METHOD TO OPERATE A MARINE PROPULSION SYSTEM IN A TROLLING MODE, CONTROL UNIT AND MARINE PROPULSION SYSTEM

Abstract

A method of operating a marine propulsion system (1) in a trolling mode. The marine propulsion system (1) comprises at least one propeller shaft (6) which can be driven by an engine (2), via a pressure operated forward clutch (4), in a forward direction or, via a pressure operated reverse clutch (5), in a reverse direction. A forward pressure is applied to engage the forward clutch (4) to a certain extent and, at the same time, a reverse pressure is applied to engage the reverse clutch (5) to a certain extent. A value of the forward pressure is different from a value of the reverse pressure so that the propeller shaft (6) is caused to rotate in a desired rotational direction. A control unit with mechanism to operate the marine propulsion system according to the method and a marine propulsion system with such a control unit are also disclosed.

Claims

1. A method of operating a marine propulsion system (1) in a trolling mode, wherein the marine propulsion system (1) comprises at least one propeller shaft (6) which can be driven by an engine (2), via a pressure operated forward clutch (4), in a forward direction or, via a pressure operated reverse clutch (5), in a reverse direction, the method comprising: applying a forward pressure to engage the forward clutch (4) to a certain extent and, at the same time, applying a reverse pressure to engage the reverse clutch (5) to a certain extent, and wherein a value of the forward pressure is different from a value of the reverse pressure, so that the propeller shaft (6) is caused to rotate in a desired rotational direction.

2. The method according to claim 1, wherein the forward pressure and the reverse pressure are determined to cause slippage in the range of 0% up to 30% at the forward clutch (4).

3. The method according to claim 1, wherein the forward pressure and the reverse pressure are determined to cause slippage in the range of 70% up to 100% at the forward clutch (4).

4. The method according to claim 1, wherein the forward pressure and the reverse pressure are determined to cause slippage in the range of 0% up to 30% at the reverse clutch (5).

5. The method according to claim 1, wherein the forward pressure and the reverse pressure are determined to cause slippage in the range of 70% up to 100% at the reverse clutch (5).

6. The method according to claim 1, wherein, before applying the forward and the reverse pressure, a prefill pressure is applied to the forward clutch (4) and to the reverse clutch (5).

7. A control unit fora marine propulsion system, wherein the control unit (9) comprises means to control the marine propulsion system (1) according to the method according to claim 1.

8. A marine propulsion system, comprising an engine (2), a transmission (8) with a pressure operated forward clutch (4) and a pressure operated reverse clutch (5), a propeller shaft (6) which can be driven by the engine (2), via the transmission (8), and a control unit (9) to control the pressure which is applied to each of said clutches (4, 5), wherein the control unit (9) is enabled to control the marine propulsion system (1) according to the method according to claim 1.

9. The marine propulsion system according to claim 8, wherein the forward clutch (4) comprises a first double acting pressure cylinder and the reverse clutch (5) comprises a second double acting pressure cylinder.

Description

[0024] The invention will now be further and more particularly described, by way of example only, and with reference to the accompanying drawings, in which:

[0025] FIG. 1 shows a simplified schematic of a marine propulsion system according to present invention and

[0026] FIG. 2 shows graphs of an example of pressure and slip control according to the invention.

[0027] The schematic of FIG. 1 shows a marine propulsion system 1 with its essential elements. The marine propulsion system 1 comprises an engine 2, a transmission 8 and a propeller shaft 6, which can be driven by the engine 2 via the transmission 8. A control unit 9 is connected by connections 10 to a pressure operated forward clutch 4 and to a pressure operated reverse clutch 5. Connections 10 symbolize hydraulic lines from corresponding hydraulic valves which are part of the control unit 9 and each one pressure chamber of the two clutches 4 and 5. In other embodiments the hydraulic valves may as well be positioned at or inside the transmission 8 near to the clutches 4, 5. In this case the hydraulic valves would be connected via electric connections to the control unit 9. The connection 11 between engine 2 and the control unit 9 is used to monitor and control the engine speed. The connection 11 can be realized as electric cable connection or as a wireless connection.

[0028] Both clutches 4, 5 are friction clutches, namely pressure operated multi-disc clutches. Each of the clutches 4 and 5 comprises an inner disc carrier 12, 14 and an outer disc carrier 13, 15. The outer disc carriers 13 and 15 are connected by spur gears 16, 17 which are fixed to the outer disc carriers 13, 15 of the two clutches 4 and 5. Propeller 7 is fixed onto propeller shaft 6 which is permanently connected to the output side of the transmission 8. The transmission 8 comprises a housing. The forward clutch 4 and the reverse clutch 5 are arranged inside the housing of the transmission 8.

