AU8452882A - A method of controlling the propulsion machinery in a ship having a variable-pitch propeller - Google Patents

Description

A METHOD OF CONTROLLING THE PROPULSION MACHINERY IN A SHIP HAVING A VARIABLE-PITCH PROPELLER

The present invention relates to a method of con¬ trolling the propulsion machinery in a ship having a variable-pitch propeller.

Increasing fuel prices have compelled ships to 5 reduce speed in order to cut down fuel consumption and thereby to compensate, to some extent, for the increased cost. However, the fuel consumption does not depend solely on the speed, but also on the weather and the state of the sea as well as on the relation between the number of revo¬ lt) lutions and the pitch of the propeller.

The relation between the number of revolutions and the pitch usually is determined by a so-called combinator, i.e. a device by which the number of revolutions and the pitch are simultaneously actuated by means of a single 5 operating lever. This means that the relation between the number of revolutions and the pitch has been established for each position of the operating lever already upon construction, and thus the fuel consumption cannot be optimized. 0 Although it is possible, if the weather conditions and the state of the sea along a planned route and also the factors referable to the ship are known, to lay down in advance suitable speeds for the different parts of the route, this method does not safely guarantee that the de- 5 sired result is obtained.

Several different methods of controlling the fuel supply, the number of revolutions and the pitch are previously known. According to these methods, however, the control is effected more or less independently of the 0 ship's speed, for which reason one cannot be sure whether an achieved cutdown in fuel consumption is the result of the control effected or whether it depends on, for example, a reduction in speed. The present invention has for its object to provide a method of the type which is mentioned by way of intro¬ duction and which makes it possible to attain maximum efficiency at a given speed of the ship.. To achieve this object, the method according to the invention is characterized in that the ship's speed is first adjusted to a value within a predetermined inter¬ val containing a desired value of the speed, by changing the number of revolutions of the propulsion machinery and the propeller pitch, whereupon the number of revolutions and the pitch are changed,while maintaining the speed within the said interval, until there is obtained a com¬ bination of the number of revolutions and the pitch which gives a minimum of fuel consumption in the propulsion machinery.

The invention will be described in more detail below, reference being had to the accompanying drawings. Fig. 1 is a flow chart showing an embodiment of a speed control comprised by the method according to this invention. Fig. 2 is a flow chart showing how the efficiency according to the invention is made as high as possible at a previously set speed. Fig. 3 shows how the method illustrated in Figs. 1 and 2 is utilized in order to attain a substantially constant fuel consumption for the distance sailed. Fig. 4 is a diagram showing the character of the relations between the number of revolutions, the power output, the speed and the propeller pitch. Fig. 5 is a block diagram of a device for carrying the method illustrated in Figs. 1-3 into effect. As will appear from Fig. 5, the method according to the invention requires for its execution detectors 1, 2 and 3 for the ship's speed, the fuel consumption and the number of revolutions. These detectors 1-3 may be of any suitable type, analog or digital, and are connected, via an interface unit 4, to a control equipment 5 which pre¬ ferably contains a computer and supplies control signals to operating means 6 and 7 for controlling the propeller pitch and the number of revolutions of the propulsion machinery, respectively, and thus- the number of revolu¬ tions of the propeller or propellers.

