US2173541A - Compound engine - Google Patents

Description

Sept. 19, 1939. w. mean m m.

GOIPOUND ENGINE Fig.

m enf Se t. 19, 1939. w. RIEGER El AL COIPOUND ENGINE Filed lay 13, 1937 2 Shuts-Shani 2 Pei 04 0,7066 M61? Mlvura Fig. 6.

Patented Sept. 19, 1939 UNITED STATES PATENT 1 OFFICE Application May 13, 1937, Serial No. 142,502 In Germany May 29, 1936 8 Claims.

This invention is directed to an improvement in compound engines of the reciprocating piston type.

It is an object of our invention to make a compound engine particularly suitable for marine work.

Another object of our invention is to form a compound engine operating economically and efficiently at loads ranging from 100 to 5000 horse power, and being readily controllable through such range.

A further object of our invention is to form a compound engine in which the steam is utilized over a substantial pressure drop so that a piston compound engine having a plurality of low pressure cylinders can obtain an efiiciency equal to or greater than that obtained by a piston engine with a low pressure turbine coupled therewith.

Still another object of our invention is to reduce the weight and size heretofore encountered in compound engines, and to construct the engine in such a manner as to eliminate substantially all vibrational effects therein.

A still? further object of our invention is to construct a compound engine having an irregular period of vibration so that the rotational forces of two or more adjoining engines will not act in rhythm or in synchronism to produce disagreeable or harmful effects upon their supporting structure, as for example upon a marine vessel.

Generally it is known to use plural expansions of steam in an engine by passing the steam through cylinders coupled either in tandem or in cross-compound relation to a drive shaft. In either of these arrangements the piston speed of the various sized pistons usually remains the same.

In the instant invention, two tandem engines are cross-compounded so that one tandem arrangement acts as the first steam pressure stage and the second tandem arrangement acts as the second steam pressure stage. As the steam pres,- sure drop between the two stages is great, the pistons of the second stage would, if the pistons of the two stages ran at the same speed, be so large as to cause critical radiation and mechanical losses, and besides would create a very bulky unit. These serious objections are avoided in our invention by causing the second stage to be operated at a higher speed than the first stage, and coupling the two stages together by power transmission means, preferably gears, proportioned to the relative speeds of the two stages.

To obtain this relationship between the two stages it is desirable that the proportion of the stroke volume per unit of time, in the first stage to the stroke volume of the second stage be at least 1: 30, that is, the volume through which the piston or pistons of the low pressure stage move (or the product of the length of the piston stroke, the area of the piston, and the number of strokes perunit of time) in a unit of time is at least 30 times the volume covered by the high pressure stage piston or pistons; while the volumes of the cylinders themselves arepreferably in a ratio ranging from 117.5 to 1:15. Thus, if the unit of time is taken as the time of one revolution of the crankshaft of the first stage, the steam volume in the first stage is equal to the volume of the first stage cylinder or cylinders, and the volume of steam in the second stage is correspondingly greater.

With the ratio of 1:30 between the stages, the sizes of the cylinders themselves are kept conveniently small by having the two stages operating at different speeds. With a gear ratio of 1:4 or 1:2 between the two stages the cylinder volumes would be in the ratio of 1:7.5 or 1:15, respectively.

Because of the elimination of radiation and mechanical losses, the steam can be exhausted from the low pressure stage at a pressure ofabout 0.2 atmosphere, with a thermodynamic efliciency equal to or greater than that obtained in an exhaust steam turbine.

The reduction in vibration is accomplished by means of the diiference in speeds in the two stages. Thus, by selecting the transmission ratio in the gears connectng the two stages, as a multiple digit or endless decimal fraction, the crankshafts of each stage will seldom or never assume the same relative positions. Consequently, a rhythm between the two shafts is prevented and harmful vibrations cannot be set up.

Further reduction in vibrational effects is obtained by mounting both stages on the same bed plate, and further by providing a common wall between the stages against which horizontal and torsional forces within the stages neutralize each other. If desirable, flywheels can be added to the crankshafts, but normally these are not necessary as other vibration dampening structure in the engine causes smooth operation without suffering the disadvantages of bulkiness and weight.

