Patent Publication Number: US-2009230765-A1

Title: System and method for delivering power to an electric motor of an automotive vehicle

Description:
BACKGROUND 
     1. Field of the Invention 
     The invention relates to systems and methods for delivering power to an electric motor of an automotive vehicle. 
     2. Discussion 
     Switches may be used to deliver power from a power source to a power sink. As an example, U.S. Pat. No. 6,211,580 to Cabuz et al. provides an electrostatic actuator and drive configuration device for use in a system requiring a long term ON state operation. The device includes a first electrostatic actuator positioned to operate in the system requiring the long term ON state upon activation of a power supply. The device also includes a second electrostatic actuator positioned to operate in the system requiring the long term ON state upon activation of the power supply. A timer is connected to the power supply to alternately select the first or the second actuator for activation to drive the selected actuator to the ON state. The timer is controlled to select the first or second electrostatic actuator on an alternating basis to prevent either electrostatic actuator from remaining in the ON state for more than a predetermined time without the other actuator being selected. The electrostatic actuators may be configured in parallel or in series, depending upon the demands of the system. 
     As another example, U.S. Pat. No. 4,769,554 to Reinartz et al. provides an electrical switching mechanism for circuits associated with hydraulic systems in automotive vehicles. The switching mechanism comprises at least one switch disposed on a printed circuit board. The at least one switch includes a sliding contact fixed to a hydraulically movable carrier. The sliding contact, in various positions along its path of displacement, provides for electrically conductive connection or disconnection. 
     As yet another example, U.S. Pat. No. 4,625,205 to Relis provides a remote control system including a central encoder for transmitting a single sequence of control pulses to a plurality of remote decoders, each of which performs a predetermined function when it has received a selected number of pulses. Reliability of the system is enhanced by including in the encoder and all of the decoders a number of electro-mechanical relays arranged in a triple redundant configuration. 
     SUMMARY 
     A system for delivering power from a power source to an electric motor of an automotive vehicle includes at least two electro-mechanical switches in parallel. Each of the electro-mechanical switches is configured to deliver power from the power source to the electric motor when activated. Each of the electro-mechanical switches has a specified number of activation cycles that defines its lifetime. The specified number of activation cycles for at least one of the electro-mechanical switches is less than an expected number of activation cycles of the electric motor for a life of the automotive vehicle. The system also includes an electronic control module that is configured to selectively activate the at least two electro-mechanical switches for an activation cycle of the electric motor. 
     A system for delivering power from a power source to an electric motor of an automotive vehicle includes a plurality of parallel electro-mechanical switches. Each of the plurality of parallel electro-mechanical switches is configured to pass power from the power source to the electric motor when activated for an activation cycle of the electric motor. Each of the plurality of parallel electro-mechanical switches has a specified number of activation cycles that defines its lifetime. The specified number of activation cycles of each of the plurality of parallel electro-mechanical switches is less than an expected number of activation cycles of the electric motor for a life of the automotive vehicle. 
     A method of providing power from a power source to an electric motor of an automotive vehicle via a plurality of parallel electro-mechanical switches includes determining whether one of the plurality of parallel electro-mechanical switches was used for a previous activation cycle of the electric motor. The method also includes activating another one of the plurality of parallel electro-mechanical switches for a current activation cycle of the electric motor. Each of the plurality of parallel electro-mechanical switches has a specified number of activation cycles that defines its lifetime. Each of the specified number of activation cycles is less than an expected number of activation cycles of the electric motor for a life of the automotive vehicle. 
     While exemplary embodiments in accordance with the invention are illustrated and disclosed, such disclosure should not be construed to limit the claims. It is anticipated that various modifications and alternative designs may be made without departing from the scope of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of a portion of a power supply system for a vacuum pump motor of an automotive vehicle according to an embodiment of the invention. 
         FIG. 2  is a flow chart of a strategy for controlling the power supply system of  FIG. 1  for an activation cycle of the vacuum pump motor of  FIG. 1  according to another embodiment of the invention. 
         FIG. 3  is a flow chart of another strategy for controlling the power supply system of  FIG. 1  for an activation cycle of the vacuum pump motor of  FIG. 1  according to yet another embodiment of the invention. 
         FIG. 4  is a flow chart of yet another strategy for controlling the power supply system of  FIG. 1  for an activation cycle of the vacuum pump motor of  FIG. 1  according to still yet another embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     Certain automotive vehicles, such as hybrid electric vehicles, may use a vacuum based braking system. A vacuum pump is often used in a vacuum based braking system. Such a vacuum pump may experience a substantial number of activation cycles, e.g., 1.2 million, during the life of the vehicle. 
     An electronically controlled solid state relay may be used to deliver power to activate a vacuum pump. Solid state relays, however, may be costly. Electro-mechanical switches are generally less costly than solid state relays. The usable life of an electro-mechanical switch, however, is typically less than the expected number of activation cycles of a vacuum pump during the life of the vehicle. 
     Referring now to  FIG. 1 , an embodiment of a portion of a power delivery system  10  includes a pair of parallel electro-mechanical switches  12 ,  14 , e.g., relays, etc., controlled by an electronic control module  16 . When activated, the switches  12 ,  14  pass electrical currents from a battery  18  to a vacuum pump motor  20  of a vacuum based braking system (not shown) for an automotive vehicle  22 . One of the switches  12 ,  14  is activated for each activation cycle of the motor  20 . In other embodiments, any number of parallel electro-mechanical switches may be controlled by the electronic control module  16 . 
