DESCRIPTION

[0001]. Field of the invention

[0002]. The present invention relates to a method of controlling a braking system, in particular of a vehicle, and to a braking system of a vehicle.

[0003]. Background art

[0004]. Motorcars and in general vehicles with more than two wheels intended to transport passengers on roads, are provided with a hand parking brake, the function of which is to lock the wheels of the vehicle thus preventing the movement thereof when it is parked.

[0005]. In modern braking systems, e.g., those provided with electronic Brake-By-Wire (BBW) technology, the hand parking brake is replaced by an Electric Parking Brake (EPB).

[0006]. For all intents and purposes, the EPB electric parking brake can be considered a sub-system of an electronic braking system with BBW technology which is used for service braking.

[0007]. In greater detail, using the EPB subsystem, the driver can activate the wheel-locking mechanism by means of an actuating device, such as an appropriate button or other automatic functions managed by an electronic processing unit, such as signal logics related to the ignition key, the gear engagement, and the accelerator pedal that, once activated, sends a request for parking- braking activation to an electronic control unit of the vehicle, which electrically actuates the brake pads to lock the brake discs and therefore the movement of the vehicle. [0008]. Vice versa, when restarting, the driver can deactivate the wheel locking mechanism by means of an actuating device that, once activated, sends a parking-braking deactivation request to an electronic control unit of the vehicle, which electrically actuates the brake pads to unlock the brake discs and therefore the movement of the vehicle.

[0009]. Moreover, in addition to replacing the parking-braking function traditionally performed by the hand parking brake, the EPB subsystem is configured to provide automatic supporting functions to the driver, including the so-called "AutoHold" function, i.e., the function allowing the wheels to be locked automatically and without the driver's request when the vehicle is stationary, e.g., uphill, and to be released as soon as the driver presses the accelerator pedal of the vehicle.

[0010]. In known disc brakes with fixed brake caliper, the two pads opposite to the brake disc are actuated by respective pistons independently actuatable by at least two actuators, at least one actuator of which being on each side of the brake disc.

[0011]. The at least two opposite actuators are independently controlled by the electronic control unit, therefore they are actuatable and controllable at the same time and independently of each other.

[0012]. For each of the two actuators, the activation of the parking braking according to a known control logic can be divided into three successive steps:

[0013]. - an inrush step, which elapses from the instant in which the electronic control unit commands the actuators, positioned at a given starting position, to begin a movement, to the instant in which the actuator starts to move, without applying any braking force to the corresponding pad;

[0014]. - an approaching step, which elapses from the instant in which the actuators start to move, without applying any braking force to the corresponding pad, to the instant in which the actuators make contact with the pad and start to apply a braking force to the pad;

[0015]. - an application step, which elapses from the instant in which the actuators start to apply and increase the braking force acting on the pad, to the instant in which the braking force applied by the actuators to the pad reaches a given predetermined reference value.

[0016]. In the known control logics, the at least two opposite actuators are configured to start the inrush step of the parking- braking activation process at the same time in order to activate an axial thrust on the two opposite faces of the brake disc being as symmetrical as possible.

[0017]. Such a symmetry is required to minimize the stresses acting on the brake disc, which could lead to cracks, damage, or rupture of the brake disc.

[0018]. In known disc brakes having at least two independently controllable opposite actuators, the wear, deterioration of mechanical components, and uncertainties related to the starting position of the two opposite actuators may result in differences in the actuation of the braking force by these two actuators, with particular reference to the time required for the two actuators to approach the respective pad and apply the respective braking force, thus generating approaching steps of different duration.

[0019]. If the duration of the approaching step of one actuator differs from the duration of the approaching step of the opposite actuator, the two actuators can start to apply a braking force but not at the same time, so that undesired and harmful asymmetric axial thrusts act on the brake disc.

[0020]. Solution

[0021]. It is the object of the present invention to provide a method of controlling a braking system and a braking system such as to obviate at least some of the drawbacks of the prior art.

[0022]. It is a particular object of the present invention to provide a method of controlling a braking system and a braking system such as to minimize the asymmetric axial thrusts actuated on the brake disc during the activation of the parking braking.

[0023]. It is a further particular object of the present invention to provide a control method of a braking system and a braking system configured to perform the control method, simplified and such as to have fewer energy and structural constraints.

