FUEL INJECTION NOZZLE

Abstract: A fuel injection nozzle includes a nozzle body 10 in which is formed a blind bore 11 at the blind end of which is a seating 12 leading into a sac volume 13 from which extends an outlet orifice 15. A valve member 16 is slidable in the bore and has a conical tip 18 engageable with the seating. The wall of the entrance 14A to the sac volume is formed concentric with the seating 12 after the nozzle body has been hardened. The bore and the sac volume are machined before the nozzle body is hardened.

Description: This invention relates to a method of making a fuel injection nozzle of the kind comprising a nozzle body defining a blind bore, a frusto conical seating at the blind end of the bore, the seating leading into a cylindrical sac volume from which extends an outlet orifice or orifices and a valve member slidable in the bore and having a conical tip shaped for engagement with the seating to prevent flow of fuel through the outlet orifice or orifices. Such a fuel injection nozzle is known from EP-A-0 283 154. In the manufacture of such a nozzle it is the practice to machine the bore and the sac volume together with the outlet orifice or orifices while the metal is in the soft state. The wall of the sac volume is of cylindrical form and is generally concentric with the bore. Following machining of the bore an enlargement is formed intermediate the ends of the bore and a passage or passages is drilled which affords communication between the enlargement and a supply groove or the like in the end face of the nozzle body remote from the seating such machining again being carried out with the nozzle body in the soft state. The nozzle body is then hardened following which at least a portion of the bore and the seating are ground, said portion of the bore forming the bearing surface for the valve member. At the end of the grinding operation the seating and said portion of the bore are substantially concentric. The valve member is ground in the usual manner and assembled into the bore. It is possible that during the hardening process limited distortion of the metal forming the nozzle body can take place resulting in slight eccentricity between the wall of the sac volume and said portion of the bore and the seating. This lack of concentricity while having little effect upon the performance of the nozzle where the valve member is moved to the fully open position to allow substantially unrestricted flow of fuel, can cause problems when the valve member is moved only a short distance away from the seating so as to form a restriction which restricts the flow of fuel through the outlet orifice or orifices. Nozzles in which the initial movement of the valve member is limited are being used to an increasing extent in fuel systems in order to improve the operating characteristics of the engine. If the wall of the sac volume is displaced during the hardening process the narrower edge of the seating no longer lies in a plane normal to the axis of the bore. In the use of the nozzle the valve member tends to rotate in the bore and if the surfaces of the valve member were concentric this would not matter. However it is found that the tip of the valve member is sometimes eccentric to a very small degree and even though the valve member is able to establish a fuel tight seal with the seating in the closed position of the valve member, in the partly open position it is found that the degree of restriction to the flow of fuel can vary as the angular position of the valve member changes in the use of the nozzle. The object of the invention is to provide a fuel injection nozzle of the kind specified and a method of making same in a simple and convenient form. According to the invention a method of making a fuel injection nozzle of the kind specified comprises machining the bore and sac volume prior to hardening the nozzle body, and following hardening, grinding a portion of the bore, the seating and at least the wall of the entrance to the sac volume so that the wall of the entrance portion is concentric with the seating. According to another aspect of the invention in a fuel injection nozzle of the kind specified at least the entrance portion of the sac volume is of enlarged diameter and is concentric with the seating. An example of a fuel injection nozzle will now be described with reference to the accompanying drawings in which: Figure 1 is a sectional side elevation of part of a known form of nozzle, Figure 2 is a view to an enlarged scale of part of the nozzle seen in Figure 1, Figure 3 is a view similar to Figure 3 showing the nozzle modified in accordance with the invention and Figure 4 shows a further modification. With reference to Figure 1 of the drawings there is shown a portion of the nozzle body 10 in which is formed a blind bore 11 at the blind end of which is formed a frusto conical seating 12 leading into a sac volume 13 having a cylindrical wall 14. Extending from the sac volume 13 are outlet orifices 15. Slidable in the bore is a valve member 16 the portion of which is illustrated is narrower in diameter than the bore to provide an annular space 17 which is connected to a fuel inlet of the nozzle, the inlet in use being connected to the outlet of a fuel injection pump. The valve member has a conical tip 18 having a cone angle which is slightly larger than that of the seating 12. Intermediate the tip 18 and the cylindrical portion of the valve member is a frusto conical portion 19 having a cone angle which is smaller than that of the seating. The valve member is biased into contact with the seating by a spring (not shown) and is lifted in known manner away from the seating by the fuel under pressure supplied to the aforesaid inlet. The nozzle body is formed from hardenable steel and while the body is in its soft state the bore 11, the seating 12 and the sac volume 13 are rough machined. In addition the outlet orifices 15 are also drilled. The body is then hardened a process which involves the use of heat and after hardening the portion of the bore which forms a bearing surface for the valve member and also the seating are ground so that they are concentric. The valve member is machined and ground to size and is assembled into the bore. It is possible that when the hardening and the grinding process have been completed, the axis of the sac volume is displaced from the axis of the ground portion of the bore and the seating with the result and as shown in Figure 2, that the transition between the narrower end of the seating and the wall 14 of the sac volume does not lie in a plane normal to the aforesaid axis. Moreover, it is often found that the tip 18 of the valve member is eccentric to a very small degree. At the same time it is still possible to obtain a satisfactory seal between the tip and the seating. The eccentricities noted above have little effect when the nozzle is of the type in which the valve member is opened to its maximum extent when fuel under pressure is supplied to the inlet. However, where the nozzle is of the type in which the valve member has two or more stages of lift the eccentricities noted above can have an effect upon the operating characteristics of the nozzle. This is because, in use, the valve member tends to rotate in the bore. If therefore the valve member is lifted by a predetermined amount from the seating the degree of restriction to the flow of fuel between the tip of the valve member and the portion of the seating adjacent the sac volume, can vary depending on the angular position of the valve member. Figure 3 in which the eccentricity is exaggerated, shows the modification to the nozzle to minimise the above problem. It will be seen from Figure 3 that the entrance portion 14A of the wall of the sac volume adjacent the seat has been machined after hardening of the nozzle body, so that it is concentric with the seating and the ground portion of the bore 11. In this manner the transition between the seating 12 and the sac volume lies in a plane normal to the axis of the ground portion of the bore and the seating. As a result the restriction to the flow of fuel between the tip 18 of the valve member and the seating 12 will remain substantially constant irrespective of the angular position of the valve member. Figure 4 in which the eccentricity is exaggerated, shows an alternative arrangement in which the entrance portion 14B to the sac volume 13 is of frusto conical form, the cone angle being smaller than that of the seating. The formation of the entrance portion 14B can be achieved using a shaped hone secured to a mandrel guided by the ground portion of the bore.