The control according to this invention is effected in two stages, the first of which is exemplified in Fig. 1. It implies that the ship's speed or velocity is made sub¬ stantially to correspond to a predetermined desired value of the speed. More particularly, the first stage causes the actual speed of the ship to be adjusted to a desired speed interval V_degired + ^_des__xeά- Adjusting the ship's speed to the desired interval is initiated by sensing the actual speed of the ship. If this speed already lies within said interval, a direct change-over to the second stage of the method according to the invention is effected, which second stage has been designated optimization in Fig. 1. If, on the other hand, the actual speed lies out¬ side the interval in question, a rough adjustment is first effected by utilizing empirical values recorded in a table. Thus, the number of revolutions of the propulsion machinery is decreased/increased to a value X corresponding approximately to a desired speed value according to the said table, and the pitch of the propeller blades is alternatively increased or decreased. The ship is then allowed to stabilize itself at its new speed, for example during 90 seconds, whereupon the ship's speed is measured during a measuring period of, for example, 90 seconds. If the speed value now measured lies within the predetermined interval, a change-over to the second stage of the method occurs, whereas otherwise the number of revolutions is increased/decreased by a predetermined amount, for in¬ stance 15 r.p.m. for each deviation of 1 knot between the actual and the desired speed value. This change in the number of revolutions is accompanied by respectively a decrease or an increase of the propeller pitch. The measuring operation previously effected is then repeated, whereupon it is again checked whether the latest measured value lies within the predetermined interval. The proce- dure is repeated until it does, unless the number of revo¬ lutions before then deviates by more than a predetermined amount, for instance 15 r.p.m., from the original roughly adjusted value, in which case an alarm is given. When a change-over to the second stage of the control method according to the invention has occurred, a flag A = 1 is set, whereupon the number of revolutions is reduced by a predetermined increment, for instance 1 r.p.m., and the propeller pitch is increased by a predetermined amount. After the ship has been allowed to stabilize its motion during a suitable interval, for example 90 seconds, the ship's speed is measured, and it is checked whether this speed lies within the above-mentioned interval. If the measured speed lies outside the interval, a return to the speed adjustment of the first stage takes place, where¬ as, if the speed lies within the interval in question, the flag³ is set to 0, and it is checked whether a cutdown in fuel consumption has occurred owing to the immediately preceding decrease in thenumber of revolutions. If this is the case, the number of revolutions is further decreased, and the pitch is again increased, and the speed is again measured to check whether it lies within the said speed interval. If the speed lies outside the interval (actually, below said interval) , the preceding change of the number of revolutions and the pitch is eliminated by a corresponding increase of the number of revolutions and decrease of the pitch, whereupon the number of revolutions and the pitch are locked. If, on the other hand, the speed lies within the interval, it is again checked whether the fuel consumption has been cut down by the latest change of the number of revolutions and the pitch. If this is the case, the preceding procedure is repeated, either until the number of revolutions and the pitch are locked in the manner described above, or until an increase in fuel consumption can be established. In the latter case, a second flag B = 1 is set, and the number of revolutions is increased by the increment of the number of revolutions

-BUREA previously utilized, for instance 1 r.p.m. , whereupon a further increase of the number of- revolutions, preferably by the same increment, and a decrease of the propeller pitch take place. The speed is then measured with a delay of, for example, 90 seconds, and it is checked whether the measured speed value lies within the above-mentioned speed interval. If this is not the case, a return to the first stage of the method, with reviewed speed adjustment, takes place. If, on the other hand, the measured speed value lies within the speed interval in question, the flag B is given the value 0, and it is checked whether the last increase in speed and the decrease in pitch have caused an increase or a cutdown in fuel consumption. If a cutdown is established, the speed is again increased and the pitch is decreased, and measuring and checking whether the speed now measured lies within the speed interval in question, are repeated. If this is not the case, the latest change of the number of revo¬ lutions and the pitch is compensated for, whereupon the number of revolutions and the pitch are locked. If, on the other hand, the measured speed value lies within the speed interval in question, the fuel consumption is again checked. The loop described above is repeated a number of times until either the measured speed value lies outside the speed interval in question or until an increase in fuel consumption is established, in which case the latest change of the number of revolutions of the propulsion machinery and the propeller pitch is eliminated by re¬ ducing the number of revolutions and increasing the pitch, whereupon these are locked.

