Abstract:
An automated gear selection apparatus for a gearbox having a linear gear selector is provided. The apparatus includes an actuator having a shaft displaceable between at least two predetermined positions corresponding to positions of the gear selector. A control means communicates with the actuator to control displacement of the shaft. The shaft is connectable to the gear selector, by means of a cable, for displacing the selector between gear selection positions. A quick release assembly secures the cable to the shaft and includes a manual operation handle. The apparatus also includes a user interface means operatively connected to the control means so that a user can selectively cause operation of the actuator and thus the gear selector. The apparatus provides a convenient and automated means for gear selection.

Description:
FIELD OF THE INVENTION  
         [0001]    This invention relates to an automated gear selection apparatus.  
         BACKGROUND TO THE INVENTION  
         [0002]    In this specification, the invention will be described with reference to gearboxes having a linear gear shifting mechanism as are commonly found in marine craft for example. Such gearboxes have a gear selector that moves linearly to select between two or more gears, such as a forward gear, a neutral gear and a reverse gear.  
           [0003]    Linear gearboxes are typically operated by means of a manually operable lever or “gearstick” that is usually coupled to the gearbox&#39;s shifting mechanism by means of a gear selector cable. In use, the lever is pushed forward to engage the forward gear, drawn into an intermediate position to engage the neutral gear and drawn fully backwards to engage a reverse gear. There are a number of disadvantages with such an arrangement.  
           [0004]    A first disadvantage is that considerable strength may be required to operate the lever. Consequently, gear changing may be awkward or clumsy, particularly for those who are unfamiliar with controlling marine craft or do not have muscular strength.  
           [0005]    A second disadvantage is that accidental shifting of the lever may have disastrous consequences. For example, inadvertently falling on or striking the gearstick will cause the craft to accelerate or decelerate in an uncontrolled and hazardous manner. Alternatively, in a recreational marine craft, a child may pull or push on the lever. Those who have had experience with boating will realize that such an event can be particularly dangerous. At present mechanical lockout mechanisms are known for preventing the inadvertent operation of the gearstick. However, mechanical lockout mechanisms are typically inconvenient and time-consuming to use.  
           [0006]    It is an object of the present invention to provide a convenient and easy to use mechanism for operating a linear gear selector and to address the disadvantages described above.  
         SUMMARY OF THE INVENTION  
         [0007]    According to the present invention there is provided an automated gear selection apparatus for a gearbox of a drive unit, the gearbox having a linear gear selector that is displaceable between at least a first position and a second position, the gear selection apparatus including:  
           [0008]    an actuator including an actuator member displaceable between at least two predetermined positions corresponding to the positions of the linear gear selector;  
           [0009]    a control means in communication with the actuator to control displacement of the actuator member, the actuator member being connectable to the gear selector for displacing said selector between at least the first and second positions; and  
           [0010]    a user interface means operatively connected to the control means so that a user can selectively cause operation of the actuator and thus the gear selector.  
           [0011]    A cable securing assembly may be attached to the actuator member for engaging a gear selector cable. Preferably the actuator member comprises a shaft that is extendible and retractable relative to a housing of the actuator. Alternatively the member may comprise a rotatable reel about which the gear selection cable may be wound.  
           [0012]    The cable securing assembly may be attached to the shaft by means of a quick release member. The cable securing assembly preferably includes a handle for manual gear selection.  
           [0013]    In a preferred embodiment the control means is configured to monitor user selection of a desired gear and in response bring the shaft to a position for selection of the desired gear. Furthermore, it is desirable that the control means is further configured to monitor the position of the shaft.  
           [0014]    Typically the control means includes a micro-controller which operates according to firmware including:  
           [0015]    instructions for monitoring signals from the user interface means;  
           [0016]    instructions for bringing the shaft towards a setpoint corresponding to a signal from the user interface means, the setpoint corresponding to selection of a gear by the linear gear selector.  
           [0017]    The firmware may further include instructions for monitoring a feedback signal indicating position of the shaft. In a preferred embodiment the feedback signal is generated by circuitry including a potentiometer coupled to the shaft.  
