Abstract:
An exhaust turbo pump of an internal combustion engine has multiple pairs of turbine and compressor wheels rotatable about a common axis, an inner pair of wheels being connected by a tubular shaft rotatable relative to a spindle connecting an outer pair of wheels. One pair of wheels comprises a turbocharger for inlet air, and another pair of wheels comprises a low pressure EGR pump.

Description:
FIELD 
     This invention relates to a turbo pump for a vehicle engine, and in particular to an exhaust driven turbo pump incorporating a turbocharger. Aspects of the invention relate to a pump, to an assembly, to a system, to an engine and to a vehicle. 
     BACKGROUND 
     Exhaust driven turbochargers for vehicle engines are well known. A turbine of the turbocharger driven by exhaust gas, drives a compressor on the inlet side, and thereby increases the charge volume of each combustion cycle of the engine. 
     Also known is the technique of exhaust gas recirculation (EGR), whereby exhaust gas is re-circulated to the inlet side of the engine to dilute the fresh air charge during a cold engine start for the purpose of reducing noxious emissions. 
     High pressure EGR provides exhaust gas from at or adjacent the exhaust manifold. This arrangement is somewhat disadvantageous since the exhaust gas stream is hot, and thereby increases the temperature of the inlet charge upon mixing therewith. Also such exhaust gas is unfiltered, and thus contains carbon and other contaminants which may cause deterioration of engine lubricant. 
     So-called low pressure EGR is an alternative which provides exhaust gas from a point in the exhaust system downstream of the usual diesel oxidation catalyst (DOC) and diesel particle filter (DPF). Such gas is relatively cool and clean, but is substantially at tail pipe pressure. The consequence of relatively low pressure is that insufficient volume may flow, or be drawn, into the engine inlet tract. A pump may thus be provided to ensure that a sufficient volume of relatively cool and clean exhaust gas can be provided to the inlet tract on demand. 
     SUMMARY OF THE INVENTION 
     It is against this background that the present invention has been conceived. Embodiments of the invention may provide an improved pump that addresses the above issues. Other aims and advantages of the invention will become apparent from the following description, claims and drawings. 
     According to one aspect of the present invention there is provided an exhaust turbo pump assembly of a vehicle engine, and having paired compressor and turbine wheels rotatable about a common axis, an inner pair of said wheels being connected by a tubular shaft rotatable relative to a spindle passing through said shaft and connecting an outer pair of said wheels, one pair of wheels comprising an exhaust driven turbocharger, and another pair of said wheels comprising an exhaust driven turbo pump for exhaust gas re-circulation to the engine inlet tract. Such a pump is referred to herein as an EGR turbo pump. 
     Such an arrangement may provide a compact turbo pump assembly in which the pairs of compressor and turbine wheels operate independently about the same rotational axis to provide a turbocharger and an EGR turbo pump. 
     In one embodiment a dual turbo pump assembly is provided. Additional pairs of turbine and compressor wheels may be provided and linked by a respective tubular shaft rotatable on the common axis. For example a triple turbo pump assembly may comprise a two stage turbocharger, and an EGR turbo pump. 
     In an embodiment of the invention, outer wheels of the turbo pump assembly are annular, the through passages providing gas flow paths to respective inner wheels. 
     In an embodiment of the invention, the EGR turbo pump is operable on demand, and includes a closure valve upstream of the turbine wheel thereof. The closure valve may be closed, so that active rotation of the turbine wheel of the EGR pump is obviated and all exhaust gas passes through the turbocharger turbine wheel. The closure valve may be opened progressively to provide for increasing flow over the EGR pump turbine wheel, so as to achieve a desired pumping effect from the EGR pump compressor wheel which is paired therewith. 
     The turbocharger may include a conventional wastegate or the like to avoid overpressure thereof and/or to divert flow which the turbocharger turbine cannot accommodate. 
     In one embodiment, the turbocharger comprises an inner pair of wheels whereas the EGR turbo pump comprises an outer pair of wheels. 
