Automotive Systems

The typical automobile consists of a multitude of components that collaborate to facilitate its operation. To comprehend the functionality of these parts more easily, they are organized into eight repair areas or fundamental operating systems, designated as A1 through A8 by ASE.

• A1. Engine Repair

• A2. Automatic Transmission and Transaxle

• A3. Manual Drive Train and Axles

• A4. Steering and Suspension System

• A5. Brakes

• A6. Electrical and Electronic Systems

• A7. Heating and Air Conditioning

• A8. Engine Performance

It should be noted that the ASE certification exams will also cover the same eight systems discussed in this program. Therefore, acquiring knowledge in these repair areas will prove valuable if you choose to pursue the ASE Student Certification and final professional certification exam in the future.

The Engine

The engine of a vehicle serves as its primary source of power, responsible for carrying out the essential functions required for the operation of all other components. Most cars are equipped with four-stroke cycle, gasoline-powered engines, while diesel engines have become increasingly popular in the automotive market due to their lower carbon dioxide emissions and improved fuel efficiency, particularly in trucks. Despite the diverse array of sizes, models, and designs in automotive engines, they all operate based on the same fundamental principles. This program will delve into the mechanics of basic four-stroke engines and explore various engine designs, providing a foundational understanding that can be applied to a wide range of automotive engines encountered in the future.

Modern Gasoline-Fueled V6 Engine (Courtesy of James Halderman)

Modern automotive engines are equipped with a multitude of electronic and computerized control systems that optimize their efficiency. Through the utilization of this advanced technology, contemporary engines are capable of achieving performance levels that were previously unattainable. These engines generate greater power while emitting fewer harmful exhaust emissions compared to older models, all while consuming less fuel. This technology offers numerous benefits, including environmental preservation, conservation of natural resources, and enhanced performance and reliability for consumers.

Upon gaining further knowledge about engines and electronic control systems, one is likely to come to the realization that these systems are not as complex as they may initially seem. In actuality, many technicians find that engines with electronic control systems are simpler to diagnose and fix compared to older models. Regardless of personal opinions on electronic controls, it is evident that they have become a permanent fixture in modern vehicles. Thus, in order to excel as an auto repair technician, it is imperative to have a comprehensive understanding of how these systems operate.

The engine system comprises not only electronic controls but also mechanical parts, which are straightforward in their design and function. Thus, it is imperative to comprehend the operational mechanisms of the mechanical components of an engine in addition to staying informed about cutting-edge electronic control systems.

The Drivetrain (Automatic and Manual Transmissions)

The drivetrain serves as the mechanism linking the engine and transmission to the wheels, with three primary types of drivetrain systems: front-wheel drive, rear-wheel drive, and four-wheel drive. These systems are distinguished based on which wheels receive power from the engine. Now let’s delve into each of these drive systems.

Front-Wheel Drive Systems

In a front-wheel drive (FWD) system, the two front wheels of the vehicle are driven by the engine. e two rear wheels rotate freely.

The front-wheel drive (FWD) system is the most commonly used drivetrain in light vehicles today. In this system, the engine drives the two front wheels while the rear wheels spin freely. Front-wheel drive is typically found in compact and mid-size cars, with the engine and transmission situated at the front above the front wheels. The FWD transaxle bears the weight, making it ideal for lighter vehicles as it is more challenging to pull weight than to push it. The majority of the vehicle’s weight is concentrated over the front wheels, allowing the front-wheel drive system to take advantage of this weight for improved traction on slippery roads. Additionally, because the entire drive system is located at the front, more interior space is available for passengers and cargo.

Rear-Wheel Drive Systems

In a rear-wheel drive (RWD) system, the engine drives only the two rear wheels of the vehicle. e two front wheels rotate freely.

The rear-wheel drive (RWD) system involves the engine powering only the rear wheels of a vehicle, with the front wheels being free to rotate. This configuration is commonly found in larger passenger cars and certain light trucks, where the rear axle propels the vehicle and bears a significant portion of its weight. RWD systems are typically designed to be more robust and able to handle heavier loads compared to front-wheel drive systems, making them the preferred choice for larger vehicles.

