Power Unit

ELECTROHYDRAULIC STEERING

bedplate. The bedplate is the top of an oil reservoir.

GEAR

Steering power is derived from either pumping

system acting alone. The system not in use serves as a

The steering gear is one of the most vital

standby source in case of an emergency.

auxiliaries aboard ship. It must be thoroughly

The two pumps (port and starboard) are identical

dependable and have sufficient capacity for maximum

in size and design and are of the variable delivery

maneuverability. The types of steering gear listed in

axial piston type. Each main pump unit includes a

the sequence of their development are (1) steam, (2)

built-in vane-type servo pump, pressure control and

electromechanical, and (3) electrohydraulic. Electro-

replenishing valves, and two main relief valves. Each

hydraulic steering gear was developed to meet the

main pump is stroked through a rotary servo control.

power requirements of naval vessels having large

displacements and high speeds with attendant increase

Each pump is driven by a 20-hp, 1200-rpm,

in rudder torques.

440-volt, 3-phase, 60-Hz induction motor through

reduction gears and a flexible coupling.

CONSTRUCTION

The pumps of the power unit are connected to the

The majority of steering gear installations in new

ram cylinders by a high-pressure piping system. The

construction naval vessels are of the electrohydraulic

two 4-way transfer valves are interposed in this

type. The electrohydraulic steering system installed in

piping, and their positions determine which pump is

one class of destroyer (fig. 11-15) consists essentially

connected to the cylinders in the ram unit. The hand

of (1) a ram unit, (2) a power unit, and (3) a remote

lever, which moves both valves simultaneously, is

control unit (not shown).

located on the power unit between the trick wheels. It

has three latched positions. The latched positions are

Ram Unit

marked P, N, and S, which denote port pump

connected, neutral (ram locked), and starboard pump

The ram unit is mounted athwartship and consists

connected, respectively.

of a single ram operated by opposed cylinders. The

ram is connected by links to the tillers of the twin

The transfer valves, which are of the ported piston

rudders. When oil pressure is applied to one end of the

type, are mounted on the power unit bedplate between

operating cylinder, the ram will move, causing each

the motors. When the valves are in the neutral (ram

rudder to move along with it. Oil from the opposite

locked) position, the ports of the pipes to the ram

end of the cylinder is returned to the suction side of

cylinders are blocked, and the two pipes from each

the main hydraulic pump in the power unit.

pump are connected through ported passages in their

respective valves. If either or both pumps are started

The tie rods that connect the two cylinders also

and put on stroke, oil will circulate through the valve

serve as guides for a sliding crosshead attached to the

and back to the pump. Movement of the transfer

ram to prevent the ram from rotating. The crosshead

valves in either direction connects the selected pump

also provides mechanical limits to the ram travel at 42

to the ram cylinders, and the opposite pump remains

of rudder angle. At this position the crosshead contacts

bypassed.

the copper facing on the stop collars and prevents

further movement.

The drain pipes from the ram cylinders lead to the

A rack is attached to the ram and engages two

reversible hand pump. It provides a means for

gears. The rotation of these gears is transmitted to the

emergency steering under limited rudder torques. The

respective differential control boxes through the

relief valve in the emergency steering system is set at

follow-up shaft.

500 psi. The oil flow is through pilot-operated

blocking valves that prevent the ram from over-

Power Unit

hauling the pump and kicking back the handles. When

you move the ram with the hand pump, set the main

The power unit has two independent pumping

transfer valves in the ram locked position and open

systems. These include two motor-driven pumps, two

the drain valves beneath the cylinders.

4-way transfer valves with operating gear, a relief

valve, two differential control boxes, two trick

The mechanical differential control box serves to

wheels, and a hand emergency gear all mounted on a

correlate the signal from the ram follow-up assembly

11-17