Abstract:
A crop sprayer control assembly includes a hand-operated control device with an up-throttle sensor operably connected to the hand-operated control device. A down-throttle sensor, an up-shift sensor and a down-shift sensor are also operably connected to the hand-operated control device.

Description:
FIELD 
       [0001]    The present invention relates generally to a crop sprayer, and more particularly to an apparatus and method for controlling rotational speed and direction of a drive shaft of a crop sprayer. 
       BACKGROUND 
       [0002]    A crop sprayer is used to distribute chemicals, such as herbicides, pesticides, and fertilizer, over crops in a field during a spraying operation. In order to maneuver the crop sprayer around the field during the spraying operation, an operator of the crop sprayer operates various controls which affect speed and direction of the crop sprayer. The speed and direction of the crop sprayer is directly related to the rotational speed and direction of a drive shaft of the crop sprayer. 
         [0003]    Typically, one control allows the operator to selectively couple and decouple an engine crankshaft of the crop sprayer from the drive shaft. Another control allows the operator to selectively change the gear ratio between the engine crankshaft and the drive shaft. Still another control allows the operator to selectively increase and decrease rotational speed of the engine crankshaft. 
         [0004]    By way of example, to control the movement of a conventional tractor, a foot activated clutch is used to selectively couple and decouple the engine crankshaft from the drive shaft, a hand actuated gear selector is used to selectively change the gear ratio between the engine crankshaft and the drive shaft, and a foot actuated throttle is used to control the rotational speed of the engine crankshaft. 
         [0005]    In addition to the controls which the operator must operate in order to maneuver a crop sprayer around a field, the crop sprayer also includes other controls which operate the chemical spraying features of the crop sprayer. By way of example, the crop sprayer generally has a boom arm control which raises, lowers, extends, and retracts a boom arm which includes a number of spray nozzles. The crop sprayer further has a spray control which adjusts the flow rate of chemicals from a storage tank through the spray nozzles mounted on the boom arm. 
         [0006]    Obviously, as the number of controls for various functions of a device increases, operation of the device becomes increasingly difficult. Moreover, coordinating operation of various controls, such as a clutch, a brake and the throttle, can be challenging, particularly when the controls are spatially separated. 
         [0007]    One approach to reduce the burden on the operator of a crop sprayer is to utilize a hydrostatic drive system in the crop sprayer. A hydrostatic drive system includes a hand lever which when manipulated causes a hydraulic fluid to be advanced within the system so as to cause rotation of the wheels of the crop sprayer at a desired rotational speed and direction. Thus, use of the hydrostatic drive system eliminates the need for an operator to (i) use his foot to activate a clutch to selectively couple and decouple the engine crankshaft from the drive shaft, and (ii) to use his foot to selectively actuate the throttle to control the speed of the engine crankshaft. A separate control may be used to selectively change the gear ratio between the engine crankshaft and the drive shaft. Consequently, the use of a hydrostatic drive system enables an operator to maneuver the crop sprayer around the field with a fewer number of separate controls thereby reducing the burden on the operator of the crop sprayer. 
         [0008]    One drawback of a hydrostatic drive system is that hydrostatic drive systems are typically heavy, complex, and expensive. The weight of a hydrostatic drive system inhibits mobility of a crop sprayer, especially in soft terrain. Wider tires can be used to distribute the weight of the crop sprayer over a larger area so as to increase mobility. The use of wider tires, however, requires an additional distance to be provided between adjacent rows of the crop in order to ensure that the crops being sprayed are not damaged by the tires during a spraying operation. This reduces the number of crops that may be planted for a given area. Alternatively, an operator may choose to maintain the same row separation resulting in a reduced clearance between the tires and the crops. Maintaining the wheels within a relatively narrow space, however, increases the required level of concentration and increases the amount of tension and fatigue experienced by an operator. 
         [0009]    What is needed therefore is an apparatus and method for reducing the number of separate controls required to control the movement and operation of a crop sprayer without significantly increasing the weight of the crop sprayer. 
