The transmission is one of the most important parts of any vehicle. It is a series of components that actually receive power from the engine and transmit this power to the wheels of the car. You may have the most powerful, most fuel-efficient engine in the world, but if you don’t have a transmission or gearbox, then all that power will simply be for naught since there is no connection between the energy generated by your engine and the wheels of your car to make it move. Keeping the transmission in tip-top shape is thus crucial to the safe and efficient operation of any modern vehicle. This begins with an in-depth understanding of what transmissions are all about, why it is important, the different parts or components of a transmission, the types of trannies, and how they work. This is the purpose of this transmission guide we have created for you.
What is a Car Transmission?
As we have mentioned in our introduction, a car transmission is that part of the vehicle that transfers or transmits the rotational power generated by the engine to the car’s wheels. It cannot get any simpler than that. Unfortunately, like the way car engines work, there are a lot of things that are occurring all at the same time in this process of transmitting the energy from the engine to the wheel. And we are going to go through them one by one so you’ll have a better grasp at just how car transmissions work, regardless of their type.
Technically, the gearbox is dependent on the power supplied by the engine. No power means it won’t be able to transmit anything to the wheel. The problem is that the power generated by internal combustion engine is quite dependent on engine speed. Power, in this case, is the usable energy or torque that can be effectively transmitted to the drivetrain. The major issue is not so much about whether there is torque or not but rather whether it is produced within a predefined engine speed or not. This range of engine speed is a requirement to producing the optimum amount of torque. The other problem is that cars typically require torque that is quite different from what the engine can produce in an optimal manner.
Let us try to dissect these issues bit by bit.
- Engine speed
We said that usable power or torque can only be produced by the engine if it is operating at a certain engine speed. This is effectively measured by the number of revolutions the crankshaft makes in a minute. That is why it is typically measured in terms of revolutions per minute or RPMs.
- Engine torque
We understand that torque is the usable energy generated by the engine. In technical terms, it describes the amount of twisting force that is generated by the engine at the crankshaft at any given rotational speed.
We understand that the topic is quite heady, so we’ll try to use an analogy instead.
Let us say you want to drive a nail straight through a wall. Speed, in this case, will be the number of times that you hit the head of the nail in one full minute. Torque, on the other hand, will be the amount of force you apply every time you hit the nail head; meaning, how hard you hit it.
Still with us? Now, let us say you want to speed up hammering the nail. Chances are you will have more misses than actual hits on the nail head because of the frenzied pace of your hand movement. Additionally, the amount of force you put into the nail is not that significant since you will have to decrease the distance between the nail and the hammer to compensate for the increase in speed. Also, your arms will probably be aching afterwards from the repetitive motion. Did you drive the nail to the wall? Perhaps you did but at what expense?
Now, let us try going slow yet very precise. Imagine hitting the nail head at a much slower rate, increasing the distance between the hammer and the nail head to allow for momentum to deliver a more forceful blow. Chances are, you will hit the nail head with each strike, but this will take you longer to drive the nail right through the wall. It really isn’t an efficient way of completing the job, is it?
The idea is to find the right pace of hammering so you’ll hit the head of the nail with just the right amount of force with each strike. This helps drive the nail without straining the muscles on your arms and hands. The trick is to do it just right. Not too slow, not too fast.
In like manner, the crankshaft of the engine needs to spin at just the right speed to provide the right amount of usable power – torque – so that it will still be able to run the car without getting damaged. This is what mechanics call the engine’s powerband. If it spins slowly, it won’t have enough torque to deliver to the wheels. If it spins like crazy, you run the risk of damaging the engine. Try revving your car’s engine towards the red line and you’ll understand what this means. You’re technically spinning the engine so fast yet you’re not really moving any faster.
Unfortunately, that only explains the first major problem of engine power. The second major issue is related to the amount of torque that is actually needed by your car in certain situations.
A good example of this is when you’re at a standstill and you need to start your car. Since you’re starting from a standstill you need the engine to deliver more power. The natural reaction of most drivers is to floor the gas pedal to send the engine crankshaft into a frenzied spin. Unfortunately, we already know that this will damage the engine. Not only that, we are not also going to move our car even an inch since spinning above the engine’s power band causes the torque to drop off. If you apply just a bit of gas, it won’t really move your car either since the torque will still be too little to move it. Remember, a slow engine spin will not deliver the right torque.
