0033] After brake pad maintenance, the control process is carried out in such a way as to determine the travel distance between the predetermined reference position at the stop and the support position and if this distance has a value equal to or above the initially stored reference distance, then it is not stored. On the other hand, if this new distance is below the initially stored reference distance, this indicates that the brake pads have changed and this new distance after maintenance is stored and replaces the previous initially stored reference distance.

[0034] Parking braking devices can have different configurations. As already mentioned, the screw of the screw / nut mechanism is mounted fixed in translation and driven in rotation by an electric motor, and it carries a nut which, under the effect of the rotation of the screw, is driven in translation along the screw, said nut being further mounted fixed in rotation in the piston.

[0035] According to one configuration of the braking device, the piston is rotated with the nut and then rests on the movable brake pad while rotating.

[0036] When the so-called mobile brake pad does not have an anti-rotation pin, during phase 1, the nut of the screw / nut mechanism is driven towards the reference position at the stop with the same speed throughout the free travel of the nut on the screw corresponding to the travel of the nut towards the reference position from either the contact position when the initial position is the parking brake position, or the inactive position when the parking brake is not activated.

[0037] The drive of the screw / nut mechanism from the initial position to the reference position at the stop causes the nut and piston to rotate towards the stop. Friction caused by the seals sealing of the piston during this rotation generates a higher current consumption, useful for detecting that the nut is in the reference position at the stop. Therefore, during phase 1, the nut is actuated in movement towards the reference position from its initial position with a high speed, up to the stop position in which the nut and the piston are also driven in rotation, the stopping of the actuation of the screw / nut mechanism then being controlled by the detection of the rotation of the nut and the piston, using means for detecting an increase in the operating current.

[0038] In this way it is possible to limit the time required to actuate the screw / nut mechanism in the reference position at the stop during phase 1 of the control process.

[0039] In another configuration of the braking device, an anti-rotation pin for the piston is provided on the brake pad. High-speed driving of the screw / nut mechanism at the reference stop position would cause very high applied forces, because the piston being blocked in rotation by the anti-rotation pin, there is a risk of damage to this pin or the piston.

[0040] In order to overcome this drawback, when the piston has an anti-rotation pin, during phase 1, the nut of the mechanism / screw nut is actuated to move towards the reference position at the stop with a first speed, in a first section of the free travel of the nut, then on a second section of screw shorter than the first section and adjacent to the stop, according to a second speed lower than the first speed.

[0041] The reference position at the stop is recognized with the detection of a current threshold exceeded. It is thus possible to carry out the implementation of the wear process without causing risks of mechanical damage while limiting the time required to actuate the screw / nut mechanism to the reference position at the stop.

[0042] The free travel of the nut on the screw corresponds to the travel of the nut towards the reference position from either the parking brake position which is the initial position when the parking brake is activated (clamping the disc), or the inactive position of the nut on the piston corresponding to the initial position when the parking brake is not activated.

[0043] In this way it is possible to limit the time required to actuate the screw / nut mechanism to the predetermined reference position while protecting the anti-rotation pin, the piston and the screw / nut mechanism from mechanical damage which would result from the nut returning against the stop element at too high a speed.

[0044] It can also be provided that the various elements: screw, nut, anti-rotation pin, are configured to resist the forces applied when the nut reaches the stop and is driven with the rotating piston.

[0045] Similarly, it is proposed to provide at the stop end of travel damping means such as a set of spring washers of the Belleville type, thus avoiding any risk of damage and the detection of the stop can be carried out on the basis of the increase in the operating current with a threshold value or a gradient. Detection can also be carried out on the motor speed.

[0046] The wear control method according to the invention can be implemented in several ways.

[0047] In a first embodiment of the control method according to the invention, the initial position of the screw / nut mechanism is the parking brake position in which the nut is located when the parking brake is active and from which it is driven in translation towards the predetermined reference position, namely the reference position at the end stop.

[0048] The wear process is then only triggered on the precondition that the following criteria and conditions are met and validated: - issuing a request to carry out a pad wear check, for example 6000 km have been covered since the last check, - the vehicle is on, the engine is not running - the driver is or is not in the vehicle, - the vehicle is stationary with the parking brake activated, and, optionally, - the vehicle is on a flat surface, i.e. on a surface with a slope of less than 8%.

