Hydraulic Drive; Brake Valve, Relief Valve; Two-Speed Select Mechanism; Parking Brake - Kubota KX080-3 Workshop Manual

WSM KX080-3 Mechanism

2. Hydraulic drive

This chapter describes the hydraulic motor, brake valve, parking brake and the hydraulic motor's two-speed
select mechanism, which are all used in the hydraulic drive.
1) Functions
1-1 Hydraulic motor
The hydraulic motor is of swash-plate axial piston type. The force of pressure oil coming from the pump
is converted to rotational movement.
1-2 Brake valve
(1) Inertial force is controlled in stopping the hydraulic motor. This helps bring the motor to a smooth halt.
(2) When the hydraulic motor is activated by an external force, this valve keeps the motor from running
out of control. In other words, hydraulic cavitation can be avoided.
(3) The valve also keeps off an excessive pressure that would occur in case of a sudden hydraulic motor
halt.
1-3 Relief valve
(1) The hydraulic motor gives out some jerk when it gets started and stopped. This valve is intended to
ease such shock as well as to avoid cavitation due to the relief action (lower braking noise).
(2) The relief valve suppresses a sudden pressure upon the hydraulic motor below its preset pressure
level. In this way, the hydraulic motor is protected against damages.

1-4 Two-speed select mechanism

The mechanism is designed to select the hydraulic motor output in two stages: high-speed, low-torque
output, and low-speed, high-torque output.

1-5 Parking brake

The parking brake keeps the at-rest hydraulic motor from starting by an external force. This friction disc
type brake is integrated with the hydraulic motor.
2) Principle and behavior
(104)
(105)
(109)
2-1 Hydraulic motor
(103)
(102)
IV-M-99
Pressure oil from the hydraulic pump flows into
the rear flange (301) of the GM motor. The pres-
sure oil is then introduced through the brake valve
and timing plate (109) into the cylinder block
(104).
The pressure oil is let into only one side of the Y1-
Y2 line that is drawn from the top dead center to
the bottom dead center of the stroke of piston
(105).
The pressure oil pushes the piston (105) in ques-
tion, which generates the force F (= P x A). This
force then acts on the slant face of swash-plate
(103). By the slanting angle
divided into component forces F2 and F3. Among
them, the radial component force F3 generates a
torque (= F3 x ri). The resultant force T (=
x ri)) of the torque of each piston (105) becomes
the turning force of the hydraulic motor. The latter
force is transmitted through the piston (105) to
drive the cylinder block (104) and shaft (102).
(102) Shaft
(103) Swash-plate
(104) Cylinder block
(105) Piston
(109) Timing plate
IV Hydraulic System
, the force F is
(F3