A distributed electro-hydraulic linear control braking system and its control method

Abstract

This invention relates to a distributed electro-hydraulic brake-by-wire system and its control method. The distributed electro-hydraulic brake-by-wire system includes wheel-end actuators located at each wheel of a vehicle. Each wheel-end actuator includes a power output mechanism, a reduction and torque amplification mechanism, a motion conversion mechanism, a hydraulic drive mechanism, a braking actuator, and a control unit. The power output mechanism outputs a rotational driving force, which, after being reduced and amplified by the reduction and torque amplification mechanism, drives the motion conversion mechanism to convert the rotational motion into a linear driving force. The linear driving force drives the hydraulic drive mechanism to generate wheel-end braking hydraulic pressure. The hydraulic drive mechanism then drives the braking actuator through hydraulic action, achieving wheel braking. This distributed electro-hydraulic brake-by-wire system effectively overcomes the shortcomings of existing technologies, reduces manufacturing costs, achieves high redundancy and rapid braking response, and improves braking control accuracy, response quality, and system robustness.

Description

Technical Field

[0001] This invention relates to the field of motor control technology, specifically to a distributed electro-hydraulic linear control braking system and its control method. Background Technology

[0002] The current mainstream directions of automotive brake-by-wire technology are mainly divided into two categories: electromechanical braking (EMB) systems and electrohydraulic braking (EHB) systems. Although both types of systems have been developed and applied to varying degrees, they both have many technical defects and cannot fully meet the high requirements of automotive braking systems for reliability, control precision, cost control and structural rationality.

[0003] The core feature of the distributed electromechanical braking (EMB) system is the complete elimination of hydraulic oil and the adoption of a distributed layout. Taking the early EMB prototypes demonstrated by companies such as Bosch as an example, the typical structure of its wheel-end actuator includes a servo motor, a planetary gear reducer, a ball screw pair, and a brake caliper integrating an electromechanical actuator. The working process of this system is as follows: after receiving the command from the electronic control unit, the motor starts to rotate. The rotational motion is amplified by the reducer and then transmitted to the ball screw. The ball screw converts the rotational motion of the motor into the linear motion of the screw nut, which in turn directly pushes the piston in the brake caliper. The piston pushes the friction plate to clamp the brake disc to achieve braking. The system achieves precise control of the braking force by precisely controlling the output torque or rotation angle of the motor.

[0004] However, existing distributed EMB systems have several significant drawbacks. In scenarios requiring continuous clamping force, such as when the vehicle is engaged in parking brake (EPB function) or waiting at traffic lights for extended periods, distributed EMB solutions can only maintain clamping by continuously outputting stall torque from the motor or relying on the screw's self-locking mechanism. Prolonged high-current stalling of the motor leads to severe overheating of the motor windings and reduction gears, placing extremely high demands on the motor's heat resistance and cooling system, and posing a risk of thermal failure. Simultaneously, during vehicle operation, road vibrations are directly transmitted back through the brake discs and friction pads to the precision roller screws and reduction gears. This high-frequency, high-intensity impact load easily causes premature fatigue damage to precision transmission components, significantly affecting the system's durability and operational reliability. Furthermore, multiple components, such as the motor, reducer, and force sensor, must be highly integrated within the space-constrained wheel hub. The structure of EMB-specific calipers is extremely complex, requiring very high standards for material properties, sealing processes, and assembly precision. Currently, the manufacturing cost of such calipers is difficult to reduce. Furthermore, existing purely mechanical EMB systems typically employ a three-loop control structure consisting of a clamping force outer loop, a speed loop, and a current loop. This control method assumes that the motor output, after being transmitted through a reducer and a lead screw, can be directly mapped to the end clamping force. However, in actual working conditions, factors such as reducer meshing errors, lead screw friction nonlinearity, changes in brake pad contact stiffness, and road impact disturbances can all interfere with this mapping link, leading to problems such as overshoot, fluctuations, and steady-state errors in clamping force control. In scenarios involving electro-hydraulic composite actuators, if this traditional three-loop control is used without separately adjusting the hydraulic build-up process, the controller will struggle to balance response speed and control stability due to the lag in hydraulic cylinder pressure build-up, the compressibility of the oil, and the elasticity of the pipeline.

[0005] Another mainstream type of centralized electro-hydraulic braking (EHB) system is the most widely used form of brake-by-wire in mass-produced vehicles. It is typically represented by Bosch's iBooster (electro-mechanical brake booster) combined with ESP (electronic stability program) or IPB (integrated power braking) system. Its typical structure includes a central motor booster (iBooster), a central hydraulic control unit (HCU, which contains a plunger pump, accumulator and multiple high-speed switching valves), and hydraulic lines connecting each wheel and traditional hydraulic calipers. The working process of this system is as follows: after the driver presses the brake pedal, the pedal displacement sensor transmits the signal to the electronic control unit (ECU). The ECU controls the iBooster motor to push the master cylinder piston to build up braking pressure, or the plunger pump in the HCU draws oil from the reservoir to build up high pressure. Then, by precisely controlling the opening and closing state of the corresponding inlet and outlet valves of each wheel cylinder, the hydraulic pressure entering each wheel hydraulic caliper is adjusted to achieve the braking function.

