General; Gear Pump; Axial Piston Pump - Husqvarna PT26D Workshop Manual

General

The machine has two hydraulic pumps with a
common hydraulic tank. The pump for work-
ing hydraulics (8) is driven from the engine's
timing gear and supplies system compo-
nents, which require hydraulic pressure irre-
spective of whether the machine is driven or
stationary. The pump is a gearwheel-pump. It
also supplies the drive system pump with
feed pressure 1.8 MPa (18 bar).
The hydraulic pump for the drive system (9)
is driven by an axle with two flexible clutches
from the engine's flywheel. It is an axial pis-
ton pump, that has a pivot box. By setting the
pivot box, the pump can be controlled to give
a variable flow with different directions. You
can then adjust the speed and drive forwards
or reverse. The pivot box is controlled by a
mechanical linkage from the drive pedals.
The hydraulic motors (7), one for each wheel,
are inverted gear motors. The displacement
of the pumps is different for forwards and
reverse. Even though the motors work in both
directions of rotation they are marked CV
clockwise), depending on the inner clutch.

Gear pump

The oil is transported from the inlet port to the
output port in the tooth gaps against the
housing wall. The play between the tooth
tops and the housing wall is the smallest pos-
sible so that no oil leaks through. The pump
flow (and thus pressure) depends on the
speed. That's why there must always be a
pressure limiting overflow vent in the pump's
outlet circuit.

Axial piston pump

The pump is of annular piston type with varia-
ble displacement. Annular piston pump dis-
placement varies with the position of the pivot
box. Displacement is determined by the pivot
box angle in relation to the drive shaft. When
the angle is 90°, displacement is zero. When
the pump is in operation, the drive shaft and
the cylinder drum rotate with the pistons. If
the pivot box is angled out, the pistons start
running in the cylinder drum. The stroke
increases as the pivot box is angled out. The
pump flow direction is changed by angling
out the pivot box to different directions.
A certain amount of oil leaks through the pis-
tons when they run. This oil cools and lubri-
cates the pump, after which it is led to the
tank.
44
English-
DESIGN AND FUNCTION
Gear pump
1. Pivot box
2. Drive shaft
Axial piston pump
8043-173
3. Piston
4. Cylinder drum
8043-239