Dump trucks have advantages such as flexibility, strong adaptability to working conditions, high labor productivity, large loading capacity, short loading and unloading time, low labor intensity, low cost and energy consumption, and good profitability. They can achieve full loading and unloading mechanization and are widely used in construction projects such as mines, hydropower projects, urbanization, roads, bridges, and pipeline networks. Due to the harsh working environment, complex and variable working conditions, rugged and difficult driving roads, frequent high-speed and heavy loading, and high frequency of use, the normal operation, maintenance, and adjustment of the lifting hydraulic system of dump trucks are particularly important, which will directly affect the safety and reliability, loading efficiency, maneuverability, and cost and energy consumption of vehicles. Therefore, the research on fault analysis and maintenance technology for the lifting hydraulic system of dump trucks has practical significance.
1. Structural principle of hydraulic lifting system
Dump trucks, commonly known as engineering trucks or dump trucks, refer to vehicles that unload goods on their own through hydraulic or mechanical lifting. The working principle of its hydraulic lifting system is to use engine power to drive the hydraulic mechanism, that is, the engine power is output by the transmission, and the hydraulic oil pump is driven by the power take-off. The hydraulic oil is pumped to the distribution valve and pressed into the hydraulic cylinder, thereby pushing the piston to lift the bucket, tilt the bucket at a certain angle, and automatically unload the cargo, and rely on the weight of the cargo box to reset it.
At present, the hydraulic lifting mechanism widely used in large tonnage dump trucks is mainly composed of lifting cylinders, control valves, lifting manual control valves, limit valves, and lifting oil pump assemblies. The lifting mechanism relies on the lifting of the lifting cylinder to complete the lifting process. The lifting cylinder is controlled by a control valve, which is operated by the driver. In order to limit the Z-tilt angle of the bucket and ensure that the bucket can be stabilized at a certain tilt position as needed, a limit valve is installed in the hydraulic system.
The hydraulic dumping mechanism is the core of a dump truck, and its performance and quality are the primary indicators for judging the quality of the dump truck. The vehicle model positioning and market positioning of the lifting and dumping mechanism are also different. When designing the lifting hydraulic system, it is necessary to comprehensively consider the power, smoothness, compactness, unloading performance, and maintenance free performance of the lifting.
2. Classification and selection analysis of lifting mechanisms for dump trucks
2.1 Main classification of lifting mechanisms for dump trucks
Usually, according to the different directions of cargo dumping, dump trucks can be divided into rear tilting, side tilting, three sided tilting, and bottom dumping types. They are mainly composed of hydraulic lifting mechanisms, car buckets, frames, and accessories. Each manufacturing and modification manufacturer has different design concepts, and their hydraulic lifting mechanisms and car bucket structures are also different. The structural types of car buckets can be divided into ordinary rectangular car buckets and mining bucket cars according to their different purposes. The ordinary rectangular hopper is used for the transportation of bulk goods, and its rear plate is equipped with an automatic opening and closing mechanism to ensure smooth unloading of the goods. The thickness of the ordinary rectangular hopper plate is 4-6 mm for the front plate, 4-8mm for the side plate, 5-8mm for the rear plate, and 6-12mm for the bottom plate; The mining bucket carriage is suitable for the transportation of large stones and other goods with larger particle sizes. Considering the impact and collision of goods, the design shape of the mining bucket carriage is complex and the materials used are thick. For example, the standard configuration plate thickness of the Jiangnan Dongfeng dump truck mining bucket carriage is 6mm in the front, 6mm in the side, and 10mm in the bottom. However, some models add angle steel to the bottom plate, which can greatly improve the rigidity and impact resistance of the carriage.
2.2 Analysis of commonly used dump truck selection
At present, foreign dump trucks are developing in the direction of large tonnage, lightweight, diversification, and serialization, and more use of high-tech research and development to develop new models, in order to shorten the design and production cycle, improve product quality, and reduce costs. With the rapid development of automotive technology and the improvement of domestic purchasing power, dump trucks are not traditional universal vehicles. In order to fully meet the strict requirements of safe, efficient, fast, convenient, and cost-effective transportation of dump trucks, various manufacturing and modification manufacturers can develop dump trucks with vastly different functions according to different goods, different working conditions, and different regions, especially their optimized design of lifting hydraulic systems and lifting mechanisms, The lifting is stable and powerful, with high work efficiency and fuel economy, which can ensure the safety and stability of the dump truck under various loads and lifting conditions.
