US2770943A - Turbines operated by free-piston gas generators - Google Patents

Description

Nov. 20, 1956 E. s. L. BEALE 2,770,943

TURBINES OPERATED BY FREE-PISTON GAS GENERATORS Filed March 18, 1952 5 Sheets-Sheet l l ATTOENEY5 Nov. 20, 1956 E. s. BEALE 2,770,943

TURBINES OPERATED BY FREE-PISTON GAS GENERATORS Filed March 18, 1952 5 Sheets-Sheet 2 ATTOENEYJ Nov. 20, 1956 E. s. L. BEALE 2,770,943

TURBINES OPERATED BY F REE-PISTON GAS GENERATORS Filed March 18, 1952 5 Sheets-Sheet 5 lNVENTOR ATTORNEYS Nov. 20, 1956 E. s. L. BEALE 2,770,943

TURBINES OPERATED BY FREE-PISTON GAS GENERATORS F'i led March- 18, 1952 5 Sheets-Sheet 5 IN VENTOR ATTORNE Y;

United States Patent TURBINES OPERATED BY FREE-PISTON GAS GENERATORS Evelyn Stewart Lansdowne Beale, Wraysbury, England,

assignor to Alan Muntz & Company Limited, Hounslow, England, a company of Great Britain Application March 18, 1952, Serial No. 277,209 Claims priority, application Great Britain March 21, 1951 15 Claims. (Cl. 60-13) The present invention relates to turbines operated by free-piston gas-generators, and particularly, but not exclusively, free-piston gas-generators f the type in which compression of the gas takes place during the compression stroke of the diesel cycle. This stroke is usually, but not necessarily, the part of the stroke when the pistons are moving inwardly and this type of free-piston gas-generator may for convenience be called the inwardcompressing type.

A difliculty met with when driving a turbine of any of the normal types from a free-piston gas-generator, particularly 'one of the inward-compressing type, is that the gas consumption of such a turbine is not great enough to accept the Whole delivery of the gas-generator when, in order to reduce the power, the delivery pressure is reduced below a certain value- In order to reduce the power below that point, some of the gas delivered by the gas-generator has to be blown off, i. e. exhausted directly to atmosphere. This point will be referred to hereinafter for convenience as the normal blow-off point. This difiiculty has been realized for many years and much effort has been devoted to overcoming it.

The reason why it has been necessary to blow off gas is that the turbine behaves, so far as gas consumption is concerned, like a nozzle of fixed area, and therefore the quantity of gas that it will consume falls progressively as the supply pressure is reduced. On the other hand, a free-piston gas-generator cannot deliver less than a certain minimum quantity of gas at any given pressure, and this minimum quantity of gas is actually greater at low delivery pressures than at high pressures. This is because the speed ofoscil'lation of the piston of a freepiston engine is fixed by the working conditions and cannot therefore be controlled independently of other factors as in a crankshaft engine. The stroke of the pistons cannot be reduced below a certain minimum value because the stroke must be great enough to open the scavenge ports of the diesel cylinder. Thus the displacement of the compressor pistons has a certain minimum value which is always quite large. delivery pressures the volumetric eiiiciency of the comp-ressor cylinders increases, because of the reduced reexpansion of the air in the clearance spaces. A gasgenerator is normally operated with gas pressures up to about lb./sq. in. gauge.

Although radial flow. turbines have been known for many years, most gas turbines in use are of the axial Moreover at low flow type and when required to operate at gas pressuresof about 40 to 50 lb./sq. in. gauge normally have three or more stages. With such turbines there is no practical way of increasing the swallowing capacity above normal. A possible way might be to use only partial gas admission at full load by closing oif part of the first stage nozzles. However, this would result in reduced efliciency over a large part of the load range from full load downwards where maximum efliciency is normally required. Blades of variable angle are not practical with such turbines for many reasons.

we 2,770,943 Patented Nov. 251*,

The present invention is based upon the realization that a single-stage, inward-flow, radial-flow turbine, when connected to a load obeying the propeller law e. g. when used for ship propulsion, can be constructed to deal efliciently with gas pressures up to about 50 lb./sq. in. gauge exhausting to atmospheric pressure; that, as has already been proposed for other purposes, it is possible to provide such a turbine with variable nozzle blades whereby the nozzle area canbe varied over a suitable range; and that in this way the swallowing capacity of the turbine can be made variable in a manner which suits the characteristics of a free-pistol gas-generator.

