GB2506921A

GB2506921A - Enhanced steering using two engine idle speeds

Info

Publication number: GB2506921A
Application number: GB1218402.4A
Authority: GB
Inventors: Neil Graham Jenkins
Original assignee: Gibbs Technologies Ltd
Current assignee: Gibbs Technologies Ltd
Priority date: 2012-10-14
Filing date: 2012-10-14
Publication date: 2014-04-16
Anticipated expiration: 2032-10-14
Also published as: WO2014057292A2; US20150266556A1; GB2506921B; US9694893B2; WO2014057292A3; CA2888156A1; GB201218402D0; CN104853986A; EP2906465A2

Abstract

A watercraft or amphibian has a prime mover operable at first and second idle speeds and a marine propulsion device which produces thrust when connected to the prime mover. A manually operated thrust control, operated by a rider, controls the amount of speed and thrust of the prime mover. A sensor determines whether the watercraft or amphibian is operating above a determined speed of travel and where the prime mover is operated above the second idle speed when the sensor determines the watercraft is operating above the determined speed such that steerable thrust is provided independently of the manual operated thrust control.

Description

ENHANCED STEERING

The present invention relates to a system, method and apparatus for enhanced steering for use in a watercraft, amphibian or other such vehicle, and in s particular, but not exclusively, where the marine propulsion is provided by means of a jet drive.

Jet drive marine propulsion systems are well known in the art and typically comprise a prime mover and jet drive combination, where the primer mover provides drive via a drive shaft which rotates an impeller arranged in a duct (conduit) of the jet drive. The duct comprises, at a first end, a proximal inlet generally arranged in the bottom surface of a hull of the watercraft or amphibian for inducting water upstream of the impeller, and, at a second end, a distal outlet generally arranged as an outlet nozzle downstream of the impellor for ejecting water as a jet. The nozzle is generally of a lesser cross-sectional area when compared to that of the duct so as to provide for pressurised and accelerated flow of the water through the duct under the action of the rotating impellor.

Propulsion is thus provided by way of a reaction force to the thrust provided by the jet of water ejected via the outlet nozzle. Unlike in watercraft where a submerged rudder is used to effect steering, with a jet drive it is conventional to provide a steering nozzle downstream (to the rear) of the outlet nozzle, and in close registration thereto, which steering nozzle is pivotable about a generally vertical axis so that it may pivot left or right under the control of the steering and direct the jet of water exiting from the outlet nozzle accordingly. Thus, steering of the watercraft or amphibian is effected as a result of the reactionary force to the thrust of the jet exiting the steering nozzle, as steered.

The thrust and steering generated by the jet drive to power and steer the watercraft or amphibian is controlled by the driver or rider by way of a manually operated throttle control device (morse throttle, twist grip biased to idle, pivotable lever biased to idle, or other suitable device) and use of a steering device (wheel, handlebar, tiller, or other suitable device). A known limitation, therefore, with jet drive marine propulsion systems is a reduced (or total lack of) steering function when the manually operated throttle is set to low or idle, or let go and biased towards idle, regardless of a steering request via the steering device, because there is low or no thrust generated by the jet drive. This can present drivers or £ riders of the watercraft or amphibians with a situation of reduced manoeuvrability and control of the watercraft or amphibian unless the manually operated throttle control is re-applied by the driver or rider. In particular, this can be a problem when travelling at speed and the manually operated throttle is let go of and returns to idle. Typically, it is then no longer possible to steer the watercraft or amphibian effectively as the thrust generated by the jet drive falls away with reduced engine speed. Such a phenomenon is known as off-throttle or off-power steering loss. A number of prior art devices and systems have been developed in particular to deal with the phenomenon of off-throttle or off-power steering loss.

Furthermore, at low speed, when attempting docking or beaching manoeuvres, a lack of meaningful steerable thrust has also been perceived by some drivers or riders as a problem, and so a number of prior art devices and systems have been developed to provide assistance with steerable thrust for low speed manoeuvres, such as docking and/or beaching. However, other drivers and riders have found steerable thrust assistance at low speed a positive hindrance as it provides steerable thrust when not intuitively expected and/or when not desired.

In the various prior art devices and systems proposed for addressing the phenomenon of off-throttle or off-power steering loss, a rapid off-throttle event and a threshold steering input is sensed, and often the speed of the watercraft is taken into consideration also. Based on these inputs, the prior art devices and systems either effect a re-application of throttle independently of the driver's or rider's use of the manual throttle control so that the jet drive generates steerable thrust, or a control system activates an elongated deceleration profile independently of the driver's or rider's use/non-use of the manual throttle control so as to slow the usual rate of throttle deceleration and thus slow the loss of steering thrust available via the jet drive.

