Patent GB-968688-A (GB)
IPC: F02C7/277
Filed: 1961-01-10
Abstract: 968,688. Engine turning gear; turbines. GARRETT CORPORATION. Jan. 10, 1961 [Jan. 11, 1960], No. 1099/61. Headings F1K and F1T. A combination engine and accessory drive apparatus includes first and second shafts for connection respectively to an engine and an accessory, a reversible variable speed motor, a transmission gearing connecting the motor to both shafts and means responsive to variations in the speed of one of the shafts for selecting the direction and rate of operation of the motor. As shown the mechanism comprises principally a main shaft 21 through which power is transmitted to and from an engine (not shown) the engine being arranged to drive an alternator part of the casing of which is shown to the right at 24. The mechanism includes a differential gear transmission 22 linking the engine and alternator together and to an auxiliary motor in the form of a reversible pneumatic turbine 23. The alternator has a tubular shaft 25 through which the main engine shaft 21 passes. With the alternator at rest the valve elements 75 of the alternator speed sensing mechanism 67 will close the radial passages 72. If manifold 77 is not at this time being supplied with fluid under pressure, the spring 96 of the pilot valve 85 will hold the valve 91 at an idle position which is disposed at the left-hand side of that occupied by the valve in Fig. 6. When fluid pressure is initially supplied to the manifold 77, some of the pressure will flow through the line 87 to the passage 73. Since the valve elements 75 of the alternator speed sensing mechanism are closed, pressure in the passage 73 will quickly increase and be transmitted to the compartment 94. This fluid pressure will urge the diaphragm 93 toward the right as viewed in Fig. 6, until the valve 91 is in position to establish communication between the inlet port 98 and port 100. In such position valve 91 also establishes communication between ports 99 and 102. Fluid may then flow from the manifold 77 through passages 87, 103 and 105 to chamber 109 of the actuator 86. This pressure will be applied to the piston 113 to move it toward the left as viewed in Fig. 6, this movement being possible since chamber' 110 is then connected with the atmosphere through passage 104 and port 102. Leftward movement of piston 113 imparts similar movement to valve elements 115 and 116. This movement of the valve 115 will establish communication between the passage 121 and the atmosphere through the connection of ports 118 and 125 and fluid may then flow from chamber 123 of valve 81 at a faster rate than the orifice in branch 121a will permit fluid to flow into the chamber. The pressure therein will fall, permitting fluid pressure in the branch 78 to move the valve element 84 away from its seat and establish fluid flow through branch 78 to the inlet duct 37 of the turbine. Such flow of fluid will cause the turbine to rotate in an anticlockwise or engine starting direction. When fluid is supplied to move the piston 113 toward the left, pressure from the passage 105 will also flow through the branch 105a to the compartment 95 in a feedback action, which will tend to return the valve spool 91 toward an intermediate or closed position in which communication between ports 98 and 100 is interrupted. Branch passage 105a communicates via capillary tube 105b with a second branch 104a extending from the passage 104 to a chamber 95a having a diaphragm 93a corresponding to the chamber 95 and its diaphragm 93 but located at the opposite end of valve 90. Fluid flowing through the tube 105b serves to equalise the pressures in the chambers 95 and 95a and permits the spool valve to assume a position determined by the balance of forces of the fluid pressure in the chamber 94 and the spring 96. Pressures in the chambers 109 and 110 of the actuator are also balanced, permitting the pistons 113 and 114 together with the valve elements 115 and 116 to remain in the positions to which they have been moved until a succeeding signal has been transmitted to the pilot valve mechanism 85. Initial counterclockwise movement of the turbine will be applied through the gear type transmission, to effect engine starting movement of the main shaft 21. As the turbine speed increases, engine speed will be correspondingly increased until the engine operation is initiated. After actual engine operation starts, the engine will accelerate and transmit torque through the shaft 21 and the gear transmission 22 to the alternator. As previously pointed out, the alternator may be loaded after the engine operation has started and the required alternator speed is reached. As the engine continues to accelerate, it will tend to increase the speed of rotation of the alternator shaft. This tendency will be sensed by the mechanism 67, causing the valve elements 75 to be unseated and permit fluid pressure to bleed from the passage 73. When this bleeding of pressure tends to exceed the volume