Internal-combustion engines – Two-cycle – Whirl through piston-controlled ports
Patent
1997-07-28
1998-09-08
Okonsky, David A.
Internal-combustion engines
Two-cycle
Whirl through piston-controlled ports
1235591, 123564, F02B 3904
Patent
active
058030271
DESCRIPTION:
BRIEF SUMMARY
This invention relates to scavenged internal combustion engines and particularly to engines wherein the scavenging is effected by a blower or the like. In particular, the invention is applicable to two stroke cycle engines and especially to direct injected two stroke cycle engines.
In blower scavenged engines, particularly those incorporating a positive displacement type blower wherein the blower is driven at a speed directly proportional to the engine speed, the rate of air supply by the blower at idle and part loads typically substantially exceeds the requirements of the engine and in this regard it is known to provide for recycling of the air output from the blower back to the inlet of the blower at such engine loads. This is typically achieved with a bypass circuit controlled by a bypass valve, this bypass valve generally being an "on-off" valve which is either completely opened to allow for the recirculation of a majority of the air output from the blower, or is alternatively completely closed to prevent any such recirculation of the air output from the blower. This bypassing arrangement has the advantage that the overall energy required to drive the blower is reduced, particularly when compared with systems where the control of the air output from the blower is achieved by throttling the output thereof.
However, at lower engine loads, the pressure drop in the bypass or recycling loop is typically higher than that through the engine. Hence, such a bypass arrangement will generally not satisfactorily control air flow to the engine at idle and low loads as the lower pressure drop through the engine than through the bypass circuit will typically result in more air than is required by the engine at such loads being delivered thereto. Accordingly, unless a slight vacuum or low pressure is created upstream of the blower to overcome the existing flow restriction in the bypass or recycling loop, more air than is required is still likely to be delivered to the engine at such lower loads.
Further, without such a restriction upstream of the blower, some difficulty may exist in regard to inputting a desired level of exhaust gas into the intake system for the purpose of exhaust emission control. In this regard and as is well known, it is in some circumstances desirable to have a high proportion of exhaust gas in the fuel and air mixture within the combustion chambers of the engine, particularly during low load operation, in order to achieve a required level of emission control.
It is therefore an object of the present invention to provide a method and apparatus for controlling the air flow to a scavenged engine that will enable the overall energy required to drive a blower supplying air thereto to be reduced and that will allow effective control of the air flow rate to the engine over the entire load range of the engine and in particular at idle and low to medium loads. It is a further object of the present invention that the air flow rate to the engine will be effectively controlled whilst the ability to provide effective exhaust gas recirculation to the engine, particularly at low and medium loads, will be improved or at least maintained.
With this object in view, there is provided a method of controlling the air supply to a scavenged internal combustion engine having a blower for supplying air thereto and bypass means for allowing a bypass air flow from the outlet side of the blower to the inlet side thereof, the method including regulating the bypass air flow through the bypass means to provide a variable rate of air flow therethrough and regulating the flow of ambient air to the blower to thereby control the pressure of the intake air supply to the blower.
Conveniently, the bypass air flow and the flow of ambient air to the blower are regulated to control the air supply to the engine at least when the engine is operating at idle and/or low loads.
Preferably, the flow of ambient air to the blower is also regulated to provide a variable rate of ambient air flow thereto.
The bypass air flow rate and the flow rat
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Bell Gregory Bruce
Malss Stephen Reinhard
Okonsky David A.
Orbital Engine Company (Australia) Pty. Limited
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