Cylinder head for an internal combustion engine

The invention relates to a cylinder-type head for an internal combustion engine, preferably an Otto-type engine, with four valves per cylinder. The cylinder head accommodates at least one combustion chamber with a pair of inlet ports situated side by side and a pair of exhaust ports, situated opposite the inlet ports. With the object of facilitating gas flowing into the combustion chamber to swirl about the cylinder axis, the invention is essentially distinguished in that the interior surface of the combustion chamber between an inlet port and an exhaust port is implemented with a swirl-generating means. At the intersection between the base plane of the cylinder head, said means form a protrusion projecting radially inwards. The remaining interior surfaces of the combustion chamber lack such protrusion at the intersection with the base plane. To reinforce the swirl generation, the inlet duct, with its port situated farthest away from the protrusion, is formed to give the gas a direction having a substantially lesser angle to the base plane than the corresponding angle of the gas direction from the second inlet duct.

The present invention relates to a cylinder head for an internal combustion 
engine having at least one cylinder with a reciprocating piston, said 
cylinder head accommodating a combustion chamber for the cylinder with 
valve-regulated ports, which, when projected on a circular surface in the 
base plane of the cylinder head facing towards the cylinder are 
distributed with a port in each of four quadrants, so that with the 
quadrants numbered clockwise, the ports of a first and a second inlet duct 
are situated in a first and a second quadrant, respectively, and so that 
the ports of a first and a second exhaust duct are situated in a third and 
a fourth quadrant, respectively. 
It is known from the U.S. Pat. No. 4,211,189 in an Otto-type engine with 
four valves per cylinder to create rotation about the cylinder axis of the 
fuel-air mixture flowing in during the induction stroke, this mixture 
being designated hereinafter "gas". This rotation, hereinafter designated 
"swirl", enables well controllable and economical combustion of the fuel 
in the engine. In the known solution one inlet duct has a substantially 
smaller throughflow area than the other inlet duct, and furthermore, the 
gas is directed from the narrow inlet duct at a relatively small angle to 
a plane normal to the cylinder axis in question. The larger duct gives the 
gas flowing into the combustion chamber from it a larger angle to the 
mentioned plane. The narrow duct thus causes the gas flowing into the 
combustion chamber to swirl, and by allowing gas flow only through the 
narrow duct at low loading and partial loading on the engine there is 
ensured swirling at these loading conditions. The other inlet valve does 
indeed open by the valve mushroom leaving its seat, but no gas flow 
appears to take place through the larger duct. Since the other inlet valve 
is sunk in a cavity, the swirl should not be affected by the valve 
opening. Gas inflow is also allowed through the other duct at greater 
loading, and the swirl is thus counteracted by this gas flow to such an 
extent that the swirl is eliminated. 
The known solution has certain disadvantages, however. Accordingly, the 
utilization of differently large inlet ducts for providing a swirl results 
in that the power obtainable from the engine will be considerably less 
than if both inlet duct ports are given a maximum configuration and are 
the same size. The implementation with differently sized valves and a 
special cavity in the combustion chamber furthermore complicates 
manufacture of the cylinder head and makes it more expensive. There is 
also the risk of unfavourable temperature concentrations in the combustion 
chamber walls. Still further, it has been found in certain types of Otto 
engines with four valves per cylinder that a reduced swirl formation at 
high loadings, which is striven for and obtained in the above-mentioned, 
known engine, results in loud combustion noise, which can be disturbing 
from the comfort aspect when the engine is used in vehicles. 
Other known methods of providing swirls in combustion chambers include 
ridges on the valve mushroom or adjacent the valve seat. The latter is the 
case in the U.S. Pat. No. 4,224,918, for example. These solutions, which 
are applied in Otto engines with two valves per cylinder, do indeed cause 
the gas flowing into the combustion chamber to swirl, but are burdened 
with the disadvantage of heavily throttling gas flow for high loading on 
the engine. Furthermore, the solutions result in relatively costly and 
troublesome manufacturing procedures for providing the ridges. 
Unfavourable wear of the valve mushroom can also be the result in the case 
where the ridge is placed on it, since here the valve is not allowed to 
rotate. 
The present invention has the task of creating a swirl in the combustion 
chamber in a simple way, with a cylinder head described in the 
introduction, while the power obtainable from the engine shall remain 
uneffected as far as possible. An essential desire is thus to provide 
swirling in the higher loading range, thereby to dampen the combustion 
noise occurring in these loading conditions. In the mentioned respects, 
the invention is distinguished substantially in that between the port of 
the second inlet duct and the port of the first exhaust duct the interior 
surface of the combustion chamber is formed with a ridge or the like which 
at its intersection with the base plane forms a protrusion extending with 
its convex delineation radially towards the cylinder axis, and in that the 
remaining interior surfaces of the combustion chamber, where intersecting 
the base plane, lack such protrusions. 
