A study on Clamping force Estimation of EMB for Fuelcell vehicle using Sliding mode observer

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1 EVS28 KINTEX, Korea, ay 3-6, 25 A study on Clamping force Estimation of EB for uelcell vehie using Sliding mode observer Kangseok Lee, Wootaik Lee 2 Graduate School, Department of Control & Instrumentation Engineering, Changwon National University, Changwon-si, Gyeongsangnam-do, , Korea, ks549@gmail.com 2 (corresponding author) Department of Control & Instrumentation Engineering, Changwon National University, Changwon-si, Gyeongsangnam-do, , Korea, wootaik@changwon.ac.kr Abstract A design and verification of sliding mode observer for estimation and control of amp-force of Electro- echanical Brake (EB) were described in this paper. Researches for elimination of a amp-force sensor from brake-by-wire system are progressed due to implementation difficulties and cost issues. In the conventional studies, amp-force is estimated from characteristic curve based on a contact point between brake pads and brake disk. In existing method, detection of accurate contact point is required. Otherwise, it causes the reduction of control performance and incorrect operation of EB. With the sliding mode observer, it is possible to estimate the contact point and control amp-force of EB with considering of ageing of EB system such as the abrasion of brake pad. The relationship between amping force and position of brake pad is made up to lookup table by learning algorithm, and amping force control algorithm is designed using the lookup table. The designed Sliding mode observer and amping force control algorithm are validated by experiments on the test bench. Keywords: EB, Electro-mechanical brake, Sliding mode Observer, Clamping force estimation, uel-cell Introduction Recently one of the primary issues of vehie electronic-control system development is applied in the x-by-wire system using communication technologies and electric motor technology. a Brake-by-wire system, Replace the hydraulic link to the brake pedal from the brake actuator used in the existing hydraulic brake system to an electrical wire, and the brake actuator is used as an electric motor electro-mechanical brake (EB) [-2]. Besides, EB has been developed as enhanced brake system by cooperation control with regenerative braking system of fuel-cell vehie. It is necessary to control EB with feedback of amping force information for precise control of amping force. By use of force sensors to measure amping force in EB or electric parking brake (EPB) systems is simple solution. However, it is difficult to install the force sensor because of the limited mounting space and the increase of cost. Therefore, amping force estimation methods without using the force sensor were proposed for EB systems. In [3], amping force estimation method from the characteristic curve between the position of brake pad and the amping force is proposed. On the other hand, amping force estimation method by analysing the relationship between motor rotation EVS28 International Electric Vehie Symposium and Exhibition

2 angles and amping force in frequency domain in [4]. And in [5], amping force estimation algorithm, considering hysteresis caused of backlash, based on the relationship curves of between motor rotation angle and amping force is proposed. In these previous studies, it is necessary to compensate the change of contact point of brake pad and disk caused of the EB system ageing such as abrasion of brake pads. To solve this problem, the contact point is estimated by using the relationship between variation of motor torque and position of brake pad in [6]. And in [7], contact point estimation method using motor angular velocity is proposed. In this paper, amping force estimation and control algorithm based on the relationship of position of brake pad and amping force is proposed. The relationship of brake pad position and amping force is defined by sliding mode observer. igure : Electro-mechanical Brake System [N] 2 System odeling The EB system inudes a caliper, brake pad and permanent magnet synchronous motor (PS). A caliper and PS are connected via gear set and ball screw. The PS generates electrical torque, and generated electrical torque converts to amping force by ball screw, brake pad and disk. Between brake pad and disk, there is a gap. The brake pad does not contact to the disk, which means no amping force generates in this section. The contact point of brake pad and disk describes as x in igure 2. Beyond contact point, amping force is generated according to position of brake pad as shown in igure 2 [3]. x x [mm] igure 2: Clamping force characteristic curve The electrical torque T is represented as shown in equation () and (2) using gear ratio and efficiency N, inertia J and friction B. Clamping - - igure 3: EB system modeling EVS28 International Electric Vehie Symposium and Exhibition 2

