Elephant Fluid Dynamics A11VO Series Variable-Axis Axial Piston Hydraulic Pump: Technical White Paper (I)

The Elephant Fluid Power A11VO series variable axial piston hydraulic pumps (including models A11VO60, A11VO75, A11VO95, A11VO130, A11VO145, A11VO190, A11VO220, A11VO260, and the high-speed A11VLO version) employ a swash plate variable design identical to that of Bosch Rexroth's A11VO/A11VLO series, featuring core technical advantages such as continuously variable displacement (with Vg max to Vg min = 0). These pumps operate at nominal pressures up to 350 bar (peak pressure: 400 bar) and are specifically designed for open-loop hydraulic systems, finding extensive applications in concrete pump trucks, earthmoving machinery, road construction equipment, compaction machines, lifting systems, mining machinery, drilling rigs, and other mobile machinery. This article systematically examines the core competitiveness of the Elephant Fluid Power A11VO series across six dimensions: technical principles, full specification parameters, control modes, application scenarios, compatibility with original Rexroth components, and supply chain benefits, providing authoritative technical guidance and procurement references for global hydraulic system integrators, construction equipment manufacturers, and end-users.

Chapter 1: Technical Principles and Core Design Advantages of the A11VO Series

1.1 Structural Principle of the Diagonal Disc Variable-Axis Axial Piston

The A11VO series hydraulic pumps feature a classic swash plate axial piston design—a decades-proven industrial standard in open-loop variable hydraulic transmission systems, specifically optimized for mobile machinery applications. Compared to bent-axis designs, the swash plate configuration offers significant advantages in compactness, cost-effectiveness, and control flexibility.

Diaphragm tilt angle variable mechanism

The cylinder centerline coincides with the drive shaft centerline, and the piston contacts the swash plate via a sliding shoe. When the swash plate's swing angle is 0°, the piston exhibits no reciprocating motion and the output flow rate is zero; as the angle increases, the piston's reciprocating stroke expands, and the output flow rate becomes proportional to the swing angle. The variable displacement mechanism achieves stepless variation in displacement from Vg_max to Vg_min = 0 by adjusting the swash plate angle (from 0° to maximum), thereby precisely controlling both output flow rate and pressure. This design ensures nearly zero flow output during standby operation, significantly reducing energy consumption and heat generation.

Static Pressure Unloading Cradle Bearing

The design employs a cradle bearing with hydrostatic pressure relief, where the swash plate is supported by a hydrostatic oil film, resulting in minimal friction loss and rapid response. This configuration ensures optimal contact between the swash plate and the piston shoe under high-pressure and high-speed conditions, achieving a volumetric efficiency of over 95% and a mechanical efficiency exceeding 90%. Even at 350 bar pressure and 2500 rpm speed, stable performance output is maintained.

Double oil discharge port design

The standard configuration features two oil discharge ports (L1 and L2), allowing flexible selection of the oil discharge pipeline routing based on installation space to simplify system design. The oil discharge pipeline must be separately connected to the oil tank to ensure housing pressure does not exceed 0.5 bar, thereby protecting the shaft seal and sealing system. For high-temperature applications, the dual-discharge port design enhances heat dissipation efficiency.

1.2 Special Design Features and Self-Suction Capability for Open Circuits

The A11VO series is specifically designed for open-circuit hydraulic systems and features the following key characteristics:

• Flow rate is directly proportional to rotational speed and displacement: output flow rate qv = Vg × n × ηv / 1000 (L/min), where Vg represents current displacement (cm³/rev), n denotes rotational speed (rpm), and ηv indicates volumetric efficiency (typically 0.95–0.97).

• Pressure is determined by external load: the pump's output pressure depends on system demand, with automatic regulation of displacement and pressure via control modes (LR/DR/LRDS/DRS/HD/EP, etc.) to achieve energy-efficient operation.

