hybrid car transmission
TRANSCRIPT
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A Simple Mechanical Transmission
System For Hybrid Vehicles
Incorporating A Flywheel
Ulises Diego-Ayala, Pablo Martinez-Gonzalez, Keith Pullen
Monday, 08 December 2008
1
Speaker: Pablo Martinez-Gonzalez
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Outline
1. Introduction
1. Transport Emissions
2. The ever-expanding global vehicle fleet2. Flywheel Technology
1. Comparison of Energy Storage Technologies
2. Flywheels in Hybrid Vehicles
3. The Mechanical Hybrid Transmission
1. The Mechanical Hybrid Transmission
2. The CVT-brake Hybrid Transmission
3. Operating Modes of the Mechanical Hybrid Powertrain
4. Simulations
1. Control Strategy
2. Vehicle and Hybrid System Specification
3. Driving Schedules4. Results
5. Summary
5. Future Work
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Transport Emissions
There is consensus among the scientific community that observed increases in global average
temperatures over the past decades were caused mostly by greenhouse emissions from human
related-activities.
Significant reductions in GHG emissions are required to mitigate the effects of climate change.
3
Power & heat
39%
Industry
16%
12% Services, etc
7%
Road
84.1%
Air
13.6%
Inland
Navigation
1.5%Rail
0.7%
Transport
26%
Total emissions, 2004Transport emissions, 2004
Households12%
Industry16%
Power &Heat 39%
Services,etc 7%
Households12%
Road83%
Rail1%
Inlandnavigation
2%
Air14%
Share of EU25 emissions by sector for year 2006
Prepared with data from the European Directorate-General for Energy and Transport
The European Parliament has promised to introduce binding legislation to limit CO2emissions for the average new car fleet to 120 g CO2/km by 2012.
These limits are deemed unfeasible by European automobile manufacturers with
current technology.
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The ever-expanding global vehicle fleet
The global vehicle fleet will continue to expand, fuelled primarily by
increased accessibility in developing countries.
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Global sales forecast for ultra-low cost vehicles
Source: A.T.Kearney
Hybrid vehicles have shown some of
the most promising advances on fuel
economy and emissions mitigation.They deliver higher fuel economy and
lower emissions than conventional
vehicles by employing regenerative
braking, by a more efficient use of the
Internal Combustion Engine (ICE),
and by shutting off the ICE when it isnot required (i.e. vehicle at rest).
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Comparison of Energy Storage Technologies
Comparison of specific energies and power of various energy storage technologies
From: O. Briat et al, Principle, design and experimental validation of a flywheel-battery
hybrid source for heavy-duty electric vehicles 5
The power density of flywheels is considerably higher than for batteries, being only
constrained by torque limitations of the transmission system.
High power density means that a much higher fraction of braking energy can be regenerated,
and that high rates of acceleration are possible.
Power density is independent of state
of charge and ambient conditions and
does not deteriorate with time.
Energy density is comparable to that ofbatteries for short-term storage, but it
is time-dependant.
Flywheels must be kept spinning in a
vacuum in order to minimise
aerodynamic losses.
Flywheels are constructed with inert
materials of easy after-life disposal.
103
102
101
100
10-1
10-2
101 102 103 104 105 106 107
Specific power, W/kg
Specificenergy,
Wh/kg
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Flywheels in Hybrid Vehicles
Hybrid Electric Vehicles (HEVs), store energy in an on-board bank of
batteries and must undergo the energy transformation: kinetic(car)-
electric(generator)-chemical(battery)-electrical(motor)-kinetic(car), with the
associated efficiency penalties.
In a hybrid powertrain with a flywheel and a mechanical transmission, the
energy transfer is solely mechanical and there is thus no energy conversionpenalties.
The power and energy capabilities of flywheels makes them better suited to
deal with the power surges of regenerative braking and acceleration rather
than as primary energy storage devices.
Flywheels can be integrated into conventional or electrical vehicles.
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The Mechanical Hybrid Transmission
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Bolt-in system. The hybrid system can be
integrated in parallel to a conventional
powertrain.
