Gears

History            

A machine consists of a power source and a power transmission system, which provides controlled application of the power. Merriam-Webster defines transmission as an assembly of parts including the speed-changing gears and the propeller shaft by which the power is transmitted from an engine to a live axle. Often transmission refers simply to the gearbox that uses gears and gear trains to provide speed and torque conversions from a rotating power source to another device.

            In British English, the term transmission refers to the whole drive train, including clutch, gearbox, prop shaft (for rear-wheel drive), differential, and final drive shafts. In American English, however, a gearbox is any device that converts speed and torque; whereas a transmission is a type of gearbox that can be "shifted" to dynamically change the speed-torque ratio such as in a vehicle.

            The most common use is in motor vehicles, where the transmission adapts the output of the internal combustion engine to the drive wheels. Such engines need to operate at a relatively high rotational speed, which is inappropriate for starting, stopping, and slower travel. The transmission reduces the higher engine speed to the slower wheel speed, increasing torque in the process. Transmissions are also used on pedal bicycles, fixed machines, and anywhere rotational speed and torque must be adapted.

            Often, a transmission has multiple gear ratios (or simply "gears"), with the ability to switch between them as speed varies. This switching may be done manually (by the operator), or automatically. Directional (forward and reverse) control may also be provided. Single-ratio transmissions also exist, which simply change the speed and torque (and sometimes direction) of motor output.

            In motor vehicles, the transmission generally is connected to the engine crankshaft via a flywheel and/or clutch and/or fluid coupling. The output of the transmission is transmitted via driveshaft to one or more differentials, which in turn, drive the wheels. While a differential may also provide gear reduction, its primary purpose is to permit the wheels at either end of an axle to rotate at different speeds (essential to avoid wheel slippage on turns) as it changes the direction of rotation.

            Conventional gear/belt transmissions are not the only mechanism for speed/torque adaptation. Alternative mechanisms include torque converters and power transformation (for example, diesel-electric transmission and hydraulic drive system). Hybrid configurations also exist.

Gearbox

A gearbox is a mechanical method of transferring energy from one device to another and is used to increase torque while reducing speed. Torque is the power generated through the bending or twisting of a solid material. This term is often used interchangeably with transmission.

            Located at the junction point of a power shaft, the gearbox is often used to create a right angle change in direction, as is seen in a rotary mower or a helicopter. Each unit is made with a specific purpose in mind, and the gear ratio used is designed to provide the level of force required. This ratio is fixed and cannot be changed once the box is constructed. The only possible modification after the fact is an adjustment that allows the shaft speed to increase, along with a corresponding reduction in torque.

            In a situation where multiple speeds are needed, a transmission with multiple gears can be used to increase torque while slowing down the output speed. This design is commonly found in automobile transmissions. The same principle can be used to create an overdrive gear that increases output speed while decreasing torque.

            A wind turbine is an example of a very large gearbox. The turbine moves at a slow rate of rotation with a great deal of torque. The transmission translates this power into the faster but lower torque rotational speed of the electricity generator. Due to the sheer size and the amount of power they can generate, wind turbines have multiple gears and stages. This feature is required to ensure that the electricity generator can provide a consistent output even as the turbine rate of rotation fluctuates.

            In an automobile, there are three types of transmission automatic, manual, or continuously variable. A manual transmission vehicle provides the best example of a simple gearbox. In both the automatic and continuously variable transmissions, the gearboxes are closed systems, requiring very little human interaction.

            Manual transmission is available in two different systems sliding mesh and constant mesh. The sliding mesh system uses straight cut spur gears. The gears spin freely and require driver manipulation to synchronize the transition from one speed to another. The driver is responsible for coordinating the engine revolutions to the road speed required. If the transition between gears is not timed correctly, they clash, creating a loud grinding noise as the gear teeth collide.

            The constant mesh system has diagonally-cut helical or double helical gear sets that are permanently meshed together. Friction cones or synchronized rings have been added to the gears to create a smoother transition when changing gears. This type of transmission is usually found in racing cars and agricultural equipment.

 

TYPES OF GEARS

There are many types of gearboxes manufactured throughout the world. One of the main differences between individual gearboxes is their performance characteristics. Choosing from the various gearbox types is application dependent. Gearboxes are available in many sizes, ratios, efficiencies and backlash characteristics. All of these design factors will affect the performance and cost of the gearbox. There are several types of gearboxes which are listed below

Bevel Gears

There are two types of bevel gearboxes which include either straight or spiral teeth gears. Straight bevel gears have straight and tapered teeth and are used in applications requiring slow speeds. Spiral bevel gears have curved and oblique teeth and are used in applications requiring high-performance, high speed applications. Straight bevel gears are used for transmitting power between intersecting shafts .They can operate under high speeds and high loads. Their precision rating is fair to good. They are suitable for 11 and higher velocity ratios and for right-angle meshes to any other angles. Their good choice is for right angle drive of particularly low ratios. However, complicated both form and fabrication limits achievement of precision. They should be located at one of the less critical meshes of the train. Wide application of the straight bevel drives is in automotive differentials, right angle drives of blenders and conveyors.

