A Novel Seamless 2-Speed Transmission System for Electric Vehicles: Principles and Simulation Results

Transcription

1 A Novel Seamless 2-Speed Transmission System for Electric Vehicles: Principles and Simulation Results Fabio Viotto, Oerlikon Drive Systems Electronic Systems for Vehicle Propulsion Symposium 8-9 November 2011 Troy (Detroit), MI 1

2 Presentation Outline Introduction Why a 2-speed Transmission for Electric Axles? The Novel Transmission Layout The Model and the Controller Results Conclusions

3 Introduction Automotive Products High performance car transmissions 4WD car power transfer units and differentials Electric vehicles gearboxes and transaxles

4 Why a 2-Speed Transmission for Electric Axles? Wheel Torque Performance benefit of a 2-speed transmission (higher torque in 1 st gear and higher speed in 2 nd gear) Constant torque region Constant power region Operating area with single-speed Base speed Vehicle Speed

5 Why a 2-Speed Transmission for Electric Axles? NEDC The optimisation of the 2 nd gear ratio permits to increase the overall efficiency of the electric powertrain 2 nd Gear Motor Downsizing 1 st Gear

6 The Novel Transmission Layout The performance benefit is achievable only in case of absence of torque gap during the gearshift The 2-speed transmission needs to be cost effective when compared to the singlespeed transmission 1 st Gear 2 nd Gear Power flow through sprag clutch Power flow through friction clutch

7 The Novel Transmission Layout Patent pending layout Single Speed Max Input Torque [Nm] Max Input Speed [rpm] (*) INSTALLATION ON VEHICLE: HORIZONTAL INSTEAD OF VERTICAL Two Speed Generation 1 Generation 2 Mass [kg] Dimensions L x W x H [mm] 330 x 260 x x 380 x x 230 x 470 (*) 1st gear ratio 8.3 : : : 1 2nd gear ratio N.A. 5.5 : : 1 Park lock (double engage) N.A. YES YES Park lock (dedicated) N.A. N.A. OPTIONAL

8 The Novel Transmission Layout UPSHIFT DOWNSHIFT Torque Electric Motor Torque Transmittable Friction Clutch Torque Sprag Clutch Torque Speed time Torque Phase Torque Phase Inertia Phase Inertia Phase Electric Motor Speed 1st Gear Speed 2nd Gear Speed

9 The Model and the Controller Dynamic Performance Model It includes: Driver model Half-shaft Dynamics Torque Demand Vehicle Speed Electric Motor Rise Time Long. Acceleration Model Therm. model Input Speed Input Torque Temperature Efficiency Model Efficiency Efficiency Model - Speed - Torque - Temperature Tyre Non-linear Dynamics (Longitudinal Force vs. Slip Ratio and Relaxation Length) V x Wheel Speed Kinematics SR theoretical Rel. Length SR del Magic Formula F x

10 The Model and the Controller Electric Powertrain Model 1st gear - 1 Degree of Freedom Friction Clutch Torque Contribution -Increased during TORQUE PHASE reducing output torque Half-Shaft Torque Contribution - Total half-shaft torque θ&& diff = T iη i η + T iη i η T iη i η T m 1 1 diff diff fc 2 2 diff diff fc 1 1 diff diff h ( ) + ( + 1) ( ) J J J J J i η i η J i η i η J J i η diff LHS RHS m diff diff b diff diff b diff diff Motor Torque Contribution Equivalent Moment of Inertia - High due to high 1 st gear ratio

11 The Model and the Controller Inertia Phase - 2 Degrees of Freedom (motor/transmission) θ&& diff = T iη i ( ) η T fc 2 2 diff diff h J + J + J + J i η i η + J i η diff LHS RHS 1b 2 2 diff diff 2 diff diff & θ m = J i T m T fc 2b + J J 2 m + 1 1η1 Low Equivalent Moment of Inertia - Due to no contribution from the Electric Motor Golden Rule: during the inertia phase of the gearshift, vehicle acceleration is controlled by the friction clutch torque, whilst electric motor dynamics are controlled by the motor torque 2nd Gear engaged θ&& diff = T iη i m 2 2 diff diff h 2 2 J 2 2 2bi2η2idiffηdiff 2 diff + LHS + RHS + m b 2 2 diff diff diff diff i1η 1 ( ) ( ) η T J J J J J J i η i η J i η Lower moment of inertia than 1 st gear due to i 2 <i 1

