Abstract:
To control both acceleration and deceleration of vehicles having an electric drive with regenerative braking, there is disclosed a control actuator which is biased to a neutral position, and which is controllably moveable between opposed positive and negative control positions relative to the neutral position to produce a control signal ranging from a value corresponding to zero when in the neutral position to a positive or negative value dependent on the amount of movement from the neutral position. The actuator may comprise a rocking foot pedal which is rotationally biased to the neutral position and which is pivotable against the bias both clockwise and anticlockwise from the neutral position to a desired positive or negative power control position. In one system, the signal produced by the actuator is treated as a power control signal and is conditioned and used to control vehicle power (i.e. energy flow from the vehicle battery the vehicle&#39;s electric drive). In another system, the signal produced by the actuator is treated as a speed changing control signal and is conditioned and used to control vehicle speed. Whatever desired speed is reached by movement of the actuator from its neutral position, the speed is sustained if the actuator is then permitted to return to its neutral position.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is related to U.S. provisional application No. 60/898,104 filed Jan. 30, 2007, entitled “Vehicle Power and Vehicle Speed Control Systems”, naming Gordon E. Dower as the inventor. The contents of the provisional application are incorporated herein by reference in their entirety, and the benefit of the filing date of the provisional application is hereby claimed for all purposes that are legally served by such claim for the benefit of the filing date. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to vehicle power control and vehicle speed control systems for vehicles which have an electric drive. The systems include cruise control systems. The vehicles include not only vehicles which are exclusively electric but also vehicles which are hybrid-electric. 
         [0003]    In conventional vehicles, the so-called “accelerator pedal” controls power, not speed. If the vehicle includes cruise control to hold the speed of the vehicle constant, cruise control settings are typically determined independently of the position of the accelerator pedal. Commonly, cruise control is engaged by a “set” button pushed by the driver at the desired speed, and disengaged by the driver pressing the brake pedal. A “resume” button returns the vehicle to the set speed. 
         [0004]    In some vehicles employing an electric drive (viz. those using an electric motor and an electric motor controller), regenerative braking may store kinetic energy in a battery that would otherwise dissipate as heat. Potential energy released when going downhill may likewise be stored to the battery. Regenerative braking may be initiated by pressing the brake pedal but it also may be activated by release of pressure on the so-called “accelerator pedal”—a somewhat confusing term in the present context, which is hereinafter avoided by instead using the term “power control pedal”. 
         [0005]    In more detail, a basic prior art power control system for a vehicle having an electric drive is representationally illustrated in  FIG. 1 . A somewhat more advanced prior art system is representationally illustrated in  FIG. 2 . The fundamental difference between the two systems is that the system illustrated in  FIG. 2  includes regenerative braking whereas the system illustrated in  FIG. 1  does not. 
         [0006]    The system shown in  FIG. 1  derives power from a battery power source  10  and includes a motor controller  11  and an electric motor  12  for providing motive power to wheels  13  of a vehicle. The system shown in  FIG. 2  similarly derives power from a battery power source  10  and includes a motor controller  21  and an electric motor  22  for providing motive power to wheels  13  of a vehicle. Both systems include a power control actuator comprising a power control pedal  25  and a displacement sensor  26  operatively connected to the power control pedal. In both cases, pedal  25  is mounted on a shaft  26 . 
         [0007]    In each system, pedal  25  is forcibly pivotable (clockwise from the position shown in  FIGS. 1 and 2 ) about an upper horizontal axis a 1  (which is also the axis of shaft  26 ) from a neutral or first pivot position where no power is to be applied to a second pivot position where maximum power is to be applied. The neutral position is maximally anticlockwise and the pedal is rotationally biased to that position by suitable biasing means (not shown). Normally, force is applied to the pedal by a user&#39;s foot  100  with the heel rested on floor  101  of the vehicle. When the force is released, then the pedal will return to its neutral position. 
         [0008]    In each system, a displacement sensor  27  produces a control signal having a variable value depending on the angular degree of rotation through which the pedal is pivoted clockwise from the neutral position. This signal is provided as an input to the motor controller ( 11 ,  21 ) which in response conditions and provides power from the battery ( 10 ,  20 ) to the electric motor ( 12 ,  22 ) depending on the measured angle. 
