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Title:
PROPULSION SYSTEM FOR A MARINE VESSEL
Document Type and Number:
WIPO Patent Application WO/2020/119945
Kind Code:
A1
Abstract:
A propulsion system (10) for a marine vessel (100) is provided. The propulsion system (10) is easy to service, as respective components of the same, i.e. an electric motor (26), a thrust bearing (30) and a fluid distribution unit (40), are provided separately and connected to each other by a plurality of couplings (32, 34). Hydraulic fluid is supplied to a propeller (24) via hydraulic conduits formed in shafts (28, 36) of the electric motor (26) and the thrust bearing (30). The propulsion system (10) can be used for marine vessels (100) of different sizes and in applications ranging from light to heavy and extreme duty applications by selecting appropriate components such as an appropriate thrust bearing (30).

Inventors:
HANSSON MATTIAS (SE)
Application Number:
EP2019/025451
Publication Date:
June 18, 2020
Filing Date:
December 10, 2019
Export Citation:
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Assignee:
CATERPILLAR PROPULSION PRODUCTION AB (SE)
International Classes:
B63H23/24; B63H3/08; B63H21/17
Foreign References:
US20050106953A12005-05-19
US2754923A1956-07-17
US9919780B22018-03-20
Attorney, Agent or Firm:
BRP RENAUD UND PARTNER MBB (DE)
Download PDF:
Claims:
Claims

1. A propulsion system (10) for a marine vessel (100), comprising:

a controllable pitch propeller (24);

a propeller shaft (22) connected to the controllable pitch propeller

(24);

an electric motor (26) including a motor shaft (28) drivably connected to the propeller shaft (22) via at least a first coupling (32);

a thrust bearing (30) provided separately from the electric motor (26), the thrust bearing (30) including a support portion (38) and a hollow shaft portion (36) rotatably supported by the support portion (38), the hollow shaft portion (36) being coupled to the motor shaft (28) via a second coupling (34); and a fluid distribution unit (40) fluidly connected to the hollow shaft portion (36) and configured to provide a flow of hydraulic fluid to the controllable pitch propeller via the hollow shaft portion (36), the motor shaft (28) and the propeller shaft (22).

2. The propulsion system of claim 1, wherein the propeller shaft (22), the motor shaft (28) and the hollow shaft portion (36) are arranged in an in-line configuration along an axial direction (L).

3. The propulsion system of claim 1 or 2, wherein the propeller shaft (22) and the hollow shaft portion (36) are coupled to the motor shaft (28) on opposite ends of the same via the first coupling (32) and the second coupling (34), respectively.

4. The propulsion system of claim 3, wherein the fluid distribution unit (40) includes a housing portion (54) detachably attached to the support portion (36) of the thrust bearing (30), and a rotatable portion (56) connected to the hollow shaft portion (36) of the thrust bearing (30).

5. The propulsion system of claim 1 or 2, wherein the hollow shaft portion (36) is connected between the propeller shaft (22) and the motor shaft (28) and coupled to the same via the first coupling (32) and the second coupling (34), respectively.

6. The propulsion system of claim 5, wherein the fluid distribution unit (40) includes a housing portion (54) detachably attached to a motor housing (58) of the electric motor (26), and a rotatable portion (56) connected to the motor shaft (28) of the electric motor (26).

7. The propulsion system of any one of claims 1 to 6, wherein at least one of the first coupling (32) and the second coupling (34) includes a flange to flange connection of the respective shafts and/or coupling members provided for the respective shafts.

8. The propulsion system of any one of claims 1 to 7, wherein at least one of the first coupling (32) and the second coupling (34) includes a sleeve coupling connecting open shaft ends of the respective shafts.

9. The propulsion system of any one of claims 1 to 8, wherein at least one of the first coupling (32) and the second coupling (34) includes a flexible element provided between the respective shafts.

10. The propulsion system of any one of claims 1 to 9, further comprising a disconnection device for disconnecting at least one of the first coupling (32) and the second coupling (34), in particular, to allow disconnection of the hollow shaft portion (36) from the motor shaft (28).

11. The propulsion system of any one of claims 1 to 10, wherein the electric motor (26) is a variable frequency electric motor, for example, a permanent magnet motor, with a rated power of between 100 and 40,000 kW, preferably between 2,000 and 6,000 kW.

