Abstract:
Apparatus and method for efficiently controlling an automatic transmission in an electric vehicle. The method may be implemented by selection of one of at least two belt clutches having different ratios. The timing for disengagement and engagement of each clutch and the proper sequencing of the disengagement and engagement of the clutches is determined to optimize the efficiency of the transmission. A direct drive motor is directly coupled to the transmission&#39;s output shaft to provide momentary power to maintain a nearly constant rate of acceleration during shifting. The method may further be applied for shifting an electric vehicle with a first motor coupled to an output shaft through a single belt clutch and a direct drive motor.

Description:
The present application claims the priority of U.S. Provisional Patent Application Ser. No. 61/142,141 filed Dec. 31, 2008, which application is incorporated in its entirety herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to electric vehicles with automatic transmissions and in particular to a new, improved method of controlling the actuation of a multi-speed transmission implementing one or more clutches. 
     Known electric vehicles with multi-speed transmissions select a transmission ratio by engaging one of two or more clutches or positively ganging members. Either of these methods generally result in frictional drag on the system due to the disengaged clutches. U.S. Provisional Patent Application Ser. No. 61/099908 filed Sep. 25, 2008 by the present inventor and incorporated herein by reference, describes an improved clutch mechanism to reduced drag on a multi-speed transmission. While the &#39;908 application provides reduced drag, it does not disclose an optimal method to efficiently disengage and engage the clutches at the proper times to minimized the time of clutch disengagement, the duration between shifts, and the wear on the drive system, and does not attempt to maximize the smoothness of the operation. 
     Additionally, disengagement of a lower ratio clutch and the subsequent engagement of a higher ratio clutch is not instantaneous and results in a period of time with no power being coupled to the drive wheels. This may results in jarring the vehicle and be an annoyance to the operator. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention addresses the above and other needs by providing apparatus and method for efficiently controlling an automatic transmission implemented by selection of one of at least two belt clutches or other mechanisms having different ratios. The timing for disengagement and engagement of each clutch and the proper sequencing of the disengagement and engagement of the clutches is determined to optimize the efficiency of the transmission. In one embodiment of the invention, at least one motor is directly coupled to the output shaft of the transmission. When multiple additional gear ratios are driven through clutches, the directly driven motor may be used to momentarily apply torque to the output shaft during the transition time when between gear selection to provide momentary power to maintain a nearly constant rate of acceleration during shifting. During this brief application of torque, the motor and controller may be driven beyond their rated sustainable power levels with there being insufficient time for these components to overheat. 
     In accordance with one aspect of the invention, there is provided a method for maintaining smooth acceleration across transmission shifts of an electric vehicle accomplished by disengaging a first belt clutch and engaging a second clutch. The method includes determining an amount of power to provide to an auxiliary motor to maintain a present acceleration of the vehicle, beginning disengagement of the first belt clutch, reducing power to a main motor, providing the determined amount of power to the auxiliary motor, beginning engagement of the second belt clutch, completing engagement of the second belt clutch, completing disengagement of the first belt clutch, returning power to the main motor, and removing power from the auxiliary motor. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
       The above and other aspects, features and advantages of the present invention will be more apparent from the following more particular description thereof, presented in conjunction with the following drawings wherein: 
         FIG. 1  is an electric vehicle suitable for application of the present invention. 
         FIG. 2  is a drivetrain according to the present invention for application with the electric vehicle. 
         FIG. 3  is a prior art electronic control system for use with the electronic vehicle. 
         FIG. 4  is an Intelligent Electronic Control System (IECS) for use with the electronic vehicle. 
         FIG. 5  shows a three speed hybrid transmission according to the present invention with direct drive capability for an internal combustion engine or a large electric motor, the hybrid transmission comprising three belt clutches each with different reduction ratios. 
         FIG. 6  is a method according to the present invention. 
     
    
    
     Corresponding reference characters indicate corresponding components throughout the several views of the drawings. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The following description is of the best mode presently contemplated for carrying out the invention. This description is not to be taken in a limiting sense, but is made merely for the purpose of describing one or more preferred embodiments of the invention. The scope of the invention should be determined with reference to the claims. 
