Auto and Shop Information Study Guide for the ASVAB

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Auto: Electrical Systems

As modern vehicles evolve, the electrical system plays an increasingly crucial role in various functionalities. Mechanically driven systems are now being redesigned to operate electrically, with several key subsystems making up the electrical system.

Battery: The Electrical System’s Backbone

The car battery provides electrical energy to start the engine and power a car’s electrical system. It converts chemical energy into electrical energy through a chemical reaction between lead and lead oxide plates immersed in an electrolyte solution of sulfuric acid and water, which is why you sometimes hear it referred to as a lead-acid battery.

When the battery is connected to the car’s electrical system, the chemical reaction causes electrons to flow through it, creating a voltage difference between its positive and negative terminals. This voltage difference powers the car’s starter motor and other electrical components.

Starting System: Engine Activation

The starting system in a car works by using the battery’s stored electrical energy to power the starter motor, which turns the engine over and starts the combustion process, allowing the engine to run on its own power.

Charging System: Powering the Electrical Components

The charging system in a car powers electrical components by converting mechanical energy from the engine into electrical energy and sending it to the battery. The main unit, the alternator, is responsible for this conversion, and a voltage regulator ensures the voltage stays safe. Rectified output from the alternator and rectified bridge circuits can also contribute to the efficient charging and distribution of electrical energy in a car.

Lighting System: Illuminating the Way

A vehicle’s lighting system consists of various lights for both interior and exterior purposes. Interior lights help the driver see the instrument panel and other areas inside the car, while headlights and taillights illuminate the road ahead and the vehicle’s rear for other drivers’ benefit. Drivers control these lights using switches that determine the electrical flow within the lighting circuit. Lighting circuits are safeguarded by fuses or circuit breakers, preventing wire overheating and potential fires by cutting off current flow when the circuit draws more than intended.

Computer System: The Nervous System of a Vehicle

The three components of a vehicle’s computer system are the electronic control unit, sensors, and actuators.

The electronic control unit (ECU) is the “brain” of the system. It is responsible for controlling and coordinating the operation of various systems and components in the vehicle, such as the engine, transmission, and brakes. When something is wrong with the car, technicians can communicate with the ECU using a scan tool via a diagnostic data link typically found near the driver’s seat.

Sensors are devices that detect and measure various physical parameters, such as temperature, pressure, and position, and send this information to the ECU for processing.

Actuators are devices that receive signals from the ECU and perform a specific action, such as opening or closing a valve, adjusting the fuel injection rate, or engaging the brakes.

Auto: Chassis Systems

As a whole, chassis systems consist of the drivetrain, which transfers power from the engine to the drive wheels, the suspension and steering systems, which control the ride quality and handling of the vehicle, and the brake system, which ensures the vehicle stops safely and predictably.

The Drivetrain System

Although the engine can generate enough power to move the vehicle, this energy must be efficiently processed and transmitted in order for the vehicle to accelerate smoothly and quickly. The vehicle’s drivetrain is in charge of transmitting power from the engine to the wheels.

Transmission Types

The transmission is a vital component of any drivetrain. The transmission is the equipment that synchronizes the engine’s speed with the vehicle’s desired speed. Automatic and manual transmissions are the two distinct types of transmissions.

Automatic Transmission

In the United States, most vehicles sold today come equipped with an automatic transmission. While automatic transmissions are more complex systems than their manual counterparts, they require less knowledge for the driver to operate.

At its core, an automatic transmission uses a series of planetary gear sets to achieve different gear ratios. Each planetary gear set consists of a central sun gear, an outer ring gear, and a set of planetary gears that rotate around the sun gear and engage with the ring gear.

When the transmission is in drive, power from the engine is transmitted through a torque converter, which is essentially a fluid coupling that allows the engine to keep running while the vehicle is stopped or idling. The torque converter then sends the power through the planetary gear sets to achieve the desired gear ratio, which determines the speed and torque delivered to the wheels.

