Ford Mustang in India

Finally after 51 years since its production began, Mustang will make an entry in the Indian market. The launch is expected to take place most probably in the second quarter of 2016. It is also the first time that Mustang will be launched with a right hand drive steering set-up.



Ford is most likely to import the completely assembled unit and will offer two engine variants: a 5 litre Ti-VCT V8 engine which can produce 420 horsepower and 542 Nm torque and the seconds option is a 2.3 litre 4 cylinder Ecoboost engine which can produce 311 horsepower and 320 Nm torque. Both the engines will have a 6 speed automatic gearbox.


The price of Mustang with 5 litre engine will be around 55 lacs to 60 lacs, and the price of the car with 2.3 litre engine is expected to be around 40 lacs to 45 lacs.

Drum Brakes (Self-Actuating Brakes)

Drum brakes work with the help of brake shoes or brake pads that use frictional force between the pads and the drum to stop the wheel. The brake pads are pressed against the inner surface of the drum to create the frictional force.

The drum brake working principle was first patented by Louis Renault, a French industrialist, in the year 1902. However, the first drum brakes were used by Maybach in the year 1900.

Design:



A drum brake consists of various components:

• A pair of brake pads with linings made of materials having high frictional coefficient. The brake pads are hinged either at a single point or independent locations not far from each other. The other ends remain in contact with the pistons in the wheel cylinder.

• Wheel drum which rotates along with the wheels. It is usually made of cast iron.

• A wheel cylinder which has a pair of pistons for each brake pad. When brake pedal is depressed, oil pressure increases and acts on the pistons. The pistons force the brake pads to press against the wheel drum.

• Brake return springs allowing the brake pads to return to their original positions once the brake pedal is released.

• Drum brakes also have an emergency brake system which can be operated through a lever by a hand brake.

• Self adjusting system to automatically re-adjust the distance required for the brake pads to travel to press against the wheel drum when brakes are applied. Brake pads start wearing with time, so self adjusting mechanism will help in changing the distance. This is the reason why they are also called self actuating brakes.

Working:

When the brake pedal is depressed by the driver, the master cylinder pressurises the hydraulic oil and sends this hydraulic pressure to the wheel cylinder. This hydraulic pressure acts on the double-acting pistons which push the brake pads outside. The brake pads press against the inner surface of the wheel drum and create friction. This friction between the brake pads and the drum brings the wheels to rest.

Once the brake pedals are released, the return springs pull the brake pads back to the original position.

Self-Actuating Mechanism:

Drum brakes are also known as self-actuating brakes. As the brake pads wears out, they have to  travel a greater distance to press against the wheel drum. Therefore, self adjusting mechanism is used to automatically re-position the resting point of the hinges on which the brake pads are hinged, so as to get them closer to the drum.

Advantage of using a drum brake:

There is only one major advantage of drum brakes, it is cheap.

Disadvantages of a Drum brake:

• Complicated design, use of several components compared to a disc brake.


• Requires regular service, especially the brake pads which wear out quickly and needs to be replaced.

Rotary Engines

Rotary engines, also known as Wankel engines is a type of internal combustion engine in which the method of operation is different compared to a conventional four stroke engine. Rotary engine adopts eccentric rotary design to complete the combustion process.

In a four stroke engine, all four jobs- intake, compression, combustion and exhaust takes place in the same volume space of the cylinder. Whereas, in a rotary engine all jobs take place at different parts of the engine housing.

History:

Wankel Rotary engine was patented by a German  engineer, Felix Wankel in 1929. NSU Motorenwerke completed a working prototype of the design in 1957.

Design:

Wankel rotary engine employs a eccentric triangular rotor instead of a cylindrical piston in order to compress and burn the air-fuel mixture. The housing is oval or epitrochoid ( as shown in fig 1, a roulette traced by a point 'p' attached to a circle of radius 'a' rolling outside the circle of a radius 'r' ) in shape. The use of a triangular rotor and the epitrochoid design of the housing creates three different volumes of gas inside the housing.

Fig 1: Epitrochoid explanation

There is an intake port on the upper left portion of the housing, and an exhaust port at the lower left portion of the housing. One or two slot(s) are provided at the mid right portion of the housing to house the spark plugs.

