Transmission

transmission of motorcycle


1       WHAT IS TRANSMISSION?

The mechanism that transmits the power developed by the engine of the automobile to the driving wheel is called the transmission system.

Main components are:

  1. Engine:
  2. Clutch
  3. Gearbox
  4. Differential

 

  • WHAT IS CLUTCH?

Clutch is a device which is used to transmit power from one shaft to another. It connects a shaft on which it mounted to another shaft which is in motion. Clutches are generally used in automobile to transmit power from engine to the driving wheels.

In cars it transmit power from the flywheel connected to the engine shaft to the clutch shaft,

And from clutch shaft it is transmitted to the rear wheels through gear shaft, propeller shaft and differential.

 

Requirements of a good clutch

  1. Gradual engagement :

The clutches should be engaged gradually so that the sudden jerks produced must be avoided.

 

  1. Torque transmission:

The clutch should be so designed, so that it can be able to transfer maximum power through it.

 

  1. Heat dissipation:

It should be so designed, so that maximum dissipation of heat takes place from it.

 

  1. Vibration damping:

The clutch be so designed, so that the noise or vibration produced in the transmission can be eliminated easily.

 

Types of clutches

  • Cone clutch
  1. Single plate clutch
  • Multi plate clutch
  1. Semi centrifugal clutch
  2. Centrifugal clutch

 

 

Components of clutch

  1. Driving members
  • The driving members of a flywheel which is mounted on the engine crankshaft
  • The flywheel is bolted to a cover which carries pressure plate, pressure springs and releasing
  • As a flywheel is bolted to the cover assembly, thus, the entire assembly of the flywheel and the cover rotate all the

 

  • The clutch housing and the cover provided with openings so the heat produced during the function dissipates
  1. Driven members
  • The driven members consists of a disc or plate called clutch
  • The clutch is free to slide on the splines of the clutch
  • It carries friction materials on both of its
  • When the clutch plate is gripped between the flywheel and the pressure plate, it rotates the clutch shaft through
  1. Operating members

The operating members consists of a foot pedal, linkage, release or throw out bearings.

 

  • TYPES OF GEARBOX IN AUTOMOBILES?

Why do we need gearbox?

When a car start, the torque provided by the engine output shaft is not enough to overcome the weight of the vehicle which make it difficult to move the car initially, so to solve this problem a gearbox is required which can provide high torque initially in order to move the vehicle.

When we go to the hill station it is essential that the vehicle should be equipped with the device that can provide a wide range of high torque, to fulfill this need a gearbox is required so that a vehicle can go to the hills.

Main parts of a gearbox

  1. Main shaft

It is the shaft used as an output shaft in a gearbox, this shaft is usually kept parallel to the lay shaft and in front of the clutch shaft or engine output shaft, the change of gear usually occur through this shaft as it usually connected to gear lever

  1. Clutch shaft

It is shaft which carries the engine output to the gearbox, the engaging and disengaging of the engine output occurs with the help of clutch.

 

 

  1. Lay shaft

It is the shaft through which the output of the engine is transferred to the main shaft by the continuous meshing of a gear on the lay shaft to the gear on the clutch shaft.

  1. Gears

They are connecting circles with teeth that rotates and meshes with another gear on the different shaft in order to transmit the circular motion between 2 different shafts, they can be – spur gear, helical gear, bevel gear and worm gear.

  1. Synchromesh shaft

They are the special devices used in modern gearbox (synchromesh gearbox) that makes the shifting of gears smooth by bringing the speed of main – shaft, lay – shaft and clutch

– shaft at the same, they doesn’t have to slide over the shaft for the shifting of the gear.

  1. Gear lever

It is the lever operated by the driver to change or shift the gear, the movement of the lever is designed in a particular fashion.

