Dynamic braking on three wheels

Abstract

An emergency braking system and method for wheels of a vehicle (1) equipped with an electric parking brake (7), which achieves emergency braking by implementing an anti-lock braking mode or an incremental braking mode. When the speeds of the two front wheels (2, 3) are unknown but the speed of only one is known, applying an anti-lock braking mode and using the known speed corrected by the reduction operation as a reference speed; an incremental braking mode is applied when no front wheel speed is known. A vehicle equipped with such a system.

Description

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

[0002] As described in document US7744166, a parking brake is electrically and / or automatically actuated by an electromechanical unit (also known as an electric actuator) associated with one or more wheels of a vehicle. Therefore, when a vehicle user wishes to engage the parking brake, they only need to press a button, for example, located on the dashboard near the steering wheel, to trigger or deactivate the parking brake's clamping around the vehicle's wheels.

[0003] The braking mode of RWU ("Rear Wheel Unlocker") is known. This mode uses the rear parking brakes to achieve dynamic braking of the vehicle when the hydraulic service brakes fail. The goal is to clamp the rear brakes to prevent them from locking up. More precisely, in the event of wheel slippage, the brakes are released to release or prevent wheel lock-up, then clamped again, and so on. This control mode is inspired by ABS (trademarked), but differs in that it uses electrical control of the brake motor.

[0004] More precisely, the RWU braking modes include cyclically performing the following operations:

[0005] - If the wheel slip is less than a first predetermined threshold known as the "low threshold", the brake is gradually tightened until the slip becomes greater than the low threshold;

[0006] - If the slip exceeds a second predetermined threshold known as the "high threshold", which is greater than the low threshold, the brake is gradually released until the slip becomes less than the high threshold;

[0007] - If the slide is greater than the low threshold and less than the high threshold, then keep the clamped at its current level.

[0008] Determining whether wheel lockup has occurred requires knowing the rotational speeds of all four wheels. Reference speeds are calculated for the two front wheels, and the speed of each rear wheel is compared to these reference speeds to determine if that rear wheel is locked: a speed significantly lower than the reference speed by a predetermined threshold indicates lockup or the onset of lockup. In other words, if the speed is less than the reference speed minus the predetermined threshold, lockup can be considered present or beginning.

[0009] If one of the rear wheels no longer provides its rotational speed, then the RWU braking mode obviously cannot be used. Therefore, the incremental braking mode must be used instead, in which the clamping of the electric parking brake is increased slightly at regular intervals in an incremental manner to avoid conditions that would cause wheel lock-up, but it is impossible to verify whether such lock-up has occurred.

[0010] However, if only one front wheel ceases to provide its rotational speed, the anti-lock braking mode is also unavailable because the reference speed used as a comparison point for the rotational speed of each rear wheel cannot be determined based on the rotational speed of only one front wheel. In fact, when a vehicle is traveling along a curved path, such as when it is turning, the difference in rotational speed between the inner and outer wheels makes comparisons with only one of the two front wheels risk yielding erroneous conclusions. For example, the speed of the inner rear wheel is always less than that of the outer front wheel. Therefore, it may appear to be constantly locked. Conversely, the speed of the outer rear wheel is always greater than that of the inner front wheel. It may decrease, i.e., begin to lock, but the speed still will not become less than that of the outer front wheel. Therefore, no lock-up is detected. For this reason, in the prior art, if the front wheels cease to provide their rotational speed, the anti-lock braking mode is abandoned and an incremental mode is used instead. Switching on the electronic parking brake in the event of a braking function failure is also known from document US2021370899A1. Furthermore, a scheme for disabling the anti-lock braking system or brake distributor of a vehicle when a fault is detected is known from document US6092879. However, none of these known schemes can overcome the problem of the front wheels no longer providing their rotational speed.

