GB2117931A

GB2117931A - Electro-hydraulic servo valves

Info

Publication number: GB2117931A
Application number: GB08306619A
Authority: GB
Inventors: Dennis William Parker
Original assignee: Dowty Hydraulic Units Ltd
Current assignee: Dowty Hydraulic Units Ltd
Priority date: 1982-03-19
Filing date: 1983-03-10
Publication date: 1983-10-19
Also published as: GB8306619D0

Abstract

An electro-hydraulic servo valve of either the moving-flapper type or the moving-jet type has any one or more of the following features:- a) a nozzle in the form of a jewel, b) a restrictor, in the flow-passage to a nozzle, in the form of a jewel, and c) a bearing, in the form of a jewel, associated with the valve spool, for engagement with a feed-back wire. t

Description

SPECIFICATION Electro-hydraulic servo valves This invention relates to electro-hydraulic servo valves.

One form of electro-hydraulic servo valve utilises a nozzle or nozzles, the flow of liquid from which is controlled by a flapper. The flapper is caused to move from a null position, by means of an electrical force motor when the latter is energised, towards or away from a nozzle in order to increase or decrease the obturating effect which the flapper has on liquid issuing from the nozzle orifice.

It is essential for such a nozzle to have an accurately-profiled shape with a sharp edge which lies in a plane parallel to the surface of the flapper when the latter is in its null position; otherwise the ability of the flapper accurately to control the flow of liquid from the nozzle orifice is impaired.

Furthermore, because of erosion which can occur on the edge of the nozzle due to a highvelocity flow of liquid, it has been necessary to make the nozzles from high-quality steels and beryllium coppers.

As a consequence nozzles for electro-hydraulic servo valves are expensive.

In such an electro-hydraulic servo valve the position of a valve spool is changed by controlling the flow of liquid from the nozzles. It is customary to use in such forms of servo valve a spring wire which is rigidly fixed at one end to the flapper and is associated, at its other end, with the valve spool so that it can move, with the valve spool, with respect to its fixed end. As the valve spool moves from its null position, consequent upon movement of the flapper from its null position, the end of the spring wire on the valve spool also moves, bending the wire and providing a feedback signal.

One such valve is described in U.K. Patent Specification No. 923839.

As shown in that patent specification, the end of the wire located on the valve spool has an accurate spherical shape which may be an accurately-made ball, which fits in an endless groove formed in the valve spool.

In practice, it is necessary to produce in the valve spool an endless groove which has the required uniform size, shape and surface finish.

For, if it is not so, the spherical end of the wire may have a tight fit when it is within one part of the groove and may have a clearance fit when it is within another part of the groove. Both can impair the performance of the servo valve and the latter can also cause accelerated wear of the parts.

It is an object of this invention to provide an improved electro-hydraulic servo valve.

According to this invention an electro-hydraulic servo valve has a nozzle made from a jewel.

Such a nozzle has a high degree of resistance to erosion to liquid flowing through and out of it at a high velocity, can be readily manufactured with the necessary high degree of accuracy and surface finish, inciuding a substantially sharp edge if necessary, and, if the jewel is an industrial jewel, is cheaper than those hitherto used.

With nozzles used previously, it has been necessary accurately to position opposed nozzles, in relation to the flapper, by a manual adjustment.

This is a precision operation which requires a high degree of skill from an operator. Nozzles made from jewels can readily be positioned accurately in and, say, cemented to, a suitable nozzle holder, which can in turn, if desired, be positioned accurately in another part of the valve and a suitably-machined flapper can then more easily be positioned accurately between the two nozzles without any need for so-called "nozzle-pushing", the technique previously used for positioning nozzles with respect to a flapper.

An electro-hydraulic servo valve may have a restrictor which restricts the flow of liquid to a nozzle. According to this invention, such a restrictor may be a jewel and will have a high degree of resistance to erosion due to liquid flow at a high velocity, can be readily manufactured to the necessary high degree of accuracy and, if the jewel is an industrial jewel, will be cheaper than those hitherto used.

Also according to this invention the feed-back wire of an electro-hydraulic servo valve is associated with the valve spool by way of a jewel bearing.

Conveniently, the jewel bearing can be in the form of a hollow tube, within which the spherical end of the feed-back wire can fit, and the hollow tube can fit in a suitable hole which can be easily machined in the valve spool.

Such a hollow tube can readily be finished to a high degree of accuracy and of surface finish. Its size can be chosen to match a certain size of high precision ball which can be fitted to the end of the feed-back wire. The quality and hardness of the jewel bearing reduces wear caused by any sliding between the feed-back wire and the spool.

If damage does occur to the jewel bearing, it can readily be removed from the valve spool and replaced. Conveniently, the jewel will be an industrial jewel which is relatively inexpensive.

