Powertrains

1. Powertrains

2. The Goal of a Transmission • The transmission allows the gear ratio between the engine and the drive wheels to change as the car speeds up and slows down

3. Components • Clutch/manual transmission or • torque converter/automatic transmission; and • differential, • driveshaft.

4. transmission is connected to the engine through the clutch. The input shaft of the transmission therefore turns at the same rpm as the engine

5. General information: gears • Purposes • Gear reduction • Overdrive • Directional change • Gear ratio: output radius/input radius Helical gear

6. How Clutches Work

7. Clutch • Purpose: connect or disconnect two shafts • Pressing pedal pushes spring; pulls plate away from flywheel • Releasing pedal allows spring to contact flywheel • Friction  wear http://www.autoparts-online.co.uk/images/feb01/clutch.jpg Animated basic Clutches

8. Automobile Clutch • flywheel is connected to the engine, and the clutch plate is connected to the transmission • the springs push the pressure plate against the clutch disc, which in turn presses against the flywheel. • This locks the engine to the transmission input shaft, causing them to spin at the same speed. Clutches explode

9. Clutches engage

10. What Can Go Wrong? • friction material on the disc wears out • similar to the friction material on the pads of brake • When most or all of the friction material is gone, the clutch will start to slip • wears while the clutch disc and the flywheel are spinning at different speeds Clutches wear

11. Other Clutches in Your Garage • automatic transmission contains several clutches, used to engage and disengage sets of planetary gears • air conditioning compressor has a magnetic clutch, allows compressor to shut off even while the engine is running

12. Compressor

13. Manual Transmission

14. Manual transmission • Purpose: optimize engine speed with varying wheel speed • Ratios (ex.): 2.3:1, 1.6:1, 1.2:1, 1:1, 0.9:1 • Parts • Input shaft • Layshaft • Gears (incl. idler) • Output shaft • Dog collars • Synchronizers

15. Manual transmission efficiency • Range: 87 to 99% overall • Factors • Time in each gear • Speed and torque values in each gear • City vs. highway • Fluid type • Mounting angle • Duty cycles • % efficiency = (input speed * input torque * 100)/(output speed * output torque) • Improvements

16. five-speed transmission applies one of five different gear ratios to the input shaft to produce a different rpm value at the output shaft

17. Very Simple Transmission

18. First Gear

19. five-speed manual transmission

22. Reverse gear is handled by a small idler gear

23. to allow collar and gear to make frictional contact before the dog teeth make contact. collar and gear synchronize their speeds before the teeth need to engage Synchronizers

25. way to let the engine turn while the wheels and gears in the transmission come to a stop • Manual transmission – engine connected to transmission by clutch • automatic transmission- have no clutch, Instead, use torque converter

26. Torque converter • Purpose: allow engine to run with trans. stopped • Fluid coupling • Parts: • Pump • Fluid • Turbine • Stator • Slippage: 2-8% power loss • Lock-up torque converters

27. fluid coupling, -- allows the engine to spin somewhat independently of transmission • slow turning or idling, engine torque passed through torque converter is very small • step on padal, the engine speeds up and pumps more fluid into the torque converter, -- more torque transmit to wheel

28. Inside a Torque Converter - Pump- Stator - Turbine- Transmission fluid

29. fins- make up the pump of the torque converter are attached to the housing

30. pump inside a torque converter is a type of centrifugal pump

31. As it spins, fluid is flung to the outside • a vacuum is created that draws more fluid in at the center

32. pump section of the torque converter is attached to the housing

33. fluid then enters the blades of the turbine, which is connected to the transmission • turbine causes the transmission to spin • blades of the turbine are curved - fluid, which enters the turbine from the outside, has to change direction before it exits the center of the turbine • directional change that causes the turbine to spin

34. turbine: the spline in the middle - connects to the transmission

35. to change the direction of a moving object, you must apply a force to that object • whatever applies the force that causes the object to turn must also feel that force, but in the opposite direction • as the turbine causes the fluid to change direction, the fluid causes the turbine to spin

36. fluid exits the turbine moving opposite the direction that the pump (and engine) are turning • If the fluid were allowed to hit the pump, it would slow the engine down, wasting power. This is why a torque converter has a stator

37. stator sends the fluid returning from the turbine to the pump. This improves the efficiency of the torque converter

38. stator resides in the very center of the torque converter. Its job is to redirect the fluid returning from the turbine before it hits the pump again • stator has a very aggressive blade design that almost completely reverses the direction of the fluid • one-way clutch (inside the stator) connects the stator to a fixed shaft in the transmission • the stator cannot spin with the fluid -- it can spin only in the opposite direction, forcing the fluid to change direction as it hits the stator blades

39. when the car gets moving. There is a point, around 40 mph (64 kph), at which both the pump and the turbine are spinning at almost the same speed • the fluid returns from the turbine, entering the pump already moving in the same direction as the pump, so the stator is not needed

41. allow the engine to operate in its narrow range of speeds while providing a wide range of output speeds

42. Automatic transmission [1] • Purpose: to keep engine within optimal rpm • Planetary gearsets • Components: • Ring • Sun • Planet carrier • Ratios created through combinations: • Reduction: sun input, planet carrier output, ring stationary • Overdrive: planet carrier input, ring output, sun stationary • Reverse: sun input, ring output, planet carrier stationary

43. key difference between a manual and an automatic transmission • manual transmission locks and unlocks different sets of gears to the output shaft to achieve the various gear ratios • automatic transmission, the same set of gears produces all of the different gear ratios • planetary gearset is the device that makes this possible in an automatic transmission

44. Automatic transmission [2] • Compound planetary gearset • One ring gear, two suns, two sets of planets • Second gear • Input 1: small sun; stationary 1: large sun (functioning as ring); output 1: planet carrier • Ratio 1: 1 + R/S, ex. 1 + 36/30 = 2.2:1 •  Input 2: planet carrier; stationary 2: large sun; output 2: ring • Ratio 2: 1/(1 + S/R), ex. 1/(1 + 36/72) = 0.67:1 • Combined ratio: Ratio 1 * Ratio 2, ex. 1.47:1

45. Planetary Gearsets • planetary gearset • set of bands lock parts of a gearset • set of three wet-plate clutches lock other parts of the gearset • hydraulic system controls the clutches and bands • large gear pump to move transmission fluid around

46. Planetary Gearsets

47. Planetary Gearsets & Gear Ratios Each of these three components can be the input, the output or can be held stationary

48. ring gear with 72 teeth and a sun gear with 30 teeth. We can get lots of different gear ratios out of this gearset Animated

49. Gears • one gear set can produce different gear ratios without having to engage or disengage any other gears • two gearsets can get the four forward gears and one reverse gear for transmission needs • compound planetary gearset

50. one ring gear always be the output of the transmission, but 2 sun gears and 2sets of planets