Patent Publication Number: US-2005115760-A1

Title: Speed control for utility vehicle operable from rearward-facing seat

Description:
TECHNICAL FIELD OF THE INVENTION  
      The invention relates to utility vehicles for industrial and agricultural use, such as utility tractors. Particularly, the invention relates to transmission control systems for such vehicles.  
     BACKGROUND OF THE INVENTION  
      Typical utility vehicles, such as compact tractors, utilize an engine operating substantially at a pre-selected speed that drives a transmission system or drive train that delivers power to one or more driven wheels. The transmission system includes a speed controllable transmission component, a gear selection component, and a differential component. The speed controllable transmission component can be, for example, a hydrostatic transmission, or a transmission that uses electro-hydraulically controlled forward and reverse clutch packs to initially accelerate the vehicle and to change vehicle direction (hereinafter referred to as a “reverser transmission”), such as a POWRREVERSER™ transmission incorporated in JOHN DEERE Series 4000 tractors.  
      When using a backhoe attachment on a compact utility vehicle, it is sometimes necessary to move the utility vehicle forward or backward by small amounts and/or at slow speeds. For example, when excavating a trench, the backhoe must be moved rearward periodically as the trench progresses. For utility vehicles having a front facing seat for driving the vehicle and a rear facing seat for operating the backhoe, or a flip seat which is alternately the front facing and the rear facing seat, the forward and reverse controls are located proximate the front facing seat. It is not practical to move the tractor using the controls without the operator having to move from the rear seat to the front seat. Thus, the operator typically moves the vehicle by planting the backhoe bucket into the ground and hydraulically moving the backhoe, by extending or retracting the backhoe boom and/or rotating the backhoe bucket to trust the vehicle forward or backward using the reaction force from the backhoe. The resultant movement of the utility vehicle is “jerky” and uncomfortable to the operator. Also, moving the utility vehicle in this manner can damage the ground or turf depending on the circumstances.  
      For a utility vehicle having a hydrostatic transmission and operated by foot controls, it is not practical to reach the foot controls while seated facing rearward while operating the backhoe. In a compact tractor that utilizes a front seat for operating the hydrostatic transmission and a rear seat for operating the backhoe, it is not practical to rotate the seat from a rearward position facing the backhoe to a frontward driving position. There is not ample room in a compact vehicle to accomplish this task. It is also not considered to be a good practice for an operator to attempt to operate the hydrostatic transmission with the front foot controls while seated facing rearward.  
      The present inventors have recognized the desirability of providing a utility vehicle that can be effectively driven at a controlled speed by an operator seated at a back of the vehicle, facing rearward.  
     SUMMARY OF THE INVENTION  
      The present invention provides a creep speed control for operating a utility vehicle while seated in a rearward facing position and operating rear mounted implements, such as a backhoe attachment. The creep speed control includes a mechanical or electronic control arrangement that allows the operator to “creep” forward or rearward at a controlled speed while operating the rear mounted implement. The speed of the utility vehicle is limited by mechanical stops or electronic control to prevent unsafe speeds while the operator is facing rearward. Additionally, an operator presence switch prevents operation of the utility vehicle when the operator is not seated.  
      When the operator is seated in the rearward orientation, movement of the utility vehicle is predicated on two independent actions that are required to actuate the creep speed control, to prevent accidental motion. Movement of the utility vehicle is however unrestricted by the creep speed control while operating the vehicle in the normal, forward facing operator position.  
      For hydrostatic transmissions that are controlled mechanically, a hand operated linkage is provided that selectively moves a hydraulic servo system that moves the swashplate of the variable displacement pump within a limited angular range to cause either forward or reverse speed.  
      For hydrostatic transmissions that are controlled electronically, a speed/direction actuator, such as a fool pedal, with a position sensor, provides an analog signal to an electronic controller. This analog signal controls the transmission speed. Ground speed can be measured by a Hall effect sensor, which produces a frequency signal by counting gear teeth on a rotating gear in the transmission. Ground speed will be a variable from zero speed to a preset maximum creep speed. The maximum creep speed, and speeds less than the maximum creep speed, will thus be controlled independently of engine speed, or the range transmission gear selection.  
      The present invention maximizes operator convenience and ergonomics. The vehicle can be operated from the rearward-facing seat in a more controlled manner, obviating the practice of positioning of the tractor using the reaction force from the backhoe. During tractor positioning, the operator may remain in the best location for operating rear-mounted implements, such as a backhoe. The operator will not be tempted to straddle the seat to engage front operated speed controls. Vehicle productivity will be increased because positioning of the vehicle will be more effectively accomplished, without interrupting operation of the rear-mounted implement.  
