Two-wheeled vehicle tail raising detection and suppression method based on hydraulic ABS

Abstract

The invention discloses a two-wheeled vehicle warped tail detection and suppression method based on a hydraulic ABS (Anti-lock Brake System), and the method comprises the steps: building a pressure model through ABS adjustment parameters, estimating the pressure of a front wheel cylinder and a rear wheel cylinder under the condition of not depending on an acceleration sensor, achieving the detection of the warped tail trend of a two-wheeled vehicle during braking through the combination of the characteristics of wheel speed, and suppressing the warped tail through reasonable pressure control. The method has the advantages of low cost, good stability and high safety.

Description

Technical Field

[0001] The invention relates to the technical field of vehicle electronic brake control, and in particular to a two-wheeled vehicle tail lift detection and suppression method based on hydraulic ABS. Background Art

[0002] Two-wheeled vehicle tail lift refers to the phenomenon that the rear wheels leave the ground and rise due to load transfer when the two-wheeled vehicle is braked in an emergency. This phenomenon often occurs when the front wheel is braked alone or the front and rear wheels are braked together. Severe tail lift can easily cause the vehicle to flip over or fall, causing injuries to the driver.

[0003] The Antilock Brake System (ABS) determines the vehicle's status by collecting wheel speeds and performing related calculations during the braking process, and then adjusts the braking force to prevent the wheels from locking and losing steering ability or tail swinging. When the vehicle is fully braked, there will be serious load transfer due to inertia, and two-wheeled vehicles are lighter, have a higher center of mass, and have a smaller front and rear wheelbase than four-wheeled vehicles, which makes it easy for two-wheeled vehicles to lift their tails during braking. If the control to prevent tail lift cannot be effectively performed, the vehicle may flip during emergency braking, which is one of the main problems affecting the safety performance of motorcycles.

[0004] At present, there are relatively few two-wheeled vehicles equipped with hydraulic ABS on the market, and the common two-wheeled hydraulic ABS is not equipped with anti-lift control function. In order to solve the problem of braking lift, the main solution of the enhanced version of ABS is to rely on the gyroscope to determine whether the rear wheel is off the ground and lifted. Summary of the invention

[0005] In order to overcome the deficiencies of the above-mentioned prior art, the present invention provides a method for detecting and suppressing tail lift of a two-wheeled vehicle based on hydraulic ABS, which detects the tail lift tendency of the two-wheeled vehicle during braking by calculating the front and rear wheel speeds and estimating the pressure difference between the front and rear wheel cylinders without relying on a gyroscope, and suppresses the tail lift by reasonable pressure control.

[0006] The technical solution adopted by the present invention is: a method for detecting and suppressing tail lift of a two-wheeled vehicle based on hydraulic ABS: the wheel speed pulse signals of the front and rear wheels are obtained respectively through the front axle wheel speed sensor and the rear axle wheel speed sensor; the ECU calculates the wheel speed signals of the front and rear wheels in real time through the wheel speed pulse signals, and further calculates the wheel acceleration signals, slip rate and vehicle acceleration signals of the front and rear wheels; when the two-wheeled vehicle brakes in an emergency, after the ABS is activated, the pressure of the front and rear wheel cylinders and the master cylinder pressure are estimated according to the increase and decrease pressure parameters of the ABS action, and then the pressure difference of the front and rear wheel cylinders is obtained; during the braking process, the vehicle deceleration, the wheel acceleration change rate and the front and rear wheel pressure difference are calculated in real time to effectively avoid bumpy roads and butted roads, and then the front and rear wheels are combined with the wheel acceleration characteristics to obtain the front and rear wheel pressure difference. The method of accurately judging the tail lift is as follows: when the vehicle is not on a bumpy road or a butted road surface, it is judged through the vehicle deceleration, the rate of change of wheel acceleration and the pressure difference between the front and rear wheels. When the wheel deceleration of the rear wheel becomes smaller and the rate of change is less than the set value, and the wheel speed difference is a positive value and greater than the set wheel speed difference, it can be judged that the vehicle is in a front axle single brake tail lift; when the wheel deceleration of the rear wheel increases sharply and the rate of change is greater than the set value, and the wheel speed difference is a negative value and less than the set wheel speed difference, it can be judged that the vehicle is in a front and rear combined brake tail lift; multiple levels of tail lift degrees are set, and according to different tail lift degrees, the corresponding front wheel decompression parameters are calculated by interpolation, and then the tail lift is suppressed by controlling the brake fluid amount of the front brake caliper.

