Recent Advancement and Challenges in Differentials-Based Vehicle Stability Control

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1 Recent Advancement and Challenges in Differentials-Based Vehicle Stability Control Jae Lew Neng Piyabongkarn John Grogg Eaton Innovation Center April 7, 26

2 Today s Topics Torque Biasing Devices Electronically-Controlled Limited Slip Differentials and Center Couplers Capable of sending torque only to the slower speed wheel Eaton EGD, Haldex LSC, BMW x-drive, GKN Torque Vectoring Devices Electronically-Controlled Dual Clutch Differentials and Center Couplers Capable of sending torque to the faster speed wheel as well as the slow speed wheel Honda S/H AWD, Mitsubishi EVO, Ricardo 1

3 Overview 1. Introduction 2. Modeling/ Characteristics of Torque Biasing Devices ELSD (Electronic Limited Slip Differential) ELSC (Electronic Limited Slip Center Coupler) 3. Effect of Torque Biasing Device on Vehicle Dynamics 4. Stability-Enhanced Traction Control Split-Mu Launching T-Junction Launching 5. Active Yaw Control 6. Rollover Mitigation 7. Conclusions 2

4 Traction Ability to move forward in rough terrain or low-µ surface (ice or sand) Typical Driveline Brake-Based Traction Diff-Based Traction Zero Traction Brake Traction Traction ICE Open Diff ICE Open Diff ICE Locking Diff Adv Limited traction No additional hardware if ABS available Better traction: serious off-road application Good traction with stability control integration (?) Disadv No Traction Brake overheat & wear: limited usage Additional hardware Jerky motion Less energy efficient 3

5 Stability Ability to keep the vehicle head in the driver s intended direction Brake-based Torque -based Adv Disadv Available on the market Less hardware if ABS is available Could be easily integrated with ABS Slow vehicle down Reactive & passive approach => slow, limit vehicle performance Intrusive to the driver Preemptive & active driveline approach => faster, enhanced vehicle performance Better handling ABS, ESP & Traction compatibility (?) No braking required Additional hardware Unable to control the torque transferred direction directly 4

6 Recent Developments using Torque- Based Methodologies Front/back controlled center coupler - Nissan V-TCS, Haldex LSC, BMW xdrive, - Bosch CCC Front/back controlled center coupler + side/side ELSD - Eaton, GKN TMD, Dana Dynamic Trak Front/back Left/right control systems (aka torque vectoring) - Honda SH-AWD, Mitsubishi AYC, Ricardo 5

7 Control System Development 1. Math Modeling and Simulation 3. Virtual Validation/ Auto Code Generation φ r [] 1 φ v [ 2] h CG z 1 y1 hr φ v mg 2. Control & Estimation Algorithms Design φ r 4. ECU and Sensor Implementation 5. Vehicle Testing 6

8 Overview 1. Introduction 2. Modeling/ Characteristics of Torque Biasing Devices ELSD (Electronic Limited Slip Differential) ELSC (Electronic Limited Slip Center Coupler) 3. Effect of Torque Biasing Device on Vehicle Dynamics 4. Stability-Enhanced Traction Control Split-Mu Launching T-Junction Launching 5. Active Yaw Control 6. Rollover Mitigation 7. Conclusions 7

9 Dynamic Modeling: ELSD T p ELSD: side to side torque transfer device The prop-shaft torque is described as T = T + p tf T diff ωl Ilr T L T tf ω E T diff T R Irr ωr The left rear and right rear axle dynamics: Clutch model: 8 Ttf = SatT CT ( C ω + K ω dt) ωr ωl ω = 2 T L T R = T = tf T + diff 2 T diff 2 = T = p T p + T 2 T 2 command clutch torque tf tf

10 ELSD Effects on Vehicle Yaw Dynamics Side-to-side torque transfer with ELSD Applying differential clutch torque during a turn Transfers torque from the faster speed wheel to the the lower speed wheel. Increases vehicle yaw understeer tendency on a constant mu surface. Turn left ω ω, R > T > L tf ω < ω Turn right, T < R L tf T tf 9

11 Dynamic Modeling: ELSC Front/back torque transfer device Clutch model c: clutch damping coefficient, k is the clutch spring coefficient, command clutch torque ω c := ω f ω r is the speed difference between the front axle and the rear axle. The front and rear axle dynamics I fω f = Tf reff Ff I ω = T r F Front & rear torques w.r.t. engine torque and CT torque Tf = Tin Ttf T r = T tf CT { ω ω } T = sat c + k dt tf c c T r r r eff r 1

