Chapter 1 Introduction to Heavy-Duty Commercial Vehicles

Chapter 1

Introduction to Heavy-Duty

Commercial Vehicles

Introduction

• Categories and configurations of commercial vehicles include:– Medium-sized delivery vehicles

– Ambulances

– Fire and rescue vehicles

– Highway semi-trailers

– Gravel haulers

– Fuel tankers

– Utility trucks

– Highway coaches

– Urban transit buses

Introduction

• In this chapter we will show you:

– A range of commercial vehicles

– Their applications

– The set of fundamental skills required for

working on them

– Their specialized requirements

Classification of Application by

Operational Characteristics

• To classify commercial vehicles:

– Consider where a commercial vehicle

performs its primary job

– Operating conditions

• Turnpike or interstate

• On-highway

• On-/off-highway or mountainous highway

• Off-highway

• Urban



• Turnpike or Interstate

– Factors: road materials, vehicle speeds,

amount of stop-and-go driving, degree of

road crown

– Vehicles designed to run on limited-access,

well-maintained, multi-lane highways made of

excellent concrete or asphalt with maximum

adverse grades not in excess of 3%



• On-Highway

– Operate on well-maintained major highways

of excellent concrete or asphalt construction

– Roads level to rolling with maximum grades

to 8%

– Vehicles must operate within legal weight and

dimensional limitations

– Vehicles able to handle steeper grades



• On-/Off-Highway or Mountainous Highway

– 20% total operating time on secondary roads

– Roads made from good concrete or asphalt

with intermittent grades of up to 12%

– Remaining time travelled on road of

well-maintained crushed rock or similar

material

– Subject to legal weight and dimensional

limitations



• Off-Highway

– 20% travel time on gravel roads or roads

with maintained crushed rock surface

– Maximum grade 12%

– Grades of 8% frequently encountered

– Not generally subject to legal weight or

dimensional limitations



• Urban

– Operating conditions primarily within cities

and suburban areas

– Subject to frequent stops and starts

– Roads of concrete, asphalt, maintained gravel

surfaces

– Greater levels of maneuverability than other

classes

– Often use engines with a lower power output

Vocational Applications

of Commercial Vehicles

• Pick-up and delivery

• Construction

• Fire service

• Heavy haul

• Intercity coach

• Line haul

• Logging

• Mining

• Refuse collection

• Rescue vehicles

• School bus

• Urban transit coach



• Pick-up and Delivery– Drop bed auto haulers

– Moving vans

– Refrigerated delivery trucks

– Beverage trucks

– Municipal trucks

– Flatbed trucks

– Newspaper delivery trucks

– Tow trucks and wreckers



• Construction

– Asphalt and gravel

trucks (dump truck)

– Flatbed trucks

– Tank trucks

– Landscape trucks

(tipper truck)

– Concrete mixers

– Snowplows



• Fire Service

– Aerial ladders and fire

trucks

– Pumpers tankers

– Aerial platforms and

special applications

– Ambulance/ paramedic



• Heavy Haul

– Equipment hauling

flatbed trailers

– Steel haulers using

high or low trailers



• Intercity Coach

– Transports people and light freight between

cities and/or suburban areas

• Tour coaches

• Cross country coaches



• Line-Haul

– General freight trucks in straight or tractor trailer configurations

– Refrigerated food trucks

– Livestock tractor trailers

– Flatbed trailers

– Side curtains



• Logging

– Wood chip haulers

either straight truck

or tractor and trailer

– Log hauling tractor

trailer combinations



• Mining

– Belly dump trailers

– Semi-end dump

hopper trailer

combinations

– Gravel hauler



• Refuse Collection

– Front-/rear-/side-

loading garbage

trucks

– Sewer/septic/vacuu

m trucks

– Liquid waste

haulers



• Rescue Vehicles

– Airport Rescue Fire

(ARF)

– Crash Rescue Fire

(CRF)

– Rapid Intervention

Vehicle (RIV)

Emergency Service



• School Bus

– Front-engine

commercial chassis

– Front- or rear-

engine integral

coach



• Urban Transit

Coach

– Airport shuttle

buses

– City transit buses

Design Factors for


• Chassis Frame

– Frame rails of a truck or bus are vehicle’s backbone

– All equipment must mount or attach to frame

– Frame must be sized and built appropriately

Design Factors for


• Engines

– Must have sufficient power to move heavy

loads and accelerate up grades while

providing good fuel economy

– Torque: twisting force applied to crankshaft

– Horsepower: how fast engine can turn while

producing torque

Design Factors for


• Engines

– Torque rise: difference between engine torque

produced at rated speed and peak torque

– High-torque-rise engines: used for line haul

applications; have a steep increase in torque

– Low-torque-rise engines: produce torque over

a wider engine RPM operating range

Design Factors for


• Power Trains

– Commercial vehicles require power trains

designed specifically for particular vocations

– Startability: capability to commence moving

forward on a specified grade

– Gradability: capability to maintain forward

motion on specified grade while sustaining a

minimum speed

Design Factors for


Design Factors for


• Power Trains

– Tractors and trucks classified according to their drive and non-drive axle configurations

– Factors influencing rear axle selection:• Gross combination vehicle weight (GCVW)