           [0018]    In a preferred embodiment the microcontroller further includes instructions for user entry of setpoints comprising actuator states corresponding to a particular gear selections.  
           [0019]    The controller may monitor a signal indicating engine revolution rate and wherein the firmware further includes instructions for determining whether or not to bring the shaft towards a setpoint on the basis of predetermined engine revolution rates.  
           [0020]    Preferably the firmware further includes instructions for user entry of the predetermined engine revolution rates. The signal indicating engine revolution rate will typically comprise a signal from an engine ignition system of the engine. However, particularly in relation to diesel engines, the signal indicating engine revolution rate may be generated by a magnetic sensor fixed relative to a magnet attached to a rotating member of the engine.  
           [0021]    The instructions for bringing the shaft towards a setpoint will preferably include:  
           [0022]    instructions for monitoring the position of the shaft;  
           [0023]    instructions for comparing the position of the shaft to a current setpoint;  
           [0024]    instructions for moving the shaft towards the setpoint at a speed that is dependent on the deviation of the position of the shaft from the setpoint in order to reduce overshoot.  
           [0025]    The user interface typically comprises a console including user data input and output means.  
           [0026]    Preferably the user interface means includes a micro-controller arranged to communicate with a micro-controller located in the control means.  
           [0027]    The interface means may include a switch means or key that is connected to the control means to provide the control means with command signals relating to a gear selected by a user. The switch means may include a console that is readily accessible by a user. The console may incorporate a number of momentary press switches or keys. Each key may correspond with one respective predetermined position of the gear selector. A discernible signal means may be provided in the control means. The discernible signal means may be in the form of a number of LED&#39;s (light emitting diodes) that correspond with respective gears.  
           [0028]    The LED&#39;s may be connected to the micro-controller to indicate to a user whether or not a particular gear has been selected.  
           [0029]    According to a further aspect of the present invention there is provided an automated gear selection apparatus for a gearbox of a drive unit, the gearbox having a linear gear selector displaceable between at least a first position and a second position, said gear selection apparatus including:  
           [0030]    an actuator means for displacing the linear gear selector between the at least a first position a second position;  
           [0031]    cable securing means releasably attached to the actuator means for securing a gear selector cable and including a handle for manual operation;  
           [0032]    control means in communication with the actuator means for controlling the actuator means; and  
           [0033]    user interface means in communication with the control means for receiving gear selections from a user.  
           [0034]    According to a final aspect of the present invention there is provided an automated gear selection apparatus for a gearbox of a drive unit, the gearbox having a linear gear selector displaceable between at least a first position and a second position, said gear selection apparatus including:  
           [0035]    a linear actuator including a movable shaft displaceable between at least two predetermined positions corresponding to at least the first position and the second position of the linear gear selector;  
           [0036]    a controller coupled to the actuator to control displacement of the shaft;  
           [0037]    a cable securing assembly attached to an end of the shaft by means of a quick release member;  
           [0038]    a user interface connected to the controller for user selection of a position of the linear gear selector.  
           [0039]    The invention is now described, by way of example, with reference to the accompanying drawings. The following description is for the purpose of illustrating an embodiment of the invention to a person of ordinary skill in the field. As such, the specific nature of the following description is not to be construed as limiting the scope of the invention described in the appended claims. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0040]    [0040]FIG. 1 is a block diagram of an automated gear selection apparatus according to a preferred embodiment of the invention.  
         [0041]    [0041]FIG. 2 is a perspective view of a linear actuator, control unit and user console according to a preferred embodiment of the invention.  
         [0042]    [0042]FIG. 3 is a side view of the linear actuator of the automated gear selection apparatus when connected to a gear selector cable.  
         [0043]    [0043]FIG. 4 is schematic diagram of circuitry located within the console of the automated gear selection apparatus of FIG. 1.  
         [0044]    [0044]FIG. 5 is a schematic diagram of circuitry located within a control unit of the automated gear selection apparatus of FIG. 1.  