Types of Gearbox‐

  1. Manual Transmission:

A manual transmission is the types of gearbox used in most of the vehicle on the road due to its low cost. It is the type of gearbox in which there are limited gear or speed ratios i.e. maximum of 6‐ speed and 1‐ reverse is there, and the shifting of gears is a manual task performs by the driver by pushing or pulling the gear lever in predefined fashion. Manual transmission always requires the use of clutch. Types of manual transmission used since the introduction of the gearbox are:

  1. Sliding Mesh Gearbox
  2. Constant Mesh Gearbox
  3. Synchromesh Gearbox

 

 

  1. Automatic Transmission or Gearbox

It is used in high‐end cars due to its high cost, in this types of gearbox infinite gear ratios can be obtained by just pressing the accelerator, the driver just need to select the mode of the drive i.e. forward or reverse, park, neutral, drive and sport, and the required gear ratios along with the timing of the meshing is obtained automatically. Automatic gearbox doesn’t require clutch pedal, so all the cars with automatic transmissions comes with only 2 pedals.

Types of automatic transmission used are‐

  1. Epicyclic Gearbox
  2. Hydraulic Torque Converter

 

  • GEAR TERMINOLOGY:
  1. Face of tooth: It is defined as the surface of the tooth above the pitch circle is known as face.
  2. Flank of tooth: The surface of the tooth below the pitch circle is known as
  3. Top land: The top most surface of the tooth is known as the top land of the
  4. Face width: Width of the tooth is known as face
  5. Pitch Circle: It is an imaginary circle which is in pure rolling action. The motion of the gear is describe by the pitch circle
  6. Pitch Circle diameter: The diameter of the pitch circle from the center of the gear is known as pitch circle diameter. The gear diameter is described by its pitch circle diameter.
  7. Pitch point: When the two gears are in contact, the common point of both of pitch circle of meshing gears is known as pitch
  8. Pressure angle or angle of obliquity: Pressure angle is the angle between common normal to the pitch circle to the common tangent to the pitch
  9. Addendum: Distance between the pitch circle to the top of the tooth in radial direction is known as
  10. Dedendum: Distance between the pitch circle to the bottom of the tooth in radial direction, is known as dedendum of the
  11. Addendum circle: The circle passes from the top of the tooth is known as addendum circle. This circle is concentric with pitch
  12. Dedendum circle: The circle passes from the bottom of the tooth is known as dedendum circle. This circle is also concentric with pitch circle and addendum
  13. Circular pitch: The distance between a point of a tooth to the same point of the adjacent tooth, measured along circumference of the pitch circle is known as circular

 

pitch. It is plays measure role in gear meshing. Two gears will mesh together correctly if and only they have same circular pitch.

  1. Diametrical pitch: The ratio of the number of teeth to the diameter of pitch circle in millimeter is known as diametrical
  2. Module: The ratio of the pitch circle diameter in millimeters to the total number of teeth is known as module. It is reciprocal of the diametrical
  3. Clearance: When two gears are in meshing condition, the radial distance from top of a tooth of one gear to the bottom of the tooth of another gear is known as clearance. The circle passes from the top of the tooth in meshing condition is known as clearance angle.
  4. Total depth: The sum of the addendum and dedendum of a gear is known as total depth. It is the distance between addendum circle to the dedendum circle measure along radial
  5. Working depth: The distance between addendum circle to the clearance circle measured along radial direction is known as working depth of the
  6. Tooth thickness: Distance of the tooth measured along the circumference of the pitch circle is known as tooth
  7. Tooth space: Distance between the two adjacent tooth measured along the circumference of the pitch circle is known as the tooth
  8. Backlash: It is the difference between the tooth thickness and the tooth space. It prevents jamming of the gears in meshing
  9. Profile: It is the curved formed by the face and flank is known as profile of the

Gear tooth are generally have cycloidal or involute profile.

  1. Path of contact: The curved traced by the point of contact of two teeth form beginning to the end of engagement is known as path of
  2. Arc of contact: It is the curve traced by the pitch point form the beginning to the end of engagement is known as arc of
  3. Arc of approach: The portion of the path of contact from beginning of engagement to the pitch point is known as arc of
  4. Arc of recess: The portion of the path of contact form pitch point to the end of the engagement is known as arc of

 

  • Gear Ratio

A gear ratio is a direct measure of the ratio of the rotational speeds of two or more interlocking gears. As a general rule, when dealing with two gears, if the drive gear (the one directly receiving rotational force from the engine, motor, etc.) is bigger than the driven gear, the latter will turn more quickly, and vice versa. We can express this basic concept with the formula Gear ratio = T2/T1, where T1 is the number of teeth on the first gear and T2 is the number of teeth on the second.