[0024]. These and other objects are achieved by a method of controlling a braking system and a braking system according to the independent claims.

[0025]. The dependent claims relate to preferred and advantageous embodiments of the present invention. [0026]. Drawings

[0027]. In order to better understand the invention and appreciate the advantages thereof, some non-limiting exemplary embodiments thereof will be described below with reference to the accompanying drawings, in which:

[0028]. - figure 1 diagrammatically shows a braking system, according to an embodiment of the invention;

[0029]. - figure 2 diagrammatically shows a supply current of a braking system actuator, and the respective force actuated on a pad of the same braking system, according to an embodiment of the invention;

[0030]. - figure 3 diagrammatically shows the supply currents and the respective forces actuated by two independently controllable actuators of a brake caliper of a braking system, according to the prior art;

[0031]. - figure 4 diagrammatically shows the supply currents and the respective forces actuated by two independently controllable actuators of a brake caliper of a braking system, according to an embodiment of the invention.

[0032]. Description of some preferred embodiments

[0033]. A method of controlling a braking system 1 of a vehicle for activating a parking-braking force actuated by the braking system 1 is described below with reference to the figures.

[0034]. The braking system 1 is of the type comprising at least: [0035]. - a brake disc;

[0036]. - a first pad and a second pad spaced apart from each other and positioned to be opposite to the brake disc;

[0037]. - a first actuator 2, configured to apply and release a first force Fa on the first pad so as to move the first pad from an open position, in which the first pad is separated from the brake disc and does not actuate a parking-braking force, to a closed position, in which the first pad is biased against the brake disc and actuates a parking-braking force;

[0038]. - a second actuator 3, configured to apply a second force Fb on the second pad so as to move the second pad from an open position, in which the second pad is separated from the brake disc and does not actuate a braking force, to a closed position, in which the second pad is biased against the brake disc and actuates a parking-braking force;

[0039]. - an electronic processing unit 4, configured to control the actuation of the first actuator 2 and the second actuator 3;

[0040]. - detection means, operatively connected to the electronic processing unit 4, configured to detect, either directly or indirectly, the value of the first force Fa actuated by the first actuator 2 on the first pad, and to detect, either directly or indirectly, the value of the second force Fb actuated by the second actuator 3 on the second pad.

[0041]. The method comprises the steps of:

[0042]. - actuating, by means of the electronic processing unit 4, both the first actuator 2 approaching against the first pad to apply the first force Fa and increase the value of the first force Fa, and the second actuator 3 approaching against the second pad to apply the second force Fb and increase the value of the second force Fb;

[0043]. - detecting, during the actuation of the first actuator 2 and the second actuator 3, and by the detection means, the value of the first force Fa and the second force Fb;

[0044]. - synchronizing the application of the first force Fa and the second force Fb on the brake disc by means of the electronic processing unit 4;

[0045]. - continuing the actuation of the first actuator 2 and the second actuator 3 until a first predetermined force value F1 is reached by the first force Fa and a second predetermined force value F2 is reached by the second force Fb;

[0046]. - stopping the first actuator 2 and the second actuator 3 by means of the electronic processing unit 4.

[0047]. Furthermore, the step of synchronizing the application of the first force Fa and the second force Fb on the brake disc comprises the steps of:

[0048]. - in a first instant of time t1 in which it is detected, by the detection means, that the first force Fa has increased to a value being substantially greater than a third predetermined force value F3, stopping the first actuator 2, and continuing the actuation of the second actuator 3;

[0049]. - in a second instant of time t2 in which it is detected, by the detection means, that the second actuator 3 applies a second force Fb with a value being substantially greater than a fourth predetermined force value F4, actuating the first actuator 2.

[0050]. Alternatively, the step of synchronizing the application of the first force Fa and the second force Fb on the brake disc comprises the steps of:

[0051]. - in a first instant of time tl in which it is detected, by the detection means, that the second force Fa has increased to a value being substantially greater than a fourth predetermined force value F4, stopping the second actuator 3, and continuing the actuation of the first actuator 2;

[0052]. - in a second instant of time t2 in which it is detected, by the detection means, that the first actuator 2 applies a first force Fb with a value being substantially greater than a third predetermined force value F3, actuating the second actuator 3.

