Product Overview
The A2FM series bent-axis fixed-displacement piston motors are a flagship product line within the Bosch Rexroth hydraulic transmission platform, classified as all-purpose high-pressure motors. Featuring a bent-axis design with axial tapered piston rotary groups, these motors are specifically engineered for hydrostatic drives in both open and closed circuits. Designed to fully comply with Rexroth A2FM Series 61 mounting and interface standards, these motors offer 100% direct interchangeability with original Rexroth units—enabling plug-and-play replacement without any管路 modifications or adapter plates, significantly minimizing downtime and retrofit costs.
The A2FM series covers an ultra-wide displacement range from 5 to 1000 cc/rev. The A2FM28 delivers 28.1 cc/rev displacement, a compact yet powerful member of the family. Sizes 10–200 are rated at 400 bar nominal pressure with 450 bar peak pressure.
The A2FM series features a 40° bent-axis design delivering very high power density, very high total efficiency, and high starting efficiency. The durable one-piece pistons with piston rings provide long service life and robust performance. Every unit undergoes 100% factory testing under simulated real-world working conditions, validating pressure, flow, and sealing performance before shipment—ensuring reliable operation from the very first start.
Model Code Interpretation:
A2FM28/61W-VBB010D-K (Part No.: R902230038)
A2FM – Series code: Bent-axis fixed displacement piston motor
28 – Displacement size: 28.1 cm³/rev
61 – Series number: Series 61
W – Rotation: Bidirectional (viewed on drive shaft)
VBB010D-K – Specific configuration code (shaft end, mounting flange, port options)
A2FM28/61W-VBB010 (Part No.: R902205656)
A2FM – Series code: Bent-axis fixed displacement piston motor
28 – Displacement size: 28.1 cm³/rev
61 – Series number: Series 61
W – Rotation: Bidirectional
VBB010 – Specific configuration code (tapered shaft with threaded pin and woodruff key DIN 6888, torque transmitted via tapered press fit)
Technical Specifications
A2FM28/61W-VBB010D-K
Model: A2FM28/61W-VBB010D-K
Part Number: R902230038
Type: Bent-axis fixed displacement piston motor (Series 61)
Geometric Displacement: 28.1 cm³/rev
Nominal Pressure: 400 bar
Maximum Pressure: 450 bar
Maximum Speed: 6300 r/min
Maximum Inlet Flow: 177 L/min
Maximum Torque (@400 bar): 179 N·m
Weight (approx.): 10.5 kg
Torsional Stiffness: 2.98 rad²
Moment of Inertia: 0.0012 kg·m²
Maximum Angular Acceleration: 6500 rad²
Rotation: Bidirectional (viewed on drive shaft)
Mounting Flange: ISO 3019-2 100B4 HW
Working Ports: SAE flange or thread
Medium: Mineral oil, synthetic hydraulic oil (HFB/HFC)
Operating Temperature Range: -20°C to +80°C
Seal Material: FKM (fluoroelastomer)
A2FM28/61W-VBB010 (Part No.: R902205656)
Model: A2FM28/61W-VBB010
Part Number: R902205656
Type: Bent-axis fixed displacement piston motor (Series 61)
Geometric Displacement: 28.1 cm³/rev
Nominal Pressure: 400 bar
Maximum Pressure: 450 bar
Maximum Speed: 6300 r/min
Weight (approx.): 10.5 kg
Drive Shaft: Tapered shaft with threaded pin and woodruff key (DIN 6888), torque transmitted via tapered press fit
Rotation: Bidirectional (viewed on drive shaft)
Working Ports: SAE flange or thread, side-mounted, with threaded plugs
Medium: Mineral oil, synthetic hydraulic oil (HFB/HFC)
Seal Material: FKM (fluoroelastomer)
A2FM Series General Parameters:
Displacement Range: 5–1000 cc/rev (5, 10, 12, 16, 23, 28, 32, 107, 125, 160, 180, 200, 250, 355, 500, 710, 1000)
Sizes 10–200: Nominal pressure 400 bar / Peak pressure 450 bar
Size 5: Nominal pressure 315 bar
Circuits: Open and closed circuits
Design: Bent-axis, 40° bent-axis design
Key Technical Advantages
1. 100% Direct Interchangeability – Zero Modification Required
The A2FM series is engineered to exact Rexroth A2FM Series 61 mounting and interface specifications, with identical dimensions, port locations, and shaft end configurations. End users can replace original units directly without any管路 modifications or adapter plates—transforming unplanned downtime into scheduled, rapid maintenance while significantly reducing spare parts procurement costs and equipment downtime losses.
