Reactivos

FUNCTION

• During compound operations, if the load pres-sure becomes lower than the other actuator and the oil flow tries to increase, compensation is received.

(When this happens, the other actuator being used for compound operation (right side) is at a higher load than the actuator on this side (left side).)

PC30MR-2

OPERATION FOR EACH FUNCTION AND VALVE

STRUCTURE, FUNCTION AND MAINTENANCE STANDARD

PC35MR, 40MR, 50MR-2

OPERATION

• If the load pressure of the other actuator (right side) becomes higher during compound opera-tions, the oil flow in actuator circuit A on this side (left side) tries to increase.

• If this happens, the LS pressure PLS of the other actuator acts on spring chamber PLS', and reducing valve (1) and flow control valve (2) are pushed to the left.

• Flow control valve (2) throttles the area of open-ing between pump circuit PP and spool upstream PPA, and pressure loss is generated between PP and PPA.

• Flow control valve (2) and reducing valve (1) are balanced in position where the difference in pressure between PLS and PA acting on both ends of reducing valve (1) and the pressure loss between PP and PPA on both sides of flow con-trol valve (2) are the same.

• In this way, the pressure difference between upstream pressure PPA and downstream pres-sure PA of both spools used during compound

OPERATION FOR EACH FUNCTION AND VALVE

10-114

PC30 – 50MR-2 STRUCTURE, FUNCTION AND

MAINTENANCE STANDARD

1. Area ratio of pressure compensation valve FUNCTION

• The pressure compensation valve determines the compensation characteristics by carrying out fine adjustment of the area ratio (S2/S1) between area S2 of reducing valve (1) and area S1 of flow control valve (2) to match the charac-teristics of each actuator.

S1: Area of flow control valve (2)

- area of piston (3) S2: Area of reducing valve (1)

- area of piston (3)

PC30MR-2

OPERATION FOR EACH FUNCTION AND VALVE

STRUCTURE, FUNCTION AND MAINTENANCE STANDARD

PC35MR, 40MR, 50MR-2

Area ratio (S2:S1) and compensation characteristics

• When ratio is 1.00:

[pump pressure PP – spool notch upstream pressure PPB] C [LS circuit pressure PLS – actu-ator circuit pressure PA (= A)] and oil flow is divided in proportion to area of opening of spool.

• When ratio is more than 1.00:

PP – PPB > PLS – PA (= A) and oil flow is divided in a proportion less than area of opening of spool.

• When ratio is less than 1.00:

PP – PPB < PLS – PA (= A) and oil flow is divided in a proportion more than area of open-ing of spool.

OPERATION FOR EACH FUNCTION AND VALVE

10-116

PC30 – 50MR-2 STRUCTURE, FUNCTION AND

MAINTENANCE STANDARD

2. LS receiving throttle of pressure compensation valve

FUNCTION

• If the other actuator is relieved during compound operations, LS introduction throttle b of reducing valve (1) divides the flow and sends more oil to the side receiving compensation.

PC30MR-2

OPERATION FOR EACH FUNCTION AND VALVE

STRUCTURE, FUNCTION AND MAINTENANCE STANDARD

PC35MR, 40MR, 50MR-2

OPERATION

• If the other actuator (right side) is relieved during compound operations, each circuit pressure (PPA, PA) of the other actuator becomes the same as the pump circuit pressure (PP = relief pressure).

• In this case, spring chamber PLS2 of the other actuator becomes the same as pump circuit pressure PP because of the balance of reducing valve (1).

• PLS2 passes through LS introduction throttle b of reducing valve (1) and becomes PLS. PLS is connected to the tank circuit T from LS bypass plug (4), so pressure loss is generated at LS introduction throttle b (the condition becomes PLS<PLS2).

• As a result, even if the other actuator is relieved, a pressure differential is created between PP and PLS, so more oil flows to actuator circuit A on this side (left side).

OPERATION FOR EACH FUNCTION AND VALVE

10-118

PC30 – 50MR-2 STRUCTURE, FUNCTION AND

MAINTENANCE STANDARD

L.H., R.H. TRAVEL JUNCTION CIRCUIT PC27MR, 30MR-2

1. When traveling in a straight line

FUNCTION

• To compensate for any difference in the oil flow in the left and right travel circuits when traveling in a straight line, the junction circuit opens when the left and right travel spools are operated.

• In this way, the flow of oil to the left and right travel motors is almost the same when traveling in a straight line, so there is no travel deviation.

• When steering the machine, the difference in the load pressure returns the reducing valve of the travel valve on the inside of the turn and the opening of the notch in the travel junction valve spool becomes smaller, so the machine can be steered.