For example:

 

  • IDLER GEAR

Idler gear is a gear wheel placed between two other gears to transmit motion from one to the other. It does not alter the speed of the output, but it does alter the direction it turns. It is used to ensure that the rotation of two gears is the same.

An idler gear is placed between two gears. The idler gear rotates in the opposite direction as the driver gear, and the follower gear rotates in the opposite direction of the idler, the same direction of the driver. It is also used to change the spacing between the input and output axles. It does not change the gear ratio between the input and output gears.

All the gears and wheels that turn inside the treads of a battle tank are all idler gears that transfer power from the input gear to the output gear to move the tread and move the tank forward. The power take off mechanism includes a gear train with an input idler gear, a first intermediate idler gear, a second intermediate idler gear and an output gear. The input idler gear receives a rotary input and the first intermediate idler gear meshes with the input gear and the second intermediate idler gear. The output gears transmit rotary power to one of the first and second axles.

 

  • CVT USED IN TWO WHEELERS

Gearless scooters have automatic transmission known continuously variable transmission (CVT) which enables it to automatically shift from low to high drive ratio using centrifugal system.

It has driver pulley, driven pulley with variable diameter and v – belt with contant length runs between these two pulleys.

High RPM is obtained by increasing diameter of driver pulley and decreasing the diameter of driven pulley. High torque is obtained by doing opposite. The system allow us to achieve infinite number of drive ratio between minimum and maximum limit.

A variator assembly is used for changing the diameter of pulley.Pulley is made up of two conical plate, one is fixed and other is free to slide along its axis, v‐ belts runs between these

 

plate.The rear side also has two two conical plate between the belts runs , one of these plate is fixed to the shaft while the other can slide sideways.

Condition of high torque and low rpm:

A compression spring forces the sliding plate to stay close to the other plate this forces the belt to stay at the maximum diameter. In the driver pulley the axial stiffness of the belt pushes the sliding cone farther apart this causes the driver pulley had min diameter.

Condition of high rpm and low torque:

to obtain high rpm the diameter of the driver pulley decreases and driven pulley increases.

  • Torque and Horse power

Torque helps a vehicle in its acceleration. Better the torque of a vehicle, better is its acceleration. In India, automobile manufacturers mostly use ‘N m‘ as a unit for torque. In some other countries, ‘pound‐foot’ (lb‐ft) is used as unit for torque.

Horse Power is one of the most important factors which determines a vehicle’s top‐speed. Higher the power of a vehicle, higher is its top speed.

Automobile manufacturers in India use ‘bhp‘ or ‘PS‘ as units for power. In some other countries, ‘kilowatt’ (kW) is used. ‘bhp’ is an abbreviation for ‘Brake Horse Power’ and ‘PS’ is an abbreviation for ‘Pferdesträrke’. PS and bhp are virtually interchangeable terms because of insignificant difference between them. 1 PS = 0.98632 bhp Torque BHP and HP are very much related.

The amount of power an engine produces at a certain rpm depends on the amount of torque produced at that rpm.

  1. HP is the output horsepower rating of an engine, while BHP is the input brake horsepower of an
  2. BHP is the measurement of an engine’s power without any power losses, while HP is BHP less the power
  3. HP is measured by hooking up the engine to a dynamometer, while BHP is measured in a controlled environment without anything attached to the
  4. Horsepower is the total power output of an engine, while torque measures the “turning/torqueing ability” of the engine. Practically, torque is a better measurement of how quickly your car will accelerate, while horsepower (relative to weight) is a better measure of your car’s top

 

  • Engine Oil v/s Transmission Oil

 

 

Both of these oils are completely different and their working conditions are different as well. In an IC Engine, the temperature is higher due to the presence of combustion chamber as compared to the transmission.

The viscosity of the engine oil is less as compared to the transmission oil.

 

Transmission Oil

 

Engine Oil

 

If we take the transmission gears, the teeth of the gears rub amongst each other. In order to sustain the smooth functioning, an oil of higher viscosity is needed so that it can sustain the pressure as well as lubricate the system in order to prevent the wear and tear.

 

 

If we put engine oil in transmission system, due to its lower viscosity, the engine oil may not be able to hold itself between the teeth and may rush away resulting in loud noise and the gear may stop functioning properly.

