Abstract:
An automatic speed control system that provides desired watercraft velocity over land. The coupled algorithms correct engine speed and torque using GPS and tachometer measurements, and the corrections are augmented and enhanced by velocity/speed and torque/speed relationships that are dynamically and adaptively programmed with real-time data collected during replicated operations of the watercraft in specified conditions.

Description:
[0001]     This patent claims priority from and incorporates by reference U.S. Patent Application Ser. No. 60/543,610, Filed Feb. 11, 2004. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention pertains to the field of watersports and boating.  
       BACKGROUND OF THE INVENTION  
       [0003]     Competitors in trick, jump, and slalom ski and wakeboard events require tow boats capable of consistent and accurate speed control. Intricate freestyle tricks, jumps, and successful completion of slalom runs require passes through a competition water course at precisely the same speed at which the events were practiced by the competitors. Some events require that a pass through a course be made at a specified speed. Such requirements are made difficult by the fact that typical watercraft Pitot tube and paddle wheel speedometers are inaccurate and measure speed over water instead of speed over land, and wind, wave, and skier loading conditions constantly vary throughout a competition pass.  
         [0004]     Marine transportation in general suffers from the lack of accurate vessel speed control. The schedules of ocean-going vessels for which exact arrival times are required, for example, are vulnerable to the vagaries of wind, waves, and changing hull displacement due to fuel depletion.  
       SUMMARY OF THE INVENTION  
       [0005]     The present invention provides consistent, accurate control of watercraft speed over land. It utilizes Global Positioning Satellite technology to precisely monitor watercraft velocity over land. It utilizes dynamic monitoring and dynamic updating of engine control data in order to be responsive to real-time conditions such as wind, waves, and loading.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]      FIG. 1  is a flow diagram of the preferred embodiment of the present invention.  
         [0007]      FIG. 2  is a flow chart of the steady state timer algorithm used in the preferred embodiment.  
         [0008]      FIG. 3  is a schematic of a watercraft utilizing the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0009]     The present invention is an electronic closed-loop feedback system that controls the actual angular velocity ω a  of a boat propeller, and, indirectly, the actual over land velocity v a  of the watercraft propelled by that propeller. The system has various configurations, but the preferred embodiment includes a global positioning satellite (GPS) velocity measurement device, a marine engine speed tachometer, four comparators, four conversion algorithms, and engine speed controls.  
         [0010]     Herein, a GPS device is one of the category of commonly understood instruments that use satellites to determine the substantially precise global position and velocity of an object. Such position and velocity measurements can be used in conjunction with timers to determine an object&#39;s instantaneous velocity and average velocity between two points. Engine speed refers to angular velocity, generally measured with a device herein referred to as a tachometer. A comparator is any analog or digital electrical, electronic, mechanical, hydraulic, or fluidic device capable of determining the sum of or difference between two input parameters, or the value of an input relative to a predetermined standard. An algorithm is any analog or digital electrical, electronic, mechanical, hydraulic, or fluidic device capable of performing a computational process. The algorithms disclosed herein can be performed on any number of devices commonly called microprocessors or microcontrollers, examples of which include the Motorola® MPC555 and the Texas Instruments® TMS320.  
         [0011]     As diagrammed in  FIG. 1  showing feedback system  100 , GPS device  10  measures the actual velocity v a  of a watercraft  50 . The GPS output v GPS  is compared in first comparator  12  to predetermined velocity v d . Comparator  12  output velocity error e v  is input to a first algorithm  14  that converts e v  to engine speed correction ω c  that is input to a second comparator  16 . Predetermined velocity v d  is input to a second algorithm  18  the output of which is ω adapt , a value of engine speed adaptively determined to be the engine speed necessary to propel watercraft  50  at predetermined velocity v d  under the prevailing conditions of wind, waves, and watercraft loading, trim angle, and attitude.  
         [0012]     The addition of engine speed correction ω c  and engine speed ω adapt  in comparator  16  results in the total desired engine speed ω d  that is input to a third comparator  20 . A sensor  24 , one of many types of commonly understood tachometers, detects the actual angular velocity ω a  of a driveshaft from an engine  53  of watercraft  50  and sends it to third comparator  20 . In third comparator  20  actual angular velocity ω a  and total desired engine speed ω d  are compared for engine speed error e ω  that is input to a third algorithm  26 . In the third algorithm  26  engine speed error e ω  is converted into engine torque correction τ c .  
         [0013]     Total desired engine speed ω d  is also input to a fourth algorithm  22  the output of which is τ adapt , a value of engine torque adaptively determined to be the engine torque necessary to operate watercraft engine  53  at total desired engine speed ω d . The addition of engine torque τ adapt  and engine torque correction τ c  in a fourth comparator  28  results in the calculated desired engine torque τ d . Calculated desired engine torque τ d  is input to controller  30  that drives a throttle control capable of producing in engine  53  a torque substantially equal to calculated desired engine torque τ d .  
         [0014]     The first and third algorithms  14  and  26 , respectively, could include any common or advanced control loop transfer function including, but not limited to, series, parallel, ideal, interacting, noninteracting, analog, classical, and Laplace types. For both the first and third algorithms  14  and  26  the preferred embodiment utilizes a simple proportional-integral-derivative (PID) algorithm of the following type (exemplified by the first algorithm  14  transfer function): 
 
