Dynamic braking on three wheels

Abstract

The problem arises when the speed of one or both front wheels cannot be obtained, making it impossible to determine the reference speed and apply anti-lock braking. This technology aims to provide a way to reliably brake the vehicle even in emergencies. 【means】 A method and system for emergency braking one of the rear wheels of a vehicle (1) equipped with an electric parking brake (7) by implementing an anti-lock braking mode or an incremental braking mode. If the speeds of the two front wheels (2 and 3) are unknown, but the speed of one is known, the anti-lock braking mode is applied using the reference speed obtained by correcting this known speed through a reduction operation. If the speed of either front wheel is unknown, the incremental braking mode is applied. A vehicle equipped with such a system.

Description

Technical Field

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

Background Art

[0002] As described in Patent Document 1, the parking brake is carried out electrically and / or automatically by an electromechanical unit (also referred to as an electric actuator) coupled to one or more wheels of the vehicle. Therefore, a vehicle user who desires to activate the parking brake only needs to press a push button arranged, for example, on the dashboard near the steering wheel, thereby starting or ending the tightening of the parking brake around the wheels of the vehicle.

[0003] The RWU (Rear Wheel Unlocker) braking mode is already known. This consists of using the parking brake on the rear wheels to perform dynamic braking of the vehicle when the service brake by the hydraulic system fails. The purpose is to tighten the brake on the rear wheels without locking. More specifically, when one wheel slips, the brake is loosened to unlock this wheel or avoid wheel locking, and then tightened again. This control mode is created by ABS (registered trademark), but is distinguished from using electric control of the brake motor.

[0004] More specifically, the RWU braking mode consists of repeatedly performing the following operations: - When the slip of the wheel is smaller than a first predetermined threshold, a so-called "low threshold", the brake is gradually tightened until the slip exceeds this low threshold. - When the slip exceeds a second predetermined threshold, a so-called "high threshold", which is larger than the low threshold, the brake is gradually loosened until the slip becomes smaller than this high threshold. - If the slip is greater than the lower threshold but less than the higher threshold, maintain the tightening at the normal level.

[0005] To determine if a wheel lock has occurred, it is necessary to know the rotational speeds of the vehicle's four wheels. The two front wheels can be used to calculate a baseline speed, and by comparing this baseline speed with the speed of each rear wheel, it is determined whether the rear wheels are locked: a speed slower than the baseline speed and below a predetermined threshold will result in a lock or the onset of a lock. In other words, if the speed is below the baseline speed which is below a predetermined threshold, the wheel can be considered locked or the onset of a lock. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] U.S. Patent No. 7744166 [Patent Document 2] U.S. Patent Application Publication No. 2021370899A1 [Patent Document 3] U.S. Patent No. 6092879 [Overview of the project] [Problems that the invention aims to solve]

[0007] If one of the rear wheels no longer provides rotational speed, it is naturally impossible to use the RWU braking mode. In that case, the system must be switched to incremental braking mode, which increases the tightening of the electric parking brake incrementally at regular intervals, thus avoiding the conditions under which the wheels would lock. However, it is not possible to verify whether or not a lock has occurred.

[0008] Incidentally, if only one front wheel is no longer supplying rotational speed, the anti-lock mode cannot be used either. This is because knowing only the rotational speed of one front wheel does not allow for the determination of a reference speed that serves as a comparison point for the rotational speeds of each rear wheel. In fact, when a vehicle follows a curved track, for example when turning, there is a difference in rotational speed between the wheels on the inside and outside of the curve, so comparing only the speed of one of the two front wheels carries the risk of drawing incorrect conclusions. For example, the speed of one inner rear wheel is always less than the speed of one outer front wheel. In this case, the inner rear wheel can always be locked. Conversely, the speed of one outer rear wheel is always greater than the speed of one inner front wheel. The outer rear wheel's speed may decrease, and thus locking may begin, but even so, this speed will not fall sufficiently below the speed of the outer front wheel. In this case, locking will not be detected. For these reasons, in conventional technology, if one front wheel is no longer supplying rotational speed, the anti-lock braking mode is abandoned and the system switches to increment mode. Similarly, Patent Document 2 describes a method for switching to an electronic parking brake in the event of a braking function malfunction. Furthermore, Patent Document 3 describes a solution for disabling the vehicle's anti-lock or brake distribution system when a malfunction is detected. However, none of these known solutions can overcome the problem of the front wheels no longer supplying rotational speed. [Means for solving the problem]