         [0009]    In the case of the system illustrated in  FIG. 1 , power control pedal  25  regulates only positive power. Resulting energy flow as depicted by cloud  14  can occur in only one direction from battery  10  to vehicle wheels  13 . In the case of the system illustrated in  FIG. 2 , power control pedal  25  may regulate negative as well as positive power. This is known as “single pedal control.” Here, as depicted by cloud  24  in  FIG. 2 , energy may flow not only from battery  10  to wheels  13  as in the case of the system illustrated in  FIG. 1 , but also from wheels  13  to battery  10  when pressure on power control pedal  25  is released. 
         [0010]    Power control pedals of the type described above are moveable in only one direction from their neutral position. Hence, they may be characterized as “unidirectional” in their operation. This limits their functionality. 
         [0011]    A conventional power control pedal in a vehicle having an electric drive with regenerative braking will not allow the vehicle to coast or freewheel when the foot is removed from the pedal (unless regenerative braking under single pedal control is disabled). Yet freewheeling under such circumstances might be desired. 
         [0012]    Also, a conventional power control pedal cannot be used to “set” a desired vehicle speed. 
       SUMMARY OF THE INVENTION 
       [0013]    Accordingly, in one aspect of the present invention, there is provided a new and improved power control system for a vehicle having an electric drive with regenerative braking, the system comprising a power control actuator which is biased to a neutral position, and which is controllably moveable between positive and negative power control positions relative to the neutral position for producing a power control signal ranging from a value corresponding to zero power when in the neutral position to a variable value dependent on the amount of movement from the neutral position. 
         [0014]    a power control actuator which is biased to a neutral position, and which is controllably moveable between positive and negative power control positions relative to the neutral position for producing a power control signal ranging from a value corresponding to zero power when in the neutral position to a variable value dependent on the amount of such movement from said neutral position. 
         [0015]    To enable freewheeling rather than regenerative braking, the system preferably includes a speed sensor for providing a speed signal corresponding to the measured speed of the vehicle and a speed holder operably connected to the power control actuator and the speed sensor. The speed holder receives a signal corresponding to the power control signal as a first input signal and a signal corresponding to the speed signal as a second input signal. In response, the speed holder produces as an output signal a modified power control signal for the motor controller, the modified signal having a variable value dependent on the difference between the first and second input signals. 
         [0016]    In a preferred embodiment, the power control actuator comprises a rocking foot pedal and a pedal rotation sensor, or an emulation of a rocking foot pedal and a pedal rotation sensor. The pedal is rotationally biased to a neutral position (e.g. by a suitable spring mechanism) relative to a pivot axis and is pivotable both clockwise and anticlockwise about the axis from the neutral position against the bias to a desired positive or negative power control position; a positive power control position normally being associated with acceleration and maintaining speed, a negative power control position normally being associated with braking. The rotation sensor is operatively connected to the pedal for producing the power control signal, the power control signal having a variable value dependent on the direction and degree of rotation of the pedal from its neutral position. When the pedal is in its neutral position, the power control actuator as a whole is in its neutral position. 
         [0017]    The pedal rotation sensor may comprise various elements. For example, it may comprise a rotary potentiometer. As another example, it may comprise optical sensing means. 
         [0018]    The orientation of the pivot axis about which rocking occurs is not considered to be critical. However, practical preferences may arise. Generally, it is contemplated that the pivot axis preferred by most users will be a horizontal axis typically located mid-way along the length of the pedal and extending transverse to the longitudinal alignment of the pedal. Normally, one&#39;s entire foot will be placed on the pedal. 
         [0019]    In another aspect of the present invention, it is recognized that a rocking foot pedal or an emulation thereof may be used not only to regulate power but also to enable speed holding without the use of other means, such as set and resume buttons as in the case of conventional cruise control. 
         [0020]    In this aspect of the invention, there is provided a vehicle speed control system for a vehicle having an electric drive with regenerative braking, the electric drive comprising an electric motor, an electric motor controller for controlling the motor, and a power source. The system comprises:
       (a) a speed changing control actuator biased to a neutral position and controllably moveable between opposed positive and negative control positions relative to the neutral position for producing a speed changing control signal having a variable value dependent on the direction and amount of such movement;   (b) a braking actuator for producing a braking signal;   (c) a resettable integrator operably connected to the control actuator for receiving an input signal corresponding to the speed changing control signal and, in the absence of a braking signal, for providing an output signal related to the input signal and the time integral of the input signal;   (d) an integrator resetter for resetting the integrator in response to a braking signal; and,   (e) a speed sensor for providing a measured vehicle speed signal to said integrator.       