     In an embodiment of the invention, the outlet of the compressor wheel of the EGR turbo pump and the outlet of the compressor wheel of the turbocharger are connected. In this arrangement exhaust gas which has been pressurized by the EGR turbo pump mixes with pressurized inlet air from the turbocharger at a location downstream of both compressor wheels. 
     In another embodiment the outlet of the compressor wheel of the EGR turbo pump and the inlet of the compressor wheel of the turbocharger are connected. In this arrangement a relatively lower pressure of exhaust gas is required for mixing in the inlet tract upstream of the turbocharger compressor wheel. 
     The compressor wheel of the EGR turbo pump is sized to provide a sufficient flow of re-circulated exhaust gas at the mixing location, and suitable pressure regulators, flow restrictors and/or non-return valves may be provided as required. 
     In an embodiment of the invention, re-circulated exhaust gas may be provided directly to the inlet tract upstream of the turbocharger compressor and without additional pressurization from the EGR turbo pump. Such an arrangement provides additional options for mixing and distributing exhaust gas to the inlet side of the engine, and may supplement exhaust gas introduced via the EGR turbo pump. Suitable diverter valves and/or flow restrictors may be incorporated to ensure that a desired proportion of exhaust gas flows via the respective paths. 
     In another embodiment, clean air from the inlet tract of the engine may be introduced into the exhaust gas re-circulation duct upstream of the compressor wheel of the EGR turbo pump. A suitable valve, which may allow flow control, thus permits dilution of re-circulated exhaust gas; this may be useful to achieve a desired proportion of re-circulated exhaust gas in the engine inlet charge. 
     The thus diluted exhaust gas subsequently passes through the EGR turbo pump compressor wheel and is directed either to the inlet tract upstream of the turbocharger compressor, or to a point downstream of turbocharger compressor and preferably upstream of an intercooler of the engine inlet tract. 
     In another embodiment a four-way valve may be provided in the exhaust re-circulation duct upstream of the EGR turbo pump compressor. Such a valve comprises an exhaust gas inlet, a fresh air inlet from the inlet tract, an outlet to the inlet tract upstream of the turbocharger compressor, and an outlet to the EGR turbo pump compressor. 
     In use the four-way valve may be closed, to prevent exhaust gas re-circulation, or may be open to permit one of:
         a) direct admission of unpressurized exhaust gas to the inlet tract of the engine;   b) direct admission of unpressurized exhaust gas to the EGR turbo pump compressor;   c) a combination of a) and b) in a desired proportion;   d) dilution of the re-circulated exhaust charge with fresh air from the inlet tract, the combined flow passing to the EGR turbo pump compressor; and   e) a combination of a) and d).       

     The various flow paths provided by embodiments of the invention allow mixing of re-circulated exhaust gas at several locations upstream and downstream of the turbocharger compressor. These variations also permit advantageous mixing of relatively hot and relatively cool gas in proportions which may also achieve a desirable gas temperature profile at locations on the engine inlet side. 
     Within the scope of this application it is envisaged that the various aspects, embodiments, examples and alternatives, and in particular the individual features thereof, set out in the preceding paragraphs, in the claims and/or in the following description and drawings, may be taken independently or in any combination. For example features described in connection with one embodiment are applicable to all embodiments, unless such features are incompatible. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: 
         FIGS. 1 &amp; 2  represent schematically a first embodiment of the invention in ‘OFF’ and ‘ON’ states; 
         FIGS. 3 &amp; 4  represent schematically a second embodiment of the invention in ‘OFF’ and ‘ON’ states; 
         FIGS. 5, 6   a  &amp;  6   b  represent schematically a third embodiment of the invention in ‘OFF’ and ‘ON’ states; 
         FIGS. 7 &amp; 8  represent schematically a fourth embodiment of the invention in ‘OFF’ and ‘ON’ states; 
         FIGS. 9, 10   a  &amp;  10   b  represent schematically a fifth embodiment of the invention in ‘OFF’ and ‘ON’ states; and 
         FIGS. 11 &amp; 12   a - 12   e  represent schematically a sixth embodiment of the invention in ‘OFF’ and ‘ON’ states. 