Four-Wheel Drive Systems

A Four-Wheel Drive (4WD) or All-Wheel Drive (AWD) System

The final category of drivetrain is the four-wheel drive (4WD) system, also known as an all-wheel drive system. In this system, the engine powers all four wheels of the vehicle, providing superior traction on slick surfaces compared to front-wheel drive (FWD) or rear-wheel drive (RWD) systems. Due to their exceptional traction, 4WD and AWD are commonly utilized in off-road scenarios where no paved road exists. These drive systems are frequently found in light duty trucks and SUVs.

The Transmission and Transaxle

Typical Automatic Transaxle (Courtesy of James Halderman)

An automobile must possess the capability to function effectively across a diverse range of speeds and terrains. It is required to navigate through urban streets at low speeds, cruise along highways at high speeds, and maintain a steady pace when ascending inclines. The transmission system of the vehicle facilitates the seamless transition between these speeds, ensuring optimal performance in various driving conditions. The illustration provided depicts a common automatic transaxle mechanism, which integrates both transmission and final drive components.

Bicycle Gears

In order to gain a deeper understanding of the function of a transmission, it is helpful to draw parallels with the operation of a bicycle. The transmission in a car can be likened to the gears on a bicycle, while the engine represents the rider of the bike. Similar to how a rider can switch gears on a bicycle while riding, a driver can adjust the transmission in a car to optimize performance. For example, when cycling on a flat surface, selecting a higher gear will increase speed, but tackling a steep incline in high gear will require more effort. In contrast, shifting to a lower gear makes it easier to pedal uphill.

The same principle applies to operating a vehicle. When driving uphill in high gear, the engine must exert a significant amount of power. Transitioning to a lower gear will facilitate the engine’s ability to navigate the incline with greater ease.

The converse of this explanation is also applicable. When a bicycle is moving downhill or on a level surface in a low gear, a rapid pedaling motion is required to generate speed, resulting in significant physical strain. Therefore, shifting to a higher gear is necessary to facilitate easier movement of the bike, enabling it to travel at a faster pace with reduced pedaling effort.

The principle of adjusting gears in a car to control engine speed is similar to the concept of shifting gears on a bicycle. When driving at higher speeds, the engine must operate at higher RPMs to propel the car forward. Without shifting gears, the engine could be subjected to excessive stress and potential damage. By shifting to a higher gear, the engine can operate at a more efficient speed, preventing any harm.

There are two primary types of transmissions commonly found in automobiles: automatic transmissions and manual transmissions. While automatic transmissions are more prevalent in today’s vehicles, manual transmissions can still be found in smaller and sportier cars, as well as light trucks. Automatic transmissions typically have a range of four to eight forward gear ratio speeds, with the gears shifting automatically with minimal driver input. On the other hand, manual transmissions usually offer either four or five gear selections, requiring the driver to manually perform each gear shift.

Automatic Transmission

An automatic transmission utilizes a combination of electronic controls, hydraulic systems, valves, sensors, and actuators to facilitate the shifting of gears for varying speeds and torque. The driver can choose a drive mode, such as reverse (R) or drive (D), which may offer multiple gear ratios, including overdrive options. Additionally, the transmission includes a neutral position, a park position, and some newer models may also feature a manual shift option for the driver to manually control gear changes.

Manual transmissions and transaxles utilize speed gears to manipulate the engine’s torque output, requiring the disengagement of the clutch during gear changes. The driver manually selects the optimal gear for the current load using a mechanical linkage. Manual transmissions typically have between four to seven forward speeds, usually including first, second, third, fourth, fifth, and sixth gears, as well as a reverse gear.

Manual Transaxle (Courtesy of James Halderman)

The choice of transmission in a vehicle is typically left to the discretion of the buyer, as most new vehicles offer the option of either type. Due to the user-friendly nature of automatic transmissions compared to manual systems, they are generally favored by the majority of customers.

Numerous contemporary vehicles, particularly those with front-wheel drive, are equipped with a specialized transmission known as a transaxle. This integrated device combines both the transmission and drivetrain components into a single unit, resulting in space efficiency, reduced weight, and simplified maintenance. These advantages make transaxles an ideal option for compact or smaller vehicles. Transaxles can be equipped with either manual or automatic transmission features.

The Suspension and Steering Systems

Basic Parts of a Steering System

The functionality of a vehicle’s suspension and steering systems enables the driver to effectively maneuver the automobile on the road. The steering system facilitates the driver in determining the vehicle’s direction, while the suspension system ensures the tires remain in contact with the road surface, even when traversing uneven terrain.

