Electronic hydraulic braking system with self-locking and pressure balancing functions

Abstract

The invention belongs to the technical field of vehicle braking, and particularly relates to an electronic hydraulic braking system with self-locking and pressure balancing functions. The system comprises a brake master cylinder unit, a pressure buildup unit, a hydraulic control unit, four brake wheel cylinder units and an ECU (electronic control unit), and the pressure buildup unit comprises a worm and gear reducing mechanism, an auxiliary motor and a gear and rack pushing and pressing mechanism. The hydraulic control unit comprises a first isolation valve, a second isolation valve, a first pressure increasing valve, a second pressure increasing valve, a third pressure increasing valve, a fourth pressure increasing valve, a first pressure reducing valve, a second pressure reducing valve, a third pressure reducing valve, a fourth pressure reducing valve, a first balance valve, a second balance valve, an oil storage pot and a pressure sensor. The brake wheel cylinder unit comprises a left front wheel cylinder, a right rear wheel cylinder, a right front wheel cylinder and a left rear wheel cylinder. According to the method, a hydraulic pressure adjusting algorithm for a control system is established, so that stable pressure output and double-wheel balanced braking can be kept under normal braking, abnormal working conditions and environment disturbance conditions.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of vehicle braking, in particular to an electronic hydraulic braking system with self-locking and pressure balancing functions. BACKGROUND

[0002] EHB belongs to one of the main types of brake-by-wire systems, specifically hydraulic brake-by-wire system, EHB brake-by-wire system cancels the traditional vacuum booster and mechanical connecting rod, and establishes hydraulic pressure through a motor-driven pressure building mechanism to achieve faster braking response. This design ensures that in the event of electronic control failure, the driver can still achieve unassisted braking through the traditional hydraulic braking system. Although it is brake-by-wire, it still retains part of the hydraulic pipeline, and uses the electric system to provide power and the hydraulic system to provide braking force.

[0003] The existing EHB wheel cylinder hydraulic pressure relies on pipeline transmission, and the same axle left and right pipelines may have different flow resistances due to different lengths and bending degrees. The response lag of the solenoid valve and the change in oil temperature may cause left and right pressure differences, leading to vehicle braking deviation. The pressure building unit uses a screw rod transmission, and when the master cylinder back pressure rises, the motor may be pushed in reverse, causing unexpected decay of the braking pressure, affecting the redundancy braking capability and the reliability of emergency braking. SUMMARY

[0004] In view of the above shortcomings of the prior art, the present application aims to provide an electronic hydraulic braking system with self-locking and pressure balancing functions to solve the problems of weak self-locking capability of the screw rod transmission pressure building unit, imbalance of the same axle left and right wheel cylinder pressure, and less automatic passive pressure balancing capability in the event of power failure.

[0005] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows: an electronic hydraulic braking system with self-locking and pressure balancing functions, comprising a brake master cylinder unit, a pressure building unit, a hydraulic control unit, four brake wheel cylinder units and an ECU control unit, the brake master cylinder unit comprising a first chamber and a second chamber, the pressure building unit comprising a worm gear reduction mechanism, an auxiliary motor and a gear rack pushing mechanism, the auxiliary motor being coaxial with the worm gear reduction mechanism, and the gear in the gear rack pushing mechanism being coaxial with the worm in the worm gear reduction mechanism, the hydraulic control unit comprising an isolation valve one, an isolation valve two, a booster valve one, a booster valve two, a booster valve three, a booster valve four, a pressure reducing valve one, a pressure reducing valve two, a pressure reducing valve three, a pressure reducing valve four, a balance valve one, a balance valve two, an oil storage pot and a pressure sensor, the brake wheel cylinder unit comprising a left front wheel cylinder, a right rear wheel cylinder, a right front wheel cylinder and a left rear wheel cylinder.

[0006] As preferred, the brake master cylinder unit adopts a tandem double-cavity structure, and each cavity contains a piston, a return spring, an oil compensation hole and a push rod limiting structure, the first cavity is communicated with the left front wheel cylinder and the right rear wheel cylinder, and the second cavity is communicated with the right front wheel cylinder and the left rear wheel cylinder.

[0007] As preferred, the ECU control unit calculates the auxiliary motor control amount according to the target pressure and the current master cylinder pressure, and the worm and gear reduction mechanism satisfies the self-locking condition:

[0008]

[0009] wherein, is a thread lead angle; is a worm pair friction factor;

[0010] The output torque of the auxiliary motor is:

[0011]

[0012] wherein, is the output torque of the auxiliary motor; is the torque constant of the auxiliary motor; is the control amount of the auxiliary motor;

[0013] The corresponding master cylinder thrust after the output torque of the auxiliary motor passes through the worm and gear reduction mechanism and the gear and rack pushing mechanism is:

[0014]

[0015] wherein, is the master cylinder thrust; is the worm and gear reduction ratio; is the transmission efficiency;

[0016] The master cylinder pressure is calculated as:

[0017]

[0018] wherein, is the master cylinder pressure; is the master cylinder piston pressure area.