12 ELSC on Vehicle Yaw Dynamics Front-to-back torque transfer with Center Coupler More complicated response Friction circle Yaw dynamics CORNERING FORCE F y B C FRONT REAR A D F y Lemma 1: Front-to-back torque transfer will generate more oversteering if and only if Lr ρ 3 sin δ + ρ1 cos δ + ρ 2 > L where ρ = F t ) F ( ) = F ( t ) F ( t ) 3 xf ( f + xf t f 2 yr yr f SLIP ANGLE Steering Input Influence [ADSC, ] ρ ρ = F t ) F ( ) 1 yf ( f yf t F xf LONGITUDINAL FORCE F x 11

13 Co-Simulation t Clock ct Goto Displa y CarSim Vehicle Model Bus _in CarSim S-Function Vehicle Code: i_i Da ta Eaton Drive line active differentials U U(E) Drive Torques Equivalent Gear Ratios bus-in wheel speeds U U(E) Modified Driveline Control Mode W/C Pres s ure M/C Pressure Vehicle Vel. Vehicle Velocity Control Mode FL,RL,FR,RR Wheel Velocity LF,RF,LR,RR Simple ABS-braking/ TC/ AYC/ RSC with ABS AYC with ABS AYC + ETM AYC Brake Actuator Model 15 Brake Pressure, mpa No ABS AYC/ No ETM AYC Pressure with ETM AYC ELSD and ELSC Model Vehicle Dynamics and Environments 12

14 Simulation Results: Effect of Locking ELSC and ELSD, On-throttle On a high friction surface (mu =.85) rear ELSD locked On-throttle turning maneuver on high friction surface 25 On-throttle turning maneuver on high friction surface 14 2 center coupler locked no torque biasing 12 Y (m) center coupler locked yaw rate (deg/s) 15 1 both devices locked rear ELSD locked 4 2 no torque biasing both devices locked X (m ) On a low friction surface (mu =.2) time (sec) 6 On-throttle turning maneuver on a low friction surface 6 On-throttle turning maneuver on a low friction surface no torque biasing 5 both devices locked 5 center coupler locked both devices locked Y (m) center coupler locked rear ELSD locked yaw rate (deg/s) rear ELSD locked no torque biasing X (m ) Vehicle Path Yaw time (sec) Rate

15 Simulation Results: Effect of Locking ELSC and ELSD, Off-throttle On a high friction surface (mu =.85) 12 1 Off-throttle turning maneuver on a high friction surface rear ELSD locked 25 2 Off-throttle turning maneuver on a high friction surface no torque biasing center coupler locked Y (m) no torque biasing center coupler locked yaw rate (deg/s) 15 1 both devices locked rear ELSD locked 2 5 both devices locked X (m ) On a low friction surface (mu=.2) Y (m) Off-throttle turning maneuver on a low friction s urface center coupler locked both devices locked no torque biasing rear ELSD locked yaw rate (deg/s ) time (sec) Off-throttle turning maneuver on a low friction surface no torque biasing center coupler locked rear ELSD locked both devices locked X (m ) Vehicle Path time (sec) Yaw Rate

16 Summary of torque-biasing effect on yaw dynamics 1. Locking ELSD induces more understeering. Less effective on a low friction surface. 2. Locking CC influences vehicle dynamics more with accelerating maneuvers and induce less understeering. Less effective with off-throttle maneuvers. 3. Compromised performance using both devices can be achieved Active Yaw Control 15

17 Overview 1. Introduction 2. Modeling/ Characteristics of Torque Biasing Devices ELSD (Electronic Limited Slip Differential) ELSC (Electronic Limited Slip Center Coupler) 3. Effect of Torque Biasing Device on Vehicle Dynamics 4. Stability-Enhanced Traction Control Split-Mu Launching T-Junction Launching 5. Active Yaw Control 6. Rollover Mitigation 7. Conclusions 16

18 Stability-Enhanced Traction Control Split-Mu Launching with ELSD T-Junction Launching with ELSC Normal Traction Control Stability- Enhancement Sensor Information Supervisory Control Yaw Damping Control ELSD / ELSC Stability-Enhanced Traction Control 17

