Brakes: Disk Brakes - Part3

In last 2 articles we covered the basic terminology and basic knowledge of brakes and in second the concepts of working principle behind the drum brakes. Our previous articles can be found on http://themechunicorn.blogspot.in/. In this article we will continue our trend with working principle of disk brakes for automobiles in bikes. Well, the disk brakes have quickly become a spotlight feature in nearly all cars and motorbikes. The reason is simple, more power, more peak force capability and surely reduced weight! Disk brakes are usually found and known as hydraulic disk brakes, while mechanical disk brakes are also present, but hydraulic disk brakes are more powerful, durable and requires very less maintenance. Also, unlike drum brakes, the disk brakes have less reciprocating/moving components and due to use of hydraulic fluid as the working medium, the disk brakes are more responsive in nature.
In construction:

The above image shows a typical single hydraulic cylinder hydraulic disk brake. In the simplest of words, the caliper holds 2 brake pads which are of frictional material and when the pressure is applied by the piston, the brake pad rubs against the disk and because of this frictional combination, the braking action is achieved. Well, there are actually 3 types of hydraulic disk brakes, single cylinder configuration, dual cylinder configuration and full disk configuration. While, the first 2 configurations are differentiated by the no. of cylinders disk caliper will be housing, the full disk configuration is rather based on surface area the brake pad will be covering! In cases of single and dual cylinder disk brakes, the brake shoe is covering a particular angled surface area of the disk, while in case of full disk configuration, a full 360^o brake pad is used.

The first image shows the full disk configuration, while the second image is the common single cylinder hydraulic disk brake. The only reason, the full disk configuration aren't popular is because of the low durability due to high surface area contact and unbalanced forces acting on the actuation rod.

Now, we will explain each component of the single cylinder disk brake.

1) Hub: Like the brake drum in drum brakes, the hub is the component of disk brakes that is connected with the wheel of the vehicle.

2) Rotor/Disk: It is the metallic disk that's been abraded to produce a frictional surface over it. The disk has to be designed in such a way that it can withstand all the frictional heat and should implement best methods of aerial cooling or ambient cooling.

3) Brake Pads: The brake pads are made of frictional material like graphite or carbon composites. the brake pads serve the same feature as served by brake shoes in the drum brakes, but are more durable in construction and usage.

4) Hydraulic Slave Cylinder: Just like the drum brakes, Slave Hydraulic Cylinder also works as an actuator in disk brakes. The pressure created inside the cylinder serves as the way to move the brake pads towards the disk.

5) Caliper Return Springs: They are mediocre to high tension springs that helps in bringing back the brake pads to their original position when the pressure from the main and slave cylinder is removed.

6) Caliper: It is the main housing in which the brake pads, hydraulic slave cylinders and caliper return springs rests and helps the whole braking system to stay rigid and in required position.

While designing a hydraulic disk brake, a lot of things need to be taken care of and every design has its own specifications, the angle covered by the brake pads, the radius of brake pads, position of them from top, frictional coefficient of the disk caliper, and many more considerations need to be taken care of while designing the braking system. In the coming series of continuing articles, we will also discuss all the equations required to design hydraulic disk brakes and their derivations, so stay tuned. Remember, educate, then excel and then only innovate.

Brakes: The General - Part1

In these series of blogs, we are gonna discuss everything and anything about brakes, starting from terminology and basics involved in first blog to its calculations and how entrepreneur designers can design their own locomotives. Since Brakes are one of the most important 3 mechanisms of any locomotive, other being power generation and steering mechanism; So, we will give time and explain everything about them gradually! So, let's start with the basics! What is a brake? In easiest words, a system or device that reduces or halts motion. Taking example of cars; brakes reduces the speed of a moving car and eventually brings it to a complete halt. Now, there are various types of braking methodologies, 1) Friction Brakes: The brakes use friction to bring out braking action and usual example include drum brakes, disk brakes, hydraulic disk brakes & pneumatic disc brakes. 2) Pumping Brakes: which use engine and engine's components friction as the required braking action! The most popular ans simple type of Pumping brake is Jake Brake which open the exhaust valve during the expansion stroke of Engine. 3) Electromagnetic Brakes: They bring about the braking action using electromagnets, they are commonly installed in hybrid/electric vehicles and is also the basis of KERS (Kinetic Energy Regeneration System) in cars. 4) Drag Brakes: These types of brakes find their application in vehicles which require deceleration through a fluid medium like air or water; the easiest example is the flaps in the wings of aircraft.

