An experimental vehicle to harvest whole-stalk sweet sorghum was designed by a university research team. At present, the harvester is a pull-type machine, meaning it is towed behind a tractor and powered via a universal joint driveline. The decision has been made to convert the harvester to a self-propelled machine. The configuration chosen is a […]
Read More…Category: Hydrostatic Transmissions
Closed-Circuit Closed-Loop Hydrostatic Transmission
The hydrostatic transmission, shown in Fig. 6.28, is operating under a constant load. Speed is set by the command voltage at 1000 rpm. The feedback transducer is a tachometer generator, which produces a voltage proportional to motor rpm. The load starts to increase, pressure increases, and the pump and motor volumetric efficiencies decrease. The motor […]
Read More…Servo Pump Operated with Flapper Nozzle Torque Motor
The servo pump shown in Fig. 6.27 is like that shown in Fig. 6.26, except a torque motor is used to position the spool of the servo valve. A torque motor rotates through several degrees of rotation, when a current is passed through the winding. The torque motor shown has a flapper attached to the […]
Read More…Manually Operated Servo Pump
Before beginning our discussion of closed-loop hydrostatic transmissions, it is necessary to first learn how a servo-controlled pump operates. A variable displacement axial piston pump will be used as an illustration. When configured for servo control, this pump will have a control piston mounted in the pump housing. When the control piston extends, it moves […]
Read More…Four-Wheel Drive Vehicle Hydrostatic Transmission
A configuration where all four wheels are powered is shown in Fig. 6.18. A single pump provides flow to four motors. This machine can be built with two or four steerable wheels. On three-wheel- and four-wheel-drive vehicles, the front wheels are configured to have a tangential velocity slightly higher (1 or 2%) than the rear […]
Read More…Three-Wheel Vehicle Hydrostatic Drive
The vehicle shown in Fig. 6.17 has three wheel motors supplied by the same pump. In the design of such a vehicle, care must be taken to size the motors and final drives such that the tangential velocity of the front and rear wheels is approximately equal. The flow does divide in such a manner […]
Read More…Vehicle with Two Hydrostatic Transmissions
The vehicle shown in Fig. 6.14 has a separate in-line hydrostatic transmission for each drive wheel. The engine delivers power via a universal joint driveline to a right-angle drive gearbox. Each side of this gearbox powers an inline hydrostatic transmission. The wheel is connected to the hydraulic motor. A final drive may or may not […]
Read More…Hydrostatic Transmission with Variable Speed Motors
As previously mentioned, it is often necessary to provide a road speed, so the machine can be moved on the highway between job sites. (Generally, these travel distances are only a few miles, so road speeds in the range of 12 to 17 mph are satisfactory.) Shifting a transmission to increase pump speed is one […]
Read More…Two Wheel Motors Hydrostatic Transmission
Wheel motors, mounted at both rear wheels (Fig. 6.12), is a variation of the configuration shown in Fig. 6.11. This arrangement eliminates the universal joint driveline, differential, and rear axle, with resultant cost and weight savings. Because the pump has low inertia, it is often possible to provide enough starting torque to start the engine […]
Read More…Hydrostatic Transmissions Advantages
A hydrostatic transmission provides improved maneuverability, but at a cost. The efficiency of a hydrostatic transmission is always lower than a discrete-gear transmission. A discrete-gear transmission will typically have an efficiency of 95% or greater, meaning that 95% of the input energy is delivered to the load (wheels). A hydrostatic transmission has an efficiency of […]
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