3 force is related with electrical torque of motor as igure 3. T J B N () J B L T T T T (2) Parameters using in this paper are shown in Table. Table : Parameters Parameter Value J 4.58e-6 kg m 2 B.9e-5 Nm/rad/s N /24 P 4EA 6.34mWb R L L m a d q 77mΩ μh 45μH 3 Sliding mode Observer Design In this chapter, the proposed sliding mode observer design, which estimates amping force of EB, is described. Equation (3) is obtained from equation () and observer for motor angular velocity is described in equation (4) which is obtained from equation (3). A constraint of a constant observer gain in equation (4) is l. The dynamic of the mismatch can be obtained using equation (5) and observer for motor angular velocity is obtained in equation (6) using dynamic of the mismatch [8-9]. J T B N (3) J T B l sign( ) (4) (5) J B N l sign( ) (6) The sliding mode reach condition is described by equation (7) [8]. The sliding mode observer gain l, to enforce the sliding mode ( s ), is determined by applying the condition of equation (7). The s represents the sliding manifold that describes the sliding condition in all equations []. (7) Therefore the sliding mode observer gain l is represented as equation (8) and (9). ( N B) l sign( ) (8) N B l (9) sign( ) And sliding mode observer gain l is represented as equation () and () considering of dynamic of the mismatch. l N B, (if ) () l ( N B), (if ) () The sliding mode observer gain l is determined as equation (2) and (3). l N B (2) l 4.2 (3) High sliding-mode observer gain helps enforce the sliding mode, and suppress influence of disturbances and uncertainties in system behavior. On the other hand, it causes oscillation in estimation result usually referred to as chattering of sliding mode observer []. Equations (4) to (6) are obtained using the concept of equivalent control [2]. After the reaching phase of the sliding mode, the dynamic of the mismatch is equal to zero. Therefore, the amping force of EB can be obtained as below in Eq. (6). J B N ( l sign( )) (4) N ( l sign( )) (5) eq ( l sign( )) eq (6) N To determine the equivalent control ( l sign( )) eq, a second-order Butterworth filter is employed. The cut-off frequency of the Butterworth filter is set to.5hz according to the minimum time of amping force rise to the max value. eq EVS28 International Electric Vehie Symposium and Exhibition 3

4 + - B sign( ) l T J LP( ) igure 4: Sliding mode observer for amping force estimation To estimate the amping force of EB, electric torque of motor has to be determined. The electric torque of motor T is determined by equation (7) which is the electric torque equation of IPS. Equation (7) and (8) are constant value for reaction torque and reluctance torque of IPS, respectively. T KTm iq KTl id iq (7) P 3 KTm m 2 2 (8) P 3 KTl ( Ld Lq ) 2 2 (9) 4 Clamping orce Control or estimation and control amping force, characteristic curve of amping force and brake pad position has to be determined. To determine the characteristic curve, amping force estimation result of designed sliding mode observer is used. Brake Pad position [mm] x x 6 x 5 x 4 3 x x 2 x s J At initialization state of EB system, EB ECU generates amping force by moving brake pad through mechanical stop which is the position of maximum amping force. And sliding mode observer estimated amping force at the same time. The lookup table can be determined using estimated amping force and position of brake pad as shown in igure 5. In the lookup table, amping force axis is divided in the same interval. The point of N amping force is contact point, and amping force is generated beyond the contact point. * Lookup x* Table - x Position v* Control - v Speed i * Control - i Current Control igure 5: Block diagram of amping force controller Using the lookup table of amping force and brake pad position, the amping force controller is designed as igure 5. With measured physical values which are the position of brake pad x, angular velocity of electric motor v and applied current of electric motor i, the feedback control is executed. The output voltage is obtained by the feedback control. 5 Experiments In this chapter, a designed sliding mode observer and amping force estimation and control algorithm are verified on the test bench. The block diagram of experiments environment is as shown igure 7. EB ECU CU 3PH Inverter Signal Conditioning Circuit CAN Transceiver i PS, PC (onitoring & Control Ref. Generation) Linear Hall sensor Load Cell Indicator Gear Set Brake Pad V o Load Cell igure 7: Block diagram of experiments environment Clamping orce [N] igure 5: Characteristic curve of amping force brake pad position There is EB ECU for Estimation amping force and control EB and it inudes 3-phase inverter for drive PS. Also, it inudes signal conditioning circuit for mensurement of physical values, and communication circuit to connect to PC for monitoring and generation of control reference. EVS28 International Electric Vehie Symposium and Exhibition 4

