Abstract:
A personal mobility vehicle is steered by handlebars. A lever is mounted on the handlebars and rotatable in either of two opposite directions by the hands holding the handlebars. A potentiometer connected to the lever comprises a wiper on a resistive track, centered by a spring. The track has a central null area formed by material of lower resistance, so that the output voltage is constant. When the lever is moved away from the centered position, the wiper moves along the track and the output voltage rises or falls. A controller controls the speed and direction of the vehicle in response to the output voltage of the potentiometer. When the wiper is on the null area, the controller stops the vehicle. The size of the null area facilitates ensuring the centered position coincides with the null area, so the vehicle stops when the lever is released.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to vehicles, and particularly to a throttle control for a vehicle, and in particular a personal mobility vehicle.  
       BACKGROUND OF THE INVENTION  
       [0002]     A personal mobility vehicle is a motorized, usually battery powered, electric vehicle, typically utilized by a person who is able to walk but is not able to walk long distances. Such vehicles typically have a seat with a back, positioned above a pair of drive wheels. Batteries power one or more drive motors, which are typically positioned below the seat. In front of the seat is a footplate, on which a person sitting in the seat can rest his or her feet. In front of the footplate is an upstanding tiller, with handlebars at the top. The tiller is connected to a front wheel, or a pair of front wheels. Rotating or moving the tiller turns the front wheel or wheels and steers the vehicle.  
         [0003]     Typically, any controls that the user needs to operate while the vehicle are positioned on the tiller, adjacent to the handlebars. (See, for example, commonly-assigned U.S. Patent Application Publication No. 20020003055.) A throttle for controlling vehicle speed and direction is often controlled by a lever pivotably mounted on the middle of the handlebars, with one end of the lever operated by the user&#39;s left hand and the other end operated by the user&#39;s right hand. As one end of the lever is squeezed, typically by the right hand, the position of the lever generates a signal commanding forward motion of the vehicle, with the speed generally proportional to how far the lever is moved. When the other end of the lever is squeezed, a signal is generated commanding reverse movement of the vehicle. When the lever is released, a restoring spring (or springs) returns it to a central position, which results in the power being cut to the motor and, typically, results in the motor being used as a brake to slow and stop the vehicle.  
         [0004]     In order to provide a null position in the control and/or to generate a control signal for motor braking, it is necessary to accurately position the lever or other throttle control. If the null or neutral position of the throttle control is not accurately located, the vehicle may experience a forward or reverse drive motion from the motors when the throttle is released. Moreover, the neutral position is desired to be sufficiently robust for practical use.  
       SUMMARY OF THE INVENTION  
       [0005]     The present invention provides a speed control device for a vehicle, preferably of the type where the user operates a control to activate electric drive motors. The speed control device includes a potentiometer that provides a signal to a motor controller to regulate the current flow to the motor. The potentiometer has variable resistance on either side of a central position. The central position defines a “dead” or null area in which a specific output is generated over a range of control positions. This specific output signals the controller to brake the vehicle to a stop. The null area needs to be sufficiently large that the self-centering mechanism reliably parks the potentiometer in the null area, even after any shift in centering or increase in play that may occur as a result of wear during normal use.  
         [0006]     The potentiometer is a rotary potentiometer. To reduce tilting of the relatively rotatable components, and consequent possible errors in the position of the potentiometer, the potentiometer has an effective length at least equal to its effective diameter. For this purpose, the effective length and effective diameter of a bearing are the length and diameter of the surface or notional surface at which the relative movement between the components occurs. If movement is not confined to a single surface, for example, because there is an intermediate component such as a roller race, then the lowest length-to-diameter ratio, usually that measured at the surface of greatest diameter, should generally be measured.  
         [0007]     In one embodiment, the rotor of the potentiometer has a wiper that contacts a continuously increasing resistive track on the stator. A central, neutral position is defined where the potentiometer has a specific resistance value. This neutral position is extended by means of a conducting layer over the resistive material, to form a null section within which the resistive track has a specific and constant value. The wiper is mounted on a shaft that is journaled in a cylindrical plain bearing in a sleeve fixed coaxial with the resistive track. The length and internal diameter of the bushing of the plain bearing then define the effective length and effective diameter of the bearing. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]     For purposes of illustrating the invention, the drawings show one or more forms in which the invention can be embodied. The invention is not, however, limited to the precise forms shown unless such limitation is expressly made in a claim. In the drawings:  
         [0009]      FIG. 1  is a perspective view of an embodiment of a personal mobility vehicle for use with the present invention.  
