An electro-hydraulic composite brake torque compensation method based on fuzzy control

Abstract

The application provides an electro-hydraulic composite brake torque compensation method based on fuzzy control and belongs to the field of new energy vehicle control. The method mainly comprises the following steps: firstly, solving the brake intensity and the required total brake torque; solving the required hydraulic brake torque and the required motor regenerative brake torque; calculating the difference between the required hydraulic brake torque and the actual hydraulic brake torque, and the difference between the required total brake torque and the actual total brake torque; superimposing the differences to the torque compensation module to perform the electro-hydraulic brake torque coordination control of the variable motor brake force; obtaining the change relationship between the reserved available motor brake torque and the brake intensity in a certain range by using the fuzzy control algorithm, adjusting the dynamic coordination coefficient, outputting the motor compensation torque, and controlling the final motor brake torque. The method improves the brake hysteresis effect of the hydraulic brake system, realizes a smooth brake process, improves the brake smoothness and safety, takes into account the brake energy recovery, and improves the brake economy.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of new energy passenger vehicle control, and particularly relates to an electro-hydraulic composite brake torque compensation method based on fuzzy control. BACKGROUND

[0002] The rapid development of industrial society has made social problems such as energy depletion increasingly prominent, and most countries and regions worldwide have developed new energy vehicle technology to solve problems such as the consumption of fossil energy such as oil by traditional internal combustion engine vehicles. Electric vehicles have advantages such as energy saving and environmental protection, and have been widely promoted, applied and developed worldwide in recent years. Regenerative braking, as a key technology for electric vehicles, will effectively reduce energy waste and achieve brake energy recovery. In typical urban driving conditions, the energy consumed by braking accounts for about 50% of the total driving energy, and even on the low-speed highway driving condition with low acceleration and deceleration frequency, the energy consumed by braking accounts for about 15%. Therefore, effectively recovering this part of energy and extending the cruising range are of great significance. At the same time, coordinated control of the electro-hydraulic braking system is also crucial because it directly relates to the stability and safety of braking on the basis of brake energy recovery. How to balance and solve the performance requirements of "economy, comfort, safety", etc. is still a problem. For example: during braking, the braking mode is switched, and the electro-hydraulic composite braking system participates in braking. Due to the inherent dynamic response characteristics of the hydraulic braking system, there is a lag effect, especially when the deceleration suddenly changes, the actual total brake torque and the target total brake torque will have a large difference, there will be a large torque impact, which will affect the braking effect, and at the same time will affect the ride comfort, and in serious cases will cause the driver to have inconsistent braking feeling, which will affect the driver's judgment, cause misoperation, and exist brake safety risk (especially for pure electric passenger cars driven by electric motors). This problem needs to be broken through and solved, so the electro-hydraulic composite brake torque compensation method under the change of brake intensity is studied, which helps to improve the braking effect, and improve the braking safety and ride comfort. Efficiently balance the economy, smoothness and safety of braking, and improve the high-quality competitiveness of the country's large number of new energy passenger vehicles.

[0003] In the prior art, the research on electro-hydraulic composite braking mainly focuses on brake force distribution, motor regenerative braking energy recovery, etc. There is little research on braking impact and jerk of electro-hydraulic composite braking. At present, there is no report on torque compensation control method considering braking economy, smoothness and safety. It has great scientific research value and practical significance to study the torque compensation control method considering braking economy, smoothness and safety. The control algorithm of "H∞ mixed sensitivity" is used for the coordinated control of torque fluctuation of electro-hydraulic composite braking system. For example, the invention patent "CN 113954796 A" published on November 16, 2021 provides an electro-hydraulic composite braking torque fluctuation coordination control system for electric vehicles. The patent provides a control algorithm of "H∞ mixed sensitivity" for suppressing torque fluctuation on this basis. The specific method is as follows: obtain the brake pedal signal, calculate the driver's target braking intensity and the required total braking torque; obtain the wheel speed and vehicle speed information, calculate the required motor regenerative braking torque and the required hydraulic system braking torque through the required total braking torque; obtain the actual motor regenerative braking torque, calculate the difference between the required hydraulic system braking torque and the actual hydraulic system braking torque, and superimpose the difference between the required motor regenerative braking torque and the actual motor regenerative braking torque on the required hydraulic system braking torque and the actual hydraulic system braking torque to input to the compensation control unit; the compensation control unit performs H∞ control to control the actual motor regenerative braking torque to follow the compensation regenerative braking torque, realize the compensation of the actual motor regenerative braking torque to the braking torque difference caused by the hysteresis effect of the actual hydraulic system braking torque, and reduce the torque fluctuation during electro-hydraulic composite braking. SUMMARY

[0004] To solve the problems existing in the prior art and consider the economy, smoothness and safety of braking, the present application designs an electro-hydraulic composite braking torque compensation method based on fuzzy control, which coordinates and compensates the regenerative braking torque, ensures that the actual total braking torque quickly follows the required total braking torque, realizes a smooth braking process, improves the braking effect, improves the braking smoothness and safety, and at the same time, considers the recovery of braking energy to improve the braking economy.

