CN112721896B - Estimation method of hydraulic pressure in master cylinder of IEHB system based on displacement pressure model - Google Patents

Abstract

The invention relates to a method for estimating hydraulic pressure of a master cylinder of an IEHB system based on a novel displacement pressure model, comprising the steps of: 1) testing the displacement pressure characteristics of the IEHB system; 2) performing polynomial fitting on the displacement pressure characteristics of the IEHB system; 3) establishing A new displacement pressure model based on rack speed compensation; 4) Estimating the master cylinder hydraulic pressure of the IEHB system according to the established new displacement pressure model based on rack speed compensation. Compared with the prior art, the present invention has the advantages of high estimation accuracy, strong versatility and the like.

Description

Estimation method of hydraulic pressure in master cylinder of IEHB system based on displacement pressure model

technical field

The invention relates to the technical field of automobile brake-by-wire, in particular to a method for estimating hydraulic pressure of a master cylinder of an IEHB system based on a displacement pressure model.

Background technique

The Integrated Electro Hydraulic Braking (IEHB) system integrates the servo electric booster with the master cylinder. While ensuring the overall compact structure, the combined hydraulic adjustment unit can quickly and accurately adjust the output. Brake pressure, and can more easily integrate the above-mentioned new vehicle active safety functions. Because the IEHB system has the ability of decoupling the hydraulic pressure of the main and wheel cylinders and the function of active pressure building, it can maximize the braking energy recovery of electric vehicles and the AEB (Autonomous emergency braking, automatic braking system), ACC (Adaptive braking system) of intelligent driving vehicles. Cruise control, adaptive cruise control system) and other automatic driving functions, the IEHB system has become the development trend of future automotive braking systems. At present, the mass-produced IEHB systems are equipped with a master cylinder hydraulic pressure sensor to realize feedback control of the master cylinder hydraulic pressure, but at the same time increase the product cost and the risk of sensor failure. Some IEHB systems use two master cylinder hydraulic pressure sensors for mutual inspection to solve the problem of sensor failure detection and backup, but further increase the system cost.

In order to improve the sensor failure safety of the IEHB system without increasing the cost as much as possible and ensure the product market competitiveness, the master cylinder hydraulic pressure estimation algorithm is particularly important. At present, the research on the IEHB system at home and abroad mainly focuses on the configuration design and the hydraulic pressure control of the master cylinder and the wheel cylinder. The displacement pressure characteristic of , and then use this polynomial (static model) to estimate the master cylinder hydraulic pressure in real time. Since the displacement pressure characteristic has hysteresis characteristics, and the polynomial fitting represents the average value of the increase and decrease . To this end, a possible method is to fit the pressure-increasing process and the decompression process of the displacement pressure characteristics respectively, but this method will have a sudden change in the estimated value of hydraulic pressure during the conversion of pressure-increase and pressure-reduction. To sum up, it is of great significance to develop the hydraulic pressure estimation of the master cylinder of the IEHB system. In addition, the core difficulty of hydraulic pressure estimation, that is, the accurate modeling of displacement pressure characteristics needs to be further improved.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a method for estimating the hydraulic pressure of the master cylinder of the IEHB system based on the displacement pressure model in order to overcome the above-mentioned defects of the prior art.

The object of the present invention can be realized through the following technical solutions:

The method for estimating the hydraulic pressure of the master cylinder of the IEHB system based on the displacement pressure model includes the following steps:

S1: Test the displacement-pressure characteristics of the IEHB system. The displacement pressure characteristic of the IEHB system refers to the relationship between the rack displacement and the hydraulic pressure of the master cylinder. Usually, the larger the rack displacement, the larger the hydraulic pressure, but the displacement pressure characteristics are affected by many factors, such as speed, temperature, etc., and there is a hysteresis characteristic, that is, there is nonlinearity and uncertainty, so the actual processing difficulty is how to Accurately model displacement pressure characteristics. Among them, in addition to the literal meaning, the rack displacement also includes the angular position of the motor or the compression volume of the IEHB system, which is only a physical quantity that differs from the rack displacement by a fixed coefficient.

