Process for controlling a hybrid naval propulsion system and hybrid propulsion system

Abstract

A method for controlling the hybrid drive system of a water craft, comprising a combustion engine (1), an electric engine/generator (2), a drive train (5) having a propeller (7) and a storage battery (3), a control unit (8) and a clutch (4). In order to increase efficiency, during travel in the upper power range the electric engine (2) is additionally operated as a generator, and during travel in the middle and lower power ranges the electric engine (2) is operated with current from a storage battery (3). The drive train is designed so that the characteristic (20) thereof lies by a defined charging capacity below the point of minimum specific fuel consumption (e.g. 25), or is steeper than the characteristic (16) of a conventional construction.

Claims

1. A propulsion system of a naval vessel, comprising a combustion engine (1), at least one electric machine (2) for being operated as a motor and as a generator, a drive train (5) with a propeller (7), a battery (3) and a control unit (8), wherein the drive train (5) is laid out in such a way that a characteristic curve (20) proceeds below the points of minimum specific fuel consumption by a distance corresponding to a given maximum charging power.

2. The propulsion system of a naval vessel according to claim 1, wherein the drive train (5) layout is such that the characteristic curve of torque over rotating speed (20) of the propeller (7) in a characteristic graph of the combustion engine is steeper than a propeller characteristic curve (16) leading to a point of rated power (15) and the characteristic curve (16) of the propeller is nearer the points of minimum specific fuel consumption of the combustion engine (1).

3. The propulsion system according to claim 2, wherein the propeller characteristic curve (20) intersects a full load curve (12) of the combustion engine (1) in a point (21), that is situated at a point of intersection of the full load curve (12) with a rated power hyperbola (14), or at a lower rotational speed.

4. The propulsion system of a naval vessel according to claim 3, wherein a steeper characteristic curve (20) of the propeller (7) is achieved by increasing its diameter.

5. The propulsion system of a naval vessel according to claim 1, wherein a ratio between power consumption or power output of the electric machine and the power of the combustion engine is a ratio range of 1:3 to 1:8.

6. The propulsion system of a naval vessel according to claim 1, wherein the electric machine (2) operated as a motor provides a torque in the lower region of rotating speed of the drive train, which does not decrease until a characteristic curve (17) of the electric machine (2) intersects a characteristic curve (20) of the drive train.

7. The propulsion system of a naval vessel according to claim 6, wherein the torque of the electric machine (2), operated as a motor, is achieved by a reduction gearbox (10) joined to the electric machine (2).

8. The propulsion system of a naval vessel according to claim 1, wherein a ratio between power consumption or power output of the electric machine and the power of the combustion engine is a ratio range of 1:4 to 1:6.

9. A method for controlling a hybrid propulsion system for a watercraft, the system comprising at least a combustion engine (1), an electric machine (2) acting as a generator and as a motor, a drive train (5) comprising a propeller (7), a battery (3) and a control unit (8), a clutch (4) being provided between the combustion engine (1) and the electric machine (2), the process comprises storing in the control unit: a characteristic curve (20) of the drive train (5) and a characteristic graph of the combustion engine including its torque and specific fuel consumption, wherein the characteristic curve (20) of the drive train (5) comprises a low and a high range and a medium range overlapping the high and the low range, including adjusting the joint load of the drive train (5) and the generator (2), during travel in the high range of the characteristic curve (20), by controlling the torque consumed by the generator (2) so that the operating point of the combustion engine in the characteristic graph is brought into a point of minimum specific fuel consumption at a prevailing rotational speed on a curve linking points of minimum fuel consumption (24), said operating point is situated above an operating point of the drive train (5) at the prevailing rotational speed; and storing electric current so generated with high efficiency in the battery (7), wherein the electric current is available for the operation of the electric machine (2) as a motor in other ranges of the characteristic curve (20).

10. The method according to claim 9, releasing the clutch, during travel in the low region of power, and operating the electric machine alone, wherein during travel in the medium region of power, the electric machine (2) assists the combustion engine (1) during acceleration.

11. The method of claim 9, wherein the electric machine assist the combustion engine in the upper range of power.

12. The method according to claim 9, wherein the torque or the power consumed by the electric machine is limited by a limiting value stored in the control unit (8) or by layout of the drive train (5).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the following, the invention will be described and commented in conjunction with the drawings, in which:

(2) FIG. 1 is a schematic representation of a propulsion system according to the state of the art and also of the present invention;

(3) FIG. 2 is a variant of the system of FIG. 1;

(4) FIG. 3 is a characteristic graph of a propulsion system according to the state of the art;

(5) FIG. 4 is the characteristic graph of FIG. 3, a characteristic curve of a propeller according to the invention being added;

(6) FIG. 5 is the complete characteristic graph of a propulsion system according to the invention.

