COMPRESSOR INLET SYSTEMS

Abstract: An internal combustion engine includes a compressor (23) to supply pressurised gas to effect injection of fuel for combustion in the engine. An intake system (17, 18, 19) includes a throttling assembly (19) to control the flow of air through the intake system. A gas inlet port to the compressor (23) is connected (31) to the air intake system (17, 18, 19) downstream of the throttling assembly (19). This lowers the pressure at the inlet port of the compressor (23) to below ambient air pressure. A method of operating an internal combustion engine of this type includes the step of lowering the pressure at the inlet port to the compressor (23) to below ambient air pressure.

Description: COMPRESSOR INLET SYSTEMS Field of the Invention This invention relates to internal combustion engines of the kind which utilise an air compressor to supply air to effect injection of metered quantities of fuel for combustion in the engine. Background Art Fuel systems for engines of this type are commonly known as dual fluid or air-assisted fuel injection systems and typically include separate fuel metering and fuel delivery devices. The fuel delivery or injection device is generally connected to a source of compressed air such as an air rail arranged to receive pressurized gas from an air compressor. Typically fuel which is metered into the injection device is subsequently delivered directly into a combustion chamber of the engine entrained in gas and in a highly atomised form. Such a dual fluid fuel injection system is described in the Applicant's United States Patent No. RE 36,768 and the Applicant's International Patent Application No. WO 99/28621 , the contents of which are hereby incorporated by cross reference. In internal combustion engines of this type, the inlet to the compressor can in certain applications be used to purge vapour from the vapour separator or "carbon canister" used to treat vapour vented from the fuel tank. An arrangement of this type is described in the Applicant's United States Patent No. 5,245,974, the contents of which are hereby incorporated by reference. In that patent, the inlet port of the compressor is arranged so that at least part of the air taken in by the compressor is drawn through that part of the vapour separator in which fuel vapour from the fuel tank, and/or fuel system in general, is accumulated so as to extract that fuel vapour. The fuel vapour is thus drawn through the compressor and delivered into the engine together with the metered quantities of fuel by the injection device. Whilst this system has proved successful, in certain applications its performance is limited by the performance of the compressor at low engine speed and particularly at idle. More particularly, the compressor is normally designed to provide an appropriate level of compressed air to the fuel injection system over the entire operating range of the engine. Consequently, it produces its highest volume of air output at higher engine operating speeds. At idle, the compressor is required to produce a relatively lesser volume of air output. At this lower operating level, the ability of the compressor to draw a sufficient volume of air and/or fuel vapour from the carbon canister may be limited and moreover may tend to fluctuate or pulsate. Further, the amount of purge capacity available is related to the required volume of the vapour separator. However, it is desirable to provide as small a volume for the separator or canister as possible to conserve space in the engine bay. Still further, such vapour purge arrangements are required to possess satisfactory high mileage durability characteristics. Disclosure of the Invention It is an object of this invention to provide an internal combustion engine having an air compressor to supply air to effect injection of the fuel for combustion in the engine which provides a more uniform and higher level of suction at the compressor inlet at low engine speeds without requiring a change in the compressor design. Accordingly, in one aspect this invention provides an internal combustion engine including a compressed gas supply means to supply pressurised gas to effect injection of fuel for combustion in the engine, an intake system for the supply of combustion air to the engine including a throttling assembly to control the flow of air through the intake system, a gas inlet port of said compressed gas supply means being connected with said air intake system downstream of the throttling assembly to lower the pressure at the inlet port of the compressed gas supply means to below ambient air pressure. Preferably, the compressed gas supply means is an air compressor which supplies pressurized air to effect the injection of metered quantities of fuel to the engine. The compressed gas supply means can also for example be a device operating from pressure generated in the operation of the internal combustion engine. In one form some of the pressure generated in a cylinder during a compression stroke may be utilised directly or used to drive a compressing system. An accumulator can be used for storage of the compressed gas. In the case of a scavenged two stroke engine, the crankcase pressure may be similarly utilised. In another aspect this invention provides a method of operating an internal combustion engine including a gas compressor having an inlet port, the compressor arranged to assist in the injection of fuel