Diesel-Powered Dynamos

Even machines have a heart. 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.

A total of up to four hydraulic pumps hooked up to the engine power the loader arms, hydraulic drive motors, auxiliary hydraulic circuits and other accessories.

This diesel heart system is an efficient and durable power source for a small piece of construction equipment like a compact loader — especially compared to a gas combustion engine that might power your car or outdoor power equipment.

“[Diesel engines] have lower revolutions per minute for longevity and direct fuel injection for a better air to fuel mixture,” explains Bill Anderson, compact equipment specialist at Volvo Equipment Co. “This creates a more complete fuel burn yielding more horsepower with less fuel consumption and with 1/3 less moving parts than a gas engine, which decreases maintenance costs.”

Power, durability and less fuel consumption are the three keys to any good diesel design. 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. Manufacturers need an engine that eats less fuel, can endure slave labor work shifts and still last for decades with the proper care.

What’s the difference between a diesel and a gas engine? Diesels only intake and compress air (a gas engine mixes both air and gas), so its compression ratio can be much higher. The higher the compression ratio, the more power is generated.

The size of the diesel engine in a compact loader is based on the size of the machine. Bobcat’s smallest skid steer is the mighty mini model 463, which touts a Kubota liquid-cooled, three-cylinder, 22.5-hp (16.8 kW) engine. The Mustang 2109 is the industry’s largest skid steer (along with its sister unit, the Gehl 7810E), sporting a Cummins liquid-cooled, four-cylinder, 99-hp (73.8 kW) engine. Minnesota compact equipment manufacturer Mustang categorizes its skid steers and track loader engines into three groups.

“There are smaller loaders, which are at 35 to 46 hp, so you have smaller displacement engines — none turbocharged.

With that, you keep the pricing as economical as possible,” explains Kelly Moore, product manager at Mustang Mfg. “Then you start moving up to mid-sized skid steers at 49 to 60 hp and then to the larger loaders at 80 hp and higher.”

Popular original equipment manufactures (OEMs) for skid steer and track loader diesel engines include Kubota, Mitsubishi, Yanmar, Deutz, John Deere, Cummins and Perkins.

“We use pretty lengthy criteria when reviewing engines,” says Moore, discussing how Mustang picks the power source for its compact loaders. “There’s multi-point criteria we take a look at that includes the sizing of the engine, power, torque output, its physical sizing to go into a loader chassis, fuel economy and parts and service support from the manufacturer. There are a large number of factors that we take a look at and weigh in order to come to the best decision when we’re looking at an engine.”

Turn Up the Turbo

Add the word “turbo” to anything and you’re sure to increase both its power and cool factors. In a skid steer or track loader engine, turbocharging not only makes a meaner machine, it also increases horsepower without decreasing engine durability, longevity and size. It’s also one of the few options you can find on today’s skid steer and track loader engines.

A turbocharger is an exhaust compressor used to increase the power output of your skid steer’s internal-combustion engine by compressing air that is entering the engine, thus increasing the amount of available oxygen. The turbocharger consists of a set of two connected fans (or turbines) that recycle energy from wasted exhaust gases. A key advantage of turbochargers is that they offer a considerable increase in engine power with only a slight increase in weight.

“Turbocharging increases the air flow into the engine creating better fuel atomization. This causes faster fuel ignition and improved fuel burn for higher horsepower output,” explains Anderson.

Turbo options do not kick in for the compact loader industry until about 50-hp diesels at the very smallest and generally in 60-hp and up categories. An extra cost of a few thousand dollars will be passed onto the customer for the benefit of a turbocharged engine. These buyers want a more powerful loader in the same size package, and often times they work in high-altitude jobsite conditions.

“A lot of customers want a little more power and performance and turbocharging can be good for them,” says Moore. “When you get into higher elevations — in the Rocky Mountain states for instance — usually turbocharging is going to be a little more advantageous. Otherwise, on a national basis, it’s just getting more power in a given engine in the same size loader.”

Tier Emission Regulations

Making clean burning and powerful engines is the goal of every manufacturer – and it’s also the goal of the Environmental Protection Agency. Currently, the EPA only regulates 0.3 percent of an engine’s total product of complete combustion. The rest (99.7 percent) of the engine exhaust is made up of natural elements in the air such as nitrogen, oxygen and water vapor. The two main emissions that are regulated by the EPA are oxides of nitrogen (NOx) and particulate matter (PM). As diesel engines move from Tier 1 to completing Tier 4 final emission regulations, NOx and PM emissions will be reduced to almost nothing. Manufacturers are also taking the opportunity to improve engine performance.

