GB2166800A - Controlling gas compressors - Google Patents

Abstract

The compressor, for use in a supercharger, comprises a gas inlet nozzle (3) leading to a centrifugal impeller (41) for accelerating gas to be compressed by the compressor, the inlet nozzle containing an axially moveable shroud (1) defining an annular clearance about an upstream portion of the impeller and being moveable to vary the annular clearance and to open and close a subsidiary gas flow path (6) defined as grooves or flutes between axial ribs supporting the shroud (1) within the nozzle (3), the movement of the shroud enabling control of maximum supercharger boost pressures. The shroud is moved by an operating lever 9 controlled in dependence on the supercharger boost pressure or on various operating parameters of an internal combustion engine supplied by the supercharger. The impeller is rotated by an epicyclic drive. <IMAGE>

Description

SPECIFICATION Gas compressors The present invention relates to improvements in the design of gas compressors, particularly in respect of inlet nozzles for such gas compressors and has particular relevance to superchargers incorporating gas compressors for use with internal combustion engines.

In a supercharger for an internal combustion engine, a gas compressor of some type is driven from a power take off from the engine to compress air to be fed to the engine. A particularly desirable form of gas compressor is a centrifugal gas compressor. Using a compressor of this type, it is possible to construct a supercharger suitable for a high capacity engine, e.g. up to 7 litres, which is of compact dimensions.

A problem which arises in connection with the use of a compressor of this type is that the compression obtained is heavily dependent upon the speed of rotation of the impeller of the compressor. Generally speaking, the compression obtained increases as the square of the rate of rotation of the crank shaft. Thus, if the desired degree of compression is obtained at relatively low engine speeds, a very high degree of compression will be obtained when the maximum rated speed of the engine is used. Alternatively, if the desired degree of compression is chosen for the maximum rated speed of the engine then, inadequate compression will be obtained at low engine speeds.

These extreme pressure differences with engine speed can cause the engine output to become unmanagable and critically effect a vehicles performance.

Centrifugal impellers for superchargers for internal combustion engines should ideally run at speed such that the tip speed of the impeller approaches 300 metres per second. Because of these high impeller speeds, inertia loading of the impeller when the engine is rapidly decelerated stresses the overdrive gearing used to produce the high impeller speeds. Some method of damping out these stresses is therefore desirable.

Previous attempts to cope with these problems have led to superchargers being produced which are over large and over complicated thus reducing the cost effectiveness of mechanically driven superchargers as well as limiting their scope of application.

As an example of an approach to problems of this nature, United States patent specification 2828907 describes a supercharger provided with a control mechanism intended to reduce the compression obtained at high engine speeds. Pressure from the supercharger is used to drive a piston to expand the hub of a variable diameter pulley to cause a reduction of the compressor impeller speed. However, the resulting mechanism is complex and bulky.

It is however in principle desirable to provide feedback from the state of operation of the engine to optimise supercharger performance so as to improve performance and reduce running costs of the engine.

Another approach to regulating the boost pressure provided by a centrifugal compressor is to throttle the air flow either upstream or downstream of the compressor. This however gives rise to undesirable effects as well as controlling the mass flow through the compressor. Amongst the undesirable effects are a rapid increase in air temperature and a decrease in the efficiency of the compressor. Where the compressor is a supercharger for an engine, the rapid increase in air temperature can raise cylinder temperatures and hence the liklihood of detonation of the air fuel mixture leading to severe engine damage such as melting of pistons.

The decrease in the efficiency of a supercharger through throttling causes the supercharger to take more and more power from the engine whilst providing less and less benefit.

An alternative solution which has been employed to regulate boost pressures is to dump excess pressure by means of a pressure relief valve. However, this is undesirable because engine power is consumed in producing the pressurised air and is simply wasted when the air pressure is dumped. This method is however often relied upon at present to deal with the excess pressures and high temperatures caused by rapid closing of the engine throttle at high engine speeds.

There is therefore still a need for a satisfactory method of regulating the boost provided by a directly driven engine supercharger.