for combustion in the engine and an intake supply system for the supply of combustion air to the engine including a throttling assembly to control the flow of air through the intake system, said method including the step of lowering the pressure at said inlet port to below ambient air pressure by connecting said inlet port with said intake system downstream of the throttling assembly. Preferably, the gas inlet part of the compressor is also connected to the intake system upstream of the throttling assembly and the flow capacities of the upstream and downstream connections are selected to achieve a predetermined pressure at the inlet port of the compressor under certain engine operating conditions. In accordance with one form of the invention, the connections to the upstream and downstream sides of the throttling assembly have flow capacities determined by selected respective aperture sizes. The aperture sizes can be selected so as to provide for an appropriate pressure level at the inlet port of the compressor over the operating range of the engine. That is, the flow capacities can be fixed at a selected level for a particular engine compressor system. The upstream and downstream connections are preferably immediately adjacent a throttle element in the throttle body. This can be achieved by the connections being in the throttle body or in the intake system immediately adjacent the throttle body. In other variations of the invention it is possible to use valves in or at the downstream and/or upstream connections to control the respective flow capacities. These valves may be arranged to provide a variable flow capacity or may simply be of an on or off type. Accordingly, such an arrangement may offer greater control of the system such that in some applications, both the upstream and downstream connections may generally be open, but the upstream connection may be restricted or closed during idle or low speed operation. Further, at high speed operation, the upstream connection might be opened or given increased volume. Still further, in some applications, it may also be desirable to close the downstream connection at higher engine speeds. It is also envisaged that the closing or adjustment of flow capacity of either or both of the connections may be by a mechanical arrangement operated in conjunction with a throttle butterfly. Further, in one possible construction, a throttle butterfly may be used to physically restrict the upstream connection. In accordance with the present invention, the pressure reduction at the inlet port of the compressor is preferably of the order of about 3.5 kPa at engine idle. It has been found that this level of pressure reduction can be achieved with a relatively low level of bypass at the throttling assembly as is constituted by the downstream connection. Further, as the amount of bypass at the throttling assembly may have an effect on throttle control at engine idle conditions, it is preferred that the amount of bypass is not substantially greater than around 2 kg per hour, however, this is of course engine capacity dependent. The present invention has primarily been developed to provide an appropriate source of suction or depression to purge fuel vapour from a carbon canister or vapour separator receiving fuel vapours from the fuel tank and/or fuel system of an internal combustion engine installation. It is however also applicable to other applications where a required and constant level of suction may be required at low engine speeds. For example, the present invention may also have applicability in regard to purging any blow-by gases which may accumulate in the crankcase of a four-stroke engine, aspects of which are discussed in the Applicant's International Patent Application No. WO 99/42711 , the contents of which are hereby incorporated by reference. Conveniently, the aperture connecting the downstream side of the throttling assembly to the inlet of the compressor is sized and located so as to be the primary aperture responsible for the creation of a lower than ambient air pressure at the inlet. That is, this aperture is the main cause of a reduction in air pressure existing at the inlet of the compressor which can be used to draw fuel vapour from the vapour separator. Conveniently, the aperture connecting the upstream side of the throttling assembly to the inlet of the compressor is sized and located so as to be the primary aperture responsible for the maintenance of a stable air flow to the compressor. Hence, a vacuum created at the inlet to the compressor by virtue of the connection downstream of the throttling assembly is used to control the pressure at the inlet of the compressor such that the fuel vapour held in the carbon canister may be delivered to the engine by way of the compressed air supply to the fuel injection system of the engine. Further, the compressor is still able to provide a stable source of pressurized air to the fuel injection system by virtue of the stable flow of air drawn by the compressor primarily through the connection upstream of the throttling assembly. It will be apparent that the primary advantage of the present invention is achieved by effectively reducing the "base" pressure from which the compressor operates at least during idle or low speeds. In the preferred form of the invention, the system can be designed so as to not significantly reduce the high speed capacity of the compressor which is critical