Seminar2 w11 Regenerative Braking

8/3/2019 Seminar2 w11 Regenerative Braking

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SEMINAR II

REGENERATIVE BRAKING

Supervisor: Dr. Mirghani

Group Member: Zafry ZainalNik Aryadi Abdul

Nor Zaini Hashim


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INTRODUCTION

For three decades now, the second commandment of

every automotive engineerright behind reduce costhas been reduce fuel consumption. The drive touse less fossil fuel has dictated the design of engines,transmissions and control systems for decades. Now,it is pushing the development of completely different

technologies for generating power. In spite of all these truly marvelous improvements, the

energy efficiency of the most modern production car isstill less than 20 percent. Most of the energy used tomove the vehicle at any speed over any distance isliterally thrown away as heat. About half of that wastedenergy goes through the brakes. Today, almost everymanufacturer is developing ways to recover asignificant portion of that wasted energy with

regenerative braking


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WHAT IS REGENERATIVE BRAKING?

A regenerative brake is an apparatus, a device orsystem which allows a vehicle to recapture part of thekinetic energy that would otherwise be 'lost' to heatwhen braking and make use of that power either bystoring it for future use or feeding it back into a powersystem for other vehicles to use.

Regenerative braking is used on hybrid gas/electricautomobiles to recoup some of the energy lost duringstopping. This energy is saved in a storage batteryand used later to power the motor whenever the car isin electric mode.


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Regenerative braking does more than simply stop the car.Electric motors and electric generators (such as a car'salternator) are essentially two sides of the same technology.Both use magnetic fields and coiled wires, but in different

configurations. Regenerative braking systems take advantageof this duality. Whenever the electric motor of a hybrid carbegins to reverse direction, it becomes an electric generator ordynamo. This generated electricity is fed into a chemicalstorage battery and used later to power the car at city speeds.

HOW IT WORKS


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Regenerative braking takes energy normally wasted duringbraking and turns it into usable energy. It is not, however, aperpetual motion machine. Energy is still lost through frictionwith the road surface and other drains on the system. Theenergy collected during braking does not restore all the energylost during driving. It does improve energy efficiency and assistthe main alternator.

Regenerative braking is a benefit of hybrid electric vehicles,whereby some of the translational energy of the vehicle iscaptured and returned to an energy storage device when thebrake pedal is applied. This is different from conventionalbraking, in which a car is slowed through friction and the energyof the car is lost through waste heat.

The energy recaptured by regenerative braking might be storedin one of three devices: an electrochemical battery, a flywheel,or in a regenerative fuel cell.


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REGENERATIVE BRAKING AND BATTERIES

The electric motor of a car becomes a generator when the

brake pedal is applied. The kinetic energy of the car is used togenerate electricity that is then used to recharge the batteries.With this system, traditional friction brakes must also be used toensure that the car slows down as much as necessary. Thus,not all of the kinetic energy of the car can be harnessed for thebatteries because some of it is "lost" to waste heat. Someenergy is also lost to resistance as the energy travels from thewheel and axle, through the drivetrain and electric motor, andinto the battery.


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REGENERATIVE BRAKING AND FLYWHEELS

the translational energy of the vehicle is transferred intorotational energy in the flywheel, which stores the energy until itis needed to accelerate the vehicle.

The benefit of using flywheel technology is that more of theforward inertial energy of the car can be captured than in

batteries, because the flywheel can be engaged even duringrelatively short intervals of braking and acceleration.

In the case of batteries, they are not able to accept charge atthese rapid intervals, and thus more energy is lost to friction.

Another advantage of flywheel technology is that the additionalpower supplied by the flywheel during acceleration substantiallysupplements the power output of the small engine that hybridvehicles are equipped with.


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REGENERATIVE BRAKING AND FUEL CELLS

The third system uses what is known as a unitized regenerative fuel cell,

which is designed to both convert hydrogen and oxygen into energy andwater, or be reversed to take the energy from the wheels, combine it withwater, and produce hydrogen and oxygen.

The system as a single unit is substantially lighter than a separateelectrolyzer and generator, which makes this system (known as a URFC)especially beneficial when weight is a factor.

When the URFC is paired up with lightweight hydrogen storage, it's energydensity of about 450 watt-hours per kilogram is ten times that of lead-acidbatteries and twice as much as any predictions for the energy density offorthcoming chemical batteries.

This means that not only will this technology make lighter hybrids available,it will also give hybrids a driving range that is comparable to that of vehicles

today that are equipped with conventional engines. Further benefits of the URFC is that it will be more cost effective than othervehicles because it will not need to be replaced, and it will provide theadditional power needed by an electric engine when accelerating onto ahighway.


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REGENERATIVE BRAKING AND LAUNCH-

ASSIST

Some of the recovered energy is stored in a package ofultracapacitors instead of the battery pack.

The ultracapacitor is charged with regenerative braking.Voltages are as high in either direction as 300 Vdc and can flowat 100 amps continuously or 200 amps for two minutes. It canbe charged and discharged quite rapidly even in urban drivecycles, and it can withstand thousands of charge/dischargecycles with no loss of performance.

In addition to extending the charge state and overall life of thebatteries, it also allows regenerative braking even when thebatteries are fully charged. At this early point in itsdevelopment, the ultracapacitor pack is large, heavy andrequires its own cooling system. However the launch-assistidea has a lot of potential, and its not limited to electric

vehicles.


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HYDRAULIC LAUNCH ASSIST (HLA) It recovers energy normally lost during deceleration and

converts it to hydraulic pressure in an accumulator, where

it is available as a source of energy during the vehicle'snext acceleration.

A variable-displacement hydraulic pump/motor is mountedon the transfer case and clutched to the output shaft that

powers the front driveshaft.

A valve block mounted on the pump contains solenoidvalves to control the flow of hydraulic fluid. A 14-gallon,high-pressure accumulator is mounted behind the rear

axle, with an almost identical low-pressure accumulatorright behind it to store hydraulic fluid.


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When the driver presses the brake pedal, a pedalmovement sensor signals the control unit, which thenoperates solenoid valves to send hydraulic fluid from thelow-pressure reservoir to the pump. The pumping action

slows the vehicle, similar to engine compression braking,and the fluid is pumped into the high-pressure reservoir.

Releasing the brake and pressing hard on the acceleratorsignals the control unit to send that high-pressure fluid

back to the pump, which then acts as a hydraulic motorand adds torque to the driveline. The system can be usedto launch the vehicle from a stop or to add torque foraccelerating from any speed.

The real advantage of hydraulics is in its power density.Hydraulics is capable of transferring energy very quicklycompared to hybrid electric system.


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REGENERATIVE BRAKING ADVANTAGES

Provide greater fuel economy

Greater improvement in emission reduction

Energy savvy (energy conversion will be carefully controlled inthe interest of maximum efficiency)

Provide ample drive power and power for sudden acceleration.

Enhance the efficiency of the engine and the overall economyof the car.


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REGENERATIVE BRAKING DISADVANTAGES

The main disadvantage of regenerative brakes when compared

with dynamic brakes is the need to closely match the electricitygenerated with the supply. With DC supplies this requires thevoltage to be closely controlled and it is only with thedevelopment of power electronics that it has been possible withAC supplies where the supply frequency must also be matched

(this mainly applies to locomotives where an AC supply isrectified for DC motors).

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Seminar2 w11 Regenerative Braking