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Journal of Science & Technology 127 (2018) 057-062 A Hydraulic Regenerative Braking System: Some Modeling and Experimental Results Luyen Van Hieu1, 2*, Ngo Sy Loc1, Tran Khanh Duong1 Hanoi University of Science and Technology – No. 1, Dai Co Viet Str., Hai Ba Trung, Ha Noi, Viet Nam 2 Hung Yen University of Technology and Education, Dan Tien, Khoai Chau, Hung Yen Received: March 27, 2018; Accepted: June 25, 2018 1 Abstract This paper presents a principle diagram of the proposed kinetic recovery system using the hydraulic accumulator. The proposed system installed on a 2.5 tone garbage specialized dump truck made in Việt Nam. The system is connected to the power take-off unit of the transmission system on the vehicle, could brake to recover kinetic energy of the vehicle. The dynamic equations of a braking process using hydraulic accumulator have been obtained and simulated using Matlab - Simulink program. The system has been tested, the experimental results are well in agreement. The influence of the accumulator initial pressure values on kinetic energy recovering process and efficiency of the system have been looked into and estimated. The system could be used to study characteristics of the hydraulic regenerative braking system extensively. Keywords: HRBS; HRB with PTO; Braking to recover kinetic energy. 1. Introduction* per the flowchart is shown in Fig. 2. The program runs and all the concerned output parameter values are recorded automatically. Conventionally, during a vehicle braking process, the kinetic energy turns to heat at the braking shoes [1]. In our study, we aim to turn the same to hydrostatic energy and store it in a hydraulic accumulator for other possible uses such as crane lifting, winching, vehicle initial accelerating.... A system for the purpose has been proposed, fabricated and installed in a 2.5 tone specialized dump truck in Việt Nam. A series of experiments have been successfully carried out. Some of the obtained results will be presented hereunder. Layout of braking pedal Pacc 4 5 6 3 8 7 9 10 V1 Kinetic energy recovery braking 2 Normal braking Power take -off 1 2. The system description CLPTO Manual transmisstion Engine The principle diagram of the proposed hydraulic regenerative braking system (HRBS) is shown in Fig. 1. The main components are: 1- oil tank; 2 - pump; 3control valve; 4- return line; 5- check valve; 6pressure transducer; 7 – pressure switch; 8- hydraulic accumulator; 9- oil reusable line; 10 – pressure indicator; 11- power take-off unit; 12- proximity sensor (electromagnetic); Br – signal from braking pedal; Pacc – signal from pressure transducer; V1 – valve control signal; CL-clutch-off control signal; CLPTO-PTO-on control signal. 11 CL V1 Control Unit Arduino uno CLPTO Pacc Br 12 CL Fig. 1 The principle diagram of the proposed HRBS As it can be seen from Fig.s 1 and 2, working of the system is very simple, the initial stroke of the braking pedal is accompanying with energy recovery process. In case of emergency, the remained part of the braking pedal stroke will activate the normal brake to stop the vehicle. The operating of the regenerative braking system includes idle mode and regenerative braking mode [2]. The entire braking process of the proposed system is controlled by an Arduino Uno card [3] operating as * Corresponding author: Tel: (+84) 1699838382 Email: vhieugt@gmail.com 57 Journal of Science & Technology 127 (2018) 057-062 av – vehicle acceleration [m/s2] Begin Pr1, Pr2 - rolling resistance of front and rear wheels [4] false Is there CL? true Connecting PTO Pr =Pr1+Pr2 = f.G (4) Pr - total rolling resistance of wheels [N] false Is there CLPTO? f- rolling resistance coefficient. true true Is there CL ? Pacc < Pmax? Pη – Friction Force of Transmission System [N]. false Pj - vehicle’s inertia force [4] which is defined as: true false Send control signal to V1 Pj = δ Reuse Mode End G dv g dt (5) where: Fig. 2 The flow chart showing working of the proposed G – weight of the vehicle [N]; HRBS t – time [s]; 3. The system modeling g - the acceleration of gravity, Limiting the system of the vehicle operating on the delta. Considering a case shown in Fig. 3: the test vehicle runs on a straight and horizontal way. When the vehicle is decelerated, the vehicle is subjected by a system of forces as shown: g = 9,81[m/s2];  - is a proportionality constant taking care of all rotating masses in the moving