Created on:2021-09-09 14:09

Construction machinery_ Maintenance of excavator_ Structure, principle and reconstruction design of hydraulic system

Construction machinery_ Maintenance of excavator_ Structure, principle and reconstruction design of hydraulic system

(1) Determination of technical transformation scheme of UH181 excavator

The working system of UH181 excavator has low pressure, large flow, large size and bulky hydraulic components; Slow movement speed; Length of mechanical transmission chain; Complex structure. The parts with high failure frequency are the main hydraulic pump and transmission box mechanism.

Compared with contemporary new models in technical parameters: the total displacement of UH181 main hydraulic pump is much larger than that of other models; When the system load is less than 17Mpa, the total flow of UH181 hydraulic pump is much greater than that of contemporary; When the system load is greater than 17Mpa, the total flow of UH181 hydraulic pump is far less than that of modern hydraulic pump; The maximum working pressure of UH181 hydraulic system is 25MPa, while that of contemporary excavators is 35MPa; UH181 works under medium and low pressure load (10 ~ 18Mpa). When it exceeds 20MPa, the system flow is very small and the working efficiency is very low.

Compared with contemporary excavators in terms of mechanism, size and performance: the hydraulic cylinder size, motion stroke, hydraulic motor size and quality of UH181 excavator are greater than those of ex400-3; The movement speed of the system actuator should not be too high, because the structural parts are huge, the oil supply is large, and the movement moment of inertia is also large, so the design movement speed is lower than that of contemporary excavators.

The motion analysis of hydraulic cylinder is shown in the table below.

 

Motion analysis of hydraulic cylinder

Serial number

液压缸

名称

动作

单位

理论工作容积/L

容积差

差额

比例

UH181

EX400-3

1

大臂液压缸

举升

s/全行程

69.87

50.5

19.38

38.36

2

斗杆液压缸

内转

s/全行程

56.7

38.89

17.81

45.8

外转

s/全行程

34.1

21.6

12.55

58.1

3

铲斗液压缸

内转

s/全行程

30.06

20.6

39.43

45.7

外转

s/全行程

20.48

10.74

9.74

90.7

 

According to q = QN, the flow is in positive proportion to the displacement; It is known from q = V / s that the greater the content product per unit time, the greater the flow required, that is, the greater the displacement of the pump. According to the movement volume of each hydraulic cylinder of UH181 compared with ex400-3, calculate the percentage of its excess, and estimate the percentage value of its displacement to be increased by the weighted average method, i.e. (38.36 + 45.8 + 58.1 + 45.7 + 90.7) / 500 × 100%=55.73%。 Since the hydraulic pump displacement of ex400-3 excavator is 180ml / R, the estimated displacement of UH181 excavator is q = 180 ×( 1+0.5573) =280.3mL/r。

Based on the above analysis results, combined with the existing domestic technical level and on-site maintenance, modification, manufacturing and commissioning conditions, it is decided to adopt the imported dual variable piston pump, install the hydraulic pump directly on the engine flywheel housing through the flexible coupling, and provide the technical transformation scheme of hydraulic main pipe, pilot control pipeline, control valve, etc. In order to ensure the quality and service life of technical transformation, it is decided to select Kawasaki hydraulic pump from Japan. After technical discussion and development with meikomas, a k3v280 double pump is customized.

(2) Structure, principle and transformation design

① Nylon tooth block coupling with flexible connection is selected for the design of the connection form between the main hydraulic pump and the engine, as shown in Figure L.

② Transformation of hydraulic pump oil supply system the original system is a three pump and three valve oil supply composite control system. Now it is intended to be transformed into a two pump oil supply system, but the block is still in the form of three valve group oil supply control. According to the working function distribution form of double pump and double circuit oil supply system of contemporary excavator, it is decided to parallel the rotary valve block system with the right valve block system and supply oil by one pump.

③ Transformation of hydraulic pump control system and compound action control oil circuit

a. The form of load feedback between raw liquid pressure pumps and between main pumps a and B is full power control and constant power regulation; A. Between pump B and rotary pump C, when the pressure of rotary pump system is less than 110MPa, it is divided power control, when it is greater than 11mpa, it is full power control, and C itself is constant power control; A. The load feedback control of pumps B and C is in the form of pilot operated secondary pressure positive flow load feedback; A. The regulator of B main pump is equipped with the minimum flow cut-off control function. See Figure M.

M.jpg

b. Now it is transformed into the control form of double pump with pilot pump: the double pump room is still constant power regulation and full power control; Pump control pressure is pilot operated secondary pressure load feedback positive flow control; The proportional solenoid valve is used to control the power of the two pumps, which matches well with the power of the engine, and can realize the multi gear control of working mode, that is, four working conditions of heavy excavation, general excavation, site leveling and micro action of hoisting.

c. The transformation design to realize the function combination of rotary valve group and right valve group. A three-way valve block is connected in series in the oil outlet pipeline of the front pump to make the oil from the front pump go to the right valve group and the rotary valve group; The rotary pilot operation control pressure oil pipe is introduced at the rear end of the standby valve block of the right valve group (the front end of the standby valve block has been refitted into the function of hydraulic crushing hammer before), so as to achieve the only purpose of parallel connection between the right valve group and the main oil circuit of the rotary valve group.

④ The transformation of the oil suction pipeline of the main pump transforms the original four branch pipelines on the main pipe into the oil suction pipes of the four hydraulic pumps respectively, into directly entering the oil suction port of the duplex pump from the main pipe, adding an oil guide arc surface at the inner wall of the right angle bend of the oil pipe, making flange joints, right angle bends, etc.

(3) Other supporting technologies to improve the performance of the whole machine after the transformation of the hydraulic system

After the technical transformation of the hydraulic system, in order to ensure the balanced technical performance, good economy, reliable use and overall improvement of the service life of the excavator, other mechanisms of the excavator have also been renovated: ① engine overhaul; ② Replace the high and low pressure rubber hose of the hydraulic system of the whole vehicle; ③ Replace the seals of hydraulic system components and assemblies; ④ Replace the engine three filters - hydraulic oil full flow filter element, bypass filter element and oil suction filter element; ⑤ Overhaul all components and assemblies of the electrical system and domestic monitoring instruments and devices; ⑥ Overhaul the four wheels of the chassis; ⑦ Domestic hydraulic oil radiator, engine water tank.

Home    Article    Construction machinery_ Maintenance of excavator_ Structure, principle and reconstruction design of hydraulic system