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Namdoo Kim, Jason C. Kwon, and Aymeric RousseauArgonne National Laboratory, USA
Nov, 2010
Tradeoff Between Powertrain Complexity and Fuel Efficiency
Introduction
2
Argonne National Laboratory - Tradeoff Between Power-train Complexity and Fuel Efficiency
Toyota Prius, and some other hybrids, use a “Power Split” system:
- Engine speed can be controlled independently from the vehicle speed
- Relatively low efficiency in the high-speed region
Combining several EVT modes in to one “Multi-mode” hybrid system, thereby increasing the number of MPs and allowing greater operation flexibility
Dozen of patents on multi-mode EVT design configuration
EVT efficiency of electro-mechanical power path increases with powertrain(PT) configuration complexity
EVT mechanical losses also increase with PT complexity
The objective is to evaluate the benefits of several multi-mode powertrain configurations from a fuel consumption and cost point of view.
MP = Mechanical point
What is an EVT ?
3
Argonne National Laboratory - Tradeoff Between Power-train Complexity and Fuel Efficiency
Electrically Variable Transmission
Continuously variable, using gearing and electric motors
Used with a battery pack in hybrid electric vehicles.
Examples:
– Single mode w/o FG : Toyota Prius04
– Single mode w/ FG : Prius10, LS600, HS 250h, Ford Escape,…
– Two mode w/o FG : Allison EP40 and EP50 bus hybrid
– Two mode w/ FGs : Saturn Vue HEV, GM Tahoe HEV
– Three&Four mode w/ FGs : Being developed by OEM
Gear Gear
BatteryEngine Wheel
Electro-Mechanical
MC2 MC1
All-Mechanical
FG = Fixed Gear
0 0.5 1 1.5 2 2.5 3-1.5
-1
-0.5
0
0.5
1
Pow
er R
atio
The ratio P-elect to P-eng (@ W-eng=1500rpm, T-eng=100Nm)
EVT1
“All-Mechanical” Power
“All-Input” Power
“Electro-Mechanical” Power“Mechanicla Point”
Ratio : 0.7054
0 1 2 3 4-1.5
-1
-0.5
0
0.5
1
1.5
Pow
er R
atio
The ratio P-elect to P-eng (@ W-eng=1500rpm, T-eng=100Nm)
EVT1EVT2
MP1MP2
0 1 2 3 4-1.5
-1
-0.5
0
0.5
1
1.5
Pow
er R
atio
The ratio P-elect to P-eng (@ W-eng=1500rpm, T-eng=100Nm)
EVT1EVT2
MP1MP2 FG1FG2
FG3
FG4
0 1 2 3 4-1.5
-1
-0.5
0
0.5
1
1.5
Pow
er R
atio
The ratio P-elect to P-eng (@ W-eng=1500rpm, T-eng=100Nm)
EVT1EVT2EVT3
MP2MP3FG2FG3
MP1FG1
Technical AccomplishmentsUnderstand Efficiency Potential of Each Multi-Mode
4
Note : Power ratio = electro-mechanical power / all-input power Minimize the power ratio, which is more efficient and transmit more power mechanically
Single Mode Two Mode(1)
AHS2 FWD
Three Mode
small values mean little recirculation, higher efficiencies
Technical AccomplishmentsUnderstand Efficiency Potential of Each Multi-Mode
5
Single Mode Two Mode(1)
AHS2 FWD Three Mode
Note : The efficiency of the multi-mode system has relatively high value Additional mode can allow to maintain high efficiency over a wider range
0 0.5 1 1.5 2 2.5 30.5
0.6
0.7
0.8
0.9
1
Eff.
Efficiency (@ W-eng=1500rpm, T-eng=100Nm)
EVT1MP
0 1 2 3 40.4
0.5
0.6
0.7
0.8
0.9
1
Eff.
Efficiency (@ W-eng=1500rpm, T-eng=100Nm)
EVT1EVT2
0 1 2 3 40.4
0.5
0.6
0.7
0.8
0.9
1
SR, the ratio of W-eng to W-out
Eff.
Efficiency (@ W-eng=1500rpm, T-eng=100Nm)
EVT1EVT2
0 1 2 3 40.4
0.6
0.8
1
SR, the ratio of W-eng to W-out
Eff.
