Dynamic braking on 3 wheels

Abstract

A method and system for emergency braking of a rear wheel of a vehicle (1) equipped with an electric parking brake (7), by implementing either an anti-lock braking mode or an incremental braking mode. When the speeds of two front wheels (2, 3) are unknown but only one is known, the anti-lock braking mode is applied with this known speed, corrected by a reduction operation, as the reference speed; and when the speed of neither front wheel is known, the incremental braking mode is applied. Vehicle equipped with such a system. Figure for the abstract: [Fig. 1]

Description

Title of the invention: Dynamic braking on 3 wheels

[0001] The present invention relates to the technical field of electric parking brakes and in particular to the field of the use of electric parking brakes during emergency braking.

[0002] As described in document US 7,744,166, a parking brake is implemented electrically and / or automatically by an electromechanical unit, also called an electric actuator, associated with one or more of the vehicle's wheels. Thus, a user of the vehicle wishing to engage the parking brake simply needs to press a push button, located for example on the dashboard near the steering wheel, to trigger or terminate the application of the parking brake around the vehicle's wheel.

[0003] We already know the RWU braking mode, for "Rear Wheel Unlocker". It consists of using the parking brake of the rear wheels to dynamically brake the vehicle when the hydraulic service brakes are faulty. The aim is to apply the brakes of the rear wheels without locking them. More precisely, in the event of a wheel slipping, the brake is released to unlock the wheel or to prevent it from locking, then it is re-tightened, etc. This control mode is inspired by ABS (registered trademark), but differs from it in that it uses electrical control of the brake motor.

[0004] More precisely, the RWU braking mode consists of executing the following operations in a loop: - if the wheel slip is below a first predetermined threshold, called the "low threshold", progressive application of the brake until the slip becomes higher than this low threshold, - if the slip is greater than a second predetermined threshold, called the "high threshold", greater than the low threshold, progressive release of the brake until the slip becomes lower than this high threshold, - if the slip is greater than the low threshold and less than the high threshold, maintaining the tightening at its current level.

[0005] Determining whether a blockage occurs requires knowing the rotational speed of the four wheels of the vehicle. The two front wheels make it possible to calculate a reference speed, to which the speed of each rear wheel is compared to determine whether this rear wheel is in a blocking situation: a speed lower than the reference speed by more than the predetermined threshold indicates a blockage or the beginning of a blockage. In other words, if the speed is lower than the reference speed less the predetermined threshold, it can be considered that there is a blockage or the beginning of a blockage.

[0006] If one of the rear wheels no longer provides its rotational speed, no use of the RWU braking mode is obviously possible. It is then necessary to fall back on an incremental braking mode, according to which the application of the electric parking brake is slightly increased incrementally at regular intervals, so as to avoid creating wheel locking conditions, without however being able to check whether this locking occurs or not.

[0007] But if it is only one of the front wheels that no longer provides its rotational speed, the anti-lock mode is also not available, because the reference speed, which serves as a point of comparison for the rotational speed of each rear wheel, cannot be determined by knowing the rotational speed of only one front wheel. Indeed, when the vehicle follows a curved trajectory, for example when it turns, the difference in rotational speed between the wheels on the inside of the bend and the wheels on the outside of the bend is such that the comparison with the speed of only one of the two front wheels risks leading to erroneous conclusions. For example, the speed of an inside rear wheel is always lower than the speed of an outside front wheel. It may then appear as always locked. Conversely, the speed of an outside rear wheel is always higher than the speed of an inside front wheel.Its speed may reduce, i.e. begin to lock, without this speed becoming sufficiently lower than the speed of the outer front wheel. The lock is then not detected. For this reason, in the state of the art, if a front wheel no longer provides its rotational speed, the anti-lock braking mode is abandoned in favor of the incremental mode. The invention

