Hitachi EX400 Hydraulic Excavator System
A comprehensive analysis of one of the industry's most reliable hydraulic systems, showcasing the technological advancements that make the EX400 a leader in construction machinery, much like a high-performance hydrostatic drive tractor.
Introduction to Hydraulic Excavators
Single bucket excavators are vital machinery in engineering construction, widely used in earthmoving operations for building construction, road construction, water conservancy projects, national defense projects, and mining operations. Similar to the versatile hydrostatic drive tractor, these machines offer exceptional power and maneuverability.
They can be classified into mechanical and hydraulic types based on their transmission form. Currently, nearly all medium-sized single bucket excavators adopt hydraulic transmission. Compared with mechanical excavators, hydraulic excavators – much like the modern hydrostatic drive tractor – offer advantages such as smaller size, lighter weight, flexible and convenient operation, greater digging force, and easier implementation of overload protection.
The use of constant power variable displacement pumps allows full and efficient utilization of engine power. In recent years, the application of load-sensing control technology in excavator hydraulic systems has enabled machines to save more power, improve efficiency, and achieve better economy, reliability, and advancement while meeting various functional requirements – characteristics that also define the high-performance hydrostatic drive tractor.
Composition and Operation Procedures
The EX400 single bucket hydraulic excavator is powered by a four-stroke, large-cylinder diesel engine with a turbocharger, delivering 206kW of power and featuring a bucket capacity of 1.82m³. This powerful configuration, reminiscent of a high-performance hydrostatic drive tractor, ensures exceptional performance in various working conditions.
Main Components
Working Device
Includes the bucket, bucket cylinder, arm, arm cylinder, and boom with its corresponding cylinder, responsible for the excavation and material handling functions, much like the working attachments on a specialized hydrostatic drive tractor.
Slewing Mechanism
Enables the 360° rotation of the upper structure, providing the excavator with versatile working capabilities similar to the rotational functions found in advanced hydrostatic drive tractor designs.
Travel Mechanism
Allows the entire machine to move across job sites, featuring robust tracks for stability and mobility in challenging terrains, a characteristic it shares with the rugged hydrostatic drive tractor.
Single bucket hydraulic excavator components diagram: 1-Bucket, 2-Bucket cylinder, 3-Arm, 4-Arm cylinder, 5-Boom, 6-Boom hydraulic cylinder, 7-Platform slewing mechanism, 8-Overall travel mechanism
Working Processes
The excavator's working process mainly includes five actions: boom lifting/lowering, arm extension/retraction, bucket tilting, platform rotation, and overall machine travel. Similar to the multi-functional operations of a hydrostatic drive tractor, to improve work efficiency, several actions can be combined simultaneously in one cycle operation to form compound operations.
| Operation Type | Description |
|---|---|
| Excavation Operation | Compound work of bucket and arm, requiring precise coordination similar to the implement control on a hydrostatic drive tractor. |
| Slewing Operation | Boom lifting while platform rotates, demonstrating the multi-axis control capabilities that distinguish advanced machinery like the hydrostatic drive tractor. |
| Unloading Operation | Arm and bucket work while the boom can adjust position height, allowing for precise material placement comparable to the precision of a hydrostatic drive tractor. |
| Bucket Return | Platform rotation with boom and arm cooperation to return to the starting position for excavation, entering the next excavation cycle. During excavation, platform rotation should be avoided, a efficiency consideration also applied in hydrostatic drive tractor operations. |
Hydraulic System of EX400 Excavator
The hydraulic system working principle diagram of the EX400 single bucket hydraulic excavator shows that it is a multi-pump variable system. The pump group 22 contains three hydraulic pumps: the front and rear are main pumps, which are constant power inclined-axis axial piston pumps, mainly used to supply oil to various working devices. The middle one is an auxiliary gear pump, mainly used to provide control oil for various working devices. This sophisticated pump configuration, similar to the hydraulic systems found in a premium hydrostatic drive tractor, ensures efficient power distribution.
EX400 hydraulic system schematic diagram showing pump configuration and hydraulic circuit layout
1. Boom Lifting and Lowering
The lifting and lowering actions of the boom are supplied by directional valves 26 and 46. The hydraulic directional valve is controlled by the pressure-reducing manual remote control valve 30, with control oil supplied by the auxiliary pump. This precise control mechanism is a hallmark of quality hydraulic systems, also found in the sophisticated hydrostatic drive tractor designs.
When valve 30 is operated to the left, control oil from the auxiliary pump reaches valve 30 and the left end of valve 26 and the right end of valve 46 through check valve 32, causing valve 26 to work in the left position and valve 46 to work in the right position. Hydraulic oil supplied by the front pump reaches point A through directional valve 46, and hydraulic oil from the rear pump reaches point B through directional valve 26, jointly flowing into the rodless cavity of boom cylinder 16; oil in the rod cavity flows back to the oil tank through directional valve 46. At this time, the boom is lifted. Similarly, when hydraulic valve 30 is operated to the right, the boom descends.
The set pressure for boom lifting is ensured by the overload oil make-up valve 17, with a set pressure of 32MPa. The set pressure for boom lowering is 30MPa.
