An intelligent control method for compound anti-lock braking based on real-time estimation of turning angle

Abstract

A composite anti-lock braking intelligent control method based on real-time estimation of turning angle relates to the technical field of vehicle braking control, and comprises the following steps: step 1, obtaining a vehicle ABS wheel speed signal and vehicle basic parameter information; step 2, estimating the vehicle turning angle θ in real time based on the Ackerman steering principle and a two-degree-of-freedom vehicle model, and identifying the vehicle turning condition; step 3, calculating the vehicle slip rate in real time; step 4, setting the activation condition of the composite anti-lock braking control strategy according to the vehicle slip rate and the relative wheel speed of the rear wheels, if the vehicle slip rate and the relative wheel speed of the rear wheels both meet the activation condition, then executing the composite anti-lock braking control strategy, otherwise executing the conventional driving braking control strategy. The present invention can estimate the vehicle turning angle in real time according to the acquired vehicle ABS wheel speed signal and vehicle basic parameter information, and accurately identify the vehicle turning condition, thereby providing accurate data support for the calculation of the vehicle slip rate.

Description

Technical Field

[0001] The invention relates to the technical field of vehicle braking control, and in particular to a composite anti-lock braking intelligent control method based on real-time estimation of turning angle. Background Art

[0002] Braking safety is an important indicator of new energy vehicles. Unlike fuel vehicles, new energy vehicles must consider not only braking efficiency but also braking energy recovery. Its braking system includes air brakes and electric brakes for energy recovery. How to coordinate the air brake force and electric brake force to achieve anti-lock control on low-adhesion roads has become the current research focus.

[0003] The Chinese patent with publication number CN116331173A discloses a segmented composite anti-lock braking control method, which controls the distribution of pneumatic and electric brake forces according to the different openings of the brake pedal during service braking, thereby taking into account the cost of the braking system and the efficient recovery of braking energy without affecting the traditional emergency braking habits. The vehicle turning condition identification and specific turning angle measurement in the patent are realized by the steering wheel angle sensor, that is, the steering angle of the front wheel is estimated by dividing the steering wheel angle read by the sensor by the steering gear ratio, thereby further calculating the vehicle slip rate, and using the vehicle slip rate as the activation condition of the composite anti-lock braking control strategy.

[0004] However, in the field of buses, the steering wheel angle sensor is still optional. Therefore, if the vehicle is not equipped with an angle-related sensor, the vehicle turning information cannot be obtained, and the vehicle driving condition and turning angle cannot be accurately judged. However, when calculating the vehicle slip rate, if the vehicle is in a turning condition, the front axle speed needs to be corrected in real time to avoid the problem of inaccurate calculation of the vehicle slip rate caused by the front axle speed being higher than the actual speed when the vehicle turns. It can be seen that if the turning condition and turning angle of the vehicle cannot be accurately obtained, the accurate vehicle slip rate cannot be calculated, which will lead to the potential problem of misjudging the vehicle on a slippery or low-adhesion road surface due to inaccurate slip rate calculation under extreme turning conditions of the compound braking anti-lock control strategy. In addition, if only the vehicle slip rate is used as the activation condition of the compound braking anti-lock control strategy, there will be problems such as insufficient judgment basis and low safety performance. Summary of the invention

[0005] The present invention provides a composite anti-lock braking intelligent control method based on real-time estimation of turning angle, the main purpose of which is to solve the problems existing in the prior art.

[0006] The present invention adopts the following technical solution:

[0007] A composite anti-lock braking intelligent control method based on real-time estimation of turning angle comprises the following steps:

[0008] Step 1: Obtain the vehicle ABS wheel speed signal and vehicle basic parameter information;

[0009] Step 2: Real-time estimation of vehicle turning angle based on Ackerman steering principle and two-degree-of-freedom vehicle model , and identify the vehicle turning condition; vehicle turning angle The calculation formula is:

[0010]

[0011] Where: is the vehicle wheelbase; is the relative wheel speed of the left front wheel; is the relative wheel speed of the right front wheel; is the front axle speed; is the front axle wheelbase; is the rear axle wheelbase;

[0012] Step 3: Calculate the vehicle slip rate in real time according to the following formula:

[0013]

[0014] Where: is the vehicle slip rate; is the longitudinal component of the front axle speed; is the relative wheel speed of the rear axle calculated based on the motor speed.