At present, traditional lifting mechanisms such as direct push, link amplification, and link composite are mostly used for dump trucks both domestically and internationally. However, common lifting mechanisms in China include T-shaped triangular frame amplification lifting mechanism, F-shaped triangular frame amplification lifting mechanism, dual cylinder lifting, front top lifting, and double-sided rollover. Among them, triangular frame amplification lifting mechanism is the most commonly used in China, with mature structure, stable lifting, and low cost, However, the length of the bucket is 4.4-6m, and the closure height between the bottom plate of the bucket and the upper plane of the main frame is relatively high, with a suitable load capacity of 8-40t; The double cylinder lifting form has a small closing height between the bottom plate of the car bucket and the upper plane of the main frame, but the hydraulic system cannot ensure synchronization between the two hydraulic cylinders, resulting in poor lifting stability and high overall stiffness requirements for the bottom plate of the car bucket. It is often used in 6 × 4 dump trucks; Most countries in Europe, America, and other countries use the front top lifting method, which has a simple structure. The closing height between the bottom plate of the car bucket and the upper plane of the main frame can be very small, and the overall stability of the vehicle is good. The hydraulic system pressure is small, making it suitable for transportation under heavy road loads, especially for transporting coal, mineral sand, and loose and easily unloaded goods; But the front top multi-stage cylinder has a large stroke and high cost; The double-sided rollover hydraulic cylinder has good force and small stroke, which can achieve double-sided rollover. However, the hydraulic pipeline design is more complex, resulting in a higher rate of lifting rollover accidents.
3. Fault analysis of lifting hydraulic system
3.1 Unstable lifting or insufficient lifting angle
Fault phenomenon: The main manifestation of this fault is insufficient oil or air mixed in the oil, and the car bucket cannot be lifted to a large angle of Z.
Fault analysis: The oil inlet pipe and pipeline joints of the oil pump are not tightly sealed, the rubber structural components are aging, and when replacing hydraulic components or opening the oil tank, air is easily mixed into the hydraulic system. During use, it is necessary to maintain the good performance and correct installation of the rubber sealing rings of the hydraulic system. Newly installed hydraulic components must be soaked and filled with oil to drain; Lip wear and elasticity? Rubber seals that have decreased or aged should be replaced in a timely manner; After changing the oil tank, during the initial operation or maintenance of the system, it is necessary to start the machine for several cycles to exhaust the air in the system; When the bucket or lifting rod is severely deformed, it must be corrected immediately; When the rotating pair is worn and lacks lubricating grease, lubricating grease must be added; When the hydraulic oil level is insufficient, it is necessary to replenish the hydraulic oil in a timely manner; When the hydraulic oil is dirty, dirty, or deteriorated, clean hydraulic oil should be replaced.
Before lifting the car bucket, try to exhaust the air mixed into the system as much as possible; When lifting the bucket to a close angle of Z, stop. First, loosen the vent plug on the upper part of the hydraulic cylinder a little to escape air. When normal oil is discharged, tighten the plug quickly. If no oil or air is discharged, it indicates that the bucket lifting angle is not enough. Continue to keep the oil pump running at low speed until normal oil is discharged. If the oil and air are mixed into foam shape and foam continues to appear, the compartment bucket can be placed at the deflation position for a period of time, and the air can be exhausted after the air gradually comes out of the foam, but the oil level should be paid attention to and the oil should be replenished.
3.2 The car bucket cannot stop in the middle after lifting
Fault phenomenon: The main manifestation of this fault is that the car hopper cannot stop at any position.
Fault analysis: When there is significant internal leakage in the directional valve or oil cylinder, the location of the leakage should be investigated and the leaking components replaced; When reversing under heavy load, the valve stem is subjected to high hydraulic power, causing the reversing valve to malfunction, resulting in occasional no intermediate stop. Therefore, the reversing valve must be turned to the slow lowering position; When the directional valve is not in place or stuck, the directional valve must be replaced; When the distribution valve and return valve are not tightly sealed, the sealing components must be tightened or replaced; When the one-way valve inside the hydraulic one-way valve is not tightly controlled, the one-way valve needs to be repaired or replaced; When the oil is too dirty, it is easy to cause the check valve to not seal tightly, and the hydraulic oil needs to be replaced; When the viscosity of hydraulic oil is too low, replace it with hydraulic oil with high viscosity; When there is oil leakage in the pipeline, it is necessary to repair the pipeline; When the manual control valve joystick is not in place, the joystick should be adjusted.
