GB2446597A

GB2446597A - Radial flow turbine control

Info

Publication number: GB2446597A
Application number: GB0702757A
Authority: GB
Inventors: Ben Finnigan; Graham Cox
Original assignee: IHI Charging Systems International GmbH; PCA ENGINEERS Ltd
Current assignee: IHI Charging Systems International GmbH; PCA ENGINEERS Ltd
Priority date: 2007-02-13
Filing date: 2007-02-13
Publication date: 2008-08-20
Also published as: GB0702757D0

Abstract

A radial flow gas turbine has a scroll 5 surrounding a turbine wheel 1, the scroll 5 having a first inlet arranged to direct gases from a gas supply manifold in a first direction A around the scroll 5. A valve 7 is movable to open or close a second inlet 6 in response to the gas pressure in the manifold, the second inlet 6 being arranged to direct gases from the gas supply manifold in a second, opposite, direction B around the scroll 5, thereby controlling the increase in rotational speed of the turbine wheel 1 as the volume of gases passing there through increases above a predetermined level. A second, smaller, scroll (11, figures 2, 3) may be provided in parallel with the scroll 5, the second scroll (11) having an inlet permanently in communication with the gas supply manifold. In this arrangement the first and second inlets of the scroll 5 may both be closed by valve 7 and all of the gas from the manifold supplied to the second scroll (11).

Description

RADIAL FLOW GAS TURBINE

Field of the Invention

This invention relates to a gas turbine, for example an exhaust gas-driven turbocharger for use with an internal combustion engine.

Background to the Invention

The use of turbochargers with internal combustion engines is becoming increasingly common, in the effort to increase engine power and efficiency.

Typically, a turbocharger will have a radial turbine surrounded by a tapering scroll by which engine exhaust gases are led into the turbine wheel. The tur-bine drives a radial air compressor which supplies compressed air to the inlet manifold for the engine.

The design of the turbocharger cannot be optimum for all engine speeds and conditions; if the turbocharger is designed to give a boost in inlet pressure, and therefore engine power, at low engine speeds, for example to improve ac-celeration from start, the boost may be excessive at higher engine speeds. On the other hand, a turbocharger designed to give a boost to power at higher en-gine speeds will not have significant effect at lower speeds. The design of the scroll is important here, because it determines the angle at which the gas flow enters the turbine wheel. The more nearly the gas flow is tangential to the cir- cumference of the turbine wheel as it enters the wheel, the greater the momen-tum imparted to the wheel.

Two strategies are typically employed to try to contrQl the turbocharger output at higher engine speeds. The most common of these is the waste gate, which is valve-controlled to dump some of the gases from the scroll back into the exhaust outlet, effectively by-passing the turbine wheel. While this limits the momentum imparted to the turbine wheel at higher engine speeds, it does also reduce the volume of exhaust gases available to do work in compressing the air supplied to the engine inlet.

An alternative, although sometimes additional, approach is to increase the angle at which the gases enter the turbine wheel with increasing engine speed. This may be achieved by the use of rotatable vanes in the scroll sur-rounding the turbine wheel, with means to increase the vane angles relative to a tangent to the periphery of the wheel with increasing engine speed and there-fore flow of exhaust gases. A problem with this approach is that the moving parts are exposed to high temperatures and are costly to manufacture, while representing a potential point of failure of the turbocharger. Because of tern-perature and cost considerations, this type of mechanism has typically been confined to use on diesel engines, where exhaust gas temperatures tend to be lower than experienced in petrol/gasoline and other spark ignition engines.

Another approach is to use a combination of two scrolls to feed exhaust gases to the turbine wheel. A smaller scroll remains open at all times, while a larger scroll is opened to the exhaust gas flow by a valve only at a predeter-mined engine speed (or exhaust manifold pressure, where the valve is operated by that pressure). While this does achieve a better uniformity of performance than a single scroll, it will typically still require a waste gate arrangement for higher speeds, since space considerations in the engine compartment around the exhaust manifold and the catalytic converter limit the size of additional scroll that can be added.

US6073447 discloses another approach, in which a smaller scroll is sur-rounded by a larger scroll communicating with the smaller scroll through angled apertures through the dividing wall between the scrolls. A valve admits gases to the outer scroll at higher engine speeds which then flow through the aper-tures into the inner scroll, thereby decreasing the flow velocity and increasing the angle at which the gases enter the turbine wheel, reducing the momentum imparted to the wheel. This arrangement, while reducing some of the disadvan- tages of the use of a single scroll or two fixed scrolls, gives rise to some disad- vantages. Firstly, the formation of the apertures requires difficult precision cast-ing techniques, and checking the results is very difficult. Secondly, because the inner scroll can communicate with the outer scroll even when the outer scroll is closed by its control valve, the turbine is less responsive to sudden peaks in pressure when accelerating from low speeds, because there is a tendency for the pressure pulse to be reduced by outward flow into the outer scroll. -3.

