GB2072269A - Controlling fluid flow nozzles - Google Patents

Abstract

A thermostatically controlled nozzle comprises a nozzle member (10) surrounded by a ring (11) of shape memory effect alloy. Between the nozzle member (10) and the SME ring (11), there is an annulus (15) which transferred strain energy from the ring (11) to the nozzle member (10) strain energy without itself storing substantial strain energy. The intermediate annulus (15) may be integral with the nozzle member (10). <IMAGE>

Description

SPECIFICATION Jet nozzles This invention relates to jet nozzles, particularly but not exclusively for use in carburettors and fuel/air metering systems of internal combustion engines.

In our British Patent Specification No.

202271 OA, we have described, and illustrated in Figure 1, a jet nozzle comprising a nozzle member circumscribed by a ring of a shape memory effect (SME) material which responds to the temperature of the fuel passing through to vary automatically the diameter of the nozzle orifice and hence the rate at which fuel is supplied to the engine. An SME material is one, the modulus of elasticity of which varies progressively and significantly in a reversible manner with a change of temperature in a transition temperature range, which is determined by the composition of the material. The SME material is usually an alloy which has been treated to exhibit a martensitic transformation and the composition of which is chosen to match the transition temperature range to the temperatures over which control of nozzle orifice is required to be exerted.

A jet nozzle as illustrated in Figure 1 of the above patent specification has been proven satisfactory in principle, but has been found to give inadequate variation in jet orifice diameter for some carburettors. Assuming that the outer diameter of the SME ring is limited by external constraints and that the diameter of the jet orifice is controlled by fuel requirements, only two parameters are available for variation: the internal diameter of the SME ring which equals the external diameter of the nozzle member, and the strain applied to the SME ring during its treatment to memory condition, and hence the potential change of diameter on temperature variation in the transition range. The actual change of diameter with temperature is of course determined by the resistance to deflection offered by the nozzle member.

It can be shown that the variation in orifice diameter is not affected significantly by the internal diameter of the SME ring, assuming that its external diameter remains unchanged.

Reducing that internal diameter reduces the resistance to deflection of the nozzle member, but also decreases the recoverable change of diameter of the SME ring, while increasing the internal diameter of the SME ring increases the recoverable change of diameter but also increases the resistance to deflection of the nozzle member.

An object of the present invention is to modify the construction of a jet nozzle to improve the change in orifice diameter with change of temperature, and, in accordance with the present invention, a jet nozzle, the effective dimensions of the outlet orifice of which are automatically controlled according to temperature, comprises a nozzle structure having a passage therethrough for the discharge of fluid and constructed to have a low resistance to compressive loading, and a ring which circumscribes and is in contact with the nozzle structure and which is made at least partly of a shape memory effect material having a modulus of elasticity which varies progressively and significantly in a reversible manner with change of temperature in a transition temperature range, the ring being so constructed that it applies to the nozzle structure a hoop stress which is dependent on temperature in the transition temperature range. By "low resistance to compressive loading" in this context is meant significantly smaller than the resistance to compressive loading of a nozzle member which is solid apart from its outlet orifice.

The nozzle structure preferably comprises a nozzle member and intermediate means interposed between the ring and the nozzle member and having the property of transferring strain energy from the SME ring to the nozzle member without itself storing substantial strain energy. The intermediate driving medium may be a low stiffness incompressible material, such as a natural or synthetic elastomer, or a slotted metal ring.

Alternatively, the nozzle assembly may comprise a nozzle member which has integral fins, so that the radial slits formed between the fins prevent the development of tensile loop stresses.

By virtue of the construction of the nozzle assembly, whether using a low stiffness incompressible material or a slotted nozzle member, a relatively large SME ring inner diameter is achieved without unduly increasing the resistance to deflection. As a result, a greater change in orifice diameter is obtainable for change of temperature in the transition range.

The invention will be more readily understood by way of example from the following description of temperature-responsive jet nozzles for carburettors and the like, reference being made to the accompanying drawings, of which Figures 1 and 2 are respectively an axial section of a jet nozzle using an elastic driving medium, and a radial section of a jet nozzle having a slotted nozzle member, and Figures 3 and 4 illustrate modifications of Figures 1 and 2, respectively.