3.3 The car bucket cannot fall after lifting
Fault phenomenon: The main manifestation of this fault is that when the car bucket is in the lifting or middle position, the manual directional valve is turned to the lowering position, and the car bucket cannot automatically fall.
Fault analysis: The main cause of the malfunction is insufficient air pressure, which prevents the distribution valve and return valve from operating, resulting in the hydraulic oil in the lower chamber of the oil cylinder not being able to smoothly return to the oil tank. This will generate a certain negative pressure and prevent the bucket from falling. The truck should be started to achieve the specified air pressure, or the manufacturing process and inspection method of the distribution valve should be improved to eliminate it by improving the design; When the manual control valve control handle is not in place, the control handle should be adjusted to make it in place; The operation is not standardized, and when the lifting angle exceeds the designed Z maximum lifting angle, it is easy to cause jamming. It is necessary to disconnect the power take-off and allow the vehicle to start and move forward before braking, and then use inertia to lower the car bucket; When dumping goods on a ramp for lifting, it is often beyond the limit of the lifting angle. At this time, it is advisable to dump on a flat road surface as much as possible; When the limit valve or safety valve malfunctions or the limit valve pipeline is damaged, immediate repair or replacement is required; When the lifting cylinder is stuck or concave, or the piston rod is bent or deformed, it is easy to get stuck on the piston rod and affect the fall of the bucket. It is necessary to straighten the piston rod or repair the cylinder body; When the lifting and dumping mechanism is not used for a long time or is contaminated by impurities, it may sometimes cause stagnation. It should be maintained, lubricated, maintained or replaced according to regulations; When there is too much hydraulic oil in the oil tank, it can also affect the bucket to fall back, so it is necessary to adjust the hydraulic oil to the normal level; When there are foreign objects blocking the hydraulic system, they should be removed, the oil tank should be cleaned, and the filter screen should be replaced.
3.4 Not lifting during heavy loads
Fault phenomenon: The main manifestation of this fault is that the bucket cannot be lifted when the truck is fully loaded with goods, but the bucket is lifted normally when the truck is empty.
Fault analysis: When the vehicle is severely overloaded, it is very easy to damage the oil pump and also cause deformation and damage to the transmission shaft. It must be strictly shipped according to the rated loading capacity, and overloading is strictly prohibited; When the vehicle is parked on a heavily sloping slope, it should be parked in a suitable position before being lifted; When the nut fastening the piston is loose, or when the oil cylinder piston ring is aligned, broken, or the piston is broken, it can cause the sealing rubber ring between the piston and the piston rod to be not tightly sealed and cause oil leakage. It is necessary to tighten the piston nut or replace the piston ring or piston; When the control valve stem is severely worn, hydraulic oil is prone to leakage from the valve stem, and it is necessary to replace the valve stem and re grind it; When there are leakage faults in the lifting cylinder, valve, and pipeline, the vehicle should be stopped to investigate the leakage location and promptly eliminate the leakage point; When the connection between the main shaft of the transmission box and the oil pump is detached or damaged, the connection between the main shaft of the transmission box and the oil pump should be replaced; When sweeping the bore of the oil pump body, it is easy to strain the pump body, causing the low-pressure and high-pressure oil chambers to connect, and reducing the oil pressure output by the gear pump. Spray welding should be used in a timely manner for repair to avoid early scrapping of the oil pump; The hydraulic oil is dirty and contains many impurities, which can easily block the control valve. It is necessary to replace all hydraulic oil and remove impurities; When the viscosity of the oil is too low, it is necessary to replace it with a suitable hydraulic oil.
3.5 Do not lift under no load or heavy load
Fault phenomenon: This fault mainly manifests as power take-off failure, lifting switch or solenoid valve failure, severe overload, or hydraulic system leakage.