to proper operation of the fuel injection system. One embodiment of the invention will now be described, by way of example only, in accordance with the accompanying drawings. Brief Description of the Drawings Figure 1 is a diagrammatic layout of a prior art fuel vapour control and compressed air assisted fuel system; Figure 2 is a diagrammatic layout of modifications to the vapour control and compressed air assisted fuel system in accordance with an embodiment of the present invention; Figure 3 is a diagrammatic layout similar to Figure 2 showing another embodiment of the present invention; Figure 4 is a diagrammatic layout similar to Figure 2 showing a further embodiment of the present invention; and Figure 5 is a more detailed schematic representation of the vapour control and compressed air assisted fuel system shown partly in Figure 2. Best Modes for Carrying out the Invention The present invention is applicable to any internal combustion engine, including those operating according to the 2 or 4 stroke cycle principle, which utilises an air compressor to supply air to effect injection of the fuel for combustion in the engine. As mentioned above, an engine of this type is described for example in the Applicant's United States Patent No. RE 36,768. In engines of this type, a significant amount of unused fuel may be returned from the fuel injection system to a fuel tank during engine operation. During such recirculation, this fuel is inevitably heated and as a result may have a greater heat input to the fuel tank relative to conventional engines. Consequently, the vapour produced by the fuel system may in certain applications be higher leading to a higher purge requirement for the fuel vapour separating system. Figure 1 shows one prior art vapour control arrangement which utilises a fuel vapour separator 10 of a conventional construction having a filter medium 11 of activated carbon and is conventionally referred to in the automotive industry as a "carbon canister". A vapour space 12 in a fuel tank 13 communicates via a conduit 14 to the input side of the separator 10. A check valve 15 located in the conduit 14 is set so as to open and permit a flow of vapour from the fuel tank 13 to the separator 10 when the pressure of the fuel vapour in the fuel tank 13 is more than a predetermined amount, such as for example 10 kPa above the pressure in the separator 10. The outlet side of the separator 10 communicates via a conduit 16 with the air induction passage 17 of an engine downstream of the conventional air box 18 and upstream of a throttle unit 19 through which air is drawn into the air induction system of the engine for combustion when the engine is in operation. Thus when the engine is in operation and the pressure in the vapour space 12 in the fuel tank 13 is sufficiently high, vapour will pass from the fuel tank 13 through the separator 10 where the fuel in the vapour will be absorbed by the activated carbon and the treated air will pass into the air induction passage 17. Whilst the engine is running, the air which enters the air induction passage 17 from the separator 10 will form part of the air carried into the engine through the air induction system 17. A conduit 20 connects the separator 10 with a conduit 21 at venturi 22. Duct 21 connects the engine air box 18 with a compressor 23. Venturi 22 results in a sub- atmospheric pressure being created as the air passes therethrough from the air box 18 to compressor 23. This reduced pressure is selectively applied to the separator 10 via conduit 20 by way of a control valve 24 which may be in the form of a solenoid operated valve provided in the conduit 20. The solenoid valve 24 is operated to open and close the conduit 20. The valve 24 is operated by the engine management ECU 25 which is programmed so that when the solenoid opens and air carrying fuel vapour is passing from the canister to the compressor 23, the ECU may make an appropriate adjustment to the metered quantity of fuel delivered to the engine. The ECU 25 also controls when fuel vapour is to be purged from the separator 10 via the compressor 23. Under normal operation, the compressor 23 draws air from the air box 18 through conduit 21 and delivers compressed air into an air rail 26 from which air is supplied to a series of fuel delivery injectors 27 to effect delivery of fuel into the engine combustion chambers. A regulator 28 controls the pressure of the air in the air rail 26 and air released by the regulator 28 is returned to the conduit 21 on the intake side of the compressor 23. When the solenoid valve 24 is opened at a particular point of the engine operating load range, the low pressure drawn on the inlet side of the compressor 23 draws fuel vapour from the separator 10 through the conduit 20. As a result, this fuel vapour is subsequently delivered to the engine via the delivery injectors 27. That is, the air delivered to the injectors 27 to entrain and atomise the metered quantities of fuel also contains a quantity of fuel vapour. In this way the fuel vapour is purged into the combustion chambers of the engine. However, as mentioned above, under some engine operating conditions, this method of canister vapour purge may not be as effective as desired due to the low level of vacuum present at the inlet of compressor 23. Typically this may be a problem at low speed engine operation and/or at engine idle speeds. Figures 2 illustrates the modifications