Control procedure for the emergency activation of a motor-driven parking brake

Abstract

The invention relates to a method for controlling a braking device of a vehicle, in particular a motor vehicle, to ensure an emergency braking function, wherein the braking device is of a type comprising at least one electrical actuator for moving a brake piston, a brake pad, a friction surface, and an electronic circuit for controlling the electrical actuator, wherein the method comprises the following steps: controlling a power (P) supplied to the electrical actuator so that the brake piston exerts a pressing force on the friction surface, measuring the deceleration of the vehicle with a deceleration detection device, then controlling the power (P) supplied to the electrical actuator of the brake piston, in particular by pulse width modulation (PWM), to generate a deceleration that is greater than a minimum deceleration and less than a deceleration thatwhich can cause the vehicle's wheels to lock up.

Description

[0001] The invention relates to a control method for the actuation of a motor-driven parking brake in an emergency situation in order to ensure emergency braking. STATE OF THE ART

[0002] The invention particularly relates to a vehicle having a service brake (operated by the driver by depressing a pedal) and a parking brake (operated by the driver by applying a handbrake). The invention is particularly applicable in emergency braking situations where the service brake is unavailable (i.e., the service brake is not functioning for various reasons).

[0003] In this case, the vehicle system controls the operation of the parking brake to brake, which can occur abruptly and lead to the wheels locking: in this case, the braking is no longer controlled.

[0004] In a vehicle, in particular a road vehicle, the function of the parking and / or emergency brake is to apply and hold brake pads, which are connected to a part rigidly connected to the chassis, against a rotating part, typically a disc or a drum, which is connected to one or more wheels.

[0005] In braking systems that utilize one or more electric actuators, it is common to use a screw-and-nut system to exert linear pressure on the brake pad, often via a piston in the case of a disc brake. This type of design is available for electric operation alone or in combination with hydraulic actuation of this or another piston. Typically, the screw-and-nut system is actuated via a gear motor.

[0006] In the event of an emergency braking of a motor vehicle, a deceleration of 1.5 m / s is required according to regulations 2 specified.

[0007] Braking systems or methods are known from existing technologies in which the rotational speed of the disc or the shaft carrying the disc is measured.

[0008] However, this type of system or method does not allow a constant deceleration of the vehicle to be achieved, especially not at the value prescribed above.

[0009] EP 2 055 541 discloses a method using a pneumatic system commonly used in trucks or trains: a spring continuously applies pressure to the brake pads, and the pneumatic system allows the brake to be released. The document provides an electric actuator, but the pressure provided is constant: the electric motor (comparable to an electric actuator) ensures that the compressed air reservoir of the pneumatic system is charged. This system only allows the brake to be released, meaning that the method used to operate the system cannot be modulated.

[0010] FR 3 111 863 discloses an improved braking method in which a processor is used to control the power supply to the electric motor (which performs the braking) through pulse-width modulation to optimize braking time. The proposed method is to apply pulse-width modulation to assist braking in a single step (second step) between an initial sharp deceleration step and a final braking step until the vehicle comes to a standstill. The document does not address emergency braking, but only braking in general.

[0011] The invention aims to propose a solution that ensures constant deceleration of the vehicle, in particular to prevent the wheels from locking and to ensure control of braking in the event of an emergency stop.

[0012] The subject of the invention is primarily a method for controlling a braking device of a vehicle, in particular a motor vehicle, in order to ensure an emergency braking function, wherein the braking device is of the type which comprises at least one electric actuator for displacing a brake piston, a brake pad, a friction surface and an electronic circuit for controlling the electric actuator, wherein the method comprises the following steps: Controlling a power delivered to the electric actuator of the brake piston so that the brake piston exerts a pressing force on the friction surface via the brake pad,

[0013] Measuring the deceleration of the vehicle with a deceleration detection device, then

[0014] Controlling the power delivered to the electric actuator of the brake piston, in particular by pulse width modulation, in such a way as to produce a deceleration which is greater than a minimum deceleration and less than a deceleration which may cause the wheels of the vehicle to lock.

[0015] Implemented in this way, the invention ensures an emergency braking function such that a constant deceleration of a vehicle is achieved.

[0016] In other words, in the method according to the invention, the controlled power delivered to the electric actuator of the brake piston is variable and lies in an optimal range defined between two limit values: the first limit value is the deceleration that causes the wheels to lock, and the second limit value is a deceleration that is minimal (for example, detected or predefined).