         [0010]      FIG. 2  is an enlarged top view of the handlebars of the vehicle shown in  FIG. 1 , partially cut away to show a potentiometer.  
         [0011]      FIGS. 3A, 3B , and  3 C are top sectional views of the potentiometer shown in  FIG. 2 , in different operating positions.  
         [0012]      FIG. 4  is a side elevation view of the potentiometer shown in  FIG. 2 , partly in section.  
         [0013]      FIG. 5  is a section along the line  5 - 5  in  FIG. 2 .  
         [0014]      FIG. 6  is a partly exploded perspective view of the potentiometer shown in  FIG. 2 .  
         [0015]      FIG. 7  is an enlarged detail of part of the potentiometer shown in  FIG. 6 .  
         [0016]      FIG. 8  is a block diagram of the drive circuit for a vehicle, incorporating the present invention.  
         [0017]      FIG. 9  is an axial section through part of the potentiometer shown in  FIG. 4 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0018]     Referring to the drawings, and initially to  FIG. 1 , one form of personal mobility vehicle of the invention is a scooter, designated generally by the reference numeral  10 . The scooter  10  has three wheels, with a pair of rear wheels  12  driven by a motor (not shown, but designated generally in  FIG. 7  as item  14 ) and a single front wheel  16 . The front wheel  16  can be steered by means of a tiller generally indicated by the reference numeral  18 . The motor drives the two rear wheels  12  through a differential (item  20  in the  FIG. 7  schematic) to allow the rear wheels to move at different speeds on curves. The motor  14  may include reduction gearing or the like (not shown) to reduce the speed of rotation of the actual motor to that of the wheels. The drive motor, differentials and reduction gearing are contemplated to take any form as desired and in the interests of conciseness are not further described herein.  
         [0019]     A seat  24  is mounted towards the rear of the scooter  10 . Between the seat  24  and the tiller  18 , a footplate  26  extends the entire width of the scooter  10 . The footplate  26  is several inches above ground level, when the scooter  10  is resting on its wheels  10  and  16 , in order to allow clearance underneath for the scooter to pass over obstacles and uneven ground. The height of the seat  24  is set so that a user (not shown) can sit on the seat with his or her feet resting on the footplate  26 .  
         [0020]     The motor is typically mounted in the rear part of the scooter  10 , behind the footplate  26  and under the seat  24 . A power supply (item  30  in the schematic of  FIG. 7 ) is typically in the form of one or more electric storage batteries, and is usually also mounted in the rear of the scooter, below the seat.  
         [0021]     The tiller  18  includes a pair of handlebars  32 , projecting from either side near the top. By rotating the handlebars and thereby turning the tiller  18  to one side or the other, the user may rotate the front wheel  16 , steering the scooter to the left or right. The mechanisms for mounting and coupling the handlebars, tiller, and front wheel so as to achieve this steering action may take any conventional form and, in the interests of conciseness, are not further described herein.  
         [0022]     Referring now to  FIGS. 2 and 3 , to control the speed of the scooter there is provided a lever  34 , pivotally mounted at  36  at the center of the handlebars  32 , and extending to either side. The ends  38 ,  40  of the lever  34  are positioned near the inner ends of the handlebars  32  and to the rear of the handlebars, that is to say, on the side towards a user sitting in the seat  24 . The ends  38 ,  40  of the lever  34  are close enough to the handlebars  32  to be reached by the thumbs of the user while also holding the handlebars, but far enough away that the user can cause an appreciable rotation of the lever  34  by squeezing one of the ends  38  or  40  against the adjacent handlebar  32 . In the construction shown in  FIG. 2 , in the rest position each end  38  or  40  of the lever  34  is approximately 4 inches (10 centimeters) from the handlebar  32 , and the lever is approximately 16 inches (40 centimeters) from end to end. The lever  34  can thus rotate through an arc of about 30° from end to end, or 15° either side of its central rest position. As shown in  FIGS. 2 and 3 , the lever  34  is mounted by being fixed to the rotor shaft  50  of a rotary potentiometer  52 .  
