GB2056553A - Directed inlet passages in I. C. engines - Google Patents

Abstract

A cylinder head 10 has a "directed" inlet passage whose inlet duct 16 is lined over at least its downstream end portion with a liner sleeve 30 which has a tongue 31 extending around about half of the circumference of the sleeve. The upper part of the tongue 31 is shaped to match the internal surface of the upper part of the bowl 13 of the inlet passage against which it abuts when the sleeve 30 is fully-inserted. The projection of the tongue 31 into abutment or close proximity with the surface of the upper part of the bowl 13 causes the tongue to act as a deflector tending to direct the airflow passing the valve seat 14 towards the cylinder wall 12, thus increasing swirl. Adjustment of the swirl can be effected by longitudinal and/or angular adjustment of the sleeve 30 in the duct 16, for example for equalisation of swirl between several cylinders. The sleeve 30 may taper downstream and may be of rectangular section with radiused corners. It may be of mild steel or plastics. <IMAGE>

Description

SPECIFICATION Directed inlet ports in l.C. engines This invention relates to internal combustion engines of the reciprocating piston type and concerns the inlet ports inthe cylinder heads of such engines. The invention is particularly although not exclusively concerned with the inlet ports of directinjection (open chamber) diesel engines, and can also be employed in certain known types of stratified-charge petrol engine.

An object ofthe invention is to provide a so-called directed inlet port arrangement having increased swirl-producing effect, and preferably also having the capability of adjustment of its swirl-producing capacity, whereby significant differences in the swirl produced in different cylinders of a multi-cylinder engine can be eliminated. Engines with inlet ports which induce swirl of the combustion gases to assist combustion normally require a precise degree of swirl in the combustion chamber in order to achieve efficient combustion. If the degree of swirl differs in different cylinders of the engine, then combustion in some cylinders will not be optimum, and fuel consumption and low exhaust emission capability may be impaired.

Two main type of inlet port which generate swirl are known, the first being the so-called helical inlet port in which the inlet gases are led through an inlet duct to enter a substantially annular volume ofthe port (referred to as the bowl) around the valve stem and above the valve seat, the inlet duct intersecting the bowl asymmetrically with respect to the axis of the valve stem and valve seat so that the outer side of the duct merges smoothly with the internal surface of the wall ofthe bowl.Thus the inlet gases are introduced in a generally circumferential direction into the bowl from the duct, whose longitudinal axis is radially-offset substantially from the axis of the valve stem (which will be considered as vertical with the valve opening downwardly from the valve seat), so thatthe gases will travel along a helical path around the valve stem in the bowl of the port and thereby acquire angular momentum before passing over the valve seat and down into the combustion chamber.

The second known kind of swirl-inducing inlet port, and that with which the present invention is concerned, is the directed inlet port which has a straight inlet duct which is downwardly-inclined towards the general plane of the valve seat (considered as horizontal with the valve stem vertical and the valve opening vertically downwardly) and leads into a circular-section inverted bowl through which the inlet valve stem extends coaxially, the valve seat being formed around the open bottom of the bowl, and the longitudinal axis of the duct intersecting or almost intersecting the axis of the valve stem in an arrangement which is symmetrical or almost symmetrical in plan, so that the inlet gases are biassed to enter the combustion space below the valve seat in a given downwardly-inclined direction which is tangential with respect to the engine cylinder, and with linear momentum which is converted into angular momentum within the engine cylinder, thereby generating swirl about the cylinder axis. In a directed port, the offset of the duct axis on either side of the valve stem axis should be no greater than 0.2D, where D is the inner diameter of the valve seat, and the angle of approach of the-duct axis, i.e. the angle which its vertical plane makes with the engine cylinder radius through the valve stem axis, should be in the range 35" to 1450 as seen in plan view.

Originally, directed inlet ports were cast in the production of the cylinder head to the required final shape, which was developed experimentally.

Experience has shown that small variations in the shape and surface finish of directed inlet ports due to quality control deficiencies in the foundry will lead to significant differences in the swirl which will be generated by them in production cylinder heads. This leads to appreciable variations in engine performance, as indicated above. To overcome this difficulty the inlet tract and inlet valve ports of the cylinder head are increasingly machined. Even with machined inlet ports of the directed kind, discrepancies can still occur between cylinders, often due to small design and/or manufacturing variations in the inlet manifold.

According to the present invention in its broadest conception, a directed inlet port in the cylinder head of an l.C. engine is provided in the bowl of the port with an insert which occludes the whole or nearly the whole ofthat part of the internal volume of the bowl which lies outside the forward projection of the internal surface of the inlet duct into the bowl and lies above the back of the head of the inlet valve, on the side of the inlet valve axis nearest to the axis of the associated engine cylinder, the insert tending to direct the air flow passing the inlet valve seat towards the wall of the engine cylinder.