Power flow is directed through a planetary
gear set (PGS), which acts as a
continuously variable transmission (CVT),
providing a wide range of speed ratios.
Control of energy flow (whether the
flywheel is being charged or delivering
power) is accomplished by applying a
torque at the ring of the PGS.
Using a brake to control the torque at the
ring gear wastes energy though, and itsoperation is limited to reducing the speed
of the ring gear. The systems has thus a
limited operability.
The brake-only mechanical-flywheel transmission
Power flow at the PGS during Regenerative Braking
Flywheel
Planetarygearset
Frictionalbrake
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The CVT-brake Hybrid Transmission
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The CVT Mechanical-Flywheel Hybrid Transmission
Adding a CVT between the carrier and ring
branches of the PGS provides an additional
control system.
The CVT transmits power to and from the
ring of the PGS, and it is able to brake or
accelerate the ring gear.
The CVT is used when possible todecelerate the ring gear, greatly reducing
the use of the frictional brake and the losses
at the ring gear.
FlywFlywFlywheel
Planetarygearset
Frictionalbrake
CVT
Clutch
The operation of the hybrid system is also extended as the CVT is also capable of
accelerating the ring gear.
However under certain conditions the CVT must be disconnected to avoid recirculation
of power.
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Vehicles speed
Flywheels speed
a) Neutral with vehicle stationary9
t
FlywheelFlywheel
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Vehicles speed
Flywheels speed
t
FlywheelFlywheel
b) Flywheel Assisted Acceleration with clutch slipping
Clutch slipping
CVT at
minimumratio
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Vehicles speed
Flywheels speed
t
FlywheelFlywheel
c) Flywheel Assisted Acceleration with CVT
CVT
increasingratio
Clutch engaged
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Vehicles speed
Flywheels speed
t
FlywheelFlywheel
d) Flywheel Assisted Acceleration with brake at ring
Ring gear deceleratedby brake
CVT at
maximumratio
Clutch disengaged
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Vehicles speed
Flywheels speed
t
FlywheelFlywheel
e) Neutral with vehicle being accelerated by engine or braked byconventional brakes
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Vehicles speed
Flywheels speed
t
FlywheelFlywheel
f) Regenerative Braking with brake at ring
Ring gear deceleratedby brake
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Vehicles speed
Flywheels speed
t
FlywheelFlywheel
g) Regenerative Braking with clutch slipping
Clutch Slipping
CVT at
maximumratio
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Vehicles speed
Flywheels speed
t
FlywheelFlywheel
h) Regenerative Braking with CVT
CVT
decreasingratio
Clutch engaged
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Simulations
A computational model of the mechanical energy storage system was developed inMatlab/Simulink and validated using experimental data. This model was then integrated
into ADVISOR.
This program was validated experimentally (see article below for details1)
To assess the performance of the mechanical energy storage system, simulations were
carried out on a conventional and a mechanical hybrid vehicle.
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1. Diego-Ayala, U, P Martinez-Gonzalez, N McGlashan, and K R Pullen. The mechanical hybrid vehicle: an investigation of aflywheel-based vehicular regenerative energy capture system. Proceedings of the Institution of Mechanical Engineers, PartD: Journal of Automobile Engineering 222, no. 11 (November 1, 2008
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Control Strategy
All the braking is provided by the regenerative system, which transfers the available
energy into the flywheel.
When the vehicle requires power, it is first provided by the flywheel reservoir.
The ICE is turned off when not in use (at rest, when braking and when the vehicle is
propelled by the energy reservoir).
The flywheel is only allowed to charge up to a maximum safety speed, and can only
assist in acceleration between a minimum and an operating speed.
