Comfortable braking method suitable for electronic mechanical braking system

Abstract

The invention relates to the technical field of vehicle braking control, in particular to a comfortable braking method suitable for an electronic mechanical braking system. Comprising the steps that first-stage control and second-stage control are executed in the initial braking stage and the later braking stage correspondingly, and the process of the first-stage control comprises the steps that the proportion of braking force on four wheels in the total braking force is distributed, so that the pitch angle of a vehicle body is restrained; the conditions for executing the second-stage control comprise that the vehicle speed is reduced to a threshold speed V1 during the execution of the first-stage control, and the V1 is in positive correlation with the initial speed V0 for executing the first-stage control and the braking force request degree Fy when the vehicle speed is reduced to a preset value V2; the second-stage control process comprises the steps that the target braking deceleration axTar is confirmed in real time, the axTar is in positive correlation with the current vehicle speed and the braking force request degree, and the actual braking force of the vehicle is controlled in real time so as to track the target braking deceleration axTar. And the braking comfort can be effectively improved.

Description

Technical Field

[0001] The invention relates to the technical field of vehicle braking control, and in particular to a comfortable braking method suitable for an electronic mechanical braking system. Background Art

[0002] At present, the mainstream comfort braking control methods are mostly based on hydraulic braking systems, and their core strategy is to alleviate the brake nodding phenomenon by adjusting the braking force distribution or delaying the pressure building rate. However, such methods have the following defects: Adaptability defects of fixed speed threshold: The existing technology usually switches to the final stage of braking control when the fixed speed threshold is preset, but does not take into account the difference in the driver's braking force request. When the braking force request is high, the fixed threshold will lead to insufficient control time in the second stage, and a steep deceleration descent curve will be used, which is easy to cause a sudden change in deceleration and create the illusion of "slipping"; conversely, when the braking force request is low, entering the second stage control too early will prolong the braking time and reduce the driving experience.

[0003] The target deceleration curve has a poor match with the working conditions: the existing method uses a fixed deceleration curve and does not dynamically adjust the curve descent gradient according to the real-time vehicle speed and braking force request. For example, in a high-speed and high-braking force request scenario, a too fast deceleration will result in an uncontrollable braking distance; while at a low speed and low-braking force request, maintaining a too high deceleration will produce an uncomfortable feeling of "nodding to a stop". Summary of the invention

[0004] In order to overcome the above-mentioned deficiencies of the prior art, the present invention provides a comfortable braking method applicable to an electronic mechanical braking system, which can effectively improve braking comfort.

[0005] In order to achieve the above object, the present invention is implemented through the following technical solutions: A comfortable braking method applicable to an electronic mechanical braking system: comprising: The first stage control and the second stage control are performed at the initial stage and the later stage of braking respectively. The first stage of control process includes: allocating the proportion of the braking force on the four wheels to the total braking force to suppress the vehicle body pitch angle; The conditions for executing the second stage control include: the vehicle speed is reduced to the threshold speed V1 during the execution of the first stage control, V1 is positively correlated with the initial speed V0 for entering the first stage control and the braking force request degree Fy when the vehicle speed drops to the preset value V2; The second stage control process includes: real-time confirmation of the target braking deceleration ax_Tar, ax_Tar is positively correlated with the current vehicle speed and braking force request, and real-time control of the vehicle's actual braking force to track the target braking deceleration ax_Tar.

[0006] Furthermore, in a comfort braking method applicable to an electronic mechanical brake system in the present application, the conditions for executing the first stage of control include detecting that the vehicle speed and the braking force request are within a preset range; The abnormal operating condition of the vehicle system that determines that the first stage control cannot be executed includes at least one of the following situations: ABS operating condition is triggered, VSC operating condition is triggered, and the vehicle system receives a downgrade request.

[0007] The downgrade request is caused by system feedback caused by other modules or hardware damage.

[0008] Furthermore, in a comfort braking method applicable to an electronic mechanical braking system in the present application, the condition for executing the second stage of control also includes that the current vehicle deceleration is within a preset range when the vehicle speed drops to a threshold speed V1.