Efficiency (@ W-eng=1500rpm, T-eng=100Nm)
EVT1EVT2EVT3
Single Mode Two Mode(1)
AHS2 FWD Three Mode
EGMC2
MC OUT
S1 C1 R1
R2 C2 R2
EGMC2
MC
OUT
CL2
CL1S1
CL4
CL3
C1 R1
R2 C2S2
S3
R3C3
Seven Configurations are Considered
6
AHS2 FWD (Two mode w/ FGs)
EGMC2
MCOUTCL1
CL2
CL3EGMC2
MCOUTCB12R
C234
CB4
C13
Two Mode w/o FGSingle Mode
P7,220,203 : 2 Electric Motors 2 Planetary Gear Sets (SPPG, DPPG) 4 Wet-Plate Clutches
P6,478,705 : 2 Electric Motors 2 Planetary Gear Sets (only SPPG) 2 Wet-Plate Clutches
AHS2 RWD (Two mode w/ FGs) Three & Four Mode w/ FGs
P6,953,409 : 2 Electric Motors 3 Planetary Gear Sets (only SPPG) 4 Wet-Plate Clutches
P7,645,206 : 2 Electric Motors 3 Planetary Gear Sets (SPPG, DPPG) 5 Wet-Plate Clutches
PRIUS : 2 Electric Motors 1 Planetary Gear Set (SPPG) no Wet-Plate Clutches
EGMC2 MC
OUT
78 30
S C R
EGMC2
MCOUTCL2
CL1S1 C1 R1
R2 C2 S2
AHS = Advanced Hybrid System (GM 2 Mode)
Single Mode w/ RG
ESCAPE : 2 Electric Motors 2 Planetary Gear Set (SPPG) no Wet-Plate Clutches
Argonne National Laboratory - Tradeoff Between Power-train Complexity and Fuel Efficiency
Modeled Different Transmissions
7
Gear System
::
Note : Transmission models developed in SimDriveline to allow for modeling of detailed losses (Transmission spin loss, Hydraulic oil loss). Low level control developed for each transmission
Local control
Plant
Argonne National Laboratory - Tradeoff Between Power-train Complexity and Fuel Efficiency
Using Argonne Powertrain System Analysis Toolkit : - forward-looking powertrain simulation environment- dynamic plant models- Matlab/Simulink/Stateflow Based
Multi Mode Leads to Smaller Component Sizes
8
Single Mode
Single Mode w/ RD
Two Modew/o FGs AHS FWD AHS RWD Three Mode Four Mode
Engine 131.5 kW 131.1 kW 125.3 kW 124.8 kW 125.3 kW 123.3 kW 123.3 kW
Motor 2 (F) 91.7 kW 80.9 kW 62.6 kW 58.1 kW 62.6 kW 61.6 kW 61.6 kW
Motor 1 (R) 91.2 kW 88.2 kW 52.4 kW 47.2 kW 52.2 kW 32.6 kW 32.6 kW
Battery NIMH, 173 cells, 1.2 volt/cell, 6
Ah
NIMH, 180 cells, 1.2 volt/cell, 6
Ah
NIMH, 170 cells, 1.2 volt/cell, 6
Ah
NIMH, 170 cells, 1.2 volt/cell, 6
Ah
NIMH, 171 cells, 1.2 volt/cell, 6
Ah
NIMH, 157 cells, 1.2 volt/cell, 6
Ah
NIMH, 157 cells, 1.2 volt/cell, 6
Ah
PC Converter Efficiency 95 % 95 % 95 % 95 % 95 % 95 % 95 %
Electrical Accessory 200 W 200 W 200 W 200 W 200 W 200 W 200 W
PGs Ratio (Zr/Zs) 2.6 2.4, 2.0 1.5, 1.5 2.36, 2.24 1.93, 1.97, 2.69
2.0, 2.0, 2.3 -
Final Drive 4.11 4.11 3.02 3.02 3.02 3.02 3.02
Wheel Radius 0.3423 m 0.3423 m 0.3423 m 0.3423 m 0.3423 m 0.3423 m 0.3423 m
Drag Coefficient 0.37 0.37 0.37 0.37 0.37 0.37 0.37
Vehicle Mass 1953 kg 1940 kg 1883 kg 1875 kg 1883 kg 1857 kg 1857 kg
Note : Baseline Vehicle Specifications : Small-size 2WD SUV Sizing results from grade(13% @ 65mph) and acceleration constraint (7.8 sec) Multi-Mode mode allows smaller electric machines
'Single' 'Single w/ RG''Two w/o FG' 'AHS2 FWD' 'AHS2 RWD' 'Three' 'Four'0
20
40
60
80
100
120
140Component Sizing
Pow
er, k
W
Mode
EngineMotor(2)Motor(1)
88.2%96.7%
95.3%100%
100%
100%
94.9% 95.3% 93.8% 93.8%99.7%
68.3%
57.5%63.4%
51.8%
68.3%
57.2%
67.2%
35.7%
67.2%
35.7%
Vehicle Level Controls All Developed Using the Same Control Philosophy
9
Controller objective: Find the power split between mechanical components (ICE, MC2, MC1) that meets the driver request for the current speed of the vehicle, while maintaining acceptable battery SOC and minimal fuel consumption
Controller has to decide on engine ON/OFF, mode and 2 other degrees of freedom
The SOC correction and engine ON/OFF conditions are properly defined.
