A variable-frequency high-precision hydraulic braking system and its control method

Abstract

The present invention discloses a variable-frequency high-precision hydraulic braking system and its control method, which includes a pedal system, a displacement detection system, a brake, a controller, and a hydraulic system composed of four solenoid valves, an accumulator, and a liquid filling system. The hydraulic system is used to adjust the pressure of the brake cylinder oil chamber; the controller acquires detection signals and controls the four solenoid valves and the liquid filling system; the actual flow output characteristics of the four solenoid valves in the frequency range of 50 Hz - 200 Hz are stored in the controller; by means of querying the database table, the controller can obtain the driving frequency required for the output characteristics corresponding to the duty ratio of the control signal of the solenoid valve. When the braking pressure approaches the target pressure, the present invention differentially controls the driving frequency at a high frequency through the double solenoid valves, so that the solenoid valves open and close in the non-linear region, thereby increasing the flow output resolution and improving the control accuracy of the braking pressure. The present invention adopts a combination scheme of large / small flow solenoid valves and has strong fault tolerance.

Description

Technical Field

[0001] The present invention belongs to the field of hydraulic braking, and particularly relates to a variable-frequency high-precision hydraulic braking system and a control method thereof. Background Art

[0002] A braking system refers to a series of devices that forcibly reduce the driving speed of a vehicle, which is composed of a power supply device, a control device, a transmission device, and a brake. Its main function is to decelerate or even stop a moving vehicle and keep the speed of a downhill vehicle stable. However, due to the different working conditions of various vehicles, high requirements are put forward for the versatility of the braking system. Especially the pressure building speed and pressure regulation control accuracy during the braking process will further affect the urgency of braking requirements and the safety of the braking vehicle.

[0003] Currently, electro-hydraulic proportional braking control technology is usually adopted for hydraulic braking. Due to the existence of a neutral dead zone in the proportional valve, the pressure response of the brake is slow and the braking process is lagged. There is internal leakage in the proportional valve, resulting in difficulty in maintaining the braking pressure stably for a long time and low control accuracy. At the same time, the spool valve structure of the proportional valve has extremely high requirements for the cleanliness of the oil. Oil pollution will cause the spool to get stuck, resulting in the inability of the brake to brake effectively, poor reliability, and difficulty in meeting the requirements of hydraulic braking under complex working conditions. The solenoid valve driving technology uses an electromagnetic switching valve as the core control element, with fast frequency response. The discrete fluid generated by high-frequency opening and closing can be comparable to the control effect of continuous fluid after being fused in the pipeline, with high control accuracy. Moreover, it has only two states of open and closed, is not sensitive to the cleanliness of the oil, so it has stronger anti-pollution ability and faster response.

[0004] Taking the ratio of the actual output flow rate of the solenoid valve to the maximum output flow rate as the flow output characteristic of the solenoid valve, Figure 2 for example, the flow output characteristic can be divided into two regions: a linear region and a non-linear region. Among them, the linear region refers to the region where the flow output characteristic of the solenoid valve changes linearly with the duty ratio of the control signal; similarly, the non-linear region refers to the region where the flow output characteristic of the solenoid valve changes non-linearly with the duty ratio of the control signal. The existing solenoid valve driving technology confines the control threshold to the linear region in order to achieve a continuous proportional output of the oil flow rate and achieve good control effects. At the same time, the higher the driving frequency, the smaller the flow pulsation and pressure shock, and the higher the control accuracy. However, as the control frequency increases, the duty ratio modulation range of the linear region further decreases, resulting in a decrease in the control threshold of the solenoid valve. In addition, the precise small oil flow output requirement does not match the working characteristics of the linear region. Therefore, based on the original control threshold, the present invention further utilizes the non-linear region flow output characteristic of the solenoid valve to expand the control region (linear region + non-linear region) of the solenoid valve and improve the flow control accuracy of the solenoid valve under high-frequency opening and closing.

[0005] In summary, the present invention proposes a variable-frequency high-precision hydraulic braking system and its control method, which realizes the braking effect of high-dynamic pressure build-up and high-precision pressure control through a multi-stage pressure build-up and pressure control method. Summary of the Invention

[0006] To solve the problems in the prior art, the present invention proposes a variable-frequency high-precision hydraulic braking system and its control method.

