GB2155542A - I.C. Engine supercharger driven via a variable ratio transmission - Google Patents

Abstract

A centrifugal compressor 2 is driven via a continuously-variable-ratio transmission (C.V.T.) such as a Kopp C.V.T. or a V-belt and variable sheave pulleys C.V.T. The ratio depends on parameters giving a measure of engine operating condition such as power output and engine revolutions. This enables power output to be increased when full power is demanded at low engine revolutions without having excessive pressurization at high engine revolutions. <IMAGE>

Description

SPECIFICATION Supercharger for internal combustion engine This invention relates to superchargers for internal combustion engines.

Such superchargers are of two types, viz., those mechanically driven from the engine or those which are exhaust driven turbines (turbochargers). Motor cars tend to use the latter if supercharging is provided because the former usually cause increased fuel consumption when the increased power available with the supercharger is not being used since the supercharger is always being driven, (unless a clutch is provided which complicates the arrangement). The mechanically-driven superchargers have however been used, for example, the "Roots" type or a mechanically driven centrifugal compressor. Although the latter increases power at high engine speeds, little or no improvement is achieved at low engine speeds.

The invention provides a supercharger for an internal combustion engine comprising a centrifugal compressor and a continuouslyvariable-ratio transmission arranged so that in use the compressor is driven from the engine via the continuously-variable-ratio transmission, the ratio of which is controlled in accordance with at least one parameter which gives a measure of engine operating condition, ac tual or demanded.

The arrangement of the invention enables increased output to be achieved at low engine speeds without having excessive pressurization at high engine speeds.

Advantageously, at the maximum power outputs for each engine speed, the ratio decreases in use with increasing engine speed over a given range of engine speeds. Preferably, at each engine speed within a given range, the ratio decreases with decreasing power output: this reduces or eliminates the increased fuel consumption encountered with previous mechanically driven superchargers in these conditions. The given range of speeds may be beteen 1 500 rpm and 5000 rpm for spark ignition engines and between 1000 rpm and 3000 rpm for compression ignition engines.

The control strategy for controlling the ratio at maximum demanded power and at idling, and at all conditions in between for all speeds can advantageously be stored in a microprocessor, but a mechanical analogue control could be used if desired.

The parameters used to control the ratio are preferably parameters giving a measure of engine speed (for example a sensor on any rotating part of the engine) and power output, actual or demanded. In steady conditions, the demanded power as determined by the diiver's foot pedal position will correspond to the actual power as measured by mass air flow. In transient conditions, the demanded power will differ from the actual power. Either may provide a signal for controlling the C.V.T.

ratio. (For example, a throttle angle sensor may be used, or a mass air flow sensor in the inlet manifold such as a hot wire or a deflectable vane, a sensor of vortices, or driver's pedal position).

Various types of continuously-variable-ratio transmissions (hereafter C.V.T.'s) may be employed such as Kopp variators employing drive balls or cones, rolling-traction type C.V.T.s, or V-belt type C.V.T.'s.

A supercharger for a spark ignition internal combustion engine will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a partly sectional view of the supercharger; Figure 2 is a view of a fragment of one part of the supercharger; and Figure 3 is of characteristic curves showing variation of mass air flow at one C.V.T. ratio, and variation of power, with engine speed.

Referring to Figure 1 of the drawings, the supercharger comprises within an outer casing 1, a centrifugal compressor indicated generally by the reference numeral 2, a step-up planetary gear mechanism indicated generally by the reference numeral 3, a Kopp C.V.T.

indicated generally by the reference numeral 4 and a pulley 5 for a drive belt from a spark ignition internal combustion engine (not shown). The compressor output feeds into the inlet manifold.

The pulley 5 is secured by bolt 6 to splined shaft 7 which together with sleeve 8 surrounding shaft 7 forms the input to the Kopp C.V.T. Sleeve 8 is integral with drive cone 9, and balls 10 are held by ring 1 0e between drive cone 9 and driven cone 1 2. The latter is integral with output sleeve 1 3 of the C.V.T.

Several such balls are provided between the cones 9,12.

