The hooklift is the key system of the demountable truck, also known as the hooklift truck. Its performance determines the merits and demerits of the whole vehicle. It has both functions of unloading goods and automatically loading and unloading the bin body, and these two functions are completed by the same vehicle-mounted working device with high working efficiency. This system can meet the specific requirements of any customer in the world. It can be widely used in sanitation and medical institutions, construction companies, public construction projects, fire departments, transportation companies, military departments, waste recycling companies, etc. According to its structural form, hooklifts can be mainly divided into small arm fixed type, telescopic type, swing arm type and composite type. The following is based on years of practical experience in installing hooklifts and sharing the key points of process control in the production and manufacture of hooklift trucks.

1.Basic structure

The hooklift equipment is an important component installed on the truck chassis, mainly used for loading and unloading the bin body. The system is equipped with a hydraulic lifting device, which can unload the bin body from the hooklift subframe and pull the bin body onto the hooklift subframe. This hooklift equipment can also be used to self-unload the bin body (the hydraulic self-unloading lock must be locked during self-unloading). The whole system drives the middle frame to overturn through the main cylinder, the telescopic arm cylinder drives the telescopic arm, and then drives the hook through the lock hook cylinder to complete the whole process of loading and unloading the bin body. Finally, the bin body is pulled onto the hooklift along the rear roller by the hook and locked by the hydraulic bin lock. The main structure of hooklift is displayed as following.

hooklift overview

Figure 1: Hooklift Overview

2. Installation process and control points of hooklift

2.1 Adjust the chassis level

When starting to modify the chassis, the truck main beam should be kept horizontal and the chassis should be free of warping. The following points should be confirmed first:

  1. Ensure that all wheels are facing forward;
  2. Ensure that the tire pressure is normal;
  3. To lift the bare chassis, at least two adjustable brackets must be used. The brackets cannot be removed during the chassis modification process.

2.2 Install hooklift subframes

If components such as gearboxes, crossbeams and brake boosters on the truck chassis exceed the plane height of the chassis and interfere with the installation position of the hooklift system parts, the interfering components can be adjusted to remove or add hooklift subframes on the chassis frame. The height of the added hooklift subframes should not exceed 100 mm.

Schematic diagram of adding hooklift subframes

Figure 2: Schematic diagram of adding hooklift subframes

2.3 Connection between hooklift and chassis

2.3.1 Installation of hooklift mounting plates

When placing the hooklift on the chassis main beam, ensure that the contact surface between the hooklift main beam and the chassis main beam has no gaps, and fixing plates must be arranged at load-concentrated positions during the movement of the hooklift. The fixing plate can be made of 8-12 mm thick plates, and the connecting bolts can be M12-M14. It is recommended that the bolt strength should be 10.9 or above. When drilling holes in the chassis main beam, the following points should be noted:

  1. Use the existing holes on the main beam as much as possible;
  2. Confirm that no damage or impact will be caused to any pipelines and wires before drilling;
  3. Use a drill bit as close to the bolt diameter as possible for drilling, for example, use a 13.9mm drill bit for M14 bolts;
  4. Do not drill holes at the edge of the side beams;
  5. Do not drill holes at the tapered end of the towing truck chassis frame;
  6. Do not weld filler at the holes of the chassis frame;
  7. The drilled holes must be primed and top-coated. The position of the main beam fixing plate is shown below.
Position diagram of sill beam fixing plate

Figure 3: Position diagram of sill beam fixing plate

2.3.2 Shorten the front part of the hooklift subframe

Before installing the hooklift on the truck chassis, the front part of the hooklift subframe should be shortened to the normal length first to ensure that the center of the rear roller is 76 mm from the rear end of the chassis main beam. The distance from the rear end of the chassis main beam to the center of the hooklift rear roller is shown in below. Arrange the front part of the hooklift subframe forward as much as possible and shorten it.