[0029] Each outer disc carrier 13, 15 is the respective input element at both clutches 4 and 5, whereas the inner disc carriers 12, 14 are the corresponding output elements. The outer disc carrier 13 of the forward clutch 4 is permanently connected to a drive shaft 3 of the engine 2. The outer disc carrier 15 of the reverse clutch 5 is driven by the outer disc carrier 13 of the forward clutch 4 by means of spur gears 16 and 17. Each of the inner disc carriers 12, 14 is permanently connected to a corresponding drive gear 18, 19. Both drive gears 18 and 19 are constantly meshing with driven gear 20 which is fixed to propeller shaft 6.

[0030] FIG. 2 shows curves of the forward pressure p.sub.FWD, reverse pressure p.sub.REV, percentage of slip in the forward clutch and the pressure difference delta P between forward and reverse pressure, during the same time period.

[0031] The two upper graphs in FIG. 2 show the forward pressure p.sub.FWD which is applied to the forward clutch and the reverse pressure p.sub.REV which is applied to the reverse clutch over a certain time period from t.sub.0 to t.sub.10.

[0032] The next graph shows the percentage of slip (SLIP.sub.FWD) in the forward clutch in the same time period from points in time t.sub.0 to t.sub.10.

[0033] The lowest graph shows the pressure difference delta P between the forward pressure and the reverse pressure. The curve of the pressure difference delta P is approximately congruent to the curve of to the rotation speed of the propeller shaft, provided that the load on the propeller stays nearly constant during the considered time.

[0034] At a starting time to there is no forward pressure p.sub.FWD applied to the forward clutch and no reverse pressure p.sub.REV is applied to the reverse clutch. Hence, both clutches are completely disengaged and no torque is transmitted. The slip in the forward clutch is at 100%.

[0035] At the time t.sub.1 a prefill pressure is applied to the forward clutch and to the reverse clutch. This causes an equal low torque on both clutches and a hold of the propeller shaft. The prefill pressure at both clutches makes them ready to transmit a higher torque very quickly, as soon as the pressure is further increased.

[0036] At the time t.sub.2 the forward pressure p.sub.FWD is further increased, while the reverse pressure p.sub.REV stays at the low prefill pressure level. This causes the forward clutch to be more engaged and to rotate the propeller shaft to a certain degree in forward direction. Hence, the percentage of slip in the forward clutch changes to about 70%. These conditions are kept until the time t.sub.3.

[0037] Between the times t.sub.3 and t.sub.4 the reverse pressure is slightly increased, so that the reverse clutch is engaged a little bit more and acts like a brake against the driving force of the partially closed forward clutch. As a result the rotation speed of the propeller shaft decreases and the percentage of slip in the forward clutch increases correspondingly to about 85%. With such pressure adjustment the propeller shaft could be driven for a longer time constantly at 85% of slippage in the forward clutch. This enables trolling maneuvers at a very low but constant speed, what is not possible with conventional methods of operation of such a propulsion system.

[0038] Between the times t.sub.4 and t.sub.5 the system is operated at the conditions before the time t.sub.3. At t.sub.5 the forward pressure is raised significantly, while the reverse pressure stays constant, so that the propeller shaft is further accelerated and the percentage of slip in the forward clutch is lowered to about 15%. However, in this low slippage range a stick-slip effect is caused which can be seen at the zigzag curve of the corresponding curve of SLIP.sub.FWD. In order to eliminate the stick-slip phenomenon the forward pressure and the reverse pressure are raised slightly after the time t.sub.7. Again the reverse clutch is engaged a little bit more and acts like a brake against the driving force of the partially closed forward clutch. This stops the stick-slip phenomenon while the percentage of slip in the forward clutch stays constant at about 15%.

[0039] The forward pressure is lowered to a certain extent after the time t.sub.8, while the reverse pressure is reduced to zero after the time t.sub.8. This causes the percentage of slip in the forward clutch to change close to zero. However, in this very low slippage a stick-slip phenomenon occurs again in the forward clutch. The stick-slip phenomenon continues until the time t.sub.9, when the forward pressure is raised to a level of 100, which corresponds to a completely engaged forward clutch. With the forward clutch being completely engaged, the percentage of slip in the forward clutch logically is zero.

[0040] In accordance with the proposed new method the described stick-slip phenomenon between the times t.sub.6 and t.sub.7 and between the times t.sub.8 and t.sub.9 can be completely avoided, if the forward pressure p.sub.FWD and the reverse pressure p.sub.REV are both raised immediately at time t.sub.6 to the higher level as can be seen in the graphs by dotted lines. So the reverse clutch can act as a counter-brake against the driving torque which is transferred via the forward clutch during this period.

REFERENCE NUMERAL

[0041] 1 marine propulsion system [0042] 2 engine [0043] 3 drive shaft [0044] 4 forward clutch [0045] 5 reverse clutch [0046] 6 propeller shaft [0047] 7 propeller [0048] 8 transmission [0049] 9 control unit [0050] 10 connection [0051] 11 connection [0052] 12 inner disc carrier [0053] 13 outer disc carrier [0054] 14 inner disc carrier [0055] 15 outer disc carrier [0056] 16 spur gear [0057] 17 spur gear [0058] 18 drive gear [0059] 19 drive gear [0060] 20 driven gear