[0015] Step 4: setting activation conditions of the compound anti-lock braking control strategy according to the vehicle slip rate and the rear wheel relative speed; if the vehicle slip rate and the rear wheel relative speed both meet the activation conditions, the compound anti-lock braking control strategy is executed; otherwise, the conventional driving brake control strategy is executed;

[0016] The activation conditions of the compound anti-lock braking control strategy are:

[0017]

[0018] Where: is the relative wheel speed of the left rear wheel; is the relative wheel speed of the right rear wheel; Setting a threshold for the rear wheel relative speed; Sets the threshold for slip rate control anti-lock braking.

[0019] Further, in step 2, the method for identifying the vehicle turning condition is: when the vehicle state satisfies the following two criteria at the same time, the vehicle is determined to be in a turning condition; otherwise, the vehicle is determined to be in a straight-ahead condition or the steering function is not working stage:

[0020] a. Vehicle turning angle Greater than the set threshold Or the absolute value of the relative speed difference between the inner and outer wheels of the front axle Exceeding the set threshold , and duration Greater than the set threshold ;

[0021] b. Front axle speed The vehicle speed is greater than the minimum threshold set for the compound braking function to be activated. .

[0022] Further, in step 3, the longitudinal component of the front axle speed Available front axle speed and vehicle turning angle The calculation formula is:

[0023] .

[0024] Furthermore, in step 3, the vehicle controller calculates the relative wheel speed of the rear axle according to the motor speed n , and its calculation formula is:

[0025] Where: is the motor speed; is the rear axle main reduction ratio; is the wheel rolling radius.

[0026] Furthermore, the calculation formula of the vehicle slip rate is:

[0027]

[0028] Further, in step 3, the compound anti-lock braking control strategy is as follows:

[0029]

[0030] Where: is the brake pedal opening; and Thresholds set for the segmented compound anti-lock braking control strategy.

[0031] further, The threshold is set at 40%. The threshold is set at 55%.

[0032] Furthermore, in step 1, the vehicle ABS wheel speed signal is obtained through the vehicle ABS wheel speed sensor, the vehicle basic parameter information is obtained through the vehicle controller, and the obtained vehicle ABS wheel speed signal and vehicle basic parameter information are filtered and the validity is judged through the vehicle controller.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] 1. The present invention provides a vehicle turning angle estimation method based on Ackerman steering and a two-degree-of-freedom vehicle model. The method can estimate the vehicle turning angle in real time according to the acquired vehicle ABS wheel speed signal and vehicle basic parameter information. , and accurately identify the vehicle's turning conditions, thereby providing accurate data support for the calculation of the vehicle's slip rate, thereby overcoming the reliance of the vehicle's turning angle measurement on the steering wheel angle sensor in the prior art, which is beneficial to reducing the manufacturing cost of the vehicle and improving the vehicle's braking safety and economy.

[0035] 2. Based on the compound anti-lock braking control strategy adjusted according to the vehicle slip rate, the present invention simultaneously introduces the rear wheel relative speed signal and sets a certain threshold as the activation condition of the electronic anti-lock braking control, thereby improving the accuracy and redundant safety of the compound anti-lock braking control.

[0036] 3. The present invention provides a low-cost, easy-to-promote, and high-engineering-value composite anti-lock braking intelligent control system, and designs a segmented composite anti-lock braking control strategy, which can prevent wheel locking while ensuring efficient braking energy recovery, thereby improving the braking stability of the vehicle. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is a control flow chart of the present invention.

[0038] Figure 2 This is a diagram of an ideal vehicle steering model in the present invention.

[0039] Figure 3 This is the two-degree-of-freedom vehicle steering model in the present invention.

[0040] Figure 4 This is a flow chart of the composite anti-lock braking control strategy of the present invention. DETAILED DESCRIPTION

[0041] The specific implementation of the present invention is described below with reference to the accompanying drawings. In order to fully understand the present invention, many details are described below, but for those skilled in the art, the present invention can be implemented without these details.