12. The propulsion system of any one of claims 1 to 11, wherein the fluid distribution unit (40) includes a rotation sensor (60) configured to detect a rotation angle of the hollow shaft portion (36).

13. The propulsion system of any one of claims 1 to 12, further comprising:

at least one fin (12) mounted to a rear portion of a hull (14) of the vessel (100), the at least one fin (12) projecting downward from the hull (14), wherein the electric motor (26), the thrust bearing (30) and the fluid distribution unit (40) are arranged inside the at least one fin (12). 14. A marine vessel (100), comprising:

a main engine or main motor; and

the propulsion system (10) of any one of claims 1 to 13, wherein the main engine or main motor (20) is configured to supply electric power to the electric motor (26) to drive the same.

15. The marine vessel of claim 14, wherein the marine vessel (100) is an arctic vessel, for example, an arctic supply vessel or an ice breaker, or an offshore vessel, a research vessel, a cruise vessel, a ferry vessel, a military vessel or a fishing vessel.

Description:
Description

PROPULSION SYSTEM FOR A MARINE VESSEL

Technical Field

[01] The present disclosure relates to marine vessels, in particular, to a

5 propulsion system for a marine vessel.

Background

[02] A marine vessel such as, for example, an offshore support vessel generally includes one or more combustion engines driving one or more main propellers for propulsion of the vessel. The one or more main propellers are 10 mechanically coupled to the one or more engines, for example, via one or more drive shafts. The one or more engines rotate at a given speed, resulting in a corresponding rotation of the one or more main propellers. For example, the vessel may include a pair of diesel engines drivably coupled to a pair of main propellers. The diesel engines and the main propellers are generally operating at 15 constant speed.

[03] For transmitting a power output of the engines to the main

propellers, a gear box may be arranged between a propulsion shaft coupled to the engine and a propeller shaft coupled to an associated propeller. The gear box is configured as a speed change mechanism that changes the speed of the

20 propulsion shaft to a speed of the propeller shaft that is suitable for rotating the propeller.

[04] US 9,919,780 B2 discloses a propulsion system for vessels

including a permanent magnet motor having an outer housing structure. A motor shaft is connected to a propeller shaft including a propeller. A thrust bearing and 25 a propeller pitch control system are integrated into the permanent magnet motor. [05] The present disclosure is directed, at least in part, to improving or overcoming one or more aspects of prior systems.

Summary of the Disclosure

[06] In one aspect of the present disclosure, a propulsion system for a

5 marine vessel comprises a controllable pitch propeller, a propeller shaft

connected to the controllable pitch propeller, and an electric motor including a motor shaft drivably connected to the propeller shaft via at least a first coupling.

A thrust bearing is provided separately from the electric motor and includes a support portion and a hollow shaft portion rotatably supported by the support 10 portion. The hollow shaft portion is coupled to the motor shaft via a second

coupling. A fluid distribution unit is fluidly connected to the hollow shaft portion and configured to provide a flow of hydraulic fluid to the controllable pitch propeller via the hollow shaft portion, the motor shaft and the propeller shaft.

[07] In another aspect of the present disclosure, a marine vessel

15 comprises a main engine or main motor and the propulsion system in accordance with the above aspect. The main engine or main motor is configured to supply electric power to the electric motor of the propulsion system to drive the same.

[08] In yet another aspect of the present disclosure, a propulsion system for a marine vessel comprises a propeller, a propeller shaft connected to the 20 propeller, and an electric motor including a motor shaft drivably connected to the propeller shaft via at least a first coupling. A thrust bearing is provided separately from the electric motor and includes a support portion and a shaft portion rotatably supported by the support portion. The shaft portion is coupled to the motor shaft via a second coupling. The propeller may be a fixed pitch propeller. 25 The thrust bearing may be disposed forward or aft of the electric motor. The propulsion system may not include a gear unit. Accordingly, the electric motor may be directly coupled to the propeller shaft via the first coupling in case the thrust bearing is disposed forward of the electric motor, or the electric motor may be directly coupled to the propeller shaft via the second coupling, the thrust bearing and the first coupling in case the thrust bearing is disposed aft of the electric motor.

[09] Other features and aspects of this disclosure will be apparent from the following description and the accompanying drawings.