Single cylinders may be cross-compounded in this manner, but the invention also contemplates the cross-compounding of cylinders mounted in tandem. The steam used may be either saturated or superheated, and preferably a condenser Cal is used in order to obtain the low pressures with which the engine may be operated.

In order that our invention may be understood more fully, a description of an engine constructed according to the objects of our invention is given.

In the drawings:

Fig. l is a vertical sectional View of a four cylinder engine taken on the line II of Fig. 3;

Fig. 2 is a side elevational view of the engine, with the casing removed to show the connecting rods and crankshaft;

Fig. 3 is a horizontal sectional view of the en gine on the line III-III of Fig. 1; r

Fig. 4 is a plan view of a five cylinderv engine;

Fig. 5 is a diagram of the torque'forces between the crankshafts;

Fig. 5a is a continuation of the diagram shown in Fig. 5, and

Fig. 6 is a plan view of a plurality of-engines having different ratios between their respective crankshafts, each engine I being .attached to a propeller shaft of a vessel.

Similar reference characters designate similar parts in the various figures.

As shown in Figs. 1-3, the engine has a high pressure stage and a lower pressure stage, both mounted upon a base plate B.

Steam enters the high pressure stage through port A into valve cylinder h for the high pressure cylinder H. Piston P in cylinder H is connected to crankshaft l by means of a connecting rod.

Exhaust steam from cylinder H is passed by valve device h to intermediate pressure cylinder M mounted in tandem with cylinder H on shaft 1. Valve cylinder m regulates the steam supply to cylinder M. From the intermediate cylinder the steam is passed to a receiver R. from which it passes to the second intermediate cylinder M the piston of which is connected to the second,

or low pressure, stage crankshaft 2, the steam passing through the regulating valve cylinder m for M Cylinder N, the piston of which is also connected to shaft 2, receives exhaust steam from cylinder M through valve cylinder, 11.. From cylinder M the steam, passes to a condenser C.

Throttled fresh steam may be supplied to the second stage alone through the valve V.

A common wall 5 separates the connecting rods for the cylinders of the two stages. As seen in Fig. 1, slide guides 6 and I are mounted on opposite sides of said wall and are preferably mounted opposite each other. Crossheads 8 and 9 connect the connecting rods of the high and low pressure stages, respectively, to the slide guides. This construction is very compact, and

because the horizontal and inertia forces set up on each slidetend to neutralize the forces on the opposite slide, vibrations are damped. A smoothly operating engine, as thus obtained, is particularly advantageous in marine engines as substantially no vibration is transmitted to the body of the vessel.

All cranks on the crankshafts l and 2, respectively, are offset from each other by 70-90 Furthermore, the crankshaft I may have a flywheel F which further insures a smoothly operpressure cylinder will preferably be from 1:7.5 to 1:30, and the ratio of the stroke volumes per unit of time between the two stages from 1:30 to 1:60.

The gears 3 and 4 are set in a ratio ranging from 1:4 to 1:2. To prevent the cranks on the crankshafts l and 2 from functioning in phase, it is desirable that the ratio between the gears be chosen as a multiple digit or endless decimal value so that the cranks will seldom, if ever, operate in phase (note Fig. 5). By this means the creation of harmful oscillations or vibrations is precluded.

Although the specific valve structures have not been shown, it is understood that valves conventional in the art are employed, for example, of the type shown in the Mechanical Engineers Handbook by Marks, or in any other standard text. Likewise, it is noted that the valve controls in each stage may be independent of the other stage. Furthermore, one high pressure cylinder may be cross-compounded with a low pressure cylinder, rather than the tandem cylinders in the two stages illustrated.

As shown in Fig. 4, it is also possible to connect three or more cylinders in tandem on the low pressure stage, for example, the cylinders M N, and N shown. On this low pressure shaft the cranks are set at 120 with respect to each other, and thus substantially no vibrations are produced.

