Turbocharger arrangement

Abstract

A twin stage turbocharger arrangement 300 comprising an exhaust manifold (400,fig.4). The arrangement comprises a first turbocharger 310 and second turbocharger 320. The first and second turbochargers

Description

Field of the disclosure The disclosure relates to the field of turbochargers for internal combustion engines. Background A turbocharger (or turbo) is a forced induction device used in an internal combustion engine. A turbocharger is powered by a flow of exhaust gases from the internal combustion engine, and uses that energy to compress intake air. The compressed intake air is pushed into the internal combustion engine, increasing the oxygen that is fed into the engine. Increasing the oxygen allows more fuel to be burned, thereby increasing power for a given engine displacement. Increasing a size of the compressor of a turbocharger (and a turbine of the turbocharger to provide adequate torque for the larger compressor) can result in high boost pressures being reached for a given airflow. This is a fundamental enabler for high power density engines as well as engines which operate at high altitude. However, with increased compressor and turbine sizes results in an increased rotating inertia. The increased inertia increases the time required to speed up the compressor of the turbocharger, which may have a detrimental effect on the engine transient response. This is known as turbo lag, and may be noticed by a driver or operator as a delay in the response of the engine upon acceleration or load acceptance, resulting in a loss of productivity. By using two or more turbochargers in a compound arrangement, it is possible to move the pressure capability versus transient response trade-off to a more favourable position in terms of engine performance. Typically, a twin stage air system comprising two turbochargers is expensive and bulky to install. Two turbochargers can take up a substantial amount of space in the engine, and typically require bulky interstage pipe work and / or brackets to support them. The typical assembly location in the engine of the two turbochargers can result in a large tolerance stack, which then is accommodated for in the interstage pipe work between the two turbochargers. The two turbochargers may typically be located away from the engine centre of gravity, resulting in addition of supporting bracketry that may amplify the tolerance stack. Summary Against this background, there is provided: a twin stage turbocharger arrangement for an internal combustion engine comprising an exhaust manifold, the twin stage turbo arrangement comprising a first turbocharger and a second turbocharger. The first turbocharger comprises a first compressor. The second turbocharger comprises a second compressor. The first and second turbochargers are each mounted to the exhaust manifold, wherein the relative orientation of the first and second turbochargers is such that the first compressor opposes the second compressor. The second turbocharger is configured to receive exhaust gas from the engine via a first chamber of the exhaust manifold. The first turbocharger is configured to receive exhaust gas from the second turbocharger via a second chamber of the exhaust manifold. In this way, twin turbochargers may be used to reduce turbo lag and increase a range of rpm at which a power increase is produced. Mounting the first and second turbochargers to the exhaust manifold allows for repurposing of existing engine components to support the turbochargers, rather than introducing additional supporting bracketry. Mounting the turbochargers to the exhaust manifold may also have the advantage that the space would not otherwise be used, and that the turbochargers do not take away space that could potentially be used by power train outlets. Both turbocharges are mounted to the same component (the exhaust manifold) meaning that the tolerances may be controlled between the two turbo chargers. A low tolerance stack may be achieved due to the join across only two components, decreasing from previous conventional arrangements that may join across 8 components and may therefore have a higher tolerance stack. Furthermore, the arrangement reduces the package size compared to a typical twin stage arrangement. The twin turbochargers of the present disclosure may be one third of the size of previous conventional arrangements. As another advantage, some or all interstage ducting may not be required due to the opposing arrangement of the first and second compressors, lowering cost. The removal of the need for additional supporting bracketry and the lower tolerance stack (and, therefore, lower complexity) may also reduce cost. There is also provided: a method of compressing intake air for an internal combustion engine comprising an exhaust manifold, the method comprising: passing intake air into a first compressor of a first turbocharger mounted to the exhaust manifold; compressing the intake air using the first compressor and outputting first compressed air; passing the first compressed air into a second compressor of a second turbocharger mounted to the exhaust manifold, wherein the second compressor opposes the first compressor; compressing the first compressed air using the second compressor and outputting second compressed air; and passing the second compressed air to an inlet manifold of the internal combustion engine; wherein: the second turbocharger is configured to receive exhaust gas from the engine via a first chamber of the exhaust manifold; and the first turbocharger is configured to receive exhaust gas from the first turbocharger via a second chamber of the exhaust