WO1992010654A1

WO1992010654A1 - Gas turbine engine power unit

Info

Publication number: WO1992010654A1
Application number: PCT/GB1991/001526
Authority: WO
Inventors: Robert Ingram Watson
Original assignee: Rolls-Royce Business Ventures Limited
Priority date: 1990-12-06
Filing date: 1991-09-06
Publication date: 1992-06-25
Also published as: GB9026547D0

Abstract

A gas turbine engine power unit (10) comprises a gas turbine engine (10a) which drives an electrical generator (22) which in turn powers an electric motor (24). The unit (10) includes a control system (34) which ensures that when the power output selector of the unit provides a command to the control system for the output power of the unit (10) to be increased, simultaneous and corresponding signals demanding an increase in power output are sent to the gas turbine engine (10a) and the electric motor (24).

Description

GAS TURBINE ENGINE POWER UNIT This invention relates to a gas turbine engine power unit and in particular to a gas turbine engine power unit which is adapted to drive a vehicle.

One way in which a gas turbine engine can be used to drive a vehicle, such as a car, is to utilise a power unit which comprises the gas turbine engine, an electrical generator driven by the gas turbine engine and one or more electric motors powered by the generator. Typically when more than one electric motor is employed, each motor is o arranged to drive one of the road wheels of the vehicle.

While such a power unit can be effective in providing satisfactory performance under steady state and slowly changing conditions, there are drawbacks when the unit is called upon to provide a rapid increase in power over a small 5 time period. Typically this would happen if rapid acceleration of a vehicle powered by the unit is selected. Such a rapid increase in power would be brought about by a correspondingly rapid increase in the amount of fuel supplied to the gas turbine engine. However gas turbine engines are 0 characterised by a time lag between an increase in fuel flow to the engine and a corresponding increase in engine power output. Clearly such a time lag is undesirable in the case of road vehicles where it would result in the vehicle performance comparing unfavourably with that of similar 5 vehicles powered directly by an internal combustion engine.

It is an object of the present invention to provide a gas turbine engine power unit in which such a ^•time lag is reduced.

According to the present invention a gas turbine engine 0 power unit comprises a gas turbine engine, an electrical generator driven by said gas turbine engine, at least one electrical motor powered by said electrical generator, a power output selector for selecting the output power of said power unit and a control system for controlling said power 5 unit, said control system being adapted to act in accordance with the output of said power output selector to control the level of electrical power directed to said at least on electric motor from said electrical generator, . an simultaneously correspondingly control the power output o said gas turbine engine. The invention will now be described, by way of example with reference to the accompanying drawing which is schematic diagram of a gas turbine engine power unit i accordance with the present invention.

Referring to the drawing, the gas turbine engine powe unit is generally indicated at 10. It comprises a primar air intake at 11 which is supplied with air from one of tw sources. One source is ambient air as indicated by the arro 12. The other is air which has been compressed by turbocharger 13 and cooled by a water cooled intercooler 14. The circumstances which dictate the choice of the particula source of air and the effects of that choice will b described later.

Air from the primary air intake 11 is directed into and compressed by a centrifugal flow compressor 15. The resultant compressed air exhausted from the compressor 15 is passed through a heat exchanger 16 which serves to increase the temperature of the air before it is directed into combustion equipment indicated at 17. There the air is mixed with fuel and the mixture combusted. The resultant combustion products then expand through and thereby drive a radial inflow turbine 18 before being directed into a power turbine 19. The turbine 18 drives the compressor 15 by means of a shaft 20 which interconnects them.

The power turbine 19 has a power output shaft 21 which drives an electrical generator 22. The electrical output of the generator 22 is directed to an electric motor 24 via a power conditioner 23 which converts that output to a form suitable for powering the electric motor 24. Although a single electric motor 24 is shown in the drawing, it will be appreciated that more than one motor 24 could be powered by the generator 22 if so desired. The exhaust efflux of the power turbine 19 is directed to a gas diverter valve assembly 25. The valve assembly 25 has first and second output ducts 26 and 27 which contain first and second flap valves 28 and 29 respectively. The first output duct 26 directs the power turbine 19 exhaust gases to the heat exchanger 16 where they are cooled by being placed in heat exchange relationship with air exhausted from the compressor 15. The gases are then directed into the turbine 30 of the turbocharger 13. The second output duct 27 also directs power turbine 19 exhaust gases to the turbocharger turbine 30, but directly, not via the heat exchanger 16.

The first and second flap valves 28 and 29 are operated in such a manner that all of the power turbine 19 exhaust gases are directed to the turbocharger turbine 30 either via the heat exchanger 16 only or not via the heat exchanger 16. After passing through the turbocharger turbine 30, the gases are exhausted to atmosphere as indicated by the arrow 31.

The turbocharger turbine 30 drives the compressor 32 of the turbocharger 13 by means of a shaft 33.

It will be seen therefore that the turbocharger 13 primary air inlet 11, compressor 15, heat exchanger 16 combustion equipment 17, turbine 18, power turbine 19 and valve system 25 constitute a gas turbine engine 10a. The gas turbine engine power unit 10 is operable at high and low power output levels. At low power output levels, the primary air intake 11 is arranged to receive ambient air 12 only i.e. .not via the turbocharger 13. Additionally the first flap valve 28 is arranged to be open and the second flap valve 29 closed. Under these conditions, the unit 10 operates thermodynamically very efficiently since the heat exchanger 16 serves to heat up air exhausted from the compressor 15 prior to combustion and additionally cool down the power turbine 19 exhaust gases. Indeed the power turbine 19 exhaust gases are cooled down to such an extent that they have a minimal effect upon the turbocharger turbine 30 as they pass through it. At high power outputs, the primary air intake 11 i arranged to receive only air which has been compressed by -th turbocharger 13 and cooled by the intercooler 14. Additionally the first flap valve 28 is arranged to be close and the second flap valve 29 open. Thus, the power turbin 19 exhaust gases, instead of being used to heat up the compressor 15 exhaust gases in the heat exchanger 16, are used to drive the turbocharger turbine 30. Consequently the air flow to the combustion equipment 17 is considerably greater than is the case in the low power mode of operation. The fuel flow to the combustion equipment 17 is increased correspondingly, thereby bringing about an increase in the amount of hot gases discharged into the power turbine 19 and in turn an overall increase in the power output of the unit 10.

