Real-time calculation method and system for hydraulic pressure of wheel cylinder of automobile electro-hydraulic braking system

Abstract

The invention discloses a wheel cylinder hydraulic pressure real-time calculation method and system of an automobile electro-hydraulic braking system. The method comprises the following steps that firstly, parameters of related parts of the electro-hydraulic braking system and signals such as the wheel cylinder hydraulic pressure value of the last period are obtained; then the brake fluid flow actually driven by the plunger pump is calculated; the flow of the brake fluid flowing back through the pressure release valve is calculated; the actual flow flowing into the wheel cylinder is obtained by subtracting the backflow flow of the pressure release valve from the flow of the brake fluid driven by the plunger pump; calculating the hydraulic pressure change gradient of the wheel cylinder according to the flow of the brake fluid flowing into the wheel cylinder; and finally calculating and recording the hydraulic pressure of the wheel cylinder at the current moment. Under the condition that the wheel cylinder hydraulic sensor fails or cannot be used, the function of the wheel cylinder hydraulic sensor is replaced, and the wheel cylinder hydraulic pressure is calculated in real time; when the wheel cylinder hydraulic pressure sensor has no fault and is normally used, the hydraulic pressure calculated value calculated by the wheel cylinder hydraulic pressure real-time calculation method provided by the invention is compared with the measured value of the sensor, so that whether the sensor has a fault or not is judged.

Description

Technical Field

[0001] The invention relates to the field of automobile brake system design, and in particular to a real-time calculation method and system for wheel cylinder hydraulic pressure of an automobile electro-hydraulic brake system. Background Art

[0002] With the rapid development of autonomous driving technology, people have higher and higher requirements for automobile safety. As an important part that affects the driving safety of automobiles, the braking system has become the focus of researchers. Among various types of braking systems, the electro-hydraulic hybrid braking system (EHB) is the most widely used. Compared with the traditional hydraulic braking system, EHB replaces some mechanical components with electronic components, which is more suitable for the development of automobile electrification. The hydraulic pressure of the electro-hydraulic braking system generally comes from the motor. The principle is to use some physical structures or components to convert the rotational motion of the motor into a linear flow of brake fluid, and then the brake fluid flows into the wheel cylinder to generate hydraulic pressure. At present, the more common combination is a ball screw plus a piston, in which the ball screw can convert the rotational motion of the motor into linear motion, and the piston connected to the ball screw also moves, thereby promoting the flow of brake fluid. Another solution is to directly use a plunger pump to connect the motor to drive the flow of brake fluid. This solution has some disadvantages, such as the periodic operation of the plunger pump and the easy generation of jitter, so there are fewer related studies, but it also has the advantages of simple structure, small overall volume, and low cost, so it can be used for redundant braking structure or auxiliary braking.

[0003] One of the important functions of the electro-hydraulic brake system is the precise control of the wheel cylinder hydraulic pressure, which requires the upper control system to obtain the actual value of the wheel cylinder hydraulic pressure in real time and adjust the control signal according to the feedback value. Generally, the wheel cylinder of a car is equipped with a hydraulic pressure sensor, which can directly obtain the hydraulic pressure signal of the sensor. However, due to the very harsh working environment of the wheel, the wheel cylinder hydraulic pressure sensor may fail or be inaccurate, or the signal may not be transmitted. Therefore, most mature commercial brake systems have the function of real-time estimation of wheel cylinder hydraulic pressure, such as Bosch's ESC system. The real-time estimation function of wheel cylinder hydraulic pressure can not only judge whether the sensor is normal by comparing the estimated value of the hydraulic pressure with the measured value of the sensor, but more importantly, it can replace the pressure sensor when the sensor fails to ensure the normal operation of the brake system.

[0004] There have been many studies on the estimation methods of the hydraulic pressure of the wheel cylinder of the electro-hydraulic brake system, but most of them are based on the motor-ball screw-piston structure, and there are few studies on the electro-hydraulic brake system using the motor-plunger pump structure. Due to the suction and pumping characteristics of the plunger pump and the change in working efficiency, the calculation of its internal liquid flow is more complicated.

