In mechanical or automotive engineering, freewheel or coupling hold is a device in the transmission that releases the driveshaft of the driven shaft when the drive shaft rotates faster than the driveshaft. Overdrive is sometimes mistakenly called freewheel, but rather unconnected.
The driven axle condition spins faster than its driveshaft on most of the bikes when the rider holds his leg, no longer pushing the pedal. In a fixed-gear bike, without a freewheel, the rear wheels will move the pedal around it.
The analogue condition is in the car with a decreased manual transmission, or situation where the driver takes his foot off the accelerator, closes the throttle; wheels want to move the engine, maybe at a higher RPM. In a two-step engine, this can be a very dangerous situation: since many two engine drives depend on the fuel/oil mixture for lubrication, a fuel shortage for the engine will result in a shortage of oil in the cylinder, and the piston will seize after a very short period of time extensive engine damage. Saab used the freewheel system in their two-stroke model for this reason and kept it in Saab 96 V4 and Saab 99 early for better fuel efficiency.
Video Freewheel
Mekanika
The simplest freewheel device consists of two saw saws, springs pressing against each other with toothed sides, much like a ratchet. Spinning in one direction, the sawtooth of the disk drive locks with the teeth of the driven disk, making it rotate at the same speed. If the drive disc slows or stops spinning, the tooth of the driven disc slips above the drive gear and continues to spin, producing a distinctive click sound proportional to the speed difference of the driven gear relative to the driving gear (more slowly).
More sophisticated and sturdy designs have spring steel rollers in an actuated cylinder. Spin in one direction, the roller locks with the cylinder so that it rotates simultaneously. Turning slower, or in the other direction, the steel roller just slips inside the cylinder.
Most bike freewheels use an internal gear drum with two springs or spring springs to squeeze the load. More pawls help spread the wear and provide greater reliability though, unless the device is made for tolerances that are not normally found in bicycle components, the simultaneous involvement of more than two pawls is rarely achieved.
Maps Freewheel
Advantages and disadvantages
Naturally, the freewheel mechanism acts as an automatic clutch, making it possible to change the gearbox in a manual gearbox, either up or down, without pressing the clutch pedal, limiting the use of manual coupling to start from stop or stop. Freewheel Saab can be involved or removed by the driver by pushing or pulling the lever. This will lock or unlock the main axle with a freewheel hub.
Freewheel also produces slightly better fuel savings on burnt engines (without fuel cessation in the engine brake) and reduces wear on the manual clutch, but leads to more damage to the brakes as there is no longer the ability to brake the engine. This can make a dangerous freewheel transmission to be used on trucks and cars driven in the mountains, since the prolonged and continuous use of the brakes to restrict the speed of the vehicle immediately leads to overheated brakes being followed immediately by a total failure.
Usage
Agricultural equipment
In agricultural equipment, oppressive clutches are commonly used on straw bales and other equipment with high inertia loads, especially when used in conjunction with tractors without take-off of life (PTO). Without a live PTO, a high inertial load can cause the tractor to continue moving even when the clutch of the foot is depressed, creating an unsafe condition. By breaking the load from the PTO under these conditions, the coping coupling improves safety. Similarly, many non-powered 'push' cylinder mowers use freewheel to propel the propellers: they are driven or driven by chains to spin at high speeds and freewheel prevent their momentum being transferred in reverse direction through the drive when the engine is stopped.
Starter engine
Freewheel assemblies are also widely used at the beginning of the machine as a kind of protective device. The starter motor usually needs to spin at 3,000 RPM to power the engine. When the lock is held in the starting position for how long after the engine starts, the starter can not rotate fast enough to follow the flywheel. Because the extreme gear ratio between the starter tooth and the flywheel (about 15 or 20: 1) it will rotate the starter armature at a dangerous high speed, causing an explosion when centripetal force acting on the coil of copper coils on the armature can no longer withstand the outer force who acted upon them. In a starter without a freewheel or overrun clutch, this would be a big deal because, with the flywheel spinning at about 1,000 RPM when idle, the starter, if involved with the flywheel, would be forced to spin between 15,000 and 20,000 RPM. Once the engine has turned and runs, the overrun clutch will release the starter from the flywheel and prevent the gear from re-meshing (such as inadvertently turning the ignition) while the machine is running. A freewheel clutch is now used in many motorcycles with an electric starter motor. It's used as a substitute for Bendix drives that are used on most auto starters because it reduces the electrical needs of the initial system.
Transmission vehicles
In addition to the above-mentioned automotive use (ie in a two-stroke engine and the initial four-step Saabs), freewheels are used in some luxury cars or luxury cars on the market (such as Rovers and Tali) from the 1930s to the 1960s.. Some period engines also tend to skip oil past the piston rings under conditions with closed throttle and high engine rotation, when a bit of vacuum in the combustion chamber is combined with high oil pressure and high splash lubrication rates from fast-turning. crankshaft will cause oil into the combustion chamber.