         [0045]    [0045]FIG. 6 is a flow chart of the firmware run by the console of the automated gear selection apparatus of FIG. 1.  
         [0046]    [0046]FIG. 7 is a flow chart of the firmware run by the control unit of the automated gear selection apparatus of FIG. 1. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0047]    [0047]FIG. 1 is a block diagram of an automated gear selection apparatus (AGSA) according to a preferred embodiment of the present invention. The AGSA includes a console  34  which is bi-directionally connected by means of electrical cable  36  to a control unit  22 . Control unit  22  is bi-directionally connected, by electrical cable  28 , to an actuator  10  that is mechanically coupled to a linear gearbox  9  by a gear selector cable  37 . Where the AGSA is installed in a marine craft, power supply  1  comprises a 12-Volt battery and power supply of the craft. The power supply is coupled to control unit  22  by electrical cable  30 . Control unit  22  distributes power by means of electrical cables  36  and  28  to console  34  and actuator  10  respectively. A number of optional modules may also be included and connections to these are shown with dashed lines in FIG. 1. For example, expansion modules in the form of auxiliary actuators  5  and sensors  7  may be connected to control unit  22  and console  34 . Similarly expansion modules in the form of auxiliary sensors  7  may be connected to control unit  22 . The auxiliary actuators and sensors may be concerned with the operation and monitoring of the marine craft&#39;s throttle for example. Micro-controller chips are located in console  34  and control unit  22  and may be conveniently programmed by means of an external In-Circuit Serial Programming Device (ICSPD)  11 .  
         [0048]    Referring now to FIG. 2, there is depicted a perspective view of console  34 , control unit  22  and linear actuator  10  prior to their installation. Console  34  has a panel bearing three gear selection keys in the form of momentary membrane press keys  38 A- 38 C. These comprise a forward key  38 A, a neutral key  38 B and a reverse key  38 C. Adjacent each key  38 A- 38 C is a light emitting diode (LED)  56 A- 56 C respectively. Console  34  further includes a buzzer  58 .  
         [0049]    Control unit  22  is encased by a watertight housing  24  which includes lugs  32  for mounting to a suitable surface of a marine craft.  
         [0050]    Linear actuator  10  includes a housing  12  from which protrudes a displaceable shaft  14 . The shaft has a 6-inch (152 mm) stroke. An assembly  63 , for securing the free end of gear selection cable  37  is located at the free end of shaft  14 .  
         [0051]    [0051]FIG. 3 is a plan view, of linear actuator  10  with cable  37  attached. Housing  12  of actuator  10  is secured to the marine craft by means of bracket  33  and bolts  49 . A flange  53  extends from bracket  33 . Flange  53  has a bore through which cable  37  is received. Cable  37  is covered by a sheath  51  that is of too large a diameter to pass through the bore in flange  53 . Cable  37  is secured to shaft  14  via adjustment assembly  64 . Assembly  64  includes a cable receiving sleeve  67  in which cable  37  is secured by tightening retaining screw  61 . The adjustment assembly is releasably coupled to the free end of shaft  14  by means of a quick release means in the form of quick release member comprising ball-lock pin  55  that passes through an aperture at the end of shaft  14 .  
         [0052]    Linear actuator  10  is a commercially available model being a Warner Linear Electrak® E050. Internally, linear actuator  10  includes a reversible 12V electric motor. The motor is connected to shaft  14  via a suitable gear assembly. Linear actuator  10  further includes a potentiometer that is mechanically coupled to shaft  14 . Control unit  24  is able to determine the position of the shaft by monitoring the voltage of the centre tap of the potentiometer.  