According to the present invention, therefore, in a freepiston gas-generator arranged to deliver gas to an inwardfiow, radial-flow turbine, the turbine is provided with variable nozzle blades and with means for automatically varying the setting of the nozzle blades in dependence upon the pressure of the gas supplied to the turbine in such a manner that at leastover a range of relatively low gas pressures the nozzle area is increased with a reduction in gas pressure. If desired, the range of variation of the nozzle blades may be made such that the direction of rotation of the turbine rotor may be changed.

With the aid of the present invention it is possible to make the swallowing capacity of the turbine match the rate of gas delivery 'of the free-piston gas-generator in such a way as to give a higher overall efiiciency than has been obtainable hitherto with a combination of freepiston gas-generator and turbine. In a practical design the nozzle area of the turbine can be increased to three times its full load value without difliculty and this would have the effect of reducing the pressure drop for a given mass flow to about one-tenth of its full load value.

The automatic control of the nozzle blades in dependence upon the gas pressure, in the case of a turbine operating with a propeller law characteristic, i. e. so that the power varies as the cube of the speed, may be arranged to function so, that the nozzle area is kept constant from full load down 'to the normal blow-oil point and thereafter the nozzle area is increased as necessary in order to reduce the power without the need for blowing off. a

The automatic control of the setting or" the nozzle blades may be effected by a servo mechanism operated by the pressure at the turbine inlet or in the enginecase of the gas-generator where the gas pressure is nearly the same as in the' turbine inlet but where the air is usually cleaner. The output member of the servo mechanism may be connected to the mechanism for actuating the nozzle blades through a cam and follower mechanism adapted to give the required relation between the position of the blades and the gas pressure.

A manual control device may be provided for moving the blades beyond the range above considered when it is required to reverse ,the direction of rotation of the turbine rotor.

As has already been stated, the invention is of particular value when the gas-generator is of the inwardcompressing type. This is because with such a gas generator there is less variation in the quantity'of gas delivered over the range of working pressures than with the outward-compressing gas-generators. However, the invention also offers advantages with the latter type of gas-generator.

In an inward-flow, radial-flow turbine, exit guide vanes are provided on therotor to reduce the whirl velocity of the gas leaving'the rotor. When such a turbine is made reversible, however, it is obvious that such exit guide vanes will face in the wrong direction for reverse running and will then increase the whirl velocity instead of decreasing it.

According to a feature of this invention, when the tur- 3 bine is provided with nozzle blades adjustable for either forward or reverse running, there are provided in the outlet of the turbine near the exit guide vanes of the rotor, further guide vanes adapted to reduce the angle of whirl of the gases leaving the turbine during forward and reverse running. This can be done by so selecting the angle of the exit guide vanes of the rotor that a suitable amount of residual Whirl remains when forward running and that this whirl is in a backwards direction, that is in a direction opposite to that of rotation of the rotor, thus providing some reaction. With this arrangement the whirl will be in the same direction for both forward and reverse running, and therefore the difference between the angles of whirl will be small. The further guide vanes in the turbine outlet are preferably made adjustable so that the angle of incidence can be made nearly correct for both directions of running.

Any given set of vanes in the turbine outlet will only be able to deflect the gas with low losses through a limited range of angles, and it is therefore important to arrange that there is not too great a difference between the angle at which the gas leaves the rotor when running forwards and in reverse.

When the turbine is running in reverse, the angle of whirl with respect to the axis is bound to be large and may be, for example, about 60 to 65. The only way of making the difference between this angle and that of forward running reasonably small is, as already stated, to make the direction of whirl the same for both directions of rotation. The small amount of reaction which is so obtained with forward running may be an advantage when using a turbine in the present invention because it will reduce the speed of rotation of the turbine rotor necessary for the maximum elficiency and for given pressure ratio between inlet and outlet. This may be valuable because the maximum permissible tip speed of the rotor may otherwise not be high enough to suit the delivery pressure of the gas-generator.

It is important to choose an amount of reaction which when running forward gives an etficiency very near to the maximum possible. This means that the angle of the exit gases must not be more than about 30 to 40 to the axis. For a given axial velocity, the total kinetic energy of the gas is proportional to 1/cos 0, where 0 is the mean angle of whirl with respect to the axis. Thus, in the example considered, the kinetic energy of the exit gases from the rotor would be increased by 33 to 70%. This kinetic energy can be recovered with good efficiency when the angle through which the gases are turned has the small value mentioned. With the vanes in the outlet so designed as to turn the gases through the angle above-mentioned, the resulting residual whirl when running forwards of up to 10 will result in very little loss. 7

When running backwards, assuming that the vanes give a turning angle of 30 to 35, there would only be a residual whirl of about 30 which would result in an increase of only about 33% in the exit kinetic energy. This would not be at all serious for reverse running when a much reduced power and efficiency in comparison with forward running is often quite acceptable. for instance in ship propulsion.