Mode selection rule is defined by maps which are computed in an offline optimization code to find the optimal engine speed and torque.
Note: Basic control concepts/constraints provided by the validation works
0 20 40 60 80 100 120 140 1600
200
400
600
800
1000
1200
1400Mode Shift Map
Vehicle Speed, mph
GB
Tor
que
Out
, Nm
EVT1EVT2EVT3FG1FG2FG3
(a)
0 20 40 60 80 100 120 140 1600
100
200
300
400
500Mode Shift Map
Vehicle Speed, mph
Eng
Spee
d O
ut, r
ad/s
ec
EVT1EVT2EVT3FG1FG2FG3
FG3
FG2FG1
(b)
Convert into the map using vehicle and engine speeds indexes
Fuel Economy Summary
10
AHS2 FWD system provides the highest fuel economy for the vehicle application considered on the small-size SUV specification.
UDDS HWFET NEDC LA92 US0620
25
30
35
40
45
50Fuel Economy Summary
Fuel
Eco
nom
y, m
pg
Single ModeSingle Mode w/ RGTwo Mode(1) w/o FGAHS2 FWDAHS2 RWDThree ModeFour Mode
15 20 25 30 35 40 45 5032
34
36
38
40
42
44
46
48
50
Average Speed, mile/h
Fuel
Eco
nom
y, m
pg
Cycle Statistics vs. FE
Single ModeSingle Mode w/ RGTwo Mode(1) w/o FGAHS2 FWDAHS2 RWDThree ModeFour Mode
0.2 0.3 0.4 0.5 0.6 0.725
30
35
40
45
50
Average Acceleration, m/s2
Fuel
Eco
nom
y, m
pg
Cycle Statistics vs. FE
Single ModeSingle Mode w/ RGTwo Mode(1) w/o FGAHS2 FWDAHS2 RWDThree ModeFour Mode
Component Average Efficiency (%) Single mode has the highest transmission efficiency
11
HWFET Single Mode
SM w/ RG
Two Mode (1)
AHS 2FWD
AHS2 RWD
Three Mode
Four Mode
Engine average Bidirectional efficiency 33.77 33.71 33.53 31.61 30.55 30.70 30.60
Motor #1 average Bidirectional efficiency 91.40 89.94 86.09 86.58 87.15 87.01 87.03
Motor #2 average Bidirectional efficiency 86.51 86.47 86.67 86.61 86.62 85.35 85.44
Transmission average Bidirectional efficiency 93.84 93.42 88.85 89.04 88.89 90.21 90.25
Powertrain Efficiency - Bidirectional 25.94 26.00 26.94 26.73 25.83 26.51 26.47
UDDS Single Mode
SM w/ RG
Two Mode (1)
AHS2 FWD
AHS2 RWD
Three Mode
Four Mode
Engine average Bidirectional efficiency, 33.32 33.37 33.05 30.89 31.09 31.94 32.02
Motor #1 average Bidirectional efficiency 86.96 87.49 86.05 86.54 86.74 86.36 86.39
Motor #2 average Bidirectional efficiency 86.17 86.13 85.95 85.99 86.02 86.68 86.86
Transmission average Bidirectional efficiency 96.12 96.39 92.85 90.48 89.54 89.11 88.70
Powertrain Efficiency - Bidirectional 33.46 33.61 33..20 31.62 30.89 30.61 30.09
Note : Transmission eff. refers only to mechanicals including final reduction gearset eff.