ω c   =K   p   e   v   +K   d ( d/dt ) e   v   +∫K   i   e   v   dt.  
 
 Where K p , K d , and K i  are, respectively, the appropriate proportional, derivative, and integral gains. 
 
         [0015]     The second and fourth algorithms  18  and  22 , respectively, provide dynamically adaptive mapping between an input and an output. Such mapping can be described as self-modifying. The inputs to the second and fourth algorithms  18  and  22  are, respectively, predetermined velocity v d  and total desired engine speed ω d . The outputs of the second and fourth algorithms  18  and  22  are, respectively, engine speed ω adapt  and engine torque τ adapt . The self-modifying correlations of algorithms  18  and  22  may be programmed during replicated calibration operations of a watercraft through a range of velocities in a desired set of ambient conditions including, but not limited to, wind, waves, and watercraft loading, trim angle, and attitude. Data triplets of watercraft velocity, engine speed, and engine torque are monitored with GPS technology and other commonly understood devices and fed to algorithms  18  and  22  during the calibration operations. Thereafter, a substantially instantaneous estimate of the engine speed required to obtain a desired watercraft velocity and a substantially instantaneous estimate of the engine torque required to obtain a desired engine speed can be fed to the engine speed and torque control loops, even in the absence of watercraft velocity or engine speed departures from desired values, in which cases the outputs of algorithms  14  and  26  may be zero.  
         [0016]     In the preferred embodiment, no adaptive data point of watercraft velocity, engine speed, or engine torque described above is programmed into algorithms  18  or  22  until it has attained a steady state condition as diagrammed in  FIG. 2 . A timer compares watercraft velocity error e v , engine speed error e ω , the time rate of change of actual watercraft velocity v a , and the time rate of change of actual engine speed ω a  to predetermined tolerance values. When the absolute value of each variable is less than or equal to its predetermined tolerance, and the time elapsed since the beginning of a sample event is greater than or equal to a predetermined validation time, ω adapt  is updated according to 
 
ω adapt ( v   d )=ω adapt ( v   d )+ k   adapt [ω d ω adapt ( v   d )]Δ t   update  
 
 where k adapt  and Δt update  are factory-set parameters that together represent the speed at which the adaptive algorithms “learn” or develop a correlated data set. The last block on the  FIG. 2  flowchart represents a correction to speed control algorithm  14 . The correction may be used to smooth iterations that may be present if algorithm  14  uses integrator action. 
 
         [0017]     When engine speed error e ω  and the time rate of change of actual engine speed ω a  decrease to predetermined tolerance values, and the time elapsed since the beginning of a sample event is greater than or equal to a predetermined validation time, τ adapt  is updated according to 
 
τ adapt (ω d )=τ adapt (ω d )+ k   adapt [τ d −τ adapt (ω d )]Δ t   update . 
 
 This is the same updating equation that is used in algorithm  18 , and it is derived in the same manner as is illustrated in  FIG. 2 . The smoothing technique described above may be used to counter the effects of integrator action in algorithm  26 . 
 
         [0018]     The substantially instantaneous estimates of engine speed and torque derived from algorithms  18  and  22  require interpolation among the discrete values programmed during watercraft calibration operation. For practice of the present invention there are many acceptable interpolation schemes, including high-order and Lagrangian polynomials, but the preferred embodiment utilizes a linear interpolation scheme. For example, algorithm  18  employs linear interpolation to calculate a value of ω adapt  for any predetermined velocity v d . From a programmed table of v d  values from v 0  to v n , inclusive of v m , and ω adapt  values from ω 0  to ω n , inclusive of ω m , a value of m is chosen so that v d &gt;v m  and v d &lt;v m+1 . Algorithm  18  calculates intermediate values of engine speed according to the equation 
 
ω adapt =ω m +[( v   d   −v   m )/( v   m+1   −v   m )](ω m+1 −ω m ). 
 