courtesy to www.images.google.com

The above image shows a typical disc-drum arrangement in a modern car and the various components involved in them! In the continuing articles we will explain functioning and detailed information about each component but for basics, I believe, its the best way to understand the braking system. Now, let's talk about some terminology one should know while studying brakes.

1) Peak Force: The peak force is the maximum amount of decelerating effect that can be achieved by the system. The peak force is usually greater than the traction limit value of tyres which results in wheel skid when brakes are applied with full force. The peak force depends on the friction coefficient between the friction components of the braking system and the time of actuation or in drag brakes case: the angle of attack i.e. at which angle the actuated component is to the streamlined fluid.

2) Continuous Power Dissipation: It is commonly affiliated with friction brakes, on actuation a lot of heat energy is produced in the system and after a particular temperature the braking system might breakdown! Thus, the maximum amount of power a braking system can dissipate without breaking down is called as Continuous Power Dissipation. The dissipation is dependent on temperature and speed of ambient cooling air.

3) Brake Fade: Because of increase in temperature, the brakes efficiency might reduce, which is technically termed as Brake fade. It is dependent on the design, and cooling system of brake plays a very important role in determining the Brake Fade of the system.

4) Smoothness: It is more of a physical term than technical term for brake application. It's all about the experience of the driver, if the brakes are harsh, worn out and exert unequal force will produce skids and would be unappreciated by the driver as such system will make him experience that he is driving on a camel.

5) Power: It is the amount of brake force the system produces with respect to the application of brake pedal! In other way, it is the ability of the system that how fast can it reach its Peak Force.

6) Drag: It is the incomplete detachment of one braking component with another because of which the unwanted braking action might be there even during full pedal release. The common causes of drag are misaligned brake shoes, broken springs, over-extended actuator wire or piston failure etc.

7) Durability: Brake systems have frictional parts that wear out at every application of brake and might needs to be replaced from time to time. The durability of systems with higher peak force is lesser.

Well, these are the most important terminology one must know in order to understand braking and braking systems! The braking system is specifically mounted on either wheel or trans-axle depending on application of the braking system. One thing that one must also know is that braking system which may/may not include supporting structure adds into weight of the body thus, it also plays an important factor depending on application. With this, we end our first article on basics of brakes and keep tuned for the next article which will briefly explain each component of braking systems and application-wise differences in them.

Everything about Turbo chargers!