In one form of the invention, a directed inlet port in an l.C. engine cylinder head is provided with an insert member mounted within the inlet duct and carrying at its inner end a projecting tongue which protrudes forwardly into and across the bowl of the port past the inlet valve stem, the tongue having a profile parts of which match the shape of the internal surface ofthe bowl and ofthe back ofthe inlet valve head in abutment with or close proximity to which the said parts lie, whereby the tongue tends to direct the air flow passing the inlet valve seat towards the wall of the engine cylinder.

Conveniently the insert member comprises a thin-walled liner shaped to lie against the internal surface of the downstream end of the duct around at least part of its circumference, the projecting tongue being formed as an extension of the wall of the liner at its inner end.

The projecting tongue or other insert within the bowl is found to increase the swirl induced in the combustion gases in the cylinder, to a degree dependent on its positioning, by acting as a baffle or deflector for the inlet gases tending to direct them towards the circumferential wall of the cylinder.

Preferably the exact position of the insert in the bowl is adjustable, enabling the degree of swirl to be varied so that any differences in the swirl induced in different cylinders can be removed or reduced.

In general the tongue or other insert should extend around at least half of the circumference of the inlet duct at the downstream end ofthe duct, in order to control the airflow direction adequately.

Preferably the insert member is longitudinallyadjustable with respect to the duct, so that the degree of protrusion into the bowl of the inlet port can be adjusted.

It is also possible to effect adjustments of the swirl induced, by rotating the insert member about the longitudinal axis ofthe downstream end portion of the duct, especially where this is of circular crosssection, so as to alterthe positioning of the insert in relation to the surface of the bowl. The possible angle of rotary adjustment depends upon the geometry of the tongue or other insert in relation to the bowl and valve stem, and will usually vary with the longitudinal position of the insert. Adjustment by rotation may be used in place of or in addition to longitudinal adjustment of the sleeve.

In one construction the insert member comprises an open-ended tubular sleeve which lines at least the downstream end of the inlet duct, the tongue being formed as a projection from the inner end of the tube on one side of the circumference. However a liner member of shell form which extends around only part of the circumference of the duct at its down stream end may also be employed.

The liner sleeve or other insert ofthe present invention may be used in conjunction with an inlet port at least part of whose internal surface is a machined surface. In some cases the whole ofthe bowl surface will have been machined. In practice at least the downstream end of the inlet duct will usually also be machined to ensure a good seat for the liner.

However the insert ofthe invention may also be used advantageously in conjunction with an inlet port which has no machined surfaces and is "as cast" provided the surface finish is suitable to allow the insert to be satisfactorily fitted.

The profile of the protruding tongue ofthe liner sleeve may vary, but as already indicated the tongue should preferably extend around approximately half of the circumference of the liner sleeve, or of the inlet duct where a complete tubular sleeve is not used, and should be shaped to conform to the portion of the internal surface ofthe bowl and of the back of the valve head remote from the cylinder into proximity with which the tongue will come when the insert is inserted as far as possible into the bowl, past the valve stem.

The invention may be carried into practice in various ways, but one specific embodiment thereof will now be described by way of example only and with reference to the accompanying drawings in which: Figure 1 shows in sectional elevation a known form of directed inlet port, not embodying the invention, in a cylinder head of a multi-cylinder direct injection diesel engine, Figure 2 is a sectional view taken approximately on the line ll-ll in Figure 1.

Figures 3 and 4 are views similar to Figures 1 and 2 respectively, showing a modified form of directed inlet port incorporating an insert sleeve as an embodiment of the present invention.

Figure 5 is a perspective view of the insert sleeve itself, and Figure 6 is a diagram showing the effect of the position of the insert sleeve on the degree of induced swirl in the cylinder and on the so-called "Gulp Factor".

