Dynamic braking on three wheels

Abstract

The invention relates to a method and system for emergency braking of a vehicle rear wheel (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 not known but only one is known, the anti-lock braking mode is applied with this known speed, corrected by a reducing operation, as a reference speed, and when the speed of neither of the front wheels is known, the incremental braking mode is applied. The invention further relates to a vehicle provided with such a system.

Description

3-wheel dynamic braking

[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 vehicle user 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 are already familiar with the RWU braking mode, for "Rear Wheel Unlocker." It involves using the rear wheel parking brake to dynamically brake the vehicle when the hydraulic service brakes fail. The goal is to apply the rear wheel brakes without locking them. More precisely, if a wheel slips, the brake is released to unlock the wheel or prevent it from locking, then it is re-tightened, etc. This control mode is inspired by ABS (registered trademark), but differs 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 lower than 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 higher than a second predetermined threshold, called the "high threshold", higher than the low threshold, progressive release of the brake until the slip becomes lower than this high threshold, - if the slip is higher than the low threshold and lower than the high threshold, maintaining the application at its current level.

[0005] Determining whether a lock-up is occurring requires knowing the rotational speed of all four wheels of the vehicle. The two front wheels allow a reference speed to be calculated, to which the speed of each rear wheel is compared to determine whether that rear wheel is in a lock-up situation: a speed lower than the reference speed by more than the predetermined threshold indicates a lock-up or the beginning of a lock-up. In other words, if the speed is lower than the reference speed minus the predetermined threshold, we can consider that there is a lock-up or the beginning of a lock-up.

[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 lock conditions, without however being able to check whether this lock occurs or not.

[0007] But if only one of the front wheels is no longer providing 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 turning, 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 comparing them to 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 if it is 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. Also known, from document US2021370899A1, is a switch to the electronic parking brake in the event of a malfunction of the braking functions. Furthermore, from document US6092879, a solution is known for neutralizing the anti-lock or the brake force distribution of the vehicle when a fault is detected. But none of these known solutions overcome the problem of a front wheel that no longer provides its rotational speed. 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 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 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 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 this description, dynamic braking request means a braking command actuated by the driver of the vehicle – human being or artificial intelligence – according to traffic requirements, while the vehicle is in motion.

[0010] In this description, wheel slip 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 slip 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 process, the reduction operation is a multiplication by a multiplying coefficient.

[0012] According to a particular mode of implementation of the emergency braking process, 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 process, 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 implementation mode 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 in order to explain the incorporation of the content of this document into the present description: where V eAR is the rear wheel speed rating, V min and V max front wheel speed ratings with and K corr is a correction coefficient, with S1 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 by reading the attached figures, which are provided as examples and are not limiting in nature, in which:

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

[0020] -represents the vehicle on a trajectory,

[0021] -is a flowchart illustrating the steps of implementing the process on the vehicle.

[0022] On the, we see from above a vehicle 1 which comprises four wheels, namely: - two front wheels 2, 3 driven and steered, a left front wheel 2 and a right front wheel 3, and - two rear wheels 4, 5 non-driven and non-steered, a left rear wheel 4 and a 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, during normal use of the vehicle 1, to slow down the latter at the request of the driver, by actuating 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 applied in two operating modes by the engine control unit 8: RWU mode (for 'Rear Wheel Unlocker' or 'rear wheel anti-lock') or 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 to an average value to suit any vehicle type 1. They can also be calibrated by vehicle type 1, or even by vehicle model 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] A portion of the trajectories of vehicle 1 and the front wheels 2, 3 left and right are shown on the map.

[0030] 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, approximately 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 on the, 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 front left wheel 2, V3 for the front right wheel 3, V4 for the rear left wheel 4, V5 for the rear right wheel 5.

[0034] As indicated on the, 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 the.

[0036] In 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 process 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 suitable 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 based on 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 apparent to those skilled in the art. List of references

[0046] 1 . . . Vehicle2 . . . Left front wheel3 . . . Right front wheel4 . . . Left rear wheel5 . . . Right rear wheel6 . . . Main brake7 . . . Parking brake8 . . . Engine control unit9 . . . Calculation means10 . . . Curved trajectory10.2… Left front wheel own trajectory10.3… Right front wheel own trajectory11 . . . Center31 . . . Verification step32 . . . Conventional braking33 . . . Verification step34 . . . Incremental braking35 . . . Verification step36 . . . Anti-lock braking37 . . . Reference speed correction step38 . . . Comparison step

Claims

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., Emergency braking method according to claim 1, wherein the reducing operation is a multiplication by a multiplying coefficient. Emergency braking method according to claim 2, in which the multiplying coefficient is between 0 and 1, for example substantially equal to 0.

84. Emergency braking method according to any one of claims 2 and 3, in which the multiplying 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]. 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]. 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. 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. 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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