manifold. Brief description of the drawings A specific embodiment of the disclosure will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 shows a prior art turbocharger arrangement. Figure 2 shows a prior art engine having a space for power train outlet appliances. Figure 3 shows a schematic diagram of a twin turbocharger arrangement according to an embodiment of the present disclosure. Figure 4 shows a schematic diagram of a twin turbocharger arrangement according to an embodiment of the present disclosure. Figure 5 shows a schematic diagram of a perspective view of a twin turbocharger arrangement according to an embodiment of the present disclosure. Figure 6 shows a schematic diagram of a perspective view of a twin turbocharger arrangement according to an embodiment of the present disclosure, in context in an engine. Figure 7 shows a schematic diagram of a side view of a twin turbocharger arrangement according to an embodiment of the present disclosure, in context in an engine. Detailed description With reference to Figure 1, a prior art turbocharger arrangement 100 is illustrated, wherein two turbochargers 110, 120 are arranged in series. The two turbochargers of the prior art turbocharger arrangement are attached to the engine via additional supporting bracketry, which may amplify a tolerance stack of the prior art turbocharger arrangement. Figure 1 illustrates interstage pipe work between the two turbochargers, which may be configured to accommodate a large tolerance stack arising from the location of the prior art turbocharger arrangement. Figure 2 illustrates an engine, with the box 210 outlining a space in which a prior art turbocharger arrangement (having two turbochargers arranged in series as in Figure 1) may typically be located. For engines that do not have twin turbochargers in series, this space is typically reserved for one or more applications run via power take-off (PTO) by taking power from the engine and transmitting power to the application(s). For example, power may be transmitted to a pump or other device. By having a prior art turbo arrangement of twin turbochargers in series, PTO can no longer be accommodated. In accordance with an embodiment of the present disclosure a twin stage turbocharger arrangement is provided for an internal combustion engine. The internal combustion engine comprises an exhaust manifold. The twin stage turbo arrangement comprises a first turbocharger and a second turbocharger, wherein the first turbocharger comprises a first compressor and the second turbocharger comprises a second compressor. The second turbocharger is configured to receive exhaust gas from the engine via a first chamber of the exhaust manifold. The second turbocharger is configured to be powered by the flow of the exhaust gas received from the first chamber. The first turbocharger is configured to receive exhaust gas from the second turbocharger via a second chamber of the exhaust manifold. The first turbocharger is configured to be powered by the flow of the exhaust gas received from the second chamber. The first turbocharger is configured to receive first intake gas and to compress the first intake gas when powered by flow of exhaust gas received from the second chamber of the exhaust manifold. The second turbocharger is configured to receive second intake gas and to compress the second intake gas when powered by flow of exhaust gas received from the first chamber of the exhaust manifold. The first and second turbochargers are each mounted to the exhaust manifold. The first turbocharger may be fluidly connected to an air intake inlet such that the first turbocharger is able to receive intake air via the air intake inlet. The second turbocharger may be fluidly connected to an inlet manifold of the engine, such that compressed air may pass from the second turbocharger to the inlet manifold of the engine. In certain embodiments, the first and second turbochargers may be mounted only to the exhaust manifold, without additional bracketry mounting the first and second turbochargers to other components of the engine. Even in embodiments where the first and second turbochargers are mounted only to the exhaust manifold, the first and second turbochargers are fluidly connected to an air intake inlet and to an inlet manifold of the engine, respectively. The relative orientation of the first and second turbochargers is such that the first compressor opposes the second compressor. The first compressor may oppose the second compressor in the sense that the orientation of the first compressor is at 180° relative to the second compressor. An inlet of the first compressor may face in an opposite direction to an inlet of the second compressor, such that a major component of the direction of flow of air into the inlet of the first compressor is opposite to a major component of the direction of flow of air into the inlet of the second compressor. The first turbocharger is configured to receive intake air and compress the intake air to output first compressed air. In certain embodiments, the second turbocharger is configured to receive the first compressed air and to compress the first compressed air to output second compressed air. With reference to Figure 3, a turbocharger arrangement 300 according to an embodiment of the present disclosure is illustrated. The turbocharger arrangement 300 comprises a first turbocharger 310 and a second turbocharger 320. The first turbocharger 310 comprises a first turbine 312 configured to receive exhaust gas from a second chamber 350 of the exhaust manifold via a first turbine inlet 314. The first turbocharger 310 further comprises a first compressor 