[0006] However, existing centralized EHB systems also have significant drawbacks. Due to the use of a central hydraulic unit (HCU), failure of the central motor, piston pump, or main control chip can lead to the complete loss of brake assist or even braking capability. Although high-end models may be equipped with two independent hydraulic circuits or even a dual-motor redundant structure, this design greatly increases the system's structural complexity and manufacturing cost. Furthermore, the complex arrangement of metal rigid pipes and rubber hoses from the central hydraulic unit to the four wheel ends not only occupies a large amount of chassis space and increases the difficulty of vehicle assembly, but also causes a certain pressure build-up delay and pressure loss along the way, thus affecting braking response speed and braking force control accuracy. In addition, traditional... EHB systems control braking pressure through pulse width modulation (PWM) of high-speed switching valves, which requires extremely high manufacturing precision for the valve body and involves complex control logic. Under harsh conditions such as low temperature and high oil viscosity, the linearity and response speed of valve control are significantly affected, further reducing control accuracy. Moreover, the pressure control of traditional EHB systems is based on the central hydraulic unit and valve control distribution, with the control focus on high pressure source pressure building and valve orifice flow distribution. Its control object is fundamentally different from the wheel-end distributed electromechanical pressure building structure, making it difficult to directly apply to the execution mode of wheel-end motor-driven local hydraulic cylinder pressure building. Therefore, existing EHB control methods cannot directly solve the problem of fine control of wheel-end independent electro-hydraulic actuators.

[0007] In summary, both of the existing mainstream automotive brake-by-wire technologies have numerous insurmountable technical defects, failing to fully meet the demands of automotive braking systems for higher reliability, higher precision, lower cost, and greater compactness. Therefore, there is an urgent need for an automotive brake-by-wire technology solution that can overcome these technical defects. Summary of the Invention

[0008] The purpose of this invention is to overcome the shortcomings of the prior art and provide a distributed electro-hydraulic brake-by-wire system. This system can solve the problems of excessive heat load and poor heat resistance caused by the need for continuous motor stall to maintain braking force in the pure electromechanical braking (EMB) system of the existing brake-by-wire system, as well as the problems of system complexity, dependence on a central high-pressure source, and difficulty in redundancy backup caused by the use of a centralized hydraulic unit in the traditional electro-hydraulic braking (EHB) system. It reduces manufacturing costs, achieves high redundancy backup and fast braking response, and improves braking control accuracy, response quality and system robustness.

[0009] The second objective of this invention is to provide a control method for the aforementioned distributed electrohydraulic line-controlled braking system.

[0010] The technical solution of the present invention to solve the above-mentioned technical problems is:

[0011] A distributed electro-hydraulic wire-controlled braking system includes wheel-end actuators mounted on each wheel of a vehicle. Each wheel-end actuator includes a power output mechanism, a reduction and torque amplification mechanism, a motion conversion mechanism, a hydraulic drive mechanism, a braking actuator, and a control unit. The power output mechanism outputs a rotational driving force, which, after being reduced and amplified by the reduction and torque amplification mechanism, drives the motion conversion mechanism to convert the rotational motion into a linear driving force. This linear driving force drives the hydraulic drive mechanism to generate wheel-end braking hydraulic pressure. The hydraulic drive mechanism then drives the braking actuator through hydraulic action, thereby achieving wheel braking.

[0012] Preferably, the power output mechanism is a servo motor.

[0013] Preferably, the speed reduction and torque amplification mechanism is a planetary gear, and the motor shaft of the servo motor is connected to the sun gear of the planetary gear; the ring gear of the planetary gear is fixed, and the planet carrier of the planetary gear is connected to the motion conversion mechanism.

[0014] Preferably, the planetary gears are in two sets, namely a first planetary gear and a second planetary gear. The sun gear of the first planetary gear is connected to the motor shaft of the servo motor, and the planet carrier of the first planetary gear is connected to the sun gear of the second planetary gear through a connecting shaft. The planet carrier of the second planetary gear is connected to the motion conversion mechanism.

[0015] Preferably, the motion conversion mechanism is a sliding lead screw, which includes a lead screw shaft and a nut sleeve sleeved on the lead screw shaft and threadedly connected to the lead screw shaft, wherein the nut sleeve is fixedly connected to the planet carrier of the planetary gear; one end of the lead screw shaft is connected to the hydraulic drive mechanism.

[0016] Preferably, the hydraulic drive mechanism is a hydraulic cylinder, and the piston rod of the hydraulic cylinder is fixedly connected to the lead screw shaft.

[0017] Preferably, the braking actuator is a hydraulic caliper, which is connected to the oil outlet of the hydraulic cylinder via an oil pipe.

[0018] Preferably, the control unit includes a clamping force outer loop, a hydraulic pressure loop, a speed loop, and a current loop. The clamping force outer loop calculates and generates a target hydraulic pressure based on the deviation between the target clamping force generated by the system and the actual clamping force. The hydraulic pressure loop calculates and generates a target motor speed based on the deviation between the target hydraulic pressure output by the clamping force outer loop and the actual hydraulic pressure. The speed loop calculates and generates a target current based on the deviation between the target motor speed output by the hydraulic pressure loop and the actual motor speed. The current loop adjusts the output voltage or PWM duty cycle of the motor driver based on the deviation between the target current output by the speed loop and the actual motor current, thereby controlling the servo motor to output the corresponding electromagnetic torque, achieving full-link closed-loop control.

