At the core of a skid steer or track loader, there’s a fiery diesel power plant pumping energy to all of the machine’s many wheels, tracks, loader arms, attachments and other functions. In the belly of the beast, this diesel engine takes in air, compresses it and then injects it with fuel. The heat of that compressed air spontaneously lights the fuel, turning it into energy. The diesel engine then transmits that energy to a set of hydraulic pumps bolted directly to the output of the engine.
These hydraulic pumps power hydraulic drive motors and charge pressure circuits and auxiliary hydraulic circuits, which power the loader arms, attachments, wheels and all of the hydro-mechanical functions on a skid steer or track loader. There is an extensive story on how the hydraulics of a skid steer work on page 54, so in this article we will concentrate on the multi-point criteria that manufacturers use to choose the right diesel engine to power their hydraulic loader — envelope, power, fuel economy, Tier 4 aftertreatment technologies — and how that all integrates.
“Perkins regularly works with OEMs and component suppliers to achieve optimum integration of the engine, electronics and hydraulic systems,” explains Oliver Lythgoe, product concept marketing manager at Perkins. “Integration of the electronic systems of operator controls, hydraulics and engine management systems is critical for a world-class skid steer or track loader. This makes a joystick controller machine that is easy to operate, safer and harder to stall. In recent years, skid steer engine technology has largely been driven by emissions regulations, but the good news is that the resulting engines are much better than their predecessors. The wide adoption of common rail fuel systems and smart turbochargers has helped increase engine power, improved cold starting and made engines more responsive.”
While your Honda Civic may only use its gas engine three or four hours a day, a skid steer’s diesel engine can be working 12-hour shifts, seven days a week, so manufacturers need a smart engine that eats less fuel, can endure slave labor work shifts, last for decades with the proper care and still have symmetry in its systems.
“Balance between the engine and hydraulic system is very important, and the correct match can result in better performance and enhanced productivity,” explains Jeff Wilke, product manager with diesel engines at Kohler. “The Kohler KDI engines have a very good load response and impressive torque starting at low rpms. This allows skid steers to dig deeper, lift faster, push harder and be more productive overall. On the maintenance side, our Kohler KDI engines meet Tier 4 Final standards without a diesel particulate filter [DPF], which significantly streamlines service. Also, oil change intervals have been extended to 500 hours because engines are running cleaner and cooler, resulting in less contaminates in the oil and less degradation due to heat. For Stage V markets where a DPF is required, we’ve extended DPF cleaning intervals, which helps to reduce replacement costs. Just make sure to always maintain your fuel and air filtration systems because contaminates in any engine can lead to potential problems.”
Today’s contractors have access to some of the cleanest engines ever built for skid steers and track loaders — emissions-compliant diesel engines — designed over decades to not only burn cleaner, but maintain fuel efficiency, add power and decrease noise and vibration.
“Look for a quiet unit,” suggests Lythgoe. “Noise is a major concern on skid steers and track loaders because the operator will spend a lot of time sitting very close to the engine. That impacts fatigue, stress and the safety of everyone around the machine.”
These clean and quiet skid steer/track loader diesel engines must now have near-zero emissions, according to EPA-mandated Tier 4 engine regulations, so these high-tech diesel engines are now engineered with aftertreatment technologies that sport names like exhaust gas recirculation (EGR), selective catalytic reduction (SCR), diesel particulate filters (DPFs) and diesel exhaust fluid (DEF). Each manufacturer applies these and other aftertreatment technologies to various power bandwidths, depending on the emissions regulations of each country. In fact, engine makers have to come up with some pretty intricate strategies to meet the globe’s varying regs.
“We just recently introduced Kohler Flex [read about it on page 14], a suite of advanced engine systems which are integrated into our KDI line — based on the specific needs of global equipment manufacturers — to meet every emissions standard in the world,” explains Wilke. “Different aftertreatment devices, including a diesel oxidation catalyst, diesel particular filter and selective catalytic reduction, are integrated in various combinations to achieve effective emissions solutions for every region.”
These relatively large and complicated systems clean the engine exhaust, yet before the fuel can even be burned and the subsequent exhaust treated properly, the fuel must first reach the combustion system safely and accurately. To supply just the right amount of fuel, highly-advanced, electronic, common rail direct injection technologies have replaced the old mechanical indirect injection systems of yore. Tier 4 engines today use a high-pressure fuel rail that’s engineered with computer controlled electronic injectors, which completely atomize the fuel for an ideal, clean, powerful burn. Those common rail fuel systems and those high-pressure injectors have an increased susceptibility to fuel contamination — water, dirt, rust, sludge and other impurities.