[0005] To achieve the above purpose, the present application provides the following technical scheme:

[0006] 1. An electro-hydraulic composite braking torque compensation method based on fuzzy control, characterized by comprising the following steps:

[0007] Step 1: Through brake intention recognition, i.e. brake pedal displacement s and pressure signal p, solve the braking intensity z and the required total braking torque T req_total ;

[0008] Step two: get the vehicle longitudinal speed v lon , longitudinal deceleration a lon , wheel speed ω whe and battery SOC, combined with the total demand braking torque T req_total , to solve the initial demand hydraulic system braking torque T req_hydraulic_initial and the initial demand motor regeneration braking torque T req_motor_initial ;

[0009] Step three: according to the initial demand hydraulic system braking torque T req_hydraulic_initial , to solve the actual hydraulic system braking torque T act_hydraulic_initial ; according to the initial demand motor regeneration braking torque T req_motor_initial and the initial actual hydraulic system braking torque T act_hydraulic_initial , to solve the actual total braking torque T act_total ; calculate the demand hydraulic system braking torque and the actual hydraulic system braking torque difference ΔT hydraulic , calculate the demand total braking torque T req_total and the actual total braking torque T act_total difference ΔT initial , which is superimposed to the torque compensation module for "motor brake force variable" electro-hydraulic braking torque coordination control, adjust the motor compensation torque T req_motor_complemental , so that the actual total braking torque T act_total follows the demand total braking torque T req_total , that is, T act_total = T req_total ;

[0010] Step four: further, the "motor brake force variable" electro-hydraulic braking torque coordination control is: to correct the reserved available motor braking torque T motor_useable , that is, Wherein, is the correction coefficient value range (0, 1), related to vehicle speed v lon and braking intensity z, which can be expressed as: Therefore, the relationship between the reserved available motor braking torque T motor_useable and the braking intensity z within a certain range can be expressed as The correction coefficient is adjusted by using fuzzy control algorithm, the longitudinal vehicle speed v lon and the braking intensity z are selected as the input variables of fuzzy control, and the reserved available motor braking torque correction coefficient is selected as the output variable of fuzzy control, and finally the reserved available motor braking torque T motor_useable is obtained. In addition, the available motor braking torque T motor_useable needs to consider the influence of motor external characteristics and battery maximum charging rate, that is

[0011] Step five: setting dynamic coordination coefficient According to the real vehicle bench test results, the dynamic coordination coefficient Is expressed by the following formula:

[0012]

[0013] Wherein, z represents the braking intensity. Case one: when the braking intensity z does not exceed the braking intensity judgment threshold Z threshold , that is, z≤Z threshold , the electro-hydraulic braking system considers braking safety and economy, the available motor braking torque T motor_useable The value is small, the motor system participation is improved, the dynamic coordination coefficient Is larger; case two: when the braking intensity z exceeds the braking intensity judgment threshold Z threshold , that is, z≥Z threshold , the electro-hydraulic braking system considers braking smoothness and safety, the available motor braking torque T motor_useable The value is large, the dynamic coordination coefficient Is smaller. The output motor compensation torque Control the final motor braking torque T req_motor_final ,

[0014] That is, T req_motor_final =T req_motor_initial +ΔT hydraulic , to compensate for the difference ΔT hydraulic Caused by the hysteresis effect of the hydraulic system braking torque.

