Bad Boy 1022H - HST System Theory of Operation

B22W-202010
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CHAPTER 4 HST SYSTEM1022H TRACTOR
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6. THEORY OF OPERATION - HYDROSTATIC SYSTEM
6.1 PUMP, MOTOR CIRCUIT (VARIABLE PUMP)
The hydrostatic system provides a means to transfer. Power from the engine to the nal drive to the wheels. It
also provides innitely variable speed control, forward or reverse, by foot pedal operation.
<Figure-a> show a rotation part of AXIAL PISTON PUMP (SWASH PLATE TYPE) With 9 pistons inserted to
cylinder block. When shaft rotates, so does cylinder block together. (Swash plate does not rotate). If Shaft Center
and Swash Plate are connected with each other vertically, as shown in <Figure-a>, Space A and B (Cylindrical
space of Cylinder Block) have the same volume so that they do not work suction and discharge, therefore there
is no pump action.
If rotating the Swash Plate ask as much as 'a', as shown in <Figure-b> each volume of Space A and B is changed
as shown in the drawing (A>B). In this condition, if rotating the shaft in the direction of θ, oil is sucked betweens
180° where piston moves from B to A.
So, if connecting suction and discharge pipe to two crescent ports, it becomes one PUMP.
In this case, Ps becomes a suction port and Pd becomes a discharge port. On the contrary, if rotating the Swash
towards, Ps becomes a discharge port and Pd becomes a suction port.
The next is about discharge capacity. As described above, in case of 'α=0', there is no suction and discharge.
The bigger the volumetric difference between Space A and B is (That is to say, as much as its slant angel).the
bigger its ow rate is.
In this case, discharge capacity of pump is calculated as follows:
Q = D PMAX · tan a · N in · η vp / tan (a Max) = (cm
3
/min)
D PMAX : Max. Capacity of PUMP (cm
3
/rev)
a : Swivel Angle of Swash Plate (deg)
a MaX : Max. Inclination Angle of Swash Plate (Swivel angle) (deg)
N in : Pump Input Rotation (rpm)
η vp : Pump Volume Efciency (%)
※ Each operation drawing is a schematic diagram, so there may be slightly differences in real product, size
and shape.
K19W085A
Figure-a
K19W086A
Figure-b
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