“With fuel injection pressure in excess of 2,000 bar [30,000 psi], it is critical that the incoming fuel is clean,” explains Eric Hoffman, application engineer for Hatz Diesel of America. “Hatz, along with most Tier 4 Final engine manufacturers, utilize a two-stage fuel filtration system. The first stage has a fuel-water separator that centrifuges the fuel to remove the water and coarse media to capture larger partials. The second stage has a fine media filter to capture particles as small as 10 microns. To minimize downtime for fuel system servicing events, it is important that operators take care to mitigate dirt and other debris from getting into the fuel tank, ensure the fuel nozzle is clean and never fill the fuel tank without the tank screen installed. It has also become standard practice to put filters on fuel tank vents to further reduce contamination.”
Other aftertreatment tech includes acronyms like EGR, which lowers an engine’s peak combustion temperature to lower NOx, one of the emissions regulated by the EPA. EGR recirculates exhaust gas by mixing it with incoming fresh air. This process reduces oxygen content, lowering combustion temperatures and reducing NOx. Cooled EGR includes the cooling of the exhaust gas by passing it through a heat exchanger prior to recirculation. EGR systems often require a diesel particulate filter (DPF), which is a through-the-wall flow device that traps and holds particulate matter (PM) in the exhaust. With the help of a catalyst, the DPF cleans or “regenerates” by oxidizing the trapped PM. There are two types of regeneration: passive and active. Everyone’s exact configuration is a little different. Here’s how Perkins breaks down its product line in North America:
• In the sub-25-hp area, Perkins offers three-cylinder 1.1- and 1.7-liter engines with simple mechanical fuel systems and no aftertreatment. This technology is sufficient to meet emissions regulations below 24 hp. At the low end, neither DPF or DOC is required.
• In the 26- to 50-hp category, Perkins offers its new Syncro 1.7-liter engines with a common rail fuel system and more advanced emissions control packages. In the 25- to 75-hp range, all Perkins engines use a DOC and certain larger engines also use DPF technology that is attractive to customers who are focused on maximizing productivity.
• Perkins has three engines in the 50- to 75-hp range, the Syncro 2.2 liter, a 2.8 liter and a 3.6 liter, all of which have four cylinders.
• Above 90 hp, Perkins offers the Syncro 3.6-liter family. See emissions tech below.
“All 75-hp and above engines in skid steer applications in areas covered by EPA Tier 4 Final requirements use DEF and SCR,” says Lythgoe. “Perkins technology minimizes DEF consumption, keeping it at about 3 percent of fuel use. So, consuming a 25-gal tank of fuel would only require about .75 gal of DEF.”
In diesel engines 75 hp and above, SCR aftertreatment technologies reduces NOx emissions by using an urea-based additive, sometimes referred to as diesel exhaust fluid or DEF. The ammonia in the urea mixes with engine exhaust gases in an SCR catalyst, converting NOx to nitrogen and water vapor. SCR will necessitate the use of DEF and will change the “total fluid consumption” of a loader.
“As a general trend, skid steer engines are getting larger due to the addition of these aftertreatment systems, which presents a challenge for equipment manufacturers,” says Wilke. “But, the compact overall design of our KDI engines, which don’t utilize a DPF in Tier 4 markets and utilize a very compact DPF in Stage V markets, provides OEMs with additional flexibility when it comes to engine integration.”
Skid steers and track loaders have unique engine requirements because these machines tend to be very compact. Early skid steers tended to be 60- to 70-hp machines, but the market has grown in both directions and the range today is between 20 and 120 hp. These are extremely versatile machines, but that versatility inevitably comes with some compromises, so be sure to talk about the diesel engine specifically when buying a skid steer or track loader.
“Check the service access,” suggests Lythgoe. “Can the operator or maintenance personnel easily access the dipstick and change filters without spillage? If those things are difficult to do, there is a good chance they won’t get done, which will negatively impact productivity and engine life. Neat wiring and waterproof electrical connectors are two other good indicators of the engine builder’s attention to detail. Finally, look at the paint quality. An engine builder that will skimp on painting may very well skimp in other places that are not readily visible.”
Hatz Diesel of America Recognized by AEM
The Association of Equipment Manufacturers recently recognized Hatz Diesel of America for its 25 years of association membership. The award was presented to Hatz president and CEO Mike Hartoonian by AEM representative Paul Malek. Hatz Diesel is a worldwide leader in the manufacture of high-quality diesel engines from 3 to 78 hp that are used in industrial, construction, military, marine, railroad, turf care, power generation, material handling, agricultural, mining, transportation, forestry and rental equipment applications. For more info, visit hatzusa.com.