Method for controlling a means for braking a motor vehicle

Abstract

The invention relates to a method for controlling a means (3) for braking a motor vehicle (1), comprising: - a first phase (P1) of automatically controlling the braking means, the braking means being controlled so as to apply a first braking torque (C1(i)), then - detecting a manual control of the braking means (3), the manual control being expressed by a control means (4) on board the vehicle, notably a brake pedal, then - a transition phase (Pt) during which the braking means is controlled so as to apply a second braking torque (C2(i)), the second braking torque being at least temporarily equal to the maximum between a first braking torque setpoint (Cs1(i)) and a second braking torque setpoint (Cs2(i)).

Description

Description Title of the invention: Method for controlling a braking system of a motor vehicle Technical field of the invention

[0001] The invention relates to a method for controlling a braking system of a motor vehicle. In particular, the invention relates to a method for controlling a braking system during a transition between a phase of automatic control of the braking system by a speed control system and a phase of manual control of the braking system, for example, by means of a brake pedal operated by a driver of the vehicle. The invention also relates to a motor vehicle comprising hardware and software configured to implement such a control method. Prior art

[0002] Motor vehicles are known to be equipped with cruise control systems. Such a cruise control system is capable of accelerating or braking the vehicle to maintain a set speed and / or to keep pace with a second vehicle in front of it. This type of system includes mechanisms for controlling the vehicle's propulsion or traction system, particularly its engine, and its braking system. For safety reasons, the braking system of a motor vehicle is generally linked to a manual control. Specifically, the motor vehicle is equipped with a brake pedal connected hydraulically to brakes, such as disc or drum brakes.

[0003] It is known that the cruise control system automatically deactivates as soon as the driver presses the brake pedal. This deactivation generally takes effect as soon as the driver begins to press the brake pedal, even just a few millimeters into its travel. The vehicle's speed, and in particular its deceleration, is then controlled manually by the driver. This manual control by the driver can be desirable when the driver feels that the cruise control is not slowing the vehicle sufficiently in a given situation.

[0004] The transition between automatic and manual braking control is problematic. When the cruise control system is deactivated, it immediately ceases to control the braking system, and the brake pedal is then only lightly depressed. This results in a transition phase during which the effective braking torque is less than The same principle applies when the cruise control system is active. This transition phase lasts until the brake pedal is sufficiently depressed, but it remains problematic: a driver who wants to regain control of the braking system because they feel the cruise control isn't slowing the vehicle down enough will briefly experience a decrease in braking power. The vehicle seems to roll forward until the brake pedal is fully depressed. This behavior encourages the driver to press the brake pedal quickly and, consequently, to modulate the braking force less precisely. The behavior of such a vehicle is therefore unsafe and uncomfortable. Presentation of the invention

[0005] The object of the invention is to provide a method for controlling a braking means which remedies the above disadvantages and improves the methods for controlling a braking means known in the prior art.

[0006] More specifically, a first object of the invention is a method for controlling a braking means allowing a safe and comfortable transition between an automatic control phase of the braking means and a manual control phase of the braking means. Summary of the invention

[0007] The invention relates to a method for controlling a braking system of a motor vehicle, comprising: - a first phase of automatic control of the braking system, by a speed regulation system on board the vehicle, the braking system being controlled so as to apply an initial braking torque, then - the detection of a manual control of the braking system, the manual control being expressed by a control means carried out in the vehicle, in particular a brake pedal, then - a transition phase during which the braking means is controlled so as to apply a second braking torque, the second braking torque being equal, at least temporarily, to the maximum between a first braking torque setpoint and a second braking torque setpoint, the first setpoint being defined by a time decay ramp, an initial value of the decay ramp at the beginning of the transition phase being equal to the first braking torque at the end of the first phase, the second setpoint being defined by the manual control of the braking means.

[0008] The second braking torque can result from the sum of said second setpoint defined by the manual control of the braking means and a supplementary braking torque, the supplementary braking torque being controlled by means of braking by the speed regulation system, the additional braking torque being defined according to said second setpoint.