The vanes in the outlet may be made movable through an angle of about 30 between their positions for forward and reverse running, so that a small angle of incidence is maintained between the gases and the leading edges of the vanes.

Any convenient means may be provided for moving the vanes, and if desired the mechanism for this purpose may be connected with that used for moving the adjustable nozzle blades between their forward and reverse running positions.

The advantage obtainable by the use of non-adjustable vanes in the outlet passages may be sufiicient for some purposes and may then be desirable because of their increased simplicity. In such a case the angle of incidence would change about 30 between forward and backward running. In order to maintain the highest possible efficiency in the forward direction, the angle of incidence would have to be kept very small, so that the angle of incidence for backward running would be about 30. This would, of course, lead to considerable loss when running in reverse, but the vanes in the outlet passage would nevertheless provide a substantial improvement as compared with an arrangement having no such vanes.

When operating a combination of free-piston gasgenerator and radial flow turbine according to this invention under conditions where it is essential to prevent the turbine speed rising appreciably when the load on it is suddenly reduced, it may be found difficult to maintain a sufficiently constant speed. An example in ship propulsion is when the propeller comes out of the water in a rough sea. The difficulty arises from the limiting rate at which the pressure delivered by the gas-generator can change. Thus, if the nozzles were suddenly opened and at the same time the fuel supply to the gas-generator were correspondingly reduced, there would be a risk of injury to the gas-generator owing to the drop in pressure caused by the opening of the nozzles. This is because the energy stored in the cushion remains momentarily high and, when this energy is returned during the compression stroke, it may result in excessive compression pressure.

Moreover, it is probably not practical to arrange, when a sudden increase in turbine speed occurs, to increase the area of the nozzles suddenly by more than say 50%, and since, with such an increase in nozzle area, the turbine will be operating with reasonable efficiency, the effect would probably be the opposite to that desired, since the gas pressure would still be high while the quantity of gas supplied would increase. The turbine speed might then be increased instead of being reduced as required.

Another difficulty that arises, when the pipe supplying gas from the gas-generator to the turbine is of substantial length, is that the energy of the gas in the pipe is not under the control of the normal speed governor which acts on the fuel control. This difficulty is aggravated by the fact that the delivery of the gas-generator cannot be reduced to less than about 50% of its full load value until the delivery pressure has dropped from the full load value.

These difficulties can be overcome or greatly reduced according to a further subsidiary feature of the invention by providing in the gas delivery pipe from the gas generator to the turbine a throttle adapted to be actuated automatically in response to a change in speed of the turbine, or in response to a rate of change of speed of the turbine exceeding a predetermined value, said throttle being interconnected with means, additional to the gaspressure-operated nozzle-blade actuating mechanism, for adjusting the nozzle blades and the arrangement being such that an increase in turbine speed results in a movement of the throttle towards its closed position accompanied by a movement of the nozzle blades towards their open position.

Provision is also preferably made to ensure that the throttle control is returned automatically to its normal setting when the rate of change of speed falls below the predetermined value.

It will be apparent that the invention avoids any risk of injury to the gas-generator through a sudden change in pressure and at the same time provides means whereby any tendency for the occurrence of a sudden increase in the turbine speed can be counteracted by the combined effect of a rapid closure of the throttle and opening of the nozzles.

Clearly, particularly when, as is desirable, the throttle is arranged close to the turbine, the use of the throttle reduces or removes the difficulty which otherwise arises from the energy of the gas in the pipe to the turbine and the inability of the gas-generator to reduce its delivery suddenly by more than a limited amount.

One way of providing a control which responds only when the rate of change of speed exceeds a predetermined value is to connect a speed-responsive deviceto the throttle through a dash-pot device so arranged that movements of the speed-responsive device at rates below the predetermined value produce relative movement between a piston and cylinder while allowing a fluid to leak away from the compression space, whereas movements of the speedor pressure-responsive device exceeding the predetermined value cause the piston to exert on the cylinder through the fluid trapped in the compression space a force sufficient to open the throttle.

When, as is usual, it is only required to correct for excessively rapid increases of speed, the throttle may be arranged to be normally fully open.

