GB2542782A

GB2542782A - Injection nozzle

Info

Publication number: GB2542782A
Application number: GB1517147.3A
Authority: GB
Inventors: Berlemont Jean-François; Martinez Jorge
Original assignee: Delphi International Operations Luxembourg SARL
Current assignee: Delphi International Operations Luxembourg SARL
Priority date: 2015-09-29
Filing date: 2015-09-29
Publication date: 2017-04-05
Anticipated expiration: 2035-09-29
Also published as: GB2542782B; GB201517147D0

Abstract

An injection nozzle (1, Fig. 1) of an internal combustion engine, comprising a nozzle body (3, Fig. 1); a piston bore (15, 115, Fig. 1) defined at least in part within the nozzle body and arranged to receive a reciprocating piston (2, Fig. 1); a piston guide 112 defining a guiding region of the piston bore for guiding movement of the reciprocating piston, respective opposite ends of the piston guide 112 defining a first end 22 and a second end 24 thereof; and a conductor assembly 32 formed on a surface of the piston guide 112 to define an electrically conductive path between the first end 22 and the second end 24, the electrically conductive path being electrically insulated from the piston guide 112. The conductive path may comprise conductive material disposed between layers of insulating material. The invention is intended to reduce the need for insulation between reciprocating surfaces that may also define an electrically conductive path, and which may be subject to wear.

Description

INJECTION NOZZLE

TECHNICAL FIELD

The present invention relates generally to fuel injection nozzles, and in particular to injection nozzles for supplying fuel to internal combustion engines, such as diesel engines.

BACKGROUND OF THE INVENTION

An example of a conventional injection nozzle 1 is illustrated in Figure 1. As shown, a piston or needle 2 is arranged within an elongate hollow nozzle body 3, and the distal end or tip 4 of the needle 2 is biased into contact with a generally conical seat 5 within the nozzle body 3 by means of a compression spring 6, so as to seal the nozzle 1. The end 7 of the nozzle body 3 is provided with one or more small apertures 8 through which fuel is injected into the engine.

In use, diesel fuel is supplied to the injection nozzle 1 from a high-pressure fuel supply in the form of a common fuel rail (not shown) fed by an injection pump (not shown). The fuel passes through a channel 9 to a first fuel accumulator volume 10 arranged around the needle 2. A second fuel accumulator volume 10a is disposed downstream of the first fuel accumulator volume 10, the first and second accumulator volumes 10, 10a being separated by a flange 2a defined by an enlarged diameter portion of the needle 2. The flange 2a is sized for a relatively close fit within the body 3 such that a clearance between the flange 2a and the body 3 is small enough to create a restriction, thereby producing a pressure drop between the first and second accumulator volumes 10, 10a. This pressure drop can be used to control movement of the needle 2.

Injection of fuel from the injection nozzle 1 is controlled by an electronic control unit (not shown). The injection nozzle 1 includes a control valve 14 (partially shown in Figure 1) which controls the movement of the needle 2 with respect to the valve seat 5 at the tip of the injection nozzle 1. The control valve 14 is operable to increase or decrease the fuel pressure in a control chamber 11 disposed at the upper end of the needle 2 as viewed in Figure 1, by controlling flow between the control chamber 11 and a low-pressure drain (not shown). The control chamber 11 is connected to the high-pressure fuel supply, so that the pressure in the control chamber 11 can be switched between the relatively high supply pressure and a relatively low pressure according to the position of the control valve 14.

When the control valve 14 is operated to connect the control chamber 11 to drain, the pressure of fuel in the control chamber 11 decreases, and the higher pressure of fuel in the accumulator volumes 10, 10a causes the needle 2 to move away from the seat 5 of the nozzle body 3. This allows the fuel to be sprayed through the apertures 8 and enter the engine. When the control valve 14 moves to prevent communication between the control chamber 11 and the drain, the pressure in the control chamber 11 increases back to the supply pressure. As a result, the needle 2 moves back on to the seat 5 so as to seal the injection nozzle 1 and cut off the fuel supply to the engine. To ensure that the pressure difference between the fuel in the control chamber 11 and the fuel in the accumulator volume 10a is sufficient to create an adequate closing force on the needle 2 during this closing operation, a flow restriction is included between the high-pressure supply and the accumulator volume 10a, which gives rise to a reduction in pressure in the accumulator volume 10a during needle closure, relative to the supply pressure.

