A Research on Thrust Ratio of Front Wheels to Rear Wheels of Front Wheel Assist Tractor

Based on dynamic analysis of Front wheel Assist (FWA) Tractor,a method for calculating the thrust Ratio of front wheels to rear wheels is described in this paper,a mathematical model is established and verified,The article introduces the definition of thrust ratio of front wheels to rear wheels,which is an important parameter affecting the tractive performance of FWA tractor.

PHENOMENON OF CARVED DRIVING WHEELS

A newly found phenomenon of carved driving wheels of a rear-wheel-drive tractor used in an airport is discussed. The circum of every driving wheel is damaged at three regions, which distribute regularly and uniformly. Everyday, the tractor tows a trailer which are times heavier than the tractor, and moves on the same road in the airport. The phenomenon is explained by the torsional self-excited vibration system of the powertrain. The simplified torsional vibration system is discribed by a 2-order ordinary differential equation, which has a limit circle. Experiments and numerical simulations show the followings： Because of the heavy trailer, the slip ratio of the tractor＇s driving wheels is very large. Therefore, there is severe torsional self-excited vibration in the tractor＇s drivetrain, and the self-excited vibration results in severe and regular fluctuations of the rear wheel＇s velocity. The severe fluctuations in velocity fastens the damage of the driving wheels. At the same time, the time interval in which an arbitrary point in the circum of the driving wheel contacts with the road twice is two times more than the period of the torsional self-excited vibration, and this times explained the existence of three damaged regions. At last, it points out that the phenomenon can be avoided when the torsional damping is large enough.

Fuel economy of multiple conditions self-adaptive tractors with hydro-mechanical CVT

Fuel economy is one of the most important properties of wheeled tractors.To improve the fuel economy,it is necessary to improve the engine fuel economy and the tractive efficiency of the driving mechanism.By analyzing the fuel economy evaluation index of wheeled tractors,the correlation among the tractor specific fuel consumption,the engine effective specific fuel consumption and the tractive efficiency of the driving mechanism were clarified in this paper.A tractor with a new type of hydro-mechanical continuously variable transmission(HMCVT)was designed and its whole model was established too.On the basis of each module’s simulation model,the binary speed ratio matching simulation model of the gearbox-engine system was obtained by the control system reconstruction,and the fuel economy simulation analysis of the wheeled tractor with HMCVT was carried out under the two typical working conditions of plowing and sowing.Compared with the current national standard,the fuel economy of the newly designed wheeled tractors with the power of 130 kW was 380 g/(kW·h),specific fuel consumption was reduced by 21.1%.The results showed that the new tractor fuel economy was greatly improved.Further,automatic navigation technology can be combined with the self-adaptive tractors to adapt to different working conditions and achieve the optimal fuel economy,which can be applied in precision agriculture.