         [0023]     Referring now to FIGS.  4  to  6 , the potentiometer  52  comprises a body  54  of electrically insulating material mounted on a threaded sleeve  56 , by means of which the potentiometer is mounted to a convenient part of the tiller  18  that is rigidly connected to the handlebars  32 . The rotor shaft  50  is journaled within the sleeve  56 , in a manner that will be described in more detail below. In known manner, the rotor shaft  50  and the sleeve  56  may be provided with flats, lugs, or other formations by which they may be easily aligned during installation. The threaded sleeve  56  is clamped by a nut  41  onto a bracket  42 , which is fixed to the tiller  18 . A cap  43  clamped to the potentiometer body  54  is also secured against rotation relative to the bracket  42  by a key  44 . The bracket has an upstanding tab  45  on one side.  
         [0024]     A collar  46 , having a tab  47  projecting down form one side, is fastened to the rotor shaft  50  by a set screw. The tab  47  overlaps axially with the tab  45 , and is of the same circumferential width as the tab  45 . A coil spring  48  is wound round the threaded sleeve  56 , and has two tangentially projecting ends  49  that rest against the sides of the tabs  45  and  47  with a torsional preload. The spring  48  thus maintains the tabs  45 ,  47  in alignment, and provides a restoring force returning them to the aligned position, and thus returning the rotor shaft  50  and the potentiometer body to a corresponding relative orientation, in the event of rotation. That relative orientation may be adjusted by releasing the set screw and rotating the potentiometer shaft  50  within the collar  46 . If that adjustment is not required, the rotor shaft  50  may be provided with a flat or recess into which the set screw can lock at a predetermined orientation.  
         [0025]     One face of the body  54  is provided with an inner, circular track  58  of electrically conductive material of low resistance, preferably silver, and an outer, horseshoe track  60  forming an almost complete circle. Three electrical leads  64 ,  66 ,  68  are respectively connected to the conductive track  58  and to each end of the arcuate track  60 . The ends of the leads  64 ,  66 ,  68  that connect to the tracks may be printed from conductive ink on the surface of the body  54 , preferably under the track  60 , provided that the end of the lead  64  is appropriately isolated from the track  60  where it crosses the radius of the latter track.  
         [0026]     Referring now also to  FIG. 7 , the arcuate track  60  consists mainly of two sections  70 ,  72  of electrically conductive material of low resistance, preferably silver, connected at one end to the leads  66 ,  68 , respectively. The other ends of the conductive sections  70 ,  72  are approximately 30° apart, and are joined by a track  74  of electrically resistive, but not fully insulating, material. At the center of the resistive track  74  is a strip of conductive material  76  covering, or recessed into, the surface of the resistive track  74 . Adjacent to each end of the resistive track  74 , the surfaces of the conductive sections  70 ,  72  are provided with roughened areas  78 . If the conductive sections are made of silver, the roughened areas may be formed by making the surface of the silver porous. Instead, an abrasive may be incorporated into the conductive material to form the roughened areas  78 .  
         [0027]     In the interests of clarity, the tracks  58  and  60  have been shown with appreciable thickness, and as projecting upward from the surface of the potentiometer body  54 . However, it is preferred to form them from layers of electrically conductive, resistive, and insulating ink of negligible thickness printed onto the surface of the body  54 . Preferably, at least the resistive track  74 , which provides the variable resistance of the potentiometer, is then printed on top of an undercoat  67  of dielectric ink, in order to provide a smooth substrate. This is found to improve the flatness of the resistive layer  74  and to produce a considerable reduction in wear and improvement in the service life of the potentiometer. The resistive layer may be printed in two or more coats. This also improves the service life of the potentiometer. Although not shown in the drawings, the ends of the resistive track  74  and the adjacent ends of the conductive sections  70 ,  72  may be overlapped.  
