Transmission, Part 2, Automotive Chassis and Transmission

* Types of Transmission:

4. SYNCHROMESH


Synchromesh transmissions are refined version of the constant mesh system, although they are less common. How it improves the system is just by adding another stage to the process of connecting the gears to the drive shaft through the dog clutch respectively.


It splits the dog clutch into two – a gear fixed to the drive shaft called the synchronizer hub, and a collar around the outside of it that could slide back and forth is called the shift sleeve.


A new component is added to the gears themselves – the synchroniser cone - and a further moving part that is called the synchronizer ring is introduced that surrounded the cone.


Now this is where it gets a little bit complicated.


Now the collars, or shift sleeves, are now the components controlled by the gear stick - and they can be slide halfway in either direction onto the synchroniser rings. This forces the rings against the synchroniser cones to get attached to the gears, and through the increased friction caused by the widening cone it can either speed up or slow down the gear to match up the speed of the shifting sleeve and synchronizer hub.


Once the speeds are matched closely enough, the sleeve can continue to slide over the blocker ring and directly mesh with both the cone and the gear, connecting everything together and transferring power to the drive shaft.


Unbelievably all of this happens in less than of a second it takes you to shift gear, providing you with an even smoother gear change.


5. Epicyclic Transmission



oyetechy, technical
Pic 1


The working principle of the epicyclic gearbox is based only on the fact that the fixing of the gears i.e. sun gear, planetary gears and annular gear is done here to obtain the required torque or speed output. As fixing of any of the above causes variation in gear ratios from high torque to high speed. So let’s see how these varied ratios are obtained


i) First gear ratio

This provide a high torque ratio to the vehicle which helps the vehicle to move from its initial state  and is obtained by fixing the annular gear which in turn causes the planet carrier to rotate or spin with the power supplied to the sun gear.

ii) Second gear ratio

This provides a high speed ratio to the vehicle which helps the vehicle to attain much higher speed during a drive, these ratios are obtained by fixing the sun gear which in turn makes the planet carrier into the driven member and annular into the driving member in order to achieve high speed ratios.

iii) Reverse gear ratio

This gear reverses the direction of the output shaft which results in reversing the direction of the vehicle, this gear is achieved by fixing the planet gear carrier which in turn here makes the annular gear into the driven member and the sun gear into the driver member.

Note- A no. of speed or torque ratios can be achieved by increasing the number planet and sun gear in epicyclic gear box.


6. Automated Manual Transmission (AMT)


The Automated Manual Transmission (AMT) a.k.a. Semi-Automatic Transmission is not essentially an automatic or a clutch-less gearbox, but rather a manual transmission that facilitates gear changes without the need for you to press the clutch. This kind of transmission unit's mechanism enrolls the use of two key parts - a hydraulic actuator system and an electronic control unit that engages and disengages the clutch while executing the gear shifts. Actually it is just a kit that can be added to any regular manual transmission, which makes it a low-cost solution for carmakers.



Pic 2


Popular Cars with Automated Manual Transmission: Maruti Suzuki Alto K10, Swift Dzire, Mahindra TUV100



Continuously Variable Transmission (CVT)



The Continuously Variable Transmission (CVT) is the most unique clutch-less gearbox compared to the others mentioned above. Mind you, it is not the best but the most unique and I say this because while other transmission units come with a certain number of gears that have to be shifted to keep in accelerating, a CVT unit doesn't have different gears like that. Ordinarily, the number of gears in a transmission, also referred to a speed, have a finite number of gear ratios that are distributed among every gear, thus to go faster all you need is to up shift beyond a point. The CVT on the other hand comes with a special gear that's variable across all driving situations and can change effortlessly through a continuous range of effective gear ratios. This allows you to controls the engine speed or RPM for accelerating or decelerating based on you throttle action. A CVT transmission is also used in two-wheelers, especially scooters where acceleration and braking is the key function. Some cars also get paddle-shifters for the convenience to drivers.



oyetechy, cvt
Pic 3



Popular Cars with Continuously Variable Transmission: Maruti Suzuki Baleno, Honda City, Jazz


* Free wheel mechanism:

Free wheel - As the name suggests , wheel should rotate freely without use of any fuel and power. Its application can be seen easily in cars when they slope down. Even in bicycles when the pedaling is stopped but wheels continue to rotate.


Why we use it?


* To reduce the wear on transmission system,

* To reduce the fuel consumption on sloping downward.
Using this, gear changing is simplified at low speed.