[0049] All of these criteria are detected and analyzed by the central control unit of the vehicle using detection means and sensors existing in the vehicle. Thus, if these criteria are all validated, a control request is sent to the central unit of the control device to start the control process and a request is sent from the parking brake wear control device to the central unit of the vehicle which sends a request to the driver to trigger said control process.

[0050] If the driver approves the request, the control process is triggered and is implemented on the parking brakes, side by side of the vehicle.

[0051] The screw / nut mechanism is therefore actuated in phase 1, from the initial position of the nut at the start of the process, here the parking brake position, to the predetermined reference position, preferably the rear stop reference position. Then in phase 2, it is actuated to drive the nut to the support position which corresponds to an intensity of the actuating motor in order to determine the distance traveled.

[0052] In phase 3, the screw / nut mechanism is actuated to drive the nut to the parking brake position, namely the initial position with the parking brake activated, or alternatively, it is actuated to drive the nut to the inactive position when the parking brake is not activated.

[0053] This mode allows the control procedure to be implemented on all four parking brakes, first on the two brakes located on the same side of the vehicle and then on the two brakes on the opposite side. In this way, parking braking is guaranteed on at least one side of the vehicle, while the other side is being checked for wear. When it has also been validated that the vehicle is parked on a flat surface, it is possible to carry out the wear check on all four parking brakes of the vehicle.

[0054] In a second mode, the initial position of the nut is the inactive position of the parking brake from which it is driven in translation towards the predetermined reference position, namely the reference position at the stop.

[0055] The triggering of the wear control process in this case is only triggered if the following criteria and conditions are met and validated: - request to carry out a pad wear check, for example when 6000 km have been covered since the last check, - the vehicle engine is running, - the driver is in the vehicle, - the vehicle is stationary with the parking brake inactive or in the low-speed rolling phase.

[0056] All of these criteria are detected and analyzed by the vehicle's central control unit using existing detection means and sensors in the vehicle. Thus, if these criteria are all validated, a control request is sent to the braking system's central unit which authorizes the sending of this request to the control system to start the control process if the operational conditions are met, for example when the vehicle speed is low.

[0057] The screw / nut mechanism is then actuated in phase 1, to drive the nut from the initial position at the start of the process, here the inactive position of the parking brake, to the predetermined reference position, preferably the reference position in rear stop. Then in phase 2, it is actuated to drive the nut to the support position which corresponds to an intensity of the actuating motor in order to determine the distance traveled. In phase 3, the screw / nut mechanism is actuated to drive the nut to the inactive position of the parking brake, namely the initial position.

[0058] If the vehicle is moving, it is then possible to perform the test procedure on all the parking brakes at the same time.

[0059] The wear control method according to the invention and its implementation device make it possible to offer a customer service allowing the latter to receive information on the estimation of the wear of the pads and discs without a sensor to be added. This invention also allows the improvement of the durability of the rear stop (e.g. during the procedure of changing the pads and provides a reinforcement of the estimation of the physical parameters using the information on the wear of the disc and the pads such as for example the loss of pressure force.

[0060] The invention also relates to a braking device acting on a motor vehicle wheel, the braking device comprising a caliper comprising a brake pad called fixed relative to the caliper and a brake pad called mobile relative to the caliper, which can be driven in abutment against a brake disc integral in rotation with the wheel, a brake piston that can be actuated hydraulically as a service brake, the braking device further comprising an electrically controlled parking brake comprising an electric motor for actuating a screw / nut mechanism intended to exert abutment against the hydraulic piston and drive said brake pad called mobile in clamping against the disc in the parking braking position, the braking device further comprising a device for monitoring the wear of the braking device according to the invention.

[0061] The invention also relates to a braking device acting on a motor vehicle wheel, the braking device comprising a caliper comprising a brake pad said to be fixed relative to the caliper and a brake pad said to be mobile relative to the caliper, which can be driven to bear against a brake disc integral in rotation with the wheel, an electrically controlled brake piston comprising an electric motor for actuating a screw / nut mechanism intended to exert a pressure against the piston and drive said brake pad said to be mobile to clamp against the disc in the parking braking or service braking position, the braking device further comprising a device for monitoring the wear of the braking device according to the invention.

[0062] The invention also relates to a motor vehicle comprising a braking device for at least one wheel comprising a device for monitoring the wear of said braking device according to the invention.