 
         [0026]    In a preferred embodiment, the integrator is a switched augmenting integrator, the integrator resetter forming a part thereof. 
         [0027]    In cases where the electric motor is a D.C. electric motor as opposed to an A.C. electric motor, the system additionally comprises a speed holder. Note that when an A.C. induction motor is used, a speed holder may not considered essential because the motor output will be a constant speed dependent on the voltage input frequency. Note also that whether the motor is D.C. or A.C. it may be a conventional motor. 
         [0028]    The power source may be a conventional power source used for electric vehicles (for example, a conventional rechargeable battery). The electric motor controller may be a conventional motor controller for directing and conditioning power flowing between the power source and the motor in response to control signals which it (the motor controller) receives. 
         [0029]    The foregoing and other features and advantages of the present invention will now be described with reference to the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0030]      FIG. 1  is a diagrammatic representation of a prior art power control system for a vehicle which does not have regenerative braking. 
           [0031]      FIG. 2  is a diagrammatic representation of a prior art power control system for a vehicle which has regenerative braking. 
           [0032]      FIG. 3  is a diagrammatic representation in side elevation view of a rocking foot pedal and a user&#39;s foot. 
           [0033]      FIG. 4  is a perspective view of the rocking foot pedal shown in  FIG. 3 . 
           [0034]      FIG. 5  is a diagrammatic representation in side elevation view of another rocking foot pedal and a user&#39;s foot. 
           [0035]      FIG. 6  is a top view of the rocking foot pedal and user&#39;s foot shown in  FIG. 5 . 
           [0036]      FIG. 7  is a diagrammatic representation of a power control system for a vehicle in accordance with the present invention. 
           [0037]      FIG. 8  is a diagrammatic representation of a vehicle speed control system in accordance with the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0038]    By way of introduction, both the embodiment shown in  FIG. 7  and that shown in  FIG. 8  include a rocking foot pedal  30  which is also illustrated in  FIGS. 3 and 4 . This pedal, mounted on a shaft  31 , is pivotable both clockwise and anticlockwise about axis a 3  which extends transverse to the longitudinal axis of the pedal and generally horizontally relative to vehicle floor  101 . The neutral or biased position of pedal  30  is shown in solid outline in both figures  FIGS. 3 and 4 .  FIG. 4  additionally shows in broken outline the upper perimeter of pedal  30  when rotated anticlockwise to a position  30 ′ from the neutral position. As well,  FIG. 4  shows, again in broken outline, the upper perimeter of pedal  30  when rotated clockwise to a position  30 ″ from the neutral position. 
         [0039]    As represented by the plus sign in  FIG. 3 , positive power control positions will result from pushing with foot  100  on pedal  30  above axis a 3  (normally with the forward portion of one&#39;s foot). As represented by the minus sign in  FIG. 3 , negative power control positions will result from pushing on the pedal below axis a 3  (normally with the rearward portion of one&#39;s foot). Of course, it will be understood that such control characteristics could be reversed. However, it is considered that such a reversal would be counter-intuitive from a user&#39;s point of view. Unlike the foot position for control of pedal  25  as illustrated in  FIGS. 1 and 2 , the foot position for control of pedal  30  as illustrated in  FIG. 3  normally will lie entirely on the pedal and above vehicle floor  101 . 
         [0040]    As one alternative to a rocking foot pedal with a horizontally extending pivot axis a 3  as described above, the pivot axis may be aligned to extend upwardly and forwardly relative to a vehicle floor. This alternative is illustrated in  FIG. 5  which representationally shows a side elevation view of a rocking foot pedal  40  and a user&#39;s foot  100 , the pedal being mounted on a shaft  41  and rotationally biased to the position shown in  FIG. 5 . The forward portion of the user&#39;s foot is rested on the pedal while the heel is rested on vehicle floor  101 . Pedal  40  is pivotable both clockwise and anticlockwise from the neutral position shown in  FIG. 5  about axis a 4  which extends upwardly and forwardly relative to floor  101 . A top view of pedal  40  illustrating in solid outline the forward portion of the user&#39;s foot  100  centrally positioned on the pedal is shown in  FIG. 6 . In this foot position, and without rotative pressure on either side of axis a 4 , pedal  40  remains in its neutral position. 
