GB2551479A - A turbocharger with sequential exhaust turbines - Google Patents

Abstract

A turbocharging system employing two turbines 3, 5 of differing sizes which may in a first embodiment be driven by exhaust gases and in a second embodiment may be augmented by an electrical motor generator (Fig 2, 1). The smaller turbine 3 is directly coupled via shaft 2 to the compressor. As the turbine is small it responds to low gas velocities. The larger turbine 5 may be connected via a selectable clutch 4 to the common drive shaft 2. As exhaust gas volumes increase the second turbine generates boost pressure. To control overboost the system employs valves (volume control dampers) 6 and 7 to allow exhaust gases to bypass turbines 3 and 5 allowing gases straight to the downstream exhaust system. The clutch 4 links the turbines and may be engaged/disengaged if pre ignition is sensed, the clutch is part of the control means which includes valves 6, 7, 10,15, a knock sensor and the engine management system.

Description

A TURBOCHARGER with SEQUENTIAL EXHAUST TURBINES.

This invention relates to inproving upon the boost pressures that can possibly be generated by conventional turbocharger systems, including compound/in-series systems, when their respective internal conbustion (i.c.> engines are operating at low/idling rpm’s, whilst also being able to, on a like-fot—like exhaust back-pressure basis, generate noeinally the sane maxi-nun boost pressures. In particular, it relates to the shaft power output of snail exhaust turbines at both high and low exhaust gas flows when operating in conjunction with one (l), or nore, larger exhaust turbines.

Dis-sinilar S-stage in-series/conpound turbochargers having smaller 1st stage turbos than 2nd stage ones are used to achieve nore boost pressure at low i.c. engine revs than would be achievable if both turbos were the sane size. To obviate excessive pressure drops across such snaller turbo’s conpressors and turbines, bypasses with motorised volune control pressure relief dampers are used to bypass exhaust gases around then as flows increase up to their nominal maximum rating. Such motoi— ised dampers being modulatingly controlled by an exhaust gas pressure sensor upstream of 1st stage turbines, set to obviate excessive exhaust back-pressures occurring - not that exhaust gas pressure sensing is necessarily the only way of controlling said motorised dampers. CGenerally as per McNulty’s patented invention US 2007/0295007 Al, excepting the last statement.3

However, where two (2), or more, radial entry in-series exhaust turbines are used there would be two (2), or more, turbo-compressors, or motoi—generators (M-G’s), involved. To simplify such a system, the present invention proposes the use of sequential multiple radial entry exhaust turbines connected to single compressors, or variable speed M—G’s, and the use of motorised volume control dampers (VCD’s) connected to secondary exhaust turbines and, optionally, a bypass with a motorised VCD around the ultimate exhaust turbine. Furthermore, when such exhaust turbines are connected to single large centrifugal turbocompressors (with/without a connected M—G) they would, thereby, spin at the same rpm as the 1st stage turbine so that significantly more turbo boost would be generated at low i.c.engine revs (boost pressure being a function of rotor tip speed) than the comparatively smaller 1st stage compressors in McNulty’s invention (on a like-foi—like exhaust turbine basis). Such increased boost pressure would also boost the power output, and economy, of intake system throttle controlled adiabatic engines (eco-boost engines) at low and idling engine rpm’s, and during cold weather start-ups intake air heated by the turbo compressor can be re-circulated around the compressor such that it compound ingly increases in temperature and reduces boost pressure upstream of the system’s adiabatic throttle, reducing its expansion cooling/freezing of charge air - in effect transferring heat from the exhaust system to the intake system. Such radial entry exhaust turbines should have de-rotating volutes fitted to their axial flow outlets to not only re-gain otherwise lost spiral energy (increasing their efficiencies by ca 30*), but to also facilitate the stacking of and rigid bolting of then together by means involving multiple separating heavy duty pla-tes, high tensile bolts, nuts and washers (a la Rover K-series engines), thereby obviating undue side loads on the ball bearings supporting the system's power transmitting shafts.

With such parallel exhaust turbines, interstage de—clutching systems should be provided so that the otherwise parasitic drag of the rotors of non—flowing turbines can thereby be prevented from adversely affecting flowing turbines. To minimise clutch wear the motorised VCD's connected to such non—flowing turbines should, ideally, be blipped open to spin—up their disconnected rotors prior to clutch engagement to allow seamless engagement prior to such VCD's then controlling flow through them, and as and when said VCD's subsequently close their respective turbine's clutch would be de-clutched. Ideally, the 1st stage tut— bines of such parallel multi-stage turbines should be small, but capable, at least, of sustaining the exhaust gas flow requirements of respective i.c.engines at idling rpm's. Also, when such parallel turbines are conected to a M-G there should, ideally, be more than two (2) parallel turbines to thereby minimise the losses generated by whichever inter-stage bypass damper/VCD is less than wide open - however, such losses can be obviated if means are incorporated for varying the transmission of power, such as continuously variable transmissions (CVT's), between any of the system's exhaust turbines whose operations are co-ordinated with their respective VCD's operations.

