Patent Publication Number: US-9409578-B2

Title: Electric drive vehicle control system

Description:
RELATED APPLICATIONS 
     This application is a continuation application of U.S. patent application Ser. No. 13/561,414, filed Jul. 30, 2012, which is a continuation application of U.S. patent application Ser. No. 12/209,074, filed Sep. 11, 2008, now U.S. Pat. No. 8,234,026, which claims priority to U.S. Provisional Patent Application No. 60/971,419, filed on Sep. 11, 2007, all of which are incorporated by reference herein in its entirety. 
    
    
     TECHNICAL FIELD 
     This application is generally related to electrically powered vehicles, and more particularly to control systems, methods and processes for electric drive mechanisms of electrically powered vehicles, such as, for example, utility vehicles. 
     BACKGROUND OF THE INVENTION 
     Utility vehicles, such as, for example, lawn tractors, have generally relied upon internal combustion engines as the prime mover transferring power through mechanical linkages (gearing or belts), hydrostatic drive(s), continuously variable transmissions (CVTs), or other similar devices to propel the vehicle. However, manufacturers of these vehicles, especially lawn tractors used for lawn mowing, are under continuously increasing pressure to reduce environmental pollution caused by vehicle emissions, as well as fluid leaks and noise from the hydrostatic transmission or engine. Hence, utility vehicles utilizing electrically-powered systems have become a primary focus to address these and other issues with combustion-engine type vehicles. 
     SUMMARY OF THE INVENTION 
     The present invention comprises systems, methods and processes for electric drive mechanisms of electrically powered vehicles, such as, for example, utility vehicles. In a particular embodiment, electronic control processes are utilized to control electronic traction and auxiliary drive systems, such as a mower deck drive mechanism. In an embodiment incorporating a mowing deck, the control processes control, among other things, vehicle travel and mower deck cutting blade speed. In such an embodiment, the electric motors receive signals from the control system of the vehicle in accordance with programmed processes to control the transmission driving speed and power take-off (PTO), and, hence, the mower deck cutting blade operation. The systems, methods and processes of the present invention have many other applications in numerous types of electrically powered vehicles. 
     A better understanding of the objects, advantages, features, properties and relationships of the invention will be obtained from the following detailed description and accompanying drawings which set forth one or more illustrative embodiments that are indicative of the various ways in which the principles of the invention may be employed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a top plan view of a vehicle incorporating an embodiment of an electrically powered vehicle with an embodiment of a typical operator control panel in accordance with the principles of the present invention. 
         FIG. 2  is a block diagram illustrating an overview of the vehicle control system in accordance with the principles of the present invention. 
         FIG. 3  is a bubble diagram of the various operating states of the electronic traction control system shown in  FIG. 2 . 
         FIG. 4  is a bubble diagram of the various operating states of the electronic mower deck drive control system shown in  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     The description that follows describes, illustrates and exemplifies one or more embodiments of the present invention in accordance with its principles. This description is not provided to limit the invention to the embodiments described herein, but rather to explain and teach the principles of the invention in order to enable one of ordinary skill in the art to understand these principles and, with that understanding, be able to apply them to practice not only the embodiments described herein, but also other embodiments that may come to mind in accordance with these principles. The scope of the present invention is intended to cover all such embodiments that may fall within the scope of the appended claims, either literally or under the doctrine of equivalents. 
     It should be noted that in the description and drawings, like or substantially similar elements may be labeled with the same reference numerals. However, sometimes these elements may be labeled with differing numbers, such as, for example, in cases where such labeling facilitates a more clear description. Additionally, the drawings set forth herein are not necessarily drawn to scale, and in some instances proportions may have been exaggerated to more clearly depict certain features. Such labeling and drawing practices do not necessarily implicate an underlying substantive purpose. As stated above, the present specification is intended to be taken as a whole and interpreted in accordance with the principles of the present invention as taught herein and understood by one of ordinary skill in the art. It should also be noted that references herein to specific manufactured components may be provided as preferred embodiments or exemplifications and should not be construed as limiting. In each case, similar or equivalent components from other manufacturers may be utilized as well. 
       FIG. 1  shows a vehicle  12  implementing one or more embodiments in accordance with the principles of the present invention. While vehicle  12  shown in  FIG. 1  is a mowing vehicle, the principles of the present invention may be applied to other vehicles as well, such as, for example, utility vehicles, tractors, or other vehicles incorporating auxiliary systems (e.g., mower blades, augers, snow throwers, tillers, sweepers, spreaders, etc.) that can benefit from integrated control with a drive system. Vehicle  12  includes a power supply  13 , a mower deck  14 , a pair of driven wheels  18  and a pair of steered wheels  25 . In an alternate embodiment (not shown), a single steered wheel may be used. In the embodiment shown, vehicle  12  also includes an electric transaxle  10  that drives a pair of output shafts or axles  16 , which in turn drive a pair of wheels  18  that provide motion to vehicle  12 . It should be noted that the use of the term wheel is intended to cover all types of wheels, as well as gears, linkages, or other mechanisms that may ultimately translate into a traction implement, such as, for example, an inner wheel of a track arrangement on a track vehicle. 
