Rexroth A2FM80 A2FM90 motor Hydraulic piston motor

Introduction to the A2FM Series

The Rexroth A2FM80 and A2FM90 are part of the renowned Series 6x fixed displacement Axial Piston Motors.

Engineered with a specialized bent-axis design, these motors are the industry standard for both open and closed circuit hydrostatic drives.

While variable motors offer flexibility, the A2FM series is favored for applications requiring absolute reliability, high starting torque, and a constant displacement-to-speed ratio.

The "80" and "90" designations refer to their displacement sizes ($80cm^3$ and $90cm^3$ per revolution), making them ideal for mid-to-heavy duty industrial and mobile machinery.

The Engineering Excellence of Bent-Axis Design

The core advantage of the Rexroth A2FM80/90 lies in its bent-axis rotary group.

Unlike swashplate designs, the bent-axis configuration reduces internal friction and allows for a more robust piston-to-shaft connection.

This results in significantly higher total efficiency ($\eta_t$), particularly during high-pressure operations.

The spherical pistons move within the cyLinder block at a fixed angle, ensuring that mechanical-hydraulic losses are kept to an absolute minimum even at maximum RPM.

Technical Specifications and Performance

Understanding the technical limits of these motors is essential for proper system integration.

1. Pressure Capabilities

Both the A2FM80 and A2FM90 are designed to operate at a nominal pressure of 400 bar (40 MPa).

They can handle peak pressures up to 450 bar (45 MPa), providing a safety buffer for high-load spikes in demanding environments.

2. Speed and Torque Output

These motors are high-speed capable, often reaching speeds up to 4500–5000 RPM depending on the specific configuration and fluid viscosity.

The fixed displacement ensures that the output torque is always directly proportional to the pressure differential across the motor.

3. Compact and Robust Housing

The housing is constructed from high-strength cast iron or specialized alloys, designed to dissipate heat efficiently while maintaining structural integrity under extreme vibration.

Key Advantages for Industrial Operations

Choosing a Rexroth A2FM80 or A2FM90 motor provides several strategic benefits for machine builders and plant operators.

Superior Starting Torque

One of the most critical metrics for a hydraulic piston motor is its ability to start under full load.

The A2FM series excels here, providing smooth, stutter-free startup torque, which is vital for winch drives and heavy-duty conveyor systems.

Interchangeability and Standardization

Rexroth adheres to strict ISO and SAE mounting standards.

The A2FM80 and A2FM90 feature standardized splined shafts and mounting flanges, making them easy to integrate into existing systems or use as drop-in replacements for older units.

Low Maintenance and Longevity

Due to the optimized lubrication paths within the bent-axis group, the internal components experience less wear.

When maintained with clean, high-quality hydraulic oil, these motors can operate for tens of thousands of hours without a significant drop in volumetric efficiency.

Common Applications

The versatility of the A2FM80 and A2FM90 makes them a staple in numerous sectors:

Construction Machinery: Drive systems for excavators, road rollers, and skid-steer loaders.

Material Handling: Powerful drive units for reach stackers and heavy-duty forklifts.

Mining & Drilling: Used in rotary heads for drilling rigs where constant speed and High Torque are required.

Marine Equipment: Ideal for deck cranes, mooring winches, and thruster drives due to their corrosion-resistant options and high-pressure tolerance.

Selection and Maintenance Tips

When selecting between the A2FM80 and A2FM90, engineers must calculate the required output torque ($T$) and flow rate ($Q$) based on the specific machine cycle.

Always ensure:

The case drain pressure does not exceed the manufacturer's limits to protect shaft seals.

The hydraulic fluid is filtered to at least 20/18/15 according to ISO 4406.

The motor is filled with hydraulic fluid before commissioning to prevent "dry start" damage to the piston shoes and cylinder block.

Conclusion

The Rexroth A2FM80 and A2FM90 represent the pinnacle of fixed displacement hydraulic bolting tools and drive technoLogy.

Their ability to deliver consistent, high-pressure performance in a compact frame makes them the preferred choice for engineers who cannot compromise on power or durability.