[0007] The technical solution of the present invention is as follows:

[0008] The present invention provides a variable-frequency high-precision hydraulic braking system, including a pedal system, a displacement detection system for detecting the displacement of the pedal system, a brake composed of a brake cylinder, a brake block, and a brake disc, and a second pressure detection system for detecting the pressure in the oil chamber of the brake cylinder; characterized in that the variable-frequency high-precision hydraulic braking system further includes a controller and a hydraulic system composed of four solenoid valves, an accumulator, and a filling system, and the hydraulic system is used to adjust the pressure in the oil chamber of the brake cylinder; a first pressure detection system for detecting the pressure of the accumulator is provided on the accumulator;

[0009] The controller is respectively connected to the displacement detection system, the second pressure detection system, and the first pressure detection system to obtain detection signals; the controller is respectively connected to the four solenoid valves and the filling system for control;

[0010] The four solenoid valves are respectively a first solenoid valve, a second solenoid valve, a third solenoid valve, and a fourth solenoid valve; wherein, the inlets of the first solenoid valve and the second solenoid valve are connected to the oil circuit at the outlet of the filling system, the outlets of the first solenoid valve and the second solenoid valve are connected to the oil chamber of the brake cylinder, the filling system is connected to the fuel tank, and the accumulator is arranged on the outlet oil circuit of the filling system; the inlets of the third solenoid valve and the fourth solenoid valve are connected to the oil chamber of the brake cylinder, and the outlets are connected to the fuel tank; the output flow rates of the first solenoid valve and the fourth solenoid valve are less than those of the second solenoid valve and the third solenoid valve;

[0011] The controller has a database therein, and the actual flow output characteristics of the four solenoid valves in the frequency range of 50 Hz - 200 Hz are stored in the database; in the way of looking up the table in the database, the controller can obtain the driving frequencies corresponding to the required output characteristics of each solenoid valve at the selected duty ratio of the control signal.

[0012] Further, the controller respectively outputs a duty ratio modulation signal and a frequency modulation signal to the four solenoid valves to control the opening and closing states and working frequencies of the solenoid valves, the duty ratio range of the duty ratio modulation signal is 0 - 100%, and the frequency range of the frequency modulation signal is 50 - 200 Hz.

[0013] Further, an accumulator pressure threshold is set in the controller. When the first pressure detection system detects that the accumulator pressure is lower than the accumulator pressure threshold, the controller controls the liquid filling system to fill the accumulator with liquid.

[0014] The present invention also provides a braking method for the above-mentioned variable-frequency high-precision hydraulic braking system, which includes the following steps:

[0015] 1) When the vehicle starts, the oil flows out of the fuel tank, and the first solenoid valve and the second solenoid valve are fully open, that is, the duty cycle modulation signals output by the controller to these two solenoid valves both have a duty cycle of 100%. The oil flows into the brake cylinder oil cavity through the first solenoid valve and the second solenoid valve; the pressure in the brake cylinder oil cavity starts to build up. When the braking pressure gradually rises to reach the pre-loaded braking pressure P pre When it reaches, the first solenoid valve and the second solenoid valve are fully closed, where the pre-loaded braking pressure P pre is less than the target braking pressure P0. At this time, the brake block generates a pre-loaded displacement Δx1; during the process of step 1), the third solenoid valve and the fourth solenoid valve always remain closed;

[0016] 2) When the displacement detection system detects a braking command signal, the controller looks up the table in the database to obtain the duty cycle corresponding to the critical dead zone point at the maximum driving frequency of 200 Hz of the solenoid valve. The critical dead zone point is the characteristic point where the flow output characteristic is just zero; based on this duty cycle, the controller increases the frequency of the first solenoid valve to 50 Hz and maintains the driving state unchanged; at the same time, at the same duty cycle, the controller increases the driving frequency of the fourth solenoid valve to 50 - 200 Hz, and adjusts the flow output characteristic of the fourth solenoid valve differentially with high precision by changing the driving frequency to make the braking pressure reach the target braking pressure P0. After reaching the target braking pressure, the first solenoid valve and the fourth solenoid valve are fully closed to maintain the braking pressure, and the brake block reaches the target displacement Δx2; during the process of step 2), the second solenoid valve and the third solenoid valve remain closed;

[0017] 3) When the braking command signal is "0", the third solenoid valve with a large flow rate starts to respond, and the excess oil returns to the fuel tank through the third solenoid valve until the pressure in the brake cylinder oil cavity returns to the pre-loaded braking pressure P pre to prepare for the next braking response;

[0018] 4) When the vehicle is turned off, the third solenoid valve is fully open, and the oil in the system returns to the fuel tank through the third solenoid valve, and the brake block returns to the displacement of 0.