      Numerous other advantages and features of the present invention will become readily apparent from the following detailed description of the invention and the embodiments thereof, from the claims and from the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is an elevational view of a utility vehicle incorporating the speed control system of the present invention;  
       FIG. 2  is a block diagram of the speed control system of the present invention applied to a hydrostatic transmission system;  
       FIG. 3  is a schematic sectional view of a mechanically controlled servo control system used in a hydrostatic transmission of  FIG. 2 ;  
       FIG. 4  is an exploded, fragmentary perspective view of the servo control system of  FIG. 2 ;  
       FIG. 5  is a schematic sectional view of a hydrostatic transmission;  
       FIG. 6  is a schematic elevational view of a first embodiment speed control system using a mechanical linkage for implementing speed control;  
       FIG. 7  is a fragmentary perspective view of a portion of the system of  FIG. 6 ;  
       FIG. 8  is a fragmentary, enlarged sectional view of a portion of the system of  FIG. 6 ;  
       FIG. 8A  is a fragmentary sectional view of an alternate embodiment creep lever;  
       FIG. 9  is a sectional view taken generally along line  9 - 9  of  FIG. 8 ;  
       FIG. 9A  is a sectional view taken generally along line  9 A- 9 A of  FIG. 8A ;  
       FIG. 10  is a sectional view taken generally along line  10 - 10  of  FIG. 9 ;  
       FIG. 11  is a block diagram of a second embodiment speed control system using an electronic control system for implementing speed control;  
       FIG. 12  is a schematic sectional view of the servo control system used in the control system of  FIG. 11 ;  
       FIG. 13  is an exploded, fragmentary perspective view of the servo control system of  FIG. 12 ;  
       FIG. 14  is a block diagram of a speed control method of the invention;  
       FIG. 15  is a fragmentary perspective view of a speed actuator and direction switches of the invention; and  
       FIG. 16  is a block diagram of an alternate speed control system of the invention has applied to a reverser transmission. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      While this invention is susceptible of embodiment in many different forms, there are shown in the drawings, and will be described herein in detail, specific embodiments thereof with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the invention to the specific embodiments illustrated.  
       FIG. 1  illustrates a utility vehicle  20 , such as a compact tractor-loader-backhoe, which incorporates a creep speed control system of the present invention. The utility vehicle includes a chassis  24  supported on a pair of front wheels  26  and larger rear wheels  28 . The chassis supports a forward-facing driver&#39;s seat  30 . The tractor shown in  FIG. 1  is outfitted with a rear-mounted implement, such as a backhoe attachment  32 , and a front mounted implement, such as a loader  34 . Direction and speed drive controls for normal, forward-facing, operation are arranged, either as foot pedals or as a control lever or actuator, operable from the driver&#39;s seat  30 .  
      The backhoe attachment  32  includes a rearward-facing operator seat  36  and backhoe controls  38 . The rearward-facing seat  36  can be a flip seat from the front-facing seat  30 . An operator console  40  is arranged on an adjacent fender  42 . According to the invention described herein, a creep speed control system  50  is arranged to be actuated by an operator sitting in the operator seat  36  (shown in  FIG. 15 ). The creep speed control system  50  allows the operator to move the utility vehicle at a controlled speed, forward or reverse, while operating the rear mounted implement.  
     Creep Speed Control For A Utility Vehicle Driven By A Hydrostatic Transmission  
       FIG. 2  illustrates, in block diagram form, the vehicle  20  incorporating the speed control system  50  of the present invention. The vehicle includes an engine  51  that drives a hydrostatic transmission  52 . The hydrostatic transmission  52  drives a range gear drive, such as a multi-speed gear transmission  54 , for transmitting power through a differential (not shown) to one or more driven wheels  56 . The tractor speed is controlled by adjustment of the speed output of the hydrostatic transmission  52 .  
      The hydrostatic transmission  52  includes a variable displacement pump  60 , and a hydraulic motor  62 . The engine  51  rotationally drives the variable displacement pump  60 . The pump  60  drives the motor  62 . The hydraulic motor drives the multi-gear transmission drive  54  interposed between the hydraulic motor  62  and the driven wheel  56 .  
      Forward and reverse pedals  72 ,  74  are mechanically connected via a linkage system  75  to a servo system  76  of the transmission  52 . A forward and reverse rear control  77  is also mechanically connected to the linkage system  75 . The pedals  72 ,  74  and the rear control  77  can be alternately operated to control transmission speed via the linkage system  75  and the servo system  76 .  