The entire housing is enclosed in coolant jackets. An eccentric shaft (output shaft) runs through the centre of the housing. It has round lobes mounted eccentrically around the output shaft, therefore making the lobes slightly offset from the axis of the output shaft.

A triangular shaped rotor is fixed over the rotor journal provided in the eccentric shaft. Internal gears are provided in the rotor that mesh with the central output shaft or the eccentric shaft.

Each face of the rotor is provided with a cavity or pocket to help in the combustion process. The cavity increases the displacement of the engine and also allows some space to the air-fuel charge.

The apex of each face acts as a seal for the three volumes of gas to the outside of the chamber.

Assembly:

The rotary engine is made of several layers:

• The outermost layer is a layer of coolant jacket. Coolant liquid flows through the passages provided in the jacket.


• The next layer from outside is the oval or epitrochoid housing layer which also has a exhaust port. This layer is very smooth so that it can help the rotor to rotate with minimum friction.


• The next layer is the centre piece which contains the inlet port.


• The centre piece has a circular port in the centre which houses the output shaft with circular lobes. The rotor rotates around the circular lobe and it also has internal gear that is meshed with a smaller gear fixed to the housing.

Working:

As the rotor rotates around the chamber, all three volumes of gas expands and compresses alternately. This alternate expansion and compression of the volumes creates a suction force for the air-fuel mixture, then compresses the fresh charge, then ignites the compressed charge with the help of spark plugs and eventually drives out the exhaust gases.


The offset lobe on the output shaft will rotate three times for every one revolution of the rotor. When the rotor rotates, the three chambers created keep varying in sizes.

• Intake :  Intake starts when one of the apex of the rotor crosses the inlet port. The volume of the chamber expands, thereby drawing in  more air-fuel mixture. The intake stroke is over when the consecutive apex crosses the inlet port and no more air-fuel charge enters the chamber.

• Compression: As the rotor continues its rotation in the housing, the volume of the chamber keeps getting reduced and the air-fuel mixture is compressed.

• Combustion: As soon as the face of the rotor makes it around the spark plugs, combustion process starts. Normally two spark plugs are employed for complete combustion. This produces enormous power that pushes the rotor in the direction that increases the volume of the chamber filled with exhaust gases unless the peak of the rotor crosses the exhaust port.

• Exhaust: Once the apex of the rotor crosses the exhaust port, the combusted gases are free to move out through the exhaust port to the tail pipe. The continuous rotation of the rotor shrinks the chamber volume and this forces the exhaust gases to move out of the chamber. Later the apex reaches the inlet port and the entire cycle starts again.

One salient feature about the rotary engine is that all three faces can act as a combustion chamber and thus three combustion or power stroke per revolution of the rotor. But the output shaft rotates thrice for every one revolution of the rotor. Therefore, one combustion stroke per revolution of the output shaft.


Advantages:

• A four stroke piston engine has a minimum of 40 moving parts including camshaft, crankshaft, valves, rockers, timing gears, etc. Whereas, rotary engines have only three main moving parts (i.e) two rotors and a output shaft.


• The entire operation is smoother. Rotary engines are balanced internally with counterweights to cut down the vibration.


• The power delivery is smooth. For every one revolution of rotor, three combustion strokes are produced.


• Rotary engines are reliable because of the slower moving parts such as the rotor which has one-third of the speed of the output shaft.

Disadvantages:

• Doesn't meet the emission norms set by the U.S government.


• Expensive in production compared to piston engines.


• Higher fuel consumption.


• Lower compression ratio.

Two Stroke Diesel Engines

The main difference between two stroke and four stroke engines is the power produced by both the engines. Two stroke engines fires once in one revolution of the crankshaft, whereas the four stroke engine fires once in 2 revolutions of the crankshaft. Therefore, the two stroke engines are capable of producing more power per revolution.

In a gasoline powered two stroke engine, we know that there is a disadvantage of some amount of gasoline escaping along with the exhaust gases without getting burnt during the process of scavenging.