[0019] As preferred, the isolation valve one and the isolation valve two are in the normally open state during normal braking, and are closed by the ECU control unit in

[0020] the pressure maintaining or failure protection mode;

[0021] The booster valve one, the booster valve two, the booster valve three and the booster valve four are opened when the master cylinder pressure is insufficient, and are closed by the ECU control unit after the master cylinder pressure reaches;

[0022] The pressure reducing valves 1, 2, 3 and 4 open when the driver releases the pedal, and are used to release the wheel cylinder pressure to the oil reservoir through the return oil line.

[0023] The balance valve one and balance valve two adjust their flow areas according to the pressure difference between the left front wheel cylinder, the right rear wheel cylinder, and the left rear wheel cylinder. The flow area adjustment satisfies the following:

[0024]

[0025]

[0026]

[0027] in, The pressure of the left wheel cylinder; This refers to the pressure of the right wheel cylinder; This is the wheel cylinder pressure equalization adjustment function; To balance the valve opening gain; To allow a pressure difference threshold, the following conditions must be met. =0.1~0.3MPa; This represents the current effective flow area of ​​the balancing valve.

[0028] Preferably, the first and second balance valves are bidirectional pressure-sensing structures, including a valve core, left and right pressure-sensing chambers, a central valve port, a return spring, and a micro-flow throttling groove. The first and second balance valves maintain a micro-flow mode under pressure-holding conditions, and their minimum flow area is 0.5% to 1% of the maximum area.

[0029] In pressure reduction mode, balance valve one and balance valve two automatically match the return oil flow according to the pressure drop speed of the left and right wheel cylinders;

[0030] In the emergency mode where the ECU control unit and auxiliary motor are both powered off, the balance valve...

[0031] The second balancing valve automatically adjusts the flow area using a mechanical pressure-sensing element to satisfy:

[0032]

[0033] in, This is the mechanical pressure sensitivity coefficient.

[0034] Preferably, the pressure sensor is located at the outlet end of the hydraulic control unit to detect the left and right pressure in real time.

[0035] The hydraulic control unit also includes an oil temperature sensor, and the ECU control unit calls a thermal compensation function based on the oil temperature to satisfy: (The text abruptly ends here, so the translation stops as well.)

[0036]

[0037] wherein, is the oil temperature pressure compensation function; is the thermal compensation coefficient.

[0038] As a preferred, the ECU control unit adopts pressure feedforward and PID closed loop control for pressure control

[0039] Algorithm:

[0040]

[0041] wherein, is the feedforward gain coefficient; is the ECU control unit instruction target pressure; is the proportional coefficient; is the pressure error, satisfying ; is the integral coefficient; is the integral term of the pressure error; is the differential coefficient; is the differential term of the pressure error;

[0042] The ECU control unit compensates pressure according to the hydraulic oil temperature drift, balances the valve one and the valve two micro flow to keep the left and right pressures consistent, and the compensation formula is:

[0043]

[0044] The ECU control unit sets the maximum opening limit of the balance valve one and the balance valve two.

[0045] Compared with the prior art, the beneficial effects of the present application are:

[0046] In the system of the present application, the mechanical self-locking pressure building mechanism, the worm gear deceleration mechanism and the gear and rack pushing mechanism are driven by irreversibility, the main cylinder back pressure cannot drive the motor to reverse, natural self-locking is realized, brake safety redundancy is improved, the main cylinder piston cannot drive the worm and auxiliary motor in reverse when it is pressed, and the brake pressure can be prevented from accidentally retreating;

[0047] In the system of the present application, through the left and right wheel cylinder dynamic pressure balancing algorithm, the balance valve and the ECU double closed loop control, the pressure difference between the left and right coaxial wheel cylinders is maintained within the error band, the pressure of the left and right wheel cylinders on the same shaft is balanced, the brake deviation is avoided, the brake stability is improved, the balance valve can monitor and adjust the pressure difference between the left and right wheel cylinders on the same shaft in real time, and the pressure imbalance problem caused by factors such as pipeline resistance difference, electromagnetic valve response delay, oil viscosity change and the like in the EHB system is offset;

[0048] The system of the application balances pressure automatically in the power-off emergency state, the balance valve adopts a bidirectional pressure sensing structure, and contains a valve core, left and right pressure sensing cavities, a center valve port, a reset spring and a micro flow throttling groove. When the pressure on either side is higher than that on the other side, the pressure sensing mechanism pushes the valve core to deviate and automatically connects the left and right channels. When the ECU and motor fail, the balance valve automatically opens the channel by using a mechanical pressure sensing structure, so as to realize self-balancing of the left and right pressures.