[0009] The additional braking torque can be calculated, at least temporarily, using the following formula: C2C(i) = max(Csl(i) - Cs2(i); 0) where: - C2C(i) denotes said additional braking torque at time i, - Csl(i) denotes the first braking torque setting at time i, - Cs2(i) denotes the second braking torque setpoint at time i.

[0010] When the difference between the first braking torque setpoint and the second braking torque setpoint is less than or equal to a predetermined threshold, the second braking torque can be equal to the maximum between the first braking torque setpoint and the second braking torque setpoint plus a third braking torque setpoint.

[0011] The third braking torque setting can be calculated using the following formula: Cs3(i) = A + B x abs(Csl(i) - Cs2(i)) where: - Csl(i) denotes the first braking torque setting at time i, - Cs2(i) denotes the second braking torque setting at time i, - abs denotes the absolute value function, - Cs3(i) denotes the third braking torque setting at time i, - A and B are constants defined such that when abs(Csl(i) - Cs2(i)) is equal to said predetermined threshold, then Cs3(i) = 0.

[0012] The second braking torque can be equal to: - to the first braking torque instruction during an initial period of the transition phase, - at most between the first braking torque setting and the second braking torque setting plus the third braking torque setting during a second period of the transition phase, the second period being subsequent to the first period, - to the second braking torque instruction during a third period of the transition phase, the third period being subsequent to the second period.

[0013] The decay ramp can be a linear ramp extending from the first braking torque at the end of the first phase to zero braking torque, in particular the duration of the decay ramp being between 0.5s and 3s inclusive and / or the slope of the decay ramp being between -1000 and -4000 Nm / s.

[0014] The control process may include, following the transition phase, a second phase of exclusively manual control of the braking means by a driver of the vehicle, via the control means on board the vehicle.

[0015] The invention also relates to a motor vehicle comprising a braking means, a speed control system capable of automatically controlling the braking means, a manual control means for the braking means, and hardware and software means configured to implement the control method as defined above.

[0016] The invention also relates to a computer program product comprising program code instructions recorded on a computer-readable medium to implement the steps of the control process as defined above when said program is running on a computer.

[0017] The invention also relates to a computer-readable data recording medium on which is recorded a computer program comprising program code instructions for implementing the control method as defined above. Presentation of the figures

[0018] These objects, features and advantages of the present invention will be described in detail in the following description of a particular embodiment, given by way of non-limiting example, with reference to the accompanying figures, among which:

[0019] Figure 1 is a schematic view of a motor vehicle according to one embodiment of the invention.

[0020] Figure [Fig. 2] is a synoptic diagram of a method for controlling a vehicle braking means according to an embodiment of the invention.

[0021] Figure 3 is a first graph illustrating the time evolution of two braking torque setpoints during the implementation of the process.

[0022] Fig. 4 is a second graph illustrating the temporal evolution, during the implementation of the process, of a curve defined by the maximum of the two instructions in Fig. 3.

[0023] Figure 5 is a third graph illustrating the time evolution of the braking torque exerted by the braking device during the implementation of the method. Detailed description

[0024] Figure 1 schematically illustrates, from a top view, a motor vehicle 1 according to an embodiment of the invention. The vehicle 1 can be of any type. For example, it can be a passenger car, a commercial vehicle, a truck, or a bus. The vehicle 1 comprises four wheels 2, each equipped with a braking means 3. Each braking means 3 can be, for example, a disc brake, i.e. that is, comprising a disc attached to the wheel and a caliper equipped with brake linings designed to rub against the disc. Alternatively, each braking system can be different, for example, a drum brake or a magnetic brake. Generally speaking, the braking system 3 is capable of generating braking torque on the vehicle's wheels 2.

