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Rexroth A6VM250HZ/63W2-VZB027B Hydraulic Motor
Overview
The Rexroth A6VM250HZ/63W2-VZB027B is a high-performance axial piston variable displacement motor manufactured by Bosch Rexroth. As part of the A6VM series, this motor features a bent-axis design and is engineered for hydrostatic transmissions in both open and closed circuits, delivering precise control of fluid flow and exceptional reliability in demanding mobile and industrial applications. The A6VM series is widely recognized for its high power density, wide control range, high overall efficiency, and long service life.
Technical Features
Bent-Axis Design with Axial Tapered Piston Rotary Group — The motor utilizes a bent-axis design with an axial tapered piston rotary group, specifically engineered for hydrostatic drives in both open and closed circuits. This design enables efficient hydraulic power conversion with high power density and smooth operation. The motor is built with a robust cast iron housing, ensuring durability under extreme conditions.
High Displacement & Pressure Capacity — The motor has a maximum geometric displacement of 250 cm³ per revolution. Due to the size classification (250 to 1000), it operates at a nominal pressure of 350 bar and can withstand maximum intermittent pressures up to 400 bar, making it suitable for high-pressure heavy-duty hydraulic systems. Smaller sizes in the A6VM series (28 to 200) offer higher pressure ratings of 400 bar nominal and 450 bar peak.
HZ Two-Point Hydraulic Control — The motor is equipped with HZ control, which is a two-point hydraulic control system. This control mechanism allows the displacement to be set to either Vg max (maximum displacement) or Vg min (minimum displacement) by switching the pilot pressure at port X on or off. When no pilot pressure is applied, the motor operates at Vg max, delivering maximum torque and minimum speed. When pilot pressure exceeds the switching threshold, the motor switches to Vg min, providing minimum torque and maximum permissible speed. The control oil is internally taken from the high-pressure side of the motor. For reliable control, an operating pressure of at least 30 bar is required. The maximum permissible pilot pressure is 100 bar.
Stepless Variable Displacement — The displacement can be infinitely changed from Vg max (maximum displacement) to Vg min (=0), providing exceptional flexibility to adjust output speed and torque according to different working requirements. The output speed depends on the pump flow rate and the motor displacement, while the output torque increases with the pressure differential between the high-pressure and low-pressure sides and with increasing displacement.
Wide Speed Range — The motor is approved for very high rotational speeds while maintaining excellent low-speed operating characteristics. The A6VM250 offers a control range that can be swiveled to zero, satisfying both high-speed and high-torque requirements.
High Flow Capacity — The motor has a maximum flow rate of approximately 675 L/min, providing substantial hydraulic power for demanding applications.
High Torque Output — The motor delivers high torque output, ensuring powerful performance in heavy-load conditions. Output torque increases with the pressure difference between the high-pressure and low-pressure sides and with increasing displacement.
High Power Density — The motor offers high power density, meaning it delivers substantial power output relative to its size and weight, contributing to space-saving installation and efficient system design. This is achieved through a compact, robust long-life bearing system.
FKM Seals for Wide Temperature Compatibility — Equipped with FKM (fluoroelastomer) seals, this motor is compatible with various hydraulic fluids and suitable for operation across a wide temperature spectrum, ensuring reliable performance in diverse operating conditions.
Series 63 Index — The 63W2 series index indicates Series 6, Index 3, Standard version with W2 configuration, representing the latest design iteration within the A6VM product family.
Good Starting Characteristics & Low Inertia — The motor features excellent starting characteristics and low moment of inertia, enabling smooth and responsive operation even under heavy starting loads.
Key Functionalities
Hydrostatic Transmission in Open and Closed Circuits — The motor is designed for hydrostatic drives in both open and closed circuits, providing versatility for various hydraulic system configurations. In closed circuit systems, the motor operates within a sealed hydraulic loop where fluid is continuously recirculated between the pump and motor, minimizing losses and leakage. In open circuit systems, fluid is supplied from a central pump through a directional control valve and returns to the reservoir after each cycle.
Two-Point Displacement Switching — The HZ control system provides a simple, reliable method for switching between two distinct displacement settings. When pilot pressure is off, the motor operates at Vg max for maximum torque and minimum speed. When pilot pressure is applied (typically >10 bar), the motor switches to Vg min for minimum torque and maximum permissible speed. This two-point control is ideal for applications requiring simple, robust speed or torque selection without the need for proportional control.
Stepless Speed and Torque Control — The motor's output speed depends on the pump flow rate and the motor displacement, while the output torque increases with the pressure differential between the high-pressure and low-pressure sides and with increasing displacement. The wide control range enables the variable motor to satisfy requirements for both high speed and high torque, with displacement infinitely adjustable from maximum to zero.
High Starting Torque — The bent-axis design naturally provides excellent starting characteristics and high starting torque, enabling the motor to easily overcome heavy breakaway loads in demanding applications such as excavators, cranes, and other heavy machinery.
Energy Efficient Operation — The variable displacement capability enables energy savings by allowing the motor to deliver only the flow and torque required by the load. By eliminating the need for gear shifts and enabling the use of smaller pumps, the A6VM series contributes to reduced energy consumption and lower operating costs.
Cost Savings Through Simplified Design — The wide control range enables cost savings through the elimination of gear shift mechanisms and the possibility of using smaller pumps, reducing overall system complexity and component costs.
High Reliability & Low Maintenance — With its robust construction, high-quality materials, wear-resistant components, and high-precision bearings, the motor ensures long-term operational stability with minimal maintenance requirements, reducing downtime and total cost of ownership.