[0049] In the system of the application, a hydraulic pressure regulating algorithm for the control system is established, so that stable pressure output and double-wheel balanced braking can be maintained under normal braking (pressurization / pressure maintenance / depressurization), abnormal working conditions (ECU failure, motor failure) and environmental disturbances (temperature rise, flow resistance difference). BRIEF DESCRIPTION OF DRAWINGS

[0050] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0051] Figure 1 is an electronic hydraulic braking system diagram of the system of the application;

[0052] Figure 2 is a brake master cylinder unit diagram of the system of the application;

[0053] Figure 3 is a pressure building unit diagram of the system of the application;

[0054] Figure 4 is a hydraulic control unit diagram of the system of the application;

[0055] Figure 5 is a brake wheel cylinder unit diagram of the system of the application;

[0056] BRIEF DESCRIPTION OF DRAWINGS: 1, brake master cylinder unit; 11, first chamber; 12, second chamber; 2, pressure building unit; 21, worm and gear reduction mechanism; 22, auxiliary motor; 23, gear and rack pushing mechanism; 3, hydraulic control unit; 31, isolation valve one; 313, isolation valve two; 33, pressure increasing valve one; 32, pressure increasing valve two; 312, pressure increasing valve three; 311, pressure increasing valve four; 35, pressure reducing valve one; 34, pressure reducing valve two; 310, pressure reducing valve three; 39, pressure reducing valve four; 37, balance valve one; 38, balance valve two; 36, oil storage pot; 314 pressure sensor; 4, brake wheel cylinder unit; 41, left front wheel cylinder; 42, right rear wheel cylinder; 43, right front wheel cylinder; 44, left rear wheel cylinder; 5, ECU control unit. DETAILED DESCRIPTION

[0057] For the convenience of those skilled in the art, the present application is further described below in conjunction with the embodiments and the accompanying drawings, and the content mentioned in the embodiments is not a limitation of the present application.

[0058] Referring to Figures 1-5 The electronic hydraulic brake system with self-locking and pressure balancing functions of the present application comprises a brake master cylinder unit, a pressure building unit, a hydraulic control unit, four brake wheel cylinder units and an ECU control unit. The brake master cylinder unit comprises a first chamber and a second chamber. The brake master cylinder unit adopts a tandem double-cavity structure, and each cavity contains a piston, a return spring, an oil compensation hole and a push rod limiting structure. The first cavity of the brake master cylinder unit generates pressure under mechanical direct pushing. The second cavity of the brake master cylinder unit passively builds pressure through hydraulic transmission. The first cavity piston moves while pushing the second cavity piston to move through hydraulic pressure. In the power-off emergency mode, the two cavities of the brake master cylinder unit cooperate to provide hydraulic oil to the brake wheel cylinder unit.

[0059] The pressure building unit comprises a worm gear reduction mechanism, an auxiliary motor and a gear and rack pushing mechanism. The auxiliary motor is coaxial with the worm gear reduction mechanism, and the gear in the gear and rack pushing mechanism is coaxial with the worm in the worm gear reduction mechanism. The auxiliary motor generates driving force, which drives the master cylinder piston through the worm gear reduction mechanism and the gear and rack pushing mechanism. The piston compresses the brake fluid in the master cylinder into the wheel cylinder. As the brake clearance disappears, the pressure of the brake system gradually increases.

[0060] The hydraulic control unit comprises isolation valve one, isolation valve two, booster valve one, booster valve two, booster valve three, booster valve four, pressure reducing valve one, pressure reducing valve two, pressure reducing valve three, pressure reducing valve four, balance valve one, balance valve two, an oil storage pot and a pressure sensor. The brake fluid flows through the brake pipeline and is regulated by each electromagnetic valve to provide the required pressure to the four wheel cylinders.

[0061] The brake wheel cylinder unit comprises a left front wheel cylinder, a right rear wheel cylinder, a right front wheel cylinder and a left rear wheel cylinder. The first chamber is in communication with the left front wheel cylinder and the right rear wheel cylinder, and the second chamber is in communication with the right front wheel cylinder and the left rear wheel cylinder. The brake wheel cylinder unit adopts a disc brake. The hydraulic oil enters the wheel cylinder to establish high pressure in the wheel cylinder chamber. The hydraulic pressure pushes the wheel cylinder piston to move. The wheel cylinder piston pushes the friction plate to compress the brake disc to achieve friction braking. When the pressure in the wheel cylinder chamber decreases, the wheel cylinder piston retreats under the action of the return spring. The friction force of the friction plate on the brake disc disappears, and the braking ends.