       SUMMARY 
       [0010]    In accordance with one embodiment of the present invention, there is provided a crop sprayer control assembly that includes a hand-operated control device. An up-throttle sensor, a down-throttle sensor, an up-shift sensor and a down-shift sensor are operably connected to the hand-operated control device. 
         [0011]    In accordance with another embodiment of the present invention, there is provided a crop sprayer speed control assembly with a joystick having a first position and a first sensor is associated with the first position. The assembly includes a memory with first stored instructions which, when executed, determine that the first sensor has sensed the joystick in the first position, issue a first signal operable to change the rotational speed of the crop sprayer engine, continue to change the rotational speed of the engine for so long as the first sensor senses the joystick in the first position, and terminates the change in the rotational speed of the engine when the first sensor no longer senses the joystick in the first position. The assembly also includes a microprocessor that executes the instructions stored in the memory. 
         [0012]    In accordance with one method of the present invention, the speed and direction of a drive shaft on a crop sprayer is controlled by moving a control stick from a first position to a second position, generating a first signal based upon the movement of the control stick to the first position, changing the rotational speed of the crop sprayer drive shaft based upon the first signal, moving the control stick from the second position to the first position, and terminating the change in the rotational speed of the drive shaft when the control stick is moved from the second position to the first position. 
         [0013]    In accordance with another method of the present invention, the drive shaft on a crop sprayer is controlled by sensing a control stick positioned in a first position with a first sensor, providing a first sensor output based upon the sensing of the control stick, changing the rotational speed of the crop sprayer drive shaft based upon the first sensor output, and terminating the change in the rotational speed of the drive shaft when the first sensor no longer senses the control stick in the first position or a first predetermined rotational speed of the drive shaft has been achieved. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  shows a perspective view of a crop sprayer in accordance with features of the present invention; 
           [0015]      FIG. 2  shows a schematic view of a drive train assembly and crop sprayer control assembly of the crop sprayer of  FIG. 1 ; 
           [0016]      FIG. 3  shows a perspective view of the control console of  FIG. 2 ; and 
           [0017]      FIG. 4  shows a schematic view of the drive train assembly and the crop sprayer control assembly of  FIG. 3 . 
       
    
    
     DESCRIPTION 
       [0018]    While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that there is no intent to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims. 
         [0019]    Referring now to  FIG. 1 , there is shown a crop sprayer  100 . The crop sprayer  100  includes a cab  102  which houses an operator and a number of controls. The crop sprayer  100  further includes a chemical tank  104  which stores chemicals, such as herbicides, pesticides, and fertilizers. The crop sprayer  100  further includes a boom arm  106  which is operable to distribute the chemicals over a wide swath in a field. In particular, the chemicals are distributed by nozzles (not shown) spaced along the boom arm  106  through which the chemicals are sprayed as the crop sprayer  100  is propelled. In alternative embodiments, the storage tank and boom assembly may be located at different locations on the crop sprayer such as at the front end of the crop sprayer. 
         [0020]    The crop sprayer  100  further includes a pair of rear wheels  108  and a pair of front wheels  110 . The rear wheels  108  are driven by a drive train assembly  112  (shown in  FIG. 2 ) so as to propel the crop sprayer  100  in the desired direction. The front wheels  110  are operable to steer the crop sprayer  100 . 
         [0021]    Referring now to  FIG. 2 , there is shown the drive train assembly  112  of the crop sprayer  100 . The drive train assembly  112  includes an engine  114 , a clutch assembly  116 , a transmission  118 , a drive shaft  120 , a rear differential  122  and a differential output shaft  124 . The clutch assembly  116 , the transmission  118 , the drive shaft  120  and the rear differential  122  and the differential output shaft  124  in this embodiment are commercially available as a matched set from International Transmissions LTD of Wrexham, United Kingdom as transmission and axle package 475/45200. 
         [0022]    The engine  114  may be a diesel engine commercially available from Cummins Engine Co. Inc., of Columbus, Ind. or Deere &amp; Company of Moline Ill. Diesel engines have several advantages including high torque output, reliability, and low fuel cost. The engine  114  generates rotational mechanical energy which is transferred to the clutch assembly  116  by a crankshaft  126  of the engine  114 . While the embodiment of  FIG. 1  shows the engine  114  mounted at the front end of the crop sprayer  100 , in alternative embodiments, the engine may be mounted elsewhere on the crop sprayer such as at the rear of the crop sprayer. 