[0019] Preferably, the wheel-end actuator further includes a sensing and detection mechanism, which includes a clamping force sensor, a pressure sensor, a motor encoder, and a current sensor. The clamping force sensor detects the actual clamping force of the braking actuator and feeds the detection signal back to the clamping force outer ring. The pressure sensor detects the actual hydraulic pressure within the hydraulic drive mechanism and feeds the detection signal back to the hydraulic pressure ring. The motor encoder detects the actual rotational speed of the power output mechanism and feeds the detection signal back to the rotational speed ring. The current sensor detects the actual current of the power output mechanism and feeds the detection signal back to the current ring.

[0020] A control method for a distributed electro-hydraulic linear braking system includes the following steps:

[0021] Step S1: The control system acquires the vehicle braking demand command, which includes at least one of the driver braking intention command, automatic driving braking command, vehicle stability control command and anti-lock braking control command, and calculates and generates the target clamping force based on the vehicle braking demand command.

[0022] Step S2: Start the clamping force outer loop control. The actual clamping force of the braking actuator is collected by the clamping force sensor. The clamping force outer loop generates the target hydraulic pressure based on the deviation between the target clamping force generated in step S1 and the actual clamping force collected by the PID calculation.

[0023] Step S3: Start the hydraulic pressure loop control. The actual hydraulic pressure in the hydraulic drive mechanism is collected by the pressure sensor. The hydraulic pressure loop generates the target motor speed by performing PID calculation based on the deviation between the target hydraulic pressure output in step S2 and the collected actual hydraulic pressure.

[0024] Step S4: Start speed loop control. The actual speed of the servo motor is collected through the motor encoder. The speed loop generates the target current through PID calculation based on the deviation between the target motor speed output in step S3 and the collected actual motor speed.

[0025] Step S5: Start the current loop control. The actual current of the servo motor is collected by the current sensor. The current loop adjusts the output voltage or PWM duty cycle of the motor driver according to the deviation between the target current output in step S4 and the actual current of the motor collected, thereby controlling the servo motor to output the corresponding electromagnetic torque.

[0026] Step S6: The electromagnetic torque output by the servo motor is reduced and increased by the deceleration and torque-increasing mechanism, and then transmitted to the motion conversion mechanism. The motion conversion mechanism converts the rotational motion into linear driving force. The linear driving force pushes the hydraulic cylinder piston to make linear motion, squeezing the brake fluid in the hydraulic cylinder to establish wheel end braking hydraulic pressure.

[0027] Step S7: The braking hydraulic pressure established in the hydraulic cylinder is transmitted to the braking actuator through the oil circuit, driving the friction pair of the braking actuator to clamp the brake disc and realize the braking operation of the corresponding wheel. During the braking process, the sensing and detection mechanism continuously collects the actual clamping force, actual hydraulic pressure, actual motor speed and actual motor current signals, and feeds them back to the corresponding closed loop in the control unit in real time. Each closed loop continuously adjusts the control quantity according to the latest deviation to realize the closed-loop correction of the entire braking link until the braking ends.

[0028] Compared with the prior art, the present invention has the following advantages:

[0029] 1. The distributed electro-hydraulic drive-by-wire braking system of this invention can effectively overcome the inherent defects of existing pure EMB systems and traditional EHB systems, achieving improvements in multiple aspects, specifically: First, through the wheel-end electro-hydraulic composite architecture and hydraulic pressure coordinated control, it can effectively solve the problem of excessive motor heat load and poor heat resistance caused by the continuous stalling of the motor due to long-term braking in pure EMB systems, thereby extending the motor's service life and improving the system's thermal management performance; Second, by utilizing the compressibility of the hydraulic medium to construct a flexible force transmission path, it can effectively mitigate the disturbance effect of road impacts on the precision transmission components at the wheel end, reduce the wear of transmission components, and thus significantly improve the overall service life and operational reliability of the system; Third, by eliminating the pure EMB system... The dedicated, highly integrated brake calipers in System B can utilize mature, mass-produced hydraulic calipers, simplifying caliper design and effectively reducing system manufacturing costs by leveraging existing mature supply chains. Fourth, the distributed wheel-end actuation architecture completely overcomes the dependence of traditional EHB systems on a central hydraulic power source. Each wheel-end actuation unit is independent and completely decoupled, meaning a single point of failure does not affect the vehicle's braking function, naturally possessing highly reliable distributed redundancy backup capabilities. Fifth, the optimized system hydraulic circuit design enables in-situ pressure build-up and local supply at the wheel ends, significantly shortening the hydraulic pressure build-up path and simplifying the hydraulic circuit structure. This effectively avoids the pipeline transmission delay problem in traditional EHB systems, achieving a more direct and faster braking response.

[0030] 2. The distributed electro-hydraulic wire-controlled braking system of the present invention adopts a four-closed-loop control architecture. By introducing a hydraulic pressure loop into the traditional three-loop control structure of "clamping force - speed - current", the clamping force target is decomposed into hydraulic pressure target, speed target and current target, realizing step-by-step closed-loop adjustment. This control architecture is highly consistent with the actual execution process of the present invention of "mechanical pushing and pressure building - hydraulic flexible transmission - caliper clamping output", which can effectively improve the braking response quality, clamping force tracking accuracy and system robustness, thereby significantly suppressing clamping force overshoot and jitter, and improving steady-state control accuracy and anti-disturbance capability. Attached Figure Description

[0031] Figures 1-3 These are schematic diagrams of the distributed electro-hydraulic line-controlled braking system of the present invention from three different perspectives.

