HST Motor
Since either of the main hydraulic lines can be high pressure, four charge check valves are used to direct the charge supply into the low pressure line. These check valves (located in the pump end cap) also incorporate the high pressure relief valve function. Any charge flow not being used for the closed circuit is discharged over a direct operating charge relief valve, through the pump and motor housings, and back to the tank.
The outer ring of the gear wheel set of HST motor is stationary part of the motor housing. This ring has internal teeth which mesh with teeth on a gear wheel or rotor which rolls inside the ring. The motion of the rotor is transmitted to the output shaft through a drive. The drive consists of a movable shaft extension with crowned involute splines at either end. These splines match the corresponding tooth system of the output shaft and rotor, resulting in a toothed coupling between rotor and drive and between drive and shaft respectively. As it rotates, the rotor causes continuous opening and closing of tooth spaces. Four of these spaces are subjected to fluid pressure, and the opposed four are connected to return line.
High Pressure Relief Valves Four combination check /high pressure relief valves are provided in the pump end cap for overload protection. These cartridge type relief valves are factory set, and are not field adjustable.
Direct Displacement Control The direct displacement control (DDC) is located on either side of the pump, and provides a simple method of control. Movement of the swashplate control shaft produces a proportional swashplate movement and change in pump flow and/or motor shaft speed and direction. The vehicle control system should be designed to return the swashplate to its neutral position.
Outer ring
Rotor
Zero Position
Bypass Valve In some applications it is desirable to bypass fluid around the pump allowing, for example, a vehicle to be moved short distance at low speed without running the engine. This is accomplished by manually operated bypass valves incorporated into the charge check/high pressure relief valves in the pump. When open (unscrewed 4 turns maximum), these valves connect both sides of the pump/motor closed circuit, allowing the motor to turn. Both valves must be opened for bypass operation and must be fully closed for normal operation. The engine should be shut down when opening or closing the bypass valves.
1/18 Shaft Rotation
1/9 Shaft Rotation IGAT074IP
Above pictures show three positions of the rotor, the corresponding rotor center movements, and the locations of pressure and return chambers respectively. Hydraulic & Hydrostatic Systems
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Systems Operation
