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Study on the Structural Configurations and Pressure Regulation Characteristics of the Automatic Pressure Regulating Valve in the Electronically Controlled Pneumatic Brake System of Commercial Vehicles
Study on the Structural Configurations and Pressure Regulation Characteristics of the Automatic...
Bao, Hanwei;Wang, Zaiyu;Wei, Xiaoxu;Li, Gangyan
2021-11-11 00:00:00
applied sciences Article Study on the Structural Configurations and Pressure Regulation Characteristics of the Automatic Pressure Regulating Valve in the Electronically Controlled Pneumatic Brake System of Commercial Vehicles Hanwei Bao , Zaiyu Wang, Xiaoxu Wei and Gangyan Li * School of Mechanical and Electrical Engineering, Wuhan University of Technology, Luoshi Road 122, Wuhan 430070, China; hanweibao@whut.edu.cn (H.B.); z623532_@whut.edu.cn (Z.W.); 259636@whut.edu.cn (X.W.) * Correspondence: gangyanli@whut.edu.cn Abstract: Based on the classification of automated driving by the SAE (Society of Automotive Engineers) and the working principle of the ECPBS (Electronically Controlled Pneumatic Brake system), the requirements and the control modes of the APRV (Automatic Pressure Regulating Valve) were concluded. Four structural configurations for APRV were proposed to meet the requirements of the ECPBS. To study the pressure regulating characteristics of the APRV of different structure configurations, a simulation model was established, and a test bench was built. Through experiments, the correctness and the reliability of the simulation model were verified. The pressure regulation Citation: Bao, H.; Wang, Z.; Wei, X.; characteristics of the APRV of different structure configurations under different control conditions Li, G. Study on the Structural were revealed, and the suitable levels in the SAE automated driving classifications for automatic Configurations and Pressure pressure regulators of different structure configurations were determined; thus, the theoretical Regulation Characteristics of the underpinning to improve driving safety and develop automated driving was provided. Automatic Pressure Regulating Valve in the Electronically Controlled Keywords: automatic pressure regulating valve (APRV); structural configuration; control condition; Pneumatic Brake System of Commercial Vehicles. Appl. Sci. 2021, pressure regulating characteristics; test bench 11, 10603. https://doi.org/10.3390/ app112210603 Academic Editor: Emanuele 1. Introduction Carpanzano In the development of driving automation, the response time of the driver for external stimuli is crucial. Even though driving people have the same cognition and control ability, Received: 1 October 2021 under larger mental loads or distracted, the driving operations may appear seriously out of Accepted: 3 November 2021 control [1–5]. Therefore, in addition to the need for an optimized strategy for the response of Published: 11 November 2021 the driver reaction time in an automated driving system, the automatic pressure regulating valve (APRV) as an actuator, its structure constructed for the safety of commercial vehicle Publisher’s Note: MDPI stays neutral driving, and the development of automatic driving is particularly critical. with regard to jurisdictional claims in The intelligentization of the brake system in commercial vehicles directly affects the published maps and institutional affil- development of driving automation, as the brake system in commercial vehicles needs iations. suitable APRV to meet the requirements of driving automation and adapt to different levels of driving automation. At present, the structural research of the APRV has mainly focused on the optimization and improvement of existing products and the analysis of the influence of the structural parameters of the APRV on its response characteristics [6], Copyright: © 2021 by the authors. while research on the structural design and working principle of the APRV is relatively Licensee MDPI, Basel, Switzerland. rare. Based on the braking requirements of the electronically controlled pneumatic brake This article is an open access article (ECPB) system of commercial vehicles, Wu S et al. proposed a new overall structure scheme distributed under the terms and of the APRV. Through a theoretical analysis, mathematical modeling and simulation, the conditions of the Creative Commons pressure response characteristics and flow characteristics of the APRV were analyzed [7,8]. Attribution (CC BY) license (https:// Bo L designed a high precision pneumatic proportional pressure valve and analyzed the creativecommons.org/licenses/by/ influence of its main physical and geometric parameters on its dynamic characteristics and 4.0/). Appl. Sci. 2021, 11, 10603. https://doi.org/10.3390/app112210603 https://www.mdpi.com/journal/applsci Appl. Sci. 2021, 11, 10603 2 of 18 control performance through a nonlinear dynamics model [9]. Sun H et al. designed an electromagnetic control pneumatic brake valve that regulated the air pressure by changing the current intensity proportionally, thus improved the reliability of the pneumatic brake system [10]. You M et al. established a mathematic model of a proportional relay valve in MATLAB/Simulink and verified the model through an open loop experiment, analyzed the effects of the main physical and geometrical parameters on the characteristics of the valve and studied the feasibility of using a pneumatic proportional valve as a pressure regulator in order to improve the pneumatic brake system of vehicles [11]. Cazzola G J et al. established a mathematical model of the ECPBS of commercial vehicles, simulated the response characteristics of the relay valve and the brake chamber and analyzed the influence of the internal structural parameters of the relay valve on the braking response time [12]. Zhao et al. studied the effects of the structural parameters on the static electromagnetic characteristics of high-speed solenoid valves [13]. The research of APRV has mainly focused on the control strategy and electric circuit. Hu Dawei et al. proposed the MPC, LQT and LPV control models in order to reduce the response time of the pressure regulating valve in the ECPBS of commercial vehicles, which was verified by the test bench and compared with the data of a PID control model, thus effectively improving the response speed of the pressure-regulating valve and the performance of the ECPBS of commercial vehicles [14–16]. Bin Zhang et al., proposed a self-correcting PWM control algorithm for high-speed on/off valves to maintain and improve the original dynamic performance under changing pressures [17]. Sorli M et al. built a nonlinear dynamic model of a pneumatic proportional pressure valve (now Parker P3P-R) under several operating conditions and downstream loads to simulate its dynamic behavior in the time and frequency domains and validated the proposed model through experiments [18]. Han J C et al. established static and dynamic simulation models of proportional relay valves of a pneumatic EBS (Electronic Braking System) for commercial vehicles with MATLAB/Simulink; then, the simulation models were verified to be correct on a test bench and, thus, can be used for the development of hardware and control algorithms of a pneumatic EBS for commercial vehicles [19,20]. Miller J I designed a new pneumatic valve to improve the response of air-actuated brakes for heavy vehicles to demand pressures generated during electronically controlled braking [21]. P X Li et al. used a double voltage driving circuit to reduce the switching time and delay time of the high- speed on/off valve, and hence, the response characteristics and the control performance were optimized [22,23]. Lee designed and manufactured an electronic valve driving circuit with fast response characteristics by using a three-power source. The new circuit shortened the switching delay time from 5 ms to 1.55 ms. Therefore, the hydraulic system with the new circuit showed excellent position tracking control performance [24]. The above research was mainly aimed at the improvement of the structure of the existing APRV or the optimization of the control strategy. The working conditions were relatively fixed in this research, and there has been no in-depth study on whether the structure of the APRV can cope with the driving conditions under special circumstances. In order to adapt to the development of driving automation and intelligentization of the brake system, the brake system in commercial vehicles is in urgent need of an APRV that can adapt to the development of driving automation and an intelligent brake system. Therefore, this paper studies the structure configurations of the APRV to ensure that the structure configuration of the APRV can adapt to more dangerous driving conditions, so