[0008] An object of the invention is a method for emergency braking of a vehicle wheel equipped with an electric parking brake, the vehicle having at least two axles and the wheel being on a first of said at least two axles, by implementing either an anti-lock braking mode or an incremental braking mode, the anti-lock braking mode being ensured by controlling the parking brake in compliance with the following rules, while the slippage of the wheel is obtained by calculating the difference between the rotational speed of the wheel and a reference speed obtained from the speed of at least one of two wheels of a second of said at least two axles of the vehicle: - if the slippage is below a first predetermined threshold, progressive application of the brake until the slippage becomes above this first threshold, - if the slip is greater than a second predetermined threshold, greater than the first threshold, progressive release of the brake until the slip becomes lower than this second threshold, - if the slip is greater than the first threshold and less than the second threshold, maintaining the application at its current level, the incremental braking method being ensured by controlling the parking brake by increasing its application in steps of predetermined durations, the method being characterized in that, when the speeds of two wheels of the second axle are not known but only one is known, the anti-lock braking mode is applied with, as reference speed, this known speed, corrected by a reduction operation, and when the speed of no wheel of the second axle is known, the incremental braking mode is applied.

[0009] In the present description, dynamic braking request means a braking command actuated by the driver of the vehicle - human being or artificial intelligence - according to the needs of the traffic, while the vehicle is in motion.

[0010] In the present description, slipping of a wheel is understood to mean that the translational speed of the wheel is greater than its rotational speed multiplied by its diameter. A method for measuring slipping is known, for example by comparing the rotational speed of the wheel (measured with the wheel rotational speed detector (WSS in English terminology)) with the speed of the vehicle.

[0011] According to a particular mode of implementation of the emergency braking method, the reduction operation is a multiplication by a multiplying coefficient.

[0012] According to a particular mode of implementation of the emergency braking method, the multiplying coefficient is between 0 and 1, for example substantially equal to 0.84.

[0013] According to a particular mode of implementation of the emergency braking method, the multiplying coefficient is calculated from the maximum steering angle and the minimum steering angle, by applying the following formula: coefficient = sin[maximum steering angle] / sin[minimum steering angle].

[0014] According to a particular embodiment of the emergency braking method, the multiplier coefficient is determined while the vehicle is moving, taking into account the actual steering angle, by applying the following formula: coefficient = sin[actual steering angle] / sin[minimum steering angle]. The application of this formula requires knowing the steering wheel rotation angle in real time, as well as the width of the vehicle and the wheel speed. Document WO202099768 A1 discloses the formula to be used to determine the speed of the rear wheel. This formula is reproduced below so as to explain the incorporation of the content of this document into the present description: Km R ~ \ -C""b " J where VeAR is the rear wheel speed estimate, Vmin and Vmax the front wheel speed estimates with and Kcoit is a correction coefficient, with Kwwr ~ 1 for < Sj, and Kcorc < 1 pOUF ■ > 53 If being a fixed threshold.

[0015] According to a particular embodiment, the first axle is a rear axle and the second axle is a front axle. Preferably, the vehicle has exactly two axles.

[0016] Another object of the invention is a braking system, characterized in that it comprises means capable of implementing the method as described above.

[0017] Another subject of the invention is a motor vehicle, characterized in that it comprises at least one braking system according to the invention. Brief description of the figures

[0018] The invention will be better understood on reading the attached figures, which are provided as examples and are not limiting in nature, in which:

[0019] - [Fig.l] is a schematic top view of a motor vehicle,

[0020] - [Fig.2] represents the vehicle of [Fig.l] on a trajectory,

[0021] - [Fig.3] is a flowchart illustrating the steps of an implementation of the method on the vehicle.

[0022] In [Fig.l], we see from above a vehicle 1 which comprises four wheels, namely: - two front wheels 2, 3 driving and steering, a left front wheel 2 and a right front wheel 3, and - two rear wheels 4, 5 non-driven and non-steered, one left rear wheel 4 and one right rear wheel 5.

[0023] Each of the front wheels 2, 3 is here equipped with a main service brake 6 controlled by the driver of the vehicle 1, and each of the rear wheels is equipped with a parking brake 7, capable of working as a parking brake and as an emergency brake. Each parking brake 7 has an electric motor (not shown) controlled by an engine control unit 8 from information relating to certain parameters of the vehicle 1 and its driving state. The engine control unit 8 is active when emergency braking becomes necessary or when parking is requested.