Fig. 4 further shows clutch couplings l and I2 mounted on shafts I and 2, through which either or both of the shafts may be connected or disconnected from the driven or propeller shaft. Obviously, this clutch construction may be applied to the engine of Fig. 1, if desired. With this connecting means, either stage may be disconnected for purposes of repair, or, for small loads, the first high pressure stage may be used alone.

Fig. 4 also illustrates another advantageous feature of our invention. Rather than have a single cylinder N of very large dimensions, it is possible to make each of the low pressure cylinders comparatively small as shown at N and N and to mount them in tandem on the shaft 2.

In such a construction the steam lines of the cylinders N, N, etc., are preferably connected in parallel as shown by the connection between the pipe 0 and the pipe p.

Fig. is a tangential force diagram wherein the line a designates the tangential forces on the shaft 2, the line b the tangential force on the high pressure shaft 1, and line 0 the summation of a and b. It is apparent from the figure that if the ratio between the gears 3 and 4 were sent to 1:2.1 that a continual displacing of the tangential forces produced will take place, and therefore an absence of a vibration producing rhythm is obtained.

Fig. 6 illustrates diagrammatically a ship Z having two or more compound engines constructed according to our invention. Each engine drives a propeller shaft S. Engine X has, however, a difierent gear ratio from engine Y. As indicated upon the drawings, for purposes of example, engine X has a gear ratio of 1:1.31 and engine Y a gear ratio of 1:133. This difference in ratios prevents the propeller shafts from rotating in rhythm and thereby causing periodically occurring vibrations, which, because of their magnitude, would produce a vibration in the vessel Z.

Having described a device illustrating and embodying the principles of our invention, we claim:

1. A cross-compound engine comprising a high pressure stage, a low pressure stage, and power transmission means connecting said stages, the stroke volumes per unit of time of said stages being in a ratio of at least 1:30 and said power transmission means having a ratio ranging substantially from 1:4 to 1:2 to maintain a proportional difierential in speed between said stages.

2. In a cross-compound engine as in claim 1, each of said stages comprising a plurality of cylinders, and pistons, a crankshaft for each stage, said cylinders being connected in tandem in each stage, and said power transmission means being mounted upon said crankshafts.

3. A cross-compound engine comprising a high pressure stage, a low pressure stage, power transmission means connecting said stages, the stroke volumes per unit of time of said stages being in a ratio ranging from approximately 1:30 to 1:60, and said power transmission means comprising gearing having a ratio ranging substantially from 1:4 to 1:2.

4. A cross-compound engine comprising a high pressure cylinder, a low pressure cylinder, a crankshaft for each cylinder, connecting rods for each cylinder, a wall between said cylinders, slide guides mounted on opposite sides of said wall, crosshead means joined to each connecting rod, said crosshead means engaging said slide guides.

5. In a cross-compound engine comprising a high pressure cylinder and a low pressure cy1inder, a crankshaft for each cylinder, a gear for each shaft, each of said gears engaging the other, the ratio of said gears being such as to preclude a periodically occurring similar angular displacement between said crankshafts.

6. In a cross-compound engine as in claim 5, a piston in each cylinder, a crank on each shaft, and connecting rods connected to the pistons and cranks, each crank being angularly displaced with respect to the other.

7. In a cross-compound engine as in claim 5, a piston in each cylinder, a crank on each shaft, connecting rods connected to the pistons and cranks, a wall between the cylinders, slide guides mounted on opposite sides of said wall, and slidable means joining said connecting rods and said slide guides.

8. A cross-compound engine comprising a low speed high pressure stage, a high speed low pressure stage, a crankshaft for each stage, a plurality of cylinders mounted in tandem with varying crank angles on said high pressure stage, a plurality of cylinders mounted in tandem with varying crank angles on said low pressure stage, connecting rods for said cylinders slidably secured to a wall between said stages, and a gear for each of said crankshafts, said gears engaging each other and being in a ratio to vary continually the angular relationship of the cranks of one stage to the cranks of the other stage.

WILLY RIEGER. OTTO H. HARTMANN.

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