MB2 - Maxma · Title: MB2.cdr Author: james Created Date: 5/4/2009 5:44:06 PM
Hydraulic Circuit (Forward, Neutral, Reverse) - Maxma · Hydraulic Circuit (Forward, Neutral,...
Transcript of Hydraulic Circuit (Forward, Neutral, Reverse) - Maxma · Hydraulic Circuit (Forward, Neutral,...
Hydraulic Circuit(Forward, Neutral, Reverse)
INTRODUCTION
Hydrostatic transmission are hydraulic systems consisting of two main components: hydraulic
pump, hydraulic motor. The pump transforms mechanical energy in hydraulic energy transferred
to the motor, which converts again the hydraulic energy in mechanical one, obtaining finally a
power transmission.
The hydrostatic transmission offers infinite control of speed and direction. The operator has
complete control of the system with one lever for starting, stopping, forward motion or reverse
motion. The lever controls the position of the swash plate of the pump Tilting the swash plate of
the variable pump produces a certain flow from the pump; this flow is transferred through high
pressure lines to the motor. The volume of flow from the pump in connection with displacement of
the motor will determine the speed of the output shaft of the motor.
Moving the swash plate of the pump to the opposite side of the neutral position, the flow from the
pump is reversed and the output shaft of the motor turns in the opposite direction. Therefore
speed of the output shaft is controlled by adjusting the control lever of the pump which acts
proportionally the swash plate, varying the displacement. Working pressure is determined by the
external load on the motor and this, together with flow produced by the pump, establishes the
power demanded by the system.
Standard Close Loop Circuit Diagram
Primary System Components
In order to avoid cavitation problems, it is foreseen a charge pump to boost all possible
suction lines. The charge pump is mounted on the rear of the main pump and draws oil
from the reservoir through a filter and provides a flow of oil under pressure to the main
pump. Charge flow exceeding the need of the circuit is by-passed through an auxiliary
relief valve normally calibrated at 13 bar.
Two check valves permit to boost the low pressure line only, isolating the high pressure
line: A and B ports are alternatively working at high pressure in function of flow direction,
which depends from the position of the main pump swash plate.
There are also two main relief valves calibrated at the highest working pressure of the
circuit: in case the external conditions force the hydrostatic transmission to overcome
the max. allowable pressure, one of the two relief valves corresponding to the high
pressure line (A or B) automatically dumps oil to the other line, preventing sustained
abnormal pressure surges in the high pressure line and cavitation in the other line.
A shuttle valve makes possible to leak a certain amount of flow to reservoir in order to
assure the oil replacement inside the closed circuit, the shuttle valve works in
combination with another relief valve calibrated normally at 11 bar. The shuttle valve
allows the flow from the charge pump to flow through the opposite check valve to
replenish internal leakage beyond what is normally supplied for oil replacement to cool
and lubricate the circuit.
At same time the relief valve combinated with shuttle valve and calibrated at 11 bar
avoids pressure dumping in the corresponding line.
The charge pump also provides oil to the servo-valve which controls the swash plate
angle of the main pump: the main pump is put into operation by a signal to the servo-
valve from the operator, and the pump is stroked into forward or reverse. At this time, the
servo-valve directs the flow from the charge pump to one servo-cylinder, which is linked
to the swash plate. The control pressure forces one of the two servo-cylinders to tilt the
swash plate in one side and it causes a high pressure flow of oil to the motor in one line
which starts rotating in one direction.
The servo-valve determines the amount of tilt of the swash plate in one or the other
direction, and it can be varied by the operator; this allows variable speed and control of
the system.
Hydraulic Circuit
Axial Piston Variable Displacement Pump
General Description
Axial piston variable displacement pump swash plate design for hydrostatic
transmission ir closed circuit.
Flow is proportional to shaft speed and pump displacement, this can be infinitely varied
as per the operator request.
Flow direction is reversed by tilting the swash plate to the opposite side of the neutral
displacement position.
Features
Axial piston variable displacement pumps are welt-engineered and easy to handle, with
high reliability proven in laboratory and field.