[0032] Figure 4 This is an architecture diagram of the control method for the distributed electro-hydraulic line-controlled braking system of the present invention.

[0033] In the diagram: 1-Servo motor; 2-First planetary gear; 3-Second planetary gear; 4-Sliding lead screw; 5-Hydraulic cylinder; 6-Hydraulic caliper; 7-Brake disc. Detailed Implementation

[0034] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto.

[0035] See Figures 1-4 The distributed electro-hydraulic wire-controlled braking system of the present invention includes wheel-end actuators installed on each wheel of a vehicle; each wheel-end actuator includes a power output mechanism, a deceleration and torque amplification mechanism, a motion conversion mechanism, a hydraulic drive mechanism, a braking actuator, and a control unit. The power output mechanism outputs a rotational driving force, which, after being decelerated and amplified by the deceleration and torque amplification mechanism, drives the motion conversion mechanism to convert the rotational motion into a linear driving force. The linear driving force drives the hydraulic drive mechanism to generate wheel-end braking hydraulic pressure, and the hydraulic drive mechanism drives the braking actuator to operate through hydraulic action, thereby achieving wheel braking.

[0036] See Figure 1The power output mechanism is a servo motor, preferably a permanent magnet synchronous servo motor or a brushless DC motor. This servo motor is the power input source for the wheel-end execution unit in this invention. Its motor shaft is connected to the input end of the reduction and torque amplification mechanism, which can convert the braking command issued by the control system into controllable rotary mechanical power. The control system precisely controls the speed, angle, and output torque of the servo motor according to commands such as brake pedal opening, vehicle stability control, or automatic driving braking. The rotary power output by the servo motor is amplified by the reduction and torque amplification mechanism, which drives the motion conversion mechanism to generate axial thrust, providing mechanical energy for hydraulic cylinder pressure build-up. Based on the rapid response of the servo motor... With its high speed and control precision, this invention can adapt to dynamic adjustment requirements under various operating conditions, including conventional braking, emergency braking, and anti-lock braking. Furthermore, it employs a distributed, independent arrangement at the wheel ends, with each wheel individually equipped with a wheel-end actuator. This eliminates reliance on a central hydraulic power source, thereby improving system redundancy and fault tolerance. Unlike traditional purely mechanical EMB structures that require the motor to be permanently stalled to maintain pressure, this invention relies on a hydraulic circuit to maintain pressure. The servo motor only participates in driving during the pressure build-up phase, significantly reducing the thermal load on the servo motor during continuous operation. This effectively improves heat dissipation and, consequently, significantly enhances the overall operational stability and service life of the machine.

[0037] See Figures 1-4 The speed reduction and torque amplification mechanism is a planetary gear, and the motor shaft of the servo motor is connected to the sun gear of the planetary gear; the ring gear of the planetary gear is fixed, and the planet carrier of the planetary gear is connected to the motion conversion mechanism.

[0038] Through the above configuration, the deceleration and torque amplification mechanism and the motion conversion mechanism in this invention are used to convert the high-speed, low-torque rotary motion output by the servo motor into a low-speed, high-thrust linear motion suitable for driving the piston rod of the hydraulic cylinder, realizing the step-by-step conversion of "electrical energy - mechanical energy - hydraulic energy". By converting the high-speed rotary output into a large axial thrust output, the high load requirements for wheel-end braking pressure can be met. Through the cooperation of the deceleration and torque amplification mechanism and the motion conversion mechanism, the small angle change of the servo motor can be mapped to the small displacement change of the piston, thereby realizing the fine adjustment of hydraulic pressure and braking force. In this embodiment, the deceleration and torque amplification mechanism and the motion conversion mechanism can adopt a coaxial series structure, which is compact and suitable for installation inside the wheel-end actuator unit near the wheel. Therefore, unlike the rigid transmission method in the existing pure EMB system where the lead screw directly pushes the brake block, the mechanical thrust output by the lead screw shaft in this invention does not directly act on the friction plate or brake block, but first acts on the piston rod of the hydraulic cylinder, and then is transmitted to the hydraulic caliper through the hydraulic medium, thereby reducing the influence of mechanical shock and transmission disturbance on the end clamping force control.

[0039] In this embodiment, the planetary gears consist of two sets: a first planetary gear and a second planetary gear. The sun gear of the first planetary gear is connected to the motor shaft of the servo motor, and the planet carrier of the first planetary gear is connected to the sun gear of the second planetary gear via a connecting shaft. The planet carrier of the second planetary gear is connected to the motion conversion mechanism. By arranging the two sets of planetary gears in series, a two-stage high reduction ratio torque amplification can be achieved. The high-speed, low-torque output power of the servo motor is gradually reduced and amplified to provide sufficient braking driving force for the downstream motion conversion mechanism. The two-stage planetary gears are coupled and transmitted step by step, resulting in smooth and uniform power transmission. This effectively suppresses speed fluctuations and transmission impacts, reduces gear meshing errors and mechanical vibrations, and improves the operational stability and service life of the transmission system.

[0040] See Figures 1-4 The motion conversion mechanism is a sliding lead screw, which includes a lead screw shaft and a nut sleeve sleeved on the lead screw shaft and threaded to the lead screw shaft. The nut sleeve is fixedly connected to the planet carrier of the planetary gear (i.e., the second planetary gear). One end of the lead screw shaft is connected to the hydraulic drive mechanism.

