GB2276211A

GB2276211A - Variable geometry turbo charger

Info

Publication number: GB2276211A
Application number: GB9405093A
Authority: GB
Inventors: Geoffrey Light Wilde
Original assignee: Individual
Current assignee: Individual
Priority date: 1993-03-16
Filing date: 1994-03-16
Publication date: 1994-09-21
Anticipated expiration: 2014-03-16
Also published as: AU6215994A; GB9405093D0; GB9305331D0; WO1994021896A1; GB2276211B

Abstract

A variable geometry turbo charger has two or more arcuate nozzle arms 58, 60 each incorporating at least one fixed nozzle vane (66 - 86) the arms being pivoted either about a common centre or closely adjacent centres. The nozzle arms can be stowed in recesses 90, 92 which form an integral part of the turbo charger housing. <IMAGE>

Description

Variable Geometrv Turbo Charqer The present invention relates to a variable geometry turbo charger.

In particular the present invention is concerned with developments relating to the turbo charger described and claimed in European patent number 0 212 834 the contents of which are hereby incorporated by way of reference.

In EP 0 212 834 there is disclosed a turbo charger for an internal combustion engine the flow through which is controlled by a variable inlet created by a number of pivoted arms each of which contains at least one fixed nozzle.

The present invention seeks to provide a similar construction of variable geometry turbo charger but particularly adapted for large capacity, typically 10 to 12 litres, diesel engines, such as are used in trucks and rail cars.

Such diesel engines require the highest possible turbo charger efficiency over the full operating engine speed range. Thus it is not only a matter of generating high engine output at low engine speeds though this is still required but the turbo charger must perform with high efficiency at high engine speeds. In comparison with a variable geometry turbo charger designed for use with automotive gasoline engines such requirements make considerable demands on the variable geometry turbo charger performance.

In the case of the diesel engine the variable geometry requirement is more exacting because the turbo charger flow rate and hence its size is matched to the top or near the top speed of the engine in the interest of obtaining high super charge pressure with high efficiency at high power engine conditions.

For the diesel engine the incorporation of an exhaust waste turbo bypass valve in order to limit the turbo charger at maximum speed would reduce overall thermo efficiency and is not suitable. The consequence is that for a given engine volumetric displacement, the turbo charger flow rate required for a diesel engine is some 50% higher than for the normal gasoline engine employing waste control. Thus for the diesel engine the problem of increasing engine output at lower engine speeds calls for a wider range of variable geometry flow rates which in turbo charger terminology is expressed as requiring higher "turn down ratio".

The present invention seeks to provide a design of variable geometry turbo charger which increases turbo charger boost and efficiency down to at least one third engine speed whilst still maintaining a good performance at top engine speed. A flow "turn down ratio" of at least 3 to 1 is expected.

According to the present invention the design aims outlined above can be achieved by providing two or more arcuate nozzle arms each incorporating at least one fixed nozzle and the arms being pivoted either about a common centre or closely adjacent centres.

When the two arcuate nozzle arms are in the fully opened positions corresponding to the diesel engine operating in the high speed range the arcuate nozzles are stowed in two recesses which form an integral part of the turbine housing.

As the arcuate nozzle arms move outwards from the fully closed position corresponding to diesel engine operation at say 25% to 30% maximum speed engine exhaust gas starts to flow into the turbine rotor of the turbo charger partly through the nozzle vanes and partly directly from the volute into tangential side feed guide vanes.

A nozzle vane at the end of the volute can be permanently fixed to the turbine housing positioned between the ends of the nozzle arms when the nozzle arms are in the closed position.

The or each fixed nozzle in the nozzle arms can be shaped to accept a gas flow from a wide range of directions.

A fixed flow directing fence can be provided on the inner wall of the housing of the turbo charger.

The gas flow to the rotor can arrange to be progressively increased using the fixed nozzles, variable nozzles and the tangential side feed guide vanes, as the nozzle arms move from the closed to the open position.