[0024] Each main brake 6 allows, in normal use of the vehicle 1, to slow down the latter at the request of the driver, by actuation of a hydraulic brake control. The hydraulic brake system is provided with control means which will not be described here.

[0025] In the event of failure of the hydraulic brakes or their control means, provision is made for an emergency switch to electric braking by the parking brakes using calculation means 9. These calculation means 9 can be centralized on the vehicle 1 or specific to the brake system.

[0026] Each parking brake 7 can be activated in two operating modes by the engine control unit 8: the RWU mode (for 'Rear Wheel Unlocker' or 'rear wheel anti-lock') or the IFA mode (for 'Incremental Force Actioning' or 'Incremental clamping actuation').

[0027] The RWU mode uses two slip thresholds, namely a first threshold (or low threshold) and a second threshold (or high threshold). These can be set on average to suit any type of vehicle 1. They can also be calibrated by type of vehicle 1, or even by model of vehicle 1. For example, the low threshold can be set to zero, which means that as soon as a wheel has a speed strictly lower than the reference speed, it is considered to be slipping on the ground.

[0028] These two operating modes, defined previously, will not be described here because they are well known to those skilled in the art.

[0029] [Fig.2] shows a portion of the trajectories of the vehicle 1 and the front wheels 2, 3 left and right.

[0030] The vehicle 1 is generally following a curved trajectory 10. For each front wheel, this curved trajectory results in a specific trajectory 10.2, 10.3, which is here assimilated to a portion of a circle with center 11.

[0031] The radius of curvature of the portion of the circle is smaller for the inner wheels, in this case the left wheels, than for the outer wheels, in this case the right wheels.

[0032] The turning radius of the front wheels 2, 3 is represented by the angles alpha and beta, measured at the tangent of the trajectory, substantially at the point of contact of the wheel with the ground. By construction of the vehicle 1, the turning angle of the inner wheel at the bend, the left front wheel 2 in [Fig. 3], is greater than the turning angle of the outer wheel at the bend, here the right front wheel 3.

[0033] Each wheel has its own rotation speed. The rotation speeds are designated as follows: V2 for the left front wheel 2, V3 for the right front wheel 3, V4 for the left rear wheel 4, V5 for the right rear wheel 5.

[0034] As shown in [Fig. 3], when the driver executes a dynamic braking request (step 30), the calculation means 9 begin by checking (step 31) whether the main brakes 6 are functioning properly. If this is the case, conventional braking is carried out (step 32).

[0035] Otherwise, the calculation means 9 trigger emergency braking by the engine control unit 8, according to the algorithm of [Fig.3].

[0036] During step 33, the calculation means 9 check whether at least one of the two front wheels 2, 3 provides its own speed. In the event of a failure in the delivery of the rotational speed of the two front wheels 2, 3, i.e. no front wheel speed is known, the method proceeds to step 34 of incremental braking.

[0037] Otherwise, during step 35, the calculation means 9 check whether the two front wheels 2, 3 provide their speed. If so, the anti-lock braking is carried out in step 36 with a reference speed calculated from the speeds of the two front wheels 2, 3, according to the emergency braking method of the state of the art.

[0038] Otherwise, one of the front wheels 2, 3 provides its speed, but the other does not. The method then moves on to step 37 of correcting the only known speed.

[0039] The single front wheel speed provided without failure is therefore corrected by applying a reduction operation to provide a corrected reference speed.

[0040] The reducing operation may consist of a multiplication by a multiplying coefficient, the value of which is less than 1. This coefficient may be fixed in advance once and for all, at a value adapted to suit any type of vehicle 1. According to the calculations and tests conducted by the inventors, the value 0.84 seems optimal as a universal coefficient.

[0041] The coefficient can also be calculated as a function of the vehicle model 1, from known geometric parameters of the latter.

