What are Hydraulics?What are Hydraulics?

Moving something by means of a Moving something by means of a liquid (water or oil) under pressure.liquid (water or oil) under pressure.

Pressure (psi) = F1/A1 = F2/A2

http://www.ph.utexas.edu/~itiq/iq/303K/ch15/15.2.3.jpg

What is the MA of this lift if

A2 = 4 X A1

Pneumatic ToolsPneumatic Tools

Moving something by means of Moving something by means of compressed aircompressed air

How do hydraulic brakes How do hydraulic brakes work?work?

The hydraulic fluid The hydraulic fluid does not compress does not compress very much. When very much. When pressurized the force pressurized the force get transmitted get transmitted throughout the system. throughout the system.

The brake fluid must The brake fluid must have a very high have a very high boiling point and not boiling point and not freeze in cold driving freeze in cold driving conditions.conditions.

http://auto.howstuffworks.com/brake3.htmClick for animation!

Using leverage and hydraulics, the braking force gets multiplied.

This lever multiplies the force on the first cylinder by four.

The diameter of the brake cylinder is 3 times larger than the pedal cylinder. This is nine times larger in area. This multiplies the force another nine times (although pressure is the same throughout). The tradeoff is that the brake piston only travels 1/9 the distance of the first pedal cylinder.

Applied Force is increased 36 times.

Disk BrakesDisk Brakes

http://auto.howstuffworks.com/drum-brake1.htmClick to animate!

http://auto.howstuffworks.com/master-brake1.htmClick for animation!

A more modern braking system uses a master cylinder with two pistons to ensure a fluid leak can be isolated to one of the

wheels.

http://auto.howstuffworks.com/power-brake2.htm

More force isRequired to operateDisk brakes. Power brakes areUsed to increaseForces on the Master cylinder.

What do brakes really do?What do brakes really do?

They stop the wheels, not the carThey stop the wheels, not the car.. If the car stops without crashing the If the car stops without crashing the

brakes absorb most of the kinetic brakes absorb most of the kinetic energy of the car, turning that energy energy of the car, turning that energy into HEATinto HEAT

High performance brakes must quickly High performance brakes must quickly shed the heat that is generated.shed the heat that is generated.

Effective braking is determined by the Effective braking is determined by the contact the wheels have with the road.contact the wheels have with the road.

Drum brakes tend to have heat build Drum brakes tend to have heat build up inside the rotating drum.up inside the rotating drum.

The rotor and brake pads used in The rotor and brake pads used in disk brake systems are exposed to disk brake systems are exposed to the outside air, making cooling the outside air, making cooling easier.easier.

Drum brakes are less expensive and Drum brakes are less expensive and have improved, so many cars still have improved, so many cars still have disk brakes in the front and have disk brakes in the front and drum brakes in the rear.drum brakes in the rear.

See article at:http://www.edmunds.com/ownership/techcenter/articles/43857/article.html

What is Friction?What is Friction?

An ‘invisible’ force that resists motion when An ‘invisible’ force that resists motion when two surfaces in contact try to move relative two surfaces in contact try to move relative to one another.to one another.

FrictionFriction is a force which causes the motion is a force which causes the motion between two surfaces to be reduced. between two surfaces to be reduced.

Because of friction people used to believe Because of friction people used to believe before Galileo and Newton that forces were before Galileo and Newton that forces were always needed to keep something in always needed to keep something in motion.motion.

Static Friction – two surfaces at rest Static Friction – two surfaces at rest with respect to each otherwith respect to each other

There are two types of There are two types of Friction:Friction:

1. 1. Static Friction Static Friction 2.2. Kinetic (sliding) Kinetic (sliding)

FrictionFriction

Tire at bottom is not moving relative to the road. Static friction between tire and road is what controls the car.

Speed of tire at top is 2X speed of the car.

Tire tread, road, and driving conditions determine the coefficient of friction.A bald tire on a dry roads has a much higher friction coefficient than on a wet road.

http://hyperphysics.phy-astr.gsu.edu

Breakaway Point

Max. Static Frictional Force

Kinetic Friction is constant.

http://www.lightandmatter.com

Kinetic FrictionStatic Friction

FStatic > FKinetic

is the friction coefficient

Static friction will counteract any applied force up to a certain threshold at which friction is overcome and the object begins to slide.