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The simple control strategy employed for the hybrid powertrain works on the following
premises:
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Vehicle and Hybrid System Specification
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The vehicle chosen for the simulations
was a Ford Focus Estate with a 1.8 turbo
diesel engine with specifications:
Hybrid System Specification
Parameter Value
Additional weight due to hybrid system (kg) 100
Flywheel inertia (kgm2) 0.11
Value of constantA for double PGS (-) 0.978
Maximum CVT ratio (-) 2.5
Minimum CVT ratio(-) 0.4
Flywheel min. speed (rad/s) 900
Flywheel operating speed (rad/s) 1100
Flywheel max. speed (rad/s) 2500
Vehicle Specification
Parameter Value
Total vehicle weight (kg) 1511
Frontal area (m2) 2.06
Radius of wheels (cm) 28.2
Rolling friction coefficient (--) 0.009
Aerodynamic drag coefficient (--) 0.312
Maximum Engine power (kW) 65 @ 4400rpm
The main specification for
the hybrid system are:
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Driving Schedules
The driving schedules used are all city cycles.
They present ample opportunities for the hybrid system to
store braking energy and to reuse it to propel the vehicle.
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Time [s]Urban Artemis Driving Schedule
0 200 400 600 800 1000
70
60
50
40
30
20
10
0
Vel[kph]
100
80
60
40
20
0
0 500 1000 1500Time [s]
Urban Dynamometer Drive Schedule
Vel[k
ph]
18
15
12
9
6
3
00 1000 2000 3000
Time [s]Indian Urban Drive Cycle
Vel[kph]
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Results
Results suggest that an important amount of the fuel economy gains derives
from tuning off the engine when the hybrid system is in operation.
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Performance of the CVT-brake hybrid vehicles following the Artemis-urban cycle. The
continuous thin black line at the top, illustrates engine operation (Engine on or off); while the
dashed thin black lines refer to flywheel maximum [upper], minimum operating and minimum
[lower] speeds of the flywheel
75
60
45
30
15
0
3000
2500
2000
1500
1000
500
00 200 400 600 800 1000
Time [s]
Flywheelspeed[rad/s]V
ehiclespeed[
km/h]
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Results
Despite carrying more weight, the use of the hybrid system resulted in improvements in
fuel economy and reductions in emissions for all the drive cycles.
The results suggest that an important amount of the fuel economy gains stem from tuning
off the engine when the hybrid system is in operation.
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UDDS ARTEMIS INDIAN
Conv MHV Conv MHV Conv MHV
Distance travelled (km) 12 12 4.9 4.9 17.6 17.6
Total Time (s) 1368 1368 993 993 2668 2668
Energy to accelerate vehicle (MJ/km) 0.43 0.46 0.6 0.66 0.39 0.42
Energy to decelerate vehicle (MJ/km) 0.19 0.2 0.39 0.4 0.19 0.2
Energy from fuel (MJ/km) 2.27 2.05 3.66 2.91 2.29 1.98
Overall efficiency vehicle (--) 0.19 0.22 0.16 0.23 0.17 0.21
Fuel economy (mpg) 44.9 49.9 28 35.2 44.7 51.6
Improvement in Fuel economy - 11% - 26% - 15%
Emissions CO2 (gr/km)1 166 149 266 212 166 144
Reductions in CO2 emissions - -10% - -20% - -13%
Time Engine on 100% 73% 100% 60% 100% 67%
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Summary
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A mechanical transmission system for hybrid vehicles incorporating a
flywheel has been proposed.
A computational model of a hybrid vehicle was developed in advisor and
validated experimentally.
Results show that under city driving savings of up to 20% can be obtained for
the system presented.
There is ample opportunity for further improvements in transmission efficiency
and operability of the system by using different powertrain configurations and
control strategies.
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Future Work
An improved version of the experimental test bed is being built a City University in
collaboration with Imperial College researchers.
This rig will be used to test different configurations of the mechanical hybrid powertrain
under various driving cycles and conditions, including the effect of road gradients.
EVT in Barcelona, Spain is currently developing a novel
type of CVT.
This transmission is based on planetary systems,
transmitting 92% of total power via mechanical means. This improves transmission efficiency while having a CVT
performance.
A transmission based on this novel CVT can also be used
for hybrid vehicles.
The rig will also be used to test a
powertrain with a hydraulic control
system intended to be used in trains.
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Questions
Thank you!