Rexroth Hagglunds UB series Rotary output type hydraulic motor

The Hägglunds VI family flips that arrangement for certain applications. Instead of (or in addition to) a shaft, the entire outer case of the motor rotates, while the internal cylinder block stays fixed. That rotating case becomes the output element — you bolt a winch drum, cable reel, or sheave directly to flanges on the case, and the motor turns the load without an intermediate shaft coupling at all.

Within this family, Bosch Rexroth uses letter codes to distinguish output configuration:

MK / MB — shaft output types, where a conventional output shaft is provided

UK / UB — rotary (rotating case) output types, where the case itself is the mounting interface for the driven component

The UB designation specifically pairs the rotating-case output with the larger-frame motor sizes in the series (mirroring the MB shaft-output frame sizes), making it the go-to choice when you need high torque delivered directly into a large-diameter rotating structure — think a winch drum wide enough to spool hundreds of meters of wire rope.

How the UB Motor Works Inside

Radial Piston, Cam Ring Architecture

The UB motor is a radial piston hydraulic motor. That architecture, rather than gear or vane design, is precisely why it can produce enormous torque at very low, controllable speeds — exactly the profile a winch or reel needs.

Inside the motor:

An even number of pistons are arranged radially in bores machined into a stationary cylinder block.

Each piston connects, via a piston rod, to a cross-head pin carrying cam rollers.

The cam rollers ride against a cam ring that is rigidly fixed to the rotating case.

A distributor, synchronized to the case through a safety coupling, times the oil delivery to each piston in sequence.

The Rotating Case Does the Work

Here's the part that distinguishes the UB: when pressurized oil pushes a piston outward, the cam roller presses against the sloped lobes of the cam ring. Because the cam ring is anchored to the case rather than to a shaft, that reaction force pushes the case itself into rotation around the stationary cylinder block, which is supported on two main bearings.

The practical result: the motor case becomes a direct-drive rotating platform. There's no shaft, no coupling, no external gearbox stage absorbing backlash or adding a failure point. The load — a drum, sheave, or rotary table — bolts straight to the case.

Why This Matters for Torque and Control

Because displacement is fixed and 100% of it is delivered through symmetrical, radially-opposed pistons, the UB motor produces smooth torque with no flow pulsation and no net centrifugal imbalance. Speed and torque are governed almost entirely by oil flow and pressure, which gives operators very fine, very low-speed control — critical when you're paying out wire rope under tension or positioning a load within millimeters.

Where the UB Series Gets Used

The Hägglunds Viking family, including UB, was originally engineered for marine deck machinery, and that heritage still shows in where it's specified today:

Marine and Offshore

Mooring and towing winches

Anchor-handling winches

Cable and umbilical reels

Crane and lifting-winch drives on vessels and platforms

Heavy Industry

Port terminal cranes and container handling equipment

Steel plant coilers and reel drives

Paper and pulp mill reel stands

Mining and mineral processing rotary equipment

Lifting and material-handling winches in general heavy machinery

The common thread across all of these: a rotating drum or reel that needs high torque, low speed, smooth control, and the ability to hold or resist load — precisely what a rotating-case radial piston motor is built to deliver.

Key Considerations When Specifying or Servicing a UB Motor

Charge Pressure and Case Pressure

Like other motors in the Hägglunds VI/Viking line, the UB requires adequate charge pressure to the working circuit and has defined limits on case pressure at standstill and during operation. Running outside these limits — particularly exceeding the permitted case pressure — risks seal damage, so charge pressure setup should always follow the specific motor's technical data sheet rather than a generic assumption.

Mounting Interface

Because the case is the output element, mounting bolt patterns, flange tolerances, and axial/radial load ratings on the case become just as critical as shaft alignment would be on a conventional motor. Undersized or misaligned mounting hardware on a UB installation puts stress directly on the main case bearings.

Direction of Rotation

As with the rest of the family, port "A" is typically the reference port: supplying oil to port A rotates the motor in the direction marked by the arrow on the housing. Confirming port assignment before commissioning avoids an embarrassing (and potentially damaging) reversed-load surprise.

Oil Cleanliness and Viscosity

Radial piston motors are precision assemblies with tight clearances between pistons, cam rollers, and cam ring. Contaminated oil or the wrong viscosity band accelerates wear on exactly the surfaces responsible for torque transfer, so filtration and viscosity specs deserve the same attention as pressure ratings.

Service Life and Inspection

Because the case itself is a load-bearing, continuously rotating structure supporting externally mounted equipment, periodic inspection of the main case bearings, the safety coupling linking the distributor to the case, and seal condition is a routine maintenance item — not an afterthought.

For more information on the UB hydraulic motor, please visit https://www.baolilaihydraulic.com/product/.

Specifications

Q1: Is the UB motor a gear motor or a piston motor?

A1: It's a radial piston motor. Pistons act on a cam ring through cam rollers and a rotating distributor, which is what allows it to generate high torque at very low, precisely controllable speeds — a very different performance profile from gear or vane motors.

Q2: What industries typically use the UB series?

A2: Primarily marine and offshore (winches, cable reels, mooring and anchor-handling equipment), as well as heavy industrial sectors like ports, steel, pulp and paper, and mining, wherever a drum or reel needs direct, high-torque, low-speed drive.

Q3: What is the price and delivery time of the UB hydraulic motor?

A3: The price and delivery time will be provided based on the model you specify.

Q4:How to purchase a UB hydraulic motor?

A4: You can visit https://www.baolilaihydraulic.com/contact/ to contact us and purchase our products via various methods.