Patent GB-1526569-A (GB)
Title: Vehicle gas turbine drive arrangement
IPC: B60K23/00
Filed: 1976-10-15
Abstract: 1526569 Gas turbine engines; controlling fuel supply DEERE & CO 15 Oct 1976 [17 Oct 1975] 43005/76 Heading F1G [Also in Division F2]  In a drive arrangement for a vehicle propelled by a gas turbine engine, in which a system for controlling engine speed and the transmission ratio of a drive gear assembly is responsive to operational conditions of the engine and to at least one operator-controlled desired value, a normally engaged clutch between the engine and the drive gear assembly is disengaged automatically under abnormal operating conditions, e.g. when the engine approaches stall as its speed falls below 55% of its rated speed. The invention is described applied to an arrangement in which a single shaft gas turbine engine is coupled through a planetary reduction gear and the automatic clutch to a service clutch followed by an infinitely variable transmission. Essential accessories such as the fuel and lubrication pumps and a drive system for power brakes are driven from a point between the reduction gear and the automatic clutch, and non-essential accessories are driven from a point between the automatic and service clutches so that the engine is substantially relieved of load when the automatic clutch is disengaged. The system is operable in two modes designated manual and automatic. Manual mode. In this mode, which is used for controlling engine speed when the vehicle is stationary or set to travel at a low ground speed, the setting of a lever of an engine speed control unit 28 determines a selected speed signal 35, 37 which is modified by a lag compensator 38, taking into account the acceleration capabilities of the engine, to produce a speed command signal 39 which is compared with the actual speed N 1 detected by a tachometer to produce an error signal 42. This error signal is modifed by a device 44 introducing proportional gain or having a proportional plus time-integral characteristic to develop an N I error signal which controls the fuel supplied to the engine 14. This signal is passed through a lowest signal selector 50 to which other signals 55, 58 are also fed, but the latter signals are of a precautionary or safety nature, and fuel control is normally exercised by the N 1 error signal. The signal 55 is produced by an electronic device 54 which receives the N 1 signal and generates a maximum fuel flow signal. The signal 58 is generated by an electronic device 60 controlled by engine exhaust temperature T5, adjusted by intake temperature T1, and cuts off fuel supply to the engine in the event of excessive adjusted exhaust temperature. The output signal 52 from the selector 50 is passed to the engine 14 through a highest signal selector 53 which also receives a minimum fuel flow schedule signal from an electronic device 65 for ensuring adequate fuel flow during start-up and idling. An emergency shut-down element 66 actuates a solenoid valve 69 to interrupt engine fuel supply on detection of an emergency condition, e.g. excessive exhaust gas temperature, engine overspeeding, non-occurrence of proper starting sequence, loss of oil pressure, &c. The transmission ratio may be adjusted by a lever of a ground speed control unit 30 when the engine is subject to the manual mode of operation. A ground speed set signal 76 is passed through an electronic device 78 which limits the rate of increase of the signal in accordance with the ability of the engine to accelerate the vehicle, and the resultant ground speed command signal 80 is passed through a summing junction 82 to the transmission 26, a feedback signal from the latter being applied to the summing junction to keep the transmission adjustment in step with the command signal. If the engine speed setting is such that insufficient power is available to meet the selected ground speed a ratio-reducing signal 96 is applied to the summing junction 82. The engine speed command signal 39 is modified by an electronic device 84 to emerge as a signal 86 which is able to increase only at a controlled rate but can respond immediately to a decrease in the signal 39, the signal 86 being compared at 90 with the actual speed signal N and the resultant error signal 92 being fed to an electronic device 94 which delivers a signal 96 to the summing junction 82 only in the sense to decrease the transmission ratio and only when the speed error signal exceeds a predetermined threshold value. Automatic mode. When the system is operated in this mode the engine speed set signal 35 remains at zero, a switch 40 is closed, and engine speed is controlled by a signal 36 derived by an electronic device 120 from adjusted exhaust temperature. A switch 130 is also closed enabling a G1 error signal obtained from the difference between the ground speed set signal 76 and an actual ground speed signal to be applied to the summing junction 82 to provide precise control over the ground speed. To guard against a sudden large increase in ground speed in the event of sudden removal of a large load, e.g. if a plough is lifted out of hard ground, an electronic device 134 provides a transmission override signal 136 which, through a maximum signal selector 100, takes over control of the transmission under large load conditions to limit the reduction in transmission ratio so that ground speed does not fall below 50% of the commanded speed. Under such conditions the engine may approach stall unless the commanded ground speed is reduced. A fixed voltage signal R MIN applied to the maximum signal selector 100 limits the lowest ratio attainable so that if the transmission 26 is of the non-slip type, application of the vehicle brakes without release of the service clutch will result in overloading of the engine which will approach stall before mechanical damage is sustained by the power train. Should engine speed fall below 55% of its rated speed, which is very near the no-load stalling speed, a device 154 delivers a signal 152 to disengage the automatic  clutch 20 which can then be re-engaged only by operation of a reset switch.