Once in motion, kinetic friction resists motion.

Static Friction depends on how squished together the two surfaces are.

Anti-lock braking systemsAnti-lock braking systems

ABS keeps the tires from skidding as long as ABS keeps the tires from skidding as long as the driver keeps the brake pedal down.the driver keeps the brake pedal down.

When slamming on the brakes, wheels can When slamming on the brakes, wheels can stop spinning much faster than a car can stop spinning much faster than a car can stop. Wheels have less kinetic energy than stop. Wheels have less kinetic energy than the car.the car.

When a wheel stops rolling it is called “lock When a wheel stops rolling it is called “lock up”. When this happens the car must now up”. When this happens the car must now skid because the wheels are not turning.skid because the wheels are not turning.

Kinetic (sliding) friction is Kinetic (sliding) friction is much lessmuch less than than static friction.static friction.

Once a car skids, the tires lose grip with Once a car skids, the tires lose grip with the road and the driver loses control.the road and the driver loses control.

Skidding results in Skidding results in reduced frictionreduced friction between tires and road.between tires and road.

Lower frictional forces reduces control. Lower frictional forces reduces control. Driver might not be able to turn the car, or Driver might not be able to turn the car, or car may spin out if one wheel is skidding car may spin out if one wheel is skidding and the others are not.and the others are not.

Safer only when used properly.Safer only when used properly. ABS functions only when brakes are not ABS functions only when brakes are not

pumped. ABS creates pedal chatter pumped. ABS creates pedal chatter which means ABS which means ABS is workingis working..

ABS doesn’t mean you will stop quicker. ABS doesn’t mean you will stop quicker. However control of the car is However control of the car is maintained, because skidding is maintained, because skidding is avoided.avoided.

The ABS controller The ABS controller (computer)(computer)

Ensures that the tires slows down at the Ensures that the tires slows down at the same rate as the car, but keeps the same rate as the car, but keeps the tires’ forces just under the point where tires’ forces just under the point where sliding would occur – just under Fsliding would occur – just under Fstatic-maxstatic-max

This maximizes the braking power.This maximizes the braking power.

http://www.youtube.com/watch?v=uq4DDMMoomU

Demo of conventional brakes vs. ABS:

How is this done?How is this done?

The system uses a computer to monitor The system uses a computer to monitor the speed of each wheel. When it the speed of each wheel. When it detects that one or more wheels are detects that one or more wheels are turning turning slowerslower than the remaining than the remaining wheels, the computer sends a signal to wheels, the computer sends a signal to momentarily remove and reapply the momentarily remove and reapply the pressure to the affected wheels to allow pressure to the affected wheels to allow them to continue turning. This them to continue turning. This "pumping" of the brakes occurs at ten or "pumping" of the brakes occurs at ten or more times a second.  more times a second. 

http://www.familycar.com/brakes.htm

The system consists of an electronic The system consists of an electronic control unit, a hydraulic actuatorcontrol unit, a hydraulic actuator**,  ,  and wheel speed sensors at each and wheel speed sensors at each wheel.  wheel. 

* An actuator is a device in a car that uses electricity to do some sort of mechanical movement- Such as power door locks or a remote trunk opener. In this case the actuator releases pressure in the brakes to pulse the brakes.

http://www.aa1car.com/library/abs1.htm

Information from wheel speedsensors is fed to the controller.

If the controller determines that one tire is If the controller determines that one tire is rotating more slowly than the other tires, rotating more slowly than the other tires,

the controller sends a signal to the wheel’s the controller sends a signal to the wheel’s actuator to lower the brake fluid pressure to actuator to lower the brake fluid pressure to

prevent skidding.prevent skidding.

www.lake-link.com

Solenoid valve closes,preventing more fluidfrom getting to the brake.It then is reopened, thuspumping the brake.

Do ABS brakes work in the Do ABS brakes work in the snow or on icy roads?snow or on icy roads?

What is the primary advantage What is the primary advantage of ABS brakes?of ABS brakes?

Heat – what a waste!!!Heat – what a waste!!!Regenerative braking Regenerative braking absorbs some of the absorbs some of the car’s kinetic energy to car’s kinetic energy to generate electricity generate electricity instead of producing instead of producing wasteful heat.wasteful heat.

The electric motor operates like a The electric motor operates like a generator during braking. generator during braking.

