Supercharged internal combustion engine

A method of controlling the air supply to a scavenged internal combustion engine having a blower for suppling 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 and controlling a supply of recirculated exhaust gas introduced upstream of the blower by controlling the flow rate of ambient air to the blower such that a requisite pressure is generated upstream of the blower to thereby control the exhaust gas flow rate.

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 rate of ambient air to the blower are 
preferably independently controlled. 
These two controls ensure that the airflow to the engine can be suitably 
controlled for any load point of the engine so that the overall power 
requirements of the blower can be minimised. Furthermore, the combined 
effect of the above two controls enables the provision of a more 
favourable environment through which desired levels of exhaust gas may be 
recirculated through the engine. That is, the pressure of the intake air 
to the blower is able to be maintained at a level to achieve the required 
level of exhaust gas recirculation (EGR) from the engine exhaust system 
back into the air intake system, particularly at idle and low loads where 
such EGR is commonly used to control the exhaust emissions. This is 
primarily achieved by controlling the flow rate of ambient air to the 
blower, and to a lesser extent by controlling the bypass air flow rate, 
such that a low pressure is generated upstream of the blower resulting in 
a more favourable condition to exist for EGR. Still further, bypassing 
sufficient air from the outlet side of the blower relieves the load on the 
blower such that it is not delivering too much air at a load point at 
which the engine does not require the blower to be working near or at its 
maximum capacity. This in turn avoids undue overheating of the air 
delivered by the blower. 
Conveniently, a valve is provided to control the bypass rate of the air 
output from the blower, the valve being configured to provide for a 
variable rate of bypassed air. Conveniently, the bypass valve is 
controlled by an electronic control unit which receives inputs indicative 
of the operating conditions of the engine, for example, from an air flow 
meter measuring the ambient air flow to the engine. The control of the 
flow rate of ambient air to the blower is preferably controlled by a valve 
actuated in response to driver inputs such as by a throttle valve actuated 
by the accelerator or throttle pedal of a vehicle. However, other control 
arrangements for each valve are also envisaged. For example, both valves 
may be controlled by the electronic control unit wherein the bypass valve 
is primarily controlled on the basis of the ambient air flow as measured 
by an air flow meter and the ambient air valve is controlled by a mapped 
position in an appropriate look-up table which has throttle or pedal 
position as a main input thereto. Alternatively, this arrangement could be 
reversed wherein the bypass valve is controlled by the mapped position 
selected as a function of throttle or pedal position and the ambient air 
valve is controlled on the basis of the measured ambient air flow. 
The typical relationship of the positioning of the bypass valve and the 
ambient air valve at idle is such that approximately 90% of the air output 
from the blower is returned through the bypass to the inlet of the blower 
whilst the ambient air valve is substantially fully closed. It should be 
noted that the bypass valve at such a load condition is preferably only 
50% open so as to give good control of the air flow rate though the bypass 
duct and hence better overall engine air flow control. Under light load 
conditions, the bypass valve is conveniently as open as possible whilst 
still maintaining good air flow control to the engine and the ambient air 
valve is substantially fully closed, whilst at full or high load 
conditions, the bypass valve is typically fully closed and the ambient air 
valve is fully opened. The ambient air valve is configured so as to give 
minor control over the air flow control system as compared to the bypass 
valve and is essentially provided to create a restriction upstream of the 
blower for more positive air flow control by the bypass valve and to 
provide a more favourable condition which will enable a flow of exhaust 
gas as desired to a point upstream of the blower, in particular at idle 
and low loads. In this regard, the restriction provided typically 
contributes to the creation of a desirable low pressure upstream of the 
blower and immediately downstream of the ambient air valve. 