Summary of the Invention

The present invention seeks to overcome these disadvantages by provid-ing a radial flow turbine having a scroll surrounding a turbine wheel, the scroll having a first inlet arranged to direct gases from a gas supply manifold in a first direction around the scroll, and a valve movable to open or close a second inlet in response to the gas pressure in the manifold, the second inlet being arranged to direct gases from the gas supply manifold in a second, opposite, direction around the scroll, thereby controlling the increase in rotational speed of the tur-bine wheel as the volume of gases passing therethrough increases above a predetermined level.

The valve may be configured to open the second inlet progressively as the manifold pressure increases, although it might alternatively be arranged to flip between an open and a closed position at a predetermined pressure. The valve may be operated by a pressure or vacuum actuator, or it may be operated electromechanically, or by a solenoid, by an electrical control system, for exam-ple an engine management computer system.

The radial flow turbine may be a small gas turbine driving an electrical generator or the like, but in a preferred embodiment the turbine forms part of a turbocharger for an internal combustion engine, suitably, but not exclusively, a spark ignition internal combustion engine driving a motor vehicle.

In a preferred embodiment, the turbine is provided with a second scroll, pref-erably of smaller volume than the first scroll, feeding gases into the turbine wheel in parallel with the first scroll, the second scroll having an inlet thereto permanently communicating with the manifold and the valve on the first scroll being arranged to be movable between a first position, in which the first and second inlets are both closed, through an intermediate position, in which the first inlet is open and the second inlet is closed to a second position, in which the second inlet is open. The valve may be moved progressively between the first and second positions or be flipped in stages from the first position to the 3o intermediate position and to the second position (and vice versa). The second scroll is suitably of smaller volume than the first scroll.

The valve preferably comprises a rotatable valve member having an L-shaped section in which the free end of the L-shape is coupled to a pivot and the cross-member of the L-shape has an outer surface which is an arc of a cir- cle whose centre coincides with the axis of the pivot, said outer surface co-operating with a correspondingly-curved valve seat over at least part of the movement thereof.

A passageway may extend between the manifold and the first and sec-ond inlets, the valve member defining a movable wall of the passageway. The first and second inlets may be separated from each other by a tapering member engaged by the cross-member of the L-shape to seal off the second inlet.

The turbine of the invention can be arranged to avoid the need for a waste gate, while keeping the turbine compact, an important consideration in the design of turbochargers for vehicle engines, where space considerations would preclude the inclusion of a larger scroll. Where a waste gate is avoided, the need for additional valve controls is also avoided, simplifying construction and potentially increasing reliability. While the design will typically be optimised to avoid the need for a waste gate, there is the possibility that such a standard design could be easily modified to extend its working range by the addition of a waste gate system if required.

BrIef Description of the Drawings

In the drawings, which illustrate an exemplary embodiment of the inven-tion: Figure 1 is a sectional plan view of the turbine part of a turbocharger; Figure 2 is a vertical section through one side of the turbocharger show-ing the additional small scroll mounted above the main scroll shown in Figure 1; and Figure 3 is a schematic perspective view showing relative positions of the scrolls.

Detailed Description of the Illustrated Embodiment

Referring first to Figure 1, the turbine wheel is indicated diagrammatically at 1, and is mounted within a housing 2 having an inlet passageway 3 which connects to an engine exhaust manifold (not shown). The passageway 3 opens, by way of a valve 4, described hereinafter, into a tapering scroll 5 which continues around the wheel through 3600 in conventional manner. However, a second inlet 6 from the passageway 3 directs exhaust gases, when opened, into the scroll 5 in the reverse direction, reducing the tangential velocity of the main gas stream and changing its angle of flow into the wheel 1. This ensures that, as the gas flow increases with increasing engine speed, the full volume of gas passes through the turbine to do work in compressing the incoming air in the compressor (not shown), but without increasing the speed of the turbine and thereby increasing the air pressure generated by the compressor. The boost in engine power produced by the turbocharger is therefore controlled, rather than increasing too rapidly.

The flow of gases into the turbine is controlled by the valve 4, which con-sists of a pivotable gate 7 having in profile an L-shape. The gate is mounted on a pivot shaft 8, which is rotated by an external actuator (not shown), which can be powered by a pressure or vacuum actuator, or by art electromechanical ac-tuator or solenoid controlled by the engine management computer, for example.

The main leg 7a of the L-shape serves, when in the fully closed position as illus-trated in Figure 1, as a barrier to the entry of the gases into the scroll 5. This configuration would only be employed when a permanently open secondary smaller scroll is provided, as hereinafter described with reference to Figures 2 and 3. The cross-member 7b of the L-shaped gate has a curved configuration, the outermost surface of which is an arc of a circle centred on the axis of the shaft 8. An extension 9 to the housing 2 is shaped to receive the gate 7 therein, so that the main leg 7a forms part of the wall of the passageway 3 when the valve is fully open. The scroll 5 is partially defined by a moulding 10 which also defines the two inlets to the turbine and which is engaged by the cross-member 7b of the gate when it is in its intermediate position closing the second inlet 6 but allowing flow into the main scroll 5.

