GB2439741A

GB2439741A - Engine load control system for regulating the power output of an i.c. engine

Info

Publication number: GB2439741A
Application number: GB0613090A
Authority: GB
Inventors: Thomas Tsoi Hei Ma
Original assignee: Individual
Current assignee: Individual
Priority date: 2006-07-01
Filing date: 2006-07-01
Publication date: 2008-01-09
Also published as: GB0613090D0

Abstract

A load control system for regulating the power output of a reciprocating internal combustion engine comprises the engine with exhaust and intake ducts and a rotary gas exchanger 10,14 connected by a first set of entry and exit ducts 22,22' to the engine exhaust duct and by a second set of entry and exit ducts 24,24' to the engine intake air duct. One branch of a bifurcated exhaust pipe 30 is connected to the exhaust side of the rotary gas exchanger 10,14 and the other branch 32 bypasses the rotary gas exchanger. A diverter valve 36 is provided at the bifurcated junction of the exhaust pipe 30 for proportioning the flow of exhaust gases between the two branches. The rotary gas exchanger 10,14 is rotated at a sufficient speed such that all the exhaust flow entering the entry duct 22 of the first set of ducts is transferred to the intake flow leaving the exit duct 24' of the second set of ducts, and the diverter valve 36 is connected for movement directly or indirectly with the accelerator pedal 56 of a vehicle and is controlled by the driver of the vehicle as the primary load control means, instead of the conventional intake throttle valve.

Description

I

ENGINE LOAD CONTROL SYSTEM

Field of the invention

The present invention relates to a load control system in an internal combustion engine, for regulating the air supply to the engine to support fuel combustion in response to a load demand.

Background of the invention

Spark ignition (SI) engines must operate within tight fuel/air ratio limits where fuel is varied in narrow proportion with air flow whilst the air flow is varied widely in response to engine load by throttling the flow in order to reduce the air pressure and the air density. This load control concept is commonly called "drive-by-air" because the primary control means responding to a load demand from the driver of a vehicle is the air throttle regulating the air flow.

In contrast, compression ignition (CI) engines can operate over much wider fuel/air ratio limits so that fuel may be varied widely in response to engine load while the air flow to the engine is essentially unregulated, i.e. unthrottled. This load control concept is commonly called "drive-by-fuel" because the primary control means responding to a load demand from the driver of a vehicle is the fuel throttle regulating the fuel flow.

At maximum and high engine loads, the difference between the above two load control concepts is small because the air density is near ambient and the fuel/air ratio is close to the stoichiometric fuel/air ratio in both cases.

At low and minimum engine loads on the other hand, the difference between the above two load concepts becomes very large where the SI engine runs at very low air density and in a fuel/air ratio region not too far from the stoichiometric fuel/air ratio, while the CI engine runs at very low fuel/air ratio and near ambient air density. This accounts for the major difference in fuel efficiency typically observed between the SI engine and the CI engine at low loads where the SI engine suffers increasing pumping losses due to increased throttling of the air flow while the CI engine remains unthrottled.

In order to improve the fuel efficiency of the SI engine at low loads, there is strong incentive to introduce new and novel load control means for the SI engine where the air flow to the engine could be varied in response to load demands without having to throttle the air flow. A known approach is "drive-by-exhaust" where the air breathing capacity of the engine is indirectly varied by partially filling the engine cylinder with exhaust gases in response to load demand. In this case, air is drawn into the engine unthrottled, but the air flow to the engine is reduced at low loads by increasing the quantity of inert fill gases already in the engine cylinder. However, whilst this proposed concept is known, there is as yet no practical system which could put the concept into practice.

Summary of the invention

According to the present invention, there is provided a load control system for regulating the power output of a reciprocating internal combustion engine, comprising the engine with exhaust and intake ducts, a rotary gas exchanger connected by a first set of entry and exit ducts forming part of the engine exhaust duct for exhaust gas flow from the engine through the gas exchanger to the ambient atmosphere and by a second set of entry and exit ducts forming part of the engine intake duct for intake air flow from the ambient atmosphere through the gas exchanger to the engine, a bifurcated exhaust pipe coming from the engine having a first branch connected to the first set of entry and exit ducts and a second branch bypassing the first set of entry and exit ducts, and a diverter valve at the bifurcated junction of the exhaust pipe for proportioning the flow of exhaust gases between the two branches, characterised in that the rotary gas exchanger is rotated at a sufficient speed such that all the exhaust flow entering the entry duct of the first set of ducts is transferred to the intake flow leaving the exit duct of the second set of ducts, and the diverter valve is connected for movement directly or indirectly with the accelerator pedal of a vehicle and is controlled by the driver of the vehicle.