If you’re already cruising at a fairly high speed, do you still need torque delivered to the wheels? You still do, but not much since the Newton’s 2nd Law of Motion is pretty much in effect. Momentum is already carrying a particularly hefty part of the workload that is supposed to be delivered by the engine. This way, the crankshaft may actually be spinning at higher speeds but the torque delivered to the wheels is not really great compared to when the car is at a standstill. Technically, the wheels will require more rotational speed but less rotational power.
What you need is something that can somehow multiply the power generated by the engine from a standstill or whenever it is needed. We also need a mechanism that will somehow reduce the amount of torque from the engine when it is absolutely not necessary such as when cruising or going downhill. Thankfully, this is where the transmission comes in.
To sum things up, it is the transmission’s job to supply the wheels with just the right amounts of power. This is achieved by transmitting torque through a variety of gears of different sizes. This is where gear ratio matters.
Inside the gearbox are a series of gears that have teeth of varying numbers depending on the size of the gear. These gears always interact with one another, typically the rotation of one gear will also rotate the other gear directly connected to it. Now, because the sizes of gears that interact with one another vary, this allows the torque to be decreased or increased without necessarily affecting the speed of the rotational power of the engine. This is made possible by gear ratios.
Let us look at two adjoining gears. Gear A has 10 teeth while Gear B has 20 teeth. Let us also say that Gear A is the input gear which is effectively the one generating the power and that Gear B is the output gear or the gear which essentially receives the power from the input gear. To turn Gear B (20 teeth), Gear A (10 teeth) must make a complete revolution twice. Relative to one another, Gear A is spinning fast while Gear B is spinning slowly yet Gear B produced more power for the simple fact that it is bigger. Computing for the gear ratio requires taking the number of teeth of the output gear and dividing this by the number of the input gear. In our example, that is 20/10 or 2. The ratio therefore is 2:1, also known as gearing down.
Conversely, if the input gear had 20 teeth and the output gear had only 10 teeth, spinning the output gear once will only require half a spin on the input gear. Computing for the gear ratio which is 10/20 = 0.5 gives us a gear ratio of 0.5:1. This is known as gearing up. If the number of teeth for both the input and output gears are the same, say each having 10 teeth, then the gear ratio is 1:1, also known as direct drive ratio.
The fact of the matter, however, is that there are more than 2 gears inside the gearbox. The good news is that using the same formula, you can actually compute for the total gear ratio for a particular system. For instance, if the input gear has 10 teeth, a second gear has 20 teeth, and a third and final gear has 30 teeth. You will need to compute for the gear ratio of each adjoining gears.
- Gear 1 to Gear 2 = 20/10 = 2 = gear ratio of 2:1
- Gear 2 to Gear 3 = 30/20 = 1.5 = gear ratio of 1.5:1
- Final gear ratio = 2 x 1.5 = 3 = gear ratio of 3:1
What this means is that the input gear will have to turn 3 times to turn the output gear (Gear 3) once. Technically, you can simply remove the 2nd gear out of the equation and just proceed to the computation of the ratio between the output and the input gears.
Putting this into the different gears in the modern car:
- 1stgear – The typical gear ratio here is 3.166:1. The RPM is usually at 947.
- 2ndgear – Gear ratio is at 1.882:1 with an RPM of 1,594
- 3rdgear – Gear ratio is 1.296:1 with an RPM of about 2,314
- 4thgear – Gear ratio is at 0.972:1 with an RPM of 3,086
- 5thgear – Gear ratio is 0.738:1 with an RPM of 4,065
If you notice, the higher the gear, the lower is the ratio. This is what we have been saying earlier about why you don’t need to drive that much power to the wheels if you are already cruising at high speeds or even downhill. The same is true if you’re heading uphill or starting from a standstill. The higher gear ratio delivers more power to the wheels without necessarily beating the engine to a pulp. Of course, this is oversimplification, but we hope you do get the point.
The Importance of a Car Transmission
Based on what we have been discussing so far, it should already be apparent why the gearbox is so important in any type of vehicle. In case you missed the point, allow us to recap.
The transmission is what helps ensure that the power generated by the engine doesn’t go to waste. It also helps ensure that the power is just right to turn the wheels. If the situation calls for more power, it goes into lower gear ratios to allow for the more efficient transfer of usable power at sufficiently low speeds. If the circumstance doesn’t really need that much energy, then it tries to compensate by reducing the power to the wheels and letting the rotational speed of the crankshaft work its magic.
The gearbox is thus, that important piece of the automotive puzzle that gives you optimum power when you need it and conserves power when there is enough momentum already occurring in the wheels. All of these are primarily designed to improve fuel efficiency and keep the integrity of your car’s engine.