 

Figure: Straight Bevel Gearbox

Figure: Spiral Bevel Gearbox

 

Physical Properties

Bevel gears are typically constructed from cast iron, aluminum alloy or other steel materials but vary between manufacturers.

            Note Gears made from steel materials can be noisy when coming into contact with other gears and also make them prone to wear.

Applications of Bevel Gears

Bevel gearboxes use bevel gears and are mainly used in right angle applications with the shafts in a perpendicular arrangement.

• Print Press

• Power Plants

• Automobiles

• Steel Plants

• Hand Drills

• Differential Drives

Advantages of Bevel Gears

• Right angle configuration

• Durable

Disadvantages of Bevel Gears

• Axes must be able to support forces

• Poorly cut teeth may result in excessive vibration and noise during operation

 Helical Gears

Helical gears are cut at angles which allow for gradual contact between each of the helical gear teeth. This type of innovation provides for a smooth and quiet operation. Gearboxes using helical gears are applicable in high horsepower and efficient applications.

Figure . Helical Gearbox

Physical Properties

helical gears are typically constructed from cast iron, aluminum allow or iron material but may vary depending on the manufacturer.

Note Gears made from steel materials can be noisy when coming into contact with other gears and also make them prone to wear.

Applications of Helical Gears

helical gears are widely used in applications which require efficiency and high horsepower.

• Oil Industry

• Blowers

• Food and Labeling

• Cutters

• Elevators

Advantages of Helical Gears

• Can be meshed in parallel or cross orientation

• Smooth and quiet operation

• Efficient

• High horsepower

Disadvantages of Helical Gears

• Resultant thrust along axis of gear

• Additives to lubrication

 Spur Gears

Spur gears are made with straight teeth mounted on a parallel shaft. The noise level of spur gears is relatively high due to colliding teeth of the gears which make spur gear teeth prone to wear. Spur gears come in a range of sizes and gear ratios to meet applications requiring a certain speed or torque output.

Figure: Spur Gearbox

Physical Properties

Spur gears are typically constructed from metals such as steel or brass, and plastics such as nylon or polycarbonate. The material used to construct spur gears may vary depending on the manufacturer.

            Note Gears made from steel materials can be noisy when coming into contact with other gears and also make them prone to wear.

Applications of Spur Gears

Spurs gears are used in applications requiring a decrease in speed with high output torque.

• Cut-to-Length

• Packaging

• Speed Control

• Construction

• Power Plants

Advantages of Spur Gears

• Cost-effective

• High gear ratios

• Compact

Disadvantages of Spur Gears

• Noisy

• Prone to wear

 Worm Gears

Worm gears are able to withstand high shock loads, low in noise level and maintenance-free but are less efficient than other gear types. Worm gears can be used in right angle configuration. The worm gearbox configuration allows the worm to turn the gear with ease; however, the gear cannot turn the worm. The prevention of the gear to move the worm can be used as a braking system. When the worm gearbox is not active, it is held in a locked position.

Figure: Worm Gearbox

Physical Properties

Worm gears are typically constructed of aluminum, stainless steel and cast iron. The material used varies depending on the manufacturer.

Applications of Worm Gears

Worm gears are used in applications requiring high speeds and loads and can be configured for right-angle applications.

• Mining

• Rolling Mills

• Presses

• Elevators/Escalator Drive Systems

Advantages of Worm Gears

• High precision

• Right-angle configurations

• Braking system

• Low noise

• Maintenance-free

Disadvantages of Worm Gears

• Limitations

• Nonreversible

• Low efficiency

 Planetary Gears

Planetary gearboxes are named so due to their resemblance to the solar system. The components of a planetary gearbox include a sun gear, ring gear and planetary gears. The sun gear is the central gear which is fixed in the center, ring gear (annulus ring) which is the outer ring with inward-facing teeth, and the planetary gears which rotate around the sun gears and mesh with both the sun and ring gear.

Figure : Planetary Gearbox

Physical Properties

the sun, ring and planetary gears of a planetary gearbox are constructed of aluminum, stainless steel or brass. The material used varies depending on the manufacturer.