[0019] Preferably, the specific content of step 2) is as follows:

[0020] 2.1) The controller obtains the real-time pressure of the brake cylinder oil chamber through the second pressure detection system, and sets the target flow output characteristics of the first solenoid valve and the fourth solenoid valve at the current moment according to the difference between the real-time pressure of the brake cylinder oil chamber and the target braking pressure;

[0021] 2.2) The controller separately searches in the database for the combinations of drive frequencies and duty cycles that satisfy the target flow output characteristics of the first solenoid valve and the fourth solenoid valve, and controls the first solenoid valve and the fourth solenoid valve with the obtained combinations of drive frequencies and duty cycles, thereby increasing the real-time pressure of the brake cylinder oil chamber; wherein, the duty cycle is the duty cycle corresponding to the critical dead zone point at the maximum drive frequency of 200 Hz of the solenoid valve, and the critical dead zone point is the characteristic point where the flow output characteristic is just zero; the drive frequency of the first solenoid valve is maintained at 50 Hz, and the drive frequency of the fourth solenoid valve is controlled within the range of 50 - 200 Hz;

[0022] 2.3) Repeat steps 2.1 and 2.2) until the real-time pressure of the brake cylinder oil chamber reaches the target braking pressure, at which time the first solenoid valve and the fourth solenoid valve are fully closed.

[0023] Further, when any one of the first solenoid valve and the second solenoid valve is damaged, the pressure is gradually increased to the preloaded braking pressure P by using the other normally working solenoid valve alone to perform the pressure building in step 1) pre and perform the pressure control in step 2) to make the pressure reach the target braking pressure P0; wherein, during the pressure control process in step 2), the controller obtains the drive frequency corresponding to the required flow output characteristic at the corresponding control signal duty cycle through looking up the table in the database, and adjusts the drive frequency of the solenoid valve in real time;

[0024] When any one of the third solenoid valve and the fourth solenoid valve is damaged, the pressure is reduced to the preloaded braking pressure P by using the other normally working solenoid valve alone to perform the pressure reduction in step 3) pre and perform the oil discharge process in step 4); wherein, during the pressure reduction process in step 3), the controller obtains the drive frequency corresponding to the required flow output characteristic at the corresponding control signal duty cycle through looking up the table in the database, and adjusts the drive frequency of the solenoid valve in real time.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1) In the prior art, the duty cycle of the control signal is usually changed to vary the magnitude of the output flow rate, and the driving frequency is increased to enhance the control accuracy of the braking system, thereby reducing the steady-state fluctuation of the braking pressure. However, the above control parameters (duty cycle + driving frequency) are limited to the linear region of the solenoid valve flow output characteristic, and this linear region decreases as the driving frequency increases, seriously affecting the dynamic and static performance of the hydraulic braking system. As the driving frequency continues to increase, in the case of a small duty cycle, when the spool has not fully opened, the falling edge of the control signal has arrived, resulting in the solenoid valve not being able to fully open, thus reducing the magnitude of the average output flow rate. At this time, the solenoid valve flow output characteristic is in the non-linear region. Therefore, the present invention takes into account the flow output characteristics of both the linear region and the non-linear region of the solenoid valve. During the pressure build-up process of the braking system, the solenoid valve opens and closes in the linear region, thereby achieving rapid pressure build-up. When the braking pressure approaches the target pressure, by regulating the driving frequency, the solenoid valve opens and closes in the non-linear region, thereby increasing the flow output resolution and further improving the control accuracy of the braking pressure.

[0027] 2) As the braking pressure gets closer and closer to the target pressure, under high-frequency driving, the flow output gradually decreases and approaches the control dead zone. The prior art cannot reliably guarantee the control accuracy of the braking pressure. Therefore, based on the existing control method, the present invention further proposes a differential configuration. Through the differential high-frequency regulation of the double solenoid valves, the influence of the control dead zone can be avoided, and finally the flow output resolution of the solenoid valve is reliably improved.