In the drawings, Figures 1 and2show a known form of directed inlet port in a cylinder head 10 of a multi-cylinder diesel engine, the axis of the associated cylinder being indicated at 11 and the position ofthe wall of the cylinder liner at 12. The inlet port comprises a bowl 13 whose upper part is of generally part-spherical form and whose divergent lower part terminates in the valve seating 14 forthe poppet valve 15, and a straight circular-section inlet duct 16 which intersects the bowl 13. The inner end portion ofthe duct 16 is cylindrical and its outer end is tapered. The axis 17 of the duct 16 is inclined downwardly towards the assumed horizontal plane of the lower face 18 of the cylinder head 10, the axis 19 of the stem 20 of the poppet valve 15 being assumed vertical.The angle between the duct axis 17 and the face 18 should be as large as is practicable within the cylinder head depth in the interest of maintaining as large a flow area as possible through the port. As seen in plan view the axis 17 ofthe duct 16 is in this case offset by a small distance E from the valve stem axis 19, as shown in Figure 2, although it could alternatively intersect that axis, and is inclined at an angle of approach ato the radial plane 22 containing the cylinder axis 11 and the valve stem axis 19, the angle a being between 35 and 145 in the projection of Figure 2.As also mentioned previously, the offset distance E should not exceed 0.2D where D is the internal diameter ofthe valve seating 14 (Figure 1.) Air entering through the duct 16 will be directed through the portto emerge pastthevalve seating in a direction which is generally tangential with respect to the cylinder liner 12 and its linear momentum will be converted into angular momentum by the swirl induced in the combustion chamber Figures 3 and 4 show a modified form of inlet port which incorporates a liner sleeve 30, the port shown in Figures 3 and 4 being an embodiment of the invention. Parts in Figures 3 and 4 which are similar to those in Figures 1 and 2 are given the same refer ence numerals. In Figures 3 and 4the axis 17 of the inlet duct 16 intersects the axis 19 of the valve stem, and the duct 16 is of cylindrical form throughout and is provided with a tubular lining sleeve 30, but in most other respects the port shown in Figures 3 and 4 is similar to that of Figures 1 and 2.

In the arrangement of Figures 3 and 4, the internal surface of the bowl 13 and the sides of the duct 16 are machined surfaces, the geometry of the arrangement lending itself readily to such machining. Moreover, an open-ended tubular cylindrical liner 30, e.g. made of 18 s.w.g. mild steel (1.2mm thick), is inserted in the duct 16 as a close sliding fit in its interior. The position of the liner 30 is adjustable longitudinally and/or by rotation in the duct, and the liner is formed at its inner end with a partcylindrical tongue 31 formed as an integral extension of its wall, and occupying approximately one half of the circumference of the liner at that end.The remaining portion 32 of the circumferential rim of the liner sleeve at that end lies in a radial plane as shown in FigureS. The liner sleeve is inserted into the bowl in an angular attitude such that the tongue 31 extends past the valve stem on the side thereof remote from the wall 12 ofthe cylinder, and when the liner is fully inserted the upper part of the edge of the tongue 31 abuts the internal surface of the bowl 13 near the axis 11 of the cylinder 12, the profile of the upper part of the tongue being shaped to conform to the concavely-curved surface of that part of the bowl. The lower part of the profile of the tongue 31 curves smoothly back in close proximity to the back radiussed surface of the valve in its closed position to join the rim portion 32 of the sleeve 30.Thus the tongue 31 acts as a baffle or deflector, masking part of that side of the bowl which is remote from the cylinder wall as seen in vertical projection, and tending to direct the air flow towards the cylinder wall as it passes the valve seating 14 and enters the engine cylinder.

The effect of the tongue 31, with the sleeve fully inserted in the orientation shown, is to increase the induced swirl in the cylinder, and also to increase the so-called "Gulp Factor" of the port. The Gulp Factor is a well-known technical term representing the resistance to air flow of the port, the higher the Gulp Factor value the lower being the resistance. For an engine operating at a given speed, the Gulp Factor is the mean inlet velocity based on the inner valve seat diameter divided by the mean discharge coefficient for the valve and port and the speed of sound at intake conditions. The mean discharge coefficient is the arithmetic mean ofthe experimentally determined values of air flow over the curve of valve lift against time.

Thus when an experimental cylinder head having a fully-machined directed inlet port having a Ricardo swirl number of 2.90 and a Gulp Factor of 0.689 was fitted with the liner sleeve in its inlet port, the sleeve in its fully inserted position increased the Ricardo swirl number to 3.93 and the Gulp Factorto 0.773.

The Ricardo swirl number is an empirical value representative of the swirl intensity generated by the inlet port/valve system. The higher the number the greater the swirl intensity.

The swirl measurements are made using a rig consisting of a source of low-pressure air at about 254mm. water which is blown through the inlet port with the inlet valve open at various fixed valve lifts up to the maximum, and with a dummy cylinder corresponding to that of the actual engine attached in the correct position below the head. The dummy cylinder contains a spinning vane anemometer whose angular speed is measured for each valve lift to give a measure of the swirl generated in the air flowing through the inlet port and valve into the cylinder. At the same time measurements of the air flow rate are made, so that the effectiveness of a particular port configuration in producing swirl can be assessed alongside the resistance to flow which in an actual engine will affect weight of air charge drawn into the cylinder in each working stroke, and hence the potential power output.Alternatively, an impulse swirl meter may be used to assess the swirl.

