Fuel control system

• US 5,083,277 A
• Filed: 01/09/1989
• Issued: 01/21/1992
• Est. Priority Date: 01/15/1988
• Status: Expired due to Term

• Current Assignee: Rolls-Royce PLC (Rolls-Royce Holdings Plc)
• Original Assignee: Rolls-Royce PLC (Rolls-Royce Holdings Plc)
• Inventors: Shutler, Arthur G.
• Primary Examiner(s): Gruber, Felix D.
• Application Number:
  US07/294,755
• Time in Patent Office: 1,107 Days
• Field of Search: 364/431.02, 364/494, 60/39.281, 60/39.03
• US Class Current: 701/100
• CPC Class Codes: F02C 9/28 Regulating systems responsive to plant or ambient parameters, e.g. temperature, pressure, rotor speed F02C9/30 - F02C9/38, F02C9/44 take precedence
• CPC Class Codes: F05D 2270/02 to control rotational speed (n)
• CPC Class Codes: F05D 2270/04 to control acceleration (u)
• CPC Class Codes: G05D 1/063 by acting on the motors
• CPC Class Codes: Y02T 50/60 Efficient propulsion technologies, e.g. for aircraft

Abstract

A gas turbine engine fuel control system comprises a microprocessor based control unit programmed to calculate the total fuel requirement to achieve a demanded engine speed on the basis of a steady state fuel requirement plus an additional overfuelling requirement. The overfuelling element is calculated in accordance with the lowest of a number of limiting variables which ensure continued engine integrity and safety and a minimum level to prevent engine flame-out and in which all variables and datums are related to an equivalent engine speed or rate of change of engine speed. The steady state fuel element is likewise calculated using a theoretical engine model based on engine acceleration characteristics. The overall system confers highly accurate control of engine speed and acceleration and enables the use of a simple fuel metering valve, in which fuel flow is directly proportional to valve position.

Claims

1. An engine fuel control system comprising:

a fuel flow metering valve arranged to control fuel flow to the engine in response to an aggregate fuel demand signal;

means for generating the aggregate fuel demand signal which comprises means for summing a steady state fuel requirement signal and an overfuelling demand signal;

engine model feedback loop means connected to receive the aggregate fuel demand signal and arranged to generate the steady state fuel requirement signal proportional to said aggregate fuel demand signal; and

means for generating the overfuelling demand signal in accordance with a pilots'"'"' thrust or speed demand signal.

2. The fuel control system as claimed in claim 1 wherein the fuel flow metering valve comprises a valve in which fuel flow is proportional to the opening of a valve member in response to the fuel demand signal.

3. The fuel control system as claimed in claim 2 wherein the valve position is controlled by an actuator driven by the fuel demand signal.

4. The fuel control system as claimed in claim 3 wherein the actuator is connected in a feedback control loop in which the actuator is energised by an error signal being the difference between the computed fuel demand signal and a feedback signal representing the opening of the valve member.

5. The fuel control system as claimed in claim 1 wherein the calculated engine speed is an estimate of a high pressure spool speed.

6. The fuel control system as claimed in claim 5 wherein the engine model loop includes a summing point operative to subtract estimated steady state fuel requirement from the fuel demand signal to determine an overfuelling demand signal.

7. The fuel control system as claimed in claim 6 wherein in the engine model loop the overfuelling demand signal is divided by the rate of change of engine speed with fuel increment to provide an engine acceleration signal which is then integrated to provide an estimated engine speed from which the estimated steady state fuel requirement is calculated.

8. The fuel control system as claimed in claim 1 wherein a maximum overfuelling demand signal is generated with regard to an engine acceleration limit signal.

9. The fuel control system as claimed in claim 8 wherein said engine acceleration limit signal is generated in accordance with the rate of change of high pressure spool speed.

10. The fuel control system as claimed in claim 1 wherein engine speed is determined periodically and a fresh fuel demand signal is computed within each period.