GB2283718A - Hydraulic rudder control unit - Google Patents

Abstract

Hydraulic rudder control unit for boats comprising a hydraulic wheel pump (11) that is hydraulically connected to a rudder actuator (9) by hydraulic flow lines (7, 8) via pressure controlled check valves and over pressure relief valves built into a wheel pump unit (10). A reversible hydraulic autopilot pump (2) is connected to the hydraulic flow lines (7, 8) in parallel with the wheel pump (11). Check valves (14, 15) are inserted between channels (3, 4) and the autopilot pump (2). A hydraulic drain line (13) is connected to a hydraulic fluid reservoir. The check valves (14, 15) have free moving balls (18, 19) as closing elements, and the travel of the balls (18, 19) are limited by adjustable stops (16, 17). The travel of the balls (18, 19) determines the amount of reverse fluid flow required to close the check valve (14, 15). Increasing the travel of the balls (18, 19) imposes an increasing closing delay which provides a dampening effect when the rudder is subject to sudden external forces. <IMAGE>

Description

HYDRAULIC RUDDER CONTROL UNIT This invention relates to a hydraulic rudder control unit for boats.

A boat rudder is usually connected to a steering wheel by a rudder control unit of some kind and autopilot control is often provided. In known hydraulic rudder control units a reversible hydraulic pump called the wheel pump has its inlet and outlet connected to the outlet and inlet of a hydraulic rudder actuator. A steering wheel is attached to the wheel pump input shaft, and when the wheel is rotated, hydraulic fluid flows from the pump outlet to the actuator inlet and at the same time fluid flows from the actuator outlet to the pump inlet.

Reversing the direction of wheel rotation reverses the pump and the direction of the fluid flow. Fluid flow powers the rudder actuator and causes the rudder to move.

The rudder actuator is often a hydraulic cylinder. The wheel pump and the hydraulic fluid reservoir are normally integrated in one unit often referred to as the wheel pump unit.

Additional pressure controlled check valves are built into the wheel pump unit. When the wheel pump is active, the output pressure deactivates, i.e. forces open, the check valve at the pump inlet side and thereby allows hydraulic fluid from the actuator outlet to enter the pump inlet and the fluid reservoir. Over pressure relief valves are normally incorporated in the wheel pump unit.

Using an autopilot with hydraulic rudder control is achieved by an additional reversible hydraulic pump, the autopilot pump, connected to the actuator in parallel with the wheel pump. The volumetric capacity of the wheel pump normally exceeds that of the autopilot pump, and if both pumps are active, the rudder is controlled by the wheel pump. Known autopilot pump arrangements have pressure controlled check valves installed between the autopilot pump and connections to the hydraulic lines leading to the rudder actuator, thereby preventing hydraulic fluid from entering the autopilot pump when it is not active. The check valves lock the rudder in position, and prevent short-circuiting flow imposed by the wheel pump. When the auto pilot pump is active, the output pressure opens the check valve at the pump inlet to allow hydraulic fluid to enter.An additional hydraulic connection is needed between the fluid reservoir and the suction side of the autopilot pump to compensate for any lack of hydraulic fluid at the pump inlet, and to ensure that the autopilot pump never runs dry.

Additional spring loaded check valves keep the autopilot pump from pumping fluid via the hydraulic connection to the fluid reservoir.

The check valve arrangement associated with known autopilot pumps complicates the rudder control system and increases the cost of the unit. More moving parts are susceptible to malfunction, and more moving parts also increase maintenance cost. It is an aim of the present invention to simplify the hydraulic rudder control system to reduce costs, increase reliability and reduce maintenance costs. It is also a purpose to achieve a dampening effect on forces acting on the boat rudder.

According to the invention there is provided a hydraulic rudder control unit for boats which comprises a hydraulic steering pump, a reversible hydraulic autopilot pump, flow valves and a hydraulic drain line; wherein the steering pump is hydraulically connected to a rudder actuator by hydraulic flow lines and the autopilot pump is connected in parallel with the steering pump; said valves are located in flow channels between the flow lines and the autopilot pump and the hydraulic drain line connects to a hydraulic fluid reservoir.

The hydraulic rudder control unit of the invention has the advantage that fewer check valves are required. The hydraulic fluid reservoir is provided to compensate for volume changes due to temperature, trapped air and internal leaks.

Flow valves may have free moving balls as closing elements, and the travel of the balls may be limited by stops preventing the balls from entering hydraulic flow lines.

Preferably, the stops are adjustable to increase or decrease the travel of the balls. The larger the distance of travel the greater the delay in preventing fluid flow. This induces a dampening effect in the system in the event of a sudden force being applied to the rudder.