         [0053]    In normal use an operator of the AGSA depresses one of the keys  38 A- 38 C on console  34 . In response, internal circuitry in console  34 , which will be described shortly, generates various signals that are conveyed to control unit  22  by means of cable  36 . The console circuitry may also light one or more of indicators  56 A- 56 C and/or activate buzzer  58  to provide feedback to the operator. Control unit  22  processes the signals from console  34  by means of internal circuitry that will be described shortly. The internal circuitry in control unit  22  generates driver currents that precisely drive the motor in linear actuator  10  in order that shaft  14  is extended or retracted. Consequently gear selector cable  37  is brought to a position corresponding to the key that was depressed. For example if key  38 A, being the “forward” key, is depressed then ultimately shaft  14  is brought to a position that causes a gear train to which it is coupled by gear selector cable  37  to select a forward gear. Alternatively, if key  38 B or  38 C is depressed then shaft  14  will be brought to a position that will cause a neutral or reverse gear position respectively to be selected. The AGSA may also be operated in a calibration mode wherein suitable shaft positions, to correspond to depression of each of the forward, neutral and reverse keys,  38 A- 38 C may be entered.  
         [0054]    Console Unit Circuit Description  
         [0055]    Referring now to FIG. 4, there is provided a schematic diagram of circuitry that is located inside console  34 .  
         [0056]    Power Supply—Power is applied via CONN 1 , which is remotely fused via the controller device (CONN 9 ). A low-pass filter (realized using R 1  and Cl) is used to reduce the effects of high frequency noise (3 dB point at 165 Hz) on the 12V supply. Diode Dl also acts to protect the device from reverse polarity connections and negative electrical spikes. Zener diode D 2  is used to protect the 5V regulator IC 1  from overvoltages of greater than  30 V. Voltage regulator IC 1  converts the conditioned 12V supply to 5V. The 5V supply produced on the output (pin  3 ) of IC 1  is stabilised via C 2  and noise is further reduced via C 3 . R 4  biases pass transistor Q 2  on under normal operating conditions. The output of IC 1  is a stabilized 5V supply that powers the micro-controller (IC 2 ), support circuitry and peripheral devices.  
         [0057]    Micro-controller and Support Circuitry—IC 2  is a general-purpose micro-controller PIC16F876 from Microchip Corporation, that operates according to inboard firmware in order to process operator commands entered via keys  38 A- 38 C. IC 2  also operates LEDS  56 A- 56 C, and exchanges data signals with control unit  22 . IC 2  receives its power supply (5V) into pin  20  and is ground referenced via pins  19  and  8 . Pin  1  of IC 2  is the !MCLR input, used to enable IC 2  or reset it under certain circumstances. It is also used as a programming voltage input when used in In-Circuit Serial Programming (ICSP) mode. Accordingly IC 2  may be programmed in-circuit by connecting an external ICSP device. Crystal X 1  sets IC 2 &#39;s internal oscillator frequency to 16 MHz. Capacitors C 4  and C 5  stabilize X 1 . R 2  is used to help limit the likelihood of input spikes causing IC 2  latch-up. D 3  enables IC 2  by applying over 2.5V to the !MCLR input. D 3  also prevents the ICSP device from placing a high voltage level onto the rest of the 5V supply during programming.  
         [0058]    Connectors and Misc. Devices—CONN 1  is the main connection to control unit  22 . Power for console  34  is received via CONN 1 . Pins  2  and  3  of CONN 1  are serial communication lines used for transmitting and receiving data. CONN 5  is a general-purpose input assigned initially as a dimmer input (to dim the indicator LEDs at low ambient lighting conditions).  
         [0059]    However, CONN 5  may be used to interface with external modules, such as the auxiliary actuators  5  and auxiliary sensors  7  of FIG. 1, for any purpose that the firmware onboard IC 2  is programmed to support. R 18  and Z 1  ensure that IC 2  is protected from noise and incorrect connections on CONN 5 . B 1  is the piezoelectric buzzer  58  visible on the panel of console  34  in FIG. 1. The buzzer is used to alert users of the console device to errors and other status information.  
         [0060]    Keypad Matrix—R 3 , R 5 , R 6 , R 9 , R 10 , R 11 , R 12  and R 13  are configured to allow the eight I/O pins  21 - 28  of micro-controller IC 2  to be used as a keypad matrix reader. The keypad matrix is set up as a 4×4 grid which may provide for up to 16 individual keys. Connection is made to console 34&#39;s three membrane keys  38 A- 38 C via pins  1 ,  2  and  3  of CONN 2 . Pin  4  of CONN 2  is the ground reference for all three membrane keys.  