 Although algorithm  22  could also utilize any of several interpolation schemes, and is not constrained to duplication of algorithm  18 , in the preferred embodiment of the present invention, algorithm  22  calculates τ adapt  using the same linear interpolation that algorithm  18  uses to calculate ω adapt . In order to implement adaptive update algorithm  18  when using a linearly interpolated table of values as the preferred interpolation embodiment, the following procedure can be followed: 
 
         [0019]     Compute a weighting factor x using the following equation: 
 
 x =[( v   d   −v   m )/( v   m+1   −v   m )]
 
         [0020]     Note that x is always a value between 0 and 1.  
         [0000]     Similar to algorithm of 18, update the two bracketing values ω m , ω m+1  in the linear table using the following equations: 
 
ω m =ω m +(1− x ) k   adapt [ω d −ω adapt   ]Δt   update  
 
ω m+1 =ω m+1 +( x ) k   adapt [ω d −ω adapt   ]Δt   update  
 
 The other values in the linear table remain unchanged for this particular update, and are only updated when they bracket the operating condition of the engine at some other time. This same procedure can be used on the engine speed vs. torque adaptive table. 
 
         [0021]     Although the preferred embodiment does not utilize extrapolation in its adaptive algorithms, the scope of the present invention could easily accommodate commonly understood extrapolation routines for extension of the algorithm  18  and algorithm  22  data sets.  
         [0022]     Adaptive algorithms  18  and  22  are not required for operation of the present invention, but they are incorporated into the preferred embodiment. Aided by commonly understood integrators, algorithms  14  and  26  are capable of ultimate control of a watercraft&#39;s velocity. However, the additional adaptive control provided by algorithms  18  and  22  enhances the overall transient response of system  100 .  
         [0023]     The following table is an example of the velocity vs. engine speed adaptive table as it might be initialized from the factory. This table is a simple linear table which starts at zero velocity and extends to the maximum velocity of the boat (60 kph) at which the maximum engine speed rating (6000 rpm) is also reached:  
                                                                 v d  (kph)   ω adapt  (rpm)                                        0   0           10   1000           20   2000           30   3000           40   4000           50   5000           60   6000                      
 
         [0024]     The following is an example of the velocity vs. engine speed adaptive after the boat has been driven for a period of time:  
                                                                 v d  (kph)   ω adapt  (rpm)                                        0   0           10   1080           20   1810           30   2752           40   3810           50   5000           60   6000                      
 
 Note that engine speed values correlating to boat speeds of 50 and 60 kph have not been modified from the original initial values. This is because the boat was never operated at these desired speeds during the period of operation between the present table and the initial installation of the controller. The following is a graphical representation of the data in the preceding tables: 
         
 
         [0025]     Controller  30  (see  FIG. 1 ) is the interface between calculated desired engine torque τ d  and the throttle control that causes the ultimate changes in engine speed. Controller  30  may interpose any number of relationships between calculated desired engine torque τ d  and engine speed, but the preferred embodiment of the present invention utilizes a direct proportionality. Other embodiments of the present invention could use controller  30  to adjust engine parameters other than throttle setting. Such parameters could include spark timing, fuel flow rate, or air flow rate. The preferred embodiment of the present invention contemplates a boat with a single speed transmission and a fixed pitch propeller. An alternate embodiment of the present invention could be used with boats having variable transmissions and/or variable pitch propellers. In these alternate embodiments, the controller  30  could adjust the transmission, pitch of the propeller, throttle setting, or a combination thereof.  
         [0026]      FIG. 3  illustrates how an operator of watercraft  50  controls the speed of engine  53  and propeller  51 . The operator supplies predetermined and desired velocity v d  through control keypad and display  59  to control module  65  that houses the algorithms and comparators of system  100 . GPS measurements from device  10  and predetermined velocity v d  values are sent to control module  65  via communications link  55 . Communication link  57  feeds engine speed measurements from a tachometer to control module  65 . System  100  may be overridden at any time through operator control of manual throttle control  61  that controls engine throttle  63 .  
         [0027]     It will be apparent to those with ordinary skill in the relevant art having the benefit of this disclosure that the present invention provides an apparatus for controlling the velocity of a watercraft. It is understood that the forms of the invention shown and described in the detailed description and the drawings are to be taken merely as presently preferred examples and that the invention is limited only by the language of the claims. The drawings and detailed description presented herein are not intended to limit the invention to the particular embodiments disclosed. While the present invention has been described in terms of one preferred embodiment and a few variations thereof, it will be apparent to those skilled in the art that form and detail modifications can be made to that embodiment without departing from the spirit or scope of the invention.