S2: Fitting IEHB displacement-pressure characteristics based on polynomials.

Further, polynomial fitting was performed on the tested IEHB displacement-pressure characteristics according to the least squares method. The specific degree of the polynomial is not limited.

S3: Establish a displacement pressure model based on rack speed compensation. specifically:

The item containing the rack speed is added to the polynomial fitting result obtained in step S2 to establish a displacement pressure model. The specific form of the item including the rack speed is not limited.

The form of the speed influencing factor has a common property, that is, it is zero during pressure increase and pressure conversion (that is, to ensure a smooth transition) and can describe the law that the actual hydraulic pressure deviates from the average value when the speed increases. Therefore, the present invention adds items related to the rack speed in the polynomial fitting result to establish a displacement pressure model.

The expression of the displacement pressure model is:

为齿条速度，k为系数，可依据试验数据进行标定。In the formula: p _m is the hydraulic pressure of the main cylinder, the unit is bar; x _r is the rack displacement, the unit is mm; A, B, C, D are the polynomial coefficients;

is the rack speed, and k is the coefficient, which can be calibrated according to the test data.

S4: Estimate the hydraulic pressure of the IEHB master cylinder according to the displacement pressure model established in S3. specifically:

According to the displacement pressure model established in step S3, the displacement of the rack and the speed of the rack are used as inputs to estimate the hydraulic pressure of the master cylinder.

Compared with the prior art, the displacement pressure model and the IEHB system master cylinder hydraulic pressure estimation method provided by the present invention at least include the following beneficial effects:

1) Compared with the traditional model, the present invention increases the speed factor, which can describe the influence law of the speed on the displacement and pressure characteristics, thereby improving the accuracy, and ensuring a smooth transition during the pressure increase and pressure reversal, and the hydraulic pressure estimation accuracy can be improved by 32.2 %.

2) Compared with the traditional model, the present invention only adds a speed compensation item, which is simple and practical, easy to implement in software and easy to debug. For hardware, such as a controller, it is easy to calculate, that is, under the situation that the calculation burden of the controller is hardly increased, A small adjustment in the software can significantly improve the hydraulic pressure estimation accuracy.

3) The dynamic model proposed in the present invention can also be used to describe the relationship between other variables (not limited to displacement pressure characteristics) with hysteresis characteristics and velocity influence characteristics, and the proposed displacement pressure model and IEHB master cylinder hydraulic pressure estimation method is reasonable Feasible, typical and universal.

Description of drawings

Fig. 1 is the main structural schematic diagram of the IEHB system adopted in the embodiment;

The labels in Figure 1 show:

1. Electronic control unit, 2. Permanent magnet synchronous motor, 3. Reduction transmission mechanism, including worm gear and rack and pinion, 4. Liquid storage tank, 5. Normally open solenoid valve, 6. Hydraulic pressure sensor, 7. Brake Wheel cylinder, 8. Brake master cylinder, 9. Decoupling cylinder, 10. Pedal simulator, 11. Pedal displacement sensor, 12. Brake pedal;

2 is a schematic diagram of the principle of an IEHB system master cylinder hydraulic pressure estimation method based on a displacement pressure model in an embodiment;

Fig. 3 is the test result of the displacement pressure characteristic under the test under two groups of normal driving conditions in the embodiment;

Fig. 4 is the polynomial fitting result of the displacement pressure characteristic in the embodiment;

Fig. 5 is the actual vehicle test result of the hydraulic pressure estimation of the master cylinder under normal driving conditions in the embodiment, wherein Fig. 5(a) is the braking test result of about 3 bar, and Fig. 5(b) is the braking test result of about 7 bar , Figure 5(c) is the result of the braking test at about 11bar, Figure 5(d) is the result of the braking test at about 15bar, and Figure 5(e) is the result of the braking test at about 30bar.

Detailed ways

The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. Obviously, the described embodiments are some, but not all, embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work shall fall within the protection scope of the present invention.

