Patent GB-868953-A (GB)
Title: Free-piston engine starter
Inventor: FALBERG ROBERT FRED
IPC: F02B71/02
Filed: 1957-11-29
Abstract: 868,953. Starting free piston engines. GENERAL MOTORS CORPORATION. Nov. 29, 1957, No. 37365/57. Classes 7(1) and 7(5). A free-piston engine has a free piston operating in a cylinder including an expansion chamber the pressure in which is increased in order to drive the piston on its firing stroke for starting purposes, a fluid pump having a suction and a discharge passage, a two-position control valve arranged to connect the chamber alternatively with the suction and discharge passages and a member whose position is controlled by the position of the piston for initiating the movement of the control valve from the position in which the suction passage is connected to the chamber to the position in which the discharge passage is connected to the chamber. The invention is applicable to free piston compressors or free piston gas generators. As particularly described it is applied to free piston gas generators supplying a turbine. Initially the piston 27 of the latch control mechanism 20 and the piston 32 of the positioning control valve 30 are at the right hand sides of their respective cylinders (Fig. 3). The pump 45 is operated whereby air is withdrawn from the cushion chamber 17 and pumped by the pump into line 47 and through vent ports 52. When the pistons 6 reach the outer part of their stroke they engage push rods 42 causing balance arm 40 to move the valve 32 to the left against the spring 39. Movement of the valve 32 to the left causes cam follower 34 to move the latch 35 against the spring 36 and when the valve reaches the end of its stroke (Fig. 2) the latch is returned by the spring 36 to its upper position blocking movement of the valve 32 to the right. With the control valve as shown in Fig. 2 pump 45 is now connected to draw air through ports 62 or 54 and passage 46 and will force it under pressure through line 47 into the passage 51. Pressure in the passage 51 acts to close the check valve 49 and also passes through check valve 57 to the chamber 53 where it acts on the piston 27 to move the links 28, 29 against the force of spring 64 to rotate shaft 22 and latch 23 to a blocking position. When the piston 27 has reached the end of its stroke to the left it pushes check valve 49 off its seat allowing pressure in the line 51 to pass into the line 26 and into the cushion chamber 17. The pressure in the chamber 17 then moves the pistons 6 inward until the synchronizer arm 24 contacts the latch 23. The pressure in the chamber 17 continues to rise and is transmitted through line 61 to act to move the cam follower 34 upward against the force of spring 37 the cam follower 34a meanwhile following the contour of latch 35. When the cam follower 34 reaches the upper portion of its stroke latch 35 is slightly depressed allowing the spring 39 to move the valve 32 rapidly to the Fig. 3 position whereupon the pressure in the chamber 53 acting to hold the latching mechanism in its locking position escapes through the passage 60. The spring 64 then moves linkage 28, 29 and 21 to move the latch 23 out of the path of linkage arm 24 and allows air under pressure in the chamber 17 rapidly to move the pistons 6 inward toward their first firing stroke. After the engine has started continued operation of it is controlled in any known manner as by the stabilizer, dephaser and other controls. The cushion chambers are connected together by suitable means 68. The pressure in the chambers after starting is controlled by a stabilizer S which is of known type. The two units Q, B would normally be connected together by conduit 66 through a normally open isolating valve I. This valve would operate to isolate the chambers after starting when a dephaser D which may be of known type would act to vary the speed of one unit relative to the other until the pistons of one unit were approximately at the inner dead centre when the pistons of the other unit were at outer dead centre. The pump 45 may be driven by an electric motor or air motor.