Analysis of the design of the hydraulic system of lifting mechanism of the dump

开篇：润墨网以专业的文秘视角，为您筛选了一篇Analysis of the design of the hydraulic system of lifting mechanism of the dump范文，如需获取更多写作素材，在线客服老师一对一协助。欢迎您的阅读与分享！

Abstract. The hydraulic lifting mechanism is one of the important working systems of the dump truck， and its structures and performances directly affect the performances and safety of the dump truck. This paper first describes the dump car， and at the same time， combined with the requirements of the design， the hydraulic systems are briefly described， as well as the design of the hydraulic lifting mechanisms and the hydraulic systems. The author introduces in details the design of the mechanical structures and the hydraulic systems of the hydraulic cylinder of the dump truck. According to the general principles and steps of the design， the author conducted the detailed design and calculation of the mechanical structures and the hydraulic systems of the hydraulic cylinder， and suitably chooses the ancillary components， and finally gets a complete set of the car dumper system meeting the requirements.

Keywords： Dump truck， mechanical design of the hydraulic cylinder， design of the hydraulic system

1. Introduction

1-1. Review of the self-discharging dumper

The dump truck is also called the tipper， which is the handling equipment developed with the use of the high-tech， emerged with the development of the times， because the handling work cannot be achieved by the humans. It is an important special automobile to rely on the engine-driven hydraulic lifting mechanism to make the container inclined to a certain angle so as to achieve the purpose of the automatic unloading， and rely on the body weight to make it reset. Its biggest advantage is that it realizes the mechanization of the discharge， so as to improve the unloading efficiency， reduce the labor intensity， and save the labor. Therefore， for decades， it has obtained the rapid development and popularity at home and abroad， and has its special automobile ownership accounting for about 25%， and is gradually perfect， becoming a series of products with multiple varieties.

There are many classifications of the dump trucks， which is generally classified in the following ways. By the usage， it can be divided into the ordinary truck for the road transportation， the heavy tipper for the non-road transport， and the special dump truck. According to the quality of the loading， it can be divided into the light truck， the medium truck and the heavy dump truck. According to the transmission type， it can be divided into the mechanical transmission， the hydraulic transmission and the electric drive. According to the classification of the unloading methods， it can be divided into the rear tipping type， the roller type， the three-side dump， the bottom and the cargo increased after tilting. According to the dumping mechanisms， it can be classified into the straight pushing type tipper； and the lever lifting tipper. According to the structures of the truck， it can be classified into the one-side open， three-side open type of the press board structure， and no-column plate （a dustpan type）. According to the shape of the cross section of the base plate， it can be divided into the moment form， the bottom type， and the arc bottom.

1-2. The lifting mechanism of the dump truck

1） The tilting mechanism of the direct push type （the hydraulic cylinder directly acts on the car chassis）

2）The tilting mechanism of the connecting rod type （the tilt hydraulic lifting cylinder through the connecting rod mechanism acts on the chassis so that it can realize the overthrow of the cars by a smaller hydraulic cylinder stroke.）

2. The design of the hydraulic system of the dump truck

2-1. Overview of the hydraulic cylinder

The dump truck is an important special automobile to rely on the engine-driven hydraulic lifting mechanism to make the container inclined to a certain angle， so as to achieve the purpose of the automatic unloading， and to rely on the body weight to make it reset. According to the characteristics of the dump truck， the hydraulic cylinder of the dump truck can be designed into the single action of the single piston rod.

The front-end cover is the hydraulic cylinder of the flange， welding type， as is shown in Figure 2-1， which is the commonly used hydraulic cylinder in the engineering machinery， and can be used as the reference map of the design of the structure of the hydraulic cylinder of the dump truck. The hydraulic cylinder in Figure 2 is rated higher， up to 25MPa.

2-2. Hydraulic System Principle Diagram

Speed control loop： The system analysis uses the throttle， and the circular form as the open method.

The direction control loop： This design uses the manual three-position three-way reversing valve to control the oil direction.

In throttle system， usually supply the oil by the quantitative pump， and adjust the required pressure by the relief valve， and maintain the constant.

The oil that the oil pumps outputs unloads in the internal reversing valve， and this design uses the three-position three-way reversing valve for unloading.

