Patent GB-711220-A (GB)
Title: Engine starting mechanism
IPC: F02N7/08
Filed: 1951-04-26
Abstract: 711,220. Turbines. GARRETT CORPORATION. April 26, 1951 [Oct. 30, 1950], No. 9737/51, Class 110(3) [Also in Group XXVII] A turbine for starting engines is contained within a housing comprising turbine casing, gear casing 10, Fig. 1. and clutch casing 13, the gear casing 10 having internal' walls 14, 15 which support a power shaft consisting of an inner tubular shaft 18 enclosed by an outer shaft 19. the two shafts being splined together at the turbine end. The outer shaft 19 is driven by the turbine through reduction gearing comprising a gear 25 on shaft 19 meshing with teeth 37 on a counter shaft 31 supported in wall 14 and connected to the turbine; more than one counter-shaft may be provided. Compressed air enters the turbine casing at inlet 44 and is axially discharged through outlet 46. The clutch casing 13, which has a thin walled extension 59. surrounds the front end of the power shaft assembly and forms the chamber 60 which is sealed from the gear casing 10 by seals 61, 62 engaging the outer surface of shaft 19; the air admitted to chamber 60 through conduit 64 acts upon the piston assembly 66 and moves it axially within extension 59, the cylindrical wall 67 of the assembly being sealed from the extension 59 by seals 68. In one of the clutch tooth faces 74 there, is provided an opening 80 which communicates with the pressure chamber 60 and is normally closed during periods of clutch engagement but upon separation of the clutch teeth the pressure in chamber 60 bleeds away. with the result that upon a given reduction in chamber pressure the spring 77 acts to disengage the clutch. The chamber 60 is also arranged to open to atmosphere in order to disconnect the clutch upon the starter exceeding a given speed when an adjustable spring-loaded valve 84, arranged radially in end wall 69. moves outwardly under centrifugal action. The clutch 73 is similarly disengaged whenever the torque imposed upon the turbine exceeds a given value, under which conditions the twisting of shaft 18 causes registration of slots in both shafts 18 and 19 and permits the pressure in chamber 60 to bleed to atmosphere through the space 98 between the shafts and tubular member 75. The turbine is arranged for push button operation with pneumatic starting control, and compressed air is supplied to the conduit 100, Fig. 7, connected with the turbine inlet whilst a pipe 101 tapped from duct 100 leads some air through a restricted orifice 102. interconnected manual control-valves 103. 104. and conduit 112 to both a diaphragm 114 which controls a valve 113 in conduit 100. and chamber 60. Upon manually operating valve 103 air is admitted to conduit 112 so that piston assembly 66 is moved to engage the clutch members 73 and 66<SP>1</SP>, and valve 113 is partially opened so allowing a limited supply of air to the turbine. As the clutch engages, the opening 80 is closed so that pressure builds up in the control conduits thereby holding the piston 105 of valve 103 in the open position whereupon the push button may be released; the increased pressure fully opens valve 113 so that the turbine rapidly accelerates to full speed. Should the clutch fail to engage and the holding pressure does not develop above piston 105 then release of the push button will close down the turbine. When the engine is self-operative the clutch teeth will begin to separate and so uncover opening 80 and reduce pressure in chamber 60 whereupon valves 103 and 113 will commence to close until the air to the control system and turbine is shut off and the piston assembly retracted by spring 77. The starting cycle may also be stopped as above described by manually actuating valve 104. In a modified electro-pneumatic control system the starting cycle is commenced by operating a push button 127, Fig. 9, which causes energization of a solenoid 121 thereby admitting air to both conduit 112 and a pneumatically-actuated switch 123 which latter closes a holding circuit to the solenoid 112 and enables push 'button 127 to be released; the shutting-down operation is automatically effected by a decrease in the pressure causing switch 123 to open. The remainder of the cycle is as previously decribed, although the starter may be also stopped by operating another switch 129.