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An Overview Of Commercial Motor Vehicle Control Systems – Part III

Welcome to Part III in our series An Overview of Commercial Motor Vehicle (CMV) Control Systems. We’re glad you could make it for this final installment in the series. We’ve covered a lot of ground so far, from engine controls to steering and braking systems.

In Part II of our series we opened the door on the various types of transmissions used on CMVs. The fact is, most CMVs will require knowledge of a manual system. Although newer transmission types are becoming increasingly popular, you will need to know how manual clutch systems work.

Once we complete our transmission section with clutch control, we will round out the series by covering secondary vehicle control systems. It’s time to dive in!

The Clutch Pedal

Sure, we could have put this at the very beginning of this series with the brake and accelerator pedals, but there is a bit more to a big rig clutch pedal. The clutch pedal is used to engage and disengage from the gears, and there are four basic positions of the clutch pedal.

They are as follows:

  • Engaged: When your foot is not pressing on the clutch pedal and it is fully released, this is considered engaged. This means the engine and drivetrain are connected and the vehicle is in gear.
  • Free play: Free play refers to the amount of movement possible without engaging or disengaging the clutch. In order to prevent premature clutch wear, free play is necessary.
  • Disengaged: When the clutch pedal is depressed around three to eight inches, it is considered disengaged. This means the engine and drivetrain are separated. In order to start the engine or shift the gears, the clutch must be disengaged.
  • Clutch brake: When it is disengaged, a CMV transmission will simply spin. Because of this, you can use the clutch brake to prevent it from turning. You will utilize this technique while at a stop. When you depress the clutch pedal to the floor, the clutch brake will then engage. It will bring the transmission to a stop and you will be able to shift into the desired gear.

Learning how to skillfully shift a big-rig truck is essential to your truck driving career. These machines shift nothing like the manual shifting function on a passenger vehicle, so additional training and technique is crucial to their successful operation.

Now that we have finished with all of the primary vehicle control systems, it’s time to move on to the secondary systems.

Secondary Vehicle Control Systems

Although these systems are called “secondary,” they are no less important. Secondary controls play a crucial role in helping you safely operate the CMV. Some will be similar to secondary controls in your car, while others will be quite different. While they differ in size and location from vehicle to vehicle, secondary control systems will generally fall into one of these four major categories:

  • Seeing: These control systems relate to how well you can peer ahead as you are operating the CMV. They generally include such components as:
    • Lights;
    • Remote mirrors;
    • Mirror heaters;
    • Windshield washers and wipers;

  • Communication. These control systems govern how well you are able to communicate with others on the road. They generally include such components as:
    • Horns;
    • Lights;
      • Turn signals;
      • Four-way flashers;
      • High beams;
      • Fog lamps;
      • Brake lights;
  • Comfort controls: Comfort controls provide the operator with the means to alter the interior climate of the cab and adjust temperature controls. They generally include:
    • The heater;
    • Air conditioner;
    • Air vents;
    • Steering wheel adjuster;
    • Seat position and adjuster.
  • Driver safety: Driver safety controls round out the safety mechanisms of a CMV. They generally include:
    • Bunk restraints;
    • Seat belts;
    • Door locks;
    • Fire extinguisher(s)
    • Warning devices, such as triangles, flares or cones.

With that, our three-part series on vehicle control systems comes to a successful close. We hope you’ve enjoyed this trip around the control systems of a CMV. Now you’ll be ready to go when the time comes to jump into the cab.

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