[0007] Compared with the prior art, the present invention has the following beneficial effects: Based on the conventional two-wheeled vehicle hydraulic ABS, without adding other hardware devices, the system can effectively monitor the tail lift trend through existing equipment and devices, quickly suppress the tail lift, greatly reduce the risk of tail lift when the two-wheeled vehicle brakes, and avoid the vehicle rushing forward, saving costs and greatly improving the safety performance of two-wheeled vehicles. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 This is a schematic diagram of the force on the whole two-wheeled vehicle during braking in the present invention; Figure 2 The figure is a force diagram of the rear wheel during single front braking (left) and a schematic diagram of the characteristics of the front and rear wheel speeds (right) in the present invention; Figure 3 The figure is a force diagram of the rear wheel during combined braking (left) and a schematic diagram of the characteristics of the front and rear wheel speeds (right); Figure 4 The figure is an overall structural diagram of the braking system of the two-wheeled vehicle in the present invention; Figure 5 A diagram showing the steps for implementing the lift detection and suppression method system provided in the present invention; Among them, 1-front axle master cylinder, 2-rear axle master cylinder, 3-front oil pipe, 4-hydraulic control unit, 5-rear oil inlet pipe, 6-front axle oil outlet pipe, 7-rear axle oil outlet pipe, 8-hydraulic ABS electronic control unit, 9-front brake caliper, 10-rear brake caliper, 11-front axle wheel speed sensor, 12-front axle wheel speed sensor signal line, 13-rear axle wheel speed sensor signal line, 14-rear axle wheel speed sensor, 15-front wheel, 16-rear wheel. Implementation

[0009] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0010] The present invention collects wheel speed pulse signals of the front and rear wheels to perform a series of calculations, and establishes a pressure model for ABS control in combination with the pressure increase and decrease parameters in the control process. The vehicle is judged to be not on a bumpy road surface or a butted road surface by the vehicle deceleration and the pressure difference between the front and rear wheels, and then the vehicle's tail lift tendency is judged by combining the pressure estimated by the pressure model, the slip rate of the front and rear wheels, and the deceleration, so as to adjust the braking pressure of the front and rear wheels. During the adjustment process, the pressure model is used to limit the amplitude of the pressure increase and decrease, effectively preventing the two-wheeled vehicle from tail lift during the braking process, and timely reducing pressure to control the tail lift tendency, while avoiding excessive pressure reduction and obvious forward movement of the vehicle, and also maintaining an ideal braking deceleration.

[0011] When a two-wheeled vehicle (taking a two-wheeled motorcycle as an example) brakes, the force on the entire vehicle is as follows: Figure 1 As shown, where m is the vehicle mass, g is the acceleration of gravity, a is the braking deceleration, and F zf is the ground support force on the front wheel, F zr is the ground support force on the rear wheel, F bf is the front wheel ground braking force, F br is the rear wheel ground braking force; H is the height of the vehicle's center of mass, L is the wheelbase, L f is the horizontal distance from the front wheel to the center of mass, L r is the horizontal distance from the rear wheel to the center of mass. Taking the center of mass as the origin, Horizontal force Σx=ma, that is, F bf +F br =ma; The vertical force Σy=0, that is, F zf +F zr =mg; The moment around the origin ΣM=0, that is, F bf *L f -F br *L r -(F bf +F br )*H=0; Can get F zf =mg*Lr / L+ma*H / L; F zr =mg*L f / L-ma*H / L; When a is equal to 0, that is, static, F zf =mg*L r / L;F zr =mg*L f / L; then the load transfer during braking is F=ma*H / L. It can be concluded that the load transfer is related to the vehicle's mass m, the vehicle's deceleration a, the vehicle's wheelbase L, and the vehicle's center of gravity height H. Therefore, when the vehicle has a serious load transfer and a tendency to lift, the vehicle's deceleration needs to be limited.