[0005] An existing method for estimating the hydraulic pressure of an electronic hydraulic brake system (CN201911413479.0) determines the current working mode of the electronic hydraulic system according to the duty cycle of the solenoid valve control signal in the previous cycle, and then determines the estimated pressure value of the hydraulic wheel cylinder starting from this week according to the current working mode of the electronic hydraulic system. This technology divides the working conditions of the electronic hydraulic system into three types: pressure-maintaining conditions, full-pressure conditions, and variable-pressure conditions. If the system is in a pressure-maintaining condition or a full-pressure condition, the estimated value of the hydraulic pressure of the wheel cylinder in the current cycle is equal to the pressure value of the hydraulic wheel cylinder in the previous cycle. When the current working condition of the electronic hydraulic system is a variable-pressure condition, the pressure conversion rate-pressure difference-duty cycle characteristic diagram under different states is directly retrieved according to the pressure increase and decrease state of the wheel cylinder and whether the wheel cylinder pressure in the previous cycle is in a linear region or a nonlinear region, and the pressure change rate of the hydraulic wheel cylinder in the previous cycle is obtained, thereby calculating the estimated value of the hydraulic pressure of the wheel cylinder in this cycle. This technology has the advantages of simple logic and strong operability, and is suitable for engineering applications, but it still has some shortcomings. For example, the calibration of the pressure change rate-pressure difference-duty cycle characteristic diagram mentioned in this technology is relatively complicated and labor-intensive; and it can be seen from the attached figure of the hydraulic pressure estimation method of the electronic hydraulic brake system that this technology is aimed at the common electronic hydraulic system based on the motor-ball screw-piston structure, rather than the electronic hydraulic system using the motor-plunger pump structure. Summary of the invention

[0006] The technical problem that the present invention aims to solve is: when the hydraulic pressure sensor at the wheel cylinder fails or there is no hydraulic pressure sensor at the wheel cylinder, the upper control system cannot accurately obtain the hydraulic pressure of the wheel cylinder. For the electro-hydraulic brake system using a plunger pump as a hydraulic drive component, the present invention provides a real-time calculation method for the hydraulic pressure of the wheel cylinder of the automotive electro-hydraulic brake system, which obtains the hydraulic pressure of the wheel cylinder by real-time calculation without calibrating the pressure change rate-pressure difference-duty cycle characteristic diagram, and the real-time calculation method for the hydraulic pressure of the wheel cylinder of the automotive electro-hydraulic brake system provided by the present invention is particularly aimed at the electronic hydraulic system using a motor-plunger pump structure, filling the gap in the calculation of the hydraulic pressure of the wheel cylinder of the electro-hydraulic brake system with a motor-plunger pump structure.

[0007] The present invention is achieved by at least one of the following technical solutions.

[0008] A method for real-time calculation of wheel cylinder hydraulic pressure of an automobile electro-hydraulic brake system comprises the following steps:

[0009] (1) In real-time calculation, the current continuous time is divided into small time slices in a discrete manner. Each time slice is a sampling cycle. Assuming that the current sampling point cycle is the kth cycle, the previous cycle is k-1, and the wheel cylinder hydraulic pressure value of the previous cycle is obtained;

[0010] (2) Open the booster valve to allow the brake fluid to flow from the reservoir into the plunger pump. At the same time, turn on the motor to drive the plunger pump to flow the brake fluid. Calculate the actual brake fluid flow driven by the plunger pump.

[0011] (3) Change the reflux flow rate by changing the opening of the pressure relief valve, open the pressure relief valve, and calculate the brake fluid flow rate returning through the pressure relief valve;

[0012] (4) obtaining the final brake fluid flow rate flowing into the wheel cylinder based on the actual brake fluid flow rate driven by the plunger pump and the brake fluid flow rate returning through the pressure relief valve;

[0013] (5) Obtain the wheel cylinder hydraulic stiffness by looking up the table based on the hydraulic pressure of the wheel cylinder at the last moment, and calculate the gradient of the wheel cylinder hydraulic pressure change;

[0014] (6) The wheel cylinder hydraulic pressure at the previous moment is obtained by adding the hydraulic pressure change to the wheel cylinder hydraulic pressure at the current moment;

[0015] (7) Record the wheel cylinder hydraulic pressure value at the current moment for calculation at the next moment; repeat steps (1) to (7) to calculate the wheel cylinder hydraulic pressure value at the next moment.

[0016] Furthermore, in step (1), if the current cycle is the first cycle, i.e., the first cycle to start real-time calculation, then w (k-1)=0, the real-time calculation of the wheel cylinder fluid pressure is started before work, and the wheel cylinder fluid pressure is 0 at this time.

