Analysis of fever in Komatsu hydraulic system

1. Heating phenomenon of hydraulic system and its harm

Komatsu excavator repairing hydraulic system heating is a phenomenon that is more common in the discovery of a variety of problems, and it is also a problem that is more complicated to analyze and deal with. Under normal working conditions of Komatsu PC200/400 excavator, the oil temperature of the hydraulic system should be below 60oC (the temperature of the oil pump is 5-10oC higher than that). If it exceeds a lot, it is called heating of the hydraulic system. Its fault characteristics are: the excavator cold car operation, various actions are relatively normal, when the machine is operated for about an hour, as the hydraulic oil temperature rises, the excavator's actuators are weak and the action is slow, especially the excavation force No, it is difficult to walk and turn.

If the hydraulic system of Komatsu excavator repairs heats up, if it cannot be dealt with in time, it will have extremely adverse effects on the system:

(1) The viscosity of the oil drops, leaks and adds, and the system heats up, forming a vicious circle;

(2) Accelerate the oxidation of the oil, form a gelatinous substance, block the small holes of the component, and make the hydraulic component malfunction or jam, making it impossible to work;

(3) Make rubber seals and hoses aging and invalid;

(4) Increase the wear of oil pump and hydraulic valve parts, or even become obsolete.

2. Case analysis of Komatsu excavator repairing the problem of heat generation in the excavator hydraulic system

For such problems, generally speaking, Komatsu excavator repair should start from the internal analysis of the external hydraulic system. The internal reason is primarily due to the unreasonable system design. Such as the unreasonable matching between components, the pipeline channels are too thin, the elbows are many, the tortuous radius is small, and the fuel tank volume is not good. Such problems should be fully considered in the design stage, otherwise the hydraulic system of the excavator will be lacking, and it will be difficult to overcome after the product is made.

2.1 Heating of the hydraulic system caused by external causes

For example, the engine of the hydraulic pump of Komatsu PC200-5 excavator is connected by the shock absorber in the shock absorber box. When dealing with a fever problem in the hydraulic system of an excavator, it was found that the oil level in the shock absorber tank greatly exceeded the oil level screw under investigation (usually about 1.5L), and the excessive oil was rolling along with the shock absorber damper. In the process, a lot of heat is generated and transferred to the hydraulic pump, causing the system to heat up.

At this moment, after the Komatsu excavator repairs and drains the shock tank oil to the standard oil level, the fault can be eliminated. There are two reasons why the oil level of the shock absorber is too high. The first is that the operator blindly refuels; the second is the aging of the oil seal at the shaft end of the hydraulic pump, which causes the hydraulic oil to leak. The latter should remove the plug and replace the oil seal.

2.2 Poor heat dissipation function of the radiator causes excessive oil temperature

The primary forms of poor heat dissipation function of the radiator are: deformation or blockage of the external heat dissipation fins, resulting in poor cooling effect; lack of cooling fans; blockage of the internal pipes of the hydraulic oil radiator. In addition to the intuitive identification of the first two, it can also be known from the small temperature difference between the upper and lower tubes of the radiator that the heat sink should be arranged at this moment, and the fan belt should be tightened. To judge the blockage of the internal pipeline of the hydraulic oil radiator, you can check the pressure difference between the two by installing a pressure gauge at the inlet and outlet oil passages of the radiator. The oil temperature is about 45oC and the pressure difference is below 0.12MPa. If it is higher than 0.12MPa, it indicates that the tubing is severely blocked, and the upper and lower covers of the radiator should be removed to clear the pipeline.

2.3 Hydraulic oil overheating caused by failure of one-way valve of hydraulic return filter element

It can be known from the schematic diagram of the hydraulic system that the hydraulic system oil return filter element check valve and the hydraulic oil radiator are connected to the outlet of the oil return filter element (see the PC200-5 hydraulic system schematic diagram). Its function is to actively open when the pressure difference of the oil return radiator is above 0.185MPa, and short-circuit the radiator to form an oil return passage. In practice, because the valve is installed at the bottom of the oil return filter element, it is difficult to check and maintain, and a single operator chooses the hydraulic oil quality incorrectly, does not change the oil for a long time, and is out of repair for a long time, resulting in severe oil pollution. The valve is stuck in the normally open position (some private companies remove this valve), so the oil return radiator has no heat dissipation effect, which will inevitably cause the oil temperature to be too high. Check whether this valve is stuck or not every time you replace the hydraulic oil.

2.4 Improper selection of hydraulic oil trademark or poor oil quality causes excessive oil temperature

In recent years, Komatsu excavators have repaired the problem that the oil temperature of the hydraulic system has risen due to the use of oil that does not conform to the rules or fake oil. For example, misuse of oil with too high viscosity will cause excessive pressure loss in the fluid flow, which is converted into heat, which will cause excessive temperature rise; misuse of hydraulic oil with too low viscosity will also cause leakage in the working hydraulic pump and hydraulic components In addition, some inferior oils have poor viscosity-temperature function, easy to emulsify and produce cavitation, fold out bubbles, etc., which will cause local high temperature in the high pressure of hydraulic oil and aggravate component wear.

2.5 System heating caused by improper adjustment of pump and hydraulic system pressure valve

Komatsu excavator repair hydraulic pump as the power source of the hydraulic system, its working condition affects the degree of heating of the system. For example, the main pump of the PC200 excavator is a plunger pump. If the valve plate in the pump and the cylinder block, sliding shoes, swash plate and plunger cylinder block are worn out, the hydraulic pump tends to heat up quickly. This can be judged by investigating that the pump heats up quickly and has the characteristics of noise. Its amendment

The pilot control pump of PC200 excavator is a gear pump. Its function is to provide operating control pressure oil for the system and adjust the size of the main pump displacement according to the load requirements. If the end face of the internal gear of the pump is worn out or the tooth gap is large, the internal leakage will increase, which will cause the pump to heat up and affect the normal operation of the main pump.

Excessive or low relief valve pressure will also cause the hydraulic system to heat up. If the pressure of the Komatsu excavator is adjusted too high, the hydraulic pump will run at a pressure exceeding the rated pressure, which will overload the pump and cause the oil temperature to rise; on the contrary, If the system pressure is adjusted too low, the operating mechanism will frequently open and unload the overflow valve under normal load, resulting in overflow and heating of the hydraulic system.