            Note Gears made from steel materials can be noisy when coming into contact with other gears and also make them prone to wear.

Applications of Planetary Gears

Planetary gearboxes are used in applications requiring low backlash, compact size, high efficiency, resistance to shock, and a high torque to weight ratio.

• Slewing Drives

• Lifts

• Cranes

• Machine Tools

• Automotive

Advantages of Planetary Gears

• High power density

• Compact

• Highly efficiency in power transmission

• Greater stability

• Load distribution among planetary gears

Disadvantages of Planetary Gears

• High bearing loads
• Complex design
• Inaccessibility

 TYPES OF GEAR BOX

Simple

The simplest transmissions, often called gearboxes to reflect their simplicity (although complex systems are also called gearboxes in the vernacular), provide gear reduction (or, more rarely, an increase in speed), sometimes in conjunction with a right-angle change in direction of the shaft (typically in helicopters, see picture). These are often used on PTO-powered agricultural equipment, since the axial PTO shaft is at odds with the usual need for the driven shaft, which is either vertical (as with rotary mowers), or horizontally extending from one side of the implement to another (as with manure spreaders, flail mowers, and forage). More complex equipment, such as silage choppers and snow blowers have drives with outputs in more than one direction.

          The gearbox in a wind turbine converts the slow, high-torque rotation of the turbine into much faster rotation of the electrical generator. These are much larger and more complicated than the PTO gearboxes in farm equipment. They weigh several tons and typically contain three stages to achieve an overall gear ratio from 401 to over 1001, depending on the size of the turbine. (For aerodynamic and structural reasons, larger turbines have to turn more slowly, but the generators all have to rotate at similar speeds of several thousand rpm.) The first stage of the gearbox is usually a planetary gear, for compactness, and to distribute the enormous torque of the turbine over more teeth of the low-speed shaft. Durability of these gearboxes has been a serious problem for a long time.

          Regardless of where they are used, these simple transmissions all share an important feature the gear ratio cannot be changed during use. It is fixed at the time the transmission is constructed.

          For transmission types that overcome this issue, see Continuously Variable Transmission, also known as CVT.

 Multi- ratio systems

Many applications require the availability of multiple gear ratios. Often, this is to ease the starting and stopping of a mechanical system, though another important need is that of maintaining good fuel efficiency.

Automotive basics

The need for a transmission in an automobile is a consequence of the characteristics of the internal combustion engine. Engines typically operate over a range of 600 to about 7000 revolutions per minute (though this varies, and is typically less for diesel engines), while the car's wheels rotate between 0 rpm and around 1800 rpm.

          Furthermore, the engine provides its highest torque and power outputs unevenly across the rev range resulting in a torque band and a power band. Often the greatest torque is required when the vehicle is moving from rest or traveling slowly, while maximum power is needed at high speed. Therefore, a system that transforms the engine's output so that it can supply high torque at low speeds, but also operate at highway speeds with the motor still operating within its limits, is required. Transmissions perform this transformation.

The dynamics of a car vary with speed at low speeds, acceleration is limited by the inertia of vehicular gross mass; while at cruising or maximum speeds wind resistance is the dominant barrier.

          Many transmissions and gears used in automotive and truck applications are contained in a cast iron case, though more frequently aluminium is used for lower weight especially in cars. There are usually three shafts a main shaft, a countershaft, and an idler shaft.

          The main shaft extends outside the case in both directions the input shaft towards the engine, and the output shaft towards the rear axle (on rear wheel drive cars front wheel drives generally have the engine and transmission mounted transversely, the differential being part of the transmission.

3. Manual transmissions

Manual transmissions come in two basic types

A simple but rugged sliding-mesh or unsynchronized/non-synchronous system, where straight-cut spur gear sets spin freely, and must be synchronized by the operator matching engine revs to road speed, to avoid noisy and damaging clashing of the gears

The now common constant-mesh gearboxes, which can include non-synchronized, or synchronized/synchromesh systems, where typically diagonal cut helical (or sometimes either straight-cut, or double-helical) gear sets are constantly "meshed" together, and a dog clutch is used for changing gears. On synchromesh boxes, friction cones or "synchro-rings" are used in addition to the dog clutch to closely match the rotational speeds of the two sides of the (declutched) transmission before making a full mechanical engagement.

The former type was standard in many vintage cars (alongside e.g. epicyclic and multi-clutch systems) before the development of constant-mesh manuals and hydraulic-epicyclic automatics, older heavy-duty trucks, and can still be found in use in some agricultural equipment. The latter is the modern standard for on- and off-road transport manual and semi-automatic transmission, although it may be found in many forms; e.g., non-synchronized straight-cut in racetrack or super-heavy-duty applications, non-synchro helical in the majority of heavy trucks and motorcycles and in certain classic cars (e.g. the Fiat 500), and partly or fully synchronized helical in almost all modern manual-shift passenger cars and light trucks.