[0009] Furthermore, in a comfort braking method applicable to an electronic mechanical braking system in the present application, it is determined that the abnormal operating condition of the automobile system that cannot execute the second stage control includes at least one of the following situations: It is detected that the driving slope exceeds the preset range, the road surface is detected to be an unpaved road, the road surface is detected to be a butt or split road, the EMB execution end temperature exceeds the preset range, a trigger drive request is detected, and a stop braking request is detected.

[0010] Further, in a comfortable braking method applicable to an electronic mechanical braking system in the present application, the process of allocating the proportion of the braking force on the four wheels to the total braking force in the first stage control includes: detecting the adhesion coefficient utilization rate of a pair of rear wheels of the vehicle, if the adhesion coefficient utilization rate of the pair of rear wheels is less than a preset threshold, then gradually increasing the proportion of the braking force of the pair of rear wheels to the total braking force under the condition that the corresponding relationship between the total braking force and the braking force request degree does not change, and the increase in the proportion of the rear wheel braking force to the total braking force is inversely correlated with the vehicle speed and the braking force request degree. As a preferred solution of the present application, if the braking force of the rear wheel is too large, it may cause the rear wheel to lock in advance. Referring to the ideal braking force curve, the adhesion coefficient of the road surface should be calculated, and the braking force should be transferred to the rear wheel as much as possible before the road surface adhesion is exhausted. The vehicle speed and the braking force request degree are used as inputs for the table lookup. The higher the vehicle speed, the smaller the increase in the proportion of the rear wheel braking force to the total braking force, and the greater the braking force request degree, the smaller the increase in the proportion of the rear wheel braking force to the total braking force.

[0011] Furthermore, in a comfortable braking method applicable to an electronic mechanical braking system in the present application, V1 can be obtained by looking up a table or calculating a function, and the calculation function is V1 = K1*Fy*(e^(K2*V0) +K3), wherein K1, K2, and K3 are all adjustable constants, and V1≤V2.

[0012] Furthermore, a comfortable braking method applicable to an electronic mechanical braking system in the present application, after the vehicle stops and the deceleration tends to a stable value, restores the actual braking force to correspond to the braking force request degree, as a preferred solution of the present application, to eliminate the influence of inertia on the vehicle body when the vehicle is just stopped.

[0013] It can be seen from the above technical solution that the present invention has the following beneficial effects: The present invention provides a comfortable braking method applicable to an electronic mechanical braking system, which makes full use of the characteristics of EMB independently controlling the braking force on each wheel, reduces the braking nodding phenomenon at the beginning of braking, and improves the braking comfort without increasing the braking distance. In the second stage control process, ax_Tar is the target deceleration of the whole vehicle in the second stage control process, which can maintain the pitch of the whole vehicle at a smaller value during braking, and at the same time, control the braking distance to achieve the purpose of braking comfort. The target deceleration is obtained through experiments and simulations under different braking force requests and different vehicle speeds, and is obtained by looking up the table by inputting the vehicle speed and the braking force request. The principle is that the greater the braking force request and the higher the speed, the shorter the amplitude of the ax_Tar front section decreases, so as to prevent the deceleration from changing suddenly, causing the passengers to feel that the braking is insufficient and the vehicle is slipping; the smaller the braking force request and the lower the speed, the greater the amplitude of the ax_Tar decreases accordingly, because at this time the vehicle is close to stopping, and there will be no abrupt braking force mutation. Moreover, the conditions for entering the final stage of vehicle braking, i.e., the second stage of control, vary with the actual conditions, i.e., V1 is a variable. Compared with the fixed speed threshold, it can ensure the adequacy of the second stage of control time to improve the comfort in the second stage of control. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 A schematic diagram of changes in speed and deceleration during braking performed by a comfortable braking method applicable to an electronic mechanical braking system in an embodiment of the present application; Figure 2 Schematic diagram of the relationship between target deceleration, braking force request and speed during the second stage control process. DETAILED DESCRIPTION