Freewheel means that the engine returns to its empty velocity on the overrun, thus greatly reducing noise both from the engine and gearbox and reducing oil consumption. Mechanisms can usually be locked to provide engine braking if required. Freewheel was also used in the original Land Rover vehicles from 1948 to 1951. Freewheel-controlled vehicles from the gearbox to the front axle, which were detached when ridden. This allows the vehicle to have a permanent 4 wheel drive system by avoiding the 'wind-up' power in the transmission. This system works, but produces unpredictable handling, especially in slippery conditions or when withdrawn, and is replaced by conventionally selectable 4WD systems.
During the Second World War, Volkswagen's military vehicles manufactured by KdF (KÃÆ'¼belwagen, Schwimmwagen) were fitted with a ZF differential system consisting of two freewheels, which sent all the engine power to the slowest rotation of two wheels.
Other car makers install freewheel between the engine and the gearbox as an automatic clutch form. After the driver releases the throttle and the freewheel-controlled vehicle will disengage and the gearchange can be made without the use of a clutch pedal. This feature appears especially in large and luxury cars that often have heavy grips and gearboxes without synchromesh because freewheel allows smoother and more subdued changes. CitroÃÆ'¼n combines freewheel and centrifugal clutch to create what is called 'TraffiClutch' where the car can start, stop and lower gears altered without using a clutch pedal. It is an option on CitroÃÆ'¡n 2CVs and its derivatives and, as the name implies, is marketed as a benefit for driving in densely populated urban areas. Similarly, Saab 93 is available with an optional Saxomat coupling.
The use of a common freewheeling mechanism is in automatic transmission. For example a traditional General Motors hydraulic transmission such as Turbo-Hydramatic 400 provides freewheeling in all lower gears of selected gear. For example, if the gear selector on a three-speed transmission is labeled 'drive' (3) - 'super' (2) - 'low' (1) and the driver has chosen 'super', the transmission will be faster if the first gear is engaged, but not in second or third gear; if in 'drive' it will freewheel at first or second; Finally, if it is low, it will not be a freewheel in any gear. This allows the driver to choose a lower range to achieve engine braking at various speeds, such as when down a steep hill.
The overdrive unit produced by Laycock de Normanville uses a freewheel to facilitate seamless gears between locked mode (1: 1) and overdrive mode without the use of conventional clutch coupling. Freewheel will lock the axle out to the exit axle in a short transition period between the cone coupling to unlocked mode and clutch for an attractive overdrive mode.
Bicycle
In an older bike style, where the freewheel mechanism is included in the gear assembly, the system is called freewheel , while the newer style, where the freewheel mechanism is in the hub, is called Freehub .
Helicopter
Freewheels are also used in rotorcraft. Because the bicycle wheel should be able to spin faster than the pedal, then the rotorcraft blades should be able to spin faster than the driving machine. This is especially important in the event of a machine failure where the freewheel on the main transmission allows the main rotor and tail systems to continue to spin independent of the drive system. It provides advanced flight control and autorotation landing.
History
In 1869, William Van Anden invented a freewheel for bicycles. The design puts the ratchet device in the front wheel hub (the wheels are moved on the 'velocipede' design of the time), allowing the rider to push himself forward without pedaling constantly. Initially, bike fans rejected the idea of ​​freewheel because they believed it would complicate the mechanical function of the bike. Cyclists believe that the bike should remain as simple as possible without additional mechanisms, such as freewheel.
Due to the lack of popularity for freewheel, it has not been continually reengineered to become more useful for decades. In 1899, the American manufacturer developed a "brake coaster", which allowed the rider to pedal backward and incorporate a freewheel mechanism. At the turn of the century, bicycle manufacturers in Europe and America incorporated a freewheel mechanism in most of their bikes, but now freewheel is included in the rear sprocket of the bike like the original design of Van Anden.
In 1924, the French bike company, Le Cyclo, introduced a gear wheel with two freewheel sprockets, which would allow the rider to ride up more easily. In the late 1920s, Le Cyclo began to use front and rear derailleur in combination with double chains that gave bicycles twice as many gears. In the early 1930s, Le Cyclo invented four freewheel sprockets and a few years later the company incorporated four spree freewheels with triple chainring giving twelve gear bikes.
In the 1970s, Japanese manufacturers introduced their own derailleur version. The Japanese bike company, SunTour introduced derailleurs behind a sloped parallelogram that tilted backwards allowing the cage to be placed farther from the freewheel than the European version. This allows the chain to shift more smoothly from the teeth to the teeth. The Japanese version of derailleur is standard and still exists today.
See also
- Sandal clip
- Clutch sprag
- Saab 96
References
Source of the article : Wikipedia
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