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What are Hydraulics?

What are Hydraulics?. Moving something by means of a liquid (water or oil) under pressure. What is the MA of this lift if A 2 = 4 X A 1. Pressure (psi) = F 1 /A 1 = F 2 /A 2. http://www.ph.utexas.edu/~itiq/iq/303K/ch15/15.2.3.jpg. Pneumatic Tools.

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What are Hydraulics?

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  1. What are Hydraulics? • Moving something by means of a liquid (water or oil) under pressure. What is the MA of this lift if A2 = 4 X A1 Pressure (psi) = F1/A1 = F2/A2 http://www.ph.utexas.edu/~itiq/iq/303K/ch15/15.2.3.jpg

  2. Pneumatic Tools • Moving something by means of compressed air

  3. How do hydraulic brakes work? The hydraulic fluid does not compress very much. When pressurized the force get transmitted throughout the system. The brake fluid must have a very high boiling point and not freeze in cold driving conditions. http://auto.howstuffworks.com/brake3.htm Click for animation!

  4. 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.

  5. Disk Brakes

  6. http://auto.howstuffworks.com/drum-brake1.htm Click to animate!

  7. 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/master-brake1.htm Click for animation!

  8. More force is Required to operate Disk brakes. Power brakes are Used to increase Forces on the Master cylinder. http://auto.howstuffworks.com/power-brake2.htm

  9. What do brakes really do? • They stop the wheels, not the car. • If the car stops without crashing the brakes absorb most of the kinetic energy of the car, turning that energy into HEAT • High performance brakes must quickly shed the heat that is generated. • Effective braking is determined by the contact the wheels have with the road.

  10. Drum brakes tend to have heat build up inside the rotating drum. • The rotor and brake pads used in disk brake systems are exposed to the outside air, making cooling easier. • Drum brakes are less expensive and have improved, so many cars still have disk brakes in the front and drum brakes in the rear. See article at: http://www.edmunds.com/ownership/techcenter/articles/43857/article.html

  11. What is Friction? • An ‘invisible’ force that resists motion when two surfaces in contact try to move relative to one another. • Friction is a force which causes the motion between two surfaces to be reduced. • Because of friction people used to believe before Galileo and Newton that forces were always needed to keep something in motion.

  12. There are two types of Friction:1.Static Friction 2. Kinetic (sliding) Friction • Static Friction – two surfaces at rest with respect to each other

  13. Speed of tire at top is 2X speed of the car. Tire at bottom is not moving relative to the road. Static friction between tire and road is what controls the car.

  14. 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

  15. Breakaway Point Kinetic Friction is constant. Max. Static Frictional Force http://www.lightandmatter.com

  16. 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 Kinetic Friction • FStatic> FKinetic • is the friction coefficient Static Friction depends on how squished together the two surfaces are.

  17. Anti-lock braking systems • ABS keeps the tires from skidding as long as the driver keeps the brake pedal down. • When slamming on the brakes, wheels can stop spinning much faster than a car can stop. Wheels have less kinetic energy than the car. • When a wheel stops rolling it is called “lock up”. When this happens the car must now skid because the wheels are not turning.

  18. Kinetic (sliding) friction is much less than static friction. • Once a car skids, the tires lose grip with the road and the driver loses control. • Skidding results in reduced friction between tires and road. • Lower frictional forces reduces control. Driver might not be able to turn the car, or car may spin out if one wheel is skidding and the others are not.

  19. Safer only when used properly. • ABS functions only when brakes are not pumped. ABS creates pedal chatter which means ABS is working. • ABS doesn’t mean you will stop quicker. However control of the car is maintained, because skidding is avoided.

  20. The ABS controller (computer) • Ensures that the tires slows down at the same rate as the car, but keeps the tires’ forces just under the point where sliding would occur – just under Fstatic-max • This maximizes the braking power.

  21. Demo of conventional brakes vs. ABS: http://www.youtube.com/watch?v=uq4DDMMoomU

  22. How is this done? The system uses a computer to monitor the speed of each wheel. When it detects that one or more wheels are turning slower than the remaining wheels, the computer sends a signal to momentarily remove and reapply the pressure to the affected wheels to allow them to continue turning. This "pumping" of the brakes occurs at ten or more times a second.  http://www.familycar.com/brakes.htm

  23. The system consists of an electronic control unit, a hydraulic actuator*,  and wheel speed sensors at each wheel.  Information from wheel speed sensors is fed to the controller. http://www.aa1car.com/library/abs1.htm * 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.

  24. If the controller determines that one tire is rotating more slowly than the other tires, the controller sends a signal to the wheel’s actuator to lower the brake fluid pressure to prevent skidding. Solenoid valve closes, preventing more fluid from getting to the brake. It then is reopened, thus pumping the brake. www.lake-link.com

  25. Do ABS brakes work in the snow or on icy roads?What is the primary advantage of ABS brakes?

  26. Heat – what a waste!!! The electric motor operates like a generator during braking. This puts energy back into the battery. Regenerative braking absorbs some of the car’s kinetic energy to generate electricity instead of producing wasteful heat.

  27. How a Parallel Hybrid car works http://www.youtube.com/watch?v=F19qeag-o_I

  28. What are benefits of Regenerative Breaking? • Have wheels turn a generator connected to a battery to capture some of the Kinetic Energy of the Car • Allows the Pruis to use a much smaller gas engine since high power demands can be supplemented by electric motor and battery. • Transfer unwanted KE into Potential Energy to be converted back into KE at a later time.

  29. Regenerative Breaking Demo

  30. How the battery and engine work together is determined by a microcontroller Scenarios: • All the engine power is not needed, so excess engine energy is used to charge the battery • Engine power is not sufficient, so battery operates an electric motor boosting power • Unwanted Kinetic Energy is used in braking to charge battery • Car only needs low power provided by electric motor, then gas engine stays off. • While at rest, all systems are off; no idle waste.

  31. Scenario 1 • Engine charges a low battery • This happens if battery is low, usually at the beginning of a trip

  32. Scenario 2 • When waiting at lights, engine and electric motor are off – no idling

  33. Scenario 3 • Engine power exceeds car’s demand, therefore engine turns generator. • Generator (i.e. electric motor) charges the battery

  34. Scenario 4 • Energy demand can be satisfied by battery only

  35. Scenario 5 • When braking, wheels turn generator that in turn charge the battery. • This also happens sometimes when coasting.

  36. Scenario 6 Engine only – energy demand equals that of gas engine.

  37. Scenario 7 • Engine and Battery working in consort to drive wheels • Demand exceeds power of gas engine

  38. Hybrid Benefits • Low emissions • Car performs well under most cases with a much smaller engine, due to reliance on the battery and electric motor for boosts in power • Very sophisticated embedded microcontrollers that manage energy demands • Captures excess energy of motor and during breaking

  39. Flywheel Storage System(FES) • Another technique for storing unwanted KE of the car • Energy is transferred to a flywheel as KE. • Flywheel turns freely and independently of until KE is needed again to propel the car.

  40. Thought question…. What are some reasons the Prius might get better mileage in stop and 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.

  41. Losses in Conventional Car http://www.consumerenergycenter.org

  42. Typical Car Prius Simulator http://priuschat.com

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