US2104802A - Pneumatic differential piston for internal combustion engines - Google Patents

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Jan. 11, 1938. E. H. HANSEN PNEUMATIC DIFFERENTIAL PISTON FOR INTERNAL COMBUSTION ENGINES Filed March 15, 1935 2 Sheets-Sheet 1 INVENTOR.

Jan. 11, 1938. E. H. HANSEN 2,104,802

PNEUMATIC DIFFERENTIAL PISTON FOR INTERNAL COMBUSTION ENGINES Filed March 15, 1935 2 Sheets-Sheet 2 I /2' \i I i M 4-il ii 27 ii i:

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FIG. 5

INVENTOR.

Patented 'Jan. 11, 1938 UNITED STATES;

PATENT orrlca PNEUMATIC DIFFERENTIAL PISTON FOR INTERNAL COMBUSTION ENGINES This invention relates to pistons for internalcombustion engines of the four and six strokecycle type, and in particular, relates to a piston, a dash-pot device, a cross-head and a connecting '5 rod, which, operating together, serve to produce strokes of variable length.

Briefly described, the invention consists of a piston having a piston-rod cast integral therewith, with a pneumatic double-acting piston at the rods other extremity. Said piston, piston rod and pneumatic piston have no mechanical or fixed attachment to the cross-head, connection being had through pneumatic means alone. The pneumatic piston reciprocates within a pneumatic cylinder which is a part of the cross-head, said cross-head being constrained to move within the engine cylinder by guides. The cross-head is journaled to the connecting-rod by means described hereinafter and shown in the drawings.

The purpose of this piston, known as the pneumatic differential piston, is to enable a more complete expansion of the initial charge, down to atmospheric pressure if desired. As is well known, the most serious deficiency in internal combustion engines to date is the lack of sufficient expansion. This results in a number of undesirable effects, among which are, wasted energy through the exhaust; back pressure through the exhaust amounting to approximately 5% of the net output; excessively high exhaust temperatures resulting in overheating and burned valves; noisy operation requiring elaborate muiiling devices, and, not the least important is the incomplete combustion of the fuel, resulting in carbon de- 5 posits and air pollution. These effects can largely be overcome by more complete expansion and a very large saving in fuel can thus be accomplished.

Up to the present time engine manufacturers, experimenting with engines using greatly increased expansion of the initial charge, have found that the theoretical gains in output and economy have been more than offset by the increase in friction losses. This being the main point to overcome in a practical manner, I will outline a means for overcoming same with a theoretical engine, having the pneumatic differential piston.

Assuming a conventional four stroke cycle englue, in which all four strokes 'per cycle are of equal length, (hereinafter called engine #1) drawing in a given volume of fuel at each suction stroke and developing a given horsepower at a given number of R. P. M. f Then assume a second four stroke cycle engine (hereinafter called engine #2) having the pneu matic differential piston. with an arbitrary cylinder area of, say, twice the cylinder area of engine #1, and drawing in the same volume of fuel at each suction stroke as engine #1. Both engines have the same ratio of compression. It will then be seen that the intake or suction stroke of engine #2 will be one-half the length of stroke in engine #1. Then, since the pneumatic differential piston makes short suction and compression strokes and long expansion and exhaust strokes, the burned gases in engine #2 are expanded to approximately twice the volume of the admitted charge. Since the expanding gases in engine #2 act upon a piston having twice the area of the piston in engine #1, the horsepower developed per cycle in engine #2 will be considerably greater than that developed in engine #1. Then, in order that engine #2 develop a horsepower output equal to that of #1, the R. P. M. of #2 will be proportionately less than that of engine #1 to achieve that result. In anycase engine #2 will operate with greater economy and less friction per horsepower produced than engine #1.

It will be found that the piston rings (the point of greatest friction in the cylinder) of engine #2 pass over but 12% greater area per cycle than the rings of #1 per cycle without, however, being subject to side-thrust.