[0041] See Figures 1-4 The hydraulic drive mechanism is a hydraulic cylinder. A hydraulic cylinder is introduced between the lead screw and the hydraulic caliper as a flexible force transmission and amplification unit. The piston rod of the hydraulic cylinder is fixedly connected to the lead screw. When the lead screw undergoes axial displacement, the piston rod of the hydraulic cylinder moves forward, pushing brake oil out of the pipe on the side of the cylinder body, thereby causing the hydraulic caliper to clamp the brake disc to achieve braking. In addition, the hydraulic cylinder also has the following functions: First, the introduction of the hydraulic cylinder avoids the lead screw directly pushing the brake block, thus eliminating motor torque fluctuations and shocks in mechanical transmission. Simultaneously, the pressure self-balancing characteristics of the hydraulic medium make the contact pressure between the brake block and the brake disc more uniform, avoiding uneven wear problems caused by machining errors or assembly deviations in rigid transmission chains. Secondly, when the brake is released, the lead screw shaft retracts to the preset position, and the piston rod of the hydraulic cylinder also returns to its original position. In this way, the brake oil in the cylinder body of the hydraulic cylinder flows back, thereby causing the piston of the hydraulic caliper to automatically retract under the action of the sealing ring return force, reaching the equilibrium position and forming the specified brake gap, without the need for manual adjustment or an additional gap adjustment mechanism.

[0042] See Figures 1-4The braking actuator is a hydraulic caliper. As the final braking actuation component, the hydraulic caliper converts the hydraulic pressure output from the hydraulic cylinder into a clamping force on the brake disc, thereby achieving vehicle deceleration or parking braking. The hydraulic caliper preferably adopts an existing, mature automotive disc hydraulic caliper structure, such as including a caliper body, caliper piston, brake pads, and a clamping mechanism that cooperates with the brake disc. The hydraulic caliper is connected to the oil outlet of the hydraulic cylinder via an oil pipe. In this embodiment, the hydraulic caliper is used to achieve end-of-line braking force output, stably converting the pressure energy in the hydraulic system into a clamping force acting on the brake disc. Furthermore, by adopting an existing, mature hydraulic caliper structure, better braking smoothness, clamping force uniformity, and engineering reliability can be obtained, thus avoiding the problems of complex structures and high development costs associated with purely EMB-specific calipers. Furthermore, since this invention completes the drive and pressure build-up through a servo motor, a reduction torque amplification mechanism, a motion conversion mechanism, and a hydraulic cylinder, the end effector can be directly matched with a mature hydraulic caliper, eliminating the need to redevelop a highly integrated dedicated electromechanical caliper. This helps to shorten the R&D cycle and reduce manufacturing costs. Finally, after the hydraulic circuit is depressurized, the hydraulic caliper can rely on the elastic deformation recovery mechanism of the original hydraulic disc brake's sealing ring to make the piston automatically return to its original position, forming a stable and repeatable braking gap, thus improving system consistency.

[0043] See Figures 1-4 The control unit includes a clamping force outer loop, a hydraulic pressure loop, a speed loop, and a current loop. The clamping force outer loop calculates and generates a target hydraulic pressure based on the deviation between the target clamping force generated by the system and the actual clamping force. The hydraulic pressure loop calculates and generates a target motor speed based on the deviation between the target hydraulic pressure output by the clamping force outer loop and the actual hydraulic pressure. The speed loop calculates and generates a target current based on the deviation between the target motor speed output by the hydraulic pressure loop and the actual motor speed. The current loop adjusts the output voltage or PWM duty cycle of the motor driver based on the deviation between the target current output by the speed loop and the actual motor current, thereby controlling the servo motor to output the corresponding electromagnetic torque, achieving full-link closed-loop control.

[0044] To achieve the above control process, the wheel-end actuator further includes a sensing and detection mechanism, which includes a clamping force sensor, a pressure sensor, a motor encoder, and a current sensor. The clamping force sensor detects the actual clamping force of the braking actuator and feeds the detection signal back to the clamping force outer loop. The pressure sensor detects the actual hydraulic pressure within the hydraulic drive mechanism and feeds the detection signal back to the hydraulic pressure loop. The motor encoder detects the actual rotational speed of the power output mechanism and feeds the detection signal back to the rotational speed loop. The current sensor detects the actual current of the power output mechanism and feeds the detection signal back to the current loop.

[0045] SeeFigures 1-4 The control method of the distributed electro-hydraulic line-controlled braking system of the present invention includes the following steps:

[0046] Step S1: The control system acquires the vehicle braking demand command, which includes at least one of the driver braking intention command, automatic driving braking command, vehicle stability control command and anti-lock braking control command, and calculates and generates the target clamping force based on the vehicle braking demand command.

[0047] Step S2: Start the clamping force outer loop control. The actual clamping force of the braking actuator is collected by the clamping force sensor. The clamping force outer loop generates the target hydraulic pressure based on the deviation between the target clamping force generated in step S1 and the actual clamping force collected by the PID calculation.

[0048] Step S3: Start the hydraulic pressure loop control. The actual hydraulic pressure in the hydraulic drive mechanism is collected by the pressure sensor. The hydraulic pressure loop generates the target motor speed by performing PID calculation based on the deviation between the target hydraulic pressure output in step S2 and the collected actual hydraulic pressure.