[0017] Furthermore, in step (2), the flow rate driven by the plunger pump is divided into the ideal flow rate Q ideal and leakage flow Q leak , Q ideal The calculation formula is Q ideal =K p ×n,Q leak The calculation formula is Q leak =K HP ×ΔP, actual brake fluid flow Q driven by the piston pump act Equal to the ideal flow minus the leakage flow, that is, Q act =Q ideal -Q leak ; where K p and K HP All are plunger pump parameters, n is the motor speed; ΔP is the liquid pressure difference between the suction end and the pump discharge end of the plunger pump.

[0018] Furthermore, the hydraulic pressure at the pump outlet of the plunger pump is equal to the hydraulic pressure of the wheel cylinder, and the hydraulic pressure value of the wheel cylinder at the previous moment is taken as P w (k-1);

[0019] The hydraulic pressure at the suction end of the plunger pump is calculated using the booster valve pressure drop formula: Where Q act (k-1) is the plunger pump outflow rate at the previous moment, K in is the boost valve parameter, which is obtained by testing the boost valve.

[0020] Furthermore, the boost valve is tested to obtain the boost valve parameter K in include:

[0021] Install hydraulic pressure sensors at both ends of the boost valve or install a hydraulic pressure sensor at only one end, and connect the other end to an external liquid storage tank to obtain the pressure difference ΔP on both sides of the boost valve. 1 , and install a flow sensor anywhere in the pipeline to obtain the brake fluid flow Q flowing through the booster valve 1 , by constantly changing Q 1 Get different ΔP 1 , using the formula Calculate K in , find the average of multiple sets of data.

[0022] Furthermore, the brake fluid flow rate returning through the pressure relief valve Where K out is the pressure relief valve parameter, obtained through testing; x represents the opening size of the pressure relief valve, P m Indicates the hydraulic pressure of the master cylinder, which is measured by the hydraulic pressure sensor at the master cylinder; P w (k-1) represents the wheel cylinder hydraulic pressure value of the kth cycle.

[0023] Furthermore, the hydraulic pressure change gradient grad_p in step (5) is w ×C w , where the wheel cylinder hydraulic stiffness C w As a wheel cylinder parameter, it needs to be obtained through testing. The wheel cylinder hydraulic stiffness C w It will change with the change of wheel cylinder hydraulic pressure. When testing the wheel cylinder hydraulic stiffness C w When the wheel cylinder hydraulic stiffness C is tested under different wheel cylinder hydraulic pressure conditions, w , so as to obtain the wheel cylinder hydraulic stiffness C under different wheel cylinder hydraulic pressure conditions w , and plotted as a wheel cylinder hydraulic pressure-stiffness curve.

[0024] Furthermore, the method of drawing a wheel cylinder hydraulic pressure-stiffness curve comprises the following steps:

[0025] A hydraulic pressure sensor is installed at the wheel cylinder to obtain the hydraulic pressure value of the wheel cylinder, and a liquid flow sensor is installed at the wheel cylinder to obtain the brake fluid flow value at the wheel cylinder;

[0026] Open the boost valve and change the wheel cylinder hydraulic pressure by controlling the motor speed and the opening of the pressure relief valve;

[0027] Control the wheel cylinder hydraulic pressure to increase from 0 to the maximum value that can be reached, record the wheel cylinder hydraulic pressure value and flow value at each point, and obtain the wheel cylinder hydraulic stiffness C at each point by dividing the wheel cylinder hydraulic pressure by the wheel cylinder volume. w The wheel cylinder hydraulic pressure value and wheel cylinder hydraulic stiffness at each point are plotted into a wheel cylinder hydraulic pressure-stiffness curve, where the horizontal axis of the curve is the wheel cylinder hydraulic pressure value, and the vertical axis of the curve is the wheel cylinder hydraulic stiffness C corresponding to each horizontal axis. w .

[0028] Furthermore, in step (6), the wheel cylinder fluid pressure P at the current moment is calculated. w (k) Formula is P w (k) = P w (k-1)+grad_p×dt, where P w (k-1) represents the wheel cylinder hydraulic pressure value at the previous moment, grad_p represents the change of the wheel cylinder hydraulic pressure within one cycle, and dt represents the duration of one cycle.

