Functional Description - Bosch rexroth A21VG 10 Series Instruction Manual

Pump
High-pressure
safeguarding
Version without boost
pump
Control

5.2.2 Functional description

Torque and rotational speed are applied to the drive shaft (1) by an diesel engine.
The drive shaft is connected by splines to the cylinder (8) to set this in motion.
With every revolution, the pistons (9) in the cylinder bores execute one stroke
whose magnitude depends on the setting of the cradle (11). The pistons hold the
slipper pads (10) onto the glide surface of the cradle with the retainer plate (2)
and guide them along. The swashplate setting during a rotation causes each piston
to move over the bottom and top dead centers and back to its initial position.
Here, hydraulic fluid is fed in and drained out through the two control slots in the
control plate (7) according to the stroke displacement. On the high-pressure side
(5) the hydraulic fluid is pushed out of the cylinder chamber and into the hydraulic
system by the pistons. At the same time, hydraulic fluid flows into the growing
piston chamber on the low-pressure side (6). In a closed circuit, supported by the
return and boost pressure.
The four high-pressure relief valves protect the hydrostatic transmission (pump and
engine) against overloading. They limit the maximum pressure in the relevant
high-pressure line and at the same time act as boost valves. High-pressure relief
valves are not working valves and are only suitable for pressure spikes or high rates
of pressure change.
In order to replenish internal leakage in the variable double pump and consumers,
port G must be connected to an external source of boost pressure. The boost
pressure-relief valve is integrated.
The swivel angle of the cradle (11) is steplessly varied. Controlling the swivel
angle of the swashplate changes the piston stroke and therefore the displacement.
Adjusting the swashplate through the neutral position will change the direction of
flow (making reversing operation possible). The swivel angle is controlled
hydraulically by means of the stroking piston. The cradle is mounted in swivel
bearings for easy motion and the neutral position is spring-centered. Increasing the
swivel angle increases the displacement; reducing the angle results in a
corresponding reduction in displacement.
Various control devices are available depending on requirements. Information
about this can be found in data sheet 93223.
RE 93223-01-B/09.2020, A21VG Series 10, Bosch Rexroth Corporation
Product description 19/56