Product Overview
The A2FM Series fixed displacement axial piston motor is a field-proven bent-axis motor platform from Bosch Rexroth, featuring an axial tapered piston rotary group of bent-axis design suitable for hydrostatic drives in both open and closed circuits. The series spans 22 displacement sizes from 5 to 1,000 cm³/rev, with nominal pressure up to 400 bar and peak pressure up to 450 bar, renowned for compact construction, excellent power-to-weight ratio, and high volumetric efficiency.
The specific model covered in this document — A2FM56/61W-VAB020 — is the 56 cm³/rev configuration with a 40° bent-axis design and bidirectional rotation capability. In the model code, A2FM designates the bent-axis fixed displacement axial piston motor; 56 indicates a theoretical displacement of 56 cm³/rev; 61 denotes the Series 61 high-pressure version (400 bar rated, 450 bar peak); W specifies bidirectional rotation; V indicates splined shaft output; A specifies SAE flange ports; B denotes the drain port position; and 020 is the sealing, installation, and design version number (NBR nitrile rubber seal). The motor is manufactured to original Bosch Rexroth specifications with 100% drop-in interchangeability, requiring no modification to mounting interfaces, port positions, or hydraulic connections. Every unit undergoes 100% simulated operating condition testing at the factory, including rated pressure loading, volumetric efficiency verification, starting efficiency validation, and seal integrity assessment prior to shipment.
Technical Specifications
A2FM56/61W-VAB020:
Series / Type: Rexroth A2FM bent-axis fixed displacement axial piston motor, Series 61
Displacement: 56.1 cm³/rev
Design: Bent-axis axial tapered piston rotary group, 40° swing angle
Nominal pressure (continuous): 400 bar (40 MPa)
Maximum pressure (intermittent): 450 bar (45 MPa)
Rated speed: 2,500 rpm
Maximum speed: 4,750 rpm
Maximum input flow (at n nom & Vg): 281 L/min
Theoretical torque (Δp = 350 bar): 312 Nm
Theoretical torque (Δp = 400 bar): 357 Nm
Direction of rotation: Bidirectional (either A or B port as inlet)
Output shaft: Splined shaft
Mounting flange: ISO 3019-2, 4-hole
Ports: SAE flange ports (A and B at side, opposite)
Drain port position: B configuration
Shaft seal material: NBR (nitrile rubber)
Circuit compatibility: Open and closed hydrostatic circuits
Housing material: High-strength cast iron
Approximate weight: 18 kg
A2FM Series displacement range (for reference):
A2FM5: 4.93 cm³/rev, max speed 11,000 rpm
A2FM10: 10.3 cm³/rev, max speed 8,800 rpm
A2FM12: 12 cm³/rev, max speed 8,800 rpm
A2FM16: 16 cm³/rev, max speed 8,800 rpm
A2FM23: 22.9 cm³/rev, max speed 6,900 rpm
A2FM28: 28.1 cm³/rev, max speed 6,900 rpm
A2FM32: 32 cm³/rev, max speed 6,900 rpm
A2FM45: 45.6 cm³/rev, max speed 6,200 rpm
A2FM56: 56.1 cm³/rev, max speed 5,500 rpm
A2FM63: 63 cm³/rev, max speed 5,500 rpm
A2FM80: 80.4 cm³/rev, max speed 5,000 rpm
A2FM90: 90 cm³/rev, max speed 5,000 rpm
A2FM107: 106.7 cm³/rev, max speed 4,400 rpm
A2FM125: 125 cm³/rev, max speed 4,400 rpm
A2FM160: 160.4 cm³/rev, max speed 4,000 rpm
A2FM180: 180 cm³/rev, max speed 4,000 rpm
A2FM200: 200 cm³/rev, max speed 3,000 rpm
A2FM250: 250 cm³/rev, max speed 2,700 rpm
A2FM355: 355 cm³/rev, max speed 2,240 rpm
A2FM500: 500 cm³/rev, max speed 2,000 rpm
A2FM710: 710 cm³/rev, max speed 1,600 rpm
A2FM1000: 1,000 cm³/rev, max speed 1,600 rpm
Note: Displacement, pressure, speed, and torque data above are sourced from the Rexroth A2FM Series official technical manual and product specification tables. For precise technical specifications of the A2FM56/61W-VAB020, always consult the official Bosch Rexroth technical manual or the product nameplate data.
Key Technical Advantages
1. 40° Bent-Axis Design for High Torque Transmission Efficiency
The A2FM56 employs a 40° large swing angle bent-axis axial tapered piston rotary group, with piston force applied directly to the output shaft socket through spherical piston ends — the torque transmission path is the shortest with minimal mechanical loss. Compared to swashplate designs, the bent-axis architecture accommodates higher working pressures at equivalent displacement and generates lower side forces between pistons and cylinder bores, reducing friction losses and wear rates in the running gear. This design is particularly suited for high-speed (3,000–5,500 rpm) and high-pressure (400 bar rated) applications, achieving overall efficiency above 90% and starting torque efficiency exceeding 85%.
