An injector nozzle and a nozzle retaining nut with a reduced effective head friction diameter

Abstract

 The invention relates to the field of fuel injectors and specifically to the nozzle retaining nut and the nozzle of the injector. The injector typically consists of a nozzle and an injector body, both fixed together with a nozzle retaining nut. During the mounting process, to fix the nozzle (106, 108) to the injector body (100, 103), a torque 112 is applied at the base of the nozzle retaining nut 116. The torque 112 generates an axial force which will press the parts 100, 103, 106 and 108 together to fit with each other and hold tightly with the help of positioning pins 104. The invention proposes a measure to increase the axial pre-load force by reduction of the effective friction diameter at the screw head (110) by means of a defined angle difference between the nozzle retaining nut 116 and the surface of the nozzle 109. This difference angle can be set at both the components alternatively by means of a variation in the angles at the surface of the nozzle or the head of the nozzle retaining nut.

Description

State of the Art

[0001] The invention relates to the field of fuel injectors and specifically to the nozzle retaining nut and the nozzle of the injector.

[0002] The fuel injectors known in the state of the art, typically comprise a nozzle, a needle moving inside the nozzle, an injector body, the nozzle being fixed to the injector body by a nozzle retaining nut. The nozzle is normally made of different parts which are manufactured separately and assembled together. The positioning pins are used to hold the different parts of the nozzle tightly in place so that the parts of the nozzle do not move with respect to each other because of the high pressure in the nozzle. The nozzle is fixed to the injector body using a nozzle retaining nut which has threads at one end and a head at the other end.

[0003] Normally there is a 90 degree shoulder at the nozzle retaining nut and the nozzle body.

[0004] Higher the operating pressure of the injector, greater is the required axial pre-load force for fixing the nozzle to the injector body with the nozzle retaining nut. But increase in the axial pre-load force increases the possibility of breaking of the positioning pins because of shear.

[0005] Other common measures for optimising the axial pre-load force for fixing the nozzle to the injector body with a nozzle retaining nut are, to have alternative surfaces or coatings. But these measures will increase the cost of the injectors.

[0006] The axial pre-load forces at any screw are influenced by the friction in the thread (thread friction) and friction at the screw head (head friction). The friction is dependent upon the effective friction diameter in the thread (pitch diameter) and the average diameter of the bearing surface. If no effective friction diameter is available, the axial pre-load force resulting from the torque is scattered.

[0007] Depending on the head friction variable, the component to be attached, which is in contact with the screw head, is heavily loaded or twisted. Thus, the load on the positioning pins increases, which can result in a malfunction of the injectors.

[0008] As for a specific example, the contact of the nozzle retaining nut is changed due to the deflection of the average friction radius depending on the screw force. In addition, the contact geometry is inclined to the so-called scores. Both of them lead to an increased dispersion of the axial pre-load force.

[0009] A coating for reducing the dispersion will result in increase in the component costs.
It also affects only a conditional improvement of the friction coefficient and is mainly effective during the initial threaded connection of the components when the retaining nut is fixed for the first time.

[0010] In case of highly loaded threaded connections ( high surface pressure at the head) and multiple threaded connections, the surface structure and the material characteristics prove mainly effective; whereas the effect of the coating wears off.

Advantages of the invention

The device according to the independent and dependent patent claims has the below mentioned advantages:

[0011] The invention generates increased axial pre-load force for a given mounting torque by reducing the friction diameter of the head, resulting in tight coupling of the different parts of the injector with each other.

[0012] The reduction of the friction diameter of the head is achieved by varying the angle between the nozzle surface and the nozzle retaining nut.

[0013] The angle difference between the surface of the head of the nozzle retaining nut and the surface of the nozzle is easily achieved by variation in the angle at the nozzle or variation in the angle of the head of the nozzle retaining nut and does not require any complex design of the nozzle retaining nut.

[0014] The angle difference to be selected is dependent on the geometry and the material of the components to be screwed.

[0015] The force acting on the nozzle is near the inner end of the nozzle retaining nut.

[0016] This measure leads to an improved distribution of the application of force and thus to a optimized surface pressure. Local surface pressure peaks, which lead to so-called scores during the threaded connection process, are prevented. Thus, the distribution of the axial pre-load force at a greater number of threaded connections is reduced and the risk of shearing off the pin attachments is minimised.

[0017] As a result, the hold-down force, which is initiated during the threaded connection process in the plate, can be reduced ( reduced load on the components). Furthermore, the use of positioning pins can be completely avoided due to this measure.