Optional Features — The motor can be equipped with optional features including an attached flushing and boost pressure valve, as well as an integrated or attached counterbalance valve, allowing customization for specific application requirements.
Application Sectors
The Rexroth A6VM250HZ/63W2-VZB027B hydraulic motor is designed for heavy-duty mobile and industrial applications requiring high-pressure, high-power hydraulic drives with simple, reliable two-point displacement control. The A6VM series is widely used across a broad spectrum of industries:
| Industry Sector | Typical Applications |
|---|---|
| Construction Machinery | Excavators, wheel loaders, bulldozers, pavers, crawler-type machines, drilling rigs, backhoes, concrete pump trucks, wheel cranes, slewing drives, track drives |
| Rotary Drilling Rigs | Main drive systems for rotary drilling rigs from major manufacturers |
| Agricultural Machinery | Combine harvesters, tractors, self-propelled agricultural equipment, heavy agricultural machinery requiring consistent torque across a wide speed range |
| Material Handling Equipment | Forklifts, pallet trucks, conveyor systems, winches, cranes (mobile and stationary), heavy material handling systems |
| Marine & Offshore | Ship propulsion systems, deck machinery, marine cranes, winches, steering gear, dredging equipment |
| Mining Equipment | Conveyor drives, crushers, excavators, material handling systems, mining machinery, drilling equipment |
| Industrial Machinery | Hydraulic presses, injection molding machines, blow molding equipment, plastic machinery, die-casting machinery, machine tool controls |
| Steel & Metallurgy | Rolling mills, continuous casting lines, steel mill hydraulic equipment |
| Forestry Equipment | Loggers, harvesters, forwarders, forestry machinery requiring high torque at low speeds |
| Waste Management & Recycling | Shredders, balers, crushers, material separators |
| Aerospace | Aerospace equipment requiring high-performance hydraulic drives |
| Petroleum & Petrochemical | Oil field equipment, drilling machinery, petrochemical processing equipment |
| Power Generation | Coal handling systems, power plant hydraulic equipment |
| Chemical Processing | Chemical mixing equipment, processing machinery |
| Ceramic Industry | Ceramic press machines, tile presses, ceramic factory hydraulic equipment |
| Paper Manufacturing | Paper mill hydraulic systems, paper machinery hydraulic components |
Performance Specifications (Model-Specific)
| Specification | Value |
|---|---|
| Manufacturer | Bosch Rexroth |
| Series | A6VM |
| Model Code | A6VM250HZ/63W2-VZB027B |
| Material Number (MNR) | R910999277 |
| Motor Type | Axial piston variable displacement motor (bent-axis design) |
| Circuit Type | Open circuit and closed circuit |
| Displacement (Vg max) | 250 cm³/rev |
| Nominal Pressure (Continuous) | 350 bar (5,076 psi) |
| Maximum Pressure (Intermittent) | 400 bar (5,800 psi) |
| Maximum Speed (at Vg max) | 2,700 rpm |
Maximum Speed (at Vg| 3,600 rpm | |
| Maximum Flow Rate | 675 L/min |
| Torque Output (at Δp = 350 bar) | 1,391 Nm |
| Control Type | HZ — Two-point hydraulic control |
| Control Function | Switches between Vg max and Vg min via pilot pressure at port X |
| Minimum Operating Pressure for Control | 30 bar |
| Maximum Pilot Pressure | 100 bar |
| Pilot Pressure Switching Threshold | >10 bar |
| Rotation Direction | Reversible |
| Housing Material | Cast iron |
| Seals | FKM (fluoroelastomer / Viton) |
| Weight | 90 kg |
| Fluid Compatibility | Mineral oil-based hydraulic fluids, various hydraulic fluids compatible with FKM seals |
| Series Index | 63W2 (Series 6, Index 3, Standard version with W2 configuration) |
Conclusion
The Rexroth A6VM250HZ/63W2-VZB027B is a high-performance axial piston variable displacement motor that exemplifies Bosch Rexroth's decades of expertise in hydraulic drive technology. With its advanced bent-axis design, HZ two-point hydraulic control, excellent suction characteristics, and robust cast iron construction, it delivers exceptional power density, precise speed and torque control, and reliable operation for demanding hydrostatic transmission applications.
The motor's defining feature is its HZ two-point hydraulic control system, which provides a simple, reliable method for switching between two distinct displacement settings — Vg max for maximum torque and minimum speed, and Vg min for minimum torque and maximum permissible speed. This control mechanism is ideal for applications requiring straightforward speed or torque selection without the need for proportional control, while still benefiting from the full range of stepless variable displacement capability when combined with pump flow control.
With high pressure capability (nominal 350 bar, maximum 400 bar), a wide control range that satisfies both high-speed (up to 3,600 rpm) and high-torque (1,391 Nm at 350 bar) requirements, high flow capacity (675 L/min), good starting characteristics, low moment of inertia, and a robust bearing system providing long service life, this motor is an ideal solution for a wide range of applications — from construction machinery, rotary drilling rigs, and agricultural equipment to material handling systems, marine propulsion, mining equipment, industrial machinery, and forestry applications.
As a proven, reliable, and energy-efficient solution for hydrostatic drives in both open and closed circuits worldwide, the A6VM250HZ/63W2-VZB027B stands out as a versatile component where consistent high-pressure performance, reliable two-point displacement control, and long-term dependability are essential requirements.
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