Two-Part Assembly
The HMG21 is made up of two main sections. The inner section is the hydraulic motor itself, containing the pistons, cylinder block, and distribution system that convert hydraulic pressure into rotational force. The outer section is a bracket that mounts to the vehicle frame or axle. The two sections are connected through sliding bearings and end covers that allow the motor to rotate relative to the bracket.
Sliding Bearings and End Covers
The sliding bearings carry the load between the motor body and the bracket. They allow smooth rotation without play that would cause vibration or misalignment. The end covers close the assembly and retain the bearings in position. This structure is what makes the motor steerable: the bracket stays fixed to the frame, while the motor body turns inside it to change the wheel's direction.
Steering Input
Steering is controlled by directing hydraulic flow to the steering circuit. When the operator turns the steering wheel, hydraulic pressure is applied to rotate the motor body within the bracket. The motor body turns to the desired angle, and the wheel mounted to the motor output shaft turns with it.
Drive Function During Steering
The motor continues to drive the wheel while it steers. There is no need to disengage the drive to change direction. The piston assembly inside the motor keeps converting hydraulic pressure into rotation, and the output shaft keeps turning the wheel. Steering and driving happen at the same time, which is essential for machines that need to turn while moving under load.
Sealing Between Rotating Parts
The interface between the rotating motor body and the fixed bracket requires sealing to prevent hydraulic fluid from leaking out and contaminants from entering. The seal arrangement is designed to withstand the pressure of the hydraulic system while allowing the rotational movement needed for steering. This is a critical design detail because a leak at this interface would affect both steering and drive performance.
No Separate Steering Cylinder
A conventional steerable drive axle uses a hydraulic cylinder to push or pull the wheel assembly into the desired angle. The HMG21 removes that cylinder entirely. Steering is built into the motor mount. This means fewer hydraulic lines, fewer fittings, and fewer points where leaks can develop.
No Steering Linkage
Mechanical steering linkages use tie rods, king pins, and steering arms to transmit force from the cylinder to the wheel. Each of these components adds weight, takes up space, and requires maintenance. The HMG21 eliminates the linkage by making the motor itself the steering mechanism.
Fewer Components, Fewer Failure Points
Every component removed from the steering system is a component that does not need to be inspected, lubricated, or replaced. For machines that operate in dusty, wet, or high-vibration environments, reducing the number of exposed moving parts lowers the risk of premature wear and unexpected downtime.
| Item | Specification |
|---|---|
| Brand | Helm Tower |
| Product | HMG21 Piston Type Steerable Drive Hydraulic Motor |
| Type | Piston type, steerable drive |
| Steering Method | Motor body rotates within mounting bracket |
| Bearing Type | Sliding bearings with end covers |
| Drive and Steer | Simultaneous drive and steering function |
| Application | Mobile machinery requiring steerable wheel drive |
Contact Helm Tower for technical details, mounting dimensions, or application support for the HMG21 Piston Type Steerable Drive Hydraulic Motor.
