Copyright NSK Ltd. All Rights Reserved
Traction Drive Speed Reducer for
high speed traction motor
International Automotive Congress 2019
APTT-02-19543
Dec. 4 , 2019
AUTOMOTIVE BUSINESS DIVISION HQ.
AUTOMOTIVE Technology Development Ctr.
2Copyright NSK Ltd. All Rights Reserved Speedy Open Creative No. APTT-02-19543
Agenda
1. Outline of NSK’s activity for EV drive system
2. Traction Drive Speed Reducer
Traction drive technology overview
High speed capability / efficiency / quietness
3. Summary
3Copyright NSK Ltd. All Rights Reserved Speedy Open Creative No. APTT-02-19543
1. Outline of NSK’s activity for EV drive system
2. Traction Drive Speed Reducer
Traction drive technology overview
High speed capability / efficiency / quietness
3. Summary
4Copyright NSK Ltd. All Rights Reserved Speedy Open Creative No. APTT-02-19543
1-1. NSK’s future vision for EV
Ball screw for e-brake booster
Key components for eAxle
Steer by wire
Parallel Link Active SuspensionWheel Hub motor
Electrification of “Driving”, “Steering” & “Braking”
Braking
Driving Steering
Steering
Driving
Traction DriveSpeed Reducer
TorqueSensor
Power Flow Switching Device
(Electric shift actuator)
C : Connected
A : Autonomous
S : Shared & services
E : Electrification
NSK’s future vision for EV
Focus on “Autonomous” and “Electrification”
Today’s topic
5Copyright NSK Ltd. All Rights Reserved Speedy Open Creative No. APTT-02-19543
1-2. NSK’s development for EV drive system
InverterBatteryInfrastructure
3 core items of EV
Highly efficient
operation of e-motor
Motor loss
reduction
Running resistance
reduction
Regenerative efficiency
improvement
Increase cruising range Minimize electric power consumption
Increase power
density
Weight
reduction
New solution for eAxle
system and components
Friction
reduction
Continuous improvement
of bearing performance
NSK’s development for EV drive system
Low
NVH
eAxle
Improvement
of quietness
Improvement
of driving
performance
e-motorGearbox
EV xxx V
6Copyright NSK Ltd. All Rights Reserved Speedy Open Creative No. APTT-02-19543
1-3. Highlighted technical trends of eAxle
Current : Gearbox with fixed reduction ratio
Near future : 15,000 ~ 20,000rpm
Current : 10,000 ~ 13,000rpm
Future : 15,000 ~ 30,000rpm
18,000rpm 21,000rpm18,000rpm17,000rpm 20,000rpm
10,500rpm 11,400rpm 12,000rpm 13,500rpm
?
2X,000rpm
?
X0,000rpm
・・・
Near future ~ : Gearbox Gearbox or transmission
2spd.
Development of high speed e-motor up to 30,000rpm
is increasing to improve the power density
(Downsizing & weight reduction)
Development of multiple speed transmission
(Mainly 2-speed) is increasing to improve the driving
performance and cruising range
2spd.
2spd.2spd.
2spd.
2spd. 2spd.
B-CVT
30,000rpm
Speed increase of e-motor Replace gearbox with transmission
Focus on the development for speed increase of e-motor and 2-speed transmission
7Copyright NSK Ltd. All Rights Reserved Speedy Open Creative No. APTT-02-19543
1-4. NSK’s development for eAxle
High speed e-motor up to 30,000rpm
for improving the power density (Downsizing & weight reduction)
Multiple speed transmission (Mainly 2-speed)
for improving driving performance and cruising range
TDSR** Traction Drive Speed Reducer
(Speed reducer for
ultra-high speed e-motor)
Ultra-high
speed e-motor
Overall
Volume
-30%
Conventional e-motor
Downsizing of packaging with TDSR and ultra-high
speed e-motor
Power transmission with low NVH by traction drive
2-speed transmission(Large gear step ratio)
Friction plates
(Brake and clutch)
PFSD*
* Power Flow Switching Device
High-functional electric
shift actuator
Seamless shifting at large gear step by torque feedback
control with Torque Sensor
Shift actuation of clutches only with 1-small e-motor by PFSD
・Installable to the powertrain
・None contact sensing
・Small size
Torque
Sensor
Downsized eAxle with TDSR 2-speed eAxle with Torque Sensor & PFSD
NSK’s development
Speed increase of e-motor Replace gearbox with transmission
Traction drive
Power transmission by shear force of
traction oil film between 2 elements,
which solidifies under high pressure
Drive roller Driven roller
Tangential force
Clamping
force
Oil film
8Copyright NSK Ltd. All Rights Reserved Speedy Open Creative No. APTT-02-19543
1. Outline of NSK’s activity for EV drive system
2. Traction Drive Speed Reducer
Traction drive technology overview
High speed capability / efficiency / quietness
3. Summary
9Copyright NSK Ltd. All Rights Reserved Speedy Open Creative No. APTT-02-19543
2-1. Traction drive overview : Principle & application
Generator
●Application 2
Kawasaki Heavy Industries,Ltd.