          Manual transmissions are the most common type outside North America and Australia. They are cheaper, lighter, and usually give better performance and fuel efficiency (although automatic transmissions with torque converter lockup and advanced electronic controls can provide similar results). It is customary for new drivers to learn, and be tested, on a car with a manual gear change. In Malaysia and Denmark all cars used for testing (and because of that, virtually all those used for instruction as well) have a manual transmission. In Japan, the Philippines, Germany, Poland, Italy, Israel, the Netherlands, Belgium, New Zealand, Austria, Bulgaria, the UK, Ireland,Sweden, Norway, Estonia, France, Spain, Switzerland, the Australian states of Victoria, Western Australia and Queensland, Finland,Latvia, Lithuania and the Czech Republic, a test pass using an automatic car does not entitle the driver to use a manual car on the public road; a test with a manual car is required. Manual transmissions are much more common than automatic transmissions in Asia, Africa, South America and Europe.

          Manual transmissions can include both synchronized and unsynchronized gearing. For example, reverse gear is usually unsynchronized, as the drive is only expected to engage it when the vehicle is at a standstill. Many older (up to 1970s) cars also lacked syncro on first gear (for various reasons—cost, typically "shorter" overall gearing, engines typically having more low-end torque, the extreme wear on a frequently used first gear synchronizer ...), meaning it also could only be used for moving away from a stop unless the driver became adept at double-declutching and had a particular need to regularly downshift into the lowest gear.

          Some manual transmissions have an extremely low ratio for first gear, called a creeper gear or granny gear. Such gears are usually not synchronized. This feature is common on pickup trucks tailored to trailer-towing, farming, or construction-site work. During normal on-road use, the truck is usually driven without using the creeper gear at all, and second gear is used from a standing start. Some off-road vehicles, most particularly the Willys Jeep and its descendents, also had transmissions with "granny first’s either as standard or an option, but this function is now more often provided for by a low-range transfer gearbox attached to a normal fully synchronized transmission.

Automatic

Most modern North American and Australian and some European and Japanese cars have an automatic transmission that selects an appropriate gear ratio without any operator intervention. They primarily use hydraulics to select gears, depending on pressure exerted by fluid within the transmission assembly. Rather than using a clutch to engage the transmission, a fluid flywheel, or torque converter is placed in between the engine and transmission. It is possible for the driver to control the number of gears in use or select reverse, though precise control of which gear is in use may or may not be possible.

          Automatic transmissions are easy to use. However, in the past, automatic transmissions of this type have had a number of problems; they were complex and expensive, sometimes had reliability problems (which sometimes caused more expenses in repair), have often been less fuel-efficient than their manual counterparts (due to "slippage" in the torque converter), and their shift time was slower than a manual making them uncompetitive for racing. With the advancement of modern automatic transmissions this has changed.

          Attempts to improve fuel efficiency of automatic transmissions include the use of torque converters that lock up beyond a certain speed or in higher gear ratios, eliminating power loss, and overdrive gears that automatically actuate above certain speeds. In older transmissions, both technologies could be intrusive, when conditions are such that they repeatedly cut in and out as speed and such load factors as grade or wind vary slightly. Current computerized transmissions possess complex programming that both maximizes fuel efficiency and eliminates intrusiveness. This is due mainly to electronic rather than mechanical advances, though improvements in CVT technology and the use of automatic clutches have also helped. A few cars, including the 2013 Subaru Impreza and the 2012 model of the Honda Jazz sold in the UK, actually claim marginally better fuel consumption for the CVT version than the manual version.

          For certain applications, the slippage inherent in automatic transmissions can be advantageous. For instance, in drag racing, the automatic transmission allows the car to stop with the engine at a high rpm (the "stall speed") to allow for a very quick launch when the brakes are released. In fact, a common modification is to increase the stall speed of the transmission. This is even more advantageous for turbocharged engines, where the turbocharger must be kept spinning at high rpm by a large flow of exhaust to maintain the boost pressure and eliminate the turbo lag that occurs when the throttle suddenly opens on an idling engine.

Semi-automatic

A hybrid form of transmission where an integrated control system handles manipulation of the clutch automatically, but the driver can still—and may be required to—take manual control of gear selection. This is sometimes called a "clutch less manual", or "automated manual" transmission. Many of these transmissions allow the driver to fully delegate gear shifting choice to the control system, which then effectively acts as if it was a regular automatic transmission. They are generally designed using manual transmission "internals", and when used in passenger cars, have synchromesh operated helical constant mesh gear sets.

