Hydrostatic Transmissions; General - MTD Garden Tractors User Manual

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HYDROSTATIC TRANSMISSIONS

6-1.

GENERAL.

For further information regarding this section,
refer to the technical service video "Hydrostatic
Drive Systems."
6-1.1 The Eaton Light Duty Hydrostatic Transmis-
sion consists of a variable displacement radial
ball piston hydraulic pump, a fixed displace-
ment radial ball piston hydraulic motor and a
system of valves all contained in one housing.
It can be used in many different types of appli-
cations where variable output speed is a
requirement. It has many advantages over
other variable speed drives (electric and
mechanical) and gear type transmissions.
1. Response. These transmissions respond
faster than other type of power-transmit-
ting system.
2. Precise speed. Has the capability of main-
taining precise speed under varying load
conditions.
3. Ease of operation. One lever controls
direction and speed smoothly without gear
change.
4. Low maintenance. Simple design keeps
maintenance to a minimum.
5. Increased productivity and versatility. It
allows complete matching or power to
load.
6. Self contained. There are no external pres-
sure lines, separate drive components,
etc.
7. Simplified final product design. It reduces
the number of mechanical drive compo-
nents.
8. Positive braking action. The lever that con-
trols speed also provides braking. The out-
put shaft speed decreases as lever is
moved toward neutral. With lever in neu-
tral, output stops.
6-1.2 Smooth Performance. This graph shows the
difference in operation of the hydrostatic trans-
mission compared to a speed gear transmis-
sion. The smooth curve represents the uniform
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matching of torque and speed requirements by
the hydrostatic transmission.
The gear transmission has only three points of
peak power while the hydrostatic transmission
offers a continuous curve without peaks and
valleys. You do not have to stop and shift down
to gain more torque, just move the control lever
toward neutral and the output torque capability
increases. See Figure 6-1.
6-1.3 Simplified Operation. A single control lever
connected to the pump section controls both
speed and direction of the transmission output
shaft. Infinite speed control is achieved by
varying the displacement ratios between the
pump and motor. Moving the control lever from
neutral to forward produces one direction of
output shaft rotation. When the lever is in neu-
tral position, output shaft rotation stops. Mov-
ing the lever from neutral to reverse produces
the opposite output shaft rotation from the for-
ward position. Output shaft speed increases as
the lever is moved from neutral.
6-1.4 Factors That May Affect Neutral Settings.
1. Unit efficiency. The more efficient a unit is,
the narrower the neutral band width will be
in a direct acting control swashplate,
unless some neutral valving device is
used.
6-1
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