     Vehicle  12  includes a plurality of systems to perform various functions, such as vehicle control system  50 , which is illustrated separately in  FIG. 2 . A general overview of the interaction between control system  50  and other portions of vehicle  12  is illustrated in the block diagram of  FIG. 2 . Traction controller  51  controls transaxle  10  and, when certain operational conditions are met, allows the operator of vehicle  12  to close PTO switch  43  to energize or allow activation of one or more functional outputs of an auxiliary controller in the form of deck controller  52 , which can drive a variety of auxiliary equipment such as mower deck  14  (illustrated), or in other embodiments, a snow thrower, a tiller, sweeper brooms, or other implements. In the illustrated embodiment, traction controller  51  is an AC-0 inverter manufactured by Zapi, Inc. of Cary, N.C. Controller terminal and pin identifiers, such as A5, A6, B7, B8, etc., are shown for reference only. Other circuit arrangements/pin assignments are possible. Alternatively, many other types of processors, programmable logic controllers (PLCs), or the like could be utilized in accordance with the principles of the present invention. 
     Referring again to  FIGS. 1 and 2 , control system  50  includes traction controller  51  that receives signals from, and sends signals to, various other portions of control system  50  and vehicle  12 . Transaxle  10  includes an electric motor  11  (which may be, for example, an asynchronous three-phase AC induction motor or any other electric motor type sufficient for driving a vehicle) that is drivingly attached to gearing within transmission  17 , thereby transmitting torque to axle or output shafts  16 , which causes rotation of driven wheels  18 . In an alternate embodiment, vehicle  12  may include two transmissions, each independently driving one of a set of opposed axles, each having an associated drive wheel, such as in a zero-turn vehicle arrangement. In yet another embodiment, vehicle  12  may include two electric direct drive motors, each independently driving one of a set of opposed wheels without transmissions, such as in a zero-turn vehicle arrangement. The principles of the present invention apply to these types of arrangements as well. 
     Referring once again to  FIGS. 1 and 2 , traction controller  51  of control system  50  controls the speed and direction of vehicle  12 . The speed of transaxle  10  can be adjusted by regulating the voltage frequency supplied to electric motor  11 . Feedback used in the control of vehicle  12  is provided to traction controller  51  by speed sensor  37  of electric motor  11  on transaxle  10 . 
     Speed sensor  37  of electric motor  11  may be a dual Hall Effect sensor that can sense and signal both a change in acceleration and rotation direction of electric motor  11 . Feedback from speed sensor  37  enables execution of programming of desired characteristics of acceleration, deceleration, neutral, and change in direction via control software in connection with traction controller  51 . The flexibility of programming allows features such as, for example, a panic stop ramped deceleration function, custom acceleration/deceleration curves, or other programmable functions to be implemented. 
     Electric motor  11  may be protected from damage by over-current and over-voltage sensors or circuitry (not shown) located in fraction controller  51 . MOSFETs (metal-oxide-semiconductor field-effect transistors) located within controller  51  are protected by the controller&#39;s capability to monitor current and temperature. A temperature sensor  36  may be located in electric motor  11  to protect electric motor  11  from overheating. Feedback from these sensors may be used to perform system checks, regulate vehicle speed, disable the PTO, initiate a controlled shutdown, sound or display a warning, or perform other functions relating to the vehicle. Additionally, in a particular embodiment, vehicle  12  may be driven in a forward or reverse direction by operator control of accelerator pedal  40 , which may be a “rocker style,” heel and toe operated pedal that includes one or more associated or integrated switches to signal direction and a potentiometer (or other signal-generating device) to signal desired speed to traction controller  51 . Alternatively, the potentiometer utilized in the accelerator pedal  40  can be utilized to generate a signal representative of both speed and direction. Optionally, a separate F-N-R (Forward-Neutral-Reverse) switch could be employed, which is used in conjunction with a simple accelerator pedal that signals desired speed only. Such a switch can be mounted on dash  20 . In yet another embodiment (not shown), two separate pedals could be used for forward and reverse directions of vehicle movement. This option allows manufacturers flexibility in choosing traditional operator controls or a different configuration. A wiring harness or assembly  54  may be used to electrically connect the various elements of control system  50 . Wiring harness  54  may be configured so that wires carrying signals are grouped together and wires carrying power and drive signals are grouped together with appropriate shielding for signal integrity. 