 

 

The transmission oil being more viscous, also absorbs the shocks being produced during the transmission of power from the engine.

 

 

Whereas, the engine oil is made such that it is able to lubricate the components at very high temperatures and ensure smooth functioning.

 

 

Hence, both of these oils serve a different purpose and should not be mixed.

 

  • Timing Chain v/s Timing Belt

In an IC Engine, the piston cylinder arrangement is attached to the crank shaft and the camshaft. Crank shaft delivers the power from the engine to the transmission and then it is transferred to the wheels. Whereas the Camshaft is responsible for controlling the intake and exhaust valve operations.

It is important that the rotation of the camshaft and the crankshaft is linked together in the engine firing order so that the four operations i.e., Intake, Compression, Combustion and Exhaust are performed correctly.

Hence, a timing chain or timing belt is used for the purpose of linking the camshaft to the crankshaft.

 

 

The timing chain functions in the same way that a timing belt does. The difference between the two is simply the material and location. One is constructed of metal and the other, a reinforced rubber. Either of these parts can be found in the internal combustion engine of a vehicle. Their responsibility is to keep the rotation of the camshaft and crankshaft synchronized.

 

 

The camshaft in the engine controls the valves to let fuel and air in and out. At the same time, the crankshaft moves the pistons up and down. This is called mechanical timing and the synchrony of these functions is imperative. If the mechanical timing is off, damage could occur to the valves, pistons, engine, or other components.

 

 

 

 

Timing Chain

 

 

The purpose of the timing belt or chain is to ensure the harmonization by keeping each turning at the precise rate. Timing chains A timing chain looks like the chain on a bicycle. The timing chain has the added advantage of durability. In fact, it should last the lifetime of your vehicle.

In contrast, a timing chain is a metal chain that unites the crankshaft and camshaft to make them revolving in‐sync. One major advantage of using timing chain over belt is its long‐lasting feature. Luckily, these chains need not be replaced after some miles. They can last until the life of your car’s engine.

Timing Belt

 

 

In addition, they contain tensioners that help to keep them working accurately and prevent loosening. Timing chains are tremendously dependent on the engine’s oil pressure. If the oil pressure is low or incoherent, it can affect the working of the chain and can impact the engine timings. As great and long lasting as timing chains are, there are a few things that might annoy you about them.

 

The biggest annoyance is the noise timing chains make. They are known for being much noisier than timing belts. That said, technology in newer vehicles has made the timing chain just as quiet as engines with a timing belt. Also, it is possible for a timing chain to break completely. Once this happens, it will cause a lot of expensive damage to your engine. You may even need to replace your engine altogether if your timing chain breaks and damages it. Engine replacement would be cheaper than engine repair in this situation. Timing Belt Timing belts have been around since the 1960s. They replaced the timing chain due to their smooth, quiet running and lower cost.

 

 

The service life of the timing belt is estimated at 60,000 to 100,000 miles or 5 to 7 years, depending on the vehicle model. Another benefit is their price. Because of their material and simple construction, timing belts are much cheaper to replace than timing chains. Like a timing chain, if a timing belt breaks, catastrophic engine damage can occur. That’s why it’s critical you follow the manufacturer’s recommended timing belt change interval. In most cases, this will be somewhere between 60,000 and 100,000 miles. They last about half as long as a timing chain.

 

  • Chain vs Belt vs Shaft Drive

 

It’s all too common to see a pair of sprockets connected through a chain, driving the rear wheel of a motorcycle. However, it’s not the only final drive system used on motorcycles. Belt drive and shaft drive are the other two final drive systems, though they are not as ubiquitous as chain drive systems. So what exactly are the various advantages and disadvantages of the three drive systems, and what is it about chain drives that make them the preferred choice?

1.  Belt Drive

 

A belt drive system isn’t as common as a chain drive system, though in terms of popularity, it stands at a distant second position. This setup comprises of a driving pulley towards the gearbox output shaft and a driven pulley at the wheel – the two pulleys are connected by a belt which has teeth, or grooves on the inner side, matching the grooves on the outer side of the pulleys.

The belt is made of a rubber‐like, but mostly a very strong synthetic material which lasts a very long time. Modern drive belts are strengthened with steel wires inside and Kevlar coating outside – such belt systems can last really long. You can expect a well‐maintained belt drive on a motorcycle to last in excess of 100,000 km or even more.