DETAILED DESCRIPTION

(7) In FIG. 1, a combustion engine has the reference number 1, an electric machine the reference number 2 and a battery reference number 3. The electric machine 2 is suitable for being operated as and engine and as a generator, or there are two electric machines, one being an engine, the other being a generator. A first separating clutch 4 is ranged between the combustion engine 1 and the electric machine 2, and a second separating clutch is ranged between the electric machine 2 and a drive train 5. The outermost end of the drive train 5 bears a propeller 7. A control unit 8 manages the combustion engine 1, the electric machine 2 and charging of the battery 3.

(8) FIG. 2 is a variant, distinguished from FIG. 1 by a high-revving electric machine 9 driving the drive train 5 via a reduction gearbox 10. The electric machine 9 can be for driving only and the generator disposed in a different manner. The high-revving motor 9 and the reduction gearbox 10 provide a high torque over a wide range of rotational speed, allowing travelling with electric drive only, the combustion engine being stopped and the coupling opened.

(9) FIG. 3 shows the characteristic graph of a combustion engine, here a diesel engine. The graph of a spark-ignited engine is somewhat similar, the curves differing in detail. On the abscissa, the rotational speed of the combustion engine 1 (which issee FIG. 1identical with that of the electric machine 2) is represented, and on the ordinate the torque. The area of the characteristic graph is limited by the full-load curve 12 on top, this curve descending with lower rotational speed (13) and at high rotational speed continues as the rated power hyperbola 14, according to the rated power. In the characteristic graph, the curves of constant specific fuel consumption are represented in a way similar to the isohypses in a geographical map. The specific fuel consumption is specified in grams per horsepower and hour. The curves of constant specific fuel consumption are referred to as conchoidal curves. It can be seen that the specific fuel consumption is a minimum in the area within the curve marked as 210. With other rotational speeds, there is also a relative minimum, corresponding each time to a maximum efficiency.

(10) Further, a propeller characteristic curve 16 of a propeller according the state of the art is shown as a broken line, being the characteristic curve of the drive train. It (16) ends in the point of rated power 15 at the intersection with the hyperbola 14 which represents the rated power of the combustion engine 1. It can be seen that when travelling with the combustion engine only operating (all points of operation being on the characteristic curve of the propeller), the characteristic curve of the propeller is throughout in regions of high specific fuel consumption (low efficiency). Slow travel, a state of operation prevailing during most of the lifetime, or idling is particularly inefficient. It is therefore desirable, to be able to use electric drive in a wide operating range.

(11) In FIG. 4, the full load curve of an electric motor/generator is shown as a semi-dotted line 17. Thanks to the invention, the electric motor/generator improves the efficiency of the entire system over the entire operating range. The electric motor can in cooperation with the combustion engine power the drive train (this is called parallel hybrid), see FIG. 1 and FIG. 2, as the case may be. It is important that the electric motor provides a high torque in the lower range and keeps the power constant over the rotational speed above its maximum power. This increases the range of operation with electric drive only, and the combustion does not operate in the range of high specific fuel consumption. This already is a measure to reduce fuel consumption. Further measures are to follow.

(12) An important measure according to the invention consists in lowering the operating rotational speed of the combustion engine, in other words to deliver a demanded torque at a lower rotational speed. By this, charging the battery with maximum efficiency of the combustion engine is achieved in a wide operating range. Lowering the rotational speed of the combustion engine is achieved by using an accordingly designed propeller 7 (e.g. a larger diameter), according to an aspect of the present invention. This lowers the operating point of maximum torque 21 in the characteristic graph towards a lower rotational speed (from 2600 to 2300 rpm). The accordingly designed propeller 7 can be designed with a larger diameter (thus also lowering losses according to the Cordier-diagram) or with blades of higher pitch, or other design measures.

(13) FIG. 4 shows the characteristic curve 20 of the drive train (essentially the propeller characteristic curve), modified according to the invention; it intersects the full load curve in point 21, at a lower rotational speed than the characteristic curve 16 of a propeller according to the state of the art, see point 15. By this, the operating points are nearer the respective points of minimum specific fuel consumption. It is important for the generation of energy to be described below that the characteristic curve of the propeller is slightly below or in the region of highest efficiency.

