How does the closed hydraulic system of the truck crane ensure that the heavy objects lifted do not

Truck crane hydraulic system.

Author. liyue browsing.

Released. 1. Overview. The truck crane is a widely used construction machinery, which can walk at a fast speed, has good mobility, strong adaptability, does not need to be equipped with power supply, can operate in the field, and is simple and flexible to operate, so it has been widely used in transportation, urban construction, fire protection, large-scale material yards, infrastructure, first aid and other fields. Hydraulic lifting technology is used on the truck crane, which has a large bearing capacity and can work under conditions of shock, vibration and poor environment.

Because the action that the actuator of the system needs to complete is relatively simple, and the position accuracy is low, the system is mainly operated manually, and for the hydraulic system of lifting machinery, it is most important to ensure reliable and safe work in the design.

The truck crane is to use the matching truck as the basic part, add the corresponding lifting functional parts on it, form a complete truck crane, and use the power provided by the car as the hydraulic system power of the crane; When the crane is working, the tires of the car are not stressed, and the whole car is lifted by relying on four hydraulic support legs, and each part of the crane is lifted for lifting operations; When it is necessary to transfer the lifting operation site, it is necessary to retract each part of the crane to the car, so that the car can be restored to the functional state of vehicle transportation and transferred. General truck cranes have the following requirements in terms of function.

1) The whole machine can be easily transferred with the car to meet the requirements of its field operation mobility, flexibility, and no need to be equipped with power supply;

2) when carrying out lifting operation, the outrigger mechanism can lift the whole vehicle, so that all tires of the car are off the ground, free from the direct action of the lifting load, and the supporting state of the hydraulic outrigger can keep the position unchanged for a long time, and prevent the soft leg phenomenon when lifting heavy objects;

3) Within a certain range, the length and depression angle of the locking boom can be adjusted and balanced arbitrarily to meet the requirements of different lifting operations;

4) make the boom within 3600 can rotate and lock arbitrarily;

5) Make the lifting weight rise and fall arbitrarily within a certain speed range, and can stop with load at any position, and there is no slip phenomenon when the load starts.

Figure 8-9 shows the structural schematic diagram of the truck crane, which is mainly composed of the following five parts.

1) Outrigger device.

During the lifting operation, the car tires are lifted off the ground, the whole vehicle is erected, the load is not pressed on the tires, and the levelness of the whole vehicle can be adjusted, which is generally a four-legged structure.

2) Boom slewing mechanism.

The boom can achieve 3600 arbitrary rotation, and it can be locked and stopped in any position.

3) Boom telescopic mechanism.

The boom is adjustable within a certain size range and can be positioned to change the working length of the boom. Generally, it is a 3-section or 4-section sleeve telescopic structure.

4) Boom luffing mechanism.

The angle of the boom can be adjusted arbitrarily between 150 800 to change the inclination angle of the boom.

5) Hook take-off and landing mechanism.

The heavy object is lifted arbitrarily within the lifting range, and the load is stopped at any position, and the lifting and descending speed is stepless adjustable within a certain range.

Because you don't take into account the g-motion (the gravity of the movable pulley), the question clearly says: "The weight of the boom, the fixed pulley, the wire rope and the friction between the wheel and the rope are not counted".

It is not said that the gravity of the moving pulley is not counted, pay attention to the topic and see the problem clearly Let the force on the wire rope be F1 and F2 before and after the water is out, the force arm of the plunger to the boom force is L1 (OF), and the force arm of the wire rope to the boom force is L2 (OB).

According to the leverage equilibrium condition, it can be seen that: N1L1=3F1L2; n2l1=3f2l2n1：n2=f1:f2

So (n2-n1): n2

Actually (f2-f1): f2

The tensile force of the wire rope before the water is f1 = 1 3 (g object - f float + g motion) after the water is f2 = 1 3 (g object + g motion) can obtain f2-f1 = 1 3f float and f2 = 1 3 (g object + g motion) so (f2-f1): f2 = f float (g object + g motion) = 5:24 i.e.:

Exactly equal to 5:24

Answer]: a, b, c

Option B is wrong, the maximum elevation angle of the boom is not more than 78 °, and the minimum is not less than 45 ° Option D, which is the cause of the mast lifting and system instability; The local pickpocketing option is the cause of the instability of the suspended member.