The stops may comprise threaded rods extending into chambers of the valves.

The rudder actuator may be a balanced actuator comprising an internal piston movable within a cylinder; said piston having a rod extending from both sides out through end walls of the cylinder. Unbalanced hydraulic cylinders have a piston rod extending from one side of the piston through one cylinder end wall. Using an unbalanced hydraulic cylinder usually requires a volumetric different fluid flow at the actuator inlet and outlet, and a large hydraulic fluid reservoir is mandatory to compensate the difference.

Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawing, which is a schematic drawing of a hydraulic control unit.

In the drawing the reference numeral 1 is assigned to a block into which an autopilot pump 2 of the twin gear type is built.

The autopilot pump 2 is powered by an autopilot controlled motor which is not shown. Channels 3, 4 in the block 1 convey hydraulic fluid between the pump 2 and ports 5, 6. The ports 5, 6 are connected to hydraulic flow lines 7, 8 between a rudder actuator 9 and a wheel pump unit 10. The rudder actuator 9 is of the balanced type and powers a rudder that is not shown. A reversible hydraulic wheel pump 11, a hydraulic fluid reservoir, check valves and over pressure relief valves are integrated in the wheel pump unit 10 as already explained.

A steering wheel 12 is attached to the input shaft of the wheel pump 11.

A hydraulic drain line 13 connects the fluid reservoir in the wheel pump unit 10 to the channels 3, 4 and consequently to the inlet and outlet of the pump 2. Ball type check valves 14, 15 inserted between the channels 3, 4 and the drain line 13, prevent hydraulic fluid flow from the pump 2 to the fluid reservoir. The check valves 14, 15 allow fluid flow from the reservoir to the pump 2 if the hydraulic pressure in the channels 3, 4 for some reason drops below the pressure in the fluid reservoir. Mechanical stops 16, 17 limit the travel of balls 18, 19 which perform the closing action of the check valves 14, 15. The balls 18, 19 are free, i.e. not spring loaded, to achieve a small closing delay and thereby provide a dampening effect if a sudden force is imposed on the rudder.

A small reverse flow is required to close an open check valve 14, 15, and the travel of the balls 18, 19 determines the amount of reverse flow needed. The mechanical stops 1G, 17 are screw threaded in the block 1 to make the travel of the balls 18, 19 adjustable.

When the wheel 12 is operated, hydraulic fluid flows from the wheel pump 11 to the actuator 9. The fluid flow causes the actuator 9 to move the rudder, while at the same time hydraulic fluid returns from the actuator 9 to the wheel pump unit 10 and the wheel pump 11. Check valves 14, 15 with balls 18, 19 prevent fluid flowing in flow lines 7, 8 to enter the drain line 13. Leakage across the autopilot pump 2 is too small to significantly degrade the power or efficiency of the actuator 9.

When the autopilot pump 2 is active, the check valves of wheel pump unit 10 prevent hydraulic fluid from entering the wheel pump unit from the hydraulic lines 7, 8. However, if the hydraulic pressure in the lines 7, 8 exceed the limit of the over pressure relief valves in the wheel pump unit 10, then the over pressure valves will bleed hydraulic fluid back to the reservoir in the wheel pump unit 10.

If the wheel 12 is operated while the autopilot pump 2 is active, the high capacity wheel pump 11 will override the lower capacity autopilot pump 2 and be in control of the rudder.

Claims (6)

CLAIMS:

1. A hydraulic rudder control unit for boats comprises a hydraulic steering pump, a reversible hydraulic autopilot pump, flow valves and a hydraulic drain line; wherein the steering pump is hydraulically connected to a rudder actuator by hydraulic flow lines and the autopilot pump is connected in parallel with the steering pump; said valves are located in flow channels between the flow lines and the autopilot pump, and the hydraulic line connects to a hydraulic fluid reservoir.

2. A hydraulic rudder control unit as claimed in claim 1, in which the flow valves have free moving balls as closing elements, and the travel of the balls is limited by stops preventing the balls entering the hydraulic flow lines.

3. A hydraulic rudder control unit as claimed in claim 2, in which the stops are adjustable to increase or decrease the travel of the balls.

4. A hydraulic rudder control unit as claimed in claim 3, in which the stops comprise threaded rods extending into chambers of the valves.

5. A hydraulic rudder control unit as claimed in any preceding claim, in which the rudder actuator is a balanced actuator.

6. A hydraulic rudder control unit as substantially hereinbefore described with reference to the accompanying drawings.