A problem, therefore, with these known prior art devices and systems is that there is a lag between the device or system sensing a rapid off-throttle event (which is a necessary precursor and sensor input), and then subsequently determining the need for off-throttle or off-power steering. Typically, a threshold steering input is also required to be sensed before the device or system is turned on or implemented. What then follows is either a re-application of throttle, or a deceleration profile is turned on or implemented so as to slow the loss of steering thrust for a predetermined period of time. The resulting effect can provide for unusual and unsettling characteristics of the watercraft or amphibian, or the systems can provide unwanted thrust, particularly in the low speed docking/beaching assist systems. This has resulted in drivers and riders of the watercraft in question switching off entirely or removing the off-throttle or off-power steering and/or low speed docking/beaching assist devices and systems.

In view of the foregoing, there remains a need for a more simplified device and system which improves upon the performance of prior art devices and systems. The present invention seeks to address this, and does so by offering a fundamentally different proposal, that of a high idle engine speed system, providing watercraft and amphibians with enhanced steering, and that does so with an intuitive response. Unlike known prior art devices and systems which are off and must be turned on or activated when certain conditions are sensed/satisfied (and require a rapid off-throttle event to be sensed), the present invention is on by default when required, but can be turned off when certain conditions are sensed/satisfied. This fundamental difference provides watercraft and amphibians with enhanced steering when required, and does so with an intuitive response.

In a first aspect, the present invention provides a watercraft or amphibian comprising: a prime mover operable with at least a first and a second idle speed; a marine propulsion device operable to generate thrust when connected to the prime mover; a manually operated thrust contrDl device operable by a rider or driver of the watercraft or amphibian to manually control in amount the speed of the prime mover and thus thrust generated by the marine propulsion device; and a sensor/determining means for sensing/determining whether or not the s watercraft or amphibian is operating at or above a determined speed of travel, wherein: the second idle speed of the prime mover is higher than the first idle speed; the marine propulsion device generates an enhanced steerable thrust when operated by the prime mover at a speed at or above the second idle speed; and the prime mover is operated with the second idle speed when the sensor/determining means senses/determines the watercraft or amphibian is operating at or above the determined speed of travel such that the marine propulsion device provides an enhanced steerable thrust independently of the manually operated thrust control device.

In a second aspect, the present invention provides a method for providing enhanced steering for a watercraft or amphibian comprising: a prime mover operable with at least a first and a second idle speed, the second idle speed being higher than the first idle speed; a marine propulsion device operable to generate thrust when connected to the prime mover; a manually operated thrust control device operable by a rider or driver of the watercraft or amphibian to manually control in amount the speed of the prime mover and thus thrust generated by the marine propulsion device; and a sensor/determining means for sensing/determining whether or not the watercraft or amphibian is operating at or above a determined speed of travel, wherein the method comprises the steps of: the marine propulsion device generating an enhanced steerable thrust when operated by the prime mover at a speed at or above the second idle speed; and the prime mover operating with the second idle speed when the sensor/determining means senses/determines the watercraft or amphibian is operating at or above the determined speed of travel such that the marine propulsion device provides an enhanced steerable thrust independently of the £ manually operated thrust control device.

In a third aspect, the present invention provides a watercraft or amphibian operable in displacement and planing modes, the watercraft or amphibian comprising: a prime mover operable with at least a first and a second idle speed; a marine propulsion device operable to generate thrust when connected to the prime mover; a manually operated thrust control device operable by a rider or driver of the watercraft or amphibian to manually control in amount the speed of the prime mover and thus thrust generated by the marine propulsion device; and a planing sensor for sensing whether the watercraft or amphibian is in a planing or a displacement mode, wherein: the second idle speed of the prime mover is higher than the first idle speed; the marine propulsion device generates an enhanced steerable thrust when operated by the prime mover at a speed at or above the second idle speed; and the prime mover is operated with the second idle speed when the planing sensor senses the watercraft or amphibian is in a planing mode in order that the marine propulsion device provides an enhanced steerable thrust independently of the manually operated thrust control device.