316 configured to receive intake air via an inlet as illustrated by arrow 317. The first compressor 316 is configured to compress the intake air, and output first compressed air via first compressor outlet 318. The second turbocharger 320 comprises a second turbine 322 configured to receive exhaust gas from a first chamber 340 of the exhaust manifold via a second turbine inlet 324. The second turbocharger 320 further comprises a second compressor 326 configured to receive air via an inlet as illustrated by arrow 327. As shown in Figure 3, the second compressor 326 is arranged to oppose the first compressor 316. The second compressor is configured to receive the first compressed air via the inlet as illustrated by arrow 327, wherein the first compressed air was output from the first compressor 316. The second compressor 326 is configured to compress the first compressed air, and output second compressed air via second compressor outlet 328. The second compressor outlet 328 may feed the second compressed air to an inlet manifold of the engine. In certain embodiments, the first turbocharger 310 may be a low pressure turbocharger and the second turbocharger 320 may be a high pressure turbocharger. The low pressure turbocharger may be configured to receive lower pressure inlet air and lower pressure exhaust gases than the high pressure turbocharger. The low pressure turbocharger may receive uncompressed inlet air to the first compressor 316. The high pressure turbocharger may receive first compressed air to the second compressor 326, wherein the first compressed air is at a higher pressure than the uncompressed inlet air. The first chamber 340 of the exhaust manifold may be a high pressure manifold duct. The second chamber 350 of the exhaust manifold may be a low pressure manifold duct. The low pressure compressor may receive exhaust gas to the first turbine 312 from the second chamber 350 that is at a lower pressure than the exhaust gas received by the second turbocharger to the second turbine from the first chamber 340. The exhaust manifold may allow for exhaust gas to pass from the first chamber 340 to the second chamber 350, via the second turbine 322 of the high pressure turbocharger. Driving the second turbine 322 may reduce the pressure of the exhaust gas entering the second chamber 350. The air to be compressed enters the first compressor of the first (low pressure) turbocharger, wherein the first compressor is powered by lower pressure exhaust gases flowing from the second chamber of the exhaust manifold. The first compressor outputs first compressed air that enters the second compressor of the second (high pressure) turbocharger, wherein the second compressor is powered by the higher pressure exhaust gases flowing from the first chamber of the exhaust manifold. Figure 4 illustrates an exhaust manifold 400, a first turbine 430 of a first turbocharger and a second turbine 440 of a second turbocharger of a turbocharger arrangement according to an embodiment of the present disclosure. The exhaust manifold 400 comprises a first chamber 410 and a second chamber 420. The first chamber 410 may comprise one or more exhaust engine ports, wherein exhaust gases feed into the first chamber 410 via the one or more exhaust engine ports. The first chamber 410 may further comprise an exhaust gas recirculation (EGR) port, wherein exhaust gas may be fed from the first chamber 410 to the EGR system via the EGR port. In the example illustrated in Figure 4, the first chamber 410 comprises an EGR port 411 and first, second, third and fourth exhaust engine ports 412,413,414 and 415. The first chamber may comprise more or fewer exhaust engine ports than illustrated in Figure 4. The exhaust gases may flow from the exhaust engine ports 412, 413, 414, 415 into the first chamber 410 of the exhaust manifold 400. The first (high pressure) chamber 410 of the exhaust manifold 400 may be configured to feed the exhaust gases from the engine exhaust ports 412, 413, 414, 415 to the turbine housing (or turbine inlet) of the second turbine 440 of the second (high pressure) turbocharger. Arrow 441 illustrates gas flow into the second turbine 440. A portion of the exhaust gases may flow out of the first chamber 410 via the EGR port 411, rather than via the second turbine 440. Powering the second turbine reduces the pressure of the exhaust gases. The exhaust gases then flow from an outlet of the second turbine 440 into the second (low pressure) chamber 420 of the exhaust manifold. Gas flow out of the second turbine 440 is illustrated by arrow 442. The exhaust gases flow from the second chamber 420 into the turbine housing (or turbine inlet) of the first turbine 430 of the first (low pressure) turbocharger. Gas flow into the first turbine 430 is illustrated by arrow 431. The exhaust gases power the second turbine 440 when flowing from the first chamber 410 to the second chamber 420. As a result, the exhaust gases in the second chamber 420 may be at a lower temperature than the exhaust gases in the first chamber 410. In a particular, non-limiting example, the exhaust gases in the first chamber 410 may be at a temperature that is around 100°C higher than the exhaust gases in the second chamber 420. For example, the exhaust gases in the first chamber 410 may be at around 750°C and the exhaust gases in the second chamber 420 may be at around 650°C. An exterior face 416 of the first chamber 410 (wherein the exterior face 416 is opposite the exhaust engine ports and / or furthest from a cylinder head of the engine) is adjacent to the second chamber 420 and is cooled by the temperature difference between the first chamber 410 and the