Marine propulsion system with efficient engine speed delta

[0001] The disclosure relates to marine propulsion systems, including engine speed control systems.

[0002] A marine engine speed control system maintains engine speed at the operator-selected engine speed. The engine has a throttle controlling engine speed according to throttle position. In response to the operator changing the operator-selected engine speed from a first-selected engine speed to a second-selected engine speed, the engine speed control system begins moving the throttle to attempt to set engine speed at the noted second-selected engine speed, and then maintain engine speed thereat.

[0003] It is common for the engine speed control system to include at least one proportional-integral-derivative (PID) controller to maintain engine speed at the operator-selected engine speed. When the operator changes the operator-selected engine speed from a first-selected engine speed to a second-selected engine speed, such change or delta causes the engine speed control system to begin moving the throttle. The amplification gain of the PID controller needs to be large enough to accommodate various deltas, including large deltas, to afford reasonably quick response time. However, large amplification gain (to accommodate a large delta) causes overshoot when attempting to set engine speed at the noted second-selected engine speed in response to the noted change of selected engine speed chosen by the operator. This can cause undesired instability or oscillation until the PID controller moves the throttle back from the overshoot position in attempting to maintain engine speed at the noted second-selected engine speed. An alternative is to limit the amount of amplification gain of the PID controller to minimize overshoot, but this approach suffers from slower response time, particularly for large deltas.

[0004] The present disclosure arose during continuing development efforts in the above technology.

[0007] FIG. 1 shows a marine propulsion system 10 having an internal combustion engine 12 for propelling a marine vessel 14, e.g. at propeller 16, in body of water 18. Engine speed is set by the operator at an engine speed control 20, e.g. a throttle lever, or the like, as is known. A central processing unit (CPU) 22 receives the engine speed command, and includes appropriate read only memory (ROM) 24 and random access memory (RAM) 26, and typically includes a proportional integral derivative (PID) controller 28, and outputs a control signal to input-output (I/O) interface 30 which in turn supplies a control signal to internal combustion engine 12 including throttle 32, all as is known.

[0008] The engine speed control system maintains engine speed at the operator-selected engine speed. Engine 12 has the noted throttle 32 controlling engine speed according to throttle position. In response to the operator changing the operator-selected engine speed at engine speed control from a first-selected engine speed to a second-selected engine speed, i.e. a change or delta, the engine speed control system begins to move the throttle to a new position to attempt to set engine speed at the noted second-selected engine speed. The engine speed control system is subject to overshoot, particularly at large deltas, when attempting to set engine speed at the noted second-selected engine speed in response to the noted change by the operator of the selected engine speed at engine speed control 20. To accommodate various deltas, including large deltas, the PID controller 28 is provided with enough amplification gain to provide desired quick enough response time to accommodate the noted change from the first-selected engine speed to the second-selected engine speed at engine speed control 20. The higher the gain the quicker the response time, however the higher gain makes the engine speed control system subject to more overshoot and instability.

Present Disclosure

[0009] In the present system, in response to the operator changing the operator-selected engine speed at engine speed control 20 from a first-selected engine speed to a second-selected engine speed, a prediction is made as to the throttle position needed to provide the noted second-selected engine speed. A feed forward signal is then provided at 34, FIG. 2, bypassing PID controller 28, and moving throttle 32 to the predicted throttle position. After the noted movement of the throttle to the predicted throttle position, the above noted engine speed control system, including PID controller 28, maintains engine speed at the noted-selected engine speed. The throttle is moved to the predicted throttle position in response to the feed forward signal, without waiting for the engine speed control system to move the throttle. The throttle is moved to the predicted throttle position in response to the feed forward signal without the above noted overshoot otherwise caused by the engine speed control system. In one embodiment, the system enables reduction of the amplification gain of the PID controller otherwise needed to accommodate the noted change or delta from the first-selected engine speed to the second-selected engine speed at engine speed control 20, and instead accommodating such change or delta by the predicted throttle position provided by the feed forward signal 34. Accordingly, the PID controller amplification gain need only be large enough to maintain engine speed at the noted second-selected engine speed, without having to accommodate the change or delta from the first-selected engine speed to the second-selected engine speed. The reduced amplification gain provides enhanced stability of the PID controller, and reduces oscillation.