     Each of the switches  12 ,  14  has a specified number of activation cycles that defines its usable life. In the embodiment of  FIG. 1 , the specified number of activation cycles for each of the switches  12 ,  14  is 600,000. Other specified numbers of activation cycles are of course also possible. The expected number of activation cycles of the motor  20  for a life of the vehicle  22  is 1,000,000. 
     While the specified number of activation cycles for any one of the switches  12 ,  14  is not sufficient to meet the expected number of activation cycles of the motor  20 , the total of the specified number of activation cycles for both of the switches  12 ,  14  is greater than the expected number of activation cycles of the motor  20 . As a result, the control module  16  uses one or the other of the switches  12 ,  14  for each activation cycle of the motor  20  for the life of the vehicle  22 . 
     Referring now to  FIGS. 1 and 2 , the control module  16  determines whether to activate the motor  20  as indicated at  24 . If no, the strategy ends. If yes, the control module  16  determines whether the switch  12  was used during the last activation cycle of the motor  20  as indicated at  26 . If no, the control module  16  activates the switch  12  to deliver power from the battery  18  to the motor  20  for an activation cycle of the motor  20  as indicated at  28 . The strategy then ends. If yes, the control module  16  activates the switch  14  to deliver power from the battery  18  to the motor  20  for an activation cycle of the motor  20  as indicated at  30 . The strategy then ends. The control strategy of  FIG. 2  thus alternately activates the switches  12 ,  14  for consecutive activation cycles of the motor  20 . 
     Referring now to  FIGS. 1 and 3 , the control module  16  determines whether to activate the motor  20  as indicated at  32 . If no, the strategy ends. If yes, the control module  16  determines whether a fault flag associated with the switch  12  is set to true as indicated at  34 . In the embodiment of  FIG. 3 , the fault flag associated with the switch  12  may be set to true if the switch  12  encountered a fault condition, e.g., not activating, etc., during a previous activation cycle of the motor  20 . If no, the control module  16  activates the switch  12  to deliver power from the battery  18  to the motor  20  for an activation cycle of the motor  20  as indicated at  36 . As indicated at  38 , the control module  16  determines whether the switch  12  is experiencing a fault condition. If no, the strategy ends. If yes, the control module  16  sets the fault flag associated with the switch  12  equal to true as indicated at  40 . As indicated at  42 , the control module  16  activates the switch  14  to deliver power from the battery  18  to the motor  20  for the activation cycle of the motor  20 . As indicated at  44 , the control module  16  determines whether the switch  14  is experiencing a fault condition. If no, the strategy ends. If yes, the control module  16  sets the fault flag associated with the switch  14  equal to true as indicated at  46 . As indicated at  48 , the control module  16  sets a vacuum supply fault flag equal to true. The strategy then ends. In the embodiment of  FIG. 3 , the vacuum supply fault flag indicates that the vacuum based braking system encountered a fault during the activation cycle of the motor  20 . 
     Referring again to step  34 , if yes, the strategy proceeds to step  42 . The control strategy of  FIG. 3  thus activates the switch  12  for consecutive activation cycles of the motor  20  unless the switch  12  is faulted. That is, the control strategy of  FIG. 3  attempts to exhaust the specified number of activation cycles of the switch  12  before using the switch  14 . 
     Referring now to  FIGS. 1 and 4 , the control module  16  determines whether to activate the motor  20  as indicated at  50 . If no, the strategy ends. If yes, the control module  16  determines whether the switch  12  was used during the last activation cycle of the motor  20  as indicated at  52 . If no, the control module  16  determines whether a fault flag associated with the switch  12  is set to true as indicated at  54 . If no, the control module  16  activates the switch  12  to deliver power from the battery  18  to the motor  20  for an activation cycle of the motor  20  as indicated at  56 . As indicated at  58 , the control module  16  determines whether the switch  12  is experiencing a fault condition. If no, the strategy ends. If yes, the control module  16  sets the fault flag associated with the switch  12  equal to true at block  60 . As indicated at  62 , the control module  16  determines whether a fault flag associated with the switch  14  is set to true. If no, the control module  16  activates the switch  14  to deliver power from the battery  18  to the motor  20  for the activation cycle of the motor  20  as indicated at  64 . As indicated at  66 , the control module  16  determines whether the switch  14  is experiencing a fault condition. If no, the strategy ends. If yes, the control module  16  sets the fault flag associated with the switch  14  equal to true as indicated at  68 . As indicated at  70 , the control module  16  determines whether the fault flag associated with the switch  12  is set to true. If no, the strategy proceeds to step  56 . If yes, the control module  16  sets a vacuum supply fault flag equal to true as indicated at  72 . The strategy then ends. 
     Referring again to step  52 , if yes, the control module  16  determines whether the fault flag associated with switch  14  is set to true as indicated at  74 . If no, the strategy proceeds to step  64 . If yes, the strategy proceeds to step  68 . 
     Referring again to step  54 , if yes, the strategy proceeds to step  62 . 
     Referring again to step  62 , if yes, the strategy proceeds to step  72 . The control strategy of  FIG. 4  thus alternately activates the switches  12 ,  14  for consecutive activation cycles of the motor  20  unless one of the switches  12 ,  14  is faulted. 
     While embodiments of the invention have been illustrated and described, it is not intended that these embodiments illustrate and describe all possible forms of the invention. For example, embodiments of the invention may be used to deliver power from a power source to any electric motor of an automotive vehicle. 
     The words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention.