A hydraulic braking system based on frequency modulation and its control method

Abstract

The present invention discloses a hydraulic brake system based on frequency modulation and a control method thereof, which belongs to the field of hydraulic brake control. During the braking stage, the hydraulic oil flows into the brake cylinder at a large flow rate to achieve the purpose of rapid pressure building; when the pressure in the brake cylinder is infinitely close to the target brake pressure, the controller outputs a high-frequency opening and closing instruction of the digital switch valve according to the pressure feedback signal in the hydraulic cylinder, so that the digital switch valve switches to a high-frequency opening and closing state. At this time, the hydraulic oil flows into the brake cylinder at a small flow rate, and the brake pressure approaches the target brake pressure at an extremely small growth rate while infinitely approaching the target brake pressure, so as to achieve the purpose of precise pressure building. When the brake system is in an emergency braking state, the actual pressure in the brake cylinder switches between the target brake pressure and the separation brake pressure, thereby increasing the contact / separation switching frequency between the brake pad and the brake disc, and increasing the effective contact time between the brake pad and the brake disc, so that the braking distance of the vehicle is effectively controlled.

Description

Technical Field

[0001] The present invention belongs to the field of hydraulic braking, and particularly relates to a hydraulic braking system based on frequency modulation 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. Its main function is to decelerate and stop a moving vehicle and keep the speed of a downhill vehicle stable. Currently, the highest technology of full hydraulic braking is the electro-hydraulic proportional braking control technology. However, the proportional valve has a dead zone in the middle position, resulting in slow pressure response of the brake and lag in the braking process. There is internal leakage in the proportional valve, making it difficult to keep the braking pressure stable for a long time and resulting in low control accuracy. 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 effectively brake, poor reliability, and difficulty in meeting the requirements of full hydraulic braking under complex working conditions.

[0003] Digital hydraulic technology uses digital on-off valves as the core control elements, with fast frequency response. The digital on-off valve makes high-frequency opening and closing actions during operation. The discrete fluid generated by the 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, being insensitive to the cleanliness of the oil, stronger anti-pollution ability, and faster response.

[0004] One opening and closing cycle of the digital on-off valve includes four stages: the valve port closing to opening, the valve port remaining open, the valve port opening to closing, and the valve port remaining closed. During the continuous opening and closing process of the valve body, when the driving voltage is constant, the durations of the two stages of the valve port closing to opening and the valve port opening to closing remain fixed. Through the driving voltage strategy, the duration of the closing and holding stage of the on-off valve is made zero. As the opening and closing frequency of the digital on-off valve gradually increases, in a single opening and closing cycle, the time for the valve port to remain open gradually shortens. Eventually, in the same opening and closing time, the higher the opening and closing frequency of the valve body, the smaller the average flow rate in the hydraulic circuit.

[0005] The traditional digital hydraulic braking system mainly has the following deficiencies:

[0006] 1) When the traditional digital hydraulic braking system receives a braking instruction from the brake pedal, it fills the hydraulic cylinder with hydraulic oil through the hydraulic circuit, causing the brake block to rub against the brake disc to achieve the braking effect. During this process, the opening and closing frequency of the digital on-off valve remains constant, so that the average flow rate remains constant. The braking pressure builds up from 0 MPa to the target value, resulting in too long braking time. When approaching the target braking pressure infinitely, the pressure rising speed in the braking system cannot be accurately controlled and is prone to deviating from the target braking pressure.

[0007] 2) In traditional digital hydraulic systems, the opening and closing frequency of digital switching valves remains constant, keeping the hydraulic oil flow rate at the oil inlet of the brake cylinder constant. As a result, the speed of the brake block during the approach to the brake disc also remains constant. If rapid pressure build-up is required, the movement speed of the brake block is relatively high, leading to excessive rigid impact when it contacts the brake disc, affecting the system lifespan and driving safety. If precise pressure build-up is needed, the movement speed of the brake block is too low to meet the requirements of rapid braking response, posing a danger.

[0008] 3) Traditional anti-lock braking systems (ABS) utilize the contact / separation switching between the brake block and the brake disc to ensure that the vehicle wheels will not be frictionally locked by the brake block during emergency braking and lose the ability to control direction. However, the contact / separation switching frequency between the brake block and the brake disc is not high, and the effective contact time between the brake block and the brake disc is short, ultimately resulting in an excessive braking distance of the vehicle, posing a danger.

[0009] 4) Since digital switching valves have only two states, "open" and "closed", there will inevitably be flow pulsation and pressure shock, further affecting the steady-state fluctuation of the braking pressure. Summary of the Invention

[0010] To solve the problems in the prior art, the present invention proposes a high-precision digital hydraulic braking system and its control method based on frequency modulation of digital switching valves. When the pressure in the brake cylinder is about to reach the target braking pressure, the digital switching valve switches from low-frequency opening and closing to high-frequency opening and closing, thereby reducing the hydraulic circuit flow rate to more precisely and rapidly approach the braking pressure. At the same time, it utilizes its high-precision pressure control advantage to achieve the function of ultra-high-frequency point braking (anti-lock).

[0011] The technical solution of the present invention is as follows:

[0012] The present invention first provides a hydraulic braking system based on frequency modulation, which includes:

[0013] A brake cylinder having a rodless chamber, a rod chamber, and a piston for separating the rodless chamber and the rod chamber. Both the rodless chamber and the rod chamber are pre-filled with oil. By adjusting the oil pressure, the piston can move in the brake cylinder. The piston is connected with a return spring and is also connected to a brake block outside the brake cylinder through a connecting rod. The brake block generates braking force by acting on an external brake disc.

[0014] A rodless chamber oil circuit connected to the rodless chamber for controlling the oil pressure in the rodless chamber of the brake cylinder.

[0015] A rod chamber oil circuit connected to the rod chamber for controlling the oil pressure in the rod chamber of the brake cylinder.

[0016] A pressure detection system for detecting the magnitude of the oil pressure in the rodless chamber of the brake cylinder.

[0017] A displacement and speed detection system for detecting the displacement and speed of an external pedal device; and

[0018] A controller for obtaining the detection signals of the pressure detection system and the displacement and speed detection system, and outputting a control signal to control the opening and closing states and working frequencies of the digital switching valves in the rodless cavity oil circuit and the rod cavity oil circuit;

[0019] The rodless cavity oil circuit and the rod cavity oil circuit are exactly the same, and both include an accumulator, an inlet oil circuit digital switching valve, an outlet oil circuit digital switching valve and a relief valve; wherein, the accumulator is arranged at the inlet of the inlet oil circuit digital switching valve to ensure the oil circuit pressure, and the relief valve is arranged at the outlet of the inlet oil circuit digital switching valve to set the maximum oil circuit pressure. The inlet oil circuit digital switching valve is used for oil inlet, and the outlet oil circuit digital switching valve is used for oil return.

[0020] The present invention also provides a frequency modulation braking method based on the above hydraulic braking system, which includes the following steps;

[0021] The displacement and speed detection system continuously detects the displacement and speed of the external pedal device;

[0022] When a displacement signal of the pedal device is received and the movement speed of the pedal device is within the set normal braking speed range; the hydraulic braking system is in a normal braking state; the normal braking state includes a rapid pressure build-up stage and a differential approaching stage; in the rapid pressure build-up stage, the inlet oil circuit digital switching valve of the rodless cavity oil circuit is fully open, and the oil enters the rodless cavity and quickly reaches the set pressure, and then enters the differential approaching stage; in the differential approaching stage, the rodless cavity oil circuit and the rod cavity oil circuit work simultaneously, and the average flow rate of the rodless cavity oil circuit is controlled to be greater than that of the rod cavity oil circuit, so that the oil pressure in the rodless cavity gradually approaches the target braking pressure p0, and the brake block contacts the brake disc to generate friction to achieve the braking purpose;

[0023] When a displacement signal of the pedal device is received and the movement speed of the pedal device is within the set emergency braking speed range; the hydraulic braking system is in an emergency braking state; the emergency braking state is divided into a rapid pressure build-up stage and an anti-lock stage. In the rapid pressure build-up stage, the inlet oil circuit digital switching valve of the rodless cavity oil circuit is fully open, and the oil enters the rodless cavity and quickly reaches the set pressure, and then enters the anti-lock stage; in the anti-lock stage, the rodless cavity oil circuit and the rod cavity oil circuit work simultaneously, and the hydraulic braking system controls the flow rates of the rodless cavity oil circuit and the rod cavity oil circuit to make the oil pressure in the rodless cavity increase or decrease periodically, so that the brake block separates from or contacts the brake disc frequently until the vehicle completes braking;

[0024] The emergency braking speed range is greater than the normal braking speed range.

[0025] As a preferred embodiment of the present invention, when the vehicle starts and the displacement and speed detection system does not detect the displacement signal of the pedal device, the piston is in the initial position under the action of the return spring, and the accumulators in the rodless chamber oil circuit and the rod chamber oil circuit are filled with liquid to the set pressure.

[0026] As a preferred embodiment of the present invention, the rapid pressure build-up stages in the normal braking state and the emergency braking state are the same;

[0027] In the rapid pressure build-up stage, the inlet digital switching valve of the rodless chamber oil circuit is fully open, the outlet digital switching valve is closed, and the oil enters the rodless chamber; the inlet digital switching valve of the rod chamber oil circuit is closed, the outlet digital switching valve is fully open, and the oil in the rod chamber flows out; when the oil pressure in the rodless chamber reaches the set percentage of the target braking pressure, the rapid pressure build-up stage ends.

[0028] As a preferred embodiment of the present invention, in the differential approaching stage of the normal braking state, the controller controls the inlet digital switching valve of the rodless chamber oil circuit to maintain the opening and closing frequency of f1, controls the return digital switching valve of the rodless chamber oil circuit to remain closed, controls the inlet digital switching valve of the rod chamber oil circuit to maintain the opening and closing frequency of f2, and controls the return digital switching valve of the rod chamber oil circuit to maintain the opening and closing frequency of f3; where f1 < f2, the greater the opening and closing frequency of the digital switching valve, the smaller its average flow rate. Therefore, the hydraulic oil flow rate at the inlet of the rodless chamber of the brake cylinder is greater than that at the inlet of the rod chamber, and its equivalent flow rate is the difference between the two. The actual effect is equivalent to the rodless chamber inlet and the rod chamber outlet, and the equivalent inlet flow rate of the rodless chamber is controlled to be less than 5% of the inlet flow rate in the rapid pressure build-up stage. The brake block contacts the brake disc with a very small impulse to generate friction and achieve the braking purpose; the digital switching valve of the rod chamber oil circuit opens and closes at the frequency of f3 to return the excess oil in the rod chamber to the fuel tank.

[0029] As a preferred embodiment of the present invention, the anti-lock stage in the emergency braking state consists of multiple anti-lock cycles, and each anti-lock cycle includes a differential working-in link and a differential fast-retreat link;

[0030] In the differential working-in link, the controller controls the inlet digital switching valve of the rodless chamber oil circuit to maintain the opening and closing frequency of f4, controls the return digital switching valve of the rodless chamber oil circuit to remain closed, controls the inlet digital switching valve of the rod chamber oil circuit to maintain the opening and closing frequency of f5, and controls the return digital switching valve of the rod chamber oil circuit to maintain the opening and closing frequency of f6; where f4 < f5, the hydraulic oil flow rate at the inlet of the rodless chamber of the brake cylinder is greater than that at the inlet of the rod chamber, and its equivalent flow rate is the difference between the two. The actual effect is equivalent to the rodless chamber inlet and the rod chamber outlet, and the equivalent inlet flow rate of the rodless chamber is controlled to be less than 5% of the inlet flow rate in the rapid pressure build-up stage. The brake block contacts the brake disc with a very small impulse to generate friction and achieve the braking purpose; the digital switching valve of the second return oil circuit opens and closes at the frequency of f6 to return the excess oil to the fuel tank;

[0031] In the differential fast-reverse link, the controller controls the digital switch valve of the oil inlet of the rodless cavity oil circuit to maintain the opening and closing frequency of f8, controls the digital switch valve of the oil return of the rodless cavity oil circuit to maintain the opening and closing frequency of f6, controls the digital switch valve of the oil inlet of the rod cavity oil circuit to maintain the opening and closing frequency of f7, and controls the digital switch valve of the oil return of the rod cavity oil circuit to remain closed; among which f7 <f8<f4<f5;由于f7<f8,制动缸无杆腔进油口的液压油流量小于有杆腔进油口的流量,其等效流量为两者的差值,实际效果等效于无杆腔出油,有杆腔进油,由于两者的流量差值相比于差动工进环节更大,制动块以极快的速度与制动盘分离;无杆腔油路的回油路的数字开关阀以f6的频率启闭,将多余油液回油至油箱。

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] (1) In the braking stage of the present invention, the digital switch valve first works in the rapid pressure building stage. At this time, the hydraulic oil flows into the brake cylinder at a large flow rate to achieve the purpose of rapid pressure building; when the pressure in the brake cylinder reaches the set value, and the set value approaches the target braking pressure (for example, 85-95% of the target braking pressure), the controller outputs a high-frequency opening and closing instruction of the digital switch valve according to the pressure feedback signal in the hydraulic cylinder, so that the digital switch valve switches to the high-frequency opening and closing state. The opening and closing frequency of the digital switch valve of the rodless cavity circuit of the brake cylinder is less than the opening and closing frequency of the digital switch valve of the rod cavity circuit of the brake cylinder, so that the filling flow of the rodless cavity circuit is greater than the filling flow of the rod cavity, and the equivalent flow rate is the difference between the two flows. The hydraulic oil flows into the brake cylinder at a small flow rate. The braking pressure approaches the target braking pressure at an extremely small growth rate while infinitely approaching the target braking pressure, so as to achieve the purpose of precise pressure building.

[0034] (2) When the present invention utilizes the low-frequency opening and closing of the digital switch valve to build pressure and approach the target braking pressure, it switches to high-frequency opening and closing, so that the operating speed of the brake cylinder drops rapidly, significantly reducing the momentum of the brake pad, effectively reducing the rigid impact of the brake system, and improving the life of the brake.

[0035] (3) Based on the frequency-flow effect characteristics of the digital switch valve, the present invention proposes an ultra-high frequency braking control strategy. Based on this characteristic, the pressure in the brake cylinder can be accurately controlled at any set value. When the brake system is in an emergency braking state, the actual pressure P in the brake cylinder is between P0 (target braking pressure) and P' (disengagement braking pressure, P xSwitch between <P' < P0). Thanks to the high-precision flow control ability of the digital switching valve under high-frequency opening and closing, P0 and P1 can be very close, thus reducing the single pressure switching time and increasing the contact / separation switching frequency between the brake block and the brake disc. The effective contact time between the brake block and the brake disc is increased, and finally the braking distance of the vehicle is effectively controlled.

[0036] (4) During the braking pressure switching process, the brake block moves differentially. The rodless cavity and the rod chamber of the brake cylinder are both supplied with oil. When the brake block approaches the brake disc, the opening and closing frequency of the digital switching valve in the rodless cavity circuit of the brake cylinder is less than that of the digital switching valve in the rod chamber circuit of the brake cylinder, so that the liquid filling flow rate in the rodless cavity circuit is greater than that in the rod chamber, and the equivalent flow rate is the difference between the two flow rates; when the brake block moves away from the brake disc, the opening and closing frequency of the digital switching valve in the rodless cavity circuit of the brake cylinder is greater than that of the digital switching valve in the rod chamber circuit of the brake cylinder, so that the liquid filling flow rate in the rodless cavity circuit is less than that in the rod chamber, and the equivalent flow rate is the difference between the two flow rates. Since the order of magnitude of this flow rate difference is smaller, the movement of the brake block will be more precisely controlled.

[0037] (5) An accumulator is added to both the two-chamber circuits of the brake cylinder in the present invention to ensure stable pressure supply in the circuit during the rapid pressure build-up stage and improve the working stability of the system. Description of the Drawings

[0038] Figure 1 It is a schematic diagram of the principle of a high-precision digital hydraulic braking system based on frequency modulation;

[0039] Figure 2 It is a schematic diagram of the working state of the hydraulic braking system of the present invention during braking preparation / ending;

[0040] Figure 3 It is a schematic diagram of the working state of the hydraulic braking system of the present invention during the rapid pressure build-up stage in the normal braking state;

[0041] Figure 4 It is a schematic diagram of the working state of the hydraulic braking system of the present invention during the differential approach stage in the normal braking state;

[0042] Figure 5 It is a schematic diagram of the working state of the hydraulic braking system of the present invention during the rapid pressure build-up stage in the emergency braking state;

[0043] Figure 6 It is a schematic diagram of the working state of the differential movement approach link of the hydraulic braking system of the present invention during the anti-lock braking stage in the emergency braking state;

[0044] Figure 7 It is a schematic diagram of the working state of the differential fast return link of the hydraulic braking system of the present invention during the anti-lock braking stage in the emergency braking state;

[0045] Figure 8 This is a timing diagram of the hydraulic braking system of the present invention in the normal braking state;

[0046] Figure 9 This is a timing diagram of the hydraulic braking system of the present invention in the emergency braking state.

[0047] Among them, 1 is the first oil return digital switch valve, 2 is the first oil inlet digital switch valve, 3 is the first accumulator, 4 is the overflow valve, 5 is the brake cylinder, 6 is the brake pad, 7 is the brake disc, 8 is the second accumulator, 9 is the second oil return digital switch valve, and 10 is the second oil inlet digital switch valve. Specific embodiments

[0048] The following further elaborates and explains the present invention in conjunction with specific embodiments. The described embodiments are only demonstrations of the disclosed content and do not delimit the scope of limitation. Without conflict, the technical features of each embodiment of the present invention can be combined accordingly.

[0049] As Figure 1 shown, the hydraulic braking system based on frequency modulation of the present invention includes: a rodless cavity oil circuit, a rod cavity oil circuit, a controller, a sensor, and a brake cylinder 5; in the figure, the P port is connected to an external liquid filling system including a hydraulic pump, and the T port is connected to the fuel tank.

[0050] The brake cylinder 5 of the present invention has a rodless cavity, a rod cavity, and a piston for separating the rodless cavity and the rod cavity. The rodless cavity and the rod cavity are both pre-filled with oil. By adjusting the oil pressure, the piston can move in the brake cylinder. The piston is connected with a return spring, and the piston is also connected with a brake pad 6 located outside the brake cylinder through a connecting rod. The brake pad generates a braking force by acting on the external brake disc 7.

[0051] The rodless cavity oil circuit and the rod cavity oil circuit of the present invention are exactly the same. Among them, the rodless cavity oil circuit includes the first accumulator 3, the first oil inlet digital switch valve 2, the first oil outlet digital switch valve 1, and the overflow valve 4; the rod cavity oil circuit includes the second accumulator 8, the first oil inlet digital switch valve 10, the first oil outlet digital switch valve 9, and the overflow valve; in the rodless cavity oil circuit and the rod cavity oil circuit, the accumulator is arranged at the inlet of the oil inlet digital switch valve to ensure the oil circuit pressure, the overflow valve 4 is arranged at the outlet of the oil inlet digital switch valve to set the maximum oil circuit pressure, the oil inlet digital switch valve is used for oil inlet, and the oil outlet digital switch valve is used for oil return. The rodless cavity oil circuit is connected to the rodless cavity and is used to control the oil pressure in the rodless cavity of the brake cylinder; the rod cavity oil circuit is connected to the rod cavity and is used to control the oil pressure in the rod cavity of the brake cylinder.

[0052] The sensor of the present invention mainly includes a pressure detection system and a displacement and speed detection system. The pressure detection system is used to detect the oil pressure magnitude in the rodless cavity of the brake cylinder; the displacement and speed detection system is used to detect the displacement and speed of the external pedal device.

[0053] The controller is the core control component of the hydraulic braking system. It is used to obtain the detection signals of the pressure detection system, as well as the displacement and speed detection systems, and output control signals to control the opening and closing states and working frequencies of the digital switching valves in the rodless cavity oil circuit and the rod chamber oil circuit.

[0054] The duty cycle modulation signal (duty cycle range 0 - 100%) of each digital switching valve in the present invention represents the time ratio of the high-level action time for driving the valve to open in a control cycle of the digital switching valve to the entire control cycle; among them, a duty cycle of 100% means that the valve is always under the action of the high level and remains open throughout the cycle, and 0 means that the valve is always closed. The driving frequency of each digital switching valve is 100 - 300 Hz. The higher the driving frequency, the more control cycles of the digital switching valve there are per unit time. An opening and closing cycle of the digital switching valve includes four stages: the valve port closes to opens, the valve port remains open, the valve port opens to closes, and the valve port remains closed. During the continuous opening and closing process of the valve body, when the driving voltage is constant, the durations of the two stages of the valve port closing to opening and the valve port opening to closing remain fixed. As the opening and closing frequency of the digital switching valve gradually increases, in a single opening and closing cycle, the time for the valve port to remain open gradually shortens, ultimately resulting in that within the same opening and closing time, the higher the opening and closing frequency of the valve body, the smaller the average flow rate in the hydraulic circuit.