The invention is illustrated diagrammatically by way of example in the accompanying drawings, in which:

Figure l is a vertical cross-section showing a free-piston gas-generator driving a radial inflow turbine,

Figure la is a fragmentary vertical cross section showing a modification in the pressure-operated control of Figure 1,

Figure 2 is a fragmentary diagram partly in elevation and partly sectioned illustrating a nozzle blade control gear,

Figure 3 is a diagram illustrating the relative positions for forward and reverse of the main control gear parts and the nozzle blades,

Figure 4 is a fragmentary diagram showing the nozzle blades adjusted radially and for different conditions of forward running,

Figure 5 is a fragmentary diagram similar to Figure 4 showing the nozzle blades adjusted for reverse running,

Figures 69 are graphs showing respectively the percentage horsepower, the percentage gas flow, the percentage nozzle area and the nozzle angle and nozzle blade chord angle plotted in each case against the working pressure,

Figure 10 is a diagram illustrating the angles of the guide vanes at the exit from the rotor for forward running,

Figure 11 is a diagram similar to Figure 10 for revers running, and

Figure 12 is a diagram illustrating a mechnaism for simultaneously controlling a throttle valve in the gas-delivery pipe from the gas generator to the turbine of Figure l, the adjustable nozzle blades of the turbine and the fuel rack of the gas-generator. The gas-generator itself has been omitted from Figure 12.

Referring to Figure l, a free-piston gas generator has two opposed diesel pistons 1, 2 working in a common diesel cylinder 3. Piston 2 is fixed to a larger diameter piston 4 working in a cylinder 5. The closed space 6 at the outer end of the cylinder 5 forms a cushion which operates in known manner to receive energy from the piston assembly 2, 4 during the power stroke of piston 2 and to restore this energy in such a manner as to bring about the compression stroke. A space 7 on the other side of piston 4 forms a compressor cylinder and is provided with inlet valves 8, 9 and delivery valves 10, 11, the latter being arranged to open into an engine case 12 surrounding the gas cylinder 3.

A compressor cylinder space 13 associated with the piston assembly which includes piston 1 has inlet valves 14, 15 and delivery valves 16, 17 which correspond to the inlet and delivery valves 3, 9 and 10, 11 respectively.

The pistons 1 and 2 co-operate in known manner with scavenge ports 18, 19, and fuel is injected in known manner through an injector nozzle 20.

Gases generated by this free-piston gas-generator are conveyed by a duct 21 to the volute 22 of a radial inflow turbine having a rotor disk 23 fixed to a driving shaft 24. The casing of the turbine is in two main parts 25, 26 which are secured together by bolts 27. One of these parts has an extension 28 which is secured by bolts 6 29 to an expansion duct 31 and supports a streamlined tail bearing housing 32 by means of fixed radial guide vanes 33. A spigot 34 on the tail end of the rotor 23 is mounted in a ball bearing 35 in the forward end of the housing 32. The rotor shaft 24 is mounted in a ball bearing 36 in the other main part 26 of the turbine casing.

The hot gases from the volnte 22 pass inwards between adjustable nozzle blades 38 by which they are directed inwards between vanes 39 formed on the rotor disk 23. On leaving the rotor disk vanes in a substantially axial direction, the gases pass between adjustable guide vanes 46 and thence between the fixed vanes 33 to the duct 31.

The adjustable nozzle blades 38 are mounted on shafts 42 parallel to the rotor axis and journalled in the casing part 26, with their leading edges approximately in alignment with the axes of these shafts (see Figure 4). On the other ends of the shafts 42 are mounted pinions 43 meshing with a toothed ring 44 which is actuated by means to be described later with reference to Figure 2.

The adjustable guide vanes 40 are mounted on radially arranged shafts 41 journalled in the extension 28 and provided on their outer ends with bevel pinions 45 meshing with a second toothed ring 46. This second toothed ring 46 is drivably connected with the first toothed ring through a transmission consising of a bevel gear wheel 48, a steel belt 49 passing round belt pulleys 50, 51, a shaft 52, a lost-motion device 53, a steel belt 54 passing round belt pulleys 55, 56, a shaft 57 and a quadrant 58.

The lost-motion device 53 is arranged so as to allow small adjustments of the adjustable nozzle blades 38 to take place without any change in the position of the guide vanes 40. Movement of the blades 38 from the forward position to the reverse position is, however, sufiicient to take up the lost motion in the device 53 so that the required adjusting movement is transmitted to the ring 46 and vanes 40.

The forward and reverse adjustment of the nozzle blades 38 in this diagrammatic illustration is by means of a hand lever 65 on the end of the shaft 57 which carries the quadrant 58 meshing with the toothed ring 44. As shown in Figure 2, the quadrant 58 engages alternatively by means of a cam follower 64 two earns 59, 59 for forward and reverse running respectively, between which it is moved manually as required by means of the hand lever 65. In its mid position, which corresponds to zero output, the quadrant 58 can be locked by the end of a plunger 60 engaging in a detent 61 in an arcuate rib 62 on the sector under the influence of a spring 63.