The present invention provides a gas compressor, for instance for use in a supercharger, comprising means defining a gas inlet path leading to an impeller for accelerating gas to be compressed by the compressor, said inlet path defining means including moveable means defining an annular clearance about an upstream portion of the impeller and being moveable selectively to vary said annular clearance.

The moveable means is preferably an annular shroud covering the inlet portion of the impeller.

As will be shown by embodiments described in detail hereafter, such an arrangement may enable control of the boost pressures produced by a super charger at high engine speeds and may assist in avoiding stress and overheating in the supercharger upon sudden throttle closing.

Optionally, the inlet path comprises means defining a main flow path for the gas from an inlet end thereof to the impeller and means defining a subsidiary flow path separated from the main flow path and extending from a downstream portion thereof, e.g. adjacent said impeller, and said moveable means selectively opens and closes said subsidiary flow path as well as varying said annular clearance.

Preferably, the subsidiary flow path has a junction with said main flow path upstream of said impeller. In such a system, the subsidiary flow path can under some operating conditions feed back gas from a downstream portion of the main flow path to an upstream portion. Under other operating conditions it may provide an additional flow path for gas flowing in the same direction as in the main flow path, thus helping to increase mass flow through the impeller.

However, alternatively the subsidiary flow path may be routed to extend into the main flow path from outside the main flow path altogether.

Even where no separate subsidiary flow path is provided in the sense of a flow path physically separated from the main flow path by a component or components of the compressor a proportion of the gas flowing through the inlet path may be permitted or caused to flow against the main stream of the gas flowing through the inlet, away from the impeller under certain operating conditions.

The moveable means may take the form of a tubular member axially slideable with respect to the impeller within means defining inlet flow path as a whole.

Such a moveable means may operate as an annular shutter over an end of a subsidiary flow path as described above.

If desired, an additional control means may be provided to close and open the end of the subsidiary flow path more remote from the impeller.

Preferably, the subsidiary flow path is defined between an interior wall of the means defining the inlet flow path and the moveable means, said moveable means being in the form of a tubular member longitudinally slidable within the inlet flow path defining means and having a portion or portions spaced therefrom to produce said subsidiary flow path.

Conveniently, the interior wall of the inlet flow path defining means is provided with one or more axially elongate radial recesses such as grooves or flutes to define the subsidiary flow path.

Suitably, the recess or recesses end at a zone contactable by the moveable means to close off the subsidiary flow path.

Alternatively, there may be an inwardly projecting ledge around the interior of the said wall against which said moveable means abuts to close said subsidiary flow path and from which it is withdrawn to open said subsidiary flow path.

Suitably, an operating member extends from said moveable means through said wall to the exterior thereof and said means is moveable to vary the annular clearance, and open or close said inlet or inlets to the subsidiary flow path if provided, by movement of said operating member.

For instance, a cam slot may be provided through a wall defining said inlet path and the operating member may be in camming engagement with said slot to govern movement of said moveable means.

In such an arrangement, the moveable means may be a tubular member longitudinally moveable to control the annular clearance and optionally the degree of opening of the subsidiary flow path but is rotatably mounted within the operating member projecting through a cam slot in the inlet flow path wall such that rotation of the tubular member by movement of the operating member causes longitudinal displacement of the tubular member in proportion to the degree of rotation.

More preferably, the tubular member is controlled for axial movement to vary the annular clearance by axially located control means. This may take the form of an axially extending control member, e.g. a control rod, joined to the tubular member by one or more webs or struts.

The control member or operating member may be moved in response to the operating conditions of an engine equipped with a supercharger according to the invention. The movement may be hydraulicly, pneumatically or mechanically produced or may be produced by a combination of these working together or in opposition. For instance, engine oil pressure, manifold pressure/vacuum, solenoids actuated by engine monitoring sensors or direct linkage to the throttle may be used to produce some or all of the desired movements.