         [0023]    The engine  114  includes a throttle  128 . The throttle  128  is operable to control rotational speed of the crankshaft  126  of the engine  114 . In particular, the throttle  128  controls the amount of air that is advanced into a combustion chamber (not shown) of the engine  114 . As the amount of air advanced into the combustion chamber is increased, the flow of fuel injected into the combustion chamber is similarly increased. By increasing the amount of fuel and air combusted in the combustion chamber of the engine  114 , the rotational speed of the crankshaft  126  of the engine  114  is increased. A signal is sent over a signal line  130  to control the position the throttle  128  during operation of the engine  114  so as to control the rotational speed of the crankshaft  126 . 
         [0024]    The clutch assembly  116  is positioned between the engine  114  and the drive shaft  120 . The clutch assembly  116  includes a torque converter which has a forward clutch  132  and a reverse clutch  134 . The forward clutch  132  is operable to selectively couple and decouple the crankshaft  126  of the engine  114  and the drive shaft  120 . In particular, when the forward clutch  132  couples the crankshaft  126  to the drive shaft  120 , the drive shaft  120  is caused to rotate in a clockwise rotational direction, as indicated by the arrow  136 . When the drive shaft  120  rotates in the clockwise rotational direction  136 , the rear wheels  108  are rotated so as to advance the crop sprayer  100  in the forward direction indicated by the arrow  138  in  FIG. 1 . Whereas, when the forward clutch  132  decouples the crankshaft  126  from the drive shaft  120 , the drive shaft  120  is not caused to rotate in the direction of the arrow  136 . As a result, when the forward clutch  132  decouples the crankshaft  126  from the drive shaft  120 , the engine  114  does not cause the rear wheels  108  to rotate so as to advance the crop sprayer  100  in the forward direction. 
         [0025]    The forward clutch  132  is actuated so as to couple the crankshaft  126  to the drive shaft  120  in response to an electric signal being received via a signal line  140 . In particular, when an “on” signal is received by the forward clutch  132  via the signal line  140 , the forward clutch  132  couples the crankshaft  126  to the drive shaft  120  so as to rotate the drive shaft  120  in the clockwise rotational direction. When an “off” signal is received by the forward clutch  132  via the signal line  140 , the forward clutch  132  decouples the crankshaft  126  from the drive shaft  120 . 
         [0026]    Similarly, the reverse clutch  134  is operable to selectively couple and decouple the crankshaft  126  of the engine  114  and the drive shaft  120 . In particular, when the reverse clutch  134  couples the crankshaft  126  to the drive shaft  120 , the drive shaft  120  is caused to rotate in a counterclockwise rotational direction, as indicated by the arrow  142 . When the drive shaft  120  rotates in the counterclockwise rotational direction, the rear wheels  108  are rotated so as to advance the crop sprayer  100  in the reverse direction as indicated by the arrow  144  in  FIG. 1 . When the reverse clutch  134  decouples the crankshaft  126  from the drive shaft  120 , the drive shaft  120  is not caused to rotate in the counterclockwise rotational direction indicated by the arrow  142 . As a result, when the reverse clutch  134  decouples the crankshaft  126  from the drive shaft  120 , the engine  114  does not cause the rear wheels  108  to rotate so as to advance the crop sprayer  100  in the reverse direction. 
         [0027]    The reverse clutch  134  is actuated so as to couple the crankshaft  126  to the drive shaft  120  in response to an electric signal being received via a signal line  146 . In particular, when an “on” signal is received by the reverse clutch  134  via the signal line  146 , the reverse clutch  134  couples the crankshaft  126  to the drive shaft  120  so as to rotate the drive shaft  120  in the counterclockwise rotational direction. When an “off” signal is received by the reverse clutch  134  via the signal line  146 , the reverse clutch  134  decouples the crankshaft  126  from the drive shaft  120 . 