Example

The present invention relates to a method for estimating the hydraulic pressure of the main cylinder of the IEHB system based on the displacement pressure model. The main structure of the IEHB system adopted in this embodiment is shown in Figure 1, which includes:

Brake pedal unit: including brake pedal 12 assembly, reflecting the driver's driving intention;

Active pressure building unit: including a motor (permanent magnet synchronous motor 2 in this embodiment), a worm gear and a rack and pinion (reduction transmission mechanism 3 in this embodiment), to convert the rotational torque of the motor into the rack the translational thrust, thereby pushing the master cylinder to generate the corresponding brake fluid pressure;

Brake execution unit: including a brake master cylinder 8, a brake wheel cylinder 7, a solenoid valve (normally open solenoid valve 5 in this embodiment), a liquid storage tank 4 and a hydraulic pipeline, which are used to connect the active pressure building unit gears. The thrust on the strip is converted into the hydraulic pressure of each wheel cylinder, and finally the friction pad at the end of the brake wheel cylinder acts on the brake disc to generate the corresponding braking torque;

Control unit: including IEHB controller (electronic control unit 1 in this embodiment), hydraulic pressure sensor 6, pedal displacement sensor 11, pedal force sensor (pedal simulator 10 in this embodiment) and related circuits for After obtaining the pedal force and pedal stroke signals, the driver's braking intention is calculated, the target braking pressure is calculated, and the target motor torque is calculated through the feedback signal of the pressure sensor to realize the pressure closed-loop control.

For the above-mentioned IEHB system, the specific implementation steps of the method for estimating the hydraulic pressure of the master cylinder of the IEHB system based on the displacement pressure model of the present invention are as follows:

Step 1: In order to study the displacement and pressure characteristics under normal working conditions, the data of the displacement of the IEHB rack and the hydraulic pressure of the master cylinder under normal driving conditions are collected through the real vehicle test. The parameters of the test vehicle equipped with IEHB are shown in Table 1. The test section is an ordinary urban highway of about 10km in Shanghai. The test results of displacement and pressure characteristics are shown in Figure 3, including two groups. Each set of tests corresponds to a mileage of 10 km, so the test data contains multiple brakings. In addition, it can be seen from the test data that under normal driving conditions, the statistical data of the displacement and pressure characteristics of the two tests have little change. Under normal driving conditions, the hydraulic pressure generally does not exceed 30bar, and from the density of data points, it can be found that the brake pressure is more concentrated in the low pressure area of 0-15bar. Five sets of data about about 11 bar, about 15 bar and about 30 bar are verified to fully illustrate the effectiveness of the present invention.

Table 1 Test vehicle parameters

Step 2: Using the first set of test data, select a cubic polynomial to fit the displacement and pressure characteristics of the IEHB system. The fitting result is shown in Figure 4, and the cubic polynomial is shown in equation (1).

Among them, p _m is the hydraulic pressure of the main cylinder, the unit is bar; x _r is the rack displacement, the unit is mm. A, B, C, and D are polynomial coefficients, and their values are as shown in formula (2):

According to the principle of least squares fitting, the values of A, B, C, and D are directly obtained from the data points of the test, and they need to satisfy: the sum of the squares of the distances between all the test data points and formula (1) is minimized.

Step 3. Considering the motion state of the rack during the braking process, it is not difficult to find that, regardless of pressure increase or decompression, when the difference between the actual hydraulic pressure and the static model is large, it often corresponds to a larger rack speed; , When decompressing and reversing, the difference between the actual hydraulic pressure and the static model gradually decreases to zero and then increases in the opposite direction, which is also consistent with the changing law of the rack speed. That is, the error between the actual hydraulic pressure and the static model is positively related to the rack speed. Therefore, the present invention proposes a new displacement pressure model as shown in formula (3):