as to better guarantee the driving safety of vehicles and the development of driving automation. Based on the classification of driving automation proposed by the SAE (Society of Automotive Engineers) and the working principle of the ECPBS of commercial vehicles, four structural configurations of APRV are proposed. The simulation model for the APRV of different structural configurations is established in AMESim, and the working condition in which the driver fails to apply sufficient braking force is simulated. Then, the pressure regulation characteristics of the APRV under different control conditions and during the switch between these conditions is studied. The correctness and the reliability of the simula- Appl. Sci. 2021, 11, x FOR PEER REVIEW 3 of 17 four structural configurations of APRV are proposed. The simulation model for the APRV of different structural configurations is established in AMESim, and the working condi- Appl. Sci. 2021, 11, 10603 3 of 18 tion in which the driver fails to apply sufficient braking force is simulated. Then, the pres- sure regulation characteristics of the APRV under different control conditions and during the switch between these conditions is studied. The correctness and the reliability of the simulation model are verified through the test bench for the pressure regulation charac- tion model are verified through the test bench for the pressure regulation characteristics of teristics of the APRV of different structural configurations. Finally, through simulation the APRV of different structural configurations. Finally, through simulation and tests, the and tests, the pressure regulation characteristics of the APRV of different structural con- pressure regulation characteristics of the APRV of different structural configurations under figurations under different control conditions are studied, and the suitable levels in the different control conditions are studied, and the suitable levels in the SAE automated driv- SAE automated driving classification for the APRV of different structural configurations ing classification for the APRV of different structural configurations are determined; thus, are determined; thus, the theoretical underpinning to improve driving safety and develop the theoretical underpinning to improve driving safety and develop driving automation driving automation is provided. is provided. 2. Pressure Regulating Requirements and Control Modes of the APRV in the ECPBS 2. Pressure Regulating Requirements and Control Modes of the APRV in the ECPBS of Commercial Vehicles of Commercial Vehicles The ECPBS of commercial vehicle is a new type of brake system that meets the The ECPBS of commercial vehicle is a new type of brake system that meets the re- requirements of automated driving. The electronic control mode is added on the basis quirements of automated driving. The electronic control mode is added on the basis of of retaining the traditional braking circuit, and the ECPBS provides decent solutions to retaining the traditional braking circuit, and the ECPBS provides decent solutions to many many problems in the traditional pneumatic brake system [25], thus ensuring driving problems in the traditional pneumatic brake system [25], thus ensuring driving safety and safety and driving comfort. As depicted in Figure 1, the APRV is the core pressure- driving comfort. As depicted in Figure 1, the APRV is the core pressure-regulating com- regulating component in the ECPBS. As the key component to ensure driving safety, ponent in the ECPBS. As the key component to ensure driving safety, its structure config- its structure configuration and the pressure-regulating function must meet the braking uration and the pressure-regulating function must meet the braking requirements of the requirements of the driver and the automated driving system. Moreover, the APRV should driver and the automated driving system. Moreover, the APRV should be able to operate be able to operate under different control modes to ensure driving safety under different under different control modes to ensure driving safety under different working condi- working conditions. tions. Front brake Rear brake chamber chamber Pneumatic line Electrical connection Pneumatic Control line Front tank Automatic pressure Automatic pressure regulator regulator Pedal valve Automatic pressure regulator Rear tank Automatic pressure Parking brake Compressor Filter regulator circuit Wet tank Rear brake Front brake Four circuit chamber chamber protection valve Figure 1. Principle drawing of the ECPBS in commercial vehicles. Figure 1. Principle drawing of the ECPBS in commercial vehicles. 2.1. Pressure Regulating Requirements of the APRV in the ECPBS of Commercial Vehicles 2.1. Pressure Regulating Requirements of the APRV in the ECPBS of Commercial Vehicles According to the description of the six levels of driving automation proposed by According to the description of the six levels of driving automation proposed by the the SAE (Society of Automotive Engineers) in 2018, the APRV should realize the follow- SAE (Society of Automotive Engineers) in 2018, the APRV should realize the following ing functions: functions: (1) The APRV can regulate the braking pressure when the vehicle is driven manually (1) The APRV can regulate the braking pressure when the vehicle is driven manually by the driver (meeting the requirements of levels 0–2 in the automated driving classification by the driver (meeting the requirements of levels 0–2 in the automated driving classifica- of the SAE). tion of the SAE). (2) The APRV can regulate the braking pressure when the vehicle is driven automat- (2) The APRV can regulate the braking pressure when the vehicle is driven automat- ically (meeting the requirements of levels 3–5 in the automated driving classification of ically (meeting the requirements of levels 3–5 in the automated driving classification of the SAE). the SAE). (3) The APRV can regulate the braking pressure when the vehicle switches between (3) The APRV can regulate the braking pressure when the vehicle switches between automated driving mode and manual driving mode (meeting the requirements of levels automated driving mode and manual driving mode (meeting the requirements of levels 1–5 in the automated driving classification of the SAE). 1–5 in the automated driving classification of the SAE). (4) The APRV can regulate the braking pressure when the electronic control system fails (meeting the requirements of levels 1–5 in the automated driving classification of the SAE). (5) The APRV can regulate the braking pressure when the braking pressure is insuffi- cient in the manual driving mode (meeting the requirements of levels 3–5 in the automated driving classification of the SAE). Appl. Sci. 2021, 11, 10603 4 of 18 2.2. Control Modes of the APRV in the ECPBS of Commercial Vehicles According to the working principle of the ECPBS of commercial vehicles and the pressure regulating requirements of the APRV, as the core pressure-regulating component of the ECPBS, the APRV should be able to be controlled directly by the driver or the automated driving system. Additionally, the APRV can operate during the switch of these two control modes or operate under a coupled control mode. Therefore, the control modes of the APRV include the manual control mode, electronic control mode and coupled control mode. The definitions are as follows: (1) Manual control mode: The pressure regulation is done by the pedal control applied by the driver. (2) Electronic control mode: The pressure regulation is done by the automated driving system via a control signal without the interference of the driver. (3) Coupled control mode: A combination of the manual control mode and the elec- tronic control mode, the pressure regulation is done by both the driver and the automated driving system. 