     As shown in  FIGS. 1 and 2 , power supply  13  is provided to operate one or more systems of vehicle  12 , including components of control system  50 . In the embodiment shown, power supply  13  consists of four 12V batteries providing 48V power. Power is distributed from power supply  13 , through power contactor  53 , to traction controller  51 . In the embodiment shown, power contactor  53  is a Model SW60 contactor manufactured by Albright International, Ltd. of Surbiton, UK (England). Power supply  13  is also in electrical communication with on-off key switch  23 . With key switch  23  in the ON position, and with the presence of power at a specified voltage threshold from power supply  13 , power contactor  53  enables traction controller  51  after diagnostic checks verify that traction controller  51  is ready to run. 
     Referring again to  FIGS. 1 and 2 , movement of rocker style accelerator pedal  40  (or other accelerator mechanism) signals traction controller  51  of an operator-directed acceleration or deceleration of vehicle  12  in either the forward or reverse direction. The input signals from accelerator pedal  40  determine the direction and speed of operation of transaxle  10 . 
     As explained above, vehicle  12  includes operator interfaces, switches, sensors, and other components that interact within control system  50  to effectuate control of vehicle  12 . Brake pedal  32  of vehicle  12  actuates a brake system located either as part of transaxle  10  or as a separate device or system. The brake system may be based on regenerative braking, mechanical braking, or a combination. Steering wheel  19  or other steering mechanism or control interface facilitates turning of vehicle  12  by mechanical, electro-mechanical, hydrostatic, or other known methods of controlling positioning of steered wheels  25 . In the illustrated embodiment, vehicle dash  20  or an equivalent includes an indicator LED (light emitting diode) or lamp  22 , vehicle key switch  23 , PTO switch  43 , cruise switch  42 , reverse operating system (ROS) switch  41 , brake switch  30 , emergency stop switch  31 , battery gauge  21  and hour meter  24 .  FIG. 2  illustrates an embodiment of some of these controls, switches, sensors and components in more detail. 
     The following description describes a representative array of elements. Some of these elements may be optional for a particular vehicle configuration. In other configurations, additional elements may be desirable. For example, a speed sensor  37  or temperature sensor  36  may be unnecessary in some applications. In another example, additional sensors may be desired to improve operator satisfaction or safety. Such sensors may include thermocouples, proximity aids, vehicle attitude or inclination sensors, and other devices relevant to the operation of a typical vehicle. Furthermore, activation of, for example, a vehicle attitude or inclination sensor may be used to initiate a secondary function, such as transmission of an emergency signal to a remote receiver in the event of a vehicle rollover. 
     In an embodiment, control system  50  controls three general categories of functionality of vehicle  12 : (1) diagnostics and start-up associated with traction controller  51  to enable control system  50  for vehicle  12 , (2) operational parameters or constraints for traction controller  51  during operation, and (3) operational parameters or constraints for other features of traction controller  51  and deck controller  52  systems. Each of these general categories is discussed below. 
     There are several control aspects related to starting and running vehicle  12 . Because vehicle  12  is accelerated electrically, a diagnostics routine is performed on the electronics prior to permitting vehicle  12  to be operated. If the battery charge does not meet the minimum threshold, fraction controller  51  will prevent start-up. Referring to  FIG. 2 , when key switch  23  is rotated to the ON position, traction controller  51  performs an array of diagnostics. Once the diagnostics have successfully been completed, a relay permits actuation of power contactor  53 . As will be noted in more detail later, traction controller  51  continuously monitors a variety of conditions and has the ability to shut down the system by way of disengaging power contactor  53 . Once power contactor  53  is engaged, functionality of the fail-safe, normally-closed brake  15  is checked. Part of this check involves verifying the brake holding capacity at start-up to ensure serviceability. Traction controller  51  drives the electric motor  11  to the required holding torque specification and monitors whether the drive wheels  18  move. If the check fails, the controller can be programmed to allow operation in a reduced power mode or disable the electric drive system. The controller can also be programmed to bypass the fail-safe holding torque check. 
     As the system continues performing diagnostics that will enable traction controller  51  and mower deck controller  52 , seat switch  34  is checked to verify operator presence. Functionality of traction controller  51  is checked and the drive state is enabled. The neutral state of vehicle  12  is verified. The inactive state of power take-off switch  43  and cruise switch  42  is also verified. The position of ROS switch  41  is checked against the drive state of vehicle  12 . After the diagnostic program passes checks, LED indicator lamp  22  indicates a “No Error” state, and power contactor  53  is switched on to enable propelling vehicle  12 . In a particular embodiment, other diagnostic options may be selectively included via software, such as, for example, limited or disabled functionality relative to battery capacity or state. 