         [0028]    The transmission  118  is interposed between the clutch assembly  114  and the drive shaft  120 . The transmission  118  in this embodiment is a four speed transmission which provides four separate gear ratios between the crankshaft  126  and the drive shaft  120 . The transmission  118  allows the operator to selectively change the gear ratio between the clutch assembly  116  and the drive shaft  120 . In particular, when an “up-shift” signal is received by the transmission  118  via the signal line  148 , the transmission  118  decouples the previously selected gear from the forward clutch  132  and couples the gear with the next highest gear ratio to the forward clutch  132  so as to rotate the drive shaft  120  at a higher rotational speed but with less torque. When a “down-shift” signal is received by the transmission  118  via the signal line  148 , the transmission  118  decouples the previously selected gear from the forward clutch  132  and couples the gear with the next lowest gear ratio to the forward clutch  132  so as to rotate the drive shaft  120  at a lower rotational speed but with more torque. Thus, the change of gear ratios allows the engine  114  to provide torque to the rear wheels  108  for a variety of operating conditions. In particular, a gear ratio may be selected that provides high torque at low crankshaft speeds whereas a different gear ratio may be selected that provides low torque at high crankshaft speeds. 
         [0029]    The drive shaft  120  is operatively coupled to the rear differential  122  and the differential output shaft  124 . The rear differential  122  splits the power from the drive shaft  120  between each of the rear wheels  108  (shown in  FIG. 1 ) in order to propel the crop sprayer  100  in the forward direction and the reverse direction. 
         [0030]    The signal lines  130 ,  140 ,  146  and  148  extend between a microprocessor  150  and the respective component. The microprocessor  150  is part of a crop sprayer control assembly  152  which is shown in more detail in  FIG. 3 . The crop sprayer control assembly  152  includes a convenience tray  154 , an arm rest  156  a joystick  158  and a control and display panel  160 . The control and display panel  160  includes a display  162  and a number of control switches  164 . The display  162  is configured to provide status and alarm information for the various systems of the crop sprayer  100  such as fuel, hydraulic system parameters, boom condition, chemical tank level, etc. The control switches  164  are used to control the various systems. 
         [0031]    The joystick  158  includes a knob  166  and a shaft  168 . A forward gear control button  170  and a reverse gear control button  172  are located on the side of the shaft  168  farthest away from the armrest  156 . The placement of the forward gear control button switch  170  and the reverse gear control button switch  172  allows the buttons to be depressed when an operator grasps the shaft  168 . Manipulation of the knob  166 , however, is unlikely to result in inadvertent manipulation of the buttons. 
         [0032]    The joystick  158  is biased toward a neutral position wherein it is aligned with the axis  174 . The joystick may be pivoted forward and backward within a first plane through the axis  174  in the directions indicated by the arrows  176  and  178 . The joystick  158  may further be pivoted from one side to the other side within a second plane through the axis  174  as indicated by the arrows  180  and  182 . Movement of the joystick  158  and manipulation of the forward gear control button switch  170  and the reverse gear control button switch  172  is detected by various sensors which are shown in  FIG. 4 . 
         [0033]    The sensors associated with the joystick  158  include an up-throttle sensor  184 , a down-throttle sensor  186 , an up-shift sensor  188 , a down-shift sensor  190 , a forward engage sensor  192  and a reverse engage sensor  194 . The up-throttle sensor  184  is configured to sense when the joystick  158  is pivoted in the direction of the arrow  176  and the down-throttle sensor  186  is configured to sense when the joystick  158  is pivoted in the direction of the arrow  178 . In this embodiment, the up-throttle sensor  184  and the down-throttle sensor  186  are configured to generate either a high signal or a low signal, depending upon whether or not the joystick  158  is sensed. Thus, the sensors provide a digital output. In an alternative embodiment, the sensors may be configured to be analog sensors, providing a varying output dependent upon the sensed magnitude of deflection of the joystick  158  toward the first or second position. This alternative configuration is useful when providing for a varying rate of throttle increase or decrease. 