(14) Lowering the rated power rotational speed according to the characteristic curve 20 of the propeller brings this characteristic curve closer to the descending branch 13 of the full load curve. This entails a lower zorque (agility) available for acceleration. With combustion engines with a significant turbo-hole this may lead to the vessel being unable to reach the rated power rotational speed, it would be unable to accelerate the vessel in the turbo-hole. The additional torque provided by the electric machine helps the combustion engine and thus the original agility with the characteristic curve 16 of the propeller is achieved again. The full load curve 22 with joint drive by the electric motor and the combustion engine is shown in FIG. 4, only a fraction of the torque of the electric motor being added.

(15) The efficiency of the generation of the electric current is essential for the economy of electric propulsion. According to the invention, it is generated in points of operation with minimum fuel consumption. In this way, the efficiency when travelling at idling speed (with propulsion by the so generated electric current) is improved by up to 40 percent, losses in the generator, inverter and the battery charging system being taken into account. The efficiency would be particularly low, if the battery were charged by the combustion engine operating at low load.

(16) FIG. 5 shows how the battery is charged with highest efficiency, resulting in cheap electric current. By the lowered points of operation the combustion engine already operates in regions of lower specific fuel consumption, see curve 20. But it is still at a distance from the curve linking points of minimum specific fuel consumption at various rotational speeds 24. The operating point of the combustion engine is brought into this curve 24 by driving the generator and in this way generating cheap electricity.

(17) As an example in the characteristic graph: At 1800 revolutions (rpm) the torque consumed by the drive train 5 in the point of operation 26 on the characteristic curve of the drive train 275 Nm (Newtonmeter). The point of operation of minimum specific fuel consumption 25 is situated at 350 Nm, thus by 75 Nm higher. In order to reach that point, the electric machine operating as a generator is controlled so as to use these 75 Nm for the generation of electric current. This corresponds to a charging current which, due to electric properties of the machine and the battery, has limits and an optimum. This maximum and optimum is considered in the layout of the drive train.

(18) Due to the propeller characteristic curve 20 being closer to the curve 24 than the characteristic curve 16 of the propeller according to the state of the art, the torque to be consumed by the generator is limited. It is much lower than it would be with the characteristic curve 16. Reaching the points of minimum consumption with a propeller according to the state of the art would require an enormous electric motor/generator.

(19) In the characteristic graph in FIG. 5, the region in which electric current is generated in addition to propelling is hatched and circumscribed by the characteristic curve 20 of the drive train, by the curve linking points of minimum specific fuel consumption at various rotational speeds 24, by a small part 12 of the full load curve 12 and by a line 27 steeply descending to the characteristic curve 20. The line 27 meets the characteristic curve 20 somewhat higher than point 28 at the intersection of the full load curve 17 of the electric engine and the characteristic curve 20 of the drive train. Up to this point, propulsion with only electric drive is possible.

(20) This additional charging power (higher torque at the same rotational speed) entails an increase of the efficiency of the combustion engine which improves the overall efficiency of propulsion directly and indirectly. Directly, because the combustion engine operates in its point of operation of maximum efficiency and indirectly, because the efficiency of the generation of electric currentand therewith of the combustion enginealso influences the efficiency of the electric machine operating as a motor. This, because the electricity is generated in the point of maximum efficiency of the combustion engine. With the so generated cheap electricity it is also economically sensible to operate the electric machine as a motor doubling the combustion engine also in other regions of operation.

(21) A windfall advantage of charging the battery also with high load is an increased freedom in dimensioning the electric machine and the battery. For instance, the size of the combustion engine can be reduced and that of the electric machine increased, leaving the capacity of the battery unchanged. In this way, the ration of the rated powers of the combustion engine and of the electric machine can be in a region of 1:3 to 1:10, preferably 1:4 to 1:6.

(22) By this layout, also the emissions can be reduced in manifold ways: The reduced fuel consumption also means a reduced quantity of exhaust gas. As higher efficiency is essentially a consequence of complete combustion, the content in CO, HC and particles of the exhaust gas is dramatically reduced. A further reduction is due to the reduced operating time of the combustion engine. If, for instance, the electric motor is operated in the lower load range during 500 hours, the energy it needs can be generated and stored in a much shorter time. The absolute value of the reduction depends, as previously said, on the load collectif (share of low-load operation), of the characteristic graph of the particular combustion engine and on the charging system of the battery. Further, servicing intervals and lifetime are increased in this way.