Fault analysis: When the connecting plug of the power take-off solenoid valve falls off or the internal coil is burned, causing the power take-off transmission shaft to not rotate, the connecting plug should be tightened or the solenoid valve should be replaced; When the solenoid valve at the rising position of the lifting bidirectional solenoid valve is damaged, emergency measures can be taken, such as replacing the air pipes of the lifting and lowering solenoid valves, and pulling the lifting switch to the lowering position to lift the bucket. When the bucket needs to be lowered, the air pipes should be replaced in their original positions. However, this method should not be used for a long time to avoid accidents; When the gear pump casing is worn, causing the low-pressure oil chamber and high-pressure oil chamber to connect, or when the W-shaped sealing ring at the rear of the gear pump is punched, the gear pump or sealing ring must be replaced in a timely manner; When the nut fastening the piston is loose, the cylinder piston is cracked, or the piston ring is broken or aligned, causing the sealing rubber ring between the piston and piston rod to be not tightly sealed and causing oil leakage, the nut should be tightened in a timely manner and replaced? Damaged piston or piston ring.
3.6 Abnormal slow or no lifting
Fault phenomenon: This fault mainly manifests as insufficient oil pressure or air mixing in the oil.
Fault analysis: Corresponding treatment methods should be taken based on different conditions. For example, when the system is out of oil, hydraulic oil needs to be added to the specified height; When there is a significant leakage in the lifting cylinder, the lifting cylinder should be repaired; When the hydraulic pipeline is damaged, it is easy to generate a large amount of leakage, leading to a serious shortage of oil in the system. It is necessary to replace the hydraulic pipeline; When the lifting oil pump is severely worn or rotates in the opposite direction, it should be repaired or replaced; When the one-way valve inside the hydraulic lifting valve has foreign objects, is not tightly closed, or is loose, detached, or obstructs the pipeline, it is necessary to clean the one-way valve; Manual control valve joystick? When in place, the distribution valve gear should be adjusted; When the viscosity of hydraulic oil is too low or deteriorates, the hydraulic oil should be replaced; When the hydraulic oil tank switch is not fully opened, it should be fully opened; When the bucket is severely overloaded and the pressure of the hydraulic system exceeds the overflow pressure of the distribution valve, the overflow valve begins to unload, causing the bucket to be unable to lift. It needs to be unloaded to the rated load before lifting; When air is mixed into the hydraulic system, it should be drained as much as possible; When the resistance of each rotating pivot is too high, methods such as adding lubricating grease to each lubrication point need to be used to solve the problem.
3.7 The carriage bucket descends by itself or the descent speed is too slow
(1) The carriage hopper descends on its own
Fault phenomenon: The main manifestation of this fault is that during the lifting process of the carriage, the manual directional valve is moved to the middle stop position (pressure maintaining state), and the carriage cannot stop lifting, but instead falls back on its own; During the lowering process, if the manual directional valve is turned to the mid stop position, the carriage cannot stop lowering.
Fault analysis: The main reason for self lowering is that there is a partial loss of pressure in the hydraulic system, and the existing pressure is difficult to overcome the weight of the bucket, resulting in the bucket lowering; The leakage inside the oil cylinder causes the hydraulic oil in the upper and lower chambers of the oil cylinder to be connected, and the hydraulic oil in the lower chamber cannot maintain pressure, causing the bucket to descend on its own; The pneumatic distribution valve body and valve core are not tightly sealed, resulting in partial communication of the hydraulic pipeline. The hydraulic oil in the oil cylinder returns to the oil tank through ports A and O, making it difficult to achieve the pressure retaining effect of the lower chamber of the oil cylinder; The one-way valve at the high-pressure oil pipe joint of the pneumatic distribution valve is stuck by foreign objects or not tightly sealed, causing the oil cylinder to fall on its own after oil return. It must be cleaned and blown clean with compressed air; When there are no foreign objects in the one-way valve, it may be due to the loose sealing of piston rings and other related components, causing oil leakage. It is necessary to tighten the nuts that fix the piston in a timely manner and replace the damaged piston or piston ring.
(2) The lowering speed of the carriage hopper is too slow
Fault phenomenon: This fault mainly manifests as a blockage or malfunction of the hydraulic system.
Fault analysis: The main cause of the fault is blockage of the hydraulic system (pipelines and hydraulic components), and when there are many impurities in the hydraulic oil, the troubleshooting method is to replace it with high-quality hydraulic oil; The movement of the valve core of the pneumatic distribution valve is not in place, causing the hydraulic oil in the hydraulic pipeline to be blocked when returning to the oil tank and passing through the A and O ports of the distribution valve during the lowering process of the bucket, forming a certain negative pressure, thereby affecting the lowering speed of the bucket; Some moving parts are stuck or burned, and the elimination method is to remove the stuck parts and add grease in a timely manner.