This is due to the fact that the cylinder area traversed in engine #2 by a stroke equal in length to the stroke of engine #1 would be approximately 1.4 times the area traversed per stroke in #1. The suction and compression strokes of #2, being one-half the length of stroke in #1 .will traverse an area approximately 0.! times that traversed during those strokes in #1. The expansion and exhaust strokes in #2, being slightly longer than the corresponding strokes in #1, will traverse an area approximately 1.54 times that traversed during those strokes in #1, thus leaving a net traversed area per cyclein engine #2 of approximately 1.12 times that traversed in engine #1. The cross-head guides of #2, although comprised of arcuate segments, also pass over a larger area per cycle than theskirt in #1, but there is opportunity for more eflicient lubrication in #2, which therefore, has less friction. In both engines an equal quantity of fuel mixture is compressed but in engine #2 compression does not start until the piston has passed more than half way up in the full stroke of the cross-head and the angularity of the connecting rod is diminishing, therefore, friction in the cylinder and other related engine friction during compression is less in #2 than in #1. In consideration of all this and-other hereinafter mentioned sources of friction economy the total friction loss per cycle of engines #1 and #2 should very nearly balance, either way. Since the expansion in engine #2 is carried farther than that in engine #1, the M. I. P. of #2 will be the lesser, but, since for an equal horsepower output engine #2 operates with less friction and exhausts against a lesser back pres-- application of the pneumatic differential piston,

due to the assumed greatly increased cylinder area and assumed greatly reduced speed making necessary a much larger engine than one to be had by a more moderate design. Such a moderated design would achieve approximately proportionate results to the above by using a more moderate increase in cylinder area, a more moderate decrease in R. P. M. and a reduction in fuel consumption per cycle in comparison to the conventional engine.

For most efilcient operation, the force of the expanding charge should be delivered through the pistonto the connecting-rod, in a direct line, axially of the piston and with a minimum of frictional resistance by all parts. This is accomplished by my invention. The piston and piston rings are not subjected to side thrust at any time, and the piston is free to rotate naturally within the cylinder, thus allowing for self-ad- Justment to any irregularities of the cylinder walls and promoting equal wear.

The working piston, piston rod and pneumatic piston are of aluminum alloy, the cross-head and guides preferably of steel, although any other suitable metals may be employed. The crosshead guides are provided with a plurality of peripheral oil-grooves on their bearing surfaces and may be machined to very close limits of cylinder clearance since they are separated from direct contact with the piston. The guides, as willbeseemareformedinpairsasaletterfl, each pair receiving thrust at alternate strokes. By transmitting the thrust through the struts, each at an angle, an equal projected bearing area may be had with less material and weight than can be had with the usual type of trunk piston skirt, and a better distribution of wear of the cylinder walls is obtained.

Recommended embodiments of my invention are illustrated in-the accompanying drawings, in which Figure lisaverticalsectionofthepistonassembly.

Figure 2 is a transverse section of the crosshead pneumatic cylinder at A-A without the connecting rod being shown.

Figure 3 is a fragmentary view of the crosshead.

Figure 4 is a diagrammatic view of the relative position of the piston during the suction stroke, at the time of opening the fuel inlet valve.

Figure 5 is a plan view of the packingspring Mel.

Referring to the drawings:

l'igure i. The working piston i is provided with a plurality of peripheral grooves ii for the reception of piston rings (not shown) and a pinrality of reinforcing ribs II, the contour of the face being optional according to the engine desisn. 'lhepiston-rodliscastintegral withthe piston I and has secured to its other extremity by screw a pneumatic double-acting piston 8 locked in place by a cotter 28, and provided with a plurality of grooves I! for the reception of piston rings. The piston-rod also has a spring ball release valve 14 fitted within the rods extremity and connecting with drilled passage 2|, said passage ll leading to a plurality of ducts 20.