[0028] 3) Aiming at the problems that in the prior art, during the pressure build-up process of the existing proportional valve, it is easy to cause the braking pressure response to lag, the braking reliability is poor, and the phenomenon of braking pressure overshoot is likely to occur. The present invention uses an electromagnetic on-off valve as the control element of the braking system, which has only two states of "open" and "closed", and has the advantages of high-speed response and strong anti-pollution ability. In addition, the present invention adopts a control scheme of a combination valve with large / small flow solenoid valves. The brake oil chamber is controlled by two groups of large / small flow solenoid valves to control the oil inlet and outlet of the hydraulic braking system respectively. At the same time, the entire braking process is divided into multiple stages to achieve the control effect of rapid pressure build-up with large flow and precise pressure control with small flow. Moreover, the present invention adds a stage of waiting for braking, and the braking pressure is pre-lifted to the pre-loaded braking pressure P pre , which is slightly less than the target braking pressure P0; when the braking command signal comes, the braking pressure can quickly reach the target braking pressure P0, thereby greatly reducing the braking time and improving the dynamic response performance of the braking stage.

[0029] 4) In the prior art, a single proportional valve is often used to control the braking pressure. When the proportional valve fails to work properly due to a fault, it will seriously affect the reliability of the braking system and the safety of the operation of the main engine equipment. The present invention adopts a combined scheme of two sets of large / small flow solenoid valves to respectively control the oil inlet and outlet of the hydraulic braking system, which has strong fault tolerance. When any one of the solenoid valves in the oil inlet and outlet circuits is damaged, the present invention can still meet the braking requirements and ensure normal and effective braking. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 is a schematic diagram of the variable-frequency high-precision hydraulic braking system of the present invention;

[0031] Figure 2 is a schematic diagram of the flow characteristics of the solenoid valve;

[0032] Figure 3 is the response of the braking pressure signal;

[0033] Figure 4 is the comparison of the brake pads and the brake disc at different stages.

[0034] In the figure, 1 - liquid filling system, 2 - first solenoid valve, 3 - accumulator, 4 - second solenoid valve, 5 - first pressure detection system, 6 - controller, 7 - displacement detection system, 8 - second pressure detection system, 9 - pedal system, 10 - brake cylinder, 11 - brake pad, 12 - brake disc, 13 - third solenoid valve, 14 - fourth solenoid valve. DETAILED DESCRIPTION OF THE INVENTION

[0035] The present invention will be further described and explained below in conjunction with the specific embodiments. The embodiments are only examples of the present disclosure and do not delimit the scope of limitation. The technical features of each embodiment of the present invention can be combined correspondingly without conflict.

[0036] As Figure 1 shown, the variable-frequency high-precision hydraulic braking system of the present invention includes a pedal system, a displacement detection system, a brake cylinder, brake pads, a brake disc, four solenoid valves, an accumulator, a liquid filling system, a first pressure detection system, and a second pressure detection system;

[0037] For the above main system components, the following detailed functional descriptions are made:

[0038] The liquid filling system 1 fills the accumulator 3 with liquid to ensure that the accumulator 3 can provide sufficient braking pressure. When the controller detects that the pressure of the accumulator is insufficient, it transmits a control signal α to the liquid filling system, and the liquid filling system fills the accumulator with liquid to supplement the pressure.

[0039] The four solenoid valves are respectively a first solenoid valve, a second solenoid valve, a third solenoid valve and a fourth solenoid valve; wherein, the inlets of the first solenoid valve and the second solenoid valve are connected to the outlet oil circuit of the liquid filling system, the outlets of the first solenoid valve and the second solenoid valve are connected to the oil chamber of the brake cylinder, the liquid filling system is connected to the fuel tank, and the accumulator is arranged on the outlet oil circuit of the liquid filling system; the inlets of the third solenoid valve and the fourth solenoid valve are connected to the oil chamber of the brake cylinder, and the outlets are connected to the fuel tank; the output flow rates of the first solenoid valve and the fourth solenoid valve are less than those of the second solenoid valve and the third solenoid valve; the four solenoid valves are all two-position two-way electromagnetic switch valves. Among them, the present invention requires that the output flow rate Q1 of the first solenoid valve 2 and the fourth solenoid valve 14 during operation is less than the output flow rate Q2 of the second solenoid valve 4 and the third solenoid valve 13 during operation, and Q2:Q1≥10:1. In an alternative embodiment, the four solenoid valves are identical solenoid valves, and only by changing the duty cycle of each valve control signal, Q2:Q1≥10:1 is achieved. In another alternative embodiment, the first solenoid valve 2 and the fourth solenoid valve 14 are selected as a small-flow solenoid valve, and the second solenoid valve 4 and the third solenoid valve 13 are selected as a large-flow solenoid valve; so that Q2:Q1≥10:1..