          Early semi-automatic systems used a variety of mechanical and hydraulic systems—including centrifugal clutches, torque converters, electro-mechanical (and even electrostatic) and servo/solenoid controlled clutches—and control schemes—automatic declutching when moving the gearstick, pre-selector controls, centrifugal clutches with drum-sequential shift requiring the driver to lift the throttle for a successful shift, etc.—and some were little more than regular lock-up torque converter automatics with manual gear selection.

          Most modern implementations, however, are standard or slightly modified manual transmissions (and very occasionally modified automatics—even including a few cases of CVTs with "fake" fixed gear ratios), with servo-controlled clutching and shifting under command of the central engine computer. These are intended as a combined replacement option both for more expensive and less efficient "normal" automatic systems, and for drivers who prefer manual shift but are no longer able to operate a clutch, and users are encouraged to leave the shift lever in fully automatic "drive" most of the time, only engaging manual-sequential mode for sporty driving or when otherwise strictly necessary.

          Specific types of this transmission include Easytronic, Tiptronic and Geartronic, as well as the systems used as standard in all ICE-powered Smart-MCC vehicles, and on geared step-through scooters such as the Honda Super Cub or Suzuki Address.

          A dual-clutch transmission alternately uses two sets of internals, each with its own clutch, so that a "gear change" actually only consists of one clutch engaging as the other disengages—providing a supposedly "seamless" shift with no break in (or jarring reuptake of) power transmission. Each clutch's attached shaft carries half of the total input gear complement (with a shared output shaft), including synchronized dog clutch systems that pre-select which of its set of ratios is most likely needed at the next shift, under command of a computerized control system. Specific types of this transmission include Direct-Shift Gearbox.

          There are also sequential transmissions that use the rotation of a drum to switch gears, much like those of a typical fully manual motorcycle. These can be designed with a manual or automatic clutch system, and may be found both in automobiles (particularly track and rally racing cars), motorcycles (typically light "step-thru" type city utility bikes, e.g., the Honda Super Cub) and quad bikes (often with a separately engaged reversing gear), the latter two normally using a scooter-style centrifugal clutch.

Bicycle gearing

Bicycles usually have a system for selecting different gear ratios. There are two main types derailleur and hub gears. The derailleur type is the most common, and the most visible, using sprocket gears. Typically there are several gears available on the rear sprocket assembly, attached to the rear wheel. A few more sprockets are usually added to the front assembly as well. Multiplying the number of sprocket gears in front by the number to the rear gives the number of gear ratios, often called "speeds".

          Hub gears use epicyclic gearing and are enclosed within the axle of the rear wheel. Because of the small space, they typically offer fewer different speeds, although at least one has reached 14 gear ratios and Fallbrook Technologies manufactures a transmission with technically infinite ratios.

          Causes for failure of bicycle gearing include worn teeth, damage caused by a faulty chain, damage due to thermal expansion, broken teeth due to excessive pedaling force, interference by foreign objects, and loss of lubrication due to negligence.

Uncommon Types

Dual clutch transmission

This arrangement is also sometimes known as a direct shift gearbox or power shift gearbox. It seeks to combine the advantages of a conventional manual shift with the qualities of a modern automatic transmission by providing different clutches for odd and even speed selector gears. When changing gear, the engine torque is transferred from one gear to the other continuously, so providing gentle, smooth gear changes without either losing power or jerking the vehicle. Gear selection may be manual, automatic (depending on throttle/speed sensors), or a 'sports' version combining both options.

Continuously variable

The continuously variable transmission (CVT) is a transmission in which the ratio of the rotational speeds of two shafts, as the input shaft and output shaft of a vehicle or other machine, can be varied continuously within a given range, providing an infinite number of possible ratios. The CVT allows the driver or a computer to select the relationship between the speed of the engine and the speed of the wheels within a continuous range. This can provide even better fuel economy if the engine constantly runs at a single speed. The transmission is, in theory, capable of a better user experience, without the rise and fall in speed of an engine, and the jerk felt when changing gears poorly.

          CVTs are increasingly found on small cars, and especially high-gas-mileage or hybrid vehicles. On these platforms, the torque is limited because the electric motor can provide torque without changing the speed of the engine. By leaving the engine running at the rate that generates the best gas mileage for the given operating conditions, overall mileage can be improved over a system with a smaller number of fixed gears, where the system may be operating at peak efficiency only for a small range of speeds. CVTs are also found in agricultural equipment; due to the high-torque nature of these vehicles, mechanical gears are integrated to provide attractive force at high speeds. The system is similar to that of a hydrostatic gear box, and at 'inching speeds' relies entirely on hydrostatic drive. German tractor manufacturer Fendt pioneered the technology, developing its 'Vario' transmission.