2. 40° Bent-Axis Design – High Power Density and Superior Efficiency
The 40° bent-axis design with axial tapered piston rotary groups delivers very high power density and very high total efficiency. The high starting efficiency makes it critical for operations requiring immediate response. The bent-axis compact design ensures minimal friction losses and superior mechanical efficiency.
3. Spherical Port Plate Technology – Self-Centering with Long Service Life
The cylinder block and port plate employ a spherical port plate design that automatically self-centers during rotation, reducing friction losses and enhancing efficiency. The durable one-piece pistons with piston rings provide long service life, while reinforced bearings and wear-resistant friction pairs deliver excellent shock and contamination resistance.
4. High-Pressure Capability with Wide Displacement Selection
Rated at 400 bar nominal pressure with 450 bar peak pressure, these motors maintain superior performance under high-load conditions. The A2FM series offers an ultra-wide displacement selection from 5 to 1000 cc/rev, allowing precise matching to specific application requirements.
5. Bidirectional Rotation with Flexible Configuration
Bidirectional rotation design (viewed on drive shaft) enables adaptation to various system requirements without the need for model changes based on rotation direction. Mounting flanges comply with ISO 3019-2 100B4 HW standards, and ports are compatible with SAE flange or thread connections. Optional integrated pressure relief valves prevent system overload, with additional optional counterbalance valves (BVD/BVE) , flushing valves, and boost-pressure valves available.
6. 100% Factory Testing Under Simulated Working Conditions
Every A2FM series unit undergoes rigorous factory testing under simulated real-world conditions, validating pressure, flow, volumetric efficiency, and sealing performance across the full operating range. Test media match actual operating conditions, ensuring each unit is ready for immediate installation and reliable operation upon delivery—eliminating the risk of “dead on arrival” components.
Application Areas
The A2FM28 series fixed displacement motors are widely deployed across the following industries and equipment types:
Construction Machinery: Small excavator travel/swing drives
Road Construction Equipment: Roller travel drives
Crane Machinery: Crane hoisting mechanisms, swing mechanisms
Mining Equipment: Mining machinery, rock drilling rigs
Agricultural Machinery: Tractor hydraulic outputs
Industrial Equipment: Injection molding machines, conveyors
Expert Maintenance Tips
1. Hydraulic Fluid Cleanliness Management
The A2FM series utilizes bent-axis piston designs with minimal clearances between pistons and cylinder bores, making them highly sensitive to fluid contamination. It is recommended to install filters with ≤10μm filtration rating, maintaining fluid cleanliness to ISO 4406 19/17/14 or better. Mineral oil and synthetic hydraulic oil (HFB/HFC) are recommended. Never use degraded or substandard hydraulic fluids.
2. Case Drain and Backpressure Control
Ensure the case drain line is unrestricted with no flow restrictions. For sizes 10–200, continuous case backpressure must not exceed 10 bar. Excessive case backpressure will cause shaft seal damage and premature bearing failure. The drain line should return directly to the reservoir, not in parallel with the return line.
3. Air Bleeding and Pre-filling Before Start-up
Always bleed air from the motor housing via the highest vent port before initial start-up or after extended shutdown periods to prevent cavitation damage. Ensure the motor housing is completely filled with hydraulic fluid prior to starting.
4. Coupling Alignment Requirements
Maintain shaft alignment within 0.05 mm concentricity and 0.5° angular deviation between the drive shaft and the load shaft. Excessive misalignment will lead to premature bearing wear and shaft seal leakage. The use of flexible couplings is recommended to compensate for minor installation deviations.
5. Rotation Direction Confirmation
The A2FM series features bidirectional rotation as viewed on the drive shaft. Verify that the system circuit direction matches the required rotation direction before installation—reversing fluid flow will reverse the motor’s direction of rotation.
6. Periodic Inspection and Maintenance
Inspect shaft seals for leakage and listen for abnormal operating noise every 1,000 operating hours or every 6 months (whichever comes first). If reduced volumetric efficiency or insufficient output torque is observed, timely overhaul of the piston assembly and valve plate is recommended.