[0025] Vehicle 1 is also equipped with a manual control means 4 for the braking means 3. Typically, the control means 4 can be a brake pedal, actuated by pressing it with the foot. Generally, the control means 4 is a device intended to be controlled by a vehicle driver to modulate the braking torque produced by the braking means 3. The control means 4 is mechanically linked to the braking means 3, specifically via a hydraulic connection. The control means 4 may be equipped with a braking force amplification device. Furthermore, the control means 4 is equipped with a sensor 5. The sensor 5 is capable of detecting the activation of the control means 4, as well as measuring a braking torque command given by the driver. Preferably, the sensor 5 is a pressure sensor for the hydraulic circuit connecting the control means 4 to the braking means 3.The sensor 5 can, for example, be installed at the level of a master cylinder of the control means 4.

[0026] The vehicle 1 also includes a modulation means 6 capable of controlling the braking means 3. The modulation means 6 is also mechanically linked, in particular hydraulically linked, to the braking means 3. The modulation means 6 may in particular include a pump capable of pressurizing a hydraulic braking circuit to activate the braking means 3. In general, the modulation means 6 is capable of controlling the braking means 3 independently of any action by the vehicle driver on the control means 4.

[0027] Finally, vehicle 1 includes a speed control system 7. The sensor 5 and the modulation means 6 are connected to the speed control system 7, for example, by electrical cable harnesses. In [Fig. 1], electrical connections are represented by dashed lines and mechanical connections by solid lines.

[0028] The speed control system 7 includes a memory 71, a microprocessor 72, and an input / output interface 73 adapted to receive data from other equipment of the vehicle 1, in particular from the sensor 5, and to send instructions to other equipment of the vehicle 1, in particular to the modulation means 6. The memory 71 of the speed control system 7 is a data storage medium on which a program is stored. a computer comprising program code instructions for implementing a method of controlling the braking means 3 according to an embodiment of the invention. The microprocessor 72 is capable of executing this method. In particular, the speed control system 7 is capable of sending control commands by means of modulation 6 via its input / output interface 73 so as to brake the vehicle. The speed control system 7 can be integrated into a single computer on board the vehicle 1, or distributed across several computers on board the vehicle 1. In this second case, the different computers are connected, for example via a data bus, so as to exchange digital information. In addition, the speed control system 7 can also be connected to a propulsion and / or traction means of the vehicle so as to control the vehicle's acceleration.The speed regulation system 7 can also be connected to means of observing the environment around the vehicle, for example a radar, a lidar or a camera.

[0029] Figure 2 now illustrates a synoptic diagram of a method for controlling braking means 3 according to an embodiment of the invention.

[0030] During the first PI phase, the braking system is automatically controlled by the speed control system 7 to apply a non-zero initial braking torque Cl(i), where i represents a given instant. This initial braking torque Cl(i) is therefore applied without any action required from the driver on the control device 4. For example, the first PI phase can be implemented to maintain a constant safety distance from a second vehicle preceding vehicle 1. Referring to [Fig. 3], it is assumed that the initial braking torque Cl(i) has a constant value. Alternatively, this value could fluctuate over time.

[0031] Next, in a first step E1, the vehicle driver activates the control means 4. Specifically, the driver presses the brake pedal with their foot. As they do so, the sensor 5 detects the pedal depressment and transmits an information signal to the cruise control system 7 in a second step E2. This information signal is interpreted as a request from the driver to regain control of the vehicle. According to the invention, rather than abruptly interrupting the application of the first braking torque Cl(i), a specific strategy will be implemented by the cruise control system 7 during a transition phase Pt, so as to ensure a safe and comfortable transition between the first phase P1 of automatic control of the braking means 3 and a second phase P2 of exclusively manual control of the braking means 3.The transition phase Pt therefore extends temporally between the first phase PI and the second phase P2. The transition phase Pt begins at time t0 when the speed control system receives. the signal emitted by sensor 5. The transition phase Pt can be relatively short, for example with a duration between 500ms and 2s inclusive.