We usually read in brochures of diesel cars, VGT or might have heard in fast and furious series the term: Turbochargers! but what exactly are they and how they work is a good question! Few car enthusiasts might be knowing something about it but in this blog, we will talk about anything and everything for Turbochargers. In this blog we will cover the basics of turbochargers, their types, cooling methodologies and finally applications. So, let's start!
Well in simple words, a turbocharger is a forced induction device i.e. it converts the linear motion of exhausts gas out from the exhaust manifold of the engine and converts it into rotary motion of turbine which in turn increases the air-intake in the inlet manifold for better performance of the engine. As we know, more air means more perfect fuel combustion which in turn increases mechanical efficiency!
The reaction involved inside combustion chamber of iso-octane with oxygen is:
C₈H₁₈ + 12.5 O₂ ------ 8 CO₂ + 9 H₂O
As, can be seen in the above equation, for every mole of iso-octane/fuel; 12.5 moles of pure oxygen is required to completely burn the fuel else:
C₈H₁₈ + 10 O₂ ------ 8 CO₂ + 4 H₂O + 5 H₂ or even,
C₈H₁₈ + 5 O₂ ------ 4 CO₂ + H₂O + CO + 3 CH₄ + 2 H₂
if the fuel if not burned properly, then there will be carbon monoxide, methane and unburned hydrogen which escape to atmosphere and is not good for environment. There are 2 air-fuel mixtures: 1) Lean i.e. more amount of air than usual 14.7:1 stoichiometric air-to-fuel ratio (AFR) or 2) Rich i.e. more amount of fuel in AFR. Well, they are there in Automobile dictionary for some reason. The reason is, lean AFR will result in more mechanical efficiency and cleaner exhaust while richer AFR will provide with more torque. But, more of something is also dangerous, the lean or rich AFR must be set optimally for best results! In an un-tuned turbocharged engine, the AFR is overly-lean which increases probability of knocking so in such-cases the AFR is made richer!
Now, there are various types of turbochargers (and I mean turbochargers; don't mix it up with superchargers or twin-chargers). The various types are:
1) Twin-Turbo - which means that two different turbochargers are used sequentially or parallel. If the turbos are parallel, it means the exhaust from different cylinders split into each i.e. let's say in a V6 arrangement: the cylinders 1,3,5 will be connected to 1st turbo while cylinders 2,4,6 will be connected to 2nd turbocharger! The main benefit of connecting two parallel turbos is that, the turbo-lag is reduced considerably while reducing the size they take up in the chassis; the other arrangement is to connect twin-turbo sequentially. This arrangement usually uses two different sized turbos, first a small turbo to reduce initial turbo lag and second big turbo to provide peak performance during full throttle, that is also the reason they are called as 2-stage twin turbo!
2) Twin-Scroll - or divided turbochargers instill the properties of 2-stage turbo into 1. The twin-scroll turbocharger has 2 exhaust-inlet manifolds and 2 nozzles. The sharp angled nozzle is for quick response and reduction in turbo-lag while the other division is for peak performance.
3) Variable Geometry - The Variable Geometry Turbocharger or VGT uses multi vane nozzle to control the exhaust-air flow to turbin and uses an actuator to control the diameter opening of nozzle. This gives a optimal power curve throughout the size which helps reduce lag without compensating for either boosted acceleration or boosted torque at peak revs!
Well, they might put you racing but without the underlying accessories, you might wanna race in tonight's race because you might loose your engine or blow off your car!
1) Intercooler: It is the most useful and essentially the most required addition you might want to install with your turbocharger! When, the air is forced into the inlet-manifold its pressure and temperature increases, thus reducing the density of oxygen in the air-fuel mixture thus, to optimise it an air charge intercooler is fitted with every turbocharger to increase the density of the air-fuel mixture and increase efficiency of the turbo-charger, also while bringing temperature under control.
2) Water Injection system: though not-popular and even very cumbersome, the water injection system is an alternative to intercooler which reduces the temperature of inlet-air through injecting water, this system was used in various automobile and aircraft applications.
3) External Waste Gate: A wastegate is a solenoid operated device that redirects excess of exhaust air away from turbine so as to regulate the power output of a small turbocharger and save engine and turbocharger from excess wear and breakdown.
4)Dump Valve: also anti-surge valve or blow off valve is a auto-pressure release valve that reduces the pressure when suddenly the throttle valve is closed in a wide-open throttle engine system. When the throttle is closed, the compressed air has no exit and without dump valve might result catastrophic in nature that is why the dump valve is an required accessory in turbochargers.
Now, since we've talked about basic working of turbo, its types, additions, then now it is right time to talk about the applications. The turbochargers have been used widely across all locomotives from production road cars to aircrafts.
1) Petrol Engines: Since 1962 Oldsmobile Jetfire Turbo to 2014 Mclaren P1, all possess petrol turbocharged engines which increase their power output by many folds.
2) Diesel Engine: The application of turbochargers in diesel engines came in 1978's with the Mercedes 300SD which drastically improved the fuel efficiency, mechanical efficiency, and driveability of diesel cars.
3) Aircrafts: Otto as well as Brayton cycle engines, both require forced induced air in one way or another; as altitude increases inversely, the density of oxygen in air increases thus making it difficult for engine to aspire, thus since 1920's research on using turbochargers with aircraft's rotary spark ignition engine started! the same concept of turbochargers is used in brayton cycle engines also where the air is compressed axially rather than using a centrifugal system.
Apart from these main uses, turbochargers have been extensively used in motorcycles, trucks, marine and land machinery etc.