The cross-head I is provided with guides s and struts ll cast integral. The guides e have a plurality of. peripheral oil grooves I for the maintenance of proper lubrication. The crosshead I is further provided with a pneumatic cylinder I cast integral. The cylinder 4 is fitted near its lower end with an automatic ball intake valve I 8, said valve ll being provided with a suggested means for lubrication consisting of an oil duct is. and an oil reservoir ll supplied by the splash system. At the upper end of the cylinder 4 there is a packing cap l2, packing spring washer II and metallic packing It. The spring washer H has radially cut slots extending from its inner circumference half-way to the outer circumference and exerts a pressure upward against the packing II. The packing cap I! is secured asshown by screw threads.

Theconnecting rod I has bushings II in its forked ends and is articulated with the crossmisemxpandrtl and contract at will on 0 any other part, a

fault common tcanmInpistonsmlusinglmwriste pins held at a r sec to piston distortion. m due in use, the piston operates as follows:

Atthe start of the in or suction stroke, withtheplston I andthecross-headlincloee proximity (as shown in igure l) at top dead center, the fuel inlet valve ll will remain closed and the exhaust valve II will be closing. The cross-head I will then descend, but since both valves 21 and II are closed, a decrease in pressure will result in the compression space, due to the piston 3, cease its descent. with the cross-head in motion downward the entrapped air within the air chamber 8| will be compressed, imparting a smoooth silent and increasing eii'ect to the movement of the pistons i and I. when the piston 3 passes the inlet port from valve ii the vacuum will be broken and air chamber will fill with air, said air drawing in lubricating oil from reservoir ll. When the cross-head 5 has descended to the relative position as shown in Figure 4, with an arbitrary air pressurein chamber It, the fuel inlet valve 21 will'then open, admitting the fuel mixture. Piston i will then descend in the usual manner drawing in a charge of fuel mixture. It willbeseenthatduetothedesignofthepackingcapi2andwasher|l,thepacking II will afiu'datightfitaboutthepistonrodl during the compression stroke of the piston 3 in the chamber 30, but will not bind on the return stroke. The length of stroke made by the piston 3 within the cylinder 4 is determined by the desired ratio of expansion.

During the following compression stroke the piston i will remain virtually idle while the crosshead 5 ascends, compressing the air within chamber 29 until a sufiicient pressure has developed to open the release valve 24. This pressure does not require any additional work on the part of the engine since it is but the resultant of the compression pressures within the engine cylinder, and the escaping air will have a cooling effect on the piston rod 2. The cross-head 5 is brought into easy, silent contact with piston 3 and the entire assembly then proceeds, with the piston face 3' in close proximity to the cross-head 5, to the end of the compression stroke. Any loss of air in chamber 30 is then replaced through inlet valve l5, which again carries lubricating oil. The expansion or power stroke and the following exhaust stroke are carried out in the usual manner, with the piston l descending the full stroke with the cross-head 5. Upon completing the exhaust stroke, the piston i is restrained from leaving the cross-head 5 (due to its inertia) by the aforesaid vacuum, or suction developed between piston 3 and the bottom of the cylinder 4 integral with the cross-head 5. Said vacuum is aided by the resistance of the exhaust gases. If there should be a slight movement by the piston I into the compression space, it would be but momentary and would aid the scavenging process.

. engine, of a working piston, and a second reciprocatory member, a dash-pot device comprising a pneumatic cylinder, a piston rod extending through one end of the cylinder and connected at one end to the working piston and at the other end to a double-acting piston adapted to reciprocate in said cylinder, and cooling means for said rod comprising a relief valve suitably disposed at one end of the piston rod.

2. The combination, in an internal combustion engine, 01' a working piston, and a second reciprocatory member, a dash-pot device comprising a cylinder, a piston rod extending through one end of the cylinder and connected at one end to the working piston and at the other end to a double-acting piston adapted to reciprocate in said cylinder, and single means for the admission of air to either side of the double-acting piston whereby said piston is under restraint of compressed air during strokes in both directions, and means for the release of air from said cylinder.

EINAR H. HANSEN.

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