At the low flow condition the inducer vanes of the turbo charger compressor are severely stalled and it should be beneficial to rotor efficiency to unstall the vanes, particularly over the high cambered outer sections. However, because the axial velocity into the inducer is so low, a large component of pre-swirl will be necessary to have a beneficial effect.

The invention proposes to generate a free-vortex pre-swirl ahead of the inducer such that the tangential velocity at the tip of the inducer is approximately half that of the inducer vane tip speed. A beneficial redistribution of flow with radius should take place through the inducer and rotor by increasing the axial velocity over the outer sections and reducing incidence angles.

The degree of pre-swirl required is large causing a significant reduction in power output of the rotor and loss of pressure ratio but that would be partially off-set by the increase in compressor efficiency obtained.

There are various ways of generating pre-swirl ahead of the compressor inducer. One of the simplest and effective ways of doing this is by means of tilting flat vanes installed in the duct of an intake elbow. The intake elbow becomes a swirl chamber at low engine speeds and air flows, and a simple elbow duct with modest or zero pre-swirl at high engine speeds and air flows. The swirl plates would be linked with the variable turbine nozzles.

The loss of torque and driving power of the turbine rotor at the low flow condition, not withstanding the high turbine nozzle velocity provided by the variable geometry nozzles, is due to the low mean efflux velocity from the exducer vanes.

Because higher rotor torque output at low flow condition is more important than high rotor efficiency at this condition, a device is suggested that might achieve an increase in rotor torque required.

Downstream of the turbine rotor it is proposed to provide an exhaust duct divided into two parts - an outer annular duct with fixed aerodynamic vanes to remove the residual swirl of the gas flow from the outer sections of the exducer, and an inner circular duct which is normally open to the gas flow from the inner sections of the exducer.

At the low flow condition this inner circular duct can be closed by rotating a circular throttle plate through 90". This forces all the flow in the rotor to enter the outer sections of the exducer and flow onwards into the outer annular duct. The outer sections of the exducer have the largest efflux angles to the axis of rotation and thereby will generate higher exducer torque reaction to augment the torque generated by the high nozzle velocity at the rotor tip.

The movement of the turbine nozzles, the compressor pre-swirl, and the turbine exducer throttle can all be linked together.

The present invention will now be more particularly described with reference to the accompanying drawings in which; Figure 1 shows a known variable geometry turbo charger.

Figure 2 shows front and side elevations of one form of variable geometry turbo charger according to the present invention with the nozzle arms in the stowed position; Figure 3 shows a view similar to figure 2 but with the arms in the fully deployed closed position; Figure 4 shows a side elevation cross-section of the turbo charger shown in figures 2 and 3; Figure 5 shows a detail of tangential side feed guide vanes of the turbo charger shown in figures 2 and 3; Figure Sa shows a detail of a flow deflecting fence of the turbo charger shown in figures 2 and 3.

Figure 6 shows a front elevation of the two nozzle arms in more detail; Figure 7 shows an end elevation of one of the arms shown in figure 6; Figure 8 shows a detail of one of the fixed nozzles in the arcuate nozzle arms; and Figure 9 shows an alternative method of mounting the arcuate nozzle arm.

Referring to figure 1 there is shown a turbine (10) having a variable inlet as described and claimed in my European patent number 0 212 834.

The turbine apparatus (10) includes a radial turbine (12) of a vehicle engine turbo charger (not shown) and has an internal entry flow passage (14). The flow passage (14) is arranged to receive motive gas for the turbine (12) from the vehicle engine exhaust and to discharge the motive gas to the inlet of the turbine rotor. In a vehicle the motive gas is usually the engine exhaust gas.

Downstream of the entry passage the flow areas are partly defined by two movable nozzle arms (16) and (18) which are pivoted respectively on spindles (20) and (22), the remainder of the passage being defined by fixed parallel walls of a casing (24) of the apparatus (10).

Each nozzle arm (16) and (18) incorporates nozzle vanes (26) (28) (30) and (32) (34) and (36) respectively.