         [0028]     Fixed to the end of the rotor shaft  50  is an insulating disc  80 , which carries a pair of wipers  82 ,  84 , one of which runs on the track  60 , and the other of which runs on the conductive track  58 . The wipers  82 ,  84  are formed from a single piece of metal, or otherwise electrically connected, and thus connect the conductive track  58  to the point on the resistive track  74  that the wiper  82  is resting on. The wiper  84  resting on the circular conductive track  58  merely needs to ensure a good contact, and has a flat contact surface  86  engaging the track  58 . The wiper  82  resting on the track  60  needs to establish contact at a precise circumferential position, because its position along the resistive track  74  determines the output of the potentiometer. Consequently, the wiper  82  is angled, with the outside of the angle forming substantially a line contact, extending radially, with the track  60 . The rotor shaft  50  is positioned in the collar  46  at an orientation such that the spring  48  centers the potentiometer with the wiper  82  on the center of the conductive strip  76 . As will be explained below, the spring  48  must reliably center the potentiometer  52  with the wiper somewhere on the conductive strip  76 . Thus, the circumferential length of the conductive strip  76  provides a tolerance for play or drift in the centering mechanism.  
         [0029]     If the leads  66 ,  68  are connected to the ends of the track  60 , and a constant voltage is imposed between the leads  66 ,  68 , a readout of the position of the wiper  82  can be obtained very simply in the form of a voltage at a high-impedance output from the lead  64 . This readout indicates the orientation of the rotor shaft  50 , and thus of the position of the lever  34 . In this arrangement, the conductive section  76  provides a substantial part of the travel of the rotor shaft  50  within which the output voltage does not change.  
         [0030]     The length of the resistive track  74  is related to the travel of the lever  34  so that, when the lever  34  is at either end of its travel, the wiper  82  rests on one of the roughened areas  78 . This has two advantages. First, the roughened areas  78  act as an abrasive to clean the wiper  82 . Second, the resistive material  74  is not very durable, and may eventually wear out entirely. If that happens, the vehicle  10  can still be operated, albeit with reduced control, by rotating the lever  34  until the wiper  82  contacts one of the conductive regions  70 ,  72 . The controller  88  will then recognize a command to drive the vehicle at full speed in the appropriate direction.  
         [0031]     When the user is not squeezing either end of the lever  34 , it is centered automatically by the spring  48 . When the lever  34  is centered by the spring  48 , the wiper  82  rests on the conductive section  76 , which forms a null area between the two halves of the resistive track  74 . This section is formed by a section of conductive ink overprinted on top of the resistive ink forming the resistive track  74 . The reading from the potentiometer is then constant while the wiper  82  is anywhere on the null area  76 . Because the null area  76  is of significant width, the precision of the centering mechanism  80  does not have to be very high.  
         [0032]     Referring now to  FIG. 8 , the leads  64 ,  66 ,  68  are connected to a controller  88 , which measures the voltage at the lead  64  relative to the voltage difference between the leads  66  and  68 . The measured voltage represents the position of the wiper  82 , and thus the desired speed and direction of the vehicle. The controller  88  controls the power supplied by the battery  30  to the motor  14  accordingly. When the wiper  82  is on the null area  76 , the output voltage at the lead  64  has a constant value, roughly in the middle of the range. As the lever  34  is rotated, once the wiper  82  is off the null area  76 , the output voltage rises, if the lever is turned one way, or falls, if the lever is turned the other way, proportionately to the distance of movement of the ends  38 ,  40  of the lever.  
         [0033]     The controller is programmed to supply power to the motor  14  to propel the vehicle at a speed proportional to the amount of movement of the lever  34  and in a direction indicated by the direction of movement of the lever  34  away from the central rest position. The controller  88  is programmed to brake the vehicle when the output from the potentiometer is in a narrow range that includes the output when the wiper  82  is on the null area  76 . If the absolute value of that output drifts over time, for example, because of uneven wear of the resistive track  64 , then it would be possible for the controller  88  to recognize the null voltage, because it will always appear as a constant output for a significant period of time as the wiper  82  crosses the null area, and recalibrate itself accordingly.  
         [0034]     Because of the very small distances traveled by the wiper  82  over the active part of the resistive track, and especially the small null area  76 , it is important to ensure that the rotor shaft  50  rotates in the threaded sleeve  56  without tilting. In particular, if the rotor shaft  50  were to tilt about a transverse axis at the end of the threaded sleeve  56  further from the body  54 , the effect could be a significant displacement of the wiper  82  along the track  60 .  