A continuous variable transmission (CVT) is a type of automatic transmission that uses a system of pulleys and belts to achieve an infinite number of gear ratios, rather than relying on discrete gear sets. This allows for smoother acceleration and better fuel efficiency, as the engine can operate at its optimal speed at all times.

Manual Transmission

Manual transmissions, also known as stick-shifts, work by using a clutch pedal and gear shifter to manually engage and disengage gears. The clutch pedal is used to disconnect the engine from the transmission, allowing the driver to shift gears using the gear shifter. The gear shifter moves a series of gears within the transmission, which vary the speed and torque delivered to the wheels. The driver must coordinate the use of the clutch and gear shifter to match the engine speed with the speed of the vehicle, which can provide greater control and performance but requires more skill and attention from the driver than an automatic transmission.

Drivetrain Types

The four different types of drivetrain are front-wheel drive, rear-wheel drive, all-wheel drive, and four-wheel drive.

Front-Wheel Drive (FWD)

Both the engine and the drive wheels are located on the front axle in FWD vehicles. Because of the benefits of space and efficiency, this is the most popular powertrain and driveline configuration for small and compact vehicles.

Rear-Wheel Drive (RWD)

The powertrain is generally mounted on the front axle, whereas the drive wheels are mounted on the rear axle in RWD vehicles. It’s also known as the “classical” driveline layout because this is how the original road vehicles were designed. RWD is standard on the majority of luxury sedans and sports automobiles.

Due to the fact that power is only transmitted through two wheels, both FWD and RWD vehicles are two-wheel drive (2WD) vehicles.

All-Wheel Drive (AWD)

The vehicle is AWD when the engine power is delivered to all four wheels all of the time. Sensors ensure power can be shifted to any wheel at any time, offering superior traction and acceleration capabilities.

Four-Wheel Drive (4WD)

Similar to AWD, 4WD in an automobile is a drivetrain system that provides power to all four wheels of the vehicle simultaneously, as opposed to a 2WD system that only powers two wheels (either the front or rear).

In a 4WD system, power from the engine is transmitted through the transmission to a transfer case, which distributes power to both the front and rear axles. This results in increased traction, better handling, and improved performance on rough terrain, slippery roads, or in off-road situations. In 4WD vehicles, sometimes called four-by-four (4X4) vehicles, there is typically an option for the driver to select AWD.

Parts of a Drivetrain

The following are common components in a FWD vehicle with a manual transmission:

clutch—The clutch enables the driver to control the power and speed of the vehicle by regulating the transfer of power from the engine to the wheels.

constant-velocity (CV) joints—A CV joint is a type of mechanical joint used in vehicles that allows power to be transmitted from the engine to the wheels at a constant speed, regardless of the angle of the joint. It is typically used in FWD and AWD vehicles to transfer power from the transaxle to the front wheels.

differential—The differential is a component of a vehicle’s drivetrain that allows the wheels to rotate at different speeds while still receiving power from the engine. It is typically located between the two rear wheels in a RWD vehicle and is also used in many AWD vehicles.

drive axle—A drive axle, also known as a live axle, is a component of a vehicle’s drivetrain that transmits power from the differential to the wheels. It is typically used in RWD vehicles and has a solid axle shaft connecting the differential to the two rear wheels.

drive shaft—The drive shaft, also known as a propeller shaft, is a component of a vehicle’s drivetrain that transmits power from the transmission or transfer case to the differential. It is typically a long, hollow, cylindrical shaft that connects the transmission output shaft to the input shaft of the differential.

half shaft—A half shaft, also known as a CV shaft, is a component of a vehicle’s drivetrain that transmits power from the differential to the wheels. It is typically used in FWD and AWD vehicles and consists of a shaft with a CV joint at either end. One end of the half shaft connects to the differential, while the other end connects to the wheel hub. As the wheels turn, the half shaft rotates and transfers power from the differential to the wheels, allowing the vehicle to move.

