Automatic Transmission / automobile gearbox /Automatic Transmission Modes/ Automatic Transmission Parts

 Automatic Transmission:

         An automatic transmission (commonly "AT" or "Auto") is an automobile gearbox that can change gear ratios automatically as the vehicle moves, freeing the driver from having to shift gears manually.

 Automatic Transmission Modes:

         In order to select the mode, the driver would have to move a gear shift lever located on the steering column or on the floor next to him/her. In order to select gears/modes the driver must push a button in (called the shift lock button) or pull the handle (only on column mounted shifters) out. In some vehicles position selector buttons for each mode on the cockpit instead, freeing up space on the central console. Vehicles conforming to U.S. Government standards must have the modes ordered P-R-N-D-L (left to right, top to bottom, or clockwise). Prior to this, quadrant-selected automatic transmissions often utilized a P-N-D-L-R layout, or similar. Such a pattern led to a number of deaths and injuries owing to un- intentional gear miss-selection, as well the danger of having a selector (when worn) jump into Reverse from Low gear during engine braking maneuvers.

           Automatic Transmissions have various modes depending on the model and make of the transmission. Some of the common modes are:
 
Park Mode (P):

         This selection mechanically locks the transmission, restricting the car from moving in any direction. A parking pawl prevents the transmission-and therefore the vehicle-from moving, although the vehicle's non-drive wheels may still spin freely. For this reason, it is recommended to use the hand brake (or parking brake) because this actually locks the (in most cases, rear) wheels and prevents them from moving. This also increases the life of the transmission and the park pin mechanism, because parking on an incline with the transmission in park without the parking brake engaged will cause undue stress on the parking pin. An efficiently-adjusted hand brake should also prevent the car from moving if a worn selector accidentally drops into reverse gear during early morning fast-idle engine warm ups.

Reverse (R):
       
          This puts the car into the reverse gear, giving the ability for the car to drive backwards. In order for the driver to select reverse they must come to a complete stop, push the shift lock button in (or pull the shift lever forward in the case of a column shifter) and select reverse. Not coming to a complete stop can cause severe damage to the transmission. Many modern automatic gearboxes have a safety mechanism in place, which does to some extent prevent (but doesn't completely avoid) inadvertently putting the car in reverse when the vehicle is moving.

       This mechanism usually consists of a solenoid-controlled physical barrier on either side of the Reverse position, which is electronically engaged by a switch on the brake pedal. Therefore, the brake pedal needs to be depressed in order to allow the selection of reverse. Some electronic transmissions prevent or delay engagement of reverse gear altogether while the car is moving.

 Neutral/No gear (N):

      This disconnects the transmission from the wheels so the car can move freely under its own weight. This is the only other selection in which the car can be started.

Drive (D):

     This allows the car to move forward and accelerate through its range of gears. The number of gears a transmission has depends on the model, but they can commonly range from 3, 4 (the most common), 5, 6 (found in VW/Audi Direct Shift Gearbox), 7 (found in Mercedes 7G gearboxes, BMW M5 and VW/Audi Direct Shift Gearbox) and 8 in the newer models of Lexus cars. Some cars when put into D will automatically lock the doors or turn on the Daytime Running Lamps.

Overdrive ([D], Od, Or A Boxed D):
       This mode is used in some transmissions to allow early Computer Controlled Transmissions to engage the Automatic Overdrive. In these transmissions, Drive (D) locks the Automatic Overdrive off, but is identical otherwise. OD (Overdrive) in these cars is engaged under steady speeds or low acceleration at approximately 35-45 mph (approx. 72 km/h). Under hard acceleration or below 35-45 mph, the transmission will automatically downshift. Vehicles with this option should be driven in this mode unless circumstances require a lower gear.

Second (2 or S):

       This mode limits the transmission to the first two gears, or more commonly locks the transmission in second gear. This can be used to drive in adverse conditions such as snow and ice, as well as climbing or going down hills in the winter time. Some vehicles will automatically up-shift out of second gear in this mode if a certain rpm range is reached, to prevent engine damage.

First (1 or L):

       This mode locks the transmission in first gear only. It will not accelerate through any gear range. This, like second, can be used during the winter season, or for towing.

      As well as the above modes there are also other modes, dependent on the manufacturer and model. Some examples include:
  
       D5:- In Hondas and Acuras equipped with 5-speed automatic transmissions, this mode is used commonly for highway use (as stated in the manual), and uses all five forward gears.

      D4:- This mode is also found in Honda and Acura 4 or 5-speed automatics and only uses the first 4 gears. According to the manual, it is used for "stop and go traffic", such as city driving.

     D3:- This mode is found in Honda and Acura 4-speed automatics and only uses the first 3 gears. According to the manual, it is used for stop & go traffic, such as city driving. This mode is also found in Honda and Acura 5-speed automatics.

