Rexroth A4VSG Axial Piston Variable Displacement Pump in TBM Hydraulic Systems: Innovative Application Solutions

1. Introduction: Core Requirements of TBM Hydraulic Systems

In modern tunnel construction, tunnel boring machines (TBMs) serve as critical equipment whose performance directly determines project efficiency and quality. The hydraulic system, functioning as the "heart" of a TBM, powers core functions including thrust, cutterhead drive, and segment erection. The Rexroth A4VSG series axial piston variable displacement pumps have become the preferred hydraulic power source for global TBM manufacturers due to their outstanding performance and reliability.

Since its development in the mid-20th century, axial piston pump technology has become an irreplaceable key component in high-pressure hydraulic systems. Compared to traditional gear pumps and vane pumps, axial piston variable displacement pumps offer significant advantages including high working pressure, volumetric efficiency, and wide flow adjustment range—making them particularly suitable for demanding TBM applications.

2. Technical Characteristics of Rexroth A4VSG Axial Piston Variable Displacement Pumps

2.1 Innovative Design Concept

The Rexroth A4VSG series features a swashplate-type axial piston variable displacement design that achieves stepless displacement adjustment by changing the swashplate angle. This design enables the pump to automatically adjust output flow according to system demands while maintaining constant rotational speed, achieving precise power matching. For equipment like TBMs with highly variable loads, this characteristic of axial piston variable displacement pumps significantly improves energy utilization efficiency.

2.2 Key Performance Parameters

· ‌Working pressure range‌: Maximum 400 bar, continuous operation at 350 bar, meeting high-pressure hydraulic requirements of TBMs

· ‌Displacement range‌: 28-1000 ml/rev, covering power requirements for various TBM specifications

· ‌Volumetric efficiency‌: Up to 98%, minimizing energy loss

· ‌Noise control‌: Optimized piston and slipper design keeps operational noise below 80 dB

2.3 Reliability Enhancement Design

Addressing the need for continuous operation in TBMs, the A4VSG axial piston pump incorporates multiple reliability-enhancing technologies:

· High-strength nodular cast iron housing with excellent impact and vibration resistance

· Hard-chrome plated pistons and specially treated cylinder bore for superior wear resistance

· Optimized bearing arrangement extending service life

· Integrated temperature and pressure sensor interfaces for condition monitoring

3. TBM Hydraulic System Architecture and A4VSG Application Positioning

3.1 Typical TBM Hydraulic System Composition

Modern TBM hydraulic systems typically consist of the following subsystems:

· ‌Main thrust system‌: Provides forward propulsion power

· ‌Cutterhead drive system‌: Powers the rotating cutting wheel

· ‌Segment erection system‌: Precisely controls segment installation manipulators

· ‌Auxiliary systems‌: Includes grouting, muck conveyance and other support functions

Among these subsystems, axial piston variable displacement pumps primarily serve the main thrust and cutterhead drive systems which have the highest power demands.

3.2 Typical A4VSG Configuration Solutions for TBMs

Configuration solutions for A4VSG axial piston pumps vary according to TBM diameter and geological conditions:

‌Small/medium diameter TBM (below φ6m) solution‌:

· Main thrust system: 2×A4VSG 250 axial piston pumps with load-sensing control

· Cutterhead drive: 1×A4VSG 500 axial piston pump with constant power control

· Total power: Approximately 500-800 kW

‌Large diameter TBM (above φ6m) solution‌:

· Main thrust system: 4×A4VSG 355 axial piston pumps with zoned pressure control

· Cutterhead drive: 2×A4VSG 750 axial piston pumps with variable frequency + constant power compound control

· Total power: 1200-2000 kW

4. Key Technical Advantages of A4VSG Axial Piston Pumps in TBMs

4.1 Precise Thrust Force Control

TBM propulsion requires real-time adjustment of thrust force and speed according to geological conditions. A4VSG axial piston pumps equipped with electronic proportional control (HD control) or load-sensing control (DA control) enable:

· Propulsion speed accuracy to 0.1 mm/s

· Independent pressure adjustment for multiple cylinder groups

· Automatic deviation correction to maintain tunneling axis precision

4.2 Efficient Power Matching

Traditional fixed displacement pump systems waste significant energy during low-load TBM operation. A4VSG axial piston variable displacement pumps achieve through constant power control or load-sensing control:

· Over 30% energy savings

· Reduced hydraulic oil temperature rise, extending fluid service life

· Decreased cooling system load

4.3 Adaptability to Complex Geology

For different geological conditions (soft soil, gravel, rock, etc.), A4VSG axial piston pumps can quickly adjust operating parameters:

· Soft soil stratum: Low pressure, high flow mode

· Hard rock stratum: High pressure, low flow mode

· Mixed stratum: Automatic mode switching

5. Intelligent Control Technology for A4VSG Axial Piston Pumps

5.1 Electronic Control System Integration

Modern A4VSG axial piston pumps can integrate multiple electronic control options:

· ‌Proportional solenoid control‌: Enables precise displacement adjustment

· ‌CAN bus interface‌: Seamless connection with TBM main control system

· ‌Condition monitoring interface‌: Real-time feedback of pump operating parameters

5.2 Intelligent Fault Diagnosis Functions

By monitoring key parameters of axial piston pumps, early fault warnings can be achieved:

· Vibration sensors detect bearing condition

· Pressure pulsation analysis identifies piston wear

· Temperature monitoring predicts seal life

5.3 Digital Twin Technology Application

Comparing A4VSG axial piston pump operational data with digital models enables:

· Performance degradation trend prediction

· Remaining life assessment

· Optimal maintenance timing determination

6. Typical Engineering Application Cases

6.1 Case 1: Urban Metro Tunnel Project

Project parameters:

· TBM diameter: 6.28 m

· Tunnel length: 3.2 km

· Geological conditions: Alternating soft soil and gravel layers

Hydraulic system configuration:

· Main thrust: 3×A4VSG 355 axial piston pumps

· Cutterhead drive: 2×A4VSG 500 axial piston pumps

Operation results:

· Average advance rate reached 12 m/day

· Zero hydraulic system failures

· 28% energy savings compared to conventional systems

6.2 Case 2: River-Crossing Tunnel Project

Project challenges:

· High water pressure (0.6 MPa)

· Long-distance tunneling (5.8 km)

· Complex geology (soft soil, rock fracture zones)

Solution:

· Redundant design using A4VSG axial piston pumps

· Intelligent pressure compensation system configuration

· Remote condition monitoring implementation

Project achievements:

· Set monthly advance record of 456 meters

· Hydraulic system reliability reached 99.98%

· Received owner's technological innovation award

7. Maintenance and Troubleshooting Guide

7.1 Routine Maintenance Points

To ensure optimal A4VSG axial piston pump performance in TBM applications:

· Check fluid cleanliness every 500 hours (ISO 4406 18/16/13)

· Inspect pump suction filter every 1000 hours

· Test pump volumetric efficiency every 2000 hours

· Regularly check coupling alignment and pipeline vibration

7.2 Common Troubleshooting

‌Issue 1: Insufficient output flow‌
Possible causes:

· Swashplate adjustment mechanism sticking

· Insufficient control pressure

· Piston wear

Solutions:

· Check control circuit pressure

· Test swashplate movement freedom

· Measure piston/cylinder block clearance

‌Issue 2: Abnormal noise‌
Possible causes:

· Cavitation due to insufficient suction

· Bearing damage

· Piston slipper wear

Solutions:

· Inspect suction filter

· Monitor bearing vibration spectrum

· Disassemble to examine critical friction pairs

8. Future Development Trends and Technological Outlook

8.1 Axial Piston Pump Technology Development Directions

· ‌Higher pressure ratings‌: Targeting 450 bar continuous operation

· ‌Intelligent adaptive control‌: Self-learning parameter optimization based on operating conditions

· ‌New material applications‌: Ceramic pistons, composite bearings, etc.

· ‌More compact designs‌: 30% higher power density

8.2 TBM Hydraulic System Innovations

· ‌Hybrid power systems‌: Combined axial piston pump and electric cylinder drives

· ‌Energy recovery technology‌: Using A4VSG in motor mode to recover braking energy

· ‌Full electro-hydraulic systems‌: Eliminating pilot hydraulics with complete electronic control

9. Conclusion

The Rexroth A4VSG axial piston variable displacement pump has become the core power component in modern TBM hydraulic systems due to its high-pressure efficiency, intelligent control, and reliable durability. Through optimized design and intelligent control technology applications, the A4VSG not only meets stringent TBM operational requirements but also demonstrates exceptional performance in energy conservation and intelligent maintenance.

As tunnel construction progresses toward deeper, longer, and more geologically complex projects, axial piston pump technology will continue innovating to provide TBMs with more powerful and intelligent power solutions. As a global leader in hydraulic technology, Rexroth remains committed to advancing axial piston pump development, driving TBM hydraulic systems toward greater efficiency, intelligence, and environmental sustainability.