     Referring again to  FIGS. 1 and 2 , when power contactor  53  is switched on, traction controller  51  is enabled. Traction controller  51  receives signals from various inputs of vehicle  12  that relate to motive operation of vehicle  12 . Initially, a check for inputs from accelerator pedal  40  is performed. If accelerator pedal  40  has been moved out of the neutral position (also referred to as PEDAL OFF in  FIG. 3 ), fail-safe brake  15  is disengaged to allow the vehicle to travel the respective speed and direction indicated. Acceleration and deceleration characteristics can be programmed via software in connection with traction controller  51 , which allows selection of acceleration or deceleration curves with different characteristics for greater operator satisfaction and control based on operator inputs or vehicle conditions. For example, deceleration curves may be programmed for a coast-to-stop function or for a panic stop function when encountering a sudden hazard. A panic-stop may be initiated by operator input or by object detection sensor (not shown) input to traction controller  51 . Other sensors or system diagnostics may also be used to initiate a system-controlled vehicle stop. The acceleration or deceleration curves can be predetermined and stored in a memory associated with the controller, or optionally can be customizable and programmed by a manufacturer (including original equipment manufacturers and authorized service technicians) given certain safety constraints. These programmed curves, at the manufacturer&#39;s election, can be made selectable by an operator of the vehicle. 
     Once fraction controller  51  is enabled, and when programmed safe operating conditions are met, PTO switch  43  can be activated to run auxiliary or deck motors  27  and  28  of mower deck  14  (or other optional attachment or implement). The current draw by drive motor  11  can be regulated for control. For example, the current draw can be regulated manually with the addition of an operator-manipulated potentiometer (e.g., knob, lever, or slide control—not shown). Optionally, the current draw can be automatically regulated via traction controller  51  to slow vehicle  12  if induced loads become high, such as when mowing thick or tall grass or when traveling up a steep grade, or if power consumption exceeds programmed parameters. This can be accomplished by enabling communication between fraction controller  51  and deck controller  52 , such as via CAN (Controller Area Network) bus or other control unit connection standard. Such regulation lowers power consumption, extends battery life between charges and optimizes operation levels to extend service life. Other signals may be desirable to enable control system  50  to provide safer and more effective operation of vehicle  12 . Traction controller  51  may provide an indication of the operating condition of the traction or deck drive systems by way of an indicator such as LED or indicator lamp  22  or by way of other operator interfaces which may be visual, audible, or a combination of visual and audible. 
     The remaining control aspects of traction controller  51  relate to operation of deck motors  27  and  28  associated with mower deck  14 . Once traction controller  51  is enabled, the operator has the ability to activate deck controller  52 . Deck controller  52  drives mower deck motors  27  and  28  which, in the embodiment shown, are controlled independently by two separate circuit boards (one for each motor) housed within deck controller  52 . Operator actuation of PTO switch  43 , when programmed safe operating conditions are met, will cause deck controller  52  to power right deck motor  27  and left deck motor  28 , which drive the cutting blades of mower deck  14 . In a particular embodiment, deck motors  27  and  28  are brushless DC (BLDC) motors, which each include Hall Effect sensors that provide feedback information to deck controller  52 . Optionally, sensorless PMSMs (permanent magnet synchronous motors) may be employed utilizing other feedback arrangements known in the art, such as motor position and timing estimates based on software algorithms. A temperature sensor (not shown) is also included in each deck motor to provide feedback to deck controller  52  to prevent overheating of deck motors  27  and  28 . Additionally, over-current and over-voltage sensors (not shown) are included in deck controller  52  to prevent damage to deck motors  27  and  28 . Again, optionally, other feedback arrangements can be utilized, such as motor position and timing estimates, voltage and current estimates, etc., based on software algorithms. In an alternate embodiment (not shown), feedback from sensors in deck motors  27  and  28  and deck controller  52  can be integrated with feedback from sensors providing information to traction controller  51  and used to regulate the speed of vehicle  12 . This integration can be used to limit power consumption and proportionately adjust for the load each drive encounters with respect to available power. As noted above, this can be accomplished by utilizing a CAN bus. Additionally, axle shafts  16  may have speed sensors (not shown) associated with them. Speed sensors may be used for several purposes, such as, for example, determining the neutral position or neutral state of transaxle  10 , which allows the controller to presume transaxle  10  is in the neutral position when the neutral position or state is sensed. Speed sensors associated with axle shafts  16  would, among other things, enhance the ability to establish the non-rotating condition of axle shafts  16 , thereby further defining the neutral position. The controller system could automatically initiate a vehicle speed reduction in the mowing state and make further adjustments under increasing loads. This can be triggered alternatively by current draw or temperature constraints. 
