Patent GB-802914-A (GB)
Title: Improvements in hydraulic transmission systems
Inventor: CARDILLO JOSEPH S
IPC: F16H61/46
Filed: 1955-10-14
Abstract: 802,914. Turning-gear. SUNDSTRAND MACHINE TOOL CO. Oct. 14, 1955, No- 29408/55. Class 7(5) [Also in Group XXIX] General. In order to drive an alternator 11, Fig. 6, at a constant speed from. an aircraft engine a hydraulic transmission, comprising swash-plate displacement-devices A and B, is provided, the former being connected to the alternator and the latter to the engine; another similar engine-driven device B' is connected to a second engine and the two devices B, B<SP>1</SP> are interconnected. The apparatus is also used for engine starting purposes by running the alternator as a motor. Engine-driven displacement devices. The devices B, B<SP>1</SP> each comprise a housing 12, Fig. 1, supporting a drive shaft 18 carrying a cylinder block 19 in which are reciprocable pistons 21, having through oil bores 29, the pistons abutting thrust plates 25 in push rods 24 that are reciprocable in a rotor 22 keyed to the shaft 18; the rods 24 contact an adjustable swash plate 35. On the discharge stroke the pistons are held against the plates 25 by discharge pressure whilst on the suction stroke this is effected by a gear pump 30 driven from the shaft 18, which pump ensures that the cylinders are always fully charged, that leakage losses are made up and the shaft is lubricated; the pump 30 has a regulating valve 46 in the discharge passage to by-pass some of the liquid into the pump intake as the engine speed and hence pump speed increases. The valve comprises a piston 48 closed by a spring 49 and pump outlet pressure tapped from an orifice whilst the piston is urged toward the open position by unmodified pump outlet pressure. Another gear pump 80 also driven from the shaft 18 is used to scavenge oil from the housing 12 to reduce drag losses. The position of the swash-plate 35 is determined by a piston 90 in a cylinder 91 and a spring-loaded pin 92 seating in a recess in the piston 90, a number of drain orifices 96 surrounding the pin seat. Liquid enters the cylinder 91 through an externally located regulating-valve 100 wherein system pressure enters a bore 101 via either one of two passages 107, depending upon whether the device is acting as a pump or motor, each incorporating a check valve, and acts upon the end 106 of the valve closure 103 and moves the latter against its spring 108, some of the liquid entering the interior 104 of the closure 103 through an orifice 109 which causes a pressure drop; the pressure differential between chamber 104 and the bore area adjacent the passages 107 also acts to move the closure 103 against its spring 108. Such movement restricts the flow from the chamber 104 through an annular groove 105 and into a passage 97 leading to the cylinder 91. An increase in system pressure produces a similar result. Control of drain fluid through the orifices 96 is effected by a poppet valve 131 having a stem 133 loosely fitting around a pin 134 secured to a spring- loaded booster-piston 135 acted upon by liquid supplied via a passage 141; a spring 139 in a recess in the piston 90 unseats the valve 131 when it is not acted upon by the booster-piston 135. Should the system pressure exceed a given value the sliding closure 158 of a relief valve 150 connects the cylinder 91 to drain into the housing interior whereupon the swash-plate 35 moves towards zero stroke position. A spring-loaded piston 170 is provided to similarly move the swashplate in the event of a supply failure. Contacts 268, 269 are actuated by weights 263 when the engine reaches a selfoperative speed to disconnect the alternator from its electrical power source so that it can no longer function as a starting motor. Alternator driving device. The device A, which has a swash-plate 185, Fig. 3, with its associated piston apparatus, and a charge gear pump 189 similar to that of the engine driven devices B, B<SP>1</SP>, is mounted upon a gear box 200 and has the drive shaft 180 connected to a gear 201 meshing with a gear 202 on the alternator shaft 203; an oil pump is driven from the gear 202 for supplying pressure liquid to accessories. The swash-plate is kept at maximum stroke when the device acts as a motor by supplying pressure liquid to a cylinder 211 in which is piston 210, the liquid being controlled by a sliding valve closure 216. For starting purposes a solenoid-atuated valveclosure 230 is provided which with the closure 216 in the position shown drains the cylinder 211 whereupon the swash-plate moves to zero stroke position. The closure 216 has a stem 240 in a cylinder 241 into which latter is admitted liquid from the outlet of the device when it is acting as a pump, the resulting rightward movement of the closure being opposed by a spring 245 the loading of which is adjustable by a cam 247 driven by the swash-plate 185 thus providing a constant or graduated change of power circuit output or torque from the device