In the conventional arrangement illustrated in Figure 1, the injection nozzle 1 is provided with upper and lower guiding regions 12, 13 which serve to centre the needle 2 within the nozzle body 3. Centring of the needle 2 is important in order to ensure proper functioning of the injection nozzle 1. The lower guiding region 13 is defined by a region of relatively small clearance between the nozzle body 3 and the needle 2, and is formed on either the needle 2 or on the nozzle body 3, or on both the needle 2 and the nozzle body 3 by a machining process. The skilled reader will appreciate that guidance may be provided in other ways, for example using bearings. The upper guiding region 12 is defined by a piston guide 12a affixed to the upper end of the body 3 and having a central bore 15 which receives an upper portion of the needle 2 and which is sized for a close fit with the needle 2, thereby providing a guiding function.

To provide timing information that enables improved control of the nozzle 1, a voltage is applied to the needle 2 using an electrical input (not shown) which may comprise an electric signal conditioning circuit that is configured to improve signal quality. As both the needle 2 and the body 3 are made from electrically conductive material, an electric circuit is closed when the tip 4 makes contact with the seat 5. The voltage applied to the needle 2 then decreases as the current flows through the closed circuit and the signal conditioning circuit. This voltage decrease indicates the precise moment at which the needle 2 contacts the seat 5, which is valuable data for optimising control of the nozzle in on-going operation. Conversely, when the needle 2 detaches from the seat 5, the electrical circuit opens which prevents a current from flowing, thereby causing the voltage on the needle 2 to increase. Each change in the needle voltage can therefore be considered as an output signal that is indicative of the state of the needle 2, i.e. whether the needle 2 is engaged with the seat 5, or at full lift.

To ensure that an output signal is not generated before the needle 2 engages or leaves the seat 5, the outer surfaces of the guide regions 12, 13 and the flange 2a are electrically insulated in areas that may contact the inner surface of the body 3, as well as the outer surfaces of the piston guide 12a.

For example, an insulating coating may be applied to external surfaces of the piston guide 12a to prevent a conductive path forming between the piston guide 12a and the body 3. Alternatively, or in addition, insulating washers may be positioned between the piston guide 12a and the body 3. Such coatings or washers cover the sealing surfaces of the piston guide 12a and so must be able to provide the dual functionality of sealing and insulating. In the context of fuel pressures exceeding 3000bar and the resulting clamping forces required between the piston guide 12a and the body 3 to provide the required seal, it has been found that such coatings quickly deteriorate leading to poor reliability for the timing data.

It would therefore be desirable to provide arrangements which overcome, or at least mitigate, these disadvantages.

SUMMARY OF THE INVENTION

Thus, in accordance with a first aspect of the present invention there is provided an injection nozzle of an internal combustion engine. The injection nozzle comprises a nozzle body, and a piston bore defined at least in part within the nozzle body and arranged to receive a reciprocating piston. The injection nozzle further comprises a piston guide defining a guiding region of the piston bore for guiding movement of the reciprocating piston, respective opposite ends of the piston guide defining a first end and a second end thereof. The injection nozzle further comprises a conductor assembly formed on a surface of the piston guide to define an electrically conductive path between the first end and the second end, the electrically conductive path being electrically insulated from the piston guide.

As the conductor assembly is electrically isolated from the piston guide, beneficially there is no need to insulate the piston guide from its surrounding components in use, for example a body of an injection nozzle. This avoids the associated reliability problems that arise in known injection nozzles where insulation material or insulating washers are used.

As the conductor assembly is formed on a surface of the piston guide, there is no need to provide additional holes in the nozzle body or a separate guide body to receive a conductor. This avoids the challenge of effectively sealing such additional holes, which by necessity extend between an area of relative high pressure and an area of lower pressure.

The piston may be, for example, a needle of the injection nozzle which is used to open or close one or more fuel dispensing apertures of the nozzle.

The conductor assembly may comprise a layer of electrically conductive material which defines the conductive path. The conductor assembly may further comprise a layer of electrically insulating material disposed between the layer of electrically conductive material and the surface of the piston guide. The conductor assembly may also comprise a further layer of electrically insulating material, in which case the layer of electrically conductive material is disposed between the two layers of electrically insulating material. In an alternative, the piston comprises a layer of electrically insulating material to prevent conduction between the conductive path and the piston.