transaxle—A transaxle is a component of a vehicle’s drivetrain that combines the functionality of a transmission and an axle into a single integrated unit. It is typically used in FWD vehicles and some AWD vehicles. The transaxle combines the transmission, which controls the gears and gear ratios, with the axle, which transmits power from the differential to the wheels.

transfer case—A transfer case is a component of a vehicle’s drivetrain that is used in 4WD and AWD vehicles to transfer power from the transmission to the front and rear axles. It is typically located between the transmission and the rear differential and consists of a set of gears that allow power to be distributed to the front and rear axles at different ratios. The transfer case allows the driver to select between different modes, such as 2WD, 4WD, and low-range 4WD, depending on the driving conditions.

transmission—The transmission is a component of a vehicle’s drivetrain that transmits power from the engine to the wheels by controlling the gear ratios.There are two main types of transmissions: manual transmissions, which are operated by the driver using a clutch pedal and a gear shifter, and automatic transmissions, which use a torque converter and a set of hydraulic clutches to shift gears automatically.

universal joints—Universal joints, also known as U-joints, are a type of mechanical joint used in a vehicle’s drivetrain to allow for the transmission of power between two shafts that are not in a straight line.

The Suspension and Steering System

The suspension and steering system is made up of various components that work together to provide stability and comfort to the driver and passengers. In this section, we will explore the different parts of the suspension and steering system, how they work, and their importance in maintaining the overall safety and performance of a vehicle.

Basic Long-Short Arm Suspension and Steering Parts

springs—The springs are the backbone of the suspension system. Made of coiled steel, their primary jobs are holding up the weight of the vehicle body and allowing up-and-down movement of the wheels while continuing to provide a smooth ride.

shock absorbers—Shock absorbers work hand in hand with the springs to provide a smooth ride. Located between the vehicle body (chassis) and the control arm, these pump-like devices give off heat and help keep the tires in contact with the road.

control arms—Often called A-arms because of their capital A shape, control arms link the chassis of the car to the steering knuckle. They allow the wheels to move up and down while keeping them properly aligned with the body of the vehicle, thus maintaining stability, steering, and handling.

control arm bushings—Control arm bushings are used to connect the upper and lower control arms to the chassis. They are typically made of soft material like rubber or polymer.

steering knuckle—The steering knuckle connects the steering and suspension components. It is typically shaped like a triangular or rectangular plate and includes attachment points for the upper and lower control arms, the steering tie rod, and the wheel hub. The steering knuckle pivots to allow the front wheels to turn left or right when the steering wheel is turned, enabling the vehicle to change direction.

ball joints—A ball joint is a mechanical component that connects the steering knuckle to the control arms of a vehicle’s suspension system. The ball joint acts as a pivot point, allowing the steering knuckle to move up and down and side to side, while maintaining a stable connection with the rest of the suspension system. Most cars have both upper and lower ball joints, which should be lubricated at least every 10,000 miles for optimal performance.

steering linkage—Steering linkage connects the steering wheel and the steering knuckle. The steering linkage includes components such as tie rods, ball joints, and control arms. Tie rods are attached to the steering knuckle and the steering rack and are responsible for transmitting the rotational motion from the steering wheel to the wheels. Ball joints connect the steering knuckle to the suspension system, allowing for the up-and-down movement of the wheels. Control arms maintain the position of the wheels.There are different steering linkage designs but the most common is rack and pinion.

wheel hub—A wheel hub is a cylindrical metal component of a vehicle’s wheel assembly that connects the wheel to the rest of the suspension system. It provides a stable mounting point for the wheel, supports the weight of the vehicle, and allows the wheel to rotate smoothly with minimal friction.