[0040] The controller is respectively connected to the displacement detection system, the second pressure detection system, and the first pressure detection system to obtain detection signals; the controller is respectively connected to the four solenoid valves and the liquid filling system for control; the first pressure detection system 5 is used to detect the pressure in the accumulator 3 in real time; the second pressure detection system 8 is used to detect the liquid pressure in the brake 10 in real time; the displacement detection system 7 detects the displacement signal of the pedal system 9 in real time, that is, the greater the displacement, the greater the current braking system's demand for braking pressure, and the greater the target braking pressure P0 will be.

[0041] The controller has a database stored with the actual flow output characteristics of the four solenoid valves in the frequency range of 50Hz - 200Hz; by looking up the table in the database, the controller can obtain the drive frequency corresponding to the required output characteristics of each solenoid valve at the selected duty cycle. Three signals from the first pressure detection system 5, the second pressure detection system 8, and the displacement detection system 7 are input into the controller 6, and control signals α for the liquid filling system 1, duty cycle modulation signals β1 (0 - 100%) and drive frequency signals f1 (50 - 200Hz) for the first solenoid valve 2, duty cycle modulation signals β2 (0 - 100%) and drive frequency signals f2 (50 - 200Hz) for the second solenoid valve 4, duty cycle modulation signals β3 (0 - 100%) and drive frequency signals f3 (50 - 200Hz) for the third solenoid valve 13, and duty cycle modulation signals β4 (0 - 100%) and drive frequency signals f4 (50 - 200Hz) for the fourth solenoid valve 14 are output.

[0042] The brake cylinder 10 is a piston cylinder. A brake block is arranged at the piston output end, and a load spring provides the restoring force for the brake block. The compression amount of the load spring is the displacement amount of the brake block. As the hydraulic pressure in the brake cylinder 10 increases, the piston push rod extends after overcoming forces such as spring force and friction force, reducing the distance between the brake block 11 and the brake disc 12. When the brake block 11 contacts the brake disc 12, a braking friction torque is generated. And the friction torque continuously increases as the normal pressure between the brake block 11 and the brake disc 12 increases.

[0043] The flow rate characteristics of the solenoid valve are shown as Figure 2 follows. The abscissa is the duty cycle of the duty cycle modulation signal output by the controller, and the ordinate is the ratio of the average output flow rate of each solenoid valve to the maximum output flow rate. In the prior art, to achieve a small flow rate output of the oil fluid, it is basically based on reducing the duty cycle of the control signal in the linear region under a fixed frequency control of a solenoid valve. For example, at a driving frequency of 50 Hz, to achieve a 5% flow rate output characteristic at this time, it is necessary to reduce the duty cycle of the control signal from the linear region to the non-linear region, and it is usually difficult to quantitatively analyze the flow rate output characteristics in the non-linear region in the prior art. In addition, if through a large amount of trial and error time, a 5% flow rate output characteristic is achieved, the duty cycle at this state is already on the verge of the dead zone, which will seriously affect the reliability of the solenoid valve flow rate output and the control accuracy. Therefore, the present invention pre-imports the actual flow rate output characteristics of each frequency (50 Hz - 200 Hz) into the controller, and the controller can feedback in real time the driving frequency corresponding to each flow rate output characteristic and the characteristic values of each duty cycle in the working area (linear region and non-linear region) of the solenoid valve by looking up the table in the database. Taking Figure 2 points A and C in it as an example for illustration, at a driving frequency of 50 Hz, the first solenoid valve inputs the flow rate with the control parameters at point A; at the same time, at a fixed duty cycle, through looking up the table and feedback in the database, the driving frequency of the fourth solenoid valve is controlled at point C to control the flow rate output. Based on the variable frequency control of the dual solenoid valves, through the way of flow rate differential, a 5% flow rate output characteristic can be achieved (the first solenoid valve inputs at point A and the fourth solenoid valve outputs at point B).