         [0034]    Continuing with  FIG. 4 , the down-shift sensor  190  is configured to sense when the joystick  158  is pivoted in the direction of the arrow  180  and the up-shift sensor  188  is configured to sense when the joystick  158  is pivoted in the direction of the arrow  182 . Finally, the forward engage sensor  192  is configured to sense depression of the forward gear control button switch  170  and the reverse engage sensor  194  is configured to sense depression of the reverse gear control button switch  172 . 
         [0035]    Each of the sensors provides a signal to the microprocessor  150  over one of the signal lines  196 ,  198 ,  200 ,  202 ,  204  or  206 . The microprocessor  150  evaluates the incoming signals from the signal lines  196 ,  198 ,  200 ,  202 ,  204  and  206  along with status data from the drive train assembly  112  and, based upon instructions stored in the memory  208 , issues control signals to actuators associated with the various components of the drive train assembly  112 . 
         [0036]    To move the crop sprayer  100  beginning with the engine  114  turning the crankshaft  126  but with no clutch engaged, an operator first manipulates either the forward gear control button switch  170  or the reverse gear control button switch  172 . When the forward gear control button switch  170  is manipulated, the forward engage sensor  192  senses the manipulation and generates a signal that is sent to the microprocessor  150  through the signal line  204 . The microprocessor  150  then determines that the forward clutch  132  is not engaged based upon a signal from the signal line  140  and that the reverse clutch  134  is not engaged based upon a signal from the signal line  146 . Therefore, based upon instructions stored in the memory  208 , the microprocessor  150  generates a control signal which is sent via the signal line  140  controlling an actuator so as to engage the forward clutch  132  and the crankshaft  126 . Thus, rotation of the crankshaft  126  is passed through the forward clutch  132  to the drive shaft  120 , causing the drive shaft  120  to rotate in the direction of the arrow  136  ( FIG. 2 ) so as to propel the crop sprayer  100  in the forward direction indicated by the arrow  138  of  FIG. 1 . 
         [0037]    In the event the forward clutch  132  is engaged when the microprocessor  150  receives a signal through the signal line  204 , the instructions stored in the memory  208  in this embodiment, when executed by the microprocessor  150  will cause a signal to be sent to the actuator for the forward clutch  132  causing the forward clutch  132  to be disengaged from the crankshaft  126 . Similarly, if the reverse clutch  134  is engaged when the microprocessor  150  receives a signal through the signal line  204 , the instructions stored in the memory  208  in this embodiment, when executed by the microprocessor  150  will cause a signal to be sent to the actuator for the reverse clutch  134  causing the reverse clutch  134  to be disengaged from the crankshaft  126 . 
         [0038]    If the reverse gear control button switch  172  is manipulated instead of the forward gear control button switch  170 , the reverse engage sensor  194  senses the manipulation and generates a signal that is sent to the microprocessor  150  through the signal line  206 . The microprocessor  150  then determines that the forward clutch  132  is not engaged based upon a signal from the signal line  140  and that the reverse clutch  134  is not engaged based upon a signal from the signal line  146 . Therefore, based upon instructions stored in the memory  208 , the microprocessor  150  generates a control signal which is sent via the signal line  146  controlling an actuator so as to engage the reverse clutch  134  to the crankshaft  126 . Thus, rotation of the crankshaft  126  is passed through the reverse clutch  134  to the drive shaft  120 , causing the drive shaft  120  to rotate in the direction of the arrow  142  ( FIG. 2 ) so as to propel the crop sprayer  100  in the rearward direction indicated by the arrow  144  of  FIG. 1 . 
         [0039]    In the event the forward clutch  132  is engaged when the microprocessor  150  receives a signal through the signal line  206 , the instructions stored in the memory  208  in this embodiment, when executed by the microprocessor  150  will cause a signal to be sent to the actuator for the forward clutch  132  causing the forward clutch  132  to be disengaged from the crankshaft  126 . Similarly, if the reverse clutch  134  is engaged when the microprocessor  150  receives a signal through the signal line  206 , the instructions stored in the memory  208  in this embodiment, when executed by the microprocessor  150  will cause a signal to be sent to the actuator for the reverse clutch  134  causing the reverse clutch  134  to be disengaged from the crankshaft  126 . 