Parts of a Car’s Transmission
Like the car engine, the transmission is composed of quite a number of parts. We have already touched on a few of them. The gearbox is actually the most complicated component of any modern-day automobile. This is especially true for automatic trannies where you don’t only have mechanical systems in the mix, you also have computer controls, electrical systems, and hydraulic systems, all working together to bring the right amount of power to the wheels without sacrificing engine integrity. However, regardless of the type of gearbox, they will always be composed of the following parts.
The input shaft is what connects the engine to the gearbox and thus, carry the same power and speed of the crankshaft of the engine.
Also called as the layshaft, the countershaft connects the input shaft to the output shaft through a fixed speed gear. Additionally, it also contains the gears for the drive gears of the car including the one for reverse.
This shaft runs parallel directly above the layshaft. The output shaft is what transmits or delivers the power of the engine to the rest of the drivetrain. The power and speed of the output shaft is dependent on the gears that are currently engaged.
These gears are located on the output shaft. They determine the ‘gear’ that your car is currently engaged in, like 1st gear, 2nd gear, and so on. Each gear is enmeshed with the gear directly underneath it mounted on the countershaft.
The first drive gear is always the largest and the fifth gear the smallest. Recalling gear ratios, the bigger the gear the slower is its spin. However, since it is larger, it actually brings more usable power or torque to the output shaft. As we have already noted in the preceding section, the higher the gear the lower the gear ratio until such time that the input and output shafts are transmitting the same amount of usable power and moving at virtually the same speed.
This gear is located between the reverse gear mounted on the output shaft and its corresponding gear mounted on the layshaft. This is what allows the vehicle to go in reverse.
Synchronizer sleeves or collars
Modern cars have synchronized gearboxes. This means that the gears mounted on both the layshaft and the output shaft are always enmeshed and are always spinning. The question most people have is that if all of the gears are somehow connected to one another and all of them are spinning at the same time, how is it possible that only one of these gears will be transmitting the right amount of usable power or torque to the output shaft. Additionally, since the input shaft is technically spinning at a different speed from the output shaft, is it even possible to obtain a smooth transmission of power? This is the work of synchronizer collars or sleeves.
All drive gears are mounted with ball bearings which allow the drive gears to spin freely while the crankshaft is spinning. To deliver power to the output shaft, the chosen gear must be ‘clamped’ onto the output shaft so only this gear will be able to transmit its power to the drivetrain. Drive gears are separated from one another by synchronizer collars. It is the job of the synchronizer collar to move over to the gear that you want to engage. Outside each gear are teeth that allow the synchronizer collar to ‘latch’ into. As soon as the synchronizer collar is enmeshed or ‘connected’ with the specific drive gear, this delivers torque to the output shaft.
This is what you move to engage your car into a gear of choice.
These rods connect the gearshift to the synchronizer collars through the shift fork. These are what actually move the synchronizer collars to the gear of your choice.
As we have already mentioned above, the shift fork is what holds your gearbox’s synchronizer collars.
In a manual transmission, the clutch can be likened to a gate valve which allows you control when to disconnect the flow of usable power from the engine to the gearbox.
A lot of folks are actually confused with the terms “engaged” and “disengaged” here. When we say “engaged”, that means the power is freely being transmitted from the engine to the drivetrain. This means that there is communication between the two components of your car. In simple terms, your foot is off the pedal. Unfortunately, when people say “engaged” they are actually thinking that you have to step on the pedal to “engage” the clutch. That is actually “disengaging” the clutch.
When you “disengage” – you put your foot on the pedal – you are actually disconnecting the transmission of torque to the drivetrain from the engine. This disconnection occurs without affecting the engine’s operation, so it keeps running. This allows you to shift your gear a lot easier since the gears have been “disengaged” from the spinning engine.
So, if you step on the clutch pedal, you are “disengaging” the clutch. If you remove your foot off the pedal, you are actually “engaging” the clutch. Hopefully, this helps.
The above parts of a car transmission are typically found in vehicles with manual trannies. In vehicles with automatic transmissions, the following are integral parts of the gearbox.
These are the equivalent of your manual’s drive gears. However, they have a few very important differences. The planetary gears are never moved physically. Additionally, they are constantly engaged to basically the same gears. The planetary gears are a collection of several gears that are contained in a carrier. At the center of the carrier is a sun gear while the periphery is surrounded by the ring gear. Smack in between the sun gear and the ring gear are several planet gears.