[0049] Step S4: Start speed loop control. The actual speed of the servo motor is collected through the motor encoder. The speed loop generates the target current through PID calculation based on the deviation between the target motor speed output in step S3 and the collected actual motor speed.

[0050] Step S5: Start the current loop control. The actual current of the servo motor is collected by the current sensor. The current loop adjusts the output voltage or PWM duty cycle of the motor driver according to the deviation between the target current output in step S4 and the actual current of the motor collected, thereby controlling the servo motor to output the corresponding electromagnetic torque.

[0051] Step S6: The electromagnetic torque output by the servo motor is reduced and increased by the deceleration and torque-increasing mechanism, and then transmitted to the motion conversion mechanism. The motion conversion mechanism converts the rotational motion into linear driving force. The linear driving force pushes the hydraulic cylinder piston to make linear motion, squeezing the brake fluid in the hydraulic cylinder to establish wheel end braking hydraulic pressure.

[0052] Step S7: The braking hydraulic pressure established in the hydraulic cylinder is transmitted to the braking actuator through the oil circuit, driving the friction pair of the braking actuator to clamp the brake disc and realize the braking operation of the corresponding wheel. During the braking process, the sensing and detection mechanism continuously collects the actual clamping force, actual hydraulic pressure, actual motor speed and actual motor current signals, and feeds them back to the corresponding closed loop in the control unit in real time. Each closed loop continuously adjusts the control quantity according to the latest deviation to realize the closed-loop correction of the entire braking link until the braking ends.

[0053] The distributed electro-hydraulic wire-controlled braking system of the present invention adopts a three-level progressive energy conversion and transmission architecture of mechanical-electrical-hydraulic. By integrating the conversion process of "electrical energy to mechanical energy" and the conversion process of "mechanical energy to hydraulic energy" in situ at the wheel end, the above two-level energy conversion modules are built into the wheel end execution unit to realize on-site energy conversion and on-site supply.

[0054] To more clearly illustrate the technical features of this embodiment, a comparative explanation is provided below in conjunction with existing technical solutions:

[0055] In existing pure electromechanical braking (EMB) solutions, energy conversion only achieves a single conversion of "electrical energy to mechanical energy." The mechanical energy output by the motor directly acts on the piston of the brake caliper, and there is no hydraulic conversion or transmission link in the entire transmission process. Although existing centralized electro-hydraulic braking (EHB) solutions involve the conversion and transmission of hydraulic energy, their hydraulic energy generation unit is centrally located in the central hydraulic module (such as iBooster or hydraulic control unit HCU), rather than integrated at the wheel end. Their energy conversion link is "electrical energy - mechanical energy - hydraulic energy - long-distance pipeline transmission - mechanical energy," which belongs to the centralized energy conversion and centralized hydraulic supply mode. In contrast, the energy conversion link of this embodiment is shorter, and the wheel end execution units of each wheel are independent and completely decoupled, thereby effectively avoiding many limitations of centralized supply.

[0056] Based on the aforementioned energy conversion architecture, this embodiment designs a composite transmission chain structure of "two-stage planetary gear reduction mechanism + motion conversion mechanism + sealed hydraulic cylinder" to specifically address the technical bottlenecks of existing mainstream braking solutions: Existing EMB actuators generally adopt a purely mechanical rigid transmission chain of "motor + planetary gear mechanism + lead screw" (such as the mainstream implementation schemes of Continental and Bosch). After the motor output torque is reduced by planetary gears, it directly drives the brake block through the ball screw. This results in the inability to attenuate disturbances such as motor torque fluctuations, gear meshing errors, and nonlinear friction of the lead screw, which are directly transmitted to the braking actuation end, leading to large overshoot in clamping force control, dynamic response jitter, and insufficient steady-state control accuracy. Although the traditional EHB solution realizes the hydraulic transmission of braking force through the hydraulic master cylinder and pipeline, its braking pressure comes from the hydraulic pump or high-pressure accumulator. The hydraulic system needs to simultaneously undertake the dual functions of generating and distributing braking pressure. The braking response speed is constrained by the hydraulic medium pressure building process and pipeline transmission delay, and the system structure is complex and the redundancy design is difficult.

[0057] To address the aforementioned issues, this embodiment introduces a sealed hydraulic cylinder and a short-distance hydraulic pipeline between the sliding screw and the hydraulic caliper. By leveraging the compressibility of the hydraulic medium, a flexible force transmission path is constructed, which can pre-isolate and effectively attenuate various transmission disturbances transmitted from the motor end. Simultaneously, through the synergistic coupling control of the mechanical thrust output by the sliding screw and the pressure in the sealed cavity of the hydraulic cylinder, the motor does not need to continuously stall to output torque during braking and pressure holding conditions. This significantly optimizes the working conditions of the servo motor, reduces the thermal load on the servo motor, and improves the thermal management performance of the system.

[0058] This embodiment adopts a distributed architecture derived from the EMB solution. Each wheel is equipped with an independent wheel-end actuator, which is driven independently and does not interfere with each other. Even if a single point of failure occurs, it will not affect the braking function of the entire vehicle, providing high redundancy and safety characteristics. At the same time, the braking actuator still uses hydraulic oil as the driving medium, inheriting the inherent advantages of hydraulic braking such as good braking smoothness and low impact noise, realizing the technical integration of "electromechanical energy conversion + hydraulic flexible transmission". In addition, this embodiment abandons the complex central hydraulic control unit (HCU) and valve island assembly in the traditional EHB system, and does not require the dedicated highly integrated brake calipers in the pure EMB solution. It adopts a modular combination of "standard servo motor + standardized reducer + micro hydraulic cylinder + mature mass-produced hydraulic caliper", which can fully rely on the existing mature supply chain system, thereby effectively reducing the R&D investment and mass production cost of the system.

