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Hydraulic Drivetrain and Regenerative Braking Team 13: Andrew Brown, Karan Desai, Andrew McGrath, Hurst Nuckols, Grant Wilson Adviser: Dr. Andrew Jackson
2012
Testing Results
Braking Efficiency (% kinetic
energy recovered) 24.73%
Drivetrain Efficiency 67.02%
Overall Efficiency 53.47%
Current Electric Hybrid
Electric Hybrid overall efficiency 75% (highway)
50.79% (city)
Sponsors
System Schematic Low Pressure
Reservior
Filter
Variable Vane Pump
Motor/Pump
Hydraulic Accumulators
Solenoid Valve
Relief Valve
Check Valve
Suction Line High Pressure Line Case Drain Line/Valve Drain Line Return/Regenerative Braking Suction Line
Since their development in 2006, hydraulic drivetrain systems
have gained considerable attention as a result of their high
efficiencies. However, due to size and weight constraints, their
application has been exclusively for large trucks and
commercial vehicles. Our senior design project investigates the
use of hydraulic drivetrains on small-scale vehicles. We have
established two main project goals: 1) to create a working
model of a hydraulic system on a go-kart, and 2) to assess the
efficiency of our hydraulic system in relation to other
mechanical and hybrid drivetrains. As with many hydraulic
drivetrain systems, our model incorporates regenerative
braking in order to further improve efficiency values. The main
components of the model include an electric motor, hydraulic
pump, hydraulic motor and two 1.5 gallon accumulators. The
present document describes the motivation, design, and
analysis of our hydraulic drivetrain system.
Abstract
0 10 20 30 40 50 600
0.5
1
1.5
Time [s]
Pow
er
[hp]
Motor Power at Full Displacement
Po = 200 psi
Po = 300 psi
Po = 400 psi
Po = 500 psi
Po = 600 psi
Po = 700 psi
0 10 20 30 40 50 600
200
400
600
800
1000
Time (s)
Hydra
ulic P
ressure
in A
ccum
ula
tor
(psi)
Hydraulic Pressure at Full Displacement
Po = 200 psi
Po = 300 psi
Po = 400 psi
Po = 500 psi
Po = 600 psi
Po = 700 psi
0 10 20 30 40 50 600
0.5
1
1.5
2
2.5
time (s)Volu
me o
f H
ydra
ulic F
luid
in A
ccum
ula
tor
(gallons)
Hydraulic Volume at Full Displacement
Po = 200 psi
Po = 300 psi
Po = 400 psi
Po = 500 psi
Po = 600 psi
Po = 700 psi
0 10 20 30 40 50 600
5
10
15
20
25
30
Time [s]
Energ
y [
kJ]
Energy at Full Displacement
Po = 200 psi
Po = 300 psi
Po = 400 psi
Po = 500 psi
Po = 600 psi
Po = 700 psi
Accumulator Simulation
𝑝𝑉𝛾 = 𝑐𝑜𝑛𝑠𝑡𝑎𝑛𝑡 𝑇 = 𝑝 ∗ 𝑑𝑖𝑠𝑝𝑙𝑎𝑐𝑒𝑚𝑒𝑛𝑡
𝑃𝑜𝑤𝑒𝑟 = 𝑇 ∗ 𝜔
Relevant Equations
0 2 4 6 8 10 12 140
5
10
15
20
Time [s]
Velo
city [
mph]
Comparison of Theoretical and Empirical Speed Tests
Theoretical based on Discharge
Maximum System Velocity
Testing
0 5 10 15 20 25 30 35 40200
400
600
800
1000
Time [s]
Pre
ssure
[psi]
Comparison of Theoretical and Empirical Pressure Discharge
Theoretical Pressure Discharge
Testing
0 2 4 6 8 10 12 140
1000
2000
3000
4000
5000
Time [s]
Energ
y [
J]
Energy Behavior
Potential Energy
Kinetic Energy
Work
400 500 600 700 800 900 10000
5
10
15
20
25
Pressure [psi]
Velo
city [
mph]
Empirical Velocity and Pressure
Theoretical Based on Discharge
Theoretical Maximum System Velocity
Testing
Validation
𝑊𝑜𝑟𝑘 = 𝐶𝑟𝑟 ∗ 𝐷𝑖𝑠𝑡𝑎𝑛𝑐𝑒 ∗ 𝐹𝑛𝑜𝑟𝑚𝑎𝑙 𝑃𝐸 + 𝐾𝐸 + 𝑊𝑜𝑟𝑘 = 𝐼𝑛𝑖𝑡𝑖𝑎𝑙 𝐸𝑛𝑒𝑟𝑔𝑦
Relevant Equations
Variable Vane Pump:
Converts rotational energy
to high pressure hydraulic
fluid flow
Variable Piston Motor/Pump:
Converts high pressure fluid flow
to rotational energy to drive
wheels; also converts kinetic of
the go-kart to high pressure fluid
flow during regenerative braking
Electric Motor: Provides
rotational energy to the
hydraulic drivetrain
Reservoir: Stores
hydraulic fluid at low
pressure
Accumulator: Stores high
pressure fluid through energy
captured from regenerative
braking as well as excess
energy produced by the engine
Decoupled Drivetrain – Unlike mechanical drivetrains, our system features no
direct mechanical linkage between the power source and the wheels. Instead,
the power source serves to charge the hydraulic accumulators. The motivation
behind this design draws from the notable efficiency losses that combustion
engines experience at non-optimal speeds. By decoupling the power source
from the wheels, the power source can be operated periodically and at its most
efficient power output, substantially reducing system losses.
Regenerative Braking – Our system incorporates a hydraulic regenerative
braking system capable of capturing 24.7% of otherwise lost kinetic energy.
The benefit to using hydraulics over electronics (batteries) for regenerative
braking is that the charge rates associated with hydraulics are not limited by the
storage device (accumulators), unlike current electronic systems.
Control System – The system is controlled by a lever to the left of the
operator that can be rotated forward or backwards. The lever controls the
swashplate angle of the variable piston motor/pump which controls the flow
direction and rate. When the user pushes the throttle button, the one-way
solenoid opens and allows flow to the hydraulic motor. The variable swashplate
allows for infinite control of the motor’s torque output. To brake and
regenerate energy, the operator must simply pull the lever backwards which
reverses the swashplate angle, reversing the flow. Reversing is achieved by
pressing the throttle button in the back position.
System Description
Our project and subsequent analysis, along with current state of the art
vehicles, show a large amount of potential for hydraulic hybrids. Given
that potential, many areas of improvement are advocated by the group:
Carbon Fiber Accumulators – Weight is at a premium on passenger
vehicles, and the heaviest component of a hydraulic hybrid is the
accumulator. Steel accumulators offer better performance currently due
to their higher maximum pressure, but an effort to make these carbon
fiber accumulators stronger would greatly improve the efficiency of the
system.
Lightweight Components – Hydraulic components are often very
heavy parts because there is often no advantage to producing lighter
ones. With results of our and other concurrent projects, it is now
obvious that engineering lightweight components could help
revolutionize the hydraulic hybrid industry.
Turbines – Turbines are capable of high efficiencies, but only in a
very narrow range of rotational speeds and loads. By powering our
system with a turbine engine, it is possible to take advantage of the
increased efficiency because the axle is decoupled from the engine in
our system.
Future Plans and Potential