       FIGS. 3 and 4  illustrate a servo system  76  that controls speed of the transmission  52 . The system  76  includes a piston  112  slidable within a cylinder  114 . A servo control lever  116  moves a spool lever  117  that forcibly slides a valve spool  118  within a spool housing  121 . The relative positioning of the spool  118  within the housing  121  directs pressurized hydraulic fluid to a select side of the piston  112  within the cylinder  114  to move the servo piston  112  in a select direction.  
      The piston  112  has a notch  125  that holds a piston follower  126  ( FIG. 4 ). The piston follower  126  controls movement of a variable displacement pump cam plate or swashplate  128 . Movement of the piston  112  causes the swashplate  128  in the hydraulic pump to rotate out of the neutral position.  
      Maximum displacement of the pump  60 , for forward direction, is attained when the servo piston  112  is moved to its extreme position, upward in  FIG. 4 . Maximum displacement of the pump  60 , for reverse direction, is attained when the servo piston  112  is moved to its extreme position, downward in  FIG. 4 . The swashplate  128  is adjustable over a range of forward and reverse positions selected by the foot pedals  72 ,  74 .  
       FIG. 5  illustrates the hydrostatic transmission  52  in more detail. The hydrostatic pump  60  illustrated is an axial piston, servo controlled, variable displacement piston pump. Input shaft splines  136  are driven via a flex plate (not shown) bolted onto the engine flywheel (not shown).  
      Changing the angle of the swashplate  128  controls fluid flow through the pump  60 , and thus controls transmission speed. The servo piston  112  controls this angle.  
      The tilting, off centerline, of the swashplate controls the distance the pistons  140  travel inside the piston bores  142  of the rotating assembly. The direction that the swashplate is rotated from center determines the direction of fluid flow (forward or reverse). The number of degrees the cam plate is deflected determines how much fluid will be displaced, i.e., the amount of deflection determines the transmission speed.  
      The hydrostatic pump  60  provides hydraulic fluid to the hydrostatic motor  60  to through the back plate  148 , to drive the hydrostatic motor. Hydraulic fluid in the power train circulates in a closed loop. Fluid leaves the hydrostatic pump  60 , flows through the hydrostatic motor  60  to, and is returned to the hydrostatic pump.  
      The hydrostatic motor  62  is a high torque axial piston motor. The motor is located on the rear of the back plate. The hydrostatic motor drives an output shaft coupled to the range transmission  54  that transfers power to the wheels. The range transmission  54  can be a multi-speed range gear transmission, such as a three-speed or four-speed gearbox.  
       FIG. 6  illustrates mechanically operated creep speed control system  50  of the present invention. The rear creep speed control  77  is activated by a creep lever  202  positioned adjacent to the operator seat  36 . The creep lever  202  is operatively connected to a linkage element, such as a bell crank  206 . The bell crank  206  is connected to a push pull cable  208  that extends through or under the vehicle body to be connected to the foot control linkage  212  as shown in  FIG. 7 . The cable  208  is surrounded by a sleeve  208   a  that is fixed to the chassis or utility vehicle body at anchors  256 ,  256   a .  FIGS. 8-10  describe the arrangement of the rear speed control  77  in more detail.  
       FIGS. 6 and 7  describe the arrangement of the front pedal controls. In normal operation from the driver&#39;s seat, the foot pedals  72 ,  74  drive a primary bell crank  216  into rotation through a forward/reverse link  218 . The primary bell crank  216  is connected to a control lever  222  via a primary push-pull rod  226 . The lever  222  is connected by a further link  230  to the servo lever  116  that, by rotation, changes in the annular position of the swashplate to drive the hydrostatic transmission at a selected speed, as illustrated in  FIGS. 3 and 4 , in either forward or reverse direction. The push pull cable  208  from the creep speed control  77  is connected to the bell crank  216  at the connection  216   a . Selective pushing or pulling of the cable  208  by the system  77  causes controlled forward or reverse speed of the utility vehicle.  
       FIG. 8  illustrates the creep lever  202  connected to the creep bell crank  206  and protruding from a console  240  mounted to the fender  42 . The console includes forward and reverse end stops  242 ,  244  that limit the speed of the vehicle by limiting the movement range of the creep controlled lever. The lever  202  is pinned, with the crank  206 , at a point  248  to the fender  42 . The crank  206  includes a hole  252  at a top thereof. The push pull rod  208  is connected to a bottom end  206   b  of the crank  206 . The anchor  256  fixes the outer sleeve  208   a  of the push pull rod  208  with respect to the tractor body or chassis.  