     An electric vehicle  10  suitable for application of the present invention is shown in  FIG. 1  and a drivetrain  50  according to the present invention and suitable for use in the vehicle  10  is shown in  FIG. 2 . The drivetrain  50  includes a drive shaft  40  and an axle  42  connected to drive wheels  12  for driving the vehicle  10 . Operator controls  18  are used by an operator to control the driving force provided by the wheels  12 . The controls  18  may be foot control, hand controls, or any form of control useable by an operator. In an instance of a remotely controlled vehicle  10 , the controls  18  may be a signal receiver. The controls  18  are connected by an operator signal cable  20  carrying an operator control signal to an electronic motor/transmission controller  22 . Batteries  24  are connected to the electronic motor/transmission controller  22  by battery power cable  26 . The electronic motor/transmission controller  22  processes the operator signal and uses Pulse Width Modulation (PWM) to control the power provided through power cable  28  to an electric motor  30 , and to generate transmission control signals provided through transmission control signal cable  32  to a transmission  36  to control gear changing and clutch engagement/disengagement and provide feedback signals from the transmission to the electronic motor/transmission controller. Power may also be carried back to the battery  24  during regenerative braking over cables  28  and  26 . 
     The motor  30  is coupled the transmission  36  through motor coupling  34 . The motor coupling  34  may be a belt, a shaft, or any other mechanical coupling for carrying mechanical power. The transmission  36  is coupled to the axle  42  by transmission coupling  40  which also may be a belt, a shaft, or any other mechanical coupling for carrying mechanical power. The vehicle  10  may be a two, three, four or more wheeled vehicle, a rear wheel drive, front wheel drive, or all wheel drive, and adaptation of the drivetrain described herein is equally applicable to any selected drive wheel(s) configuration. In the embodiment shown in  FIG. 2 , the front wheels  14  are used for steering only. 
     A prior art electronic control system  60  for the electric vehicle  10  is shown in  FIG. 3 . Power and braking actuators  62   a  and  62   b  respectively are mechanically coupled to a power signal transducer  18   a  and a braking signal transducer  18   b  respectively. A power signal  20   a  and a braking signal  20   b  are generated by the transducers  18   a  and  18   b  and provided to the electronic motor/transmission controller  22 . The electronic motor/transmission controller  22  controls a flow of current from the battery  24  to the electric motor  30  for providing power in response to the power signal  20   a , and controls a flow of current from the electric motor  30  to the battery  24  for providing electricity to recharge the battery  24  in response to the braking signal  20   b . During the application of power, the electric motor  30  provides mechanical power to the transmission  36  through the coupling  34  and the transmission  36  provides mechanical power to the vehicle  10  through the coupling  40 . While the electronic control system  60  may prove adequate in some instance, it does not always result in power and braking which accurately mimics the positions of the power and braking actuators  62   a  and  62   b.    
     An Intelligent Electronic Control System (IECS)  64  is shown in  FIG. 4  which includes an intelligent controller  66  which provides adjusted operator power and braking signals  68   a  and  68   b  to the electronic motor/transmission controller  22  to provide power and regenerative braking which mimic the positions of the power and braking actuators  62   a  and  62   b . The power signal  20   a  and the braking signal  20   b , along with motor voltage and current signals  70 , are provided to an intelligent controller  66 . The intelligent controller  66  computes and provides adjusted power and braking signals  68   a  and  68   b  to the electronic controller, and transmission control signals  74  to the transmission  36 , to provide acceleration and braking which mimic the positions of the power and braking actuators  62   a  and  62   b . The motor voltage and current signals  70  are obtained from voltage and current sensors  72  residing between the electronic motor/transmission controller  22  and the electric motor  30 . 