[0029] A system for realizing the real-time calculation method of wheel cylinder hydraulic pressure of an automobile electro-hydraulic brake system includes a fluid storage tank, a master cylinder, a brake pedal, a master cylinder fluid pressure sensor, a pressure relief valve, a boost valve, a motor, a plunger pump, and a brake wheel cylinder. The fluid storage tank and the master cylinder are connected by a hydraulic hose, the brake pedal is connected to the master cylinder by a connecting rod and a piston, the master cylinder fluid pressure sensor is connected to the master cylinder to measure the master cylinder fluid pressure, the pressure relief valve and the boost valve are connected to the master cylinder by a hydraulic steel pipe, the motor drives the plunger pump through a cam structure, and the plunger pump is connected to the boost valve, the pressure relief valve and the brake wheel cylinder by a hydraulic steel pipe.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] 1) With regard to the electro-hydraulic brake system which uses a plunger pump as a hydraulic drive component and which is less studied currently, the present invention provides a method for real-time calculation of the wheel cylinder hydraulic pressure of the electro-hydraulic brake system, which can replace the function of the wheel cylinder hydraulic sensor when the wheel cylinder hydraulic sensor fails or cannot be used, and calculate the wheel cylinder hydraulic pressure in real time.

[0032] 2) When the wheel cylinder hydraulic pressure sensor has no faults and is in normal use, the hydraulic pressure calculated by the real-time calculation method of the wheel cylinder hydraulic pressure provided by the present invention can be compared with the measured value of the sensor to determine whether the sensor is faulty. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 is a method flow chart of a method for real-time calculation of wheel cylinder hydraulic pressure of an electro-hydraulic brake system provided by an embodiment;

[0034] Figure 2It is a hydraulic diagram of an electro-hydraulic brake system using a plunger pump as a hydraulic drive component provided by an embodiment of the present invention;

[0035] Figure 3 The embodiment of the present invention provides Figure 2 The important brake fluid flow diagram when the electro-hydraulic brake system is working is shown;

[0036] Figure 4 It is a calculation flow chart of the real-time calculation method of the wheel cylinder hydraulic pressure of the automobile electro-hydraulic brake system provided by the present invention;

[0037] Figure numerals: 1-fluid reservoir; 2-master cylinder; 3-brake pedal; 4-master cylinder fluid pressure sensor; 5-pressure relief valve; 6-boost valve; 7-motor; 8-plunger pump; 9-wheel cylinder. DETAILED DESCRIPTION

[0038] In order to make the objectives, technical solutions and advantages of the present invention more clear and explicit, the present invention is further described in detail below with reference to the accompanying drawings and embodiments.

[0039] like Figure 2 As shown, the electro-hydraulic brake system using a plunger pump as a hydraulic drive component in this embodiment includes a fluid reservoir 1, a master cylinder 2, a brake pedal 3, a master cylinder fluid pressure sensor 4, a pressure relief valve 5, a pressure boosting valve 6, a motor 7, a plunger pump 8, and a wheel cylinder 9. The fluid reservoir 1 and the master cylinder 2 are connected by a hydraulic hose, the brake pedal 3 is connected to the master cylinder 2 by a connecting rod and a piston, the master cylinder fluid pressure sensor is connected to the master cylinder so as to measure the master cylinder fluid pressure, the pressure relief valve 5 and the pressure boosting valve 6 are connected to the master cylinder by a hydraulic steel pipe, the motor 7 drives the plunger pump 8 by a cam structure, and the plunger pump 8 is connected to the pressure boosting valve 6, the pressure relief valve 5, and the brake wheel cylinder by a hydraulic steel pipe. In the hydraulic control system in this embodiment, the input variables are the motor speed and the opening of the pressure relief valve, the output variable is the brake wheel cylinder fluid pressure, and there is a master cylinder pressure sensor that can measure the fluid pressure at the master cylinder. In addition to the variables mentioned above, the other variables mentioned in this embodiment are all parameters of the system components themselves or calculated variables.

[0040] like Figure 1 , Figure 4 As shown, the present embodiment provides a method for real-time calculation of wheel cylinder hydraulic pressure of an automobile electro-hydraulic brake system, comprising the following steps:

[0041] (1) In real-time calculation, the current continuous time (the time in real-time calculation) is divided into small time slices in a discrete manner. The time spent in each time slice is dt. The smaller dt is, the more accurate the calculation result is. Each time slice is a sampling cycle. Assuming that the current sampling point cycle is the kth cycle, the previous cycle is k-1. Obtain the wheel cylinder hydraulic pressure P of the previous cycle w(k-1), the acquisition method is as follows: If the current cycle is the first cycle (i.e., the first cycle to start real-time calculation), then P w (k-1) = 0 (generally, the real-time calculation of wheel cylinder hydraulic pressure is started before the brake system starts working, and the wheel cylinder hydraulic pressure is 0 at this time); if the current cycle is not the first cycle, the wheel cylinder hydraulic pressure P of the previous cycle can be obtained according to step (7) w (k-1) has been recorded and can be used directly.