5 Clamping orce [N] Clamping orce - Lookup Table [N] Brake Pad Position [mm] or the verification, additional load cell and indicator for measurement of the amping force is inuded in the experiments environment. Power Supply Oscilloscope The lookup table based on the amping force estimation result using sliding mode observer is as igure. In igure, the contact point is determined on the.97mm. In the region between ~.97mm, it is the gap of brake pad and disk, which means there is no amping force in this region. 2.8 Load cell, Indicator EB ECU EB.8 igure 8: Test bench In igure 9, it is comparison of amping force estimated with sliding mode observer and amping force measured with load cell. In the result of estimation of amping force with sliding mode observer, there is difference from measured amping force below N. It is the exuded region of lookup table as low generated torque of electric motor. The amping force aspect of estimation with sliding mode observer and measurement with load cell is similar, particularly between N to 7N which is primary operating region. The maximum simultaneous error is below 4N Required Clamping orce [N] igure : Lookup table of amping force brake pad position igure shows the relationship between amping force measured using load cell and calmping force estimated using lookup table. The maximum simultaneous error is below 4N. This means that it is possible to use this lookup table for estimation and control amping force instead force sensor such as load cell Load Cell Sliding ode Observer Brake Pad Position [mm] igure 9: Clamping force estimation result by sliding mode observer and load cell Clamping orce - Load Cell [N] igure : Comparison of amping force by lookup table and load cell igure 2 shows the result of proposed estimation and control algorithm of amping force. Control references of amping force are 2N, 4N and EVS28 International Electric Vehie Symposium and Exhibition 5

6 Clamping orce [N] 7N, respectively. The maximum response time is.5sec, maximum steady state error is 2N easured Clamping force Reference Clamping force Time [sec] igure 2: Clamping force control result 6 Conusion Recently, amping force estimation methods without using the force sensor were proposed in many researches. However it is necessary to compensate the change of contact point of brake pad and disk caused of the EB system ageing such as abrasion of brake pads in previous researches. In this paper, amping force estimation and control algorithm based on the relationship of position of brake pad and amping force with sliding mode observer is proposed. Designed sliding mode observer is verified by experiment on the test bench. By using designed sliding mode observer, it can be possible to estimate the amping force. The amping force and contact point can be estimated with considering of ageing of EB system such as the abrasion of brake pad. Acknowledgments This research was financially supported by the Industrial Strategy Technology Development Program of inistry of Knowledge Economy (No ) References [] Dominguez-Garcia AD, Kassakian JG, Schindall JE, A backup system for automotive steer-by-wire, actuated by selective braking. Power Electronics Specialists Conference, ISSN , 24. [2] Schenk D., Wells R., iller J., Intelligent braking for current and future vehies. SAE Technical Paper 95762, doi:.427/95762, 995 [3] Schwarz, R., Isermann, R., et al., Clamping force estimation for a brake-by-wire actuator, SAE Technical Paper, doi:.427/ , 999 [4] Stephen S., Bab-Hadiashar A., Hoseinnezhad R., Clamp-force estimation for a brake-by-wire system: A sensor-fusion approach, IEEE Transactions on Vehicular Technology, ISSN , 28 [5] J.Y. Choe, Y.H. Ki, J.H. Jeon, S.. Lee, H.S. Ahn, Design and implementation of a new type of a amping force estimator for EB systems, 2 KSAE Conference, pp 75-8, 2 [6] C. Jo, S. Hwang, H. Kim, Estimation of amping- -force and development of gap-distance control algorithm for electro-mechanical brake, KSAE conference, pp , 29 [7] Y.O. Lee, W. Lee, C.W. Lee, C.C. Chung, Y. Son, Novel amping force control for electric parking brake systems, 7th Asian Control Conference, pp , 29 [8] V. Utkin, Variable Structure Systems with Sliding odes, IEEE Transactions on Automatic Control, Vol. 22, Issue 2, pp , 977 [9] K. Lee, K. Bae, W. Lee, Retraction control of motorized seat belt system with sliding mode observer, SAE Technical Paper, doi:.427/ , 22 [] I. Husain, R.J. Veillette, and C. Batur, Design and performance analysis of sliding-mode observers for sensorless operation of switched reluctance motors, IEEE transactions on Control Systems Technology, Vol., No. 3, pp , 23 [] V. Utkin, Sliding mode control design principles and applications to electric drives, IEEE Transactions on Industrial Electronics, Vol. 4, No., pp , 993 [2] N.K. 'sirdi, A. Rabhi, L. ridman, J. Davila, Y. Delanne, Second order sliding mode observer for estimation of velocities, wheel sleep, radius and stiffness, American Control Conference, doi:.9/acc , 26 EVS28 International Electric Vehie Symposium and Exhibition 6

7 Authors Kangseok Lee received the.s. degrees in control and instrumentation engineering from Changwon National University, Changwon, Korea, in 2. He is currently working toward the Ph.D. degree in the Graduate School of Control and Instrumentation Engineering, Changwon National University. His research interests inude software development of automotive control systems. Wootaik Lee received the Ph.D. degree in automotive engineering from Hanyang University, Seoul, Korea, in 22. Since 23, he has been with the Department of Control and Instrumentation Engineering, Changwon National University, where he is currently a Professor. His research interests inude design and implementation of embedded realtime control systems, and motorbased automotive control systems. EVS28 International Electric Vehie Symposium and Exhibition 7