[0032] During this transition phase Pt, a second braking torque C2(i) is applied by the braking means 3. This second braking torque C2(i) can result from the sum of a braking torque applied manually by the driver by actuating the control means 4, and a supplementary braking torque C2C(i) generated by the modulation means 6. As we will see in more detail later, the transition phase Pt includes a third step E3 during which the supplementary braking torque C2C(i) is calculated, and a fourth step E4 of transmitting a control command from the speed regulation system 7 via the modulation means 6 to apply the supplementary braking torque C2C(i). The supplementary braking torque C2C(i) is calculated to obtain a second torque C2(i) corresponding to a very specific profile.

[0033] During the transition phase Pt, the second braking torque C2(i) is equal, at least temporarily (i.e. at least over a sub-period of the transition phase Pt), to the maximum between a first braking torque setpoint Csl(i) and a second braking torque setpoint Cs2(i).

[0034] The first setpoint Csl(i) is illustrated in [Fig. 3] by a dashed line. The first setpoint Csl(i) is defined by a time decay ramp. An initial value of the decay ramp at the beginning of the transition phase Pt is equal to the first braking torque Cl(i) at the instant the transition phase begins, i.e., Cl(t0). Preferably, the decay ramp is a linear ramp extending from the first braking torque Cl(t0) to zero braking torque. For example, the duration of the decay ramp can be between 500 ms and 2 s inclusive. For example, the slope of the decay ramp can be between 1000 Nm / s and 4000 Nm / s. These values ​​can be adapted according to the value of the first braking torque Cl(t0). For low values, the ramp can be shorter and / or the slope can be shallower.The characteristics of the decay ramp can be defined during a vehicle development phase. The first setpoint Csl(i) can be stored in the memory of the speed control system 7 as a linear equation. The first setpoint Csl(i) can be calculated at any time by the equation Cs(i) = n. i + p, where n and p are parameters such that Cs(t0) = Cl(t0) and Cs(t2) = 0, t2 being the time at which the transition phase Pt ends.

[0035] The second setpoint Cs2(i) is illustrated in [Fig. 3] by a second dashed line. The second setpoint Cs2(i) is defined by the manual control of the braking means 3. The second setpoint is therefore not controllable by the speed regulation system 7 since it depends solely on the manner in which The control means 4 is used by the driver. The second setpoint Cs2(i) can nevertheless be measured in real time, for example by means of the sensor 5 integrated into the control means 4. This pressure value can be transmitted to the speed control system 7 and converted, for example by means of a conversion table or a formula, into a braking torque. According to the example shown in [Fig. 3], the second setpoint Cs2(i) follows a generally parabolic shape. Alternatively, the shape of this curve could be different depending on how the driver actuates the control means 4.

[0036] Figure 4 illustrates the curve Lp, corresponding to the maximum between the first setpoint Csl(i) and the second setpoint Cs2(i), with a solid line. As long as the first setpoint Csl(i) is greater than or equal to the second setpoint Cs2(i), the maximum between the first setpoint Csl(i) and the second setpoint Cs2(i) is equal to the first setpoint Csl(i). As soon as the second setpoint Cs2(i) becomes greater than or equal to the first setpoint Csl(i), the maximum between the first setpoint Csl(i) and the second setpoint Cs2(i) becomes equal to the second setpoint Cs2(i).

[0037] A transition phase Pt, during which the second torque C2(i) follows the curve Lp, offers several advantages. First, it prevents a complete interruption of the braking torque. The driver does not feel the vehicle being released forward, which is reassuring. The driver may occasionally feel a brief drop in braking torque, but this drop is small and very short, therefore not bothersome. A second advantage is preventing undesirable excessive braking torque. Such a phenomenon could occur if the interruption of the torque controlled by the cruise control system were simply delayed, since the second torque C2(i) would then be equal to the torque command set by the cruise control system plus the torque command expressed by the driver when pressing the brake pedal.A third advantage is to avoid any prolonged situation in which the actual braking torque produced by the braking means varies while the driver has stabilized his control, that is to say, he has stabilized the position of his foot on the brake pedal.