The nozzle vanes of the arm (16) defines fixed nozzles (38) and (40) and the vanes on the arm (18) defines fixed nozzles (42) and (44).

The nozzle arms (16) has a variable inlet R and the nozzle arm (18) has a variable outlet V, and there is a variable area passage U between the nozzle arms (16) and (18).

The nozzle vane arms (16) and (18) are shown connected by a three element link system (46) which can be operated by a lever (48) so that upon movement of the lever (48) both vane arms (16) and (18) will pivot on their respective spindles (20) and (22) and the variable areas R, U and V will be altered to control the speed of the radial turbine (12). As an alternative a cam and lever system could be used to regulate the movements of the nozzle vane arms (16) and (18).

As shown the nozzle vane arms are actuated through the lever and link mechanism (26) to regulate the turbo charger speed in order to maintain the required engine supercharge pressure from 100% of crank shaft speed down to about 25% of maximum engine crank shaft speed.

The provision of the two nozzle vane arms enables a series of nozzles to be introduced immediately upstream of the turbine rotor (12) of much reduced flow area at low engine crank shaft speed compared with the volute casing area. In figure 1 the two nozzle vane arms (16) and (18) are in a position which corresponds to the maximum engine crank shaft speed and the turbine rotor (12) operates with vortex flow as in current superchargers.

The motive gas flows both through the fixed area nozzles (38) and (40) and (42) and (44) of the nozzle vane arms (16) and (18) and through the variable area passage inlet and outlets R,U and V.

The whole of the motive gas flows through the casing (24) of the turbine and none flows through a waste gate valve bypassing the turbine.

A throttle valve can be incorporated in the casing downstream of the turbine to enable the levels of the pressure at inlet and outlet of the turbine to be raised to reduce the volumetric flow of gas through the turbine should this be found to be necessary when adapting a particular design and size of turbine rotor to match the chosen engine gas flow.

As has been stated the form of variable inlet to the turbine rotor (12) shown in figure 1 was designed specifically for a gasoline automotive engine. The principal object of the variable geometry feature is to increase engine output at low engine speed to overcome the well known turbo charger engine performance deficiency of "turbo lag" in automobiles.

In applying the design to a diesel engine the variable geometry requirement is more exacting because the turbo charger flow rate and hence its size is matched to the top or near top speed of the engine in the interests of obtaining high supercharge pressure with high efficiency at high power conditions. For a diesel engine the incorporation of an exhaust waste gate turbo bypass valve to limit the turbo charger at maximum speed would reduce overall thermal efficiency and is therefore rejected in the present design.

The consequence is that for a given engine volumetric displacement the turbo charger flow rate required for a diesel engine is some 50% higher than for the normal gasoline engine employing waste gate control.

Hence for a diesel engine the problem of increasing output torque at low engine speeds calls for a wider range of variable geometry flow rate which in turbo charger terminology is expressed as requiring higher "turn down ratio".

The design of variable geometry turbo charger shown in figures 2 to 9 aims to increase turbo charger boost and efficiency down to at least one third engine speed whilst still maintaining a good performance at top engine speed.

Referring to the drawings and in particular to figures 2 and 3 there is shown a turbine apparatus (10) having a casing (52) which can be cast in two parts about an appropriate split line A-A.

The casing (52) has an inlet (54) and contains a turbine rotor (56) and two nozzle vane arms (58) and (60) which are pivoted on concentric spindles (62) and (64).

The nozzle vane arms (58) and (60) each have fixed nozzles (66), (68), (70), (72), (74); and (76), (78), (80), (82), (84) and (86) respectively.

A fixed nozzle vane (88) is fixed to the housing (52) between free ends (58A) and (60A) of the nozzle vane arms (58) and (60).

Flow passages X and Y are defined between the free ends (60A) and (58A) respectively and the fixed vane (88). A flow passage Z is defined between the opposite free ends (58B) and (60B) of the nozzle vane arms (58) and (60) respectively.