       FIG. 9  illustrates the creep lever console  240  and creep lever  202 , in rear view, mounted on the vehicle fender  42 . A leaf spring  262  holds the creep lever  202  in a direction away from the fender  42 . In order for the creep lever  202  to turn the bell crank  206 , it must be pushed toward the fender  42  for a peg  266  on the lever to engage the hole  252  in the bell crank  206 . Once the peg  266  and the hole  252  are engaged, the lever  202  and the bell crank  206  pivot together.  
       FIG. 10  additionally shows the console  240  includes a neutral position notch  274 . The leaf spring holds the creep lever  202  in the neutral position notch  274  when the lever reaches the neutral position and outward hand force (toward the fender  42 ) on the lever  202  is removed. An outward hand force on the lever  202  toward the fender  42  frees the lever from the notch  274 .  
       FIGS. 8A and 9A  illustrate an alternate embodiment mechanical arrangement to that shown in  FIGS. 8 and 9 . A creep lever  202   a  includes an upper lever portion  202   b  fixed to a lower L-shaped lever portion  202   c . The lever  202   a  is pivotable on a stud  248   a  that carries a low friction Teflon washer  248   b , a bell crank  206   c , a wave spring  248   c , a flat washer  248   d , and a jam nut  248   e.    
      A hand knob  202   d  on a top of the upper lever portion  202   b  includes an activation button  202   e  supported on an internal coil spring  202   f . The button is connected to a rod  202   g  which extends below of the upper lever portion  202   b , forming a peg  202   h.    
      The bell crank  206   c  includes a notch  206   d  which must be engaged by the peg  202   h  in order for the lever  202   a  and the bell crank  206   c  to be pivoted together in forward or reverse direction from the neutral (zero speed) position shown in  FIG. 8A .  
      The push pull rod  208  moves the primary bell crank  216  as illustrated in  FIGS. 6 and 7 , to move the servo lever  116 . Thus, movement of the push pull rod  208  by the lever  202  causes angular movement of the swashplate  128 .  
      While operating the creep speed control, a “backup alarm” can be provided to sound while the creep system is in use, either in forward or reverse direction, as a warning of vehicle movement.  
       FIG. 11  illustrates a second embodiment wherein a speed control system  350  of the invention is accomplished using electronic control. The control system  350  includes a controller  366 , such as a microprocessor-based microcontroller. For normal, forward-facing operation, the control system  350  includes the forward pedal  72  and the reverse pedal  74 . The forward pedal  72  is operatively engaged with a potentiometer  382  to produce a forward pedal position signal, and the reverse pedal  74  is operatively engaged with a potentiometer  384  to produce a reverse pedal position signal. The potentiometers  382 ,  384  are signal-connected to the controller  366 .  
      The controller  366  is signal-connected, through appropriate signal conditioning or amplifying circuitry (not shown), to a solenoid  406   a  of a forward drive proportional pressure control valve  406  and to a solenoid  408   a  of a reverse drive proportional pressure control valve  408 . The output current to energize the forward or reverse pressure control valves  406 ,  408  is substantially proportional to the corresponding pedal position signal.  
      For creep speed control from a rear of the vehicle, the system  350  includes a creep speed control actuator  420  and direction switches  424 ,  428 . The direction switches  424 ,  428  are preferably momentary switches that must be continuously pressed to remain activated. Only one of the switches  424 ,  428  can be activated at a given time. In this regard, the switches  424 ,  428  can be formed by a toggle switch, pivoted to either engage switch  424  or switch  428  and which spring returns to a neutral position, neither switch activated, when neither switch is pressed.  
      The actuator  420  includes a slide lever  421  operatively associated with a lever position sensor, such as a potentiometer  434 . The potentiometer  434  is signal-connected to the controller  366 . The controller  366  is preprogrammed to send a proportional speed signal, in response to, and proportional to, a signal from the potentiometer  434 , to the respective solenoid  406   a ,  408   a , depending on which switch  424 ,  428  is activated. The proportional speed signal ranges from a zero speed signal up to a preprogrammed maximum speed signal corresponding to the maximum travel or position of the actuator  420 .  
      To enable the creep control system  350 , particularly the actuator  420  and switches  424 ,  428 , a seat switch  435  must first detect the presence of an operator sitting in the rear seat  36 .  