[0038] To calculate the additional braking torque C2C(i) required to obtain a second braking torque C2(i) equal to the maximum between the first setpoint Csl(i) and the second setpoint Cs2(i), we can use the following formula: C2C(i) = max (Csl(i) - Cs2(i) ; 0)

[0039] This calculation is simple to implement and does not require significant computing power. It is therefore understood that the additional braking torque is calculated based on the second setpoint Cs2(i), which allows for a more consistent performance, particularly at the beginning of the Pt transition phase.

[0040] In [Fig. 4], we observe that the Lp curve includes a well-defined inflection point Px. This inflection point is positioned at time tl when the first setpoint Csl(i) is equal to the second setpoint Cs2(i). Therefore, Csl(tl) = Cs2(tl). The presence of such an inflection point in the torque profile exerted by the braking system 3 could result in a slight jolt perceptible to the vehicle driver. Thus, an improvement is also proposed to smooth the inflection point Px in order to avoid any unwanted jolt.

[0041] To achieve this, when the difference between the first setpoint Csl(i) and the second setpoint Cs2(i) is less than or equal to a predetermined threshold S, the second braking torque C2(i) is equal to the maximum of the first setpoint Csl(i) and the second setpoint Cs2(i) plus a third braking torque setpoint Cs3(i). In other words: C2(i) = max (Csl(i) - Cs2(i); 0) + Cs3(i). The threshold S can be a value set by parameterization, for example, a value between 200 Nm and 800 Nm inclusive.

[0042] The third setpoint Cs3(i) can be calculated, for example, using the following formula: Cs3(i) = A + B x abs(Csl(i) - Cs2(i)) where: - Csl(i) denotes the first braking torque setting at time i, - CSs(i) denotes the second braking torque setting at time i, - Cs3(i) denotes the third braking torque setting at time i, - "abs" denotes the absolute value function, and - A and B are constants defined by parameterization such that when abs (Csl(i) - Cs2(i)) is equal to the predetermined threshold S, then Cs3(i) = 0, that is, A+B x S = 0

[0043] More specifically, the smoothing of the second torque C2(i) can be obtained by calculating the complementary braking torque C2C(i) with the following algorithm:

[0044] Finally, applying the above algorithm to calculate the complementary braking torque C2C(i) yields a second torque C2(i) during the transition phase Pt, as shown in [Fig. 5]. Compared to the Lp curve, the profile of the second torque C2(i) includes a much less pronounced inflection point and The amplitude of the derivative of the second torque is reduced. Therefore, there is no sudden variation in braking torque that could cause a jolt perceptible to the driver.

[0045] The transition phase Pt can thus be decomposed into three successive periods: Ptl, Pt2, and Pt3. During the first period Ptl, defined as long as Csl(i) >= Cs2(i) + S, the second torque C2(i) is equal to the first braking torque setpoint Csl(i). During this first period, the second torque C2(i) is decreasing. During the second period Pt2, defined as long as abs(Csl(i) - Cs2(i)) <= S, the second torque C2(i) is defined by the formula C2(i) = max(Csl(i) - Cs2(i); 0) + Cs3(i). During this second period, the second torque C2(i) is decreasing until time tl and then increasing. During a third period Pt3, defined as soon as Cs2(i) >= Csl(i) + S, the second torque C2(i) is equal to the second braking torque setpoint Cs2(i). During this third period, the second torque C2(i) is increasing.

[0046] Thanks to the invention, we therefore benefit from a safe and comfortable transition between an automatic control phase of the braking means 3 and a manual control phase of the braking means 3.