By forming the conductor assembly from one or more layers, the thickness of the assembly can be minimised, thereby minimising the impact of the conductor assembly on the piston guide and the likelihood that it may obstruct other components such as the reciprocating piston.

In some embodiments, the conductor assembly is formed on a surface of the piston bore, for example a portion of the piston bore in the guiding region defined by the piston guide. This configuration conveniently avoids passing the conductor across any sealing surfaces of the injection nozzle which would complicate manufacture. In such embodiments, the conductor assembly may substantially cover the surface of the piston bore.

Alternatively, the conductor assembly may be formed within a groove defined in a surface of the piston guide. Advantageously, the groove may have a depth that is less than or substantially equal to the thickness of the conductor assembly, for example to prevent the creation of a leakage path.

In other embodiments, the conductor assembly is formed on an external surface of the piston guide. In such embodiments, the conductor assembly may substantially cover the external surface of the piston guide.

The piston guide may be integral with the nozzle body, in which case the piston bore is wholly defined by the nozzle body. For example, the piston guide may be defined by a narrowed section of the piston bore defining a guiding function. In this case the lower end of the piston guide may be defined by a stepped or inclined end face created at the lower end of the narrowed section of the piston bore.

Alternatively, the piston guide may be defined by a guide body that is distinct from and attached to the nozzle body. In such embodiments, the piston bore is defined by both the nozzle body and the guide body, and the conductive path is electrically insulated from the guide body.

The conductor assembly may comprise a first terminal disposed at the first end of the piston guide, and a second terminal disposed on the second end of the piston guide, in which case the first terminal and the second terminal define respective end points of the conductive path. The first and second terminals may each comprise a region of exposed electrically conductive material that is electrically insulated from the piston guide. In such embodiments, the second end of the piston guide may define a spring seat for a spring that biases the piston, in use, in which case the second terminal engages the spring so as to provide electrical communication between the first terminal and the piston through the spring.

The conductor assembly may be formed using a deposition, coating, painting or printing process, for example.

In a second aspect of the invention, there is provided a fuel injector comprising an injection nozzle of the previous aspect of the invention, and an actuator for controlling the injection nozzle. The fuel injector may include a piezoelectric actuator or a solenoid (electromagnetic) actuator, or any other type of actuation means, and is typically suitable for use in a compression ignition internal combustion engine.

It will be appreciated that preferred and/or optional features of the first aspect of the invention may be incorporated alone or in appropriate combination in the second aspect of the invention also.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a schematic illustration of a known injection nozzle and has already been described. The present invention is now described by way of example only with reference to the remaining drawings in which:

Figure 2 is a perspective view of a piston guide as seen from above, for use in an injection nozzle according to an embodiment of the invention;

Figure 3 corresponds to Figure 2 but shows the piston guide in longitudinal cross-section;

Figure 4 corresponds to Figure 3 but shows the piston guide from below;

Figure 5 shows a conductor assembly of the piston guide of Figures 2 to 4 in cross-section; and

Figure 6 is a schematic illustration of an injection nozzle according to another embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the description of the preferred embodiments below, the terms “lower” and “upper” are used to refer to the relative positions of components of the injection nozzle as shown in the drawings, and are not in any way intended to refer to the positions or orientations of these components in use.

Referring to Figures 2 to 4, an injection nozzle according to an embodiment of the invention forms the lower part of a fuel injector, such as a piezoelectric or solenoid fuel injector, which also includes an actuator (not shown) for controlling movement of a piston or needle 2 of the nozzle. The fuel injector is of the type suitable for use in delivering high pressure fuel to a combustion chamber of a compression ignition internal combustion (diesel) engine.

The injection nozzle may be of the type described above with reference to Figure 1 and is described in that context below. The injection nozzle includes a piston/needle guide 112 for the injection nozzle needle 2. For the avoidance of doubt, the piston guide described below is not the same as that included in the known injection nozzle shown in Figure 1 and described above. It is also noted that although the piston guide 112 described below is defined by a separate, dedicated body, in other embodiments the piston guide 112 is formed integrally with the nozzle body 3, for example as a narrowed portion of the central bore 3.

The piston guide 112 of the embodiment shown in Figures 2 to 4 comprises a generally cylindrical guide body 16 having a base portion 18, shown as uppermost in Figures 2 to 4, and a nose portion 20 of reduced diameter extending axially downwardly from the base portion 18. The guide body 16 is therefore T-shaped in cross-section, as shown in Figures 3 and 4.