         [0061]    External Module Adapter—CONN 4  and CONN 6  are 25-way DB connectors that may be used to interface to external expansion modules such as the auxiliary sensors and actuators shown in FIG. 1. Such modules may comprise, for example, a throttle controller, thruster controller, or other modules as desired. Also, either CONN 4  or CONN 6  may be used to connect to the In-Circuit Serial Programming (ICSP) device for loading firmware onto IC 2 .  
         [0062]    External Module Detection Input—Pin  5  of IC 2  is configured as an analog input, which is read on power-up to determine which modules are connected to console  34  and which firmware needs to be run in order to control them. R 20  sets a baseline for external Plug-n-Play connections to be made by providing a 10K pull-up resistor to 5V. Micro-controller IC 2  then interprets 5V on pin  5  to signify that no external modules are connected, and in response runs firmware related to the AGSA. If additional expansion modules are connected then they must each have a different valued pull-down resistor, which divides the voltage down as seen on pin  5  of IC 2  in a unique pattern, such that controller IC 2  is able to unambiguously determine which external modules it is connected to.  
         [0063]    In-Circuit Serial Programming (ICSP) Power Supply Isolation—Transistor Q 2  acts as a blocking device to voltages appearing at Vcc, so that only micro-controller IC 2  receives power from the ICSP device. C 6  stabilises the 5V supply from the ICSP device for stable operation while programming. During programming, no power is connected to the rest of the circuit—only IC 2  is operational. Pins  7  and  19  provide a power supply of 5V to IC 2  during programming. Pins  8 ,  20  and  21  of CONN 6  and CONN 4  are used to make a data connection between an externally connected ICSP device and IC 2 .  
         [0064]    LED Indicator Matrix—Pins  11 ,  12 ,  13  and  14  of IC 2  are set up to drive up to twelve LED indicators, although in the preferred embodiment only three LEDs  56 A- 56 C are fitted. The LEDs are pulsed with a high current in turn as required in very quick procession, giving the appearance that all required LEDs are on simultaneously, whereas only one LED is really on at any point in time. Three LEDs, L 2 , L 3  and L 4  are included in console  34  being visible in FIG. 1 as items  38 A- 38 C.  
         [0065]    Control Unit Circuit Description  
         [0066]    Referring now to FIG. 5, there is provided a schematic diagram of the circuitry within control unit  22 .  
         [0067]    Power Supply—Power is applied via CONN 9 , which is fused via F 2 . A low-pass filter (realized using R 2  and C 7 ) is used to reduce effects of relatively high frequency noise (3 dB point at 165 Hz) on the 12V supply. Diode D 4  protects the device from reverse polarity connections and negative electrical spikes. Zener diode D 5  protects the 5V regulator IC 3  from receiving a voltage higher than it is specified to take (30V). This can occur with high-powered and/or low frequency (frequencies significantly less than input low pass filter  3  dB point) ‘spikes’ on the 12V supply. Regulator IC 3  converts the conditioned 12V supply to 5V which is then stabilised via C 8  and filtered via C 9 . R 39  is used to keep Q 11  pass transistor on. The stabilized 5V supply powers micro-controller (IC 4 ), support circuitry and peripheral devices.  
         [0068]    Micro-controller and Support Circuitry—Micro-controller IC 4  is a PIC16F876 from Microchip Corporation operates according to onboard firmware in order to process user commands received from console  34 . IC 2  receives its supply (5V) into pin  20  and ground referenced via pins  19  and  8 . Pin  1  of IC 4  is the !MCLR input, used to enable the device or reset it under certain circumstances. It is also used as a programming voltage input when used in In-Circuit Serial Programming (ICSP) mode. Accordingly, IC 4  can be programmed in-circuit by means of an external ICSP device. Crystal X 2  sets IC 4 &#39;s internal oscillator frequency to 16 MHz and is stabilized by capacitors C 10  and C 11 . R 25  is used to help reduce IC 4  latching-up. D 10  enables IC 4  by applying over 2.5V to the !MCLR input. D 10  also protects the ICSP device from placing a high voltage level onto the rest of the 5V supply during programming.  