[0042] For example, from the maximum steering angle (that of the inner wheels), from the minimum steering angle (that of the outer wheels), we can determine a coefficient by the following formula: - coefficient = 1 / sin[maximum steering angle] / sin[minimum steering angle] where the minimum steering angle and the maximum steering angle are chosen from alpha and beta depending on the direction of the turn (right turn or left turn).

[0043] Finally, the coefficient can also be determined while the vehicle 1 is running, taking into account the actual steering angle, by applying the following formula: coefficient = 1 / sin[actual steering angle] / sin[minimum steering angle] where the minimum steering angle is chosen from alpha and beta depending on the direction of the turn (right turn or left turn).

[0044] This corrected speed is then compared, during step 38, to the speeds of each of the rear wheels 4, 5 for application of braking in RWU mode of the rear wheels 4, 5, which takes this corrected speed as the reference speed.

[0045] The invention is not limited to the embodiments presented and other embodiments will become clear to those skilled in the art. List of references

[0046] 1 . . . Vehicle 2 . . . Left front wheel 3 . . . Right front wheel 4 . . . Left rear wheel 5 . . . Right rear wheel 6 . . . Main brake 7 . . . Parking brake 8 . . . Engine control unit 9 . . . Means of calculation 10 . . . Curved trajectory 10.2... Clean trajectory of the left front wheel 10.3... Clean trajectory of the right front wheel 11... Center 31... Verification step 32 . . . Conventional braking 33 . . . Verification step 34 . . . Incremental braking 35 . . . Verification step 36 . . . Anti-lock braking 37 . . . Reference speed correction step 38 . . . Comparison step

Claims

Claims

1. Method for emergency braking of a vehicle wheel (1) equipped with an electric parking brake (7), the vehicle having at least two axles and the wheel being on a first of said at least two axles, by implementing either an anti-lock braking mode or an incremental braking mode, the anti-lock braking mode being ensured by controlling the parking brake (7) in compliance with the following rules, while the slip of the wheel is obtained by calculating the difference between the rotational speed of the wheel and a reference speed obtained from the speed of at least one of two wheels (2, 3) of a second of said at least two axles of the vehicle: - if the slip is less than a first predetermined threshold, progressive application of the brake until the slip becomes greater than this first threshold, - if the slip is greater than a second predetermined threshold, greater than the first threshold,progressive release of the brake until the slip becomes lower than this second threshold, - if the slip is higher than the first threshold and lower than the second threshold, maintaining the application at its current level, the incremental braking method being ensured by controlling the parking brake (7) by increasing its application in steps of predetermined durations, the method being characterized in that, when the speeds of the two wheels (2, 3) of the second axle are not known but only one is known, the anti-lock braking mode is applied with, as reference speed, this known speed, corrected by a reduction operation, and when the speed of no wheel of the second axle is known, the incremental braking mode is applied.,

2. An emergency braking method according to claim 1, wherein the reducing operation is a multiplication by a multiplying coefficient.

3. Emergency braking method according to claim 2, in which the multiplying coefficient is between 0 and 1, for example substantially equal to 0.

84.

4. An emergency braking method according to any one of claims 2 and 3, wherein the multiplier coefficient is calculated from the maximum steering angle and the minimum steering angle, by applying the following formula: coefficient = 1 / sin[maximum steering angle] / sin[minimum steering angle].

5. Emergency braking method according to any one of claims 2, 3 and 4, in which the multiplying coefficient is determined while the vehicle (1) is moving, taking into account the actual steering angle, by applying the following formula: coefficient = 1 / sin[actual steering angle] / sin[minimum steering angle].

6. An emergency braking method according to any one of claims 1, 2, 3, 4 and 5, wherein the first axle is a rear axle and the second axle is a front axle and, preferably, the vehicle has exactly two axles.

7. Braking system, characterized in that it comprises means capable of implementing the method as described above according to any one of claims 1, 2, 3, 4, 5 and 6.

8. Motor vehicle (1), characterized in that it comprises at least one braking system according to the invention according to claim 7.

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