• Excellent self-priming performance: The pump operates under self-priming conditions and functions normally whether the oil tank is pressurized or equipped with an integrated booster pump (centrifugal pump/impeller pump). The optimized oil suction port design and plunger return mechanism ensure outstanding self-priming capability under standard installation conditions (oil suction height ≤ 800 mm).

• High-speed A11VLO version: Available in sizes ranging from 130 to 260 mm, this model can be equipped with an impeller pump (A11VLO) for exceptionally high rotational speeds, meeting the demands of high-speed mobile machinery.

1.3 Advantages of Axial Drive and System Integration

100% shaft-driven capability

The A11VO series pumps feature through-shaft drive capability, supporting either gear pumps or axial piston pumps of equivalent specifications (100% through-shaft drive). This design offers: – The ability to connect a make-up pump, gear pump, or auxiliary piston pump in series after the main pump, simplifying hydraulic system layout; – Elimination of additional installation space and couplings, reducing system complexity; – Direct power delivery from the main pump's drive shaft to the auxiliary pump, enhancing overall transmission efficiency; – For closed-loop applications, the make-up pump can be installed directly behind the main pump, creating a compact static hydraulic drive unit.

1.4 Summary of Core Competitive Advantages

Chapter 2: Detailed Explanation of Full Specification Technical Parameters for the Elephant Fluid Dynamics A11VO Series

2.1 Product Models and Displacement Matrix

The A11VO series comprises two structural sub-series:   -A11VO Standard Version (60–260 specifications): features standard rotational speeds, suitable for general engineering machinery and industrial applications;   -A11VLO High-Speed Version (60–260 specifications): an optimized high-speed variant that can be equipped with a built-in impeller pump (centrifugal pump) to achieve exceptionally high speeds, ideal for high-speed mobile machinery.

The technical specifications for the standard model of the Elephant Fluid Dynamics A11VO series are as follows:

Note: The above data are theoretical values based on operating conditions of drive speed n = 1500 rpm, oil viscosity v = 36 mm²/s, and oil temperature t = 50 °C. Actual values should account for efficiency losses and manufacturing tolerances.

2.2 Technical Specifications of the A11VLO High-Speed Version

The A11VLO series enhances high-speed performance over the A11VO model and can be equipped with an integrated impeller pump (centrifugal pump) to achieve exceptionally high rotational speeds.

2.3 Key Performance Calculation Formulas

Pump discharge rate (proportional to displacement and driving speed): qv = Vg × n × ηv / 1000 (L/min)

Where: Vg is the current displacement (cm³/rev), n is the driving speed (rpm), and ηv is the volumetric efficiency (typically 0.95–0.97).

Pump output torque (proportional to displacement and pressure difference): T = Vg × Δp / (20π × η_mh) (Nm)

Where: Δp is the pressure difference (bar), and η_mh is the mechanical-hydraulic efficiency (typically 0.90–0.93).

Pump input power: P = qv × Δp / (600 × η_t) (kW)

Where: η_t represents total efficiency (typically ranging from 0.85 to 0.90).

The core principle of variable control is as follows: when high flow demand occurs (e.g., rapid extension of a hydraulic cylinder), the displacement Vg increases automatically; when pressure maintenance is required (e.g., hydraulic clamping), Vg decreases automatically to near zero. This on-demand oil supply mechanism ensures the system operates consistently in its highest efficiency zone, reducing overall energy consumption by 20–30% compared to a fixed-displacement pump plus relief valve configuration.

Chapter 3: In-depth Analysis of Ten Control Methods

The core competitiveness of the A11VO series lies in its extensive range of control options. Elephant Fluid Power fully replicates all control features available in the Rexroth A11VO/A11VLO series.

3.1 LR – Power Control (Direct Control)

How it works: Equipped with a built-in power control valve that limits the pump's output power within a preset range. When system pressure rises, it automatically reduces displacement to maintain constant power; when pressure drops, it increases displacement to boost flow rate. Power control settings can be adjusted externally even during operation.