Claims

Demands

1. A method for controlling a braking means (3) of a motor vehicle (1), characterized in that it comprises: - a first phase (PI) of automatic control of the braking means, by a speed regulation system (7) on board the vehicle, the braking means being controlled so as to apply a first braking torque (Cl(i)), then - the detection of a manual control of the braking means (3), the manual control being expressed by a control means (4) carried out in the vehicle, in particular a brake pedal, then - a transition phase (Pt) during which the braking means is controlled so as to apply a second braking torque (C2(i)), the second braking torque being equal, at least temporarily, to the maximum between a first braking torque setpoint (Csl(i)) and a second braking torque setpoint (Cs2(i)), the first setpoint (Csl(i)) being defined by a time decay ramp, an initial value (Csl(tO)) of the decay ramp at the beginning of the transition phase being equal to the first braking torque (Cl(tO)) at the end of the first phase, the second setpoint (Cs2(i)) being defined by the manual control of the braking means.

2. Control method according to the preceding claim, characterized in that the second braking torque (C2(i)) results from the sum of said second setpoint (Cs2(i)) defined by the manual control of the braking means and a complementary braking torque (C2C(i)), the complementary braking torque being controlled to the braking means (3) by the speed control system (7), the complementary braking torque being defined as a function of said second setpoint (Cs2(i)).

3. A control method according to the preceding claim, characterized in that the additional braking torque (C2C(i)) is calculated, at least temporarily, with the following formula: C2C(i) = max(Csl(i) - Cs2(i) ; 0) where: - C2C(i) denotes said additional braking torque at time i, - Csl(i) denotes the first braking torque setting at time i, - Cs2(i) denotes the second braking torque setpoint at time i.

4. A control method according to any one of the preceding claims, characterized in that, when the difference between the first braking torque setpoint (Csl(i)) and the second braking torque setpoint (Cs2(i)) is less than or equal to a predetermined threshold (S), the second braking torque (C2i)) is equal to the maximum between the first braking torque setpoint (Csl(i)) and the second braking torque setpoint (Cs2(i)) plus a third braking torque setpoint.

5. A control method according to the preceding claim, characterized in that the third braking torque setpoint (C3(i)) is calculated by the following formula: Cs3(i) = A + B x abs(Csl(i) - Cs2(i)) where: - Csl(i) denotes the first braking torque setting at time i, - Cs2(i) denotes the second braking torque setting at time i, - abs denotes the absolute value function, - Cs3(i) denotes the third braking torque setting at time i, - A and B are constants defined such that when abs(Csl(i) - Cs2(i)) is equal to the predetermined threshold (S), then Cs3(i) = 0.

6. A control method according to claim 4 or 5, characterized in that the second braking torque (C2(i)) is equal to: - at the first braking torque setting (Csl(i)) during a first period (Ptl) of the transition phase (Pt), - at most between the first braking torque setpoint (Csl(i)) and the second braking torque setpoint (Cs2(i)) plus the third braking torque setpoint during a second period (Pt2) of the transition phase (Pt), the second period being subsequent to the first period, - to the second braking torque instruction (Cs2(i)) during a third period (Pt3) of the transition phase (Pt), the third period being subsequent to the second period.

7. A control method according to any one of the preceding claims, characterized in that the decay ramp is a linear ramp extending from the first braking torque (Cl(tO)) at the end of the first phase to zero braking torque, in particular the duration of the decay ramp being between 0.5s and 3s inclusive and / or the slope of the decay ramp being between -1000 and -4000 Nm / s.

8. A control method according to any one of the preceding claims, characterized in that it comprises, following the transition phase, a second phase (P2) of exclusively manual control of the braking means (3) by a driver of the vehicle, via the control means (4) mounted in the vehicle.

9. Motor vehicle (1) comprising a braking means (3), a speed control system (7) capable of automatically controlling the braking means (3), a control means (4) manual of the braking means (3), and of the hardware and software means configured to implement the control method according to one of the preceding claims.

10. Product computer program comprising program code instructions recorded on a computer-readable medium to implement the control process steps according to any one of claims 1 to 8 when said program is running on a computer.

Images