OPERATION

• When left and right travel spools (1) are oper-ated, the pump discharge flows from pump cir-cuit PP and circir-cuits PA to actuator circir-cuits B.

• When traveling in a straight line, to make actua-tor circuits PA equal, left and right reducing valves (2) are pushed to the right by the same amount, and notch a and the travel junction cir-cuit are opened.

• In this way, the left and right travel actuator cuits are interconnected by the travel junction cir-cuit, so if any difference occurs in the flow of oil to the left and right travel motors, the compensa-tion is carried out to prevent any deviacompensa-tion in travel.

OPERATION FOR EACH FUNCTION AND VALVE

(3)

STRUCTURE, FUNCTION AND MAINTENANCE STANDARD

2. Steering when traveling

OPERATION

• When traveling in a straight line, if left travel spool (L. H. 1) is returned to the neutral position and the steering is operated, a difference (R. H.

B > L. H. B) is generated in the load pressure of left and right travel actuator circuits PA, and LS pressure PLS becomes the same pressure as R.

H. B.

• As a result, flow control valve (3) on the left travel side is pushed to the left by LS circuit PLS.

Because of this, the opening of the left notch a is made smaller, so it becomes possible to operate the steering when traveling.

• Damper b is provided in the circuit to damper any excessive characteristics in the opening or closing of the travel junction circuit if the spool is operated suddenly.

OPERATION FOR EACH FUNCTION AND VALVE

10-120

PC30 – 50MR-2 STRUCTURE, FUNCTION AND

MAINTENANCE STANDARD

PC35MR, 40MR, 50MR-2

1. During straight travel

FUNCTION

• An interconnection circuit is installed to correct the flow error in both travel circuits during straight travel.

• With this circuit, the flow rates in both travel motors become almost the same during straight travel to reduce travel deviation.

• Dampers b are installed to ease the transient characteristics of sudden opening and closing of the interconnection circuit when the machine is steered and the spools are operated sharply.

OPERATION

• Bridge circuits PA of both travel circuits are con-nected to each other by interconnection circuit L.

Accordingly, if there is difference between the oil flow rates in both travel motors, it is corrected to reduce the travel deviation.

OPERATION FOR EACH FUNCTION AND VALVE

STRUCTURE, FUNCTION AND MAINTENANCE STANDARD

2. Steering when traveling

OPERATION

• When the right travel spool (R. H. 1) is returned to the neutral position to steer the machine in the straight travel state, the load pressures in both travel actuator circuits PA become different (L.

H. A > R. H. A).

• Since the main pump is separated at this time, oil flows in both travel motors according to the opening area of the spool.

OPERATION FOR EACH FUNCTION AND VALVE

10-122

PC30 – 50MR-2 STRUCTURE, FUNCTION AND

MAINTENANCE STANDARD

SELF-PRESSURE REDUCING VALVE PC27MR, 30MR-2

1. When the control valve is held

FUNCTION

• This valve reduces pump discharge pressure PP and supplies the pilot main pressure of 2.90 MPa {30.0 kg/cm²} to the PPC valve.

• When the actuator circuit pressure is low, the self-pressure sequence valve is closed to raise pump discharge pressure PP to secure the pilot main pressure.

OPERATION

• Unload spool (1) moves and pump discharge pressure PP is set to 2.90 MPa {30.0 kg/cm²}.

(See the explanation of the unload valve.)

• Pump discharge pressure PP is reduced to 2.90 MPa {30.0 kg/cm²} by self-pressure reducing spool (2) and self-pressure reducing pilot relief valve (3), and the main pressure oil is supplied through the PC port to the PPC valve.

OPERATION FOR EACH FUNCTION AND VALVE

(3)

STRUCTURE, FUNCTION AND MAINTENANCE STANDARD

2. When the control valve is operated

OPERATION

• Unload spool (1) moves to the left and pump dis-charge pressure PP becomes higher than the LS pressure by the LS differential pressure. (See the explanation of unload valve.)

• When pump discharge pressure PP is higher than 2.90 MPa {30.0 kg/cm²}, it is reduced to 2.90 MPa {30.0 kg/cm²} by self-pressure reduc-ing spool (2) and self-pressure reducreduc-ing pilot relief valve (3), and the pressure oil is supplied through the PC port to the PPC valve.

• At this time, self-presser sequence valve (4) is kept open.

OPERATION FOR EACH FUNCTION AND VALVE

In document UNIVERSIDAD NACIONAL DE SAN MARTÍN (página 43-0)