made to the arrangement of Figure 1 in accordance with the present invention. Instead of conduit 21 being connected with the air induction system 17 downstream of and adjacent to the air box 18, it is connected via a T-piece 30 and two passages to the air induction system 17 either side of a throttle butterfly 33 which is housed in the throttle body or unit 19. As shown, connections to the induction system 17 are made at the throttle body 19 itself, but in practice connections anywhere upstream and downstream of the throttle butterfly 33 may be sufficient. A damping volume 34 for noise vibration harshness purposes is provided in the conduit 21 to attenuate any noise and vibration which may be generated in the system. The locating of the connection 31 on the downstream side of the throttle butterfly 33 results in the compressor inlet via conduit 21 being depressed by the engine intake vacuum. This level of vacuum is controlled by adjusting a bypass flow rate through connection 32 on the upstream side of the throttle butterfly 33. By appropriately dimensioning the connections 31 and 32, the compressor inlet depression level can be set as desired. This in turn ensures an appropriate flow rate available to the separator 10 at idle whilst ensuring a stable air flow rate to the compressor 23 and the fuel injection system. In particular, it has been found that this arrangement can be implemented without significantly affecting the pressure in the air rail 26 provided by the compressor 23 during normal operation and in particular at high speed operation. Further, control over the engine idle speed is not compromised and does not require any additional hardware to counter-act the impact of the connections 31 and 32. In the embodiment shown in Figure 3 control valves 41 , 42 are fitted to connections 31 and 32. A throttle position sensor 43 is also provided on the throttle body 19. The valves 41 , 42 and position sensor 43 are connected to the engine management ECU 25. The ECU 25 is used to control the level of vacuum by adjustment of valves 41 , 42 to control the flow of air through connections 31 and 32. This allows the level of vacuum to be optimised according to engine speed and/or load. For example the upstream connection 32 may be restricted or closed using valve 42 during idle or low speed operation. At high engine speed the upstream connection 32 via valve 42 can be opened or adjusted to give increased flow. The valve 41 in connection 31 can in some applications be closed at high speed. Figure 4 shows a further variation of the invention. In this arrangement control valves 41, 42 are fitted to the connections 31 and 32 as for the embodiment shown in Figure 3. A mechanical connection is provided as indicated by arrow 44 between the throttle butterfly 33 and the control valves 41 , 42. The control valves 41 , 42 are adjusted according to the movement of the throttle butterfly 33. Any suitable form of mechanical linkage can be used to effect adjustment of the valves 41 , 42. The mechanical linkage can for example be arranged so that for high speed operation corresponding to the butterfly 33 being moved toward the fully open position valve 41 can be closed and valve 42 fully opened. Conversely at idle the linkage can be arranged such that valve 42 is closed or restricted and valve 41 is fully opened. In other variations of the invention only one of the valves shown in Figures 3 and 4 may be employed. Flow through the connection without a valve is controlled by aperture size as described in relation to the Figure 2 embodiment. Figure 5 shows a more detailed schematic representation of the system. The same reference numerals have been used in Figure 5 to identify the components described in relation to Figures 1 to 4. In operation the vapour purge system operates as described in respect of Figure 1. When the ECU 25 determines that the solenoid valve 24 should be opened to permit the purging of some of the fuel vapour from the vapour separator 10, the compressor 23 draws a fuel vapour and delivers this to the engine by way of the air rail 26 and delivery injectors 27. It will be apparent that the aperture sizes of connections 31 and 32 may required to be tuned for each particular engine compressor combination. In testing of the invention on a 1.8 litre dual overhead cam engine fitted with the Applicant's direct dual fluid fuel injection system, it has been possible to achieve a fuel vapour idle flow rate from the separator 10 of about 6 litres per minute whilst still providing sufficient differential pressure across the throttle butterfly 33 to properly control engine idle speed. In the engine tested this corresponded to an aperture size of 2mm in diameter at the downstream connection 31 and an aperture size of 4mm in diameter at the upstream connection 32. Testing of this system has shown the capacity to provide a high purge volume without significant compressor flow loss, and irrespective of any compressor flow pulsations. The foregoing describes only one embodiment of the invention and modifications can be made without departing from the scope of the invention. For example, whilst the invention has in the main been discussed with respect to automotive applications, it may also have applicability to other vehicle and engine applications, such as motorcycles and scooters, where there may also exist the need to purge fuel vapour isolated by a fuel vapour separation means.

