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2018-09-21 17:11:24·  来源:洞云书屋
(注:本文是译文,Original author: Anupam Singhal)Drive shaft is a mechanical part of transmission system which is used to transfer the power from engine to the wheel. It comprises two constant velocity (CV) joints and t
(注:本文是译文,Original author: Anupam Singhal)

Drive shaft is a mechanical part of transmission system which is used to transfer the power from engine to the wheel. It comprises two constant velocity (CV) joints and the actual shaft is almost universally used in front wheel drive (FWD) vehicles. The usage of drive shaft as a power transmitter in automobile is more convenience because it is less likely to become jammed or broken compared to chain-drives. In operation, drive shaft is generally subjected Torsional and bending stress due to which fatigue and fractural failures may occur. Some common causes of failures are manufacturing, design, maintenance, raw material, and the user originated faults.

The movement of vehicles can be provided by transferring the torque produced by engines to wheels after some modification. The transfer and modification system of vehicles is called as power transmission system and have different constructive features according to the vehicle’s driving type which can be front wheel drive.

Most automobiles today use rigid driveshaft to deliver power from a transmission to the wheels. A pair of short flexible driveshaft is commonly used in cars to send power from a differential to the wheels.

There are different types of drive shafts in Automotive Industry:
One-piece driveshaft
Two-piece driveshaft
Slip in Tube driveshaft

Drive shafts are carriers of torque. They are subject to torsion and shear stress, equivalent to the difference between the input torque and the load. They must therefore be strong enough to bear the stress, whilst avoiding too much additional weight as that would in turn increase their inertia.

In front wheel drive operation, two universal joints (CV joints) are used for drive a shaft at constant angular velocity with a large misalignment angle. The inner end of the driveshaft has very little misalignment relative to the transmission housing, while the outer end of the driveshaft is attached to the front wheel and must continue to transmit torque whilst turning through angles up to 40 degrees.

FWD drive shaft can be solid or tubular, equal or unequal length, come with or without damper weight. Equal length shafts are used in some vehicles to help reduce torque steer. The intermediate shaft is used as a link from transaxle to the half shaft. The outer ends have a support bracket and bearing assembly. Looseness in the bearing or bracket can create vibrations. The small damper weight is called torsional damper, that is sometimes attached to one half shaft serves to dampen harmonic vibrations in the drivetrain and to stabilize the shaft as it spins, not to balance the shaft.

The outer joints generally wear faster than inner joints because of the increased range of operating angles to which they are subjected. Inner joint angles may change only 10 to 20 degrees as outer joint can undergo changes up to 40 degrees in addition to jounce and rebound as the wheels are steered.

All CV joints are encased in a protective rubber (neoprene, natural and silicon) or thermoplastic boot. The job of the boot is to retain grease and to keep dirt and water out. The importance of the boot cannot be overemphasized because without its protection the joint does not survive. once CV joint packed with grease and installed, it requires no further maintenance. A loose or missing boot clamp, or a slit, tear, or a small puncture in the boot itself allows grease to leak out and water or dirt to enter. A milky or foamy appearance indicates water contamination. A gritty feeling when rubbed between the fingers indicates dirt. It Results, the joint is destroyed.

Countries, where the average atmospheric temperature is approximate 40 degree, the failures mainly occur by changing the properties of grease. Grease must change its property on increasing of temperature because of changing in chemical composition. Grease becomes hard and thick on high temperature and does not operates normally. Oil present in grease may leak or vaporized which results failure of joint.

On the other side, road conditions are firmly effect the drive shaft. Domestic cars are manufactured on the basis of smooth road conditions but some developing countries have very rough road conditions so that premature failure may occur. A rough road condition causes the drive shaft work continuously on bumps and dips. Rough road have more dirt and dust particles, which are accumulated on the boot and in the grease. Which results abrasion of balls or tripods and joint may fail before time.

Generally it seems that 80 % of the problems in CV joints are caused by a change in the working distance of the side shaft, 8 % by faults or negligence during installation. 8 % come from cracked axle boots which lead to a loss of lubricant, resulting in soiling of the joint. only the remaining 4 % of all joint failures have been caused by jolts and normal wear and tear of the parts.