In a fourth aspect the present invention provides a method for providing enhanced high speed steering for a watercraft or amphibian comprising: a prime mover operable with at least a first and a second idle speed, the second idle speed being higher than the first idle speed; a marine propulsion device operable to generate thrust when connected to the prime mover; a manually operated thrust control device operable by a rider or driver of the watercraft or amphibian to manually control in amount the speed of the prime mover and thus thrust generated by the marine propulsion device; and a planing sensor for sensing whether the watercraft or amphibian is in a planing or a displacement mode, wherein the method comprises the steps of: the marine propulsion device generating an enhanced steerable thrust when operated by the prime mover at a speed at or above the second idle speed; and the prime mover operates with the second idle speed when the planing sensor senses the watercraft or amphibian is in a planing mode in order that the marine propulsion device provides an enhanced steerable thrust independently of the manually operated thrust control device.

Preferred embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings, in which: Figure 1 is a schematic flow diagram of a first preferred embodiment of enhanced steering according to the present invention; Figure 2 is a schematic flow diagram of a further preferred embodiment of enhanced steering according to the present invention; and Figure 3 is a schematic flow diagram of a yet further preferred embodiment of enhanced steering according to the present invention.

The system, method and apparatus for enhanced steering according to the present invention provides a high idle engine speed when the watercraft or amphibian is operated in marine mode at or above a given speed of travel, which given speed of travel may be settable or programmable (and either fixed or dynamic in use), providing a "determined speed of travel". With the high idle engine speed active at or above the determined speed of travel, the engine always provides a steerable thrust via the jet drive since the engine speed cannot fall below a speed at which steerable thrust is no longer provided via the jet drive, even in the event of a rider or driver accidentally or intentionally letting go of the manually operated throttle. The enhanced steering is active and available when the watercraft or amphibian is travelling at or above the determined speed of travel in marine mode, e.g. travelling at high speed on water and steering is required. The high idle engine speed can, however, be switched off by a driver or rider, or the control system.

Referring first to Figure 1, there can be seen a schematic flow diagram illustrating an operating mode of a first preferred embodiment of enhanced steering according to the present invention for use in watercraft, amphibians and other such vehicles, in this first preferred embodiment, the prime mover (not shown) is a conventional spark ignition combustion engine having a normal" idle speed of approximately 1300 revolutions per minute (rpm), a "high" idle speed of approximately 4100 rpm, and can operate at approximately 8000 rpm at full is throttle. The throttle can be controlled manually by the rider or driver to operate the engine in the range from 1300 rpm to 8000 rpm. The system can, independently of the rider or driver, set a high idle speed such that the throttle cannot fall below the high idle speed, provided certain conditions are met, as will now be described by way of example only. The flow diagram illustrates a first step 100 of the sequence at "Start of Loop". Next, at step 120 "In Marine Mode?", the system determines either by way of sensing using a suitable sensor and/or by way of other suitable determination (e.g. mode selection) if the watercraft or amphibian is in a marine mode. If it is determined that the watercraft or amphibian is not in a marine mode, then the normal idle speed of 1300 rpm is operational, as shown at step 125 "Normal Idle Speed 1300 rpm", and the system returns to step 100 of the sequence at "Start of Loop".

Alternatively, if it is determined that the watercraft or amphibian is in a marine mode, then the system moves to the next step 130 Is Vehicle Planing (or at/above Determined Speed)?". Here, the system determines either by way of sensing using a suitable sensor (e.g. speed of travel sensor) and/or by way of other suitable determination if the watercraft or amphibian is at or above the determined speed of travel. In this first embodiment, the determined speed of travel is when the watercraft or amphibian is planing (although, as described above, the determined speed of travel may be set at any speed of travel lower or higher than a planing speed). Preferably, the sensor used is a water presence sensor and is positioned in the watercraft or amphibian such that it is substantially dry when planing, and wet when in a displacement condition. If it is determined that the watercraft or amphibian is not planing (water presence sensor is wet), then the normal idle speed of 1300 rpm is operational, as shown at step 135 "Normal Idle Speed 1300 rpm", and the system returns to step 100 of the sequence at "Start of Loop". Alternatively, if it is determined that the watercraft or amphibian is planing (water presence sensor is substantially dry), then the high idle speed of 4100 rpm is operational, as shown at step 150 "High Idle Speed 4100 rpm Active", and the system returns to step 100 of the sequence at "Start of Loop". With the high idle speed of 4100 rpm active when planing (or at/above the determined speed of travel) in the marine mode, the engine always is provides a steerable thrust in this state via the let drive since the engine speed cannot fall below a speed at which steerable thrust is no longer provided via the jet drive, even in the event of a rider or driver accidentally or intentionally letting go of the manually operated throttle. In short, the system is always default "on" when in marine mode, and is turned "off" when the speed of travel falls below the determined speed of travel.

