The Machines of the Heavy Equipment Industry Explained

Picture an excavator, one of the classic workhorses of heavy industries, used for digging, moving, pushing, all sorts of tasks. What really is an excavator? A vehicle? A machine? A tool? Well, yes, something like all of that. Heavy equipment products are in a league and industry of their own. These products are geared to do two distinct things. Driving, a.k.a. acting as a vehicle, and working, a.k.a. acting as a tool. There are indeed some stationary products, like tower cranes and certain types of drilling rigs, that don't do any driving, but we can generalize driving and working as the two distinct activities of heavy equipment. Driving relies on either wheels or tracks. Tracks operate via a system of chains and sprockets. The wheels versus tracks distinction is a major one. Wheels move faster and with more control on even terrain, like roadways. They're also typically less expensive and less prone to breaking down over time, given they have fewer moving parts. Tracks, conversely, are more stable and can crawl well over uneven terrain. Tracked excavators are often called crawlers accordingly. However, tracks are more complex and require more maintenance and repair over time. Plus, most track systems cannot be driven on roadways. Tracks are commonly covered with a steel track shoe, which damages the driving surface. Smaller excavators can, however, be used on roads by fitting them with rubber tracks or track pads. Working relies on other tools and attachments, and this varies widely by the type of equipment. Excavators, for example, use a shovel called the bucket, attached to an arm, and then to a boom that reaches overhead. All of this is controlled by the operator who sits in the cab. Driving and working are two distinct uses of the equipment's power. How about the source of the power? That can vary. There are two common ones, diesel and electricity. Diesel is a high-density energy source, and diesel engines output a lot of power. The classic diesel engine system uses combustion, much like the internal combustion engine in a car. Controlled explosions of diesel move pistons in cylinders, which turn a system of gears that create some mechanical action, like spinning wheels. This is called a diesel mechanical system and is a high-power, reliable, and relatively lower-cost approach. Increasingly, diesel systems take a second approach, converting the diesel into electricity via an onboard generator, then applying the electrical power. This is called a diesel-electric system. Electrified systems like this—no, electrified does not necessarily mean diesel-free—have several benefits. They're more fuel-efficient, combustion wastes energy to heat, and provide greater control over power distribution. Consider how smoothly electric cars accelerate relative to gas cars. The downside is that diesel-electric systems tend to be costlier and more complex, and are more prone to breaking down under operational stress. Of course, electrified systems can draw their power fully or partially from batteries. However, with current technology, battery-only systems are not practical solutions for creating the power needed for the largest heavy equipment. Plus, many equipment use cases are far off-grid, away from the electrical infrastructure needed for recharging. So, while battery-diesel hybrids are increasingly common in heavy equipment, battery-only systems are typically limited to smaller equipment, such as forklifts. So how does the power get from the source to the end-use? Well, there are a few different mechanisms at play. First, let's cover the mechanisms used to make the driving possible. Diesel-mechanical systems use a transmission, which uses a series of gears and shafts. This works like a very heavy-duty car. Diesel-electric and fully-electric engines similarly work like very heavy-duty EVs. Power is sent via an electric drivetrain, which doesn't rely on gears in the same way. The working elements rely on an entirely different mechanism, hydraulics. Hydraulic systems are force amplifiers. A small input gets turned into a more forceful output. This is like how a long lever can lift heavy objects, but it works via pressurized systems. Take a simplified example, a small cylinder of liquid connected to a large cylinder. Now, add pistons, like pumps, to both. Pumping the small piston down will create a massive amount of pressure in the small cylinder. This pressure will push out the larger piston with a larger force. This is how heavy equipment can do such heavy lifting. Hydraulics are used in other applications as well, like industrial presses and modern elevators. In fact, the driving elements of equipment can sometimes rely on hydraulics as well, particularly when tracks are used. And the opposite is true in some cases as well. The working elements are powered not by hydraulics, but by direct transmission from the engine. Here, the rotary motion generated in the engine is simply transmitted as is to the associated attachments, often called implements. This is the case with agricultural tractors, which usually connect directly to their implements through a shaft called PTO, power takeoff. This simplifies the connection mechanism and allows the same tractor to work with many different implements. The hydraulics can be powered either by diesel mechanical systems, where pumps are moved by the engine in a mechanical way, or electrified systems, where the pumps are moved by electricity. The specifics of the equipment design, what power sources and various mechanisms are used, will of course depend on the equipment in question and its use cases. We'll explore these in the next chapter.