3. Theoretical Analysis and Structural Configurations of the APRV in the ECPBS of Commercial Vehicles 3.1. Mathematical Model of the APRV The mathematical model of the APRV includes a solenoid valve subsystem and relay valve subsystem. The key points of the model are the movement of the valve core and piston and the relationship between the pressure and mass flow rate. The movement of the valve core in the solenoid valve is determined by electromagnetic force, spring force, damping force and flow force. The dynamic equation of the valve core of the solenoid valve is as follows: d x dx dx 1 1 1 m = F k (x + x ) sgn( ) c( ) (P P )pr (1) e 1 0 1 c 1 in dt dt dt where F is the electromagnetic force (N), m is the mass of the valve core in the solenoid valve, k is the stiffness of the spring (N/m), c is the coefficient of the viscous damping 1 1 (Nm s ), P is the pressure of the inlet port (Pa), P is the pressure of the control cavity in c (Pa), r is the effective radius of the flow area (m), x is the displacement of the valve core 1 1 in the solenoid valve (m) and x is the initial shape variable of the spring (m). The movement of the piston and valve core in the relay valve includes the processes of pressurization and decompression. In the pressurization process of the APRV, the piston and the valve core stay in contact and, hence, can be considered as a whole. The dynamic equation of the piston and valve core is as follows: d x dx dx dx (m + m ) = P A PA (k x + F ) sgn( ) (c + c ) sgn( ) F + (m + m )g (x 0) (2) p c c 1 2 x2 0 1 2 p c dt dt dt dt In the process of decompression, the piston and the valve core detach. The dynamic equation of the piston is as follows: d x dx dx dx m = P A PA sgn( ) c sgn( ) F + m g (x < 0) (3) p c 2 p 1 1 f dt dt dt dt where x is the displacement of the piston (m), m is the mass of the piston in the relay valve (kg), m is the mass of the valve core in the relay valve (kg), A is the upper surface 2 2 area of the piston (m ), A is the lower surface area of the piston (m ), k is the stiffness 2 x2 of the spring (N/m), F is the preload force of the spring (m), c is the viscous damping 0 1 1 1 coefficient of the piston (Nm s ), c is the viscous damping coefficient of the valve core 1 1 (Nm s ) and F is the friction force (N). The processes of pressurization and decompression in the APRV can be considered the inflation and the deflation processes of a variable-volume chamber. These processes Appl. Sci. 2021, 11, x FOR PEER REVIEW 5 of 17 d x dx dx dx (3) m =− P A PA− sgn()⋅⋅ c − sgn() F + m g( x<0) pc 2 12 1 f p dt dt dt dt where x is the displacement of the piston (m), is the mass of the piston in the relay valve (kg), m is the mass of the valve core in the relay valve (kg), A is the upper sur- c 1 2 2 face area of the piston (m ), A is the lower surface area of the piston (m ), k is the 2 x 2 stiffness of the spring (N/m), F is the preload force of the spring (m), c is the viscous 0 1 −1 −1 damping coefficient of the piston (N·m ·s ), c is the viscous damping coefficient of the −1 −1 valve core (N·m ·s ) and is the friction force (N). Appl. Sci. 2021, 11, 10603 5 of 18 The processes of pressurization and decompression in the APRV can be considered the inflation and the deflation processes of a variable-volume chamber. These processes happen in an extremely short time and, therefore, can be regarded as adiabatic processes, happen in an extremely short time and, therefore, can be regarded as adiabatic processes, so the relationship between the pressure and mass flow rate [6] is as follows: so the relationship between the pressure and mass flow rate [6] is as follows: dp R Rθ P dV P dV =− kq θ kq −(1 k− ) − (4) in in out d p R Rq P dV P dV dt V V V dt V dt = kq q kq (k 1) (4) out in in dt V V V dt V dt where is the volume of the chamber (m ), q is the inlet mass flow rate (kg/s), q in out where V is the volume of the chamber (m ), q is the inlet mass flow rate (kg/s), q is the in out is the outlet mass flow rate (kg/s), is the adiabatic index and θ is the temperature of in outlet mass flow rate (kg/s), k is the adiabatic index and q is the temperature of the air in the air that flows through the orifice (K). that flows through the orifice (K). 3.2. 3.2. Str Structural uctural Configura Configurations tions of the of the APRV APRV Based on the working principle of the ECPBS of commercial vehicles shown in Figure 1, Based on the working principle of the ECPBS of commercial vehicles shown in Figure the pressure-regulating requirements and the control modes of the APRV, four structural 1, the pressure-regulating requirements and the control modes of the APRV, four struc- configurations of the APRV (shown in Figure 2) are proposed. tural configurations of the APRV (shown in Figure 2) are proposed. Powe r supply Fee dback signal Power supply Feedback signal Controller Controller Target signal Target signal High-speed inlet valve High-speed High-spee d High-spee d (normal open) inlet valve exhaust valve exhaust valve Inle t port Inle t port (ele ctronic control) (m anual control) EXH EXH High-speed on- Inle t port off valve (ele ct ronic control) High-speed sw itching valve Inle t port (m anual control) EXH EXH SUP OUT SUP OUT EXH EXH Structure construction I Structure construction II Power supply Feedback signal Power supply Feedback signal Controller Controller Target signal Tar get signal High-speed inlet valve High-spee d inlet valve (normal open) (normal open) High-speed High-speed exhaust valve High-speed exhaust valve Inle t port Inle t port sw itching valve (ele ctronic control) EXH (manual control) EXH Inle t port Inle t port (ele ctronic control) (m anual control) Switchi ng valve EXH EXH High-spee d inlet valve SUP OUT SUP OUT EXH Pneumatic li ne EXH Structure construction III Structure construction IV Electri cal connectio n Si gna l lin e Figure 2. Principle drawing of the different structural configurations of the APRV. Figure 2. Principle drawing of the different structural configurations of the APRV. First of all, the APRV must ensure independent pressure regulation by the driver or the automated driving system, namely support for the manual control mode and electronic control mode. Additionally, through the optimization of the structural configuration and the control strategy, the coupled control mode and the switch between the two control modes can be realized. As shown in Figure 2, the lower valve bodies in the four structural configurations are the same, and the electronic control circuits are similar. In these configurations, the pressure regulation is done by the control of high-speed solenoid valves, which serve as switch valves or high-speed inlet/exhaust valves, and the difference is that different configurations apply different types of solenoid valves, namely normally open (NO) ones and normally Appl. Sci. 2021, 11, 10603 6 of 18 closed (NC) ones. Correspondingly, the manual control circuit of each configuration differs. In configuration I, the manual control circuit and the electronic control circuit are in parallel. In configurations II and III, the switch between the control modes is done by the control of the switch valves, which are, respectively, a two-position three-way solenoid valve in configuration II and a three-position three-way solenoid valve in configuration III. In configuration IV, a high-speed inlet valve is applied between the inlet port and the lower valve body on the basis of configuration II. Therefore, two electronic control circuits are set up to implement the coupled control mode. The configurations are elucidated in Table 1. Table 1. Features of the different structural configurations of the APRV. High-Speed Support for Support for Support for Structural High-Speed Inlet/Exhaust Manual Control Electronic Control Coupled Control Configuration Switch Valve Valve Mode Mode Mode I Not available 1 NO and 2 NCs Yes Yes Yes two-position three-way II 1 NO and 1 NC Yes Yes No solenoid valve three-position three-way III 1 NO and 1 NC Yes Yes Yes solenoid valve two-position three-way IV 1 NO and 2 NCs Yes Yes Yes solenoid valve 4. Test Bench for the Pressure Regulation Characteristics and Control Conditions of the APRV of Different Structural Configurations in the ECPBS of Commercial Vehicles 4.1. Equivalent Models of the APRV of Different Structural Configurations and the Test Bench for the Pressure Regulation Characteristics To analyze the pressure regulation characteristics of the APRVs of different structural configurations under different control conditions, a test bench for the pressure regulation characteristics of the APRVs of different structural configurations was built. As shown in Figure 3, a pedal valve, the equivalent models, air tanks, a computer, an NI acquisition card, etc. were included in the test bench, and the specific piping and components of the test bench were consistent with that of the ECPBS (Figure 1) to ensure compliance with the requirements of the braking system. The pressure signal and the control signal Appl. Sci. 2021, 11, x FOR PEER REVIEW were acquired by the NI acquisition card and processed in real time, and thus, the test 7 of for 17 equivalent models of the APRV of different structural configurations could be carried out. Air tank Regulator (Manual control) Air tank (Electronic control) High-speed High-speed switching valve inlet valve High-speed inlet valve High-speed (normally open) exhaust valve Structural configuration I Structural configuration II Structure Relay valve construction power supply Control box Pedal Brake chamber valve NI data acquisition card Computer Structural configuration III Structural configuration IV Figure 3. Test bench for the pressure regulation characteristics of the APRV of different structural Figure 