When delivering power, the gas load on the nozzle blades tends to move them so as to reduce the nozzle area, thereby causing the cam follower 64 to be pressed up against the corresponding cam 59 or 59'.

The adjustable nozzle blades 38 preferably have a pressure-operated control, in addition to a manual control such as that provided by the hand lever 65 in Figure 1, so as to keep the nozzle blades at the best angle to suit the conditions at low outputs. This pressure-operated control (see Figures 1 and 2) includes a piston 66 working in a cylinder 67 which is in communication through a pipe 68 with the engine case 12 of the gas-generator. In the modification of Figure la the cylinder 67 is in com munication through a pipe 68a with the duct 21; the pressure in the engine case 12 is substantially the same as that in the turbine inlet duct 21. It is preferred to have pipe 68 communicate with the engine case 12, as shown in Figure 1, because the air in the engine case 12 is cleaner than that in the duct 21. The gas pressure acting against one side of the piston 66 is opposed by the pressure of a spring 69 acting against the other side thereof. A piston rod 78 and connecting rod 71 couple the piston 66 to 21 depending arm 73 integral with the cam 59. Each of the two cams 59 and 59 is pivotally mounted the former on a bracket 74 and the latter on a bracket 75, and a con necting rod 76 interconnects these cams for rotation in opposite directions respectively.

Figure 3 shows the positions of the nozzle blades 38 and the cam follower 64 both for forward and reverse running.

The radius of the quadrant 58 in this embodiment is twice the diameter of the pinions 43. Since, therefore, the total change of angle of the blades 38 between the full load forward position (shown in full lines) and the full load reverse position (shown in broken lines) is 170, the corresponding change of angle of the quadrant is 85. The change of nozzle blade angle between the full load position and the position for of full load indicated by reference 38 in Figure 4, is about 24 for forward running and 36 for reverse running. Consequently, the corresponding quadrant angles will be 12 and 18 respectively. In Figure 3, the cam 59 and cam follower 64 are shown in broken lines in their full load forward positions and in chain-dotted lines in the positions they occupy at 5% of full load. The reverse cam 59, is shown only in the full load reverse position, with the cam follower in the full load reverse position in broken lines. The cam follower 64 is also shown however in chain dotted lines displaced through 18" to its 5% of full load reverse position.

The connecting rod 76 has been omitted from Figure 3 for the sake of simplicity.

Figure 4 shows the adjustable nozzle blades 38 in the positions for full load and 5% of full load forwards, the former being shown in full lines and indicated by reference 38 while the latter is shown chain dotted and indicated by reference 38. In the same figure, these blades are also shown in the radial position, indicated in chain dotted lines at 38", which would give zero power output if there were no reaction. Arrow 78 indicates the direction of the axis of the jet at the throat of the nozzle formed between the two adjacent blades 38 when they are in the full load forward position. The corresponding nozzle angle 79 is then 15, whilst in the 5% of full load forwards position, it is increased to approximately 40. In Figure 5, which shows the blades 38 in the full load reverse position, the direction of the jet axis at the nozzle throat is indicated by arrow 80, the nozzle angle 81 in this case being 30. The angle 81 just referred to does not take into account the effect of the reversed curvature of the blades, which will in practice make the true jet angle appreciably smaller. The values of the blade chord angle, i. e. the angle between the chord and radius drawn through the centre of the trailing edge radius are 1' for full load forward, 25 for 5% of full load forward and 6 for full load reverse.

The total change in blade angle between full load forward and full load reverse is 173 in the example illustrated in Figures 4 and 5. This angle would be slightly reduced, e. g. to approximately 170 if the blades were made with an aerofoil section instead of a uniform thickness as shown.

The curves of Figures 6 and 7 show the characteristics of the free-piston gas-generator with the gas pressure at full load selected at 45 lb./sq. in. gauge. From these it is possible to calculate the required nozzle areas (see Figure 8), which in turn determine the nozzle angles (Figure 9) and the blade angles of blades 38.

It will be seen that these angles remain unchanged from full load down to 18 lb./sq. in. gauge where the horse-power is approximately 28% of full power. This would be about the normal blow-oft point with an axial flow turbine, and the nozzle area is therefore increased below this pressure to avoid blowing off. The rate of increase in nozzle area and change of blade angle increases progressively until the rate of change is very great at the minimum power output at about 3 lb./sq. in gauge. At this pressure the gas horse-power is about 6% of full power, but owing to the greatly reduced turbine efficiency under these conditions the shaft horse-power is only about 2%.

