Question: A mobile machine has two hydrostatic transmissions. One hydrostatic transmission propels the machine, and the other transmission powers a rotary mechanism on the machine. A diesel engine drives a twin pump mount at 2000 rpm. Pump A (propel transmission) is mounted on the right side of the pump mount, and Pump B (rotary mechanism transmission) is mounted on the left side. These transmissions are specified as follows:
Pump A: Variable displacement pump 4.57 in3/rev maximum displacement Fixed displacement motor 4.57 in3/rev displacement Charge pump displacement 1.03 in3/rev Charge pump relief 350 psi Case pressure 40 psi
Pump B: Fixed displacement pump 2.56 in3/rev displacement Fixed displacement motor 2.56 in3/rev displacement Charge pump displacement 0.86 in3/rev Charge pump relief 290 psi Case pressure 40 psi
Average operating pressure for the Pump A circuit is estimated to be 1600 psi. Pump and motor overall efficiencies are estimated to be 93.5%, and volumetric efficiencies are estimated to be 97.5%. The pump will operate most of the time at 75% of maximum displacement. Average operating pressure for the Pump B circuit is estimated to be 3600 psi. Pump and motor overall efficiencies are estimated to be 92% and volumetric efficiencies are estimated to be 95.5%. Maximum ambient temperature is 95°F, and we must design for a maximum fluid temperature of 140°F. You may use the following assumptions:
1. The overall heat transfer coefficient for all heat transfer surfaces is U = 30 Btu/h⋅ft2⋅F.
2. 25% of the total heat generated is dissipated from the surface of the lines and components:
a. Calculate total heat generated by the two hydrostatic transmissions.
b. Design the reservoir with a capacity equal to four times the total reservoir flow (both circuits). You may use any shape you like. Calculate the total heat dissipated by the system (qsys) and reservoir (qres). If additional heat exchange is needed, write the specifications for a finned-tube oil cooler for the machine.