[0042] The present invention discloses a composite anti-lock braking intelligent control method based on real-time estimation of turning angle. In order to more clearly explain the design concept of the control method, this embodiment takes a rear-mounted rear-wheel drive 4x2 central drive pure electric bus as an example to explain the control method in detail. However, the control method is also applicable to pure electric vehicles with other configurations such as rear single tire (2x2). The process of composite anti-lock braking intelligent control based on real-time estimation of turning angle of real-time road conditions is shown in Figure 1 , during the service braking process, the specific implementation steps are as follows:

[0043] Step 1: Obtain the vehicle ABS wheel speed signal and vehicle basic parameter information.

[0044] Specifically, the vehicle ABS wheel speed signal includes the front axle speed , Left front wheel relative speed , Relative wheel speed of left rear wheel , right front wheel relative speed Relative wheel speed to right rear wheel , obtained through the vehicle ABS wheel speed sensor. The basic vehicle parameter information includes motor speed , Vehicle wheelbase , front wheelbase and rear axle wheelbase Etc., obtained through the vehicle controller.

[0045] In order to improve the accuracy of the signal, this step also requires the vehicle controller to filter and determine the effectiveness of the collected wheel speed signal and motor speed signal. The specific processing method and determination method can be implemented based on the existing technology and will not be elaborated here.

[0046] Step 2: Real-time estimation of vehicle turning angle based on Ackerman steering principle and two-degree-of-freedom vehicle model , and identify the vehicle turning condition, vehicle turning angle The calculation formula is:

[0047]

[0048] Where: is the vehicle wheelbase; is the relative wheel speed of the left front wheel; is the relative wheel speed of the right front wheel; is the vehicle front axle speed; is the front axle wheelbase; is the rear axle wheelbase.

[0049] Step 2.1: Real-time estimation of vehicle turning angle based on Ackerman steering principle and two-degree-of-freedom vehicle model .

[0050] When the vehicle turns at medium or low speed, the lateral acceleration is very small. At this time, it can be approximately considered that the vehicle satisfies the Ackerman steering model. The vertical lines of the inner and outer wheel turning angles of the ideal Ackerman steering trapezoid intersect at the extension line of the rear axle. The intersection is the instantaneous steering center, which achieves stability and smoothness of the vehicle when turning. Figure 2 The ideal Ackerman steering trapezoid ignores the effect of the suspension, assumes that the wheel is an absolute rigid body, and assumes that the tire side slip characteristics are linear. At the same time, it is assumed that when the car turns, all wheels roll around the steering center at a certain angular velocity. Driving.

[0051] The formula for the turning radius of each wheel and the center of mass, the vehicle speed, and the vehicle rotation angular velocity is:

[0052]

[0053] Where: is the turning radius of the left front wheel; is the turning radius of the right front wheel; is the left front wheel speed; is the right front wheel speed; It is the angular velocity of the vehicle around the instantaneous turning center, that is, the angular velocity of the vehicle's rotation.

[0054] In the vehicle, the vehicle controller obtains the front axle speed collected by the ABS wheel speed sensor , Left front wheel relative speed and right front wheel relative speed , the absolute value of the relative wheel speed difference between the inner and outer wheels of the front axle is expressed as , then the vehicle's angular velocity The calculation formula is:

[0055]

[0056] Where: It is the difference between the rotation radius of the left and right wheels of the vehicle.

[0057] Relative wheel speed difference between inner and outer wheels of front axle The calculation formula is:

[0058]

[0059] Buses usually turn at low to medium speeds. During a turn, the outer wheel speed is greater than the inner wheel speed, and the front wheel speed is greater than the rear wheel speed. According to the Ackerman steering four-link structure, the steering angle of the inner wheel is slightly larger than that of the outer wheel, usually 2 to 4 degrees larger. Through trigonometric functions, the difference in the rotation radius of the left and right wheels of the vehicle is It can be simplified to the following formula:

[0060]

[0061] Where: is the front axle wheelbase; is the rear axle wheelbase.

[0062] Under steady-state steering conditions, in vehicle steering analysis, the angle turned by the center of the vehicle can be equal to the average of the left and right wheel angles, that is:

[0063]

[0064] Where: is the left front wheel rotation angle, is the rotation angle of the right front wheel; is the rotation angle corresponding to the center of the front axle, that is, the required turning angle of the vehicle.