5 Brief Description of the Drawings

[10] The accompanying drawings, which are incorporated herein and constitute a part of the specification, illustrate exemplary embodiments of the disclosure and, together with the description, serve to explain the principles of the disclosure. In the drawings:

10 Fig. 1 shows a partial side sectional view of a marine vessel

including a propulsion system in accordance with the present disclosure; and

Fig. 2 shows an enlarged partial view of a thrust bearing in accordance with the present disclosure.

Detailed Description

[UK] The following is a detailed description of exemplary embodiments of the present disclosure. The exemplary embodiments described herein and illustrated in the drawings are intended to teach the principles of the present disclosure, enabling those of ordinary skill in the art to implement and use the present disclosure in many different environments and for many different 20 applications. Therefore, the exemplary embodiments are not intended to be, and should not be considered as, a limiting description of the scope of patent protection. Rather, the scope of patent protection shall be defined by the appended claims.

[12] The present disclosure may be based in part of the realization that,

25 in order to fulfil demands for, e.g., silent operation of a propulsion system of a marine vessel and reducing mechanical and energy convertion losses, it may be desirable to provide an electric motor for driving a main propeller of the vessel.

In particular, it has been realized that this can be achieved without providing a reduction gearbox system between the electric motor and a propeller shaft of the propeller.

[13] Further, it has been realized that an integration of, for example, a thrust bearing and/or a fluid distribution unit into the electric motor of the

5 propulsion system limits the application of the propulsion system to light duty and small vessels, as the integrated thrust bearing cannot receive loads associated with heavy duty and large vessels. In addition, it has been realized that an integrated system is needlessly complex and difficult to service and maintain.

[14] Accordingly, it has been realized that it is advantageous to

10 separate the individual components of the propulsion system, in particular, the electric motor, the hydraulic unit and the thrust bearing. This allows using the system in vessels of any size, for example, small to medium up to large scale vessels, and in applications ranging from light to heavy and extreme duty operation. In this manner, the propulsion system is easier to service and maintain,

15 and replacement of individual parts is much easier. In some cases, it may be

possible to replace parts of the system in the field, without interrupting the operation of the vessel.

[15] In addition, it has also been realized that the propulsion system disclosed herein can be retrofitted to marine vessels, for example, by providing

20 the propulsion system in a fin attached to a hull of the vessel. In some

applications, a plurality of propulsion systems and respective fins can be provided to achieve a desired output power.

[16] Further, it has been realized that the propulsion system is

especially advantageous when a controllable pitch propeller is used, as it is

25 possible to provide hydraulic lines for supplying hydraulic fluid to the

controllable pitch propeller inside the respective shafts of the propulsion system, which are appropriately coupled to each other to achieve a fluid connection between, for example, control chambers in a hub of the propeller and the fluid distribution unit, which may be disposed forward of the electric motor and the propeller shaft.

[17] In the following, an exemplary propulsion system for a marine vessel is described with respect to Figs. 1 and 2. Fig. 1 shows a partial side

5 sectional view of a marine vessel 100 having a propulsion system 10, and Fig. 2 shows an enlarged partial view of the propulsion system illustrating a thrust bearing in accordance with the present disclosure.

[18] As shown in Fig. 1, marine vessel 100, which may be an arctic vessel, for example, an arctic supply vessel, or a multi-purpose offshore vessel,

10 comprises a hull 14. Further, marine vessel 100 includes one or more main

engines or motors 20. Each main engine 20 may be an internal combustion engine configured to burn a supply of gaseous and/or liquid fuel to produce a mechanical output. For example, each main engine 20 may be a diesel engine, a gaseous fuel engine or a dual fuel engine configured to bum both gaseous fuel 15 and liquid fuel, for example, diesel oil. Alternatively, each main engine 20 may be configured as an electric motor powered by a generator. Each main engine 20 may be a variable speed engine that is configured to operate at varying speeds, or may be a constant speed engine configured to operate at a constant speed.

[19] An alternator (not shown) may be mechanically connected to main 20 engine 20. For example, an input of the alternator may be mechanically

connected to a flywheel (not shown) of engine 20. The alternator may be configured to receive a mechanical output from the associated engine 20 and convert the same to electrical power. The electrical power generated by the alternator may be provided to an electric motor 26 of a propulsion system 10 as 25 described below, and, optionally, an electric motor (not shown) associated with a front tunnel thruster provided at a bow of vessel 100, which may generate a water jet resulting in a steering force which facilitates maneuvering of vessel 100. Likewise, the electrical power generated by the alternator may be provided to an electric motor (not shown) associated with a rear tunnel thruster. In addition, electrical power output by the alternator may be supplied to one or more other electrical loads (not shown) of vessel 100. For example, the electrical loads may be heating systems, pumps, navigation and bridge systems or other auxiliary systems on vessel 100.