[0044] When the braking pressure rises from the preloading pressure value to the target pressure value, a dual solenoid valve variable frequency driving mode is adopted. The first solenoid valve is always at point A (the corresponding point at a fixed duty cycle of the 100 Hz critical dead zone point in the 50 Hz flow rate characteristic curve), and the fourth solenoid valve is at point B of the 200 Hz critical dead zone point. As the pressure difference continuously approaches, the driving frequency and the control signal duty cycle of the first solenoid valve remain unchanged. Based on looking up the table in the database, the driving frequency of the fourth solenoid valve is reduced in real time until the driving frequencies of the first solenoid valve and the fourth solenoid valve are the same (50 Hz). At this time, the braking pressure difference is 0, that is, the target pressure value is reached. Subsequently, the first solenoid valve and the fourth solenoid valve are closed to keep the braking pressure value unchanged.

[0045] Therefore, the present invention can improve the maximum controllable duty ratio of the solenoid valve, expand the drive control range, and based on the variable-frequency differential flow output, greatly improve the flow output resolution, improve the flow control accuracy, and effectively avoid phenomena such as overshoot in the valve control system.

[0046] The following describes the braking process of the present invention in conjunction with Figure 3 and Figure 4 as shown in Figure 3 When the vehicle starts at time t1, the hydraulic oil flows out from the P port, the first solenoid valve 2 and the second solenoid valve 4 are fully open (both β1 and β2 are 100%), and the hydraulic oil flows into the brake chamber after passing through the solenoid valve. At time t2, pressure building starts, and during the process of the braking pressure gradually rising, the preloading braking pressure P pre is reached at time t3, which is slightly less than the target braking pressure P0, P pre = P0 * (90% - 95%), and the load spring is gradually compressed to the target pre-compression amount Δx1 (as shown in Figure 4 ). At this time, the first solenoid valve 2 and the second solenoid valve 4 are fully closed (both β1 and β2 are 0).

[0047] When the braking command signal arrives at time t4, the controller, through the database, based on the variable-frequency technology, real-time regulates the driving frequency f1, duty ratio β1 of the small-flow first solenoid valve 2 and the driving frequency f4, duty ratio β4 of the small-flow fourth solenoid valve 14, and differentially controls the pressure with high precision. At time t5, the braking system quickly builds pressure and reaches the target braking pressure P0 at time t6. At this time, the first solenoid valve 2 and the fourth solenoid valve 14 are fully closed, and the braking pressure is maintained, and the load spring is gradually compressed to the target pre-compression amount Δx2.

[0048] When the braking command signal is "0" at time t7, the large-flow third solenoid valve 13 starts to respond at time t8, and the excess hydraulic oil returns to the fuel tank (T port) through the third solenoid valve 13, and reaches the preloading braking pressure P pre at time t9, preparing for the next braking response. When the vehicle is turned off at time t 10 , the third solenoid valve 13 is fully open (β3 is 0), and the hydraulic oil in the system returns to the fuel tank through the third solenoid valve 13. The compression amount of the load spring returns from the target pre-compression amount Δx1 to the compression amount 0.

[0049] The present invention adopts a combined scheme of two sets of large / small flow solenoid valves to separately control the oil inlet and outlet of the hydraulic braking system, and has strong fault tolerance. When any one of the solenoid valves in the inlet and outlet oil circuits is damaged, the present invention can still meet the braking requirements and ensure normal and effective braking.

[0050] Taking the damage of the first solenoid valve 2 with a small flow rate in the inlet oil circuit and the third solenoid valve 13 with a large flow rate in the outlet oil circuit as an example, a specific description is given. At this time, the multi-stage pressure building and pressure control processes are simplified. When the controller receives the vehicle start signal, the second solenoid valve 4 is fully opened. When the braking pressure reaches the preloading pressure P pre When it reaches, the second solenoid valve 4 is closed, and the preloading pressure P pre is maintained.