during engine starting as the speed is increased. When the swashplate attains the maximum angle the cam 247 no longer influences the setting of the spring 245. Governor control. The gear pump 189 drives flyweight 275, Fig. 5, associated with a rod and a switch arm 283 co-operating with alternator under and over speed contacts 287 and 288, respectively. Contact 288 controls energization of a solenoid valve 290, Fig. 6 which directs pressure liquid into a tank 84; a latch is embodied in valve 290 to prevent the alternator from being again rotated until the failure has been corrected. The fly-weight 275, Fig. 5, is mounted on a bevel gear 295 by means of which the drive is taken to the governor 271. The governor shaft 301, which has located therein a sliding pilot valve closure 305, is provided with flyweights 307, the arms 308 of which are secured to the valve closure 305. Opposing the action of the flyweights is an adjustable spring 309 the lower end abutting the closure 305 and the upper end contacting a plunger 313 forming part of a solenoid 315 which when energized moves the closure 305 down. The shaft 301 incorporates drain passages 316, outlets 317 and inlets 318 whilst the upper part of its bore is enlarged to form a cylinder 319 for a piston 320 secured to the closure 305. A spring-centred buffer piston 323 is reciprocable in a cylinder 322 to one side of the governor casing 300, the cylinder having pairs of ports 326 and 327 therein. Pressure liquid from the gear pump 189, Fig. 3, is introduced into the inlets 318 and in the event of the alternator being loaded and experiencing a speed drop the valve closure 305 is moved down so uncovering outlets 317 whereupon liquid from the inlets flows therethrough into passages 331 and 332 and enters cylinder 319 and acts on piston 320 to provide a restoring force urging the closure 305 upwardly so partially closing outlets 317 and repositioning the flyweights 307. From passage 332 the liquid enters lower ports 326 and lifts the buffer piston 323 forcing the liquid above the latter out via upper ports 327 into the cylinder 319 above the piston 320 to oppose the restoring force and by passages 336, 337 and valve 290, Fig. 6, to the booster cylinder 136, Fig. 1 whereupon the disposition of the swash-plate 35 is charged to increase the pump displacement and the alternator speed returns to normal; the buffer piston 323, Fig. 5, similarly returns to a central position at a rate determined by a needle valve 328 in the passage 337. Upon a load decrease obtaining the alternator speed rises and the flyweights 307 raise the closure 305 and connect to atmosphere the portion of cylinder 319 beneath the piston 320 and the similar portion of buffer cylinder 322 through drain ports and passages 316, 345, 346; pressure liquid on top of piston 320 lowers the closure 305 partially closing the control ports 317, concomitantly pressure liquid also lowers the buffer piston 323 producing a pressure on the under side of the piston 320 that opposes the restoring force on the top thereof. As the buffer piston 323 is lowered liquid is drawn from the booster cylinders 136, Fig. 1, via port 338, Fig. 5, to unseat the poppet valves 131, Fig. 1, and so adjust the swash-plate 35 in a direction to decrease the pump displacement and enable the alternator speed to return to normal, the buffer piston 323, Fig. 5, returning as previously described. A pressure regulating valve may be disposed between the gear pump and the pilot valve. When an extreme load charge occurs the buffer piston 323 is forced above the lowermost ports 327 or below the uppermost ports 326 and permits direct flow of liquid to the booster piston through the buffer cylinder. Interconnecting hydraulic system. The outlet of device A is connected to a conduit 350, Fig. 6, ,and the inlet to a conduit 351, the conduit 350 opening into a branch 352 leading to solenoid-actuated blocking valves 353, 355 controlling conduits 354, 356 connected to the inlets of the devices B, B', the valve 355 also controlling the outlets of both of the latter through conduits 357, 357<SP>1</SP>; the conduit 351 leads to conduit 357<SP>1</SP>. The valve 353 is used to cut out the device B<SP>1</SP> during engine starting whilst the valve 355 is provided to establish communication between the device A and B or B and B<SP>1</SP>. Operational cycle. The alternator is connected to a source of electrical power and runs as a motor thereby driving the shaft 180, Fig. 3, and the solenoid 231 is energized to lower the pressure in the cylinder 211 and move swash-plate 185 to zero strokeposition; upon the device A attaining a speed of 6,000 r.p.m. the solenoid 231 is deenergized so that pressure liquid enters the cylinder 211 and increases the displacement of the device until the constant output cam 247 becomes effective. Governor solenoid 315, Fig. 5, is then energized to move the closure 305 to maximum strokeposition, which directs liquid into conduits 339, 340, Fig. 6, to correspondingly move t