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In recent years, small diesel engines for industrial use are required to achieve still higher power output per engine size (high power density) and to have the performance to comply with stringent exhaust emissions standards as well. To meet these social demands and market requirements, there are various engineering tasks yet to accomplish. In this paper, two important technical issues have been focused, those are, combustion system improvement to enable lower exhaust emissions and higher power output than conventional models and new cooling system as a solution for increased heat load issue accompanying the progress of high power density. Firstly, for combustion system improvement, the swirl adjustment technique has been developed that will optimize the swirl ratio for each engine application with different load and speed condition.

The latest frequency-conversion system, as typified by inverter power generator, is capable of providing superb fuel economy and NVH characteristics by means of real-time control of the engine speed according to its load condition. The current mechanical governor, however, can difficultly achieve that demand of performance. In order to meet these requirements, we have developed the electronic governor system having high control flexibility and response for small diesel engines for agricultural and industrial use. In developing this electronic governor system, we have adopted a method that can minimize modification of current engines. We have successfully developed the electronic governor system by means of a post-assembly installation, in which dedicated functional devices are installed to complete engine while keeping intact the current highly reliable PFR type fuel-injection pump and the mechanical governor.

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.

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.

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.

The New Kubota Grand L30 Series Compact Tractors are powerful, user-friendly compact tractors that have advanced functions to provide the maximum performance. Many new features such as IntelliPanel enable users to obtain high workability, comfort, and operability. IntelliPanel is an advanced function that displays information on a liquid crystal display to help users' with operation and maintenance. An electronically controlled multi-gear GST (Glide Shift Transmission) enables users to choose gears for 12 travel speeds using one lever, during travel without operating a clutch. An ECU (Electric Control Unit) controls solenoid valves and a proportional reducing valve to allow for smooth gear changes.

The RTV900 utility vehicle with tractor technology features the first Variable Hydro Transmission (VHT) with auxiliary hydraulics, power steering and wet disc brakes. The VHT comes equipped with a servo-type variable capacity pump, linked in parallel with fixed capacity and variable capacity motors on the same axle. This variable motor enables an increased driving force with auto-deceleration. Additionally, the RTV900 uses hydraulic power steering that is commonly used on tractors. The RTV900's power steering decreases heavy kickback in rough terrain and allows the operator to maneuver and drive the machine with minimal effort. Wet disk brakes resolve the problems of mud and water that can infect dry-type brakes, improving safety and reliability in bad road conditions. With its sealed VHT components, power steering and wet disk brakes, the RTV900 will provide farmers, vineyards, nurseries, orchards and golf courses increased power, lower maintenance costs and easy, safe operation.

Hydraulic fluid (HF) specifications for mobile construction equipment called JCMAS HK and HKB have been established by the Fuels and Lubricants Committee of Japan Construction Mechanization Association (JCMA). The specifications are designated by two viscosity categories of single grade and multigrade. Each category has ISO viscosity grade (VG) 32 and 46. The JCMAS HK oils are recommended for use in hydraulic systems designed at pressure up to 34.3MPa(5000psi) and to heat hydraulic fluid up to 100 °C. These oils also provide wear control, friction performance, oxidation and rust protection, seal swell control and filterability performance. Two piston pump test procedures were developed to evaluate lubricating performance of these oils under high pressure conditions. The JACMAS HKB oils are classified as environmentally friendly oils due to the additional requirement for biodegradability.

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.