     The intelligent controller  66  further controls the powering of a primary motor  31  which is mechanically coupled to the coupling (or output shaft)  40  to directly drive the output shaft  40 . The intelligent controller  66  provides a second power signal  69  to the electronic motor/transmission controller  22  to provide a flow of power through second power cable  29  to the motor  31 . The motor  31  may be connected to the output shaft  40  on either side of the transmission  36  (see  FIG. 5 ) and may be connect through a clutch, for example a one way clutch which automatically engages when the speed of the motor  31  exceeds the speed of the output shaft  40  and automatically disengages when the speed of the motor  31  is less than the speed of the output shaft  40 . The intelligent controller  66  may also use the power signal  69  in a regenerative mode to draw power from the motor  31  to recharge the batteries  24  when the transmission down shifts during regenerative braking when the one way clutch is not present. 
     A three speed hybrid transmission  36  with direct drive capability for the primary motor  31 , comprising three belt clutches  80 ,  82 , and  84  each with different reduction ratios, is shown in  FIG. 5 . The motors  30  and  31  and the three speed hybrid transmission  36  are controlled by the intelligent controller  66  to provide smooth and efficient power to the output shaft  40 . Examples of suitable belt clutches  80 ,  82 , and  84  are of a type described in U.S. Provisional Patent Application Ser. No. 61/099,908 filed Sep. 25, 2008 by the present inventor, and incorporated above by reference. The belt clutches  80 ,  82 , and  84  are fixedly connected together with spacers  76  between them to create space for actuators  78 , and share the common input shaft  34  and the common output (or drive) shaft  40 . The output shaft  40  is operatively connected to at least one wheel  12  to drive the vehicle  10  (see  FIG. 2 ). The electric motor  30  is mounted to the belt clutch  36  and drives the shaft  34 . The primary motor  31  is connected either directly to the output shaft  40  or disengageably through a clutch  86 . The clutch  86  may be a uni-directional clutch, such as a clutch bearing or the like, so that when the electric motor  30  alone is driving output shaft  40  through one of the belt clutches  80 ,  82 , and  84 , the motor  31  does not need to turn. 
     In some examples where the highest ratio belt clutch is less than 1:1 ratio, the primary motor  31  may provide an additional higher ratio operation, creation basically a fourth speed for a transmission comprising three belt clutches. 
     The engagement of the belt clutches  80 ,  82 , and  84  is monitored to prevent the possibility of engaging multiple clutches having different ratios simultaneously, which could cause damage to the transmission  36 . In one embodiment, the clutches  80 ,  82 , and  84  are engaged and disengaged by moving actuators which apply and release tension on the belt. In order to fully disengage each clutch  80 ,  82 , or  84 , the clutch actuators must move sufficiently to assure that the corresponding belts are completely separated from pulleys on the shafts  34  and  40 . As the clutches are engaged, there is a range where the clutch will be in the process of engaging but until it is fully engaged, the friction will not be adequate to drive the system. While vehicle  10  is under power and the transmission  36  shifts to a higher transmission ratio, during partial clutch engagement, the motor  30  may be dynamically braked to a speed close to the speed it will rotate when the subsequent gear is engaged or may only receive adequate power to maintain a desired rotational motor speed. 
     While not essential to the utility of the present invention, the direct drive motor  31  may be used as the primary motor in a high gear. In this embodiment, as the intelligent controller  66  signals the transmission  36  to transition the clutches  80 ,  82 , or  84  from being either fully engaged or disengaged there is period of time between being fully engaged and disengaged where there is partial engagement, and no power may be applied from the from motor  30  through the clutches to output shaft  40  without experiencing belt slippage. Such belt slippage increases wear on belts, creates heat, and wastes energy. During the shifts, the intelligent controller  66  applies current to the motor  31  at a level to maintain a reasonably constant level of acceleration while the motor  30  is not driving the output shaft  40 . Because of the short duration which the motor  31  applies power, the current applied to the motor  31  may be allowed to exceed the continuous rating of the motor  31  or motor controller  22 . For optimal smooth operation of the vehicle  10 , the current applied to the motor  31  during the shift will be enough to maintain the desired level of acceleration throughout the shifting process. After the clutch  80 ,  82 , or  84  is engaged, the current provided to the motor  30  and/or motor  31  as applicable will be increased at rate determined to provide a smooth increase in torque until the acceleration which was applied prior to the shift is achieved, or the maximum available current is applied to the motor  30  and/or motor  31  as applicable. 