vehicle [4]. To simplify the calculation, an assumption has been made namely only vehicle wheels are to be taken into account, neglecting the contribution of the others rotating parts, hence: v Pj Pw e Y G h δ = 1+ x Mbxp bx rbx Pr1 A Z1 Pr2 B Z2 b a O bxi i m.rbx2 (6) For a vehicle wheel, it’s angular and linear velocities depend on each other by: Ppp L Fig. 3. Forces acting on the test vehicle ωbx = Balancing equation of forces acting on the test vehicle when brakes in a horizontal way have the following form: Pj - Pw - Pr1 - Pr2 - Pη - Ppp=0 J v rbx (7) Ppp - The braking force acting on the rear wheels by the system (1) Ppp = where: Pw is air resistance [4]: M bxp (8) rbx where: Pw = KFv2 (2) K- Coefficient of air resistance; Mbxp - Braking torque at the wheels by the system [N.m] F - The vehicle cross-sectional area [m2]; rbx – The working radius of the wheels[m] v - The vehicle braking speed [5] which is defined as: a relation between the braking torque at wheels and the pump driving torque i.e., at the power take-off (PTO)’s output shaft, is defined as: t v = v 0 -  a v dt (3) M bxp = 0 where: vo – initial braking speed [m/s] and 58 M p i trp η tr (9) Journal of Science & Technology 127 (2018) 057-062 plp1 - pressure losses in pipe [7] where: Mp - torque at the shaft of pump [Nm] Δplp1 = 10.(λ tr - the efficiency of the force transmission itrp - transmission ratio from pump shaft to the wheel shaft of the vehicle: i trp = ωp Δp lp2 = 10. ξ j j =1 ρ.vdi2 2.g (16) ρ.v d2 2.g (17) where: where:  - the density of the hydraulic oil [kg/m3] p - the angular velocity of the pump shaft [rad/s] lp - length of the charging line [m] bx - the angular velocity of the wheel shaft [rad/s] - d + ξv ) plp2 – Total local pressure losses [7] (10) ω bx lp v - pressure loss coefficient at the entrance of the charging line Model of the hydraulic pump: Torque equation [6]: Mp = j - local line pressure loss coefficient at a j place d p .Δpp (11) 2π.ηmp  - a dimensionless friction factor depending on Reynold number (Re), from the case of laminar flow [8]: Flow rate equation [6]: Qp = d p .ωp .ηvp = (12) 2 where: 64 Re Re = (18) vd .d 3 dp - pump displacement (m /rev). (19)  pp - Pump pressure (N/m2) where: vp – pump volumetric efficiency. d – the internal diameter of the pipe [m] mp – pump mechanical efficiency  - oil kinetic viscosity [m2/s] vd – average oil velocity [m/s] - Model of the pipeline is written in the form of pressure loss [7]: vd = plpvao - total pressure loss from the oil tank to the pump; - plp- total pressure loss from the pump to the accumulator. pg , Vg pao ,Vao pgo ,Vgo a b V = Vgo-Vg If plpi is total line pressure loss, then the pump pressure may be defined as: plp=plp1 + plp2 c (13) Fig. 4. The hydraulic accumulator and state of chargeSOC: a--The initial SOC, b- The low operating pressure and c – The high operating pressure (14) Neglecting any heat transfer may be presented in the energy recovering process, the following model for the accumulator could be arrived [9]: pvaop – pressure at the pump inlet pvaop = −plpvao (20) π.d 2 Model for the fluid accumulator In order to minimize the total pressure losses in the system, the cross dimension of the pipelines should be chosen in such a way that the oil will flow in the laminar regime. pp = (Δplp + pg - p vaop ) 4.Qp (15) 59 Journal of Science & Technology 127 (2018) 057-062 k k pao .Vao = p go .Vgo = p g .Vgk 4. Method of calculation (21) Begin where: Input parameters and dt k – the adiabatic exponent which can be assumed at 1,4 [9] for two-atom gases such as nitrogen. Assign pg, av and v Vao – effective gas volume (m3) false v   true pao – the pre-charge pressure (N/m2) Calculate parameters Vgo - gas volume at the minimum operating pressure (m3) Output pgo – the minimum operating pressure (N/m2) (the initial pressure of accumulator) Draw parameters versus time graphs End pg – the operating pressure (N/m2) Fig. 5. The flow chart showing calculating steps in the proposed HRBS during the braking process Vg – gas volume at the working pressure (m3) From equation (21) and Fig. 4, pg can be found as: Vgo pg = pgo .