T-IDG®
(Toroidal CVT)
●Application 1
Nissan Motor Co.,Ltd
EXTROID-CVT ®
(Toroidal CVT)
Drive roller Driven roller
Thin oil film
thickness is 1 μm
Tangential force for
transmitting torqueFt = μt・Fc
μt ; Traction coefficient
Fc ; Clamping forceCreep : Cr
Thin oil film
Tangential force:Ft
Drive roller
Driven roller
Clamping force : Fc
・Power is transmitted by shear force of oil film between 2 rollers
・Key technology on traction oil which behaves as solid material
under high pressure
PrincipleTraction drive
ApplicationTraction drive
10Copyright NSK Ltd. All Rights Reserved Speedy Open Creative No. APTT-02-19543
2-2. Reliability in automotive market
Traction oil durability
×104
0.000
0.050
0.100
0 4 8 12 16
Mileage ,km
Tra
ctio
n c
oef
fici
ent
at
12
0o
C
●: Fleet
◇: Bench80,120, 140oC
Pressure (Pmax)
Velocity
Oil Temp.
1.24 GPa
6.8 m/s
5.0%Slip Ratio
80,120, 140oC
Pressure (Pmax)
Velocity
Oil Temp.
1.24 GPa
6.8 m/s
5.0%Slip Ratio
Driver
Driven
Traction coefficient was not changed
before and after endurance test
Traction surface durability
300:1
Magnification
1000:1
Running sectionNon-running section
Observation
area
Grinding direction Grinding
mark
Oil film in
operation
Evaluation of traction coefficient by Idemitsu Kosan Co., Ltd.
Grinding marks remained, so existence of
oil film in operation was confirmed
Traction Drive is reliable for automotive market because traction oil and traction surface keep original properties
Toroidal CVT disc after running
118,500 km in the market
11Copyright NSK Ltd. All Rights Reserved Speedy Open Creative No. APTT-02-19543
2-3. Comparison between traction drive and gear
Contact patch・Low sliding speed・Smooth and silent
Normal force
Tangential force
DriveDriven
Traction drive Gear
High speed operation +++ - - -
Sliding speed @50m/s 0.1 [m/s] 20~30 [m/s]
Quietness (NVH) +++ - - -
Vibration in meshing order No Yes
Backlash (rattle noise) No Yes
Torque capacity (vs weight) + ++
Normal force / tangential force 15~20 < 2
Clamping mechanism Required Not required
Advantage of traction drive High speed capability High quietness (Low NVH) High controllability due to backlash-less
12Copyright NSK Ltd. All Rights Reserved Speedy Open Creative No. APTT-02-19543
2-4. High speed capability
Fluid temp ; 100degC
Operating zone
Traction curve
Traction drive characteristic (traction curve)
Sliding speed at operating condition is quitelow (approx. 0.2% of creep ratio)
Traction drive characteristics under operating condition are almost unaffected by tangential speedIt keeps similar property as 10m/s even in 70m/s
Traction drive device is able to operate under high speed condition keeping high performance
13Copyright NSK Ltd. All Rights Reserved Speedy Open Creative No. APTT-02-19543
2-5. Traction Drive Speed Reducer : structure & power flow
Specification
The pinion rollers are
held with the flexibility
on radial direction
Generation of clamping force linear to transmission torque
Optimum clamping force achieved with less creep and
frictional loss
Generation of clamping forceStructure of Traction Drive Speed Reducer
• Maximum input rotation speed : 32,000 [rpm]
• Capacity of transmit power : 125 [kW]• Reduction ratio : 4.0
• Weight of main components : 10 kg
Pinion roller
Carrier
Loading cam
Ring roller(Low speed side)
Sun roller(High speed side)
Input
Output
Fixed
Power pathways
Fa : Clamping force
T : Force by torque
θ : Cam angle
𝑭𝒂 = 𝑻/ 𝐭𝐚𝐧𝜽
14Copyright NSK Ltd. All Rights Reserved Speedy Open Creative No. APTT-02-19543
2-6. Efficiency
Calculated efficiency at traction surface
Latest proto (Gen.3 modified)
Current proto (Gen.3)
Target
Measurement result
Target
Beyond 97 %
Next proto (Gen.4)Further optimization for efficiency improvement
The evaluation testing is to be started at Dec. 2019
Calculation
Next proto (Gen.4)
Good correlation between