[0042] (2) Calculate the actual brake fluid flow driven by the piston pump: Figure 2 As shown, the boost valve 6 is opened to allow the brake fluid to flow from the reservoir into the plunger pump 8, and the motor 7 is turned on to drive the plunger pump 8 to drive the brake fluid to flow. Figure 3 As shown in the figure, the actual brake fluid flow rate driven by the plunger pump 8 is the brake fluid flow rate flowing through the plunger pump. Based on the working characteristics of the plunger pump suction-pumping cycle, under normal circumstances, there will be a certain pressure difference between the suction side and the pumping side of the plunger pump 8, which will lead to a decrease in its working efficiency. Therefore, the flow rate driven by the plunger pump is divided into the ideal flow rate Q ideal and leakage flow Q leak The ideal flow rate Q ideal It is proportional to the motor speed and the calculation formula is Q ideak =K p ×n, leakage flow Q leak It is proportional to the pressure difference at both ends of the plunger pump, and the calculation formula is Q leak =K HP ×ΔP, and the hydraulic pressure on the suction side of the plunger pump is given by the formula Calculate the actual brake fluid flow rate Q act Equal to the ideal flow minus the leakage flow, that is, Q act =Q ideal -Q leak .

[0043] Where n is the motor speed, which can be obtained in real time; ΔP is the hydraulic pressure at the outlet of the plunger pump minus the hydraulic pressure at the suction end of the plunger pump, that is, the hydraulic pressure difference. The hydraulic pressure at the outlet of the plunger pump can be approximately considered to be equal to the hydraulic pressure of the wheel cylinder (the pipeline pressure drop is very small), and the wheel cylinder hydraulic pressure value P at the previous moment can be taken. w (k–1); P m Indicates the hydraulic pressure of the master cylinder, measured by the hydraulic pressure sensor at the master cylinder. K p and K HP These are plunger pump parameters, which are determined by the characteristics of the plunger pump itself and are measured through experiments. p It is the ideal flow coefficient of the plunger pump, which is numerically equal to the volume of the plunger pump cavity and can be obtained by multiplying the plunger rod cross-sectional area and the plunger rod stroke. K HPis the piston pump leakage coefficient, which can be obtained through testing. The testing process is as follows: first, install a hydraulic pressure sensor at both ends of the piston pump to obtain the pressure difference ΔP at both ends of the piston pump (or install a hydraulic pressure sensor at only one end, and connect the other end to an external liquid storage tank, with the hydraulic pressure being 0), and install a flow sensor anywhere in the pipeline to obtain the actual flow rate Q pumped out by the piston pump act , given a certain motor speed n, according to the formula Q act =K p × HP ×ΔP can calculate the piston pump leakage coefficient K HP .Q act (k–1) is the pumping flow rate of the plunger pump at the previous moment, K in is the boost valve parameter, obtained by testing the boost valve. The test process is: install a hydraulic pressure sensor at both ends of the boost valve (as another embodiment, only install a hydraulic pressure sensor at any one end, and the other end is connected to an external liquid storage tank, and the hydraulic pressure is 0) to obtain the pressure difference ΔP on both sides of the boost valve 1 , and install a flow sensor anywhere in the pipeline to obtain the brake fluid flow Q flowing through the booster valve 1 , by constantly changing Q 1 Different ΔP can be obtained 1 , and then use the formula K can be calculated in , you can find the average value of multiple sets of data.

[0044] (3) Calculate the brake fluid flow rate returning through the pressure relief valve: Figure 3 As shown, when the pressure relief valve 5 is closed, all the brake fluid pumped out by the plunger pump will flow into the wheel cylinder. At this time, the brake fluid flow rate returning through the pressure relief valve is 0; when the pressure relief valve 5 is opened, in addition to flowing to the wheel cylinder, a portion of the brake fluid pumped out by the plunger pump will flow back into the fluid storage tank 1 through the pressure relief valve. The brake fluid flow rate returning through the pressure relief valve is the brake fluid flow rate flowing through the pressure relief valve in the figure. According to the pressure drop characteristics of the solenoid valve, the flow rate passing through the solenoid valve is proportional to the square root of the pressure difference at both ends of the solenoid valve. The pressure relief valve adopts a linear solenoid valve. The change of its opening x causes the liquid flow area of ​​the pressure relief valve to change, thereby affecting the physical parameters of the pressure relief valve. Therefore, the calculation formula for the return brake fluid flow rate is: Where K out It is the pressure relief valve parameter, which is measured through experiments. The test process is: install a hydraulic pressure sensor at both ends of the pressure relief valve 5 (or install a hydraulic pressure sensor at only one end, and connect the other end to an external liquid storage tank, and the liquid pressure is 0) to obtain the pressure difference ΔP on both sides of the pressure relief valve 2 , and install a flow sensor anywhere in the pipeline to obtain the brake fluid flow Q flowing through the pressure relief valve 5 2 , by constantly changing Q 2Different ΔP can be obtained 2 , and then use the formula K can be calculated out , multiple sets of data can be averaged. x represents the opening size of the linear solenoid valve, ranging from 0 to 1, which can be obtained in real time; P m Indicates the hydraulic pressure in the master cylinder, measured by the hydraulic pressure sensor at the master cylinder.

[0045] (4) Calculate the actual flow rate into the wheel cylinder: Figure 3 As shown in the figure, the actual flow rate flowing into the wheel cylinder is the brake fluid flow rate flowing into the wheel cylinder. The actual brake fluid flow rate driven by the plunger pump minus the brake fluid flow rate returning through the pressure relief valve is obtained to obtain the final brake fluid flow rate Q flowing into the wheel cylinder. w =Q act -Q out .

[0046] (5) Calculate the wheel cylinder hydraulic pressure gradient: wheel cylinder hydraulic stiffness C w It will change with the change of wheel cylinder hydraulic pressure. When testing the wheel cylinder hydraulic stiffness C w When the wheel cylinder hydraulic stiffness C is tested under different wheel cylinder hydraulic pressure conditions, w , and plotted as a wheel cylinder hydraulic pressure-stiffness curve.

[0047] As an embodiment, the curve test method is: install a hydraulic pressure sensor at the wheel cylinder to obtain the wheel cylinder hydraulic pressure value, and install a liquid flow sensor at the wheel cylinder to obtain the brake fluid flow value at the wheel cylinder fluid. Open the boost valve, and change the wheel cylinder hydraulic pressure by controlling the motor speed and the opening of the pressure relief valve. Control the wheel cylinder hydraulic pressure to increase from 0 to the maximum value that can be achieved. Record the wheel cylinder hydraulic pressure value and flow value at each point in the process, and obtain the wheel cylinder hydraulic stiffness C at each point by dividing the wheel cylinder hydraulic pressure with the wheel cylinder volume (the wheel cylinder volume is the initial volume of the wheel cylinder plus the volume of the brake fluid flowing in after the pressure starts to build up). w The wheel cylinder hydraulic pressure value and wheel cylinder hydraulic stiffness at each point are plotted into a wheel cylinder hydraulic pressure-stiffness curve, where the horizontal axis of the curve is the wheel cylinder hydraulic pressure value, and the vertical axis of the curve is the wheel cylinder hydraulic stiffness C corresponding to each horizontal axis. w According to the wheel cylinder hydraulic pressure P at the last moment w (k–1) and combined with the wheel cylinder hydraulic pressure-stiffness curve, the wheel cylinder hydraulic pressure is obtained as P w Wheel cylinder hydraulic stiffness C under (k–1) condition w , calculate the hydraulic pressure gradient grad_p = Q w ×C w .

[0048] (6) Calculate the current wheel cylinder hydraulic pressure: The current wheel cylinder hydraulic pressure can be obtained by adding the wheel cylinder hydraulic pressure at the previous moment to the hydraulic pressure change. The calculation formula is Pw (k) = P w (k-1)+grad_p×dt, where P w (k-1) represents the wheel cylinder hydraulic pressure value at the previous moment, grad_p represents the change of the wheel cylinder hydraulic pressure within one cycle, and dt represents the duration of one cycle.

[0049] (7) Record the wheel cylinder hydraulic pressure at the current moment for calculation at the next moment. Repeat steps (1) to (7) to calculate the wheel cylinder hydraulic pressure value at the next moment.