The water sensor may take any suitable form, but in this first preferred embodiment is an optical sensor providing an electrical output signal based on refractive measurements. The electrical output signal from the water sensor is then processed to take account of the effects of splash and transients, e.g. when moving from wet to dry conditions and vice-versa. For example, the water sensor may determine a WET output if it is wet for more than a preset number of seconds W, where W is programmable. Alternatively, or in addition, an EWMA co-efficient may be used. Where the determined speed of travel is set lower than a speed where the watercraft or amphibian is planing, the electrical output signal from the water sensor may be processed differently to take account of the determined speed of travel to be measured. Alternatively, or in addition, other suitable sensors may be beneficially employed. For example, a paddle wheel speed sensor may be used to detect the speed of travel by measuring the water flow through vanes of the paddle wheel which acts to rotate the paddle wheel.

Alternatively, or additionally, a global positioning system (GPS) or a pressure sensing system (e.g. pitot tube, hull pressure sensor, or jet drive pressure sensor etc.) may be used.

The speed of the engine is effected by controlled opening of an air inlet valve, typically a butterfly valve, as is conventional in the art. Opening of the inlet air valve permits air to be admitted and mixed with fuel for combustion in one or more cylinders of the engine. The degree of opening of the air inlet valve controls the amount of air admitted for combustion, which in turn controls the resulting speed (rpm) of the engine. The air inlet valve or valves are actuated by the manually operated throttle control device and/or a solenoid actuator, both of which are mechanically coupled to the air inlet valve or valves. In the first preferred embodiment, the manually operated throttle control device takes the form of a manually operated lever, biased to a closed position, mounted on handlebars and which is mechanically coupled to the engine throttle via a pull cable. Opening of the throttle, thus increasing the engine speed, is effected by the rider or driver moving the lever against its bias and pulling the cable. In turn, the cable pulls open the throttle, opening the air inlet valve(s), thereby admitting more air for combustion. The speed of the engine is thus dependent upon the degree of actuation of the lever, subject to the position of the solenoid actuator (see below). The biasing action serves to return the lever, cable and throttle to a closed position, again subject to the position of the solenoid actuator, when the driver eases or releases the lever, ultimately back to idle (normal idle or high idle, as appropriate). In addition, a solenoid actuator is provided and is also mechanically coupled to the to the engine throttle. The stroke of the solenoid is sufficient to effect opening of the throttle to a desired position. The electronic control unit (ECU) provides a command signal to the solenoid, and when commanded, the solenoid holds open the throttle at the desired position. In this first preferred embodiment, the desired position (at full stroke) equates to the high -10 idle speed of 4100 rpm. Consequently, when commanded, the solenoid actuator provides a high idle speed of 4100 rpm, above which the manually operated throttle control device can function as normal, but below which the solenoid actuator takes precedence. Alternatively, when not commanded, the solenoid actuator is retracted (at zero stroke) and does not affect the usual low idle speed of 1300 rpm, above which the manually operated throttle control device can function as normal.

It will be appreciated, however, that in alternative embodiments, the speed of the prime mover may be controlled or throttled by way of any suitable control means. For example, where a combustion engine is used, throttling may be effected by way of control of air and/or fuel admission/injection, combustion timing, or any other suitable control (including ECU controlled) devices.

Alternatively, where an electric motor is used, the supply of current may be controlled, or any other suitable control (including ECU controlled) device employed.