Unlike chain drive, which requires very frequent cleaning, tightening and maintenance, belt drives are relative maintenance free. They run clean as they don’t have to be lubricated with sticky lubes and don’t require cleaning either. Belt drive systems also run much smoother, with much less jerks as compared to chain drives, and produce incomparably less noise too.

 

 

2.  Shaft drive

 

 

To start off, shaft drive systems are the most expensive of the three systems we have here, and by some margin. They are, however, the sturdiest of the three, very smooth, and hardly ever need any maintenance. If designed and engineered well, drive shafts often last the life of a motorcycle without requiring any servicing or maintenance whatsoever.

 

 

 

This system, as the name suggests, comprises of a shaft that’s connected to the gearbox output via a universal joint, which is essentially a coupling that facilitates transmission of rotary power at any selected angle. At the other end, the shaft is connected to the rear wheel hub via a spiral bevel gear. The bevel gear turns the direction of rotation of the shaft by 90 degrees to make the wheel turn.

This entire drive system is bathed in oil for lubrication and sealed to protect it from any external elements, which makes it totally maintenance free.

Since shaft drive systems are heavy, expensive, and by themselves require more torque to work efficiently, they are not used on low‐capacity or economy‐oriented motorcycles. They are used on large capacity (generally 600cc or above) motorcycles which produce good amounts of torque.

Also, since shaft drive systems are very sturdy and reliable, they are often used in motorcycles built for the purpose of adventure, sports touring or adventure touring. In essence, these systems lend themselves very well for applications where the motorcycles have to run for very long distances, or in treacherous conditions, where minimizing breakdown possibility is top priority.

 

 

3.  Chain Drive

 

Now that brings us to the trusty old chain drive systems. Comprising of a simple chain of linkages connecting sprockets, this is the drive system that an overwhelming majority of motorcycles implement. The sprocket connected to the gearbox output shaft is the driving sprocket and the one

 

at the rear wheel is the driven sprocket, both are connected through a chain, which also comes in a variety of designs, but we’ll leave that discussion to some other day.

Now a chain drive system requires you to tighten it from time to time as the chain has a tendency to increase in length with time. There is an in‐built provision in the swing‐arm in motorcycles with chain drive systems to allow the rear wheel to move backwards by a limited extent.

One has to check the motorcycle every 500‐700 km for slack and adjust it if required. In addition, since chain drive systems are generally open to the elements and catch a lot of dust and grime, they have to be cleaned and lubricated every 500‐700 km. This makes chain drive systems pretty service intensive and bothersome to an extent.

 

12         Why one gear down and four gears up in a bike?

 

 

This topic has always grabbed the attention of biker’s enthusiasts that why in almost all new bikes the gearboxes are becoming “1 Down 4 Up gear shift patterns” or “1 Down 5 Up gear shift patterns”. It has been seen that sequential gearboxes are favourite for motorcycles as they occupy less space and makes it easy to change gear while riding. While earlier these sequential type gearboxes were having a changing sequence of all gear up type, which is nowadays replaced to 1 down 4 up gear shift patterns. The reason behind this change is both ergonomics and technical. Since if one is willing to reduce the speed to lowest, then the rider has to lower the gear to 1st gear. While riding a bike with all UP type changing sequence bike, the rider may end up in Neutral. In most of the cases, he/she will be thinking that bike is in first gear and when throttles results are nothing else than a roaring engine, resulting in irritation and a panic change of gear and throttling which may result into an accident.

 

13         Right speed to change gears

 

First gear is not the running gear. It is used to bring the car from standing position to running position. Ideal speed range of the gear is from 0‐15 kmph.

Second gear ideal speed is from 15‐30 kmph. Third gear ideal speed range is from 30‐40 kmph.

Fourth gear ideal speed range is from 40‐50/55 kmph. Fifth gear ideal speed range is 50/55+ kmph.

 

If we adhere to these limits then, the fuel economy of the vehicle increases.