In figure 2 the nozzle vane arms are shown in the fully open position whilst in figure 3 the nozzle vane arms are shown in fully closed position. The casing (52) is provided with two pockets or recesses (90) and (92) for stowing the nozzle vane arms (58) and (60) when the vane arms are in the fully open position.

Referring particularly to figures 4 and 5 the casing (52) is provided with tangential flow passages (94) which are arranged to feed motive gas into the zone of the rotor tips of the turbine (56). The provision of the passages (94) enables a more progressive variation of nozzle flow from the lowest engine speed to the middle engine speed range as will be described below.

The casing (52) incorporates a fixed flow deflecting fence (96) (figures 2 and 5A) the purpose of which is to encourage motive gas to flow towards the rotor tip zone as will be described below.

Referring particularly to figures 6 and 7 the nozzle vane arms (58) and (60) are shown with more clarity though omitting the fixed nozzles in each arm. It will be noted that the nozzle vane arms (58) and (60) are a close fit within the casing (52) and seals can be provided between the arms and the casing walls if necessary. Also the arrangement of co-axial spindles (62) and (64) for the nozzle vane arms (58) and (60) respectively are shown more clearly, including the provision of ceramic bushes.

Referring to figure 8 the shape of the fixed nozzles in the nozzle vane arms (58) and (60) is shown more clearly. In comparison with the fixed nozzles as shown in figure 1 the design of the present fixed nozzles take account of two important factors.

At low engine speeds where the nozzle vane arms are in the closed or near closed position flow velocities in the volute are low and the flow direction indeterminate. There will be a large flow acceleration into the fixed nozzle passages so that the leading edges of the vanes defining the passages need to be able to accept the flow over a wide range of gas angles. The present fixed nozzles have a large radius to accept directional change.

The comparatively large size of the present turbo charger with that shown in figure 1 makes it possible to increase the number of nozzles to in the present case, twelve, and place the throat of the nozzles nearer to the tips of the rotor blades of the turbine (56). There should be an improvement in the circumferential distribution of flow to improve turbine efficiency and ensure that the high velocity jets issuing from the fixed nozzles impinge more directly and uniformally onto the turbine rotor blades to generate higher torque.

The vanes defining the fixed nozzles are precision cast integrally with the nozzle vane arms. The vane trailing edges have been reduced to a thickness of approximately lmm to increase the efficiency of the nozzle flow into the turbine rotor.

Referring to figure 9 instead of the nozzle vane arms (58) and (60) being mounted on a common centre they can be mounted on spindles at a closely adjacent centres as shown.

Initially the nozzle vane arms (58) and (60) are in the closed position as shown in figure 3 and as engine speed increases the arms are moved progressively outwardly until at maximum engine speed the nozzle vane arms are stowed in the recesses (90) and (92) in the housing (52).

There are three stages in the development of the gas flow to the turbine rotor tips from the closed position of the nozzle arms to the intermediate position of the nozzle arms covering the engine speed range from approximately 25% speed to approximately 50% engine speed. These stages are: 1). flow through twelve equal nozzles only when the nozzle vane arms are in the closed position (figure 3); 2). flow through nine fixed nozzle throats augmented by flow through the three variable nozzles X, Y and Z.

3). flow from 1 and 2 above augmented by the tangential gas flow through the passages (94) at the side fed directly from the volute.

As the nozzle vane arms move further outwards the flow through the nine fixed nozzles reduces to a negligible proportion, the flow increasing progressively directly from the volute.

In the half way positions between the nozzle vane arms being fully closed and fully open, the arms cause some blockage to the flow from the volute at certain angular positions around the volute. This blockage will generate some additional losses and a reduction of turbine expansion efficiency. The present design aims to minimise these losses. As the nozzle vane arms move to fully open positions they withdraw into the pockets (90) and (92) away from the vortex in the volute. This is assisted by the flow deflecting fence (96) which encourages the vortex flow to flow towards the rotor tip zone leaving the nozzle vane arms stored in a relatively ambient region of the flow.