         [0041]    Control may be achieved by placing the forward portion of one&#39;s foot on pedal  40  in a position bridging axis a 4  while the heel is rested on the vehicle floor  101 , then turning the foot to the left or right while pressing on the pedal. A foot turn to the right is illustrated in broken outline at  100 ′ in  FIG. 6 . A foot turn to the left is illustrated in broken outline at  100 ″. As indicated by the plus sign in  FIG. 6 , positive power control positions preferably are associated with foot turns to the right; negative power control positions preferably are associated with foot turns to the left. Although this control could be reversed, it is considered intuitively preferable because the left side of pedal  40  will be in closest proximity to where a conventional brake pedal is typically located relative to a conventional accelerator pedal. 
         [0042]    Persons wearing high heels may find it awkward to place their entire foot on a rocking foot pedal such as pedal  30 , and may therefore favor a pedal such as pedal  40 . 
         [0043]    Of course, it will be understood by persons of ordinary skill in the art that a rocking pedal movement could be designed to occur on a axis other than axis a 3  or a 4  as described above. 
         [0044]    Further, persons of ordinary skill in the art will appreciate that the control which can be achieved with an actuator which comprises any one of the rocking foot pedals described above can be emulated in a variety of ways. The use of one&#39;s foot is not necessarily required. For example, a suitable actuator may have a pivotal or linear movement emulating a pivotal movement designed for control by hand rather than by foot. The prior art is replete with devices for detecting movement and for measuring the amount of movement. 
         [0045]    Referring now to  FIG. 7 , there is illustrated a power control system for a vehicle having an electric drive, the electric drive comprising a battery power source  70 , a motor controller  71 , and an electric motor  73  for providing motive power to wheels or at least one wheel  13  of the vehicle. The system comprises a power control actuator  75  comprising a rocking foot pedal  30  as shown in  FIGS. 3 and 4 , and a pedal rotation sensor  76 . Further, the system comprises a speed sensor  77  and a speed holder  78 . 
         [0046]    It will be understood by persons of ordinary skill in the art that a rocking foot pedal such as foot pedal  40  could be substituted in  FIG. 7  for pedal  30  to generally achieve the same function or similar control as that provided by pedal  30 . 
         [0047]    Speed holder  78  receives two input signals, the first being a power control signal from power actuator  75  via the output of pedal rotation sensor  76 , the second being a speed signal from speed sensor  77  corresponding to the measured speed of the vehicle. In response, the speed holder (which, for example, may comprise an operational amplifier) produces as an output signal a modified power control signal for motor controller  71 , the modified signal having a variable value dependent on the difference between the two input signals. 
         [0048]    Referring now to  FIG. 8 , there is illustrated a speed control system for a vehicle having an electric drive, the electric drive comprising a battery power source  80 , a motor controller  81 , and a D.C. electric motor  82  for providing motive power to wheels  13  of the vehicle. The system comprises a speed changing control actuator  90  comprising a rocking foot pedal  30  as shown in  FIGS. 3 and 4 , a rotary potentiometer  91 , and a buffer amplifier  95 . Further, the system comprises a speed sensor  96 , a speed holder  97 , a switched augmenting integrator  100  which includes an integrator resetter  101 , and a braking actuator  110 . 
         [0049]    Since actuator  90  of the present embodiment serves to control speed rather than power, it is referred to herein as a speed changing control actuator rather than as a power control actuator. However, as will be understood by persons of ordinary skill in the art, actuator  90  as depicted in  FIG. 8  may readily be regarded from a structural point of view as a species of actuator  75  as depicted in  FIG. 7 . Further, it will be understood that this species is merely an example. 
         [0050]    In further regard to actuator  90 , and as in the case of the embodiment shown in  FIG. 7 , it will be understood by persons of ordinary skill in the art that a rocking foot pedal such as foot pedal  40  could be substituted in  FIG. 8  for pedal  30  to generally achieve the same function as that provided by pedal  30 . 
         [0051]    In more detail, rotary potentiometer  91  of actuator  90  is mounted with pedal  30  on shaft  31  and includes two terminals; firstly, terminal  92  normally wired to a positive DC voltage source and, secondly, terminal  92  normally wired to a negative DC voltage source. The positive and negative sources are of equal magnitude whereby the voltage on line  94  at the output of the potentiometer is zero when pedal  30  is in its neutral position. This output is also the input to buffer amplifier  95  which in the present embodiment is an operational amplifier wired as a voltage follower. Together, potentiometer  91  and amplifier  95  may be considered as part of a pedal rotation sensor. 