The diverter valve may be connected for movement via mechanical linkages with the accelerator pedal.

Alternatively, it may be connected to an actuator which moves in response to a load demand signal from the accelerator pedal.

In the invention, the driver of the vehicle has direct command of the power output of the engine by operating the diverter valve as the primary load control means, regulating the quantity of exhaust gases transferred to the engine intake duct in inverse proportion to engine load, thereby reducing the quantity of ambient air that could be drawn into the engine to support fuel combustion in proportion to engine load. In short, the proposed system operates according to the load control concept of drive-by-exhaust.

The invention is an extension of Patent Application GB0609674.7 for an EGR dispensing system in an internal combustion engine. In GB0609674.7 substantial quantities of exhaust gases may be transferred without relying on an EGR pipe to mix with the engine intake air as a means for reducing NOx emissions during combustion. Any quantity of EGR may be transferred as required which is calibrated over a range of engine speed and load operating conditions and is then controlled according to an EGR demand signal derived from the calibration map at each speed and load operating point, where the operating point has already been set by a separate load control system based on drive-by-air or drive-by-fuel. The present invention takes advantage of the unique and highly flexible gas exchange characteristics of the EGR dispensing system of GB0609674.7 but changes the control priority to drive-by-exhaust so that the quantity of exhaust gases transferred to the engine intake air stream is no longer controlled by the EGR calibration, but is controlled in direct response to a load demand from the driver of the vehicle.

Preferably the rotary gas exchanger is driven at a constant speed which is sufficiently high for the diverter valve to control the full range of speeds and loads of the engine according to the load control concept of drive-by-exhaust. Alternatively it may be driven at a variable speed in proportion with engine speed, and the speed is sufficiently high for the diverter valve to control the full range of loads of the engine at each engine speed.

Thus the driver of the vehicle controls the engine along a load continuum which follows the inverse of the exhaust gas exchange continuum regulated by the diverter valve and there is no need to throttle the intake air flow of the engine to reduce load. Any specific demand for EGR using the rotary gas exchanger will be ignored in this load control strategy of drive-by-exhaust, which overrides any EGR control strategy described in GB0609674.7.

Of course the drive-by-exhaust strategy will have an effect on combustion and exhaust emissions similar to that with EGR but this will be a passive consequence of the load control because load control takes first priority. This may cause difficulty in a conventional spark ignition engine which cannot tolerate high levels of exhaust gas dilution, but the new generation of combined spark ignition and controlled auto-ignition engine will be able to take advantage of the invention by running in the spark ignition mode at high loads when the exhaust gas dilution is low, and going through smooth transitions to the controlled auto-ignition mode and the spark-assisted auto-ignition mode at low loads with higher exhaust gas dilution, while following an exhaust gas exchange continuum controlled by the driver of the vehicle by means of the diverter valve.

Brief description of the drawings

The invention will now be described further by way of example with reference to the accompanying drawings in which Figure 1 is a schematic view of a system for dispensing EGR according to GB0609674.7, Figure la is a schematic view of an alternative system for dispensing EGR according to GB0609674.7, Figure 2 is a schematic axial cross-section of the EGR dispensing system of Figure 1, adapted to provide a load control system of the present invention, Figure 2a is a developed view of the rotary gas exchanger in the load control system of Figure 2, and Figure 3 is a schematic lateral cross-section of the rotary gas exchanger of Figure 2.