         [0040]    Additional data may be considered by the microprocessor  150  prior to engaging or disengaging a clutch. By way of example, the speed and direction of rotation of the drive shaft  120  may be provided to the microprocessor  150 . Accordingly, an instruction may be stored in the memory  208  the execution of which only allows a clutch to be engaged if the drive shaft  120  is not rotating. Alternatively, a small amount of rotation in the direction opposite to the clutch to be engaged may be allowed. This reduces wear on the system in the event one of the gear control button switches is inadvertently depressed twice. In one embodiment, a clutch is allowed to be engaged so long as the drive shaft  120  is rotating in the opposite direction at a speed corresponding to about 3 miles per hour. 
         [0041]    Deflection of the joystick  158  in the direction of the arrow  182  of  FIG. 3  is sensed by the up-shift sensor  188  and a signal is sent to the microprocessor  150  over the signal line  200 . The microprocessor  150  then determines the status of the forward clutch  132 , the reverse clutch  134  and the transmission  118  using one or more inputs from the signal lines  140 ,  146  and  148 , respectively. If the reverse clutch  134  is engaged, then the microprocessor  150  ignores the signal since, in this embodiment, there is only a single reverse gear. Likewise, if the forward clutch  132  is not engaged, the signal is ignored. Alternatively, a warning signal may be sent to the display  162 . In the event more than one reverse gear is available, then the microprocessor will command the drive train components  112  in a manner similar to the following process which is performed when the forward clutch  132  is engaged. 
         [0042]    If the microprocessor  150  determines that the forward clutch  132  is engaged, the actual gear in the transmission  118  that is engaged to the crankshaft  126  through the forward clutch  132  is determined. If the engaged gear in the transmission  118  is the gear with the highest gear ratio then the signal from the up-shift sensor  188  is ignored. If the gear that is engaged in the transmission  118  is not the gear with the highest gear ratio, then the microprocessor  150 , based upon stored instructions in the memory  208 , sends a signal over the line  140  so as to control the actuator for the forward clutch  132  to disengage the forward clutch  132  from the crankshaft  126 . Then, a signal is sent over the signal line  148  to the transmission  118  selecting the gear with the next highest gear ratio compared to the previously engaged gear. Finally, the microprocessor  150  sends a signal over the line  140  so as to control the actuator for the forward clutch  132  to engage the forward clutch  132  with the crankshaft  126 . Thus, rotational movement of the crankshaft  126  is passed through a gear in the transmission  118  with a higher gear ratio. 
         [0043]    Deflection of the joystick  158  in the direction of the arrow  180  of  FIG. 3  is sensed by the down-shift sensor  190  and a signal is sent to the microprocessor  150  over the signal line  202 . The microprocessor  150  then determines the status of the forward clutch  132 , the reverse clutch  134  and the transmission  118  using signals from the signal lines  140 ,  146  and  148 , respectively. If the reverse clutch  134  is engaged or the forward clutch  132  is not engaged, the signal is ignored or a warning signal may be generated. 
         [0044]    If the microprocessor  150  determines that the forward clutch  132  is engaged, the actual gear in the transmission  118  that is engaged to the crankshaft  126  through the forward clutch  132  is determined. If the engaged gear in the transmission  118  is the gear with the lowest gear ratio then the signal from the down-shift sensor  190  is ignored. If the gear that is engaged in the transmission  118  is not the gear with the lowest gear ratio, then the microprocessor  150 , based upon stored instructions in the memory  208 , sends a signal over the line  140  so as to control the actuator for the forward clutch  132  to disengage the forward clutch  132  from the crankshaft  126 . Then, a signal is sent over the signal line  148  to the transmission  118  selecting the gear with the next lowest gear ratio compared to the previously engaged gear. Finally, the microprocessor  150  sends a signal over the line  140  so as to control the actuator for the forward clutch  132  to engage the forward clutch  132  with the crankshaft  126 . Thus, rotational movement of the crankshaft  126  is passed through a gear in the transmission  118  with a lower gear ratio. 