Such parallel multi-stage turbines, particularly where there are more than 2-stages, represent a viable alternative to positive displacement reverse acting exhaust superchargers and, almost certainly, means that could rotate at much higher rpm than such superchargers to thereby afford the possibility of shaft powering high rpm intake system centrifugal compressors (with ca 30% efficiency increasing pre-rotating volutes) that, in any case, would be simpler than alternative lower rpm intake system superchargers, and likely more efficient and lighter. And with this system, in which centrifugal charge-air compressors can be generating some boost pressure at low and even idling rpm*s, said centrifugal compressors (with ca 30% efficiency increasing pre-rotating volutes) can be operating much like positive displacement superchargers whilst also being more efficient, lighter and more durable (having no tip seals).

Two (2), or more, such parallel exhaust turbine systems may be required where the i.c.engine has two (2), or more, exhaust systems. And such parallel exhaust turbine systems may be in-series/compounded for diesel engines, and with bypasses around they could be sequentially operated and/or bypassed if one of them has a fault or function failure.

The invention will now be described by way of example with reference to the accompanying schematic drawings in which:

Figure 1 shows a turbocharger system with an electric throttle valve, which could be a compression-expansion adiabatic engine, for spark ignition i.c.engines.

Figure 2 shows an emission controlled turbine exhaust throttling system for hybrid electric—diesel i.c.engines.

In figure 1, centrifugal intake air compressor 1 is connected via shaft 2 to exhaust turbine 3 which is connected via clutch 4 (**> to exhaust turbine S. Combustion ’knock1 (the product of high turbo-boost and high exhaust back pressures) sensors, or a sensor, connected via an electronic control unit (ECU), modu-latingly controls, when combustion pre-ignition is sensed, the actuator of VCD 8 and actuates clutch 4’s actuator, and when VCD & is wide-open modulatingly controls the actuator of VCD 7. With a self-learning programmed ECU such incipient combustion pre-ignition control can be more closely controlled if such a self-learning ECU is also connected to other sensors sensing such engine operating conditions as turbo-boost pressure, exhaust back-pressure, exhaust temperature, combustion chamber temperature, ambient temperature, charge-air temperature, etc, learns how to maintain i.c.engine combustion chamber at a preset limit optimally just short of (destructive) pre-ignition — such learnt software may be prototype obtained and used as a basis for a core/default production self-learning software programme. Throttle valve Θ is controlled by a throttle control system (TCS) connected to the ECU. Intercooler 9*s charge-air cooling is inhibited during cold start-ups, and partial bypass VCD 10 is also opened during such start-ups so that turbo compressor heated charge-air is re—circulated around centrifugal compressor 1 such that such compression heating is compounded. Pre-rotating volute 11 significantly reduces the losses othet— wise occurred at the intake of compressor 1*s rotor, and de-ro— tating volutes IS and 13 also recover most of the otherwise lost spiral energy discharged from from turbines 3 and 5. (**) Alternatively, to minimise the parasitic drag losses of turbine S when flow through it is less than sufficient to rotate it at the same rpm as comressor 1, motorised clutch 4 should be a motorised de-clutching CVT whose control is coordinated with VCD 6’s operations. Also, at idle and low revs, VCD’s 7 and 10 are opened and VCD’s 15 and 6 closed to not only bypass the parasitic drags of compressor 1 and turbines 3 and 5, but to also minimise heat sink into the turbo system, but which are, ideally, overridden when an ECU’s TCS’s throttle position sensor (TPS) sensor senses accelerated throttle movement, although such VCD operations should be obviated where electric throttle valve 8 is a positive displacement adiabatic compression-expansion engine (as in eco-boost engines).