[0017] According to an advantageous embodiment, the minimum deceleration is 1.5 m·s -2 or essentially 1.5 m·s -2 .

[0018] Preferably, according to a first embodiment of the method, the current supplied to the electric actuator is controlled as a function of the applied deceleration.

[0019] Even more preferably, according to a further embodiment, the current for supplying the electric actuator is controlled as a function of the rotational speed of the electric actuator.

[0020] Advantageously, the width of the pulse width modulation is variable.

[0021] Furthermore, the output power is controlled in the form of a constant voltage.

[0022] Advantageously, the deceleration detection device implemented by the method is an accelerometer or a Doppler sensor. DESCRIPTION OF THE CHARACTERS

[0023] Further features and advantages of the invention will become apparent from the detailed description of a non-limiting embodiment and the accompanying drawings, in which: [ Fig. 1] a diagram illustrating the deceleration of a vehicle after performing a first procedure, [ Fig. 2] another diagram illustrating the deceleration of a vehicle after carrying out a first method according to the invention, and [ Fig. 3] another diagram illustrating the deceleration of a vehicle after carrying out a second method according to the invention. EMBODIMENTS

[0024] Fig. Figure 1 shows several characteristic curves, particularly illustrating the vehicle's speed 1 during an emergency braking situation. The figure illustrates the control process by influencing pulse width modulation: A first diagram (top) shows a characteristic curve 2, which represents the state of an emergency braking request over time. A second diagram (middle) shows several characteristic curves, including the characteristic curve representing the vehicle's speed 1 over time. A third diagram (bottom) shows the state of an actuator (characteristic curve 3) over time.

[0025] A dashed vertical 4 demarcates two cases: - to the left of line 4 are the speed 1 of the vehicle, the current 5 and the force 6 exerted during emergency braking if the pulse width modulation (PWM) is 100%, - right of line 4 - the profiles of the characteristics for current 5, force 6 and speed 1 of the vehicle are shown in dashed lines for the case where the pulse width modulation remained at 100%, and - the profiles of the characteristics for current 5, force 6 and speed 1 of the vehicle are shown as solid lines for the case where the pulse width modulation is set to x%.

[0026] The scheme in Fig. 1 is to be read as follows: A situation is illustrated in which a vehicle designed to carry out the method according to the invention comprises a service brake and a parking brake, and in which the vehicle travels at a certain speed V.

[0027] The vehicle comprises at least one electric actuator for displacing a brake piston, a brake pad, a friction surface and an electronic circuit for controlling the electric actuator.

[0028] The user wants to slow down the vehicle, but the service brake no longer works.

[0029] In order to ensure an emergency braking function, an initial power is first controlled, which is delivered to the electric actuator of the brake piston so that the brake piston exerts a pressing force on the friction surface via the brake pad.

[0030] The control of the first power is symbolized by the demand R (characteristic curve 2), which occurs simultaneously with the increase in the power P of the actuator (characteristic curve 3).

[0031] At the same time, the current 5 also increases (see Peak I).

[0032] A reduction in the speed of the vehicle can be observed at the time when the force exerted on the friction surface increases and the current intensity rises again.

[0033] Then, the deceleration of the vehicle is measured with a deceleration sensing device, such as an accelerometer or a Doppler sensor, and the power P delivered to the electric actuator of the brake piston is controlled by modulating the pulse width so that the speed remains above a threshold speed to avoid wheel locking - in Fig. 1 symbolized by the star (in other words, the deceleration is controlled so that it remains below a deceleration that leads to the locking of the wheels).

[0034] It should also be noted that both characteristics are identical and that by modulation the strength of the current 5 and the applied force 6 can be reduced in order to achieve a constant deceleration.

[0035] Fig. Figure 2 shows what happens when a first method is implemented, in which the pulse width is modulated according to the invention. The current supplying the electric actuator is controlled as a function of the electric actuator's speed.

[0036] Reference symbols used in the characteristic curves in Fig. 1 are used in Fig. 2 to make reading easier.

[0037] The same scenario can be observed: the user wants to slow down the vehicle, but the service brake no longer works.

[0038] In order to ensure an emergency braking function and according to the second embodiment of the method according to the invention, as Fig. 2 shows, a first power is initially controlled, which is delivered to the electric actuator of the brake piston, so that the brake piston exerts a pressing force on the friction surface via the brake pad.

[0039] The control of the first power is symbolized by the demand R, which occurs simultaneously with the increase of the power P of the actuator.

[0040] At the same time, the current 5 also increases (see Peak I).