[0055] The braking process of the hydraulic braking system is to change the oil pressure in the rodless cavity of the brake cylinder to reach the target braking pressure p0, so that the brake block acts on the external brake disc 7 to generate braking force. The magnitude of the target braking pressure p0 is determined by the stroke of the pedal device, that is, the greater the stroke distance, the greater the target braking pressure p0.

[0056] The following describes the braking process of the hydraulic braking system of the present invention.

[0057] As Figure 2 shown, when the controller does not receive the braking command signal from the displacement detection system, the system is in the braking preparation state. The controller collects the corresponding detection signals in real time through the displacement, speed detection system, and pressure detection system. The controller controls the relay of the first inlet oil circuit digital switching valve 2 to lose power and maintain the right position (closed), controls the relay of the first return oil circuit digital switching valve 1 to lose power and maintain the right position (closed), and the hydraulic oil charges the first accumulator 3 by the external liquid filling system P1 to prepare for braking. The controller controls the relay of the second inlet oil circuit digital switching valve 10 to lose power and maintain the right position (closed), controls the relay of the second return oil circuit digital switching valve 9 to lose power and maintain the right position (closed), and the hydraulic oil charges the second accumulator 8 by the external liquid filling system P2.

[0058] Normal braking state:

[0059] When the speed of the pedal device received by the displacement and speed detection system is within the normal braking range, the system brakes normally. The normal braking state is divided into a rapid pressure build-up stage and a differential approach stage.

[0060] In the rapid pressure build-up stage (such as Figure 3 ), the controller controls the relay of the first oil inlet digital switch valve 2 to be energized and switches to the left position (open). The hydraulic oil flows from the external liquid filling system P1 through the first accumulator 3 and the left position of the first oil inlet high-speed switch valve 2 into the rodless cavity of the brake cylinder 5, quickly building pressure. At the same time, the controller controls the relay of the second oil return digital switch valve 9 to be energized and switches to the left position. The oil in the rodless cavity of the brake cylinder flows into the oil tank T2 through the left position of the second oil return digital switch valve 9. The pressure detection system continuously detects the pressure in the rodless cavity of the brake cylinder.

[0061] When the pressure detection system detects that the pressure in the rodless cavity of the brake cylinder reaches the set value (this set value can generally be set to 85-95% of the target braking pressure p0), the system enters the differential approach stage (such as Figure 4 ). At this time, the controller controls the first oil inlet digital switch valve 2 to maintain the opening and closing frequency of f1, controls the first oil return digital switch valve 1 to maintain the right position (closed), controls the second oil inlet digital switch valve 10 to maintain the opening and closing frequency of f2, and controls the second oil return digital switch valve 9 to maintain the opening and closing frequency of f3. Among them, f1 < f2. The greater the opening and closing frequency of the digital switch valve, the smaller its average flow rate. Therefore, the hydraulic oil flow rate at the oil inlet of the rodless cavity of the brake cylinder is greater than that at the oil inlet of the rod chamber, and its equivalent flow rate is the difference between the two. The actual effect is equivalent to oil inlet in the rodless cavity and oil outlet in the rod chamber. The equivalent oil inlet flow rate in the rodless cavity is controlled to be less than 5% of the oil inlet flow rate in the rapid pressure build-up stage (specifically, it can be selected according to the control accuracy. The smaller the flow rate difference, the more accurate the control, but the time to approach the target braking pressure will be longer); because the flow rate difference between the two is extremely small, the brake block contacts the brake disc with a very small impulse to generate friction, achieving the braking purpose. The second oil return digital switch valve 9 opens and closes at the frequency of f3 to return the excess oil to the oil tank T2.

[0062] Emergency braking state:

[0063] When the speed of the pedal device received by the displacement and speed detection system is within the emergency braking range, the system brakes emergently. The emergency braking state is divided into a rapid pressure build-up stage and an anti-lock stage. The anti-lock stage consists of multiple consecutive anti-lock cycles. Each anti-lock cycle is divided into two links: differential working feed and differential fast return. Multiple differential working feed links and differential fast return links alternate and cycle to form the anti-lock stage.

[0064] Rapid pressure build-up stage (such as Figure 5) The controller energizes the relay of the first oil inlet digital switch valve 2 to switch to the left position. The hydraulic oil flows from the external liquid filling system P1 through the first accumulator 3 and the left position of the first oil inlet high-speed switch valve 2 into the rodless cavity of the brake cylinder, quickly building pressure. At the same time, the controller energizes the relay of the second oil return digital switch valve 9 to switch to the left position, and the oil in the rodless cavity of the brake cylinder flows into the oil tank T2 through the left position of the second oil return digital switch valve 9. The pressure detection system continuously detects the pressure in the rodless cavity of the brake cylinder.

[0065] When the pressure detection system detects that the pressure in the rodless cavity of the brake cylinder reaches the set value (this set value can generally be set to 85 - 95% of the target braking pressure p0), the system enters the anti-lock braking stage. Each anti-lock braking cycle in the anti-lock braking stage is divided into two links: differential working feed and differential fast retraction.

