Patent GB-698112-A (GB)
Title: Improvements relating to means for controlling the length of stroke in free-piston internal combustion engines
IPC: F02B71/00
Filed: 1948-02-18
Abstract: 698,112. Free piston engines. BALDWINLIMA-HAMILTON CORPORATION. Feb. 18. 1948 [Sept. 12, 1945], No. 4718/48. Classes.7 (i) and 7 (ii). A. stroke control device for a free-piston engine comprises a member controlled by movement of the piston and which in turn controls inlet valve means for admitting gas under pressure to the accumulator chamber of the engine upon the compression stroke, being shorter than normal and vent valve means for venting the accumulator chamber upon the stroke being longer than normal the arrangement being such that under short stroking conditions in which repeated strokes differ from normal by only a small amount a succession of repeated short strokes are required to effect operation of the inlet valve whereas the vent valve is operable immediately to release the accumulator chamber pressure on the occurrence of a single overstroke in excess of a predetermined magnitude. In Fig. 2, 10 and 11 are rack bars. Racks similar to these are frequently connected to the pistons of free-piston engines to synchronize the movement thereof. An opposed free-piston engine is described. The rack bar 10 carries cam surfaces comprised by a depression 13 and a projection 14 which actuate a follower 15 which in turn through the devices shown actuates valves 28, 32 which control respectively supply of air from a line 29 to a pipe 30 or. release of air from the pipe 30 to a vent pipe 33. The pipe 30 leads to the pneumatic energy accumulator space of the engine. When the follower 15 drops into the depression 13 a piston 22 is moved to the left, and when the projection 14 contacts the follower the piston 22 is moved to the right. During leftward movement of the piston after a port 46 has been covered liquid from a chamber 35 is forced past a non- return valve 37 into a chamber 24 at the left hand side of a piston 25 forcing the piston to the right and during rightward movement of the piston after a port 49 has been covered liquid is forced into a chamber 23 at the right hand side of the piston 25 and moves this piston to the left. The movements of the piston 25 are not normally sufficient to operate levers 31, 27 connected to the valves 32, 28 respectively. During normal operation for one complete reciprocation of the engine pistons the piston 22 moves to the left due to the follower entering the depression 13 and the piston 25 is moved to the right, next the piston 22 is shifted to the right by contact of the projection 14 with the follower and the piston 25 is moved to the left, The follower then enters the depression again and the piston 22 is again moved to the left and the piston 25 to the right. The arrangement is such that the movement to the left of the piston 25 due to the action of the projection 14 is twice the amount of movement to the right due to the action of the depression 13 so that the piston is returned to its central position again without having operated either of the valves 28, 32. However if the stroke varies from the normal the piston 25 is moved out of its central position to actuate one of the valves but this actuation may not occur due to one stroke only varying from the normal. If the variation of stroke from the normal is repeated then only a slight variation on each stroke will have a cumulative effect so that the piston 25 moves to one or other side to actuate one of the valves. In a modification the cam instead of having a depression and a projection has two projections and there are only two pumping strokes (one in each direction) of the piston 22 for each reciprocation of the engine pistons. In another modification applicable where but little stroke variation is expected there is a single inclined cam surface on the rack bar. Air vents 67 and 68 are provided. In a modification the cam could be carried by any part which moves in fixed relation to the movement of the piston. A pump 52 is used for making up leakage. The line 54 is shown connected to the fuel pump associated with the engine fuel injector. Fig. 5 shows, means for preventing hunting of the engine. Piston 25' corresponds to piston 25 of Fig. 2 and carries smaller pistons 85 which co-operate with chambers 86, 87 to supply oil to actuate a valve 92. Thus if the piston 25' is moved to the left by oil supplied to a chamber 23' the piston 85 causes oil to be supplied from the chamber 87 to a chamber 89 and move the valve 92 to the right so that it uncovers an elongated port 96 and connects a chamber 23' at the right of the piston 25' to a passage 97 leading to a pipe 99 which is connected to an atmospheric pressure relief such as an oil tank. Thus further supply of oil to the chamber 23' moves the piston 25' very gradually. The valve 92 resumes its neutral position on cessation of movement of the piston 25'. A return movement of the piston is also retarded by a similar action to that described above.