US3601989A

US3601989A - Marine propulsion system

Info

Publication number: US3601989A
Application number: US854236A
Authority: US
Inventors: Kenneth A Austin
Original assignee: Avco Corp
Current assignee: Avco Corp
Priority date: 1969-08-29
Filing date: 1969-08-29
Publication date: 1971-08-31
Anticipated expiration: 1988-08-31

Abstract

A marine propulsion system including a multistage, ducted pump creating a jet of propelling water is driven from conventional power plants one being a relatively low horsepower Diesel; the other a high output gas turbine. The former is connected to a single, large diameter first pump stage; the latter to both the single large diameter stage and the second smaller diameter stage, whereby the second state is operated at a higher rotational speed. Suitable clutch means, preferably over running clutches provide for smooth transition from the Diesel to turbine power mode and vice versa.

Description

United States Patent Inventor Kenneth A. Austin Hove, England Appl. No. 854,236

Filed Aug. 29, 1969 Patented Aug. 31, 19711 Assignee Avco Corporation Stratford, Conn.

MARINE PROPULSION SYSTEM 9 Claims, 3 Drawing Figs.

[1.8. Ci 60/221, 74/661,115/11,415/61,417/2,4l7/16,417/247 Int. Cl ..B63h 23/10, B63h 21/28 Field of Search 417/2, 16,

[56] References Cited UNITED STATES PATENTS 2,223,592 12/1940 Bartonetal. 415/61 3,153,907 10/1964 Griffith 60/39.15

Primary Examiner-Mark M. Newman Assistant Examiner-Warren Olsen Attorneyr-Charles M. Hogan and Irwin P. Garfinkel ABSTRACT: A marine propulsion system including a multistage, ducted pump creating a jet of propelling water is driven from conventional power plants one being a relatively low horsepower Diesel; the other a high output gas turbine. The former is connected to a single, large diameter first pump stage; the latter to both the single large diameter stage and the second smaller diameter stage, whereby the second state is operated at a higher rotational speed. Suitable clutch means, preferably over running clutches provide for smooth transition from the Diesel to turbine power mode and vice versa.

MARINE PROPULSION SYSTEM This invention is concerned with marine propulsion systems of the general type including a water jet, as distinguished from conventional propellors, as a means for propelling waterborne craft.

Reference to U.S. Pat. No. 3,328,961 will illustrate the basic fundamentals of a propulsion system having the requisite capabilities of providing jet propulsion of water sustained craft and wherein there is provided a housing defining a propulsion duct which houses a craft driving, multistage pump or turbine in such fashion that both the stages, in this case two, are driven from a common power source at different rotational speeds. In addition the turbine stages differ in diametric dimension, the second or following stage being smaller than the first stage and driven at higher rotational velocities than the first stage. Control of the discharge through the duct is afiected by a reverse scoop or diverter and steering vanes direct to the energized fluid so as to provide for turning and reversal of the craft to which the system is applied, reference again being made to aforesaid US. Pat. No. 3,328,961 and additionally earlier issued, to US. Pat. No. 3,251,185.

While the described system is highly effective to provide high speeds for watercraft as, for example, for use in patrol craft adapted for military, police or other purposes, this result is not accomplished without some sacrifices, most notable of which is inefficient low speed operation, speed as measured in terms of velocity per unit fuel consumed per ton mile. This adverse, yet inherently present result, is generated because the various parameters such as power plant capability, mass flow rate, nozzle exit velocity, system weight, inlet suction head and pump design among others, are all considered and carefully coordinated by calculation to satisfy one basic end result, namely, maximum speed for given load and available power, irrespective of any other consideration.

The present invention, then, while recognizing the result desired in respect of maximum craft velocity with respect to available power, also overcomes the disadvantages mentioned above by permitting efficient operation of the propulsion system at low craft speeds, adequate maneuverability at virtually all velocities, and, at the same time, satisfies the requirement of optimum performance in terms of maximum design velocity of the craft in which installed.

By way of illustration and explanation of a manner of prac ticing the invention, reference is made to the drawing wherein FIG. 1 is a partial, sectional, elevational view through the stern of watercraft to which the present invention is applied.

FIG. 2 is a graphic plot illustrating the thrust requirements at speed; speed and thrust being expressed in percent of design maximum and maximum available power, respectively, while FIG. 3 is a graphical plot of propulsive efficiency versus velocity ratio, the former expressed in percent, the latter being the ratio of velocity energy imported to the jet AV over boat speed Vk.

