Studies on Feedback Power and Power Transmission Systems of Closed-loop for Rotary-Tilling Tractor

Abstract

Recent popularization of rotary tillage in Japan is quite remarkable along with riding tractors. Insufficient knowledge on the characteristics of power transmission of a rotary tilling tractor may causes inappropriate tractor design, test method and so on. The authors studied the power transmission characteristics including external forces acting on a rear-wheel drive and a four-wheel drive tractor in rotary tillage. The results obtained are as follows:
1) The power transmission system of a rotary tilling tractor forms a closed-loop.
2) The rotary axle power achieves tillage work in which reaction forces from soil act to the machine. The reaction forces as the external forces on the tractor act as the tractor-travel-power calculated by the equation (40-3) and feedback-power calculated by the equation (70) through drive-wheels into the closed-loop transmission system of the tractor.
3) The sum of both tractor-travel-power and feedback-power is named return-power of the rotary tilling tractor. The ratio η_r of the return-power to the rotary axle power is several percent according to the example calculated by the equation (40-2). (6% in example)
4) The ratio of the rotary axle power L₃ to the engine output power L_E in the closed-loop system is L₃/L_E and denoted by η_R for the rear-wheel drive tractor and η_A for the four-wheel drive tractor, and calculated by the equation (42) and (65) respectively. Here η_R and η_A are named “overall power transmission efficiency of the closed-loop system” of the rotary tilling tractor.
5) There is negligible difference between the overall power transmission efficiency η_R of the rear-wheel drive tractor and η_A of the four wheel drive tractor. The velocity difference between the rear and front wheels also gives negligible influence to the overall power transmission efficiency.
6) These efficiencies η_R and η_A are several percent larger than the efficiency η′ in the open-loop system without any feedback from the return-power of the rotary axle power. This percentage will be about a half of the ratio it η_r of the return-power in general.
7) Among many factors in the equation (42) and (65), the efficiencies of each power transmission element η₁, η₂ and so forth, rotary tiller weight W_R, tractor weight W_T are more sensitive than other factors to the changing value of η_R and η_A. Thus, increasing n1, n2 and so forth and decreasing W_R and W_T in the range of tractor motion stability are important design factors to get better overall power transmission efficiency.
8) It is necessary to realize the field condition of rotary tillage which forms a closed-loop power transmission system to conduct the tractor bench test such as durability test. One method for this purpose is to give several percent larger engine power than the original engine power to the transmission input shaft of the tractor. The other is to give additional drive power calculated by the equation (70) to the wheel drive axles by another power source.