Referring now to Figures 2 and 3, the smaller permanently-open scroll 11 is mounted above the scroll 5, but opens at its centre into the same turbine wheel, so that the gases from it act upon the wheel substantially tangentially so as to achieve the greatest momentum from the initial relatively low flow achieved when the engine is accelerating from low speed. This ensures a satis-factory starting boost. The smaller scroll 11 has its own inlet passageway 12, connected to the manifold separately. In Figure 3, the inlets to the scroll 5 are shown as separated along their entire length. It will be appreciated, however, that these are more conveniently interconnected as illustrated in Figure 1.

In use, when the flow through the smaller scroll 11 approaches its maxi-mum, the gate 7 is rotated to open the scroll 5 to allow the additional flow through to act on the turbine without excessively increasing its speed. This may be done progressively in response to the increase in engine speed, i.e. partially opening the inlet to the scroll 5 initially and then gradually increasing the degree of opening, or it may be done stepwise, with the gate 7 rotating to open the inlet to the scroll 5 fully while keeping the second inlet 6 closed until the gas pres-sure tends towards the point at which excessive rotational speed of the turbine is likely to ensue, at which point the gate 7 is further rotated to open the second inlet 6, allowing some of the incoming gases to flow into the scroll 5 in the re-verse direction, causing lower velocities of the gases swirling around the scroll from the main inlet and increasing the angle at which the gases enter the tur- bine wheel. This in turn reduces the efficiency of energy extraction in the tur- bine wheel so that the increased gas flow through it does not result in a continu-ing increase in rotational speed, with corresponding excessive boost in inlet pressure to the engine.

The movement of the gate 7 at this stage may also be progressive, or in a step to open the second inlet fully. With a fall-off of engine speed, the move-ment of the gate 7 would be reversed to avoid the turbocharger boost dropping off too rapidly. In this way, the performance of the turbocharger can be matched more closely to what is required over a given flow range while still enabling a relatively compact turbocharger to be employed.

Claims

1. A radial flow gas turbine having a scroll surrounding a turbine wheel, the scroll having a first inlet arranged to direct gases from a gas supply manifold in a first direction around the scroll, and a valve movable to open or close a second inlet in response to the gas pressure in the manifold, the second inlet being arranged to direct gases from the gas supply manifold in a second, opposite, direction around the scroll, thereby controlling the increase in rota-tional speed of the turbine wheel as the volume of gases passing therethrough increases above a predetermined level.

2. A turbine according to Claim 1, wherein the valve is configured to open the second inlet progressively as the manifold pressure increases.

3. A turbine according to Claim 1, wherein the valve is configured to flip between an open and a closed position at a predetermined pressure.

4. A turbine according to Claim 1, 2 or 3, wherein the valve is oper-ated by a pressure or vacuum actuator.

5. A turbine according to Claim 1, 2 or 3, wherein the valve is be op-erated electromechanically, or by a solenoid.

6. A turbine according to Claim 5, wherein the valve is controlled by an electrical control system, such as an engine management computer system.

7. A turbine according to any preceding claim, provided with a sec-ond scroll feeding gases into the turbine wheel in parallel with the first scroll, the second scroll having an inlet thereto permanently communicating with the mani-fold and the valve on the first scroll being arranged to be movable between a first position, in which the first and second inlets are both closed, through an in-termediate position, in which the first inlet is open and the second inlet is closed to a second position, in which the second inlet is open.

8. A turbine according to Claim 7, wherein the second scroll is of smaller volume than the first scroll.

9. A turbine according to any preceding claim, wherein the valve comprises a rotatable valve member having an L-shaped section in which the free end of the L-shape is coupled to a pivot and the cross-member of the L-shape has an outer surface which is an arc of a circle whose centre coincides with the axis of the pivot, said outer surface co-operating with a correspond-ingly-curved valve seat over at least part of the movement thereof.

10. A turbine according to Claim 9, wherein a passageway extends between the manifold and the first and second inlets and the valve member de-fines a movable wall of the passageway.

11. A turbine according to Claim 10, wherein the first and second inlets are separated from each other by a tapering member engaged by the cross-member of the L-shape to seal off the second inlet.

12. A radial flow gas turbine, substantially as described with reference to, or as shown in, the drawings.

13. A turbocharger, comprising a radial flow gas turbine according to any preceding claim coupled to a compressor to compress air supplied to the cylinders of an internal combustion engine.

14. An internal combustion engine incorporating a turbocharger ac-cording to Claim 13.

15. An engine according to Claim 14, which is a spark-ignition engine.

16. A motor vehicle having an engine according to Claim 14 or 15.