[0065] In vehicle steering analysis, the present invention simplifies the complex four-wheel system into a two-degree-of-freedom vehicle model, such as Figure 3 The vehicle is simplified into two wheels. At this time, the vehicle has only two degrees of freedom: lateral motion and yaw motion, which is suitable for dynamic analysis of low-speed driving. Based on the following approximations and assumptions:

[0066] A. Ignoring the vertical motion and coupling of the vehicle, it is assumed that the vehicle moves in a two-dimensional plane.

[0067] B. Assume that the vehicle is traveling at a relatively slow speed and ignore the transfer of loads between the front and rear axles;

[0068] C. Assume that the vehicle structure is rigid;

[0069] D. Ignore the influence of the steering system and take the front wheel angle as input;

[0070] E. Ignore the effect of the suspension and assume that the vehicle only moves in a plane parallel to the ground, lateral motion on the y-axis and yaw motion around the z-axis.

[0071] After simplification, based on the principle of trigonometric function, the vehicle wheelbase and the vehicle front axle center turning radius are Bring in:

[0072]

[0073] In the formula, , are the distances from the vehicle's center of mass to the front and rear axles, respectively; is the vehicle wheelbase; It is the rotation radius of the vehicle's front axle center.

[0074] From formula 1.6, we can know that in order to solve the vehicle turning angle First, we must find the front axle center rotation radius Combining the above steps, we can see that according to the vehicle rotation angular velocity and front axle speed The rotation radius of the vehicle's front axle center can be calculated , so combining formulas (1.2), (1.3) and (1.4) yields:

[0075]

[0076] Furthermore, the vehicle turning angle can be calculated by combining equations (1.6) and (1.7) The calculation formula is:

[0077]

[0078] Step 2.2: The vehicle controller identifies the vehicle turning condition according to the established steering judgment standard.

[0079] Finding the vehicle turning angle After that, the vehicle controller can identify the vehicle turning condition. Specifically, the steering judgment standard formulated in this implementation is:

[0080] a. Vehicle turning angle Greater than the set threshold Or the absolute value of the relative speed difference between the inner and outer wheels of the front axle Exceeding the set threshold , and duration Greater than the set threshold ;

[0081] b. Front axle speed The vehicle speed is greater than the minimum threshold set for the compound braking function to be activated. .

[0082] When the vehicle state meets the above two criteria at the same time, the vehicle is judged to be in a turning condition, otherwise it is judged to be in a straight-ahead condition or the steering function is not working. That is, the judgment criteria for the vehicle being in a turning condition are:

[0083]

[0084] It can be seen that the vehicle turning angle can be calculated based on the Ackerman steering principle and the two-degree-of-freedom vehicle model. The calculation formula is as follows, and the vehicle turning angle can be estimated in real time based on the vehicle ABS wheel speed signal and vehicle basic parameter information obtained in step 1. , thereby providing accurate data support for the identification of vehicle turning conditions, thereby overcoming the reliance of the vehicle turning angle measurement on the steering wheel angle sensor in the prior art, and helping to reduce the manufacturing cost of the entire vehicle.

[0085] Step 3: Calculate the vehicle slip rate in real time according to the following formula:

[0086]

[0087] In the formula, is the vehicle slip rate; Front axle speed longitudinal component; Rear axle relative wheel speed calculated from the motor speed.

[0088] When the vehicle controller determines that the vehicle is in the process of turning, it will adjust the front axle speed Real-time correction is performed to avoid the problem that the front axle speed is higher than the actual speed when the vehicle is turning, which leads to inaccurate slip rate calculation. The longitudinal component of the front axle speed of the whole vehicle Available front axle speed and vehicle turning angle Calculated, that is:

[0089]

[0090] When the vehicle controller determines that the vehicle is moving straight, The longitudinal speed is the front axle speed collected by the ABS wheel speed sensor. .

[0091] The vehicle controller calculates the relative wheel speed of the rear axle according to the motor speed n obtained in step 1 , the formula is:

[0092]

[0093] Where: is the motor speed; is the rear axle main reduction ratio; is the wheel rolling radius.

[0094] Combining formulas (3.1) to (3.3), the formula for calculating the vehicle slip rate is:

[0095]

[0096] Step 4: Set the activation condition of the compound anti-lock braking control strategy according to the vehicle slip rate and the relative wheel speed of the rear wheels. If the vehicle slip rate and the relative wheel speed of the rear wheels both meet the activation conditions, the compound anti-lock braking control strategy is executed, otherwise the conventional driving brake control strategy is executed.