2-3. Diagram of the hydraulic system

The hydraulic system diagram using the hydraulic cylinder to realize the three processes of the lifting， the intermediate phase and falling of the carriage is shown in the following chart. The names of each component are： 1--single rod hydraulic cylinder， 2--throttling valve， 3--hand-operated direction valve， 4--fuel tank， 5--overflow valve， 6--hydraulic pump， 7--non-return valve， 8―filter.

2-3-1. Lifting （Fig. 4）

The reversing valve 3 is in the lifting position， and the pressure oil is pumped through the one-way valve 7 into the cylinder chamber， and pushes the piston up through the triangular arm mechanism， so that the car roars. Until the limiting valve in the piston opens， the pressure oil that the fuel pump output flows back to the fuel tank， and the lifting straps， and the relief valve can be used to regulate the maximum pressure of the system.

The valve is in the intermediate phase， the oil that the pump output is unloading in the internal reversing valve， without pressure. There is no pressure of the oil in the cylinder， it will not lift the oil cylinder， and at the same time， the oil in the cylinder has been closed， so the truck is in the intermediate phase， and the carriage is in the stationary state.

The valve is in the foaling position， and the lower oil in the cylinder is connected to the oil tank. Under the weight of the compartment， the piston moves down. The cylinder oil runs back to the fuel tank through the throttle valve 2， and the falling speed can be adjusted by the throttle valve and in this process， we can make the pump stop rotating.

3. Analysis of the fluid pressure of the hydraulic cylinder and the selection of the rated pressure

3-1. Analysis of the fluid pressure

Assume that there is no pressure in the liquid returning cavity in the hydraulic cylinder， the fluid pressure of the hydraulic cylinder has two forms. One is the fluid pressure acting on the piston， that is， the thrust， and the other is the fluid pressure acting on the annular area of the piston rod side， that is， the pulling force.

3-4. Comprehensive structural parameters of the hydraulic cylinder

The outer diameter D of the piston and the diameter d of the piston rod are the basic structural parameters of the hydraulic cylinder. In addition to D and d， the structural parameters of the hydraulic cylinder are the piston stroke S， the cylinder length L1， the piston width B， the length of the piston rod L and the structural types and sizes of the heads and tails of the piston rod， the orientation distance H， the oil inlet diameter d0 and the size of the thread interface （or flange）. The stroke of the hydraulic cylinder should be set according to the needs of the work， and in order to simplify the manufacturing process and reduce the manufacturing cost， we should adopt the series parameters of the standard travel size. In order to reduce the deflection of the axis of the cylinder when the cylinder piston rod extends out， the hydraulic cylinder should have the reasonable orientation length.

3-5. The selection of the safety coefficient

After determining the structural parameters of the hydraulic cylinder （at least once again after eventually settled down）， we can carry out the specific design of the structure： the shape and size of the parts and the processing requirements， the material， the connection methods and the strength checking， in order to design reasonably， and then it involves the choice of the safety coefficient.

The choice of the safety coefficient is not mandatory， but we must try to choose a smaller number in the safe condition. If the safety factor is too large， not only will it cause the unnecessary waste， and improve the cost， but it will also cause the hydraulic cylinder dimensions large， and so is the weight， which often cannot meet the job requirements. But the safety factor should not be too low， in order to avoid the accidents.

3-6. The design of the cylinder tube

3-6-1. The connection form of the cylinder tube and the cylinder head

The structural forms of the cylinder， that is， the connecting mode of the cylinder and the front-end cap is associated with its usages of the hydraulic cylinder， the working pressure， the working environment and the installation requirements and other factors.

The end cover is composed of the front cover and the rear end cover. The front cover will seal off the piston rod cavity （the plunger）， and plays the roles of the orientation， seal and dustproof for the piston rod. The back cover， which is the cylinder bottom， seals off the inner cavity of the cylinder at one end， and usually plays the role of connecting the hydraulic cylinder with the other parts of the machine.

There are eight common ways of the connecting models between the cylinder and the end cover： the pull rod type， the flange type， the welded type， the internal and external thread types， the inner ring and the outer ring type and the steel retainer ring type， among which the welding type is only suitable for the connection of the cylinder and the back cover.

For the fixed machinery， if the size and the quality have no special requirements， we recommend the use of the flange connection， and the connection mode has the advantages of simple structure， easy processing， easy handling， and widely used. The cylinder and the cylinder head are connected by the welding flange connection.