[0010] Current marine internal combustion engines are typically airflow lead, meaning that the demand from the operator requests a certain throttle percentage or throttle position. The throttle percent or position can be translated into an airflow request. For a marine propulsion system, the operator requests a particular engine speed, at engine speed control 20. By predicting the throttle percent or position needed to get to the operator requested engine speed or RPM (engine revolutions per minute), the otherwise poor transient performance of a PID-only controller is improved. To predict the needed throttle percent or position, the airflow at a given throttle percent or position, engine speed, and engine load is predicted. The flow through a throttle is affected by engine speed, barometric pressure, and engine load. In one embodiment, in response to the operator changing the operator-selected engine speed at engine speed control 20 from a first-selected engine speed to a second-selected engine speed, throttle position is predicted as needed to provide requisite engine airflow per cylinder (APC) needed to provide the noted second-selected engine speed. In a further embodiment, a normalized APC calculation is used to predict required throttle position to achieve the noted second-selected engine speed. In one embodiment, a normalized APC calculation is used as follows:

[0011] $\left(\mathrm{normalized}\mathrm{APC}\right)=K\frac{\left(\mathrm{corrected}\mathrm{APC}\right)-\left(\mathrm{minimum}\mathrm{APC}\right)}{\left(\mathrm{maximum}\mathrm{APC}\right)-\left(\mathrm{minimum}\mathrm{APC}\right)}$
where K is a normalization function, and minimum APC and maximum APC are predetermined according to the particular marine internal combustion engine in the marine propulsion system, e.g. by an empirical data look-up table. Normalization function K can change based on barometric pressure, manifold pressure, and intake air temperature. In one embodiment, engine load is predicted at the second-selected engine speed, and the predicted engine load is converted to a predicted APC, and a corrected APC is calculated by compensating the predicted APC for a given parameter, and the normalized APC is calculated from the corrected APC. In one embodiment, where the vessel may be subject to operation at various altitudes, the corrected APC is calculated by compensating the predicted APC for different altitudes. For example, a given throttle position or percent results in different APC's at different altitudes, e.g. a throttle position at 40% open in one test provided an APC of 276 milligrams at 10,000 feet altitude, and an APC of 400 milligrams at 750 feet altitude. This variation in airflow at a given throttle position or percent due to barometric pressure, engine RPM, etc., may make the above noted correction desirable. Other parameters for correction may include differing propellers, differing vessel loads, etc. The noted normalization is desired to provide greater predictive accuracy at higher throttle settings, particularly when the pressure ratio across the throttle increases above 0.8 and approaches 1.0. Compressible flow predictions are difficult to use at pressure ratios greater than 0.8.

[0012] The present system provides a method for efficiently changing controlled engine speed of a marine internal combustion engine in a marine propulsion system for propelling a marine vessel, wherein the engine is operated at an operator-selected engine speed and an engine speed control system maintains engine speed at the operator-selected engine speed, the engine having a throttle controlling engine speed according to throttle position, the method including responding to the operator changing the operator-selected engine speed, from a first-selected engine speed to a second-selected engine speed, by predicting throttle position needed to provide the second-selected engine speed, providing a feed forward signal moving the throttle to the predicted throttle position, after the movement of the throttle to the predicted throttle position, using the engine speed control system to maintain engine speed at the second-selected engine speed. In a further embodiment, wherein the engine speed control system moves the throttle, in response to the operator changing the operator-selected engine speed from the first-selected engine speed to the second-selected engine speed, to attempt to set engine speed at the second-selected engine speed, the method includes moving the throttle to the predicted throttle position in response to the feed forward signal, without waiting for the engine speed control system to move the throttle. In a further embodiment, wherein the engine speed control system is subject to overshoot when attempting to set engine speed at the second-selected engine speed in response to the operator changing the operator-selected engine speed from the first-selected engine speed to the second-selected engine speed, the method includes moving the throttle to the predicted throttle position in response to the feed forward signal without the overshoot otherwise caused by the engine speed control system. In a further embodiment, wherein the engine speed control system includes at least one PID controller, the method includes reducing the amplification gain of the PID controller otherwise needed to accommodate the change from the first-selected engine speed to the second-selected engine speed, and instead accommodating the change by the predicted throttle position provided by the feed forward signal, whereby the PID controller amplification gain need only be large enough to maintain the engine speed at the second-selected engine speed, without having to accommodate the change from the first-selected engine speed to the second-selected engine speed, the reduced amplification gain providing enhanced stability of the PID controller. In a further embodiment, the method includes responding to the operator changing the operator-selected engine speed, from the first-selected engine speed to the second-selected engine speed, by predicting throttle position needed to provide requisite engine airflow per cylinder, APC, needed to provide the second-selected engine speed, using a normalized APC calculation to predict required throttle position to achieve the second-selected engine speed. In a further embodiment, the method includes using a normalized APC calculation as follows:

[0013] $\left(\mathrm{normalized}\mathrm{APC}\right)=K\frac{\left(\mathrm{corrected}\mathrm{APC}\right)-\left(\mathrm{minimum}\mathrm{APC}\right)}{\left(\mathrm{maximum}\mathrm{APC}\right)-\left(\mathrm{minimum}\mathrm{APC}\right)}$
where K is a normalization function, and minimum APC and maximum APC are predetermined according to the particular the marine internal combustion engine in the marine propulsion system. In a further embodiment, the method includes predicting engine load at the second-selected engine speed, converting the predicted engine load to a predicted APC, calculating a corrected APC by compensating the predicted APC for a given parameter, calculating the normalized APC from the corrected APC. In a further embodiment, wherein the engine speed control system moves the throttle, in response to the operator changing the operator-selected engine speed from the first-selected engine speed to the second-selected engine speed, to attempt to set engine speed at the second-selected engine speed, the method includes moving the throttle to the predicted throttle position in response to the feed forward signal, without waiting for the engine speed control system to move the throttle, wherein the engine speed control system includes at least one PID controller, and the method includes reducing the amplification gain of the PID controller otherwise needed to accommodate the change from the first-selected engine speed to the second-selected engine speed, and instead accommodating the change by the predicted throttle position provided by the feed forward signal, whereby the PID controller amplification gain need only be large enough to maintain the engine speed at the second-selected engine speed, without having to accommodate the change from the first-selected engine speed to the second-selected engine speed, the reduced amplification gain providing enhanced stability of the PID controller, responding to the operator changing the operator-selected engine speed, from the first-selected engine speed to the second-selected engine speed, by predicting throttle position needed to provide requisite engine airflow per cylinder, APC, needed to provide the second-selected engine speed, using a normalized APC calculation to predict required throttle position to achieve the second-selected engine speed, predicting engine load at the second-selected engine speed, converting the predicted engine load to a predicted APC, calculating a corrected APC by compensating the predicted APC for barometric pressure(eg for altitude compensation), and calculating the normalized APC from the corrected APC.

[0014] The disclosure provides a system for efficiently changing controlled engine speed of a marine internal combustion engine in a marine propulsion system for propelling a marine vessel, the engine being operated at an operator selected engine speed and an engine speed control system maintaining engine speed at the operator-selected engine speed, the engine having a throttle controlling engine speed according to throttle position, the system including a control circuit having a processor, a memory, and an input/output interface, wherein the control circuit responds to the operator changing the operator-selected engine speed, from a first-selected engine speed to a second-selected engine speed, by predicting throttle position needed to provide the second-selected engine speed, and provides a feed forward signal moving the throttle to the predicted throttle position, and after the movement of the throttle to the predicted throttle position, uses the engine speed control system to maintain engine speed at the second-selected engine speed. The control circuit including at CPU 22, ROM 24, RAM 26, includes a computer-readable medium having computer-executable instructions for performing the above noted method, including the steps set forth above.

[0015] In further embodiments, the disclosure is applicable to hybrid marine propulsion systems having both an internal combustion engine and an electric propulsion system, including an electric motor, for propelling a marine vessel. The system and method of the present disclosure is used for efficiently changing controlled engine speed of the marine internal combustion engine in the hybrid marine propulsion system.

[0016] In the foregoing description, certain terms have been used for brevity, clearness, and understanding. No unnecessary limitations are to be inferred therefrom beyond the requirement of the prior art because such terms are used for descriptive purposes and are intended to be broadly construed. The different configurations, systems, and method steps described herein may be used alone or in combination with other configurations, systems and method steps. It is to be expected that various equivalents, alternatives and modifications are possible within the scope of the appended claims. Each limitation in the appended claims is intended to invoke interpretation under 35 U.S.C. §112, sixth paragraph, only if the terms “means for” or “step for” are explicitly recited in the respective limitation.