3.8 When lifting, the bucket tilts or the cylinder is pulled out
(1) Dipper tilt
Fault phenomenon: The main manifestation of the tilting fault of the car bucket during lifting is that the car bucket tilts to one side during lifting.
Fault analysis: When the car bucket pin is dropped, the car bucket must be quickly lowered and returned to the warehouse for repair; When the tire is severely out of air or has a flat tire, it is necessary to inflate the tire to standard pressure or replace the tire; When the stabilizer rod ball head breaks or the pin falls off, the stabilizer rod ball head should be replaced and the pin tightened; Truck suspension fracture is a malignant fault, and structural design should be improved to strengthen the suspension system and improve its reliability; Lifting the car bucket on sloping ground should be avoided, and the vehicle should be parked on flat ground before lifting.
(2) Cylinder extraction
Fault phenomenon: The main manifestation of the cylinder pulling fault during lifting is that when the car bucket is lifted to the rear section of Z, it cannot control the automatic lifting.
Fault analysis: When the lifting angle of the trunk bucket is too small and the rear suspension is too long, the vehicle needs to be redesigned and installed; When the installation position of the limit valve is incorrect, the installation position of the limit valve should be readjusted. If the cargo is a large object and the lifting angle is too small, the lifting angle must be adjusted to achieve a Z angle of travel; When the fixing bolts of the bucket limit switch are loose, they should be tightened in a timely manner; The lifting limit switch is a vulnerable component with a high failure rate. When the clearance of the lifting limit is too large or deviated, it can easily lead to the failure of the lifting cylinder to pull out the cylinder, which can break and damage electrical components, engines, and oil pipes, and even lead to major safety accidents. The maintenance intensity is high, the cost is high, and it seriously affects the vehicle's operability. To avoid the failure of lifting the cylinder, when the bucket is lifted to the set height, the lifting operation should be immediately stopped; At the same time, strengthen daily inspections to eliminate potential accident hazards in their early stages.
3.9 The carriage bucket falls in the "mid stop position"
Fault phenomenon: The main manifestation of this fault is that the carriage hopper will fall at any position.
Fault analysis: When the one-way valve of the gear pump is not tightly sealed, it is necessary to repair the gear pump and one-way valve; When the control valve or directional valve malfunctions, repair or replace the control valve or directional valve; When there is leakage inside the hydraulic cylinder, causing the pressure to be unable to be maintained, the hydraulic cylinder piston and piston ring should be repaired, and the hydraulic cylinder should be replaced if necessary.
3.10 There is traction when lifting the car bucket
Fault phenomenon: The main manifestation of this fault is that the vehicle has traction after unloading the ore and rock without overtaking the switch.
Fault analysis: The main cause of the fault is the proximity switch and circuit failure of the car bucket; Some vehicles have traction after lifting, which is a normal phenomenon for GE company due to vehicle safety considerations, and the speed is limited to 5mph.
3.11 The bucket does not land or the landing is not flexible
Fault phenomenon: This fault mainly manifests as excessive lifting angle, hydraulic cylinder or control valve failure.
Fault analysis: When the lifting angle is too large, if the dump truck is unloading on a slope and the bucket exceeds the stable point, the vehicle needs to be parked on flat ground before lowering the bucket; When the sealing pressure at the head of the hydraulic cylinder is too tight, adjust the compression nut to ensure that there is no oil leakage at the head of the hydraulic cylinder; If the hydraulic cylinder bracket is not installed properly, readjust the installation; When the piston rod is bent, it must be corrected or replaced; When the lifting control valve fails and cannot return, the control valve should be repaired or replaced; When the lifting control circuit is disconnected or the control lever is broken, it is necessary to repair the circuit or replace the control lever.
3.12 Shaking when lifting the trunk bucket
Fault phenomenon: This fault mainly manifests as shaking during the test drive lifting after system maintenance or replacement of high-pressure oil pipes, but it rarely occurs during heavy vehicle lifting and strong lifting.