Technical Parameters:   – Power range: Set according to the motor/engine's rated power   – Control behavior: Prioritizes flow demand within the power limit; automatically reduces pressure or flow when reaching the limit   – External adjustment: The power setting can be adjusted via external devices even during pump operation

Typical application: Engine-driven mobile machinery designed to prevent engine overload-induced shutdown, such as excavators, loaders, and bulldozers.

3.2 DR – Constant Pressure Control (Direct Control)

Working principle: Equipped with a built-in pressure control valve that limits the pump's maximum output pressure within a preset range. When system pressure reaches the set value, the pump automatically reduces its displacement to deliver only the flow required to maintain the pressure, eliminating overflow losses.

Technical Parameters:   – Pressure setting range: Standard adjustable, covering the entire operating pressure range   – Hysteresis and pressure rise: Δp_max ≈ 4 bar   – Control deviation decreases as the set pressure value decreases

Typical applications: Systems requiring constant pressure, such as hydraulic clamping devices, hydraulic test benches, press pressure maintenance systems, and concrete pump truck pressure control systems.

3.3 LRDS – Power Control + Pressure Cut-off + Load-Sensitive Control

Working Principle: Integrates three functions—power control, pressure cutoff, and load sensitivity. The pump simultaneously maintains the set power, limits maximum pressure, and responds to load-sensitive signals, achieving comprehensive control of "constant power – pressure limitation – load sensitivity".

Technical Parameters: -Power Control: Same as LR characteristics, externally adjustable-Pressure Cut-off: Automatically cuts flow output when system pressure reaches the set upper limit-Load Sensitivity: Responds to LS signals, delivering only the required flow rate to eliminate throttling losses-Control Range: Multiple selectable levels for varying power and pressure requirements

Typical application: Main pumps for high-end construction machinery, such as large excavators, concrete pump trucks, and mining dump trucks, delivering optimal energy efficiency and engine protection.

3.4 DRS – Pressure Control + Load-Sensitive Control

Working principle: Integrates dual functions of pressure control and load-sensitive control. The pump simultaneously maintains the set pressure and responds to load-sensitive signals, achieving "constant-pressure-load-sensitive" control.

Technical Parameters:   – Pressure Control: Same as DR characteristics   – Load Sensitivity: Responds to LS signals and delivers only the required flow rate   – Fast response time, ideal for hydraulic systems requiring rapid response

Common applications: Systems requiring simultaneous pressure control and response to load variations, such as cranes, aerial work platforms, and forestry machinery.

3.5 HD – Hydraulic Control (related to pilot pressure)

Working principle: The pump displacement is proportionally regulated by an external pilot pressure signal. Increased pilot pressure leads to increased displacement and consequently higher output flow rate. This hydraulic proportional control system features rapid response and high precision.

Technical parameters: -Control pressure differential: 10 bar or 25 bar (selectable) -Control starting point: Vg min (minimum displacement) corresponding to 0 bar pilot pressure-Control ending point: Vg max (maximum displacement) corresponding to 10/25 bar pilot pressure-Response time: <0.3 seconds

Common applications: Systems requiring hydraulic pilot control, such as excavator pilot control, loader pilot control, and crane pilot control.

3.6 EP – Electric Proportional Control (Proportional Electromagnet)

Working principle: The device receives current signals (12 V DC or 24 V DC) via an electroproportional electromagnet, converting the electrical signal into mechanical displacement to regulate pump displacement. It can be directly interfaced with PLCs or industrial control computers for digital control.

Technical Parameters:   -EP1: 12 V DC, adjustable control current range   -EP2: 24 V DC, adjustable control current range   -Response time: <0.2 seconds   -Control accuracy: ±1% displacement

Common applications: automated construction machinery, remotely controlled devices, electro-hydraulic integrated systems, and CNC hydraulic equipment.

3.7 DH – Hydraulic Control (related to pilot pressure; special version)

How it works: Similar to HD, but a specialized hydraulic control version designed for specific hydraulic system requirements. Control features can be customized according to customer needs.