[0062] The ECU control unit calculates the auxiliary motor control amount according to the target pressure and the current master cylinder pressure to achieve master cylinder pressure building. The worm gear reduction mechanism meets the self-locking condition.

[0063]

[0064] wherein, is the thread lead angle; is the worm pair friction factor;

[0065] Back pressure cannot push back the auxiliary motor → natural mechanical self-locking, when the ECU control unit fails, the pressure remains and does not automatically decay;

[0066] The output torque of the auxiliary motor is:

[0067]

[0068] wherein, is the output torque of the auxiliary motor; is the torque constant of the auxiliary motor; is the control amount of the auxiliary motor;

[0069] The corresponding main cylinder thrust of the output torque of the auxiliary motor after the worm and gear reduction mechanism and the gear and rack pushing mechanism is:

[0070]

[0071] wherein, is the main cylinder thrust; is the worm and gear reduction ratio; is the transmission efficiency;

[0072] The main cylinder pressure is calculated as:

[0073]

[0074] wherein, is the main cylinder pressure; is the main cylinder piston pressure area.

[0075] The isolation valve one and the isolation valve two are in a normal open state during normal braking, and are closed by the ECU control unit in the pressure maintaining or failure protection mode;

[0076] The booster valve one, booster valve two, booster valve three, and booster valve four are opened when the main cylinder pressure is insufficient, and are closed by the ECU control unit after the main cylinder pressure reaches;

[0077] The pressure reducing valve one, pressure reducing valve two, pressure reducing valve three, and pressure reducing valve four are opened when the driver releases the pedal, and are used to release the wheel cylinder pressure to the oil storage pot through the oil return line;

[0078] The balance valve one and the balance valve two adjust the flow area of the balance valve one and the balance valve two according to the pressure difference of the left front wheel cylinder, the right rear wheel cylinder, the right front wheel cylinder and the left rear wheel cylinder, maintain the balance of the left and right wheel cylinder pressure, and the flow area adjustment satisfies:

[0079]

[0080]

[0081]

[0082] Wherein, is the left wheel cylinder pressure; is the right wheel cylinder pressure; is the wheel cylinder pressure balance adjustment function;

[0083] is the balance valve opening gain; is the allowable pressure difference threshold, satisfying = 0.1-0.3MPa; is the current effective flow area of the balance valve.

[0084] The balance valve one and the balance valve two are bidirectional pressure sensing structures, including a valve core, left and right pressure sensing cavities, a center valve port, a reset spring and a micro flow restriction groove, when the pressure of any one side is higher than that of the other side, the pressure sensing mechanism pushes the valve core to deviate and automatically connects the left and right channels, the balance valve one and the balance valve two maintain the micro flow mode in the pressure maintaining state, the minimum flow area is 0.5%-1% of the maximum area, which is used for compensating the pressure fluctuation caused by thermal expansion and cold contraction of the oil;

[0085] In the pressure reducing mode, the balance valve one and the balance valve two automatically match the oil return flow according to the left and right wheel cylinder pressure drop speed, so as to realize the synchronous pressure reduction of the left and right wheel cylinders;

[0086] In the emergency mode that the ECU control unit and the auxiliary motor are all powered off, the balance valve one and the balance valve

[0087] two rely on the mechanical pressure sensing element to automatically adjust the flow area, realize the passive balance of the left and right wheel cylinder pressure, and satisfy:

[0088]

[0089] Wherein, is the mechanical pressure sensing coefficient.

[0090] The pressure sensor is arranged at the outlet end of the hydraulic control unit, which is used for real-time detection of the left and right wheel cylinder pressure, the hydraulic control unit further includes an oil temperature sensor, and the oil temperature sensor is arranged near the balance valve one and the balance valve two, the ECU control unit calls a thermal compensation function for pressure drift correction according to the oil temperature, and satisfies:

[0091]

[0092] wherein, is the oil temperature pressure compensation function; is the thermal compensation coefficient.

[0093] The ECU control unit adopts pressure feedforward and PID closed-loop control algorithm for pressure control:

[0094]

[0095] wherein, is the feedforward gain coefficient; is the ECU control unit command target pressure; is the proportional

[0096] coefficient; is the pressure error, satisfying ; is the integral coefficient; is the integral term of the pressure error; is the differential coefficient; is the differential term of the pressure error;

[0097] The ECU control unit compensates pressure according to the hydraulic oil temperature drift, balances the left and right pressures of the valve one and valve two, and keeps the micro flow consistent, and the compensation formula is:

[0098]

[0099]

[0100] The ECU control unit sets the maximum opening limit of the balance valve one and the balance valve two, so that the left and right wheel cylinders will not produce secondary pressure fluctuation due to excessive compensation during emergency braking.