3. Test bench for the pressure regulation characteristics of the APRV of different struc- configurations. tural configurations. The test covers a pressurization–decompression test under manual control, a pres- surization–decompression test under electronic control, a switch test between the manual and electronic control modes during pressurization and a switch test between the manual and coupled control modes during pressurization. Considering the significant effect of the control strategy on the pressure response, the equivalent model is set to operate at the full open condition or full close condition to avoid such influence. The switch tests between modes are planned to simulate the conditions in which the brake force is insufficient ow- ing to the false operation of the driver or a malfunction of the pedal valve so that the automated driving system takes over and switches the control mode to the electronic con- trol mode or coupled control mode. A stopping block is installed on the pedal valve to set the opening of the valve at a fixed point to simulate a condition in which the brake force is insufficient and make sure the pressure is the same before the control mode is switched to the electronic control mode or coupled control mode. The software interface of the test bench was developed with LabVIEW. As shown in Figure 4, the interface is made up of a display section, control section, data storage section and signal selection section. Display interface Control section Data s torage section Signa l selection sectio n Figure 4. Software interface of the test bench for the pressure regulation characteristics of the APRV of different structural configurations in the ECPBS of commercial vehicles. Appl. Sci. 2021, 11, x FOR PEER REVIEW 7 of 17 Air tank Regulator (Manual control) Air tank (Electronic control) High-speed High-speed switching valve inlet valve High-speed inlet valve High-speed (normally open) exhaust valve Structural configuration I Structural configuration II Structure Relay valve construction power supply Control box Pedal Brake chamber valve NI data acquisition card Computer Structural configuration III Structural configuration IV Appl. Sci. 2021, 11, 10603 7 of 18 Figure 3. Test bench for the pressure regulation characteristics of the APRV of different structural configurations. TThe test cove he test covers ars pra pre essurs iz surization–decom ation–decompressipre on tssion est un test der m under anual man contru oal control, l, a pressuriza pres- ation– decompr surization ession –decompression test under electr test under electroni onic control, a c switch control test , a swi between tch test between the the manual and ma elec- nual tronic control modes during pressurization and a switch test between the manual and and electronic control modes during pressurization and a switch test between the manual coupled control modes during pressurization. Considering the significant effect of the and coupled control modes during pressurization. Considering the significant effect of the control strategy on the pressure response, the equivalent model is set to operate at the full control strategy on the pressure response, the equivalent model is set to operate at the full open condition or full close condition to avoid such influence. The switch tests between open condition or full close condition to avoid such influence. The switch tests between modes are planned to simulate the conditions in which the brake force is insufficient owing modes are planned to simulate the conditions in which the brake force is insufficient ow- to the false operation of the driver or a malfunction of the pedal valve so that the automated ing to the false operation of the driver or a malfunction of the pedal valve so that the driving system takes over and switches the control mode to the electronic control mode or automated driving system takes over and switches the control mode to the electronic con- coupled control mode. A stopping block is installed on the pedal valve to set the opening trol mode or coupled control mode. A stopping block is installed on the pedal valve to set of the valve at a fixed point to simulate a condition in which the brake force is insufficient the opening of the valve at a fixed point to simulate a condition in which the brake force and make sure the pressure is the same before the control mode is switched to the electronic is insufficient and make sure the pressure is the same before the control mode is switched control mode or coupled control mode. to the electronic control mode or coupled control mode. The software interface of the test bench was developed with LabVIEW. As shown in The software interface of the test bench was developed with LabVIEW. As shown in Figure 4, the interface is made up of a display section, control section, data storage section Figure 4, the interface is made up of a display section, control section, data storage section and signal selection section. and signal selection section. Display interface Control section Data s torage section Signa l selection sectio n Figure 4. Software interface of the test bench for the pressure regulation characteristics of the APRV Figure 4. Software interface of the test bench for the pressure regulation characteristics of the APRV of different structural configurations in the ECPBS of commercial vehicles. of different structural configurations in the ECPBS of commercial vehicles. 4.2. Control Conditions of the Test for the Pressure Regulation Characteristics of the APRV of Different Structural Configurations in the ECPBS of Commercial Vehicles The test is done by replacing the equivalent models of the APRV of different structural configurations. In the test bench, the air source pressure is set to 700 kPa, the power source voltage is 220 V, the nominal voltage of the solenoid valve is 24 V and the voltage of the control signal is 5 V. 4.2.1. Control Conditions of the Test for the Pressure Regulation Characteristics of the APRV of Structural Configuration I The equivalent model of the APRV of the structural configuration is connected to the test bench, and the pressure is controlled by the pedal valve and the switch of the high-speed solenoid valves. The control condition of each solenoid valve is shown in Table 2. Appl. Sci. 2021, 11, 10603 8 of 18 Table 2. Control conditions for the test of the pressure regulation characteristics of the APRV in structural configuration I. Structural Configuration Control Condition Pedal Valve High-Speed Inlet Valve 1 High-Speed Exhaust Valve High-Speed Inlet Valve 2 Pressurization decompression Fully open ! release Deactivated Deactivated Deactivated test under manual control Pressurization decompression Release Activated ! deactivated Deactivated ! activated Activated test under electronic control Switch test between manual Configuration I and electronic control modes Driven to the fixed point Deactivated ! activated Deactivated Deactivated ! activated during pressurization Switch test between manual and coupled control modes Driven to the fixed point Deactivated ! activated Deactivated Deactivated during pressurization Appl. Sci. 2021, 11, 10603 9 of 18 In the pressurization–decompression test under manual control, all the high-speed solenoid valves are deactivated. The pressurization and decompression processes are controlled by the pedal valve. When the outlet pressure is near 700 kPa, the pedal is released, and the test for the manual control is over. In the pressurization–decompression test under electronic control, the high-speed inlet valve 1 and the high-speed inlet valve 2 are activated simultaneously to perform the pressurization test. When the pressure is near 700 kPa, the high-speed inlet valve 1 is deactivated, and the high-speed exhaust valve is activated; thus, the test for the electronic control is over. In the switch test between manual and electronic control modes during pressurization, the pedal of the pedal valve is driven to the fixed point. When the outlet pressure settles, the high-speed inlet valve 1 and the high-speed valve 2 are activated simultaneously, and the switch test between manual and electronic control modes during pressurization is over. In the switch test between the manual and coupled control modes during pressuriza- tion, the pedal of the pedal valve is driven to the fixed point. When the outlet pressure settles, the high-speed inlet valve 1 is activated, and the switch test between manual and coupled control modes during pressurization is over. 4.2.2. Control Condition of the Test for the Pressure Regulation Characteristics of the APRV of Structural Configurations II, III and IV Since the working principles of the manual control mode and electronic control mode of the APRV of structural configurations II, III and IV are the same, the tests or manual control mode, electronic control mode and the switch between the two modes are performed in the same test on the equivalent model of structural model IV. Since the coupled control mode is not supported in structural configuration II but in structural configurations III and IV, the switch test between the manual control mode and coupled control mode is not performed in this circuit. The control condition of each solenoid valve is shown in Table 3. In the pressurization–decompression test under manual control, all the high-speed solenoid valves are deactivated. The pressurization and decompression processes are controlled by the pedal valve. When the outlet pressure is near 700 kPa, the pedal is released, and the test for the manual control is over. In the pressurization–decompression test under electronic control, the high-speed switch valve is activated, and the high-speed inlet valve is connected to the air tank (electronic control). When the outlet pressure is near 700 kPa, the high-speed inlet valve and the high-speed exhaust valve are activated simultaneously, and the test for the electronic control is over. In the switch test between the manual and electronic control modes during pressur- ization, the pedal of the pedal valve is driven to the fixed point. When the outlet pressure settles, the high-speed switch valve is activated, and the switch test between the manual and electronic control modes during pressurization is over. In the switch test between the manual and coupled control modes during pressuriza- tion, the pedal of the pedal valve is driven to the fixed point. When the outlet pressure settles, the high-speed inlet valve 2 is activated, and the switch test between the manual and coupled control modes during pressurization is over. 4.2.3. Control Conditions of the Test for the Pressure Regulation Characteristics of the APRV of Structural Configuration III Since the working principles of the manual control mode and electronic control mode of the APRV of structural configurations II, III and IV are the same, the tests or manual control mode, electronic control mode and the switch between the two modes are not performed in the test for configuration III. The key test program for configuration III is the switch test between the manual and coupled control modes. The control conditions for each solenoid valve are shown in Table 4. Appl. Sci. 2021, 11, 10603 10 of 18 Table 3. Control conditions for the test of the pressure regulation characteristics of the APRV in structural configurations II, III and IV. High-Speed Inlet Valve Structural Configuration Control Condition Pedal Valve High-Speed Switch Valve High-Speed Exhaust Valve High-Speed Inlet Valve (Normally Open) Pressurization decompression Fully open ! release Deactivated Deactivated Deactivated Deactivated test under manual control Pressurization decompression Structural configuration II, Release Activated Deactivated ! activated Deactivated ! activated Deactivated test under electronic control III, IV Switch test between manual and electronic control modes Driven to the fixed point Deactivated ! activated Deactivated Deactivated Deactivated during pressurization Switch test between manual Structural configuration IV and coupled control modes Driven to the fixed point Deactivated Deactivated Deactivated Deactivated ! activated during pressurization Table 4. Control conditions for the test of the pressure regulation characteristics of the APRV in structural configuration III. High-Speed Inlet Valve 1 Structural Configuration Control Condition Pedal Valve High-Speed Switch Valve High-Speed Exhaust Valve High-Speed Inlet Valve 2 (Normally Open) Switch test between manual control mode and Structural configuration III Driven to the fixed point Deactivated Deactivated Deactivated Deactivated ! activated electronic control mode during pressurization Appl. Sci. 2021, 11, x FOR PEER REVIEW 10 of 17 Table 4. Control conditions for the test of the pressure regulation characteristics of the APRV in structural configuration III. High-Speed Structural Pedal High-Speed Inlet Valve 1 High-Speed High-Speed Control Condition Configuration Valve Switch Valve (Normally Exhaust Valve Inlet Valve 2 Open) Switch test between Driven Structural manual control mode and to the Deactivated → configuration Deactivated Deactivated Deactivated electronic control mode fixed activated III during pressurization point Appl. Sci. 2021, 11, 10603 11 of 18 In the switch test between the manual and coupled control modes, the pedal of the pedal valve is driven to the fixed point. When the outlet pressure settles, the high-speed inlet valve 2 is activated, and the switch test between manual and coupled control modes In the switch test between the manual and coupled control modes, the pedal of the is completed. pedal valve is driven to the fixed point. When the outlet pressure settles, the high-speed inlet valve 2 is activated, and the switch test between manual and coupled control modes 5. is completed. Simulation Model for the Pressure Regulation Characteristics of the APRV of the Different Structural Configurations 5. Simulation Model for the Pressure Regulation Characteristics of the APRV of the Based on the structural configurations of the APRV, the simulation model is estab- Different Structural Configurations lished, and the pressure regulation characteristics are studied. To study all the structural Based on the structural configurations of the APRV, the simulation model is estab- configurations shown in Figure 2 in one simulation model, the AMESim simulation mod- lished, and the pressure regulation characteristics are studied. To study all the structural els of high-speed solenoid valves (Components SC_1 and SC_3,) and pedal valve (Com- configurations shown in Figure 2 in one simulation model, the AMESim simulation models ponent SC_2) are established. The simulations for the tests of the manual control mode, of high-speed solenoid valves (Components SC_1 and SC_3,) and pedal valve (Component electronic control mode, coupled control mode and the switch between the control modes SC_2) are established. The simulations for the tests of the manual control mode, electronic are done by switching the control signals of components SC_1, SC_2 and SC_3. The sim- control mode, coupled control mode and the switch between the control modes are done by ulation switching mo the decontr l for th ol e signals pressure of components regulation char SC_1, acteri SC_2 stics ando SC_3. f the A The PRV simulation is shown model in Figure for the pressure regulation characteristics of the APRV is shown in Figure 5. Electronic control Manual control Component SC_1: Simulation model of high-speed solenoid valve Component SC_2: Simulation model of pedal valve Component SC_3:Simulation model of high-speed switch valve Figure 5. Simulation model for the pressure regulation characteristics of the APRV of the different Figure 5. Simulation model for the pressure regulation characteristics of the APRV of the different st str ru uctural ctural configurations configurations in in the the ECPBS ECPBS of of commer comm cial ercivehicles. al vehicles. The main structural parameters of the simulation model for the pressure regulation The main structural parameters of the simulation model for the pressure regulation characteristics of the APRV of the different structural configurations in the ECPBS of characteristics of the APRV of the different structural configurations in the ECPBS of com- commercial vehicles are shown in Table 5. mercial vehicles are shown in Table 5. Table 5. Main structural parameters of the simulation model for the pressure regulation characteristics of the APRV of different structural configurations in the ECPBS of commercial vehicles. Seal-Ring Volume of Parameter Air Source Pressure Hole Diameter Maximum Travel Diameter Control Cavity Values 0.7 MPa 7 mm 6 mm 0.04 L 0.24 mm Parameter Number of coil turns Winding resistance Spring rate Preload force Mass of the valve core Values 1000 50 Ohm 2000 N/m 10 N 5 g To verify the correctness of the simulation model of the APRV, a series of tests are done on the test bench for the pressure regulation characteristics of the APRV of different structural configurations in the ECPBS of commercial vehicles, and the curves of the Appl. Sci. 2021, 11, x FOR PEER REVIEW 11 of 17 Table 5. Main structural parameters of the simulation model for the pressure regulation character- istics of the APRV of different structural configurations in the ECPBS of commercial vehicles. Air Source Seal-Ring Hole Volume of Maximum Parameter Pressure Diameter Diameter Control Cavity Travel Values 0.7 MPa 7 mm 6 mm 0.04 L 0.24 mm Number of Winding Mass of the Parameter Spring rate Preload force coil turns resistance valve