Common applications: specialized hydraulic systems, such as marine hydraulic systems, aviation ground equipment, and military hydraulic systems.

3.8 LG – Lever Control (Mechanical Control)

Working principle: The pump displacement is directly adjusted via a mechanical lever. It is simple and reliable, requiring no external control of oil or power sources, and operates solely through mechanical control.

Typical applications: Simple mechanical control scenarios, such as small agricultural machinery, basic construction equipment, and manual hydraulic devices.

3.9 DH.D/DH.G – Hydraulic Control (Special Version)

Working Principle: DH.D and DH.G are specialized hydraulic control versions with unique operational characteristics, designed for specific applications. DH.D represents the dynamic control version, while DH.G denotes the gain control version.

Common applications: Systems requiring specialized dynamic response, such as high-speed injection molding machines, high-speed die-casting machines, and vibration-sensitive equipment.

3.10 EP.D / EP.G – Electric Proportional Control (Special Version)

Working principle: EP.D and EP.G are specialized versions of electric proportional control with distinct characteristics. EP.D employs dynamic electric proportional control, while EP.G uses gain-based electric proportional control.

Common applications: High-precision electro-hydraulic control systems, such as servo hydraulic systems, CNC machining centers, and precision testing equipment.

3.11 Control Method Selection Decision Matrix

Chapter 4: In-depth Comparison of Compatibility with the Bosch Rexroth A11VO Series

4.1 Dimensions and Installation: 100% Interchangeability

The Elephant Fluid Dynamics A11VO series strictly adheres to Rexroth's original design specifications, ensuring complete physical interchangeability.

• Installation flange: Compliant with ISO 3019-2 standards, available in 2-hole and 4-hole configurations, with installation dimensional tolerance controlled within ±0.1 mm.

• Drive shaft end: Available in three options – DIN 6885 flat key shaft, DIN 5480 splined shaft, and ANSI B92.1a splined shaft – fully compatible with Rexroth's corresponding models.

• Oil port connection: SAE flanged oil port compliant with ISO 6162 standard, available in both metric and UNC thread options

• Control interfaces: LR/DR/LRDS/DRS/HD/EP/DH/LG – The control of oil port positions is fully compatible with Rexroth's original specifications.

• Oil discharge ports: Standard configuration includes two oil discharge ports (L1 and L2), positioned identically to those of the original Rexroth components.

• Axial drive: 100% axial drive capability (same specifications), compatible with series connection of gear pumps or axial piston pumps; flange and hub dimensions match those of original Rexroth components.

• Oil replenishment pump interface: The A11VLO series (specifications 130–260) can be equipped with a built-in impeller pump (centrifugal pump); the interface dimensions match those of the original Rexroth components.

4.2 Performance Parameters: Third-party Benchmark Testing

Through comparative testing conducted by the internationally renowned hydraulic testing institution (TUV Rheinland certification laboratory), the performance comparison between the Elephant Fluid Power A11VO series and Rexroth's original products is as follows:

Note: Test conditions include a mineral oil medium, ISO VG46 standard, oil temperature of 40°C, nominal pressure of 350 bar, and operating speed of 1500 rpm.

4.3 Complete Reproduction of Control Methods

The Elephant Fluid Dynamics A11VO series fully supports all control modes of the Rexroth A11VO/A11VLO series.

• LR: Power control, externally adjustable

• DR: Constant Pressure Control, Direct Operation

• LRDS: Power control + Pressure cut-off + Load-sensitive control

• DRS: Pressure control + load-sensitive control

• HD: Hydraulic proportional control, dependent on pilot pressure

• EP: Electric proportional control, 12V/24V DC

• DH: Hydraulic Control, Special Version

• LG: Lever control, mechanical control

• DH.D/H/G: Hydraulic control, Dynamic/Gain version

• EP.D/EP.G: Electric proportional control, dynamic/gain version

The response characteristics, control curves, and electromagnet parameters of all control modes are identical to those of Rexroth's original components, enabling direct replacement without requiring reconfiguration of the control system.

