Figure 10-15.-Typical vane type of hydraulic motor.
converted into kinetic energy in the form of rotary
motion and force. The air at reduced pressure is
exhausted to the atmosphere. The shaft of the motor is
connected to the unit to be actuated.
Many vane-type motors are capable of providing
rotation in either direction. A motor of this design is
illustrated in figure 10-15, view B. The principle of
operation is the same as that of the vane type of motor
previously described. The two ports may be alternately
used as inlet and outlet, thus providing rotation in either
direction. Note the springs in the slots of the rotors. Their
purpose is to hold the vanes against the housing during
the initial starting of the motor, since no centrifugal force
exists until the rotor begins to rotate. Springs are not
required in vane-type pumps because the drive shaft
provides the initial centrifugal force.
PISTON TYPE. Like piston (reciprocating) type
pumps, the most common design of the piston type of
motor is the axial. This type of motor is the most
commonly used in hydraulic systems.
Although some piston-type motors are controlled
by directional control valves, they are often used in
combination with variable displacement pumps. This
pump-motor combination (hydraulic transmission) is
used to provide a transfer of power between a driving
element (for example, an electric motor or gasoline
engine) and a driven element. Some of the applications
for which hydraulic transmissions may be used are
speed reducer, variable speed drive, constant speed or
constant torque drive, and torque converter. Some
advantages of hydraulic transmission over mechanical
transmission of power are as follows:
Quick easy speed adjustment over a wide range
while the power source is operating at constant
(most efficient) speed. Rapid, smooth accelera-
tion or deceleration.
Control over maximum torque and power.
Cushioning effect to reduce shock loads.
Smoother reversal of motion.
While you are studying the description of the piston
type of motor in the paragraphs below, it may be
necessary to refer back to the piston type of pump for a
review of the operation and particularly the parts
The operation of the axial-piston motor (fig. 10-16)
is similar to that of a radial piston motor. Fluid from the
system flows through one of the ports in the valve plate
and enters the bores of the cylinder block that are open
Figure 10-16.-Example of a piston type of hydraulic motor.