However the movement is produced, it is preferably related to the engine operation conditions so that the following status is achieved: Engine Condition Annular clearance low to mid range engine speeds with part throttle enlarged low to mid range engine speeds with the throttle fully or substantially open preferably reduced high engine speed with throttle open reduced high engine speeds with throttle shut (i.e. full engine braking) enlarged At idle the annular clearance is of less importance but is preferably enlarged.

Preferably the impeller is an unshrouded centrifugal impeller.

The compressor preferably further comprises a power input shaft, a planetary epicyclic gear having a planet carrier connected to be rotated by the power input shaft, a fixed annulus and a sun wheel drivingly connected to the impeller.

Preferably, the planet carrier is engaged with a plurality of balls as planetary elements and said sun wheel comprises a ball race which is frictionally engaged by said balls.

Preferably, the annulus is restrained from rotation by friction means such that the annulus will rotate if subjected to heavy torque.

A friction drive mechanism of this general kind for rotating an impeller is described in United States patent specification 2828907 and a modification of the type of drive described there is described in detail hereafter.

The invention includes a supercharger containing a compressor as described above and further includes internal combustion engines provided with such a supercharger.

The invention also includes motor vehicles incorporating such internal combustion engines, particularly wheeled vehicles such as motor cars, trucks and buses.

The invention will be illustrated by the following description of preferred embodiments thereof with reference to the accompanying drawings in which.

Fig. 1 shows a cross-sectional view on the main rotational axis of a supercharger according to the invention; and Figure 2 shows a cut away view of a second type of supercharger according to the invention.

As shown in the Fig., a supercharger according to the invention has an air inlet nozzle 3 defining a main flow path for air to a centrifugal impeller 41 mounted for rotation to be driven directly from the internal combustion engine upon which the supercharger is mounted by a mechanism to be described hereafter. Air passing through the nozzle is accelerated by the impeller into a central diffuser 12 and passes out of the supercharger through an outlet nozzle diffuser 11. The accelerated air is slowed by the diffuser causing a conversion of kinetic energy to produce an increase in pressure. The use of the outlet nozzle diffuser enables the convolute central diffuser 12 to be of reduced size.

In more detail, the supercharger illustrated comprises a circular section air inlet nozzle 3 defined by an outer cylindrical wall member 5 mounted coaxially on a cylindrical wall portion 5a of an upper casing member 33 forming part of the casing of the supercharger.

A longitudinally moveable inner tubular member 1 having a cylindrical exterior shape is slidably mounted within the cylindrical wall 5 and extending down as a close sliding fit into the cylindrical mouth 5a of the casing member 33. A plurality of axially extending grooves or flutes in the mouth of the casing member 33 produce with the cylindrical shutter a plurality of passageways 6 constituting a subsidiary gas flow path between the tubular member and the casing member 33 and leasing up to an annular space 2 between tubular member 1 and wall member 5. At the very base of the cylindrical mouth 5a of the casing member 33 the grooves terminate at the level indicated by numeral 49 where the inboard end of the tubular member 1 can seal against the mouth 5a in a gas tight manner.An outwardly projecting annular bead 4 is formed on the exterior of the tubular member 1 above the level of the cylindrical mouth 5a of the casing portion 33. Bead 4 abuts the top of the cylindrical mouth 5a of the casing member 33 when the tubular member is moved to its innermost position such that its inboard end seals the ends of the passageways 6.

Tubular member 1 carries an operating lever 9 which protrudes through a cam slot 8 in the casing 33 for connection to an actuator (not shown). Movement of the operating lever 9 in the cam slot 8 rotates the tubular member 1 and also moves the tubular member 1 longitudinally in the cylindrical mouth 5a of the casing member 33. The operating lever 9 is attached to the tubular member 1 at a portion thereof which contacts the mouth 5a in a region without the grooves producing the air passages 6 but which is a sealing fit against the cylindrical mouth portion of the casing member 33 so that there is no air escape path through the cam slot 8.

The range of movement of the tubular member 1 is indicated by the shaded area 7.