[0050] When the wheel cylinder hydraulic pressure sensor is fault-free and in normal use, the hydraulic pressure calculated by the real-time calculation method of the wheel cylinder hydraulic pressure provided by the present invention can be compared with the measured value of the sensor to determine whether the sensor is faulty. If the difference between the hydraulic pressure value and the measured value of one wheel cylinder among the four wheel cylinders of the vehicle is outside the acceptable range set in advance, while the difference between the hydraulic pressure value and the measured value of the wheel cylinders of other wheels is within the acceptable range set in advance, it is considered that the pressure sensor at the wheel cylinder is faulty, and the hydraulic pressure value of the wheel cylinder at this location adopts the calculated value instead of the measured value.

[0051] The preferred embodiments of the present invention disclosed above are only used to help explain the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to the specific implementation methods described. Obviously, many modifications and changes can be made according to the content of this specification. This specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present invention, so that those skilled in the art can understand and use the present invention well.

Claims

1. A real-time calculation method for wheel cylinder hydraulic pressure of an automobile electro-hydraulic brake system, characterized in that: The following steps are involved: (1) In real-time calculation, the current continuous time is divided into small time slices in a discrete manner. Each time slice is a sampling cycle. Assuming that the current sampling point cycle is the kth cycle, the previous cycle is k-1, and the wheel cylinder hydraulic pressure value of the previous cycle is obtained; (2) Open the booster valve to allow the brake fluid to flow from the reservoir into the plunger pump. At the same time, turn on the motor to drive the plunger pump to flow the brake fluid. Calculate the actual brake fluid flow driven by the plunger pump. (3) Change the reflux flow rate by changing the opening of the pressure relief valve, open the pressure relief valve, and calculate the brake fluid flow rate returning through the pressure relief valve; (4) obtaining the final brake fluid flow rate flowing into the wheel cylinder based on the actual brake fluid flow rate driven by the plunger pump and the brake fluid flow rate returning through the pressure relief valve; (5) Obtain the wheel cylinder hydraulic stiffness by looking up the table based on the hydraulic pressure of the wheel cylinder at the last moment, and calculate the gradient of the wheel cylinder hydraulic pressure change; (6) The wheel cylinder hydraulic pressure at the previous moment is obtained by adding the hydraulic pressure change to the wheel cylinder hydraulic pressure at the current moment; (7) Record the wheel cylinder hydraulic pressure value at the current moment for calculation at the next moment; repeat steps (1) to (7) to calculate the wheel cylinder hydraulic pressure value at the next moment.

2. The method for real-time calculation of wheel cylinder hydraulic pressure of an automobile electro-hydraulic brake system according to claim 1, characterized in that: In step (1), if the current cycle is the first cycle, i.e., the first cycle to start real-time calculation, then P w (k-1)=0, the real-time calculation of the wheel cylinder fluid pressure is started before work, and the wheel cylinder fluid pressure is 0 at this time.

3. The method for real-time calculation of wheel cylinder hydraulic pressure of an automobile electro-hydraulic brake system according to claim 1, characterized in that: In step (2), the flow rate driven by the plunger pump is divided into the ideal flow rate Q ideal and leakage flow Q leak , Q ideal The calculation formula is Q ideal =K p ×n,Q leak The calculation formula is Q leak =K HP ×ΔP, actual brake fluid flow Q driven by the piston pump act Equal to the ideal flow minus the leakage flow, that is, Q act =Q ideal -Q leak ; where K p and K HP All are plunger pump parameters, n is the motor speed; ΔP is the liquid pressure difference between the suction end and the pump discharge end of the plunger pump.

4. The method for real-time calculation of wheel cylinder hydraulic pressure of an automobile electro-hydraulic brake system according to claim 3, characterized in that: The hydraulic pressure at the pump outlet of the plunger pump is equal to the hydraulic pressure of the wheel cylinder. Take the hydraulic pressure value of the wheel cylinder at the previous moment, P w (k-1); The hydraulic pressure at the suction end of the plunger pump is calculated using the booster valve pressure drop formula: Where Q act (k-1) is the plunger pump outflow rate at the previous moment, K in is the boost valve parameter, which is obtained by testing the boost valve.

5. The method for real-time calculation of wheel cylinder hydraulic pressure of an automobile electro-hydraulic brake system according to claim 4, characterized in that: Test the boost valve to obtain the boost valve parameter K in include: Install hydraulic pressure sensors at both ends of the boost valve or only install hydraulic pressure sensors at any one end, and connect the other end to an external fluid storage tank to obtain the pressure difference ΔP1 on both sides of the boost valve, and install a flow sensor anywhere in the pipeline to obtain the brake fluid flow Q1 flowing through the boost valve. By continuously changing Q1, different ΔP1 can be obtained, using the formula Calculate K in , find the average of multiple sets of data.