• Type of terrain

• Road speed

• Tire size

• Axle ratio required and transmission ratios

• Engine torque and speed

Design Factors for


• Power Trains

– Trucks categorized by number of wheel

positions and drive axles

– Common configuration is tandem axle; uses

two drive axles

– Pusher axle is non-driving and located in front

of a drive axle

– Tag axle located behind the drive axles

Design Factors for


Design Factors for


• Cab

– Designed for specific types of usage

– Include some type of aerodynamic fairings

and wind deflectors to improve fuel economy

– Conventional cab: engine placed in front of

the cab

– Location of front axle can influence turning

radius of a vehicle and affect ride quality

Design Factors for


Design Factors for


• Suspensions

– Transmits braking and drive forces to chassis

– Enables articulation or movement of axles to

adapt to road conditions

– Promotes proper vehicle tracking while

enabling safe steering and minimization of

tire wear

Other Chassis Equipment

• Fuel tanks

• Exhaust

• Hitching devices and fifth wheels

• Batteries

• Auxiliary power supplies

• Auxiliary heaters

• Back of cab access

• Day cab or sleeper cab

• Seating

• Power take-off’s

• Steps

• Lighting and conspicuity markings

• Deck plates

• Braking systems

• Auxiliary braking devices

• Aerodynamic fairings

• Tires

Classification of Heavy Vehicles by

Weight and Length

• Federal Bridge Gross Weight Formula

– Gross weight limits: maximum legal weight of

a vehicle that can travel on roads and bridges

– Federal Bridge Gross Weight Formula (Bridge

Formula B and Federal Bridge Formula)

– Formulas established maximum weights for

commercial motor vehicle (CMV) based on

number of axles vehicle had and spacing

between those axles


Weight and Length

• Vehicle Weight Ratings

– Gross vehicle weight (GVW): maximum

design weight of a vehicle including full tank

of fuel, fully loaded to its capacity, with all

passengers

– Gross vehicle weight rating (GVWR): design

rating specified by a manufacturer as

recommended maximum weight of a vehicle

when fully loaded


Weight and Length

• Vehicle Weight Ratings

– Gross combined weight rating (GCWR):

specific maximum weight limit determined by

vehicle manufacturer

Classification of Heavy

Vehicles by Combination

• Combination vehicles

– Two or more combined or coupled vehicle units

• Full trailer

– Trailer supported at both ends with an axle and

does not rest on fifth wheel

• Semi-trailer

– Coupling method where some of trailer’s load is

carried by tractor through connection known as a

fifth wheel



• A-Train

– Second trailer is full trailer unit connected by draw bar to single hitch point on lead trailer

• B-Train

– Tractor pulling semi-trailer and a second, semi-trailer behind the first semi-trailer

• C-Trains

– Similar to A-train except that it has two drawbars and is more stable





• Hitching Devices

– Fifth wheels: plate-type coupling device designed

to support weight of semi-trailer

– Draw bars: connect tow vehicles to tractor or lead

towing unit

– Pintle hooks: fixed towing horn that connects with

drawbar eye attached to towed vehicle

– Couplers: look similar to pintle hooks; towing horn

pivots and is not fixed

– Ball hitches: used with tongue-trailer draw bars

Common Terms and Conventions

• Vehicle Identification Number (VIN)

– Unique serial number composed of 17

characters (letters and digits) assigned to

each vehicle produced

– Located on frame, engine, inside driver's door

on information sticker, on some components

and in vehicle's computer modules.

Summary

• Commercial vehicles perform variety of

revenue-generating tasks having unique and

even unusual functions.

• To properly maintain and service commercial

vehicles, important to understand the ways

commercial vehicles are classified and

configured.

• Helpful way to classify commercial vehicles is

considering where it performs its primary job.

Summary

• When classifying commercial vehicles by operating conditions, five categories used:

– Turnpike or interstate; on-highway; on-/off-highway or mountainous highway; off-highway; and urban.

• Vehicles classified by their vocation.

• Depending on operating conditions and job performed, commercial vehicle will have a particular chassis, engine, power train, cab, and suspension.

Summary

• Frames sized and built appropriately to be

capable of supporting loads applied to it while

adapting to forces that bend and twist frame.

• Heavy-vehicle engines must have sufficient

power to move heavy loads and accelerate up

grades while providing good fuel economy.

• Commercial vehicles require power trains

designed specifically for particular vocations.

• Tractors and trucks classified according to their

drive and non-drive axle configurations.

Summary

• Common configuration is tandem axle combination, which uses use two drive axles.

• Commercial vehicles classified by weight and length.

• Federal Bridge Gross Weight Formula: legal calculation that establishes maximum allowable weight of commercial vehicle traveling on roads and bridges.

• Classification system for heavy vehicles uses their gross vehicle weight (GVW).

Summary

• In North America, vehicle’s weight per axle is

regulated.

• Heavy vehicles classified by combination:

tractor/semi-trailer, truck/full trailer, truck/pole

trailer.

• Combinations have multiple trailers, referred

to as A-trains, B-trains, C-trains; differentiated

by hitching mechanism connecting the

trailers.

Summary

• Best solution to enable transportation of

heavier and larger loads is to add more axles

to vehicle configuration.

• Fifth wheel is point of articulation between

trailer and tractor and enables trailer and

tractor to turn effectively.

• Vehicle classifications by hitching device rely

on gross trailer rate and tongue weight.

Documents

Chapter 1 Introduction to Heavy-Duty Commercial Vehicles