     According to another aspect, deck controller  52  allows for a programmable timeout if vehicle  12  is stopped for a set period of time. Other power conservation and safety features can be readily programmed, such as a multi-stage shutdown sequence to protect and manage power supply  13  when the charge has deteriorated to specified levels. In a particular embodiment, the first time the specified minimum voltage level is reached and sensed for a predetermined period (5 seconds, for example), the deck motors  27  and  28  associated with deck  14  are disabled and a reduced vehicle speed is implemented to reduce the load on power supply  13 . If the voltage then draws down to the minimum voltage level and is sensed for more than a predetermined period a second time, the traction drive speed is reduced again (to 20% of maximum, for example). If the minimum charge level is reached and sensed for a predetermined period a third time, the traction drive may be disabled, stopping the vehicle. Optionally, the vehicle may enter a hibernation state wherein travel modes are disabled, but minimal power is still available to energize, for example, a visual display, emergency lights, or an emergency signal transmitter while key switch  23  remains in the ON position. 
     An alarm to remind the operator to recharge power supply  13  can be employed at vehicle shutdown to help prevent deep battery discharge and prepare vehicle  12  for next use. A plug-in “smart” charger may be used to charge power supply  13 . This “smart” charger may be on-board vehicle  12  or external to vehicle  12 . Another optional feature is employment of regenerative braking of the electric motor(s) to charge the system power supply during braking or when the vehicle is coasting. 
     When attempting to move in reverse with a mower deck engaged, a reverse operating system (ROS) typically stops the blades of the mower deck by removing power from an electric clutch-brake or by killing the prime mover to stop the vehicle. In the embodiment shown, closing ROS switch  41  allows the operator to bypass this function to permit operation of deck motors  27  and  28  and associated mower blades when accelerator pedal  40  is moved to a position indicating reverse travel of vehicle  12 . This ROS function is facilitated by the interaction between traction controller  51  and deck controller  52 . The ROS function allows uninterrupted mowing in reverse without worry of a time-out condition. Only when vehicle  12  is shifted out of reverse will the ROS function be deactivated. Once shifted out of reverse, this mode can only be reinitiated by activating ROS switch  41  before shifting vehicle  12  back into reverse. The vehicle must be in either neutral or forward to activate the ROS switch  41 . A 2-position ROS switch  41  is indicated in  FIG. 2 , but a momentary switch or other switch forms could be substituted. Alternatively, an ROS position can be added to key switch  23 , thereby eliminating the need for separate ROS switch  41 . Additionally, traction controller  51  can be programmed to automatically slow vehicle  12  when moving in reverse and/or when mowing in reverse. Audible and/or visual alarms (which may include error codes), object detection systems, etc., may also be activated when moving and/or mowing in reverse. 
     Software switches can be used to slow the vehicle, stop the vehicle or blades automatically, or enable auxiliary functions when certain operating, alarm, or emergency conditions are met or encountered while operating vehicle  12 . As an additional safety feature, brake  15  may be configured to engage traction drive motor  11  when vehicle  12  is stopped or stalled. A manual release cable (or other linkage) may be used with brake  15  to allow the operator to disengage the brake in order to move vehicle  12 . The manual release cable may be combined with an integrated switch in communication with controller  51  to ensure that vehicle  12  is disabled when moving vehicle  12 . Functionally, this gives the operator a bypass option to push or tow the vehicle. 
     The flexible programming capability of mower deck controller  52  driving the blades in mower deck  14  allows inclusion of a slight delay and/or ramping up to optimal cutting speed for both safety and energy conservation. Another feature that can be implemented is a blade stop function that performs a controlled stop of mower blades when either PTO switch  43  is deactivated or when key switch  23  is deactivated. For example, a capacitor in deck controller  52  can latch power so that when key switch  23  is switched off before PTO switch  43  is deactivated, mower deck controller  52  can back-drive deck motors  27  and  28  to stop mower blades within a programmed interval instead of allowing them to coast to a stop. For example, this programmed interval may be specified as 5 seconds or some other specification corresponding to an industry standard such as ANSI (American National Standards Institute) or an OEM (original equipment manufacturer) specification. Controlled braking of mower blades can also be accomplished by utilizing regenerative braking or mechanical braking. 
     Additionally, deck controller  52  may receive a signal from traction controller  51  to stop deck motors  27  and  28  when vehicle  12  has not moved for a programmed time interval, or if vehicle  12  exceeds a programmed maximum travel speed (axle speed sensors, for example, can enable both of these functions), or if other vehicle operational parameters are exceeded. 
     Turning now to  FIG. 3  (the traction controller  51  state map), various combinations of actuator and switch positions define various states for traction, PTO, ROS, cruise, key switch, sensors and errors while utilizing operating control system  50  functions as illustrated. Illustrated are 10 different preferred states of operation for traction controller  51  and interrelationships of these states. 
     The first state  100  is the vehicle OFF state in which vehicle  12  is powered down and controllers are disabled with key switch  23  in the OFF position. When key switch  23  is turned to the ON position, control passes to state  101 , in which traction controller  51  is powered and begins processing. 