[0101] Example 1: Normal pressurization process (the whole process of the system performing normal pressurization according to the command after the driver generates braking intention)

[0102] 1) Driver braking intention acquisition

[0103] Pedal travel Pedal force ECU calculates target pressure 10 mm 120N 1.2 MPa 20 mm 220N 2.0 MPa 35 mm 380N 3.2 MPa

[0104] The ECU control unit converts the target braking pressure according to the pedal force and stroke characteristic curve:

[0105]

[0106] The pedal force-pressure conversion relationship after calibration is embodied.

[0107] 2) Build-up unit start and mechanical transmission details​

[0108] Motor rated current: 20A

[0109] Motor output torque: 0.5 N-m / A → 10 N-m

[0110] Worm transmission ratio: 18:1

[0111] Transmission efficiency: 0.82

[0112] Main cylinder area:

[0113] The auxiliary motor drives the worm to rotate, and the torque is output through the worm gear, and the main cylinder piston is pushed through the rack to build pressure thrust:

[0114]

[0115] Pressure is generated in the main cylinder cavity:

[0116]

[0117] The motor can achieve a brake pressure of more than 5 MPa.

[0118] 3) Pressurization path opening and oil propulsion

[0119] Pressurization valve flow coefficient: = 0.65

[0120] Valve opening: = 0.4

[0121] Oil density: = 870 kg / m3

[0122] Wheel cylinder pressure: = 1.5 MPa

[0123] The ECU control unit first opens the isolation valve to cut off the oil return path of the main cylinder and the reservoir, and then opens the pressurization valve to make the main cylinder pressure act quickly on the left and right wheel cylinders;

[0124] Liquid flow:

[0125]

[0126] The left and right wheel cylinders have a volume of about 6 ml, so the pressurization can be completed in about 0.36 s.

[0127] 4) Pressure equalization and compensation

[0128] Initial pressure imbalance:

[0129] Left wheel: = 3.2 MPa

[0130] Right wheel: = 2.9 MPa

[0131] Difference: ΔP = 0.3 MPa

[0132] If satisfied:

[0133]

[0134] The balance valve keeps a small flow (about 0.5% - 1%), otherwise, according to:

[0135]

[0136] The automatic adjustment balance valve makes the left and right pressures tend to be consistent:

[0137] After opening for 150 ms: the difference drops to 0.12 MPa;

[0138] After opening for 300 ms: the difference drops to 0.03 MPa (satisfies <0.05 MPa requirement).

[0139] 5) Reach target pressure and safety check

[0140] Worm friction angle:

[0141]

[0142] Self-locking factor meets the conditions;

[0143] Back thrust (max 200N) cannot drive reverse rotation;

[0144] Main cylinder pressure decay rate:

[0145]

[0146] ECU control unit enters pressure maintenance preparation state, self-locking worm structure eliminates auxiliary motor back thrust, and the current pressure is mechanically maintained.

[0147] In the normal pressure mode, the ECU control unit calculates the target wheel cylinder pressure according to the braking intention, and sends instructions to the pressure building unit. The auxiliary motor will drive the worm and gear reduction mechanism to achieve speed reduction and torque increase, and the gear rack will convert the worm rotation torque into rack translation thrust, so as to push the brake master cylinder unit piston to build up the brake pressure. At this time, the master cylinder pressure is greater than the wheel cylinder pressure, and the two isolation valves and four pressure increasing valves are in the open state, so the brake fluid flows from the brake master cylinder unit through the isolation valve and the pressure increasing valve into the brake wheel cylinder unit, and the left front and right rear wheel cylinders are pressurized. The pressure sensor feedbacks that the left and right wheel cylinder pressures reach the target value, and the ECU control unit controls the isolation valve to close and the pressure increasing valve to close. The left and right balance valves immediately lock the valve opening degree in the micro flow state (only 0.5%~1% flow area is reserved), preventing abnormal oil movement between the left and right wheel cylinders and ensuring the stability of the pressure balance state in the pressurization stage.

[0148] Example 2: Pressure maintaining process (the process of keeping the system stable after reaching the target pressure)

[0149] 1) Electromagnetic valve state switching

[0150] After the ECU control unit determines that the target pressure 3.0MPa is reached:

[0151] Isolation valve leakage test: <0.02ml / min

[0152] Pressure increasing valve closing leakage: <0.015ml / min

[0153] Pressure reducing valve leakage: <0.02ml / min

[0154] The master cylinder and the wheel cylinder form a closed hydraulic chamber, and the pressure can be maintained for more than 10 minutes.