Infinitely variable

The IVT is a specific type of CVT that includes not only an infinite number of gear ratios, but an infinite range as well. This is a turn of phrase; it actually refers to CVTs that are able to include a "zero ratio", where the input shaft can turn without any motion of the output shaft while remaining in gear. Zero output implies infinite ratios, as any "high gear" ratio is an infinite number of times higher than the zero "low gear".

          Most (if not all) IVTs result from the combination of a CVT with an epicyclic gear system with a fixed ratio. The combination of the fixed ratio of the epicyclic gear with a specific matching ratio in the CVT side results in zero output. For instance, consider a transmission with an epicyclic gear set to 1−1 gear ratio; a 11 reverse gear. When the CVT side is set to 11 the two ratios add up to zero output. The IVT is always engaged, even during its zero output. When the CVT is set to higher values it operates conventionally, with increasing forward ratios.

In practice, the epicyclic gear may be sent to the lowest possible ratio of the CVT, if reversing is not needed or is handled through other means. Reversing can be incorporated by setting the epicyclic gear ratio somewhat higher than the lowest ratio of the CVT, providing a range of reverse ratios.

Electric variable

The Electric Variable Transmission (EVT) combines a transmission with an electric motor to provide the illusion of a single CVT. In the common implementation, a gasoline engine is connected to a traditional transmission, which is in turn connected to an epicyclic gear system's planet carrier. An electric motor/generator is connected to the central "sun" gear, which is normally un-driven in typical epicyclic systems. Both sources of power can be fed into the transmission's output at the same time, splitting power between them. In common examples, between one-quarter and half of the engine's power can be fed into the sun gear. Depending on the implementation, the transmission in front of the epicyclic system may be greatly simplified or eliminated completely. EVTs are capable of continuously modulating output/input speed ratios like mechanical CVTs, but offer the distinct benefit of being able to also apply power from two different sources to one output, as well as potentially reducing overall complexity dramatically.

          In typical implementations, the gear ratio of the transmission and epicyclic system are set to the ratio of the common driving conditions, say highway speed for a car, or city speeds for a bus. When the drivers presses on the gas, the associated electronics interprets the pedal position and immediately sets the gasoline engine to the RPM that provides the best gas mileage for that setting. As the gear ratio is normally set far from the maximum torque point, this set-up would normally result in very poor acceleration. Unlike gasoline engines, electric motors offer efficient torque across a wide selection of RPM, and are especially effective at low settings where the gasoline engine is inefficient. By varying the electrical load or supply on the motor attached to the sun gear, additional torque can be provided to make up for the low torque output from the engine. As the vehicle accelerates, the power to the motor is reduced and eventually ended, providing the illusion of a CVT.

          The canonical example of the EVT is Toyota's Hybrid Synergy Drive. This implementation has no conventional transmission, and the sun gear always receives 28% of the torque from the engine. This power can be used to operate any electrical loads in the vehicle, recharging the batteries, powering the entertainment system, or running the air conditioning. Any residual power is then fed back into a second motor that powers the output of the drive train directly.

GEARBOX MECHANISM

 

Working of Gearbox

All gearboxes work in a similar fashion. The directions the gears rotate are dependent on the input direction and orientation of the gears. For example, if the initial gear is rotating in a clockwise direction, the gear it engages will rotate counterclockwise. This continues down the line for multiple gears. The combination of different size gears and the number of teeth on each gear plays a significant role in the output torque and speed of the shaft. High gear ratios allow for more output torque and lower speeds, while lower gear ratios allow for higher output speed and less output torque.

            A planetary gearbox works relatively the same. A planetary gearbox system is constructed with three main components a central sun gear, a planet carrier (carrying one or more planet gears) and an annulus (an outer ring). The central sun gear is orbited by planet gears (of the same size) mounted to the planet carrier. The planet gears are meshed with the sun gear while the outer rings teeth mesh with the planet gears. There are several configurations for a gearbox system. Typical configurations consist of three components the input, the output and one stationary component.

            For example one possible configuration is the sun gear as the input, the annulus as the output and the planet carrier remaining stationary. In this configuration, the input shaft rotates the sun gear, the planet gears rotate on their own axes, simultaneously applying a torque to the rotating planet carrier that in turn applies torque to the output shaft (which in this case is the annulus). The rate at which the gears rotate (gear ratio) is determined by the number of teeth in each gear. The torque (power output) is determined by both the number of teeth and by which component in the planetary system is stationary.

