GB2204094A - Multiple intake ducts to i.c. engine cylinder intake valves - Google Patents

Abstract

Each intake valve 18 is provided with a first pair of relatively large diameter diametrically opposed intake ducts 22, 24 serving to induct air into the engine cylinder at full throttle, and a second pair of relatively small diameter diametrically opposed intake ducts, 32, 34 disposed transversely of the first pair of ports and serving to induct air into the engine cylinder under part throttle. Fuel may be supplied to all or only certain of the ducts by carburation or fuel injection. The ducts 32, 34 may impart swirl to the charge. <IMAGE>

Description

INTERNAL COMBUSTION ENGINE The present invention relates to internal combustion engines and seeks to improve the induction of the charge into the combustion chamber, with the aim of improving lean burn capability.

According to the present invention, there is provided an internal combustion engine having separate intake and exhaust valves for each cylinder, wherein an intake valve is provided with a first pair of relatively large diameter diametrlically opposed ports serving to induct air into the engine cylinder at full throttle, and a second pair of relatively small diameter diametrically opposed ports disposed transversely of the first pairof ports and serving to induct air into the .engine cylinder under part tbrotle.

Preferably, each intake port is provided with a first throttle for controlling the air flow through the smaller ports and a second throttle ganged with the first throttle and arranged to open at higher loads than the first throttle and controlling the air flow through the -larger ports.

The small diameter ports are opened progressively sunder part load while the large diameter ports remain shut.

In this way, charge velocity- is maximized to prompte lean burn capability. With increasing speed, the large ports open progressively and admit larger air masses with the smaller ports playing a diminishing role as their flow resistance is greater than the larger ports.

One large port and one small port may be connected to a twin choke carburettor but alternatively fuel injection may be employed. In the latter case, fuel may be injected into both ports but it may suffice in some engines to inject only into the small port.

The small ports may be angled relative to one another in such a manner as to promote swirl about an axis parallel to that of the valve guide. Such swirl will only be effective at partial throttle. Under open throttle conditions, the toroidal flow resulting from the induction of a large air mass is adequate to ensure good burning characteristics. The small ports may alternatively rely exclusively upon toroidal vortices or may be designed to combine the toroidal vortex with swirl in order to maximize lean burn capability by maximizing the energy stored in the charge prior to its being trapped and compressed to cause turbulence.

As an alternative to a carburettor, the engine may be fuel injected. The effect of even induction of air around the circumference of the inlet valve is to promote toroidal flow. This flow results from gases curling off the edge of the inlet valve and breaking away from the valve when it reaches a certain size.

After breaking away, the toroid moves into the cylinder.

The gas flow resembles that of smoke rings blown by cigarette smokers in which the rotation of the gases is such that particles in the gas stream thread in and out of the ring defined by the toroid. By the nature of this flow, gases can remain localised in one region and this can be used to advantage to obtain a stratified charge.

Thus it is possible to position the injectors in the one or more of the ports in a manner to increase the charge density in the vicinity of the spark plug. In this way, though the overall mixture strength may be lean, there is no problem experienced in igniting the mixture in the region of the spark plug. Of course, once ignited, the flame can readily propagate through a weaker mixture. It is probable that injection to achieve a stratified charge would need to be into one of the larger ports.

The invention will now be described further, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a partly sectioned perspective view of a cylinder head of an engine constructed in accordance with the invention, Figure 2 is a schematic side view of the embodiment shown in Figure 1, Figure 3 is a schematic rear end view of the embodiment of the Figures 1 and 2, and Figure 4 is view similar to Figure 1 of an alternative embodiment in which -the secondary ports are positioned in a manner to promote swirl.

Figure 1 shows a partial sect-ion through a cylinder head 10 in the region of an inlet valve 18 (Figure 2). The valve guide is designated 12 and part of the valve seat 14 is shown. The upper endof the valve guide 12 opens onto a recess 16 for receiving cam follower buckets (not shown) and these act between an overhead camshaft and the upper ends of the poppet valves. As so far described,- the cyli-nder head is of course conventional and further more detailed description is not deemed necessary. The cylinder head also includes a water cooling jacket and exhaust valves but these are not illustrated as they are not germane to the invention.

The invention is concerned with the p-orting .leading to the inlet valves and aims to provide porting which improves the volumetric efficiency at high load and which improves lean burn capability at part load and low load conditions.

The porting is symmetrical and at high load the air is supplied by the two main -intake ports 22 and 24 which open onto diametrically opposed sides of the inlet valve seat 14. These two ports are of relatively large diameter and one (22) opens onto a manifold arranged on the side of the engine while the other (24) is to be connected to a manifold on the top of the engine. The two main ports are balanced so that equal quantities of air reach the combustion chamber from both directions and this has been shown experimentally to increase the breathing efficiency under high load operating conditions. The increased volumetric efficiency is believed to stem first from the better usage of the entire skirt area of the poppet valve.

