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We have found that most commercially available biodegradable hydraulic oils show low static friction coefficients not depending on the kinds of wet friction materials. Since hydraulic motors of a hydraulic excavator contain wet parking brakes, the most commercially available biodegradable hydraulic oils can not provide enough brake torque capacity to park safely. Furthermore, all kinds of commercially available biodegradable hydraulic oils do not have adequate oil performance for a hydraulic system of construction eq ipment. Thus we have developed a n high performance biodegradable hydraulic oil. To obtain a high static friction coefficient and compatibility with elastomers, a new synthetic ester base fluid has been developed. To improve oxidation stability and to attain compatibility with mineral oil based hydraulic oils,. an additive formulation has also been developed.

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.