core Values 1000 50 Ohm 2000 N/m 10 N 5 g Appl. Sci. 2021, 11, 10603 12 of 18 To verify the correctness of the simulation model of the APRV, a series of tests are done on the test bench for the pressure regulation characteristics of the APRV of different structural configurations in the ECPBS of commercial vehicles, and the curves of the pres- pressure regulation characteristics of the pressure regulator under manual control mode sure regulation characteristics of the pressure regulator under manual control mode and and electronic control mode are shown in Figure 6. electronic control mode are shown in Figure 6. (a) (b) Figure 6. Verification of the simulation model for the pressure regulation characteristics of the APRV of the different Figure 6. Verification of the simulation model for the pressure regulation characteristics of the APRV of the different structural configurations in the ECPBS of commercial vehicles: (a) manual control and (b) electronic control. structural configurations in the ECPBS of commercial vehicles: (a) manual control and (b) electronic control. The experiments results and the simulation results show the same trends, similar re- The experiments results and the simulation results show the same trends, similar sponse times and consistent key values; thus, the simulation model fits well with the test response times and consistent key values; thus, the simulation model fits well with the test Appl. Sci. 2021, 11, x FOR PEER REVIEW 12 of 17 bench. The simulation is done by changing the control signals of components SC_1, SC_2 bench. The simulation is done by changing the control signals of components SC_1, SC_2 and SC_3, and the parameters of the simulations for each control condition are shown in and SC_3, and the parameters of the simulations for each control condition are shown in Table 6. Table 6. In Table 6, the signal value 0 is the deactivation signal, and signal value 1 is the In Table 6, the signal value 0 is the deactivation signal, and signal value 1 is the acti- Table 6. Parameters of the simulation models for the pressure regulation characteristics of the APRV of the different struc- activation signal. It is difficult to simulate the switch from the manual control mode to vation signal. It is difficult to simulate the switch from the manual control mode to another tural configurations in the ECPBS of commercial vehicles. another mode. To simulate the insufficient pressure during manual-controlled braking, the mode. To simulate the insufficient pressure during manual-controlled braking, the maxi- maximum outlet pressure in the manual control mode is set to 0.3 MPa. In the simulation Pressure of Air Pressure of Air mum outlet pressure in the manual control mode is set to 0.3 MPa. In the simulation for Parameter Signal Source Signal Source Signal Source Structural for the switch test between the control modes, the control mode is switched from the Tank (Electronic Tank (Manual the switch test between the control modes, the control mode is switched from the manual Control Condition (SC_1) (SC_2) (SC_3) Configuration manual control mode to the electronic control mode or coupled control mode in 0.5 s. The Control) Control) control mode to the electronic control mode or coupled control mode in 0.5 s. The simula- simulation results are illustrated in Figure 7. Electronic control 1 0 0 0.7 MPa 0 tion results are illustrated in Figure 7. All structural Manual control (0.3 MPa) 0 1 1 0 0.3 MPa configuration Manual control (0.7 MPa) 0 1 1 0 0.7 MPa Coupled control 1 1 1 0.7 MPa 0.7 MPa 0–0.5 s: 0 0–0.5 s: 1 0–0.5 s: 1 Switch between manual and 0.7 MPa 0.3 MPa Structural electronic control modes 0.5–1 s: 1 0.5–1 s: 0 0.5–1 s: 0 configuration I,III,IV 0–0.5 s: 0 0–0.5 s: 0 0–0.5 s: 0 Switch between manual and 0.7 MPa 0.3 MPa coupled control modes 0.5–1 s: 1 0.5–1 s: 1 0.5–1 s: 1 Figure 7. Figure 7.Simulation curves of the pressure regulation Simulation curves of the pressure regulationcharacterist characteristics ics of th of the e APRV of the APRV of thedifferent different structural configurations in the ECPBS of commercial vehicles. structural configurations in the ECPBS of commercial vehicles. In the simulation results, when the control mode switches from the manual control mode to the coupled control mode, the pressure response time increases, and the outlet pressure cannot reach the target level. One possible explanation is that the outlet of the pedal valve is connected to the air tank (electronic control), and the outlet pressure of the pedal valve is higher than the inlet pressure; thus, the air leaks. Compared with switching to the coupled control mode, switching to the electronic control mode avoids such phe- nomenon, and the pressure response is better. To verify the correctness of the simulation results, the equivalent models for the APRV of the different structural configurations are built to perform tests of the pressure regulation characteristic under different control modes and verify the simulation results. 6. Test-Based Comparative Analysis on the Pressure Regulation Characteristics of the APRV of the Different Structural Configurations in the ECPBS of Commercial Vehi- cles According to the performance requirements of the commercial vehicle braking sys- tem, the time when the pressure reaches 75% of the target pressure is taken as the index to evaluate the pressure regulation characteristics of the APRV of the different structural configurations under different control conditions. 6.1. Pressurization–Decompression Test under Manual Control The test results of the pressurization–decompression test of the APRV of the different structural configurations under manual control are illustrated in Figure 8. Appl. Sci. 2021, 11, 10603 13 of 18 Table 6. Parameters of the simulation models for the pressure regulation characteristics of the APRV of the different structural configurations in the ECPBS of commercial vehicles. Parameter Signal Source Signal Source Signal Source Pressure of Air Tank Pressure of Air Tank Structural (SC_1) (SC_2) (SC_3) (Electronic Control) (Manual Control) Configuration Control Condition Electronic control 1 0 0 0.7 MPa 0 All structural Manual control (0.3 MPa) 0 1 1 0 0.3 MPa configuration Manual control (0.7 MPa) 0 1 1 0 0.7 MPa Coupled control 1 1 1 0.7 MPa 0.7 MPa 0–0.5 s: 0 0–0.5 s: 1 0–0.5 s: 1 Structural Switch between manual and electronic control modes 0.7 MPa 0.3 MPa 0.5–1 s: 1 0.5–1 s: 0 0.5–1 s: 0 configuration 0–0.5 s: 0 0–0.5 s: 0 0–0.5 s: 0 I, III, IV Switch between manual and coupled control modes 0.7 MPa 0.3 MPa 0.5–1 s: 1 0.5–1 s: 1 0.5–1 s: 1 Appl. Sci. 2021, 11, 10603 14 of 18 In the simulation results, when the control mode switches from the manual control mode to the coupled control mode, the pressure response time increases, and the outlet pressure cannot reach the target level. One possible explanation is that the outlet of the pedal valve is connected to the air tank (electronic control), and the outlet pressure of the pedal valve is higher than the inlet pressure; thus, the air leaks. Compared with switching to the coupled control mode, switching to the electronic control mode avoids such phenomenon, and the pressure response is better. To verify the correctness of the simulation results, the equivalent models for the APRV of the different structural configurations are built to perform tests of the pressure regulation characteristic under different control modes and verify the simulation results. 6. Test-Based Comparative Analysis on the Pressure Regulation Characteristics of the APRV of the Different Structural Configurations in the ECPBS of Commercial Vehicles According to the performance requirements of the commercial vehicle braking system, the time when the pressure reaches 75% of the target pressure is taken as the index to evaluate the pressure regulation characteristics of the APRV of the different structural configurations under different control conditions. 