Unit Three Chassis

1、Text Drive line(shown in Fig.3-1) carries power from the engine crankshaft to the driving wheels, so the wheels rotate and the automobile moves. The typical drive line comprises clutch, transmission, drive shaft, final drive, differential and the driving wheels. Clutch The clutch has the task of con

2、necting and disconnecting the engine and the transmission, both during starting up and during shifting. Friction plates route the rotation of the engine crankshaft to the gears, and then to the wheels. In a manual transmission, you disengage the clutch when you press the pedal down. The pedal works

3、the thrust pad, and it presses levers in the middle of the clutch cover. Doing all this lifts the pressure plate away from the clutch plate. The flywheel which is turned by the crankshaft gets disconnected with the transmission shaft. When you lift the clutch pedal, springs force the pressure plate

4、and clutch plate against the flywheel. The clutch plate friction linings allow it to slide before becoming engaged. The sliding causes a smooth start instead of jolt. Manual Transmission The manual transmission is a speed and power changing device installed at some point between the engine and drivi

5、ng wheels of the vehicle. It provides a means of varying the ratio between engine rpm and driving wheels rpm to best meet each particular driving situation. A manual transmission requires a clutch to apply and remove the engine torque to the transmission input shaft. The clutch allows this to happen

6、 gradually so that the car can be started from a complete stop. Modern manual transmission do not disengage any of the forward drive gears. They are simply connected to their shafts through the use of “synchronizers”. Reverse is achieved through reverse idler gears. Which are engaged to move the car

7、 backwards. Automatic Transmission In an automatic transmission, gear ratios are changed automatically. This eliminates the need for the driver to operate the clutch and manually “shift gears”. The typical automatic transmission combines a fluid torque converter, a planetary- gear system, and a hydr

8、aulic control system in a single unit. As car speed changes, various gear ratios between the crankshaft and the wheels are selected and then changed automatically. Automatic controls inside the transmission supply the proper ratio for the driving condition. In addition to the forward-gear ratios, ne

9、utral, and reverse the automatic transmission has a PARK position. This locks the transmission to prevent the car from moving or rolling away while parked. Drive Shaft The drive shaft, or propeller shaft, connects the transmission output shaft to the differential pinion shaft. Since all roads are no

10、t perfectly smooth, and the transmission is fixed, the drive shaft has to be flexible to absorb the shocks of bumps in the road. Universal, or “U-joints” allow the drive shaft to flex when the drive angle changes. The drive shafts are usually hollow in order to weigh less, but of a large diameter to

11、 that they are strong. High quality steel, and sometimes aluminum are used in the manufacture of the drive shaft. The shaft must be quite straight and balanced to avoid vibrating. Since it turns at the engine speeds, a lot of damage can be caused if the shaft unbalanced, or bent. Damage can be also

12、caused if the U-joints are worn out. Differential When the car is on straight road, the ring gear, differential case, differential pinion gears, and two differential side gears all turn as a unit without any relative motion(shown in Fig.3- 5). The two differential pinion gears do not rotate on the p

13、inion shaft. This is because they exert equal force on the two side gears. As a result, the side gears turn at the same speed as the ring gear, which causes both drive wheels to turn at the same speed also. However, when the car begins to round a curve, the differential pinion gears rotate on the pinion shaft. This permits