[0012] First, we need to accurately identify the tail lift trend. The driving wheel of a two-wheeled vehicle is the rear wheel. There are two types of tail lift conditions: one is to brake only the front wheel; the other is to brake the front and rear wheels together. When only the front wheel is braked, the rear wheel is in a normal driving state. Figure 2 (left), F f is the rolling resistance, in N; W is the vertical load on the wheel, F z is the normal reaction force of the ground on the wheel, in N. When there is a tendency to lift, the normal reaction force and rolling resistance of the ground on the rear wheel are both 0, and the wheel speed deceleration of the rear wheel becomes smaller under the action of the inertia force torque. The specific wheel speed performance is as follows Figure 2 (Right) During the braking process of a single front axle, the wheel speeds of the front and rear wheels decrease simultaneously until the deceleration of the rear wheel decreases midway, and the positive wheel speed difference V between the rear and front wheels r -V f It becomes larger, that is, there is a tail trend.

[0013] In the case of combined front and rear braking, the rear wheel is in a braking state. During the operation of ABS, the movement of the entire wheel can be approximated as pure rolling. Figure 3 (Left), the force equation during braking is as follows: F b ≈ F u ;u a is the driving direction, F b is the ground braking force, F u is the braking force of the brake, in N; T u is the braking friction torque of the wheel, in N·m; W is the vertical load of the wheel, F z is the normal reaction force of the ground on the wheels, in N. When the car is tilting right, the ground braking force and the normal reaction force of the ground on the wheels are both 0. The rear wheel speed drops sharply under the braking force, and the deceleration increases rapidly. The negative wheel speed difference V between the rear wheel and the front wheel r -Vf It becomes smaller, that is, there is a tail trend.

[0014] When the two tail-lifting tendencies are detected, the front wheels should be decompressed to reduce the vehicle's deceleration, thereby reducing the load transfer F= ma*H / L to alleviate the tail-lifting tendencies.

[0015] The overall structure of the braking system of a two-wheeled vehicle is as follows: Figure 4 As shown, the electronic control unit (ECU) 8 of the hydraulic ABS obtains the wheel speed pulse signals of the front wheel 15 and the rear wheel 16 in real time. The wheel speed pulse signals are obtained by the front axle wheel speed sensor 11 and the rear axle wheel speed sensor 14 respectively and transmitted to the ECU by the front axle wheel speed sensor signal line 12 and the rear axle wheel speed sensor signal line 13 respectively. Through the wheel speed pulse signals, the ECU can calculate the wheel speed signals of the front and rear wheels, the wheel acceleration signals of the front and rear wheels, the slip rate and the acceleration signal of the vehicle in real time. In the case of emergency braking, after the ABS is activated, the pressure difference between the front and rear wheels is estimated according to the increase and decrease pressure parameters of the ABS action. The front axle master cylinder 1 and the rear axle master cylinder 2 of the two-wheeled vehicle can brake separately, and the brake fluid enters the hydraulic control unit 4 through the front oil pipe 3 and the rear oil pipe 5 respectively; then the ECU determines how much brake fluid is distributed to the front and rear wheels respectively through the wheel acceleration and slip rate, and the distributed brake fluid reaches the front brake caliper 9 through the front axle oil outlet pipe 6 or reaches the rear brake caliper 10 through the rear axle oil outlet pipe 7, thereby achieving effective braking. During braking, the real-time calculated vehicle deceleration and front and rear wheel pressure difference can effectively avoid bumpy roads and butted roads. Combined with the wheel acceleration characteristics of the front and rear wheels and the wheel speed difference of the front and rear wheels, it is determined whether there is a tendency of tail lift, and then the brake fluid volume of the front brake caliper 9 is controlled to suppress the tail lift.

[0016] Specifically, the entire vehicle lift detection and lift suppression process includes the following steps: S1. Initialize each ABS module In this step, ABS will detect the wheel speed signal received and the internal hydraulic unit. First, ABS will detect the wheel speed sensor signal to determine whether there is a hardware fault in the wheel speed sensor; when the vehicle reaches a speed of 5km / h, the wheel speed signal fault detection is completed, so that it can be confirmed from both hardware and signal aspects that the wheel speed signal received by ABS is credible. Then ABS will detect the pressure increasing and decreasing valve and motor to ensure that the pressure can be effectively adjusted during braking.