       This is the manual selection of gears for automatics, such as Porsche's Tiptronic. This feature can also be found in Chrysler and General Motors products such as the Dodge Magnum and Pontiac G6. The driver can shift up and down at will, by toggling the shift lever (console mounted) like a semi-automatic transmission. This mode may be engaged either through a selector/position or by actually changing gear (e.g. tipping the gear-down paddles mounted near the driver's fingers on the steering wheel).

     The predominant form of automatic transmission is hydraulically operated, using a fluid coupling/ torque converter and a set of planetary gear-sets to provide a range of torque multiplication.

Automatic Transmission Parts :

 
        A hydraulic automatic transmission consists of the following parts:

1. Torque Converter/Fluid Coupling

2. Planetary Gear Set

3. Clutch packs & Bands

4. Valve Body

5. Hydraulic or Lubricating Oil

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What is Differential Unit ? How Differential Unit work.

 Differential Unit:

Differentials are a variety of gearbox, almost always used in one of two ways. In one of these, it receives one input and provides two outputs: this is found in every automobile. In automobile and other wheeled vehicles, the differential allows each of the driving wheels to rotate at different speeds, while supplying equal torque to each of them. In the other, less commonly encountered, it combines two inputs to create an output that is the sum (or difference) of the inputs. In automotive applications, the differential and its housing are sometimes collectively called a "pumpkin" (because the housing resembles a pumpkin).

Purpose:

The differential gear box has following functions:

1. Avoid skidding of the rear wheels on a road turning.

2. Reduces the speed of inner wheels and increases the speed of outer wheels, while drawing a curve.

3. Keeps equal speeds of all the wheels while moving on a straight road.

4. Eliminates a single rigid rear axle, and provides a coupling between two rear axles.

The following description of a differential applies to a "traditional" rear- or front-wheel-drive car or truck: Power is supplied from the engine, via the transmission or gearbox, to a drive shaft termed as propeller shaft, which runs to the differential. A spiral bevel pinion gear at the end of the propeller shaft is encased within the differential itself, and it meshes with the large spiral bevel ring gear termed as crown wheel.

 The ring and pinion may mesh in hypoid orientation.The ring gear is attached to a carrier, which holds what is sometimes called a spider, a cluster of four bevel gears in a rectangle, so each bevel gear meshes with two neighbors and rotates counter to the third that it faces and does not mesh with. Two of these spider gears are aligned on the same axis as the ring gear and drive the half shafts connected to the vehicle's driven wheels.

These are called the side gears.The other two spider gears are aligned on a perpendicular axis which changes orientation with the ring gear's rotation. These two gears are just called pinion gears, not to be confused with the main pinion gear. (Other spider designs employ different numbers of pinion gears depending on durability requirements.)

As the carrier rotates, the changing axis orientation of the pinion gears imparts the motion of the ring gear to the motion of the side gears by pushing on them rather than turning against them (that is, the same teeth stay in contact), but because the spider gears are not restricted from turning against each other, within that motion the side gears can counter- rotate relative to the ring gear and to each other under the same force (in which case the same teeth do not stay in contact).

Thus, for example, if the car is making a turn to the right, the main ring gear may make 10 full rotations. During that time, the left wheel will make more rotations because it has further to travel, and the right wheel will make fewer rotations as it has less distance to travel. The side gears will rotate in opposite directions relative to the ring gear by, say, 2 full turns each (4 full turns relative to each other), resulting in the left wheel making 12 rotations, and the right wheel making 8 rotations.

The rotation of the ring gear is always the average of the rotations of the side gears. This is why if the wheels are lifted off the ground with the engine off, and the drive shaft is held (preventing the ring gear from turning inside the differential), manually rotating one wheel causes the other to rotate in opposite direction by the same amount.

When the vehicle is travelling in a straight line, there will be no differential movement of the planetary system of gears other than the minute movements necessary to compensate for slight differences in wheel diameter, undulations in the road (which make for a longer or shorter wheel path), etc.

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HOW DRIVE SHAFT WORK

 The Drive Shaft.

The drive shaft, or propeller shaft, connects the transmission output shaft to the differential pinion shaft. Since all roads are not perfectly smooth, and the transmission is fixed, the drive shaft has to be flexible to absorb the shock of bumps in the road. Universal, or "U-joints" allow the drive shaft to flex (and stop it from breaking) when the drive angle changes.

Drive shafts are usually hollow in order to weigh less, but of a large diameter so that they are strong. High quality steel, and sometimes aluminum are used in the manufacture of the drive shaft. The shaft must be quite straight and balanced to avoid vibrating. Since it usually turns at engine speeds, a lot of damage can be caused if the shaft is unbalanced, or bent. Damage can also be caused if the U-joints are worn out.

There are two types of drive shafts, the Hotchkiss drive and the Torque Tube Drive. The Hotchkiss drive is made up of a drive shaft connected to the transmission output shaft and the differential pinion gear shaft. U-joints are used in the front and rear. The Hotchkiss drive transfers the torque of the output shaft to the differential. No wheel drive thrust is sent to the drive shaft. Sometimes this drive comes in two pieces to reduce vibration and make it easier to install (in this case, three U-joints are needed).The two-piece types need ball bearings in a dustproof housing as center support for the shafts. Rubber is added into this arrangement for noise and vibration reduction.