[0011] This invention

[0012] One object of the present invention is an emergency braking method for the wheels of a vehicle equipped with an electric parking brake, the vehicle having at least two axles and the wheels located on a first axle of the at least two axles, the method achieving emergency braking by implementing an anti-lock braking mode or an incremental braking mode, the anti-lock braking mode being ensured by controlling the parking brake to simultaneously comply with the following rules, wherein wheel slippage is obtained by calculating the difference between the rotational speed of the wheel and a reference speed, the reference speed being based on the speed of at least one wheel of the two wheels of the second axle of the at least two axles of the vehicle:

[0013] - If the sliding is less than a predetermined first threshold, the brake is gradually clamped until the sliding becomes greater than the first threshold;

[0014] If the sliding exceeds a predetermined second threshold, and the second threshold is greater than the first threshold, then the brake is gradually released until the sliding becomes less than the second threshold;

[0015] If the sliding is greater than the first threshold and less than the second threshold, then the clamping is maintained at its current level.

[0016] The incremental braking method ensures that the parking brake is controlled by gradually increasing the clamping of the parking brake over a predetermined period of time.

[0017] The method is characterized in that when the speeds of the two wheels of the second axle are unknown but only one is known, the anti-lock braking mode is applied, and the known speed is corrected by a reduction operation and used as a reference speed; while when the speeds of all wheels of the second axle are unknown, the incremental braking mode is applied.

[0018] In this specification, "dynamic braking request" refers to braking control initiated by the vehicle driver—a human or artificial intelligence—based on traffic demand while the vehicle is in motion.

[0019] In this specification, "wheel slippage" refers to the translational speed of a wheel being greater than its rotational speed multiplied by its diameter. Methods for measuring this slippage are known, such as comparing the wheel's rotational speed (measured using a wheel rotation speed detector (WSS)) with the vehicle's speed.

[0020] According to a particular implementation of the emergency braking method, the reduction operation is multiplied by a multiplier coefficient.

[0021] According to a particular embodiment of the emergency braking method, the multiplier coefficient is between 0 and 1, for example, approximately equal to 0.84.

[0022] According to a specific implementation of the emergency braking method, the multiplier coefficient is calculated based on the maximum steering angle and the minimum steering angle by applying the following formula: coefficient = sin[maximum steering angle] / sin[minimum steering angle].

[0023] According to a specific embodiment of the emergency braking method, the multiplier coefficient is determined during vehicle travel by applying the following formula, taking into account the actual steering angle: coefficient = sin[actual steering angle] / sin[minimum steering angle]. The application of this formula requires real-time knowledge of the steering wheel rotation angle, vehicle width, and wheel speed. Document WO202099768A1 discloses a formula for determining the rear wheel speed. This formula is presented below to clearly indicate that the content of that document is incorporated herein by reference:

[0024]

[0025] Among them, V eAR It is the evaluation value of the rear wheel speed, V min and V max It is an evaluation value of the front wheel speed and

[0026] V min ≤V max ,

[0027] Kcorr It is a correction factor, and

[0028] for K corr =1; and for K corr ≤1.

[0029] S1 is a fixed threshold.

[0030] In one particular embodiment, the first axle is a rear axle, and the second axle is a front axle. Preferably, the vehicle has exactly two axles.

[0031] Another object of the present invention is a braking system, characterized in that the braking system includes means capable of implementing the method described above.

[0032] Another object of the present invention is a motor vehicle, characterized in that it includes at least one braking system according to the present invention. Attached Figure Description

[0033] The invention will be better understood by reading the accompanying drawings, which are provided as examples and are not intended to be limiting. In the drawings:

[0034] - Figure 1 It is a schematic top view of a motor vehicle;

[0035] - Figure 2 Showing the trajectory Figure 1 The vehicles;

[0036] - Figure 3 This is a flowchart illustrating the steps of one implementation of the method on a vehicle.

[0037] Figure 1 In the image above, vehicle 1 can be seen to have four wheels, namely:

[0038] - The two drive and steering front wheels 2 and 3, namely the left front wheel 2 and the right front wheel 3; and

[0039] - Two non-driving and non-steering rear wheels 4 and 5, namely the left rear wheel 4 and the right rear wheel 5.

