In any motor vehicle (whether automobile, water craft, off road vehicle or airplane), the drive train refers to the components that generate and transfer energy from a crude stored state into kinetic energy. This conversion is accomplished through traction on a given surface, which causes the forward motion of the vehicle over hard surfaces, air, or even water. To simplify, the drive train consists of a motor vehicle’s engine, transmission, drive shafts, differentials and drive axels. The drive axels are also commonly known as the final drive, which can be drive wheels, continuous tracks (like on a tank), propellers, etc. These drive types are all mechanisms that take part in converting the fuel that is injected into the vehicle into physical energy that ultimately causes the vehicle to move.
The drive train can be broken down into two categories. One category is known as the powertrain, which typically includes all the parts of the engine and transmission. The other category is known as the driveline, which refers to the remaining parts of the drive train. The driveline includes the components that come after the transmission, such as the axel, drive shafts, and the differentials. The set up of these vehicle parts can vary based on whether or not the vehicle is front wheel drive, rear wheel drive, or four wheel drive/all wheel drive.
Front wheel drive was created by Sir Alec Issigonis and is typically the most common form of drive train. With front wheel drive the engine is essentially mounted sideways under the hood of the car, with the transaxle attached towards the back bottom of the engine. The transaxle is one unit and contains both the transmission and the differential. It is important to note that front wheel drive vehicles must have what is called a constant velocity joint (homo kinetic/CV joint) attached to the half shafts. The CV joint allows for power to be distributed smoothly and evenly to both tires, allowing for maintained control of the vehicle while disbursing power simultaneously.
Rear wheel drive has the engine mounted vertically or perpendicular to the driveshaft. The transmission is attached directly to the engine, which sends torque, or power, down the driveshaft to the differential unit. The differential unit is connected to the drive shaft by a part called a U-joint. Via the U-joint, the differential unit then distributes power to the back two wheels.
Four / all wheel drive takes elements from both front wheel drive and rear wheel drive and is a little more complex. The front and back wheels are only rotating at the same speed when the vehicle is traveling in a perfectly straight line. This fact means that two different differentials are needed to control power distribution, one in the front and one in the rear. There is a distinction however, between AWD and 4WD (all wheel drive and four wheel drive). The distinction is that in all wheel drive there are two differentials added to help evenly distribute power; one center compact differential and one in the rear of the vehicle. With four wheel drive there are two individual differentials controlled by a transfer case and there is no center differential.
Although front wheel drive is the most common type of drive train, each of the different systems are commonly used and can be considered complex and intricate. Each different drive train style contains similarities and differences which correlate with their pros and cons. To summarize the different types of drive trains some of the pluses and minuses of each can be considered. Front wheel drive is appealing because it makes the vehicle lighter, which increases gas mileage. FWD also allows for more room for personal space in the vehicle, and it gives the driver better maneuvering control in adverse weather conditions. The downsides are that the engine is more cramped because the entire drive train is up front. This limitation of space makes repair and maintenance more of a hassle. Second, steering while excessively accelerating can become somewhat challenging because of the distribution of torque. Third, FWD requires more frequent rotation of the front tires because there is more weight in the front of the vehicle.
The pros and cons of rear wheel drive are simply the opposite of that of those of front wheel drive. Weight distribution is superior in RWD as a result of how the components are configured on the car. When driving in normal weather conditions rear wheel drive gives better steering ability because the force is exerted from the back of the vehicle. There is less wear and tear on the front tires and suspension. And finally, there is more room where the engine is, which leads to greater ease of repair. As for all wheel drive and four wheel drive, there is really only one pro and that is greater traction, so if your vehicle contains this drive train, happy off-roading!