6.1. Pressurization–Decompression Test under Manual Control Appl. Sci. 2021, 11, x FOR PEER REVIEW 13 of 17 The test results of the pressurization–decompression test of the APRV of the different structural configurations under manual control are illustrated in Figure 8. (a) (b) Figure 8. Test results of the pressurization–decompression test under manual control: (a) pressurization test and (b) de- Figure 8. Test results of the pressurization–decompression test under manual control: (a) pressurization test and (b) decom- compression test. pression test. Though there is one more orifice in structural configurations II, III and IV than struc- Though there is one more orifice in structural configurations II, III and IV than struc- tural configuration I, all the configurations show no significant difference in the manual- tural configuration I, all the configurations show no significant difference in the manual- controlled pressurization response, because the volume ratio between the air tank and the controlled pressurization response, because the volume ratio between the air tank and the control cavity is rather big. The response time for structural configurations II, III and IV control cavity is rather big. The response time for structural configurations II, III and IV to to reach reach 75% 75% ofof the thtar e tar get get pr p essur ressure e isis 0.15 0.15 s,s, and and response response time time for for str struct uctural uralconfiguration configuration I Ito tor rea each chthat that is 0 is 0.16 .16 s. s. In In th the e manual-contr manual-contro olled lled decompr decompress ession ion test, test the , th contr e cont olrol cavity cavi of ty the of APR the V AP exhausts RV ex- haust the air s th toe the airouter to thenvir e outer onment, environmen and the t, pr and essur the e in pres the sur cavity e in th changes e cavity grchange eatly. Limited s greatlby y. Limited the number by th of e orifices, number the of orifices decompr , th ession e decom response pression time respon of str suctural e time of configurations structural con II, fig III - and IV is 0.54 s, and the decompression response time of structural configuration I is 0.38 s. urations II, III and IV is 0.54 s, and the decompression response time of structural config- Though the decompression speed of structural configurations II, III and IV is slower, it still uration I is 0.38 s. Though the decompression speed of structural configurations II, III and meets the requirements of the commercial vehicle braking system. IV is slower, it still meets the requirements of the commercial vehicle braking system. 6.2. Pressurization–Decompression Test under Electronic Control 6.2. Pressurization–Decompression Test under Electronic Control The test results of the pressurization–decompression test of the APRV of the different The test results of the pressurization–decompression test of the APRV of the different structural configurations under electronic control are illustrated in Figure 9. structural configurations under electronic control are illustrated in Figure 9. (a) (b) Figure 9. Test results of the pressurization–decompression test under electronic control: (a) pressurization test and (b) decompression test. The response time for structural configurations II, III and IV to reach 75% of the target pressure of 0.7 MPa is 0.13 s, and the response time for structural configuration I to reach that is 0.12 s. Since the working principle of electronic-controlled decompression in all the structural configurations is the same, the decompression response curves fit quite well. The decompression response time of structural configurations II, III and IV is 0.36 s, and Appl. Sci. 2021, 11, x FOR PEER REVIEW 13 of 17 (a) (b) Figure 8. Test results of the pressurization–decompression test under manual control: (a) pressurization test and (b) de- compression test. Though there is one more orifice in structural configurations II, III and IV than struc- tural configuration I, all the configurations show no significant difference in the manual- controlled pressurization response, because the volume ratio between the air tank and the control cavity is rather big. The response time for structural configurations II, III and IV to reach 75% of the target pressure is 0.15 s, and response time for structural configuration I to reach that is 0.16 s. In the manual-controlled decompression test, the control cavity of the APRV ex- hausts the air to the outer environment, and the pressure in the cavity changes greatly. Limited by the number of orifices, the decompression response time of structural config- urations II, III and IV is 0.54 s, and the decompression response time of structural config- uration I is 0.38 s. Though the decompression speed of structural configurations II, III and IV is slower, it still meets the requirements of the commercial vehicle braking system. 6.2. Pressurization–Decompression Test under Electronic Control Appl. Sci. 2021, 11, 10603 15 of 18 The test results of the pressurization–decompression test of the APRV of the different structural configurations under electronic control are illustrated in Figure 9. (a) (b) Figure 9. Test results of the pressurization–decompression test under electronic control: (a) pressurization test and (b) Figure 9. Test results of the pressurization–decompression test under electronic control: (a) pressurization test and (b) decompression test. decompression test. The response time for structural configurations II, III and IV to reach 75% of the target The response time for structural configurations II, III and IV to reach 75% of the target pressure of 0.7 MPa is 0.13 s, and the response time for structural configuration I to reach pressure of 0.7 MPa is 0.13 s, and the response time for structural configuration I to reach Appl. Sci. 2021, 11, x FOR PEER REVIEW 14 of 17 that is 0.12 s. Since the working principle of electronic-controlled decompression in all the that is 0.12 s. Since the working principle of electronic-controlled decompression in all the structural configurations is the same, the decompression response curves fit quite well. structural configurations is the same, the decompression response curves fit quite well. The decompression response time of structural configurations II, III and IV is 0.36 s, and The decompression response time of structural configurations II, III and IV is 0.36 s, and the decompression response time of structural configuration I is 0.39 s. Therefore, in the the decompression response time of structural configuration I is 0.39 s. Therefore, in the pressurization–decompression test under electronic control, all the structural configura- pressurization–decompression test under electronic control, all the structural configurations tions show no significant differences. show no significant differences. 6.3. Switch Test between Manual and Electronic Control Modes during Pressurization 6.3. Switch Test between Manual and Electronic Control Modes during Pressurization Due to the limitation of the stopping block, the outlet pressure settles at 0.26 MPa in Due to the limitation of the stopping block, the outlet pressure settles at 0.26 MPa in 6.42 s, and the control mode is switched to the electronic control mode, and the pressure 6.42 s, and the control mode is switched to the electronic control mode, and the pressure increases to 75% of the target pressure of 0.7 MPa in 0.08 s. The test results of the switch test increases to 75% of the target pressure of 0.7 MPa in 0.08 s. The test results of the switch between the manual and electronic control modes during the pressurization of structural test between the manual and electronic control modes during the pressurization of struc- configuration I are shown in Figure 10a. tural configuration I are shown in Figure 10a. (a) (b) Figure 10. Results of the switch test between the manual control mode and electronic control mode during pressurization: Figure 10. Results of the switch test between the manual control mode and electronic control mode during pressurization: (a) structural configuration I and (b) structural configurations II, III and IV. (a) structural configuration I and (b) structural configurations II, III and IV. Due to the limitations of the stopping block, the outlet pressure settles at 0.26 MPa in Due to the limitations of the stopping block, the outlet pressure settles at 0.26 MPa in 5.32 s, and the control mode is switched to the electronic control mode, and the pressure 5.32 s, and the control mode is switched to the electronic control mode, and the pressure increases to 75% of the target pressure of 0.7 MPa in 0.11 s. The test results of the switch increases to 75% of the target pressure of 0.7 MPa in 0.11 s. The test results of the switch test between the manual and coupled control modes during the pressurization of struc- test between the manual and coupled control modes during the pressurization of structural tural configurations II, III and IV are shown in Figure 10b. configurations II, III and IV are shown in Figure 10b. 6.4. Switch Test between Manual and Coupled Control Modes during Pressurization In structural configurations I, III and IV, when the control mode is switched from the manual control mode to the coupled control mode, the control cavity of the APRV, air tank (manual control), air tank (electronic control) and the pedal valve is connected alto- gether. At this moment, the outlet pressure of the pedal valve is higher than the inlet pres- sure, so the air from the air tank (electronic control) leaks through the pedal valve contin- uously, and the pressure of the brake chamber can only reach 0.55 MPa instead