Asymmetry in the combustion chamber is created by the presence of this 
ridge, thus enabling the gas flow from the first inlet duct port to 
provide a swirl which is not eliminated by the gas flow from the second 
inlet duct port. The swirl-generating ridge may be readily formed in the 
wall of the combustion chamber and its swirl-generating effect rather than 
otherwise increases with increased gas flow, i.e. increased engine load. 
An advantageous embodiment of the invention is characterized in that both 
inlet ducts are formed such that the first inlet duct gives the gas a 
direction with a substantially less angle to the base plane than the 
corresponding angle of the gas direction from the second inlet duct. 
A further swirl-generating effect is obtained by the asymmetrical 
implementation of the inlet ducts, and this effect may be added to that 
obtained by the ridge mentioned above. It is essential here that it is the 
first inlet duct, which is thus situated farthest from the ridge, that 
guides the gas at a small angle to the base plane of the cylinder head. 
The second inlet duct, which is situated adjacent the ridge, consequently 
has a greater incident angle to the base plane, for avoiding inter alia by 
coaction with the ridge, direct confrontation with the swirl generated by 
the gas flow from the first inlet duct.

The inventive cylinder head 1 illustrated in the figures is intended for an 
Otto-type engine for operation in vehicles. The view in FIG. 1 of the base 
plane 2 of the cylinder head 1 illustrates a combustion chamber 3, which 
includes two inlet duct ports 4, 5, two exhaust duct ports 6, 7 and an 
opening 8 for an ignition means (not shown). The inlet duct ports 4, 5 are 
equally as large, and are somewhat larger than the exhaust duct ports 6, 
7, which in turn are also equally as large. The ports 4-7 are distributed 
with a port in each of four quadrants 14-17 of a circle 10 defined by the 
diameter of the cylinder 11 in question. A piston 12 is arranged for 
conventionally executing reciprocatory motion in the cylinder 11. The 
piston motions are synchronized with the movements of customary valves 18, 
19 regulating the inlet and exhaust ports 4-7 in a way well known for an 
internal combustion engine working on the Otto principle. 
The quadrants 14-17 are indicated by chain dotted lines in FIG. 1, and are 
numbered clockwise so that the inlet port 4 is situated in the first 
quadrant 14, the inlet port 5 in the second quadrant 15, the exhaust port 
6 in the third quadrant 16, and the exhaust port 7 in the fourth quadrant 
17. The center of the circle is coincident with the central axis 20 of the 
cylinder and the center of the ignition means opening 8. 
Where intersecting the base plane 2 of the cylinder head, the walls of the 
combustion chamber 3 form substantially straight side edges 22-24. The 
inlet quadrant 15 and the exhaust quadrant 16 are however mutually 
connected by a side edge 25, formed with a protrusion 26 located halfway 
between the duct ports 5, 6. The protrusion 26 extends from an imagined 
straight side edge situated symmetrically with the side edge 24, radially 
inwards towards the cylinder axis 20 a distance equalling at least 5 
percent of the distance between the cylinder axis 20 and the straight side 
edge 24. To advantage, this distance is between 8 and 16 percent of the 
distance mentioned. The inwardly directed crest of the protrusion 26 has a 
radius approximately equal to that of the inlet port. 
The protrusion 26 extends along the combustion chamber wall and forms an 
inwardly extending ridge 28 between the inlet duct port 5 and the exhaust 
duct port 6 (see Figures 2 and 3). For a lesser requirement of 
swirl-generation, the ridge 28 may in its entirety lie radially outside a 
dashed line 29 in FIG. 1 between the centers of the exhaust and inlet 
ports 5 and 6. For increased swirl-generation the ridge 28 should, 
however, extend past the line 29 towards the ignition means opening 8. In 
a section through the line 29, the height of the ridge 28 relative the 
corresponding combustion chamber portion between the valves 4 and 7 may be 
up to about thirty percent of the through-flow radius of the inlet duct 
port. 
The combustion chamber 3 depicted in the figures also has an implementation 
where the inlet and exhaust ports 4, 5 and 6, 7, respectively, are 
situated in planes intersecting each other and forming equal angles to the 
base plane 2 (see FIG. 4). The directions of motion of the inlet and 
outlet valves 18 and 19 also form equal angles to the base plane. It will 
also be seen from FIGS. 1 and 2 that between the side edges 22-25 and the 
cylinder circle 10 there are formed so-called squish surfaces, which at 
the end phase of the piston compression stroke conventionally create 
microturbulence in the combustion chamber 3 favourable to combustion. 