Turning first to FIG. 1, it will be seen that the aft section of a waterborne craft is shown in phantom line 20. Transom 21 is designed to provide for emergence of the exit nozzle 22 of a duct having its entrance mouth 24 disposed downwardly and opening through thebottom of the craft. Transom 21 also is provided with reverse scoop 23 operated by operator 25. Maneuvering of the craft is affected by operation of the reverse scoop and additional steering vanes 23, the system in general being the subject of previously issued patents.

In accordance with known practice, the mouth 24 of duct 30 is quite large in area as compared with the exit nozzle 22; the duct 10 tapering gradually between these openings.

Disposed within the duct 10 and intermediate of its open ends is a turbine type pump 30. The pump 30 is of multistage design having a small diameter, bladed rotor 26 disposed toward the exit nozzle 22 and a larger diameter, bladed rotor 28 disposed ahead of rotor 26. Suitable stator blades 32, to im port some control over the liquid vortex created by rotor 28 may be interposed between the two rotors.

As also shown in the drawing, a suitable power transmission 40 including a housing 42 is provided within the hull of of the craft 20. This transmission 40 is located outside of the duct 30 but is connected to the turbine or pump stages by a pair of

concentric shafts

34 and 36, which pass through the wall of duct 30. Suitable seal means, conventional in the art, are provided between the duct 10 and transmission housing 42 to prevent passage of water from the duct into the housing 42 and lubricating oil or grease from the housing to the duct and vice versa.

As previously stated

shafts

34 and 36 are concentric; one being carried within the other on suitable bearings whereby pump rotor 26 is driven by shaft 36 and pump rotor 28 is carried on and driven by shaft 34 completely independently of rotor 26 and shaft 36. The mechanical details of bearing and seal location and design are also purely conventional and need not be discussed in detail.

As shown in FIG. 1, the transmission end of shaft 36 extends through transmission housing 42 and is connected to a prime mover 50 (only partially shown) through a conventional clutch 44. The clutch 44 simply provides for operation of the prime mover 50 without load, as when being started, or when it is desired to operate the prime mover without driving the craft for such other reasons as are readily apparent to one familiar with operation of any waterborne craft.

In driven engagement with shaft 36 through the medium of an overrunning clutch assembly 48, is a gear 46. Gear 46 is, in turn, in meshing and driving engagement with a driven gear 52 keyed on and supported by a countershaft 54.

Counter shaft 54 is supported by the housing 42, the

usual journals

56 and 58 being provided for this purpose as is shown in the drawings.

Also keyed onto and driven by countershaft 54 is a gear 62. Gear 62 is shown as supported on shaft 54 approximately midway of the ends of the shaft. Gear'62 is also in meshed, driving engagement with a rotor drive gear 64 which is keyed on or, perhaps may form, the terminal end of drive shaft 34.

With the described arrangement then, power developed by prime mover 50 will be transmitted, through clutch 44, gear 46, overrunning clutch 48, gear 52, gear 62 to turbine rotor shaft 34. Power is also transmitted through clutch 44 directly to rotor shaft 36 to the record stage rotor 26 of the propulsion pump 30. It should be noted that,'as of particular importance, the gear ratio established through the gear chain to rotor 26 is such that the relative difference in rotational speed between

turbine rotors

26 and 28 to produce the desired propulsion energy is maintained. In other words, rotor 26 will be driven at a higher rate of speed than rotor 28 when prime mover 50 is operating.

Further consideration of the drawing will show a second prime mover also operatively connected to transmission 40. This prime mover, (only a portion thereof being shown), is mounted in the hull 211 of craft at a slight angle downwardly from the stern and is coupled to transmission 40 through a conventional marine forward and reverse transmission, not shown, via a conventional drive shaft 66 having thereon the usual

flexible couplings

68, 72 to allow for slight misalignment between prime mover and transmission, if same occurs. Shaft 66 is connected to a transmission shaft 74 which is journaled in the transmission housing 42 by any suitable and usual antifriction bearing means 76, 76'. Shaft 66 is also disposed at an angle with respect to countershaft 54, but: is mechanically coupled thereto by a pair of frustoconical shaped gears 78, 82 and an additional overrunning clutch 84 disposed between gear 78 and shaft 74. Gear 82 is, however, keyed on countershaft 54 such that any rotational effort through overrunning clutch 84 will be transmitted to this shaft and hence through

gears

62 and 64 to pump shaft 34 thus turning the first stage impeller 28 of pump 30.