[0053]. Advantageously, the control method according to the present invention minimizes the asymmetric axial thrusts actuated on the brake disc during the activation of the parking braking.

[0054]. This is achieved as a result of the synchronization of the application of the first and second forces Fa, Fb on the two opposite faces of the brake disc, which synchronization is obtained by sharing between the two actuators, by means of the electronic processing unit, the detection when the contact is made between one of the two actuators with the respective pad, which results in the temporary stop of the actuator pending the next detection of contact occurred between the other of the two actuators with the respective pad.

[0055]. As can be seen by comparing figures 6 and 7, showing a control method according to the present invention, with figures 4 and 5, showing a control method according to the prior art, the method according to the present invention drastically reduces the asymmetric axial thrusts actuated on the brake disc, i.e., reduces the difference between the opposite forces applied by the respective actuators upon completion of the activation of the parking braking.

[0056]. Advantageously, the control method according to the present invention is applicable to braking systems comprising at least one fixed brake caliper.

[0057]. According to an embodiment of the invention, the third predetermined force value F3 is substantially equal to the fourth predetermined force value F4.

[0058]. According to an embodiment of the invention, the third predetermined force value F3 is equal to zero.

[0059]. According to an embodiment, the fourth predetermined force value F4 is equal to zero.

[0060]. According to an embodiment, both the third predetermined force value F3 and the fourth predetermined force value F4 are equal to zero.

[0061]. According to an embodiment of the invention, both the first predetermined force value F1 and the second predetermined force value F2 are greater than the third predetermined force value F3 and the fourth predetermined force value F4.

[0062]. Furthermore, the first predetermined force value F1 and the second predetermined force value F2 are equal to a force value such as to complete the activation of a parking-braking force.

[0063]. According to an embodiment of the invention, the first predetermined force value F1 is substantially equal to the second predetermined force value F2.

[0064]. According to an embodiment of the invention, the step of detecting, by the detection means, the value of the first force Fa comprises:

[0065]. - detecting, by the detection means, the angular position of the first actuator 2; and

[0066]. - calculating, by means of the electronic processing unit

4, the value of the first force Fa based on the angular position of the first actuator 2; or

[0067]. - detecting the value of a first supply current ia supplying the first actuator 2; and

[0068]. - calculating, by means of the electronic processing unit

4, the value of the first force Fa based on the value of the first supply current ia supplying the first actuator 2.

[0069]. According to an embodiment, the step of detecting, by the detection means, the value of the second force Fb comprises:

[0070]. - detecting, by the detection means, the angular position of the second actuator 3; and

[0071]. - calculating, by means of the electronic processing unit

4, the value of the second force Fb based on the angular position of the second actuator 3; or

[0072]. - detecting the value of a second supply current ib supplying the second actuator 3; and

[0073]. - calculating, by means of the electronic processing unit

4, the value of the second force Fb based on the value of the second supply current ib supplying the second actuator 3. [0074]. According to an embodiment of the invention, the step of actuating, by means of the electronic processing unit 4, both the first actuator 2 approaching against the first pad to apply the first force Fa and increase the value of the first force Fa, and the second actuator 3 approaching against the second pad to apply the second force Fb and increase the value of the second force Fb, is actuated upon reception, by the electronic processing unit 4, of a parking-braking force activation request signal.

[0075]. The parking-braking force activation request signal is sent by an actuating device operatively connected to the electronic processing unit 4, upon actuation of said actuating device.

[0076]. The actuating device is actuatable by a user.

[0077]. According to an embodiment of the invention, the method comprises, after the step of continuing the actuation of the first actuator 2 and the second actuator 3 until a first predetermined force value F1 is reached by the first force Fa and a second predetermined force value F2 is reached by the second force Fb, the step of:

[0078]. - sending, from the electronic processing unit 4 to a signaling device operatively connected to the electronic processing unit 4, a complete parking-braking force activation signal.

[0079]. Optionally, the complete parking-braking force activation signal is viewable by a user by means of the signaling device.

[0080]. According to an embodiment, the step of synchronizing the application of the first force Fa and the second force Fb on the brake disc is performed in an iterative manner. Preferably, the iteration time is between 5 and 10 ms.

[0081]. According to an embodiment, during the step of synchronizing the application of the first force Fa and the second force Fb on the brake disc, the value of the first force Fa and/or the value of the second force Fb is detected every 5-10 ms.

