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In recent years, since the demands for comfortable operation and low fuel consumption are increasingly enhanced on the industrial machines, non-road engines as power sources on agriculture, landscape and construction applications are required to be achieved high power, low fuel consumption and low noise. Also, even for small engines, it is necessary to keep up with the trend of electronic control devices on these machines. Based on such backgrounds, we developed new non-road direct injection diesel engines with common rail system to satisfy those demands. This paper reviews the technologies to achieve the adoption of common rail system onto such small displacement industrial engines and to optimize the combustion system and injection characteristics.

In these days, not only low exhaust emission but also carbon dioxide reduction is required to achieve carbon neutrality toward resolution of climate change. Though examination of electrification and decarbonized fuel is progressing, industrial machines have issues for high load factor and infrastructure development. Therefore, trends of off-road powertrain are expected to be diversified depending on usage environment or applications. As a result, in terms of diesel engines below 19 kW, it should be the best way for satisfying the social needs to develop new diesel engines which have high environmental performance by optimizing engine combustion. In the case of diesel engines below 19 kW, it is difficult for the engines to adopt the direct injection (DI) combustion system and the common rail system (CRS). The fuel spray of these small displacement engines by DI or CRS easily attaches the wall surface of combustion chamber due to the small bores and causes increasing fuel consumption.

In this paper, the features of V3300 heavy-duty diesel engine series and the technologies to achieve the concepts are introduced. V3300 series is the vertical water-cooled 4 cycle IDI diesel engine for agricultural and industrial use. Its output is the highest in our company's IDI diesel engines. V3300 series was developed based on the concepts of our conventional series (low vibration, low noise, clean exhaust emissions and good fuel efficiency). V3300 series adopts 3 valves system for the first time in agricultural and industrial diesel engines. This 3 valves system is composed of 2 intake valves and 1 exhaust valve per cylinder. V3300 series also adopts the new combustion system which succeeded to the KUBOTA's original combustion system. The volumetric efficiency, the fuel efficiency and the exhaust emission performance are improved by these systems. The comfort level is achieved by reduction of the vibration and the noise by adoption of the built-in balancer.

KUBOTA has been marketing M Series tractors to the world since 1955. As shown in Fig.1, this series consists of five models ranging from 33.6 to 59.7kW (45-80) PTO horsepower. The four configurations are equipped with either ROPS or ROPS cabin, and an optional 4-wheel drive for each model is available. In this series, we have pursued “excellent-stability, high-productivity superior-mobility, and good operator-comfort” with a renewed effort to remove the bulky image of tractors regarding mobility. The New M series tractors were developed to meet multi purpose requirements of the market place. In this paper, the author will introduce the technologies utilized to enhance the concepts of “excellent-stability, high-productivity, superior-mobility and good operator-comfort”. We pursued this course of development for the new generation M series tractors.

Recently, EU StageV emissions regulations have been enforced in the European market since 2019, increasing environmental requirements for diesel engines. EU StageV has been tightened compared to EPA Tier4 regulation, which demand PM (Particulate Matter) reduction and added new PN (Particle Number) regulations. Until the previous regulation EU Stage IIIA, the power category of 19kW or more and less than 37 kW had adopted mechanical IDI (Indirect-Injection). This mechanical engine is characterized by compactness and lightweight because of simple structure. Therefore, this engine is appreciated by customer with easy installation. On the other hand, to achieve EU StageV, it is necessary to adopt the electronic direct injection common rail system with more precise fuel injection and advanced exhaust gas aftertreatment device.

Off-road engines are requested with limited space due to variety of end products, and it is also requested reasonable costs for the limited end products prices. For that purpose, several small off-road engines have to comply with emission legislations by only engine modifications. However, the additional engine control and devices (=High pressure direct injection, combustion chamber modification, electrical control, turbo charging control, etc.) must be expensive, and increasing the total engine costs and manpower for developments. These are very critical issues for long term possibility of same engine productions which cover to new legislations in each country. Thanks to drastic fuel condition improvement for passenger cars / trucks around the world, it would be aroused one of the best solution by DOC (Diesel Oxidation Catalyst) systems rather than the engine modifications.