[0066] In the differential working feed link ( Figure 6 ), the controller controls the first oil inlet digital switch valve 2 to maintain the opening and closing frequency of f4, controls the first oil return digital switch valve 1 to maintain the right position, controls the second oil inlet digital switch valve 10 to maintain the opening and closing frequency of f5, and controls the second oil return digital switch valve 9 to maintain the opening and closing frequency of f6. Among them, f4 < f5. The greater the opening and closing frequency of the digital switch valve, the smaller its average flow rate. Therefore, the hydraulic oil flow rate at the oil inlet of the rodless cavity of the brake cylinder is greater than that at the oil inlet of the rod cavity, and its equivalent flow rate is the difference between the two. The actual effect is equivalent to the rodless cavity inlet and the rod cavity outlet, and the equivalent inlet flow rate of the rodless cavity is controlled to be less than 5% of the inlet flow rate in the rapid pressure build-up stage; due to the extremely small difference in the flow rates of the two, the brake block contacts the brake disc with a very small impulse to generate friction, achieving the braking purpose. The second oil return digital switch valve 9 opens and closes at the frequency of f6 to return the excess oil to the oil tank T2.

[0067] In the differential fast retraction link ( Figure 7 ), the controller controls the first oil inlet digital switch valve 2 to maintain the opening and closing frequency of f8, controls the first oil return digital switch valve 1 to maintain the opening and closing frequency of f6, controls the second oil inlet digital switch valve 10 to maintain the opening and closing frequency of f7, and controls the second oil return digital switch valve 9 to maintain the right position. Among them, f7 < f8 < f4 < f5. Since f7 < f8, the greater the opening and closing frequency of the digital switch valve, the smaller its average flow rate. The hydraulic oil flow rate at the oil inlet of the rodless cavity of the brake cylinder is less than that at the oil inlet of the rod cavity, and its equivalent flow rate is the difference between the two. The actual effect is equivalent to the rodless cavity outlet and the rod cavity inlet, and the flow rate difference between the two can be controlled to be larger than that in the differential working feed stage (for example, 5% - 20% of the inlet flow rate in the rapid pressure build-up stage), and the brake block separates from the brake disc at a very high speed. The first oil return digital switch valve 1 opens and closes at the frequency of f6 to return the excess oil to the oil tank T1.

[0068] A differential working stroke link and a differential quick return link constitute an anti-lock cycle. The entire emergency braking process consists of multiple anti-lock cycles until the vehicle completes braking. Compared with a general ABS anti-lock system, the extremely high-frequency point braking of this system makes the proportion of the effective braking time of the system in the entire braking cycle larger, so the braking distance is shorter than that of a general ABS anti-lock system.

[0069] As Figure 8 shown is the timing diagram of the normal braking state. Before time t0, the system is in the braking preparation state, and the first inlet oil circuit digital switch valve 2 and the second inlet oil circuit digital switch valve 10 are closed. At time t0, the brake pedal acts, and the displacement and speed detection system sends a braking signal to the controller. The controller controls the first inlet oil circuit digital switch valve 2 to remain open, controls the first return oil circuit digital switch valve 1 to remain closed, controls the second inlet oil circuit digital switch valve 10 to close, and controls the second return oil circuit digital switch valve 9 to remain open. The circuit starts to build pressure rapidly, and the hydraulic oil flow rate in the rodless cavity of the brake cylinder rises to Q1 at time t1. Before time t2, the pressure detection system detects that the pressure in the rodless cavity of the brake cylinder is the set value P x (infinitely close to the target braking pressure P0 but the brake block has not yet contacted the brake disc), the controller issues an instruction to control the first inlet oil circuit digital switch valve to switch to the opening and closing frequency of f1, and control the second inlet oil circuit digital switch valve 10 to switch to the opening and closing frequency of f2 (f1 is slightly less than f2), so that the oil inflow in the rodless cavity of the brake cylinder is slightly greater than the oil inflow in the rod cavity. The final effect is equivalent to the rodless cavity of the brake cylinder inletting oil and the rod cavity outlettng oil, and the oil inflow and outflow is the difference between the two flow rates. The brake block starts to approach differentially. At time t2, the flow rate of the first inlet oil circuit digital switch valve 2 reaches Q2, and the braking pressure reaches the target braking pressure P0, and the vehicle starts to brake and decelerate. At time t3, the vehicle braking is completed, and the braking pressure then drops to 0 MPa.

[0070] As Figure 9 shown is the schematic timing diagram of the emergency braking state. Before time t0, the system is in the braking preparation state, the first inlet oil circuit digital switch valve 2 and the second inlet oil circuit digital switch valve 10 are closed, and the first accumulator and the second accumulator are charged. At time t0, the brake pedal acts, and the displacement and speed detection system sends a braking signal to the controller. The controller controls the first inlet oil circuit digital switch valve 2 to remain open, controls the first return oil circuit digital switch valve 1 to remain closed, controls the second inlet oil circuit digital switch valve 10 to close, and controls the second return oil circuit digital switch valve 9 to remain open to build pressure rapidly. Before reaching time t2, the pressure detection system detects that the pressure in the rodless cavity of the brake cylinder is the set value P x(Infinitely close to the target braking pressure P0 but the brake pads have not yet contacted the brake disc), the controller issues an instruction to control the opening and closing frequency of the first oil inlet digital switch valve 2 to f1, and control the opening and closing frequency of the second oil inlet digital switch valve 10 to f2 (f1 is slightly less than f2), so that the oil inflow in the rodless cavity of the brake cylinder is slightly greater than the oil inflow in the rod cavity. The final effect is equivalent to the rodless cavity of the brake cylinder being filled with oil and the rod cavity discharging oil, and the oil inflow and outflow are the difference between the two flows, and the brake pads start to approach differentially. At time t2, the braking pressure reaches the target braking pressure P0, and the vehicle starts to brake and decelerate and enters the anti-lock braking stage.