      A rotation speed sensor  436 , such as a Hall effect sensor, is arranged adjacent to a rotating part of the range transmission, such as a gear  437  that rotates in direct proportion to the vehicle ground speed. The controller  366  receives a frequency signal from the sensor  436  and adjusts the output speed signal to the proportional pressure reducing valve solenoids  406   a ,  408   a  to maintain the preprogrammed speed selected by the pedals  72 ,  74  or by the actuator  420 .  
      Ground speed will be variable from zero speed to a preset maximum safe speed for creep operation, given that the vehicle is being operated slowly, temporarily from the rear.  
      This maximum allowable speed will be independent of engine speed, or of range transmission gear selection. The ground speed sensed by the Hall effect sensor is used as a feedback signal to the controller so that the selected speed is maintaining regardless of the range transmission gear selection or engine speed.  
       FIGS. 12 and 13  illustrate the hydrostatic transmission servo control in more detail. Given an engine drive speed and a range transmission gear selection, the hydrostatic transmission provides variable speed control, forward and reverse, by operation of the foot pedals  72 ,  74  during normal operation, and by the actuator  420  during creep operation. Each valve  406 ,  408  is connected to a source of pressurized hydraulic fluid S and a return channel R at a reduced pressure. Preferably, the return channel R recirculates hydraulic fluid back to the vehicle&#39;s hydraulic system reservoir.  
      Depressing the forward foot pedal  72  during normal operation, or pushing the actuator  420  and the forward switches  424  during creep operation, causes an electrical output signal or voltage of the potentiometer  382  to be transmitted to the controller  366 . The controller  366 , through software, sends an electrical signal to energize the solenoid  406   a  of the forward drive proportional valve  406 . The proportional valve  406  is opened according to the electrical signal, allowing pressurized hydraulic fluid, fed from the source S into the inlet  407  of the valve  406 , to flow through the valve  406  to pressurize a servo cylinder  114  on one side of a servo piston  112  that is slidably housed in the cylinder  114 . The other valve  408  allows fluid to flow from within the cylinder  114 , from an opposite side of the servo piston  112 , to the return channel R.  
      When the reverse pedal  74  is pressed during normal operation, or the actuator  420  is pushed and the reverse switch  428  is activated during creep operation, the potentiometer  384  sends an electrical output signal or voltage to the controller  366 . The controller  366 , through software, sends an electrical signal to energize the solenoid  408   a  of the reverse drive proportional valve  408 . The reverse drive proportional valve  408  is opened, according to the electrical signal, to allow pressurized hydraulic fluid, fed into an inlet  419  of the valve  408  from the source S, to flow through the valve  408  to pressurize the servo cylinder  114  on an opposite side of the servo piston  112  within the cylinder  114 . The other valve  406  allows fluid to flow from within the cylinder  114 , from the one side of the servo piston  112 , to the return channel R.  
      Preferably, the valve solenoids  406   a ,  408   a  are driven by pulse width modulation type currents and causes pressure to be modulated at the outlet proportionally, according to the controlled width of step pulses of current applied. While the frequency of the pulses remains substantially the same, the pulse widths are changed to modulate the valves.  
      During creep operation, the swashplate  128  can only be moved by the actuator  420  and the switches  424 ,  428 , via the valves  406 ,  408 , over a preprogrammed limited range, set in the controller software, to limit vehicle speed.  
      To actuate the system, the operator must:  
      1. Be sitting at the rear operator&#39;s seat to enable creep drive.  
      2. Select a direction using the switches  424 ,  428 , either forward or reverse, for vehicle movement.  
      3. While holding the direction switch  424  or  428 , move the speed actuator lever  421 . This lever, via the potentiometer  434 , will provide an analog signal to the controller  366 . This signal will control transmission and vehicle speed.  
      While operating the creep speed control, i.e., while one of the switches  424 ,  428  are pressed, a “backup alarm” can be provided to sound while the creep system is in use, either in forward or reverse direction, as a warning of vehicle movement.  
       FIG. 14  illustrates a proportional, derivative, integral (PID) algorithm programmed within the controller  366  software for using the sensor  436  as feedback to correct the vehicle speed based on the ground speed of the vehicle. The measured ground speed from the sensor is compared to the selected speed dictated by the actuator position and an error between the two signals will be used to increase or decrease the output signal to the proportional control valves  406 ,  408  to increase or decrease tractor speed.  