     State  101  is a diagnostic and preparation to operate state, which includes a ready or standing state, if diagnostics pass. If diagnostics fail, state  101  passes to error state  102  and an alarm is actuated. Any of the following states described herein can pass to error state  102  if they fail any of the conditions outlined for operation within a particular state. State  101  consists of key switch  23  on, internal diagnostics pass, PTO switch  43  off, ROS switch  41  off, cruise switch  42  off, operator in seat (actuating seat switch  34 ), foot off accelerator pedal  40  (in neutral), and manual brake switch  30  off. Also, electric brake  15  coil resistance is measured to determine presence of the coil. Optionally, the brake holding capacity check, as previously described, may be employed as well. If all of these conditions are met, power contactor  53  is closed. If the operator then actuates PTO switch  43 , control passes to state  110  and the PTO timeout timer is set. Alternatively, if the operator first actuates the accelerator pedal  40 , a test of brake  15  is performed. If the brake test is passed, the controller  51  passes control to state  103 . 
     State  102  is an error state in which errors can be categorized as recoverable or non-recoverable. For non-recoverable errors, control remains in state  102  until key switch  23  is turned off. Recoverable errors can be resolved without cycling key switch  23  and, when resolved, the alarm is deactivated. Non-recoverable errors occur when the controller shuts off the PTO, shuts down the vehicle for not meeting a specified minimum voltage requirement, a hardware failure is detected, a diagnostic failure occurs, seat switch  43  is detected open in a state other than state  101  (recoverable error in state  101 ), or a test of brake  15  fails. Recoverable errors may be defined to include, for example, a condition when the operator is not in the seat, an accelerator is not in neutral, a manual brake release switch is in an ON position, etc. Any alarm or emergency condition (for both recoverable and non-recoverable errors) encountered by traction controller  51  or deck controller  52  will result in passing control to state  102  and stopping of both vehicle  12  and deck  14  blades. If PTO switch  43  was on before entering error state  102 , it will be necessary to cycle PTO switch  43  after recovery from the error in order to resume operation of mower deck  14  motors  27  and  28 . 
     State  103  is a transport state where vehicle  12  is in a travel-only mode. State  103  consists of key switch  23  on, internal diagnostics pass, PTO switch  43  off, ROS switch  41  on or off, cruise switch  42  on or off, operator in seat (actuating seat switch  34 ), accelerator pedal  40  in either forward or reverse and maximum speed enabled. The sequence starts with the operator closing seat switch  34  and then actuating accelerator pedal  40 . A test of brake  15  is performed by traction controller  51  and, if passed, brake  15  is released and electric motor  11  is started in the direction signaled by the operator&#39;s input. If the PTO is activated while in state  103 , controller  51  passes control to state  104 ,  105 ,  108 , or  111 , depending on a combination of accelerator pedal  40  position (forward or reverse) and ROS switch  41  position (on or off). If traction controller  51  determines it should pass control to state  105  (attempted reverse mowing with ROS off), then either vehicle  12  speed is greatly reduced and mowing is allowed (referenced as “105 Opt 1” in  FIG. 3 ), or, if a reverse cut-off function is selected in the software, then mowing is not allowed (referenced as “105 Opt 2” in  FIG. 3 ) and a non-recoverable error is generated and control passes to state  102 . If control passes to state  104 ,  108 , or  111 , vehicle  12  speed is limited to a programmed forward mowing speed. Cruise switch  42  will only function if traveling forward and then the speed is maintained while traveling forward. Activating cruise switch  42  while traveling forward “freezes” the actual current vehicle speed. The cruise condition is terminated if brake pedal  32  is depressed, or accelerator pedal  40  is moved into reverse, or accelerator pedal  40  is pressed forward further than the “frozen” position, or cruise switch  42  is actuated while the accelerator pedal is in neutral. While in cruise mode, if accelerator pedal  40  is pressed forward and cruise switch  42  is actuated again, the “frozen” cruise value will be updated, reflecting the new accelerator position. When accelerator pedal  40  is moved into the neutral position (represented by the PEDAL OFF notations in  FIG. 3 , as mentioned previously), vehicle  12  stops, and when accelerator pedal  40  remains in the neutral position for a specified, programmed time interval (such as, for example 0.4 seconds), traction controller  51  will return to state  101  and engage brake  15 . If manual brake switch  30  is activated, controller  51  overrides accelerator pedal  40 , forces electric motor  11  to zero rpm, stops vehicle  12  and engages brake  15 . When operating in state  103 , if ROS switch  41  is in the ON position and PTO switch  43  is then switched to the ON position, traction controller  51  will jump to state  111  if moving forward and state  108  if moving in reverse. Conversely, if ROS switch  41  is in the OFF position and PTO switch  43  is then switched to the ON position, traction controller  51  will jump to state  104  if moving forward and state  105  if moving in reverse. 