         [0045]    If desired, the microprocessor  150  may be configured to further process available data prior to actually shifting gears in the manner described above. By way of example, a signal corresponding to the current rotational speed and direction of the drive shaft  120  may be provided to the microprocessor  150 . Based upon the rotational speed of the drive shaft  120 , the microprocessor may delay the actual gear shift, particularly when up-shifting, until the rotational speed of the drive shaft  120  has been increased to a predetermined level. This reduces the amount of shock to the system because of the change in torque resulting from the higher gear ratio. Additional inputs, such as current torque on various parts of the system, may also be used. 
         [0046]    Deflection of the joystick  158  in the direction of the arrow  176  of  FIG. 3  is sensed by the up-throttle sensor  184  and a signal is sent to the microprocessor  150  over the signal line  196 . The microprocessor  150  then determines the status of the throttle  128  using a signal from the signal line  130 . If the throttle  128  is fully open or at the upper limit, then the signal is ignored or a warning signal may be generated. 
         [0047]    If the microprocessor  150  determines that the throttle  128  is not fully opened, then the microprocessor  150 , based upon stored instructions in the memory  208 , sends a signal over the line  130  so as to control the actuator for the throttle  128  to control the throttle  128  toward the full open position at a predetermined rate of opening. The microprocessor  150  controls the throttle  128  so as to continue opening for so long as the up-throttle sensor  184  senses that the joystick  158  is deflected. As the throttle  128  is opened, the amount of fuel introduced into the combustion chambers of the engine  114  is increased causing an increase in the rotational speed of the crankshaft  126 . Thus, the rotation of the driveshaft  120  is increased, causing the crop sprayer  100  to accelerate. 
         [0048]    Once the desired speed is achieved, the operator releases the joystick  158  which is biased toward the neutral position. As the joystick  158  moves to the neutral position, the up-throttle sensor  184  will lose the ability to sense the joystick  158  and the signal is removed from the signal line  196 . The microprocessor  150  then removes the signal from the signal line  130  and the throttle  128  is maintained at the resulting position. 
         [0049]    Alternative instructions may be stored in the memory  208  for execution by the microprocessor  150 . By way of example, but not of limitation, the microprocessor may be configured to modify a speed set point based upon the deflection of the joystick  158 . In one such embodiment, a set point speed is indicated on the display  162 . In response to a deflection of the joystick  158 , the set point speed is increased. When the desired set point speed is displayed, the operator releases the joystick. Meantime, the microprocessor determines a discrepancy between the set point speed and the actual speed, and controls the throttle as necessary to increase the actual speed to the set point speed. 
         [0050]    Deflection of the joystick  158  in the direction of the arrow  178  of  FIG. 3  is sensed by the down-throttle sensor  186  and a signal is sent to the microprocessor  150  over the signal line  198 . The microprocessor  150  then determines the status of the throttle  128  using a signal from the signal line  130 . If the throttle  128  is at its lower limit, then the signal is ignored or a warning signal may be generated. 
         [0051]    If the microprocessor  150  determines that the throttle  128  is not at the lower limit, then the microprocessor  150 , based upon stored instructions in the memory  208 , sends a signal over the line  130  so as to control the actuator for the throttle  128  to control the throttle toward the full shut position at a predetermined rate of closing. The microprocessor  150  controls the throttle  128  so as to continue closing for so long as the down-throttle sensor  186  senses that the joystick  158  is deflected. As the throttle  128  is closed, the amount of fuel introduced into the combustion chambers of the engine  114  is decreased causing a decrease in the rotational speed of the crankshaft  126 . Thus, the rotation of the driveshaft  120  is decreased, causing the crop sprayer  100  to decelerate. 
         [0052]    Once the desired speed is achieved, the operator releases the joystick  158  which is biased toward the neutral position. As the joystick  158  moves to the neutral position, the down-throttle sensor  186  will lose the ability to sense the joystick  158  and the signal is removed from the signal line  198 . The microprocessor  150  then removes the signal from the signal line  130  and the throttle  128  is maintained at the resulting position. 
         [0053]    While the invention has been illustrated and described in detail in the drawings and foregoing description, the same should be considered as illustrative and not restrictive in character. It is understood that only the preferred embodiments have been presented and that all changes, modifications and further applications that come within the spirit of the invention are desired to be protected.