This disclosure relates to fuel injectors and specifically to needle and nozzle arrangements therefor. Background to the invention

A typical fuel injector comprises an actuator controlled valve needle adapted to be moved away from a valve seat so as to allow fuel to be dispensed into a combustion chamber. Generally the needle is located along a central axis within a cylindrical nozzle body portion of the fuel injector These components work together as a valve to control fuel injection events. Both the nozzle body/seat and needle may have conical co-operating surfaces. When the needle is seated on the valve seat of the nozzle body, an edge seal is formed stopping high pressure fuel going into the combustion chamber.

The needle may be hydraulically controlled by the pressure of the fuel supplied to the injector. High fluid forces thereby act on the needle to drive its motion, particularly towards its closed position where the distal end, e.g. the conical surface of the needle tip, engages the (nozzle body) valve seat. The closing of such a needle valve arrangement is typically driven to be as fast as possible for the purpose of injector delivery requirements. Hence, this results in high velocity impact of the needle with the valve seat e.g. after every main injection; this leads to wear of the seat. Furthermore, seat wear results in changes to the total area exposed to high pressure fuel. This alters the degree of hydraulic force exerted on the needle resulting in performance drift. In extreme cases, for example regarding pilot injection where activation of the valve is for a very short periods, injection may be missed altogether as a result of seat wear.

Currently, seat wear is typically suppressed by hardening the impact surface of the nozzle body seat and needle seat via material processes such as nitriding heat treatment and DLC coating. However this increases production costs. Alternatively, seat wear can be minimised by driving the needle so that it closes slower - this however has a detrimental effect on injector performance. It is an object of the invention to overcome problems with seat wear.

Statement of the Invention

In one aspect is provided a nozzle arrangement for a fuel injector including a nozzle body having a longitudinal axis, and including a valve seat located towards the distal end thereof, and housing a needle located within said nozzle body and wherein said nozzle body and said needle define a nozzle body volume at the distal end of said nozzle, said needle adapted to be slidable within said nozzle body along said axis, to a closed position where the tip of the needle is in contact with the valve seat, and an open position where the needle tip is in a position away form said valve seat, characterized wherein said needle comprises a needle main portion and a separate needle tip portion, said needle main portion including a recess located at its distal end for location of said needle tip portion, and having spring means located between main portion and tip portion, said tip portion adapted to move along said axis relative to said needle main portion, wherein the proximal portion of said needle tip and said recess form a pressure chamber, and wherein the distal end of the needle main portion includes at least one orifice or flow channel fluidly connecting said pressure chamber to said nozzle body volume.

The said orifice may be located in a side wall defining said recess. The recess is preferably cylindrical, and wherein the proximal end of the needle tip portion includes a widened piston portion, the recess and the end of the piston portion defining said pressure chamber.

The nozzle arrangement may include means to limit the movement of said needle tip away from said main needle body. The limiting means may be provided by an internal collar at the end of said recess.

Preferably the said spring is pre-stressed.

Brief Description of the Drawings

The invention will now be described by way of example and with reference to the following figures:

Figure 1 shows the distal end of a fuel injector according to one example; Figure 2 shows the nozzle arrangement of the figure 1 example in more detail; and,

Figure 3 illustrates the operational stages of the figure 1 and 2 examples.

In one example the problem of nozzle seat wear in a common rail system is solved by using a hydraulic suspension needle (HSN) arrangement wherein the (mass of the) needle is divided into two portions, a main portion and a tip portion. The tip portion impacts with the seat as normal while the rest of the needle will be gradually slow down by spring force. As a result, the needle impact momentum is reduced as the mass is less which minimise seat wear.

Figure 1 shows a schematic view of the distal end of a fuel injector (nozzle capsule) 1 according to one example. It shows a needle upper control chamber 2, where fuel pressure acts to operate the main needle portion 3. The

(injector) nozzle capsule includes a main housing 4 and a nozzle body (housing) 5 within which are located a main needle (portion) 3 as well as a needle tip portion 6. A nozzle return spring 7 is located as shown. Figure 2a shows a view of the distal portion of the needle of the figure 1 design in more detail including main needle (portion) 3, and needle tip portion 6. Figure 2b shows a cross sectional view of figure 2a, and figure 2c shows an enlarged portion of the figure 2b view.

As can be seen the needle main portion 3 includes a recess 8 at its distal end, which in the example is formed as an open cylinder, and within this is located a separate needle tip portion 6. Thus the cylindrical "hollow" portion can be considered as a housing for the needle tip portion. Thus the needle tip is located within the housing provided by the recess (hollow cylinder) of the needle main portion, and thus forming a (hydraulic) chamber 9, bounded by the recess 8 (hollow cylinder) formed in the distal portion of the main needle portion and the proximal (upper surface in the figure) of the needle tip portion 3. Between the upper surface 9 of the closed portion of the cylinder and the proximal portion of the needle tip portion is located a spring 10. The spring may be considered a return spring. The spring does not have to be fixed at either end but may be supported in order to prevent uneven loading or rubbing. Preferably it is supported radially at one end. The needle tip and needle main portion (housing) can move relatively to each other in the axial direction.