Essentially this is a matrix of paraliel tubes, whose length is greater in comparison with their diameter, the matrix being mounted at the exit from the cylinder and being restrained from free rotation by a torque measuring device. The swirling air flow entering the matrix has its angular momentum destroyed, and at the same time a torque proportional to the swirl is imposed on the matrix. Swirl measurements were also made on the experimental cylinder head referred to above with the inlet sleeve 30 progressively retracted in stages from its fully-inserted position, and the effect of the position of the sleeve is indicated graphically in Figure 6. This is a graph showing the Ricardo swirl number and the Gulp Factor plotted against the linear displacement in millimetres of the liner sleeve 30 from its fully-inserted position.It will be seen that the swirl number falls substantially linearly from its maximum value as the sleeve is progressively retracted. The Gulp Factor rises slightly to a maximum of 0.78 art a sleeve retraction of about 1.3 mm and falls slowly thereafter to reach a value of 0.755 at 4 mm retraction, still well above the value for the unlined inlet port.

Whilst it is convenient in most cases to make the liner sleeve of circular cross-section constant along its length, this is not essential. A liner sleeve of nominally rectangular section with radiused corners could be used. Again, the liner sleeve could be axially-tapering in the downstream direction. It is not necessary for the whole of the outer surface of the liner sleeve to lie flush against the surface of the duct 16, so the sleeve need not conform precisely to the cross-sectional shape of the duct 16.

Instead of being made of mild steel, the sleeve 30 could be made of a plastics material having adequate strength to resist the aerodynamic turbulent forces acting on the tongue and adequate durability at the engine operating temperature. Either a simple plastic moulding, or a filled or fibre-reinforced plastic could be used.

Afterthe longitudinal and/or angular position of the sleeve 30 in the duct 16 has been adjusted to the optimum setting as regards swirl induction, or swirl equalisation as the case may be, the sleeve may be fixed in position by means of a drop of a suitable adhesive.

Claims (10)

1. A cylinder head of an l.C. engine having at least one inlet port of the directed port type which is provided with an inlet valve of mushroom-headed poppet type, and with an insert in the bowl of the port which occludes the whole or nearly the whole of that part of the internal volume of the bowl which lies outside the forward projection of the internal surface of the inlet duct into the bowl and lies above the back of the head of the inlet valve, on the side of the inlet valve axis nearest to the axis of the associated engine cylinder, the insert tending to direct the airflow passing the inlet valve seat towards the wall ofthe engine cylinder.

2. A cylinder head of an I.C. engine having at least one inlet port of the directed port type which is provided with an inlet valve of mushroom-headed poppet type, and with an insert member mounted within the inlet duct and carrying at its inner end a projecting tongue which protrudes forwardly into and across the bowl of the port past the inlet valve stem, the tongue having a profile parts of which match the shape of the internal surface ofthe bowl and the back of the head of the valve, in abutment with or close proximity to which the said parts ofthe profile lie when the insert member is in or closeto its innermost position, whereby the tongue tends to direct the air flow passing the inlet valve seat towards the wall ofthe engine cylinder.

3. A cylinder head as claimed in Claim 2, in which the insert member comprises a thin-walled liner shaped to lie against the internal surface ofthe downstream end of the duct around at least a part of its circumference, the projecting tongue being formed as an extension ofthe wall of the liner at its inner end.

4. A cylinder head as claimed in Claim 2 or Claim 3, in which the insert member is longitudinallymovable in the duct of the inlet port, so that the degree of protrusion of its tongue into the bowl of the inlet port can be adjusted.

5. A cylinder head as claimed in Claim 3 or Claim 4, in which the duct is of circular cross-section at its inner end, and in which the liner is angularly adjustable in the duct about the duct axis so that the relative position of the tongue in the bowl can be adjusted.

6. A cylinder head as claimed in any one of Claims 3 to 4, in which the insert member comprises an open-ended tubular sleeve which lines at least the downstream end of the inlet duct, the tongue being ,formed as a projection from the inner end of the tube which extends around part on one side only of its circumference.

7. A cylinder head as claimed in Claim 6, in which the tongue extends around at least one half of the circumference of the liner.

8. A cylinder head as claimed in Claim 6 or Claim 7, in which the insert sleeve is longitudinally-slidably and/or rotatably-adjustable in the duct, for the pur pose of adjusting the position of its tongue in the bowl.

9. A cylinder head as claimed in any one ofthe preceding Claims, in which at least part of the inter nal surface of the inlet port is a machined surface.

10. A cylinder head having a directed inlet port with a liner sleeve substantially as specifically described herein with reference to Figures 3,4 and 5 ofthe accompanying drawings.