It will be appreciated that the above described method affords a combination of the number of revolutions and the pitch which provides for minimum fuel consumption in the propulsion machinery for speeds within the speed interval in question. In some cases, it may be desirable to maintain the fuel consumption constant at a desired level per unit of length for the distance sailed. An embod-lment of the

^"fUREΛ

OJWPI method according to the present invention, by which this desideratum is realized, is shown in Fig. 3. In accord¬ ance with what is shown in Fig. 3, there is calculated, in a first step, a suitable speed value according to the formula

in which B is the fuel consumption per unit of length for the distanc sailed, m a second step, the speed control illustrated in Fig.1 is carried out on the basis of the calculated speed value. It is then checked whether the actual fuel consumption lies within an interval containing the desired value of the fuel consumption, for instance ^B _c>_esi_re(3 ± 1%» If this is the case, the fuel consumption is optimized by effectin the control as illustrated in the flow chart according to Fig. 2. If, on the other hand, the fuel consumption lies outside the interval in question, a suitable speed value is again calculated in accordance with the above formula, whereupon the procedure is repeated until the number of revolutions and the pitch are locked.as shown in the chart according to Fig. 2.

It appears from the diagram shown in Fig. 4 that the power output depends upcn the number of revolutions and the pitch. However, the above described mechanized method ensures that the minimum fuel consumption for a given desired speed is attained. A corresponding manual control by means of instruments indicating the speed, the fuel consumption, the pitch and the number of revolutions is not possible in actual practice because the control requires constant supervision and attention which can only be effected by automatic means.

As has been mentioned above, the detectors 1, 2 and 3 for the ship's speed, fuel consumption and number of revolutions, respectively, may be of any suitable type. However, the detector 3 for the number of revolutions preferably is an inductive detector and may comprise soft iron gears mounted around the periphery of the shaft, the revolutions of which are to be measured, and an inductive transducer which is so mounted that it detects the passage of the gears and, thus, the number of revolutions of the shaft. Such revolution detectors are available from Verkon Electronics AB, Sweden. The fuel consumption detector 2 may be a flow-meter of the type utilizing ultrasonic pulses. Such a flow-meter is avail¬ able under the designation EMUF from Danfoss A/S, Denmark. The operating means 6 and 7 may consist of electro- pneumatic transducers, for instance of the type 346 018 from Wabco Westinghouse.

Claims (5)

1. A method of controlling the propulsion machinery in a ship having a variable-pitch propeller, c h a r a c t e r i z e d in that the ship's speed is first adjusted to a value within a predetermined interval containing a desired value of the speed, by changing the number of revolutions of the propulsion machinery and the propeller pitch, whereupon the number of revolutions and the pitch are changed,while maintaining the speed within the said interval, until there is obtained a combination of the number of revolutions and the pitch which gives a minimum of fuel consumption in the propulsion machinery.

2. A method as claimed in claim 1, c h a r a c ¬ t e r i z e d in that the fuel consumption is measured after the speed adjustment, that the speed is measured after each change in the number of revolutions and the pitch, following upon the speed adjustment, for checking that the speed still lies within said interval, and that the fuel consumption is measured after each such change and is compared with the immediately preceding measure- ment of the fuel consumption, if the speed after said change was within the said interval.

3. A method as claimed in claim 2, c h a r a c ¬ t e r i z e d in that further changes in the number of revolutions are made in the same direction as the pre- ceding change, if this change implied a cutdown in fuel consumption, until either an increase in fuel con¬ sumption is recorded or the speed lies outside the said interval.

4. A method as claimed in any one of claims 1-3, c h a r a c t e r i z e d in that the first change in the number of revolutions, after the speed adjustment, is a reduction in the number of revolutions.

'BUREA OMPI

5. A method as claimed in any one of claims 1-4, c h a r a c t e r i z e d in that^" the actual value of the speed is selected on the basis of a desired fuel consumption value per unit of length for the distance sailed, that it is checked, after said speed adjustment, whether the fuel consumption lies within a predetermined second interval containing the desired fuel consumption value, and that a new desired value is calculated for a further speed adjustment, if the fuel consumption, after the speed adjustment, lies outside said second interval.

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