19 Overview 1. Introduction 2. Modeling/ Characteristics of Torque Biasing Devices ELSD (Electronic Limited Slip Differential) ELSC (Electronic Limited Slip Center Coupler) 3. Effect of Torque Biasing Device on Vehicle Dynamics 4. Stability-Enhanced Traction Control Split-Mu Launching T-Junction Launching 5. Active Yaw Control 6. Rollover Mitigation 7. Conclusions 18

20 Yaw Control Algorithm Target yaw rate calculation Normal Traction Control Stability- Enhancement Sensor Information Supervisory Control Yaw Damping Control ELSD Yaw Damping Control 19

21 Simulation Results: Yaw Control - 6mph, mu=.6 (wet) - only simulation can perform this with consistency ELSD Applied Clutch Torque clutch torque (Nm) time (sec) Double lane change at 1 km/h yaw rate (deg/s ) desired yaw rate with yaw control without yaw control time (sec)

22 Test Results: Slalom Maneuver Constant speed (w/ cruise control) Global Displacement Speed Yaw Rate Oversteering leads to unstable response Oversteering regions Yaw Control Blue: no yaw control Red: with yaw control 21

23 Overview 1. Introduction 2. Modeling/ Characteristics of Torque Biasing Devices ELSD (Electronic Limited Slip Differential) ELSC (Electronic Limited Slip Center Coupler) 3. Effect of Torque Biasing Device on Vehicle Dynamics 4. Stability-Enhanced Traction Control Split-Mu Launching T-Junction Launching 5. Active Yaw Control 6. Rollover Mitigation 7. Conclusions 22

24 Rollover Mitigation NHTSA Rollover Statistics (In USA, 22) xml DOT 1 DOT xml no nopag d d Types of Rollover Tripped - uneven road surface as a vehicle leaves the paved road surface. e.g. soft soil, guard rail, steep slope Un-tripped - high speed maneuver Electronic Stability Control - Keep the vehicle head in the driver s intended direction - Utilize individual wheel braking and throttle down Un-Tripped 5% Tripped 95% 23

25 NHTSA Rollover Rating Static Stability Factor (SSF) Dynamic Rollover Test (DRT) xml DOT 1 no Pag d SSF = T/2H 24 NHTSA Rollover Rating SSF: Passenger Car(1.3~1.5), SUVs & Pick-Ups (1.~1.3) DRT: Un-tripped rollover rating under Fishhook maneuver Measure of dynamic rollover propensity of vehicles (including driveline, tire, suspension, handling, etc) Can reduce both tripped and un-tripped rollovers 24 Eaton Confidential and Proprietary

26 Rollover Index z Direct measurement of roll => Too late! TTR (Time-to-Rollover) CE (Critical Energy) LTR (Lateral Load Transfer Ratio) φ LTR y F zr mg F zl h h R where LTR = F F zr zr + F F zl zl 2 Ay = ( h + h + hφ R ) d g 2( h A A R + h) y 1 y = d g SSF g d /2 T SSF = = ( h+ h ) 2H R Lateral Accel SSF is the NHTSA (National Highway Traffic Safety Administration) static rollover index. 25

27 Simulation Results (NHTSA Fishhook) - SUV with Eaton ELSD at the rear - constant speed: 6 Km/h - asphalt surface 1 1 Dashed Line: W/O Roll Control Solid Line: W/ Roll Control LTR.5 Lateral Acceleration (g) Time (sec) Lateral load transfer ratio Time (sec ) Vehicle lateral acceleration Yaw Rate (deg/s ec) 1 Roll (deg) Time (sec) Vehicle yaw rate Time (sec) Vehicle roll angle 26

28 Conclusion Demonstrated that ELSD and ELSC can improve vehicle stability (stability-enhanced traction, yaw control, rollover mitigation) as well as traction control. Developed electro-hydraulic ELSD and ELSC hardware and control algorithms for various commercial SUVs. Investigated the possibility of integrating with ABS/ESC system. ELSD and ELSC could be a cost effective solution for active torquebased vehicle stability control. Note: ELSD - Electronically Controlled Limited Slip Differential ELSC - Electronically Controlled Limited Slip Center Coupler ABS - Anti-Lock Brake System ESC - Electronic Stability Control System 27