The torque tube drive shaft is used if the drive shaft has to carry the wheel drive thrust. It is a hollow steel tube that extends from the transmission to the rear axle housing. One end is fastened to the axle housing by bolts. The transmission end is fastened with a torque ball. The drive shaft fits into the torque tube. A U-joint is located in the torque ball, and the axle housing end is splined to the pinion gear shaft. Drive thrust is sent through the torque tube to the torque ball, to transmission, to engine and finally, to the frame through the engine mounts. That is, the car is pushed forward by the torque tube pressing on the engine.

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HOW U-Joint WORK ?

 

U- Joint:

Hooke's joint is a linkage that transmits rotation between two non parallel shafts whose axes are coplanar but not coinciding., and is commonly used in shafts that transmit rotary motion. It is used in automobiles where it is used to transmit power from the gear box of the engine to the rear axle.The driving shaft rotates at a uniform angular speed, where as the driven shaft rotates at a continuously varying angular speed.        

            A complete revolution of either shaft will cause the other to rotate through a complete revolution at the same time. Each shaft has fork at its end. The four ends of the two fork are connected by a centre piece, the arms of which rest in bearings, provided in fork ends. The centre piece can be of any shape of a cross, square or sphere having four pins or arms. The four arms are at right angle to each other.

When the two shafts are at an angle other than 180° (straight), the driven shaft does not rotate with constant angular speed in relation to the drive shaft: the more the angle goes toward 90° the jerkier the movement gets(clearly, when the angle β = 90° the shafts would even lock).

However, the overall average speed of the driven shaft remains the same as that of driving shaft, and so speed ratio of the driven to the driving shaft on average is 1:1 over multiple rotations.

The angular speed ω2 of the driven shaft, as a function of theangular speed of the driving shaft ω1 and the angle of the driving shaft φ1,is found using:

         

Components of Hooke’s Joint

Slip Joint in the Propeller Shaft:

 Hook Jointin the Propeller Shaft:

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 HOW INTERCOOLER WORKS 

An intercooler is a heat exchanger that’s fitted between the engine’s super or turbo charger and the intake manifold. Its job is to absorb and dissipate the heat in the charge air in order to provide the engine with the coolest and most dense air possible.

Air has a mass or a weight that changes based on the temperature and pressure of the air. The lower the temperature – the higher the mass. The higher the pressure – the higher the mass. 

At 15 degrees Celsius and at sea level 1 litre of air weighs around 1.225 grams. Of that around 0.245 grams is oxygen – the stuff we want to cram into the engine.

In order to get more air, thus more oxygen into the engine, we either need to compress the intake charge (turbo or supercharging), cool the intake charge, or both!

This is where things get tricky because the process of compressing the air also heats it up, so we need to cool it before it makes its way into the engine.

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 What is alternator and what works?

An alternator is a type of electrical machine that converts mechanical energy into alternating electric energy.  Hence it is also called synchronous generators or AC generator.  If you have a car or a heavy and big vehicle, then if your headlights are slightly dimmed, and your car is not always starting.  And you are worried because what is the reason for this, then maybe the cause of alternator malfunction can also happen, because this small piece of machinery is very useful for you, which produces electricity from mechanical energy.

 Also, alternators also charge the battery of your vechiles while you are driving it.  If they are not working, then your battery will slowly die.  Your car needs a lot of power to start working, and if your battery is not getting recharged, then it will die easily very soon.  Therefore, the alternator has a very important function in a vechile.

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STARTING SYSTEM: COMPONENTS AND WORKING PRINCIPLES

The engine can’t “start” rotational movement on its own. It needs an electric motor to get it up to a minimal RPM to run, then the engine can run under its power. The starter is the biggest load on the vehicle's electrical system. We cannot simply run all that current through the ignition switch, in most systems a relay is used to activate the starter solenoid, and the starter solenoid itself acts as another relay to engage the starter motor (explained later). Before electric starters, automobile owners needed to crank the engine over themselves! This was not ideal for any kind of quick getaway.

The starter motor is an electric motor that rotates your engine to allow the spark and fuel injection systems to begin the engine's operation under its power. Typically, the starter is a large electric motor and stator coil mounted to the bottom (generally to one side) of the vehicle's transmission bell housing where it connects to the engine itself. The starter has gears that mesh with a large flywheel gear on the backside of the engine, which turns the central crankshaft. Because this is a lot of physical weight and friction to overcome, starter motors are generally powerful, high-speed motors and use an ignition coil to ramp up their power before engaging.


COMPONENTS OF STARTING SYSTEM

1. Battery

2. Ignition Switch

3. Neutral Safety Switch

4. Starter Relay

5. Battery Cables

6. Starter Motor

Starter motor parts

1. Starter Solenoid

2. Starter Motor

3. Starter Drive Pinion

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