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　　Construction machinery bulldozer is one of the commonly used working machines in shovel transport machinery. It is a self-propelled construction machine that installs bulldozer and operating mechanism in front of track tractor or tyre tractor. It is mainly used for excavating cut, constructing road lifting, backfilling, removing obstacles, etc. It can also complete shovel and accumulation of short-distance loose materials.Bulldozers are equipped with scarifiers to loosen hard soil, soft rock or chisel bedrock for excavation by scrapers and bulldozers, and to assist graders or scrapers in completing joint construction operations to improve the operational efficiency of these machines.

　　There are many types of bulldozers, which can be classified according to power class, walking device, installation mode, transmission mode and use of bulldozer shovel.

　　(1) According to engine power level.

　　1. Small bulldozer: with power below 75 kW and low productivity, it is used for small area or sporadic earthwork sites.

　　2. Mid-sized bulldozer: 75-239 kW for general earthwork.

　　3. Large bulldozer; with power over 239 kW and high productivity, it is used in large earthworks in hard soil or deep frozen soil.

　　(2) According to the way of walking.

　　1. Crawler bulldozer: with high traction, low ground pressure, strong climbing ability, suitable for harsh working environment and excellent operation performance, it is a multi-purpose machine.

　　2 Tyre bulldozer: fast driving, good maneuverability, short working cycle, convenient and quick transfer, no damage to the ground, especially suitable for urban construction and road maintenance works.

　　Bulldozers can be divided into the following types by means of transmission:

　　1) Mechanical drive bulldozer: The bulldozer with mechanical drive works reliably, is easy to manufacture, has high transmission efficiency and is easy to repair, but its operation is laborious, and its adaptability to load is poor. It is easy to cause engine stalling and reduce operation efficiency. It has been adopted less.

　　2) Hydraulic-mechanical transmission bulldozer: Hydraulic torque converter and power shift transmission combined transmission are used, which has the ability of adaptive stepless speed variation, automatic adaptation to external load changes. The engine is not easy to stall, and the load can be shifted with less shifting times, portability and high efficiency. It is the transmission type mostly used by modern large and medium-sized bulldozers.

　　3) Fully hydraulic drive bulldozer: driven by hydraulic motor, the driving force is transmitted directly to the walking mechanism.Because there is no drive component such as main off-table, transmission, drive axle, etc., the structure is compact, the general arrangement is convenient, the whole machine is light in weight, simple in operation and can realize in-situ steering. However, the full hydraulic bulldozer mechanism causes high cost, poor durability and reliability, and is only used on medium power bulldozers at present.

　　4) Electrically driven bulldozer: the mechanical energy output from the diesel engine is first converted into electrical energy, and then the electric motor is driven by cable, which drives the walking device and working device. The bulldozer is compact in structure, convenient in general arrangement and flexible in operation.Stepless speed change and in-place steering of the whole machine are possible.However, the machine is of high quality and high manufacturing cost, and it is only used on a few high-power wheel dozers at present.