         [0052]    As shown in  FIG. 8 , braking actuator  110  comprises a conventional brake pedal  111  (which has associated conventional mechanical components not shown) and also a brake application sensor  112  for producing braking signals upon a driver&#39;s activation of the brake pedal. One braking signal from the brake application sensor is provided as a reset signal on line  115  to switched augmenting integrator  100 ; another as a signal on line  113  to motor controller  81 . The input to brake application sensor  112  from pedal  111  may be a simple voltage generated when pedal  111  moves to close a switch, (generally similar to conventional cruise control or brake-light systems). Although not shown, it of course will be understood that brake pedal  111  is connected to the vehicle brakes as well as brake application sensor  112 . 
         [0053]    Switched augmenting integrator  100  receives a proportionate actuator displacement signal from speed changing control actuator  90  and adds to it the time integral of that signal to provide a signal to operatively connected speed holder  97 . It also receives a signal from integrator resetter  101  to adjust its output to correspond to any post-braking speed. In more detail, switched augmenting integrator  100  comprises operational amplifier OA 1 , capacitor C l , resistors R 1  and R 2 , and triple-pole double-throw switch SW 1 . One end of resistor R 1  is connected to the output of buffer amplifier  95  of speed changing control actuator  90 ; the other to an input of amplifier OA 1 . 
         [0054]    The switch position shown in  FIG. 8  is a BRAKE OFF position where capacitor C 1  and resistor R 2  are connected by switch SW 1  in series in a feedback loop around amplifier OA 1  from the output of amplifier OA 1 . This is the normal (viz. unactivated) position of switch SW 1 . In this position, the relationship between the output voltage v 2  of amplifier OA 1  and the input voltage v 1  from the output of buffer amplifier  95  as a function of time (t) can be simply expressed as follows: 
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         [0055]    If the vehicle is starting from rest, then v 1 (0) will be zero. 
         [0056]    When switch SW 1  is activated by a reset signal from braking actuator  110 , then the switch toggles and capacitor C 1  and resistor R 2  are removed from the feedback loop of amplifier OA 1 . A zero resistance/impedance appears in the feedback path around OA 1 . Fundamentally OA 1  is now wired as a voltage follower. This is a BRAKE ON position and results when coil  116  of switch SW 1  receives an energizing reset signal on line  115  from brake  111  via brake application sensor  112 . In this switch position, the output on line  98  from speed sensor  96  becomes effective. The voltage across capacitor C 1  will drive towards the voltage output from speed sensor  96 . Meanwhile, on line  113 , brake application sensor  112  signals motor controller  81  to provide neither positive or negative energy to motor  82 . 
         [0057]    When brake  111  is released and the reset signal from braking actuator  110  ends, SW 1  becomes deactivated. Capacitor C 1  and resistor R 2  will be once again in the feedback loop of amplifier OA 1 . The resulting initial voltage input to speed holder  97  from OA 1  will depend upon the voltage across capacitor C 1  at the time the reset signal from braking actuator  110  was terminated. 
         [0058]    Speed sensor  96  provides a signal proportional to the vehicle&#39;s measured speed. One of its two outputs is provided as an input to integrator resetter  101  on line  98 ; the other to speed holder  97  on line  99 . 
         [0059]    Speed holder  97  is operatively connected to the output of switched augmenting integrator  100 , speed sensor  96 , and motor controller  81 . Its output depends upon the difference between the inputs received from the outputs of integrator  100  and speed sensor  96 . 
         [0060]    More particularly, using the speed signal from speed sensor  96 , speed holder  97  signals motor controller  81  to provide positive or negative energy to D.C. electric motor  82  to or from battery  80  so as to maintain a constant speed signal in proportion to the speed holder&#39;s setting. That setting matches and tracks the output of integrator  100 . Speed holder  97  may be an operational amplifier used as a voltage follower in which motor controller  81 , electric motor  82 , vehicle wheels  13  and speed sensor  96  constitute a chain in its feedback loop. 