[0009] The object of the present invention is a method for emergency braking one of the wheels of a vehicle equipped with an electric parking brake by implementing an anti-lock braking mode or an incremental braking mode, wherein the vehicle has at least two axles, the wheel is on the first of these at least two axles, and the anti-lock braking mode is ensured by controlling the parking brake in accordance with the following rules, while the slip of the wheel is obtained by calculating the difference between the rotational speed of this wheel and a reference speed obtained based on the speed of one of the at least two wheels on the second axle of the vehicle: -If the slip is less than a first predetermined threshold, gradually tighten the brake until the slip exceeds this first threshold. -If the slip exceeds a second predetermined threshold which is greater than the first threshold, gradually release the brakes until the slip becomes less than this second threshold. - If the slip is greater than the first threshold but less than the second threshold, the tightening is maintained at the normal level. The incremental braking method is performed by controlling the parking brake while gradually increasing the tightening for a predetermined duration. This method is characterized in that, if the speeds of the two wheels on the second axle are unknown but the speed of one of them is known, the anti-lock braking mode is applied using the known speed modified by a reduction operation as the reference speed, and if the speeds of both wheels on the second axle are unknown, the incremental braking mode is applied.

[0010] In this description of the present invention, a dynamic braking request means braking control that is activated by the vehicle driver (human or artificial intelligence) in response to traffic needs while the vehicle is in motion.

[0011] In this description of the present invention, wheel slip means that the translational speed of the wheel exceeds the rotational speed multiplied by the wheel diameter. Methods for measuring slip are known, for example, by comparing the rotational speed of the wheel (measured by a wheel speed sensor (WSS)) with the vehicle speed.

[0012] According to one specific embodiment of the emergency braking method, the reduction operation is multiplication by a multiplier coefficient.

[0013] According to one specific embodiment of the emergency braking method, the multiplier coefficient is between 0 and 1, for example, approximately equal to 0.84.

[0014] According to one particular embodiment of the emergency braking method, the multiplier coefficient is calculated by applying the following formula based on the maximum and minimum steering angles: coefficient = sin[maximum steering angle] / sin[minimum steering angle].

[0015] According to one specific embodiment of the emergency braking method, the multiplication coefficient is determined during the running of the vehicle, and considering the actual steering angle, the following formula: coefficient = sin[actual steering angle] / sin[minimum steering angle] is applied. To apply this formula, the real-time rotation angle of the steering wheel, the vehicle width, and the wheel speed must be known. International Publication No. 202099768 A1 pamphlet discloses the formula to be used for determining the speed of the rear wheels. This formula is incorporated herein by reference, and the content of the above-mentioned document is incorporated into the description of the present invention for explanation.

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[0019] According to one specific embodiment, the first axle is the rear axle and the second axle is the front axle. Preferably, the vehicle has exactly two axles. Another object of the present invention is a braking system, characterized by including means capable of implementing the above method.

[0020] Another object of the present invention is a motor vehicle, characterized by including at least one braking system according to the present invention.

[0021] This invention is not limiting in any way and will be better understood by referring to the accompanying drawings provided as examples. [Brief explanation of the drawing]

[0022] [Figure 1] This is a schematic diagram of a car viewed from above. [Figure 2] This figure shows the vehicle in Figure 1 on the track. [Figure 3] This flowchart shows the steps for implementing the method in a vehicle. [Modes for carrying out the invention]

[0023] Figure 1 shows vehicle 1, which has four wheels, i.e., the following: -Two electric power steering front wheels 2 and 3, namely left front wheel 2 and right front wheel 3 -The two rear wheels are not electric or power-steering, namely the left rear wheel 4 and the right rear wheel 5.