Tires

Typically made of rubber and other materials, tires come in different sizes, shapes, and tread patterns. They are an essential component of any vehicle and require regular maintenance and replacement to ensure safe and efficient operation. The most common type of tire design from the 1940s onward has been the radial tire. Radial tires are made of the following components:

beads—This is the part of the tire that is in contact with the rim of the wheel. It is made of steel wire and helps to hold the tire in place on the rim.

rim—The outer edge of a wheel that holds the tire is referred to as the rim. The bead serves as the mounting point for the tire on the rim.

body plies—Body plies run from bead to bead and make up the tire’s main body.

wheel well liner—This term refers to a sealed surface that protects the mechanical underside of the car from road damage caused by rocks, water, slush, etc., that are thrown up as the tires roll.

sidewalls—A tire’s sidewall is designed to prevent air from escaping while protecting the body plies.

tread—The rubber on the tire that makes contact with the road is known as the tread. The tread on tires wears down over time, reducing its ability to provide traction.

belts—Belts are employed between the plies and the tread to stabilize the tire’s footprint (where it makes contact with the ground).

Proper tire inflation is an important and often overlooked part of car maintenance. An overinflated tire can have uneven wear, leading to loss of traction and a less smooth ride. An underinflated tire can lead to reduced fuel economy, handling, and braking ability. Either extreme can lead to a dangerous situation, such as a tire blowout. To ensure tires are in good condition, have them inspected and rotated frequently, and make sure they stay in the manufacturer’s recommended range of inflation, typically between 30 and 35 psi.

Parts of the Brake System

The brake system is one of the most critical systems in any vehicle. Its primary function is to bring the vehicle to a complete stop, preventing accidents and ensuring safety on the road. Here are the major parts of any brake system:

Brake Pedal

The brake pedal is the part of the braking system that the driver uses to activate the brakes. When the driver presses the brake pedal, it transmits mechanical force to the master cylinder.

Master Cylinder

The master cylinder generates the hydraulic pressure that applies the brakes to the wheels. It converts the force from the brake pedal into hydraulic pressure by pushing brake fluid through the brake lines.

Brake Fluid Reservoir

The brake fluid reservoir is a container that holds the brake fluid used by the braking system. The master cylinder draws fluid from the reservoir as needed.

Brake Lines

Brake lines are metal or rubber hoses that carry the brake fluid from the master cylinder to the brake assemblies at the wheels. The brake lines must be strong and flexible to withstand the hydraulic pressure generated by the master cylinder.

Brake Assemblies

Brake assemblies are located at each wheel and contain brake pads (in disc brake systems) or brake shoes (in drum brake systems) that are pressed against the brake rotor or drum to slow or stop the vehicle. Hydraulic pressure from the master cylinder causes the brake pads or shoes to press against the rotor or drum, creating friction that slows the vehicle down. Disc brakes are superior to drum brakes because they are better at rejecting heat energy.

Brake System Operation

The brake system is hydraulically operated. When the driver presses the brake pedal, a pumping piston in the master cylinder puts pressure on the brake fluid. The brake fluid flows through the brake lines and moves the pistons in the brake assemblies to operate the brakes. As the driver presses the brake pedal harder, higher fluid pressure develops, and more braking power is produced.

Brake System Options

There are two brake system options that enhance vehicle control during a hard stop.

Power Brakes

Power brakes, also known as power-assisted brakes, are a type of braking system in which a device called a brake booster is used to amplify the force applied to the brake pedal by the driver. The brake booster uses an engine vacuum or a hydraulic pump to increase the force applied to the master cylinder, which generates the hydraulic pressure that operates the brakes. Power brakes require less force to operate than non-power brakes, making it easier for the driver to bring the vehicle to a stop.

Anti-Lock Brake System (ABS)

An ABS provides superior vehicle control during a hard stop. The majority of cars now come with ABS, which helps prevent wheels from locking under hard braking conditions. The ABS includes speed sensors on each wheel to communicate the relative speeds of each wheel to a computer. If the ABS computer detects a greater than predetermined difference in wheel speed, it uses the ABS’s pumps and valves to modify the brake pressure for the affected wheel or wheels.

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