(1) H55 hydraulic excavator and failure
The Carter excavator uses German SMS technology and adopts full hydraulic transmission and control. The whole machine runs quickly, flexibly, and has high digging efficiency (2.5ni3 per shovel). The car is equipped with a 220 hp (1 hp-735.499W) diesel engine One, the oil source is equipped with two A7VT0200 type constant power variable hydraulic pumps. The maximum working pressure is 30MPa, and the maximum flow rate is 564L / min (the two pumps can be combined to provide an oil source for the stick cylinder, boom cylinder, and maximum speed rotation).
A H55 hydraulic excavator has been working for nearly half a year, and its failure rate has gradually increased, and even the whole vehicle sometimes cannot run.After 0.5 hours of regular work, it needs to be stopped for maintenance.
Its main faults:
①The temperature of the hydraulic system of the Carter excavator does not match the design temperature. After running for 1500h, it works for 30min. When the ambient temperature is 35 degrees, the temperature of the main components of the whole machine is measured by the far infrared thermometer.
②The excavator cannot work normally. The speed of the whole machine is slowed down (such as walking, slewing, boom, stick, excavation, etc.), and even some parts sometimes do not move, and basically can not work.
③The seal is not good. The oil seal and seal of the hydraulic cylinder and pipe joint are damaged seriously.
④ Tubing and joints often burst.
⑤ The hydraulic pump is badly damaged.
(2) Causes of heat failure of excavator
1) Poor working conditions in harsh environments and high temperatures. Excavator work site environment is harsh, such as when the summer environment temperature is 35 degrees, the work site temperature is high.
2) The working environment cannot meet the design conditions. The H55 hydraulic excavator adopts German SMS technology, and the working environment temperature of the excavator considered in the design is low (about 25cC), which is suitable for excavation of gravel and soft soil, and it is intermittent Working system, when the foundation is removed, the concrete volume is large and the hardness is high, which is different from the design conditions, so the original design of the hydraulic system heat dissipation setting is simple, such as the capacity of the oil tank is small (400L); the capacity of the heat dissipation cooler is small, and the heat dissipation area is small ( 26m3); the radiator used is a plate-fin air-cooled type, this radiator channel is easily blocked by the gel in the oil, and the effect is poor. In addition, the radiator is installed on the top of the engine (the temperature of the engine itself is high, when (When the ambient temperature is 35 degrees, the engine temperature is 92 degrees), so the hydraulic system can hardly dissipate heat through the cooler. The cooling effect is extremely poor, which is the main reason for the heating of the hydraulic system.
3) The oil source of the H55 hydraulic excavator uses two A7VT0200 constant power variable piston pumps. The pump has the characteristics of high power, high use pressure, strong anti-pollution ability, compact structure, flexible variable methods, etc. In order to understand the hydraulic pump Damage situation, first of all, the volumetric efficiency test of the hydraulic pump, when the hydraulic pump pressure is loaded to 20MPa (oil temperature at 500C). After measurement and calculation, the volumetric efficiency was 0.78. The hydraulic pump was disassembled and tested, and it was found that the hydraulic pump rotating rigid body distribution surface and the cylinder plunger hole were worn, and the maximum clearance between the individual cylinder plunger hole and the plunger was 0.08mm ( (It should not be greater than 0.02mm), the parts in the pump have obvious blackening, which is caused by the high oil temperature of the hydraulic system and the main reason for the wear of the hydraulic pump.
According to the analysis of the actual situation on the spot, the main reason for the failure of the H55 excavator is the overheating of the hydraulic system, which caused the damage of the hydraulic components of the excavator, which caused the excavator to not work properly.
(3) Improvement of hydraulic system of excavator
1) Increase the heat dissipation area. Expand the volume of the fuel tank from the original 400L to 1200L, which increases the oil storage capacity and heat dissipation area of the fuel tank.
2) Redesign the radiator. Change the installation position of the original radiator (the original radiator is installed on the top of the engine), and redesign the cooler ventilation channel to ensure sufficient cooling air volume.
3) Add two radiators to increase the heat dissipation area from 26m2 to 52rr12.
4) Change the connection form of the oil return circuit of the cooling system of the hydraulic system. The original radiator and a one-way valve are installed in parallel on the return oil circuit. When the oil resistance of the radiator oil path increases, and the liquid resistance is slightly greater than the opening pressure of the one-way valve At the time, the oil return is directly returned to the tank through the check valve without the radiator. Change the cooling oil return circuit of the hydraulic system, install the two newly added radiators in series with the original radiator, then the hydraulic system returns all the oil By paralleling two stages of heat dissipation and returning to the oil tank, this ensures the heat dissipation effect of the oil return of the hydraulic system.
The H55 hydraulic excavator has been used in the original site under good working conditions. The oil temperature of the hydraulic system is controlled within 80 degrees, which overcomes the damage of hydraulic components and pipelines caused by the heating of the hydraulic system, improves the efficiency of the excavator, and reduces failures. Rate, the effect is ideal.
