limited-rotation hydraulic motors

LIMITED-ROTATION HYDRAULIC MOTORS

1. What are Limited-Rotation Hydraulic Motors?

• The limited-rotation motors provide an oscillating power output. In other words, limited-rotation motors provide rotary output motion over a finite angle.

• Usually the rotation of the shaft of these motors is 90°, 180°, or 270°.

• Types: The two types of limited-rotation motors used to obtain an oscillatory output are:

1. Vane type limited-rotation motors, and

2. Piston type limited-rotation motors.

2. Vane Type Limited-Rotation Motors

There are two types of limited-rotation vane motors, the single-vane and the double-vane. Fig.5.13 and 5.14 illustrate the operation of a typical single-vane and double-vane rotation motors respectively. In both the single- and the double-vane units, seals are maintained between the rotor and the barriers, and between the vanes and the housing.

1. Single-Vane Rotation Motor

As shown in Fig.5.13, the single-vane unit consists of a cylindrical housing, a shaft with a single vane, a barrier which limits the vane rotation, and end pieces which support the shaft. Pressurised liquid enters on the side of the vane, forcing the vane to rotate to the barrier. The single-vane unit produce the rotation of approximately 280°.

2. Double-Vane Rotation Motor

In the double-vane unit, the pressurised fluid enters on one side of a vane and is ported through the shaft to the corresponding side of the other vane, as shown in Fig.5.14. A rotation of about 100° can be obtained with the double-vane unit.

3. Analysis of Torque Capacity in a Single-Vane Type Limited-Rotation Motor 

The torque producing capacity of a single-vane type limited-rotation motion can be determined as below.

Let

T = Torque developing capacity in N-m,

F = Hydraulic force acting on vane in N,

P = Hydraulic pressure in N/m2,

A = Surface area of vane in contact with liquid in m2,

RR = Outer radius of rotor in m,

RV  = Outer radius of vane in m, and

L = Width of vane in m.

Area of vane surface, A = (RV - RR) L

We know that the torque developing capacity,

T = Vane force × Mean radius of the vane

Combining equations (5.8) and (5.9), we get

It can be noted from Equation (5.10) that torque capacity depends only on the hydraulic pressure and the volumetric displacement.

4. Ranges

The limited-rotation vane motors are available with torque output ranging from less than 1 N-m at 4 bars to nearly 85 kN-m at 200 bars.

3. Piston Type Limited-Rotation Motors

Fig.5.15 illustrates a typical piston type limited-rotation motor called helix-spline rotary motor.

As shown in Fig.5.15, the helix-spline unit employs a shaft with a helical screw which passes through the piston. A guide rod prevents rotation of the piston. Also a self-locking helix angle prevents rotation when an external torque is applied. This type of motors can obtain any desired rotation angle. Both lesser and greater than 360° are possible.

4. Applications of Limited-rotation Hydraulic Motors

The important applications of limited-rotation hydraulic motors include conveyor sorting, valve turning, air bending operations, flip over between work stations, positioning for welding, lifting, rotating, and dumping.