The inner surface of the tubular member 1 is so configured that the cross-section of the main flow path progressively decreases on moving inwards along the flow path and then rapidly increases toward the lower, inboard end of the tubular member 1. This compliments the shape of the inlet side of the centrifugal impeller 41 coaxially mounted in the nozzle 3 at the inboard end thereof and having a plurality of vanes protruding from a central hub bearing a nose cone 42.

The diameter of the impeller increases sharply on moving further into the supercharger, i.e.

downwards in the Figure.

The annular clearance between the upstream portion of the impeller and the tubular member may be enlarged by moving the tubular member up and may be reduced by moving it down.

The tubular member serves as a variable position shroud about the top of the impeller 41.

An exhaust path for compressed gas is formed in a central casing member 34 to which the casing member 33 is attached by bolts. An annular central diffuser 12 for the compressed gas is provided in the central casing member 34 and a continuous flow path is provided through the nozzle 3, over the impeller 41 and out through the tips of the impeller into the central diffuser 12. An outlet nozzle diffuser 11 is provided in the upper casing member 33 in communication with a part of the central diffuser 12.

The drive mechanism for the impeller 41 is contained within the central casing member 34 and a lower casing member 35 secured to the central casing member 34 on a side opposite to the upper casing member 33.

The drive mechanism is similar in principle to that described in United States patent specification 2828907 but is greatly improved in compactness and simplicity and provides an epicyclic drive to the impeller.

A low speed power input shaft 27 is positioned coaxial with the impeller and enters the lower casing member 35 through a central apperture therein. Shaft 27 is provided with a smaller diameter portion at step 40 for mounting a pinion or pulley (not shown) for driving the shaft.

Shaft 27 is supported at its entry to the casing 35 in a ball race 29 retained in place by circlips 31 and provided with an oil seal 32 itself retained by a circlip 30. At its inboard end shaft 27 is supported with a roller bearing 28. Within casing portion 35 a high speed shaft 15 extends coaxially from the impeller and terminates in a reduced diameter portion in the form of pilot shaft 25 received in a counter bore in the inboard end of low speed shaft 27 in a needle roller bearing 26. In its central area, the high speed shaft 15 is provided with an enlarged diameter portion constituting an inner ball race 24 in engagement with which are a plurality of balls 17. A pair of annular ball races 16, 18 are positioned on either side of the median plane of the ball race 24 and the associated balls 17.The upper race 16 is a friction fit in an appropriate bearing housing formed in the central casing member 34. The lower race 18 is a friction fit in a similar bearing housing formed in an annular thrust member 19 supported on a plurality of coil springs 20 circumferentially disposed about the thrust member 19 and each received in a respective cup 21 formed in the lower surface thereof. The other end of each coil spring 20 is received in a respective cup 21 formed in the upper surface of the lower casing member 35. By this arrangement, the balls 17 are pinched between annular races 16, 18 and pressed against the ball race 24 of the high speed shaft.

A planet carrier member 23 is mounted by bolts 22 on a flange at the inboard end of the low speed shaft 27 and is provided with a plurality of fingers extending between balls 17. Rotation of the low speed shaft and therefore of the planet carrier 23 therefore forces planetary rotation of the balls 17 in rolling contact with the races 16, 18 producing a higher rate of rotation of the high speed shaft 15.

At its upper end, i.e. toward the impeller, the high speed shaft 15 is mounted in roller bearings 14.

A network of oil distribution channels 36, 37, 38, 39, 46, 47 provide an oil mist to the bearings and the planetary epicyclic gear. The oil is fed in under pressure through passageway 36 and exits through passageway 37 immediately below the air outlet nozzle 11. The space 48 between the thrust member 19 and the lower casing member 35 constitutes an oil expansion cavity.

The upper casing member 33 is provided with strengthening and cooling webs 43, the central casing member with webs 44 and the lower casing member 35 is provided with strengthening and cooling webs 45.

The form of drive described provides a very compact and mechanically straight forward, high efficiency, high speed drive to the impeller 41. Should the impeller 41 be jammed, high torque will be applied to the annular races 16, 18. Since these are only held still in normal operation by friction under the force of springs 20, they will revolve under high torque against their frictional loading to prevent the mechanism being damaged.