[0071] At time t2, the system enters the anti-lock braking stage (only one cycle of the anti-lock braking link is described below). At time t2, the system enters the differential quick return link of the anti-lock braking stage. The controller controls the opening and closing frequency of the second oil inlet digital switch valve 10 to f7, controls the second oil return digital switch valve 9 to remain closed, controls the opening and closing frequency of the first oil inlet digital switch valve 2 to f8, and controls the opening and closing frequency of the first oil return digital switch valve 1 to f6 (f7 is slightly less than f8), so that the oil inflow in the rodless cavity of the brake cylinder is slightly less than the oil inflow in the rod cavity. The final effect is equivalent to the rod cavity being filled with oil and the rodless cavity discharging oil, and the oil outflow is the difference between the two flows, and the brake pads start to perform differential quick return.

[0072] Until time t3, the pressure detection system detects that the pressure in the rodless cavity of the brake cylinder drops to P'. The differential quick return link ends, and the system enters the differential work feed link. The controller controls the opening and closing frequency of the first oil inlet digital switch valve 2 to f4, controls the first oil return digital switch valve 1 to remain closed, controls the opening and closing frequency of the second oil inlet digital switch valve 10 to f5, and controls the opening and closing frequency of the second oil return digital switch valve 9 to f6 (f4 is slightly less than f5), so that the oil inflow in the rodless cavity of the brake cylinder is slightly greater than the oil inflow in the rod cavity. The final effect is equivalent to the rod cavity discharging oil and the rodless cavity being filled with oil, and the oil outflow is the difference between the two flows, and the brake pads start to perform differential work feed. When the pressure detection system detects that the pressure in the brake cylinder reaches the target braking pressure P0 again, the controller issues a corresponding signal, and the system enters the differential quick return link of the anti-lock braking stage again. At time t5, the vehicle braking is completed, and the system braking pressure then drops to 0 MPa.

