Drivetrain – Lesson 1 | Manual Transmission and Drivetrain

Drivetrain – Lesson 1 | Manual Transmission and Drivetrain

 

Manual Transmission and Drivetrain : Lesson 1 – Drivetrain

Drivetrain – General

Objectives

Upon completion of this lesson, you will be able to:

! Explain the purpose and function of a drivetrain.

! Describe a drivetrain and identify the types.

! Identify the components of a drivetrain.

! Explain the theory and operation of a drivetrain.

 

Introduction – Basic drivetrain

This course describes the purpose, function, theory, and operation of the basic drivetrains that are used in many cars and light trucks. The drivetrain consists of a transmission, driveshaft, and axle/differential or transaxle. To understand the purpose and function of the drivetrain it is essential to have an understanding of some basic terms that are common in any discussion of drivetrains. Those terms are power, torque, and power flow.

 

Power

Power is the rate or speed of doing work. Adding power gets work done more quickly. For example, when a horse is connected to a plow and is plowing a field, it would take that single horse a certain amount of time to plow each row in the field. If another horse was attached to the plow, the two horses might be able to plow the field in half the time. In other words, the addition of more power reduced the amount of time needed to do the same amount of work.

The internal combustion engine creates the power that is transferred through the drivetrain to the wheels. The engine, however, only develops power within a very narrow range of rpm (revolutions per minute). In fact, most automotive engines only develop power between 1,000 and 6,000 rpm. As you will see, the drivetrain enables the vehicle to overcome the engine’s power limitations.

 

Torque

As well as producing the power, the engine also produces torque. When the burning of fuel takes place in the engine’s cylinders, the pistons and connecting rods force the crankshaft to turn. This rotary force is called torque. In simple terms, torque is a turning or twisting effort. When a technician uses a tool to tighten a bolt, torque is applied to the bolt.

When the bolt is tight, the technician may not be able to turn it anymore, but even though the bolt does not turn, the technician is applying torque. Torque then is the force that produces, or tries to produce rotation. Torque is measured in Newton-meters (Nm) or foot-pounds (lb-ft).

The drivetrain multiplies the engine’s torque to allow the vehicle to operate. The drivetrain does both of these things by using gears in different combinations.

As we describe the operation of components of the drivetrain, we are concerned with the flow of power. The flow of power, or power flow, is the path the power takes from the engine to the wheels that drive the vehicle.

Understanding the power flow through a drivetrain component is basic to understanding how the component works. The technician must understand how a component works in order to properly diagnose and repair a drivetrain concern.

 

Drivetrain – At a glance

Basic drivetrain

The purpose of the drivetrain is to transfer power from the engine to the drive wheels. There are many different combinations of drivetrain, but most fit into four basic types: Rear-Wheel Drive (RWD),

Front-Wheel Drive (FWD), Four-Wheel Drive (4WD), or All-Wheel Drive (AWD).

 

Basic rear-wheel drive

On RWD vehicles power is transferred from the engine to the rear wheels by way of the transmission, driveshaft, and rear axle/differential.

 

manual transmission and drivetrain
rear-wheel drive
  1. Engine
  2. Transmission
  3. Driveshaft
  4. Rear differential
  5. Rear-axle
  6. Universal joints
  7. Tires
  8. Clutch and flywheel

 

Basic drivetrain (continued)

Basic drivetrain front-wheel drive

On FWD vehicles, power is transferred from the engine to the front wheels by way of the transaxle and half shafts.

 

drivetrain front-wheel drive
  1. Left hand halfshaft
  2. Right hand halfshaft
  3. Transaxle

 

Basic four-wheel drive

 

Basic four-wheel drive
Basic four-wheel drive

 

  1. Rear-axle
  2. Rear driveshaft
  3. Transfer case
  4. Front driveshaft
  5. Locking hubs
  6. Front differential
  7. Engine
  8. Front axle
  9. Transmission
  10. Slip yoke
  11. Rear differential

On 4WD vehicles, power is transferred from the engine to the rear wheels by way of the transmission, transfer case, driveshaft, and rear axle/differential. Using an electronic switch or manual lever, the vehicle driver may also choose to have power delivered to the front wheels. Power is transferred to the front wheels by way of the transmission, transfer case, front driveshaft, and front axle/differential.

 

Basic drivetrain (continued)

Basic all-wheel drive

 

Basic all-wheel drivetrain with a transaxle

  1. Power take-off
  2. Rear-axle
  3. Driveshaft
  4. Transaxle
  5. Half shafts

 

On AWD vehicles, power may be transferred from the engine to the drive wheels in many ways depending on the vehicle. All AWD vehicles have a transaxle or transmission.

AWD vehicles with a transaxle transfer power to the front wheels by way of the transaxle and half-shafts. Power is sent to the rear wheels by way of the transaxle, Power Take-Off (PTO) driveshaft, and rear axle/differential.

AWD vehicles with transmissions transfer power to the rear wheels by way of the transmission, transfer case, driveshaft, and rear axle/differential. Power is transferred to the front wheels by way of the transmission, transfer case, front driveshaft, and front axle/differential.

The typical 4WD vehicle can be switched between 2WD, 4WD High, and 4WD low. The typical AWD vehicle cannot be switched between 2WD and 4WD.

The transfer case is only used on 4WD or AWD vehicles. The purpose of the transfer case is to transmit power to the rear axle and to the front axle. Many transfer cases include a gear reduction mechanism to provide a lower range.

Driveshaft

The driveshaft transfers the rotation torque of the transmission or transfers the case output shaft to the axle(s) and differential(s).

Rear-axle and differential

The rear axle serves many purposes. It serves as a mounting point for suspension components and transfers power from the driveshaft to the rear wheels via the axle shafts. The rear axle also provides a gear reduction.

The purpose of the rear differential is to allow the rear axle shafts to be able to turn at different speeds

 

Drivetrain – Components

Basic drivetrain components

Clutch

The clutch connects and disconnects the engine from the transmission or transaxle.

Manual transmission

A manual transmission is a housing containing a number of gears. The gears in the transmission multiply the engine’s torque to get the vehicle moving. The transmission also provides reverse gear for the vehicle. Manual transmissions are used on some rear-wheel drive and 4-wheel drive vehicles.

 

Manual transaxle

The manual transaxle contains gears to multiply engine torque received through the clutch. It also provides the differential action required by powered wheels that are rotating at different speeds. So basically it serves the same function as both the transmission and differential. Some all-wheel-drive vehicles use a transaxle.

 

Read More…

Clutch – Lesson 2 | Manual Transmission and Drivetrain

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