       FIG. 15  illustrates the location of the creep speed control actuator  420 , the lever  421  and the direction switches  424 ,  428 . As can be seen, the speed control lever  421  and direction switches  424 ,  428  are located in a convenient location (refer to  FIG. 1 ) for the rear implement operator to reach slightly back and to the side with his left hand to control the actuator  420  and one of the direction switches  424 ,  428  to commence creep forward or creep reverse of the utility vehicle.  
     Creep Speed Control For A Utility Vehicle Driven By A Reverser Transmission  
       FIG. 16  illustrates, and a block diagram form, the creep speed control system of the present invention incorporated in a reverser transmission. A reverser transmission is described in detail in U.S. Ser. No. 09/905,645 filed Jul. 13, 2001, herein incorporated by reference. The reverser transmission uses hydraulically actuated forward and reverse clutch packs, to commence forward and reverse movement. According to the creep speed control system of the present invention, as applied to a reverser transmission, the operator actuates a direction switch and a speed actuator and a proportional speed signal is sent to the controller. The controller modulates the clutch pack proportional pressure reducing valves to initiate movement of the vehicle at a controlled and limited rate of speed.  
       FIG. 16  illustrates a control system  550  for use with a reverser transmission  552  of the type that uses electro-hydraulic control of clutch packs to engage forward or reverse tractor driving direction, for example as embodied in the POWRREVERSER™ transmission used in John Deere Series 4500 PRT and 4600 PRT tractors.  
      The reverser transmission  552  is driven by an engine drive  553 . The reverser transmission  552  drives a range transmission  554  that drives one or more wheels via a differential (not shown).  
      A controller  556 , such as a microprocessor-based microcontroller or an electronic control module, is signal-connected to forward and reverse proportional pressure control valves  562 ,  566 , which in turn are pressure-fluid-connected to forward and reverse clutch packs  572 ,  576 .  
      For normal operation from the forward-facing seat, a forward-neutral-reverse lever  602  is used to commence movement of the vehicle. The lever  602  is connected to switches  608 , which are signal-connected to the controller  556 . A clutch switch  634  and pedal position sensor, such as a potentiometer  638 , are mounted to a clutch or “inching” pedal and signal-connected to the controller  556 .  
      The forward and reverse clutch packs  572 ,  578  are hydraulically engaged and spring-released. The torque capacity of the clutch packs is thus a function of the hydraulic pressure supplied to the clutch packs. The proportional valves  562 ,  566  produce a downstream hydraulic pressure that is proportional to the current applied to the respective valve&#39;s solenoid, and thus control the hydraulic pressure supplied to the respective forward or reverse clutch pack.  
      The controller  556  controls the current to the correct valve  562 ,  566  and at the correct level to satisfy the clutch torque being commanded by the operator. Based on the operator&#39;s command via the vehicle direction selector  602 , the forward, reverse, or neither control valve  562 ,  566  is energized.  
      Based on the signal from a potentiometer  638 , connected to a clutch pedal or “inching pedal”  639 , the current to the respective control valve  562 ,  566  is also modulated as a function of clutch pedal position. The controller compares the output signal that is commanded by the preprogrammed speed/time profile triggered by a signal from the direction switch  608 , with an output signal that is commanded from the clutch pedal position signal from the potentiometer  638 , and modulates the output signal to the valves  562 ,  566  according to the smaller of the two speed commands.  
      A switch  612  senses the presence of an operator on the rear seat  36  and must be activated to enable the creep system, including the actuator  420  and the switches  424 ,  428 . The actuator  420  sends a speed demand signal, proportional to the position of the lever  421 , for a direction dictated by the direction switches  424 ,  428 , to the controller  556 . The controller  556  sends a control signal, proportional to the speed demand signal, to the valves  562 ,  566  to modulate clutch pressures. The controller  556  modulates the control signal according to the feedback signal from the speed sensor  436  and the maximum speed for creep mode, preprogrammed in the controller  556 .  
      The ground speed of the vehicle is sensed by the sensor  436  and a signal from the sensor  436  is used as a feedback signal to the controller  556  so that the selected speed is maintaining regardless of the range transmission gear selection or engine speed.  
      While operating the creep speed control, i.e., while one of the switches  424 ,  428  are pressed, a “backup alarm” can be provided to sound while the creep system is in use, either in forward or reverse direction, as a warning of vehicle movement.  
      From the foregoing, it will be observed that numerous variations and modifications may be effected without departing from the spirit and scope of the invention. It is to be understood that no limitation with respect to the specific apparatus illustrated herein is intended or should be inferred. It is, of course, intended to cover by the appended claims all such modifications as fall within the scope of the claims.