[0015] Compared with the prior art, the present application has the following beneficial effects:

[0016] 1. The electric-hydraulic composite brake torque compensation method based on fuzzy control fully considers that different braking intensities correspond to braking demand targets (low braking intensity considers braking safety and energy recovery, medium and high braking intensity considers braking safety and smoothness) during braking, ensures the motor system participation during braking, improves energy recovery rate and braking economy;

[0017] 2. The electric-hydraulic composite brake torque compensation method based on fuzzy control reduces the error between the actual total braking torque and the demand total braking torque to a certain extent during braking mode switching, realizes smooth braking process, and improves braking smoothness and ride comfort;

[0018] 3. The electric-hydraulic composite braking torque compensation method based on fuzzy control according to the present application, sets the available motor braking torque coordination coefficient according to the braking intensity change, ensures the dynamic adjustment of the electric-hydraulic composite braking torque, shortens the braking distance, and improves the braking effect and braking safety. BRIEF DESCRIPTION OF DRAWINGS

[0019] The description of the embodiments will become more readily apparent when taken in conjunction with the accompanying drawings, in which:

[0020] Figure 1 The braking torque-time curve of the electric-hydraulic composite braking torque compensation method provided according to the embodiment of the present application;

[0021] Figure 2 The braking torque-time curve of the electric-hydraulic composite braking system according to the prior art;

[0022] Figure 3 The flowchart of the electric-hydraulic composite braking torque compensation method provided according to the embodiment of the present application.

[0023] Figure 4 The strategy diagram of the electric-hydraulic composite braking torque compensation method provided according to the embodiment of the present application. DETAILED DESCRIPTION

[0024] To further illustrate the technical solutions adopted by the present application and the technical problems solved, the embodiments of the present application are described in detail, and the same reference numerals are maintained throughout the drawings. The described embodiments are merely illustrative, are limited to explanation and illustration, and cannot be understood as limiting the present application.

[0025] A electric-hydraulic composite braking torque compensation method based on fuzzy control is described below with reference to the accompanying drawings, but the present application is not limited to these embodiments.

[0026] Referring to the accompanying drawings, Figure 1 , the braking torque-time curve of the electric-hydraulic composite braking torque compensation method provided according to the present application is shown;

[0027] Referring to the accompanying drawings, Figure 2 , the braking torque-time curve of the electric-hydraulic composite braking system according to the prior art is shown;

[0028] Referring to the accompanying drawings, Figure 3 , the flowchart of the electric-hydraulic composite braking torque compensation method provided according to the embodiment of the present application is shown.

[0029] Referring to the accompanying drawings, Figure 4The application discloses a fuzzy control-based electro-hydraulic composite braking torque compensation method.

[0030] The electro-hydraulic composite braking torque compensation method is specifically described as follows:

[0031] Step one: through braking intention recognition, i.e. brake pedal displacement s and pressure signal p, the braking intensity z and the required total braking torque T are solved req_total ;

[0032] Step two: the vehicle longitudinal speed v lon , the longitudinal deceleration a lon , the wheel speed ω whe and the battery SOC are acquired, the initial required hydraulic system braking torque T req_hydraulic_initial and the initial required motor regenerative braking torque T req_motor_initial are solved in combination with the required total braking torque T req_total ;

[0033] Step three: the actual hydraulic system braking torque T act_hydraulic_initial is solved according to the initial required hydraulic system braking torque T req_hydraulic_initial ; the actual total braking torque T act_total is solved according to the initial required motor regenerative braking torque T req_motor_initial and the initial actual hydraulic system braking torque T act_hydraulic_initial ; the difference ΔT hydraulic between the required hydraulic system braking torque and the actual hydraulic system braking torque is calculated, the difference ΔT initial between the required total braking torque T req_total and the actual total braking torque T act_total is calculated, and the difference is superimposed to the torque compensation module to perform the electro-hydraulic braking torque coordination control of the "variable motor braking force", the motor compensation torque T req_motor_complemental is adjusted, so that the actual total braking torque T act_total quickly follows the required total braking torque T req_total , i.e. T act_total =T req_total ;

[0034] Step four: further, the electro-hydraulic braking torque coordination control of the "variable motor braking force" is specifically: the available motor braking torque T motor_useable is corrected, i.e. wherein, is a correction coefficient value range (0, 1), which is related to the vehicle speed v lon and the braking intensity z, and can be expressed as: Therefore, the available motor braking torque T motor_useableThe relationship between the following braking intensity z and the range can be expressed as The correction coefficient is adjusted by using a fuzzy control algorithm, and the longitudinal vehicle speed v lon and the braking intensity z are selected as the input variables of the fuzzy control, and the reserved available motor braking torque correction coefficient is selected as the output variable of the fuzzy control, and finally the reserved available motor braking torque T motor_useable is obtained. In addition, the available motor braking torque T motor_useable needs to consider the influence of the motor external characteristic and the maximum charging rate of the battery, that is

[0035] Step five: setting the dynamic coordination coefficient According to the results of the real vehicle bench test, the dynamic coordination coefficient is expressed by the following formula:

[0036]

