GB2309262A

GB2309262A - Flow control valve

Info

Publication number: GB2309262A
Application number: GB9601165A
Authority: GB
Inventors: Thomas Tsoi-Hei Ma
Original assignee: Ford Motor Co
Current assignee: Ford Motor Co
Priority date: 1996-01-20
Filing date: 1996-01-20
Publication date: 1997-07-23
Also published as: GB9601165D0

Description

Flow Valve Field of the invention The present invention relates to a flow valve and is particularly concerned with a flow valve that can be used as a fuel injector to regulate the quantity of fuel supplied to the combustible charge of an internal combustion engine.

Background of the invention A fuel injector is conventionally constructed as a solenoid operated pintle valve which is expensive to manufacture and presents problems on account of the inertia of the pintle that acts as a closure member. The valve takes time to open, time to close, can suffer from sealing problems and is prone to valve bounce when operated at high frequency. The valve is also required to atomise the fuel which it does not do particularly well unless additional steps are taken to break up or scatter the fuel flow.

Summary of . the invention With a view to mitigating the foregoing disadvantages of known fuel injectors, the present invention provides, in accordance with a first aspect, a valve comprising a rigid housing having an inlet connectable to a pressurised supply and an outlet, an elastomeric body mounted in the rigid housing and formed with a flexible walled passage leading from the inlet to the outlet, and a piezoelectric element for compressing the elastomeric body against the housing, the compression force on the elastomeric body being variable by applying an electrical excitation voltage to the piezoelectric element between a first level in which the passage is deformed and sealingly closed and a second lower level in which pressurised fluid can flow through the passage.

The passage in the elastomeric body may either be formed as a bore or as a slit. A bore, which can be formed by material removal or can be incorporated in the elastomeric body during moulding, is normally open and is closed by the application of a compressive force. The flexible walls of a bore can be sealed against each other but this is difficult when the bore has a large diameter. In this case, a rod can be positioned inside the bore and the walls of the bore may seal against the rod when the elastomeric body is compressed.

A slit, on the other hand, is just a cut that is normally closed but is capable of being forced open by fluid pressure. The walls of the slit can seal against each other regardless of the size of the slit, thereby avoiding the need for a rod. The compressive force in this case is merely required to oppose the fluid pressure so as to prevent the valve from being opened.

While the piezoelectric element may be designed to apply compression to the elastomeric body in any direction, it is advantageous for the compression force of the piezoelectric element to act parallel to the axis of the passage, the deformation of the elastomeric body being confined by the housing and the piezoelectric element to displace the walls of the passage transverse to the axis of the passage.

Conveniently, the housing may comprise a cup containing the elastomeric body and an annular cap acting to clamp the piezoelectric element against the surface of the elastomeric body. The clamping force exerted by the cap should preferably serve to precompress the elastomeric body such that the passage is closed when no excitation voltage is applied to the piezoelectric element, excitation of the piezoelectric element serving to relax the compression and open the valve.

The piezoelectric element of the preferred embodiment of the invention has the form of a disc with a central aperture surrounding the mouth of the passage, excitation of the element resulting in the disc being deformed into a dished or conical shape thereby relaxing the compression in the elastomeric body.

It is desirable for the passage to be closed near its mouth rather than along its entire axial length. This can be achieved if the elastomeric body in its uncompressed state has an annular protrusion surrounding the mouth of the passage, compression of the protrusion by the piezoelectric element serving to create a greater deformation of the passage near the mouth of the passage than along the remainder of the axial length of the passage.

In accordance with a second aspect of the invention, there is provided a fuel injector comprising a rigid housing defining a fuel inlet connectable to a pressurised fuel supply and a fuel outlet, an elastomeric body mounted within the rigid housing and having a passage leading from the fuel inlet to the fuel outlet, and a piezoelectric element that is deflectable upon application thereto of an electrical excitation voltage, which piezoelectric element when not excited acts to compress the elastomeric body against the housing to deform the passage and prevent fuel flow therethrough, excitation of the piezoelectric element serving to relax the compression of the elastomeric body whereby to permit fuel flow to the fuel outlet from the pressurised fuel supply through the passage.

The valve of the invention lends itself particular well to use as a fuel injector because the piezoelectric element can be excited at high frequency and this results in very fine atomisation of the fuel flow. The valve has hardly any moving parts in the conventional sense, the movement being the vibration of a piezoelectric element and the variable compression of the elastomeric body. The sealing is effected by the elastomeric body rather than between accurately machined metal parts, making for a less expensive and more robust construction.

Brief description of the drawings The invention will now be described further, by way of example, with reference to the accompanying drawings, in which : Figure 1 shows an axial section through an uncompressed elastomeric body of a fuel injector of the invention, Figure 2 is an axial section through a fuel injector comprising the elastomeric body of Figure 1, the injector being shown in its closed, unexcited condition with the elastomeric body fully compressed, and Figure 3 is a similar axial section through the same injector as in Figure 2, showing the piezoelectric element in its excited condition in which the injector is open and the compression of the elastomeric body is relaxed.

