Tansmissions & Gears

Well long break i would say before i wrote something on my this blog....the other one still gets my attention at times. However, the reason for that was lack of time and also lack of interest i could garner from my readers. However, looks like i want to try again and give it one more shot to make this blog useful enough to folks in order to get some interest from them.
The topic for today is "Transmissions"
Why do we need a transmission...or do we need one?
Frankly we would not need one, we could simply control the speed of a motor the same way we control the speed in our ceiling fan. However, unfortunately our automobiles use motors which are not electricity powered. They are IC's or Internal combustion engines which run most efficiently in a fixed narrow range of RPM. They are not able to produce the same amount of torque at all the RPM's and of course are not efficient at all RPM ranges. At very low RPM the engines suffer from lower dynamic torque and hence we need to somehow use the same RPM to get the needed torque demands. At cruising speeds we require lesser torque as compared to when we are climbing a hill. All these means that the IC engine has to meet various requirements of torque, speed and efficient operation. This can be achieved very easily using a Transmission. A transmission ensure that the Engine can be run in a narrow band of RPM where it runs most efficiently and uses gears to meet the driver request of torque or speed.
How does it do it?
A simple transmission "conceptually" is a set of gears with different gear ratio's. If the engine is running at x RPM using a gear ration you can get y RPM at you transmission shaft based on the following formula:
X * GR = Y
GR = Gear Ratio
X =   Engine RPM
Y =   Transmission Shaft RPM
However, this is an ideal case....losses will come into picture like in any system.
if GR>1 then Y is greater than X. This is rarely done since this means that Transmission shaft RPM is higher than engine RPM. This basically means that your car is completely free. This condition is called Overdrive and mostly seen in higher end car with ECU's and TCU's which keep monitoring if everything is still under control.
What are gears and gear ratio's?
A picture speaks more than words...so here is the picture

Ever wondered why the car or bike will not climb a steep incline when we are on a higher gear as compared to a lower gear? At a higher gear the transmission transfers most of the engine speed to the tires as compared to the torque. If we consider power delivered by engine constant then either we can have higher torque or angular velocity. Hence at the higher gear ( more angular velocity) we need to really rev the engine hard to make the vehicle climb ( more revs more power output) in order to meet the higher torque requirement.

In coming blogs it will try to explain what different transmission can do and how they do it. But basics are these...
1. For a constant power by the engine i.e. constant RPM on engine shaft we should be able to get different torques and output speeds.
2. Gears are one of the mechanism's for doing what we need in point (1). There are other methods like use of pulleys, belts and electro mechanical couplings.

4 - pack ABS - The ones your car has!!

Now that from a few posts we have discussed only "C" I thought this time will get back to some automotive basics.
Topic this time is Vehicle stability and we will towards the end talk a bit about ABS.
The vehicle undergoes various kinds of forces when it is in motion. We will talk about stability when in motion in this post. The simplest to understand is horizontal forces. i.e when the car moves forward then there is Pseudo-Force that acts backwards ( which makes the driver go backwards when the car moves forward). This force acts in the opposite direction on braking. That is the reason the front of the car will dip when we brake hard. Now assuming that you are going on a straight road when you brake the wheels will reduce their speed continuously till they come to stand still. Here there are some concepts that we need to understand.

1. Why does the car move forward when the wheels turn? - The answer to this lies in friction. If there was no friction, there was no reason for the car to move forward. So who is really driving the car ahead....well it is the friction force. If the wheel moves too fast then it tends to slip. This is because the surface friction cannot keep up. This means when you have low friction, the best thing to do is to let your wheels spin slowly rather than fast. Why Slow?  The force acting at the point of contact is proportional to the wheel speed. So footing the accelerator always doesn't mean more speed.
   
2. What happens when we brake ? - The brakes when engaged bring down the speed of the wheel. This means we are reducing the force at the point of contact. In which the surface will offer us lesser friction force. This means that our vehicle will slow down. However, when will we start slipping? This will occur if the rest of the body of the car is still much faster ....and that drags our wheels. This situation worsens when the brakes are jammed hard and the wheels lock. After the lock the friction equation changes. From Rolling friction it changes to sliding friction. This sliding motion will reduce/ remove the steer-ability. Once the steering capability is lost all that will happen is that the vehicle will move in the direction of the force it had when the tires are locked. 
3. Other Problems ? - The brakes work quite great when we are on a straight road. However, when we brake when we are on a curve we have to worry about other forms of forces apart from horizontal. They are the lateral forces that tend to push the car in other directions than the one intended by the driver. This however, is not controlled by having a ABS.

Yeah, finally we are talking about the ABS. The ABS or the Anti Lock Braking systems will help a lot in number (2) above. It will ensure that the wheels never are locked. This helps in the following ways

• Wheels are not locked so you can steer the vehicle till the last minute.
• Wheels are braked and released at very fast rate which means that the wheels are approximately maintained at a point where they get maximum braking efficiency ( approx 20 -30 % slip). This happens because the wheels have more friction when they are rolling then when they are slipping. However, this makes you wonder if slip has lesser resistance then why not make my vehicle slip all the while. That would have been a good idea if the area's of contact while slipping and rolling where the same. Since they are not in effect under normal circumstances the slipping tyre would give you a lot more resistance. Also we got to think about the life of the tyre. However, when we are braking this works better to have the tyre rolling rather than slipping.
  
• If you have 4 way ABS system ( lucky you) then each wheel can be individually controlled to ensure best braking force through the 4 wheels so that the vehicle can be stopped easily even on µ-Split surfaces too. Btw, 4 way ABS means that each tyre has a wheelspeed sensor and has a control valve that can be controlled to lock or unlock the brakes. 3 way ones have front 2 wheels individual and rear wheel both have a single control valve.

Ok i will stop here to take  a breather. More later.
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