Before explaining the operation of the invention it is believed essential to note that both overrunning clutches are of available commercial types and in and of themselves are completely standard items such as might be manufactured by various organizations such as, for example, Borg Warner Corporation of Chicago, Ill.

In respect of the

prime movers

50 and 70 it should also be noted that while many variations are possible, the inventive concept is best accomplished where prime mover 70 is a lightweight, high efficiency Diesel engine such as, for example, a model GM-4-53 Diesel of approximately 140 hp. sold by General Motors Corporation, Detroit, Mich., for marine propulsion and various other applications.

Prime mover 50 is preferably a high output, lightweight, gas turbine capable of developing approximately 1500 hp., an example of which is that available from Lycoming Division of Avco Corporation, Stratford Stratford, and identified as a Lycoming T F Turbine.

The combination of power plant types represents an advantageous arrangement in practicing the invention since, as is well known, gas turbines, while possessed of extremely high power capabilities per unit weight have also a rather high consumption of fuel when operated at low power. On the other hand, Diesel engines are well known for efficient fuel consumption per horsepower output, but suffer from the disadvantages of rapidly increasing size and weight per unit horsepower developed as power capabilities are increased. As will be apparent the capabilities of these diverse types of power plants or prime movers are thus matched to the capabilities of the jet pump propulsion system.

Turning now to FIGS. 2 and 3, it may be seen that for a given hull design, it is anticipated that most routine operations will occur at less than 30 percent of maximum design speed. Within this area of operation the thrust required to propel the craft will be approximately 20 percent of the total available thrust from the propulsion system. Since it is economically unsound to operate a gas turbine under such conditions the turbine is shut down and power is derived from the Diesel engine driving through shaft 66, etc., overrunning clutch 84 gears 78, 82, shaft 54 gears 62, 64 to the first stage pump rotor 28. Because of the presence of overrunning clutch 48 between gear 46 and shaft 36, this gear simply idles on the shaft 36 and with clutch 44 disengaged the turbine may be shut down.

As is evident, however, from an inspection of FIG. 3, thrust requirements increase rapidly as craft speed is increased, so

that, at about 20 percent of design speed the Diesel would be operating at maximum capability.

At this point, or, for example, when it is known that maximum speed will be desired, the turbine may be started and clutch 44 engaged. Thus the second stage or rotor 26 of the jet propulsion pump 30 in energized. Also as the power output from the turbine is increased, it will bring the rotational speed of shaft 36 up to a point where overrunning clutch 48 will engage so that power is transmitted via gear 46 and gear 52 to shaft 54 with the result that both stages of pump 30 are driven from the turbine since overrunning clutch 84 will automatically disengage the Diesel engine from the power train. At this point the Diesel is simply shut down or left in idle standby, as may be desired.

It will now be apparent that with full turbine power available the full capabilities of the craft may be attained in respect of 100 percent of design maximum speed. It might be noted that the dip in the speed vs. thrust serve plotted in FIG. 2 represents the point where the craft begins to plane, i.e., the design of the hull is such that at about 65 percent design speed a transition point is reached where the hull no longer acts as a pure displacement hull but rather becomes a planning hull to enable high speed of the craft with almost constant thrust up to about 70 percent-75 percent of design maximum. Above 70 percent-75 percent of design speed the thrust requirements again become almost a one-to-one ratio and, as plotted, the speed-thrust curve reflects this relationship.

The advantages of a two engine propulsion system having been established, attention is now invited to FIG. 3 in connection with operation of pump 30 as a single or multiple stage device. In FIG. 3, propulsive efficiency is plotted against velocity ratio VR which is the ratio of jet velocity VJ-boat speed VK to boat speed VK for a series of loss coefficients per given pump design, inlet area, etc. In all cases the propulsive efficiency of the pump bears direct relation to the jet velocity ratio VR, such that as VR increases, optimum design points occur at higher loss coefiicient values and propulsive efficiency decreases. Thus, having in mind that thrust is a product of mass flow through the pump times jet velocity VJ, it may be deduced that the higher the mass flow through the pump and the lower is jet velocity VJ the greater is propulsive efficiency. Thus, a slow speed, large diameter pump stage is more efficient and adequate for low speed operation than a smaller faster turning pump stage. Thus during low speed operation the coupling of a highly efficient, low horsepower Diesel is adequate to provide the required low speed thrust.