Each ball 10 is rotatable about a spindle 1 0a, which is guided by carrier 11 in an axial plane. One end of the spindle 1 0a is movable in a groove 1 Ob in a scroll 14 in order to vary the angle of inclination of the axis about which the balls can rotate. The spindles 1 0a of all the balls nest in the other spiral grooves in the annular-shaped scroll 1 4. Each groove (Figure 2) starts from the inner diameter of the scroll (where the spindle 1 0a rests in Figure 1) and runs towards the outer diameter of the scroll in a spiral.Consequently, if the scroll 1 4 is rotated, the spindle 1 Oa is gradually moved to the outer diameter of the scroll, while remaining in the same axial plane, for example, the plane of the paper, passing through the position occupied by groove 1 Oc in Figure 1 and ending up in the position occupied by groove 1 Od in Figure 1.

The ratio of the Kopp C.V.T. depends on the angle of inclination of the spindles 10a, since the diameters of the circles described on the balls 10 by the cones 9, 1 2 determine the drive ratio. Thus, as illustrated, the input cone 9 runs on a circle whose diameter (2A) is approximately half the diameter of the ball, and the output cone 12 runs on a circle whose diameter (2B) is only slightly less than the diameter of a ball.

Consequently the Kopp C.V.T. would give an overall reduction in speed of the output relative to the input.

If the spindle was where the groove lOb is Figure 1, the ratio would be 1:1, and if it was where the groove 1 Oc is in Figure 1, a corresponding increase in speed would be achieved.

The outer periphery of the annular scroll 14 is provided with gear teeth, and worm 1 5 can be rotated to rotate the scroll.

It is desired that the end loading forcing the cones 9, 1 2 together against the balls should vary in step with the torque transmitted by the C.V.T. This is achieved by virtue of the input shaft consisting of two parts, the shaft 7 and the sleeve 8, interconnected by a helical thread on the shaft 7 meshing with helical grooves 18 in the sleeve 8. Thus, cone 12 and output sleeve 1 3 are located against axial movement to the right as seen in Figure 1 relative to the shaft 7 because of thrust bearing 1 6 (relative rotational movement is of course permitted).

Also, increased torque applied to pulley 5 causes, because of the helical thread and groove, increased axial force on the sleeve 8.

Consequently, increased torque at the input shaft causes increased end loading across the drive balls 1 0.

The output of the C.V.T. is taken from output sleeve 1 3 and the two-stage gearing 3 steps it up to give an approximately 9:1 speed increase. Such a high step-up permits the use of a small centrifugal compressor with a corresponding low inertia. Teeth on the outside of output sleeve 1 3 mesh with a planetary gear 1 9 which is free to rotate on a fixed shaft 20 and which is axially connected to an additional planetary gear 21. Three such pairs of gears 19, 21 are provided around the output sleeve 1 3 equally spaced around its circumference. The additional planetary gears 21 mesh with and support against radial movement, sun gear 23, thereby avoiding the need for a bearing for the sun gear. Sun gear 23 is formed integrally with shaft 22 which forms the input to the compressor 2.

It will thus be seen that the compressor 2 is driven from the engine via pulley 5 and C.V.T. 4, and that the speed of the compressor 2 relative to the pulley 5 is controlled by rotating the annular scroll 1 4.

Two sensors (not shown) have outputs which are fed into a microprocessor (not shown) which in turn controls a motor (not shown) connected to the worm 1 5. The parameter measured by one sensor is engine rotational speed, and that measured by the other is throttle angle in the engine inlet manifold, the latter giving a measure of power output.

Referring to Figure 3, A shows the characteristic power curve of the engine without the supercharger, and B shows the power curve with the supercharger. C represents another alternative for the power curve which, given a suitable control strategy, could be obtained.

Curve D shows the mass air flow characteristic curve of the centrifugal compressor at the highest ratio of the C.V.T. This curve illustrates the problems of prior art centrifugal compressor superchargers which operate at a fixed ratio. If, as shown in Figure 3, a useful increase in mass air flow is obtained at low engine revolutions, the compressor cannot be used since severe over-pressurisation at high engine revolutions would result. If, on the other hand, over-pressurisation at high engine revolutions is avoided, little or no boost would be obtained at low revolutions.