         [0035]     Referring now to  FIG. 9 , the rotor shaft  50  is located axially within the threaded sleeve  56  by two C-clips  90  and  92  set in grooves  94 ,  96  in the rotor shaft. One of the C-clips  90  is positioned within a recess  98  in the body  54  of the potentiometer, inside the conductive track  58 . The abutment between the C-clip  90  and the bottom of the recess  98  acts as a thrust bearing, receiving the axial force produced by the springiness of the wipers  82  and  84 . The axial force is not large, but to give smoother rotation a washer  100  is provided between the C-clip  90  and the bottom of the recess. The other C-clip  92  engages the free end of the threaded sleeve  96 . A washer similar to the washer  100  is preferably also provided under the C-clip  92 .  
         [0036]     Seated in a recess inside the free end of the threaded sleeve  56 , and retained in position by the C-clip  92 , is a sleeve  102  that forms a plain bearing for the rotor shaft  50 . The bearing sleeve  102  is preferably made of bearing bronze or other copper alloy that provides a smooth bearing on the metal, typically steel, of the rotor shaft  50 . The bearing sleeve  102  fits into the threaded sleeve  56  as snugly as is consistent with ease of assembly, and fits the rotor shaft  50  as closely as is consistent with easy rotation, in order to minimize play. To minimize tilting of the rotor shaft  50 , the bearing sleeve  102  is longer than the diameter of the shaft, preferably about 1½ times as long as the inside diameter of the shaft. The part of the inner bore of the threaded sleeve  56  between the bearing sleeve  102  and the first C-clip  90  is of diameter slightly wider than the internal diameter of the bearing sleeve, so that the rotor shaft  50  is journaled in the bearing metal of the bearing sleeve  102 , and not in the metal, typically steel, of the threaded sleeve  56 .  
         [0037]     The C-clip  92 , including any washer, is preferably of sufficiently large outside diameter that it overlaps the threaded sleeve  56  outside the bearing sleeve  102 , and is of sufficiently small diameter that it does not hinder threading of the nut  41  onto and off the threaded sleeve.  
         [0038]     An  0 -ring  104  is seated in a groove  106  in the rotor shaft  50 . The  0 -ring  104  serves to seal the only opening into the interior of the potentiometer. The  0 -ring  104  engages either the bearing sleeve  102  or the interior wall of the threaded sleeve  56  between the bearing sleeve  102  and the first C-clip  90 . Preferably, as shown in  FIG. 9 , the  0 -ring may be positioned so that it rests on the end of the bearing sleeve  102 , exerting a slight axial pressure that further reduces play in the mounting of the rotor shaft  50 . However, this may result in increased wear of the  0 -ring from contact with the angular rim of the bearing sleeve  102 . Alternatively, therefore, the  0 -ring may be spaced away from the bearing sleeve  102 , and may engage the slightly wider part of the central bore of the threaded sleeve  56 .  
         [0039]     Although a specific embodiment of the invention has been described, various modifications are possible. For example, the part of the resistive track  74  under the conductive strip  76  could be omitted, so that the two halves of the resistive track  74  are separate. This would allow a thicker conductive strip  76  without an undesirably high bulge in the track surface that the wiper  82  runs on.  
         [0040]     Alternatively, the layer  76  could be formed of dielectric material, instead of conductive material. The central rest position of the potentiometer may then be recognized as a position in which no output signal is received. The part of the resistive layer under the dielectric layer  76  may then be omitted, so that the two halves of the resistive track  74  are separate. In this arrangement, the controller  88  measures the resistances between the lead  64  and each of the leads  66 ,  68  (one of which resistances should be very high) to identify the desired direction and speed of movement.  
         [0041]     The construction shown in the drawings, with the lever  34  mounted directly on the rotor shaft  50  of the potentiometer  52 , is mechanically very simple and reliable. However, it does involve a very small travel of the wiper  82  on the track  60 , approximately 30° of arc as shown in the drawings, and consequently requires precise manufacture of the potentiometer. It would be possible instead to increase the travel of the wiper  82 , for example, by introducing gearing between the lever  34  and the rotor shaft  50 .  
         [0042]     Further, although the vehicle  10  has been described and illustrated as a three-wheeled scooter, it will be appreciated that the speed control of the invention could be applied to a four-wheeled scooter, or indeed to any vehicle with a speed control that is moved away from a central rest position in one direction to command forward motion and in the opposite direction to command backward motion, with the amount of movement of the control commanding the speed of movement.  
         [0043]     The present invention may be embodied in other specific forms without departing from the spirit thereof and, accordingly, reference should be made to the appended claims, rather than to the foregoing specification, as indicating the scope of the invention.