[0041] At the moment when the force 5 exerted on the friction surface increases and the current I increases again, a reduction in the vehicle speed can be observed.

[0042] At the same time, the delay 8 increases.

[0043] In order to maintain the deceleration 8 (and thus achieve a constant deceleration - see stage P1, which reaches the characteristic curve 8), the deceleration of the vehicle is measured with a deceleration detection device, for example with an accelerometer or a Doppler sensor (as in the case of the Fig. 1), and the power P delivered to the electric actuator of the brake piston is controlled (regulated) by modulating the pulse width so that the speed 1 of the vehicle remains above a threshold speed in order to avoid locking of the wheels.

[0044] However, the deceleration must be greater than a minimum deceleration of 1.5 m s -1 (lower level P2).

[0045] The supply current (characteristic curve 5) of the electric actuator is controlled depending on the speed of the electric actuator.

[0046] The characteristic curves 5 and 6 (which correspond respectively to the current supplied to the actuator and the force exerted on the friction surface) initially follow a common rise.

[0047] By influencing the modulation of the pulse width (starting from the dashed vertical "X%"), the speed of the electric actuator is brought to a constant deceleration (see curve 8, which reaches a plateau), with the power supply of the actuator then being interrupted (characteristic curve 5 simultaneously goes to zero when characteristic curve 8 reaches its plateau).

[0048] More specifically, the deceleration is monitored so that when the deceleration falls below a minimum deceleration of 1.5 m / s -2 falls, the procedure is repeated to achieve the minimum deceleration of 1.5 m / s -2 to reach.

[0049] At this point, speed 1 decreases steadily.

[0050] In the Fig. 1 or Fig. In the examples shown in Figure 2, it should be noted that the width of the pulse width modulation is variable and that the control of the output power is in the form of a constant voltage.

[0051] In Fig. 3 shows another method according to the invention.

[0052] In this example, the current I supplying the electric actuator is controlled as a function of the applied deceleration 8: a force is applied in steps (see between the two dashed vertical lines, each of which generates an intensity peak at each transition from a given force level 6 to a higher force level). The transition from one level to a higher level is determined by the deceleration level achieved.

[0053] It is also possible to note the P3 level in Fig. 3, as in Fig. 2.

[0054] From the above description it is clear how the invention enables constant deceleration of the vehicle in the event of emergency braking.

[0055] However, it must be understood that the figures illustrate two particular embodiments of the method according to the invention and that the method could have further features without departing from the scope of the invention. List of reference symbols: 1 speed characteristic curve 2 Demand curve 3 Characteristic curve of the actuator 4 Straight line symbolizing pulse width modulation 5 Characteristic curve of the strength of the power transmitted to the actuator 6 Characteristic curve of the force exerted on the friction surface 8 Delay characteristic R requirement V speed I current P Power of the actuator P1 maximum delay level P2 Minimum delay level P3 level reached by the applied force QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] EP 2 055 541

[0009] FR 3 111 863

[0010]

Claims

[1] Method for controlling a braking device of a vehicle, in particular a motor vehicle, to ensure an emergency braking function, the braking device being of the type comprising at least one electric actuator for displacing a brake piston, a brake pad, a friction surface and an electronic circuit for controlling the electric actuator, the method comprising the following steps: Controlling a power (P) delivered to the electric actuator of the brake piston so that the brake piston exerts a pressing force on the friction surface via the brake pad, Measuring the deceleration of the vehicle with a deceleration detection device, then gradually controlling the power (P) delivered to the electric actuator of the brake piston, in particular by pulse width modulation (PWM), by controlling the supply current (I) of the electric actuator as a function of the measured deceleration in such a way as to produce a deceleration which is greater than a minimum deceleration and less than a deceleration which may cause the wheels of the vehicle to lock. [2] Control method according to claim 1, characterized by that the minimum delay is 1.5 ms -2 amounts. [3] Control method according to claim 1 or 2, characterized by that the supply current (I) of the electric actuator is controlled as a function of the applied delay (8). [4] Control method according to claim 1 or 2, characterized by that the supply current (I) of the electric actuator is controlled as a function of the speed (8) of the electric actuator. [5] Control method according to one of claims 1 to 4, characterized by that the width of the pulse width modulation (PWM) is variable. [6] Method according to one of the preceding claims, characterized by that the control of the output power (P) takes place in the form of a constant voltage. [7] Method according to one of the preceding claims, characterized by that the deceleration detection device is an accelerometer or a Doppler sensor.

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