flowing through restriction 89, pressure will be decreased in the compartment 94 of the pilot valve mechanism 85 and the spring 96 will then move the valve spool 91 to the left, as viewed in Fig. 6, completely to interrupt the flow of fluid from the manifold 77 through the passages 103 and 105 to the chamber 109 but establish flow from the manifold 77 through the passages 103 and 104 to the chamber 110 of the actuator 86. When this flow is established, the piston 114 will be moved to the right as viewed in Fig. 6, such movement being possible because the chamber 109 of the actuator will then be vented to the atmosphere through the passage 105 and the port 101. When the piston 114 moves to the right, similar movement will be imparted to the valve element 115, causing it to move towards a position in which communication between chamber 123 of the turbine control valve 81 and the atmosphere, through line 121 and port 125, will be decreased. As this communication is decreased, fluid flowing from the manifold 77 through the passages 121a and 121 will apply force to the piston 83 of the valve 81 and move the valve element 84 towards a closed position to modulate the flow of fluid under pressure through branch 78 to the turbine. This modulation of fluid flow will decrease the rate of operation of the turbine whereby the speed of the alternator will be trimmed to maintain the current being generated by the alternator at the desired frequency. As the engine continues to accelerate, the pilot valve 85 will be repeatedly operated in the same manner to cause the valve 78 to continue to decrease the flow of motivating fluid to the turbine. It will therefore be apparent that if the speed of operation of the alternator should decrease, such change will be sensed by the mechanism 67 to cause the pilot valve 85 to so actuate the valve 81 that the flow of fluid to the turbine will be increased whereby the alternator speed will be adjusted to maintain the required frequency of the current. Thus one can say that initially the gear formed by the stationary ring 51, the gears 48 and 49 and the planet carrier 42 will act purely as a fixed gear giving a fixed speed ratio from the turbine to the engine and the torque to the alternator is shared differentially between the turbine and the engine. Once the engine starts however the torque applied to the engine by the turbine gradually drops and the engine correspondingly takes an increasing share of the torque to the alternator. Eventually the planet gears 55, 56 and 54 will reverse their direction of rotation and the system will act as a differential with no parts fixed since the gear 57 will then rotate in a clockwise direction. During this time the alternator speed will have continued to accelerate and this will be sensed by the mechanism 67; the signals generated thereby will cause the pilot valve 85 to continue to move the valve 81 toward the closed position. The flow of fluid to the turbine through passage 78 will eventually be completely interrupted. Before this condition occurs, however, the forces exerted by the engine and the air applied through nozzles 40 to the turbine will be balanced, causing the turbine to stop rotating in an anticlockwise direction and start to be driven by the engine in a clockwise direction in opposition to the air issuing from the nozzles 40. This clockwise operation of the turbine causes the gear transmission further to trim the speed of the alternator and absorbs some of the power delivered by the engine. The amount of power absorbed, however, is at a minimum, and the ratio of the gears is so calculated that the engine will be operating at or near a cruise condition. If the engine is caused to accelerate beyond the crusing speed and tends further to increase the speed of the alternator, this tendency will be sensed by the mechanism 67 and a signal will be transmitted to the pilot valve mechanism 85, which will then cause the actuator 86 to move to a position wherein the chamber 124 of valve 82 will be partially vented to the atmosphere. At this time the valve element 84 of the valve 82 will be moved by fluid under pressure in the branch 80 towards an open position to cause fluid to flow through this branch to the duct 38 of the air turbine. Fluid flow into this duct will be admitted through nozzles 41 to the turbine wheel to increase the rate of rotation in a clockwise direction. The tendency of the alternator speed to increase will be further counteracted by the clockwise rotation of the turbine. It will be realised that when the engine speed is decreased, the speed of the alternator will tend to decrease and be sensed by the mechanism 67 through the closing movement of valve elements 75. This action will cause pressure in the compartment 94 to increase and move the valve 91 in a direction to make the actuator 86 operate the valve 82 to reduce the flow of fluid to the turbine nozzle 41. The clockwise rate of operation of the turbine will decrease to cause alternator