[0015] Combination Figure 1 A comfort braking method applicable to an electronic mechanical braking system is shown, comprising: The first stage control and the second stage control are performed at the initial stage and the later stage of braking respectively. The first stage of control process includes: allocating the proportion of the braking force on the four wheels to the total braking force to suppress the vehicle body pitch angle; The conditions for executing the second stage control include: the vehicle speed is reduced to the threshold speed V1 during the execution of the first stage control, V1 is positively correlated with the initial speed V0 for entering the first stage control and the braking force request degree Fy when the vehicle speed drops to the preset value V2; The second stage control process includes: real-time confirmation of the target braking deceleration ax_Tar, combined with Figure 2 As shown, ax_Tar is positively correlated with the current vehicle speed and braking force request Fx, and the actual braking force of the vehicle is controlled in real time to track the target braking deceleration ax_Tar.

[0016] Based on the above method, this embodiment makes full use of the characteristics of EMB independently controlling the braking force on each wheel, and starts to reduce the braking nodding phenomenon at the beginning of braking, and improves the braking comfort without increasing the braking distance. During the second stage control process, ax_Tar is the target deceleration of the whole vehicle during the second stage control process. This deceleration can keep the pitch of the whole vehicle at a smaller value during braking, and at the same time, control the braking distance to achieve the purpose of braking comfort. The target deceleration is obtained through experiments and simulations under different braking force requests and different vehicle speeds, and is obtained by looking up the table by inputting the vehicle speed and braking force request. The principle is that the greater the braking force request and the higher the speed, the shorter the amplitude of the ax_Tar front section decreases, preventing the deceleration from changing suddenly, giving passengers a feeling of insufficient braking and slipping; the smaller the braking force request and the lower the speed, the greater the amplitude of the ax_Tar decreases accordingly, because at this time the vehicle is close to stopping, and there will be no abrupt braking force mutation. Among them, the principle of tracking the target braking deceleration ax_Tar is to perform closed-loop control based on the difference err_ax between ax_Tar and the actual deceleration of the vehicle. In addition, the conditions for entering the final stage of vehicle braking, that is, the second stage of control, vary with the actual situation, that is, V1 is a variable, which can ensure the adequacy of the second stage of control time compared to the fixed speed threshold, so as to improve the comfort in the second stage of control. Specifically, in a car that requests braking through the brake pedal, the degree of braking force requested is positively correlated with the travel of the car's brake pedal.

[0017] In this embodiment, the conditions for executing the first stage control include detecting that the vehicle speed and the braking force request are within a preset range; The abnormal operating condition of the vehicle system that determines that the first stage control cannot be executed includes at least one of the following situations: ABS operating condition is triggered, VSC operating condition is triggered, and the vehicle system receives a downgrade request.

[0018] The downgrade request is caused by system feedback caused by other modules or hardware damage.

[0019] Furthermore, in this embodiment, the condition for executing the second stage control also includes that when the vehicle speed decreases to the threshold speed V1, the current vehicle deceleration is within a preset range. In one embodiment, the current vehicle deceleration is within a preset range of -0.5g to -0.05g.

[0020] In this embodiment, the abnormal operating condition of the automobile system that determines that the second stage control cannot be executed includes at least one of the following situations: It is detected that the driving slope exceeds the preset range, the road surface is detected to be an unpaved road, the road surface is detected to be a butt or split road, the EMB execution end temperature exceeds the preset range, a trigger drive request is detected, and a stop braking request is detected.

[0021] In this embodiment, the process of allocating the proportion of the braking force on the four wheels to the total braking force in the first stage control includes: detecting the adhesion coefficient utilization rate of a pair of rear wheels of the vehicle, if the adhesion coefficient utilization rate of the pair of rear wheels is less than the preset threshold, then gradually increasing the proportion of the braking force of the pair of rear wheels to the total braking force under the condition that the corresponding relationship between the total braking force and the braking force request degree does not change, and the increase in the proportion of the rear wheel braking force to the total braking force is inversely correlated with the vehicle speed and the braking force request degree. If the braking force of the rear wheel is too large, it may cause the rear wheel to lock in advance. Referring to the ideal braking force curve, the adhesion coefficient of the road surface should be calculated, and the braking force should be transferred to the rear wheel as much as possible before the road surface adhesion is exhausted. The vehicle speed and the braking force request degree are used as inputs for the table lookup. The higher the vehicle speed, the smaller the increase in the proportion of the rear wheel braking force to the total braking force, and the greater the braking force request degree, the smaller the increase in the proportion of the rear wheel braking force to the total braking force.