( )1.4 t Vgo -  Q p .dt o (22) Based on the above obtained system of equations from 1 to 26 and using the Matlab - Simulink programme to model the braking kinetic energy recovering process. The calculating process is shown by the flow chart, Fig. 5. (23) 5. Some modeling and experimental results 1 Vgo = Vao ( po k ) p go 5.1 The system parameter values Hence the ratio of recoverable energy  is: E  = a max 100% E v The parameter values of the testing vehicle are shown in Table 1. (24) Table 1: Values of the testing vehicle parameters where: Names Eamax – The maximum energy that may be recovered and stored in the hydraulic accumulator during braking process: Ea (J) Ea =  pg Qp dt Vehicle mass Vehicle wheel’s radius Inertial torque of the wheel The cross-sectional area of the vehicle (25) Ev – The testing vehicle kinetic energy available at the moment of starting to brake (i.e., the vehicle velocity is vo), can be defined as [10]: ΔE v = [ 2 o n m.v J .ω +  bxi 2 2 i=1 2 bxoi ] The coefficient of air resistance [11] The transmission ratio from PTO’s shaft to the vehicle wheels (number lever 3) The total length of the pipe from pump to H.A. Inside diameter of the pipe Number of wheels Volume of oil that pump made in 1 rotation Gas volume at the precharge pao The pre-charge pressure of gas (26) where: n – the number of the vehicle wheels. The average braking acceleration of the vehicle: avtb, can be defined as: a vtb v = o t ph (27) where: vo – The vehicle braking velocity (m/s) tph - Braking time (s) 60 Desig nation m rbx Values Units 2400 0,355 kg m Jbx 5,222 Kg.m2 F 2,4 K 0,58 itrp3 7,8 l 1,5 m d 0,0127 m n 6 m2 dp 14.10^(-6) m3/rev Vao 0,025 m3 pa0 70 bar Journal of Science & Technology 127 (2018) 057-062 5.2 The results 150 Pressure pg(bar) After 5 times measuring in the test and calculating on the modeling, the results obtained in the braking process when the vehicle was running at a velocity vo of 30km/h till stop, are shown in Fig.s 6, 7, 8 and 9. 100 Test, pgo=95bar Modeling ,pgo=95bar Test, pgo=85bar Modeling ,pgo =85bar Test, pgo=75bar Modeling, pgo =75bar 50 0 0 5 10 time(s) 15 20 Fig. 7. Pressure versus braking time in the proposed HRBS: modelling and experimental results 2,60 2,51 2,33 2,40 2,14 2,20 2,00 Fig. 6. Velocity versus time in the HRBS measured at various working pressures 1,80 Test, pgo=75barTest, pgo=85barTest, pgo=95bar As it has been clearly shown in Fig. 6 that, the higher the pressure the shorter the braking times: Oil volume DV (lit) Case 1: at a pressure of pgo=75 bar, braking time is 16s and the average acceleration avtb is of 0,52 (m/s2); Fig. 8. The oil volume recovered in the proposed HRBS: experimental results under various pressure pgo Case 2: at a pressure of pgo=85 bar, braking time is 15s and the average acceleration avtb is of 0,56 (m/s2); Case 3: at a pressure of pgo= 95 bar, braking time is 14s and the average acceleration avtb is of 0,60 (m/s2); When brakes the test vehicle running at a velocity of 30km/h, the available kinetic energy Ev as per equation 26 is 91937(J), Fig. 9 shows that: Case 1: at a pressure of pgo=75 bar, the maximum accumulated pressure is 88(bar), the recovered volume of oil is 2,51(lít), the recovered energy is 21600(J) and the percentage of energy recovered is 23.49%; Fig. 9. Percentages of energy recovered in the proposed HRBS: experimental results under various pressure pgo 6 Conclusions Case 2: at a pressure of pgo=85 bar, the maximum accumulated pressure is 99.63(bar), the recovered volume of oil is 2,33(lít), the recovered energy is 22809(J) and the percentage of energy recovered is 24.81%; Based on the presented above results, the following conclusions can be made: - The HRBS proposed in this study is a rational and profitably applicable in practice. Case 3: at a pressure of pgo=95 bar, the maximum accumulated pressure is 111.26(bar), the recovered volume of oil is 2,14(lít), the recovered energy is 23408(J) and the percentage of energy recovered is 25.46%; - In an operating pressure range around 100bar, the percentage of recovered kinetic energy is about 25%. - Installation of the HRBS in a traditional vehicle will not adversely affect its safety 61 Journal of Science & Technology 127 (2018) 057-062 - It is advisable to use the Matlab-Simulink programme to simulate and evaluate the desired HRBS’s characteristics before doing the actual design of the system. References [1]. Châu Thành Trí - Châu Ngọc Thạch (2005), Hệ thống thắng trên xe ô tô, Nhà xuất bản trẻ. [2]. Luyện Văn Hiếu, Ngô Sỹ Lộc, Trần Khánh Dương (2018). Giới thiệu hệ thống thực nghiệm phanh thu hồi năng lượng động năng bằng bình tích năng thủy lực trên xe ô tô chuyên dùng, Tạp chí Cơ khí Việt Nam, số 3 năm 2018. tr. 58-65. [3]. "Arduino," [Online]. 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