Cálculo de acciones y dimensionado de la cimentación

• Right pressure 9.80 MPa {100 kg/cm²} x Right flow rate (50.0 l/min) + Left pressure 9.80 MPa {100 kg/cm²} x Left flow rate (50.0 l/min) = 8.10 kW {11.0 PS} + 8.10 kW {11.0 PS} = 16.2 kW {22.0 PS}

When the machine is steered:

• Right pressure 19.6 MPa {200 kg/cm²} x Right flow rate (50.0 l/min) + Left pressure 9.80 MPa {100 kg/cm²} x Left flow rate (40.0 l/min) = 16.2 kW {22.0 PS} + 6.60 kW {9.0 PS} = 22.8 kW {31.0 PS}

Since the pump input horsepower is larger than the engine horsepower, the PC control starts (to prevent the engine from stalling).

• Right pressure 19.6 MPa {200 kg/cm²} x Right flow rate (30.0 l/min) + Left pressure 19.6 MPa {200 kg/cm2} x Left flow rate (20.0 l/min) = 9.60 kW {13.0 PS} + 6.60 kW {9.0 PS} = 16.2 kW {22.0 PS}

The average flow rate of both sides is reduced from 50.0 l/min to 25.0 l/min (Reduction by 50%).

2) When the double pump system is used When the machine travels straight:

• Right pressure 9.80 MPa {100 kg/cm²} x Right flow rate (50.0 l/min) + Left pressure 9.80 MPa {100 kg/cm²} x Left flow rate (50.0 l/min) = 8.10 kW {11.0 PS} + 8.10 kW {11.0 PS} = 16.2 kW {22.0 PS}

When the machine is steered:

• Right pressure 19.6 MPa {200 kg/cm2} x Right flow rate (50.0 l/min) + Left pressure 4.90 MPa {50 kg/cm²} x Left flow rate (40.0 l/

min) = 16.2 kW {22.0 PS} + 2.90 kW {4.0 PS}

= 19.1 kW {26.0 PS}

Since the pump input horsepower is larger than the engine horsepower, the PC control starts (to prevent the engine from stalling).

• Right pressure 19.6 MPa {200 kg/cm2} x Right flow rate (43.0 l/min) + Left pressure 4.90 MPa {50.0 kg/cm²} x Left flow rate (33.0 l/min) = 14.0 kW {19.0 PS} + 2.20 kW {3.0 PS} = 16.2 kW {22.0 PS}

The average flow rate of both sides is reduced from 50.0 l/min to 38.0 l/min (Reduction by 24.0%).

When the machine having the ordinary single pump system is steered, the flow rate is reduced by 50%. If the double pump system is used, however, the reduction of the flow rate is only 24%.

HYDRAULIC PUMP

(3)

STRUCTURE, FUNCTION AND MAINTENANCE STANDARD

VALVE ASSEMBLY

T : Drain

GH : Gear pump HI signal (a2) GL : Gear pump LO signal (b2) P1 : Pump signal pressure PE : Control piston pressure

PH : Pump shuttle pressure (Pump pressure) P1L : Pump pressure input

PLS : LS pressure input

PAVE : Pump average pressure (Pump pressure)

1. Locknut 2. Plug 3. Spring 4. Spool 5. Sleeve 6. Piston 7. Seat 8. Plug 9. Lever 10. Spool 11. PC valve

HYDRAULIC PUMP

10-68

MAINTENANCE STANDARD

FUNCTION 1. LS valve PC35MR-2

• The LS valve controls the discharge of the pump according to the stroke of the control lever, or the demand flow for the actuator.

• The LS valve calculates the demand flow for the actuator from differential pressure PLS between pump discharge pressure PP and control valve outlet pressure PLS, and controls pump discharge Q.

(PP is called the pump discharge pressure, PLS called the LS pressure, and PLS called the LS differential pressure.)

• That is, the pump discharge is controlled accord-ing to the demand flow for the actuator by the following method; The pressure loss made when the oil flows through the opening of the control valve spool (LS differential pressure PLS) is sensed and pump discharge Q is so controlled that the pressure loss will be constant.

• The demand flow for the actuator is always sup-plied, however, as long as it does not exceed the maximum pump discharge in the fine control mode, etc. Accordingly, the pump discharge is kept at the same level, regardless of the engine speed. To prevent this, the LS differential pres-sure is automatically set low and the pump dis-charge is reduced when the engine speed is low.

PC40MR, 50MR-2

• The LS valve controls the pump discharge according to the stroke of the control lever, or the flow rate required by the actuator.

• This valve determines the flow rate required by the actuator from differential pressure PLS between main pump discharge pressure P1L and control valve outlet pressure PLS, then con-trols main pump discharge Q.

(P1L is called the pump pressure, PLS LS pres-sure, and PLS LS differential pressure.)

• To put it concretely, the LS valve senses the pressure loss (= LS differential pressure PLS) caused by the flow of oil from the pump through

the opening of the control valve spool, then con-trols pump discharge Q so that this pressure loss will be constant. Consequently, the LS valve sup-plies the oil according to the demand of the con-trol valve.

• In the range of fine control, etc. where the oil flow rate does not exceed the pump capacity, the pump discharge is kept constant even if the engine speed is low or full, since the LS valve always secures the oil flow rate required by the control valve. To solve this problem, the LS dif-ferential pressure is automatically set low to reduce the discharge when the engine speed is low.

• The engine speed is sensed by checking pres-sures GH and GL before and after the fixed throttle (metering throttle) of the discharge pas-sage of the swing gear pump, and those pres-sures are applied to the third and fourth pressure receiving chambers a2 and b2 in the LS valve to change the setting of the LS valve.

• When the engine speed is low, the swing pump discharge is reduced and pressures GH and GL before and after the metering throttle are almost the same (the metering differential pressure cal-culated by GH – HL is low). On the other hand, when the engine is running at the full speed, the swing pump discharge is increased and the metering differential pressure becomes high.

• When the metering differential pressure is high (the engine speed is high), the LS pressure is set higher than the normal value. When the meter-ing differential pressure is low (the engine speed is low), the LS pressure is set lower than the nor-mal value.

• The LS valve receives pump pressure P1L, LS pressure PLS, and pressures GH and GL before and after the metering throttle of the swing gear pump. The relationship between LS differential pressure PLS and pump discharge Q is shown at right.

HYDRAULIC PUMP

STRUCTURE, FUNCTION AND MAINTENANCE STANDARD

2. PC valve

• When pump discharge pressure P1/PAVE rises, the stroke of the control valve spool is increased and the opening area is increased and pump dis-charge Q is increased. At this time, the PC valve limits pump discharge Q according to discharge pressure P1/PAVE so that the pump absorption horsepower will not exceed the engine horse-power. In other words, the PC valve performs approximate constant-horsepower control.

• That is, if the load on the actuator is increased and pump discharge pressure P1/PAVE rises during operation, the PC valve reduces pump discharge Q. If the pump discharge pressure lowers, the PC valve increases pump discharge Q.

• The relationship between pump discharge pres-sure P1/PAVE and pump discharge Q is shown below.

• When the machine swings, since the swing pump and main pump are installed tandem, the torque absorbed in the main pump is lowered by the part absorbed in the swing pump.

• When the swing pump operates, the total of the main pump absorption torque and swing pump absorption torque is the total absorption torque (100%)

HYDRAULIC PUMP

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MAINTENANCE STANDARD