[0051] When the rising edge of the braking command signal comes, the drive frequency f2 and the duty cycle β2 at the initial point of the second solenoid valve are switched to point A. At this time, the drive frequency f2 is 50 Hz, and the duty cycle β2 is the duty cycle value corresponding to the critical dead zone point of 200 Hz. Subsequently, the controller looks up the table through the database and adjusts the drive frequency f2 of the second solenoid valve 4 in real time based on the frequency conversion technology, continuously increasing the drive frequency until 200 Hz, and accurately raising the preloading pressure P pre to the target braking pressure P0, then the second solenoid valve 4 is closed, and the target braking pressure P0 is maintained.

[0052] When the falling edge of the braking command signal comes, the fourth solenoid valve 14 starts to respond, reducing the braking pressure to the preloading pressure P pre to prepare for the next braking response. When the controller receives the vehicle stop signal, the fourth solenoid valve 14 responds, and the oil in the system returns to the fuel tank through the solenoid valve 14.

[0053] In summary, based on the fault tolerance of the braking system of the present invention, the braking requirements can still be met, ensuring normal and effective braking.

[0054] The above-described embodiments only represent several implementation manners of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the patent of the present invention. For those of ordinary skill in the art, without departing from the concept of the present invention, several deformations and improvements can still be made, and these all belong to the protection scope of the present invention.