second chamber 420. Typically, the hottest point on exhaust manifold is the face furthest away from the cylinder head. Arranging the second chamber 420 (that is acting as interstage ducting between the second turbine and the first turbine) adjacent to the face of the exhaust manifold that is furthest from the cylinder head therefore allows for cooling of the hotspot of the exhaust manifold. This may improve robustness of the exhaust manifold to high exhaust gas temperatures. In certain embodiments, this may allow for lower grade materials to be used to manufacture the exhaust gas manifold. Furthermore, the exhaust gases passing through the second chamber 420 may be heated by the temperature difference between the first chamber 410 and the second chamber 420, thereby recovering some of the energy lost in the second turbine 440 that may then be used in the first turbine 430. As described, the first and second turbochargers may be arranged such that the air to be compressed first enters a lower pressure compressor of the first turbocharger and is then ducted to the higher pressure compressor of the second turbocharger. In certain embodiments, the duct may be cast into both first and second compressor housings with a sealing joint between them. In this way, there is no interstage ducting as the ducting is included in the compressor housing, such that the first compressed air passes directly from the first turbocharger to the second turbocharger. In other embodiments, another form of ducting may be used. In certain embodiments, interstage ducting may be used, such that the first compressed air passes from the first turbocharger to the second turbocharger via compressor interstage ducting. The opposing arrangement of the first and second compressors allows for minimal or no interstage ducting, since the outlet of the first compressor is adjacent to or close to the inlet of the second compressor. The inlet of the second compressor may be aligned with a direction of air flow out of the outlet of the first compressor. In certain embodiments, the first and second compressors may rotate in opposite directions. One of the first and second compressors may rotate clockwise and the other of the first and second compressors may rotate anticlockwise. In this way, overall size (also referred to as packaging size) of the turbocharger arrangement may be reduced. The centre of gravity of the turbocharger arrangement may be located closer to the centre of gravity of the engine. Figure 5 shows a perspective view of a turbocharger arrangement according to an embodiment of the present disclosure. The turbocharger arrangement 500 comprises a first turbocharger, wherein the first turbocharger comprises a first compressor 510 having an inlet 511 and an outlet 512. The first turbocharger further comprises a first turbine 520 configured to power the first compressor 510. The turbocharger arrangement 500 comprises a second turbocharger, wherein the first turbocharger comprises a second compressor 530 having an inlet 531 and an outlet 532. The second turbocharger further comprises a second turbine 540 configured to power the second compressor 530. In use, intake air enters the first compressor 510 via inlet 511. The intake air is compressed by the first compressor and first compressed air exits the first compressor via outlet 512 and enters the second compressor via inlet 531. The first compressed air is compressed by the second compressor 530 and second compressed air exits the second compressor via outlet 532, to be passed to an inlet manifold of the engine. An exhaust manifold 550 is also illustrated, wherein exhaust gases from the exhaust manifold pass into the second turbine 540 and then to the first turbine 530, via the second chamber of the exhaust manifold (not visible). The turbocharger arrangement 500 is also shown in Figure 6 from a different angle, and with other engine components behind it. Figure 7 illustrates the turbocharger arrangement 500 from the side, to show the opposing arrangement of the first and second compressors. The first (lower pressure) compressor 510 is supported by the right hand side of the exhaust manifold as illustrated, and the second (higher pressure) compressor 530 is supported by the left hand side of the exhaust manifold as illustrated. Having the first and second compressors arranged to be opposing in this way allows for the structural connection of the first and second turbochargers to be at opposite ends of the exhaust manifold. As a result, the modal mass of the system is split and the natural frequency of the arrangement is increased. A method of compressing intake air for an internal combustion engine comprising an exhaust manifold, is provided. The method may comprise any of the steps described above with relation to the turbocharger arrangement. The method comprises passing intake air into a first compressor of a first turbocharger mounted to the exhaust manifold. The intake air is compressed using the first compressor and first compressed air is output. The first compressed air is passed into a second compressor of a second turbocharger mounted to the exhaust manifold, wherein the second compressor opposes the first compressor. The first compressed air is compressed using the second compressor and second compressed air is output. The second compressed air is passed to an inlet manifold of the internal combustion engine. The second turbocharger is configured to receive exhaust gas from the engine via a first chamber of the exhaust manifold. The first turbocharger is configured to receive exhaust gas from the first turbocharger via a second chamber of the exhaust manifold.