[0082]. According to a further aspect of the invention, a braking system 1 of a vehicle configured to activate a parking-braking force, comprises at least:

[0083]. - a brake disc;

[0084]. - a first pad and a second pad spaced apart from each other and positioned to be opposite to the brake disc;

[0085]. - a first actuator 2, configured to apply and release a first force Fa on the first pad so as to move the first pad from an open position, in which the first pad is separated from the brake disc and does not actuate a parking-braking force, to a closed position, in which the first pad is biased against the brake disc and actuates a parking-braking force;

[0086]. - a second actuator 3, configured to apply a second force

Fb on the second pad so as to move the second pad from an open position, in which the second pad is separated from the brake disc and does not actuate a braking force, to a closed position, in which the second pad is biased against the brake disc and actuates a parking-braking force;

[0087]. - an electronic processing unit 4, configured to control the actuation of the first actuator 2 and the second actuator 3;

[0088]. - detection means, operatively connected to the electronic processing unit 4, configured to detect, either directly or indirectly, the value of the first force Fa actuated by the first actuator 2 on the first pad, and to detect, either directly or indirectly, the value of the second force Fb actuated by the second actuator 3 on the second pad.

[0089]. The braking system 1 is configured to activate the parking-braking force by performing a method as described above.

[0090]. Advantageously, a braking system 1 thus configured allows minimizing the asymmetric axial thrusts actuated on the brake disc when activating the parking braking.

[0091]. With added advantage, a braking system 1 thus configured has reduced energy and structural constraints.

[0092]. Advantageously, the braking system comprises at least one fixed brake caliper.

[0093]. According to an embodiment of the invention, the braking system 1 comprises an actuating device operatively connected to the electronic processing unit 4.

[0094]. The electronic processing unit 4 is configured to actuate both the first actuator 2 approaching against the first pad to apply the first force Fa and increase the value of the first force Fa, and the second actuator 3 approaching against the second pad to apply the second force Fb and increase the value of the second force Fb upon reception, by the electronic processing unit 4, of a parking- braking force activation request signal.

[0095]. The parking-braking force activation request signal is sent by the actuating device upon actuation of said button. [0096]. The actuating device is actuatable by a user.

[0097]. Advantageously, the actuating device is positionable in the passenger compartment of the vehicle close to the position occupied by the user.

[0098]. The actuating device can be, by way of example, an appropriate button, an ignition key, a gear shift actuator, an acceleration pedal or different pedal, or a device connected to automatic functions managed by the electronic processing unit 4 or an appropriate electronic processing unit.

[0099]. According to an embodiment, the braking 1 comprises a signaling device operatively connected to the electronic processing unit 4.

[00100]. The electronic processing unit 4 is configured to send a complete parking-braking force activation signal to the signaling device.

[00101]. The parking-braking force activation signal is viewable by a user by means of the signaling device.

[00102]. The signaling device can be, for example, a warning light, or a digital screen positioned inside the passenger compartment of the vehicle close to the position occupied by the user.

[00103]. According to an embodiment, the detection means comprise an angular position detector, preferably an encoder, configured to detect the angular position of the first actuator 2 and/or the second actuator 3.

[00104]. Alternatively or additionally, the detection means comprises a current detector, preferably an ammeter, configured to detect the value of a supply current supplying either the first actuator 2 or the second actuator 3.

[00105]. The electronic processing unit 4 comprises a calculator configured to calculate the value of the first force Fa and/or the second force Fb based on the angular position of the first actuator 2 or the second actuator 3, respectively.

[00106]. Alternatively or additionally, the calculator is configured to calculate the value of the first force Fa and/or the second force Fb based on the value of the supply current supplying the first actuator 2 or the second actuator 3, respectively.

[00107]. Obviously, those skilled in the art will be able to make changes or adaptations to the present invention, without however departing from the scope of the following claims.

LIST OF REFERENCE SIGNS

1. Braking system

2. First actuator

3. Second actuator

4. Electronic processing unit

Fa. First force

Fb. Second force

F1. First predetermined force value

F2. Second predetermined force value

F3. Third predetermined force value

F4. Fourth predetermined force value ia. First supply current ib. Second supply current t1. First time instant t2. Second time instant