[0063] The invention will now be described in more detail with reference to the drawing in which the figures represent:

[0064] [Fig. 1] a longitudinal sectional view of the preferred example of a motor vehicle brake according to the invention;

[0065] [Fig. 2] a diagram illustrating during the phases of the control method according to the invention and as a function of time, the current intensity curve of the actuating motor and the travel of the nut of the screw / nut mechanism;

[0066] [Fig. 3] a linear schematic representation of the travel of the nut of the screw / nut mechanism during the control method according to the invention according to Figure 2;

[0067] [Fig. 4] a diagram illustrating during the phases of the control method according to the invention and as a function of time the current intensity curve of the actuating motor and the travel of the nut of the screw / nut mechanism according to a variant of the mode of figure 2;

[0068] [Fig. 5] a linear schematic representation of the travel of the nut of the screw / nut mechanism during the control method according to the invention according to Figure 4;

[0069] [Fig. 6] a diagram illustrating during the phases of another mode of the control method according to the invention and as a function of time the current intensity curve of the actuating motor and the travel of the nut of the screw / nut mechanism;

[0070] [Fig. 7] a linear schematic representation of the travel of the nut of the screw / nut mechanism during the control method according to the invention according to Figure 6;

[0071] [Fig. 8] a schematic representation of a control device according to the invention; and

[0072] [Fig. 9] a top view of a vehicle equipped with a control device according to the invention.

[0073] The method for monitoring the wear of a motor vehicle brake pad according to the invention makes it possible to more specifically monitor the wear of the brake pad or lining carried by the brake pad.

[0074] The motor vehicle V comprises a braking device acting on each wheel R of said vehicle, the braking device or brake F as shown in Figure 1 comprises a caliper E carrying two brake pads P1, P2 facing each other, one P1 is said to be fixed relative to the caliper E and the other P2 said to be mobile relative to the caliper E is operable in translation to be brought into abutment against a brake disc D integral in rotation with the wheel. The brake F is mounted at each wheel so as to overlap the disc D to position each brake pad Pl, P2 on one side of the disc. The translational actuation of the movable brake pad P2 allows the disc D to be clamped by the two brake pads Pl, P2 using a brake piston 1. This piston 1 can be actuated hydraulically or electrically.

[0075] The brake F also includes an electrically controlled parking brake comprising an electric motor M for actuating a screw / nut mechanism to exert pressure and drive the piston 1. The nut 21 is driven in translation along the screw 22 to come to bear against the brake piston 1 and therefore exert pressure on the brake pad P2 to tighten it against the disc D which is against the brake pad PI in the parking braking position.

[0076] The nut 21 of the screw / nut mechanism 2 constitutes the driving part of the piston 1 moving along the screw 22 to exert pressure against the piston 1 towards the brake pad P2, the clamping of the brake disc D by the pads Pl, P2 as well as the release of the piston 1 to stop the braking.

[0077] When the electric parking brake is operating, the operating current I of the actuating motor M can be measured by a specific detection circuit and the measured values ​​can be transmitted to an electronic control unit of the braking device.

[0078] When parking braking is required, the actuating motor M is activated to start. The nut 21 is generally at an initial position, corresponding to a position Pi of the nut 21 in which the parking braking is inactive. The intensity I of the starting current is generally high, as represented by a current peak ID in Fig. 3. After the current peak ID, the intensity I of the operating current drops to an operating value corresponding to a "free" stroke of the nut 21 on the screw 22.

[0079] Then, the nut 21 presses on the piston 1, the intensity I of the operating current undergoes a variation at this contact position Pc in which the nut / piston is pressing on the brake pad P2 and again an increase linked to this pressing force of the pad P2 on the disc D. Once the brake piston 1 presses on the brake pad P2, the intensity of the current increases rapidly up to the position Ps of the nut 21 corresponding to an activated parking brake, where a peak Is of the intensity of the operating current is again observed and the actuation of the screw / nut mechanism is then stopped. The brake piston 1 is thus held in the activated parking brake position using the screw / nut mechanism 2.

[0080] When the parking brake is deactivated, the actuating motor M of the screw / nut mechanism 2 drives the nut 21 in translation in the opposite direction to an inactive position Pi, a position in which the parking brake is inactive, the nut 21 ceasing to hold the piston 1 against the brake pad P2, and therefore the clamping of the disc D.

[0081] The control method according to the invention therefore uses the measurement of the intensity I of the operating current of the actuating motor M of the screw / nut mechanism 2 to estimate at time intervals the distance traveled by the nut 21.

