"IKTESNAL COMBUSTION ΞKGEE " A2ID C II>.2ϊ?. HEAD THΞ?ZH)R. i _ This invention relates to internal combustion engines, and cylinder heads therefor.

Conventional internal combustion engines comprise a cylin¬ der head having a recess therein, a cylinder block having a piston - reciprocable in an open-ended cylinder therein, the cylinder being positioned to register with the recess in the head to define a combustion chamber, and inlet and o tlet valves mountsc in valve openings in the recess for axial movement relative to the cylinder head to open and close the valve openings. It is known to shape the recess e.g. by forming a cusp in one side wail, which projects between the inlet and outlet, valves along the range of covenent of the inlet valve so as to impart a swirling moticn to gases flowing into the combustion chamber through the inlet valve. The swirling motion assists in mixing fuel and air within the combustion chamber and improves combustion.

However, we have observed that such cusps also restrict the free flow of gases into the chamber and therefore reduce the maximum amount of gas which can be drawn into the combustion chamber. The maximum power of the engine is therefore reduced. According to the present invention, there is provided a cylinder head for an internal combustion engine comprising a recesβ for cooperating with a piston and cylinder in a cylinder block to define a combustion chamber and inlet and outlet apertures for seating inlet and outlet valves, the walls of the recess around the inlet aperture being shaped to impart a swirling action to gases flowing therethrough into the chamber, characterised in that the walls of the recess around the inlet aperture are shaped to impart the swirling action only when the inlet valve is partially open. Since the walls of the recess are shaped to impart the swirling action only when the inlet valve is partially open, e.g. from one quarter to one half open, gases can flow more freely into the recess when the inlet valve is fully open. Consequently a

smaller reduction in- aximum power of the engine is achieved.

Nevertheless the swirling action imparted to the ~~.se 3 whilst the inlet valve is partially open is sufficient to improve the combustion in the engine. In the preferred embodiment of the invention, the swirling action is produced by a cusp on one side of the recess which projects radially across the recess between the inlet and outlet apertures, but extends a iaily from the inlet aperture a distance less than the axial movement of the inlet valve between its open and closed positions. Preferably the distance by which the cusp extends beyond the inlet aperture is no more than half, but preferably at least one quarter of the a a movement of the inlet -valve between its open and closed positions.

The invention also includes an internal combustion engine- -- incorporating a cylinder head in accordance with the invention. A preferred embodiment of the invention will now be described, by way of example only with reference to the accompany¬ ing drawings, in which: -

Figure 1 is a vertical- cross- section through part of an internal combustionengine in accordance with the invention;

Figure 2 is a bottom view of a cylinder head incorporated in the engine of Figure 1.

He-farin to the drawings, an internal a-smbusticn engine 1 comprises a cylinder head 2 having a number of cardiodal recesses, one of whichis shown at 3_.ia its lower surface, secured to a cylinder block having a similar number of pistons 5 an cylinders

6 therein each positioned to register with a respective cne of the recesses 3- T e.space enclosed by the cylinder β, piston 5 and recess !*. defines a combustion chamber 7. ^s best seen in Figare 2, fuel and air mixture may be introduced into the combustion chamber

7 through an inlet aperture 3 which is opened and closed by movement of an inlet valve 9, between the t-wo positions indicated in broken lines in Figure 1. The fuel and air mixture can be ignited in the combustion chamber by a sparking plug (net shown) retained in a threaded bore 11 in the roof of the recess 3 _*

The products of co abas ion may be exhaus ted roa the coabustion chaaber 7 through an exhaust aperture 12 , «hich is opened and closed by aoveaent of an exhaus t valve 13 in a conventional manner. One side wall, of the recess 4- includes a cusp 14. which proj ects between the inlet a nd outlet aperture s 3, 12. As best s~en in Figure 1 , the cusp extends axially downwardly oa the inlet aperture in the roof of the recess 3 by a distance equal to about one third of the aoveaent cf the inlet valve 9 between its

•_» open and closed positions.

In use, when the inlet is fully open, air and fuel mixture is free to flow over the cusp 14. into the cccbus ion chamber. As the inlet valve closes however, the air and fuel aixture i3 directed by the cusp 14. into a swirling action in the coabustion chaaber so that the air ard fuel is thoroughly aixsa iaaediately prior to coabustion.

As a result, the avourable effect of a swirling gas and fuel mixture on coabustion is achieved with little adverse influence on the aaxiaum rate offlow of gas into the coabustion chaaber.

BAD ORIGINAL _.