[0097] Step 4.1: Set the activation condition of the compound anti-lock braking control strategy according to the vehicle slip rate and the relative wheel speed of the rear wheels.

[0098] The composite anti-lock braking control strategy of the present invention is adjusted according to the real-time slip rate of the vehicle, and the relative wheel speed of the rear wheels (including the relative wheel speed of the left rear wheel) is synchronously introduced. Relative wheel speed to right rear wheel ), a certain threshold is set as the activation condition of the compound anti-lock braking control strategy to improve the accuracy and redundant safety of the compound anti-lock braking control.

[0099] Specifically, the activation condition of the composite anti-lock braking control strategy set in this embodiment is: when the absolute value of vehicle slip is Greater than the set threshold The vehicle slips more and more seriously, and the absolute value of the relative speed of the rear wheels (i.e. the absolute value of the relative speed of the left rear wheel) Or the absolute value of the right rear wheel speed ) is greater than the set threshold , the vehicle is judged to be on a low-adhesion road surface and the compound braking function is activated; otherwise, the vehicle is judged not to be on a low-adhesion road surface and the conventional driving brake control strategy is executed.

[0100] The activation conditions of the compound anti-lock braking control strategy are as follows:

[0101]

[0102] Where: Setting a threshold for the rear wheel relative speed; Thresholds are set for slip rate control anti-lock braking. The specific values ​​of the two set thresholds can be determined by low-attachment calibration and are not explicitly defined here.

[0103] Step 4.2: Compound anti-lock braking control strategy.

[0104] The segmented composite anti-lock braking control strategy of the present invention is formulated according to the brake pedal opening and the air brake intervention, with the goal of maximizing electric brake energy recovery.

[0105] Specifically, based on the fixed pedal opening-air brake pressure relationship curve, the brake pedal is designed with a certain amount of idle travel. Therefore, in the idle travel stage, the air brake force does not intervene in the brake control, and the motor is used for anti-lock control, so that the electric recovery can be maximized on the basis of ensuring the low-adhesion controllable state; after the electric brake force reaches the maximum, the air brake force begins to cooperate with the electric brake force to participate in the braking process.

[0106] Reference Figure 4 The composite anti-lock braking control strategy adopts segmented braking control according to the brake pedal opening size, which is divided into anti-lock control under small opening, anti-lock control under medium opening and anti-lock control under large opening:

[0107] (1) Anti-lock control at small opening: At this stage, the compound braking control is completely realized by electric braking, that is, at this stage, the vehicle controller performs anti-lock control on low-adhesion roads according to the vehicle slip rate and the relative wheel speed of the rear wheels to prevent the vehicle from locking, skidding and drifting.

[0108] (2) Anti-lock control at medium opening: The vehicle's composite brake anti-lock control is controlled by electric brake and pneumatic brake together, and the pneumatic brake ABS controls the vehicle's anti-lock function. In this stage, the vehicle controller synchronously adjusts the electric brake to control the vehicle's slip rate, thereby preventing the vehicle from locking, sliding, and drifting. According to the pedal opening size and the air brake intervention, the pedal opening threshold of the gas-electric hybrid stage is set The setting of this threshold is determined based on the calibration of the low-attachment test field to avoid the threshold being set too small, which may cause the air brake to provide insufficient deceleration and lead to braking forward; at the same time, avoid the threshold being set too large, which may cause the air-electric hybrid stage to be lengthened, affecting the control effect of the compound brake.

[0109] (3) Anti-lock control at large opening: At this time, the air brake plays a major role. When the ABS is activated on low-adhesion roads, the electric brake removes torque at a fixed slope according to the ABS activation flag to ensure the braking effect and stability of the vehicle on low-adhesion roads.

[0110] Therefore, the segmented compound anti-lock braking control strategy is set as follows:

[0111]

[0112] Where: is the brake pedal opening; and Thresholds set for the segmented compound anti-lock braking control strategy.