[0024] Each of the front wheels 2 and 3 is equipped with a main service brake 6, which is controlled here by the driver of vehicle 1, and each of the rear wheels is equipped with a parking brake 7 that can function as both a parking brake and an emergency brake. Each parking brake 7 has an electric motor (not shown) controlled by a motor control unit 8 based on information about several parameters of vehicle 1 and its driving state. The motor control unit 8 is activated when emergency braking is required or when parking is requested.

[0025] Each main brake 6 allows the vehicle 1 to be decelerated by the operation of hydraulic brake control at the driver's request during normal use. The hydraulic brake system includes control means, but these will not be described here.

[0026] An emergency switching mechanism is provided that uses a calculation means 9 to switch to electric braking via the parking brake in the event of a failure of the hydraulic brakes or their control means. These calculation means 9 may be integrated into the vehicle 1 or may be specific to the brake system.

[0027] Each parking brake 7 is operated by a motor control unit 8 according to two operating modes: RWU ("Rear Wheel Unlocker" or "Rear Wheel Locking Device") mode or IFA ("Incremental Force Actioning" or "Incremental Tightening Action") mode.

[0028] The RWU mode uses two slip thresholds: a first threshold (or low threshold) and a second threshold (or high threshold). These can be determined on average to fit all types of vehicle 1. They can also be calibrated for each type of vehicle 1, and even for each model of vehicle 1. For example, the low threshold can be set to zero, which means that as soon as the speed of one wheel falls below a reference speed, that wheel is considered to be slipping on the road surface.

[0029] The two operating modes described above are well-known to experts in the relevant technology and will not be explained here.

[0030] Figure 2 shows vehicle 1 and a portion of the left and right front wheels 2 and 3.

[0031] Vehicle 1 is in the process of following a curved track 10 as a whole. For each front wheel, this curved track is represented here as a specific track 10.2, 10.3 which is identified with a portion of the circle of the center 11.

[0032] The radius of curvature of the circular portion described above is smaller for the inner wheel (in this case, the left wheel) than for the outer wheel (in this case, the right wheel).

[0033] The steering radii of front wheels 2 and 3 are indicated by angles α and β, measured at approximately the point of contact between the road surface and the wheel, tangent to the track. Due to the design of vehicle 1, the steering angle of the inner wheel in a curve, the left front wheel 2 in Figure 1, is greater than that of the outer wheel in a curve, in this case the right front wheel 3.

[0034] Each wheel has its own unique rotational speed. Therefore, the rotational speeds are shown as follows: V2 for the left front wheel 2, V3 for the right front wheel 3, V4 for the left rear wheel 4, and V5 for the right rear wheel 5.

[0035] As shown in Figure 3, when the driver makes a dynamic braking request (step 30), the calculation means 9 begins to verify whether the main brake 6 is working properly (step 31). If it is working properly, conventional braking is performed (step 32).

[0036] Otherwise, the calculation means 9 initiates emergency braking by the motor control unit 8 according to the algorithm in Figure 3.

[0037] In step 33, the calculation means 9 verifies whether at least one of the two front wheels 2, 3 is supplying its own inherent speed. If there is a malfunction in supplying the rotational speed of the two front wheels 2, 3, that is, if the speed of the front wheels is completely unknown, the method proceeds to the incremental braking step 34.

[0038] Otherwise, in step 35, the calculation means 9 verifies whether the two front wheels 2, 3 are supplying their speed. If yes, in step 36, antilock braking is activated at a reference speed calculated based on the speeds of the two front wheels 2, 3, according to the emergency braking method of the prior art.

[0039] If the answer is no, one of the front wheels 2 or 3 is supplying the speed, but the other is not. In that case, the process moves on to step 37, which corrects only the known speed.

[0040] Therefore, the single front wheel speed, which was supplied without any malfunction, is corrected by the application of the reduction operation, and the corrected reference speed is supplied.

