The characteristics of the dump truck engine are based on the working conditions of the dump truck, requiring a large torque reserve in the low-speed section of the engine to be equipped and a fast speed response. At the same time require that the clutch, air compressor, starter and other accessories have a good adaptability. For example, a 4102 naturally-aspirated engine of an engine factory was originally a mature model for flat panel cars. However, when it was originally equipped with a dump truck, it found that the torque reserve in the low-speed stage was insufficient, the speed responsiveness was poor, and some accessories could not be adapted to the requirements of the dump truck. The failure rate is high. In the later stage, a series of adaptability improvements to the engine and accessories have obvious effects and can better meet the working conditions of the dump truck. The following is an example of the 4102 engine for analysis. Medium-high speed performance is superior, but low-speed performance is relatively poor. Governor initial state: With two-pole governor, only control the maximum speed and the minimum speed, between the highest speed and the lowest speed governor. Improved state: Reconfigure the whole speed governor, not only can control the maximum speed and minimum speed Under the supply of fuel, and can control the maximum rotational speed and the minimum rotational speed between the supply of fuel at any speed, more effectively adapt to the characteristics of dump trucks frequently changing speed. It has been verified that the improved engine speed response capability has improved significantly.
Clutch initial state: with φ275 diaphragm clutch, friction plate (outer diameter × inner diameter) φ275×φ180, torque capacity 400N.m, pressing force 6500N. Failure mode: Clutch slipping, burning and other faults. Analysis of reasons: Dump truck overload is more serious, especially starting or climbing conditions and other sliding conditions produce a larger work force, and the smaller pressing force will make the clutch slip, φ275 diaphragm clutch thermal capacity can not meet the requirements of such conditions The clutch heat capacity and platen pressing force should be increased to increase the reserve factor.
Improvement status: The φ300 diaphragm clutch was reconfigured, the friction plate (outer diameter × inner diameter) φ300×φ190, the torque capacity was increased to 480 N.m, and the pressing force was increased to 7500N. In view of the fact that the friction coefficient of the original friction plate decays rapidly with increasing temperature, the formula of the friction plate material is improved, the friction coefficient is increased, and the wear rate is reduced. After the improvement, it was verified that the clutch slippage, burning and other defects were significantly reduced. The performance of the friction plates before and after the improvement is shown in Table 1.
Due to the high reliability of pneumatic brakes in air compressors, most dump truck engines are currently equipped with air compressors. Initial state: With air-cooled air compressor, single cylinder, piston diameter φ65, intake unloading mode, working pressure 0.8MPa, rated displacement 125L/min. The air compressor comes with a small air filter.
Failure mode: The unloading valve is stuck, the engine oil is not used, the pumping speed is slow, and the failure rate is high. Some of the small air filters that were discovered during the inspection were clogged with dust and some had a sticky cylinder. Analysis of the causes: The possible causes of the failure of the unloading valve such as stuck and not pumping are: after long-term use, the unloading valve lacks lubricating oil or sticks more dust, and the friction force increases causing the unloading valve to become stuck.
The air-cooled air compressor has poor cooling effect in a low-speed working environment. The long-time working heat load is large, and the valve plate is easily deformed under high temperature. Small air filter filter effect is not good, in the absence of timely maintenance (a lot of users ignore the maintenance of the air compressor comes with a small air filter), no air intake leads to not cheer.
Small air filter filter results in poor dust will cause the unloading valve plunger stuck, resulting in the plunger is not reset in the normally open state, do not pump. The possible causes of engine oil failure are: poor air filter filtration results in premature wear of the piston ring. The piston ring wears badly.
Improved status: Reconfigured water-cooled air compressor, single cylinder, piston diameter φ65, exhaust unloading mode, working pressure 0.8Mpa, rated displacement 125L/min. The cylinder head of the air compressor is cooled by the engine's circulating water to ensure reliable operation under conditions with poor conditions and to improve the cooling effect of the air compressor. And cancel the air compressor comes with a small air filter, the air compressor from the engine intake manifold or engine after the air filter to ensure air compressor clean intake. At the same time, the width of the scraper ring was changed from 0.8 to 0.35, and the surface of the piston ring was treated to improve wear resistance. Fig. 1 Improved front and rear engine torque characteristics comparison curve.