     
    
    
     DETAILED DESCRIPTION 
     In the accompanying drawings, a dual turbo pump assembly is illustrated schematically. Paired turbine and compressor wheels,  11 ,  12  and  13 ,  14  are mounted for rotation about a common axis, the inner pair  11 ,  12  being coupled by a tubular shaft  15 , and the outer pair  13 ,  14  being coupled by a shaft (not shown) running within the tubular shaft  15 . 
     Each pair of wheels is independent of the other, and the outer pair  13 ,  14  are annular to permit flow to and from the inner pair, as will become apparent from the following description. 
     In use flow control valves are provided to direct flow to one or other turbine wheel, and to one or other compressor wheel. The inner pair of wheels  11 ,  12  comprise a conventional turbocharger of an internal combustion engine, and the outer pair of wheels comprise a pump for low pressure exhaust gas which is re-circulated to the engine inlet side (an EGR turbo pump). 
     With reference to  FIG. 1 , the dual turbo pump assembly consists of exhaust driven turbines  12 ,  14  supplied with exhaust gas from the exhaust manifold  19  of a diesel engine (not shown). After passing through the turbine stages, exhaust gas passes through a diesel oxidation catalyst  16  and a diesel particulate filter  17  to an exhaust tailpipe  18 . In the tailpipe exhaust gas pressure may be characterized as low, compared with exhaust gas pressure upstream of the turbo pump assembly. 
     In the drawings potential flow paths are indicated by dotted line whereas actual flow paths are indicated by solid line. 
       FIG. 1  illustrates a configuration where the turbine  14  associated with the EGR turbo pump is not active—an exhaust stream supply valve  21  is closed, and all exhaust gas flow is via the turbine  12  which forms part of the engine turbocharger. Exhaust flow passes through a central aperture in the turbine  14 , but imparts no substantial rotational force thereto, though some free-wheeling may be intentionally permitted to ensure lubrication of the bearings thereof. 
     In this arrangement, the compressor wheel  11  of the turbocharger operates conventionally to charge the inlet manifold  20  of the engine, and receives inlet air through a central aperture of the compressor wheel  13 , which may freewheel due to the connection to the turbine  14 . 
     An exhaust gas re-circulation tract  22  directs exhaust gas toward the compressor wheel  13 , but the tract is closed in this embodiment by valve  23 . 
     Thus in the embodiment of  FIG. 1 , the EGR pump is ‘off’. 
     In  FIG. 2 , the EGR pump is ‘on’, and the valve  21  permits flow via the turbine  14 , which in turn drives the compressor wheel  13 . The valve  23  is also open to permit the compressor wheel  13  to draw EGR gas via duct  22  and pump it to the inlet manifold  20  so as to supplement pressurized air from the compressor wheel  11 . Mixing of EGR gas and inlet air preferably occurs upstream of a conventional air to air intercooler (not shown), located upstream of the inlet manifold  20 . 
     This embodiment permits re-circulation of exhaust gas which is at too low a pressure to flow effectively into the inlet manifold without pumping. 
     Design and specification of suitable turbine and compressor wheels, valves, flow rates and other variables is within the ability of an appropriately skilled person, and need not be further described here. 
     In the event that the temperature of re-circulating exhaust gas is too high, a suitable cooler  24  may be incorporated into the EGR duct, for example a gas/water cooler associated with the engine cooling system. 
     An alternative arrangement is illustrated in  FIGS. 3 and 4 . The same components are given identical reference numerals. 
     This embodiment corresponds to that of  FIGS. 1 and 2  save that pressurized exhaust gas passes from the compressor wheel  13  to mix with inlet air upstream of the compressor wheel  11 .  FIG. 3  shows the ‘off’ configuration in which valves  21  and  23  are closed.  FIG. 4  shows the ‘on’ configuration in which low pressure exhaust gas is pumped to the air inlet duct. The arrangement of  FIGS. 3 and 4  may provide better mixing of gases, and an alternative configuration for installing within a congested engine compartment. 