Claims: A method of making a fuel injection nozzle of the kind comprising a nozzle body (10) defining a blind bore (11), a frusto conical seating (12) at the blind end of the bore, the seating leading into a sac volume (13) from which extends an outlet orifice or orifices (15) and a valve member (16) slidable in the bore (11) and having a tip (18) shaped for engagement with the seating to prevent flow of fuel through the outlet orifice or orifices (15) the method being characterised by the steps in the following order, machining the bore (11) and the sac volume (13), hardening the nozzle body (10), and grinding a portion of the bore (11), the seating (12) and at least the wall of the entrance portion (14A, 14B) to the sac volume, so that the wall of the entrance portion is concentric with the seating (12). A method according to Claim 1 in which the method further comprises the step of using the ground portion of the bore (11) as a guide for a mandrel carrying a shaped hone which forms the entrance portion (14B) to the sac volume. A fuel injection nozzle made according to the method of Claim 1 comprising a nozzle body (10) defining a blind bore (11), a frusto conical seating (12) at the blind end of the bore, the seating leading into a cylindrical sac volume (13) from which extends an outlet orifice or orifices (15), and a valve member (16) slidable in the bore (12) and having a conical tip (18) shaped for engagement with the seating to prevent flow of fuel through the outlet orifice or orifices, said conical tip (18) defining with the seating (12) when the valve member is partly lifted from the seating a restriction to the flow of fuel through said outlet orifice or orifices (15), characterised in that at least the wall of the entrance portion (14A, 14B) of the sac volume is of enlarged diameter and is concentric with the seating (12). A fuel injection nozzle according to Claim 3 characterised in that said entrance portion (14A) is of cylindrical form and is of larger diameter than the remaining portion of the sac volume. A fuel injection nozzle according to Claim 3 characterised in that said entrance portion (14B) is of frusto conical form and has a cone angle which is smaller than the cone angle of the seating (12).

Inventors: HARDY, MARTIN PAUL
Applicants: LUCAS INDUSTRIES PUBLIC LIMITED COMPANY
Application year: 1990
Main classification: F02M61
IPC codes: F02M61