2. High Starting Torque and Excellent Low-Speed Performance
The bent-axis architecture delivers high torque instantaneously upon startup without requiring oil film pressure build-up, with excellent starting efficiency. For travel drive applications involving frequent start-stop cycles and heavy-load starting — such as vibratory roller travel systems, winch drives, and swing mechanisms — this characteristic significantly simplifies drivetrain design and reduces energy losses from intermediate transmission stages. The A2FM56 achieves a theoretical torque of 357 Nm at Δp = 400 bar and 312 Nm at 350 bar, with torque density leading its class among 56 cm³/rev displacement motors.
3. Spherical Flow Distribution for High Volumetric Efficiency
The A2FM Series employs spherical flow distribution, with a stable oil film maintained between the valve plate and cylinder barrel face under high pressure to preserve high volumetric efficiency and minimize internal leakage. Pistons feature an integral tapered design with piston ring sealing. The laminated piston ring adapts to micro-deformation of the cylinder bore under high pressure, maintaining consistent sealing contact. Under thermal cycling, its thermal expansion compensation far exceeds that of solid piston rings. This design maintains high efficiency across a wide temperature and pressure envelope, minimizing energy loss and heat generation from internal leakage.
4. Compact Construction with High Power Density
The A2FM56/61W-VAB020 achieves 56 cm³/rev displacement capability and 400 bar working pressure in a unit weighing only approximately 18 kg, delivering an excellent power-to-weight ratio. The bent-axis rotary group is compact with a small envelope, suited to space-constrained mobile machinery and industrial equipment. Motor output speed is proportional to input flow, and drive torque increases with the pressure differential between high-pressure and low-pressure sides, providing flexible system design. The ISO 3019-2 standard 4-hole flange and SAE flange ports ensure high standardization for system integration and spare parts interchangeability.
Application Areas
Construction equipment: Vibratory roller travel drives (Sany and comparable brands), excavator swing drives, mini loader travel systems, transit mixer drum drives
Lifting and transport machinery: Winch motors, truck crane swing drives, aerial work platform travel systems
Drilling equipment: Rotary drilling rig auxiliary drives, anchor drilling rig swing drives
Marine and offshore: Deck machinery, windlass drives, fishing vessel winches
Industrial hydraulic systems: High-pressure high-flow industrial hydraulic equipment, industrial devices requiring high-torque fixed displacement rotary drives
Agricultural machinery: Combine harvester auxiliary drives, self-propelled sprayer travel systems
Expert Maintenance Tips
1. Fluid Cleanliness Management Is the Primary Task
The A2FM56 operates with micron-level clearances between pistons and cylinder bores and between the valve plate and cylinder barrel face. Particulate contamination in hydraulic fluid is the leading cause of piston scoring and valve plate wear. Systems must be equipped with filtration rated to ISO 4406 18/16/13 or better, with periodic monitoring of moisture and particle contamination levels. In dusty construction machinery environments, consider shortening fluid change intervals accordingly.
2. Case Drain Line Configuration Requirements
Case drain from the A2FM56 must be routed to the reservoir through the highest drain port, with case pressure strictly controlled within specified limits. Excessive case pressure will cause shaft seal failure; insufficient pressure will reduce lubrication and heat rejection effectiveness. The case drain line must terminate below the minimum oil level in the reservoir to maintain positive return flow under all operating conditions. Note: this model features a B-configuration drain port — verify correct drain port position during installation.
3. Pre-Start Case Filling and Air Purging
Before first startup after installation or repair, the motor case must be filled with clean hydraulic fluid through the highest case port until fluid overflows. The A2FM56 bent-axis axial piston architecture creates a complex internal case cavity geometry; starting an un-purged motor can cause dry friction damage between piston ball ends and socket bushings, leading to irreversible premature wear.
4. Splined Shaft and Mounting Alignment
This model features a splined shaft output (V configuration). During installation, verify that the output shaft spline is properly aligned with the mating component, and that spline engagement length meets design requirements. Installation misalignment will cause abnormal spline wear and bearing side loading, significantly shortening service life. The ISO 3019-2 standard 4-hole flange requires mounting bolts to be tightened in stages to the specified torque value, with re-checking after 500 operating hours. Always use the correct O-ring seal at the SAE flange port interface.
5. Shaft Seal Inspection and Replacement
The shaft seal is a wear component on the A2FM56. Replace the shaft seal every 5,000 operating hours or when leakage exceeds 10 drops per minute. During replacement, ensure correct installation orientation with the lip facing the housing interior. For systems using water glycol or other special fluids, select a seal version compatible with the medium.
6. Restart Procedure After Extended Shutdown
If the motor has been idle for more than three months, manually rotate the output shaft to confirm freedom of movement, and inspect the case oil level and shaft seal for leakage before restarting. Extended shutdown can cause oil film drainage from piston-slipper interfaces, creating a dry-start risk. Before restarting, replenish clean hydraulic fluid through the case fill port and operate at low speed and reduced load for 10–15 minutes before returning to normal duty.