Claims: CLAIMS 1. An internal combustion engine including a compressed gas supply means to supply pressurized gas to effect injection of fuel for combustion in the engine, an intake system for the supply of combustion air to the engine including a throttling assembly to control the flow of air through the intake system, a gas inlet port of said compressed gas supply means being connected with said air intake system downstream of the throttling assembly to lower the pressure at the inlet port of the compressed gas supply means to below ambient air pressure. 2. An internal combustion engine according to claim 1 wherein said compressed gas supply means is an air compressor which supplies pressurized air to effect the injection of metered quantities of fuel to the engine. 3. An internal combustion engine according to claim 2 wherein the gas inlet port of said compressor is also connected to the intake system upstream of the throttling assembly and the flow capacities of the upstream and downstream connections are selected to achieve a predetermined pressure at the inlet port of the compressor under certain engine operating conditions. 4. An internal combustion engine according to claim 3 wherein said connections to the upstream and downstream sides of the throttling assembly have flow capacities determined by selected respective aperture sizes. 5. An internal combustion engine according to claim 2 wherein said connections are immediately adjacent a throttling element in the throttling assembly. 6. An internal combustion engine according to claim 4 or claim 5 wherein the flow capacity of the connection to the downstream side of the throttling assembly substantially determines the pressure at the inlet port. 7. An internal combustion engine according to any one of claims 4 to 6 wherein the flow capacity of the connection to the upstream side of the throttling assembly substantially determines the stability of air flow to the inlet port. 8. An internal combustion engine according to claim 3 wherein at least one of said connections to the upstream and downstream sides of the throttling assembly includes a valve to control the respective flow capacity thereof. 9. An internal combustion engine according to claim 8 wherein said valve(s) provide a variable flow capacity. 10. An internal combustion engine according to claim 8 wherein said valve(s) are of an on or off type. 11. An internal combustion engine according to claim 3 wherein the closing or adjustment of flow capacity of either or both of the connections to the upstream and downstream sides of the throttling assembly is effected by movement of a throttle butterfly. 12. An internal combustion engine according to claim 11 wherein said throttle butterfly can operate to physically restrict the upstream connection. 13. An internal combustion engine according to any one of claims 3 to 12 wherein the amount of bypass of the throttling assembly is not substantially greater than around 2 kg per hour. 14. An internal combustion engine according to any one of claims 1 to 13 wherein said inlet port is connected to purge fuel vapour from a vapour separator receiving fuel vapours from a fuel system. 15. An internal combustion engine according to claim 14 wherein the vapour separator is a carbon canister and the inlet port of the compressor is also connected to an outlet side of the canister. 16. A method of operating an internal combustion engine including a gas compressor having an inlet port, the compressor arranged to assist in the injection of fuel for combustion in the engine and an intake supply system for the supply of combustion air to the engine including a throttling assembly to control the flow of air through the intake system, said method including the step of lowering the pressure at said inlet port to below ambient air pressure by connecting said inlet port with said intake system downstream of the throttling assembly. 17. A method of operating an internal combustion engine in accordance with claim 16 further including connecting said inlet port to the intake system upstream of the throttling assembly and controlling the flow of air from the respective connections to provide a selected pressure at said inlet port. 18. A method of operating an internal combustion engine according to claim 17 wherein said flow of air is controlled by fixed apertures respectively determining the flow from the connections. 19. A method of operating an internal combustion engine in accordance with claim 17 wherein said flow of air is controlled by way of at least one adjustable valve controlling the flow of air from the respective connections. 20. A method of operating an internal combustion engine in accordance with claim 17 further including the step of controlling the flow of air from the respective connections in accordance with engine operating speed and/or load. 21. A method of operating an internal combustion engine in accordance with claim 20 wherein flow from the connection to said intake system upstream of the throttling assembly is restricted during low speed engine operation. 22. A method of operating an internal combustion engine in accordance with claim 20 or claim 21 wherein flow from the connection to said intake system upstream of the throttling assembly is increased during high speed engine operation. 3. A method of operating an internal combustion engine in accordance with any one of claims 20 to 22 wherein flow from the connection to said intake system downstream of the throttling assembly is prevented during high speed engine operation.

Inventors: YANG KOON CHUL, YANG, KOON, CHUL
Applicants: ORBITAL ENG PTY, YANG KOON CHUL, ORBITAL ENGINE COMPANY (AUSTRALIA) PTY LTD, YANG, KOON, CHUL
Application year: 2000
Main classification: F02M67
IPC codes: F02M25, F02M67