Fault analysis: During the test drive after maintenance, it is necessary to repeatedly lift the hydraulic system several times to eliminate any air mixed in; When the power take-off or oil pump is damaged, it is necessary to replace the power take-off or oil pump; When the connecting devices such as the car bucket and auxiliary beam are deformed, improvements or repairs should be made; When the flow rate of the oil inlet pipe changes too much, it is necessary to check the oil circuit; When there is an internal leak in the oil pump, it should be promptly repaired or replaced; When the hydraulic oil tank is short of oil, it is necessary to replenish the specified model of hydraulic oil. If the hydraulic oil is too dirty or there are many impurities in the hydraulic oil tank, it is necessary to remove the impurities in the system, clean the oil tank, and then replace it with a new filter and hydraulic oil.
3.13 The car bucket cannot be overturned
Fault phenomenon: The main manifestation of this fault is a lack of hydraulic oil in the fuel tank; Oil pump, valve?? Or control the cylinder to mix air, etc.
Fault analysis: When the oil level in the hydraulic oil tank is insufficient and the bucket is in its original position, it is necessary to add enough oil to the specified value; When the circuit breaker valve is stuck, it is necessary to use a lever to adjust the valve to its original position or replace the valve; When the oil pump connected to the transmission cannot operate normally, the sealing of the oil circuit from the transmission housing to the control cylinder should be checked; When the hydraulic distribution valve is not working or malfunctioning, some pipelines should be loosened, and the control cylinder should be checked for air mixing. The control cylinder needs to be disassembled for cleaning, and then replaced with a new distribution valve.
3.14 Hydraulic cylinder or rod pulled or leaking oil
Fault phenomenon: This fault mainly manifests as the damage of oil cylinder components or the failure of sealing components in actual work, resulting in the inability of the oil cylinder to function properly.
Fault analysis: When the vehicle is biased, the goods must be unloaded correctly; When the clearance of the oil cylinder bracket exceeds the tolerance or the installation of the oil cylinder is not vertical, the bracket clearance should be adjusted properly; When the cylinder is lifted and interfered with or damaged by other components, it needs to be redesigned and installed; After overturning, when continuing production, the damaged parts related to the oil cylinder should be replaced; When unloading, the roadbed is uneven and must be strictly operated and used in accordance with the requirements and standards; When the nut at the top of the oil cylinder is loose, tighten the nut at the top of the oil cylinder according to the torque; When the fit clearance between the oil cylinder trunnion and the bracket hole is too large, damaged components should be replaced; When the hydraulic oil is dirty, the oil filter and hydraulic oil must be replaced.
When the vehicle deviates multiple times, it is necessary to load the goods correctly and replace the sealing kit; When the cylinder is pulled, it is necessary to replace the cylinder and sealing kit; When the installation position of the oil cylinder does not meet the requirements, the cylinder barrel should be replaced and the position of the oil cylinder should be readjusted; Avoid illegal operations and do not lower the oil cylinder while driving; Seals are prone to accelerated aging and failure in high-temperature environments, and oil seals or sealing rings must be replaced in a timely manner; When the air filter of the fuel tank is dirty, the air filter must be replaced; When the oil cylinder air port overflows, if the oil level in the tank exceeds the liquid level gauge, a small amount of oil in the tank can be drained; When the hydraulic oil model is incorrect, a suitable hydraulic oil should be replaced.
3.15 Air control valve or limit valve stuck
Fault phenomenon: The main manifestation of this fault is the sudden failure of the air control valve or limit valve.
Fault analysis: When impurities are mixed into the air control valve, it should be cleaned or replaced; When the limit valve core fails, the limit valve needs to be replaced; When the air pipe is damaged and leaks, tighten the joint or replace the air pipe; When there is a bending phenomenon in the trachea, it is necessary to rearrange the direction of the trachea.
3.16 Oil pump leaking, not rotating, or burnt
Fault phenomenon: This fault mainly manifests as increased oil pump noise, insufficient or no pressure in the hydraulic system, insufficient or no displacement of the oil pump, and high temperature.
Fault analysis: When the heavy load of the carriage bucket drops too quickly, the oil chamber pressure is too high, or the spline shaft scratches the self tightening oil seal at the oil pump journal, it is easy to damage the oil seal and cause leakage; Due to uneven force on the "O" type sealing ring between the oil pump and the transition plate, leakage can occur, which can also increase the noise of the oil pump and reduce the pump oil pressure. Therefore, when installing the journal oil seal, it is important to be cautious and ensure that the low-pressure chamber pressure is within the rated range; When the fastening bolts between the oil pump transition plate and the distribution valve are loose or the sealing ring is damaged, there is a significant leakage, and the sealing ring needs to be replaced and tightened; When impurities are mixed into the joint surface, it is usually possible to tighten the high-pressure side bolts, replace the sealing ring, clean the 2 mating surfaces, and then apply sealant.