In the case of diesel powered two stroke engines, only air is used as a fresh charge, so there is no fuel wastage. Diesel is injected with the help of a fuel injector only after the air is compressed up to 1/18th of the cylinder volume. The compression of air increases the temperature and pressure inside the combustion chamber high enough to burn the diesel without the application of spark plugs.

Working:

The two stroke diesel engine has an air inlet port through which air is constantly tried to be pushed inside the combustion chamber with the help of an air pump. Two or four exhaust valves are provided at the top which open at the same time to let the exhaust gases to escape. A diesel injector is provided at the top to inject the diesel at the precise timing. There is no spark plug.

Power Stroke:

1. When the piston starts moving towards the Bottom Dead Centre (BDC) from the Top Dead Centre (TDC), the exhaust valve opens by means of camshaft and the exhaust gases escape out through it.


2. Further moving down, the piston uncovers the air inlet port and allows the air to fill inside the combustion chamber. The fresh air charge also drives out the remaining exhaust gases out of the exhaust valve.

Compression Stroke:

1. After reaching the BDC, the piston starts moving towards the TDC. The exhaust valve is closed and no more fresh air escapes out through the exhaust valve.


2. Further moving up, the piston covers the air inlet port and starts compressing the air trapped inside the combustion chamber to almost 1/18th of its volume.


3. The temperature and pressure rises inside the combustion chamber and just before the piston reaches TDC, diesel is injected inside the combustion chamber.


4. The fuel is burnt and tremendous amount of energy is released and the steps in the power stroke repeats itself.

A two stroke diesel engine must have a turbocharger or a supercharger to push more air inside the combustion chamber. Thus it is more expensive than a two stroke gasoline engine.

Torsen Limited Slip Differential

Torsen Limited Slip Differential houses a set of complicated gear system, but is the most effective of all the LSDs. This product is the trademark of the JTEKT corporation. Torsen was first patented by Gleasman in 1958.

Construction:


The components used inside torsen are unique and they provide the most brilliant way of providing differential action and also overcoming the traction difference problem.

It has a pair of specially designed gear assembly. These are designed on the basis of spur gear (Worm wheel) and worm gear assembly. This is the basic principle behind the working of a torsen. The unique feature of worm gear and worm wheel assembly is that the spinning worm gear can rotate the worm wheel, whereas the vice-versa is not possible. It means that the rotating worm wheel cannot spin the worm gear (the assembly is locked in this case).

A pair of this worm wheel and worm gear assembly is attached to the differential case. The half output shafts are connected on either side of the worm gears that drive the wheels.

The power from the transmission is transferred to the pinion and ring gear assembly which is standard in any differential. The worm wheels rotate along with the ring gear. Each end of the worm wheels is fitted with a spur gear. The spur gears are meshed so that both the worm gears rotate at the same speed and in opposite directions.

Case 1 (Vehicle moving straight):

In this case, the power from the ring gear is directly transferred to the output shafts via the differential casing. The worm wheels and worm gears are locked and rotate as a single solid unit. The worm wheels do not spin on its own axis and the worm gears do not rotate about its own axis. Equal amount of power is distributed to the wheels.

Case 2 (Vehicle taking a right turn):

In this case, the left wheel has to rotate at a higher speed compared to right wheel. The worm gear of the faster moving left axle will rotate the corresponding worm wheel about its own axis at a higher speed. Whereas, the right axle rotates in opposite direction when considering its relative motion with the left axle. Thus the right worm wheel will rotate in the opposite direction.

The spur gears which are meshed at the end of worm wheels will make sure that the worm gears rotate at the same speeds but in opposite direction. This ensures a perfect differential action.

Case 3 ( One wheel on a slippery surface and the other on a non slippery surface ):

In this case, a vehicle equipped with a conventional differential will allow majority of the power to be transferred to the slippery wheel. Therefore the vehicle will get stuck.

In a torsen LSD, the excessive speed of the slipping wheel can be used to its advantage. As the slipping wheel ( say the right wheel) starts spinning at a higher speed, this speed increase will be transferred to the right worm wheel via the right worm gear. The right worm wheel starts rotating in its own axis, therefore transferring the power to the left worm wheel as they both are connected with the help of spur gears.

