Drive shaft

A drive shaft, driving shaft, propeller shaft, or Cardan shaft is a mechanical device for transferring power from the engine or motor to the point where useful work is applied. Most engines or motors deliver power as torque through rotary motion: this is extracted from the linear motion of pistons in a reciprocating engine; water driving a water wheel; or forced gas or water in a turbine. From the point of delivery, the components of power transmission form the drive train.

Drive shafts are carriers of torque: they are subject to torsion and shear stress, which represents the difference between the input force and the load. They thus need to be strong enough to bear the stress, without imposing too great an additional inertia by virtue of the weight of the shaft.

Automotive drive shafts

Vehicles

Most automobiles today use rigid drive shafts to deliver power from a transmission to the wheels. A pair of short drive shafts is commonly used to send power from a central differential, transmission, or transaxle to the wheels.

In front-engined, rear-drive vehicles, a longer drive shaft is also required to send power the length of the vehicle. Two forms dominate: The torque tube with a single universal joint and the Hotchkiss drive with two or more joints. This system became known as Système Panhard after the automobile company, Panhard et Levassor patented it.

Early automobiles often used chain drive or belt drive mechanisms rather than a drive shaft. Some used electrical generators and motors to transmit power to the wheels.

In British English, the term "drive shaft" is restricted to a transverse shaft which transmits power to the wheels, especially the front wheels. A drive shaft connecting the gearbox to a rear differential is called a propeller shaft, or prop-shaft. A prop-shaft assembly consists of a propeller shaft, a slip joint and one or more universal joints. Where the engine and axles are separated from each other, as on four-wheel drive and rear-wheel drive vehicles, it is the propeller shaft that serves to transmit the drive force generated by the engine to the axles.

A drive shaft connecting a rear differential to a rear wheel may be called a half shaft. The name derives from the fact that two such shafts are required to form one rear axle.

There are different types of drive shafts in Automotive Industry:

• 1 piece drive shaft
• 2 piece drive shaft
• Slip in Tube drive shaft

The Slip in Tube Drive shaft is the new type which also helps in Crash Energy Management. It can be compressed in case of crash. It is also known as a collapsible drive shaft.

Drive shaft for Research and Development (R&D)

The automotive industry also uses drive shafts at testing plants. At an engine test stand a drive shaft is used to transfer a certain speed / torque from the combustion engine to a dynamometer. A "shaft guard" is used at a shaft connection to protect against contact with the drive shaft and for detection of a shaft failure. At a transmission test stand a drive shaft connects the prime mover with the transmission.

Motorcycle drive shafts

Drive shafts have been used on motorcycles almost as long as there have been motorcycles. As an alternative to chain and belt drives, drive shafts offer relatively maintenance-free operation and long life. A disadvantage of shaft drive on a motorcycle is that gearing is needed to turn the power 90° from the shaft to the rear wheel, losing some power in the process. On the other hand, it is easier to protect the shaft linkages and drive gears from dust, sand and mud.

The best known motorcycle manufacturer to use shaft drive for a long time — since 1923 — is BMW. Among contemporary manufacturers, Moto Guzzi is also well-known for its shaft drive motorcycles. The British company, Triumph and all four Japanese brands, Honda, Suzuki, Kawasaki and Yamaha, have produced shaft drive motorcycles.

The first use of a drive shaft on an off-road motorcycle was in the Tote Gote Nova series. It used a straight shaft powering a worm gear which then turned a gear. The outer casing was aluminum, and was supported by two rubber bushings. The engine faced forward in the frame.

Motorcycle engines positioned such that the crankshaft is longitudinal and parallel to the frame are often used for shaft driven motorcycles. The requires only one 90° turn in power transmission, rather than two. Moto Guzzi, BMW, Triumph, and Honda use this engine layout.

Motorcycles with shaft drive are subject to shaft effect where the chassis climbs when power is applied. This is counteracted with systems such as BMW's Paralever, Moto Guzzi's CARC and Kawasaki's Tetralever.

Marine drive shafts

On a power-driven ship, the drive shaft, or propeller shaft, usually connects the transmission inside the vessel directly to the propeller, passing through a stuffing box or other seal at the point it exits the hull. There is also a thrust block, a bearing to resist the axial force of the propeller. As the rotating propeller pushes the vessel forward, any length of drive shaft between propeller and thrust block is subject to compression, and when going astern to tension. Except for the very smallest of boats, this force isn't taken on the gearbox or engine directly.

Cardan shafts are also often used in marine applications between the transmission and either a propeller gearbox or waterjet.

Drive shafts in Bicycles

The drive shaft has served as an alternative to a chain-drive in bicycles for the past century, although never becoming very popular. A shaft-driven bicycle is described as "acatane". When used on a bicycle, a drive shaft has several advantages and disadvantages:

Advantages

• Drive system is less likely to become jammed or broken, a common problem with chain-driven bicycles
• The use of a gear system creates a smoother and more consistent pedaling motion
• The rider cannot become dirtied from chain grease or injured by the chain from "Chain bite", which occurs when clothing or even a body part catches between the chain and a sprocket
• Lower maintenance than a chain system when the drive shaft is enclosed in a tube, the common convention
• More consistent performance. Dynamic Bicycles claims that a drive shaft bicycle consistently delivers 94% efficiency, whereas a chain-driven bike can deliver anywhere from 75-97% efficiency based on condition.
• Greater clearance: with the absence of a derailleur or other low-hanging machinery, the bicycle has nearly twice the ground clearance
• For bicycle rental companies, a drive-shaft bicycle is less prone to be stolen, since the shaft is non-standard, and both noticeable and non-maintainable. This type of bicycle is in use in several major cities of Europe, where there have been large municipal funded, public (and automatic) bicycle rental projects.

Disadvantages

• A drive shaft system weighs more than a chain system, usually 1-2 pounds heavier
• At optimum upkeep, a chain delivers greater efficiency
• Many of the advantages claimed by drive shaft's proponents can be achieved on a chain-driven bicycle, such as covering the chain and gears with a metal or plastic cover
• Use of lightweight derailleur gears with a high number of ratios is impossible, although hub gears can be used
• Wheel removal can be complicated in some designs (as it is for some chain-driven bicycles with hub gears).

See also

• Universal joint