[2(5] As shown in Fig. 1, a fin 12 is formed in a rear portion of hull 14 and projects downward from hull 14. In some embodiments, fin 12 may be formed integrally with hull 14. In other embodiments, fin 12 may be a separate member fastened to hull 14 by appropriate fastening means, for example, by being bolted or welded to hull 14. It will be appreciated that a plurality of fins 12 10 may be provided, for example, two, three or four fins 12, if desired. In this case, each fin 12 accommodates a corresponding propulsion system 10. Likewise, it will also be appreciated that, in other embodiments, no fin 12 may be present, and propulsion system 10 may be provided in hull 14, or in another hull appendage, for example, a gondola or the like. Also in this case, a plurality of propulsion 15 systems 10 may be provided, if desired.

[21] It will be readily appreciated that each fin 12 may have any

appropriate shape that provides an inner space formed inside each fin 12 that can accommodate propulsion system 10 while providing extra buoyancy for vessel 100. Therefore, the present disclosure is not limited to the shape of fin 12 shown

20 in Fig. 1.

[22] As also shown in Fig. 1, propulsion system 10 of marine vessel 100 further includes a propeller 24, for example, a controllable pitch propeller, a propeller shaft 22 connected to controllable pitch propeller 24, an electric motor 26 including a motor shaft 28 drivably connected to propeller shaft 22 via a first

25 coupling 32, and a thrust bearing 30 provided separately from electric motor 26 and including a support portion 38 mounted to an appropriate mounting structure arranged inside fin 12 and a hollow shaft portion 36 rotatably supported by support portion 38. Hollow shaft portion 36 is coupled to motor shaft 28 via a second coupling 34. [23] In addition, a fluid distribution unit 40 is fluidly coupled to hollow shaft portion 36 of thrust bearing 30 and configured to provide a flow of hydraulic fluid, for example, hydraulic oil, to control the pitch of the blades of propeller 24 via hollow shaft portion 36, motor shaft 28 and propeller shaft 22.

[24] As shown in Fig. 1, in the exemplary propulsion system 10,

propeller shaft 22, motor shaft 28 and hollow shaft portion 36, i.e. thrust bearing 30, are arranged in sequence along an axial direction L in an in-line

configuration. In particular, in the example shown in Fig. 1, propeller shaft 22 and hollow shaft portion 36 are coupled to motor shaft 28 on opposite ends of

10 motor shaft 28. This means that, in the exemplary propulsion system 10, electric motor 26 is arranged between thrust bearing 30 and propeller shaft 28 and coupled to the same via the respective couplings 32, 34. Further, in the example, fluid distribution unit 40 is detachably mounted to thrust bearing 30 on the side that is opposite to the side where the connection to the motor shaft 28 via

15 coupling 34 is made.

[25] As shown in Fig. 2, fluid distribution unit 40 includes a housing portion 54 detachably attached to support portion 36 of thrust bearing 30, and a rotatable portion 56 connected to hollow shaft portion 36 of thrust bearing 30 to rotate together with the same. Fluid distribution unit 40 is configured to supply

20 hydraulic fluid to inner spaces (control chambers) provided in a propeller hub 46 (see Fig. 1) of propeller 24 to actuate corresponding actuators for changing the pitch angle of the blades of propeller 24 in a known manner. To this end, thrust bearing 30 includes hollow shaft portion 36 as a rotatable member coupled to motor shaft 28, which is also configured as a hollow shaft including a plurality of 25 inner bores or conduits (not shown) for transporting the hydraulic fluid. Likewise, propeller shaft 22 also includes a corresponding plurality of hydraulic conduits (inner bores) for supplying the hydraulic fluid received via motor shaft 28 to the inner spaces formed in propeller hub 46. The hydraulic fluid is received by fluid distribution unit 40 from one or more hydraulic pumps via corresponding conduits (not shown) and distributed to propeller hub 46. It will be appreciated that appropriate seals may be provided to obtain a fluid-tight connection between the respective conduits. Details of a corresponding fluid supply in order to adjust the pitch angle of the blades of propeller 24 are known to the skilled person and 5 will therefore not be described in detail.