Distance from the rear end of the chassis main beam to the center of the hooklift rear roller

Figure 4: Distance from the rear end and hooklift rear roller

The schematic diagram of shortening is shown in Figure 5. For vehicles without rear supporting iron wheels, the hooklift should be installed close to the cab to avoid the truck from tilting its head. The distance from the rear axle center to the center of the hooklift rear roller is shown in Figure 6. In the figure, L is the distance from the rear axle center to the center of the hooklift rear roller. The shorter L is, the less likely the truck is to tilt its head.

shortening the front beam of the auxiliary beam

Figure 5: Shortening the front beam of the auxiliary beam

Distance from the rear axle center to the center of the hooklift rear roller

Figure 6: Distance from the rear axle center to the center of the hooklift rear roller

2.4 Installation of oil pump and drive shaft

If the truck gearbox is equipped with an additional take-off device and there is enough space between the drive shaft and the crossbeam, the method of installing a direct pump additional device can be adopted. The key is to ensure that the rotation direction of the oil pump and the connection position of the take-off device and the pump match. Since the rotation direction of the oil pump is usually counterclockwise, if the directions do not match, the rear cover needs to be disassembled and rotated 180° to make it compatible. If a flange take-off device is used, an adjustable pump cannot be used. Instead, a drive shaft flange should be used. In this case, a special bracket should be used to assemble the flange hub to the oil pump shaft, and then the pump should be installed on the truck chassis. According to the product instructions, the drive shaft bracket must be fixed. An adapter can be installed between the pump and the take-off device. Since the installation positions of the oil pump and valves are movable, flexible hoses need to be used to connect the hydraulic system pipelines.

2.5 Installation of oil tank and oil circuit connection diagram

The hydraulic system of the hooklift is a high-pressure connection system with the highest working pressure of 35 MPa. High-pressure hoses are connected between the hydraulic pump and the main control valve, and these hoses are prohibited from vibrating. In addition, the hydraulic oil tank should be installed as high as possible, but the filter element of the return oil circuit must be easy to replace. Refuel from here when refueling by removing the cover. The working principle of the oil circuit is that the hydraulic pump obtains power from the chassis through the take-off device, pressurizes the hydraulic oil in the oil tank into high-pressure hydraulic oil, and then transmits the pressure to the main control valve body through high-pressure oil pipes. The main control valve controls the stroke of various cylinders on the hooklift to realize the loading and unloading operation of the hooklift. At the same time, the returned hydraulic oil is sent back to the oil tank through the return oil pipe. The oil circuit connection diagram is shown in Figure 7.

2.6 Installation of rear axle support

Rear axle supports include “rear axle support cylinders” and “rear axle support rollers”, which are mainly used to reduce the rear overhang load of the chassis main beam and prevent the truck from tilting its head during hooklift operation.

Oil circuit connection diagram

Figure 7: Oil circuit connection diagram

2.6.1 Rear axle support cylinders

The rear axle support cylinders are suitable for rear axle support forms on softer and harder ground. Pay attention to the following points during installation:

  1. There are 1 rear axle support cylinder on the left and right, installed above the steel plate springs of the last axle of the chassis and as far back as possible;
  2. In the unladen state, ensure that there is a distance of 30-50 mm between the fully extended cylinder rod of the support cylinders and the steel plate springs;
  3. The connecting plates of the rear axle support cylinders cannot be welded to the chassis main beam to facilitate the disassembly of the cylinders.

2.6.2 Rear axle support rollers

Rear axle support rollers are suitable for rear axle support forms on harder ground. Pay attention to the following points during installation:

  1. The rear axle support rollers should be as far back as possible;
  2. Usually, when loading and unloading on a horizontal road surface, maintain a ground clearance of 100-150 mm at the lowest point of the rear roller;
  3. The roller frame should have the same width as the chassis and be connected to the chassis with connection plates with a thickness of 12 mm and at least 8 M14 bolts.

Conclusion

In the installation of the hooklift, first ensure that the chassis model matches the hooklift; secondly, strictly implement the consistency requirements of the product in the whole special truck modification process.

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This blog is translated from the article “Control Points of Hooklift in Manufacturing Process of Hooklift Truck” by Qizhong Yao 2011.