The angular positions of the nozzle vane arms (58) and (60) are arranged to maintain substantially constant engine supercharge pressure from approximately 25% engine speed to 100% speed and an operating mechanism for the nozzle vane arms (58) and (60) can be provided to achieve this objective Referring to figure 10 there is shown a compressor (100) of the turbo charger comprising a casing (102), a compressor rotor (104) arranged to drive the turbine of the turbo charger, the casing including an elbow (106) and an inlet (108).

Disposed within the inlet (108) there are shown two swirl vanes (110) in the low engine speed position. In this position a free vortex pre-swirl is provided to the inlet gasses before entering the compressor rotor (104). At the low engine speed condition the vanes of the compressor rotor are severely stalled, and the pre-swirl applied to the intake gasses has the effect of unstalling at least in part these vanes.

Referring to figure 11 the exhaust from the turbine rotor of the turbo charger flows into an exhaust duct (110) which is divided into two parts by means of a shroud (112) which is supported from the wall of the exhaust duct (110) by a number of equi-spaced exducer efflux vanes (114). Disposed within the shroud is a valve (116) which is shown in the closed position.

The shroud divides the exhaust duct into an outer annular duct (118) with fixed aerodynamic vanes in order to remove the residual swirl of the gas flow from the outer sections of the exducer and an inner circular duct (120) which is normally open to the gas flow from the inner sections of the exducer.

At the low flow condition the inner circular duct is closed by the valve (116) so that it is in the position shown in figure 11.

All the flow is thus forced to enter the outer section of the exducer and flow into the outer annular duct (118). The outer sections of the exducer have the largest efflux angles to the axis of rotation and will thereby generate higher exducer torque reaction to augment the torque generated by the high nozzle velocity at the rotor tip.

Claims

1. A variable geometry turbo charger of the type disclosed in my European patent number 0 212 834 having two or more arcuate nozzles each incorporating at least one fixed nozzle characterised in that the arms are pivoted either about a common centre or closely adjacent centres.

2. A turbo charger as claimed in claim 1 characterised in that when the two arcuate nozzle arms are in the fully open position corresponding to an engine operating in the high speed range the arcuate nozzles are stowed in two recesses which form an integral part of the turbine housing of the turbo-charger.

3. A turbo charger as claimed in claim 1 or claim 2 characterised in that as the arcuate nozzle arms move outwards from the fully closed position corresponding to the engine operation at approximately 25 to 35% maximum speed engine exhaust gas starts to flow into the turbine rotor of the turbo charger partly through the nozzle vanes and partly directly from the volute into tangential side feed guide vanes.

4. A turbo charger as claimed in any one of the preceding claims characterised in that there is provided a nozzle vane at the end of the volute which is permanently fixed to the turbine housing and positioned between the ends of the nozzle arms when the nozzle arms are in a closed position.

5. A turbo charger as claimed in any one of the preceding claims characterised in that the or each fixed nozzle in the nozzle arms are shaped to accept the gas flow from a wide range of directions.

6. A turbo charger as claimed in any one of the preceding claims characterised in that there is provided a fixed flow directing fence on the inner wall of the housing of the turbo charger.

7. A turbo charger as claimed in any one of the preceding claims characterised in that the compressor of the turbo charger has an inlet including gas swirl means.

8. A turbo charger as claimed in claim 7 characterised in that the swirling means comprise two or more swirl vanes which can be moved between a position in which zero swirl is imparted to the incoming gases to a position where swirl is imparted to the intake gasses.

9. A turbo charger as claimed in any one of the preceding claims characterised in that the exhaust duct of the turbine of the turbo charger includes blocking means.

10. A turbo charger as claimed in claim 9 characterised in that the exhaust duct of the turbine is divided into an outer annular duct and a central circular duct, valve means being provided within the central circular duct, the valve means being operable between a position allowing gas to flow both through the outer annular duct and the central circular duct and to a closed position in which the exhaust flow is directed principally through the outer annular duct.