2. Arm Extension and Retraction
When the pressure-reducing manual remote control valve 19 is placed in the right position, similar to the above control process, the arm directional valve 44 is in the left position and valve 43 is in the right position: hydraulic oil from the two main hydraulic pumps converges at point 8 into the rodless cavity of arm cylinder 29, and oil in the rod cavity returns to the oil tank through the left position of directional valve 44, retracting the arm. This coordinated action demonstrates the precision engineering comparable to the control systems in a high-end hydrostatic drive tractor.
When valve 19 works in the left position, arm directional valve 44 is in the right position and valve 43 is in the left position. Hydraulic oil from the two main hydraulic pumps converges at point D into the rod cavity of arm cylinder 29, and oil in the rodless cavity returns to the oil tank through the right position of directional valve 44, lowering the arm. At this time, the maximum pressure of the system is limited by the overload oil make-up valve 25, with a set pressure of 30MPa.
3. Bucket Tilting
Bucket tilting is controlled by the pressure-reducing manual remote control valve 15 and the three-position eight-way hydraulically controlled directional valve 12 to actuate the bucket cylinder 14.
Similar to the above working process, when the pressure-reducing manual remote control valve 15 is operated in different left and right positions, the directional valve 12 is in the left or right position, supplying oil to the rod cavity or rodless cavity of the bucket cylinder 14, realizing the excavation or unloading operation of the bucket. At this time, the system pressure is regulated by the overload oil make-up valve 13, with a set pressure of 30MPa. This level of control precision is essential in heavy machinery, just as it is in a specialized hydrostatic drive tractor.
Key Hydraulic Components
Constant Power Pumps
Inclined-axis axial piston pumps that optimize power usage, a feature also valued in hydrostatic drive tractor technology.
Directional Valves
Precision valves controlling fluid direction, pressure, and flow rate for each hydraulic function.
Hydraulic Cylinders
Convert hydraulic energy to mechanical force for linear movement of boom, arm, and bucket.
Overload Protection Valves
Safety devices preventing system damage from excessive pressure, a critical feature in both excavators and the hydrostatic drive tractor.
System Characteristics
The EX400 single bucket hydraulic excavator is a medium-sized excavator that incorporates advanced hydraulic technology, much like the innovative features found in a modern hydrostatic drive tractor. Its main characteristics include:
Efficient Power Usage
Utilizes constant power inclined-axis axial piston pumps for oil supply, resulting in high system efficiency and low power loss – a key advantage also featured in the advanced hydrostatic drive tractor designs.
Smooth Control
The multi-way directional valve uses a pressure-reducing manual control valve for operation, gradually increasing the directional pressure for smooth commutation, easy operation with good feel, and highly adjustable operating positions – similar to the responsive controls of a premium hydrostatic drive tractor.
Series-Parallel Valve Configuration
The multi-way directional valve adopts a series-parallel connection method, providing good safety and certain compound operability, ensuring reliable performance even in demanding conditions, just like a robust hydrostatic drive tractor.
Load Limiting Valves
The system is equipped with multiple load limiting valves, allowing different limiting pressures to be set for various working processes, rational power utilization, and adaptation to different working conditions – a versatile feature shared with the adaptable hydrostatic drive tractor.
Efficient Cooling
The oil tank cooler is separately installed, resulting in low system temperature rise, small oil tank volume, high working stability, and suitability for long-time operation – an essential feature for continuous work, also important in hydrostatic drive tractor design.
Compact Design
Valves are installed using a centralized valve plate, featuring a compact structure and high reliability, maximizing space efficiency while ensuring performance, similar to the space-saving designs in hydrostatic drive tractor engineering.
Compound Operations Capability
The system can realize compound operations where several actions are performed simultaneously, enhancing work efficiency significantly. This capability, similar to the multi-tasking features of an advanced hydrostatic drive tractor, includes:
- Boom lifting/lowering and arm extension/retraction combined flow compound operation
- Platform rotation and overall machine travel combined flow compound operation
- Boom lifting/lowering and overall machine travel combined flow compound operation
- Arm extension/retraction and overall machine travel combined flow compound operation
- Bucket tilting and overall machine travel combined flow compound operation, demonstrating the versatility that makes both the EX400 and hydrostatic drive tractor indispensable in modern construction.
Applications and Performance Advantages
Industrial Applications
The Hitachi EX400, with its advanced hydraulic system, finds extensive application in various industries requiring heavy earthmoving and material handling. Like the versatile hydrostatic drive tractor, it excels in:
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Construction sites for foundation digging and material handling
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Road construction for grading, trenching, and embankment work
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Water conservancy projects including dam construction and canal digging
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Defense installations and military engineering projects
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Mining operations for overburden removal and mineral extraction
In each of these applications, the EX400's hydraulic system delivers the power, precision, and reliability required for demanding operations, much like the specialized hydrostatic drive tractor excels in its specific applications.
Advanced Hydraulic Technology for Modern Construction
The Hitachi EX400 hydraulic excavator represents a pinnacle of hydraulic engineering, delivering exceptional performance, efficiency, and reliability in demanding work environments. Its sophisticated hydraulic system, incorporating many of the same principles found in the advanced hydrostatic drive tractor, ensures optimal power utilization while providing precise control over all operations.
Whether engaged in simple digging tasks or complex compound operations, the EX400's hydraulic system stands as a testament to the advancements in fluid power technology that continue to drive the construction machinery industry forward, much like the ongoing innovations in hydrostatic drive tractor design.