Referring next to Figure 2, there can be seen a schematic flow diagram illustrating an operating mode of a further preferred embodiment of enhanced steering according to the present invention for use in watercraft, amphibians and other such vehicles. In this further preferred embodiment, the system functions as described above in relation to the first preferred embodiment, save for the introduction of an additional input, a manual over-ride button for the rider or driver to positively select the low idle speed to turn the system off. Accordingly, as before, the flow diagram illustrates a first step 200 of the sequence at "Start of Loop". Next, at step 220 "In Marine Mode?", the system again determines either by way of sensing using a suitable sensor and/or by way of other suitable determination (e.g. mode selection) if the watercraft or amphibian is in a marine mode. If it is determined that the watercraft or amphibian is not in a marine mode1 then the normal idle speed of 1300 rpm is operational, as shown at step 225 Normal Idle Speed 1300 rpm", and the system returns to step 200 of the sequence at "Start of Loop". Alternatively, if it is determined that the watercraft or -11 -amphibian is in a marine mode, then the system moves to the next step 230 "Is Vehicle Planing (or at/above Determined Speed)?". Here, the system determines either by way of sensing using a suitable sensor (eg. speed of travel sensor) and/or by way of other suitable determination if the watercraft or amphibian is s planing. While, again, the determined speed of travel is when the watercraft or amphibian is planing, as described above the determined speed of travel may be set at any speed of travel lower (or higher) than a planing speed. Preferably, the sensor used is a water presence sensor and is positioned in the watercraft or amphibian such that it is substantially dry when planing, and wet when in a displacement condition. If it is determined that the waterciaft or amphibian is not planing (water presence sensor is wet), then the normal idle speed of 1300 rpm is operational, as shown at step 235 Normal Idle Speed 1300 rpm", and the system returns to step 200 of the sequence at Start of Loop". Alternatively, if it is determined that the watercraft or amphibian is planing (water presence sensor is substantially dry), then the system moves to the next step 240 "Did Rider Over-ride High Idle?". Here, the system determines by way of sensing using a suitable sensor if the over-ride button or switch has been operated while the watercraft or amphibian is planing. Preferably, the sensor used is a prominent button or switch and is positioned in the watercraft or amphibian such that it provides ease of access to a rider or driver. If it is determined that a high idle speed is not desired by the rider or driver (button or switch activated when at/above determined speed of travel), then the normal idle speed of 1300 rpm is operational, as shown at step 245 "Normal Idle Speed 1300 rpm", and the system returns to step 200 of the sequence at "Start of Loop". Alternatively, if it is determined that a low idle speed is not desired by the rider or driver (button or switch not activated when at/above determined speed of travel), then the high idle speed of 4100 rpm is operational, as shown at step 250 "High Idle Speed 4100 rpm Active", and the system returns to step 200 of the sequence at "Start of Loop". With the high idle speed of 4100 rpm active when planing (or at/above the determined speed of travel) in the marine mode and not over-ridden, the engine always provides a steerable thrust in this state via the jet drive since the engine speed cannot fall below a speed at which steerable thrust is no longer provided via the jet drive, -12 -even in the event of a rider or driver accidentally or intentionally letting go of the manually operated throttle. In short, the system is default on" when in marine mode, and is turned "off' when the speed of travel falls below the determined speed of travel and/or the rider or driver turns it off using the button or switch.

Referring next to Figure 3, there can be seen a schematic flow diagram illustrating an operating mode of a yet further preferred embodiment of enhanced steering according to the present invention for use in watercraft, amphibians and other such vehicles. In this preferred embodiment, the system functions as described above in relation to the further preferred embodiment of Figure 2, save for the substitution of the manual over-ride button or switch with an alternative method of switching the system off, namely a steering request/no request determination, for the rider or driver to positively select the low idle speed by turning the system off. Accordingly, as before, the flow diagram illustrates a first is step 300 of the sequence at "Start of Loop". Next, at step 320 "In Marine Mode?", the system again determines either by way of sensing using a suitable sensor and/or by way of other suitable determination (e.g. mode selection) if the watercraft or amphibian is in a marine mode. If it is determined that the watercraft or amphibian is not in a marine mode, then the normal idle speed of 1300 rpm is operational, as shown at step 325 "Normal Idle Speed 1300 rpm", and the system returns to step 300 of the sequence at Start of Loop".

Alternatively, if it is determined that the watercraft or amphibian is in a marine mode, then the system moves to the next step 330 "Is Vehicle Planing (or at/above Determined Speed)?". Here, the system determines either by way of sensing using a suitable sensor (e.g. speed of travel sensor) and/or by way of other suitable determination if the watercraft or amphibian is planing. While, again, the determined speed of travel is when the watercraft or amphibian is planing, as described above the determined speed of travel may be set at any speed of travel lower (or higher) than a planing speed. Preferably, the sensor used is a water presence sensor and is positioned in the watercraft or amphibian such that it is substantially dry when planing, and wet when in a displacement condition. If it is determined that the watercratt or amphibian is not planing (water 13 -presence sensor is wet), then the normal idle speed of 1300 rpm is operational, as shown at step 335 "Normal Idle Speed 1300 rpm", and the system returns to step 300 of the sequence at "Start of Loop". Alternatively, if it is determined that the watercraft or amphibian is planing (water presence sensor is substantially dry), then the system moves to the next step 340 "Does Rider Request Steering".