[0022] In this embodiment, V1 can be obtained by looking up a table or calculating a function, and the calculation function is V1 = K1*Fy*(e^(K2*V0) +K3), where K1, K2, and K3 are all adjustable constants. In one embodiment, the range of V1 is [1.5m / s, V2]. In one embodiment, V2 is 3m / s.

[0023] Combination Figure 2 As shown, in this embodiment, after the vehicle stops and the deceleration tends to a stable value, the actual braking force is restored to correspond to the braking force request degree, so as to eliminate the influence of the inertia of the vehicle body when the vehicle stops.

[0024] The technical principles of the present invention are described above in conjunction with specific embodiments. These descriptions are only for explaining the principles of the present invention and cannot be interpreted as limiting the scope of protection of the present invention in any way. Based on the explanations herein, those skilled in the art can associate other specific implementations of the present invention without creative work, and these methods will fall within the scope of protection of the present invention.

Claims

1. A comfortable braking method applicable to an electronic mechanical braking system, characterized in that: include: The first stage control and the second stage control are performed at the initial stage and the later stage of braking respectively. The first stage of control process includes: allocating the proportion of the braking force on the four wheels to the total braking force to suppress the vehicle body pitch angle; The conditions for executing the second stage control include: the vehicle speed is reduced to the threshold speed V1 during the execution of the first stage control, V1 is positively correlated with the initial speed V0 for entering the first stage control and the braking force request degree Fy when the vehicle speed drops to the preset value V2; The second stage control process includes: real-time confirmation of the target braking deceleration ax_Tar, ax_Tar is positively correlated with the current vehicle speed and braking force request, and real-time control of the vehicle's actual braking force to track the target braking deceleration ax_Tar.

2. A comfortable braking method applicable to an electronic mechanical braking system according to claim 1, characterized in that: The conditions for executing the first stage control include detecting that the vehicle speed and the braking force request are within a preset range; The abnormal operating condition of the vehicle system that determines that the first stage control cannot be executed includes at least one of the following situations: ABS operating condition is triggered, VSC operating condition is triggered, and the vehicle system receives a downgrade request.

3. A comfortable braking method applicable to an electronic mechanical braking system according to claim 1, characterized in that: The condition for executing the second stage control also includes that the current vehicle deceleration is within a preset range when the vehicle speed decreases to the threshold speed V1.

4. A comfortable braking method applicable to an electronic mechanical braking system according to claim 1, characterized in that: The abnormal operating condition of the vehicle system that determines that the second stage control cannot be executed includes at least one of the following situations: It is detected that the driving slope exceeds the preset range, the road surface is detected to be an unpaved road, the road surface is detected to be a butt or split road, the EMB execution end temperature exceeds the preset range, a trigger drive request is detected, and a stop braking request is detected.

5. A comfortable braking method applicable to an electronic mechanical braking system according to claim 1, characterized in that: The process of distributing the proportion of the braking force on the four wheels to the total braking force in the first stage of control includes: detecting the adhesion coefficient utilization rate of a pair of rear wheels of the vehicle. If the adhesion coefficient utilization rates of the pair of rear wheels are both less than a preset threshold, then gradually increasing the proportion of the braking force of the pair of rear wheels to the total braking force while the corresponding relationship between the total braking force and the braking force request degree does not change. The increase in the proportion of the rear wheel braking force to the total braking force is inversely correlated with the vehicle speed and the braking force request degree.

6. A comfortable braking method applicable to an electronic mechanical braking system according to claim 1, characterized in that: V1 can be obtained by looking up a table or calculating a function, where the calculation function is V1 = K1*Fy*(e^(K2*V0) +K3), wherein K1, K2, and K3 are all adjustable constants, [V1≤V2].

7. A comfortable braking method applicable to an electronic mechanical braking system according to claim 1, characterized in that: After the vehicle stops and the deceleration tends to a stable value, the actual braking force is restored to correspond to the braking force request degree.

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