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An Overview Of The Commercial Motor Vehicle – Part V

We’ve been taking you on a comprehensive journey through the commercial motor vehicle (CMV). With so much ground already covered, we are continuing on through some of the most vital components of a CMV.

Large commercial trucks are technologically advanced vehicles. But even as the digital age brings change to legacy components, it’s still important to have a good working knowledge of the basics of how a CMV operates.

In our last installment, we were taking a look at the electrical system. Today we will finish with the electrical system and start in on the real power behind a CMV: The drive train. So, let’s dive right in!

Electrical Circuits

Finishing out the electrical system includes covering the various circuits. First up is the cranking circuit. This is the circuit that moves electricity from the battery to a starter motor. You start the process by depressing a starter switch inside the vehicle.

Next up is the ignition circuit. The ignition circuit provides the sparks for each cylinder. The spark ignites the fuel and air mixture within the engine itself. For diesel engines, an ignition circuit is not needed.

Finally, you’ll have to consider lighting and accessory circuits. These circuits provide electricity for the CMV’s horn, lights, instruments, wipers and more.

The Drive Train

Well, with the electrical system in our review mirror, it’s time to move on to the drive train. This is the part of the CMV that powers everything from the belly of the beast. The drive train is essentially a series of connected mechanical parts which convert power generated by the engine into torque and applies it to power the vehicle’s wheels.

There are several basic components of a typical drive train setup:

  • Clutch;
  • Transmission;
  • Drive shaft;
  • Universal joints;

So without further ado, let’s take a look at each individual component of a CMVs drive train.

The Clutch

The clutch allows the operator to connect or disconnect the engine from the power train. This is what allows the truck driver to shift gears.

The clutch itself will generally be comprised of the following major parts:

  • Clutch housing;
  • Flywheel;
  • Clutch disc(s);
  • Pressure plate;
  • Release assembly;

In most truck setups, the clutch has three plates. One plate will be squeezed tightly between the other two. The plate in the middle is called the clutch disk and is connected to the shaft leading out to the transmission.

The other two plates are called driving members and are connected directly to the engine. A powerful spring or set of springs tightens the grip on the two driving members and forces them all to turn as one unit.

The engine flywheel is used in conjunction with the first driving member. It has a smooth surface where the pressure plate pushes up against it. Without this component, the engine would not be able to properly power the vehicle.

The pressure plate is a cast iron ring which is smooth on one side. It is fastened to the cover and then bolted to the flywheel. The way it is fastened allows it to slide back and forth.

Finally, the driven plate is a flat steel disk with friction on one side. The plate is fastened by splines to a shaft that snakes into the transmission. Once there, it fits into grooves on the shaft. This allows them all to turn together, but doesn’t prevent the plate from sliding back and forth. The driven plate is designed to wear out before other components. In fact, this prevents damage to other parts of the clutch system.

We hope you’ve enjoyed our most recent look into the vital components of a CMV.

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