US2912965A - Free piston machine - Google Patents

Description

Nov. 17, 1959 J. s. CAMPBELL 2,912,965

FREE. PIs'roN MACHINE Filed July 14', 195e `ATTORNEY v 2,912,965 FREE PIsroN MACHINE James S. Campbell, Kingston, Ontario, Canada, assigner toQueens University, Kingston, Ontario, Canada Application July '14, 1958, Serial No. 748,312

2 Claims. l (C1. 12S-H46) This invention relates to free piston machines such as compressors and gasifiers.

IIn conventional free piston gasifiers and compressors,

the pistons are returned after the firing stroke by energy stored in bounce cylinders in which air is trapped and compressed.

In compressing air part of the energy absorbed in the air is transferred to heat and lost. Moreover, piston rings are depended upon to trap the air and these are not fully eicient as a result of which it is usual to replace the lost air after every stroke. The mechanism necessary to effect this step further complicates the mechanical arrangement of the structure design.

It is an object of this invention to provide a simple mechanical means of greater efl'iciency for returning the pistons of a free piston structure after the firing stroke.

To this end, the invention contemplates the provision, in a free piston machine having a pair of piston assemblies, of a mechanical spring arranged to store energy in response to the firing stroke of each piston assembly, such spring on completion of the firing stroke being arranged to effect the compression stroke of the piston assembly.

The invention will be described with reference to the accompanying drawing, in which- Figure l is a longitudinal sectional elevation of a free piston structure incorporating the spring arrangement of the present invention,

Figures 2, 3, 4, and 6 are partial longitudinal elevations of modified forms of the arrangement,

Figure 7 is a partial sectional elevation of the arrangement of Figure 5 in another position, and

Figure 8 is a partial sectional elevation of an associated starting device.

Referring to Figure 1, 1 is a power cylinder and 2 and 3 compressor cylinders axially arranged with respect to the power cylinder one at each end thereof, the compressor cylinders being of larger diameter than that of the power cylinder. A pair of piston assemblies each comprising a power piston 4 and a larger diameter compressor piston 5 are reciprocatingly mounted in the cylinders, all in accordance with conventional practice. In the structure shown, the general frame of the machine includes an inner aligning disc 6 for each compressor cylinder with air inlet openings 7 therein, an outer closure plate 8 with valve controlled compressed air outlets 9, a cover 10 forming a compressed air passage 11, and a duct 12 leading from passage 11 to an air intake 13 in the power cylinder. Also, as shown, each compressor piston has valved openings 14 therein and the power cylinder has a fuel injection nozzle 15 and a scavenging air outlet 16.

In accordance with the invention, a hollow cylindrical member or sleeve 17 is mounted in each cover member 10, such sleeve having a portion extending partially into a cylindrical recess 18 in the adjacent compressor cylinder and in which it has a sliding t. A compression spring 19 is positioned within the sleeve 17 and recess 18 and has I one endseated on an annular flange 20 carried 'by the outer end of sleeve 17 and its other end engaging a seat 21 fixed in piston .5 at the base of recess 18. As shown, v

the recess 18 is open to atmosphere through the open end of the sleeve. It will be apparent that, on the firing stroke of the piston assemblies, the springs 19 will be compressed" and, on completion of the firing stroke, will function to move the piston assembliesv inwardly to perform the com#v pression stroke thereof. It will be understood that springs of suitable strength to carry out this step will Abe lemployed. l l

An advantage of the structure described resides in the fact that a substantial interior area vof the piston assembly? is exposed to atmosphere and facilitates a cooling of the y pistons. This exposed area also makes possible the proi 22 is located betweenthecoinpressor pistons 5 and has" its ends connected to the confronting faces'of such pistons as by rods 23. v l

In the modificatonof Figure 4, a4 separate tension spring 24 is connected to the inner faceof each compressor piston 5, the inner ends of both springs being attached to a frame member 25.

It will be understood that a plurality of springs 22 or pairs of springs 24 may be symmetrically arranged about the axis of the pistons.