         [0069]    Connectors and Misc. Devices—CONN 7  is the main connection to the console device, being connected directly to CONN 1  of FIG. 4. Power for the console device is sent via CONN 7 . Pins  2  and  3  of CONN 7  are the serial communications lines used for transmitting and receiving data.  
         [0070]    Motor Control Drivers and Logic—Transistors Q 7 , Q 8 , Q 9  and Q 10  are Metal Oxide Semiconductor Field Effect Transistor (MOSFET) devices used to directly drive the motor in linear actuator  10 . The four transistors are configured so that the linear actuator (connected to CONN 8 ) may be driven either forward or backward by changing the polarity of the voltage appearing across the CONN 8  terminals. To drive the linear actuator forward requires Q 8  and Q 9  to be switched into conduction. During this time Q 7  and Q 10  are switched to high impedance and so are effectively switched off thereby placing +12V on pin  1  of CONN 8  and 0V on pin  2  of CONN 8 . To reverse the polarity of the voltage appearing across pins  1  and  2  of CONN 8 , and therefore reverse the direction of the linear actuator, requires Q 8  and Q 9  being switched to high impedance and Q 7  and Q 10  switched into conduction. This places 0V on pin  1  of CONN 8  and +12V on pin  2  of CONN 8 . Zener diodes D 6 , D 7 , D 8  and D 9  are placed across the outputs of drive transistors Q 7 , Q 8 , Q 9  and Q 10  to protect them from reverse voltage induced across the linear actuator&#39;s motor when the transistors momentarily switch states. To quickly switch Q 7 , Q 8 , Q 9  and Q 10  (to reduce power consumption during switching), transistors Q 3 , Q 4 , Q 5  and Q 6  are used to amplify the signal from IC 4 . This allows for a higher current drive signal facilitating quicker switching of the drive transistors. R 21  is placed between the drive transistors and ground (0V) to provide a current shunt for measuring current through the linear actuator. LED L 5  is used for testing only.  
         [0071]    External Sensor Adapter—25-way DB connector CONN  10  provides an interface to external sensors such as the auxiliary sensors  7  of FIG. 1. CONN 10  may also be used to connect to the In-Circuit Serial Programming (ICSP) device for loading firmware onto IC 4 .  
         [0072]    Current Sense Amplifier—Operational amplifier IC 3 :B is an operational amplifier configured to amplify and scale the signal from R 21  so that IC 4  is able to measure the current drawn by linear actuator  10 . IC 4  may be programmed to detect if linear actuator  10  is drawing current indicative of an error state, and in that case, warn the operator of an abnormal situation by means of buzzer  58 , for example.  
         [0073]    Linear Actuator Position Sensor—CONN 3  is connected to the linear feedback potentiometer inside linear actuator 10.5 volts is placed across the potentiometer and the resulting voltage on the center tap terminal of the potentiometer is monitored by analogue input pin  2  of IC 4 . Accordingly, IC 4  is able to determine the position of shaft  14  by monitoring the voltage on pin  2  of CONN 4 .  
         [0074]    In-Circuit Serial Programming (ICSP) Power Supply Isolation—Transistor Q 11  acts as a blocking device to voltages appearing at Vcc, so as only micro-controller IC 4  receives power from the ICSP device. C 14  stabilizes the 5V supply from the ICSP device for stable operation while programming. During programming, no power is connected to the rest of the circuit—only IC 4  is operational. Pins  7  and  19  provide a power supply of 5V to IC 4  during programming. Pins  8 ,  20  and  21  of CONN 10  are where the data is transmitted from the ICSP device to IC 4 .  