     State  104  is the forward mowing state with ROS off, traveling at a reduced working speed. State  104  consists of key switch  23  on, internal diagnostics pass, PTO switch  43  on, ROS switch  41  off, cruise switch  42  on or off, operator in seat (actuating seat switch  34 ), accelerator pedal  40  in forward and working speed reduction enabled. When accelerator pedal  40  is moved into the neutral position, vehicle  12  stops, and when accelerator pedal  40  remains in the neutral position for a specified, programmed time interval, traction controller  51  jumps to state  110  and engages brake  15 . When PTO switch  43  is switched off, traction controller  51  jumps to state  103  and sends a signal to the deck controller  52  (or other auxiliary controller, depending on configuration) to stop deck motors  27  and  28 . When accelerator pedal  40  is moved to the reverse position, control jumps to state  105  and vehicle  12  transitions from forward travel to reverse travel, if allowed by software settings. Alternatively, when accelerator pedal  40  is moved to the reverse position, control jumps to state  105  and then to error state  102  if not allowed by software settings. If ROS switch  41  is switched on, traction controller  51  jumps to state  111 . If a momentary ROS switch  41  is used (referenced in  FIG. 3  as “ROS Opt 2”), the timeout feature is set before transferring to state  111 . 
     State  105  is the attempted reverse mowing with ROS off state. State  105  consists of key switch  23  on, internal diagnostics pass, PTO switch  43  on, ROS switch  41  off, cruise switch  42  off, operator in seat (actuating seat switch  34 ), accelerator pedal  40  in reverse and either a speed reduction function or a cut-off function enabled. Depending on software settings, state  105  either allows mowing in reverse at reduced speed when accelerator pedal  40  is in the reverse position (referenced in  FIG. 3  as “105 Opt 1”), or it does not allow any mowing (referenced in  FIG. 3  as “105 Opt 2—Reverse Cut-Off”) and control is passed to state  102  and an alarm is generated. If reduced speed mowing is allowed in state  105 , the reduced speed may be programmed at, for example, approximately one foot per second maximum for safety, or other specification corresponding to an industry standard such as ANSI or an OEM specification. If not allowed, and control is passed to state  102  as mentioned above, this is a non-recoverable error, so key switch  23  must be turned off and back on to proceed. ROS switch  41  is disabled while in state  105 , so it will not function if switched on while in state  105 . Under “105 Opt 1”, when accelerator pedal  40  is moved to the neutral position, vehicle  12  stops, and when accelerator pedal  40  remains in the neutral position for a specified, programmed time interval, fraction controller  51  jumps to state  110  and brake  15  is applied. If PTO switch  43  is switched off, control jumps to state  103  and deck motors  27  and  28  are stopped. If accelerator pedal  40  is moved into forward position, traction controller  51  jumps to state  104  and vehicle  12  transitions from reverse travel to forward travel. 
     State  108  is the reverse mowing state with ROS on, operating at a reduced working speed. State  108  consists of key switch  23  on, internal diagnostics pass, PTO switch  43  on, ROS switch  41  on, cruise switch  42  off, operator in seat (actuating seat switch  34 ), accelerator pedal  40  in reverse and working speed reduction enabled. When PTO switch  43  is switched off, traction controller  51  jumps to state  103  and deck motors  27  and  28  are stopped. If a latching ROS switch  41  is used (under “ROS Opt 1”), when accelerator pedal  40  is moved into the neutral position, vehicle  12  stops, and when accelerator pedal  40  remains in the neutral position for a specified, programmed time interval, traction controller  51  jumps to state  110  and brake  15  is applied. If accelerator pedal  40  is moved into forward position, traction controller  51  jumps to state  104  (under “ROS Opt 1”) and vehicle  12  transitions from reverse travel to forward travel. If a momentary ROS switch is used (under “ROS Opt 2”), when accelerator pedal  40  is moved to the neutral position, vehicle  12  stops, and when accelerator pedal  40  remains in the neutral position for a specified, programmed time interval, traction controller  51  jumps to state  112  and brake  15  is applied. If accelerator pedal  40  is moved into forward position, traction controller  51  jumps to state  111  (under “ROS Opt 2”) and vehicle  12  transitions from reverse travel to forward travel. 
     State  110  is a temporary, stationary vehicle state with PTO switch  43  on and ROS switch  41  off. State  110  consists of key switch  23  on, internal diagnostics pass, PTO switch  43  on, ROS switch  41  off, cruise switch  42  off, operator in seat (actuating seat switch  34 ), accelerator pedal  40  in neutral, working speed reduction enabled and electric brake  15  applied. When the PTO timeout has elapsed, PTO switch  43  is switched off by the software and traction controller  51  jumps to state  101 . If accelerator pedal  40  is moved into the forward position, fraction controller  51  will jump to state  104  or, if moved into the reverse position, to state  105 . If ROS switch  41  is switched on, traction controller  51  will jump to state  112 . If a momentary ROS switch  41  is used (“ROS Opt 2”), traction controller  51  sets the ROS timeout timer before transfer to state  112 . 
