The excavator undercarriage typically consists of the lower frame/track frame, four wheels, and one track (comprising the drive wheel, idler wheel, track rollers, track idler, and tracks). It also includes the final drive (travel motor and reduction gearbox) and the tensioning device. Some models also feature attachments like dozer blades. Engineering terminology collectively refers to the drive sprocket, idler sprocket, track rollers, track idler, and tracks as the “four wheels and one belt,” which collectively form the critical wear components of the undercarriage.
Key Components
- Track Frame / X-Frame: Supports the weight of the upper structure, connects the left and right tracks, and mounts the four wheels and one belt, serving as the primary structural element of the undercarriage.
- Track Group / Track Assembly:: Composed of track links and track plates, it increases ground contact area, distributes weight, and enables movement.
- Sprocket (Drive Wheel): Engages with the track to receive final drive torque, propelling the vehicle forward or steering.
- Idler (Front Idler): Works with the tensioning device to maintain chain tension and guide track movement.
- Track Roller (Bottom Roller): Supports the entire machine's weight and evenly distributes the load to the ground-contacting tracks.
- Carrier Roller (Top Roller): Supports the return side of the track, ensuring smooth operation and suppressing oscillation.
Power and Transmission
- The travel motor converts hydraulic energy into mechanical energy. After torque amplification by the travel reduction gearbox, it is transmitted to the drive wheel, forming the final drive of the chassis.
- Typically located at the tail sprocket, this assembly serves as the core power component for chassis mobility.
Tensioning and Guidance
- The tensioning device (grease cylinder + return spring) adjusts track tension by shifting the idler position, absorbing shocks, and preventing derailment.
- Combined with track guards and guide components, it reduces track deviation while enhancing durability and stability.
Optional and Variant Components
- Mini excavators often feature dozer blades for grading and support, representing common undercarriage attachments.
- Some references include the central swivel joint and slewing ring in undercarriage listings, while others classify them under the upper structure—reflecting differing categorization standards.
- Wheeled undercarriages replace the track system with axles and tires, offering higher mobility but differing cross-country performance—representing a distinct chassis type.
Inspection Checklist
- Lower frame/track frame (X-frame)
- Four wheels and one track: Sprocket (or Drive Wheel)，Idler (or Idler Wheel)，Track Roller (or Bottom Roller)，Carrier Roller (or Top Roller)，Track (or Track Chain, Track Assembly)
- Final drive: Travel motor + travel reducer
- Tensioning device (grease cylinder + spring)
- Attachments: Dozer blade, protective plates/cleaners, etc.