In use, drive is taken from the engine to the pulley mounted on shaft 27 abutting step 40 and the rate of rotation of the shaft 27 is substantially magnified by the epicyclic planentary gear to drive the impeller 41 at a substantial rate. Ideally, at maximum engine speeds, the impeller reaches a speed of rotation such that its linear tip speed is about 300 metres per second.

Operating lever 9 is connected to a linear actuator which in turn is connected to a monitoring system checking chosen aspects of the engine performance. The monitoring system may simply measure a single aspect of engine performance such as the boost pressure of the supercharger.

In such a case, as the boost pressure increases, so the operating lever 9 is drawn leftwards in the Fig. by the linear actuator toward to position indicated by the numeral 10 thus causing the tubular member 1 to fall and turn in the cylindrical mouth of the upper casing member 33 decreasing the annular clearance from the impeller and closing the ends of the grooves in the mouth 5a. This has the effect of accelerating the flow of air to the impeller blades by reducing the cross sectional area of the flow path through the upstream portion of the impeller and nozzle. This results both from the decrease in annular clearance and from shutting of air flow to the impeller through passageways 6. This has the effect of reducing the boost pressure derived from the supercharger at these high engine speeds.Although this effect may be regardable as a throttling the flow to the impeller, it does not appear to produce the same harmful effects as placing a simple throttle upstream of the impeller. Because the flow rate is axually governed by the cross-sectional area of the passages in the impeller itself, excessive heat need not be produced if the mass flow of the impeller is high in relation to the dischaged velocity.

When the throttle is suddenly closed at high engine speeds, the tubular member is preferably lifted by rightward movement of the actuator. This alleviates the stresses on the impeller and the surges of gas flow and pressure likely to be produced under these conditions by providing an enlarged escape path for gases from the vicinity of the impeller.

The linear actuator may of course be operated in connection with a combination of engine operating conditions using information gathered by a plurality of sensors.

Factors which may be used to control the operation of the actuator include brake and throttle operation, engine sensors that detect knock, pressure, temperature, engine speed, engine load and air density. Information gathered by sensors relating to these factors may be subjected to an algorithm by suitable microprocessor or computer apparatus to provide a signal to the linear actuator appropriate to the instantaneous engine conditions.

By this means, it is possible to optimise the performance of the engine. Different algorithms may be used to concentrate on improving engine performance or engine economy or to obtain a particular pattern of engine performance for a particular type of operation. The mechanism described is however particularly suitable for increasing the torque and economy obtained from an internal combustion engine.

Fig. 2 shows a second embodiment in which no gas passages 6 are provided. The tubular member 1 is a sealing fit with the mouth 5a but on being raised is moved further away from the impeller allowing increased mass flow to the impeller under open throttle conditions to produce greater boost at lower engine speeds and, under shut-throttle conditions allowing back flow of gas in space 7 opened up by the tubular member's movement.

Fig. 2 also shows a preferred configuration of impeller, also preferred for use in superchargers as shown in Fig. 1. The tips of the blades are curved back with respect to the direction of rotation whilst the roots are curved forward. This type of impeller can be designed to enhance the effect of the nozzles described above and leads to a greater peak efficiency range.

The embodiments described above provide mechanically driven superchargers having a particularly high output for their size, simple in design, efficient to run and inexpensive to produce.

The use of the moveable tubular member described above allows the regulation of the boost pressure of a supercharger independently of impeller speed, without dumping compressed air through a pressure release valve. Rather the mass flow is increased or decreased by adjustment of the cross sectional area of the flow path through the impeller.

In contrast to using a throttling control upstream of the impeller, reducing the mass flow in this way may reduce the air temperature instead of increasing it, thereby increasing compressor efficiency instead of decreasing it.

Excessive back pressure caused by rapidly closing the engine throttle at high engine speeds may be relieved without dumping the compressed air by virtue of diverting air away from the impeller to prevent excessive temperature levels occurring.