Detailed description of the preferred embodiment

Referring to the EGR dispensing system described in GB0609674.7, Figure 1 (also Figure la) shows a reciprocating internal combustion engine 100 with intake manifold 114 admitting intake air from the ambient atmosphere through an air blower 124 and a housing 14 containing a flow guiding matrix 10 to the engine cylinders along an intake duct comprising elements 124, 24, 14, 10, 24t, 114 in the flow direction indicated by arrows, and exhaust manifold 112 discharging exhaust gases from the engine cylinders through the housing 14 and matrix 10 to the ambient atmosphere via an exhaust turbine 122 along an exhaust duct comprising elements 112, 22, 14, 10, 22', 122 in the flow direction also indicated by arrows. The matrix 10 is supported for rotation within the housing 14 with good seals at each end of the matrix 10 butting against the end walls of the housing 14.

The above configuration of engine exhaust and intake ducts 112, 22, 22' and 24, 24', 114 respectively, connected directly to separate parts of a rotary gas exchanger 14, 10 (with or without the turbo-charger 122, 124) constitutes a system for dispensing EGR with the conspicuous absence of an EGR pipe connecting between the exhaust duct and the intake duct of the engine as in a conventional EGR system. EGR is delivered from the exhaust duct to the intake duct, not by a connecting flow, but by transport of discrete packages of exhaust gases trapped within the flow guiding passages of the matrix from one part of the housing to another part of the housing as the matrix rotates. When the matrix 10 is stationary, no package is transferred and the exhaust and intake streams will simply flow past one another along separate parts of the matrix 10. When the matrix 10 is rotated at a variable speed driven by an electric motor or by the engine drive train (not shown), discrete packages of exhaust gases will be intercepted from the exhaust gas stream 22, 22', trapped locally within part of the matrix 10, carried across to the intake air stream 24, 24' as the matrix rotates, and deposited into the intake air stream.

Thus EGR is dispensed according to the rotating speed of the matrix and this could take place at any exhaust or intake pressure, not relying on delta-P to drive a connecting flow as in a conventional EGR system. Very large quantities of EGR gases may to transferred to the engine intake air without increasing the engine exhaust back pressure or decreasing the engine intake air induction pressure, thus maintaining high volumetric efficiency and low pumping work in the engine.

Figures 2 and 3 show a rotating matrix 10 of thin wall structure forming a plurality of flow passages aligned substantially parallel with the axis of rotation of the matrix for guiding a flow of gases from one exposed end of the matrix to the other exposed end of the matrix. A flow passage element 20 fed with an advancing column of exhaust gases is highlighted as example in Figure 2. The matrix 10 is contained within a housing 14 which seals the ends of the unconnected part of the matrix and supports the matrix for rotation about an axis 12 driven by a variable speed motor or by the engine drive train (not shown). This assembly constitutes a rotary gas exchanger and is a key part of the EGR dispensing system of Figure 1 (also Figure la) with like components annotated by the same numerals.

The housing 14 has two sets of entry and exits ducts labelled generally 22, 24 in Figure 3. A first set of entry and exit ducts 22, 22' respectively in the housing 14 connects an engine exhaust gas stream from the engine exhaust system (112) through the housing 14 and matrix 10 to the ambient atmosphere. A second set of entry and exit ducts 24, 24' respectively in the housing 14 connects an engine intake air stream from the ambient atmosphere through the housing 14 and matrix 10 to the engine intake system (114). In the invention, the respective sets of ducts are disposed in the housing 14 with the entry and exit ducts of each set opposite one another facing the ends of the rotating matrix 10 and positioned eccentrically to the axis of rotation of the matrix 10 apart from and in rotational sequence with the other set of entry and exit ducts. Each set of entry and exit ducts in the housing 14 can only make through flow connection via a passing group of flow passages in the matrix 10 which are instantaneously aligned with the flow cross-sections of the said ducts as the matrix rotates, such that the passing flow passages are sequentially exposed to the exhaust gas stream in the ducts 22, 22' and then to the intake air stream in the ducts 24, 24', thereby intercepting and isolating a quantity of exhaust gases trapped within the lengths of the passing flow passages in the matrix 10 from the exhaust gas stream in the ducts 22, 22', and carrying and depositing the said exhaust gases into the intake air stream in the ducts 24, 24' as the matrix rotates. For example the flow passage element 20 containing a trapped package of a column of exhaust gases is carried laterally from the duct 22 to the duct 24 along a locus indicated by the rotation arrow in Figure 3.