Figures 10 and 11 illustrate diagrammatically the conditions at the exit from the rotor for forwards and reverse running respectively.

Referring to Figure 10, the angle 83 is the angle made by the rotor guide vanes 39 to the axial direction of the turbine. In the two velocity triangles shown in the same figure, 84, 85, 86, 87 and 88 represent respectively the absolute gas velocity, the gas exit angle, the absolute whirl at exit, the mean vane velocity and the relative gas velocity. 89 is the final gas angle at which the gases leave the adjustable guide vanes 40 and 90 is the gas turning angle. Arrow 91 indicates the forward running direction.

The angles, velocities and the like corresponding to 83 to 91 in Figure 10 are indicated in the reverse running diagram of Figure 11 by references 83' to 91 respectively.

The diagrams of Figures 10 and 11 are intended to be illustrative rather than quantitative.

Figure 12 illustrates a control mechanism which automatically controls the setting of a throttle valve in the gas delivery pipe 21 from the gas-generator to the turbine in Figure l in response to changes in the speed of the turbine, while at the same time providing an interconnection between the throttle and the adjustable nozzle blades whereby the nozzles are caused to open as the throttle closes.

In Figure 12, a shaft 95 drivably connected with the turbine shaft 24 (Figure 1) drives the shaft 96 of a mechanical governor by means of skew gears 97, 98. An axially sli-dable grooved collar 99 alters its position with changes in the speed of the shaft 96 under the control of centrifugal fly-weights 101 of the governor. Engaged in the groove of the collar 99 is the lower end of a lever 102 which pivots about a vertical fixed point 103 con nected by a rod 104 to the end-piece 105 on the piston rod of a pilot valve having a casing 106. The upper end of the lever 102 is slotted at 107 to receive a pin 108 on the end of a rod 109 on which is fixed a double-acting piston 111 working in a servo-cylinder 112. A link 113 connects the rod 109 to the upper end of a rocking lever 114 pivoted at 115. The lever 114 is connected at a point nearer to its pivot mounting 115 than to its upper movable end by means of a link 116 to the fuel rack 117 of the fuel pump 118.

A butterfly throttle valve 119, arranged in the gas dclivery duct 21 from the gas-generator to the turbine, is mounted on a spindle 121 for rotation with an arm 122 which is movable between a minimum throttle opening stop 123 and a maximum throttle opening stop 124. A spring 125 constantly pulls the arm 122 in the direction towards the stop 124. The lower end of arm 122 is connected by a link 128, to a dash-pot cylinder 129 housing a double-acting dash-pot piston 131 on the end of rod 109 remote from the end carrying the pin 108. Also connected to the lower end of lever 122 is one end of a further link 132 the other end of which is connected to an arm 133 fixed for rotation about a pivot 134 with a cam 135. A cam follower roller 136 on a toothed sector 137 transmits movements imparted to it by the cam to the said sector 137 which, like the sector 53 (Figure 2) meshes with the toothed ring 44 and controls the opening and closing movements of the nozzle blades 38.

Either of the two earns 59 (Figure 2) or 135 (Figure 12) can operate independently of the other to move the nozzle blades towards the open position. In case the cam follower roller 64 (Figure 2) of the cam 59 effects movement of the nozzle blades towards the open position and the cam 135 (Figure 12) is not operated by its associated mechanism shown in Figure 12, then rotation of the toothed ring 44 with consequent rotation of the toothed sector 137 will move the cam follower roller 136 out of engagement with its cam 135. Similarly, in case cam follower roller 136 is operated to move the nozzle blades towards the open position, then rotation of the toothed ring 44 with consequent rotation of the toothed sector 58 will move the cam follower roller 64 out of engagement with its cam 59.

The two ends of the dash-pot cylinder 129 intercommunicate with one another through a duct 138 in which is arranged an adjustable valve 139 which controls the rate at which the dash-pot fluid can leak through the duct 138 from one side of the piston 131 to the other. Pipes 151, 152 communicating respectively with the two ends of the dash-pot cylinder are interconnected by two ducts 153, 154 fitted with oppositely directed springloaded non-return valves 155, 156.

A pair of ducts 141,'142 communicating respectively with opposite ends of the servo-cylinder 112 are connccted to the casing 106 of the pilot valve, one on each side of the mid position along the length of said casing. An oil supply line 143 for an oil pump 144 opens into the casing 106 at its mid position and two return pipes 145, 146 connect the two outer ends respectively of the casing 106 with the suction connection of the oil pump 144. Two lands 147, 148 on the pilot valve 149 when in the normal rest position shown in Figure 12 mask the openings in the casing 106 leading to the ducts 141 and 142.