As power requirements increase because of demand for higher boat velocity VK, it should be apparent that the fixed parameters of duct size, rotor size, etc., place limitations on the mass flow through the system with the result that higher jet velocity V] must be developed irrespective of loss in propulsive efficiency as distinguished from total thrust developed. Even this expedient is subject to limitations because, as explained in the before mentioned U.S. Pat. No. 3,328,961, a condition of pump cavitation develops, which condition is intolerable due to its adverse effects on pump power unit and propulsive thrust. If, however, the second stage rotor 26 of pump 30 is started and the ratio of its speed to that of the first stage rotor maintained higher than one-to-one, having in mind its smaller diameter, the problems attendant to high speed operation of a single stage may be avoided and extremely high jet velocities obtained, this being accompanied by increased craft speeds.

Much, if not all of the material relating to the effectiveness of a two stage jet propulsion system is to be found in said U.S. Pat. No. 3,328,961 but is discussed herein, by way of explanation of the fundamental principles underlying the inventive concept herein disclosed. Further it is believed that a complete understanding of the principles of the propulsive system, per se, enables a more complete understanding of the advantages of the use of dual power plants of distinct modes of power generation.

Having described the invention in full and complete terms, it will be apparent that various modifications will be practiced by those skilled in the art. Such changes and modifications are, however, to be considered within the spirit and scope of the concept herein described, which is limited only as defined in the appended claims, wherein, I claim:

1. In a marine propulsion system including a tapered duct having a large entrance port and pump means contained therein, said pump means including at least two turbine-type stages, one behind the other, and driven at different rotational speeds, the improvement comprising drive means for said pump means, said drive means including two prime movers, one of which is operable to drive a single stage of said pump means, the other of which is operable to drive all stages of said pump means and means between said prime movers and said pump means whereby only one stage of said pump means may be driven for one mode of operation and whereby both stages of said pump means may be driven for a second mode of operation.

2. The improved marine propulsion system of claim I wherein said means between the prime movers and said pump means is a gear drive having clutch means therein for selectively disengaging one stage of said pump means from the prime movers.

3. The marine propulsion system of claim 1, wherein one of said prime movers is a conventional Diesel engine and the other of said prime mover is a gas turbine, the latter being operatively connected to both pump stages; the former being drivingly connected to only a single pump stage.

4. The marine propulsion system of claim 1 wherein the operative connection of said prime mover to all of said pump stages include overrunning clutch acting to automatically engage or disengage said prime mover from its driving connection to one of the pump stages.

5. The marine propulsion system of claim ll wherein said leading pump stage is of larger diameter than said trailing pump stage and is operated at all times during propulsion of a vehicle in which the system is installed and said trailing pump stage is operated selectively at a rotational speed greater than that of said leading pump stage to provide greater propulsive effort when desired.

6. A marine propulsion system including a tapered open ended duct having a turbine type multistage pump therein, one stage of which is of larger diameter than any succeeding stage; a pair of prime movers; means operatively connecting said prime movers to said pump for operation of the pump stages in accordance with a given set of conditions, said means comprising a gear case; a pair of coaxial driven shafts carried thereby, each shaft driving a single pump stage, one of said shafts driving said larger of said pump stages and being operatively connected to both prime movers, the other of said shafts being connected to only one of said prime movers, said operative connection between said one of said shafts and both of said prime movers including clutches whereby power to said shaft may be obtained from either one of said prime movers selectively.

7. A marine propulsion system as defined in claim 6 wherein said clutches are automatically engaged when the power output of either of said prime movers exceeds that of the other of said prime movers and vice versa.

8. A marine propulsion system as defined in claim 7 wherein the prime mover driving both of said pump stages is a gas turbine and the prime mover driving only said large diameter stage is a Diesel engine.

9. A marine propulsion system as defined in claim 7 wherein said gear case includes further a countershaft mounted therein, said countershaft carrying gear means thereon, a first of said gear means being keyed thereon and driven by one of said movers, a second gear means keyed thereon and driving said turbine driving shaft; a third gear keyed thereon and driven by said second prime mover, the driving engagement of each prime mover to said first and third gear means including overrunning clutches.

Claims

2. The improved marine propulsion system of claim 1 wherein said means between the prime movers and said pump means is a gear drive having clutch means therein for selectively disengaging one stage of said pump means from the prime movers.

5. The marine propulsion system of claim 1 wherein said leading pump stage is of larger diameter than said trailing pump stage and is operated at all times during propulsion of a vehicle in which the system is installed and said trailing pump stage is operated selectively at a rotational speed greater than that of said leading pump stage to provide greater propulsive effort when desired.