We know that the unique feature of worm wheel and worm gear arrangement is that the worm wheel cannot spin the worm gear. This principle is applied in the torsen as the left worm wheel cannot spin the left worm gear and the entire mechanism gets locked. As a result, both the left and right wheels start rotating at the same speed.

To withstand the heavy vehicle load, two more pairs of worm gear and worm wheel assembly is added to the differential case.

Electronic Limited Slip Differential (eLSD)

Introducing electronics into any technology improves its accuracy. Electronic limited slip differential (eLSD) is just like a normal LSD having pressurized hydraulic clutches, fine tuned with electronics.

An eLSD employs Electronic Control Unit (ECU) to provide sufficient torque to each wheel. Wheel sensors sense the wheel speeds and provide inputs to the ECU. In the event of slipping of wheels, the ECU actuates the hydraulic clutches allowing it to transfer more torque to the wheel having more traction. An eLSD also allows for better control over a vehicle while taking a turn or changing the lane with the help of Electronic Stability Program (ESP).

An eLSD prevents a vehicle from excessive yaw. From the top view, yaw is defined as the rotation of a vehicle around its central point. Rear wheel eLSD monitors whether the rear wheels are moving in the same direction as the front wheels while turning or changing the lane. If the yaw is more than the limit, then the vehicle could go for a spin. Hence, an eLSD prevents the vehicle from spinning.

Limited Slip Differential (LSD)

What is LSD?

The limitations in differential is overcome by using Limited Slip Differential (LSD). It is a mechanical differential gear system used in automobiles to limit the relative motion between the wheels.

In a car with the conventional differential, if only one wheel is stuck on a slippery surface, then one wheel will be slipping freely over the slippery surface while the other wheel motion ceases. Limited Slip Differential overcomes it by transferring more torque to the non slipping wheel. This helps the vehicle escape a ditch easily.

LSD Construction:



One of the most commonly used technology for LSD is clutch pack based. The differential case has the same components that are used in a conventional differential. A pinion from the propeller shaft meshed to the ring gear, allowing 90 degree power transfer. The sun gears and planet gears are also meshed with each other. Planet gears rotate around the axis of the ring gear and also in its own axis. The sun gears are connected to the 2 half output shafts connected to each wheel. It has a series of friction and steel plates arranged alternately and packed together on either side between the sun gears and the differential case. There is a pre-load spring fitted between the sun gears.

LSD Working:

Friction discs are locked with the sun gears. Therefore, friction discs and side gear will always rotate together. Steel plates have external teeth and are made to fit in the grooves provided in the differential casing. Therefore, both steel plates and case rotate together.

If the clutch assembly is well pressed, then the entire clutch and case assembly will move together. Therefore, motion from the case is directly transferred to the half output shafts. The pre-load spring fitted between the sun gears will provide a side thrust and press the clutch discs together.

The sun and planet gear assembly is a bevel gear assembly. In a bevel gear system, axial forces are also induced apart from tangential forces. The axial force tries to push the sun gears against meshing with the planet gears. In the differential casing, a small allowance is provided to the sun gears for axial movement. Therefore, during high torque transfer, there is a huge amount of axial force acting on the sun gears that push it outwards towards the clutch pack. This axial thrust presses the clutch discs against the wall of the casing.

Vehicle with one wheel on a slippery surface:

Lets consider the case where one wheel is on slippery surface and the other is on a non slippery surface. Due to higher traction on the non slippery surface, the torque transferred towards the non slipping wheel will be higher. As a result, more axial thrust is created on the non slippery side and the clutch assembly on that side is locked. So power from the transmission is transmitted directly towards the non slippery surface via the clutch pack assembly.

On the slippery side, the axial force is not enough to lock the clutch pack. Therefore, power flow towards the slippery side is limited. As a result, the vehicle will overcome the traction difference problem.

While taking a turn:

While taking a turn, the LSD acts as a normal differential. In this case, the clutch pack won't come to use as the axial force developed will be less. As a result, the left and right wheels will turn at different speeds just like the conventional differential.