[0041] The reduction operation can consist of multiplication by a multiplier coefficient less than 1. The multiplier coefficient can be predetermined to a value suitable for all types of vehicles 1, but only once for the whole. According to calculations and tests performed by the inventor, a value of 0.84 appears to be optimal as a universal coefficient.

[0042] The coefficient can also be calculated based on the geometric parameters that can be determined from the model of vehicle 1.

[0043] For example, based on the maximum steering angle (steering angle of the inner wheel) and the minimum steering angle (steering angle of the outer wheel), the coefficient can be determined by the following formula: -Coefficient = 1 / sin[maximum rudder angle] / sin[minimum rudder angle] Here, the minimum and maximum steering angles are selected from α and β depending on the direction of the turn (right curve or left curve).

[0044] Furthermore, the coefficient can also be determined while vehicle 1 is in motion, and the following formula is applied, taking into account the actual steering angle: Coefficient = 1 / sin[actual steering angle] / sin[minimum steering angle] Here, the minimum steering angle is selected from α and β depending on the direction of the turn (right curve or left curve).

[0045] Next, in step 38, this corrected speed is compared with the speed of each rear wheel 4 and 5, and braking in RWU mode is applied to rear wheels 4 and 5, with this corrected speed being set as the reference speed.

[0046] The present invention is not limited to the embodiments described above, and other embodiments will become apparent to experts in the art. [Explanation of Symbols]

[0047] 1 vehicle 2 Front left wheel 3. Right front wheel 4. Left rear wheel 5 Right rear wheel 6. Main Brake 7. Parking brake 8 Motor control unit 9 Means of calculation 10 Curved track 10.2 The left front wheel's inherent trajectory 10.3 The inherent trajectory of the right front wheel 11 center 31 Verification Steps 32 Conventional braking 33 Verification Steps 34 Incremental braking 35 Verification Steps 36 Anti-lock braking 37. Steps to correct the reference speed 38 Comparison Steps

Claims

1. A method for emergency braking one of the wheels of a vehicle (1) equipped with an electric parking brake (7) by performing an anti-lock braking mode or an incremental braking mode, wherein the vehicle has at least two axles, the wheel is on the first axle of the at least two axles, and the anti-lock braking mode is ensured by controlling the parking brake (7) in compliance with the following rules, wherein the slip of the wheel is obtained by calculating the difference between the rotational speed of the wheel and a reference speed, the reference speed is obtained based on the speed of one of the at least two wheels (2, 3) on the second axle of the at least two axles of the vehicle. - If the slip is less than a first predetermined threshold, the brake is gradually tightened until the slip exceeds this first threshold. - If the slip is greater than a second predetermined threshold, the brake is gradually released until the slip becomes less than the second threshold. - If the slip is greater than the first threshold and less than the second threshold, the tightening is maintained at a normal level. The increment braking method is performed by controlling the parking brake (7) while gradually increasing the tightening for a predetermined duration, in a method in which, A method characterized in that, when the speeds of the two wheels (2, 3) of the second axle are unknown but the speed of one of them is known, the anti-lock braking mode is applied using the known speed corrected by a reduction operation as the reference speed, and when the speeds of both wheels of the second axle are unknown, the incremental braking mode is applied.

2. The emergency braking method according to claim 1, wherein the reduction operation is multiplication by a multiplier coefficient.

3. The emergency braking method according to claim 2, wherein the multiplication coefficient is between 0 and 1, for example, approximately 0.

84.

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

5. The multiplication coefficient is determined while the vehicle 1 is in motion, and taking into account the actual steering angle, the following formula is used: Coefficient = 1 / sin[actual rudder angle] / sin[minimum rudder angle] The emergency braking method according to any one of claims 2, 3, or 4, to which the following applies.

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

7. A braking system characterized by including means capable of carrying out the method described in any one of claims 1, 2, 3, 4, 5, or 6.

8. An automobile (1) characterized by including at least one braking system according to the present invention as described in claim 7.

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