Semi-Truck

Overview

The semi-truck is a Class 8 diesel tractor unit, the heaviest class of on-highway vehicle, built to haul a semi-trailer over long distances. It is a tractor only: it carries no cargo itself but couples to and pulls trailers through a fifth-wheel plate. A sleeper cab lets drivers rest during multi-day routes, and the 6×4 tandem-drive layout delivers the traction and load capacity needed for combined weights up to 80,000 lb.

Construction

Motive power comes from the Diesel Engine, a 15-liter inline-six diesel with a variable-geometry turbocharger and full emissions aftertreatment. Its torque is managed by the 18-Speed Transmission, an 18-speed manual whose closely-spaced ratios keep the engine in its narrow efficient band under heavy load. Drive passes through the Driveshaft to the Drive Axle tandem, while the Front Steer Axle carries the steered wheels.

Heavy vehicles rely on compressed air rather than hydraulics for braking: the Air Brake System supplies spring-brake chambers and slack adjusters at every wheel, with ABS control. Trailers couple to the Fifth Wheel Coupling, whose locking jaw grips the trailer kingpin. The driver lives and works in the Sleeper Cab, a sleeper cab with bunk, seats, and full instrumentation. Supporting systems include the Cooling System circuit sized for sustained full-load operation, recirculating-ball Steering System, a Suspension combining front leaf springs with rear air ride, and the Fuel System's dual aluminum saddle tanks for long-haul range.