Typically, the ring gear is connected to the input shaft while the planetary carrier is connected to the output shaft. Meanwhile, the sun gear is locked in its position in the center of the planetary carrier. Turning the ring gear will move the planet gears along the sun gear. This causes the planetary carrier to spin the output shaft, albeit at a slower speed since the planetary carrier has a much bigger diameter than the ring gear. This is similar to the 1st gear in a manual transmission.
If the sun gear is unlocked and any two elements are locked, all three elements will spin at effectively the same speed. This causes the output shaft to spin at the same speed as that of the input shaft. This is equivalent to a manual transmission on a 3rd or even higher gear.
If the planetary carrier is locked and power is applied to the ring gear, this spins the sun gear in the opposite direction to give you the reverse gear.
As we have explained above, the ring gear is connected to the input shaft while planetary carrier is connected to the output shaft. The planetary carrier also connects to a clutch pack. The sun gear connects to a drum that is surrounded by a band. The function of the band is to prevent the drum from turning the sun gear if needed. The drum is also connected to the clutch pack.
The torque converter is the equivalent of the clutch in a manual car transmission. It is located between the transmission and the engine and it functions, like the clutch, in allowing the engine to keep on running even if your car has already come to a complete stop. Imagine you have 2 electric fans facing each other, one plugged and the other unplugged. If the plugged fan is spinning, it will blow air into the blades of the unplugged fan, causing it to turn as well. If you grab the unplugged fan’s blade, this will stop it from spinning. However, once you let go, the unplugged fan will start spinning again, mimicking the speed of the spin of the plugged fan. This is essentially the same with a torque converter. The only difference is that instead of air blowing into the other side of the torque converter, you have transmission fluid spinning this side of the device.
The torque converter is essentially composed of three parts that work seamlessly together to bring power from the engine to the drivetrain. The pump is located in the converter housing on the side of the engine. The turbine is connected to the transmission’s input shaft to bring power to the wheels. The stator is connected to a one-way clutch that can freely spin only in one particular direction. All three elements have fins allowing each to direct transmission fluid through the torque converter.
This is an integral component of an automatic transmission system as it provides the oil needed for the automatic gearbox to remain fully functional. This is mounted on the transmission case and connected to the torque converter housing via a flange. The oil pump provides pressure every time the engine is running.
This is a network of tubes and passages that deliver transmission fluid to all the critically sensitive parts of the transmission.
This is considered the control center of a car’s automatic transmission. It effectively directs transmission fluid to the various valves that activate different components of the transmission like the band servo or the clutch pack.
Modern automatic transmissions already come with sophisticated computer controls that integrate all the information obtained from various sensors such as vehicle speed, engine load, throttle position, brake pedal position, engine speed, and a whole lot more. The car’s computer controls the very precise points upon which shifts have to be made to make changing gears a lot smoother. All the information gathered by the sensors are synthesized and sent to the solenoid pack located inside the automatic transmission. The solenoids present in the pack will redirect the transmission fluid to the appropriate servo or clutch pack to manage or control shifting.
Governor, throttle cable, and vacuum modulator
If your car has an automatic transmission but doesn’t have computer controls yet, then you will most likely have the governor, the throttle cable, and the vacuum modulator.
The governor controls hydraulic pressure depending on the speed of your car. This is accomplished by spinning hinged weights against several pull-back springs by using centrifugal force. As the springs are pulled farther outwards, increasing oil pressure acts on the shift valves which in turn signal the correct shift to be made.
The vacuum modulator and the throttle cable works like the governor except that they are reliant on engine load. The throttle cable tracks the gas pedal’s position while the vacuum modulator monitors the presence or absence of vacuum in the engine. If the engine is running lightly, it registers high vacuum readings. If the engine is running heavy, the vacuum reads zero.
Seals and gaskets
Moving the different components of an automatic transmission is largely the role of the transmission fluid. However, it should also be understood that in order for it to exercise its functions optimally, it needs to be circulated under pressure. Loss of pressure simply means the transmission fluid will not be able to move through the rest of the transmission. This is where seals and gaskets play a very important role in maintaining the integrity of an automatic transmission. These prevent the hydraulic system from failing, maintaining optimum pressure throughout the system.
Types of Car Transmissions
In the past, learning how to work the clutch pedal was largely considered as a rite of passage. With the passing of time, however, improvements in gearbox technology have clearly moved the transmission well beyond the archetypal manual tranny. Let’s try to understand the different types of car transmissions in an effort to understand the development of this integral part of the modern automobile.
