Abstract:
Methods and apparatus are provided for preventing over-shifting in electric vehicles having a multi-gear transmission and an electric motor operable in a drive mode and a regenerative braking mode. The method includes: (a) predicting the speed of the electric motor resulting from downshifting from a current gear being used to a next lower gear based on a current speed of the electric vehicle, a current speed of the electric motor, and a gear ratio of the next lower gear; (b) determining if the speed of the electric motor predicted in (a) will cause an overvoltage condition from regenerative braking or an overspin condition in the electric motor; (c) preventing downshifting to the next lower gear when it is determined that the downshifting will cause an overvoltage condition or an overspin condition in the electric motor; and (d) repeating steps (a), (b), and (c) a plurality of times.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority from U.S. Provisional Patent Application No. 61/754,161 filed on Jan. 18, 2013 entitled METHOD AND APPARATUS FOR INHIBITING OR PREVENTING OVER-SHIFTING ON ELECTRIC VEHICLES, which is hereby incorporated by reference. 
     
    
     BACKGROUND 
       [0002]    The present application relates generally to electric vehicles such as, e.g., electric motorcycles, tricycles, and all-terrain vehicles (ATVs). More particularly, the application relates to methods and apparatus for preventing over-shifting on such vehicles. 
         [0003]    One benefit of electric vehicles is the ability to re-capture energy during braking or on a downhill descent, often called regenerative braking—or “regen” for short. An electric motor, when supplied energy, will drive the traction wheel(s) of the vehicle, which then propel the vehicle forwards. When no energy is supplied to the motor, but the traction wheel(s) supply mechanical motion to the motor, the motor itself will become a generator supplying energy that can be used to assist in recharging the vehicle battery system. The higher the motor rotor is spun by mechanical means, the larger the voltage produced as a result. 
         [0004]    For electric vehicles with a fixed gear system, the motor speed and corresponding output voltages are generally closely matched for the system it is designed into. With a gearbox equipped electric vehicle that supports selection between multiple gears, an issue arises that if a too low gear is quickly selected at high speeds, the resulting regen voltages become excessively large as the motor spins above maximum rated revolutions per minute (RPM). An example of this is a motorcycle with a multi-gear transmission traveling in one particular gear at maximum motor RPM, which then quickly downshifts one or more gears while maintaining the same or similar speed. The result would be the motor spinning faster than the maximum RPM speed allowed (overspin) with a resulting voltage generation that exceeds system design parameters (overvoltage), which can cause damage to the vehicle. 
       BRIEF SUMMARY OF THE DISCLOSURE 
       [0005]    In accordance with one or more embodiments, methods and apparatus are provided to determine whether the effects of a new gear selection in an electric vehicle is safe or excessive before that gear is entered. If the new gear is determined to result in excessive regenerative voltages being produced, a mechanism is actuated to prevent the shift from completing. Two exemplary mechanical implementations for preventing shifting are described: one external to the gearbox and the other internal to the gearbox. The techniques for preventing over-shifting can be predictive (preventing shifting before it occurs) or reactive (preventing shifting after the shift sequence has initiated). 
         [0006]    In accordance with one or more embodiments, a method is provided for preventing over-shifting in an electric vehicle having a multi-gear transmission and an electric motor operable in a drive mode and a regenerative braking mode. The method includes the steps of: (a) predicting the speed of the electric motor resulting from downshifting from a current gear being used to a next lower gear based on a current speed of the electric vehicle, a current speed of the electric motor, and a gear ratio of the next lower gear; (b) determining if the speed of the electric motor predicted in (a) will cause an overvoltage condition from regenerative braking or an overspin condition in the electric motor; (c) preventing downshifting to the next lower gear when it is determined that the downshifting will cause an overvoltage condition or an overspin condition in the electric motor; and (d) repeating steps (a), (b), and (c) a plurality of times. 
         [0007]    An electric vehicle in accordance with one or more embodiments comprises an electric motor operable in a drive mode and a regenerative braking mode, at least one drive wheel, a multi-gear transmission connected to the electric motor and the at least one drive wheel for transmitting torque therebetween, an energy storage system for providing power to the electric motor in the drive mode and being rechargeable by the electric motor in the regenerative braking mode, a downshifting prevention apparatus, and a vehicle control unit to prevent over-shifting in the electric vehicle. The vehicle control unit is configured to (a) predict the speed of the electric motor resulting from downshifting from a current gear being used to a next lower gear based on a current speed of the electric vehicle, a current speed of the electric motor, and a gear ratio of the next lower gear; (b) determine if the speed of the electric motor predicted in (a) will cause an overvoltage condition from regenerative braking or an overspin condition in the electric motor; (c) actuate the downshifting prevention apparatus to prevent downshifting when the vehicle control unit determines that downshifting to the next lower gear will cause an overvoltage condition or an overspin condition in the electric motor; and (d) repeat (a), (b), and (c) a plurality of times. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a simplified diagram illustrating select components of an electric vehicle in accordance with one or more embodiments in a drive mode. 