3-6-2. The requirements of the cylinder

The cylinder is the main part of the hydraulic cylinder， and together with the end cover and the piston， they constitute the sealing cavity， to accommodate the pressure oil， and the driving load and power， and there are the requests on the strength， stiffness， sealing and other aspects.

3-6-3. The selection of the cylinder materials

（1） The steel cylinder blank generally adopts the seamless steel tubes by annealing， cold drawn or rolling， and there are the semi-finished products already on the market whose inner holes are honed or finished， and we should just cut the seamless steel pipes according to the required length， and the materials are the No. 20， 35， 45 steel and the 27SiMn alloy steel.

（2） For the hydraulic cylinder whose working temperature is lower than -50℃， we must use 35 or 45 steel， and they will be treated.

（3） The cylinder welded to the flange or the cylinder head， we should use the 35 steel， and after the machinery processing， we can quench and temper it. For the cylinder that will not be wielded with other parts， we should use the quenched and tempered 45 steel.

（4） For the cylinder with thicker walls， we should use the cast iron or the foregoing， or use the thick steel plate to roll into a cylinder shape， and anneal seam after welded， and we should use the rays for the magnetic examination.

3-6-4. The geometric tolerance of the cylinder

The roundness， the conical degree and the cylindricity of the inner diameter of the cylinder should be not more than half of the diameter tolerances， and the error of the straightness of the cylinder axis should be not more than 0.03mm/500mm. The circular run-out of the cylinder end facing the axis is less than 0.04mm /100mm.

3-7. The design of the cylinder head and the oil inlet

3-7-1. The design of the oil inlet

The problems related to the design of the oil export are： the port size， the position， size， and the external connection methods. The external connection method of the oil outlet is mainly the ordinary fine thread， and the oil outlet connecting thread of the hydraulic cylinder should conform to the provisions of the GB/T2878-1993. The oil inlet of this hydraulic cylinder is usually offered in the cylinder， and the structure and the size are shown in the chart on the parts.

3-8. The design of the piston assembly

3-8-1. The materials and technical requirements of the piston rod

There are two kinds of the piston rods， the hollow type and the solid type. The outside diameter tolerance of the piston rod is mainly f8， and the surface roughness is generally Ra=（0.16～0.63）μm. When the requirement for the precision is high， select Ra≤（0.1～0.2）μm. The coaxial tolerance of the shaft neck matched with the inner holes of the piston and the diameter of the piston rod is not more than （0.01～0.02）mm， and the perpendicularity tolerance of the shaft shoulder to fit the piston and the axis of the piston rod is not more than 0.04mm/100mm.

3-8-2. The orientation of the piston rod

In the front cover of the cylinder， there installs the guide sleeve to guide the piston rod and the sealing elements to seal off the cylinder and the dust ring to prevent the dirt， moisture and impurities into sealing elements when the piston rod shrinks.

The tubing used in the hydraulic system consists of the hard tubes and the hoses， and the casing pipes should have the sufficient flow sections and the bearing capacities， and at the same time， we should try to shorten the pipelines， and avoid the sharp turns and the abrupt changes of the cross-sections.

5. Conclusion

Firstly， combined with the needs of the design， this paper expounds the hydraulic system， and introduces in detail the mechanical structures of the hydraulic cylinder of the dump truck and the design of the hydraulic system. According to the general principles and steps of the design， the author conducts the detailed design and calculation of the mechanical structures of the hydraulic cylinder and the hydraulic system， and the ancillary components are also calculated and selected. Finally， we can get a complete set of the car dumping system that can meet the requirements. There are a lot of the methods to design the hydraulic lifting mechanism of the dump truck， and this paper does not put forward the creative point of view， and then there must be more exploration.

References

[1] Liu Aiyun， Yuan Jianchang. Analysis and repair of the faults of the hydraulic system of the lifting mechanisms of the dump trucks [J]， Value engineering， 2011， （05）

[2] Yin Liang. The hydraulic cylinder of the new model of the dump truck [J]， Special vehicles， 2010， （03）

[3] Xu Gening， Zuo Yifan， Wang Jingchuan. The computer aided optimum design of the rod-connecting type of the lifting mechanism of the dump truck [J]， Construction machinery， 2008， （09）

[4] Liu Bo. Analysis of hydraulic dumping mechanism of the domestic dump truck [J]， Building， 2008， （20）