In operation, if the speed of the turbine increases, the grooved collar 99 of the mechanical governor will move to the right as seen in Figure 12. The pilot valve 149 will then also move to the right so that oil from the pump 144 will pass via the supply line 143, the casing 106, and the duct 142 into the right-hand end of the servo-cylinder 112. The double-acting piston 111 will move to the left and oil will pass down duct 141 through casing 106 and back to the pump 144 via the return pipe 145. Then, after the upper end of lever 102 has moved a predetermined distance to the left as seen in Figure 12, the lands 147, 148 will have been pulled back by the rod 104 into the rest position in which the lands 147, 148 close the lower ends of ducts 141 and 142. In the meantime, the movement of rod 109 to the left will have transmitted a movement in the same direction t the fuel rack 117 so as to reduce the rate of fuel delivery to the gas-generator. The same movement of the rod 109 will also have been simultaneously transmitted to the butterfly throttle valve 119 and to the nozzle blades 38 via the dash-pot piston 131 and cylinder 129.

If the valve 139 is adjusted to allow the dash-pot fluid to pass only at a very low rate, the consequent closing movement of the throttle valve 119 and opening movement of the nozzle blades will be substantially proportional to the increase in the speed of the turbine rotor, andboth the throttle valve 119 and the nozzle blades 38 will be returned to their original positions by the action of the spring 125 after a considerable interval of time. If, however, this valve 139 is adjusted to allow the dashpot fluid to pass at a relatively fast rate, the valve 119 and nozzle blades will not undergo any appreciable movement, unless the rate of change of speed exceeds a certain predetermined value.

The provision of the non-return valves 155, 156 enables the rod 109, when the throttle arm 122 is already against one of the stops 123 or 124, to move further in the direction for moving the said arm towards the said stop, in order to operate the fuel rack 117 to increase or reduce the supply of fuel to the gas generator.

The position of the piston 111 in the cylinder 112 at normal maximum speed at full load, is indicated by chain dotted line 157. At normal minimum speed the piston occupies a position at the right-hand end of the cylinder 112 as seen in the drawing, while the over-speed range is between the line 157 and the left-hand end of the cylinder 112.

I claim:

1. A power unit comprising, in combination, a freepiston gas-generator, an inward flow, radial flow turbine, said turbine having variable nozzle blades in the inlet thereof, gas-delivery means connecting said gas-generator with said turbine inlet, and nozzle blade-actuating means responsive to the pressure of the gas supplied to said turbine to increase automatically the areas between '10 said nozzle blades with reduction in the pressure of said gas at least over a range of relatively low gas pressures.

2. A power unit as claimed in claim 1, wherein said nozzle blade actuating means are non-responsive to changes in said gas pressure above a predetermined value.

3. A power unit as claimed in claim 1, wherein said nozzle blade actuating means comprise a nozzle blade actuating mechanism and a gas connection between said gas-generator and said mechanism to apply gas pressure to actuate said mechanism.

4. A power unit as claimed in claim 1, wherein said nozzle blade actuating means comprise a nozzle blade actuating mechanism and a gas connection between said turbine inlet and said mechanism to apply gas pressure to actuate said mechanism.

5. A power unit as claimed in claim 1, wherein said nozzle blade actuating means are operable automatically over a predetermined range and wherein said combination comprises a manually-operable control for moving said nozzle blades to a setting outside said range to effect reversal of the direction of rotation of the turbine rotor.

6. A power unit as claimed in claim 1, wherein said nozzle blade actuating means are operable automatically over a predetermined range and wherein said combination comprises a manually-operable control for moving said nozzle blades to a setting outside said range to effect reversal of the direction of rotation of the turbine rotor, and wherein said turbine has exit guide vanes in the outlet thereof and wherein said turbine comprises, near said exit guide vanes, further guide vanes positioned to reduce the angle of whirl of gases leaving the turbine, and means for adjusting the angles of said further guide vanes with respect to the direction of movement of the said gases.

7. A power unit as claimed in claim 1, wherein said nozzle blade actuating means are operable automatically over a predetermined range and wherein said combination comprises a manually-operable control for moving said nozzle blade to a setting outside said range to efiect reversal of the direction of rotation of the turbine rotor, and wherein said turbine has exit guide vanes in the outlet thereof and wherein said turbine comprises, near said exit guide vanes, further guide vanes positioned to reduce the angle of whirl of gases leaving the turbine, means for adjusting the angles of said further guide vanes with respect to the direction of movement of the said gases, and means coupling said adjusting means with said manually-operable control.