           [0009]      FIG. 2  is a simplified diagram illustrating select components of an electric vehicle in accordance with one or more embodiments in a regen mode. 
           [0010]      FIG. 3  is a graph showing typical gear selection when shifting up through various speeds. 
           [0011]      FIG. 4  is a graph showing typical gear selection when downshifting through various speeds. 
           [0012]      FIG. 5  is a graph showing exemplary voltage generation during a regenerative mode. 
           [0013]      FIG. 6  is a graph showing an example of overvoltage when double shifting down (motor overdrive). 
           [0014]      FIG. 7  is a graph showing an example of overvoltage from shifting down too early (motor overdrive). 
           [0015]      FIG. 8  is a simplified diagram illustrating an exemplary gear position sensor. 
           [0016]      FIG. 9  is a flowchart illustrating an exemplary predictive gear selection process in accordance with one or more embodiments. 
           [0017]      FIG. 10  is a flowchart illustrating an exemplary reactive gear selection process in accordance with one or more embodiments. 
           [0018]      FIG. 11  is a simplified diagram illustrating an exemplary shift lever mechanically coupled with a gearbox. 
           [0019]      FIG. 12  is a simplified diagram illustrating an exemplary shift lever, a gearbox, and a regen protection solenoid in accordance with one or more embodiments. 
           [0020]      FIG. 13A  is a perspective view of an exemplary shift lever with external regen protection solenoid in accordance with one or more embodiments. 
           [0021]      FIG. 13B  is a perspective view of an alternate exemplary shift lever with external regen protection solenoid in accordance with one or more embodiments. 
           [0022]      FIG. 14  is a perspective view of an exemplary gearbox with an internal regen protection lock mechanism with one or more embodiments. 
           [0023]      FIG. 15A  is a side view of the internal regen protection lock mechanism of  FIG. 14  showing normal gear selection with the overdrive lockout disabled. 
           [0024]      FIG. 15B  is a side view of the internal regen protection lock mechanism of  FIG. 14  showing the overdrive lockout enabled, resulting in downward gear selection being blocked. 
           [0025]      FIG. 15C  is a side view of the internal regen protection lock mechanism of  FIG. 14  showing the shift lever/gear in a neutral position and the overdrive lockout enabled. 
       
    
    
     DETAILED DESCRIPTION 
       [0026]      FIG. 1  is a simplified diagram showing select components of a typical electric vehicle. The flow of power starts from the vehicle&#39;s battery system  4  which then goes to the motor controller  3 , where it is modified to drive the motor  7  depending on a variety conditions. The vehicle&#39;s throttle  2  regulates the speed and is interpreted by the motor controller  3 , which then adjusts the flow of energy  6  to the motor. Additional conditions such as the position of the key switch, drive modes (economy, sport, etc.), error conditions (e.g., kickstand down on a motorcycle) are controlled by the vehicle&#39;s control unit  1  have additional control over the vehicle state and thus will influence what the motor controller delivers to the motor. Drive linkage  8  to the drive wheel  10  can be through a variety of mechanical mechanisms (e.g., chains, belts, shafts), and the particular drive linkage is not a limitation of this patent. In addition, the Battery/Energy Storage System  4  can be generally any form of rechargeable energy storage and is not a limitation of this patent. 
         [0027]    In  FIG. 2 , the flow is reversed as the vehicle is using mechanical energy from braking to drive the motor  7 , which then generates electricity  11  transferred to the motor controller  3  where it can then use that energy  12  to re-charge the vehicle&#39;s battery system  4 . 
         [0028]      FIG. 3  is a simplified diagram illustrating the normal sequence for shifting upwards in gears. This example uses a 6-speed gearbox transmission (shown as gears 1 through 6). However, it should be understood that that methods and apparatus in accordance with various embodiments can be applied to transmission gearboxes with any number of multiple gears. Conversely, for downshifting (shown in  FIG. 4 ), the sequence is reversed. (For clarity, the horizontal axis in  FIG. 4  is reversed in direction from that shown in  FIG. 3 ). 