6. The method for real-time calculation of wheel cylinder hydraulic pressure of an automobile electro-hydraulic brake system according to claim 1, characterized in that: Brake fluid flow rate returning through the pressure relief valve Where K out is the pressure relief valve parameter, obtained through testing; x represents the opening size of the pressure relief valve, P m Indicates the hydraulic pressure of the master cylinder, which is measured by the hydraulic pressure sensor at the master cylinder; P w (k-1) represents the wheel cylinder hydraulic pressure value of the kth cycle.

7. The method for real-time calculation of wheel cylinder hydraulic pressure of an automobile electro-hydraulic brake system according to claim 1, characterized in that: The hydraulic pressure change gradient in step (5) is grad_p = Q w ×C w , where the wheel cylinder hydraulic stiffness C w As a wheel cylinder parameter, it needs to be obtained through testing. The wheel cylinder hydraulic stiffness C w It will change with the change of wheel cylinder hydraulic pressure. When testing the wheel cylinder hydraulic stiffness C w When the wheel cylinder hydraulic stiffness C is tested under different wheel cylinder hydraulic pressure conditions, w , so as to obtain the wheel cylinder hydraulic stiffness C under different wheel cylinder hydraulic pressure conditions w , and plotted as a wheel cylinder hydraulic pressure-stiffness curve.

8. The method for real-time calculation of wheel cylinder hydraulic pressure of an automobile electro-hydraulic brake system according to claim 7, characterized in that: The method for drawing a wheel cylinder hydraulic pressure-stiffness curve comprises the following steps: A hydraulic pressure sensor is installed at the wheel cylinder to obtain the hydraulic pressure value of the wheel cylinder, and a liquid flow sensor is installed at the wheel cylinder to obtain the brake fluid flow value at the wheel cylinder; Open the boost valve and change the wheel cylinder hydraulic pressure by controlling the motor speed and the opening of the pressure relief valve; Control the wheel cylinder hydraulic pressure to increase from 0 to the maximum value that can be reached, record the wheel cylinder hydraulic pressure value and flow value at each point, and obtain the wheel cylinder hydraulic stiffness C at each point by dividing the wheel cylinder hydraulic pressure by the wheel cylinder volume. w The wheel cylinder hydraulic pressure value and wheel cylinder hydraulic stiffness at each point are plotted into a wheel cylinder hydraulic pressure-stiffness curve, where the horizontal axis of the curve is the wheel cylinder hydraulic pressure value, and the vertical axis of the curve is the wheel cylinder hydraulic stiffness C corresponding to each horizontal axis. w .

9. The method for real-time calculation of wheel cylinder hydraulic pressure of an automobile electro-hydraulic brake system according to claim 1, characterized in that: In step (6), calculate the current wheel cylinder hydraulic pressure P w (k) Formula is P w (k) = P w (k-1)+grad_p×dt, where P w (k-1) represents the wheel cylinder hydraulic pressure value at the previous moment, grad_p represents the change of the wheel cylinder hydraulic pressure within one cycle, and dt represents the duration of one cycle.

10. A system for implementing the method for real-time calculation of wheel cylinder hydraulic pressure of an automobile electro-hydraulic brake system according to any one of claims 1 to 9, characterized in that: The invention comprises a fluid storage tank (1), a master cylinder (2), a brake pedal (3), a master cylinder fluid pressure sensor (4), a pressure relief valve (5), a pressure boosting valve (6), a motor (7), a plunger pump (8), and a brake wheel cylinder (9). The fluid storage tank (1) and the master cylinder (2) are connected via a hydraulic hose, the brake pedal (3) is connected to the master cylinder (2) via a connecting rod and a piston, the master cylinder fluid pressure sensor (4) is connected to the master cylinder (2) to measure the master cylinder fluid pressure, the pressure relief valve (5) and the pressure boosting valve (6) are connected to the master cylinder (2) via a hydraulic steel pipe, the motor (7) drives the plunger pump (8) via a cam structure, and the plunger pump (8) is connected to the pressure boosting valve (6), the pressure relief valve (5) and the brake wheel cylinder (9) via a hydraulic steel pipe.

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