The various variable features of the gas turbine engine power unit 10 are controlled by a control unit 34. Thus the control unit 34 receives input signals from the power output lever 36 and the power turbine 19 output shaft and sends output signals to the primary air inlet 11, the valve assembly 25, the fuel flow control system for the combustion equipment 17 and to the electric motor 24.

The control unit 34 controls the power unit 10 in such a way that the primary air inlet 11, the fuel flow to the combustion equipment 17 and the first and second flap valves 28 and 29 are caused to operate as described earlier in a manner appropriate to whether high or low power operation is required. Thus if the power output selector 36 is moved to a high or low power position then the control unit 34 causes the power unit 10 to react accordingly. Additionally, if the load driven by the power unit 10 should change, the rotational speed of the power turbine 19 output shaft 21 will change accordingly. This will result in an appropriate signal being sent from the output shaft 21 to the control unit 34 causing the control unit 34 to increase or decrease the power output of the power unit 10 as necessary.

When it is desired to increase the power output of the power unit 10, the power output selector 36 is moved to an high power setting. This results in an appropriate sig being sent from the power output 36 to the control unit 3 The control unit 34 then reacts to that signal as describ earlier by sending appropriate signals to the primary a inlet 11, the valve assembly 25 and the fuel flow to t combustion equipment 17. While this would result in eventual increase the power output of the gas turbine engi 10a there would be an inevitable time lag as its vario rotational parts increase in rotational speed. In order to compensate for this time lag, the contr unit 34 additionally and simultaneously sends a signal to t electric motor 24 to cause it to increase its power inpu This has the effect of providing an immediate increase in t power output of the electric motor 24. It also has t effect of causing the electric motor 24 to extract more pow from the electrical generator 22, thereby causing both t generator 22 and the power turbine 19 to slow down. Howev the rotational parts of the power turbine 19 and t electrical generator 22 together with the shaft 21 whi interconnects them are arranged to be of high rotation inertia. This is achieved by ensuring that their mass sufficiently high to ensure that their inertia does n permit the rotational speed of the generator 22 to drop bel a predetermined level before the previously mentioned ti period has passed. Clearly the predetermined level is t minimum speed which is necessary for the generator 22 supply the power requirements of the electric motor 24.

The effect of using the power output lever 36 initiate simultaneous and corresponding power increa signals to the gas turbine engine 10a and the electric mot 24 is a very fast power output increase response from t electric motor 24.

It may be found under certain circumstances that t mass of the rotary portions of the power turbine 19 and t generator 22 together with that of their interconnecti shaft is insufficient to provide the • necessary inertia overcome the time lag of the gas turbine engine 10a. In su cases, the power turbine 19 could be arranged to rotate at speed which is greater than would otherwise be necessary i order that the necessary level of inertia can be achieved.

Although the present invention has been described wit reference to a gas turbine engine 10a which is provided wit a turbocharger and associated equipment to enable it to operate at different power levels, a conventional gas turbine engine could be employed if so desired.

Claims

Claims:-

1. A gas turbine engine power unit (10) comprising a g turbine engine (15,17,18), an electrical generator (2 driven by said gas turbine engine (15,17,18), at least o electric motor (24) powered by said electrical generat (22), a power output selector (36) for selecting the outp power of said power unit (10), and a control system (34) f controlling said power unit (10), characterised in that sa control system (10) is adapted to act in accordance with t output of said power output selector (36) to control t level of electrical power directed to said at least o electric motor (24) from said electrical generator (22), a simultaneously correspondingly control the power output said gas turbine engine (15,17,18), said electrical generat (22) and the portions of said gas turbine engine (15,17,18 which rotate therewith being of such a combined mass th when an increase in the power output of said power unit (10 is demanded, in the -period between the initiation of sai demand and said gas turbine engine (15,17,18) respondin thereto, they have sufficient inertia to ensure that thei rotational speed does not fall below the level necessary fo said generator (22) to satisfy the power requirements of sai at least one electric motor (24).

2. A gas turbine engine power unit as claimed in claim characterised in that said power unit (10) includes turbocharger (13) driven by the exhaust efflux of said ga turbine engine (15,17,18), said turbocharger (13) optionall increasing the airflow to said gas turbine engine (15,17,18 to thereby increase its power output.

3. A gas turbine engine power unit as claimed in claim characterised in that said power unit (10) includes a hea exchanger (16) to optionally place the exhaust efflux of sai gas turbine engine (15,17,18) in heat exchange relationshi with air which has been compressed by said gas turbine engin (15,17,18) prior to being directed into the combustio equipment (17) of said engine (15,17,18).

4. A gas turbine engine (15,17,18) power unit as claimed in claim 3 characterised in that said power unit (10) includes valve means (25) adapted to direct the exhaust efflux of said gas turbine engine (15,17,18) either into said heat exchanger (16) and thence into said turbocharger (13) or directly into said turbocharger (13).

5. A gas turbine engine power unit as claimed in any one preceding claim characterised in that said power unit (10) includes a power turbine (19), said power turbine (19) being driven by the exhaust efflux of said gas turbine engine (15,17,18) and adapted to drive said electrical generator (22).