[26] A rudder 48, which forms part of a steering system of vessel 100, is provided aft of propeller 24 and used to steer vessel 100 in a known manner.

[27] Propulsion system 10 further includes a protective guard 50

mounted forward of propeller 24, and an aft seal 44 provided forward of

10 protective guard 50. The rear part of propeller shaft 22 is radially supported by a stem tube assembly 42, and a forward seal 52 is arranged at the front end of stem tube assembly 42.

[28] Propulsion system 10 further comprises a shaft earthing device 18 and a break system 16 configured to break propeller shaft 22, if necessary. These

15 components and their functions are known, such that a detailed description

thereof will be omitted herein.

[29] As shown in Fig. 1, electric motor 26 includes a motor housing 58 supported on a corresponding mounting structure inside fin 12. Likewise, thrust bearing 30 is also mounted on a corresponding mounting structure inside fin 12

20 and radially supports the shaft system including propeller shaft 22, motor shaft 28 and hollow shaft portion 36 while, at the same time, receiving axial loads acting on said shaft system. Due to thrust bearing 30 being arranged separately from electric motor 26, any appropriate thrust bearing 30 can be used, depending on the application, with any given size or configuration, as long as hollow shaft

25 portion 36 is provided in order to supply hydraulic fluid to propeller 24. It will be appreciated that, in some embodiments, a conventional thrust bearing may be used and modified accordingly, for example, by providing an inner bore inside the same to form hollow shaft portion 36 or installing hollow shaft portion 36 in order to provide the respective hydraulic lines or conduits. A configuration of thrust bearings is known, and it will readily apparent to the skilled person how to modify a given thrust bearing, if necessary, in order to provide hollow shaft portion 36. Likewise, it will be also readily apparent to the skilled person how to attach, for example, a fluid distribution unit to support portion 38 of thrust 5 bearing 30 such that the rotatable portion 56 of the same can rotate with hollow shaft portion 36.

[30] At least one of first coupling 32 and second coupling 34 may

include a flange to flange connection of the respective shafts and/or coupling members provided for said shafts. For example, such a shaft to shaft coupling

10 could be provided between motor shaft 28 and hollow shaft portion 34. Of

course, it will be readily apparent to the skilled person that any appropriate coupling can be used for each of first coupling 32 and second coupling 34. For example, at least one of first coupling 32 and second coupling 34 may include a sleeve coupling connecting open shaft ends of the respective shafts. For example, 15 such a sleeve coupling may be used as coupling 32 between propeller shaft 22 and motor shaft 28. Corresponding couplings are well-known and will therefore not be described in detail herein. Likewise, it will be appreciated that at least one of first coupling 32 and second coupling 34 may include a flexible element or damping element provided between the respective shafts in order to reduce 20 vibrations and the like. In the same manner, one or more disconnection devices for disconnecting at least one of first coupling 32 and second coupling 34 may be provided. This facilitates disconnection of, for example, hollow shaft portion 36 from motor shaft 28, or disconnection of motor shaft 28 from propeller shaft 22. In this manner, the individual components of propulsion system 10 are easier to 25 service or repair, where necessary.

[31] Electric motor 26 is a variable speed electric motor. In other

embodiments, electric motor 26 may be a constant speed electric motor. For example, electric motor 26 may be a permanent magnet motor including a rotor integrated with motor shaft 28 and a stator arranged, for example, radially outwards of the rotor. A rated power of electric motor 26 may be between 100 and 40,000 kW, preferably between 2,000 and 6,000 kW. Of course, it will be readily appreciated that any type of electric motor can be used as electric motor 26, for example, a DC motor, an AC motor, a synchronous or asynchronous 5 motor, etc. In some embodiments, a plurality of electric motors may be drivably coupled to propeller shaft 22, for example, in series, with an appropriate arrangement of thrust bearing 30 and fluid distribution unit 40 in the above- described manner.

[32] In some embodiments, fluid distribution unit 40 may include a

10 rotation sensor 60 configured to detect a rotation angle of hollow shaft portion 36 and, accordingly, propeller shaft 22. In this manner, fluid distribution unit 40 can be controlled in an appropriate manner to supply the hydraulic fluid to the respective chambers inside propeller hub 46. In addition, in some embodiments, one or more lubrication supply channels may be formed inside the respective 15 shafts in order to supply a lubricant, for example, mineral oil or the like, to

propeller hub 46.