8. A power unit as claimed in claim 1, comprising a throttle in said gas-delivery means, further nozzle bladeactuating means to vary the areas between said nozzle blades, speed-sensitive means responsive to change of speed of said turbine, and couplings between said throttle and said speed-sensitive means, said couplings increasing the areas between said nozzle blades and moving said throttle toward its closed position in response to an increase in turbine speed.

9. A power unit as claimed in claim 1, comprising a throttle in said gas-delivery means, further nozzle blade-actuating means to vary the -areas between said nozzle blades, speed-sensitive means responsive to a rate of change of turbine speed exceeding a predetermined value, and couplings between said throttle and said speed-sensitive means, said couplings increasing the areas between said nozzle blades and moving said throttle tonozzle blades, speed-sensitive means responsive to a rate of change of turbine speed exceeding a predetermined value, and couplings between said throttle and said speedsensitive means, said couplings increasing the areas hetween said nozzle blades and moving said throttle toward its closed position in response to a rate of change of turbine speed exceeding said predetermined value, and wherein said couplings comprise means opening said throttle automatically when the rate of change of turbine speed falls below said predetermined value.

11. A power unit as claimed in claim 1, comprising a throttle in said gas-delivery means, further nozzle blade-actuating means to vary the areas between said nozzle blades, speed-sensitive means responsive to a rate of change of turbine speed exceeding a predetermined value, and couplings between said throttle and said speedsensitive means, said couplings increasing the areas between said nozzle blades and moving said throttle toward its closed position in response to a rate of change of turbine speed exceeding said predetermined value, and wherein the coupling between said throttle and said speed-sensitive means comprises a dash-pot device.

12. A power unit comprising, in combination, a freepiston gas-generator, an inward flow radial flow turbine, said turbine having variable nozzle blades in the inlet thereof, gas delivery means connecting said gas-generator with said turbine inlet, nozzle blade actuating means to vary the areas between said nozzle blades, a throttle in said gas delivery means, speed-sensitive means responsive to change of speed of said turbine and coupling means between said throttle and said speed-sensitive means, said coupling means increasing the areas between said nozzle blades and moving said throttle toward its closed position in response to an increase in turbine speed.

13. A power unit comprising, in combination, a freepiston gas-generator, an inward flow radial flow turbine, said turbine having variable nozzle blades in the inlet thereof, gas delivery means connecting said gasgenerator with said turbine inlet, nozzle blade actuating means to vary the areas between said nozzle blades, a throttle in said gas delivery means, means controlling the supply of fuel to said gas-generator, speed-sensitive means responsive to change of speed of said turbine, and coupling means between said throttle, said speed-sensitive means, and said means for controlling the supply of fuel to said generator, said coupling means increasing the areas between said nozzle blades; moving said throttle towards its closed position and reducing the supply of fuel to said gas-generator in response to an increase in turbine speed.

14. A power unit comprising, in combination, a freepiston gas-generator, an inward flow radial flow turbine, said turbine having variable nozzle blades in the inlet thereof, gas delivery means connecting said gas-generator with said turbine inlet, nozzle blade actuating means to vary the areas between said nozzle blades, a throttle in said gas delivery means, speed-sensitive means responsive to a rate of change of turbine speed exceeding a predetermined value, and couplings between said throttle and said speed-sensitive means, said couplings increasing the area between said nozzle blades and moving said throttle towards its closed position in response to rate of change of turbine speed exceeding said predetermined value.

15. A power unit as claimed in claim 14, in which said couplings comprise/means opening said throttle automatically when the rate of change of turbine speed falls below said predetermined value.

References Cited in the file of this patent UNITED STATES PATENTS 895,603 Trow et a1 Aug. 11, 1908 2,091,669 Bryant Aug. 31, 1937 2,132,286 Carbonara Oct. 4, 1938 2,147,935 Steiner Feb. 21, 1939 2,200,892 Pateras Pascara May 14, 1940 2,219,994 Jung Oct. 29, 1940 2,283,175 Berger May 19, 1942 2,412,365 Sollinger Dec. 10, 1946 2,421,445 Waller June 3, 1947 2,428,830 Birmann Oct. 14, 1947 2,464,434 Chittenden Mar. 15, 1949 2,518,660 Browne Aug. 15, 1950 FOREIGN PATENTS 591,555 Great Britain Aug. 21, 1947 952,321 France May 2, 1949

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