A very small minimum clearance is maintained between the end faces of the rotating matrix 10 butting with the end walls of the housing 14 in order to stop to all intents and purposes any gas leakage at the perimeters of the entry and exit ducts 22, 22' and 24, 24', and to maintain different gas pressures within each set of duct5. The walls of the flow passages in the matrix 10 may be constructed of thin foils of stainless steel or extruded ceramic in a honeycomb f low guiding structure. The walls may also be porous allowing seepage of gases from one passage to an adjacent passage while guiding a flow of gases from one exposed end of the matrix to the other exposed end of the matrix.

Figure 2 also shows a bifurcated exhaust pipe 30 coming from the engine exhaust system (112) with one branch connected to the entry and exit ducts 22, 22' and another branch 32 bypassing the entry and exit ducts 22, 22'. A diverter valve 36 is provided at the bifurcated junction for proportioning the flow of exhaust gases between the two branches. In the position shown, the diverter valve 36 diverts substantially the full flow of exhaust gases towards the duct 22. When the valve 36 is moved in the direction of the arrow, a smaller proportion of the exhaust gas flow will be diverted to the duct 22.

This enables the dispensing of EGR to be controlled by diverting a predetermined proportion of the engine exhaust gas stream to the entry duct 22 and rotating the matrix 10 at a sufficient speed to transfer all the diverted gases to the intake air stream out of the exit duct 24' so that the diverter valve 36 sets the quantity of EGR. Of course when no EGR is required, the diverter valve 36 may be moved to divert all the exhaust gases to the branch 32 completely bypassing the housing 14.

It should be noted that an inherent feature of the system in Figure 1 (also Figure la) is that the exhaust gas stream leaving the exit duct 22' will have ambient air carried across and deposited into it in the same way as the intake air stream leaving the exit duct 24' will have EGR gases carried across and deposited into it as the matrix 10 rotates. In Figure 2, because of the sufficiently high rotating speed of the matrix 10, the gas stream discharged from the exit duct 22' will be entirely air and this may be released immediately to the ambient atmosphere as shown by the stub pipe 22'.

The above operation is better illustrated in Figure 2a which is a developed view of the rotating matrix shown in Figure 2 moving in the direction of the dashed arrows and carrying the flow passages past the entry and exit ducts 22, 22' which take the exhaust gases from the engine, and then past the entry and exit ducts 24, 24' which take the intake air to the engine. Following one flow passage element moving from left to right, it has initially a column of air trapped between the sealed ends. When this flow passage element is carried past the cross-section of the entry and exit ducts 22, 22', exhaust gases (shown shaded) will enter the passage as an advancing column pushing the air content out of the passage. The extent by which the exhaust gas column fills the length of the flow passage element would depend on the speed of the gas flow along the element and -10 -time available for the element to traverse laterally the cross-section of the entry and exit ducts 22, 22'. In Figure 2a where the speed of rotation of the matrix 10 is sufficiently high in relation to the speed of the gas flow, there is no breakthrough of the exhaust gas column reaching the exit duct 22' in the time available so that the gases leaving the exit duct 22' will be entirely air.

When the flow passage element is carried completely past the cross-section of the entry and exit ducts 22, 22', the column is sealed again at both ends and transported laterally until it reaches the cross-section of the entry and exit ducts 24, 24' where intake air will enter the passage as an advancing column and push the exhaust gas content out of the flow passage element into the exit duct 24'. These exhaust gases would join with more air breaking through the flow passage element and reaching the exit duct 24' in the time available according to the speed of rotation of the matrix 10, and the mixture is delivered to the engine as EGR mixed with intake air. Thus EGR is dispensed by the dispensing system comprising the engine exhaust and intake ducts connected directly to separate parts of a rotary gas exchanger, without relying on flow along an EGR pipe.

It should be noted that whilst Figure 2a shows the exhaust gas stream and intake air stream arranged in counter-flow directions as in Figure 1, the EGR dispensing system will operate to similar effectiveness when the two streams are arranged in the same flow direction as shown in Figure la.

Having described the EGR dispensing system of GB0609674.7, Figure 2 shows the adaptation made to the system to create an engine load control system by connecting the diverter valve 36 via mechanical linkages 46 for movement with the accelerator pedal 56 of a vehicle controlled by the driver of the vehicle. Alternatively, the -11 -diverter valve 36 may be connected to an actuator (not shown) which moves in response to a load demand signal from the accelerator pedal.