         [0061]    As indicated above, the switched augmenting integrator shown in  FIG. 8  includes a triple-pole double-throw switch SW 1  which has BRAKE ON and BRAKE OFF positions. The position will be determined by the presence or absence of a reset signal on line  115  from brake application sensor  112 . If there is no reset signal from the brake application sensor, then the signal will correspond to a BRAKE OFF signal. If there is a reset signal, then the signal will correspond to a BRAKE ON signal. 
         [0062]    When the system shown in  FIG. 8  is in use, motor controller  81  is operatively connected to speed holder  97 , battery  80 , and D.C. electric motor  82 . Motor controller  81  responds proportionally to the output of speed holder  97  by regulating the energy flow in either direction between battery  80  and electric motor  82 . Regenerative braking occurs when the motor controller causes energy to flow from the motor to the battery. Motor controller  81  is also operatively connected along line  113  to brake application sensor  112  of braking actuator  110  whose braking signal causes the motor controller to reduce motor energy flow to zero whenever, and so long as, brake pedal  111  is pressed. 
         [0063]    Electric motor  82  is operatively connected to motor controller  81  and drive wheels  13 . It causes energy to flow from battery  80  to the drive wheels and vice versa, according to its input from the motor controller. 
         [0064]    In preferred embodiments, the system illustrated in  FIG. 8  functions as follows when in use: 
         [0065]    Starting from rest, the driver applies toe pressure to pedal  30  thereby causing a positive displacement from its neutral or default position. This produces a positive output from actuator  90  proportional to the degree of displacement. Fed to switched augmenting integrator  100  as an input, this output immediately results in a corresponding time dependent output that passes to speed holder  97  which is thereby “set” and compares this set signal to the speed signal from speed sensor  96 , which will be zero if the vehicle has not yet started to move. Based on the comparison, the speed holder signals the motor controller to cause a proportionate energy flow from battery  80  to motor  82  and thence to vehicle wheels  13 . 
         [0066]    The vehicle accelerates causing speed sensor  96  to generate an increasing signal that is fed to speed holder  97 . The feedback loop is closed (in the absence of a brake signal) and the vehicle&#39;s speed increases until the comparison reduces so that the flow of energy from battery  80  balances frictional, drag, and gravitational forces acting on the vehicle. However, the speed at which the comparison goes to zero is influenced by any change in the signal received from switched augmenting integrator  100  and this depends on the driver&#39;s pressure on pedal  30 . If the driver immediately removes his or her foot, the output of integrator  100  will stay constant because of the absence of any time over which to integrate. If the driver maintains constant toe pressure, and therefore constant displacement of pedal  30 , then the output of integrator  100  will not return to zero but will, instead, gradually increase as the integral of the displacement signal increases over time. The vehicle will gradually accelerate and continue to do so to the limits of the system. To counter this, a driver typically will intuitively gradually relax foot pressure and the vehicle will ease into a constant speed, maintained by speed holder  97 , once the foot has been removed from the pedal. If the driver now applies heel pressure, the speed setting signal fed to speed holder  97  will decline. Eventually, motor controller  81  may be called upon to begin regenerative braking to the point of zero speed. If the driver continues to apply heel pressure, the set signal will be or will become negative and the vehicle will eventually begin travelling backwards. This characteristic reflects another advantage of the present invention. In addition to obviating the need for separate speed holding buttons for cruise control, it renders unnecessary a separate control for driving in reverse. 
         [0067]    When brake pedal  111  is applied, a braking signal is generated and fed to motor controller  81  causing it to interrupt energy flow between battery  80  and drive wheels  13 . Such braking as now takes place is mechanical and non-regenerative. The integrator  100  is switched so that its output, governed by the speed signal from speed sensor  96 , declines to a value equal to whatever corresponds to the current speed. Consequently, when the driver removes his or her foot from brake pedal  111 , there is a new set speed such that the vehicle&#39;s speed is now held at the post-braking speed. The means by which this may be achieved is illustrated by the embodiment shown in  FIG. 8 . 
         [0068]    If an A.C. motor was employed instead of D.C. motor  82  shown in  FIG. 8 , then it will be understood by persons of ordinary skill in the art that speed holder  97  as shown in  FIG. 8  and its connection (line  99 ) from speed sensor  96  can be excluded. Necessarily, the connection from amplifier OA 1  to speed holder  97  will instead extend as an input to motor controller  81   
         [0069]    Various modifications and changes to the embodiments shown in the drawings are possible and undoubtedly will occur to persons of ordinary skill in the art.