STRUCTURE AND FUNCTION

Principle of operation

•The PVH Series travel motor consists of the fixed part which consists of hydraulic motor (2) and hydraulic valve and the rotary part which consists of simple planetary reduction gear unit (1).

a b1consists of 4 planetary gears and b2 consists of 3 planetary gears.

1.Simple planetary reduction gear unit

2.Hydraulic motor

3.Hydraulic motor Automatic 1st valve

4.Counterbalance valve

5.No. 2 reduction

1.Reduction gear unit

Function

•The reduction gear unit consists of 2 stages of simple planetary gears. It converts the high-speed revolution from the hydraulic motor into low-speed higher torque to obtain revolution of the case.

Operation

•In the following figure, gear s2 is coupled with the hydraulic motor output shaft by spline (of by a shaft). The speed of rotation of gear s2 is reduced by gears s2, b2 and a2.

•The reduced revolution is further reduced through gears s1, b1 and a1, coupled with carrier 2 (5) by spline.

•This revolution is transmitted through internal gears a1 and a2 to the rotary part and used for travel.

•The reduction ratio of the 2 stages of the simple planetary gears is generally given by the following expression.

R = Zs1 (Zs1 + Za1) x Zs2 (Zs2 + Za2)

Zs1, Zs2: Number of teeth of gears s1 and s2

Za1, Za2: Number of teeth of gears a1 and a2

•Since the body of the PHV Series travel motor revolves, the above reduction ratio is given by the following expression.

R' = 1/(1-1/R)

2.Hydraulic motor

Function

•This hydraulic motor is an axial piston motor (rotary cylinder swash plate type). It converts the hydraulic energy from the pump into rotary movement.

Operation

•The hydraulic oil flowing in through the hydraulic valve is supplied to valve plate (3).

•The hydraulic oil supplied to port A flows into the cylinder port in cylinder barrel (2) corresponding to port A and pushes piston (1).

•The pushing force of the above hydraulic oil is converted through rocker cam (4) into rotary force and output to shaft (5) coupled with cylinder barrel (2).

•The return oil in the cylinder port flows out through port B of valve plate.

•When the motor revolves in reverse, the hydraulic oil flows in through port B and the return oil flows out through port A

Structure And Function

Operation of 2nd motor

•Rocker cam (4) has 2 faces of A and B on the opposite side to the face on which shoe (6) slides. It is supported on 2 balls (7) fixed to body (8).

•Balls (7) are installed a little higher than the axis. Accordingly, in the 1st gear speed, face A is pressed against body (8) by the hydraulic force applied to piston (1) and the force of spring (9), and swash plate angle is set to a and the delivery of the motor is increased.

•If the 2nd gear lever is set, hydraulic oil P is led through the 2nd spool into control chamber (10).

•The control piston (11) moves to the right ( ) until face Bof rocker cam (4) contacts the travel motor body (8), and then rocker cam (4) is fixed at swash plate angle b. At this time, the delivery of the motor is reduced.

•While the engine is stopped, control chamber (10) is connected through the 2nd spool to the drain port.

•As a result, rocker cam (4) is returned to the 1st gear speed position by spring (9), thus the 1st gear speed is always selected when the machine starts travel.

3.Hydraulic valve

1)Counterbalance valve

Operation

•If the hydraulic oil is supplied through port A, it pushes check valve (2) open and flows in port A’ on the inlet side of the hydraulic motor.

•On the other hand, the hydraulic oil flows through choke C into chamber D and moves spool (3) to the right against spring (4).

•As a result, the oil on the return side of the hydraulic motor flows in through port B' and returns through body (1) and opening E of spool (3) to port B to rotates the hydraulic motor.

•If the hydraulic oil is supplied through port B, each part operates in the opposite direction and the hydraulic motor revolves in reverse.

•If the hydraulic oil from port A is stopped, spool (3) moved to the (3) is returned to the left by the force of spring (4).

•At this time, the oil in chamber D controls the speed of spool (3) returning to the left with choke C

•Even if the hydraulic oil from port A is stopped, the hydraulic motor continues revolution by inertia.

•At this time, the return oil is controlled gradually by the changing speed and shape of the cut of spool (3) to stop the hydraulic motor smoothly.

2)Automatic 1st valve

Operation

•If the 2nd pilot switch is turned ON, the 2nd pilot pressure is led through port PP into hydraulic pressure pilot (1) and force F1 is generated.

•Force F1 moves automatic 1st valve (5) to the right against force F4 and sets the system in the 2nd gear speed.

•On the other hand, the drive pressure is led into pilots (2) and (3) to generate forces F2 and F3

•Since the pressure receiving area of hydraulic pilot (3) is larger than that of (2), force F3 is larger than force F2 . As the drive pressure is increased, the difference between forces F2 and F3 is increased.

•If drive pressure is increased from the 2nd gear speed level to the set pressure of the 1st gear speed, the total of rightward forces F1 and F2 is exceeded by the total leftward forces F3 and F4. As a result, automatic 1st valve (5) moves to the left and sets the system in the 1st gear speed.

•If drive pressure is reduced from the 1st gear speed level to the set pressure of the 2nd gear speed, the total of rightward forces F1 and F2 exceeds the total leftward forces F3 and F4. As a result, automatic 1st valve (5) moves to the right and set the system in the 2nd gear speed.

4.Parking brake

Function

•When the travel motor is stopped, the parking brake fixes the hydraulic motor output shaft mechanically.

Operation

•While the hydraulic oil is not supplied to port A or B, spring (7) presses brake piston to the left.

•At this time, disc plate (3) fixed by the semi lunar groove of cylinder barrel (1) is fixed between steel plate (4) which is also fixed to body (2).

•As a result, cylinder barrel (1) cannot revolve because of the friction force of disc plate (3) and steel plate (4) and the hydraulic motor output shaft is fixed.

•If the hydraulic oil is supplied to port A or B, hydraulic oil P is led into chamber (5). Hydraulic oil P moves brake piston (6) to the right against the force of spring (7).

•As a result, disc plate (3) and steel plate (4) is released and the friction force is lost and cylinder barrel (7) can revolve.

Structure And Function

Cylinders

STRUCTURE AND FUNCTION CYLINDERS

Boom swing cylinder

Blade cylinder

Variable gauge cylinder