 

  • Is it bad to switch gears without pressing the clutch

 

 

The clutch is a disc in your motorcycle that is able to connect and disconnect engine torque from the transmission. This connect and disconnect is what can make smooth riding possible. Just like anything on a motorcycle, the clutch can be susceptible to premature wear and even failure. Shifting gears without using the clutch is bad for the internal components on a motorcycle. Although clutch less shifting is possible, it could damage the transmission and/or cause premature wear on the clutch and should only be done during emergencies.

 

15         Why is there no reverse gear for a motorcycle

 

 

The front fork of all bikes has an rake angle which assist in keeping it going straight and make it easy to correct balance without falling over. This does not work in reverse very well, as the rear wheel is fixed. You can train yourself to ride backwards, but it is very difficult. In addition, it would be dangerous on a motorcycle. Since, motorcycles have a tight turning radius. Rather, you can simply push it backwards with your feet There are reverse gears for motorcycles.

They aren’t standard because you can easily push your bike backwards with your feet. They exist because when bikes get larger, such as trikes, they become necessary. You see them all the time in vehicles equipped for delivery and handicapped equipped bikes… because they are all trikes.

Most bikes simply do not require a reverse. It is very difficult to ride backwards on a bike, so you rather need that to move the thing back for one vehicle length or so. If the bike is lighter, most people do not have problems doing that with their feet. You would never move backwards a bike for 100 yards voluntarily. You would rather turn it around, which is far easier than turning around a car. Some motorcycles have a reverse gear. The last three generations of the Honda Gold Wing (GL1500, old GL1800, current GL1800) have reverse. In the first two it’s an electric reverse utilizing the starter motor to creep the bike in reverse.

 

16         Why clutch plate of a bike malfunction frequently

 

 

The following might be the reasons of malfunctioning of the clutch plate

  • When the speed of the bike is reduced, the driver does not switch to a low gear. This increases the wear and tear of the clutch plate and the pressure plate which increases the friction between
  • When the idle speed of the bike is low, the engine might have a tendency to stop at lower speed or when the bike is standing in a traffic. Thus, in order to prevent this, the driver applies the clutch and accelerator at the same time which again in turn increases the wear and tear of the components of the
  • At high speeds, the driver presses the clutch and then applies the brakes. This also increases the wear and tear of the It is recommended to press the brakes first and then press the clutch at high speeds.
  • When the driver presses the clutch partially then as well, the components are subjected to wear and tear and it may in turn reduce the life of the
  • When the driver suddenly releases the clutch while starting the bike, it may also result in malfunctioning of the

 

17 Why do bikes don’t have automatic transmission

 

 

The main reason why automatic transmission isn’t popular on motorcycles is that those on the low end of the displacement scale are popular for fuel efficiency, which is less with automatic transmissions. Now you can make automatic transmission so advanced it can offer better fuel efficiency than manual, but then the cost of such transmissions means they no longer remain cheap, economical bikes. At the high end of the market, motorcyclists want power and performance, and manual gearbox helps rider to ride the way they want ‐ rev to the redline or ride the torque curve, use engine braking etc., which you can’t do with an automatic transmission

 

 

Fuel Economy

Many tests were done for comparing automatic and manual gearbox. Results shown that manual gearbox had always a slight (sometimes pretty decent) advantage over automatic. Usually, fuel consumption numbers are lower on ~ 10% percent, so manual transmission is more efficient. But it isn’t always true. If you are inexperienced driver, you could over‐rev your engine and shift in wrong times, then fuel economy with automatic could be even better, plus with it you will not be stressing your motorcycle so much.

 

 

Acceleration

 

Generally manual transmission beats the automatic one in this field. It happens because manual gearboxes weight less, has more speeds to choose from (gear ratios) and there is no torque converter, which “devours” some of the overall torque.

 

 

Price

Automatic will be always more expensive due to more technological parts like torque converter, or the planetary gearset. So, expect that the bike with automatic transmission will cost you more than the same bike with manual.

 

 

Reliability

It’s another important factor, and usually manual transmission proves itself better in this area. It is because automatic transmission has much more parts and other sophisticated mechanics that could fail. Manual gearbox is much simpler. Also, there are some things like towing or driving on snow (well that is not completely applicable for bikes) that could easily burn your transmission if you don’t know how to properly use it under such conditions. In addition, automatic is much “pickier” than the manual, you need to use only suitable high‐quality oils for it.

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