Detailed description of the Dreferred embodiment The drawings show a fuel injector 10 comprising a housing 12 formed of a cup 12a and an annular cap 12b. The cup 12a contains an elastomeric body 14 shown in its uncompressed form in Figure 1. The body 14 has a stepped bore comprising of a lower portion 14a of larger diameter and an upper portion 14b of smaller diameter. The surface of the body 14 is not flat but has an annular protrusion 14c that surrounds the mouth of upper portion 14b of the bore.A piezoelectric element 16 in the form of a disc with a central aperture surrounding the mouth of the upper portion 14b of the bore is clamped by the cap 12b against the surface of the body 14 thereby deforming the protrusion 14c, the resulting deformation of the body 14 causing the mouth of the upper bore portion 14b to seal against a rod 18 that is mounted on an inlet 20 fitted within the lower portion 14a of the bore.

When an alternating excitation voltage is applied across the piezoelectric element 16 by electrodes on its opposite surfaces, it is deflected at the same frequency as the applied voltage between the closed position shown in Figure 2 and the open position shown in Figure 3. In Figure 3, the element 16 is dished outwards to relax the compression on the body 14 resulting in the valve being open.

In use the inlet 20 is connected to a pressurised source of fuel at typically 3 bar pressure and the compression by the clamping of the element 16 against the surface of the body 14 is sufficient to prevent egress of fuel. When fuel is to be injected, an alternating excitation voltage is applied to the element 16 to cause the element 16 to oscillate between its open and closed positions resulting in a fuel flow that is forced through the valve by fuel pressure and is atomised by the oscillation. The quantity of fuel delivered may be varied by modifying the duration of excitation of the element 16 and/or regulating the fuel pressure.

The invention has been particularly described by reference to a passage constructed as a bore but it will be clear that the passage may comprise a slit instead of a bore. In this case, it is not necessary to include a rod in the passage as the walls of a slit can seal easily against each other. It will also be clear that a plurality of passages may be used and that the invention is not therefore restricted to the use of a single passage in the elastomeric body.

Claims

1. A valve comprising a rigid housing having an inlet connectable to a pressurised supply and an outlet, an elastomeric body mounted in the rigid housing and formed with a flexible walled passage leading from the inlet to the outlet, and a piezoelectric element for compressing the elastomeric body against the housing, the compression force on the elastomeric body being variable by applying an electrical excitation voltage to the piezoelectric element between a first level in which the passage is deformed and sealingly closed and a second lower level in which pressurised fluid can flow through the passage.

2. A valve as claimed in claim 1, in which the passage comprises a bore formed by material removal or incorporated in the elastomeric body during moulding.

3. A valve as claimed in claim 2, wherein a rod is positioned inside the bore, the walls of the bore sealing against the rod when the elastomeric body is compressed.

4. A valve as claimed in claim 1, wherein the passage comprises a normally closed slit, the walls of which may be forced apart by fluid pressure.

5. A valve as claimed in any preceding claim, wherein the compression force of the piezoelectric element acts parallel to the axis of the passage and the deformation of the elastomeric body is confined by the housing and the piezoelectric element to displace the walls of the passage transverse to the axis of the passage.

6. A valve as claimed in any preceding claim, in which the housing comprises a cup containing the elastomeric body and an annular cap acting to clamp the piezoelectric element against the surface of the elastomeric body.

7. A valve as claimed in claim 6, in which the clamping force exerted by the cap serves to precompress the elastomeric body such that the passage is closed when no excitation voltage is applied to the piezoelectric element, excitation of the piezoelectric element serving to relax the compression and open the valve.

8. A valve as claimed in claim 7, wherein the piezoelectric element is in the form of a disc having a central aperture surrounding the mouth of the passage, excitation of the element resulting in the disc being deformed into a dished or conical shape thereby relaxing the compression in the elastomeric body.

9. A valve as claimed in claim 8, wherein the elastomeric body in its uncompressed state has an annular protrusion surrounding the mouth of the passage, compression of the protrusion by the piezoelectric element serving to create a greater deformation of the passage near the mouth of the passage than along the remainder of the axial length of the passage.

10. A fuel injector comprising a rigid housing defining a fuel inlet connectable to a pressurised fuel supply and a fuel outlet, an elastomeric body mounted within the rigid housing and having a passage leading from the fuel inlet to the fuel outlet, and a piezoelectric element that is deflectable upon application thereto of an electrical excitation voltage, which piezoelectric element when not excited acts to compress the elastomeric body against the housing to deform the passage and prevent fuel flow therethrough, excitation of the piezoelectric element serving to relax the compression of the elastomeric body whereby to permit fuel flow to the fuel outlet from the pressurised fuel supply through the passage.

11. A fuel injector constructed, arranged and adapted to operate substantially as herein described with reference to and as illustrated in the accompanying drawings.