What it is?



oyetechy, free wheel mechanism
Pic 4



Free wheel is a device which is installed between propeller shaft and the gear box. (Also there is overdrive between propeller shaft and gearbox.) Free wheel makes the wheel to rotate wheel freely when propeller shaft is disengaged from the the engine or gear box.


Working and mechanism?



As you can see in diagram (very badly made , sorry for that but cant make better than that), there is driving member and driven member. Driven member is attached to the propeller shaft and driving member is attached to the gear box (which is attached to the center of the freewheel). It has spring and three different size balls (or rollers) attached to the spring.


Now when the freewheel rotates the spring elongates and the rollers tends to move outwards creating friction between driving member and driven member. This friction causes the driven member to move with driving member. And this transfers the power to propeller shaft.


Now what happens when the car slope down



When the car slopes down, driver disengages the clutch. But the driven member keeps rotating as the car is going down. This time this outer driven member has no contact with the inner driving member and inner driving member doesn’t rotate. Thus the freewheel isolates the engine and the transmission from the driving wheel which leads to less wear on transmission.

*i) The principle of operation of overdrives.


Overdrive is a device used to set up the gear ratio in the car. It is fitted in between the transmission & propeller shaft. This results into less wear of the engine parts & decreases vibration & noise. As the friction lesses at lower speeds are less. There is a saving of fuel also with the use of overdrive. Overdrive is generally fitted onto top gear only.


Working:

To understand the working of an overdrive. It consists of an epicyclic gear train in which the Sun gear is free to rotate on the input shaft,while the cartier can move on splines on the input shaft. A free wheel clutch is also fitted onto the input shaft splines. Then the output shaft is connected to ring.
When the Sun gear is locked with casing i.e it becomes stationary, the speed of output shaft is increased i.e overdrive is engaged. When, the sun gear is locked with carrier or to ring. A Solid drive through the gear train is obtained. Thus, depending onto the locking of the sun gear with casing or with the carrier, the overdrive is the normal direct drive is obtained.

There is an another possible control of mechanism i.e when the sun wheel is free to rotate on the input shaft. In this case, there is direct drive through the free wheel clutch when the engine develops power.

* ii) The Working of torque converter.


The construction of torque converter is somewhat similar to that of fluid flywheel: the only difference here is being that it has an additional stationary member called as the stator or the reaction member & all the members have blade/vane of specific shape.


The operation of two however is not similar, where as the fluid flywheel transmits the same torque as given to it by the engine shaft. The torque converter increases the torque in a ratio from about 2:1 to 3:1. Thus, it serves as the same purpose as that of a gearbox & that too in way better way where as in the gearbox here the torque variation is only in finite no. of steps, while in the case of torque converter torque output variation is continuous. However, the efficiency of the torque converter is high only with narrow limits of speed.



A Single stage torque converter consists of 3 main parts:
i) Impeller or called as the driving member which is connected to engine.
ii) turbine or driven member which is connected to the road where through the transmission gears & driveline.
iii) starter fixed to the frame through a free wheels.
In addition to this, there is a transmission oil pump which is used to keep the converter full of oil under pressure. Here Pressure is necessary to keep the converter full of oil when rotating. Due to this rotation the centrifugal force pushes the oil in the outward direction & this tends to form air pockets near the center of the converter . This phenomenon of forming small air pocket due to low pressure is called cavitation, to avoid such the converter pressure is kept between 200 to 1200 KPa. 

Working: When the engine is started, the impeller starts to rotate. Initially, the oil here from the impeller is pushed into the turbine because of the higher centrifugal forces at the impeller, due to this being driven by the engine & turbine being at stationary. Thus oil, having taken the high kinetic energy from the engine through the impeller, hits out the outer edge of the turbine.


This flow of high energy oil provides the forces that tends to rotate the turbine. These forces increases with the increase in engine speed. When it is great enough, the turbine starts to rotate & the vehicle moves. The turbine blade angle is set such that it changes the directions of oil flow so that when it comes out of the turbine at the centre , its directions is effectively backwards.


If there were no stator & it were to enter the impeller just directly, it will push the impeller in the opposite direction & hence will thus cause a loss of power.

Note: There are certain concepts that do not have such importance as per the point of view of exam and hence are not explained here. For any queries or questions you can directly mail me. Or just dm me on instagram @chakitg. 



Regards:  

Er. Chakit Gupta
Transmission, Part 2, Automotive Chassis and Transmission Transmission, Part 2, Automotive Chassis and Transmission Reviewed by Oyetechy.com on November 06, 2019 Rating: 5

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