Automotive Information

The Parts of an Engine

Connecting rod – Connects the piston to the crankshaft. The connecting rod rotates at both ends, changing its angle as the piston moves and the crankshaft rotates.

Crankshaft – Converts the up-down motion of the pistons into circular motion.

Cylinders – the core of an engine. Most cars have more than one, and they can be arranged in a single row (inline), at an angle to each other (V), or horizontally opposite one another (flat).

Piston – The cylindrical piece of metal that moves up and down inside the cylinder.

Piston rings – Flexible metal rings that seal the outer edge of the piston and the inner edge of the cylinder. Piston rings keep the air/fuel mixture and exhaust in the combustion chamber from leaking out during compression and combustion. They also keep oil from leaking into the cylinder.

Spark plug – Supplies the spark that ignites the air/fuel mixture.

Sump – Surrounds the crankshaft to contain lubricating oil, which collects in the bottom of the sump.

Valves – The intake and exhaust valves let in the air and fuel and let out exhaust fumes. Both valves are closed during the compression and combustion strokes.

An automobile’s engine power comes from the burning of a small amount of gasoline and air in an enclosed space. This process is called combustion. When this mixture is ignited, it burns quickly, like a mini explosion that pushes energy out in all directions. This chemical energy is made from the fuel and air converted into heat energy. The propulsion force that results is used to move a part of the engine. The moving part is then used to turn the wheels of the automobile, giving the vehicle movement.

The movement of the crankshaft is similar to your legs turning the pedals of a bike, turning the wheels, and creating forward motion. The piston needs to keep moving up and down so the power stroke can be repeated, keeping the car moving.

The bike example describes a two pistol arrangement attached to the crankshaft. Modern motor vehicle engines can have four, six, eight, and even twelve cylinders.

Once the pistons give moving power to the wheels, the new air-fuel mixture needs a way into the cylinder and the burnt exhaust gases need a way out of it. Above the piston, there are two holes at the top of the cylinder. Each hole has a tight metal disc that acts as a plug or a stopper. One disc will open, allowing fresh air-fuel mixture into the cylinder. Once it is closed, and combustion has moved the piston down the cylinder, the other disc will open, allowing the exhaust gases to leave the cylinder as the piston comes back up, making room for the next fresh air-fuel mixture. These metal discs that open and close are called valves. Valves are controlled by a rod assembly, rocker arm, and camshaft. The camshaft connected to the pistons is driven by the crankshaft, moving at one-half the speed of the crankshaft to open and close valves at the precise moment.

Remember, while the camshaft and valves help the engine create power, the crankshaft takes that power and gives it to the vehicle. The crankshaft converts reciprocating motion (the up and down of the pistons) into rotational motion that rotates the gears in the transmission, which, through other gears, rotate the wheels.

Air Fuel System

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To trigger an explosion in the cylinder and move the piston downward, the appropriate amount of air-fuel mixture must be applied. This is the function of the carburetor. A fuel pump sends the fuel from the storage tank to the part of the carburetor called the float bowl. Air is sucked into the carburetor through the air filter, caused by the downward motion of the pistons, increasing speed as it passes through a passageway in the carburetor called the venturi. The air rapidly passes the opening to the float bowl, where it sucks a small amount of fuel with it. This air-fuel mixture becomes a mist and passes through the open valve in the cylinder and into the chamber above the piston. Timing is everything during this process.

Connected to the throttle valve at the base of the carburetor is the accelerator pedal, which determines how much air-fuel mixture the engine will need. A ratio of approximately 15:1 pounds of air to pounds of fuel is always needed to keep the mixture proportioned for combustion.

The Powertrain

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The powertrain refers to all of the components that convert the engine’s power into movement. These include the engine, transmission, driveshaft, differentials, and axles. In general the powertrain includes everything from the engine through to the rotating wheels.

Drivetrain

The drivetrain is the group of components that deliver power to the wheels. Unlike the powertrain, it typically refers to everything that comes after the engine. The drivetrain includes all the pieces between the engine and wheels that produce, develop, or assist in moving the wheels.