Typical Front and Rear Suspension Systems

In order to facilitate smoother driver control, the majority of steering systems in modern vehicles are equipped with power assist. This technology assists drivers by reducing the effort required to turn the steering wheel, commonly known as power steering. Historically, power assist was achieved through hydraulic systems that pressurized fluid to aid in steering. However, present-day steering systems predominantly utilize electric power steering (EPS) systems, where an electric motor provides the necessary assistance to the driver instead of hydraulic mechanisms.

The suspension system of a vehicle utilizes springs, shock absorbers, and struts to dampen bumps and ensure a comfortable ride on uneven terrain. In addition to maintaining tire contact with the road, the suspension system also aims to provide a seamless journey for passengers. By absorbing bumps and maintaining stability, modern suspension systems are engineered to deliver a smooth ride both at high speeds on highways and at lower speeds. It is crucial for the suspension system to strike a balance between comfort and road grip to ensure safe handling by the driver.

The Brake System

The majority of individuals are aware that the brake system in a vehicle is responsible for decelerating or halting the rotation of its wheels. What is less commonly understood is that the vast majority of brakes can be categorized into either drum brake systems or disc brake systems. A comprehensive examination of both types of systems will be provided in future lessons.

Modern Antilock Braking System (ABS)

Historically, the automotive brake system faced a significant drawback where sudden braking would often result in wheel lock-up, leading to the car sliding on the road surface. This presented two major safety concerns: increased stopping distance and loss of steering control, both of which heightened the risk of accidents.

Due to this rationale, the majority of modern vehicles are outfitted with electronically-managed brake systems known as antilock brake systems (ABS). ABS technology effectively prevents wheel lock during abrupt stops by utilizing electronic monitoring and control of braking functions. These sophisticated systems have significantly enhanced vehicle safety and minimized accident occurrences.

The Electrical and Electronic Systems

!e Electrical and electronic systems are the “brains” of modern cars. For many years, a car’s electrical system contained only the battery, the battery charging system, and the lights or accessories on the vehicle. Today, almost every part of a vehicle is in some way powered or controlled by an electrical or electronic system. Today’s modern car has a wire and a computer connected to almost everything. Electrical and electronic systems manage everything from engine operation to the temperature inside the car. Some of the electrical and electronic systems found in a typical vehicle are as follows:

• Battery and battery-charging system
• Headlight and directional signal circuits
• Starter system
• Windshield wiper, horn, radio, and other accessory circuits
• Engine control systems
• Transmission/transaxle shifting system
• Accessories control systems

Electrical or electronic systems control or power almost every part of modern vehicles.

The comprehensive coverage of all electrical systems, their functionalities, and maintenance procedures will be provided in the later stages of the program. In the meantime, it may be beneficial to grasp some fundamental concepts about these systems. It is essential to understand that automotive electrical systems function on direct current (DC), which offers a constant voltage supply. This stable voltage is sourced from the vehicle’s battery and charging system. Direct current is the type of current commonly used to power cordless appliances and battery-operated devices. Typically, around 12.6 volts are needed to operate the electrical systems in most cars, significantly higher than the voltage of a typical flashlight battery. Although similar in operation to household batteries, car batteries have a significantly higher voltage capacity.

The functionality of all electrical and electronic components within a vehicle is reliant upon the battery. In addition, the car is equipped with a charging system that collaborates with the other electrical systems to replenish the battery’s power while the engine is in operation. Typically, this charging system prolongs the lifespan of a car battery, allowing it to remain functional for several years before needing to be replaced.

The Heating and Air Conditioning Systems

Automotive systems serve various functions beyond propulsion, with some dedicated to improving passenger comfort. One such example is the heating and air-conditioning system, which allows passengers to adjust the temperature inside the vehicle. Most vehicles are equipped with heating systems to keep passengers warm in cold weather, and many also include air conditioning systems for cooling in hot weather. The heating system utilizes heat generated by the engine to warm the cabin, while the air conditioning system works to lower the temperature inside the vehicle during warmer weather.

Heating, Ventilation, and Air-Conditioning (HVAC) System

While many vehicle systems offer passengers the ability to manually adjust heating or cooling levels, some are designed to automatically regulate desired temperatures. In fact, certain modern vehicles feature advanced systems that enable individual temperature settings for both the driver and passengers in separate seating areas within the vehicle.