[0073] 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 hydraulic braking system based on frequency modulation, characterized in that, Comprising: A brake cylinder having a rodless chamber, a rod chamber, and a piston for separating the rodless chamber and the rod chamber. The rodless chamber and the rod chamber are both pre-filled with hydraulic fluid. The piston can be moved within the brake cylinder by adjusting the hydraulic fluid pressure. The piston is connected with a return spring and is also connected through a connecting rod to a brake block located outside the brake cylinder. The brake block generates a braking force by acting on an external brake disc; A rodless chamber oil circuit connected to the rodless chamber for controlling the hydraulic pressure within the rodless chamber of the brake cylinder; A rod chamber oil circuit connected to the rod chamber for controlling the hydraulic pressure within the rod chamber of the brake cylinder; A pressure detection system for detecting the magnitude of the hydraulic pressure in the rodless chamber of the brake cylinder; A displacement and speed detection system for detecting the displacement and speed of an external pedal device; And A controller for obtaining the detection signals of the pressure detection system and the displacement and speed detection system, and outputting control signals to control the opening and closing states and operating frequencies of digital switching valves in the rodless chamber oil circuit and the rod chamber oil circuit; The rodless chamber oil circuit and the rod chamber oil circuit are exactly the same, and each includes an accumulator, an inlet oil circuit digital switching valve, an outlet oil circuit digital switching valve, and a relief valve. Among them, the accumulator is arranged at the inlet of the inlet oil circuit digital switching valve to ensure the oil circuit pressure, the relief valve is arranged at the outlet of the inlet oil circuit digital switching valve to set the maximum oil circuit pressure, the inlet oil circuit digital switching valve is used for oil inlet, and the outlet oil circuit digital switching valve is used for oil return; The displacement and speed detection system continuously detects the displacement and speed of the external pedal device; When a displacement signal of the pedal device is received and the moving speed of the pedal device is within the set normal braking speed range; the hydraulic braking system enters the normal braking state. The normal braking state includes a rapid pressure build-up stage and a differential approaching stage. In the rapid pressure build-up stage, the inlet oil circuit digital switching valve of the rodless chamber oil circuit is fully open, and the hydraulic fluid enters the rodless chamber and quickly reaches the set pressure, and then enters the differential approaching stage. In the differential approaching stage, the rodless chamber oil circuit and the rod chamber oil circuit work simultaneously, and the average flow rate of the rodless chamber oil circuit is controlled to be greater than that of the rod chamber oil circuit, so that the hydraulic pressure in the rodless chamber gradually approaches the target braking pressure p0, and the brake block contacts the brake disc to generate friction, achieving the braking purpose; When a displacement signal of the pedal device is received and the moving speed of the pedal device is within the set emergency braking speed range; the hydraulic braking system enters the emergency braking state. The emergency braking state is divided into a rapid pressure build-up stage and an anti-lock stage. In the rapid pressure build-up stage, the inlet oil circuit digital switching valve of the rodless chamber oil circuit is fully open, and the hydraulic fluid enters the rodless chamber and quickly reaches the set pressure, and then enters the anti-lock stage. In the anti-lock stage, the rodless chamber oil circuit and the rod chamber oil circuit work simultaneously, and the hydraulic braking system controls the flow rates of the rodless chamber oil circuit and the rod chamber oil circuit, so that the hydraulic pressure in the rodless chamber periodically increases or decreases, causing the brake block to be separated from or contact the brake disc at a high frequency until the vehicle completes braking; The speed range of the emergency braking is greater than that of the normal braking; In the differential approximation stage of the normal braking state, the controller controls the inlet digital switching valve of the rodless chamber oil circuit to maintain the opening and closing frequency of f1, controls the return digital switching valve of the rodless chamber oil circuit to remain closed, controls the inlet digital switching valve of the rod chamber oil circuit to maintain the opening and closing frequency of f2, and controls the return digital switching valve of the rod chamber oil circuit to maintain the opening and closing frequency of f3; where f1 < f2, the greater the opening and closing frequency of the digital switching valve, the smaller its average flow rate. Therefore, the hydraulic oil flow rate at the inlet of the rodless chamber of the brake cylinder is greater than that at the inlet of the rod chamber, and its equivalent flow rate is the difference between the two. The actual effect is equivalent to the rodless chamber inlet and the rod chamber outlet, and the equivalent inlet flow rate of the rodless chamber is controlled to be less than 5% of the inlet flow rate in the rapid pressure build-up stage. The brake pad contacts the brake disc with a very small impulse to generate friction, achieving the braking purpose; the digital switching valve of the rod chamber oil circuit opens and closes at the frequency of f3, returning the excess oil in the rod chamber to the fuel tank; The anti-lock stage in the emergency braking state consists of multiple anti-lock cycles, and each anti-lock cycle includes a differential working-in link and a differential fast-retreat link; In the differential working-in link, the controller controls the inlet digital switching valve of the rodless chamber oil circuit to maintain the opening and closing frequency of f4, controls the return digital switching valve of the rodless chamber oil circuit to remain closed, controls the inlet digital switching valve of the rod chamber oil circuit to maintain the opening and closing frequency of f5, and controls the return digital switching valve of the rod chamber oil circuit to maintain the opening and closing frequency of f6; where f4 < f5, the hydraulic oil flow rate at the inlet of the rodless chamber of the brake cylinder is greater than that at the inlet of the rod chamber, and its equivalent flow rate is the difference between the two. The actual effect is equivalent to the rodless chamber inlet and the rod chamber outlet, and the equivalent inlet flow rate of the rodless chamber is controlled to be less than 5% of the inlet flow rate in the rapid pressure build-up stage. The brake pad contacts the brake disc with a very small impulse to generate friction, achieving the braking purpose; the digital switching valve of the second return oil circuit opens and closes at the frequency of f6, returning the excess oil to the fuel tank; In the differential fast-retreat link, the controller controls the inlet digital switching valve of the rodless chamber oil circuit to maintain the opening and closing frequency of f8, controls the return digital switching valve of the rodless chamber oil circuit to maintain the opening and closing frequency of f6, controls the inlet digital switching valve of the rod chamber oil circuit to maintain the opening and closing frequency of f7, and controls the return digital switching valve of the rod chamber oil circuit to remain closed; where f7 < f8 < f4 < f5; since f7 < f8, the hydraulic oil flow rate at the inlet of the rodless chamber of the brake cylinder is less than that at the inlet of the rod chamber, and its equivalent flow rate is the difference between the two. The actual effect is equivalent to the rodless chamber outlet and the rod chamber inlet. Since the flow rate difference between the two is larger than that in the differential working-in link, the brake pad separates from the brake disc at a very high speed; the digital switching valve of the return oil circuit of the rodless chamber oil circuit opens and closes at the frequency of f6, returning the excess oil to the fuel tank.

2. The hydraulic braking system based on frequency modulation according to claim 1, wherein, The opening and closing voltages of each digital switching valve in the rodless chamber oil circuit and the rod chamber oil circuit are fixed values in different opening and closing cycles, and the controller controls the output flow rate of each digital switching valve by changing the working frequency of each digital switching valve.

3. The hydraulic braking system based on frequency modulation according to claim 1, characterized in that, Each digital switching valve in the rodless chamber oil circuit and the rod chamber oil circuit is a two-position two-way digital switching valve.

4. A hydraulic braking system based on frequency modulation according to claim 1, characterized in that, The controller detects the pressure of the accumulators in the rodless chamber oil circuit and the rod chamber oil circuit in real time. When the pressure of the accumulator is less than the set value, the controller issues an alarm or fills the under-pressure accumulator with liquid through an oil pump to maintain the pressure of the accumulator.

5. A hydraulic braking system based on frequency modulation according to claim 1, characterized in that; When the vehicle starts and the displacement and speed detection system does not detect the displacement signal of the pedal device, the piston is in the initial position under the action of the return spring, and the accumulators in the rodless chamber oil circuit and the rod chamber oil circuit are filled with liquid to the set pressure.

6. The hydraulic braking system based on frequency modulation according to claim 1, characterized in that; The rapid pressure build-up phases in the normal braking state and the emergency braking state are the same; In the rapid pressure build-up phase, the inlet digital switching valve of the rodless chamber oil circuit is fully open, the outlet digital switching valve is closed, and the oil enters the rodless chamber; the inlet digital switching valve of the rod chamber oil circuit is closed, the outlet digital switching valve is fully open, and the oil in the rod chamber flows out; when the oil pressure in the rodless chamber reaches the set percentage of the target braking pressure, the rapid pressure build-up phase ends.

Images