Figure 5 shows an arrangement wherein, instead of the tension spring 22, a compression spring 26 is arranged to act as a tension spring. As shown, the spring is received within a tubular member 27 with one end thereof seated on an annular flange 28 at one of the members, the other end of which is connected to one piston 5 as by a rod 29. A rod 30 connected to the other piston 5 extends through the member 27 and spring 26 and has a cross bar 31 on which the other end of the spring is seated. This arrangement may be desirable under certain circumstances since compression springs have greater fatigue characteristics than tension springs, particularly at high speeds.

Figures 6 and 7 show a modification wherein a conical coil compression spring 32 is interposed between the outer face of each piston 5 and the closure plate 8. This arrangement is possible because of the relatively small space required by use of such a spring.

Figure 8 illustrates a manner of associating starting device with a structure such as shown in Figure l. A rod 33 is mounted axially within the spring 19, sleeve 17, and recess 18 by screwing its end portion into the piston wall at the base of the recess as indicated at 34. The rod 33 has a screw-threaded portion 35 projecting outwardly from the recess and mounted thereon is a hand wheel 36 the hub portion of which engages the spring retaining ange 20. To start the engine, the hand wheel 36 is turned to reciprocate the rod 33 outwardly bringing with it the piston 5 while compressing spring 19. When the pistons are in outermost position, they may be locked therein by means of a detent which engages the teeth of a pinion 38 forming part of a piston synchronizing means which also includes a rack 39. The rod and handwheel may now be removed from each piston assembly and, on tripping the detents, the springs 19 force the piston assemblies together rapidly to sta-rt the engine. It will be apparent that the use of piston return springs, as described, makes readily possible such an engine starting procedure as well as other similar engine starting prov cedures,

Patented Nov. 17, 1959 Y YWhile a single helical compression spring 19 is shown for use in an embodiment such as illustrated in Figure l, it will be understood that such spring may be of either unitary or composite form. '-fMoreover, in order to provide adequate energy'and/or to avoid surgi-ng under high speed, a plurality of springs'niay be associated together in various arrangements, three of which are illustrated in Figures 9, 10 and 1l by way of example.

Figure 9 shows a pairY of concentric'ally arranged springs 40 andv 41 with opposed helix angles.

Figure l() shows a pair vof concentrically arranged springs 42 and 43 with their helices wound in the same direction. I

Figure ll shows a pair of springs 44 and 4S of the same pitch and mean diameter threaded together.

A It will be understood that any suitable spring stock cross section may be employed for the springs.-

Moreoven the coil pitch and/or mean diameter of the springs may be varied as desired to reduce spring surge where the engine speed is such as to induce springA surge.

Dampening of spring surge may also be accomplished by allowing the springs to rub against their guides or in multiple spring installations against each other. Furthermore,- combinations of pitchvariation, mean diameter variation, and frictional contact may be employed to avoid spring surge.

I claim:

1. In a free piston machine having a power cylinder, compressor cylinders; a pair of piston assemblies mounted in said cylinders, and a cover enclosing the end of each of said compressor cylinders, said piston assemblies being movable towards each othersto perform a compression stroke and away from each other to perform a tiring stroke, each said piston assembly having an axial recess in the outer face thereof, a sleeve ixed to each said cover and projecting into said recess for sliding engagement with the wall thereof, and at least one spring in said sleeve and recess and bearing upon an inner face of one of said piston assemblies to urge said piston assemblies towards each other to perform said compression stroke, said springs being loaded in response Ito said firing stroke to constitute a source of energy for performance of said compression stroke.

2. A free piston machine as dened in claim l, including means for moving each said piston assembly against the action of said spring comprising a rod extending axially through said cover and spring and having one end bearing on said piston assembly, and a'member threadedly mounted on said rod exteriorlyA of said cover.

References cited in the fue of this patent UNITED STATES PATENTS 790,325 Steele as May 23, 1905 FOREIGN PATENTS 353,587 Germany May 22, 1922 1,119,336 France Y. Apr. 3, 1956

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