An upper face of the base portion 18, as viewed in Figures 2 and 3, defines a first end of the guide body 16 at end face 22. The end of the nose portion 20, visible in Figure 4, defines a planar second end face 24 of the guide body 16 which defines a second end of the guide body 16. The second end face 24 defines a spring seat for the spring 6 that is used to bias the needle 2 into engagement with the seat 5, in use. An annular lower surface of the base portion 18 extending radially from the junction between the base portion 18 and the nose portion 20 defines an overhang 25. In use, a radially outer portion of the overhang 25 bears against the body 3 of the injection nozzle 1 to act as a sealing surface. A central piston bore 115 extends axially through the guide body 16 between the first and second end faces 22, 24. In use, the central piston bore 115 aligns with the central bore 15 of the nozzle body 3 so that together the central piston bore 115 and the central bore 15 define a nozzle piston bore which is arranged to receive the reciprocating piston or valve needle 2 of the injection nozzle 1. The central piston bore 115 of the piston guide 112 is sized for a close fit with the needle 2 so as to provide a guiding function and so define a guide region of the nozzle piston bore. Moreover, the clearance between the needle 2 and the surface of the piston bore 115 is minimised so as to prevent significant leakage between the needle and the guide body 16 during operation.

The first end face 22 of the guide body 16 is generally planar aside from a horseshoe recess 26 that partially surrounds the piston bore 115. The remainder of the first end face 22 defines a sealing surface 28 which, in use, bears against a body of the control valve 14 of the injection nozzle 1 to create a high pressure seal to prevent leakage of fuel towards the piston bore 115.

Two holes 30 extend through the base portion 18 of the guide body 16, one to each side of the piston bore 115. At the upper end of the guide body 16, each hole 30 opens into the horseshoe recess 26 to define hole openings that are offset below the plane of the sealing surface 28 of the first end face 22. The holes 30 are disposed radially outward of the nose portion 20 such that they open onto the overhang 25. In use, the holes 30 are arranged to receive dowel pins extending from the surface of the body of the control valve 14, thereby orienting the guide body 16 correctly relative to the control valve 14. The dowel pins may be integral with the body of the control valve 14, or may locate in corresponding holes in the body of the control valve 14. The horseshoe recess 26 facilitates assembly by guiding the dowel pins.

In an alternative embodiment, the surface of the body of the control valve 14 may include a horseshoe recess to provide guidance for dowel pins extending from the guide body 16, in which case the first end face 22 of the guide body 16 may be generally flat. A further hole extends through the base portion 18 of the guide body 16, this further hole being disposed outside the horseshoe recess 26 and defining the fuel channel 9 that delivers fuel to the accumulator volume 10 beneath the piston guide 112.

As shown in Figure 3 and 4, a conductor assembly 32 is formed lengthwise on the tubular internal surface of the piston bore 115 and is used to create an electrically conductive path between the first and second ends of the guide body 16. This conductive path is used to apply a voltage to the piston or needle 2 so as to extract injection timing data as described above. As shall become clear in the description that follows, the conductive path is electrically isolated from the guide body 16 so as to prevent an electrical short circuit through the guide body 16 to the injection nozzle body 3, in use.

As shown in Figure 3, the conductor assembly 32 comprises a first terminal 34 located on the first end face 22 of the guide body 16 within the horseshoe recess 26. By locating the first terminal 34 in the horseshoe recess 26, electrical connection can be made to the first terminal 34 without making contact with the body of the control valve 14 when the injection nozzle 1 is assembled. This avoids creation of an electrical short circuit, while also preserving the integrity of the hydraulic seal between the piston guide 112 and the control valve 14. In some embodiments, the first terminal 34 is configured to connect to a wire or pin which extends from an electrical connector of the injection nozzle 1 and through the body of the control valve 14, for example. A second terminal 36 of the conductor assembly 32 is positioned on the second end face 24, as shown in Figure 4. In use, the spring 6 engages the second terminal 36 as it bears against the second end face 24, which as noted above acts as a spring seat. As the spring 6 is conductive and bears against the injection nozzle needle 2, a voltage can be applied to the needle 2 through the conductive path via the second terminal 36.

The first and second terminals 34, 36 define end points for the conductive path and enable connection from an electrical input (not shown) above the piston guide 112 to the needle 2 through the spring 6.