[0113] Preferably, The threshold is set at 40%. The threshold is set to 55%. In the application, and The value of is adjusted according to the actual vehicle pedal idle travel and the vehicle deceleration that the air brake can provide under the threshold state. Assume that the corresponding opening of the pedal design theoretical idle travel is , The corresponding brake pedal opening is when the air brake does not intervene in the braking process. According to the difference between the driving state and the stationary state, there are usually Slightly less than .

[0114] 4.3 Conventional driving brake control strategy

[0115] Conventional driving brake control strategy means that the vehicle controller outputs the corresponding braking torque in real time based on the real-time vehicle speed and brake pedal opening according to the system's built-in brake MAP diagram, and does not actively adjust or intervene based on the slip rate.

[0116] The above is only a specific implementation of the present invention, but the design concept of the present invention is not limited thereto. Any non-substantial changes to the present invention using this concept shall be deemed as an infringement of the protection scope of the present invention.

Claims

1. An intelligent control method for compound anti-lock braking based on real-time estimation of turning angle, characterized in that: The steps include: Step 1: Obtain the vehicle ABS wheel speed signal and vehicle basic parameter information; Step 2: Real-time estimation of vehicle turning angle based on Ackerman steering principle and two-degree-of-freedom vehicle model , and identify the vehicle turning condition; vehicle turning angle The calculation formula is: Where: is the vehicle wheelbase; is the relative wheel speed of the left front wheel; is the relative wheel speed of the right front wheel; is the front axle speed; is the front axle wheelbase; is the rear axle wheelbase; The method for identifying the vehicle turning condition is as follows: when the vehicle state satisfies the following two criteria at the same time, the vehicle is determined to be in a turning condition; otherwise, the vehicle is determined to be in a straight-ahead condition or the steering function is not working stage: a. Vehicle turning angle Greater than the set threshold Or the absolute value of the relative speed difference between the inner and outer wheels of the front axle Exceeding the set threshold , and duration Greater than the set threshold ; b. Front axle speed The vehicle speed is greater than the minimum speed threshold set for compound braking function activation. ; Step 3: Calculate the vehicle slip rate in real time according to the following formula: Where: is the vehicle slip rate; is the longitudinal component of the front axle speed; is the relative wheel speed of the rear axle calculated according to the motor speed; Step 4: Set the activation conditions of the compound anti-lock braking control strategy according to the vehicle slip rate and the relative wheel speed of the rear wheels. If the vehicle slip rate and the relative wheel speed of the rear wheels both meet the activation conditions, the compound anti-lock braking control strategy is executed, otherwise the conventional driving brake control strategy is executed; the activation conditions of the compound anti-lock braking control strategy are: Where: is the relative wheel speed of the left rear wheel; is the relative wheel speed of the right rear wheel; Setting a threshold for the rear wheel relative speed; Sets the threshold for slip rate control anti-lock braking.

2. The intelligent control method for compound anti-lock braking based on real-time estimation of turning angle according to claim 1, characterized in that: In step 3, the longitudinal component of the front axle speed Using front axle speed and vehicle turning angle The calculation formula is: 。 3. The intelligent control method for compound anti-lock braking based on real-time estimation of turning angle according to claim 2, characterized in that: In step 3, the vehicle controller calculates the relative wheel speed of the rear axle according to the motor speed n , and its calculation formula is: Where: is the motor speed; is the rear axle main reduction ratio; is the wheel rolling radius.

4. The intelligent control method for compound anti-lock braking based on real-time estimation of turning angle according to claim 3, characterized in that: The calculation formula of vehicle slip rate is: 。 5. The intelligent control method for compound anti-lock braking based on real-time estimation of turning angle according to claim 1, characterized in that: In step 3, the compound anti-lock braking control strategy is as follows: Where: is the brake pedal opening; and Thresholds set for the segmented compound anti-lock braking control strategy.

6. The intelligent control method for compound anti-lock braking based on real-time estimation of turning angle according to claim 5, characterized in that: The threshold is set at 40%. The threshold is set at 55%.

7. The intelligent control method for compound anti-lock braking based on real-time estimation of turning angle according to claim 1, characterized in that: In step 1, the vehicle ABS wheel speed signal is obtained through the vehicle ABS wheel speed sensor, the vehicle basic parameter information is obtained through the vehicle controller, and the vehicle ABS wheel speed signal and vehicle basic parameter information obtained are filtered and judged for validity through the vehicle controller.

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