[0037] Wherein, z represents the braking intensity. Case one: when the braking intensity z does not exceed the braking intensity judgment threshold Z threshold , that is, z≤Z threshold , the electro-hydraulic braking system considers both braking safety and economy, the available motor braking torque T motor_useable takes a small value, improves the participation of the motor system, and the dynamic coordination coefficient is large; case two: when the braking intensity z exceeds the braking intensity judgment threshold Z threshold , that is, z≥Z threshold , the electro-hydraulic braking system considers more braking smoothness and safety, the available motor braking torque T motor_useable takes a large value, and the dynamic coordination coefficient is small. The output motor compensation torque controls the final motor braking torque T req_motor_final , that is, T req_motor_final =T req_motor_initial +ΔT hydraulic , to compensate for the difference ΔT hydraulic caused by the hysteresis effect of the hydraulic system braking torque.

Claims

1. An electro-hydraulic composite brake torque compensation method based on fuzzy control, characterized by, The relationship between the reserved available motor braking torque and the braking intensity is determined, the motor compensation torque control of the "variable motor braking torque" is divided into two cases, and the braking economy, smoothness and safety are considered; the size relationship between the current braking intensity and the braking intensity judgment threshold is judged, and the motor compensation torque is dynamically adjusted according to the difference between the required total braking torque and the actual total braking torque, so that the actual total braking torque quickly follows the required total braking torque; Specifically includes the following steps: Step one: Solve the braking intensity z and the required total braking torque T by braking intention recognition, i.e. brake pedal displacement s and pressure signal p req_total ; Step two: get the vehicle longitudinal speed v lon , longitudinal deceleration a lon , wheel speed ω whe and battery SOC, combined with the total required braking torque T req_total , solve the initial required hydraulic system braking torque T req_hydraulic_initial and the initial required motor regenerative braking torque T req_motor_initial ; Step three: according to the initial demand hydraulic system braking torque T req_hydraulic_initial , solve the actual hydraulic system braking torque T act_hydraulic_initial ; according to the initial motor regenerative braking torque T req_motor_initial and the initial actual hydraulic system braking torque T act_hydraulic_initial , solve the actual total braking torque T act_total ; calculate the difference ΔT hydraulic between the demand hydraulic system braking torque and the actual hydraulic system braking torque, calculate the difference ΔT initial between the demand total braking torque T req_total and the actual total braking torque T act_total , superimpose it to the torque compensation module for "motor braking force variable" electro-hydraulic braking torque coordination control, adjust the motor compensation torque T req_motor_complemental , so that the actual total braking torque T act_total follows the demand total braking torque T req_total as soon as possible, that is, T act_total =T req_total ; Step 4: The electro-hydraulic braking torque coordination control of the "variable motor power" specifically refers to: controlling the reserved available motor power torque T motor_useable Make corrections, that is... in, The correction factor has a range of values ​​(0,1), which is related to the vehicle speed v. lon It is related to the braking intensity z, and can be expressed as: Therefore, the reserved available electric motor torque T motor_useable The relationship between the following braking intensity z and its variation within a certain range can be expressed as follows: Using fuzzy control algorithm to adjust the correction coefficient Adjustments are made, and the longitudinal vehicle speed v is selected. lon The braking intensity z is used as the input variable for fuzzy control, and the reserved available motor torque correction coefficient is... As the output variable of fuzzy control, the reserved available motor driving torque T is finally obtained. motor_useable Additionally, the electric motor's torque T can be used. motor_useable The effects of motor external characteristics and the maximum battery charging rate need to be considered, i.e. Step five: set the dynamic coordination coefficient θ, according to the real vehicle bench test result, the dynamic coordination coefficient θ is expressed by the following formula: Wherein, z represents the braking intensity; case one: when the braking intensity z does not exceed the braking intensity judgment threshold Z threshold , that is, z≤Z threshold , the electro-hydraulic braking system considers braking safety and economy, the available motor braking torque T motor_useable is small, the motor system participation is improved, and the dynamic coordination coefficient θ is large; case two: when the braking intensity z exceeds the braking intensity judgment threshold Z threshold , that is, z≥Z threshold , the electro-hydraulic braking system more considers braking smoothness and safety, the available motor braking torque T motor_useable is large, and the dynamic coordination coefficient θ is small; the output motor compensation torque T req_motor_complemental ≤θT motor_useable , the final motor braking torque T req_motor_final is controlled, that is, T req_motor_final =T req_motor_initial +ΔT hydraulic , to compensate for the difference ΔT caused by the hysteresis effect of the hydraulic system braking torque hydraulic .

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