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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 60 0 0.5 1 1.5 Time [s] Power [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 60 0 200 400 600 800 1000 Time (s) Hydraulic Pressure in Accumulator (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 60 0 0.5 1 1.5 2 2.5 time (s) Volume of Hydraulic Fluid in Accumulator (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 60 0 5 10 15 20 25 30 Time [s] Energy [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 = = ∗ = ∗ Relevant Equations 0 2 4 6 8 10 12 14 0 5 10 15 20 Time [s] Velocity [mph] Comparison of Theoretical and Empirical Speed Tests Theoretical based on Discharge Maximum System Velocity Testing 0 5 10 15 20 25 30 35 40 200 400 600 800 1000 Time [s] Pressure [psi] Comparison of Theoretical and Empirical Pressure Discharge Theoretical Pressure Discharge Testing 0 2 4 6 8 10 12 14 0 1000 2000 3000 4000 5000 Time [s] Energy [J] Energy Behavior Potential Energy Kinetic Energy Work 400 500 600 700 800 900 1000 0 5 10 15 20 25 Pressure [psi] Velocity [mph] Empirical Velocity and Pressure Theoretical Based on Discharge Theoretical Maximum System Velocity Testing Validation = ∗ ∗ + + = 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

2012 Hydraulic Drivetrain and Regenerative Braking · Hydraulic Drivetrain and Regenerative Braking Team 13: Andrew Brown, ... System Description Our project and subsequent analysis,

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Page 1: 2012 Hydraulic Drivetrain and Regenerative Braking · Hydraulic Drivetrain and Regenerative Braking Team 13: Andrew Brown, ... System Description Our project and subsequent analysis,

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