1、Transmission System A Basic Parts of the transmission system The transmission system applies to the components needed to transfer the drive from the engine to the road wheels. The main components and their purposes are (1) Clutch - to disengage the drive - to provide a smooth take-up of the drive (2
2、) Gearbox - to increase the torque applied to the driving road wheels - to enable the engine to operate within a given range of speed irrespective of the vehicle speed - to give reverse motion of the vehicle - to provide a neutral position so that the engine can run without moving the vehicle (3) Fi
3、nal drive - to turn the drive through 90 - to reduce the speed of the drive by a set amount to match the engine to the vehicle (4) Differential - to allow the inner driving road wheel to rotate slower than the outer wheel when the vehicle is cornering, whilst it ensures that a drive is applied equal
4、ly to both wheels. B Clutch and Clutch Service In order to transmit the power of the engine to the road wheels of a car, a friction clutch and a change-speed gearbox are normally employed. The former is necessary in order to enable the drive to be taken up gradually and smoothly, while the latter pr
5、ovides different ratios of speed reduction from the engine to the wheels, to suit the particular conditions of running, A clutch performs two tasks: (1) it disengages the engine from the gearbox to allow for gear changing. (2) it is a means for gradually engaging the engine to the driving wheels, wh
6、en a vehicle is to be moved from rest the clutch must engage a stationary gearbox shaft with the engine； this must be rotating at a high speed to provide sufficient power or else the load will be too great and the engine will start (come to test). C Clutch Action To start the engine, the driver must
7、 depress the clutch pedal. This disengages the gearbox from the engine. To move the car, the driver must reengage the gearbox to the engine. However, the engagement of the parts must be gradual. An engine at idle develops little power. If the two parts were connected too quickly, the engine would st
8、all. The load must be applied gradually to operate the car smoothly. A driver depresses the clutch pedal to shift the gears inside the gearbox. After the driver releases the clutch pedal, the clutch must act as solid coupling device. It must transmit all engine power to the gearbox, without slipping
9、. The clutch mechanism include three basic parts: driving member, driven member, operating members. The driving member The driving member consists of two parts: the flywheel and the pressure plate. The flywheel is bolted directly to the engine crankshaft and rotates when the crankshaft turns. The pr
10、essure plate is bolted to the flywheel. The result is that both flywheel and pressure plate rotate together. The driven member The driven member, or clutch disc, is located between the flywheel and pressure plate. The disc has a splined hub that locks to the splined input shaft on the gearbox .Any r
11、otation of the clutch disc turns the input shaft .Likewise, any motion of the input shaft moves the clutch disc. The splines allow the clutch disc to move forward and backward on the shaft as it engages and disengages. The inner part of the clutch disc, called the hub flange, has a number of small c
12、oil springs. These springs are called torsional springs. They let the middle part of the clutch disc turn slightly on the hub. Thus, the springs absorb the torsional vibrations of the crankshaft. When the springs have compressed completely, the clutch moves back until the springs relax. In other wor
13、ds, the clutch absorbs these engine vibrations, preventing the vibrations from going through the drive train. Operating Members These are the parts that release pressure from the clutch disc. The operating members consist of the clutch pedal, clutch return spring, clutch linkage, clutch fork, and th
14、rowout bearing. The clutch linkage includes the clutch pedal and a mechanical or hydraulic system to move the other operating members. When the clutch pedal is depressed, the clutch linkage operates the clutch fork .The clutch fork, or release fork, moves the throwout bearing against the pressure pl
15、ate release levers. These levers then compress springs that normally hold the clutch disc tightly against the flywheel. At this point, the torque of the engine cannot turn the gearbox input shaft. The gears in the gearbox may be shifted or the vehicle can be brought to a full stop. When the clutch p
16、edal is released, the pressure plate forces the clutch disc against the flywheel. The clutch return spring helps raise the pedal. D Clutch Service The major parts of the clutch assembly need no maintenance or lubrication during normal service. However, all linkage parts need lubrication at points of
17、 contact. The linkage itself must be adjusted to prevent wear of the clutch disc. Free-play Adjustment You can make only one adjustment on the clutch linkage the free-play adjustment. Free play is the allowable space between the throwout bearing and the pressure plate release levers. This space is i
18、mportant because it prevents pressure on the levers that could keep the clutch from engaging fully. In other words, the throwout bearing must be slightly away from the pressure plate levers so that the bearing applies no pressure on the levers. On the other hand, there must not be too much free play between the bearing and the levers. With too much clearance, the clutch cannot fully disengaged when the driver press the clutch pedal to the floor. In most cases, you measure the free play at the clutch pedal, rather than at the bell housing.