4.4 Quality Certification System

• ISO 9001:2015 Quality Management System Certification

• CE certification complies with the EU Machinery Directive 2006/42/EC.

• RoHS certification: Compliance with the Directive on Restrictions of Hazardous Substances

• ATEX certification optional (II 2G Ex h IIC T4-T1 Gb X / II 3G Ex h IIC T4-T1 Gc X)

• China Classification Society (CCS) certification applies to ships and marine engineering applications

• TUV Rheinland Performance Testing Certification (optional)

Chapter 5: Industry Application Scenarios and Solutions

5.1 Hydraulic System of Concrete Pump Trucks

Main Pump for Concrete Pumping Vehicles (A11VO130/A11VO145/A11VO190)

Concrete pump trucks typically employ A11VO130, A11VO145, or A11VO190 as the main pump. Through LRDS power control combined with pressure cutoff and load-sensing regulation, the system achieves the following functions: -Pumping phase: High-flow rapid pumping (Vg max); LRDS controls maximum power to prevent engine overload; -Pressure maintenance phase: High-pressure, low-flow pressure stabilization (reduced Vg while maintaining pressure); DR pressure cutoff ensures pumping pressure does not exceed safety limits; -Switching phase: Rapid response switching; load-sensing control provides only the required flow rate to eliminate throttling losses; -Energy-saving standby mode: Automatic reduction of displacement to near zero during pumping intervals, minimizing energy consumption and heat generation; -External power adjustment: Power settings can be modified via external devices even during operation to accommodate different concrete grades and delivery distances.

Compared to the conventional pump-and-overflow valve configuration, the A11VO variable pump reduces energy consumption by 25%–35%, lowers oil temperature rise, extends seal lifespan, and enhances the continuous operating capability of pump trucks.

5.2 Excavator Hydraulic System

Excavator main pump (A11VO60/A11VO75/A11VO95)

20–40-ton excavators typically employ a dual-pump system (one left and one right pump, either A11VO75 or A11VO95). Through LR power control or LRDS integrated control, the system achieves: – Compound operation: Independent control of both pumps enables coordinated movement of the boom, dipper mast, and rotation; LR control limits individual pump power to prevent engine stall. – Excavation force control: When excavation resistance increases, LR control automatically reduces displacement while maintaining constant power output for stable engine operation. – Travel drive: Combined with an A6VM variable motor, it utilizes closed-loop static hydraulic transmission for high efficiency and energy savings. – External power adjustment: Operators can modify power settings via external controls to switch between "Economic Mode" and "Power Mode" based on working conditions.

Main pumps for large excavators (A11VO130/A11VO145/A11VO190)

Large excavators in the 40–100-ton class typically employ A11VO130, A11VO145, or A11VO190 as their main pumps. The LRDS integrated control system delivers:   – Ultra-high digging power: 350 bar high-pressure output for exceptional excavation capability;   – Precise power control: LRDS dynamically matches engine power curves to achieve optimal fuel efficiency;   – Load-sensitive response: rapid adaptation to load changes for precise operation.

5.3 Excavator and Loader Hydraulic Systems

Loader Hydraulic System (A11VO60/A11VO75/A11VO95)

-wheel loaders typically employ single-pump or dual-pump systems (A11VO75 or A11VO95). Through LR power control or DRS pressure-load sensitive control, the following functions are achieved: -Excavating operations: high-flow rapid loading (Vg max); LR control limits power to prevent engine overload; -Lifting operations: high-pressure lifting (reduced Vg with maintained pressure); DRS control ensures stable lifting force; -Travel drive: combined with an A6VM variable motor, it enables closed-loop static hydraulic transmission for high efficiency and energy savings; -Steering system: a through-shaft-driven series gear pump provides independent hydraulic power to the steering system.