[0082] Thus, the control method according to an embodiment illustrated in figures 2 and 3 comprises a phase 1 which consists of actuating in displacement the nut 21 driving the piston 1 towards a predetermined reference position in rear stop PREF in which the rear of the nut 21 is brought into abutment against the collar 23 of the rod 22, from its initial position Pi, that is to say the position in which the nut 21 is located at the time of starting the control method, corresponding in this mode to the position P s of nut 21 in which the parking brake is active.

[0083] As can be seen, the intensity I of the current of phase 1 is generally high, as represented by the current peak ID in Fig. 2. After the current peak ID, the intensity I of the operating current drops to an operating value corresponding to a "free" stroke of the nut 21 on the screw 22 towards the collar 23 forming a stop. Once at the stop, the intensity shows a peak IB, then drops again. Once the nut 21 is brought to a stop against the collar 23, during phase 2 of the control method, the screw / nut mechanism 2 is actuated again, and when reversing the drive to return the nut 21 to the support position PA, the intensity shows a reversal peak IINV and then again the intensity I of the operating current drops to an operating value corresponding to the "free" stroke of the nut 21 on the screw 22 towards the piston 1.The nut 21 is moved from the reference position PREF to a support position PA in which the piston 1 resting on the brake pad P2 drives the brake pad P2 into support with the brake disc D of the brake F but without having reached its parking position Ps. Before this support position PA, the intensity increases again to the contact position Pc when the nut 21 presses against the piston 1 and the brake pad P2. The nut 21 is driven in phase 3 to the parking braking position Ps.

[0084] Thus, the given intensity value defined as the support intensity IA, corresponds to the operating intensity IF + a defined intensity value such as 2 amperes. From this intensity value, the travel time between PREF and PAPPUI is estimated and the distance traveled by the nut 21 between these two positions can then be determined.

[0085] This determined distance D is then compared with a predetermined reference distance DREF, and the calculation of a difference between the two distances makes it possible to determine the loss of thickness of the brake pad P.

[0086] This mode of the control process is implemented when the vehicle meets certain conditions and performance criteria which are: - request to carry out a pad wear check, for example 6000 km have been covered since the last check, - the vehicle is on, - the vehicle is stationary with the parking brake activated, and - the vehicle is on a flat surface.

[0087] The flat surface condition is achieved when a slope of less than 8% is determined. An additional condition that the driver is in the vehicle can also be considered.

[0088] Figures 4 and 5 represent a variant of this mode in which phase 3 of the method drives the nut 21 from the support position PA to the inactive position Pi and not to the initial parking braking position Ps.

[0089] Diagram 5 illustrates the variations in intensity during the phases of this process.

[0090] Figures 6 and 7 show another mode of the process in which phase 1 is initiated from the inactive position of the brake and phase 3 returns the screw / nut mechanism to this inactive position.

[0091] The wear control process mode in this case is only triggered if the following criteria and conditions are met and validated: - request to carry out a pad wear check, for example when 6000 km have been covered since the last check, - the vehicle engine is running, - the driver is in the vehicle, - the vehicle is stationary with the parking brake inactive or in the low-speed rolling phase.

[0092] Phases 1.1 of figures 4 and 6 represent the brake release stroke and phases 1.2 the free stroke of nut 21.

[0093] In Figures 6 and 7 is illustrated a mode of the method according to the invention in which the initial position is the inactive position Pi to which the screw / nut mechanism 2 is returned from the support position PA.

[0094] This control method is implemented using a control device 100 shown in Figure 8 which comprises an electronic control unit 100 of the parking brake, comprising a first control module 101 configured to actuate the screw / nut mechanism 2 from an initial position of the nut 21 at the time of starting the control method to a reference position PREF; a second module 102 configured to actuate the screw / nut mechanism 2 from the reference position PREF of the nut 21 to a support position PA of the nut 21 in which the piston 1 is in contact with the brake pad P2, said support position PA being located, in the tightening direction, after the contact position Pc in which the piston 1 comes into contact with the brake pad P2 and before the parking braking position Ps in which the brake pads P1, P2 are in the parking braking position of the brake (in tight contact with the disc D);a third module 103 configured to determine an estimated distance d between the reference position PREF and the support position PA; a fourth module 104 configured to compare the estimated distance d and a predetermined reference distance d EF and to determine the difference between these two distances to estimate the loss of thickness of the brake pad P2.;

[0095] As can be seen in Figure 9, a vehicle V according to the invention comprises a braking device or brake F at at least one, preferably each wheel R, as well as a control device according to the invention.

