Fuel Injector Assembly between Fuel Rail Cup and Intake Manifold Groove

Fuel Injector Assembly between Fuel Rail Cup and Intake Manifold Groove

Co-axiality and Concentricity:

Intake Manifold Injector Sitting Hole must be co-axial to Rail Hole; but as rail itself is mounted on intake manifold, geometric tolerances with maximum material condition must be used to define location of rail mounting hole with respect of Injector Hole in Intake Manifold. 

After a certain level of co axiality and concentricity if injector is inclined further then fuel start leaking. This Inclination is called Permissible Inclination Angle. At the centre (middle of length) of Injector this inclination cause a gap called permissible positional gap.

Measure	Spec	Remark
Permissible  Positional Gap	0.6 mm	If Co-axiality and Concentricity is not maintained then these values will increase and this leads to fuel leak.
Permissible  Inclination Angle	1.4  °

Above two parameters are drawn in below image -

To maintain above not only single part design tolerance but also stack up tolerance must be in low range. Ideally there should not be any tolerance in machining of intake manifold, Fuel Rail and Injector. But It is impossible to get 100 % component having same dimension up to 0.01 mm level. So Groove, Chamfer and Surface Finish are taken into consideration to provide freedom in tolerance and avoid fuel leakage : - 

Intake Manifold Groove Dimension, Chamfer and Surface Finish Requirement:

Injector sitting whole dimension have fixed reference:

1.    Fix mounting hole of Rail on Intake Manifold for dimension measurement 

2.    Fix Intake Manifold mounting hole on Cylinder Head for dimension measurement    

Manifold Design	Spec mm	Remark
Injector O Ring D / d	15.2 / 3.5	Used for Intake Grove Design
Injector sitting area tolerance	+/-0.1	On surface b, z, d4 surface
Injector sitting surface finish	Ra 6.3	On surface b, z,a,d4 surface
Chamfer  Angle (α)	25 ° +/- 1	To avoid cutting of O Ring
Chamfer Height z	2 + 0.5/ -0
Stopper Surface for Injector	7 +/- 0.23	Injector O Ring cannot slide in to intake hole