[0155] 2) Master cylinder self-locking

[0156] Maximum return oil pressure: 3.0MPa

[0157] Counter thrust:

[0158]

[0159] The worm self-locking can resist ≥1000N thrust, and the master cylinder back pressure cannot push the auxiliary motor and the piston position Fixed and not back, hydraulic pressure Not change with auxiliary motor disturbance.

[0160] 3) Temperature rise compensation

[0161] Typical brake temperature rise: ΔT=15℃

[0162] Oil volume expansion coefficient: = 0.015 MPa / °C

[0163] Pressure drift:

[0164]

[0165] ECU control unit automatically reduces target pressure by 0.2 MPa, ensuring that the vehicle does not slide forward.

[0166] 4) Pressure equalization maintenance

[0167] The balance valve compensates for the left-right difference using the following steady-state model:

[0168]

[0169] Left and right pressure maintenance process example:

[0170] Time left wheel right wheel Difference 0s 3.00 2.95 0.05 5s 2.99 2.98 0.01 10s 2.98 2.97 0.01

[0171] By achieving left and right wheel cylinder pressure equality through minimal flow, the pressure difference is stabilized within ±0.01 MPa.

[0172] 5) Leak pressure compensation

[0173] When the ECU control unit detects a sudden drop in pressure on either side of the wheel cylinder:

[0174]

[0175] The ECU control unit performs pressure compensation action:

[0176] Motor start-up time: 0.03 s

[0177] Pressure compensation current: 2 A

[0178] It takes 60-80 ms to restore the pressure to the target

[0179] The ECU control unit automatically triggers short-term pressure compensation, and stabilizes through auxiliary motor fine-tuning.

[0180] When the target brake pressure is equal to the actual pressure and is not zero, the system enters pressure maintenance mode. When the ECU control unit determines that the braking intention is stable braking, it will keep the pressure reducing valve, pressure increasing valve, and isolation valve closed. The brake fluid is kept between the wheel cylinder and the isolation valve. The system enters the pressure maintenance stage. At this time, the pressure sensing elements of the left and right balance valves continue to monitor the left and right wheel cylinder pressures, and the valve port is in a low flow resistance locking state, which does not allow a large amount of oil to flow, and at the same time can offset the pressure changes caused by thermal expansion and contraction of oil through a small gap.

[0181] ​Example 3: Pressure reduction process (how the system safely and smoothly reduces pressure when the vehicle requires less deceleration or the driver releases the brake pedal)

[0182] 1) Trigger condition

[0183] ECU control unit triggers according to any of the following conditions:

[0184] Pedal displacement Fast rise;

[0185] Target pressure drop:

[0186]

[0187] Original target pressure: 3.0 MPa

[0188] New target pressure: 1.0 MPa

[0189] TCS (Traction Control), ESP request for pressure reduction

[0190] 2) Reduction valve opening control

[0191] Valve opening maximum: 0.5 mm2

[0192] Initial opening: 0.15 mm2

[0193] Flow:

[0194]

[0195] Total wheel cylinder volume 6 ml, single pressure reduction: 0.27 s from 3.0 MPa to 1.0 MPa.

[0196] 3) Avoid impact

[0197] ECU control unit uses hysteresis PID control during pressure reduction:

[0198]

[0199] But only used for auxiliary buffering, not involved in the main pressure reduction action;

[0200] By adjusting the slope of the pressure reduction valve opening:

[0201]

[0202] Keep the pressure drop slope at:

[0203]

[0204] Actual monitoring:

[0205] Time Pressure (MPa) (dP / dt) 0s 3.0 — 0.05s 2.65 -7 MPa / s 0.1s 2.3 -7 MPa / s

[0206] 4) Balance valve synchronous decompression

[0207] Balance valve continuously detects pressure difference during decompression:

[0208]

[0209] Original imbalance:

[0210] Left wheel: 3.0 MPa

[0211] Right wheel: 2.7 MPa

[0212] And according to:

[0213]

[0214] After opening the balance valve:

[0215] Time Left wheel Right wheel 0.1s 2.45 2.35 0.2s 1.95 1.93 0.3s 1.10 1.08

[0216] Difference always <0.05 MPa.

[0217] 5) End condition

[0218] System detects wheel cylinder pressure:

[0219]

[0220] System automatically closes decompression valve and enters zero pressure maintenance state.

[0221] In normal decompression mode, the driver releases the pedal, the ECU control unit calculates the target decompression amount, the wheel cylinder and decompression valve are opened, the boost valve and isolation valve remain closed, and the hydraulic oil in the wheel cylinder flows back to the oil reservoir through the decompression valve and oil return pipeline. At this time, the left and right balance valves are synchronized to return the oil to the left and right wheel cylinders to avoid one side decompressing faster and the other side decompressing slower. When the pressure sensor feedbacks the left and right wheel cylinder pressure drops to normal pressure, the ECU control unit controls the decompression valve to close, and the left and right balance valves reset the valve port to the initial closed state, ready for the next brake.