Here, the system determines by way of sensing using a suitable sensor if the steering nozzle or handlebars have been moved to a substantially "straight ahead" position from a "steering desired" position when the watercraft or amphibian is planing. Preferably, the sensor used is a rheostat and is positioned in the watercraft or amphibian such that it provides a variable electrical output dependent upon the degree of steering (from zero to full lock in both the left and right hand directions). If it is determined that the watercraft or amphibian is not desired to be steered (rheostat output signal), then the normal idle speed of 1300 rpm is operational, as shown at step 345 "Normal Idle Speed 1300 rpm", and the is system returns to step 300 of the sequence at "Start of Loop". As such, the rider or driver can turn the system off when no steering is desired by moving the steering nozzle or handlebars to a substantially "straight ahead" position.

Alternatively, if it is determined that the watercraft or amphibian is desired to be steered (rheostat output signal), then the high idle speed of 4100 rpm is operational, as shown at step 350 "High Idle Speed 4100 rpm Active", and the system returns to step 300 of the sequence at "Start of Loop". With the high idle speed of 4100 rpm active when planing (or at/above the determined speed of travel) in the marine mode and when steering is desired, the engine always provides a steerable thrust in this state via the jet drive since the engine speed cannot fall below a speed at which steerable thrust is no longer provided via the jet drive, even in the event of a rider or driver accidentally or intentionally letting go of the manually operated throttle. In short, the system is default "on" when in marine mode, and is turned "off" when the speed of travel falls below the determined speed of travel and/or the rider or driver sets the steering straight ahead.

-14 -In the preferred embodiments described, the high idle engine speed is provided under the control of the ECU based on determining the necessary sensor inputs. It will be appreciated, however, that the various sensors described may take any suitable form (by way of supplementation and/or substitution), provided they serve to sense and provide the necessary inputs required for the ECU to make a determination. For example, the water sensor may take the form of a global positioning system (GAS) for use in determining if the watercraft or amphibian is operating at/above the determined speed of travel. Alternatively, the GAS may be provided in addition as a backup. Further, a pressure sensor or sensor array in the jet drive may be used in place of, or in addition to, these to determine if the watercraft or amphibian is is operating at/above the determined speed of travel. In such a case, the pressure sensor or sensors may be calibrated to detect pressure thresholds above which a determination can be made on whether the watercraft or amphibian is operating at/above the determined speed of travel (e.g. planing) or not. Indeed, it will appreciated that calibration of any of the sensors employed, and the use of signal processing techniques, may be beneficially employed to optimise the system implemented in a particular watercraft or amphibian. For example, in the preferred embodiment of Figure 3 which additionally senses that steering is desired, this may require sensing that the steering angle of the steering nozzle or handlebar is turned beyond an absolute steering threshold (which is adjustable/programmmable) of typically greater than, say, 5, 10, 15 or 20 degrees in either direction from the straight ahead position (0 degrees), where the total steering angle range is, say, -25 to +25 degrees. However, alternative methods of processing the desire for steering exist, such as measuring the acceleration of the steering nozzle or handlebars when turned, and using algorithms or variations thereof. In scenarios where electrical interference may be a threat to the reliability of the sensors used, or the sensed signals, mechanical means may be employed in addition to, or in place of, electrical means. For example, a paddle wheel speed sensor may be used to detect whether or not the watercraft or amphibian is operating at/above the determined speed of travel. Similarly, mechanical switches may be -15 -positioned in close proximity on either side of the steering nozzle so as to be activated by a turned steering nozzle to detect a desired steering input.

A further refinement, which provides for additional calibration of the S system, is to employ programmable timers (or delays) for the various functions or for sensing of the sensed parameters. For example, if a rider or driver lets go of the manually operable throttle control and effects a steering action, in certain scenarios it may prove useful for the high idle speed to be active only for a determined amount of time, e.g. ito 3 seconds, sufficient to make the desired manoeuvre before coming down off the plane and slowing to a halt. Similarly, the transition from planing to displacement mode, and vice versa, can take some seconds (depending upon whether the watercraff or amphibian is being turned -more resistance, quicker to stow -or travelling straight ahead), and so this can also be relevant in terms of the time it takes for a dry water sensor (planing) to is detect water (displacement), and this can be taken advantage of in terms of how the system is calibrated.