Further, it is envisaged that the relationship of the positioning of the 
bypass valve and the ambient air valve will enable the level or amount of 
EGR used for exhaust emission control to be varied as desired. That is, 
for various different arrangements of the bypass valve and ambient air 
valve positions, different flow rates of exhaust gas to the point 
immediately downstream of the ambient air valve are possible. For example, 
a certain combination of bypass and ambient air valve positioning will 
provide for a certain air flow rate through the bypass and for a certain 
resultant air flow rate to the blower. A second combination of bypass and 
ambient air valve positioning may also result in a similar resultant air 
flow rate to the blower but will typically provide for a different air 
flow rate through the bypass and through the ambient air valve. In the 
case where exhaust gas is input to the point immediately downstream of the 
ambient air valve and upstream of the point of communication of the bypass 
with the main air intake duct, a different low pressure will exist 
immediately downstream of the ambient air valve than did for the previous 
positions of the ambient air and bypass valves. Hence, even though the 
blower receives the same air flow rate as for the previous valve position 
settings, a different rate of exhaust gas is able to be delivered to the 
point upstream of the blower. In this regard, a manifold vacuum sensor may 
be arranged to be the primary input for controlling the bypass valve and 
the ambient air valve to ensure that a sufficiently low pressure or vacuum 
exists upstream of the blower for EGR purposes. 
It should be noted that typically, the ambient air valve will be configured 
such that when it is fully closed a minimum amount of ambient air will 
still be able to pass through the valve to enable effective and correct 
operation of the air flow control system. In particular, this minimum 
amount of air will typically be that required to minimise the low pressure 
or slight vacuum created on the engine side of the ambient air valve by 
the blower such that it is just sufficient to enable suitable air flow 
control for the engine and to create a favourable environment to enable a 
flow of exhaust gas to the engine via the upstream side of the blower, 
particularly at idle and low engine loads. This minimum amount of ambient 
air may, for example, conveniently be provided by the provision of one or 
more orifices or slits in the standard butterfly type valve used in such 
air intake systems or by providing a butterfly valve with a blade which 
when fully closed does not closely match the internal profile or perimeter 
of the duct in which it is located. Alternatively, the ambient air valve 
may simply be configured to not be able to fully close. The partial or 
slight minimisation of the low pressure produced on the engine side of the 
ambient air valve by the minimum amount of ambient air able to flow 
therethrough ensures that the blower is not operating inefficiently as it 
would if it were to operate against a near vacuum which would be the case 
if the ambient air valve was to completely prevent the flow of ambient air 
therethrough to the engine. 
There is further provided by the present invention, a blower scavenging 
arrangement for an internal combustion engine including a blower for 
supplying air to the engine, a bypass air control means for regulating a 
bypass air flow from the outlet side of the blower to the inlet side 
thereof to thereby provide a variable rate of bypass air flow, and an 
ambient air control means for regulating the flow rate of ambient air to 
the blower, wherein said regulation by said bypass air control means and 
said ambient air control means thereby controls the pressure of the intake 
air supply to the blower. 
Because the bypass air control means provides for a variable rate of air 
flow through a bypass circuit or loop, the bypass air control means is 
able to provide better control of the rate of flow of bypass air in 
contrast to certain prior art systems which simply provide for the bypass 
loop to be fully open or fully closed. Similarly, the ambient air control 
means is also preferably able to provide for a variable rate of flow of 
ambient air to the blower. 
Preferably, the bypass air control means and the ambient air control means 
are interactive to control the pressure of the intake air supply to the 
blower in response to engine operating conditions. 
Conveniently, the bypass air control means is controlled by an electronic 
control unit which receives inputs indicative of the operating conditions 
of the engine such as engine load. Typically, the ambient air control 
means for adjusting the ambient air flow is actuated in response to driver 
load demand such as would be indicated by vehicle throttle or pedal 
position. However, as previously indicated, other control arrangements for 
each valve are also envisaged. 
The above described method of and arrangement for controlling the air flow 
to and hence the operation of the blower ensures that a suitable amount of 
air is delivered to the engine at any load point over the entire operating 
regime of the engine, particularly at low and medium loads where the air 
requirements are not as high in comparison to high load operation. This 
minimises the overall power requirements of the blower. That is, by 
bypassing the output air via the bypass valve, the power consumption of 
the blower will be lower than when compared with, for example, an 
arrangement where the air output from the blower is merely throttled. 
Furthermore, the described method also ensures that effective exhaust gas 
recirculation can be achieved throughout the operating range of the 
engine, and particularly at idle and low load conditions. Further, the 
method also ensures that the blower is not unduly overloaded at any engine 
load point and does not unduly overheat, such as for example, when the 
ambient air valve is fully closed.