“These new regulations are forcing many engine manufactures to develop new ways of maximizing engine performance, while lowering pollutant output. Many new engine air/fuel induction improvements have come due to Tier 2 regulations,” says Anderson.

Each tier is aimed at reducing harmful emissions by phasing in cleaner burning engines through various horsepower ranges. So, to use Tier 3 as an example: 175- to 750-hp engines had to be compliant with specific emission regulations by 2006; 100- to 175-hp engine standards will take effect in 2007; and 50- to 100-hp engines will have to meet Tier 3 standards by 2008.

For compact equipment, a 50-hp engine commonly used in a skid steer loader or track loader has to meet Tier 3 emissions by January 2008. Regulations for engines smaller than 50 hp skip Tier 3 altogether and go straight to Interim Tier 4. The same is true for engines larger than 750 hp.

While complying with engine regulations will end up costing end-users more money in the end (alas, research and technology are not free), there will be obvious environmental positives, as well as other added end-user benefits.

An Evolving Power Source

Fueled by bigger applications, increasing commercial demands and emission regulations, skid steer and track loader diesel engines have evolved into more vigorous and efficient power plants over the last 50 years. Technologies like direct injection fuel systems (developed to better atomize the fuel mixture with air in the cylinder) have created diesel engines that are engineering marvels. Today’s compact loader diesels burn much cleaner, they’re not nearly as noisy or smoky and have better cold starting capability (when a diesel engine is cold, the compression process may not raise the air to a high enough temperature to ignite the fuel).

Although there are not many choices when it comes to choosing your machine’s power source (except for options like turbocharging or an anti-stall device), your OEM brand of diesel engine is bound to be a quality power source. Each skid steer and track loader manufacturer picks their specific brand — Bobcat uses Kubota engines, Mustang capitalizes on Yanmar and Cummins and ASV utilizes Perkins engines.

“Certainly the horsepower and torque are key specifications when looking at engines in various compact loaders,” says Brad Lemke, ASV director of new product development. “You don’t want to buy a big heavy machine that doesn’t have the horsepower to back it up. Power-to-weight ratio is critical for performance. Turbocharged engines can be very nice and a lot of customers choose them. Cold starting is also something that is important in certain parts of the country.”

Buyers should quiz their dealer on why the machine manufacturer has chosen a certain brand and see if that philosophy fits their working style. For example, the engine power curve should match the contractors operating approach. Many operators like to run the machine at half or three-quarters throttle. They should make sure the engine will have the power they need at the rpm at which they want to work.

Your compact loader engine also needs to be powerful enough to turn the hydraulic pumps efficiently without wasting fuel. As the machine works the load, the pumping process will vary. The engine must have enough oomph to handle the peak load, yet be responsive enough to compensate for pump variations. The pump and engine rpm must match as the engine should not over-speed to get maximum pump output.

Fuel efficiency is also of monumental concern.

“Fuel consumption is as varied as the conditions and work loads required from the machine,” says Anderson. “Skid steer loaders do not use miles per gallon as a measurement — gallons per hour is the typical usage measurement. Typical fuel cells will hold between 12 to 25 gal. Any given fuel cell should hold enough fuel to complete eight to 10 hours of operating time under normal operating conditions.”

One of the more high-tech diesel engine features on the market is called an anti-stall device. This device allows the pumps that power the wheels, tracks and implements to sense various loads, so they won’t exceed the power capacity of the engine.

“Some manufacturers go beyond just putting good, reliable power into their compact loaders. ASV, for instance, includes a feature they call Posi-Power in the powertrain of many of their rubber track loaders,” explains Lemke. “Posi-power is a power management system that helps prevent engine stalls by automatically adjusting the hydraulic pump output based on available engine horsepower.”

Easy engine maintenance is as imperative as good fuel economy and as advantageous as an anti-stall device. Although the engine, cooling system and other accessories are tightly packed into the back of a compact loader, the engine compartment is designed to make maintenance

easy on your machine’s ticker. The use of flip-up cabs and swing- or tilt-out radiators will give good access to the engine. On many models, the door on the back opens wide and the radiator and fan tilt up to allow clear access to the engine and all of the maintenance items such as filters.

With routine engine maintenance on your diesel power plant, you can ensure your engine will last up to 6,000 to 8,000 hours, which could mean decades of work for you and your compact tool carrier.

Keith Gribbins is managing editor of Compact Equipment.