of the target pressure of 0.7 MPa. The test results of the switch test between the manual and coupled control modes during pressurization are shown in Figure 11. Appl. Sci. 2021, 11, 10603 16 of 18 6.4. Switch Test between Manual and Coupled Control Modes during Pressurization In structural configurations I, III and IV, when the control mode is switched from the manual control mode to the coupled control mode, the control cavity of the APRV, air tank (manual control), air tank (electronic control) and the pedal valve is connected altogether. At this moment, the outlet pressure of the pedal valve is higher than the inlet pressure, so the air from the air tank (electronic control) leaks through the pedal valve continuously, and the pressure of the brake chamber can only reach 0.55 MPa instead of the target pressure of Appl. Sci. 2021, 11, x FOR PEER REVIEW 15 of 17 0.7 MPa. The test results of the switch test between the manual and coupled control modes during pressurization are shown in Figure 11. (a) (b) (c) Figure 11. Results of the switch test between the manual and coupled control modes during pressurization: (a) structural Figure 11. Results of the switch test between the manual and coupled control modes during pressurization: (a) structural configuration I, (b) structural configuration III and (c) structural configuration IV. configuration I, (b) structural configuration III and (c) structural configuration IV. 7. Discussion 7. Discussion To investigate the situation in which the driver fails to apply sufficient braking force, To investigate the situation in which the driver fails to apply sufficient braking force, simulation and experiment research are done to study the pressure regulation character- simulation and experiment research are done to study the pressure regulation character- istics of the APRV. Combining the simulation and the experiment, the suitable structural istics of the APRV. Combining the simulation and the experiment, the suitable structural configuration is determined, and the theoretical underpinning to develop active safety configuration is determined, and the theoretical underpinning to develop active safety and and driving automation is provided. driving automation is provided. Through Through a co a comparative mparative an analysis, alysis, tthe he co conclusions nclusions ar are e fol follows: lows: ((1) 1) In the manual In the manual-contr -contrololled led or the el or the ectron electronic-contr ic-controlled pressuriza olled pressurization tion processes, processes, all structur all structural al conf configurations igurations showed no sign showed no significant ificant differe difn fer ces. Howeve ences. However r, in the man , in the u manu al-con- al- controlled decompression test, the response time of structural configurations II, III and IV trolled decompression test, the response time of structural configurations II, III and IV was was 42 42.1% .1% longer longer t than han t that hatof of st structural ructural configuration configuratioI. n I. Such Such a dif a di ferffer ence ence is no is noticeable, ticeab but le, both the results meet the requirements of the braking system. but both the results meet the requirements of the braking system. (2) When the pressure of the electronic control circuit is higher than that of the manual (2) When the pressure of the electronic control circuit is higher than that of the man- control circuit, leaks happen, and the pressure cannot reach the target value; thus, the ual control circuit, leaks happen, and the pressure cannot reach the target value; thus, the driving safety of the vehicle is seriously affected. Since the coupling control mode pro- posed in this paper has the possibility of air leakage during braking, the APRV in the ECPBS described in this paper cannot use this control mode. (3) Structural configurations I, III and IV have varying degrees of the possibility of air leakage during braking. Since air leakage during braking in commercial vehicles causes extremely serious accidents, it will lead to an insufficient braking force and be un- able to ensure the safety of the vehicle. Therefore, structural configurations II, III and IV are not recommended for use in the ECPBS described in this paper. In summary, the coupled control mode is not supported in structural configuration II, but the manual control mode and electronic control mode and the switch between these Appl. Sci. 2021, 11, 10603 17 of 18 driving safety of the vehicle is seriously affected. Since the coupling control mode proposed in this paper has the possibility of air leakage during braking, the APRV in the ECPBS described in this paper cannot use this control mode. (3) Structural configurations I, III and IV have varying degrees of the possibility of air leakage during braking. Since air leakage during braking in commercial vehicles causes extremely serious accidents, it will lead to an insufficient braking force and be unable to ensure the safety of the vehicle. Therefore, structural configurations II, III and IV are not recommended for use in the ECPBS described in this paper. In summary, the coupled control mode is not supported in structural configuration II, but the manual control mode and electronic control mode and the switch between these two modes are supported, so the regulation of the braking pressure can be done successfully. Specifically, when the driver cannot apply sufficient braking force, the driving safety of the vehicle can still be guaranteed; thus, the system is consistent with the development of driving automation. 8. Conclusions The pressure regulating requirements and the control modes of the APRV in the ECPBS of commercial vehicles were proposed, and the structural configurations of the APRV were designed. The simulation model of the control modes of the APRV was es- tablished in AMESim; then, the pressure regulation characteristics under different control conditions were analyzed. Specifically, leaks happen when the driver cannot apply suf- ficient braking force and the control mode is switched from the manual control mode to the coupled control mode, so structural configurations II, III and IV are not recommended for use in the ECPBS described in this paper. The simulation was verified to be correct through experiments on the test bench for the pressure regulation characteristics of the APRVs of different structural configurations. Finally, the best structural configuration was determined, and the theoretical underpinning to improve the driving safety and driving automation was provided. The driving conditions and driving tasks that were not covered will be studied, and more factors concerning the driver and the environment will be considered in future works to improve the active safety and driving automation. Moreover, new sample products of the APRV will be made and tested. The hardware in the loop test and field test will be tested to gather more experiment data and provide better data and theoretical support. Author Contributions: Conceptualization, G.L. and H.B.; methodology, H.B. and G.L.; software, H.B., X.W. and Z.W.; validation, G.L. and H.B.; investigation, H.B. and Z.W.; resources, G.L.; data curation, H.B., Z.W. and X.W.; writing—original draft preparation, H.B.; writing—review and editing, H.B., G.L. and Z.W.; visualization, H.B. and G.L.; supervision, G.L.; project administration, G.L. and funding acquisition, G.L. All authors have read and agreed to the published version of the manuscript. Funding: This research was funded by the China Postdoctoral Science Foundation (2018M642937) and Project 20202h0184, which cooperated with the SMC Corporation. Institutional Review Board Statement: Not applicable. Informed Consent Statement: Not applicable. Data Availability Statement: The study did not report any data. Acknowledgments: We would like to sincerely thank all our previous and current teachers and classmates who laid the basis for this research, namely Gangyan Li, Jian Hu, Jun Xu, Zaiyu Wang and Xiaoxu Wei. Conflicts of Interest: The authors declare no conflict of interest. Appl. Sci. 2021, 11, 10603 18 of 18 References 1. Ariansyah, D.; Caruso, G.; Ruscio, D.; Bordegoni, M. Analysis of autonomic indexes on drivers’ workload to assess the effect of visual ADAS on user experience and driving performance in different driving conditions. J. Comput. Inf. Sci. Eng. 2018, 18, 031007. [CrossRef] 2. Chen, H.; Zhao, F.K.; Huang, K.; Tian, Y.T. Driver Behavior Analysis for Advanced Driver Assistance System. In Proceedings of the 2018 IEEE 7th Data Driven Control and Learning Systems Conference, Enshi, China, 25–27 May 2018. 3. Elizabeth, R.V. Classification and overview of advanced driver assistance systems according to the driving process. 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