The engine 5 is a multi-cylinder reciprocating piston engine of generally 
conventional construction having exhaust ducts 6 communicating the engine 
cylinders with an exhaust pipe 7 via a catalytic exhaust treatment means 8 
of conventional construction. The combustion chamber of each cylinder 
communicates with the air inlet manifold 9 which distributes air to each 
combustion chamber in timed relation to the combustion cycle thereof. 
Whilst the present invention is described with respect to a multi-cylinder 
engine, it should be noted that it is equally applicable to single 
cylinder engines. Further, it is to be noted that the engine 5 as depicted 
in FIG. 1 is intended to represent a multi-cylinder two stroke cycle 
engine wherein the fuel is injected directly into the combustion chambers 
of the engine 5. However, the blower 10 and control system thereof is 
equally applicable to four stroke cycle engines or to an engine wherein 
the fuel is injected at a location close to or at the area of entry of the 
fuel to the respective cylinders of an engine and particularly to 
stratified charge or variable displacement engines. That is, the blower 
and control system therefor is not limited to engines wherein the fuel is 
delivered to the engine independently of the air supply. Equally, the 
invention is applicable to both spark-ignition and compression-ignition 
engines. 
The blower 10 is of the positive displacement type such as a Roots blower 
or the like. The blower 10 draws in air via the intake duct 11 which is 
connected to the ambient air duct 12 and the bypass duct 13. Between the 
ambient air and intake ducts 11 and 12 respectively is a control valve 14. 
A further control valve 15 is positioned in the bypass duct 13. The 
ambient air duct 12 receives air substantially at ambient pressure from an 
air filter box 16. 
The air flow from the ambient air duct 12 to the intake duct 11 is 
controlled by the valve 14 which is conveniently of the butterfly type, 
but which may be of any suitable construction. As illustrated, the valve 
14 is of the butterfly type and is arranged to be actuated by the driver 
such as via a throttle pedal 33. The valve 14 is constructed so that even 
when in the "closed" position, a restricted flow of air may pass from the 
ambient air duct 12 to the intake duct 11. This may be achieved in 
relation to the valve 14 as illustrated by the provision of apertures 18 
in a blade 19 of the butterfly valve 14. The apertures 18 are sized so 
that when the engine 5 is operating at idle, the air flow to the blower 10 
is sufficient for the engine 5 to operate, and to also draw exhaust gas 
via EGR duct 21 and EGR control valve 22 from the engine exhaust system to 
be recirculated into the engine combustion chambers at a desired rate when 
required. The apertures 18 may alternatively be in the form of orifices or 
slits. An appropriate cooling means or heat exchanger 23 may be provided 
to enable cooling of the exhaust gas prior to being input to the engine 5 
via the intake duct 11. 
The provision of apertures 18 ensures that the low pressure or slight 
vacuum created on the engine side of the valve 14 within the intake duct 
11 is minimized to enable control of both air flow to the blower 10 and 
exhaust gas flow into the intake duct 11. In particular, the size of the 
apertures 18 should be selected such that the minimization of the slight 
vacuum on the engine side of the valve 14 is so as to reduce the pressure 
drop within the bypass duct 13 to an acceptable level such that air will 
be enticed to flow into the bypass duct 13 and not the engine 5 when the 
bypass valve 15 is opened. The total area of the apertures 18 may be up to 
40% of the maximum flow area through the valve 14 after which too much air 
is likely to flow into the intake duct 11 to provide a suitable low 
pressure in this region. The minimum area may be 0% of the maximum flow 
area, however, as previously mentioned, this would probably cause the 
blower 10 to operate inefficiently and possibly overheat. Accordingly, the 
minimum area should be sufficient to provide a suitable minimum air flow 
into the intake duct 11. This will ensure that the blower 10 does not 
unduly overheat. 
The bypass duct 13 has incorporated therein a bypass control valve 15, 
which may be of the butterfly type, and which is operable to control the 
rate of flow of air bypassed from the downstream or outlet side of the 
blower 10 to the upstream or inlet side thereof. The control valve 15 
comprises a blade 20 and is constructed so that in the closed position, 
there is substantially no flow through the bypass duct 13. 