[0059] Compared with existing mainstream solutions, the core technical features of this embodiment are as follows: Compared with the traditional EHB solution, the braking pressure in this embodiment comes from the mechanical thrust output by the servo motor after deceleration, torque amplification, and motion conversion. The hydraulic cylinder only undertakes the flexible transmission and buffering function of force and is not a unit for generating braking pressure. Compared with the purely mechanical EMB solution, this embodiment avoids the problem of direct transmission of disturbances in rigid transmission chains from a physical level by constructing a flexible transmission link through hydraulic medium, effectively improving the stability and accuracy of braking control.

[0060] For the electromechanical-hydraulic composite actuator structure of "motor-driven locally sealed hydraulic cylinder actively building pressure" at the wheel end in this embodiment, this embodiment further designs a four-closed-loop control system that couples the compressibility of the hydraulic medium, the dynamic characteristics of hydraulic cylinder pressure building, and the nonlinear characteristics of sliding screw friction, in order to adapt to the physical transmission mechanism of the electromechanical-hydraulic composite actuator and improve control performance.

[0061] Existing purely mechanical EMB solutions generally adopt a three-loop control architecture of "clamping force outer loop - speed loop - current inner loop". The controlled object is only a purely mechanical rigid transmission chain. Although nonlinear disturbances in the transmission system can be compensated through closed-loop control algorithms such as PID, fuzzy PID, and three-loop PI control, the inherent defect of rigid transmission chains without flexible buffer links cannot fundamentally solve the problem of insufficient control accuracy caused by direct transmission of disturbances. The pressure control core of traditional EHB solutions is the central hydraulic source and valve-controlled pressure distribution. The control coupling is high, and the braking response speed is limited by the pressure build-up of the hydraulic system and the valve group action delay.

[0062] The core difference between the four-closed-loop control architecture of this embodiment and the existing three-closed-loop control architecture lies in the addition of a hydraulic pressure control loop between the outer loop of clamping force control and the middle loop of speed control. Hydraulic pressure is incorporated as an independent intermediate state variable into the closed-loop regulation system, enabling the controller to independently and precisely regulate the pressure build-up process of the hydraulic cylinder. This ensures that the control logic is fully matched with the physical transmission mechanism of the electro-hydraulic composite actuator in this embodiment. This four-closed-loop control architecture can significantly suppress overshoot and oscillation during the dynamic response of clamping force, improving the steady-state control accuracy and anti-disturbance capability of the system. Under braking and pressure-holding conditions, the hydraulic pressure control loop can be used to maintain the stability of the hydraulic cylinder cavity pressure, significantly alleviating the heat generation problem caused by continuous motor stall. Under dynamic braking and ABS anti-lock braking conditions, smoother wheel-end pressure regulation and more stable braking force output can be achieved. Therefore, this embodiment significantly outperforms the EMB scheme using a purely mechanical three-closed-loop control in terms of clamping force control accuracy, dynamic response smoothness, thermal management performance, and system reliability.

[0063] Finally, the essential differences between the control scheme of this invention and existing control schemes are mainly reflected in two aspects: First, the control object of existing pure mechanical EMB is a rigid electromechanical transmission chain, while the control object of this invention is an electromechanical-hydraulic composite system that includes mechanical transmission and hydraulic transmission coupling links, and the physical mechanism of the control architecture and the actuator are highly matched; Second, compared with the pressure control system of traditional EHB, the hydraulic pressure control loop of this invention is not based on a central hydraulic source and valve-controlled pressure distribution architecture, but on the execution mechanism of active pressure building by a wheel-end servo motor through a reduction torque amplification mechanism and a sliding screw driving a hydraulic cylinder. That is, the pressure control core of traditional EHB is valve-controlled pressure distribution, while the pressure control core of this invention is the integrated and coordinated control of active pressure building by wheel-end electromechanical system and flexible hydraulic output. This core difference gives this invention unparalleled technical advantages over traditional EHB systems in terms of distributed independent control, direct braking response, and system redundancy safety.

[0064] The above are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above content. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A distributed electro-hydraulic linear control braking system, characterized in that, The system includes wheel-end actuators mounted on each wheel of the vehicle. Each wheel-end actuator comprises a power output mechanism, a reduction and torque amplification mechanism, a motion conversion mechanism, a hydraulic drive mechanism, a braking actuator, and a control unit. The power output mechanism outputs a rotational driving force, which is reduced and amplified by the reduction and torque amplification mechanism to drive the motion conversion mechanism to convert the rotational motion into a linear driving force. The linear driving force drives the hydraulic drive mechanism to generate wheel-end braking hydraulic pressure. The hydraulic drive mechanism then drives the braking actuator through hydraulic action to achieve wheel braking.

2. The distributed electro-hydraulic linear control braking system according to claim 1, characterized in that, The power output mechanism is a servo motor.