[0222] Example 4: Mechanical equalization emergency braking in the case of ECU control unit or auxiliary motor power failure (system working mode after complete loss of ECU control unit, auxiliary motor, and electromagnetic valve power supply)

[0223] 1) Fault state

[0224] ECU control unit failure

[0225] Main power failure <10 ms

[0226] All solenoid valves return to default state: response time 25-35 ms.

[0227] 2) Mechanical brake pressure

[0228] The driver pushes the master cylinder piston by pedal mechanical force:

[0229]

[0230] Driver pedal force: 350 N

[0231] Master cylinder area: 2.7 x 10-4m2

[0232] Brake pressure:

[0233]

[0234] Satisfy ordinary braking needs.

[0235] 3) Self-locking holding pressure

[0236] Back pressure 1.3 MPa

[0237] Back thrust: 351 N

[0238] The maximum self-locking of the worm can resist 1000 N back thrust, and the self-locking structure still satisfies:

[0239]

[0240] 4) Mechanical equalization ability of balance valve

[0241] The balance valve adopts a mechanical pressure difference driving structure, and still works according to the following model after the ECU control unit fails:

[0242]

[0243] Initial imbalance of left and right wheel cylinders:

[0244] Left wheel cylinder: 1.3 MPa

[0245] Right wheel cylinder: 1.0 MPa

[0246] Mechanical equalizing valve automatically adjusts the opening (0.04 mm2), after 20 ms:

[0247] Time Left wheel Right wheel 20 ms 1.24 1.18 40 ms 1.21 1.20

[0248] 5) Emergency braking effect

[0249] Pressure difference between left and right wheel cylinders: 0.016 MPa (satisfies pressure difference <0.3-0.5 MPa);

[0250] Braking deceleration: 4.0 m / s2(satisfies regulations ≥2.44 m / s2)

[0251] Vehicle run-off angle speed: <1.2 ° / s (regulation requirement <2 ° / s).

[0252] In the power-off emergency braking mode, if the auxiliary motor is powered off, the ECU control unit fails or the electromagnetic valve is disabled, the EHB system is switched to the emergency braking mode, the force of the driver's pedal directly pushes the brake master cylinder unit piston, the hydraulic oil in the master cylinder enters the left and right wheel cylinders through the master cylinder-isolation valve-wheel cylinder pipeline, at this time, the left and right balance valves have no brake master cylinder unit command, and only rely on the built-in mechanical structure to realize passive pressure balance, the pressure output by the master cylinder enters the wheel cylinder pipeline, if the left wheel cylinder is supplied with oil by the first cavity of the master cylinder first, the pressure rises first and is greater than that of the right wheel cylinder, the mechanical pressure sensing part of the balance valve will be pushed by the high pressure of the left cylinder, and the channel from the left cylinder to the right cylinder is automatically opened, so that the oil in the left cylinder flows to the right cylinder, until the pressure of the left and right cylinders is balanced.

[0253] In summary, the application constructs a set of hydraulic pressure regulation algorithm for the control system, so that it can maintain stable pressure output and balanced braking of the double wheels under the conditions of normal braking (pressurization / pressure maintenance / depressurization), abnormal working conditions (ECU failure, auxiliary motor failure), environmental disturbance (temperature rise, flow resistance difference), and offset the pressure imbalance problem caused by the difference in pipeline resistance, electromagnetic valve response delay, oil viscosity change and other factors in the EHB system.

[0254] The above is only a specific embodiment of the present application, but the protection scope of the present application is not limited thereto, any person skilled in the art can easily think of changes or replacements within the technical range disclosed in the present application, which should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. An electronic hydraulic brake system having self-locking and pressure equalization functions, comprising a brake master cylinder unit, a pressure building unit, a hydraulic control unit, four brake wheel cylinder units, and an ECU control unit, characterized in that, The brake master cylinder unit comprises a first chamber and a second chamber, the pressure building unit comprises a worm gear deceleration mechanism, an auxiliary motor and a gear rack pushing mechanism, the auxiliary motor is coaxial with the worm gear deceleration mechanism, and the gear in the gear rack pushing mechanism is coaxial with the worm in the worm gear deceleration mechanism, the hydraulic control unit comprises an isolation valve one, an isolation valve two, a pressure increasing valve one, a pressure increasing valve two, a pressure increasing valve three, a pressure increasing valve four, a pressure decreasing valve one, a pressure decreasing valve two, a pressure decreasing valve three, a pressure decreasing valve four, a balance valve one, a balance valve two, an oil storage pot and a pressure sensor, and the brake wheel cylinder unit comprises a left front wheel cylinder, a right rear wheel cylinder, a right front wheel cylinder and a left rear wheel cylinder.