It will be appreciated that while the prime mover has been described as a spark ignition internal combustion engine, drive (power) to the jet drive may be provided by any one or more suitable power sources in any combination such as, for example without limitation, a compression ignition engine, an electric motor, a hydraulic motor, a hybrid engine or a jet engine. It will also be appreciated that the figures of i300 rpm, 4i00 rpm and 8000 rpm described above for low idle engine speed, high idle engine speed and maximum engine speed are typical only and not fixed. Indeed, each, some or all may be varied to suit and optimise the particular configuration of prime move and jet drive used. As such, all engine speeds are indicative only.

Furthermore, in the foregoing description, reference has been made to a watercraft and an amphibian, and this is intended to include also within its scope, without limitation, vehicles with all-terrain and amphibious capability, personal watercraft, boats and the like.

-16 -The known limitation of reduced (or total lack of) steering function in marine propulsion systems when a manually operated throttle is set to low or idle, or let go and biased towards idle, regardless of a steering request via the steering device, is not limited to jet drives. It is also experienced to one degree or another with propeller, z-drive, outboard motor and other marine propulsion systems. In these marine propulsion systems, however, an appendage, typically a rudder or fin, is usually provided in the water at all speeds to provide some degree of steerage. Nevertheless, the present invention can also be beneficially employed in watercraft or amphibians provided with these marine propulsion systems.

Although different embodiments of enhanced steering according to the present invention have been described above, any one or more or all of the features described (and/or claimed in the appended claims) may be provided in isolation or in various combinations in any of the embodiments. As such, any one or more these features may be removed, substituted and/or added to any of the feature combinations described and/or claimed. For the avoidance of doubt, any of the features of any embodiment may be combined with any other feature from any of the embodiments.

Accordingly, whilst preferred embodiments of the present invention have been described above and illustrated in the drawings, these are by way of example only and non-limiting. It will be appreciated by those skilled in the art that many alternatives are possible within the ambit, spirit and scope of the invention, as set out in the appended claims.

Claims

-17 -CLAIMS1. A watercraft or amphibian comprising: a prime mover operable with at least a first and a second idle speed; a marine propulsion device operable to generate thrust when connected to the prime mover; a manually operated thrust control device operable by a rider or driver of the watercraft or amphibian to manually control in amount the speed of the prime mover and thus thrust generated by the marine propulsion device; and a sensor/determining means for sensing/determining whether or not the watercraft or amphibian is operating at or above a determined speed of travel, wherein: the second idle speed of the prime mover is higher than the first idle speed; the marine propulsion device generates a steerable thrust when operated by the prime mover at a speed at or above the second idle speed; and the prime mover is operated with the second idle speed when the sensor/determining means senses/determines the watercraft or amphibian is operating at or above the determined speed of travel such that the marine propulsion device provides a steerable thrust independently of the manually operated thrust control device.
2. A watercraft or amphibian as claimed in claim 1 wherein the prime mover is an internal combustion engine.
3. A watercraft or amphibian as claimed in claim 1 or claim 2 wherein the marine propulsion device is at least one jet drive.
4. A watercraft or amphibian as claimed in any one of the preceding claims wherein the sensor/determining means comprises any one or more of a water sensor, a global positioning system, a paddle wheel sensor, and/or a pressure sensor.

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5. A watercraft or amphibian as claimed in any one of the preceding claims wherein the determined speed of travel is either fixed or variable, and when variable is set or programmed in use.
6. A watercraft or amphibian as claimed in any one of the preceding claims wherein the determined speed of travel is a planing speed of the watercraft or amphibian.
7. A watercraft or amphibian as claimed in any one of the preceding claims, the watercraft or amphibian further comprising a manual over-ride operable by the rider of driver, wherein the prime mover is operated with the second idle speed when the sensor/determining means senses/determines the watercraft or amphibian is operating at or above the determined speed of travel and the manual over-ride has not subsequently been operated by the rider of driver.
8. A watercraft or amphibian as claimed in claim 7, wherein the manual over-ride operable by the rider of driver is a switch or button.
9. Awatercraft or amphibian as claimed in claim 7 or claim 8, wherein the manual over-ride operable by the rider of driver is or further comprises a steering device.
10. A watercraft or amphibian as claimed in any one of the preceding claims, the watercraft or amphibian further comprising a steering sensor for sensing whether or not steering is desired, wherein the prime mover is operated with the second idle speed when the sensor/determining means senses/determines the watercraff or amphibian is operating at or above the determined speed of travel and the steering sensor senses that steering is desired.
11. A watercraft or amphibian as claimed in any one of the preceding claims, the watercraft or amphibian further comprising means for determining if the -19 watercraft or amphibian is operating in a marine mode, and whereinthe prime mover is operated with the second idle speed when it is determined that the watercraft or amphibian is in a marine mode and the sensor/determining means senses/determines the watercraft or amphibian is operating at or above the s determined speed of travel.
12. A watercraft or amphibian as claimed in any one of the preceding claims, wherein the prime mover is operated with the first idle speed when not operated with the second idle speed.
13. A watercraft or amphibian as claimed in any one of the preceding claims, wherein the operation of the prime mover with the second idle speed is time limited, following which the prime mover is operated with the first idle speed.
14. A watercraft or amphibian as claimed in any one of claims 10 to 13, wherein the steering sensor determines if steering is desired via movement of a steering nozzle.
15. A watercraft or amphibian as claimed in any one of the preceding claims, wherein the first idle speed of the prime mover is in the range of 0 to 1499 rpm and the second idle speed of the prime mover is in the range of 1500 to 8000 rpm.
16. A watercraft or amphibian as claimed in any one of the preceding claims, wherein the first idle speed of the prime mover is in the range of 0 to 1300 rpm and the second idle speed of the prime mover is in the range of 1400 to 8000 rpm.
17. A watercraft or amphibian as claimed in any one of the preceding claims, wherein the first idle speed of the prime mover is substantially 1300 rpm and the second idle speed of the prime mover is substantially 4100 rpm.