The control strategy contained in the microprocessor has the effect that, for maximum power developed by the engine at each speed (i.e. full load conditions): at very low engine revolutions, the C.V.T. has its highest ratio and the compressor 2 is rotated the quickest relative to the pulley rotational speed; for increasing engine revolutions, the C.V.T. gradually reduces in ratio; at maximum engine revolutions, the C.V.T. ratio is lowest and the speed of the compressor is lowest relative to the pulley rotational speed. For minimum loads of the engine at each speed (eg the power supplied by the engine when idling) the C.V.T. ratio remains at its lowest throughout the entire range of engine speeds. Thus, at each engine speed within a given range, the ratio decreases with decreasing power output.

For such part-load conditions, the ratio of the C.V.T. lies between its extreme values and depends on the magnitude of the part load.

By appropriate choice of control strategy, the exact form of the supercharged characteristic may be selected, for example, curve B or curve C.

Various modifications may of course be made without departing from the scope of the invention. Thus, the Kopp C.V.T. may be replaced by a C.V.T. consisting of a V-belt running between a pair of variable-sheave pulleys.

Equally, instead of sensing power output by means of throttle angle, the engine power output may be sensed by means of mass air flow in the inlet tract, detected by means of a deflecting vane sensor, a hot wire sensor, or a vortex shedder (detector). Instead of measuring engine speed to reduce the C.V.T. ratio with increasing speed (for maximum power output), a feedback system using the pressure generated by the compressor could be used to regulate the C.V.T. ratio.

Thus, if desired, the scroll 1 5 could be directly controlled by the varying parameters such as a linkage from the throttle indicative of throttle angle and the pressure generated by the compressor.

If desired, the control strategy could be such as to compensate for thin air conditions by a degree of pressurisation, in dependence upon a barometer. Also, means could be provided to detect the onset of knock and reduce the supercharging accordingly.

The arrangement described is suitable for spark ignition or compression ingnition engines, except that the pressure generated by the compressor is not a suitable signal for controlling the latter.

Claims (12)

1. A supercharger for a spark ignition internal combustion engine comprising a centrifugal compressor and a continuously-variableratio transmission arranged so that in use the compressor is driven from the engine via the continuously-variable-ratio transmission, the ratio of which is controlled in accordance with at least one parameter which gives a measure of engine operating condition, actual or demanded.

2. A supercharger as claimed in claim 1, wherein at the maximum power outputs for each engine speed, the ratio decreases in use with increasing engine speed over a given range of speeds.

3. A supercharger as claimed in claim 1 or claim 2, wherein at each engine speed within a given range, the ratio decreases with decreasing power output.

4. A supercharger as claimed in any one of claims 1 to 3, wherein one parameter gives a measure of power output, actual or demanded.

5. A supercharger as claimed in claim 4, wherein another parameter gives a measure of engine speed.

6. A supercharger as claimed in claim 4, wherein another parameter gives a measure of pressure generated by the compressor.

7. A supercharger as claimed in any one of claims 1 to 6, wherein the output of the continuously-variable-ratio transmission engages fixed planetary gears, each of which is connected to an axially spaced additional planetary gear, a sun gear meshing with the additional planetary gears and being connected to the compressor.

8. A supercharger as claimed in claim 7, wherein the sun gear is located against radial movement by the additional planetary gears.

9. A supercharger as claimed in any one of claims 1 to 8, wherein the continuously-variable-ratio transmission is a Kopp variator.

10. A supercharger as claimed in claim 9, wherein the input to the Kopp variator is via relatively movable helical surfaces arranged so that changes in torque at the input cause relative axial movement which adjusts the end load across the drive members of the variator.

11. A supercharger as claimed in any one of claims 1 to 8, wherein the continuouslyvariable-ratio transmission is a V-belt and a pair of variable sheave pulleys.

1 2. A supercharger substantially as hereinbefore described with reference to the accompanying drawings.

1 3. A spark ignition internal combustion engine having a supercharger as claimed in any one of claims 1 to

12.