Figure 5 is a cross-sectional view of the conductor assembly 32 on the surface of the guide body 16. This figure shows that the conductor assembly 32 is a multi-layer assembly comprising a conductive layer 38 formed from conductive material encased between first and second insulating layers 40, 42 of insulating material.

The conductive layer 38 defines the conductive path that enables an electric current to flow between the first and second end faces 22, 24 of the guide body 16 when the injection nozzle needle 2 engages the seat 5 to close an electric circuit.

The first insulating layer 40, shown uppermost in Figure 5, provides electrical insulation between the conductive layer 38 and the needle 2, and the second insulating layer 42, which is lowermost in Figure 5, is disposed between the conductive layer 38 and the guide body 16 to provide electrical insulation between the conductive layer 38 and the guide body 16. In this way, the conductive path is electrically isolated from both the needle 2 and the guide body 16, and thus there is no electrical short circuit between the needle 2 and the piston guide 112, in use.

In this embodiment, the layers 38, 40, 42 of the conductor assembly 32 are relatively narrow such that the assembly 32 takes the general form of a strip or wire. However, in other embodiments the layers 38, 40, 42 may be of any width and may even cover the entire surface of the piston bore 115.

The first and second terminals 34, 36 are defined by openings in the first insulating layer 40 which expose a region of the conductive layer 38, enabling electrical connections to be made.

Each of the layers of the conductor assembly 32 may be formed in a variety of ways. For example, a vapour deposition process may be used, in which case the layers are formed from materials that are suitable for such processes. For example, the insulating layers may be formed from an oxide such as an aluminium oxide, and the conductive layer 38 could comprise any electrically conductive deposition material, such as gold. Other processes that may be used to form the layers 38, 40, 42 of the conductor assembly 32 include coating, painting or printing processes.

There is typically a clearance of approximately 5pm between the surface of the piston bore 115 of the piston guide 112 and the outer surface of the injection nozzle needle 2; this close fit enables the piston guide 112 to provide its guiding function. Accordingly, the thickness of the conductor assembly 32 is smaller than this clearance to avoid obstructing the needle 2. This is readily achievable with any of the above processes. Alternatively, in an embodiment in which the conductor assembly 32 covers the entire surface of the piston bore 115, the diameter of the piston bore 115 can be adjusted accordingly to maintain the required clearance.

In a further alternative embodiment to that shown in Figures 2 to 4, a longitudinal groove may be created in the surface of the piston bore 115, in which groove the conductor assembly 32 can be formed to ensure that the conductor assembly 32 does not obstruct the needle 2. For example, the groove may have a depth substantially equal to the thickness of the conductor assembly 32 such that the conductor assembly 32 sits flush with the surface of the piston bore 115. Sizing the depth of the groove to be less than or equal to the thickness of the conductor assembly 32 has the benefit that the conductor assembly 32 substantially fills the groove, thereby avoiding the creation of a leakage path between the first and second end faces 22, 24 through the groove.

The conductor assembly 32 of this embodiment beneficially avoids the need to provide electrical insulation between the piston guide 112 and the injection nozzle body 3, because the conductive path is isolated from the guide body 16. This means that the reliability problems noted above for known injection nozzles where the piston guide 112 is insulated from the injection nozzle body 3 can be avoided, as can the challenges with sealing an additional bore through the guide body 16 for the alternative arrangement in which a wire is fed through the additional bore.

As the needle 2 of the injection nozzle 1 is typically a continuous metallic body, once a voltage is applied to the needle 2 through the conductor assembly 32 and the spring, the entire needle 2 has a higher electric potential than the surrounding components. Therefore, as the piston guide 112 is not insulated from the nozzle body 3, in this embodiment the needle 2 is insulated from the piston guide 112 to prevent an electric short circuit developing between the two.

This may be achieved by coating the portion of the needle 2 that is received in the piston bore 115 with an insulating material. If this is done, optionally the first insulating layer 40 of the conductor assembly 32 can be dispensed with. Alternatively, or in addition, the surface of the piston bore 115 may be coated with insulating material. For example, an insulating coating may be applied to the piston bore 115 before the conductor assembly 32 is created. Alternatively, at least one of the first and second insulating layers 40, 42 of the conductor assembly 32 may be extended to cover the entire surface of the piston bore 115 and thereby provide the required insulation.

