Trucks are an American institution, the acknowledged Kings of the Road. They travel to and from all corners of the continent day after day, covering millions of miles between them, often forming spectacular convoys on the roads. The heavy-duty truck is the type that springs to mind when we mention the word truck, and it’s those that we are talking about today. In fact, we are going to talk about the braking system of a heavy-duty truck which differs to most other road vehicles.
Heavy trucks are just one of a class of trucks that are defined by the weight they can carry, which is what we will talk about now before we start to look at the braking system of a heavy-duty truck and what make it special. So, what is a heavy truck?
When you see a large articulated truck, one that has a separate cab and trailer, it’s more than likely a heavy-duty truck. These are the biggest of the truck classifications on the roads of the USA. There are 8 classes of truck starting from light trucks – Class 1 and including the likes of Ford F150 and similar everyday trucks – up to Class 8, which includes the biggest trucks of all.
Classes 7 and 8 are the heavy truck groups, and they include models from legendary names such as Mack, International and the market leader Freightliner. The latter is the biggest manufacturer of trucks in the USA. Others include Volvo, Peterbilt and various national and international companies known for their trucks.
The classes are defined by weight. A Class 8 heavy duty truck, for example, has a minimum weight allowance of 33,000lbs. They can carry up to 80,000lbs including load, driver, trailer and cab. That should give you a good idea of why heavy duty is the chosen name. So, the braking systems of a heavy-duty truck: check out Haldex – one of the leading names in the business – for an idea of the components involved and we’ll give you a simple explanation in the following section.
The history of the truck in the USA is a story of evolving innovation and ideas, and begins with the development of the motor car in the late 1800’s. The internal combustion engine changed transport in every way, and it was Henry Ford who was at the leading edge of cars for the masses with the legendary Model T.
This would make the basis of home-made trucks, with commercial users converting Model T’s by adding a carrying platform where the rear body should be. Soon, Ford and other manufacturers recognised the demand for load carrying vehicles and commercial vans and began making them in-house.
These very early trucks used the same running gear as the cars they were based upon and this included the brakes. However, as manufacturers began catering for the demand for ever-bigger commercial trucks it became clear that the stopping power provided by automobile brakes was not enough.
Fast forward to the latter part of the 20th century and the answer came about in the form of air brakes. Your standard vehicle braking system will use hydraulic fluid to push in a piston when the pedal is depressed, which instigates the other parts of the system to do their bit and exert the pressure through a disc or pad that slows the vehicle the difference with heavy trucks is that they use compressed air to do the job, so let’s try and explain how it works I simple terms.
A heavy-duty truck is also known as a semi-truck. This is because it consists of two sections: the tractor cab that has the driver, engine and power train and the trailer, which is a separate entity. The air brake system covers all the wheels – both those on the cab and those on the trailer – and is activated by way of compressed air through a series of hoses. The air is provided by the engine when it’s running and stored, but the hoses need to be connected when a trailer is linked and disconnected when the trailer is dropped at its destination.
The brakes themselves can be either drum or disc variety. Drum brakes use a set of pads applied to the drum of the wheel hub assembly to slow the vehicle, while the disc brake set up utilises discs and callipers – as do most modern cars – to bring the vehicle to a stop. The best option will be that decided upon by the manufacturer who will naturally designed vehicle for efficient running and with the safety of all involved in mind.
Brakes on heavy trucks are among the most important of safety appliances and will be regularly maintained by the users. The current breed of trucks carries perhaps the most powerful form of braking system of all road vehicles, and it is certainly a long way from those trucks of old! What does the future hold for the heavy truck? Let’s finish by looking at the potential future of the heavy truck market.
There is plenty of concern regards the future of the heavy truck market with emissions controls being tightened all the time. Heavy trucks carry the vast majority of domestic freight within the USA and will continues to do so for the foreseeable future, as electric vehicles do not have the range needed to replace the present fleet.
As far as truck safety and brakes are concerned there will be further developments in these areas without a doubt as everyone wants to see trucks and all road vehicles as safe as possible, while increases to efficiency can only be welcomed. Heavy trucks, beloved by small children and adults alike, are not going to disappear from the roads of the USA anytime soon as they form the backbone of commercial distribution in the USA and are essential to the smooth running of the USA.