         [0029]    In the regen mode, the motor produces a voltage output proportional to the speed (RPM) of the motor. The voltage produced is defined as: 
         [0000]      Motor Voltage=Ke×RPM
 
         [0000]    where Ke is the Motor Voltage constant and RPM is the revolutions per minute of the motor. 
         [0030]    Due to this linear relationship between the motor&#39;s RPM and the voltage output, the voltages produced during regen when shifting down have a similar shape to the motor&#39;s speed. The voltage output of the motor is shown in  FIG. 5  and is similar in shape to the RPM shown in  FIG. 4 . The higher the RPM of the motor, the greater the voltage produced. 
         [0031]    When a driver shifts from a higher gear at maximum motor RPM to a lower gear (or double-shifts two gears at once) downward, the motor can spin beyond parameters designed for the motor itself. In addition, due to the excessive spinning of the motor, the voltages produced on the output, e.g., at  20 , can be higher than the designed maximum  21  for the system as shown in  FIG. 6 . 
         [0032]    The same effect can also come from downshifting too early at  30 , which can cause a motor to spin faster than the system is designed to handle, and thus cause an overvoltage condition at  31  as shown in  FIG. 7 . 
         [0033]    To prevent this overspin or overvoltage condition, the gears selected should be within specified motor RPM ranges, and no gear should be selected that would cause the motor to enter overspin or produce a voltage greater than what the system is designed for. 
         [0034]    The current gear selection can be determined by a gear position sensor. As an example, a resistive sensor is discussed in embodiments illustrated herein, but it should be understood that a variety of other sensors (optical, magnetic, etc.) can also be used. An exemplary resistive sensor is shown in  FIG. 8  with corresponding gears. In this example, the higher the gear selection, the higher the voltage output from the sensor. As the output is linear (analog), intermediate positions can also be determined, including the direction of the shift before it shifts completely out of the current gear and into the next. Digital sensors have also been developed for gear position sensors, and can be used in this application. 
         [0035]    Exemplary algorithms for an electric motorcycle (or tricycle or ATV) overdrive lockout are shown in the flowcharts of  FIGS. 9 and 10 . These algorithms can be performed by the electric motorcycle&#39;s control unit (Vehicle Control Unit or Engine Control Unit), which knows the current gear being used in the gearbox, the vehicle&#39;s speed, and the motor&#39;s RPM. From this information, it can calculate what the next gear selection would do to the motor&#39;s speed. 
         [0036]    The algorithm of  FIG. 9  is predictive in operation and, in which, calculations are repeatedly done to predetermine if the next lower gear were to be selected, whether it would cause an overspin/overvoltage condition. If an overspin/overvoltage could take place, then actions are taken to prevent downshifting before it happens. The gear ratio for the next lower gear position is looked up at  40 . At  41 , the motor RPM is calculated by taking the current vehicle speed, the motor voltage constant (Ke), and the next lower gear ratio from what is currently being used. The output voltage is calculated at  42 , and is then compared to the known system maximum parameters at  43 . If it exceeds the maximum, then action is taken to prevent downshifting at  44 , e.g., a solenoid is energized to prevent downshifting. This method works with both digital and analog gear position sensors. 
         [0037]    With some sensors, the direction of the shift can be determined before the actual gear is selected, and the corrective action can take place if it is determined that the shift would produce a condition where the motor would overspin or produce an overvoltage that exceeds design parameters. 
         [0038]    A reactive algorithm using this example is shown in  FIG. 10 . This time, the process starts with determining the direction of the shift in process (which can be accomplished if the gear sensor provides analog or linear position information through the gear shift range) at  50 . If the shift direction is upward, the algorithm quickly exits. If the shift direction is downward, then the algorithm looks up the new lower gear ratio at  51 . The current speed of the vehicle and the new gear ratio can then be used to calculate the new motor RPM value at  52 . With the motor&#39;s calculated new RPM, the new voltage output can be calculated at  53  and then compared to see an overspin/overvoltage would result at  54 . If the new gear produces an overspin/overvoltage condition  55 , then action is taken to prevent the shift from completion and to remain in the current gear at  56 . 