Another advantage of symmetrical porting has been found to be the improved burning characteristics of the charge. The fact that the charge enters from all round the skirt area of the valve tends to cause toroidal vortices, that is to say rings of gas rotating in the manner of smoke rings and remaining in an annulus while moving away from the valve. This increases the stored energy in the charge and increases the turbulence upon compression of the mixture. The improved mixing promotes faster burn and increases the lean burn capability.

The two large ports 22 and 24 do not maximize performance under low speed conditions. The air velocity under low speed conditions is low and this stores less energy and produces less turbulence. The invention therefore proposes two further symmetrical ports 32, 34 of smaller diameter than the ports 22, 24. The ports 32 and 34 open onto opposite sides of the skirt of the valve but on a line orthogonal to the line of the large ports 22, 24. The configuration of the four ports is clearer in the views of Figures 2 and 3 which use the same reference numerals as Figure 1 but only show the dispositions of the ports relative to the inlet Valve when viewed from the side and from the read end of the engine respectively.

The larger ports 22 and 24 are controlled by a first throttle while the smaller ports 32 and 34 are commonly controlled by a second throttle separate from the throttle for the larger ports 22 and 24.~The throttles are arranged to open at different times and a-rephased so that the air flows through the smaller ports 32 and 34- under low speed and low load conditionsand the lar-ger ports are opened progressively to meet the demand under high load conditions. In this way, air speed is optimized throughout the load range improving lean burn capability. Even under low load conditions, the air flow is symmetrical to the valve and all the advantages. previously described as being the result of dual porting are still achieved even when the large ports are fully throttled.

The embodiment of Figures 1 to 3 is designed such that air always flows in a plane containing the axis of the inlet valve and there is no component of air flow tending to cause swirl about the vertical axis of the valve. The embodiment of Figure 4 is generally similar to the previously described embodiment and differs from it in that the smaller ports 32' 34' are intentionally angled at 40 to promote such swirl at low engine loads.

The gas flow will 'in this case consists of a mixture of toroidal flow and swirl, i.e. a ring which simultaneously spins about the axis of the valve.

The fuelling of the different ports may be achieved in a variety of ways. For example, the smaller ports may be connected to one throat of a twin choke carburettor while the larger ports are connected to the other. This allows the mixture strength to be adjusted -separ-ately for low load and high load conditions. Alternatively, fuel may be fed to only the smaller of the ports, which operate under all conditions, while clean air is inducted through the larger ports. In this case, any metering device in the flow path of the smaller ports must make allowance for the air entering via the other two ports.

In the case of fuel being metered by a carburettor, only one large port and one small port from each inlet need be connected to the carburettor. The other two ports must be connected to throttles for matching the air flow with that flowing through the carburettor but fuel need only be introduced through one set of ports. This avoids the need for more than one carburettor, thereby eliminating an unnecessary additional expense and complication.

Fuel injection offers an alternative suitable system for metering fuel to the engine. The fuel may be injected in this case at any suitable desired position and furthermore the injection point may be selected to achieve a stratified charge which is richer in the vicinity of the spark plug after compression.

The improved burning characteristics potentially permits operation with leaner mixtures to improve fuel economy, though ignition timing must be adjusted to gain the full benefit from the lean mixture. Furthermore, the increased power under full load may exceed requirements and in this case it would be possible to adjust the valve timing to reduce maximum power output while simultaneously increasing bottom end torque. Thus the improvement of the invention can be reflected in the output power of the engine and in increased economy and drivability. If torque output exceeds requirement over the driving range, then of course transmission ratios can be altered to increase economy still further while reducing output torque at the wheels.

Claims (6)

1. An interna-l combustion engine having separate intake and exhaust valves for each cylinder, wherein an intake valve is provided with a first pair of relatively large diameter diametrically opposed ports serving to induct air into the-engine cylinder at full throttle, and a second pair of relatively small diameter diametrically opposed pprts disposed transversely of the first pair of ports and serving to induct air into the engine cylinder under part throttle.

2. An engine as claimed in claim 1, wherein each intake port is provided with a first throttle for controlling the air flow through the smaller ports and a second throttle ganged with the first throttle and arranged to open at higher loads than the first throttle and controlling the air flow through the larger ports.

3. An eng-ine as claimed in claim 2, wherein the small ports are angled relative to one another in such a manner as to promote swirl about an axis parallel to that of the valve guide.

4. An engine as claimed in any preceding claim, wherein a carburettor is provided for metering fuel to the cylinder, the carburettor being a twin choke carburettor having one throat supplying a fuel/air mixture to one small port and the other throat to one large port, the remaining large port and small port of the cylinder being connected to receive only air by way of respective throttles matching the carburettor throttles.

4. An engine as claimed in any of claims 1 to 3, wherein the cylinder is fuelled by fuel injection into at least one the smaller ports.

5. An engine as claimed in claim 4, wherein the injector or one of the injectors is positioned in a manner to increase the charge density in the vicinity of the spark plug.

6. An engine constructed and adapted to operate substantially as herein described with reference to and as illustrated in the accompanying drawings.