Controlling of Gearbox

The output of a motor (i.e. stepper, brushless, AC and brush motors) is used as the input of the gearbox and controls the speed at which the gearbox rotates. The configuration below illustrates the driver controlling the external motor, which is connected as the input shaft of the gearbox. As a result, when the driver is powered, the motor shaft rotates inside the gearbox causing the output shaft of the gearbox to rotate. The output speed and torque is dependent on the internal configuration of the gearbox.

 Selection of the Appropriate Gearbox

When considering a gearbox, many factors need to be considered to meet specific application requirements

Gear Ratio
Gear ratios are defined as the correlation between the numbers of teeth of two different gears. Commonly, the number of teeth a gear has is proportional to its circumference. This means that the gear with a larger circumference will have more gear teeth; therefore the relationship between the circumferences of the two gears can also give an accurate gear ratio. For example, if one gear has 36 teeth while another gear has 12 teeth, the gear ratio would be 31.

Output Torque
Output torque is dependent on the gear ratio used. To obtain a high output torque, a large gear ratio would be selected. Using a large gear ratio will lower the output shaft speed of the motor. Inversely, using a lower gear ratio, a smaller output torque value would be delivered into the system, with a greater motor speed at the output shaft.

Speed (RPM)
Speed is proportional to the gear ratio of the system. For example, if the input gear has more teeth than the output gear, the result will be an increase in speed at the output shaft. On the other hand, having the reverse scenario with more gear teeth at the output compared to the input will result in a decrease of speed at the output shaft. In general, the output speed can be determined by dividing the input speed by the gear ratio.

Gear Arrangement
Gear arrangement is an ingenious engineering design that offers various benefits over the traditional fixed axis gear system design. The unique combination of both power transmission efficiency and compact size allows for a lower loss in efficiency. The more efficient the gear arrangement, (i.e. spur, helical, planetary and worm) the more energy it will allow to be transmitted and converted into torque, rather than energy lost in heat.

            Another application factor to be taken into account is load distribution. Since the load being transmitted is shared among multiple planets, the torque capacity is increased. The higher number of planets in a gear system will increase the load ability and enhance torque density. 

 
                               Figure: Fixed-Axis vs. Planetary Gear System

            In Figure 8, the gear arrangement on the left is a traditional fixed axis gear system with a pinion driving a larger gear on an axis parallel to the shaft. On the right, is a planetary gear design system with a sun gear (pinion) surrounded by more than one gear (planet gears) and is encompassed in an outer ring gear. The two systems are similar in ratio and volume, but the planetary gear design has three times the higher torque density and three times the stiffness due to the increased number of gear contacts.

Fixed Axis Gear System
Volume = 1, Torque = 1, Stiffness = 1

Planetary Gear System
Volume =1, Torque = 3, Stiffness = 3

Other gear arrangements as mentioned in the Types of Gearboxes segment of this guide are bevel, helical, cycloid, spur and worm.

Backlash
Backlash is the angle in which the output shaft of a gearbox can rotate without the input shaft moving, or the gap between the teeth of two adjacent gears. It is not necessary to consider backlash for applications which do not involve load reversals. However, in precision applications with load reversals like robotics, automation, CNC machines, etc., backlash is crucial for accuracy and positioning.

Advantages of a Gearbox

• Low noise level

• High efficiency

• High reduction ratios

• Increase in output torque

• Decrease in output speed

• Durable

Disadvantages of a Gearbox

• More costly than other drive systems

• Proper lubrication is necessary for smooth running

• Poorly cut teeth may result in excessive vibration and noise during operation

• Quality matters and adds to cost

Troubleshooting

Problem Gearbox Becomes Hot
Solution The exterior temperature of the gearbox may become hot due to several reasons. Please refer to the following information, take the necessary steps to solve this issue. If the gearbox temperature is excessive, please consult the manufacturer.

1. Ambient temperature is above advised level - If the ambient temperature is too high, it may diminish the efficiency of the gearbox. Install a cooling fan or move the application to a more viable location.

2. Proper ventilation - Proper ventilation is necessary, not only for the gearbox but for all electrical/mechanical equipment to function properly. Ensure that there is adequate air flow in the area of the equipment to allow for system cooling.

3. Improper shaft alignment - The first step is to check the alignment of the input shaft of the motor to the gearbox. It is necessary that the input shaft of the motor be aligned with the gearbox to ensure the proper use of the gearbox.