Figure 6 shows an injection nozzle 100 according to another embodiment, in which a piston guide 113 is an integral part of the body 3 of the injection nozzle. In this embodiment, the piston bore is formed wholly within the nozzle body 3, and the piston guide 113 is defined by a narrowed section of the piston bore to create a guiding region. In this embodiment the conductor assembly 32 provides the same function of creating a conductive path between a first end and a second end of the piston guide 113, which in this case are defined by stepped or inclined faces resulting from a change in diameter of the bore (i.e. the step/inclined face at respective ends of that region which guides the piston). As in the previous embodiment, the conductive path is insulated from the nozzle body 3 and the control valve.

It is noted that in the integrated arrangement of Figure 6 there is no spring below the guiding region. Therefore, the electrical connection to the needle 2 is different to the earlier embodiment, and is made, for example, by way of a radial contact (not shown) provided below the guiding region to contact the needle 2 directly.

Although preferred embodiments of the present invention have been described above, it will be apparent that numerous modifications could be made without departing from the scope of the present invention which is defined solely by the claims below. For example, the conductor assembly 32 could alternatively be formed on the external surface of the guide body 16 instead of inside the piston bore 115. In such embodiments, the conductor assembly 32 may cover the entire outer surface of the guide body 16.

Claims

1. An injection nozzle (1) of an internal combustion engine, the injection nozzle (1) comprising: a nozzle body (3); a piston bore (15, 115) defined at least in part within the nozzle body (3) and arranged to receive a reciprocating piston (2); a piston guide (112) defining a guiding region of the piston bore (15, 115) for guiding movement of the reciprocating piston (2), respective opposite ends of the piston guide (112) defining a first end (22) and a second end (24) thereof; and a conductor assembly (32) formed on a surface of the piston guide (112) to define an electrically conductive path between the first end (22) and the second end (24), the electrically conductive path being electrically insulated from the piston guide (112).

2. The injection nozzle (1) of claim 1, wherein the conductor assembly (32) comprises a layer of electrically conductive material (38) which defines the conductive path.

3. The injection nozzle (1) of claim 2, wherein the conductor assembly (32) comprises a layer of electrically insulating material (42) disposed between the layer of electrically conductive material (38) and the surface of the piston guide (112).

4. The injection nozzle (1) of claim 3, wherein the conductor assembly (32) comprises a further layer of electrically insulating material (40), and wherein the layer of electrically conductive material (38) is disposed between the two layers of electrically insulating material (40, 42).

5. The injection nozzle (1) of any preceding claim, wherein the conductor assembly (32) is formed on a surface of the piston bore (115).

6. The injection nozzle (1) of claim 5, wherein the conductor assembly (32) substantially covers the surface of the piston bore (115).

7. The injection nozzle (1) of any of claims 1 to 4, wherein the conductor assembly (32) is formed within a groove defined in a surface of the piston guide (112).

8. The injection nozzle (1) of claim 7, wherein the groove has a depth that is less than or substantially equal to the thickness of the conductor assembly (32).

9. The injection nozzle (1) of any of claims 1 to 4, wherein the conductor assembly (32) is formed on an external surface of the piston guide (112).

10. The injection nozzle (1) of any preceding claim, wherein the piston guide (112) is integral with the nozzle body (3) and wherein the piston bore (15, 115) is wholly defined by the nozzle body (3).

11. The injection nozzle (1) of any of claims 1 to 9, wherein the piston guide (112) is defined by a guide body (16), wherein the piston bore (15, 115) is defined by both the guide body (16) and the nozzle body (3), and wherein the conductive path is electrically insulated from the guide body (16).

12. The injection nozzle (1) of any preceding claim, wherein the conductor assembly (32) comprises a first terminal (34) disposed at the first end (22) of the piston guide (112), and a second terminal (36) disposed on the second end (24) of the piston guide (112), and wherein the first terminal (34) and the second terminal (36) define respective end points of the conductive path.

13. The injection nozzle (1) of claim 12, wherein the first and second terminals (34, 36) each comprise a region of exposed electrically conductive material that is electrically insulated from the piston guide (112).

14. The injection nozzle (1) of claim 12 or claim 13, wherein, in use, the second end (24) of the piston guide (112) defines a spring seat for a spring (6) that biases the piston (2), and wherein the second terminal (36) engages the spring (6) so as to provide electrical communication between the first terminal (34) and the piston (2) through the spring (1).

15. A fuel injector comprising an injection nozzle (1) as claimed in any of claims 1 to 14 and an actuator for controlling the injection nozzle.