         [0039]    To prevent a gear change from completing, a method to mechanically stop the shift takes place. Two examples follow: one external to the gearbox, and the other internal to the gearbox. There are numerous possible variations to each of these implementations, but it is understood that using generally any mechanical or other method (internal or external to the gearbox) to stop shifting would fall under the scope of this disclosure. In this application,  FIGS. 11-13  describe an external approach to preventing a gear change, whereas FIGS.  14  and  15 A-C describe an internal approach to preventing a gear change. 
         [0040]    The external approach to stopping a gear change shown in  FIGS. 11-13  utilizes an electromagnetic solenoid under the shift lever of the vehicle. A typical shift lever  74  for a motorcycle is shown in  FIG. 11 . The lever is foot operated, and by moving the lever upward  60 , a higher gear is selected. Conversely, a downward movement  61  on the lever will select a lower gear. 
         [0041]    The modified version with the solenoid is shown in  FIG. 12 . The shift lever  74  pivots around the shift shaft in which the movement will cause selection of the next gear. 
         [0042]    Adjacent to the shift lever is a metal plate  70  with a hole  71  slightly larger than the diameter of the solenoid piston in the center. This metal plate is attached to the vehicle frame  72 . When the solenoid  73  is engaged, the solenoid&#39;s piston extends out and through the metal plate hole. This provides a mechanical reinforcement to prevent further downward motion of the shift lever. When the solenoid is de-energized, the piston retracts and the shift lever can move downward freely. Thus, by energizing and de-energizing the solenoid  73 , the shift lever&#39;s downward movement can be respectively disabled or enabled. 
         [0043]    Two variations are shown in  FIGS. 13A and 13B . The difference between the two is that  FIG. 13B  shows a more mechanically robust version as the pin is re-enforced on both sides  80  of the shift lever  74  when the solenoid piston is extended. 
         [0044]    An internal approach to stopping a gear change is shown in FIGS.  14  and  15 A- 15 C.  FIG. 14  shows the gearbox assembly, which includes the Shift Lever  90 , shift shaft  91 , shift shaft gear  92 , shift lock  93 , shift lock spring  94 , and solenoid  95 , which is discussed in further detail below. The shift shaft gear, shift lock, shift lock spring, and solenoid are internal to the gearbox unit, with the shift shaft extending from inside to the outside of the gearbox unit before being attached to the shift lever. 
         [0045]      FIG. 15A  shows the shift shaft gear  92  in normal operation with the shift lock  93  inactive. The Solenoid piston is retracted due to the solenoid spring  97  expansion when the solenoid  95  is not energized, thus the shift shaft gear is able to freely move in either the up or down direction. 
         [0046]      FIG. 15B  shows the overdrive lockout enabled by energizing the solenoid  95 , which extends the solenoid piston  98 . Because the algorithm described in  FIG. 9  is constantly being executed, it is likely that the algorithm would immediately use the new lower gear (that has just engaged) as the selected gear before the driver fully releases the Shift Lever. In this case, the shift shaft gear  92  is allowed to spring back to a neutral position shown in  FIG. 15A  as the Shift Lever returns to Neutral position. However once the Shift Lever is in Neutral position, the Shift Lock spring  94  forces the Shift Lock  93  into place and prevents further downshifting until the overspin condition is removed. Once the potential overspin condition has been calculated to be removed, the Solenoid  95  can be de-energized which allows the Solenoid Spring  97  to un-compress and the solenoid piston will then retract and unlock the Shift Shaft Gear. 
         [0047]    The algorithms for preventing over-shifting described above may be implemented in software, hardware, firmware, or any combination thereof. The processes are preferably implemented in one or more computer programs executing on a programmable device (e.g., in the vehicle control unit or engine control unit) including a processor and a storage medium readable by the processor (including, e.g., volatile and non-volatile memory and/or storage elements). Each computer program can be a set of instructions (program code) in a code module resident in the storage medium. 
         [0048]    Having thus described illustrative embodiments, it is to be appreciated that various alterations, modifications, and improvements will readily occur to those skilled in the art. Such alterations, modifications, and improvements are intended to form a part of this disclosure, and are intended to be within the spirit and scope of this disclosure. While some examples presented herein involve specific combinations of functions or structural elements, it should be understood that those functions and elements may be combined in other ways according to the present disclosure to accomplish the same or different objectives. In particular, acts, elements, and features discussed in connection with one embodiment are not intended to be excluded from similar or other roles in other embodiments. 
         [0049]    Additionally, elements and components described herein may be further divided into additional components or joined together to form fewer components for performing the same or similar functions. 
         [0050]    Accordingly, the foregoing description and drawings are by way of example only, and are not intended to be limiting.