[0040] Each of the front wheels 2 and 3 is equipped with a main service brake 6 controlled by the driver of vehicle 1, and each of the rear wheels is equipped with a parking brake 7, which can function as both a parking brake and an emergency brake. Each parking brake 7 has an electric motor (not shown), which is controlled by a motor control unit 8 based on information related to certain parameters of vehicle 1 and its driving state. The motor control unit 8 is activated when emergency braking becomes necessary or parking is required.

[0041] During normal use of vehicle 1, each main brake 6 can decelerate the vehicle by actuating the hydraulic braking control upon the driver's request. The hydraulic braking system is equipped with a control device, which will not be described in detail here.

[0042] In the event of a failure of the hydraulic brake or its control device, an emergency switch is provided, allowing switching to electric braking implemented by the parking brake via a computing device 9. This computing device 9 may be integrated into the vehicle 1 or be dedicated to the braking system.

[0043] Each parking brake 7 can be requested by the motor control unit 8 according to two operating modes: RWU ("Rear Wheel Unlocker") mode or IFA ("Incremental Force Actioning") mode.

[0044] The RWU mode utilizes two slip thresholds: a first threshold (or low threshold) and a second threshold (or high threshold). These thresholds can be set in an average manner to apply to any type of vehicle 1. They can also be calibrated by the type of vehicle 1 or even by the model of vehicle 1. For example, the low threshold can be set to zero, meaning that once a wheel has a speed strictly less than a reference speed, it is considered that the wheel is slipping on the ground.

[0045] The two operating modes defined above will not be elaborated further here, as they are well known to those skilled in the art.

[0046] Figure 2 The image shows a portion of the trajectory of vehicle 1, as well as the left front wheel 2 and the right front wheel 3.

[0047] Vehicle 1 is generally moving along curved trajectory 10. For each front wheel, this curved trajectory is represented by dedicated trajectories 10.2 and 10.3, which here approximate as an arc with a center 11.

[0048] The radius of curvature of the arc of the inner wheel (left wheel in this case) is smaller than the radius of curvature of the arc of the outer wheel (right wheel in this case).

[0049] The turning radii of the front wheels 2 and 3 are represented by angles α and β, which are measured at the tangent to the trajectory, approximately at the point of contact between the wheel and the ground. Due to the construction of vehicle 1, the inner wheel ( Figure 3 The steering angle of the left front wheel (2) is greater than the steering angle of the outer wheel (in this case, the right front wheel (3)).

[0050] Each wheel has its own rotational speed. Therefore, the rotational speeds are expressed as: 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.

[0051] like Figure 3 As shown, when the driver makes a dynamic braking request (step 30), the computing device 9 begins to check (step 31) whether the main brake 6 is operating normally. If so, conventional braking is performed (step 32).

[0052] Otherwise, the computing device 9 according to Figure 3 The algorithm initiates emergency braking through the motor control unit 8.

[0053] In step 33, the computing device 9 checks whether at least one of the two front wheels 2 and 3 provides its own speed. If the provision of rotational speed by both front wheels 2 and 3 fails, i.e., no front wheel speed is known, the method proceeds to step 34 of incremental braking.

[0054] Otherwise, in step 35, the computing device 9 checks whether both front wheels 2 and 3 are providing their speeds. If so, then in step 36, according to the emergency braking method of the prior art, anti-lock braking is performed using a reference speed calculated based on the speeds of the two front wheels 2 and 3.

[0055] Alternatively, if one of the front wheels 2 and 3 provides its speed while the other does not, then the method proceeds to step 37, which involves correcting for the only known speed.

[0056] Therefore, the single front wheel speed that is provided without failure is corrected by applying a reduction operation to provide a corrected reference speed.

[0057] The correction operation can be multiplied by a multiplier coefficient, the value of which is less than 1. This coefficient can be pre-set once and for all to apply to any type of vehicle. According to calculations and tests conducted by the inventors, a value of 0.84 appears to be optimal as a universal coefficient.

[0058] This coefficient can also be calculated based on the known geometric parameters of vehicle 1, according to the model of vehicle 1.