2. The electronic hydraulic brake system with self-locking and pressure balancing functions according to claim 1, characterized in that, The brake master cylinder unit adopts a tandem double-cavity structure, and each cavity contains a piston, a return spring, an oil compensation hole and a push rod limiting structure, the first chamber is communicated with the left front wheel cylinder and the right rear wheel cylinder, and the second chamber is communicated with the right front wheel cylinder and the left rear wheel cylinder.

3. The electronic hydraulic brake system with self-locking and pressure balancing functions according to claim 1, characterized in that, The ECU control unit calculates the auxiliary motor control amount according to the target pressure and the current master cylinder pressure, and the worm gear deceleration mechanism satisfies the self-locking condition: wherein is the thread lead angle; is the worm pair friction factor; The output torque of the auxiliary motor is: wherein, is an output torque of the assist motor; is a torque constant of the assist motor; is a control amount of the assist motor; After the output torque of the auxiliary motor is transmitted through the worm gear deceleration mechanism and the gear rack pushing mechanism, the corresponding master cylinder pushing force is: wherein, is the master cylinder thrust force; is the worm gear reduction ratio; is the transmission efficiency; The master cylinder pressure is calculated as: wherein, Pc is the master cylinder pressure; A is the master cylinder piston pressure area.

4. The electronic hydraulic brake system with self-locking and pressure balancing functions according to claim 1, characterized in that, The isolation valve one and the isolation valve two are in the normally open state in the normal braking process, and are closed by the ECU control unit in the pressure maintaining or failure protection mode; The pressure increasing valve one, the pressure increasing valve two, the pressure increasing valve three and the pressure increasing valve four are opened when the master cylinder pressure is insufficient, and are closed by the ECU control unit after the master cylinder pressure reaches; The pressure decreasing valve one, the pressure decreasing valve two, the pressure decreasing valve three and the pressure decreasing valve four are opened when the driver releases the pedal, and are used to release the wheel cylinder pressure to the oil storage pot through the oil return pipeline; The balance valve one and the balance valve two adjust the flow area of the balance valve one and the balance valve two according to the pressure difference of the left front wheel cylinder, the right rear wheel cylinder, the right front wheel cylinder and the left rear wheel cylinder, and the flow area adjustment satisfies: wherein, is the left wheel cylinder pressure; is the right wheel cylinder pressure; is the wheel cylinder pressure equalization adjustment function; is the equalization valve opening gain; is the allowable pressure difference threshold value, satisfying = 0.1 ~ 0.3 MPa; is the current effective flow area of the equalization valve.

5. The electronic hydraulic brake system with self-locking and pressure balancing functions according to claim 4, characterized in that, The balance valve one and the balance valve two are bidirectional pressure sensing structures, and comprise a valve core, left and right pressure sensing cavities, a center valve port, a return spring and a micro flow throttling groove, the balance valve one and the balance valve two maintain the micro flow mode in the pressure maintaining state, and the minimum flow area is 0.5% to 1% of the maximum area; In the pressure decreasing mode, the balance valve one and the balance valve two automatically match the oil return flow according to the left and right wheel cylinder pressure drop speed; In the emergency mode that the ECU control unit and the auxiliary motor are all powered off, the balance valve one and the balance valve two automatically adjust the flow area by relying on the mechanical pressure sensing element, and satisfy: The pressure sensor is arranged at the outlet end of the hydraulic control unit, and is used for real-time detection of the left and right wheel cylinder pressures, the hydraulic control unit further comprises an oil temperature sensor, the ECU control unit calls a thermal compensation function according to the oil temperature, and satisfies: wherein is the mechanical pressure sensing coefficient.

6. The electronic hydraulic brake system with self-locking and pressure balancing functions according to claim 1, characterized in that, The ECU control unit adopts a pressure feedforward and PID closed loop control algorithm for pressure control: wherein, is an oil temperature rise pressure compensation function; is a thermal compensation coefficient.

7. The electronic hydraulic brake system with self-locking and pressure balancing functions according to claim 1, characterized in that, The ECU control unit performs pressure compensation according to the hydraulic oil temperature drift, the balance valve one and the balance valve two maintain the left and right pressures consistent in the micro flow state, and the compensation formula is: wherein, is a feedforward gain coefficient; is an ECU control unit command target pressure; is a proportional coefficient; is a pressure error, satisfying ; is an integral coefficient; is an integral term of the pressure error; is a differential coefficient; is a differential term of the pressure error; The ECU control unit sets the maximum opening limit of the balance valve one and the balance valve two. ​

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