2. Motor swash plate angle (capacity) at minimum (Hi speed)
a. When the solenoid valve is excited, the pilot pressure oil from the main pump flows the port P, and pushes regulator valve (9) to the left in the direction of the arrow
b. Because of this, the main pressure oil from the control valve passes through passage d in regulator valve (9), enters regulator piston (15) at the bottom, and pushes regulator piston (15) to the right in the direction of the arrow.
c. As a result, swash plate (4) moves in the minimum swash plate angle direction, the motor capacity be-comes minimum.
STRUCTURE AND FUNCTION TRAVEL MOTOR
Operation of parking brake 1. When starting the travel
a. When the travel lever is operated, the pressurized oil from the pump actuates counterbalance valved spool (19), opens the circuit to the parking brake, and flows into chamber A of brake piston (12). It overcomes the force of spring (11), and pushes piston (12) to the left in the direc-tion of the arrow. When this happens, the force pushing plate (13) and disc (14) to-gether is lost, so plate (13) and disc (14) separate and the brake is released.
2. When stopping travel
a. When the travel lever is placed in neutral, counterbalance valve spool (19) returns to the neutral position and the circuit to the parking brake is closed. The pressurized oil in chamber A of brake piston (12) is drained is pushed to the right in the direc-tion of the arrow by spring (11). As a result, plate (13) and disc (14) are pushed to-gether, and the brake is applied. A time delay is provided by having the pressu-rized oil pass through a throttle in slow turn valve (22) when the brake piston re-turn, and this ensures that the brake is still effective after the machine stops.
STRUCTURE AND FUNCTION TRAVEL MOTOR
Operation of brake valve
• The brake valve consists of a suction safety valve (18A), counterbalance valve (18) in a cir-cuit as shown in the diagram on the right.
• The function and operation of each component is as given below.
STRUCTURE AND FUNCTION TRAVEL MOTOR
1. Counterblalance valve, check valve a. Function
i. When travelling downhill, the weight of the machine makes it try the travel faster than the speed of the motor. As a result, if the machine travel with the engine at low speed, the motor will ro-tate without load and the machine will run away, which is extremely danger-ous. The prevent this, these valves act the make the machine travel accord-ing to the engine speed (pump dis-charge amount).
b. Operation when pressure oil is supplied i. When the travel lever is operated, the
pressurized oil from the control valve is supplied the port PA. It pushes open suction safety valve (18A) and flows from motor inlet port MA the motor outlet port MB. However, the motor outlet port is closed by suction safety valve (18B) and spool (189), so the pressure at the supply side rises.
ii. The pressurized oil at the supply side flows from orifice E1 and E2 in spool (19) the chamber S1. When the pres-sure in chamber S1 goes above the spool switching pressure, spool (19) is pushed to the right in the direction of the arrow. As a result, port MB and PB are connected, the outlet port side of the motor is opened, and the motor starts the rotate.
STRUCTURE AND FUNCTION TRAVEL MOTOR
c. Operation of brake when traveling downhill i. If the machine tries the run away when traveling downhill, the motor will turn under no load, so the pressure at the motor inlet port will drop, and the pressure in chamber S1 through ori-fices E1 and E2will also drop. When the pressure in chamber S1 drops be-low the spool switching pressure, spool (19) is returned tot the left in the direction of the arrow by spring (20), and outlet port MB is throttled. As a result, the pressure at the outlet port side rises, resistance is generated to the rotation of the motor, and this pre-vents the machine from running away.
In other words, the spool moves the a position where the pressure at outlet port MB balances the pressure at the inlet port and the force generated by the weight of the machine. It throttles the outlet port circuit and controls the travel speed according to the amount of oil discharged from the pump.
2. Safety valve a. Function
i. When travel is stopped (or when trav-elling downhill), the circuits at the inlet and outlet ports of the motor are closed by the counterbalance valve, but the motor is rotated by inertia, so the pressure at the outlet port of the motor will become abnormally high and damage the motor or piping. The safety valve acts the release this ab-normal pressure and send it to the in-let port side of the motor the prevent damage to the equipment.
b. Operation when travel is stopped (or when traveling downhill, rotating to the right) i. When the motor inlet port pressure
(pressure PA) goes down, the pres-sure in chamber S1 also goes down.
When it goes below the switching pressure of the spool, spool (19) is re-turned to the left by spring (20), and outlet port passage B1 is throttled.
When this happens, the motor contin-ues the rotate under inertia, so the outlet pressure (pressure MB) rises.
STRUCTURE AND FUNCTION TRAVEL MOTOR
ii. If the pressure goes above the set pressure of suction-safety valve (18A), the poppet opens. The oil then passes through large notch A1 in counterbalance valve spool (19) and flows the chamber MA in the circuit on the opposite side.
c. When rotating to the left
i. The operation is the reverse of when rotating to the right.
d. When starting travel (or during normal travel)
i. When the travel lever is operated, the pressurized oil from the pump moves counterbalance valve spool (19) to the right. When this happens, the passage to the suctionsafety valve becomes the circuit flowing through the small notch in the counterbalance valve spool. As a result, a big difference in pressure is created, and the pump pressure rises the provide a powerful drawbar pull.
STRUCTURE AND FUNCTION
1. Travel PPC valve 2. Service PPC valve 3. Service pedal 4. L.H. travel lever 5. R.H. travel lever 6. R.H. PPC valve 7. R.H. work
equip-ment lever 8. Solenoid valve 9. Accumulator