4. Overload - Decrease the load of the gearbox and observe if the temperature lowers. If not, your application may require a larger gearbox model.

5. Lubrication – Poor lubrication for the bearings and gears. Consult with the manufacturer regarding warranty information.

6. Improperly mounted bearings - Reassembly may be required of the gearbox. Consult with the manufacturer regarding warranty information.

Problem Loud/Vibration Noise
Solution Loud or vibration noises can be due to many different sources discussed in this section.

Improper installation - Improper installation may be a result of loose bolts or misalignment between the motor and gearbox. Tightening loose bolts and aligning the motor and gearbox may solve the issue of excessive noise.

2. Input speed too high - Lowering the input speed may help reduce the noise.

3. Overload - Decreasing the load may help reduce the noise. If not, a larger-sized model gearbox will be required.

4. Worn or damaged bearings - Worn or damaged bearings may need to be replaced. Consult with the manufacturer regarding warranty information.

5. Lubrication - Gears/bearings need to be properly lubricated for cohesiveness. Consult with the manufacturer regarding warranty information.

Problem Input/output Shafts Do Not Rotate
Solution Before going through the below instructions, ensure the motor shaft rotates to isolate any problem with the motor or gearbox.

1. Proper installation - Ensure that all bolts connecting the motor to the gearbox are securely fastened.
2. Gear teeth are worn - Need to replace worn gears. Consult your dealer for warranty information.

3. Gears in locked position - Gears may need to be replaced due to wear and tear. Another possibility would be that a foreign object may need to be removed from within the gearbox, causing the gears to be in the locked position. Consult your dealer for warranty information.

Problem Gear Teeth Wear
Solution Wear and tear on gearboxes is natural occurrences. Proper use and system maintenance can help extend their lifetime of the gearbox.

1. Proper installation - Ensure that all bolts connecting the motor and the gearbox are securely fastened.

2. Excessive load - Wear and tear on the gear is caused by contact with other gears. Reducing the load will lower the tension the gears make with one another. If a higher load is required, using a larger gearbox may be necessary.

3. Input speed too high - Lowering the input speed may help reduce the amount of wear and tear on the gears.

4. Ambient temperature is above the advised level - If the ambient temperature is too high, it may diminish the efficiency of the gearbox. Installing a cooling fan or moving the application to a more viable location may resolve this application.

Cost of a Gearbox

The price of a gearbox varies and is typically affected by size, accuracy specifications, backlash, and the gear ratio, as well as the specific manufacturer. Gearboxes with a backlash in the range of 30 arc-minutes may cost as low as $500. The cost for gearboxes with a backlash value under 5 arc-minutes will cost more than gearboxes with high backlash values. Below is a list of gearbox products offered by Anaheim Automation? Comprehensive specifications and pricing is available on our website at AnaheimAutomation.com, for each of the offered types

• Economy Gearboxes

• High-Grade Gearboxes

• Right-Angle Planetary Gearboxes

• Rotating Output Flange Gearboxes

Formulas

Motor Torque x Gear Ratio = Torque at the Wheel

Input Shaft Speed (RPM) / Gear Ratio = Output Shaft Speed

Gear Ratio = Teeth on one gear Teeth on a second gear

Example If one gear has 60 teeth and a second gear has 20 teeth the gear ratio would be 31

Use of gearbox

Advancements in technology and the evolution of gears have made more efficient and powerful gearboxes to be developed and manufactured at lower costs. Toothed gear systems have evolved from fixed axis gear systems to new and improved gears including helical, cycloid, spur, worm and planetary gear systems. Gearboxes are widely used in applications that require desired output speed (RPM), control the direction of rotation, and to translate torque or power from one input shaft to another.

Gearboxes are used in a variety of industries

• Aerospace – In the aerospace industry, gearboxes are used in space and air travel, i.e. airplanes, missiles, space vehicles, space shuttles and engines.
• Agriculture – In the agriculture industry, gearboxes are used for plowing, irrigation, pest and insect control, tractors and pumps.
• Automotive – In the automotive industry, gearboxes are used in cars, helicopters, buses and motorcycles.
• Construction – In the construction industry, gearboxes are used in heavy machinery such as cranes, forklifts, bulldozers and tractors.
• Food Processing – In the food processing industry, gearboxes are used in conveyor systems, the processing of meat and vegetable products, and packaging applications.
• Marine Industry – In the marine industry, gearboxes are used on boats and yachts.
• Medical – In the medical industry, gearboxes are used in surgical tables, patient beds, medical diagnostic machines, dental equipment and MRI and CAT scan machines.
• Power Plants – In power plants, gearboxes are implemented in transformers, generators and turbines.