Claims

1. A twin stage turbocharger arrangement for an internal combustion engine comprising an exhaust manifold, the twin stage turbo arrangement comprising a first turbocharger and a second turbocharger, wherein:the first turbocharger comprises a first compressor;the second turbocharger comprises a second compressor;the first and second turbochargers are each mounted to the exhaust manifold, wherein the relative orientation of the first and second turbochargers is such that the first compressor opposes the second compressor;the second turbocharger is configured to receive exhaust gas from the engine via a first chamber of the exhaust manifold; andthe first turbocharger is configured to receive exhaust gas from the second turbocharger via a second chamber of the exhaust manifold.

2. The twin stage turbocharger arrangement of claim 1, wherein:the first turbocharger is configured to receive intake air and compress the intake air to output first compressed air; andthe second turbocharger is configured to receive the first compressed air and compress the first compressed air to output second compressed air.

3. The twin stage turbocharger arrangement of claim 2, wherein the first compressed air passes from the first turbocharger to the second turbocharger via compressor interstage ducting.

4. The twin stage turbocharger arrangement of claim 2, wherein the first compressed air passes directly from the first turbocharger to the second turbocharger.

5. The twin stage turbocharger arrangement of any preceding claim, wherein: the second turbocharger comprises a second turbine configured to receive exhaust gas from the first chamber of the exhaust manifold and output exhaust gas to the second chamber of the exhaust manifold; andthe first turbocharger comprises a first turbine configured to receive exhaust gas from the second chamber of the exhaust manifold.

6. The twin stage turbocharger arrangement of any preceding claim, wherein one of the first and second compressors rotates clockwise and the other of the first and second compressors rotates anticlockwise.

7. The twin stage turbocharger arrangement of any preceding claim, wherein the firstchamber of the exhaust manifold is adjacent to the second chamber of the exhaust manifold such that heat transfer between the first and second chamber is enabled.

8. The twin stage turbocharger arrangement of any preceding claim, wherein a connection between the first turbocharger and the exhaust manifold is at a first end of the exhaust manifold and a connection between the second turbocharger and the exhaust manifold is at a second end of the exhaust manifold opposite the first end.

9. A method of compressing intake air for an internal combustion engine comprising an exhaust manifold, the method comprising:passing intake air into a first compressor of a first turbocharger mounted to the exhaust manifold;compressing the intake air using the first compressor and outputting first compressed air;passing the first compressed air into a second compressor of a second turbocharger mounted to the exhaust manifold, wherein the second compressor opposes the first compressor;compressing the first compressed air using the second compressor and outputting second compressed air; andpassing the second compressed air to an inlet manifold of the internal combustion engine;wherein:the second turbocharger is configured to receive exhaust gas from the engine via a first chamber of the exhaust manifold; andthe first turbocharger is configured to receive exhaust gas from the first turbocharger via a second chamber of the exhaust manifold.

10. The method of claim 9, wherein:the first turbocharger receives intake air and compresses the intake air to output first compressed air; andthe second turbocharger receives the first compressed air and compresses the first compressed air to output second compressed air.

11. The method of claim 10, wherein the first compressed air passes from the first turbocharger to the second turbocharger via compressor interstage ducting.

12. The method of claim 10, wherein the first compressed air passes directly from the first turbocharger to the second turbocharger.

13. The method of any preceding claim, wherein:the second turbocharger comprises a second turbine, wherein the second turbine receives exhaust gas from the first chamber of the exhaust manifold and output exhaust gas to the second chamber of the exhaust manifold; andthe first turbocharger comprises a first turbine, wherein the first turbine receives exhaust gas from the second chamber of the exhaust manifold.

14. The method of any preceding claim, wherein one of the first and second compressors rotates clockwise and the other of the first and second compressors rotates anticlockwise.

15. The method of any preceding claim, wherein the first chamber of the exhaust manifold is adjacent to the second chamber of the exhaust manifold such that heat transfer between the first and second chamber is enabled.

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