During the engine induction stroke the inlet valves 18 with their mushrooms 
21 (see FIG. 4) uncover the ports 4, 5 so that the gas can flow into the 
combustion chamber 3. The mushrooms 21 guide the gas along the combustion 
chamber walls and the gas flowing in from the port 4 after about half a 
revolution, reaches the ridge 28 and the protrusion 26, which then guide 
the gas radially inwardly downwardly and prevent it from directly 
colliding with the gas flowing in from the other inlet port 5. The 
last-mentioned gas flow is confronted by the ridge 28 immediately after 
the mushroom 21 spreads the gas along the walls of the combustion chamber. 
The ridge 28 prevents the tendency of this gas flow to form a swirl 
counter-directed to the gas from the first inlet port 4. The gas flow from 
the inlet port 5 is given a considerable axial component by the guiding 
effect of the ridge 28, and this together with the guidance by the ridge 
28 of the gas flow from the first inlet duct port 4 results in that the 
swirl generated by the latter gas flow may be retained for full load on 
the engine as well. The mentioned swirl-generation is reinforced in the 
invention by a differently shaped implementation of the inlet ducts 34, 
35, consideration also having been paid to the location of the ridge 28 in 
the combustion chamber 3. The inlet ducts 34, 35 depart from an opening 31 
common to both ducts and situated in the side wall 32 of the cylinder 
head, the ducts subsequently being divided by an intermediate wall 33 cast 
in the cylinder head 1 into two essentially parallel ducts 34, 35 leading 
to the respective port 4 and 5, as will be seen from FIGS. 1 and 4. The 
duct 34 has a lower wall portion 36 which is depressed relative the 
corresponding wall portion 37 of the duct 35. An upper wall portion in the 
duct 34 opposite to the wall portion 36 is formed as a ramp 38 (see FIG. 
5). The ramp 38 together with the opposing wall portion 36 directs the gas 
flow at a relatively small angle to the base plane 2 of the cylinder head. 
The angle of the ramp 38 to the base plane 2 is to advantage between 
14.degree. and 20.degree., and its angle to the valve motion direction 
should be between 40.degree. and 60.degree.. The ramp 38 is situated 
upstream of a valve guide 41 projecting into the duct. There is no 
counterpart to the ramp 38 in the inlet duct 35, and the implementation of 
the upper portion of this duct is entirely conventional, which is apparent 
from the dashed line in FIGS. 4 and 5. The different implementation of the 
inlet ducts 34, 35 and the presence of the ramp 38 in the duct 34 also 
result in that the valve guide 41 projecting into the duct 34 has a 
considerably shorter distance to the port 4 than the distance prevailing 
between the valve guide 42 in the duct 38 and its port 5. Coolant ducts 39 
included in the engine cooling system are also illustrated in FIGS. 1 and 
4. 
During the induction stroke, when the inlet valves 18 are kept open and the 
exhaust valves 19 closed, gas flows through the ducts 34, 35 and their 
ports 4, 5 and past the valve mushrooms 21 into the combustion chamber 3. 
The ramp 38 and the depressed wall portion 36 in the duct 34 then give the 
gas flow a direction which results in that the major portion of the gas 
flow is urged past the upper portion of the inlet valve mushroom 21. The 
chief gas flow thus obtains a direction having a comparatively small angle 
to the base plane 2 of the cylinder head, and the gas flow will thus sweep 
along the combustion chamber walls and be guided by the ridge 28 so that 
swirl generation is reinforced. On the other hand, the gas flowing through 
the inlet duct 35 is given a direction having at the port 5 a relatively 
large angle to the base plane 2. The direction can be regarded as 
substantially that of the motion of the inlet valve 18. The gas flow will 
thus distribute itself relatively uniformly past the valve mushroom and 
there is thus avoided the generation of a swirl counter-directed to the 
swirl achieved by the gas flow from the inlet port 4. Since the gas flow 
from the inlet port 5 is also guided by the ridge 28 so that a 
counter-directed swirl generation is prevented, there is ensured a desired 
swirl generation for high loading of the engine also. A desired 
comparatively quiet combustion is thus obtained in the inventive engine, 
which is achieved by the inventive introduction of asymmetry in the 
combustion chamber and inlet ducts connected therewith. 
The embodiment example described above may not be considered to restrict 
the invention, which within the scope of the following claims may be 
modified in a plurality of embodiments.