     In the configuration illustrated in  FIGS. 5 and 6   a , the exhaust side is unchanged.  FIG. 5  represents an ‘off’ state whereas  FIG. 6 a    shows an ‘on’ state whereby exhaust gas passes directly to the air inlet tract, and is unboosted. A second valve  25  of the EGR duct closes a flow path to the compressor wheel  13 . 
     The mixture of EGR gas and air is boosted by the compressor wheel  11 , to supply the inlet manifold  20 . 
     In the embodiment of  FIG. 6 b   , the valve  25  is also opened to permit a proportion of exhaust gas to be boosted directly to the inlet tract downstream of the compressor wheel  11 . Flow restrictors, or other means may be provided to determine the flow proportions of the two pathways for the EGR gas stream. 
     Yet another arrangement is illustrated in  FIGS. 7 and 8 . The exhaust side is unchanged.  FIG. 7  represents the ‘off’ state, and  FIG. 8  the ‘on’ state. 
     An additional valve  26  is incorporated in the air inlet tract whereby air may be directed to mix with the EGR gas upstream of the compressor wheel  13 . Again, flow restrictors or other means may be provided to determine the proportion of air directed towards valve  23  for mixing with the EGR stream. 
     Whilst the valve  26  can be open in  FIG. 7 , it will be understood that it may also be closed in order to obviate any risk of back flow through the EGR duct  22 . When the valves  26  and  23  are open ( FIG. 8 ), the EGR stream mixes with fresh air in a desired proportion. 
       FIGS. 9, 10   a  and  10   b  illustrate another embodiment having valves  23 ,  27  corresponding closely to  FIGS. 7 and 8 , but a flow path for boosted EGR gas which is directed to the air inlet upstream of the compressor wheels. The exhaust side is unchanged. 
     Thus in the ‘off’ configuration of  FIG. 9 , valves  23  and  27  are closed, and EGR flow is prevented. 
     In the ‘on’ configuration of  FIG. 10 a   , valve  23  is opened to permit exhaust gas to be boosted by compressor wheel  13  and admitted to the air inlet tract (this arrangement also corresponds to  FIG. 4 ). 
     In the ‘on’ configuration of  FIG. 10 b   , the valve  27  is also opened to permit dilution of the exhaust gas entering compressor wheel  13 . 
     Another embodiment is illustrated in  FIGS. 11 and 12   a - 12   e .  FIG. 11  represents an ‘off’ configuration, whereas  FIGS. 12 a -12 e    illustrate various ‘on’ configurations. In these embodiments, a 4-way valve  28  is provided in the EGR duct. 
     In the first ‘on’ condition ( FIG. 12 a   ) exhaust gas is directed to the inlet duct upstream of the compressor wheel  11  (also corresponding to  FIG. 6 a   ) and is unboosted. 
     In  FIG. 12 b   , exhaust gas is boosted via the compressor wheel  13  (also corresponding to  FIG. 2 ). 
     In  FIG. 12 c   , exhaust gas is both boosted and supplied directly to the inlet tract (also corresponding to  FIG. 6 b   ). 
     (In  FIG. 12 d   , the valve  28  directs inlet air to mix with exhaust gas upstream of the compressor wheel  13  (also corresponding to  FIG. 8 ). 
     In  FIG. 12 e   , inlet air and exhaust gas are mixed, and proportions supplied to both the inlet tract upstream of compressor wheel  13  and to compressor wheel  11 . 
     The different flow paths permitted by the configurations described herein can both accommodate installations in engine compartments which are congested, and permit mixing of exhaust gas and fresh air in suitable proportions to achieve a desirable charge to the inlet manifold. In particular it may be possible to achieve desirable temperatures of an inlet charge in addition to a desired proportion of exhaust gas and air.