The full length shaft with- a highly efficient tapered roller bearing arrangement offers a
high loading capacity for external radial forces.
The hydro-mechanical servo displacement control maintains the selected swash plate
position and hence pump displacement.
The low noise level, the high ratio power / weight permit to approach the widest range of
applications
Axial Piston Variable Displacement Pump
Servo Displacement Control - Reversing time
Regulated by the control handle on the servo valve, the swashpalte can be infinitely
varied in both directions with the help of the servosystem.
The pump displacement results from the control handle position.
Time for the directional change of max flow in one side to max flow in the other side
(across neutral position) is depending on the size of the control orifice fitted in the supply
port to the servo valve.
The values given assume movement of the control handle directly from one end position
to the other.
Adjustment time of handle: < minimum reversing time
Operating pressure: 210 bar
Speed: 1450 rev / min2Viscosity: 35 mm / sec
Axial Piston Variable Displacement Pump
Effcien curves
Legend: Series1 = Total efficiency at 350 barSeries2 = Total efficiency at 210 barSeries3 = Volumetric efficiency at 350 barSeries4 = Volumetric efficiency at 210 bar
Axial Piston Variable Displacement Pump
Effcien curves
Legend: Series1 = Total efficiency at 350 barSeries2 = Total efficiency at 210 barSeries3 = Volumetric efficiency at 350 barSeries4 = Volumetric efficiency at 210 bar
Axial Piston Variable Displacement Pump
Effcien curves
Legend: Series1 = Total efficiency at 350 barSeries2 = Total efficiency at 210 barSeries3 = Volumetric efficiency at 350 barSeries4 = Volumetric efficiency at 210 bar
Axial Piston Variable Displacement Pump
Effcien curves
Legend: Series1 = Total efficiency at 350 barSeries2 = Total efficiency at 210 barSeries3 = Volumetric efficiency at 350 barSeries4 = Volumetric efficiency at 210 bar
Axial Piston Variable Displacement Pump
Axial Piston Variable Displacement Pump
Axial Piston Variable Displacement Pump
Outline Drawing of Axial PistonVariable Displacement Pump
Causes high pressure in "A" port in anticlockwise pump
B: Causes high pressure in "B" port in clockwise pump
Causes high pressure in "B" port in anticlockwise pump
A: Causes high pressure in "A" port in clockwise pump
Direction of flow related to position of control lever:
Axial Piston Fixed Displacement Motor
General Description
These types of hydraulic motors are of swash plate design with fixed displacement. The
output speed is proportional to the inlet flow and inversely proportional to displacement
of the motor.
The output torque is proportional to the displacement and the drop pressure across the
motor.
The direction of output shaft rotation depends upon the - flow direction, which port is
boosted by high pressure. These motors are mainly designed for closed circuit
application, because a purge valve is normally installed on the rear of the port block.
Features
These motors have high performances and easy to handle, because of the very high
ratio power / weight.
The shaft is supported by two roller bearings and the torque is transferred by the cylinder
block to the shaft through a splined connection.
High efficiency is guaranteed by the simple construction and the accurate mechanical
design, combined with the constant quality of production and assembling.
High case pressure can be achieved because of the special design of the front shaft seal.
AXIAL PISTON FIXED DISPLACEMENT SWASH PLATE MOTOR
Axial Piston Fixed Displacement Motor
Axial Piston Fixed Displacement Motor
Motor dimensions
Outline Drawing of Axial PistonFixed Displacement Motor (valve block)
VALVE BLOCK
VALVE BLOCK
The valve block is installed on the rear cover of the motor.
This block has induded two relief valves which protect the circuit preventing sustained
pressure surges in the high pressure line and cavitation in the other line.
A shuttle valve makes possible to leak a certain amount of flow to reservoir in order to assure
the oil replacement inside the dosed circuit, the shuttle valve works in combination with
another relief valve calibrated normally at 11 bar, which avoids pressure dumping in the
corresponding line.
VALVE BLOGK WITH BY-PASS VALVE
This valve assures the same performances of the standard one, further on the by-pass makes
possible the connection of two high pressure lines; so that the entire hydrostatic transmission is
in idle position.