In figure £, variable speed M-G 1 is connected to exhaust tu»— bine £ by shaft 3 which also connects, via de-clutching CVT’s 4 and 5, to exhaust turbines & and 7. M-G 1 is also connected via power transmitting means to an M-G mechanically connected to a respective to diesel engine and/or to M-G’s connected to a respective vehicle’s drive system/s. De-rotating volutes 8, 9 and 10 recover spiral energy otherwise lost from the axial outlets of radial entry exhaust turbines £, & and 7. Lambda/OE sensor 11 is connected via the respective diesel engine’s ECU to M-G l’s speed controller 1£, the actuators of CVT’s 13 and 14 and those of VCD’s 15, 18 and 17. The said ECU controls speed controller 1£ between iero (not obtained unless the respective diesel engine stops) and a programmed maximum such that M-G I outputs power, unless such maximum is overridden by inputs to said ECU from its TCS’s throttle position sensor (TPS) sensing heavy/accelerated throttle movement (**). IdeaLly the ECU1s system. In any case, the ECU sequentially controls speed controls speed controller 12, the actuators of CVT’s 13 and 14 together with the actuators of their respective VCD’s IS and 16, the actuator of VCD 17 and the diesel engine’s throttle controlled fuel injection system (inhibiting it if exhaust emissions are not to be increased). («*) Such operation reduces, at least, M-G 1’s power (generation) output, and if oversped beyond unity speed absorbs power from any one, or more, power sources it may be connected to such that the passage of exhaust gases through turbines 2, & and 7 would be accelerated. Vice versa, M-G 1’s speed would decelerate upon abrupt throttle lift-off and where there are power accumulating-discharging means, such as a battery-pack, M-G I’s potential power output can be absorbed during such throttle lift-offs - and absorb power outputs from an M-G braking the aforesaid respective diesel engine and its connected drive line, or hub-mounted M-G1 s braking wheels, when such M-G1s speeds are controlled by said engine’s respective vehicle’s brake control system.

In all cases, ideally, there should be means for minimising the transfer of exhaust heat to such items as clutches, CVT’s and M—G’s comprising of such means as hollow carbon fibre composite power transmission shafts and means for thermally insulating said items from exhaust flowing items. Ideally, de-rotators should be finned, or ribbed and/or coolant/water jacketed (**> to cool the exhaust gases in them to not only reduce heat-sink into system components, but to also cause static pressure regain by reducing the volume of exhaust gases in them such that outlet discharge velocities reduce. [(**> Ideally, coolant and exhaust gas flow should be in counterflow, and coolant should be spirally rotated in the jacketing.] Similarly, such cooling means should be applied to the turbines to reduce pressure inside them and, thereby, back-pressure in the exhaust system upstream of them - such cooling would not, however, reduce the velocity of the so far uncooled hot exhaust gases impinging upon the tips of the turbine’s rotors such that their power outputs would not be reduced either. However, respective i.c.engines’ exhaust systems upstream of the turbines of this system should, ideally, be thermally insulated with means having a heat reflective outer surface to thereby minimise any reduction in exhaust gas volume entering this system’s turbines, and, thereby, any reduction in the velocity of the exhaust gases impinging upon said turbines’ rotor tips, and to also minimise exhaust heat radiation into the engine bays of said engine’s respective vehicles, or plant rooms, that otherwise would likely heat a respective engine’s intake air.

Claims (1)

1. CLAIMS: 1) Sequential multi-stage exhaust turbine systems for internal combustion (i.c.) engines comprising of, at least, a radial entry exhaust turbine having a de—rotating volute with a power transmission shaft connected to a centrifugal air compressor having a pre-rotating volute in a respective i.c.engine’s air intake system, or connected to variable power transmission means, or connected to both such said compressors and power transmission means, and which is also connected via one <1), or more, clutches to the shafts of one (1), or more, other exhaust turbines having de-rotating volutes, exhaust gas volume control dampers (VCD’s) connected to said other exhaust turbines, actuators connected to, means for varying the aforesaid variable power transmission means where applicable, said clutches and VCD’s, and means for connecting said actuators to control means connected to one (1>, or more, means for sensing the respective i.c.engine’s operating conditions. £) Sequential multi-stage turbine systems according to claim 1 in which there are means for varying the transmission of shaft power between turbines that have actuating means connected to claim l’s control means and control means that outputs a signal when said varying means input and output shaft speeds are the same. 3) Sequential multi-stage turbine systems according to claim 1, or claim 2, in which there are means for by-passing exhaust gases around the exhaust turbines having a VCD with actuating means connected to claim l’s control means. 4) Sequential multi-stage turbine systems according to any of the preceding claims, in which there are means for insulating a respective i.c.engine’s exhaust system upstream of the claimed system's exhaust turbines. 5) Sequential multi-stage turbine systems according to any of the preceding claims, in which there are means for minimising the transfer of exhaust heat to a system item. 6) Sequential multi-stage turbine systems according to any of the preceding claims, in which turbines and/or de-rotators are finned, or ribbed and/or coolant jacketed.