         [0075]    External Watchdog Timer (WDT) Device—The circuitry between pin  6  of IC 4  and CONN 11  is configured to generate a failsafe output signal should IC 4 , or any external modules fail in an unsafe manner (e.g. while the marine craft is under full throttle). High current loads, as may be associated with solenoids and motors, may be switched by connection to CONN 5 .  
         [0076]    For example, it is possible to connect an additional linear actuator to a throttle, rather than a gear train, via a solenoid-controlled link. In which case the solenoid would be energized by connection to CONN 11 . Under normal operating conditions, the solenoid is energized, thereby allowing the throttle to remain connected to the linear actuator and therefore, under full control of IC 4 . Should IC 4  detect a fault condition, IC 4  depowers pin  1  of CONN 5  thereby switching off the solenoid and in turn decoupling linear actuator  10  from the throttle so that the throttle returns to its idle state.  
         [0077]    During standard operation Pin  6  of IC 4  sends an oscillating signal to the input of the WDT circuit. The oscillation is at a predetermined rate that must remain constant for the WDT to remain in a controlled active state. In this state, any device connected to the output of the external WDT will be held ON. In the case of an electrical system failure, controller device failure, fuse trip, system crash, or any other circumstance occurring that affects the integrity of the controller device&#39;s operation, the external WDT will be de-asserted. Any device attached to the output switch controlled by the external WDT will be switched OFF. IC 4  already has an internal WDT, which is used to recover from software glitches and can recover very quickly. The external WDT is a ‘last resort’ safety feature designed to avert major system failures.  
         [0078]    Firmware Description—Console  
         [0079]    The micro-controllers IC 2  and IC 4  in both console  34  and control unit  24  respectively contain on-board firmware that includes instructions for execution by the micro-controllers. FIG. 6 is a flowchart of the firmware in console  34 . At box  60  controller chip IC 2  in console  34  is initialized for operation. At box  62  the controller chip IC 2  determines whether or not calibration mode has been entered. In the event that calibration mode has not been entered then control passes to box  64  wherein the controller chip IC 2  monitors for a key press. If no key press is detected then control diverts to box  68 , at which the state of indicators  56 A- 56 C is updated. For example, if console  34  has received a signal from control unit  22  indicating that actuator shaft  14  has reached a reverse gear setpoint then LED  56 C will be lit.  
         [0080]    Alternatively, if a key press is detected at box  64  then control passes to box  66  wherein a signal identifying the pressed key is transmitted to control unit  22 . Indicators informing a console operator of the state of the linear actuator are updated at box  70 . At box  70  the controller chip IC 2  checks to determine if any additional plug-in modules have been connected. The additional modules may comprise auxiliary actuators  5  (FIG. 1.) for example. If additional modules have been connected then firmware routines to support the operation of the additional modules may be called.  
         [0081]    Returning now to box  62 , in order to enter calibration mode the console operator must take the AGSA through a predetermined sequence that is recognized by the console firmware as indicating that the calibration mode is to be entered. In the preferred embodiment the sequence is as follows. Firstly, the AGSA is disconnected from power, then while holding down the neutral key  38 B the power is reconnected. In response the console firmware directs micro-controller chip IC 2  to light all three LEDs  56 A- 56 C. The console operator must then release neutral key  38 B within three seconds of all of the LEDs being illuminated to correctly enter the calibration mode. After three seconds has elapsed all LEDs are then turned off and LED  56 B is repeatedly flashed to indicate that the firmware has proceeded to box  72  of the flowchart of FIG. 6.  
         [0082]    The AGSA firmware may include instructions for preventing gear changes above a certain engine RPM as a safety feature. It follows that the AGSA must be able to determine engine RPM. In order to do so the AGSA monitors the engine ignition system via CONN 10  of the control unit. Depending on the number of cylinders, and whether the ignition system is a dual-fire type or not, a varying number of pulses per revolution will be generated by the ignition system. Accordingly, at box  72  the number of pulses that are generated per revolution must be entered into console  34  so that the AGSA can determine the engine RPM. (Where the AGSM is to be fitted to a diesel powered craft, which does not include an electronic ignition system, a magnet may be placed on the drive unit&#39;s axle and a suitable sensor located adjacent. The sensor is arranged to generate a signal for interpretation by the AGSM each time the axle rotates.) To vary the pulses-per-revolution parameter the forward and reverse keys  38 A and  38 C are operated to increment and decrement the parameter respectively. The number of revolutions that have been entered are confirmed by LED  56 B flashing a corresponding number of times in quick succession. Once the correct value has been entered the neutral key  38 B is depressed thereby passing the firmware to second calibration step  74  of FIG. 6.  