This puts energy back into the This puts energy back into the battery.battery.

http://www.youtube.com/watch?v=F19qeag-o_I

How a Parallel Hybrid car How a Parallel Hybrid car worksworks

What are benefits of What are benefits of Regenerative Breaking?Regenerative Breaking?

Have wheels turn a generator connected Have wheels turn a generator connected to a battery to capture some of the Kinetic to a battery to capture some of the Kinetic Energy of the CarEnergy of the Car

Allows the Pruis to use a much smaller gas Allows the Pruis to use a much smaller gas engine since high power demands can be engine since high power demands can be supplemented by electric motor and supplemented by electric motor and battery.battery.

Transfer unwanted KE into Potential Transfer unwanted KE into Potential Energy to be converted back into KE at a Energy to be converted back into KE at a later time.later time.

Regenerative Breaking Regenerative Breaking DemoDemo

How the battery and engine How the battery and engine work together is determined by work together is determined by

a microcontrollera microcontroller

Scenarios:Scenarios:

All the engine power is not needed, so excess All the engine power is not needed, so excess engine energy is used to charge the batteryengine energy is used to charge the battery

Engine power is not sufficient, so battery Engine power is not sufficient, so battery operates an electric motor boosting poweroperates an electric motor boosting power

Unwanted Kinetic Energy is used in braking to Unwanted Kinetic Energy is used in braking to charge batterycharge battery

Car only needs low power provided by electric Car only needs low power provided by electric motor, then gas engine stays off.motor, then gas engine stays off.

While at rest, all systems are off; no idle waste.While at rest, all systems are off; no idle waste.

Scenario 1Scenario 1 Engine charges a low batteryEngine charges a low battery This happens if battery is low, usually at the beginning of a This happens if battery is low, usually at the beginning of a

triptrip

Scenario 2Scenario 2 When waiting at lights, engine and When waiting at lights, engine and

electric motor are off – no idlingelectric motor are off – no idling

Scenario 3Scenario 3 Engine power exceeds car’s demand, therefore Engine power exceeds car’s demand, therefore

engine turns generator.engine turns generator. Generator (i.e. electric motor) charges the batteryGenerator (i.e. electric motor) charges the battery

Scenario 4Scenario 4

Energy demand can be satisfied by battery onlyEnergy demand can be satisfied by battery only

Scenario 5Scenario 5 When braking, wheels turn generator that in turn charge the When braking, wheels turn generator that in turn charge the

battery.battery. This also happens sometimes when coasting.This also happens sometimes when coasting.

Scenario 6Scenario 6

Engine only – energy demand equals that of gas Engine only – energy demand equals that of gas engine.engine.

Scenario 7Scenario 7 Engine and Battery working in consort to drive wheelsEngine and Battery working in consort to drive wheels Demand exceeds power of gas engineDemand exceeds power of gas engine

Hybrid BenefitsHybrid Benefits

Low emissionsLow emissions Car performs well under most cases with a Car performs well under most cases with a

much smaller engine, due to reliance on the much smaller engine, due to reliance on the battery and electric motor for boosts in powerbattery and electric motor for boosts in power

Very sophisticated embedded microcontrollers Very sophisticated embedded microcontrollers that manage energy demandsthat manage energy demands

Captures excess energy of motor and during Captures excess energy of motor and during breakingbreaking

Flywheel Storage SystemFlywheel Storage System(FES)(FES)

Another technique for storing unwanted Another technique for storing unwanted KE of the carKE of the car

Energy is transferred to a flywheel as KE.Energy is transferred to a flywheel as KE. Flywheel turns freely and independently Flywheel turns freely and independently

of until KE is needed again to propel the of until KE is needed again to propel the car.car.

Thought question….Thought question….

What are some reasons the Prius What are some reasons the Prius might get better mileage in stop and might get better mileage in stop and go conditions than on the highway?go conditions than on the highway?

http://www.getrichslowly.org/blog/2007/05/30/how-to-improve-your-gas-mileage-23-top-tips-for-better-fuel-economy/http://www.consumerenergycenter.org/transportation/consumer_tips/vehicle_energy_losses.html

Good sources of information.

http://www.consumerenergycenter.org

Losses in Conventional Car

Typical Car

PriusSimulator

http://priuschat.com