3. The distributed electro-hydraulic linear control braking system according to claim 2, characterized in that, The speed reduction and torque amplification mechanism is a planetary gear, and the motor shaft of the servo motor is connected to the sun gear of the planetary gear; the ring gear of the planetary gear is fixed, and the planet carrier of the planetary gear is connected to the motion conversion mechanism.

4. The distributed electro-hydraulic linear control braking system according to claim 3, characterized in that, The planetary gears are in two sets, namely a first planetary gear and a second planetary gear. The sun gear of the first planetary gear is connected to the motor shaft of the servo motor, and the planet carrier of the first planetary gear is connected to the sun gear of the second planetary gear through a connecting shaft. The planet carrier of the second planetary gear is connected to the motion conversion mechanism.

5. The distributed electro-hydraulic linear control braking system according to claim 3, characterized in that, The motion conversion mechanism is a sliding lead screw, which includes a lead screw shaft and a nut sleeve sleeved on the lead screw shaft and threadedly connected to the lead screw shaft. The nut sleeve is fixedly connected to the planet carrier of the planetary gear. One end of the lead screw shaft is connected to the hydraulic drive mechanism.

6. The distributed electro-hydraulic linear control braking system according to claim 5, characterized in that, The hydraulic drive mechanism is a hydraulic cylinder, and the piston rod of the hydraulic cylinder is fixedly connected to the lead screw shaft.

7. The distributed electro-hydraulic linear control braking system according to claim 6, characterized in that, The braking actuator is a hydraulic caliper, which is connected to the oil outlet of the hydraulic cylinder via an oil pipe.

8. The distributed electro-hydraulic line-controlled braking system according to claim 7, characterized in that, The control unit includes a clamping force outer loop, a hydraulic pressure loop, a speed loop, and a current loop. The clamping force outer loop calculates and generates a target hydraulic pressure based on the deviation between the target clamping force generated by the system and the actual clamping force. The hydraulic pressure loop calculates and generates a target motor speed based on the deviation between the target hydraulic pressure output by the clamping force outer loop and the actual hydraulic pressure. The speed loop calculates and generates a target current based on the deviation between the target motor speed output by the hydraulic pressure loop and the actual motor speed. The current loop adjusts the output voltage or PWM duty cycle of the motor driver based on the deviation between the target current output by the speed loop and the actual motor current, thereby controlling the servo motor to output the corresponding electromagnetic torque, achieving full-link closed-loop control.

9. The distributed electro-hydraulic linear control braking system according to claim 8, characterized in that, The wheel-end actuator further includes a sensing and detection mechanism, which includes a clamping force sensor, a pressure sensor, a motor encoder, and a current sensor. The clamping force sensor detects the actual clamping force of the braking actuator and feeds the detection signal back to the clamping force outer loop. The pressure sensor detects the actual hydraulic pressure within the hydraulic drive mechanism and feeds the detection signal back to the hydraulic pressure loop. The motor encoder detects the actual rotational speed of the power output mechanism and feeds the detection signal back to the rotational speed loop. The current sensor detects the actual current of the power output mechanism and feeds the detection signal back to the current loop.

10. A control method for the distributed electro-hydraulic linear control braking system as described in claim 9, characterized in that, Includes the following steps: Step S1: The control system acquires the vehicle braking demand command, which includes at least one of the driver braking intention command, automatic driving braking command, vehicle stability control command and anti-lock braking control command, and calculates and generates the target clamping force based on the vehicle braking demand command. Step S2: Start the clamping force outer loop control. The actual clamping force of the braking actuator is collected by the clamping force sensor. The clamping force outer loop generates the target hydraulic pressure based on the deviation between the target clamping force generated in step S1 and the actual clamping force collected by the PID calculation. Step S3: Start the hydraulic pressure loop control. The actual hydraulic pressure in the hydraulic drive mechanism is collected by the pressure sensor. The hydraulic pressure loop generates the target motor speed by performing PID calculation based on the deviation between the target hydraulic pressure output in step S2 and the collected actual hydraulic pressure. Step S4: Start speed loop control. The actual speed of the servo motor is collected through the motor encoder. The speed loop generates the target current through PID calculation based on the deviation between the target motor speed output in step S3 and the collected actual motor speed. Step S5: Start the current loop control. The actual current of the servo motor is collected by the current sensor. The current loop adjusts the output voltage or PWM duty cycle of the motor driver according to the deviation between the target current output in step S4 and the actual current of the motor collected, thereby controlling the servo motor to output the corresponding electromagnetic torque. Step S6: The electromagnetic torque output by the servo motor is reduced and increased by the deceleration and torque-increasing mechanism, and then transmitted to the motion conversion mechanism. The motion conversion mechanism converts the rotational motion into linear driving force. The linear driving force pushes the hydraulic cylinder piston to make linear motion, squeezing the brake fluid in the hydraulic cylinder to establish wheel end braking hydraulic pressure. Step S7: The braking hydraulic pressure established in the hydraulic cylinder is transmitted to the braking actuator through the oil circuit, driving the friction pair of the braking actuator to clamp the brake disc and realize the braking operation of the corresponding wheel. During the braking process, the sensing and detection mechanism continuously collects the actual clamping force, actual hydraulic pressure, actual motor speed and actual motor current signals, and feeds them back to the corresponding closed loop in the control unit in real time. Each closed loop continuously adjusts the control quantity according to the latest deviation to realize the closed-loop correction of the entire braking link until the braking ends.

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