Although the illustrative electro-hydraulic servo valves described above have been of the so called nozzle/flapper type, those electro-hydraulic servo valves of the so-called moving-jet type could also have nozzles and/or restrictors and/or feed-back bearings in the form of jewels.

Claim

1. An electro-hydraulic servo valve having any one or more of the following features:-

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

SPECIFICATION Electro-hydraulic servo valves This invention relates to electro-hydraulic servo valves.

One form of electro-hydraulic servo valve utilises a nozzle or nozzles, the flow of liquid from which is controlled by a flapper. The flapper is caused to move from a null position, by means of an electrical force motor when the latter is energised, towards or away from a nozzle in order to increase or decrease the obturating effect which the flapper has on liquid issuing from the nozzle orifice.

It is essential for such a nozzle to have an accurately-profiled shape with a sharp edge which lies in a plane parallel to the surface of the flapper when the latter is in its null position; otherwise the ability of the flapper accurately to control the flow of liquid from the nozzle orifice is impaired.

Furthermore, because of erosion which can occur on the edge of the nozzle due to a highvelocity flow of liquid, it has been necessary to make the nozzles from high-quality steels and beryllium coppers.

As a consequence nozzles for electro-hydraulic servo valves are expensive.

In such an electro-hydraulic servo valve the position of a valve spool is changed by controlling the flow of liquid from the nozzles. It is customary to use in such forms of servo valve a spring wire which is rigidly fixed at one end to the flapper and is associated, at its other end, with the valve spool so that it can move, with the valve spool, with respect to its fixed end. As the valve spool moves from its null position, consequent upon movement of the flapper from its null position, the end of the spring wire on the valve spool also moves, bending the wire and providing a feedback signal.

One such valve is described in U.K. Patent Specification No. 923839.

As shown in that patent specification, the end of the wire located on the valve spool has an accurate spherical shape which may be an accurately-made ball, which fits in an endless groove formed in the valve spool.

In practice, it is necessary to produce in the valve spool an endless groove which has the required uniform size, shape and surface finish.

For, if it is not so, the spherical end of the wire may have a tight fit when it is within one part of the groove and may have a clearance fit when it is within another part of the groove. Both can impair the performance of the servo valve and the latter can also cause accelerated wear of the parts.

It is an object of this invention to provide an improved electro-hydraulic servo valve.

According to this invention an electro-hydraulic servo valve has a nozzle made from a jewel.

Such a nozzle has a high degree of resistance to erosion to liquid flowing through and out of it at a high velocity, can be readily manufactured with the necessary high degree of accuracy and surface finish, inciuding a substantially sharp edge if necessary, and, if the jewel is an industrial jewel, is cheaper than those hitherto used.

With nozzles used previously, it has been necessary accurately to position opposed nozzles, in relation to the flapper, by a manual adjustment.

This is a precision operation which requires a high degree of skill from an operator. Nozzles made from jewels can readily be positioned accurately in and, say, cemented to, a suitable nozzle holder, which can in turn, if desired, be positioned accurately in another part of the valve and a suitably-machined flapper can then more easily be positioned accurately between the two nozzles without any need for so-called "nozzle-pushing", the technique previously used for positioning nozzles with respect to a flapper.

An electro-hydraulic servo valve may have a restrictor which restricts the flow of liquid to a nozzle. According to this invention, such a restrictor may be a jewel and will have a high degree of resistance to erosion due to liquid flow at a high velocity, can be readily manufactured to the necessary high degree of accuracy and, if the jewel is an industrial jewel, will be cheaper than those hitherto used.

Also according to this invention the feed-back wire of an electro-hydraulic servo valve is associated with the valve spool by way of a jewel bearing.

Conveniently, the jewel bearing can be in the form of a hollow tube, within which the spherical end of the feed-back wire can fit, and the hollow tube can fit in a suitable hole which can be easily machined in the valve spool.

Such a hollow tube can readily be finished to a high degree of accuracy and of surface finish. Its size can be chosen to match a certain size of high precision ball which can be fitted to the end of the feed-back wire. The quality and hardness of the jewel bearing reduces wear caused by any sliding between the feed-back wire and the spool.

If damage does occur to the jewel bearing, it can readily be removed from the valve spool and replaced. Conveniently, the jewel will be an industrial jewel which is relatively inexpensive.

Although the illustrative electro-hydraulic servo valves described above have been of the so called nozzle/flapper type, those electro-hydraulic servo valves of the so-called moving-jet type could also have nozzles and/or restrictors and/or feed-back bearings in the form of jewels.

Claim

1. An electro-hydraulic servo valve having any one or more of the following features:- (a) a nozzle or nozzles made from a jewel, (b) a restrictor made from a jewel, and (c) a bearing for a feed-back wire in the form of a jewel.