         [0083]    At item  74  the maximum number of RPM at which a gear change may be made is entered, once again by means of the forward and reverse keys, in 100 RPM increments. Once again, LEDs on console  34  are flashed a number of times in quick succession to confirm the number, in hundreds, of RPM that have been entered.  
         [0084]    At the third calibration step  76 , the shaft positions or “setpoints” for each of the forward, reverse and neutral gear selection positions may be entered. Upon entering this state, the LED next to the reverse key flashes thereby indicating that the reverse gear position is ready to be positioned. The forward and reverse keys must then be operated to bring the actuator shaft to the position that is to correspond to the reverse key. The actuator will be extended or retracted as the forward and reverse keys are depressed. Once the correct position for proper engagement of the reverse gear is arrived at, the neutral key should be depressed. The AGSA then stores the linear actuator setpoint and will return back to this setpoint every time the reverse button is subsequently depressed in standard use.  
         [0085]    LED  56 B, i.e. the LED adjacent neutral key  38 B will flash to indicate that the neutral actuator shaft position is being set. A similar procedure is used to set the shaft position that is to correspond to forward and neutral gear selections. After all three of the shaft positions have been set the calibration steps are completed and control diverts back to box  64 .  
         [0086]    Firmware Description—Control Unit  
         [0087]    Referring now to FIG. 7, there is depicted a flowchart of the inboard firmware of control unit  22 . At startup the micro-controller in control unit  22  is initialized at box  80 . Then, at box  82  the controller determines whether or not calibration mode has been entered. In the event that calibration mode has not been entered then control passes to box  84  where the controller determines whether or not a keypress has been received from console  34 . In the event that a keypress has been received then control diverts to box  86  and a setpoint corresponding to the button that has been depressed is set. At box  88  the control unit determines whether or not the linear actuator shaft  18  is at the setpoint. If the linear actuator shaft is at the setpoint then control diverts back to box  84 . Alternatively, if the linear actuator is not at the current setpoint then control diverts to box  90 . At box  90  micro-controller IC 4  sends appropriate biasing signals to MOSFETS Q 3 -Q 6  which in turn bias Q 7 -Q 10  so that motor driver currents are sent via CONN 8  to drive the motor in linear actuator  10  and bring shaft  14  towards the current setpoint.  
         [0088]    Box  90  includes instructions for the control unit to check how far away the linear actuator is from the setpoint. If the actuator shaft is far away from the setpoint then the controller moves the actuator rapidly towards the setpoint. As the actuator shaft gets closer to its desired position the controller moves it more slowly thereby decreasing the degree of overshoot.  
         [0089]    In the presently described embodiment the position of actuator shaft  14  is updated one thousand times per second, thereby ensuring sharp and accurate control of the position of the shaft without recourse to computationally intensive proportional integro-differential (PID) controllers.  
         [0090]    It will be realized that the automated gear selection apparatus of the present invention has been described in relation to a preferred embodiment. However, many other embodiments are possible. For example, rather than use a linear actuator a rotary actuator might instead be used to wind cable  37  precise distances about an actuator reel. Furthermore, it will be realized that a single, suitably programmed, micro-controller might be used rather than the two micro-controllers, one for the console and one for the control unit, of the preferred embodiment. Indeed the console and the control unit may be integrated into a single assembly if required. Other embodiments and variations of the invention will be apparent to those skilled in the art. Accordingly, the following claims are to be constructed broadly and not restricted merely to the preferred embodiment that is discussed herein.