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  • Kubota OC60-E4; A Unique Naturally Aspirated Industrial Diesel Engine

Kubota OC60-E4; A Unique Naturally Aspirated Industrial Diesel Engine

Kubota’s Unique Naturally Aspirated Single-Cylinder Industrial Engine

John Lehenbauer
Nov 7, 2017
Photographers: Courtesy of Manufacturer
The Kubota Corporation began as a foundry in Osaka, Japan, in 1890. Thirty-two years later, the company produced its first engine, a horizontal, liquid-cooled, kerosene-fueled powerplant designed for agricultural use. That first unit laid the groundwork for Kubota’s design and development of new diesel engines, but the company didn’t start marketing these little oil-burners in the U.S. until 1976.
Since its early beginnings, Kubota has built diesel engines that are competitive alternatives to their gasoline counterparts. By 1999, demand for its powerplants had grown large enough for the company to form a new division, Kubota Engine America. Today, Kubota Engine America engineers and builds a broad assortment of compact oil-burners as part of the division’s powerplant lineup. Many of these engines are designed for use with generators and industrial equipment, while others are nonspecific power sources that can be adapted for any number of applications. The OC60-E4 is one of Kubota’s smallest diesels. It is a single-cylinder, normally aspirated, indirect-injected industrial engine that measures 18 inches long, 16 inches wide, and 18 inches high. The condensed unit tips the scales at only 84 pounds. The OC60 produces 6 hp and 10 lb-ft of torque and meets Tier 4 emissions standards. The small size and low weight make it an ideal alternative to gasoline engines in applications like generators and pumps.
Kubota was able to keep the size and weight down by eliminating the need for water cooling, instead using a unique system called the Advanced Cooling Three Vortex. The ACTV uses an air-cooled cylinder and oil-cooled cylinder head to regulate engine temperature. By using oil to cool the cylinder head, ideal combustion temperature can be maintained and noise is significantly reduced. The cooling oil also helps lower the temperature of the injector’s nozzle, extending its service life. Oil temperature is regulated with a small, finned cooler mounted on top of the engine that receives airflow from the fan that cools the cylinder. Eliminating water cooling also reduces the amount of routine maintenance needed.
Photo 2/2   |   The single-cylinder Kubota OC60-E4’s unique Advanced Three Vortex Cooling system uses a combination of air and oil to maintain ideal temperature and eliminate the need for water cooling.
Working in conjunction with the ACTV to lower emissions and increase efficiency is the Three Vortex Combustion System. The TVCS works inside the cylinder to create three swirls of air and fuel in a specially designed spherical vortex chamber during the combustion stroke. The swirling improves the combustion effectiveness of the indirectly injected fuel.
An inherent problem with single-cylinder engines is vibration. The vibration comes from two major sources. One of the sources is the inertia force generated by the piston and the small end of the connecting rod as they are reciprocating. The other comes from the centrifugal force (a kind of inertia force) generated as the connecting rod’s large end turns on the crankshaft. The OC60’s two inertial force vibrations are offset with a uniaxial balancer. The balancer shaft works by rotating a counterweight at the same speed in the opposite direction of the crankshaft to neutralize the vibrations.
Another design feature of the OC60 is its die-cast-aluminum crankcase. The case uses oil galleries to lubricate the crankshaft and feed oil to the sides of the cast-iron cylinder liner. Surrounding the cylinder liner with oil reduces liner temperatures and low-end noise.
To guarantee oil circulates efficiently throughout the engine, a trochoid-style pump is used. The pump uses inner and outer rotors (housed inside the body) to draw in oil, pressurize it, and then discharge the pressurized lubricant into passages that run throughout the engine.
An NC-type mini injection pump is used to pressurize fuel. It’s a small, lightweight, plunger-type unit that is actuated by the camshaft via a tappet roller. Fuel delivery is increased or decreased to the injector by the movement of the pump’s control rack. The injector uses a throttle-style injection nozzle that gradually increases fuel for smoother, quieter combustion events.

SPECIFICATIONS

Engine: Kubota OC60-E4
Displacement: 0.276L (16.8 ci)
Engine Layout: Single cylinder
Valvetrain: 2 valves
Bore x Stroke: 2.83 x 2.68 inches (72 x 68 mm)
Compression Ratio: 24.5:1
Head material: Cast iron
Block material: Die-cast aluminum
Piston material: Aluminum
Power: 6 hp
Torque: 10 lb-ft
Emissions: EPA Tier 4
Induction: Naturally aspirated
Exhaust: Cast iron
Cooling System: Oil-and-air cooled
Fuel System: Indirect injection
Lubrication System: Wet sump
Lubrication Capacity: 1.4 quarts (1.3 L)
Dry Weight: 84 pounds (38 kg)
Length: 18.15 inches
Width: 15.87 inches
Height: 18.03 inches

Sources

Kubota Engine America
kubotaengine.com
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