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Axial Piston Pumps, Motors, and Transmissions
Series 70 / 15 Series
Description of Operation for Series 70 and 15 Series Products
Basic Pump/Motor Circuit
A typical hydrostatic transmission consists of a vari-
able displacement axial piston pump connected in
closed circuit to a fixed displacement axial piston
motor. There are two basic arrangements of hydro-
static transmissions:
1. A split system in which the pump and motor are
mounted separately. Pressurized fluid is con-
tained and directed through hoses or tubing.
2. An integral system in which the pump and motor
are contained in the same housing with pressur-
ized fluid internally contained.
The variable pump (PV) is driven by a prime mover,
typically an internal combustion engine. The fixed
motor (MF) drives the vehicle transmission or other
work function. Direction of rotation and speed of the
motor shaft depends on the output flow of the pump.
System pressure is dependent upon vehicle tractive
resistance or other work function requirements.
Variable Displacement Pump
The variable displacement pump (PV) is an axial
piston design. It has a mechanical control connected
to the swashplate. In operation, as the machine
operator moves the control handle, the swashplate
tilts. This tilting results in fluid flow from the pump, with
the amount of fluid flow being proportional to the
swashplate tilt angle. The direction in which fluid is
pumped depends on input rotation and the side of
neutral that the swashplate is tilted or stroked. Re-
versing the swashplate angle reverses the flow of
fluid.
Fixed Displacement Motor
The fixed displacement motor (MF) is an axial piston
motor that has the swashplate at a fixed angle, giving
it a fixed displacement. The direction of motor shaft
rotation depends on the direction of fluid flow through
the motor. Changing the direction of fluid flow through
the motor causes opposite motor shaft rotation.
Direct Displacement Control
The variable displacement pump swashplate in both
the Series 70 and 15 Series transmissions is directly
controlled. For the Series 70 pump, any movement of
the control shaft results in a proportional movement of
the swashplate, with 21 degrees of control rotation
resulting in 15 degrees of swashplate rotation. For the
15 Series pump, any movement of the control shaft
results in equivalent swashplate movement, with 15
degrees of control shaft rotation resulting in 15 de-
grees of swashplate rotation.
Basic Closed Circuit
RESERVOIR
INPUT
PV
OUTPUT
MF
CASE DRAIN
FLOW (BI-DIRECTIONAL)
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