[0096] Of course, the invention is not limited to the examples which have just been described and numerous adjustments can be made to these examples without departing from the scope of the invention.

[0097] NOMENCLATURE F disc brake (braking device) E stirrup V vehicle PI brake pad fixed relative to the caliper P2 brake pad movable relative to the caliper D disk 1 piston 2 screw / nut mechanism 21 nut 22 screws 23 collar M electric motor PA support position PC contact position PREF reference position Pi inactive parking brake position P s Active parking brake position Start intensity ID IB stop intensity IINV motor reversing current IF operating intensity Is Parking intensity IA support intensity d estimated distance dREF reference distance

Claims

Claims 1. Method for checking the wear of a braking device (F) acting on at least one wheel (R) of a motor vehicle (V), the braking device (F) comprising: a caliper (E) comprising two brake pads, one (PI) called fixed relative to the caliper (E) and the other (P2) called mobile relative to said caliper (E) drivable in abutment against the brake disc (D) integral in rotation with the wheel and positioned between the brake pads (P1, P2), the braking device comprising an electrically controlled parking brake comprising an electric motor (M) for actuating a screw / nut mechanism (2) intended to exert abutment against a brake piston (1) in abutment against the so-called mobile brake pad (P2) and thus drive said so-called mobile brake pad (P2) in clamping against the disc (D) and the fixed brake pad (PI), in the parking braking position;the method comprising: a phase 1 comprising driving the nut (21) of the screw / nut mechanism (2) from an initial position (Pi) to a reference position (PREF);a phase 2 comprising the driving in movement of the nut (21) of the screw / nut mechanism (2) from the reference position (PREF) to a support position in which the so-called mobile brake pad (P2) is supported against the brake disc (D) (F), said support position (PA) being before the parking braking position (Ps) in which the parking brake is applied, said method comprising the determination of the distance (d) traveled by the nut of the screw / nut mechanism (2) between the reference position (PREF) and said support position (PA), the comparison of the determined distance (d) and a predetermined reference distance (dREF), and the calculation of a difference between the two distances to determine the wear of the braking device linked to the loss of thickness of the so-called mobile brake pad (P2), of the disc (D) and / or of the fixed brake pad (PI).; 2. Method according to claim 1, characterized in that it comprises a phase 3 comprising driving the nut (21) of the screw / nut mechanism (2) from the support position (PA) to a final position.

3. Method according to claim 1 or 2, characterized in that the reference position (PREF) corresponds to a position in which the nut (21) of the screw / nut mechanism (2) is spaced from the piston (1) and is in rear abutment against a stop element provided on the screw (22).

4. Method according to one of claims 1 to 3, characterized in that the initial position is the position of the nut (21) along the screw (22) of the screw / nut mechanism when implementing the control method, this initial position (Pi) being either the parking braking position (Ps) of the nut (21) when the parking brake is activated (clamping of the disc), or the inactive position (Pi) of the nut (21) when the parking brake is not activated.

5. Method according to one of claims 1 to 4, characterized in that the reference distance (dREr) is the distance of movement of the nut (21) of the screw / nut mechanism (2) from the reference position (PREF) to the parking braking position (Ps), said reference distance being determined when the so-called movable brake pad (P2), the disc (D) and the so-called fixed brake pad (PI) respectively have a known thickness.

6. Method according to one of claims 1 to 5, characterized in that the intensity of the current of the motor actuating the screw / nut mechanism (2) is measured, and in particular variations in the intensity of the current, to estimate the different positions of the nut (21) along its travel on the screw (2) such as the reference position at the stop, the support position and the tightening position.

7. Method according to claim 6, characterized in that the support position (PA) is defined by a current intensity of the electric motor reaching a support intensity value (IA) corresponding to the intensity of the operating current during its “free” travel from the reference position (PREF) to which is added a predefined intensity constant at least equal to 0.5 amps and less than 23 amps, preferably between 2 and 4 amps.

8. Method according to claim 7, characterized in that in phase 1, the nut (21) of the screw / nut mechanism (2) is driven from the initial position (Pi) to the reference position (PREF) in rear stop against the stop element of the screw (22), then in phase 2, from the reference position (PREF) to the support position (PA) identified by reaching the support intensity measurement (IA), then from the support position (PA) to a final position.