Shovel excavator hydraulic system (A11VO95/A11VO130)

Excavators typically employ the A11VO95 or A11VO130 as their main pump. Through LRDS integrated control, they achieve:   – Excavation, loading, transportation, and unloading: multi-functional pump operation with LRDS control adapting to varying power and flow requirements under different conditions;   – Continuous operation: high-reliability design designed for sustained performance in harsh environments such as mines and construction sites.

5.4 Hydraulic Systems for Road Surface Machinery and Compaction Machinery

Roller Hydraulic System (A11VO60/A11VO75)

Vibration rollers typically employ A11VO60 or A11VO75 as the main pump. Through DR constant-pressure control or LR power control, the system achieves:   – Travel drive: Constant-pressure control maintains a steady travel speed to ensure uniform compaction;   – Vibration system: LR power control limits vibration intensity to prevent engine overload;   – Steering system: A shaft-driven gear pump provides independent hydraulic power for the steering mechanism.

Paver Hydraulic System (A11VO75/A11VO95)

Asphalt pavers typically employ the A11VO75 or A11VO95 as their main pump. Through DRS pressure and load-sensing control, they achieve:   – Paving speed control: Load-sensing control precisely matches paving speed requirements to ensure quality;   – Tamping plate control: Constant-pressure regulation maintains uniform pressure on the tamping plate for smooth paving surface;   – Material delivery system: High-flow delivery (Vg max) enhances operational efficiency.

5.5 Hydraulic Systems for Lifting Machinery

Automobile Crane Hydraulic System (A11VO95/A11VO130/A11VO145)

Automotive cranes typically employ A11VO95, A11VO130, or A11VO145 as the main pump. Through DRS pressure-load sensitive control or LR power control, the system achieves: -Lifting operations: load-sensitive control precisely matches lifting speed requirements for safe and smooth performance; -Telescoping operations: constant-pressure control maintains stable pressure during telescoping to ensure smooth movement; -Rotating operations: power control limits rotational torque to prevent engine overload; -Leg control: a through-shaft-driven series gear pump provides independent hydraulic power to the leg system.

Crawler Crane Hydraulic System (A11VO130/A11VO145/A11VO190)

Large crawler cranes typically employ A11VO130, A11VO145, or A11VO190 as the main pump. Through LRDS integrated control, the system achieves:   – Ultra-high lifting capacity: 350 bar high-pressure output for exceptional lifting force;   – Precise power control: LRDS dynamically matches engine power curves to optimize fuel efficiency;   – Multi-mechanism coordination: load-sensing control enables synchronized operation of lifting, luffing, and slewing functions.

5.6 Hydraulic Systems for Mining Machinery and Drilling Equipment

Hydraulic System for Mine Self-Dumping Trucks (A11VO130/A11VO145/A11VO190)

Large mining dump trucks typically employ A11VO130, A11VO145, or A11VO190 as the main pump. Through LRDS integrated control, the system achieves: -Lifting and unloading: high-flow rapid lifting (Vg max), with LRDS controlling power limits and maximum pressure to ensure safety; -Steering system: independent hydraulic power supplied via a through-shaft-driven series gear pump; -Braking system: independent hydraulic power provided by a through-shaft-driven series gear pump; -Continuous operation: a highly reliable design tailored for demanding continuous performance in harsh mining conditions.

Hydraulic Systems for Drilling Equipment (A11VO145/A11VO190/A11VO220/A11VO260)

Large drilling equipment typically employs A11VO145, A11VO190, A11VO220, or A11VO260 as the main pumps. Through DR constant-pressure control or LR power control, the system achieves:   – Drilling fluid supply: Constant-pressure control maintains a stable supply pressure to ensure drilling quality;   – Rotational drive: Power control limits rotational load to prevent engine overload;   – Mud circulation: High-flow mud circulation (Vg max) enhances drilling efficiency;   – Continuous operation: A highly reliable design meets the demands of continuous operations under harsh field conditions.