(1) H55 hydraulic excavator and fault
Carter excavator uses German Simak technology and adopts full hydraulic transmission and control The whole machine runs quickly and flexibly with high excavation efficiency (2.5ni3 per shovel) The vehicle is equipped with one 220 HP (1 hp-735.499w) diesel engine and two a7vt0200 constant power variable hydraulic pumps The maximum working pressure is 30MPa and the maximum flow is 564l / min (two pumps can be combined to provide oil source for 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 can not run sometimes. After working for 0.5h, it needs to stop for maintenance
Main faults:
① The hydraulic system temperature of Carter excavator is inconsistent with the design temperature Operate for 30min after 1500h When the ambient temperature is 35 ℃, the temperature of main parts of the whole machine measured by far infrared thermometer
② The excavator does not work properly The speed of the whole machine slows down (such as walking, slewing, boom, stick, excavation, etc.), and even some parts sometimes don't act and basically can't work
③ Poor sealing The oil seal and seal of hydraulic cylinder and pipe joint are seriously damaged
④ Oil pipes and joints often burst
⑤ The hydraulic pump is severely damaged
(2) Causes of excavator heating failure
1) Poor working condition in harsh environment and high temperature The working environment of the excavator is bad. For example, when the ambient temperature is 35 degrees in summer, the working site temperature is high
2) The working environment cannot meet the design conditions H55 hydraulic excavator adopts German Simak technology. The working environment temperature of the excavator considered in the design is low (about 25CC), which is suitable for excavating gravel and soft earth rock. It belongs to intermittent working system. When removing the foundation, the concrete has large volume and high hardness, which is different from the design conditions. Therefore, the heat dissipation setting of the original design hydraulic system is relatively simple, such as small oil tank capacity (400L); The cooling cooler has small capacity and small cooling area (26m3); The radiator used is plate fin air-cooled type. This kind of radiator channel is easy to be blocked by colloids in 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 the ambient temperature is 35 ℃, the engine temperature is 92 ℃), so the hydraulic system can hardly dissipate heat through the cooler The cooling effect is very poor, which is the main reason for the heating of the hydraulic system
3) The oil source of H55 hydraulic excavator uses two a7vt0200 constant power variable piston pumps The pump has the characteristics of high power, high operating pressure, strong anti pollution ability, compact structure and flexible variable mode In order to understand the damage of the hydraulic pump, the volumetric efficiency test of the hydraulic pump is carried out first. When the pressure of the hydraulic pump is loaded to 20MPa (the oil temperature is 500C), the volumetric efficiency is 0.78 after measurement and calculation The hydraulic pump was disassembled and tested. It was found that the port surface of the rotating rigid body of the hydraulic pump and the plug hole of the cylinder block were worn. The maximum clearance between the plug hole of individual cylinder block and the plunger was 0.08mm (no more than 0.02mm). The parts in the pump were obviously blackened, which was 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 site, the main cause of the failure of H55 excavator is the overheating of the hydraulic system, which causes the damage of the hydraulic components of the excavator and makes the excavator unable to work normally
(3) Improvement of hydraulic system of excavator
1) Increase the heat dissipation area The volume of the oil tank is expanded from 400L to 1200L, which increases the oil storage capacity and heat dissipation area of the oil 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 duct to ensure sufficient cooling air volume
3) Add two radiators to expand the heat dissipation area from 26m2 to 52rr12
4) Change the connection form of heat dissipation and oil return circuit of hydraulic system The original radiator is installed on the oil return circuit in parallel with a one-way valve When the hydraulic resistance of the radiator oil circuit increases and the hydraulic resistance is slightly greater than the opening pressure of the check valve, the return oil will directly return to the oil tank through the check valve without passing through the radiator By changing the heat dissipation and oil return circuit of the hydraulic system and installing the two newly added radiators in series with the original radiator, the oil return of the hydraulic system will return to the oil tank after two-stage heat dissipation in parallel, so as to ensure the heat dissipation effect of the oil return of the hydraulic system
After modification, H55 hydraulic excavator works well on the original site, and 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 working efficiency of the excavator, reduces the failure rate, and the effect is ideal