The jet nozzle of Figure 1 of the accompanying drawings is similar to that of Figure 1 of the above-mentioned patent specification, in that it includes a nozzle member 10 and an SME ring 11 which surrounds a part of the length of the nozzle member. As before, the nozzle member 10 has a bore 12 forming an outlet orifice. In the present case, the ring 11, instead of being in intimate contact with the exterior of the nozzle member 10, is separated from the nozzle member by an elastic driving medium 13 in the form of a cylinder of a low stiffness incompressible material, which is advantageously a natural or synthetic elastomer.

The ring 11 is made of an SME alloy which is heat treated to bring it into memory condition and which is strained when at a temperature below the transition temperature range by forcing a taper mandrel through the bore. The alloy is chosen to have a transition temperature range encompassing the temperature over which the nozzle is to be controlled. On increase in temperature, the recovered strain, i.e. the decrease in internal diameter of the ring 10, is transferred through the medium 13 to the nozzle member 10 and results in compression of that member and a progressive reduction in the diameter of that part of the bore 12 within the ring. Transfer of the recovered strain to the nozzle member is achieved without substantial loss because the elastomer of the driving medium 1 3 is incompressible and therefore does not store any part of the strain.

It will be observed that the inner diameter of the ring 11 is no longer the same as the outer diameter of the nozzle member 10; the ratio of recoverable strain to compressive resistance of the nozzle member is thus increased compared with the arrangement of the earlier patent application.

To ensure minimum loss of recovered strain in the driving medium 13, longitudinal straining of that medium resulting in axial extrusion of the elastomeric material should be kept as low as possible, as by the empioyment of rigid end caps preventing axial extrusion. Alternatively, as shown in Figure 3, a long cylinder 1 3A of the elastomer may be utilised so that end losses are minimal.

Not only does the jet nozzle of the accompanying Figure 1 or Figure 3 achieve a greater change in the bore 12 for unit change of temperature within the transition range compared with that of Figure 1 of the earlier specification, but in addition manufacture is facilitated in the elimination of the need for precision machining of the nozzle member outer diameter and the SME ring inner diameter.

Instead of using an elastomeric material for the driver medium 13, a rigid driving medium may be employed, provided it is shaped in such a way that losses of recovered strain are minimised. For example, the cylinder 13 may be replaced by a metal ring having radial slots that minimise resistance to deformation. The slotted metal ring may be formed integral with the nozzle member as shown in Figure 2. In that Figure, the nozzle member is indicated at 1 5 and has an unstrained external diameter equal to the inner diameter of the ring 11 when at a temperature below the transition range. The nozzle member has a number of radial slots 16 which, over the entire axial length of the member, extend from the periphery of the nozzle member to points spaced from the bore 12.

Alternatively, the slotted metal ring may be independently made, as illustrated in Figure 4 where the slotted ring is indicated at 1 7 between the SME ring 11 and the separate nozzle member 10.

Claims (7)

1. A jet nozzle comprising a nozzle structure having a passage therethrough for the discharge of fluid and constructed to have a low resistance to compressive loading, and a ring which circumscribes and is in contact with the nozzle structure and which is made at least partly of a shape memory effect material having a modulus of elasticity which varies progressively and significantly in a reversible manner with change of temperature in a transition temperature range, the ring being so constructed that it applies to the nozzle structure a hoop stress which is dependent on temperature in the transition temperature range.

2. A jet nozzle comprising a nozzle member having a passage therethrough for the discharge of fluid; a ring surrounding, but spaced from, the nozzle member and made at least partly of a shape memory effect material having a modulus of elasticity which varies progressively and significantly in a reversible manner with change of temperature in a transition temperature range; and intermediate means interposed between the nozzle member and the ring, the intermediate means having the property of transferring strain energy from the ring to the nozzle member without its storing substantial strain energy; the ring being so constructed that it applies to the intermediate means, and thence to the nozzle member, a hoop stress which is dependent on temperature within the transition temperature range.

3. A jet nozzle according to claim 2, in which the intermediate means is integral with the nozzle member.

4. A jet nozzle according to claim 2, in which the intermediate means is independent of the nozzle member.

5. A jet nozzle according to claim 3 or claim 4, in which the intermediate means is a metal annulus which is slotted radially.

6. A jet nozzle according to claim 2, in which the intermediate means is an annulus of a low stiffness incompressible material, so designed that the hoop stress applied by the ring is transferred to the nozzle member without substantial loss.

7. A jet nozzle substantially as herein described with reference to the accompanying drawings.