The use of the spring loaded epicyclic friction drive described above provides a compact overdrive mechanism and offers excellent damping against inertia and shock loads. Using high speed bearings lubricated by oil mist optimises the efficiency of the compressor.

Whilst the invention has been described with reference to specific characteristics of the illustrated embodiment, many modifications and variations of this are possible. For instance, nozzles as described in connection with mechanically driven superchargers may equally be used in conjunction with exhaust turbine driven superchargers.

Claims (23)

1. A gas compressor comprising means defining a gas inlet path leading to an impeller for accelerating gas to be compressed by the compressor, said inlet path defining means including moveable means defining an annular clearance about an upstream portion of the impeller and being moveable selectively to vary said annular clearance.

2. A compressor as claimed in Claim 1 which comprises means defining a main flow path for the gas from an inlet end thereof to the impeller and means defining a subsidiary flow path separated from the main flow path and extending from a downstream portion thereof and wherein said moveable means selectively opens and closes said subsidiary flow path as well as varying said annular clearance.

3. A compressor as claimed in Claim 2 in which the subsidiary flow path has a junction with said main flow path upstream of said impeller.

4. A compressor as claimed in Claim 2 in which the subsidiary flow path is routed to extend into the main flow path from outside the main flow path.

5. A compressor as claimed in any preceding claim in which the moveable means takes the form of a tubular member axially slideable with respect to the impeller within means defining inlet flow path as a whole.

6. A compressor as claimed in Claim 5, in which the moveable means operates as an annular shutter over an end of a subsidiary flow path separated from the main flow path and extending from a downstream portion thereof.

7. A compressor as claimed in Claim 6, in which the subsidiary flow path is defined between an interior wall of the means defining the inlet flow path and the moveable means, said moveable means being in the form of a tubular member longitudinally slidable within the inlet flow path defining means and having a portion or portions spaced therefrom to produce said subsidiary flow path.

8. A compressor as claimed in Claim 7, in which the interior wall of the inlet flow path defining means is provided with one or more axially elongate radial recesses such as grooves or flutes to define the subsidiary flow path.

9. A compessor as claimed in Claim 8, in which the recess or recesses end at a zone contactable by the moveable means to close off the subsidiary flow path.

10. A compressor as claimed in Claim 8, in which there is an inwardly projecting ledge around the interior of the said wall against which said moveable means abuts to close said subsidiary flow path and from which it is withdrawn to open said subsidiary flow path.

11. A compressor as claimed in any one of Claims 5 to 10, in which an operating member extends from said moveable means through said wall to the exterior thereof and said means is moveable to vary the annular clearance, and open or close said inlet or inlets to the subsidiary flow path if provided, by movement of said operating member.

12. A compressor as claimed in Claim 11, in which a cam slot is provided through a wall defining said inlet path and the operating member is in camming engagement with said slot to govern movement of said moveable means.

13. A compressor as claimed in any one of Claims 5 to 10 in which the tubular member is controlled for axial movement to vary the annular clearance by axially located control means.

14. A compressor as claimed in Claim 13, in which the axial control means takes the form of an axially extending control member joined to the tubular member by one or more webs or struts.

15. A compressor as claimed in any preceding claim, in which the impeller is an unshrouded centrifugal impeller.

16. A compressor as claimed in any preceding claim further comprising a power input shaft, a planetary epicyclic gear having a planet carrier connected to be rotated by the power input shaft, a fixed annulus and a sun wheel drivingly connected to the impeller.

17. A compressor as claimed in Claim 16, in which the planet carrier is engaged with a plurality of balls as planetary elements and said sun wheel comprises a ball race which is frictionally engaged by said balls.

18. A compressor as claimed in Claim 16, in which the annulus is restrained from rotation by friction means such that the annulus will rotate if subjected to heavy torque.

19. A gas compressor substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

20. A supercharger containing a compressor as claimed in any preceding claim.

21. A supercharger substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

22. An internal combustion engine provided with a supercharger as claimed in Claim 20 or Claim 21.

23. A motor vehicle incorporating an internal combustion engine as claimed in Claim 23.