Brief descriptions of the drawings

[0018] 

Figure 1

shows a fuel injector

Figure 2

shows the schematic of the injector

Figure 3 to 6

shows the detailed view of the invention

Description of the embodiments

[0019] Shown in Fig. 1 is a typical fuel injector comprising of an injector body, a nozzle and a nozzle retaining nut 116. The nozzle comprises of different parts 106 and 108, fixed to each other using the positioning pins 104. The positioning pins 104 ensure that the parts 106 and 108 do not move with respect to each other during the operation of the nozzle which involves high pressures in the nozzle.

[0020] The nozzle ( 106, 108 ) is fixed to the injector body ( 100, 103 ) with the nozzle retaining nut 116 with the help of threads 102, 90 and a contact at the head 110.

[0021] During the mounting process, to fix the nozzle ( 106, 108 ) to the injector body ( 100, 103 ), a torque 112 is applied at the base of the nozzle retaining nut 116. The torque 112 generates an axial force which will press the parts 100, 103, 106 and 108 together to fit with each other and hold tightly with the help of positioning pins 104.

[0022] The torque 112 applied at the base of the nozzle retaining nut gets split into the head friction torque 114 and the thread friction torque 118.

[0023] The invention proposes a measure to increase the axial pre-load force by reduction of the effective friction diameter at the screw head ( 110 ) by means of a defined angle difference between the nozzle retaining nut 116 and the surface of the nozzle 109.

[0024] The following formula is valid for a uniform surface pressure in rotationally symmetrical components:

T ...	Head friction torque (114)
F ...	Axial force
µh ...	Friction co-efficient head
Df ...	effective average friction diameter

[0025] For a given torque T, reduction of the friction diameter D_f causes an increase in the axial force F.

[0026] Shown in Fig. 2 is the schematic of the injector.

[0027] The Fig. 3 show the detailed view of the invention. Shown in the figure is the cross sections of a part of the nozzle 108 and the head of the nozzle retaining nut 116. The head 110 of the nozzle retaining nut 116 makes contact with the nozzle surface 109. The effective diameter of the head of the nozzle nut is defined as the distance between the inner contact points between the head surface 110 and the surface of the nozzle 109. The effective diameter 300 of the head of the nozzle retaining nut 116 for a given force is varied by varying the angle 201 between the head 110 and the surface of the nozzle 109 where the head is in contact. The effective diameter 300 increases when the retaining nut is turned depending on the axial force.

[0028] The Fig. 4 shows as an illustration how the change in the angle 201 changes the effective diameter 300 of the head.

[0029] This difference angle can be set at both the components alternatively by means of a variation in the angles at the surface of the nozzle or the head of the nozzle retaining nut.

[0030] Fig. 5 shows the surface of the nozzle 109 having 90 degrees with vertical axis and head surface 110 of the nozzle retaining nut having less than 90 degrees with vertical axis. Variation of these angles will vary the effective friction diameter of the head surface.

[0031] Fig. 6 shows the surface of the nozzle 109 having less than 90 degrees with vertical axis and head surface 110 of the nozzle retaining nut having 90 degrees with vertical axis.

[0032] According to the loading case or the required axial force, the angle difference and the tolerance window is to be set in such a way that the average friction diameter at the surface does not shift outwards in a major way during the threaded connection process. On the other hand, the angle difference is to be limited in such a way that it cannot result in local increase in pressures and in plastification.

Claims

1. An injector with a nozzle retaining nut (116) having threads (102) at inner side of one end and a head (110) at the other end, the threads (102) being threaded to a nozzle, the head (110) being in contact with the nozzle, the said nozzle retaining nut (116) characterised by a defined angle difference between the surface of the head and the surface of the nozzle body.

2. The nozzle retaining unit (116) according claim 2 wherein the increase in axial force generated during the mounting process will result in tight coupling of different parts of the nozzle.

3. The nozzle retaining nut (116) according to claim 1 wherein the angle difference between the surface of the head and the surface of the nozzle is set either by variation in the angle at the nozzle or variation in the angle of the nozzle retaining nut (116), one being at 90 degrees and the other being conical or tapered in shape.

4. The nozzle retaining unit (116) according to claim 1 wherein the angle difference and the tolerance is set in such a way that the average friction diameter at the surface does not shift outwards in a major way during the mounting process.

5. The angle difference is 0,5 degree to 3 degrees typical being 1,5 to 2,0 degrees

6. The surface of the retaining nut has the shape of the circular ring and the surface of the nozzle is of conical or tapered shape.

Drawing