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18. A watercraft or amphibian as claimed in any one of the preceding claims, the watercraft or amphibian further comprising an idle actuator operable to control whether the primer mover operates with the first or the second idle speed.
19. A watercraft or amphibian as claimed in any one of the preceding claims, the watercraft or amphibian further comprising an electronic control unit and wherein the electronic control unit controls/determines whether the prime mover is operated with the second idle speed or the first idle speed.
20. A method for providing enhanced steering for a watercraft or amphibian comprising: a prime mover operable with at least a first and a second idle speed, the second idle speed being higher than the first idle speed; a marine propulsion device operable to generate thrust when connected to is the prime mover; a manually operated thrust control device operable by a rider or driver of the watercraft or amphibian to manually control in amount the speed of the prime mover and thus thrust generated by the marine propulsion device; and a sensor/determining means for sensing/determining whether or not the watercraft or amphibian is operating at or above a determined speed of travel, wherein the method comprises the steps of: the marine propulsion device generating a steerable thrust when operated by the prime mover at a speed at or above the second idle speed; and the prime mover operating with the second idle speed when the sensor/determining means senses/determines the watercraft or amphibian is operating at or above the determined speed of travel such that the marine propulsion device provides a steerable thrust independently of the manually operated thrust control device.
21. Awatercraft or amphibian operable in displacement and planing modes, the watercraft or amphibian comprising: a prime mover operable with at least a first and a second idle speed; -21 -a marine propulsion device operable to generate thrust when connected to the prime mover; a manually operated thrust control device operable by a rider or driver of the watercraft or amphibian to manually control in amount the speed of the prime mover and thus thrust generated by the marine propulsion device; and a planing sensor for sensing whether the watercraft or amphibian is in a planing or a displacement mode, wherein: the second idle speed of the prime mover is higher than the first idle speed; the marine propulsion device generates a steerable thrust when operated by the prime mover at a speed at or above the second idle speed; and the prime mover is operated with the second idle speed when the planing sensor senses the watercraft or amphibian is in a planing mode in order that the marine propulsion device provides a steerable thrust independently of the manually operated thrust control device.
22. A method for providing enhanced high speed steering for a watercraft or amphibian comprising: a prime mover operable with at least a first and a second idle speed, the second idle speed being higher than the first idle speed; a marine propulsion device operable to generate thrust when connected to the prime mover; a manually operated thrust control device operable by a rider or driver of the watercraft or amphibian to manually control in amount the speed of the prime mover and thus thrust generated by the marine propulsion device; and a planing sensor for sensing whether the watercraft or amphibian is in a planing or a displacement mode, wherein the method comprises the steps of: the marine propulsion device generating a steerable thrust when operated by the prime mover at a speed at or above the second idle speed; and the prime mover operates with the second idle speed when the planing sensor senses the watercraft or amphibian is in a planing mode in order that the -22 -marine propulsion device provides a steerable thrust independently of the manually operated thrust control device.
23. A watercraft or amphibian substantially as hereinbefore described with reference to or as shown in the accompanying drawings.
24. A method for providing enhanced high speed steering for a watercraft or amphibian substantially as hereinbefore described with reference to or as shown in the accompanying drawings.