The bypass valve 15 is automatically controlled by an electronic control 
unit (ECU) 30 which receives inputs 31 related to at least the ambient air 
flow into the engine 5, engine speed, throttle pedal position (load) and 
engine temperature. The position of the butterfly valve 14 is varied in 
response to the position of the accelerator pedal 33 via a cable 34 in a 
known manner. The position of the butterfly valve 14 is therefore a 
function of the load on the engine 5 and this position can also be 
determined, typically by feedback means to the ECU 30, to provide a 
further input thereto related to the load on the engine 5. The air flow is 
measured by an air flow meter 32 mounted in the ambient air duct 12 
immediately downstream of the air filter box 16. The bypass valve 15 is 
principally controlled in dependence on the measured ambient air flow as 
measured by the air flow meter 32. The ECU 30 is programmed to close the 
valve 15 when the engine 5 is operating in the medium to high load range 
as the rate of air supply required by the engine 5 is high and is able to 
be supplied by the blower 10 without the need to bypass any of the output 
air therefrom. At these conditions, the full air output of the blower 10 
is typically required by the engine 5. Further, the resulting 
sub-atmospheric pressure in the intake duct 11 is sufficiently high to 
effectively provide the required level of EGR into the respective 
combustion chambers of the engine 5. 
However, when the engine 5 is operating at low loads or at idle, the ECU 30 
is programmed to open the bypass valve 15 to return air from the high 
pressure or delivery side of the blower 10 to the intake air duct 11 to be 
recycled through the blower 10. At such low loads, the valve 14 is 
typically substantially closed and air control to the blower 10 and hence 
engine 5 is primarily via bypass valve 15. This bypassing of air maintains 
the blower 10 operating with a full supply of air, while also not having 
an excess of air being delivered to the engine 5. That is, the ambient air 
valve 14 essentially serves to create a low pressure or slight vacuum 
upstream of the blower 10 which creates a condition where it is more 
favourable for air to pass through the bypass duct 13 as opposed to 
passing through the engine 5. 
Further and as previously alluded to hereinbefore, the positioning of the 
ambient air valve 14 and the bypass valve 15 may be utilised to provide 
for different levels of exhaust gas to the engine 5 via the EGR means. 
That is, for similar air flow rates to the blower 10, different levels of 
exhaust gas can be drawn into the intake duct 11 for subsequent delivery 
to the engine 5. This can be deduced from a consideration of FIG. 1 
wherein the EGR duct 21 communicates with the intake duct 11 upstream of 
the point of communication of the bypass duct 13 with the intake duct 11. 
Accordingly, from different position settings of the valves 14 and 15 
which provide for a similar air flow rate to the blower 10, a different 
level of low pressure will exist immediately downstream of the ambient air 
valve 14. Hence, different levels of EGR are able to be used for emission 
control. 
Modifications and variations as could be made by a skilled addressee are 
deemed to be within the scope of the present invention. For example, the 
ambient air valve 14 may be spring loaded in a similar manner to a vehicle 
choke and may further include a mechanism to retain the blade 19 thereof 
in the fully opened position at wide open throttle or full load only. This 
may be achieved for instance by a cable connecting the blade 20 of the 
bypass valve 15 with the blade 19 of the ambient air valve 14 and a lost 
motion mechanism being incorporated on the blade 20. In operation, at idle 
and low load operation, the blade 19 is in the fully closed position 
whilst the blade 20 is typically as open as possible. As the engine 5 goes 
from low to medium and then to high load operation, the blade 20 begins to 
move to the fully closed position. Initial movement in this regard has no 
effect on the blade 19 as the lost motion mechanism takes up this 
movement. Further movement however, typically corresponding to the engine 
5 moving into high load operation, causes the blade 20 to move to the 
completely closed position and to also move the blade 19 via the 
connecting cable into the fully opened position. Other mechanical or 
hybrid mechanical/electronic arrangements for actuating the air valves 14 
and 15, whether independently or jointly, are deemed to be within the 
scope of the present invention.