12 The Model and the Controller Inertia Phase - Upshift Electric Motor Torque Control (according to the Golden Rule) y t upshift 1 [DTD = DRIVER TORQUE DEMAND] θ & m,1 st _ gear i 2 / i 1 0 t upshift,end t upshift T m, driver θ& = θ& y reference, m m,1 st _ gear (motor ref speed) θ & ( m (motor speed) DTD Feedback (PID) Feedforward ( DTD) T m, ref (follow ref speed profile)

13 The Model and the Controller Inertia Phase - Upshift Friction Clutch Torque Controls (according to the Golden Rule) Control 1 The friction clutch transmits the same amount of torque the electric motor would generate according to: Driver Torque Demand (unmodified) actual motor speed

14 The Model and the Controller Inertia Phase - Upshift Friction Clutch Torque Controls (according to the Golden Rule) Control 2 Friction Clutch Torque T fc, saturation The friction clutch transmits the same amount of torque the electric motor would generate according to: Torque Phase DOES NOT CHANGE significantly during the inertia phase Inertia Phase Driver Torque Demand (unmodified) motor speed in 2nd gear First gear Second gear Time

15 The Model and the Controller Torque Phase Upshift Control 3 Motor Torque Demand Reduction of wheel torque during power transition from sprag clutch to friction clutch Increase of motor torque that compensate the reduction of wheel torque during power transition from sprag clutch to friction clutch Torque Phase Inertia Phase OBVIOUSLY UP TO MAX TORQUE Common for Control 1 and 2 First gear Second gear Time

16 Results Upshift in the constant torque region of the electric motor Motor Torque B A Motor Speed Complete absence of torque gap during the upshift Control 1 equivalent to Control 2 [m/s 3 ] Acceleration [m/s 2 ] Speed and Acceleration Vehicle - Driver's Demand 20% 20 actuator deactivation upshift end 10 inertia phase start Vehicle Acceleration [m/s 2 ] upshift demand Max Jerk During Upshift: [m/s 3 ] Mean Jerk During Upshift: 0.60 [m/s 3 ] Time [s] Jerk - Driver's Demand 20% Vehicle Speed [km/h] upshift demand inertia phase start upshift end actuator deactivation Time [s] Jerk [m/s 3 ] Speed [km/h]

17 Results Upshift in the constant power region of the electric motor Motor Torque 8000 Motor Speed Dynamics During Gearshift - Driver's Demand 100% Upshift Time: 0.56 [s] B A Speed [rpm] st Gear Speed [rpm] 2 nd Gear Speed [rpm] Reference Speed [rpm] Motor Speed [rpm] actuator deactivation upshift end inertia phase start upshift demand Time [s] Torque Dynamics During Gearshift - Driver's Demand 100% Motor Speed Torque [Nm] st Gear Torque [Nm] 2 nd Gear Torque [Nm] Motor Torque [Nm] actuator deactivation upshift end inertia phase start upshift demand Control 2 Time [s]

18 Results Upshift in the constant power region of the electric motor Control 1 Motor Torque B A Motor Speed Control 1: torque gap during the inertia phase and low jerk Control 2 Control 2: no torque gap during the inertia phase but high jerk (in any case always within a tolerable threshold i.e. < 25 m/s^3)

19 Results Sensitivity Analyses Control 1 vs Control 2 vs Control 3 Torque Demand km/h km/h Upshift time Mean acceleration during upshift Mean jerk during upshift 80% Control s 4.03 s 0.95 s 1.82 m/s m/s 3 Control s 3.84 s 0.70 s 2.25 m/s m/s 3 Control s 3.82 s 0.74 s 2.31 m/s m/s 3 Low acceleration times and jerk values with control 3 Friction Clutch Actuator Rise Time (longitudinal acceleration test at 100% of driver torque demand) Motor Time Constant

20 Results Development Vehicles Control 1 Control 2 UPSHIFT in CONSTANT TORQUE REGION Torque Phase Inertia Phase LCV LCV event event UK UK (September) (September)

21 Conclusions The adoption of a 2-speed transmission can be an effective way to increase the performance and the efficiency of an electric axle A novel 2-speed transmission system design is proposed, based on the control of a friction clutch and a sprag clutch The implemented simulation models demonstrate the effectiveness of the transmission concept The novel transmission system permits the independent control of the electric motor dynamics and the vehicle acceleration dynamics during the gearshift The main parameters affecting the gearshift dynamics are: motor inertia friction clutch actuator dynamics (rise time) and motor dynamics The prototypes of the novel transmission system are under testing on a vehicle demonstrator and on the Hardware-In-the-Loop powertrain rig of the University of Surrey