为齿条速度；系数k可依据试验数据进行标定。式(3)表明，新型的位移压力模型不但能体现位移压力特性受制动速度的影响规律，在增减压换向时也能平稳过渡。即增减压换向时，速度因子减小后反向增大，相当于动态模型与静态模型的差值也是减小后反向增大，而静态模型是连续的且输入输出一一对应，因此静态模型本身是平滑过渡的，而在动态模型增减压转化的一瞬间，速度影响因子为零，和静态模型相同，因此可以实现平滑过渡。in,

is the rack speed; the coefficient k can be calibrated according to the test data. Equation (3) shows that the new displacement pressure model can not only reflect the influence law of the displacement pressure characteristics by the braking speed, but also can make a smooth transition when the pressure and pressure are reversed. That is to say, when the pressure and pressure are reversed, the speed factor decreases and then increases in the opposite direction, which is equivalent to the difference between the dynamic model and the static model also decreases and then increases in the opposite direction, while the static model is continuous and the input and output are in one-to-one correspondence. Therefore, the static model itself has a smooth transition, and at the moment when the dynamic model increases and decreases the pressure, the speed influence factor is zero, which is the same as the static model, so a smooth transition can be achieved.

In addition, it is found through experiments that when the pressure difference between the actual pressure and the static model is large, the rack speed is often larger. Therefore, the speed factor added in the present invention can also characterize this characteristic, thereby improving the pressure estimation accuracy.

Step 4. According to the established displacement pressure model, in a real vehicle, the hydraulic pressure of the master cylinder can be estimated in real time by using the rack position and the rack speed.

In order to verify the validity of the proposed model, the displacement pressure model and the traditional static displacement pressure model were calibrated through the first set of test data, and verified through the second set of test data, and the estimated effects under different hydraulic pressures were selected for specific analysis. As shown in Figures 5(a) to 5(e). Among them, Figure 5(a) is the braking test result of about 3bar, Figure 5(b) is the braking test result of about 7bar, Figure 5(c) is the braking test result of about 11bar, and Figure 5(d) is The result of the braking test at about 15bar, Figure 5(e) is the result of the braking test at about 30bar.

It can be seen that due to the addition of rack speed compensation, the new model has higher response speed and hydraulic pressure estimation accuracy at the beginning and end of each braking than the traditional static model; Maintaining a smooth transition, the RMS value of the overall hydraulic pressure estimation error is 1.28 bar, which is 32.2% lower than the traditional model's 1.89 bar.

The above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited to this. Any person familiar with the technical field can easily think of various equivalents within the technical scope disclosed by the present invention. Modifications or substitutions should be included within the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims (4)

1. The IEHB system master cylinder hydraulic pressure estimation method based on displacement pressure model is characterized in that, comprises the following steps: 1) Test the displacement pressure characteristics of the IEHB system; 2) Polynomial fitting of the displacement and pressure characteristics of the IEHB system; 3) Establish a displacement pressure model based on rack speed compensation; 4) Estimate the hydraulic pressure of the master cylinder of the IEHB system according to the established displacement pressure model based on rack speed compensation; The specific content of step 3) is: In the polynomial fitting result obtained in step 2), the item containing the rack speed is added to establish a displacement pressure model; the item containing the rack speed is the parameter related to the rack speed in the IEHB system; The expression of the displacement pressure model is:

In the formula: p _m is the hydraulic pressure of the main cylinder, x _r is the rack displacement,

is the rack speed, A, B, C, D are the polynomial coefficients, and k is the coefficient. 2 . The method for estimating the hydraulic pressure of the master cylinder of the IEHB system based on the displacement pressure model according to claim 1 , wherein the displacement pressure characteristics of the IEHB system are the displacement of the rack of the IEHB system and the hydraulic pressure of the master cylinder of the IEHB system. 3 . The relationship between. 3. The method for estimating the hydraulic pressure of the main cylinder of the IEHB system based on the displacement pressure model according to claim 1, in step 2), polynomial fitting is performed on the displacement pressure characteristics of the tested IEHB system according to the least square method. 4. the IEHB system master cylinder hydraulic pressure estimation method based on displacement pressure model according to claim 1, the concrete content of step 4) is: According to the displacement pressure model established in step 3), the displacement of the rack and the speed of the rack are used as inputs to estimate the hydraulic pressure of the master cylinder.

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