In fact, the damper cooling wind speed is often less than 13m/s. From Table 2, it can be seen that the air-cooled air compressor has a significantly higher temperature than the water-cooled air compressor, which has a greater negative impact on the life of the air compressor. In addition, when matching, ensure that the air compressor exhaust is sufficient. Otherwise, measures such as increasing the working volume of the air compressor or increasing the speed of the air compressor should be taken to increase the displacement. After verification by the market, the failure rate of the improved air compressor has been significantly reduced. Starter initial state: With ordinary starter, power 4.5kW, voltage 24V. Failure mode: The starter hits the teeth and the electromagnetic switch has a high failure rate. Analysis of reasons: Dump trucks are mostly short-haul transportation, and the engine startup is more frequent, requiring higher reliability of the starter. Radial and axial clearances of starter gears and flywheel ring gears are not suitable, or starter power or voltage drops are large and can cause teeth to fail. Improved state: Increase starter power to 5kW and voltage 24V. The chamfering structure of the starter pinion and the ring gear is improved, and the size chain and the tolerance band that affect the meshing stroke of the starter gear and the flywheel ring gear are strictly controlled. At the same time, electromagnetic switches and other components are optimized to improve the reliability of electrical devices. Verified by the market, the failure rate of the starter is significantly reduced after the improvement.
The initial state of the pump: The rated flow of the pump is 200L/min, and the speed of the water pump shaft and the crankshaft is 1.0. Use an ordinary seven-leaf plastic fan. Failure mode: The high temperature of the engine when the engine is running at low speed for a long time. The temperature difference between the inlet and outlet of the radiator is measured at 4.8°C. Analysis of the reason: The temperature difference between the inlet and outlet of the radiator is 4.8°C, which means that the radiator itself has enough cooling capacity. The cooling capacity of the engine itself is not sufficient to dissipate the heat generated in time and further improvement is needed. Improved state: The ratio of the water pump shaft to the crankshaft speed is increased to 1.15, which increases the circulation speed of the cooling water and the water flow rate of the pump while increasing the air flow. At the same time, the fan tooth angle is adjusted to improve the suction capacity. After verification, the water temperature is higher than the troubleshooting. The initial state of the flywheel housing and the clutch housing: The material of the flywheel housing is not reinforced by the protruding parts of the starter.
Failure mode: Fracture phenomenon in the flywheel housing or clutch housing (particularly in the starter area). Analysis of the reasons: Due to the working conditions of the dump truck, the generated vibrations are transmitted to the flywheel housing or the clutch housing. Fatigue cracks are easily formed in the structurally weak parts. Strengthened structures and weak parts should be strengthened in terms of structure and material. Improve the status: Change the material of the flywheel housing and clutch housing to further improve the mechanical performance. At the same time, the ribs are added to the stressed parts of the flywheel housing to optimize the structure. After the improvement, the failure rate of the flywheel housing and the clutch housing is significantly reduced.
Conclusion To sum up, in order to adapt to the special working conditions of the dump truck, the engine should meet the following requirements; the overload of the dump truck is serious, the design strength of the whole machine (especially the running parts) must be increased, and the clutch reserve coefficient must be large. Dump trucks have poor road conditions. They are frequently used in the middle and low-speed sections, and the maximum torque points are appropriately adjusted. The low-speed torque reserve in the engine is sufficient. The speed change of the dump truck is frequent and the speed response is better, and the full speed governor should be matched. Dump trucks are mainly used for short-distance transportation and start-up is frequent. The reliability of the starter is higher. Dump trucks operate at medium and low speeds. The engine must have strong heat dissipation capacity, and the pump and oil cooler must have large flow. The driving environment of the dump truck is bad, and the braking performance is required to be high. The displacement of the air compressor is large and the reliability is high. The vibration of the dump truck is large, the rigidity and strength of the body are high, and the flywheel housing, clutch housing and other components should be designed in terms of material, structure, etc.
Semi Automatic Soldering Machine
SUZHOU DEGU MACHINERY CO.,LTD , https://www.deguwindingmachine.com