[0059] For example, based on the maximum steering angle (maximum steering angle of the inner wheel) and the minimum steering angle (minimum steering angle of the outer wheel), the coefficient can be determined using the following formula:

[0060] - Coefficient = 1 / sin[maximum steering angle] / sin[minimum steering angle]

[0061] The minimum steering angle and the maximum steering angle are selected from α and β according to the turning direction (right turn or left turn).

[0062] Finally, this coefficient can also be determined during vehicle 1's driving by applying the following formula while taking into account the actual steering angle: coefficient = 1 / sin[actual steering angle] / sin[minimum steering angle], where the minimum steering angle is selected from α and β according to the steering direction (right or left).

[0063] Then, in step 38, the corrected speed is compared with the speed of each of the rear wheels 4 and 5 to apply RWU mode braking to the rear wheels 4 and 5, which uses the corrected speed as a reference speed.

[0064] This invention is not limited to the described embodiments, and other embodiments will be apparent to those skilled in the art.

[0065] List of reference numerals

[0066] 1...vehicles

[0067] 2...Left front wheel

[0068] 3...Right front wheel

[0069] 4...Left rear wheel

[0070] 5...Right rear wheel

[0071] 6... Main brake

[0072] 7... Parking brake

[0073] 8...Motor control unit

[0074] 9...Computing device

[0075] 10...curved trajectory

[0076] 10.2...Dedicated track for the left front wheel

[0077] 10.3... Right front wheel exclusive trajectory

[0078] 11...center

[0079] 31... Inspection steps

[0080] 32...Conventional braking

[0081] 33... Inspection steps

[0082] 34...Incremental Braking

[0083] 35... Inspection steps

[0084] 36...Anti-lock Braking

[0085] 37... Correction steps for reference speed

[0086] 38... Comparison Steps

Claims

1. An emergency braking method for a wheel of a vehicle (1) equipped with an electric parking brake (7), the vehicle having at least two axles and the wheel located on a first axle of the at least two axles, the method achieving emergency braking by implementing an anti-lock braking mode or an incremental braking mode, the anti-lock braking mode being ensured by controlling the parking brake (7) to simultaneously comply with the following rules, wherein wheel slippage is obtained by calculating the difference between the rotational speed of the wheel and a reference speed, the reference speed being based on the speed of at least one wheel of two wheels (2, 3) of the second axle of the at least two axles of the vehicle: - If the sliding is less than a predetermined first threshold, the brake is gradually clamped until the sliding becomes greater than the first threshold; If the sliding exceeds a predetermined second threshold, and the second threshold is greater than the first threshold, then the brake is gradually released until the sliding becomes less than the second threshold; If the sliding is greater than the first threshold and less than the second threshold, then the clamping is maintained at its current level. The incremental braking method ensures that the parking brake (7) is controlled by gradually increasing the clamping of the parking brake (7) over a predetermined period of time. The method is characterized in that when the speeds of two wheels (2, 3) of the second axle are unknown but the speed of only one is known, the anti-lock braking mode is applied, and the known speed is corrected by a reduction operation and used as a reference speed; while when the speeds of all 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 multiplied by a multiplier coefficient.

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

84.

4. The emergency braking method according to any one of claims 2 and 3, wherein, The multiplier coefficient is calculated using the following formula based on the maximum and minimum steering angles: Coefficient = 1 / sin[maximum steering angle] / sin[minimum steering angle].

5. The emergency braking method according to any one of claims 2, 3, and 4, wherein, The multiplier coefficient is determined during the driving of the vehicle (1) by applying the following formula and taking into account the actual steering angle: Coefficient = 1 / sin[actual steering angle] / sin[minimum steering angle].

6. The 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; preferably, the vehicle has exactly two axles.

7. A braking system, characterized in that, The braking system includes means adapted to implement the method as described in any one of claims 1, 2, 3, 4, 5, and 6.

8. A motor vehicle (1), characterized in that, The motor vehicle (1) includes at least one braking system according to the invention as claimed in claim 7.

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