     State  111  is the forward mowing state with ROS on (and which enables a timeout function for the ROS under “ROS Opt 2”). State  111  consists of key switch  23  on, internal diagnostics pass, PTO switch  43  on, ROS switch  41  on, cruise switch  42  on or off, operator in seat (actuating seat switch  34 ), accelerator pedal  40  in forward and working speed reduction enabled. If accelerator pedal  40  is moved into reverse position, traction controller  51  jumps to state  108  and vehicle  12  transitions from forward travel to reverse travel. When PTO switch  43  is switched off, traction controller  51  jumps to state  103  and deck motors  27  and  28  are stopped. When accelerator pedal  40  is moved to the neutral position, vehicle  12  stops, and when accelerator pedal  40  remains in the neutral position for a specified, programmed time interval, traction controller  51  jumps to state  112  and brake  15  is applied. If ROS switch  41  is switched off, traction controller  51  jumps to state  104 . If a momentary ROS switch  41  is used (“ROS Opt 2”), and if the ROS timeout elapses, controller  51  jumps to state  104 . 
     State  112  is a temporary, stationary vehicle state with ROS switch  41  and PTO switch  43  both on (and which enables a timeout function for the ROS under “ROS Opt 2”). State  112  consists of key switch  23  on, internal diagnostics pass, PTO switch  43  on, ROS switch  41  on, cruise switch  42  off, operator in seat (actuating seat switch  34 ), accelerator pedal  40  in neutral and working speed reduction enabled. When the PTO timeout elapses, traction controller  51  jumps to state  101  and deck motors  27  and  28  are stopped. If accelerator pedal  40  is moved into the forward position, traction controller  51  will jump to state  111  or, if moved into the reverse position, to state  108 . If ROS switch  41  is switched off, fraction controller  51  jumps to state  110 . If a momentary ROS switch  41  is used (“ROS Opt 2”), and if the ROS timeout elapses, controller  51  jumps to state  110 . 
     Turning now to  FIG. 4  (the deck controller  52  state map), various combinations of actuator and switch positions define various states for the PTO, key switch and errors while utilizing operating controller system functions as illustrated. Illustrated are 5 different states of operation for deck controller  52  and the interrelationships of these states. 
     State  100 , as previously described above, is the vehicle OFF state in which vehicle  12  is powered down and controllers are disabled with key switch  23  in the OFF position. When key switch  23  is switched on, and after diagnostics have passed, deck controller  52  is enabled by controller  51  and deck control passes to state  202 . 
     In state  202 , deck controller  52  is enabled with key switch  23  on and PTO switch  43  off. When PTO switch  43  is switched on, deck controller  52  jumps to state  203 . 
     In state  203 , deck controller  52  is enabled with key switch  23  on and PTO switch  43  on to power mower deck motors  27  and  28 . From state  203 , deck controller  52  transfers control to one of two possible states, error state  204  or PTO disabled state  205 . 
     State  204  is the error state which is entered if one or more deck motors  27  and  28  are outside the programmed allowable temperature, current, or voltage range. Once the error is removed, operator cycling of PTO switch  43  once (after a programmed delay of approximately 5 to 10 seconds to prevent overheating of MOSFETs or other sensitive electronic components) will return control to state  203  and start deck motors  27  and  28  running again. If key switch  23  is placed in the OFF position while in state  204 , deck controller  52  will jump to state  100 . 
     In state  205 , the PTO is disabled. Mower deck  14  cutting blades are stopped (within a programmable time limit governed by industry standards or OEM specifications for safety) by pulse width modulation (PWM) control of deck motors  27  and  28 . When PTO switch  43  is switched off (thereby removing the PTO ground), deck controller  52  jumps to state  202  from state  205 . If PTO switch  43  is switched back on and the ground signal is reapplied at state  205  before the motor stopping function is completed, deck controller  52  returns to state  203 . If the key remains off in state  205 , deck controller  52  returns to state  100 . 
       FIGS. 1 and 2  illustrate some of the various inputs that may be connected via operator-actuated switches to traction controller  51 . Traction controller  51  as illustrated allows an operator to use an emergency stop switch  31 , brake switch  30 , or the key switch  23  OFF position to initiate engagement of fail-safe brake  15  on electric motor  11 . Cruise switch  42  can be engaged to maintain a constant travel speed input which is cancelled upon receiving a brake pedal  32  or accelerator pedal  40  input signal outside a set or programmed range. If the set range is exceeded, cruise switch  42  must be turned off and back on again to reactivate the cruise function. As mentioned previously, a separate F-N-R switch may be added if rocker style accelerator pedal  40  (shown) is replaced by a different type of accelerator pedal. Optionally, hand-operated lever or joystick controls may be used in lieu of pedal(s) and steering wheel. 
     While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the invention which is to be given the full breadth of the appended claims and any equivalent thereof.