Created on:2021-09-06 10:32

Construction machinery_ Fault analysis and improvement of D375A-2 bulldozer blade lifting slowly

Construction machinery_ Fault analysis and improvement of D375A-2 bulldozer blade lifting slowly

(1) Fault analysis of blade lifting slowly

The movement speed of the hydraulic cylinder piston depends on the flow into the cylinder. From the above oil circuit analysis, it can be seen that the flow of oil into the blade lifting hydraulic cylinder is not only related to the moving position of blade lifting valve 3, but also related to the position of 4 (i.e. the load feedback pressure). If the blade lifting valve 3 is fully opened and the pressure loss is minimum, the flow of feedback oil flowing through the shuttle valve 19 is the largest, and the flow and pressure are also the largest after flowing through the throttle valve 6, so that the left oil pressure of the control oil of the flow control valve 4 is equal to the right oil pressure, the elastic force of the spring pushes the flow control valve to the right, and all the combined oil of the large and small pumps enters the hydraulic cylinder; If the feedback oil of blade lifting valve 3 flows through throttle valve 6 through shuttle valve 19 and reaches the left side of flow control valve 4, there will be a lot of flow loss and a lot of pressure loss. The left control oil pressure of flow control valve 4 is less than the right oil pressure. The spring is compressed and the flow control valve moves to the left. A lot of oil from large and small pumps will flow back to the oil tank rather than into the hydraulic cylinder, The hydraulic cylinder will only move slowly.

① Due to the particularity of load feedback oil circuit: small pipe diameter, many flow points and long line; It is throttled at throttle valve 6. Therefore, it is not difficult to see that the real cause of blade lifting fatigue is the leakage in the load feedback oil circuit, resulting in differential pressure. The left control oil pressure of flow control valve 4 is less than the right oil pressure, the flow control valve moves to the left, and the oil of large and small pumps flows back to the oil tank through this valve without all entering the hydraulic cylinder.

② When the bulldozer is just started, the viscosity is relatively high (the viscosity of the oil is inversely proportional to the temperature), the leakage of the load feedback oil circuit is less, and the fault is not obvious. With the increase of the oil temperature, the leakage increases, the time required for each lifting of the blade increases, and the working time of the hydraulic pump (running with load) also increases, accelerating the rising speed of the oil temperature, At the same time, the fault of slow blade lifting is obvious.

③ After long-term use of the hydraulic control valve, there are varying degrees of wear between the valve core and the valve body and at the cone of the valve core of the main overflow valve 5; In addition, the load feedback oil circuit flows through many points, the pipeline is narrow, and there is throttling at throttle valve 6, which increases the leakage and has the most obvious impact on the system. When the wear reaches a certain level, the problem of slow blade lifting begins to appear. With the increase of wear, the fault becomes more and more obvious, so that it can not be used.

(2) Improvement measures

Measure 1: the simplest way to eliminate such faults is to replace the hydraulic control valve and main overflow valve assembly. However, the hydraulic valve is always very expensive, and the spare parts depend on imports, which has a long arrival cycle and affects the production.

Measure 2: take effective measures to compensate the leakage in the load feedback oil circuit, so as to solve the problem that the flow control valve is not in place.

Specific implementation: remove the plug at the left end of the main overflow valve, and use a drill bit to expand the orifice C to 2 ~ 2.5mm (the original aperture is 1.5mm). Due to the increase of the flow section at C, the pressure difference before and after the orifice is reduced. After field test, the effect is very obvious.

(3) Conclusion

① This method can prolong the service life of the hydraulic control valve. Due to the compensation of the load feedback pressure, the problem that the flow control valve is not in place is solved. The time of each work cycle (lifting of the working mechanism) of the hydraulic pump is shortened, the efficiency is improved, and the oil temperature tends to be normal, which greatly improves the working environment of the hydraulic pump and seals, prolongs the service life of the and seals, and improves the service efficiency of the bulldozer. Using this scheme, four D375A-2 bulldozers have been improved successively. The application for more than two years shows that the scheme is feasible.

② This method is more suitable for bulldozer models without scarifier (because there is a piston valve on the piston of blade lifting hydraulic cylinder). For models with scarifier, pay attention not to expand the orifice C too large. Gradually increase the aperture (0.1mm each time) and conduct tests until the lifting weakness fault disappears and the hydraulic system pressure does not increase. Make records to prevent mixing.

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