The core working principle of an excavator lies in a three-stage linkage process: "Engine provides power → Hydraulic system transmits power → Working device and travel device execute movements". It converts the mechanical energy of the engine into precisely controllable hydraulic energy, ultimately realizing operational actions such as excavation, lifting, rotation, and travel. Essentially, it is a collaborative process of "power conversion and precise transmission". Specifically, it can be broken down into three core links: power source, power transmission, and action execution.

I. First Link: Power Source – The Engine Outputs Basic Mechanical Energy

The engine is the "power heart" of the excavator, whose main function is to convert the chemical energy of fuel (diesel) into mechanical energy to provide power for the entire equipment.

Core Function

When the engine operates, it outputs torque through the crankshaft. On one hand, it drives the hydraulic pump (to supply energy to the main hydraulic system); on the other hand, it drives the generator (to supply power to the electrical system and cab control panel). At the same time, it drives the operation of auxiliary components such as the cooling fan and fuel pump to ensure the basic operation of the equipment.

Key Characteristics

Most excavators adopt diesel engines (which have high torque and are resistant to heavy loads) and can automatically adjust the speed according to the operational load (e.g., low speed for fuel efficiency during light loads, high speed to enhance power during heavy loads), avoiding power waste or insufficiency.

II. Second Link: Power Transmission – The Hydraulic System Converts Mechanical Energy into Controllable Hydraulic Energy

The hydraulic system is the "power transmission hub" of the excavator and the core that distinguishes it from ordinary machinery. It can convert the "continuous mechanical energy" output by the engine into "precisely controllable hydraulic energy" and then distribute it to various executive components (boom, arm, bucket, crawler, etc.). The core of this link is the collaboration of "hydraulic pump - hydraulic valve - hydraulic cylinder/motor":

1. Hydraulic Pump: Converts Mechanical Energy into Hydraulic Energy ("Power Generator")

The engine drives the hydraulic pump (usually a piston pump, which has high pressure and stable flow) to operate. Through the "oil suction - oil pressure" action, the hydraulic pump draws hydraulic oil from the hydraulic oil tank and then delivers it to the hydraulic pipeline at high pressure (usually 20-35MPa, equivalent to a pressure of 200-350 kg/cm²).

Different operational actions correspond to different hydraulic pumps: Some excavators are equipped with a "main pump + pilot pump" – the main pump supplies high-pressure oil for "major movements" such as the boom, arm, and crawler; the pilot pump provides low-pressure control oil for the operating lever (the operator pushes the lever to control the opening of the main hydraulic valve), enabling "precise control".

2. Hydraulic Valve: Controls the Direction, Pressure, and Flow of Hydraulic Oil ("Power Distributor")

The hydraulic valve is equivalent to a "switch and regulating valve". Installed in the hydraulic pipeline, it controls the flow direction, pressure, and flow rate of high-pressure hydraulic oil according to the operator's control instructions (pushing the operating lever):

• Direction Control: For example, when the operator pushes the "boom lift" lever, the hydraulic valve guides high-pressure oil into the "rodless cavity of the boom hydraulic cylinder", pushing the piston rod of the hydraulic cylinder to extend and driving the boom to lift; if the operator pushes the "boom lower" lever, the hydraulic valve guides oil into the "rod cavity", the piston rod retracts, and the boom lowers.

• Pressure Control: When the operational load is too high (e.g., the bucket hits hard rock), the pressure of the hydraulic system will exceed the safety value. At this time, the "relief valve" will open automatically, diverting excess hydraulic oil back to the oil tank to prevent damage to the hydraulic pump and pipeline due to overpressure (protecting system safety).

• Flow Control: The greater the amplitude of the operator's lever push, the larger the opening of the hydraulic valve, and the more hydraulic oil flows into the hydraulic cylinder/motor, resulting in faster movement speed (e.g., gently pushing the lever makes the boom lift slowly, while pushing it hard makes the boom lift quickly), realizing "precise adjustment of movement speed".

3. Hydraulic Cylinder/Hydraulic Motor: Converts Hydraulic Energy into Mechanical Energy ("Power Executor")

After being distributed by the hydraulic valve, the hydraulic oil is finally delivered to the "hydraulic cylinder" (for linear movements, such as the lifting/expansion of the boom, arm, and bucket) or "hydraulic motor" (for rotational/travel movements, such as the rotation of the slewing platform and crawler travel), converting hydraulic energy into mechanical movements:

• Hydraulic Cylinder (Linear Movement): Taking the boom hydraulic cylinder as an example, after high-pressure oil enters the cylinder block, it pushes the piston rod to make a linear movement. One end of the piston rod is connected to the boom, which in turn drives the boom to rotate around the hinge point (realizing lifting/lowering). The working principles of the arm and bucket are consistent with this, and the three cooperate to complete the composite action of "excavation - lifting".

• Hydraulic Motor (Rotational/Travel Movement): The rotation of the slewing platform relies on the "slewing motor" – high-pressure oil drives the rotor inside the motor to rotate, and the rotor drives the slewing bearing (the component connecting the platform and the chassis) to rotate after gear reduction, realizing 360° rotation; crawler travel relies on the "travel motor", which drives the crawler drive wheel to rotate, thereby driving the crawler to roll and enabling the equipment to move forward/backward and turn.

III. Third Link: Action Execution – The Working Device and Travel Device Complete Operations

The executive components driven by the hydraulic system finally realize specific operations through the "working device" and "travel device":

1. Working Device: Completes Core Actions of Excavation and Loading

The working device consists of the "boom, arm, and bucket" (commonly known as the "three-stage structure"). All three are driven by hydraulic cylinders and cooperate to complete the excavation action:

During excavation: First, adjust the bucket angle (with the bucket teeth touching the ground), and contract the arm hydraulic cylinder to drive the bucket to cut into the soil layer; at the same time, slightly adjust the boom hydraulic cylinder to control the excavation depth; after the bucket is full, extend the boom hydraulic cylinder (to lift the bucket), the slewing motor drives the platform to rotate (turning to the transport vehicle), and finally contract the bucket hydraulic cylinder (to tilt the bucket) to unload the material onto the transport vehicle, completing one excavation cycle.

2. Travel Device: Enables Equipment Movement and Operational Position Adjustment

The travel device of a crawler excavator consists of the "crawler, drive wheel, track roller, and idler wheel" and is driven by the travel motors on the left and right sides respectively:

• Forward/Backward: The left and right travel motors rotate forward (forward movement) or reverse (backward movement) simultaneously, driving the crawlers on both sides to roll synchronously;

• Turning: One travel motor rotates forward and the other reverses (or one stops rotating), creating a speed difference between the crawlers on both sides. The equipment rotates around one side of the crawler (realizing small-radius turning), facilitating position adjustment in narrow spaces.

Summary of the Core Logic

The working principle of an excavator can be simplified as:Fuel chemical energy → Engine mechanical energy → Hydraulic pump hydraulic energy → Hydraulic valve distribution → Hydraulic cylinder/motor mechanical energy → Working device/travel device movements

The key to the entire process is the "precise control of the hydraulic system" – through the adjustment of the pressure and flow of hydraulic oil, the "speed, force, and direction" of movements are controllable. This not only meets the high-power demand for heavy-load excavation (such as hard rock breaking) but also enables small-amplitude movements for fine operations (such as slope trimming), ultimately achieving efficient and flexible operational results.