We’ve already managed to explain how this type of transmission, somehow in the preceding sections. This is generally the oldest and the simplest type of transmission known to man. You step on the clutch pedal to disengage the drivetrain from the engine without loss of power from the engine. You then shift the gear, release the pedal, and the whole system engages again, transmitting power to the drivetrain from the engine. Performance-wise, it’s preferred over other transmission types. It’s also fuel efficient. However, what really makes the manual transmission a well-loved type even today is the feeling of being a ‘real’ driver where the skill is tied to the ability to shift the gear in one fluid, perfectly timed motion. No automatic or CVT can ever duplicate that feeling.
The automatic tranny has definitely taken the reins off the once-ubiquitous manual. The principle of power transmission is essentially the same. The only difference is that instead of a clutch you have a torque converter and instead of a fixed set of drive gears arranged in a linear fashion, you have a planetary arrangement. Because there really is no clutch to worry about, the automatic is the preferred choice for beginners as well as those who prefer a more relaxed ride. Even with today’s advanced automatic transmissions, they still cannot match the fuel efficiency of the manual. Also, the automatic’s rather complicated construction makes it very expensive to fix once broken.
Continuously Variable Transmission (CVT)
One can look at the Continuously Variable Transmission or CVT as a modified version of an automatic tranny. However, the main difference is that it doesn’t actually come with ring, sun, and planet gears. Instead, the gear ratios are achieved through a system of pulleys and belts (they should thus, be called pulley ratios?). One of the most important advantages of the CVT over the AT is fuel economy. In fact, the CVT even fares a lot better than the manual transmission when it comes to fuel economy. Additionally, the design of the CVT is a lot simpler than an AT, making it less prone to mechanical failure and as such giving it exceptional economy when it comes to maintenance and repairs, although it still cannot beat the manual in this department. The downside to the CVT is the lack of feedback to the driver. It would be like riding on a car that has a single gear operating on all speeds. The gearshift that you somehow feel in both manuals and automatics is simply not there.
Semi-Automatic and Dual Clutch Transmissions
These types of transmissions marry the pluses of both the manual and the automatic trannies. A semi-automatic uses a variety of actuators and pneumatics to shift gears within a typical layout of a manual. On the other hand, a dual clutch transmission has separate clutches for the even- and odd- numbered gears. This allows for ultra-fast shifting. Think of the paddle shift on the steering wheels of F1 race cars. These types of transmissions are reserved for the elite – F1 race cars, luxury, sports, exotic and supercars. They’re very expensive. And since the technology is so advanced and complicated, mechanical failure is definitely a very big and costly concern.
Tiptronic Transmission: How Does Work?
There are an increasing number of modern vehicles that now integrate the Tiptronic transmission pioneered by Porsche, although you can perhaps hear from other car manufacturers that they coined the term Sportmatic or even Steptronic. Whatever the case, they all mean the same thing. The Tiptronic transmission is essentially a type of automatic transmission that can be either computer-controlled or driver-managed.
When driving it like an automatic, the Tiptronic really does work like an automatic transmission, allowing the on-board computer to determine the correct shifting. However, if the driver so decides to take control of when to shift, such as what applies in a manual transmission, all he needs to do is to flip on a switch to activate the Tiptronic system. The power to the gearbox and the drivetrain is now under the direct control of the driver. You can look at the Tiptronic as a manual transmission that has an automatic component or an auto tranny with manual tranny features. Whichever the case, the point is the driver ultimately decides when to up-shift or down-shift.
This is accomplished rather easily. Paddle shifters are integrated into the steering column of the car. There are two of these paddle shifters, one each for upshifting and downshifting. There are also some car brands that provide additional features to the Tiptronic mechanism. For example, they may integrate a performance setting whereby gear shifts are initiated only at higher RPMs. This helps give a feeling of driving a performance sports car. Another is the rev-match function where the engine speed is increased as you shift to a lower gear.
The transmission or the gearbox is one of the most important parts of any vehicle since it transfers usable power from the engine’s crankshaft to the drivetrain to turn the wheels and allow the car to move. It is also through the transmission that it is able to keep the engine running even though the vehicle has already come to a dead stop. The tranny allows the more efficient transfer of power to the wheels when the circumstances call for it such as when going up an incline or starting from a standstill. It is also this part of the car that allows you to coast seamlessly on highways without putting too much power in the wheels, conserving energy in the process.
Since the transmission is basically what drives your car’s wheels, it is thus very important that you keep it in excellent condition. Learning how it works and its different components should give you a fair understanding of how you can take care of your car’s transmission.