Claims

1. A variable-frequency high-precision hydraulic braking system, comprising a pedal system, a displacement detection system for detecting the displacement of the pedal system, a brake consisting of a brake cylinder, a brake block and a brake disc, and a second pressure detection system for detecting the pressure in the oil chamber of the brake cylinder; characterized in that, The variable-frequency high-precision hydraulic braking system further includes a controller and a hydraulic system composed of four solenoid valves, an accumulator, and a liquid filling system. The hydraulic system is used to adjust the pressure of the oil chamber of the brake cylinder. A first pressure detection system for detecting its pressure is provided on the accumulator. The controller is respectively connected to the displacement detection system, the second pressure detection system, and the first pressure detection system to obtain detection signals, and is respectively connected to the four solenoid valves and the liquid filling system for control. The four solenoid valves are respectively a first solenoid valve, a second solenoid valve, a third solenoid valve, and a fourth solenoid valve. Among them, the inlets of the first solenoid valve and the second solenoid valve are connected to the oil circuit at the outlet of the liquid filling system. The outlets of the first solenoid valve and the second solenoid valve are connected to the oil chamber of the brake cylinder. The liquid filling system is connected to the fuel tank, and the accumulator is arranged on the outlet oil circuit of the liquid filling system. The inlets of the third solenoid valve and the fourth solenoid valve are connected to the oil chamber of the brake cylinder, and the outlets are connected to the fuel tank. The output flow rates of the first solenoid valve and the fourth solenoid valve are smaller than those of the second solenoid valve and the third solenoid valve. The controller has a database stored with the actual flow output characteristics of the four solenoid valves in the frequency range of 50 Hz - 200 Hz. By looking up the table in the database, the controller can obtain the drive frequency corresponding to the required output characteristics of each solenoid valve at the selected duty cycle of the control signal. 1) When the vehicle starts, the hydraulic fluid flows out of the fuel tank. The first solenoid valve and the second solenoid valve are fully open, that is, the duty cycle modulation signals output by the controller to these two solenoid valves both have a duty cycle of 100%. The hydraulic fluid flows into the brake cylinder oil chamber through the first solenoid valve and the second solenoid valve. The brake cylinder oil chamber starts to build pressure. When the brake pressure gradually rises to reach the preloading brake pressure P pre When, the first solenoid valve and the second solenoid valve are fully closed, where the preloading brake pressure P pre is less than the target brake pressure P0. At this time, the brake pads generate a preloading displacement Δx1. During the process of step 1), the third solenoid valve and the fourth solenoid valve always remain closed; 2) When the displacement detection system detects a braking command signal, the controller looks up the table in the database to obtain the duty cycle corresponding to the critical dead zone point at the maximum drive frequency of 200 Hz of the solenoid valve. The critical dead zone point is the characteristic point where the flow output characteristic is just zero. Based on this duty cycle, the controller increases the frequency of the first solenoid valve to 50 Hz and maintains the drive state unchanged. At the same time, at the same duty cycle, the controller increases the drive frequency of the fourth solenoid valve to 50 - 200 Hz, and differentially and highly precisely controls the pressure by adjusting the flow output characteristic of the fourth solenoid valve, so that the braking pressure reaches the target braking pressure P0. After reaching the target braking pressure, the first solenoid valve and the fourth solenoid valve are fully closed to maintain the braking pressure, and the brake block reaches the target displacement Δx2. During the process of step 2), the second solenoid valve and the third solenoid valve remain closed. The specific content of step 2) is as follows: 2.1) The controller obtains the real-time pressure of the oil chamber of the brake cylinder through the second pressure detection system, and sets the target flow output characteristics of the first solenoid valve and the fourth solenoid valve at the current moment according to the difference between the real-time pressure of the oil chamber of the brake cylinder and the target braking pressure. 2.2) The controller respectively searches in the database for combinations of drive frequencies and duty cycles that satisfy the target flow output characteristics of the first solenoid valve and the fourth solenoid valve, and controls the first solenoid valve and the fourth solenoid valve with the obtained combinations of drive frequencies and duty cycles, thereby increasing the real-time pressure of the oil chamber of the brake cylinder. Among them, the duty cycle is the duty cycle corresponding to the critical dead zone point at the maximum drive frequency of 200 Hz of the solenoid valve. The critical dead zone point is the characteristic point where the flow output characteristic is just zero. The drive frequency of the first solenoid valve is maintained at 50 Hz, and the drive frequency of the fourth solenoid valve is controlled within the range of 50 - 200 Hz. 2.3) Repeat steps 2.1 and 2.2) until the real-time pressure in the brake cylinder oil chamber reaches the target braking pressure, at which time the first solenoid valve and the fourth solenoid valve are fully closed; 3) When the braking command signal is "0", the third solenoid valve with a large flow rate starts to respond, and the excess oil returns to the fuel tank through the third solenoid valve until the pressure in the oil chamber of the brake cylinder returns to the preloaded specified pressure P pre , preparing for the next braking response; 4) When the vehicle is turned off, the third solenoid valve is fully open, and the oil in the system returns to the fuel tank through the third solenoid valve, and the brake pads return to the displacement of 0; When any one of the first solenoid valve and the second solenoid valve is damaged, the other solenoid valve that is working normally is used alone to build pressure in step 1) so that the pressure gradually rises to reach the preloaded braking pressure P pre , and step 2) is performed to control the pressure so that the pressure reaches the target braking pressure P0; wherein, during the pressure control process of step 2), the controller obtains the drive frequency corresponding to the required flow output characteristic at the duty ratio of the corresponding control signal by looking up the table in the database, and adjusts the drive frequency of the solenoid valve in real time; When any one of the third solenoid valve and the fourth solenoid valve is damaged, the other solenoid valve that is working normally is used alone to reduce the pressure in step 3) so that the pressure drops to the preloaded braking pressure P pre , and the oil drainage process of step 4) is carried out; wherein, during the pressure reduction process of step 3), the controller obtains the driving frequency corresponding to the required flow output characteristic at the duty ratio of the corresponding control signal by looking up the table in the database, and adjusts the driving frequency of the solenoid valve in real time; When each solenoid valve is in the open state, the ratio of the output flow rates of the second solenoid valve and the third solenoid valve to the output flow rates of the first solenoid valve and the fourth solenoid valve is ≥ 10:

1.

2. The variable-frequency high-precision hydraulic braking system according to claim 1, wherein The four solenoid valves are all two-position two-way electromagnetic on-off valves, and have only two working states: open and closed.

3. The variable-frequency high-precision hydraulic braking system according to claim 1, wherein The controller outputs a duty cycle modulation signal and a frequency modulation signal to the four solenoid valves respectively to control the opening and closing states and the working frequencies of the solenoid valves. The duty cycle range of the duty cycle modulation signal is 0 - 100%, and the frequency range of the frequency modulation signal is 50 - 200 Hz.

4. The variable-frequency high-precision hydraulic braking system according to claim 1, characterized in that An accumulator pressure threshold is set in the controller. When the first pressure detection system detects that the accumulator pressure is lower than the accumulator pressure threshold, the controller controls the liquid filling system to fill the accumulator with liquid.

5. The variable-frequency high-precision hydraulic braking system according to claim 1, characterized in that The preloaded braking pressure is 90 - 95% of the target braking pressure.

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