Thus the driver of the vehicle has direct command of the power output of the engine by operating the diverter valve 36 as the primary load control means, regulating the quantity of exhaust gases transferred to the engine intake duct in inverse proportion to engine load, thereby reducing the quantity of ambient air that could be drawn into the engine to support fuel combustion in proportion to engine load. In short, the system operates according to the load control concept of drive-by-exhaust.

Preferably the rotary gas exchanger 14, 10 is driven at a constant speed which is sufficiently high for the diverter valve 36 to control the full range of speeds and loads of the engine according to the load control concept of drive-by-exhaust. Alternatively it may be driven at a variable speed in proportion with engine speed, and the speed is sufficiently high for the diverter valve 36 to control the full range of loads of the engine at each engine speed.

Thus the driver of the vehicle controls the engine along a load continuum which follows the inverse of the exhaust gas exchange continuum regulated by the diverter valve 36 and there is no need to throttle the intake air flow of the engine to reduce load. Any specific demand for EGR using the rotary gas exchanger 14, 10 will be ignored in this load control strategy of drive-by-exhaust, which overrides any EGR control strategy described in GB0609674.7.

Of course the drive-by-exhaust strategy will have an effect on combustion and exhaust emissions similar to that with EGR but this will be a passive consequence of the load control because load control takes first priority. This may cause difficulty in a conventional spark ignition engine -12 -which cannot tolerate high levels of exhaust gas dilution, but the new generation of combined spark ignition and controlled autoignition engine will be able to take advantage of the invention by running in the spark ignition mode at high loads when the exhaust gas dilution is low, and going through smooth transitions to the controlled auto-ignition mode and the spark-assisted auto-ignition mode at low loads with higher exhaust gas dilution, while following an exhaust gas exchange continuum controlled by the driver of the vehicle by means of the diverter valve 36.

Claims

-13 -

CLAIMS

1. A load control system for regulating the power output of a reciprocating internal combustion engine, comprising the engine with exhaust and intake ducts, a rotary gas exchanger connected by a first set of entry and exit ducts forming part of the engine exhaust duct for exhaust gas flow from the engine through the gas exchanger to the ambient atmosphere and by a second set of entry and exit ducts forming part of the engine intake duct for intake air flow from the ambient atmosphere through the gas exchanger to the engine, a bifurcated exhaust pipe coming from the engine having a first branch connected to the first set of entry and exit ducts and a second branch bypassing the first set of entry and exit ducts, and a diverter valve at the bifurcated junction of the exhaust pipe for proportioning the flow of exhaust gases between the two branches, characterised in that the rotary gas exchanger is rotated at a sufficient speed such that all the exhaust flow entering the entry duct of the first set of ducts is transferred to the intake flow leaving the exit duct of the second set of ducts, and the diverter valve is connected for movement directly or indirectly with the accelerator pedal of a vehicle and is controlled by the driver of the vehicle.

2. A load control system as claimed in claim 1, wherein the diverter valve serves as the primary load control means for the engine in response to a load demand from the driver of the vehicle, regulating the quantity of exhaust gases transferred to the engine intake duct in inverse proportion to engine load, thereby reducing the quantity of ambient air that could be drawn into the engine to support fuel combustion in proportion to engine load.

3. A load control system as claimed in claim 1, wherein the diverter valve is connected for movement by mechanical linkages with the accelerator pedal.

-14 - 4. A load control system as claimed in claim 1, wherein the diverter valve is connected to an actuator which moves in response to a load demand signal from the accelerator pedal.

5. A load control system as claimed in any preceding claim, wherein the rotary gas exchanger is driven at a constant speed which is sufficiently high for the diverter valve to control the full range of speeds and loads of the engine.

6. A load control system as claimed in any one of claims 1 to 4, wherein the rotary gas exchanger is driven at a variable speed in proportion with engine speed, and the speed is sufficiently high for the diverter valve to control the full range of loads of the engine at each engine speed.

7. A load control system as claimed in any preceding claim, used for load control in a combined spark ignition and controlled auto-ignition internal combustion engine.