Single Mode
Single Mode w/ RG
Two Mode (1)
AHS2 FWD
AHS2 RWD
Three Mode
Four Mode
Single Mode
Single Mode w/ RG
Two Mode (1)
AHS2 FWD
AHS2 RWD
Three Mode
Four Mode
The energy loss results of the transmission under UDDS and HWFET
Argonne National Laboratory - Tradeoff Between Power-train Complexity and Fuel Efficiency
Impact of Powertrain on Operation
12
0 10 20 30 40 50 600
50
100
150
200
Vehicle Speed, mph
Engi
ne S
peed
, rad
/s
UDDS - Operating points (HEV and propelling)
M.P.
0 10 20 30 40 50 600
50
100
150
200
250
Vehicle Speed, mph
Engi
ne S
peed
, rad
/s
UDDS - Operating points (HEV and propelling)
M.P.1M.P.2FG1FG2FG3FG4EVT1EVT2FG2FG3FG4
0 10 20 30 40 50 600
50
100
150
200
250
Vehicle Speed, mph
Engi
ne S
peed
, rad
/s
UDDS - Operating points (HEV and propelling)
M.P.1M.P.2M.P.3FG1FG2FG3EVT1EVT2EVT3FG2FG3Mechanical Points Line
(SR=0.7222)
FG2 (MP1)
FG3
FG4(MP2)
FG1 FG1(MP1)
FG3(MP3)
FG2(MP2)
AHS2 FWD
Single-mode
Three-mode
0 10 20 30 40 50 600
50
100
150
Vehicle Speed, mph
Engi
ne S
peed
, rad
/s
HWFET - Operating points (HEV and propelling)
M.P.
0 10 20 30 40 50 600
50
100
150
200
Vehicle Speed, mph
Engi
ne S
peed
, rad
/s
HWFET - Operating points (HEV and propelling)
M.P.1M.P.2FG1FG2FG3FG4EVT1EVT2FG3FG4
0 10 20 30 40 50 600
50
100
150
200
Vehicle Speed, mphEn
gine
Spe
ed, r
ad/s
HWFET - Operating points (HEV and propelling)
M.P.1M.P.2M.P.3FG1FG2FG3EVT1EVT2EVT3FG2FG3
FG2 (MP1)
FG3
FG4(MP2)
MPFG3
(MP3)
FG2(MP2)
AHS2 FWDSingle-mode Three-mode
UDDS :
HWFET :
0 0.5 1 1.5 2 2.5-2
-1.5
-1
-0.5
0
0.5
1
1.5
SR, the ratio of W-eng to W-out
Pw
r R
atio
The ratio P-elect to P-eng, Single Mode EVTConstant Engine Torque and Engine Speed (@ W-eng=1500rpm, T-eng=120Nm)
EVT1
0 0.5 1 1.5 2 2.5
0.65
0.7
0.75
0.8
0.85
0.9
0.95
1
SR, the ratio of W-eng to W-out
Eff
.
Efficiency
EVT1
“Electro-Mechanical” Power
“All-Mechanical” Power
“Mechanical Point”ratio :0.72
“All-Input” Power
Single Mode Single Mode
Single mode system has relatively lower system efficiency in primary operating region As transmission reaches higher overdrive, electro-mechanical power increases sharply.
Conclusion
13
Argonne National Laboratory - Tradeoff Between Power-train Complexity and Fuel Efficiency
The fuel efficiency potential of several multimode systems (1 to 4 modes) has been defined.
Detailed transmission models, including spin losses and hydraulic oil losses have been developed along with their low level controllers.
Vehicle level control strategies have been defined for several multi-mode systems.
For the small SUV application considered, the results show impact on component sizing and component operating conditions.
Multi-mode system has more fuel economy advantage during high speed cycle. When the cycle is more aggressive, multi-mode with FG has advantage.
Future work will focus on:
- Additional vehicle classes (e.g., compact, midsize car, midsize SUV…)
- Take into account additional Vehicle Technical Specifications (i.e., towing, passing…)
- Other configurations options (e.g., for series, compare series vs. GM Volt…)
Tradeoff Between Powertrain Complexity and Fuel Efficiency
Contact / Website
Namdoo Kim, nkim@anl.gov
Aymeric Rousseau, arousseau@anl.gov
http://www.autonomie.net/
Argonne National Laboratory, 9700 South Cass, Argonne IL 60439, USA
Acknowledgements
Activity sponsored by Lee Slezak from the U.S. Department of Energy
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