The spring may be positioned within the chamber by a needle tip projectionl4 in the proximal portion of the needle tip portion having a smaller diameter than the tip portion. The spring is preferably preloaded

The needle tip portion includes a widened piston portion 11 dimensioned similar to the diameter of the housing such that it forms generally a seal therewith. The needle tip portion can reciprocate like a piston within the chamber 9 formed by the housing/recess in the main body portion. Thus, axial

(reciprocating) motion of the needle tip is guided within by way of the

piston/widened portion and this acts as a seal, such that the needle tip and needle housing form a pressure chamber. The pressure chamber is fluidly connected to the rest of the

hydraulic/fuel system, in particular the nozzle body volume 20 via flow channel(s) such as in the example in the figure, by an orifice 12. This is seen more clearly in figure 3 Thus, the arrangement provides damping, and the control of the amount of damping is by adjusting various dimension of e.g. the orifices, the spring constant and such like, - thereby controlling the amount of damping (pressure increase within the chamber). The skilled person would understand that spring preload and the size and number of orifices may be varied to achieve the required damping effect.

An internal collar 13 may be provided on the extreme distal end of the needle main portion i.e. at the open end of the cylinder recess portion in order to limit downward travel of the needle tip portion relative to the needle main portion. Thus his can be regarded as hook means. The skilled person would understand that alternative designs can be provided to provide the limiting travel of the needle tip downwards relative to the main needle portion or more generally speaking to limit the distance the tip portion can move away from the main needle portion.

In refined or alternative examples there may be a mechanism provided to limit the movement of the needle tip in a direction towards the needle main portion i.e. to ensure a minimum clearance/distance between the needle tip portion vis a vis the upper face of the main body portion/closed end of the

recess/ cylinder.

By appropriate design, (e.g. of the spring so that overall rate and preload is kept), the arrangement behaves exactly like a normal needle in most conditions except during closing impact conditions.

Figure 3 (a, b, c ), shows cross sectional views of the injector distal portion including the arrangement of figure 1 , and shows the needle main portion tip portion and (hydraulic suspension) spring 10 located within the nozzle body. The views shows the operation stages. During a needle closing impact event, needle accelerates from open position (fig 3a) towards the nozzle body /valve seat. The needle tip impacts nozzle body same as a typical needle but without the mass of the needle main portion. The needle main body will continue to travel and decelerated by the force provided by the spring (fig 3c). Once the needle main portion has come to a stop, the needle main portion /housing hydraulic force reaches equilibrium as the (hydraulic suspension needle) chamber pressure equals to the rest of the system (including the upper control chamber). The only force acting on needle portions is the return spring, which effectively extends the control chamber (fig 3b) ready for next injection. The needle tip remains shut throughout this process due to needle control chamber pressure.

The spring 10 preload is an important parameter. This spring may be considered a hydraulic suspension needle spring. The preload determines the amount of force due to needle main portion 3 motion is transmitted to the needle tip portion 6. If the needle main portion motion results in less force than the spring preload, there will be no further travel for the needle main portion and the main and tip potion acts like a single needle unit. If the spring preload is too high, all the loading from the needle main portion will be transmitted to the needle tip portion and the arrangement will act as a single unit, and thus there would be no advantage over a conventional needle. If the spring preload is too low, the needle main portion would travels further and would require more time to return to its nominal position (fig 3b). A spring preload between 100N to 1500N is preferred. When the control chamber orifice 12 is designed to be restrictive, motion of the needle main portion generates a pressure increase within the needle pressure chamber 9 due to a piston effect. This pressure generates a force acting against the needle main portion motion and decelerates the needle main portion more quickly. The amount of pressure increase can be tuned by the size of the control chamber orifice(s) or coefficient of discharge (Cd) of the orifice. It is worth noting that the restriction of the control chamber is not necessary feature. It is useful in minimising the amount of travel of the housing and hence reducing the time to return to nominal position (fig 2b). For a non-restrictive orifice, an area equivalent to a single 1mm diameter hole should be sufficient. For restrictive orifice, an area equivalent to a single orifice hole is estimated in a range of 0.05mm to 0.25mm diameter. This varies depends on the needle closing velocity and the control chamber 9 volume. The clearance of the piston portion 11 should also be closely controlled if orifice is restrictive, and preferably with less than ΙΟμιη clearance, as leakage affects the control chamber 9 pressure.

When the engine is shut down and there is no system pressure to the fuel injector, the needle will be in its closed position (fig 3b). The needle tip 6 is fully extended from the needle main portion 3 under the spring 10 preload. When engine is on but no injection occurs, the arrangement is in its closed position (fig 3b) with needle tip fully extended from the needle main portion. The needle upper control chamber 2 and the needle hydraulic control chamber 9 have the same pressure and hence no hydraulic load acting on the needle housing. The needle tip portion will be fully extended from the needle main portion. When needle is lifts from the seat to an open position, the needle upper control chamber 2 has a low pressure whilst control chamber 9 remains high pushes the needle housing and needle tip apart.