SECTION 3. MAJOR COMPONENT OF THE HYDRAULIC SYSTEM

1.HYDRAULIC SYSTEM

General Description

This valve is installed to bypass working fluid of a specified pressure from the main circuit into the PTO circuit through a fixed orifice.It includes a changeover valve for engaging and disengage the PTO clutch by means of a solenoid and a sequential valve for PTO circuit's over the main circuit.

(1) Flow-divider

(2) Transmission case

(3) Relief Valve

(4) Pressure control valve

(1)Solenoid

This solenoid is switched on or off by operating the PTO switch.With this lever operation,the solenoid shifts the changeover valve to the left or the right to bypass or block the flow to port B.

(2)PTO

Changeover Valve

This valve is composed of the spool and spring.When the solenoid is switched on,the spool is moved to the left by overcoming the spring force and allows the fluid from the pump to flow from port P to port B through the fixed orifice.

-When the solenoid is switched 「ON」

The fluid from the pump flows to port B through port P,the pressure-reducing valve,and the changeover valve.

The pressure of the PTO clutch circuit and that of passage(2) are the same and will be set as P₂.The pressurized fluid acts on the left-hand side of the valve,passing through port ; its pressure will be set as P₁.

As passage (1) and passage (2) are interconnected,then P₁=P₂.

The force imposed upon the left-hand side of the valve is P1 whereas the force imposed upon the right side of the valve is P1 plus the spring force.Consequently the spool is pushed leftwards. Here port A is blocked, so the fluid from the pump is branched off to the PTO clutch.

(1)Passage 1

(2)passage 2

(3)Pressure-reducing valve

(4)Changeover valve

(5)PTO clutch

(6)To control valve.

-When the solenoid is switched 「OFF」:

The fluid in the PTO clutch is unloaded to the bank through port B.Consequently pressure P2 at passage(2) becomes zero,whereas the pressure at passage (1) is P1.Then the force imposed upon the left side of spool (P1)overcomes the force imposed upon the right side (P2+spring force),so that the spool is pushed rightwards to connect port P and part A. Therefore no fluid from the pump is branched off to the PTO clutch; that is,all fluid flows to the control valve.

(1)Passage (1)

(2)Passage (2)

(3)Pressure-reducing valve

(4)Changeover valve

(5)PTO clutch

(6)To control valve

Fig. 9-5 PTO solenoid switch 「OFF」position

(1) Pressure-reducing valve.

This valve is composed of the spool,spring,and piston and bleeds off the surplus fluid from the pump into the tank by actuating the spool when the fluid pressure exceeds the regulated pressure at port B

(2) Fixed orifice

This orifice controls the fluid flow at B in accordance with the pressure differential between the secondary pressure of the pressure reducing valve and the PTO clutch actuating pressure.