Vehicles come in a variety of “drives.” There are front-wheel, rear-wheel, all-wheel, and four-wheel drive vehicles. The drivetrain configurations of these types of vehicles differ due to the way the engines deliver power to the wheels.

Transmission

The manual transmission consists of the clutch and gearbox. The role of the clutch is to engage or disconnect the running engine from the gearbox. The clutch is particularly important to keep the engine idling when bringing a vehicle to a stop. Without a clutch, the engine’s rotation would be locked to the gearbox, causing the engine to slow to a shuddering halt or to stall.

The transmission gears are used to harness and optimize an engine’s power regardless of the vehicle’s speed. A manual transmission may have from 3 to 6 or even 8 gears, each with a different mechanical ratio.

The mechanical ratio for low gear (first gear) produces more force at lower vehicle speeds and is needed for starting from a stop. However, that gear ratio will reach the maximum engine revolution at a very low speed. Ratios in the higher gears produce less force and require fewer engine revolutions to achieve higher speeds.

Driveshaft

Four Types of Transmission

1. Manual – The operator must manually select the desired gears using the stick shift; the operator’s left foot is used to engage the clutch.

2. Conventional automatic transmission – Uses a complex set of gears that are controlled by the vehicle’s computer, thus taking the manual selection process away from the operator. Automatic transmissions have no conventional clutch; instead, a device called a torque converter performs this task.

3. Semi-automatic and dual-clutch transmissions – These combine both manual and automatic transmissions. In a semi-automatic system, gears can still be selected by the driver, but there is no clutch pedal because the car’s computer performs this function. This system is often called the “clutchless manual.” A variation of this is the dual-clutch transmission, which uses a separate clutch for the odd and even gears. Therefore, while one gear is in use, the next gear—be it higher or lower—is ready to go at a moment’s notice. This means the vehicle can handle extremely rapid shifts.

4. Continuously variable transmission (CVT) – Does not use gears. Instead, this system employs a pulley system controlled by the car’s computer to offer the optimum gear ratio for any given driving situation.

Rear-wheel drive vehicles with front-mounted engines require a long driveshaft. The driveshaft is a rotating shaft that runs all the way down the center of a vehicle, bringing the power from the engine/transmission through a differential to the wheels. Vehicles that are front-engined with front-wheel drive have a combined transmission/differential system called a transaxle.

Differentials

The differential has a gear set called a ring and pinion. Its pinion gear is driven by the driveshaft and rotates the differential’s ring gear. The differential assembly accepts the inside end of the rear wheel axles, which are rotated by the ring gear. Wheels and tires are at the outer end of the rear axles.

An additional and important feature of the differential is that it allows the driven wheels to rotate at different speeds, increasing grip. Without a differential, the driven wheels would be locked together and forced to spin at the same speed. While a vehicle moving in a straight line would not have much of a problem, a vehicle that is taking corners, particularly ones that are tight, or that is maneuvering with high speed would encounter difficulty. In these scenarios, one wheel would spin uselessly. A differential helps split the power out into the two wheels.

There are other more noticeable reasons why it is important for driven wheels to rotate at different speeds.

Wheels on a single axle, or on individual axles connected by a rigid differential, would not turn at different speeds when cornering. When turning a corner with wheels that are allowed to rotate freely on an axle, the inside wheel will rotate slower than the outside wheel because the outside wheel must go a longer distance (it is at a bigger radius than the inside wheel). Without the differential, corners would be much noisier due to tires squealing because they are forced to corner at different distances. Also, rear tires would wear out much faster.

Axles

A wheel won’t turn unless it’s connected to a vehicle by an axle. The axle is the shaft on which a wheel or a gear rotates. The axle for front wheels is called a spindle, which is part of the front suspension. The front suspension includes features that allow the vehicle to be steered.

And we arrive—and finish—at the wheels.