[0017] S2. Signal collection and real-time monitoring of vehicle status In this step, ABS captures and calculates the wheel speed signal V of the front and rear wheels through the wheel speed sensor. f and V r , the wheel acceleration a can be obtained by calculating the wheel speed signalf and a r and the vehicle's reference speed V ref , and then the slip rate S of the front and rear wheels can be calculated f and S r , the vehicle's deceleration a v By comprehensively judging the wheel acceleration and slip rate, the vehicle's logical braking signal f can be obtained. b Then, when the wheel acceleration and slip rate reach the ABS activation threshold, the ABS function is activated, and the pressure increase and decrease time during the ABS pressure adjustment process is used to estimate the pressure of the front and rear wheel cylinders and the master cylinder pressure, and then the pressure difference between the front and rear wheel cylinders is obtained.

[0018] S3, tail lift detection According to the basic characteristics of braking, high adhesion coefficient road tire locking requires high wheel cylinder pressure and high vehicle deceleration; low adhesion coefficient road tire locking requires low wheel cylinder pressure and low vehicle deceleration. Analysis shows that when the vehicle's wheelbase and center of gravity height are constant, it is the vehicle's deceleration that affects the vehicle's tail lift, and the judgment of tail lift needs to be combined with the wheel speed difference between the front and rear wheels. Actual tests show that in low adhesion coefficient road conditions and docking conditions (high adhesion coefficient road enters low adhesion coefficient road), there is also a large difference in front and rear wheel speeds. Therefore, it is necessary to avoid low adhesion coefficient road conditions and docking conditions. Combining the wheel cylinder pressure difference parameters and the vehicle's deceleration can effectively judge these two conditions and ensure that the tail lift trend can be accurately identified.

[0019] When the wheel cylinder pressure difference is small and the vehicle deceleration is large, the rear wheel deceleration and the front and rear wheel speed difference are judged in real time. r -V f When the rear wheel deceleration increases sharply and the rate of change is greater than the set value, and the wheel speed difference V r -V f When it is a negative value and is less than the set wheel speed difference, it can be determined that the vehicle is in a tail lift due to front and rear combined braking.

[0020] S4, tail lift suppression After determining the lift-off condition, according to the previous analysis, the most effective way to suppress it is to reduce the vehicle's deceleration. When the vehicle lifts, the rear wheels are off the ground, and the most effective way to reduce the vehicle's deceleration is to decompress the front wheels. Set 5 levels of lift-off degree, analyze the lift-off degree, and calculate the corresponding front wheel decompression parameters through interpolation, so as to suppress the lift-off by reasonably decompressing the front axle, while also avoiding the vehicle from jumping forward when the lift-off is suppressed.

Claims

1. A method for detecting and suppressing tail lift of a two-wheeled vehicle based on hydraulic ABS, characterized in that: The detection and suppression method comprises: The wheel speed pulse signals of the front wheels and the rear wheels are obtained respectively through the front axle wheel speed sensor and the rear axle wheel speed sensor; Through the wheel speed pulse signal, the ECU calculates the wheel speed signals of the front and rear wheels in real time, and further calculates the wheel acceleration signals, slip rate and vehicle acceleration signals of the front and rear wheels; When a two-wheeled vehicle is braked urgently and the ABS is activated, the pressure of the front and rear wheel cylinders and the master cylinder pressure are estimated based on the increase and decrease pressure parameters of the ABS action, and then the pressure difference between the front and rear wheel cylinders is obtained; During braking, real-time calculation of vehicle deceleration, wheel acceleration change rate and front and rear wheel pressure difference can effectively avoid bumpy roads and butted roads. Combined with the front and rear wheel acceleration characteristics and the front and rear wheel speed difference, it can accurately determine whether there is a tail lift trend. Set multiple levels of tail lift, calculate the corresponding front wheel decompression parameters through interpolation according to the different tail lift levels, and then suppress the tail lift by controlling the brake fluid volume of the front brake caliper.

2. A two-wheeled vehicle lift detection and suppression method based on hydraulic ABS according to claim 1, characterized in that: The method to accurately judge the tail lift is: when the vehicle deceleration, wheel acceleration change rate and front and rear wheel pressure difference are used to judge that the vehicle is not on a bumpy road or a butt road, when the wheel deceleration of the rear wheel becomes smaller and the change rate is less than the set value, and the wheel speed difference is a positive value and greater than the set wheel speed difference, it can be judged that the vehicle is in a front axle single brake tail lift; when the wheel deceleration of the rear wheel increases sharply and the change rate is greater than the set value, and the wheel speed difference is a negative value and less than the set wheel speed difference, it can be judged that the vehicle is in a front and rear combined braking tail lift.

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