Although bulldozers and excavators are both common construction machinery and both use crawler undercarriage, their functional positioning is completely different, which directly leads to significant differences in their undercarriage designs.
Let's conduct a detailed comparison from several key dimensions:
1. Differences in Core Functions and Design Concepts
Core Functions:
Bulldozer undercarriage: Provides huge ground adhesion and a stable support platform for toppling operations.
General excavator undercarriage: Provides a stable and flexible base for the upper device to perform 360° rotary excavation operations.
Design Concept:
Bulldozer undercarriage: Integrated operation: The vehicle body is rigidly connected with the working device (scythe). The chassis needs to bear the huge toppling reaction force.
General excavator undercarriage: Split operation: The lower vehicle undercarriage is the mobile carrier, and the upper device is the working body. They are connected through a swivel support.
Relationship with the Working Device:
Bulldozer undercarriage: The working device (scythe) is directly rigidly hinged to the undercarriage frame. The push force is entirely borne and transmitted by the undercarriage.
General excavator undercarriage: The working device (arm, bucket, bucket) is installed on the upper vehicle platform. The excavation force is mainly borne by the upper vehicle structure, and the undercarriage mainly bears the overturning moment and weight.
2. Specific Structures and Technical Differences
Walking Frame and Chassis Structure
Bulldozer:
• Uses an integrated rigid undercarriage: The undercarriage system is usually a solid structure connected rigidly to the main undercarriage
• Purpose: To ensure that the huge reaction force during toppling operations can be directly and without loss transmitted to the entire undercarriage, ensuring the stability and powerful operation capability of the machine.
Excavator:
• Uses X-shaped or H-shaped lower vehicle frame, connected to the upper device through swivel supports.
• Purpose: The undercarriage system mainly undertakes the functions of support and movement. Its design should ensure that the weight of the upper vehicle platform and the excavation reaction force can be evenly distributed during 360° rotation. The X/H structure can effectively disperse stress and provide installation space for the swivel device.
Track and Load-bearing Wheel Layout
Bulldozer:
• Track gauge is wide, undercarriage is low, and the center of gravity is low.
• The number of track rollers is large, the size is relatively small, and they are closely arranged, almost covering the entire track ground length.
• Purpose: To maximize the ground contact area, reduce ground pressure, provide excellent stability, and prevent tipping or overturning during toppling. The close load-bearing wheels can better transfer the weight to the track plate and adapt to uneven ground.
Excavator:
• Track gauge is relatively narrow, the undercarriage is higher, facilitating steering and crossing obstacles.
• The number of track rollers is small, the size is large, and the spacing is wide.
• Purpose: To improve throughability and flexibility while ensuring sufficient stability. Larger load-bearing wheels and wider spacing help to disperse the impact loads generated during dynamic excavation.
Drive and Transmission Method
Bulldozer:
• Traditionally, it mostly uses hydraulic mechanical transmission. Engine power passes through a torque converter, gearbox, central transmission, steering clutch, and final drive, ultimately reaching the track and sprocket.
• Characteristics: High transmission efficiency, can provide continuous and powerful traction, suitable for the constant power output required for toppling operations.
Excavator:
• Modern excavators generally use hydraulic transmission. Each track is driven by an independent hydraulic motor.
• Characteristics: Can achieve in-place steering, excellent maneuverability. Precise control, easy to adjust position in narrow spaces.
Tension and Suspension System
Bulldozer:
• Usually uses rigid suspension or semi-rigid suspension. There is no or only a small buffer travel between the load-bearing wheels and the chassis.
• Purpose: In flat ground operations, rigid suspension can provide the most stable support, ensuring the quality of flat operations.
Excavator:
• Generally uses an oil-gas tensioning device with an air suspension. The load-bearing wheels are connected to the chassis through hydraulic oil and nitrogen gas buffering.
• Objective: To effectively absorb the impact and vibration during digging, traveling, and walking, protect the precise vehicle structure and hydraulic system, and improve operational comfort and machine lifespan.
Wear characteristics of the "four rollers and one track"
Tractor:
• Due to frequent steering and diagonal movement operations, the sides of the front idler and the chain tracks of the tracks are relatively severely worn.
Excavator:
• Due to frequent in-place rotation operations, the wear of the track rollers and top rollers is more prominent, especially the rim part.
3.Summary:
• The tractor undercarriage is like the lower body of a heavyweight sumo wrestler, solid and stable, firmly rooted in the ground, with the purpose of pushing the opponent forward.
• The excavator undercarriage is like a flexible crane base, providing a stable base for the upper boom and being able to adjust the direction and position as needed.