When the sealing ring inside the oil pump is damaged or the input shaft end frame oil seal is damaged, spare parts must be replaced; When the loose bearing at the input end of the gear oil pump causes scratches on the pump body and gear, it is necessary to replace the bearing and grind the scratched parts of the pump body; When the gear oil pump drive shaft skeleton oil seal is damaged, causing oil leakage at the drive shaft, a new skeleton oil seal should be replaced; When the sealing surface of the oil outlet flange is poor, and the sealing surface or sealing ring is damaged, it needs to be repaired or replaced; When the sealing surface of the joint between the rear cover and the shell is poor and oil leaks, it is necessary to check the sealing surface for scratches, burrs, deformation, dirt, etc., and make appropriate repairs; When there is abnormal noise in the oil pump or the pump oil pressure is low, timely maintenance or replacement should be carried out.
When the transmission mechanism or gear shaft sleeve of the oil pump is damaged, cannot operate, or has severe internal leakage, it is necessary to immediately replace the spare parts and repair them; When the connecting sleeve between the oil pump and the power take-off breaks, the connecting sleeve must be replaced; When the oil pump is stuck or the power take-off malfunctions, it is necessary to repair or replace the oil pump or power take-off; When the power take-off operating system malfunctions, timely maintenance should be carried out; When the hydraulic oil is insufficient, dirty or severely deteriorated, it should be promptly replenished or replaced with clean hydraulic oil; The oil pump operates without load for a long time, and the power take-off is required to shift out of gear when it is not working.
3.17 Insufficient or no oil absorption
Fault phenomenon: The main manifestation of this fault is that the hydraulic system is slow or unable to rise and fall (forward and backward); During the lifting (forward and backward) process, the hydraulic system pressure is unstable or generates noise, and the oil in the tank emits bubbles; Damaged gear pump or sudden increase in oil temperature.
Fault analysis: The oil suction pipe is too thin or too long, and there are dead corners at the bend. When there are too many bends, the oil suction pipe must be thickened or shortened to prevent dead corners and reduce bends; When the oil suction pipe leaks, it is necessary to identify the leak and handle it; The oil suction filter screen and oil suction pipe are blocked, clean the filter screen and remove the blockage; When the oil level in the fuel tank is too low or there is no oil, oil must be added to the specified height; When the viscosity of the oil is too high, hydraulic oil recommended by the manufacturer should be used; When the sealing surface of the oil suction flange is poor, it is necessary to check the sealing surface for deformation, burrs, scratches or dirt, and make appropriate corrections; When inhaling air from the oil seal of the driving journal framework of the gear pump, it is necessary to remove the gear pump, check if the framework seal is damaged, and replace the framework seal if necessary.
3.18 No-load noise or hydraulic system howling
Fault phenomenon: The fault of the vehicle making noise when unloaded is mainly manifested as the slow sinking of the car hopper when the vehicle is unloaded, and intermittent noise will be generated, but this phenomenon is a normal phenomenon. What are the main causes of hydraulic system howling faults? When overloading the vehicle, it will cause the system pressure to be too high, the safety valve to open, and accompanied by a sharp howling sound.
Fault analysis: The main reason for the no-load noise fault is that the clearance between the transmission shaft and the shaft sleeve is small, the lubrication is not sufficient, and the friction force is high, causing the vehicle to sink intermittently. Intermittent sliding and noise are generated due to friction. This type of fault will gradually disappear after the sliding surface is fully lubricated during use.
Other sounds usually occur when the oil pump is under overload, and at this time, it must be operated at reduced load. If the handling capacity is appropriate, it is due to the low setting pressure of the safety valve causing it to open, and the opening pressure can usually be adjusted according to regulations.
4. Conclusion
The lifting hydraulic system is a key working system for dump trucks, and its performance is superior?? The main performance indicators that affect the vehicle are related to its safety, transportation function, and self unloading function. The quality of its working state is related to the vehicle's work efficiency and engineering progress. Therefore, conducting in-depth research on the fault analysis and control technology of the lifting hydraulic system of dump trucks can significantly improve the operational efficiency, integrity rate, and operability of vehicles.
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2023-09-08