     In the embodiment described above with the direct drive motor  31  being used in conjunction with the selection of ratios using the clutches  80 ,  82 , and  84 , when a specific ratio is selected, the proper level of current determined to supply the desired amount of acceleration may be provided to the motor  31  as the power is remove from the motor  30 , even before the currently engaged clutch  80 ,  82 , or  84  is disengaged. For other embodiments, some other predetermined acceleration may be achieved for the specific gear ratio transition for all input variables considered for a desired level of efficiency, safety consideration and/or feel for the operator. 
     Similarly, when the vehicle  10  is under power and it is desired for the transmission  36  to shift from a higher ratio clutch to a lower ratio in order to maintain power or efficiency, power will be removed from the motor  30  as the higher ratio clutch is disengaged. The lower ratio clutch will begin engagement with timing which allows the lower ratio clutch to begin to couple power from the motor  30  to the output shaft  40  as the higher ratio clutch is being disengaged and is reducing the amount of power coupled through the higher ratio clutch from the motor  30  to the output shaft  40 . At the same time, enough power may be applied to the motor  30  to achieve a desired rotational speed to approximately equal the speed it will be rotating once the lower ratio clutch is engaged. Once the lower ratio clutch is completely engaged to a point that it can couple the necessary torque to power the vehicle  10 , the current will be provided to the motor  30  at a smooth rate to achieve the desired level of acceleration determined for the inputs given to the intelligent controller  66 . In the case of the system which implements a direct drive motor  31  in conjunction with the motor  30 , power may be maintained by the motor  31  until the clutch  80 ,  82 , or  84  is fully engaged and power is reapplied to the motor  30 , and when necessary, power may be applied to the direct drive motor  31  after the lower ratio clutch is engaged, to maintain the desired level of acceleration. 
     In another embodiment, when all power is removed from the drive system, resulting in the vehicle  10  being allowed to coast, none of the clutches  80 ,  82 , or  84  will be engaged until power is again applied as determined by the intelligent controller  66 . At that time, the engagement process described above will be applied. When the vehicle  10  has come to a complete stop, then the lowest ratio clutch will be engaged with the motor  30  at zero RPM to anticipate the vehicle  10  being accelerated again. 
     In the situation where regenerative braking is being employed through the drivetrain, the vehicle  10  will be shifted into lower ratios as the vehicle  10  slows down at the point determined to provide a desired deceleration while maximizing power battery recharging. The shifting sequence during deceleration will be the same as described above while power is being applied, with the exception of the power flow before and after the disengagement of the higher ratio and engagement of the lower ratio will be flowing from the motors  30  and  31  to the battery rather than into the motor or motors. 
     While the transmission  36  is described above in the context of a three speed transmission, a vehicle  10  having any transmission comprising at least one belt clutch is intended to come within the scope of the present invention. Further, while the invention is herein described having a single motor  30 , in other embodiments the motor  30  may be replaced by two or more motors, and any electric vehicle with a motor or motors driving an input shaft of a transmission, and having an auxiliary motor connected directly to an output shaft of the transmission for maintaining acceleration during shifting and power the vehicle in high gear is intended to come within the scope of the present invention. 
     A method for maintaining constant acceleration across transmission shifts according to the present invention is described in  FIG. 6 . The shifting is accomplished by disengaging a first belt clutch having a first ratio, and engaging a second belt clutch having a second ratio of a transmission coupling a first motor to an output shaft. The method includes determining an amount of power to provide to a direct drive motor to maintain a present acceleration of the vehicle during shifting at step  100 , beginning disengagement of the first belt clutch at step  102 , reducing power to first motor at step  104 , providing the determined amount of power to the direct drive motor at step  106 , beginning engagement of the second belt clutch at step  108 , completing engagement of the second belt clutch at step  110 , completing disengagement of the first belt clutch at step  112 , returning power to the first motor at step  114 , and removing power from the direct drive motor at step  116 . 
     While the invention herein disclosed has been described by means of specific embodiments and applications thereof, numerous modifications and variations could be made thereto by those skilled in the art without departing from the scope of the invention set forth in the claims.