calculation and measurement result Latest proto (Gen.3 modified)
Latest proto (Modified current proto)
Partially achieved the target efficiency (96% 98.5% )**
** Achieve full range with next proto
15Copyright NSK Ltd. All Rights Reserved Speedy Open Creative No. APTT-02-19543
Gen.4 Gen.3
Output Side
Carrier(Fixed)Loading Cam(Torque-sensitive
clamping mechanism)
Sun Roller
(High speed side)
Pinion Roller
Ring Roller
(Low speed side)
Power 150kwMax torque 130Nm / Max rotation speed 30,000rpmReduction ratio 5.0 / Weight 9.3kg
Gen.4 prototype
2-7. Next prototype Gen.4
Contact
profile
optimization
16Copyright NSK Ltd. All Rights Reserved Speedy Open Creative No. APTT-02-19543
1st meshing order
2nd meshing order
Planetary gear
TDSR
2-9. Quietness
Traction Drive Speed Reducer
(TDSR)
NVH comparison test between
planetary gear and TDSR (Proceeding)
Planetary gear
Verification test Initial testing result (Vibration comparison)
Input torque :
20 Nm
Acceleration pick-up
(Side of test-box)
Input speed :
7500 rpm
Sun roller rotating speed [rpm]
Vib
ration [
m/s
2]
Order [-]
Even at rotation speeds less than 10,000rpm,
significant reduction in vibration was observed
Vib
ration [
m/s
2r]
Acceleration pick-up
(Side of test-box) Planetary gear
TDSR
17Copyright NSK Ltd. All Rights Reserved Speedy Open Creative No. APTT-02-19543
Inverter
E-motor
Φ200
14
0
Volume = 14.8 L
140
296
175
Volume=9.54L(1.64 + 7.90 L)
・110kw
・320Nm
・10,500rpm
StatorStator
Φ200
Φ252
Φ210
Φ156
Φ150
・150kw
・130Nm
・30,000rpm
TDSR
Even with higher power, 36% downsizing of e-motor incl. TDSR could be achieved
36% Down
22886
TDSRe-motor
NSK TDSR + Ultra-high speed e-motorConventional e-motor
2-10. NSK’s downsizing assumption
18Copyright NSK Ltd. All Rights Reserved Speedy Open Creative No. APTT-02-19543
2-11. Proposal : Installation of Traction Drive Speed Reducer to eAxle
Vehicle
performance
20,000rpm or higher
NSK eAxle concept with TDSR
Reduction ratio
= 16.0 (Overall)
Superior
quietness
2 lay
axes*2
Improved
power density
of e-motor*1
Current eAxle
e-motor
eAxle
system
Calculation base
Vehicle segment : C
Vehicle weight : 1,600 kg
Wheel radius : 0.34 m
e-motor : 150 kW
Downsized
system *1,*2
13,000rpm
Vehicle speed
Drive
(w
he
el) t
orq
ue
Reduction ratio
= 10.5 (Overall)
3 lay
axes
160
km/h
Acceleration
(0.65G)
3,450Nm
Traction Drive
Speed Reducer
Reduction ratio
of TDSR= 5.0
Vehicle speed
Drive
(w
he
el) t
orq
ue
160
km/h
Acceleration
(0.65G)
3,450Nm
19Copyright NSK Ltd. All Rights Reserved Speedy Open Creative No. APTT-02-19543
1. Outline of NSK’s activity for EV drive system
2. Traction Drive Speed Reducer
Traction drive technology overview
High speed capability / efficiency / quietness
3. Summary
20Copyright NSK Ltd. All Rights Reserved Speedy Open Creative No. APTT-02-19543
3. Summary
• Traction Drive Speed Reducer (TDSR) enables power transmission with higher reliability
and quietness under extremely high speed operation like 20000rpm or higher.
• High-speed traction motor equipped with TDSR is expected to be approximately 30-40%
smaller and lighter than conventional traction motor.
• Gen.3 TDSR partially achieved 98.5% of efficiency and Gen.4 TDSR with further
improvement is expected to achieve full range by end of 2019.
Traction Drive Speed Reducer
21Copyright NSK Ltd. All Rights Reserved Speedy Open Creative No. APTT-02-19543
Seamless 2-speed eAxle concept : Technical specification
Technical specification
Max. e-motor power 150 kW
Max. e-motor torque 130 Nm
Max. e-motor speed 30,000 min-1
Reduction ratio of
traction drive speed reducer5.0
Reduction ratio of
2-speed transmission
Low: 2.5
High: 1.0
Max. drive torque 4,000 Nm
Max. vehicle speed 250 km/h
Traction Drive Speed
Reducer
22Copyright NSK Ltd. All Rights Reserved Speedy Open Creative No. APTT-02-19543
Thank you for your attention.