[33] Although in the exemplary propulsion system 10 described above, thrust bearing 30 is arranged forward of electric motor 26 and connected to fluid distribution unit 40 on the opposite side, in other embodiments, thrust bearing 30

20 may be provided aft of electric motor 26. For example, thrust bearing 30 may be provided such that hollow shaft portion 36 of the same is connected between propeller shaft 22 and motor shaft 28 via first and second couplings 32, 34, respectively. In this case, housing portion 54 of fluid distribution unit 40 may be detachably attached to motor housing 58 of electric motor 26, and rotatable 25 portion 56 of the same may be connected to motor shaft 28 of electric motor 26.

The hydraulic fluid is then supplied to propeller 24 via motor shaft 28, hollow shaft portion 36 and propeller shaft 22 in this order. The remaining configuration is essentially the same as described above. It should be noted, however, that in this configuration vibrations of, for example, electric motor 26 may be transmitted to fluid distribution unit 40. If this is not desired, the previously described configuration should be used instead.

[34] Although marine vessel 100 has been described above as an arctic vessel, it will be readily appreciated that the engine room arrangement disclosed

5 herein may be used in any other type of marine vessel, for example, (multi

purpose) offshore vessels, research vessels, cruise and ferry vessels, military vessels, cargo vessels, fishing vessels etc.

[35] In addition, although propeller 24 has been described above as a variable pitch propeller, in other examples, propeller 24 may be a fixed pitch

10 propeller. It will be appreciated that fluid distribution unit 40 will be omitted in this case, and the respective shafts will not be hollow shafts. The remaining configuration may be the same as in the embodiments described above.

Industrial Applicability

[36] The propulsion system for a marine vessel disclosed herein is 15 applicable to marine vessels in general for improving the serviceability and

maintenance of a propulsion system of the same, in particular, in case the propulsion system includes an electric motor directly coupled to a propeller shaft without a gear unit.

[37] An exemplary operation of marine vessel 100 having propulsion

20 system 10 will be described in the following with reference to Figs. 1 and 2.

[38] Main engine 20 may combust a fuel such as liquid fuel and/or gaseous fuel to provide output power. The output power provided by main engine 20 is converted into electrical power and supplied to electric motor 26 to rotate the same. The rotation of motor shaft 28 is transmitted to propeller shaft 22 via

25 coupling 32, and the rotation of propeller shaft 22 rotates propeller 24. The thrust provided by propeller 24 can be controlled by varying the rotation speed of electric motor 26. In addition, the thrust provided by propeller 24 can also be controlled by changing a pitch angle of the blades of controllable pitch propeller 24 in an appropriate manner. To this end, fluid distribution unit 40 may supply hydraulic fluid to respective control chambers provided in propeller 46 via hollow shaft portion 36, motor shaft 28 and propeller shaft 22, more particularly, via corresponding hydraulic conduits or passages provided therein. In this manner, a desired thrust can also be set by an appropriate control of the pitch 5 angle of the blades of propeller 24.

[39] Axial loads received by shafts 22, 28 and 36 are received by thrust bearing 30. Accordingly, fluid distribution unit 40 is decoupled from, for example, vibrations produced by propeller 24 and electric motor 26.

[40] In case one or more components of propulsion system 10 are to be 10 serviced or repaired, the corresponding components can be separated from the remaining components by disconnecting, for example, couplings 32 and/or 34. This facilitates easy servicing and repair of, for example, fluid distribution unit 40, hydraulic lines provided within the respective shafts, etc.

[41] Although the preferred embodiments of this invention have been 15 described herein, improvements and modifications may be incorporated without departing from the scope of the following claims.

Terms such as“about“,“around“,“approximately^ or“substantially” as used herein when referring to a measurable value such as a parameter, an amount, a temporal duration, and the like are meant to encompass variations of ±10% or 20 less, preferably ±5% or less, more preferably ±1% or less, and still more

preferably ±0.1% or less of and from the specified value, insofar as such variations are appropriate to perform the disclosed invention. It is to be understood that the value to which the modifier“about” refers is itself also specifically, and preferably, disclosed. The recitation of numerical ranges by 25 endpoints includes all numbers and fractions subsumed within the respective ranges, as well as the recited endpoints.