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In 1994, the Kubota Corporation launched the Grand “L” Series of compact tractors to the worldwide market. SAE J1150 -TERMINOLOGY FOR AGRICULTURAL EQUIPMENT defines compact tractor as a small agricultural tractor equipped with a 540rpm rear PTO (SAE J1170) and a three-point hitch designed for Category I (SAE J715)implements only. These tractors generally weigh less than 1800kg, have less than 30 PTO kw, and are primarily designed and advertised for use with mowers and light-duty material handling equipment. The concept behind the development of this series of tractors comprises of 4 basic types with PTO power ranging from 18.7 to 27.6 kW (25 to 37 HP). It offers operator comfort, excellent dexterity, and high performance efficiency in a compact tractor configuration. The tractor performs well without any special skill by the operator. Further, it can utilize with equal efficiency such varied applications as light construction, grounds maintenance, and agriculture.

Kubota introduced a 14.9kw(20HP) multi-purpose compact tractor in 1989. This tractor was developed to perform light duty applications requiring loader, backhoe, and scraper capabilities as well as operations that require a 3-point hitch or a rear PTO. The design of tractor, loader, and backhoe was originally targeted to be especially suitable for agricultural and light duty industrial applications. The effort was to improve operating efficiency, ease of operation, and operator comfort. “AUTORETURN” system was adapted into the backhoe. Electro-hydraulic control technology reduces the need for operator skills. The detailed description of this technology as applied to multi-purpose compact tractor is described in the body of this report.

This paper describes a new technology of an electronically controlled transmission for mid-size agricultural tractors. The most notable feature is a electro hydraulically controlled wet multi-disk clutch that is employed to change transmission speeds. This clutch provides for continuous, smooth speed changes regardless of load. The speed change is accomplished by three steps of control: 1) overlap control where the pressure applied to the hydraulic clutch is overlapped, 2) load detection control where the load is determined by monitoring the engine rpm and the governor setting, and 3) shock reduction control where the hydraulic clutch pressure is reduced according to the load.

Kubota has developed a lawn tractor series that will be produced in the USA with good cost to performance ratio and with new features for improved control and comfort. We believe this is the first in the industry of lawn tractor series that features the Cushion Ride system, Auto Throttle Advance system and other features. The new models, that were introduced this spring, were designed concurrently with a horizontal-axis water-cooled diesel engine and a vertical-axis water-cooled gasoline engine. Another new feature is the Electric Power Steering system. I will now discuss these newly introduced technologies.

Recently most of the Japanese tractors (10 - 40kw) have been equipped with an electro-hydraulic system for automatic depth and tilt control for the rotary tiller. This is a typical implement for the Japanese rice farming. The improved performance was needed to deal in the following areas. 1. In the muddy and rough soil pan condition, the tillage depth has to be kept at the satisfactory level while the engine speed stays within the operating range. 2. An automatic depth control must apply to rough tillage without using the conventional depth sensor (i.e. rotary tiller rear cover angle sensor). To meet these requirements, an automatic depth and tilt control system was developed. The two control modes (called MC-AUTO and E-AUTO) for the automatic depth control were developed by combining the conventional control method plus a load control method based on the fuzzy control theory.