COMPONENT

<When bypassed >

OPERATION ／ HST Pump

When the force generated by the low pressure circuit [A] plus the spring force (3) becomes smaller than the force generated by the charging circuit [B], the valve sheet (8) is pressed up to the position shown in the figure and the oil in the charging circuit [B] will be drawn into the low pressure circuit [A].

<When towing (engine stops)>

The poppet (7) is pressed down to the position shown in the figure by tightening the rod (1), the oil in the high pressure circuit [A] will be drawn into the charging circuit [B].

COMPONENT OPERATION ／ HST Pump

・Low-pressure relief valve

This valve controls the charging pressure. During the machine operation, it is always working. The relieved oil goes through the HST pump housing then goes to the HST motor, oil cooler and oil tank for their lubrication and cooling.

COMPONENT OPERATION ／ HST Pump

・DA control system（UCHIDA ／ Serial No. 4501 ～）

（１）Features

① The discharging direction can be changed by using the solenoid valve.The travel direction can be changed the forward and reverse easily by the switch.

② The discharge amount is controlled according to the engine speed. Only the accelerator operation can continuously control the machine speed.

③ Torque Fixing Control. When the load is increased, engine overload is prevented by controlling the oil discharge amount.

（２）DA valve

The gear pump is connected to the HST pump for charging and piloting. The gear pump discharge is increased or decreased according to the engine speed. The flow rate is led to the charge circuit through the orifice on the full flow DA valve. Using as an indicator the differences in pressures caused at the front and rear of the orifice, according to the flow rate change, the DA valve decompresses the charging pressure and generates the pilot pressure. It means that the pump tilt is controlled along with the pressure almost in proportion to the engine speed. A certain volume, which is directly proportional to the engine speed, of oil will be drawn from the charging pump into the charging circuit [C] through the port [A]. DA valve can be activated with signals which indicate the spring force by the spring (4) and the pressure difference between foreand-aft the orifice (6) to reduce the pressure of the charging circuit [C] and generate a control pressure in the control circuit [B].

1-Control cartridge

2-O-ring

3-Adjusting screw

4-Adjusting Spring

5-Differential piston

6-Orifice

Ａ-DA valve, primary (from charging pump)

Ｂ-DA valve, secondary (to control circuit)

Ｃ-DA valve, secondary (to charging circuit)

Ｄ-DA valve drain