9. Method according to claim 8, characterized in that the method is triggered on the precondition that the following criteria and conditions are met and validated: - issuing a request to carry out a pad wear check, - the vehicle is on, the engine is not running - the vehicle is stationary with the parking brake activated, and, optionally, - the vehicle is on a flat surface.

10. Method according to one of claims 1 to 9, characterized in that, when the so-called mobile brake pad (P2) comprises an anti-rotation pin, during phase 1, the nut (21) of the screw / nut mechanism (2) is driven towards the reference position (PREF) in abutment with a first speed, in a first section of the free travel of the nut (21), then on a second screw section (22) shorter than the first section and adjacent to the reference position (PREF) in abutment, according to a second speed lower than the first speed, the free travel of the nut (21) on the screw (22) corresponding to the travel of the nut (21) towards the reference position (PREF) from either the contact position (Pc) when the initial position is the parking brake position (Ps), or the inactive position (Pi) when the parking brake is not activated.

11. Method according to one of claims 1 to 9, characterized in that, when the so-called mobile brake pad (P2) does not include an anti-rotation pin, during phase 1, the nut (21) of the screw / nut mechanism (2) is driven towards the reference position (PREF) in abutment with the same speed throughout the free travel of the nut (21) on the screw (22) corresponding to the travel of the nut (21) towards the reference position (PREF) from either the contact position (Pc) when the initial position is the parking braking position (Ps), or the inactive position (Pi) when the parking brake is not activated.

12. Device for monitoring the wear of the brake pads (P1, P2) and the disc (D) of a braking device acting on at least one wheel of a motor vehicle, the braking device comprising a caliper (E) comprising two brake pads, one said to be fixed relative to the caliper (E) and the other said to be movable relative to said caliper (E) drivable in bearing against the brake disc (D) integral in rotation with the wheel and positioned between the brake pads (P1, P2), the braking device comprising an electrically controlled parking brake comprising an electric motor (M) for actuating a screw / nut mechanism intended to exert a bearing against a brake piston (1) bearing against the so-called movable brake pad and thus drive said so-called movable brake pad (P2) in clamping against the disc and the fixed brake pad, in the parking braking position;the control device being configured to implement the method according to one of claims 1 to 11, and comprising an electronic control unit (100) of the parking brake, said unit comprising: a first control module (101) configured to actuate the mechanism; screw / nut (2) and drive the nut (21) along the screw (22) from an initial position of the nut (21) to a predetermined reference position of said nut (21); a second module (102) configured to actuate the screw / nut mechanism (2) and drive the nut (21) from the reference position (PREF) to a support position (PA) of the nut (21) in which the so-called movable brake pad (P2) is in support with the brake disc (D) (F), said support position (PA) being before the parking braking position (Ps) of the nut (21) in which the parking brake is applied; a third module (103) configured to determine a distance (d) between the reference position (P EF) and the support position (PA);a fourth module (104) configured to compare the determined distance (d) and a predetermined reference distance (dREF) and to calculate a difference between the two distances to determine the wear of the so-called mobile brake pad (P2) as well as of the disc (D) and of the second so-called fixed brake pad (PI).; 13. Braking device acting on a motor vehicle wheel, the braking device comprising a caliper (E) comprising a so-called fixed brake pad (PI) and a so-called mobile brake pad (P2) which can be driven in abutment against a brake disc (D) integral in rotation with the wheel, a brake piston (1) which can be actuated hydraulically as a service brake, the braking device further comprising an electrically controlled parking brake comprising an electric motor (M) for actuating a screw / nut mechanism (2) intended to exert abutment against the piston in abutment against the so-called mobile brake pad (P2), to drive said mobile brake pad (P2) in clamping against the disc (D) in the parking braking position, the braking device further comprising a device for monitoring the wear of the mobile brake pad (P2) according to claim 12.

14. Braking device (F) acting on a motor vehicle wheel, the braking device (F) comprising a caliper (E) comprising a so-called fixed brake pad (PI) and a so-called mobile brake pad (P2) drivable in translation to be brought into abutment against a brake disc (D) integral in rotation with the wheel, an electrically controlled brake piston comprising an electric motor (M) for actuating a screw / nut mechanism (2) intended to exert abutment against the piston and drive said so-called mobile brake pad (P2) into clamping against the disc (D) in the parking braking or service braking position, the braking device (F) further comprising a device for monitoring the wear of the braking device (F) according to claim 12.

15. Motor vehicle comprising at least one braking device according to one of claims 13 or 14.

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