Design And Testing Of A New Form Of Positive Displacement Hydraulic Drive To Give Optimum Full Speed Characteristics

Hydrostatic transmission is the only method of providing high output torque throughout an infinitely variable speed range with a constant input velocity. Most drives use separate pumps and motors but an integral pump/motor drive nit would enable many novel configurations to be used. Hydrostatic drives normally employ piston pumps and motors as they operate at higher oil pressures with greater efficiency. Vane pumps deliver a larger volume of oil for their size, so if the vane geometry were improved to contain higher pressures, then a vane pump/motor drive unit would be more competitive. For many applications a variable speed drive spends a greater proportion of running time at the velocity of A ton Unfortunately, the oil velocity, and the sliding velocity of the components, are maximum at this ratio. It is possible, however, using certain inversions to improve these conditions and this thesis follows the development of a new vane geometry and its adaptation into an inversion to form the basis of a variable speed hydrostatic drive. A test drive unit was designed to a given specification and manufactured to evaluate the potential of this novel variable speed drive. The work included investigation into, the port timing for the new vane geometry, the oil flow from the multi-chambered unit, and the development of a self-adjusting seal for the ports. The tests provided velocity ratios within 3% of the theoretical values but the unit only transmitted minimal power due to internal leakage. The faults were analysed and recommendations were made for certain modifications to rectify these shortcomings. Unfortunately, the modifications were too extensive to complete and retest within the time available.